OIL-PRESSURE DEVICE FOR OIL-PRESSURE SHOVEL

PURPOSE:To raise the performance of an oil-pressure device by controlling the capacity of a slewing motor on the basis of necessary strokes of an oil- pressure cylinder and the slewing angle of the slewing motor by a method in which the capacity of the slewing motor is allowed to change only when the slewing motor and the oil-pressure cylinder for boom are operated concurrently. CONSTITUTION:A pilot pump 9 controls the discharge flow rate of a slewing motor 1 by supplying pilot pressure to the control actuator 12 of the motor 1 through an electromagnetic proportional reduced-pressure control valve 11 to be operated on command signals from a regulator 10. Pressure oil from the main pump 16 is supplied in parallel to a switching valve 13 for slewing direction and a two-speed switching valve 14 for boon. Only when limit switches (a) and (b) provided to these valves 13 and 14 are operated together, an operating valve 11 is actuated through contact points (a') and (b'). The capacity of the motor 1 is optimumly controlled on the basis of necessary stroke of an oil-pressure cylinder 2, slewing angle of the motor 1, drive pressure of the cylinder 2 for boom, and inertial moment of the slewing body.