JPH07317706A - Hydraulic circuit for construction machine - Google Patents

Abstract

PURPOSE:To prevent composite controllability and energy efficiency from being decreased by making a structure wherein a negative control variable- displacement pump is controlled through upstream pressure of a pressure generating means. CONSTITUTION:A directional control valve for a large inertia actuator 32 is formed into an open center type, and directional control valves for small inertia actuators 34, 36 are formed into a closed center type. An oil pressure bypass line 62 communicated with a tank line 54 is connected to a bypass passage 60a of the open center-type directional control valve 60, and a pressure compensated flow control valve 64 and a pressure generating means 66 are provided on this bypass line 62 from the upstream. Upstream pressure of the control valve 64 is applied to the pressure compensated flow rate control valve 64 in its opening direction, and load pressure of the small inertia actuators 34, 36, to be generated by the closed-type directional control valves 22, 24 and/or the maximum load pressure and spring pressure are applied in its closed direction, so as to control a negative control variable-displacement pump 10 through upstream pressure of the pressure generating means 66.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a hydraulic circuit for a construction machine,
In particular, the present invention relates to a hydraulic circuit including a relatively large inertial actuator, and further to an improvement of a hydraulic circuit capable of achieving improved combined operability and energy efficiency in such a circuit.

[0002]

2. Description of the Related Art Conventionally, this type of hydraulic circuit is preferably constructed as a load sensing circuit, and such a circuit is generally known.

FIG. 4 shows a hydraulic circuit of this type. In the illustrated example, only two actuator systems are shown. However, in FIG. 4, the discharge pressure oil from the pump line 12 of the negative control variable displacement pump 10 is supplied to the respective branch pump lines 14 and 1.
6, via the directional control valves 20, 22 and actuator lines 26, 28, respective actuators 32,
A hydraulic circuit for supplying / discharging to / from 34 in parallel is shown. Therefore, each directional valve (closed center type) 20,
The flow control valves 38 and 40 are provided at the inlets of the valve 22, and the pressure of the outlet side oil passages 14a and 16a of the flow control valves 38 and 40 in the closing direction is set to the respective signal lines 38a. , 40a, and the load pressure of the actuators 32, 34 generated in the directional control valves 20, 22 in the opening direction is applied via the signal lines 42, 44, respectively. On the other hand, in the flow rate control mechanism 10a of the variable displacement pump 10, the higher pressure of the load pressures is selected by the high pressure selecting means 48 and the signal line 5.
It is configured to be introduced via 0. In the figure, reference numeral 52 is a relief valve, and 54 is a tank line.

Therefore, according to such a configuration, generally, when each of the directional control valves 20 and 22 is operated, the pump oil amount corresponding to the opening degree of each directional control valve 20 and 22 is obtained.
2, 34. Moreover, this oil amount is always kept constant even if the load pressure of each actuator 32, 34 fluctuates. As described above, in this type of hydraulic circuit, the drive speed of the actuator is set in proportion to the operation amount of the directional control valve, and this speed is always kept constant regardless of the fluctuation of the load pressure. It is possible to greatly improve the operability of the hydraulic circuit, that is, the machine, particularly the combined operability.

[0005]

However, the conventional hydraulic circuit described above has the following drawbacks, especially when the circuit includes a relatively large inertial actuator.

That is, in the conventional hydraulic circuit (see FIG. 4), for example, when the actuators 32 and 34 are for a large inertia swing and a small inertia boom, respectively, the actuators 32 and 34 are operated simultaneously. In order to (combine operation), the two-way switching valves 20 and 22 are simultaneously operated by half-lever, for example (in this case, the discharge capacity of the pump 10 is sufficient to drive both actuators 32 and 34 simultaneously). Assuming that (Yes), the pump discharge pressure gradually increases. As a result, first, the drive pressure of the boom actuator 34 (for example, 130b
ar), the boom actuator 34 is driven, and then the drive pressure of the swing actuator 32 (for example, 250 b
ar), the swing actuator 32 is driven.

