Automatic control for hydraulic power transmission

Claim 1

In a fluid energy transmission system which includes a driven variable displacement pump, a movable element for varying the displacement of the pump, a servo means having a piston operably connected to move the movable element to vary the pump displacement in response to different pressures and a pair of conduit means interconnecting the pump to a control valve and thence to a motor in a driving, recirculating relation, an improved control for such system comprising: a flow-to-pressure transducer means which incorporates a flow restriction interposed in the control valve capable of generating a pressure differential upstream and downstream of the restriction which is proportional to the flow through the conduit means; a first sensing line affording communication between the servo and the control valve at a point downstream of the flow restriction whereby the pressure actuates the servo piston to increase or decrease pump displacement to maintain a predetermined flow rate through the conduit means; a bleed orifice venting the first sensing line to atmosphere; a valve means in the first sensing line having a first position unrestricting flow in the first sensing line and a second position blocking flow in the first sensing line; said valve means including an actuating piston connected through a second sensing line to said motor whereby when a certain static load is experienced on said motor, the actuating piston actuates the valve means moving it to its second position blocking flow in the first sensing line causing the pump to stroke back to a standby condition.