Abstract
The objective of this work is the development of a methodology for modeling a collapsing seal lip and integrating said model in the global dynamic simulation model of a hydraulic brake. A collapsing seal is a seal that is designed so that, in some given pre-defined situations, it allows a certain amount of fluid to break the sealing and flow into the main hydraulic chamber in order to compensate excessive vacuum levels and facilitate the return motion of the brake.
This methodology combines finite element models of the rubber seal for the calculation of the lip deformation as a function of the surrounding pressure and finite volume models for the calculation of the flow rate around the collapsed lip. Based on a detailed analysis of the results of these distributed parameter models, a reduced-order parametric model is developed for the calculation of the lip displacement and the flow as a function of the operating conditions, the main geometric parameters, and the fluid properties. From the finite volume model results, the critical sections of the flow path are identified and the Reynolds number dependent loss coefficients are calculated. The reduced order model divides the fluid domain in several volumes, where, through an iterative procedure, the pressure is calculated, and consequently the mass flow rate through the fluid path and the seal lip displacement. Finally, the parametric model is integrated in the lumped parameter transient model of the complete hydraulic system in order to take into account the seal collapse and its effects in the dynamic performance of the global braking system.
The result is an advanced, lumped-parameter dynamic model that allows a detailed but computationally effective modeling of the seal collapse process. If the seal material or geometry is modified, a new set of FE simulations must be run in order to characterize the seal deformation.
In summary, a parametric model for the seal collapse has been developed, based on CFD flow results and FE seal deformation results. The novel model predicts the recuperation flow and its effects more accurately, and allows its use for different cylinder sizes and temperature conditions.
KEYWORDS – Brakes, Master Cylinders, Seals, Simulation, Parametric Models