JPH05195930A - Knocking detecting device and engine control device - Google Patents

Abstract

PURPOSE:To enhance the output of an engine and its fuel efficiency by constituting a knocking detecting device and an engine control device in such a way that the ignition timing is calculated both by an ignition-timing correcting value that is calculated on the basis of the output of a comparison means for judging the presence of the occurrence of knocking and by a basic ignition timing that is calculated on the basis of the conditions of the engine. CONSTITUTION:A device in which ignition timing is controlled on the basis of the detected value of knocking caused at the time of combustion of an engine 7 is provided with a vibration sensor 151 for detecting the vibration of the engine 7 or the internal-pressure vibration inside the cylinder, and a comparison means by which the vibration included therein is compared with a predetermined knock judging index for judging the presence of the occurrence of knocking. And the device is constituted in such a way that the correction value is calculated on the basis of the output of the comparison means, and a basic ignition timing is calculated on the basis of the conditions of the engine, and that the ignition timing is calculated on the basis of this correction value and the basic ignition timing. In this case, the judgment of comparison means and respective calculations are carried out in a control unit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a knock detection device and an engine control device having a knock detection means.

[0002]

2. Description of the Related Art When knocking occurs in an engine, vibration having a characteristic resonance frequency component is generated. The presence or absence of knocking is detected by separating and distinguishing from the engine vibration detected by the vibration sensor, the vibration caused by the knocking and the background vibration generated other than knocking. That is, in the conventional knocking detection device, as described in, for example, Japanese Unexamined Patent Publication (Kokai) No. 58-45520, a specific resonance frequency component of 1 or 2 within a range of 8 to 15 KHz is predetermined from engine vibration.
Separation was performed using a bandpass filter tuned to the frequency, and the presence or absence of knocking was determined by determining whether or not the level exceeded a predetermined level.

[0003]

In the above-mentioned prior art, since the presence or absence of knocking is determined by using only the specific frequency component contained in the output of the vibration sensor, the background vibration becomes high. The fluctuation of the background vibration becomes larger than the vibration caused by knocking at the time of high-speed load operation. For this reason, the vibration due to knocking and the background vibration cannot be separated from the output of the vibration sensor, and it is impossible to determine whether knocking occurs.

An object of the first invention is to provide a knocking detection device capable of determining whether or not knocking has occurred even under high load and high speed operation.

A second object of the present invention is to provide a knocking detection device capable of determining whether or not weak knocking occurs in all engine operating states.

Furthermore, in the above-mentioned prior art, since the resonance frequency of the knocking sensor is set to about 13 KHz, it is difficult to separate and use the resonance frequency component near 13 KHz, and it is determined whether knocking occurs. Could not be used for. For this reason, the background vibration becomes small during high-load high-speed operation.
The frequency band up to about 0 KHz cannot be used to determine whether knocking has occurred. Therefore, it was not possible to determine whether knocking occurred during high-load and high-speed operation.

A third object of the present invention is to provide a knocking detection device capable of determining whether or not knocking has occurred even during high load and high speed operation.

In the above prior art, the knocking judgment cannot be made during the high load high speed operation of the judging means for judging the occurrence of knocking for the calculation of the ignition timing. Therefore, during high-load high-speed operation, the ignition timing must be retarded to a region where knocking never occurs, and engine output and fuel efficiency cannot be improved. A fourth object of the present invention is to provide an engine control device capable of improving engine output and fuel efficiency during high-load and high-speed operation.

In the above prior art, the FFT (FastFoFoFo) is used because the determination means for determining the occurrence of knocking for the calculation of the ignition timing is composed of an analog circuit.
It was not possible to execute complicated arithmetic processing such as urier transform) in real time. Therefore, the information contained in the vibration sensor cannot be fully utilized, it is not possible to determine with high accuracy whether knocking has occurred, and the ignition timing cannot be controlled so that the engine output and the fuel efficiency are optimized.

A fifth object of the present invention is to provide an engine control device capable of effectively utilizing the information contained in the vibration sensor and controlling the ignition timing to optimize the engine output and the fuel efficiency.

[0011]

To achieve the above first object, the first invention includes a vibration sensor for detecting engine vibration or cylinder internal pressure vibration and an output of the vibration sensor based on digital frequency analysis. The determination means for determining the presence or absence of knocking from at least two frequency components is provided.

