Run-flat tire with three carcass layers

The weight, space and convenience advantages of a run-flat tire can be substantial. This is especially true for the urban-economy car or family type vehicles which have limited space available for a spare tire and inadequate space for the removed flat tire. These vehicles also have higher comfort requirements that must be addressed. The mini-spare solution to the flat tire problem has very limited performance capabilities. Other solutions include major modifications in the rim and/or the tire, which are not cost effective or compatible with a conversion to standard tires on the same rims. The run-flat tire of this invention includes thickened sidewall portions, a belt package with a cap ply, lower sidewall rubber support portions, a specially designed bead seat area with a rim seat ply and three carcass layers. The classical problems of inflated vs. deflated performance tradeoffs in ride comfort, handling, radial stiffness and endurance of the tire are substantially improved. This is accomplished with a run-flat tire having relatively small weight increases over a standard tire and a rim that can be used interchangeably with the standard tire. The run-flat tire system of this invention is capable of maximum lateral accelerations under nominal operations of approximately 0.90 g.sup.S and extended operating efficiency (i.e., handling and durability) at higher speeds for longer distances.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a radial pneumatic tire and more specifically to 
an improved self-supporting run-flat tire. 
2. Description of the Prior Art 
There is a current ongoing effort by automobile manufacturers to eliminate 
the spare tire in order to reduce vehicle curb weight, increase available 
space within the vehicle and provide operator convenience. This is 
particularly true for vehicles having higher comfort specifications such 
as conventional luxury, family or urban-economy type vehicles. For 
example, new generation electrical and hybrid type vehicles have critical 
space and weight restrictions. 
One solution to increase trunk space and reduce weight of the spare tire is 
the mini-spare. This tire is a specifically designed and constructed 
narrow tire mounted on a special rim. The tire has a slightly smaller 
diameter than the standard factory equipment tire. These tires are very 
limited in the number of travel miles permitted and the speed of the 
vehicle. They are intended to get the vehicle to a service station so the 
standard tire can be repaired. Special mini-spare standards are provided 
by the Tire and Rim Association (T&RA) of Copley, Ohio and are based on 
vehicular weight and performance. The mini-spare is not the best solution 
because the tire loses air over time (by permeation) and will not have the 
performance characteristics of a properly inflated mini-spare. 
Furthermore, space for the removed flat tire is frequently not available. 
Another recent solution is the run-flat tire. The advantage of this tire is 
to eliminate the need of a spare tire and ancillary equipment, achieving 
substantial savings in vehicle weight and increasing the space for other 
automotive systems and cargo. Numerous variations of run-flat tires have 
been developed. These involve changes to the structure of the tire itself 
and modifications to the rim to hold and support the flat tire. Each 
variation is limited by safety restrictions on vehicle speed, length of 
travel, zero inflation pressure handling and the magnitude of the lateral 
accelerations that force the bead of the tire off the rim seat. Further, 
the best solutions are those which do not affect the vehicle's nominal 
performance. Therefore, the need for improvements in the design of 
run-flat tires continues. 
A number of generic features of run-flat tires have been disclosed which 
yield improvements, although limited, in vehicle performance. These 
features include thickened tire sidewalls, sidewall reinforcing plies, 
tire bead seat and vehicle rim configuration modifications, tire sidewall 
to rim flange contact and tire belt package edge modifications. Each of 
these features can be used to help solve known run-flat performance 
problems. 
One feature of some run-flat tires is thickened sidewalls to support the 
vehicle after loss of inflation pressure. Such a sidewall, as the tire is 
viewed in cross-section, presents a crescent-shaped mass of rubber to the 
inside of the carcass reinforcing. On complete deflation of the tire, the 
crescent-shaped mass is put into compression while the carcass cord 
reinforcement is in tension; thereby preventing collapse of the sidewall. 
The respective inner wall surfaces of the tire do not contact one another 
and the rolling radius of the tire is maintained at a relatively large 
percentage of the inflated rolling radius of the tire. Seven patents that 
disclose a thick sidewall design are U.S. Pat. Nos. 4,067,374; 4,779,658; 
5,058,646; and 5,217,549, European Patent No. 456,437 (EP), Japanese 
Patent No. 1-30809 (JP) and French Patent No. 2,469,297 (FR). 
U.S. Pat. No. 4,067,374 discloses the use of a crescent-shaped sidewall 
reinforcing rubber portion inside the carcass layer which has a high 
dynamic modulus with low hysteresis properties and high aging properties. 
The crescent-shape sidewall reinforcing rubber is put into compression 
while the cords of the carcass are put into tension, thereby inhibiting 
collapse of the sidewall. A cap ply located outside the belt package 
cooperates with the sidewall construction to increase the run-flat 
performance of the tire. The patent also discloses a lower sidewall 
support on the tire that contacts a rim flange when the tire is in an 
uninflated mode. 
In European Patent No. 458,437, the inner sidewalls of the tire have a 
crescent-shaped reinforcing rubber with a specified radius of curvature of 
the axially inner face in relation to the section height of the tire. Two 
radial carcass plies are turned up around the bead cores from the inside 
to the outside. Two cap plies are positioned radially outward of two belt 
plies. In addition, this run-flat tire design includes an extension of the 
bead area to form a bead toe for a bead retaining system. 
The crescent-shaped reinforcement rubber portion of the run-flat tire in 
U.S. Pat. No. 4,779,658 has two layers; i.e., an anticrack layer adjacent 
to the carcass and a reinforcing layer inside the anticrack layer. The 
reinforcing layer provides more support for the tire when deflated and the 
anticrack layer is stated to provide a balance between ride comfort and 
crack resistance. This tire also has a protruding rubber bead toe portion 
supported by a rubber chafer and a fabric member made of textile cord. 
U.S. Pat. No. 5,058,646 is similar to EP 458,437 but discloses a 
three-layer crescent-shaped cushion on the inner sidewall in terms of 
thickness of the layers. A hard rubber bead filler is further disclosed 
for the bead area of the tire. 
The pair of crescent-shaped elastomeric reinforcing members disclosed in 
U.S. Pat. No. 5,217,549 are preferably for high profile tires having a 
section height of 5 inches (127 millimeters) or greater. Sidewall 
stiffness is achieved by a single high modulus crescent-shaped member in 
each sidewall with a reinforcing bias ply strip on the inside or the 
outside surface of the two carcass plies. These bias ply strips are bias 
at 60 degrees and reinforcing members are of a nylon material. 
