JPH07190003A - Hydraulic driving circuit for construction machine - Google Patents

Abstract

PURPOSE:To rationalize a flow rate distribution to each actuator so as to improve workability by disposing a flow rate limiting variable throttle part on the downstream side of a pressure compensatory part and linking the throttle opening thereof with the operation of another throttle part. CONSTITUTION:A pressure compensatory part 262 is disposed on the upstream side of a group of throttle parts formed of an operation variable throttle part 222 for adjusting a flow rate supplied to an actuator 206 and a flow rate limit variable throttle part 261 for keeping small a difference in pressure between the front and the rear of this throttle part 222 and limiting the flow rate thereof and thus a difference in pressure among the front and the rear of the group of throttle parts is kept at a specified level. At the same time, the flow rate limit variable throttle part 261 is additionally provided and the throttle opening thereof is caused to be changed by linking this with the operation of an operation variable throttle part 223. Therefore, even when saturation is generated due to the composite driving of the actuators 206 and 207, in order to supply the sufficient amount of pressure oil to the actuator 207, the supply of a flow rate to the actuator 206 is rationally limited and any trouble of specified work is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic drive circuit of a construction machine for controlling the drive of an actuator of the construction machine and performing load sensing control, and is particularly useful for a hydraulic excavator or a hydraulic crane. .

[0002]

2. Description of the Related Art In a construction machine such as a hydraulic excavator or a hydraulic crane, a plurality of actuators are appropriately driven by a hydraulic pump at the same time, or one actuator is driven while the other actuator is additionally driven. Frequent maneuvers that require so-called compound drive are performed. In this way, in a hydraulic drive path of a construction machine that requires multiple drive of multiple actuators with a hydraulic pump, in order to smoothly drive all the actuators that are to be combined, It is necessary to constantly supply enough hydraulic pressure to drive the most loaded actuator. Therefore, in such a hydraulic drive circuit, control called load sensing control is performed. In short, load sensing control is a hydraulic drive circuit having such an actuator that is driven in combination, and detects the maximum load pressure from the load pressures of the actuators that are driven in combination, and determines the discharge pressure of the hydraulic pump. Is a control system in which the discharge capacity of the hydraulic pump is controlled so as to be higher than the maximum load pressure by a predetermined value. By adopting such a control system, not only is sufficient hydraulic pressure supplied to each actuator,
The hydraulic pump will constantly supply the hydraulic pressure to the required limit and keep the power consumption low.

However, in a hydraulic drive circuit for performing load sensing control, when hydraulic pressure is introduced from a main pipe line through a branch passage without providing pressure oil distribution means, the pressure oil is guided to an actuator having a lower load. There is a tendency to be broken, and the appropriate allocation cannot be made. Therefore, in such a hydraulic drive circuit, a flow rate control device, which is means for appropriately distributing pressure oil to each actuator, is provided.

Hereinafter, these technical contents will be described with reference to FIGS.
It will be described based on 5. FIG. 10 is a hydraulic circuit diagram showing a hydraulic drive circuit of a first conventional construction machine, and FIG. 11 is a hydraulic circuit diagram showing a hydraulic drive circuit of a second conventional construction machine.
2 is a hydraulic circuit diagram showing a hydraulic drive circuit of a construction machine of a third conventional example, FIG. 13 is a hydraulic circuit diagram showing a hydraulic drive circuit of a construction machine of a fourth conventional example, FIG. 14 is a third conventional example, A hydraulic circuit diagram of a hydraulic pilot operating device for operating a directional control valve in a hydraulic drive circuit of a construction machine of a fourth conventional example, FIG.
5 is a hydraulic circuit diagram showing a hydraulic drive circuit of a hydraulic excavator which is a hydraulic drive circuit of a construction machine of a fifth conventional example. In these drawings, the portions denoted by the same reference numerals represent the same portions, and therefore the portions denoted by the same reference numerals will be described only in the hydraulic circuit diagram relating to the first conventional example.

First, a hydraulic circuit diagram relating to the first conventional example will be described with reference to FIG.
Reference numeral 01 is a variable displacement hydraulic pump, reference numeral 202 is a variable displacement hydraulic pump 201, and a tilt control device for controlling the discharge capacity of the pump 201 and thus the discharge pressure. The details will be described later. Reference numeral 203 denotes a main pipe line connected to the discharge port of the variable displacement hydraulic pump 201 for guiding pressure oil of the pump, 203
Reference numerals a and 203b are branch passages for branching the pressure oil guided to the main pipe 203 to the actuators 206 and 207 described later through the flow control devices 220 and 221 described later, respectively.
Reference numerals 4 and 205 denote load conduits that connect the bottom sides of the actuators 206 and 207 to the flow rate control devices 220 and 221, respectively, and serve as oil passages for driving the actuators 206 and 207. 206 and 207 are branch paths 203a and 203b. Flow control devices 220 and 221 respectively provided in the
Actuators whose speeds are respectively controlled by, for example, equipment such as booms, arms of hydraulic excavators, and hydraulic cylinders for driving buckets. Load line 204,
205 supplies the pressure oil whose flow rate is adjusted by each flow rate control device 220, 221 to the bottom side of each actuator 206, 207 to operate the actuators 206, 207 upward. FIG. 10 illustrates a one-way actuated actuator in which only one load conduit 204, 205 is provided for each actuator 206, 207 in order to simplify the structure and facilitate understanding. However, the actuators of almost all construction machines, including the actuators of hydraulic excavators, actually require bidirectional operation. An example of a hydraulic drive circuit that is provided with such a bidirectional actuator is
This will be described later with reference to FIGS. 12 to 14. 210, 2
11 is a check valve, 212 is each load pipeline 204, 205
Of the actuators 206 and 207, the higher load pressure, that is, the highest load pressure is detected, and the highest load pressure is detected.
Lead to 2. This maximum load pressure detection path 212 is connected to the connection line 2
08 and 209 are connected to the load pipelines 204 and 205, respectively. In that case, the check valves 210 and 21 are connected.
Since it is connected through the check valve 1, the pressure oil flows back to the load pipes 204, 205.
The actuators 206 and 20 are blocked by the maximum load pressure detection path 212.
If the higher load pressure of the seven load pressures is introduced, as a result, the lower load pressure cannot be introduced.
As a result, during the combined driving of these actuators 206 and 207, the higher load pressure of these load pressures is always selected and guided to the maximum load pressure detection path 212. Reference numeral 213 is a pressure control valve called an unload valve, and 214 is a discharge pressure detection path that connects the tilt control device 202 and the main pipe 203, and guides the discharge pressure of the variable displacement hydraulic pump 201 to the tilt control device 202. Pressure control valve 21
3 does not operate the flow rate control devices 220 and 221 described below, thereby minimizing the discharge amount and discharge pressure of the variable displacement hydraulic pump 201 when the actuators 206 and 207 are not driven. It controls so that it saves power.

In the hydraulic drive circuit for performing such load sensing control, as described above, the means for distributing the pressure oil is not provided, and the main conduit 203 is branched into the branch conduits 203a, 20a.
When the hydraulic pressure is guided to the actuators 206 and 207 through the actuator 3b, the pressure oil tends to be guided to the actuator having a lower load.
A flow control device is provided as a means for appropriately distributing the pressure oil to 6, 207 to control the supply flow rate to the actuator. Therefore, the configuration of this flow control device will be described. 220 and 221 are the branch paths 203a,
Flow rate control devices 222 and 222 respectively provided in 203b.
Reference numeral 223 denotes an operation variable throttle section having a function of adjusting a supply flow rate to the actuator by being operated by an operation lever as a means for operating the construction machine, and 224 and 225 denote upstream sides of the respective operation variable throttle sections 222 and 223. Is a pressure compensator having a function of controlling the differential pressure across the throttles of the operation variable throttles 222 and 223 to a constant value. Each of the operation variable diaphragm sections 222 and 223 is operated by the operator operating the operation lever, and a predetermined diaphragm opening degree is given according to the operation amount. Flow controller 2
Reference numeral 20 includes an operation variable throttle section 222 and a pressure compensating section 224. The flow rate control device 221 includes an operation variable throttle section 2
23 and a pressure compensator 225. For these flow rate control devices 220 and 221, the operation variable throttle section 222 and the pressure compensating section 224, and the operation variable throttle section 223 and the pressure compensating section 225 are separately shown in FIG. However, in reality, they form an inseparable valve unit as an assembly of different functional parts. Reference numeral 226 denotes a signal conduit for opening the pressure compensating portion 224, which connects the first signal receiving portion of the pressure compensating portion 224 and the load conduit 204 via a part of the connecting conduit 208, and 227 denotes pressure compensation. The signal line 228 for closing the pressure compensator 224 connecting the second signal receiving part of the part 224 and the upstream line 215 of the variable throttle part 222 for operation is a spring as a differential pressure setting means. A preset amount of displacement is preset at the time of initial setting to open the oil passage of the pressure compensator 224. The signal line 226 for the opening operation is the load line 20.
The load pressure of No. 4 is guided to the first signal receiving portion of the pressure compensation unit 224, and a control force in the opening direction is applied together with the spring 228 so as to open a variable orifice provided in the pressure compensation unit 224. The signal pipe line 227 for closing operation guides the upstream pressure of the variable throttle portion 222 for operation to the second signal receiving portion of the pressure compensating portion 224, and applies a control force in the closing direction thereto. The pressure compensating section 224 adjusts the opening amount by the control force in the opening direction and the closing direction so that the differential pressure across the throttle of the operating variable throttle section 222 becomes a constant value set by the spring 228, as described later. It works to control. 229 is the pressure compensator 22
The signal pipe for opening the pressure compensating portion 225, which connects the first signal receiving portion of No. 5 and the load pipeline 205 via a part of the connecting pipeline 209 and guides the load pressure similarly to the signal pipeline 226. Road 2
Reference numeral 30 is a signal conduit for closing the pressure compensating portion 225, which is similar to the signal conduit 227 and connects between the second signal receiving portion of the pressure compensating portion 225 and the upstream conduit 216 of the operating variable throttle portion 223. Reference numerals 231 are springs similar to the spring 228, which are preset to open the oil passage of the pressure compensation unit 225.
The signal pipe line 229 for opening operation gives a control force in the opening direction to the pressure compensating part 225 together with the spring 231, and the signal pipe line 230 for closing operation gives a control force in the closing direction to the pressure compensating part 225. . Similar to the pressure compensator 224, the pressure compensator 225 functions as the pressure compensator 224 by adjusting the opening amount by the control force in the opening direction and the closing direction.

First, load sensing control will be described based on the hydraulic drive circuit described above.

Now, the variable displacement hydraulic pump 201 is operated and the operating variable throttles 222 and 223 are operated by the operator, so that the hydraulic pressure is the main pipe line 203 and each branch line 203.
a, 203b, and the respective load pipes 204, 205 are supplied to the actuators 206, 207, and if these pressures are used to drive them in combination, the higher load pressure of the actuators 206, 207, that is, the maximum The load pressure is from the pipe line on the highest load pressure side of the load pipe lines 204, 205 to the connecting pipe line 20 corresponding to this pipe line.
It is guided to the maximum load pressure detection path 212 through one of the Nos. 8 and 209, and then to the tilt control device 202. on the other hand,
The discharge pressure of the variable displacement hydraulic pump 201 is also determined by the main pipeline 20.
3 through the discharge pressure detection path 214, the tilt control device 202
Be led to. Then, the displacement control device 202 has means for controlling the displacement of the variable displacement hydraulic pump 201 based on these pressure signals, so that the discharge pressure of the variable displacement hydraulic pump 201 is set to the maximum load pressure. The displacement of the pump 201 is controlled so as to decrease the discharge capacity of the pump 201 when the value is higher than the value obtained by adding the so-called load sensing differential pressure, and to increase it when the value is low. As a result, in the variable displacement hydraulic pump 201, the discharge capacity is controlled so that the discharge pressure becomes higher than the maximum load pressure by a predetermined specified value, and so-called load sensing control is performed. When only one of the actuators 206 and 207 is independently driven, the load pressure of the independently driven actuator becomes the maximum load pressure, and the same control is performed.

Next, the operation of the flow rate control device of the first conventional example will be described based on the hydraulic drive circuit of FIG. 10 for performing such load sensing control.

Now, assuming that the load sensing control is performed and the actuators 206 and 207 are driven in combination, the load pressures in the load pipes 204 and 205 are transmitted through the signal pipes 226 and 229 to the pressure compensating units. 224,
225 are respectively guided to the first signal receiving portions of
8, 231 provides a control force in the opening direction, while the upstream pressure of each operation variable throttle section 222, 223 passes through each signal conduit 227, 230 to the second signal receiving section of each pressure compensating section 224, 225. Each of them is guided to give control force in the closing direction. Then, when the upstream pressure of the operating variable throttle portions 222, 223 becomes higher than a predetermined value in consideration of the load pressure and the spring force, the control force in the closing direction is strengthened accordingly and the opening of the pressure compensation valves 224, 225 is increased. Immediately before reducing and closing the opening, the upstream pressure of the variable throttle units 222 and 223 for operation is almost equal to the sum of the load pressure and the spring force. As a result, the differential pressure across the operating variable throttles 222 and 223 is obtained by subtracting the load pressure, which is the downstream pressure of the operating variable throttles 222 and 223, from the upstream pressure of the operating variable throttles 222 and 223. The value is the value corresponding to the spring force. In such a state, if the load pressure increases or the upstream pressure of the variable throttle units 222 and 223 for operation decreases, the control force of the pressure compensating valves 224 and 225 in the opening direction relatively increases and the opening increases. The variable throttle section 22 for operation
The opening amount is self-adjusted so as to increase the upstream pressure of 2,223. Further, when the load pressure or the upstream pressure tries to return to the original state again, the control force in the closing direction relatively increases and the opening is reduced, so that the upstream pressure of the variable throttle units 222 and 223 for operation is reduced. Self-adjust the opening amount. As described above, in the pressure compensators 224 and 225, the signal lines 226 and 229 are used.
The control force in the opening direction due to the load pressure applied through the control valve and the control force in the closing direction due to the upstream pressure of the variable throttle portions 222 and 223 for operation applied via the signal conduits 227 and 230 cooperate to control the upstream pressure. The load pressure is changed according to the change and self-adjustment is performed so that the pressure difference between the two is constant, and the springs 228 and 231 play a role of setting the pressure difference to a predetermined value. . Thus, the variable throttle unit 22 for operation
The upstream pressure of 2,223 is always maintained at a pressure higher than the load pressure by the amount corresponding to the spring force by the pressure adjusting function of the pressure compensating valves 224,225. Therefore, the pressure difference across the throttles 222 and 223 for operation can be compensated by the pressure compensating valves 224 and 225 so as to be always constant regardless of the load pressure. As a result, the operation variable diaphragm units 222 and 223 are operated by the actuator 20.
The flow rate of the pressure oil supplied to the actuators 206 and 207 is adjusted to be constant according to the throttle opening degree without being influenced by the load pressures of the actuators 6 and 207. The operating speed of 207 is also kept constant.

In order to explain this more accurately, the pressure compensating units 224 and 225 are expressed as mathematical expressions.
In this way, in this way, the operation variable diaphragm units 222, 2
The differential pressure between the upstream pressure of 23 and the actuators 206 and 207 is controlled to be equal to the biasing force due to the displacement of the springs 228 and 231. Is substantially equal to the differential pressure across the throttles of the operating variable throttle portions 222 and 223, and thus can be expressed by the equation (1).

[0012] _{a (Pz i -Pl i) =} k i (xo i + x i) ∴Pz i -Pl i = (xo i + x i) k i / a = ΔPv i ‥‥‥‥‥‥‥‥‥ ( 1) The meaning of each symbol in these formulas is as follows.

Pz _i ; variable aperture sections 222, 22 for each operation
3 upstream pressure (secondary pressure of each pressure compensating portion 224, 225) Pl _i ; Downstream pressure of each operation variable throttle portion 222, 223 (load pressure of each actuator 206, 207) a; Pz _i , Pl _i Each pressure compensator 224,22
5 pressure receiving area k _i ; spring constant xo _i ; each spring 228, 231 given at the time of initial setting
Displacement x _i of each spring 22 generated by applying a control force
Displacement amount of 8, 231 ΔPv _i ; Differential pressure before and after throttling of each operation variable throttle section 222, 223 On the other hand, discharge of the variable displacement hydraulic pump 201 that supplies pressure oil to the upstream side of the operation variable throttle section 222, 223 Pressure Ps
Is controlled by the load sensing control to be higher than the maximum load pressure Plmax by a predetermined value, that is, the load sensing differential pressure ΔP _LS , as shown in the following equation (2).

Ps = Plmax + ΔP _LS (2) That is, the discharge pressure Ps of the variable displacement hydraulic pump 201.
Is controlled to always maintain a constant load sensing differential pressure ΔP _LS by load sensing control.
This load sensing differential pressure ΔP _LS is set so as to generally follow (3) below.

ΔP _LS = ΔPv _i (3) Then, the differential pressure across the throttles of the operating variable throttle sections 222 and 223 is the actuator in both the maximum load pressure side and the low load pressure side. The load sensing differential pressure Δ is almost not affected by the circuit pressure such as the load pressure of 206 and 207 or the discharge pressure of the variable displacement hydraulic pump 201.
A pressure equal to P _LS will be maintained. As a result, the passage flow rate Qv _i ′ in the variable throttle units 222 and 223 for operation
Can be set to a value proportional to the throttle opening degree given to each operation variable throttle section 222, 223 without being affected by the circuit pressure, as shown in the following equation (4). If the degree is constant, a constant value can always be maintained.

[0016] _{Qv i '= N · A i} √ (Pz i -Pl i) = N · A i √ (ΔPv i) = N · A i √ (ΔP LS) ‥‥‥‥ (4) In addition, this ( The meanings of the symbols used in the equation 4) other than the symbols already described are as follows.

Qv _i ′; Variable throttle parts 222, 2 for each operation
Opening N aperture of each operating variable throttle 222 and 223; flow rate through A _i at 23 when the hydraulic circuit diagram explaining about the second conventional example on the basis of a constant 11, the hydraulic drive circuit of the second conventional example, Variable displacement hydraulic pump 201, main conduit 203, branch conduit 203
a, 203b, and a plurality of one-way actuated actuators 206, 207 driven by the hydraulic pressure of the variable displacement hydraulic pump 201 supplied through the load pipelines 204, 205, these actuators 206, 20
The maximum load pressure of the load pressures of 7 is the maximum load pressure detection path 21.
2 to detect the discharge pressure of the variable displacement hydraulic pump 201 through the tilt control device 2 according to the pressure signals of the detection path 212 and the discharge pressure detection path 214 so that the discharge pressure of the variable displacement hydraulic pump 201 becomes higher than the maximum load pressure by a predetermined value. The point that the discharge capacity of 201 is controlled to perform load sensing control. A hydraulic drive circuit for performing such load sensing control is provided with a flow rate control device including a variable throttle portion for operation and a pressure compensating portion. In this respect, there is no difference in the basic configuration from the hydraulic drive circuit of the first conventional example, and only the configuration relating to the flow control device is different from the hydraulic drive circuit of the first conventional example. Therefore, regarding the hydraulic circuit diagram relating to the second conventional example, only the flow rate control device will be described.

In FIG. 11, reference numerals 240 and 241 are flow control devices provided in the respective branch paths 203a and 203b, and reference numerals 242 and 243 have a function of operating the operation lever to adjust the flow rate supplied to the actuator. Similar to the variable diaphragm units 222 and 223, the variable diaphragm units for operation 244 and 245 are the variable diaphragm units 222 and 223 for operation.
The pressure compensating unit is similar to the pressure compensating units 224 and 225 and is disposed on the downstream side of the H.223, and has a function of controlling the differential pressure across the throttles of the operating variable throttle units 242 and 243 to a constant value. The flow rate control device 240 includes the variable flow restrictor 242 and the pressure compensator 244 for controlling the flow rate control device 24.
1 is composed of an operation variable throttle section 243 and a pressure compensating section 245, respectively, and in that it is composed of an operation variable throttle section and a pressure compensating section, the flow rate control devices 220 and 22 of the first conventional example.
There is no difference from 1. These flow rate control devices 240, 241
Is similar to the flow control devices 220 and 221 of the first conventional example.
It forms the valve unit. Reference numeral 246 denotes a signal pipe line for closing the pressure compensating unit 244, which connects the first signal receiving unit of the pressure compensating unit 244 and the maximum load pressure detecting line 212 via a part of the connecting pipe line 208. Pressure compensator 24
The signal line 248 for opening the pressure compensating part 244 connecting between the second signal receiving part 4 and the downstream line 217 of the variable throttle part 242 for operation sets the pressure compensating part 244 to the closed state. A spring for this purpose is preset so as to close the oil passage of the pressure compensator 244 by giving a slight amount of displacement at the time of initial setting. The signal pipe line 246 for closing operation guides the maximum load pressure of the maximum load pressure detection line 212 to the first signal receiving part of the pressure compensating part 244 so as to close a variable orifice provided in the pressure compensating part 224. In addition, a control force in the closing direction is applied together with the spring 248. The signal line 247 for the opening operation is
The downstream pressure of the variable throttle portion 242 for operation is guided to the second signal receiving portion of the pressure compensating portion 244 and a control force in the opening direction is given to this. The pressure compensating unit 244 functions to control the opening amount by the control force in the closing direction and the opening direction to control the differential pressure across the throttle of the operation variable throttle unit 242 to a constant value as described later. Numeral 249 is a pressure compensating section for connecting the first signal receiving section of the pressure compensating section 245 and the maximum load pressure detecting path 212 via a part of the connecting conduit 209 to guide the maximum load pressure like the signal conduit 246. 245 is a signal line for closing operation, 250 is a second signal receiving part of the pressure compensating part 245 and the variable throttle part 2 for operation.
Signal line 24 connecting between 43 and the downstream line 218.
A signal line for opening the pressure compensator 245, which is similar to that of No. 7, 2
Reference numeral 51 is a spring similar to the spring 248, which is preset to close the oil passage of the pressure compensation unit 245. The signal pipe line 249 for closing operation gives a control force in the closing direction to the pressure compensating portion 245 together with the spring 251, and the signal pipe line 250 for opening operation gives a control force in the opening direction to the pressure compensating portion 245. . Similar to the pressure compensating unit 244, the pressure compensating unit 245 adjusts the opening amount by the control force in the closing direction and the opening direction, and functions similarly to the pressure compensating unit 244.

The operation of the second conventional flow control device will be described.

Assuming that the load sensing control is performed and the actuators 206 and 207 are driven in combination, the maximum load pressure of the maximum load detection path 212 is passed through the signal lines 246 and 249 to the pressure compensating sections 244 and 244. Two
45 are respectively guided to the first signal receiving portions, and the springs 248,
251 is applied together with the control force in the closing direction.
The second of each pressure compensator 244, 245 through 7,250
The control force in the opening direction is applied by being guided to the signal receiving portions. Then, when the downstream pressure of the variable throttle portions for operation 242, 243 becomes higher than a predetermined value in consideration of the maximum load pressure and some spring force, the control force in the opening direction is strengthened accordingly, and the pressure compensating portions 244, 245 are provided. Enlarge the opening of actuator 2
A hydraulic pressure of a pressure value sufficient to drive these is supplied to 06 and 207. In such a state, if the maximum load pressure decreases, the variable throttle units 242, 243 for operation are operated.
If the downstream pressure of the pressure rises further, the pressure compensators 244, 2
The reference numeral 45 self-adjusts the opening amount so as to further expand the opening to reduce the downstream pressure, and conversely, when the maximum load pressure increases or the downstream pressure is about to decrease, the opening is reduced and the downstream pressure decreases. The amount of opening is self-adjusted so as to increase. Thus, the downstream pressures of the variable throttle portions 242, 243 for operation are controlled by the pressure compensation functions of the pressure compensating portions 244, 245 such as the load pressure of the actuators 206, 207 and the discharge pressure of the variable displacement pump 201. The pressure slightly higher than the maximum load pressure is always maintained without being affected by the pressure fluctuation. That is, the operation variable diaphragm units 242, 2
The differential pressure across the throttle 43 is influenced by the opening degree of the variable throttle portions 242 and 243 for operation and the load fluctuation of the actuators 206 and 207 together with the control of the discharge pressure of the variable displacement hydraulic pump 201 by the load sensing control. Pressure compensation is performed so that the pressure is always constant. As a result, the variable throttle units 242, 243 for operation can adjust the flow rate constantly according to the throttle opening degree without being affected by the fluctuation of the circuit pressure.

Therefore, in order to explain this more accurately, the pressure compensating portions 244 and 245 are first provided with the downstream pressure Pz of the operating variable throttle portions 242 and 243 disposed upstream thereof. _i is controlled so as to follow the equation (1).

Pz _i = Plmax + k _i / a (Zo _i + Z _i ) = Plmax + Co _i ................................................ (5) The symbols in the equation (5) have the following meanings.

