Study On Gasoline Engine Transient Air-Fuel Ratio Based On Fuzzy Sliding Mode Control

The birth of the car not only brings convenience to people,but also lead to the resources and environmental problems.In recent years,the environmental problems have become more and more serious and the petrochemical resources have been reduced drastically,so the calls for energy saving and emission reduction are getting increasingly strong.The three-way catalytic conversion technology can convert the harmful components of exhaust gas into harmless gas by redox reaction,and is still the main technology for purifying automobile exhaust gas today.However,the exhaust gas purification efficiency of the three-way catalytic converter is affected by the air-fuel ratio of the engine.Relevant studies show that the purification efficiency of the three-way catalytic converter can be optimized only when the air-fuel ratio of the engine remains close to the theoretical value.Therefore,the precise control of the air-fuel ratio of the engine,especially under transient conditions,has become the key to achieving energy-saving and emission reduction of the gasoline engine.Under this background,the investigations the transient air-fuel ratio control strategy for gasoline engine are carried out.The main highlights of this paper are as follows:Firstly,the air intake model and fuel dynamic model are established according to the mean model of the engine,and the engine simulation model is built in Simulink.Secondly,the fuel injection of engine is divided into the basic fuel injection and compensated fuel injection.In order to obtain the air flow and the basic fuel injection,the method of Unscented Kalman Filter(UKF)is used to design an air flow observer.In addition,to obtain the compensated fuel injection,the sliding mode surface and control rate are designed using the sliding mode control algorithm(SMC).At the same time,the buffeting of SMC is reduced using fuzzy control algorithm to calculate the switching gain of sliding mode control rate,then the model of compensated fuel injection based on fuzzy-SMC control algorithm is established.Finally,the control strategy for the transient air fuel ratio of the engine is put forward by combining the air flow observer,the fuel injection compensator and the engine model.The simulation model of the transient air fuel ratio is built in Simulink and the results are discussed by comparing with other control strategies.The results show that the output buffeting problem of SMC is effectively suppressed by combining the fuzzy and SMC control algorithm.Moreover,with the discussion of the simulation results,it can be seen that the transient air fuel ratio under the fuzzy sliding mode control strategy are very close to the theoretical value,which verifies the superiority of the transient air fuel ratio control strategy proposed in this thesis.