Torque ripple free electric power steering

• US 6,498,451 B1
• Filed: 09/06/2000
• Issued: 12/24/2002
• Est. Priority Date: 09/06/2000
• Status: Expired due to Term

• Current Assignee: GM Global Technology Operations Incorporated (Motors Liquidation Co. GUC Trust), Steering Solutions IP Holding Corporation (Nexteer Automotive Group Ltd.)
• Original Assignee: Delphi Technologies, Inc. (BorgWarner Incorporated)
• Inventors: Bernard, Bruno Patrice, Nehl, Thomas Wolfgang, Chen, Shaotang, Namuduri, Chandra Sekhar, Henry, Rassem Ragheb, Boules, Nady
• Primary Examiner(s): Dang, Khanh
• Application Number:
  US09/656,116
• Time in Patent Office: 839 Days
• Field of Search: 318/254, 318/138, 318/661, 318/685, 318/715, 310/44, 310/45, 310/46
• US Class Current: 318/661
• CPC Class Codes: B62D 5/0403 characterised by constructional features, e.g. common housing for motor and gear box
• CPC Class Codes: H02K 29/03 with a magnetic circuit specially adapted for avoiding torque ripples or self-starting problems
• CPC Class Codes: H02K 29/08 using magnetic effect devices, e.g. Hall-plates, magneto-resistors H02K29/12 takes precedence
• CPC Class Codes: H02K 7/116 with gears
• CPC Class Codes: H02P 2209/07 Trapezoidal waveform
• CPC Class Codes: H02P 6/10 Arrangements for controlling torque ripple, e.g. providing reduced torque ripple

Abstract

Disclosed is an electric motor system with reduced torque ripple comprising a sinusoidally magnetized permanent magnet, a sinusoidal inverter, a higher resolution position sensor, a composite iron stator yoke, a composite reinforced plastic rotor core and shaft; and a high gear ratio gear reduction box. The novel combination of magnet, inverter, sensor, plastic rotor core and shaft and high gear ratio gear box substantially reduces the torque ripple on the shaft of said motor system.

Claims

1. An electric motor system with reduced torque ripple comprising:

an electric motor having a stator and a rotor and at least one windings;

said electric motor comprising;

permanent magnetic means effective in generating an essentially sinusoidal magnetic field; and

a higher-resolution position sensor effective in sensing the angular position of said rotor; and

a sinusoidal inverter coupled to said electric motor to drive at least one winding current through said at least one windings of said electric motor wherein said sinusoidal inverter is adapted to receive angular position information from said higher-resolution position sensor to control said at least one winding currents to be essentially sinusoidal.

2. The invention of claim 1 wherein said permanent magnetic means further comprises at least one sinusoidally magnetized permanent magnets.

3. The invention of claim 1 wherein said electric motor further comprises slotless airgap windings.

4. The invention of claim 1 wherein said at least one windings of said electric motor are located in slots separated by teeth.

5. The invention of claim 1 wherein said stator is made from a powdered iron composite.

6. The invention of claim 5 wherein said stator is also the motor housing.

7. The invention of claim 1 wherein said rotor further comprises a composite reinforced plastic shaft.

8. The invention of claim 1 wherein said rotor further comprises a composite iron shaft.

9. The invention of claim 1 wherein said electric motor system further comprises a torque command, wherein said control of said at least one winding currents is responsive to said torque command, and wherein said control is a current-mode control.

10. The invention of claim 1 wherein said electric motor system further comprises a torque command, wherein said control of said at least one winding currents is responsive to said torque command, and wherein said control is a voltage-mode control.

11. The invention of claim 1 wherein said higher-resolution position sensor further comprises:

an incremental position sensor; and

an absolute position sensor defining a reference angle.

12. The invention of claim 11 wherein said absolute position sensor further defines one or more electronic signal, where said one or more electronic signal each includes a first level and a second level, and said reference angle is based upon a transition from said first level to said second level of one said electronic signal when said motor is rotating clockwise, and is based upon a transition from said second level to said first level of said one electronic signal when said motor is rotating counterclockwise.

