Engine misfire, knock of roughness detection method and apparatus

• US 5,269,178 A
• Filed: 06/24/1991
• Issued: 12/14/1993
• Est. Priority Date: 12/10/1990
• Status: Expired due to Fees

• Current Assignee: Sensortech LP
• Original Assignee: Sensortech LP
• Inventors: Vigmostad, Erik B., Klauber, Robert D., Sprague, Frederick P.
• Primary Examiner(s): Williams, Hezron E.
• Assistant Examiner(s): DOMBROSKE, GEORGE M
• Application Number:
  US07/720,240
• Time in Patent Office: 904 Days
• Field of Search: 73/116, 73/117.2, 73/117.3, 73/35 R, 73/35 KR, 73/35 K, 73/35 KS, 73/35 J, 73/35 M, 73/35 O, 73/35 P, 73/DIG. 2, 364/431.08
• US Class Current: 73/114.15
• CPC Class Codes: B60G 17/019 characterised by the type of sensor or the arrangement thereof B60G17/01941 takes precedence
• CPC Class Codes: B60G 2204/11 Mounting of sensors thereon
• CPC Class Codes: B60G 2400/30 Propulsion unit conditions
• CPC Class Codes: B60G 2400/60 Load
• CPC Class Codes: B60G 2400/91 Frequency
• CPC Class Codes: B60G 2401/172 Hall effect
• CPC Class Codes: B60G 2600/602 high pass
• CPC Class Codes: B60G 2600/604 low pass
• CPC Class Codes: B60G 2800/802 Diagnostics
• CPC Class Codes: G01D 3/028 mitigating undesired influences, e.g. temperature, pressure
• CPC Class Codes: G01L 23/223 using magnetic or magnetostrictive means
• CPC Class Codes: G01L 3/102 involving magnetostrictive means magnetostrictive sensors H10N35/101
• CPC Class Codes: G01L 3/105 involving inductive means G01L3/102, G01L3/104 take precedence
• CPC Class Codes: G01M 15/042 by monitoring a single specific parameter not covered by groups G01M15/06 - G01M15/12
• CPC Class Codes: Y10S 73/02 Magnetostrictive

Abstract

Disclosed are a method and apparatus for comparing torsional stress/strain states of a power transmitting member of an internal combustion engine to detect an abnormal combustion condition, including misfire, knock or roughness. Statistical processing steps may be used to detect an abnormal combustion event including: calculating a mean and standard deviation for a set of signals related to the torsional stress induced in the power transmitting member, calculating a difference between a later signal and the mean, calculating a ratio of the difference to the standard deviation, and comparing the ratio to a threshold. The ratio so obtained from a given cylinder may further be compared with one or more other such ratios from other cylinders. A magnetostrictive sensor may preferably be used to obtain the signals relating to the torsional stress in the power transmitting member, such as the engine crankshaft. In addition, the magnetostrictive sensor may include windings to cancel induced electromagnetic interference signals.

Claims

1. A method for detecting torque variation in a power transmitting member which experiences torque variation, the method comprising the steps of:

obtaining a first set of signals related to torsional stress in the power transmitting member during a first time period;

determining a first at least one value from said first set of signals;

obtaining a second signal related to torsional stress in the power transmitting member during a second time period wherein said second time period may comprise a portion of the first time period;

computing a second at least one value, at least in part from the second signal;

wherein said values are computed without directly computing the torque;

comparing the second at least one value to the first at least one value wherein said step of comparing may comprise, at least in part, the step of calculating a ratio of the second at least one value and the first at least one value; and

thereby detecting torque variation in the power transmitting member.

2. The method of claim 1 wherein said torque variation results from an abnormal combustion event, such as misfire, knock, or roughness, in an internal combustion engine which produces a series of combustion events and which transmits power through the power transmitting member;

wherein said first set of signals obtaining step comprises the step of obtaining a first set of signals related to the torsional stress in the member produced by a first series of combustion events;

wherein said determining step comprises the step of calculating a mean and a standard deviation for the first set of signals;

wherein said second signal obtaining step comprises the step of obtaining a second signal related to the torsional stress in the member produced by a second combustion event;

wherein said calculating step comprises the steps of;

calculating a difference between the second signal and the mean of the first set of signals; and

calculating a ratio of the difference and the standard deviation; and

wherein said detecting step comprises the step of comparing the ratio to a threshold to detect an abnormal combustion event.

