Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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ASYMMETRIC DIRECTIONAL PNEUMATIC AGRICULTURAL TIRE
Technical Field
This invention relates to a directional pneumatic agricultural tire for use on
farm tractors
and similar agricultural type vehicles.
Background Art
Tractor tires must have good vibration characteristics on and off the road
while maintaining
good traction or draw bar characteristics. Such tires must also provide for
the removal of soil,
mud, etc., during infield use.
The tractive power propelling the vehicle is primarily provided through and
transmitted by
large lugs that are typically oriented in a directional pattern. This
directional pattern generally
employs the use of what is commonly called or referred to as long bars or a
combination of long
bars and short bars. Typically, these patterns of lugs are designed to have
two rows of shoulder
lugs, one row extending from each shoulder of the tire towards the equatorial
plane. The
volumetric space between the lugs is commonly referred to as the soil
discharge channels. These
channels provide a means for compacted soil to discharge over the tire
shoulder. This feature
prevents the tire from packing with mud and enables the tire to maintain a
self cleaning capability.
Generally, these tires having two rows of shoulder lugs are arranged such that
the lugs create a V
or chevron-type pattern, these patterns usually are centered about the
equatorial plane. If they are
not centered they are typically alternating such that the chevron is on one
side of the equatorial
plane and the next set of circumferentially adjacent lugs have a chevron which
is on the opposite
side of the equatorial plane. This alternating pattern is repeated such that
there is a balancing effect
of the chevrons. For the proposes of this invention, these alternating
chevrons on one side or the
other of the equatorial plane in a repeating fashion are considered
symmetrical in that as the tire
passes through its footprint, that is the portion of the tire contacting the
ground surface, the soil
' discharge channels within the footprint typically average out such that the
average volume within
the channel is equal on the left side of the equatorial plane versus the right
side of the equatorial
plane. Such a tire demonstrating a long bar/short bar combination is exhibited
in U.S. Patent No.
4,383,567 and is commonly referred to in the commercial market place as the
Goodyear
DynaTorque II radial tire.
Another tire using a similar long bar/short bar combination is taught in U.S.
Patent No.
4,534,392. This tire is commonly referred to as the Goodyear DynaTorque Radial
and the Kelly-
Springfield PowerMac IJS Radial Tractor Tire. This particular tire used a
combination of two
3S long bars separated by a short bar and repeated by two long bars and this
pattern is repeated on
both sides of the tire. This tread pattern is such that it again exhibits a
combination of chevrons
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that have a resultant pattern such that the soil discharge channels as the
tire passes through the
footprint tend to equalize.
The prior art tires typically had several characteristics in common. One being
the
employment of a large number of lugs where at least one of the lugs would
always cross the
centerline of the tire. These tires had several beneficial tractive
performance characteristics in that
they were good in most soil conditions and provided good draw bar traction.
The problem that
was prevalent in these types of designs is that the short bar would tend to
wear out more rapidly
than the long bars. The resultant effect is that an uneven wear pattern would
be generated in the
tire after a period of time. This meant that the farmer would perceive the
tire as being irregularly
worn and therefore he considered the employment of a short bar detrimental to
the performance of
the product.
In 1992, The Goodyear Tire & Rubber Company introduced a new tractor tire
having two
sets of primary and secondary lugs. The tire was commercially identified as a
DT710 and is
described in U.S. Patent No. 5,046,541. As described in the patent, this tire
has good traction,
vibration and cleaning characteristics. These primary and secondary lugs are
shorter in length than
most tractor tire lugs. The tire effectively increased the number of lugs and
therefore an increase
in lug surface area resulted. This increased the performance capabilities of
the tire. The flexible
nature of these relatively short lugs also helped reduce the soil compaction
potential of the tire even
though more lug surface area was employed.
In 1995, U.S. Patent No. 5,411,067 taught that the tire described above as
U.S. Patent No.
