The present invention relates to a pressure compensating valve, an unloading pressure control valve, and a hydraulically operated device.
FIG. 25 depicts a hydraulically operated device described in Japanese Unexamined Patent Application 1-247805.
In this hydraulically operated device, a variable delivery pump A is connected to a low pressure hydraulic cylinder D via a pressure compensating valve B and a directional control valve (operating valve) C. The pump A is also connected to a high pressure cylinder Dxe2x80x2 via a pressure compensating valve Bxe2x80x2 and a directional control valve Cxe2x80x2.
An actuator E for changing the displacement volume and a flow regulating valve F for controlling the actuator E are attached to the hydraulic pump A.
The higher load pressure among the load pressures that are produced during the operation of the cylinders D and Dxe2x80x2 is sensed by a shuttle valve G as the maximum load pressure PLS, and this maximum load pressure PLS is output as the pilot pressure to the flow regulating valve F.
The flow regulating valve F controls the actuator E so that the discharge pressure PP of the pump A is always greater than the maximum load pressure PLS.
The cylinders D and Dxe2x80x2 are jointly operated by the simultaneous operation of directional control valves C and Cxe2x80x2 in the hydraulically operated device. At this time, the pressure compensating valve B controls the amount of oil supplied to the cylinder D so that the difference between the input pressure and the output pressure of the directional control valve C is constant, and the pressure compensating valve Bxe2x80x2 similarly controls the amount of oil supplied to the cylinder Dxe2x80x2 so that the difference between the input pressure and the output pressure of the directional control valve Cxe2x80x2 is constant.
The hydraulically operated device equipped with the pressure compensating valves B and Bxe2x80x2 can prevent the disadvantage of pressured oil accumulating and being supplied to the cylinder with the lighter load among the operating valve cylinders D and Dxe2x80x2.
According to the aforementioned Japanese Unexamined Patent Application 1-247805, however, the discharge pressure of pump A decreases upon the supply of large amounts of pressured oil to the hydraulic cylinder D with the lower pressure during periods of considerable control input to the directional control valves C and Cxe2x80x2. In such cases, the pressure difference before and after the pressure compensating valve B fails to reach the compensated pressure difference, and the pressure compensating valve B thus fails to achieve pressure compensation. That is, the pressure compensating valve B remains open.
While the pressure compensating valve B fails to achieve pressure compensation, the amount of pressured oil supplied to the hydraulic cylinder D with the lower pressure is uncontrolled, so no pressurized oil is supplied to the hydraulic cylinder Dxe2x80x2 with the higher pressure, and the hydraulic cylinder Dxe2x80x2 with the higher pressure is thus not operated. The operator must then operate the directional control valve C in the slightly open direction to control the flow rate to the hydraulic cylinder D with the lower pressure.
To prevent such a situation from developing, the aforementioned hydraulically operated device is provided with a pressure difference sensing device H for sensing the pressure difference PPxe2x88x92PLS between the pressure PP of the pressured oil discharged from the hydraulic pump A and the maximum load pressure PLS, a control force set device I for setting the control force fc based on the pressure difference PPxe2x88x92PLS and the relationship depicted in FIG. 26, and an electromagnetic valve J that is operated by means of the output signals from the control force setting device I.
The control force fc is given by the following equation.
fc=fxe2x88x92xcex1(PPxe2x88x92PLS)
Where f: the pressing force of springs b and bxe2x88x92 in pressure compensating valves B and Bxe2x80x2
xcex1: constant
The electromagnetic valve J allows pressured oil corresponding to the control force fc to act on the pressure receiving components of the pressure compensating valves B and Bxe2x80x2 when the pressure difference PPxe2x88x92PLS is at or below the specific pressure difference Pm shown in FIG. 26.
This allows the control force fc against the pressing force f of the aforementioned springs b and bxe2x88x92 to be exerted on the springs in the pressure compensating valves B and Bxe2x80x2. The force fc increases the discharge pressure of the pump A by increasing the flow resistance of the pressure compensating valves B and Bxe2x80x2, allowing pressured oil to be supplied to the hydraulic cylinder Dxe2x80x2 with the higher pressure.
