Thermal Brake Judder Investigations Using a High Speed Dynamometer

This paper is concerned with addressing the problems experienced with the thermo-elastic behaviour of the disc - that of optimum heat dissipation, and equally important, even heating of the disc blade. The primary objective is to develop a more temperature-stable brake disc.
The work presented approaches the problems of thermal judder through benchmarking the current situation. This is approached by modelling the current brake and its validation by means of vehicle and laboratory testing. The empirical work is centred on a bespoke high speed brake dynamometer which incorporates the full vehicle suspension for an accurate yet controlled simulation of brake and vehicle operating conditions. The dynamometer is housed in a purpose built laboratory with both CCTV and direct visual access. It is capable of dynamic measurement of DTV, caliper pressure fluctuations, disc surface temperature and vibration measurements at discrete points about the rig. This information is presented and supported by thermal imaging of the brake during a heavy brake application and subsequent thermal judder. The results also include surface scanning of the disc which is carried out at appropriate stages during testing to identify disc deformation including disc warping, “ripple” and the effects of “hot spotting”.
Disc run-out measurements via non-contacting displacement transducers show the disc taking up varying orders of deformation ranging from first to third order during high speed testing. The state of cold deformation of the disc is also shown to vary with the disc returning to first or second order deformation upon cooling.
Thermal images of the brake disc have shown vane patterns to show through to the disc surface identifying uneven heat distribution.