The Research Of Air Fuel Ratio Control Strategy Based On Transient Air Charge Estimation For Gasoline Engine

Engine transient air-fuel ratio control has great and far-reaching significance for alleviating energy shortage problem and reducing emissions. Accurate estimation for transient cylinder air charge is an effective method for improving the accuracy of transient air-fuel ratio control of engine. This paper focuses on engine transient cylinder air charge estimation and air-fuel ratio control based on the estimated transient cylinder air charge.First of all, the system composition and operating principle of engine is analyzed and nonlinear mean value model for engine transient cylinder air charge estimation is constructed based on mean value engine model. The estimation model for transient cylinder air charge which includes the crankshaft rotation velocity dynamic besides the intake manifold pressure dynamic and the parameters of the model is identified by linear integral filter identification method.Secondly, air-charge estimation algorithm based on Kalman filter is proposed for the problem that transient cylinder air charge of engine cannot be measured directly, and the transient air-fuel ratio controller is designed based on the proposed air-charge estimation algorithm. Considering the influence of pumping fluctuations, the digital ?lter with nonlinear moving average is adopted. In consideration of nonlinear characteristics of engine model, unscented Kalman filter is used to estimate the system state and then cylinder air charge can be accurately estimated. Then, air-fuel ratio feedforward-feedback controller is designed based on the accurate estimated cylinder air charge. Simulation comparison in MATLAB is given between the estimation algorithm based on unscented Kalman filter with the existing estimation algorithm for the cylinder air charge in order to validate the algorithm performance. Meanwhile simulation experiments of air-fuel ratio control demonstrate effectiveness of the controller.Finally, considering the engine fuel injection delay and delay of air-fuel ratio control system, air charge prediction algorithm and air-fuel ratio controller are designed. In order to compensate the engine fuel injection delay, the kalman prediction algorithm is adopted for air charge prediction. On the basis of air charge prediction, considering the time delay existing in the air-fuel ratio model and sensor dynamic, minimum variance controller is designed to realize the accurate control of the air-fuel ratio. The simulation carried out in the condition of MATLAB demonstrate the effectiveness of the proposed prediction algorithm and controller.