Noise reduction technology is a hot topic among tire engineers. During yesterday's (Sept. 12) International Tire Exhibition and Conference in Akron, Ohio, Naoki Yukawa of Sumitomo Rubber Industries Ltd. gave an in-depth presentation on how his company has succeeded in reducing tire cavity resonance.
His speech, "Special Silent Technology for Radial Passenger Car Tires," is excerpted below.
Summary
In January 2006, Sumitomo Rubber Industries Ltd. (SRI) in Japan released a tire with sponge that absorbed tire cavity noise.
Together with existing noise reduction technology, SRI succeeded in reducing cavity resonance due to the resonance of air inside the tire that till now had been very difficult to eliminate.
Through this technology, SRI was able to give a tire unprecedented silence, and a new sense of values.
Introduction
This new noise reduction technology is applied to the Dunlop Le Mans S LM703 range, which is sold as an aftermarket product in Japan. The positioning of this tire in the Japanese aftermarket is as a general-purpose tire which has balanced handling and driveability.
It is one of the main product lines of Dunlop for car models ranging from compact car, through minivan to luxury sedan, and resides in a category where competition is intense.
Recently, marketing research results for summer tire performance suggest that there is a requirement for refined characteristics and safety in Japan.
SRI paid special attention in particular to the noise performance that was required for comfort and satisfaction for a user. Users were requested to, see and understand it, touch and understand it, ride and understand it.
As a result, Sumitomo Rubber Industries' advanced technology was used to develop a special low noise tire that included the world's first noise-absorbing sponge.
Technology
There are three main factors influencing the noise inside of a car.
* Pattern noise (pitch noise) of 100-500Hz band.
* Road noise of 125-315Hz band.
* Cavity resonance of 200-315Hz band. (The cavity resonance is a noise of narrow frequency band caused by resonance of the air inside the tire.)
Approach
Reduction of these noise charactristics was examined, while considering the following questions:
1. Is it only necessary to delete the noise characterisitc that is most dominant?
2. Does the secondary noise now beome dominant if only the one noise is eliminated?
3. Is there another case that subsequest noise charateristics become unacceptable when the primary sources are eliminated?
Ultimately therefore, it was decided to attempt to reduce all three main noise factors significantly.
The following three technologies were adopted:
* a pattern noise improvement pattern to reduce the pattern noise in the 100-500Hz band.
* a PEN (Polyethylene naphthanate) combination cap-ply to reduce road noise in the 125-315Hz band.
* a special sponge material which absorbs noise to reduce cavity resonance in the 200-315Hz band.
Through this, a noise reduction result was achieved that could easily be detected by a general user.
Pattern noise (pitch noise) improvement pattern: The flow of a pattern is regarded as important when designing a pattern for low noise generation. Additionally it was planned to reduce pitch noise by adopting five kinds of random pitch.
With simulation, optimization of a shift in the pattern to further reduce pattern noise was also incorporated.
As a result, the LM703 was able to demonstarte a significant improvement in pitch noise over the previous LM702 in the 100Hz-500Hz band.
PEN combination cap-ply layer to improve road noise: PEN was adopted as a cap-ply layer to reduce road noise mainly in the 160Hz and 250Hz range.
Polyethylene naphthanate is a high strength fiber, being some four times higher than general nylon.
Road noise was able to be reduced by adopting this material as the cap-ply. The reason that this is effective in noise reduction of the 250Hz band is that the power to restrict the edge part of a belt increases by adopting this material as a cap layer.
As a result, resonance of a tire can be shifted in a higher direction from the neighborhood of 250Hz where the noise was easily generated by the vehicle. Consequently, 'Gaa' Noise is reduced significantly in the 250Hz region.
The reason that this is also effective in the 160Hz band is that there is a resonance related to the tread twisting mode in this frequency band. Again, power to restrict the edge part of a belt increases by adopting the PEN material as a cap-ply layer.
As a result, the tire deformation due to this resonance can be suppressed and 'Goh' Noise can be reduced in the 160Hz region.
As discussed, it is necessary to restrict the edge part of the belt to show noise reduction effects. On the other hand, the need to restrict the center part of the belt is small.
In addition, power to restrict the belt center becomes high when PEN is used for the entire cap-ply. This results in high tread rigidity, and ride comfort is degraded.
Therefore, a normal nylon cap-ply layer is used for the center part of the tread with minimal effect on the noise reduction. It is a so-called combination cap-ply layer structure and is compatible with both noise performance and ride comfort.
Technology to eliminate cavity resonance: The technology eliminates the noise due to the resonance of air inside the tire, by arranging a sponge material in the tire cavity.
The effect of this is great and can completely erase the cavity resonance peak in the 220Hz neighborhood. Till now, the technique used to improve this noise was by lowering tread strength. However, in many cases improvement was difficult since handling was often reduced in exchange.
Additionally, in recent years noise reduction technology of vehicles has also developed and become very sophisticated. However, because this particular noise was a peak, it stands out from the surrounding background noise and becomes a problem.
So using this technology, SRI has succeeded in completely erasing the cavity resonance that was difficult to improve by changes to the structure of the tire.
For the shape (of the noise absorbing sponge material), a double humped profile was adopted which was compatible both with the effect of absorbing noise and also with durability.
The material adopted was a special ether polyurethane sponge having both light weight and durability. Several types of material were evaluated, but considering performance from the point of view of the severe environment inside the tire and from the consideration of cost, it is believed that the light weight sponge material is the optimum.
The placement position of the sponge was selected as the underside of the tread by using (SRI simulation technology). This is because vibration of air in that region is large.
These simulation techniques were also extremely useful in deciding an optimizated shape for the sponge in the tire on a size-by-size basis.
The LM703 shows a noise reduction effect of about 3dB in comparison with the old pattern LM702 on a smooth road surface. On a specific road noise generating surface, there was a noise reduction effect of about 4dB.
Conclusion
A new product, the Dunlop Le Mans LM703, was released which concentrated all the noise reduction technology of Sumitomo Rubber Industries Ltd. in to the one tire. This tire was able to significantly reduce noise generation when compared with previous conventional technology tires.
Sale of this tire range was started in January 2006 in Japan. So far, LM703 sales are good and the reaction from the market is good, too.