When the cylinders D and Dxe2x80x2 are cylinders that operate an operating device in construction machinery (such as a hydraulic shovel boom, arm, or bucket), the pressure compensation characteristics of the pressure compensating valves B and Bxe2x80x2 are preferably modified in some cases to improve the operating characteristics, depending on the operating configuration of the aforementioned operating device.
A technique that is capable of changing the throttle levels for each pressure compensating valve and that is capable of suitably changing the pressure difference before and after the directional control valves C and Cxe2x80x2 has been disclosed in the aforementioned patent publication. That is, in this technique, electromagnetic valves J as described above are provided for the pressure compensating valves B and Bxe2x80x2, and the control force fc for the pressure compensating valves B and Bxe2x80x2 are individually adjusted by these electromagnetic valves J. Accordingly, the throttle levels of the pressure compensating valves B and Bxe2x80x2 are individually changed; that is, the pressure differences before and after the direction control valves C and Cxe2x80x2 are different from each other.
A state in which the required flow rate is distributed completely irrespective of load is also referred to in particular as a fully compensated state.
The conventional devices described above suffer from the following drawbacks, however.
In some cases, pressure compensation is not possible when the mechanism for producing control force fc to modify the pressure compensation characteristics malfunctions. Furthermore, the electromagnetic valves J are operated by computations after the pressure difference has been sensed by a pressure difference detector 21H, resulting in poor response.
In view of the foregoing, a first object of the present invention is to provide a pressure compensating valve that allows the pressure compensation characteristics to be arbitrarily modified, that has good response, and that is highly reliable.
FIG. 27 depicts a hydraulically operated device described in Japanese Unexamined Patent Application 4-250226. When the operating device A in this hydraulically operated device is operated, a flow regulating valve (operating valve) B is operated, by means of the pilot pressure produced by the operating device A, to an extent corresponding to the extent to which the operating device A has been operated, and the discharged pressured oil from a hydraulic pump D is consequently supplied to a hydraulic cylinder (hydraulic actuator) C.
A pressure compensating valve E for keeping the pressure difference before and after the flow regulating valve B at a constant level is located between the hydraulic pump D and the flow regulating valve (operating valve) B.
An operating device Axe2x80x2, flow regulating valve (operating valve) Bxe2x80x2, hydraulic motor (hydraulic actuator) Cxe2x80x2, and pressure compensating valve Exe2x80x2 each correspond to the operating device A, flow regulating valve (operating valve) B, hydraulic cylinder C, and pressure compensating valve E.
An unloading pressure control valve F is connected in parallel to the hydraulic pump D. The higher pressure between the load pressure acting on the hydraulic cylinder C and the load pressure acting on the hydraulic motor Cxe2x80x2 is sensed as the maximum load pressure by a shuttle valve G, and this maximum load pressure is allowed to act on the unloading pressure control valve F.
The unloading pressure control valve F is provided to return the discharged oil from the hydraulic pump D to the tank. The amount of the aforementioned discharged oil returned by the unloading pressure control valve F is set by the difference between the maximum load pressure and the discharge pressure of the hydraulic pump D, and by control signals output from a control unit J.
A computer H connected to the control unit J computes the difference xcex94PLS between the discharge pressure of the hydraulic pump D and the load pressure of the hydraulic cylinder C or hydraulic motor Cxe2x80x2 based on the functional relation shown in FIG. 28 and the output of sensors a1, a2 and a1xe2x80x2, a2xe2x80x2 for sensing the control input of the operating devices A and Axe2x80x2.
The function shown in FIG. 28 defines a relation in which the pressure difference xcex94PLS increases proportionally until the control input St of the operating device A reaches a set value, and the pressure difference xcex94PLS stays at a value xcex94PLS1 when the control input St is at or beyond the set value.
When the control input St is 20%, for example, the pressure difference xcex94PLS is computed by the computer H, so a control signal corresponding to a pressure difference xcex94PLS2 is output from the control unit J, and the unloading start pressure of the unloading pressure control valve F is set to pressure difference xcex94PLS2. As a result, the amount of pressured oil supplied through the pressure compensating valve Exe2x80x2 and flow regulating valve Bxe2x80x2 to the hydraulic motor Cxe2x80x2 is the amount defined by the pressure difference xcex94PLS2.
