• Brake Judder - An Investigation of the Thermo-elastic and Thermo-plastic Effects during Braking

      Bryant, David; Fieldhouse, John D.; Talbot, C.J. (2011)
      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 design advice that provides uniform heating of the disc, and equally important, even dissipation of heat from the disc blade. The material presented emanates from a combination of modeling, on-vehicle testing but mainly laboratory observations and subsequent 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. Advanced 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. This surface interrogation during braking identifies disc deformation including disc warping, 'ripple' and the effects of 'hot spotting'. 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 static surface scanning, or geometry analysis, of the disc which is carried out at appropriate stages during testing. The work includes stress relieving of finished discs and subsequent dynamometer testing. This identifies that in-service stress relieving, due to high heat input during braking, is a strong possibility for the cause of disc 'warping'. It is also seen that an elastic wave is established during a braking event, the wave disappearing on release of the brake.
    • The Influence of Pad Abutment on the Generation of Brake Noise

      Fieldhouse, John D.; Bryant, David; Talbot, C.J. (2011)
      The paper overviews the modes of vibration of the principal component parts of a brake and their contribution to system instability during noise generation. It is shown that both in-plane and out-of-plane vibration is present and that both can be related to the vibration of the pad. It is further shown that the pad and its region often provide a solution or 'fix' towards noise prevention and it is this area that forms the focus of this investigation. The collective evidence, proposals and associated theory are applied to real brake case studies when it is demonstrated that disc/pad interface 'spragging' may be the source of brake noise. Measurements of the position of the dynamic centre of pressure (CoP) support the theoretical predictions that a leading CoP induces brake noise. Design proposals are suggested that may be applied early in the design phase as a means to reduce the propensity of a brake to generate noise.