JPH06280809A - Control device for hydraulically-operated machine - Google Patents

Abstract

PURPOSE:To improve operational property of a hydraulically-operated machine by detecting hydraulic pump delivery pressure or a plural number of operation machine actuator load pressure and motor speed and making the differential pressure set value higher, the higher the detected pressure gets and lower the detected motor speed gets. CONSTITUTION:Control pressure added to a control valve 37 varys in accordance with the control signal added to a control valve 36 and thereby differential pressure varys. A controller 33 memorizes the relation between the operating amount of an operating lever and the differential pressure when a pump 2 delivery pressure is low, medium and high and the revolution of and engine 1 is low and high. A corresponding differential pressure based on pump delivery pressure detected by a pump pressure sensor 44 and engine speed detected by a revolution sensor 32 is read and a control signal is output to the control valve 36 to obtain such differential pressure. The result thereof is that a desired operational characteristic can be maintained without causing any change to the operational characteristic of the lever even if there is pressure oil leakage. It is also possible to vary the differential pressure based on the load of an operation machine.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a controller for a hydraulically driven machine including a construction machine such as a power shovel, and more particularly, to a change amount of a driving speed of a working machine actuator per constant operation amount of a flow operation valve. The present invention relates to a control device that can be changed according to the operating state of a hydraulic drive machine.

[0002]

2. Description of the Related Art Conventionally, a pressure difference between a discharge pressure of a hydraulic pump and a load pressure of a working machine actuator is instructed from the outside in order to obtain operability of an operating lever according to a work content of a construction machine. A technique for controlling so as to change according to a work mode indicating a work type is disclosed in, for example, Japanese Patent Laid-Open No. 2-7690.
No. 4 publication.

In the technique described in this publication, when the work mode is changed from the "normal work" mode to the "fine operation" mode, the differential pressure becomes smaller than that in the "normal work", and the operation lever is constantly operated. The amount of change in the drive speed of the work implement actuator per amount is smaller than during "normal work",
It is possible to perform more detailed work suitable for the "fine operation" mode.

As a control method of this kind, Japanese Patent Laid-Open No.
There is one disclosed in Japanese Patent No. 164941, in which the so-called metering region, which becomes smaller as the engine speed decreases, is enlarged by controlling the differential pressure so as to decrease as the engine speed decreases. The dead band, which increases as the number of revolutions decreases, is made smaller), and the operability of the operating lever is improved.

[0005]

As described above, in these prior arts, the differential pressure is changed according to the work mode or the engine rotation, whereby the relationship between the operation lever operation amount and the work machine actuator speed (hereinafter referred to as "operation characteristic"). )) To improve the operability of the operating lever, but these conventional techniques only change the differential pressure uniquely according to the work mode or engine rotation, The control is not performed in consideration of the influence of the pressure oil leak in the actual hydraulic circuit.

That is, as the load applied to the work implement actuator increases, pressure oil leakage (leakage) increases in the hydraulic line between the operating valve (flow control valve) and the work implement actuator, and the hydraulic pump Substantially lower volumetric efficiency. Moreover, as the engine speed decreases, the ratio of the leak flow rate to the pump discharge flow rate increases, and the above-mentioned volumetric efficiency significantly decreases. For this reason, the actual speed of the work implement actuator decreases, and the relationship of the actual operating characteristics changes significantly. Therefore, desired operating characteristics cannot be obtained, and operability deteriorates.

Further, in the prior art, although the differential pressure is reduced according to the work mode or the engine speed, it is not controlled according to the actual operating state of the operating lever. For example, when all the plurality of operation valves (flow control valves) are in the neutral position and the conventional technique is applied as it is, the so-called work machine actuator suddenly starts moving when the operation lever is operated at high engine speed. The phenomenon of "jumping out" will occur, and when the engine is running at low speed, dead time and dead zone will increase when the operation of the operating lever is started, and in both cases, operability will be deteriorated.

The present invention has been made in view of these circumstances, and even if there is a pressure oil leak, the operability is not deteriorated, and when the operation lever is operated from the neutral position. It is an object of the present invention to provide a device that does not cause deterioration in operability.

