JP3298139B2 - Knock detection device - Google Patents

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 for determining whether or not knock has occurred based on a signal from a knock sensor.

[0002]

2. Description of the Related Art Generally, in this type of knock detection apparatus, knock detection is performed using one or a plurality of band-pass filters. One example is disclosed in JP-A-55-16196.
The knock detection device applied to the ignition timing control device disclosed in Japanese Patent Application Laid-Open No. 9-29139 is provided with a plurality of filters having frequency characteristics different from each other, and configured to receive the output of the knock sensor and selectively use the filters. ing. A knock detection device using such a band-pass filter is frequently used because it can be configured at low cost.

[0003] On the other hand, in Japanese Patent Application Laid-Open No. 3-47449,
A knock detection device that performs frequency analysis using frequency analysis means such as fast Fourier transform (FFT), separates and determines each frequency based on the frequency analysis, and determines whether or not knock has occurred is disclosed.

[0004]

However, in the knock detection device disclosed in Japanese Patent Application Laid-Open No. 55-161969,
The center frequency of the pass frequency band is fixed at a preset frequency. Therefore, when there is a shift in the center frequency of knock due to the type, individual difference, engine speed, etc. of the internal combustion engine, there is a problem that the filter frequency cannot follow the shift.

Further, the knock detection device disclosed in Japanese Patent Application Laid-Open No. 3-47449 has a problem that it is difficult to perform a fast Fourier transform process at a high rotation speed. That is, since the interval of the ignition cycle is short at the time of high rotation and the knock vibration information collected thereby is small, the accuracy of the fast Fourier transform is significantly reduced (for example, when sampling at 50 kHz at 6000 rpm, about 100 points are obtained). Since only data is obtained, the accuracy of the fast Fourier transform is 500 Hz). In addition, since the interval of the ignition cycle is short at the time of high rotation, there is a problem that the time required for the calculation of the fast Fourier transform is not secured, or a very high-speed and expensive computer is required.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a knock detecting device capable of following a change in knock frequency and performing digital processing with high accuracy. To provide.

[0007]

In order to achieve the above object, a knock detection device according to the present invention comprises: a knock sensor for detecting a vibration generated in an internal combustion engine; and a signal from the knock sensor. Frequency characteristic variable type filter means for passing a signal in a frequency band, and the filter
The knock signal that has passed through the
Determining means, an engine speed detecting means for detecting an engine speed of the internal combustion engine, and a knock signal from the knock sensor when the engine speed by the engine speed detecting means is equal to or less than a predetermined speed. Digital signal processing means for performing frequency analysis processing, and frequency characteristics for changing the frequency characteristics of the filter means such that the frequency having the maximum intensity as a result of the frequency analysis by the digital signal processing means includes the signal passing region of the filter means. and summarized in that with a changing means.

[0008]

According to the above arrangement, the knock signal from the knock sensor is subjected to frequency analysis processing by the digital signal processing means only when the engine speed detected by the engine speed detection means is equal to or lower than the predetermined speed. Then, the frequency characteristic of the filter unit is changed by the frequency characteristic change unit so that the frequency having the maximum intensity as a result of the frequency analysis by the digital signal processing unit includes the signal passing region of the filter unit. Further, the presence / absence of knock occurrence is determined by the determination means based on the knock signal passed through the filter means.

That is, by changing the filter characteristic of the filter means by frequency analysis, the frequency characteristic of the filter means follows the knocking frequency at which the deviation has occurred. Further, by performing the frequency analysis processing only at the time of low rotation, deterioration of digital processing is avoided.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a diagram showing the configuration of the present embodiment. Knock sensor 1 is provided in a cylinder block of an internal combustion engine, and detects vibration generated in the internal combustion engine and converts the vibration into an electric signal. As the knock sensor 1, for example, a piezoelectric ceramic element is used.

A pre-filter 2 is connected to the knock sensor 1, and a detection signal from the knock sensor 1 is
Is input to The pre-filter 2 amplifies the output signal of the knock sensor 1 as necessary, and cuts unnecessary high-frequency components (generally, 20 kHz or more). An A / D converter 3 is connected to the pre-filter 2 and converts a signal passed through the pre-filter 2 (analog output) into a digital value. Note that A
The signal converted by the / D converter 3 is prevented from being mixed with aliasing noise by the pre-filter 2.

A digital signal processor (hereinafter, referred to as DSP) 4 is connected to the A / D converter 3.
The DSP 4 receives a knock signal from the knock sensor 1 via the pre-filter 2 and the A / D converter 3 and outputs a determination signal for determining whether or not knock has occurred.

