A Computational and Experimental Investigation on the Effect of Bleed Slits for a Shim Stack Type Hydraulic Damper

As the automotive industry undergoes significant changes in the dynamic behavior of vehicles and increasing demand for rapid product design, accurate prediction of product performance in the early stages has become more crucial than ever in the competitive environment. Shim-stack-type hydraulic dampers are widely used in automotive parts for both internal combustion engine (ICE) vehicles and electric vehicles (EV). EVs are even more sensitive to damper performance as ICE, which is a major NVH source has been removed. However, the industry still faces challenges in obtaining accurate models of dampers due to their highly nonlinear hydro-mechanical behavior. Bleed slits in a shim-stack-type hydraulic damper play a key role in determining the blow-off characteristics of dampers, and therefore, accurate prediction of the blow-off characteristics is crucial in evaluating the damping performance of a vehicle. Bleed flow analyses are conducted at two levels: component level and assembly system level. For the component level analysis, computational fluid dynamics (CFD) is utilized to analyze bleed flow characteristics corresponding to various bleed slits, which are validated by conducting experimental flow bench tests. For the assembly system level analysis, a dynamic 1-dimensional (1-D) system model is developed for a target passive hydraulic damper to evaluate the effect of bleed slits on the assembly level. The damper characteristic of the proposed method and a conventional method with a constant discharge coefficient are compared. An experimentally measured damper characteristic from a dynamo is used to validate the system model.