Patent ID: 7562615
Filing Date: 2009-07-21
Classification: E02F,F15B,Y02P

Abstract:
1. A hydraulic working machine provided with a main pump, a working element, a double-acting hydraulic cylinder arranged for extension or contraction by pressure oil, which is delivered from a main pump, to drive said working element, a directional control valve for controlling flows of pressure oil to be fed from said main pump to a bottom chamber and rod chamber of said hydraulic cylinder, and a control unit for performing a change-over control of said directional control valve, characterized in that said hydraulic working machine is provided with: a jack-up selector valve for being changed over when a bottom pressure on said hydraulic cylinder has reached a predetermined pressure, and a flow-line changing means for changing a flow-line for pressure oil, which is to be fed from said main pump to a meter-in port of said directional control valve, from an open side to a closed side in response to a change-over control of said jack-up selector valve, wherein, when the bottom pressure on said hydraulic cylinder is equal to or higher than the predetermined pressure upon lowering said working element, said jack-up selector valve is changed over to a first selected position to change over said flow-line changing means to the closed side such that pressure oil delivered from said main pump is not fed to said rod chamber of said hydraulic cylinder, and when the bottom pressure on said hydraulic cylinder is lower than the predetermined pressure upon lowering said working element, said jack-up selector valve is changed over to a second selected position to change over said flow-line changing means to the open side such that pressure oil delivered from said main pump is fed to said rod chamber of said hydraulic cylinder via said directional control valve.