This invention relates to pneumatic radial-ply runflat
tires and ways to increase the bending stiffness of sidewall wedge inserts.
BACKGROUND OF THE INVENTION
Various methods have been devised for enabling the safe,
continued operation of unpressurized or underpressurized vehicle tires with the
intent of minimizing further damage to the uninflated tire and without simultaneously
compromising vehicle handling over a distance from the location where the tire has
lost its pressure to a place desired by the driver, such as a service station where
the tire can be changed. Loss of tire pressure can result from a variety of causes,
including puncture by a foreign object such as a nail or other sharp object piercing
the pneumatic tire installed on a vehicle.
Pneumatic tires designed for sustained operation under
conditions of unpressurization or underpressurization are also called runflat tires,
as they are capable of being driven in the uninflated, or what would generally be
called the "flat" condition. A conventional pneumatic tire collapses upon itself
when it is uninflated and is carrying the weight of a vehicle. The tire's sidewalls
buckle outward in the circumferential portion of the tire where the tread contacts
the ground, making the tire "flat".
The term "runflat" is generally used to describe a tire
that is designed such that the tire structure alone, in particular the structure
of the sidewalls, has sufficient rigidity and strength to support the vehicle load
when the tire is operated without being inflated. The sidewalls and internal surfaces
of the tire do not collapse or buckle onto themselves, and the tire does not otherwise
contain or use other supporting structures or devices to prevent the tire from collapsing.
In general, runflat tires incorporate sidewalls that are
thicker and/or stiffer than a conventional non-runflat tire so that the tire's load
can be carried by an uninflated tire with minimum adverse effects upon the tire
itself and upon vehicle handling until such reasonable time as the tire can be repaired
or replaced. The typical methods used in sidewall thickening and stiffening include
the incorporation of circumferentially disposed wedge inserts in the inner peripheral
surface of the sidewall portion of the carcass, which is the region in the tire
usually having the lowest resistance to deformation under vertical loading. In such
runflat tire designs, each sidewall is thickened in such a way that its overall
thickness is increased in the region between the bead and the tread shoulder. The
inserts in each sidewall, in combination with the plies, add rigidity to the sidewalls
in the absence of air pressure during runflat operation. Such reinforced sidewalls,
when operated in the uninflated condition, experience a net compressive load in
the region of the sidewall that is in the road-contacting portion of the tire. Also,
the bending stresses on the sidewalls are such that the outer portions of the reinforced
sidewalls experience tensile forces while the inner portions experience compression
stresses during runflat operation.
U.S. Pat. No. 5,368,082 ('082) of Oare et al
, having a common assignee with the present invention, discloses a low
aspect ratio, runflat, pneumatic radial ply tire which employs special sidewall
inserts to improve stiffness. Approximately six additional pounds of weight per
tire was required to support an 800 lb load in this uninflated tire. This earlier
invention, although superior to prior attempts at runflat tire design, still imposed
a weight penalty that could be offset by the elimination of a spare tire and the
tire jack. However, this weight penalty becomes even more problematic in the design
of tires having higher aspect ratios. The '082 Patent teaches a sidewall construction
for runflat tires in which the tire is constructed with two plies, an inner liner
and two reinforcing wedge inserts in each sidewall. The two inserts in each sidewall
are disposed such that one insert is located between the two plies while the other
insert is located between the inner liner and the first or innermost ply.
U.S. Patents Nos. 5,427,166
5,511,599 of Willard, Jr
., and assigned to Michelin Corporation disclose the addition of a third
ply and the addition of a third insert in the sidewall to theoretically improve
the runflat performance of a runflat tire over that of the '082 Patent discussed
above. These two Michelin patents discuss some of the load relations that occur
in the uninflated condition of the tire and demonstrate that the principle disclosed
in the `082 patent can be applied to additional numbers of plies and inserts.
However, use of large amounts of rubber to stiffen the
sidewall members, as in the Michelin patents previously discussed, usually increase
flexure heating and lead to earlier tire failure during runflat operation. This
is especially so when the tire is operated at high speeds. Therefore, one goal of
runflat tire design is to minimize the number of wedge inserts used to stiffen each
sidewall and reduce the total amount of elastomeric wedge insert material used in
a runflat tire.
