JPH0526721A - Detecting device for knocking - Google Patents

Abstract

PURPOSE:To enable decision of knocking irrespective of a state of operation by extracting three kinds of frequency components, at least, for each of a plurality of extracted frequency components and by varying a central frequency in accordance with the frequency out of them which has a maximum amplitude level. CONSTITUTION:Frequency components S1 and S3 according to each of a plurality of knocking vibration modes are extracted from an output signal of a knocking sensor. In three kinds of frequency analysis processings 111 to 113, on the occasion, frequency components of S11=f1-DELTAf, S12=f1 (central frequency matched with each component frequency f0) and S13=f1+DELTAf are extracted for each of the components S1 and S3. When the component S13 (S11) out of them shows a maximum, amplitude level, the frequency f1 is made high (low) by DELTAf. When the amplitude level of the component S12 is the maximum the frequency f1 is shifted by DELTAfX(x) ((x)=0 to 1) to the one of the components S11 and S13 which has the larger amplitude level. Since the central frequency follows automatically a change in each of the vibration modes, in this way, decision of knocking can always be performed irrespective of the state of operation of an engine.

Description

Detailed Description of the Invention

[0001]

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 suitable for a gasoline engine for automobiles.

[0002]

Knocking on an engine (also called knock)
Occurs, vibration with a specific resonance frequency component is generated. Therefore, the occurrence of knocking can be determined by detecting this vibration with a knock sensor.
Therefore, in the conventional knocking detection device, a bandpass filter is used to extract only the specific frequency component with the highest frequency of occurrence from the frequency components included in the signal from the knock sensor, and the level of the extracted signal Whether or not there was knocking was determined by the size of the. An apparatus related to this is disclosed in JP-A-59-737.
50, JP-A-59-125034, JP-A-60-2
No. 04969, and those described in JP-A Nos. 1-178773.

[0003]

In the above-mentioned prior art, the fact that knocking has a plurality of vibration modes is not taken into consideration, and some of the vibration modes when knocking occurs are treated as noise. However, the knocking detection capability is limited, the operating range of the engine that can detect knocking is limited, and there is a problem in reliable knocking detection.

That is, in the conventional device, only a specific frequency is detected from the signals included in the knock sensor signal by using the bandpass filter, but in the actual knocking phenomenon, only a single frequency component is used. Rather than occurring, there are multiple knocking vibration modes.

That is, as shown in FIG. 6, the cylinder of the engine is cylindrical as its name suggests. Therefore, as vibration modes in the cylinder, nodes (dividing lines) and antinodes (dividing lines) of pressure fluctuations in the radial direction and the circumferential direction are used. -) Exists, and as a result, five types of frequency components appear as a resonance phenomenon in the cylinder due to knocking. However, in the conventional technique, only the specific frequency that is most likely to resonate is extracted from these frequencies, and this limits the knocking detection capability.

The frequency of knocking vibration also changes depending on the properties of the gas in the combustion chamber. That is, the resonance wavelength of the cylinder is determined by the shape of the combustion chamber serving as the resonance cavity, but if the combustion temperature or the compression ratio increases, the speed of sound in the combustion gas also increases and the frequency rises. Furthermore, when the compression ratio of the engine increases, not only does the combustion temperature rise, but the shape of the resonance cavity changes and the resonance mode also changes.

With respect to this point, the conventional technique using a bandpass filter can be dealt with by widening the band of this filter, but as a result, noise can be easily picked up, and reliable detection of knocking can be achieved. There was a problem with. An object of the present invention is to provide a knocking detection device capable of always reliably determining knocking regardless of the operating state of the engine and enabling easy and accurate knocking control.

[0008]

In order to achieve the above-mentioned object, frequency component extraction means for independently extracting a signal component of each of a plurality of predetermined knock vibration modes based on the output of a knock sensor is provided. Whether or not knocking has occurred is determined by comprehensive determination of a plurality of signal components,
At this time, as the signals extracted by the frequency component extracting means, at least three kinds of signals having frequencies close to each other are obtained, and the deviation of the frequency components to be detected is obtained from the amplitude level of these signals, and the frequency is detected. The center frequency of the component extracting means is changed.

