Decoding an alternator output signal

• US 20050251369A1
• Filed: 05/07/2004
• Published: 11/10/2005
• Est. Priority Date: 05/07/2004
• Status: Active Grant

• Current Assignee: Snap-On Incorporated
• Original Assignee: Snap-On Incorporated
• Inventors: Stoffels, Nicolaas M. J., DeCarlo, Robert D., Mutzabaugh, Dennis M.
• Granted Patent: US 7,162,397 B2
• Time in Patent Office: Days
• US Class Current: 702/190
• CPC Class Codes: G01L 23/085 by measuring fluctuations of starter motor current or of battery voltage battery testing arrangements G01R31/36; testing of electrical installation on transport means G01R31/005; battery testing arrangements G01R31/36

Abstract

An engine diagnostic system is provided that enables a service technician to evaluate engine cylinder contribution to output power. The service technician couples one or more signal leads to the vehicle'"'"'s battery, alternator, or accessory receptacle (e.g., cigarette lighter receptacle) to provide an alternator output signal to a signal analyzer. The signal analyzer processes the alternator output signal to generate an engine signature, which represents engine cylinder contribution to engine output power.

Claims

1. An apparatus for filtering an alternator output signal to reduce interference, the apparatus comprising:

a bandpass filter circuit coupled to the alternator output signal and configured to generate a diode ripple signal by attenuating frequency components below a first cutoff frequency and above a second cutoff frequency;

a transformer coupled to the diode ripple signal and configured to amplify the diode ripple signal; and

a direct current (DC) coupling circuit coupled to the alternator output signal and the amplified diode ripple signal and configured to add the amplified diode ripple signal with the alternator output signal to generate a filtered ripple signal.

2. The apparatus of claim 1, further comprising:

a signal analyzer coupled to the filtered ripple signal and configured to demodulate the filtered ripple signal.

3. The apparatus of claim 1, wherein the bandpass filter circuit includes a high pass filter portion and a low pass filter portion.

4. The apparatus of claim 1, wherein the first cutoff frequency is from about 155 Hz to about 215 Hz.

5. The apparatus of claim 1, wherein the second cutoff frequency is from about 27.5 KHz to about 37.5 KHz.

6. The apparatus of claim 1, wherein the transformer has a gain of about 10.

7. A method for filtering an alternator output signal to reduce interference, the method comprising:

bandpass filtering the alternator output signal to generate a diode ripple signal, the diode ripple signal having attenuated frequency components below a first cutoff frequency and above a second cutoff frequency;

amplifying the diode ripple signal to generate an amplified diode ripple signal; and

adding the amplified diode ripple signal with the alternator output signal to generate a filtered ripple signal, the filtered ripple signal including a direct current (DC) component coupled to the amplified diode ripple signal.

8. The method of claim 7, further comprising:

coupling the filtered ripple signal to a signal analyzer configured to demodulate the filtered ripple signal.

9. The method of claim 7, wherein the first cutoff frequency is from about 155 Hz to about 215 Hz.

10. The method of claim 7, wherein the second cutoff frequency is from about 27.5 KHz to about 37.5 KHz.

11. A signal processing system for angle demodulating a ripple signal obtained from an alternator output signal, the system comprising:

an analog-to-digital converter configured to sample the ripple signal to generate a diode ripple data stream;

a bandpass filter configured to receive the diode ripple data stream and further configured to filter the signal to generate a complex time domain diode tone; and

an angle demodulator configured to generate a phase demodulated signal by receiving the complex time domain diode tone and demodulating the diode tone.

12. The signal processing system of claim 11, further comprising:

an input conditioning module configured to receive the diode ripple data stream and to adjust dynamic range before the analog-to-digital converter samples the ripple signal to generate a diode ripple data stream.

13. The signal processing system of claim 11, further comprising:

a filter/amplifier circuit configured to receive the alternator output signal and to filter the alternator output signal to reduce interference before the analog-to-digital converter samples the ripple signal to generate a diode ripple data stream.

