JPH07306119A - Knocking detector for internal combustion engine - Google Patents

Abstract

PURPOSE:To detect the attaching looseness of a knocking sensor quickly and accurately. CONSTITUTION:The output based on the knocking generated in an internal combustion engine from a knocking sensor 8 is amplified by a gain switch 12. The output is divided into a plurality of frequency bands by a digital filter 5 provided in a DSP 13. The abnormality of the knocking sensor 8 is detected by a knocking judging means 6 provided in the DSP 13 by using the specified frequency band among a plurality of the frequency bands. In this way, the attaching looseness of the knocking sensor 8 is accurately detected by using the specified frequency band in the output characteristics in detection of the knocking generated in the internal combustion engine from the knocking sensor 8.

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 an internal combustion engine capable of detecting a failure (fault) of a knock sensor for detecting knock in a knock control system.

[0002]

2. Description of the Related Art Conventionally, as prior art documents relating to a knock detection device for an internal combustion engine, those disclosed in Japanese Utility Model Publication No. 60-29703 and Japanese Patent Publication No. 59-119067 are known.

Among them, Japanese Utility Model Publication No. 60-29703 discloses a method of judging a failure when the output of the knock sensor signal from the integrator is smaller than a predetermined value. Further, Japanese Patent Laid-Open No. 59-119067 discloses a method for detecting a failure based on a peak hold output of a knock sensor signal.

[0004]

In the fail detection method described above, the fail determination level must be set low in consideration of the difference in the internal combustion engine (engine) and the variation in the sensor output. Fail detection can only be performed when there is a marked decrease in output due to wire breakage or sensor element breakage.

Now, the knock phenomenon will be described.

Knock is a phenomenon in which unburned gas in a cylinder is compressed by the combustion gas, self-ignites, and rapidly burns to cause resonance in the cylinder. This resonance phenomenon has a natural frequency determined by the bore diameter and sound velocity of the internal combustion engine, and when the resonance vibration mode is Pnm when the cylinder radial direction order is n and the circumferential direction order is m, FIG. ，
It is predicted that a knock component will be generated at the frequency shown in (b). If vibration can be detected for each of these resonance signal modes, the accuracy of knock detection is improved. Further, if this knock is controlled at a minute level, fuel consumption can be improved without damaging the internal combustion engine.

As a result of the experiments conducted by the inventors, the sensor signal output when the knock sensor is installed by an inappropriate tightening torque, that is, when the installation is loose, the output of the knock sensor is decreased without the knock, and the knock signal is decreased. It was found that the vibration mode of high frequency remarkably appeared in some cases. FIG.
[Fig. 4] is a characteristic diagram showing a relationship between frequency and spectrum intensity when sensor mounting states are different. Here, in FIG.
(A) shows the case where there is looseness in the installation, and
Comparing with (b), it can be seen that a frequency band fa passing through a BPF (Band Pass Filter) appears to have a magnitude larger than the knock spectrum intensity.

FIG. 17 is a sectional view showing the structure of knock sensor 80.

The operating principle of the knock sensor 80 is that the vibration of the internal combustion engine (engine) is transmitted from the mounting seat surface 81a of the knock sensor 80 to the piezoelectric element 82 through the housing 81 and generates a voltage proportional to the vibration. Is.
Therefore, unless the mounting seat surface 81a of the knock sensor 80 is brought into close contact with the internal combustion engine block E / GB with a predetermined torque, not only the internal combustion engine vibration is transmitted but, on the contrary, it is amplified by resonance due to rattling or the like. It will end up. In other words, due to the structure of the knock sensor used for knock detection, a normal sensor signal cannot be obtained unless it is installed with an appropriate tightening torque, and quick detection cannot be performed even if the installation is loosened for some reason. There was a problem.

Therefore, the present invention has been made to solve such a problem, and an object of the present invention is to provide a knock detection device for an internal combustion engine capable of quickly and appropriately detecting looseness in mounting of a sensor.

[0011]

A knock detection device for an internal combustion engine according to a first aspect of the present invention comprises a knock detection means for detecting a knock generated in an internal combustion engine, and an amplification means for amplifying an output from the knock detection means. It comprises a filter means for separating the output from the amplifying means into a plurality of frequency bands, and an abnormality detecting means for detecting an abnormality of the knock detecting means by using a predetermined frequency band separated by the filter means. is there.

According to a second aspect of the present invention, there is provided a knock detection device for an internal combustion engine, wherein the filter means comprises a plurality of filters in addition to the means of the first aspect.

In the knock detection device for an internal combustion engine according to claim 3, in addition to the means provided in claim 1, the filter means has a variable center frequency in the frequency band.

According to a fourth aspect of the present invention, there is provided a knock detection device for an internal combustion engine, in addition to the means provided in the first to third aspects,
The predetermined frequency band used by the abnormality detection unit is a frequency band different from the frequency band used by the knock detection unit for knock determination.

According to a fifth aspect of the present invention, there is provided a knock detection device for an internal combustion engine, in addition to the means provided in the first to third aspects,
The predetermined frequency band used by the abnormality detection means is a frequency band on the higher frequency side than the frequency band used by the knock detection means for knock determination.

According to a sixth aspect of the present invention, there is provided a knock detection device for an internal combustion engine, in addition to the means provided in the first to third aspects,
The abnormality detecting means makes the knock detecting means abnormal when the output from the knock detecting means in the predetermined frequency band separated by the filter means exceeds a predetermined level for a predetermined number of times.

