U.S. patent application number 09/467485 was filed with the patent office on 2001-12-27 for heavy duty tire.
Invention is credited to MATSUURA, SHINICHI, TSUDA, SATOSHI.
Application Number | 20010054463 09/467485 |
Document ID | / |
Family ID | 18479002 |
Filed Date | 2001-12-27 |
United States Patent
Application |
20010054463 |
Kind Code |
A1 |
MATSUURA, SHINICHI ; et
al. |
December 27, 2001 |
HEAVY DUTY TIRE
Abstract
A heavy duty tire comprises a pair of axially outermost
circumferential rows of shoulder blocks, each of the shoulder
blocks provided with a circumferentially extending narrow groove,
the narrow groove subdividing the shoulder block into an axially
inner wide main part and an axially outer narrow lateral part, and
the narrow groove is curved convexly so that the narrow lateral
part is narrower in a middle region than both the circumferential
end regions, whereby the heel and toe wear and shoulder wear and
resistance to tear-off can be improved.
Inventors: |
MATSUURA, SHINICHI;
(KOBE-SHI, JP) ; TSUDA, SATOSHI; (AKASHI-SHI,
JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH LLP
P O BOX 747
FALLS CHURCH
VA
220400747
|
Family ID: |
18479002 |
Appl. No.: |
09/467485 |
Filed: |
December 20, 1999 |
Current U.S.
Class: |
152/209.18 ;
152/209.27 |
Current CPC
Class: |
B60C 11/11 20130101;
B60C 11/01 20130101; B60C 2011/1213 20130101; Y10S 152/902
20130101; Y10S 152/03 20130101 |
Class at
Publication: |
152/209.18 ;
152/209.27 |
International
Class: |
B60C 027/00; B60C
011/13 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 21, 1998 |
JP |
10-363304 |
Claims
1. A heavy duty tire comprising a pair of axially outermost
circumferential rows of shoulder blocks disposed in a tread, each
of the shoulder blocks provided with a circumferentially extending
narrow groove, the narrow groove subdividing the shoulder block
into an axially inner wide main part and an axially outer narrow
lateral part, and the narrow groove curved convexly so that said
narrow lateral part is narrower in a middle region than both
circumferential end regions in the circumferential direction.
2. The heavy duty tire according to claim 1, wherein a minimum
axial width of said narrow lateral part in the middle region is in
the range of from 5 to 8% of the average axial width of the
shoulder block.
3. The heavy duty tire according to claim 1, wherein said narrow
lateral part has a minimum axial width in the range of from 5 to 8%
of the average axial width of the shoulder block, and a maximum
axial width in the range of from 7 to 12% of the average axial
width.
4. The heavy duty tire according to claim 1, 2 or 3, wherein the
narrow groove comprises a central convexly curved part and a pair
of circumferential end parts, and the circumferential end parts are
substantially straight.
5. The heavy duty tire according to claim 1, 2 or 3, wherein the
narrow groove comprises a central convexly curved part and a pair
of circumferential end parts, and the circumferential end parts are
concavely curved.
6. The heavy duty tire according to claim 4 or 5, wherein the
circumferential end parts are inclined so that the axial width of
the narrow lateral part gradually increases towards both the
circumferential ends thereof.
7. The heavy duty tire according to claim 4 or 5, wherein the
circumferential end parts extends substantially parallel with the
circumferential direction.
8. The heavy duty tire according to claim 4 or 5, wherein the
circumferential length of the convexly curved part is not less than
50% of the circumferential length of the narrow groove.
9. The heavy duty tire according to claim 4 or 5, wherein the
convexly curved part has a radius of curvature in the range of from
0.8 to 2.0 times the average axial width of the shoulder block.
10. The heavy duty tire according to claim 1, wherein the narrow
groove has a width in the range of from 1.5 to 3.0 mm.
Description
[0001] The present invention relates to a heavy duty tire having an
improved tread structure capable of preventing uneven wear.
[0002] In recent years, tread patterns comprising blocks such as
block pattern, rib-block pattern and the like are widely used in
not only passenger car tires but also heavy duty tires such as
pneumatic tires for trucks, buses and the like.
[0003] In the heavy duty tires, the load of each block is
relatively heavy, and accordingly uneven wear is very liable to
occur. For example, uneven wear between axially outer part and
inner part of a block caused by a difference in the rolling
diameter of the tire is liable to occur in axially outer blocks
such as shoulder blocks. This type of uneven wear is called
shoulder wear. Uneven wear at the circumferential edges (heel and
toe) of a block is called heel and toe wear, and this type of
uneven wear occurs in every block, but the degree is higher in the
axially outer blocks such as shoulder blocks.
[0004] In order to improve the shoulder wear, it has been proposed
to subdivide each shoulder block into an axially outer narrow width
part and an axially inner wide part by a narrow groove extending
straight in the tire circumferential direction so as to concentrate
the wear on the axially outer narrow width part.
