GB2044693A

GB2044693A - A Radial Carcass Pneumatic Tyre for Heavy Vehicles

Info

Publication number: GB2044693A
Application number: GB8009554A
Authority: GB
Original assignee: Compagnie Generale des Etablissements Michelin SCA
Current assignee: Compagnie Generale des Etablissements Michelin SCA
Priority date: 1979-03-22
Filing date: 1980-03-21
Publication date: 1980-10-22
Also published as: SE8002211L; DE3011024A1; LU82281A1; BR8001700A; SE444290B; AR222697A1; IT8067437A0; FR2451834B1; CA1126634A; FR2451834A1; AU5676880A; EG14647A; IT1128071B; JPS55127208A; AU530018B2; MX148912A; GB2044693B; ES8100170A1; ES489769A0; BE882312A

Abstract

A radial pneumatic tyre for heavy vehicles comprises a radial carcass reinforcement 2 and a crown reinforcement which is formed of at least two plies 24,25 of cords and which is parallel to the carcass reinforcement along a mid- circumferential zone less wide than the crown reinforcement. The neutral fibre of each side wall of the carcass reinforcement at least radially outwardly from points 22 follows a natural equilibrium profile the continuation 2' of which is located below the crown reinforcement in the radial direction. This profile passes through a point 21 at which tangent T is parallel to the rotational axis YY' of the tyre and which point is spaced from the mid-circumferential plane by a distance d greater than the axial half width I of the zone of parallelism between the reinforcement and the carcass. <IMAGE>

Description

SPECIFICATION A Radial Carcass Pneumatic Tyre for Heavy Vehicles This invention relates to pneumatic tyres for large load-carrying road vehicles. In particular, the invention relates to tyres having a radial carcass reinforcement and a crown reinforcement.

Usually, such pneumatic tyres have carcass and crown reinforcements reinforced with steel cables. The carcass reinforcement is a single ply of cords and the crown reinforcement is of the triangulated type. Thus, it is essentially formed by two plies known as the working plies which are inclined at small angles to the longitudinal direction and one ply known as the triangulation ply which is inclined at a large angle, e.g. 60 to 800 to the longitudinal direction. This triangulation ply, which is arranged radially inside the working plies, may be interrupted along a mid-circumferential zone. This triangulation ply is then formed from two narrow plies, the axially inner edges of which are spaced in the axial direction and the axially outer edges of which are located axially inside the edges of the working plies.

Present day use of such tyres on roads which become less and less winding every year or have only negligible bends, i.e. virtually straight motorways, means that there is less and less justification for the presence of a triangulation ply in the crown reinforcement. In fact, such a ply constitutes an extra stiffening which is in addition to that provided by the working plies. This additional stiffening serves essentially to reduce the wear on the tread when the tyre is subjected to high drift angles, i.e. cornering.

Moreover, the use of two plies of reduced width may accidentally result either in one of them being forgotten or in one of them being fitted non-symmetrically relative to the midcircumferential plane. Moreover, the provision and fitting of two narrow plies which come into effect only on rare occasions increases the cost of such tyres needlessly. Finally, the presence of unnecessary plies in zones reputed to be critical because they are located between the edges of the working plies and the carcass reinforcement results in a harmful increase in the temperature of the elastomer during travel.

Purely and simply omitting these narrow plies which triangulate the crown reinforcement is not sufficient to avoid these disadvantages in such tyres.

In tyres of this kind where the crown reinforcement is provided with narrow triangulation plies, the neutral fibre of the carcass reinforcement follows, on either side of the midcircumferential plane, the line of a natural equilibrium profile in which the point having a tangent parallel to the rotational axis is located at a distance which is at least equal to the outer radius of the crown reinforcement as measured at the mid-circumferential plane. As a result, the crown reinforcement constitutes a belt which contracts and counteracts the tendency of the neutral fibre of the carcass reinforcement to assume its natural maximum radius when the tyre is inflated to its normal pressure. Therefore, a harmful distribution of stresses is established in the spaces contained between the marginal zones of the crown reiniforcement and the carcass reinforcement.This harmful distribution persists when the narrow triangulation plies are omitted.

The neutral fibre of the carcass reinforcement takes on a profile which is difficult to control and which also leads to an increase in the diameter of the edges of the tread and causes wear.

It is an object of the invention to eliminate or reduce these disadvantages.

