Knock signal detection in automotive systems

• US 20090118989A1
• Filed: 11/07/2007
• Published: 05/07/2009
• Est. Priority Date: 11/07/2007
• Status: Active Grant

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: Padhi, Kabi P., Menter, Patrick W.
• Granted Patent: US 7,594,423 B2
• Time in Patent Office: Days
• US Class Current: 701/111
• CPC Class Codes: G01L 23/225 circuit arrangements therefor

Abstract

In an automotive system (300), a knock detection scheme is provided for detecting knock events in an internal combustion engine that are sensed by a transducer structure, such as a non-intrusive acoustic accelerometer sensor (310) to generate sensor signal information which is processed by a signal processing structure (312, 316, 318, 326) which extracts digital signal parameters from the sensor signal information to identify a predetermined pitch frequency (330) and any short-term energy increase (328) in the digital signal information which in combination are used to provide a positive indication of engine knock behavior. When a short term Fourier transform (324) is used to extract the digital signal parameters, time frequency resolution may be improved by appropriately windowing the digital signal being transformed.

Claims

1. A system for detecting knock signals in an internal combustion engine, comprising:

a sensor structure operatively coupled to the internal combustion engine for generating sensor signal information in response to engine vibrations; and

a signal processing structure operatively coupled to the sensor structure for extracting digital signal information from the sensor signal information to identify a predetermined pitch frequency and any short-term energy increase in the digital signal information which in combination are used to generate a knock detection signal.

2. The system of claim 1, where the sensor structure comprises an accelerometer sensor.

3. The system of claim 1, where the sensor structure comprises a non-intrusive acoustic sensor for attachment to an engine cylinder.

4. The system of claim 1, where the signal processing structure comprises:

an analog-to-digital converter for sampling the sensor signal information into a digital sensor signal;

an anti-aliasing filter for digitally filtering the digital sensor signal into a filtered digital sensor signal;

a decimator for down-sampling the filtered digital sensor signal into a decimated filtered digital sensor signal;

a short time Fourier transform module for extracting instantaneous frequency and amplitude information from the decimated filtered digital sensor signal; and

a knock detection module for detecting a predetermined pitch frequency and a short-term energy increase from the instantaneous frequency and amplitude information, where the knock detection module generates a knock detection signal if both the predetermined pitch frequency is detected and if a short-term energy increase is detected.

5. The system of claim 4, where the short time Fourier transform module applies a Blackman Harris window to the decimated filtered digital sensor signal to reduce frequency smearing.

6. The system of claim 4, where the knock detection module comprises a pitch detection module for computing a pitch frequency from the instantaneous frequency and amplitude information using a two-way mismatch error computation.

7. The system of claim 4, where the knock detection module comprises an energy computation module for computing a frame energy value from the instantaneous frequency and amplitude information.

8. The system of claim 7, where the knock detection module comprises a knock decision module for computing a short-term energy increase by comparing the frame energy value with a frame energy value from one or more previous frames.

9. A method for obtaining engine knock data from an internal combustion engine, comprising:

acquiring analog vibration signal information from a cylinder in the internal combustion engine using a knock sensor;

processing the analog vibration signal information by frame to generate an anti-aliased, down-sampled digital time domain signal;

short term Fourier transforming the digital time domain signal into a digital frequency domain signal, thereby generating instantaneous frequency and amplitude information for each frame;

detecting a predetermined pitch frequency in a frame from the instantaneous frequency and amplitude information;

detecting a predetermined energy increase in a frame from the instantaneous frequency and amplitude information; and

generating an engine knock detection signal if both the predetermined pitch frequency is detected and if the predetermined energy increase is detected.

10. The method of claim 9, where acquiring analog vibration signal information comprises lowpass filtering the analog vibration signal information to remove high frequency components.

11. The method of claim 9, where processing the analog vibration signal information comprises:

digitally sampling the analog vibration signal information into a digital sensor signal;

lowpass digitally filtering the digital sensor signal into a filtered digital sensor signal; and

decimating the filtered digital sensor signal into a decimated filtered digital sensor signal.

12. The method of claim 9, where short term Fourier transforming the digital time domain signal comprises multiplying the digital time domain signal and a Blackman Harris window.

13. The method of claim 9, where detecting a predetermined energy increase comprises comparing a first energy value for a current frame with a second energy value for a previous frame.

14. The method of claim 9, where detecting a predetermined energy increase comprises comparing a first energy value for a current frame with an average energy value for two or more previous frames.

15. The method of claim 9, where detecting a predetermined pitch frequency comprises computing a two-way mismatch error value to select from a set of candidate pitch frequencies.

16. A method of detecting engine knocks, comprising:

generating an analog sensor signal from an accelerometer which senses engine vibrations; and

extracting by frame a digital signal from the analog sensor signal to identify a predetermined pitch frequency and any short-term energy increase in the digital signal;

generating a knock detection signal if both the predetermined pitch frequency and a short-term energy increase are detected in a frame.

17. The method of claim 16, where extracting by frame a digital signal comprises:

sampling the analog sensor signal into a digital sensor signal;

anti-aliasing filtering the digital sensor signal into a filtered digital sensor signal;

decimating the filtered digital sensor signal into a decimated filtered digital sensor signal;

extracting instantaneous frequency and amplitude information from the decimated filtered digital sensor signal by applying a windowed short time Fourier transform; and

detecting a predetermined pitch frequency and a short-term energy increase from the instantaneous frequency and amplitude information.

18. The method of claim 17, where applying a windowed short time Fourier transform comprises applying a Blackman Harris window to the decimated filtered digital sensor signal.

19. The method of claim 17, where detecting a predetermined pitch frequency and a short-term energy increase comprises computing a pitch frequency from the instantaneous frequency and amplitude information using a two-way mismatch error computation.

20. The method of claim 17, where detecting a predetermined pitch frequency and a short-term energy increase comprises computing a current frame energy value from the instantaneous frequency and amplitude information, and comparing the current frame energy value to a frame energy value from one or more previous frames.