3. The method of claim 2 wherein said step of obtaining the second signal is performed sufficiently close in time to said step of obtaining the first set of signals so as to obtain the second signal and the first set of signals under substantially constant engine ambient conditions.

4. The method of claim 2 wherein said step of calculating a standard deviation comprises calculating a moving standard deviation, and wherein said step of calculating a mean comprises calculating a moving mean.

5. The method of claim 2 wherein said step of obtaining the first set of signals comprises obtaining each of the first set of signals from a first combustion chamber.

6. The method of claim 1 wherein said torque variation results from an abnormal combustion event, such as misfire, knock or roughness, in an internal combustion engine which produces a series of combustion events and which transmits power through the power transmitting member;

wherein said first set of signals obtaining step comprises the step of obtaining a first set and a second set of signals related to the torsional stress in the member produced by a first series and second series of combustion events respectively;

wherein said determining step comprises the step of calculating a means and a standard deviation for the first and second sets of signals respectively;

wherein said second signal obtaining step comprises the steps of;

obtaining a third signal and a fourth signal related to the torsional stress in the member produced by a third and a fourth combustion event respectively;

calculating a first difference between the third signal and the mean of the first set of signals;

wherein said calculating step comprises the steps of calculating a first ratio of the first difference to the standard deviation for the first set of signals;

calculating a second difference between the fourth signal and the mean of the second set of signals; and

calculating a second ratio of the second difference to the standard deviation for the second set of signals; and

wherein said detecting step comprises the step of comparing the first ratio to the second ratio to detect an abnormal combustion event.

7. The method of claim 6 wherein said step of obtaining the first set of signals and the third signal comprises obtaining each from a first combustion chamber, and wherein said step of obtaining the second set of signals and the fourth signal comprises obtaining each from a second combustion chamber.

8. The method of claim 7 wherein the steps of calculating the mean and the standard deviation for the first and second sets of signals comprise the steps of calculating a moving mean and a moving standard deviation for the first set of signals for the first combustion chamber and the second set of signals for the second combustion chamber respectively, wherein the first and second ratios define a first relativity number and a second relativity number respectively, and wherein the step of comparing the first ratio to the second ratio comprises the step of comparing the first and second relativity numbers to detect an abnormal combustion event.

9. The method of claim 1 wherein said torque variation results from an abnormal combustion event, such as misfire, knock or roughness, in an internal combustion engine which produces a series of combustion events and which transmits power through the power transmitting member;

wherein said first set of signals obtaining step comprises the step of obtaining a first set of signals related to the torsional stress in the member produced by a first series of combustion events;

wherein said determining step comprises the step of calculating a mean and a variance for the first set of signals;

wherein said second signal obtaining step comprises the step of obtaining a second signal related to the torsional stress in the member produced by a second combustion event;

wherein said calculating step comprises the steps of;

calculating a square of a difference between the second signal and the means of the first set of signals; and

calculating a ratio of the square of the difference and the variance; and

wherein said detecting step comprises the step of comparing the ratio to a threshold to detect an abnormal combustion event.

10. The method of claim 1 wherein said torque variation results from an abnormal combustion event, such as misfire, knock or roughness, in an internal combustion engine which produces a series of combustion events and which transmits power through the power transmitting member;

wherein said first set of signals obtaining step comprises the step of obtaining a first set and a second set of signals related to the torsional stress in the member produced by a first series and a second series of combustion events respectively;

wherein said determining step comprises the step of calculating a mean and a variance for the first and second sets of signals respectively;

wherein said second signal obtaining step comprises the step of obtaining a third signal and a fourth signal related to the torsional stress in the member produced by a third and a fourth combustion event respectively;

wherein said calculating step comprises the steps of;

calculating a first square of the difference between the third signal and the mean of the first set of signals;

calculating a first ratio of the first square of the difference and the variance for the first set of signals;

calculating a second square of a difference between the fourth signal and the mean of the second set of signals; and

calculating a second ratio of the square of the second difference to the variance for the second set of signals; and

wherein said detecting step comprises the step of comparing the first ratio to the second ratio to detect an abnormal combustion event.

11. The method of claim 10 wherein said step of obtaining the first set of signals and the third signal comprise obtaining each from a first combustion chamber, and wherein said step of obtaining the second set of signals and the fourth signal comprise obtaining each from a second combustion chamber.

