VIBRATION ANALYSIS OF A MACPHERSON TYPE SUSPENSION SYSTEM

The road surface disturbs the pneumatic tyre in the contact patch with different frequencies. The disturbing frequency depends on the speed of the vehicle and the wavelength of the road irregularities. In the current study, the propagation of the vibrations created at the contact patch through the suspension is presented. The oscillations are transmitted to the car body through the rubber mounts and the support joints. When these vibrations reach body panels (roof and floor panels, windows, etc.), they are transmitted to the air and, thus, the structure-borne noise in the passenger compartment is created. The structure-borne noise defines the vehicle comfort for the frequency range up to 400 Hz. The main task of noise, vibration, and harshness engineers is to avoid coupling between tyre and chassis elements’ natural modes, which significantly increases the level of structural noise in the passenger compartment. The accelerations of the oscillations were measured for different points of the suspension and the car body. The measurements were taken for two sets of tyres (summer and winter) of the same size and mounted on the same rims. The disturbing frequency was in the range of the tyre’s natural modes. The results for the two sets of tyres were compared. The measurements were taken for different air pressure in them. This comparison shows the effect of the tyre type on the structure-borne propagation and determines whether increased noise levels are due to the resonance of the tyre or a suspension element. In addition, a finite element analysis (FEA) was conducted. The model points out the exact element responsible for the high levels of vibrations. Thus, the coupling between the tyre and suspension natural modes can be avoided.