Power plants – Pressure fluid source and motor – Condition responsive control of pump or motor displacement
Patent
1991-06-18
1992-07-14
Michalsky, Gerald A.
Power plants
Pressure fluid source and motor
Condition responsive control of pump or motor displacement
60427, 91451, 91518, 13759613, F15B 1308
Patent
active
051292297
ABSTRACT:
A hydraulic drive system for a civil-engineering and construction machine, includes an unloading valve connected to a discharge line of a hydraulic pump for relieving a hydraulic fluid from the hydraulic pump to a tank when a differential pressure between a delivery pressure of the hydraulic pump and a load pressure of an actuator exceeds a first predetermined value, for controlling the differential pressure. The unloading valve has a spool, a first receiving chamber arranged adjacent to one end of the spool, and a second pressure receiving chamber arranged adjacent to the other end of the spool, the delivery pressure of the hydraulic pump being introduced into the first pressure receiving chamber and the load pressure of the hydraulic actuator being introduced into the second pressure receiving chamber. The unloading valve is provided with a restrictive communication path for selectively communicating the first pressure receiving chamber and the second pressure receiving chamber with each other, whereby when a phase deviation exists between the delivery pressure P.sub.s of the hydraulic pump and the maximum load pressure P.sub.L transmitted to the unloading valve as signal pressures, oscillation of the unloading valve is prevented.
REFERENCES:
patent: 3976097 (1976-08-01), Brakel
patent: 4153075 (1979-05-01), Budzich
patent: 4617854 (1986-10-01), Kropp
patent: 4727793 (1988-03-01), Hall
Olhydraulik und Pneumatik, H. Lodige, vol. 33, No. 9, 1988, pp. 608-613, "Optimierung eines LS Wegeventilsystems".
Nakamura Kazunori
Tanaka Hideaki
Hitachi Construction Machinery Co. Ltd.
Michalsky Gerald A.
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