GB2024738A

GB2024738A - Radial carcass pneumatic tyre

Info

Publication number: GB2024738A
Application number: GB7923840A
Authority: GB
Original assignee: Compagnie Generale des Etablissements Michelin SCA
Current assignee: Compagnie Generale des Etablissements Michelin SCA
Priority date: 1978-07-10
Filing date: 1979-07-09
Publication date: 1980-01-16
Also published as: DE2925846A1; ES8202293A1; FR2430858A1; SE7905965L; ES482347A0; BR7904374A; AU4876579A; BE877441A; LU81474A1; IT7968434A0; NL7905333A; JPS5511996A

Abstract

A radial carcass pneumatic tyre for vehicle wheels comprising a carcass reinforcement and a crown reinforcement (not illustrated) is such that the shape 21 of the carcass reinforcement at rated inflation pressure and under no load differs from the shape 22 of the carcass reinforcement when the tyre is at 5 to 10% of its rated inflation pressure and under no load. The axial distance Lo from the equatorial plane ZZ being not more than the distance L1 and the radial distance RBo from the tyre rotation axis YY' being at least equal to radial distance RB1 wherein Bo and B1, are the intersections of the carcass reinforcement shapes 22,21 with the trace UU' of the plane parallel to the equatorial plane and at the edge of the crown reinforcement. <IMAGE>

Description

SPECIFICATION Radial carcass pneumatic tyre The invention relates to pneumatic tyres having a radial carcass reinforcement and more particularly to the carcass and crown reinforcements of such tyres.

A radial tyre comprises a carcass reinforcement formed by at least one ply of radial wires or cables anchored to at least one bead wire in each bead and a crown reinforcement formed by at least two plies of wires or cables which are parallel in each ply and cross from one ply to the next and form acute angles of less than 45" with the longitudinal direction of the tyre.

The endurance of the reinforcements of radial tyres frequently depends on the endurance of the rubber between the edges of the crown reinforcement regarded as a whole and the carcass reinforcement, and more particularly on the endurance of the bonds between the edges of the different plies which constitute the crown reinforcement. The endurance of the rubber connection between the edges of the plies of the crown reinforcement depends not only on the driving conditions to which the tyre is subjected, but also on the degree of prestressing caused by the inflation pressure of the tyre (as specified by the standards) in the rubber mixture located between the edges of the crown plies. These prestresses comprise shearing stresses to which the rubber mixtures currently used are highly susceptible.

A number of arrangements have been proposed in order to reduce these shearing stresses. The object of the arrangements is to improve the life of the region between the edges of the different crown plies and/or between the edges of the crown reinforcement and the underlying carcass reinforcement. The arrangements may consist in vulcanising the tyre in a mould so that the meridian curvature of the carcass reinforcement increases in the side walls and decreases in the shoulders when the tyre is inflated to its rated pressure.

These arrangements are unsatisfactory because they do not take into account the local variations which occur in the geometry of the crown reinforcement and the plies which constitute it; during inflation of the tyre to its rated pressure.

In fact, the meridian profile of the tyre when not under load, but mounted on a rim and inflated to about 5 to 10% of the rated pressure, is different from the profile of the tyre when inflated to 100% of the rated pressure. The entire crown is dilated when inflated. The angles formed by the wires or cables of the crown plies with the longitudinal direction of the tyre decrease, causing a reduction in the axial width of the plies and hence in the overall axial width of the crown reinforcement. These deformations on inflation result in a state of prestressing at the edges of the crown reinforcement, which is prejudicial to the endurance of the tyres of this kind.

It is an object of the invention to reduce the harmful deformations of the edges of the crown reinforcement which occur in an inflated tyre.

Therefore according to the invention there is provided a pneumatic tyre comprising a carcass reinforcement formed by at least one ply of radial wires or cables anchored to at least one bead wire in each bead, and a crown reinforcement comprising at least two plies of wires or cables which are parallel in each ply and cross from one ply to the next, forming acute angles of less than 45" with the circumferential direction of the tyre, in which when the tyre is mounted on a rim, inflated at 5 to 10% of the rated pressure and not under load, the radial distance RAo of the intersection Ao of the carcass reinforcement with the trace ZZ' of the equatorial plane is less than the radial distance RA1 of this intersection A1 from the rotation axis W' of the tyre when the pressure is equal to the rated pressure, the intersection Bo of the carcass reinforcement with the trace UU' of the plane parallel to the equatorial plane and at a tangent to the corresponding edge of the crown reinforcement is located at an axial distance L0 from the trace ZZ' of the equatorial plane of not more than the axial distance L1 of this intersection B1 when the pressure is equal to the rated pressure, and at a radial distance RBo from the rotation axis YY' of the tyre at least equal to this radial distance RB1 when the pressure is equal to the rated pressure, so that the length 2TTRBo of the circle described about the rotation axis YY' by the intersection Bo of the carcass reinforcement with the trace UU' of the plane parallel to the equatorial plane and at a tangent to the corresponding edge of the crown reinforcement is at least equal to the same length when the pressure is equal to the rated pressure.

