JPH0734954A - Knock detecting device for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent the occurrence of erroneous detection of a knock by a method wherein a frequency zone is varied to a direction in which no output is generated during a specified period in which knock vibration is not detected, in a switched capacitor filter to pass only a signal of a given frequency zone outputted from a knock sensor. CONSTITUTION:Vibration generated by an internal combustion engine is detected by a knock sensor 1 and only a signal of a given frequency zone of detecting signals therefrom is caused to pass by means of a switched capacitor filter 2. Only a specified signal is fed, in order, to a knock detecting circuit, a fail circuit 28, and a knock suppression circuit 29 through an amplifier 26, and knock detection, fail detection, and knock suppression are executed, in the order. In this case, the characteristics of the filter 2 are variable by means of the frequency of a switching drive signal and the frequency is variable by means of a detecting signal from a crank angle sensor 24. In which case, during a given period in which knock vibration is not detected, a frequency zone different from that in a period in which knock vibration is detected is selected by a frequency characteristic controller 17.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a knock detecting device for detecting a knock generated in an internal combustion engine and controlling ignition timing, air-fuel ratio and the like.

[0002]

2. Description of the Related Art Generally, a knock detecting device in a multi-cylinder internal combustion engine (engine) detects a vibration in a combustion cycle of each cylinder by one vibration pickup mounted on an engine block, and detects a vibration in the output voltage of the vibration pickup. , The knock vibration component is extracted by a filter including a resistor and a capacitor, and the output voltage from the filter is compared with the knock discrimination voltage.

Then, for example, when knocking detection of a 4-cylinder 4-cycle engine is performed, as shown in FIG.
Since the ignition interval is long in the low engine speed region, the vibration output in the combustion cycle of each cylinder is separated, and knock detection for each cylinder can be performed by comparing this vibration output with the knock determination voltage. . However, FIG.
As shown in (b), since the ignition interval is short in the high engine speed region, the vibration output due to the combustion cycle of each cylinder continues until the period of the combustion cycle of the next cylinder, and the knock of the target cylinder for which knock is to be detected is detected. The vibration output and the vibration output of the previous cylinder overlap. Therefore, the vibration output due to the combustion cycle of the target cylinder cannot be accurately detected.

The continuation of the oscillation output of the pre-combustion cycle is caused by the response delay of the filter, that is, the oscillation accumulated in a circuit by the electric charge accumulated in the capacitor forming the filter. For this reason, Japanese Patent Laid-Open No. 1-182556 discloses a knock detection device which removes the electric vibration component inside the filter for a predetermined period irrelevant to the vibration in the combustion cycle of each cylinder.

[0005]

However, in the above method, since the output before the period required for knock detection is removed, the filter output in the period required for knock detection is delayed in response, and accurate knock detection is not possible. There is a problem that it can not be done. Furthermore, for a predetermined period unrelated to knock vibration,
It requires multiple analog switches to remove the electrical oscillatory components inside the filter.

If mechanical noise such as valve noise such as A in FIG. 12 (b) occurs before the knock detection period in FIG. 12 (a), the filter output is delayed as shown in B in FIG. 12 (c). There is a problem in that knock detection cannot be performed accurately because mechanical noise appears during the knock detection period. The present invention does not require multiple analog switches, and
An object of the present invention is to provide a knock detection device for an internal combustion engine, which can accurately perform knock detection even at high engine speed.

[0007]

Therefore, as shown in FIG. 1, the present invention provides a knock sensor for detecting a vibration generated in an internal combustion engine, and a switched capacitor for passing a signal in a predetermined frequency band output from the knock sensor. Based on the signal from the crank angle detecting means for detecting the crank angle of the internal combustion engine, and the crank angle detecting means, a predetermined period of the period in which knock vibration is not detected is the pass frequency band of the switched capacitor filter. As a second aspect, there is provided a knock detection device for an internal combustion engine, comprising: a frequency band selection unit that selects a frequency band different from a frequency band in a period in which knock vibration is detected.

[0008]

The switched capacitor filter passes the signal in the predetermined frequency band output from the knock sensor.
Then, the frequency band selecting means, based on the signal from the crank angle detecting means, a frequency band of a period in which knock vibration is detected as a frequency band that can pass through the switched capacitor filter for a predetermined period among periods in which knock vibration is not detected. Select a frequency band different from.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment embodying the present invention will be described below with reference to the drawings. FIG. 2 shows an overall configuration diagram of this embodiment. In FIG. 2, a knock sensor 1 is attached to an internal combustion engine (engine), and this knock sensor 1 detects a vibration generated in the engine.