12. The method of claim 1 wherein said torque variation results from an abnormal combustion event, such as misfire, knock or roughness, in an internal combustion engine which produces a series of combustion events and which transmits power through the power transmitting member;

wherein said first set of signals obtaining step comprises the step of obtaining a first set of signals related to the torsional stress in the member produced by a first series of combustion events;

wherein said determining step comprises the step of calculating a means for the first set of signals;

wherein said second signal obtaining step comprises the step of obtaining a second signal related to the torsional stress in the member produced by a second combustion event;

wherein said calculating step comprises the steps of;

calculating a difference between the second signal and the means of the first set of signals; and

calculating a ratio of the difference and the mean; and

wherein said detecting step comprises the step of comparing the ratio to a threshold to detect an abnormal combustion event.

13. The method of claim 1 wherein said torque variation results form a torque producing event in said power transmitting member which experiences a series of torque producing events;

wherein said first set of signals obtaining step comprises the step of obtaining a first set of signals related to the torsional stress in the member produced by a first series of torque producing events;

wherein said determining step comprises the step of calculating a mean and a standard deviation for the first set of signals;

wherein said second signal containing step comprises the step of obtaining a second signal related to the torsional stress in the member produced by a second torque producing event;

wherein said calculating step comprises the steps of;

calculating a difference between the second signal and the mean of the first set of signals; and

calculating a ratio of the difference and the standard deviation; and

wherein said detecting step comprises the step of comparing the ratio to a threshold to detect a relative difference in the second torque producing event.

14. The method of claim 1 wherein said torque variation results from a torque producing event in said power transmitting member which experiences a series of torque producing events;

wherein said first set of signals obtaining step comprises the step of obtaining a first set of signals related to the torsional stress in the member produced by a first series of torque producing events;

wherein said determining step comprises the step of calculating a mean for the first set of signals;

wherein said second signal obtaining step comprises the step of obtaining a second signal related to the torsional stress in the member produced by a second torque producing event;

wherein said calculating step comprises the steps of;

calculating a difference between the second signal and the mean of the first set of signals; and

calculating a ratio of the difference and the mean; and

wherein said detecting step comprises the step of comparing the ratio to a threshold to detect a relative difference in the later torque producing event.

15. The method of claim 1 wherein said torque variation results from an abnormal combustion event, such as misfire, knock or roughness, in an internal combustion engine which produces a series of combustion events and which transmits power through the power transmitting member;

wherein said first set of signals obtaining step comprises the step of obtaining a first signal related to the torsional stress in the member for a first combustion chamber and produced during starting rotation of the engine prior to engine ignition;

wherein said determining step comprises the step of setting said at least one value equal to said first set of signals;

wherein said second signal obtaining step comprises the step of obtaining a second signal related to the torsional stress in the member produced by a combustion event for the first combustion chamber and after engine ignition;

wherein said calculating step comprises the step of dividing a difference between the first and second signals by a threshold to detect an abnormal combustion event in the first combustion chamber.

16. The method of claim 15 further comprising the steps of:

obtaining a third signal related to the torsional stress in the member for a second combustion chamber produced during starting rotation of the engine prior to engine ignition;

obtaining a fourth signal related to the torsional stress in the member produced by a combustion event for the second combustion chamber and after engine ignition; and

comparing a difference between the first and second signals with the difference between the third and fourth signals to detect an abnormal combustion event in one of the first and second combustion chambers.

17. The method of claim 16 wherein said step of comparing a difference between the first and second signals with the difference between the third and fourth signals comprises the steps of comparing the differences to a threshold.

18. The method of claim 1 wherein said torque variation results from an abnormal combustion event, such as misfire, knock or roughness, in an internal combustion engine which produces a series of combustion events and which transmits power through the power transmitting member;

wherein said first set of signals obtaining step comprises the step of obtaining a first signal related to the torsional stress produced in the member during a peak portion of a combustion event;

wherein said determining step comprises the step of setting said at least one value to said first signal;

wherein said second signal obtaining step comprises the step of obtaining a second signal related to the torsional stress produced in the member during a non-peak portion of a combustion event;

wherein said calculating step comprises the step of calculating a ratio between the first and second signals; and

wherein said detecting step comprises the step of comparing the ratio to a threshold to detect an abnormal combustion event.