A knock detecting device for an internal combustion engine according to a seventh aspect of the present invention is a knock detecting means for detecting a knock occurring in the internal combustion engine, and a filter for separating an output from the knock detecting means into a plurality of frequency bands in time series. Means, amplification means for amplifying the output from the filter means, and abnormality detection means for detecting abnormality of the knock detection means using a predetermined frequency band amplified by the amplification means.

[0018]

According to the first aspect of the present invention, the output of the knock detecting means based on the knock generated in the internal combustion engine is amplified by the amplifying means, and the output is separated into a plurality of frequency bands by the filter means. The abnormality of the knock detection means is detected by the abnormality detection means by using. That is, the abnormality of the knock detection means is detected by using the predetermined frequency band corresponding to the output characteristic of the knock detection generated from the knock detection means in the internal combustion engine.

In addition to the function of claim 1, the filter means of the knock detecting device for an internal combustion engine according to claim 2 comprises a plurality of filters, and the output from the amplifying means is separated into a plurality of frequency bands. It is possible to obtain the output of each frequency band suitable for the normal knock detection of the knock detection means and the abnormality detection of the knock detection means.

According to the filter means of the knock detecting device for an internal combustion engine of claim 3, in addition to the operation of claim 1, the center frequency of the frequency band is made variable so that the knock detecting means detects the frequency band to be separated. It can be adapted to the characteristics of the installed internal combustion engine.

The predetermined frequency band used by the abnormality detecting means of the knock detecting device for an internal combustion engine according to claim 4 is the frequency band used for knock determination of the knock detecting means in addition to the functions of claims 1 to 3. Is a different frequency band,
The normal knock detection of the knock detection means and the abnormality detection of the knock detection means can be accurately performed.

The predetermined frequency band used in the abnormality detection means of the knock detection device for an internal combustion engine according to claim 5 is in addition to the functions of claims 1 to 3, the frequency band used for knock determination of the knock detection means. The frequency band on the high frequency side.
For this reason, the knock detection means can use the normal knock detection frequency band, and the abnormality detection of the knock detection means can accurately detect them by using the frequency bands on the higher frequency side than the normal knock detection frequency band. it can.

According to the abnormality detecting means of the knock detecting device for the internal combustion engine of the sixth aspect, in addition to the functions of the first to third aspects, the output from the knock detecting means in the predetermined frequency band separated by the filter means is output. When the predetermined level is exceeded a predetermined number of times, the knock detection means is abnormal. Therefore, the abnormality can be reliably determined based on the output from the knock detection means.

According to another aspect of the present invention, the output of the knock detection means based on the knock generated in the internal combustion engine is separated into a plurality of frequency bands in time series by the filter means, and the plurality of frequency bands are amplified by the amplification means. The abnormality of the knock detecting means is detected by the abnormality detecting means using a predetermined frequency band among them. That is, the abnormality of the knock detection means is detected by using the predetermined frequency band in the output characteristic of the knock detection generated from the knock detection means in the internal combustion engine.

[0025]

EXAMPLES The present invention will be described below based on specific examples.

<First Embodiment> FIG. 1 is an overall configuration diagram showing a knock detection device for an internal combustion engine according to a first embodiment of the present invention.

In FIG. 1, a knock sensor 8 for achieving knock detection means converts the vibration of the internal combustion engine body into an electric signal, and in this embodiment, it is necessary to be a non-resonant sensor for frequency analysis. is there. This knock sensor 8
The input circuit 9 connected to adjusts the impedance of the sensor signal from the knock sensor 8. LPF (Low Pass Filter) connected to this input circuit 9
10 prevents aliasing noise. HPF (High Pass Filter) 1 connected to this LPF 10
1 removes a low frequency component signal unrelated to knocking. The LPF 10 outputs a signal having a frequency of 20 KHz or less to H
The PF 11 is configured to pass a frequency of 1 KHz or higher. The gain switcher 12 that achieves the amplification means connected to the HPF 11 adjusts the input signal to an appropriate size. An A / D converter (Analog to Digital Converter) with high resolution may be used without using the gain switcher 12, but it is expensive. DS connected to this gain switcher 12
The P (Digital Signal Processor) 13 can perform multiplication processing faster than a microcomputer. The DSP 13 includes an A / D converter 14 and a PiO (parallel I / D).
O) 15. In this embodiment, the number of A / D converters 14 is 1.
Providing a dynamic range equivalent to 6 bits and wider than the conventional one, the PiO 15 communicates with the gain switcher 12 and the host CPU 16 described later. B to achieve the filter means
The digital filter 5 composed of PF1, BPF2 and BPF3 and the knock determination means 6 for achieving the abnormality detection means are D
It is constituted by software in the SP 13, the filter means 5 performs digital filter processing, and the knock determination means 6 performs knock determination from the result of digital filter processing. The host CPU 16 controls the ignition timing output to the ignition device 17 and the fuel injection amount (not shown) in response to the result of the presence or absence of knocking from the DSP 13.

FIG. 2 is a timing chart for explaining the operation of the DSP 13 shown in FIG.

As shown in FIG. 2, A indicates a reference position signal, and the fall of the signal indicates the BTDC (Be of each cylinder.
fore Top Dead Center: Before top dead center) 10 ° CA (crank angle), which causes a from time t1 in FIG.
The reference position interrupt process described later is executed during the period (see FIG. 4).
reference). Further, B of FIG. 2 shows a knock determination section, and b,
c indicates a period of a timer 1 interrupt process, which will be described later, executed at times t2 and t3 (see FIG. 5). Furthermore, d in FIG.
Indicates the period of a timer 2 interrupt process, which will be described later, executed from time t2.

