Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02100480 2000-06-15
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BELT REINFORCED PNEUMATIC RADIAL TIRE
US Patent 4,926,919, issued May 22, 1990, to Hopkins
et al. discloses a cord of four filaments each having a
diameter of 0.30 mm in a belt structure of a tire having
two plies or layers each with cords of at least 820
Newtons and preferably 890 Newtons plus or minus 65
Newtons (at page 4) break strength in a light truck (LT)
tire.
The present invention relates to radial tires for
vehicles, i.e., those tires wherein the cords of the
carcass plies which extend from one bead to the other lie
substantially on radial planes.
Particularly, the present invention relates to light
truck tires having less weight favoring low rolling
resistance to absorb less horsepower while maintaining
the strength of the previous heavier construction as well
as ride and handling.
Assignee's prior application, now published as EP 0
237462 on September 16, 1987, discloses a two ply
passenger tire belt having cords of 2x3.OHT construction.
The high tensile material used was the save as that being
used herein and was described as high carbon steel with a
carbon content by weight of greater than 0.800.
Also related to this application is Assignee's U.S.
Statutory Registration No. H1333 disclosing 0.35
filaments both untwisted and twisted of ST material in a
cord for a reinforcement particularly for radial medium
truck
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tires, and PCT/US 90/01906 filed March 21, 1991 on
which a request has recently been filed to enter the
national stage in the U.S. disclosing further, bunched
construction of super tensile cord particularly for
radial medium truck tires in Load Range F-J.
Previous light truck tires had three different
cords to reinforce the belt package for Load Ranges B,
C and D. While the known 2x.30HT, above, was useful
to replace 2+2x.25NT at 20 EPI for Load Range B tires,
2+2x.30HT was chosen for Load Range C tires. Load
Range D tires and above previously used
3x.265/9x245HT+1 (compact, i.e., single twist all in
the same direction) cord with a wrap wire at 10 EPI.
After considerable study, effort, testing and
time, the present invention provided a single cord for
both Load Ranges C and D which substantially reduced
the number of filaments for Load Range D and,
surprisingly, resulted in a larger cord diameter for
Load Range C with the same number of filaments. While
a reduction in the number of filaments would lead one
to expect a reduction in weight, this would not be the
case where the filament size was increased and the
number of filaments maintained. As a result, a single
cord was found for use in both Load Ranges C and D by
varying the ends per inch (EPI) in the plies of the
belt. Other advantages which exist in the present
invention include improved rolling resistance in at
least one instance and a reduction in the cord gum
coat gauge between the cord layers in the belt in
another instance. A weight reduction due to reduction
in weight of reinforcement as well as reduction in an
amount of gum gauge also result in a reduction in cost
for the tire of the present invention. Further, the
new belt structure gives greater rolling resistance
perhaps because of the higher stiffness of the new
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cord over the old cord being used for reinforcement in
the belt structure.
This invention provides the above advantages in a
pneumatic radial tire with a carcass having radial cords
and two sidewalk spaced apart a distance which in the
axial direction determines the width of the tire section.
The tire has two beads each one of which around which are
turned up, from the inside toward the outside, the ends
of the cords of the carcass. A tread is disposed on the
crown of the circumferentially inextensible is interposed
between the tread and the carcass. The belt structure
has a width that is substantially equal to that of the
tread and has two radially overlapped layers of
elastomeric fabric reinforced with metallic cords. The
metallic cords are parallel to each other in each layer
and crossed with the cords of the facing layer and
inclined at an angle between 16 and 30°. The gauge of
the gum between two facing cords on the plane of a cross
section of the tire preferably is not larger than 0.064
cm throughout the entire width of the annular reinforcing
structure. The metallic cords are two twisted filaments
twisted with parallel filaments all filaments of about
0.30 mm diameter high tensile steel and being distributed
in each layer with a density of (13 EPI) 5.1 ends per
centimeter for Load Range C to (17 EPI) 6.7 ends per
centimeter for Load Range D.
