Investigation of tire stiffness and damping coefficients effects on automobile suspension system

In this paper, we analyzed the vibration of an automobile suspension system. The influence of tire pressure and arc angle, vehicle velocity, and road impact frequency on the tire stiffness and damping coefficient was considered in this analysis. Moreover, an experimental formula for tire damping coefficient based on automobile velocity and impact frequency was proposed. In addition, the effects of the automobile’s mass, mass moment of inertia, unsprung mass, and center of gravity on the amplitude and period of vibration were investigated. The body was considered rigid, and the tires and other unsprung-loaded accessories were particles of a four-degree-of-freedom system. The equations of motions were solved by the analytical Laplace transform method and validated using Runge-Kutta numerical method. Based on outcomes for an initial displace of the front axle, increasing the tire pressure from 0.2 to 0.8 MPa leads to a 40% increase and 70% decrease in front and rear axles, and declining tire arc angle from 50° to 30° increases the maximum displacement of the front axle by 13% and halves the period. Different excitation frequency values (5, 10, 50, and 100 Hz) were applied to the system, which produced a 31%, 8%, and 9% rise in amplitudes. We understood that the tire damping coefficient decreases on a logarithmic scale for an automobile with a speed between 1 and 25 m/s. Furthermore, alternation in mass does not affect body rotation, and the alternation of mass moment of inertia does not influence body displacement significantly.