First, the reference position interrupt processing a is executed at the fall of the reference position signal at time t1 in FIG. 2, and the start time of the knock determination section is set in the timer 1 as indicated by f. As a result, the timer 1 interrupt process b is executed at the judgment section start time of time t2. This allows timer 2
The end time of the knock determination section is reset as indicated by g, and the timer 2 interrupt processing d is executed to perform A / D conversion of the knock signal and digital filter processing.

The knock signal is A / D converted every 20 μs, and digital filter processing is performed each time. After filtering each frequency band, the output (gate section t2 to t3
The maximum value (in) is held respectively.

In addition to the interruption of the timers 1 and 2, the peak hold value is reset (initialized) at the beginning of the gate section by the main routine, and the gate section t2
After t3, knock determination process f and fail determination process h
Is performed and the result is sent to the host CPU 16. After that, a process g for initializing the A / D conversion value to 0 is executed.

3 to 12 are flowcharts showing the flow of the program of the DSP 13.

<Initialization Routine: See FIG. 3> Simultaneously with power-on, initialization is performed in step S101, then the process proceeds to step S102, cylinder discrimination is performed, and this routine ends. Note that this routine is first executed only once.

<Reference Position Interrupt Routine: See FIG. 4> FIG.
At time t1 of, the angle interruption at the reference position is performed. Here, the reference position indicates the crank angle of the internal combustion engine, which is BTDC 10 ° CA (crank angle) of each cylinder, and is sent from the host CPU 16. First, in step S201, cylinder discrimination is performed, and a value corresponding to the distance from the cylinder that is currently ignited to the knock sensor is output. This signal is also a signal sent from the host CPU 16, and the first (#
1) It is set to 1 only for a cylinder, and other cylinders are calculated using a counter. Next, in step S202,
The engine speed is calculated based on the time required from the previous reference signal to the present reference signal. Next in step S20
In step 3, the input gain setting, fail determination, timer setting, and the like are performed as preprocessing. Next in step S20
4, the timer 1 is set to wait for the crank angle set in advance according to the engine speed, and this routine ends. Here, usually, knock occurs at ATDC (After Top Dead Center) 15-
Since it is about 70 ° CA (crank angle), a time corresponding to a value of about 10 ° CA (crank angle) ATDC, which is slightly before, is set in step S204.

<Timer 1 Interrupt Routine: See FIG. 5> FIG. 4
When the time set in step S204 (time t2 shown in FIG. 2) is reached, it is determined in step S301 that the knock determination interval flag, which will be described later, is 1, and the process proceeds to step S302. The knock determination section end flag is set to 0. Next, in step S303, the timer 1 is reset to a time corresponding to a value of ATDC 70 ° CA (crank angle), and then the process proceeds to step S304 to start A / D conversion and digital filter processing. Timer 2 is set and activated. After that, the routine proceeds to step S305, the main routine is started, and this routine is ended.

On the other hand, when the reset time of the timer 1 (time t3 shown in FIG. 2) is reached, it is determined in step S301 that the knock determination end flag is 0 this time, which is the knock determination end interval, and step S306. Moved to
After setting the knock determination section end flag to 1, step S
The process proceeds to 307, the operation of the timer 2 is stopped, the A / D conversion and the digital filter / peak hold processing are ended, and this routine is ended.

<Timer 2 Interrupt Routine: See FIG. 6> This timer 2 interrupt routine is executed every 20 μs.
After the A / D conversion of the knock signal by the A / D converter 14 is started in step S401, the process proceeds to step S402, and the value A / D converted by the A / D converter 14 is taken into the DSP 13. . Next, the process proceeds to step S403, and the captured A / D converted value is stored and accumulated in a RAM (Random Access Memory) (not shown) in the DSP 13 in time series, and the process proceeds to step S404. -Peak hold processing is performed, and this routine ends.

<Digital Filter / Peak Hold Processing Routine: See FIG. 7> In step S501, digital filter processing is performed according to the following equation.

Vi

[0] = {b0 ・ VAD

[0] + b1.VAD [1] + b2.VAD [2] -a1.VAD [1] -a2.VAD [2]} / a0 where i is the type of frequency band (for example, 6 to 8 KHz →
0, 9 to 11 KHz → 1, 13 to 15 KHz → 2). Also, Vi

[0] is the RAM value after digital filtering in each frequency band i, and the numbers in [] indicate time (for example, 0: current value, 1: AD one time before,
2: Value before 2 AD cycles). VAD

[0] indicates the RAM value after A / D conversion. a0 to a2 and b0 to b2 are constants determined by the order and frequency band of the filter.

Next, the process proceeds to step S502, and each RAM value Vi calculated in step S501.

It is determined whether [0] exceeds the maximum value (peak hold value) VMAXi in each frequency band. When the expression in step S502 is satisfied, the process proceeds to step S503 and Vi

[0]
Is stored (peak hold) as VMAXi. When the expression in step S502 is not satisfied, VMAXi is left as it is, and the process proceeds to step S504, where the next A / D conversion and digital filter processing is performed as a reference.
The RAM values of Vi and VAD are sequentially fed, and this routine ends.

