JP2933806B2 - Hydraulic drive for construction machinery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load sensing system provided in a construction machine such as a hydraulic shovel for controlling a flow rate of a hydraulic pump so that a pump discharge pressure is larger than a maximum load pressure of a plurality of actuators by a predetermined pressure. And a hydraulic drive device provided with a left running motor for operating a left crawler belt and a right running motor for operating a right crawler belt.

[0002]

2. Description of the Related Art As a hydraulic drive for a construction machine of this type, the one shown in FIG. 9 has been conventionally proposed. FIG.
2 shows a circuit of a hydraulic drive device of the hydraulic shovel. The prior art shown in FIG. 9 includes a prime mover 1, a variable displacement hydraulic pump 2 driven by the prime mover 1, and a control actuator 15 for controlling a tilt angle of a swash plate of the hydraulic pump 2.
And a flow control valve 14 for controlling the driving of the control actuator 15. Control actuator 1
5 and the flow control valve 14 constitute a control means for controlling the flow rate of the hydraulic pump 2 so that the pump discharge pressure Ps becomes a predetermined pressure greater than the maximum load pressure Pamax of each actuator.

In this prior art, a boom is driven in addition to a left running motor 3 for driving a left crawler belt (not shown) forming a running body, a right running motor 4 for driving a right crawler belt (not shown) forming a running body. Boom cylinder not shown,
A plurality of actuators such as an arm cylinder (not shown) for driving the arm are provided. Also, a left traveling flow control valve 6 for controlling the flow of pressure oil supplied from the hydraulic pump 2 to the left traveling motor 3, and a right traveling for controlling the flow of pressure oil supplied to the right traveling motor 4 from the hydraulic pump 2. Flow control valve 8, a flow control valve (not shown) for controlling the flow of pressure oil supplied to an actuator (not shown), a flow control valve 6 for the left travel, a flow control valve 8 for the right travel, and a flow control valve (not shown). The vehicle includes a left traveling pressure compensation valve 7, a right traveling pressure compensating valve 9, and a pressure compensating valve (not shown) for controlling a differential pressure between the upstream pressure and the downstream pressure.

[0004] For example, one driving portion 7a of the above-mentioned left traveling pressure compensating valve 7 is provided with a discharge pressure P of the hydraulic pump 2.
s and the downstream pressure P _{L1 of the} left traveling flow control valve 6, and the other driving unit 7 b supplies the maximum load pressure Pamax of the load pressure of each actuator and the upstream pressure P _{L of the} left traveling flow control valve 6 to the other driving unit 7 b.
_Z1 is given, on one of the driving portion 9a of the right travel pressure compensation valve 9 described above, the downstream pressure P _L2 of delivery pressure Ps and the left travel flow control valve 8 for the hydraulic pump 2 is supplied, the other drive Part 9
b is the maximum load pressure of the load pressure of each actuator
Pamax and the upstream pressure P _{Z2 of the} left traveling flow control valve 8 are provided. The pump discharge pressure Ps is given to one drive unit of the above-described flow control valve 14 shown in FIG. 9, and the other drive unit is provided with the maximum load pressure Pama of the actuator.
x is given. Further, the maximum load pressure Pamax of each actuator is taken out via the shuttle valve 12.

[0005] In the thus configured are the prior art, the differential pressure between the maximum load pressure Pamax of the flow control valve 14 is a discharge pressure Ps and the actuator of the hydraulic pump 2, i.e. depending on the load sensing differential pressure [Delta] P _LS by being controlled Te, control actuator 15 is controlled in response to the differential pressure [Delta] P _LS, the flow rate to a predetermined differential pressure balance the pressure difference [Delta] P _LS to the force of the spring biasing the flow control valve 14 is a hydraulic Discharge from the pump 2. Further, the differential pressure across the flow control valves 6, 8 and the like by the pressure compensating valves 7, 9 and the like becomes the differential pressure between the discharge pressure Ps of the hydraulic pump 2 and the maximum load pressure Pamax of the actuator, that is, the same differential pressure as each other. Pressure ΔP _LS . Therefore, if the combined operation including running is performed by simultaneously switching the flow control valves 6, 8, etc., the opening of each flow control valve 6, 8, etc. is not affected by the fluctuation of the load pressure of other actuators. The flow rate discharged from the hydraulic pump 2 is diverted to each of the left traveling motor 3, the right traveling motor 4, and another actuator (not shown), and a combined operation including this traveling can be performed.