19. The method of claim 18 wherein said steps of obtaining said first and second signals are performed sufficiently close in time so as to obtain both signals under substantially constant engine ambient conditions.

20. The method of claim 1 wherein said torque variation results from an abnormal combustion event, such as misfire, knock or roughness, in an internal combustion engine which produces a series of combustion events and which transmits power through the power transmitting member;

wherein said first set of signals obtaining step comprises the step of obtaining a first signal and a second signal related to the torsional stress produces in the member during a non-peak portion of two respective combustion events;

wherein said determining step comprises the step of setting said at least one value to said first and said second signals;

wherein said second signal obtaining step comprises the step of obtaining a third signal related to the torsional stress produced in the member during a peak portion of a combustion event;

wherein said calculating step comprises the step of multiplying the third signal by the ratio of the first and second signals; and

wherein said detecting step comprises the step of comparing the multiplied third signal to a threshold to detect an abnormal combustion event.

21. The method of claim 20 further comprising the steps of obtaining a fourth signal related to the torsional stress in the member produced by a combustion event, and comparing the fourth signal to the third signal multiplied by the ratio of the first and second signals to determine an abnormal combustion event.

22. The method of claim 21 wherein said steps of obtaining said second, third and fourth signals are performed sufficiently close in time so as to obtain each signal under substantially constant engine ambient conditions.

23. The method of claim 21 wherein said step of obtaining the first signal comprises obtaining an average of a plurality of signals related to the torsional stress produced in the member during a non-peak portion of a plurality of combustion events.

24. The method of claim 1 wherein said torque variation results from an abnormal combustion event, such as misfire, knock or roughness, in an internal combustion engine which produces a series of combustion events and which transmits power through the power transmitting member;

wherein said first set of signals obtaining step comprises the step of obtaining a first set of signals related tot he torsional stress in the member produced by a first series of combustion events;

wherein said determining step comprises the step of calculating a mean and an estimated standard deviation for the first set of signals;

wherein said second signal obtaining step comprises the step of obtaining a second signal related to the torsional stress in the member produced by a second combustion event;

wherein said calculating step comprises the step of calculating a difference between the second signal and the mean of the first set of signals; and

wherein said detecting step comprises the step of comparing the difference to the estimated standard deviation to detect an abnormal combustion event.

25. The method of claim 24 wherein the step of calculating an estimated standard deviation comprises the steps of calculating a difference between each signal in the first set of signals and the means, calculating a summation of the absolute values of the differences, and dividing the summation by the number of signals in the first set of signals.

26. The method of claim 24 wherein the step of comparing the difference to the estimated standard deviation comprises the steps of:

calculating a ratio of the difference and the estimated standard deviation; and

comparing the ratio to a threshold to detect an abnormal combustion event.

27. The method of claim 1 wherein said torque variation results from an abnormal combustion event, such as misfire, knock or roughness, in an internal combustion engine which produces a series of combustion events and transmits power through the power transmitting member;

wherein said first set of signals obtaining step comprises the step of obtaining a first set of signals related to the torsional stress in the member produced by a first series of combustion events;

wherein said determining step comprises the step of calculating a mean and an estimated variance for the first set of signals;

wherein said second signal obtaining step comprises the step of obtaining a second signal related to the torsional stress in the member produced by a second combustion event;

wherein said calculating step comprises the step of calculating a square of the difference between the second signal and the mean of the first set of signals; and

wherein said detecting step comprises the step of comparing the square of the difference to the estimated variance to detect an abnormal combustion event.

28. The method of claim 1 wherein said torque variation results from an abnormal combustion event, such as misfire, knock or roughness, in an internal combustion engine which produces a series of combustion events and which transmits power through the power transmitting member,

wherein said first set of signals obtaining step comprises the step of obtaining a first set of signals related to torsional stress in the member produced by a first series of combustion events;

wherein said determining step comprises the step of calculating an expected value of the second signal from the first set of signals and using said expected value to obtain the first at least one value;

where in said second signal obtaining step comprises the step of obtaining a second signal related to torsional stress in the member produced by a second combustion event.

