JPH0635941B2 - Knocking detection device for internal combustion engine - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a knocking detection device for an internal combustion engine, and more particularly to a knocking detection device that can accurately detect knocking occurrence from a detection signal of engine vibration.

<Prior Art> When knocking at a predetermined level or higher occurs in an internal combustion engine, not only the output is reduced, but also shock is absorbed.
There is an ignition timing control device that detects knocking and corrects the ignition timing so as to avoid knocking quickly because it adversely affects the exhaust valve and the piston (Japanese Patent Laid-Open No. 58-105036). (See gazette, etc.).

Knocking detection for correcting ignition timing due to occurrence of such knocking is performed as follows.

That is, as shown in FIG. 9, the knock sensor 11 that outputs a detection signal corresponding to the vibration level by the piezoelectric element is installed in the engine 12
Mounted on a cylinder block, etc., the detection signal from the knock sensor 11 is input to the bandpass filter 13 to pass only the signal near the center frequency peculiar to knocking, and half-wave rectification is performed, and then the predetermined value is determined by the integrator 14. In the integration section (for example, ATDC 10 ° -60 °), and the peak value of the integrated value in the integrator 14 (sum of specific frequency component intensities in the integration section) is A / D converted by the A / D converter 15. Input to the microcomputer 16. The microcomputer 16 determines whether knocking occurs based on the difference between the peak of the integrated value when knocking occurs and the peak of the integrated value when knocking does not occur (mechanical vibration level).

<Problems to be Solved by the Invention> In such a conventional general knocking determination method, knocking determination is performed based on the intensity of one specific frequency component. However, actually, only one frequency component contributes to knocking. Therefore, the knocking determination accuracy was poor.

In consideration of this point, attempts are being made to detect knocking by detecting the intensities of a plurality of specific frequency components.

By the way, since the degree of contribution to knocking of these specific frequency components (hereinafter referred to as frequency contribution rate) is different, unless the intensity detection is performed by changing the weighting by frequency contribution rate for each frequency component, knocking detection accuracy It was found from experiments by the applicant of the present application that the value cannot be sufficiently increased.

However, the frequency contribution rate varies depending on the cylinder and also varies depending on the engine speed. Therefore, if a constant frequency contribution rate is given to the frequency components, the accuracy decreases due to the variation due to these factors. I also found out.

The present invention has been made in view of the above problems, and provides a knocking detection device in which the knocking detection accuracy is increased as much as possible by setting the frequency contribution rate for each cylinder and each engine speed region. To aim.

<Means for Solving the Problems> Therefore, the 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 an engine body to detect engine vibration, and a specific frequency component extracting means extracts a specific frequency component from a detection signal of the vibration sensor.

The intensity sampling means samples the intensities of the plurality of extracted specific frequency components within a predetermined section.

The frequency contribution rate setting means sets, for each specific frequency component, a frequency contribution rate that contributes to knocking of the specific frequency component according to at least one of cylinders and engine speed regions.

The intensity correction means corrects the intensities of the plurality of specific frequency components sampled by the intensity sampling means with the corresponding frequency contribution rates set by the frequency contribution rate setting means.

The knocking determination means determines the presence or absence of knocking based on the intensities of the plurality of specific frequency components corrected by the intensity correction means.

<Operation> According to such a configuration, the intensity of each frequency component is obtained by correcting the frequency contribution rate set in accordance with at least one of each cylinder and each engine speed region, so that it depends on each cylinder and engine speed. Since the vibration intensity that contributes to knocking can be detected with high accuracy while avoiding variations, the knocking determination accuracy can be increased as much as possible based on the detection result.

<Examples> Examples of the present invention will be described below.

In FIG. 2 showing one embodiment, a knock sensor (vibration sensor) 1 attached to a cylinder block of an internal combustion engine (not shown) has a built-in piezoelectric element and outputs a detection (voltage) signal having a waveform corresponding to engine vibration. To do.

The detection signal (analog signal) of the knock sensor 1 is A
It is A / D converted by the / D converter 2 and input to the comb filter 3.