[0006] Generally, in each of the flow control valves 6, 8 and the like, as shown in FIG. Due to such variations in the opening areas of the flow control valves 6, 8 and the like, and delicate oil leaks inevitably occurring in the pipelines constituting the circuit, for example, the left traveling motor 3 and the right traveling The flow rates flowing into each of the motors 4 generally vary as shown in FIG. In other words, it is desirable that the operating speed of each of the traveling motors 3 and 4 is essentially constant with respect to the operation amount of an operation lever (not shown) for switching each of the flow control valves 6 and 8, but in practice it is not necessarily constant. Can not.

However, when the traveling operation is straight traveling, the maximum flow rate that can be discharged from the hydraulic pump 2 becomes smaller than the sum of the required flow rates of the traveling motors 3 and 4, that is, saturation occurs. As shown in FIG. 7, each of the traveling motors 3 and 4 is equally supplied with a flow rate that is の of the maximum flow rate of the hydraulic pump 2 described above.
Since the flow rate of / 2 is a constant flow rate, after all, stable straight running can be realized without being affected by the variation of the opening areas of the flow control valves 6 and 8 described above.

[0008]

However, during steering (turning), only the left traveling operation lever of the left / right traveling operation levers (not shown) was operated to the full stroke, and the right traveling operation lever was half-operated, for example. Sometimes, the sum of the required flow rates of the left and right traveling motors 3 and 4 becomes smaller than the maximum flow rate of the hydraulic pump 2, so that the flow rate supplied to the left traveling motor 3 is as shown by the solid line in FIG. Generally, the flow rate is larger than the pump flow rate during the straight running, that is, the flow rate which is １ ／ of the maximum flow rate of the pump 2. Therefore, in the prior art shown in FIG. 9 described above, the traveling speed at the time of steering becomes faster than that at the time of straight traveling, and the traveling speed may be extremely changed, for example, when shifting from straight traveling to steering traveling. There is a problem in operability.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances in the prior art, and has as its object a stable operation without being affected by variations in the opening area due to manufacturing errors of the flow control valves for right and left traveling and the like. An object of the present invention is to provide a hydraulic drive device for a construction machine that can realize straight traveling and suppress an increase in traveling speed during steering.

[0010]

In order to achieve this object, the present invention provides a variable displacement hydraulic pump, a plurality of pumps including a left traveling motor and a right traveling motor driven by hydraulic oil discharged from the hydraulic pump. And a left traveling direction switching valve for controlling the flow of pressure oil supplied from the hydraulic pump to the left traveling motor, and controlling the flow of pressure oil supplied to the right traveling motor from the hydraulic pump. Right traveling direction switching valve, and control means for controlling a discharge flow rate of the variable displacement hydraulic pump in accordance with a load sensing differential pressure which is a differential pressure between a pump discharge pressure and a maximum load pressure of the load pressure of the actuator. In the hydraulic drive system for a construction machine, the control means controls the target difference as the target value of the load sensing differential pressure as the pump discharge pressure increases. It is a configuration including the target differential pressure changing means capable of changing the value of the target differential pressure so decreases.

[0011]

In general, the driving pressure is relatively low because both the left crawler belt and the right crawler belt rotate at the same rotational speed when traveling straight, while one side rotates more when steering, and the vehicle runs while turning. Therefore, it is known that the driving pressure is higher than that when traveling straight ahead, and the maximum load pressure during steering is determined by the load pressure of the traveling motor related to the side that rotates a lot, and the pump discharge pressure is governed by the maximum load pressure. Have been.

