WO2020025685A1

WO2020025685A1 - Pneumatic tire with optimized crown architecture

Info

Publication number: WO2020025685A1
Application number: PCT/EP2019/070652
Authority: WO
Inventors: Frederic Bourgeois; Bruno Guimard
Original assignee: Compagnie Generale Des Etablissements Michelin
Priority date: 2018-08-03
Filing date: 2019-07-31
Publication date: 2020-02-06

Abstract

Disclosed is a pneumatic tire (1) which has an overall axial width LT and a maximum diameter Rm, and the tread (2) of which has an axial width L and comprises two working plies (41, 42) and a reinforcement ply (5). The reinforcement ply (5) is formed by helically winding a strip of reinforcing elements, the width LB of which, measured perpendicularly to the reinforcing elements, is at most 0.09*LT and which has a constant thickness excluding any extra thickness of the reinforcement ply, but without excluding possible discontinuities. The axial width LF of the reinforcement ply (5) is greater than the axial width (L41, L42) of the working plies (41, 42). The minimum axial distance between the axially outermost points (511, 512) of the reinforcement ply and the crown plies is at least 0.38*LB and at most 1.25*LB.

Description

Tires with optimized crown architecture

FIELD OF THE INVENTION

The present invention relates to a tire intended to be mounted on a passenger vehicle, and more particularly the top of such a tire.

[0003] A tire having a geometry of revolution relative to an axis of rotation, the geometry of the tire is generally described in a meridian plane containing the axis of rotation of the tire. For a given meridian plane, the radial, axial and circumferential directions respectively designate the directions perpendicular to the axis of rotation of the tire, parallel to the axis of rotation of the tire and perpendicular to the meridian plane. The median circumferential plane, called the equator plane, divides the tire into two substantially symmetrical half toroids, the tire possibly having asymmetries in tread, in architecture, linked to manufacturing precision or to sizing.

In what follows, the expressions "radially inside" and "radially outside" mean respectively "closer to the axis of rotation of the tire, in the radial direction, than" and "further from the axis of rotation of the tire, in the radial direction, that ". The expressions "axially inside of" and "axially outside of" mean respectively "closer to the equator plane, in the axial direction, than" and "further away from the equator plane, in the axial direction, than". A "radial distance" is a distance from the axis of rotation of the tire, and an "axial distance" is a distance from the equatorial plane of the tire. A "radial thickness" is measured in the radial direction, and an "axial width" is measured in the axial direction.

A tire comprises a crown comprising a tread intended to come into contact with the ground by means of a running surface, two beads intended to come into contact with a rim and two sidewalls connecting the crown to the beads. In addition, a tire comprises a carcass reinforcement comprising at least one carcass layer, radially interior at the top and connecting the two beads.

The tread is further formed by one or more mixtures or rubber compounds. The expressions “rubber mixture” or “rubber compound” designates a rubber composition comprising at least one elastomer and a filler.

The crown comprises at least one crown reinforcement radially inside the tread. The crown reinforcement comprises at least one reinforcement of work comprising at least one working layer composed of reinforcing elements parallel to each other forming, with the circumferential direction, an angle between 15 ° and 50 °. The invention relates to tires, the crown reinforcement of which comprises a hooping reinforcement comprising at least one hooping layer composed of reinforcing elements forming, with the circumferential direction, an angle between 0 ° and 10 °, the hooping reinforcement being most often but not necessarily radially external to the working layers.

For any layer of crown reinforcement elements, working, or other, a continuous surface, said radially outer surface (SRE) of said layer, passes through the most radially outer point of each element of reinforcement, of each meridian. For any layer of reinforcement elements of crown reinforcement, of work, or other, a continuous surface, called radially inner surface (SRI) of said layer, passes through the most radially inner points of each reinforcement element, of each meridian. The radial distances between a layer of reinforcing elements and any other point, are measured from one or the other of these surfaces and so as not to integrate the radial thickness of said layer. If the other measurement point is radially outside the layer of reinforcing elements, the radial distance is measured from the radially exterior surface SRE at this point, and respectively from the radially interior surface SRI at the other measurement point if this is radially inside the layer of reinforcing elements. This makes it possible to take coherent radial distances from one meridian to another, without having to take into account the possible local variations linked to the shapes of the sections of the reinforcing elements of the layers.

In order to obtain wet grip performance, cutouts are placed in the tread. A cutout designates either a well, a groove, an incision, or a circumferential groove and forms a space opening onto the rolling surface and delimited radially internally by a cutout bottom.

