Toyo Tire & Rubber Co., Ltd. announced that it has developed a new device that effectively reduces resonance in tyre cavities, a source of interior noise, based on the new technology called “Toyo Silent Technology” to solve the issue of sound that is transmitted from the tyre to the interior of a vehicle.
Noise is generated by the vibration of air. Tyres mounted to the vehicle are structures that are internally filled with air. For that reason, input to the tyres that is generated by contact with the road surface during vehicle travel causes the air inside the tyre to vibrate. These vibrations are transmitted to the vehicle interior as noise via the axle.
The company conducted simulations to visualise what the status of the air inside the tyre which is presumed to generate the noise, is like when the vehicle is actually traveling. Through these simulations, they ascertained that the air itself generated flow in the circumferential direction, and flow in the vertical direction.
One method for reducing tyre cavity noise is internally mounting material that has a sound-absorbing effect. This has been implemented in the tyre industry as a leading technology. However, the research team focused on the fact that air flow is generated inside the tyre, so they incorporated a unique approach to reduce noise by utilising the flow of air.
Originally, noise is reduced when it passes through the pore. There are two attenuation mechanisms, namely, friction generated at the wall faces of the pore that the air passes through, and a vortex generated by the sound passing through the pore.
Using the flow of air when sound passes through the hole further increases the noise-reduction effect. So the researchers arranged a porous film to face the flow of air (the pathway of the air) that they ascertained from visualisation, and studied disposing a structure through which generated sound can pass.
In order to handle the flows in both the vertical and circumferential directions, the break-through point that the company devised was to mount an arch-shaped perforated film device.
Tyre cavity noise is in the frequency band of 200 Hz to 250 Hz. To check the efficacy of this device in reducing noise targeting this frequency band, researchers ran actual vehicle tests using tyres the company manufactures and markets.
The results of these measurements of noise levels inside the vehicle, showed that tyre cavity noise on a passenger vehicle traveling using tyres implemented with this device was notably reduced to a maximum level of -12 dB in the frequency range of 200 Hz to 250 Hz, compared to driving on current tyres that do not have this device installed.
Based on these results, Toyota Tires plans to continue to study commercialisation of tires equipped with this device in the future, and to expand the market.