A Computational and Experimental Investigation on the Effect of Bleed Slits for a Shim-Stack-Type Hydraulic Damper 2023-01-1059

As automotive industry experiences a significant change in terms of the dynamic behavior of vehicles and an increasing demand for rapid design of products, accurate prediction of product performances in the early stages has become even more vital 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), and EVs are even more sensitive to the damper performance as ICE, a major NVH source is removed. However, the industry still struggles to obtain accurate models of the dampers due to their highly nonlinear hydro-mechanical behaviors. Bleed slits for a shim-stack-type hydraulic damper play a key role in determining the blow-off characteristics of a damper, and, consequently, accurate prediction of the blow-off characteristics is crucial in evaluating the damping performance of a vehicle. The bleed flow analyses are carried out in 2 ways: component level and assembly system level. For the component level analysis, the bleed flow characteristics corresponding to various bleed slits are analyzed using computational fluid dynamics (CFD) and validated by conducting experimental flow bench tests. For the assembly system level analysis, a dynamic 1-dimensional (1-D) system model for a target passive hydraulic damper is developed 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.