The present invention focuses on this point,
Due to the above-described configuration, when the vehicle is traveling straight, the target differential pressure changing means generates a relatively large target differential pressure, for example, the target differential pressure in the related art, as the pump discharge pressure is relatively low. The target differential pressure having the same value as that of the load sensing differential pressure is set as the load sensing differential pressure, whereby the flow rate of の of the maximum flow rate of the hydraulic pump is supplied to each of the left traveling motor and the right traveling motor in the same manner as in the related art. Stable straight running can be realized without being affected by variations in the opening area due to manufacturing errors of the flow control valve and the like.

Also, during steering, as the pump discharge pressure becomes higher than during straight running, the target differential pressure changing means sets the target differential pressure smaller than that during straight running as the load sensing differential pressure. Accordingly, the flow rate discharged from the hydraulic pump is controlled so as to be smaller than when traveling straight, and the flow rate supplied to the traveling motor forming the side that rotates more is also suppressed as compared with the related art. 1/2 of the maximum flow rate of the hydraulic pump during traveling
It can be reduced to the extent. As a result, an increase in the traveling speed during steering can be suppressed, and for example, a traveling speed equivalent to the traveling speed during straight traveling can be achieved.

[0014]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of a hydraulic drive device for a construction machine according to the present invention. FIG. 1 is a circuit diagram showing one embodiment of a hydraulic drive device for a construction machine according to the present invention, FIG. 2 is a diagram showing a main part configuration of a controller provided in the embodiment shown in FIG. 1, and FIG. 3 is a controller shown in FIG. FIG. 4 is a diagram showing a functional relationship between a pump discharge pressure and a target differential pressure set by a function generator included in FIG. 4, and FIG. 4 is a diagram showing characteristics obtained in the embodiment shown in FIG.

In these figures, the same elements as those shown in FIG. 9 are denoted by the same reference numerals. That is,
Also in the embodiment shown in FIG. 1, a prime mover 1, a variable displacement hydraulic pump 2 driven by the prime mover 1, a left traveling motor 3 driving a left crawler belt (not shown) forming a traveling body, and a traveling body are formed. A right traveling motor 4 for driving a right crawler belt (not shown), a left traveling flow control valve 6 for controlling the flow of pressure oil supplied from the hydraulic pump 2 to the left traveling motor 3,
The upstream and downstream pressures of the right traveling flow control valve 8, the left traveling flow control valve 6, and the right traveling flow control valve 8, which control the flow of hydraulic oil supplied from the hydraulic pump 2 to the right traveling motor 4. The pressure compensating valve 7 for left traveling and the pressure compensating valve 9 for right traveling are provided for controlling the front-rear differential pressure, which is the difference between the two.

In the embodiment shown in FIG. 1, a hydraulic cylinder 5 such as a boom cylinder or an arm cylinder is illustrated as an actuator other than the traveling motors 3 and 4. The drive of the hydraulic cylinder 5 is controlled by a hydraulic cylinder flow control valve 10, and the differential pressure across the hydraulic cylinder flow control valve 10 is controlled by a hydraulic cylinder pressure compensation valve 11. Load pressure of left traveling motor 3 and right traveling motor 4
The larger one of the load pressures is taken out by the shuttle valve 12, and the larger one of the load pressure taken out by the shuttle valve 12 and the load pressure of the hydraulic cylinder 5 is taken out by the shuttle valve 13. Further, in this embodiment, a main relief valve 22 that regulates the magnitude of the discharge pressure Ps of the hydraulic pump 2 and a pilot pump 21 that is driven by the prime mover 1
And a pilot relief valve 2 for defining the magnitude of the pilot pressure Pso discharged from the pilot pump 21.
3 and solenoid valves 32, 33 and 34 for reducing the pilot pressure Pso and outputting the control pressure Pc, respectively.

