U.S. patent number RE30,549 [Application Number 05/953,653] was granted by the patent office on 1981-03-24 for pneumatic tire.
This patent grant is currently assigned to Uniroyal, Inc., Uniroyal S.A.. Invention is credited to Henri J. Mirtain, Jonathan Mishory.
United States Patent |
RE30,549 |
Mirtain , et al. |
March 24, 1981 |
Pneumatic tire
Abstract
A belted pneumatic tire is disclosed in which an annular
protuberance projects axially from the buttress region on each side
of the tire. The protuberances are positioned radially inward of
the tire tread and the lateral edges of the belt or breaker extend
into the protuberances such that the breaker edges are removed from
the vicinity of the tread-ground contact patch to thereby improve
uniformity and edge separation problems. A relatively wide breaker
having a low cross-sectional curvature is also utilized to thereby
provide firm support to the tread and consequent improved
performance characteristics.
Inventors: |
Mirtain; Henri J. (Compiegne,
FR), Mishory; Jonathan (Birmingham, MI) |
Assignee: |
Uniroyal, Inc. (Middlebury,
CT)
Uniroyal S.A. (Clairoix, FR)
|
Family
ID: |
25494330 |
Appl.
No.: |
05/953,653 |
Filed: |
October 23, 1978 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
489687 |
Jul 18, 1974 |
03976115 |
Aug 24, 1976 |
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Current U.S.
Class: |
152/531;
152/209.16; 152/454; 152/537; 152/538 |
Current CPC
Class: |
B60C
9/20 (20130101); B60C 11/00 (20130101); B60C
11/01 (20130101); B60C 11/0083 (20130101); Y10T
152/1081 (20150115) |
Current International
Class: |
B60C
9/20 (20060101); B60C 11/00 (20060101); B60C
11/01 (20060101); B60C 009/22 () |
Field of
Search: |
;152/361R,29WT,29D,29R,353R,352R,360,154,354 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Love; John J.
Assistant Examiner: Underwood; Donald W.
Attorney, Agent or Firm: Posin; Jack
Claims
What is claimed is:
1. A pneumatic tire comprising a cord reinforced carcass, a tread
overlying the crown region of said carcass, a reinforcing breaker
.Iadd.having a cross-sectional curvature along its entire width
only in a radially inward direction for all normal operating
conditions of said tire and .Iaddend.comprising a plurality of
rubberized layers interposed between said tread and the crown
region of said carcass, each layer having parallel cords oriented
at an angle in the range of greater than 0.degree. to 30.degree.
relative to the median equatorial plane of the tire, the angle of
the cords in each layer being opposed relative to the angle of the
cords in another layer, first and second buttress regions disposed
radially inward of and adjacent to the respective first and second
shoulders of the tread, first and second axially directed annular
protuberances formed in the corresponding first and second buttress
regions, each of said protuberances having a radially external
surface positioned radially inward of the surface of said tread
while the tread is in engagement with the road surface in a
non-flotation situation and the tire is carrying normal load and in
normal operation including straight line running, cornering or
breaking, and the lateral side edges of the cords in each layer of
said reinforcing breaker extend into said protuberances. .[.2. The
tire of claim 1 wherein the tread has a width and the lateral side
edges of the reinforcing breaker are positioned axially outside of
the tread width..]. .[.3. The tire of claim 1 wherein said radially
outward surfaces of the protuberances are disposed radially inward
of the grooves in said tread..]. .[.4. The tire of claim 1 wherein
the cords in each layer of said reinforcing breaker are oriented at
an angle in the range of 15.degree. to 30.degree. relative to the
median equatorial plane of the tire..]. .[.5. The tire of claim 1
wherein the edges of each reinforcing breaker layer extend into a
protuberance in an axial direction beyond the width of the surface
of said tread a distance in the range of about 9% to 12% of the
cross-sectional width of the tire..]. .[.6. The tire of claim 1
wherein, said tire has first and second sidewalls defining the
maximum width of the tire, said tread has first and second
shoulders defining the width of the tread, said first protuberance
is disposed in an axial direction between the first shoulder and
the first sidewall and the second protuberance is disposed in an
axial direction between the second shoulder and the second
sidewall, said breaker has a width in the range of 85% to 100% of
the maximum width of the tire..]. .[.7. The tire of claim 1 wherein
the reinforcing breaker has a crown radius ratio of 100 to 400%..].
