JP2786941B2 - Hydraulic drive for work machines - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a hydraulic drive device for a working machine such as a hydraulic shovel or a hydraulic crane, and more particularly to a work having a pressure compensating means for maintaining a differential pressure across a flow control valve at a specified value. The present invention relates to a hydraulic drive for a machine.

2. Description of the Related Art Some work machines are provided with a plurality of work members necessary for performing a desired work. A typical example is a hydraulic excavator. The hydraulic shovel includes a lower traveling body for moving the hydraulic shovel, an upper revolving body pivotally mounted on the lower traveling body, and a front mechanism including a boom, an arm, and a bucket.
Various equipment such as a driver's cab, a prime mover, and a hydraulic pump are mounted on the upper swing body, and a front mechanism is attached.

By the way, by controlling the pump discharge amount such that the pump discharge pressure becomes higher than the load pressure of the hydraulic actuator by a constant value, the hydraulic drive device used in this type of working machine can control only the flow rate necessary for driving the actuator. From a hydraulic pump. This load sensing system typically responds to the discharge pressure of a hydraulic pump and the maximum load pressure of a plurality of actuators extracted in a detection line, for example, as described in JP-A-60-11706. Having a pump control switching valve that operates and controls the supply and discharge of pressure oil, and a working cylinder that is driven by the pressure oil controlled by the switching valve and changes the displacement of the hydraulic pump It has a regulator. The switching valve is provided with a spring for biasing the switching valve in a direction opposite to the pressure difference between the pump discharge pressure and the maximum load pressure. In this pump regulator, when the maximum load pressure rises, the switching valve operates to drive the working cylinder,
Increasing the displacement of the hydraulic pump increases the pump discharge flow and increases the pump discharge pressure. As a result, the pump discharge pressure is controlled to be higher than the maximum load pressure by a specified value determined by the spring.

In a load sensing system, a pressure compensating valve is generally disposed upstream of the flow control valve, whereby the differential pressure across the flow control valve is maintained at a specified value determined by the spring of the pressure compensating valve. . By arranging the pressure compensating valve in this way and maintaining the differential pressure across the flow control valve at a specified value, when a plurality of actuators are driven simultaneously, the differential pressure across the flow control valves for all of the actuators increases. Since the value is maintained at the specified value, the flow rate can be accurately controlled irrespective of the fluctuation of the load pressure, and the combined driving of the actuator can be stably performed at a desired driving speed.

Further, in the load sensing system described in Japanese Patent Application Laid-Open No. 60-11706, a means for opposing the pump discharge pressure and the maximum load pressure is provided instead of the spring of the pressure compensating valve, and the differential pressure between the two is provided. Is used to set the specified value. As described above, the pump discharge pressure and the maximum load pressure are maintained at specified values determined by the spring of the switching valve. As a result, the specified value can be set also by the differential pressure between the pump discharge pressure and the maximum load pressure, and the composite driving of the actuator can be stabilized in the same manner as described above. When the differential pressure is used instead of the spring, when the hydraulic pump is saturated and the discharge flow rate is insufficient with respect to the required flow rate, the differential pressure between the pump discharge pressure and the maximum load pressure decreases. Since the reduced differential pressure is applied to all the pressure compensating valves, the differential pressure across all the flow control valves is uniformly maintained at a value smaller than the specified value. As a result, when the pump discharge flow rate is insufficient, it is avoided that a large flow rate is preferentially supplied to the actuator on the low load side, and the pump discharge flow rate is divided at a ratio corresponding to the required flow rate ratio. The drive speed ratio of the actuator is appropriately controlled. For this reason, even when the hydraulic pump is saturated, stable combined driving of the actuator is possible.

However, the above-described conventional hydraulic drive has the following problems.

Generally, in a work machine, there is a work that needs to control the strength of a force applied to a work target. For example,
Taking a hydraulic excavator as an example of a working machine, when filling a concrete pipe in a groove, a swing motor is driven to rotate the revolving body to push the concrete pipe at the tip of a bucket and adjust the angular position of the concrete pipe. Work corresponds to this. In such an operation, the speed control of the swing motor is not important, and it is desirable that force control for slightly moving the concrete pipe by the swing operation lever can be performed.

The conventional hydraulic circuit that does not employ a load sensing system uses an open center type flow control valve, which controls the pump discharge pressure by adjusting the throttle amount on the pressure oil discharge side, and implements force control. Was. However, in the load sensing system, the pump discharge pressure is controlled to be higher than the load pressure by a specified value regardless of the position of the flow control valve, so that the pump discharge pressure is uniquely determined by the load pressure. However, force control by the operation lever could not be performed. If this is described in the above example of an operation, the revolving structure driven by the revolving motor has a very large inertia, so that the load pressure of the revolving motor at the time of start-up rises to the set pressure of a relief valve installed in the circuit, and at this pressure, Since the revolving body is driven, a large revolving force is generated, and the revolving force moves the concrete pipe, so that the pressing force is too strong and the concrete pipe may be damaged. In addition, since a large turning force is generated as described above, the revolving body is rapidly accelerated, and it is difficult to turn at a slight angle. In the case of the above operation, it is difficult to slightly move the concrete pipe.

Another example in which force control is desirable is a work in which a certain object is pressed against the ground or a fixed part by a work member such as a bucket during work, and is held. In the case of this work, in the load sensing system, a phenomenon occurs in the same manner as when the work member is directly pressed against the fixed portion, the load pressure increases to the relief pressure, a large force is generated, and the object is damaged. There is fear. Therefore, such an operation is not possible. Such problems are not only in excavators,
This is a problem that occurs in various other work machines.

An object of the present invention is to provide a hydraulic drive device for a work machine that employs a load sensing system and enables force control.

DISCLOSURE OF THE INVENTION In order to achieve the above object, the present invention provides a hydraulic pump,
At least one hydraulic actuator that is driven by pressure oil discharged from the hydraulic pump, and a flow control valve that is driven in accordance with an operation amount of operation means and controls a flow of pressure oil supplied to the actuator from the hydraulic pump. Detecting pipe means for extracting the load pressure of the actuator, and a differential pressure between the pressure on the upstream side of the flow control valve and the load pressure of the actuator, which is connected to the detecting pipe means, is maintained at a specified value. A hydraulic drive device for a working machine having a pressure compensating means, wherein the load pressure of the actuator, which is provided for the detecting pipe means and is extracted by the detecting pipe means, is determined according to an operation amount of the operating means. It has pressure limiting means for limiting the following.

Preferably, the pressure limiting means is connected between a throttle provided in the detection pipe means and a downstream side of the throttle and a tank, and changes a set pressure according to an operation amount of the operation means, A variable relief valve for preventing the pressure downstream of the throttle from exceeding its set pressure.

Alternatively, the pressure limiting unit may be configured to include a variable pressure reducing unit installed in the detection conduit unit and configured to reduce the load pressure to a value determined according to an operation amount of the operation unit. In this case, preferably, the variable pressure reducing means is a variable pressure reducing valve that changes a set pressure according to an operation amount of the operating means and reduces the load pressure to the set pressure. Instead, the variable pressure reducing means is provided in the detection pipe means, and changes a degree of opening in accordance with an operation amount of the operating means, a first variable throttle, and a downstream side of the first variable throttle and a tank. A second variable throttle connected between the first and second variable throttles, the first and second variable throttles cooperating with each other to change an opening degree according to an operation amount of the operating means. The pressure may be reduced to a value determined according to the operation amount of the operation means.

