Optimal Suspension Damping for Improved Driver- and Road- Friendliness of Urban Buses

Dynamic interactions of urban buses with urban roads are investigated in view of the vibration environment for the driver and dynamic tire forces transmitted to the roads. The static and dynamic properties of suspension component and tires are characterized in the laboratory over a wide range of operating conditions. The measured data is used to derive nonlinear models of the suspension component, and a tire model as a function of the normal load and inflation pressure. The component models are integrated to study the vertical and roll dynamics of front and rear axles of the conventional and modern low floor designs of urban buses. The resulting nonlinear vehicle models are thoroughly validated using the fieldmeasured data on the ride vibration and tire force response of the buses. A weighted performance index is formulated on the basis of frequency-weighted vertical and roll rms accelerations due to vibration transmitted to the driver, and dynamic load coefficients due to tire forces. The influence of variations in different operating conditions, which are known to be wide for urban buses, on the performance index is investigated to identify operating factors that affect the performance most significantly. The results show that variations in suspension damping, tire pressure and road roughness, considered within specified design constraints, affect the performance most significantly. Constrained multivariable optimization techniques are used to determine optimal values of low- and high-speed rebound and compression damping to minimize the performance index. The results of the study are used to propose optimal damping properties for both front and rear axle suspensions under a wide range of variations in the passenger load.