U.S. patent application number 13/249407 was filed with the patent office on 2012-05-10 for pneumatic tire with tread having ground contact shape and uneven wear sacrificial protrusion.
This patent application is currently assigned to BRIDGESTONE CORPORATION. Invention is credited to Naomichi FUNATO, Mie NONAKA.
Application Number | 20120111467 13/249407 |
Document ID | / |
Family ID | 35781756 |
Filed Date | 2012-05-10 |
United States Patent
Application |
20120111467 |
Kind Code |
A1 |
NONAKA; Mie ; et
al. |
May 10, 2012 |
PNEUMATIC TIRE WITH TREAD HAVING GROUND CONTACT SHAPE AND UNEVEN
WEAR SACRIFICIAL PROTRUSION
Abstract
A pneumatic tire with an air pressure corresponding to maximum
loading, such that the ground contact shape has a gradually
decreasing circumferential direction length from the tire width
direction center to the portion corresponding towards the tire
width direction outermost circumferential groove, followed by the
ground contact shape having a gradually increasing circumferential
direction length towards the tire width direction outside. In the
ground contact shape, the relationships
0.02.ltoreq.(A-B)/L.ltoreq.0.1, and 0.02.ltoreq.(C-B)/L.ltoreq.0.1
are satisfied, in which A is the maximum length in the
circumferential direction of the tire width direction outermost
rib, L is the circumferential direction length of the tire width
direction center, and B and C are distances in a tire
circumferential direction which depend on the width of the tire
width direction outermost rib and the width of the second rib from
the outside in the tire width direction.
Inventors: |
NONAKA; Mie; (Tokyo, JP)
; FUNATO; Naomichi; (Tokyo, JP) |
Assignee: |
BRIDGESTONE CORPORATION
Tokyo
JP
|
Family ID: |
35781756 |
Appl. No.: |
13/249407 |
Filed: |
September 30, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11630576 |
Jul 17, 2007 |
8056591 |
|
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PCT/JP05/11410 |
Jun 22, 2005 |
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13249407 |
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Current U.S.
Class: |
152/209.18 |
Current CPC
Class: |
Y10S 152/901 20130101;
B60C 2011/013 20130101; B60C 11/01 20130101 |
Class at
Publication: |
152/209.18 |
International
Class: |
B60C 11/00 20060101
B60C011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 23, 2004 |
JP |
2004-185055 |
Claims
1. A pneumatic tire provided with a tread including a plurality of
ribs separated by at least two circumferential direction grooves
extending in a circumferential direction wherein: when looking at
the tread ground contact shape under conditions that the pneumatic
tire is mounted onto a rim with maximum loading, and with an air
pressure corresponding to maximum loading, the ground contact shape
has a gradually decreasing circumferential direction length from
the tire width direction center to the portion corresponding
towards the tire width direction outermost circumferential groove,
followed by the ground contact shape having a gradually increasing
circumferential direction length towards the tire width direction
outside, and in the ground contact shape, the following
relationships are satisfied: 0.02.ltoreq.(A-B)/L.ltoreq.0.1, and
0.02.ltoreq.(C-B)/L.ltoreq.0.1, wherein L is the circumferential
direction length of the tire width direction center, A is the
maximum length in the circumferential direction of the portion
corresponding to the tire width direction outermost rib, Ws is the
width of the portion corresponding to the tire width direction
outermost rib, W.sub.2 is the width of the portion corresponding to
the second rib from the outside in the tire width direction, B is
the distance in the tire circumferential direction between two
points that are intersections of border lines of circumferential
direction sides of the portion corresponding to the outermost rib,
intersecting with a first virtual line extending in the tire
circumferential direction and at a distance of 0.076 Ws in the tire
width direction to the outside from a border line of the portion
corresponding to the outermost rib, the border line corresponding
to an edge of a circumferential direction groove on the inside of
the outermost rib in the tire width direction, and C is the
distance in the tire circumferential direction between two points
that are the intersections of border lines of circumferential
direction sides of the portion corresponding to the second rib from
the outside in the tire width direction, intersecting with a second
virtual line that extends in the tire circumferential direction and
is a distance of 0.112 W.sub.2 to the inside in the tire width
direction from a border line corresponding to the tire width
direction outside circumferential direction groove edge of the
portion corresponding to the second rib from the outside in the
tire width direction.