14. The signal processing system of claim 11, further comprising:

a slew rate limiter configured to receive the diode ripple data stream and to apply a slew rate limit to identify an impulse in the diode ripple data stream, the slew rate limiter further configured to reduce the impulse magnitude before the bandpass filter processes the frequency domain signal; and

a spectrum analyzer operatively coupled to the band pass filter and configured to determine a center frequency for the band pass filter.

15. The signal processing system of claim 14, wherein the spectrum analyzer is further configured to determine a center frequency of the diode tone, and the slew rate limiter includes a threshold computed by the center frequency of the diode tone.

16. The signal processing system of claim 11, further comprising:

a Fourier transform module configured to receive the diode ripple data stream and to convert the diode ripple data stream from a time domain signal to a frequency domain signal;

a bandpass filter operatively coupled to the Fourier transform module and configured to filter the frequency domain signal; and

an inverse Fourier transform module operatively coupled to the band pass filter and configured to transform the filtered frequency domain signal into the diode tone, the diode tone comprising a complex time domain signal.

17. The signal processing system of claim 11, wherein the angle demodulator further comprises:

an arctangent calculator configured to calculate the arctangent of the diode tone to produce a phase signal; and

a phase differentiator operatively coupled to the arctangent calculator and configured to differentiate the phase signal to yield the phase demodulated signal.

18. The signal processing system of claim 11, further comprising:

a slope rate limiter configured to receive the phase demodulated signal and to identify a discontinuity in the phase demodulated signal.

19. The signal processing system of claim 18, wherein the slope rate limiter further comprises:

a first derivative module configured to calculate a first derivative of the phase demodulated signal;

a second derivative module operatively coupled to the first derivative module and configured to calculate a second derivative of the phase demodulated signal;

an adder operatively coupled to the first and the second derivative modules and configured to add the absolute values of the first derivative and the absolute value of the second derivative to produce a slope metric signal;

a comparator operatively coupled to the adder and configured to determine an impulse duration by comparing the slope metric signal to a reference value; and

an interpolator operatively coupled to the comparator and configured to receive the phase demodulated signal, the interpolator further configured to reconstruct the phase demodulated signal to remove the discontinuity for the impulse duration.

20. The signal processing system of claim 11, further comprising:

an indexer configured to sample the phase demodulated signal to produce indexed engine data.

21. The signal processing system of claim 20, wherein the time base of the indexed engine data is independent of engine RPM and diode ripple tone frequency.

22. The signal processing system of claim 20, further comprising:

a storage unit configured to receive the indexed engine data and to store the indexed engine data for subsequent processing.

23. A method for angle demodulating a ripple signal obtained from an alternator output signal, the method comprising:

sampling the ripple signal to generate a diode ripple data stream;

filtering the diode ripple data stream to generate a diode tone; and

performing an angle demodulation on the diode tone to obtain a phase demodulated signal.

24. The method of claim 23, wherein the alternator output signal is obtained from a connection between a first ground point and a second ground point.

25. The method of claim 24, wherein the first ground point comprises an alternator housing and the second ground point comprises a negative battery terminal.

26. The method of claim 23, further comprising:

conditioning the diode ripple data stream to adjust dynamic range before sampling the ripple signal to generate a diode ripple data stream.

27. The method of claim 23, further comprising:

filtering the diode ripple data stream to reduce interference before sampling the ripple signal to generate a diode ripple data stream.

28. The method of claim 23, further comprising:

applying a slew rate limit to the diode ripple data stream to identify an impulse and to reduce the impulse magnitude before filtering the diode ripple data stream to generate a diode tone.

29. The method of claim 28, further comprising:

transforming a time domain signal into a frequency domain signal;

performing a spectrum analysis on the frequency domain signal to determine a center frequency for the filtering.

