Offset Prediction of an Asymmetric Force Damper on Harmonic Base Excitation Isolation System

Abstract

An asymmetric force damper, commonly known as a dual-rate shock absorber, is basically designed to improve ride-comfort quality of the vehicles. The damping forces for extension and compression direction are not equal. In general, the damping force for compression is much less than that for extension. This is to absorb immediate shock caused by road input during the compression stroke and to prevent the car body or isolated mass from oscillating during the extension stroke. However, the asymmetric force damper can be found in the application of the harmonic base excitation isolation systems. This is because the damper can be easily found commercially. Such the applications, the isolated mass will be shifted and oscillating about a new equilibrium position. This occurrence may cause failure to other connected component due to misalignment. This study focuses on seeking simply analytical method in order to predict the level of offset resulting from the difference of damping forces. The analytically predicted offset is compared to the that obtained using numerical simulation. The results are all in good agreement. It found that the greater in the difference of damping force as well as the higher excitation frequency cause the greater level of offset. This information can be used prior the decision in using the automotive shock absorber in the harmonically base excited vibration isolation.