JP2612365B2 - 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 result device suitable for a gasoline engine for an automobile.

[Conventional technology]

In an internal combustion engine, particularly a gasoline engine for an automobile, it is desirable to operate at a knocking limit in order to improve the performance.

However, this requires the application of high-precision knock control, and of course, the use of a high-precision knock detection device is indispensable.

By the way, as this knocking detection device, a method of using a sensor for detecting vibration of an engine (internal combustion engine) and determining knocking from a detection signal of the sensor has been widely adopted. That is, a knocking phenomenon caused by abnormal combustion in the combustion chamber of the engine causes vibration having a plurality of resonance frequency components peculiar to the engine block, and the occurrence of knocking is detected by capturing the vibration energy.

However, in this method, it is difficult to distinguish it from mechanical noise caused by the mechanical movement of the engine itself, and as a method for determining this, a method of extracting only the above-described resonance frequency component has been devised.

For example, Japanese Patent Application Laid-Open No. 63-219874 describes a method in which a plurality of filters are provided, a specific resonance frequency component including a plurality of frequency components is extracted, and knocking is detected.

Here, examples of using a plurality of filters include a method of configuring an analog filter or the like with discrete components, and a method of detecting a plurality of frequencies by applying a digital filter.

As a conventional method of using a plurality of filters as described above, a technique of changing a sampling clock is known. For example, in Japanese Patent Application Laid-Open No. Sho 64-54227, a band is changed. I have.

However, if the sampling clock is changed, the band-pass characteristic changes, and the clock of the microcomputer is usually used as this clock. In this case, the calculation processing time by the microcomputer also changes. There was a problem.

[Problems to be Solved by the Invention] In the above-mentioned conventional technology, the point that the center frequency has to be fixed in the analog filter and the digital filter is not considered, and the change in the operation state of the engine and the engine itself are not considered. It has been difficult to properly adjust the center frequency to the resonance frequency due to the change of the resonance frequency with the aging of the sensor, and there has been a problem in improving the accuracy of knocking detection.

Further, in the above-described conventional technology, when the filter is an analog filter, no consideration is given to the necessity of using discrete parts by the number of frequencies to be extracted. There was.

An object of the present invention is to provide a knocking detection device that can always perform high-accuracy detection regardless of the operating state or aging of the engine without increasing the number of components.

[Means for solving the problem]

The object is to simultaneously use a sensor for detecting vibration of an internal combustion engine and a filter having a pass band of a frequency based on a plurality of vibration modes, and simultaneously detect at least two types of specific frequency components having different frequencies from the detection signal of the sensor. Extraction, a timbre index corresponding to a predetermined vibration mode generated in the combustion chamber of the internal combustion engine is obtained based on these specific frequency components, and knocking detection of the internal combustion engine is determined based on the timbre index. In the apparatus, selecting means for detecting a frequency having a maximum level value from among spectral components in the vicinity of each predetermined frequency which is preset in correspondence with the at least two kinds of specific frequency components, respectively The frequency detected by the selection means is used for calculating the tone index every time the frequency is detected. Used as wave number components, it is accomplished as slide into updating the timbre index.

According to the embodiment, a sensor for detecting the vibration of the engine block or the fluctuation of the internal pressure in the combustion chamber is provided, and the detection signal of the sensor is reduced to a sufficient level necessary for analyzing the knocking signal. A preamplifier is provided to amplify up to

The amplified signal is converted into a digital value by an AD converter and sampled by a microcomputer.

Then, the occurrence of knocking is determined by analyzing the frequency of the AD conversion result of the knocking signal by a microcomputer.

In order to detect the aging of the engine, means for integrating the operating time of the engine or the traveling distance is provided.

[Action]

The knocking sensor has a flat frequency response over a sufficiently wide band including the signal required to detect knocking, and contains a plurality of unique frequency components generated when knocking occurs. Occurrence can be detected.

In addition, by accumulating the operating time or mileage of the engine, it is possible to estimate the deterioration of the engine, and it is possible to track the frequency used for frequency analysis for the shift of the specific frequency when knocking occurs due to the deterioration, and to detect knocking. Can be optimized.

Further, by analyzing the sampling result by the microcomputer, the occurrence of knocking can be detected in real time, and the engine output and the combustion efficiency can be optimized.

Further, by the frequency analysis in the microcomputer, a plurality of frequency components can be analyzed at the same time, and a band with a slightly different frequency can also be analyzed.

In addition, since a plurality of frequencies are analyzed, all vibration modes at the time of occurrence of knocking can be captured, so that knocking can be detected reliably.

〔Example〕

Hereinafter, a knocking detection device for an internal combustion engine according to the present invention will be described in detail with reference to the illustrated embodiment.

