PNEUMATIQUE EN ELASTOMERE SANS ARMATURE

PNEUMATIC TIRE OF ELASTIC MATERIAL WITHOUT REINFORCEMENT

Abrégé anglais

ABSTRACT OF THE DISCLOSURE:
A pneumatic tire comprising a tread at a crown and
a body which comprises, on both sides of the crown, a shoulder
extended by a sidewall terminated by a bead, and formed of
elastic material without reinforcement is characterized by
the fact that the radius of curvature pm of the meridian
profile of the inner wall follows the law
<IMG>
at least in the portion of the pneumatic tire located radially
outward of the points where the meridian profile reaches its
greatest axial distance from the equatorial line.

Revendications

The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:
1. A pneumatic tire having an equatorial line, an
axis of rotation and comprising a tread at a crown and a body
which comprises, on both sides of the crown, a shoulder
extended by a sidewall terminated by a bead, and formed of
elastic material without reinforcement, characterized by the
fact that the radius of curvature ?m at a point A of the
meridian profile of the inner wall of said tire follows the law
(a) <IMG>
at least in the portion of the pneumatic tire located radially
outward of the points where the meridian profile reaches its
greatest axial distance from the equatorial line; wherein
? is the angle formed by a tangent to
said meridian profile at said point A with
a straight line passing through said point A
and being parallel to said axis of rotation;
y is the distance of said point A from
said axis of rotation, measured parallel to
said equatorial line, and
Re is the radius of the point of said
meridian profile located at the greatest
axial distance from said equatorial line.
2. A pneumatic tire according to claim 1,
characterized by the fact that the radius of curvature ?m of
the meridian profile of the inner wall is located between the
two limits defined by the following relationships:

(b) <IMG> and
(c) <IMG>
3. A pneumatic tire according to claim 1 or claim 2,
characterized by the fact that the radius of curvature pm of
the meridian profile of the inner wall follows the said law
from one bead to the other.
4. A pneumatic tire according to claim 1 or claim 2,
characterized by the fact that its tread consists of a suitable
tread material which is different from the material or
materials of the body of the pneumatic tire.

Description

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The present invention relates to improvements in
pneumatic tires of elastic material without reinforcement. The
absence of reinforcement, however, does not exclude the use,
in the beads of these tires, of bead rings whose function is
to assure the seating and possibly the tightness of the beads
on the rim.
The crown of such tires may be formed of a single
elastic material, for instance, the material forming the side-
walls. However, it may also be formed of several superimposed
elastic materials adhering to each other, for instance, at
least two materials one of which, arranged radially outward,
is suitable to form the tread, while the other, arranged
radially on the inside of the tread, is suitable to form the
; mechanically resistant body of the tire in the region of the
crown.
Tires of the type under consideration may assume
as a result of the inflation pressure, shapes which are very
different from the shapes of the uninflated tires.
It particular, the region of the crown may thus
show a considerable increase in curvature. An exaggeration
of the curvature may cause-an unfavorable distribution of the
wear of the tread. This drawback may, under the effect of
the fatigue and/or thermal stresses to which the region of
the crown is subjected during the travel of the tire, be
amplified by the increase, creepage or failure of the rigidity
of the material forming the mechanically resistant part of
the crown region.
In order to overcome these drawbacks, it has been
proposed to provide said region with a reinforcement or
reinforcing elements or to increase its thickness. These
~-~ solutions result, in particular, in an increase in the cost
of the tires o~ the type in question and/or a decrease in
the comfort upon travel, due to the increase in the stiffness
., . ~

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of the crown.
It is furthermore important to note the shape,
and more particularly the meridian profile, assumed by the
body of such tires under the influence of a given inflation
pressure. This, for instance, in order to determine their
outside diameter in use or the meridian contour to be imparted
to the tread. This determination requires the use and employ-
ment of expensive means of computation.
The object of the present invention is to avoid
these deformations upon inflation and therefore the drawbacks
which they entail.
The fundamental ide~ of the invention consists
therefore in providing the meridian profile of the inner wall
of the tire with a radius of curvature Pm such that the
circumferential deformation ~c is zero. The determination of
such a profile requires the use of costly computation means.
This is why a preferred variant of the present invention
consists in using, in first approximation, the relationships
serving for the calculation of membranes in order to evaluate
the meridian radius of curvature of such a profile. This
radius then follows the law
Y_ ~
(a) Pm = 2 cos ~ ~ 2
3 + ~
In the accompanying drawing, which is intended,
together with the corresponding portion of the present
specification, to facilitate an understanding of the invention,
- Fig. 1 shows schematically half of a meridian
profile of the inner wall of a tire in accordance with the
invention with dimensions utilizing the parameters which
appear in the above-indicated law of variation, and

-
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- Fig. 2 illustrates a radial half section through
a tire in accordance with the invention.
Fig. 1 shows, in part, half of a meridian profile 1
of the inner wall ~11 of Fig. 2) of a pneumatic tire in
a~cordance with the invention. The running point A of this
profile is located at a distance y from the axis of rotation
X-X' of the tire. The distance y is measured parallel to the
trace Y-Y' of the equatorial plane of the tire. ~e is the
radius of the point E of the inner wall which is located at
the greatest axial distance from the equatorial line Y-Y'.
Rs is the radius of the point S of the crown which is furthest
from the axis of rotation X-X'. ~ is the angle formed by
the tangent AT to the inner profile 1 at the point A with
the straight line AD passing through the point A and parallel
to the axis of rotation X-X'. Pm is the meridian radius of
~ curvature at the point A of the inner profile 1.
; The calculation of the coordinates of the different
points constituting the profile 1 is advantageously effected
by means of a computer.
The tire 2 in accordance with the invention shown
in radial half section in Fig. 2 is a pneumatic tire of
millimeter size 135-330. It comprises a tread 3 at a crown 5
and a body 4 which compris0s, on both sides of the crown 5,
a shoulder 6 extended by a sidewall 7 terminated by a bead 8.
~ The bead 8 is reinforced by at least one bead ring 9 and rests
; on a rim 10 (shown in part). The inner wall 11 has a trace inaccordance with the invention. The value Rs of the radius
at the crown is equal to 273 mm and the ratio Re/RS is equal
to 0.79. The rim 10 is a standard 4-inch rim.
0 The object of the invention being essentially to
avoid the creation of a state of circumferential deformations
in the region of the crown and of the shoulders as a result of
_ 3 -
'' .

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the placing under pressure of the tire, it may be sufficient
to impart to the inner wall 11 a profile in accordance with
the invention in the crown, the shoulders and the portions of
the sidewalls radially outward of the points E where the inner
- wall 11 reaches its greatest distance from the equatorial
line Y-Y`. ~lowever, it is preferable that the inner wall 11
follow the said meridian profile from one bead 8 to the other.
The inner wall of the tire can be given a meridian
curvature in accordance with the invention at the time of the
manufacture of the tire. The tire can also be manufactured
in such a manner that the meridian curvature in accordance
with the invention is reached only when the tire is in position
on its rim, but not inflated.
The tread may be of a suitable material different
from the material or materials of the body of the tire, all
of these materials adhering to each other.
In practice, the advantages of the invention are
obtained when the meridian radius of curvature Pm defined
above by law (a) is located between the two limits defined
by the following relationships:
'
(b) Plm 3 cos ~ Re2 and
5 + 2
R 2
::: 1 _ e2
(c) ~2m = 11 cos ~ R 2
15 + 7 2