Pz _i ; variable aperture parts 242, 24 for each operation
3 downstream pressure (primary pressure of each pressure compensator 244, 245) Plmax; maximum load pressure a; pressure compensator 244, 2 for Plmax, Pz _i
45 pressure receiving area k _i ; spring constant Zo _i ;
Amount of displacement Z _i ; displacement amount of each spring generated by applying control force Co _i ; constant Co _i in the equation (5) is the biasing force k _i / a (Zo _i + Z _i ) of the springs 248 and 251. Is regarded as a constant and replaced. The biasing force of the springs 248 and 251 is
In this second conventional example, a slight amount of displacement is applied at the time of initial setting to set the pressure compensating units 244, 245 to the closed state, and the downstream pressure of the variable throttle units 242, 243 for operation is kept slightly higher than the maximum load pressure. The pressure compensating portions 244 and 245 are adjusted to such a small value that they can be almost ignored. Therefore, in the pressure compensating portions 244 and 245, the downstream pressure Pz _{i of the} operation variable throttle portions 242 and 243 is adjusted. Is controlled to be approximately equal to the maximum load pressure Plmax. On the other hand, the discharge pressure Ps of the variable displacement hydraulic pump 201 that supplies pressure oil to the upstream side of the variable throttle units 242 and 243 for operation is determined by the load sensing control as shown in the equation (2). The discharge pressure Ps is controlled to be Plmax + ΔP _LS , which is higher than the load sensing differential pressure ΔP _LS than Plmax.
a, 203b are sent to the operation variable diaphragm sections 242, 24
3 upstream pressure. Then, each flow control device 24
In a state in which an arbitrary opening degree is given to the operation variable throttle units 242 and 243 of 0 and 241, the differential pressure Ps-Pz between the upstream pressure and the downstream pressure of each operation variable throttle unit 242 and 243.
_i is the following (6) from the equations (2) and (5).
As shown in the equation, a constant value that is close to the load sensing differential pressure ΔP _LS is always maintained.

Ps−Pz _i = (Plmax + ΔP _LS ) − (Plmax + Co _i ) = ΔP _LS −Co _i ≈ΔP _LS (6) That is, In each of the variable throttle parts on the maximum load pressure side and the low load pressure side, the pressure is controlled and pressure-compensated by the pressure compensating parts 244 and 245 so that the pressure substantially equal to the load sensing differential pressure ΔP _LS is always maintained. As a result, as shown in the following expression (7), the variable throttle units for operation 242, 24
The passage flow rate Qv _i ′ in No. 3 is not affected by the fluctuation of the circuit pressure, and the variable throttle valves for operation 242, 243 are operated.
It becomes possible to make the value proportional to the aperture opening given to the above, and if the aperture opening is constant, it is possible to always keep a constant value.

Qv _i ′ = N · A _i √ (Ps−Pz _i ) = N · A _i √
(ΔP _LS ) ····························································································· (7).

Qv _i ′; Variable throttle parts 242, 2 for each operation
Flow rate A _{i at} 43; throttle opening degree of each variable throttle portion 242 and 243 for operation N; constant The hydraulic drive circuits of the first conventional example and the second conventional example shown in FIGS. In each case, each actuator 206, 207 is provided with only one load conduit 204, 205, and
Although it can only be operated in two directions, in a hydraulic drive circuit of a construction machine such as a hydraulic excavator or a hydraulic crane, it is necessary to allow the actuator to be operated in two directions. Therefore, the hydraulic drive circuits of the third conventional example and the fourth conventional example in which the actuator can be operated in two directions will be described below with reference to FIGS. 12, 13 and 14.

First, the hydraulic circuit diagram of the third conventional example will be described with reference to FIGS. The hydraulic drive circuit of the third conventional example is the hydraulic drive circuit of the first conventional example modified so that the actuators 206 and 207 can be operated in two directions. The hydraulic drive circuit of the third conventional example includes a variable displacement hydraulic pump 201, a main pipe line 203, and a branch line 2.
03a, 203b, and a plurality of actuators 206, 207 driven by the hydraulic pressure of the variable displacement hydraulic pump 201 supplied through the load pipelines 204, 205. The highest load pressure among them is detected by the highest load pressure detection path 212, and the discharge pressure of the variable displacement hydraulic pump 201 is determined by the pressure signals of the detection path 212 and the discharge pressure detection path 214 through the tilt control device 202. The discharge capacity of the pump 201 is controlled so as to be higher by a predetermined value than the above, and load sensing control is performed. In the hydraulic drive circuit for performing such load sensing control, an operation variable throttle unit and It is arranged on the upstream side of this variable throttle for operation,
Control force in the opening and closing directions is applied by load pressure, spring force, and upstream pressure of the variable throttle for operation to adjust the opening amount, and the differential pressure across the throttle of the variable throttle for operation is controlled to a constant value. There is no difference in the basic configuration from the hydraulic drive circuit of the first conventional example in that a flow rate control device including the pressure compensating units 224 and 225 is provided, and the flow rate is higher than that of the hydraulic drive circuit of the first conventional example. The only difference is the configuration relating to the variable throttle portion for operation and the load conduit of the control device. Therefore, the third
Regarding the hydraulic circuit diagram of the conventional example, only the configuration relating to these parts will be described in detail.

Referring to FIG. 12, the configuration relating to the load conduit will be described. 204a and 204b connect the bottom side and rod side of the actuator 206 to the directional control valve 272 of the flow rate control device, respectively, and connect the oil path for driving the actuator 206. Forming a pair of load conduits 5a and 205b, which connect the bottom side and rod side of the actuator 207 to the directional control valve 273 of the flow control device.
It is a pair of load pipelines similar to 4b. Each of the pair of load pipelines 204a, 204b, 205a, 205b supplies the pressure oil whose flow rate is adjusted by each flow rate control device to each of the actuators 206, 207 through one of them, and at that time, the inside of each actuator 206, 207 Drain the pressure oil through the other. The hydraulic drive circuit of the third conventional example is such a pair of load conduits 204a, 204b, 205a.
By arranging 05b, each actuator 20
6,207 can be operated in two directions up and down in desired directions. Actuator 20 that operates in such two directions
In order to be able to control 6, 207, it is necessary to modify the flow rate adjusting device, in particular, the part corresponding to the variable throttle and its operating mechanism. The configuration relating to this point will be outlined based on FIGS. 12 and 14. 270 and 271 are hydraulic pilot operating devices that output pilot pressure by operating the operating lever, and 272 and 273 are output from the hydraulic pilot operating devices 270 and 271. It is a closed center type directional control valve for two-way drive of a hydraulic pilot operation type that is operated by each pilot pressure. The variable throttle parts 222, 223 for operation in the first conventional example and the operation in the second conventional example are used. This is a portion corresponding to the variable diaphragm portions 242 and 243. These directional control valves 272, 273
Is switched depending on the operating direction of the operating lever of each hydraulic pilot operating device 270, 271, and the opening amount is adjusted according to the operating amount of each operating lever. Third
In the conventional hydraulic drive circuit, each actuator 2
The flow control devices 06 and 207 include the hydraulic pilot operating device 270 and the directional control valve 272 and the pressure compensating unit 224, and the hydraulic pilot operating device 271 and the directional control valve 273 and the pressure compensating unit 225, respectively. Direction control valves 272 of the pressure compensators 224 and 225
Looking at the arrangement with respect to 273, each pressure compensating portion 224, 225 has a respective directional control valve 27, similar to the arrangement with respect to the variable throttle portions 222, 223 for operation in the first conventional example.
It is arranged on the upstream side of 2,273.

Referring to FIG. 14, the hydraulic pilot operating device 2
Describing the configuration of 70 and 271 in detail, P is a pilot pump as a pilot pressure generation source, and 270a is a control lever 270c to which the pressure oil of the pilot pump P is introduced.
Is operated in the direction of the arrow L to output the pilot pressure P _1, and the pressure reducing valve 270b outputs the pilot pressure P ₂ by operating the operating lever 270c in the direction of the arrow R. The pressure reducing valves 270d and 270e are the same. Pressure reducing valve 27
0a and 270b are pilot conduits that lead the pilot pressures P ₁ and P ₂ output to the signal receiving portions of the directional control valve 272, respectively. The hydraulic pilot operating device 270 operates the pressure reducing valve 270a or the pressure reducing valve 270b via the spring 270f or the spring 270g by operating the operating lever 270c in the arrow L direction or the arrow R direction, and the pilot valve is operated from one of the pressure reducing valves. The pilot pressure P ₁ or the pilot pressure P is applied to the pipeline 270d or the pilot pipeline 270e.
Output ₂ Hydraulic pilot operating unit 271 is also pressure reducing valve 270a for outputting a pilot pressure P _3, P ₄ by operating the operation lever 271c directed pressure oil of the pilot pump P, a 270b, the respective pilot pressure P _3,
It is provided with pilot conduits 271d and 271e for guiding P ₄ to the respective signal receiving portions of the directional control valve 273, and has the same configuration as the hydraulic pilot operating device 270. Therefore, like the hydraulic pilot operating device 270, by operating the operating lever 271c in the arrow L direction or the arrow R direction, the pressure reducing valve 271a or 271b is operated via the spring 271f or the spring 271g, and one of the pressure reducing valves is operated. Outputs the pilot pressure P ₃ or the pilot pressure P ₄ to the pilot pipe line 271d or the pilot pipe line 271e. Further, the hydraulic pilot operating device 270 and the hydraulic pilot operating device 271 are respectively provided with the operating lever 2
70c and the operating lever 271c operation amount, the springs 270f and 270g and the springs 271f and 271g are changed in displacement amount to set the secondary pressure of the pressure reducing valves 270a and 270b and the pressure reducing valves 271a and 271b to arbitrary values. Therefore, the pilot pipe lines 270d and 270e and the pilot pipe line 271 can be changed according to the respective operation amounts.
It is possible to adjust the pilot pressures P ₁ and P ₂ and the pilot pressures P ₃ and P ₄ output to the d and 271e, respectively, and to output the pilot pressure of a desired value.

Next, the configuration of the directional control valves 272 and 273 will be described in detail. The directional control valve 272 and the directional control valve 2 will be described.
Reference numeral 73 is a variable aperture section 222, 223 for operation of the first conventional example.
Variable throttle parts 222a, 22 for operation having the same function as
2b and operating variable diaphragm portions 223a and 223b are incorporated respectively. When the operating lever 270c of the hydraulic pilot operating device 270 is operated in the L direction, the directional control valve 272 is switched from the neutral position in the figure to the 1 position by the pilot pressure P ₁ , and when the operating lever 270c is operated in the R direction, the pilot control valve 272 is operated. R from the neutral position in the figure due to pressure P ₂
Switched to position. The directional control valve 273 also operates the operating lever 271c of the hydraulic pilot operating device 271 in the L direction,
When operated in the R direction, the pilot pressures P ₃ and P ₄ are switched to the 1 position and the r position, respectively, like the direction control valve 272. When the directional control valves 272 and 273 are switched to the 1 position, the upstream conduits 215 and 216 are routed through the respective operating variable throttle portions 222a and 223a.
To communicate with the respective one of the load pipes 204a and 205a, and the pressure oil of the variable displacement hydraulic pump 201 is supplied to the bottom side of each of the actuators 206 and 207. At the same time, the other load pipes 204b and 205b are respectively communicated with the tank ports so that the actuators 206 and 2 are connected.
The pressure oil on the rod side of 07 is released to the tank, thus driving the actuators 206 and 207 upward. When the position is switched to the r position, each directional control valve 27
2, 273 of the variable diaphragm portions 222b, 2 for operation respectively
The upstream pipelines 215, 216 are respectively connected to the respective one of the load pipelines 204b, 205b via 23b, so that the pressure oil of the variable displacement hydraulic pump 201 is supplied to each actuator 20.
Supply to the rod side of 6,207. At the same time, the other load pipes 204a, 205a are respectively connected to the tank ports to allow the pressure oil on the bottom side of each actuator 206, 207 to escape to the tank.
Drive 06 and 207 downward. In that case, the directional control valve 272 and the directional control valve 273 are the values of the pilot pressures P ₁ and P ₂ and the pilot pressures P ₃ and P ₄ output from the hydraulic pilot operating device 270 and the hydraulic pilot operating device 271, that is, the operating lever. 270c and operating lever 27
The movement amount of the spool is adjusted according to the operation amount of the 1c in the L direction and the R direction, and the opening amount thereof, that is, the variable diaphragm 222.
A, 222b and the respective aperture openings of the variable apertures 223a, 223b are set.

Since the hydraulic drive circuit of the third conventional example has such a configuration, the hydraulic pilot operating device 27
0, 271 are simultaneously operated by the operation levers 270c, 271c, the directional control valves 272, 273 are operated by the operation lever 2
The position is switched to the 1 position or the r position according to each operation direction of 70c and 271c, and the aperture opening of the operation variable aperture section is adjusted according to each operation amount. Then, the pressure oil introduced from the variable displacement hydraulic pump 201 to the respective branch pipelines 203a and 203b through the main pipeline 203 is
The variable throttle portion 222 for operating the directional control valve 272, respectively.
a, 222b and one of the variable throttle portions 223a, 223b for operation of the directional control valve 273, and the one of the pair of load pipelines 204a, 204b and one of the pair of load pipelines 205a, 205b. Each actuator 2
It is supplied to the bottom side or rod side of 06, 207 at a flow rate according to the opening amount. At the same time, each actuator 20
The pressure oil stored on the other side of 6, 207 is discharged to the tank through the other load pipeline. As a result, the actuators 206 and 207 are combinedly driven and driven in the forward and reverse predetermined directions according to the respective operating directions of the operating levers 270c and 271c, and at the same time, the operating levers 270c and 271.
It is driven at a predetermined speed according to each operation amount of 1c. In that case, the variable throttle portion 222a for operating the directional control valve 272,
222b and variable throttle portion 22 for operating the directional control valve 273
Similarly to the hydraulic drive circuit of the first conventional example, the pressure compensating section 224 and the pressure compensating section 2 are provided on the upstream side of 3a and 223b.
25 is arranged and the load sensing control is performed.
In addition, the differential pressure across the throttle of the operating variable throttle portions 223a and 223b that is operating is the actuator 20 regardless of the throttle portion on the maximum load pressure side or the low load pressure side.
The pressure substantially equal to the load sensing differential pressure ΔP _LS is maintained regardless of fluctuations in the circuit pressure such as the load pressure of 6,207 and the discharge pressure of the variable displacement hydraulic pump 201. As a result, the variable diaphragm units 222a, 222b, 223a for operation,
The passage flow rate Q _i in 223b can be changed in proportion to the throttle opening degree given to each operation variable throttle portion without being affected by the fluctuation of the circuit pressure, and the actuators 206 and 207 are always operated. Operating levers 270c, 271
It is possible to drive at a speed according to the operation amount of c.

Next, the hydraulic circuit diagram of the fourth conventional example will be described with reference to FIGS. 13 and 14. The hydraulic drive circuit of the fourth conventional example is a modification of the hydraulic drive circuit of the second conventional example so that the actuators 206 and 207 can be operated in two directions. The hydraulic drive circuit of the fourth conventional example includes a variable displacement hydraulic pump 201, a main pipe line 203, and a branch line 2.
03a, 203b, and a plurality of actuators 206, 207 driven by the hydraulic pressure of the variable displacement hydraulic pump 201 supplied through the load pipeline, the highest of the load pressures of these actuators 206, 207. The load pressure is detected by the maximum load pressure detection path 212, and the detection path 2 is detected.
12 and the pressure signal of the discharge pressure detection path 214 are used to control the discharge capacity of the variable displacement hydraulic pump 201 through the tilt control device 202 so that the discharge pressure of the variable displacement hydraulic pump 201 becomes higher than the maximum load pressure by a predetermined value. The point that load sensing control is performed is that the hydraulic drive circuit that performs such load sensing control is arranged with the variable throttle portion for operation and the downstream side of this variable throttle portion for operation. A pressure compensating unit 244 for controlling the opening amount by controlling pressures in the closing direction and the opening direction by the downstream pressures of the operation variable throttle unit and controlling the differential pressure across the throttle of the operation variable throttle unit to a constant value. , 245, there is no difference in the basic configuration from the hydraulic drive circuit of the second conventional example, and the flow control device of the second conventional example is different from that of the hydraulic drive circuit of the second conventional example. Action variable throttle portion, the pressure compensator 24
The only difference is the configuration of the pipelines around 4,245 and the load pipelines. Further, as compared with the hydraulic drive circuit of the third conventional example, each actuator 206, 207 is provided with a pair of load pipelines 204a, 204b, 205a, 205b, and the flow control device of each actuator 206, 207 is a hydraulic pilot. There is no difference in the basic configuration in that it is composed of an operating device, a directional control valve, and a pressure compensator, and because the pressure compensator is provided on the downstream side of the directional control valve, the pipe around the pressure compensator is The only difference is the configuration of the path and directional control valve. Therefore, regarding the hydraulic circuit diagram of the fourth conventional example, only these configurations will be described in detail below.

The configuration of the pipes around the pressure compensator will be described. The primary side of the pressure compensators 244 and 245 is provided with a directional control valve having the function of a variable throttle for operation via the downstream pipes 217 and 218. 274,275 connected to the second
The hydraulic drive circuit of the conventional example is aligned with the hydraulic drive circuit, but the secondary side of the hydraulic drive circuit is again provided with the directional control valve 2 via the pipe lines 252 and 253.
It is connected to the devices 74 and 275 and employs a configuration that is not found in any hydraulic drive circuit of the conventional example. To describe the configuration of the directional control valve, the directional control valve 274 and the directional control valve 275 are the variable throttle portions 242 for operation of the second conventional example.
A variable aperture section 242 for operation having the same function as 243.
a, 242b and operating variable diaphragm portions 243a, 243b
Each has a built-in. Direction control valves 274,275
Is a closed center type directional control valve for two-way drive of a hydraulic pilot operating system, similar to the directional control valves 272 and 273 of the third conventional example.
When the operating levers 270c and 271c of the 271 are operated in the L direction, the pilot pressures P ₁ and P ₃ are respectively switched from the neutral position to the 1 position as in the direction control valves 272 and 273 of the third conventional example. , Their operating levers 27
When 0c and 271c are operated in the R direction, the pilot pressures P ₂ and P ₄ are switched from the neutral position in the figure to the r position. When the directional control valves 274 and 275 are switched to the 1 position, the operation variable throttle portions 242a and 242 are respectively operated.
3a, the branch pipes 203a, 203b are connected to the downstream pipes 217, 218, respectively, and the pipes 252, 253 are connected to the load pipes 204a, 205a, respectively. Pressure oil is supplied to the bottom side of each actuator 206, 207. At the same time, the other load pipes 204b and 205b are respectively communicated with the tank ports so that the actuators 206 and 2 are connected.
The pressure oil on the rod side of 07 is released to the tank, thus driving the actuators 206 and 207 upward. When the position is switched to the r position, each directional control valve 27
4,275 operating variable diaphragm portions 242b, 2
The branch pipes 203a and 203b are respectively connected to the downstream pipe lines 217 and 218 via 43b, and the pipe lines 252 and 253 are connected to the load pipe lines 204b and 205b, respectively. Pressure oil is supplied to the rod side of each actuator 206, 207. At the same time, the other load pipes 204a and 205a are respectively communicated with the tank ports so that the actuators 206 and 2 are connected.
The pressure oil on the bottom side of 07 is released to the tank, thus driving each actuator 206, 207 downward. In that case, the direction control valves 274, 275 are similar to the direction control valves 272, 273 of the third conventional example, and the operation levers 270c, 2
The moving amount of the spool is adjusted according to the operation amount of the 71c in the L direction and the R direction, and the opening amount thereof, that is, the operation variable diaphragm units 242a and 242b and the operation variable diaphragms 243a and 243a, 2
Each throttle opening degree of 43b is set.

Since the hydraulic drive circuit of the fourth conventional example has such a structure, the hydraulic pilot operating device 27
0, 271 are simultaneously operated by the operation levers 270c, 271c, the directional control valves 274, 275 move the operation lever 2
The position is switched to the 1 position or the r position according to each operation direction of 70c and 271c, and the aperture opening of the operation variable aperture section is adjusted according to each operation amount. In that case, if the directional control valves 274, 275 are switched to the 1 position, the pressure oil guided from the variable displacement hydraulic pump 201 to the respective branch pipe lines 203a, 203b is respectively supplied to the directional control valves 274, 275. Variable throttle unit 242 for operation
a, 243a passing through the openings of the downstream pipes 217, 21
Guided to 8. The pressure oil guided to each of the downstream pipelines 217 and 218 is controlled to a prescribed pressure and each pressure compensating section 24.
4, 245, and the load pipes 204a, 20 from the pipes 252, 253 through the direction control valves 274, 275.
5a, and is supplied to the bottom side of each actuator 206, 207 at a flow rate according to the opening amount. at the same time,
The pressure oil accumulated on the rod side of each actuator 206, 207 is discharged to the tank from the load pipes 204b, 205b through the tank ports of the directional control valves 274, 275. If the directional control valves 274 and 275 are switched to the r position, the variable displacement hydraulic pump 20
The pressure oil guided from 1 to the branch pipes 203a and 203b passes through the openings of the variable throttle portions 242b and 243b for operation of the directional control valves 274 and 275, respectively, and is guided to the downstream pipes 217 and 218. . Each of these downstream pipelines 217, 2
The pressure oil guided to 18 passes through the pressure compensating units 244 and 245 while being controlled to a prescribed pressure, and the pipelines 252 and 253.
Through the direction control valves 274 and 275 to the respective load pipelines 20.
4b, 205b, each actuator 206,
It is supplied to the rod side of 207 at a flow rate according to the opening amount. At the same time, the pressure oil accumulated on the bottom side of each actuator 206, 207 is transferred to the load pipelines 204a, 205.
It is discharged from a through the tank port of each directional control valve 274, 275 to the tank.

Therefore, the actuators 206, 20
7 is the operation lever 2 as in the hydraulic drive circuit of the third conventional example.
70c and 271c are driven in predetermined forward and backward directions according to the respective operating directions, and the operating levers 270c and 271c are also driven.
Is driven at a predetermined speed according to each operation amount. In that case, the variable throttle portions 242a, 242a, 2 for operating the directional control valve 274 are operated.
42b and variable throttle 243 for operating the directional control valve 275
The pressure compensating section 244 and the pressure compensating section 24 are respectively provided on the downstream side of a and 243b similarly to the hydraulic drive circuit of the second conventional example.
5 is arranged and the load sensing control is performed, the operation variable diaphragm units 242a, 242b,
The passing flow rate Qv _i ′ at 243a and 243b can be changed in proportion to the throttle opening degree given to each operation variable throttle portion without being affected by the fluctuation of the circuit pressure,
The actuators 206 and 207 are always operated by the operation lever 2
It is possible to drive at a speed according to the operation amount of 70c, 271c.

The above-mentioned third shown in FIG. 12 to FIG.
Both the hydraulic drive circuits of the conventional example and the fourth conventional example are capable of operating two actuators in two directions. For example, a hydraulic excavator or a hydraulic crane can perform such two-direction operation. It is necessary to provide many actuators. Since increasing the number of actuators requires a large flow rate in this way, a plurality of hydraulic pumps should be installed, and the pressure oils of the hydraulic pumps should be combined appropriately and supplied to each actuator. Is required. Thus, an example of a hydraulic drive circuit of a hydraulic excavator in which a plurality of actuators can be operated in two directions by arranging pressure oils of a plurality of hydraulic pumps to be supplied to the actuators in this way is illustrated. 15 shows a fifth conventional example, and the technical contents thereof will be described below with reference to FIG. The hydraulic drive circuit of the fifth conventional example is basically the same as the hydraulic drive circuits of the first conventional example to the fourth conventional example, but the specific configuration thereof is a variable displacement hydraulic pump or actuator. However, when assigning the reference numerals to the configuration, all the explanations will be given with new reference numerals regardless of those of the conventional examples.

In the hydraulic drive circuit of the fifth conventional example, in the hydraulic drive circuit of the fourth conventional example, two variable displacement hydraulic pumps are installed, and the pressure oils of the hydraulic pumps are merged and supplied to the actuator. This corresponds to a configuration in which a large number of actuators are modified so that they can operate in two directions. The outline of the configuration of the hydraulic drive circuit of the fifth conventional example will be described with reference to FIG. 15. The hydraulic drive circuit of the fifth conventional example relates to a hydraulic excavator, and includes a swing hydraulic motor 31, an arm cylinder 32, and a boom cylinder as actuators. 33, a bucket cylinder 34, a first traveling motor 35, and a second traveling motor 36. To each of these actuators 31 to 36, the pressure oil of the two variable displacement hydraulic pumps 1 and 2 is respectively connected to the upper and lower discharge pipe lines 1.
a, 2a from the left and right main conduits 11, 12 and the respective branch conduits 20a, 20b through the actuators 31-3.
6, the pressure compensating portions 4a, 4b having signal pipes 9a, 10a, 9b, 10b, etc., respectively, which are provided on the downstream side after being branched to the variable throttle portion for operation of each directional control valve 3. Through the merging connection pipeline 5, and is led to either one of the pair of load pipelines 6a and 6b to be supplied. In addition, these actuators 3
The maximum load pressure among the load pressures of the actuators driven by the variable displacement hydraulic pumps 1 and 2 among 1 to 36 is detected by the maximum load pressure detection paths 8a and 8b.
The discharge pressures of the two variable displacement hydraulic pumps 1 and 2 are increased by a predetermined value from the maximum load pressure through the tilt control devices 41 and 42 according to the pressure signals of a and 8b and the discharge pressure detection paths 43a and 43b. By controlling the discharge capacity of the pump as described above, load sensing control is performed. Therefore, the hydraulic drive circuit of the fifth conventional example is arranged on the operation variable throttle section and on the downstream side of the operation variable throttle section, and is controlled by the maximum load pressure, the spring force and the downstream pressure of the operation variable throttle section. A flow rate control device is provided, which is provided with a control force in the closing direction and the opening direction to adjust the opening amount and controls the differential pressure across the throttle of the operating variable throttle unit to a constant value. In the above, there is no difference in the basic configuration between the hydraulic drive circuit of the fourth conventional example and the hydraulic drive circuit of the second conventional example.
Further, in that the load sensing control is performed, there is no difference in the basic configuration from the hydraulic drive circuit of the fourth conventional example and the conventional example already described. Therefore, regarding the hydraulic drive circuit of the fifth conventional example, only the main points will be described regarding the configuration relating to these points, and only the other points will be described in detail.