Note that the pilot pressure Pso of the pilot pump 21 and the downstream pressure P _{L1 of the} left traveling flow control valve 6 are given to one drive section 7a of the above-mentioned left traveling pressure compensating valve 7, while the other driving section is driven. The control pressure Pc output from the solenoid valve 32 and the upstream pressure P _{Z1 of the} left traveling flow control valve 6 are given to the section 7b, and one driving section 9a of the above-mentioned right traveling pressure compensating valve 9 has: Pilot pressure Pso of pilot pump 21
And the downstream pressure P _{L2 of the} left traveling flow control valve 8, and the control pressure P output from the solenoid valve 33 is applied to the other drive unit 9 b.
c and the upstream pressure P _{Z2 of the} left traveling flow control valve 8 are provided.

Further, in this embodiment, the pump discharge pressure P
s, and a load sensing differential pressure ΔP _LS that is a differential pressure between the pump discharge pressure Ps and the maximum load pressure Pamax among the load pressures of the actuators including the traveling motors 3 and 4. And a differential pressure detector 27.

Further, in the embodiment shown in FIG. 1, the discharge flow rate of the hydraulic pump 2 is controlled in accordance with the load sensing differential pressure ΔP _LS which is the differential pressure between the pump discharge pressure Ps and the maximum load pressure Pamax of the actuator. control means, the pump according to the discharge pressure Ps increases, the load sensing differential pressure [Delta] P _LS target value at which the target differential pressure [Delta] P can change the value of the target differential pressure [Delta] P to decrease a target differential pressure changing means Is included. The target differential pressure changing means includes, for example, a control actuator 20 for controlling the displacement of the hydraulic pump 2, and a small-diameter chamber 20 a of the control actuator 20, that is, a small-diameter chamber 20 a connected to the pilot pump 21 and a large-diameter chamber. An electromagnetic switching valve 24 arranged in a conduit communicating with the control actuator 20b;
An electromagnetic switching valve 26 disposed in a conduit connecting the large-diameter chamber 20b to the tank 25, and having a logical judgment and arithmetic function,
The pump discharge pressure signal detected by the pump discharge pressure detector 90 and the differential pressure signal detected by the differential pressure detector 27 are input to corresponding ones of the solenoid valves 32, 33, and 34 and the electromagnetic switching valve 24. , 26 and a controller 30 that outputs a drive signal to each of them.

The controller 30 described above, for example, as shown in FIGS. 2 and 3, functional relationship to the target differential pressure [Delta] P is the target value of the load sensing differential pressure [Delta] P _LS accordance pump delivery pressure Ps increases decreases Is set in advance, and a function generator 30a that outputs a target differential pressure ΔP corresponding to the pump discharge pressure Ps detected by the pump discharge pressure detector 90
And the target differential pressure ΔP output from the function generator 30a.
Calculating means for calculating a deviation ΔS from the load sensing differential pressure P _LS detected by the differential pressure detector 27, for example, a target differential pressure ΔP with a negative sign “−”, and a differential pressure detector An adder 30b for adding the load sensing differential pressure P _LS detected at 27; and increasing or decreasing the pump flow rate according to the deviation ΔS output from the adder 30b.
Judgment processing means 30c for judging whether to keep the current state and outputting a drive signal corresponding to the judgment result to electromagnetic switching valves 24, 26
.

The operation of the embodiment configured as described above is as follows. In general, at the time of traveling operation, when traveling straight ahead, both the left crawler belt (not shown) driven by the left traveling motor 3 and the right crawler belt (not shown) driven by the right traveling motor 4 rotate at the same rotational speed, so that the driving pressure, that is, the pump discharge pressure Ps is relatively low. On the other hand, at the time of steering, one side turns a lot, and the vehicle travels while turning the vehicle body, so that the driving pressure, that is, the pump discharge pressure Ps becomes higher than that during the straight traveling. Further, the maximum load pressure Pamax at the time of steering is determined by the load pressure of the traveling motor on the side that rotates a lot, and in a hydraulic drive device having a load sensing system as in this embodiment, the pump discharge pressure Ps is the maximum. It is governed by the load pressure Pamax. From such a viewpoint, the function relationship preset in the function generator 30a of the controller 30 is, for example, as shown in FIG. 3, the target differential pressure ΔP is set to a relatively high constant value in a low pressure region associated with straight running, that is, the conventional relationship. The target differential pressure is set to a value equivalent to the target differential pressure in the technology, and the target differential pressure ΔP is set to a constant value lower than the target differential pressure in the low pressure region in the high pressure region accompanying the steering travel, and the above-mentioned high constant value is set. To a low constant value.

