JPH062340A - Driving circuit of hydraulic operation machine - Google Patents

Abstract

PURPOSE:To make good composite drive of both system by providing a variable differential pressure compensating valve to a directional control valve belonging to a high pressure hydraulic pump, providing a constant differential pressure compensating valve to a directional control valve belonging to low pressure pump, and connecting both systems selectively through a control valve. CONSTITUTION:For example, when traveling is separately controlled, pressure oil for a variable capacity hydraulic pump 30a is supplied to a left traveling directional control valve 5 and a variable differential pressure compensating valve 20e, and pressure oil for a hydraulic pump 30b is supplied to a right traveling directional control valve 6 and a variable differential pressure compensating valve 20f to separately travel. At that time, the maximum load pressure of a left traveling motor is applied to the variable differential pressure compensating valve 20e and a differential pressure detector 32a, and flow rate of the pump 30a is so controlled that discharge pressure of the pump 30a is higher than the maximum load pressure by DELTAPLS. Flow rate of the pump 30 is controlled by the compensating valve 20f and a differential pressure detector 32b even in the case of a right traveling motor. According to the constitution, in the case of composite drive of both systems, better driving can be made without requiring any adjustment of metering.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit for a hydraulic working machine such as a hydraulic excavator, and more particularly to a directional control valve for controlling an actuator, which is provided with a differential pressure between an upstream pressure and a downstream pressure of the directional control valve. The present invention relates to a drive circuit of a hydraulic working machine including a pressure compensating valve for controlling a differential pressure across the vehicle.

[0002]

2. Description of the Related Art As a conventional technique equipped with this type of pressure compensating valve, for example, there is a drive circuit for a hydraulic working machine disclosed in International Publication No. WO90 / 00683.

This prior art is provided for a hydraulic pump, a plurality of actuators driven by pressure oil discharged from the hydraulic pump, and the actuators respectively corresponding to these actuators. A plurality of directional control valves for controlling the flow of pressure oil, and attached to these directional control valves to control the differential pressure across the directional control valves, which is the differential pressure between the upstream pressure and the downstream pressure. It has a plurality of pressure compensating valves, and has a basic configuration in which the discharge pressure of the hydraulic pump is controlled to be a constant pressure higher than the load pressure of the actuator.

Further, in a drive circuit for a general hydraulic working machine having the basic structure as exemplified above, a directional control valve for controlling each actuator when driving a plurality of actuators having different load pressures in combination. If all are equipped with a constant pressure differential pressure compensating valve that constantly controls the differential pressure across the directional control valve as a pressure compensating valve,
When the sum of the required flow rate of each actuator is larger than the flow rate discharged from the hydraulic pump, in the saturated state,
Although the flow rate supplied to the low-voltage side actuator is kept constant, the flow rate supplied to the high-voltage side actuator decreases. That is, it is well known that the low pressure side actuator priority drive is compensated by providing the constant differential pressure / pressure compensation valve.

Further, in a drive circuit for a general hydraulic working machine having the basic structure as exemplified above, a directional control valve for controlling a plurality of actuators having different load pressures is used. As a pressure compensating valve, variable differential pressure pressure compensation that can control the differential pressure across the directional control valve to match the differential pressure between the hydraulic pump discharge pressure and the maximum load pressure of the actuator When a valve is attached, when the sum of the required flow rate of each actuator increases and it is about to reach a saturated state, each variable differential pressure is adjusted according to the degree of decrease in the discharge pressure of the hydraulic pump due to the increase of the required flow rate. The pressure compensating valve controls the differential pressure across each directional control valve so that it becomes smaller than that before, so that the flow rate of each variable differential pressure compensating valve becomes smaller than before. The occurrence of the above-mentioned saturated state is prevented, and the flow rate discharged from the hydraulic pump is completely diverted to the high-pressure side actuator and the low-pressure side actuator. Can hold That is, it is well known that the drive of the high-pressure side actuator is compensated by providing the variable differential pressure compensating valve.

[0006]

In the prior art as described above, when various actuators having different load pressures are combined to drive various works, the combined works are performed according to the kind of work to be performed. It is necessary to drive both of the driven actuators well.

In this case, for example, when it is intended to perform combined drive of the high-pressure side actuator and the low-pressure side actuator in a drive circuit in which the pressure compensating valves are all constant differential pressure pressure compensating valves, the constant differential pressure Good driving of the low-pressure side actuator can be realized due to the essential function of the compensation valve, but good driving of the high-pressure side actuator cannot be realized.

Further, when the pressure compensating valve is a drive circuit consisting of variable differential pressure compensating valves altogether and it is intended to carry out combined driving of the high-pressure side actuator and the low-pressure side actuator, the variable differential pressure compensating valve is operated as described above. Good driving of the high-voltage side actuator can be realized according to the function inherently possessed, but good driving of the low-voltage side actuator cannot be realized.

Therefore, in the prior art, by adjusting the metering in such a case, it is possible to realize the driving of the actuator which cannot be driven well. However, in reality, such adjustment of the metering is extremely complicated and requires a lot of labor, which makes it difficult. In some cases, it may not be possible to drive the actuator with high accuracy despite the adjustment of the metering, and as a result, good workability may not be obtained.

The present invention has been made in view of the above-mentioned circumstances in the prior art, and an object of the present invention is to combine a high-voltage side actuator and a low-voltage side actuator with each other, without requiring adjustment of metering. It is to provide a drive circuit of a hydraulic working machine capable of realizing various drives.

[0011]

In order to achieve this object, a first aspect of the present invention is a hydraulic pump and a plurality of hydraulic pumps driven by pressure oil discharged from the hydraulic pump. Actuators, a plurality of directional control valves provided corresponding to each of these actuators, for controlling the flow of pressure oil supplied from the hydraulic pump to the actuators, and provided in association with these directional control valves. And a plurality of pressure compensating valves for controlling a front-rear differential pressure which is a differential pressure between the upstream pressure and the downstream pressure of the directional control valve, and the discharge pressure of the hydraulic pump is higher than the load pressure of the actuator by a constant pressure. In the drive circuit of the hydraulic working machine that is controlled so that any one of the plurality of pressure compensation valves described above always controls the differential pressure across the corresponding directional control valve to be constant. A constant differential pressure pressure compensating valve, and the other one of the plurality of pressure compensating valves determines the differential pressure across the corresponding directional control valve among the discharge pressure of the hydraulic pump and the load pressure of the actuator. The variable pressure differential pressure compensating valve is controllable so as to match the differential pressure with the maximum load pressure.