In FIG. 15, reference numerals 1 and 2 denote a first variable displacement hydraulic pump and a second variable displacement hydraulic pump for joining pressure oils and supplying them to the actuators 31 to 36, respectively.
The pressure oil discharged from these variable displacement hydraulic pumps 1 and 2 is discharged from each discharge pipe line 1 connected to each discharge port.
First main pipeline 1 located on the left and right in the figure through a and 2a
It is guided to the first and second main pipelines 12. The first main pipe line 11 and the second main pipe line 12 on the left and right form a meter-in circuit for shunting the pressure oil guided to each main pipe line to the variable throttle portion for operation of each directional control valve 3. 1 branch pipe 20a, second
A large number of the branch pipes 20b are connected in parallel with each other. The left and right first flow dividing pipes 20a and second flow dividing pipes 20b are provided in pairs for the respective directional control valves, and the variable displacement hydraulic pressures introduced to the main pipes 11 and 12 are provided. The pressure oils of the pumps 1 and 2 are divided into the flow dividing pipes 20a and 20b, respectively.
The flow can be divided into the respective directional control valves 3 through. Reference numeral 3 denotes a closed center type directional control valve for two-way merging drive connected to both of the flow dividing pipes 20a and 20b, and 4a and 4b are arranged on the left and right sides of the directional control valve 3 in pairs to form a pair. The first pressure compensating unit and the second pressure compensating unit include the directional control valve and the left and right pressure compensating units 4.
a and 4b are provided corresponding to each of the actuators 31 to 36. Since the directional control valve 3 is provided, when the switching operation is performed, the respective pressure oils divided into the left and right flow dividing pipes 20a and 20b are guided to the left and right pressure compensating portions 4a and 4b, and the merging connection pipe 5 is provided. The combined pressure oil is introduced into one of the load pipes 6a or 6b to be supplied to the actuators 31 to 36, and at the same time, the actuator 31
The pressure oil in 36 to the other load pipeline 6b or load pipeline 6a
Can be discharged to the tank through.

The directional control valve 3 for two-way merge drive will be described in detail. The directional control valve 3 is operated by a hydraulic pilot operating device similar to the hydraulic pilot operating device 70.
When it is operated to the left, it is switched from the neutral position in the figure to the r position, and when it is operated to the right, it is switched from the neutral position to the l position in the figure, and the directional control valves 72, 73 in the third conventional example and the fourth conventional example, Similar to the 74 and 75, a pair of left and right variable aperture parts for operation are incorporated at any position of l and r. As in the third conventional example and the fourth conventional example, the pair of operating variable throttle portions at the l and r positions respectively open the throttle according to the operation amount in each direction of the operating lever of the hydraulic pilot operating device. The degree is set. When the directional control valve 3 is switched to the 1 position, the pressure oil of the first variable displacement hydraulic pump 1 that is diverted to the left diversion pipe 20a and the second variable displacement that is diverted to the right diversion pipe 20b are provided. The pressure oil of the hydraulic pump 2 is supplied to the left and right pressure compensating portions 4a through the left and right variable throttle portions for operation which are built in at the 1 position.
4b to the primary side, and each pressure compensator 4
The pressure oil that has passed through a and 4b and merged in the merged connection pipe line 5,
It is guided to the load pipe line 6b through an inverted U-shaped flow passage built in at the right end of the l position. At the same time, the other load pipeline 6a is connected to the tank via the tank port at the left end of the 1 position. Further, when the position is switched to the r position, the pressure oil of the first variable displacement hydraulic pump 1 that is branched to the left distribution pipe 20a and the second variable displacement hydraulic pump 2 that is distributed to the right distribution pipe 20b are divided. The pressure oil is guided to the primary side of each of the left and right pressure compensating portions 4a and 4b through the left and right variable throttle portions for operation which are built in at the r position, and passes through each pressure compensating portion 4a and 4b. The pressure oil merged in the merging connection conduit 5 is guided to the load conduit 6a through an inverted U-shaped flow path built in at the left end at the r position. At the same time, the other load pipeline 6b is connected to the tank via the tank port at the right end of the r position.

The pressure compensating portions 4a and 4b will be described in detail. When the directional control valve 3 is switched between the 1 position and the r position, the first variable throttle portion for operation which is built in the 1 position,
The second variable throttle section or the first variable throttle section for operation built in the r position, and the variable pressure for each operation so that each pressure oil that has passed through the second variable throttle section can be merged and guided to the actuator. Two output pipes are provided which communicate with the secondary side of the throttle portion and are connected to the confluent connection pipe 5. The first pressure compensator 4a and the second pressure compensator are provided in these two output pipes. The parts 4b are arranged respectively. A load signal relating to the maximum load pressure is guided to the first pressure compensating unit 4a from a signal line 9a for closing operation, which connects the first signal receiving unit and the maximum load pressure detecting route 8a, and is initialized. A control force in the closing direction is applied together with the spring force for. In addition, the first of the directional control valve 3
A pressure signal relating to its own primary pressure is transmitted from a signal line 10a for opening operation, which connects between an output pipe line communicating with the secondary side of the operating variable throttle unit and a second signal receiving unit of the pressure compensation unit 4a. It is guided and a control force in the opening direction is given. Pressure compensator 4a
Adjusts the opening amount by the control force in the closing direction and the opening direction, and controls the differential pressure across the throttle of the first operation variable throttle unit to a constant value regardless of switching to the 1 position or the r position. Work. A pressure signal relating to the maximum load pressure is guided to the pressure compensating section 4b from a signal line 9b for closing operation, which connects the first signal receiving section and the maximum load pressure detecting path 8b, and is used for initial setting. A control force in the closing direction is applied together with the spring force. Further, the signal line 1 for opening operation connecting between the output line communicating with the secondary side of the second variable throttle part for operation of the directional control valve 3 and the second signal receiving part of the pressure compensating part 4b.
A pressure signal relating to its own primary pressure is derived from 0b and a control force in the opening direction is applied. The pressure compensator 4b adjusts the opening amount by the control force in the closing direction and the opening direction, and keeps constant the differential pressure across the throttle of the second operation variable throttle unit regardless of switching to the l position or the r position. Acts to control the value of. The configurations and functions of the pressure compensating units 4a and 4b described above are basically the same as those of the pressure compensating unit in the second conventional example described above.

The control means for carrying out the load sensing control will be described. In order to detect the load pressure of each of the actuators 31 to 36, a load pressure introducing passage 5c is provided in each of the merging connection pipes 5 corresponding to the actuators 31 to 36. Six actuators 31 to 36 are connected to each other, and six actuators 31 to 36 are provided. The maximum load pressure detection paths 8a, 8b for controlling each tilting of the variable displacement hydraulic pumps 1, 2 are
Each of the six load pressure introducing paths 5c is connected to the load signal conduits 5a and 5b. The load signal conduits 5a and 5b are provided with check valves 7a and 7b in the same manner as the above-described conventional connection conduits 208 and 209.
Is provided, and the highest load pressure, which is the highest pressure among the load pressures of the six actuators 31 to 36, is determined by the same principle as that already described in the first conventional example. It can be detected by 8b. Therefore, the maximum load pressures in the maximum load pressure detection paths 8a and 8b and the discharge pressures of the variable displacement hydraulic pumps 1 and 2 in the discharge pressure detection paths 43a and 43b are respectively passed through the tilt control devices 41 and 42. The variable displacement hydraulic pumps 1 and 2 are controlled so that the displacements of the variable displacement hydraulic pumps 1 and 2 are controlled so that the discharge pressures of the variable displacement hydraulic pumps 1 and 2 become higher than the respective maximum load pressures by a predetermined value. , 2 can be controlled to perform the load sensing control described above.

Since the hydraulic drive circuit of the fifth conventional example has such a structure, when any one of the directional control valves 3 is simultaneously operated by each operation lever, the directional control valves 3 operated simultaneously are operated. Is switched to the 1-position or the r-position according to the operating direction of each operating lever to drive the actuator in a predetermined direction, and the first and first built-in actuators are provided at the corresponding position according to the operation amount of each operating lever. The diaphragm openings of the left and right operation variable diaphragm parts 2 are simultaneously adjusted to drive the actuator at a predetermined speed. Arm cylinder 32
The flow of the pressure oil will be described by taking the case where the directional control valve 3 is switched to the r position as an example. From the variable displacement hydraulic pumps 1 and 2 to the discharge pipes 1a and 2a and the left and right main pipes 11 and 12, branch pipes are provided. The respective pressure oils guided to the passages 20a and 20b pass through the openings of the left and right operation variable throttle portions built in the r position of the directional control valve 3 of the arm cylinder 32 and reach the respective secondary sides thereof. It is led to the left and right communicating output lines. The respective pressure oils guided to the left and right output pipelines pass through the left and right pressure compensating portions 4a and 4b while being controlled to a prescribed pressure, and merge in the merge connection pipeline 5, and then from the merge connection pipeline 5. , The load conduit 6a through the built-in inverted U-shaped flow path at the left end of the position
And is supplied to the bottom side of the arm cylinder 32 to drive the piston downward. Further, when the directional control valve 3 of the arm cylinder 32 is switched to the 1 position, the variable displacement hydraulic pump 1, which is guided to the branch pipelines 20a, 20b.
Each pressure oil of No. 2 is, in turn, at the l position of the directional control valve 3,
Similarly to the above, the flow is controlled and guided to the load pipe line 6b and supplied to the rod side of the arm cylinder 32 to drive the piston upward. The same applies to the direction control valves of the other actuators. According to the hydraulic drive circuit of the conventional example, the control means of the construction machine are simultaneously operated to join and drive the plurality of actuators in two directions. be able to.

In this conventional example, all actuators are
The variable displacement hydraulic pumps on the stand are configured to be combined and driven by the pressure oil, but depending on the type and design of the construction machine, part of the actuator may be driven by only one hydraulic pump. . Further, even when the merge drive is performed, the merge drive may be performed by a larger number of hydraulic pumps. In that case, the number of main pipes is increased according to the number of the hydraulic pumps, and each of r and l is increased. It suffices to incorporate a number of variable throttle portions for operation at positions corresponding to the number of merged pressure oils, and increase the number of output conduits and pressure compensating portions communicating with the secondary side thereof.

The hydraulic drive circuit of the fifth conventional example is arranged downstream of the first variable throttle portion for operation and the second variable throttle portion for operation when the directional control valve 3 is switched to the 1 and r positions. On the side, as in the second conventional flow control device, the pressure compensator 4a is provided.
Since the pressure compensating section 4b is arranged and the load sensing control is performed, the actuators 31 to 36 are not affected by the fluctuation of the circuit pressure.
Can be always driven at a speed according to the operation amount of the operation lever.

[0045]

As described above, in each of the hydraulic drive circuits of the construction machines of the first conventional example to the fifth conventional example, the power consumption can be kept low by the load sensing control. At the same time, the actuator can always be driven at a predetermined speed according to the operation amount of the operation lever without being affected by the fluctuation of the circuit pressure, which is preferable in this limit. However,
In conventional hydraulic drive circuits that drive such actuators in combination, when the actuators are driven in combination, the discharge flow rate of the variable displacement hydraulic pump depends on the combination of the actuators and the required flow rate of the directional control valve that controls those actuators. The phenomenon of less than the sum of so-called saturation may occur. When such saturation occurs, depending on the work content of the actuator, the supply flow rate to that one actuator will be insufficient until it exceeds the limit necessary to perform the work, and the decrease in the drive speed will be significant. , There may be a fatal problem in work.

Taking a hydraulic excavator as an example, a simple example is shown. In the hydraulic excavator, when leveling a level ground, the boom cylinder and the arm cylinder are simultaneously driven to perform horizontal pulling by a combined operation of pulling the arm and raising the boom. However, if the supply flow rate to the boom cylinder for raising the boom, which has a larger load than the arm pulling, decreases, the arm pulling precedes the boom raising and the arm adjusts downward. , The blade edge of the bucket at the end of the arm falls to the ground, which makes smooth grounding work impossible. Furthermore, when performing such leveling work on the slope, unless the boom raising amount is given priority over the arm pulling amount over the work on level ground, the blade edge of the bucket will cut into the slope. There will be a significant hindrance to the ground preparation work.

In a hydraulic excavator, when a wetland is encountered during running, the arm is used like a crutch to move forward while pulling forward, but when saturation occurs during such work, relative movement occurs. As a result, the flow rate of supply to the arm cylinder, which has a large load, is reduced, and the speed at which the arm is retracted is significantly reduced, making it difficult to smoothly perform wetland escape work. In addition, although carrying work is also carried out by hanging the luggage while moving it with a bucket, when trying to change the height of the hanging load by raising the arm or boom while traveling, the flow rate supplied to the traveling motor will decrease and the traveling speed will decrease. The sudden drop in the height causes the problem of swinging of the suspension and spilling or collapse of the load. As described above, in the conventional hydraulic drive circuit that only performs uniform flow rate distribution, depending on the work content, the supply flow rate to the actuator, which is the main focus of the work, is insufficient, and that work is hindered. There was a problem. Problems associated with saturation during combined drive of such actuators are not limited to the problems exemplified above, and occur in various aspects of construction work with the recent increase in complexity of work sites of construction machinery and diversification of applications. .

The present invention solves such a problem found in the hydraulic drive circuit of the conventional construction machine. Therefore, even when saturation occurs during combined drive of the actuators,
An object of the present invention is to provide a hydraulic drive circuit for a construction machine capable of rationally distributing a flow rate to each actuator so as not to hinder the work.

[0049]

The above objects of the present invention are as follows:
“A variable displacement hydraulic pump, a plurality of actuators driven by the hydraulic pressure of the variable displacement hydraulic pump, and the maximum load pressure of the load pressures of these actuators are detected to determine the discharge pressure of the variable displacement hydraulic pump. A control means that performs load sensing control that controls the discharge capacity of the pump so that it is higher than the maximum load pressure by a predetermined value, and an operation that is operated by the operation means of the construction machine to adjust the supply flow rate to the actuator Variable throttle portion, and an opening direction control force based on the load pressure of the actuator, which is arranged on the upstream side of the operation variable throttle portion, the opening direction control force set by the differential pressure setting means, and its own secondary pressure. A control force in the closing direction based on the control is applied to adjust the opening amount, and the secondary pressure of itself is increased by a constant value above the load pressure of the actuator by the differential pressure setting means. In the hydraulic drive circuit of the construction machine, which has a pressure compensating unit for controlling so as to control the supply flow rate to the actuator, and which is provided corresponding to each actuator in the hydraulic drive circuit of the construction machine. A flow restricting variable throttle unit as a means for restricting the flow rate passing through the operation variable throttle unit is arranged downstream of the pressure compensating unit in some of the flow rate controlling devices, and the flow restricting variable throttle unit is provided. The throttle opening of the throttle unit is set so as to decrease in accordance with the increase of the throttle opening of the variable throttle unit for operation of another flow rate control device, in conjunction with the operation of the variable throttle unit for operation. '' A hydraulic drive circuit for a construction machine as set forth in claim 1 characterized in that "a variable displacement hydraulic pump and a plurality of hydraulic pumps driven by the hydraulic pressure of the variable displacement hydraulic pump. Load sensing that detects the maximum load pressure of the actuator and the load pressure of these actuators, and controls the discharge capacity of the variable displacement hydraulic pump so that it is higher than the maximum load pressure by a specified value. In addition to providing control means for controlling, a variable throttle part for operation that is operated by the control means of the construction machine to adjust the flow rate supplied to the actuator, and a variable throttle part for operation that is arranged on the downstream side of Based on the control force in the closing direction, the control force in the closing direction for initial setting, and the control force in the opening direction based on the primary pressure of the self, the opening amount is adjusted to adjust the primary pressure of the self to the maximum load pressure side. A pressure compensator for controlling the actuator to a constant value sufficient to drive the actuator, and a flow controller for controlling the supply flow rate to the actuator. In the hydraulic drive circuit of the construction machine provided corresponding to the actuator, the variable throttle portion for operation is provided on the upstream side of the pressure compensating portion in some of the flow control devices provided corresponding to the actuators. A variable flow restricting throttle unit is arranged as a means for restricting the passage flow rate of the flow restrictor, and the throttle opening of this variable flow restricting throttle unit is adjusted according to the increase of the throttle opening of the variable throttle restrictor for operation of another flow control device. The hydraulic drive circuit for a construction machine as set forth in claim 2 is characterized in that it is set in association with the operation of the operating variable throttle portion so as to decrease. “A plurality of variable displacement hydraulic pumps, and at least one actuator that is jointly driven by merging and supplying pressure oil of the plurality of variable displacement hydraulic pumps,
The maximum load pressure is detected for each of the actuators driven by the pressure oil and each variable displacement hydraulic pump, and the discharge pressure of each variable displacement hydraulic pump is higher than the maximum load pressure. A control means for performing load sensing control for controlling the discharge capacity of each variable displacement hydraulic pump is provided so as to be increased by a predetermined value, and it is operated by the operation means of the construction machine corresponding to the combined drive actuator. A plurality of variable throttles for operation that adjust the supply flow rate to the actuator are built in so as to match the number of confluences of the pressure oil to the actuator, and the flow path of the pressure oil is arranged so that the actuator can be driven in two directions by the control means. A directional control valve for two-way merging drive that can be switched, and corresponding to the remaining actuator Bidirectional drive capable of switching the flow path of pressure oil so that the actuator can be driven in two directions by the operating means by incorporating a variable throttle portion for operation that is operated by the vertical means to adjust the supply flow rate to the actuator. A directional control valve is provided to control the opening amount by applying a closing direction control force based on the maximum load pressure, a closing direction control force for initial setting, and an opening direction control force based on its own primary pressure. The pressure compensator that controls its own primary pressure to a constant value sufficient to drive the actuator on the maximum load pressure side, in each of the flow paths communicating with the secondary side of each variable throttle for operation. In the hydraulic drive circuit of the installed construction machine, the operation variable throttle is provided upstream of some of the pressure compensation sections of the pressure compensation section respectively arranged in the flow path communicating with the secondary side of each operation variable throttle section. Part of flow At least one flow restricting variable throttle section is arranged as a means for restricting the flow rate so that the throttle opening of this flow restricting variable throttle section decreases in accordance with the increase of the throttle opening degree of the other operation variable throttle section. The hydraulic drive circuit for the construction machine according to claim 5 is characterized in that it is set in conjunction with the operation of the variable throttle portion for operation. Variable displacement hydraulic pump and second variable displacement hydraulic pump, and swing motor, arm cylinder, boom cylinder, bucket cylinder, first actuator as actuators driven by pressure oil of these variable displacement hydraulic pumps
First maximum load pressure detecting means for detecting the maximum load pressure by a load signal relating to the load pressure of the traveling motor and the second traveling motor and the actuator driven by the first variable displacement hydraulic pump, and the second variable displacement type The maximum load pressure is detected by the second maximum load pressure detection means that detects the maximum load pressure by the load signal related to the load pressure of the actuator driven by the hydraulic pump, and the discharge pressure of each variable displacement hydraulic pump is the maximum load. Control means for performing load sensing control for controlling the discharge capacity of each variable displacement hydraulic pump so as to be higher than the pressure by a predetermined value, and the pressures of the first variable displacement hydraulic pump and the second variable displacement hydraulic pump. A first main pipe line and a second main pipe line for respectively guiding oil, and respectively provided corresponding to the above-mentioned actuators, and operated by the operating means of the hydraulic excavator. The first variable throttle portion for operation and the second variable throttle portion for operation, which adjust the supply flow rate to the actuator, are respectively incorporated in the two switching positions, and the actuator is operated by switching to the two switching positions. Directional control valve for swing motor, directional control valve for arm cylinder, boom cylinder that has the function as a directional control valve for two-way merging drive that can switch the flow path of pressure oil so that it can drive merging in two directions The directional control valve, the directional control valve for the bucket cylinder, the directional control valve for the first traveling motor, and the directional control valve for the second traveling motor, and the respective pressure oils introduced into the first main pipeline and the second main pipeline, respectively. A directional control valve for a swing motor, a directional control valve for an arm cylinder, and a boom cylinder for branching the flow into the first variable throttle portion for operation and the second variable throttle portion for operation of each directional control valve. Da directional control valve,
At the two switching positions of the directional control valve for the bucket cylinder, the first directional control valve for the first traveling motor and the first diverting pipeline for the directional control valve for the second traveling motor, and the second diverting pipeline. The directional control valve is arranged in each output pipe that communicates with the secondary sides of the first operation variable throttle section and the second operation variable throttle section, respectively, and is arranged in the closing direction by the load signal related to the maximum load pressure. Control force, closing direction control force for initial setting, and opening direction control force by the pressure signal related to the own primary pressure are applied to adjust the opening amount, and the own primary pressure drives the actuator on the maximum load pressure side. A hydraulic drive circuit for a construction machine including a first pressure compensating unit and a second pressure compensating unit which are controlled so as to have a constant value that is sufficient to have a circuit switching unit and a load signal switching unit. A switching valve is installed to When a valve other than the directional control valve for the engine and the directional control valve for the second traveling motor is being switched, the circuit switching unit of this switching valve causes the pressure oils in the first main pipe and the second main pipe to be supplied respectively. The load signal switching unit of the switching valve is configured so as to be switched so as to be divided into the first diversion conduit of the second traveling motor directional control valve and the second diversion conduit of the first traveling motor directional control valve. Thus, the load signal of the first traveling motor acts as a load signal for detecting the maximum load pressure by the second maximum load pressure detecting means, and relates to the maximum load pressure detected by the second maximum load pressure detecting means. The load signal acts as a load signal for applying a control force in the closing direction to the second pressure compensator corresponding to the first traveling directional control valve, and the maximum load detected by the first maximum load pressure detecting means is detected. Load signal for pressure The first directional control valve for the first traveling motor and the second directional control valve for the second traveling motor are configured to be switched so as to act as a load signal for applying a control force in the closing direction to the first pressure compensating portion corresponding to the second traveling directional control valve. When the valves other than the directional control valve for the traveling motor are not switched, the circuit switching portion of the switching valve causes the pressure oil in the first main pipe and the second main pipe to divide into the second shunt of the first traveling motor, respectively. The load signal switching section of the switching valve allows the load signal of the first traveling motor and the load signal of the second traveling motor to be switched so that the flow is divided into the pipe and the first branch pipe of the second traveling motor. Are switched so as to act as load signals for detecting the maximum load pressure by the first maximum load pressure detection means and the second maximum load pressure detection means, respectively, and the directional control valve for the swing motor and the arm cylinder are provided. The first main conduits on the downstream side of the first diversion conduit of the directional control valve for upstream and on the upstream side of the other first diversion conduit are respectively linked to the operation of the respective directional control valves. Direction for the first traveling motor when the flow restricting variable restrictor for restricting the flow rate of the first operation variable restrictor of the directional control valve is arranged and the pressure oil in the second main pipe is diverted Second control valve
Of the directional control valve and the second main pipeline on the downstream side of the second diverter pipeline of the second travel motor directional control valve and on the upstream side of the remaining second diverter pipeline. A flow restricting variable restrictor for restricting the flow rate of the second operable variable restrictor of the remaining directional control valve that is interlocked with each operation of the boom cylinder directional control valve and the boom cylinder directional control valve. In the second main pipe line upstream of the second diversion pipe line of the swing motor directional control valve and the arm cylinder directional control valve on the downstream side of the second diversion pipe line of A flow restricting variable throttle section for restricting a flow rate passing through the second operation variable throttle section of the swing motor directional control valve and the arm cylinder directional control valve is arranged in association with the operation of the bucket cylinder directional control valve, Variable for each of the above flow rate restrictions The throttle opening of the throttle is reduced so that the throttle opening of the operation variable throttle of the directional control valve interlocked with the flow restricting variable throttle decreases as the throttle opening increases. The hydraulic drive circuit for a construction machine as set forth in claim 6 characterized in that "the first variable displacement hydraulic pump and the first variable displacement hydraulic pump 2 variable displacement hydraulic pumps, and a swing motor, an arm cylinder, a boom cylinder, a bucket cylinder as an actuator driven by the pressure oil of these variable displacement hydraulic pumps, a first cylinder,
First maximum load pressure detecting means for detecting the maximum load pressure by a load signal relating to the load pressure of the traveling motor and the second traveling motor and the actuator driven by the first variable displacement hydraulic pump, and the second variable displacement type The maximum load pressure is detected by the second maximum load pressure detection means that detects the maximum load pressure by the load signal related to the load pressure of the actuator driven by the hydraulic pump, and the discharge pressure of each variable displacement hydraulic pump is the maximum load. Control means for performing load sensing control for controlling the discharge capacity of each variable displacement hydraulic pump so as to be higher than the pressure by a predetermined value, and the pressures of the first variable displacement hydraulic pump and the second variable displacement hydraulic pump. A first main pipe line and a second main pipe line for respectively guiding oil, and respectively provided corresponding to the above-mentioned actuators, and operated by the operating means of the hydraulic excavator. The first variable throttle portion for operation and the second variable throttle portion for operation, which adjust the supply flow rate to the actuator, are respectively incorporated in the two switching positions, and the actuator is operated by switching to the two switching positions. Directional control valve for swing motor, directional control valve for arm cylinder, boom cylinder that has the function as a directional control valve for two-way merging drive that can switch the flow path of pressure oil so that it can drive merging in two directions The directional control valve, the directional control valve for the bucket cylinder, the directional control valve for the first traveling motor, and the directional control valve for the second traveling motor, and the respective pressure oils introduced into the first main pipeline and the second main pipeline, respectively. A directional control valve for a swing motor, a directional control valve for an arm cylinder, and a boom cylinder for branching the flow into the first variable throttle portion for operation and the second variable throttle portion for operation of each directional control valve. Da directional control valve,
At the two switching positions of the directional control valve for the bucket cylinder, the first directional control valve for the first traveling motor and the first diverting pipeline for the directional control valve for the second traveling motor, and the second diverting pipeline. The directional control valve is arranged in each output pipe that communicates with the secondary sides of the first operation variable throttle section and the second operation variable throttle section, respectively, and is arranged in the closing direction by the load signal related to the maximum load pressure. Control force, closing direction control force for initial setting, and opening direction control force by the pressure signal related to the own primary pressure are applied to adjust the opening amount, and the own primary pressure drives the actuator on the maximum load pressure side. A hydraulic drive circuit for a construction machine including a first pressure compensating unit and a second pressure compensating unit which are controlled so as to have a constant value that is sufficient to have a circuit switching unit and a load signal switching unit. A switching valve is installed to When a valve other than the directional control valve for the engine and the directional control valve for the second traveling motor is being switched, the circuit switching unit of this switching valve causes the pressure oils in the first main pipe and the second main pipe to be supplied respectively. The load signal switching unit of the switching valve is configured so as to be switched so as to be divided into the first diversion conduit of the second traveling motor directional control valve and the second diversion conduit of the first traveling motor directional control valve. Thus, the load signal of the first traveling motor acts as a load signal for detecting the maximum load pressure by the second maximum load pressure detecting means, and relates to the maximum load pressure detected by the second maximum load pressure detecting means. The load signal acts as a load signal for applying a control force in the closing direction to the second pressure compensator corresponding to the first traveling directional control valve, and the maximum load detected by the first maximum load pressure detecting means is detected. Load signal for pressure The first directional control valve for the first traveling motor and the second directional control valve for the second traveling motor are configured to be switched so as to act as a load signal for applying the control force in the closing direction to the first pressure compensating portion corresponding to the second directional control valve for traveling. When the valves other than the directional control valve for the traveling motor are not switched, the circuit switching portion of the switching valve causes the pressure oil in the first main pipe and the second main pipe to divide into the second shunt of the first traveling motor, respectively. The load signal switching section of the switching valve allows the load signal of the first traveling motor and the load signal of the second traveling motor to be switched so that the flow is divided into the pipe and the first branch pipe of the second traveling motor. Are switched so as to act as load signals for detecting the maximum load pressure by the first maximum load pressure detection means and the second maximum load pressure detection means, respectively, and the pressure oil in the second main pipeline is diverted. Place In the downstream side of the second diversion conduit of the first traveling motor directional control valve and the second diversion conduit of the second traveling motor directional control valve in the remaining upstream side of the second diversion conduit. A flow rate in the second main pipe line that interlocks with the operation of the directional control valve having the maximum operation amount of these directional control valves and limits the flow rate of the remaining directional control valve through the second variable throttle portion for operation. Arranging the variable throttle for restriction, and operating it so that the throttle opening of the variable throttle for flow restriction decreases with the increase of the throttle opening of the variable throttle for operation of the directional control valve with the maximum operation amount. Is set in association with the operation of the variable throttle portion for use in the swivel motor, and the directional control valve for the swing motor and the directional control valve for the arm cylinder are provided on the downstream side of the first diversion conduit of the remaining first diversion conduit. The first main line on the upstream side and the direction control valve for the boom cylinder and the direction for the bucket cylinder In the main conduit of one of the second main conduits on the downstream side of the second branch conduit of the control valve and on the upstream side of the second branch conduit of the swing motor directional control valve and the arm cylinder directional control valve, A flow rate limiting means having a variable flow rate limiting variable throttle section capable of selectively forming a throttle is provided, and the maximum operation amount of the operation amounts of the swing motor directional control valve and the arm cylinder directional control valve and the boom cylinder direction are provided. If the maximum operation amount of the former is larger than the maximum operation amount of the operation amounts of the control valve and the bucket cylinder directional control valve, the first operation amount is first.
Is formed in the main pipeline of the second main pipeline, and when the latter has a larger maximum operation amount, the throttle is formed in the second main pipeline, and the throttle formed in the main pipeline by the flow restricting variable throttle section. The hydraulic drive circuit of the hydraulic excavator is characterized in that the throttle opening degree is set so as to decrease in accordance with an increase in the operation amount of the difference between the two maximum operation amounts. This is achieved by a hydraulic drive circuit of each construction machine of a hydraulic drive circuit of a construction machine as set forth in claim 7.