In order to achieve the second object, in the second invention, a vibration sensor for detecting engine vibration or cylinder pressure vibration, a crank angle sensor for detecting an engine crank angle, and a first crank angle are provided. From the second crank angle to the second crank angle at predetermined time intervals, sampling means for sampling the digital value of the output of the vibration sensor, a memory for storing the sampled value, and a frequency component contained in the vibration sensor based on the stored contents of the memory. And a determining means for determining the presence or absence of knocking in accordance with the frequency component.

In order to achieve the third object, in the third aspect of the invention, a vibration sensor having a substantially constant detection sensitivity from 5 KHz to 18 KHz, and a judging means for judging whether knocking occurs based on the output of the vibration sensor. Was established.

In order to achieve the fourth object, in the fourth invention, a vibration sensor for detecting engine vibration or cylinder internal pressure vibration, an A / D converter for converting the output of the vibration sensor into a digital signal, and a digital signal are provided. A determination means for determining whether or not knocking has occurred by discriminating the other vibration and the vibration based on knocking by digital processing by taking in a signal, and an ignition timing control means for controlling the ignition timing by the output of the determination means are provided.

In order to achieve the fifth object, in the fifth invention, a vibration sensor for detecting engine vibration or cylinder pressure vibration, a first storage means for storing a program, and an output of the vibration sensor are fetched. , A first microcomputer for determining whether knocking has occurred according to the program of the first storage means and storing the determination result in the second storage means, an engine state sensor for detecting the engine state, and a program And a second microcomputer for calculating the ignition timing according to the program of the third storage means on the basis of the output of the engine state sensor and the stored contents of the second storage means.

[0016]

According to the first aspect of the present invention, at least two resonance frequency components included in the output of the vibration sensor are obtained by digital frequency analysis, and it is determined whether knocking occurs. As a result, the presence or absence of knocking can be compositely determined from at least two resonance frequency components included in the vibration sensor, so that the vibration and the background vibration caused by knocking occur even during high-load high-speed operation in which the background vibration becomes large. It is possible to determine whether or not knocking has occurred, and it is possible to determine whether knocking has occurred.

According to a second aspect of the invention, the digital value of the output of the vibration sensor is sampled at a predetermined time interval from the first crank angle to the second crank angle, stored in a memory, and the frequency component is analyzed based on the stored contents. , Whether or not knocking has occurred is determined based on the frequency component. As a result, an arbitrary frequency component included in the output of the vibration sensor can be obtained, and the presence or absence of knocking is determined using the frequency component in which the most noticeable vibration according to the engine operating state appears. Therefore, it is possible to determine whether weak knocking occurs in all operating states of the engine.

According to a third aspect of the present invention, the engine vibration is detected substantially uniformly in the range of 5 KHz to 18 KHz, and the presence or absence of knocking is determined based on this detection. As a result, it is possible to determine whether or not knocking has occurred in a frequency range in which background vibration is small, such as during high-load and high-speed operation, so that it is possible to determine whether or not knocking has occurred even during high-speed and high-load operation.

According to a fourth aspect of the present invention, the presence or absence of knocking is determined by converting the output of the vibration sensor into a digital signal, and by using this digital signal, the other vibrations and the vibration due to knocking are separated and discriminated by the digital processing. The ignition timing is controlled based on this determination. In this way, since the separation determination by the digital processing can be performed, it is possible to reliably determine the presence or absence of knocking even at high load and high speed, control the ignition timing advance and retard, and improve engine output and fuel efficiency. .

In a fifth aspect of the invention, the first microcomputer determines whether or not knocking has occurred according to the program of the first storage means based on the digital value of the vibration sensor, and based on the presence or absence of knocking, the first microcomputer The second microcomputer calculates the ignition timing according to the program of the third storage means. As a result, the first microcomputer performs complicated processing according to the program.
Moreover, since it can be done in real time, the information contained in the vibration sensor can be effectively utilized, and the ignition timing can be controlled so that the engine output and the fuel efficiency are optimized.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the principle of determining whether knocking occurs in the present invention will be described. The vibration of the engine contains many vibration components. For example, there are vibration components due to piston friction, crankshaft rotation, valve operation, and the like. Further, these vibration components change depending on the engine state.

When knocking occurs in the engine, vibration unique to knocking occurs. Whether or not knocking has occurred is determined by separating the vibration characteristic of knocking from the overall vibration of the engine detected by the vibration sensor.

