Kinematics characteristics of unsprung mass in a double wishbone suspension based on velocity transformation

The transformation from multibody models to lumped-parameter models is a crucial aspect of vehicle dynamics research. The velocity transformation method is adopted in this research, and the suspension multibody model is described using only one degree of freedom. It is found that the equivalent mass of the system is time-dependent during the simulation process, as observed in numerical simulations. Further symbolic calculations are conducted to derive the analytical form of the equivalent mass, and the results show that once the static parameters are determined, the equivalent mass of the suspension system is determined solely by the vertical position of the suspension upright, which reveals the kinematics characteristic of the equivalent mass of the suspension system. It is found that the equivalent mass experiences smaller changes when the suspension is compressed from the middle position, but larger changes when the suspension is extended. Furthermore, by comparing the multibody model, the lumped-parameter model with static mass, and the proposed lumped-parameter model considering the kinematics characteristic of the equivalent unsprung mass, the proposed model produces simulation results that more closely match the original multibody model than the model with static mass. The improvements in accuracy can be up to 20% under certain evaluation metrics.