In the JP 1-30809 patent a crescent-shaped low heat generating rubber with 
a specified maximum thickness of 1.0 to 1.5 times the sidewall rubber plus 
the carcass thickness is arranged inside the sidewall. The crescent-shaped 
run-flat strip extends radially inward and overlaps the apex of the bead 
filler rubber by 10 millimeters or more. 
A two part crescent-shaped sidewall reinforcing ply of FR 2,469,297 has a 
relatively thick mass. The exterior portion adjacent the carcass plies is 
of a flexible cellular structure having a relatively low density and Shore 
A hardness. Preferably the neutral axis of the sidewall during bending is 
located in the interior portion of the reinforcing ply. 
A critical and limiting feature of the run-flat tire is the ability of the 
deflated tire to stay on the rim during cornering maneuvers of the 
vehicle. This is known in the art as resistance to bead-unseating or bead 
retention. Bead unseating resistance is improved by extending or recessing 
the toe portion of the bead area to engage a rim having an extended or 
recessed portion. This feature of run-flat tires is noted in European 
Patent 456,437 (EP), U.S. Pat. Nos. 4,554,960; 4,779,658; and 4,917,164 
and Japanese Patent No. 2-179513 (JP). 
In patent EP 456,437, each bead area has a relatively thin rubber portion 
shaped axially inward of the carcass to form a bead toe. The toe extends 
radially inward to be inserted into a rim groove at the axially inner end 
of a tapered bead seat of a wheel rim. The base of the bead of the tire is 
further provided with a groove immediately axially outside the bead toe 
and inside a bead core. The groove fits into a hump formed in the bead 
seat of the rim for which the tire is designed. 
U.S. Pat. No. 4,779,658 also shows a protruding rubber member which serves 
to reinforce the bead area to prevent the bead from unseating during 
run-flat travel. The protruding rubber seats the tire to a rim which is 
modified to receive the protruding rubber member. U.S. Pat. No. 5,058,646 
discloses a similar protruding member that seats in a modified rim. 
The extended rubber toe portion of each bead area disclosed in U.S. Pat. 
No. 4,917,164 is a hard rubber member bonded to the crescent-shaped 
reinforcing layer. The toe portion has a preferred elastic modulus at 100 
percent unit strain of 75 to 95 kilograms per square centimeter. A fabric 
reinforcing member or ply is attached to the exterior of the toe portion 
as an interface to the rim seat. Another rubber member is bonded to the 
heel portion at the rim interface. All these components help to maintain 
the tire on the rim after it becomes deflated. 
The problem of maintaining the tire on the rim with a loss in inflation 
pressure is also discussed in U.S. Pat. No. 4,554,960. To resist 
bead-unseating, this patent discloses a specially designed bead area base 
and precise placing of the beads on the rim seats. A rim hump is formed on 
a standard rim with a circumferential hump having radially a cylindrical 
generatrix. Japanese Patent No. 2-179513 also discloses the modification 
of the bead toe portion as well as the rim seat. 
With the extensive flexing of the run-flat tire and the large deflections 
associated with the deflated rolling tire, the various components within 
the run-flat tire undergo gradual breakdown. High component temperatures 
also contribute to the breakdown of the materials in the run-flat tire. 
Efforts to give the crescent-shaped sidewall supporting members additional 
performance improvements are disclosed in U.S. Pat. Nos. 3,994,329 and 
4,287,924, Japanese Patent No. 3-14370 (JP) and French Patent Nos. 
1,502,689 and 2,458,407. Improvements include better heat conduction from 
the thickened sidewall portions, limited flexing or sagging of the 
deflated tire and reductions in the required thickness of the 
crescent-shaped reinforcement. 
The chambers of the tire disclosed in U.S. Pat. No. 3,994,329 are 
lenticular in shape. These chambers are filled with a flexible cellular 
material and are bounded on both lateral sides by reinforcing layers, such 
as plies of the carcass. These layers form walls that render the sidewalls 
suitable to support the load of a wheel with limited sagging of the tire. 
In U.S. Pat. No. 4,287,924 a two part crescent-shaped member has a heat 
conducting sheet or layer between the two parts. The layer extends over 
the whole height of the crescent-shaped portions and the two 
crescent-shaped parts are of different flexibility. The heat conducting 
layer may have parallel metallic cords extending radially to assist in the 
heat conductivity. The height of the tire is 31 percent of its inflated 
height when the inflation pressure is zero. 
The cord reinforcing unit on the interior surface of the sidewall 
crescent-shaped reinforcing member in JP 3-143710 consists of at least one 
reinforced ply. The crescent member and the reinforced ply provides the 
overall sidewall support for run-flat performance. Also, the bead area has 
a rubber toe portion that fits into a rim recess for bead seat retention. 
The FR 1,502,689 patent discloses a very thin crescent-shaped member at the 
interior of the sidewall which is heavily reinforced by one or two plies 
having reinforcing members. These reinforcing members are at an angle of 
.+-.30 degrees with the radial plane to help support the sidewall by 
triangulation with the radial reinforcing members of the carcass in the 
sidewall. This tire is designed for resistance of the sidewall to 
punctures. 
A portion of the crescent-shaped reinforcing member in FR 2,458,407 is 
positioned inside the innerliner rubber (FIG. 3). This interior portion 
has some load bearing abilities, but also becomes an interior sealant 
material. The total thickness of the sidewall portion at an median plane 
of the tire is expressed as a function of the load on the tire, the 
section width of the tire and the radial distance from the axis of 
rotation to the median plane. 
The features discussed above can be used in the design of a run-flat tire 
having some run-flat endurance capability. However, even combining all of 
such features will provide a run-flat tire with only limited performance 
capabilities. There remains a need to have improved tire performance to 
permit additional travel distances and especially to achieve improved load 
supporting capabilities for the vehicles using higher aspect ratio tires. 
Problems continue to inhibit run-flat tire performance when vehicle ride 
comfort of the inflated tire is considered. The need is to add features to 
create a run-flat tire which has little or no influence on the vehicle 
during inflated tire running but which have a significant influence after 
loss of tire inflation pressure, particularly in improvements to the load 
supporting and cornering comfort capabilities of the vehicle. 