An incision or a groove has, on the running surface, two main characteristic dimensions: a width W and a length Lo, such that the length Lo is at least equal to twice the width W. An incision or a groove is therefore delimited by at least two main lateral faces determining its length Lo and connected by a bottom face, the two main lateral faces being distant from each other by a non-zero distance, called width W of the incision or the groove. The depth of a cutout is the maximum distance between the running surface and the bottom of the cutout. This maximum distance being measured in a direction orthogonal both to the rolling surface and to the bottom of the cut.

In what follows, the expression "overhanging" means, "for each meridian, radially exterior within the limit of the axial coordinates delimited by". Thus "the most radially outer points of the hooping layer overhanging the most axially outer points of the most radially outer working layer" denote for each meridian, the set of the most radially outer points of the hooping layer radially exterior to the most axially exterior points of the most radially exterior working layer, within the limit of the axial coordinates of the latter.

STATE OF THE ART

A tire must meet multiple performance criteria relating to phenomena such as endurance, uniformity, rolling resistance. To meet endurance performance at high speed, a large number of tires are fitted with a hoop layer. These hooping layers have a very high rigidity in extension in the circumferential direction and allow the centrifugal forces to be taken up at high speed. To improve productivity, the hooping layer is placed in a strip of several wires of a width LB measured perpendicular to the reinforcing elements of said strip. The wider the strip, the less turns it takes and therefore the manufacturing time to go continuously from one of the axial ends of the crown reinforcement to the other. The difficulty is that the wider the strip of the hooping layer, the greater the edge effects because the width from the axial end of the hooping layer to the equatorial plane varies around the wheel from the width of the laying strip. . This variation has an influence on the uniformity of tires and their endurance at high speed.

To solve this problem, tire manufacturers have devised many solutions. Some begin with one or more turns, at 0 ° so-called dead turns, of the hooping strip on the most axially outer zone of the working layers or shoulder of the tire, as for example in JP2016 / 066809, to generate layer thicknesses hooping of the hooping layer in the shoulder area. However, the impact of these solutions on the other performances is not negligible because this extra thickness of the hooping layer is located in an area where the volume of the rubbery materials or the reinforcing elements is constrained between the layer of carcass, the dimensioning of which is determined by the pressure equilibrium curve and the tread profile determined by the balance between wear and tear in the central area of the tread and wear and tear in the shoulder area.

For optimized rolling resistance, the working layers must have a substantially constant radius between the center and the shoulders of the tire, which facilitates flattening. The extra thickness of a dead turn of the band of the hooping layer is closer to the rolling surface than the hooping layer in the center of a tire, and could be attacked when rolling over an object on the ground. of rolling. In addition, this extra thickness reduces the volume of the tread on the shoulder area. The tires thus designed arrive at the wear limit in more than 80% of the cases with the shoulder zones at the wear limit and a central zone that can still cover several thousand kilometers.

The solution used in the state of the art is therefore to design the tire such that the radius of the working layers decreases appreciably from the center towards the shoulder by degrading the rolling resistance of the tire.

SUMMARY OF THE INVENTION

The main objective of the present invention is therefore to distribute the volume of the hoop layer at the shoulder without degrading the endurance of the tire.

This objective is achieved by a tire, intended to be mounted on a mounting rim of a wheel of a passenger vehicle, the tire having an overall axial width LT mounted on a nominal rim and inflated to a pressure nominal and comprising:

An axis of rotation (R), an equator plane (P) which is the circumferential plane passing through the center of gravity of the tire and perpendicular to the axis of rotation (R),

• a crown comprising a tread, intended to come into contact with the ground via a running surface and a crown reinforcement, comprising three layers of reinforcing elements, the tread being radially external to the 'crown frame,

The crown reinforcement comprising two working layers composed of reinforcing elements parallel to each other forming, with the circumferential direction, an angle between 15 ° and 50 °, The crown reinforcement also comprising a hooping layer composed of textile reinforcing elements forming, with the circumferential direction, an angle between 0 ° and 10 °, the hooping layer being radially external to the working layers, and d an axial width LF equal to the axial distance between the two most axially outer points of the hooping reinforcement,

• two beads intended to come into contact with a rim and two sides connecting the top to the beads,

A carcass reinforcement comprising at least one carcass layer, radially interior at the top and connecting the two beads,

The hooping layer being constituted by the helical winding of a strip of reinforcing elements whose width LB measured perpendicular to the reinforcing elements is at most equal to 0.09 ^* LT,

Each axial distance between the most axially external points of the hooping layer and the most axially external points of each working layer located on the same side of the equator plane being at least equal to 0.38 ^* LB and at most equal to 1 25 ^* LB

• the hooping layer being of constant thickness and the axial width LF of the hooping layer being greater than the axial widths of the working layers.

The overall axial width LT of the tire is measured on a tire mounted on a nominal rim and inflated to a nominal pressure as defined in the regulations. For example, the overall axial width LT is defined as the maximum overall flange size in SG service as defined by ETRTO in the document "ETRTO, STANDARDS MANUAL, 2005".

