Research On Control Strategy For Transient Air-fuel Ratio Of Exhaust Gas Dilution CAI Gasoline Engine

The exhaust gas dilution CAI can improve fuel economy and achieve low NOx emission level, thus it draws wide attention from the field of internal combustion engine. A way to realize the exhaust gas dilution CAI is that adjusting the exhaust gas though negative valve overlap by adjustment mechanism. In IVO timing, the residual gas which is recompressed by the piston can lead to intake backflow. Furthermore, this combustion technology is sensitive to boundary conditions and its air-fuel ratio can be affected by the disturbance easily in transient conditions.In transient conditions, the key points to realize the effective control for transient AFR are the acquisition of in-cylinder air charge and effective feedback control method. This paper proposes a control method which combines dynamic intake observer with active disturbance rejection control(ADRC). The observer can online estimate the certainty part of the intake by physical modeling. The intake backflow model is added to the intake manifold dynamic model to design the intake observer. Then the dynamic characteristics of the temperature and pressure are analyzed. The simulation results show that the observer realizes an accurate track to the volumetric efficiency and can be easily transplanted to different engines. For the feedback aspect, ADRC contains two parts: a basic control method and a linear extended state observer(ESO). The deviation of intake model, fuel dynamic and other external disturbance can be equivalent to the total disturbance and be estimated by the ESO. The basic control method can compensate the total disturbance in the input port to reject the disturbance.A LTC engine experimental platform is built to test the control result of this algorithm. It is also compared with the traditional static feedforward and PID feedback method. The transient conditions can be represented by the variation of ETC and VVT in both idle and constant speed conditions. Experimental results show that this method can reduce the overshoot and realize fast stabilization for AFR in transient conditions compared with static feedforward and PID feedback method. So this method shows more advantage in controlling the transient AFR.