FIG. 29 shows the relation between the amount of oil Q supplied to the hydraulic motor Cxe2x80x2 and the pressure difference xcex94P before and after the flow regulating valve Bxe2x80x2 when the control input St is 20%.
As shown in FIG. 29, the pressure compensating valve Exe2x80x2 supplies pressured oil in a constant oil amount q2 to the hydraulic motor Cxe2x80x2 so that the pressure difference xcex94P of the flow regulating valve Bxe2x80x2 is kept at a constant pressure difference xcex94Pc+xcex94PLS (xcex94PLS is the pressure loss of the pressure compensating valve Exe2x80x2). However, while the pressure difference xcex94P has not yet reached the constant pressure difference xcex94Pc+xcex94PLS (compensated pressure difference), the pressured oil is supplied to the hydraulic motor Cxe2x80x2 in the oil amount q1 defined by the unloading start pressure xcex94PLS2 of the unloading pressure control valve F.
Thus, according to this hydraulically operated device, when the control input of the operating device A is set to about 20% for moderate acceleration of the hydraulic motor Cxe2x80x2, the amount of oil supplied to the hydraulic motor Cxe2x80x2 is limited to the amount of oil q1 defined by the unloading start pressure xcex94PLS2, and the hydraulic motor Cxe2x80x2 is thus moderately accelerated.
Furthermore, in the case of the load sensing circuit of a variable delivery pump, when the unloading start pressure of the unloading pressure control valve F is pre-modified, the amount of pressured oil discharged from the hydraulic pump D is increased in advance. The response of the hydraulic cylinder C when operated by the operating unit A is thus better.
The unloading start pressure of the unloading pressure control valve F is variable. However, the unloading start pressure is set through the computer H and the control unit J. It is accordingly always set after the output from the sensors a1, a2 and a1xe2x80x2, a2xe2x80x2 of the operating devices A and Axe2x80x2, and a resulting problem is the poor response in terms of the hydraulic cylinder C or the hydraulic motor Cxe2x80x2. More specifically, when the fluctuations in the load pressure of the hydraulic cylinder C or hydraulic motor Cxe2x80x2 are estimated, the unloading start pressure is hopefully pre-modified rapidly irrespective of the control input of the operating devices A and Axe2x80x2. For the reasons described above, however, the unloading start pressure is difficult to modify in advance.
In view of the foregoing, a second object of the present invention is to provide an unloading pressure control valve allowing the unloading start pressure to be preset so as to improve the response in terms of a hydraulic actuator.
A pump discharge pressure control means for controlling the displacement volume of a hydraulic pump (discharge volume per revolution) is provided in a hydraulically operated device in which the pressured oil discharged from a variable delivery pump is supplied to a hydraulic actuator such as a hydraulic cylinder by the operation of an operating valve. This pump discharge pressure control means is designed so as to control the displacement volume of a hydraulic pump based on the discharge pressure of a hydraulic pump and the load pressure acting on a hydraulic actuator, so that the aforementioned discharge pressure is greater by a specific pressure than the aforementioned load pressure.
According to the hydraulically operated device equipped with the pump discharge pressure control means, when the load pressure is increased during the operation of the operating valve, the displacement volume of the hydraulic pump immediately increases to a magnitude corresponding to the load pressure. The actuator is also connected via a pressure compensating valve. A flow rate corresponding to the control input of the operating valve can thus be supplied, irrespective of the magnitude of the load pressure, to the actuator.
To be supplied at flow rate corresponding to the control input is, in other words, a matter of the action of pressure corresponding to the load. The control input of the operating valve at this time and certain actuator conditions sometimes result in rapid start up with shocks.
When the aforementioned hydraulic actuator is a hydraulic motor or cylinder driving an operating unit in construction machinery (such as the revolving superstructure, boom, arm, or bucket in the case of a hydraulic shovel, for example), the rapid start up of the aforementioned hydraulic actuator results in lower operating performance, depending on the operating configuration.
Hydraulically operated devices such as the following have been proposed in patent publications.
That is, in the hydraulically operated device proposed in Japanese Unexamined Patent Application 9-222101, for example, a bleed valve is connected to the discharge channel of the aforementioned hydraulic pump, and part of the pressured oil discharged by the hydraulic pump is bled through the bleed valve to the tank.