The addition of sidewall components, such as harder rubber bead fillers and 
reinforcing plies have been disclosed in standard T&RA tires to improve 
handling. However, these components in a tire degrade the ride comfort or 
other performance characteristics of the inflated tire. 
There is a need for a new run-flat tire having improved performance 
characteristics that overcome some of the limitations discussed in the 
art. A run-flat tire that has less deflection when deflated allows the 
trip to continue and permits the continuation of almost normal operation 
of the vehicle. This is a particular need for a luxury car, family or 
urban-economy vehicle and the like. A durable run-flat tire is also needed 
that has an acceptable response to steering inputs at zero inflation 
pressure yet capable of adequate inflated ride comfort with a relatively 
soft vehicle suspension system. Furthermore, vehicles of the family or 
urban-economy type have available space problems as a result of their 
overall dimensions and the relatively large size of the passenger and 
luggage spaces. 
SUMMARY OF THE INVENTION 
Space, weight and convenience problems associated with spare tires are 
solved by a run-flat tire. An object of this invention is to provide a 
run-flat tire which demonstrates improved vehicle performance under 
deflated conditions and yet achieves the same vehicle performance as a 
standard tire when inflated. 
A further object of this invention is to provide a run-flat tire which can 
be constructed by conventional manufacturing techniques, requiring few 
additional manufacturing steps and procedures, thereby having a cost 
effective tire which will achieve the required long travel distances at 
relatively high speeds and with minimum changes in vehicular steering 
feel. 
A still further object is to prevent premature stress cracking from being 
produced during run-flat travel in or near the boundaries between the 
crescent-shaped reinforcing members and the reinforced carcass layers in 
the load bearing sidewall portions of the run-flat tire. 
In particular, the run-flat tire of this invention introduces an essential 
third inner carcass layer that preferably extends from bead to bead and 
bisects two crescent-shaped reinforcing members in each sidewall. Other 
bead portion and belt package features and components are disclosed that 
are a part of the total combination that yields improved run-flat tire 
performance. This run-flat tire improves deflated tire running and yet 
maintains good ride comfort and handling during inflated tire running. 
This higher profile run-flat tire is particularly useful on luxury, family 
and urban-economy type cars. Tires for these vehicles have aspect ratios 
in the range of 40 to 65 percent. Aspect ratio is defined as the tire 
section height as a percent of the overall tire width. 
The preferred embodiment tire of this invention is easily mounted on a 
standard rim of a vehicle and is capable of sustaining vehicle loads at 
the tire's contact patch with the loss of inflation pressure. The tire has 
a crown portion with a tread. A belt package is located radially inward of 
the tread. An innerliner portion covers the interior surface of the tire. 
There are a pair of bead portions each having a bead core and a bead 
filler. 
A pair of load bearing sidewall portions are each disposed radially between 
a respective lateral edge of a crown portion of the tire and a respective 
bead portion. Each sidewall portion has first and second crescent-shaped 
reinforcing members disposed outside the innerliner portion. 
A middle carcass layer radially inward of the belt package extends between 
each bead has its end portions turned up from inside to outside around 
each bead core in such a manner to at least partially encompass the bead 
core and a respective bead filler. An outer carcass layer is disposed 
outside the middle carcass layer and the turned-up portion and extends 
radially inward to at least a point axially exterior and adjacent to each 
bead core. 
An inner carcass layer is disposed inside of the middle carcass layer and 
is positioned between the first and second crescent-shaped members in each 
sidewall portion. The inner carcass layer extends radially inward to at 
least a point axially interior and adjacent to each bead core. The carcass 
layers each have a plurality of substantially parallel reinforcing members 
and a curvilinear configuration. 
In one embodiment of the invention at least a pair of carcass-shaped 
reinforcing members can be separated by any interface portion that 
achieves the objects of this invention by its position within the sidewall 
portions. The position of the interface portion (i.e. inner carcass layer) 
between at least two crescent-shaped reinforcing members provides a radial 
stepwise stress distribution between the two crescent-shaped reinforcing 
members axially across the interface portion on a median plane adjacent a 
central radial plane of a contact patch. The position of the interface 
portion also reduces the maximum deflection of the deflated tire due to 
vehicle loads. Three total carcass layers, with the inner carcass layer 
providing the interface portion, are preferred to provide extra 
reinforcement for the severe operating conditions during abnormal deflated 
running, such as curb impact, high temperatures or extreme deformations. 
In an embodiment of this invention a belt package is located radially 
outward from a crown portion of the outer carcass layer. In this 
embodiment, a first belt of the belt package is located radially outward 
of the crown portion of the carcass layers. At least one other belt is 
located radially outward of the first belt. The first belt is wider than 
the other belts. A cap ply is located outward of the other belts and 
inward of a tread portion. The cap ply is wider than both the first and 
other belts. The tread portion is located radially outward of the belt 
package for contacting a ground surface. 
In a further embodiment of this invention, a rim seat ply contacts the rim 
at each tire/rim interface and has a square woven fabric as reinforcing 
members. A rubber seat portion is positioned to support the rim seat ply 
at each bead portion. A second rubber toe portion is located axially and 
radially inward of the bead core. The toe portion also supports the rim 
seat ply and helps keep the tire on the rim at a tire/rim interface. 
Finally, a pair of rubber support portions are disposed to assist the rim 
seat ply in contacting a flange of the rim at the tire/rim interface when 
the tire is deflated. 
Another embodiment includes a tire and rim system capable of sustaining 
vehicle loads effectively with the loss of inflation pressure. The tire 
and rim system includes the preferred run-flat tire including the rim seat 
ply, the first rubber seat portion and the second rubber toe portion which 
is mounted on a rim having a hump disposed at the axially innermost end of 
the rim seat ply of the tire. The rim seat ply may engage the rim hump so 
that the tire remains seated on the rim during vehicle maneuvers as well 
as during straight ahead running.

