JPH0768966B2 - Hydraulic pump controller - Google Patents

Description

TECHNICAL FIELD The present invention relates to a control device for a hydraulic pump of a load sensing control hydraulic drive circuit used for a hydraulic machine such as a hydraulic excavator, a hydraulic crane, etc., and particularly to a discharge pressure of the hydraulic pump. The present invention relates to a control device for a hydraulic pump, which controls so as to maintain a value higher than a maximum load pressure of a hydraulic actuator by a constant differential pressure.

[Conventional technology]

In recent years, in a hydraulic drive system for a construction machine including a plurality of hydraulic actuators that drive a plurality of driven bodies such as a hydraulic excavator and a hydraulic crane, the discharge pressure of a hydraulic pump is controlled in association with a load pressure or a required flow rate. At the same time, a pressure compensating valve is arranged in relation to the flow control valve, and the pressure compensating valve controls the differential pressure across the flow control valve to stably control the supply flow rate during combined drive. There is. this house,
There is load sensing control as a typical example of controlling the discharge pressure of the hydraulic pump in conjunction with the load pressure.

Load sensing control controls the discharge rate of the hydraulic pump so that the discharge pressure of the hydraulic pump is higher than the maximum load pressure of multiple hydraulic actuators by a certain value. Economical operation becomes possible by increasing or decreasing the discharge amount of the hydraulic pump.

FIG. 9 shows an example of a conventional hydraulic pump control device used for load sensing control, together with a hydraulic drive circuit in which it is used. This control device is, for example, DE-A1-3422165
(Corresponding to JP-A-60-11706).

In FIG. 9, the hydraulic drive circuit is connected between the hydraulic pump 1, the hydraulic actuator 2 driven by the hydraulic pressure discharged from the hydraulic pump 1, the hydraulic pump 1 and the actuator 2, and operates the operating lever 3a. The flow rate control valve 3 for controlling the flow rate of the pressure oil supplied to the actuator 2 by means of the flow rate control valve 3 and the differential pressure upstream and downstream of the flow rate control valve 3, that is, the differential pressure across the flow rate control valve 3 is kept constant, and the flow rate through the flow rate control valve 3 is controlled. Valve 3
The pressure compensating valve 4 is controlled so as to be proportional to the opening of the pressure compensating valve 4, and the pressure compensating flow rate controlling valve is constituted by one set of the flow rate controlling valve 3 and the pressure compensating valve 4. The hydraulic pump 1 has a displacement variable mechanism, for example, a swash plate 1a. Although only one hydraulic actuator is shown in FIG. 9, there are actually a plurality of actuators, and correspondingly there are a plurality of pressure compensating flow valves.

The control device of the hydraulic pump 1 includes a load sensing regulator 70 that controls the displacement of the hydraulic pump 1, that is, the position of the swash plate 1a.
Switches the switching valve 72 according to a difference signal between the discharge pressure Pd of the hydraulic pump 1 and the maximum load pressures PL of a plurality of actuators selected by the shuttle valve 9, and controls the inflow and outflow of the hydraulic pressure to and from the swash plate drive cylinder 71. The tilt position of the swash plate 1a, that is, the discharge amount of the hydraulic pump 1 is controlled so that the difference between the discharge pressure of the hydraulic pump 1 and the maximum load pressure of the actuator becomes a constant value indicated by the spring 72a.

[Problems to be Solved by the Invention]

However, the conventional hydraulic pump control device has the following problems.

In a conventional general open-circuit service hydraulic circuit that does not perform load sensing control, when it is desired to raise the hydraulic oil temperature immediately after startup in cold weather to protect hydraulic equipment, the pressure discharged from the hydraulic pump 1 is used. The oil is returned to the tank through the throttle of the directional control valve, etc., and the energy loss increases the oil temperature.

However, in the load sensing type hydraulic circuit including the load sensing regulator 70, the differential pressure ΔP between the pump discharge output Pd and the maximum load pressure PL of the actuator is the set value of the spring 72a, and thus is always a constant value. . Therefore, when the discharge pressure Pd of the hydraulic pump 1 is increased to generate the energy loss, the load sensing regulator 70 operates to decrease the discharge amount of the hydraulic pump 1 so that the differential pressure ΔP becomes constant. Since the energy loss acts like tears, the hydraulic oil temperature cannot be raised. That is, there is a drawback that warm-up operation is difficult to perform during normal work.