.[.8. The tire of claim 7 wherein the reinforcing breaker has a
crown radius ratio of about 180%..]. .[.9. The tire of claim 1
wherein said protuberances each have a radially outward surface
disposed radially inward of the surface of said tread, each of said
surfaces having a rectilinear projection when viewed in
cross-section, said rectilinear projection having an angle in the
range of 0.degree. to 10.degree. relative to the axis of the tire,
said angle being inclined radially outward in the direction of said
tread when greater than 0.degree...]. .[.10. The tire of claim 9
wherein said radially outward surfaces comprise rubber having a
modulus greater than 100 kg/cm.sup.2 and
a tensile strength greater than 160 kg/cm.sup.2..]. 11. A pneumatic
tire comprising a cord reinforced carcass, a tread overlying the
crown region of said carcass, a reinforcing breaker interposed
between said tread and the crown region of said carcass and having
parallel cords oriented at an angle in the range of 0.degree. to
30.degree. relative to the median equatorial plane of the tire,
said breaker having a crown radius ratio of 100% to 400% and being
contiguous to the carcass over a range of 25% to 60% of the
cross-sectional width of the tire, first and second buttress
regions disposed radially inward of and adjacent to the respective
first and second shoulders of the tread, first and second axially
directed annular protuberances formed in the corresponding first
and second buttress regions, each of said protuberances having a
radially external surface positioned radially inward of the surface
of said tread while the tread is in engagement with the road
surface in a non-flotation situation and the tire is carrying
normal load and in normal operation including straight line
running, cornering or braking, and the lateral side edges of
said reinforcing breaker extend into said protuberances. 12. A
pneumatic tire comprising a cord reinforced carcass, a tread
overlying the crown region of said carcass and having a width of
less than 80% of the cross-sectional width of the tire, a
reinforcing breaker interposed between said tread and the crown
region of said carcass, said breaker having a width of at least 85%
of the cross-sectional width of the tire and having parallel cords
oriented at an angle in the range of 0.degree. to 30.degree.
relative to the median equatorial plane of the tire, said breaker
having a crown radius ratio of 100% to 400% and being contiguous to
said carcass along a width of at least 40% of the cross-sectional
width of the tire, first and second buttress regions disposed
radially inward of and adjacent to the respective first and second
shoulders of the tread, first and second axially directed annular
protuberances formed in the corresponding first and second buttress
regions, each of said protuberances having a radially external
surface positioned radially inward of the surface of said tread
while the tread is in engagement with the road surface in a
non-flotation situation and the tread is carrying normal load and
in normal operation including straight line running, cornering or
braking, and the lateral side edges of said reinforcing breaker
extend into said protuberances. .[.13. A pneumatic tire comprising
a cord reinforced carcass, a tread overlying the crown region of
said carcass, a reinforcing breaker interposed between said tread
and the crown region of said carcass and having parallel cords
oriented at a angle in the range of 0.degree. to 30.degree.
relative to the median equatorial plane of the tire, first and
second buttress regions disposed radially inward of and adjacent to
the respective first and second shoulders of the tread, first and
second axially directed annular protuberances formed in the
corresponding first and second buttress regions, each of said
protuberances being continuous along a buttress region and having a
radially external surface positioned radially inward of the surface
of said tread while the tread is in engagement with the road
surface in a non-flotation situation and the tire is carrying
normal load and in normal operation including straight line
running, cornering or braking, each of said surfaces having a
sculptured tread design formed therein, and the lateral side edges
of said reinforcing breaker extend into said protuberances..].