DETAILED DESCRIPTION OF THE INVENTION AND ITS PREFERRED EMBODIMENTS 
The unique features of the run-flat tire of this invention, which yield the 
improvements needed for a vehicle to overcome the above described 
limitations of state-of-the-art tires, include the load bearing sidewall 
portions each having first and second crescent-shaped reinforcing members 
bisected by an essential third inner carcass layer. Each of the essential 
three reinforced carcass layers extend from the bead to at least a crown 
point below the belt package, and preferably extend the full width and 
depth of the tire from bead to bead. The bias of the carcass reinforcing 
members from a radial plane is determined by the vehicle application. The 
run-flat tire is a radial tire having carcass reinforcing bias angles from 
about 75 degrees to 90 degrees. Other structural features in combination 
with the unique sidewall portions include a belt package with at least two 
belt plies and a cap ply as well as a pair of bead portions each including 
a relatively high modulus bead core, a bead filler, a rubber support 
portion, a rubber seat portion, a rubber toe portion and a rim seat ply at 
the tire/rim interface that may engage a hump on a rim of the vehicle. 
The run-flat tire 10 of this invention has a cross-sectional configuration 
in a radial plane containing an axis of rotation A of the tire as 
illustrated in FIG. 1. This figure shows half the cross-section which is 
symmetrical about the midcircumferential plane P. The tire having this 
cross-sectional configuration is readily mounted on a rim of a vehicle. 
A pair of bead portions 20 are axially spaced apart and each include a bead 
core 22, a bead filler 24, a rubber support portion 34, a first rubber 
seat portion 26, a second rubber toe portion 28 and a rim seat ply 27. A 
carcass portion 60 has an middle carcass layer 62, an outer carcass layer 
64 and an inner carcass layer 68. The middle carcass layer 62 has a 
turned-up portion 66 which extends around the bead core 22 from inside to 
outside of the tire 10 to a distance G radially outside the bead reference 
D, as illustrated in FIG. 2. The distance G is in a range of 15 to 40 
percent, and preferably equal to about 30 percent, of the section height 
H. The bead reference D is established by a line parallel to the axis of 
rotation A from the intersection of a radial line 23 from the center of 
the bead core 22 and the innermost surface of the rim seat ply 27 at point 
25. The inner carcass layer 68 is positioned uniformly between the middle 
carcass layer 62 and the innerliner portion 44 in each bead portion 20 and 
extends radially inward to at least a point 67 axially inward and adjacent 
to the bead core 22. The outer carcass layer 64 of the tire is located 
axially outside the middle carcass layer 68 and the turned-up portion 66 
and extends radially inward to at least a point 61 axially outward and 
adjacent to the bead core 22. The bead filler 24 contacts the outermost 
surface of the bead core 22 and extends a distance F radially outward of 
the bead reference D. The bead filler 24 is contoured to assume a 
predetermined optimum profile. An apex 29 of the bead filler 24 is 
preferably at the distance F in a range of 40 to 60 percent, and 
preferably about 50 percent, of the section height H. 
A load bearing sidewall portion 40 extends from a belt package 80 of the 
tire to the bead portion 20 at both axial edges of a crown portion 14. 
Each sidewall portion 40 includes a pair of crescent-shaped rubber 
reinforcing members 54,56 as shown in FIGS. 1 and 2. The profile shape of 
the crescent-shaped reinforcing members may also be lenticular within the 
scope of this invention. The first crescent-shaped reinforcing member 56 
is disposed between the middle carcass layer 62 and the inner carcass 
layer 68. The second crescent-shaped member 54 is disposed between the 
inner carcass layer 68 and an innerliner portion 44 of the tire 10. The 
sidewall portions 40 help maintain the crown portion 14 radially separated 
from the bead portion 20 when the tire has a loss of inflation pressure. A 
tread rubber portion 12 has a surface 16 for contacting a ground surface 
during running of the tire. 
The rubber in the tread rubber portion 12 and a sidewall rubber portion 42 
may be of any suitable compound based on natural or synthetic rubber or 
any suitable combination thereof known in the art. The innerliner portion 
44 is preferably of a halobutyl rubber. 
The overall profile of the sidewall portions 40 are shaped in a manner to 
provide the best equilibrium curve for generating normal and lateral 
forces on the tire during inflated running. A thickness of the load 
bearing sidewall portion including a sidewall rubber 42, the inner, middle 
and outer carcass layers 68, 62, 64, the first and second crescent-shaped 
reinforcing members 56, 54, the bead filler portion 24 and the innerliner 
portion 44 is approximately constant over its radial extend and such 
sidewall portion 40 has a width of about 6 percent to about 8 percent of a 
section width SW of the tire 10. The crescent-shaped members 54,56 have a 
profile geometry including a thickness distribution to produce optimum 
inflated and deflated tire performance. The crescent-shaped members extend 
to a crown point 58 in the crown area of the tire axially inward of the 
axial extent of the belt package 80 at least 20 millimeters. A preferred 
thickness distribution of the crescent-shaped members is that second 
member 54 has a thickness substantially equal to that of first member 56. 
The properties of these crescent-shaped members are discussed later. 
The belt package 80 is located radially outward of the carcass layers 62, 
64 and 68 in the crown portion 14 of the tire 10. In an embodiment of this 
invention, the belt package has a wide inner belt 82 and at least one 
narrower outer belt 84 (FIG. 1). A cap ply 86 having a width to axially 
extend beyond both lateral edges of the innermost belt 82, is included as 
part of the preferred belt package 80. These belt components allow the 
lateral areas of the crown portion 14 to be more compliant in compression, 
which improves the endurance of the tire when running deflated. This 
results in a redistribution of the load so that the tread portion 12 at 
its two shoulder regions can fully support the loads from the sidewall 
portions 40. Reinforcing members of the inner belt 82 are preferably of an 
metallic (i.e. steel) material. Reinforcing members in each of the outer 
belts 84 are also preferably of a aromatic polyamide or a metallic (i.e., 
steel) material. Belt reinforcing members are at an acute angle with 
respect to the midcircumferential plane P. The cap ply 86 has reinforcing 
members preferably of a polyamide multi-filament (i.e., nylon) material 
which are approximately parallel to the midcircumferential plane. Other 
belt package and cap ply materials that maintain structural integrity of 
the tire may be used for the reinforcing members within the scope of this 
invention. 
The overall section height H is measured from the bead reference D (FIG. 
2). The overall section width SW is measured in the maximum width median 
plane M. The ratio of the section height H to the overall section width SW 
is the aspect ratio of the tire. Aspect ratios between approximately 0.40 
to 0.65 are preferred values for the cured run-flat tire of this invention 
(FIG. 1). 
