Brake noise reduction on a heavy duty vehicle using rotor asymmetry

This paper considers the introduction of asymmetry onto a heavy duty
commercial disc brake to alleviate an undesirable high amplitude noise at 2400 Hz, the rotor
vibrating with a 5-diametral mode order. It is shown that by adding mass to the free-free
mode of vibration the amplitude at the undesirable frequency is reduced considerably and a
mode split is observed.
Increasing the asymmetry shows the frequency split to increase from a few hertz to several
hundred. A test rig is used to determine the full effect of the staged modifications when it is
seen the noise is eliminated. On-vehicle tests demonstrate the effectiveness of the technique
when it is seen the condition goes from one where the vehicle cannot travel a few metres
without excessive noise to a situation where the vehicle passes whole day trials without a
noise issue. It is seen that under normal driving conditions thermal concerns have not been an
issue. In the first instance asymmetry is introduced by drilling holes, radially, into the disc
blade but a bespoke cast disc is produced which exaggerates asymmetry, the resulting
frequency split being 769Hz.
Finite element analysis complements the experimental results where it is seen that the two
normal modes split wit h one of the rotor modes posit ioned at the location of the drilled holes
whereas the second is located between the holes.