The performance of a vehicle braking system can be seriously undermined by excessive increase in temperature in the brake components, especially in the brake disc itself. This rise in temperature is produced by the heat generated from the relative sliding at the friction interface. The resulting thermo-elastic deformation within the disc can change the distribution of contact pressure and lead to thermal localization such as hot-banding and hot-spotting. The phenomenon is called thermo-elastic instability, and if severe, this can cause judder, as well as decrease in fatigue life of the disc.
In addition, since weight reduction has become a major topic in the automotive industry due to the environmental impacts of carbon emissions, it is imperative to ensure that the thermal performance of a disc brake is optimized in a weight efficient method. With the advent of electric vehicles, there are even more reasons to reduce total vehicle mass in order to extend the range of the vehicle. Furthermore, the brake disc constitutes part of the vehicle's unsprung mass, so minimizing this mass helps to improve ride comfort and reduce damage to the road surface.
This paper describes how structural optimization techniques have been deployed in the redesign of a ventilated brake disc used on a high performance passenger vehicle with the view of improving thermal performance, while minimizing mass. Two types of optimization strategy have been investigated: shape (parametric) and topology (non-parametric).
In the parametric optimization study, a coupled thermal-structural analysis was first developed to predict the thermo-mechanical behaviour of the existing disc for given braking conditions. Using a Design of Experiment approach, the geometry of the existing disc was then parametrized into shape variables and the influence of each design variable on temperature distribution and distortion of the disc was studied using a Response Surface methodology. This enabled derivation of optimum values of these geometric parameters, thereby yielding an improved thermal performance as well as a reduced mass compared with the existing disc design.
In the second topology optimization study, a baseline ground structure was formulated to enable new conceptual vane geometries for both improved thermal performance and lower disc mass to be derived. This approach allowed novel disc designs not previously considered to evolve. Although possibly more difficult to manufacture than the conventional disc, the potential performance benefits of this more radical optimization strategy are clearly demonstrated.
Ahmed Oshinibosi, Research student, University of Leeds; Prof. David Barton, University of Leeds; Dr. Peter Brooks, University of Leeds