Also, as a special warm-up operation method, the operation lever 3a is operated to drive the actuator 2 until the stroke end is reached, and the circuit pressure is increased until the relief valve that controls the maximum pressure of the circuit is operated. Although there is a method, there is a problem that normal work cannot be performed during that time and high pressure is applied to the hydraulic equipment, which adversely affects the equipment.

It is an object of the present invention to perform a warm-up operation so that the oil temperature automatically rises when the hydraulic oil temperature is low, and to perform normal work during the warm-up operation. It is to provide a control device for a pump.

[Means for Solving the Problems]

In order to achieve the above object, the present invention provides at least one hydraulic pump provided with displacement volume varying means, a plurality of hydraulic actuators driven by pressure oil discharged from the hydraulic pump, and between the hydraulic pump and each actuator. And a flow rate control valve for controlling the flow rate of the pressure oil supplied to the actuator in accordance with the operation amount of the operating means, in a hydraulic pump control device in a load sensing control hydraulic drive circuit, First detection means for detecting a pressure difference between the pressure and the maximum load pressure of the plurality of actuators; and when the pressure difference between the discharge pressure of the hydraulic pump and the maximum load pressure of the plurality of actuators is about to exceed a predetermined value, The discharge amount of the hydraulic pump is discharged to the tank, and the unload valve that regulates the maximum value of the differential pressure and the temperature of the hydraulic oil are detected. Based on the differential pressure detected by the second detection means and the first detection means, the first target of the hydraulic pump that holds the differential pressure at a constant value lower than the maximum value of the differential pressure regulated by the unload valve. Corresponding to the first means for determining the displacement volume and the temperature of the hydraulic oil detected by the second detecting means, it is necessary to raise the oil temperature by the throttle loss generated in the unload valve during warm-up operation. A second means for determining a second target displacement of the hydraulic pump valve for giving a flow rate; and a third means for selecting a larger value of the first and second target displacements, And a control means for controlling the displacement of the hydraulic pump based on the target displacement selected by the third means.

[Action]

In the present invention thus constituted, when the temperature of the hydraulic oil is low, the first target of the hydraulic pump is determined by the first means from the differential pressure between the discharge pressure of the hydraulic pump and the maximum load pressure of the actuator. The second target displacement determined by the temperature of the hydraulic oil by the second means is larger than the displacement, and the second target displacement is selected by the third means. Therefore, the pump discharge amount corresponding to the difference between the first target displacement and the second target displacement is released from the unload valve, and the throttle loss that occurs at this time increases the oil temperature. When the oil temperature rises to the normal state, the second target displacement is smaller than the first target displacement, and the third means selects the first target displacement. As a result, the original load sensing control is automatically performed, and the amount of oil released from the unload valve disappears, so energy loss during normal work is avoided.

Further, when the maximum load pressure is increased by operating the operating means during the warm-up operation, and the first target displacement determined by the first means becomes larger than the second target displacement,
In the third means, the first target displacement is selected, and in this case also, the automatic load sensing control is automatically performed.
Normal work can be performed even during warm-up operation. Furthermore, the unload valve controls the maximum value of the differential pressure between the discharge pressure of the hydraulic pump and the maximum load pressure of multiple actuators to perform warm-up operation, so the pump pressure does not rise to the maximum pressure and The effect of is avoided.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS.

In FIG. 1, a hydraulic drive circuit according to the present embodiment is connected between a hydraulic pump 1, a hydraulic actuator 2 driven by pressure oil discharged from the hydraulic pump 1, and between the hydraulic pump 1 and the actuator 2. , A flow rate control valve 3 that controls the flow rate of pressure oil supplied to the actuator 2 by operating the operation lever 3a, and a differential pressure upstream and downstream of the flow rate control valve 3, that is, a differential pressure across the flow rate control valve 3, And a pressure compensation valve 4 for controlling the passage flow rate of the pressure control valve 3 so as to be proportional to the opening degree of the flow rate control valve 3.
The pressure compensating flow rate control valve is configured as a set. Hydraulic pump 1
Has a displacement volume variable mechanism, that is, a swash plate 1a.
Although only one hydraulic actuator 2 and one pressure compensation flow control valve 3 and 4 are shown in FIG. 1, there are actually a plurality of actuators, and a plurality of pressure compensation flow control valves are correspondingly provided. is there.

