Air-Charge Estimation for Variable Cam Timing Engines

摘要

Because of the time delay between fuel injection and the air-fuel ratio measurement by the exhaust oxygen sensor, transient accuracy of the air-fuel ratio regulation system significantly depends on the feedforward component, that is, on cylinder air-charage estimation. For this reason, the topic of air-charge estimation has attracted continued attention in powertrain control system design. Variable cam timing introduces an additional challenge due to the speed with which engine pumping coefficients change and, in some cases, due to unmeasured back-flow of the exhaust gas into the intake manifold. The objective of this paper is to illuminate some of these issues and suggest new algorithmic solutions to air-charge estimation problems.