13. The invention of claim 12 wherein a power-up phase of said electric motor further includes the steps of:

determining an angular interval from said one or more electronic signals from said absolute position sensor;

exciting one or more said winding from said motor according to said determined angular interval; and

,

controlling said winding currents to be essentially sinusoidal after one of said electronic signals from said absolute position sensor has effected a transition from one of said first and second levels to the other of said first and second levels.

14. The invention of claim 11 wherein said at least one motor windings of said electric motor is arranged into one or more phases, and said absolute position sensor further comprises one electronic signal for each said motor phase.

15. The invention of claim 1 wherein said higher-resolution position sensor comprises:

a magnetoresistor;

a toothed track; and

said magnetoresistor(s) and toothed track(s) mounted in said motor such that relative rotational motion between said rotor and said stator results in relative rotational motion between said magnetoresistor(s) and said toothed track(s); and

wherein said magnetoresistor(s) is disposed sufficiently close to said toothed tracks(s) so as to be effective in detecting said relative motion.

16. The invention of claim 2 wherein said electric motor further comprises slotless air gap windings.

17. The invention of claim 16 wherein said at least one winding of said electric motor are located in slots separated by teeth.

18. The invention of claim 17 wherein said stator is made from a powdered iron composite.

19. The invention of claim 18 wherein said stator is also the motor housing.

20. The invention of claim 19 wherein said rotor further comprises a composite reinforced plastic shaft.

21. The invention of claim 19 wherein said rotor further comprises a composite iron shaft.

22. The invention of claim 21 wherein said electric motor system further comprises a torque command, wherein said control of said at least one winding current is responsive to said torque command, and wherein said control is a current-mode control.

23. The invention of claim 21 wherein said electric motor system further comprises a torque command, wherein said control of said at least one winding current is responsive to said torque command, and wherein said control is a voltage-mode control.

24. The invention of claim 22 wherein said higher-resolution position sensor further comprises:

an incremental position sensor; and

an absolute position sensor defining a reference angle.

25. The invention of claim 24 wherein said absolute position sensor further defines one or more electronic signal, where said one or more electronic signal each includes a first level and a second level, and said reference angle is based upon a transition from said first level to said second level of one said electronic signal when said motor is rotating clockwise, and is based upon a transition from said second level to said first level of said one electronic signal when said motor is rotating counterclockwise.

26. The invention of claim 25 wherein a power-up phase of said electric motor further includes the steps of:

determining an angular interval from said one or more electronic signals from said absolute position sensor;

exciting one or more said winding from said motor according to said determined angular interval; and

,

controlling said winding currents to be essentially sinusoidal after one of said electronic signals from said absolute position sensor has effected a transition from one of said first and second levels to the other of said first and second levels.

27. The invention of claim 24 wherein said at least one motor windings of said electric motor is arranged into one or more phases, and said absolute position sensor further comprises one electronic signal for each said motor phase.

28. The invention of claim 27 wherein said higher-resolution position sensor comprises:

a magnetoresistor;

a toothed track; and

said magnetoresistor(s) and toothed track(s) mounted in said motor such that relative rotational motion between said rotor and said stator results in relative rotational motion between said magnetoresistor(s) and said toothed track(s); and

wherein said magnetoresistor(s) is disposed sufficiently close to said toothed tracks(s) so as to be effective in detecting said relative motion.

29. An electric motor system with reduced torque ripple for power assisted steering in a motor vehicle comprising:

an electric motor having a stator and a rotor and at least one windings;

said electric motor comprising;

permanent magnetic means effective in generating an essentially sinusoidal magnetic field; and

a higher-resolution position sensor effective in sensing the angular position of said rotor; and

a sinusoidal inverter coupled to said electric motor to drive at least one current through said at least one windings of said electric motor wherein said sinusoidal inverter is adapted to receive angular position information from said higher-resolution position sensor to control said at least one winding current to be essentially sinusoidal.

30. The invention of claim 29 wherein said permanent magnetic means further comprises at least one sinusoidally magnetized permanent magnets.

31. The invention of claim 29 wherein said electric motor further comprises slotless airgap windings.

32. The invention of claim 29 wherein said at least one windings of said electric motor are located in slots separated by teeth.