29. The method of claim 28 wherein the step of calculating the expected value of the second signal comprises the steps of:

calculating an expected value for a third signal selected from the first set of signals, the third signal occurring prior to the second signal;

weighting each of the third signal and the expected value of the third signal with respective weighting coefficients; and

summing the weighted third signal and the weighted expected value of the third signal to produce the expected value of the second signal.

30. The method according to claim 29 wherein the weighting coefficients total unity.

31. The method of claim 1 wherein said torque variation results from an abnormal combustion event, such as misfire, knock or roughness, in an internal combustion engine which produces a series of combustion events and which transmits power through the power transmitting member;

wherein said first set of signals obtaining step comprises the step of obtaining a first set of signals related to the torsional stress in the member produced by a first series of combustion events;

wherein said determining step comprises the step of calculating a first series of differences between each successive pair of signal in the first set of signals and calculating a mean from the first series of differences;

wherein said second signal obtaining step comprises the step of obtaining a second signal related to the torsional stress in the member produced by a second combustion event;

wherein said calculating step comprises the step of calculating a second difference between the second signal and a third signal selected from the first set of signals, the third signal occurring prior to the second signal; and

wherein said detecting step comprises the step of comparing the second difference to the mean from the first series of differences to detect an abnormal combustion event.

32. The method of claim 31 wherein the step of comparing the second difference to the mean from the first series of differences comprises the steps of:

calculating a ratio of the second difference and the mean from the first series of differences; and

comparing the ratio to a threshold to detect an abnormal combustion event.

33. The method of claim 1 wherein said torque variation results from a repetitive abnormal combustion event, such as repetitive misfire, knock or roughness, in an internal combustion engine which produces a series of combustion events and which transmits power through the power transmitting member;

wherein said first set of signals obtaining step comprises the step of obtaining a set of signals related to the torsional stress in the member produced by a series of combustion events;

wherein said determining step comprises the step of calculating a series of differences between each successive pair of signals in the set of signals and calculating a mean from the series of differences;

wherein said calculating step comprises the step of determining a high and a low value of a difference from the series of differences; and

wherein said detecting step comprises the step of comparing the mean to at least one of zero and a difference between the high and low values to detect a repetitive abnormal combustion event.

34. The method of claim 1 wherein said torque variation results from an abnormal combustion event, such as misfire, knock or roughness, in an internal combustion engine which produces a series of combustion events and which transmits power through the power transmitting member;

wherein said first set of signals obtaining step comprises the step of obtaining a first set of signals related to the torsional stress in the member produced by a first series of combustion events;

wherein said determining step comprises the step of calculating a standard deviation for the first set of signals;

wherein said second signal obtaining step comprises the step of obtaining a second signal related to the torsional stress in the member produced by a second combustion event;

wherein said calculating step comprises the steps of;

calculating a difference between the second signal and a third signal selected from the first set of signals, the third signal occurring immediately prior to the second signal; and

calculating a ratio of the difference and the standard deviation; and

wherein said detecting step comprises the step of comparing the ratio to a threshold to detect an abnormal combustion event.

35. The method of claim 34 wherein the step of calculating the standard deviation comprises the step of calculating a moving standard deviation.

36. The method of claim 1 wherein said first set of signals and said second signal are obtained from at least one magnetostrictive sensor adjacent the power transmitting member.

37. The method of claim 36 wherein said obtaining a first set of signals step comprises the steps of:

obtaining a third set of signals related to torsional stress in the power transmitting member during the first time period;

passing said third set of signals through a tuned filter having at least one of a variable high pass element, a variable low pass element, and a variable center frequency;

sensing the rotational speed of the power transmitting member; and

tuning at least one of the high pass, low pass and center frequency elements of said tuned filter, responsive to the sensed rotational speed of the power transmitting member, to thereby produce said first set of signals.

38. The method of claim 36 wherein said obtaining a second set of signals step comprises the steps of:

obtaining a fourth signal related to torsional stress in the power transmitting member during the second time period;

passing said fourth signal through a tuned filter having at least one of a variable high pass element, a variable low pass element, and a variable center frequency;

sensing the rotational speed of the power transmitting member; and

tuning at least one of the high pass, low pass and center frequency elements of said tuned filter, responsive to the sensed rotational speed of the power transmitting member, to thereby produce said second signal.

39. The method of claim 38 wherein a high pass frequency for the high pass element is proportional to the sensed rotational speed of the power transmitting member.