.[.14. The tire of claim 13 wherein said radially external surfaces
comprise rubber having a modulus greater than 100 kg/cm.sup.2 and a
tensile strength greater than 160 kg/cm.sup.2..]. .[.15. A
pneumatic tire comprising a cord reinforced carcass, a tread
overlying the crown region of said carcass and having first and
second shoulders defining the maximum width of the tread, a
reinforcing breaker comprising a plurality of rubberized layers
interposed between said tread and the crown region of said carcass,
each layer having parallel cords oriented at an angle in the range
of greater than 0.degree. to 30.degree. relative to the median
equatorial plane of the tire, the angle of the cords in each layer
being opposed relative to the angle of the cords in another layer,
first and second sidewalls attached to the carcass and defining the
maximum width of the tire, first and second buttress regions
connected to and disposed radially outward of the sidewalls and
radially inward of and adjacent to the respective first and second
shoulders of the tread, first and second annular protuberances
formed in the corresponding first and second buttress regions and
extending axially from said buttress regions, the first
protuberance being disposed in its entirety between a plane
parallel to said median equatorial plane and passing through the
first shoulder and a plane tangential to the first sidewall at the
maximum width point of the tire and the second protuberance being
disposed in its entirety between a plane parallel to said median
equatorial plane and passing through the second shoulder and a
plane tangential to the second sidewall at the maximum width point
of the tire, each of said protuberances having a radially external
surface positioned radially inward of the surface of said tread
while the tread is in engagement with the ground and the tire is
carrying normal load, and the lateral side edges of the cords in
each layer of said reinforcing breaker extend into
said protuberances..]. 16. A pneumatic tire comprising a cord
reinforced carcass, a tread overlying the crown region of said
carcass, a reinforcing breaker .Iadd.comprising a plurality of
rubberized layers .Iaddend.interposed between said tread and the
crown region of said carcass and having .Iadd.a cross-sectional
curvature along its entire width only in a radially inward
direction for all normal operating conditions of the tire, each
layer of the reinforcing breaker having .Iaddend.parallel cords
oriented at an angle in the range of 0.degree. to 30.degree.
relative to the median equatorial plane of the tire, .Iadd.the
angle of the cords in each layer being opposed relative to the
angle of the cords in another layer, .Iaddend.first and second
sidewalls attached to the carcass and defining the maximum width of
the tire, first and second buttress regions connected to and
disposed radially outward of the sidewalls and radially inward of
and adjacent to the respective first and second shoulders of the
tread, first and second annular protuberances formed in the
corresponding first and second buttress regions and extending
axially between the planes tangential to the sidewalls at the
maximum width of the tire, each of said protuberances having a
radially external surface positioned radially inward of the surface
of said tread while the tread is in engagement with the ground and
the tire is carrying normal load, the lateral side edges of
.Iadd.each layer of .Iaddend.said reinforcing breaker extend into
said protuberances, said buttresses each having a surface
positioned radially outward of a protuberance, and first and second
recesses each formed by a buttress surface and a radially external
surface of the protuberance whereby deformation of the tread is
decoupled from each protuberance and the .[.breaker edge.].
.Iadd.edges of the breaker layers .Iaddend.located in the
protuberances. .[.17. The tire of claim 16 wherein said
protuberances each have a radially inward surface, and further
comprising first and second sidewalls attached to said carcass, and
third and fourth recesses each formed by a radially inward surface
of a protuberance and one of said sidewalls whereby deformation of
each sidewall is decoupled from the adjoining protuberance and the
breaker edge located in the protuberance..]. .Iadd. 18. A pneumatic
tire comprising a cord reinforced carcass, a tread overlying the
crown region of said carcass, a reinforcing breaker having a
substantially constant direction of curvature along its entire
width and comprising a plurality of rubberized layers interposed
between said tread and the crown region of said carcass, each layer
having parallel cords oriented at an angle in the range of greater
than 0.degree. to 30.degree. relative to the median equatorial
plane of the tire, the angle of the cords in each layer being
opposed relative to the angle of the cords in another layer, first
and second buttress regions disposed radially inward of and
adjacent to the respective first and second shoulders of the tread,
first and second axially directed annular protuberances formed in
the corresponding first and second buttress regions, each of said
protuberances having a radially external surface positioned
radially inward of the surface of said tread while the tread is in
engagement with the road surface in a non-flotation situation and
the tire is carrying normal load and in normal operation including
straight line running, cornering or breaking, and the lateral side
edges of the cords in each layer of said reinforcing breaker extend
into said protuberances. .Iaddend.
Description
BACKGROUND OF THE INVENTION
This invention relates to pneumatic tires and more particularly to
a pneumatic tire having a wide reinforcing breaker or belt
extending into an annular protuberance in the buttress region of
the tire.
The tread reinforcement component commonly referred to as a belt or
breaker is disposed between the tread and the carcass in the crown
region of the tire. Typically, a breaker or belt is constructed of
one or more plies of rubberized cord fabric. Each cord in the
fabric is generally of a substantially non-extensible material such
as metallic wires or strands, glass filaments, or rayon filaments.
