JPH0465636A - Knocking detector for internal combustion engine - Google Patents

Abstract

PURPOSE:To save the quantity of parts and a matching time and to detect a waveform change with time in real time by taking out the intensity for plural kinds of specific frequency components by a so-called digital filter consisting of a comb filter and a resonator. CONSTITUTION:The resonators 6a, 6b,... are made to resonate respectively based on a digital signal processed by the comb filter 3, and the continuation of resonance for each resonator 6a, 6b,... is restrained in accordance with the signal offset by an adding device 5, then the intensity of each frequency component is successively obtained. In the case the plural kinds of frequency components, the knocking vibration of which become remarkable, are extracted, the intensity (amplitude) of each frequency component can be obtained in real time without requiring a large memory capacity, as compared with the case the specific frequency components are taken out by a fast Fourier transform calculation from the detection signal inputted to a microcomputer 7.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a knocking detection device for an internal combustion engine, and more particularly to a technique for improving a device that detects the occurrence of knocking from an engine vibration detection signal.

<Prior art> When knocking occurs above a predetermined level in an internal combustion engine, it not only reduces the output but also causes suction and
Since this affects the exhaust valves and pistons, some engines are equipped with an ignition timing control device that detects knocking and corrects the ignition timing to promptly avoid knocking (Japanese Patent Laid-Open No. 58 (Refer to Publication No.-105036, etc.).

Knocking detection for correcting the ignition timing due to the occurrence of knocking has conventionally been performed as follows. That is, as shown in FIG. 5, a knock sensor 11 that outputs a detection signal according to the vibration level using a piezoelectric element is attached to a cylinder block of an engine, etc., and band pass filters 13 and 14 are set at mutually different center frequencies. .15, frequency components specific to knocking are extracted from the detection signal of the knock sensor 11, passed through a noise filter consisting of a resistor R and a capacitor C, and then analog/digital (hereinafter simply referred to as A/D). ) A/D conversion is performed by the converter 16 and input to the microcomputer 17.

The microcomputer 17 then uses a bandpass filter 13. 14. The occurrence of knocking is detected based on the level difference between the non-knocking time and the knocking time of each frequency component obtained in step 15, the temporal change characteristics of the waveform of a specific frequency, and the like.

Further, as shown in FIG. 6, the detection signal of the knocking sensor 11 is A/D converted by the A/D converter 16 and inputted to the microcomputer 17, which then performs fast Fourier transform (FFT), etc. In some cases, the occurrence of knocking is detected as described above by performing signal analysis through calculations and extracting frequency components specific to knocking.

<Invention or Problem to be Solved> By the way, in the case of a configuration in which a band-pass filter is used to extract frequency components that are noticeable as knocking vibrations, as shown in FIG. 5 above, when trying to detect knocking using multiple types of frequency components, , the number of parts increases accordingly, and the number of filters increases, which requires matching time, resulting in an increase in cost.

In addition, when performing signal analysis such as fast Fourier transform calculations in a microcomputer using the configuration shown in Figure 6 to obtain a frequency spectrum as shown in Figure 7, the number of parts and matching time increase. Although the disadvantages of using an analog bandpass filter can be overcome, it requires a large amount of memory capacity for calculations, and it is not possible to obtain the temporal transition of the extracted waveform of a specific frequency in real time. There is a problem in that knocking detection can only be performed based on the temporal transition of the waveform.

The present invention has been made in view of the above problems, and it is possible to reduce the number of parts and matching time when extracting multiple types of specific frequency components from the detection signal of a vibration sensor (knock sensor) and detecting knocking. Another object of the present invention is to enable real-time detection of the temporal transition of the extracted waveform of a specific frequency.

<Means for Solving the Problems> Therefore, a knocking detection device for an internal combustion engine according to the present invention is configured as shown in FIG.

In Fig. 1, a vibration sensor is attached to the engine body to detect engine vibration, and the detection signal of this vibration sensor is
A/D conversion is performed by a converter to obtain digital data of engine vibration.

This digital data of engine vibration is then input to a comb filter and processed. This comb filter is
A multi-stage delay element inputting an A/D-converted detection signal, data A/D-converted by the A/D converter, and data delayed by the multi-stage delay element after A/D conversion. It is configured to include an adder that performs addition.

The data processed by the comb filter is input to a plurality of resonators that resonate with mutually different frequency components, and a knocking discrimination means is used based on the mutually different specific frequency components obtained from each of the plurality of resonators. Determine the occurrence of knocking.