A switched capacitor filter 2 is connected to the knock sensor 1. FIG. 3 shows a specific configuration of the switched capacitor filter 2. As shown in the figure, a second-order switched capacitor filter is used as the switched capacitor filter 2 of this embodiment. That is, the switched capacitor filter 2 includes the capacitors 3 to 9 and the switching element (FE).
T) 10 to 14 and operational amplifiers 15 and 16.

Further, in the switched capacitor filter 2, a kind of resistance is realized as a filter by switching the switching elements 10 to 14 between the state shown by the solid line and the state shown by the broken line (switching operation). Function. In the case of the circuit of FIG. 3, the filter center frequency f ₀ is f ₀ = f _CLK / 20. However, f _CLK is the frequency of the switching drive signal.

In FIG. 2, a frequency characteristic controller 17 as a filter control circuit is connected to the switched capacitor filter 2. The frequency characteristic controller 17 includes a microcomputer 18 and
The drive signal generator 19 shown in FIG. 4 is provided. The drive signal generator 19 comprises a counter 20, a compare register 21, an inverting latch circuit 22 and a setter 23. The counter 20 inputs a 1 MHz pulse signal from a crystal oscillator. Then, as shown in FIG. 5, the counter 20 increments the count value by "1" for each rising edge of the pulse signal. Setting device 23
Is to set n corresponding to the number of frequency divisions of the oscillation signal (pulse signal), and in this embodiment, n = 0 or n = 3 is set. The compare register 21 compares the count value of the counter 20 with the set value n of the setter 23, and when both values match, the counter 2
The count value of 0 is reset (= 0). As shown in FIG. 5, the inversion latch circuit 22 generates and outputs a drive signal that is inverted every time the counter 20 is reset.

In FIG. 2, the frequency characteristic controller 1
A crank angle sensor 24 and a cylinder discriminating sensor 25 for discriminating a cylinder are connected to 7 to detect an engine speed, a crank angle and a cylinder, and transmit a detection signal to the frequency characteristic controller 17. An amplifier 26 is connected to the switched capacitor filter 2, and the amplification factor of this amplifier 26 is controlled by an amplification factor controller 27. A knock detection circuit / fail detection circuit 28 composed of a microcomputer 18 is connected to the amplification factor controller 27. The circuit 28 transmits a detection signal corresponding to the knock sensor output to the amplification factor controller 27, and the controller 27 knocks. The amplification factor of the amplifier 26 is changed according to the sensor output.

On the other hand, the amplifier 26 is connected to a knock detection circuit / failure detection circuit 28. Knock detection circuit 28a
Makes a knock determination level from the output signal of the amplifier 26,
If the output signal is higher than the knock determination level, it is determined that knock has occurred in the engine and a knock detection signal is output.
A knock suppressing circuit 29 is connected to the knock detecting circuit 28a, and the knock suppressing circuit 29 retards the ignition timing by a predetermined amount in order to suppress the knock by inputting the knock detecting signal.

The fail detection circuit 28b produces a fail detection level from the output signal of the amplifier 26, and if 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. A knock suppression circuit 29 is connected to the fail detection circuit 28b.
Receives a fail detection signal and controls the ignition timing by a predetermined amount until a safe ignition timing.

Next, the operation of the knock detecting device for the internal combustion engine configured as described above will be described. A signal of engine vibration detected by knock sensor 1 is input to switched capacitor filter 2. Switched capacitor filter 2
Then, of this input signal, only the frequency band specific to knock is passed. Then, this signal is amplified to a proper size by the amplifier 26, and based on the amplified signal, a knock detection circuit
The fail detection circuit 28 and the knock control circuit 29 perform knock detection, fail detection, and knock suppression control.

At this time, the filter characteristic of the switched capacitor filter 2 can be changed by the frequency f _CLK of the switching drive signal, and this f _CLK is changed by the frequency characteristic controller 17 according to the crank angle sensor signal and the cylinder discrimination signal. You can The flowchart of FIG. 6 shows the processing for changing f _CLK executed by the microcomputer 18 of the frequency controller 17. Hereinafter, description will be given according to this flowchart.
It should be noted that this flowchart is executed for each predetermined crank angle.

