BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates generally to pneumatic tires, and more
specifically to pneumatic tires designed to remain affixed to and in operative
association with the vehicle wheel even upon deflation of the tire. Some varieties
of these tires include devices designed to support the vehicle when the tire loses
inflation pressure. Such tires are commonly known as "run flat" tires.
2. Description of the Prior Art
One basic problem with pneumatic tires is that the performance of
the tires depends on the retention of pressurized air within the tire. Upon a
condition where the pressurized air in the tire escapes, such as when the tire
is punctured by a nail or other road hazard, performance of the tire can diminish
rapidly. In most cases, the vehicle can only be driven a very short distance before
the it becomes inoperable.
Because of this deficiency, tire designers have long sought to develop
a tire able to provide good driving characteristics and performance even upon
deflation of the tire.
One of the key problems in providing such continued performance upon
deflation is that of retaining the tire to the wheel. Since the tire is normally
retained on the wheel by the pressurized air within the tire pushing the beads
and sidewalls of the tire outwardly against a wheel flange, the escape of the
pressurized air through puncture or other road hazard eliminates the inner pressure.
Absent this pressure, the tire tends to become disconnected and disassociated
from the wheel and control of the vehicle becomes more difficult.
Previous efforts to address this deficiency have required a special
wheel/tire combination. For various reasons this solution has not proven to be
acceptable. One of the chief reasons for the ineffectiveness of the solution is
the high cost of the special wheels which were required. These tire/wheel combinations
have typically cost several times the cost of the typical tire and wheel combination.
Other tire/wheel combinations required special mounting procedures and/or equipment.
As such, they have never been commercially acceptable.
There was perceived a need for a new tire which could stay connected
to a conventional wheel, even in a deflated condition, without the requirement
of a special wheel. In other words, a tire which could be mounted to any conventional
wheel, but which would be retained upon the wheel upon tire deflation and would
continue to provide acceptable driving performance for an acceptable distance.
Efforts by others to address this need include European Patent application
0 475 258 A1, US Patent 5,131,445, US Patent 3,954,131, US Patent 4,193,437, US
Patent 4,261,405, and European Patent application 0 371 755 A2.
In addition, several other attempts have sought to develop a bead
configuration having certain advantageous properties and configurations. For example,
in US Patent 4,203,481 a run flat tire is disclosed which is to be used in association
with a special rim. In US Patent 1,914,040, a tire bead is disclosed having a
rectangular configuration. Further, in US Patent 1,665,070, a tire bead is disclosed
having a triangular configuration.
In commonly-owned copending application serial no. 07/954,209, which
is incorporated here by reference, an innovative runflat device utilizing the
herein disclosed inventive bead core is disclosed.
SUMMARY OF THE INVENTION
The present invention relates to a pneumatic tire which can be used
on a conventional wheel and which will be retained on the wheel even upon deflation
of the tire. The inventive tire is a vulcanized radial ply pneumatic tire having
a pair of axially spaced beads. At least one radial ply extends between the beads
and is turned radially outwardly around the beads. The tire has a toroidal shape.
Each of the beads has a bead core which comprises a coil of round wire filaments
which, in the toroidally-shaped tire prior to its vulcanization, has a polygonal
cross-sectional area defined by imaginary lines segments contacting the outer
surfaces of the outer filaments in the bead core. The bead core is further characterized
by the polygonal cross-sectional area having a radially-inward base side, a radially
outward point or side, a first side and a second side. The first and second sides
extend between the base side and the radially outermost point or side. The first
side intersects the base side at a first edge to form an included acute angle
α. The second side intersects the base to form an included acute angle β,
with α being greater than or equal to β.
According to another aspect of the invention, the inventive tire
can be used in connection with a wheel having a flange and a hump. A bead heel
surface on the tire can be configured to have a length between 85% and 100% of
the distance W between the hump and an axially inward surface of the flange, contributing
to the tire remaining on the wheel during a deflated condition. Wire filaments
in a first layer of the bead core can be configured so that a relatively wide,
stiff first layer of filaments can be constructed, further contributing to the
retention of the tire on the wheel upon a deflated tire condition.