While the increased resistance to compression deflection
of the multiple inserts tends to prevent the collapse of the uninflated loaded tire,
the use of multiple plies and more than one reinforcing wedge insert in each sidewall,
has drawbacks which include the above mentioned increase in tire weight and flexure-induced
heat build up. Such designs also increase the tire's complexity in ways that adversely
affect manufacturing and quality control.
U.S. Patent No. 3,464,477 of Henri Verdier
, assigned to Michelin Corporation and considered as being the closest
prior art to the tire of claim 1, discloses a pneumatic tire particularly for off-highway
(OTR) use wherein the inflated tire is to be protected against damage such as cuts
and abrasion to the sidewalls when the tire is used on rocky or rough ground. Although
this is not a runflat design, there are useful teachings presented since the inventor
has determined that sidewall damage from such OTR operation can be ameliorated by
reinforcing the tire sidewalls:
- "surprisingly ... the sidewalls should be reinforced inwardly of the carcass
plies." The disclosed reinforcement of each sidewall is a single reinforcing wedge
insert ("elastomeric reinforcement") which has a maximum thickness at the mid height
of the sidewall of the tire between about 1% and 3% of the overall maximum width
of the tire, the reinforcement tapering toward its edges, that is toward the tread
and toward the corresponding bead of the sidewall and extending about half of the
height of the tire. The elastomeric composition is not very important other than
that it should not have a hysteretic loss greater than 25%. The elastomer may contain
one or more plies of elastic cords of metallic or non-metallic type arranged radially
or only slightly inclined to the radial direction, for example at an angle between
about 10 and 30 degrees to the radial (claim 3 reads "not more than 30 degrees").
Suitable elastic cords for reinforcing the internal layer of the tire are polyamide
cords, such as nylon, or elastic metallic cables, preferably having a modulus of
elasticity less than 5000 DaN/mm2. The preferred embodiment of the sidewall
reinforcement "layers" is summarized in claim 6 and includes "a pair of plies of
elastic polyamide cords, ... the cords of one ply crossing the cords of the other
ply, said layers and said plies therein terminating short of said bead and the edge
of said tread adjacent to said sidewall." There is no discussion or specification
of the length or position of the ends of one ply relative to the other ply in the
pair of plies. The disclosed design, with specific limits on insert thickness and
insert ply cord angles, provides sidewall reinforcement suitable for providing "surprisingly
increased resistance to damage ... [such as] cutting or gashing by cutting objects"
when operating an inflated tire on rocky terrain.
Clearly, the goal in runflat tire design is to provide
a low-cost, light-weight tire that gives good runflat vehicle handling as well as
good service life during runflat operation.
OBJECTS OF THE INVENTION
It is an object of the present invention to provide a pneumatic,
radial runflat ply tire as defined in one or more of the appended claims and, as
such, having the capability of being constructed to accomplish one or more of the
following subsidiary objects.
One object of the present invention is to provide a pneumatic
radial runflat ply tire with a simplified design that allows for improved manufacturing
Another object of the present invention is to provide a
pneumatic radial runflat ply tire having a reduced weight as compared with prior
Another object of the present invention is to provide a
pneumatic radial runflat ply tire having a reduced heat generating potential during
runflat operation as compared with prior art designs.
Still another object of the present invention is to provide
a pneumatic radial runflat ply tire having good normal inflation handling and ride
characteristics as well as good runflat handling properties and runflat durability
and operational life.
