Resilient tires and wheels – Tires – resilient – Pneumatic tire or inner tube
Reexamination Certificate
1999-03-29
2001-11-20
Johnstone, Adriene C. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Pneumatic tire or inner tube
C152S539000, C152S547000, C152S552000, C152S554000
Reexamination Certificate
active
06318431
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a heavy duty radial tire of which bead portions can be improved in durability.
BACKGROUND OF THE INVENTION
With the recent improvements in road networks and vehicles' performance, high running performance is required even in heavy duty tires for trucks, buses and the like. In recent years, radial carcass and heavy duty radial tires in which the outside of the radial carcass is tightened by a rigid belt are widely employed. Such heavy duty radial tires are high in the rigidity of the tread portion and excellent in high speed performance, and further they show an excellent wear resistance, mileage and the like.
By the way, during running, a heavy duty radial tire is repeatedly subjected to the large stress in a region from the sidewall portion to bead portion. In this region, very small cracks (hereinafter referred “cracks” simply) are liable to occur due to such stress and ozone in the atmosphere.
The cracks make it impossible to recycle the tires, and there is a possibility that a carcass ply separation is caused if cracks are grown inwardly of the tire.
It becomes clear that, in heavy duty radial tires, especially those which are mounted on a five-degree-taper rim j of which bead seats j
1
are tapered at five degrees with respect to the tire axial direction as shown in
FIG. 12
, since the outer surface of the bead portions comes into contact with a curved surface j
2
of the rim flange over a wide range (for example 80% or more), a large strain is produced and heat generation occurs in the contacting part during running.
Such strain and heat, by their multiplier effect, harden or deteriorate the rubber in the bead portions which causes early damages such as cracks, carcass ply separation and the like.
DESCRIPTION OF THE INVENTION
In the inventions set forth in claims
1
to
3
, it is an object to provide a heavy duty radial tire in which, by controlling cracks, especially those liable to occur on the surface of the bead portion over a long time period, the bead portions can be improved in durability.
The present inventors discovered that the larger the maximum principal strain at the tire outer surface, the greater the possibility of cracks occurring when the tire mounted on a regular rim is inflated. Further, it was discovered that cracks are liable to concentrate upon spots where strain is relatively large when a maximum principal strain &egr;m is at the tire outer surface in a region between a maximum tire width point at which the tire outer surface is axially outmost and an outer contact point which is the radially outmost point of a contacting region where the bead portion contacts with the rim flange, and
when the difference (&egr;m−&egr;p) of the maximum principal strain &egr;m from a maximum principal strain &egr;p at the above-mentioned maximum tire width point are large.
To be effective for controlling maximum principal strain it was discovered
to turn up the carcass ply around the bead core from axially inside to outside to form a turnup portion, and
to dispose the turnup portion adjacent to and parallel with a main portion to form a parallel portion, and to limit the parallel portion to a length of 1.0 to 8.0 times the maximum section width CW of the bead c ore.
Further, it is an object to further improve the durability of the bead portion by preventing carcass ply separations and preventing cracks. For this purpose, a side packing rubber having a 100% modulus of 14 to 65 kgf/sq.cm more preferably 47 to 60 kgf/sq.cm is disposed on the axial outer surface of the carcass ply turnup portion, and the position of the radially outer end thereof is limited.
Furthermore, in order to further prevent the above-mentioned cracks and separations, the ratio (St/S) of a contact length St of the outer surface of the bead portion with the curved flange surface and a curved length S of the curved flange surface is set to be 0.2 to 0.70, more preferably 0.4 to 0.65.
In this specification, the “regular rim” is a rim having dimensions specified an a standard rim specified by JATMA, a “Design Rim” by TRA, or a “Measuring Rim” by ETRTO. The “regular inner pressure” is a maximum air pressure specified by JATMA, a maximum value specified in the “Tire Load Limits At Various Cold Inflation Pressures” table of TRA, or a “Inflation Pressure” specified by ETRTO.
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Asano Kenji
Nakagawa Tsuneyuki
Numata Kazuki
Shiraishi Masaki
Ueyoko Kiyoshi
Birch & Stewart Kolasch & Birch, LLP
Johnstone Adriene C.
Sumitomo Rubber Industries Ltd.
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