Brake judder can be split into two distinct groups - "˜hot' and "˜cold' judder, both of which can be classed as a mechanically induced vibration. Until recently research efforts regarding brake judder have been overshadowed by other brake related issues such as brake noise for example squeal and groan. Although brake noise still remains a problem for vehicle manufacturers, past research effort has led to a greater understanding of the mechanism which creates the noise and solutions are now more readily available. This is not the case with brake judder as past research has been less focussed towards its occurrence or cause. As brake performance and reduced packaging demands increase then the thermal issues of braking become more of an issue. It is this aspect of thermal judder, rather than cold judder, which is most difficult to investigate as this can manifest itself as high frequency (often referred to as drone) or low frequency excitation, the latter causing excessive vibration in the suspension and steering systems. The principal reason for past research priorities and the recent interest in judder is because of the increased demands being placed on brakes - higher power absorption with lighter structures. In this paper the dynamic distortion of the brake disc prior to, during and post braking is analysed. Thermo-elastic wave-like deformation is shown to occur during the process of a single braking event with the order of deformation corresponding to the brake pressure variation. The order of this wave-like deformation is shown to be linked to the amount of energy transferred into the braking system with higher energy braking events resulting in higher-order deformation.
Bryant, David; Fieldhouse, John; - University of Bradford Claffey, Enda; - Bentley Motors Limited