Resilient tires and wheels – Tires – resilient – Pneumatic tire or inner tube
Reexamination Certificate
2001-07-25
2004-10-12
Johnstone, Adrienne C. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Pneumatic tire or inner tube
C152S510000, C152S526000, C152S527000, C152S531000, C152S555000, C152S556000
Reexamination Certificate
active
06802350
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a pneumatic radial tire, and more particularly to a pneumatic radial tire in which the weight reduction of the tire is realized by a reinforcing structure using a monofilament cord as a cord constituting a belt layer and the degradation of belt durability is advantageously controlled by rationalizing a rubber gauge between the monofilament cords located in the adjacent belt layers.
2. Description of Related Art
In the pneumatic radial tire, the rigidity of the belt is considerably increased for improving so-called hoop effect, so that the weight is generally heavier than that of a pneumatic bias tire. As a result, the degradation of the fuel consumption become a problem. In the radial tire, therefore, various attempts are made for solving such a problem to reduce the tire weight.
For example, as shown in
FIG. 3
a
, there is widely used a belt layer
21
formed by rubberizing metal twisted cords or organic fiber twisted cords as a cord of the belt layer from the old time. Considering a case that the belt layer
21
is replaced with a belt layer
22
formed by rubberizing monofilament cords and having the same elastic modulus as in the belt layer
21
within a usable region thereof as shown in
FIG. 3
b
, a diameter d
2
of the monofilament cord can be made smaller than a diameter d
1
of the twisted cord and hence the thickness of the belt layer constituted by the cords and the coating rubber can be decreased, so that the weight reduction of the tire can be attained.
Moreover, the term “monofilament cord” used herein means a cord consisting of a single filament without twisting.
However, if it is intended to reduce the tire weight by merely changing the design from the belt layer
21
into the belt layer
22
as mentioned above, the flexible followability of the cord to the coating rubber in case of using the twisted cord is not realized in the deformation of the belt layer using the monofilament cords, so that the shearing strain between the belt layers becomes large and the separation failure between the monofilament cord and the coating rubber is apt to be easily caused at both side end portions of the belt layer by heat generation resulted from such a shearing strain and hence there is a drawback that the durability of the belt lowers.
Therefore, even if the weight reduction of the tire is attempted by using the monofilament cord instead of the twisted cord as a cord of the belt layer as mentioned above, it is strongly demanded to develop a new technique capable of ensuring the sufficient belt durability.
SUMMARY OF THE INVENTION
It is, therefore, an object of the invention to solve the above problem for satisfying such a demand, and to provide a pneumatic radial tire capable of realizing the weight reduction of the tire and effectively controlling the degradation of the belt durability by using a monofilament cord as a cord constituting the belt layer.
According to the invention, there is the provision of in a pneumatic radial tire comprising an innerliner, a carcass toroidally extending between a pair of bead portions and externally contacting with the innerliner, a belt arranged at an outer circumference side of a crown portion of the carcass, one or more cap layers covering the belt over substantially a full width thereof, and a tread arranged at an outer circumference side of the cap layer, an improvement wherein the belt is comprised of at least two belt layers each formed by covering metal monofilament cords or organic fiber monofilament cords with a coating rubber, and a rubber gauge between the monofilament cords located in the adjacent belt layers is made 1.5-5 times of a diameter of the monofilament cord.
In the tire according to the invention, the weight reduction of the tire can be attained by constituting the belt layer with the metal monofilament cords or organic fiber monofilament cords. And also, the rubber gauge between the monofilament cords in the adjacent belt layers is made 1.5-5 times, preferably 2.5-5 times of the diameter of the monofilament cord, so that the rubber gauge between the cords is sufficiently ensured while keeping the above effect of reducing the tire weight, and also the occurrence of the separation failure between the monofilament cord and the coating rubber at both side edge portions of the belt layer based on the heat generation resulted from the shearing strain between the belt layers can be prevented in the deformation of the belt layer, whereby the degradation of the belt durability can effectively be controlled.
When the rubber gauge between the monofilament cords located in the adjacent belt layers exceeds 5 times of the diameter of the monofilament cord, the sufficient weight reduction can not be achieved with the increase of the rubber gauge, while when it is less than 1.5 times, the effect for dispersing the shearing strain between the belt layers by the coating rubber is hardly obtained, and as a result, once the separation occurs between the monofilament cord and the coating rubber at both side end portions of the belt layer, the progress of the separation is fast and the early degradation of the belt durability is worried and hence the sufficient belt durability can not be ensured.
When the belt layer is constituted by arranging a plurality of cord groups, each of which groups being comprised of plural monofilament cords arranged side by side, in parallel to each other, for example, when a plurality of cord groups each comprised of 3-5 straight monofilament cords having a circular section are arranged in parallel to each other, a distance between the cord groups in the belt layer can sufficiently be ensured, so that even if the separation once occurs between the monofilament cord and the coating rubber at both side edge portions of the belt layer, the progress of the separation can be controlled.
In addition to the weight reduction by the belt as mentioned above, it is advantageous to further promote the weight reduction as a whole of the tire by reducing the weight of the innerliner. Concretely, the thickness of the innerliner is preferable to be made a range of 0.15-0.8 mm as a range enabling both the reservation of a sufficient air tightness and the achievement of the weight reduction of the tire.
The carcass is preferable to be comprised of at least one carcass ply containing rubberized polyethylene naphthalate cords therein.
When the weight reduction of the tire is realized by changing design from the belt layer using the twisted cord into the belt layer using the monofilament cord and having the same elastic modulus as in the former belt layer within the usable region thereof and the degradation of the belt durability is advantageously controlled by rationalizing the rubber gauge between the monofilament cords located in the adjacent belt layers, there is a tendency of lowering a breaking tenacity of the belt. In such a pneumatic radial tire, however, when the carcass is comprised of at least one carcass ply containing high-rigidity rubberized poly-ethylene naphthalate cords therein, the lowering of the breaking tenacity of the belt -can be compensated by the increase of the breaking tenacity of the carcass to mitigate the tension bearing ratio of the belt.
And also, when the belt is reinforced with a cap layer of rubberized polyethylene naphthalate cords extending substantially in a circumferential direction of the tire, the cap layer can sufficiently bear bending rigidity in the deformation of the belt and the like as compared with a case of applying a usually used cap layer of nylon cords, whereby heat generation resulted from the shearing strain between the belt layers is controlled to advantageously prevent the separation failure between the monofilament cord and the coating rubber at both side edge portions of the belt layer and hence the degradation of the belt durability can be avoided.
Furthermore, the lowering of the breaking tenacity of the belt as a weak point when the belt layer using the monofilament cords is used instead
Bridgestone Corporation
Johnstone Adrienne C.
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