FIG. 1 is a block diagram of an engine system to which an embodiment of the present invention is applied. In FIG. 1, reference numeral 1 denotes an engine.
An engine control unit 10 comprising U11, ROM12, RAM13, I / O14, etc., is provided. The output voltage of the intake air meter (H / W) 2, the crank angle sensors 3, 4, the water temperature sensor 5, and the throttle valve The output of the opening degree sensor 6 and the like are taken in, the combustion injection amount and the ignition timing optimum for the operation of the engine are measured, and the measurement result is output from the I / O 14 to drive the injector 7 and the ignition coil 8 to drive the engine 1 Performs fuel supply control and ignition control.

These controls will be described in more detail below.

The air taken by the engine is an air cleaner (not shown)
And enters the combustion chamber through ducts, slots, suction pipes and suction valves. The intake air amount is measured by the intake air amount meter 2 and input to the engine control unit 10 as a voltage corresponding to the intake amount per unit time.

From the crank angle sensors 3 and 4, a cylinder is determined, and two types of signals, a reference signal Ref indicating the top dead center and a position signal pos indicating the crank angle, are generated. Used for measuring the rotation speed.

The temperature Tw of the engine cooling water is measured by the water temperature sensor 5 and is used for correcting the engine control.

The CPU 11 calculates the fuel injection amount by dividing the intake air amount by the number of revolutions and adding a correction such as a water temperature.

On the other hand, the basic value of the ignition timing is determined by the fuel injection amount and the rotation speed, and is corrected by the behavior of the water temperature and the rotation speed.

Next, the knock sensor 9 is a sensor for detecting vibration attached to the cylinder block of the engine 1, and has a function of converting the vibration accompanying the occurrence of knock into an electric signal.

The knock sen 9 may be attached together with the ignition plug 8a instead of the illustrated position.

Further, the knock sensor 9 may be a sensor for detecting in-cylinder pressure attached to the combustion chamber, which is a system that takes out a variation in the in-cylinder pressure as a knocking signal, and is represented by 9a.

Further, in this embodiment, a timer 20 is provided in the engine control unit 10 so as to obtain the total operating time of the engine.

A vehicle speed sensor 21 is provided on the wheels of the vehicle. The vehicle speed signal VSP from the vehicle speed sensor 21 is integrated by an integrator 22 in the engine control unit 10 to obtain the total driving distance.

The total operation time and total operation distance are stored by a non-volatile ROM (not shown) or a backup by a built-in battery, so that the total operation time and the total operation distance are retained even when the power of the engine control unit 10 is turned off.

Next, the knocking detection according to the present invention will be described.

First, the vibration in the combustion process of the engine has the frequency value ρmn, where m is the degree in the circumferential direction of the cylinder and n is the degree in the radial direction of the cylinder, and the resonance frequency fmn exists correspondingly. For example, in the case of the engine used in this embodiment,
The values are as shown in FIG.

Therefore, in the case of the present embodiment, the number of times ρ10 indicates a case where the order in the circumferential direction of the cylinder is 1 and the order in the radial direction is 0.

 Here, the frequency value ρmn is a name of the vibration mode.

The frequency characteristics of the knock sensor 9 attached to the cylinder block of the engine 1 include all the above-mentioned specific frequencies generated when knocking occurs, and have a uniform sensitivity over the range.

Therefore, when a certain knocking signal is analyzed, a distribution as shown in FIG. 2B is obtained.

Therefore, if it is known in advance that the frequency characteristics are not uniform, the frequency characteristics can be evenly flattened by providing the preamplifier described later with characteristics opposite to the frequency characteristics.

Next, the processing of the knocking signal will be described with reference to FIG.

The knocking signal s is amplified through the preamplifier 30. As described above, the frequency characteristic is changed by the equalizer 31 in accordance with the frequency characteristic of Knocksen, and is amplified by the variable amplifier 33 within a range not exceeding the input voltage range of the AD converter 34. It is assumed that the amplification value of the variable amplifier 33 can be changed according to the level of the input signal or the number of rotations in accordance with an instruction from the I / O 14. However, the amplification value is set to be constant in the frequency analysis section of the knocking signal.

Here, the section for analyzing the knocking signal is started from a predetermined angle (time point) θopen after the top dead center where the knocking phenomenon easily occurs, as shown in FIG. The angle θopen can be determined by setting the rising of the reference signal Ref to zero and counting the position signal Pos, as shown in the figure.

When the count value matches the angle θopen, the AD conversion end interrupt is permitted, and the processing by the AD converter 34 is started (third processing).
Figure).

As shown in FIG. 4, the AD conversion is performed at regular intervals τ, and the microcomputer is interrupted at the end of the AD conversion, and is sequentially and sequentially transferred to the RAM within the AD conversion end interrupt.

Here, the period τ of the AD conversion is set so that the frequency represented by the reciprocal thereof is twice or more that of the highest frequency to be analyzed here.