According to the hydraulically operated device described in this patent publication, the rapid start up of the hydraulic actuator is controlled, resulting in better operating performance.
However, the bleed valve used in the hydraulically operated device of the aforementioned patent publication bleeds off part of the pressured oil discharged from the hydraulic pump to the tank. In other words, a large amount of the pressured oil that is supposed to be supplied to the hydraulic actuator ends up being returned to the tank when bled off. This results in significant energy loss.
Other resulting problems are the need for large-scale machines because of the large amounts of pressured oil that are bled off, poor sensitivity, and difficulties in achieving high-precision control.
In view of the foregoing, a third object of the present invention is to provide a hydraulically operated device that allows energy loss to be minimized to control rapid start up of hydraulic actuators, and that also allows machinery to be made more compact and high-precision control to be achieved.
Another object of the present invention is to simultaneously achieve the first and second objects.
Still another object of the present invention is to simultaneously achieve the first and third objects.
Yet another object of the present invention is to simultaneously achieve the second and third objects.
And finally another object of the present invention is to simultaneously achieve the first, second, and third objects.
To achieve the first object, the first of the present inventions is a pressure compensating valve through which passes pressured oil that is fed from a hydraulic pump 1 to a hydraulic actuator 5, characterized by comprising a main valve 20 that is operated in such a way as to increase the area of the opening between an inlet port 24 and an outlet port 25 by means of pressure acting on a first pressure receiving component 21, that is also operated in such a way as to reduce the area of the opening by means of pressure acting on a second pressure receiving component 22 and pressure acting on a third pressure receiving component 23, and that is designed to allow the pressure Pa of the pressured oil flowing to the inlet port 24 to act on the first pressure receiving component 21 and the pressure Pb of the load 5 driven by the pressured oil flowing from the outlet port 25 to act on the second pressure receiving component 22; and control pressure producing means 7B for allowing control pressure Pe resulting from a reduction in the pressure Pa of the inlet port 24 to act on the third pressure receiving component 23.
The first invention allows the desired pressure compensation characteristics to be obtained by changing the control pressure Pe because the pressure compensation characteristics are changed according to the magnitude of the control pressure Pe.
Because the control pressure Pe resulting from a reduction in the pressure of the inlet port 24 is allowed to act on the third pressure receiving component 23 of the main valve 20, fluctuations in the control pressure Pe also correspond to fluctuations in the pressure of the inlet port 24. The pressure compensation characteristics are thus unaffected by the pressure fluctuation of the inlet port 24 of the main valve 20.
To achieve the second object described above, the second invention is an unloading pressure control valve for introducing discharged pressured oil from a hydraulic pump 1 to a tank according to the pressure difference between the discharge pressure PP of the hydraulic pump 1 and the load pressure PLS of a hydraulic actuator 5, characterized by comprising a main valve 100 that is constructed in such a way as to operate in the communicating direction by means of the discharge pressure PP of the hydraulic pump 1 acting on a first pressure receiving component 123, to operate in the cut-off direction upon load pressure PLS to a second pressure receiving component 124, and to change the balance of the operating force in each of the directions by means of control pressure Pg acting on a third pressure receiving component 125; and control pressure producing means 101 for producing the control pressure Pg.
The second invention allows the unloading start pressure to be set by means of the control pressure Pg acting on the third pressure receiving component 125. The control pressure Pg is produced by means of the control pressure producing means. Accordingly, the unloading start pressure can be preset by the control pressure producing means, and the amount of pressured oil discharged from the hydraulic pump 1 can be increased in advance to improve the response in terms of the hydraulic actuator 5.
To achieve the third object described above, the third invention is a hydraulically operated device comprising a plurality of hydraulic actuators 5 to which pressured oil discharged from a variable delivery pump 1 is supplied via pressure compensating valves 7 and directional control valves 4; means for outputting pressure PLS to a load pressure sensing passage 9 according to the maximum load pressure among the load pressures acting on the actuators; and pump discharge pressure control means for controlling the discharge pressure of the hydraulic pump 1 based on the pressure PLS; wherein the hydraulically operated device is characterized in that a variable bleed valve 11 is located in the load pressure sensing passage 9.
