Recently, reduction of a vehicle noise (for example, an airflow noise or machine sound) in a vehicle such as a passenger car has been further developed. However, according to continually increasing of needs for a comfortable riding environment, a necessity for a reduction of tire noise has increased more than before.
In order to reduce a noise of tread with respect to a road, various shapes of tread have been developed. A purpose of such a noise reduction technique is for dispersing noise frequencies generated by the tread to wideband frequencies, so as to reduce the noise near to a level of so-called white noise.
Further, relatively high temperature heat is generated from the tire mounted on the vehicle due to a high-speed rotation thereof or friction with the road surface. However, rubber which is a major component of the tire has a low heat dissipation performance due to the material characteristics thereof. For this reason, heat generated from the tire is not properly transmitted to an outside, therefore the lifespan of each component may be shortened, and the tire may be separated or ruptured due to a serious deterioration in tire durability. In particular, radial tires for trucks or buses which are used in harsh conditions, or run-flat tires for the purpose of traveling in an emergency situation are greatly influenced by durability due to a temperature.
When the run-flat tire travels in an emergency situation (in the case that pressure inside the tire is 0 psi), a periodically fluctuating load is applied to the tire, which causes a bending and stretching motion of the sidewall. When the inside of the tire is filled with air, a degree of bending and stretching motion in the sidewall is relatively small, but when the run-flat tire travels in an emergency situation of 0 psi, the degree thereof becomes large. In this case, heat is generated from the side wall by the continuously repeated large bending and stretching motion and thermal stress is continuously applied to sidewall reinforcing rubber for supporting the tire against load, causing a rupture in the tire.
In order to solve the problems, techniques for forming protruded cooling fins on the sidewall have been developed. For example, Korean Patent Laid-Open Publication No. 10-2010-0070796 discloses a pneumatic tire including blade-shaped structures and cooling fins formed on a sidewall for improving heat dissipation performance. However, these techniques have a problem that a resonance phenomenon occurs by an airflow noise generated during high speed air collapsing due to the cooling fins, and thereby the noise is significantly increased.
Accordingly, a technique capable of reducing an amount of heat convection in the sidewall from which a lot of heat is generated, as well as decreasing the airflow noise is required for a pneumatic tire.
In addition, for a conventional tire, since cooling fins are formed at fixed intervals for reducing heat generation and turbulence regularly generated by the collision of high speed air is insufficient for effectively radiating heat. That is, if sufficient turbulence is not generated, the air resistance does not easily decrease.
Accordingly, there is still a need for the pneumatic tire to reduce the amount of heat convection in the sidewall from which a lot of heat is generated, as well as efficiently decrease the air resistance.