Sumitomo Rubber Industries Ltd. has developed technology to suppress tire cavity noise-a growing problem in certain original equipment fitments-using polyurethane foam mounted to the tire´s inner liner.
Sumitomo is marketing a line of quiet tires-the Dunlop LeMans LM703-in Japan using the technology along with a noise-optimized tread pattern and a belt overlay of polyethylene naphthanate, or PEN, yarn, which the company claims works better than nylon to suppress noise.
Sumitomo focused on tire cavity noise because it is considered a peak noise, or one that stands out from the surrounding background noise, according to Naoki Yukawa, manager, material technology department at Sumitomo´s Tyre Technical HQ in Kobe, Japan.
He made a presentation on the technology at ITEC 2006, held in Akron Sept 14-16.
Previously, Yukawa said, tire companies tried to address tire cavity noise by lowering tread depth, but this presented tradeoffs in mileage and handling.
By attaching a double-humped strip of PU foam sponge (which resembles corrugated sheeting in profile) circumferentially to the inner liner at the center of the tread, Sumitomo claims it can erase cavity resonance, Yukawa said.
In tackling the problem, SRI researchers looked at the three main factors influencing noise inside the car, he said:
— Pattern noise (pitch noise) of 100-500 Hertz band.
— Road noise of 125-315Hz band. (It is from a ´Goh´ noise around 160Hz Zone and ´Gaa´ noise around 250Hz zone.)
— Cavity resonance of 200-315 Hz band. (The cavity resonance is a noise of narrow frequency band caused by resonance of the air inside the tire.)
They then wondered whether it is necessary to delete only the most dominant noise characteristic, or must they also consider secondary noise sources that become more noticeable if the dominant noise source is eliminated.
In the end, SRI attacked all three, changing the tread pattern to address pitch noise, adding the PEN cap-ply to cut road noise and building in the PU sponge to absorb cavity noise.
The result is a tire that generates about 3 to 4 dB less noise than the comparative previous SRI tire, Yukawa said, depending on road surface.
Thus far SRI has focused on selling the tire in the aftermarket, a spokesman said, while continuing to work with Japanese OEMs on fitments.