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:
Aug. 12, 2014
Filed:
Dec. 17, 2007
Kazunori Nakamura, Tsuchiura, JP;
Kazunori Nakamura, Tsuchiura, JP;
Hitachi Construction Machinery Co., Ltd., Tokyo, JP;
Abstract
[Problem] To provide a hydraulic drive system for a hydraulic excavator, which makes it possible to efficiently perform grading work by using residual energy of pressure oil in a hydraulic circuit although no attention has been paid to the residual energy in conventional technologies. [Solution] A hydraulic drive system for a hydraulic excavator is provided with a boom cylinderand arm cylinder, a main hydraulic pumpfor feeding pressure oil to both the cylinders, a directional control valvefor a boom and directional control valvefor an arm to control flows of pressure oil to be fed to the boom cylinderand arm cylinder, respectively, and a reservoir lineconnecting the directional control valvefor the arm with a working oil reservoir. A flow-rate control valvecapable of selectively closing the reservoir lineis arranged and, when a rod-side hydraulic pressure of the arm cylinderhas increased to a preset value or greater while grading work is performed by a combined operation of boom raising and arm crowding, the reservoir lineis closed by the flow-rate control valveto prevent drainage of rod-side pressure oil from the arm cylinderto the working oil reservoirand to feed the rod-side pressure oil to a bottom side of the boom cylinder