energies Article Intake Air Mass Observer Design Based on Extended Kalman Filter for Air-Fuel Ratio Control on SI Engine Lei Meng , Jie Luo, Xu Yang * and Chunnian Zeng * School of Automation, Wuhan University of Technology, Wuhan 430070, China * Correspondence: [email protected] (X.Y.); [email protected] (C.Z.) Received: 13 August 2019; Accepted: 3 September 2019; Published: 6 September 2019 Abstract: Air-fuel ratio (AFR) control is important for the exhaust emission reduction while using the three-way catalytic converter in the spark ignition (SI) engine. However, the transient cylinder air mass is unable to acquire by sensors directly and it may limit the accuracy of AFR control. The complex engine dynamics and working conditions make the intake air estimation a challenge work. In this paper, a novelty design of intake air observer is investigated for the port-injected SI engine. The intake air dynamical modeling and the parameter fitting have been carried out in detail. Extended Kalman Filter (EKF) has been used to optimize the instantaneous cylinder charge estimation and minimize the effort of pump gas fluctuation, random noise, and measurement noise. The experiment validation has been conducted to verify the effectiveness of the proposed method. Keywords: intake air mass observer; Extended Kalman Filter; air-fuel ratio control; SI engine 1. Introduction The spark ignition (SI) engine emission is reduced by using the three-way catalytic converter (TWC) based on electronic fuel injection control to meet the strict emission requirements. However, the conversion efficiency of TWC depends on the engine air-fuel ratio (AFR) significantly. The maximum converter efficiency and fuel economy could be guaranteed by regulating the AFR at a very narrow band around the stoichiometric value. One of the important practical aspects for the accurate AFR control is the correct intake air mass estimation in the engine cylinder [1]. However, the transient cylinder air mass is difficult to measure by sensors, due to the intake manifold dynamics. Practically, there are two kinds of method for the intake air measurement on production engines. Using the mass air flow (MAF) sensor that was installed before the throttle can directly measure the mass flow entering the intake system, but the result has a tremendous error against the actual cylinder air mass under the transient state. The other method is using the manifold air pressure (MAP) sensor to calculate the cylinder air mass based on the speed-density approach, which is widely used on the existing engine control system, has a faster response time, and costs less. Both of the technical methods mentioned above could not directly acquire the instant cylinder air mass. In addition, the complex engine working conditions and tremendous measurement noise make the cylinder air mass estimation a challenging task and have captured enormous attention recently. On the production engine management system, the intake air mass estimation is based on the well-calibrated look-up tables at different engine operating states. However, the dramatic change of intake dynamics and parameter varying makes a challenging problem for the traditional air estimation. Many approaches have been proposed in the literature on the air charge estimation to improve the accuracy at both the transient and steady state [2,3]. Hendricks [4] has emphasized that the pressure transducer response time existed and it was impossible to follow rather slow throttle angle transients and proposed the necessary of intake air observer to eliminate the sensor response characteristic. 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FigureFigure 1.1. StructureStructure ofof thethe SISI engineengine airair path.path. EnergiesEnergies 20192019, 11, ,12 x ,FOR 3444 PEER REVIEW 3 of3 12 of 12 However, the cylinder air mass, which is controlled by the inlet and outlet valves, is difficult to However, the cylinder air