SUMMARY OF THE INVENTION
The present invention relates to a pneumatic radial ply
runflat tire having a tread, a carcass comprising a radial ply structure, a belt
structure located between the tread and the radial ply structure, an inner liner
and two sidewalls each reinforced by a single wedge insert that contains a pair
of wedge-insert stiffener layers circumferentially disposed therein as defined in
BRIEF DESCRIPTION OF THE DRAWINGS
The structure, operation, and advantages of the invention
will become further apparent upon consideration of the following description taken
in conjunction with the accompanying drawings, wherein:
FIGURE 1 is a cross-sectional view of a prior art runflat tire design incorporating
multiple wedge inserts in each sidewall and multiple plies in the ply structure;
FIGURE 2 is a cross-sectional view of a runflat tire in accordance with the
FIGURE 3A is a cross-sectional detail view of the reinforced sidewall wedge
insert for the runflat tire of the present invention;
FIGURE 3B shows the crossed wires of the respective wedge-insert stiffening
FIGURE 4A shows a square section beam being loaded in compression and deformed;
FIGURE 4B shows a cross-sectional view of the beam of FIGURE 4A;
FIGURE 4C is a diagram of the stresses within the beam of FIGURE 4A;
FIGURE 5A shows a square section beam, with compression-bearing elements,
being loaded in compression and deformed;
FIGURE 5B shows a cross-sectional view of the beam of FIGURE 5A; and
FIGURE 5C is a diagram of the stresses within the beam of FIGURE 5A.
"Apex" means an elastomeric filler located radially above
the bead core and between the plies and the turnup plies.
"Aspect Ratio" means the ratio of the section height of
a tire to its section width; also refers to the cross-sectional profile of the tire;
a low-profile tire, for example, has a low aspect ratio.
"Axial" and "Axially" means the lines or directions that
are parallel to the axis of rotation of the tire.
"Bead" or "Bead Core" generally means that part of the
tire comprising an annular tensile member of radially inner beads that are associated
with holding the tire to the rim; the beads being wrapped by ply cords and shaped,
with or without other reinforcement elements such as flippers, chippers, apexes
or fillers, toe guards and chafers.
"Belt Structure" or "Reinforcement Belts" or "Belt Package"
means at least two annular 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 18° to 30° relative to the equatorial plane of
"Breakers" or "Tire Breakers" means the same as belt or
belt structure or reinforcement belts.
"Carcass" means the tire structure apart from the belt
structure, tread, undertread over the plies, but including the beads.
"Casing" means the carcass, belt structure, beads, sidewalls
and all other components of the tire excepting the tread and undertread.
"Circumferential" most often means circular lines or directions
extending along the perimeter of the surface of the annular tread perpendicular
to the axial direction; it can also refer to the direction of the sets of adjacent
circular curves whose radii define the axial curvature of the tread, as viewed in
"Cord" means one of the reinforcement strands, including
fibers, with which the plies and belts are reinforced.
"Crown" or "Tire Crown" means the tread, tread shoulders
and the immediately adjacent portions of the sidewalls.
"Equatorial Plane" means the plane perpendicular to the
tire's axis of rotation and passing through the center of its tread; or the plane
containing the circumferential centerline of the tread.
"EMT" means "extended mobility tire," which means the same
as "runflat tire."
"Footprint" means the contact patch or area of contact
of the tire tread with a flat surface at a given speed and under a given load and
"Gauge" refers to thickness.
"Inner liner" means the layer or layers of elastomer or
other material that form the inside surface of a tubeless tire and that contain
the inflating fluid within the tire.
"Insert" means the same as "wedge insert," which is the
crescent-shaped or wedge-shaped reinforcement typically used to reinforce the sidewalls
of runflat-type tires; it also refers to the elastomeric non-crescent-shaped insert
that underlies the tread.
"Lateral" means a direction parallel to the axial direction.
"Normal inflation pressure" means the specific load at
a specific inflation pressure assigned by the appropriate standards organization
for the service condition of the tire.
"Normal load" means the specific load at a specific inflation
pressure assigned by the appropriate standards organization for the service condition
for the tire.
"Ply" means a cord-reinforced layer of rubber-coated radially
deployed or otherwise parallel cords.
"Radial" and "radially" mean directions radially toward
or away from the axis of rotation of the tire.
"Radial ply structure" means the one or more carcass plies
or which at least one ply has reinforcing cords oriented at an angle of between
65° and 90° with respect to the equatorial plane of the tire.