According to a fifth aspect of the present invention, a hydraulic pump, a plurality of actuators driven by pressure oil discharged from the hydraulic pump, and the respective actuators are provided. A plurality of directional control valves that are provided to control the flow of pressure oil supplied from the hydraulic pump to the actuator, and are provided in association with these directional control valves, and have an upstream pressure and a downstream pressure of the directional control valve. And a plurality of pressure compensating valves for controlling the front-back differential pressure which is the differential pressure of the hydraulic pump, and a drive circuit of a hydraulic working machine controlled so that the discharge pressure of the hydraulic pump is higher than the load pressure of the actuator by a constant pressure. In the pressure compensating valve, the differential pressure across the corresponding directional control valve is set to the discharge pressure of the hydraulic pump and the actuator according to a predetermined external signal. From a variable differential pressure pressure compensating valve that can be controlled to match the differential pressure with the maximum load pressure of the load pressure, to a constant differential pressure pressure compensating valve that constantly controls the differential pressure across the directional control valve. The pressure compensating valve is variable or can be changed from a constant differential pressure compensating valve to a variable differential pressure compensating valve.

[0013]

When a constant differential pressure pressure compensating valve and a variable differential pressure compensating valve are mixed in the hydraulic pump system as in the invention described in claim 1, a plurality of actuators having different load pressures are provided. When a constant differential pressure compensating valve is attached to each of the directional control valves for controlling the above, good driving of the low-pressure side actuator is compensated. Further, when a variable differential pressure compensating valve is attached to each of the directional control valves that control a plurality of actuators having different load pressures, good driving of the high-pressure side actuator is compensated. Then, among the directional control valves for controlling a plurality of actuators having different load pressures, a predetermined directional control valve is attached with a constant differential pressure pressure compensating valve, and another directional control valve is attached with a variable differential pressure compensating valve. A good drive of the actuator controlled by the directional control valve, to which a constant differential pressure pressure compensating valve is attached, is compensated. For example, when driving multiple actuators with different load pressures,
When the directional control valve for controlling the high-pressure side actuator is equipped with a variable differential pressure compensating valve, and the directional control valve for controlling the low-pressure side actuator is equipped with a constant differential pressure compensating valve, the Drive can be realized. Further, for example, when the directional control valve for controlling the low pressure side actuator is equipped with a variable differential pressure / pressure compensation valve and the directional control valve for controlling the high pressure side actuator is equipped with a constant differential pressure / pressure compensation valve, It is possible to realize good driving of.

Therefore, in the invention according to claim 1 of the present invention, the combination of each actuator and the variable differential pressure compensating valve or the constant differential pressure compensating valve is appropriately selected in advance in consideration of the type of work. By simply setting, when performing composite driving of a plurality of actuators having different load pressures, good composite driving of the corresponding actuator can be realized without any adjustment of metering.

Further, in the invention described in claim 5 of the present invention, similarly to the invention described in claim 1, each actuator and the variable differential pressure compensating valve or the constant value is preliminarily considered in consideration of the kind of work. By appropriately setting the combination of differential pressure and pressure compensating valves, it is possible to realize good combined drive of the relevant actuators without the need for metering adjustment, and by applying external signals to the pressure compensating valves. When you want to change the combination of the actuator and the variable differential pressure compensating valve or the constant differential pressure compensating valve, and you want to implement a work mode in which the high-pressure side actuator and the low-pressure side actuator are reversed. Therefore, it is possible to easily cope with the circuit structure that has already been assembled, without requiring replacement work.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of a drive circuit for a hydraulic working machine according to the present invention will be described below with reference to the drawings. 1 is a circuit diagram showing a configuration of a first embodiment of the present invention, FIG. 2 is a diagram showing pressure-flow rate characteristics of a system including a variable differential pressure compensating valve provided in the embodiment shown in FIG. 1, and FIG. FIG. 2 is a diagram showing pressure-flow rate characteristics of a system including a constant differential pressure pressure compensation valve provided in the embodiment shown in FIG. 1.
The first embodiment shown in FIGS. 1 to 3 corresponds to claims 1 and 2 of the present invention.

The first embodiment shown in FIG. 1 shows, for example, a drive circuit for a hydraulic excavator, which comprises a first variable displacement hydraulic pump 30a and a second variable displacement hydraulic pump 30b. The hydraulic pump 30a controls an attachment directional control valve 1 for controlling the drive of an attachment actuator (not shown), a bucket directional control valve 2 for controlling the drive of a bucket cylinder (not shown), and a drive of an arm cylinder (not shown). Directional control valve for arm 3
And a boom directional control valve 4 for controlling the drive of a boom cylinder (not shown) and a left directional control valve 5 for controlling the drive of a left traveling motor (not shown) are connected, and
It is connectable to a right traveling directional control valve 6 for controlling driving of a right traveling motor (not shown) via the electromagnetic switching valve 33. These directional control valves 1, 2, 3, 4, 5, 6 have
The differential pressure across the directional control valve, which is the differential pressure between the upstream pressure and the downstream pressure, is defined as the discharge pressure P _S1 of the hydraulic pump 30a and the load pressure of each actuator to which the pressure oil discharged from the hydraulic pump 30a is supplied. Variable differential pressure compensating valve that can be controlled so as to match the differential pressure ΔPLS with the maximum load pressure P _LM1 , of which, namely, attachment variable differential pressure compensating valve 20a, bucket variable differential pressure compensating valve 20b, arm. A variable differential pressure / pressure compensating valve 20c, a boom variable differential pressure / pressure compensating valve 20d, a left traveling variable differential pressure / compensating valve 20e, and a right traveling variable differential pressure / compensating valve 20f are respectively attached.

