Carl Beveridge

Investigation of drum brake noise from a brake mounted on a half vehicle test rig

The paper considers a drum brake mounted on a 1/2 vehicle test rig including suspension, cross beam and transmission differential. It is a continuation of earlier work and so reviews the characteristics of a drum brake when generating noise on a 1/4 vehicle test rig and compares them to those found on the 1/2 vehicle rig. Frequencies of 960, 850, 1400 and 4600 Hz are examined in some detail using the technique of holographic interferometry. It is seen that the modes of vibration of the component parts vary notably over the frequency range considered. This observation allows the significance of each part to be evaluated for each frequency range. With the accumulated information it was possible to predict other possible unstable frequencies and although these were not observed within this series of tests the predicted instability frequencies have been observed on earlier work

Comparison of Disc and Drum Brake Rotor Mode Movement

Disc brake noise is generally accompanied by a movement of the rotor mode of vibration. It is shown that the speed of mode movement is related to the frequency of noise generation divided by the rotor vibration mode order, the direction being the same as disc rotation. The same type of movement is also seen in a drum brake generating low frequency noise. The backplate is shown to have a moving mode with a speed that is twice the noise frequency divided by the mode order. A possible drum mode is indicated and it is suggsted that this rotates at the frequency of noise and in the direction of drum rotation. It is proposed that the mechanism involved with disc mode movement and drum/backplate mode movement may have a common explanation. It is explained that this mode movement is the result of two contra-rotating waveforms of differing amplitudes - this being an explanation for both brake types as a feature of brake noise.

A visual experimental noise investigation of a twin calliper disc brake

A twin caliper brake system is investigated using the whole body visual technique of holographic interferometry. It is shown that the disc mode of vibration has a preferred position where a disc antinode is situated under one caliper and a disc node under the second caliper. The maximum angular space occupied by the pad antinode is, as predicted by the theoretical study of the disc/pad interface geometry, the angle subtended by the pad length. For a four- piston opposed caliper the minimum distance is slightly larger than the piston centers. There is evidence that the disc mode position, in relation to the two calipers, may be antinode/node, node/node or antinode/antinode. With these arrangements an accompanying revised theoretical study of the disc/pad interface geometry predicts two stable conditions are possible - if the calipers are positioned either at an angle between 125\mD to 130\mD or 165\mD to 175\mD. The smaller angle was not tested but the brake became quiet at angles greater than 166\mD. A brief study of the caliper modes and pad spring retainer is included in the holographic results.