JP2001050202A - Hydraulic control system for hydraulic working machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydraulic control system for a hydraulic working machine which restrains relief pressure drop at the time of cut-off control. SOLUTION: This hydraulic control system comprises a variable displacement hydraulic pump 2, a regulator 3, a controller 6 for generating control signals to drive the regulator 3, a boom hydraulic cylinder 12, a revolving motor 13, a variable main relief valve 18, a pressure sensor 19 for detecting working pressure of an actuator, a solenoid proportional valve 20 for controlling the main relief pressure of the main relief valve 18, and a cut-off set pressure indicator 40. A function generating section is also included in the system, which section outputs a command current (i) for controlling the solenoid proportional valve 20 to increase the main relief pressure up to predetermined pressure when the controller 6 drives the regulator 3 to execute cut-off control for reducing the suction torque of the variable displacement hydraulic pump 2 because the pressure detected by the pressure sensor 19 exceeds the cut-off set pressure PCM.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic control device for a hydraulic working machine such as a hydraulic shovel, and more particularly to a hydraulic working machine capable of cutting off a discharge flow rate of a variable displacement hydraulic pump for supplying pressure oil for driving an actuator. To a hydraulic control device.

[0002]

2. Description of the Related Art A conventional hydraulic control device for a hydraulic working machine capable of cutting off the discharge flow rate of a variable displacement hydraulic pump is disclosed in Japanese Patent Application Laid-Open No. 63-195403.

[0003] This prior art includes a variable displacement hydraulic pump,
A displacement control means for controlling the absorption torque of the variable displacement hydraulic pump, that is, a swash plate drive actuator, and a displacement control signal generating means for generating a control signal for driving the swash plate drive actuator, that is, a controller; An actuator driven by pressure oil discharged from the pump, that is, a hydraulic motor and a hydraulic cylinder,
A directional control valve for controlling the flow of pressure oil supplied from the variable displacement hydraulic pump to these actuators, that is, an operation valve, and operation means for switching these operation valves, that is, an operation lever, are provided.

A main relief valve for defining a main relief pressure corresponding to the maximum pressure of the variable displacement hydraulic pump,
An overload relief valve that defines an overload relief pressure corresponding to the maximum load pressure of the actuator described above, and a pressure sensor that detects the operating pressure of the actuator, that is, the discharge pressure of the variable displacement hydraulic pump, are provided. .

In this prior art, when a pressure detected by a pressure sensor exceeds a predetermined cutoff set pressure, a swash plate drive actuator is controlled by a signal output from a controller, and the absorption torque of a variable displacement hydraulic pump is controlled. Is controlled so as to reduce the displacement volume, that is, the discharge flow rate of the pump is reduced, thereby reducing the energy loss when the pressure oil from the pump is relieved and returned to the tank. .

[0006]

Normally, the characteristics of a relief valve such as a main relief valve or an overload relief valve, as shown by a characteristic A in FIG. )have. Therefore, when the discharge flow rate of the pump decreases due to the cutoff control described above, the relief pressure tends to gradually decrease.

As described above, when the relief pressure decreases,
Conversely, control for increasing the flow rate is performed this time. In other words, in the above-described conventional technology, hunting that repeatedly reduces and increases the flow rate discharged from the pump is likely to occur due to the override characteristic inherent to the main relief valve or the overload relief valve, so that the pressure oil from the pump is supplied. However, there is a problem that the drive control accuracy of the actuator is easily deteriorated.

In the prior art, when the cutoff control is activated and the pump discharge flow rate is reduced, the relief pressure is slightly reduced, and accordingly, the operating force of the actuator is reduced. There is also a problem that it is easy for the operator operating the actuator to feel uncomfortable.

SUMMARY OF THE INVENTION The present invention has been made in view of the above situation in the prior art, and has as its object to provide a hydraulic control device for a hydraulic working machine which can suppress a decrease in relief pressure during cutoff control. It is in.

[0010]

In order to achieve the above object, an invention according to claim 1 of the present application comprises a variable displacement hydraulic pump, a tilt control means for controlling an absorption torque of the variable displacement hydraulic pump, Displacement control signal generating means for generating a control signal for driving the displacement control means, an actuator driven by pressure oil discharged from the variable displacement hydraulic pump, and a main unit corresponding to a maximum pressure of the variable displacement hydraulic pump. A main relief valve that regulates a relief pressure; and a pressure detection unit that detects an operating pressure of the actuator. A pressure detected by the pressure detection unit is a predetermined cutoff setting pressure that is smaller than the main relief pressure. Is exceeded, the tilt control signal generating means controls the tilt control means to reduce the absorption torque of the variable displacement hydraulic pump. In the hydraulic control device for a hydraulic working machine, the main relief valve comprises a variable-type main relief valve, and includes a main relief-pressure control means for controlling the main relief pressure of the variable-type main relief valve. A configuration including main relief pressure increase control means for controlling the main relief pressure control means so as to increase the main relief pressure by a predetermined pressure when driving the rotation control means to reduce the absorption torque of the variable displacement hydraulic pump. It is.

According to the first aspect of the present invention, when the operating pressure of the actuator detected by the pressure detecting means exceeds a predetermined cutoff set pressure smaller than the main relief pressure, a tilt control signal is generated. A control signal for driving the displacement control means is output from the means, and the displacement control means drives the variable displacement hydraulic pump to reduce the absorption torque, that is, to reduce the displacement of the variable displacement hydraulic pump. As a result, cutoff control for reducing the discharge flow rate of the variable displacement hydraulic pump is performed.

At the time of the cutoff control, the main relief pressure rise control means operates the main relief pressure control means. Thereby, the main relief pressure is increased by a predetermined pressure,
Irrespective of a decrease in the discharge flow rate of the variable displacement hydraulic pump, a decrease in pressure due to the override characteristic of the main relief valve is corrected, and a decrease in main relief pressure during the cutoff control can be suppressed. Therefore, it is possible to prevent the occurrence of hunting that repeatedly reduces and increases the pump discharge flow rate during the cutoff control, and to suppress a decrease in the operating force of the actuator during the cutoff control.

[0013] In order to achieve the above object, the invention according to claim 2 of the present application is based on the invention according to claim 1,
The actuator comprises a plurality of actuators,
Operation detection means for detecting the operation of these actuators, and an overload relief valve for defining an overload relief pressure corresponding to the maximum load pressure of each of the actuators, the overload relief valve,
An overload relief pressure control means for controlling the overload relief pressure of the variable overload relief valve, the variable overload relief valve including a variable overload relief valve for defining the overload relief pressure according to a predetermined actuator among the actuators; and An overload relief pressure increase control means for controlling the overload relief pressure control means so as to increase the overload relief pressure by a predetermined pressure, and driving the tilt control means to absorb the variable displacement hydraulic pump. When reducing the torque,
One of the main relief pressure increase control means and the overload relief pressure increase control means is controlled to increase the pressure of a corresponding one of the main relief pressure and the overload relief pressure by a predetermined pressure.

