Effects of Kingpin Inclination and Caster Angle on Kinematics and Lateral Dynamics of Long Wheelbase School Bus

Camber angle of steered wheels varies with steering angle as a function of the kingpin inclination angle (KPIA) and caster angle. Thus, the aim of the study herein was to understand the possibility of control of KPIA and caster angle and thus also control camber angle during turn. Hence a detailed study has been done to evaluate the effects of KPIA and caster angle on kinematics and lateral dynamics of the school bus. TruckSim® simulation tool has been used to carry out a simulation study on an 8.5 tonne 6.45 m wheelbase bus model. This open loop study was done to evaluate individual and combined effects of the aforementioned input variables on camber angle which directly influences the kinematic and dynamic response of the bus. Thus, for both KPIA and caster angle variation, handling response metrics were studied for three different manoeuvres, namely straight path driving, steady-state circles and double lane change. The handling response metrics which were analysed include radius of turn, tyre side-slip angles, body slip angle, steering effort as well as aligning moments and forces at tyre road contact. Furthermore, the effect on understeer gradient was evaluated to understand the variation in handling behaviour of the bus with respect to changes in input variables. To determine the effects of caster angle and kingpin inclination angle on the above-mentioned handling metrics, the design of experiments (DOE) has been carried out. A full factorial DOE for a 2-variable (caster angle and KPIA) and 5-level simulation was done to understand the trend of the output parameters. Validation of the results from this work has been done against work presented in the literature. Thus, the outcome of the work helps in assessing the sensitivity of handling response metrics to the input variables discussed here.