Investigation of Drum Brake Noise from a Brake Mounted on a Half Vehicle Test Rig 2002-01-2613
The paper considers a drum brake mounted on a ½ vehicle test rig including suspension, cross beam and transmission differential. It is a continuation of earlier work (1) and so reviews the characteristics of a drum brake when generating noise on a ¼ vehicle test rig and compares them to those found on the ½ vehicle rig. Frequencies of 960, 850, 1400 and 4600Hz 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 test the predicted instability frequencies have been observed on earlier work.
The suspension system parts are seen to play an important role at 960Hz and 1400Hz but at the higher frequency they appear less significant. It is suggested that the mode of vibration of the backplate, and its associated interface mounting with the suspension, may provide an answer as to why this is so. Additionally it is suggested that there is an influencing relationship between the trailing arm, the spring pan and the main cross beam, the spring pan exhibiting a complex mode. The same may be said in general terms for the frequency at 850Hz where the suspension spring pan is seen as the dominant feature. A series of time related holograms at the lower frequency allows the phase relationship of the spring pan structure, sidewall to base, to be established at 76°.
A time series of holograms at 4600Hz shows a moving mode of vibration but with each nodal position moving at a different, varying rate. It is suggested that this may be due to in-plane vibration.
A noise “fix” is suggested for the low frequency noise and additional suggestions are made to reduce the influence of the suspension system through basic design changes.