According to the second aspect of the present invention, for example, the overload relief pressure for defining the maximum load pressure of the predetermined actuator is set smaller than the main relief pressure, and It is assumed that the overload relief pressure that defines the maximum pressure of the load pressure of another actuator that is different from the main relief pressure is set, and only the operation of another actuator described above is temporarily detected by the operation detection unit. If it is assumed that the pressure detecting means detects that the operating pressure of the other actuator has exceeded a predetermined cutoff set pressure smaller than the main relief pressure, in this case, the present invention relates to the above-described claim 1. It has the same effect as in the invention.

That is, a control signal for driving the tilt control means is output from the tilt control signal generating means, and the tilt control means reduces the absorption torque of the variable displacement hydraulic pump, ie, the variable displacement hydraulic pump Drive to reduce displacement. As a result, cutoff control for reducing the discharge flow rate of the variable displacement hydraulic pump is performed.

At the time of the cutoff control, the main relief pressure increase control means operates the main relief pressure control means. Thereby, the main relief pressure is increased by a predetermined pressure,
Irrespective of a decrease in the discharge flow rate of the variable displacement hydraulic pump, a decrease in pressure due to the override characteristic of the main relief valve is corrected, and a decrease in main relief pressure during the cutoff control can be suppressed. Therefore, it is possible to prevent the occurrence of hunting that repeatedly reduces and increases the pump discharge flow rate during the cutoff control, and to suppress a decrease in the operating force of the another actuator during the cutoff control.

Also, differently from the above, only operation of a predetermined actuator is detected by the operation detecting means, and a predetermined cutoff setting in which the operating pressure of the predetermined actuator is smaller than the overload relief pressure of the variable type overload relief valve. Assuming that the pressure value has been detected by the pressure detecting means, a control signal for driving the tilt control means is output from the tilt control signal generating means, and the tilt control means outputs the absorption torque of the variable displacement hydraulic pump. , I.e., to reduce the displacement of the variable displacement hydraulic pump. As a result, cutoff control for reducing the discharge flow rate of the variable displacement hydraulic pump is performed.

At the time of the cutoff control in this case, the overload relief pressure increase control means operates the overload relief pressure control means. As a result, the overload relief pressure of the variable overload relief valve is increased by a predetermined pressure, and despite the decrease in the discharge flow rate of the variable displacement hydraulic pump, the pressure drop due to the override characteristic of the variable overload relief valve is reduced. The overload relief pressure of the variable overload relief valve at the time of this cutoff control is corrected. Therefore, it is possible to prevent the occurrence of hunting that repeatedly reduces and increases the pump discharge flow rate during the cutoff control, and to suppress a decrease in the operating force of a predetermined actuator during the cutoff control.

The operation detecting means detects that the predetermined actuator and another actuator have been operated, and determines that the operating pressure of the other actuator has exceeded a predetermined cutoff set pressure smaller than the main relief pressure. Assuming that the pressure is detected by the pressure detecting means, the same operation as in the first aspect of the present invention is achieved in this case.

That is, a control signal for driving the tilt control means is output from the tilt control signal generating means, and the tilt control means reduces the absorption torque of the variable displacement hydraulic pump, ie, the variable displacement hydraulic pump Drive to reduce displacement. As a result, cutoff control for reducing the discharge flow rate of the variable displacement hydraulic pump is performed.

At the time of the cutoff control, the main relief pressure increase control means operates the main relief pressure control means. Thereby, the main relief pressure is increased by a predetermined pressure,
Irrespective of a decrease in the discharge flow rate of the variable displacement hydraulic pump, a decrease in pressure due to the override characteristic of the main relief valve is corrected, and a decrease in main relief pressure during the cutoff control can be suppressed. Therefore, it is possible to prevent the occurrence of hunting that repeatedly reduces and increases the pump discharge flow rate during the cutoff control, and to suppress a decrease in the operating force of the another actuator during the cutoff control.

Further, in order to achieve the above object, the invention according to claim 3 of the present application is characterized in that in the invention according to claim 2,
The predetermined actuator is constituted by a turning motor.

According to another aspect of the present invention, there is provided a variable displacement hydraulic pump, a tilt control means for controlling an absorption torque of the variable displacement hydraulic pump, and a tilt control device. A tilt control signal generating means for generating a control signal for driving the means, an actuator driven by pressurized oil discharged from the variable displacement hydraulic pump, and an overload relief pressure corresponding to the maximum load pressure of the actuator. A prescribed overload relief valve,
Pressure detecting means for detecting an operating pressure of the actuator, wherein when the pressure detected by the pressure detecting means exceeds a predetermined cutoff set pressure smaller than the overload relief pressure, the tilting is performed. In the hydraulic control device for a hydraulic working machine, wherein the tilt control means is controlled by a control signal generating means so as to reduce the absorption torque of the variable displacement hydraulic pump, the overload relief valve is a variable type overload relief. And an overload relief pressure control means for controlling the overload relief pressure of the variable overload relief valve, and driving the tilt control means to reduce the absorption torque of the variable displacement hydraulic pump. At this time, the overload relief pressure of the variable overload relief valve is increased by a predetermined pressure. It is the configuration with overload relief pressure increase control means for controlling the overload relief pressure control means.

According to the present invention, the tilt control signal is output when the operating pressure of the actuator detected by the pressure detecting means exceeds a predetermined cutoff set pressure smaller than the overload relief pressure. A control signal for driving the displacement control means is output from the generation means, and the displacement control means drives the variable displacement hydraulic pump to reduce the absorption torque, that is, to reduce the displacement of the variable displacement hydraulic pump. . As a result, cutoff control for reducing the discharge flow rate of the variable displacement hydraulic pump is performed.

At the time of the cutoff control, the overload relief pressure rise control means operates the overload relief pressure control means. As a result, the overload relief pressure is increased by a predetermined pressure, and regardless of a decrease in the discharge flow rate of the variable displacement hydraulic pump, a decrease in pressure due to the override characteristic of the variable overload relief valve is corrected. , A decrease in the overload relief pressure can be suppressed. Therefore, it is possible to prevent the occurrence of hunting that repeatedly reduces and increases the pump discharge flow rate during the cutoff control, and to suppress a decrease in the operating force of the actuator during the cutoff control.

