Recent Improvements in Road Noise Control 2007-01-2358

In the recent years, reduction of engine noise as well as aerodynamic noise makes vehicle road noise predominant in numerous operating conditions. Fortunately, experimental and numerical improvements now allow a better understanding of road noise generation and propagation. This paper will focus on two specifics improvements related to this matter.

First, excitations are now extracted from the wheel blocking forces. As road noise is a random phenomenon, a component analysis is performed to extract a limited number of uncorrelated excitation patterns (magnitude and phase) at the five fixed Degrees of Freedom at the wheel center. The relevance of such excitations is proved when comparing computed blocking forces at the body-suspension interface to measurements. Implicitly, this comparison also validates the numerical model (Finite Elements) of the suspension.

Second, one introduces a road noise indicator at the body-suspension interface in order to synthesize multiple degrees of freedom interactions. The indicator is based upon the power injected by the suspension in the car body. The vibroacoustic coupling with the acoustic cavity is then no longer needed to assess the suspension design. This approach has been tested experimentally on a front axle of a mid-size passenger car. Interaction forces have been computed using an inverse method while velocities were measured on the body side. Both are combined to calculate the vibratory power. This power is compared to the noise measured directly at the front and rear passengers' ears. It appears that the indicator and the averaged quadratic sound pressure are very similar. Several elastic mounts with different stiffness have been used to check the sensitivity of the indicator versus interior noise. These results suggest that even at low frequencies, rather simple energetic views of vehicle vibroacoustic problems may be of great interest.