JPH04247131A - Hydraulic control device for hydraulic construction equipment - Google Patents

Abstract

PURPOSE:To save fuel consumption as well us to enhance operability by assuming optimum load sensing control of respective valves even if a first and a second hydraulic actuator which are controlled by paired control valves made under, at least, a common specification, are different in required maximum flow rate. CONSTITUTION:This device is applied to a hydraulic circuit in which the required maximum flow rate of a first actuator 4 is greater than the required maximum flow rate of a second actuator 21, the difference in pressure between the discharge pressure of a pump 1 and the maximum loading pressure of the first or second hydraulic actuators 4 and 21 is detected, and a displacement volume is changed so that the difference in pressure is turned out to be a target value set in advance. The operating condition is detected of the first and second actuators 4 and 21, and when the operating condition of the first hydraulic actuator 4 is to be detected, the target value for the difference in pressure is to be set higher than that of the case when the second hydraulic actuator 21 is operated.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic control system for hydraulic construction machinery capable of so-called load sensing control and input torque limiting control.

0002

2. Description of the Related Art An example of a hydraulic construction machine equipped with this type of hydraulic control device is a wheeled hydraulic excavator as shown in FIG. In the figure, reference numeral 4 denotes a hydraulic motor for driving, and the rotation of this hydraulic motor 4 causes the rear wheel to move through the transmission 101 and the propeller shaft 102.
03 is driven and the vehicle runs. Further, as the boom cylinder 21 expands and contracts, the boom 104, which is a part of the front attachment, is raised and lowered.

FIG. 7 is a diagram showing a hydraulic circuit for traveling and working of a conventional wheeled hydraulic excavator that performs the above-mentioned load sensing control and input torque limiting control.
is a variable displacement hydraulic pump driven by the engine 27. The rotational speed of the engine 27 is controlled by rotating a governor lever 27b of a governor 27a by a pulse motor 28 in accordance with the amount of depression of a fuel lever or a travel pedal 6a (not shown). Then, the variable displacement hydraulic pump 1 is driven according to the engine rotation speed, and the discharged oil is guided to the hydraulic motor 4 via the travel control valve 2, and is also sent to the boom drive oil cylinder via the work control valve 20. 2
I am guided by 1.

Load sensing control refers to the pressures before and after the travel control valve 2 or the work control valve 20, that is, the inlet pressure (pump pressure) and outlet pressure (load of the hydraulic motor 4 and hydraulic cylinder 21) of the control valves 2 and 20. The displacement volume (hereinafter also referred to as the tilting angle) of the variable displacement hydraulic pump 1 is adjusted so that the differential pressure between the pressure on the high pressure side selected by the shuttle valve 29 and referred to as the load sensing pressure becomes a constant value. ) to maintain the pump pressure higher than the load sensing pressure by a predetermined target value.

[0005] Therefore, a load sensing regulator 11 is provided which switches according to the differential pressure between the pump pressure and the load sensing pressure, and when the differential pressure between the pump pressure and the load sensing pressure exceeds the pressure set by the spring 11a, The load sensing regulator 11 switches toward position b in response to the pressure. At this position b, servo cylinder 1
Pump pressure is introduced to the pump 2, and the displacement of the hydraulic pump 1 becomes smaller due to the extension of the servo cylinder 12, and the pump discharge flow rate is reduced. On the other hand, when the differential pressure becomes less than the pressure set by the spring 11a, the load sensing regulator 11 is switched to position a, and the servo cylinder 12 is connected to the tank. As a result, the displacement volume increases and the pump discharge flow rate increases.

By carrying out the load sensing control as described above, the pump tilting angle is controlled so that the pump discharge flow rate becomes the flow rate required by the control valve 2 or 20, and an excess flow rate is not discharged. Since there is no waste due to loss, fuel efficiency is improved and operability is also improved.

Next, the operation of the traveling circuit will be explained. Now, for example, if you switch the forward/reverse switching valve 8 to forward (position F) and operate the pedal 6a of the pilot valve 6, the engine speed will be controlled according to the amount of pedaling, and the oil discharged from the hydraulic pump 5 will be controlled by the pilot valve. The hydraulic pressure is guided to the pilot port 2a of the hydraulic pressure control valve 2, and the control valve 2 is switched at a stroke amount according to the pilot oil pressure. As a result, oil discharged from the variable displacement hydraulic pump 1 is supplied to the hydraulic motor 4 via the pipe 91, the pressure compensation valve 23, the control valve 2, the pipe 92 or 93, and the counterbalance valve 3, and the vehicle runs. The speed of the vehicle depends on the amount of depression of the travel pedal 6a.