[0050]

The invention constituted by the matters described in claims 1, 2, 5, 6, and 7 of the claims is thus the variable displacement hydraulic pump and , Which has a plurality of actuators that are combinedly driven by the pressure oil of this variable displacement hydraulic pump, is provided with means for performing load sensing control, and is operated by the operating means of the construction machine to adjust the supply flow rate to the actuators. In a hydraulic drive circuit of the type shown in each of the claims, wherein a variable throttle section for operation and a pressure compensation section are provided,
A flow rate limiting variable throttle section as a means for limiting the flow rate of the operating variable throttle section is arranged on the downstream side or upstream side of a part of the pressure compensating section according to the type of the hydraulic drive circuit,
The operation of the variable throttle portion for operation is controlled so that the throttle opening degree of the variable throttle portion for flow rate restriction decreases in accordance with the increase of the throttle opening degree of the specific variable throttle portion for operation different from the variable throttle portion for operation. When the saturation is caused by the combined drive of the actuators, the aperture of the specific variable throttle for operation is made relatively large, which is the main focus of the work. When a large flow rate is to be supplied to one of the actuators, the throttle opening degree of the flow rate limiting throttle section is set to relatively decrease in association with the operation of the specific operation variable throttle section. As a result, the supply flow rate to the other actuator is
The flow restricting throttle restricts the flow rate of the variable displacement hydraulic pump in accordance with an increase in the throttle opening of the specific operation variable restrictor, so that the pressure oil of the variable displacement hydraulic pump is given priority to one of the actuators, which is the main focus of the work. Will be supplied to. Further, when the throttle opening degree of the specific operation variable throttle section is made relatively small, the throttle opening degree of the flow rate limiting throttle section is relatively increased in association with the operation of the operation variable throttle section. Since the pressure oil of the variable displacement hydraulic pump is preferentially supplied to one actuator, the supply flow rate to the other actuator is not unnecessarily limited and is within a reasonable range. Limited by. Therefore, according to the present invention, the pressure oil of the variable displacement hydraulic pump is not only preferentially supplied to one of the main actuators, but also the flow rate distribution of the pressure oil to each actuator is rationalized. Even if saturation occurs during combined driving of the actuators, the work will not be hindered. The same applies to each invention constituted by the matters described in claims 3 and 4 of the claims which respectively depend on the above claims 1 and 2.

[0051]

Embodiments of the present invention will be described with reference to FIGS. FIG. 1 is a hydraulic circuit diagram showing a hydraulic drive circuit of a construction machine according to a first embodiment of the present invention, and FIG. 2 is a hydraulic drive circuit of a construction machine according to the first embodiment of the present invention. Characteristic diagram showing characteristics of differential pressure across the throttle of the variable throttle portion for operation when the variable throttle portion for operation is attached, and FIG. 3 illustrates characteristics of the hydraulic drive circuit of the construction machine according to the first embodiment of the present invention. FIG. 4 is a hydraulic circuit diagram showing a hydraulic drive circuit for a construction machine according to a second embodiment of the present invention, and FIG. 5 is a hydraulic circuit diagram showing a hydraulic drive circuit for a construction machine according to a third embodiment of the present invention. Circuit diagram, FIG. 6 is a hydraulic circuit diagram showing a hydraulic drive circuit of a construction machine according to a fourth embodiment of the present invention, and FIG. 7 is a hydraulic operating mechanism for realizing the operation of the switching valve in the hydraulic drive circuit of FIG. Fig. 8 is a hydraulic circuit diagram showing a concrete example of Fig. 8, and Fig. 8 is a hydraulic circuit diagram showing a hydraulic drive circuit of a construction machine according to a fifth embodiment of the present invention. Road view, and FIG. 9 is a hydraulic circuit diagram showing a specific example of a hydraulic mechanism for realizing the operation of the switching valve in the hydraulic drive circuit of FIG. 1 and 4 to 9
In FIG. 10, the parts denoted by the same reference numerals as those in FIGS. 10 to 15 represent the same parts as those in these figures, and therefore those parts will not be described in detail in order to avoid redundant description.

First, an outline of the hydraulic drive circuit for a construction machine according to the first embodiment of the present invention will be described with reference to FIG. 1. As apparent from FIG. 1, the hydraulic drive circuit according to the present embodiment is shown in FIG.
In comparison with the hydraulic drive circuit of the first conventional example of FIG.
Variable displacement hydraulic pump 2 whose discharge capacity is controlled by 2
01 and a plurality of actuators 206 and 207 that are combinedly driven by the variable displacement hydraulic pump 201, and the maximum load pressure among the load pressures of these actuators 206 and 207 is detected by the maximum load pressure detection path 212. Through the tilt control device 202, the maximum load pressure and the discharge pressure of the variable displacement hydraulic pump 201 detected by the discharge pressure detection path 214 make the discharge pressure higher than the maximum load pressure by a predetermined value. There is no difference in the basic configuration in that the discharge capacity of the variable displacement hydraulic pump 201 is controlled to perform load sensing control. The greatest feature of the hydraulic drive circuit of the present embodiment is that in the hydraulic drive circuit of the first conventional example shown in FIG. 10, one of the flow rate control devices 220, 221 is provided with one of the flow rate control devices 220.
The point 61 is added so that it is interlocked with the variable throttle unit 223 in the other flow rate control device 221. Therefore, regarding the hydraulic drive circuit of the first embodiment of FIG.
This point will be mainly described.

In FIG. 1, reference numeral 260 is provided in the branch passage 203a and corresponds to the flow control device 220 in the hydraulic drive circuit of the first conventional example to which the flow restricting variable throttle portion 261 is added. It can be considered as a kind of flow rate control device because it controls the supply flow rate of. On the other hand, reference numeral 221 denotes a flow rate control device that is provided in the branch path 203b and controls the flow rate supplied to the actuator 207, which is exactly the same as the flow rate control device in the first conventional example. Reference numeral 261 denotes an operating lever, that is, a variable throttle portion 22 for operation which is operated by the operating means of the construction machine.
2, a variable flow restricting portion 262 for suppressing the differential pressure across the throttle for controlling the variable throttle portion 222 for operation to restrict the flow rate of passage, 262 is further provided than the variable restricting portion 261 for flow rate limiting. Located on the most upstream side of the upstream,
It is a pressure compensating unit that operates similarly to the pressure compensating unit 224. When comparing the characteristics with the flow rate control device according to the first conventional example, the flow rate control device 260 according to the present embodiment includes a group of throttle parts including an operation variable throttle part 222 and a flow rate limiting variable throttle part 261 and this throttle part. It may be considered to be configured with the pressure compensating unit 262 arranged on the upstream side of the group. The variable flow restricting throttle portion 261 of the flow control device 260 is connected to the operating variable throttle portion 223 of the other flow control device and the interlocking means 2.
The aperture opening is changed in conjunction with the operation of the operation variable aperture section 223. In this case, the throttle opening degree of the variable flow restricting throttle portion 261 is set in association with the operation of the operation variable throttle portion 223 so as to decrease in accordance with the increase of the throttle opening degree of the operation variable throttle portion 223. I am trying to do it. As for the configuration of the pressure compensating unit 262, reference numeral 263 is a signal pipe of the pressure compensating unit 262 that connects the first signal receiving unit of the pressure compensating unit 262 and the load pipe line 204 through a part of the connecting pipe line 208. Reference numeral 264 denotes a signal conduit of the pressure compensating portion 262, which connects the second signal receiving portion of the pressure compensating portion 262 and the secondary side of the pressure compensating portion 262, that is, the upstream of the flow restricting variable throttle portion 261. A spring as a differential pressure setting means for setting a differential pressure between the upstream pressure and the downstream pressure of the throttle unit, that is, a differential pressure between the front and rear, which is a spring 22 in FIG.
Similar to No. 8, presetting is performed so that a predetermined displacement amount is applied at the time of initial setting to open the oil passage of the pressure compensation unit 262. The signal conduit 263 guides the load pressure of the load conduit 204, that is, the downstream pressure of the throttle unit group, to the pressure compensator 262, and imparts a control force in the opening direction together with the spring 265. The signal line 264 guides the secondary pressure of the pressure compensating unit 262, that is, the upstream pressure of the throttle unit group, to the pressure compensating unit 262, and applies a control force in the closing direction to the pressure compensating unit 262. The pressure compensating unit 262 adjusts the opening amount by the control force in the opening direction and the closing direction so that the differential pressure across the throttle unit is maintained at a constant value initially set by the spring 265 as described later. It works to control.

The flow rate control device 260 in the hydraulic drive circuit of the first embodiment has the operation variable throttle section 222 for adjusting the flow rate supplied to the actuator 206 by operating the operation lever in this way, and this operation variable throttle section. A pressure compensating section 262 is arranged upstream of a throttling section group consisting of a flow restricting variable throttling section 261 which functions to suppress the differential pressure across the throttle 222 and restrict its flow rate.
At the signal receiving portion, the control force in the opening direction due to the downstream pressure of the throttle portion group, the control force in the opening direction set by the spring 265 as the differential pressure setting means, and the control force in the closing direction due to the upstream pressure of the throttle portion group. By imparting and adjusting the opening amount thereof, the differential pressure across the throttle unit is constantly maintained at a predetermined value initially set by the spring 265. In other words, the upstream pressure of the throttle unit is adjusted to the upstream pressure. Is controlled so that it is always higher than the downstream pressure of the actuator 206, that is, the load pressure of the actuator 206 by a predetermined value set by the spring 265. Therefore, the upstream pressure of the throttle unit is the same as in the conventional example. Depending on the load pressure, the pressure value is constantly adjusted to the limit value required to drive the actuator 206, and power can be saved. At the same time, the flow control device 260 controls the flow restricting variable throttle unit 2
61 is attached, and its throttle opening degree is controlled by the variable throttle portion 223 for operation.
As described in detail later, even if saturation occurs when the actuators 206 and 207 are driven in combination, the differential pressure across the throttle of the operating variable throttle section 222 can be suppressed. It is possible to rationally limit the supply flow rate to the other actuator 206 so that the pressure oil is sufficiently distributed to the one actuator 207, which is the main object, so that the predetermined work is not hindered. In order to more accurately show the characteristics of the flow rate control device 260 in the hydraulic drive circuit of the present embodiment, the characteristics thereof will be described below using mathematical expressions.

First, in the pressure compensator 262, as described above, the pressure difference between the upstream pressure of the flow restricting variable throttle portion 261 and the downstream pressure of the operating variable throttle portion 222, that is, the differential pressure across the throttle portion group is set as a spring. Since it is controlled so as to be equal to the urging force of H.265, the relationship is expressed as a mathematical expression as follows, and the differential pressure is equal to the differential pressure across the throttle unit group. Can be expressed as

[0056] _{a (Pz i -Pl i) =} k i (xo i + x i) ∴ Pz i -Pl i = (xo i + x i) k i / a = ΔPo i ‥‥‥‥‥‥‥‥ (8 ) The meaning of each symbol in these formulas is as follows.

Pz _i : upstream pressure of the throttle group (pressure compensator 26
Load pressure) a downstream pressure of the throttle unit (actuator 206; 2 of the secondary pressure) Pl _i Pz _i, the pressure receiving area k _i of the pressure compensator 262 relates Pl _i; granted during initialization; spring constant xo _i Displacement amount x _i of spring 265; Displacement amount of spring 265 generated by applying control force Po _i ; Differential pressure across throttle unit group On the other hand, variable displacement hydraulic pressure that supplies pressure oil to the primary side of pressure compensation unit 262 The discharge pressure Ps of the pump 201 is controlled by the load sensing control so as to be higher than the maximum load pressure Plmax by a predetermined value, that is, the load sensing differential pressure ΔP _LS , as shown in the equation (2). To be done. That is, the discharge pressure Ps of the variable displacement hydraulic pump 201 is controlled by the load sensing control so as to always maintain a constant load sensing differential pressure ΔP _LS , as described in the description of the first conventional example. The load sensing differential pressure ΔP _LS is set to be equal to the front-rear differential pressure ΔPo _i of the throttle group so as to substantially follow (9) below.

ΔP _LS = ΔPo _i (9) As is clear from these equations (8) and (9), in the pressure compensator 262, the differential pressure across the throttle unit is applied to the spring 265. Since the load sensing differential pressure is set to be equal to this biasing force, the pressure compensating portion 262 eventually has a differential pressure ΔPo across the throttle portion group. _i is approximately load sensing differential pressure Δ
This means that the control is carried out so as to maintain a constant value equal to P _LS . The differential pressure ΔPo _i across the throttle group and the differential pressure ΔPv across the variable throttle section 222 for operation in the throttle group.
_i and throttling differential pressure ΔP of the variable throttle unit 261 for flow rate restriction
Looking at the relationship with m _i , this relationship can be expressed by the following equation.

[0059] _{ΔPo i = ΔPv i + ΔPm i} ‥‥‥‥‥ (10) thereof (9), (10) from the differential pressure .DELTA.Pm _i stop flow restriction variable throttle portion 261, operating variable throttle portion Two
The differential pressure ΔPv _i before and after the throttle can be expressed by the following equation.

ΔPm _i = ΔPo _i −ΔPv _i = ΔP _LS −
ΔPv _i ····························································· (11)
And the differential pressure .DELTA.Pm _i diaphragm pv _i and the flow regulating variable throttle portion 261, passes through the flow rate Qv _i in the operation variable throttle portion 222 and the flow regulating variable throttle portion 261, each relationship between Qm _i, the following equation Can be expressed as

[0061] _{Qv i = N · A i √} (ΔPv i) ‥‥‥‥‥ (12) Qm i = N · B i √ (ΔPm i) ‥‥‥‥‥ (13) Each of these formulas The symbols have the following meanings.

Qv _i : Flow rate in variable throttle portion 222 for operation Qm _i : Flow rate in variable throttle portion 261 for flow rate A _i ; Opening degree B _i of variable throttle portion for operation 222; 261 throttle opening degree N; constant flow rate Qv _i in these variable throttle portions 222 for operation
And the passing flow rate Qm _i in the flow restricting variable throttle unit 261
Are the flow rates of the pressure oil that flow through the same flow path and are equal to each other, the following equation can be obtained from the equations (11), (12), and (13). 22
The differential pressure ΔPv _i before and after the throttle can be expressed by the following equation (14).

N · A _i √ (ΔPv _i ) = N · B _i √ (ΔPm _i ) = N · B _i √ (ΔP _LS −ΔPv _i ) ∴ΔPv _i = (B _i / A _i ) ² / {1+ (B _i / A _i ) ² } · ΔP _LS = χ _i ² / (1 + χ _i ² ) · ΔP _LS ‥‥‥‥‥‥‥‥ (14) where χ _i is the flow rate to the variable throttle portion 222 for operation. It means the aperture area ratio (B _i / A _i ) of the limiting variable diaphragm 261.

Further, the passage flow rate Qv _i in the variable throttle portion 222 for operation of the flow rate control device of this embodiment is as follows (1)
It can be represented by the formula 5).

Qv _i = N · A _i √ (ΔPv _i ) = N · A _i √ {χ _i ² / (1 + χ _i ² ) · ΔP _LS } = √ {χ _i ² / (1 + χ _i ² )} · N・ A _i √ (ΔP _LS ) = √ {χ _i ² / (1 + χ _i ² )} ・ Qv _i '... (15) The symbols used in this equation (15) have the following meanings. It is as follows.

Qv _i : Variable aperture section 22 for operation of this embodiment
Flow rate Qv _i ′ in 2; variable throttle units 222, 22 for operation of the first conventional example
3 is a graph showing the relationship expressed by the equation (14), that is, the characteristic of how the differential pressure ΔPv _i across the throttle of the operating variable throttle unit 222 changes depending on the opening area ratio χ _i . It becomes like 2. The variable throttle unit 22 for operation shown in FIG.
The characteristic of No. 2 can be roughly described as follows.
Variable throttle portion 261 for flow rate restriction with respect to the throttle opening A _{i of} 2
The larger the ratio of the throttle opening B _i is, the larger the differential pressure ΔPv _i across the variable throttle portion 222 for operation becomes, and becomes a value close to the load sensing differential pressure ΔP _LS (compensation pressure by the pressure compensating portion 262). As the ratio is smaller, the effective differential pressure in the variable throttle portion 222 for operation is reduced and the differential pressure ΔPv _i before and after the throttle is reduced. Further, according to the characteristics shown in FIG. 2 and the equation (15), the flow rate control device of the first embodiment has the flow restricting variable throttle section for the throttle opening A _i of the operation variable throttle section 222. The larger the ratio of the throttle opening B _i of 261 is, the larger the flow rate that is closer to the flow control device of the first conventional example is secured, and the smaller the ratio is, the first
A suppressed flow rate obtained by reducing the flow rate of the flow rate control device of the conventional example can be obtained.

The hydraulic drive circuit of the present embodiment is provided with the flow rate control device 260 having such a flow rate characteristic, and the throttle opening of the flow rate limiting variable throttle section 261 is controlled by the operation variable throttle section 223.
Since it can be changed in conjunction with the operation of the operation, when the saturation is generated by the combined drive of the actuators 206 and 207, the operation variable diaphragm unit 223.
When a large flow rate is to be supplied to one of the actuators 207, which is the main focus of the work, by making the throttle opening degree of No. 2 relatively large, the flow restricting throttle unit 223 is interlocked with the operation of the operation variable throttle unit 223. The throttle opening degree of 261 is set to relatively decrease. As a result, the flow rate supplied to the other actuator 206 is limited by the flow rate limiting throttle section 261 in accordance with an increase in the throttle opening degree of the operation variable throttle section 223, and the pressure oil of the variable displacement hydraulic pump 201 is reduced. It is preferentially supplied to one of the actuators 207, which is the main focus of the work. Further, when the throttle opening degree of the variable throttle portion 223 for operation is made relatively small, the throttle opening degree of the throttle portion 261 for flow restriction is relatively increased in conjunction with the operation of the variable throttle portion 223 for operation. Since the hydraulic oil of the variable displacement hydraulic pump 201 is preferentially supplied to one actuator 207, the flow rate supplied to the other actuator 206 is not unnecessarily limited and is rational. It is limited within the range. Therefore, according to the hydraulic drive circuit of this embodiment, the one actuator 20 whose main focus is the pressure oil
7 is not only preferentially supplied to the actuators 7, but also the flow rate of the pressure oil can be rationally distributed to the actuators 206 and 207, and even when saturation occurs during combined driving of the actuators 206 and 207, There will be no hindrance to the work.