2. The pneumatic tire according to claim 1 wherein an uneven wear
sacrificial protrusion with a peak portion thereof positioned lower
than the road surface and that contacts the road surface during
ground contact is formed at at least the bottom of the tire width
direction outermost circumferential groove.
3. The pneumatic tire according to any one of claims 1 wherein
indentation portions are formed in the tire width direction
outermost rib at the side face thereof outside in the tire width
direction of the tread ground contact shape edge, reducing the
rigidity of the rib.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation of U.S. application Ser. No.
11/630,576 filed Jul. 17, 2007 which is a National Stage Entry of
PCT Application No. PCT/JP2005/011410 filed Jun. 22, 2005, and
which claims priority to Japanese Patent Application No.
2004-185055 filed Jun. 23, 2004. The entire disclosures of the
prior applications are hereby incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to a pneumatic tire, and in
particular to a pneumatic tire that can suppress uneven wear that
easily develops when the pneumatic tire is used on the steering
axel of a heavily loaded vehicle.
BACKGROUND ART
[0003] In general, the shape of the ground contact portion
(footprint) of a pneumatic tire is, for example, as shown at
numeral 100 in FIG. 8, such that the length of the ground contact
portion gradually reduces from the central portion toward the
shoulder portion. However, with the rib pattern of the ground
contact shape 100 uneven wear due to dragging in the vicinity of
tread ground contact edge 102E is easily generated, and in order to
suppress the above uneven wear the ground contact shape can be made
close to a rectangular shape.
[0004] However, if the ground contact shape gets closer to
rectangular, due to the variation in the conditions of tire
manufacture and conditions of use, the length of the ground contact
increases from the central portion to the shoulder portion to give
the ground contact shape 104, and rib punch wear easily develops in
the vicinity of the outer edge in the tire width direction at the
second rib from the outer side rib 106 (the shaded portion of FIG.
9).
[0005] In order to solve this problem, a pneumatic tire has been
proposed (see Patent Publication 1) with a ground contact pattern
where the ground contact length first gets shorter from the central
portion in the tire width direction to the tread ground contact
edge side, and then the ground contact length gradually gets longer
up to the tread ground contact edge.
Patent Publication 1: Japanese Patent Application Laid-Open (JP-A)
No. 5-77608.
DESCRIPTION OF THE INVENTION
Problem to be Solved by the Invention
[0006] The pneumatic tire in Patent Publication 1, by considering
the ground contact shape, can suppress uneven wear due to dragging
in the vicinity of the tread ground contact edge and suppress
shoulder scrubbing as a side force makes the tread edge rounded and
this wear then progresses towards the center.
[0007] However, there is strong market demand to further suppress
uneven wear.
[0008] The invention has been made with regard to the above problem
to be solved and an object of the invention is to provide a
pneumatic tire that is able to suppress uneven wear further than
conventionally.
Means to Solve the Problems
[0009] As a result of carrying out a series of investigations and
experiments, the inventors have been able to find a significant
improvement in uneven wear by optimizing the relative proportions
of the dimensions of the ground contact portions of the ribs
separated by the circumferential grooves.
[0010] An aspect of an exemplary embodiment provides: a pneumatic
tire provided with a tread including plural ribs separated by at
least two circumferential direction grooves extending in a
circumferential direction. When looking at the tread ground contact
shape under conditions that the pneumatic tire is mounted onto a
rim with maximum loading, and with an air pressure corresponding to
maximum loading, the ground contact shape has a gradually
decreasing circumferential direction length from the tire width
direction center to the portion corresponding towards the tire
width direction outermost circumferential groove, followed by the
ground contact shape having a gradually increasing circumferential
direction length towards the tire width direction outside. In the
ground contact shape, the following relationships are
satisfied:
0.02.ltoreq.(A-B)/L.ltoreq.0.1, and 0.02.ltoreq.(C-B)/L.ltoreq.0.1.