The third invention allows the amount discharged from the hydraulic pump 1 to be controlled by bleeding off the pressured oil in the load pressure sensing passage 9. The amount flowing in the load pressure sensing channel 9 is generally quite low. The pump pressure is controlled according to the pressure of the load pressure sensing passage 9, whereas the pressure of the load pressure sensing passage 9 is the pressure corresponding to the load pressure of the actuator and thus reacts exactly to the fluctuations in the load pressure of the actuator. It also reacts promptly to fluctuations in the load pressure. Energy loss can thus be minimized, and machines can be made more compact. The amount discharged from the hydraulic pump 1 can be controlled with greater precision.
To achieve the first and second objects described above, the fourth of the inventions is a hydraulically operated device comprising a pressure compensating valve through which passes pressured oil that is fed from a hydraulic pump 1 to a hydraulic actuator 5; and an unloading pressure control valve for introducing discharged pressured oil from the hydraulic pump 1 to a tank according to the pressure difference between the discharge pressure PP of the hydraulic pump 1 and the load pressure PLS of the hydraulic actuator 5; wherein the hydraulically operated device is characterized by comprising a pressure compensating valve 7 itself comprising a pressure compensated main valve 20 that is operated in such a way as to increase the area of the opening between an inlet port 24 and an outlet port 25 by means of pressure acting on a first pressure receiving component 21 for a pressure compensating valve, that is also operated in such a way as to reduce the area of the opening by means of pressure acting on a second pressure receiving component 22 for a pressure compensating valve and pressure acting on a third pressure receiving component 23 for a pressure compensating valve, and that is designed to allow the pressure Pa of the pressured oil flowing to the inlet port 24 to act on the first pressure receiving component 21 for a pressure compensating valve and the pressure Pb of the load 5 driven by the pressured oil flowing from the outlet port 25 to act on the second pressure receiving component 22 for a pressure compensating valve, and control pressure producing means 7B for allowing control pressure Pe resulting from a reduction in the pressure Pa of the inlet port 24 to act on the third pressure receiving component 23 for a pressure compensating valve; and an unloading pressure control valve 10 itself comprising a main valve 100 for an unloading pressure control valve, that is constructed in such a way as to operate in the communicating direction by means of the discharge pressure PP of the hydraulic pump 1 acting on a first pressure receiving component 123 for an unloading pressure control valve, to operate in the cut-off direction upon load pressure PLS to a second pressure receiving component 124 for an unloading pressure control valve, and to change the balance of the operating force in each of the directions by means of control pressure Pg acting on a third pressure receiving component 125 for an unloading pressure control valve, and control pressure producing means 101 for producing the control pressure Pg.
According to the fourth invention, the pressure compensation characteristics are changed according to the magnitude of the control pressure Pe, allowing the desired pressure compensation characteristics to be obtained by changing the control pressure Pe.
Because the control pressure Pe resulting from a reduction in the pressure of the inlet port 24 is allowed to act on the third pressure receiving component 23 for a pressure compensating valve in the main valve 20 for a pressure compensating valve, the control pressure Pe also fluctuates according to the fluctuations in the pressure of the inlet port 24. The pressure compensation characteristics are thus unaffected by the pressure fluctuations in the inlet port 24 of the main valve 20.
Furthermore, the unloading start pressure can be set by means of the control pressure Pg acting on the third pressure receiving component 125 for an unloading pressure control valve. The control pressure Pg is produced by the control pressure producing means. The unloading start pressure can thus be preset by the control pressure producing means, and the amount of pressured oil discharged from the hydraulic pump 1 can be increased in advance to improve the response in terms of the hydraulic actuator 5.
