Note: Descriptions are shown in the official language in which they were submitted.
1~4~63
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The foregoing abstract is not to be taken as
limiting the invention of this application, and in
order to understand the full nature and extent of
the technical disclosure of this application, refe-
rence must be made to the accompanying drawings inthe following detailed description.
Back~round of the Invention
This invention relates to a pneumatic tire, and
more particularly, to a novel and improved pneumatic
- 10 tire.
It is well known in the prior art that it is
desirable to cure a tire in a configuration such that
the carcass ply structure follows the natural equili-
; brium curve for at least a portion of its length. The
natural equilibrium curve is the shape the carcass plystructure tends to assume as prescribed by its cord
path and dimensions when mounted on the rim for which
it is designed and inflated to design inflation pres-
sure. This concept is thoroughly discussed and ex-
plained in "Mathematics Underlying The Design ofPneumatic Tire" by John F. Purdy. U.S. Patent Nos.
3,757,844; 3,910,336; and 3,938,575 are illustrative
of the prior art wherein at least a portion of the
carcass ply structure follows the natural equilibrium
curve.
During normal operation of a pneumatic tire, the
~ bead area is subject to torsional forces and stress
- concentrations which can substantially detract from
~; the durability, handling and overall performance of
the tire. The prior art does not take into account
these forces. In the prior art the carcass ply layers
are all immediately adjacent one another or are dis-
posed at positions symmetrically about the natural
equilibrium curve in the bead area. The carcass ply
structure does not contribute to the lateral stability
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463
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of the tire or improve bead durability under la~eral
forces.
Applicant has designed an improved pneumatic tire
which has the advantages of a tire having the carcass
plies located at the natural equilibrium curve while
at the same time providing improved handling and
durability.
Summary of the Invention
In accordance with the present invention, there
is provided a pneumatic tire comprising a ground
engaging tread portion, said tread portion terminating
in a pair of shoulder portions, one at each lateral
end thereof, a pair of sidewall portions extending
radially inward from said shoulder portions
terminating in a pair of bead portions respectively,
each of said bead portions having at least one
inextensible bead core, a first carcass reinforcing
ply structure extending from bead core to bead core,
the terminal ends of said first carcass ply structure
each being wrapped adjacent the axially inner surface
of each respective bead core and, a second carcass
reinforcing ply structure extending from bead core to
bead core the terminal ends of said carcass reinforced
ply structure being wrapped adjacent the axially
outermost surface of said respective bead cores,
characterized by said tire being cured in the
configuration such that the neutral contour line of
each of said first and second carcass reinforcing ply
structures coincides with the respective natural
equilibrium curve of said structures.
Description of the Figures
Fig. 1 is a radial cross-sectional view of a
pneumatic tire made in accordance with the present
invention; and
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Fig. 2 is a radial cross-sectional view of the
tire of Figure 1 when experiencing a lateral force.
Detailed Description of the Invention
_
Reerring to Fig, 1, there is illustrated a
pneumatic tire lO made in accordance with the present
invention. The tire 10 has a circumferentially
extending ground engaging tread portion 12 which
terminates in a pair of shoulder portions 14,15 at the
lateral ends thereof. A pair of sidewall portions
16,17 extend radially inward from said shoulder
portions 14,15 respectively terminating in a pair of
bead portions 18,19. Each of the bead portions 18,19
have embedded therein a substantially inextensible
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11 ~4463
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bead core 20, 21 respectively. The bead cores 20,
21 in the embodiment illustrated are preferably
made of steel wires. A carcass reinforcing ply
structure 22 extends from bead portion 18 through
sidewall 16, tread portion 12 and sidewall 17 to bead
portion 19. The reinforcing ply structure 22 com-
prises two reinforcing ply structures 23 and 24.
The carcass reinforcing structure 22 is of the one-up
one-down construction, that is, wherein the ends of
the axially innermost ply structure 23 are wrapped
adjacent the axially innermost surface of each of the
bead cores 20, 21 in each of the respective bead
areas 18 and 19 and the ends of the axially outermost
ply structure 24 is wrapped adjacent the axially outer-
most surface of each of the bead cores 20, 21 in each
respective bead area 18, 19. In the particular em-
bodiment illustrated, the reinforcing ply structures
23 and 24 each comprise one layer of rubber ooated
fabric. The fabric comprises of a pIurality of
parallel cords which may be made of any material
used for rubber reinforcement, for example, and not
by way of limitation, rayon, nylon, polyester and
steel and may form many desired angles with respect
to the mid-circumferential centerplane CP of the tire.
The cords of reinforcing ply structures 23 and 24
form an angle of from about 75 to about 90 with
respect to the mid-circumferential centerplane CP.
While the particular embodiment illustrated shows
reinforcing ply structures 23 and 24 as having a
single layer each, it is understood that each ply
structure 23 and 24 may be comprised of any multiple
of layers, preferably ply structures 23 and 24 each
having the same number of fabric layers.
Placed circumferentially about the radially
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outermost surface of the carcass ply structure 22
is a tread reinforcing belt structure 28 having two
cut reinforcing plies 30, 32 of parallel cords coated
with a thin layer of rubber. The cords of plies 30,
5 32 may be comprised of any material used for rubber
reinforcement, for example, and not by way of limi-
tation, nylon, rayon, steel and aramid. While the
belt structure 28 is shown as having two cut plies
30, 32 belt structure 22 may be of any desired con-
figuration and be omitted entirely if desired. Thecords of plies 30 and 32 preferabl~ form an angle of
from about 15 to 30 with respect to the mid-circum-
ferential centerplane CP of the tire and in the
particular embodiment illustrated is approximately
21. Preferably the plies 30 and 32 are oriented
such that the cords of ply 30 form an anglè equal and
opposite to the angle formed by the cords of belt ply
32.