33. The invention of claim 29 wherein said stator is made from a powdered iron composite.

34. The invention of claim 33 wherein said stator is also the motor housing.

35. The invention of claim 29 wherein said rotor further comprises a composite reinforced plastic shaft.

36. The invention of claim 29 wherein said rotor further comprises a composite iron shaft.

37. The invention of claim 29 wherein said electric motor system further comprises a torque command, wherein said control of said at least one winding currents is responsive to said torque command, and wherein said control is a current-mode control.

38. The invention of claim 29 wherein said electric motor system further comprises a torque command, wherein said control of said at least one winding currents is responsive to said torque command, and wherein said control is a voltage-mode control.

39. The invention of claim 29 wherein said higher-resolution position sensor further comprises:

an incremental position sensor; and

an absolute position sensor defining a reference angle.

40. The invention of claim 39 wherein said absolute position sensor further defines one or more electronic signal, where said one or more electronic signal each includes a first level and a second level, and said reference angle is based upon a transition from said first level to said second level of one said electronic signal when said motor is rotating clockwise, and is based upon a transition from said second level to said first level of said one electronic signal when said motor is rotating counterclockwise.

41. The invention of claim 40 wherein a power-up phase of said electric motor further includes the steps of:

determining an angular interval from said one or more electronic signals from said absolute position sensor;

exciting one or more said winding from said motor according to said determined angular interval; and

,

controlling said winding currents to be essentially sinusoidal after one of said electronic signals from said absolute position sensor has effected a transition from one of said first and second levels to the other of said first and second levels.

42. The invention of claim 39 wherein said at least one motor windings of said electric motor is arranged into one or more phases, and said absolute position sensor further comprises one electronic signal for each said motor phase.

43. The invention of claim 29 wherein said higher-resolution position sensor comprises:

a magnetoresistor;

a toothed track; and

said magnetoresistor(s) and toothed track(s) mounted in said motor such that relative rotational motion between said rotor and said stator results in relative rotational motion between said magnetoresistor(s) and said toothed track(s); and

wherein said magnetoresistor(s) is disposed sufficiently close to said toothed tracks(s) so as to be effective in detecting said relative motion.

44. The invention of claim 29 wherein said electric motor system with reduced torque ripple is mounted on the steering column of said motor vehicle.

45. The invention of claim 30 wherein said electric motor further comprises slotless air gap windings.

46. The invention of claim 45 wherein said at least one winding of said electric motor are located in slots separated by teeth.

47. The invention of claim 46 wherein said stator is made from a powdered iron composite.

48. The invention of claim 47 wherein said stator is also the motor housing.

49. The invention of claim 48 wherein said rotor further comprises a composite reinforced plastic shaft.

50. The invention of claim 48 wherein said rotor further comprises a composite iron shaft.

51. The invention of claim 49 wherein said electric motor system further comprises a torque command, wherein said control of said at least one winding current is responsive to said torque command, and wherein said control is a current-mode control.

52. The invention of claim 49 wherein said electric motor system further comprises a torque command, wherein said control of said at least one winding current is responsive to said torque command, and wherein said control is a voltage-mode control.

53. The invention of claim 51 wherein said higher-resolution position sensor further comprises:

an incremental position sensor; and

an absolute position sensor defining a reference angle.

54. The invention of claim 53 wherein said absolute position sensor further defines one or more electronic signal, where said one or more electronic signal each includes a first level and a second level, and said reference angle is based upon a transition from said first level to said second level of one said electronic signal when said motor is rotating clockwise, and is based upon a transition from said second level to said first level of said one electronic signal when said motor is rotating counterclockwise.

55. The invention of claim 54 wherein a power-up phase of said electric motor further includes the steps of:

determining an angular interval from said one or more electronic signals from said absolute position sensor;

exciting one or more said winding from said motor according to said determined angular interval; and

,

controlling said winding currents to be essentially sinusoidal after one of said electronic signals from said absolute position sensor has effected a transition from one of said first and second levels to the other of said first and second levels.