For example, when each of the operating levers of the left traveling flow control valve 6 and the right traveling flow control valve 8 is switched to a full stroke in order to perform straight traveling, the hydraulic oil discharged from the hydraulic pump 2 Are respectively connected to the left traveling motor 3 and the right traveling motor 4 via the left traveling pressure compensating valve 7 and the left traveling flow control valve 6, and via the right traveling pressure compensating valve 9 and the right traveling flow control valve 8, respectively. , Whereby the left crawler belt and the right crawler belt (not shown) are driven, and straight traveling is performed. At this time, the discharge pressure P of the hydraulic pump 2
s is detected by the pump discharge pressure detector 90 and output to the controller 30. Further, the differential pressure between the pump discharge pressure Ps and the maximum load pressure Pamax which is the maximum value of the traveling load pressure detected through the shuttle valves 12 and 13, that is, the load sending differential pressure ΔP _LS is determined by the differential pressure detector 27. And is input to the controller 30.

The controller 30 in, determine the maximum load pressure Pamax by calculating means for example (not shown) based on the load sensing differential pressure [Delta] P _LS outputted from the differential pressure detector 27, the electromagnetic valve drive signal corresponding to the maximum load pressure Pamax 32 and 33. Thereby, the solenoid valve 3
Each of the control units 2 and 33 controls the control pressure obtained by reducing the pilot pressure Pso discharged from the pilot pump 21, that is, the control pressure Pc corresponding to the maximum load pressure Pamax, by the driving unit 7b of the left traveling pressure compensating valve 7 and the right traveling pressure. It outputs to each of the drive parts 9b of the pressure compensating valve 9. The driving section 7a of the left traveling pressure compensating valve 7 and the driving section 9a of the right traveling pressure compensating valve 9 are each provided with a pilot pressure P of the pilot pump 21.
so is given as is. Therefore, each of the left traveling pressure compensating valve 7 and the right traveling pressure compensating valve 9 is controlled by the same differential pressure (Pso−Pc).
The front-rear differential pressure (P _Z1 -P _L1 ) of the left traveling flow control valve 6 and the front-rear differential pressure (P _Z2 -P _L2 ) of the right traveling flow control valve 8 are equally controlled, and the left traveling motor 3 and the right traveling A flow rate corresponding to the opening area of the left traveling flow control valve 6 and the right traveling flow control valve 8 can be supplied to each of the motors 4 without being affected by load fluctuations of other actuators.

Further, in the controller 30, based on the pump discharge pressure Ps output from the pump discharge pressure detector 90, the target differential pressure ΔP is selected by the function generator 30a shown in FIG. Since the vehicle is traveling straight ahead, the pump discharge pressure P
s is located in the low pressure region shown in FIG. 3, and a relatively high value is selected as the target differential pressure ΔP. FIG. 2 shows the target differential pressure ΔP output from the function generator 30a with a minus sign “−” and the load sensing differential pressure ΔP _LS output from the differential pressure detector 27 as described above. The addition is performed by the adder 30b, and the deviation ΔS is obtained. Next, based on the deviation ΔS output from the adder 30b by the determination processing means 30c, it is determined whether the pump flow rate should be maintained as it is, increased or decreased, that is, the deviation ΔS becomes zero. A determination is made to make ΔP _LS equal to ΔP.

In this judgment processing means 30c, when the deviation ΔS is 0, the load sensing differential pressure ΔP _LS is
P, and the solenoid-operated switching valves 24, 24 shown in FIG.
26 is output. Thereby, the control actuator 20 is kept stopped, and the current flow rate is discharged from the hydraulic pump 2.