As shown in FIG. 3, the preamplifier 30 is
It is assumed that a low-pass filter 32 having a sufficient attenuation for a frequency f cut of 1 / (2t) or more is included.

Thus, the number of AD-converted data, at time t _0, which has become ^the 2 ⁿ for example, as shown in FIG. 4, and ends the AD conversion end interrupt, sets a frequency analysis flag at this time t ₀ Then, the frequency analysis process is started.

As shown in FIG. 3, this frequency analysis is performed, for example, by a fast Fourier transform 35 from a ²ⁿ number of sampled data A in a butterfly calculation (calculation method is, for example, “manual utilizing FFT” (published by Japan Management Association 60.10.30, Kido) This is started by obtaining 2 ⁿ different frequency data B.

And, of these 2 ⁿ number of revolutions, by preliminary experiments,
Spectral components S ₁ corresponding to _k (k> 1) frequencies f _{1 to} f _k determined as frequencies specific to knocking occurrence
SS _k as data C. This is a tone index corresponding to knocking.

Next, processing 36 is performed on these spectral components S _{1 to} S _k .
, The knocking signal strength I is _obtained by multiplying the weighting amounts W _{1 to} W _k , respectively.

Then, in the comparison process 37, the signal intensity I is changed to a reference intensity I ₀ representing the intensity at the time when the knocking phenomenon does not occur.
It is determined that knocking has occurred when the value is larger than.

In this manner, when it is determined that knocking has occurred, as shown in FIG. 4, a known ignition timing control is performed in which the ignition timing is delayed by a predetermined angle θref, and thereafter, the ignition timing is returned by a predetermined angle, for example, + 1 ° every predetermined period Tadv. It is.

Next, the processing of the microcomputer required for these calculations will be described with reference to FIG.

First, the processing of FIG. 5A is executed in response to the rise of the reference signal, and after the cylinder is determined, the predetermined angle θopen
Set.

At the same time, an angle interrupt is generated when the position signal is counted by the angle of θopen from the rise of the reference signal, thereby generating an angle interrupt, as shown in FIG.
, The AD conversion end interrupt is permitted within this angle interrupt, the sampling counter is set to zero, and the sampling data storage pointer is initialized to the head address of the storage area.

The processing of FIG. 5C is started by the AD conversion end interrupt. In this processing, first, the AD conversion value is stored in the address indicated by the sampling data storage pointer, and the pointer and the sampling counter are incremented (50). ).

And when the sampling counter reaches 2 ⁿ ,
The AD conversion end interrupt is stopped, and the frequency analysis flag is set (51).

On the other hand, the processing shown in FIG. 5 (d) is provided as a timer task which is started at regular intervals. In this processing, the frequency analysis flag is checked. A conversion subroutine is started (52).

After fast Fourier transform completed, the execution process (53) for taking out the spectral components S ₁ to S _k corresponding to the frequency f ₁ ~f _k.

However, specific frequency of knocking occurrence is slightly instead Te cowpea the rotational speed and the ignition timing, and for varying in position of the piston at the time of knocking, it was used as the value of the spectral components S ₁ to S _k Therefore, the knocking phenomenon cannot be accurately determined.

Therefore, in this embodiment, as shown in FIG. 6, the maximum peak point is determined from among the spectral components in the range corresponding to f ± Δf, which are adjacent to the specific frequency consisting of the frequencies f _{1 to} f _k. , so that the use in place of the specific frequencies of them from the frequency f ₁ ~f _k.

Note that an average value of spectral components within a range corresponding to f ± Δf that is immediately before and after the specific frequency may be used instead.

Further, the frequency giving the maximum peak spectrum amount selected from f ± Δf for each ignition may be used as the center frequency for the next ignition.

Calculated knocking intensity I on the spectral components S ₁ to S _k thus obtained is multiplied by a weighting factor W ₁ to _W-k, respectively (5
4), it is compared with a reference intensity I ₀ (55).

When the knock intensity I becomes larger than the reference intensity I ₀ is the make knocking occurrence flag (56).

FIG. 5 (c) shows an ignition timing calculation task. As described above, when the knocking occurrence flag is set, the ignition timing is delayed by the angle θret, and the ignition timing holding timer is set to the timing Tad.
Set to v (57).

Then, the period Tsdv is subtracted for each period of the timer task,
At the time when it reaches zero, the angle θret is reduced by one degree. If the angle θret does not become zero here, the period Tadv
Set. By this series of operations, the ignition timing is retarded every time knocking occurs, and as a result, knocking control is obtained (58).

By the way, the specific frequency f ₁ to knock detection
f _k is accompanied by aging as shown in FIG.

Therefore, in this embodiment, as described in FIG.
A timer 20 and a vehicle speed sensor 21 are provided in the engine control unit 10, and the total operation time of the engine and the total operation distance of the vehicle are obtained by these. The total operation time and the total operation distance are calculated by the engine control unit 10. It will be saved even if the power is turned off.

