Resilient tires and wheels – Tires – resilient – Pneumatic tire or inner tube
Reexamination Certificate
1999-11-19
2004-08-24
Yao, Sam Chuan (Department: 1733)
Resilient tires and wheels
Tires, resilient
Pneumatic tire or inner tube
C152S539000, C152S541000, C152S547000, C152S555000, C152S516000
Reexamination Certificate
active
06779573
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a pneumatic tire, and more particularly to a pneumatic radial tire belonging to a category known as so-called run-flat tire and capable of running over a given distance at a state that an internal pressure becomes zero (atmospheric pressure) or near to zero due to puncture or the like. Preferably, the invention relates to a pneumatic radial tire having a ratio of section height to section width or an aspect ratio of not less than 60 and an excellent run-flat durability (“run-flat” means the running at a punctured state) when being run at a high speed over a relatively long distance at the punctured state while holding a low cost and a handling easiness.
2. Description of Related Art
The run-flat type radial tire (hereinafter abbreviated as run-flat tire) is mainly used in vehicles such as passenger cars and the like under a relatively small loading applied to the tire. It is demanded that when the tire becomes a flat (punctured) state, even if it suddenly occurs during not only the running on general road but also the high-speed running on an expressway, the run-flat tire can safely be run without considerably degrading the steering stability of the vehicle, particularly a passenger car, and even if the running is continued at the punctured state over the relatively long distance, the run-flat tire can be safely and surely run over a given distance, for example, 80-160 km to an intended place without detaching from a rim used (approved rim) and causing the tire breakage.
For this end, there are proposed run-flat tires having various structures, which are often combined with a contrived approved rim. The tires for such proposals are roughly classified into a super low-section profile tire having an aspect ratio of less than 60 and a low-section profile tire having an aspect ratio of 60-80 in which the section height is relatively high.
As to the super low-section profile tire, an example (
20
) of run-flat tires put into practical use in the market at most is shown in FIG.
5
. This tire
20
is a tire having a structure that a thick rubber reinforcing layer
9
having a crescent shape in section is arranged at an inner surface side of an innermost carcass ply
6
-
1
over a zone ranging from a bead portion
2
through a sidewall portion
3
to an end of a tread portion
4
. Such a tire is often mounted onto a vehicle premising high-speed running such as a sports car, a sports-type car or the like.
In order to mitigate a degree of collapse deformation as far as possible when the tire
20
having the thick rubber reinforcing layer
9
is run at a flat state under loading, a radial carcass
6
is constituted by two or more plies comprising a turnup ply
6
-
1
wound around a bead core
5
from an inside of the tire toward an outside thereof and a down ply
6
-
2
enveloping the turnup ply
6
-
1
from the outside thereof, and a hard stiffener rubber
8
is arranged so as to extend from an outer peripheral surface of the bead core
5
up to a position near to a maximum tire width, and as the case may be, a rubberized layer of Kevlar cords or steel cords (which is called as an insert ply) is disposed in a zone ranging from the bead portion
2
to the sidewall portion
3
.
On the other hand, the low-section profile tire having a relatively high section height is recently and frequently mounted onto an imported or domestic high-grade passenger car having a relatively great displacement. This type of the tire is possible to be run at the run-flat state in cooperation with a rim to be assembled, wherein an incorporation of a protect member for pushing a bead portion of the tire toward a rim flange onto the rim is the main current. Because, a height of a sidewall portion
3
in the low-section profile tire (see
FIG. 5
) is considerably higher than that of the super low-section profile tire and the sidewall portion
3
violently bends by a height difference between both the tires and as a result the desired run-flat durability can not be obtained.
In the tire
20
having the above construction as shown in
FIG. 5
, it is proposed and practiced to increase the thickness or the height of the rubber reinforcing layer
9
, or to largely increase the hardness or modulus of rubber itself for improving the durability in the run-flat running. However, they have a limitation on manufacture and a limitation on the rising width of the cost, so that when the internal pressure is suddenly at a state of zero, it is particularly insufficient to ensure the steering stability of the vehicle in the high-speed running and also the durability is insufficient in the continuation of the running at the run-flat state. Therefore, it is desired to develop tires holding the above performances and improving the run-flat durability to a level causing no problem in practical use.
In the case of incorporating the protect member onto the rim, there is firstly a problem in so-called rim assembling operability because it is not easy to assemble the tire onto a wheel. Secondly, it is unavoidable to largely increase the weight in the tire-wheel assembly, which brings about significant increase of unsprung mass in the vehicle and hence the ride comfort of the vehicle against vibrations is considerably degraded, so that it is unsuitable as the tire for use in a high-grade passenger car.
The inventors have thoroughly investigated a position and a cause of tire trouble generated in time series during the run-flat running of the tire
20
shown in
FIG. 5
with respect to the run-flat durability and confirmed that a position of trouble most quickly generated in the tire is an end portion of &ggr;-region in the belt
7
(see
FIG. 5
) and then such a trouble successively causes a trouble of the rubber reinforcing layer
9
in &bgr;-region of the sidewall portion
3
(see
FIG. 5
) and a trouble of the stiffener rubber
8
in &agr;-region of the bead portion
2
(see FIG.
5
). Therefore, the inventors have already proposed a pneumatic tire
21
A having particularly an aspect ratio of not less than 60, in which a cushion rubber
10
as shown in
FIG. 6
is interposed between the end portion of the belt
7
and the outermost carcass ply
6
-
2
(see
FIG. 5
) and tan &dgr; of the cushion rubber
10
is made not more than that of a coating rubber for the cords of the carcass ply
6
as described in Japanese Patent Application No. 10-121422. This tire
21
A is demonstrated that the remarkable improvement of the durability can advantageously be realized in the end portion of the belt
7
during the run-flat running to attain an excellent run-flat durability.
However, it is demanded to further improve the run-flat durability without stop at the present time. The run-flat durability satisfying the above demand is conditioned to satisfy that it is possible to at least run over a distance of 80-160 km as previously mentioned under the continuation of running at an upper level of limit speed at the run-flat state on the expressway even in the pneumatic tire having the aspect ratio of not less than 60. Under such a severer condition, it is the present state that it is required to more further improve the run-flat durability improved in the aforementioned pneumatic tire
21
A.
SUMMARY OF THE INVENTION
It is, therefore, an object of the invention to provide a pneumatic tire having particularly an aspect ratio of not less than 60 which controls the cost to a level not causing trouble in practice, holds the handling easiness for rim assembling operability or the like and maintains the ride comfort within an acceptable range without causing inconvenience in the production applying the conventional thick rubber reinforcing layer, and guarantees the safe running of the vehicle such as passenger car or the like even if air is rapidly released due to the puncture or the like, and does not cause fatal trouble even if the high-speed running on the expressway is continued at a limit speed or a speed near thereto for a long time, and can develop a highly excellent run-fl
Kobayashi Kazuomi
Matsuo Kenji
Nishikawa Tomohisa
Bridgestone Corporation
Fischer Justin
Yao Sam Chuan
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