JP3330340B2 - Control device for hydraulic drive machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Conventionally, a differential pressure between a discharge pressure of a hydraulic pump and a load pressure of a working machine actuator is externally designated in order to obtain operability of an operating lever according to the work content of a construction machine. For example, Japanese Patent Application Laid-Open No. Hei 2-7690 discloses a technique for controlling a work mode to be changed according to a work mode indicating a work type.
No. 4 discloses this.

[0003] In the technique described in this publication, when the operation mode is changed from the "normal operation" mode to the "fine operation" mode, the differential pressure becomes smaller than that in the "normal operation", and the operation lever is constantly operated. The amount of change in the drive speed of the work machine actuator per amount is smaller than during "normal work",
It is possible to perform more detailed work suitable for the "fine operation" mode.

Further, as a control method of this type, there is another control method disclosed in Japanese Patent Application Laid-Open No. 2-1649491. By controlling the engine so as to reduce the differential pressure in response to a decrease in the engine speed, the engine is controlled. Increase the so-called metering area, which decreases as the rotation decreases,
(In other words, the dead band which increases as the rotational speed decreases is reduced to improve the operability of the operation lever.

[0005]

As described above, in these prior arts, the differential pressure is changed in accordance with the operation mode or the engine rotation, and thereby the relationship between the operation lever operation amount and the work machine actuator speed (hereinafter referred to as "operation characteristics"). )) To improve the operability of the operation lever. However, these conventional techniques only change the differential pressure uniquely according to the operation mode or the engine rotation. It does not control in relation to the actual load on the actuator.

However, in general, in a hydraulic power shovel or the like, horsepower control or the like is performed such that the absorption torque of the hydraulic pump matches the output torque of the engine (see FIG. 7C). An apparatus for controlling the discharge amount of the hydraulic pump according to a so-called PQ curve shown in FIG. 7B is provided so that an absorption torque value at the matched point is obtained. Note that such a device is a known device mainly configured with a TVC valve, for example.

However, when the torque is controlled so as to be limited to a certain value or less, P2 (>) in FIG.
As shown in P1), when the hydraulic pump discharge pressure Pp, that is, the load on the work implement actuator is large, the discharge amount Qp of the hydraulic pump decreases. For this reason, as shown in FIG. 7A, when the load pressure Pp is large as P2 as compared with the case where the load pressure Pp is small as P1, the driving speed v of the work implement is affected by the small discharge amount Qp. As a result, it is limited to a small value as indicated by the broken line, the dead band is increased, and the lever operability is extremely deteriorated.

Further, in the prior art, although the differential pressure is controlled according to the work mode, it is not controlled according to the actual driving state of the work machine by the work machine. That is,
When there are a plurality of working machines, the required operating characteristics are different for each working machine, and if the differential pressure is uniquely determined according to the working mode, this demand cannot be met. For example, there is a case where the demands are different, for example, a work machine actuator for excavation is to be driven as “normal work”, but a work machine actuator for traveling is to be driven as “fine operation” due to uneven terrain. In this case, conventionally, every time the excavation work shifts to the traveling work and vice versa, the operation mode instruction must be manually changed, which makes the operation complicated. However, there is a problem that the burden on the operator is increased.

The present invention has been made in view of such a situation, and the operability is conventionally improved by controlling the differential pressure according to the load applied to the working machine actuator, the driving state of each working machine, and the like. It is an object of the present invention to provide a control device that can be improved more than the above.

[0010]

Therefore, according to a first aspect of the present invention, a hydraulic pump driven by a prime mover and a discharge pressure oil of the hydraulic pump are supplied through a pressure oil supply passage. A plurality of hydraulic actuators driven by the pressure oil supply path, a plurality of flow control valves for controlling the flow rate of the pressure oil supplied to the plurality of working machine actuators according to the operation amount, Control of a hydraulically driven machine having a hydraulic pump, wherein the hydraulic pump controls the discharge flow rate of the hydraulic pump so that the differential pressure between the discharge pressure of the hydraulic pump and the load pressure of the plurality of working machine actuators becomes a set value. A device for selecting a work mode; a pressure detecting device for detecting a discharge pressure of the hydraulic pump or a load pressure of the plurality of work machine actuators; An operation amount detecting means for detecting each operation amount of the valve; and an operation for detecting a current operation state by detecting a type and a driving direction of a currently operated operation device actuator among the plurality of operation device actuators. State detection means, the operation mode selected by the selection means, the pressure detected by the pressure detection means, each operation amount detected by the operation amount detection means, and the operation mode detected by the operation state detection means Means for changing the differential pressure set value based on the current work state.