Further, for example, when the large inertial swing actuator 32 is controlled at a fine speed, the directional control valve 20 is first operated to the left at the time of starting, so that the pressure oil discharged from the pump 10 is supplied to the flow control valve 38 and the direction. Assuming a case in which the actuator 32 is supplied via the switching valve 20 to drive the actuator 32, and then the directional switching valve 20 is returned to a slightly neutral position in order to decelerate the same, the area of the opening throttle passage is reduced. Since the differential pressure in the throttle passage 20a increases, the pressure in the signal line 42 relatively decreases as compared with the pressure in the oil passage 14a, so that the flow control valve 38 moves in its closing direction. Result Pump 10 to Actuator 32
The amount of pressure oil supplied to is reduced. That is, the actuator 32 is decelerated.

However, in the case of the above-mentioned operation, in the conventional hydraulic circuit, the actuator 32 is
In the former case (combined operation), the actuator 32 is immediately activated even if the driving pressure is increased, because the state is maintained or the movement is continued due to the large inertia of itself. And due to this, a high voltage is generated in the circuit. In the latter case, the actuator 32 does not immediately decelerate even if the pressure oil supply amount to the actuator 32 decreases,
Due to this, abnormal pressure is generated in the circuit, and cavitation and hunting repeatedly occur. When the pressure is high, the relief valve 52 often operates, and the pressure oil is wasted.

Therefore, in any of the conventional hydraulic circuits, the operability is lowered due to the generation of the high pressure or the abnormal pressure, and the energy efficiency is lowered due to the consumption of the pressure oil. Further, particularly in the former case, the boom actuator 34 on the low load pressure (small inertia) side is driven by the drive pressure and the pump discharge pressure due to the start-up delay of the large inertia actuator 32, that is, until steady driving. Since the differential pressure (250-130 = 120 bar) between and is wastefully consumed as a pressure loss of the flow control valve 40, there is a drawback that the energy efficiency is further reduced.

SUMMARY OF THE INVENTION An object of the present invention is to provide a hydraulic circuit for a construction machine including a relatively large inertial actuator, which is capable of preventing deterioration of combined operability and energy efficiency.

[0011]

In order to achieve the above object, a hydraulic circuit of a construction machine according to the present invention includes one relatively large inertia actuator and one or more relatively small inertia actuators. In the hydraulic circuit of the construction machine, in which the discharge pressure oil from the negative control variable displacement pump is supplied to and discharged from these actuators in parallel via the branch pump line, the directional control valve and the actuator line, respectively. The directional control valve for the inertial actuator is formed as an open center type having a bypass passage, while the directional control valve for the small inertial actuator is formed as a closed center type, and the bypass passage of the open center type directional control valve is formed. Connect the pressure oil bypass line that communicates with the tank line, and use this pressure oil bypass line. Is provided with a flow control valve with pressure compensation and a pressure generator in order from the upstream side, and the flow control valve with pressure compensation is applied with the upstream pressure of the control valve in the opening direction and is closed in the closing direction. By applying the load pressure of the small inertia actuator and / or the maximum load pressure and spring pressure therein, which is generated in the center type directional control valve, the negative control variable displacement pump is operated via the pressure on the upstream side of the pressure generating means. It is characterized in that it is configured to control.

In the above hydraulic circuit, the open center type directional control valve can have the bypass throttle passage in the throttle communication state even in the full stroke operation position.

Also, most commonly, the large inertia actuators may be pivot actuators and the small inertia actuators may be boom, arm and / or other actuators.

[0014]

According to the present invention, the negative control variable displacement pump is linked to the closed center type directional control valve for the small inertia actuator and is also subordinate to the open center type directional control valve for the large inertia actuator. Controlled through. Therefore, according to the present invention,
Each of these actuators can be smoothly driven without loss even when the large and small inertia actuators are simultaneously driven. That is, it is possible to prevent a decrease in combined operability and energy efficiency, which are difficult points in the conventional hydraulic circuit of this type.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of a hydraulic circuit for a construction machine according to the present invention will be described in detail below with reference to the accompanying drawings. For convenience of explanation, the same components as those of the conventional structure shown in FIG. 4 are designated by the same reference numerals, and detailed description thereof will be omitted.