[0009]

Therefore, the first aspect of the present invention
In the invention, a hydraulic pump driven by a prime mover, a plurality of hydraulic actuators driven by supply of pressure oil discharged from the hydraulic pump through a pressure oil supply passage, and the hydraulic oil supply passage are provided, A plurality of flow rate control valves for controlling the flow rate of the pressure oil supplied to the plurality of work machine actuators according to an operation amount, and a discharge pressure of the hydraulic pump and a load pressure of the plurality of work machine actuators. In a control device for a hydraulically driven machine configured to control the discharge flow rate of the hydraulic pump so that the differential pressure between the hydraulic pressure pump and the load pressure of the plurality of work machine actuators Pressure detecting means for detecting, and rotation speed detecting means for detecting the rotation speed of the prime mover,
And a means for changing the differential pressure setting value such that the differential pressure setting value increases as the pressure detected by the pressure detecting means increases and the rotation speed detected by the rotation speed detecting means decreases. I have to.

According to a second invention of the present invention, in the same device as the first invention, a neutral position detecting means for detecting that the respective operating positions of the plurality of flow control valves are in the neutral positions, and the prime mover. And a plurality of flow rate control means for detecting the number of rotations of the plurality of flow control valves, and the neutral position detection means for detecting that all the operating positions of the plurality of flow control valves are in the neutral position. The differential pressure setting value is smaller than the differential pressure setting value when one of the flow rate control valves is being operated, and the differential pressure setting value becomes smaller as the rotation speed detected by the rotation speed detecting means increases. And a means for changing the set value.

[0011]

According to the structure of the first aspect of the invention, the differential pressure setting value is increased so that the greater the pressure detected by the pressure detecting means and the smaller the rotational speed detected by the rotational speed detecting means are. The set value changes. That is, since the differential pressure setting value changes according to the factors that affect the pressure oil leak in the hydraulic circuit, such as the pressure and the rotational speed of the prime mover, the operability of the flow control valve (the operating lever for operating the flow control valve) is improved.

Further, according to the structure of the second invention, when the neutral position detecting means detects that all the operating positions of the plurality of flow control valves are in the neutral positions, the plurality of flow control valves are provided. Is smaller than the differential pressure set value when one of the flow rate control valves is operated, and the differential pressure set value becomes smaller as the rotation speed detected by the rotation speed detection means becomes larger. Changes. That is, even if the flow control valve is started from the neutral position, the differential pressure at the neutral position is smaller than the differential pressure at the positions other than the neutral position and is set according to the rotational speed of the prime mover. Occasionally, the "jump out" phenomenon at the start of the operation does not occur, and the dead time and the dead zone do not increase even at low rotation speed, and the operability at the start of the operation is improved.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a control device for a hydraulically driven machine according to the present invention will be described below with reference to the drawings. In the embodiments, a power shovel is assumed as the hydraulically driven machine.

FIG. 1 shows the construction of a working machine hydraulic circuit for driving two kinds of working machines (boom and arm) among working machines of a power shovel. It should be noted that, in the embodiment, two types of working machines are used to avoid complication of the drawings.
Only one operating valve is shown.

As shown in the figure, the variable displacement hydraulic pump 2
Is driven by the engine 1, and the swash plate 2a of the swash plate 2a is moved according to the movement of the piston 12a of the regulator 12 for driving the swash plate.
The tilt angle of is changed. Then, the discharge flow rate D (cc / rev) per one rotation of the hydraulic pump 2 is changed according to the change of the tilt angle of the swash plate 2a. The engine 1 is provided with a rotation sensor 32 for detecting the rotation speed (r · p · m) ωE of the engine 1, and the detection signal ωE of the rotation sensor 32 is applied to the controller 33.

The pressure oil discharged from the hydraulic pump 2 is supplied to the operation valve 7 via the pipe 9 and the pipes 9a and 9b branching the pipe 9.
8 respectively. The spools of the operation valves 7 and 8 are driven according to the operation amounts S1 and S2 of an operation lever (not shown),
The opening area A of each operation valve is adjusted according to the moving amount of the spool.
1 and A2 change, and the pressure oil having a flow rate corresponding to the change is supplied to the hydraulic cylinders 3 and 4 as the working machine actuators. At this time, the pressure oil flowing out from the operation valve 7 is the conduit 3
It is supplied to the extension side cylinder chamber and the compression side cylinder chamber of the hydraulic cylinder 3 via a and 3b, respectively, to extend and retract the hydraulic cylinder 3, respectively.