In a further aspect of the present invention, the
annular reinforcement structure of the above defined tire
has a stiffness ratio in relation to control structure of
equal to at least 1.05.
In a still further aspect of the invention, it has
been found that for Load Range E the size
CA 02100480 1999-11-19
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reduction and openness of a 2+2 type construction could also
be obtained by use of 2+2x.35ST cord which has a higher
material strength than the high tensile of the 2+2x.30 cord
being of super tensile material such as that disclosed in
Assignee's US Patent No. 4,960,473.
Yet another aspect of the present invention is as
follows:
A load range E pneumatic radial tire with a carcass
having radial cords, two sidewalls spaced apart a distance,
which in the axial direction, determines the width of the tire
section, two beads each one of which around which are turned
up, from the inside toward the outside, the ends of the cords
of the carcass, and a belt structure that is circumferentially
inextensilble interposed between the tread and the carcass,
the belt structure having a width that is substantially equal
to that of the tread and having at least two radially
overlapped layers of elastomeric fabric reinforced with
metallic cords, the metallic cords being parallel to each
other in each layer at a density of 14 to 20 EPI (5.5 to 7.8
ends per centimeter) and crossed with the cords of the facing
layer and inclined at an angle of between 16° and 30° with
respect to the equatorial plane of the tire, comprising the
gauge of the gum between two facing cords, on the plane of a
cross section of the tire being between 0.019 inches (0.05 cm)
and 0.033 inches (0.084 cm) throughout the entire width of the
belt structure, the metallic cords being two twisted filaments
twisted with two parallel filaments all filaments of 0.32 to
0.40 mm diameter super tensile steel.
The features of the present invention which are believed
to be novel are set forth with particularity in the appended
claims. The present invention both as to its structure and
CA 02100480 1999-11-19
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manner of operation may best be understood by reference to the
following detailed description, taken in accordance with the
accompanying drawings in which:
Fig. 1 is a cross sectional view of a tire in a plane
that contains the axis of rotation of the tire and in
accordance with the present invention;
Fig. 2 is an enlarged schematic of the annular
reinforcing portion of the tire shown in Fig. 1; and
Fig. 3 is an enlarged cross sectional view of a cord from
the structure portion of the tire in Fig. 2.
As used herein and in the claims:
"Axial" and "axially" are used herein to refer to lines
or directions that are parallel to the axis of rotation of the
tire.
"Bead" means that part of the tire comprising an annular
tensile member wrapped by ply cords and shaped, with or
without other reinforcement elements such as flippers,
chippers, apexes, toeguards and chafers, to fit the design
rim.
"Belt structure" means at least two layers or plies of
parallel cords, woven or unwoven, underlying the tread,
unanchored to the bead, and having both left and right cord
angles in the range from 16 degrees to 30 degrees with respect
to the equatorial plane of the tire.
- 5 - 214~4~~
"Carcass" means the tire structure apart from the
belt structure, tread, undertread, and sidewall rubber
over the plies, but including the beads.
"Cord" means one or more of the reinforcement
elements, formed by one or more filaments/wires which
may or may not be twisted or otherwise formed which
may further include strands so formed which strands
may or may not be also so formed, of which the plies
in the tire are comprised.
"Crown" means that portion of the tire within the
width limits of the tire tread.
"Density" means quantity per unit length.
"Equatorial plane (EP)" means the plane
perpendicular to the tire's axis of rotation and
passing through the center of its tread.
"Gauge" means material thickness.
"High Tensile Steel (HT)" means a carbon steel
with at least 0.80% carbon by weight, or a tensile
strength of at least 3240 Mpa.
"Super Tensile Steel (ST)" means a carbon steel
with a content by weight of between 0.78% and 0.86%
carbon, 0.3% to 1.0% Si and between 0.1% and 0.5% of
an alloying element from a class of the following
elements: Cr, Ni, Co, W, V and Nb, and any combination
thereof, the balance being iron and residuals, or a
tensile strength of at least 3380 Mpa.