In these relationships: L is the circumferential direction length
of the tire width direction center; A is the maximum length in the
circumferential direction of the portion corresponding to the tire
width direction outermost rib; Ws is the width of the portion
corresponding to the tire width direction outermost rib; W.sub.2 is
the width of the portion corresponding to the second rib from the
outside in the tire width direction; B is the distance in the tire
circumferential direction between two points that are intersections
of border lines of circumferential direction sides of the portion
corresponding to the outermost rib, intersecting with a first
virtual line extending in the tire circumferential direction and at
a distance of 0.076 Ws in the tire width direction to the outside
from a border line of the portion corresponding to the outermost
rib, the border line corresponding to an edge of a circumferential
direction groove on the inside of the outermost rib in the tire
width direction; and C is the distance in the tire circumferential
direction between two points that are the intersections of border
lines of circumferential direction sides of the portion
corresponding to the second rib from the outside in the tire width
direction, intersecting with a second virtual line that extends in
the tire circumferential direction and is a distance of 0.112
W.sub.2 to the inside in the tire width direction from a border
line corresponding to the tire width direction outside
circumferential direction groove edge of the portion corresponding
to the second rib from the outside in the tire width direction.
[0011] Next, the operation of the pneumatic tire will be
explained.
[0012] Uneven wear in the vicinity of the tread edge due to
dragging and shoulder scrubbing wear can be suppressed more than
conventionally. Under conditions that the pneumatic tire is mounted
onto a rim with maximum loading, and with an air pressure
corresponding to maximum loading, the ground contact shape has a
gradually decreasing circumferential direction length from the tire
width direction center to the portion corresponding towards the
tire width direction outermost circumferential groove, followed by
the ground contact shape having a gradually increasing
circumferential direction length towards the tire width direction
outside, and satisfies the following relationships:
0.02.ltoreq.(A-B)/L.ltoreq.0.1, and 0.02.ltoreq.(C-B)/L.ltoreq.1
0.1. In these relationships: L is the circumferential direction
length of the tire width direction center; A is the maximum length
in the circumferential direction of the portion corresponding to
the tire width direction outermost rib; Ws is the width of the
portion corresponding to the tire width direction outermost rib;
W.sub.2 is the width of the portion corresponding to the second rib
from the outside in the tire width direction; B is the distance in
the tire circumferential direction between two points that are
intersections of border lines of circumferential direction sides of
the portion corresponding to the outermost rib, intersecting with a
first virtual line extending in the tire circumferential direction
and at a distance of 0.076 Ws in the tire width direction to the
outside from a border line of the portion corresponding to the
outermost rib, the border line corresponding to an edge of a
circumferential direction groove on the inside of the outermost rib
in the tire width direction; and C is the distance in the tire
circumferential direction between two points that are the
intersections of border lines of circumferential direction sides of
the portion corresponding to the second rib from the outside in the
tire width direction, intersecting with a second virtual line that
extends in the tire circumferential direction and is a distance of
0.112 W.sub.2 to the inside in the tire width direction from a
border line corresponding to the tire width direction outside
circumferential direction groove edge of the portion corresponding
to the second rib from the outside in the tire width direction.
[0013] Here, if (A-B)/L<0.02 then uneven wear in the vicinity of
the edge of the ground contact of the outermost rib in the tire
width direction due to dragging easily occurs.
[0014] On the other hand, if (A-B)/L>0.1 then uneven wear in the
vicinity of the inside edge portion of the tire width direction
outermost rib due to dragging easily occurs.
[0015] Further, if (C-B)/L<0.02, then uneven wear in the
vicinity of the edge of the ground contact of the second rib from
the outside in the tire width direction due to dragging easily
occurs.
[0016] On the other hand, (C-B)/L>0.1 then uneven wear in the
vicinity of the inside edge portion of the tire width direction
outermost rib easily occurs.
