Abstract:
Exterior noise is the only acoustic attribute regulated for passenger cars and light trucks. The primary procedure used to quantify this noise is an outdoor passby test conducted under full-throttle acceleration. Unless specified noise levels are met under this procedure, a vehicle may not be sold in a given market jurisdiction. Recent reduction of European regulatory limits by 3 dB has re-enforced many of the technical challenges faced in designing and testing vehicles to meet these new requirements. These challenges include: better understanding and control of test and environmental variables, more accurate methods of noise prediction, and improved techniques for isolating and reducing individual source contribution. In recent investigations, sound intensity has been employed to isolate tire/pavement interaction noise for vehicles under passby conditions. This has led to the determination that tires can produce significantly higher noise levels under the torque of acceleration than under cruise conditions. As a result, tires are often the major noise source when the total vehicle noise approaches the new regulatory limits. This paper reviews the variables associated with the passby test procedure, the effects of vehicle acceleration on tire/pavement interaction noise, and the needs for improved predictive methods.