[0009]

The vibration detection means can detect all modes of knocking vibration generated in the combustion chamber, and the frequency component extraction means can separately detect each vibration mode. At this time, by performing knock determination for each vibration mode, it is possible to incorporate into the knock detection the signal that has been conventionally excluded as a noise component, so that the knocking detection capability can be improved. Then, since the center frequency of the frequency component extraction means automatically tracks according to the change of the vibration mode,
The knock can always be reliably determined, and accurate knock control can be performed.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The knocking detection device according to the present invention will be described in detail below with reference to the illustrated embodiments. FIG. 5 is a block diagram of an engine control device to which an embodiment of the present invention is applied. In the figure, 1 is an engine control unit, 2 is an engine cylinder, 3 is an intake pipe, 4 is an exhaust pipe, and 5 is a throttle. A valve, 6 is a fuel injection valve, 7 is an ignition plug, 8 is an ignition coil, 9 is a distributor, 10 is an air flow sensor for measuring an intake air flow rate, 11 is a reference sensor for cylinder discrimination, and 12 is a rotation angle. Position sensor, 13
Is an opening sensor that detects the throttle valve, 14 is an O ₂ sensor that detects the air-fuel ratio, 15A is a knock vibration sensor, 15B is a seat pressure sensor, and 15C is an in-cylinder pressure sensor.

The engine control unit 1 is composed of various electronic circuits including a microcomputer, and has an intake air flow meter 10, a reference angle sensor 11, a position angle sensor 12, and a throttle valve opening sensor 1.
3. In addition, the signals from various sensors such as the air-fuel ratio sensor 14 necessary for knowing the operating state of the engine are taken in,
Various drive signals are created by predetermined arithmetic processing, the fuel injection valve 6 and the ignition coil 8 are operated, and the engine is controlled.

Knock vibration sensor 15A and seat pressure sensor 15
B, and the in-cylinder pressure sensor 15C are all provided as knock signal detecting means. First, the knock vibration sensor 15A is attached in the vicinity of the combustion chamber of the cylinder block of the engine, and the vibration caused by combustion of the engine is detected. The seat pressure sensor 15B is provided on the washer portion of the spark plug 7 and serves to directly convert the vibration in the combustion chamber into an electric signal. And
The in-cylinder pressure sensor 15C is attached by making a hole in a part of the cylinder head of the combustion chamber, and also functions to directly capture the vibration in the combustion chamber and convert it into an electric signal.

In the embodiment of the present invention, the knock signal detecting means need only be one system. Therefore, actually, any one of the knock vibration sensor 15A, the seat pressure sensor 15B, and the in-cylinder pressure sensor 15C is used. Only one will be used.

By the way, as described above, the vibration mode and frequency when knocking occurs are as shown in FIG. That is, as vibrations of the cylinder in the combustion chamber, resonance states occur between the nodes (dividing lines) and the antinodes (+ or −) in the radial direction and the circumferential direction, and only specific frequency components are generated.
Since the knock signal detecting means detects the vibration due to the knock thus generated, the output thereof includes signals of a plurality of vibration modes.

Therefore, it is desirable that the knock vibration sensor 15A, the washer sensor 15B, or the in-cylinder pressure sensor 15C serving as the knock signal detecting means has a uniform sensitivity over the entire band including the frequencies shown in FIG. In addition, a piezo-type piezoelectric detection type sensor using a piezoelectric ceramic or crystal is generally used. Therefore, this sensor is also used in this embodiment.

As described above, the engine control unit 1
Supplies a drive signal to the fuel injection valve 6 and the ignition coil 8 to control the engine. In this embodiment, any one of the knock vibration sensor 15A, the seat pressure sensor 15B, and the in-cylinder pressure sensor 15C is used. The knocking determination process is performed by taking in a signal (knock signal) from one or more knock signal detecting means, and based on the result, the knocking control given by delaying the ignition timing in a predetermined manner is performed. The knock determination process by the engine control unit 1 at this time will be sequentially described below.

First, the signal from the knock signal detecting means (hereinafter referred to as the knock sensor 15) is input to a predetermined frequency analyzing means, separated into respective frequency components and extracted.