The control device for the hydraulic pump 1 according to this embodiment includes a pressure control valve 80.
A differential pressure detector 5, a swash plate tilt position detector 6, a hydraulic pressure detector 90, a control unit 7, and a swash plate controller 8.

The pressure control valve 80 is connected to the discharge line of the hydraulic pump 1 and has a maximum differential pressure ΔP between the discharge pressure Pd of the hydraulic pump 1 and the maximum load pressures PL of a plurality of actuators including the actuator 2 selected by the shuttle valve 9. It is an unload valve that regulates the value, and when the differential pressure ΔP tries to exceed a certain value instructed by the spring 80a, the discharge amount of the hydraulic pump 1 is discharged to the tank, and the maximum value of the differential pressure ΔP is set by the spring 80a. Keep below the value.

The differential pressure detector 5 detects the differential pressure between the maximum load pressure PL of a plurality of hydraulic actuators including the actuator 2 selected by the shuttle valve 9 and the discharge pressure Pd of the hydraulic pump 1, and controls it as an electric signal ΔP. Output to unit 7. The swash plate tilt position detector 6 detects the tilt position of the swash plate 1a of the hydraulic pump 1 and outputs this to the control unit 7 as an electric signal θ. The oil temperature detector 90 detects the temperature of the hydraulic oil and outputs it as an electric signal t to the control unit 7. The oil temperature detector 90 is arranged in, for example, a tank. The control unit 7 controls the hydraulic pump 1 based on the electric signal ΔP, θ, t.
The drive signal of the swash plate 1a is calculated, and this drive signal is output to the swash plate control device 8. The swash plate control device 8 includes a control unit 7
The swash plate 1a is driven by the drive signal from.

The swash plate control device 8 can be configured as an electro-hydraulic servo hydraulic drive device, for example, as shown in FIG.

That is, the swash plate drive device 8 has a servo piston 8b for driving the swash plate 1a of the hydraulic pump 1, and the servo piston 8b is housed in the servo cylinder 8c. The cylinder chamber of the servo cylinder 8c is divided into a left chamber 8d and a right chamber 8e by the servo piston 8b, and the cross-sectional area of the difference chamber 8d is the right chamber 8e.
Is formed larger than the cross-sectional area d.

The left chamber 8d of the servo cylinder 8c is communicated with a hydraulic source 10 such as a pilot pump via a pipe line 8f.
The right side chamber 8e is connected to the hydraulic source 10 via the line 8i,
8f is connected to tank 11 via return line 8j. A solenoid valve 8g is installed in the pipeline 8f, and a solenoid valve 8h is provided in the return pipeline 8i.
Is installed. These solenoid valves 8g, 8h are normally closed solenoid valves (functions of returning to a closed state when not energized), and are switched by a drive signal from the control unit 7.

When the solenoid valve 8g is excited (turned on) and switched to the switching position B, the left chamber 8d of the servo cylinder 8c communicates with the hydraulic power source 10c, and the servo piston 8b moves to the second position due to the area difference between the left chamber 8d and the right chamber 8e. Move to the right as seen in the figure. As a result, the tilt angle of the swash plate 1a of the hydraulic pump 1 increases and the discharge amount increases.
When the solenoid valves 8g and 8h are demagnetized (OFF) and both return to the switching position A, the oil passage of the left chamber 8d is shut off, and the servo piston 8b is held stationary at that position. As a result, the tilt angle of the swash plate 1a of the hydraulic pump 1 is kept constant, and the discharge amount is kept constant. When the solenoid valve 8h is excited (turned on) and switched to the switching position B, the left chamber 8d
And the tank 11 communicate with each other, the pressure in the left side chamber 8d decreases, and the servo piston 8d is moved leftward in FIG. 2 by the pressure in the right side chamber 8e. As a result, the tilt angle of the swash plate 1a of the hydraulic pump 1 decreases, and the discharge amount also decreases.

The control unit 7 is composed of a microcomputer, and as shown in FIG. 3, the differential pressure signal ΔP output from the differential pressure detector 5, the position signal θ output from the swash plate tilt position detector 6 and the oil temperature. An A / D converter 7a that converts the oil temperature signal t output from the detector 90 into a digital signal, and a central processing unit (CP
U) 7b and read-only memory (ROM) 7c for storing control procedure programs. A random access memory (RAM) 7d for temporarily storing numerical values during calculation, an output I / O interface 7e, and amplifiers 7g, 7h connected to the solenoid valves 8g, 8h are provided.

