Preliminary investigation of dilution strategies to control engine torque during transient events

A continuously variable transmission (CVT) allows a powertrain controller the freedom to develop a required output power at a range of engine torque and speed conditions. This flexibility can be used to maximise fuel efficiency. Due to low frictional and pumping losses a gasoline engine's fuel efficiency is maximised at low speed, high torque conditions. However due to the reduced torque margin available, controlling a gasoline engine in this region compromises transient vehicle response. Dilution torque control, using EGR or lean burn, has the potential to maintain the economy gains available using a CVT powertrain whilst improving a vehicle's driveability. This paper introduces preliminary work that has been undertaken to investigate the potential of charge dilution to control steady state engine torque. A test rig has been developed based around an engine fitted with variable cam phasing and an external EGR system. The paper contains a discussion of initial results of a lean dilution test program used to demonstrate the principle