JPH0486533A - Detecting apparatus for knocking of internal combustion engine - Google Patents

Abstract

PURPOSE:To enhance knocking detection accuracy by discriminating the generation of knocking by comparing the intensity change of a detected specific frequency component with a set standard change characteristic. CONSTITUTION:The detection signal of a knocking sensor 1 is inputted to a comblike filter 3 through an A/D converter 2. In the filter 3, the data delayed by a delay circuit 4 is subtracted from the data allowed to bypass the circuit 4 and the frequency corresponding to a delay time is erased by an adder 5 and becomes comblike as a frequency characteristic. By this constitution, it is prevented that a resonator 6 (6a - 6e) is continuously resonated on the basis of the signal from the adder 5 and the intensity of each frequency component is obtained. The output of the resonator 6 is inputted to a microcomputer 7 and, in the microcomputer 7, the intensity change of the characteristic frequency component of the sensor 1 inputted through the resonator 6 is compared with a set standard change characteristic on the basis of the detection signal from a crank angle sensor 8 and the generation of knocking is discriminated.

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
Some engines are equipped with an ignition timing opening device that detects knocking and corrects the ignition timing to quickly avoid knocking, since it has a negative effect on exhaust valves and pistons (Japanese Patent Laid-Open No. 58-105036). (Refer to official bulletins, etc.)

Knocking detection for correcting the ignition timing due to the occurrence of knocking has been performed as follows.

That is, as shown in FIG. 7, a knock sensor 11 that outputs a detection signal according to the vibration level using a piezoelectric element is attached to the cylinder block of the engine 12, etc., and the detection signal from this knock sensor 11 is sent to a bandpass filter 13. After inputting the signal and passing only the signal near the center frequency peculiar to knocking and performing half-wave rectification, the integrator 14 integrates only a predetermined integration interval, and the peak value of the integrated value in the integrator 14 is sent to the A/D. The converter 15 performs A/D conversion and inputs the signal to the microcomputer 16. microcomputer 16
Then, it is determined whether or not knocking is occurring based on the difference between the peak of the integral value when knocking occurs and the peak of the integral value when knocking does not occur.

<Problems to be Solved by the Invention> However, in the configuration described above in which the occurrence of knocking is determined based on the peak level (frequency intensity level) of the integral value, it is desirable that there be sufficient changes in intensity depending on the presence or absence of knocking. In reality, depending on the shape of the engine, the mounting position of the knock sensor, etc., it may not be possible to obtain a sufficient amount of the change in strength. There were times when I ended up.

By the way, in the above integration interval, when knocking occurs, the intensity of the frequency component that picks up the knocking vibration changes as the knocking pressure vibration attenuates, and when knocking does not occur, the mechanical vibration level is maintained and the intensity hardly changes. It has the following characteristics. The present applicant has focused on such characteristics and has proposed a device that detects knocking by detecting the characteristics of the actual intensity change in an interval that substantially coincides with the above-mentioned integral interval, and has determined whether the level of the frequency intensity is This makes it possible to detect knocking even under conditions that do not change significantly depending on whether the vehicle is present or not.

In knocking detection based on such intensity changes, frequency intensity data input at predetermined time intervals within a predetermined section are sequentially integrated, and the initial value is integrated assuming that the intensity is manually applied at the first time in the predetermined section and does not change thereafter. The change characteristics obtained by doing this are set as the standard change characteristics. Then, by detecting the deviation between the change in the integrated value of the actual strength and the reference change characteristic, and detecting knocking by detecting the degree of change in the actual strength based on this deviation, the absolute value of the strength can be detected. This allows knocking to be detected regardless of the level.

However, if the standard change characteristics are determined based on the intensity input at the first time of a predetermined section as described above, the timing at which combustion oscillations appear within the predetermined section due to the difference in distance between each cylinder with respect to the knock sensor Since the frequency varies from cylinder to cylinder, it may not be possible to accurately set the standard change characteristic for detecting changes in frequency intensity depending on the cylinder.