4,534,392 the Goodyear DynaTorque Radial and Kelly-Springfield PowerMac LS
Radial Tractor
tires could be modified by the employment of a notch in at least each of the
long bars across the
equatorial plane. This notch could be of partial or full depth. By notching
the long bar the tire
achieved increased flexibility and reduced soil compaction while further
enhancing the tractive
capability of the tire. This pattern had the resultant effect of the
directional symmetrical patterned
tires in that the soil discharge channels throughout the footprint on average
from left side to right
side were equal as the tire rolled through the soil.
Each of the tires described above had several key limitations; one being that
the
employment of short lugs in combination with long bar lugs inherently results
in a potential
nonuniform treadwear problem. Alternatively, the employment of short lugs such
as the DT7I0
although resulting in very uniform wear has bars that are substantially
shorter than the typical lugs
and as a result the tread although wearing uniformly is perceived by the
farmer to have the
potential of wearing out quickly because the lugs are substantially shorter
than the conventional
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lugs. This in spite of the fact that there is a larger surface area in the use
of the DT710 type short
lugs with the resultant effect of more lug surfacing contact as the tire molls
therefore enhancing the
wear and durability of this particular tire. Nevertheless, the customer
perceives the potential for
fast wear due to the use of short lugs.
The tire of the present invention has a unique asymmetric directional tread
pattern such that
the soil discharge channels between the lugs on one side of the tire are
uniformly greater than the
soil discharge channels created on the opposite side of the tire. This creates
a unique asymmetric
soil discharge channel. Additionally, the inventive tire has two rows of
shoulder lugs, the lugs
being of substantially equal lengths which enables the tire to exhibit very
uniform wear patterns.
Summary of the Invention
A pneumatic agricultural tine 20 having a maximum section width (SV~, an axis
of rotation
(R), an equatorial plane (EP) centered between the maximum section width (SV~
and
perpendicular to the axis (R) is described. The tire 20 has a casing having a
carcass 21 having one
or more plies 22 reinforced with robber coated cords 22A and has a rubber
tread 32 disposed
radially outwardly of the casing. The tread 32 has first and second lateral
tread edges 32A,33B;
the distance between the lateral tread edges 33A,33B defines the tread width
('TW). The tread 32
has an inner tread 34 and a plurality of lugs 50A,50B,50C projecting radialiy
outwardly from the
inner tread 34. The tread lugs 50A,50B and 50C have a length 1, and a width
1", the ratio of the lug
length 1, to lug width la,, is at least three times, preferably at least three
times.
The tread 32 has a plurality of shoulder lugs 50A and 50B. The plurality of
shoulder lugs
50A,50B are divided into a first row of shoulder lugs 50A extending from the
first lateral edge
33A respectively towards the equatorial plane and a second row of shoulder
lugs 50B extending
from the second lateral edge 33B. The lugs 50A of the first row are
ci>,cumferentially offset
relative to the lugs 50B of the second row. A plurality of similarly oriented
central lugs 50C are
arranged in row and each central lug 50C extends across the equatorial plane
EP. The lugs of the
first row of shoulder lugs 50A are substantially aligned with the central lugs
50C along their
respective lug lengths 1,, while the shoulder lugs 50B of the second row are
similar but oppositely
oriented relative to the first row of shoulder lugs 50A. The combination of
shoulder lugs 50A,50B
and central lugs 50C form an asymmetric chevron pattern 70,72 having a point
74 of the chevron
70,72 located between the equatorial plane EP and the second lateral edge 33B.
A primary leg 76
of the chevron 70,72 lies along the substantially aligned lengths of the
shoulder lugs 50A of the
first row and the central lugs 50C. A secondary leg 78 of the chevron 70,72
lies along the length
of the shoulder lugs 50B of the second mw and the point 74 of the chevron
70,72.
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In the preferred embodiment each of the shoulder lugs SOA of the first mw are
similar in
shape and length. Similarly, each of the shoulder lugs SOB of the second row
are of similar shape
and length. It is most preferred that both the shoulder lugs SOA and SOB of
the first and the second
row are of similar shape and length. This is believed to improve the uniform
wear of this tread
pattern.
