A study of thermal judder on a laboratory dynamometer

This paper considers a study of the thermo-elastic behaviour of a disc brake during heavy braking. The work is concerned with working towards developing a situation (or design) that provides uniform heating of the disc, and equally important, even dissipation of heat from the disc blade. The approach is through a combination of modelling, on-vehicle testing but mainly laboratory investigations. The experimental work makes use of a purpose built high speed brake dynamometer which incorporates the full vehicle suspension for controlled simulation of the brake and vehicle operating conditions. Extensive instrumentation allows dynamic measurement of brake pressure fluctuations, disc surface temperature and discrete vibration measurements. Disc run-out measurements using non-contacting displacement transducers show the disc taking up varying orders of deformation ranging from first to third order during high speed testing. The mechanical measurements are complemented by thermal imaging of the brake, these images showing the vane and vent patterns on the surface of the disc. The results also include surface scanning, or topographical analysis, of the disc which is carried out at appropriate stages during testing. This surface interrogation identifies disc deformation including disc warping, "ripple" and the effects of "hot spotting".