Simulation For Air-Fuel Ratio Control Of Electronic Controlled Gasoline Engine

Rapid development of electronic and control technology applied to the engine controlsystem more and more, so that the engine development towards to the goal of power andenergy-saving. Increasingly stringent emission regulations put forward higher requirementsfor the engine control system, and improve the air-fuel ratio control accuracy is the key linkto improve the engine power, fuel economy and reduce exhaust pollution.Based on the theory of mean value engine model, we establish a inlet channelsub-model and a fuel evaporation sub-model. The inlet channel sub-model was verified byusing with the si_s4engine model which provided by en-DYNA engine dynamicssimulation software; The dynamic characteristics of the fuel evaporation sub-model wassimulated and analyzed, and illustrates the need for compensation on the dynamiccharacteristics of the fuel transfer when the engine is in the acceleration and decelerationoperating, and set up the fuel transfer dynamic characteristics compensator. Lastly, thedynamic characteristics compensator with good results is verified by simulation.In our study, the target is that the air-fuel ratio to be the theoretical air-fuel ratio whenengine is in stable conditions and transitional conditions. For the stable conditions, theair-fuel ratio open-loop control method was given firstly, but it requires the high accuracy ofequipment and be vulnerably disturbed, so we used the oxygen sensor to control the actualair-fuel ratio based on the PID closed-loop feedback.To the transition conditions, the accurately predict the gas flow is the key to preciselycontrol the air-fuel ratio, and the prediction of intake air was via the inlet pressureprediction. So we focused on the inlet pressure prediction algorithm, and improved the inletpressure prediction algorithm of some relevant literature, and proposed a variation of inletpressure range forecast prediction algorithm. The algorithm can adjust forecast range by theengine speed, the forecast range is far at low speed, in order to improve the accuracy of theprediction; forecast range is near at high speed, in order to ensure the engine ECU hasenough time for the calculation of the prediction algorithm. The simulation results show that the inlet pressure prediction algorithm has higher precision, so the inlet pressure to predictthe value of the predictive cycle gas mass value also with high precision, and use the targetair-fuel ratio to calculate the fuel injection quantity and compensate fuel transmissiondynamic characteristics, in order to achieve the accurate air-fuel ratio control in thiscondition.This study is not to describe the variety of air-fuel ratio control methods, but to studythe air-fuel ratio control algorithm for the purpose of practical application, and give arigorous derivation and validation to the algorithms, so this study can give reference to theair-fuel ratio control development of engine ECU’s software.