Numerical and Experimental Investigation of Brake Bleeding Performance Improvements in an EPB Caliper 2018-01-1876
Brake bleeding in an EPB (Electric Parking Brake) caliper is the procedure of removing any air bubbles performed on hydraulic brake systems including the brake pipes, hoses and brake fluid. This is very crucial because air bubbles are compressible gas and their presence in the brake system greatly reduces the hydraulic pressure and thus has a considerable impact on brake pedal feel. The critical cause of sharply deteriorating the brake bleeding performance has been confirmed to be entrapped air existing in very tiny gap between caliper components and the flow resistance due to the gap prevents totally allowing air the escape outside. In this paper, it is reported on numerical and experimental investigations into the topic of “bleeding performance improvements”. Both simulation calculations and experimental verifications have been carried out with the goal of describing the compressibility mechanism of compressible brake fluid within the caliper. The multiphase simulations with three-phases (air, brake fluid and its vapor) were performed to achieve a better understanding of the pressure rise and release characteristics of the brake fluid. The caliper performance tester was used to measure the fluid consumption amount on the baseline and improved caliper models under standard braking conditions. In the analysis of deriving the unique property with the entrapped air from the measured data in a hollow cylinder, the correlation between the fluid consumption curve characteristics according to the bulk modulus and air mass fraction values is described. The correlated values are extensively applied to all the simulations for property input. The numerical calculations result in an improved understanding of the components improvements on bleeding performance issue. Regarding the performance reduction by manual bleeding, critical fluid compressibility mechanism has identified in order to draw effective components shape for improving the bleeding performance.