Research On Air Fuel Ratio Control Of Engine Based On MAP Self-calibration

Extended-range engine is a key component of series hybrid power system.In order to achieve good economy,power performance and emission characteristics,the air-fuel ratio system of engine needs to be further studied to achieve the optimal control of air-fuel ratio.Vehicle engines often run under various working conditions,and their air-fuel ratio system has the characteristics of nonlinearity,time variation and time delay,which will bring difficulties to the modeling of the system,thereby affecting the control effect of air-fuel ratio,so it is of great significance to study the control strategy considering the characteristics of the air-fuel ratio system.Aiming at the air-fuel ratio control of BMW F800 GS engine,the relevant intake estimation algorithm is designed and the extended range engine test bench is built.Then,the air-fuel ratio system of the engine is modeled,and the air-fuel ratio controller is designed based on the feedback linearization control method,so that the air-fuel ratio of the engine can be stabilized at the target value through the intake estimation algorithm and air-fuel ratio controller.Finally,the effectiveness of the intake estimation algorithm,air-fuel ratio system modeling and air-fuel ratio controller is verified by experiments.The research work of this paper mainly includes the following aspects:Firstly,aiming at the engine intake estimation,the main reasons for the poor accuracy of intake estimation are the effect of throttle charging and exhaust and the nonlinearity of intake system.In order to improve the accuracy of intake estimation,a map self-learning engine intake estimation algorithm is designed.Firstly,the timevarying volumetric efficiency related to engine working conditions is described as a map table related to engine speed and intake pressure to achieve local linearization of the nonlinear model of the intake system.Secondly,the piecewise bilinear interpolation algorithm is used to calculate the volume efficiency,and the adaptive observer is combined to estimate the system state and volume efficiency in real time,and the convergence of the observer is proved.Finally,the engine intake flow is estimated by the velocity density model.Secondly,the modeling of air-fuel ratio system is studied.Considering that the air-fuel ratio system has time-varying nonlinear characteristics,and the time-varying characteristics of the wet wall effect are the most obvious,this paper adopts recursive least square method to identify the parameters of the wet wall model online.Then,considering that the actual air-fuel ratio system is affected by a large number of disturbances,an extended state observer is designed to estimate the modeling errors of the system,and the real-time model of the air-fuel ratio system can be obtained.Based on the above research,this paper proposes a control strategy of air-fuel ratio system based on feedback linearization control method.Finally,an intake estimation experiment is designed on the experimental bench under transient conditions of the engine,and the convergence of the observer is ensured by adjusting the parameters of the control algorithm online.Experimental results show that the observer can estimate the system state and volumetric efficiency in real time,and verify that the proposed algorithm can improve the intake estimation accuracy of the engine system under transient engine conditions.Then the model verification experiment of engine air-fuel ratio system is designed,and the accuracy of the model is verified by changing the throttle angle and changing the fuel injection pulse width.Finally,two sets of air-fuel ratio control experiments are designed,respectively changing the target air-fuel ratio in the case of fixed throttle and changing the throttle angle in the case of fixed target air-fuel ratio.The experimental results show that the air-fuel ratio control method proposed in this paper is effective.