FIG. 3 illustrates the characteristics of the hydraulic drive circuit of this embodiment as a concrete example. Figure 3
(I), the abscissa means the input to the variable diaphragm section, that is, the operation amount of the operating means of the variable diaphragm section, which is brought by the operator, and the ordinate means the opening area of the variable diaphragm section, that is, the diaphragm opening of the variable diaphragm section. , A ₁ and A ₂ are aperture openings given to the operation variable aperture section 222 and the operation variable aperture section 223 by their inputs, and B ₁ is given in conjunction with the operation of the operation variable aperture section 223. The throttle opening degree of the flow restricting variable throttle portion 261 is shown. When the hydraulic drive circuit according to the present embodiment is driven in combination, the throttle openings of the operation variable throttle section 222, the operation variable throttle section 223, and the flow rate limiting variable throttle section 261 are shown in (I) of FIG. The conditions are set as those given by the relations A ₁ , A ₂ , and B ₁ , and the differential pressure ΔPv _i before and after the throttle with respect to the variable throttle portion 222 for operation, the flow rate Qv _i, and the input to the variable throttle portion 223 for operation are set. Looking at the respective relationships, the relationships shown in (II) and (III) of FIG. 3 are obtained. That is, the operating variable diaphragm unit 22
2 when the actuator 206 is independently operated, the differential pressure ΔPv _i across the throttle of the operating variable throttle unit 222 is the flow restricting variable throttle unit 261 that is fully opened, and the throttle opening is for operation. Since it is equal to the opening of the variable throttle unit 222 when it is fully opened, it is always constant as in the conventional example, as shown by the solid line in (II) of FIG. As a result, the passage flow rate Qv _i in the operation variable throttle unit 222 is input to the operation variable throttle unit 222, that is, the operation amount of the operation means, as in the conventional example, as shown by the solid line in (III) of FIG. It will increase or decrease in direct proportion to. Further, when the actuators 206 and 207 are combinedly driven, the differential pressure ΔPv _i across the throttle of the operation variable throttle unit 222 is shown by a chain line in (II) of FIG. 3 as the input to the operation variable throttle unit 223 increases. To decrease. As a result, the passage flow rate Qv _i in the operation variable throttle unit 222 increases in a suppressed state as the input to the operation variable throttle unit 223 increases, as indicated by the solid line in (III) of FIG. Therefore, the pressure oil of the variable displacement hydraulic pump 201 is fed to one actuator 207.
While being preferentially supplied to the other actuator 206
There is no unnecessarily limited supply flow rate. As described above, according to the hydraulic drive circuit of the present embodiment, when the actuator 206 is independently driven, the actuator 206 can be driven according to the operation amount of the operation lever without being affected by the fluctuation of the circuit pressure, as in the conventional example. Not only can be driven at a predetermined speed, but when saturation occurs during combined driving, the pressure oil of the variable displacement hydraulic pump 201 can be preferentially supplied to one of the main actuators 207,
In addition, it exhibits an excellent characteristic that the flow rate can be distributed to the actuators 206 and 207 rationally. Therefore, in the hydraulic drive circuit of the construction machine,
The actuators 206, 20 are designed by designing such excellent characteristics to be utilized as needed.
It is possible to effectively prevent the occurrence of troubles due to saturation during composite driving of No. 7.

In this embodiment, for convenience of explanation, the flow restricting variable throttle portion 261 is always operated in conjunction with the operation of the operating variable throttle portion 222. However, depending on the work content, the actuator may be operated. In some cases, there is no possibility that saturation will occur during the combined drive of 206 and 207, or troubles associated with saturation will occur, so in such a case, the interlocking means 266 can be attached and detached to release the interlocking operation appropriately. You can Further, in the flow rate control device of the present embodiment, the flow rate limiting variable throttle portion 261 is arranged upstream of the operation variable throttle portion 222 to form the throttle portion group. As long as it is arranged on the downstream side of the pressure compensating section 262, even if the positional relationship between the flow rate limiting variable throttle section 261 and the operation variable throttle section 222 is reversed, there will be no effect on the above-mentioned mathematical expressions. It is clear that the characteristics of the flow rate control device do not fluctuate depending on the positional relationship.

The hydraulic drive circuit of the first embodiment described above has the operation variable throttle portions 222 and 223 and the pressure compensating portion 22.
A plurality of flow rate control devices 220, 22
Although the hydraulic drive circuit of the first conventional example in which the load sensing control is performed by providing No. 1 is improved, the hydraulic drive circuit of the second conventional example also has a common configuration in this respect. Therefore, the configuration of the hydraulic drive circuit of the first embodiment can naturally be applied to the hydraulic drive circuit of the second conventional example. The mode of application will be described. When this is applied to the hydraulic drive circuit of the second conventional example, in the hydraulic drive circuit of the second conventional example of FIG. A flow restricting variable throttle section 261 similar to that of the first embodiment is additionally provided on the upstream side so as to configure a restrictor group together with the operation variable restrictor section 242. The flow restricting variable throttle section 261 is used in the first embodiment. The other flow rate control device 24 using the interlocking means 266 similar to the example.
By connecting to the first variable throttle portion 243 for operation, the throttle opening degree of the variable throttle portion 261 for flow restriction may be changed in conjunction with the operation. In that case, the throttle opening degree of the flow restricting variable throttle portion 261 is the same as in the first embodiment.
The operation variable throttle unit 223 is set so as to decrease in accordance with an increase in the aperture opening of the operation variable aperture unit 223 in association with the operation of the operation variable aperture unit 223.

The hydraulic drive circuit constructed as described above, which is an improvement of the hydraulic drive circuit of the second conventional example, can be considered according to the first embodiment. Therefore, although not particularly shown in the drawings, the hydraulic drive circuit is not shown. The overall configuration of the above is represented based on FIG. 11 which is the drawing of the second conventional example (the flow restricting variable throttle portion and the reference numerals of the interlocking means are the same as those of the first embodiment of FIG. 1). Also used as reference numerals 261 and 266).

"Variable displacement hydraulic pump 206, a plurality of actuators 206 and 207 driven by the hydraulic pressure of the variable displacement hydraulic pump 206, and the maximum load pressure among the load pressures of these actuators 206 and 207 is the maximum load. The pressure detection path 212 is detected, and the maximum load pressure and the discharge pressure of the variable displacement hydraulic pump 201 detected by the discharge pressure detection path 214 are varied so that the discharge pressure becomes higher than the maximum load pressure by a predetermined value. A control means for performing load sensing control for controlling the discharge capacity of the positive displacement hydraulic pump 201 is provided, and variable throttle portions 242, 243 for operation which are operated by the operation lever to adjust the flow rate supplied to the actuators 206, 207, This operating variable diaphragm unit 2
42, 243 are arranged on the downstream side, and control force in the closing direction by the load signal of the signal lines 246, 249 relating to the maximum load pressure, control force in the closing direction by the force of the springs 248, 251 for initial setting, and self-control. Signal line 24 for primary pressure
A control force in the opening direction is applied by the pressure signal of 7,250 to adjust the opening amount so that the primary pressure of the self becomes a constant value sufficient to drive the actuators 206, 207 on the maximum load pressure side. Controlling pressure compensator 244, 245
In the hydraulic drive circuit of the construction machine such as the second conventional example having the flow control devices 240, 241 for controlling the supply flow rates to the actuators 206, 207, among the flow control devices 240, 241 Flow controller 2
40, a flow rate limiting variable throttle section 261 as a means for limiting the flow rate passing through the operation variable throttle section 242 is arranged on the upstream side of the pressure compensating section 244 in 40. By the interlocking means 266, the variable throttle portion 2 for operation is so arranged as to decrease in accordance with an increase in the aperture opening of the variable throttle portion 243 for operation of the other flow rate control device 241.
The setting is made in association with the operation of 43. When the hydraulic drive circuit of the second conventional example is improved to have such a structure, the flow rate control device provided with the variable flow rate restricting throttle portion 261 has the operation variable throttle portion 242 and the flow rate restricting variable throttle portion. It can be considered that it is composed of a throttle portion group including a portion 261 and a pressure compensating portion 244 arranged on the downstream side of the throttle portion group. Since the present flow rate control device has the same characteristics as the flow rate control device 260 in the first embodiment, the present hydraulic drive circuit improved in the second conventional example is similar to the first embodiment in FIG. The characteristics as shown in can be exhibited. In order to confirm this, it will be clarified by using mathematical formulas that the present flow rate control device has the same characteristics as the flow rate control device 260 in the first embodiment, similarly to the description in the first embodiment. .

First, in the pressure compensator 244, the primary pressure of itself, that is, the downstream pressure Pz _i of the throttle unit arranged on the upstream side of the pressure compensator 244, is made to follow the following equation (16) as in the previous equation (5). Have control.

Pz _i = Plmax + Co _i ‥‥‥‥‥‥‥‥‥‥‥ (16) The symbols in the equation (16) have the following meanings.

Pz _i : Downstream pressure of the throttle group (pressure compensator 24
4 primary pressure) Plmax; maximum load pressure Co _i ; constant Co _i in the equation (16) is adjusted to be a negligible small value as in the second conventional example. In the compensating unit 244, the downstream pressure Pz _i of the throttle unit is controlled so as to be substantially equal to the maximum load pressure Plmax, that is, a constant value that is the minimum required to drive the actuator on the maximum load pressure side. become.
On the other hand, the discharge pressure Ps of the variable displacement hydraulic pump 201 that supplies pressure oil to the upstream side of the throttle unit group is determined by the load sensing control as shown in the above equation (2).
Pl higher than load sensing differential pressure ΔP _LS than max
The discharge pressure Ps is controlled to be max + ΔP _LS , and this discharge pressure Ps is sent to the branch paths 3a and 3b and becomes the upstream pressure of the throttle unit group. Then, in the state in which an arbitrary valve opening degree is given to the variable throttle portion 242 for operation of the present flow control device,
The differential pressure Ps-Pz _i of the pressure difference i.e. throttle portion groups the upstream pressure and the downstream pressure of the throttle portion groups, before (2), always as shown in equation (16) from both of the following formula (17) A constant value close to the load sensing differential pressure ΔP _LS will be maintained.

Ps−Pz _i = (Plmax + ΔP _LS ) − (Plmax + Co _i ) = ΔP _LS −Co _i ≈ΔP _LS (17) This load sensing differential pressure ΔP _LS and the operating variable in the throttle group. Looking at the relationship between the differential pressure .DELTA.Pm _i stop before and after the diaphragm of the diaphragm portion 242 differential pressure Pv _i and the flow regulating variable throttle portion 261, this relationship can be expressed with the following equation.

[0077] _{ΔP LS = ΔPv i + ΔPm i} ‥‥‥‥‥ (18) Further, the differential pressure across the diaphragm of the operating variable restrictor 242 Pv _i and the differential pressure .DELTA.Pm _i stop flow restriction variable throttle portion 261
And the passage flow rate in the variable throttle portion 242 for operation and the variable throttle portion 261 for flow rate restriction are as follows.
Like the expressions 2) and (13), it can be expressed by the following expression.

Qv _i = N · A _i √ (ΔPv _i ) ·································································· (19) Qm _i = N · B _i √ (ΔPm _i ). The symbols have the following meanings.

[0079] Qv _i; passing the operating variable throttle portion 242 flow Qm _i; passing the flow restriction variable throttle portion 261 flow A _i; throttle operation variable throttle portion 242 opening B _i; flow restriction variable throttle portion The throttle opening degree of the air conditioner 261 is a constant; the passage flow rate Qv _i in the constant operation variable throttle unit 242 and the passage flow rate Qm _i in the flow rate limiting variable throttle unit 261 are
Since the flow rates of the pressure oils flowing through the same flow path are equal to each other, the following equation can be obtained from the equations (18), (19), and (20), and as a result, the variable throttle portion 242 for operation can be obtained. The differential pressure ΔPv _i across the throttle can be expressed by the following equation (21).

N · A _i √ (ΔPv _i ) = N · B _i √ (ΔPm _i ) = N · B _i √ (ΔP _LS −ΔPv _i ) ∴ ΔPv _i = (B _i / A _i ) ² / {1+ (B _i / A _i ) ² } · ΔP _LS = χ _i ² / (1 + χ _i ² ) · ΔP _LS ‥‥‥‥‥‥‥‥ (21) where χ _i is the flow rate to the operating variable throttle 242. It means the opening area ratio (B _i / A _i ) of the limiting variable diaphragm 261.

Further, the passage flow rate Qv _i in the variable throttle portion 242 for operation of the present flow rate control device can be expressed by the following equation (22).

Qv _i = N · A _i √ (ΔPv _i ) = N · A _i √ {χ _i ² / (1 + χ _i ² ) · ΔP _LS } = √ {χ _i ² / (1 + χ _i ² )} · N・ A _i √ (ΔP _LS ) = √ {χ _i ² / (1 + χ _i ² )} ・ Qv _i ′ ··························································· (21) Since it is substantially the same as the relationship represented by, the characteristic of the differential pressure across the throttle ΔPv _i of the variable throttle portion 242 for operation of the present flow rate control device is as follows.
Similar to the first embodiment, the result is as shown in FIG. Then, as a natural result, the passage flow rate Qv _i in the variable throttle portion 242 for operation of the present flow rate control device expressed by the expression (22) is the same as that of the first embodiment expressed by the expression (15). Since it is substantially the same as,
As in the case of the first embodiment, the larger the ratio of the throttle opening B _i of the flow restricting variable throttle portion 261 to the throttle opening A _i of the operating variable throttle portion 242, the larger the flow control device in the second conventional example. The closer the flow rate is secured, and the smaller the ratio is, the more suppressed the flow rate obtained by reducing the flow rate of the flow rate control device in the second conventional example is obtained. This hydraulic drive circuit
As described above, since the flow rate control device has the same flow rate characteristics as the flow rate control device in the first embodiment, the throttle opening degree of the flow rate limiting variable throttle portion 261 is changed to the operation variable throttle portion 243.
It is apparent that the characteristics as shown in FIG. 3 can be exerted if they can be changed in conjunction with the operation of, like the first embodiment. Therefore, the first conventional hydraulic drive circuit has
Also in the present hydraulic drive circuit improved by applying the configuration of the hydraulic drive circuit of the embodiment, when the actuator 206 is driven independently, it can be operated without being affected by the fluctuation of the circuit pressure as in the conventional example. The variable displacement hydraulic pump 2 can be driven not only at a predetermined speed according to the operation amount of the lever, but also when saturation occurs during composite driving.
One of the main actuators 207 is the pressure oil 01.
To each actuator 206,
It is possible to exert an excellent characteristic that the flow rate can be distributed to the 207 rationally. In addition, in the above description, in attaching the flow restricting variable throttle portion 261 to the flow control device 240 of the second conventional example, only disposing it on the upstream side of the pressure compensating portion 244 is described.
Flow restricting variable throttle 261 and operating variable throttle 242
Although the positional relationship with the flow rate control device is not clarified, as long as the flow restricting variable throttle section 261 is arranged on the upstream side of the pressure compensating section 244, no matter what the positional relationship is, It is clear from the above description in the first embodiment that the fluctuation does not occur.

Next, the hydraulic drive circuit for the construction machine of the second embodiment of the present invention will be described with reference to FIG. 4. The hydraulic drive circuit of the present embodiment is the hydraulic drive circuit of the third conventional example shown in FIG. This is improved by using the same method as in the first embodiment. The hydraulic drive circuit of the first embodiment corresponds to an improved hydraulic drive circuit of the first conventional example that controls the flow rate supplied to an actuator that operates in one direction. The hydraulic drive circuit of the third conventional example shown in FIG. 12 is modified so that the supply flow rate to the bidirectional actuator can be controlled. Therefore, the configuration of the hydraulic drive circuit of the first example is the same as that of the third conventional example. Of course, it can be applied to the hydraulic drive circuit. As is apparent from FIG. 4, the hydraulic drive circuit of the second embodiment includes a variable displacement hydraulic pump 201 whose discharge displacement is controlled by a tilt control device 202, as compared with the hydraulic drive circuit of the third conventional example shown in FIG. , A plurality of actuators 2 that are driven in combination by this variable displacement hydraulic pump 201
06, 207 and these actuators 20
The maximum load pressure among the 6,207 load pressures is detected by the maximum load pressure detection path 212, and the maximum load pressure and the discharge pressure detection path 2 are detected.
Based on the discharge pressure of the variable displacement hydraulic pump 201 detected by 14, the discharge displacement of the variable displacement hydraulic pump 201 is controlled through the tilt control device 202 so that this discharge pressure becomes higher than the maximum load pressure by a predetermined value. However, it is common to the hydraulic drive circuit of the third conventional example in that the load sensing control is performed. Further, the variable throttle portions 222a, 222 for operation which are operated by the hydraulic pilot operating device 270 to adjust the flow rate supplied to the actuator 206.
Hydraulic pilot operating device 2 with b built in the 1 and r positions
70 is operated by a closed center type directional control valve 272 for two-way drive and a hydraulic pilot operating device 271 that can switch the flow path of pressure oil so that the actuator 206 can be driven in two directions by the actuator 207. Variable throttle part 2 for operation that adjusts the supply flow rate of
23a and 223b are built in the l position and the r position, and a similar directional control valve 273 that can switch the flow path of the pressure oil so that the actuator 207 can be driven in two directions by the hydraulic pilot operating device 271 is provided. Signal line 2 for load pressure of actuators 206 and 207
26, 229 control signals in the opening direction by the load signals, control forces in the opening direction set by the springs 228, 231, which are differential pressure setting means, and signal conduits 227 relating to the secondary pressure of itself.
The control force in the closing direction is applied by the pressure signal of 230 to adjust the opening amount, and the secondary pressure of itself is controlled by the springs 228 and 231 to be higher than the load pressure of the actuators 206 and 207 by a certain value. Pressure compensator 224,22
5 is also arranged upstream of the directional control valves 272 and 273, respectively, which is also common to the hydraulic drive circuit of the third conventional example. Further, in this way, each actuator 206,
Since 207 can be driven in two directions,
As a matter of course, like the hydraulic drive circuit of the third conventional example,
A pair of load conduits 204a, 204b that connect the bottom side and rod side of the actuator 206 to the directional control valve 272 to form an oil path for bidirectional driving of the actuator 206;
A pair of load conduits 2 that connect the bottom side and rod side of the actuator 207 to the directional control valve 273 to form a similar oil path.
05a and 205b. Therefore, regarding the hydraulic drive circuit of the second embodiment of FIG. 4, description of the configuration relating to these points is omitted, and only the improvements of the hydraulic drive circuit of the third conventional example will be described.

In FIG. 4, 267 is a pressure compensator 224.
Is a flow rate limiting variable throttle section that is arranged on the downstream side of the directional control valve 272 and that acts to suppress the differential pressure across the throttle of the operation variable throttle section 222a or the operation variable throttle section 222b to limit the flow rate thereof. The operation variable throttle unit 222a or the operation variable throttle unit 222b forms a throttle unit group, and constitutes a kind of flow rate control device together with the pressure compensation unit 224.
The flow restricting variable throttle section 267 has a variable throttle section 267a and a variable throttle section 26 at its left and right positions, respectively.
7b and is connected to the spool of the direction control valve 273, it is switched to the left position or the right position in conjunction with the operation of the control valve 273. That is, when the directional control valve 273 is in the non-operation state, the directional control valve 273 is in the neutral state and is in the fully open state, and the directional control valve 273 is in the 1 position or the r position.
When the switch is operated to the position, it is switched to the left position or the right position, and the throttle openings of the variable throttle parts 267 and 267b at the left and right positions of the variable throttle parts 223a and 223b for operation of the directional control valve 273. This operating variable throttle unit 2 is designed to decrease as the throttle opening increases.
It is set in conjunction with the operation of 23a and 223b. Therefore, the flow restricting variable throttle portion 267 is in the fully open state when the one directional control valve 273 is in the non-operation state, so that the other variable directional throttle portion 22 of the directional control valve 272 is in the open state.
When the one directional control valve 273 is switched to the 1 position without any limitation on the flow rates of 2a and 222b, the variable throttle part 267a at the left position is switched by being switched to the left position in accordance with the switching operation. Of the directional control valve 272 serves to suppress the differential pressure across the throttle of the operating variable throttle portion of the operating variable throttle portions 222a and 222b on the operating side to limit the passing flow rate, and the r position When it is switched to the right position, the variable throttle unit 267b at the right position restricts the differential pressure across the throttle of the operating variable throttle unit on the operating side to limit the passage flow rate. Work. In this way, the flow restricting variable throttle unit 2
67, when one of the directional control valves 273 is switched to either the l position or the r position, it operates in conjunction with the switching operation, and the variable squeezing portion 222a for operation of the other directional control valve 272, It can serve to limit the flow rate through 222b. The flow restricting variable throttle portion 267 is different from the flow restricting variable throttle portion 261 in the above-described first embodiment in this respect, but there is no substantial difference in its function, and the operation variable throttle portion 267 is the same. The characteristics of 222a and 222b are set to the flow restricting variable throttle portion 261 in the first embodiment.
Similar to the above, it can be changed to one having the characteristics shown in FIG.

Since the hydraulic drive circuit of the second embodiment has such a structure, for example, the direction control valve 272 is
By switching to the position, the directional control valve 273 is switched to the 1 position or the r position in a state where one actuator 206 is being driven upward through the variable throttle portion 222a for operation, and the other one which is the main focus for the work. If the actuator 207 is driven upward or downward for composite driving, the flow restricting variable throttle section 267 is switched to the left position or the right position in conjunction with the switching operation, and the flow restricting variable throttle section 267 of The variable throttle portion 267a or the variable throttle portion 267b at the left position or the right position is the directional control valve 27.
A throttle unit group is formed on the downstream side of the pressure compensation unit 224 together with the variable throttle unit 222a for operation in No. 2. As a result, the variable throttle portion 267a or the variable throttle portion 267b of the flow rate limiting variable throttle portion 267 is operated by the variable throttle portion 223a or the variable throttle portion 223b for operation of the directional control valve 273, respectively.
The differential pressure across the throttle of the variable throttle portion 222a for operation is suppressed according to the throttle opening degree to limit the flow rate thereof, and the pressure oil of the variable displacement hydraulic pump 201 is preferentially supplied to the actuator 207 which is the main target thereof. . Further, by switching the directional control valve 272 to the r position, the directional control valve 273 is switched to the 1 position or the r position in a state where one actuator 206 is driven downward through the operation variable throttle portion 222b. Assuming that the other actuator 207, which is the main object, is driven upward or downward for compound driving, the flow restricting variable throttle portion 267 is switched to the left position or the right position in conjunction with the switching operation, and similarly, Variable throttle part 267a of variable throttle part 267 for flow rate restriction or variable throttle part 26
7b are variable throttle portions 2 for operating the directional control valve 273.
23a or the flow rate of the variable throttle portion 222b for operation is restricted according to the throttle opening degree of the variable throttle portion 223b for operation, and the pressure oil of the variable displacement hydraulic pump 201 is preferentially supplied to the actuator 207 which is the main object. Therefore, in the hydraulic drive circuit of this embodiment, the actuator 20
In any case of vertically driving 6 and 207, when the saturation occurs during the compound driving, the pressure oil of the variable displacement hydraulic pump 201 can be preferentially supplied to one actuator 207 which is the main focus of the work. Moreover, it is possible to exhibit the same excellent characteristics as the hydraulic drive circuit of the first embodiment that the flow rate can be distributed to the actuators 206 and 207 rationally.

A hydraulic drive circuit for a construction machine according to a third embodiment of the present invention will be described with reference to FIG. 5. The hydraulic drive circuit of the present embodiment is the hydraulic drive circuit of the fourth conventional example shown in FIG. Using a method similar to the example, the actuator 20
Even if the 6 and 207 are combined and driven in any direction, the first
The hydraulic drive circuit is improved so as to exhibit the same excellent characteristics as the hydraulic drive circuit of the embodiment. As is apparent from FIG. 5, the hydraulic drive circuit of the third embodiment includes a variable displacement hydraulic pump 201 whose discharge displacement is controlled by a tilt control device 202, as compared with the hydraulic drive circuit of the fourth conventional example shown in FIG. , Having a plurality of actuators 206 and 207 that are driven in combination by the variable displacement hydraulic pump 201,
The maximum load pressure of the load pressures of the actuators 206 and 207 is detected by the maximum load pressure detection path 212, and the maximum load pressure and the discharge pressure of the variable displacement hydraulic pump 201 detected by the discharge pressure detection path 214 are detected. Accordingly, the displacement of the variable displacement hydraulic pump 201 is controlled through the tilt control device 202 so that the discharge pressure becomes higher than the maximum load pressure by a predetermined value, and the load sensing control is performed. 4 It is common to the hydraulic drive circuit of the conventional example. Further, the variable throttle portions 242a and 242b for operation, which are operated by the hydraulic pilot operating device 270 to adjust the flow rate supplied to the actuator 206, are built in at the l position and the r position, and the actuator 206 is driven in two directions by the hydraulic pilot operating device 270. A closed center type directional control valve 274 for two-way drive and a hydraulic pilot operating device 27 capable of switching the pressure oil flow path as much as possible.
The variable throttle portions 243a and 243b for operation, which are operated by No. 1 to adjust the supply flow rate to the actuator 207, are built in the l position and the r position, so that the hydraulic pilot operating device 271 can drive the actuator 207 in two directions. A similar directional control valve 275 capable of switching the flow path is provided, and the control force in the closing direction by the load signals of the signal lines 246 and 249 relating to the maximum load pressure, the force of the springs 248 and 251 for initial setting. Signal lines 247, 250 relating to the control force in the closing direction and the primary pressure of the self
The control force in the opening direction is applied by the pressure signal of No. 1, and the opening amount is adjusted to control the primary pressure of the self so that the primary pressure of the self becomes a constant value sufficient to drive the actuators 206 and 207 on the maximum load pressure side. The compensating portions 224 and 225 are arranged downstream of the directional control valves 274 and 275, respectively, which is also common to the hydraulic drive circuit of the fourth conventional example. Further, since the actuators 206 and 207 can be driven in two directions as described above, the bottom side and the rod side of the actuator 206 are naturally directed in the same direction as the hydraulic drive circuit of the fourth conventional example. A pair of load conduits 204a and 204b which are connected to the control valve 272 to form an oil passage for two-way driving of the actuator 206, and a bottom side and a rod side of the actuator 207 are connected to the directional control valve 273 to form a similar oil path. Forming a pair of load pipes 205a, 2
05b and. Therefore, regarding the hydraulic drive circuit of the third embodiment of FIG. 5, description of the configuration relating to these points will be omitted, and only the improvements of the hydraulic drive circuit of the fourth conventional example will be described.