Preferably, the pressure compensating means operates in response to the discharge pressure of the hydraulic pump and the limited load pressure, and controls the pump discharge pressure so that the pressure difference between the two is maintained at a specified value. Including pump control means. In this case, preferably, the pump control means is a pump regulator that controls a discharge flow rate of the hydraulic pump so as to maintain the specified value, and consequently controls a pump discharge pressure. Alternatively, the pump control means may be an unload valve connected to the discharge line of the hydraulic pump and directly controlling the pump discharge pressure.

The pressure compensating means is connected to the upstream side of the flow control valve, and operates in response to the inlet pressure of the flow control valve and the limited load pressure, so that the pressure difference between the two is maintained at a specified value. It may be a pressure compensating valve for controlling the inlet pressure of the flow control valve.

More preferably, the operating means is a means for generating a pilot pressure proportional to the operation amount, means for driving the flow control valve by the pilot pressure, the pressure limiting means, means for extracting the pilot pressure, Means that operates based on the extracted pilot pressure and limits the load pressure to a value determined according to the operation amount of the operation means.

Alternatively, the operation means may be a means for generating an electric signal proportional to the operation amount, and in this case, the pressure limiting means may be a value determined according to the operation amount of the operation means based on the detected value. And means for outputting a corresponding electric signal, and means for operating based on the electric signal to limit the load pressure to the calculated value or less.

Preferably, the apparatus further comprises means for selecting operation of the pressure limiting means.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a hydraulic drive device according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing details of the pump actuator.

FIG. 3 is a schematic diagram of a hydraulic drive device according to a second embodiment of the present invention.

FIG. 4 is a schematic diagram of a hydraulic drive device according to a third embodiment of the present invention.

FIG. 5 is a diagram showing the relationship between the primary pressure and the secondary pressure of the variable pressure reducing valve.

FIG. 6 is a schematic diagram of a hydraulic drive device according to a fourth embodiment of the present invention.

FIG. 7 is a flowchart showing a processing procedure of the control device.

FIG. 8 is a schematic diagram of a hydraulic drive device according to a fifth embodiment of the present invention.

FIG. 9 is a flowchart showing a processing procedure of the control device.

FIG. 10 is a schematic diagram of a hydraulic drive device according to a sixth embodiment of the present invention.

FIG. 11 is a schematic diagram of a hydraulic drive device according to a seventh embodiment of the present invention.

FIG. 12 is a schematic view of the pump control means of the hydraulic drive device according to the eighth embodiment of the present invention.

FIG. 13 is a schematic diagram of a hydraulic drive device according to a ninth embodiment of the present invention.

FIG. 14 is a characteristic diagram showing the relationship between the opening degree and the pilot pressure of the first and second variable throttles.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings, taking a hydraulic shovel as an example of a working machine.

First Embodiment First, a first embodiment of the present invention will be described with reference to FIG. 1 and FIG.

Configuration In FIG. 1, reference numeral 1 denotes a variable displacement hydraulic pump. The hydraulic pump 1 has a displacement displacement mechanism (hereinafter, represented by a swash plate) 1a, and the amount of displacement of the swash plate 1a (displacement displacement). ) Is controlled by a load sensing type pump regulator 2. The hydraulic pump 1 is connected with a swing motor 3 for driving an upper swing body of a hydraulic shovel and a boom cylinder 13 for driving a boom, and constitutes a hydraulic drive device.

The drive of the swing motor 3 is controlled by a flow control valve 4,
A pressure compensating valve 5 is provided upstream of the flow control valve 4. Relief valves 6a and 6b are provided in the main circuit of the swing motor 3, and regulate the maximum load pressure of the swing motor 3. Similarly, the drive of the boom cylinder 13 is controlled by a flow control valve 14, a pressure compensating valve 15 is installed upstream of the flow control valve 14, and relief valves 16a, 16
b is provided. Flow control valves 4, 14 and pressure compensating valves 5, 15
Between the swing motor 3 and the boom cylinder 13
Check valves 11 and 18 for preventing backflow of pressure oil from the pump are provided.

The flow control valve 4 has driving units 4x, 4y connected to the pilot lines 4p1, 4p2, and the pilot lines 4p1, 4p2 are connected to the operating device 4a of the swing motor 3. The operating device 4a has an operating lever 4b and pilot valves 4c and 4d. When the operating lever 4b is operated, the pilot valves 4c and 4d are operated according to the operating direction.
Is activated, a pilot pressure corresponding to the operation amount is generated, and the pilot pressure is applied to the line 4p1 or 4
The flow control valve 4 is introduced into the drive unit 4x or 4y of the flow control valve 4 via p2, and sets the flow control valve 4 to an opening corresponding to the operation amount.
The same applies to the flow control valve 14, and the pilot line 14
Drive units 14x and 14y are connected to p1 and 14p2,
p1 and 14p2 are connected to an operating device 14a of the boom cylinder 12 including an operating lever 14b and pilot valves 14c and 14d.

The flow control valves 4 and 14 have detection lines 7a and 17 for extracting the load pressure of the swing motor 3 and the boom cylinder 13, respectively.
Is connected, the load pressure extracted to the detection line 7a is output to the detection line 7b via the pressure limiting unit 20, and the higher one of this pressure and the load pressure extracted to the detection line 17 is Is selected by the shuttle valve 8 and output to the detection pipe 9.

The pressure compensating valves 5 and 15 are respectively connected to the driving units 5x and 1 on one side.
5x is loaded with the load pressure (pressure on the outlet side of the flow control valves 4 and 14) of the swing motor 3 and the boom cylinder 13 extracted to the detection pipes 7a and 17 via the pipes 5a and 15a and the other side. Drive unit
The pressures on the inlet sides of the flow control valves 4 and 14 are applied to 5y and 15y via conduits 5b and 15b. Further, springs 5c, 15c are provided on the pressure compensating valves 5, 15 on the side where the load pressure is applied. Thereby, the pressure compensating valves 5 and 15 control the differential pressures before and after the flow control valves 4 and 14 to be maintained at specified values determined by the springs 5c and 15c, respectively.