"Radial ply tire" means a belted or circumferentially-restricted
pneumatic tire in which at least one ply has cords which extend from bead to bead
and are laid at cord angles between 65° and 90° with respect to the equatorial
plane of the tire.
"Runflat" or "runflat tire" is a pneumatic tire that is
designed to provide limited service while uninflated or underinflated.
"Section height" means the radial distance from the nominal
rim diameter to the outer diameter of the tire at its equatorial plane.
"Section width" 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 sidewalls due to labeling, decoration or protective bands.
"Shoulder" means the upper portion of sidewall just below
the tread edge.
"Sidewall" means that portion of a tire between the tread
and the bead.
"Tangential" and "tangentially" refer to segments of circular
curves that intersect at a point through which can be drawn a single line that is
mutually tangential to both circular segments.
"Tread cap" refers to the tread and the underlying material
into which the tread pattern is molded.
"Tread width" means the arc length of the tread surface
in the plane includes the axis of rotation of the tire.
"Wedge insert" means the same as "insert," which is the
sidewall reinforcement used in runflat tires.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Prior Art Embodiment
With reference to FIGURE 1, a cross section of a
typical prior art, pneumatic radial runflat tire 10 is illustrated. The tire
10 has a tread 12, a belt structure 14 comprising belts
24,26, a pair of sidewall portions 16,18, a pair of bead regions
20a,20b and a carcass structure 22. The carcass 22 comprises
a first ply 30 and second ply 32, a gas-impervious inner liner
34, a pair of beads 36a,36b, a pair of bead filler apexes
21a,21b, a first pair of sidewall wedge inserts 40a,40b, and a second
pair of inserts 42a,42b. The first or innermost wedge inserts 40a,40b
are located between the inner liner 34 and the first ply 30, and the
second wedge inserts 42a,42b are located between the first ply
30 and second ply 32. The fabric overlay 28 is disposed beneath,
or radially inward of, tread 12 and on top of, or radially outward from,
belt structure 14. The reinforced sidewall portions 16,18 of carcass
structure 22 give the tire 10 a limited runflat capability.
As can be seen from FIGURE 1, the structural reinforcement
in the sidewall area of the tire 10, i.e., the wedge inserts 40a,40b,42a,42b,
substantially increase the overall thickness of the sidewall portions
16,18. This generalized prior art runflat tire design shows the more or less
uniformly thickened sidewalls that characterize runflat tire designs. The insert-reinforced
sidewalls are necessary to support the tire's load with minimal sidewall deflection
when the tire 10 is in an uninflated or underinflated state. Such runflat
tire designs provide good vehicle handling and performance under conditions of full
inflation, and they give acceptable runflat vehicle handling and runflat operational
life when the tire is underinflated or uninflated. Runflat tires generally weigh
more than equivalent non-runflat-capable tires, and their greater structural complexity
results in additional time consuming manufacturing and quality control.
FIGURE 2 shows a cross-sectional view of a tire 50 employing the features
of the present invention. The tire 50 differs from prior art tire
10 of FIGURE 1 in one significant way: it has only a single wedge
insert 59a,59b in each sidewall 77,78, respectively, and each of those
individual wedge inserts is reinforced by two stiffening reinforcement layers
72a,72b and 73a,73b, respectively, which are herein referred to as
wedge-insert stiffeners. The structural details of the wedge-insert stiffeners
72a,72b are shown in greater detail in FIGURES 3A and 3B. Basically,
each set of wedge-insert stiffeners 72a,73a is made of parallel-aligned nylon
or wire monofilaments or metal cords which are arranged as shown in FIGURE 3B.