"Load Range D and E" means load and inflation
limits for a given tire used in a specific type of
service as defined by tables in The Tire and Rim
Association Inc.. 1989 Year Book.
"Radial" and "radially" are used to mean
directions radially toward or away from the axis of
rotation of the tire.
"Section width" means the maximum linear distance
parallel to the axis of the tire and between the
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~~.~v~~:~'
exterior of its sidewalls when and after it has been
inflated at normal pressure for 24 hours, but
unloaded, excluding elevations of the sidewalls due to
labeling, decoration or protective bands.
"Stiffness Ratio" means the value of the control
belt structure stiffness divided into the value of
another belt structure when the values are determined
by a fixed three (3) point bending test having both
ends of the cord fixed and flexed by a load centered
between the fixed ends.
"Tread" means that portion of a tire that comes
into contact with the road when the tire is normally
inflated and under normal load.
Referring to Figs. 1 to 3, there is illustrated,
by means of a working example, a tire of size
LT215/85R15 Load Range D according to a preferred
embodiment, and all actual dimensions related therein
are for a tire of said size. A pneumatic tire (10)
according to the invention has what is commonly
referred to in the tire art as a radial ply carcass
structure. For the purposes of the present invention,
a tire has a radial ply carcass structure when the
cords of the carcass reinforcing ply, or plies 11, 12,
are oriented at angles in the range of 75° to 90° with
respect to the equatorial plane (EP) of the tire.
A tire 10 according to the invention has a pair
of substantially inextensible annular beads 13, 14
which are axially spaced apart from one another. Each
of the beads 13, 14 is located in a bead portion of
the tire which has exterior surfaces configured to be
complimentary to the bead seats and retaining flanges
of a rim (not shown) upon which the tire is designed
to be mounted. A radial ply carcass structure, in the
preferred embodiment comprising two plies 11, 12 of
side-by-side reinforcing cords of polyester material,
7
extends between the beads with an axially outer
portion of the carcass structure folded about each of
the beads. While in the preferred embodiment, the
carcass ply structure comprises two plies of
reinforcing material, it is understood that one or
more carcass plies of any suitable material may be
employed without deviating from the scope of the
present invention.
Preferably, a tire according to the invention is
a tubeless tire having a layer of a low permeability
material 9 disposed inwardly of the carcass plies 11,
12 and contiguous to an inflation chamber defined by
the tire and rim assembly. Elastomeric sidewalls 15,
16 are disposed axially outwardly of the carcass
structure. A circumferentially extending belt
structure 17 comprising two layers 18, 20 (Fig. 2),
each of which preferably comprises steel reinforcing
cords 22 (Fig. 3) characterized by the cords 22 having
filaments 24, 26, 28 and 30 with a breaking strength
of at least 3240 Mpa. The cords 22 used in the
working example have a structure of four filaments 24,
26, 28 and 30 of 0.30 mm diameter high tensile steel
wire and a cord 22 break strength of 890 Newtons plus
or minus 65 Newtons. Each cord 22 has two filaments
24, 26 twisted together with a 16 mm lay length and
these two filaments 24, 26 are twisted at a 16 mm lay
length together with the remaining two filaments 28,
which are untwisted and parallel to each other when
twisted together with the twisted filaments 24, 26 all
30 in the same twist direction. This cord is designated
as 2+2x.30HT. The 2+2 construction is known for its
openness and good rubber penetration resulting from
the openness. The .30 designates the filament
diameter in millimeters and the HT designates the
material being high tensile.
More particularly, initially Load Range C tires
were built with two belts as illustrated in Fig. 3
with 2+2x.30HT cords at 6.3 ends per centimeter (16
EPI) with the angle 0 of one ply being approximately
21° and the other ply having an identical but opposing
angle. The next build of this tire in this load range
altered the end count from the above 6.3 ends per
centimeter (16 EPI) to 5.1 ends per centimeter (13
EPI) resulting in an increase in belt stiffness and
the gum gauge (g) between the cords in opposing layers
18, 20 in comparison to a production reinforcement
which it is to replace of 2+2x.25NT (Normal Tensile)
at 7.9 ends per centimeter (20 EPI) in a control tire.