The run-flat tire 10 is mounted on a rim 70 as illustrated in FIG. 2. The 
rim 70 can be a standard T&RA rim but preferably has a hump 72 added to 
help retain the bead portion 20 of the tire on the rim 70. The nominal rim 
diameter DR is measured to a rim reference D which is associated with the 
size of the tire. The reinforced rim seat ply 27 contacts the rim at the 
tire/rim interface 76. The contour of the rubber seat 26 has been designed 
to obtain a more uniform pressure distribution at the tire/rim interface 
76. The increase of frictional forces between the tire rim seat ply 27 and 
the rim 70 at the tire/rim interface 76 helps maintain the tire 10 seated 
on the rim 70. The rim seat ply 27 also contacts the hump 72 near a base 
point 75. The design of rubber seat and toe portions is disclosed in U.S. 
Pat. No. 4,554,960, which is incorporated herein by reference thereto. The 
rim seat ply 27 has essentially square woven fabric reinforcing members at 
.+-.45 degrees with the radial plane and extends circumferentially around 
the tire. Square woven fabric standard in the industry can be used. The 
rim seat ply reinforcing members are preferably of a textile material 
(i.e. aromatic polyamide, polyester, rayon or nylon). 
The symmetric hump 72 on the rim 70 is referred to as an "SH contour" rim. 
The diameter to the outermost surface of the hump 72 is at least at the 
same radial extent as the bead reference D. This profile provides 
additional axial support to keep the bead portions 20 from being unseated. 
The run-flat tire 10, as well as a standard T&RA tire, is easy to mount 
and dismount on this rim 70. 
A gap between a flange 74 of the rim 70 and the tire 10, as observed in 
FIG. 1, is provided to prevent contact between the inflated tire 10 and 
the rim 70. Contact between the inflated tire and the rim in this region 
when the vehicle is cornering will affect the handling characteristics of 
the vehicle. The gap is maintained between the rim seat ply 27 with its 
rubber support portion 34 and the flange 74 of the rim 70 during inflated 
running conditions. A sidewall rubber 42 is preferably positioned to the 
exterior of the each support portion 34 and is spaced from the flange 74 
by the same gap. 
A loaded and deflated run-flat tire 10 in contact with a ground surface 90 
is illustrated in FIG. 4. The crown portion 14 of the tire 10 has a tread 
12 with a tread design or sculpture wherein surface areas 16 make contact 
with the ground surface 90. The radial section height H of the free tire 
10 (FIG. 2) is compressed to a run-flat height HF, with both heights being 
measured from a bead reference D. The crescent-shaped portions are under 
compression and bending and the rim seat ply 27, backed-up by the rubber 
support portion 34, is in contact with the flange 74 of the rim 70. In 
addition, the distance from the center of the bead core 22 to a base point 
75 (FIG. 2) on the hump 72 of the rim is in a range of 12 to 16 
millimeters. The carcass turn-up portions 66 of the middle carcass layer 
62 now extend outward from the bead reference D a distance G (FIG. 2) in 
the range of 25 to 40 percent of the deflated section height SH of the 
tire. This configuration helps transmit the radial loads from the surface 
areas 16 to the rim 70 of the vehicle. 
The physical properties and shape of the various portions of the tire 10 
are important to increase both the lateral and radial stiffness of the 
deflated tire 10. For example, the rubber seat portion 26 and the rubber 
toe portion 28 are contoured to provide a continuous footing of the rim 
seat ply 27 on rim 70 at the tire/rim interface 76 (FIG. 4) for the 
reasons discussed above. 
Preferably the tire 10 is optimized so that the forces and moments 
schematically shown in FIG. 3A operate to ensure equilibrium of the lower 
sidewall and bead portions of the mounted and inflated tire. A 
sufficiently small finite circumferential length of one of the lower 
sidewall and bead portions is considered in this analysis such that force 
changes on radial planar surfaces 52 have limited influence relative to 
the moment and forces shown in FIG. 3A and, therefore, are not 
illustrated. The internal inflation pressure IP produces a relatively 
large axial force LI at the bead to rim interface. The section face 50 at 
the median plane M has a resulting normal tension force NI to resist the 
internal pressure IP. The tension force NI resultant comprises membrane 
tension forces TC in the three carcass layers as well as tension forces TR 
in the rubber components, as illustrated in FIG. 3B. The relative 
magnitude of these tension forces can vary from one component to another 
within the scope of this invention. The moment MI from the forces on 
surface 50 at the median plane M about a moment axis perpendicular to the 
radial plane surface 52 at inner point 51 is clockwise, as shown in FIG. 
3A. This is a result of the tension forces TC and TR. The resulting radial 
force VI at the tire/rim interface 76 is sufficient to maintain the 
inflated tire in substantially air tight contact with the rim, whereby the 
inflation pressure IP in the cavity 12 of the tire 10 does not diminish. 
The response to the inflation pressure IP pushing the tire 10 away from 
the rim 70 the tension in the bead core 22 holds the tire on the rim as a 
result of the cured tire's diameter being smaller than the diameter DR of 
the relatively rigid rim 70. This vertical force VI will increase in the 
region of the external load (tire's contact patch) for the rolling tire on 
the vehicle. This increased vertical force VI is insufficient to produce a 
resulting compression force (-NI) on the median plane surface 50 with a 
nominal inflation pressure IP. 
With the total loss of inflation pressure (i.e. IP=0) the force 
distribution on the lower sidewall and bead segment changes dramatically, 
as illustrated in FIG. 5A. The membrane tension is lost and the resultant 
radial force VF at the tire/rim interface 76 increases from the value of 
the radial force VI, which exists in a fully inflated tire situation as 
illustrated in FIGS. 3A and 3B, to a value equal to essentially half of a 
symmetrical load supported by the tire. The axial force LF is reduced from 
the fully inflated tire axial load LI due to the now substantially 
nonexistent need to react any axial component of the inflation pressure 
inside the tire. The section face 50 at the median plane M' moves axially 
outward and radially inward as the tire deforms to a section height HF 
(FIG. 4). The eccentricity EF of the radial force VF is the axial distance 
to the inner point 51 on the section face 50. This distance is larger than 
an eccentricity EI for the mounted and inflated tire of FIG. 3A. The 
efficiency or effectiveness of the run-flat tire at zero inflation 
pressure can be quantified by the magnitude of the change in eccentricity 
from EI to EF. That is, the smaller the change in eccentricity (EF-EI) the 
more effective the run-flat tire design. Alternately stated, the more 
efficient run-flat tire will support a larger radial force VF at the same 
change in eccentricity EF-EI than a less efficient run-flat tire. The 
run-flat tire of this invention is designed to be relatively efficient. 
