Influence of Shim Bending Mode on Damping Force Variation of a Hydraulic Twin Tube Shock Absorber 2014-01-0045
Automotive shock absorber shims are subjected to deformation while generating the pressure differential across the rebound and compression chambers. Considering the contact, large deflection, and material this shim stack deformation will be nonlinear throughout the working velocity of shock absorbers. The deformation of shim stack mainly depends on number and geometry of deflection disk, number and geometry of ports, and clamping disk geometry on which shims are rested.
During the rebound and compression stroke of the shock absorber, the oil flows through the piston and base valve ports. High pressure oil developed during mid and high velocity of shock absorber results in deflection of shim stack in piston and base valve assembly. This deflection leads to oil leakage through the shim stack which results in change in damping force by the shock absorber. The fluid pressure from the flow passage (well) acting over surface area of shim differs while causing an elastic bending of the shims. The oil leakage depends on shim bending mode which in turn depends piston port position and resting/clamping size of back up disk on which shims are rested.
The bending mode of shim changes, if the piston/base valve port positions are varied which in turn changes the pressure differential across shims. This will results in variation of damping force trend. This paper presents different porting positions of piston/ base valve and its effect on bending mode of shim stack & damping force trend. Structural simulation is carried out to substantiate the bending mode shape and experimental trails are carried out to demonstrate the damping force changes.