JP2006022648A - Knock detection device for internal combustion engine, knock detection method, ignition timing adaptation method and ignition timing control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To automatically perform reliable knock judgment corresponding to human's audibility by using standard knock wave form having characteristics common knock phenomena without depending on an engine operation condition. <P>SOLUTION: A cylinder pressure sensor 12 is attached on the engine, knock is judged by evaluating correlation (similarity) of signal wave form of the cylinder pressure sensor 12 and the standard knock wave form created beforehand by mutual correlation method. The standard knock wave form has constant magnitude and frequency dropping as time passes. Consequently, reliable knock judgment corresponding to human's audibility can be automatically done by using the standard knock wave form having characteristics common in knock phenomena without depending on the engine operation condition. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a knock detection device, a knock detection method, an ignition timing adaptation method, and an ignition timing for an internal combustion engine, in which knock is determined by evaluating the correlation between the waveform of the output signal of the knock signal output means and a reference knock waveform prepared in advance. The invention relates to a control method.

In recent years, as shown in Patent Document 1 (Japanese Patent Laid-Open No. 2003-314349), in order to automatically perform knock determination corresponding to human hearing, the output signal is determined according to knock generated during operation of the internal combustion engine. Using a knock signal output means whose waveform changes (for example, an in-cylinder pressure sensor, a microphone, a knock sensor, etc.), the correlation between the waveform (detection waveform) of the output signal of this knock signal output means and a reference knock waveform created in advance A technique for evaluating knock and making a knock determination has been studied. This Patent Document 1 describes that a reference knock waveform is created by experiment or simulation.
JP 2003-314349 A (paragraph [0034] etc.)

  In the knock detection method of Patent Document 1, in order to improve the detectability and reliability, it is necessary to give the reference knock waveform a common feature of a knock phenomenon that does not depend on engine operating conditions. However, the above Patent Document 1 only describes that the reference knock waveform is created by experiment or simulation. Specifically, what kind of knock phenomenon common characteristics should be given to the reference knock waveform? Was an unresolved issue.

  Accordingly, an object of the present invention is to automatically perform highly reliable knock determination corresponding to human hearing, using a reference knock waveform having a common characteristic of a knock phenomenon that does not depend on driving conditions. Is to do so.

  In order to achieve the above object, the present invention provides a signal waveform output from a knock signal output means in which a waveform of an output signal changes according to a knock generated during operation of an internal combustion engine, and a reference knock waveform created in advance. In the case of performing the knock determination by evaluating the correlation, the vibration waveform whose frequency changes with the passage of time is used as the reference knock waveform. In order to optimize the reference knock waveform, the present inventor analyzed the signal waveform at the time of knock occurrence under various operating conditions and analyzed the frequency change and the amplitude change. As a result, the amplitude change of the signal waveform at the time of knock occurrence As for, it became clear that a complicated change occurred according to the operating conditions and no common features appeared. On the other hand, regarding the frequency change of the signal waveform at the time of knock occurrence, it has been found that common characteristics appear even if the operating conditions change. In this case, a common feature regarding frequency change is that the frequency decreases with time. Focusing on this feature, the present invention uses, as the reference knock waveform, a vibration waveform whose frequency changes with time, and thereby provides a common feature of the knock phenomenon that does not depend on operating conditions. Using the provided reference knock waveform, it is possible to automatically perform a highly reliable knock determination corresponding to human hearing.

  In this case, as described above, for the amplitude change of the signal waveform at the time of knock occurrence, a complicated change occurs according to the operating conditions and no common features appear, so even if the amplitude of the reference knock waveform is changed, It doesn't seem to make much sense. Therefore, it is preferable that the amplitude of the reference knock waveform is constant and only the frequency is changed. Thus, if the amplitude of the reference knock waveform is constant, the creation of the reference knock waveform is facilitated, and a product-sum operation for evaluating the correlation between the signal waveform of the knock signal output means and the reference knock waveform, etc. The calculation processing is easy, and there is an advantage that the calculation load can be reduced.

  The knock detection method of the present invention may be applied to a process for adjusting the ignition timing at the design and development stage of the internal combustion engine. In the ignition timing adaptation process, if the ignition timing is adapted while checking the knock allowable range based on the knock determination result obtained by the knock detection method of the present invention, the knock determination corresponding to the human audibility is made to the human audibility. This can be done automatically without relying on, significantly reducing the number of man-hours for ignition timing and shortening the adaptation time, and shortening the vehicle design and development period.