As shown in FIG. 2, the pump regulator 2 is connected to a swash plate 1a of the hydraulic pump 1 and has an operating cylinder 2a for driving the swash plate 1a.
2b is connected to the discharge line 1b of the hydraulic pump 1 and the bottom side chamber is connected to the line 2b and the tank 10 via two switching valves 2c and 2d.
Can be selectively communicated with

The first switching valve 2c is a switching valve for load sensing control, and a pump discharge pressure is applied to a driving unit 2e on one side from a pipe 2b, and a detection pipe 9 is applied to a driving unit 2f on the other side. Thus, the pressure selected by the shaft valve 8 is applied. In addition, a spring 2g is installed on the drive unit 2f side of the switching valve 2c. Assuming that the pressure selected by the shuttle valve 8 is the load pressure of the swing motor 3, when the load pressure increases, the switching valve 2c is driven to the left in the figure, and the switching valve 2c
The bottom side chamber of 2a is connected to the tank 10, whereby the working cylinder 2a is driven in the contracting direction to increase the amount of tilt of the swash plate 1a. As a result, the discharge flow rate of the hydraulic pump 1 increases,
Pump discharge pressure increases. When the pump discharge pressure increases, the switching valve 2c is returned to the right side in the figure, and when the differential pressure between the pump discharge pressure and the load pressure reaches a specified value determined by the spring 2g, the switching valve 2c stops, and the drive of the working cylinder 2a is started. Stop.
Conversely, when the load pressure decreases, the switching valve 2c is driven rightward in the drawing, and the switching valve 2c connects the bottom side chamber of the working cylinder 2a to the line 2b.
, The working cylinder 2a is driven in the extension direction by the pressure receiving area difference between the bottom chamber and the rod chamber, and the tilt amount of the swash plate 1a is reduced. As a result, the discharge flow rate of the hydraulic pump 1 decreases, and the pump discharge pressure decreases. When the pump discharge pressure decreases, the switching valve 2c is returned to the left in the figure, and when the differential pressure between the pump discharge pressure and the load pressure reaches a specified value determined by the spring 2g, the switching valve 2c stops, and the operating cylinder 2a Stop driving. Thus, the pump discharge pressure is controlled to be higher than the load pressure of the swing motor 3 by a specified value determined by the spring 2g.

The second switching valve 2d is a switching valve that performs horsepower limiting control,
It is configured as a servo valve that feeds back the tilt position of the swash plate 1a. Thus, when the pump discharge pressure increases and exceeds a predetermined value, the pump discharge flow rate is controlled so that the maximum possible discharge flow rate of the hydraulic pump 1 decreases as the discharge pressure increases.

Returning to FIG. 1, the pressure limiting unit 20 is composed of a throttle 20a installed in the detection pipe 7a, and a variable relief valve 20b installed in a pipe 21 connecting the downstream side of the throttle 20a to the tank 10. I have. The variable relief valve 20b has a spring 20c and a drive unit 20d as means for setting a relief pressure. A switching valve 22 that selectively opens and closes the pipeline 21 and selects an operation mode is provided downstream of the variable relief valve 20b in the pipeline 21. When the switching valve 22 is in the closed position, the normal operation mode is selected, and when the switching valve 22 is in the open position, the force control mode is selected.

Pipelines 23a and 23b branch off from pilot pipes 4p1 and 4p2,
The pilot pressure transmitted to either one of the pipes 23a and 23b is extracted by the shuttle valve 24 and transmitted to the pipe 25. The pipeline 25 is connected to the drive unit 20d of the variable relief valve 20b, and the pilot pressure extracted by the shuttle valve 24 is applied to the drive unit 20d. As a result, the pilot pressure generated by the operating device 4a, that is, the operating lever
The set pressure is changed in accordance with the operation amount of 4b, and accordingly, when the switching valve 22 is at the open position, the pressure downstream of the throttle 20a does not exceed the set pressure. That is, the load pressure extracted in the detection line 7a is limited to a value determined according to the operation amount of the operation lever 4b, and the limited load pressure is transmitted to the shuttle valve 8 via the detection line 7b. .

Operation Next, the operation of the present embodiment configured as described above will be described.

During normal operation, the operator switches the switching valve 22 to the closed position, and disconnects the communication between the variable relief valve 20b and the tank 10. In this state, since the variable relief valve 20b does not function, the load pressure of the swing motor 3 extracted in the detection pipe 7a always appears in the detection pipe 7b. Therefore,
The operation in this case is the same as that of the conventional load sensing system without the pressure limiter 20, and the speed control is performed according to the operation amount of the operation lever 4b when the swing motor 3 is driven independently.

That is, when the operator operates the operation lever 4b, a pilot pressure is generated in one of the pilot lines 4p1 and 4p2, for example, the pilot line 4p1, and the flow control valve 4
Is switched to the position on the left side of the drawing at an opening degree corresponding to the operation amount of the operation lever 4b, and the pressure oil of the hydraulic pump 1 passes through the variable throttle of the pressure compensating valve 5 and the flow control valve 4 to the left side of the turning motor 3 in the drawing. The turning motor 3 is supplied from the main pipeline to the turning motor 3 and starts turning in one direction. In this case, since the inertia of the upper swing body is extremely large, most of the pressure oil to be supplied to the swing motor 3 at the start of swing is discharged to the tank 10 via the relief valve 6a and the load appearing in the detection pipe 7a. The pressure becomes the set pressure of the relief valve 6a. This load pressure is
a, is introduced into the driving portion 2f of the switching valve 2c of the pump regulator 2 via the detection pipe 7b, the shuttle valve 8 and the detection pipe 9, and as described above, the tilt amount of the swash plate 1a is increased and the pump discharge is performed. The pressure is controlled to be higher than the load pressure of the swing motor 3 by a specified value determined by the spring 2g. At this time, since the load pressure of the swing motor 3 is high, the increase in the amount of tilt of the swash plate 1a is limited by the switching valve 2d that performs the horsepower limiting control.

When the swing motor 3 is gradually accelerated in this manner, the amount of oil relieved from the relief valve 6a also gradually decreases accordingly. After reaching the rotation speed, the load pressure rapidly decreases to a value far lower than the set pressure of the relief valve 6a. Also at this time, the pump regulator 2 controls the discharge flow rate according to the low load pressure so that the differential pressure between the discharge pressure of the hydraulic pump 1 and the load pressure is maintained at a specified value determined by the spring 2g.

In the above-described independent drive of the swing motor 3, the spring 5c of the pressure compensating valve 5 normally has a difference between the pump discharge pressure and the load pressure in which the differential pressure across the flow control valve 4 is controlled by the pump regulator 2 as described above. Since the pressure compensating valve 5 is set to be substantially equal to the differential pressure, the pressure compensating valve 5 is almost fully opened. That is, the pressure compensating valve 5 does not function when the swing motor 3 is driven alone.

The independent drive of the boom cylinder 13 also operates according to this.

In the case of a combined operation in which the swing motor 3 and the boom cylinder 13 are simultaneously driven, when the operation levers 4b and 14b are simultaneously operated, the flow control valves 4 and 14 are opened at an opening corresponding to the operation amounts thereof, and the swing motor 3 and the boom cylinder 13 are opened. The pressurized oil is supplied to the boom cylinder 13, whereby the swing motor 3 and the boom cylinder 13
Are driven simultaneously. The higher one of the load pressures of the swing motor 3 and the boom cylinder 13, for example, the load pressure of the swing motor 3 is selected by the shuttle valve 8 and output to the detection line 9. This load pressure is introduced into the drive portion 2g of the switching valve 2c of the pump regulator 2, and the discharge of the hydraulic pump 1 is maintained such that the differential pressure between the load pressure and the pump discharge pressure is maintained at a specified value, as in the case of single drive. The flow rate is controlled.

