Study on AFR Control for a PFI Air-Cooled Motorcycle Engine

Abstract

For PFI (Port Fuel Injection) SI engine, accurate AFR (Air-fuel Ratio) control would keep TWC (Three-Way Catalyst) work in high efficiency range to achieve low pollutants emission. For ZS157FMI-3 motorcycle engine equipped with ZH600 ECS (Electronic Control System), a control strategy with close-loop feedback mode and feed-forward mode was designed for transient, quasi-steady and steady work states. One switching oxygen sensor was installed to form the close loop for quasi-steady and steady work states, and feed-forward control strategy based on a simplified fuel-film model was implemented to cope with transient AFR control. TP (Throttle Position) change rates were selected to be the determinant of which AFR control mode should be activated. For the validation of the control methods, bench tests were carried out in three typical work procedures. The results showed that AFR values of close-loop were close to stoichiometric one with relative error below 3%. AFR in acceleration or deceleration process may exhibit slight fluctuations, but the crest would be eliminated immediately. It concluded that the strategy designed in the study is able to cope with AFR control on variety of operation conditions for the experimental engine.