Coded data generation or conversion – Analog to or from digital conversion – Analog to digital conversion
Reexamination Certificate
2002-11-19
2004-06-15
Williams, Howard L. (Department: 2819)
Coded data generation or conversion
Analog to or from digital conversion
Analog to digital conversion
C123S406340, C701S111000, C073S035030, C708S319000
Reexamination Certificate
active
06750798
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for processing a knock sensor signal and a design method of the same. More particularly, the present invention relates to a signal-processing apparatus for digitally processing an analog signal generated by a knock sensor for detecting a knocking.
2. Related Art
A knocking detection apparatus of an internal combustion engine is disclosed in documents such as Japanese Patent No. 2764495 (JP-A No. H5-248937).
In the apparatus disclosed in the document, an analog signal generated by a knock sensor is analyzed by being subjected to a wavelet conversion process in order to detect generation of a knocking. Thus, the analog signal generated by the knock sensor is subjected to an A/D conversion process in an A/D converter at a fixed sampling period, and time-axis data obtained as a result of the A/D conversion process is supplied to a frequency sampling filter to generate a processing result, which is then used as a basis for detecting generation of a knocking. The frequency sampling filter is a digital filter having an impulse response equal to the output of a predetermined basic wavelet function.
That is, in the implementation of a wavelet conversion process, a frequency F to serve as a processing object of a filter for determining whether or not a knocking exists by the wavelet conversion process is determined in advance, and a frequency sampling filter reacting to the frequency F, which is referred to as a filter frequency, is provided. A frequency sampling filter for wavelet conversion is designed so that, in general, the impulse response of the filter has a waveform H with a basic wavelet function's frequency (or the so-called scale) matching the frequency F serving as an object of the filter. (That is, the waveform H is the waveform of a wavelet function having the F frequency). Thus, the output value of a frequency sampling filter designed in this way increases when the frequency of the input waveform Hin, which is the waveform of supplied time-axis data obtained as a result of an A/D conversion process, is equal to the frequency F serving as an processing object of the filter, and the input waveform Hin substantially exceeds the waveform H in the upward and downward directions. The more substantially the input waveform Hin exceeds the waveform H, the more the output value of the frequency sampling filter increases. The output value of the frequency sampling filter having such a characteristic is analyzed to determine whether or not a knocking exists.
By the way, in the apparatus disclosed in the document, the frequency sampling filter is designed to comprise a comb-type filter and a resonator to reduce the number of multiplications in the frequency sampling filter.
However, the document includes a statement saying: “If a wavelet conversion process is carried out using 50 wavelet functions with different scales, the number of multiplications is 750 per sample.” Thus, in the sampling frequency filter disclosed in the document, for each sample, 15(=750/50) multiplications are required.
Assume for example that an attempt is made to carry out filter processing (strictly, digital filter processing) up to a maximum frequency of 14 kHz. In this case, it is necessary to set the sampling frequency (that is, the reciprocal of the sampling period) at a value at least equal to 28 kHz in accordance with the sampling theorem. As a matter of fact, it is desirable to set the sampling frequency at about 100 kHz in order to give a high degree of precision with which a knocking is detected. Then, let 3 frequencies including 14 kHz be each a processing object of the filter. In this case, if the frequency sampling filter disclosed in the document is used, for each period of 10 microseconds, which corresponds to a frequency of 100 kHz, 45 (=3×15) multiplications are required so that, the processing load becomes excessively large if an ordinary microcomputer is to be used for carrying out the filtering process, that is, if an ordinary microcomputer is to be used to function as a digital filter. For this reason, a special-purpose microcomputer such as a DSP is required.
SUMMARY OF THE INVENTION
It is thus an object of the present invention addressing the problems to reduce the filter processing load borne by a knock sensor signal processing apparatus used in a knocking detection system for detecting generation of a knocking by analyzing a signal generated by a knock sensor.
In accordance with a first aspect of the present invention, there is provided a knock sensor signal processing apparatus comprising:
an A/D converter for converting a knock-sensor signal generated by a knock sensor provided in an internal combustion engine from an analog signal into a digital signal in an A/D conversion process carried out at a fixed sampling period; and
a digital filter for sequentially inputting sampled data obtained as a result of the A/D conversion process carried out by the A/D converter and processing the sampled data.
The digital filter is an FIR (Finite Impulse Response) filter. In addition, filter coefficients h (k) of the digital filter are set in such a way that the filter coefficient h(m)=0 in case the sign of the filter coefficient h(m−1) is different from the filter coefficient h(m+1) where k=0 to n and n is a positive integer.
In accordance with such a knock sensor signal processing apparatus, the filter load to process the knock signal can be reduced effectively.
That is, in general, an FIR filter includes a delay-unit group comprising a plurality of delay units connected to each other in series. The delay unit at the first stage receives pieces of sampled data sequentially with a present input piece of sampled data delayed from the immediately preceding input piece of sampled data by a sampling period. The subsequent delay units following the delay unit at the first stage receive pieces of sampled data from the immediately preceding delay units. The output of each delay unit in this group is multiplied by a coefficient h(k) referred to as a filter coefficient or a filter constant to produce a product. A sum of such products for the delay units, that is, a result of processing to sum up the weighted outputs of the delay units, is the output of the filter.
In an implementation of the knock sensor signal processing apparatus according to the first aspect of the present invention, if the sign of an (m−1)th filter coefficient h(m−1) is different from the sign of an (m+1)th filter coefficient, the mth filter coefficient h(m) between the (m−1)th filter coefficient h(m−1) and the (m+1)th filter coefficient h(m+1) is 0. Thus, the output of a delay unit corresponding to the mth filter coefficient h(m) of 0 does not have to be subjected to filter processing.
In other words, if the sign (or the polarity) of a filter coefficient of a digital filter changes, a zero point is deliberately used in order to reduce a computation load.
Concretely, in designing an FIR filter reacting to a processing-object frequency f of the filter, that is, in designing a FIR filter with a filter frequency f, the filter coefficients h(k) of the FIR filter are set at values equal to values of their respective mince points set on a predetermined reference waveform having a frequency equal to the filter frequency f by mincing the waveform starting from a start of the waveform at intervals each equal to a sampling period to provide a FIR filter having an output value, which increases when the frequency of the waveform representing pieces of time-axis data input sequentially matches the filter frequency f. In this case, zero-cross points of the reference waveform are used as some of the mince points. By doing so, the multiplicand filter coefficients for delay units corresponding to the mince points at the zero-cross points are zero so that, for the outputs of such delay units, no processing is required.
In such an implementation, the filter-processing
Denso Corporation
Nixon & Vanderhye P.C.
Williams Howard L.
LandOfFree
Apparatus for processing knock sensor signal does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus for processing knock sensor signal, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus for processing knock sensor signal will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3312930