As a result of such control, the differential pressure between the pump discharge pressure and the load pressure of the boom cylinder 13 on the low load pressure side becomes larger than the above specified value. Therefore, if no care is taken, the discharge flow rate from the hydraulic pump 1 is preferentially supplied to the low load pressure side boom cylinder 13 and the flow rate supplied to the high load pressure side swing motor 3 is remarkable. Therefore, the driving of the swing motor 3 becomes difficult. In such a situation, the pressure compensating valve 15 functions to ensure that the turning motor 3 is supplied with a flow rate corresponding to the operation amount of the operation lever 4a. That is, the pressure compensating valve 15 is throttled by the increase of the pump discharge pressure, and the pressure difference before and after the flow control valve 14 is reduced by the spring 15c.
The pressure difference between the flow control valves 4 and 15 is substantially equalized. As a result, the flow rate supplied to the swing motor 3 and the boom cylinder 13 is controlled to a flow rate according to the operation amounts of the operation levers 4b and 14b, and a smooth composite operation can be performed.

Next, when performing force control, the switching valve 22 is switched to the open position to select the force control mode. As a result, force control is performed as follows.

When the operation lever 4b for turning is operated, for example, when a pilot pressure corresponding to the operation amount is introduced into the pilot pipeline 4p1, the flow control valve 4 is switched to the position on the left side in the figure. At the same time, the pilot pressure is introduced into the drive unit 20d of the variable relief valve 20b via the pipe 23a, the shuttle valve 24, and the pipe 25, and the set pressure of the variable relief valve 20b is changed from the value determined only by the spring 20c to the spring 20c. Change to a value determined by the pilot pressure. This set pressure changes according to the magnitude of the pilot pressure. The larger the pilot pressure, the larger the set pressure, and the smaller the pilot pressure, the smaller the set pressure. After all, if the operation amount of the operation lever 4b is large, the set pressure is large, and if the operation amount is small, the set pressure is small.

Now, assuming that the turning motor 3 is in a stopped state and the operation amount of the operation lever 4b is small, the pilot line 25
The pilot pressure extracted to the low, variable relief valve 20
The set pressure of b becomes a small value. On the other hand, pressurized oil is supplied to the swing motor 3 by switching the flow control valve 4 described above.
Since the revolving structure has a large inertial load, the load pressure of the revolving motor 3 tends to increase to the relief pressure of the relief valve 6a as described above, and the above-described set pressure of the variable relief valve 20b is higher than the relief pressure of the relief valve 6a. Since the pressure is much smaller, a load pressure higher than the set pressure of the variable relief valve 20b tends to appear in the detection line 7a. This load pressure is guided to the variable relief valve 20b via the throttle 20a, and the variable relief valve 20b releases a part of the pressure oil downstream of the throttle 20a to the tank 10, and reduces the pressure downstream of the throttle 20a to the variable relief valve. To the set pressure. That is, the load pressure extracted in the detection pipeline 7a is limited to a value determined according to the operation amount of the operation lever 4b, and the limited low pressure is guided to the detection pipeline 7b. This pressure is introduced via the shuttle valve 8 and the detection line 10 into the drive 2f of the switching valve 2c of the pump regulator 2, so that the pump discharge pressure is lower than this limited low pressure by the specified value determined by the spring 2g. And the discharge pressure of the pump is controlled by the variable relief valve 20b.
Becomes a low pressure obtained by adding the specified value to the set pressure of This pressure is constant as long as the operation amount of the operation lever 4b is constant.

As a result of controlling the pump discharge pressure to a low constant pressure as described above, the increase in the load pressure of the swing motor 3 up to the relief pressure of the relief valve 6a is suppressed, and the load pressure is reduced to the above-described set pressure of the variable relief valve 20b. There will be approximately equal low pressure. Thus, the swing motor 3 is driven with a small force according to the operation amount of the operation lever 4b, and the upper swing body of the hydraulic excavator is also gradually driven with a small force. That is, sudden acceleration of the upper-part turning body is prevented.

When the operation amount of the turning lever is further increased from this state, the set pressure of the variable relief valve 20b increases accordingly, and the increased set pressure appears in the detection pipeline 7b. For this reason, the discharge pressure of the hydraulic pump 1 also increases, and the swing motor 3 is driven by the increased force.

As described above, in the present embodiment, the set pressure of the variable relief valve 20b is changed in accordance with the operation amount of the operation lever 4b,
Since the pressure on the downstream side of 20a does not exceed this set pressure, the load pressure of the swing motor 3 extracted to the detection pipe 7a is limited to a value determined according to the operation amount of the operation lever 4b, and the load By employing a sensing system and controlling the load pressure of the swing motor 3 according to the operation amount of the operation lever 4b, the force control of the swing motor 3 can be performed.

Therefore, for example, when the concrete pipe is filled in the groove, when the work of adjusting the angular position of the concrete pipe by pushing the concrete pipe at the tip of the bucket by driving the swing motor to swing the swing body, the operation lever is used. Since the operation amount of the concrete pipe can be reduced and the concrete pipe can be pushed little by little with a small force, damage to the concrete pipe can be prevented and fine adjustment of the angular position of the concrete pipe becomes possible. In addition, when a certain object is pressed against the ground or the fixed portion by a work member such as a bucket by the rotation of the upper revolving unit and the work is held, the pressing force can be controlled according to the operation amount of the operation lever. Therefore, an appropriate pressing force can be selected according to the characteristics of the object, and the object can be pressed and held without being damaged.

Further, even in a normal turning operation in which the direction of the front attachment is changed, the turning acceleration can be controlled in accordance with the operation amount of the operation lever. Excellent operability is obtained. Further, since the acceleration pressure can be reduced, the durability of various hydraulic devices and pipes can be expected to be improved.

Second Embodiment A second embodiment of the present invention will be described with reference to FIG. In the figure, the same parts as those shown in FIG. 1 are denoted by the same reference numerals. In this embodiment, the force control is performed using a pressure compensating valve.

In FIG. 2, the drive unit 5x of the pressure compensating valve 5A is connected to the detection line 7b via the line 5d, and as a result, the drive unit 5x applies the load pressure of the swing motor 3 extracted to the detection line 7a. However, the load pressure limited by the pressure limiting unit 20 is applied. Other configurations are the same as those of the first embodiment.

In this embodiment, the operation when the switching valve 22 is in the closed position for selecting the normal operation mode is the same as that in the first embodiment. When the switching valve 22 is in the open position for selecting the force control mode, operations other than the pressure compensating valve 5A are the same as those in the first embodiment. When the switching valve 22 is in the open position, the load pressure limited by the pressure limiting unit 20 in the detection pipe 7b is introduced into the drive unit 5x of the pressure compensating valve 5A via the pipe 5d. For this reason the pressure compensating valve
5A operates so that the differential pressure between the pressure on the inlet side of the flow control valve 4 and the pressure of the detection pipe 7b is maintained at a specified value determined by the spring 5c. That is, the pressure on the inlet side of the flow control valve 4 is equal to the detection line
Is controlled to be a pressure obtained by adding a prescribed value determined by the spring 5c to the pressure of the above. Here, the pressure of the detection pipe 7b has a low constant value according to the operation amount of the operation lever 4b (see FIG. 1) due to the action of the variable relief valve 20b. Therefore, the pressure on the inlet side of the flow control valve 4 is also controlled to a constant low pressure. As a result, the pressure on the inlet side of the flow control valve 4 is controlled to a low and constant pressure. As a result, the load pressure of the swing motor 3 also decreases, and force control according to the operation amount of the operation lever can be performed.