[0017] An aspect of another exemplary embodiment provides a
pneumatic tire provided with a tread including plural ribs
separated by at least two circumferential direction grooves
extending in a circumferential direction wherein: R1 is less than
R2, where, when looking at a cross-section of the tire along the
rotational axis, R1 is a radius of curvature of a first running
surface of the tread located on the tire equatorial plane side of a
tire width direction outermost circumferential groove, and R2 is a
radius of curvature of a second running surface of the tread
located to the shoulder side of a tire width direction outermost
circumferential main groove; the second running surface is located
to the inside in the tire diameter direction of a virtual extension
line of the first running surface; and further db is less than da,
where da is a step height between the first running surface and a
virtual extension line of the second running surface, and db is a
step height at the edge of the ground contact of the tread between
the second running surface and the virtual extension line of the
first running surface. By being as above, the ground contact shape
of the tread under conditions that the pneumatic tire is mounted
onto a rim with maximum loading, and with an air pressure
corresponding to maximum loading, has a gradually decreasing
circumferential direction length from the tire width direction
center to the portion corresponding towards the tire width
direction outermost circumferential groove, followed by the ground
contact shape having a gradually increasing circumferential
direction length towards the tire width direction outside, and in
the ground contact shape, the following relationships are
satisfied: 0.02.ltoreq.(A-B)/L.ltoreq.0.1, and
0.02.ltoreq.(C-B)/L.ltoreq.0.1. In these relationships: L is the
circumferential direction length of the tire width direction
center; A is the maximum length in the circumferential direction of
the portion corresponding to the tire width direction outermost
rib; Ws is the width of the portion corresponding to the tire width
direction outermost rib; W.sub.2 is the width of the portion
corresponding to the second rib from the outside in the tire width
direction; B is the distance in the tire circumferential direction
between two points that are intersections of border lines of
circumferential direction sides of the portion corresponding to the
outermost rib, intersecting with a first virtual line extending in
the tire circumferential direction and at a distance of 0.076 Ws in
the tire width direction to the outside from a border line of the
portion corresponding to the outermost rib, the border line
corresponding to an edge of a circumferential direction groove on
the inside of the outermost rib in the tire width direction; and C
is the distance in the tire circumferential direction between two
points that are the intersections of border lines of
circumferential direction sides of the portion corresponding to the
second rib from the outside in the tire width direction,
intersecting with a second virtual line that extends in the tire
circumferential direction and is a distance of 0.112 W.sub.2 to the
inside in the tire width direction from a border line corresponding
to the tire width direction outside circumferential direction
groove edge of the portion corresponding to the second rib from the
outside in the tire width direction.
[0018] Next, the operation of the pneumatic tire will be
explained.
[0019] R1 is less than R2, where, when looking at a cross-section
of the tire along the rotational axis, R1 is a radius of curvature
of a first running surface of the tread located on the tire
equatorial plane side of a tire width direction outermost
circumferential groove, and R2 is a radius of curvature of a second
running surface of the tread located to the shoulder side of a tire
width direction outermost circumferential main groove; the second
running surface is located to the inside in the tire diameter
direction of a virtual extension line of the first running surface;
and further db is less than da, where da is a step height between
the first running surface and a virtual extension line of the
second running surface, and db is a step height at the edge of the
ground contact of the tread between the second running surface and
the virtual extension line of the first running surface. By being
as above, the ground contact shape of the tread under conditions
that the pneumatic tire is mounted onto a rim with maximum loading,
and with an air pressure corresponding to maximum loading, can be
made to have a gradually decreasing circumferential direction
length from the tire width direction center to the portion
corresponding towards the tire width direction outermost
circumferential groove, followed by the ground contact shape having
a gradually increasing circumferential direction length towards the
tire width direction outside. That is, it is possible to easily
obtain such a ground contact shape by the running surface
cross-section, without depending on the internal structure of the
tire.
[0020] Uneven wear in the vicinity of the tread edge due to
dragging and shoulder scrubbing wear can be suppressed more than
conventionally by the ground contact shape of the tread, under
conditions that the pneumatic tire is mounted onto a rim with
maximum loading, and with an air pressure corresponding to maximum
loading, having a gradually decreasing circumferential direction
length from the tire width direction center to the portion
corresponding towards the tire width direction outermost
circumferential groove, followed by the ground contact shape having
a gradually increasing circumferential direction length towards the
tire width direction outside, and the following relationships being
satisfied:
0.02.ltoreq.(A-B)/L.ltoreq.0.1, and 0.02.ltoreq.(C-B)/L.ltoreq.0.1.