It is believed preferable that the circumferentially adjacent chevrons 70,72
have a
cincumferential overlap (O) as measured by axially extending Iines 84,86, the
overlapping (O)
distance between these lines 84, 86 at the extremes of the circumferential
overlap being at least 25
of the total circumferential extent (Tj of a chevron 70,72 enables the tire 20
to achieve extremely
uniform ride and handling characteristics. The shoulder lugs SOA,SOB each have
an axially outer
end 53 and an axially inner end 51. The axially outer ends 53 of the shoulder
lugs SOA of the first
row are circumferentially offset relative to the axially outer ends 53 of the
shoulder lugs SOB of the
second row as measured as the distance X circumferentially between axial lines
90,92 tangent to
the extremes of the axially outer ends 53. The cincumferential offset distance
X is at least 75 % of
the circumferential distance between the axially inner 51 and axially outer
ends 53 of the shoulder
lugs SOA of the first row. In a preferred embodiment of the tire 20, the tire
20 has a net gross
ratio as measured around the entire circumference of the tire of Iess than 35
% , preferably about
22 % .
In order to maintain this open tread pattern, each tread lug SOA,SOB,50C is
spaced a
minimum distances) of 1.5 the lug width (lw) from an adjacent lug SOA,SOB, or
SOC.
Brief Description of Drawings
The following is a brief description of the drawings in which like parts bear
like reference
numerals and in which:
Fig. 1 is a perspective view of the preferred tire according to the present
invention.
Fig. 2 is a plan view of the preferred tire according to the present
invention.
Fig. 3 is a fragmentary view of the tread portion of the preferred tire
according to the
present invention.
Fig. 4 is a cress-sectional view of the preferred tire taken along lines 5-5
of Fig. 2.
Fig. 5 is a plan view of a portion of the contact patch of the preferred tire
according to the
present invention.
Fig. 6A and Fig. 6B are fragmentary view of a tread portion of a first and
second
embodiment of the inventive tire.
Fig. 7A and 7B are schematic view of the tire according to the invention
mounted to a
,.
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vehicle.
Definitions
"Aspect ratio" of the tire means the ratio of its section height (SH) to its
section width
(SW) multiplied by 100 % for expression as a percentage.
5 "Axial" and "axially" means 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, toe guards and chafers, to fit the design rim.
"Belt reinforcing structure" means at least two layers of 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 17 degrees to 27 degrees with respect to the
equatorial plane of the
tire.
"Carcass" means tile tire structure apart from the belt structure, tread,
undertread, and
sidewall rubber over the plies, but including the beads.
"Circumferential" means lines or directions extending along the perimeter of
the
surface of the annular tread perpendicular to the axial direction.
"Design rim" means a rim having a specified configuration and width. For the
purposes of this specification, the design rim and design rim width are as
specified by the
industry standards in effect in the location in which the tire is made. For
example, in the
United States, the design rims are as specified by the Tire and Rim
Association. In Europe,
the rims are as specified in the European Tyre and Rim Technical Organization -
Standards
Manual and the term design rim means the same as the standard measurement
rims. In Japan,
the standard organization is The Japan Automobile Tire Manufacturer's
Association.
"Design rim width" is the specific commercially available rim width assigned
to each
tire size and typically is between 75 % and 90% of the specific tire's section
width.
"Equatorial plane (EP)" means the plane perpendicular to the tire's axis of
rotation and
passing through the center of its tread.
"Footprint" means the contact patch or area of contact of the tire tread with
a flat
surface at zero speed and under normal load and pressure.
"Inner" means toward the inside of tile tire and "outer" means toward its
exterior.
"Lateral edge" means the axially outermost edge of the tread as defined by a
plane
parallel to the equatorial plane and intersecting the outer ends of the
axially outermost traction
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lugs at the radial height of the inner tread surface.
"Leading" refers to a portion or part of the tread that contacts the ground
first, with
respect to a series of such parts or portions, during rotation of the tire in
the direction of
travel.
