Research On Knock Vibration Feature Extraction And Intensity Evaluation For Gasoline Engine

Knock detection is the premise and foundation of the ignition closed-loop control in gasoline engine.Knock feature extraction and intensity evaluation is the premise of knock detection and control.Severe knock could make the power coastdown and fuel consumption increase,even damage mechanical parts while light knock can improve the power performance of an engine.Vibration detection technology is the most commonly used method of knock detection,but the existing knock detection method can not evaluate knock intensity accurately,so it is difficult to achieve precise control of the knock.Detecting knock timely and effectively has important theoretical significance and engineering practical value.This dissertation researched the non-stationary and non-linear vibration signal analysis and feature extraction method,including: Wavelet transform,empirical mode decomposition,higher order statistics theory,fractal theory and mathematical morphology,etc.Thesis researched signal analysis methods in the field of engine vibration signal analysis and detonation feature extraction and intensity evaluation.The main research results of the full text are as follows:In view of the randomness in the direction of propagation of cylinder pressure high-frequency oscillation and the non-linear vibration of engine structure block,this paper proposes a detonation characteristic analysis method based on the fusion of multiple directions vibration.The highly sensitive vibration direction of engine knock is proved by analyzing the influence rule of the in-cylinder pressure high-frequency oscillation on the vibration.On the basis of ensemble empirical mode decomposition & wavelet packet transformation principles and their calculation research,this paper works out signal abstraction method and further extracts the time-frequency characters and space distribution principles of vibration signals.The method,which overcomes the problem of the decomposition of wavelet packet frequency components without physical meaning and the too wide frequency band of the IMF component,can detect knock and evaluate the intensity effectively.When the engine knock is at different intensity,the distribution intensity and morphology of non-Gaussian components of vibration signals will change in bi-frequency domain along with the knock.Through the analysis of the characteristics of the vibration signal with different knock intensity,Knock feature extraction and intensity evaluation are effectively implemented by using bi-spectrum slice and singular value decomposition.The calculation method of box counting dimension and generalized dimension is discussed based on fractal geometry analysis.The single fractal and multi-fractal is studied in the application of knock detection.The fractal box dimension and generalized dimension of different knock conditions at different time are successfully extracted.This paper proposes a signal feature extraction method based on multi-domain united technologies,including dual de-noising ability of wavelet domain bi-spectrum analysis method,highlighted characteristic of knock impact based on kurtosis criterion and EEMD-Bispectrum feature extraction method,accurate description of knock non-Gaussian ingredients intensity distribution in bispectrum image based on fractal dimension analysis method,and quantization of based on kurtosis criterion& EEMD & mathematical morphology.These methods analyze knock vibration characteristic from different domain,such as time-frequency domain,instantaneous frequency domain,dual frequency domain and mathematical morphology geometrical.Derived from the above method,knock intensity factor has been developed and the relevance of the proposed criterion for characterizing different levels of knock has been investigated.The results reveal that the new method proposed is feasible in knock feature extraction and knock detection of gasoline engine.