JPH0675001B2 - 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 detect the degree of 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.
Some of them are equipped with an ignition timing control device which can prevent knocking promptly by detecting knocking and correcting the ignition timing because it adversely affects the exhaust valve and the piston (Japanese Patent Laid-Open No. 58-105036). Etc.).

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

That is, as shown in FIG. 6, the knock sensor 11 that outputs a detection signal according 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. Integration interval of
A / D converter 15 performs A / D conversion of the peak value of the integrated value (accumulation of the amplitude of the specific frequency component in the integration section) in the integrator 14 that integrates only ATDC 10 ° to 60 °) and inputs it to the microcomputer 16. Let In the microcomputer 16, 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,
It is determined whether knocking has occurred.

<Problems to be Solved by the Invention> By the way, in the configuration in which the occurrence of knocking is determined by the peak level of the integrated value as described above, it is desirable that there is a sufficient difference in the peak level of the integrated value depending on the presence or absence of knocking. Actually, there is a case where the difference cannot be sufficiently secured in an operating region or a cylinder where the signal level is particularly small depending on the shape of the engine or the mounting position of the knock sensor. Knocking was sometimes erroneously detected because there was no clear difference in peak level.

Further, conventionally, the presence / absence of knocking can be determined on / off based on the integrated value, but there is a problem that the degree of knocking occurrence cannot be determined.

The present invention has been made in view of the above problems, and an object thereof is to provide a knocking detection device capable of highly accurately detecting the degree of occurrence of knocking even when the signal level from the knocking sensor is low. To do.

<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 the engine body to detect engine vibration, and a specific frequency extraction means extracts a specific frequency component from the detection signal of the vibration sensor.

The amplitude change detection means detects a change on the time axis of the amplitude of the specific frequency component extracted by the specific frequency extraction means within a predetermined backbone.

Then, the knocking degree setting means sets the degree of belonging to knocking occurrence based on the difference between the change in the amplitude of the detected specific frequency component on the time axis and the predetermined reference change characteristic.

Here, the amplitude change detection means is configured to integrate the amplitude of the specific frequency component extracted by the specific frequency extraction means, and a predetermined reference change characteristic is set as a change characteristic of the integrated value of the amplitude, and knocking is performed. The degree setting means may be configured to set the degree of knocking occurrence based on a value obtained by accumulating the deviation of the integrated value at each amplitude sampling timing.

<Operation> According to such a configuration, the amplitude of the specific frequency component extracted from the detection signal of the vibration sensor changes on the time axis within the predetermined period during the knocking occurrence, or when the knocking does not occur. Since it is determined whether there is a change, the knocking vibration and the mechanical vibration can be separated independently of the signal level, and even if the signal level is small, only the knocking vibration can be extracted and knocking detection can be performed. Also, it is possible to obtain the degree of belonging to knocking occurrence as a difference with respect to a predetermined reference change characteristic.

<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 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 arranged to resonate with mutually different frequency components, and in this embodiment, the resonance frequency is 7kHz, 8kHz according to the frequency range 7kHz to 9kHz in which knocking vibration is said to appear remarkably. , 9kHz, 10kHz, 11kHz.

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 amplitude of each frequency component can be sequentially obtained.

In this embodiment, the characteristic 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 means is the above comb filter 3
And resonators 6a to 6e. However, analog band-pass filters may be provided corresponding to the number of required frequencies, and the output of each band-pass filter may be A / D converted and read by the microcomputer 7. In this case, The bandpass filter corresponds to the specific frequency extracting means.

The output of each of the resonators 6a to 6e, that is, the amplitude signal of each frequency component is input to the microcomputer 7, and the microcomputer 7 is based on the detection signal from each crank sensor 8. While detecting the occurrence of knocking in an internal combustion engine (not shown) based on the characteristic frequency component of the knock sensor 1 input through the resonators 6a to 6e in a predetermined frequency component section to be detected,
The ignition timing in the addition device 9 is corrected and controlled based on the detection result.

The contents of knocking occurrence detection performed by the microcomputer 7 will be described below with reference to the flowchart of FIG.

In this embodiment, the functions of the amplitude change detecting means and the knocking degree setting means are provided by the microcomputer 7 as software as shown in the flowchart of FIG.

The knocking occurrence detection shown in the flowchart of FIG.
It is performed in a predetermined frequency analysis section (predetermined engine), and the predetermined frequency analysis section is a section in which combustion vibration of each cylinder can be sampled while avoiding ignition noise, for example, in a 6-cylinder engine, ATDC10゜ ~ ATDC
The angle is set to 60 °, and the predetermined frequency analysis section is detected based on the detection signal from the crank angle sensor 8.

