DISC BRAKE VIBRATION AND SQUEAL
Brakes are critical safety and performance components in vehicles. Most of the kinetic energy of a travelling vehicle is dissipated as heat through friction when the brake is applied and about 10% of the kinetic energy is converted to vibration/sound energy. Friction can induce a number of brake noises (judder, moan, groan, squeal, squeak, to name a few) defined in different frequency bands. The most offensive of all brake noise is squeal, which is a sustained noise above 1 kHz. Brake noise may give the false impression that there is a serious fault in the operation of the brake and at least causes the customer to believe that the brake, and possibly the vehicle, is of poor quality. It is a source of irritation and complaint. The noise, vibration and harshness (together known as NVH in automotive industry) generate warranty cost estimated to be about US$ 1 billion a year to the automotive industry in North America alone. A squealing brake is difficult and expensive to correct. Alleviation and even elimination of vehicle brake squeal will enhance customer comfort and the wellbeing of the general public.
The study of brake squeal has a history of over a century. Extensive research started in the 1950’s and the early pioneers were mostly British. Now all car manufacturers and brake and friction material suppliers spend a large amount of money dealing with brake noise. Abendroth and Wernitz noted that many makers of materials for brake pads spend up to 50% of their engineering budgets on NVH issues.
The investigation of disc brake squeal at Liverpool started in the late 1980’s. Since then Liverpool has been awarded three EPSRC and three industrial grants. Liverpool is now recognised as a scientific leader in this research area.
A typical (floating caliper) disc brake
An unstable mode of about 4.1 kHz from a large finite element model (by Dr Q Cao)
The expertise required for studying brake noise and vibration includes vibration theory, contact mechanics, friction, mechanics of materials, modal testing, theory of elasticity and the finite element method. The researcher has to use large finite element software packages, such as MSC/Nastran or ABAQUS.
ã Dr H Ouyang 2003, 2004