Rotor Asymmetry Used to Reduce Disc Brake Noise 2004-01-2797

Asymmetry is applied to a heavy-duty commercial twin calliper disc brake rotor as a means to alleviate an undesirable high amplitude noise. The problematic frequency is 2400 Hz, the rotor blade exhibiting a 5-diametric mode order of vibration. The asymmetry is introduced by drilling sets of radial holes into the disc rim. Modal analysis is carried out over a range of frequencies using added masses applied magnetically to the rim of the rotor This 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 vibration amplitude at 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 at very close frequencies but when asymmetry is introduced, by drilling holes in the rim of the disc, there is a noticeable frequency decoupling of the 2 normal modes This is also accompanied by a distinct positioning of the antinodes with the antinodes of one mode positioning at the sets of drilled holes, the other mode antinodes being 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.