First, when it is detected that the frequency analysis section has been entered, the amplitude of each frequency component input via each of the resonators 6a to 6e is stored as an initial value (S1).

Then, it is assumed that the initial values stored for each frequency component do not change, respectively, and that the amplitude of a constant level continues in the frequency analysis section, and the time axis change of the integrated value of the amplitude at this time, the resonator 6a ~ The linear change characteristic is set based on the output interval (sampling period) from 6e and the initial value, and is used as the reference change characteristic when no knocking occurs (S2).

Next, the amplitude of each frequency component to be input at every predetermined time in the frequency analysis section is stored, and the temporal transition of the amplitude (amplitude change pattern) is detected for each frequency component (fourth). See figure).

Then, based on such detection, the amplitude is integrated for each sampling period on the time axis, and the pattern of amplitude change in the frequency analysis section is observed as the slope of the integrated value (S3).

Then, as described above, the reference change characteristic for each frequency component obtained assuming that the amplitude is unchanged and the characteristic of the change in the amplitude integral value for each frequency component actually detected are compared, and both are compared. The amount of deviation is calculated, for example, as plus on the increasing side and minus on the decreasing side with respect to the normative change characteristic, and is accumulated at each sampling interval of the amplitude so that the accumulated value E represents the amount of deviation of the actual change with respect to the normative change characteristic. (S4).

In addition, when the deviation of the change in the integrated value is accumulated as described above, the change characteristic due to the knocking vibration may not be correctly shown at the beginning of the analysis section due to the change in the timing of occurrence of the knocking vibration. Further, it is preferable to accumulate the deviation amount after the integrated amplitude value for each frequency component becomes equal to or less than a predetermined value.

Here, the reference change characteristic is linearly increased because it is premised that there is no change in amplitude. On the other hand, when the change pattern of the amplitude integrated value obtained based on the actual detection signal does not match. It is estimated that since the frequency component contains knocking vibration, the amplitude is not stable at a constant amplitude. However, the amplitude integrated value based on the actual detection signal is substantially the same as the reference change characteristic. In the case of linearly increasing change, it can be estimated that the frequency component is only mechanical vibration (see FIG. 5).

That is, as shown in FIG. 5, in the same frequency component,
When the knocking vibration is included, the knocking vibration due to abnormal combustion is gradually attenuated. Therefore, the amplitude of the frequency component is also gradually gradually attenuated to the level of mechanical vibration only. Conversely, the knocking vibration is included. If not, the amplitude changes at a substantially constant mechanical vibration level. Therefore, when knocking vibration is not included, the initial amplitude of the analysis section is substantially maintained, and the integrated value of the amplitude increases substantially linearly.

Therefore, as described above, assuming that the initial amplitude of the analysis interval does not change thereafter, if the time-based change of the integrated value of the amplitude is estimated, this change characteristic (predetermined normative change characteristic) shows that knocking does not occur. When the actual amplitude is integrated on the time axis when knocking occurs,
As shown in FIG. 5, a change pattern that does not match the change characteristic estimated to correspond to the non-occurrence of knocking is shown, and the clearer the occurrence of knocking, the greater the difference in change characteristic. . Therefore, it is possible to detect the probability of occurrence of knocking (degree of occurrence of knocking) by obtaining an integral value of the actual amplitude on the time axis, comparing it with that when the knocking is not occurring, and accumulating the difference. It is a thing.

In this way, since knocking can be detected based on the amplitude change pattern of the specific frequency component, it is possible to identify even when the signal level is low, and even in the high rotation range where mechanical vibration becomes strong, It is possible to easily detect knocking by distinguishing between knocking vibration and mechanical vibration.

Note that depending on the frequency, there is a frequency range in which the amplitude becomes weaker than the engine vibration level due to occurrence of knocking and returns to the engine vibration level as the knocking vibration attenuates. Since it does not exhibit a linear change which is a change characteristic when the knock does not occur, the probability of occurrence of knocking can be detected. In addition, although the change characteristic when knocking is not generated is set by setting the amplitude in the initial part of the frequency analysis section to be constant, the amplitude change (decreasing change or increasing change) when knocking vibration is included for each frequency component in advance. In order to show the degree of non-knocking, compare the amplitude change characteristics expected to appear in the first knocking politics with the amplitude change pattern for each frequency component found from the actual detection signal. It is also possible to obtain the cumulative amount of deviation between the two.