The present embodiment is effective when the force control of the swing motor 3 is necessary in the combined operation of driving the swing motor 3 and the boom cylinder 13 at the same time. When the swing motor 3 and the boom cylinder 13 are driven at the same time, the pump regulator 2 supplies the high pressure selected by the shuttle valve 8 out of the limited pressure of the detection line 7 b and the load pressure of the boom cylinder 13 of the detection line 17. However, when the load pressure of the boom cylinder 13 is higher, force control cannot be performed in the first embodiment. In this embodiment, in such a case, the pressure compensating valve 5A functions as described above to limit a rise in pressure on the inlet side of the flow control valve 4 and to execute force control of the swing motor 3.

As described above, in the present embodiment, the limited load pressure generated by the pressure limiting unit 20 is introduced into the pressure compensating valve instead of the conventional load pressure. Also, the force control of the swing motor can be performed without any support during the combined operation.

Third Embodiment A third embodiment of the present invention will be described with reference to FIGS. In the present embodiment, a configuration different from that of the above-described embodiment is adopted for the pressure limiting means.

In FIG. 3, a hydraulic drive device according to the present embodiment includes a hydraulic pump 31, an actuator driven by hydraulic oil discharged from the hydraulic pump 31, such as a swing motor 32 and left and right travel motors 33 and 34, and a hydraulic pump. Flow control valves 35, 36, and 37 are provided for controlling the flow of pressure oil supplied to these actuators 32, 33, and 34 from 31.

Actuators 32, 3 are attached to flow control valves 35, 36, 37, respectively.
Detection lines 39, 40, 41 for extracting the load pressures of 3, 34 are connected, and the detection lines 39, 40 are connected to another detection line 43 via a shuttle valve 42, and the detection lines 41, 41 are connected. The detection line 43 is connected to another detection line 45 via a shuttle valve 44, and the detection line 45 and the detection line 46 for the load pressure related to another actuator not shown are connected via a shuttle valve 47. It is communicated to the detection line 48.

The hydraulic pump 31 has a displacement displacement mechanism, that is, a swash plate 31.
A variable displacement type having a, and the amount of displacement (displacement) of the swash plate 31 is a load sensing type pump regulator 38.
Is controlled by The pump regulator 38 is a hydraulic pump 31
The swash plate 31a includes an actuator 38a that drives the swash plate 31a, and a switching valve 38b that controls the driving of the actuator 38a. The actuator 38a includes a piston 38c having different pressure receiving areas at both ends, a first chamber 38d in which a piston end having a large pressure receiving area is located, and a second chamber 38e in which a piston end having a small pressure receiving area is located. The first chamber 38d is connected to a switching valve 38b via a line 38f, and the switching valve 3
8b is a discharge line 31b of the hydraulic pump 31 via lines 38g and 38h.
And a tank 49 via a line 38i.
With this configuration, the first chamber 38d can be selectively communicated with the discharge pipe line 31b of the hydraulic pump 31 and the tank 48 by the switching valve 38b. Further, the second chamber 38e is always in communication with the discharge line 31b of the hydraulic pump 31 via the line 38h.

The switching valve 38b is provided with two opposing driving sections 38j and 38k, one pumping section 38j receives a pump discharge pressure from a pipe 38m, and the other driving section 38k receives the pressure of the above-described detection pipe 48. Is loaded. Further, a spring 38n is provided on the drive unit 38k side of the switching valve 38b.

The above-described configuration of the pump regulator 38 by the combination of the actuator 38a and the switching valve 38b has a configuration excluding the second switching valve 2d for controlling the horsepower of the pump regulator 2 shown in FIG. 2 according to the first embodiment. The discharge flow rate of the hydraulic pump 31 is controlled so that the pump discharge pressure is higher than the pressure appearing in the detection pipe 48 by a specified value determined by the spring 38n.

The flow control valves 35, 36, and 37 are of a pilot operation type driven by pilot pressure as in the first embodiment, and are pilot pipes 35a, 35 connected to the drive unit of the flow control valve 35.
Pipes 50a and 50b branch from b, and the pipes 50a and 50b communicate with a pipe 52 via a shuttle valve 51. With this configuration,
The pilot pressure transmitted to one of the pipes 50a and 50b is extracted by the shuttle valve 51 and transmitted to the pipe 52.

A variable pressure reducing valve 53 is provided in the detection conduit 39 relating to the flow control valve 35. The pressure-reducing valve 53 uses the load pressure extracted to the detection pipe 39 as a primary pressure and reduces the pressure to output a secondary pressure. Like a general pressure-reducing valve, a secondary pressure is applied to one side. And a spring 53b as one of means for setting the value of the secondary pressure on the other side. Further, on the side of the pressure reducing valve 53 where the spring 53b is located, a driving unit 53c is further installed as another means for setting the value of the secondary pressure, and the pilot pressure transmitted to the pipeline 52 to the driving unit 53c is provided. Is loaded.

The variable pressure reducing valve 53 thus configured has characteristics as shown in FIG. That is, when the pilot pressure is low, the primary pressure P1 (the load pressure extracted in the detection line 39) is reduced to a relatively small secondary pressure P2, and when the pilot pressure is high, the secondary pressure P2 is reduced accordingly. Make it higher. Thus, the variable pressure reducing valve 53 changes the set pressure in accordance with the pilot pressure, and correspondingly reduces the load pressure of the actuator 32 extracted in the detection line 39, thereby extracting the load pressure in the detection line 39. The applied load pressure is limited to a value determined according to the operation amount of an operation lever (not shown) related to the hydraulic motor 32 as in the first embodiment.

The operation of the present embodiment configured as described above is as follows. If a not-shown operation lever related to the hydraulic motor 32 is operated with a small operation amount to drive a revolving structure not shown,
When the flow control valve 35 is switched, a small pilot pressure generated according to the small operation amount is extracted by the shuttle valve 51 and supplied to the drive unit 53c of the variable pressure reducing valve 53 via the pipe 52. As a result, assuming that the load pressure of the hydraulic motor 32 extracted in the detection pipe 39 at this time, that is, the primary pressure of the variable pressure reducing valve 53 is P1a, the primary pressure P1a is relatively high as shown in FIG. Reduced to a small secondary pressure P2a, this 2
The next pressure P2a is supplied to the drive unit 38k of the switching valve 38b via the shuttle valves 42, 44, 47 and the detection pipe 48. Thereby, the swash plate 31a of the hydraulic pump 31 is tilted such that the pump discharge pressure is higher than the pressure appearing in the detection pipe 48, that is, the secondary pressure P2a of the variable pressure reducing valve 53 by a specified value determined by the spring 38n. (Displacement volume) is controlled, and since the secondary pressure P2a of the variable pressure reducing valve 53 is a low constant value determined according to the operation amount, the pump discharge pressure is obtained by adding a prescribed value determined by the spring 38n to the constant value. Similarly, it is controlled to a relatively low constant value.

