Electronically controlled power steering system

• US 5,307,892 A
• Filed: 04/13/1992
• Issued: 05/03/1994
• Est. Priority Date: 08/03/1990
• Status: Expired due to Fees

• Current Assignee: Techco Corp.
• Original Assignee: Techco Corp.
• Inventors: Phillips, Edward H.
• Primary Examiner(s): HILL, MITCHELL
• Application Number:
  US07/868,087
• Time in Patent Office: 750 Days
• Field of Search: 180/79.1, 180/132, 180/141, 180/142, 180/143, 364/424.05, 91/375 A
• US Class Current: 180/422
• CPC Class Codes: B62D 5/09 characterised by means for actuating valves
• CPC Class Codes: B62D 6/008 Control of feed-back to the steering input member, e.g. simulating road feel in steer-by-wire applications
• CPC Class Codes: B62D 6/02 responsive only to vehicle speed
• CPC Class Codes: B62D 6/08 responsive only to driver input torque

Abstract

An electronically controlled power steering system for motor vehicles is disclosed for steering dirigible wheels in response to an input torque applied to a steering wheel. The power steering system includes a mechanical steering gear mechanism coupled to the steering wheel for generating a mechanically derived steering force in response to the input torque. A power cylinder is coupled to the mechanical steering gear mechanism for producing a hydraulically derived steering force which augments the mechanically derived steering force. A control valve is provided which is in fluid communication with the power cylinder for generating differential pressure applied to the power cylinder. A first signal is generated which is indicative of the input torque applied to the steering wheel. A signal processing unit generates an output signal in response to the first signal. The signal processing unit is operable to selectively actuate the control valve in response to the output signal for selectively regulating the hydraulically derived steering force generated by the power cylinder.

Claims

1. An electronically controlled power steering system for motor vehicles of the type used for steering dirigible wheels in response to an input torque applied to a steering wheel, comprising:

mechanical steering gear means coupled to said steering wheel for generating a mechanically derived steering force in response to said input torque;

a power cylinder coupled to said mechanical steering gear means for producing a hydraulically derived steering force for augmenting said mechanically derived steering force;

first transducer means for generating a first signal indicative of said input torque applied to said steering wheel;

control valve means in fluid communication with said power cylinder for generating a differential pressure applied to said power cylinder;

means for supplying fluid to said control valve means; and

signal processing means for generating an output signal in response to said first signal, said signal processing means operable to selectively actuate said control valve means in response to said output signal for selectively regulating said hydraulically derived steering force generated by said power cylinder said signal processing means being adapted to amplify and selectively manipulate said first signal such that said output signal is a function of said input torque applied to said steering wheel.

2. The electronically controlled power steering system of claim 1 wherein said control valve means includes a control valve and valve actuation means for selectively actuating said control valve in response to said output signal.

3. The electronically controlled power steering system of claim 1 wherein said signal processing means includes means for generating said output signal as a function of vehicular speed.

4. The electronically controlled power steering system of claim 1 wherein said signal processing means includes means for amplifying said first signal so as to increase a system gain at relatively low input torque levels and decrease said gain at relatively high input torque levels.

5. The electronically controlled power steering system of claim 1 wherein said first transducer means is a torque transducer associated with said mechanical steering gear means.

6. The electronically controlled power steering system of claim 1 further including second transducer means for generating a rate signal indicative of the velocity of an output motion of said steering gear means, said rate signal being fed back to said signal processing means for selectively modifying said output signal.

7. The electronically controlled power steering system of claim 6 wherein said second transducer means is associated with said mechanical steering gear means.

8. The electronically controlled power steering system of claim 6 wherein said rate signal is frequency compensated and amplified by said signal processing means.

9. The electronically controlled power steering system of claim 8 wherein said rate signal is non-linearly amplified by said signal processing means as a function of one of its first own magnitude and magnitude of said first signal.

10. The electronically controlled power steering system of claim 8 wherein said rate signal is non-linearly amplified by said signal processing means as a function of its own first magnitude and a second magnitude of said first signal.

11. The electronically controlled power steering system of claim 6 wherein said signal processing means includes means for amplifying said rate signal as a function of vehicular speed for generating a rate derived - speed sensitive power steering.

12. The electronically controlled power steering system of claim 2 further comprising fluid pressure measurement means for measuring differential fluid pressure applied to said power cylinder upon actuation of said control valve and generating a pressure signal in response thereto.

