Resilient tires and wheels – Tires – resilient – Pneumatic tire or inner tube
Reexamination Certificate
2003-01-13
2004-11-30
Johnstone, Adrienne C. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Pneumatic tire or inner tube
C152S539000
Reexamination Certificate
active
06823914
ABSTRACT:
TECHNICAL FIELD
This invention relates to a heavy duty pneumatic radial tire, and more particularly to tires suitable for use in vehicles such as trucks, buses and the like, and particularly it relates to a heavy duty pneumatic radial tire in which an organic fiber cord layer is used in a bead portion of the tire used under severe conditions of load, running speed and the like as a reinforcing layer effective for the bead portion to improve a bead portion durability.
BACKGROUND ART
In the heavy duty pneumatic radial tire suitable for use in trucks, buses and the like, it is common to reuse a base tire for recapping when a tread rubber reaches a service limit in the wear because it is not desirable to use a new tire only once. Referring to
FIG. 16
, illustrating a section of a main part of the conventional tire inclusive of a bead portion, there is often observed a case of causing a long and large crack or a separation failure accompanied with the growth of the crack in an end
4
te
of a turnup portion
4
t
of a carcass
4
or an outer end
6
e
of a rubberized steel cord layer (generally called a wire chafer)
6
as a reinforcing layer for a bead portion
1
among members constituting the bead portion
1
. The used tire having such defects is unsuitable as a base tire and it is obliged to give up recapping thereof. When the service conditions are very severe, the aforementioned crack or separation failure is caused even in the new tire on the way of the service life.
The aforementioned long crack or separation failure in an end portion such as end
4
te,
end
6
e
or the like results from the concentration of large strain in such end portion. Referring to
FIG. 17
showing a section of another conventional tire, in order to eliminate this strain, there is widely used means where one or more organic fiber cord layers, two layers in the illustrated embodiment, for example, nylon cord layer
15
(
15
-
1
,
15
-
2
) generally called a nylon chafer are arranged outside the turnup portion
4
t
of the carcass
4
alone in case of
FIG. 16
or together with the steel cord layer
6
as the reinforcing layer in the case of FIG.
18
and adjacent thereto at a height sufficiently covering the above end portion in a radial direction of the tire.
However, the application or addition of the organic fiber cord layer
15
does not develop an effect to an intended extent and reasons thereof are investigated to elucidate the following facts.
That is, as a part of the two organic fiber cord layers
15
-
1
,
15
-
2
(see
FIG. 17
,
FIG. 18
) is perspectively shown in
FIG. 19
showing a half lower-side of a tire running under loading at a zone ranging from a leading edge of a contact patch to a trailing edge thereof, cords C
R
(upward to the right in the figure) and cords C
L
(upward to the left in the figure) of the organic fiber cord layers
15
-
1
,
15
-
2
are arranged so as to cross with each other between the layers in a bead portion
1
corresponding to a ground contact region of the tire tread rotating under a given air pressure and under loading, so that even in either case of arrangements upward to the left and the right, the cords have to be always subjected to compression deformation at the leading side or the trailing edge of the contact patch.
Although detailed reasons of always causing the compression deformation will be described later, the degree of compression deformation becomes higher when the traction force and braking force are further applied to the tire. When an axial compression force is applied to the cord in the organic fiber cord layer
15
, the modulus of the organic fiber cord becomes very low to the axial compression, so that the rigidity required for developing a stress mitigating function of the organic fiber cord layer
15
naturally intended to the turnup end
4
te
of the carcass
4
or the end
6
e
of the reinforcing layer
6
is largely diminished. According to experiments, a ratio of axial compression modulus to tensile modulus in the organic fiber cord layer embedded in rubber is only about 0.1.
And also, it has been confirmed that cracking failure is caused in an end portion of the organic fiber cord layer
15
toward the outside of the tire. As a result of an investigation on the cause of the cracking failure, it is elucidated to be caused by a large tensile strain applied to rubber in the vicinity of the end
15
e
of the organic fiber cord layer
15
toward the outside of the tire. That is, air pressure filled in the heavy duty pneumatic radial tire mainly used in truck and bus is as high as 7.00~9.00 kgf/cm
2
, for example, at room temperature and is further increased by a rising of tire temperature accompanied with the running of the vehicle. As shown in
FIG. 18
, a large tension T is applied to the carcass
4
by a higher internal pressure, and the large tension T produces pulling forces a, b of arrow direction in not only the turnup portion
4
t
of the carcass
4
, but also the bead portion reinforcing layer
6
and the organic fiber cord layer
15
and hence the turnup portion
4
t
, bead portion reinforcing layer
6
and organic fiber cord layer
15
are forcibly displaced in the acting direction of the pulling forces a, b. Such a forced displacement particularly causes a large tensile strain e in rubber near to the end
15
e
of the organic fiber cord layer
15
. The tensile strain e is further increased by bending deformation of the bead portion
1
under loading shown by a phantom line. Consequently, a fatigue crack is created in rubber near to the end
15
e
of the organic fiber cord layer
15
by repetitive action of strain amplitude of the tensile strain e accompanied with the rotation under loading, which grows to finally cause the separation failure.
In addition, it is strongly demanded to form a lower section profile of radial ply tires for recent trucks and buses, from which it tends to increase low-section tires. In the low-section tire used under heavy load, the deformation of the bead portion
1
is particularly increased and the strain amplitude quantity of the tensile strain e is considerably increased, so that there is high-lighted cracking failure or separation failure in the end
15
e
of the organic fiber cord layer
15
located toward the outside of the tire, which has hardly been observed in the conventional tire. This type of the failure is a recent tendency and an effective improving countermeasure does not exist at the present time.
It is, therefore, an object of the invention to provide a heavy duty pneumatic radial tire in which the organic fiber cord layer advantageously develops the rigidity as a stress mitigating layer to the end of the turnup portion of the carcass and the end of the bead portion reinforcing layer made of the steel cord layer extending over the turnup end outward in the radial direction of the tire and also the resistance to cracking in the end of the organic fiber cord layer is largely improved even in a tire having a small aspect ratio to considerably improve the bead portion durability and recapping property as compared with the conventional tire.
SUMMARY OF THE INVENTION
In order to achieve the above object, a first aspect of the invention lies in a heavy duty pneumatic radial tire comprising a carcass of at least one rubberized cord ply of radial arrangement toroidally extending between a pair of bead core embedded in bead portions and wound around the bead core from inside of the tire toward outside to form a turnup portion, and at least one rubberized organic fiber cord layer extending outside the turnup portion over an end of the turnup portion outward in a radial direction of the tire, in which the organic fiber cord layer is arranged so as to extend from a position near to an outside of the bead core over the end of the turnup portion toward the outside of the tire and spread apart to the turnup portion.
In a preferable embodiment of the first aspect of the invention, the organic fiber cord layer has a first bent portion acutely bending toward the outside of the tire with respe
Bridgestone Corporation
Johnstone Adrienne C.
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