First, the arrangement of the actuator system of the hydraulic circuit according to the present invention has the same structure as that of the conventional hydraulic circuit. Therefore, in this embodiment, an actuator having three actuator systems is shown. That is, FIG.
In the hydraulic circuit, basically, the discharge pressure oil from the pump line 12 of the negative control variable displacement pump 10 is supplied to the respective branch pump lines 14, 16, 18, the directional control valves 60, 22, 24 and the actuator lines. The actuators 26, 28 and 30 are configured to supply and discharge in parallel to the respective actuators 32, 34 and 36. It should be noted that here, the actuator has one relatively large inertia, most commonly a swing actuator 32, and one or more (two in the illustrated embodiment) relatively small inertia, for example, Boom and arm actuators 34, 36.

However, in the present embodiment, in such a structure, first, the directional control valve 60 for the turning actuator 32 having a large inertia is formed as an open center type having a bypass passage 60a. , And the small inertia inertia boom and arm actuator 3
The directional control valves 22 and 24 for 4 and 36 are formed in a normal closed center type. The direction switching valves 60, 22 and 24 are connected in parallel. Further, a pressure oil bypass line 62a communicating with the tank line 54 is connected to one side of the bypass passage 60a of the open center type directional control valve 60, and a pressure generating means 66 is provided on the downstream side pressure oil bypass line 62a, and the other side. Direction switching valve 60 connected to the pump line 12 of
A flow control valve 64 with pressure compensation is provided on the pressure oil bypass line 62 on the upstream side. The flow control valve with pressure compensation 6
As shown by the broken line, 4 may be provided on the upstream side of the pressure generating means 66 in the pressure oil bypass line 62a on the downstream side of the direction switching valve 60. The flow control valve 64 with pressure compensation
Is applied to the upstream side pressure of the control valve 64 through the signal line 64a in the opening direction, and the small inertia actuators 34, 36 generated in the closed center type directional control valves 22, 24 are closed in the closing direction. The maximum load pressure among the load pressures (or the load pressure when there is one small inertia actuator) is set to the signal lines 42 and 44 and the high pressure selecting means 48.
Spring 64b via and in addition to signal line 50
Is applied. Furthermore, the flow rate control mechanism 10a of the variable displacement pump 10 is configured to apply the upstream pressure of the pressure generating means 66, that is, the pressure of the downstream pressure oil bypass line 62a via the signal line 68. Further, reference numeral 52 in the drawing indicates a relief valve, and 54 indicates a tank line.

Next, the operation of the hydraulic circuit of the present invention having the above construction will be described. First, with all the directional control valves 60, 22, 24 in the neutral position, the signal lines 42, 4 of the closed center directional control valves 22, 24 are shown.
Since 4 is connected to the tank lines 54 and 54, respectively, the pressure of the signal line 50 is kept low. Accordingly, the flow control valve with pressure compensation 64 is maintained in the open state by the pressure of the pressure oil bypass line 62 applied via the signal line 64a, so that the pressure of the downstream side pressure oil bypass line 62a, that is, the signal line 68. Is maintained at the high pressure of the pump line 12, this high pressure is guided to the flow rate control mechanism 10a of the variable displacement pump 10, and when the control pressure is high, the discharge flow rate of the variable displacement pump 10 is reduced by the negative control. Is kept to a minimum.

In the above state, when the closed center type directional control valve 22 is operated to the left side in the figure, for example, to the half lever position in order to drive the small inertia boom actuator 34 at a fine speed, the discharge from the pump 10 is performed. Pressure oil is pump line 12, branch pump line 1
6, and is supplied to the actuator line 28 through the throttle passage 22a of the direction switching valve 22. However, at this time, the pressure oil pressure, that is, the actuator 3
The load pressure of 4 is the signal line 42, the high pressure selecting means 48,
It acts via the signal line 50 in the direction of closing the flow control valve 64 with pressure compensation. Therefore, the pressure-compensated flow rate control valve 64 controls the discharge flow rate of the pump 10 to increase through the signal line 68 and the flow rate control mechanism 10a.
As a result, the discharge flow rate of the pump 10 is the same as that of the throttle passage 22.
It is automatically adjusted so that the differential pressure at a is always constant, that is, the amount of oil supplied to the actuator 34 is always constant regardless of the load pressure. That is, the actuator 34 is always operated independently at a constant speed regardless of the fluctuation of the load pressure.

