Displacement control device for a hydraulic unit such as a hydrostatic transmission of skid-steer loader

摘要

A bias coupling is operatively interposed between a displacement varying movable member, an actuator, and a control valve assembly (14) which has a spool (26) and sleeve (22) that are displaceable with respect to each other. The bias coupling provides a preload force which must be overcome before the sleeve and spool can move with respect to each other and thus apply hydraulic assistance for stroking the unit. The sleeve moves synchronously with the spool until a feedback force exceeds a preload force whereupon relative displacement of the spool and the sleeve occurs so as to generate a control signal to a servo (16), which causes the servo to supplement the operator input force in moving the movable member to vary the fluid displacement of the unit.