In these relationships: L is the circumferential direction length
of the tire width direction center; A is the maximum length in the
circumferential direction of the portion corresponding to the tire
width direction outermost rib; Ws is the width of the portion
corresponding to the tire width direction outermost rib; W.sub.2 is
the width of the portion corresponding to the second rib from the
outside in the tire width direction; B is the distance in the tire
circumferential direction between two points that are intersections
of border lines of circumferential direction sides of the portion
corresponding to the outermost rib, intersecting with a first
virtual line extending in the tire circumferential direction and at
a distance of 0.076 Ws in the tire width direction to the outside
from a border line of the portion corresponding to the outermost
rib, the border line corresponding to an edge of a circumferential
direction groove on the inside of the outermost rib in the tire
width direction; and C is the distance in the tire circumferential
direction between two points that are the intersections of border
lines of circumferential direction sides of the portion
corresponding to the second rib from the outside in the tire width
direction, intersecting with a second virtual line that extends in
the tire circumferential direction and is a distance of 0.112
W.sub.2 to the inside in the tire width direction from a border
line corresponding to the tire width direction outside
circumferential direction groove edge of the portion corresponding
to the second rib from the outside in the tire width direction.
[0021] Here, if (A-B)/L<0.02 then uneven wear in the vicinity of
the edge of the ground contact of the outermost rib in the tire
width direction due to dragging easily occurs.
[0022] On the other hand, if (A-B)/L>0.1 then uneven wear in the
vicinity of the inside edge portion of the tire width direction
outermost rib easily occurs.
[0023] Further, if (C-B)/L<0.02, then uneven wear in the
vicinity of the edge of the ground contact of the second rib from
the outside in the tire width direction due to dragging easily
occurs.
[0024] On the other hand, (C-B)/L>0.1 then uneven wear in the
vicinity of the inside edge portion of the tire width direction
outermost rib easily occurs.
[0025] An uneven wear sacrificial protrusion with a peak portion
thereof positioned lower than the road surface and that contacts
the road surface during ground contact is formed at at least the
bottom of the tire width direction outermost circumferential
groove.
[0026] Since there is a difference in the diameter of the tread
running surface an the diameter of the peak portion of the uneven
wear sacrificial protrusion, when the tire is rotated and contacts
the road surface, there is dragging of the uneven wear sacrificial
protrusion relative to the road surface and abrasion of the uneven
wear sacrificial protrusion, and uneven wear of the ribs that are
adjacent to the circumferential groove can be further suppressed.
Furthermore, progression of uneven wear towards the center side can
be suppressed.
[0027] Indentation portions are formed in the tire width direction
outermost rib at the side face thereof outside in the tire width
direction of the tread ground contact shape edge, reducing the
rigidity of the rib.
[0028] Next, the operation of the pneumatic tire will be
explained.
[0029] By forming indentation portions in the tire width direction
outermost rib at the side face thereof outside in the tire width
direction of the tread ground contact shape edge, the rigidity of
the rib in the vicinity of the tread ground contact edge is
reduced, and the frictional force with the road surface is reduced,
and so generation of uneven wear can be suppressed.
EFFECT OF THE INVENTION
[0030] By the above construction of the pneumatic tires an
excellent effect can be obtained that, as explained above, uneven
wear can be suppressed more than conventionally.
[0031] By the above construction of the pneumatic tire an excellent
effect can be obtained that uneven wear of the ribs, adjacent to
the circumferential groove in which the uneven wear sacrificial
protrusion is formed, can be further suppressed, and progression of
uneven wear towards the center side can be suppressed.
