The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Jun. 04, 2002
Filed:
Aug. 02, 2000
Yasutaka Tsuruga, Ryugasaki, JP;
Takashi Kanai, Kashiwa, JP;
Junya Kawamoto, Tsuchiura, JP;
Kenichiro Nakatani, Tsuchiura, JP;
Kiwamu Takahashi, Tsuchiura, JP;
Satoshi Hamamoto, Toyama-ken, JP;
Yasuharu Okazaki, Takaoka, JP;
Yukiaki Nagao, Toyama, JP;
Hitachi Construction Machinery Co., Ltd., Tokyo, JP;
Abstract
A hydraulic drive system includes a pump control unit for controlling a pump delivery rate such that a pump delivery pressure is held at a predetermined value higher than a maximum load pressure among actuators . Pressure compensating valves are each constructed to set, as a target compensation differential pressure, a differential pressure between the delivery pressure of a hydraulic pump and the maximum load pressure among the actuators . The pressure compensating valve is given such a load dependent characteristic that the target compensation differential pressure is reduced when a load pressure rises. A lower limit setting spring for limiting the target compensation differential pressure from becoming smaller than a predetermined value is provided in the pressure compensating valve for the swing section.