This build was followed by a build of Load Range D
tires with a belt package as described above for the
Load Range C tires except the reinforcement in the two
belt layers 18, 20 now was increased to 6.7 ends per
centimeter (17 EPI) resulting in an increase in
stiffness but a decrease in the gum gauge (g) between
the cords in opposing layers 18, 20 in comparison to a
production reinforcement which it is to replace of
3x.265/9x.245HT+1 at 3.9 ends per centimeter (10 EPI)
in a control tire.
Recently, a tire of size LT235/85R16 Load Range E
extended the above application in a tire of similar
construction by using 2+2x.35ST cord as the belt
reinforcement. The belt structure, similar to belt
structure 17 and therefore not illustrated, has two
layers each having cords with filaments of a breaking
strength of at least 3380 Mpa. Preferably, the cords
have four filaments of 0.35 mm diameter super tensile
steel wire and a cord break strength of 1200 Newtons
plus or minus 100 Newtons. Each cord has two
filaments twisted together with a 15 mm lay length and
these two filaments are twisted at 16 mm lay length
~100~80
_ g _
together with the remaining two filaments which are
untwisted and parallel to each other when twisted
together with the twisted filaments all in the same
twist direction. The two belt layers had cords at
17.5 EPI (6.9 ends per cm) resulting in a decrease in
wire coat gauge from 0.072" (0.183 cm) to 0.60" (0.153
cm) while also reducing the gum gauge (g) between the
cords in opposing layers in comparison to a production
reinforcement which it is to replace of
3x.265/9x.245HT+1 at 12 EPI (4.1 ends per cm) from
.031" to .019" (.084 cm to .050 cm). It is
anticipated that metallic cord density in the belt
layers from 14 to 20 EPI will be useful for load range
E tires with the filament diameter ranging from 0.32
to 0.40 mm. The above tire selections came only after
extensive study and testing which included the lab
test results in Tables I and II below.
to - 2~~~~~~1
TABLE
I
Test
Tire
- LT225/75R16
WRL
ST
2+2z.25NT 2+2z.30HT2+2z.30HT 2+2z.30HT2+2z.30HT
7.9 endlcm4.7 ends/cm5.5 ends/cm6.3 ends/cm7.1 ends/cm
CORD (20 EPI) (12 EPn (14 EPn (16 EPI) (18 EPI)
ROLLING
RESISTANCE
LRC
IN
COMPARISON
TO CONTROL
(CONTROL)
RATED 101 102 100 ** **
LOAD
1300 102 103 100 ** **
LB
LOAD
ROLLING
RESISTANCE
LRD
RATED ** ** 100 107 106
LOAD
1300 ** ** 100 108 108
LB
LOAD
TREADWEAR
IN COMPARISON
TO
2 CONTROL
0
(CONTROL)
LRC 100 113 - - 113
PROJECT
ED
2 WEAR
5
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TABLE II
Test Tire
- LT235/85R16
LR E
3X.265/9X.245+1HT2+2XL35ST
12 EPI 17.5 EPI
CORD (4.6 ENDS/CIVi)(6.9 ENDS/CIvn
(CONTROL)
PLUNGER 100 110
ROLLING 100 100
RESISTANCE
(RATED LOAD)
TREADWEAR 100 105
(TEST TRACIn
For the tires of Table I, it was found that none
of the tires failed as a result of the belt structure
in either the HS (High Speed) Outdoor Resilometer or
DOT Extended Tests. The force test for both Load
Ranges were within three points of each other for Load
Range C and one point for Load Range D. From Table I,
it was concluded that for the Rolling Resistance Test,
under Load Range C, 2+2x.25NT, 2+2x.30HT at 12 EPI and
2+2x.30HT at 14 EPI were within 2% of each other while
2+2x.30HT at 16 EPI was 8% better. Tread wear was
improved with 2+2x.30HT at 12 EPI over 2+2x.25NT at 20
EPI under Load Range C.
