Synthesis of Structure Borne Vehicle Interior Noise due to Tire/Road Interaction

Abstract

The pneumatic tire is one of the important sources of noise and vibration in a vehicle. Modern vehicles have implemented good preventive and control measures for power unit and aerodynamic NVH. Hence, the tire/road interaction has become a dominant source. Riegel and Wiedemann [1] have reported the dominance of tire/road interaction over engine and wind sources, in contributing to vehicle interior noise. Vehicle interior noise due to tire/road interaction consists of two components, namely structure borne noise caused due to low frequency excitation (below 500 Hz) and air borne component which are due to mid and high frequency excitation (above 500 Hz). Experimental Transfer Path Analysis (TPA) is a tool to identify whether the source or transmission path needs to be altered for reducing the cabin noise. This paper describes the successful implementation of experimental TPA to synthesize structure borne vehicle interior noise due to tire/road interaction on a sedan class passenger car. As a first step, the required local structural Frequency Response Functions (FRFs) and Noise Transfer Functions (NTFs) are determined in the laboratory for the vehicle without tire/wheel assembly by hammer impact test, by hitting at the spindle interface (paths). The second step is to repeat the test with tire/wheel assembly by an impact on the tire at the contact patch to get the same set of structural FRFs. The third step is to conduct a road test. The operational acceleration responses as well as interior sound pressure levels are measured for both engine on and off conditions for the same measurement points considered during the laboratory tests. These operational data are further combined with local structural FRFs of the vehicle to estimate the operational loads at the transfer paths using matrix inversion method. Then, the NTFs are multiplied with operational loads to synthesis the contribution of individual paths to the total structure borne vehicle interior noise. Lastly, path and vector contribution analysis are carried out from the TPA results to identify the critical paths for the critical frequencies. Moreover in this work the TPA is not only used to synthesize the structure borne interior noise, but also to estimate the road input excitation. Hence the tire force transmissibility from contact patch to vehicle spindle is determined. The estimated road excitation can be used in a parametric study to address the influence of tire design in contributing to structure borne vehicle interior noise.