For each frequency component corresponding to each of the resonators 6a to 6e, the cumulative value E of the deviation amount with respect to the reference change characteristic corresponding to the non-knock of the actual amplitude change in the frequency analysis section is obtained as described above. The sum of the absolute values of the cumulative value E obtained in step 1 or the average value, and further the maximum value are obtained. Then, from the deviation amount cumulative value E for each frequency component, the absolute value of the deviation amount cumulative value E finally set, that is, the degree of belonging to knocking occurrence (probability of knocking occurrence)
In the present embodiment, the mode of knocking occurrence is divided into three to be the final detection result based on the value that indicates

First, the preset cumulative value E of the knocking occurrence level is compared with the actually detected cumulative value E (S5), and when the knocking occurrence level is exceeded, it is determined that knocking has occurred (S6). . On the other hand, when it is equal to or lower than the cumulative value E of the knocking occurrence level, the preset cumulative value E of the knocking non-occurrence level is compared with the actually detected cumulative value E (S7), and the knocking non-occurrence level is higher than the knocking non-occurrence level. When it is small, the knocking non-occurrence state is determined (S8), but when the actually detected cumulative value E is an intermediate value between the knocking occurrence level and the knocking non-occurrence level, it is determined that knocking has occurred. It is determined that knocking has not occurred, and it is determined that knocking may occur (S9).

It should be noted that, based on the cumulative value E obtained for each frequency component as described above, the modes of knocking occurrence for each frequency component are classified into the above three, and the most number of determinations among the determined knocking occurrence modes is performed. You may make it select many things finally.

As described above, when the knocking occurrence modes are classified into three types based on the cumulative value E that indicates the knocking degree, for example, when the knocking occurrence is determined, the ignition timing is retarded by a predetermined crank angle. In order to avoid knocking, the ignition timing is advanced by a predetermined crank angle when knocking is not detected to increase the engine output, and when it is determined that knocking may occur, the current ignition timing is set. Try to keep it.

In this way, if it is determined that knocking may occur in addition to the presence or absence of knocking, it is possible to perform control for maintaining the current state in addition to advance angle correction and retard angle correction as ignition timing control. The controllability is improved as compared with the case where the ignition timing is advanced or retarded based on the presence / absence determination.

As described above, it is the simplest method to classify the knocking occurrence modes into three types, and further classify the knocking level into four or more from the cumulative value E indicating the degree of knocking, and according to each classification result. If the correction amount of the ignition timing is set, the ignition controllability for avoiding knocking is further improved.

In this embodiment, the detection signal from the knock sensor 1 is 7 kH
Although five kinds of frequency components of z, 8kHz, 9kHz, 10kHz and 11kHz are extracted, the frequencies to be extracted are not limited. Further, it is not necessary to say the number of frequencies, and the knocking degree may be detected according to the flowchart shown in FIG. 3 using only one frequency component.

<Effects of the Invention> As described above, according to the present invention, the occurrence of knocking can be detected regardless of the detection signal level of the vibration sensor, and the probability of occurrence of knocking can be detected. For example, it is possible to finely execute the ignition timing correction for avoiding knocking, and there is an effect that the accuracy of the ignition timing control for avoiding knocking is improved.

[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 flow chart showing the contents of knocking detection control in the same embodiment, and FIG. FIG. 5 is a diagram showing an example of an amplitude change of a specific frequency component in a frequency analysis section in the same embodiment, FIG. 5 is a time chart for explaining knocking determination based on an amplitude change pattern of a specific frequency, and FIG. It is a block diagram showing an example of a 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 (2)

[Claims] 1. A vibration sensor attached to an engine body for detecting engine vibration, a specific frequency extracting means for extracting a specific frequency component from a detection signal of the vibration sensor, and a specific frequency extracted by the specific frequency extracting means. Amplitude change detecting means for detecting a change in the amplitude of the component on the time axis within a predetermined period, and knocking based on the difference between the amplitude change of the specific frequency component detected by the amplitude change detecting means and the predetermined reference change characteristic. An knocking detection device for an internal combustion engine, comprising: knocking degree setting means for setting a degree of occurrence. 2. The amplitude change detection means is configured to integrate the amplitude of the specific frequency component extracted by the specific frequency extraction means, and the predetermined normative change characteristic is a change characteristic of an integrated value of the amplitude. 2. The internal combustion engine according to claim 1, wherein the knocking degree setting means is configured to set the degree of belonging to knocking occurrence based on a value obtained by accumulating the deviation before integration for each amplitude sampling timing. Knocking detection device.