Analysis and Reduction of Abnormal Suspension Noise in Sports Utility Vehicle

This paper focuses on reducing abnormal noise originating from suspension when driving on rough road at the speed of 20 kmph. The test vehicle is a front wheel driven monocoque SUV powered by four cylinder engine. Cabin noise levels are higher between 100 to 800 Hz when driven on rough road at 20 kmph. Vibration levels are measured on front and rear suspension components, front and rear subframe, subframe connections on body to identify the noise source locations. Since the noise levels are dominant only in certain rough patches at very narrow band of time, wavelet analysis is used for identification of frequency at which the problem exist. Based on wavelet analysis, it is identified that the vibration levels are dominant on front lower control arm (LCA). The dynamic stiffness of LCA bushes is reduced by ~ 40% to improve the isolator performance which reduced the noise levels by ~ 9 dB (A) at the problematic frequency band. Modal analysis is conducted on front suspension components to identify the modes and mode shapes and to correlate with underbody noise. Dynamic stiffness of the LCA is increased by ~ 2.5 times which reduced the noise levels by ~ 1.5 dB (A). Noise transfer function and point mobility measurements are conducted at the suspension connection point on body to identify the structurally weak path. Dynamic stiffness at the identified paths is improved by ~ 2 times which further reduced the noise levels to acceptable level. Criteria that should be considered during suspension design to avoid underbody noise are elaborated.