Investigation of the Disc Deflection Behavior of Shim Valves in Vehicle Shock Absorbers

Todays tuning of hydraulic vehicle shock absorbers is mainly an empirical iterative process performed in time-consuming and expensive ride tests, whereas the majority of damper simulation models used for investigating vehicle ride behavior is based on an abstract parameterization. For the manufacturing of automotive dampers, however, the valve code is essential. Minor changes in the valve code describing the shim stack in the hydraulic valves may have a noticeable impact on the damper characteristics, while the physical effects are still not sufficiently understood. Therefore, the paper presents a detailed physics-based structural model to investigate the pressure-deflection behavior of shim stacks and the influence of specific discs in the stack. The model includes a variety of effects like friction and preload, and is capable to predict the damper characteristics. The modeling approach has no limitations on geometric quantities like disc diameter and thickness or the number of discs. Short computational time, fully automated preprocessing, simulation and post processing may reduce the time for damper tuning drastically, enable investigations of tolerance influence on damper forces or application of numerical optimization for stack design, where millions of potential shim stack designs may be investigated to find the best combination. A special test rig was built to validate finite element, contact and friction modeling. Also comparisons of simulation data with force-velocity measurements of the assembled damper were performed and the influence of disc variations is studied.