Further, in order to achieve the above object, the invention according to claim 5 of the present application is characterized in that in the invention according to claim 4,
The actuator is constituted by a turning motor.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a hydraulic control device for a hydraulic working machine according to the present invention will be described below with reference to the drawings. Figures 1-3
FIG. 1 is a view for explaining a first embodiment of a hydraulic control device for a hydraulic working machine corresponding to claim 1 of the present invention. FIG. 1 is a hydraulic circuit diagram showing an overall configuration of the first embodiment, and FIG. FIG. 3 is a block diagram illustrating a configuration of a main part of a controller provided in the embodiment, and FIG. 3 is a diagram illustrating characteristics of an electromagnetic proportional valve that is provided in the first embodiment and controls a main relief pressure of a main relief valve.

The first embodiment shown in FIGS. 1 to 3 is provided, for example, in a hydraulic excavator, and includes an engine 1, a variable displacement hydraulic pump 2 driven by the engine 1, and a pilot pump 4. ing. Also,
The tilt control means for controlling the absorption torque of the hydraulic pump 2, that is, the regulator 3, the actuator discharged from the hydraulic pump 2, for example, the boom cylinder 12, the swing motor 13, and the hydraulic pump 2 from the boom cylinder 12, the swing motor 13 A boom directional switching valve 10, a turning directional switching valve 11 for controlling the flow of pressure oil supplied to each,
A boom operating device 8 for switching the boom direction switching valve 10 and a turning operation device 9 for switching the turning direction switching valve 11 are provided.

A variable main relief valve 1 for defining a main relief pressure corresponding to the maximum pressure of the hydraulic pump 2
8, a pressure detecting means for detecting the operating pressure P of the actuator, that is, a pressure sensor 19, a pilot relief valve 5 for regulating the pilot relief pressure of the pilot pump 4, and a maximum pressure of the load pressure of the boom cylinder 12. Overload relief valves 14 and 15 for defining an overload relief pressure to be applied, and overload relief valves 16 and 17 for defining an overload relief pressure corresponding to the maximum load pressure of the swing motor 13.

Further, a main relief pressure control means for controlling the main relief pressure of the variable type main relief valve 18, for example, an electromagnetic proportional valve 20, and a cutoff for instructing a predetermined cutoff setting pressure PCM smaller than the main relief pressure. A set pressure indicator 40, a cutoff set pressure PCM output from the cutoff set pressure indicator 40,
And a predetermined arithmetic processing is performed by inputting the actuator operating pressure P output from the pressure sensor 19 described above,
The controller 6 outputs a target displacement signal PX to the regulator 3 and outputs a command current i for driving the electromagnetic proportional valve 20.

As shown in FIG. 2, the controller 6 sets the relationship between the actuator operating pressure P and the pump tilt amount θ in advance, and sets the pump tilt corresponding to the actuator operating pressure P output from the pressure sensor 19 as shown in FIG. Shift amount θ
And a calculation unit 63 that subtracts the cutoff setting pressure PCM of the cutoff setting pressure indicator 40 from the actuator operating pressure P detected by the pressure sensor 19 and outputs a calculation value PS. The relationship between the operation value PS output from the operation unit 63 and the tilt correction value ε is set in advance, and the function generation unit 64 that outputs the tilt correction value ε according to the operation value PS, and the function generation unit 61 described above. Subtracting the displacement correction value ε, which is the output value of the function generator 64, from the pump displacement amount θ, which is the output value of the above, and outputting the target displacement signal PX, which is the calculated value, as a signal for controlling the regulator 3. A function generating unit that presets a relationship between the calculation value PS of the calculation unit 63 and the command current i, and outputs the command current i corresponding to the calculation value PS as a signal for controlling the electromagnetic proportional valve 20 And a 5.

When the calculated value PS reaches the first set value PS1, the function generating section 64 increases the tilt correction value ε to a predetermined value. From such a state, the calculated value PS changes to the first set value PS1. A hysteresis loop that decreases the tilt correction value ε when the value decreases to the second set value PS2 that is smaller than the second set value PS2. Similarly, the function generator 65 described above calculates the operation value PS
When the value of the command current i reaches the first set value PS1, the value of the command current i is increased to a predetermined value.
It has a hysteresis loop that reduces the command current i when the value decreases to the second set value PS2 smaller than the set value PS1.

The relationship between the command current i output from the function generator 65 and the output pressure PO of the proportional solenoid valve 20 is as follows:
For example, as shown in FIG. 3, while the value of the command current i gradually increases and the opening area of the electromagnetic proportional valve 20 gradually increases,
The output pressure PO that increases almost proportionally is output, and when the electromagnetic proportional valve 20 is fully opened, a substantially constant large output pressure PO is output.

A function generator 61 for outputting the pump displacement θ in the configuration of the controller 6 described above, and a calculated value PS
, A function generator 64 that outputs a tilt correction value ε, and a calculator 62 that outputs a target tilt signal PX.
As a result, the pressure detected by the pressure sensor 19 is smaller than the main relief pressure by a predetermined cutoff set pressure PC
A cut-off control unit that controls the regulator 3 to perform cut-off control so as to reduce the absorption torque of the hydraulic pump 2 when the pressure exceeds M is configured.

An operation unit 63 for outputting an operation value PS.
When the regulator 3 is driven to reduce the absorption torque of the hydraulic pump 2 by the function generation unit 65 that outputs the command current i, the main proportional valve 20 is controlled to increase the main relief pressure by a predetermined pressure. Relief pressure rise control means is provided.

The operation of the first embodiment configured as described above will be described below. First, a predetermined cutoff setting pressure PCM smaller than the main relief pressure of the main relief valve 18 is input to the controller 6 by operating the cutoff setting pressure indicator 40 in advance.

In this state, the engine 1 is driven, the hydraulic pump 2 and the pilot pump 4 are operated,
By operating the boom operating device 8 or the turning operating device 9, the boom direction switching valve 10 or the turning direction switching valve 1 is operated.
1, the pressure oil discharged from the hydraulic pump 2 is supplied to the boom cylinder 12 or the swing motor 13,
The boom cylinder 12 or the swing motor 13 is driven to rotate a boom (not shown) or a swing body to perform a corresponding operation such as an excavation operation of earth and sand or a suspended load operation.

During the operation, the pressure sensor 19 detects the actuator operating pressure P.
Input to the controller 6. As shown in FIG. 2, the function generation unit 61 outputs to the calculation unit 62 a pump tilt amount θ that decreases as the actuator operating pressure P increases.
When the actuator operating pressure P exceeds a cutoff set pressure PCM smaller than the main relief pressure, P-PC
M = PS> 0, and the calculated value PS is used as the function generator 6
4 and 65.