According to the invention there is provided a pneumatic tyre for large load-carrying road vehicles having a radial carcass reinforcement anchored at each end to at least one beadwire and a crown reinforcement parallel to the carcass reinforcement along a mid-circumferential zone of parallelism, the width of which is less than the axial width of the crown reinforcement, the crown reinforcement being formed by at least two plies of cords, the cords being parallel to one another in each ply, the cords of one ply being crossed relative the next ply, the cords in the plies of the crown reinforcement forming angles of from 1 5 to 300 with the longitudinal direction of the tyre in which, when the tyre is mounted on its designed rim and inflated normally to its designed pressure, the neutral fibre of the carcass reinforcement on either side of the mid-circumferential plane at least radially outside the point where the carcass reinforcement attains its maximum axial width, follows a natural meridian equilibrium profile defined by the equation:

in which P is the angle formed by the tangent to that profile of equilibrium and the rotational axis of the tyre at a point located at a distance R from the rotational axis, Re is the distance from the rotational axis of the point where the equilibrium profile attains its maximum axial width, and Rs is the distance from the rotational axis of the point where the extension of the equilibrium profile has a tangent parallel to the rotational axis, this point being located axially at a distance from the midcircumferential plane of the tyre which is greater than the axial half-width of the midcircumferential zone of parallelism and not more than the axial half-width of the narrowest ply of the crown reinforcement, and this point being located at a radial distance Rs from the rotation axis which is less than the radial distance RB of the edges of the mid-circumferential zone of parallelism.

A carcass reinforcement in a pneumatic tyre according to the invention does not tend to attain its maximum radius Rs under the effect of the inflation pressure since the point through which the neutral fibre or the extension thereof passes and attains its maximum radius R8 is located on either side of and radially inside the zone of parallelism of the carcass and crown reinforcements. The crown reinforcement is therefore not stressed by expansion forces coming from the carcass reinforcement. The same is true of the spaces contained between the marginal zones of the crown reinforcement and the carcass reinforcement and the edges of the tread.

In order that the neutral fibre of the carcass reinforcement follows the natural equilibrium profile as faithfully as possible, it is preferable to use a single-ply carcass reinforcement, e.g. a single ply of steel cords. Furthermore, in conjunction with such a carcass reinforcement, it is sufficient to use a crown reinforcement formed by only two working plies, preferably formed by steel cords.

It is known to use, in cooperation with a carcass reinforcement in which the neutral fibre follows its natural equilibrium profile from the beads to its point of contact with the crown reinforcement, a crown reinforcement having specially stiffened edges to which the carcass reinforcement is at a tangent, at a small angle relative to the rotational axis of the tyre. The aim of this arrangement is to prevent the formation of stresses at the point of contact between the carcass reinforcement and the crown reinforcement and to maintain the value of this contact angle even at high speeds. Starting from the point of contact, the carcass reinforcement tends to expand radially outwards to reach the natural equilibrium profile of its neutral fibre.In view of the fact that the point of contact is located axially inside the corresponding edge of the crown reinforcement, the critical space contained between the marginal zone of the crown reinforcement and the carcass reinforcement is unfavourably affected, which is not the case in a tyre according to the invention.

It is also known to use a carcass reinforcement in which the neutral fibre follows its natural equilibrium profile from the point of contact of the carcass reinforcement with the beadwire to its point of contact with the crown reinforcement, the crown reinforcement having specially stiffened edges and the beadwire having an exceptionally high torsional rigidity. The aim of this arrangement is to avoid harmful stresses at the points of contact between the crown reinforcement and carcass reinforcement when the choice of an aspect ratio of not more than 0.6 leads to excessive shortening of the length of the cords in the carcass reinforcement. This arrangement has the same disadvantages as the previous solution whereas in the case of a tyre according to the invention the solution adopted is independent of the value of the aspect ratio.

The invention will now be illustrated, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a radial section through the reinforcements of a known tyre with a triangulated crown reinforcement; and Figure 2 is a radial section through the reinforcements of a pneumatic tyre according to the invention.

The prior known tyre whose reinforcements are schematically shown in Figure 1 has a radial carcass reinforcement 2 formed by a single ply of steel cords. This reinforcement 2 is anchored in place by being bent round a beadwire 3 in each tyre bead 3'.

A crown reinforcement 1 is located radially outside the carcass reinforcement 2 and is formed by three superimposed plies 4, 5 and 6, each formed of steel cords. The cords of the two adjacent plies 5 and 6 radially outside the ply 4 form small angles, of the order of 200 with the longitudinal direction of the tyre. Those of the ply 4 form a relatively large angle, of the order of 650, with the longitudinal direction.

The extension 2' of the neutral fibre shown in broken lines from the carcass reinforcement 2 has a maximum radius R's which is greater than the external mid-circumferential radius RA of the crown reinforcement. Thus, as can be seen, the crown reinforcement imposes on the carcass reinforcement 2, a profile shown by solid line 2"' located radially inside the neutral fibre 2'. This profile starts from points 2" close to the crown reinforcement when the tyre is mounted on a rim 7 (only the edges of which are shown) and inflated normally. The crown reinforcement 1 opposes the expansion of the carcass reinforcement 2 towards its natural equilibrium profile shown by the extension 2' of the neutral fibre.