<Preprocessing Routine: See FIG. 8> This routine is a flowchart of the preprocessing in step S203 of FIG. In step S601, the gain of the gain switch 12 is adjusted so that the input signal has an appropriate magnitude. As the signal for this gain switching, the knock sensor signal immediately after the A / D converter 14 is used without using the signal after digital filtering. This is because the knock sensor signal is attenuated after passing through the digital filter unless the signal has a frequency that exactly matches the center frequency f0 of the digital filter.

<Main Routine: See FIG. 9> This routine is a flowchart of the main routine started in step S305 of FIG. First, step S701
Then, the RAM value VMAXi that stores the maximum value is cleared, the process proceeds to step S702, and the knock determination section end flag =
After waiting until it becomes 1, the routine proceeds to step S703, where knock determination is made for each ignition. Then step S704
After the sensor mounting abnormality is detected, the process proceeds to step S705, the A / D conversion value (Vi, VAD) is initialized to 0, and this routine ends.

<Knock Judgment Routine: See FIG. 10> This routine is a detailed flowchart of the knock judgment in step S703 of FIG. Step S801 to Step S
In 803, knock determination for each ignition is performed for each frequency band based on the peak value after output of the digital filter for each frequency band in each knock determination region. Here, in step S801, the frequency band is 0 (6 to 8).
KHz), in step S802, frequency band 1 (9 to 11)
KHz), in step S803, frequency band 2 (13 to 1
Each knock determination for 5 KHz) is performed. Next, the process proceeds to step S804, the knock determination results in steps S801 to S803 are put together and a comprehensive knock determination is made, the result is output to the host CPU 16, and this routine ends.

<Knock determination routine in frequency band 0: see FIG. 11> This routine is a detailed flowchart of knock determination in frequency band 0 in step S801 of FIG. Note that step S802 and step S8 in FIG.
Since the determination routine of 03 is basically the same as this routine, the description thereof will be omitted.

In step S901, the peak value VMAX0 of the output after digital filtering is smoothed using the previous value Vm0 and stored in Vm0 as a RAM value. Next, in step S902, it is determined whether VMAX0 exceeds a value obtained by multiplying Vm0 by K0. When the inequality sign in step S902 is satisfied, the process proceeds to step S903, 1 is stored in KNK0, and when the inequality sign in step S902 is not satisfied, the process proceeds to step S904,
0 is stored in KNK0, and this routine ends. Here, KNK0 = 1 indicates knocking, KNK0 = 0 indicates no knocking, and K0≈5.

<General Knock Judgment Routine: See FIG. 12>
This routine is a detailed flowchart of the comprehensive knock determination in step S804 of FIG. Step S1001
Then, after the knock determination result in each frequency band is added and stored in the RAM value KNK as the total knock determination result, the process proceeds to step S1002, the result is output to the host CPU 16 as a port, and this routine ends. To do. In this way, when KNK is 1 or more, it is determined that there is knock.

<Sensor Attachment Abnormality Detection Routine: See FIG. 13> This routine is a detailed flowchart of the sensor attachment abnormality detection in step S704 of FIG. Step S1
In 101, if the knock determination result of the mode 0 is “1”, the process proceeds to step S1102, and if the knock determination result of the mode 2 is “1”, the process proceeds to step S1103, KNK0 = 1, KNK2. When the condition of = 1 is continuously detected a predetermined number of times, the process proceeds to step S1104, and it is determined that the sensor is attached abnormally. Note that step S
If any of the conditions from 1101 to S1103 is not satisfied, the process proceeds to step S1105, and it is determined that the sensor is normally attached.

<Sensor Attachment Abnormality Detection Routine: See FIG. 14> This routine is a detailed flow chart of a modified example of the sensor attachment abnormality detection of step S704 of FIG. 9 instead of FIG. When VMAX1 exceeds the predetermined value α in step S1201 and is continuously determined a predetermined number of times (for example, 3 times), the process proceeds to step S1202, it is determined that the sensor is attached abnormally, and the determination condition of step S1201 is satisfied. If not, the process proceeds to step S1203, and it is determined that the sensor is normally attached.

As described above, the knock detection device for an internal combustion engine of this embodiment amplifies the knock detection means achieved by the knock sensor 8 for detecting the knock generated in the internal combustion engine and the output from the knock detection means. Amplification means achieved by the gain switching device 12, filter means achieved by the digital filter 5 composed of BPF1, BPF2, and BPF3 for separating the output from the amplification means into a plurality of frequency bands, and the filtering means. And an abnormality detecting means achieved by the knock determining means 6 for detecting an abnormality of the knock detecting means by using a predetermined frequency band separated by the above. This is an embodiment of claim 1. be able to.

Therefore, the output from the knock sensor 8 based on the knock generated in the internal combustion engine is amplified by the gain switcher 12, and the output is separated into a plurality of frequency bands by the digital filter 5 achieved by the DSP 13. Abnormality of the knock sensor 8 is detected by the knock determination means 6 achieved by the DSP 13 using the predetermined frequency band. That is, the abnormality of the knock sensor 8 is detected by using the predetermined frequency band in the output characteristic of the knock detection generated from the knock sensor 8 in the internal combustion engine.

Therefore, by using the predetermined frequency band in the output characteristic of the knock detection generated from the knock sensor 8 in the internal combustion engine, the loose attachment abnormality of the knock sensor 8 can be accurately detected.

Further, in the knock detecting apparatus for the internal combustion engine of the present embodiment, the filter means achieved by the digital filter 5 of the DSP 13 has a plurality of BPF1, BPF2, BPF3.
The present invention can be an embodiment of claim 2. Therefore, the outputs of the respective frequency bands suitable for the normal knock detection of the knock sensor 8 and the abnormality detection of the knock sensor 8 are obtained, and the loose attachment abnormality of the knock sensor 8 is accurately detected.