The function generator 64 outputs the corresponding tilt correction value ε to the calculator 62 when the value of the calculator PS becomes equal to or greater than the first set value PS1. The calculation unit 62 calculates θ−ε = PX, and outputs the corrected target tilt signal PX to the regulator 3. As a result, the regulator 3 is driven so as to reduce the absorption torque of the hydraulic pump 2, that is, to reduce the displacement of the hydraulic pump 2, and cutoff control for reducing the discharge flow rate of the hydraulic pump 2 is performed.

At this time, the function generating section 65 also sends the corresponding command current i to the electromagnetic proportional valve 20 when the calculated value PS output from the calculating section 63 becomes equal to or greater than the first set value PS1.
Output to Thereby, the electromagnetic proportional valve 20 is switched to the lower position direction in FIG. 1, and the pilot pressure of the pilot pump 4 is changed via the electromagnetic proportional valve 20 to the main relief valve 1.
8 starts to be supplied to the drive unit. That is, the output pressure PO having the characteristic shown in FIG. 3 is applied to the drive unit of the main relief valve 18, and the main relief pressure of the main relief valve 18 is increased by a predetermined pressure as exemplified by the characteristic B in FIG.

In the first embodiment configured as described above, the main relief pressure is increased by a predetermined pressure by the output pressure PO of the solenoid proportional valve 20 irrespective of the decrease in the discharge flow rate of the hydraulic pump 2 during cutoff control. Thus, a decrease in pressure due to the override characteristic of the main relief valve 18 is corrected, and a decrease in main relief pressure during the cutoff control can be suppressed. Therefore, when the pump discharge flow rate during the cut-off control decreases, the control for increasing the pump discharge flow rate is suppressed, and the occurrence of hunting that repeatedly reduces and increases the pump discharge flow rate can be prevented. The pressure oil can be supplied with a relatively stable flow rate change that does not repeatedly increase or decrease the flow rate, and the drive control of the actuator can be performed with high accuracy.

Further, a decrease in the operating force of the actuator during the cut-off control can be suppressed, and the operator operating the actuator does not feel uncomfortable due to such a reduction in the operating force, thereby obtaining good operability. Can be

FIGS. 4 and 5 are views for explaining a second embodiment of a hydraulic control device for a hydraulic working machine according to claims 4 and 5 of the present invention. FIG. 4 is a hydraulic diagram showing the overall configuration of the second embodiment. FIG. 5 is a circuit diagram, and FIG. 5 is a block diagram showing a configuration of a main part of a controller provided in the second embodiment.

The second embodiment shown in FIGS. 4 and 5 is also provided in a hydraulic shovel, for example. 4 and 5, the same reference numerals as those shown in FIGS. 1 and 2 denote the same components.

In the second embodiment, in particular, the overload relief valves 16 and 17 for defining the overload relief pressure corresponding to the maximum load pressure of the swing motor 13 are composed of variable overload relief valves. . Further, an overload relief pressure control means for controlling the overload relief pressure of the variable overload relief valves 16 and 17, for example, an electromagnetic proportional valve 21, a predetermined cutoff setting pressure smaller than the overload relief pressure, ie, A cutoff setting pressure indicator 41 for indicating a predetermined cutoff setting pressure PCO smaller than the main relief pressure of the relief valve 18, and operation detecting means for detecting that the turning operation device 9 has been operated, for example, an operation detection switch 23
And

As shown in FIG. 5, the controller 6
A function generator 6 in which the same relation between the actuator operating pressure P and the pump displacement θ is set as in the embodiment.
1, calculation units 62 and 63, calculation value PS and tilt correction value ε
And a function generator 65 that sets the relationship between the operation value PS and the command current i and outputs the command current i as a signal for controlling the above-described electromagnetic proportional valve 21. In addition to the above, a switching unit 67a is provided in a connection path between the cutoff setting pressure indicator 41 and the calculation unit 63, and opens and closes this connection path. The switching unit 67a is closed when the operation signal SW2 from the operation detection switch 23, that is, the operation signal SW2 indicating that the turning operation device 9 has been operated is input, and the cutoff setting pressure indicator 41 And the arithmetic unit 63 are made conductive. Therefore, the operation unit 63
Performs an operation of subtracting the cutoff set pressure PCO from the operating pressure P.

When the regulator 3 is driven to reduce the absorption torque of the hydraulic pump 2 by the switching unit 67a, the operation unit 63 that outputs the operation value PS, and the function generation unit 65 that outputs the command current i. Further, an overload relief pressure increase control means for controlling the electromagnetic proportional valve 21 so as to increase the overload relief pressure of the overload relief valves 16 and 17 by a predetermined pressure is configured.

In the other constructions, those having the same reference numerals as those shown in FIG. 1 described above have been described in connection with FIG. 1 and will not be described here.

The operation of the second embodiment configured as described above will be described below. First, a predetermined cutoff set pressure PCO smaller than the main relief pressure of the main relief valve 18 is input to the controller 6 by operating the cutoff set pressure indicator 41 in advance.

In this state, the engine 1 is driven, the hydraulic pump 2 and the pilot pump 4 are operated,
When the boom operating device 8 or the turning operating device 9 is operated, the boom cylinder 12 or the turning motor 13 is driven as described in the first embodiment, and
Applicable works such as excavation work and suspended load work are carried out.

During the operation, the pressure sensor 19 detects the actuator operating pressure P.
Input to the controller 6. As shown in FIG. 5, the function generator 61 outputs to the calculation unit 62 a pump tilt amount θ that decreases as the actuator operating pressure P increases.
Here, when the turning operation device 9 is operated and the operation signal SW2 is output from the operation detection switch 23, the switching unit 67a of the controller 6 shown in FIG. 5 is closed by the operation signal SW2. In such a state, when the actuator operating pressure P exceeds the cut-off set pressure PCO smaller than the main relief pressure, P-PCO = PS> 0, and the calculated value PS is calculated by the function generators 64 and 65. Output to both sides.

The function generating section 64 outputs the corresponding tilt correction value ε to the calculating section 62 when the calculated value PS becomes equal to or more than the first set value PS1. The calculation unit 62 calculates θ−ε = PX, and outputs the corrected target tilt signal PX to the regulator 3. As a result, the regulator 3 is driven to reduce the absorption torque of the hydraulic pump 2, that is, to reduce the displacement of the hydraulic pump 2, and cutoff control for reducing the discharge flow rate of the hydraulic pump 2 is performed.