Stresses in Wedge Inserts
FIGURE 3A shows a schematic, detailed cross-sectional view of the wedge insert
59a depicted in FIGURE 2. Wedge insert 59b has essentially
the same construction as wedge insert 59a and therefore is not discussed
in detail herein. When the tire 50 of FIGURE 2 is partially or completely
deflated, the portion of the wedge insert 59a that is in the ground-contacting
portion of the tire 50 experiences large vertical compressive forces that
cause the wedge insert to bend as the sidewall undergoes partial collapse. In
FIGURE 3A, the neutral bending axis A-A, which is the interface between
the portions of the wedge insert 59a that are in compression and tension,
is shown. More specifically, referring to FIGURE 3A, the portion of the wedge
that is to the right of the neutral axis A-A undergoes compressive stresses,
while the portion to the left of the neutral axis experience tensile stresses. The
two stiffening reinforcements 72a,73a are located in the compression-load-bearing
side of the neutral bending axis A-A within the wedge insert 59a.
The wedge-insert stiffeners 72a,73a provide the
wedge insert 59a with additional resistance to compression-induced strain.
If the wedge insert 59a were not reinforced with the stiffening reinforcements,
the bending stresses would be such that a maximum compressive stress would arise
in the approximate center of the right-most (or inner-most) edge of the elastomeric
compound of which the circumferentially disposed wedge insert 59a is made.
Such compressive stresses would be of a cyclical nature during runflat operation.
That is, during runflat operation, the combination of extreme compressive stresses
of a cyclical nature with the inherent hysteresis of the elastomeric compound, induce
heat buildup and fatigue of the elastomeric material of which the wedge insert
59a is made. Failure during runflat operation is, in other words, hastened
by a combination of cyclical-flexure-induced heating and flexure fatigue failure
of the elastomeric material.
The incorporation of the compression-load-bearing wedge-insert
stiffeners 72a,73a allows a large portion of the cyclical compressive loading
on the wedge insert 59a to be borne by the stiffeners which remove a large
portion of the cyclical compressive loading from the elastomeric compound of which
the wedge insert 59a is made. Accordingly, the maximum magnitude of the compressive
stresses in the wedge insert can be reduced, which means that the amount of flexure-induced
heating will be reduced, as will the cyclical maximum compression stress which otherwise
contributes to fatigue failure during runflat operation. The tire will thereby achieve
an improvement in its runflat service life. Additionally, the wedge-insert stiffeners,
when made of metal, will, by means of thermal conductivity, tend to distribute and
dissipate flexure-induced heating to a larger portion of the total tire body.
Structure of the Invention
The reinforcing layer 72a, shown in FIGURE 3A,
comprises parallel cords 76, shown in FIGURE 3B. The reinforcing layer
73a, shown in FIGURE 3A, comprises substantially parallel cords
75, shown in FIGURE 3B. The cords are preferably aligned in a parallel
configuration because it leads to the best shear stress distribution, which provides
the best resistance to compression. Referring to FIGURE 3A, the vertical
extent of the wedge-insert stiffener 72a is preferably in the range of 25
percent to 60 percent and most preferably in the range of 30 percent to 50 percent
of the total radially oriented span L of the respective wedge insert
59a (and 59b in FIGURE 2). The vertical extent of the stiffener
72a is no greater than 60 percent because the inflated handling of the tire
will be affected by the too high sidewall stiffness and it is no less than 25 percent
because the contribution to compression resistance would be negligible. The vertical
extent of the wedge-insert stiffener 73a is preferably in the range of 60
percent to 90 percent and most preferably in the range of 70 percent to 80 percent
of the total radially oriented span L of the wedge insert 59a (and
59b in FIGURE 2). The vertical extent of wedge-insert stiffener
73a is no greater than 90 percent because of the risks of reduced durability
at the edge of the stiffener and no less than 60 percent because of the necessity
for a step off from 72a to prevent the localization of two weak points at
the edges of the stiffener 73a, which could cause a high stress concentration.