The comb filter 3 includes a delay circuit 4 including a plurality of stages of unit delay elements, and an adder 5 that subtracts output data of the delay circuit 4 from data bypassing the delay circuit 4. To the filter 3, a circuit in which a number of resonators 6a to 6e corresponding to the number of frequencies desired to be extracted from the detection signal of the knock sensor 1 are connected in parallel is vertically connected.

The resonators 6a to 6e are adapted to resonate with mutually different frequency components, and in the present embodiment, the resonance frequencies are 7 kHz and 8 kHz according to the frequency range 7 kHz to 9 kHz in which knocking vibration is said to appear remarkably. ，
They are 9 kHz, 10 kHz, and 11 kHz.

In the comb filter 3, by subtracting the data delayed by the delay circuit 4 from the data bypassed by the delay circuit 4, the detection signal level is totally attenuated, and in particular, the frequency corresponding to the delay time is added. They are erased by the device 5 to obtain a so-called comb-shaped result as a frequency characteristic.

As a result, the resonators 6a to 6e can be prevented from continuing to resonate based on the signals canceled by the adder 5, and the intensities of the respective frequency components can be successively obtained. The comb-shaped filter 3 and the resonators 6a to 6e constitute the specific frequency component extracting means in this embodiment.

In this embodiment, the specific frequency component is extracted from the signal from the knock sensor 1 by the configuration of the comb filter 3 and the resonators 6a to 6e as described above. The band pass filters may be provided in correspondence with the number of required frequencies, and the output of each band pass filter may be A / D converted and read by the microcomputer 7.

The output of each of the resonators 6a to 6e, that is, the intensity signal of each frequency component is input to the microcomputer 7, and the microcomputer 7 is based on the detection signal from the crank angle sensor 8. The occurrence of knocking in an internal combustion engine (not shown) is detected based on a specific frequency component of the knock sensor 1 input through the resonators 6a to 6e in a predetermined frequency analysis section to be detected.

The content of such knocking occurrence detection will be described below with reference to the flowchart of FIG. In this example,
The functions of the intensity sampling means, the frequency contribution rate setting means, the intensity correction means, and the knocking determination means are the same as those of the third
As shown in the flowchart of the figure, the microcomputer 7 is provided as software.

The knocking occurrence detection shown in the flowchart of FIG.
This is performed in a predetermined frequency analysis section, and the predetermined frequency analysis section is, for example, a section in which combustion vibration of each cylinder can be sampled while avoiding ignition noise. For example, in a 6-cylinder engine, ATDC 10 ° to ATDC 60 °. Can be decided like.

Therefore, the predetermined frequency analysis section is detected based on the detection signal from the crank angle sensor 8, and the cylinder in the combustion stroke is determined by the cylinder determination signal included in the detection signal. The engine speed is detected based on the number of times the signal is output per unit time or the output cycle of the reference crank angle signal output for each cylinder stroke phase difference (S1).

When the frequency analysis section is entered, the frequency spectra output from the resonators 6a to 6e at predetermined time intervals (predetermined time intervals) as shown in FIG. As described above, the intensity (f ₀₀ , of the angular frequency component f _j (j = 0 to n) obtained at every predetermined time in the analysis section,
f ₁₀ , f ₂₀ , f ₃₀ ··· f _m0 ), (f ₀₁ , f ₁₁ , f ₂₁ , f
₃₁ ... f _m1 ), (f ₀₂ , f ₁₂ , f ₂₂ , f ₃₂ ... F _m2 )
_.. (f _0n , f _1n , f _2n , f _2n , f _3n, ... F _mn ) are sampled (S2). This function corresponds to intensity sampling means.

Next, based on the cylinder and the engine circuit in the combustion stroke detected in S1, the map table of the frequency contribution rate stored in the ROM incorporated in the microcomputer using the cylinder and the engine speed as parameters for each frequency component ( from the seventh see figure), retrieves the frequency contribution of KF _j of each frequency component f _j (S3). That is, the ROM that stores the frequency contribution rate KF _j
And the cylinder discrimination and engine speed detection of S1 and the S
The frequency contribution rate setting means is configured by the function of frequency contribution rate search 2 above.

Based on these sampled intensity data, the maximum intensity level KSi of all frequencies is calculated by the following equation (S4).

