A Research Of Automobile Engine Misfire Fault Diagnosis Based On Crankshaft Speed

With the development of automobile industry and the improvement of people’s livingstandard, the amount of the automobile in society is increasing year by year. The automobileindustry has not only promoted the society development but also made our personal lifemore convenient, simultaneously the exhaust emissions cause the environment pollution, somore and more people focus on the environment problem. Therefore the emission controland fault diagnosis of automobile have highlighted more important significance. In order tomonitor the running state of the engine and exhaust gas treatment system, the OBD systemwas invented by foreigners in the last century80’s, and China has successively promulgatedrelevant laws and regulations after learning this technology.In the thesis I analyzed the reason of engine misfire fault, point out the importance ofthe engine fault diagnosis, and analyze the influences of the misfire fault on the crankshafttorque and the crankshaft speed. The four cylinder engine is the research object. when engineload changes, road ups and downs lead to automobile load changes, to design of the misfirefault diagnosis system, ensure engine misfire fault can be timely detected. The core of thefault diagnosis system is the sliding mode observer. It used the method of the sliding modevariable structure control theory. This method has strong robustness to the parametervariation and the system perturbation.The design of engine misfire fault diagnosis system is divided into three steps: first,design the sliding mode observer base on the numerical model of the engine, according tothe crankshaft speed estimate the crankshaft torque, and analyzed the stability of the slidingmode observer; secondly, analyzed the spectrum of the estimated crankshaft speed anddesign of Butterworth low pass filter; At last, the fault diagnosis logic was designed, theestimated torque and the speed deviation was inputted to the fault diagnosis logic.In AMESim established four cylinder engine physical model, to simulate the change ofengine throttle, load variations, the misfire fault and other conditions, access the data of thecrankshaft speed in these conditions. To detect the misfire fault in Simulink.Simulation in MATLAB/Simulink and AMESim, had detected the pre-set misfire faultcorrectly. Verified the effectiveness of the misfire fault diagnosis system designed based onsliding mode observer and Butterworth filter.