Further, in the single operation state, if the direction switching valve 60 is operated to the left in the figure, for example, to the half lever position in order to simultaneously drive (composite operation) the large inertial swing actuator 32, as shown in FIG. As can be seen from the hydraulic symbol diagram at the half lever position shown in
The pressure oil bypass line 62 is also connected to the downstream pressure oil bypass line 62a via the throttle passage 60b, and the throttle passage 60b.
It is also connected in parallel to the actuator line 26 via c. Therefore, in this state, in addition to the flow rate control by the pressure-compensated flow rate control valve 64, the flow rate is also throttled in the throttle passage 60a, so that the amount of pressure oil flowing to the downstream side pressure oil bypass line 62a is larger than that during the boom actuator 34 is operated independently. As a result, the pressure in the signal line 68 decreases, and the discharge flow rate of the variable displacement pump 10 increases due to the negative control via the flow rate control mechanism 10a, and this increased pressure oil component tries to drive the swing actuator 32.

At this time, however, the actuator 32
Does not drive immediately because of its large inertia, and therefore the pressure in the pump line 12 tends to rise due to the increase in the discharge flow rate of the pump. However, the increase in the discharge flow rate is
Since it is not due to the flow control valve with pressure compensation 64 but due to the reduction of the area of the bypass passage 60a of the directional control valve 60, the bypass flow rate to the pressure oil bypass line 62a on the downstream side is accompanied by the pressure increase of the pump line 12. Can be increased, resulting in a decrease in pump discharge flow. That is, the pressure in the pump line 12 does not rise abnormally. In other words, during combined operation of both actuators 34, 32, the operating pressure acts on the swing actuator 32 while the boom actuator 34 is operating, and as a result, the swing actuator 32 is driven slowly and smoothly. That is, both actuators 32, 34
Does not reduce its operability and energy efficiency.

When the heavy load actuator 32 is operated independently, the actuator 32 is subjected to center bypass bleed-off control via the open center type directional control valve 60 in accordance with normal negative control, so that the actuator 32 is driven smoothly and without loss. It is clear that this will be done.

As described above, according to the hydraulic circuit of the present invention, the negative control variable displacement pump is interlocked with the closed center type directional control valve for the small inertia actuator and the open center type directional control valve for the large inertia actuator. Since the control is performed via the pressure compensation flow rate control valve that also depends on the above, even when the large and small inertia actuators are simultaneously driven, these actuators can be driven smoothly and without loss. That is, it is possible to reliably prevent the deterioration of the composite operability and energy efficiency, which are the drawbacks of the conventional hydraulic circuit of this type.

Next, FIG. 3 shows another embodiment of the hydraulic circuit according to the present invention. In this embodiment, the bypass throttle passage 70b of the open center type directional control valve 70 is formed so as to be in the throttle communication state even at the full stroke operation position of this valve. This is because the swing actuator 32 generally does not require high-speed driving unlike the other actuators 34 and 36 such as a boom and an arm.
8 (see FIG. 1) signal pressure is always maintained at a predetermined pressure,
The maximum amount of oil supplied to the swing actuator 32 (maximum drive speed) can be configured to be smaller than that of the other actuators 34, 36.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and many design changes can be made without departing from the spirit of the present invention.