As a result of the pump discharge pressure being controlled to a low constant pressure as described above, the load pressure also becomes a low pressure, and the hydraulic motor 32 is driven with a small force according to the operation amount of the operation lever, as in the first embodiment. The revolving superstructure of the hydraulic excavator is also gradually driven by a small force.

When the operation amount of the operation lever increases and the pilot pressure increases accordingly, the drive of the variable pressure reducing valve 53 also increases, and a larger secondary pressure P2b is taken out for the same primary pressure P1a. The next pressure P2 is given to the drive section 38k of the switching valve 38b. As a result, the swash plate 31a of the hydraulic pump 31 causes the pump discharge pressure to exceed the
The displacement (displacement volume) is controlled so as to increase by the specified value determined by the
The pressure is controlled by adding Pb to a specified value determined by the spring 38n. As a result, the hydraulic motor 32 is driven with a larger force than the above-described case according to the operation amount of the operation lever, and the upper swivel is driven with a faster acceleration.

Therefore, also in this embodiment, the force control of the hydraulic motor 32 can be performed similarly to the first embodiment, and the same effect as that of the first embodiment can be obtained.

Fourth Embodiment A fourth embodiment of the present invention will be described with reference to FIGS. In the drawing, members equivalent to those shown in FIG. 4 are denoted by the same reference numerals. This embodiment employs electronic control as a part of the pressure limiting means.

In FIG. 4, an electromagnetically operated variable pressure reducing valve 53A is provided in the detection pipe 39, and the variable pressure reducing valve 53A has an electromagnetic driving unit 53d instead of the driving unit 53c in FIG. I have. Further, an electric operation lever 60 is provided as operation means of the hydraulic motor 32, and the electric operation lever 60 is provided with an input unit 61a,
The control unit 61 is connected to a control device 61 having an output unit 61b, a storage unit 61c, and a calculation unit 61d. The control unit 61 is connected to an electro-hydraulic converter 62 and a driving unit 53d for the pressure reducing valve 53A. The electro-hydraulic converter 62 is for generating a pilot pressure for driving the flow control valve 35. Other configurations are substantially the same as those of the third embodiment shown in FIG.

In the present embodiment configured as described above, when the electric operation lever 60 is slightly operated with the intention of turning the revolving body slowly, as shown in step S1 in FIG. The operation amount x is read into the calculation unit 61d via the input unit 61a. Next, the procedure moves to step S2, where the storage unit 61
The relationship between the operation amount x stored in advance in c and the command signal I for the solenoid valve 53A is read, and the command signal I corresponding to the operation amount x read in step S1 is calculated. Here, the relationship between the operation amount x and the command signal I is such that the command signal I increases in proportion to the operation amount x, and the command signal I takes a maximum value during a full stroke. Next, proceed to step S3.
The command signal I obtained in S2 is output to the driving section 53d of the pressure reducing valve 53A, and the pressure reducing valve 53A is driven. At the same time, a command signal to the flow control valve 35 corresponding to the operation amount x of the electric operation lever 60 is calculated, and is output from the output unit 61b of the control device 61 to the electro-hydraulic converter 62. In the electro-hydraulic converter 62, a pilot pressure corresponding to the operation amount x is generated based on the command signal, and the pilot pressure is given to the drive unit of the flow control valve 35, and the flow control valve 35 is switched.

The load pressure generated by driving the hydraulic motor 32 based on the discharge flow rate supplied from the hydraulic pump 31 is detected by the detection pipeline.
Guided to 39 as the primary pressure of the variable pressure reducing valve 53A, the pressure reducing valve 53A
Is supplied to the drive section 38k of the switching valve 38b in the same manner as in the third embodiment described above.

Even in the present embodiment configured as described above, when the operation amount x of the electric operation lever 60 is small, the value of the command signal I given to the pressure reducing valve 53A is small, and thus, as in the third embodiment, The secondary pressure reduced by 53A is relatively small, and the discharge pressure of the hydraulic pump 31 is relatively small by the control using this secondary pressure. Therefore, the hydraulic motor
32 can be driven with a small force corresponding to the operation amount x of the electric operation lever 60, and the revolving unit can be driven with a small force.

Fifth Embodiment A fifth embodiment of the present invention will be described with reference to FIGS. In the drawings, members equivalent to those shown in FIGS. 4 and 6 are denoted by the same reference numerals. In this embodiment, the pressure reducing valves are installed at different positions.

In FIG. 8, the hydraulic drive device of the present embodiment includes hydraulic cylinders 32A, 33A, which provide a boom cylinder, an arm cylinder, and a bucket cylinder as actuators, respectively.
34A and an electric operation lever 60 that outputs electric signals of operation amounts xa, xb, xc as operation means of these hydraulic cylinders, respectively.
a, 60b, and 60c. Also, hydraulic cylinders 32A, 33
A variable pressure reducing valve 53B having an electromagnetic drive unit 53b is installed in the detection line 45 from which the maximum load pressure of A and 34A is extracted.
The electric operation levers 60a, 60b, 60c are connected to a control device 61A, and the control device 61A is connected to the electrohydraulic conversion devices 62a, 62b, 62c and the drive unit 53d of the variable pressure reducing valve 53B. The electro-hydraulic converters 62a, 62b, 62c are for generating pilot pressure for driving the flow control valves 35, 36, 37.
Further, there is provided a selection switch 63 which is turned on during a horizontal pulling operation for moving the tip of the bucket of the hydraulic shovel in parallel with the ground and turned off during a normal excavation operation. The other structure is substantially the same as the fourth embodiment shown in FIG.

Generally, in a hydraulic shovel, when a boom, an arm, and the like are simultaneously operated to perform a horizontal pulling operation, it is known that an operation amount of a boom operation lever is relatively small and a load pressure of a boom cylinder is highest. Therefore, in the fifth embodiment, when performing the horizontal pulling operation, the selection switch 63 is turned on, and the following control is performed.

When the electric operation levers 60a, 60b, 60c are operated during the horizontal pulling operation, the control device 61A as shown in step S10 of FIG.
Manipulated variables xa, xb,
xc is read. Next, the process proceeds to step S11, where it is determined whether the selection switch 63 is ON or OFF. Now this selection switch 6
Since 3 is ON, the process proceeds to step S12, in which the arithmetic element y controls the driving of the hydraulic cylinder 32A which is the boom cylinder for driving the boom among the operation amounts xa, xb, xc of the electric operation levers 60a, 60b, 60c. Operating lever corresponding to the flow control valve 35
The operation amount xa of 60a is set to the operation element y, and then the process proceeds to step S13. In this step S13, the relationship between the operation element y stored in the storage section 61c in advance and the command signal I to the pressure reducing valve 53B is read out, and the operation element y set in step S12, that is, the electric operation lever 60a A command signal I corresponding to the operation amount xa is produced. Here, the relationship between the calculation element y and the command signal I to the pressure reducing valve 53B is such that the command signal I increases in proportion to the calculation element y, and the calculation element y takes the maximum value during a full stroke. I have. Next, proceeding to step S14, the command signal I obtained in step S13 is output from the output unit 61b of the control device 61A to the pressure reducing valve.
The pressure is output to the drive unit of 53B, and the pressure reducing valve 53A is driven.

