Method and apparatus for enhancing stability in servo systems comprising hydro-mechanically driven actuators

• US 5,544,715 A
• Filed: 12/15/1994
• Issued: 08/13/1996
• Est. Priority Date: 06/01/1993
• Status: Expired due to Fees

• Current Assignee: Edward H Phillips-Techo Corporation
• Original Assignee: Edward H Phillips-Techo Corporation
• Inventors: Phillips, Edward H.
• Primary Examiner(s): FOCARINO, MARGARET ANN
• Application Number:
  US08/357,158
• Time in Patent Office: 607 Days
• Field of Search: 180/132, 180/135, 180/140, 180/150, 180/156, 180/160, 384/215, 403/203, 403/225, 403/291, 267/140.3, 267/140.5, 267/141.2, 267/141.3, 267/141.4, 267/141.5, 267/141.7, 464/180
• US Class Current: 180/417
• CPC Class Codes: B60G 2204/1222 Middle mounts of stabiliser on vehicle body or chassis
• CPC Class Codes: B62D 5/06 fluid, i.e. using a pressurised fluid for most or all the force required for steering a vehicle
• CPC Class Codes: F16F 15/02 Suppression of vibrations of non-rotating, e.g. reciprocating systems; Suppression of vibrations of rotating systems by use of members not moving with the rotating systems F16F15/005 takes precedence ; layered products B32B; suppression of vibration in ships B63; relieving load on bearings, using magnetic means F16C39/06
• CPC Class Codes: Y10T 403/405 Flexible intermediate member
• CPC Class Codes: Y10T 403/455 Elastomer interposed between radially spaced members

Abstract

Methods and devices for enhancing shudder stability in servo systems comprising hydro-mechanically driven actuators are disclosed. Series damping devices forming compliant couplings having series damping characteristics are disclosed. The series damping devices are utilized for mounting the hydro-mechanically driven actuators or coupling them to load elements which they position. The improvement consisting of providing series damping associated with the hydro-mechanically driven actuators for absorbing sufficient energy to provide adequate gain and phase margins for the open-loop feedback characteristics of systems utilizing the hydro-mechanically driven actuators in order to substantially prevent high frequency shudder from occurring during operation of the systems.

Claims

1. A series damping device for enhancing a shudder stability in a hydro-mechanical system, said damping device comprising:

a frame;

a hydraulic actuator having a driven member reciprocally displaceable along an axis;

a linkage assembly connected to said driven member of said actuator;

means for compliantly coupling said hydraulic actuator to one of said frame and said linkage assembly, said means for compliantly coupling having at least one first biasing element and at least one second biasing element positioned to exert a biasing force along said axis, said first biasing element being preloaded and having a first predetermined stiffness, said at least one second biasing element having a second predetermined stiffness which is less than said first predetermined stiffness, and applied only when said driven member is axially displaced by said hydraulic actuator to exert a force upon said means for coupling greater than said first predetermined stiffness of said at least one biasing member.

2. The series damping device of claim 1 wherein each at least one first biasing member has non-linear load deflection value.

3. The series damping device of claim 1, wherein said at least one first biasing member is a Belleville washer.

4. The series damping device of claim 1, wherein said at least one first biasing member comprises a plurality of Belleville washers.

5. The series damping device of claim 1 wherein said at least one second biasing member is formed of a lossy material.

6. The series damping device of claim 5, wherein said lossy material has a damping coefficient value of generally 50 lb. sec/in.

7. The series damping device of claim 1 wherein said at least one second biasing member comprises an elastomeric bumper.

8. The series damping device of claim 1, further comprising a pair of spaced apart bushings mounted to said driven member, said at least one first and at least one second biasing members being disposed between said bushings.

9. The series damping device of claim 1, wherein said first biasing member is partially compressed when said drive member is exerting no force upon said means for coupling.

10. A method for enhancing shudder stability in power steering systems, said method comprising the steps of:

compliantly coupling one of a linkage assembly and a frame to a driven member of a hydraulic actuator with at least one biasing member having a predetermined stiffness in an axial direction; and

coupling a second biasing member to said first biasing member in an axial direction said second biasing member having a second predetermined stiffness lower in value than said first predetermined stiffness when said driven member exerts a force greater than said predetermined force of said first biasing member.