By the way, as the frequency analysis means,
Conventionally, bandpass filters using analog circuits have been mainly used, but when trying to extract multiple frequency components at the same time, the same number of analog circuits as the number of types of frequency components to be extracted are required. Increasing scale and complication of circuit adjustment processing are inevitable. Therefore, in this embodiment, the knock signal is AD-converted, and the frequency component of the AD conversion result is extracted by a digital filter. Since the frequency shown in FIG. 6 changes depending on the engine type, combustion chamber shape, bore diameter, etc., adjustment can be simplified by configuring the frequency extracting means 17 with a digital filter as in this embodiment.

As the digital filter, there are a non-regressive filter shown in FIG. 2 and a regressive filter shown in FIG. 3, and either digital filter may be used in this embodiment. Further, as shown in FIG. 4, the digital filter may be a filter that takes the difference between the output of the all band pass filter and the output of the band elimination filter for each characteristic frequency. In FIG. 4, the delay circuit functions as an all-pass filter. Then, as many filters as the number of frequency components to be extracted are prepared, and the required types of frequency components are simultaneously extracted.

By the way, the sampling interval τ _s for performing AD conversion is the reciprocal of the frequency that is at least twice the maximum frequency to be extracted by the sampling theorem, and in the example of FIG. 6, the maximum extraction frequency is 18 Since it is 0.1 kHz,
This interval τ _s may be set so as to satisfy the following equation.

[0021]

[Equation 1]

The coefficients ai and bi in the non-regressive filter shown in FIG. 2 and the regression filter shown in FIG. 3 are prepared in advance in accordance with the digital filter design procedure.

On the other hand, a fast Fourier transform is known as a frequency analyzing means, but in this case, the number of samples of 2n is necessary. For this reason, the section for frequency analysis, that is, the sampling section becomes a double or 1/2 discrete section and becomes a discontinuous section.

Therefore, in order to solve this problem, there is a method of multiplying each AD sample value by a Fourier coefficient, without being limited by the number of 2 n samplings, and there is a method. One example is shown in FIG.
That is, the frequency analysis means based on the Fourier series shown in FIG. 7 sets the frequency to be extracted as f, and sets the Fourier coefficient ci as in the following equation. To extract.

[0025]

[Equation 2]

At this time, as is apparent from FIG. 7, in this embodiment, the correction means 40 is provided, and the combustion in the cylinder is performed in accordance with the operating state of the engine, for example, the fuel injection width T _P and the rotational speed N. Estimate the temperature and calculate the frequency f
Is changed so that an appropriate frequency component can always be extracted.

By the way, in the present invention, the non-regressive digital filter of FIG. 2 and the regressive digital filter of FIG.
Alternatively, each of the frequency components S _{1 to} S ₅ by either the filter shown in FIG. 4 or the frequency analysis means based on the Fourier series shown in FIG.
In the extraction process of ......, at least three types of frequency components are respectively extracted centering on each characteristic frequency, and the frequency having the maximum amplitude level among these is determined as the corresponding characteristic frequency component. , And the fact that the center frequency of the filter is moved based on the relationship between this and at least two remaining frequency components, and the tuning of the filter is always given in accordance with each characteristic frequency. Below, about the means for this,
This will be described with reference to FIG.

In FIG. 1, processes 111 to 114, excluding the knock sensor and sampling process, are the non-regressive digital filter of FIG. 2, the regression digital filter of FIG. 3, the filter of FIG. 4, or the Fourier series of FIG. It corresponds to each of the extraction processing of each frequency component in the frequency analysis means.

First, as the procedure here, as shown in FIG. 1, three types of frequency analysis processing 111, 112, 113 are performed.
As shown in the spectrum diagram in the lower left of the figure, S ₁₁ = f ₁ −Δf, S ₁₂ = f ₁ , S ₁₃ = f for each characteristic frequency.
Extract three frequency components of ₁ + Δf. Here, f ₁ is a center frequency matched with the characteristic frequency f ₀ , and on the other hand, the value of Δf may be set to about several hundred Hz, although it depends on the value of the center frequency f ₁ .

If the frequency component S ₁₃ has the maximum level among these three types of frequency components, it means that the characteristic frequency is shifted to the higher side by at least Δf. , Center frequency f ₁
Is increased by Δf. On the contrary, if the frequency component S ₁₁ has the maximum level among these three types of frequency components, it means that the characteristic frequency is shifted to the lower side by at least Δf at this time. The frequency f ₁ is lowered by Δf.

