Abstract
Keywords: CFD, Brakes, Parametric
As passenger vehicles have become more refined, the consumer has become more discerning. This has put considerable pressure on automotive manufacturers to develop ever quieter cars, especially within the area of brake refinement. Of the different classifications of brake noise brake judder is now considered the most concerning of all; accounting for 75% of brake refinement issues (Thompson, 2006). This equates to a cost to the industry of $100 million (US) per annum in warranty claims alone (Akebono Braking Technology, 2005), so the magnitude of the problem is evident.
Judder manifests itself as a strong pulsation of the brake pedal which can be accompanied by vibration of the steering wheel and floor pan as well as a drumming sound within the cabin upon application of the brakes. The mechanism of judder is a forced vibration with a frequency directly related to wheel speed. The vibration emanates from variations in circumferential disc thickness (DTV), this results in variations in brake pressure (BPV) and high amplitude vibration of the wheel hub and suspension system. Judder may be categorised under two headings of "cold judder" and "hot judder". Cold judder is caused by permanent disc thickness variation that result from excessive run-out leading to off brake wear or corrosion of the rotor; as such these mechanisms are well understood with a variety of available solutions. Hot or thermal judder however is a much more complex problem; it results from disc thickness variations caused by thermo-elastic deformation of the rotor or an effect known as `hot spotting´. To avoid the occurrence of thermal judder excessive heating of the rotor must be avoided, whilst minimising temperature variation across the rotor.