At this time, the function generation unit 65 also sends the corresponding command current i to the electromagnetic proportional valve 21 when the operation value PS output from the operation unit 63 becomes equal to or greater than the first set value PS1.
Output to Thereby, the electromagnetic proportional valve 21 is switched to the lower position direction in FIG. 4, and the pilot pressure of the pilot pump 4 starts to be supplied to the drive units of the overload relief valves 16 and 17 via the electromagnetic proportional valve 21. That is, the output pressure PO having the same characteristic as the characteristic shown in FIG. 3 is given to the drive units of the overload relief valves 16 and 17,
The overload relief pressures of the overload relief valves 16 and 17 have characteristics equivalent to the characteristics B in FIG.

Also in the second embodiment constructed as described above, when the turning operation device 9 is operated, regardless of the decrease in the discharge flow rate of the hydraulic pump 2 during the cut-off control, the electromagnetic proportional valve is operated. 21, the overload relief pressure of the overload relief valves 16, 17 is increased by a predetermined pressure, and the overload relief valves 16, 1 are increased.
The decrease in pressure due to the override characteristic of 7 is corrected, and the decrease in overload relief pressure during the cutoff control can be suppressed. Therefore, even in the second embodiment, as in the first embodiment described above, when the pump discharge flow rate during cutoff control decreases, control to increase the pump discharge flow rate is suppressed, Hunting, which repeatedly reduces and increases the pump discharge flow rate, can be prevented.
The pressure oil having a stable flow rate change which does not repeatedly increase and decrease the flow rate can be supplied, and the drive control of the swing motor 13 can be performed with high accuracy.

Further, similarly to the first embodiment described above, in the second embodiment as well, it is possible to suppress a decrease in the operating force of the swing motor 13 during cutoff control, and to operate the swing motor 13. Good operability can be obtained without giving an uncomfortable feeling due to such a decrease in the operating force to the operating operator.

FIGS. 6 and 7 are views for explaining a third embodiment of a hydraulic control device for a hydraulic working machine according to claims 2 and 3 of the present invention. FIG. 6 is a hydraulic diagram showing the overall configuration of the third embodiment. FIG. 7 is a circuit diagram, and FIG. 7 is a block diagram showing a configuration of a main part of a controller provided in the third embodiment.

The third embodiment shown in FIGS. 6 and 7 is also provided in a hydraulic shovel, for example. 6 and 7, the same reference numerals as those shown in FIGS. 1 and 2 denote the same components.

Also in the third embodiment, the overload relief valves 16 and 17 for defining the overload relief pressure corresponding to the maximum load pressure of the predetermined actuator, that is, the swing motor 13, are composed of variable overload relief valves. ing. In addition, another actuator, that is, the overload relief valves 14 and 15 for defining the overload relief pressure of the boom cylinder 12 are composed of fixed overload relief valves. Further, in addition to the electromagnetic proportional valve 20 for controlling the main relief pressure of the variable main relief valve 18 equivalent to that in the first embodiment, the overload relief pressure of the variable overload relief valves 16 and 17 is controlled. Overload relief pressure control means,
For example, an electromagnetic proportional valve 21 is provided.

Further, there is provided a cutoff set pressure indicator 42 for indicating the cutoff set pressure PC1, and a cutoff set pressure indicator 43 for indicating a cutoff set pressure PC2 different from the cutoff set pressure PC1. . For example, if the main relief pressure of the main relief valve 18 is P1,
Overload relief valve 1 according to boom cylinder 12
Assuming that the overload relief pressures of the overload relief valves 4 and 15 are P2 and the overload relief pressures of the overload relief valves 16 and 17 related to the swing motor 13 are P3, the relationship of P3 <P1 <P2 is set in advance. According to this setting, the cut-off setting pressure PC1 set by the above-described cut-off setting pressure indicator 42 is preset and set by the cut-off setting pressure indicator 43 so that PC1 <P1. Cut-off setting pressure PC
2 is set in advance so that PC2 <P3 and PC2 <PC1.

Operation detecting means for detecting that the boom operating device 8 has been operated, for example, the operation detecting switch 2
2, and an operation detecting means for detecting that the turning operation device 9 is operated, for example, an operation detecting switch 23.

As shown in FIG. 7, the controller 6
A function generator 6 in which the same relation between the actuator operating pressure P and the pump displacement θ is set as in the embodiment.
1, calculation units 62 and 63, calculation value PS and tilt correction value ε
And a function generator 65 in which the relationship between the operation value PS and the command current i is set and the command current i is output as a control signal. A switching unit 66 connected to the pressure indicator 42 and closed by an operation signal SW1 output from the operation detection switch 22, and an operation signal SW2 connected to the cutoff setting pressure indicator 43 and output from the operation detection switch 23. Switching unit 6 closed by
7 and a maximum value selection unit 68 that selects the maximum value PC of the cutoff set pressures output from the switching units 66 and 67 and outputs the selected value to the calculation unit 63.
Furthermore, when the operation signals SW1 and SW2 output from the operation detection switches 22 and 23 are input, it is determined that only the operation signal SW1 is input, and both the operation signal SW1 and the operation signal SW2 are input. A determination unit 69 that outputs a selection signal SWA when it is determined that the operation signal SW2 is input, and outputs a selection signal SWB when it is determined that only the operation signal SW2 is input; and when the selection signal SWA is output from the determination unit 69. And a switching unit 70 that connects the function generation unit 65 to the drive unit of the electromagnetic proportional valve 21 when the selection signal SWB is output from the determination unit 69. Have.

The regulator 3 is driven by the switching unit 66, the maximum value selecting unit 68, the calculating unit 63, the function generating unit 65 for outputting the command current i, the determining unit 69, and the switching unit 70. When reducing the absorption torque of the hydraulic pump 2, the main relief pressure increase control means for controlling the electromagnetic proportional valve 20 so as to increase the main relief pressure of the main relief valve 18 by a predetermined pressure is configured.
Switching section 67, maximum value selection section 68, and operation section 6
3, the function generating unit 65, the discriminating unit 69, and the switching unit 70, when the regulator 3 is driven to reduce the absorption torque of the hydraulic pump 2, the overload relief pressure of the overload relief valves 16, 17 is reduced. The overload relief pressure increase control means for controlling the electromagnetic proportional valve 21 so as to increase the pressure by a predetermined pressure is configured.

In the other structures, those having the same reference numerals as those shown in FIG. 1 described above have been described in FIG. 1 and will not be described here.