Further, in the knock detecting device for the internal combustion engine of this embodiment, the filter means achieved by the digital filter 5 of the DSP 13 makes the center frequency of the frequency band variable, and the center frequency of the frequency band is variable. It can be an example. For this reason, the frequency band to be separated is set to knock sensor 8
Can be adapted to the characteristics of the internal combustion engine in which it is arranged.

Furthermore, in the knock detecting device for the internal combustion engine of the present embodiment, the predetermined frequency band used in the abnormality detecting means achieved by the knock determining means 6 of the DSP 13 is the frequency band used in the knock determination of the knock sensor 8. Is another frequency band, and this can be the embodiment of claim 4. Therefore, the normal knock detection of the knock sensor 8 and the abnormal attachment looseness detection of the knock sensor 8 can be accurately performed.

In addition, in the knock detecting device for the internal combustion engine of the present embodiment, the knock sensor 8 has a predetermined frequency band used by the abnormality detecting means achieved by the knock determining means 6 of the DSP 13.
This is a frequency band on the higher frequency side than the frequency band used for the knock determination of (1), and this can be the embodiment of claim 5. Therefore, the knock sensor 8 can use the normal knock detection frequency band, and the abnormality detection of the knock sensor 8 can accurately detect them by using the higher frequency band than the normal knock detection frequency band. it can.

In addition, in the knock detecting apparatus for the internal combustion engine of this embodiment, the abnormality detecting means achieved by the knock determining means 6 of the DSP 13 is the digital filter 5 of the DSP 13.
The knock sensor 8 is made abnormal when the output from the knock sensor 8 in the predetermined frequency band separated by the filter means, which has been achieved in step 1, exceeds a predetermined level a predetermined number of times. Can be an example. Therefore, based on the output from the knock sensor 8, it is possible to accurately detect the abnormality in the looseness of the sensor mounting.

<Second Embodiment> FIG. 18 is an overall configuration diagram showing a knock detecting device for an internal combustion engine according to a second embodiment of the present invention.

In FIG. 18, two knock sensors 21, 22 are attached to the internal combustion engine (engine),
Knock sensors 21 and 22 detect vibrations generated in the internal combustion engine. A multiplexer 23 is connected to the knock sensors 21 and 22. A multiplexer controller 28 is connected to the multiplexer 23 as a control circuit. A rotational speed sensor 33 for detecting the engine rotational speed Ne and a cylinder discrimination sensor 34 for discriminating a cylinder are connected to the multiplexer controller 28.
Based on these signals, the multiplexer 23 is controlled so as to switch and output the output signals of the knock sensor 21 and the knock sensor 22. A switched capacitor filter 24 is connected to the multiplexer 23.

A specific structure of the switched capacitor filter 24 will be described with reference to FIG. As the switched capacitor filter 24 of this embodiment, a secondary switched capacitor filter is used. That is, the switched capacitor filter 24 includes capacitors 41, 42, 43, 4
4,45,46,47 and switching element (FET)
48, 49, 50, 51, 52 and operational amplifiers 53, 5
4 and. In the switched-capacitor filter 24, the switching elements 48 to 52 are connected to each other as shown in FIG.
By switching (switching operation) between the state shown by the solid line and the state shown by the broken line in FIG. 9, a kind of resistance is realized and functions as a filter. In the case of the circuit of FIG. 19, the filter center frequency f0 is f0 = fCLK / 20. However, fCLK is the frequency of the switching drive signal.

In FIG. 18, a frequency characteristic controller 30 as a filter control circuit is connected to the switched capacitor filter 24. The frequency characteristic controller 30 is provided with a microcomputer 31 and a drive signal generator 32 shown in FIG. The drive signal generator 32 comprises a counter 32a, a compare register 32b, an inverting latch circuit 32c and a setter 32d, and the counter 32a inputs a pulse signal of 1 MHz from a crystal oscillator. Then, the counter 32a increments the count value by "1" at each rising edge of the pulse signal, as shown in FIG. The setter 32d sets n corresponding to the number of divisions of the oscillation signal (pulse signal), and in this embodiment, n = 2 or n = 3 or n = 4 is set. There is. The compare register 32b uses the count value of the counter 32a and the setter 3
When the set value n of 2d is compared and both values match, the count value of the counter 32a is reset (= 0). As shown in FIG. 21, the inversion latch circuit 32c generates and outputs a drive signal that is inverted every time the counter 32a is reset.

In FIG. 18, a rotation speed sensor 33 and a cylinder discrimination sensor 34 are connected to the frequency characteristic controller 30, and a detection signal for detecting the engine rotation speed Ne and the cylinder is sent to the frequency characteristic controller 30.

An amplifier 25 is connected to the switched capacitor filter 24, and the amplification factor of this amplifier 25 is controlled by an amplification factor controller 35. This amplification factor controller 35 includes a knock detection circuit composed of a microcomputer.
The fail detection circuit 26 is connected, and the knock detection circuit / fail detection circuit 26 sends a detection signal corresponding to the knock sensor output to the amplification factor controller 35. The amplification factor controller 35 outputs the detection signal of the amplifier 5 according to the knock sensor output. Change the amplification factor.

