Shock absorber friction testing on a MacPherson suspension considering realistic mounting situation

Abstract

Due to the specific layout of MacPherson suspension systems, the shock absorber is subject to a varying amount of load perpendicular to its own axis of displacement and is therefore generating a certain amount of friction. Especially at the presence of lateral forces at the tire contact patch, for example, in cornering situations, additional friction is generated. In order to accurately consider the actual amount of friction regarding vehicle dynamics and comfort, it is crucial to study shock absorber friction depending on the acting shear force. However, there is a shortage of knowledge considering realistic load situations of the shock absorber as present in the vehicle. Consequently, no commonly established test method exists to take the shear force into account. With the help of a static finite element analysis a test rig set-up is developed to investigate shock absorber friction replicating the suspension mounting situation. In the first step, a full suspension is transferred to a finite element model by a reverse engineering approach. Special attention is given to the spring forces, which show to be strongly multiaxial in terms of shear force reduction. Subsequently, the stress characteristics of the shock absorber tube, piston and the inner housing of the twin-tube shock absorber are investigated. Regarding various possible load cases for shock absorber testing under shear force, it becomes evident that one specific test set-up is able to reproduce the real load situation accurately. This test layout is implemented on a hydropulser test rig and allows the study of load-dependent friction characteristics.