The operation of the third embodiment configured as described above will be described below. First, by operating the cutoff setting pressure indicator 42 in advance, a cutoff setting pressure PC1 smaller than the main relief pressure P1 of the main relief valve 18 is input to the controller 6, and by operating the cutoff setting pressure indicator 43, The cutoff set pressure PC2, which is smaller than the overload relief pressure P3 of the load relief valves 16 and 17 and smaller than the cutoff set pressure PC1, is input to the controller 6.

In this state, when the engine 1 is driven, the hydraulic pump and the pilot pump 4 are operated, and, for example, only the boom operating device 8 is operated, the boom cylinder 12 is driven, and a boom (not shown) is operated and a desired boom is operated. Work is performed.

During the operation, the pressure sensor 19 detects the actuator operating pressure P.
Input to the controller 6. As shown in FIG. 7, a pump tilt amount θ that decreases as the actuator operating pressure P increases is output from the function generator 61 to the calculator 62. An operation signal SW1 is output from the operation detection switch 22 in accordance with the operation of the boom operating device 8, and the operation signal SW1 closes the switching unit 66 of the controller 6 shown in FIG. Therefore, the cut-off set pressure PC1 set by the cut-off set pressure indicator 42
Is input to the maximum value selection unit 68, and the maximum value selection unit 68
Is output to the calculation unit 63 from the maximum value PC (= PC1). The operation signal SW1 output from the operation detection switch 22 is input to the determination unit 69. The determination unit 69 determines that only the operation signal SW1 is input, and outputs the selection signal SWA. The switching unit 70 is switched by the selection signal SWA so as to connect the function generation unit 65 and the drive unit of the electromagnetic proportional valve 20. In this state, the actuator operating pressure P becomes the main relief pressure P1
When the pressure exceeds the cut-off set pressure PC1 smaller than P1, the calculation in the calculation unit 63 becomes P-PC1 => 0, and the calculation value PS is output to both the function generation units 64 and 65.

The function generator 64 outputs a corresponding tilt correction value ε to the calculator 62 when the calculated value PS becomes equal to or greater than the first set value PS1. The calculation unit 62 calculates θ−ε = PX, and outputs the corrected target tilt signal PX to the regulator 3. As a result, the regulator 3 is driven to reduce the absorption torque of the hydraulic pump 2, that is, to reduce the displacement of the hydraulic pump 2, and cutoff control for reducing the discharge flow rate of the hydraulic pump 2 is performed.

At this time, at the same time, when the operation value PS output from the operation unit 63 becomes greater than or equal to the first set value PS1, the corresponding command current i is also transmitted to the function of the electromagnetic proportional valve 20 via the switching unit 70. Output to the drive unit. Thereby, the solenoid proportional valve 20 is switched to the lower position direction in FIG. 6, and the pilot pressure of the pilot pump 4 starts to be supplied to the drive unit of the main relief valve 18 via the solenoid proportional valve 20. That is, the output pressure PO having the above-described characteristic shown in FIG. 3 is applied to the drive section of the main relief valve 18, and the main relief pressure of the main relief valve 18 becomes the characteristic B in FIG.

As described above, when only the boom operating device 8 is operated, regardless of the decrease in the discharge flow rate of the hydraulic pump 2 during the cut-off control, the output pressure PO of the electromagnetic proportional valve 20 increases. The main relief pressure of the main relief valve 18 is increased by a predetermined pressure, and a decrease in pressure due to the override characteristic of the main relief valve 18 is corrected, so that a decrease in the main relief pressure during the cut-off control can be suppressed. Therefore, when the pump discharge flow rate decreases during the cutoff control, the control for increasing the pump discharge flow rate is suppressed, and the occurrence of hunting that repeatedly reduces and increases the pump discharge flow rate can be prevented. The pressure oil having a relatively stable flow rate change that does not repeatedly increase or decrease the flow rate can be supplied, and the drive control of the boom cylinder 12 can be realized with high accuracy. Further, a decrease in the operating force of the boom cylinder 12 at the time of the cut-off control can be suppressed, and the operator operating the boom cylinder 12 does not feel uncomfortable due to such a decrease in the operating force, thereby obtaining good operability. .

For example, when the hydraulic pump 2 and the pilot pump 4 are operated as described above,
When only the turning operation device 9 is operated, the turning motor 13 is driven, and a turning body (not shown) turns, and a desired operation is performed.

During the operation, the pressure sensor 19 detects the actuator operating pressure P,
Input to the controller 6. As shown in FIG. 7, a pump tilt amount θ that decreases as the actuator operating pressure P increases is output from the function generator 61 to the calculator 62. An operation signal SW2 is output from the operation detection switch 23 in accordance with the operation of the turning operation device 9, and the switching unit 67 of the controller 6 shown in FIG. 7 is closed by the operation signal SW2. Therefore, the cutoff set pressure PC2 set by the cutoff set pressure indicator 43 is input to the maximum value selection unit 68, and the maximum value PC (= PC2) is output from the maximum value selection unit 68 to the calculation unit 63. Also, an operation signal SW output from the operation detection switch 23
2 is input to the determination unit 69, and it is determined by the determination unit 69 that only the operation signal SW2 is input, and the selection signal S
WB is output. The switching unit 70 has a selection signal SW
By B, the function generator 65 and the drive of the electromagnetic proportional valve 21 are switched to be connected. In this state, the actuator operating pressure P is changed to the overload relief valve 1
When the pressure exceeds the cutoff set pressure PC2 smaller than the overload relief pressures P3 of FIGS. 6 and 17, the calculation in the calculation unit 63 becomes P-PC2 = PS> 0, and the calculated value P
S is output to both of the function generators 64 and 65.

The function generator 64 outputs the corresponding tilt correction value ε to the calculator 62 when the calculated value PS becomes equal to or larger than the first set value PS1. The calculation unit 62 outputs θ-ε = PX as an operator and outputs the corrected target tilt signal PX to the regulator 3. As a result, the regulator 3 is driven to reduce the absorption torque of the hydraulic pump 2, that is, to reduce the displacement of the hydraulic pump 2, and cutoff control for reducing the discharge flow rate of the hydraulic pump 2 is performed.

At this time, at the same time, when the operation value PS output from the operation unit 63 becomes greater than or equal to the first set value PS1, the corresponding command current i is also transmitted to the electromagnetic proportional valve 21 via the switching unit 70. Output to the drive unit. Thereby, the electromagnetic proportional valve 21 is switched to the lower position in FIG. 6, and the pilot pressure of the pilot pump 4 starts to be supplied to the drive units of the overload relief valves 16 and 17 via the electromagnetic proportional valve 21. That is, the output pressure PO having the same characteristic as the characteristic shown in FIG. 3 described above is given to the drive units of the overload relief valves 16 and 17, and the overload relief pressure of the overload relief valves 16 and 17 is changed as shown in FIG. The characteristic becomes equivalent to the characteristic B and the predetermined pressure is increased.

