Vehicle Performance Simulation and Optimization Including Tire Slip

A dynamic simulation has been developed to predict the acceleration of a manual-transmission vehicle at wide-open throttle. A notable feature of the model is that tire slip is included, and the coefficient of friction varies with slip. This allows the simulation to start from zero vehicle speed and include the dynamics of gear shifting. The model was used in optimization studies for 3-speed, 4-speed, and 5-speed transmissions which indicated that fastest times, for the vehicle studied, are obtained when the mass center is as close to the drive axle as possible, and gear ratios are selected so that the engine speed brackets the horsepower peak. Also, optimal gear ratios deviate slightly from a geometric progression by closer spacing in higher gears and wider spacing in low gears, a common practice in gear box design.