According to the invention, the crown reinforcement of the kind described above is elongated in the circumferential direction near the equator when the transition is made from inflation of 5 to 10% of the rated pressure to inflation of 100% of the rated pressure. Consequently, for meridian curvatures of the carcass reinforcement measured at the intersection of the carcass reinforcement with the equatorial plane and between 50 and 300%, preferably between 50 and 150%, of the equatorial circumferential curvature, the difference between the radial distances from the axis of rotation of this said intersection, measured at 100% and at 5 to 10% of the rated pressure, is equal to not more than 2% and preferably not more than 1% of the radial distance from the rotation axis of the said intersection measured at 5 to 10% of the rated pressure.It is easy to keep below such limits, for example by using cables made from steel wires for the crown reinforcement. The equatorial circumferential curvature is, by convention, equal to the value 2 where D is the equatorial diameter of the carcass reinforcement at 100% of the rated inflation pressure.

Also, the difference between the axial distances of the equatorial plane and the plane parallel to the equatorial plane at a tangent to the corresponding edge of the crown reinforcement, measured at 100% and at 5 to 10% of the rated pressure, is not more than 10%, preferably not more than 5% of the said distance measured at 5 to 10% of the rated pressure.

The invention thus proposes a means of preventing the formation of harmful shearing stresses during inflation, for example by using a mould with a suitable meridian profile or by some other means. It also makes it possible to reduce the length of the circle described by the edge of the crown reinforcement when the tyre is inflated to its rated pressure. This reduction in length is equivalent to compressing the edge zone of the crown reinforcement. This is advantageous, particularly in tyres wherein the carcass reinforcement has an equatorial meridian curvature which is less than the equatorial circumferential curvature in cases where the crown of the tyre in use is subjected to substantial variations in meridian curvature.

The invention will now be described with reference to the accompanying drawings in which: Figure 1represents a meridian section through a known pneumatic tyre of the radial kind, with an additional plan view of a portion of a cable of each of the plies constituting the crown reinforcement, and Figure 2 shows the corrections proposed according to the invention to the meridian profile of the carcass reinforcement.

The tyre 1 has a carcass reinforcement 2 extending from one bead wire 3 to the other 3'. Outside the carcass reinforcement 2 is located the crown reinforcement 4. The carcass reinforcement 2 is formed by a ply of steel cables. The crown reinforcement is formed by three plies 41, 42, 43 of steel cables; these plies are usually of different widths. The cables in ply 41, which is nearest the carcass reinforcement, form an angle a of more than 45Q with the longitudinal direction of the tyre; the cables of the two plies 42,43 form angles ss, y of less than 45 , preferably between 10 and 30 , with the longitudinal direction. Usually, the ply 41 is termed the triangulation ply and the plies 42 and 43 are termed the working plies.Thus, the ply 41 triangulates the set of three plies 41 to 43 which form the crown reinforcement 4. However, the invention also covers cases where the triangulation ply 41 is not provided and the portion of the carcass reinforcement 2 located beneath the working plies 42 and 43 acts as the triangulation ply. The widest working ply, in this case ply 42, defines the width W of the crown reinforcement 4. In Figure 2, which will be described hereinafter, the width L1 corresponds to W/2. The edge of this ply 42 is designated by reference numberal 45.

These two types of crown reinforcement, which are known per se, may be covered by protective plies consisting of elastic reinforcing members whose function is to protect the plies of the crown reinforcement from damage.

The carcass reinforcement 2 makes contact with the bead wires 3, 3' at points C and C'. The distance from C to C' is the length of this reinforcement between the bead wires of the carcass reinforcement 2. This length is defined by the external dimensions of the tyre and the geometry of the crown. These dimensions are themselves defined by the standards currently in use for the rated inflation pressure. The tyre 1 is mounted on a rim 5 and inflated to its rated pressure.The carcass reinforcement 2 (or its mean fibre in the case of a carcass reinforcement formed by a plurality of superimposed radial plies) follows the meridian profile imposed on it by its length, the inflation pressure, the crown reinforcement and the bead wires, whilst the invention is independent of the h/b ratio of the radial height h of the carcass reinforcement 2 in relation to the nominal radius of the rim to the maximum axial width b of the carcass reinforcement 2.