Based on the control procedure program stored in the ROM 7c, the control unit 7 determines the differential pressure target tilt position θ _p0 of the swash plate 1a of the hydraulic pump 1 from the differential pressure signal ΔP output from the differential pressure detector 5.
And the target tilt position θ _t0 for warm-up operation is calculated from the oil temperature signal t output from the differential pressure detector 90, and the two target tilt positions θ _p0 and θ _t0 are compared, and the maximum Select a value and set this as the command value θ ₀ of the target tilt position,
₀ and the position signal θ output from the swash plate tilt position detector 6 generate a drive signal that makes the deviation between the two zero, and use this as I /
Output from the amplifiers 7g, 7h to the solenoid valves 8g, 8h of the swash plate control device 8 via the O interface 7e. As a result, the swash plate 1a of the hydraulic pump 1 is controlled so that the tilt position signal θ coincides with the target tilt position command value θ ₀ .

The operation of this embodiment will be described in detail below with reference to the flowchart of the control procedure program stored in the ROM 49c shown in FIG.

First, in step 100, the outputs of the differential pressure detector 5, the tilt / tilt position detector 6, and the oil temperature detector 90 are input via the A / D converter 7a, and the differential pressure signal ΔP, the tilt position signal θ, It is stored in the RAM 7d as the oil temperature signal t.

Next, in step 110, the differential pressure tilt target position θ _p0 is calculated from the differential pressure signal ΔP. FIG. 5 shows details of the procedure 110.
First, in step 111, the differential pressure deviation Δ (ΔP) between the differential pressure target value ΔP ₀ and the differential pressure signal ΔP input in step 100 is calculated. Here, the target value ΔP ₀ of the differential pressure is the maximum value of the differential pressure ΔP regulated by the pressure control valve 80, that is, the spring 80.
Set slightly lower than the value set by a. Next, in step 112, a preset control coefficient Ki is multiplied by a differential pressure deviation Δ (ΔP) to obtain an increment Δθ of the differential pressure target tilt position.
Calculate _ΔP . The control coefficient Ki is a so-called integral coefficient, and is preset so that the control device functions optimally. Further, if the time (cycle time) required for programming from steps 100 to 140 in FIG. 4 is t _c , the increment Δθ _ΔP of the differential pressure target tilt position is the difference pressure target tilt position within t _c time. It will be an increment.

Next, in step 113, the increment Δθ _ΔP is added to the previously calculated target tilt position command value θ ₀ −1 to calculate the new differential pressure target tilt position θ _p0 .

Next, returning to FIG. 4, in step 120, the target tilt position θ _t0 for warm-up operation is calculated. Here, the target tilt position θ _t0 for warm-up operation is the pressure control valve (unload valve) 80 during warm-up operation.
It is set as a value that gives the flow rate required to raise the oil temperature due to the throttling loss that occurs in. The contents of this calculation will be described below with reference to FIG.

In FIG. 6, the horizontal axis is the value of the oil temperature t read in step 100, and the vertical axis is the target tilt position θ _t0 for warm-up operation. As shown by the solid line, the target tilt position θ _t0 for warm-up operation is set so that the target tilt position θ _t0 decreases as the oil temperature t rises. As shown by the broken line, the target tilt position θ _t0 is constant when the oil temperature is t _n ° C or lower, and θ when t _n ° C or higher.
_It may be set such that _t0 = 0. This functional relationship is stored in advance in the ROM 7c shown in FIG. 3, and in any case, in step 120, the ROM read using the t read in step 100 is used.
It reads the target tilting position theta _t0 for warming up from the functional relationship which is stored to c.

Returning to FIG. 4 again, in step 130, the larger of the differential pressure target tilt position θ _p0 and the warm-up target tilt position θ _t0 obtained in steps 110 and 120 is selected, and the target tilt position is set. Command value θ ₀
And

Next, in step 140, tilting position control of the swash plate 1a of the hydraulic pump 1 is performed. The details are shown in FIG. In step 141 of FIG. 7, the deviation Z between the command value θ ₀ of the target tilt position calculated in step 130 and the tilt position signal θ read in step 100 is calculated.