That is, in the case shown in FIG. 6, for example, if the standard change characteristic corresponding to the non-occurrence of knocking is set based on the intensity input for the first time in a predetermined interval (frequency analysis interval) in which intensity changes are detected (frequency analysis interval), The actual intensity change (the line connecting the ○ marks with a solid line in Fig. 6) and the actual intensity change (the line connecting the ○ marks with a dotted line in Fig. 6) cannot be correctly detected as deviations from the standard change characteristic. In the case shown in Figure 6, it is desirable to set the standard change characteristic (the line connecting the x marks with a solid line in Figure 6) based on the intensity input second after entering the analysis interval. In rare cases, even if the standard change characteristic is set based on the third input intensity (the line connecting the Δ marks with a solid line in Figure 6), it will still not be possible to detect the desired intensity change. .

Therefore, in the case shown in Fig. 6, the standard change characteristic is set based on the second input intensity, in other words, the intensity that will be maintained at that level during normal combustion immediately before knocking vibration appears. However, in cylinders that are further away from the sensor, the intensity change characteristics shown in Figure 6 may be detected later by the sensor, and conversely, in cylinders that are closer to the sensor, the intensity change characteristics may be detected earlier. Therefore, even if the analysis intervals are matched as shown by the dotted line in Figure 6 so that a desired standard change characteristic can be obtained for one particular cylinder, it may not be possible to set the desired standard change characteristic for other cylinders. It was there.

The present invention has been made in view of the above problems, and provides an apparatus for detecting knocking by comparing a change in frequency intensity detected within a predetermined interval with a reference change characteristic.
It is an object of the present invention to improve knocking detection accuracy by allowing the reference change characteristic to be set with high precision based on the intensity obtained in the predetermined section.

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

The intensity change of the specific frequency component in a predetermined interval is detected by the intensity change detection means, and the initial intensity sampling means is configured to determine the intensity of the specific frequency component extracted by the specific frequency extraction means in advance for each cylinder in the predetermined interval. Samples the intensity when the set slice level is exceeded for the first time.

Here, the standard change characteristic setting means sets a standard change characteristic of the intensity of the specific frequency component in the predetermined period, assuming that the intensity sampled by the initial intensity sampling means does not change in the predetermined period.

The knocking determining means compares the intensity change of the specific frequency component detected by the intensity change detecting means with the standard change characteristic set by the standard change characteristic setting means to determine the occurrence of knocking.

<Operation> According to this configuration, the intensity of the specific frequency component extracted from the detection signal of the vibration sensor changes in a predetermined interval with a characteristic when knocking does not occur that substantially matches the standard change characteristic, or Since it is possible to determine whether the characteristics change when knocking occurs, which are significantly different from the Even in this case, knocking can be detected by extracting only the knocking vibration.

However, when setting the reference change characteristic to be compared with the intensity change detected in a predetermined section based on the initial intensity of the predetermined section, it is necessary to set the preset slice level for each cylinder after entering the predetermined section. Since the setting is based on the intensity when the vibration is exceeded for the first time, the distance from the vibration sensor to each cylinder is different, and the intensity data input in a given section may have a delay or advance between cylinders. Even if the intensity levels are different, the intensity level during normal combustion can be sampled to set the reference change characteristic, and thereby the actual intensity change can be detected with high accuracy.

<Example> The present invention will be explained in detail 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 waveform detection (voltage) signal according to engine vibration. do.

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

The comb filter 3 is composed of a delay circuit 4 consisting of a plurality of stages of unit delay elements, and an adder 5 that subtracts the output data of the delay circuit 4 from the data that has bypassed the delay circuit 4. 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 or parallel-connected circuits are vertically connected to the shaped filter 3.

The resonators 6a to 6e are designed to resonate with mutually different frequency components, and in this embodiment, the resonant frequencies are set according to a frequency range of 7kHz to 9kHz in which knocking vibrations are considered to be noticeable. 7kHz,
8kHz, 9kHz, 10kHz
z.

The frequency is 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 detected signal level is attenuated as a whole, and in particular, the frequency corresponding to the delay time is added. They are canceled in the unit 5 to obtain a so-called comb-shaped frequency characteristic.

Thereby, it is possible to prevent each of the resonators 6a to 6e from continuing to resonate based on the signals canceled by the adder 5, and the intensity of each frequency component can be obtained sequentially. Therefore,
The specific frequency extraction means in this embodiment is the A/D converter 2. Comb-shaped filter 3. It is composed of resonators 6a to 6e.

