JPH05332192A - Knocking control device for engine - Google Patents

Abstract

PURPOSE:To avoid obstacle in judgment even in case that data number is varied in every engine speed by judging knock generation in a mean level of a spectrum. CONSTITUTION:Analog-to-digital conversion S22 of a knock sensor signal is started at the starting time of knock gate. In every A/D conversion, the converted value is Fourier transformed (S23). Then, mean spectrum of a specified frequency corresponding to a knock is obtained (S24) from the result of the Fourier-transformation S23. This operation is repeated during the knock gate period in every specified time. Presence of knock generation is judged from the mean level of the spectrum of the specified frequency corresponding to the knock during the knock gate period.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a knock control device for an engine, which executes a multiplication of a twiddle factor of a Fourier transform and a previous A / D conversion value during A / D conversion to average spectrum intensities for knock determination. Regarding

[0002]

2. Description of the Related Art As a conventional technique, the power of a plurality of frequencies associated with knock vibration is calculated by FFT (Fast Fourier Transform: Fas).
There is a technique of detecting knock by calculating with t Fourier Transform (for example, Japanese Patent Laid-Open No. 3-47449).

However, this method has a limitation in the gate period because the number of samples needs to be 2 ⁿ . FFT is DFT (mixed state Fourier transform: Dis
Less computational effort than creat Fourier Transform),
Even so, it is difficult to finish the calculation between the end of one gate period and the start of the next gate period, since the calculation is started after all the sampling is completed. Here, if it is attempted to make the calculation in time, it is necessary to reduce the number of data, and the accuracy deteriorates. R for sampled data
It must be stored in AM, and RAM is increased in large quantities. In order to maintain the accuracy of FFT, it is necessary to widen the gate period (processing period of the knock sensor signal), but if the gate period is widened, noise components other than knock increase as shown in FIG. Becomes worse. There are problems such as.

[0004]

SUMMARY OF THE INVENTION The present invention provides a DF when only a few spectral intensities are important, such as knock.
The processing load of T may be smaller than that of FFT.
With the DFT, there is no limit to the number of data, so the knock gate can be set freely. Since DFT can proceed with calculation even during data sampling, the time from the end of sampling to knock determination can be shortened.
In the case of knock detection, since the duration of knock vibration, that is, the number of data is different for each engine speed, knock detection should be performed by averaging the power per data rather than knock detection by the total power. The S / N can be improved by calculating the maximum value of the vibration power in the middle of the gate using the DFT. Focusing on this point, by using the time during A / D conversion, the twiddle factor of the Fourier transform corresponding to a plurality of specific frequencies is multiplied by the A / D converted data, and based on this, one spectral data The object is to solve the above-mentioned problem by obtaining an average level per hit and performing knock determination based on this average level.

[0005]

Therefore, according to the present invention, as shown in FIG. 1, a knock sensor for detecting vibrations according to knock of an engine, a low-pass filter for attenuating a high frequency component of the knock sensor signal, and a A / D converter for A / D converting the output in a predetermined cycle, specific frequency selecting means for selecting a specific frequency for knock determination, and timing for setting a gate period of A / D conversion for knock determination Control means and A / D of the A / D converter
Fourier transforming means for Fourier transforming the transformed value for each A / D conversion, and averaging for averaging the spectrum obtained by Fourier transforming by the Fourier transforming means for each A / D conversion of the A / D converter Means, knock determination means for performing knock determination based on the result of the averaging, and knock control means for controlling knock according to the knock determination result of the knock determination means are provided.

[0006]

The timing control means opens the knock gate to start A / D conversion and initialize the spectrum. A /
A plurality of knock frequencies are selected from the specific frequency selection means by taking in the D conversion value, and the Fourier transform corresponding to this is executed by the Fourier transform means. This conversion is A / D
It is executed between conversion and A / D conversion. Based on the result of the Fourier transform, averaging of the spectrum is performed in the averaging means. Knock determination and knock control are performed according to the average level.

[0007]

EXAMPLES The present invention will be described below with reference to examples. In FIG. 3, reference numeral 1 denotes a knock sensor that detects vibrations according to the knock of the engine, and has a flat output characteristic with respect to frequency. Reference numeral 2 is a low-pass filter for detecting return noise. Reference numeral 3 is a DSP (digital signal processor) having a built-in A / D converter 3a for digitally processing the knock sensor signal and determining knock. Four
Is an ECM (engine control microcomputer) that calculates a control amount of a knock control factor such as an engine ignition timing and an air-fuel ratio according to a knock determination result from the DSP 3.

FIG. 4 shows a DSP executed at a certain angle, for example, a timing of 10 ° C. after top dead center (BTDC).
The processing contents of No. 3 are shown. When this routine starts from S10, the A / D conversion start timing is set to set the gate period of A / D conversion in S11. This A / D
The A / D conversion start and end timings for setting the conversion gate period are determined by the engine speed as shown in FIG. 7, for example. RAM value for calculating the spectrum of the specific frequency selected for knock determination in S12 (average level XRM (k), X of the real part and imaginary part of the spectrum)
IM (k) and maximum power value PMAX (k)) are cleared. This routine ends in S13.

FIG. 5 shows the processing contents of the DSP 3 executed at the A / D conversion start timing. When this routine starts from S20, the A / D conversion end timing is set in S21. In S22, the output signal of knock sensor 1 at that time is A / D converted. This A / D conversion value X in S23
Fourier transform (n). Since this is one of the points of the present invention, it will be described in detail. The conversion formula of DFT is

[0010]

[Equation 1] Here, X (n) is time series data, n is time series data X
(N) is an index indicating the order, N is the total number of time series data, k is an index that defines the frequency, and X (k) is k.
The spectrum of the frequency determined by, W _N is the twiddle factor,

[0011]

[Equation 2]

[0012] This twiddle factor W _N is

[0013]

[Equation 3]

Kn = N, W _N ^kn goes around once, and then repeats. For example, if N = 128 and A / D sampling frequency fs = 50 KHz, the frequency resolution Δf is Δf = 50 KHz / 64. Frequency f = 1
Focusing on 2.5 KHz (corresponding to k = 16), n = 1
28/16 = 8, that is, W _N ^kn makes one round with 8 data.