In FIG. 5, reference numeral 268 is a pressure compensator 224.
Of the directional control valve 274, which is arranged further upstream of the directional control valve 274 arranged upstream of the directional control valve 274.
42a or the variable throttle portion for operation 242b is a variable throttle portion for restricting a flow rate that acts to suppress the differential pressure across the throttle and restricts the flow rate thereof. The variable throttle portion for operation 242a or the variable throttle portion for operation 242b restricts The pressure compensating section 244 constitutes a kind of flow rate control device. The flow restricting variable throttle portion 268 has a variable throttle portion 268a and a variable throttle portion 268b at its left position and right position, respectively, and is connected to the spool of the directional control valve 275 to operate the control valve 275. The operation is switched to the right position or the left position in conjunction with. That is, when the directional control valve 275 is in the non-operation state, it is in the neutral state and is in the fully open state, and when the directional control valve 275 is switched to the 1 position or the r position, the left position or the right position. The variable diaphragm portion 26 at the left and right positions while being switched to the position
8a and 268b so that the throttle opening degree of the directional control valve 275 decreases in accordance with the increase of the throttle opening degree of the operation variable throttle portions 243a and 243b.
It is set in association with the operation of a and 243b. Therefore, the flow restricting variable throttle portion 268 is different from the flow restricting variable throttle portion 267 in the second embodiment only in the spool of the directional control valve connected thereto, and there is substantially no difference in the functions of both. Therefore, the operating variable diaphragm units 242a, 242a, 2
The characteristic of 42b is the same as that of the flow restricting variable throttle 267.
The characteristics can be changed to those shown in FIG.

Since the hydraulic drive circuit according to the third embodiment has such a structure, the variable throttle portion 242 for operation can be operated by switching one of the directional control valves 274 to the l position or the r position.
In the state where one actuator 206 is driven upward or downward through a or the variable throttle portion 242b for operation, the other directional control valve 275 is switched to the 1 position or the r position, and the other one that is the main focus for the work. If the actuator 207 is driven upwards or downwards for composite driving, the flow restricting variable throttle section 268 is switched to the left position or the right position in conjunction with the switching operation, and the flow restricting variable throttle section 268. The variable throttle 268a or the variable throttle 268b in the left or right position of the control valve together with any one of the operating variable throttle 242a and the operating variable throttle 242b of one directional control valve 274 being operated. A throttle unit group is formed on the downstream side of the compensation unit 244. As a result, the variable throttle portion 268a or the variable throttle portion 268b of the flow restricting variable throttle portion 268 is changed according to the throttle opening degree of the operation variable throttle portion 243a or the operation variable throttle portion 243b of the other directional control valve 275. One of the directional control valve 274, the variable throttle portion 242a for operation and the variable throttle portion for operation 242b, is controlled to suppress the differential pressure across the throttle to limit the flow rate thereof, and a variable displacement hydraulic pump. The pressure oil 201 is preferentially supplied to the main actuator 207. Therefore, in the hydraulic drive circuit of this embodiment, the actuators 206, 20
When the composite drive of 7 is performed in any of the up and down directions, when the saturation occurs during the composite drive, the pressure oil of the variable displacement hydraulic pump 201 can be preferentially supplied to the actuator 207, which is the main focus of the work, and The same excellent characteristics as the hydraulic drive circuit of the first embodiment that the flow rate can be distributed to the actuators 206 and 207 rationally can be exhibited. In this example,
Although the flow restricting variable throttle portion 268 is arranged on the upstream side of the directional control valve 274, it may be arranged in the downstream pipe line 217 provided between the directional control valve 274 and the pressure compensating portion 244. The fact that the same characteristics can be exhibited is apparent from what has already been described in the first embodiment.

In any of the flow rate control devices of the first and second embodiments described above, the variable flow restricting throttle portion is arranged upstream of the operating variable throttle portion. Even if the relationship is reversed, the same effect can be achieved,
It is clear from what has already been described in the first embodiment and the like, as long as the arrangement of the flow restricting variable throttle portion with respect to the pressure compensating portion is specified in the relationship as described in the hydraulic drive circuit of each embodiment. Since it is good, it is a matter of design choice how to make those positional relationships. Further, in these examples, for convenience of explanation, only an example of a hydraulic drive circuit provided with two actuators and operating variable throttles corresponding thereto is shown, but by providing three or more of these,
It is of course possible to dispose the variable flow restricting throttle portion with respect to a part of the variable throttle portion for operation, and link this with the operation of another variable throttle portion for operation. In such a case, a plurality of flow rate limiting variable throttle portions that are interlocked with the operation of such other operating variable throttle portions may be arranged with respect to the same variable throttle portion for operation, as will be apparent from the following embodiments. You can also do it.

A hydraulic drive circuit for a construction machine according to a fourth embodiment of the present invention will be described with reference to FIG. 6. The hydraulic drive circuit of the present embodiment is an improvement of the hydraulic drive circuit of the fifth conventional example shown in FIG. Equivalent to a thing. The hydraulic drive circuit of the fourth embodiment relates to the hydraulic excavator as in the fifth conventional example, and as can be seen from FIG.
Two variable displacement hydraulic pumps 1 and 2 whose discharge displacements are respectively controlled by 1, 42, and a swing hydraulic motor 31, an arm cylinder 32, as actuators driven by these two variable displacement hydraulic pumps 1 and 2. A boom cylinder 33, a bucket cylinder 34, a first traveling motor 35, and a second traveling motor 36 are provided, and the maximum load pressure detection paths 8a and 8a are provided for the actuator groups driven by the variable displacement hydraulic pumps 1 and 2, respectively. The maximum load pressure is detected at 8b, and the maximum load pressure and the discharge pressures of the variable displacement hydraulic pumps 1 and 2 detected at the discharge pressure detection paths 43a and 43b make the discharge pressures higher than the maximum load pressures. Also, each displacement of the variable displacement hydraulic pumps 1 and 2 is controlled through the tilt control devices 41 and 42 so as to increase by a predetermined value, and load sensing control is performed. In terms are Unishi, in common with the hydraulic drive circuit of the fifth conventional example of FIG. 15. In addition, the actuators 31 to 36 are operated by the hydraulic pilot operating device corresponding to the actuators 31 to 36.
A pair of right and left operation variable throttles for adjusting the supply flow rate to the pressure control valve 36 are installed at the r position and the left position, respectively, so that the pressure oil flow passage is formed so that the actuators 31 to 36 can be combined and driven in two directions by the hydraulic pilot operating device. A closed center type directional control valve 3 for two-way merging drive capable of switching operation is provided, and signal lines 9a, 9 relating to the maximum load pressure are provided.
The control force in the closing direction by the load signal of b, the control force in the closing direction by the spring force for the initial setting, and the control force in the opening direction by the pressure signal of the signal lines 10a and 10b regarding the primary pressure of the self are given to open. The pressure compensators 4a and 4b for adjusting the amount of the self-adjustment so that the self-primary pressure is set to a constant value sufficient to drive the actuator on the maximum load pressure side are provided on the secondary side of each operation variable throttle unit. It is also common to the hydraulic drive circuit of the fifth conventional example in that it is arranged in each of the left and right output conduits that communicate with. Further, since the actuators 31 to 36 can be driven to merge in two directions in this manner, it goes without saying that the actuators 31 to 36 pass through the pressure compensating portions 4a and 4b as in the hydraulic drive circuit of the fifth conventional example. The combined pressure oil is merged in the merge connection pipe line 5, and the merged pressure oil is guided to one of the load pipe lines 6a or 6b to be supplied to the actuators 31 to 36, and at the same time, the actuators 31 to 31.
The pressure oil in 36 can be discharged to the tank through the other load pipeline 6b or the load pipeline 6a. Therefore, in the hydraulic drive circuit of the fourth embodiment of FIG. 6, description of the configuration relating to these points will be omitted, and only the remaining points will be described. Hereinafter, in describing the embodiments of the present invention, the directional control valve 3 for two-way merging drive provided corresponding to each actuator 31 to 36.
Respectively, a swing motor directional control valve, an arm cylinder directional control valve, a boom cylinder directional control valve, a bucket cylinder directional control valve, a first traveling motor directional control valve, and a second traveling motor directional control valve. Call.

In the hydraulic drive circuit of the fourth embodiment, the base hydraulic circuit is slightly changed from the hydraulic drive circuit of the fifth conventional example. First, this point will be explained. The circuit divides the pressure oil introduced into the first main pipe line 11 and the second main pipe line 12 into the first variable throttle portion for operation and the second variable throttle portion for operation of each directional control valve. In contrast to the first and second diversion pipes of each directional control valve, which are always fixedly connected to the first main pipe 11 and the second main pipe, respectively. In the hydraulic drive circuit, the second diversion conduit 20b of the first traveling motor directional control valve and the first diversion conduit 20a of the second traveling motor directional control valve are operated by the switching valve 60 described in detail later. , If control valves other than these directional control valves are activated, Each is connected to the second main pipe line 12 and the first main pipe line 11, so as when otherwise connected to its opposite. In FIG. 6, reference numeral 51 is a variable flow restricting portion for restricting the flow rate, which is interlocked with the operation of the swing motor directional control valve and the arm cylinder directional control valve, two of which are arranged in the first main pipeline 11, and 52 is the second. For limiting the flow rate, four of which are arranged in the main pipeline 12 are linked to the operation of the boom cylinder directional control valve, the bucket cylinder directional control valve, the first traveling motor directional control valve, and the second traveling motor directional control valve. The variable diaphragm unit. Flow restricting variable throttle parts 51, 52 which are interlocked with the operation of these directional control valves 3.
Both are in the neutral state and in the fully open state when the directional control valve 3 is in the non-operation state, and when the directional control valve 3 is switched to the 1 position or the r position. , The left or right position is switched, and the throttle opening of the variable throttle at the left and right positions thereof is decreased in accordance with the increase of the throttle opening of the variable throttle for operation built in the directional control valve 3. It is set in conjunction with the operation of the operation variable aperture section. Therefore, the flow restricting variable throttle parts 51 and 52 show the characteristics of the operation variable restricting part in the directional control valve 3 on the downstream side thereof in the same manner as the flow rate restricting variable restrictor part 268 in the third embodiment shown in FIG. It can be changed to one with such characteristics. When the two flow restricting variable throttles 51 interlocked with the operation of the swing motor directional control valve and the arm cylinder directional control valve are arranged in the first main conduit 11, the swing motor directional control valve and the arm cylinder Downstream of the first diversion pipe 20a of the directional control valve, upstream of the remaining first diversion pipe 20a, that is, the directional control valve for the boom cylinder, the directional control valve for the bucket cylinder, and the direction for the first traveling motor. The control valve and the second travel motor directional control valve are arranged on the upstream side of the first branch pipe 20a. In the case where the flow restricting variable throttling portion 52 interlocked with the operation of the first traveling motor directional control valve and the second traveling motor directional controlling valve among the four flow restricting variable throttling portions 52 is arranged in the main pipeline 12. ,
The second flow dividing pipe 20b and the second flow dividing pipe 20b of the first traveling motor directional control valve when the pressure oil in the second main pipe 12 is divided.
Downstream of the second diversion pipe 20b of the traveling motor directional control valve and upstream of the other second diversion pipe 20b, that is, a slewing motor directional control valve, an arm cylinder directional control valve, and a boom cylinder directional control. The valve and the bucket cylinder directional control valve are arranged on the upstream side of the second flow dividing pipe 20b. Four
Among the individual flow restricting variable throttles 52, the flow restricting variable throttles 52 interlocked with the operation of the boom cylinder directional control valve and the bucket cylinder directional control valve are arranged in the main pipe line 12 when these bidirectional control valves are arranged. Second branch line 20b of
Is arranged on the downstream side of the second branch pipe 20b of the swing motor directional control valve and the arm cylinder directional control valve. The flow restricting variable throttling portion 51 is connected to the downstream diversion conduit 20a in accordance with an increase in the throttling opening of the operating variable throttling portion at each of the l and r positions of the directional control valve interlocking with the flow restricting variable throttle portion 51. The directional control valve 3 provided on the upstream diversion conduit 20a is limited by limiting the flow rate of the first variable throttle portion for operation at each position of l and r of each directional control valve provided on the upstream side. Through, the pressure oil of the variable displacement hydraulic pump 1 is preferentially supplied to the actuator. The flow restricting variable throttle portion 52 is connected to the downstream diversion conduit 20b in accordance with an increase in the throttle opening of the operating variable throttle portion at each of the l and r positions of the directional control valve interlocking with the flow restricting variable throttle portion 52.
The directional control valve 3 provided in the upstream diversion conduit 20b is limited by limiting the passage flow rate of the second variable throttle portion for operation at each position of l and r of each directional control valve provided in Through, the pressure oil of the variable displacement hydraulic pump 2 is preferentially supplied to the actuator.

Reference numeral 60 denotes a circuit switching unit 61 and a load signal switching unit 6
A directional control valve for a swing motor, a directional control valve for an arm cylinder, a directional control valve for a boom cylinder, and a directional control valve for a bucket cylinder, that is, the first traveling motor. When the directional control valves other than the directional control valve for the second drive motor and the directional control valve for the second traveling motor are being switched, the directional control valve is moved to the right and switched to the left position, and at other times, the neutral position on the right side. Switched to position. The mechanism for realizing the switching will be described in detail later with an example. Since the switching valve 60 performs such a switching operation, the pressure from the main pipe lines 11 and 12 to the diversion pipe line 20b of the first traveling motor directional control valve and the diversion pipe line 20a of the second traveling motor directional control valve is reduced. The flow of oil is switched by the circuit switching unit 61, and the load signal switching unit 62 switches the flow of load signals of the load signal pipe 5a and the signal pipes 9a, 9b for closing operation for these directional control valves. can do. More specifically, the structure will be described. In the circuit switching unit 61 of the switching valve 60, the two branch ports 20b on one side are provided with the second branch pipe 20b and the first main pipe of the directional control valve for the first traveling motor. Is connected to the path 11, and to the two ports on the other side,
A diversion introducing pipe for guiding the pressure oil in the second main pipe 12 to the first diversion pipe 20a of the second traveling motor directional control valve or the second diversion pipe 20b of the first traveling motor directional control valve. Road 1
3 and the first diversion line 20 of the directional control valve for the second traveling motor
and a are connected. Load signal switching unit 6 of switching valve 60
2, two ports on one side are provided with a maximum load pressure detection extension path 6 that can be an extension of the maximum load pressure detection paths 8a and 8b.
3 and the first maximum load pressure detection path 8a are connected, and two ports on the other side are provided for closing the first pressure compensating portion 4a corresponding to the directional control valve for the second traveling motor. The signal line 9a and the second maximum load pressure detection line 8b are connected. In addition, in the maximum load pressure detection extension path 63, a second pressure compensating portion 9b corresponding to the first traveling motor directional control valve is provided.
The signal line 9b for closing operation and the load signal line 5a are connected in series.

This switching valve 60 is moved from the illustrated position to the left position by a mechanism as will be illustrated later, when the valves other than the first traveling motor directional control valve and the second traveling motor directional control valve are switched. The first main pipe line 11 is introduced into the first diversion pipe line 20a of the second traveling motor directional control valve, and the first diversion pipe line is introduced into the second diversion pipe line 20b of the first traveling motor directional control valve. In order to connect the pipelines 13 via the flow paths in the circuit switching unit 61, respectively, the first main pipeline 11
And the pressure oil in the second main pipe 12 is divided into the first diversion pipe 20a of the second traveling motor directional control valve and the second diversion pipe 20b of the first traveling motor directional control valve, respectively.
At the same time, the second maximum load pressure detection path 8b is provided in the maximum load pressure detection extension path 63, and the second maximum load pressure detection path 8b is provided in the signal line 9a for closing the first pressure compensation section 4a corresponding to the second travel motor directional control valve. 1
The maximum load pressure detection paths 8a of the first traveling motor 3 are connected to each other via the flow paths in the load signal switching unit 62.
The load signal of No. 5 becomes a load signal for detecting the maximum load pressure on the second maximum load pressure detection path 8b, and the load signal related to the maximum load pressure on the second maximum load pressure detection path 8b is the first traveling. Second pressure compensator 4b corresponding to the directional control valve
Is applied to the signal pipe 9b of the first direction to apply a control force in the closing direction, and the load signal relating to the maximum load pressure of the first maximum load pressure detection path 8a corresponds to the second traveling directional control valve. The compensator 9a is switched to the signal line 9a of the compensator 9a so as to apply the control force in the closing direction. Further, when the valves other than the first traveling motor directional control valve and the second traveling motor directional control valve are not switched, the switching valve 60 is switched to the position shown in the drawing, whereby the first traveling motor directional control valve is switched. The first main pipe line 11 is provided in the second diversion pipe line 20b of the control valve, the diversion introduction pipe line 13 is provided in the second diversion pipe line 20a of the second traveling motor directional control valve, and the flow in the circuit switching unit 61 is increased. So that the pressure oils in the first main pipe 11 and the second main pipe 12 are respectively connected via the passages, the second diversion pipe 20b and the second drive motor direction of the first traveling motor directional control valve are respectively supplied. The flow is divided into the first flow dividing pipe 20a of the control valve. At the same time, the first maximum load pressure detection path 8a is added to the maximum load pressure detection extension path 63.
The second maximum load pressure detection path 8b is connected to the signal line 9a for closing the first pressure compensating section 4a corresponding to the directional control valve for the second traveling motor, and the flow path in the load signal switching section 62. , The load signal of the first traveling motor 35 becomes a load signal for detecting the maximum load pressure in the first maximum load pressure detection path 8a, and the first maximum load pressure detection path is detected. The load signal relating to the maximum load pressure of 8a is introduced to the signal line 9b of the second pressure compensating portion 4b corresponding to the first traveling directional control valve to give the control force in the closing direction, and the second maximum load. The load signal relating to the maximum load pressure of the pressure detection path 8b is guided to the signal line 9a of the first pressure compensating section 9a corresponding to the second traveling directional control valve and is switched so as to apply the control force in the closing direction. .

An example of a mechanism for realizing such a switching operation will be described with reference to FIG. In FIG. 7, the parts denoted by the same reference numerals as those in FIG. 6 represent the same parts as those in FIG. In FIG. 7, only the essential parts of the directional control valve 3 which are indispensable for the description are shown for convenience of description, but the directional control valves 3 shown in FIG. A directional control valve similar to that shown,
In order from the bottom, a swing motor directional control valve, an arm cylinder directional control valve, a boom cylinder directional control valve, a bucket cylinder directional control valve, a first traveling motor directional control valve,
The directional control valve for 2nd traveling motors is represented. In FIG. 7, reference numeral 80 is a pilot pump as a pilot pressure generation source for generating a pilot pressure introduced to the signal receiving portion of the switching valve 60, 81 is a discharge line of the pilot pressure, and 82
Is a throttle, 84 is a relief valve provided in the discharge pipe 81,
Reference numeral 90 denotes a pilot operating device for outputting pilot pressure to the pilot conduits 91a and 91b to switch the directional control valve 3, and has a mechanism similar to that of the pilot operating devices 270 and 271 already described in FIG. . Although not shown in FIGS. 6 and 15, the directional control valve 3 is provided with a flow path for communicating the pilot pressure bypass conduit 83b with the tank in the neutral position. for that reason,
When all of the swing motor directional control valve, the arm cylinder directional control valve, the boom cylinder directional control valve, and the bucket cylinder directional control valve are in a neutral position, the downstream pilot pipe from the pilot conduit 83 is provided. The pilot pressure, which is about to be guided to the signal receiving portion of the switching valve 60 through the passage 83a, is released to the tank through the pilot pressure bypass pipe passage 83b so that the switching valve 60 cannot be switched to the left position. Further, when the directional control valves are switched to either of the left and right positions,
It is designed to shut off the pilot pressure bypass line. Therefore, when at least one of the directional control valve for the swing motor, the directional control valve for the arm cylinder, the directional control valve for the boom cylinder, and the directional control valve for the bucket cylinder operates, the pilot pressure bypass line 83b is shut off. As a result of the pilot pressure from the pilot conduit 83 acting on the signal receiving portion of the switching valve 60 via the downstream pilot conduit 83a, the switching valve 60 is switched to the left position. The switching operation of the switching valve 60 described above can be realized by such a mechanism.

Since the hydraulic drive circuit of the hydraulic excavator of the fourth embodiment has the above-mentioned structure, the pressure oils of the variable displacement hydraulic pumps 1 and 2 are distributed in the following priority relationship. Distribute to the directional control valve 3.

(1) Directional control valves for swing motor and arm cylinder For the first branch pipe 20a of the direction control valve for swing motor and the direction control valve for arm cylinder, the respective directional control valves are provided. The first variable displacement hydraulic pump 1 is configured to suppress the flow of the pressure oil to the remaining first flow dividing pipes 20a by the two flow restricting variable throttle portions 51 which are respectively interlocked with each other.
Pressure oil is preferentially supplied. Further, for the second branch pipe 20b of the swing motor directional control valve and the arm cylinder directional control valve, a boom cylinder directional control valve, a bucket cylinder directional control valve, and a first traveling motor directional control valve. When at least one of the second traveling motor directional control valves is operated in a combined manner, the flow rate limiting variable throttle portion 52 interlocking with the operated directional control valve suppresses the shunt of the pressure oil. The pressure oil of the second variable displacement hydraulic pump 2 is non-priority supplied.

(2) Boom Cylinder and Bucket Cylinder Directional Control Valves For the first branch pipe 20a of the boom cylinder directional control valve and the bucket cylinder directional control valve, a slewing motor directional control valve and When at least one of the arm cylinder directional control valves is operated in combination, the flow restricting variable throttle section 51 interlocking with the operated directional control valve suppresses the shunt of the pressure oil, so that The pressure oil of the variable displacement hydraulic pump 1 is non-priority supplied.
At least one of the first traveling motor directional control valve and the second traveling motor directional control valve is connected to the second branch pipe 20b of the boom cylinder directional control valve and the bucket cylinder directional control valve. When one of the second variable displacement hydraulic pumps 2 is operated in a combined manner, the flow rate restricting variable throttle portion 52 interlocking with the combined operated directional control valve suppresses the shunting of the pressure oil. Non-priority supply, otherwise, by the two flow restricting variable throttles 52 respectively linked with the boom cylinder directional control valve and the bucket cylinder directional control valve, the swing motor directional control valve and the arm cylinder. Second direction control valve
Of the pressure oil to the flow dividing pipe 20b
The pressure oil of the variable displacement hydraulic pump 2 is preferentially supplied.

(3) Directional control valves for the first traveling motor and the second traveling motor When only traveling is performed, the circuit switching portion 61 of the switching valve 60 is kept in the illustrated state. The pressure oil of the first variable displacement hydraulic pump 1 is supplied to both of the flow dividing pipes 20a and 20b of the first traveling motor directional control valve, and at the same time, the second traveling motor directional control valve The pressure oil of the second variable displacement hydraulic pump 2 is supplied to both of the flow dividing pipes 20a and 20b, so that the hydraulic excavator can run at a desired speed. Also,
When at least one of the directional control valve for the swing motor, the directional control valve for the arm cylinder, the directional control valve for the boom cylinder, and the directional control valve for the bucket cylinder is operated in combination with these directional control valves for the traveling motors, Since the circuit switching unit 61 of the switching valve 60 is switched from the position shown in the drawing to the left position, for the second branch pipe 20b of the first traveling motor directional control valve and the second traveling motor directional control valve, The two variable displacement hydraulic pumps 2 for suppressing the flow of the pressure oil to the other second flow dividing pipes 12b are controlled by the two flow restricting variable throttles 52 which are interlocked with the respective directional control valves. Pressure oil is preferentially supplied. At the same time, for the first branch pipe 20a of the directional control valve for the first traveling motor and the directional control valve for the second traveling motor, the combined directional control valve is the directional control valve for the swing motor and the arm cylinder. If it is at least one of the directional control valves, the flow restricting variable throttle portion 51 interlocking with the directional control valve suppresses the shunt of the pressure oil, so that the pressure oil of the first variable displacement hydraulic pump 1 is controlled. Is supplied non-priority,
Further, if it is either the boom cylinder directional control valve or the bucket cylinder directional control valve, it is appropriately supplied according to the operation amount regardless of whether the directional control valve has priority or non-priority.

