SE434574B - Arrangement for detecting unwanted combustion processes in internal combustion engines working with ignition systems by means of an acceleration sensor - Google Patents

Abstract

The invention relates to an arrangement for detecting unwanted combustion processes in internal combustion engines working with ignition systems by means of an acceleration sensor and a bandpass filter tuned to the frequency of the knocking vibrations, the output signal of which is intended to be compared with a reference value and the result obtained thereby being assigned to the unwanted combustion processes that are to be detected. In order to avoid the need for recurrent adjustments of the device's setting, it is proposed according to the invention that a rectifier 4 is arranged for the base noise signal UE received by the acceleration sensor 1 and passed through the bandpass filter 3, in which rectifier 4 this signal is rectified to a knocking signal UK, that a band block filter 5 tuned to the frequency of the knocking vibrations fK is series- connected to an effective-value rectifier 6a and an amplifier 6b for conversion of the base noise signal UE received by the acceleration sensor 1 into a reference signal UR, and that a comparator 7 is arranged for comparison of the reference signal UR with the knocking signal UK, whereby an output signal UA is obtained if the knocking signal UK exceeds the reference signal UR. <IMAGE>

Description

3004267-4 adaptation to the given conditions, it may be appropriate to the gain of the reference signal is linear or non-linear.

The s.k. The "nailing" of an internal combustion engine occurs when the fuel mixture is not incinerated on its own from the ignition spark but also a self-ignition occurs in front the flame front being widespread due to pressure and the temperature rise. This uncontrolled combustion is harmful for the engine and causes increased mechanical and thermal loads.

This "nailing" can be induced, among other things, by changing the tower load. An opportunity to recover from this condition is to adjust the ignition. IN The noise spectrum caused by the "nailing" is within the frequency range around 7 kHz. Complicating the detection is that similar noise, for example arising from valve knocks, likewise lies within this frequency range and that the entire noise level over the speed range from idle up to the maximum speed changes approximately by a factor of 10.

The invention is described in more detail below with reference to an embodiment.

In the drawing, which shows a block diagram of the device according to the invention, an acceleration sensor 1 is shown, for example a piezocrystal sensor, which picks up the body sound and which is arranged in a suitable place in the engine, for example at the cylinder head. After this sensor follows an input amplifier 2, the output of which is bound with a bandpass filter 3 and a bandpass filter 5. After the bandpass filter 5 follows a rectifier H and after the bandpass filter is provided an effective value rectifier 6a and a linear amplifier « 6b. This amplifier may or may not have a non-linear strengthening or also omitted altogether in certain applications.

The outputs of the rectifier D and the amplifier 6b go to the inputs on a comparator 7. The bandpass filter 3 and the bandpass filter 5 are set to the clock frequency fK at 7 kHz. This means that the bandpass filter amplifies and the bandpass filter suppresses it frequency.

The body audio signal_UE from acceleration sensor 1 is amplified in the input amplifier 2 to the required level and early to the two filters. In the bandpass filter 3, one is amplified any existing signal with the frequency fx (while all others frequencies intestine) and in imskearm 4 mother this signal for biwanaa of

Claims (2)

8004267-4 knock signal UK. In the band-blocking filter 5, on the other hand, any signals are attenuated with the frequency fK. The remaining signal constituents, after passing the effective value rectifier, form the mean value of the body sound signal, which after linear amplification in the amplifier 6b forms a threshold value for the knock signal, which constitutes a reference signal UR. Both signals are compared with each other in the comparator 7. If the knock signal UK exceeds the reference signal UR t for shifting the ignition timing. The comparator always gives a signal UA, if oscillations within the frequency range fK are recorded with the input signal UE and these exceed a certain level in relation to the other frequencies. A relative comparison is obtained which eliminates the need for an ilfiå; then the comparator emits an output signal UA, which can, for example, renew continuous adjustment. _ P a t e n t k r a v Device for detecting unwanted combustion processes; in the case of internal combustion engines operating by means of an ignition system by means of a H0C @ 1 @ Patí0HS9ÜßIê.Ü) ms¿ assign a reference value and the result obtained; This undesired combustion process, which is to be detected, is characterized in that a rectifier (4) is arranged for the body sound signal (UE) received by the acceleration sensor (1) and passed through the bandpass filter (3), in which this signal is rectified. to a knock signal (UK), that a band-blocking filter (5) tuned to the frequency of the knock oscillations (fw) is connected in series with an effv value rectifier (6a) and an amplifier (öb) for converting the structure received by the current signal (1). ) to a reference signal (UR), and that a comparator (T) is arranged may, ï; - move the reference signal (UR) with the knock signal (UK), whereby an output signal (UA) is obtained if the knock signal (UK) exceeds the reference signal (FROM). Device according to claim 1, characterized in that the amplifier (öb) has a linear gain. . Device according to claim 1, characterized in that the amplifier (6b) has a non-linear gain.