Pressure compensating valve, unloading pressure control valve and hydraulically operated device

Abstract

A pressure compensating valve (7) comprises 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 driven by the pressured oil flowing from the outlet port (25) to act on the second pressure receiving component (22); and control pressure producer (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). An unloading pressure control valve comprises 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 direction by means of control pressure (Pg) acting on a third pressure receiving component (125); and control pressure producer (101) for producing the control pressure (Pg). A hydraulically operated device has a variable bleed valve (11) located in a load pressure sensing passage (9). This allows pressure compensated characteristics to be changed as desired. The unloading start pressure is also preset so as to improve response in terms of the hydraulic actuators. Energy loss can also be minimized, allowing the rapid start-up of the hydraulic actuators to be controlled, machines can be made smaller, and high precision control can be achieved.

Description

[0001] The present invention relates to a pressure compensating valve, an unloading pressure control valve, and a hydraulically operated device.DESCRIPTION OF THE RELATED ART[0002] FIG. 25 depicts a hydraulically operated device described in Japanese Unexamined-Patent Application 1-247805.[0003] 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 D' via a pressure compensating valve B' and a directional control valve C'.[0004] 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.[0005] The higher load pressure among the load pressures that are produced during the operation of the cylinders D and DT is sensed by a shuttle valve G as the maximum load pressure P.sub.LS, and this maxi...

AI Technical Summary

Benefits of technology

The system enables reliable pressure compensation, rapid start-ups with reduced energy loss, and high-precision control, enhancing the performance and compactness of construction machinery.

Problems solved by technology

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.

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 pressured oil is supplied to the hydraulic cylinder D' with the higher pressure, and the hydraulic cylinder D' with the higher pressure is thus not operated.

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.

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 a1', a2' of the operating devices A and A', and a resulting problem is the poor response in terms of the hydraulic cylinder C or the hydraulic motor C'.

For the reasons described above, however, the unloading start pressure is difficult to modify in advance.

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.

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.

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.

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