As described above, when only the turning operation device 9 is operated, regardless of the decrease in the discharge flow rate of the hydraulic pump 2 during the cut-off control, the output pressure PO of the electromagnetic proportional valve 21 changes. Overload relief valve 1
6, 17 overload relief pressure is increased by a predetermined pressure,
A decrease in pressure due to the override characteristics of the overload relief valves 16 and 17 is corrected, and a decrease in overload relief pressure during the cutoff control can be suppressed. Therefore, when the pump discharge flow rate during the cutoff control decreases, control to increase the pump discharge flow rate is suppressed, and the occurrence of hunting that repeatedly reduces and increases the pump discharge flow rate can be prevented,
Pressure oil having a relatively stable flow rate change that does not repeatedly increase or decrease the flow rate can be supplied to the swing motor 13.
Drive control can be performed with high accuracy. Further, a decrease in the operating force of the swing motor 13 during the cutoff control can be suppressed, and the operator operating the swing motor 13 does not feel uncomfortable due to such a decrease in the operating force, so that good operability can be obtained. Can be

Further, for example, as described above, the hydraulic pump 2
When both the boom operating device 8 and the swing operating device 9 are operated in a state where the pilot pump 4 is operated, the boom cylinder 12 and the swing motor 13 are driven, and a boom (not shown) is vertically rotated. In addition, the revolving body turns, and desired operations such as earth and sand excavation work and suspended load work are performed.

While such operations are being performed, the actuator operating pressure P is detected by the pressure sensor 19,
Input to the controller 6. As shown in FIG. 7, a pump tilt amount θ that decreases as the actuator operating pressure P increases is output from the function generator 61 to the calculator 62. The operation signal SW1 is output from the operation detection switch 22 in accordance with the operation of the boom operation device 8, and the switching unit 66 of the controller 6 shown in FIG. Accordingly, the operation signal SW2 is output from the operation detection switch 23, and the switching unit 67 is closed by the operation signal SW2. Therefore, the cut-off setting pressure indicator 4
The cut-off set pressure PC1 set at 2 and the cut-off set pressure PC2 set at the cut-off set pressure indicator 43 are input to the maximum value selection unit 68. Where P
Since there is a relationship of C1> PC2, the maximum value selecting unit 68
, The cut-off set pressure PC1 is selected as the maximum value PC and is output to the calculating section 63. The operation signal SW1 output from the operation detection switch 22 and the operation signal SW2 output from the operation detection switch 23 are input to the determination unit 69, and both the operation signals SW1 and SW2 are input to the determination unit 69. And the selection signal SWA is output. The switching unit 70 is switched by the selection signal SWA so as to connect the function generation unit 65 and the drive unit of the electromagnetic proportional valve 20. In this state, if the actuator operating pressure P exceeds the cut-off set pressure PC1 which is smaller than the main relief pressure P1 of the main relief valve 18, the calculation in the calculation unit 63 will be P-PC1 = P
S> 0, and this operation value PS is output to the function generators 64 and 65.
Is output to both.

The function generating section 64 outputs the corresponding tilt correction value ε to the calculating section 62 when the calculated value PS becomes equal to or more than the first set value PS1. The calculation unit 62 calculates θ−ε = PX, and outputs the corrected target tilt signal PX to the regulator 3. As a result, the regulator 3 is driven to reduce the absorption torque of the hydraulic pump 2, that is, to reduce the displacement of the hydraulic pump 2, and cutoff control for reducing the discharge flow rate of the hydraulic pump 2 is performed.

At this time, at the same time, when the operation value PS output from the operation unit 63 becomes greater than or equal to the first set value PS 1, the corresponding command current i is also transmitted to the electromagnetic proportional valve 20 via the switching unit 70. Output to the drive unit. Thereby, the solenoid proportional valve 20 is switched to the lower position direction in FIG. 6, and the pilot pressure of the pilot pump 4 starts to be supplied to the drive unit of the main relief valve 18 via the solenoid proportional valve 20. That is, the output pressure PO having the above-described characteristic shown in FIG. 3 is applied to the drive unit of the main relief valve 18, and the main relief pressure of the main relief valve 18 becomes the characteristic B in FIG.

As described above, even when both the boom operating device 8 and the turning operating device 9 are operated, regardless of the decrease in the discharge flow rate of the hydraulic pump 2 during the cut-off control, the electromagnetic proportional valve is operated. The output pressure PO of 20 increases the main relief pressure of the main relief valve 18 by a predetermined pressure, and corrects a decrease in pressure due to the override characteristic of the main relief valve 18. Can be suppressed.
Therefore, when the pump discharge flow rate decreases during the cut-off control, control for increasing the pump discharge flow rate is suppressed, and the occurrence of hunting that repeatedly reduces and increases the pump discharge flow rate can be prevented. It is possible to supply pressure oil having a relatively stable flow rate change that does not repeatedly increase or decrease the flow rate, so that the drive control of the boom cylinder 12 can be performed with high accuracy. Further, a decrease in the operating force of the boom cylinder 12 during the cut-off control can be suppressed, and the operator operating the boom cylinder 12 does not feel uncomfortable due to such a reduction in the operating force, so that good operability can be obtained. Can be

In each of the above embodiments, for simplicity of explanation, the turning motor 1 is used as an actuator.
Although only the example 3 and the boom cylinder 12 have been illustrated, the hydraulic excavator is equipped with various other actuators. Therefore, the present invention is not limited to the configuration including the swing motor 13 and the boom cylinder 12 as in the above-described embodiments, but may include another actuator such as an arm cylinder, a bucket cylinder, or the like. For example, the third
As another actuator in the embodiment, an arm cylinder may be provided instead of the boom cylinder 12.

[0081]

According to the invention of each claim of the present invention,
It is possible to suppress the reduction of the relief pressure at the time of the cut-off control, which has occurred conventionally, and to prevent the occurrence of hunting which repeatedly reduces and increases the pump discharge flow rate at the time of the cut-off control. Pressure oil having a relatively stable flow rate change that does not cause the repetition of increase and decrease of the pressure can be supplied, and the drive control of the actuator can be performed with higher precision than in the past.

Further, it is possible to suppress a decrease in the operating force of the actuator during the cut-off control, which has conventionally occurred, and to prevent the operator operating the actuator from feeling uncomfortable due to such a decrease in the operating force. Excellent operability is obtained as compared with the above.