FIGS. 11A and 11B are diagrams showing the output of the vibration sensor when knocking does not occur and the analysis result of the frequency component of the output of the vibration sensor. On the other hand, FIGS. 11C and 11D are diagrams showing the analysis result of the output of the vibration sensor and the frequency component of the output of the vibration sensor when knocking occurs.

As shown in Table 1, when the resonance vibration mode is ρ _nm , where n is the radial direction of the cylinder and m is the circumferential direction thereof, there is a resonance frequency f _nm corresponding thereto.

As can be seen by comparing (b) and (d) of FIG. 11, when the knocking occurs, the resonance frequency components of the respective resonance frequency components are higher than when the knocking does not occur. It's getting bigger.

[0026]

[Table 1]

Determination of the presence or absence of knocking using the knocking determination index will be described with reference to FIG. In order to explain the principle operation, the resonance frequency f ₁₀ (6.3K
The frequency components of Hz) and f ₀₁ (13.0 KHz) will be described. However, it is not restricted to this,
Whether or not knocking has occurred can be determined using any two or more resonance frequency components.

The vibration sensor combines and detects vibration including knocking and background vibration.
Therefore, knocking determination index I is determined include vibration I _k due to the occurrence of background vibration I _b and knocking when index I _b becomes defined in the background vibration, the knocking occurs when a knocking has not occurred It is the index I to be used.

When the above knocking determination index I is mathematically expressed using the main resonance frequency components, the following equation is obtained.

I = ω ₁₀ P (f ₁₀ ) + ω ₂₀ P (f ₂₀ ) + ω ₀₁ P (f ₀₁ ) + ω ₃₀ P (f ₃₀ ) + ω ₁₁ P (f ₁₁ ) ... (1) where ω is the engine Takes a real value determined by the number of revolutions. It is also possible to take a binary value of 1 or 0. P is the vibration intensity (power spectrum) of each resonance frequency component.

As shown in FIG. 12, the knock determination index I _b indicated by the resonance frequency component of the background vibration and the index I _k indicated by the resonance frequency component of the vibration due to the occurrence of knocking are different in direction and magnitude. . This is because, as is apparent from a human hearing test, the engine sound when there is no knock is distinct from the engine sound when there is knock, and the tone color is different depending on whether there is knock.

When the vibration due to knocking is added to the background vibration, the knock determination index I by the f ₀₁ and f ₁₀ components included in the vibration sensor is shown in FIG. 12 (a).
In the case of, the existence of knocking can be determined by entering the region below the knock determination threshold I ₀₁ and going outside the threshold I ₀₂ in FIG.

In the present specification, not only the five terms on the right side of the equation (1), but also any combination of a plurality of resonance frequency components included in the output of the vibration sensor is defined as a knocking determination index. To do.

As described above, when the knocking determination index is used, the configuration of the specific frequency component due to the occurrence of knocking with respect to the background vibration is taken into consideration, so that the presence or absence of knocking can be determined even if the background vibration becomes large. ..

Further, the present invention is based on the knowledge explained below obtained from the engine combustion experiment. That is,
First, the resonance vibration table for knocking occurrence is unique to the engine model. Secondly, when knocking occurs, the components of each resonance frequency have their respective intensities (power spectra), but the energy generated by knocking can be grasped as the sum of these intensities (power spectra). Thirdly, as shown in FIG. 13, the frequency distribution of the energy and the component of the resonance frequency that fluctuate in each combustion cycle is observed as a non-central distribution with respect to the energy generated by knocking.

Following the principle of determining whether knocking has occurred, a specific configuration will be described. FIG. 1 is a system configuration diagram. Air enters from the inlet of the air cleaner 1,
Duct 3, Throttle body 5 with throttle valve 5, Intake pipe 6
And is sucked into the cylinder of the engine 7. The intake air amount is detected by the hot-wire air flow meter 2 provided in the duct 3, and the detection signal is input to the control unit 9.

On the other hand, fuel is injected from a fuel tank (not shown) through the injector 16, mixed with intake air in the intake passage and supplied into the cylinder of the engine 7.
The air-fuel mixture is compressed by the engine 7, ignited by the ignition plug 15 and expelled from the exhaust pipe 8 after explosion. The exhaust pipe 8 is provided with an exhaust sensor 11, and a detection signal is input to the control unit 9.