[0032] By the above construction of the pneumatic tire an excellent
effect can be obtained that the generation of uneven wear of the
tire width direction outermost rib in the vicinity of the tread
ground contact edge can be further suppressed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 shows a ground contact shape of a pneumatic tire
according to a first embodiment of the invention;
[0034] FIG. 2 is a tread cross-section along the tire rotational
axis direction of a pneumatic tire of the first embodiment of the
invention;
[0035] FIG. 3 is a tread cross-section along the tire rotational
axis direction of a pneumatic tire of a second embodiment of the
invention;
[0036] FIG. 4 is a tread cross-section along the tire rotational
axis direction of a pneumatic tire of a third embodiment of the
invention;
[0037] FIG. 5 is a tread cross-section along the tire rotational
axis direction of a pneumatic tire of a Comparative Example 1;
[0038] FIG. 6 is a tread cross-section along the tire rotational
axis direction of a pneumatic tire of a Comparative Example 2;
[0039] FIG. 7 is a graph showing the experimental results of wear
tests;
[0040] FIG. 8 is a tread plan view showing a conventional ground
contact shape;
[0041] FIG. 9 is a tread plan view showing another conventional
ground contact shape.
BEST MODE OF THE INVENTION
First Embodiment
[0042] Details of a pneumatic tire 10 according to a first
embodiment of the invention will be explained below with reference
to the drawings.
[0043] The first embodiment of the invention will be explained with
reference to FIG. 1 and FIG. 2.
[0044] As shown in FIG. 2, the tread 12 of the pneumatic tire 10 is
provided, on each side in the tire width direction (in the
direction of arrow A) of the equatorial plane of the tire CL, with
a first circumferential direction main groove 14 extending around
the periphery of the tire (one side is omitted in FIG. 2), and, on
the outside of the first circumferential direction main groove 14
in the tire width direction, a second circumferential direction
main groove 16 extending around the periphery of the tire (one side
is omitted in FIG. 2).
[0045] The first circumferential direction main groove 14 and the
second circumferential direction main groove 16 of the first
embodiment of the invention both extend linearly with a constant
width around the tire circumferential direction.
[0046] FIG. 1 shows the ground contact shape 12F of the tread 12 of
this pneumatic tire 10 under conditions that the pneumatic tire is
mounted onto a rim with maximum loading, and with an air pressure
corresponding to maximum loading.
[0047] As is shown in FIG. 1, the circumferential direction length
of the ground contact shape 12F gradually decreases from the center
in the tire width direction towards the second circumferential
direction main groove 16 at the outside in the tire width
direction. After that, the circumferential direction length of the
ground contact shape 12F then gradually increases towards the
outside in the tire width direction.
[0048] In this ground contact shape, the circumferential direction
length of the tire width direction center is designated L, the
maximum length in the circumferential direction of the border line
18F of the ground contact shape of shoulder rib 18 is designated A,
the width of the border line 18F of the ground contact shape of
shoulder rib 18 is designated Ws, the width of the border line 20F
of the ground contact shape of second rib 20 is designated W.sub.2,
and in the ground contact shape of the shoulder rib 18, B is
designated for the distance in the tire circumferential direction
between two points Psa and Psb that are the intersections of a
first virtual line FLs (that extends in the tire circumferential
direction and is a distance of 0.076 Ws to the outside in the tire
width direction from the border line 18Fi corresponding to the edge
of the second circumferential direction main groove 16) and the
border line 18F.
[0049] In the ground contact shape of the second rib 20, C is
designated for the distance in the tire circumferential direction
between two points P.sub.2a and P.sub.2b that are the intersections
of a second virtual line FL.sub.2 (that extends in the tire
circumferential direction and is a distance of 0.112 W.sub.2 to the
inside in the tire width direction from the border line 20Fo
corresponding to the edge of the second circumferential direction
main groove 16) and the border line 20F.
[0050] The relationships are satisfied that:
0.02.ltoreq.(A-B)/L.ltoreq.0.2, and
0.02.ltoreq.(C-B)/L.ltoreq.0.18.
[0051] It is more preferable that these relationships are
satisfied:
0.05.ltoreq.(A-B)/L.ltoreq.0.15, and
0.03.ltoreq.(C-B)/L.ltoreq.0.13.
[0052] In order to provide such ground contact shapes, the
sectional shape of the tread 12 of the pneumatic tire 10 of the
current embodiment is set in the following manner.