BRIEF DESCRIPTION OF THE DRAWINGS
Other aspects of the invention will become apparent from the following
descriptions when read in conjunction with the accompanying drawings wherein:
DESCRIPTION OF THE PREFERRED EMBODIMENT
- Figure 1 is a cross-sectional view of one half of a tire according to the invention,
the tire being cut along its equatorial plane;
- Figure 2 is a cross-sectional view of a bead core according to the invention;
- Figure 3 is a schematic view of the cross-sectional bead core of Figure 2 with
line segments drawn to show the perimeter, angles, and geographical characteristics
of the bead core of Figure 2; and,
- Figure 4 is an enlarged cross-sectional view of a portion of Figure 1 showing
the bead core and bead area of the tire as it fits onto an associated wheel rim.
- Figure 5 is a cross-sectional view of the design rim.
Invention also may be better understood in the context of the following
definitions, which are applicable to both the specification and to the appended
"Pneumatic tire" means a laminated mechanical device of generally
toroidal shape (usually an open-torus) having beads and a tread and made of rubber,
chemicals, fabric and steel or other materials. When mounted on the wheel of a
motor vehicle, the tire through its tread provides traction and contains the fluid
that sustains the vehicle load.
"Radial-Ply tire" means a belted or circumferentially-restricted
pneumatic tire in which the ply cords which extend from bead to bead are laid
at cord angles between 65 degrees and 90 degrees with respect to the equatorial
plane of the tire.
"Equatorial plane (EP)" means the plane perpendicular to the tire's
axis of rotation and passing through the center of its tread.
"Carcass" means the tire structure apart from the belt structure,
tread, under tread, and side wall rubber over the sides, but including the bead.
"Belt structure" means at least two layers or plies of parallel cords,
woven or unwoven, underlying the tread, unanchored to the bead and having both
left and right cord angles in the range from 17 degrees to 27 degrees with respect
to the equatorial plane of the tire.
"Sidewall" means that portion of the tire between the tread and the
"Tread" means a molded rubber component which when, bonded to a tire
casing, includes that portion of the tire that comes into contact with the road
when the tire is normally inflated and under normal load.
"Tread width" means the arc length of the tread surface in the axial
direction, that is, the plane passing through the axis of rotation of the tire.
"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, decorations, or protective bands.
"Section height" means the radial distance from the nominal rim diameter
to the maximum outer diameter of the tire at the road contact surface nearest
its equatorial plane.
"Aspect ratio" of the tire means the ratio of its section height
to its section width.
"Axial" and "axially" are used herein to refer to the lines or directions
that are parallel to the axis of rotation of the tire.
"Radial" and "radially" are used to mean directions radially toward
or away from the axis of rotation of the tire.
"Inner" means toward the inside of the tire.
"Outer" means toward the tire's exterior.
In the drawings the same numbers are used for the same components
or items in the several views. With particular reference now to Figure 1, there
is illustrated a pneumatic tire 10. The preferred embodiment of the invention has
been successfully incorporated into passenger car tires of size P255/45ZR17 and
P285/40ZR17 although it is believed the invention is applicable to other types
and sizes of tires. The pneumatic tire 10 comprises a tread 12, a sidewalls 14,
a carcass 16, and a pair of annular tensile members, commonly referred to as bead
cores 20. In the preferred embodiment, the tire 10 includes a runflat device 18
in the sidewalls of the tire 10. It is believed that a tire incorporating the
hereafter disclosed invention will remain in operative association with the vehicle
wheel and rim whether or not a runflat device 18 is present in the tire. For ease
of illustration, only one half of the tire 10 is shown, with the tire being split
along its equatorial plane EP. With reference to Figures 4 and 5, the tire 10
fits onto and works in conjunction with an associated design wheel or rim 22, which
will be discussed later in this disclosure.
With reference to Figure 2, a preferred arrangement of bead core
filaments is shown. The bead core 20 is shown in cross-section in Figure 2 and
comprises a series of wire filaments 26. The bead core 20 is preferably comprised
of a single continuous filament which is repeatedly annularly wound into an annulus.
In other words, each of the filaments 26 shown in cross-section in Figure 2 are
a part of the same continuous filament wound into the bead core 20. Although a
single continuous filament is the preferred embodiment of the invention, it is
believed the invention can be successfully practiced in the case of separate,
discrete filaments wound into a similar annular configuration. One common such
configuration is known as "strap beads."