The cords within the breaker plies are oriented parallel to each
other and substantially parallel to the plane of the beads and thus
circumferentially of the tire, or at a small bias angle. In a
single ply breaker construction, the small bias angle can be
0.degree.. Where the breaker is a multi-ply structure, however, the
small bias angle is in the range of about 15.degree.-30.degree.
with respect to the median equatorial plane of the tire, and may be
oppositely disposed in successive plies.
The development of a reinforcing belt or breaker for use in
pneumatic tires added a number of benefits to tires including
considerable improvement to tire durability. On the other hand, the
breaker also introduced some new problems of its own. The lateral
edges of a breaker in a typical tire, due to their location between
the tire tread and carcass at a position of continually changing
stress, tend to separate from the carcass or themselves. Improper
positioning of the breaker results in the uniformity problems of
increased lateral force variation and conicity.
Another benefit of a reinforcing breaker is improved tread wear due
to the greater stiffness imparted to the tire tread. Of course,
this benefit is enhanced by utilizing a "flat" tread having no
convex cross-sectional curvature so that the relative movement
between the center portion of the tread and the axially outward
portions is minimized thereby resulting in an even wear pattern. A
serious drawback of a tread designed to have no convex
cross-sectional curvature lies in the fact that a tire which is
vulcanized with such a shape, when cured, may inflate to a concave
tread cross-section rather than a flat cross-section. Elimination
of this problem can be accomplished by constructing and vulcanizing
the tire such that the tread has at least a small convex
cross-sectional curvature, that is, a large crown radius ratio,
when the cured tire is inflated to its rated inflation
pressure.
In the detailed description of the invention following hereinafter,
the cross-sectional curvature of the tread and breaker of the tire
are discussed in terms of "crown radius ratio" and "crown radius."
The term "crown radius" as used herein either with respect to the
tread or breaker, means the radius of the arc of a circle which
best approximates the arc of curvature of the tread surface or the
breaker as the case may be of a tire. The crown radius is commonly
determined by the formula ##EQU1## where "leg set" is the axial
distance measured along a line tangent to the tread or breaker at
its midpoint between the shoulders of the tread or edge of the
breaker, or predetermined points axially equidistance inward of the
shoulders or breaker edges. Shoulder drop is the perpendicular
distance from the aforementioned tangent line to the tread
shoulders or said predetermined points. In the case of a breaker,
shoulder drop may be considered as the perpendicular distance
between the line tangent to the breaker at its midpoint and the
edges of the breaker. The "crown radius ratio" is the ratio of the
crown radius of either the tread or breaker to the nominal
cross-sectional width of the tire and as used herein is expressed
in terms of percent.
Either a belted radial or a belted bias tire construction is
suitable for use in the present invention. The radial type tire is,
however, the preferred embodiment. A radial tire is inclusive of
various tire constructions which typically comprise a carcass or
body having one or more reinforcement plies of cord fabric
extending from bead to bead wherein the cords in each ply are
substantially radial in orientation, that is, the cords are
oriented substantially normal to the beads and the crown centerline
of the tire. In a single ply radial tire construction, the carcass
cords normally have a 90.degree. bias angle, that is, in the
unshaped carcass they extend perpendicular to the planes of the
beads. In a two-ply radial tire construction, the cords in each
carcass ply are parallel to the cords in the other carcass ply.
However, the cords in each ply may be oriented at oppositely
disposed angles of 70.degree. or more with respect to the median
equatorial plane of the tire and thus the angle between cords in
different plies is between 0.degree. and 40.degree.. In more than
two ply radial ply tire constructions, similar cord arrangements in
successive carcass plies is usually employed.
With regard to the prior art, U.S. Pat. No. 3,450,182 discloses a
tire having a flat tread cross-section, wide protuberances
extending beyond the width of the tire sidewalls, a tread surface
in normal engagement with the ground between the lateral edges of
the protuberances and a breaker extending laterally beneath the
tread to positions adjacent the edges of the protuberances. This
patent does not, however, disclose a breaker having its lateral
edges removed from the stress area of contact by the tread with the
ground or a convex cross-sectional tread curvature facilitating the
manufacture of a tire. Moreover, the extreme lateral extension of
the protuberances beyond the tire sidewall will result in a high
degree of tread shoulder wear and breaker separation due to
centrifugal force moving the protuberances radially outward during
tire rotation.