  Further, the knock detection device of the present invention is mounted on a vehicle, and the ignition timing is controlled while confirming the knock allowable range based on the knock determination result obtained by the knock detection method of the present invention during operation of the internal combustion engine. Anyway. In this way, knock control corresponding to the driver's audibility can be performed, and the ignition timing is advanced within a range where the driver does not feel uncomfortable in all driving regions, thereby improving output and fuel consumption. be able to.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment embodying the best mode for carrying out the invention will be described with reference to the drawings.

  First, the system configuration of the entire knock detection apparatus will be described with reference to FIG. An in-cylinder pressure sensor 12 for detecting the in-cylinder pressure is attached to the cylinder head of the engine 11 that is an internal combustion engine as a knock signal output means. The in-cylinder pressure sensor 12 may be integrated with the spark plug 13 or may be configured separately from the spark plug 13. The output signal of the in-cylinder pressure sensor 12 is taken into the knock determination computer 16 (correlation evaluation means, knock determination means) via the high-pass filter 14 and the A / D converter 15. As shown in FIG. 2, only the vibration component (knock component) of the in-cylinder pressure is extracted from the waveform of the output signal of the in-cylinder pressure sensor 12 by the high-pass filter 14.

  The knock determination computer 16 determines the knock by evaluating the correlation (similarity) between the signal waveform of the in-cylinder pressure sensor 12 and the reference knock waveform created in advance by the cross-correlation method. In such a knock detection method, in order to improve the detectability and reliability, it is necessary to give the reference knock waveform a common feature of a knock phenomenon that does not depend on engine operating conditions.

  Therefore, in order to optimize the reference knock waveform, the inventor analyzed the signal waveform at the time of occurrence of the knock under various engine operating conditions, and analyzed the frequency change and the amplitude change. Analysis of the frequency component of the signal waveform of the in-cylinder pressure sensor 12 revealed that a lot of knock secondary frequency components (frequency components near 14 kHz) are commonly included under various engine operating conditions. This seems to be because the vibration of the secondary frequency of the knock occurs in the vertical direction in the cylinder (that is, the installation direction of the in-cylinder pressure sensor 12).

  From the analysis result of the frequency component, in this embodiment, the frequency change and the amplitude change are analyzed focusing on the secondary frequency component of the knock. FIG. 3 shows the results of measuring the change in amplitude of the signal waveform when knocking occurs under various engine operating conditions. As is clear from this measurement result, it has been found that the amplitude change of the signal waveform at the time of knock occurrence has a complicated change depending on the engine operating condition, and no common feature appears. Therefore, since it seems that there is not much meaning even if the amplitude of the reference knock waveform is changed, the amplitude of the reference knock waveform is assumed to be constant.

  On the other hand, the measurement results as shown in FIG. 4 were obtained for the change in frequency of the signal waveform when knocking occurred. Looking at the secondary frequency component of knock, the frequency of θ1 (25 ° C. A) at the initial occurrence of knock becomes approximately 14 to 15 kHz under various engine operating conditions, and this frequency decreases almost linearly with time. It has been found that the predetermined crank angle θ2 (50 ° C. A) at which the vibration is sufficiently attenuated is about 10 to 11 kHz, and the frequency change degree is the same as the crank angle even if the engine operating conditions are changed.

Next, the mechanism of frequency change will be considered. The resonance frequency Fr in the bore direction in the cylinder is calculated by the following equation.
Fr = C · ρ / (π · bore diameter)
Here, C is the speed of sound and ρ is the gas density.

The speed of sound C is calculated by the following equation.
C = √ (κ ・ R ・ T)
Here, κ is a gas constant, R is a specific heat ratio, and T is a temperature.

The change in the volume of the combustion chamber due to the movement of the piston during the combustion stroke is regarded as an adiabatic change, and from the initial knock generation θ1 (25 ° C. A) to the predetermined crank angle θ 2 (50 ° C. A) in which the knock vibration is sufficiently damped. When the temperature change (T1 → T2) is calculated by the gas state equation, the following relationship is obtained.
T2 = 0.630 · T1
Here, T1 is the temperature at the initial occurrence of knocking θ1 (25 ° C. A), and T2 is the temperature at the time of knock vibration attenuation (50 ° C. A).