On the other hand, the amplifier 25 is connected to the knock detection circuit / fail detection circuit 26. Knock detection circuit 2
6a produces a knock determination level from the output signal of the amplifier 25, and if the output signal is higher than the knock determination level, it outputs a knock detection signal as the occurrence of knock in the internal combustion engine. A knock suppressing circuit 27 is connected to the knock detecting circuit 26a, and the knock suppressing circuit 27 retards the ignition timing by a predetermined amount in order to suppress the knock based on the input of the knock detecting signal.

The fail detection circuit 26b produces a fail detection level from the output signal of the amplifier 25, and when the fail detection level is lower than a preset fail judgment level, it outputs a fail detection signal because the knock sensor signal system has failed. Further, a knock suppressing circuit 27 is connected to the fail detecting circuit 26b, and the knock suppressing circuit 27 delays a predetermined amount until safe ignition timing by inputting a fail detecting signal.

Next, the operation will be described.

The switched capacitor filter 2 in which vibrations of the internal combustion engine are detected by the knock sensors 21, 22 and the knock sensor output signal is selected by the multiplexer 23.
4 is input and only the frequency band peculiar to knock is passed.
This signal is amplified by the amplifier 25 to an appropriate size, and the knock detection circuit / fail detection circuit 26 and the knock suppression circuit 27 perform knock detection, fail detection, and knock suppression control based on the amplified signal. At this time,
The filter characteristic of the switched capacitor filter 24 can be changed by the frequency fCLK of the switching drive signal, and this fCLK is changed and output by the frequency characteristic controller 30 according to the engine speed Ne and the cylinder discrimination signal.

Microcomputer 3 of frequency characteristic controller 30
No. 1 executes the process shown in FIG. 22 every predetermined time. First,
In step S1301, it is determined whether a predetermined ignition has elapsed since the previous fail determination (sensor looseness determination).
When the determination condition of step S1301 is not satisfied,
In step S1302, the engine speed Ne from the rotation speed sensor 33 is read, and in step S1303, the engine speed Ne is equal to the predetermined speed Neo (for example, 40
Is less than 00 rpm). Step S1
When the expression in 303 is satisfied, step S130
4, the setting device 32d is set to n = 4, and when the inequality sign in step S1303 is not satisfied, the process proceeds to step S1305 and the setting device 32d is set to n = 3. On the other hand, when the determination condition of step S1301 is satisfied, the process proceeds to step S1306, and the setter 32d is set to n = 2. Then, after step S1304, step S1305, or step S1306, this routine ends.

Here, when n = 4 is set in the setter 32d, as shown in FIG. 21, the counter 3 of FIG.
2a increments the count value by "1" at each rising edge of the pulse signal from the crystal oscillator (FIG. 21).
T1, t2, t3, t4, ...). In addition, the compare register 32
When b compares the count value of the counter 32a with the set value n (= 4) of the setter 32d and both values match, the count value of the counter 32a is reset (= 0) (FIG. 2).
1 t4). At this reset timing, the inverting latch circuit 32c generates and outputs the inverting switching drive signal. In this way, when n = 4, a switching drive signal of 250 KHz, which is 1 MHz divided by 4, is obtained.

On the other hand, when n = 3 is set in the setter 32d, as shown in FIG. 21, the counter 32 of FIG.
a increments the count value by "1" at each rising edge of the pulse signal from the crystal oscillator (t1, t2, t3, t4, ... In FIG. 21). In addition, the compare register 32b
Compares the count value of the counter 32a with the set value n (= 3) of the setter 32d, and when both values match, the count value of the counter 32a is reset (= 0) (FIG. 21).
T3). At this reset timing, the inverting latch circuit 32c generates and outputs the inverting switching drive signal. In this way, when n = 3, the switching drive signal of 333 KHz, which is the 1/3 frequency division, is obtained. Similarly, when n = 2, a switching drive signal of 500 KHz is obtained.

In this way, the frequency-divided switching drive signal is sent to the switched capacitor filter 24, and the switching elements 48 to 52 of the switched capacitor filter 24 are switched by this signal. On this occasion,
In the switched capacitor filter 24, the impedance changes and the filter characteristic changes by switching the switching frequency. That is, the switched capacitor filter 24 becomes a filter having a center frequency of 6.25 KHz as shown in FIG. 23 when the switching drive signal of 250 KHz is input, and becomes 8.3 KHz when the switching drive signal of 333 KHz is input. It becomes a filter having a center frequency, and when a switching drive signal of 500 KHz is input, it becomes a filter having a center frequency of 12.5 KHz. That is, when the engine speed Ne is smaller than the predetermined speed Neo, the filter has a center frequency of 6.25 KHz, and the engine speed Ne is the predetermined speed N.
When it is larger than eo, it becomes a filter having a center frequency of 8.3 KHz, and further 12.5 K at every predetermined number of ignitions.
It becomes a filter having a center frequency of Hz.

