Development of semi-active suspension for Formula SAE vehicle 2018-36-0224
The design of passive suspension systems is being improved since the early days of the automotive industry in order to obtain the best tradeoff between ride comfort and handling. In this context, passenger cars tend to prioritise ride comfort whilst racing cars tend to focus on handling. On the other hand, Formula SAE is a series of undergraduate competitions in which the students design, build and compete with small, formula-style, mono-seated vehicles. As part of the competition events, the vehicle experiences tight corners and short-length slaloms. The minimum turning diameter and the shortest length of slalom period conducted by Formula SAE prototypes are 9 m and 7.6 m, respectively. Therefore, high controllability of vehicle dynamic behaviour is required in order to enhance the cornering speed, this is achievable by working on the dampers to optimise the rates of load transfer in cornering. This paper describes the development of semiactive control algorithms to optimise the handling performance of a Formula SAE vehicle by reducing the non-suspended mass displacements and tyre load variations, which are meant to be implemented utilising magnetorheological dampers. A magnetorheological fluid is usually described as a functional fluid whose effective viscosity can be dramatically varied reversibly by submitting it to the presence of a magnetic field. The control algorithms (groundhook two-state and groundhook linear) have been developed in MATLAB/Simulink. The full-vehicle multibody models have been implemented in MSC ADAMS/Car. The control and mechanical systems have been afterwards co-simulated in order to evaluate the effectiveness of the control approaches over the vehicle overall performance through single lane-change and swept-sine steer manoeuvres. The influence of the groundhook linear tuning parameter was also studied. The metrics for ride comfort and handling considered were RMS chassis vertical acceleration and RMS tyre vertical displacement, respectively. The outcomes of the present work have shown that for a tuning parameter of 0.6 the best handling performance is achieved whilst for a tuning parameter of 0.8 the best trade-off between handling and ride comfort is achieved. Additionally, it could be concluded that both semi-active suspensions present better performance than the passive one concerning handling and ride comfort. However, the groundhook two-state algorithm achieved an overall better compromise when submitted to different manoeuvres and can be considered more suitable to Formula SAE vehicles.