[0053] The running surface of tread 12, as seen in FIG. 2 cross
section of tread 12 along the tire rotational axis direction, has a
radius of curvature R1 (with the center of curvature on the tire
inside) of the running surface 12A at the side of the equatorial
plane CL of the second circumferential direction main groove 16,
and a radius of curvature R2 (with the center of curvature on the
tire inside) that is larger than R1 of the running surface 12B at
the shoulder side of the second circumferential direction main
groove 16.
[0054] Further, the running surface 12B is positioned overall to
the inside in the tire diameter direction of a virtual line 12Af
that is an extension of the running surface 12A.
[0055] In order to satisfy 0.02.ltoreq.(A-B)/L.ltoreq.0.1, and
0.02.ltoreq.(C-B)/L.ltoreq.0.1, for example, the height of the
running surface 12B of the shoulder rib 18, the slope angle of
running surface 12B, and the radius of curvature of running surface
12B may be adjusted in correspondence with the second rib 20 on the
inside.
[0056] For the pneumatic tire 10 of the present embodiment, as seen
in FIG. 2, the ground contact shape 12F as shown in FIG. 1 is
obtained by setting the amount of step to be da at the edge portion
of the second circumferential direction main groove 16 on the
equatorial plane CL side between the running surface 12A and a
virtual extension line 12Bf extended out from running surface 12B,
and setting the amount of step to be db (<da) at the tread
ground contact edge 12E between the virtual extension line 12Af
extended out from running surface 12A and the running surface
12B.
[0057] Here, in the first embodiment, first circumferential
direction main groove 14 and the second circumferential direction
main groove 16 extend linearly at a constant width in the
circumferential direction, however, they may extend in a zig-zag
shape.
[0058] For example, if the first circumferential direction main
groove 14 and the second circumferential direction main groove 16
are a zig-zag shape, then border line 18Fi, border line 20Fo and
border line 20Fi are zig-zag shape, and in this case Ws and W.sub.2
are calculated using the average positions around one circumference
of the tire.
(Operation)
[0059] By setting the above cross section shape and ground contact
shape of tread 12, uneven wear in the vicinity of the tread edge by
dragging and shoulder scrubbing wear can be suppressed more than
conventionally.
[0060] Here, if (A-B)/L<0.02, since ground contact length A
becomes shorter, uneven wear due to dragging in the vicinity of the
tread edge of shoulder rib 18 easily arises.
[0061] On the other hand, if (A-B)/L>0.1, the ground contact
length A becomes longer than necessary, and uneven wear of the
tread edge portion on the inside in the tire width direction of
shoulder rib 18 easily arises.
[0062] If (C-B)/L<0.02, since ground contact length C becomes
shorter, uneven wear due to dragging in the vicinity of the tread
edge of second rib 20 easily arises
[0063] On the other hand, if (C-B)/L>0.1, the ground contact
length B becomes shorter, and uneven wear of the tread edge portion
on the inside in the tire width direction of shoulder rib 18 easily
arises.
[0064] Here, for the tread ground contact edges of the present
embodiment, the pneumatic tire 10 was mounted on a standard rim as
defined in the JATMA YEAR BOOK (the Japan Automobile Tyre
Manufacturers Association Specifications; 2003 Edition), inflation
was to an air pressure (maximum air pressure) of 100% of the air
pressure corresponding to the maximum permissible load (bold load
figures in the table of internal pressure against load bearing
ability) in the application size ply rating according to the JATMA
YEAR BOOK, at the time of loading with the to the maximum
permissible load. In the location of use and manufacturing
locations, when TRA Specifications and ETRTO Specifications are
used, various specifications are followed.
Second Embodiment
[0065] Next, a pneumatic tire 10 according to the second embodiment
will be explained with reference to FIG. 3. Here, similar
structures to the first embodiment are given the same numeral, and
explanation thereof is omitted.
[0066] As can be seen from FIG. 3, in the groove bottom of the
second circumferential direction main groove 16 is formed a uneven
wear sacrificial protrusion 22 with a peak portion thereof that is
set at a position that is lower than the running surfaces 12A, B,
and that is in contact with the road surface during ground
contact.