The hydraulic pump 30b is provided with a swing direction control valve 7 for controlling the drive of a swing motor (not shown), a boom direction control valve 8 for controlling the drive of a boom cylinder (not shown), and an arm cylinder (not shown). An arm directional control valve 9 for controlling, a bucket directional control valve 10 for controlling driving of a bucket cylinder (not shown), and an attachment directional control valve 11 for controlling driving of an attachment actuator (not shown) are connected, Also,
It is connectable to a right traveling directional control valve 6 for controlling driving of a right traveling motor (not shown) via the electromagnetic switching valve 33. The directional control valves 7, 8, 9, 10, 11 described above are
A constant differential pressure pressure compensating valve that always controls the differential pressure across the corresponding directional control valve to be constant, that is, a swing constant differential pressure pressure compensating valve 21a, a boom constant differential pressure compensating valve 21b, an arm constant differential pressure pressure. Compensation valve 21c, constant differential pressure pressure compensation valve 21d for bucket, constant differential pressure pressure compensation valve 2 for attachment
1e is attached respectively.

The maximum load pressure among the load pressures of the actuators belonging to the hydraulic pump 30a is detected by the first maximum load pressure detection circuit 34a and is given to the first differential pressure detection device 32a as the pressure P _LM1 . The first differential pressure detection device 32a _obtains the differential pressure ΔPLS between the discharge pressure P _S1 of the hydraulic pump 30a and the maximum load pressure P _LM1 and determines the differential pressure ΔPLS.
A drive signal according to LS is given to the first ejection amount control means 31a. The discharge amount control means 31a controls the displacement of the hydraulic pump 30a according to the drive signal. As a result, in the circuit belonging to the hydraulic pump 30a, the discharge pressure P
Load sensing control is performed in which _S1 is larger than the maximum load pressure P _LM1 of the load pressure of the actuator driven by the pressure oil discharged from the hydraulic pump 30a by the differential pressure ΔPLS.

Similarly, the maximum load pressure of the load pressures of the actuators belonging to the hydraulic pump 30b is detected by the second maximum load pressure detection circuit 34b, and is given to the second differential pressure detection device 32b as the pressure P _LM2 . To be The second differential pressure detection device 32b is provided with a discharge pressure P of the hydraulic pump 30b.
The differential pressure ΔPLS between _S2 and the maximum load pressure P _LM2 is obtained, and a drive signal corresponding to this differential pressure ΔPLS is given to the second discharge amount control means 31b. The discharge amount control means 31b controls the displacement of the hydraulic pump 30b according to the drive signal. As a result, in the circuit belonging to the hydraulic pump 30b,
Load sensing control is performed in which the discharge pressure P _S2 is larger than the maximum load pressure P _LM2 of the load pressure of the actuator driven by the pressure oil discharged from the hydraulic pump 30a by the differential pressure ΔPLS.

The electromagnetic switching valve 33 described above connects the hydraulic pump 30b to the right traveling directional control valve 6 and cuts off the connection between the hydraulic pump 30a and the right traveling directional control valve 6; The pump 30a has a right position that connects the right traveling directional control valve 6 and cuts off the connection between the hydraulic pump 30b and the right traveling directional control valve 6, and is not shown due to the switching to the left position. A switching position that guides the load pressure of the right traveling motor to the second maximum load pressure detection circuit 34b, and the load pressure of the right traveling motor (not shown) to the first maximum load pressure detection circuit 34a in association with the switching to the right position. And a switching position for guiding. The electromagnetic switching valve 33 is switched to the left position shown in FIG. 1 when the direction control valves 7 to 11 are not operated, and to the right position when the direction control valves 7 to 11 are operated.

Here, the variable pressure difference pressure compensating valve 20 described above is used.
a, 20b, 20c, 20d, 20e, 20f characteristics and constant differential pressure pressure compensating valves 21a, 21b, 21c, 21
The characteristics of d and 21e will be described with reference to FIGS.

As mentioned above, the constant pressure difference pressure compensating valve 21
a to 21e control the differential pressure across the directional control valves 7 to 11 to be constant.

On the other hand, the variable differential pressure compensating valves 20a ...
20f is suitable for load sensing system, and each directional control valve 1
Load sensing differential pressure ΔPLS (= discharging pressure _PS1 of hydraulic pump 30a-maximum load pressure _PLM1 )
Control to match. That is, the hydraulic pump 3
When the sum total of the required flow rates of the actuators belonging to 0a increases and the discharge pressure P _S1 of the hydraulic pump 30a decreases, the differential pressure ΔPLS decreases, but at this time, the variable differential pressure compensating valves 20a to 20f correspond. Each directional control valve 1 to 6
The pressure difference between the front and rear is reduced so as to match the reduced pressure difference ΔPLS, whereby the flow rate passing through the corresponding directional control valves 1 to 6 is reduced and saturation is prevented.

The constant differential pressure pressure compensating valves 21a to 21e simply keep the differential pressure constant, and therefore the above-mentioned differential pressure ΔP.
When the change in LS cannot be dealt with and the total sum of the required flow rates of the actuators belonging to the hydraulic pump 30b increases, a saturated state is reached.