56. The invention of claim 55 wherein said at least one motor windings of said electric motor is arranged into one or more phases, and said absolute position sensor further comprises one electronic signal for each said motor phase.

57. The invention of claim 56 wherein said higher-resolution position sensor comprises:

a magnetoresistor;

a toothed track; and

said magnetoresistor(s) and toothed track(s) mounted in said motor such that relative rotational motion between said rotor and said stator results in relative rotational motion between said magnetoresistor(s) and said toothed track(s); and

wherein said magnetoresistor(s) is disposed sufficiently close to said toothed tracks(s) so as to be effective in detecting said relative motion.

58. The invention of claim 57 wherein said electric motor system with reduced torque ripple is mounted on the steering column of said motor vehicle.

59. A electric power assisted steering system for a motor vehicle including an electric motor system, the steering system comprising:

a steerable wheel coupled to a movable rack-pinion gear assembly;

a reduced torque ripple electric motor having a stator and a rotor and at least one windings coupled to said movable rack and a steering wheel;

said electric motor comprising;

permanent magnetic means effective in generating an essentially sinusoidal magnetic field; and

a higher-resolution position sensor effective in sensing the angular position of said rotor; and

a sinusoidal inverter coupled to said electric motor to drive at least one current through said at least one windings of said electric motor wherein said sinusoidal inverter is adapted to receive angular position information from said higher-resolution position sensor to control said at least one winding current to be essentially sinusoidal;

wherein said motor applies an assist torque to said rack-pinion assembly responsive to a command, said command responsive to torque applied to said steering wheel.

60. The steering system of claim 59 wherein said permanent magnetic means further comprises at least one or more sinusoidally magnetized permanent magnets.

61. The steering system of claim 60 wherein said electric motor further comprises slotless airgap windings.

62. The steering system of claim 59 wherein said at least one windings of said electric motor are located in slots separated by teeth.

63. The steering system of claim 59 wherein said stator is made from a powdered iron composite.

64. The steering system of claim 63 wherein said stator is also the motor housing.

65. The steering system of claim 59 wherein said rotor further comprises a composite reinforced plastic shaft.

66. The steering system of claim 59 wherein said rotor further comprises a composite iron shaft.

67. The steering system of claim 59 wherein said electric motor system further comprises a torque command, wherein said control of said at least one winding currents is responsive to said torque command, and wherein said control is a current-mode control.

68. The steering system of claim 59 wherein said electric motor system further comprises a torque command, wherein said control of said at least one winding currents is responsive to said torque command, and wherein said control is a voltage-mode control.

69. The steering system of claim 59 wherein said higher-resolution position sensor further comprises:

an incremental position sensor; and

an absolute position sensor defining a reference angle.

70. The steering system of claim 69 wherein said absolute position sensor further defines one or more electronic signal, where said one or more electronic signal each includes a first level and a second level, and said reference angle is based upon a transition from said first level to said second level of one said electronic signal when said motor is rotating clockwise, and is based upon a transition from said second level to said first level of said one electronic signal when said motor is rotating counterclockwise.

71. The steering system of claim 70 wherein a power-up phase of said electric motor further includes the steps of:

determining an angular interval from said one or more electronic signals from said absolute position sensor;

exciting one or more said winding from said motor according to said determined angular interval; and

,

controlling said winding currents to be essentially sinusoidal after one of said electronic signals from said absolute position sensor has effected a transition from one of said first and second levels to the other of said first and second levels.

72. The steering system of claim 69 wherein said at least one motor windings of said electric motor is arranged into one or more phases, and said absolute position sensor further comprises one electronic signal for each said motor phase.

73. The steering system of claim 59 wherein said higher-resolution position sensor comprises:

a magnetoresistor;

a toothed track; and

said magnetoresistor(s) and toothed track(s) mounted in said motor such that relative rotational motion between said rotor and said stator results in relative rotational motion between said magnetoresistor(s) and said toothed track(s); and

wherein said magnetoresistor(s) is disposed sufficiently close to said toothed tracks(s) so as to be effective in detecting said relative motion.

74. The steering system of claim 59 wherein said electric motor system is mounted on the steering column of said motor vehicle.