<Operation> According to this configuration, the analog detection signal from the vibration sensor is A/D converted by the A/D converter, and this A/D converter converts the analog detection signal from the vibration sensor.
A so-called digital filter consisting of a comb filter and a resonator extracts the intensities (amplitudes) of a plurality of specific frequency components from the digital detection signal obtained by /D conversion.

In other words, in a comb filter, a signal delayed by a delay element and a signal bypassed by the delay element are added together in an adder to cancel a specific frequency, thereby canceling the resonance of the resonator. By providing multiple stages of such a configuration, the intensities of multiple types of frequency components can be extracted.

Therefore, it is possible to detect in real time a change in the intensity of a frequency component that becomes noticeable as knocking, without requiring a large memory capacity.

<Example> The present invention will be explained in detail below.

In FIG. 2 showing one embodiment, a knock sensor (
Vibration sensor) ■ has a built-in piezoelectric element and outputs an analog voltage signal with a waveform corresponding to engine vibration.

The detection signal of the knock sensor l is converted into an A/D converter 2 by an A/D converter 2.
By performing D conversion, unnecessary high frequency components are cut and then input to the comb filter 3.

The comb filter 3 is composed of a plurality of stages of delay elements 4a-, 4b, . . . corresponding to the number of frequencies to be extracted, and an adder 5.
4b, . . . and the data whose polarity is reversed and the delay elements 4a, 4b.

By adding the data bypassed by the adder 5, the detected signal level is attenuated overall, and the adder 5 cancels out the frequencies corresponding to the delay time in particular, thereby improving the frequency characteristics. As a result, a so-called comb-shaped result is obtained.

The comb filter 3 includes a plurality of resonators 6a connected in parallel and provided corresponding to the number of frequencies used for knocking detection.
, 6b, ... are connected in series to
The output of the comb filter 3 is a plurality of resonators 6a, 6b having mutually different resonance frequencies.

... are input to each, a delay element, and an adder.

Resonators 6a, 6b, ... consisting of multipliers
resonates with each specific frequency component and outputs the amplitude value (intensity) of each frequency in real time.

In this way, if the resonators 6a, 6b, . 6a, 6b, . . . are prevented from continuing to resonate, and the intensity of each frequency component can be obtained sequentially.

Here, the resonator 6 is adjusted to correspond to the type of frequency required.
a, 6b, . . . are provided, and the number of delay elements 4a, 4b, .
Appropriately select from 7 kHz to 9 kHz and its surrounding frequency range where knocking vibration becomes noticeable, for example, 7 kHz.
, 8kHz, 9kHz, IQkHz,
It is preferable to use about 5 types of 11 kHz.

the fourth from each resonator 6a, 6b, .
The output data as shown in the figure is input to a microcomputer 7 as a knocking determination means, and the microcomputer 7 detects knocking according to a program stored in a ROM in advance.

In this configuration, in order to extract a plurality of types of frequency components in which knocking vibration becomes noticeable from the detection signal from the knock sensor 1, a
Since the so-called digital filter consisting of 6b, . . . is used, the microcomputer 7
Compared to extracting a specific frequency component from a detection signal input into the system by fast Fourier transform, the intensity (amplitude) of each frequency component can be obtained in real time without requiring a large amount of memory capacity. (see figure 4),
Further, unlike the case where an analog filter such as a bandpass filter is used, a large number of matching steps are not required.

Knocking determination based on the information on intensity changes for each specific frequency component obtained as described above is performed, for example, as shown in the flowchart of FIG. 3.

The knocking occurrence detection shown in the flowchart of Fig. 3 is as follows:
This is carried out in a predetermined frequency analysis section, and the predetermined frequency analysis section is, for example, a section in which combustion vibrations of each cylinder can be sampled while avoiding ignition noise. For example, in a 6-cylinder engine, ATDCIO° ~ A T D
C60°, and such a predetermined frequency analysis section is detected based on a detection signal from a crank angle sensor (not shown).

First, when it is detected that the frequency analysis section has entered, each of the resonators 6a, 6. The intensity (amplitude) of each frequency component input via b, . . . is stored as an initial value (Sl).

Then, assuming that the initial values stored for each frequency component do not change and that the intensity continues at a constant level in the frequency analysis interval, the time axis change of the integrated value of the intensity at this time is calculated as the sampling period and the initial value. This is set based on the value and is set as the standard change characteristic for each frequency component (S2).

Next, based on the time course of the intensity determined for each frequency component that is actually input (see Figure 4), the intensity is integrated for each sample period on the time axis, and the intensity is integrated within the frequency analysis interval. Detect the characteristics of the intensity change in (S3).

Then, as mentioned above, the standard change characteristic for each frequency component obtained assuming that the intensity remains unchanged is compared with the characteristic of the change in the intensity integral value for each frequency component actually detected ( S4).