According to a second aspect of the present invention, in the control apparatus for a hydraulically driven machine similar to the first aspect, the working state detecting means detects a working state of each of the plurality of flow control valves to detect a working state. It is characterized in that the type of the machine actuator is detected.

According to the first and second aspects of the present invention, the work mode selected by the selection means, the pressure detected by the pressure detection means, each operation amount detected by the operation amount detection means, The differential pressure set value changes based on the current work state detected by the state detection means. That is, although the required operation characteristics vary depending on the working state of the working machine, the demand can be met by changing the differential pressure according to the current working state. If the current work state does not correspond to the work mode selected by the selection means, the differential pressure set value selected in the work mode is changed to a differential pressure set value according to the current work state. .

According to the present invention, the differential pressure is changed in accordance with the load applied to the working machine actuator, the operation amount of the working machine actuator, and the current working state. Efficiency is dramatically improved than before.

[0014]

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

FIG. 1 shows the configuration of a working machine hydraulic circuit for driving various working machines (boom, arm, etc.) among working machines of a power shovel. In the embodiment, only two operation valves respectively corresponding to two types of working machines are shown in order to avoid complication of the drawings.

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

The hydraulic oil discharged from the hydraulic pump 2 is supplied to the operating valve 7 via the pipe 9 and the pipes 9a and 9b which branch off the pipe 9.
8 respectively. The spools of the operation valves 7 and 8 are driven in accordance with the operation amounts S1 and S2 of an operation lever (not shown),
The opening area A of each operation valve according to the amount of movement of the spool
1, A2 changes, and hydraulic oil of a flow rate corresponding to the change is supplied to the hydraulic cylinders 3, 4 as working machine actuators, respectively. At this time, the pressure oil flowing out of the operation valve 7 is
The hydraulic cylinder 3 is supplied to the cylinder chamber on the extension side and the cylinder chamber on the contraction side of the hydraulic cylinder 3 via a and 3b, respectively, to extend and contract the hydraulic cylinder 3 respectively.

Similarly, the pressure oil flowing out of the operation valve 8 is supplied to the cylinder chamber on the extension side and the cylinder chamber on the contraction side of the hydraulic cylinder 4 through the pipelines 4a and 4b, thereby extending and contracting the hydraulic cylinder 4 respectively. Let it.

The operating valves 7 and 8 comprise positions N, M and L,
In 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 state halfway 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. Variable aperture of lot ring 20
Is squeezed. 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, ie, the pipelines 3a, 3b, 4a and 4
b, pressure reducing valves 25a, 25b, 26a respectively
And 26b are directed to the check valves 21 and 22 via the port R, respectively.

The check valve 21 is connected to a pilot line 23a, and this pilot line 23a is connected to a pilot line 23b. The check valve 22 is connected to the pilot line 23b. The pilot line 23b is connected to the pilot line 24. Therefore, the hydraulic oil on the high-pressure PLS side of the hydraulic cylinders 3 and 4 is guided to the pilot pipeline 24 through one of the check valves 21 and 22. The pilot line 24 is connected to the spring position side of the pressure reducing valves 25a, 25b, 26a and 26b, and eventually, the pressure reducing valves 25a, 25b, 26
The load pressure PLS on the high pressure side of the hydraulic cylinders 3 and 4 is applied to the spring position sides of a and 26b. On the side facing the spring, the pressure oil on the inlet side of the pressure reducing valve, that is, the operation valve 7,
The pressure at the outlet side of No. 8 is applied as pilot pressure. In addition, the pipeline 10 supplies the pressure oil of the operation valves 7 and 8 to the tank 11.
Is provided for relief.