That is, the variable differential pressure compensating valves 20a-2
When the actuators controlled by the directional control valves 1 to 6 attached with 0f are combinedly driven, the discharge flow rate of the hydraulic pump 30a is completely diverted to the corresponding combinedly driven actuators. In this case, the flow rate supplied to the high-pressure actuator Q _H, the flow rate supplied to the low pressure side actuator Q _L, the opening area A _H of the directional control valve for controlling the driving of the high pressure side actuator, driving the low-pressure side actuator the opening area of the directional control valve for controlling the a _L, the proportionality constant and xi], a _{Q H = ξ · a H √} (ΔPLS) (1) Q L = ξ · a L √ (ΔPLS) (2) . That is, as shown in FIG. 2, the sum of the required flow rate Q _HO of the high-pressure side actuator and the required flow rate Q _LO of the low-pressure side actuator is P− as indicated by point P at a predetermined load sensing differential pressure setting value ΔPLSO. If it is larger than the Q curve, the load sensing differential pressure ΔPLS
Decreased, the flow rate Q _L supplied flow rate Q _H is supplied to the high pressure side actuator and the low pressure side actuator accordingly, reduced as shown in the above (1) (2), automatically P -Settle at the stable point Q on the Q line. In contrast,
During combined driving of the actuators controlled by the constant pressure difference pressure compensation valves 21a to 21e, as shown in FIG. 3, the discharge pressure P _S2 of the hydraulic pump 30b decreases from the virtual operating point P and balances at the point R. . This constant differential pressure pressure compensation valve 21
In the case of a~21e _{is, Q H = ξ · A H} √ (ΔPLSO) (3) Q L = because it is _{ξ · A L √ (ΔPLSO)} (4), the flow rate Q supplied to the high-pressure actuator
_H, the flow rate Q _L is supplied to the low pressure side actuator is essentially unchanged. However, in reality, as shown in FIG. 3, the flow rate Q _H supplied to the high-pressure side actuator decreases from point S to point T due to the influence of saturation, while the flow rate Q _H supplied to the low-pressure side actuator is reduced. _L keeps a constant value.

In this way, the variable differential pressure compensating valves 20a ...
When the actuators controlled by the directional control valves 1 to 6 attached with 20f are combinedly driven, the pressure oil of the hydraulic pump 30a is completely divided and supplied to each of the corresponding actuators, and the discharge pressure P _{S1 of the} hydraulic pump 30a is supplied. Is held up to high pressure. Therefore, the driving of the low-voltage side actuator is not sacrificed, but the high-voltage side actuator can be driven well. On the other hand, the directional control valve 7 having the constant pressure difference pressure compensating valves 21a to 21e attached thereto
When the actuators controlled by 9 to 9 are combinedly driven, the actuators are not divided completely, but the low-voltage side actuators can be driven well.
Although not shown in FIG. 1, the directional control valve to which the variable differential pressure compensating valve is attached and the directional control valve to which the constant differential pressure compensating valve is attached are simultaneously operated to operate the corresponding actuator. When the combined drive is performed, good drive of the actuator controlled by the directional control valve to which the constant differential pressure compensating valve is attached is compensated regardless of the magnitude relationship of the load pressure.

In the first embodiment shown in FIG. 1, the functions of the constant differential pressure compensating valves 21a to 21e, the functions of the variable differential pressure compensating valves 20a to 20f, and the various operations carried out by the hydraulic excavator are described. In consideration of
The attachment actuators, bucket cylinders, arm cylinders, boom cylinders, left traveling motors (not shown) belonging to 0a and variable differential pressure compensation valves 20a to 20e for compensating good driving of the high-pressure side actuator are set to be combined, A swing motor, a boom cylinder, an arm cylinder, a bucket cylinder, and an attachment cylinder (not shown) belonging to the hydraulic pump 30b,
It is set so as to be combined with the constant differential pressure compensating valves 21a to 21e for compensating good driving of the low-pressure side actuator, and in consideration of traveling alone driving, and traveling and combined driving of other booms, arms, etc., The variable differential pressure compensating valve 20f and the right traveling motor (not shown) connectable to both the hydraulic pump 30a and the hydraulic pump 30b via the electromagnetic switching valve 33 are set to be combined.

In the embodiment constructed as described above, the electromagnetic switching valve 33 is kept in the state shown in FIG. 1 during the traveling alone operation, so that the hydraulic fluid of the hydraulic pump 30a is controlled to the left traveling direction. The pressure oil of the hydraulic pump 30b is supplied to the valve 5 and the variable differential pressure compensating valve 20e, and the right traveling directional control valve 6 is provided.
The variable differential pressure is supplied to the pressure compensating valve 20f, so that it is supplied to both the left traveling motor and the right traveling motor (not shown),
The desired traveling alone can be realized. At this time, the load pressure of the left traveling motor is set as the maximum load pressure P _LM1 via the first maximum load pressure detection circuit 34a and the variable differential pressure compensating valve 2
0e pressure chamber and the first differential pressure detection device 32a, and the variable differential pressure pressure compensating valve 20e causes the differential pressure across the left traveling direction control valve 5 to change to the discharge pressure P of the hydraulic pump 30a.
The pressure is controlled to be a differential pressure between _S1 and the load pressure of the left traveling motor (maximum load pressure P _LM1 ), and the first discharge amount is determined according to the signal output from the first differential pressure detection device 32a. The control means 31a controls the flow rate of the hydraulic pump 30a so that the discharge pressure P _S1 of the hydraulic pump 30a becomes higher than the maximum load pressure P _LM1 by ΔPLS. Similarly, the load pressure of the right traveling motor is set as the maximum load pressure P _LM2 via the second maximum load pressure detection circuit 34b, and the variable differential pressure compensating valve 20.
the pressure chamber of f, given to each of the second differential pressure detecting device 32b, the discharge pressure of the differential pressure across the hydraulic pump 30b of the right travel directional control valve 6 by the variable differential pressure pressure compensating valve 20f P _S2
And the right traveling motor are controlled to have a load pressure (maximum load pressure P _LM2 ), and according to a signal output from the second differential pressure detection device 32 b, the second discharge amount control means 31.
b is the hydraulic pump 3 so that the discharge pressure P _S2 of the hydraulic pump 30b is higher than the maximum load pressure P _LM2 by ΔPLS.
Control the flow rate of 0b.

Further, when the high pressure side actuator and the low pressure side actuator having different load pressures are combinedly driven, for example, the combined drive of the boom cylinder forming the high pressure side actuator and the arm cylinder forming the low pressure side actuator is intended. When the control valves 3 and 4 and the directional control valves 8 and 9 are operated, first, the electromagnetic switching valve 33 is switched to the right position in accordance with the operation of the directional control valves 8 and 9. As a result, the directional control valve 6 that controls the drive of the right traveling motor is connected to the hydraulic pump 30a.