Note that 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 into the microcomputer 7.

The outputs of the resonators 6a to 6e, that is, the intensity signals for each frequency component, are input to a microcomputer 7. The occurrence of knocking in an internal combustion engine (not shown) is detected based on the specific frequency components of the knock sensor 1 input via the respective resonators 6a to 6e in a predetermined detected frequency analysis section, and ignition is performed based on the detection result. By controlling the ignition timing in the device 9, the ignition timing is advanced while quickly avoiding knocking.

The details of the knocking detection performed by the microcomputer 7 will now be described in accordance with the flowchart shown in FIG.

In this embodiment, the intensity change detection means, the initial intensity sampling means, and the reference change characteristic setting means.

The function as a knocking determination means is provided by the microcomputer 7 in the form of software, as shown in the flowchart of FIG.

The program shown in the flowchart of FIG. 3 is a program for detecting the knocking intensity based on the intensity change pattern of the specific frequency component of the detection signal of the knock sensor 1, and is executed in a predetermined frequency analysis section (predetermined section). The predetermined frequency analysis section is, for example, a section in which combustion vibrations of each cylinder can be sampled while avoiding ignition noise, and for example, in a six-cylinder engine, ATDCIO° to A
The TDC 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 interval has entered, slice levels Y#1 to Y are set in advance for each cylinder.
Slice level Y corresponding to the current combustion cylinder is selected from #4, and whether the intensity of the frequency component inputted first through each resonator 6a to 6e exceeds the slice level Y or not. (Sl).

The slice level Y is used to compensate for the fact that the timing of combustion vibration appearing in the frequency analysis section differs between cylinders due to the difference in distance between each cylinder with respect to the knock sensor 1.

In this embodiment, the frequency intensity during normal combustion immediately before knocking vibration appears is sampled, and knocking is then detected by whether the sampled value is maintained or the intensity changes due to the occurrence of knocking. For example, in a cylinder far from the knock sensor 1, the frequency intensity data detected within the frequency analysis period may be delayed. The intensity data input at the beginning of the frequency analysis interval will be the intensity during normal combustion depending on the cylinder, but in other cylinders the sampling may be too early or may be delayed, resulting in the intensity being during normal combustion. Sampling becomes impossible.

Therefore, in order to sample the intensity data during normal combustion for each cylinder, slice levels Y#l-Y#4 have been set for each cylinder in advance through experiments, and slice levels Y#1 to Y#4 are set in advance for each cylinder. If the intensity does not exceed slice level Y, it is determined whether the next input intensity exceeds slice level Y or not.

Then, the intensity exceeds the slice level Y for the first time, that is,
The intensity detection value during normal combustion, which is sampled after compensating for the difference in the distance of each cylinder to the knock sensor l, is stored as an initial value for each frequency (S2).

Next, assuming that the initial values stored for each frequency component do not change and the intensity continues at a constant level in the frequency analysis interval, the time-axis change in the integrated value of the intensity at this time is calculated as the sampling period and the This is set based on the initial value, and this is set as the standard change characteristic corresponding to when knocking does not occur (
S3).

Next, based on the temporal change in intensity determined for each frequency component that is actually input (see Figure 4), each intensity is integrated for each sample period on the time axis, and The characteristics of the intensity change are detected (S4).

Then, as mentioned above, the standard change characteristics corresponding to the non-occurrence of knocking for each frequency component obtained assuming that the intensity remains unchanged, and the characteristics of the change in the intensity integral value for each frequency component actually detected. (S5).

Here, the standard change characteristic assumes that there is no change in intensity, so it increases linearly.On the other hand, if the change characteristic of the intensity integral value obtained based on the actual detection signal does not match, Since the frequency component includes knocking vibration, it is assumed that the intensity is not stable at a constant level and the occurrence of knocking is determined (S6), or the intensity integral value based on the actual detected a signal is determined. If the frequency component increases substantially linearly as in the standard change characteristic, it is assumed that the frequency component is only mechanical vibration and knocking is not occurring (S7). Such a determination is made for each frequency component corresponding to each of the resonators 6a to 6e, and the final determination is made, for example, by a majority vote of whether knocking or non-knocking is determined for each frequency component.

