Investigation of damping properties of telescopic shock absorber and its rubber mounts in frequency range 50-150 Hz

Abstract

The pneumatic tyre is excited by the road unevenness at a frequency close to its first radial mode for the speeds of 50-60 km•h-1. The first resonance of the belt of a radial-type pneumatic tyre has a frequency about 100 Hz. These oscillations are associated with amplitudes of displacement less than 1 mm. The vibrations at the resonance frequency go through the suspension elements and reach the vehicle body without noticeably reducing their amplitude. These high frequency vibrations have a major role in the vibro-acoustic comfort in the passenger compartment of a vehicle. The telescopic shock absorber is one of the suspension components. In the frequency range up to 20 Hz, it has a fundamental role in damping the oscillations generated by the road unevenness. In the frequency range of the natural modes of both sprung and unsprung masses (0.9-12 Hz), the displacements between both ends of a shock absorber are over 5 mm. High-frequency vibrations with an amplitude less than 1 mm do not activate the shock absorber damping properties. The amplitudes are not big enough to create the necessary pressure drop between the two chambers above and under the piston and to provide viscous damping. Other elements that have an influence on damping vibrations with frequencies above 50 Hz are the rubber mounts of the shock absorber. The work explores the behaviour of a telescopic shock absorber and its rubber mounts in the frequency domain determined by the resonances of the pneumatic tyre belt. A method for obtaining the damping coefficient of the rubber mounts for the shock absorberis presented. The purpose of the work is to determine the influence of the damping properties of the shock absorber and its rubber mounts on the vibrational behaviour of the suspension in the frequency range 50-150 Hz. The results of the work can be used to select a proper shock absorber and its rubber mounts, in order to improve the vibro-acoustic comfort of the passenger compartment.