Fluid–structure interaction and dynamic stability of shock absorber check valves

Shock absorbers, also known as dampers, are a crucial part of most vehicles produced today and ensure both safety and comfort of passengers by absorbing displacement changes through fluid–structure interaction (FSI) between the contained mineral oil and elastic metal valves. In this study, the two most common types of shock absorber valves, namely the spring valve and the shim valve, are investigated in both compression and rebound operation of a typical motorcycle suspension system. Depending on the flow direction, different properties of the valve system are desired, which are demonstrated for realistic boundary conditions. By using both high-order FSI simulations as well as a low-order analytical model, stability and nonlinear dynamics of the valve are computed within the system’s parameter space and the opening and closing characteristics are obtained for typical volumetric flow rates. Additionally, the adhesion force due to viscous stiction between valve plate and seat area by the damper fluid is taken into account, causing delay of opening especially at high excitation velocities and frequencies. It is demonstrated that significant pressure losses of more than 95% during compression take place in the small gap region between shim valve and piston due to frictional effects. Additionally, the check valve response time during transition from rebound to compression is reduced from 3.7ms down to 0.4ms by optimizing spring properties, which limit hysteresis effects. Linear stability analysis using the Routh–Hurwitz criterion shows the onset of instabilities at a flow rate of 95.9Lmin−1 for the baseline setup, with parameters such as damping and valve opening section negatively affecting stability at lower values. Finally, frequencies of valve vibrations during rebound are calculated and their dependence on the most important parameters of the valve, such as pretension and stiffness, are examined.