_{KSi = f m0 (max) ×} KF 0 + f m1 (max) × KF 1 + ··· + f mn (max) × KF n Here, f _mj (max) sampling the intensity of the frequency component f _j (f _0j, f _1j , f _2j , f _3j ··· f _mi ) is the maximum value, and KF _j is the above-mentioned frequency contribution rate.

This maximum level KSLi is a value that serves as an index indicating the magnitude of knocking.

Next, based on the intensity data, the average intensity level SLi of all frequencies is calculated by the following equation (S
5).

SLi = {KF ₀ / m Σf _m0 + KF ₁ / m Σf _m1 + ... KF _n / m Σf _mn } In this arithmetic expression, the frequency contribution rate KF _{j is used} to correct each frequency component. That is, both the maximum level KSLi and the average level SLi are intensity-corrected by the frequency contribution rate KF _j. Therefore, in the functions of S3 and S4,
Intensity correction means are included.

Maximum level KSLi and average level thus obtained
The presence or absence of knocking is determined by comparing the difference with SLi with the background BGLi (S6). That is, BGLi + α <KSi
When −SLi, it is determined that knocking has occurred (S7), and BGLi ≧ KSLi−SLi + α (α is a threshold value)
If it is, it is determined that knocking has not occurred (S8). This function corresponds to knocking determination means.

The background level BGLi is obtained by performing a weighted average calculation of the difference between the maximum level KSi compared with the BGLi and the average level SLi by the following equation when it is determined that there is no knocking in the knocking determination ( S9).

According to such knocking discrimination, the difference between the maximum level KSi and the average level SLi is basically the sum of the differences between the maximum value and the average value of the vibration level, and when knocking occurs, the above-mentioned knocking vibration is locally detected. This difference increases due to the property of increased vibration levels.

On the other hand, the background level BGLi is a weighted average value of the sum of the differences between the maximum level KSi and the average level SLi when not knocking.

Therefore, when knocking occurs, the value of (KSi-SLi) becomes sufficiently larger than that of BGLi, and accurate knocking determination can be performed even for a signal with a low level.

Then, as a configuration according to the present invention, a plurality of specific frequencies having a high contribution rate to knocking are selected, and weighting is performed by using a frequency contribution rate that avoids variations set for each cylinder for each frequency component and each engine speed region. The knocking detection accuracy is remarkably improved because the sum is calculated.

In this embodiment, the knocking strength determination is performed by sampling the frequency analysis section at predetermined time intervals to obtain the maximum level and the average level, but the present invention is not limited to this. For example, as an example applied to a conventional general knocking detection method, the sum of values obtained by multiplying the integral value of each frequency component in all sections by the frequency contribution rate is set as the integral value at the time of non-knocking determination of all vibration components. The knocking determination may be performed by comparing the background level with the background level.

Next, an embodiment will be described in which knocking vibration characteristics are more accurately captured and distinction from mechanical vibration is made clearer to perform knocking determination.

In this method, when the average level SLi is calculated, the total sum of intensity average values for each frequency obtained in the same manner as in the above-described embodiment is corrected with a value that is an intensity change correction coefficient KLP. Also, when calculating BGLi, the weighting x is set as a function of the intensity change correction coefficient KLP. A routine for setting the intensity correction coefficient KLP will be described with reference to the flowchart of FIG.

First, the intensity for each frequency component is sampled at predetermined time intervals in the same manner as S1 in FIG. 3 (S11), and the intensity of each specific frequency component (f ₀₀ , f ₁₀ .. f _n0 ) are stored as initial values (S12).

Then, it is assumed that the initial values stored for each frequency component do not change, respectively, and that the intensity of a constant level continues in the frequency analysis section, and the time axis change of the integrated value of the intensity at this time is compared with the sampling period and the initial value. The value is set on the basis of the value and it is set as a reference change characteristic (S13).

Next, based on the temporal transition of the intensity obtained for each frequency component that is actually input (see FIG. 7), the intensity is integrated for each sampling period on the time axis, and within the frequency analysis interval. The characteristic of intensity change is detected (S14).

Then, as described above, the normative change characteristic for each frequency component obtained assuming that the intensity is unchanged is compared with the actually detected change characteristic of the intensity integral value for each frequency component (S15). ).

