Circuit arrangement to detect knocking

Details Circuit arrangement to detect knocking Circuit arrangement to detect knocking

1991-10-18

1994-08-02

Chapman, John E.

Measuring and testing

Engine detonation

Combustion signal compared to reference signal varied by a...

G01L 2322

Patent

active

053334892

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention is related to a circuit arrangement to detect knocking in an internal combustion engine, and particularly, to a circuit arrangement having a knock sensor which is connected with an evaluating circuit via a filter effecting a separation of the knock frequency.
In automotive engineering, knocking in an internal combustion engine is a dangerous operating state which can lead to damage in the long run. Therefore, circuit arrangements to detect knocking in an internal combustion engine are known which determine the frequency spectrum of the internal combustion engine by means of a knock sensor and, after filtering out the relevant knock frequency, feed it to a circuit arrangement which, when knocking is detected, changes the operating parameters of the internal combustion engine in such a way that knock-proof operation is brought about. Increasingly greater demands are made with respect to the detecting and evaluating devices of the known circuit arrangements. For example, increasingly higher knock frequencies must be determined and evaluated as a result of modern internal combustion engine construction. This conflicts with the relatively low limit frequencies of the evaluating circuits presently in use. In addition, there is a demand for arrangements for evaluating the knock sensor signals which are constructed in a particularly simple manner.


SUMMARY OF THE INVENTION

In contrast to the known circuit arrangements, the circuit arrangement according to the invention has the advantage that a simple and accordingly inexpensive construction of the entire circuit arrangement is possible in spite of the relatively high frequency of the knock sensor signal, since a frequency reduction is effected so that a relatively simple technique can be used. According to the invention, the reduction in frequency is effected with a means for superposing which works according to the principle of superposition (beat principle, superheterodyne principle) and accordingly lowers the frequencies of the knock sensor signal components. This reduced frequency mixed signal is then fed to the evaluating circuit via filter means.
According to a further development of the invention, the means for superposing receives another signal at an oscillator frequency of the same magnitude as the predominant knock frequency for mixing or superposition with the knock sensor signal. The advantage of this consists in that a mixed signal is available at the output of the superposing means which corresponds to the envelope curve of the knock signal.
It is also possible to operate the superposing means with an oscillator frequency which diverges from the knock sensor signal frequencies in such a way that the mixed signal frequencies of the output signal of the mixer stage is less than the sensor signal frequencies. This frequencies reduction then enables a further processing of the signal using simple means. The oscillator frequency can be below or above the frequency of the anticipated knock signal by an amount corresponding to the desired filter frequency of a subsequently arranged filter means (band-pass filter). As has already been mentioned, the advantage of this signal processing consists in that knock signals of very high frequencies can be processed, wherein no special demands are to be made on the further signal processing with respect to the frequency processing characteristics.
The means for superposing comprises a mixer stage multiplier. The knock sensor signal, which is composed of ground noise and possible knock signals, and the oscillator frequency--as additional input quantity--are fed to this mixer stage multiplier. The output of the multiplier is connected to the evaluating circuit.
In particular, a level stabilizing circuit can be connected between the superposition means and the knock sensor. This ensures that the knock sensor signal, whose amplitude depends on the operating state of the internal combustion engine, is brought to a constant level and then subjected to further processing. Fluctua

REFERENCES:
patent: 3393557 (1968-07-01), Brown et al.

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