Abstract: A torque control for a hydrostatic piston pump that provides for a servo piston rod that is connected to the swashplate of the pump and connected to a servo piston within a first cavity that receives compensation pressure that urges the servo piston toward the swashplate. The servo piston has a stem that extends into a bore and is in contact with the stem of a maximum displacement piston that extends into a second cavity that is acted upon by system pressure to urge the maximum displacement piston toward the swashplate. Additionally, within the second cavity is a set of Bellville washers that surround the stem of the maximum displacement piston to limit the movement of the maximum displacement piston toward the swashplate.

Abstract: 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.