The respective parallel-aligned monofilaments, aligned nylon or wire monofilaments
or metal cords 75, 76 of each set of wedge-insert stiffeners 72a, 73a,
respectively, are preferably oriented at an angle of between 20 degrees and 55 degrees
(extending through the insert and centerline C-L as shown in Figure 2) with
respect to the circumferential direction (CD), as shown by the angles &agr;
and &bgr; in FIGURE 3B, which is a view of the wedge-insert stiffeners
from a direction that is more or less perpendicular to the curved plane of the two
sets of layers of stiffening reinforcements 72a,73a. The parallel-aligned
cords 75, 76 of inserts 59a,59b respectively, lie in transverse relation
to each other. While shown as being nearly perpendicular to each other, it is within
the terms of the invention to change their relation with the angle ranges mentioned
before. The angle of the wedge-insert stiffeners 72a,73a is no more than
55 degrees with respect to the circumferential direction because the monofilament
or cords may be affected by a poor durability to buckling and no less than 20 degrees
because the resistance to compression will be negligible.
Before explaining in detail the compression-bearing dynamics
of operation of the wedge-insert stiffeners, it should be borne in mind that the
radial ply 70 shown in FIGURE 2 experiences and bears cyclical tensile
loading during normal inflated operation and especially during runflat operation
when the portion of the sidewalls that are most adjacent to the ground-contacting
portion of the tire undergo the greatest deformation.
Dynamics of Operation of the Inventive Concept
The dynamics of operation of the inventive concept that
underlies the use of wedge-insert stiffeners can be understood by reference to
FIGURES 4A, 4B, and 4C and FIGURES 5A, 5B, and 5, which
show the compressive stresses associated with the bending of elastomeric beams that
are subjected to opposing forces of compression.
FIGURE 4A shows a square-section beam 80 of elastomeric material that
is loaded in compression, and deflected in bending, by opposing forces
F. Beam 80 represents an idealized segment of the wedge insert
59a shown in FIGURES 2 and 3A without the wedge-insert stiffeners
of the present invention. It should, of course, be acknowledged that the actual
wedge inserts 59a,59b are crescent-shaped in cross section and, being circumferentially
deployed, are essentially endless. FIGURE 4B shows the beam 80 in
cross section. The main body 82 of beam 80 is an elastomeric material
while the upper region is a tensile-stress-bearing layer 84 that corresponds
to the radial ply layer 70 of the tire 50 shown in FIGURE 2.
Tensile-stress-bearing radial cords 85 are shown in cross section in layer
84 of FIGURE 4B. FIGURE 4C shows a stress distribution curve for the
cross-sectional portion shown in FIGURE 4B; the location of the neutral axis
is chosen for diagrammatic purposes only and does not reflect actual stress-strain
The stress distribution curve shown in FIGURE 4C
reflects the predominance of compressive stresses in that the area 88, which
lies on the compression-stress side of the stress diagram, is much larger than the
corresponding tensile-stress area 86. For the sake of clarity, it is acknowledged
that the integrated multiplicative product of the compressive (or tensile) stress
and the corresponding distance from the neutral axis is related directly to the
resistance of beam 80 to bending flexure. In other words, the area
88 represents a compressive force which acts through a moment arm that is
distributed across the region located between the neutral axis and the point &sgr;
where maximum compressive stress is experienced in the elastomeric material
of main body 82. A corresponding moment arm for tensile stresses also exists,
but for the purposes of explaining the benefits of this invention, the limiting
of the maximum compressive stress &sgr;
is of specific interest.
FIGURES 5A, 5B, and 5C represent the effects of the incorporation
of the present invention upon a compression-loaded beam 90 that is otherwise
comparable to the beam 80 depicted in FIGURE 4A. In FIGURE 5A,
opposing forces F place the beam 90 in compression and in a bent state
of deflection which, as with the beam 80 of FIGURE 4A, induces compressive
and tensile stresses that are described in more detail as follows. FIGURE 5B
shows the beam 90 in cross section. In particular, FIGURE 5B shows
the tensile bearing layer 92, which corresponds to the radial ply layer
70 of the tire 50 shown in FIGURE 2 and cords 97 embedded
in elastomer 91 and corresponding to the radially aligned reinforcing cords
of the radial ply layer 70. FIGURE 5B also includes an idealized view of
the two layers that correspond to the stiffening reinforcement layers
72a,72b,73a,73b shown in FIGURE 2 and FIGURE 3A. Referring
to FIGURE 5B, layer 93 corresponds to stiffening reinforcement
73a in FIGURE 3A and layer 94
corresponds to stiffening reinforcement 72a.