The constant displacement hydraulic pump 34 discharges pressure oil at a predetermined pressure. The discharge pressure oil is supplied to a pipeline 35 and a control valve 36 (a so-called "LS-EPC valve").
Is supplied to the pilot port 37a of the control valve 37 as a control pressure Pc as pressure oil. Here, the control valve 36 is
The valve position is changed according 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 line 35. When the pressure of the pressure oil discharged from the hydraulic pump 34 exceeds the pressure set by the relief valve 38, the relief valve 38 releases the relief valve 38. Is done.

The pipeline 9 on the discharge side of the hydraulic pump 2 is branched into a pilot pipeline 14. The pilot pipeline 14 is connected to a cylinder chamber on the small diameter side of the regulator 12 and is connected to a pilot port 37 b of a control valve 37. It is connected. The pilot line 23b is extended to extend the pilot port 37 on the side where the spring 37d of the control valve 37 is located.
c. For this reason, 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 provided. The pressure PLS on the high pressure side of the load pressure is used as the pilot pressure.
The biasing force of the spring 37d is applied as an offset pressure. In the control valve 37, the valve position is switched according to the differential pressure of the pressure applied to each end of the control valve 37, and the hydraulic oil of the discharge amount corresponding to the switching position is supplied to the large-diameter cylinder chamber of the regulator 12. And the tilt angle of the swash plate 2a is controlled.

In this case, the tilt angle of the swash plate 2a is controlled such 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
In response to a 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 stop 20.

The engine 1 has a fuel injection pump 38.
And governor 39 are also provided. The fuel control lever 39a of the governor 39 is driven by a motor 40, and the drive position of the lever 39a is detected by a position sensor 41. The detection signal of the position sensor 41 is applied 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 applied to the controller 33. The monitor panel 43 selects and indicates a work mode M performed by a power shovel, that is, a “heavy excavation” mode M1, an “excavation” mode M2, a “straightening” mode M3, and a “fine operation” mode M4. And the selected work mode M1,
Signals indicating M2, M3 and M4 are applied to the controller 33.

A pump pressure sensor 44 is connected to the pipe 14.
The pressure of the pressure oil in the pipeline 14, that is, the discharge pressure oil Pp of the hydraulic pump 2 is detected by the sensor 44. This detected value Pp is applied to the controller 33.

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 amounts") S1 and S2, respectively.
1, S2 is applied to the controller 33.

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

On the other hand, the controller 33 executes an arithmetic process as described later based on the various signals inputted,
The control signal obtained as a result is transmitted 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, ie, the hydraulic pump 2
Is controlled in the discharge amount D (cc / rev). In this case, the controller 33 outputs a control signal for setting the absorption horsepower of the hydraulic pump 2 to a constant value. That is, the hydraulic pump 2
Outputs a control signal to the control valve 36 so as to obtain a constant horsepower according to the input work mode M1.
7, the swash plate 2a of the hydraulic pump 2 is controlled. In this way, the matching point moves to the most efficient point according to the current load state (F in FIG. 7C).
reference).

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 the differential pressure as well as the pump absorption horsepower by the same control signal. In this case, the controller 33 controls the pilot port 37a of the control valve 37 according to the control signal applied to the solenoid 36a of the control valve 36. The applied control pressure Pc changes, which changes the differential pressure ΔPLS. In this embodiment, the operability of the operation levers (not shown) of the operation valves 7 and 8 is improved by changing the differential pressure ΔPLS according to various controls described later. Hereinafter, the contents of the variable control of the differential pressure ΔPLS will be described in detail.

First control In the first control, the operability is improved by changing the differential pressure ΔPLS according to the load currently applied to the work implement actuator.