When the pedal 6a is released while the vehicle is running, the pilot valve 6 shuts off the pressure oil and its outlet port is communicated with the tank 10. As a result, the pressure oil acting on the pilot port 2a returns to the tank 10 via the forward/reverse switching valve 8, the slow return valve 7, and the pilot valve 6. At this time, since the return oil is throttled by the throttle 7a of the slow return valve 7, the pilot type control valve 2 is gradually switched to the neutral position and the vehicle is gradually decelerated.

Furthermore, when the operating switching valve 20 is switched to the "B" position or the "C" position using the operating lever 20a,
The oil discharged from the hydraulic pump 1 is connected to the pipe 94 and the pressure compensation valve 24.
and a boom driving hydraulic cylinder 2 via a control valve 20.
1, the boom 104 shown in FIG. 6 moves up and down as the hydraulic cylinder 21 expands and contracts. Here, the pressure compensation valve 23,
24 is used to compensate for the independent operation of the hydraulic motor 4 and the hydraulic cylinder 21, and causes the hydraulic pump 1 to discharge a pressure higher than the maximum load pressure of each of these actuators by a predetermined pressure. be.

Reference numeral 25 denotes a torque control servo valve for performing input torque limit control. The discharge pressure of the hydraulic pump 1 is introduced as a pilot pressure to this servo valve 25, and this pilot pressure is applied to a limit torque setting spring 25a. When the pressure becomes higher than the set pressure, the position is switched from the position c to the position d shown in the figure. As a result, the discharge pressure of the hydraulic pump 1 acts on the servo cylinder 12, the displacement volume of the hydraulic pump 1 is reduced by the servo cylinder 12, and the torque of the hydraulic pump 1 is limited to within the range of the output torque of the engine 27. Overloading the engine 27 is prevented. This is input torque limiting control, and is shown, for example, as a PQ diagram as shown in FIG.

That is, according to the above configuration, the target displacement volume (first target displacement volume) by load sensing
The displacement volume of the hydraulic pump is controlled to be the smaller of the target displacement volume (second target displacement volume) based on the input torque limit control, thereby improving fuel efficiency and operability. Overload of the engine 27 is prevented. Note that 26 is an unload valve, 31a and 31b are crossover relief valves, and CJ is a center joint.

0012

[Problems to be Solved by the Invention] By the way, in the traveling and working hydraulic circuit shown in FIG. 7, the maximum required flow rate during traveling is generally larger than the maximum required flow rate during working. The control valves 2 and 20 are valves with common specifications. Therefore, the maximum discharge flow rate of the hydraulic pump 1 is determined from the maximum required flow rate during running, and the pressure loss at the maximum stroke of the control valve 2 at the maximum flow rate is, for example, 18 kg.
・If f/cm2, the target differential pressure due to the spring 11a of the load sensing regulator 11 is 18Kg・f/cm2.
It is set to cm2. Therefore, when the work control valve 20 is operated to the maximum stroke, the differential pressure between the pump pressure and the load sensing pressure increases to its target value of 18 Kg·f/cm2.
The hydraulic pump 1 is operated at its maximum tilt angle so that As a result, pressure loss at the control valve 20 increases due to unnecessary discharge flow rate, resulting in poor fuel efficiency and poor operability.

Therefore, if the above-mentioned target differential pressure is set to, for example, 15 Kg·f/cm2 based on the maximum required flow rate during work, even if the control valve 2 is operated to the maximum stroke, the differential pressure between the pump pressure and the load sensing pressure will remain as above. The target differential pressure is 15Kg・
f/cm2, and the hydraulic pump 1 is not controlled to its maximum tilt angle, making it impossible to obtain the flow rate required during travel. However, the control valves 2 and 20 are made with different specifications, and the travel control valve 2 is made larger so that the pressure loss at the maximum stroke is equal to that of the work control valve 20 (15
Kg・f/cm2), parts cannot be standardized,
Not only does this lead to an increase in costs, but the valve itself becomes larger.

An object of the present invention is to increase the size of the valves without increasing costs even when the required maximum flow rates of the first and second hydraulic actuators controlled by at least one pair of common specification control valves are different. It is an object of the present invention to provide a hydraulic control device for hydraulic construction machinery that improves fuel efficiency and operability by performing optimal load sensing control on each valve without causing any problems.