Similarly, the pressure oil flowing out from the operation valve 8 is supplied to the extension side cylinder chamber and the contraction side cylinder chamber of the hydraulic cylinder 4 via the conduits 4a and 4b, and the hydraulic cylinder 4 is extended and contracted respectively. Let

The operating valves 7 and 8 consist of positions N, M and L,
At the neutral position N, the pump port into which the pressure oil discharged from the pump 2 flows is in a closed state, and in the intermediate state from the switching position N to the switching positions L and M, the pressure oil flowing through the operation valve is provided on the spool. Rotating ring variable aperture 20
Squeezed with. Further, at the switching positions L and M, the throttle 20 has a constant area, and at each position, the load pressure of the hydraulic cylinders 3 and 4, that is, the pipelines 3a, 3b, 4a and 4 are provided.
b pressure reducing valves 25a, 25b, 26a respectively disposed in b
The pressures on the outlet side of and 26b are introduced to the check valves 21 and 22 via the port R, respectively.

The check valve 21 is connected to a pilot pipe line 23a, and this pilot pipe line 23a is connected to a pilot pipe line 23b. The check valve 22 is connected to the pilot line 23b. The pilot conduit 23b is connected to the pilot conduit 24. Therefore, the pressure oil on the high pressure PLS side of the hydraulic cylinders 3 and 4 is guided to the pilot conduit 24 through either of the check valves 21 and 22. The pilot line 24 is connected to the pressure reducing valves 25a, 25b, 26a and 26b on the side of the spring position, and as a result, the pressure reducing valves 25a, 25b, 26 are connected.
The load pressure PLS on the high pressure side of the hydraulic cylinders 3 and 4 is applied to the spring position side of a and 26b. On the side facing the spring, pressure oil on the inlet side of the pressure reducing valve, that is, the operating valve 7,
The pressure on the outlet side of 8 is applied as the pilot pressure. In addition, the pipeline 10 uses the pressure oil of the operation valves 7 and 8 for the tank 11
It is provided for relief.

The constant displacement hydraulic pump 34 discharges pressure oil of a predetermined pressure, and this discharge pressure oil is a conduit 35 and a control valve 36 (so-called "LS-EPC valve").
Is supplied to the pilot port 37a of the control valve 37 as a pressure oil of the control pressure Pc. Here, the control valve 36 is
The valve position is changed in response to a control signal applied from the controller 33 to the electromagnetic solenoid 36a, whereby the flow rate of the pressure oil supplied to the pilot port 36a is changed.

A relief valve 38 is provided in the pipe 35, and when the pressure of the hydraulic oil discharged from the hydraulic pump 34 becomes equal to or higher than the pressure set by the relief valve 38, the relief valve 38 causes the relief. To be done.

The discharge-side pipe line 9 of the hydraulic pump 2 is branched into a pilot pipe line 14, which is connected to the cylinder chamber on the small diameter side of the regulator 12 and to the pilot port 37b of the control valve 37. It is connected. The pilot line 23b is extended to the pilot port 37 on the side where the spring 37d of the control valve 37 is located.
connected to c. Therefore, the spring 37 of the control valve 37
The discharge pressure Pp of the hydraulic pump 2 and the control pressure Pc from the control valve 36 are provided at the end on the side where there is no d, and the hydraulic cylinders 3 and 4 are provided at the end on the side where the other spring 37d of the control valve 37 is present. The pressure PLS on the high pressure side of the load pressure is the pilot pressure,
Further, the biasing force of the spring 37d is applied as an offset pressure. Then, in the control valve 37, the valve position is switched according to the pressure difference applied to each end of the control valve 37, and the discharge amount of the pressure oil corresponding to the switching position is changed to the cylinder chamber on the large diameter side of the regulator 12. Is supplied or discharged to the swash plate 2a and the tilt angle of the swash plate 2a is controlled.

In this case, the tilt angle of the swash plate 2a is controlled so that the pressure difference ΔPLS between the hydraulic pump pressure Pp and the cylinder load pressure PLS is maintained at a set value as described later. In this case, the set value of the differential pressure ΔPLS is the control pressure P
c, that is, from the controller 33 to the electromagnetic solenoid 36a
Is changed according to the control signal applied to the.

At this time, the relationship between the pressures Pp and PLS and the discharge amount (volume) D of the hydraulic pump 2 is expressed by the following equation (1).

D = CA√ (Pp-PLS) (1) where C is a constant and A is the aperture area of the diaphragm 20.

The engine 1 has a fuel injection pump 38.
Governor 39 is attached. The fuel control lever 39a of the governor 39 is driven by the motor 40, and the drive position of the lever 39a is detected by the position sensor 41. The detection signal of the position sensor 41 is added to the controller 33 as a feedback position signal when driving and controlling the motor 40.

