Experimentally validated dynamic results of a relaxation type quarter car suspension with an adjustable damper

Models of varying degree of sophistication are used in vehicle dynamic studies. For ride comfort, Kelvin-Voigt arrangement is preferred and for impact harshness analysis, a relaxation type suspension model, Zener or Maxwell type is used. The non-consideration of relaxation type models in ride comfort studies can result in significant errors for frequencies below ~30Hz. The object of the paper is to show the influence of the series stiffness on the effective suspension damping both experimentally and numerically. A frequency domain analysis of 2- DOF Zener quarter car model is performed to find the complex relation between effective damping coefficient and the limiting value of damping ratio for a given series stiffness. The nonlinear relation between shock absorber damping and the natural frequencies is clearly illustrated. A novel four post rig setup is used to validate the results by measuring transmissibilities, giving damping ratios for varying shock absorber settings. A closed form solution, based on a simplified partial model, of optimal damping coefficient, which is a nonlinear function of stiffnesses, shows good agreement with numerical simulations of the complete system. The nonlinearities in shock absorbers also influence the outcome. These findings can be a great value at early design stage