The high voltage generated in the ignition coil 13 is distributed to each cylinder by the distributor 14 and supplied to the ignition plug 15. The rotation state of the engine is detected by the crank angle sensor 12, and the crank angle sensor 12 outputs a Ref signal indicating an absolute position for each rotation and a P _OS signal indicating a position moved by a predetermined angle from the absolute position. The Ref signal and the P _OS signal are input to the control unit 9. A vibration sensor 151 that detects vibration is attached to the engine 7, and a detection signal is input to the control unit 9.

The control unit 9 calculates the fuel supply amount and the ignition timing based on the signals from the respective sensors, and outputs the control signal to the injector 16 and the ignition coil 13. FIG. 2 is a diagram showing details of the control unit 9. Control unit 9 includes CPU 20, A / D converter 21, ROM 22, input I / O 23, RAM 24, DP
A control block 34 including a RAM 25, an output I / O 26 and a bus 37, a CPU 29, a port 27,
Timing circuit 28, A / D converter 30, ROM 31,
RAM 32, clock 33, operational circuit 3
8 and a block 35 for knocking detection composed of a bus 36. Here, CPU20, CPU
The exchange of 29 data is a dual port RAM DPRA
It is done through M25.

The intake air amount Q _a detected by the hot wire type flow meter 2 is converted into a digital value by the A / D converter 21 and taken into the CPU 20. The Ref signal and the P _OS signal detected by the crank angle sensor 12 are taken into the CPU 20 through the input I / O 23. C
The PU 20 performs arithmetic processing according to the program stored in the ROM 22, and the arithmetic result is the fuel injection time signal T _i , which means the fuel injection amount from the output I / O 26, and the ignition timing signal θ.
_Informed to each actuator as an _ign . The RAM 24 holds necessary data during arithmetic processing.

On the other hand, the timing circuit 28 has a TDC in which the operation circuit 35 indicates the top dead center.
When the signal is generated, the CPU 20 divides the periodic signal generated by the clock 33 according to the content input to the port 27 to generate a sampling signal. When the sampling signal is generated, the A / D converter 30 converts the output signal of the vibration sensor 15 into a digital value.

A conventional vibration sensor for detecting knocking resonates at around 13 KHz as shown in FIG. 3A, but at least 18 to 20 K in this embodiment.
In order to obtain a resonance frequency component up to Hz, one that resonates at 18 KHz or higher as shown in FIG. 3B is used.

The CPU 29 outputs the digital value sampled in accordance with the program held in the ROM 31 to RA.
The data is stored in M32, and frequency analysis is performed based on the stored data to determine whether knocking has occurred. The determination result of whether or not knocking has occurred is C via DPRAM25.
Informed to PU20.

The CPU 20 will explain the calculation operation of the ignition timing for each ignition cycle with reference to the flowchart of FIG. The operation of this flow chart is activated every fixed time period, for example, every 10 msec. RAM in step 201
The engine speed N and the intake air amount Q are read from a predetermined register set in 24. In step 202, the intake air amount Q / N per unit speed is calculated, and Q / N is calculated.
The fuel injection time width T _i is obtained from N, and the basic ignition timing θ _base is obtained from the basic ignition timing map as shown in FIG. In step 203, it is determined whether knocking occurs based on the content of a knock flag determined by the flowchart of FIG. 10 described later. If knocking has occurred, then in step 213 a predetermined retardation amount Δθ _ret is subtracted from the ignition timing θ _adv . The ignition timing is retarded by this subtraction. In step 214, RAM2
4 and compare the ignition timing retarded by knocking with a predetermined number of times, for example 50 (step 2
In 05), decide the pace to recover. The count data A is initialized and the process proceeds to step 208.

Here, the retard amount Δ in step 213
In the calculation of θ _ret , a case in which the retard amount Δθ _ret is variable based on the number of revolutions as shown in the flowchart of FIG. 6 will be described in order to suppress the occurrence of sudden knocking during high speed rotation. That is, if knocking has occurred in step 203, it is determined in step 231 whether the engine speed N is higher than a predetermined speed N ₂ . If it is smaller than the predetermined rotation speed N ₂ , step 23
In step 2, the predetermined retard angle amount Δθ _ret 1 is set as the retard angle value Δθ _ret . In the case larger than the predetermined rotational speed N ₂ retard amount large [Delta] [theta] _ret 2 from [Delta] [theta] _ret 1 in step 233 delta
By setting θ _ret , it is possible to set an appropriate retard amount that suppresses knocking.