[0015]

[Means for Solving the Problems] The present invention will be explained in conjunction with FIGS. 1 to 3 showing one embodiment. The present invention comprises a variable displacement hydraulic pump 1 driven by a prime mover 27, and a The first and second hydraulic actuators 4, 21 are provided between the hydraulic pump 1 and the first and second hydraulic actuators 4, 21, and the hydraulic actuators 4, 21 are driven by oil discharged from the hydraulic pump 1. The first and second control valve means 2, 20A respectively control the flow rate of pressure oil supplied to the hydraulic pump 1 and the discharge pressure of the hydraulic pump 1.
and differential pressure detection means 54 for detecting the differential pressure between the maximum load pressure of the second hydraulic actuators 4 and 21, and displacement volume changing means 40 for changing the displacement volume of the hydraulic pump 1;
and a first displacement volume control means 61 that controls the displacement volume changing means 40 so that the differential pressure becomes a predetermined target value, and the required maximum flow rate of the first actuator 4 is adjusted to the required maximum flow rate of the second actuator 21. It is applied to hydraulic control devices of hydraulic construction machinery whose flow rate is set higher than the required maximum flow rate. and,
The above purpose is to operate the first and second hydraulic actuators 4, 2
When the state detecting means 64 detects the state of use of the first hydraulic actuator 4 and the state of use of the first hydraulic actuator 4 is detected,
This is achieved by including target differential pressure changing means 61c that sets the target value of the differential pressure higher than when using the second hydraulic actuator 21. The invention of claim 2 is:
A second displacement volume control means 62 is provided for controlling the displacement volume changing means 40 so that the pump input torque does not exceed the prime mover output torque based on the discharge pressure of the hydraulic pump 1,
When the first hydraulic actuator is used, the maximum displacement volume that can be set by the first displacement volume control means 61 is larger than the maximum displacement volume that can be set by the second displacement volume control means 62. The target value of the differential pressure is set. The first hydraulic actuator in claim 3 is a travel hydraulic motor. The state detecting means in claim 4 detects that the operating means of the travel hydraulic motor 4 is being operated, and in response to this detection, the target differential pressure changing means 61c increases the target value of the differential pressure. .

[0016]

[Operation] When the first hydraulic actuator 4 with a large required maximum flow rate is used, a large target differential pressure is set, and when the second hydraulic actuator 21 with a small required maximum flow rate is used, a small target differential pressure is set. Ru. Therefore, when the first hydraulic actuator is used, the tilting angle of the hydraulic pump 1 is maximized to obtain a sufficient discharge flow rate, and when the second hydraulic actuator is used, the tilting angle of the hydraulic pump 1 is controlled to the maximum. Only the maximum flow rate required for that actuator is delivered.

[0017] In the section of means and effects for solving the above-mentioned problems that explains the structure of the present invention, figures of embodiments are used to make the present invention easier to understand. It is not limited to.

[0018]

[Embodiment] An embodiment of the present invention will be explained with reference to FIGS. 1 to 4. FIG. 2 is a diagram showing the overall configuration of a hydraulic control device for a wheeled hydraulic excavator, and FIGS. 1 and 3 are partially enlarged diagrams, and the same parts as in FIG. 7 are given the same reference numerals. Mainly explain the differences.

In this embodiment, the tilting angle, ie, the displacement volume, of the variable displacement hydraulic pump 1 is controlled by a tilting angle control device 40. The tilt angle control device 40 includes a hydraulic pump 41 driven by an engine 27, a pair of electromagnetic valves 42,
43, and the hydraulic pump 4 according to switching of the solenoid valves 42 and 43.
The hydraulic pump 1 has a servo cylinder 44 whose piston position is controlled by pressure oil from the hydraulic pump 1, and the tilt angle of the hydraulic pump 1 is controlled according to the piston position of the servo cylinder 44. Here, the pair of solenoid valves 42 and 43 are switched and controlled by a controller 50.

Further, the forward/reverse selector valve 8A is of an electromagnetic type, and the forward/reverse selector valve 8A changes from the N position in response to switching of the forward/reverse selector switch SW1 provided in the driver's seat from the N position to the F position and then to the R position. Switches to F position and R position respectively. When this forward/reverse changeover switch SW1 is in the N position, a high level signal is output from this switch SW1. Further, the work control valve 20A is of a hydraulic pilot type, and the operation lever 58
The switching is performed by the pressure reduced by the pressure reducing valve 59 in response to the operation. SW2 is a brake switch, which is turned on when working and turned off when driving. When the brake switch SW2 is turned on, both a parking brake and a service brake (not shown) are operated, and when it is turned off, the service brake can be operated by operating the brake pedal. When this brake switch SW2 is turned on, a high level signal is output from this switch SW2.

