Resilient tires and wheels – Tires – resilient – Pneumatic tire or inner tube
Reexamination Certificate
1998-07-08
2002-07-02
Johnstone, Andrienne C. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Pneumatic tire or inner tube
C152S526000, C152S528000, C152S531000, C152S537000
Reexamination Certificate
active
06412534
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to pneumatic redial tires, and more particularly to a heavy duty pneumatic radial tire used from small-size truck to middle- to large-size vehicles such as trucks, buses and the like which improves a belt durability when being run on good roads exemplified by paved road surface or the like at a relatively higher speed and is excellent in the resistance to tire damage based on exterior input such as cut burst, shock burst or the like which is liable to be caused when being run on bad roads exemplified by non-paved road surface.
2. Description of Related Art
Recently, high-speed running and diversification for running mode progress with the advance of improving the performances of vehicles, while the lowering of deck height in the vehicles is generalized. Therefore, the service conditions for pneumatic tires used in these vehicles, particularly pneumatic radial tires used in vehicles of from small-size truck to truck and bus tend to become more severer as compared with the conventional service conditions. On the other hand, the demand for recapped tires is increasing in the middle- to large-size vehicles, and particularly tires capable of conducting the recapping several times is demanded.
Under the above situations, since belt durability in the pneumatic radial tire is particularly an important performance, not only the occurrence of separation failure from a belt end in a new tire but also the occurrence of large cracks in the belt end of a used base tire to be recapped becomes a problem. Such a lacking of belt durability is particularly serious in low-section profile tires used in low deck vehicles.
Among vehicles such as small-size truck, usual-size truck and the like, there is a dump truck mainly running on non-paved road. Further, sightseeing buses and so on are obliged to sometimes run on non-paved road apart from city buses. Although it is unavoidable that protuberant pebble stones and quarrying are scattered on the non-paved road, foreign matters such as metallic pieces having a sharp edge may be existent even on a paved road surface. Therefore, when the tire mounted on these vehicles rides on the foreign matter such as protuberant pebble stones, quarrying, metallic piece and the like, there may be caused cut damage arriving at the belt or burst failure based on the cut damage, or there may be caused shock burst prior to the cut damage.
It need scarcely be said that the structure of the belt is deeply concerned in the aforementioned problems on the belt durability and on the cut burst or shock burst. In general, the conventional belt has a structure shown by symbol
6
A in FIG.
10
. The belt
6
A is comprised of four steel cord layers
6
A-
1
to
6
A-
4
, in which at least two adjacent layers are cross cord layers, cords of which layers being crossed with each other with respect to an equatorial plane E of the tire.
In the belt
6
A of the conventional tire, an inclination angle of steel cord with respect to the equatorial plane E is 50-70° in an innermost layer
6
A-
1
and 15-25° in middle layers
6
A-
2
,
6
A-
3
, and that of an outermost layer
6
A-
4
is the same as in the middle layer
6
A-
3
. The middle layers
6
A-
2
,
6
A-
3
are cross cord layers, and the outermost layer
6
A-
4
has the same cord inclining direction as the middle layer
6
A-
3
and serves as a protection layer to external wound. In the tire having such a belt
6
A, however, interlaminar shearing strain in end portions of the middle layers
6
A-
2
and
6
A-
3
having a large cord crossing angle is remarkably large during running under loading and interlaminar separation failure based thereon is liable to be caused and also durability to heat generation is lacking, so that the outermost layer
6
A-
4
does not sufficiently play a role as the protection layer. Also, this tire has a problem that cut burst failure or shock burst failure is substantially defenseless. These problems are serious in low-section profile tires having a small aspect ratio.
In order to solve the above problems, JP-A-57-201704 proposes a heavy duty pneumatic radial tire used under a higher internal pressure in which at least two circumferential cord layers are disposed on an outer circumference of a carcass and two or more cross cord layers are disposed on a circumference thereof, and cords of the circumferential cord layer have a relative elongation before fracture of at least 8% and a heat shrinkage of at least 1.25% prior to the inflation of air pressure, and cords of each of the cross cord layers have an inclination angle of 45-90° with respect to the equatorial plane of the tire and are extensible and heat shrinkable, and JP-A-2-81706 proposes a heavy duty pneumatic tire in which a belt is comprised of a first strip disposed on an outer circumference of a carcass and containing wavy or zigzag reinforcing elements arranged along the equatorial plane, and a second strip of at least two layers, cords of which layers being crossed with each other at an inclination angle of 30-60° with respect to the equatorial plane.
However, the tires disclosed in these publications generate a large shearing strain in end portions of the cross cord layers during the running under loading because the belt is provided with the adjoining laminated cross cord layers, cords of which layers being crossed with each other with respect to the equatorial plane. As a result, the interlaminar separation failure is liable to be caused in the end portions of the cross cord layers, so that the belt structure disclosed in these publications is naturally critical in the improvement of the belt durability and hence the anticipated belt durability can not be obtained. In the tire of JP-A-57-201704, organic fiber cords are used as a reinforcing element for the belt, so that there is also a problem that the resistance to cut burst or shock burst is lacking.
In relation to the problem on the separation at the end portions of the cross cord layers as mentioned above, JP-A-2-81705 proposes a belt structure comprised of a first strip containing wavy or zigzag reinforcing elements arranged along the equatorial plane of the tire, and a second strip of a single layer containing cords arranged at an inclination angle of 15-70° with respect to the equatorial plane. JP-A-8-318706 proposes a belt structure comprised of a single slant belt layer disposed on an outer circumference of a carcass and containing a plurality of cords or filaments inclined with respect to the equatorial plane, and at least one circumferential belt layer disposed at an outside of the slant belt layer and containing a plurality of organic fiber cords arranged in parallel to the equatorial plane.
The tires having the belt structure disclosed in the latter two publications are concerned with a pneumatic radial tire for passenger car and are designed to establish the reduction of weight and cost and the improvement of performances for passenger tire such as cornering property, durability, high-speed durability and the like. They do not have cross cord layers, so that there is not an anxiety of causing the separation at the end portions of the cross cord layers. However, they are not used at a considerably high air pressure under a large load such as heavy duty pneumatic radial tire of the invention here, so that they have no concern with the improvement of performances in the heavy duty pneumatic radial tire such as belt durability, resistance to cut burst, resistance to shock burst and the like.
SUMMARY OF THE INVENTION
It is, therefore, an object of the invention to provide heavy duty pneumatic tires having mainly an aspect ratio of not more than 75% which have a sufficient resistance to belt separation in a new tire and improve a durability of belt end, which is unacceptable in repetitive recapping after use, to provide a belt durability sufficiently durable to reuse as a recap tire, and have excellent resistances to cut burst and shock burst and are capable of largely prolonging total service life of the tire.
A
Kimura Takahiro
Kohno Yoshihide
Tsuruta Makoto
Bridgestone Corporation
Johnstone Andrienne C.
Sughrue & Mion, PLLC
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