Next, in step 142, it is determined whether the absolute value of the deviation Z is within the dead zone Δ of the swash plate tilt position control. here
If it is determined that | Z | is smaller than the dead zone Δ (| Z | <Δ), go to step 144, output the OFF signal to the solenoid valves 8g and 8h, and set the swash plate 1a.
Fix the tilt position of. In step 142, | Z | is the dead zone Δ
If it is determined that it is larger (| Z | ≧ Δ), the procedure goes to step 143.
In step 143, the sign of Z is determined. If it is determined that Z is positive (Z> 0), go to step 145. In step 145, turn on solenoid valve 8g and turn on solenoid valve 8h to move the tilt position of the swash plate in the large direction.
Outputs an OFF signal.

When it is determined in step 143 that Z is negative (Z ≦ 0), the procedure goes to step 146, and the solenoid valve 8g is turned off to output the ON signal to the solenoid valve 8h to move the tilt position of the swash plate in the small direction. .

Through the above steps 141 to 146, the tilt position of the swash plate 1a is controlled so as to match the command value θ ₀ of the target tilt position.

A block diagram of the above configuration is shown in FIG.
Shown with 0. Here, the block 201 corresponds to the procedure 111, the block 202 corresponds to the procedure 112, the blocks 203 and 204 correspond to the procedure 113, and the block 205 corresponds to the procedure 120. Block again
206 corresponds to step 130, and blocks 207, 208, and 209 are step 140.
Equivalent to.

In other words, step 110 (steps 111-113) or block 2
01 to 204 are constant values ΔP ₀ lower than the maximum value of the differential pressure regulated by the pressure control valve 80, based on the differential pressure between the discharge pressure of the hydraulic pump 1 and the maximum load pressure of the plurality of actuators 2. A first means for determining the first target displacement θ _p0 of the hydraulic pump 1 to be held at step 120 or block 205 is a hydraulic pressure corresponding to the temperature of the hydraulic oil detected by the oil temperature detector 90. A second means for determining the second target displacement, θ _t0 , of the pump 1 constitutes a procedure 130 or block 2
06 constitutes a third means for selecting a larger value of the first and second target displacements.

In the present embodiment constructed as described above, since the target tilting position theta _t0 for relatively large warming up in step 120 is calculated when the working oil temperature is low, the differential pressure target tilting position theta _{Even if p0} is small, the target tilt position θ _t0 for warm-up operation is selected in step 130. As a result, the flow rate discharged from the hydraulic pump 1 is increased by a flow rate corresponding to θ _t0 −θ _p0 from the original flow rate of the load sensing control based on the target tilt position θ _p0 , and the flow rate corresponding to θ _t0 −θ _p0 is increased. It is released from the control valve 80. Therefore, the pressure control valve 80 causes a throttling loss to raise the temperature of the hydraulic oil, so that the warm-up operation is quickly achieved. In addition, since the pressure control valve 80 sets the maximum value of the differential pressure to be slightly higher than the target differential pressure ΔP _0, the load lever (maximum load pressure) is also operated by operating the operating lever 3a during warm-up operation.
As a result, the differential pressure target tilt position θ _p0 calculated in step 110 becomes larger than the target tilt position θ _t0 for warm-up operation, and in step 130 the differential pressure target tilt position θ _p0 is selected. .
At this time, the pressure control valve 80 sets the maximum value of the differential pressure to the target differential pressure ΔP ₀
Since it is set slightly higher, the flow rate corresponding to θ _p0 discharged from the hydraulic pump is supplied to the hydraulic actuator 2 without being discharged from the pressure control valve. Therefore, the original load sensing control is automatically performed, and normal work can be performed even during the warm-up operation. In addition, the pressure control valve 80
Since the warm-up operation is performed by limiting the maximum value of the differential pressure between the discharge pressure of the hydraulic pump 1 and the maximum load pressure of a plurality of actuators, the pump pressure does not rise to the maximum pressure and adversely affects hydraulic equipment. Is avoided.

If the oil temperature rises and warming up is no longer required, proceed to step 120.
The target tilting position θ _t0 for warm-up operation calculated in step 1 becomes smaller, and in step 130, the original target differential pressure tilting position θ _p0 is selected. As a result, the original load sensing control is automatically performed and the amount of oil released from the pressure control valve 80 is eliminated, so that energy loss due to the pressure control valve 80 is eliminated during normal work, and there is an energy saving effect.

