Patent ID: 7921642

Claim:
An inertial body drive system, comprising: a hydraulic pressure source; a hydraulic motor supplied with pressurized oil from said hydraulic pressure source to rotationally drive an inertial body; first and second main conduits connecting said hydraulic motor with said hydraulic pressure source; a directional control valve connected between said main conduits and adapted to open the supply of pressurized oil to said hydraulic motor from said hydraulic pressure source when switched from a neutral position to a changeover position and to stop the supply of pressurized oil to said hydraulic motor when returned to said neutral position; and overload relief valves connected between said main conduits, at a position between said directional control valve and said hydraulic motor to limit a maximum pressure in said main conduits to a first preset pressure value; characterized in that said inertial body drive system comprises: a pressure selector means connected between said main conduits, at a position between said directional control valve and said hydraulic motor to connect one of said main conduits, on a high pressure side to a high pressure conduit while connecting the other main conduit on a low pressure side to a low pressure conduit when switched from a neutral position to a changeover position; a valve means connected between said high pressure conduit and said low pressure conduit and comprised of a spool to be put in sliding displacement between an open position and a closed position and said spool being constantly biased toward said closed position under a biasing action of a biasing member, and said spool being switched from said closed position to said open position against the biasing action of said biasing member upon pressurization of oil in an oil pressure chamber; a pressurized oil supply means comprised of an oil reservoir chamber in communication with said oil pressure chamber of said valve means and adapted to supply pressurized oil in said oil reservoir chamber to said oil pressure chamber of said valve means as soon as a pressure in said high pressure conduit drops below a second pressure value lower than a first pressure value preset by said overload relief valves; a passage connecting said oil reservoir chamber of said pressurized oil supply means and said oil pressure chamber of said valve means constantly to a low pressure reservoir; and a flow resisting means provided in said passage to throttle a flow of operating oil to be discharged toward said reservoir.