Patent ID: 7197872
Filing Date: 2007-04-03
Classification: E02F,F15B

Abstract:
1. A hydraulic circuit in a work vehicle, comprising: an undercarriage; a revolving superstructure rotatably mounted atop the undercarriage; a hydraulic source disposed at the revolving superstructure; at least a plurality of work hydraulic cylinders disposed at the undercarriage, that are to be driven by pressure oil from the hydraulic source; a control valve that controls flow of pressure oil from the hydraulic source to the work hydraulic cylinders; an operating device that issues a command for drive of the control valve; valve devices each comprising a check valve, each provided in correspondence to one of the plurality of work hydraulic cylinders to allow and prohibit outflow of pressure oil from a work hydraulic cylinder; a commanding device that outputs one of a command for allowing extension/contraction and a command for prohibiting extension/contraction for each of the work hydraulic cylinders; a control device that controls each of the valve devices so as to allow outflow of pressure oil from the work hydraulic cylinder by invalidating a check valve function thereof in response to the command for allowing extension/contraction output from the commanding device and an operation of the operating device, and so as to prohibit outflow of pressure oil from the work hydraulic cylinder with the check valve in response to the command for prohibiting extension/contraction output by the commanding device, wherein the control device also prohibits outflow of pressure oil from the work hydraulic cylinder with the check valve while the operating device is not operated.