Resilient tires and wheels – Tires – resilient – Pneumatic tire or inner tube
Reexamination Certificate
1999-02-26
2001-01-09
Johnstone, Adrienne C. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Pneumatic tire or inner tube
C156S117000
Reexamination Certificate
active
06170547
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a pneumatic radial tire; in particular, it pertains to a pneumatic radial tire which is capable of suppressing irregular wear of the tread by an improved helical belt that is arranged on the outer peripheral side of the carcass.
BACKGROUND ART
The tread patterns of pneumatic radial tires are often determined mainly in view of the desired performance of the tire, such as maneuvering stability and wet performance. Also, it is conventional practice that the tread is formed with a plurality of grooves extending in the circumferential direction and widthwise direction of the tire, to thereby define discrete land portions in the form of blocks. In this instance, there is a tendency that the tread undergoes irregular wear. One may then consider that the block configuration can be modified for the purpose of preventing irregular wear of the tread, though such modifications are not practically carried out. This is because modification of the block configuration makes it difficult to preserve the maneuvering stability, wet performance and the like, which are required as the basic performance of the tire. Accordingly, it would be desirable to suppress irregular wear of the tread by improving the belt structure.
SUMMARY OF THE INVENTION
The present invention is based on recognition obtained with respect to pneumatic radial tires in which there is arranged, on outer peripheral side of a radial carcass, a winding layer or so-called helical belt layer wherein a ribbon comprised of a plurality of cords embedded in a rubber is successively wound in helical manner with a predetermined angle relative to the circumferential direction of the tread portion. In connection with such pneumatic tires, it has been conceived that the helical belt can be improved so as to effectively suppress irregular wear of the tread without modification of the block configuration.
The inventor thus conducted through investigations on the mechanism of occurrence of irregular wear of the tread portion, as well as countermeasures for suppressing and preventing the same. The result of such investigations can be summarized as follows.
First of all, it is considered that irregular wear of a tire tread portion due to the driving force occurs under the following causal relationship. That is, as illustrated in
FIG. 1
, attention is directed to the relative positional relationship between an arbitrary point P on the outermost layer
11
of a tire
10
, i.e., a helical belt layer, and a point Q on the tread region which is intersected by a normal line of the outermost belt layer passing through the point P. In this case, when the tire
10
is applied with a driving force, the tread rubber
12
undergoes a shearing deformation within the ground contact surface so that a point Q
1
on the tread region, which is located on the normal line passing through a point P
1
on the belt layer
11
outside the ground contact surface, is shifted to a retracted point Q
2
in the ground contact surface, which is retraced rearwards of a point P
2
in the rotational direction R. That is the relationship indicated by the line segment P
1
-Q
1
, which is perpendicular to the belt layer
11
outside the ground contact surface, changes to the relationship indicated by the line segment P
2
-Q
2
, which is inclined relative to a normal line n intersecting the point P
2
on the belt layer
11
within the ground contact surface, during which the tread rubber
12
undergoes a shearing deformation. This relationship is maintained until immediately before the tread region comes out of the ground contact surface as shown by a line segment P
3
-Q
3
. Then, as soon as the tread region comes out of the ground contact surface, the tread rubber
12
is restored to the original state so that the relationship indicated by a line segment P
4
-Q
4
is recovered wherein the point Q
4
on the tread region is located on the normal line intersecting the point P
4
on the belt layer
11
as is the case with the point Q
1
, for the line segment P
1
-Q
1
. This recovery causes the shear strain of the tread rubber
12
to be rapidly released, thereby causing a sliding movement of the tread rubber
12
and a resultant increase in the wear amount of the edge portion, particularly at the kick-out side of the block. This is a main factor of so-called “heel-and-toe wear”.
It can be therefore understood that, by reducing the shear strain of the tread rubber, which is caused immediately before the tread region comes out of the ground contact surface, it is possible to suppress the heal-and-toe wear. The inventor has experimentally confirmed that the deformation of the tread rubber caused immediately after the tread region steps into the ground contact surface does not significantly depend on the belt structure of the tire. Based on such recognition, the inventor found that the wear of the tread rubber can be suppressed by reducing the relative displacement between the outermost belt layer
11
and the tread, so that the shear strain indicated by the line segment P
3
-Q
3
in
FIG. 1
at the kick-out side of the tread region is reduced to the deformation which is indicated by the line segment P
3A
-Q
3A
in FIG.
2
.
Furthermore, the inventor noted that the tread portion undergoes a marked bending deformation in the vicinity of a portion which is applied with the load when the tire is pressed against the road surface, and the bending deformation causes a compressive deformation along a circumferential direction of the belt layer with a longitudinal center line of the tread portion as the center. The inventor then considered that, by arranging the outermost belt layer at a location spaced from the bending-neutral plane by as increased distance as possible, it would be possible to reduce the compressive deformation amount of the belt layer and thereby reduce the relative displacement between the outermost belt layer and the tread. Thus, in order to have the outermost belt layer arranged at a location spaced from the bending-neutral plane by as increased distance as possible, a trial has been conducted in which a rubber layer of approximately 1 mm in thickness was arranged between the outermost belt layer and the second belt layer as seen from the outer side, though an intended function could not have been achieved.
Investigations were further conducted with respect to the cause thereof, and it has been revealed that the compressive deformation of the outermost belt layer due to the bending deformation of the tread portion is absorbed by the deformation (so-called buffer deformation) of the belt layer arranged inside of the outermost belt layer, so that the outermost belt layer does not sufficiently undergo a compressive deformation. Thus, in order to suppress such buffer deformation of the rubber and arrange the outermost belt layer at a location spaced from the bending neutral plane by as increased distance as possible, a trial has been made in which a helical layer was formed by successively winding, helically in the axial direction of the tire, a ribbon comprised of a rubber layer of about 2 mm in thickness, for example, and cords which are dispersed within the rubber layer not only in the width direction thereof but also in the radial direction of the tire, in the manner to be more fully described below with reference to illustrated embodiments. As a result, it became possible to achieve a large compressive deformation of the outermost belt layer as indicated by outlined arrows in
FIG. 2
, and increase the compressive deformation amount by approximately 25% particularly in a region adjacent to the center of the ground contact surface. This is because the rubber material of the outermost belt layer is substantially divided by the cords and such arrangement of the cords contributes to suppression of the buffer deformation. Moreover, it has been found that, by suitably setting the distance between the peak and the bottom of the cord-arrangement, due to the dispersion of cords in the radial direction of the tire, there is no
Bridgestone Corporation
Johnstone Adrienne C.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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