If knocking occurs in step 203, the count data A is incremented by 1 in step 204. The count data A is used to determine whether it is time to recover the ignition timing θ _adv retarded by the occurrence of knocking by the advance amount Δθ _adv . In step 205, the count data A is the predetermined value 50.
Judge whether it has become equal to. The flow shown in FIG. 4 is 1
The count data A is 50 because it is activated every 0 msec.
When 0.5 seconds has passed since the count data A was initialized, the count data A is recovered every 0.5 seconds. In step 205, if the count data A is not equal to 50, the process proceeds to step 206.
In step 206, the retard angle value θ _adv is set to the predetermined advance angle amount Δθ.
Add _adv . The ignition timing is recovered by this addition.

In addition, in step 206, the amount of advance angle Δθ _adv may be made variable according to the number of revolutions as shown in the flowchart of FIG. 5 in order to suppress the sudden knocking by setting an appropriate amount of advance angle change. That is, step 2
If A = 50 in 05, it is determined in step 221 whether the engine speed is higher than the predetermined speed N ₁ . When a predetermined greater than the rotational speed N ₁ is the advance value [Delta] [theta] _adv a predetermined advance amount [Delta] [theta] _adv 1 at step 222. If not greater than the predetermined rotation N _1, at step 223, to change the bit by bit advance a small amount of advance [Delta] [theta] _adv 2 than [Delta] [theta] _adv 1 as advance value [Delta] [theta] _adv.

Therefore, the occurrence of knocking due to a sudden change in the advance angle can be prevented.

In this way, in step 208, the ignition timing θ _ign is calculated by adding the ignition timing θ _adv obtained as described above to the basic ignition timing θ _base . Step
At 209, the maximum advance value θ _res is obtained according to the engine speed N and the intake air amount Q / N per unit speed. The maximum advance value θ _res is read out from the maximum advance value map stored in the ROM 31. In step 210, it is determined whether the ignition timing θ _ign exceeds the maximum advance value θ _res . If not, proceed to step 211. If the maximum advance value θ _res is exceeded, the advance angle is too large. Therefore, in step 211, the maximum advance value θ _{res is set} to the ignition timing θ.
_ign .

Before executing step 202, as shown in the flowchart of FIG. 7, the number of revolutions N,
A case where the reliability of the vibration sensor is improved by determining the abnormality of the vibration sensor based on the output of the vibration sensor after taking in the intake air amount Q will be described. If the vibration sensor is abnormal, the abnormality is processed.

After the engine speed N and the intake air amount Q are acquired in step 201, the engine speed N is acquired in step 231.
There is determined whether a predetermined larger rotational speed N _3. If the rotation speed is lower than the predetermined rotation speed N ₃ , the output of the vibration sensor is not large enough to detect an abnormality.
Go to 2.

If the engine speed is higher than the predetermined speed N _{3 in} step 231, it is determined in step 232 whether the vibration sensor is higher than the predetermined level K or not. If it is larger, the vibration sensor is determined to be normal and the process proceeds to step 202. If the output of the vibration sensor is smaller than the predetermined level, it is determined that the vibration sensor is abnormal, and in step 234, the ignition timing for the abnormality of the vibration sensor is obtained. Step two
At 34, the ignition timing θ _irr at the time of abnormality according to the rotation speed N and the intake air amount per unit rotation is searched from the map stored in the ROM ₂₂ . The retrieved abnormal ignition timing θ _irr is a value that is sufficiently retarded from the value stored in the basic ignition timing map, and knocking does not occur. In step 235, θ _irr is set as the basic ignition timing θ _base, and the flow is terminated without calculating the ignition timing by knocking detection.

After the ignition timing θ _ign has been set as described above, in step 212, depending on the engine state,
Delay time t _d , number of sampling points n _s , frequency division ratio t _s
Is output to the port 27. In step 213, the main comparison resonance frequency f is set in the DPRAM 25 according to the engine state, and the flow is ended.

The frequency division ratio t _s determines the sampling cycle of the digital value of the output of the vibration sensor, and the number of sampling points n _s determines the number of sampling points.