To achieve the first and third objects described above, the fifth of the inventions is a hydraulically operated device comprising a plurality of hydraulic actuators 5 to which pressured oil discharged from a variable delivery pump 1 is supplied via pressure compensating valves and directional control valves 4; means 8 for outputting pressure PLS to a load pressure sensing passage 9 according to the maximum load pressure among the load pressures acting on the actuators 5; and pump discharge pressure control means 12 for controlling the discharge pressure of the hydraulic pump 1 based on the pressure PLS; wherein the hydraulically operated device is characterized by comprising a pressure compensating valve 7 itself comprising a main valve 20 that is operated in such a way as to increase the area of the opening between an inlet port 24 and an outlet port 25 by means of pressure acting on a first pressure receiving component 21, that is also operated in such a way as to reduce the area of the opening by means of pressure acting on a second pressure receiving component 22 and pressure acting on a third pressure receiving component 23, and that is designed to allow the pressure Pa of the pressured oil flowing to the inlet port 24 to act on the first pressure receiving component 21 and the pressure Pb of the load 5 driven by the pressured oil flowing from the outlet port 25 to act on the second pressure receiving component 22, and control pressure producing means 7B for allowing control pressure Pe resulting from a reduction in the pressure Pa of the inlet port 24 to act on the third pressure receiving component 23; and a variable bleed valve 11 is located in the load pressure sensing passage 9.
According to the fifth invention, the pressure compensation characteristics are changed according to the magnitude of the control pressure Pe, allowing the desired pressure compensation characteristics to be obtained by changing the control pressure Pe.
Because the control pressure Pe resulting from a reduction in the pressure of the inlet port 24 is allowed to act on the third pressure receiving component 23 of the main valve 20, the control pressure Pe also fluctuates according to the fluctuations in the pressure of the inlet port 24. The pressure compensation characteristics are thus unaffected by the pressure fluctuations in the inlet port 24 of the main valve 20.
Furthermore, the amount discharged from the hydraulic pump 1 can be controlled by bleeding off the pressured oil in the load pressure sensing passage 9. The amount flowing in the load pressure sensing channel 9 is generally quite low. The pump pressure is controlled according to the pressure of the load pressure sensing passage 9, whereas the pressure of the load pressure sensing passage 9 is the pressure corresponding to the load pressure of the actuator and thus reacts exactly to the fluctuations in the load pressure of the actuator. It also reacts promptly to fluctuations in the load pressure. Energy loss can thus be minimized, and machines can be made more compact. The amount discharged from the hydraulic pump 1 can be controlled with greater precision.
To achieve the second and third objects described above, the sixth of the present inventions is a hydraulically operated device comprising a plurality of hydraulic actuators 5 to which pressured oil discharged from a variable delivery pump 1 is supplied via pressure compensating valves 7 and directional control valves 4; means 8 for outputting pressure PLS to a load pressure sensing passage 9 according to the maximum load pressure among the load pressures acting on the actuators 5; pump discharge pressure control means 12 for controlling the discharge pressure of the hydraulic pump 1 based on the pressure PLS; and an unloading pressure control valve for introducing discharged pressured oil from the hydraulic pump 1 to a tank according to the pressure difference between the discharge pressure PP of the variable delivery pump 1 and the load pressure PLS of the hydraulic actuators 5; wherein the hydraulically operated device is characterized by comprising an unloading pressure control valve 10 itself comprising a main valve 100 that is constructed in such a way as to operate in the communicating direction by means of the discharge pressure PP of the hydraulic pump 1 acting on a first pressure receiving component 123, to operate in the cut-off direction upon load pressure PLS to a second pressure receiving component 124, and to change the balance of the operating force in each of the directions by means of control pressure Pg acting on a third pressure receiving component 125, and control pressure producing means 101 for producing the control pressure Pg; and a variable bleed valve 11 is located in the load pressure sensing passage 9.
According to the sixth invention, the unloading start pressure can be set by means of the control pressure Pg acting on the third pressure receiving component 25. The control pressure Pg is produced by means of the control pressure producing means. Accordingly, the unloading start pressure can be preset by the control pressure producing means, and the amount of pressured oil discharged from the hydraulic pump 1 can be increased in advance to improve the response in terms of the hydraulic actuator 5.
The amount discharged from the hydraulic pump 1 can be controlled by bleeding off the pressured oil in the load pressure sensing passage 9. The amount flowing in the load pressure sensing channel 9 is generally quite low. The pump pressure is controlled according to the pressure of the load pressure sensing passage 9, whereas the pressure of the load pressure sensing passage 9 is the pressure corresponding to the load pressure of the actuator and thus reacts exactly to the fluctuations in the load pressure of the actuator. It also reacts promptly to fluctuations in the load pressure. Energy loss can thus be minimized, and machines can be made more compact. The amount discharged from the hydraulic pump 1 can be controlled with greater precision.