And according to these total driving time and total driving distance,
The specific frequencies f _{1 to} f _k for knocking detection are configured to be shifted in a direction to cancel the aging shown in FIG. 7, so that the knocking detection can be performed with higher accuracy.

By the way, in the above embodiment, the frequency analysis is performed by the fast Fourier transform. However, instead of the fast Fourier transform, another frequency analysis method, for example, a Walsh-Hadamard transform may be used.

According to the Walsh-Hadamard transform, the specific frequencies f _{1 to} f _k can be _obtained without extracting 2 ⁿ spectra, and the calculation time can be shortened.

The Walsh-Hadamard transformation is described in "Transactions of the Society of Instrument and Measurement Engineers, Vol. 18, No. 10," p. 38-p.
You may refer to Moon, Kurihara, etc.

Still another frequency analysis method, for example, for f ₁ ~f _k to advance required, constitutes a digital bandpass filter, by shifting each coefficient in Z transform, applying the method of shifting the center frequency of the bandpass You may.

Also, the center frequency at the time of knocking varies depending on the cooling water temperature, intake air temperature, humidity, and operating conditions.
If the center frequency is moved in accordance with these conditions, knock detection accuracy can be further improved.

〔The invention's effect〕

According to the present invention, a specific frequency at the time of occurrence of knocking can be tracked in accordance with the operating state of the engine, knocking can always be determined with high accuracy, and accurate knocking control can be obtained.

Further, by selecting a plurality of frequencies, a high load, can be detected by high speed rotation even appropriate frequency, in the knocking generation time and knocking non occurrence, a large ratio of the knocking intensity I and the reference intensity I ₀ And the knocking determination can be made accurately.

Further, since the knocking control can be applied to high loads and high revolutions, the operating point of the engine can be brought close to the ignition timing required by the MBT control, and the engine output and the fuel consumption rate can be improved.

[Brief description of the drawings]

1 is a block diagram showing an engine system to which a knocking detection device for an internal combustion engine according to the present invention is applied, FIG. 2 is an explanatory diagram of a vibration mode, and FIG. 3 is a description of a knocking detection process according to an embodiment of the present invention. FIG. 4, FIG. 4 is a waveform diagram for explaining the operation, FIG. 5 is a flowchart showing a knocking detection processing procedure according to an embodiment of the present invention, FIG. 6 is a characteristic diagram showing a frequency for knocking detection, and FIG. FIG. 6 is a characteristic diagram illustrating a secular change of a knocking detection frequency. 1 ... engine, 2 ... intake air meter (H / W), 3, 4
... Crank angle sensor, 5 ... Water temperature sensor, 6 ... Water temperature sensor, 7 ... Injector, 8 ... Ignition coil, 9 ...
... knock sensor, 10 ... engine control unit, 11 ...
Microcomputer CPU, 12… ROM, 13… RAM, 1
4 ... I / O.

Claims (4)

(57) [Claims] 1. A sensor for detecting vibration of an internal combustion engine, and a filter having a pass band of frequencies according to a plurality of vibration modes, wherein at least two types of specific frequency components having different frequencies from a detection signal of the sensor are provided. Simultaneously extracted, based on these specific frequency components to determine a tone index corresponding to a predetermined vibration mode generated in the combustion chamber of the internal combustion engine,
In the knocking detection device for an internal combustion engine, which is configured to determine the presence or absence of knocking based on the timbre index, in the vicinity of each predetermined frequency set in advance corresponding to the at least two kinds of specific frequency components, A selecting means for detecting a frequency indicating the maximum level value from among the spectral components of each of the spectral components is used.The frequency detected by the selecting means is used as a specific frequency component used for calculating the timbre index each time the detection is performed. A knocking detection device for an internal combustion engine, characterized in that the tone color index is updated. 2. The invention according to claim 1, further comprising operating state detecting means for detecting an operating state of the internal combustion engine including at least one of a cooling water temperature, an intake air temperature, and an intake air humidity of the internal combustion engine. Knocking detection of an internal combustion engine, wherein each predetermined frequency set in advance corresponding to the at least two kinds of specific frequency components is changed in accordance with a detection result of an operating state detecting means. apparatus. 3. The invention according to claim 1, further comprising: time counting means for accumulating the operation time of said internal combustion engine from a predetermined point in time, and corresponding to said at least two kinds of characteristic frequency components according to a detection result of said time counting means. A knocking detection device for an internal combustion engine, wherein each of the predetermined frequencies set in advance is changed. 4. The invention according to claim 1, wherein said selecting means multiplies a plurality of spectra including said neighboring spectral components by respective predetermined weighting coefficients, and obtains said spectral components by summing them. A knocking detection device for an internal combustion engine, characterized in that: