JPH0523374B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a knock sensor for detecting vibrations of an internal combustion engine, a knock filter that passes a signal supplied from the sensor at least in the frequency range of an expected knock signal, a comparator, and a retriggerable monostable multivibrator downstream of the knock filter, the one input side of the comparator being connected to the output side of the knock filter; The other input side is supplied with a signal from the knock sensor via a rectifier stage, the time constant of the monostable multivibrator being set in such a way that it is kept active by the minimum frequency of the knock filter. The present invention relates to a knock detection device.

BACKGROUND OF THE INVENTION A method and a device for detecting an engine knock are already known from DE 32 15 683 A1. This device has a knock sensor that measures engine vibration and converts the measured vibration into a corresponding electrical signal, and a knock filter whose frequency band of this electrical signal is a passband, and a knock sensor that detects the measured knock phenomenon. A comparator is provided, which outputs a signal when a valid measurement value is recognized by the device.

Problems to be Solved by the Invention Conventional devices have problems in that the suppression of background noise is uneven, especially at low rotational speeds, and that the dynamic characteristics are poor at relatively high rotational speeds. be. This is because the engine knock signal at the input side of the comparator inevitably contains a background noise component due to the bandpass filter and rectifier. On the other hand, the background noise signal supplied to the other input side of the comparator includes a signal that is integrated through the second smoothing circuit and delayed with respect to the knock signal, and this causes the above-mentioned insufficient signal. This causes dynamic characteristics.

Means for Solving the Problems The above drawbacks are solved according to the invention by configuring the rectifier stages to be non-integrating rectifiers.

Embodiment In the embodiment of the invention shown in FIG. 1, the knock sensor 1 is connected to the input terminal 2;
is connected to the input side of the knock filter 4 and the input side of the rectifier 9 together with the test signal terminal 3. The output side of the knock filter 4 is connected to the non-inverting input side of the comparator 5, while the inverting input side is connected to the output side of the rectifier 9 and to the background noise terminal 10. The output of the comparator 5 is connected via a knock signal terminal 6 to a retriggerable monostable multivibrator 7, the output of which is connected to the input of a microcomputer 8. The output side of the microcomputer 8 is connected to the test signal terminal 3 via a test line 12. An error reporting stage 13 is connected to the background noise terminal 10, and the error reporting stage itself is connected to the microcomputer 8 via a reporting line 14.

The device evaluates the output signal of a knock sensor 1 mounted on the engine block and sends a logic signal to a knock signal terminal 6 when a knock is occurring during combustion. For this purpose, the output signal, which simultaneously contains a background noise component and a knock signal component, is filtered by a knock filter 4 tuned to the mechanical resonance frequency of the engine during knock combustion.
The knock filter 4 has a fixed amplification factor. In addition, the output signal of the knock sensor 1 is also supplied to a rectifier 9. The rectified signal obtained by this is the comparator 5
The level at the inverting input side of is shifted in the positive direction depending on the sensor output voltage amplitude. In order to obtain a certain reset characteristic in the output signal of the comparator 5,
Has a small input offset. The hysteresis characteristic suppresses the background noise signal of knock filter 4. In other words, the comparator 5 constitutes an amplitude filter, the passage area of which depends on the amplitude of the output signal of the knock sensor 1.

The level shift due to the background noise rectification value on the inverting input side of the comparator 5 is inevitably caused by temporal changes in engine noise such as changes in bearing play or valve play, and product variations and aging of sensor 1. The function is to automatically adapt the response sensitivity of the device to the fluctuations in the output signal amplitude of the knock sensor 1 that occur. In that case, the level shift is
The variation of the background noise at the output of the noise filter 4 is carried out in parallel against the proportional level shift at the input of the comparator 5. Thereby, background noise is suppressed to the extent necessary to avoid unnecessarily lowering the response sensitivity. By correspondingly adjusting the amplification of the knock filter 4, an optimum condition between detection accuracy and error probability can be found.

Therefore, a pulsed signal is applied to the knock signal terminal 6 during knock combustion, and this signal triggers the retriggerable monostable multivibrator 7. The time constant of the multivibrator 7 is selected in such a way that at least the lowest passing frequency of the knock filter 4 keeps this multivibrator active. The output signal of the multivibrator 7, ie the pulse width, is therefore a suitable measure of the duration of the knocking process or of the strength of the knocking. This signal is detected by the microcomputer 8 and its duration is summed. The microcopy computer 8 can, of course, also be directly connected to the comparator 5, and it can also be determined by hardware or software whether or not the measured knocks are valid. Via an interrupt input, the pulse length or the number of oscillation sequences of the output signal of the comparator 5 is counted and compared with a predetermined threshold value.
In this case, the microcomputer 8 is a part of the vehicle's computer, and this computer performs various functions important to the operation of the engine, such as controlling the knobs related to changes in ignition timing. This embodiment is not shown in the figures for the sake of simplicity.

The microcomputer 8 is connected to the test signal terminal 3 via a test line 12 and cyclically sends one test signal to the test signal terminal 3 every 100 combustions. Based on that, microcomputer 8
When the device detects one pulse of the multivibrator 7, the knock detection function of the device is checked.
In the case of inspection in a factory, a predetermined type of signal can be applied to the test signal terminal 3 in order to inspect the frequency characteristics, sensitivity, etc. of the device.