When the deviation ΔS <0, ΔP _LS <Δ
In the state of P, the electromagnetic switching valve 24 is turned ON, the electromagnetic switching valve 2
6 is turned off. Thereby, the large-diameter chamber 20b and the tank 25 of the control actuator 20 shown in FIG.
a and the pilot pressure P of the pilot pump 21
so is supplied to both the small diameter chamber 20a and the large diameter chamber 20b,
Due to the pressure receiving area difference between the large-diameter chamber 20b and the small-diameter chamber 20a, the piston of the control actuator 20 moves to the left in FIG. 1, the tilt angle increases, and the flow rate discharged from the hydraulic pump 2 increases. Control is performed. Along with this,
ΔP _LS gradually increases to approach ΔP, and finally coincides.

When the deviation ΔS> 0, ΔP _LS > Δ
In the state P, a signal for turning off the electromagnetic switching valve 24 and turning on the electromagnetic switching valve 26 is output. Thus, the large-diameter chamber 20b and the small-diameter chamber 20a of the control actuator 20 are formed.
Is cut off, the large-diameter chamber 20b communicates with the tank 25, and the pilot pressure Pso applied to the small-diameter chamber 20a causes the piston of the control actuator 20 to move rightward in FIG. As a result, control for reducing the flow rate discharged from the hydraulic pump 2 is performed. Along with this,
ΔP _LS gradually decreases to approach ΔP, and finally coincides.

The relationship between the strokes of the operation levers of the flow control valves 6 and 8 for traveling when the vehicle is traveling straight as described above and the flow rate of the fluid flowing into the traveling motors 3 and 4, that is, the traveling speed is shown by a solid line in FIG. As in the prior art described above, in the full stroke state, a flow rate that is の of the maximum flow rate of the hydraulic pump 2 is equally supplied to each of the left traveling motor 3 and the right traveling motor 4. .

On the other hand, when the operation lever of the left traveling flow control valve 6 is operated to a full stroke and the operation lever of the right traveling flow control valve 8 is half-operated, for example, in order to perform steering traveling, the hydraulic pump 2 Is supplied via a left traveling pressure compensating valve 7 and a left traveling flow control valve 6, and via a right traveling pressure compensating valve 9 and a right traveling flow control valve 8. That is, a relatively large flow rate is supplied to the left traveling motor 3 and a small flow rate is supplied to the right traveling motor 4, whereby the left crawler belt (not shown)
The right crawler turns and steering is performed.

At this time, in the controller 30, the target differential pressure ΔP is selected by the function generator 30a shown in FIG. 2 based on the pump discharge pressure Ps output from the pump discharge pressure detector 90. Because it is a run,
The pump discharge pressure Ps is located in the high pressure region shown in FIG. 3, and a relatively low value is selected as the target differential pressure ΔP. The target differential pressure ΔP output from the function generator 30a has a negative sign “−”.
And the load sensing differential pressure ΔP _LS output from the differential pressure detector 27 are added by the adder 30b shown in FIG. 2 to obtain the deviation ΔS. Based on the deviation ΔS, as described above, the judgment processing means 30c determines whether the pump flow rate is to be maintained as it is, increases or decreases, that is, the deviation ΔS becomes 0 and ΔP _LS matches ΔP. The determination for the termination and the output of the corresponding drive signal are performed.

In this case, since the target differential pressure ΔP selected by the function generator 30a is low, and the deviation ΔS output from the adder 30b tends to ΔS> 0, the pump flow reduction processing is mainly performed. Then, a signal for turning off the electromagnetic switching valve 24 and turning on the electromagnetic switching valve 26 is output from the judgment processing means 30c of the controller 30. Thereby, as described above, the large-diameter chamber 20b of the control actuator 20
The large-diameter chamber 20b and the tank 25 communicate with each other, the pilot pressure Pso applied to the small-diameter chamber 20a causes the piston of the control actuator 20 to move rightward in FIG. Control is performed such that the turning angle is reduced and the flow rate discharged from the hydraulic pump 2 is reduced. That is, the flow rate discharged from the hydraulic pump 2 is slightly suppressed as compared with the straight traveling. Accordingly, the flow rate supplied to the left traveling motor 3 is smaller with respect to the stroke of the operation levers of the traveling flow control valves 6 and 8 than during the straight traveling described above. For example, as shown by the dashed line in FIG.
At the time of the full stroke, it is possible to obtain a characteristic that coincides with a flow rate that is の of the pump maximum flow rate, which is the flow rate during the straight running described above.