In U.S. Pat. No. 2,477,754, an aircraft tire is shown in which a
tread and breaker have a substantial convexly curved cross-section
when the tire is inflated and the breaker has edges positioned
within protuberances extending from the side of the tire. When this
tire is loaded (but not impacted), the tread-ground contact area is
in the crown area of the tread only and consequently the tread wear
and traction of the tire will be relatively poor. Moreover, when
the tire is subject to the normal type of impaction and very heavy
loading which aircraft tires receive, the lateral edges of the
breaker rotate through the tread-ground contact area to cause edge
separation of the breaker. A further defect in the tire of U.S.
Pat. No. 2,477,754 is that the circumferential breaker cords along
the lateral sides of the breaker will carry the entire breaker load
under deflection so that these breaker cords will break after a
small amount of such use.
SUMMARY OF THE INVENTION
It is an important object of the present invention to provide an
improved pneumatic tire having a construction which overcomes the
aforementioned disadvantages.
It is a further object of this invention to provide a tire having a
breaker and characterized by a high degree of uniformity and
resistance to edge separation and a high amount of traction.
It is another object of the invention to provide a tire
construction having a radially convex cross-sectional curvature
which can be reliably attained during manufacture of the tire and
which provides an optimum disposition of contact between the tire
tread and the ground as the tire rotates.
It is another object of the invention to provide a tire
construction having a high degree of hazard resistance.
It is yet another object of this invention to provide a tire
construction having an auxiliary tread or other pattern in the
buttress region of the tire normally out of engagement with the
ground and engaging the ground only under predetermined conditions
such as in mud or snow, during low inflation or after wear of the
main tread surface to a predetermined level.
In general, the objectives of the invention are accomplished by the
provision of a pneumatic tire having an annular protuberance in
each buttress region, a wide breaker having its lateral edges
extending into the protuberances and a cross-sectional curvature of
the tread and breaker such that a maximum amount of the tread
surface engages the ground when the tire is inflated and
loaded.
The protuberances are normally out of engagement with the ground so
that placing the breaker edges in the protuberances removes the
edges from the treadground contact area. This results in the
minimization of breaker edge separation and the elimination of tire
uniformity problems due to improper placement of the breaker. A
tread and breaker with a small amount of radially outward
curvature, that is, convex curvature, facilitates manufacture of
the tire and permits an optimum disposition of the tread to thereby
enhance the wearing properties of the tire. Placing the edges of
the breaker in the protuberances assists in attaining the low
breaker curvature and consequently the improved tread wear.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other objects and features of the present
invention will be more clearly understood from the following
detailed description thereof when read in conjunction with the
accompanying drawings, in which:
FIG. 1 is a cross-sectional elevation view of a pneumatic tire in
accordance with this invention;
FIG. 2 is a plan view of a section of the tire of FIG. 1 showing
the tire tread and viewing the tire in a direction radially inward
toward the axis of the tire;
FIG. 3 is a view similar to that of FIG. 2 showing another
embodiment of the invention;
FIG. 4 is a cross-sectional elevation, broken away, showing a
portion of the tire embodiment of FIG. 3 and
FIG. 5 is cross-sectional elevation view showing the tire of FIG. 1
in an inflated, normally loaded condition.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring generally to the drawings, there is illustrated a tire 2
including a carcass 3 having two radial or substantially radial
superposed carcass plies 4 and 6, sidewalls 8 and 10 overlying the
respective lateral regions of the carcass and terminating at their
radially inwardmost edges in a pair of beads 12 and 14. It may be
noted that the planes tangential to the widest points on the
sidewalls 8 and 10 preferably define the maximum width of the tire
2, however, it is not intended that the tire be limited to a
maximum width defined only by the sidewalls. Moreover, the term
"sidewall" is considered herein to include any variations in the
sidewall such as a buffing rib, raised letters or other figures,
and sculptured patterns or designs in the sidewall. A tread 20
overlies the crown region of the carcass and a pair of buttress
regions 16 and 18 are positioned between and connect the tread 20
and sidewalls 8 and 10. The buttress regions 16 and 18 respectively
have continuous, annular protuberances 56 and 58 extending axially
or laterally from the tire, i.e., in a direction away from the
median equatorial plane of the tire. A breaker ply 22 having
breaker layers 26 and 28 for providing reinforcing support to the
tread 20 is disposed between the crown region of the carcass 3 and
the tread 20. The breaker ply 22 includes lateral sides 34 and 36
and has lateral edges 30 and 32 extending into the protuberances 56
and 58 in an axial direction, i.e., in a direction away from the
median equatorial plane of the tire. A fluid-impervious liner 24 is
located radially inward of the carcass 3 and extends from bead 12
to bead 14. A pair of insert supports 38 and 40 are interposed
between sides 34 and 36 of the breaker ply 22 and the carcass 3.
