Study of Evaluation Index Characterizing Dynamic Friction Characteristics in Shock Absorber

Abstract

The dynamic characteristics of the shock absorber, which is a component of the suspension, have a large influence on the dynamic performance such as the steering stability and riding comfort of the automobile. The damping force of the shock absorber which is the deciding factor of the exercise performance is the sum of the hydraulic damping force generated at the valve portion and the frictional force generated at the sliding portion between the piston rod and the oil seal or the piston and the cylinder. So far, it has been required to reduce friction as much as possible to the sliding parts of shock absorbers. However, recent studies have revealed that reducing friction is not necessary for improvement in the performance. When the suspension deforms, vibration damping force is generated as the piston of the shock absorber moves, but a time difference occurs before the large hydraulic damping force rises. On the other hand, the frictional force in the shock absorber is thought to play an important role in generating effective damping force against deformation of the suspension, since its generated force itself is small but its response is high. Although the frictional force in the shock absorber occurs in reciprocating motion in various speed ranges from minute amplitude of 1mm or less to large amplitude of several tens of mm, its behavior changes dynamically and complicatedly and sufficient understanding has not been advanced. Therefore, in this study, we developed a device that can measure the speed dependence of friction in reciprocating motion with high accuracy with the aim of grasping dynamic friction characteristics in shock absorber. We investigated the evaluation index for extracting the features of the dynamic friction characteristics from the measured data.