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.

Friction of a MacPherson suspension system at various load cases

“…In the suspension design of modern MacPherson systems specialized springs, so-called side load springs, are frequently used to compensate the shear force partially or even completely, as demonstrated by (Frendo et al, 2006;Gotoh and Imaizumi, 2000;Hamano et al, 2001;Liu et al, 2008;Wünsche et al, 1994). (Deubel et al, 2022) present the compensating effect of the coil spring used in the vehicle of this study, which primarily consists of a deflectiondependent force F c, y in the lateral direction of the vehicle and thus in the plane of Figure 1(a). Consequently, the effective shear force F s, e is simply expressed as…”

“…In consequence, the shock absorber eventually is subject to shear forces and bending (Deubel et al, 2022). According to (Lizarraga et al, 2008), the friction in the shock absorber may be greatly influenced by the shear force.…”

“…Alternatively, the shock absorber’s perpendicular load can more accurately be calculated using a multi-body simulation, taking into account the third dimension.In the suspension design of modern MacPherson systems specialized springs, so-called side load springs, are frequently used to compensate the shear force partially or even completely, as demonstrated by (Frendo et al, 2006; Gotoh and Imaizumi, 2000; Hamano et al, 2001; Liu et al, 2008; Wünsche et al, 1994). (Deubel et al, 2022) present the compensating effect of the coil spring used in the vehicle of this study, which primarily consists of a deflection-dependent force normalFc,y in the lateral direction of the vehicle and thus in the plane of Figure 1(a). Consequently, the effective shear force normalFs,e is simply expressed asFinally, from Figure 1(b), neglecting any spring moments, the inner normal contact forces can be calculated at the piston rod bearing normalFi,1 and at the piston normalFi,2.…”

“…The compensating spring force increases only degressively as shown in Figure 9(a), owed to a general saturation of the spring’s lateral force. Furthermore, the increasing angle between the top mount and the shock absorber (from slightly negative to more positive) weakens the spring’s lateral force increase (Deubel et al, 2022). Therefore, theoretically the effective shear force increases progressively.…”

Strength analysis and structural improvement of the connection between rear shock absorber support and frame of a city bus based on Hypermesh

“…The shock absorbers and supports connected to the axle not only bear the weight of various components installed on the bus frame but also suppress the repeated bouncing of the shock absorption spring after absorbing various impacts brought by the road surface to accelerate the attenuation of the spring's natural vibration. Therefore, its reliability is not only related to the normal operation of the entire vehicle but also to the safety of the vehicle [1] .…”