Knock signal detection in automotive systems
View Patent ↗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.
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.