HYDRAULIC DRIVE DEVICE AND DIRECTION SWITCHOVER VALVE FOR HYDRAULIC MACHINE

摘要

A hydraulic drive device which has a closed center type direction switching valve (2) which is connected to a hydraulic pump (50) through a pressure oil feed passage (3) to control flow of a pressure oil fed to an actuator (51). The hydraulic drive device comprises a throttle shutoff means (11) provided on an unload circuit (10), which connects the pressure oil feed passage (3) to a tank (53), for throttling and shutting off the unload circuit (10) in accordance with a control input of the direction switching valve (2), the throttle shutoff means comprising a logic valve (12) having a feedback slit (12b), of which opening area is increased or decreased in accordance with an amount of movement of a valve disc (12a), and a pilot variable throttle (13) for controlling an amount of pilot flow passing through the feedback slit (12b) in accordance with a control input of the direction switching valve (2). Accordingly, the closed center type direction switching valve is shortened in axial length of a spool of the direction switching valve as compared with an open center type direction switching valve, achieves an improvement in working accuracy and compactness, and can function in an equivalent manner to an open center type direction switching valve without the use of any controller. <IMAGE>