The Effect of Stiffness and Damping of the Suspension System Elements on the Optimisation of the Vibrational Behaviour of a Bus

The effects of spring stiffness and shock absorber damping on the vertical acceleration of the driver’s body, suspension deformation and dynamic wheel load were investigated, with the purpose to define recommendations for selecting oscillation parameters while designing the suspension system of a (intercity) bus. Oscillatory responses were analysed by means of a bus oscillatory model with linear characteristics and three degrees of freedom, with excitation by the Power Spectral Density (PSD) of the roughness of asphalt-concrete pavement in good condition. The analysis was conducted through a simulation, in frequency domain, using statistical dynamics equations. A programme created in the software pack MATLAB was used to analyse the transfer functions, spectral density and RMS of oscillatory parameters. The results of the analysis show that the parameters which ensured good oscillatory comfort of the driver were conflicting with the parameters which ensured the greatest stability of the bus and the corresponding wheel travel. In terms of the driver’s oscillatory comfort, the bus suspension system should have a spring of small stiffness and a shock absorber with a low damping coefficient. In terms of active safety, it should have a spring of small stiffness and a shock absorber with a high damping coefficient, while minimum wheel motion requests for springs of great stiffness and shock absorbers with a high damping coefficient.