Toyo Tire & Rubber Co., Ltd. has developed a new device that effectively reduces resonance in tyre cavities, a source of interior noise.
The new device is based on new technology called “Toyo Silent Technology” which solves the issue of sound that is transmitted from the tyre to the interior of a vehicle.
As hybrid vehicles become more popular, the mobility environment is becoming dramatically transformed as can be seen in the shift from the internal combustion engine that uses petrol as a source of power for passenger vehicles, to motor drives.
For that reason, there is a growing trend in the demand for high levels of comfort in vehicle interiors. It has accumulated abundant knowledge with regard to tyres, the one part of a vehicle that touches the ground for the vehicle to travel. Toyo says it will utilize that knowledge to incorporate Toyo Silent Technology into the products it will develop to provide drivers and passengers with a comfortable space with greater silence.
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.
Noise that is generated by air that is filled inside the tyre being vibrated by the tyre receiving external input (the road surface) is called tyre cavity resonance, and is one source of vehicle interior noise.
For example, when a vehicle is traveling at high speed and it drives over seams in the road, one can hear a bumping sound. However, road-surface unevenness is inputted to the tyre that is rolling. This is tyre cavity noise that is generated by the phenomenon of vibrating air inside the tyre.
Toyo says it has conducted simulations to visualize what the status of the air inside the tyre which is presumed to generate the noise, is like when the vehicle is actually traveling, in other words, when the tyre is rolling in contact to the ground. Through these simulations, Toyo says it has 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 the idea of internally mounting material that has a sound absorbing effect. However, the company says it has focused on the fact that air flow is generated inside the tyre so Toyo incorporated its unique approach to reduce noise by utilizing the flow of air.
Originally, noise is reduced when it passes through the pore. There are two attenuation mechanisms, friction is generated at the wall facing the pore that the air passes through, and a vortex is 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, Toyo says it arranged a porous film to face the flow of air (the pathway of the air) that it ascertained from visualization, 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.
Toyo says it also arranged cylindrical foam at 16 base points around the tyre circumference to hold the archshaped devices. The hollow structure of the cylindrical foam has a sound-attenuation effect. For that reason, a synergistic effect with the perforated film further enhances their noise reduction effect.
The audible range for humans is said to be approximately 20 Hz to 20,000 Hz. 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, Toyo says it ran actual vehicle tests using tyres it manufactures and markets. The results of its 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 reduce 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, Toyo says it plans to continue to study commercialization of tyres equipped with this device in the future, and to expand the market.