Abstract
A concept for an fuel efficient engine drivetrain control system that can attain fewer exhaust emissions and higher fuel economy was investigated. The system integrates a lean burn engine, an electric machine for power assist, and an electronically controlled synchromesh gear transmission or a power shift transmission with centrifugal force clutch. Driving modes, smooth switching of the power source, the air-fuel ratio and torque control during gear shift were analyzed for their ability to cut exhaust emissions and improve fuel economy.