Power drive unit and control system therefor

• US 4,635,441 A
• Filed: 05/07/1985
• Issued: 01/13/1987
• Est. Priority Date: 05/07/1985
• Status: Expired due to Term

• Current Assignee: Sundstrand Corporation (Raytheon Technologies Corporation d/b/a RTX)
• Original Assignee: Sundstrand Corporation (Raytheon Technologies Corporation d/b/a RTX)
• Inventors: Ebbing, Steven J., Beneditz, Bruce D., Hermans, Robert J., Vicari, John J.
• Primary Examiner(s): Croyle, Carlton R.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US06/731,663
• Time in Patent Office: 616 Days
• Field of Search: 60/450, 60/911, 60/445, 91/506
• US Class Current: 60/450
• CPC Class Codes: F16H 61/423 Motor capacity control by fluid pressure control means
• CPC Class Codes: H02P 29/0016 Control of angular speed of one shaft without controlling the prime mover
• CPC Class Codes: Y10S 60/911 Fluid motor system incorporating electrical system

Abstract

A power drive unit and control system therefor avoiding performance degradation which can occur in control of the variable displacement hydraulic motor of the power drive unit by measurement of the angle of a displacement-setting wobbler of the motor and the speed of the motor. This is avoided by sensing flow through the motor which provides an indirect measure of wobbler position and speed of motor operation. The power drive unit and control system therefor has a variable displacement hydraulic motor with a displacement-setting wobbler positioned by pressure applied to a servo piston by an electro-hydraulic servo valve. The control system responds to a speed command having a value dependent upon a position loop which determines the relation between the actual position of a load and a commanded position, with the control providing for a maximum possible speed of motor operation under a particular load condition with a substantially constant rate of fluid flow through the motor. As the load varies, the flow through a flow-regulator valve varies and flow is sensed by a linear variable differential transformer associated with the valve member of the flow regulator. The linear variable differential transformer outputs a control voltage indicative of a variation in either direction from the desired rate of fluid flow through the motor which is used to adjust the angle of the wobbler to bring the flow to the desired rate and the motor is caused to operate at a maximum possible speed. The control, by using a speed command responsive to a position loop, provides a controlled snubbing action to reduce the speed of the motor as the load approaches the commanded position.

Claims

1. A hydraulic power drive unit having a variable displacement motor for moving a load under both aiding and opposing load conditions at the maximum speed possible for the load condition with a substantially constant desired rate of fluid flow throug the motor comprising, means for adjusting motor displacement, means for regulating fluid flow from the motor including a flow-regulating valve having a valve member positionable in response to a flow responsive pressure differential, and means responsive to a variation in said desired rate of fluid flow as detected by the flow-regulating means for operating said motor displacement adjusting means including a circuit having a linear variable differential transformer movable by said valve member.

2. A hydraulic power drive unit as defined in claim 1 including means for operating said motor displacement adjusting means to reduce the motor speed as the load approaches a desired position.

3. A hydraulic power drive unit as defined in claim 1 including means for increasing the displacement of the motor to reduce the motor speed as the motor-driven load approaches a commanded position.

4. A control for a variable displacement motor to achieve maximum possible motor speed with a substantially uniform rate of fluid flow through the motor operable with both aiding and opposing loads comprising, displacement-varying means for the motor, control means for the displacement-varying means, flow-responsive means for sensing the rate of fluid flow from the motor including a flow-regulating valve having a valve member positionable in response to a flow responsive pressure differential, and means operable when the rate of fluid exceeds a predetermined value for causing said control means to operate the displacement-varying means to reduce the displacment of the motor including a circuit having a linear variable differential transformer movable by said valve member.

5. A control valve as defined in claim 4 wherein said valve member has an orifice through which the fluid flow from the motor passes to create a pressure difference variable with the rate of fluid flow.

6. A control as defined in claim 4 wherein said control means includes means operable to increase the motor displacement as the motor-driven load approaches a commanded position to reduce motor speed for a controlled snubbing action.

7. A hydraulic power drive unit having a variable displacement motor and means for controlling the displacement of the motor to maximize the speed of the motor operating under varying loads and supplied with motive fluid at a substantially uniform rate of flow comprising, a flow-regulating valve through which fluid flows from the motor, adjustable means for setting the displacement of the motor, control means for said setting means to maintain a rate of flow through the flow-regulating valve within a predetermined range, and means including a linear variable differential transformer operable by the flow-regulating valve for sensing the rate of flow through said flow-regulating valve in excess of said predetermined range for causing said displacement-setting means to reduce the displacement of the motor and increase the speed of the motor.

8. A hydraulic power drive unit having an adjustable variable displacement motor responsive to a speed command for moving a load under both aiding and opposing load conditions at the maximum speed possible for the load condition with a substantially constant desired rate of fluid flow through the motor comprising, an electro-hydraulic servo control coupled to a wobbler and responsive to a speed signal for positioning the wobbler, a flow-regulating valve connected to said motor for regulating fluid flow from the motor and having a valve member positionable in response to a flow-induced pressure differential which varies with the load on the motor, a linear variable differential transformer connected to said valve member for outputting an output signal when the valve member has moved to shift the linear variable differential transformer from a null position, and control circuit means including said electrohydraulic servo control and said linear variable differential transformer for summing said output signal with the speed signal to control said servo control for setting the position of the wobbler.