In the preferred embodiment, the filaments are comprised of a single
strand of 0.050" diameter wire which is individually coated with 0.005" of elastomeric
material. Therefore, the preferred embodiment filament 26 has an overall diameter
In the preferred embodiment, the bead core 20 comprises five layers
30,32,34,36,38 of filaments 26. The first layer 30 is the most radially inward
layer and comprises eight filaments 26.
The second layer 32 is radially outward of the first layer 30 and
comprises seven filaments 26. It is important that the filaments of adjoining
layers, 30, 32, be "nested" together. In other words, the filaments 26 are offset
axially by a distance equal to one half the diameter of a filament 26 so that
the radially inwardmost portion of the outer surfaces of the filaments 26 in the
second layer 32 lie radially inwardly of the radially outwardmost portion of the
outer surface of filaments 26 in the first layer 30.
The third layer 34 comprises six filaments, the fourth layer 36 comprises
four filaments and the radially outwardmost layer, the fifth layer 38, comprises
two filaments. As can be seen best in Figures 2 and 3, the two filaments 26 of
the fifth layer 38 are offset toward the first side 48 of the bead core 20.
The bead core 20 has a perimeter 42. The perimeter 42 comprises the
lengths of imaginary line segments contacting and tangent to outer surfaces of
a base side 44, a radially outermost point or side 46, a first side 48, and a
second side 50. The radially outermost point or side 46 can have a variety of
configurations without significantly affecting the performance of the inventive
bead core 20. For example, the bead core 20 could take the form of an isosceles
triangle or the top surface of a rhombus. In the first case, the radially outermost
surface 46 would take the form of a line (or a point in cross-section).
The base side 44 is the radially innermost side of the bead core
20 and is approximately parallel to the tire's axis of rotation as well as the
mating surface of the wheel 22. In the preferred embodiment, the first side 48
is axially inward of the second side 50, although the relative orientation of
the first and second sides 48,50 is not believed to be critical for the successful
practice of the invention.
The first side 48 extends between the base side 44 and the radially
outermost point or side 46 and intersects the base side 44 at a first edge 54.
The first side 48 intersects the base side 44 to form an included acute angle
The second side 50 extends between the base side 44 and radially
outermost side 46 and intersects the base side 44 at a second edge 56, forming
thereby an included acute angle β. In the preferred embodiment, angle α
is greater than or equal to β.
The perimeter 42 of the bead core 20 defines a cross-sectional area
of the bead core. The area of the inventive bead core 20 is less than the area
of an isosceles triangle having acute angles equal to α. Further, the area
of the bead core 20 is less than the area of a trapezoid having angles α
and β and a height equal to the distance from the base side 44 of the bead
core 20 to an imaginary line parallel to the base side 44 and tangent to the radially
outermost filament 26 in the cross-section of the bead core 20. In the preferred
embodiment, the bead core perimeter 42 has at least five sides, with the longest
side being the base side 44.
In the preferred embodiment, the length of the base side of the bead
core 22 is between 0.3" and 0.65". In the preferred embodiment, the length of
the base side 44 of the bead core 20 is 0.48".
With reference to Figure 4, the tire 10 has a bead area which includes
a bead heel surface 60. The bead heel surface 60 cooperates with the associated
wheel 22. An important aspect of the invention is that the wheel 22 is the conventional,
design rim as specified for the tire by industry standards, such as the
Tire and Rim Association Yearbook, which is incorporated herein by reference.
For example, the wheel used with the preferred embodiment of the tire in the sizes
referred to earlier (i.e., P255/45ZR17) is a drop center, 5 degree "J" rim as
specified in the Tire and Rim Association Yearbook.
The wheel 22 comprises an axially inner surface 74 of the wheel flange
76. The wheel 22 also comprises a safety hump 80 which lies axially inwardly of
the wheel flange 76. The distance between the safety hump 80 and the axially inward
surface 74 of the wheel flange 76 is referred to herein as the rim seat 62 and
has a width equal to a distance W. The distance W is a standard for the various
wheels designed for various vehicles. This information has been standardized in
the industry and is obtainable from the Tire and Rim Association Yerbook.
In the design wheels to be used with the preferred embodiment of the inventive
tire, W is equal to 0.790".