Figure 2 shows one half of the meridian profile 21 of a conventional carcass reinforcement corresponding to a tyre which is not under load, mounted on a rim and inflated to 100% of the rated pressure. This profile 21 is at a tangent to the bead wire at C and passes through point A1, the intersection of the trace ZZ' of the equatorial plane with the profile 21. The length CC' between bead wires is equal to twice the length CA1. The point B1 which denotes the intersection between the carcass reinforcement and the trace UU' of the plane at a tangent to the corresponding edge of the crown reinforcement and parallel to the equatorial plane of trace ZZ' is at an axial distance L1 from the trace ZZ' and at a radial distance RB1 from the rotation axis W' of the tyre.

Moreover, according to the invention, when the tyre is fitted but not under load and is inflated to 5 to 10% of its rated pressure, the profile 22 of the carcass reinforcement should be chosen so that the point Bo of the intersection of the carcass reinforcement with the trace UU' is located radially outside and axially inside the imaginary point B1 belonging to the meridian profile 21 of the carcass reinforcement under the same conditions but at the rated pressure.The point Bo is at an axial distance L0, less than L1, from the trace ZZ' of the equatorial plane and at a radial distance RBo, greater than RB1, from the rotation axis W'. On the other hand, owing to the circumferential contraction of the crown reinforcement; the point A1 where the profile 21 of the carcass reinforcement intersects the trace ZZ' occurs at Ao. The point is at a radial distance RAo from the rotation axis YY' which is less than the radial distance RA1 from point A1.

In the tyre according to the invention, inflated to the rated pressure, the length (2aRB) described by the imaginary point B1 of the edge of the crown reinforcement is less than the length (2xRBo) described by the imaginary point Bo at 5 to 10% of the rated inflation pressure.

There is a special case when RBo = RB1. In this case, between 5 to 10% of the rated pressure and 100% of the rated pressure, the radial distances of points Bo and B1 from the rotation axis YY' do not vary.

In practice, although the curvature at the shoulder decreases and the curvature of the side walls of the carcass reinforcement according to the invention increases during inflation, it is preferable to use a carcass reinforcement having the same length C C' between the bead wires, i.e. comprising at least one radial ply of almost inextensible cables, e.g. made of steel wires. The radial position of point Bo (Figure 2) can be determined experimentally or using a computer. However, it is also possible to calculate the radial position of point Bo as a first approximation.

If rO is the equatorial radius of the widest working ply 42 the cables of which form an angle Po of less than 45" relative to the equatorial plane when the tyre is mounted, inflated to about 5 to 10% of rated pressure and not under load, if r3 is the radius of the edge 45 of this ply 42, taking into account the meridian profile of the carcass reinforcement 2 determined by the rated inflation pressure, the length of the carcass reinforcement and the position of the bead wires according to current standards, and if r1 is the equatorial radius of the same working ply 42 elongated by the effect of the rated inflation pressure (with rO determined experimentally or taken, by hypothesis, to be not more than r1/1.02, preferably not more than r1/1.01 ), this elongation having brought the value of the angle ss0 of the wires to ss1, and assuming that the effect of the meridian curvature on the angle P1 is negligible, it is possible to calculate, as a first approximation which is adequate for practical purposes, the value of the radius r2 of the edge 45 and the value of the angle P2 at this edge of the ply 42, when the tyre is mounted, inflated to about 5 to 10% of the rated pressure and not under load, using the following equation: cos P2 r2 = r3 COS ss1 sin P2 = 2 sin 131-sin Por r1 COS =-cos130.

r0 Thus, it is sufficient to deduce, from the length r2, the radial distance separating the carcass reinforcement 22 from the edge 45 of the widest working ply 42 in order to obtain the radial distance of point B0 from the rotation axis YY' of the tyre 1 and position the carcass reinforcement 22 according to the invention.