[0005] In this proposition, however, the heel and toe wear can not
be improved, and as the rigidity of the axially outer narrow width
part is low, this part is liable to be torn off.
[0006] Therefore, it is an object of the present invention to
provide a heavy duty tire in which the heel and toe wear as well as
shoulder wear is effectively improved and the resistance to
tear-off is increased.
[0007] According to the present invention, a heavy duty tire
comprises
[0008] a pair of axially outermost circumferential rows of shoulder
blocks,
[0009] each of the shoulder blocks provided with a
circumferentially extending narrow groove,
[0010] the narrow groove subdividing the shoulder block into an
axially inner wide main part and an axially outer narrow lateral
part, wherein
[0011] the narrow groove is curved convexly so that the narrow
lateral part is narrower in a middle region than both
circumferential end regions in the circumferential direction.
[0012] Preferably, the narrow groove has a width in the range of
from 1.5 to 3.0 mm. The narrow lateral part has a minimum axial
width in the range of from 5 to 8% of the average axial width of
the shoulder block, and a maximum axial width in the range of from
7 to 12% of the average axial width.
[0013] Embodiments of the present invention will now be described
in detail in conjunction with the accompanying drawings.
[0014] FIG. 1 is a developed view showing a tread pattern according
to the present invention.
[0015] FIG. 2 is a cross sectional view taken along a line A-A in
FIG. 1.
[0016] FIG. 3 is a plan view of a shoulder block showing an example
of the narrow groove.
[0017] FIG. 4 is a plan view of a shoulder block showing another
example of the narrow groove.
[0018] FIGS. 5(A) and 5(B) to FIGS. 7(A) and 7(B) are graphs
showing test results.
[0019] According to the present invention, a heavy duty tire 1 is
provided in the tread 2 with at least two circumferential grooves 3
extending continuously in the tire circumferential direction and
axial grooves 4 extending therefrom to the tread edges E.
[0020] In this embodiment, the tire is a radial ply tire of size
11R22.5 for trucks and buses. In a meridian section of the tire,
the tread 2 has a single radius curvature TR as shown in FIG.
2.
[0021] In FIG. 1, The circumferential grooves 3 include a pair of
axially outermost grooves 3c, a pair of axially inner grooves 3b,
and a central groove 3a on the tire equator C. Each circumferential
groove 3 is a zigzag groove. But various grooves, e.g. straight
groove, wavy groove and the like can be used.
[0022] The axial grooves 4 include axially outer grooves 4c
extending between the outermost circumferential grooves 3c and
tread edges E, axially inner grooves 4a extending between the
central circumferential groove 3a and the inner circumferential
grooves 3b, and middle grooves 4b extending between the inner
circumferential grooves 3b and outermost circumferential grooves
3c.
[0023] By the circumferential grooves 3 and axial grooves 4, a
block pattern made up of a plurality of blocks 5 is formed in the
tread 2. These blocks 5 are arranged in a plurality of
circumferential rows including two rows R1 of inner blocks 5a
between the axially inner grooves 3b, two rows R2 of middle blocks
5b between the axially outermost grooves 3c and the axially inner
grooves 3b, and two rows R3 of shoulder blocks 5c axially outside
the axially outermost grooves 3c.
[0024] Preferably, the circumferential grooves 3 and axial grooves
4 have a width of at least 2% of the tread width TW between the
tread edges E.
[0025] Here, the tread width TW is the maximum axial width of the
ground contacting area under a standard condition in which the tire
is mounted on a standard rim and inflated to a standard load and
then loaded with a standard load. The standard rim is the "standard
rim" specified in JATMA, the "Measuring Rim" in ETRTO, the "Design
Rim" in TRA or the like. The standard pressure is the "maximum air
pressure" in JATMA, the "Inflation Pressure" in ETRTO, the maximum
pressure given in the "Tire Load Limits at Various Cold Inflation
Pressures" table in TRA or the like. The standard load is the
"maximum load capacity" in JATMA, the "Load Capacity" in ETRTO, the
maximum value given in the above-mentioned table in TRA or the
like.
[0026] Each of the shoulder blocks 5c is provided with a narrow
groove 9, whereby the shoulder block 5c is subdivided into an
axially inner wide main part 6 and an axially outer narrow lateral
part 7. The narrow groove 9 has a width in the range of from 1.5 to
3.0 mm (in this embodiment about 2.0 mm) and a depth GD1 in the
range of not less than 30%, preferably 50 to 100%, more preferably
55 to 80% of the depth GD2 of the axially outermost circumferential
grooves 3c. Both the circumferential ends thereof are opened to the
outer axial grooves 4c circumferentially adjacent to the shoulder
blocks 5c.
[0027] FIG. 3 shows an example of the narrow groove 9, wherein the
narrow groove 9 comprises a central convex part 9A and a pair of
circumferential end parts 9B.