With continuing reference to Figure 4, the tire 10 has a bead area
which includes a bead heel surface 60. The bead heel surface 60 cooperates with
and is the point of interface with the wheel 22. In the preferred embodiment of
the invention, the width of the bead heel surface 60, measured in the axial direction,
is substantially equal to the distance W between the hump 80 and the axially inner
surface 74 of the wheel flange 76. This area of the wheel 22 will be herein referred
to as the rim seat 62. The width of the bead heels of prior art tires were significantly
smaller than the inventive bead heel 60. The configuration of the bead core 20,
along with the increased width of the bead heel surface 60, causes the tire 10
to remain in operative association with the wheel 22, even in situations where
such operative association is uncommon, such as deflation of the tire 10.
Through testing of various designs, the applicant has learned that
one the key elements of the tire/wheel design which keeps the tire 10 affixed
to the wheel 22 in cases of tire deflation is the design of the base side 44 of
the bead core 20 and the bead heel surface 60.
One of the key elements of the design is the relationship of the
width of the bead heel surface 60 to the distance W between the hump 80 and the
axially inward surface 74 of the wheel rim 22. Prior art designs allowed for significant
variation in the two dimensions, allowing for some slippage of the bead heel surface
60 of the tire 10 relative to the rim seat 62 of the wheel 22. For example, the
width of the bead heel 60 of one relevant prior art design was 0.650". The bead
heel 60 of the inventive tire has a width of 0.750". The area of the wheel 22
between the axially inward surface 74 of the wheel 22 and the hump 80 is referred
to herein as the rim seat 76. Since the width of the rim seat 76 (the distance
W) is 0.790", the preferred tire 10 has a bead heel width equal to 95% of the
distance W. It is believed that the width of the bead heel 60 must be between 85%
and 100% of the distance W for the tire 10 to remain on the wheel 22 upon tire
deflation. By filling, or nearly filling, the width of the rim seat 62 with the
bead heel 60, the axially inwardmost portion of the bead heel 60 never begins
to ride over the hump 80, at any point around the circumference of the bead heel
Another important element of the successful inventive tire 10 is
the width of the first layer 30 of the bead core 20. Relevant prior art designs
used first layers 30 of widths of 0.276" while the width of the first layer 30
of the inventive bead core 20 is 0.480". Since the width of the rim seat (i.e.
"W") is 0.790", the width of the first layer 30 is 61% of W. It is believed that
the width of the first layer 30 of the bead core 20 must be between 50% and 75%
of the distance W.
Another important aspect of the bead core 20 is the linearity of
the first layer 30. By configuring the filaments 26 of the first layer 30 so that
their axial centerlines lie in a common plane, the compressive force between the
first layer 30 and the rim seat 62 is more uniform than was possible in prior
art designs. The more uniform stress between the first layer 30 and the rim seat
62, tends to secure the bead heel 60 to the rim seat 62.
Another important aspect of the inventive design is the dimensional
integrity of the bead core 20. Analysis of cut cured tire sections indicate that
first layer 30 of the bead core 20 retains its linearity throughout the vulcanization
process. Prior art bead cores 20 often deform when the carcass 16 "turns up" during
the tire building and vulcanization process. The filaments 26 in the inventive
bead core 20 are of a larger diameter (0.050") than is typical (i.e., 0.037") in
relevant prior designs. It is believed the larger diameter filaments 26 contribute
to the dimensional stability of the bead core 20. Another important element to
the dimensional stability is the continuous filament 26 of the bead core 20, as
compared with the prior art strap beads. The first layer 30 is configured to be
approximately parallel to the tire's axis of rotation and/or the rim seat 62. In
the preferred wheel, a 5 degree, drop center "J" rim, as per the 1990
Tire and Rim Association Yearbook, the first layer 30 is parallel to the
rim seat 62, which in turn makes an angle of 5 degrees with the tire's axis of
The inventive tire 10 mounts onto a typical drop center rim 22 as
any conventional prior art tire would. No special wheels or rims are required,
nor are any special mounting procedures.
It is also believed that the innovative tire 10 disclosed herein
will be retained on the wheel 22 with nearly any effective design of a runflat
device 18. Although the runflat device 18 disclosed is effective and is preferred,
the bead design disclosed herein should work with other runflat devices.