Design And Implementation Of Engine Knock Control System Based On Wavelet Transform

With the continuous development of the automobile electronic technology,knock control technology in automotive engine control system application gradually becomes to the standard configuration from the previous high-grade car.Although the engine controllers has been used to do a series of calibration experiment(including the ignition advance angle calibration)in the factory,The reasons such as aging of the engine,carbon increasing in cylinders,spark plug ignition performance degradation,will affect the engine performance,and may lead to engine knock occurrence so as to reduce the output torque,power loss and bad emission,even damage the engine if seriously.Therefore,knock control is particularly important.At present,there are many researches and implementation ways about knock control.On the market,the special chip for knock sensor signal are used in engine controllers.The method is low-cost but requires a lot of threshold calibration work.FPGA and DSP are also used in some studies,but it costs too much.This paper solves these problems by using cheap MCU STM32F103 with wavelet transform,which has great abilities in signal analysis field.The knock control system will be realized based on wavelet transform.The control strategy software will be developed based on model and Simulink.Through the analysis and comparison of the current research situation of the domestic and foreign research on the knock control system,this paper has worked out the basic development routes as follows.First of all,the knock signal test system has been built by use of the engine control unit(ECU)developed independently,engine test bed and dynamometer.The knock signals happened and non-happened are collected to study the engine knock mechanism and analysis the signal frequency spectrum.Secondly,the wavelet filter is designed to obtain knock characteristic signal on the basis of studying the wavelet theory and Mallat wavelet fast algorithm,which will be analyzed to obtain the knock determination index combined with the relative energy determination method of knock signal.Thirdly,the knock controller hardware system is constructed by STM32 micro controller,the software of which is implemented by building knock control model in Simulink according to the wavelet filtering and the knock determination method researched before.Then a fixed-point processing will be done to improve the efficiency of the code.The target file system and embedded code template file are configured for code generation.The code generated will be run on the target hardware system and be analyzed for real-time;Finally,the knock controller is experimented combined with the engine controller(ECU)to verify its function.As a result,through experimental verification,the knock controller can control the ignition advance angle in detonation critical region,which can effectively eliminate the Knock phenomenon by adjusting ignition advance angle when it occurs.At the same time,the output power and torque of the engine can reach the maximum.