Knock control using resonant vibration of combustion has been spread through spark-ignition engines. In a lean burn engine, it is especially important in order to keep ignition timing the optimal. However, the improvement in a performance at the time of acceleration of a car continues being a subject. It is because that the conventional method has the delay of knock detection. This paper proposes a quick detection method for precise knock control.
The resonant vibration of pressure in cylinder can be measured by vibration sensors at the cylinder block or in-cylinder pressure sensors. Although which sensor could be used, it decided to use a pressure sensor here. Knock phenomenon can appear and disappear in a very short time. On the other hand, the conventional method using the Fourier transform will ask for an average over the whole of one combustion stroke. In order to improvement in sensitivity, the wavelet transform with the advantage of catching a momentary state change is applied effectively. The simulation was carried out in order to select the mother function for the detection of resonant vibration. The result showed Morlet function was more suitable than Meyer function and others.
Wavelet transform has the practical subject that the load of calculation is large. The load is mitigated by omitting the calculation range of the symmetrical mother function by 50%. According to our results of wavelet analyses with an in-cylinder pressure sensor, it became clear that a knocking combustion has single resonant vibration mode, and that two or more resonant vibration modes are not produced simultaneously. Based on this fact, the method of comparing a scale-spectrum obtained by wavelet transform according to a crank angle was examined.
From the results of engine tests and its off-line analysis, it was proved that a knock is detectable in one combustion using our method of scale-spectrum comparison.