Toyo Tire & Rubber Co Ltd, which is known for the Toyo Tires brand, says it has developed a technology to reduce noise caused by tires.
Specifically, it can reduce road noises such as (1) low noise generated at the time of traveling on a rough road surface and (2) road noise generated at the time of going over road seams by up to 75%, contributing to realizing a comfortable in-vehicle space. It is expected to be applied to tires to be released in early 2019.
There are two kinds of noise caused by tires at the time of driving a vehicle. One is road noise. When tires are being shaken due to irregularities on the road surface, the vibration is transmitted to the axles, causing road noise.
The other is pattern noise. When sound generated between tires and the road surface is transmitted to the in-vehicle space via the body and windows, it becomes pattern noise.
This time, Toyo Tire & Rubber aimed to reduce the former (road noise). While the level of pattern noise is determined by the shape of the tire grounding surface, road noise is caused partly by the vibration of air inside tires. What causes the noise is a phenomenon called "cavity resonance," in which air resonates inside like a drum.
It was difficult to reduce road noise, so Toyo Tire & Rubber considered that the reduction of road noise would result in a great improvement.
Toyo Tire & Rubber focused on the airflow inside a tire. By carrying out fluid simulations many times, the company succeeded in visualizing air moving inside a rotating tire and found that there are two flows. One is in the circumferential direction (the direction of the rotation), and the other is in the vertical direction (the direction toward the center of the tire).
With the knowledge of airflow, it becomes possible to know the flow of sound generated by the resonance.
Noise reduced by passing it through hole
To reduce cavity resonance and, thus, road noise, Toyo Tire & Rubber developed a device made of polyurethane and attached it along the inner circumference of a tire. The device consists of a porous film and 16 cylindrical sponges. Each sponge weighs 10-12g (mass), and the polyurethane has a higher durability than commonly-used industrial polyurethanes.
The sponges pull the porous film in the vertical direction to form the shape of an arch in the aim of increasing the area in which the resonance sound contacts the porous film and sponges.
When sound passes through a hole, its volume diminishes. When resonance sound passes through the porous film or cylindrical sponge, part of the sound turns into frictional heat. The rest of the sound, which does not turn into frictional heat, stays near the hole as if it is swirling. As a result, the sound does not spread, and its volume decreases.
"Our technology is different from other companies' technologies in that it utilizes airflow," Toyo Tire & Rubber said.
Other companies attach a sound-absorbing material to the inner circumference of a tire.
Toyo Tire & Rubber prototyped a tire by using the new technology, applied it to a minivan and tested the vehicle. As a result, compared with conventional tires that are not equipped with the device, noise was reduced by up to about 12dB in a low-frequency band of 200-250Hz. This is equivalent to a noise reduction of 75%, according to a calculation made by the company.
There is a strong demand for such technologies from automakers, especially Europe-based luxury car manufacturers, because they are expected to realize a high-quality, comfortable in-vehicle space, said Manabu Moriya, executive officer of Toyo Tire & Rubber.
Several overseas manufactures have already employed other tire manufacturers' technologies that attach a sound-absorbing material, etc, for mass-produced vehicles. For example, Audi AG and Tesla Inc are increasingly using those technologies, he said. On the other hand, Japanese automakers do not seem to be actively using them.
Toyo Tire & Rubber, which is a new comer in the field, targets the new technology at the market for electric vehicles (EVs). EVs, which use a motor in place of an engine, are much quieter than normal gasoline vehicles. However, the low noise level can be a problem because noises caused by tires can be heard more clearly.
The use of EVs is expected to spread in tandem with autonomous driving technologies. In-vehicle spaces where no one has to take the wheel will become like living rooms. To enhance its presence in the field of next-generation vehicles, the company plans to strengthen the technological development of the "quiet tire."© Nikkei Technology Online