The number of sampling points is 32 and the sampling period is 25 μsec, 26.4 μsec and 25.9 μs.
Table 2 shows the frequency components that can be set and analyzed in DMRAM25 when ec is set.

In order to obtain a frequency component that coincides with the main resonance frequency in the above-mentioned Table 1 like the frequency marked with * in this table, for example, if f ₁₁ = 18.1 KHz, If the sampling timing is set to 25.9 μsec, 18.098 KHz is obtained in the wave number 15, and accurate frequency analysis at 18.1 KHz becomes possible.

[0057]

[Table 2]

As described above, the resolution of frequency analysis is determined by the sampling period and the number of sampling points. The t _d , t _s , and n _{s that} are set in step 212 are determined and set according to the operating state of the engine so as to obtain the resonance frequency component necessary for determining whether knocking has occurred.

FIG. 9 is a timing diagram of the timing circuit 28 and its operation. The timing circuit 28 is the delay counter 4
1, sample rate count 42, sample counter 4
4. An AND gate 43 having an inverter at its input terminal. The TDC signal is input to the set terminal of the delay counter 41 and the set terminal of the sample counter 44. The output of the clock 33 is input to the enable terminal of the delay counter 41 and the terminal of the AND gate 43 including the inverter. The output of the AND gate 43 is input to the enable terminal of the sample rate counter 42. The zero output of the sample rate counter 42 is input to the enable terminal of the sample counter 44. It is also input to the set terminal of the sample rate counter 42 itself, and is further output as a sampling signal. The zero output of the sampling counter 44 is input to the AND gate 43.

When the delay time t _d , the sampling number n _s , and the frequency division ratio t _s are output from the CPU 20 to the port 27, the delay counter t _d , the sample rate counter t _s , the sample counter n _s , Each is set as an initial value of the down counter 4. When a signal is input to the set terminal of each counter, the zero terminal becomes 1, and each counter counts down every time a signal is input to the enable terminal. When the count becomes zero, the zero terminal output becomes zero.

TD is set to the set terminal of the delay counter 41.
When the C signal is input, the zero output becomes 1 and the clock 3
Each time the signal No. 3 is input to the enable terminal, the counter sequentially counts down. The TDC signal is a signal output when the angle of the crankshaft reaches an angle corresponding to the top dead center (top dead center). The TDC signal is output from the Ref signal and the Po _s signal output from the crank angle sensor in the hardware or the CPU 20. Made by software. When the down count value of the delay counter becomes zero, the zero output of the delay counter becomes zero, and 1 is input to the AND gate 43. In this state, since the sample counter 44 has already received the TDC signal and the zero output is 1, the output signal of the clock 33 is directly input to the enable terminal of the sample rate counter 42.

The sample rate counter 42 counts down each time a clock signal is generated, and outputs a sampling signal each time the count value becomes zero. Further, the count value again t _d inputs the signal to its set terminal.
The zero output is input to the enable terminal of the sampling counter 44. Down count and sample counter 44
When the counter value of 0 becomes zero and the zero output becomes zero, the clock signal cannot pass through the AND gate and the sampling signal is not output.

The operation of the arithmetic processing of the CPU 29 for determining whether knocking has occurred will be described with reference to the flowchart of FIG. The operation of this flowchart is executed each time in successive explosion cycles, and is started immediately after the end of the predetermined number of times n _s of A / D conversion started by the TDC signal. That is, when a predetermined number of output digital values of the vibration sensor 15 are held in the memory of the RAM 32, that is, when the zero terminal output of the sample counter 44 falls from 1 to 0, an interrupt signal is output to the CPU 29. Is activated.

First, in step 300, frequency analysis is performed on the measurement data of the vibration sensor by FFT. The data to be analyzed is a sampling value held in a predetermined memory of the RAM 32. In order to analyze the resonance frequency component included in the output of the vibration sensor, the FFT is performed from the sampling value.
Perform the method (Fast Fourier Transform). Note that W
Frequency analysis can also be performed using the FT method (Walsh to Fourier Transform). The resonance frequency f used when calculating the knocking determination index I by the equation (1) in step 301
Select. This selection method is based on the power spectra P (f ₀₁ ), P (f ₂₀ ), P (f ₀₁ ), and P (f ₀₁ ), for five resonance frequencies.
From the largest one of P (f ₃₀ ) and P (f ₁₁ ) n (n
Only ≦ 5) is selected. Next, step 302
Then, the knocking determination index I is calculated.