First, in step 1, the microcomputer 18
Reads the crank angle detected by the crank angle sensor 24. Next, at step 2, it is judged from this crank angle whether or not it is currently in the knock detection period. Here, the knock detection period is ATDC (after top dead center) 10 ° C
A (crank angle) to 70 ° CA. If it is within the knock detection period, proceed to step 3, and if not within the knock detection period, proceed to step 4. In step 3, the set value of the setter 23 is set to "3", and this routine ends. In step 4, the set value of the setter 23 is set to "0" and this routine ends. That is, in step 4, the frequency of the switching drive signal is not divided.

By executing the above processing, when n = 3 is set in the setter 23 (during the knock detection period), as shown in FIG. 5, the counter 20 of FIG. The count value is incremented by "1" at each rising edge of the pulse signal from (1) (t1, t2, t3 in FIG. 5). In addition, the compare register 21 sets the count value of the counter 20 and the set value n (=
3) is compared and if both values match, the counter 20
The count value of is reset (= 0) (t in FIG. 5).
3). At this reset timing, the inverting latch circuit 2
A switching drive signal in which 2 is inverted is generated and output.

In this way, when n = 3, a switching drive signal of 167 kHz, which is 1 MHz divided by 6, can be obtained. On the other hand, when n = 0 is set in the setter 23 (outside the knock detection period), the pulse signal from the crystal oscillator is output as the switching drive signal. In this way, when n = 0, no frequency division is performed, so that a switching drive signal of 1 MHz is obtained.

The thus-divided switching drive signal is sent to the switched capacitor filter 2, and the switching elements 10 to 14 of the switched capacitor filter 2 are switched by this signal. At this time, in the switched capacitor filter 2, the impedance is changed by switching the switching frequency, so that the filter characteristic is changed. That is, the switched capacitor filter 2 becomes a filter having a center frequency of 8.3 kHz, which is a frequency band peculiar to knocking, as shown in FIG. 7, when a switching drive signal of 167 kHz is input during the knocking detection period. Outside, it becomes a filter having a center frequency of 50 kHz when a switching drive signal of 1 MHz is input.

By performing the above-described processing, the knock-specific frequency band is output only during the knock detection period, and the output is set to almost 0 V AC because the knock-specific frequency band is not passed in other periods. You can This allows
The influence of the filter output outside the knock detection period can be eliminated. Furthermore, if the frequency band that can pass outside the knock detection period is set to a high frequency band, the higher the signal passing frequency band, the faster the signal response, and therefore the signal responsiveness can be improved.

In the above-described first embodiment, the crank angle sensor 24 corresponds to the crank angle detecting means and the step 2 corresponds to the frequency band selecting means, and functions. In the first embodiment, the signal pass frequency band of the switched capacitor filter 2 is changed in all the periods other than the knock detection period, but it may be changed only in a part of the period. For example, in the flowchart shown in FIG. 8, the signal pass frequency band of the switched capacitor filter 2 is changed only for a predetermined period before the start of the knock detection period. The second embodiment will be described below with reference to the drawings. This flowchart is executed for each predetermined crank angle. In addition, in the flowchart of FIG.
The same step numbers are assigned to the steps that execute the same processing as the steps shown in the flowchart of FIG.

When this routine is executed, step 1
At, read the crank angle. Then, in the next step 5, whether the knock detection period has started (that is,
ATDC 10 ° CA), and if so, go to step 3, otherwise go to step 6. In step 3, the set value of the setter 23 is set to "3" and this routine is finished.

In step 6, it is judged whether the knock detection period has ended (whether it is ATDC 70 ° CA). If it has ended, step 7 is reached. If it has not ended, this routine ends. In step 7, it is determined whether or not a predetermined time has elapsed since the knock detection period ended. If the time has not passed, this process is continued until the time passes. If the time has passed, go to step 4. In step 4, the set value of the setter 23 is set to "0" and this routine ends.

Even if the above processing is executed, the same effect as that of the first embodiment can be obtained. In addition, the first,
In the second embodiment, the center voltage of the knock sensor output signal may be input to the switched capacitor filter 2 instead of the knock sensor output signal outside the knock detection period. Here, the center voltage of the knock sensor output signal means 0 V of alternating current of the sensor output. For example, in FIG. 13A, the knock sensor output signal oscillates with 0 V as a reference. Become. In addition, for example, in FIG. 13B, since 5V is oscillating as a reference, this 5V becomes the center voltage. The third embodiment will be described below.

FIG. 9 is a block diagram of this embodiment. In this figure, a signal from either knock sensor 1, 1 ′ or knock sensor center voltage generator 30 is input to switched capacitor filter 2 after being selected by multiplexer 31. The multiplexer 31 is the microcomputer 18
The signal is selected based on the control signal from.
The other configuration is similar to that of FIG.
The processing executed by the microcomputer 18 in such a configuration will be described with reference to the flowchart shown in FIG. The flowchart of the present embodiment is obtained by adding step 8 between step 5 and step 3 and step 9 between step 6 and step 7 of the flowchart shown in FIG.