In the embodiment constructed as described above, when the vehicle travels straight ahead, when the operation levers of the traveling flow control valves 6 and 8 are fully stroked, the required flow rates of the left traveling motor 3 and the right traveling motor 4 are increased. Is larger than the maximum flow rate of the hydraulic pump 2, the flow rate １ ／ of the pump maximum flow rate is equally supplied to the left travel motor 3 and the right travel motor 4 as described above, In the same manner as described above, stable straight running can be realized without being affected by variations in the opening area due to manufacturing errors of the flow control valves 6 and 8 for running.

During steering, by supplying a smaller flow rate than the pump flow rate during straight running to the running motors 3, 4, the running speed during steering is suppressed to, for example, the same speed as during straight running. Can be
Extreme operability can be ensured without causing an extreme change in traveling speed when moving from straight traveling to steering traveling.

In the above description, for example, the case where the operation lever of the left traveling flow control valve 6 is made full-stroke at the time of steering has been described. Left traveling motor 3 due to variations in the opening area of control valve 6
Although the running speed may vary, the slope of the metering characteristic becomes gentler as shown in FIG. 4 as compared with the prior art, and the running speed at the time of steering can be reduced, thereby ensuring excellent safety. can do.

In the above embodiment, the pump discharge pressure detector 90 is provided. Instead of providing the pump discharge pressure detector 90, the maximum load pressure Pamax of the actuator including the traveling motors 3, 4 is detected. A maximum load pressure detector is provided, and the controller 30 has a function generator 30a shown in FIG.
In addition to the adder 30b and the judgment processing means 30c, a configuration having pump discharge pressure calculating means for obtaining the pump discharge pressure Ps based on the maximum load pressure detected by the above-described maximum load pressure detector is provided, and the function generator 30a It may be configured to output the target differential pressure ΔP corresponding to the pump discharge pressure Ps obtained by the above-described pump discharge pressure calculating means. In this way, those configurations, the negative sign to the target differential pressure [Delta] P that is output from the function generator 30a "-" if added to the load sensing differential pressure [Delta] P _LS in adder 30b are denoted by the following operation described above The embodiment shown in FIG. 1 has substantially the same operation and effect as the embodiment shown in FIG.

[0036]

According to the present invention having the above-described structure, it is possible to realize a stable straight running without being affected by the variation of the opening area due to a manufacturing error of the flow control valve for right and left running and the like. An increase in running speed during steering can be suppressed, and operability during steering can be improved as compared with the conventional case.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a main configuration of a controller provided in the embodiment shown in FIG. 1;

3 is a diagram showing a functional relationship between a pump discharge pressure set by a function generator included in the controller shown in FIG. 2 and a target differential pressure.

FIG. 4 is a diagram showing characteristics obtained in the embodiment shown in FIG. 1;

FIG. 5 is a diagram showing variations in the opening area of a traveling flow control valve that generally occur.

FIG. 6 is a diagram showing a variation in a traveling motor inflow flow rate which generally occurs.

FIG. 7 is a view showing a traveling motor inflow flow rate during a conventional straight traveling.

FIG. 8 is a diagram showing an inflow flow rate to one traveling motor during conventional steering.

FIG. 9 is a circuit diagram showing a conventional hydraulic drive device for a construction machine.