The throttle dial 42 is for setting a target rotation speed of the engine 1, and a throttle signal corresponding to the target rotation speed ωTH is added to the controller 33. Further, the monitor panel 43 selects and instructs a work mode M performed by the power shovel, that is, a "heavy excavation" mode M1, a "excavation" mode M2, a "rectification" mode M3, and a "fine operation" mode M4. And the selected work mode M1,
Signals indicating M2, M3, M4 are applied to controller 33.

A pump pressure sensor 44 is provided in the pipe line 14.
The sensor 44 detects the pressure of the pressure oil in the conduit 14, that is, the pressure oil Pp discharged from the hydraulic pump 2. This detected value Pp is added to the controller 33.

Further, the operation valves 7 and 8 are provided with operation amount sensors 45 and 46 for detecting operation stroke amounts (hereinafter referred to as "operation amount") S1 and S2, respectively.
1, S2 are added to the controller 33.

The controller 33 outputs a drive control signal to the motor 40 based on various input signals,
The output torque of the engine 1 is controlled. That is, as shown in FIG. 5, the motor 40 is set so that the regulation lines l1, l2, l3 ... According to the input target revolution speed ωTH and the current engine revolution speed ωE detected by the engine revolution sensor 32 are set. A drive control signal is applied to the fuel control lever 39a and the fuel control lever 39a is activated.

On the other hand, the controller 33 executes arithmetic processing as will be described later based on various input signals,
The control signal obtained as a result is applied to the solenoid 3 of the control valve 36.
6a, and the tilt angle of the swash plate 2a of the hydraulic pump 2 via the control valve 37 and the regulator 12, that is, the hydraulic pump 2
The discharge amount D (cc / rev) of is controlled.

In this case, the controller 33 outputs a control signal for making the absorption horsepower of the hydraulic pump 2 a constant value.
That is, the hydraulic pump 2 receives the input work mode M1.
A control signal for obtaining a constant horsepower corresponding to the ... Is output to the control valve 36, and the swash plate 2a of the hydraulic pump 2 is controlled via the control valve 37. In this way, the matching point moves to the most efficient point according to the current load state (see F in FIG. 5).

On the other hand, the controller 33 outputs a control signal for obtaining the differential pressure ΔPLS set as described later. That is, the controller 33 controls not only the pump absorption horsepower but also the differential pressure by the same control signal. In this case, the solenoid 3 of the control valve 36 is controlled.
The control pressure Pc applied to the pilot port 37a of the control valve 37 changes according to the control signal applied to 6a, and the differential pressure ΔPLS changes accordingly. In this embodiment, the differential pressure ΔPLS is changed as described later to improve the operability of the operation levers (not shown) of the operation valves 7 and 8.

The details of the variable control of the differential pressure ΔPLS will be described below.

First Control In the first control, the above-mentioned so-called "pressure oil leak" is caused by changing the differential pressure ΔPLS in accordance with the load currently applied to the work implement actuator and the engine speed. Even if there is, it tries to perform control that does not impair the lever operability.

By the way, in general, the influence of the above-mentioned pressure oil leak on the operation characteristics is that the ratio qL of the leak amount qL in the hydraulic line of the hydraulic pump 2 to the discharge amount Q (cc / min).
It is said to be proportional to / Q. By increasing the ratio qL / Q, the substantial volumetric efficiency of the hydraulic pump 2 decreases, and the actual speed of the work machine actuator decreases.
The operating characteristic of the operating lever changes from the desired operating characteristic in the direction in which the differential pressure decreases. Therefore, the above ratio qL / Q
By reducing the value, the operating characteristic can be maintained at a desired characteristic and the lever operability can be maintained.

Now, the pump discharge amount Q is Q = DωE (2), which is proportional to the engine speed ωE. On the other hand, it is known that the leakage amount qL itself is proportional to the load applied to the work machine actuators 7 and 8, that is, the discharge pressure Pp of the hydraulic pump 2. Therefore, the ratio qL /
Q is expressed as qL / Q = Pp / ωE (3), and in the end, as the hydraulic pump discharge pressure Pp increases, the ratio qL / Q also increases. By correcting the differential pressure to increase as Pp increases, desired operating characteristics can be maintained, and the ratio qL / Q increases as the engine speed ωE decreases, resulting in a decrease in differential pressure. In order to prevent this, the desired operating characteristic can be maintained by correcting the differential pressure so that it becomes larger as the rotational speed ωE becomes smaller.

