Experimental characterization and numerical modelling of an innovative hydropneumatic suspension system

Today most of the vehicles are equipped with a suspension system to guarantee a good comfort level while providing enough handling capability. All the suspension systems where a shock absorber and a spring are employed are subjected to the well known "ride-handling compromise", since comfort and handling require opposite settings of the suspension parameters. This thesis deals with an innovative suspension system, the AirTender, that allows to overcome this compromise thanks to the introduction of an hydropneumatic spring in series to a coil spring into the original suspension structure. Thanks to the two springs working in series a dynamic change of the equivalent spring rate during the shock absorber travel is obtained. The main aim of this thesis is to develop a mathematical model capable to capture the fundamental dynamics of the AirTender system in order to be able to study the way it works under different initial conditions and to study the changes of the main physical parameters. Furthermore, focusing on the implementation of the system on a Honda CRF 1000 motorcycle, this thesis also wants to investigate the effects of the AirTender on the vehicle dynamics. The research work started with an experimental test campaign aimed at the characterization of the shock absorber installed on the motorbike and of the AirTender system, to get all the data needed to study the system and to develop the mathematical model. Indeed some parameters of the model cannot be directly computed and they need to be estimated from the experimental data. The physical model of the AirTender suspension system has been then developed starting from the fundamental equations describing the coil and hydropneumatic spring behaviour and comparing the numerical simulations to the experimental data, leading in the end to the development of a linear model able to represent the AirTender dynamics with a good accuracy.