The knocking determination index I is calculated based on the equation (1) by the selected PMs. For example, if P (f ₁₀ ) and P (f ₀₁ ) are selected, the state of calculation of the index I is as shown in FIG.

Here, a value standardized by the average value PM of the power spectrum can be used instead of P in the equation (1). For example P (f ₁₀₎ in place of P (f ₁₀₎ /
PM (f ₁₀ ) may be used. PM is calculated by the following equation (2) from the value of P calculated in each explosion.

PM = a · PM + (1-a) · P (2) where a is the contribution rate of the conventional value of PM. This PM update is executed only when it is not determined that knocking has occurred. The initial value of PM is preset in the ROM 31 and can be obtained by reading it.

In step 303, the engine speed N and the intake air amount Q are read from the RAM 32. Step 304
Then, based on the table stored in the ROM 31,
A threshold value I ₀₁ or I ₀₂ is calculated from the engine speed N and the intake air amount Q.
Select.

If the knocking determination index I is larger than I ₀₁ or I ₀₂ , it is determined in step 305 that knocking has occurred.
If the knock flag is 1, the knocking determination index I is small, it is determined that knocking has not occurred, the knock flag is set to 0, and the writing flow to the DPRAM 25 ends.

The routine of FIG. 10 is executed before the routine of FIG. 4 is started. That is, the routine of FIG. 4 is a program that determines the ignition timing of a cylinder before the explosion process, and is normally executed in the compression process or the intake process, whereas the routine in FIG. 10 is executed immediately after the explosion.

[0071]

According to the first aspect of the present invention, since the presence or absence of knocking can be determined from the knocking index, the presence or absence of knocking can be determined even at a high load and high speed when background vibration becomes large.

Since the second invention can use an arbitrary frequency component included in the vibration sensor, it is possible to determine whether or not knocking occurs by using an appropriate resonance frequency component according to the operating state of the engine. Therefore, it is possible to determine whether or not weak knocking occurs in all engine operating states.

In the third aspect of the present invention, since it is possible to determine whether knocking occurs or not by using the resonance frequency component in which the background vibration becomes small at high load and high speed, it is possible to determine whether knocking occurs even at high load and high speed.

According to the fourth aspect of the present invention, it is possible to determine whether or not knocking has occurred at a high load and a high speed, so engine output and fuel efficiency can be improved.

In the fifth aspect of the present invention, the information contained in the output of the vibration sensor can be effectively utilized, so that the engine output and the fuel efficiency can be controlled to be optimum.

[Brief description of drawings]

FIG. 1 is a system diagram.

FIG. 2 is a diagram showing a control unit.

FIG. 3 is a diagram showing characteristics of a vibration sensor.

FIG. 4 is a flowchart showing calculation of ignition timing.

FIG. 5 is a flowchart showing the calculation of ignition timing.

FIG. 6 is a flowchart showing the calculation of ignition timing.

FIG. 7 is a flowchart showing the calculation of ignition timing.

FIG. 8 is a basic ignition timing map.

FIG. 9 is a timing circuit and its operation diagram.

FIG. 10 is a flowchart showing the operation of knocking determination.

FIG. 11 is a diagram showing an output signal of a vibration sensor and a frequency analysis result.

FIG. 12 is a diagram showing a knocking determination index.

FIG. 13 is a diagram showing a relationship between knocking occurrence frequency and knocking strength.

[Explanation of symbols]

9 ... Control unit, 12 ... Crank angle sensor,
15 ... Vibration sensor, 28 ... Timing circuit, 30 ... A /
D converter, 33 ... Clock.

Claims (1)

[Claims] 1. A vibration sensor for detecting engine vibration or cylinder internal pressure vibration, which detects a knocking phenomenon occurring during combustion of an engine and controls ignition timing based on the detected value, and the vibration sensor is included in the vibration sensor. A comparison means for comparing the vibration with a predetermined knock determination index to determine whether knocking has occurred, a correction calculation means for calculating a correction value of the ignition timing based on the output of the comparison means, and an engine state. An engine control device comprising: a basic ignition timing calculating means for calculating a basic ignition timing based on the above; and an ignition timing calculating means for calculating an ignition timing based on the correction value and the basic ignition timing.