|
This paper presents a detailed analysis of the deflection of the shim stacks used in hydraulic dampers. In hydraulic
dampers, a stack of circular disks (shims) is mounted on each side of the main piston to create a pressure drop as the
hydraulic oil is passed through the piston from one side to the other. A stiff shim stack creates a high pressure drop
across the piston, resulting in high damping. A softer shim stack creates less pressure drop and smaller damping. In
practice, shims can be added or removed from the shim stack assembly to tune the damper and generate the desired
damping force characteristics as a function of velocity. Tuning a damper requires taking the damper apart, making the
changes to the shim stack assembly, and putting the damper back together. This takes a considerable amount of time and
effort. Therefore, mathematical modeling of the shim stack assembly becomes a crucial part of the analysis of hydraulic
dampers. The goal of the study presented here is to provide a model of the shim stack assembly in order to accurately
predict the level of damping for different configurations of the shim stack. The shims that are stacked on each other will
deflect under the pressure created by the hydraulic oil, and at the same time, slide against each other. This important
characteristic of the shim stack needs to be accounted for in the mathematical model and makes the analysis complicated.
For the sake of simplicity, in past studies the shim stack is approximated by the deflection of a single disk and formulas for a single disk are used. This, however, introduces a significant amount of error in the damper hydraulic model. In this paper, the deflection of shim stacks is analyzed and compared with the single disk approximation. It is found that this approximation fails to agree with the more accurate model of representing the shims individually. Therefore, a more detailed and accurate model is necessary for better simulating the damping characteristics of hydraulic dampers as a function of relative velocity across the damper.
|