Since the hydraulic drive circuit of this embodiment distributes the pressure oil of the variable displacement hydraulic pumps 1 and 2 to the directional control valve 3 in such a priority relationship, for example, the arm cylinder 32 and the boom cylinder 33 are separated from each other. When the combined drive is performed, the pressure oil of the first variable displacement hydraulic pump 1 responds to the operation amount of the directional control valve for the arm cylinder by the function of the flow restricting variable throttle portion 51 that is interlocked with the operation. And is preferentially supplied from the first branch pipe 20a. At the same time, with respect to the boom cylinder directional control valve, the pressure oil of the second variable displacement hydraulic pump 2 moves to the second direction according to the operation amount by the action of the flow restricting variable throttle portion 52 which is interlocked with its operation. Is preferentially supplied from the diversion pipe 20b. Therefore, even if the operation amount of the boom 33 is increased and the drive speed thereof is increased, a required amount of pressure oil is supplied from the second variable displacement hydraulic pump 2 according to the operation amount of the boom cylinder directional control valve. "Is a problem that the invention is trying to solve."
Even if the work requires the boom raising height as well as the arm operation like the slope leveling work described in the above section, the work is not hindered.

Traveling motors 35 and 36 and arm cylinder 3
As for the case where the two are combinedly driven, in this case, the switching valve 60 is switched from the position shown in the drawing to the left position by operating the arm cylinder directional control valve, and the first main pipe line 11 and the second The pressure oil in the main pipeline 12 is passed through the circuit switching unit 61 to the first diversion pipeline 20a of the second traveling motor directional control valve and the second of the first traveling motor directional control valve.
The flow is divided into the flow dividing pipe 20b. as a result,
With respect to the first traveling motor directional control valve and the second traveling motor directional control valve, the second variable displacement hydraulic pump is operated by the action of the two flow rate limiting variable throttle portions 52 which are interlocked with the respective operations. The second pressure oil is preferentially supplied from the respective second flow dividing pipes 20b in accordance with the respective operation amounts, and the pressure oil of the first variable displacement pump 1 is also reduced in the respective first flow amounts although the amount thereof is small. Support is supplied from the pipeline 20a. At the same time, for the arm cylinder directional control valve, the pressure oil of the first variable displacement hydraulic pump 1 operates in accordance with the operation amount of the first variable displacement hydraulic pump 1 due to the operation of the flow restricting variable throttle portion 51 interlocking with its operation. In addition to being preferentially supplied from the second distribution pipe 20a, the pressure oil of the second variable displacement hydraulic pump 2 is also supplied from the second distribution pipe 20b in a small amount. Therefore, even if the operation amount of the arm is increased, a necessary amount of pressure oil can be preferentially supplied from the first variable displacement hydraulic pump 1 to the arm cylinder directional control valve according to the operation amount. Even if the work requires a large amount of operation of the arm while traveling, such as the above-mentioned wetland escape work, the arm can be operated at a desired speed suitable for the work, and It can be done smoothly. On the contrary, when the operation amount of the arm is small, the first traveling motor 35 and the second traveling motor 3
For 6, the pressure oil of the second variable displacement hydraulic pump 2 is preferentially supplied, and in addition, the pressure oil of the first variable displacement hydraulic pump 1 is also supplied to a considerable extent. Since it is possible to reduce the shock caused by the traveling speed drastically decreasing due to the arm operation, it is possible to prevent the problems such as the spillage and the collapse of the load, which are seen in the above-mentioned suspended load carrying work. .

Traveling motors 35 and 36 and boom cylinder 3
Looking at the case where 2 and 2 are combinedly driven, in this case as well,
By operating the boom cylinder directional control valve, the switching valve 60 is switched from the illustrated position to the left position in the same manner as described above, and the pressure oil in the first main pipe line 11 and the second main pipe line 12 is changed to the second position. First diversion line 20 of directional control valve for travel motor
a and the second diversion conduit 2 of the directional control valve for the first traveling motor
Divide to 0b. As a result, the pressure oil of the second variable displacement hydraulic pump 2 is supplied to the first traveling motor directional control valve and the second traveling motor directional control valve by two variable flow rate limiting variables that are interlocked with their respective operations. Due to the function of the throttle portion 52, each of the flow dividing pipes 20b according to the respective operation amount.
Is preferentially supplied to the boom cylinder directional control valve from the flow dividing pipe 20b.
At the same time, the pressure oil of the first variable displacement hydraulic pump 1 is
The directional control valve for the traveling motor and the directional control valve for the second traveling motor are given priority or non-priority to the directional control valve for the boom cylinder, and are appropriately supplied from the flow dividing pipes 20a according to the operation amount. Therefore, in addition to the pressure oil of the second variable displacement hydraulic pump 2 being preferentially supplied to the first traveling motor directional control valve and the second traveling motor directional control valve, the first variable displacement Since the pressure oil of the hydraulic pump 1 is also appropriately supplied, even when a combined operation with the boom is performed instead of the arm in the above-described suspended load carrying work, the traveling speed changes rapidly as in the case of the combined operation with the arm. It can reduce the shock.

As described above, in the hydraulic drive circuit according to the present embodiment, the pressure oil of the variable displacement hydraulic pump can be changed when saturation is generated during the combined drive, regardless of whether the actuators are combined and driven in any direction. It can be preferentially supplied to the actuator, which is the main focus of the work, and
It is possible to exhibit the same excellent characteristics as the hydraulic drive circuits of the second and third embodiments in that the flow rate of the pressure oil can be rationally distributed to each actuator. Even in that case, the pressure oils of the two pumps are merged and supplied to each actuator, and the selection of whether or not the pressure oil is preferentially supplied to the actuators is made in two ways for each actuator. Since it is possible to perform the pressure oil of the pump, there is more room for selection, and the flow rate of the pressure oil to the actuator can be distributed more rationally. In this embodiment, all of the actuators can be combined and driven, but depending on the type and model of the construction machine that employs this type of hydraulic drive circuit, some of them should not be combined and driven. It is also possible, and which one of them is to be combined and driven is a matter of design choice.

The hydraulic drive circuit for the construction machine of the fifth embodiment will be described with reference to FIGS. 8 and 9. The hydraulic drive circuit of the present embodiment is an improvement of the hydraulic drive circuit of the fifth conventional example shown in FIG. The hydraulic drive circuit of the fourth embodiment is of the same system. The hydraulic drive circuit of the present embodiment is the fourth
This is equivalent to the hydraulic drive circuit of the embodiment in which the flow restricting variable throttle parts 51 and 52 are eliminated and the flow restricting variable throttle part 64, the switching valve 70, and related structures thereof are provided. Therefore, since the hydraulic drive circuit serving as the base is common to the hydraulic drive circuit of the fourth embodiment, the hydraulic drive circuit of the fifth embodiment will be described focusing on the points relating to the flow restricting variable throttle portion 64 and the switching valve 70. To do. Note that, in FIGS. 8 and 9, parts given the same reference numerals as those in FIGS. 6 and 7 represent parts equivalent to those figures.

In FIG. 8, reference numeral 64 designates the second diversion pipe 20b and the second traveling motor directional control valve of the first traveling motor directional control valve when the pressure oil in the second main pipe 12 is diverted. A flow restricting variable throttle portion arranged in the second main pipe line 12 on the downstream side of the second diversion pipe line 20b and on the upstream side of the remaining second diversion pipe line 20b. The flow rate of the remaining directional control valve passing through the second variable throttle portion for operation is limited in conjunction with the operation of the directional control valve having the maximum operation amount. When the first traveling motor directional control valve and the second traveling motor directional control valve are in the non-operating state, the flow rate limiting variable throttle portion 64 is in the neutral state and is in the fully open state. When the directional control valve is switched, it is switched to the left position, and the throttle opening of the flow restricting variable throttle at that left position increases the throttle opening of the variable throttle for operation with the maximum operation amount. It is set in association with the operation of the operating variable diaphragm unit in such a relationship that it decreases in accordance with. Therefore, the flow restricting variable throttle unit 64
Is the characteristic of the variable throttle portion for operation of the directional control valve 3 on the downstream side of the variable throttle portion for operation of the maximum operation amount of the first travel motor directional control valve and the second travel motor directional control valve. The characteristic can be changed to that shown in FIG. 3 in relation to the manipulated variable. The mechanism for actually operating the flow restricting variable throttle portion 64 and the switching valve 70 described below is
Detailed description will be given later based on FIG. 9.

Reference numeral 70 is a switching valve having a circuit switching unit 71 and a first load signal switching unit 72a and a second load signal switching unit 72b attached to both ends of the spool.
The circuit switching unit 71 is provided on the downstream side of the first diversion conduit 20a of the swing motor directional control valve and the arm cylinder directional control valve and on the first upstream side of the remaining first diversion conduit 20a.
The second branch pipe of the swing motor and the arm cylinder directional control valve at the downstream side of the main pipe 11 and the second branch pipe 20b of the boom cylinder directional control valve and the bucket cylinder directional control valve. It is arranged astride the second main pipeline 12 on the upstream side of 20b. The flow restricting variable restrictor of FIG. 6 is provided with a flow restricting variable restricting portion capable of selectively forming a restrictor in one of the first main conduit 11 and the second main conduit 12. Similar to the portions 51 and 52, the first operation variable throttle portion and the second operation variable throttle portion of each directional control valve 3 provided on the downstream pipelines 11a and 12b side in each of the main pipelines 11 and 12, respectively. It becomes a flow rate limiting means for limiting the flow rate of the flow through the section. To describe these configurations in detail, the circuit switching unit 71 is provided at its left position with the first operation variable throttle unit of the directional control valves other than the swing motor directional control valve and the arm cylinder directional control valve. The first flow rate limiting variable throttle section for limiting the passing flow rate is built-in, and the flow rate of the second operation variable throttle section of the swing motor directional control valve and the arm cylinder directional control valve is provided at the right position thereof. A second flow rate limiting variable throttle section for limiting the flow rate is built in, and the first flow rate limiting variable throttle section is switched to the left position to form a throttle in the first main pipe line 11, or a right position. It is possible to form a throttle in the second main pipe line 12 by switching to the second variable flow rate limiting variable throttle section.
Then, the maximum operation amount of the operation amounts of the swing motor directional control valve and the arm cylinder directional control valve is compared with the maximum operation amount of the boom cylinder directional control valve and the bucket cylinder directional control valve. When the maximum operation amount of the former is larger than the maximum operation amount of the latter, the switch is switched to the left position, and the first main pipe line 11 is formed with the throttle by the first flow restricting variable throttle unit. Is larger, the throttle valve is switched to the right position to form a throttle in the second main conduit 12 by the second flow restricting variable throttle portion. In this case, the opening of the throttle formed by each of the first variable flow restricting portion for flow rate restriction and the second variable flow restricting portion for flow rate restriction decreases in accordance with an increase in the operation amount of the difference between the two maximum operation amounts. The tendency is to set. For example, the directional control valve for the swing motor is operated in combination with the directional control valve for the arm cylinder with a larger operation amount, and both the directional control valve for the boom cylinder and the directional control valve for the bucket cylinder are operated. If not, it is switched to the left position and the first main line 1
A throttle is formed in the first flow restricting variable throttle portion. In this case, the opening of the throttle formed by the first variable flow restricting portion for flow rate restriction is set to be relatively small when the operation amount of the swing motor directional control valve is relatively large. If it is small, it will be relatively large. Further, for example, the swing motor directional control valve is operated with a larger operation amount than the arm cylinder directional control valve, and the boom cylinder directional control valve is operated with a larger operation amount than the bucket cylinder directional control valve. In the case where all of the above are operated in combination, when the operation amount of the boom cylinder directional control valve is larger than the operation amount of the swing motor directional control valve, it is switched to the right position and the second main pipe 12 A throttle is formed by the variable throttle portion for restricting the flow rate. In this case, the opening of the throttle formed by the second variable flow restricting throttle portion is the operation amount obtained by subtracting the operation amount of the swing motor directional control valve from the operation amount of the boom cylinder directional control valve, that is, the maximum operation. When the operation amount of the difference in amount is relatively large, it is relatively small, and when it is relatively small, it is relatively large, and it is set such that it decreases in accordance with the increase of the maximum operation amount. In addition,
The circuit switching unit 71 of the switching valve 70, when none of the swing motor directional control valve, the arm cylinder directional control valve, the boom cylinder directional control valve, and the bucket cylinder directional control valve is operated, In the neutral position as shown in FIG. 6, neither the first variable flow restricting portion for restricting the flow rate nor the second variable restricting portion for restricting the flow rate works.

First load signal switching unit 72 of switching unit valve 70
a is a first high load pressure detection path 73a for detecting a higher one of the load pressures of the boom cylinder 33 and the bucket cylinder 34, and a first high load pressure detection path 73a for connecting it to the first maximum load pressure detection path 8a. It connects and disconnects with the connection path 74a. In addition, the second load signal switching unit 72b of the switching valve 70 detects the higher load pressure of the swing motor 31 and the arm cylinder 32.
The high load pressure detection path 73b and the connection path 74b connecting the high load pressure detection path 73b to the second maximum load pressure detection path 8b are connected or disconnected. The first load signal switching unit 72a, when in the neutral position and when switched to the left position,
The first high load pressure detection path 73a and the first connection path 74a are disconnected from each other, and only when they are switched to the right position, they are communicated with each other. That is, only when the pressure oil of the second variable displacement hydraulic pump 2 is to be preferentially supplied to the boom cylinder 33 and the bucket cylinder 34, the load pressures of the second maximum displacement pressure detection passage 8a and the first maximum load pressure detection path 8a. In the load sensing control of the first variable displacement hydraulic pump 1, the load signal for detecting the maximum load pressure is reflected. Further, the second load signal switching unit 72b disconnects between the second high load pressure detection path 73b and the first connection path 74b when it is in the neutral position and when it is switched to the right position, Only when they are switched to the left position, communication is established between them. That is,
The pressure oil of the first variable displacement hydraulic pump 1 is supplied to the swing motor 31.
And, in the case where the arm cylinder 32 is to be preferentially supplied, those load pressures act as load signals for detecting the maximum load pressure in the second maximum load pressure detection path 8b, This is reflected in the load sensing control of the second variable displacement hydraulic pump 2.

On the other hand, as described above, the first load signal switching unit 72a or the second load signal switching unit 72b is switched to the right position or the left position, and the second variable displacement hydraulic pump 2 is operated.
Alternatively, the first variable displacement hydraulic pump 1 or the second variable displacement hydraulic pump, in which the load signal of one actuator to which the pressure oil of the first variable displacement hydraulic pump 1 is preferentially supplied is the other pump While the second load signal switching unit 72b or the first load signal switching unit 72a is being reflected on the second load sensing control, the second high load pressure detection path 73b and the second connection are connected. Between road 74b or first
The high load pressure detection path 73a and the first connection path 74a are disconnected from each other, and the pressure oil of the second variable displacement hydraulic pump 2 or the first variable displacement hydraulic pump 1 is supplied non-priority. The load signal of the other actuator being operated is not reflected in the load sensing control of its respective pump. As a result, the other actuator is operated from the second variable displacement hydraulic pump 2 or the first variable displacement hydraulic pump 1 only when the load pressure is lower than the maximum load pressure of the one actuator. The first variable displacement hydraulic pump 1 or 2
The variable displacement hydraulic pump 2 is driven by receiving an appropriate distribution of pressure oil according to its operation amount.

An example of a mechanism for actually operating the flow restricting variable throttle portion 64 and the switching valve 70 described above is shown in FIG.
It will be described based on. In the figure, 100a is a shuttle valve for inputting pilot pressures from the pilot operating device 90, which are output to the pilot conduits 91a, 91b, and preferentially outputting the higher pilot pressure of these pressures. Pilot operation device 9 for motor directional control valve, arm cylinder directional control valve, boom cylinder directional control valve, bucket cylinder directional control valve, first traveling motor directional control valve, and second traveling motor directional control valve
It is provided corresponding to 0. When the pilot operating device 90 is operated by the operating lever, it is practically impossible that the pilot pressure is simultaneously output from the left and right pressure reducing valves. Therefore, the shuttle valve 100a is operated substantially by the operating lever. It works to detect the pilot pressure of the side pressure reducing valve. The value of the pilot pressure of the pressure reducing valve determines the operation amount of each directional control valve 3 and thus the throttle opening of the variable throttle portion for operation thereof. Therefore, the operation amount and throttle opening of the directional control valve are determined. Has the same meaning as. Reference numeral 100b denotes a shuttle valve which inputs each pilot pressure output from the two shuttle valves 100a adjacent to each other and preferentially outputs a pilot pressure higher than these pressures, and is a directional control valve for a swing motor. Each pilot pressure to the arm cylinder directional control valve, each pilot pressure to the boom cylinder directional control valve and the bucket cylinder directional control valve, to the first traveling motor directional control valve and the second traveling motor directional control valve For each pilot pressure, the higher pilot pressure is selected and output.

Of these selected and output pilot pressures, the pilot pressures for the first traveling motor directional control valve and the second traveling motor directional control valve are applied to the signal receiving portion of the flow restricting variable throttle portion 64. The higher pilot pressure selected from among the above is introduced through the pilot pressure detection path 101c and imparts a control force that opposes the spring 65. as a result,
The flow restricting variable throttle unit 64 is switched to the left position,
A throttle having a predetermined opening degree according to the pilot pressure is formed in the second main pipe line 12. In that case, the throttle opening is set in such a relationship that it becomes relatively smaller as the pilot pressure becomes relatively larger. The switching operation of the flow restricting variable throttle portion 64, which has already been described in the description of FIG. 8, can be realized by such a mechanism.

On the other hand, in the first signal receiving portion on the left side of the switching valve 70, the higher pilot pressure selected from the pilot pressures for the swing motor directional control valve and the arm cylinder directional control valve is used. The switching valve 7 is guided through the detection path 101a and imparts a control force that opposes the force of the spring 75b.
To the second signal receiving portion on the right side of 0, the higher pressure selected from the pilot pressures for the boom cylinder directional control valve and the bucket cylinder directional control valve is introduced through the pilot pressure detection path 101b. , And provides a control force that opposes the spring 75a. As a result, the circuit switching unit 7 of the switching valve 70
1 is switched to the left position or the right position by the differential pressure between the pilot pressure introduced from the pilot pressure detection passage 101a and the pilot pressure introduced from the pilot pressure detection passage 101b, and the first main passage 11 or the second main passage A diaphragm is formed at 12. In that case, the throttle opening degree of the variable flow restricting throttle portion in the circuit switching portion 71 is set in such a relationship that it becomes relatively smaller as the differential pressure becomes relatively larger. At the same time, the first load signal switching unit 72a of the switching valve 70
Similarly, the second load signal switching unit 72b is also switched to the left position or the right position, and the second high load pressure detection path 73b and the first high load pressure detection path 73a are respectively connected to the second connection path 74b. Also, the second maximum load pressure detection path 8b and the first maximum load pressure detection path 8a can be connected or disconnected through the first connection path 74a. The switching operation of the switching valve 70, which has already been described in the description of FIG. 8, can be realized by such a mechanism. The hydraulic circuit of FIG. 9 is also provided with the switching valve 60 already described in the explanation of FIG. 6, but the mechanism of FIG. 9 for realizing the switching operation of this switching valve is already shown in FIG. Since the mechanism is the same as that described, the description is omitted.

Since the hydraulic drive circuit of the hydraulic excavator of the fifth embodiment has the above-mentioned configuration, when the actuators 31 to 36 are combinedly driven, each variable displacement type drive is given the following priority relationship. By distributing the pressure oil of the hydraulic pumps 1 and 2 to each directional control valve 3, it is possible to overcome the problems associated with saturation that occur in various operations.

(1) Combined drive of one or both of a swing motor and an arm cylinder and one or both of a boom cylinder and a bucket cylinder For example, one or both of a boom and a bucket and an arm are combined to excavate earth and sand. In this case, the switching valve 70 operates according to the differential pressure between the pilot pressure applied to the boom cylinder directional control valve or the bucket cylinder directional control valve and the pilot pressure applied to the arm cylinder directional control valve. And
When excavating earth and sand, the arm first performs the excavation operation, and then the boom and bucket perform the excavation operation to raise and excavate, but the arm first becomes the center. When the amount of operation of the arm is made larger than the other during excavation operation, the switching valve 70 is switched to the left position, and the pressure oil of the first variable displacement hydraulic pump 1 corresponding to the load pressure of the arm cylinder 32 is switched. Is preferentially supplied to the arm, and at the same time, the pressure oil of the second variable displacement hydraulic pump 2 is distributed to the operated one of the boom cylinder directional control valve and the bucket cylinder directional control valve. Depending on the manipulated variable, it is distributed to the arm cylinders 32 regardless of whether it is prioritized or not. Therefore, the arm cylinder 32 can obtain a desired speed and pressure, and the desired excavation work centered on the arm can be smoothly achieved. Next, when the boom or bucket digs up around the center and the digging up is performed and any one of the operation amounts is relatively increased, the switching valve 70 is switched to the right position, and the actuators 33 and 34 are operated. On the other hand, the second
In addition to preferentially supplying the pressure oil of the variable displacement hydraulic pump 2 of No. 1, the pressure oil of the first variable displacement hydraulic pump 1 is distributed in proportion to the boom cylinder 33 and the non-priority. The bucket cylinder 34 can obtain a desired speed and pressure and can smoothly achieve the desired excavation work.

Further, for example, in the case of a dump loading work of excavated soil and the above-mentioned leveling work, a combined operation of the swivel base and the arm and the boom is performed. In that case, the direction control valve for the swivel motor or the direction for the arm cylinder is used. The switching valve 70 operates according to the pressure difference between the pilot pressure applied to the control valve and the pilot pressure applied to the boom cylinder directional control valve. Then, when performing such a composite operation, the boom raising height is required, and when the boom operation amount is increased, the switching valve 70 is switched to the right position, and the second variable capacity is changed with respect to the boom cylinder 33. Type hydraulic pump 2 preferentially supplies pressure oil, and at the same time,
Since the pressure oil of the first variable displacement hydraulic pump 1 is also distributed to the swing motor 31 and the arm cylinder 32 regardless of priority or non-priority, the boom cylinder 33 obtains a desired speed and height. The desired work can be achieved smoothly.

Further, when one or both of the swivel base and the arm and one or both of the boom and the bucket are operated in combination, the pilot pressure to the swivel motor directional control valve or the arm cylinder directional control valve and the boom. When no differential pressure is generated between the directional control valve for the cylinder or the pilot pressure for the directional control valve for the bucket cylinder, and the switching valve 70 is held and operated in the state as shown in FIG.
In this case, the first load signal switching unit 72 of the switching valve 70
a and the first load signal switching unit 72b connect between the first high load pressure detection path 73a and the first connection path 74a and between the second high load pressure detection path 73b and the second connection path 74b, respectively. Since the space is cut off, the load sensing control of the first variable displacement hydraulic pump 1 is performed based on the load pressure of the swing motor 31 and the arm cylinder 32, and the boom cylinder 3
The load sensing control of the second variable displacement hydraulic pump 2 is performed based on the load pressure of the bucket cylinder 34 and the load pressure of the bucket cylinder 34. Now, assuming that such control is performed during the combined operation of the swing and boom raising operations, the pressure oil of the first variable displacement hydraulic pump 1 corresponding to the high load pressure of the swing motor is the high load swing motor. 31 and the low load boom cylinder 33, and the pressure oil of the second variable displacement hydraulic pump 2 corresponding to the low load pressure of the boom cylinder 33 is generated by the circuit switching unit 71 of the switching valve 70 in the second main pipeline. Although the downstream pipe line 12a in 12 and the most downstream pipe line 12b communicate with each other, the swing motor 31 has a higher load pressure than the boom cylinder 33.
However, the entire amount is supplied to the boom cylinder 33. Therefore, not only can the swivel motor 31 with a high load pressure be driven, but also the speed for raising the boom of the boom cylinder 33 with a low load pressure need not be reduced, and a necessary and sufficient boom raising height can be secured. Also,
Under such a condition that there is a load pressure difference between the swing motor 31 and the boom cylinder, the boom cylinder directional control valve is switched with a larger operation amount, that is, a driving speed, than that of the swing motor directional control valve. The same is true when the valve 70 is switched to the right position. According to the hydraulic drive circuit of the present embodiment, the pressure oils of the variable displacement hydraulic pumps 1 and 2 are not only generated when there is a difference in the operation amount between the actuators that are compositely driven, but also when there is a load pressure difference. Can be reasonably distributed to each of the actuators, and good composite drive can be realized.