FIG. 24 is a flow chart for execution processing by the microcomputer of the fail detection circuit 26b. In the present embodiment, the timing at which this processing is executed is from the start of the fail determination section where n = 2 is switched. First, in step S1401, the amplification factor controller 35 sets the amplification factor of the amplifier 25 to the maximum value in order to accurately perform fail detection. Next, the process proceeds to step S1402, and a predetermined period elapses until there is no influence when the output signals of the knock sensors 21 and 22 are switched by the multiplexer 23 or when the signal passing frequency band of the switched capacitor filter 24 is switched. Wait until step S1
The process proceeds to 403, and Timer is reset to 0. Next, proceeding to step S1404, it is determined whether the sensor signal of the amplifier 25 exceeds the fail detection level VFAIL. When the expression in step S1404 is satisfied, the process proceeds to step S1405, and the fail detection level VFAIL is incremented. When the expression in step S1404 is not satisfied, step S1405 is skipped and the process proceeds to step S1406. Step S1
At 406, it is determined whether Timer has exceeded the predetermined period TLEV. When the expression in step S1406 is not satisfied, that is, it is determined that the predetermined period TLEV has not yet elapsed and it is a fail detection period, and steps S1404 to S1406 are repeated. Here, step S1404
The process of step S1406 is executed in a cycle in which each peak of the sensor signal from the amplifier 25 can be appropriately detected. Further, the predetermined period TLEV is the width of the fail detection period.

When the expression in step S1406 is satisfied, the process proceeds to step S1407, and the fail detection level VFAIL after the fail detection period is set in advance according to the operating condition of the internal combustion engine such as the engine speed. It is determined whether it is less than. Step S1
When the inequality sign of 407 is established, it is determined that the knock sensor signal system has failed, and the process shifts to step S1408 to output a fail detection signal to the knock suppression circuit 27, and then shift to step S1409. Then, in step S1409, a predetermined value (for example, 3) is subtracted from the fail detection level VFAIL, and this routine ends. On the other hand, when the expression in step S1407 is not satisfied, it is determined that the signal systems of the knock sensors 21 and 22 are normal, and step S1408 is skipped and nothing is done, the process proceeds to step S1409, and the fail detection level VFAIL is detected.
A predetermined value (for example, 3) is subtracted from this, and this routine is ended.

As described above, the knock detecting device for the internal combustion engine according to the present embodiment includes the knock detecting means achieved by the knock sensors 21 and 22 for detecting the knock occurring in the internal combustion engine,
Filtering means achieved by the switched capacitor filter 24 for separating the output from the knock detecting means into a plurality of frequency bands in time series, and amplification means achieved by the amplifier 25 amplifying the output from the filtering means. And an abnormality detecting means achieved by a knock detecting circuit / fail detecting circuit 26 for detecting an abnormality of the knock detecting means using a predetermined frequency band amplified by the amplifying means. Can be the embodiment of claim 7.

Therefore, the output from the knock sensors 21, 22 based on the knock generated in the internal combustion engine is separated into a plurality of frequency bands in time series by the switched capacitor filter 24, and the output is amplified by the amplifier 25. The knock detection circuit / fail detection circuit 26 detects an abnormality in the knock sensors 21 and 22 using a predetermined frequency band. That is, the abnormality of the knock sensors 21, 22 is detected by using the predetermined frequency band in the output characteristic of the knock detection generated from the knock sensors 21, 22 in the internal combustion engine.

Therefore, by using the predetermined frequency band in the output characteristic of the knock detection generated from the knock sensors 21 and 22 in the internal combustion engine, the loose attachment abnormality of the knock sensors 21 and 22 can be accurately detected.

[0077]

As described above, according to the knock detecting device for the internal combustion engine of claim 1, the output of the knock detecting means based on the knock generated in the internal combustion engine is amplified by the amplifying means, and the output is filtered. The means separates into a plurality of frequency bands, and the abnormality detection means detects the abnormality of the knock detection means using a predetermined frequency band among them. At this time, a predetermined frequency band corresponding to the output characteristic of knock detection generated in the internal combustion engine from the knock detection means is used. Thereby, the abnormality of the knock detection means can be accurately detected.

According to the knock detecting device for the internal combustion engine of the second aspect, in addition to the effect of the first aspect, since the filter means is composed of a plurality of filters, the normal knock detection of the knock detecting means and the knock detecting means can be realized. The output of each frequency band suitable for abnormality detection is obtained. Thereby, the abnormality of the knock detection means can be accurately detected.

According to the knock detecting device for the internal combustion engine of the third aspect, in addition to the effect of the first aspect, since the center frequency of the frequency band of the filter means is variable, the knock detecting means detects the frequency band to be separated. Can be adapted to the characteristics of the internal combustion engine in which it is arranged. Thereby, the abnormality of the knock detection means can be accurately detected.

According to the knock detecting device for the internal combustion engine of the fourth aspect, in addition to the effects of the first to third aspects, the predetermined frequency band used by the abnormality detecting means is the frequency used for knock determination of the knock detecting means. Since the frequency band is different from the band, the normal knock detection of the knock detection means and the abnormality of the knock detection means can be accurately detected.

According to the knock detecting device for the internal combustion engine of the fifth aspect, in addition to the effects of the first to third aspects, the predetermined frequency band used by the abnormality detecting means is the frequency used for knock determination of the knock detecting means. The frequency band is higher than the band. As a result, the knock detection means can use the normal knock detection frequency band, and the knock detection means abnormality detection can accurately detect them by using the frequency bands on the higher frequency side than the normal knock detection frequency band. it can.

According to the knock detecting device for the internal combustion engine of the sixth aspect, in addition to the effects of the first to third aspects, the abnormality detecting means is provided from the knock detecting means in the predetermined frequency band separated by the filter means. When the output exceeds a predetermined level a predetermined number of times, the knock detection means is made abnormal. As a result, the reliability of the output from the knock detection means increases, and the abnormality can be reliably determined based on the output.