Forces LF, VF, and the toe force LT are reacted at the section face 50 at 
the median plane M'. The toe force LT helps hold the bead area 20 in 
contact with the rim 70 and will be discussed in more detail later in this 
disclosure. The greater the radial force VF and its eccentricity EF plus 
the axial force LF and its radial moment arm SF the greater the moment 
around the moment axis at the inner point 51 on the section face 50 of the 
median plane M'. The loads on the section face 50 produce a resulting 
force NF and a moment MF to resist the loads and the moments caused by 
loads at the tire/rim interface 76, as well as inertial forces by the 
rotating tire. 
The distribution of loads on the section face 50 of the median plane M', as 
illustrated in FIG. 5B, are essential in support of the vehicle by the 
deflated tire 10 of FIG. 4. The reinforced sidewall support members 54, 56 
are used in the tire to support the vehicle loads by compressive forces. 
In accordance with the present invention, the run-flat tire has an 
additional ply positioned to assist the crescent-shaped members 54, 56 in 
support of these compressive loads. This ply is preferably in the form of 
a reinforced inner carcass layer 68. The resultant compressive force C1 
acting on the first crescent-shaped member 56 and the resultant 
compressive force C3 acting on the second crescent-shaped member 54 are 
schematically illustrated in FIG. 5B. Although the schematic 
representations of the compressive forces C1 and C3 are not intended to 
represent any particular absolute values of the forces, the schematic 
representations are provided to illustrate the relatively greater value or 
magnitude of the compressive force C3 on the second crescent-shaped member 
54 as compared to the compressive force C1 on the first crescent-shaped 
member 56. The addition of this reinforced carcass layer has numerous 
advantages as follows: 
(1) the compressive forces C1 and C3 of the first and second crescent 
shaped members 56 and 54, respectively, can be reduced by the compressive 
force C2 on the inner carcass layer 68; 
(2) a stepwise reduction 55 in the compressive stress distribution 53 from 
the compressive force C3 is made possible by the compressive load C2 on 
the inner carcass layer 68; 
(3) the magnitude of radial shear forces at the interfaces between the 
crescent-shaped members 54, 56 and carcass layers 62, 64 and 68 are 
reduced to provide improved endurance of the run-flat tire of this 
invention; and 
(4) it restrains the counter deflection magnitude and, therefore, the 
deradialization of all carcass reinforcing members at the leading and 
trailing edges of the contact patch. 
The compressive stress distribution 53 can vary from the linear 
distribution illustrated in FIG. 5B, but a stepwise reduction 55 will 
continue to exist in the tire of this invention. 
The position of the inner carcass layer 68 from the moment axis at inner 
point 51 in FIG. 5B is defined by the distance DC. This distance can be 
selected to provide the proper advantages or improvements in the run-flat 
tire's ability to support itself. The axial distance DC to the inner 
carcass layer 68 from the moment axis at inner point 51 on the median 
plane M' can be optimized. Other planes through the tire sidewall portion 
can also be selected and the position of the inner carcass layer 
determined. The selection of the distance DC at the median plane M' is 
optimized based on the following: 
1) the carcass reinforcing members 69 of the inner carcass layer 68 are 
able to develop their full compression capability; 
2) the absolute sum of tension forces T1+T2+T3 and compression forces 
C1+C2+C3 are equal to the total compression force NF on the cross-section 
50; and 
3) the sum of the counterclockwise moments from compression forces C1-C3 
and the clockwise moments from the tensile forces T1-T3 must equal the 
resisting moment MF which is clockwise and approximately equal in 
magnitude to the moment from forces at the tire/rim interface 76. 
An increase in the axial distance DC adversely affects the resisting moment 
MF, and a decrease in the axial distance DC to near zero (inner carcass 
layer near the innerliner) can cause the carcass reinforcing members 69 to 
be subjected to buckling due to the increased compression forces exerted 
thereon. The axial distance DC for most run-flat tires 10 resulted in an 
optimum location such that approximately equal thicknesses of the first 
crescent-shaped reinforcing member 56 and second crescent-shaped 
reinforcing member 54 are preferred at the median plane M'. 
The two crescent-shaped reinforcing members 54,56 can be formed of a 
substantially identical material to enhance the ease of manufacture in the 
tire building operation. The run-flat tire can thus be constructed with 
only a limited number of additional products and manufacturing procedures. 
By providing end positions 58,59 of the crescent-shaped reinforcing 
members which are displaced axially and radially from one another the 
performance of the run-flat tire can be further adjusted for vehicle 
suspension variations. The preferred tire has end positions 58,59 of the 
crescent-shaped members adjacent to one another as shown in FIG. 2. The 
result is a cost-effective run-flat tire for family and urban-economy type 
vehicles. 
The crescent-shaped reinforcing members 54,56 can have the same material 
property or two different material properties. In one embodiment different 
materials include a soft rubber first crescent shaped member 56 adjacent 
to the middle carcass layer 62 to act as a cushion for the inner carcass 
layer 68 and a hard rubber second crescent shaped member 54. The hard 
rubber second crescent shaped member 54 can support the same load on a 
reduced cross-sectional area and thereby effectively decreases the total 
mass of the tire required to support the load of the vehicle. The 
following physical properties of the crescent-shaped reinforcing members 
54,56 insure a stepwise reduction in the stress distribution and help 
inhibit catastrophic failures when the tire is running deflated. The soft 
rubber first crescent shaped member 56 has a Shore A hardness in the range 
of approximately 40 to 55 and preferably 50 to 52. The first crescent 
shaped member 56 has a modulus of elasticity in compression at a ten 
percent unit strain in a range of approximately 2.0 to 4.0 megaPascals 
(MPa) and preferable equal to about 2.3 MPa. A second crescent shaped 
member 54 is innermost to the inner carcass layer 68 and first crescent 
shaped member 56 and in contact with the outside face of the innerliner 
portion 44. The second crescent shaped member 54 has a Shore A hardness in 
the range of approximately 70 to 90 and a modulus of elasticity in 
compression at a ten percent unit strain in a range of approximately 7.0 
to 15.0 MPa. The preferred Shore A hardness of the second crescent shaped 
member 54 is 75-80 and its preferred modulus of elasticity is 8 to 10 MPa. 