In the above embodiment, the pressure control valve 80 for warming up is specially provided. However, generally, in the load sensing control hydraulic circuit, an unload valve is installed in order to avoid an increase in circuit pressure due to a delay in response when the load sensing regulator 70 controls the constant differential pressure. This unload valve sets the target differential pressure so that the differential pressure between the discharge pressure of the hydraulic pump 1 and the maximum load pressure of the actuator 2 is slightly higher than the target differential pressure ΔP ₀ of the load sensing control. There is. Therefore, in the hydraulic circuit equipped with this unloading valve, the pressure control valve 80
It is preferable that the unload valve is also used as a pressure control valve for warm-up operation without providing the above.

〔The invention's effect〕

According to the present invention, warm-up operation is performed so that the oil temperature automatically rises when the hydraulic oil temperature is low, and normal work can be performed during the warm-up operation, so workability in cold weather is improved. The energy loss due to the warm-up operation can be minimized while being greatly improved. Moreover, since the pump pressure does not rise to the maximum pressure during the warm-up operation, the life of the hydraulic device can be improved.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a load sensing control hydraulic drive system including a hydraulic pump control system according to an embodiment of the present invention, and FIG. 2 is a schematic diagram of the configuration of a swash plate tilt position control system. FIG. 3 is a schematic diagram showing the configuration of the control unit, FIG. 4 is a flow chart showing the control procedure performed by the control unit, and FIG. 5 shows the details of the procedure for calculating the differential pressure target tilt position. 6 is a flowchart showing the relationship between the oil temperature and the target tilt position for warm-up operation, and FIG. 7 shows the details of the procedure for controlling the tilt position of the swash plate of the hydraulic pump. FIG. 8 is a flowchart showing the configuration of the above-described embodiment in a block form, and FIG. 9 is a schematic diagram showing a load sensing control hydraulic drive circuit including a conventional hydraulic pump control device. Is. DESCRIPTION OF SYMBOLS 1 ... Hydraulic pump 2 ... Hydraulic actuator 3 ... Flow control valve 4 ... Pressure compensating valve 3a ... Operating lever 7 ... Control unit (control means) 8 ... Swash plate control device (control means) 80 ...... Pressure control valve 90 ...... Oil temperature detector 110 …… Procedure (first means) 120 …… Procedure (second means) 130 …… Procedure (third means) θ _p0 …… _Differential pressure target Tilt position (first target displacement) θ _t0 …… Target tilt position for warm-up operation (second target displacement) θ ₀ …… Target tilt position command value

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Toichi Hirata Inoue Hirata, 650 Jinritsucho, Tsuchiura, Ibaraki Prefecture Tsuchiura Plant, Hitachi Construction Machinery Co., Ltd. Machinery Company Tsuchiura Plant (72) Inventor Hideaki Tanaka 650 Kintachimachi, Tsuchiura City, Ibaraki Prefecture Hitachi Construction Machinery Company Tsuchiura Plant (72) Inventor Yu Onou 650 Kintatemachi, Tsuchiura City, Ibaraki Hitachi Construction Machinery Co., Ltd. Ceremony Company Tsuchiura Factory (56) References JP-A-60-11706 (JP, A) Actually developed 60-184617 (JP, U)

Claims (2)

[Claims] 1. At least one hydraulic pump having displacement means, a plurality of hydraulic actuators driven by pressure oil discharged from the hydraulic pump, and a hydraulic pump connected to each actuator for operation. A control device for a hydraulic pump in a load-sensing control hydraulic drive circuit, comprising: a flow rate control valve that controls a flow rate of pressure oil supplied to an actuator in accordance with an operation amount of a means. First detection means for detecting a pressure difference from the maximum load pressure of the actuator; and a discharge amount of the hydraulic pump when the pressure difference between the discharge pressure of the hydraulic pump and the maximum load pressure of the plurality of actuators exceeds a predetermined value. An unloading valve that discharges the oil to the tank and regulates the maximum value of the differential pressure; and a second detecting means that detects the temperature of the hydraulic oil. A first target displacement volume of the hydraulic pump for holding the differential pressure at a constant value lower than the maximum value of the differential pressure regulated by the unload valve, based on the differential pressure detected by the first detecting means; 1 and the hydraulic pump that provides a flow rate required to raise the oil temperature due to the throttle loss generated in the unload valve during warm-up operation, corresponding to the temperature of the hydraulic oil detected by the second detection means. A second means for determining a second target displacement and a third means for selecting a larger value of the first and second target displacements, the target selected by the third means. A controller for controlling the displacement of the hydraulic pump based on the displacement, and a control device for the hydraulic pump. 2. The hydraulic pump control device according to claim 1, wherein the second target displacement is set to be smaller as the oil temperature rises.