Further, a spark plug 6 is connected to the DSP 4 via an ignition control circuit 5, and the ignition control circuit 5
4, the ignition timing of the ignition plug 6 is controlled. Further, the DSP 4 is connected to a rotation speed sensor 7 as an engine rotation speed detecting means. The sensor 7 detects the engine rotation speed of the internal combustion engine and outputs a detection signal to the DSP 4.

FIG. 1 shows a functional block diagram of the DSP 4. The DSP 4 has a bandpass filter (hereinafter, referred to as BPF) 8 and a fast Fourier transform circuit (hereinafter, referred to as FFT).
9, a knock determination circuit 10 and a learning control circuit 11.

The BPF 8 forms a filter means, receives a knock signal (digital signal) from the knock sensor 1, and receives only a knock frequency band (usually 6 kHz to 8 kHz).
z). Further, the filter coefficient of the BPF 8 is variable.

The FFT 9 constitutes a digital signal processing means, receives a knock signal (digital signal) from the knock sensor 1, performs a frequency analysis process, and outputs the processing result to a knock determination circuit 10 and a learning control circuit 11.

The learning control circuit 11 constitutes frequency characteristic changing means, and outputs the engine speed signal from the speed sensor 7 and the FFT 9
When the engine speed is smaller than a predetermined speed (for example, 3000 rpm), the FFT
9, the filter coefficient of the BPF 8 is changed. That is, the center frequency of the BPF 8 is made variable by the learning control circuit 11.

The knock determination circuit 10 has a BPF 8, an FFT
In response to the output signal of No. 9, it is determined whether or not knock has occurred, and the result of the determination is output to the ignition control circuit 5. Next, the operation of the present embodiment will be described.

FIG. 3 is a flowchart showing a routine for determining whether or not knock has occurred. This routine is executed by the DSP 4 at predetermined intervals or at predetermined crank angles.

First, the DSP 4 detects the engine speed by the speed sensor 7 at step 100, compares the engine speed with a predetermined speed (3000 rpm in the present embodiment), and determines whether the internal combustion engine has a high speed. It is determined whether the rotation speed is low or low. Then, the DSP 4 proceeds to Step 110 when the engine speed is high, and proceeds to Step 150 when the engine speed is low.

At step 110, the DSP 4 outputs the B signal of the knock signal detected by the knock sensor 1.
Only the knock signal having the frequency of the pass frequency band of PF8 is passed. Then, the DSP 4 proceeds to step 120,
A knock signal that has passed through the BPF 8 is compared with a predetermined threshold value (knock determination level) to determine whether knock has occurred. That is, when the knock signal level becomes equal to or higher than the threshold value and the knock is determined to be “present”, the DSP 4 outputs a knock “present” signal to the ignition control circuit 5 in step 130. If the DSP 4 determines that the knock signal level is smaller than the threshold value and the knock is “absent”, the DSP 4 proceeds to step 1.
At 40, a signal indicating that knock is “absent” is output to the ignition control circuit 5. Then, after the knock determination in steps 130 and 140, the DSP 4 ends the routine.

On the other hand, steps 100 to 150
In step 150, the DSP 4 searches for the maximum intensity value of the FFT 9 at step 150. FIG. 4 shows an example of the output result of the frequency analysis in the FFT 9 at that time. In FIG. 4, the solid line shows the output result when knock occurs, and the broken line shows the output result when no knock occurs.

Then, the DSP 4 determines in step 160 that the FF
The maximum intensity value (intensity A in FIG. 4) at T9 is compared with a threshold to determine whether knock has occurred. That is,
The DSP 4 determines that the knock is “present” when the maximum strength is equal to or larger than the threshold, and determines that the knock is “absent” when the maximum strength is smaller than the threshold. If it is determined in step 160 that the knock is “present”, the DSP 4 outputs a knock “present” signal to the ignition control circuit 5 in step 170. If it is determined in step 160 that the knock is “no”, the DSP 4 outputs a signal of the knock “no” to the ignition control circuit 5 in step 180. DSP4 is Step 1
After the processes in steps 70 and 180, the process proceeds to step 190.

Next, the DSP 4 determines in step 190 that the FF
The frequency characteristic of the BPF 8 is changed so that the frequency having the maximum intensity (frequency B in FIG. 4) as a result of the frequency analysis by T9 includes the signal passing region of the BPF 8. That is, FIG.
, The filter coefficient of the BPF 8 is changed such that the maximum intensity in the analysis result of the FFT 9 becomes the center frequency of the BPF 8 as shown by the two-dot chain line. Then, after executing the process of step 190, the DSP 4 ends a series of routines.