Further it was learned that between
3x.265/9x.245HT+1 at 12 EPI, the previous production
cord, and 2+2x.30HT at 16 EPI, the rolling resistance
and tread wear are equal, but the tire weight is 6%
less.
From the above data, by extrapolation, it was
determined that for Load Range C, 13 EPI would be the
preferred count while for Load Range D, 17 EPI would
~~Ofl4~~
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be preferred to extend the use of 2+2x.30HT cord over
both Load Ranges C and D where previously 2+2x.25NT at
20 EPI was used for Load Range C and 3x.245/9x.245HT+1
at 10 EPI was used for Load Range D. The reduction in
weight came in Load Range D and the rolling resistance
for Load Range D was 8% better. For example, on a
LT215/85R16 tire, Load Range D, the weight savings are
up to 5% per tire.
A factory process trial build of 19,000 tires was
made and sold on approximately May 12, 1988, to
determine factory handling characteristics.
The weight savings are from a reduction in not
only the weight of the reinforcing cord but in some
instances also from a reduction in the gum between the
reinforcing cord layers. Turning to Fig. 2, it can be
appreciated that if the coating for a given cord
decreases with the cord diameter (d) then the gauge
(g) of the gum between the cord layers will be reduced
as well. For example, if the cord diameter is the
average diameter of the smallest surrounding circle
around a normal cross section of the cord, the Load
Range D previous cord of 3x.265/9x.245HT+1 has a cord
diameter of 0.040 inches while the 2+2x.30HT cord has
a diameter of 0.031 inches. As a result, the gum
gauge (g) for 3x.265/9x.245HT+1 is 0.033 inches while
for 2+2.x30HT the gum gauge (g) is 0.025 inches, a 24%
reduction. The above reduction made production of
reinforcement for tires in Load Ranges C and D more
economical, and resulted in 2+2x.30HT cord being
useful over both Load Ranges C and D for light truck
tires.
Lastly, it has been observed for Load Range D the
belt structure for a LT215/85R16 tire with 2+2x.30HT
at 17 EPI and a belt gum gauge of 0.025 inches (0.064
mm) has a stiffness of 11.04 Newtons on a laboratory 3
~~t~~4~~1
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point bending, i.e., fixed ends center impingement,
stiffness test as compared to 10.2 Newtons for its
predecessor, 3x.265/9x.245HT+1 at 10 EPI on the same
test. This is a ratio of 1.10 of the new belt
stiffness over the old (control). While not proven,
it is possible that the belt stiffness is responsible
for, or at least contributes to, the 8% improvement in
rolling resistance noted above. The same phenomenon
for belt edge stiffness can be observed for Load Range
C, although not as predominant, which might explain
why the advantage in rolling resistance was not
observed in Load Range C. Here the new belt structure
using 2+2x.30HT at 13 EPI had a stiffness of 8.16
Newtons as compared to 7.7 Newtons for the control
which was the predecessor, 2+2x.25NT at 20 ends per
inch. The above stiffness values give a stiffness
ratio of 1.06 for the Load Range C.
From Table II, it was concluded that for the
Rolling Resistance Test, under Load Range E, 2+2x.35ST
c~ 17.5 EPI was equal to 3x.265/9x.245+1HT c~ 12 EPI,
but Treadwear was directionally better and Plunger
improved by 10%. These results were achieved while
reducing the weight of the 2+2x.35ST tire by 1.44 lbs.
(3%) and an accompanying cost savings.
Again the weight savings are from a reduction in
not only the weight of the reinforcing cord, but from
a reduction in gum coat and gum between the
reinforcing cord layers.
In accordance with the provisions of the patent
statutes, the principle and mode of operation of the
tire have been explained and what is considered to be
its best embodiment has been illustrated and
described. It should, however, be understood that the
invention may be practiced otherwise than as
w~l~~~~
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specifically illustrated and described with out
departing from its spirit and scope.