Both the first and second crescent-shaped reinforcing members exhibit a 
relatively low hysteresis. Based on actual performance results the 
preferred embodiment of this invention is with the crescent-shaped members 
54,56 having essentially the same material physical properties, similar to 
that of the harder second crescent shaped reinforcing member 54. The 
presence of the inner carcass layer 68 between the first and second 
crescent-shaped members 54,56 provides a stepwise stress distribution 55 
(FIG. 5B) between these crescent-shaped members at the inner carcass layer 
68 as discussed above. This inner carcass layer 68 provides the necessary 
stress reduction in the first crescent-shaped reinforcing member 56 
without the cost of having two different material properties for the 
crescent-shaped reinforcing members 54 and 56. A lower modulus of 
elasticity for the axially outer first crescent-shaped reinforcing member 
56 of this invention is not preferred as it further reduces the ability of 
this crescent shaped member 56 to resist compressive loads and at the same 
time have a reduced mass. 
During run-flat rolling of the deflated tire 10, the length L of the 
contact patch or footprint of the tire on the ground surface 90 is 
increased as illustrated in FIG. 6A. This length L can range from 2 to 5 
times the footprint length of the inflated tire. In the process of the 
tire being deflated, there is a transfer of the essential normal load 
supporting portions of the tire from tension in the outer and middle 
carcass layers 64,62 to compression in the inner carcass layer 68 as well 
as the crescent-shaped reinforcing members 54,56 of the tire 10. The 
reinforcing members 65,63 of the outer and middle carcass layers 64,62 
respectively are cords made of any suitable material from the group 
consisting of rayon, nylon, polyester, aromatic polyamide and polyethylene 
naphthalate. The large deformations of the run-flat tire 10 are 
illustrated in FIG. 6A by the differences between the dashed line for the 
loaded and deflated tire and the solid lines for the unloaded and deflated 
tire. Another result of this large deformation is that the section height 
HF of the deflated and loaded run-flat tire is approximately 40 to 60 
percent of the initial cured tire section height H, for the preferred 
embodiment tire (FIG. 2). Section height H is the mounted, inflated and 
unloaded section height of the run-flat tire 10. Section height H is in a 
range of approximately 96 to 98 percent of a cured section height of the 
tire (FIG. 1). 
Another important characteristic of the deflated run-flat tire of the 
invention is the deradialization of the sidewall portions 40, including 
the crescent-shaped reinforcing members 54,56 and the three carcass layers 
62,64,68 during running. At the radial plane R in FIG. 6A the 
deradialization is small and the tire sidewall portion 40 is under a 
relative maximum compression deformation. 
The deformation in a radial direction RD (counter deflection) as a function 
of the angular position B from the radial plane R is illustrated in FIG. 
6B. The maximum radial deformation RD1 is at the radial plane R and 
decreases to zero near the edges 2 and 4 of the contact patch having a 
length L. Outside both contact patch edges 2,4 there is a positive counter 
deflection (increasing RD) of the tread surface 16 of the crown portion 14 
to a maximum value RD2 of radial deformation. A major angular portion of 
the crown portion 14 has a small positive value RD3 of radial deformation. 
The radial deformation is approximately symmetrical about angular position 
B=180 degrees for a stationary or slow rolling tire. 
The radial displacement RD verses angular position B curve 6 of FIG. 6B is 
useful in visualizing the forces that support the deflated run-flat tire 
10. At radial plane R the inner carcass layer 68 and the crescent-shaped 
reinforcing members 54,56 are in compression. At the angular position of 
the maximum positive counter deflection (radial deformation RD2), the 
inner carcass layer 68 and the crescent-shaped members are in tension. 
Another primary function of the inner carcass layer is to limit the 
maximum positive counter deflection RD2 near the leading edge 4 and 
trailing edge 2 of the contact patch 14 (FIG. 6). The load supporting 
components (crescent-shaped members and inner carcass layer) cycle from 
tension to compression and back to tension as the tire rotates and the 
crown portion 14 contacts the ground surface 90. Therefore, 
crescent-shaped members and the inner carcass layer having both excellent 
tensile and excellent compression strength properties are preferred. The 
tension and compression physical properties of most non-reinforced rubber 
products used in tires are known to be approximately equal. The tensile 
strength properties of the inner carcass layer are much better than its 
compressive strength properties, due to the reduced strength of its 
reinforcing members in compression. Some reinforcing members are much 
better in compression than others. The preferred reinforcing members 69 
are cords made of any suitable material from the group consisting of 
nylon, rayon, aromatic polyamide and polyethylene naphthalate. A hybrid 
reinforcing member which is more stable at higher temperatures is also 
within the scope of this invention. These reinforcing members 69 of the 
inner carcass layer 68 (FIG. 5B), being supported by the adjacent 
crescent-shaped reinforcing members 54,56, have an increased compressive 
strength as a result of this confinement. The strength (modulus of 
elasticity) in compression of the inner carcass layer 68 is from about 55 
megaPascals (MPa) to about 95 MPa using a 1100 decitex 2 ply polyester or 
a 1840 decitex 2 ply rayon reinforcing material. The rubber skim layers 
are of a material standard in the industry. The preferred modulus of 
elasticity in compression for the inner carcass layer 68 is at least 75 
MPa. 
A critical performance characteristic of the run-flat tire 10 is the 
ability of the tire to achieve relatively high lateral forces without 
unseating from the rim 70. The essential components or features of the 
run-flat tire 10 of this invention, which are most helpful in achieving 
improved unseating performance during lateral cornering maneuvers of the 
vehicle included in each bead portion 20, are the rubber toe portion 28, 
the bead core 22, the rubber seat portion 26 and especially the rim seat 
ply 27. The rubber seat portion 26 has a preferred tension modulus of 
elasticity at 10 percent strain in a range of approximately 6.5 to 9.0 
megaPascals (MPa) and the rubber toe portion has a preferred tension 
modulus of elasticity at 10 percent unit strain in a range of 
approximately 45 to 60 MPa. Other components such as the crescent-shaped 
reinforcing members 54,56 and the bead filler 24 are also important, but 
somewhat less critical, in keeping the run-flat tire on the rim. However, 
all of these features contribute to the run-flat performance of the tire 
of the invention. Even without special modifications to the rim (i.e., 
using standard T&RA rim specifications) the tire of this invention will 
remain seated up to a lateral acceleration of at least 0.60 g.sup.S with 
nominal vehicle operation. 