[0067] Since there is a difference between the diameter of the
tread 12 running surfaces and the diameter of the peak portion of
uneven wear sacrificial protrusion 22, when the tire is rotating
and in contact with the road surface, the uneven wear sacrificial
protrusion 22 drags relative to the road surface and wears, and
uneven wear can be suppressed in the vicinity of the edge portion
at the second circumferential direction main groove 16 side of the
shoulder rib 18 and in the vicinity of the edge portion at the
second circumferential direction main groove 16 side of second rib
20.
[0068] Further, progression of the uneven wear of shoulder rib 18
toward the center side can be suppressed.
Third Embodiment
[0069] Next, a pneumatic tire 10 according to the third embodiment
will be explained with reference to FIG. 4. Here, similar
structures to the first embodiment are given the same numeral, and
explanation thereof is omitted.
[0070] As shown in FIG. 4, the pneumatic tire 10 of the present
embodiment has a fine groove 24 formed on the side face of shoulder
rib 18 further to the tire axel direction side than the tread
ground contact edge 12E.
[0071] By this fine groove 24, the rigidity in the vicinity of the
tread ground contact edge of shoulder rib 18 is reduced, and a
frictional force with the road surface is lowered, and the
generation of uneven wear in the vicinity of the tread ground
contact edge of shoulder rib 18 can be suppressed.
[0072] Here, the fine groove 24 may be formed to be intermittent in
the circumferential direction, and may be substituted by forming
plural holes (indentations).
(Experimental Tests)
[0073] In order to verify the effect of the invention two types of
conventional pneumatic tire, and Examples of two types of pneumatic
tire according the invention were prepared, and abrasion testing
was carried out.
[0074] The cross section of the Comparative Example 1, as can be
seen in FIG. 5, has a uniform radius of curvature of the running
surfaces (R1). The relationships of A, B, C and L are shown in
Table 1 below.
[0075] The cross sectional shape of Comparative Example 2, as can
be seen from FIG. 6, the radius of curvature of the running surface
12A on the tire equatorial plane CL side of the second
circumferential direction main groove 16 is R1, and the running
surface 12B on the tread ground contact edge 12E side has a radius
of curvature R2, and the running surface 12B is disposed toward the
outside in the tire diameter direction to a virtual extension line
12Af that is an extension of running surface 12A. The relationships
of A, B, C and L are shown in Table 1 below.
[0076] Pneumatic tires of Examples 1, 2 have cross sections
according to FIG. 2. The relationships of A, B, C and L are shown
in Table 1 below.
[0077] The tire sizes are all 295/75R22.5, and the rim sizes are
all 8.25.times.22.5.
[0078] The abrasion test method and evaluation method were: North
American market, after mounting the test tires to test vehicles (5
vehicles for each test) and running for 100,000 km, the amount of
abrasion was measured. In the evaluation, shown is an inverse
(reciprocal) index with the amount of abrasion of the Comparative
Example 1 set at 100, and the larger the figure shown the higher
the performance (change-over life).
[0079] The experimental results are shown in the Table 1 below and
FIG. 7.
TABLE-US-00001 TABLE 1 Comparative Comparative Example Example
Example 1 Example 2 1 2 (A - B)/L -0.05 0.01 0.04 0.07 (C - B)/L 0
-0.01 0.05 0.04 Portion Shoulder Second Shoulder Shoulder
developing I/W Rib Rib Rib Rib Change-over 100 90 120 125 life
index
[0080] It can be seen from the results of the tests that uneven
wear in the tires according to the invention is not as much as the
uneven wear of the tires of the Comparative Examples, and the
change-over life is longer.
INDUSTRIAL APPLICABILITY
[0081] By optimizing the ground contact shape it is possible to
suppress uneven wear that can easily develop on tires when used on
the steering axel of a heavily loaded vehicle, and it is applicable
when uneven wear suppression is desired.
EXPLANATION OF THE NUMERALS
[0082] 10 pneumatic tire
[0083] 12 tread
[0084] 12E tread ground contact edge
[0085] 14 first circumferential direction main groove
[0086] 16 second circumferential direction main groove
[0087] 18 shoulder rib
[0088] 20 second rib
[0089] 22 uneven wear sacrificial protrusion
[0090] 24 fine groove (indentation)
* * * * *