Here, the standard change characteristic assumes that there is no change in intensity, so it increases linearly, but on the other hand, if the change characteristic of the intensity integral value obtained based on the actual detection signal does not match, Since knocking vibration is included in the frequency component, knocking occurrence is determined by estimating that the intensity is not stable at a constant level (S5), or the intensity integral value based on the actual detection signal is also determined as described above. If the frequency component increases substantially linearly as in the standard change characteristic, it is assumed that the frequency component is only due to mechanical vibration, and knocking does not occur (S6).

Such determination is performed for each frequency component corresponding to each resonator 6a, 6b, . . . , and, for example, when knocking is determined at a majority of frequencies, it is finally determined that knocking has occurred.

Note that the comparison between the standard change characteristic and the change characteristic based on the actual detection signal can be performed, for example, by accumulating the differences in integral values on the same time axis and checking whether the accumulated value is greater than or equal to a predetermined value. .

The operation of detecting the occurrence of knocking by the control shown in the flowchart of FIG. 3 will now be described.

That is, when knocking vibration is included in the same frequency component, the knocking vibration due to abnormal combustion is gradually attenuated, so the intensity of the frequency component included in the knocking vibration is also initially greatly attenuated and gradually reduced to the level of only mechanical vibration. On the other hand, when knocking vibration is not included, the intensity changes at a substantially constant mechanical vibration level. Therefore, when knocking vibration is not included, the initial intensity of the analysis section is approximately maintained, and the integrated value of the intensity increases approximately linearly.

Therefore, as mentioned above, if the initial strength of the analysis interval is assumed to be constant and the time axis change in the integrated value of the strength is estimated, this change characteristic (predetermined engine change characteristic) will be calculated when knocking does not occur. and when knocking occurs,
When the actual intensity is integrated on the time axis, it shows a change characteristic that does not match the change characteristic estimated as corresponding to the time when knocking does not occur. Therefore, knocking can be detected by calculating the integral value of the actual intensity on the time axis and comparing it with the value when no knocking occurs.

In this way, knocking is detected based on changes in the intensity of specific frequency components, so it can be identified even when the signal level is low, and even in the high rotation range where mechanical vibration is strong. Knocking can be detected by easily distinguishing between knocking vibration and mechanical vibration.

In addition, there may be frequencies where the intensity becomes weaker than the mechanical vibration level due to the occurrence of knocking, and then returns to the mechanical vibration level as the knocking vibration decays. It is preferable that the increase/decrease in level is influenced by knocking vibration.

However, the knocking determination based on the temporal transition of each of the plurality of frequency components output from each resonator 6a, 6b, . . . is not limited to the logic shown in the flowchart of FIG. 3 above.

<Effects of the Invention> As explained above, according to the present invention, when multiple types of frequency components are extracted from a vibration sensor, intensity changes for each frequency component can be obtained in real time, and the intensity changes It has the advantage of requiring only a small amount of memory when observing the time course of the noise, and provides an optimal preprocessing device especially when detecting knocking based on intensity changes of multiple types of frequency components included in the detection signal. can.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the configuration of the present invention, Fig. 2 is a system schematic diagram showing an embodiment of the present invention, Fig. 3 is a flowchart showing the details of knocking detection in the above embodiment, and Fig. 4 is the same as above. A diagram showing an example of the output of each resonator in the embodiment, FIGS. 5 and 6 are block diagrams each showing an example of a conventional knocking detection device, and FIG. 7 shows a diagram of the frequency spectrum obtained in the configuration shown in FIG. It is a diagram showing an example. l... Knock sensor (vibration sensor) 3... (rhone filter 4a, 4b, ... - Delay element 5... Adder 6a, 6b, 6c, ・
...Resonator 7...Microcomputer patent applicant Japan Electronics Co., Ltd. Representative Patent attorney Fujio Sasashima Figure 4

Claims (1)

[Claims] A vibration sensor attached to an engine body to detect engine vibration; an analog/digital converter for converting a detection signal from the vibration sensor from analog to digital; /Contains a plurality of stages of delay elements into which a digitally converted detection signal is input, and an adder which adds the data delayed by the plurality of stages of delay elements and the output data of the analog/digital converter. A comb-shaped filter, a plurality of resonators each inputting the output of the comb-shaped filter and resonating with mutually different frequency components, and knocking generation based on mutually different specific frequency components obtained from the plurality of resonators. A knocking detection device for an internal combustion engine, comprising: a knocking determination means for determining knocking; and a knocking detection device for an internal combustion engine.