51 is a tilt angle sensor for detecting the tilt angle θs of the hydraulic pump 1; 52 is the discharge pressure Pp of the hydraulic pump 1;
A pressure sensor 53 detects the rotation speed N of the engine 27.
A rotation speed sensor 54 detects the discharge pressure of the hydraulic pump 1 and the maximum load pressure of the actuator (hydraulic motor 4
This is a differential pressure sensor that detects the differential pressure ΔPLS between the load pressure of the hydraulic cylinder 21 and the load pressure of the hydraulic cylinder 21, which is the larger value selected by the shuttle valve 29. Further, 55 is a potentiometer that detects the amount of rotation Nθ of the governor lever 27b, and 56 is a pressure sensor that detects the pressure Pt of the pilot valve 6 according to the amount of operation of the travel pedal 6a.The detection results of each of these sensors are as follows. The output signals of the forward/reverse changeover switch SW1 and the brake switch SW2 are input to the controller 50. 57 is a rotation speed setting device that commands a target rotation speed X according to manual operation of the fuel lever 57a, and the command signal is also input to the controller 50.

The controller 50 has a first control circuit section 60 as shown in FIG. , minimum value selection section 63, and comparator 64a
and a determination section 64 comprising an AND gate circuit 64b;
It consists of a servo control section 65.

The comparator 64a constituting the determination section 64 outputs a high level signal when the pilot pressure Pt detected by the pressure sensor 56 is higher than a predetermined pressure, and the output signal is an AND signal. Gate circuit 6
It is input to the non-inverting input terminal of 4b. Further, the inverting input terminal of the AND gate circuit 64b is connected to the brake switch SW.
2 and a signal from the forward/reverse selector switch SW1 are respectively input. And ■brake switch SW
2 is turned off (switch SW2 outputs a low level signal).
), ■ The forward/reverse selector switch SW1 is in the F or R position other than the N position (switch SW1 outputs a low-level signal), ■ The pilot pressure Pt is higher than a predetermined value (the comparator 64a outputs a high-level signal (output), that is, when the vehicle is running, the output of the AND gate circuit 64b is at a high level, and when the vehicle is working, the output of the AND gate circuit 64b is at a low level.

The LS control unit 61 controls the target differential pressure ΔPLSR1.
The target differential pressure ΔPLSR1 is set by the setting unit 61a of the target differential pressure ΔPLSR1, the setting unit 61b of the target differential pressure ΔPLSR2 which is lower than the target differential pressure ΔPLSR1, and the signal that the determination unit 64 determines to be running (the output of the AND gate circuit 64 is at a high level). A selection switch SW that selects the target differential pressure ΔPLSR2 based on a signal that determines work (the output of the AND gate circuit 64 is low level)
61c. Then, the deviation Δ(PLS) between the differential pressure ΔPLSD detected by the differential pressure sensor 54 and the target differential pressure is calculated by the deviation device 61d, and the target value is changed by the function generator 61e based on this deviation Δ(PLS). Calculate the amount ΔθL. Further, the amount of change ΔθL in this target value is integrated and output as a target pump tilt angle (first target displacement volume) θL for load sensing control.

The torque control unit 62 controls the engine rotation speed Nr detected by the rotation speed sensor 53 and the potentiometer 5.
Speed sensing is performed by calculating the deviation ΔT from the governor lever position Nθ detected in step 5 using a deviation device 62a, and based on this deviation ΔT, a target torque calculation unit 62b calculates a target torque Tpo for preventing an engine stall. . Then, the reciprocal number of the pump discharge pressure Pp detected by the pressure sensor 52 is determined by the reciprocal number calculation unit 62c, and the multiplier 62d multiplies this reciprocal number by the target torque Tpo to determine θps. Furthermore, this θps is filtered by the first-order delay element to obtain the target pump tilt angle (second
The target displacement volume is output as θT.

The minimum value selection unit 63 selects the smaller value of the two target tilt angles θL and θT, and inputs the tilt angle command value θr to the servo control unit 65. Servo control section 6
5, the deviation Δθ between the input tilting angle command value θr and the tilting angle feedback value θs detected by the tilting angle sensor 51 is determined by the deviation device 65a, and the function generating section calculates the deviation Δθ based on this deviation Δθ. On/off signals for the electromagnetic valves 42 and 43 are output from 65b. Thereby, the tilting angle control device 40 is controlled so that the pump tilting angle θs matches the tilting angle command value θr.

