Both automakers and customers keep on pursuing better fuel economy, performance and driveability. A "mild" hybrid drivetrain is of great interest due to its potential capability on improving these targets. This drivetrain contains a spark ignition (SI) engine, an integrated starter/alternator (ISA), a torque converter (TC), a continuously variable transmission (CVT), a final drive (FD), a driveshaft, a brake-by-wire (BBW) system and wheels. While the challenge is to model and to develop an optimal control algorithm for this hybrid electric vehicle (HEV), this paper will focus only on the modeling aspect. Model-based control design and the nature of human perceptible driveability issues require low-frequency dynamic models. Therefore, a nonlinear control-oriented model which is sufficiently accurate but not excessively complicated is proposed here. Simulation results demonstrate that this model is effective to capture the main behaviors of vehicle dynamics and to evaluate fuel economy, performance and driveability objectively.
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