Resilient tires and wheels – Tires – resilient – Anti-skid devices
Reexamination Certificate
1998-04-08
2001-03-27
Maki, Steven D. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Anti-skid devices
C152S209280
Reexamination Certificate
active
06206064
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pneumatic tire having inclined grooves at the tread, and in particular, to a pneumatic tire in which both wet properties are improved and pattern noise is reduced.
2. Description of the Related Art
In the field of pneumatic tires, there is an increasing number of examples of pneumatic tires utilizing an inclined main groove pattern in order to achieve both wet properties and a reduction in pattern noise.
However, in such conventional pneumatic tires, it is easy for uneven wear to occur at the blocks which are defined by the inclined main grooves in vicinities of the end portions of the tread. When the tire is new, both wet properties and low pattern noise are achieved, but as uneven wear occurs, the pattern noise worsens.
Further, after the tire becomes worn, the superior reduction in pattern noise which the tire exhibits over a conventional straight pattern tire disappears, and in some cases, the conventional tire may even be superior with regard to reducing pattern noise.
SUMMARY OF THE INVENTION
In view of the aforementioned, an object of the present invention is to provide a pneumatic tire which aims to achieve both wet properties and reduced pattern noise, and in which uneven wear of blocks at the tread end portion sides of an inclined groove pattern is improved, and in which pattern noise at the time of wear is also improved.
A first aspect of the present invention is a pneumatic tire in which a plurality of inclined main grooves are disposed in a tire circumferential direction from positions spaced apart from one another at both sides of a tire equatorial plane toward tread end sides so as to extend in opposite directions at either side of the tire equatorial plane and so as to be inclined with respect to the tire circumferential direction, wherein each of said inclined main grooves extends at an angle of inclination of 15 to 45° with respect to the tire circumferential direction; at a vicinity of a tread end side final end, each of said inclined main grooves extends at an angle of inclination of 75 to 105° with respect to the tire circumferential direction, and opens with a narrow width at a tread end; at a vicinity of a tire equatorial plane side final end, each of said inclined main grooves extends, in a circular-arc-shape convex toward a tire equatorial plane side, toward an intermediate portion of an inclined main groove which is adjacent in the tire circumferential direction, so as to open at the adjacent inclined main groove; at a tread side region, said inclined main grooves which are aligned in the tire circumferential direction are communicated by auxiliary grooves which are more narrow than said inclined main grooves; a rib which is continuous along the tire circumferential direction is defined on a tire equatorial plane, and a plurality of blocks which are aligned in the tire circumferential direction are defined at both sides of the rib; and given that an angle of inclination of a groove wall surface of said inclined main groove at a block step-in end side with respect to a normal line which passes through an opening end and is perpendicular to a tread stepping surface is &thgr;1 and an angle of inclination of a groove wall surface of said inclined main groove at a block kick-out end side with respect to a normal line which passes through an opening end and is perpendicular to the tread stepping surface is &thgr;2, &thgr;1<&thgr;2 from a tread center to said auxiliary groove and &thgr;1>&thgr;2 from said auxiliary groove to the tread end.
The operation of the pneumatic tire of the first aspect of the present invention will be described hereinafter.
First, operation relating to the water-removing ability will be discussed.
On a wet road surface, water within the tread stepping surface behaves as follows. At the vicinity of the step-in side of the tread stepping surface, in the vicinity of the tread center region, water flows forward in the tire circumferential direction or forward at less than 20° with respect to the tire circumferential direction. Next, at the tread intermediate region, water flows forward at 20 to 40° with respect to the tire circumferential direction. At the tread side region, water flows toward the outer side of the tire at an angle exceeding 40° with respect to the tire circumferential direction.
In the pneumatic tire of the first aspect of the present invention, the tread stepping surface is sectioned by inclined main grooves as follows. At the tread intermediate region, the inclined main groove extends at an angle of inclination of 15 to 45° with respect to the tire circumferential direction. At the final end of the inclined main groove which final end extends toward the tread center region, the inclined main groove extends in a circular-arc-shape, i.e., the inclination thereof with respect to the tire circumferential direction is small. At the final end of the inclined main groove which final end extends toward the tread end side, the inclined main groove extends substantially along the tread transverse direction, i.e., the inclination thereof with respect to the tire circumferential direction is large. The inclined main groove thus extends in directions coinciding with the above-described behavior of water within the tread stepping surface. Thus, an excellent water-removing ability is ensured.
Next, operation with respect to the pattern noise will be discussed.
An example of pattern noise of a tire is the striking sound made at the time of step-in of the block.
In the pneumatic tire of the first aspect of the present invention, at the portion of the inclined main groove from the tread center to the auxiliary groove, the angle of inclination &thgr;1 of the groove wall surface at the block step-in end side is set to be smaller than the angle of inclination &thgr;2 of the groove wall surface at the block kick-out end side. Therefore, at the blocks which are defined by the inclined main grooves from the tread center to the auxiliary grooves, the rigidity of the step-in end side is less than the rigidity of the kick-out end side.
In this way, because the rigidity of the step-in end of the block is smaller, the impact at the time of step-in of the block when the pneumatic tire is rolling can be lessened, and the striking sound can be decreased.
If the tread is divided into a tread central region at the tread center side and tread side regions positioned at the both sides of the central region, the tread central region (about the same as the region from the tread center to the auxiliary grooves) is a region at which there is no uneven wear of the blocks. Therefore, due to the aforementioned decrease in the striking sound at the time of step-in, pattern noise can be reduced over the entire lifetime of the tire.
From the auxiliary grooves to the tread ends, the angle of inclination &thgr;1 of the block step-in end side groove wall surface is greater than the angle of inclination &thgr;2 of the block kick-out end side groove wall surface. Therefore, at the blocks which are defined by the inclined main grooves from the auxiliary grooves to the tread ends, the rigidity of the kick-out end side is lower than the rigidity of the step-in end side.
It is easy for uneven wear to occur at the blocks at the regions at the tread end sides of the tread, i.e., the blocks at the tread side regions. (Uneven wear is wear in which the kick-out end side of the block is worn, and is also called heel-and-toe wear.) It is known that when uneven wear occurs, pattern noise increases.
While the tire is rolling, the blocks deform as they contact the road surface, and return to their original shapes as they move apart from the road surface. Heel-and-toe wear is wear which occurs at the time the block moves apart from the road surface, i.e., due to the sliding at the time of kick-out from the road surface.
In the pneumatic tire of the first aspect of the present invention, at the blocks which are defined by the portions of the inclined main grooves from the auxiliary groove
Bridgestone Corporation
Maki Steven D.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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