In this embodiment, the load sensing control section 6
1 and the torque control unit 62, and the minimum value selection unit 63 selects whichever is smaller, but the maximum value of the target tilt angle output from the load sensing control unit 61 is the torque Each part is set to be larger than the maximum value of the target tilt angle output from the control part 62. This point will be explained.

The P-Q diagram indicated by A-B-C-D in FIG. 4 is a P-Q diagram that can be set by the torque control section 62, and its maximum flow rate is Qt. Here, as described above, the target differential pressure set by the load sensing control unit 61 is ΔPLSR1 during driving, and ΔPLSR smaller than that during work.
It is 2. Now, assuming that the tilting angle of the hydraulic pump 1 becomes very large, the target differential pressure ΔPLSR1 during traveling
The maximum discharge flow rate of the hydraulic pump 1 according to the equation is shown in FIG. 4 as Qt'. In other words, the target differential pressure ΔPLS during driving is set so as to command a tilting angle such that Qt' is larger than Qt.
The value of R1 is determined. With such settings, when the specification of the maximum discharge flow rate of the hydraulic pump 1 is set to Qt, it is possible to always discharge Qt even if it is affected by errors in various parts. On the other hand, since the maximum discharge flow rate during work is Qd limited by the target differential pressure ΔPLSR2,
The P-Q diagram during operation is shown as E-F-C-D in FIG. 4.

Next, the operation of this embodiment configured as above will be explained. During work, the brake switch SW2 is on and the forward/reverse selector switch SW1 is in the N position (neutral position), so the AND gate circuit 64b of the determination unit 64
The output of is low level. Therefore, the selection switch 61c selects the small target differential pressure ΔPLSR2. On the other hand, when driving, the brake switch SW2 is off and the forward/reverse selector switch SW1 is switched to the F or R position other than the N position. The output of the circuit 64b becomes high level. Therefore, the selection switch 61c selects a large target differential pressure ΔPLSR.

Therefore, the maximum discharge flow rate of the hydraulic pump 1 is Qt when running due to the target differential pressure ΔPLSR1, and Qd when working due to the target differential pressure ΔPLSR2.
(<Qt). As a result, when driving, the performance of the hydraulic pump 1 can be fully demonstrated and the flow rate necessary for driving can be discharged, and when working, the hydraulic pump 1 is not controlled to the maximum tilt, and the flow rate necessary for the work can be discharged. Since the above amount of pressure oil is not discharged, pressure loss at the control valve 20A can be suppressed, and there will be no deterioration in fuel efficiency or operability. Furthermore, the traveling control valve 2 and the working control valve 20A can be made common, and the cost and size of parts do not increase.

In the configuration of the above embodiment, the engine 2
7 is the prime mover, the hydraulic pump 4 and the hydraulic cylinder 21 are the first and second hydraulic actuators, and the control valves 2 and 2 are
0A is the control means, the differential pressure sensor 54 is the differential pressure detection means, the tilting angle control device 40 consisting of the servo cylinder 44 and the electromagnetic valves 42 and 43 is the displacement volume changing means, and the load sensing control section 61 is the The first displacement volume control means, the determination section 64 constitutes a state detection means, and the selection switch 61c constitutes a target differential pressure change means.

In the above embodiment, the load sensing control section and the input torque limit control section are provided in the controller, and the tilting angle control is performed by a solenoid valve, and the judgment section in the controller is also used to determine whether traveling or working. Although the configuration is described above, it may be configured as shown in FIG. That is, the load sensing control section and the input torque limit control section are configured by the load sensing regulator 111 and the torque regulator 25, respectively, and the tilting angle control is configured by each regulator.
This may be done by hydraulic pressure using the cylinders 111 and 25. In this case, the spring force of the target differential pressure setting spring 111a provided in the load sensing regulator 111 can be changed by the electromagnetic proportional solenoid 111b, and when it is determined that the vehicle is traveling, the controller turns on the electromagnetic proportional solenoid 111b. Increase the spring force. Furthermore, when it is determined that work is to be done, the electromagnetic proportional solenoid 111b is turned off to reduce the spring force. As a result, as in the above-described embodiment, the target differential pressure during traveling is set larger than the target differential pressure during work, and similar effects can be obtained.

