Holographic interferometry used to investigate noise from a drum brake mounted on a half vehicle test rig

摘要

The paper is a continuation of earlier work (1) and so reviews the characteristics of a drum brake when generating noise on a 1/4 vehicle test rig and compares the results to the same drum brake mounted on a 1/2 vehicle test rig. Holographic interferometry is used to provide whole body visual information of the modes of vibration of the component parts. Although the principal frequency discussed is 850Hz there is consideration and comment provided for frequencies of 1400 Hz & 4600 Hz. 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 frequencies have been observed on earlier work. The suspension system plays an important role at the lower frequencies but less so at the higher frequencies. 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. A series of time related holograms allows the phase relationship of the spring pan structure to be established at 76°. 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.