However, when the amplitude level of the frequency component S ₁₂ is the maximum, the center frequency f is the one having the larger amplitude level among the frequency components S ₁₁ and S ₁₃ on both sides.
₁ is shifted by Δf × x (x = 0 to 1). Therefore, the above processing is as shown in the processing 114 of FIG. 1, and at this time, as a concrete method for shifting the frequency, in the above digital filter, the respective coefficients ai, bi, ci are It only needs to be changed, and it is extremely easy to realize.

When the extraction of the respective frequency components S _{1 to} S ₅ is finished in this way, the knock determination means shown in FIG. First, in the processes 80 and 81, the respective frequency components S _{1 to} S ₅ of the knock vibration are average values S ₁ to S ₅ of the frequency components S _{1 to} S ₅ when it is determined that there is no knock by then.
S ₅ (indicated by the superscript bar in the following equation and FIG. 8)
Respectively, and the ratio or difference (zero in the case of negative) is calculated, and those values are set to SN ₁ to SN ₅ .

Next, in process 82, these values SN ₁
~ SN ₅ , the sum of them, or the top m sums when arranged in descending order of the value, is taken and the knock index IK is calculated.
Output as. Then, this knock index IK is processed 8
3, when the knock index IK signal corresponding to the upper y% of the cumulative frequency distribution of the knock index IK signal shown in the lower right of FIG. 8 is compared with the level of the sensory test in knock control, the knock index IK signal is knocked. Determined to occur. Here, the cumulative frequency distribution in the lower right of this figure shows that the level with a large index is 0
%, From which all index levels are added up to the lower index level.

Next, if it is determined that no knocking, in the process 84 is performed to update the average value S ₁ ~ S ₅ frequency components S ₁ to S ₅ in the following manner.

[0035]

[Equation 3]

Here, K is a coefficient for obtaining a moving average, and a numerical value between K = 4 and 64 is used. Next, the frequency component extraction timing process will be described. First, FIG. 9 shows the configuration required for this processing. The knock signal from the knock sensor 15, the reference signal from the reference angle sensor 11, and the position signal from the position angle sensor 12 are input and the position signal is input. Count the rise of the signal,
Counter 10 cleared at the rising edge of the reference signal
0 and a compare register 101 that compares the count value of the counter 100, an interrupt controller 102 that requests an interrupt to the CPU 103 when the count values of the counter 100 and the compare register 101 match, and AD conversion that AD converts the knock signal. And the container 104.

Next, the processing operation will be described with reference to the flowchart of FIG. 10 and the timing chart of FIG. 11. First, as shown in FIG. 10A, the CPU 103 is interrupted at the rising edge of the reference signal Ref. AD
The angle θ _{K at} which the conversion operation by the converter 104 should be started is set in the conveyor register 101.

The counter 100 has a reference signal Ref.
Is cleared at the rising edge of and the position signal Pos starts counting from zero. And the count value of the counter 100 is θ _K
10B, the process by the coincidence interrupt of FIG. 10B starts, and the AD conversion by the AD converter 104 is started in the process, and the AD conversion interrupt is permitted at the same time. Then, the ending angle θ _N of AD conversion is set in the compare register 101.

Further, every time AD conversion is completed, an AD conversion interrupt request is issued to the CPU, the processing of FIG. 10 (c) starts, and the product-sum calculation of the digital filter is performed within this AD conversion interrupt. This sum of products operation is performed by the AD conversion value ADi and the coefficient
It is a calculation for multiplication with i, bi, ci, etc. and the sum thereof, and is performed until the crank angle reaches θ _N.

When the count value of the counter 100 counting the position signal Pos coincides with θ _N , a coincidence interrupt request is again issued, and the AD conversion interrupt is stopped in this request, and the sum of products up to that point is added. The calculated values are the frequency components S _{1 to} S ₅ .

Then, as shown in FIG. 8, the ratio or difference SN _{1 to} S between these frequency components S _{1 to} S ₅ and the average value.
N ₅ is obtained, and the knock index IK is calculated from these values.

After that, by the process 83 of FIG. 8, when the knock index IK is larger than the level SL in the sensory test, it is judged that there is knock, when it is smaller, it is judged that there is no knock, and then an output indicating the presence or absence of knock is output. , As shown in FIG. 11, the signal is output before the next reference signal Ref rises.