Next, consider the change in the speed of sound C in the cylinder (C1 → C2).
C2 = √ (κ ・ R ・ T2)
= √ (κ ・ R ・ 0.630 ・ T1)
= 0.794 · √ (κ · R · T1)
= 0.794 · C1
Here, C1 is the speed of sound at the initial occurrence of knock θ1 (25 ° C. A), and C2 is the speed of sound when knock vibration is attenuated (50 ° C. A). In the above equation, it is assumed that there is no change in the gas constant κ and the specific heat ratio R. However, in actuality, the specific heat ratio R changes in the direction of decreasing due to the increase in CO ₂ due to the combustion of the air-fuel mixture.

From the relationship of the change in the sound speed C (C1 → C2) described above, the change in the resonance frequency Fr (Fr1 → Fr2) is expressed by the following equation.
Fr2 = 0.794 · Fr1 [theoretical value]
Here, Fr1 is the resonance frequency at the initial occurrence of knock θ1 (25 ° C. A), and Fr2 is the resonance frequency at the time of knock vibration attenuation (50 ° C. A).

According to the experiment result of the present inventor, the change (Fr1 → Fr2) of the resonance frequency Fr is expressed by the following equation.
Fr2 = 0.727 · Fr1 [Experimental value]
The reason why the experimental value is different from the theoretical value is considered to be that the frequency decrease width becomes large due to the temperature decrease due to the cooling water. Thus, although there is a slight difference between the experimental value and the theoretical value, the characteristic that the frequency change degree is the same with respect to the crank angle is not changed regardless of the engine operating conditions.

  Focusing on this feature, in this embodiment, a vibration waveform in which the amplitude is constant and only the frequency decreases with time is used as the reference knock waveform. FIG. 5 shows a reference knock waveform with respect to the secondary frequency of the knock. The vibration waveform has a frequency of 14 kHz at the initial occurrence of the knock (25 ° C. A) and a frequency of 10.5 kHz at the time of knock vibration attenuation (50 ° C. A). Used as a reference knock waveform.

  FIG. 6 is a reference knock waveform for the 1.5th order frequency of the knock. The frequency at the time of knock generation (25 ° C. A) is 11 kHz, and the frequency at the time of knock vibration attenuation (50 ° C. A) is 8.25 kHz. This vibration waveform may be used as the reference knock waveform.

  FIG. 7 shows a reference knock waveform with respect to the primary frequency of the knock, in which the frequency at the initial occurrence of the knock (25 ° C. A) is 6.7 kHz, and the frequency when the knock vibration is attenuated (50 ° C. A) is 5 kHz. The waveform may be used as a reference knock waveform.

  Since the signal waveform at the time of occurrence of knocking in the in-cylinder pressure sensor 12 has a correlation (similarity) with the reference knock waveform, as shown in FIG. 8, the signal waveform is an observed waveform and a search waveform. A product-sum operation is performed on the reference knock waveform y (n) to obtain a cross-correlation value Rxy (k) between the two. This cross-correlation value Rxy (k) is expressed by the following equation.

  The waveform of the cross-correlation value Rxy (k) is a waveform obtained by extracting a knock component from the signal waveform x (n) and the reference knock waveform y (n). This cross-correlation value Rxy (k) corresponds to a measured value of knock strength, and the relationship between the knock strength due to human hearing and the cross-correlation value Rxy (k) is measured as shown in FIG. As is apparent from the measurement data of FIG. 9, the cross-correlation value Rxy (k) and the knocking intensity due to hearing have a substantially linear relationship. Therefore, the cross-correlation value Rxy (k) is used as a measurement value of the knocking intensity. For example, the measured value of the knock intensity can be made to substantially correspond to the knock intensity based on the sense of hearing, and it is not necessary for the person to hear the knock noise from the engine operating noise in the ignition timing adapting process. Thereby, the adaptation man-hour of the ignition timing can be significantly reduced, the adaptation time can be shortened, and the vehicle design and development period can be shortened.

