Conditions of Frictional Contact in Disk Brakes and their Effects on Brake Judder

In automotive disk brake systems, frictional heat is not uniformly distributed due to various reasons such as thermal expansion and imperfections in geometry. It is well known that thermoelastic distortion due to frictional heating affects the contact pressure distribution and can lead to thermoelastic instability or TEI, where the contact load is concentrated in one or more small regions on the brake disk surface. These regions then reach very high temperatures and the passage of these hot spots moving under the brake pads can cause low frequency vibration called brake judder. Disk thickness variation (DTV) will further promote the localized contact. Nonuniform contact can also be generated by disk lateral runout (LRO). This study investigated the effects of various contact conditions on the heating patterns and judder characteristics of a disk brake by using a state of the art infrared camera technology and vibration measurements. The baseline friction material used in the study was modified based on the theory of thermoelastic instability and dynamometer testing confirmed that the modified material had better judder performance.