According to the knock detecting device for the internal combustion engine of claim 7, the output of the knock detecting means based on the knock generated in the internal combustion engine is separated into a plurality of frequency bands in time series by the filter means, and the plurality of frequency bands are separated. The frequency band is amplified by the amplification means, and the abnormality detection means detects the abnormality of the knock detection means using a predetermined frequency band of the amplified frequency band. At this time, a predetermined frequency band in the output characteristic of knock detection generated in the internal combustion engine from the knock detection means is used. Thereby, the abnormality of the knock detection means can be accurately detected.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing a knock detection device for an internal combustion engine according to a first embodiment of the present invention.

FIG. 2 is a timing chart explaining the operation of the DSP of FIG.

FIG. 3 is a flowchart showing an initial setting routine of the knock detection device for an internal combustion engine according to the first embodiment of the present invention.

FIG. 4 is a flow chart showing a reference position interrupt routine of the knock detection device for an internal combustion engine according to the first embodiment of the present invention.

FIG. 5 is a flowchart showing a timer 1 interruption routine of the knock detection device for an internal combustion engine according to the first embodiment of the present invention.

FIG. 6 is a flowchart showing a timer 2 interruption routine of the knock detection device for an internal combustion engine according to the first embodiment of the present invention.

FIG. 7 is a flowchart showing a digital filter / peak hold processing routine of the knock detection device for an internal combustion engine according to the first embodiment of the present invention.

FIG. 8 is a flowchart showing a pre-processing routine of the knock detection device for an internal combustion engine according to the first embodiment of the present invention.

FIG. 9 is a flowchart showing a main routine of the knock detection device for an internal combustion engine according to the first embodiment of the present invention.

FIG. 10 is a flowchart showing a knock determination routine of the knock detection device for an internal combustion engine according to the first embodiment of the present invention.

FIG. 11 is a flowchart showing a knock determination routine in frequency band 0 of the knock detecting device for an internal combustion engine according to the first embodiment of the present invention.

FIG. 12 is a flow chart showing a general knock determination routine of the knock detecting device for an internal combustion engine according to the first embodiment of the present invention.

FIG. 13 is a flowchart showing a sensor mounting abnormality detection routine of the knock detection device for an internal combustion engine according to the first embodiment of the present invention.

FIG. 14 is a flow chart showing a modified example of a sensor mounting abnormality detection routine of the knock detection device for an internal combustion engine according to the first embodiment of the present invention.

FIG. 15 is a frequency characteristic diagram showing a relationship between a frequency of engine vibration and a spectrum intensity detected by a conventional knock detection device for an internal combustion engine.

FIG. 16 is a characteristic diagram showing a relationship between frequency and spectrum intensity when the conventional sensor mounting state is different.

FIG. 17 is a cross-sectional view showing a mounted state of a conventional knock sensor.

FIG. 18 is an overall configuration diagram showing a knock detection device for an internal combustion engine according to a second embodiment of the present invention.

FIG. 19 is a circuit diagram showing a specific configuration of a switched capacitor filter of a knock detection device for an internal combustion engine according to a second embodiment of the present invention.

FIG. 20 is a block diagram showing a drive signal generation device of a knock detection device for an internal combustion engine according to a second embodiment of the present invention.

FIG. 21 is a time chart showing signal states in a counter and the like of the knock detection device for an internal combustion engine according to the second embodiment of the present invention.

FIG. 22 is a flowchart showing a processing routine of the microcomputer of the frequency characteristic controller of the knock detection device for an internal combustion engine according to the second embodiment of the present invention.

FIG. 23 is a characteristic diagram showing a relationship between frequency and gain by a BPF in a knock detection device for an internal combustion engine according to a second embodiment of the present invention.

FIG. 24 is a flowchart showing a processing routine of the microcomputer of the fail detection circuit of the knock detection device for an internal combustion engine according to the second embodiment of the present invention.

[Explanation of symbols]

 8 Knock sensor (knock detection means) 12 Gain switcher (amplification means) 13 DSP (filter means / abnormality detection means)

Claims (7)

[Claims] 1. A knock detecting means for detecting a knock generated in an internal combustion engine, an amplifying means for amplifying an output from the knock detecting means, and a filter means for separating an output from the amplifying means into a plurality of frequency bands. An abnormality detection device for an internal combustion engine, comprising: an abnormality detection unit that detects an abnormality of the knock detection unit using a predetermined frequency band separated by the filter unit. 2. The knock detection device for an internal combustion engine according to claim 1, wherein the filter means comprises a plurality of filters. 3. The knock detection device for an internal combustion engine according to claim 1, wherein the filter means has a variable center frequency in the frequency band. 4. The predetermined frequency band used by the abnormality detection means is a frequency band different from the frequency band used for knock determination of the knock detection means. The knock detection device for an internal combustion engine according to any one of claims. 5. The predetermined frequency band used by the abnormality detecting means is a frequency band on a higher frequency side than a frequency band used for knock determination of the knock detecting means. The knock detection device for an internal combustion engine according to any one of claims. 6. The abnormality detecting means sets the knock detecting means to be abnormal when the output from the knock detecting means in a predetermined frequency band separated by the filter means exceeds a predetermined level a predetermined number of times. Claim 1 characterized by
The knock detection device for an internal combustion engine according to claim 3. 7. A knock detecting means for detecting knock occurring in an internal combustion engine, a filter means for separating an output from the knock detecting means into a plurality of frequency bands in time series, and an output from the filter means is amplified. A knock detection device for an internal combustion engine, comprising: an amplification unit that performs the above; and an abnormality detection unit that detects an abnormality of the knock detection unit using a predetermined frequency band amplified by the amplification unit.