Resilient tires and wheels – Tires – resilient – Anti-skid devices
Reexamination Certificate
2001-07-31
2004-01-27
Maki, Steven D. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Anti-skid devices
C152S209270, C152S209230, C152S523000
Reexamination Certificate
active
06681823
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a heavy load pneumatic radial tire which has plural of ribs divided by plural of main grooves in the circumferential direction on the tread surface of the tread portion and in more detail, relates to a technique of preventing uneven wear from being generated on the shoulder rib surface which runs on both sides of the tread surface of the said tread portion.
2. Description of the Prior Art
As heavy load pneumatic radial tires loaded on trucks, buses, or the like, which are driven on the well-paved road, as tread patterns, tires with ribs are employed more frequently than tires with blocks, from the viewpoint of wear resistance, ride quality, fuel cost, or the like. However, at the grounding part with loading, due to the bending of the side wall, particularly as for tires having ribs on the tread portion, due to the partially heavy pressure at the end part in the tire width direction of the shoulder rib, the abrasion of the part is promoted, and the shoulder rib wears earlier than the other ribs, thereby sometimes causing “side dropped abrasion” in which shoulder rib sinks like a step.
Such uneven wear begins at the external end part in the tire width direction in the shoulder rib of the tread portion and as the mileage increases, the uneven wear expands into the internal side in the tire width direction, and winds its way in the tire circumferential direction as well, thereby causing uneven wear which is so called “river wear”. When the mileage further increases, ribs in the shoulder portion as a whole are worn. Consequently, a step is generated between the adjacent ribs of the shoulder portion set inside in the tire width direction interposing the main groove therebetween, thereby causing “side dropped abrasion”. This “side dropped abrasion” is not preferable since it generates defective appearance and short duration of tire life.
Heretofore, in order to improve uneven wear, for example, a tire as shown in
FIG. 7
has been provided.
FIG. 7
shows an example of the conventional heavy load pneumatic radial tire and shows a schematic local sectional view of the right half in the tire width direction from the center line CL which vertically and equally divides the cross sectional view into two.
FIG. 8
shows a schematic local sectional view of the tread portion showing the non-grounding state at the time of filling standard pressure in the conventional tire.
FIG. 9
shows a schematic local sectional view of the tread portion showing the grounding state of the tire shown in FIG.
8
.
FIG. 10
shows an enlarged schematic local sectional view of the tread portion showing the grounding state near the shoulder portion shown in FIG.
9
.
FIG. 11
shows a schematic top view representing the tread pattern of the conventional tire.
A tire shown in
FIG. 7
is provided with the carcass CC, the tread portion
100
which covers the crown region of the carcass CC, and the belt
106
having plural of belt cords between the tread
100
and the crown region of the said carcass CC. In addition, a tire shown in
FIG. 7
is a tire having plural of main grooves
102
which run circumferentially at the tread surface
111
of the said tread portion
100
and plural of ribs
103
divided by these main grooves
102
. In the tire in
FIG. 7
, as shown in
FIGS. 7 and 8
, a circular fine groove
150
is provided in the side region
140
A of the shoulder portion
140
running on both sides of the surface
111
of the tread portion
100
with the aperture
151
whose one end is opened to the side region
140
A. This fine groove
150
is the fine groove of straight groove sectional view having substantially the same groove width from the aperture
151
to the groove bottom
154
. In other words, this fine groove
150
comprises the external wall
152
of the external side in the tire diameter direction leading to the external side
141
in the tire diameter direction of the side region
140
A of the shoulder portion
140
, the internal wall
153
of the internal side in the tire diameter direction leading to the internal side
142
in the tire diameter direction of the side region
140
A of the shoulder portion
140
, and the groove bottom
154
leading to the said external wall
152
and the said internal wall
153
. The said external wall
152
and the said internal wall
153
extend to the groove bottom in a substantially parallel manner.
In this conventional tire, the said fine groove
150
decreases the partially heavy grounding pressure on the surface of the said rib
103
S, particularly on the surface of the end portion (rib
103
A) of the external side in the tire width direction since the force F to the external part in the tire width direction of the rib
103
S in the shoulder portion
140
which causes uneven wear, is diminished by the force required to fill the gap of the said fine groove.
However, when this conventional tire is filled with air at standard pressure and then loaded on the vehicle and driven, as shown in
FIGS. 9 and 10
, and when this tire contacts the ground surface G, the force F transmitted from the side wall SW which affects the rubber surrounding the said fine groove
150
makes the external wall
152
and the internal wall
153
of the fine groove
150
contact each other and acts as a force f
1
indicated by arrow blocking in from the aperture
151
to the vicinity of the groove bottom.
Therefore, such force f
1
, as shown in
FIG. 10
, acts as the force to push the rib
103
S in the shoulder portion
140
in the grounding state into the internal side in the tire width direction (that is, the side of a center line which vertically and equally divides the cross sectional view of the tire into two), and in the surface of the said rib
103
S, its grounding pressure, particularly at the end of the tire width direction gets high on the ground surface. On the other hand, in accordance with the revolution of the tire at the time of driving, when the grounding state of the rib
103
S in the said shoulder portion
140
comes to be released, since the action by the force f
1
against the said rib
103
S is gone, the fine groove
150
which has been compressed between the external wall
152
and internal wall
153
recovers to the initial state, the gains of the said grounding pressure on the surface of the said rib
103
S are released.
Thus, the above described phenomena are repeated in the conventional tire whenever the grounding and the non grounding state are repeated. Consequently, the conventional tire, as described above, although trying to prevent uneven wear, reducing the grounding pressure of the rib
103
S in the shoulder portion
140
by the said fine groove
150
, right after the external wall
152
and the internal wall
153
in the fine groove
150
contact each other and block up, the grounding pressure begins to rise. Therefore, even if the conventional tire is provided with such fine grooves, it cannot be said that the tire fully prevents uneven wear which is likely to occur on the surface of the rib
103
S in the shoulder portion
140
.
In addition, in the conventional tire, as described above, when it contacts the ground surface G, the force f
1
makes the external wall
152
and internal wall
153
of the fine groove
150
contact and makes them block up from the aperture
151
to the vicinity of the back of the groove. Then by such force f
1
, the groove bottom
154
is compressed, leaving little gap of the fine groove
150
, making the curvature of the groove bottom
154
big and making the deformation of groove bottom
154
big. And when the grounding state in this rib
103
S is released, the state recovers again to the state shown in FIG.
8
and the blocked-up state of the fine groove
150
is released. Therefore, since these phenomena are repeated at the time of driving, cracks are likely to be generated on groove walls, in particular, on groove bottom
154
, and the tire life is likely to be damaged. These phenomena remarkably appear in the heavy load pneuma
Maki Steven D.
Merchant & Gould P.C.
Toyo Tire & Rubber Co., Ltd.
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