The tyre whose reinforcements are schematically shown in Figure 2 has the same dimensions as the one in Figure 1. It also has a carcass reinforcement 2 formed by a single ply of steel cords which is anchored in position by being bent round beadwires 3 in each tyre bead 3'. The crown reinforcement TO is formed by two plies 24 and 25 of steel cords which are parallel to one another in each ply and cross from one ply to the other. The plies 24 and 25 form angles of 200 and +200, respectively, with the longitudinal direction of the tyre. Between the crown reinforcement 10 and the carcass reinforcement 2 there is a mid-circumferential zone of parallelism having a width 2A. The crown ply 25 radially outside the crown ply 24 is the narrower of the two; its width is 2L. The carcass reinforcement 2 attains its maximum axial width B/2 from the mid-circumferential plane X-X' of the tyre at a point 22 located at a distance Re ((p=900) from the rotational axis Y-Y', when the tyre is inflated normally after being mounted on a rim 7 identical to the rirri 7 used with the tyre shown in Figure 1.

According to the invention, the carcass reinforcement 2 follows its natural equilibrium profile radially outside the points 22 whose radius is Re. However, the carcass reinforcement 2 can also follow its natural equilibrium profile starting from the bead 3' or even from its point of contact 20 with the beadwire 3.

The extension 2', shown by broken lines, of the equilibrium profile of the carcass reinforcement 2 has a tangent T parallel to the rotational axis Y Y' at a point 21 located radially at a distance Rs from the rotation axis Y-Y', which is less than the distance RB of the edge of the zone of parallelism between the crown reinforcement 10 and the carcass reinforcement 2. Advantageously, the difference RBR5 is greater than 0% and not more than 3% of RB. Preferably, this difference is not more than 1% of RB.

Transversely or axially, the point 21 is located at a distance dfrom the mid-circumferential plane .X-X' which is greater than the distance I of the edge of the zone of parallelism between the carcass reinforcement 2 and the crown reinforcement 10 and not more than the width L of the edge of the narrowest crown ply 25 from the plane X-X'. Advantageously, the axial distance of this point 21 from the midcircumferential plane X-X' is from 40% to 100% of the distance L. Preferably, this distance d is not more than 60% of the distance L.

Instead of having two separate crown plies 24 and 25, the crown reinforcement 10 could be formed by a single ply folded back on itself.

Claims

1. A pneumatic tyre for large load-carrying road vehicles having a radial carcass reinforcement anchored on each end to at least one beadwire and a crown reinforcement parallel to the carcass reinforcement along a midcircumferential zone of parallelism, the width of which is less than the axial width of the crown reinforcement, the crown reinforcement being formed by at least two plies of cords, the cords being parallel to one another in each ply, the cords of one ply being crossed relative the next ply, the cords in the plies of the crown reinforcement forming angles of from 15 to 300 with the longitudinal direction of the tyre, in which, when the tyre is mounted on its designed rim and inflated normally to its designed pressure, the neutral fibre of the carcass reinforcement on either side of the mid-circumferential plane at least radially outside the point where the carcass reinforcement attains its maximum axial width, follows a natural meridian equilibrium profile defined by the equation:

in which (p is the angle formed by the tangent to that profile of equilibrium and the rotational axis of the tyre at a point located at a distance R from the rotational axis, Re is the distance from the rotational axis of ohe point where the equilibrium profile attains its maximum axial width, and Rs is the distance from the rotational axis of the point where the extension of the equilibrium profile has a tangent parallel to the rotational axis, this point being located axially at a distance from the mid-circumferential plane of the tyre which is greater than the axial half-width of the midcircumferential zone of parallelism and not more than the axial half-width of the narrowest ply of the crown reinforcement, and this point being located at a radial distance R5 from the rotation axis which is less than the radial distance RB of the edges of the mid-circumferential zone of parallelism.

2. A pneumatic tyre as claimed in Claim 1 in which the difference between RB and Re is greater than 0% and not more than 3% of the distance RB.

3. A pneumatic tyre as claimed in Claim 2 in which the difference between RB and Re is not more than 1% of the distance RB.

4. A pneumatic tyre as claimed in any preceding claim in which the carcass reinforcement is formed by a single ply of cords, and the crown reinforcement is formed by two plies of cords.

5. A pneumatic tyre as claimed in Claim 4 in which the cords of the carcass reinforcement and of the crown reinforcement are steel cords.

6. A pneumatic tyre as claimed in any preceding claim in which the point where the equilibrium profile of the carcass reinforcement has a tangent parallel to the rotational axis of the tyre is located at an axial distance from the midcircumferential plane of from 40 to 1 00% of the axial distance of the edge of the narrowest crown ply from the mid-circumferential plane.

7. A pneumatic tyre as claimed in Claim 6 in which the point where the equilibrium profile of the carcass reinforcement has a tangent parallel to the rotational axis of the tyre is located at an axial distance from the mid-circumferential plane of not more than 60% of the axial distance of the edge of the narrowest crown ply from the midcircumferential plane.

8. A pneumatic tyre as claimed in any preceding claim in which the carcass reinforcement follows its natural equilibrium profile radially inside the point with the radius Re.

9. A pneumatic tyre as claimed in any of claims 1 to 7 in which the carcass reinforcement follows its natural equilibrium profile up to the point of contact with the beadwire.

10. A pneumatic tyre for large load-carrying road vehicles, substantially as herein described with reference to Figure 2 of the accompanying drawings.