1997-07-30
1999-08-10
Lopez, F. Daniel
60368, F15B 2102
Patent
active
059341769
ABSTRACT:
A hydraulic operating system has a cylinder which is actuated to raise, hold or lower a load against the force of gravity. An electromagnetic 3/2 valve connects a working chamber of the cylinder to a hydraulic reservoir when not energized, and permits flow from a pump to the working chamber when energized. A non-return valve prevents flow from the working chamber to the pump when the valve is energized. A three position switch operates an electric control unit to raise, lower or hold the load in an intermediate position. When holding in an intermediate position, the control unit constantly energizes the valve during a first period, after which the control unit intermittently energizes and deenergizes the valve so as to lower the load in stepwise fashion during a second period.
REFERENCES:
patent: 3908515 (1975-09-01), Johnson
patent: 4416187 (1983-11-01), Nystrom
patent: 4773302 (1988-09-01), Mizota et al.
patent: 5170021 (1992-12-01), Martini
patent: 5375418 (1994-12-01), Shelhart et al.
patent: 5454292 (1995-10-01), Oudelaar
Applicant's Exhibit A--Patent Cooperation Treaty Report Concerning Novelty Search of International Type for Netherland Application No. 9500181, dated Feb. 1, 1995.
Applicant's Exhibit B--English translation of Applicant's Exhibit A.
Applicant's Exhibit C--Patent Cooperation Treaty International Search Report for International Application No. PCT/NL96/00047, dated May 15, 1996.
Mentink Laurentius A. G.
Wind Roelof Jan
Applied Power Inc.
Lopez F. Daniel
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