Brake noise reduction using rotor asymmetry

This paper considers the application of an asymmetry to a heavy-duty commercial twin calliper disc brake rotor as a means to alleviate an undesirable high amplitude noise at 2400 Hz, the rotor blade exhibiting a 5-diametric mode order of vibration. In this instance asymmetry is introduced by drilling sets of radial holes into the disc rim. Modal analysis carried out over a range of frequencies using added masses shows the amplitudes at set frequencies to reduce considerably when asymmetry is introduced. When a set of 5 masses is added to the rotor the occurrence of the troublesome frequency is seen to be considerably reduced. Finite element analysis complements the experimental results. The analysis of a plain disc initially shows the two normal modes but when asymmetry is introduced by drilling holes in the rim of the disc there is a noticeable frequency shift accompanied by a distinct positioning of the antinodes with the antinodes of one mode fixing to the sets of drilled holes with the other mode antinodes between the holes. When an asymmetric disc is fitted to the vehicle the noise is eradicated. Significant testing of the vehicle has since being undertaken without noise being generated.