At this time, the variable differential pressure compensating valves 20c and 20d attached to each of the directional control valves 3 and 4 and the first differential pressure detecting device 32a have a maximum load pressure of the boom cylinder on the high pressure side. The load pressure P _LM1 is given via the first maximum load pressure detection circuit 34a, and the first discharge amount control means 31a causes the discharge pressure P _S1 of the hydraulic pump 30a to be larger than the maximum load pressure P _LM1 by ΔPLS. The variable differential pressure compensating valves 20c and 20d control the differential pressure across the directional control valves 3 and 4 to control the flow rate of the hydraulic pump 30a and the discharge pressure P _S1 and the maximum load pressure P of the hydraulic pump 30a.
The difference from _LM1 is controlled, that is, ΔPLS, which is a changeable differential pressure. As a result, the pressure oil discharged from the hydraulic pump 30a is completely shunted to each of the direction control valves 3 and 4, and particularly good driving of the boom cylinder, which is a high-pressure actuator, is also compensated. On the other hand, the constant pressure difference pressure compensating valves 21b, 21 attached to the directional control valves 8, 9
c and the second differential pressure detection device 32b, the load pressure of the boom cylinder on the high pressure side is given as the maximum load pressure P _LM2 via the second maximum load pressure detection circuit 34b, and the second discharge amount control is performed. The means 31b controls the flow rate of the hydraulic pump 30a such that the discharge pressure P _S2 of the hydraulic pump 30b becomes larger than the maximum load pressure P _{LM 2} by ΔPLS, and the constant differential pressure compensating valves 21b and 21c discharge the pressure. Pressure P
Regardless of the change in differential pressure between _S2 and maximum load pressure P _{LM 2} ,
The differential pressure across the directional control valves 8 and 9 is controlled to be a constant differential pressure ΔPLSO set in advance. This allows
The pressure oil discharged from the hydraulic pump 30b is the directional control valve 8,
Although divided into 9, the constant pressure difference pressure compensating valves 21b, 2
By providing 1c, good driving of the arm cylinder, especially on the low pressure side, is compensated. By combining these operations, excellent combined drive of both the boom cylinder, which is the high-pressure side actuator, and the arm cylinder, which is the low-pressure side actuator, can be realized.

Further, when the direction control valves 5 and 6 are operated with the intention of the combined drive in which the traveling is further performed during the combined drive of the boom and the arm as described above, the combined drive of the boom cylinder and the arm cylinder is performed, and The pressure oil of the hydraulic pump 30a is supplied to both the left traveling motor and the right traveling motor via the left traveling directional control valve 5 and the right traveling directional control valve 6,
The load pressure of these left traveling motor and right traveling motor is also the first
Of the maximum load pressure detection circuit 34a. As for the downstream pressures of the left traveling directional control valve 5 and the right traveling directional control valve 6, the maximum load pressure P _LM1 detected by the first maximum load pressure detection circuit 34a is applied to the variable differential pressure compensating valves 20e, 20f. Controlled by If the load pressure of the left drive motor and the right drive motor is maximum, the load pressure is the first
_{Is the} maximum load pressure P _LM1 detected by the maximum load pressure detection circuit 34a. In this way, the combined drive of the boom, the arm and the traveling can be realized. The composite drive of other actuators can be performed in the same manner as above.

In the first embodiment constructed as described above, the pressure compensation valves on the actuator side belonging to the hydraulic pump 30a are variable differential pressure pressure compensation valves 20a to 20f, and the pressure compensation valves on the actuator side belonging to the hydraulic pump 30b are arranged. By using the constant pressure difference pressure compensating valves 21a to 21e, as described above, when compound driving of a plurality of actuators having different load pressures is performed, good compound driving of the corresponding actuator is realized without requiring any metering adjustment. It is possible to obtain good workability.

FIG. 4 is a circuit diagram showing the configuration of the second embodiment of the present invention. This second embodiment also corresponds to claims 1 and 2. The second embodiment is functionally equivalent to the first embodiment described above, but the directional control valve block is different in form. That is, in the above-described first embodiment, the directional control valves 1 to 5 belonging to the hydraulic pump 30a are included in one control valve, and these directional control valves 1 to 5 are operated by one spool, and the hydraulic pump is operated. 30b
The directional control valves 6 to 11 belonging to 1) are included in another one control valve, and these directional control valves 6 to 11 are included in the other 1 control valve.
Although it is structured to operate with a spool of books, in the second embodiment shown in FIG. 4, each directional control valve 1a, 2a, 3a,
4a, 5, 6, and 7 are included in one control valve, and the whole structure is operated by one spool.
Each of the attachment direction control valve 1a, the bucket direction control valve 2a, the arm direction control valve 3a, and the boom direction control valve 4a is configured to include two direction control valves. Variable differential pressure compensating valves 20a, 20b, 20c, 2 are provided on one side of each of the directional control valves.
The corresponding one of 0d is attached, and the corresponding one of the constant differential pressure compensating valves 21e, 21d, 21c, 21b is attached to the other.

In the second embodiment constructed as described above, the same operational effects as those in the first embodiment described above are obtained, and in addition to the two hydraulic pumps 30a, 30b, the spool is installed. Since only one valve is provided, the overall shape of the control valve including each directional control valve can be made compact.

FIG. 5 is a circuit diagram showing a third embodiment of the present invention. The third embodiment corresponds to claims 5 and 6. This third embodiment is similar to the second embodiment shown in FIG.
In the same manner as in the second embodiment, only one spool is provided for the two hydraulic pumps 30a and 30b, and the constant differential pressure / pressure compensation valve 21b in the second embodiment described above is used.
21c, 21d, 21e instead of the pressure compensation valve 100,
101, 102, 103 are provided, and these pressure compensating valves 100 to 103 can be changed from the variable differential pressure pressure compensating valve to the constant differential pressure pressure compensating valve, or can be changed from the constant differential pressure pressure compensating valve to the variable differential pressure pressure. The pressure compensating valve that can be changed to the compensating valve is used. Then, the electromagnetic switching valve 9 is provided in the pressure chamber to which the pressure for operating the valve element of each pressure compensation valve 100 to 103 is introduced.
0, 91, 92, 93 are connected to each other, and these electromagnetic switching valves 90 to 93 generate a pressure ΔP _E according to the calculated value calculated by the adder 40.
Connected to. In addition, the adder 40 uses the load sensing set differential pressure ΔPLS output from a command device (not shown).
The calculation for obtaining the difference between O and ΔPLS which is the actual load sensing differential pressure detected by the second differential pressure detecting device 32b is performed. That is, the pressure ΔP _E described above is equal to ΔPL
Corresponds to SO-ΔPLS.

