Disturbance rejection in SI engines with variable cam timing

Variable cam timing (VCT) systems in SI engines are being used to reduce the emissions, increase the peak torque, and improve fuel economy. However, cam timing transients introduce variations in the cylinder air charge which negatively affects drivability and emissions. In this paper we present an analysis of the problem and propose a nonlinear controller which reduces the effect of variable cam timing on cylinder air charge. The compensation improves drivability, and, because a more aggressive cam timing schedule can be used, may lead to improved fuel efficiency and reduced emissions