Study of dynamic modelling and stability of passenger cars

Vibration in automobiles is very undesirable as it causes discomfort to the vehicle occupants and can also lead to fatigue and failure of the vehicle. Therefore, study and analysis of vehicle suspension dynamics has been an integral part of automobile research ever since the invention of automobiles. Vehicle vibration is related to the passenger comfort, safety and vehicle stability. Many researchers have analysed vehicle vibration by considering various models like quarter car, half car and full car models with different types of excitation. In continuation, this research investigates the responses of the quarter car and a half car model as the vehicle ride performance is generally assessed at the design stage by simulating the vehicle response to road excitation. This requires the development of a vehicle model to analysis their responses. The disturbances from the road are assumed to be constant or step function and the time responses and frequency responses of the sprung and unsprung masses have been studied. Simple yet, in practice, meaningful state-space formulations of the optimal suspension control problem for a half-car 2-DOF and 4-DOF vehicle models are given. Using an efficient equivalent representation, a complete analytical solution of the system was obtained.

The problem structure and associated analytical results are used to deduce the optimal solution. The optimal solution here is the damping, which has been optimised with the given set of fixed parameters. This research provides an insight on the suspension dynamics of the two most extensively used models in vehicle dynamics with their complete state space realisation, simulated using a code developed in Matlab platform. The codes developed in this research can be used to analyse the suspension system responses to road inputs. However, accuracy of the results obtained will depend on how accurately and effectively the system parameters have been measured. An experimental validation can be done for obtaining experimental responses in real situation, as it can provide better insight on the system responses and it will be interesting to compare responses obtained in both the ways. The models can be coupled with various control technologies to check their effectiveness and also to obtain the responses with different road excitations.