A SIMULATION-MODEL OF A CHASSIS DYNAMOMETER - MODEL DEVELOPMENT AND CYCLES APPLICATION

An appropriate chassis dynamometer simulation of an actual vehicle roa d load is essential if a realistic emissions assessment is to be obtai ned. This requires a full understanding of the effects of actual road load parameters and the factors associated with their determination, a s well as an accurate model to predict the dynamometer dissipated powe r at each vehicle speed of the testing cycle. In this study, details o f the model which predicts the performance of an emissions testing fac ility are described. The model, based on a combination of fundamental energy balance relations and calibration data, includes predictions of the dissipated energy of the system's main components. This energy is mainly attributed to friction rubbing between mating parts and pumpin g losses. A quadratic least square fit for dissipated torque measured at different steady-speed calibration tests is provided, and the physi cal meaning of each term is discussed. Employing the lumped thermal ca pacitance method, the subsystems' temperature profiles are predicted. The developed model is made to simulate the dynamometer's performance during selected driving test cycles. Cycles are categorized as either being actual or synthesized after an evaluation of their events. A sca le of fourteen parameters has been used to characterize each of the se lected test cycles. Results of the simulation are pesented, which incl ude the total energy consumed, flywheel wall shear losses, power absor ber blower pumping work, the rubbing losses of the dynamometer main co mponents, and predictions of the temperature history for each subsyste m. The effect of the tested vehicle weight on the dynamometer's perfor mance is also investigated.