To ensure correct uniformity and endurance for the tire, it is essential that the hooping layer, of constant thickness, has an axial width LF greater than the maximum axial width of the working layers. By axial width LF is meant the maximum axial distance between the ends on either side of the equator plane of the most axially outer points of the hooping layer on the entire tire. These points can be determined by non-destructive examinations (MRI or other) or by destructive examination by removing the materials radially outside the hoop layer. This involves measuring the axial distance between the most axially outermost points of the corresponding hooping layer at the beginning or end of fitting of the hooping strip. This condition makes it possible to ensure a minimum circumferential rigidity at the ends of the working layers so as to ensure the endurance of the tire at high speed, usually provided by an extra thickness.

The minimum axial distance between the most axially outer points of the hooping layer on the circumference of the tire and the most axially outer points of the working layers is at least equal to 0.38 ^* LB in order to ensure a minimum of circumferential stiffness in this area and limit the deformation of the working layers on the shoulders in high speed centrifugation and at most equal to 1.25 ^* LB, because just as the working layers need the stiffness of the hooping layer at their ends to withstand the extreme stresses of centrifugation, in the same way the hooping layer needs the working layers in this zone there to withstand the stresses linked to the inflation and to the transverse stresses, in the case where no excess thickness of the hooping layer is present on the shoulder area, that is to say, where the thickness of the hooping layer is constant, with variations close to the diameter be reinforcing elements of the hooping layer.

The hooping layer is of constant thickness means that the hooping layer has substantially the same thickness at each axial point of the hooping layer in each meridian plane. In each meridian plane, the thickness of the hooping layer at an axial point is measured by considering the axially closest reinforcing element of the hooping layer and by measuring the distance between the radially outermost point of the layer of hooping and the radially innermost point of the hooping layer, this distance being measured along a straight line perpendicular to a line passing through the center of all the reinforcing elements of the hooping layer and passing through the center of the element reinforcing the axially closest hooping layer. Thus the invention excludes any radial excess thickness of the hooping layer in the axial width of the hooping layer but does not exclude in the center a greater pitch between the turns of the strip of the hooping layer generating gaps or spaces between two reinforcing elements of the hooping layer, in particular around the pla n equatorial. Thus, the hooping layer is devoid of any double radial winding of the strip.

For the same reason it is essential that the width of the strip for applying the hooping layer, measured perpendicular to the elements of reinforcement is limited. Its maximum width must be at most 0.09 ^* LT. To measure the width LB, it suffices to position itself at the start or end points of laying the hooping layer either by using a suitable non-destructive control means, or by removing the materials radially external to the hooping layer.

One of the technical means of the invention being to avoid any excess thickness of the hooping layer in the shoulder zone, no excess thickness being necessary in the center of the tire, the latter is of a substantially constant radial thickness over its entire axial width, therefore without dead tower or curling. On the other hand is included in the invention a variant or the pitch of laying of the strip of the hooping layer would be variable over the width, minimum at the shoulders and maximum at the center bringing empty spaces between two radially successive reinforcing elements of the layer hooping, that is to say that the thickness of the hooping layer is substantially constant over its axial width to variations in the diameter of the reinforcing elements.

It will be noted that, in one embodiment, the most radially outer point of the tire is distant from the axis of rotation (R) by a radial distance Rm, measured on the equator plane, the tire being mounted on a nominal rim and inflated to a nominal pressure.

It will also be noted that in one embodiment, the most radially outer working layer has an axially outermost point, the projection of which is perpendicular to the running surface on the running surface, is at a radial distance Re from the axis of rotation R, Re being measured, the tire being mounted on a nominal rim and inflated to a nominal pressure, and said spray being at a distance d2 from the most axially outer point of the most radially outer working layer. In other words, in this embodiment, d2 is the straight distance between the most axially outside point of the most radially outside working layer in the equator plane, this point being on the radially outside surface SRE of the most radially outer working layer, and projected from this point perpendicular to the running surface on the running surface.

The nominal pressure is the recommended working pressure. Such pressure is for example defined as the basic pressure as defined by ETRTO in the document "ETRTO, STANDARDS MANUAL, 2005".

The nominal rim is the rim compatible with the use of the tire under normal conditions of use. Such a rim is for example defined as a measuring rim as defined by ETRTO in the document "ETRTO, STANDARDS MAN UAL, 2005".

One of the preferred modes of the invention is that the radial distance d1 of the most radially outer working layer at the most radially outer point of the tire is at least equal to d2 +0.2 ^* (Rm-Re) . d 1, Rm and Re are measured on the equatorial plane of a tire mounted on a nominal rim and inflated to nominal pressure. In other words, d1 is the straight distance between the most radially outside point of the most radially exterior working layer in the equator plane, this point being on the radially exterior surface SRE of the working layer the most radially outer, and the projected from this point perpendicular to the running surface on the running surface, this projected this being on the equator plane.