That is, in general, in the system shown in FIG. 1, the output torque of the engine 1 and the absorption torque of the hydraulic pump 2 are matched at a matching point as shown in FIG. The discharge amount Q (cc / min) of the pump 2 is controlled according to a PQ curve as shown in FIG. By performing the equal horsepower control in this manner, engine stall is prevented. However, on the other hand, FIG.
As shown in (1), the pump discharge amount Q decreases as the load PLS applied to the work implement actuators 3 and 4, that is, the discharge pressure Pp of the hydraulic pump 2 increases. Therefore, when the load is large, the engine stall prevention function acts as a limiter of the pump discharge amount (volume) (cc / rev).

FIG. 7A shows the operation amount S (S
1, S2) and the driving speed v of the working machine actuators 3, 4
(V1, v2), which generally shows the relationship between (v1, v2), the work equipment actuator having a large load is driven, and the discharge pressure P
When p increases from P1 to P2 (see FIG. 7B),
Accordingly, as shown by a broken line, the discharge amount is limited,
As a result, the driving speed is limited, and the so-called dead band (dead stroke) increases.

Therefore, in this embodiment, as the discharge pressure Pp detected by the pump pressure sensor 44, that is, the load PLS of the working machine actuators 3, 4 increases, the differential pressure ΔPLS
Is output to the control valve 36 so that the control signal 36 becomes smaller.

That is, FIG. 2 shows the operation amounts S1 and S2 and the working machine actuator driving speed v by this "first control".
1 and v2. The graph shows that the differential pressure .DELTA.PLS decreases as the load Pp increases, so that even if the load Pp increases, the characteristic (b) does not shift to the characteristic (b) having a large dead band. (C), the dead band remains small as in the case of the characteristic (a) when the load Pp is small, and good lever operability is maintained.

Second control In the above-described first control, the differential pressure ΔPLS is changed according to the pump discharge pressure Pp. However, the differential pressure ΔPLS is uniquely changed only by the pump discharge pressure Pp. In this case, the load is likely to fluctuate in the work implement actuator fine speed region where the operation amount is small, and the fluctuations in the speeds v1 and v2 due to the load fluctuation give the operator an uncomfortable feeling. Therefore, in this embodiment, the operation amount sensors 45, 46
By outputting a control signal to the control valve 36 such that the differential pressure determined by the pump discharge pressure Pp becomes the minimum value and the differential pressure ΔPLS becomes smaller as the manipulated variables S1 and S2 detected respectively in the above steps become larger, the above-mentioned uncomfortable feeling is obtained. Has been eliminated.

The operation characteristic (c) 'shown in FIG. 3 shows the relationship between the operation amounts S1 and S2 by the "second control" and the working machine actuator drive speeds v1 and v2. , S2 is increased, the differential pressure ΔPLS is decreased, so that the operation amount S1,
When the drive speeds v1 and v2 are not suddenly limited when S2 rises, the drive speeds v1 and v2 gradually increase in accordance with the operation amounts S1 and S2 rise.
The drive speeds v1 and v2 change so as to approach the limit value of v2. In this case, the operation amount S of the work implement actuator
1. When S2 is small, the differential pressure .DELTA.PLS becomes large. Even if the load is large, the characteristic is almost the same as the characteristic (a) when the load is small. In other words, in the slow-speed region, the differential pressure hardly changes with the load fluctuation,
It is possible to obtain good operability in which the driver does not feel uncomfortable due to fluctuations in the driving speeds v1 and v2. Eventually, the manipulated variables S1, S2
As the pressure increases, the differential pressure ΔPLS decreases (the gradient decreases in characteristics), finally reaches a differential pressure (minimum value) determined by the pump discharge pressure, and a dead stroke state occurs.

The differential pressure ΔPLS is changed according to the larger one of the operation amounts S 1 and S 2 of the operation valves 7 and 8. Further, since the manipulated variables S1 and S2 mean the opening areas A1 and A2 of the operation valves, these may be detected.