"Net-to-gross ratio" means the ratio of the normally loaded and normally
inflated tire
tread rubber that makes contact with a hard flat surface, divided by the area
of the tread,
including non-contacting portions such as grooves as measured around the
entire
circumference of the tire.
"Normal inflation pressure" refers to the specific design inflation pressure
and Ioad
assigned by the appropriate standards organization for the service condition
for the tire.
"Normal load" refers to the specific design inflation pressure and load
assigned by the
appropriate standards organization for the service condition for the tire.
"Radial" and "radially" means directions radially toward or away from the axis
of
rotation of the tire.
"Radial-ply tire" means a belted or circumferentially restricted pneumatic
tire in which
the ply cords, which extend from bead to bead are laid at cord angles between
b5~ and 90~
with respect to the equatorial plane of the tire.
"Section height" {SH) means the radial distance from the nominal rim diameter
to the
outer diameter of the tire at its equatorial plane.
"Section width" (SW) means the maximum linear distance parallel to the axis of
the
tire and between the exterior of its sidewalls when and after it has been
inflated at normal
pressure for 24 hours, but unloaded, excluding elevations of the sidewalk due
to labeling,
decoration or protective bands.
"Tire design load" is the base or reference load assigned to a tire at a
specific inflation
pressure and service condition: other load-pressure relationships applicable
to the tire are
based upon that base or reference.
"Trailing" refers to a portion or part of the tread that contacts the ground
last, with
respect to a series of such parts or portions during rotation of the tire in
the direction of travel.
"Tread arc width" (TAW} means the width of an arc having its center located on
the
plane (EP) and which substantially coincides with the radially outermost
surfaces of the
various traction elements (lugs, blocks, buttons, ribs, etc.) across the
lateral or axial width of
the tread portions of a tire when the tire is mounted upon its designated rim
and inflated to its
specified inflation pressure but not subjected to any load.
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"Tread width" means the arc length of the tread surface in the axial
direction, that is,
in a plane passing through the axis of rotation of the tire.
"Unit tread pressure" means the radial load borne per unit area (square
centimeter or
square inch) of the tread surface when that area is in the footprint of the
normally inflated and
normally loaded tire.
Detailed Description of the Invention
Now referring to Fig. 5, a tire is shown in cross-section view generally as
reference
numeral 20. The pneumatic tire 20 has a carcass 21 having one or more carcass
plies 22
extending circumferentially about the axis of rotation of the tire 20. The
carcass plies 22 are
anchored around a pair of substantially inextensible annular beads 24. A belt
reinforcing
structure 26 comprising one or more belt plies 28 is disposed radially
outwardly from the
carcass plies 22. The belt plies 28 provide reinforcement for the crown region
of the tire 20.
A circumferentially extending tread portion 32 is located radially outwardly
of the belt
reinforcing structure 26.
A sidewall portion 33 extends radially inwardly from each axial or lateral
tread edge
33A,33B of the tread to an annular bead portion 35 having the beads 24 located
therein.
The carcass plies 22 preferably have textile or synthetic cords 22A
reinforcing the plies
22. The cords 22A are preferably oriented radially. Most preferably, the cords
22A are made
of polyester or nylon material. Typically, the tire 20 may have two, three or
four plies 22,
each constmction increasing in load carry capability as a function of the
number of plies.
The belt reinforcement structure 26 preferably includes at least two belts 28
reinforced
by synthetic cords of rayon or aramid.
Now referring to Figs. 1-5, a tire 20 according to the present invention is
illustrated.
The tire 20 according to the present invention has a unique tread 32. The
tread 32 has a first
tread edge 33A and a second tread edge 33B. Disposed between the tread edges
33A,33B is
an inner tread 34 and a plurality of Iugs SOA,SOB and 50C extending radially
outwardly from
the inner tread 34.
As illustrated in Fig. 4 each lug 50A,SOB and 50C has a radially outer surface
58, a
first edge 52, second edge 54 and a centerline 63 between the first and second
edges. Each
lug 50A and 50B extends generally axially inwardly from an axially outer end
51 to an axially
inner end 53. Each lug 50 intersects the equatorial plane EP and has an
orientation
substantially aligned with the lugs SOA as shown.
