Intrinsic Performance Limitations of Torque Generation in a Turbocharged Gasoline Engine

Abstract

The main control variable for combustion engines is the generated torque, as it has to follow the driver’s desire. For turbocharged gasoline engines, the torque generation is directly related to the air charge in the cylinder, since for emission reduction a stoichiometric ratio of fuel and air has to be met. However, controlling the air charge by the actuators in the air path, an inverse response behavior of the torque may be observed. This indicates an unstable zero dynamics or non-minimum phase behavior of the system. Plants with unstable zero dynamics impose limitations in achievable control performance and many control methods are not applicable. Therefore, a semi-physical mean value model of the engine is investigated to determine the existence and stability of zero dynamics and the consequences for control.