FIG. 6 is a diagram illustrating the structure of the switching means provided in the third embodiment shown in FIG. 5, for example, the vicinity of the electromagnetic switching valves 90 and 91. In FIG. 6, 60 is a spool, and 3a and 4a are the arm directional control valve and the boom directional control valve shown in FIG. 5, respectively. 3A is an arm cylinder controlled by the arm directional control valve 3a, 9
Reference numerals 0, 91, 100, and 101 denote the electromagnetic switching valve, the electromagnetic switching valve, the pressure compensation valve, and the pressure compensation valve shown in FIG. 5, respectively. Of these, the pressure compensating valve 100 is connected to a valve body 100a and a second maximum load pressure detection circuit 34b (not shown), and is connected to a back pressure chamber 100b to which the maximum load pressure P _LM2 is introduced and an electromagnetic switching valve 90. Equipped with a pressure chamber 100c
Similarly, the pressure compensating valve 101 is connected to the valve body 101a and a second maximum load pressure detection circuit 34b (not shown), and is connected to the back pressure chamber 101b to which the maximum load pressure P _LM2 is introduced and the electromagnetic switching valve 91. The pressure chamber 101c is provided. In FIG. 5, P _Z1 and P _Z2 represent the downstream pressures of the directional control valves 4a and 3a, respectively.

When the electromagnetic switching valves 90 and 91 are kept in the upper position as shown in FIG. 6, the pressure ΔP _E from the pressure generator 80 is the pressure chamber 100 of the pressure compensating valves 100 and 101.
The pressure compensating valves 100 and 101, which are not applied to the hydraulic pressure pumps c and 101c, determine the differential pressure across the directional control valves 4a and 3a as the discharge pressure P _S2 of the hydraulic pump 30b and the maximum load pressure P.
_It functions as a variable differential pressure compensating valve that controls the pressure difference ΔPLS with _LM2 .

In such a state, when the load sensing set differential pressure ΔPLSO is output from the command device (not shown) and, for example, the electromagnetic switching valve 90 is switched to the lower position in FIG. 6, the pressure generator shown in FIG. The pressure ΔP _E generated at 80 is introduced into the pressure chamber 100c of the pressure compensation valve 100. Here, the pressure receiving area of the back pressure chamber 100b and the pressure chamber 100
Assuming that the pressure receiving area of c is set to be equal, P _Z1 = P _LM2 −ΔP _E = P _LM2 − (ΔPLSO −ΔPLS) = P _LM2 −ΔPLSO + P _S2 −P _LM2 = P _S2 −ΔPLSO, and the direction control is performed. The differential pressure across the valve 4a becomes P _S2 −P _Z1 = ΔPLSO, and the pressure compensating valve 100 is changed from the variable differential pressure compensating valve to the constant differential pressure compensating valve.

Another pressure compensation valve 101, 10 shown in FIG.
Similarly for 2 and 103, the variable differential pressure compensating valve can be changed to the constant differential pressure compensating valve or the constant differential pressure compensating valve to the variable differential pressure compensating valve.

In the third embodiment thus constructed, the pressure compensating valves 100, 1 are switched by switching the electromagnetic switching valves 90, 91, 92, 93 from the positions shown in FIG.
01, 102, 103 are constant pressure difference pressure compensating valves, and have the same effect as the second embodiment.

By setting any one of the electromagnetic switching valves 90 to 93 to the state shown in FIG. 5, the corresponding one of the pressure compensating valves 100 to 103 is made a variable differential pressure compensating valve. Therefore, if you want to implement a work mode in which the high-voltage side actuator and low-voltage side actuator are reversed, you can easily deal with the parts without changing the already assembled circuit structure. it can.

FIG. 7 is a circuit diagram showing the configuration of the fourth embodiment of the present invention. The fourth embodiment corresponds to claims 1 and 3.

In the fourth embodiment, as in the first embodiment described above, the hydraulic pump 30a includes a directional control valve for attachment 1, a directional control valve for bucket 2, a directional control valve for arm 3 and a directional control valve for boom. Control valve 4, left traveling directional control valve 5,
And the right running directional control valve 6 are connected to each other, and variable differential pressure compensating valves 20a to 20f are provided as pressure compensating valves for controlling the differential pressure across the directional control valves 1 to 6, respectively. Further, the hydraulic pump 30b includes the right traveling directional control valve 6, the turning directional control valve 7, the boom directional control valve 8, the arm directional control valve 9, and the bucket directional control valve 1 described above.
0, the directional control valve 11 for attachment is connected, and constant differential pressure pressure compensating valves 21a to 21e are provided as pressure compensating valves for controlling the differential pressure across the directional control valves 7 to 11, respectively. Further, an electromagnetic switching valve 33 that selectively connects the hydraulic pumps 30a and 30b and the right traveling directional control valve 6 is provided, and the first discharge amount control means 31a that controls the discharge amount of the hydraulic pump 30a and the hydraulic pressure. Second discharge amount control means 31b for controlling the discharge amount of the pump 30b is provided.

In the fourth embodiment, the above-mentioned first
Is different from the embodiment described above in that the center bypass passage 30A connected to the discharge pipe of the hydraulic pump 30a and the hydraulic pump 30
It has a center bypass passage 30B connected to the discharge pipe line b, and the hydraulic system is formed in a center bypass system. Then, the center bypass passages 30A, 3
0B is the center bypass passage 30
Flow rate detection means 33 for detecting the flow rate flowing through A and 30B
a and 33b are provided. These flow rate detecting means 33
Signals corresponding to the flow rates detected by a and 33b are given to the output means 32A and 32B. These output means 33
A and 33B output a pump displacement command signal, which is substantially inversely proportional to the signal given from the flow rate detection means 33a and 33b, to the discharge amount control means 31a and 31b, respectively. Therefore, the discharge amount control means 31a, 31b control these hydraulic pumps 30a, 30b so that the hydraulic pumps 30a, 30b discharge a flow rate that is substantially inversely proportional to the flow rate in the center bypass passages 30A, 30B. .

