Investigation and Phenomenological Modeling of Degraded Twin-Tube Shock Absorbers for Oil and Gas Loss

Degraded shock absorbers have a negative effect on the safety-critical driving dynamics of passenger cars. Oil and gas loss due to leaks at the shock absorber seals are the most common degradation mechanisms of vehicle shock absorbers. This paper presents degraded twin-tube shock absorber measurement results. Eight different twin-tube shock absorbers for passenger cars were modified and measured for this purpose. Based on this analysis, a semi-physical phenomenological model is derived which can represent the properties of a twin-tube shock absorber in the event of oil and gas loss. The model is parameterized based on quasi-static and dynamic harmonic measurements and is validated using harmonic and stochastic signals. The data analysis and a simulation study show that an oil loss of just 10 % can reduce the damping work performed by the shock absorber to 50 % compared to an intact shock absorber. Similarly, an oil loss of 50 % can lead to a reduction of the shock absorber work to zero. Oil foaming and cavitation must be taken into account when modeling the shock absorber characteristics in the event of oil and gas loss. It can be summarized that particularly long-lasting excitations at high shock absorber velocities, such as those that occur when driving on uneven roads, lead to a significant loss of damping work. This in turn leads to increased wheel load fluctuations and lower transmittable horizontal tire forces and unsteady driving behavior.