To achieve the first, second, and third objects described above, the seventh of the present inventions is a hydraulically operated device comprising a plurality of hydraulic actuators 5 to which pressured oil discharged from a variable delivery pump 1 is supplied via pressure compensating valves and directional control valves 4; means 8 for outputting pressure PLS to a load pressure sensing passage 9 according to the maximum load pressure among the load pressures acting on the actuators 5; pump discharge pressure control means 12 for controlling the discharge pressure of the variable delivery pump 1 based on the pressure PLS; and an unloading pressure control valve for introducing discharged pressured oil from the variable delivery pump 1 to a tank according to the pressure difference between the discharge pressure PP of the variable delivery pump 1 and the load pressure PLS of the hydraulic actuators 5; wherein the hydraulically operated device is characterized by comprising a pressure compensating valve 7 itself comprising a pressure compensated main valve 20 for a pressure compensating valve, that is operated in such a way as to increase the area of the opening between an inlet port 24 and an outlet port 25 by means of pressure acting on a first pressure receiving component 21 for a pressure compensating valve, that is also operated in such a way as to reduce the area of the opening by means of pressure acting on a second pressure receiving component 22 for a pressure compensating valve and pressure acting on a third pressure receiving component 23 for a pressure compensating valve, and that is designed to allow the pressure Pa of the pressured oil flowing to the inlet port 24 to act on the first pressure receiving component 21 for a pressure compensating valve and the pressure Pb of the load 5 driven by the pressured oil flowing from the outlet port 25 to act on the second pressure receiving component 22 for a pressure compensating valve, and control pressure producing means 7B for allowing control pressure Pe resulting from a reduction in the pressure Pa of the inlet port 24 to act on the third pressure receiving component 23 for a pressure compensating valve; and an unloading pressure control valve 10 itself comprising a main valve 100 for an unloading pressure control valve, that is constructed in such a way as to operate in the communicating direction by means of the discharge pressure PP of the hydraulic pump 1 acting on a first pressure receiving component 123 for an unloading pressure control valve, to operate in the cut-off direction upon load pressure PLS to a second pressure receiving component 124 for an unloading pressure control valve, and to change the balance of the operating force in each of the directions by means of control pressure Pg acting on a third pressure receiving component 125 for an unloading pressure control valve, and control pressure producing means 101 for producing the control pressure Pg; and a variable bleed valve 11 is located in the load pressure sensing passage 9.
According to the seventh invention, the pressure compensation characteristics are changed according to the magnitude of the control pressure Pe, allowing the desired pressure compensation characteristics to be obtained by changing the control pressure Pe.
Because the control pressure Pe resulting from a reduction in the pressure of the inlet port 24 is allowed to act on the third pressure receiving component 23 for a pressure compensating valve in the main valve 20 for a pressure compensating valve, the control pressure Pe also fluctuates according to fluctuations in the pressure of the inlet port 24. The pressure compensation characteristics are thus unaffected by the fluctuations in the inlet port 24 of the main valve 20 for a pressure compensating valve.
Furthermore, the unloading start pressure can be set by means of the control pressure Pg acting on the third pressure receiving component 125 for an unloading pressure control valve. The control pressure Pg is produced by means of the control pressure producing means. Accordingly, the unloading start pressure can be preset by the control pressure producing means, and the amount of pressured oil discharged from the hydraulic pump 1 can be increased in advance to improve the response in terms of the hydraulic actuators 5.
The amount discharged from the hydraulic pump 1 can be controlled by bleeding off the pressured oil in the load pressure sensing passage 9. The amount flowing in the load pressure sensing channel 9 is generally quite low. The pump pressure is controlled according to the pressure of the load pressure sensing passage 9, whereas the pressure of the load pressure sensing passage 9 is the pressure corresponding to the load pressure of the actuators and thus reacts exactly to the fluctuations in the load pressure of the actuators. It also reacts promptly to fluctuations in the load pressure. Energy loss can thus be minimized, and machines can be made more compact. The amount discharged from the hydraulic pump 1 can be controlled with greater precision.