13. The electronically controlled power steering system of claim 12 wherein said pressure signal is fed back to said signal processing means for selectively modifying said output signal in response thereto, and wherein said differential fluid pressure applied to said power cylinder is a function of said input torque applied to said steering wheel.

14. The electronically controlled power steering system of claim 6 further comprising fluid pressure measurement means for measuring said differential fluid pressure applied to said power cylinder upon actuation of said control valve and generating a pressure signal in response thereto.

15. The electronically controlled power steering system of claim 14 wherein said pressure signal is fed back to said signal processing means for selectively modifying said output signal in response thereto and wherein said differential fluid pressure applied to said power cylinder is a function of said input torque applied to said steering wheel.

16. The electronically controlled power steering system of claim 15 wherein said fluid pressure measurement means is a pressure transducer associated with said control valve.

17. The electronically controlled power steering system of claim 2 wherein said control valve is an open-centered rotary valve and said valve actuation means is a torque motor coupled to said rotary valve and operable to selectively control fluid flow therethrough.

18. The electronically controlled power steering system of claim 17 wherein said open-centered rotary valve and said torque motor are remotely located from said steering gear means.

19. The electronically controlled power steering system of claim 18 wherein said open-centered rotary valve and said torque motor form a control valve assembly.

20. The electronically controlled power steering system of claim 6 wherein said control valve is an open-centered rotary valve and said valve actuating means is a torque motor coupled to said rotary valve and operable to selectively control fluid flow therethrough.

21. The electronically controlled power steering system of claim 14 wherein said control valve is an open-centered rotary valve and said valve actuating means is a torque motor coupled to said rotary valve and operable to selectively control fluid flow therethrough.

22. The electronically controlled power steering system of claim 2 wherein said mechanical steering gear means includes an input shaft coupled to a steering shaft to which said steering wheel is secured, an actuation member generally coaxially aligned with said input shaft and a rotationally compliant member adapted to interconnect said input shaft to said actuation member for transmitting said input torque thereto, said input torque being transferred from said actuation member to a driven member for producing said mechanically derived steering force.

23. The electronically controlled power steering system of claim 22 wherein said first transducer means is operably associated with said input shaft and said actuation member for generating said first signal indicative of the torque transmitted to said actuation member.

24. The electronically controlled power steering system of claim 23 wherein said first transducer means comprises first and second proximity transducers secured on one of said input shaft and said actuation member which are adapted to measure the distance between complimentary facing surfaces on the other of said input shaft and said actuation member and wherein said compliant member elastically deflects in a substantially linear manner with respect to said input torque upon rotation of said input shaft so as to define a corresponding change in said proximate distance between said first and second proximity transducers and said complimentary facing surfaces, respectfully, which is concomitant with said input torque, said signal processing means adapted to manipulate signals generated by said first and second proximity detectors to define said first signal.

25. The electronically controlled power steering system of claim 24 wherein said first and second proximity transducers are mounted in opposed relation within a plurality of first jaw teeth formed on an end of one of said input shaft and said actuation member which are loosely fitted with a plurality of complimentary second jaw teeth formed in juxtaposed relation on an end of the other of said input shaft and said actuation member and wherein said first and second jaw teeth form a mechanical backup steering assembly such that when said input torque is substantially zero said first and second jaw teeth are substantially centered in a non-contacting orientation.

26. The electronically controlled power steering system of claim 25 wherein said first and second proximity transducers are redundant such that their respective output signals are compared by said signal processing means whereby upon an excessively divergent value thereof said mechanical backup steering assembly provides mechanically derived steering during conditions of substantially no hydraulically derived steering force being generated.

27. The electronically controlled power steering system of claim 22 wherein said mechanical steering gear means further includes second transducer means for generating a rate signal representative of the rotational velocity imparted on said actuation member relative to said input shaft.

28. The electronically controlled power steering system of claim 27 wherein said second transducer means comprises a tachometer.

29. The electronically controlled power steering system of claim 28 wherein said rate signal is fed back to said signal processing means for modifying said output signal so as to enhance a system stability whereby an unstable motion of said dirigible wheels is attenuated through a modification of said output signal.

30. The electronically controlled power steering system of claim 29 wherein said output signal from said signal processing means is applied to said valve actuating means for selective actuation of said control valve in a manner which is substantially linearly related to said output signal.

31. The electronically controlled power steering system of claim 30 wherein said valve actuating means includes a torque motor which is actuated to elastically deflect a torsion bar for selectively regulating flow characteristics of said control valve with respect to said power cylinder.

32. The electronically controlled power steering system of claim 31 wherein output from said control valve is a differential right and a left fluid flow to opposite ends of said power cylinder for generating said hydraulically derived steering force.