After determining whether or not knock has occurred in this manner, the determination signal is input to the ignition control circuit 5.
Then, the ignition timing is corrected in accordance with the knock determination signal, and the ignition of the ignition plug 6 is controlled at the corrected ignition timing.

As described above, in the knock detection device of this embodiment, the knock signal from knock sensor 1 is subjected to frequency analysis processing by FFT 9 only when the engine speed detected by speed sensor 7 is equal to or lower than a predetermined speed. With FF
The frequency characteristic of the BPF 8 is changed by the learning control circuit 11 so that the frequency at which the maximum intensity of the frequency analysis result of T9 includes the signal passing region.

As a result, in the conventional knock detection device, the frequency characteristic of the filter could not follow the shift of the center frequency of the knock caused by the type, individual difference, engine speed, etc. of the internal combustion engine. By BPF
Since the frequency characteristics of the BPF 8 are changed, the center frequency of the BPF 8 can reliably follow the center frequency of the knock even if a frequency shift occurs. Further, in the conventional apparatus, the FFT processing at the time of high rotation was sometimes difficult, but in the present embodiment, the frequency analysis was performed only at the time of low rotation, and B
Since learning of PF8 is performed, F
Deterioration of the processing accuracy of the FT processing can be avoided, and the processing accuracy can be improved in the entire rotation range.

The present invention is not limited to the above embodiment, but can be embodied in the following modes. (1) When determining the maximum intensity of the FFT 9, a plurality of intensity values near the maximum value are added, and a center frequency at which the maximum intensity is obtained is obtained from the added value. (2) As a filter means, a low-pass filter (LP
F) or use of a high-pass filter (HPF). (3) As the digital signal processing means, other processing other than the fast Fourier transform is performed.

[0029]

According to the present invention, an excellent effect of being able to follow a change in knock frequency and performing digital processing with high accuracy is exhibited.

[Brief description of the drawings]

FIG. 1 is a functional block diagram of a DSP.

FIG. 2 is a diagram showing an ignition timing control device using a knock detection device.

FIG. 3 is a flowchart for determining whether knock has occurred.

FIG. 4 is a diagram illustrating a processing result of FFT and a frequency characteristic of a BPF.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Knock sensor, 4 ... Digital signal processor (DSP), 7 ... Rotation speed sensor as engine speed detection means, 8 ... Band pass filter (BPF) as filter means, 9 ... High-speed Fourier as digital signal processing means Conversion circuit (FFT), 10: knock determination circuit as determination means, 11: learning control circuit as frequency characteristic change means.

Continuation of front page (56) References JP-A-2-223652 (JP, A) JP-A-61-23871 (JP, A) JP-A-4-8850 (JP, A) JP-A-59-67441 (JP) JP-A-3-47449 (JP, A) JP-A-59-65728 (JP, A) JP-A-62-203434 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB Name) F02D 45/00 368

Claims (4)

(57) [Claims] A knock sensor for detecting a vibration generated in an internal combustion engine; a filter means of a variable frequency characteristic type that receives a signal from the knock sensor and passes a signal in a predetermined frequency band ; Knocked by knock signal passed
First determining means for determining the presence or absence of a boil, engine speed detecting means for detecting the engine speed of the internal combustion engine, and when the engine speed by the engine speed detecting means is equal to or less than a predetermined speed, Digital signal processing means for performing frequency analysis processing of the knock signal by the knock sensor; and so that the frequency having the maximum intensity in the frequency analysis result by the digital signal processing means includes the signal passing region of the filter means. knock detecting apparatus characterized by comprising a frequency characteristic changing means for changing the frequency characteristics. 2. The knock detection device according to claim 1, wherein said filter means is a band pass filter. 3. The knock detection device according to claim 1, wherein said digital signal processing means is a fast Fourier transform (FFT). 4. The frequency by said digital signal processing means.
The second to determine whether knock has occurred based on the numerical analysis result
Determination means, wherein the engine speed detected by the engine speed detection means is a predetermined engine speed.
When the following conditions are satisfied, the knock is determined based on the second determination means.
The engine speed by the engine speed detecting means.
When the rotation speed is higher than the predetermined rotation speed, the first determination is performed.
The presence or absence of a knock is determined based on the determining means.
Knock detection according to any one of claims 1 to 3,
apparatus.