Identifying tyre influence on tyre/road noise emission using Close-proximity (CPX) method

Abstract

Previous research results show that tyre properties including tyre structure and tread pattern have significant impacts on tyre/road noise. With the advance of measuring technology, it is now possible to objectively measure the tyre rubber hardness, which reflects the tyre aging, with a durometer. Some laboratory studies found that each unit of tyre rubber hardness (in terms of shore A value) increase can cause about 0.2 dB(A) increase in overall tyre/road noise level, in which, frequencies between 1000 Hz and 3000 Hz are mostly affected. However, these findings have limitations, i.e., a) the studies are laboratory based which may not reflect the real on-road situations and b) the rubber hardness may change as the tyre runs on the road surface. This study aims at studying the tyre effects on tyre/road noise emissions using a Close-proximity (CPX) trailer fabricated and certified at the Hong Kong Polytechnic University. This study included two parts, firstly, 3 pairs of tyres (SRTT, AVON and Yokohama) were tested on 35 road sections including 5 road surface materials (PMFC 10/30, FC 10/30, SMA, WC, and C) at speed 50 km/h, 70 km/h and 80 km/h, total 420 tyre/road noise measurements were conducted to study the effect of the tread pattern and the relationship between tyre/road noise emission and the tyres. Secondly, this part involved aging a pair of tyres by two different methods to increase the rubber hardness. Total 288 tyre/road noise measurements are made on dense surfaces (SMA and C) with these two tyres at regular interval to identify the effect of tyre aging on road noise. This study has two main findings: a) The tread pattern design, especially the ventilation of the grooves and tread blocks, is closely related to the air pumping effect which affects the tyre/road noise level at higher frequencies between 1000 Hz and 4000 Hz. b) The relationship between the tyre rubber hardness and tyre/road noise level does not follow a linear relationship. And the influence of the tyre rubber hardness is not significant; the variations on tyre/road noise level owing to changes in the tyre rubber hardness between 62 °shore to 71 °shore are within 1 dB(A). And many researchers such as Sandberg and Ejsmont (2007) found harder rubber generate higher noise level at higher frequency between 1000 to 3000 Hz. This study also shows softer rubber produces lower noise level at this frequency range.