Reliability-based design optimisation of vehicle drivetrain dynamic performance

A vehicle drivetrain is designed to meet specific vehicle performance criteria, which usually involve trade-offs among conflicting performance measures. This paper describes a methodology to optimise the drivetrain design including the axle ratio, transmission shift points and transmission shift ratios considering uncertainty. A complete vehicle dynamic model is developed using the bond graph method. The model includes the vehicle, engine, transmission, torque converter, driveline and transmission controller. An equivalent MATLAB Simulink model performs the non-linear dynamic analysis. In order to reduce the computational effort, a time-dependent metamodel is developed based on principal component analysis using singular value decomposition. The optimisation is performed using both the Simulink vehicle dynamic model and the metamodel. A deterministic optimisation first determines the optimum design in terms of fuel economy, without considering variations or uncertainties. Subsequently, a reliability-based design optimisation determines the optimum design under uncertainty. A vehicle example illustrates the design methodology.