In each of the bead portions 18, 19 there is
20 provided a hard rubber reinforcement 34, 36 - respec-
tively which extends radially outward from the
respective bead core in between the carcass rein-
forcing ply structures 23 and 24. The hard rubber
reinforcement 34 and 36 extend radially outward
25 terminating a distance A from the nominal rim diameter
NRD of at least twenty-five (25) percent of the car-
cass section height CSH, preferably at least thirty (30)
percent and in the particular embodiment illustrated
the distance A is about thirty-six (36) percent of the
30 maximum carcass section height CSH. For the purposes
of this invention, the nominal rim diameter NRD is
the distance from the axis of rotation as designated
in the size designation of the tire and the maximum
carcass section height CSH is the maximum radial dis-
35 tance between the neutral contour of the carcass rein-
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63
forcing structure 22 beneath the tread portion 12and the nominal rim diame-ter NRD. The hard rubber
reinforcement 34 and 36 comprises a material having
a dynamic modulus of elascity of at least 125 Kg/cm2.
The dynamic modulus being determined by the Goodyear
Vibra Tester (ASTM-22331).
The tira 10 is cured in configuration such that
the neutral contour line of each of the reinforcing
ply structures 23, 24 follow its respective natural
equilibrium curve. Preferably the reinforcing ply
structures 23 and 24 follow the natural equilibrium
curve radially outward to wherein it first meets the
belt structure 28.
For the purposes of this invention the neutral
contour line of each carcass reinforcing ply structure
23, 24 respectively, is the line located midway be-
tween the outermost and innermost reinforcing ply
of each reinforcing ply structure 23, 24.
The natural equilibrium curve for each of the
reinforcing ply structures 23 and 24 are determined
in accor,dance with the~,following relationship:
~0 ~c .e~
Y- I .~ -- P
~ (/Da~ e
wherein y is the perpendicular distance from the
mid-circumferential plane of radius ~o to any
point on the tire carcass for any specified ~ ;
~ is the distance from the axis of rotation to
a point on the tire;
~ m is the radius from the axis of rotation
to the point on the tire carcass where y is maximum;
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qC is the cured cord angle, the outer angle
which the cord makes with the circumference of
; any circle in the circumferential direction of the
tire;
~o is the radius from the axis of rotation of
the tire to a point determined by an iterative
method such that the curve defined by equation (1)
will pass through a point ~s, Ys (specified in
the shoulder areaj and tangent to a line determined
by Ym, ~ b, Yb determined for the carcass structure
in the bead area;
s is the distance from the axis of rotation
to a point in the shoulder area where the carcass
contour deviates from equation (l);
Yb, ~ b is the point at which the carcass
: contour deviates from equation (l~;
b is the distance from the axis of rotation
. to the point on the tire carcass in the bead area;
~:: Yb is the distance from the mid-circumferential
: ; 20 plane of radius ~o to the point on the tire carcass
bead area;
The above equation is used when a belt rein-
forcing structure 28 is present in the tire 10.
: : When there is no belt reinforcing structure the ~ o
term is replaced by the ~ o term which is defined
as the radius from the axis of rotation to a point
on the tire at the tread center.
For the purposes of this invention, the maxi-
mum carcass section width CSW is the maximum distance
measured parallel to the axis of rotation of the tire
between the neutral contour of the reinforcing struc-
ture 22.
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During normal operation of a pneumatic tire,
the bead area is subject to torsional forces and
stress concentrations which can substantially
detract from the durability and handling charac-
teristics of a tire. This is of particularimportance in tires of radial type construction,
that is, a tire in which the cords form an angle
of from about 75 to 90 with respect to the mid-
; circumferential centerplane. The carcass ply
layers of a radial tire do not contribute sub-
stantially to the lateral stability of the tire
on proved bead durability under lateral forces.
The one-up one-down carcass ply construction
provides bead durability and improves the lateral
; 15 stability of the tire during turning maneuvers.
Referring to Fig. 2, there is illustrated the
tire 10 undergoing a lateral force. The one-up
one-down construction puts one of the reinforcing
ply structures 23 or 24 in compression while the
other is in tension depending upon which bead portion
is being considered. The reinforcing ply structure
that is being put under tension adds to the stability
of the tire. Curing the tire ln the configuration
such that each of the reinforcing ply structures
follow its own natural equilibrium curve minimizes
the stresses and tension variations in the cords of
each ply~structure while at the same time allows the
carcass reinforcing ply structures to go into tension
as the condition requires improving lateral stability
of the tire. A tire made in accordance with the
present invention exhibits improved lateral stability
and bead durability without adversely affecting the
~ normal performance characteristics of the tire.
-~ Applicant's invention is particularly well suited
~ 35 for radial type tires, that is,tires wherein the
11~4463
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cords of the reinforcing ply structure form an
angle from about 75 to 90 with respect to the
mid-circumferential plane of the tire, wherein
improved lateral stability is desired~
While certain representative embodiments and
: details have been shown for purposes if illustrat-
ing the invention, it will be apparent to those
skilled in the art that various changes and modifi-
cations may be made therein without departing
from the spirit or scope of the invention.
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