As illustrated in Figs. 6A and 6B the radially outer surface 58 when viewed
from the
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contact patch has a polygonal shape. The surface 58 when encompassed by a
rectangle 65
exhibits the approximate orientation of the lug 50A,50B,SOC. For purposes of
this invention
the centerline 63 of the lugs 50A,50B or 50C is approximated by a line
extending substantially
parallel to the first and second edges 52,54 and being generally equidistanced
between these
edges.
It is important to note that lugs have a length 1, at least three times their
width I",
whereas block elements have a width greater than one-third the length of the
element. A lug
for purposes of this invention has a length 1, at least 10% of the section
width (SW) of the tire
20.
The distance along the centerline 63 between the axially outer and inner ends
51,53
defines the length (l~ of the lug 50.
The distance extending substantially perpendicularly between the first and
second edges
52,54 of the lug define the lug width (la,). The radial distance extending
between the inner
tread 34 and the edges 52,54 of the lug 50 defines the radial lug height (1,~.
Preferably, the
ratio of the shoulder lug width (la,) to lug radial heights (1~ is less than
two-thirds over at least
70 % of the lug length (1~.
As the shown in Figs. 6A and 6B the lugs 50A,SOB, and 50C are oriented in such
a
fashion that the shoulder lug 50A and the central lug 50C form the primary leg
76 of a
chevron shape 70,72 while the shoulder lug 50B is oppositely inclined and
forms a portion of
the secondary leg 78 of the chevron 70,72. The lug 50B when connected to the
inner point 74
of the chevron 70,72 at the end 53 of the central lug 50C forms the entire
secondary leg 78 of
the chevron 70,72.
A centerline 63 drawn between the leading edges 52 and trailing edges 54 of
each lug
50A,50B and 50C established the general shape of the chevron pattern 70,72.
In the preferred embodiment the chevron 70,72 appearance is similar to a pair
of bird
wings on the peak of a downward stroke wherein one wing is longer than the
opposite wing.
This arcuate shape of each leg of the chevron 70,72 creates soil discharge
channels 80,82
between the lugs 50A,50B and 50C. The soil discharge channel 80 extending
outward
through the first lateral edge 33B is substantially larger than the soil
discharge channel 82
extending outward through the second lateral edge 33B. Each leg, primary and
secondary
76,78 can preferably be spaced an equal distance from a circumferendally
adjacent respective
primary or secondary leg 76,78. In other words, the chevron patterns 70,72 can
be uniformly
repeated around the circumference of the tire 20.
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The total circumferential extent of the chevrons 70,72 is shown in Figs. 6A,6B
as T.
Circumferentially adjacent chevrons 70,72 overlap a distance e, g being at
least 25 % of T as
measured between the axial extending 84, 86 and 88. The shoulder lug SOB as
shown is
circumferentially offset from the shoulder lug SOA by a distance X, X being
measured as the
S distance between axial lines 90,92 as shown in Fig. 6A,6B and wherein X is
at least 50%
preferably about 75 % of the circumferential extent of the shoulder lug SOA as
measured
between lines 92 and 84.
In one embodiment of the invention these tires 20 are made in two distinct
molds such
that the short secondary legs 78 of the chevron 70 are positioned closest to
the lateral edge
nearest the tractor 10 when the tires 20 are mounted as shown in Fig. 7A. The
resultant effect
is that the two tires 20A and 20B working combination push more solid
laterally away from
the vehicle 10. The lateral forces are balanced and thus offset while the
displaced soil act
upon the tires tending to give a resultant forward propulsion. This feature
would be
noticeable in very wet loose or mucky soil conditions.
Interestingly, for cost and performance efficiency it has been found that the
tires 20
can be produced in a single mold and mounted as shown in Fig. 7B wherein the
primary leg
76 of the chevron 70,72 is positioned such that tire 20A has the primary leg
76 outboard of
the vehicle while tire 20B has the primary leg 76 inboard of the vehicle 10.