FIG. 2 shows operation lever operation amounts S1 and S2 (or operation valve opening area S for performing the first control).
1 and S2) and the differential pressure ΔPLS, when the pump discharge pressure Pp is small (FIG. 2A), when the pump discharge pressure Pp has an intermediate value (FIG. 2B), the pump discharge pressure Pp is It is shown separately when it is large (FIG. 2 (c)), and when the engine speed ωE is small (dashed line A) and when the engine speed ωE is large (solid line B).

As is clear from FIG. 2, from FIG. 2A to FIG. 2B, and then to FIG. 2C, the greater the pump discharge pressure Pp, the greater the differential pressure ΔPLS, and from B to A. It can be seen that the smaller the engine speed ωE, the larger the differential pressure ΔPLS is set.

The contents of FIG. 2 are previously stored in a memory (not shown) in the controller 33, and the pump discharge pressure Pp detected by the pump pressure sensor 44 and the rotation sensor 3 are stored.
2, the differential pressure ΔPLS corresponding to the detected values in FIG. 2 is read out based on the engine speed ωE detected in 2,
A control signal is output to the control valve 36 so as to obtain this differential pressure ΔPLS. As a result, the operating characteristics of the lever do not change even if a pressure oil leak occurs, and the desired operating characteristics are maintained.

In the first control, the differential pressure is changed based on the discharge pressure Pp of the hydraulic pump 2, but the point is that the differential pressure can be changed based on the load applied to the working machine. It is of course possible to change the differential pressure based on the load PLS of the working machine.

Second Control In this second control, the differential pressure ΔPLS is set to be smaller than the set differential pressure when the operating valve is in the neutral position and at a position other than the neutral position, and the engine speed is set. Depending on the above, "jumping out" at high engine speed and "increasing dead time" at low engine speed as described above
It is intended to effectively prevent the occurrence of the above and improve the operability at the time of starting the lever operation.

Now, as described above, JP-A-2-1649
In No. 41, the operability is improved by controlling the differential pressure ΔPLS so as to decrease according to the decrease in the engine speed, but all the operation valves are in the neutral position N.
Assuming that the above control is performed as it is while the engine is being operated, the high engine speed as shown by H in FIG. 3 (b) at the start of the operation of the operation lever as shown by G in FIG. 3 (a). Since the differential pressure ΔPLS is sometimes large, a “pop-out” phenomenon occurs in which the drive speed of the work machine actuator rises rapidly. This is the differential pressure set at the neutral position N and the neutral position N.
This is because there is no difference between the pressure difference and the pressure difference set when the lever is operated to a position other than that. As shown in I of FIG. 3 (c), the pressure difference ΔPLS rises sharply at the start of lever operation. It is caused by.

Therefore, if the differential pressure when the operating lever, that is, the operating valves 7 and 8 is in the neutral position N is ΔPLSn, and the differential pressure in the operating state other than the neutral position N is ΔPLSa, then ΔPLSn <ΔPLSa ... ( 4) As shown in Fig. 3C, the differential pressure ΔPLSn during neutral is smaller than the differential pressure ΔPLSa during operation, so that there is a transition with a gentle gradient as shown by the broken line J in Fig. 3C. The pressure rises, and the "pop-out" phenomenon is eliminated as shown by the broken line K in FIG. 3 (b).

On the other hand, when the engine speed is low, in the above-mentioned conventional engine, even at the neutral position N, the differential pressure ΔPLS becomes smaller as the engine speed decreases, as shown in FIG.
As indicated by the alternate long and short dash line L, the drive speed of the work implement actuator does not readily rise at the start of lever operation, resulting in increased dead time and dead zone. Therefore, when the neutral position N is set, the dead pressure is increased by increasing the differential pressure ΔPLSn according to the decrease of the engine speed ωE as shown in FIG. 4, contrary to the other positions. The inconvenience of can be eliminated. Further, as shown in FIG. 4, the differential pressure ΔPLSn is changed so as to decrease in accordance with the increase of the engine speed ωE, thereby effectively preventing the “pop-out” phenomenon which becomes remarkable as the engine speed increases. You can

After all, as shown in the equation (4) and FIG. 4, when either of the operating valves 7 and 8 is in the neutral position N, one of the operating valves 7 and 8 is operated. The differential pressure ΔPLSn is set so that it is smaller than the differential pressure ΔPLSa when the lever is being operated, and becomes smaller as the engine speed ωE increases, eliminating any of the above inconveniences and improving the operability at the start of lever operation. be able to.