40. The method of claim 38 wherein a low pass frequency for the low pass element is proportional to the sensed rotational speed of the power transmitting member.

41. The method of claim 37 wherein a high pass frequency for the high pass element is proportional to the sensed rotational speed of the power transmitting member.

42. The method of claim 37 wherein a low pass frequency for the low pass element is proportional to the sensed rotational speed of the power transmitting member.

54. The method of claim 28 wherein said first set of signals and said second signal are obtained from at least one magnetostrictive sensor adjacent the power transmitting member.

55. The method of claim 28 wherein the step of comparing comprises, at least in part, the step of calculating a ratio of the second at least one value and the first at least one value.

56. The method of claim 29 wherein said first set of signals and said second signal are obtained from at least one magnetostrictive sensor adjacent the power transmitting member.

57. The method of claim 29 wherein the step of comparing comprises, at least in part, the step of calculating a ratio of the second at least one value and the first at least one value.

43. A method for detecting an abnormal combustion event, such as misfire, knock or roughness, in an internal combustion engine which produces a series of combustion events and which transmits power through a power transmitting member, said method comprising the steps of:

obtaining a first set of signals related to the torsional stress in the member produced by a first series of combustion events;

obtaining a second signal related to the torsional stress in the member produced by a second combustion event;

calculating an expected value of the second signal from the first set of signals;

calculating a difference between the expected value of the second signal and the second signal;

calculating an expected value of a moving standard deviation;

dividing the difference between the expected value of the second signal and the second signal by the expected value of the moving standard deviation to obtain a ratio; and

comparing the ratio to a threshold to detect an abnormal combustion event.

44. The method of claim 43 wherein said first set of signals and said second signal are obtained from at least one magnetostrictive sensor adjacent the power transmitting member.

45. The method of claim 43 wherein the step of calculating the expected value of the second signal comprises the steps of:

calculating an expected value for a third signal selected from the first set of signals, the third signal occurring prior to the second signal;

weighting each of the third signal and the expected value of the third signal with respective weighting coefficients; and

summing the weighted third signal and the weighted expected value of the third signal to produce the expected value of the second signal.

46. The method according to claim 45 wherein the respective weighting coefficients of the weighted third signal and the weighted expected value of the third signal sum to unity.

47. A method for detecting torque variation in a power transmitting member which experiences torque variation, said method comprising the steps of:

obtaining a first set of signals related to the torsional stress in the power transmitting member during a first time period;

obtaining a second signal related to the torsional stress in the power transmitting member during a second time period;

calculating an expected value of the second signal from the first set of signals;

calculating a difference between the expected value of the second signal and the second signal;

calculating an expected value of a moving standard deviation;

dividing the difference between the expected value of the second signal and the second signal by the expected value of the moving standard deviation to obtain a ratio; and

comparing the ratio to a threshold to detect torque variation in the power transmitting member.

48. The method of claim 47 wherein said first set of signals and said second signal are obtained from at least one magnetostrictive sensor adjacent the power transmitting member.

49. The method of claim 47 wherein the step of calculating the expected value of the second signal comprises the steps of:

calculating the expected value for a third signal selected from the first set of signals, the third signal occurring prior to the second signal;

weighing each of the third signal and the expected value of the third signal with respective weighing coefficients; and

summing the weighted third signal and the weighted expected value of the third signal to produce the expected value of the second signal.

50. The method according to claim 49 wherein the weighted coefficients total unity.

51. A method for detecting an abnormal combustion event, such as misfire, knock or roughness, in an internal combustion engine which produces a series of combustion events and which transmits power through a power transmitting member said method comprising the steps of:

obtaining a first set of signals related to torsional stress in the power transmitting member produced by a first series of combustion events during a first time period;

calculating an expected value for a third signal selected from the first set of signals, the third signal occurring prior to a second signal where in said second signal is related to torsional stress in the power transmitting member during a second time period;

weighting each of the third signal and the expected value of the third signal with respective weighting coefficients; and

summing the weighted third signal and the weighted expected value of the third signal to produce an expected value of the second signal;

obtaining the second signal; and

calculating a ratio of the second signal and the expected value of the second signal to determine abnormal combustion.

52. The method according to claim 51 wherein the weighting coefficients total unity.

53. The method according to claim 51 wherein said first set of signals and said second signal are obtained from at least one magnetostrictive sensor adjacent the power transmitting member.