The braking performance of pads for high-speed train with rigid and flexible structure on a full-scale flywheel brake dynamometer

Abstract

The performance of two brake pads with rigid structure (Rigid pad) and flexible structure (Flex pad) were systematically compared and analyzed by braking test on a full-scale flywheel brake dynamometer. 109 brakes were conducted according to test program in China Railway Production Certification (CRCC) standard, including dry condition, recovering brake, static brake, wet condition, and continuous brake, as well as various clamping force to simulate the service of pad on the high-speed train from 50 km/h to 275 km/h of initial brake speed (IBS). Two pads displayed similar tendency of coefficient of friction (COF) when braking at IBS below 200 km/h under dry condition. However, the obvious fading and fluctuation of COF was detected on Rigid pad when the IBS was higher than 200 km/h, stability of COF was just 77%, lower than 91% of Flex pad. More severely, the total wear rate of Rigid pad was 0.13 cm3/MJ, which was 3 times more than 0.04 cm3/MJ of Flex pad. Nevertheless, Rigid pad presented more stable and higher COF under wet condition, and the minimum COF for Rigid pad was 0.262 when braking with 25 L/h of water flow, 2 times higher than 0.12 of Flex pad. All these differences attributed to the adjusting function of pad structure, which gave different contact status on rubbing surface. Flex pad contributed to an intimate contact status with brake disc during braking by adjusting friction elements, resulting in a uniform temperature distribution and stable COF. On the other hand, the intimate contact benefited to the formation of water film during wet braking, decreasing COF observably. This study provides useful information for the structural design of brake pad and braking control strategy for high-speed train.