[0026]

As described above, the hydraulic circuit of the construction machine according to the present invention comprises one relatively large inertial actuator and one or a plurality of relatively small inertial actuators. On the other hand, in the hydraulic circuit of the construction machine that supplies and discharges the pressure oil discharged from the negative control variable displacement pump in parallel via the branch pump line, the direction switching valve and the actuator line, the direction switching valve for the large inertia actuator. Is formed as an open center type having a bypass passage, while the directional control valve for the small inertia actuator is formed as a closed center type, and the bypass passage of the open center type directional control valve is provided with a pressure oil communicating with a tank line. Connect the bypass line and press the pressure oil bypass line in order from the upstream side. A compensating flow control valve and a pressure generating means are provided, and the pressure compensating flow control valve applies the upstream pressure of the control valve in the opening direction and the closed center type directional control valve in the closing direction. The negative control variable displacement pump is configured to be controlled by applying a generated load pressure of the small inertia actuator and / or a maximum load pressure and a spring pressure therein, via the pressure on the upstream side of the pressure generating means. To control the negative control variable displacement pump via the closed center type directional control valve for small inertia actuator and the flow control valve with pressure compensation which is also subordinate to the open center type directional control valve for large inertia actuator. Even when simultaneously driving large and small inertia actuators, these actuators can be driven smoothly and without loss. Rukoto is possible.

That is, according to the present invention, it is possible to surely prevent the deterioration of the composite operability and energy efficiency which has occurred in the conventional hydraulic circuit of this kind. Also,
The hydraulic circuit of the present invention has the advantage of being relatively simple to construct.

[Brief description of drawings]

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

FIG. 2 is a hydraulic pressure symbol diagram at a half lever position of the open center type directional control valve for the large inertial (turning) actuator of the hydraulic circuit shown in FIG.

FIG. 3 is a hydraulic symbol diagram showing another embodiment of the open center type directional control valve for the large inertia (swing) actuator of the hydraulic circuit shown in FIG.

FIG. 4 is a hydraulic system diagram showing a configuration example of a hydraulic circuit of a conventional construction machine.

[Explanation of symbols]

 10 variable displacement pump 10a flow control mechanism 12 pump line 14, 16, 18 branch pump line 22, 24 closed center type directional control valve 22a throttle passage 26, 28, 30 actuator line 32 large inertia (swing) actuator 34 small inertia (boom) ) Actuator 36 Small inertia (arm) actuator 42, 44 Signal line 48 High pressure selection means 50 Signal line 52 Relief valve 54 Tank line 60 Open center type directional control valve 60a Bypass passage 60b, 60c Throttle passage 62 Pressure oil bypass line 62a Downstream side Pressure oil bypass line 64 Flow control valve with pressure compensation 64a Signal line 66 Pressure generating means 70 Open center type directional control valve 70a Bypass passage 70b Throttle passage

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location F15B 11/05 A 8512-3H

Claims (3)

[Claims] 1. A comparatively large inertial actuator and one or a plurality of comparatively small inertial actuators, to which a discharge pressure oil from a negative control variable displacement pump is branched. In a hydraulic circuit of a construction machine that supplies and discharges in parallel via a pump line, a direction switching valve and an actuator line, the direction switching valve for the large inertia actuator is formed as an open center type having a bypass passage, while the small inertia actuator is used. The directional switching valve for use is formed as a closed center type, and a pressure oil bypass line communicating with the tank line is connected to the bypass passage of the open center type directional switching valve. A flow control valve with pressure compensation and a pressure generating means are provided in sequence, and the pressure compensation The flow rate control valve with a load is applied with the upstream pressure of the control valve in the opening direction, and the load pressure of the small inertia actuator generated in the closed center type directional control valve in the closing direction and / or the maximum load pressure therein. A hydraulic circuit for a construction machine, which is configured to apply a load pressure and a spring pressure to control the negative control variable displacement pump via the pressure on the upstream side of the pressure generating means. 2. The hydraulic circuit for a construction machine according to claim 1, wherein the open center type directional control valve has a bypass throttle passage formed in a throttle communication state even in a full stroke operation position. 3. The hydraulic circuit for a construction machine according to claim 1, wherein the large inertia actuator is a swing actuator, and the small inertia actuator is a boom, arm and / or other actuator.