The tread 20 includes a tread surface 44, a plurality of grooves 46
and shoulders 48 and 50 which respectively define the line of
connection between buttress region 16 and tread 20 and buttress
region 18 and tread 20.
Describing the cord ply components of the tire 2 in a radially
outward direction, carcass plies 4 and 6 are layers of rubberized
cords or cables made of any suitable natural or synthetic fiber
such as nylon, rayon, polyester, metal wire, glass fiber, etc., and
each of the carcass plies 4 and 6 extends from bead to bead. In the
carcass plies illustrated, the cords in each carcass ply are
oriented at oppositely disposed small and normally equal angles of
up to about 20.degree. with respect to true radial planes. Thus the
respective carcass plies have bias angles of between 70.degree. and
90.degree. with respect to the median equatorial plane of tire 2.
The breaker layers 26 and 28 are layers of rubberized, parallel
reinforcing elements which preferably are metal cords such as
steel, but can also be cords of other high modulus material such as
rayon, glass fiber or Kevlar. The cord reinforcing elements in each
breaker ply are preferably oriented at, but not limited to, a
substantial bias angle of between about 15.degree. and 30.degree.
to the median equatorial plane of the tire. However, the breaker
layer reinforcing elements may be at an angle of substantially
0.degree. to the median equatorial plane of the tire and may be of
the type in which the cords are wound onto the carcass of the
tire.
Referring now to FIGS. 1 and 5, the extension of the edges 30 and
32 of the breaker ply 22 in an axial direction into the
protuberances 56 and 58 and the positioning of the protuberances 56
and 58 such that they do not normally contact the ground or road
surface during normal operation and maximum rated loading of the
tire effectively removes the edges 30 and 32 from the area between
the carcass 3 and the tread-ground contact patch as the tire
rotates. The width of the tread-ground contact patch is defined by
the shoulders 48 and 50 of the tread 20 and, as can be seen in
FIGS. 1 and 5, the breaker ply edges 30 and 32 are axially outward
of the shoulders 48 and 50 and thus the contact patch. One of the
advantages of this construction is elimination of the well known
effect of improper positioning of the breaker and variations in the
breaker edges on the uniformity of the tire. Another advantage of
this construction is the removal of the breaker ply edges from the
high stress area radially inward of the contact patch due to the
repetitive loading and unloading of the tire tread as it rotates
through the tread patch. The effect of this stressing is to subject
the breaker ply edge to continuous movement and high heat,
particularly at high speed, and ultimately cause its separation
from the carcass. In order to obtain this advantage, it is
important that the width of the breaker ply 22 be greater than the
width of the tread 20. The width of the tread 20 is not greater
than 80% of the maximum cross-sectional width of the tire and may
be 68% to 72% of the nominal cross-sectional width of the tire.
Thus, the breaker ply 22 should be greater than the width of the
tread of a particular tire as designated above, and may be as wide
as 95% of the width of the tire.
It is advantageous for a tread to have a low cross-sectional
curvature, i.e., a large crown radius ratio, in that the tread will
thereby have a more optimally shaped contact patch with the ground
or road. Such a contact patch is one in which the entire leading
edge of the contact patch simultaneously engages the ground as the
tire rotates. This type of road contact results in increased tread
wear resistance and therefore increased tire mileage. For the same
reason, a breaker ply should have a large crown radius ratio and
preferably a crown radius ratio which positions the cross-section
of the breaker parallel to the tread. The breaker ply may, however,
have a crown radius ratio larger than that of the tread. The
location of the protuberances 56 and 58 on the buttress regions 16
and adjacent to the tread 20 permits not only a wide breaker ply
but also one which can have a large crown radius ratio. Stating the
cross-sectional curvature of the tread 20 in terms of crown radius
ratio, the tread may have a crown radius ratio of 120 to 400% and a
preferable optimum value of 180%. The breaker 22 should have a
crown radius ratio of between 100 and 400% and a preferred optimum
value such that the breaker is parallel to the tread surface.