[0028] The convex part 9A is curved convexly towards the axially
outside, and the axially outermost point T (defined on the groove
center line) lies in the middle range X of the circumferential
length L of the block. Therefore, the narrow lateral part 7 has a
narrow width part 10 in the middle range X and wide parts
(hereinafter heel part 11 and toe part 12) in the circumferential
ends. Here, the middle range X is, as shown in FIG. 3, a 30% length
range centered on the circumferential midpoint P.
[0029] Preferably, the convex part 9A has a radius Rw of curvature
(defined by the groove center line) in the range of from 0.8 to 2.0
times the average width of the shoulder block.
[0030] Further, the convex part 9A has a circumferential length Lw
not less than 50%, preferably not less than 60% of the
circumferential length L of the narrow groove 9 (in this embodiment
about 80%).
[0031] Accordingly, the rigidity of the narrow lateral part 7
varies in the tire circumferential direction. Therefore, even if a
large tangential force is applied to the top of the shoulder block
5c when contacting or leaving the ground for example, excessive
deformation and tear-off of the narrow lateral part 7 can be
avoided because the wide heel part 11 and toe part 12 can resist
such deformation and tear-off, and the narrow groove 9 can be
closed to increase the apparent rigidity of the narrow lateral part
7. Further, wear energy concentrates on the narrow lateral part 7
and wear energy to the main part 6 decreases and uneven wear as a
whole is improved.
[0032] If the minimum axial width Wmin in the narrow part 10 is too
small, such advantageous effects can not be obtained. Therefore,
the minimum axial width Wmin is preferably set in the range of from
5 to 8% of the average axial width of the shoulder block 5c.
[0033] In FIG. 3, the wide heel part 11 and toe part 12 have a
constant axial width W because the circumferential end parts 9B of
the narrow groove 9 and the axially outer edge E of the shoulder
block 5c are substantially parallel with the tire circumferential
direction.
[0034] FIG. 4 shows another example of the narrow groove 9. In this
example, the heel part 11 and toe part 12 have a variable axial
width gradually increasing towards the respective circumferential
ends, In this case, the circumferential end parts 9B of the narrow
groove 9 are oblique and preferably formed in a linear shape or
slightly concavely curved shape.
[0035] Preferably, the axial width W of the narrow lateral part 7
measured at the circumferential ends (thus which is usually a
maximum width) is set in the range of from 7 to 12% of the
above-mentioned average width of the shoulder block and more than
the above-mentioned minimum width Wmin. If more than 12%, the wear
energy to the main part 6 increases. If lass than 7%, the rigidity
decreases and the above-mentioned effects can not be obtained.
[0036] In the example shown in FIG. 1, the above-mentioned narrow
grooves 9 are provided on only the axially outermost shoulder
blocks 5c. However, it is possible to further provide the narrow
grooves 9 on the second outermost blocks (in this example middle
blocks 5b) such that that the narrow lateral part 7 faces the
outermost circumferential groove 3c.
[0037] Comparison Test
[0038] Truck/bus radial tires of size 11R22.5 (Wheel rim:
22.5.times.7.50) having the same tread pattern shown in FIG. 1
except for the narrow grooves were made as test tires and tested
for wear energy. Example tire was provided with the narrow grooves
9 shown in FIG. 1. Reference tire 1 was provided with straight
narrow grooves instead of the curved narrow grooves 9. Reference
tire 2 was not provided with the narrow groove.
[0039] Using a combination sensor capable of measuring a share
stress and slip and their directions, the share stress and slip
were measured at the heel and toe of various blocks (measuring
points are indicated in FIG. 1 as {circle over (1)} to {circle over
(12)}), and the wear energy was computed by multiplying these
values. The test conditions are as follows:
[0040] Slip angle: 0 and 1 degrees
[0041] Inner pressure: 850 kPa
[0042] The results are shown in FIGS. 5(A)-5(B) to FIGS. 7(A)-7(B).
From the test results, it was confirmed that the tire according to
the present invention can be decreased in the difference in wear
energy between the heel and toe and thus the wear energy can be
evened in the circumferential direction.
[0043] Further, the average of the wear energies at the
above-mentioned twelve measuring points, and the ratio of the
average of the wear energies at the six toe-side measuring points
to the average of the wear energies at the six heel-side measuring
points were computed. The results are shown in the following Table
1.
1 TABLE 1 Tire Ex. Ref.1 Ref.2 Average wear energy (J/sq.m) Slip
angle 0 deg. 295.9 278.7 326.2 Slip angle 1 deg. 1011.4 1180.8
1081.6 Wear energy ratio 1.5 1.56 1.8
[0044] Example tire was slightly increased in the average wear
energy in comparison with Reference tire 1, but the wear energy
ratio was effectively reduced. Therefore, Example tire could be
improved in the wear resistance in its entirety.
* * * * *