Power plants – Pressure fluid source and motor – Having condition responsive control in a system of distinct...
Reexamination Certificate
1999-03-03
2002-01-01
Lopez, F. Daniel (Department: 3745)
Power plants
Pressure fluid source and motor
Having condition responsive control in a system of distinct...
C060S452000, C060S468000
Reexamination Certificate
active
06334308
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a pressure compensating valve, an unloading pressure control valve, and a hydraulically operated device.
DESCRIPTION OF THE RELATED ART
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 D′ via a pressure compensating valve B′ and a directional control valve C′.
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 D′ is sensed by a shuttle valve G as the maximum load pressure P
LS
, and this maximum load pressure P
LS
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 P
P
of the pump A is always greater than the maximum load pressure P
LS
.
The cylinders D and D′ are jointly operated by the simultaneous operation of directional control valves C and C′ 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 B′ similarly 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.
The hydraulically operated device equipped with the pressure compensating valves B and B′ 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 D′.
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 C′. 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 D′ with the higher pressure, and the hydraulic cylinder D′ 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 P
P
−P
LS
between the pressure P
P
of the pressured oil discharged from the hydraulic pump A and the maximum load pressure P
LS
, a control force set device I for setting the control force fc based on the pressure difference P
P
−P
LS
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=f−&agr;
(P
P
−P
LS
)
Where f: the pressing force of springs b and b
−
in pressure compensating valves B and B′
&agr;: 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 B′ when the pressure difference P
P
−P
LS
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 b
−
to be exerted on the springs in the pressure compensating valves B and B′. The force fc increases the discharge pressure of the pump A by increasing the flow resistance of the pressure compensating valves B and B′, allowing pressured oil to be supplied to the hydraulic cylinder D′ with the higher pressure.
When the cylinders D and D′ 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 B′ 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 C′ 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 B′, and the control force fc for the pressure compensating valves B and B′ are individually adjusted by these electromagnetic valves J. Accordingly, the throttle levels of the pressure compensating valves B and B′ are individually changed; that is, the pressure differences before and after the direction control valves C and C′ 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
21
H, 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 A′, flow regulating valve (operating valve) B′, hydraulic motor (hydraulic actuator) C′, and pressure compensating valve E′ 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 hydrauli
Sato Yasuhiro
Wakisaka Ryoji
Yoshida Nobumi
Komatsu Ltd.
Lopez F. Daniel
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