FIG. 4 shows the run-flat tire 10 in a deflected position, typical of the 
tire in a deflated condition. This deflected position will become deformed 
laterally (or axially) when the vehicle is cornering. The outer side 
(opposite the location of the turn axis or turn center of the vehicle 
trajectory) is critical as the tire is being forced to the inside of the 
rim 70. In this maneuver, the hard rubber toe portion 28 acts in 
compression and helps keep the bead portion 20 from being displaced to the 
interior of the rim 70. In a preferred embodiment, the rim seat ply 27 
engages a hump 72 at the contact point 75 on the rim 70 which acts to 
apply a further restraining and compressive force to the rubber toe 
portion 28. The hard rubber toe portion 28 resists deformation and helps 
maintain the bead core 22 a fixed distance removed from the hump 72. The 
rubber toe portion 28 has a modulus of elasticity at 10 percent unit 
strain in a range of approximately 45 to 60 MPa, preferably from 50 to 57 
MPa. 
To unseat the run-flat tire 10 from the rim 70, the bead core 22 must 
negotiate, or be displaced in an axial direction to a position axially 
inward of, the hump 72. In addition, the bead core 22 will rotate when it 
is displaced to a location over the hump 72 of the rim 70. Therefore, the 
tensile strength and torsional rigidity of the bead core 22 are important 
parameters in maintaining the tire on the rim 70, particularly during 
cornering maneuvers of the vehicle. The bead core 22 is preferably of a 
metallic or aromatic polyamide material. The tensile strength at one 
percent unit strain of the bead core is in a range of approximately 900 to 
2500 Newtons per square millimeter and is preferably 2000 Newtons per 
square millimeter. The torsional stiffness of the bead core is the moment 
or torsion necessary to produce a rotation at a unit shear strain of 
0.0436 radians (2.5 degrees). The torsional stiffness of the bead core of 
this invention is at least 90 Newton meters per radian and is preferably 
at least 125 Newton meters per radian for a 100 millimeter long test 
sample. Various bead core cross-sectional configurations are within the 
scope of this invention, such as circular and rectangular. The torsional 
moment of inertia for the cross-sectional area of the bead core is at 
least 125 millimeters to the fourth power and further shall be in a range 
of about 125 to about 350 millimeters to the fourth power, and preferably 
at least 140 mm.sup.4. These physical parameters are defined in the 
American Society of Testing Materials (ASTM) of Philadelphia, Pa. 
Standards D885 and E6, which are incorporated herein by reference thereto. 
TEST RESULTS 
The run-flat tire of this invention exhibits improved vehicle performance, 
especially when one tire has a loss of inflation pressure. The critical 
ride comfort problem has also been substantially resolved by providing a 
run-flat tire with little change in the radial stiffness of the inflated 
run-flat tire. Lateral accelerations of the vehicle up to approximately 
0.65 g.sup.S with an unmodified (standard) rim and up to the vehicle's 
lateral limit of approximately 0.85 g.sup.S with a modified rim (having a 
hump 72) have been achieved without the bead area 20 becoming unseated 
from the rim 70. 
The deflated radial stiffness of various run-flat tires of the same size 
were obtained as shown in the first Table below. Tire A was a control tire 
having a construction similar to the tire of this invention, except the 
inner carcass ply was omitted to provide only two carcass layers. This 
control tire is good in ride comfort when inflated but has a relatively 
large deflection when loaded and deflated. The object of this invention is 
to produce a new run-flat tire that maintains the radial stiffness of the 
control tire when inflated but increases the radial stiffness above that 
of the control tire when deflated. Tire B is the same two carcass layer 
tire of tire A but has a steel reinforced run-flat stiffener ply between 
the carcass turned-up portion and the bead filler. Tire C is a run-flat 
tire having three carcass layers as described in this invention. 
______________________________________ 
RADIAL STIFFNESS VALUES (kg/mm) 
TIRE deflated (0 b) 
% change inflated (2.4 b) 
% change 
______________________________________ 
A(ref.) 
23.4 ref. 33.9 ref. 
B 29.5 +21 37.4 +10 
C(inv.) 
27.9 +15 35.3 +04 
______________________________________ 
It is clear from this table that the tire of this invention (tire C) is one 
that provides the closest ride comfort to the control tire A and yet 
provides a much improved support for vehicle loads. 
The cornering stiffness of the tires can also be measured to obtain the 
relative ability of the various run-flat tires in their ability to provide 
lateral forces that maneuver the vehicle. The Table below shows the same 
run-flat tires as described above where the improved cornering stiffness 
from a vehicle test with the tires deflated is given with respect to the 
two carcass ply tire A. The higher the value the better the run-flat tire 
corners. 
______________________________________ 
CORNERING STIFFNESS 
VALUES (kg/deg.) 
TIRE deflated (0 bars) 
% change 
______________________________________ 
A (ref.) 60 ref. 
B 90 +50 
C (invention) 83 +38 
______________________________________ 
The tire of this invention (tire C) provides better cornering values with 
respect to the control tire. Hence, the inventive tire (tire C) is a good 
compromise for luxury, family or urban-economy vehicles and the like. The 
addition of a run-flat stiffener ply (tire B) is more suited to sport or 
performance type vehicles which sacrifice ride comfort for high cornering 
requirements and because of the greater rear axle load bias. These 
vehicles have a load distribution being nearer to a 50/50 (front/back) 
percentage load distribution which requires higher cornering stiffness 
values for the rear tires to keep the vehicle from having a steering 
stability problem. 
Providing the improved bead portion components of the rubber support 
portion 34, the reinforced rim seat ply 27, the first rubber seat portion 
26 and the second rubber toe portion 28 improved the run-flat tire's 
cornering force magnitude. A P225/60 R16 deflated run-flat tire with these 
four added components had a fifty (50) percent increase in the cornering 
force over a tire without these components when tested at a 2 degree slip 
angle. A five (5) percent increase in radial stiffness was also obtained 
with these three components added to this run-flat tire. 
From the above description of the preferred embodiments of the invention, 
those skilled in the art will perceive other improvements, changes and 
modifications within the skill of the art which are essentially covered by 
the appended claims.