Third control In the first and second controls described above, the pump discharge pressure Pp
Alternatively, the differential pressure ΔP is set so that a predetermined operation characteristic is uniquely obtained according to the operation amounts S1 and S2 (whichever is larger).
Although the LS is changed, in the case of a power shovel having a plurality of working machines, required operation characteristics differ depending on which working machine is being driven. Therefore, in the third control, which of the working machines is driven in which direction is detected by the operation amount sensors 45 and 46,
An operation characteristic is selected according to the detected work machine (boom, arm, etc.), and control is performed so as to obtain the selected operation characteristic, thereby satisfying the above-mentioned demand.
In this case, the various operating characteristics are a three-dimensional map showing the relationship among the lever operation amount Si (or the opening area Ai of the operation valve), the pump discharge pressure Pp, and the differential pressure ΔPLS for each type of the working machine being driven. 4 is stored in advance in a memory (not shown) in the controller 33 as shown in FIG. Note that the shape of the three-dimensional map E in FIG. 4 is actually different for each driving state of the work machine, and FIG. 4 is merely an example.

FIGS. 5A, 5B and 5C two-dimensionally show a three-dimensional map E as shown in FIG.
The case where the load Pp is small (FIG. 5A), the case where the load Pp takes an intermediate value (FIG. 5B), and the case where the load Pp is large (FIG. 5C) are shown separately. Driving state,
In other words, when the boom is raised (broken line C), when the arm is excavated in the straightening mode M3 (dashed-dotted line B), otherwise (solid line A)
It is shown for each.

As is clear from this figure, when the driving state of the work machine is detected as "boom rising", the differential pressure ΔPLS is constant irrespective of the detected value of the load Pp. This is because the load is always large when the boom rises,
This is because there is no problem in operability even if the operation characteristics are determined only by the driving state of the work implement without depending on the detected value of the load Pp.

Further, the operation characteristic (differential pressure) to be selected may be changed according to the magnitude of the absorption torque of the hydraulic pump.

For example, when it is revealed by the controller 33 that the absorption torque of the hydraulic pump 2 is set to be small, the characteristics A, B, and C shown in FIG. Change to B ', C'. In this case, the characteristic A 'in FIG.
The reason why the differential pressure ΔPLS is reduced as i increases is that the power of the engine 1 is limited when the lever is fully operated.

By the way, even in the same working mode, the working machine actuator for excavating work such as a boom is driven and the working machine actuator for traveling is driven as the working machine actuator. However, the operation characteristics required by each work machine actuator are different, and if the operation characteristics are uniquely determined according to the operation mode, it may be inconvenient. That is, the “digging mode” M
Even when operating in 2, the drive speed of the actuator for the boom and arm is to be driven at the normal drive speed according to the `` digging mode '', but during the excavation work Therefore, in consideration of safety, it is necessary to reduce the speed difference between climbing and descending a hill and to reduce the driving speed of the traveling actuator, that is, a demand for driving at a driving speed corresponding to the "fine operation mode" M4. There is.

In this case, assuming that the excavation mode M2 is currently selected as the work mode, the operation amount sensor 4
Based on the detected values of 5 and 46, it is determined which of the work implement actuators is currently being driven, and if the vehicle is currently running, the inclination is small as shown in the characteristic (c) of FIG. If an operation characteristic having a low driving speed (equivalent to the fine operation mode M4) is selected, and if it is determined that the boom or the like is currently driven and excavating, the currently selected “excavation mode” is selected. The operation characteristic as shown in the characteristic (a) of FIG. 2 having a larger inclination and a higher driving speed according to M2 is selected. When it is determined that the excavating actuator and the traveling actuator are simultaneously driven as the working machine actuators, the driving speed is reduced for safety as shown in a characteristic (c) of FIG. Operating characteristics are selected.

When the contents of the third control described above are generalized, the pump discharge pressure Pp and the manipulated variables S1 to S1
A function G having Sn (1 to n mean various working machines) as a variable is determined in advance, and the differential pressure ΔPLS is thereby determined.

ΔPLS = G (Pp, S1 to Sn) (2) In this case, the map E in FIG. 4 is a three-dimensional representation of the function G.

The differential pressure ΔPLS determined by the function G
Must not exceed a preset maximum differential pressure ΔPLSmax at low load, as shown in the following equation (3):
And can be restricted.