Here, the reference change characteristic is linearly increased because it is premised that there is no change in intensity. On the other hand, when the change characteristic of the intensity integral value obtained based on the actual detection signal does not match. Is estimated to be unstable at a constant intensity because the frequency component of the noise includes knocking vibration. Therefore, it is determined whether or not the intensity integral value matches the reference variation characteristic for each predetermined time for each frequency component, and the total number C in the case where they do not match within the detection section is measured by the counter.

Then, the intensity change correction coefficient KLP is set according to the total number C. Specifically, the larger the total number C, the greater the proportion of knocking vibrations included, and therefore the direction in which knocking determination is likely to occur, that is, the average level SLi is decreased to a small value to increase the difference from the maximum level KSi. Yes (S16).

Then, the intensity change correction coefficient set as described above
The average level SLi is set by KLP by multiplying the value obtained in the above embodiment by the intensity change correction coefficient KLP as in the following equation.

SLi = {KF ₀ / m Σf _m0 ＋ KF ₁ / m Σf _m1 ＋ ・ ・ ・ KF _n / m Σf _mn } ・ KLP In addition, the weighting coefficient x used for the update calculation of the background level BGLi is set to the strength correction coefficient KLP. Set as a function. Specifically, the larger KLP is, the smaller the proportion including knocking vibration is. Therefore, the weighting coefficient x is set to a small value in order to increase the weight of KSi-SLi and calculate BGLi.

As described above, by using the intensity correction coefficient KLP, it is possible to detect the intensity change characteristic of knocking and perform knocking detection with higher accuracy.

In this embodiment, the intensity change correction coefficient KLP is set as a value for correcting the average level, but it may be set as a value for correcting the maximum level.

Further, in the embodiment shown above, the frequency contribution rate was obtained with high accuracy by searching from the three-dimensional map table with the cylinder and the engine speed as parameters, but in order to reduce the memory amount, the frequency contribution rate becomes the basic frequency contribution rate. The correction coefficient for correcting the variation for each cylinder may be multiplied by the correction coefficient for correcting the variation for each engine speed region to perform the correction. Further, the present invention includes the one in which the frequency contribution rate is set according to only one of the cylinders and the engine speed range, and it is possible to considerably improve the accuracy thereof.

<Effects of the Invention> As described above, according to the present invention, the intensities of a plurality of specific frequency components are corrected from the detection signal from the vibration sensor by using the frequency contribution rate set for each cylinder and each engine rotation region. Since the knocking determination is performed using the value, there is an effect that the knocking determination accuracy can be increased as much as possible.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of the present invention, FIG. 2 is a system block diagram showing an embodiment of the present invention, FIG. 3 is a flowchart showing the contents of knocking detection control in the same embodiment, FIG. FIG. 5 is a time chart showing how intensity is sampled for each specific frequency component in the same embodiment, FIG. 6 is a diagram showing an example of a frequency spectrum in the same embodiment, and FIG. 7 is also for each frequency component. Stored frequency contribution ratio map table, 8th
FIG. 9 is a flowchart showing the contents of knocking detection control in another embodiment, and FIG. 9 is a block diagram showing an example of a conventional knocking detection device. 1 ... Knock sensor (vibration sensor), 2 ... A / D converter, 3 ... Comb filter, 4 ... Delay circuit, 5 ... Adder, 6a-6e ... Resonator, 7 ... Micro Computer, 8 ... Crank angle sensor

Claims (1)

[Claims] 1. A vibration sensor attached to an engine body for detecting engine vibration, a specific frequency component extracting means for extracting a plurality of specific frequency components from a detection signal of the vibration sensor, and an extraction by the specific frequency component extracting means. Intensity sampling means for sampling the intensities of the plurality of specified frequency components respectively within a predetermined section, and a frequency contribution rate that contributes to knocking of the specific frequency components for each specific frequency component at least for each cylinder and each engine speed region A frequency contribution rate setting unit that sets the intensity of a plurality of specific frequency components sampled by the intensity sampling unit with a corresponding frequency contribution rate set by the frequency contribution rate storage unit. Means and a knocker based on the intensities of the plurality of specific frequency components corrected by the intensity correcting means. Device for detecting knocking in an internal combustion engine, characterized in that it is configured to include a knock determining means for determining the presence or absence of grayed, the.