The output signal of the rectifier 9 is taken out from the background noise terminal 10 by means of an error reporting stage 13. The error reporting stage detects a failure of the knock sensor or a break in the sensor cable by the absence of background noise appearing at the background noise terminal 10. In case of failure, error notification stage 1
3 emits an optical or acoustic signal to the driver and transmits the notification via a notification line 14 to the vehicle's computer. The computer accordingly interrupts the knock control and adjusts the internal combustion engine to a non-hazardous operating state in any case, for example by adjusting the ignition timing delay. The technical aspects of such an error reporting stage, such as the smoothing of background noise at the input of a threshold switch, are well known to those skilled in the art and are therefore not shown in the figures for the sake of simplicity.

The embodiment of FIG. 2 has largely the same construction as the embodiment of FIG. 1, and these are designated by the same symbols. The essential difference is that a filter 11 is connected between the input terminal 2 and the input side of the rectifier 9. This filter 11 is tuned to the frequency band of background noise. The increased resonance no longer interferes with the amplitude filtering action of the comparator 5.

The knock detection device for an internal combustion engine of the present invention can be used for both an external ignition type internal combustion engine and a self-ignition type internal combustion engine. Depending on the criteria of the desired embodiment, the knock signal at the knock signal terminal 6 acts as the actual value of the knock control, for example on the ignition timing or the injection timing, or on the intake pressure of the intake air of the internal combustion engine to be charged. According to a particularly advantageous embodiment of the invention, the device according to the invention can be mounted together with the knock sensor 1 in one housing in the engine. The knock signal is then supplied via one line to a transistor ignition system, such as is used in many automobiles, for adjusting the ignition timing.

Effects of the Invention Compared to the conventional technology, the knock detection device of the present invention has the following advantages:
This has the advantage that the output signal of the knock sensor is not integrated. Therefore, the background noise superimposed on the knock signal no longer affects the output signal level. This results in particularly good background noise suppression, especially at low engine speeds. A further advantage is that the manufacturing costs are lower than before. Furthermore, the device of the present invention can be easily integrated.

In embodiments of the invention, the hysteresis characteristic of the comparator acts to suppress background noise signals at the output frequency of the knock filter. The comparator offset has the advantage that it can be used to achieve a constant reset characteristic of the comparator output signal. By tuning the filter to a passband above the engine's resonant frequency, sudden, resonance-induced rises in the background noise signal no longer interfere with detection. The filter can be implemented very simply with one short circuit or a buffer amplifier. The test signal terminal makes it very easy to test the knock detection function at the factory or to monitor the knock detection function during engine operation by periodically generating a test signal by the vehicle's computer. A retriggerable monostable multivibrator at the output of the comparator produces a pulse as an output signal that is immediately applicable to processing by a microcomputer, the duration of which is a good measure of the strength of the knock. A fault reporting stage connected to the background noise terminal has the advantage that the knock sensor or its lead can be easily monitored. If no voltage is applied to the background noise terminal, the error notification stage emits an optical or acoustic signal to the vehicle driver or the like and applies a signal to the vehicle's computer. In response, the computer interrupts the knock control and shifts the ignition timing to a safe value.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram of a first embodiment of a knock detection device with a trigger stage and a microcomputer, and FIG. 2 is a second embodiment of the device according to the invention with a filter on the background noise circuit side. FIG. 3 is an example block circuit diagram. 1...Knock sensor, 3...Test signal terminal, 4
...Knock filter, 5... Comparator, 7... Monostable multivibrator, 9... Rectifier, 10...
Background noise terminal, 11...filter, 13...error notification stage.

Claims (1)

[Claims] 1 Knock sensor 1 for detecting vibrations of an internal combustion engine
a knock filter 4 which passes the signal supplied by the sensor at least in the frequency range of the expected knock signal; a comparator 5; and a retriggerable monostable multivibrator 7 downstream of the comparator 5. One input side of the comparator 5 is connected to the output side of the knock filter 4, and the other input side of the comparator 5 is connected to a rectifier stage from the knock sensor 1. In the knock detection device, the monostable multivibrator 7 is supplied with a signal via the knock filter 4, and the time constant of the monostable multivibrator 7 is set to be kept active by the minimum frequency of the knock filter 4. Knock detection device characterized in that the rectifier stage is a non-integrating rectifier 9. 2. The device according to claim 1, wherein the comparator 5 has a hysteresis characteristic. 3. The device according to claim 1 or 2, wherein the comparator 5 has an offset. 4. Claim 1, wherein a filter 11 is connected between the knock sensor 1 and the rectifier 9.
The apparatus according to any one of items 1 to 3. 5. The filter 11 is tuned to the background noise of the internal combustion engine.
Apparatus described in section. 6. According to any one of claims 1 to 5, a test signal terminal 3 is connected to the knock filter 4, and a test signal is supplied to the knock detection device via the terminal 3. The device described. 7. The device according to claim 6, wherein a test signal is periodically supplied to the knock detection device via the test line 12, and the failure or function of the knock detection device is checked from the response of the comparator 5 to this signal. Device. 8. A background noise terminal 10 is connected to the output side of the rectifier 9, and an error notification stage 13 is connected to the background noise terminal 10. Claims 1 to 7 provide at least one notification that a failure of the knock sensor 1 and/or a failure of the lead wire of the knock sensor 1 occurs when the knock sensor 1 falls below a predetermined level. The device described. 9. A patent in which it is determined whether or not a knock has been effectively identified by counting the pulse length or the number of series of oscillations of the output signal from the output signal of the comparator 5 and comparing it with a predetermined threshold value. Claim No. 8
Apparatus described in section.