Abstract
Noise emissions from a four piston opposed calliper disc brake are investigated using the whole body visual technique of holographic interferometry. The brake, as used on a substantial off road vehicle, was mounted on a semi-rigid test rig with mirrors mounted to provide a view of the disc and sides of the calliper and pads.
A self generated braking noise of 2750 Hz was investigated and it may be seen that the pads behave in a similar manner but 180a out-of-phase.
The disc is seen to exhibit a 4 diameter mode order during noise generation and a series of time related holograms show that this mode rotates around the disc, in the direction of rotation, at a rate related to the noise frequency divided by the disc mode order. The rate is not uniform, more periodic, which gives rise to a variation in disc vibration amplitude. This mode movement is in keeping with other holographic work where a sliding fist type calliper was investigated during noise generation at 10750 Hz. The rate of movement is typical of two waveforms travelling in opposite directions, one significantly stronger than the other.
Additional work with the brake includes a noise matrix test using a variety of friction materials and noise fix shims where it is demonstrated that a full face shim proves most effective in reducing noise.