[0033] In the above example, the traveling hydraulic motor 4 and the working hydraulic cylinder 20A are provided as hydraulic actuators, but three or more control valves with common specifications drive three hydraulic actuators with different maximum flow rates. The present invention can also be applied to things. That is, the present invention can be applied to hydraulic construction machines other than the embodiments as long as they are each controlled by at least a pair of common control valves and include at least a pair of hydraulic actuators with different maximum required flow rates.

[0034]

According to the present invention, when load sensing control is performed on at least a pair of hydraulic actuators having different maximum required flow rates, such as those used for traveling and work, the target for the first hydraulic actuator with a larger required maximum flow rate is determined. Since the differential pressure is made larger than that of the second hydraulic actuator, which requires a smaller maximum flow rate, when the first hydraulic actuator is used, the maximum tilting angle of the hydraulic pump can be increased to obtain the desired discharge flow rate. When using the second hydraulic actuator, reduce the maximum tilt angle of the hydraulic pump to prevent pressure oil from flowing in excess of the required flow rate.
Therefore, pressure loss can be suppressed. Therefore, by standardizing the control valves, it is possible to perform appropriate load sensing control without deteriorating fuel efficiency, reducing operability, increasing costs, or increasing the size of parts. In addition, in a device that uses input torque limit control in combination, by setting the maximum displacement commanded by load sensing control to be larger than the maximum displacement volume set by input torque limit control,
The performance of the hydraulic pump can be maximized.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the main parts of a hydraulic control device according to an embodiment of the present invention.

[Fig. 2] Diagram showing the overall configuration of the above hydraulic control device

[Figure 3]
Partial enlarged view of Figure 2

[Figure 4] P-Q diagram of the variable displacement hydraulic pump in Figure 2

[Figure 5
] Diagram showing an example of a hydraulic load sensing control unit and input torque limit control unit

[Figure 6] Side view of wheeled hydraulic excavator

[Figure 7] Diagram showing a conventional hydraulic control device

[Explanation of symbols]

1 Variable displacement hydraulic pump 2 Travel control valve 4 Hydraulic motor 8A forward/backward switching valve 20A work control valve 21 Hydraulic cylinder 40　Tilt angle control device 41 Hydraulic pump 42, 43 Solenoid valve 44 Servo cylinder 50 Controller 51 Tilt angle sensor 52 Pressure sensor 53 Rotation speed sensor 54 Differential pressure sensor 55 Potentiometer 56 Pressure sensor 57 Rotation speed setting device 57a Fuel lever 60 First control circuit section 61 LS control section 61a, 61b Target differential pressure setting section 61c selection switch 62 Torque control section 63 Minimum value selection section 64 Judgment section 65 Servo control section SW1　Forward/forward selector switch SW2 Brake switch

Claims (4)

[Claims] 1. A variable displacement hydraulic pump driven by a prime mover; first and second hydraulic actuators driven by oil discharged from the hydraulic pump; and the hydraulic pump and the first and second hydraulic actuators. first and second control valve means provided between the valve means and controlling the flow rate of pressure oil supplied to these hydraulic actuators, respectively; and a difference between the discharge pressure of the hydraulic pump and the maximum load pressure of the hydraulic actuator. a pressure difference detection means for detecting pressure; a displacement volume change means for changing the displacement volume of the hydraulic pump; and a displacement volume change means for controlling the displacement volume change means so that the pressure difference becomes a predetermined target value. 1, and the required maximum flow rate of the first actuator is set to be larger than the required maximum flow rate of the second actuator,
, a state detecting means for detecting a usage state of the second hydraulic actuator; and when the usage state of the first hydraulic actuator is detected, the target differential pressure is higher than when the second hydraulic actuator is used. 1. A hydraulic control device for hydraulic construction machinery, comprising: target differential pressure changing means for setting a high value. 2. The hydraulic control device according to claim 1, wherein the displacement volume is controlled based on the discharge pressure of the hydraulic pump so that the pump input torque does not exceed the prime mover output torque. a first control means;
The maximum displacement volume that can be set with the displacement volume control means of
Hydraulic control for hydraulic construction machinery, characterized in that the differential pressure target value when using the first hydraulic actuator is set so as to be larger than the maximum displacement volume that can be set by the second displacement volume control means. Device. 3. The hydraulic control device for hydraulic construction machinery according to claim 1, wherein the first hydraulic actuator is a travel hydraulic motor. 4. The control device according to claim 3, wherein the state detecting means detects that the operating means of the travel hydraulic motor is operated, and in response to this detection, the target differential pressure changing means changes the differential pressure. A hydraulic control device for hydraulic construction machinery characterized by increasing a pressure target value.