Even in the fourth embodiment having the above-described structure, as in the case of the first embodiment described above, excellent composite drive of each actuator can be performed without the need for adjusting the metering. , Good workability can be obtained. Further, since it is formed in the center bypass system, it is not necessary to consider a complicated combination of tandem and parallel circuits for performing the combined drive of the actuators, and the circuit configuration can be relatively simplified from this viewpoint.

FIG. 8 is a circuit diagram showing the configuration of the fifth embodiment of the present invention. The fifth embodiment corresponds to claims 5 and 7.

The fifth embodiment is set to the center bypass system like the fourth embodiment shown in FIG. 7, and the directional control valves 1 to 11 and the center bypass passage 30 are provided.
A, 30B, flow rate detection means 33a, 33b, output means 3
2A, 32B and variable differential pressure compensating valves 20a-20f. However, unlike the fourth embodiment, the pressure compensating valve for controlling the differential pressure across the directional control valve 7 is composed of the variable differential pressure compensating valve 7a, and the directional control valves 8-1.
The pressure compensating valve for controlling the differential pressure between the front and rear is pressure that can be changed from the variable differential pressure compensating valve to the constant differential pressure compensating valve, or from the constant differential pressure compensating valve to the variable differential pressure compensating valve. It consists of compensating valves 100-103. Accordingly, the electromagnetic switching valves 90 to 93, the pressure generator 80, and the adder 4 which are the same as those in the third embodiment shown in FIG.
0, a differential pressure detector 32b is provided. The differential pressure detector 32b is _supplied with the maximum load pressure P _LM2 for detecting the maximum load pressure of the actuators belonging to the hydraulic pump 30b together with the discharge pressure P _S2 of the hydraulic pump 30b.

With this structure, the same effect as that of the above-described fourth embodiment is obtained, and the same effect as that of the above-mentioned third embodiment is also obtained. That is, when it is desired to perform a work mode in which the high-voltage side actuator and the low-voltage side actuator are reversed, it is possible to easily cope with the operation without replacing the already assembled circuit structure parts.

FIG. 9 is a circuit diagram showing the configuration of the sixth embodiment of the present invention. The sixth embodiment corresponds to claims 5 and 8.

The sixth embodiment is formed in the closed center system, whereas the fifth embodiment is formed in the center bypass system. Then, the operation amount detecting means 110a for outputting an operation amount signal according to the operation amount of the operation lever for operating the directional control valves 1 to 6, and the directional control valves 6 to.
Operation amount detection means 110b for outputting an operation amount signal corresponding to the operation amount of the operation lever for operating 11, and a pump tilt command signal substantially proportional to the operation amount signals output from these operation amount detection means 110a, 110b. Discharge amount control means 3
Output means 111a and 111b for outputting to 1a and 31b are provided. Therefore, the discharge amount control means 31a, 31
The b controls the hydraulic pumps 30a and 30b so that the hydraulic pumps 30a and 30b each discharge a flow rate that is substantially proportional to the operation amount of the operation lever described above. The other structure is almost the same as that of the fifth embodiment described above.

In the sixth embodiment having the above-mentioned structure, similar to the first embodiment, good composite driving of the actuator can be performed, and good workability can be obtained. Similar to the fifth embodiment, the working mode in which the high-pressure side actuator and the low-voltage side actuator are reversed can be easily dealt with, and the pressure associated with the load sensing system as in the first embodiment described above can be easily applied. Since it is not necessary to consider stabilization of the servo system, the circuit configuration can be simplified as compared with the first embodiment.

Incidentally, as in the first embodiment shown in FIG.
The pressure compensation valve on the hydraulic pump 30a side is a variable differential pressure compensation valve, the pressure compensation valve on the hydraulic pump 30b side is a constant differential pressure compensation valve, and the closed center system is used. As described above, each hydraulic pump 30a is operated in accordance with the operation amount of the operation lever of the directional control valve,
It can also be configured to control the discharge amount of 30b.

[0054]

Since the present invention is configured as described above, when compound driving of a plurality of actuators having different load pressures is performed, good compound driving of the corresponding actuator is realized without any adjustment of metering. Therefore, good workability can be surely obtained without requiring labor and complexity associated with the adjustment of the metering.

Further, in the invention described in claim 5, in particular, in addition to the above-described action and effect, it is desired to carry out a working mode in which the high-voltage side actuator and the low-voltage side actuator are reversed. In addition, it is possible to easily cope with the circuit structure that has already been assembled, without requiring replacement work.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a pressure-flow rate characteristic of a system including a variable differential pressure compensating valve provided in the embodiment shown in FIG.

FIG. 3 is a diagram showing a pressure-flow rate characteristic of a system including a constant differential pressure compensating valve provided in the embodiment shown in FIG.

FIG. 4 is a circuit diagram showing a configuration of a second exemplary embodiment of the present invention.

FIG. 5 is a circuit diagram showing a configuration of a third exemplary embodiment of the present invention.

FIG. 6 is a switching means for switching from the variable differential pressure compensating valve provided in the third embodiment shown in FIG. 5 to the constant differential pressure compensating valve, or from the constant differential pressure compensating valve to the variable differential pressure compensating valve. It is a figure which shows an example.

FIG. 7 is a circuit diagram showing a configuration of a fourth exemplary embodiment of the present invention.

FIG. 8 is a circuit diagram showing a configuration of a fifth exemplary embodiment of the present invention.

FIG. 9 is a circuit diagram showing a configuration of a sixth exemplary embodiment of the present invention.