The purpose of the wedge-insert stiffeners 72a,72b,73a,73b
is to bear significant portions of the compressive stresses which the wedge insert
59a, as shown in FIGURE 3A, experiences during runflat operation.
Accordingly, the stress distribution curve shown in FIGURE 5C shows the respective
layers 93,94 (which correspond to the stiffening reinforcements
72a,72b,73a,73b of FIGURES 2 and 3) bearing large portions
of the compressive load of the deflected compression-loaded beam 90 of
FIGURES 5A and 5B. The maximum stress &sgr;
experienced by the elastomeric material 91, at the location most distant
from the neutral axis, is less than the corresponding &sgr;
shown in FIGURE 4C, wherein wedge-insert stiffeners are not used to
carry the cyclical compressive loading.
Since the maximum compressive stress &sgr;
is less in the instance wherein the wedge-insert stiffeners of the present
invention are deployed within the wedge inserts than when such stiffeners are not
used, the elastomeric component of the wedge insert undergoes a reduced magnitude
of cyclical compression, especially during runflat operation. Thus the incorporation
of wedge-insert stiffeners in the wedge inserts, as set forth in the present invention,
reduces the maximum compressive stress &sgr;
and accordingly reduces the heat buildup due to the cyclical nature of the
compressive loading during runflat operation. Fatigue failure resulting from cyclical
flexure is also reduced because the maximum strain associated with the stress &sgr;
is also reduced.
The respective parallel-aligned cords 75,76 within
the stiffening reinforcements 72a,73b (FIGURE 2) can be made from
solid wire monofilaments or from metal cords. The inventors recognize that instead
of wire monofilaments or metal cords, the wedge-insert stiffeners can also be made
of nylon monofilaments, which also have substantial compression-load-bearing capacity
in comparison to the elastomeric material 91 (FIGURE 5B) of which
the wedge inserts are made.
The inventors also recognize that by designing an appropriate
sidewall wedge gauge distribution in conjunction with the physical properties (e.g.,
rigidity, tensile-stress-bearing properties) of the wire/cord wedge-insert stiffeners
72a,72b,73a,73b, the tire designer can tailor the operational properties
of tire 50 (FIGURE 2) to a variety vehicle types and tire use applications
as well as ride characteristics and vehicle handling characteristics in both normal-inflated
operation and in runflat operation.
The present invention also includes the incorporation of
the wedge-insert stiffeners 72a,72b,73a,73b with the tire designs having
two or more radial plies that are reinforced with metal wires/cords and/or organic
fibers/cords or combinations of metal and organic reinforcing fibers/wires/cords.
Manufacturing Sequence, Compared to Prior Art Tire
Another benefit of the present invention is its contribution
to a potentially reduced number of manufacturing steps and the corresponding quality
control associated with each. The manufacture of prior art tires having a multiplicity
of sidewall inserts 40a,40b,42a,42b, as shown in prior art tire
10 shown in FIGURE 1, entails the following sequence of manufacturing
steps in the part of the manufacturing process that takes place upon a tire assembly
drum. First, the inner liner 34 is laid upon a conventional tire building
drum (not shown), followed by the beads 36a,36b, followed by inserts
40a,40b, then by ply layer 30, inserts 42a,42b and then ply
layer 32. Other tire components, which are not a part of the present invention,
such as for example, the outermost elastomeric portions of the sidewall portions
77,78 and bead filler apexes 38a,38b can then be added.
In the present invention, as shown in FIGURE 2,
the use of a single wedge insert 59a,59b, each containing two stiffening
reinforcement layers 72a,72b,73a,73b, accordingly simplifies the manufacturing
process. That is, the use of single wedge inserts within each sidewall, eliminates
the need to orient the two or more inserts in each sidewall portion such that they
are optimally and uniformly positioned in relationship to one another and to the
other tire structures.
The invention is intended to embrace all such alternatives,
modifications and variations as fall within the scope of the appended claims.