Note that the comparison between the standard change characteristic and the change characteristic based on the actual detection signal is performed by, for example, integrating the differences in integral values on the same time axis and checking whether the integrated value is greater than or equal to a predetermined value. . Here, the mode of occurrence of knocking may be determined into three or more types based on the integrated value of the differences, or the degree of occurrence of knocking may be set.

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

As shown in Fig. 5, when knocking vibration is included in the same frequency component, the knocking vibration gradually attenuates from the occurrence of abnormal combustion in the frequency analysis interval, so the intensity of the frequency component also initially becomes large and gradually decreases. The vibration will attenuate and return to the level of only mechanical vibration. Conversely, when knocking vibration is not included, the intensity will remain 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 intensity of the analysis interval is assumed to be constant and the time axis change in the integrated value of intensity is estimated, this change characteristic will be the one when knocking does not occur, and if knocking occurs. When the actual strength is integrated on the time axis, as shown in Figure 5, 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.

However, as shown in FIG. 6, the standard change characteristics vary greatly depending on the sampling of the initial values, and input data at different times may be used as the standard as the initial value depending on the variation in the distance between each cylinder and the knock sensor 1. Is it necessary to set the change characteristic? In this embodiment, by controlling the initial value sampling according to the slice level Y for each cylinder as described above, it is possible to eliminate variations in the distance between each cylinder and the knock sensor 1. Since the setting accuracy of the standard change characteristic is ensured through compensation, the accuracy of knocking detection as described above by comparing the standard change characteristic with the actual intensity change is improved.

Depending on the frequency, there may be a frequency range that exhibits characteristics such that the intensity becomes weaker than the engine vibration level due to the occurrence of knocking, and then returns to the engine vibration level as the knocking vibration attenuates. Knocking can be detected because it does not show the linear change characteristic when knocking occurs.

In addition, in this example, whether multiple frequency components were used or one
Knocking may be determined only based on changes in the intensity of one specific frequency component, and when determining knocking by detecting changes in the intensity of each of multiple frequency components, the final determination is not limited to a majority vote. .

<Effects of the Invention> As explained above, according to the present invention, a specific frequency component is extracted from a detection signal from a vibration sensor that detects engine vibration, and based on the change in the intensity of the specific frequency component in a predetermined interval. In a device that detects knocking,
When setting the reference change characteristic to be compared with the actual intensity change based on the initial input data of a predetermined interval, it is possible to compensate for the deviation in the input timing of the intensity data due to variations in the distance between each cylinder and the vibration sensor. Therefore, the setting accuracy of the reference change characteristic can be improved, and the knocking detection accuracy can be improved.

[Brief explanation of drawings]

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. FIG. 5 is a diagram showing an example of the temporal change in the intensity of a specific frequency component in the example. FIG. 5 is a diagram showing how the intensity integral value changes depending on the presence or absence of knocking.
The figure is a diagram showing problems in the setting control of the reference change characteristic shown in Figure 5, and Figure 7 is a block diagram showing an example of a conventional knocking detection device. l...Knock sensor (vibration sensor) 2...A
/D converter 3...Comb filter 6a to 6e
...Resonator 7...Microcomputer 8
...Crank angle sensor patent applicant Fujio Sasashima, agent of Japan Electronics Co., Ltd., patent attorney

Claims (1)

[Scope of Claims] A vibration sensor attached to an engine body to detect 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 component extracted by the specific frequency extracting means. an intensity change detection means for detecting an intensity change in a predetermined interval of a frequency component; and an intensity change detection means for detecting an intensity change in a predetermined interval of a frequency component; initial intensity sampling means for sampling intensity; and norm change characteristic setting for setting a norm change characteristic of the intensity of the specific frequency component in the predetermined interval assuming that the intensity sampled by the initial intensity sampling means remains unchanged in the predetermined interval. and a knocking determination means for determining the occurrence of knocking by comparing the intensity change of the specific frequency component detected by the intensity change detection means with the reference change characteristic set by the reference change characteristic setting means. A knocking detection device for an internal combustion engine configured.