ΔPLS = min (G (Pp, S1 to Sn), ΔPLSmax) (3) This maximum differential pressure ΔPLSmax is a differential pressure that determines a cycle time, and when this value is small, the cycle time is delayed. . For example, by changing the maximum differential pressure ΔPLSmax according to the work mode, the cycle time can be made to correspond to the work mode.

In the embodiment, the discharge pressure P of the hydraulic pump 2
Although the differential pressure is changed based on p, the point is that it is only necessary to be able to change the differential pressure based on the load of the work equipment, and it is naturally possible to change the differential pressure based on the load PLS of the work equipment. .

It should be noted that the prior art relating to the first to third controls and the differential pressure control described above (for example, the above-mentioned JP-A-2-76).
904 and JP-A-2-1649491). In this case, for example, even when the differential pressure is changed according to the load Pp so as to obtain the characteristic (c) shown in FIG. 2, the degree of the change is made different according to the work mode M1 selected on the monitor panel 43. It is conceivable to do so.

As described above, according to this embodiment,
Since the differential pressure ΔPLS is changed according to the load Pp applied to the work equipment actuator, optimal lever operability suitable for the current work condition is obtained, and the work efficiency is dramatically improved compared to the past. Can be.

[Brief description of the 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 hydraulic drive machine according to the present invention.

FIG. 2 is a graph showing a relationship between an operation amount of an operation lever and a driving speed of a work implement actuator in the embodiment.

FIG. 3 is a graph showing a relationship between an operation amount of an operation lever and a driving speed of a work implement actuator in another embodiment.

FIG. 4 is a diagram three-dimensionally showing contents stored in the controller of FIG. 1;

FIG. 5 is a diagram two-dimensionally illustrating the contents of FIG. 4 and illustrates how a relationship between a lever operation amount, a pump discharge pressure, and a differential pressure changes according to a driving state of a work machine. FIG.

FIG. 6 is a diagram corresponding to FIG. 5 showing a relationship when the absorption torque of the hydraulic pump is small.

FIG. 7 is a graph used to explain a conventional technique relating to differential pressure control.

[Explanation of symbols]

 2 Hydraulic pump 3 Hydraulic cylinder 4 Hydraulic cylinder 7 Operating valve 8 Operating valve 12 Regulator 33 Controller 36 Control valve 37 Control valve 44 Pump pressure sensor 45 Operating amount sensor 46 Operating amount sensor

──────────────────────────────────────────────────続 き Continuation of the front page Examiner Naoshi Fujiwara (56) References JP-A-4-194383 (JP, A) JP-A-2-76904 (JP, A) JP-A-2-1644941 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) F15B 11/00-11/22 E02F 9/20-9/22 F04B 49/06

Claims (2)

(57) [Claims] 1. A hydraulic pump driven by a prime mover, a plurality of hydraulic actuators driven by a discharge pressure oil of the hydraulic pump being supplied through a pressure oil supply path, and a plurality of hydraulic actuators provided in the pressure oil supply path. A plurality of flow control valves for controlling the flow rate of the pressure oil supplied to the plurality of working machine actuators in accordance with an operation amount; and a discharge pressure of the hydraulic pump and a control of the plurality of working machine actuators. A control unit for controlling a discharge flow rate of the hydraulic pump so that a differential pressure with respect to a load pressure becomes a set value; a selection unit for selecting a work mode; and a discharge pressure of the hydraulic pump. A pressure detection unit that detects a load pressure of the plurality of work machine actuators; an operation amount detection unit that detects each operation amount of the plurality of flow control valves; A work state detection unit that detects a current work state by detecting a type of a work machine actuator that is currently being driven among the tutors and a driving direction thereof; a work mode selected by the selection unit; and the pressure detection. Means for changing the differential pressure set value based on the pressure detected by the means, each operation amount detected by the operation amount detection means, and the current work state detected by the work state detection means. The control device of the hydraulic drive machine equipped. 2. The control device for a hydraulically driven machine according to claim 1, wherein said work state detection means detects the type of work machine actuator by detecting each operation state of said plurality of flow control valves.