Joseph E. Louis - Panora IA
Gary R. Lingenfelter - Nevada IA
A displacement control device for a hydraulic unit includes: an actuator for applying operator input force to a movable member for varying displacement of the unit; a control valve having a spool and a sleeve displaceable with respect to each other, one of these being coupled with the movable member and the other being coupled with the actuator, the control valve being capable of generating a control signal based upon the relative displacement of the spool and sleeve; a servo which is operatively connected to the movable member and receives the control signal so as to move the movable member and change the fluid displacement of the unit in response to the control signal; and a bias coupling connecting the spool and the sleeve of the control valve. Thus, a preload force is interposed between and the spool and the sleeve such that relative displacement between the spool and the sleeve takes place when the feedback force exceeds the preload force. Thus, the sleeve moves synchronously with the spool until the feedback force exceeds the preload force.