This means that
the large soil discharge channels 82 are not working in opposite or a balanced
configuration as
shown in Fig. 7B. Ordinarily one would speculate that the tires 20A,20B would
create a
slippage moment around the vehicle 10. Interestingly it has been found that
the tire 20B
anchors the tractor 10 while tire 20A working with tire 20B propel the vehicle
forward.
Historically, farm tire designers had heretofore always tried to balance the
soil
discharge channels 80, in the contact patch such that the amount of soil
channeled on each side
of the equatorial plane (EP) was equal. This design factor has been the
convention even when
unequal channels were employed circumferentially. The designer always
attempted to achieve
this balanced loading effect by alternating the large and small channels on
each side of the
tread.
The tire 20 of the present invention clearly breaks from that conventional
practice, it
has an asymmetric directional tread pattern that can maintain the vehicles
traction even though
employing an imbalanced soil discharge volume, one side of the tire having
chevrons 80 being
substantially greater than the opposite side 82.
As shown in Figs. 3 and 5 the preferred tire 20 has both shoulder lugs SOA,SOB
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oriented similarly but opposite in hand. The centerline 63 is broken into an
axially inner
portion 63A and an axially outer portion 63B, the outer portion being inclined
at an ~,o, ao
being in the range of 60~ to 90~ relative to the equatorial plane EP. The
axially inner portion
63A is inclined at an angle ai of about 45~.
5 The central Iug 50C has a centerline 63 divided into three parts
63A,63B,63C. The
ends 63A and 63B being inclined similarly at a very steep angle ~3, wherein ~,
is less than 45~
relative to the equatorial plane preferably about 30~. The central portion 63B
of the central
lug is oriented at an angle 8 of about 45~ relative to the equatorial plane.
As shown in Fig. 6B an alternative embodiment of the tire 20 is shown wherein
the
10 lugs 50A,50B and 50C are shown as curvilinear lugs. The lugs 50A and 50C
follow a
generally singular curvature and are generally aligned along their lengths.
Shoulder lug 50B
is oriented such that the leading edge 52 intersects the point 74 of the
chevron 72. As can be
more readily seen the soil discharge channels 80, 82 similarly exhibit the
volumetric imbalance
taught in the preferred embodiment tire of Figs. 1-6A.
A most beneficial feature exhibited in both tires is that the resultant lug
lengths 1, are
quite long as a result of the use of the asymmetric chevron patterns 70,72.
When one compares the inventive tire to the prior art tires, the following is
observed in
a 480/80842 (18.4842) size:
Shoulder Lugs l, Central Lugs l,
Inventive Tire 7.87 in. (20 cm) 5.74 (14.6 cm)
DT710 6.50 in. (16.5 cm) 5.55 (14.1 cm)
DynaTorque 7.36 avg. (18.7 cm) NONE
(8.64 in. long 6.07 in. short)
As can be seen the shoulder lugs are longer than typically can be employed
while at the
same time being equal in length. This means that the tire will wear uniformly
while also
achieving no degradation in tractive performance. As can be seen the tire
according to the
present invention has the lug length of the shoulder lugs greater than the
average of the long
burl short bar prior art tires i. e. , 1, > 'h (L~ + L9) .
Also due to the use of the asymmetric chevron 70,72 less lugs are needed to
create the
beneficial circumferential overlap to reduce harsh ride and vibrational
problems associated
with long bar/short har tread patterns i.e., N shoulder lug 50A and 50B < N
(L,_,+ LS) while
N shoulder lug 50A,50B + central lugs 50C > N (LL + LS). Accordingly, the
total surface
areas (SA) at the center two-thirds of the tread width (TW) is greater than
the total surface
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area in the same center two-thuds region of the prior art long bar/short bar
tread pattern.
This means that overall wear durability as well as improved ride
characteristics are achieved
by the inventive tire when compared to the prior art tires.
It must be appreciated that the actual shape of the individual lugs can be
varied as well
as their orientation without departing from the spirit of the invention.
Furthermore, it is
understood that the point 74 of the chevron can lie on one or the other tread
half but not both.