[Explanation of symbols]

2 Variable displacement hydraulic pump 3 Left traveling motor (actuator) 4 Right traveling motor (actuator) 6 Left traveling flow control valve 7 Left traveling pressure compensating valve 8 Right traveling flow control valve 9 Right traveling pressure compensating valve 20 Control Actuator 20a Small-diameter chamber 20b Large-diameter chamber 21 Pilot pump 24 Electromagnetic switching valve 25 Tank 26 Electromagnetic switching valve 27 Differential pressure detector 30 Controller (control means) 30a Function generator 30b Adder (deviation calculating means) 30c Judgment processing means 32 Electromagnetic Valve 33 Solenoid valve 34 Solenoid valve 90 Pump discharge pressure detector Ps Pump discharge pressure Pamax Maximum load pressure ΔP _LS load sensing differential pressure ΔP Target differential pressure ΔS deviation

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) E02F 9/22 F15B 11/00 F15B 11/05

Claims (3)

(57) [Claims] 1. A variable displacement hydraulic pump, a plurality of actuators including a left running motor driven by pressure oil discharged from the hydraulic pump and operating a left crawler belt, and a right running motor operating a right crawler belt; A left traveling direction switching valve for controlling the flow of pressure oil supplied from the hydraulic pump to the left traveling motor, and a right traveling direction switching for controlling the flow of pressure oil supplied to the right traveling motor from the hydraulic pump. A construction comprising a valve and a control means for controlling a discharge flow rate of the variable displacement hydraulic pump in accordance with a load sensing differential pressure which is a differential pressure between a pump discharge pressure and a maximum load pressure of the load pressure of the actuator. In the hydraulic drive device for a machine, as the control means increases the pump discharge pressure, the target differential pressure, which is the target value of the load sensing differential pressure, decreases. Hydraulic drive system for a construction machine which comprises the target differential pressure target differential pressure changing means capable of changing the value of the so that. 2. A pump discharge pressure detector for detecting the pump discharge pressure, and detecting the load sensing differential pressure which is a differential pressure between the pump discharge pressure and a maximum load pressure of the load pressure of the actuator. A differential pressure detector, wherein the control means includes a control actuator for controlling a displacement of the variable displacement hydraulic pump, an electromagnetic switching valve for controlling the drive of the control actuator, and a logic judgment and calculation function. A controller that inputs a pump discharge pressure signal detected by the pump discharge pressure detector, and a differential pressure signal detected by the differential pressure detector, and outputs a drive signal to the electromagnetic switching valve. The controller has a function relationship in which the target differential pressure, which is the target value of the load sensing differential pressure, decreases as the pump discharge pressure increases, and is set in advance, A function generator that outputs a target differential pressure corresponding to the pump discharge pressure detected by the pump discharge pressure detector, a target differential pressure output from the function generator, and a load detected by the differential pressure detector A deviation calculating means for calculating a deviation from the sensing differential pressure, and determining whether to increase, decrease, or hold the current value of the pump flow rate according to the deviation output from the deviation calculating means. The hydraulic drive device for a construction machine according to claim 1, further comprising a determination processing unit that outputs a drive signal. 3. A maximum load pressure detector for detecting a maximum load pressure of the actuator, and a load sensing differential pressure which is a differential pressure between the pump discharge pressure and a maximum load pressure of the load pressure of the actuator. A control actuator for controlling the displacement of the variable displacement hydraulic pump, an electromagnetic switching valve for controlling the drive of the control actuator, a logical judgment and an arithmetic operation. A controller which has a function, receives a pump discharge pressure signal detected by the pump discharge pressure detector, and a differential pressure signal detected by the differential pressure detector, and outputs a drive signal to the electromagnetic switching valve. A controller for calculating a pump discharge pressure based on the maximum load pressure detected by the maximum load pressure detector; A function relationship in which the target differential pressure, which is the target value of the load sensing differential pressure, decreases as the pressure value increases is set in advance, and a target differential pressure corresponding to the pump discharge pressure obtained by the pump discharge pressure calculating means is calculated. A function generator for outputting, a deviation calculating means for calculating a deviation between a target differential pressure output from the function generator and a load sensing differential pressure detected by the differential pressure detector, and an output from the deviation calculating means. And a judgment processing means for judging whether to increase, decrease, or keep the current value of the pump flow rate according to the deviation, and outputting a drive signal corresponding to the judgment result. Construction machinery hydraulic drive.