CA1105364A

CA1105364A - Pneumatic tire of elastic material without reinforcement

Info

Publication number: CA1105364A
Application number: CA322,050A
Authority: CA
Inventors: Yves Herbelleau
Original assignee: Compagnie Generale des Etablissements Michelin SCA
Current assignee: Compagnie Generale des Etablissements Michelin SCA
Priority date: 1978-02-21
Filing date: 1979-02-21
Publication date: 1981-07-21
Also published as: IT7967373A0; AU4438979A; IT1118390B; DE2906780A1; LU80941A1; JPS54122503A; BR7901137A; FR2417403A1; GB2014915A; SE7901495L; GB2014915B; AU525473B2; FR2417403B1; ES477865A1; NL7901354A; BE874133A

Abstract

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 reaius of curvature ?m of the meridian profile of the inner wall follows the law

Description

1~5364 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.
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. Thus the meridian curvature of such a tire may undergo considerable variation.
This may cause an unfavorable transverse distribution of the wear of the tread. This drawback may, under the effect of the fatigue and/or thermal stresses to which the tire is subjected in travel, be amplified either by the increase of the inflation pressure due to the heating of the tire or by creepage or failure of the rigidity of the nonreinforced material.
It is furthermore important to know the shape, more particularly the meridian profile, assumed by the body of such tires under the influence of a given inglation pressure.
The object of the present invention is to avoid the said deformations upon inflation and therefore the drawbacks which they entail, for example, by determining the outside diameter of the tires in use or the meridian contour to be imparted to the tread. This determination requires the use and employment of costly computation means.
However, one may, in first approximation and using the relationships serving for the calculation of membranes, defines structures which make it possible to cancel out the deformations ~r in the radial direction.
In order to produce a tire which is free of radial deformation the invention consists in imparting to the meridian profile of the inner wall of the tire a radius of curvature ~ .

-5~6~

Pm such that this radius follows the law (a) Pm = 1 -Y~ -- ( y2 - 1).

2 cos ~ Re2 In the accompanying drawing, which is intended 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 wlth dimensions utilizing the parameters which appear in the above-indicated law of variation, and - Fig. 2 illustrates by way of example a radial half section of a pneumatic tire in accordance with the invention.
Fig. 1 shows, in part, half of a meridian profile 1 of the inner wall (11 in Fig. 2) of a pneumatic tire in ac-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. Re is the radius of the point E of the inner wall which is located at the greatest axial distance from the equatoria] 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~. ~m is the meridian radius of cur-vature 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 milli-meter size 135-330. It comprises a tread 3 at a crown 5 and a body 4 which comprises, on both sides of the crown 5, a shoulder 6 extended by a sidewall 7 terminated by a bead 8.

-` 11(~5364 The bead 8 i~ reinforced by at least one bead ring 9 and rests on a rim 10 (shown in part). The inner wall 11 has a trace in accordance with the invention. The value R of the radius at the crown is equal to 273 mm and the ratio R /R
is equal to 0.80. The rim 10 is a standard 4-inch rim.
Since it is essential to avoid at least the deforma-tion of the crown during the inflation of the tire, it may be sufficient to impart to the inner wall 11 a profile in ac-cordance with the invention between the points E and S, that is to say in the crown, the shoulders and the portions ofthe sidewall radially outward from the points E where the inner wall 11 reaches its greatest a~ial distance from the equatorial line Y-Y~. However, 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 reach 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:
Re2 (b) ~lm 7 cYS ~ Y and y2 11~5364 ( C ) P2 = Y YZ
m -cos ~ 3 Re2 _ 1 Y , .

Claims

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) 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) and (c)

3. A pneumatic tire according to claim 1 or claim 2, characterized by the fact that the radius of curvature ?m 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 material which is different from the material or materials of the body of the pneumatic tire.