Road Induced Interior Noise: Use of OTPA to Determine Tire Contribution and Vehicle Sensitivity

Customers' expectations concerning noise and comfort inside a vehicle are getting higher, as an image of the quality of the vehicle. Because of optimization of engine noise during the past years,Customers' expectations concerning noise and comfort inside a vehicle are getting higher, as an image of the quality of the vehicle. Because of optimization of engine noise during the past years, the contribution of road noise to interior noise has increased. The road noise performance is mainly due to the vibrations coming from the wheels and going inside the car through the frame. Thus, it depends on the good coupling between the tire and the vehicle, to avoid bad filtering or mode resonance. The OTPA (Operational Transfer Path Analysis) is a powerful tool to investigate quickly the sound inside the cabin of the vehicle, and to determine the contributions of the main sources of it. Then it is possible to find the link between a disturbance inside the cabin and its origin. One of the usage of this tool for Michelin is to investigate specific claims of customers concerning the interior noise of the car. For road noise, it makes it possible to find the wheel responsible for the disturbance, and to separate the input (wheel accelerations) from the path (car transmissibility). The cause of the sound can be determined: high source level from the wheel, or low filtering from the car on the specific disturbance. An example of study showing how the method is implemented in the case of road noise is presented.