33. The electronically controlled power steering system of claim 32 wherein said rate signal is selectively increased as a function of vehicular speed for generating a rate derived speed sensitive steering.

34. A method for controlling a power steering system of the type used in motor vehicles for steering a pair of dirigible wheels, said method comprising the steps of:

applying an input torque to a power steering unit by applying a steering torque to a steering wheel coupled thereto;

generating a mechanically derived steering force in response to said input torque;

generating a hydraulically derived steering force in response to said input torque for augmenting said mechanically derived steering force;

summing said mechanically derived steering force and said hydraulically derived steering force to define a total steering force which is applied to the dirigible wheels;

sensing a first signal indicative of said input torque;

amplifying and modifying said first signal to generate an output signal which is a function of said input torque applied to said steering wheel;

applying said output signal to a control valve assembly; and

selectively actuating said control valve assembly in response to said output signal for regulating said hydraulically derived steering force as a function of said input torque.

35. The method of claim 34 wherein said power steering unit includes mechanical steering gear means coupled to said steering wheel for generating said mechanically derived steering force in response to said input torque and a power cylinder coupled to said mechanical steering gear means for producing said hydraulically derived steering force, said power cylinder fluidly communicating with said control valve assembly.

36. The method of claim 35 wherein said step of generating said output signal includes providing signal processing means for generating said output signal for selectively actuating said control valve assembly so as to selectively regulate said hydraulically derived steering force generated by said power cylinder.

37. The method of claim 36 wherein said control valve assembly includes a valve apparatus and a valve actuation means for selectively actuating said valve apparatus in response to said output signal from said signal processing means.

38. The method of claim 34 wherein said step of generating said output signal includes means for generating said output signal as a function of vehicular speed.

39. The method of claim 34 wherein said step of generating said output signal includes selectively amplifying said first signal so as to increase system gain at relatively low input torque levels and decrease system gain at relatively high input torque levels.

40. The method of claim 35 wherein said step of sensing said first signal includes providing a torque transducer within said mechanical steering gear means.

41. The method of claim 36 further comprising the step of sensing the velocity of an output motion of said steering gear means and generating a rate signal indicative thereof and inputting said rate signal to said signal processing means for selectively modifying said output signal with respect to said first signal and said rate signal.

42. The method of claim 41 wherein said step of sensing the velocity of an output motion of said steering gear means includes providing a tachometer in association with said mechanical steering gear means.

43. The method of claim 41 wherein said rate signal is manipulated and amplified by said signal processing means.

44. The method of claim 41 wherein said rate signal is non-linearly amplified as a function of one of its own magnitude and the magnitude of said first signal.

45. The method of claim 41 wherein said rate signal is non-linearly amplified as a function of its own magnitude and the magnitude of said first signal.

46. The method of claim 41 wherein said rate signal is amplified as a function of vehicular speed for generating rate derived speed-sensitive power steering.

47. The method of claim 36 further including the step of measuring the differential fluid pressure applied to said power cylinder and generating a pressure signal in response thereto.

48. The method of claim 47 said pressure signal is fed back to said signal processing means for selectively modifying said output signal in response thereto such that said differential fluid pressure applied to said power cylinder is a function of said input torque applied to said steering wheel.

49. The method of claim 41 further including the step of measuring the differential fluid pressure applied to said power cylinder and generating a pressure signal in response thereto.

50. The method of claim 49 said pressure signal is fed back to said signal processing means for selectively modifying said output signal in response thereto such that said differential fluid pressure applied to said power cylinder is a function of said input torque applied to said steering wheel.

51. The method of claim 50 wherein said step of measuring said differential fluid pressure includes providing a pressure transducer between said valve apparatus and said power cylinder.

52. An electronically controlled power steering system for motor vehicles of the type used for steering dirigible wheels in response to an input torque applied to a steering wheel, comprising:

mechanical steering gear means coupled to said steering wheel for generating a mechanically derived steering force in response to said input torque;

a power cylinder coupled to said mechanical steering gear means for producing a hydraulically derived steering force for augmenting said mechanically derived steering force;

first transducer means for generating a first signal indicative of said input torque applied to said steering wheel;

control valve means in fluid communication with said power cylinder for generating a differential pressure applied to said power cylinder;

means for supplying fluid to said control valve means;

a source of pressurized hydraulic fluid adapted to supply hydraulic fluid to said control valve means;

signal processing means for generating an output signal in response to said first signal, said signal processing means operable to selectively actuate said control valve means in response to said output signal for selectively regulating said hydraulically derived steering force generated by said power cylinder; and

second transducer means for generating a rate signal indicative of the velocity of an output motion of said mechanical steering gear means, said rate signal being fed back to said signal processing means for selectively modifying said output signal said signal processing means being adapted to amplify and selectively manipulate said first signal such that said output signal is a function of said input torque applied to said steering wheel.