As previously indicated, the breaker ply 22 may comprise cords
wound at substantially 0.degree. to the median equitorial plane of
the tire 2. A drawback of substantially 0.degree. breaker plies is
that they tend to make a tire unstable in a forward rolling
direction when the tire is subjected to lateral forces. Increasing
the width of such 0.degree. breakers decreases this problem,
however, as the width of the breaker plies increases, their
cross-sectional curvature typically also increases. The result is
that upon deflection of the breaker radially inward, the entire
tire load is transferred to the axially outward breaker cords which
are not deflected so that these cords are quickly weakened and
break. The use of a protuberance in the butress region of a tire 2
permits an extra wide breaker and at the same time allows the
breaker to have a high crown radius ratio. Consequently, the
present problems of 0.degree. wound breakers will be minimized in
the breaker ply 22 when it utilizes substantially 0.degree. wound
cord reinforcing elements.
The edges of a breaker ply positioned axially within the width of
the tread of a tire are located at one of the regions of higher
breaker ply stress. Removal of the breaker ply edges 30 and 32
axially outside of the tread width into protuberances 16 and 18
removes the edges from the high stress region. However, a region of
high stress on the breaker ply 22 continues adjacent to the areas
located by the edges of the contiguous width of the breaker ply 22
and carcass 2. This contiguous width is defined by the axially 3,
circumferential edges 42 and 44 of the insert supports 38 and 40
and also by the points along the cross-section of the breaker ply
22 and carcass 3 where the crown radii of the latter are
substantially equal. As the tread 20 rotates through the tread
contact patch, the change in stress on the breaker ply 22 will tend
to cause separation of the breaker ply 22 from the carcass 3 at the
edges of the contiguous width of the latter two tire components.
The aforementioned width of contiguity is centered on the median
equatorial plane of the tire and is preferably, but not
necessarily, 25 to 60% of the cross-sectional width of the
tire.
With reference to FIGS. 1, 2 and 5, the protuberances 56 and 58
respectively have radially inward surfaces 51 and 53 and radially
outward continuous circumferential surfaces 54 and 52 positioned
radially inward of the surface 44 of tread 20. The surfaces 54 and
52 are substantially parallel to the axis of the tire 2, as shown
in FIGS. 1 and 5, but may be inclined toward the shoulders 48 and
50 of the tread 20. It is critical, however, that the surfaces 54
and 52 are not inclined such that they connect directly to the
tread 20 at shoulders 48 and 50 but rather join the buttress
surfaces 60 and 62 radially inward of the shoulders 48 and 50. In
effect, this construction provides a decoupling of the
protuberances 16 and 18 from the tread 20 such that the
protuberances do not also distort and deflect with the tread 20 as
the tread goes into and comes out of the tread-ground contact
patch. The rubber that forms the surfaces 54 and 52 preferably has
a dynamic modulus greater than 100 kg/cm.sup.2 and a tensile
strength greater than 160 kg/cm.sup.2. This rubber may also be
reinforced with floc material such as steel, Kevlar, polyester,
fiberglas or other suitable organic or inorganic material.
As shown in FIG. 3, the surfaces 52 and 54 of protuberances 18 and
16 may have formed in them a sculptured design which may be an
additional tread 64 suitable for extra traction in floatation
situations such as in snow and mud. Also, the tread 64 may be of a
design which creates a high level of noise or vibration while
rotating on the road surface and which, due to its radially inward
position relative to tread 20 as shown in FIG. 4, becomes operative
only under low inflation conditions of the tire 2 or after the
tread 20 has worn to a level such that tread 64 engages the road
surface. The vibration or noise generated will be discernible to
the vehicle operator such that he can correct the problem
indicated. It should be emphasized, however, that the tread 64 is
radially inward of tread surface 44 and does not normally engage
the road.
It will be understood that the foregoing description of the
preferred embodiment of the present invention is for purposes of
illustration only, and that the various structural and operational
features as herein disclosed are susceptible to a number of
modifications and changes none of which entail any departure from
the spirit and scope of the present invention as defined in the
hereto appended claims.
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