In addition, in this embodiment, since the amplitude of the reference knock waveform is made constant, the creation of the reference knock waveform becomes easy and the correlation between the signal waveform x (n) and the reference knock waveform y (n) is evaluated. It is easy to perform arithmetic processing such as sum-of-products calculation, and there is an advantage that the calculation load can be reduced.
However, it goes without saying that the present invention may change the amplitude of the reference knock waveform.

  In this embodiment, the in-cylinder pressure sensor 12 is used as the knock signal output means. However, the present invention is not limited to this. A knock sensor for detecting vibration of the cylinder block of the engine 11 is attached to the engine 11 and the knock sensor The correlation between the signal waveform and the reference knock waveform may be evaluated, and a microphone for detecting a sound generated during engine operation is installed at an appropriate interval with respect to the engine 11. The correlation between the signal waveform of the collected sound and the reference knock waveform may be evaluated. Alternatively, an ion current detection system that detects the ion current generated in the cylinder during combustion through a spark plug or the like is used as a knock signal output means, and the correlation between the waveform of the ion current detection signal and the reference knock waveform is obtained. You may make it evaluate.

  Further, any one of the above knock signal output means may be mounted on the vehicle, and the ignition timing may be controlled while confirming the knock allowable range by the same method as in this embodiment during engine operation. In this way, knock control corresponding to the driver's audibility can be performed, and the ignition timing is advanced within a range where the driver does not feel uncomfortable in all driving regions, thereby improving output and fuel consumption. be able to.

It is a figure explaining the system configuration | structure of the whole knock detection apparatus in one Example of this invention. It is a figure explaining an example of a cylinder pressure waveform and a knock waveform extracted from this. It is a figure showing the result of having measured the amplitude change of the signal waveform at the time of knock generation on various engine operating conditions. It is a figure explaining the analysis result of the frequency change with respect to time. It is a figure explaining the reference | standard knock waveform about the secondary frequency of knock, and its frequency change. It is a figure explaining the reference | standard knock waveform about the 1.5th-order frequency of a knock, and its frequency change. It is a figure explaining the reference | standard knock waveform about the primary frequency of a knock, and its frequency change. It is a figure explaining the method of calculating | requiring the cross-correlation value Rxy (k) of both by performing product-sum operation on the signal waveform x (n) and the reference | standard knock waveform y (n). It is an experimental data figure showing the relationship between a cross correlation value and the knock level by hearing.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Engine (internal combustion engine), 12 ... In-cylinder pressure sensor (knock signal output means), 13 ... Spark plug, 16 ... Knock determination computer (correlation evaluation means, knock determination means)

Claims (6)

A knock signal output means whose output signal waveform changes according to a knock generated during operation of the internal combustion engine, and a correlation between the waveform of the output signal of the knock signal output means and a reference knock waveform prepared in advance is evaluated. In a knock detection device for an internal combustion engine comprising a correlation evaluation unit and a knock determination unit that performs a knock determination based on the correlation evaluated by the correlation evaluation unit,
The knock detection device for an internal combustion engine, wherein the reference knock waveform is a vibration waveform whose frequency changes with time.   2. The knock detection device for an internal combustion engine according to claim 1, wherein the reference knock waveform is a vibration waveform having a constant amplitude and only a frequency changing. An internal combustion engine that performs knock determination by evaluating the correlation between a signal waveform output from a knock signal output means that changes the waveform of an output signal in response to a knock that occurs during operation of the internal combustion engine and a reference knock waveform that has been created in advance. In the engine knock detection method,
A knock detection method for an internal combustion engine, wherein a vibration waveform whose frequency changes with time is used as the reference knock waveform.   4. The knock detection method for an internal combustion engine according to claim 3, wherein the reference knock waveform is a vibration waveform whose amplitude is constant and only the frequency changes.   When adapting the ignition timing at the design and development stage of the internal combustion engine, adapt the ignition timing while confirming the knock allowable range based on the knock determination result obtained by the knock detection method according to claim 3 or 4. A method for adapting ignition timing of an internal combustion engine characterized by the above.   An ignition timing of an internal combustion engine, wherein the ignition timing is controlled while confirming a knock allowable range based on a knock determination result obtained by a knock detection method according to claim 3 or 4 during operation of the internal combustion engine. Control method.

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