Experimental study on tire vibrations and induced noise

Tire-pavement induced vibrations are among the main sources of vehicle exterior noise. Its dominant spectral content is approximately within 500–1500 Hz. For these frequencies, previous studies have proposed the existence of travelling waves along the tire’s circumferential direction, as opposed to a modal behavior. This distinctive structural response generates acoustic waves that propagate into the environment. Unfortunately, no noise measurements above 500 Hz that can be used to validate this assumption have been conducted. In this work, a methodic measurement approach for tire vibrations and noise within the frequency range of interest is presented. Two tires of different size and construction were horizontally suspended over a test rig inside an anechoic room. In order to avoid the interference with the rig’s rigid body modes, they were hanged with low stiffness cords. The tires were then excited with an impulse input by using an impact hammer. Noise was measured using a 19 microphone arc array. The array formed a semi-circle around the tire’s cross section, thus providing noise levels induced by both sidewall and tread band vibrations. The arc was then rotated around the tire in order to capture tire noise directivity patterns. On the other hand, vibrations measurements were performed by using accelerometers on a set of 35 equally spaced points along the mid-tread line of the tires. A chirp signal was implemented as an input in order to fully characterize the tire response within the frequency range of interest. Noise measurements show the expected levels decay along the circumferential direction, whereas structural tire responses suggest the existence of waves that propagate along this direction.