(2) Composite drive of travel motor and other actuators The hydraulic drive circuit of the fourth embodiment exhibits the same function as that of the third embodiment when the travel motor and other actuators are compositely driven. To do. For example, regarding the case where the traveling motors 35 and 36 and the arm cylinder 32 are combinedly driven, in this case, the switching valve 60 is switched from the position shown in the drawing to the left position by operating the directional control valve for the arm cylinder, The pressure oils of the first main pipe line 11 and the second main pipe line 12 are respectively passed through the circuit switching unit 61 to the first diversion pipe line 20a of the second directional control valve for the traveling motor and the first diverter control valve for the first traveling motor. The flow is divided into the second flow dividing pipe 20b. At the same time, the switching valve 7 is operated by operating the directional switching valve for the arm cylinder.
The circuit switching unit 71 of 0 is switched to the left position, and the first flow restricting variable throttle unit forms a throttle in the first main pipe line 11, and the second main pipe line 12 restricts the flow amount. The variable throttle portion 64 for operation operates in conjunction with the operation of the directional control valve for the first traveling motor or the directional control valve for the second traveling motor to form a throttle. As a result, with respect to the first traveling motor directional control valve and the second traveling motor directional control valve, the pressure oil of the second variable displacement hydraulic pump 2 is removed by the action of the flow restricting variable throttle portion 64. In accordance with the maximum operation amount of the operation amount of the directional control valve 3, the second flow dividing pipes 20b are preferentially supplied, and the pressure oil of the first variable displacement pump 1 is small in amount. It is supported and supplied from the first branch pipe 20a. At the same time, with respect to the arm cylinder directional control valve, the pressure oil of the first variable displacement hydraulic pump 1 is operated in accordance with the operation amount by the action of the first flow restricting variable throttle portion of the circuit switching portion 71. While being preferentially supplied from the first distribution pipe 20a, the pressure oil of the second variable displacement hydraulic pump 2 is also supplied from the second distribution pipe 20b in a small amount. Therefore, even if the operation amount of the arm is increased, a necessary amount of pressure oil can be preferentially supplied from the first variable displacement hydraulic pump 1 to the arm cylinder directional control valve according to the operation amount. Even in work such as wetland escape work that requires arm operation with a large amount of operation while traveling, the arm can be operated at a desired speed, and work can be performed smoothly. On the contrary, when the operation amount of the arm is small, the pressure oil of the second variable displacement hydraulic pump 2 is preferentially supplied to the first traveling motor 35 and the second traveling motor 36. Variable displacement hydraulic pump 1
Since a considerable amount of pressure oil is also supplied from the support, it is possible to alleviate the shock caused by the drastic decrease in the traveling speed due to the arm operation, so the problems described in the above-mentioned suspended load carrying work do not occur. .

As described above, the hydraulic drive circuit according to the present embodiment can exhibit the same excellent characteristics as the hydraulic drive circuit according to the fourth embodiment, and the most drive speed which is the main focus in the process of the work. , Which constantly selects large actuators and distributes the flow rate of pressure oil to adapt to the operation amount of the directional control valve, it is possible to smoothly perform a wide range of various operations required for modern hydraulic excavators. it can.

In each of the hydraulic drive circuits related to the present invention illustrated above, even when saturation occurs during combined driving of actuators, the pressure oil of the variable displacement hydraulic pump is preferentially given to the actuator which is the main focus of the work. And the ratio of the flow rate to each actuator can be distributed rationally. Therefore, it is possible to solve the problem that the work is hindered by the occurrence of saturation as in the conventional hydraulic drive circuit. The characteristic that the pressure oil of the hydraulic pump is preferentially supplied to the main actuators and the flow rate can be distributed to each actuator in this way functions most effectively when saturation occurs. It goes without saying that it functions effectively not only when saturation occurs, but also when the actuator is normally driven in combination.

In the flow rate control devices of the first to fifth embodiments described above, when the control force is applied to the pressure compensating portion, the load pressure of the actuator, the primary pressure and the secondary pressure of the actuator are applied to the signal receiving portion. The so-called hydraulic pilot operation method is used to guide the pressure and maximum load pressure as pilot pressure, but it is also possible to apply control force using an electromagnetic pilot operation method or an electromagnetic operation method based on these pressures. Since it suffices to apply a control force based on these pressures to the pressure compensator, it does not matter what kind of operation method is used. In these embodiments, the spring is used to preset the pressure compensating unit, but the same purpose can be achieved by using the hydraulic pilot pressure or the like, that is, a means that can give a desired control force at the time of initial setting. If so, it doesn't matter what kind. In these embodiments, the flow restricting variable throttle unit is always operated in conjunction with the operation of the operating variable throttle unit. However, depending on the work content, saturation may occur during the combined driving of the actuators, or the saturation may occur. In some cases, there is no risk of trouble, so a means may be provided that allows the interlocking operation to be canceled as appropriate.

[0119]

As is apparent from the above description, the present invention has a variable displacement hydraulic pump and a plurality of actuators that are driven in combination by pressure oil of the variable displacement hydraulic pump, and perform load sensing control. Claims 1 and 2 in the scope of the claims, in which a variable throttle portion for operation and a pressure compensating portion which are operated by the steering means of the construction machine to adjust the flow rate supplied to the actuator are provided in addition to the means for performing
In the various types of hydraulic drive circuits shown in claim 5, claim 6, and claim 7, a flow restricting variable throttling portion as a means for restricting the flow rate of passage through the operating variable throttling portion,
According to the type of the hydraulic drive circuit, as shown in each claim, it is arranged on the downstream side or the upstream side of a part of the pressure compensating section, and the throttle opening degree of the flow restricting variable throttle section is Since the setting is made in conjunction with the operation of other variable throttle units for operation, even if saturation occurs during combined driving of actuators, the flow distribution to each actuator does not hinder the work. Thus, it is possible to provide a hydraulic drive circuit for a construction machine that can be rationalized.

[Brief description of drawings]

FIG. 1 is a hydraulic circuit diagram showing a hydraulic drive circuit of a construction machine according to a first embodiment of the present invention.

FIG. 2 is a characteristic diagram showing characteristics of differential pressure across the throttle of the operation variable throttle when the flow restrictor is provided with the flow restricting variable throttle in the hydraulic drive circuit for the construction machine according to the first embodiment of the present invention. It is a diagram.

FIG. 3 is a characteristic diagram for explaining the characteristics of the hydraulic drive circuit for the construction machine according to the first embodiment of the present invention.

FIG. 4 is a hydraulic circuit diagram showing a hydraulic drive circuit for a construction machine according to a second embodiment of the present invention.

FIG. 5 is a hydraulic circuit diagram showing a hydraulic drive circuit for a construction machine according to a third embodiment of the present invention.

FIG. 6 is a hydraulic circuit diagram showing a hydraulic drive circuit for a construction machine according to a fourth embodiment of the present invention.

FIG. 7 is a hydraulic circuit diagram showing a specific example of a hydraulic operating mechanism for realizing the operation of the switching valve in the hydraulic drive circuit of FIG.

FIG. 8 is a hydraulic circuit diagram showing a hydraulic drive circuit for a construction machine according to a fifth embodiment of the present invention.

9 is a hydraulic circuit diagram showing a specific example of a hydraulic operating mechanism for realizing the operation of the switching valve in the hydraulic drive circuit of FIG.

FIG. 10 is a hydraulic circuit diagram showing a hydraulic drive circuit of a construction machine of a first conventional example.

FIG. 11 is a hydraulic circuit diagram showing a hydraulic drive circuit of a construction machine of a second conventional example.

FIG. 12 is a hydraulic circuit diagram showing a hydraulic drive circuit of a construction machine of a third conventional example.

FIG. 13 is a hydraulic circuit diagram showing a hydraulic drive circuit of a construction machine of a fourth conventional example.

FIG. 14 is a hydraulic circuit diagram of a hydraulic pilot operating device for operating a directional control valve in a hydraulic drive circuit of a third conventional example and a fourth conventional example.

FIG. 15 is a hydraulic circuit diagram showing a hydraulic drive circuit of a hydraulic excavator which is a hydraulic drive circuit of a construction machine of a fifth conventional example.

[Explanation of reference signs] 1, 2 Variable displacement hydraulic pump 3 Directional control valves 4a, 4b Pressure compensator 5 Confluent connection conduits 5a, 5b Load signal conduit 5c Load pressure introduction conduit 6a, 6b Load conduit 7a, 7b Check Valves 8a, 8b Maximum load pressure detection passages 9a, 9b Signal pipe lines for closing operation 10a, 10b Signal pipe lines for opening operation 11, 12 Main pipe passage 13 Dividing flow introducing pipe passages 20a, 20b Dividing pipe passage 31 Swing motor 32 Arm Cylinder 32 Boom cylinder 34 Bucket cylinder 35 First traveling motor 36 Second traveling motor 41, 42 Tilt control device 43a, 43b Discharge pressure detection path 51, 52 Flow rate limiting variable throttle portion 60 Switching valve 61 Circuit switching portion 62 Load signal Switching unit 63 Maximum load pressure detection extension 64 Variable flow restricting throttle unit 70 Switching valve 71 Circuit switching unit 72a, 72b Load signal off Part 201 Variable displacement hydraulic pump 202 Tilt control device 203 Main line 203a, 203b Branch line 204, 205 Load line 206, 207 Actuator 208, 209 Connection line 210, 211 Check valve 212 Maximum load pressure detection line 214 Discharge pressure Detection path 222, 223 Operation variable throttle section 222a, 223b, 223a, 223b Operation variable throttle section 224, 225 Pressure compensation section 226, 229 Opening operation signal conduit 227, 230 Closing operation signal conduit 228, 231 Spring 242a , 242b, 243a, 243b Correcting variable throttle section 244, 245 Pressure compensating section 246, 249 Signal line for closing operation 247, 250 Signal line for opening operation 248, 251 Spring 260 Flow control device of the first embodiment 261 Flow Restriction Variable Throttle 262 Pressure Compensation 263 signal pipe for opening 264 signal pipe for closing 265 spring 266 interlocking means 267 flow restricting variable throttle 267a, 267b variable throttle 268 flow restricting variable throttle 268a, 268b variable throttle 266a, 266b open operation Signal lines 67a, 67b for closing signal lines 268a, 268b for closing operation Spring

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display area F15B 11/16

Claims (7)

[Claims] 1. A variable displacement hydraulic pump, a plurality of actuators driven by the hydraulic pressure of the variable displacement hydraulic pump, a maximum load pressure among load pressures of these actuators, and a variable displacement hydraulic pump A control means for performing load sensing control that controls the discharge capacity of the pump so that the discharge pressure is higher than the maximum load pressure by a predetermined value is provided, and the flow rate supplied to the actuator is operated by the control means of the construction machine. Is arranged on the upstream side of the variable throttle for operation and the variable throttle for operation,
The control force in the opening direction based on the load pressure of the actuator, the control force in the opening direction set by the differential pressure setting means, and the control force in the closing direction based on the own secondary pressure are applied to adjust the opening amount, And a pressure compensator for controlling the secondary pressure of the actuator so as to be higher than the load pressure of the actuator by a constant value by means of the differential pressure setting means. In the hydraulic drive circuit of the construction machine that is provided as a component, the flow rate of the variable throttle part for operation is set to the downstream side of the pressure compensating part in some of the flow rate control devices provided corresponding to the actuators. A flow restricting variable throttle section is arranged as a means for restricting, and the throttle opening of this flow restricting variable throttle section decreases in accordance with the increase of the throttle opening of the variable throttle section for operation of another flow rate control device. Hydraulic drive circuit for a construction machine, characterized in that it has to be set in conjunction with the operation of the operation variable throttle portion in earthenware pots. 2. A variable displacement hydraulic pump, a plurality of actuators driven by the hydraulic pressure of the variable displacement hydraulic pump, a maximum load pressure of load pressures of these actuators, and a variable displacement hydraulic pump A control means for performing load sensing control that controls the discharge capacity of the pump so that the discharge pressure is higher than the maximum load pressure by a predetermined value is provided, and the flow rate supplied to the actuator is operated by the control means of the construction machine. And a variable throttle portion for operation for adjusting, and arranged on the downstream side of the variable throttle portion for operation,
The control force in the closing direction based on the maximum load pressure, the control force in the closing direction for the initial setting, and the control force in the opening direction based on the own primary pressure are applied to adjust the opening amount to maximize the own primary pressure. A construction machine having a pressure compensator for controlling the load pressure side actuator to a constant value sufficient to drive the actuator, and a flow rate control device for controlling the supply flow rate to the actuator provided for each actuator. In the hydraulic drive circuit of the above, as means for limiting the passage flow rate of the variable throttle portion for operation on the upstream side of the pressure compensating portion in a part of the flow rate control device provided in correspondence with each actuator. A variable throttle for flow restriction is placed, and the throttle opening of this variable throttle for flow restriction is adjusted so that it decreases as the throttle opening of the variable throttle for operation of another flow control device decreases. Aperture Hydraulic drive circuit for a construction machine, characterized in that it has to be set in conjunction with the operation of the. 3. A direction control capable of switching a flow path of pressure oil so that a variable throttle portion for operation, which is operated by a control means of a construction machine and adjusts a flow rate supplied to an actuator, can switch a flow path of pressure oil so as to drive the actuator in two directions. The hydraulic drive circuit for a construction machine according to claim 1 or 2, wherein the hydraulic drive circuit is formed in each flow path of the valve so that the flow path can be switched by a control means of the construction machine. 4. A plurality of flow restricting variable restrictors are arranged as a means for restricting the flow rate of the operation variable restrictor.
The flow rate of passage of at least one variable throttle portion for operation is limited, and claim 1 and claim 2 characterized by the above-mentioned.
Alternatively, the hydraulic drive circuit for the construction machine according to claim 3. 5. A plurality of variable displacement hydraulic pumps, and at least one actuator that is jointly driven by joining and supplying pressure oils of these plurality of variable displacement hydraulic pumps, and is driven by the pressure oil. The maximum load pressure is detected for each of the multiple actuators and the actuator groups driven by each variable displacement hydraulic pump so that the discharge pressure of each variable displacement hydraulic pump becomes higher than the maximum load pressure by a predetermined value. Is equipped with a control means for performing load sensing control for controlling the discharge capacity of each variable displacement hydraulic pump, and corresponding to the combined drive actuator, the flow rate supplied to the actuator is operated by the operation means of the construction machine. A plurality of variable throttles for operation to be adjusted are built in so as to match the number of confluences of pressure oil to the actuator, and the control means is A directional control valve for two-way merging drive that can switch the flow path of pressure oil so that the actuator can be driven in two directions. Direction for two-way drive that can be operated to change the flow path of pressure oil so that the actuator can be driven in two directions by its control means. A control valve is provided to control the opening amount by controlling the closing force based on the maximum load pressure, the closing direction control force for initial setting, and the opening direction control force based on the own primary pressure. A pressure compensator for controlling the primary pressure to a constant value sufficient to drive the actuator on the maximum load pressure side is arranged in each of the flow paths communicating with the secondary side of each variable throttle for operation. In the hydraulic drive circuit of the installation machine, a part of the pressure compensating section arranged in the flow path communicating with the secondary side of each operation variable throttling section is provided upstream of a part of the pressure compensating section. At least one flow restricting variable throttle section is arranged as a means for restricting the flow rate of passage, and the throttle opening of this flow restricting variable throttle section decreases in accordance with the increase of the throttle opening of the other operation variable throttle section. As described above, the hydraulic drive circuit for the construction machine is characterized in that it is set in association with the operation of the variable throttle portion for operation. 6. A first variable displacement hydraulic pump and a second variable displacement hydraulic pump, and a swing motor, an arm cylinder, a boom cylinder as an actuator driven by the pressure oil of these variable displacement hydraulic pumps, The first load pressure is detected by a load signal relating to the load pressure of the bucket cylinder, the first traveling motor, the second traveling motor, and the actuator driven by the first variable displacement hydraulic pump.
Of the maximum load pressure detecting means and the second maximum load pressure detecting means for detecting the maximum load pressure by the load signal relating to the load pressure of the actuator driven by the second variable displacement hydraulic pump. Control means for performing load sensing control for controlling the discharge capacity of each variable displacement hydraulic pump so that the discharge pressure of each variable displacement hydraulic pump becomes higher than each maximum load pressure by a predetermined value; and a first variable displacement type A first main line and a second main line for guiding the pressure oil of the hydraulic pump and the second variable displacement hydraulic pump, respectively, are provided corresponding to the actuators, respectively, and are operated by the operating means of the hydraulic excavator. And a second variable throttle portion for operation for adjusting the flow rate supplied to the actuator
Both of the operating variable throttle parts are built in at the two switching positions, and by switching between the two switching positions, the flow path of the pressure oil can be switched so that the actuator can be merged in two directions. A swing motor directional control valve having a function as a merging drive directional control valve, an arm cylinder directional control valve, a boom cylinder directional control valve, a bucket cylinder directional control valve, a first traveling motor directional control valve, and a first directional control valve. 2 traveling motor directional control valve, the first operation variable throttle portion and the second operation of each of the directional control valve the pressure oil introduced into the first main pipeline and the second main pipeline respectively Slewing motor directional control valve for branching to variable throttle, arm cylinder directional control valve, boom cylinder directional control valve, bucket cylinder directional control valve, first traveling motor directional control And a first diversion conduit and a second diversion conduit of the directional control valve for the second traveling motor, and a first operation variable throttle portion of each directional control valve at two switching positions of each directional control valve, The control force in the closing direction according to the load signal related to the maximum load pressure, the control force in the closing direction for the initial setting, and the self-controlling force are arranged in the respective output pipes respectively communicating with the secondary side of the second operation variable throttle unit. A control force in the opening direction is applied by a pressure signal related to the primary pressure to adjust the opening amount, and the primary pressure of the self is controlled to be a constant value sufficient to drive the actuator on the maximum load pressure side. In a hydraulic drive circuit for a construction machine having a first pressure compensating section and a second pressure compensating section, a switching valve having a circuit switching section and a load signal switching section is provided, and a first traveling motor directional control valve and a first traveling motor 2 Valves other than directional control valve for traveling motor When the switching operation is performed, the circuit switching portion of the switching valve causes the pressure oil in the first main pipe and the second main pipe to flow into the first branch pipe and the first branch pipe of the second traveling motor directional control valve, respectively. The traveling motor directional control valve is switched so as to be branched to the second branch pipe, and the load signal switching section of the switching valve causes the load signal of the first traveling motor to detect the second maximum load pressure detecting means. The second pressure compensation in which the load signal relating to the maximum load pressure detected by the second maximum load pressure detecting means corresponds to the first traveling directional control valve. Acting as a load signal for applying a control force in the closing direction to the section, and the load signal relating to the maximum load pressure detected by the first maximum load pressure detecting means corresponds to the second traveling directional control valve. Close to pressure compensator When the valves other than the first traveling motor directional control valve and the second traveling motor directional control valve are not switched, the switching valve can be switched to act as a load signal for applying the control force of By the circuit switching unit of
Of the main hydraulic line and the second main hydraulic line of the first traveling motor and the second diversion conduit of the first traveling motor, respectively. The load signal switching unit of the valve causes the load signal of the first traveling motor and the load signal of the second traveling motor to be the first
Of the directional control valve for the swing motor and the directional control valve for the arm cylinder so that the maximum load pressure detecting means and the second maximum load pressure detecting means can be switched so as to act as a load signal for detecting the maximum load pressure. The first main conduits on the downstream side of the first diversion conduit and on the upstream side of the remaining first diversion conduit are linked to the operation of the respective directional control valves, respectively. A second flow restricting valve for the first traveling motor in the case where the flow restricting variable restricting unit for restricting the flow rate passing through the first operating variable restricting unit is arranged to divert the pressure oil in the second main pipeline. The second main conduit on the downstream side of the second branch conduit of the diversion conduit and the second diversion conduit of the second traveling motor, and on the second main conduit on the upstream side of the remaining second diversion conduit of this directional control valve The second variable throttle section for operation of the other directional control valve that is interlocked with each operation A flow restricting variable throttle that restricts the passing flow rate is arranged, and the swing motor directional control valve and the arm cylinder directional control are provided downstream of the second diversion conduit of the boom cylinder directional control valve and the bucket cylinder directional control valve. The second main pipeline on the upstream side of the second diversion pipeline of the control valve is connected to the operation of the boom cylinder directional control valve and the bucket cylinder directional control valve, respectively, and is associated with the swing motor directional control valve and the arm cylinder directional control valve, respectively. A flow restricting variable restrictor that restricts the flow rate of the second operation variable restrictor of the directional control valve is arranged, and the throttle openings of the flow restricting variable restrictors are set to the flow restricting variable restrictors. It is characterized in that it is set in conjunction with the operation of the variable throttle part for operation so that it decreases in accordance with the increase in the throttle opening of the variable throttle part for operation of each directional control valve that is in interlocking relation with the parts. To Hydraulic drive circuit of the setting machine. 7. A first variable displacement hydraulic pump, a second variable displacement hydraulic pump, and a swing motor, arm cylinder, boom cylinder as an actuator driven by the pressure oil of these variable displacement hydraulic pumps, The first load pressure is detected by a load signal relating to the load pressure of the bucket cylinder, the first traveling motor, the second traveling motor, and the actuator driven by the first variable displacement hydraulic pump.
Of the maximum load pressure detecting means and the second maximum load pressure detecting means for detecting the maximum load pressure by the load signal relating to the load pressure of the actuator driven by the second variable displacement hydraulic pump. Control means for performing load sensing control for controlling the discharge capacity of each variable displacement hydraulic pump so that the discharge pressure of each variable displacement hydraulic pump becomes higher than each maximum load pressure by a predetermined value; and a first variable displacement type A first main line and a second main line for guiding the pressure oil of the hydraulic pump and the second variable displacement hydraulic pump, respectively, are provided corresponding to the actuators, respectively, and are operated by the operating means of the hydraulic excavator. And a second variable throttle portion for operation for adjusting the flow rate supplied to the actuator
Both of the operating variable throttle parts are built in at the two switching positions, and by switching between the two switching positions, the flow path of the pressure oil can be switched so that the actuator can be merged in two directions. A swing motor directional control valve having a function as a merging drive directional control valve, an arm cylinder directional control valve, a boom cylinder directional control valve, a bucket cylinder directional control valve, a first traveling motor directional control valve, and a first directional control valve. 2 traveling motor directional control valve, the first operation variable throttle portion and the second operation of each of the directional control valve the pressure oil introduced into the first main pipeline and the second main pipeline respectively Slewing motor directional control valve for branching to variable throttle, arm cylinder directional control valve, boom cylinder directional control valve, bucket cylinder directional control valve, first traveling motor directional control And a first diversion conduit and a second diversion conduit of the directional control valve for the second traveling motor, and a first operation variable throttle portion of each directional control valve at two switching positions of each directional control valve, The control force in the closing direction according to the load signal related to the maximum load pressure, the control force in the closing direction for the initial setting, and the self-controlling force are arranged in the respective output pipes respectively communicating with the secondary side of the second operation variable throttle unit. A control force in the opening direction is applied by a pressure signal related to the primary pressure to adjust the opening amount, and the primary pressure of the self is controlled to be a constant value sufficient to drive the actuator on the maximum load pressure side. In a hydraulic drive circuit for a construction machine having a first pressure compensating section and a second pressure compensating section, a switching valve having a circuit switching section and a load signal switching section is provided, and a first traveling motor directional control valve and a first traveling motor 2 Valves other than directional control valve for traveling motor When the switching operation is performed, the circuit switching portion of the switching valve causes the pressure oil in the first main pipe and the second main pipe to flow into the first branch pipe and the first branch pipe of the second traveling motor directional control valve, respectively. The traveling motor directional control valve is switched so as to be branched to the second branch pipe, and the load signal switching section of the switching valve causes the load signal of the first traveling motor to detect the second maximum load pressure detecting means. The second pressure compensation in which the load signal relating to the maximum load pressure detected by the second maximum load pressure detecting means corresponds to the first traveling directional control valve. Acting as a load signal for applying a control force in the closing direction to the section, and the load signal relating to the maximum load pressure detected by the first maximum load pressure detecting means corresponds to the second traveling directional control valve. Close to pressure compensator When the valves other than the first traveling motor directional control valve and the second traveling motor directional control valve are not switched, the switching valve can be switched to act as a load signal for applying the control force of By the circuit switching unit of
Of the main hydraulic line and the second main hydraulic line of the first traveling motor and the second diversion conduit of the first traveling motor, respectively. The load signal switching unit of the valve causes the load signal of the first traveling motor and the load signal of the second traveling motor to be the first
When the pressure oil in the second main pipeline is diverted so that it can be switched so as to act as a load signal for detecting the maximum load pressure by the maximum load pressure detection means and the second maximum load pressure detection means Second directional control valve for the first traveling motor
Of the directional control valve and the second main pipeline on the downstream side of the second diverter pipeline of the directional control valve for the second traveling motor and on the upstream side of the remaining second diverter pipeline. Of the directional control valve having the maximum operation amount of the other directional control valve, a variable flow restricting portion for restricting the flow rate of the second variable throttle portion for operation of the remaining directional control valve is arranged to restrict the flow rate. The throttle opening of the variable throttle unit is set in conjunction with the operation of the variable throttle unit for operation so that it decreases in accordance with the increase of the throttle opening of the variable throttle unit for operating the directional control valve with the maximum operation amount. And the direction for the boom cylinder and the direction for the boom cylinder on the downstream side of the first diversion conduit of the swing motor directional control valve and the arm cylinder directional control valve on the upstream side of the remaining first diversion conduit. Swirling on the downstream side of the second branch pipe of the control valve and the directional control valve for the bucket cylinder The in the second upstream side of the distribution pipe path over motor directional control valve and the arm cylinder directional control valve 2
In one of the main conduits of the above, a flow restricting means having a variable restricting portion for restricting a flow capable of selectively forming a restrictor is provided,
The maximum operation amount of the operation amounts of the swing motor directional control valve and the arm cylinder directional control valve is compared with the maximum operation amount of the boom cylinder directional control valve and the bucket cylinder directional control valve. When the maximum operation amount of is larger, the throttle is formed in the first main pipeline, and when the latter is larger, the throttle is formed in the second main pipeline. It is characterized in that the throttle opening degree of the throttle formed in the main pipe by the limiting variable throttle portion is set so as to decrease in accordance with an increase in the operation amount of the difference between the two maximum operation amounts. Hydraulic drive circuit for construction machinery.