53. The electronically controlled power steering system of claim 52 wherein said control valve means includes a control valve and valve actuation means for selectively actuating said control valve in response to said output signal.

54. The electronically controlled power steering system of claim 52 wherein said signal processing means includes means for generating said output signal as a function of vehicular speed.

55. The electronically controlled power steering system of claim 52 wherein said signal processing means includes means for amplifying said first signal so as to increase a system gain at relatively low input torque levels and decrease said system gain at relatively high input torque levels.

56. The electronically controlled power steering system of claim 52 wherein said first and second transducer means are associated with said mechanical steering gear means.

57. The electronically controlled power steering system of claim 52 wherein said rate signal is selectively manipulated and amplified by said signal processing means.

58. The electronically controlled power steering system of claim 57 wherein said rate signal is non-linearly amplified by said signal processing means as a function of one of a first magnitude of said rate signal and a second magnitude of said first signal.

59. The electronically controlled power steering system of claim 57 wherein said rate signal is non-linearly amplified by said signal processing means as a function of a first magnitude of said rate signal and a second magnitude of said first signal.

60. The electronically controlled power steering system of claim 52 wherein said signal processing means includes means for amplifying said rate signal as a function of vehicular speed for generating a rate derived - speed sensitive power steering.

61. The electronically controlled power steering system of claim 53 further comprising fluid pressure measurement means for measuring the differential fluid pressure applied to said power cylinder upon actuation of said control valve and generating a pressure signal in response thereto.

62. The electronically controlled power steering system of claim 61 wherein said pressure signal is fed back to said signal processing means for selectively modifying said output signal in response thereto and wherein said differential fluid pressure applied to said power cylinder is a function of said input torque applied to said steering wheel.

63. The electronically controlled power steering system of claim 62 wherein said fluid pressure measurement means is a pressure transducer associated with said control valve.

64. The electronically controlled power steering system of claim 53 wherein said control valve is an open-centered rotary valve and said valve actuation means is a torque motor coupled to said rotary valve and operable to selectively control fluid flow therethrough.

65. The electronically controlled power steering system of claim 61 wherein said control valve is an open-centered rotary valve and said valve actuation means is a torque motor operable to selectively control fluid flow through said reaction valve.

66. The electronically controlled power steering system of claim 53 wherein said mechanical steering gear means includes an input shaft coupled to a steering shaft to which said steering wheel is secured, an actuation member generally coaxially aligned with said input shaft and a rotationally compliant member adapted to interconnect said input shaft to said actuation member for transmitting said input torque thereto, said input torque being transferred from said actuation member to a driven member for producing said mechanically derived steering force.

67. The electronically controlled power steering system of claim 66 wherein said first transducer means is operably associated with said input shaft and said actuation member for generating said first signal indicative of the torque transmitted to said actuation member and wherein said first transducer means comprises first and second proximity transducers secured on one of said input shaft and said actuation member which are adapted to measure the distance between complimentary facing surfaces on the other of said input shaft and said actuation member and wherein said compliant member elastically deflects in a substantially linear manner with respect to said input torque upon rotation of said input shaft so as to define a corresponding change in said proximate distance between said first and second proximity transducers and said complimentary facing surfaces, respectfully, which is concomitant with said input torque, said signal processing means adapted to manipulate signals generated by said first and second proximity detectors to define said first signal.

68. The electronically controlled power steering system of claim 67 wherein said first and second proximity transducers are mounted in opposed relation within a plurality of first jaw teeth formed on an end of one of said input shaft and said actuation member which are loosely fitted with a plurality of complimentary second jaw teeth formed in juxtaposed relation on an end of the other of said input shaft and said actuation member and wherein said first and second jaw teeth form a mechanical backup steering assembly such that when said input torque is substantially zero said first and second jaw teeth are substantially centered in a non-contacting orientation.

69. The electronically controlled power steering system of claim 68 wherein said first and second proximity transducers are redundant such that their respective output signals are compared by said signal processing means whereby upon an excessively divergent value thereof said mechanical backup steering assembly provides mechanically derived steering during conditions of substantially no hydraulically derived steering force being generated.