Therefore, the engine control unit 1 inputs the presence / absence of this knock at the next rise of the reference signal Ref, and if there is knock, delays the ignition timing at the time of setting the next ignition timing, etc. to avoid known knocking. It exercises control.

As described above, according to this embodiment, the occurrence of knocking can always be detected with certainty, so that accurate knocking avoidance control can be performed and engine performance can be sufficiently improved.

Further, according to this embodiment, since the information contained in the output of the vibration sensor can be effectively utilized, the engine output and the fuel efficiency can be controlled to be optimum.

[0046]

According to the present invention, a plurality of frequency components can be analyzed at the same time according to the vibration mode in the cylinder, and the analysis result becomes the signal strength included in the analysis section. Since it can be simplified and the degree of freedom in frequency selection is increased, there is an effect that it can respond even if the specifications of the target engine change.

Further, according to the present invention, the analysis frequency is automatically fine-tuned according to the vibration mode in the cylinder, and automatically tracks the changes in the analysis frequency, so that it is possible to prevent secular changes in the engine. Nevertheless, the knock can always be detected reliably and highly accurate knock control can be obtained.

Further, the sampling range is not limited to the n-th power of 2 called Fast Fourier Transform, and the sampling range can be freely selected, so that the frequency analysis section can be freely set according to the engine speed, and knocking detection can be performed. The accuracy can be improved sufficiently.

[Brief description of drawings]

FIG. 1 is a block diagram showing frequency analysis means in an embodiment of a knocking detection device according to the present invention.

FIG. 2 shows a first filter means according to an embodiment of the present invention.
It is a block diagram showing an example of.

FIG. 3 is a second filter means according to an embodiment of the present invention.
It is a block diagram showing an example of.

FIG. 4 is a third filter means according to an embodiment of the present invention.
It is a block diagram showing an example of.

FIG. 5 is a configuration diagram of an engine control device to which an embodiment of a knocking detection device according to the present invention is applied.

FIG. 6 is an explanatory diagram of a knocking frequency mode.

FIG. 7 is a fourth filter means according to an embodiment of the present invention.
It is a block diagram showing an example of.

FIG. 8 is a block diagram of knocking determination means in one embodiment of the present invention.

FIG. 9 is a block diagram of a timing control means according to an embodiment of the present invention.

FIG. 10 is a flowchart illustrating a timing control operation in the embodiment of the present invention.

FIG. 11 is a timing chart illustrating a timing control operation in the embodiment of the present invention.

[Explanation of symbols]

1 Engine control unit 2 engine cylinders 3 intake pipe 4 exhaust pipe 5 Throttle valve 6 Fuel injection valve 7 Spark plug 8 ignition coil 9 distributor 10 Intake air flow meter 11 Reference angle sensor 12 Position angle sensor 13 Throttle valve opening sensor 14 Air-fuel ratio sensor 15A knock vibration sensor 15B Seat pressure sensor 15C cylinder pressure sensor

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location G01M 15/00 A 7324-2G

Claims (3)

[Claims] 1. A frequency component extracting means for independently extracting at least two predetermined frequency components included in an output signal of a knock sensor for detecting at least one of engine vibration and cylinder internal pressure vibration, and this frequency component extracting means. A knock index calculating means for calculating a knock index from a calculation result of at least two outputs given by the above, and by making the at least two frequency components coincide with the resonance frequency components determined by the respective resonance modes appearing in the cylinder of the engine. In a knocking detection device of a type that determines occurrence of knocking based on the knock index, frequency analysis means for extracting at least three types of signals of frequencies close to each other of the at least two frequency components, and at least three types of these signals. The frequency of the signal with the maximum amplitude level of And a processing means for changing the center frequency of the frequency analysis means, and the center frequency of the frequency analysis means is configured to automatically track the frequency change of the resonance frequency component. 2. The knocking detection device according to claim 1, wherein the frequency component extracting means is composed of at least two kinds of digital filters. 3. The invention according to claim 2, further comprising means for calculating the speed of sound in the atmosphere in the cylinder from the operating state of the engine, and changing the center frequency of the digital filter according to the result of calculation of the speed of sound by this means. A knocking detection device having the above structure.