On the other hand, the operation amounts xa, xb, xc of the electric operation levers 60a, 60b, 60c
Is output from the output unit 45 of the control device 61A to the electro-hydraulic converters 62a, 62b, 62c, and the pilot pressure generated by these electro-hydraulic converters 62a, 62b, 62c, that is, the operation amount xa, Pilot pressures corresponding to xb and xc are supplied to the drive units of the respective flow control valves 35, 36 and 37, and these flow control valves 35, 36 and 37 are switched. Thereby, the hydraulic pump 31
Hydraulic cylinders 32A, 33A, 34A with pressure oil supplied from
Is driven to perform a horizontal pulling operation. The maximum value of the load pressure generated by driving the hydraulic cylinders 32A, 33A and 34A supplied from the hydraulic pump 31, that is, the primary pressure of the variable pressure reducing valve 53B The pressure is reduced by the pressure reducing valve 53A, and the reduced secondary pressure is supplied to the drive unit 38k of the switching valve 38b.
As a result, the discharge pressure of the hydraulic pump 31 is controlled to a pressure corresponding to the operation amount of the electric operation lever 60a for the boom, and the load pressure of the boom cylinder is correspondingly adjusted.
It is controlled to a value corresponding to the operation amount of 60a.

In general, in the case of normal excavation work in a hydraulic excavator, the load pressure of the boom cylinder is not always the highest, and the load pressure of the arm cylinder or the bucket cylinder may increase. Therefore, in the fifth embodiment, when performing excavation work, the selection switch 63 is turned off, and the following control is performed.

First, after reading the operation amounts xa, xb, and xc of the electric operation levers 60a, 60b, and 60c related to the excavation work in step S10, the process proceeds to step S15 because the determination in step S11 in FIG. 8 is not satisfied. In this step S15, a process of setting the operation element 6y to the maximum value of the manipulated variables xa, xb, xc, that is, max (xa, xb, xc) is performed. Next, the procedure proceeds to the above-described procedure S13, where the command signal I corresponding to the computation element y corresponding to the maximum value of the same manipulated variables xa, xb, xc as described above is computed, and then the procedure proceeds to the procedure S14, which is obtained in the procedure S13. The command signal I is output from the output unit 61b of the control device 61A to the drive unit 53d of the pressure reducing valve 53B, and the pressure reducing valve 53B is driven.

On the other hand, the operation amounts xa, xb, xc of the electric operation levers 60a, 60b, 60c
The pilot pressure is generated in the electro-hydraulic converters 62a, 62b, 62c in response to the pressure, and the flow control valves 35, 36, 37 are switched according to these pilot pressures, and the pressure is supplied by the hydraulic oil supplied from the hydraulic pump 31. The hydraulic cylinders 32A, 33A, 34A to be driven are driven to perform excavation work. The maximum value of the load pressure generated by driving the hydraulic cylinders 32A, 33A, and 34A by the discharge flow rate supplied from the hydraulic pump 31, that is, the largest pressure among the load pressures of the boom cylinder, the arm cylinder, and the bucket cylinder Is guided as the primary pressure of the pressure reducing valve 53B via the pipe line 45, the pressure is reduced by the pressure reducing valve 53B, and the reduced secondary pressure is supplied to the drive section 38k of the switching valve 38b. Thereby, the discharge pressure of the hydraulic pump 31 is controlled to a pressure corresponding to the maximum value of the operation amounts xa, xb, xc of the electric operation levers 60a, 60b, 60c, and the load pressure of the boom cylinder, the arm cylinder, and the bucket cylinder is controlled. Is correspondingly controlled.

In the present embodiment configured as above, when the selection switch 63 is selected to be ON and the horizontal pulling operation is intended, the load pressure of the boom cylinder, which is usually the largest in this horizontal pulling operation, is relatively small. Since it is reduced according to the operation amount of the boom operation lever, the boom can be driven with a small force at the time of starting the horizontal pulling operation, and the fine operability is improved. Further, when the selection switch 63 is selected to be OFF and the excavation work is intended, one of the load pressures of the boom cylinder, the arm cylinder, and the bracket cylinder, which is the largest in this excavation work, depends on the largest operation amount of the operation lever. As a result, the reduction of the load pressure is minimized, and a powerful excavation operation with a small decrease in work efficiency can be performed.

Sixth Embodiment A sixth embodiment of the present invention will be described with reference to FIG. In the figure, the same reference numerals are given to members equivalent to those shown in FIG. In this embodiment, force control can be performed on all actuators.

In FIG. 10, electromagnetically operated variable pressure reducing valves 53C, 53D, 53E are installed in all of the detection lines 39, 40, 41 for extracting the load pressure of the hydraulic cylinders 32A, 33A, 34A. Further, in the control device 61B, the operation amounts xa, xb, of the electric operation levers 60a, 60b, 60c are
Based on each of xc, a command signal for the corresponding pressure reducing valve is calculated and output according to the procedure shown in FIG. The selection switch 63 shown in FIG. 8 is not provided. Other configurations are the same as those of the fifth embodiment.

In this embodiment configured as described above, the load pressure can be limited according to the operation amount of the electric operation lever for each hydraulic cylinder having different load pressure and metering characteristics, and force control can be performed. Control can be realized.

Seventh Embodiment A seventh embodiment of the present invention will be described with reference to FIG. In the drawing, members equivalent to those shown in FIG. 4 are denoted by the same reference numerals. In this embodiment, the concept of the second embodiment is introduced into the third embodiment shown in FIG.

That is, in FIG. 11, pressure compensating valves 71, 72, 73 are provided upstream of the flow control valves 35, 36, 37. Pressure compensation valve
72, 73 is a general one, the outlet side pressure (load pressure of the corresponding actuator) and the inlet side pressure of the flow control valves 36, 37 are applied to the opposing drive units 72x, 72y and 73x, 73y,
The differential pressure across the flow control valves 36, 37 is maintained at a specified value determined by springs 72a, 73a. The pressure compensating valve 71 is
The secondary pressure reduced by the variable pressure reducing valve 53 is applied to x, the input side pressure of the flow control valve 35 is applied to the drive unit 71y, and the differential pressure between the two is maintained at a specified value determined by the spring 71a.
The other structure is the same as that of the third embodiment shown in FIG.

The configuration of the present embodiment thus configured is different from that of the second embodiment shown in FIG. 3 except that the configuration of the pressure limiting means adopts that of the third embodiment shown in FIG. The second embodiment is substantially the same, so that the same effect as that of the second embodiment can be obtained. That is, in the combined operation of simultaneously driving the hydraulic motors 32, 33, and 34, even if the load pressure of the actuators other than the hydraulic motor 32 increases and the force control by the pump regulator 38 cannot be performed, the operation of the pressure compensating valve 71 The increase in pressure on the inlet side of the flow control valve 35 is limited. Therefore, the hydraulic motor 32
Force control can be performed.

Another Embodiment Still another embodiment of the present invention will be described with reference to FIGS.

FIG. 12 shows an eighth embodiment of the present invention, in which the displacement of a variable displacement hydraulic pump is controlled as pressure means for maintaining a differential pressure between a pump discharge pressure and a load pressure at a specified value. Instead of the above-described pump regulator that controls the discharge flow rate and the discharge pressure of the hydraulic pump, an unload valve that directly controls the pump discharge pressure is used.