The above equation (4) and the contents of FIG. 4 are stored in advance in a memory (not shown) in the controller 33.
Based on the outputs of the operation amount detection sensors 45 and 46, it is detected that both the operation valves 7 and 8 are in the neutral position N, and when the neutral position N is detected, the output ωE of the rotation sensor 32 is detected. The differential pressure ΔPLSn is read from the memory, and a control signal is output to the control valve 36 so as to obtain the differential pressure ΔPLSn. As a result, the above-mentioned "pop-out" phenomenon and the like at the start of the lever operation are eliminated, and the operability is improved as compared with the conventional case.

The second control is not limited to the case of applying the conventional technique of reducing the differential pressure according to the decrease in the engine speed, but the differential pressure is set during the lever operation without depending on the engine speed. It is obvious that it is suitable to be applied to the case.

[0049]

As described above, according to the present invention,
The greater the load on the work implement actuator,
Moreover, since the differential pressure is changed so that the differential pressure decreases as the engine speed decreases, it is possible to maintain good operability that is not affected by the pressure oil leak.
Further, according to the present invention, when the operating valve is in the neutral position, the differential pressure is set to be smaller than the differential pressure when the operating valve is operated, and the differential pressure becomes smaller as the engine speed increases. Since it is changed, the operability at the time of starting the operation of the operation lever is improved and the work efficiency is improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a working machine hydraulic circuit in an embodiment of a control device for a hydraulically driven machine according to the present invention.

FIG. 2 is a graph showing how the differential pressure changes according to the engine speed and the pump discharge pressure.

FIG. 3 is a graph showing changes in the operating amount of the operating lever, the driving speed of the working machine actuator, and the time difference of the differential pressure, respectively, in order to explain the effect of this embodiment in comparison with the prior art. It is the graph used.

FIG. 4 is a graph showing the relationship between the engine speed and the differential pressure setting value when the operating lever is in the neutral position.

FIG. 5 is a graph showing the relationship between the engine speed and the output torque, which is used for explaining the equal horsepower control in the embodiment.

[Explanation of symbols]

 2 hydraulic pump 3 hydraulic cylinder 4 hydraulic cylinder 7 operation valve 8 operation valve 12 regulator 33 controller 36 control valve 37 control valve 44 pump pressure sensor 45 operation amount sensor 46 operation amount sensor

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Internal reference number FI Technical display location F15B 11/16 Z 9026-3H (72) Inventor Hideki Kunichi 2597 Shinnomiya, Hiratsuka-shi, Kanagawa Komatsu Co., Ltd. Factory Electronics Division, Electronic Systems Division

Claims (2)

[Claims] 1. A hydraulic pump driven by a prime mover, a plurality of hydraulic actuators driven by supplying pressure oil discharged from the hydraulic pump through a pressure oil supply passage, and a plurality of hydraulic actuators provided in the pressure oil supply passage. And a plurality of flow rate control valves for controlling the flow rate of the pressure oil supplied to the plurality of working machine actuators according to the operation amount, and the discharge pressure of the hydraulic pump and the plurality of working machine actuators. In a control device for a hydraulically driven machine configured to control a discharge flow rate of the hydraulic pump so that a pressure difference between the load pressure and the set pressure is a set value, a discharge pressure of the hydraulic pump or a load of the plurality of working machine actuators Pressure detection means for detecting the pressure, rotation speed detection means for detecting the rotation speed of the prime mover, the greater the pressure detected by the pressure detection means, and the A control device for a hydraulically driven machine, comprising means for changing the differential pressure setting value such that the differential pressure setting value increases as the rotational speed detected by the rotational speed detecting means decreases. 2. A hydraulic pump driven by a prime mover, a plurality of hydraulic actuators driven by supplying pressure oil discharged from the hydraulic pump through a pressure oil supply passage, and the hydraulic oil supply passage. And a plurality of flow rate control valves for controlling the flow rate of the pressure oil supplied to the plurality of working machine actuators according to the operation amount, and the discharge pressure of the hydraulic pump and the plurality of working machine actuators. In a controller of a hydraulically driven machine configured to control a discharge flow rate of the hydraulic pump so that a pressure difference between the load pressure and the set pressure is a set value, each operation position of the plurality of flow rate control valves becomes a neutral position. Position detecting means for detecting that the number of rotations of the prime mover is high, a rotational speed detecting means for detecting the rotational speed of the prime mover, When it is detected that all the operating positions of are in the neutral position, the difference is smaller than the differential pressure set value when one of the plurality of flow control valves is operated, A control device for a hydraulically driven machine, further comprising means for changing the differential pressure setting value such that the differential pressure setting value decreases as the rotation speed detected by the rotation speed detecting means increases.