30. The method of claim 29, further comprising:

synthesizing a band pass filter based on the center frequency.

31. The method of claim 23, wherein filtering the diode ripple data stream to generate a diode tone further comprises:

transforming a filtered frequency domain signal into the diode tone, the diode tone comprising a time domain signal.

32. The method of claim 23, wherein performing an angle demodulation on the diode tone to obtain a phase demodulated signal further comprises:

calculating an arctangent of the diode tone to produce a phase signal; and

differentiating the phase signal to yield the phase demodulated signal.

33. The method of claim 23, further comprising:

applying a slope rate limit to the phase demodulated signal to identify a discontinuity in the phase demodulated signal.

34. The method of claim 33, wherein applying a slope rate limit to the phase demodulated signal to identify a discontinuity in the phase demodulated signal further comprises:

calculating a first and a second derivative of the phase demodulated signal;

adding the absolute value of the first derivative and the absolute value of the second derivative to produce a slope metric signal;

comparing the slope metric signal to a reference value to determine an impulse duration; and

reconstructing the phase demodulated signal to remove the discontinuity for the impulse duration.

35. The method of claim 34, wherein reconstructing the phase demodulated signal to remove the discontinuity for the impulse duration comprises a sample and hold routine.

36. The method of claim 23, further comprising:

sampling the phase demodulated signal by the diode tone to produce indexed engine data.

37. The method of claim 36, wherein the time base of the indexed engine data is independent of engine RPM and diode ripple tone frequency.

38. The method of claim 36, further comprising:

storing the indexed engine data for subsequent processing.

39. The method of claim 38, wherein the subsequent processing comprises at least one of non-real-time processing and interfacing with a computing device.

40. A method for decoding a ripple signal obtained from an alternator output signal, the method comprising:

detecting a first zero crossing of a diode tone;

signaling a counter when the first zero crossing is detected;

detecting a second zero crossing of the diode tone; and

responsive to detecting the second zero crossing, storing the value of the counter.

41. The method of claim 40, further comprising:

producing indexed engine data based on the stored value of the counter.

42. The method of claim 41, wherein the time base of the indexed engine data is independent of engine RPM and diode ripple tone frequency.

43. A signal processing system for generating indexed engine data, the system comprising:

a computing device including a communications interface and a processor;

wherein the communications interface is configured to receive an alternator output signal and the processor is configured to decode the alternator output signal to generate the indexed engine data.

44. An apparatus for obtaining a diode ripple signal from a vehicle, the apparatus comprising:

a first terminal configured to be coupled to a first ground point; and

a second terminal configured to coupled to a second ground point.

45. The apparatus of claim 44, wherein the first ground point comprises an alternator housing and the second ground point comprises a negative battery terminal.

46. An apparatus for filtering an alternator output signal to reduce interference, the apparatus comprising:

means for bandpass filtering the alternator output signal to generate a diode ripple signal, the diode ripple signal having attenuated frequency components below a first cutoff frequency and above a second cutoff frequency;

means for amplifying the diode ripple signal to generate an amplified diode ripple signal; and

means for adding the amplified diode ripple signal with the alternator output signal to generate a filtered ripple signal, the filtered ripple signal including a direct current (DC) component coupled to the amplified diode ripple signal.

47. A signal processing system for angle demodulating a ripple signal obtained from an alternator output signal, the system comprising:

means for sampling the ripple signal to generate a diode ripple data stream;

means for filtering the diode ripple signal to generate a complex time domain diode tone; and

means for generating a phase demodulated signal by receiving the complex time domain diode tone and demodulating the diode tone.

48. An apparatus for decoding a ripple signal obtained from an alternator output signal, the apparatus comprising:

means for detecting a first zero crossing of a diode tone;

means for signaling a counter when the first zero crossing is detected;

means for detecting a second zero crossing of the diode tone; and

means for storing the value of the counter responsive to detecting the second zero crossing.