That is, in FIG. 12, reference numeral 80 denotes a fixed displacement hydraulic pump, and a discharge pipeline 81 of the hydraulic pump 80 is connected to a tank 83 via an unload valve 82. The unloading valve 82 has opposing driving parts 82x and 82y and a spring 8 for setting the unloading pressure.
2a, the pump discharge pressure is applied to the drive section 82x via the pipe 84, and the limited load pressure is applied to the drive section 82y via the detection pipe 9 or 48 of the above-described embodiment. Has been.

Also in the present embodiment configured as described above, the pump discharge pressure can be detected by the known function of the unload valve 82.
Or, since it is controlled to be higher than the limited load pressure appearing at 48 by the specified value determined by the spring 82a, the load sensing system can be configured in the same manner as the previous embodiment, and the same effect can be obtained. Can be.

FIGS. 13 to 15 show a ninth embodiment of the present invention, in which a variable throttle is used instead of using a relief valve or a pressure reducing valve for directly controlling pressure as pressure limiting means.

That is, in FIG. 13, a first variable throttle 90 is installed in a load pressure detection pipe 39 related to the hydraulic motor 32, and a second variable throttle 90 is provided between the downstream side of the first variable throttle 90 and the tank 49. A variable throttle 91 is provided, and the downstream side of the first variable throttle 90 is connected to the shuttle valve 42. First and second variable apertures
The pilot pressure extracted to the pipe 52 is guided to 90 and 91, and the opening is changed according to the pilot pressure. The relationship between the pilot pressure and the opening is as shown in FIG. 14. In the first variable throttle 90, the opening is minimum when the pilot pressure is zero, and the opening increases as the pilot pressure increases. In the second variable throttle 91, on the contrary, the opening is maximum when the pilot pressure is zero,
The opening degree decreases as the pilot pressure increases. Note that the first variable stop 90 may be a fixed stop. Other configurations are the same as those of the third embodiment shown in FIG.

Also in this embodiment in which the pressure limiting means is configured in this manner, the first and second variable throttles 90 and 91 cooperate to control the pressure on the downstream side of the first variable throttle 90 corresponding to the pilot pressure. Since the pressure is reduced to a value determined according to the operation amount of the operation lever, the load pressure can be limited according to the operation amount of the operation lever in the same manner as when a variable relief valve or a variable pressure reducing valve is used. Can be obtained.

INDUSTRIAL APPLICABILITY As described above, according to the present invention, the pressure limiting means for limiting the load pressure of the actuator extracted to the detection pipe means to a value determined according to the operation amount of the operation means is provided. Therefore, a load sensing system can be adopted and force control can be performed, and operability is significantly improved.

Claims (12)

(57) [Claims] A hydraulic pump (1), at least one hydraulic actuator (3) driven by pressure oil discharged from the hydraulic pump, and a hydraulic pump (3) driven in accordance with an operation amount of an operation means (4a); A flow control valve (4) for controlling the flow of pressure oil supplied from the hydraulic pump to the actuator, detection pipe means (7a, 7b) for extracting the load pressure of the actuator, and connected to the detection pipe means; And a pressure compensating means (2 or 5) for maintaining a differential pressure between a pressure upstream of the flow control valve and a load pressure of the actuator at a specified value. Pressure limiting means (7a, 7b) for limiting the load pressure of the actuator (3) extracted to the detection conduit means to a value determined according to the operation amount of the operation means (4a) or less. 20) Hydraulic drive system characterized in that it comprises. 2. A hydraulic drive device for a working machine according to claim 1, wherein said pressure limiting means (20) is provided with a throttle (20a) provided in said detection pipe means (7a) and said throttle. Between the downstream side of the throttle and the tank (10), and changes the set pressure according to the operation amount of the operating means (4a) so that the pressure downstream of the throttle does not exceed the set pressure. A hydraulic drive device comprising a variable relief valve (20b). 3. A hydraulic drive system for a working machine according to claim 1, wherein said pressure limiting means is provided in said detection pipe means (39), and said load pressure is reduced by an operation amount of said operating means. Variable pressure reducing means (53; 5
3A; 53B; 53C-53E). 4. A hydraulic drive system for a working machine according to claim 3, wherein said variable pressure reducing means changes a set pressure according to an operation amount of said operating means, and reduces said load pressure to said set pressure. A hydraulic drive device characterized by being a variable pressure reducing valve (53). 5. A hydraulic drive device for a working machine according to claim 3, wherein said variable pressure reducing means is provided in said detection pipe means (39), and said variable pressure reducing means adjusts an opening in accordance with an operation amount of said operating means. A first variable throttle (90) to be changed, and a second variable throttle connected between the downstream side of the first variable throttle and the tank (49) and changing the opening in accordance with the operation amount of the operation means. A throttle (91), wherein the first and second variable throttles cooperate to lower the pressure downstream of the first variable throttle to a value determined according to the operation amount of the operating means. Hydraulic drive. 6. The hydraulic drive system for a working machine according to claim 1, wherein said pressure compensating means is responsive to a discharge pressure of said hydraulic pump (1; 31; 80) and said limited load pressure. Pump control means (2; 38; 82) for controlling the pump discharge pressure so that the pressure difference between the two is maintained at a specified value.
A hydraulic drive device comprising: 7. A hydraulic drive system for a working machine according to claim 6, wherein said pump control means controls a discharge flow rate of said hydraulic pump so as to maintain said specified value, and as a result, a pump discharge pressure is reduced. A hydraulic drive device comprising a pump regulator (2; 38) for controlling. 8. The hydraulic drive system for a working machine according to claim 6, wherein said pump control means is connected to a discharge line (81) of said hydraulic pump (80) and directly controls a pump discharge pressure. A hydraulic drive device, which is an unload valve (82). 9. The hydraulic drive system for a work machine according to claim 1, wherein said pressure compensating means is connected to an upstream side of said flow control valve (4; 35), and is adapted to control an inlet pressure of said flow control valve. A pressure compensating valve (5A; 71) that operates in response to the limited load pressure and controls an inlet pressure of the flow control valve such that a differential pressure between the two is maintained at a specified value. Hydraulic drive. 10. A hydraulic drive system for a working machine according to claim 1, wherein said operating means generates a pilot pressure proportional to said operation amount, and said pilot pressure causes said flow control valve (4; 35) to operate. Means (4a) for driving
The pressure control means operates based on the extracted pilot pressure and means for extracting the pilot pressure (24, 25; 51, 52), and determines the load pressure according to the operation amount of the operation means. Means to limit to below value (20b; 53; 90,9
1) A hydraulic drive device comprising: 11. A hydraulic drive system for a working machine according to claim 1, wherein said operating means is means for generating an electric signal proportional to said operation amount (60; 60a), and said pressure limiting means is A means (61; 61A; 61B) for calculating a value determined according to the operation amount of the operating means based on the detected value and outputting a corresponding electric signal; Means for limiting the calculated value to not more than (53)
A; 53B; 53C-53E). 12. The hydraulic drive system for a work machine according to claim 1, further comprising means (22) for selecting an operation of said pressure limiting means.