Therefore, when DFT is performed on a stationary signal of 12.8 KHz, the average of the results up to the first 8 data and 1
All 28 data have the same value as the DFT average.
That is, as long as the number of data is large to some extent, it is possible to capture the essence with a smaller number of data without processing N = 128 data. Therefore, a reasonable value can be obtained even when N = 128 or N = 100 up to the DFT.

W _N ^kn is calculated in advance by RO
DF by writing in M and reading the appropriate value
It becomes possible to calculate T. Considering this W _N ^kn simply,
128 × 2 = 256 pieces are required for the real part and the imaginary part for each k, but using the periodicity of W _N ^kn , 8 × 2 = 16 pieces can be obtained if f = 12.8 KHz. Na ROM
The efficiency of can be improved.

In S23, at a specific k,

[0018]

## EQU00004 ## XR (k) = X (n) cos (2.pi./N.k.n) XI (k) = X (n) sin (2.pi./N.k.n) is calculated.

In S24, spectrum averaging is executed as follows.

[0020]

[Equation 5] In S25, the power is calculated by the following formula.

[0021]

## EQU00006 ## P (k) = XRM (k) .XRM (k) + XIM (k) .XIM (k) In S26, the power calculated this time is the maximum value RM up to now.
If larger than Ax (k), replace P (k) with PMAX (k). By doing so, the power at the time of knocking can be captured, and the S / N can be improved. In S27, it is determined whether or not the A / D conversion end timing has come. If YES, the process proceeds to S29, and if NO, the process proceeds to S28. In S28, time adjustment is performed to set the A / D conversion sampling period (execution period of S22) to a predetermined value, and the process returns to S22. This routine ends in S29.

FIG. 6 is a flowchart showing the processing contents at the A / D end timing. When this routine starts from S30, the knock determination level is calculated in S31, for example, by the following equation.

[0023]

V _KD (k) = KVAL (k, cyl) × VMEAN (k, cyl) where k is a frequency index, cyl is a cylinder index, and V _KD (k) is a knock determination level. K
VAL (k, cyl) is an engine condition, frequency, a coefficient set for each cylinder, and VMEAN (k, cyl) is an average level of PMAX (k) for each frequency and each cylinder.

By doing so, the knock determination level can be created for each cylinder and each frequency, and the knock detection accuracy can be improved. In S32, the maximum value PAX (k) of the vibration power for each frequency and the knock determination level V
_KD (k) is compared, and if PMAX (k) is V _KD (k) or more, it is determined to be a knock. The steps S31 and S32 are executed for a plurality of knock frequencies. Then, as a result of knock determination at a plurality of knock frequencies, if knock is determined even at one frequency, it is determined that there is knock during the current combustion.

In S33, the result is output to the port. For example, if there is a knock, a certain port is set to 0, and if not, it is set to 1. The ECM 4 reads this port and performs knock control according to ignition timing and the like. This routine ends in S35.

[0026]

Since the present invention has the following effects, it is possible to perform knock control with high accuracy. You can freely set the knock gate.

Since the time from the end of the gate to the knock determination is short, the knock determination result can be quickly reflected in the ignition timing and the like. Since knock determination is performed at the average level of the spectrum, the determination is not hindered even if the number of data changes for each rotation speed.

Since the maximum value of the vibration power in the gate section can be obtained, the S / N can be improved.

[Brief description of drawings]

FIG. 1 is a diagram corresponding to a claim of the present invention.

FIG. 2 is a waveform diagram of a gate period and a knock sensor signal.

FIG. 3 is a block diagram showing an embodiment of the device of the present invention.

FIG. 4 is a DS executed at BTDC 10 ° C. timing.
It is a flowchart which shows the processing content of P.

FIG. 5 is a DSP executed at A / D conversion start timing.
5 is a flowchart showing the processing contents of FIG.

FIG. 6 is a DSP executed at the end timing of A / D conversion.
5 is a flowchart showing the processing contents of FIG.

FIG. 7 is a diagram showing A / D conversion start and end timings.

[Explanation of symbols]

 1 Knock sensor 2 Low pass filter 3 Digital signal processor 3a A / D converter 4 Engine control microcomputer

Claims (3)

[Claims] 1. A knock sensor for detecting vibrations according to engine knock, a low-pass filter for attenuating a high-frequency component of the knock sensor signal, and an A / D for A / D converting the output of the filter at a predetermined cycle.
A converter, a specific frequency selecting means for selecting a specific frequency for knock determination, a timing control means for setting a gate period of A / D conversion for knock determination, and an A / D converter for the A / D converter. Fourier transforming means for Fourier transforming the D-converted value for each A / D conversion, and averaging for averaging spectra obtained by Fourier transforming by the Fourier transforming means for each A / D conversion of the A / D converter Knocking means for making knock determination based on the result of this averaging, and knock control means for controlling knock in accordance with the knock determination result of this knock determining means. Control device. 2. The Fourier transform means executes the Fourier transform by utilizing the time between the A / D conversion of the A / D converter and the A / D conversion. Knock control device for engine. 3. The knock control device for an engine according to claim 1, wherein the knock determination means determines the knock based on the maximum power of the average level of the spectrum within the gate period.