Claims

1. A pneumatic tyre comprising, a carcass reinforcement formed by at least one ply of radial wires or cables anchored to at least one bead wire in each bead, and a crown reinforcement comprising at least two plies of wires or cables which are parallel in each ply and cross from one ply to the next, forming acute angles of less than 45" with the circumferential direction of the tyre, in which when the tyre is mounted on a rim, inflated to from 5 to 10% of the rated pressure and not under load.

the radial distance RAo of the intersection Ao of the carcass reinforcement with the trace ZZ' of the equatorial plane is less than the radial distande RA1 of this interesection A1 from the rotation axis W' of the tyre when the pressure is equal to the rated pressure, the intersection Bo of the carcass reinforcement with the trace UU' of the plane parallel to the equatorial plane and at a tangent to the corresponding edge of the crown reinforcement is located, at an axial distance L0 from the trace ZZ' of the equatorial plane of not more than the axial distance L1 of this intersection B1 when the pressure is equal to the rated pressure, and at a radial distance RBo from the rotation axis W' of the tyre at least equal to this radial distance RB1 when the pressure is equal to the rated pressure, so that the length 2RB0 of the circle described about the rotation axis YY' by the intersection Bo of the carcass reinforcement with the trace UU' of the plane parallel to the equatorial plane and at a tangent to the corresponding edge of the crown reinforcement is at least equal to the same length when the pressure is equal to the rated pressure.

2. A pneumatic tyre as claimed in Claim 1, in which the meridian curvature of the carcass reinforcement at the equator, measured at rated pressure, is between 50 and 300% of the circumferential curvature at the equator, and the difference between the radial distances RA1 and RAo between the rotation axis W' and the intersections A1 and Ao of the carcass reinforcement with the trace ZZ' of the equatorial plane, measured at 100% and at 5 to 10%, respectively, of the rated inflation pressure, is equal to not more than 2% of the radial distance RAo, measured at 5 to 10% of the rated pressure, between the rotation axis YY' and the said intersection Ao.

3. A pneumatic tyre as claimed in Claim 2 in which the meridian curvature of the carcass reinforcement at the equator, measured at the rated pressure, is between 50 and 150% of the circumferential curvature at the equator.

4. A pneumatic tyre as claimed in Claim 2 or Claim 3 in which the difference between the radial distance RA1 and RAo between the rotation axis YY' and the intersections A1 and Ao of the carcass reinforcement with the trace ZZ' of the equatorial plane, measured at 100% and at 5 to 10% respectively of the rated inflation pressure, is equal to not more than 1% of the radial distance RAo measured at 5 to 10% of the rated inflation pressure, between the rotation axis W' and the said intersection Ao.

5. A pneumatic tyre as claimed in any preceding claim in which the crown reinforcement is made from steel cables.

6. A pneumatic tyre as claimed in any preceding claim in which the difference (L1 - L0) between the axial distances L1 and L0 of the equatorial plane from the plane parallel to the equatorial plane and at a tangent to the corresponding edge of the crown reinforcement, measured at 100% and at 5 and 10%, respectively, of the rated pressure, is equal to not more than 10% of the said distance L0 measured at 5 to 10% of the rated pressure.

7. A pneumatic tyre as claimed in Claim 6 in which the difference (L1 - L0) between the axial distances L1 and Lo of the equatorial plane from the plane parallel to the equatorial plane and at a tangent to the corresponding edge of the crown reinforcement, measured at 100% and at 5 and 10%, respectively, of the rated pressure, is equal to not more than 5% of the said distance L0 measured at 5 to 10% of the rated pressure.

8. A pneumatic tyre as claimed in any preceding claim in which the radial distances RBo and RB1, respectively, from the rotation axis of the tyre, of the intersections Bo and B1, respectively, of the carcass reinforcement with the plane parallel to the equatorial plane and at a tangent to the corresponding edge of the crown reinfornement remain constant when the inflation pressure increases from 5 to 10% of rated pressure to 100% of rated pressure.

9. A pneumatic tyre as claimed in any preceding claim in which the carcass reinforcement is substantially inextensible.

10. A pneumatic tyre as claimed in Claim 9 in which the carcass reinforcement comprises at least one radial ply of steel cables.

11. A pneumatic tyre as claimed in any preceding claim in which as a first approximation, the radial distance r2 of the edge of the widest working ply of the crown reinforcement from the rotation axis W' of the tyre at 5 to 10% of rated pressure is equal to the value of the term cos 132 2 = r3Cosss1' cos Pi' in conjuction with the terms sin 132 = 2 sin ss1 - sin po, cos pill. cos Pc, rO where rO is the radial distance of the widest working ply from the rotation axis, measured in the equatorial plane, po is the angle of the wires of this ply with the equatorial plane at about 5 to 10% of rated pressure, r1 is the equatorial radial distance and P1 is this equatorial angle of the wires at 100% of rated pressure, and r3 is the radial distance of the edge of the working ply at 100% of rated pressure.

12. A pneumatic tyre substantially as herein described with reference to Figure 2 of the accompanying drawings.