[Brief description of the drawings]

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

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

FIG. 3 is a diagram showing characteristics of an electromagnetic proportional valve provided in the first embodiment shown in FIG. 1 and controlling a main relief pressure of a main relief valve.

FIG. 4 is a hydraulic circuit diagram showing an overall configuration of a second embodiment of the present invention.

FIG. 5 is a block diagram showing a configuration of a main part of a controller provided in the second embodiment shown in FIG. 4;

FIG. 6 is a hydraulic circuit diagram showing an overall configuration of a third embodiment of the present invention.

FIG. 7 is a block diagram showing a configuration of a main part of a controller provided in the third embodiment shown in FIG. 6;

FIG. 8 is a view showing override characteristics found in a general relief valve.

[Explanation of symbols]

Reference Signs List 1 engine 2 variable displacement hydraulic pump 3 regulator (tilt control means) 4 pilot pump 5 pilot relief valve 6 controller 7 tank 8 operating device for boom 9 operating device for turning 10 direction switching valve for boom 11 turning direction switching valve 12 boom Cylinder (another actuator) 13 Swing motor (predetermined actuator) 14 Overload relief valve 15 Overload relief valve 16 Overload relief valve 17 Overload relief valve 18 Main relief valve 19 Pressure sensor (pressure detecting means) 20 Electromagnetic proportional valve (Main relief pressure control means) 21 Electromagnetic proportional valve (overload relief pressure control means) 22 Operation detection switch (operation detection means) 23 Operation detection switch (operation detection means) 40 Cut-off setting pressure indicator 41 Cut-off Set pressure indicator 42 Cut-off set pressure indicator 43 Cut-off set pressure indicator 61 Function generation unit 62 Operation unit 63 Operation unit (main relief pressure increase control unit) (overload relief pressure increase control unit) 64 Function generation unit 65 Function generator (main relief pressure rise control means)
(Overload relief pressure rise control means) 66 Switching section (Main relief pressure rise control means) 67 Switching section (Overload relief pressure rise control means) 67a Switching section (Overload relief pressure rise control means) 68 Maximum value selection section ( Main relief pressure increase control means) (Overload relief pressure increase control means) 69 Determination unit (Main relief pressure increase control means) (Overload relief pressure increase control means) 70 Switching unit (Main relief pressure increase control means) (Overload Relief pressure rise control means) A characteristic B characteristic P Actuator operating pressure θ Pump displacement amount PS Calculated value ε Displacement correction value i Command current PX Target displacement signal PO Output pressure PCM Cutoff set pressure PCO Cutoff set pressure PC1 Cut Off set pressure PC2 Cutoff set pressure PC maximum value SW1 operation signal SW2 operation signal SWA selection signal SWB selection signal

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takeshi Nakamura 650, Kandate-cho, Tsuchiura-shi, Ibaraki F-term inside the Tsuchiura Plant of Hitachi Construction Machinery Co., Ltd. 2D003 AA01 AB05 AC09 AC11 BA01 BA08 CA03 DA03 DA04 DB02 3H089 AA27 AA71 CC01 CC08 CC11 DA03 DA13 DB03 DB33 DB47 DB49 EE17 EE22 EE36 FF07 FF12 GG02 JJ02

Claims (5)

[Claims] A variable displacement hydraulic pump, a tilt control means for controlling an absorption torque of the variable displacement hydraulic pump, a tilt control signal generating means for generating a control signal for driving the tilt control means, An actuator driven by pressure oil discharged from the variable displacement hydraulic pump, a main relief valve for defining a main relief pressure corresponding to a maximum pressure of the variable displacement hydraulic pump, and pressure detection means for detecting an operating pressure of the actuator. When the pressure detected by the pressure detection means exceeds a predetermined cutoff set pressure smaller than the main relief pressure, the tilt control signal generation means controls the tilt control means by the tilt control signal generation means. In the hydraulic control device for a hydraulic working machine controlling the absorption torque of the variable displacement hydraulic pump to be small, the main relief valve A variable main relief valve, comprising main relief pressure control means for controlling the main relief pressure of the variable main relief valve, and driving the tilt control means to reduce the absorption torque of the variable displacement hydraulic pump. And a main relief pressure increase control means for controlling the main relief pressure control means so as to increase the main relief pressure by a predetermined pressure. 2. An actuator comprising: a plurality of actuators; an operation detecting means for detecting an operation of these actuators; and an overload relief defining an overload relief pressure corresponding to a maximum load pressure of each of the actuators. A valve, wherein the overload relief valve includes a variable overload relief valve that regulates the overload relief pressure of a predetermined actuator among the actuators, and the overload relief of the variable overload relief valve is provided. An overload relief pressure control means for controlling the pressure, and an overload relief pressure increase control means for controlling the overload relief pressure control means to increase the overload relief pressure by a predetermined pressure; Drive the above When reducing the absorption torque of the variable displacement hydraulic pump, one of the main relief pressure rise control means and the overload relief pressure rise control means is controlled, and one of the main relief pressure and the overload relief pressure is controlled. 2. The hydraulic control device for a hydraulic working machine according to claim 1, wherein the pressure of a corresponding part is increased by a predetermined pressure. 3. The hydraulic control device for a hydraulic working machine according to claim 2, wherein said predetermined actuator is a swing motor. 4. A variable displacement hydraulic pump, a tilt control means for controlling an absorption torque of the variable displacement hydraulic pump, a tilt control signal generating means for generating a control signal for driving the tilt control means, An actuator driven by pressure oil discharged from a variable displacement hydraulic pump, an overload relief valve for defining an overload relief pressure corresponding to a maximum load pressure of the actuator, and a pressure detection for detecting an operating pressure of the actuator The pressure control means generates the pressure by the displacement control signal generating means when the pressure detected by the pressure detecting means exceeds a predetermined cutoff set pressure smaller than the overload relief pressure. In the hydraulic control device of the hydraulic working machine for controlling the variable displacement hydraulic pump to reduce the absorption torque. The overload relief valve comprises a variable overload relief valve, and includes overload relief pressure control means for controlling the overload relief pressure of the variable overload relief valve, and driving the tilt control means Overload relief pressure increase control means for controlling the overload relief pressure control means to increase the overload relief pressure of the variable overload relief valve by a predetermined pressure when reducing the absorption torque of the variable displacement hydraulic pump. A hydraulic control device for a hydraulic working machine, comprising: 5. The hydraulic control device for a hydraulic working machine according to claim 4, wherein said actuator is a turning motor.