Test methodologies for mapping tyre exterior noise in semi-anechoic chamber

Tyre exterior noise is the result of the combination of many complex phenomena taking place at tyre/road contact. Tread impact, stick/slip of the tread blocks and air-pumping are only some of the excitation mechanisms, whose effect can be amplified by the tyre structural vibrations, by the pipe resonances of the longitudinal grooves in the contact patch and by the aerodynamic phenomena in the leading and trailing footprint regions. Indoor tests are of fundamental support in the development of new products, in terms of optimization of both tread pattern design and structural solutions. This paper illustrates the test methodologies developed within a research cooperation between Politecnico di Milano and Pirelli Tyre, for mapping the noise generated by a rolling tyre during the experiments carried out in semi-anechoic chamber. Noise source identification is performed through microphone array techniques, while the radiated sound field is characterized in terms of directivity patterns for variable frequency. In both cases the measurement equipment is fitted with a robotic handling system to speed up the stepped positioning of the microphones.