Hydraulic control circuit for a hydraulic lifting cylinder

Motors: expansible chamber type – With motive fluid valve – Independent control of bypass between opposed working chambers

Reexamination Certificate

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C091S451000

Reexamination Certificate

active

07104181

ABSTRACT:
A hydraulic control circuit for a hydraulic cylinder is described for the raising and lowering of a boom on a telescopic loader. First and second chambers of the hydraulic cylinder are connected to a control valve over first and second supply lines and are selectively connected to either a hydraulic pressure source or to a hydraulic reservoir. The circuit includes on-off valves for controlling the flow through a first hydraulic line extending between the first chamber of the cylinder and the hydraulic reservoir, and through a second hydraulic line extending between the second chamber and the hydraulic reservoir in such a way that a floating position can be provided. Furthermore, a load-holding valve arrangement is provided in the first supply line at a location between the control valve and the first chamber of the cylinder. To provide assurance against uncontrolled lowering of the boom during switching to the floating position under load, a valve arrangement is provided that controls the flow rate as a function of the flow rate.

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Patent Abstracts of Japan vol. 1998, No. 04, Mar. 31, 1998 & JP 09 317706 A, Dec. 9, 1997.
Patent Abstracts of Japan vol. 1998, No. 11, Sep. 30, 1998 * JP 10 168949 A, Jun. 23, 1998.

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