Certifying a twin-wheeler CPX vehicle for tyre/road noise measurement

A twin-wheeler tyre/road noise measuring vehicle with a trailing acoustic enclosure was designed and fabricated in Hong Kong in 2009. This vehicle has undergone the specified certification tests in the draft ISO/CD 11819-2 for measuring tyre/road noise at Close Proximity (CPX). The first test ensures minimal reflections within the acoustic enclosure. An artificial omni-directional sound source was devised and placed at the tyre/road contact patch to mimic the noise source. The noise measured with and without the enclosure was compared. The second test is for ensuring the background noise from the test vehicle itself is negligible compared to the tyre/road noise. A long trailer was specifically designed to perform the "removed" tyre testing runs. The noises measured with and without the two test tyres on the same porous asphalt road section were compared. The third test ensures that the noise from the on-road pass-by vehicles has minimal effect on the measured tyre/road noise. The noises measured when the CPX vehicle was parked on the near side lanes were compared to that measured when the CPX vehicle ran on the same road sections. The results show that the devices tailored made for these certification tests worked well; this twin-wheel CPX vehicle successful passed all certification tests and these specified certification tests are practicable.