[Explanation of symbols]

 1 Directional Control Valve for Attachment 1a Directional Control Valve for Attachment 2 Directional Control Valve for Bucket 2a Directional Control Valve for Bucket 3 Directional Control Valve for Arm 3a Directional Control Valve for Arm 3A Arm Cylinder 4 Directional Control Valve for Boom 4a Directional Control Valve for Boom Valve 5 Left traveling directional control valve 6 Right traveling directional control valve 7 Swing directional control valve 7a Swing variable differential pressure pressure compensating valve 8 Boom directional control valve 9 Arm directional control valve 10 Bucket directional control valve 11 Attachment Directional control valve 20a Attachment variable differential pressure compensating valve 20b Bucket variable differential pressure compensating valve 20c Arm variable differential pressure compensating valve 20d Boom variable differential pressure compensating valve 20e Left traveling variable differential pressure compensating valve 20f Variable differential pressure compensating valve for right traveling 21a Constant differential pressure compensating valve for turning 21b Boom one Constant differential pressure compensating valve 21c Constant differential pressure compensating valve for arm 21d Constant differential pressure compensating valve for bucket 21e Constant differential pressure compensating valve for attachment 30A Center bypass passage 30B Center bypass passage 30a First variable displacement hydraulic pump 30b Second variable displacement hydraulic pump 31a First discharge amount control means 31b Second discharge amount control means 32A Output means 32B Output means 32a First differential pressure detection device 32b Second differential pressure detection device 33 Electromagnetic switching valve 33a Flow rate detection means 33b Flow rate detection means 34a First maximum load pressure detection circuit 34b Second maximum load pressure detection circuit 40 Adder 60 Spool 80 Pressure generator 90 Electromagnetic switching valve 91 Electromagnetic switching valve 92 Electromagnetic switching valve 93 Electromagnetic switching valve 100 pressure compensation valve 101 pressure compensation valve 102 pressure compensation valve 103 pressure compensation valve 100a valve body 100b back pressure chamber 100c pressure chamber 101a valve body 101b back pressure chamber 101c pressure chamber 110a operation amount detection means 110b operation amount detection means 111a output means 111b output means

Claims (8)

[Claims] 1. A hydraulic pump, a plurality of actuators driven by pressure oil discharged from the hydraulic pump, and pressures provided corresponding to the actuators and supplied from the hydraulic pump to the actuators. A plurality of directional control valves that control the flow of oil, and a plurality of pressures that are attached to these directional control valves and that control the differential pressure across the directional control valve, which is the differential pressure between the upstream pressure and the downstream pressure. In the drive circuit of the hydraulic working machine, which is provided with a compensating valve and is controlled so that the discharge pressure of the hydraulic pump is higher than the load pressure of the actuator by a constant pressure, any one of the plurality of pressure compensating valves is provided. , A constant differential pressure pressure compensating valve that constantly controls the differential pressure across the directional control valve to be constant, and other ones of the plurality of pressure compensating valves are applicable. A differential differential pressure compensating valve that can be controlled to match the differential pressure across the directional control valve to the differential pressure between the discharge pressure of the hydraulic pump and the maximum load pressure of the load pressure of the actuator. The drive circuit of the characteristic hydraulic working machine. 2. A differential pressure detecting device for detecting the differential pressure between the discharge pressure of the hydraulic pump and the maximum load pressure, and a discharge for controlling the discharge amount of the hydraulic pump according to the differential pressure detected by this differential pressure detecting device. A drive circuit for a hydraulic working machine according to claim 1, further comprising: an amount control means. 3. A center bypass passage connected to a discharge pipe of a hydraulic pump, a flow rate detecting means for detecting a flow rate flowing through the center bypass passage, and a pump tilt according to a signal output from the flow rate detecting means. The output means for outputting a command signal, and the discharge amount control means for controlling the discharge amount of the hydraulic pump according to the pump displacement command signal output from this output means are provided. Drive circuit for hydraulic working machine. 4. An operation amount detecting means for setting a closed center system and outputting an operation amount of an operation lever for operating a directional control valve, and a pump tilt according to an operation amount signal output from the operation amount detecting means. The output means for outputting a rotation command signal, and the discharge amount control means for controlling the discharge amount of the hydraulic pump according to the pump displacement command signal output from the output means are provided. Drive circuit of the hydraulic working machine. 5. A hydraulic pump, a plurality of actuators driven by pressure oil discharged from the hydraulic pump, and pressures provided corresponding to the actuators and supplied from the hydraulic pump to the actuators. A plurality of directional control valves that control the flow of oil, and a plurality of pressures that are attached to these directional control valves and that control the differential pressure across the directional control valve, which is the differential pressure between the upstream pressure and the downstream pressure. In a drive circuit of a hydraulic working machine that is provided with a compensating valve and is controlled so that the discharge pressure of the hydraulic pump is higher than the load pressure of the actuator by a constant pressure, the pressure compensating valve responds to a predetermined external signal. The corresponding differential pressure across the directional control valve to the differential pressure between the discharge pressure of the hydraulic pump and the maximum load pressure of the actuator load pressures. Can be changed to a constant differential pressure pressure compensating valve that constantly controls the differential pressure across the corresponding directional control valve, or a constant differential pressure variable compensating valve A drive circuit for a hydraulic working machine, comprising a pressure compensation valve that can be changed to the pressure compensation valve. 6. A differential pressure detecting device for detecting a differential pressure between a discharge pressure of a hydraulic pump and a maximum load pressure, and a discharge for controlling a discharge amount of the hydraulic pump according to the differential pressure detected by the differential pressure detecting device. A drive circuit for a hydraulic working machine according to claim 5, further comprising: an amount control means. 7. A center bypass passage connected to a discharge conduit of a hydraulic pump, a flow rate detecting means for detecting a flow rate flowing through the center bypass passage, and a pump tilt according to a signal output from the flow rate detecting means. The output means for outputting a command signal, and the discharge amount control means for controlling the discharge amount of the hydraulic pump in accordance with the pump displacement command signal output from this output means are provided. Drive circuit for hydraulic working machine. 8. An operation amount detecting means for setting a closed center system and outputting an operation amount of an operation lever for operating a directional control valve, and a pump tilt according to an operation amount signal output from the operation amount detecting means. The output means for outputting a rotation command signal, and the discharge amount control means for controlling the discharge amount of the hydraulic pump according to the pump displacement command signal output from this output means are provided. Drive circuit of the hydraulic working machine.