That is, when it is determined in step 5 that the knock detection period has started, the routine proceeds to step 8, where the output of the knock sensor 1 or the knock sensor 1 ′ is switched to the switched capacitor filter 2 based on the cylinder discrimination sensor signal 25.
The switch of the multiplexer 31 is switched so as to input to Further, when it is determined in step 6 that the knock detection period has ended, in step 9 the signal from the knock sensor center voltage generator 30 (in the present embodiment,
The switch of the multiplexer 31 is switched so that the 0 V signal) is input to the switched capacitor filter 2.

By executing the above-mentioned processing, the output of the switched capacitor filter 2 can be made to be 0 V AC more quickly and surely, so that the output outside the knock detection period is more effective than in the first and second embodiments. Influence of filter output,
Also, the influence of the filter output in all ignition can be eliminated. If there are multiple knock sensors,
If one of them fails, the original output should be 0, but if the knock sensor used in the pre-ignition cycle is not broken, the pre-ignition is due to the delay in the response of the filter output. Since the filter output of the cycle remains until the next ignition cycle, fail detection cannot be accurately performed. However, in this embodiment, the signal of output 0 is input to the filter, and the signal passing frequency of the filter is switched to a high frequency so that the response of the filter becomes faster. Therefore, the filter output of the previous ignition cycle quickly becomes 0. In addition, there is an excellent effect that the fail can be accurately detected in the next ignition cycle in which the knock sensor is out of order.

[0030]

As described above, according to the present invention,
The switched capacitor filter changes the frequency band in the direction in which the output is not output during the period when no knock vibration is detected, so even if knock detection is continuously performed at high engine speed, the knock vibration in the previous ignition cycle causes ignition after the ignition. It does not remain in the cycle. Therefore, it is possible to prevent erroneous detection of knock due to knock vibration of the pre-ignition cycle when the internal combustion engine is rotating at high speed.

[Brief description of drawings]

FIG. 1 is a block diagram showing constituent features of the present invention.

FIG. 2 is a system configuration diagram of the first embodiment.

FIG. 3 is a circuit diagram of a switched capacitor filter.

FIG. 4 is a configuration diagram of a frequency characteristic controller.

FIG. 5 is a time chart for explaining signal processing.

FIG. 6 is a flowchart showing a process executed by a microcomputer.

FIG. 7 is a correlation diagram showing frequency-gain characteristics of the switched capacitor filter.

FIG. 8 is a flowchart showing a process executed by a microcomputer in the second embodiment.

FIG. 9 is a system configuration diagram of a second embodiment.

FIG. 10 is a flowchart showing processing executed by a microcomputer in the third embodiment.

FIG. 11 is a time chart for explaining a conventional technique.

FIG. 12 is a time chart for explaining a conventional technique.

FIG. 13 is a time chart for explaining a center voltage.

[Explanation of symbols]

 1 Knock Sensor 2 Switched Capacitor Filter 17 Frequency Characteristic Controller 18 Microcomputer 24 Crank Angle Sensor 28 Knock Detection Circuit / Fail Detection Circuit 29 Knock Suppression Circuit 30 Center Voltage Generator 31 Multiplexer

Claims (3)

[Claims] 1. A knock sensor for detecting a vibration generated in an internal combustion engine, a switched capacitor filter for passing a signal in a predetermined frequency band output from the knock sensor, and a crank angle detecting means for detecting a crank angle of the internal combustion engine. Based on the signal from the crank angle detecting means, of the period in which knock vibration is not detected, a predetermined period is a frequency band different from the frequency band of the period in which knock vibration is detected as the pass frequency band of the switched capacitor filter. A knock detection device for an internal combustion engine, comprising: a frequency band selecting means for selecting. 2. The switched capacitor filter passes a signal in one of frequency bands of a knock-specific frequency band output from the knock sensor and a signal in a high frequency band other than the knock. The knock detection device for an internal combustion engine according to claim 1. 3. A center voltage generating means for generating a center voltage of a signal output from a knock sensor, an output from the knock sensor based on a signal from the crank angle detecting means, and a center voltage generating means from the center voltage generating means. 3. The knock detection device for an internal combustion engine according to claim 1, further comprising input signal selection means for inputting one of the output signal and the output signal to the switched capacitor filter.