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Displacement control with load feedback and stroke control for a hydraulic unit

  • US 6,119,456 A
  • Filed: 01/21/1998
  • Issued: 09/19/2000
  • Est. Priority Date: 01/21/1998
  • Status: Expired due to Fees
First Claim
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1. A displacement control device for a variable displacement hydraulic unit having a movable member disposed therein for varying the fluid displacement of the unit comprising:

  • an actuator for applying an operator input force to the movable member;

    a control valve having a spool and a sleeve displaceable with respect to each other, one of the spool and the sleeve being mechanically coupled with the movable member, the other of the spool and the sleeve being mechanically coupled with the actuator, the control valve being capable of generating a control signal based upon the relative displacement of the spool and the sleeve;

    a servo for receiving the control signal from the control valve and being operatively connected to the movable member so as to forcibly move the movable member and thereby vary the fluid displacement of the hydraulic unit in response to the control signal;

    the control valve and the servo being structurally separate and distinct elements;

    a yieldable bias coupling comprising a spring operatively interposed between the spool and the sleeve of the control valve whereby a preload force is interposed between the spool and the sleeve;

    the spring being remote from the servo and free from engagement therewith;

    the spring being continuously operatively connected to the actuator and to at least one of the spool and the sleeve and being of sufficient load bearing capacity to provide load force and position feedback of the movable member as well as direct control of movement of the movable member anywhere between a position of no fluid displacement and a position of maximum fluid displacement;

    whereby the sleeve moves synchronously with the spool until a load force on the movable member exceeds the preload force of the bias coupling whereupon relative displacement of the spool and the sleeve occurs so as to generate the control signal to the servo and cause the servo to supplement the operator input force in moving the movable member to vary the fluid displacement of the unit and wherein the preload force is sufficient to provide direct control of movement of the movable member throughout a range of positions between a position of no fluid displacement and maximum fluid displacement.

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