Rm represents the radius of the most radially exterior point, generally located on the equator plane, where is measured d 1, the distance between the running surface and the most radially exterior working layer. Re and d2 represent the same characteristics as Rm and d1 but at the axial end of the most radially outer working layer.

Re represents the radius of the tread surface perpendicular to the axial end of the most radially outer working layer, and d2, the distance between the tread surface and the most radially outer working layer at the same point. The condition limits the curvature of the most radially outer working layer over the width of the crown as a function of the variation in the thicknesses of the tread between the shoulder and the center of the tire, slight variations due to the balance of wear and this in order to guarantee that the working layers have the smallest possible variation in radius, a condition made possible by the constant nature of the thickness of the hooping layer, knowing that the hooping layer is present at the places where Rm, Re, d 1, d2 are measured since the axial width of the hooping layer is at least equal to the width of the most radially outer working layer.

This constancy of the radius facilitates flattening and improves the rolling resistance.

To further improve this flattening, it is advantageous for the tire to comprise a rubber compound, said compound for decoupling the carcass from the crown, a rubber compound being radially outside the carcass reinforcement and radially inside the layer of most radially inner work, of which the most axially interior point is axially interior at the most axially exterior point of the most radially interior working layer and whose most axially exterior point of said decoupling compound from the crown carcass, is axially exterior at the most axially exterior point of the hooping reinforcement. This allows the ends of the working layers to be kept at a substantially constant radius although the radius of the carcass layer at the shoulder decreases sharply due to the deformation due to inflation.

A preferred solution is that the shortest distance (d3) from the most axially outside point of the working layer most radially outside the hooping layer, is at least equal to 0.75 times the distance (d4) la shortest from the most axially outside point of the working layer most radially inside the hooping layer and at most equal to 1.25 times the shortest distance (d4) from the most axially outside point of the most working layer radially inside the hooping layer. This characteristic associated with the previous one on Re, Rm, d1, d2, ensures that the two working layers both keep a radius as constant as possible in the width of the crown reinforcement.

In other words, in this solution, d3 is the straight distance between the most axially outer point of the most radially outer working layer, this point being on the radially outer surface SRE of the working layer the most radially outer and projected from this point on the radially inner surface SRI of the hoop layer perpendicular to the radially inner surface SRI of the hoop layer. Also in other words, d4 is the straight distance between the most axially outer point of the most radially inner working layer, this point being on the radially outer surface SRE of the most radially inner working layer, and the projection of this point on the radially inner surface SRI of the hooping layer perpendicular to the radially inner surface SRI of the hooping layer.

In order to guarantee good endurance to attacks from the tread during driving in the presence of obstacles on the road surface, it is preferred that, when the tire according to the invention, includes cutouts in the tread overhanging the most axially outer points of the most radially outer working layer, then the shortest distance (d5) from the most radially outer point of the hooping layer overhanging the most axially outer point of the most radially outer working layer at the bottom of said overhanging cutout, is at least equal to 1.5 mm and at most equal to 3 mm, preferably at least equal to 2 mm and at most equal to 2.5 mm. This thickness of rubber compound between the bottom surface of the cutouts and the reinforcing elements of the crown reinforcement makes it possible to protect the reinforcing elements of the hooping layer as well as the reinforcing elements of the working layers.

In other words, in this preferred embodiment, d5 is the straight distance between the most radially outer point of the hooping layer, point which is located on the radially outer surface SRE of the hooping layer, overhanging the most axially outer point of the most radially outer working layer and the projection of this point on the bottom of the cutout perpendicular to the bottom of the cutout.

It is advantageous that at least two rubber compounds are radially outside the hooping layer and the most radially inner rubber compound is radially inside at the most radially inner points of the cutouts. The fact that the most radially inner rubber compound is internal to the bottom surfaces of the cutouts implies that this rubber compound is not intended to touch the ground. This rubber compound therefore does not have the characteristics of a rubber compound suitable for this use, this makes it possible to use rubber compounds of low resistance to wear or without any particular characteristic with respect to adhesion performance. This rubber compound will preferably be chosen for its resistance to attack and its low rolling resistance.

To reduce the rolling resistance of the tire, it is preferred that at least one radially outer rubber compound at the most radially inner points of the cutouts has a dynamic tanô loss, measured according to the same standard ASTM D 5992-96, a temperature of 23 ° C and under a stress of 0.7 MPa at 10 Hz, at most equal to 0.30, preferably at most equal to 0.25.

The invention being intended for a passenger tire, the tire preferably comprises cutouts in the tread and their maximum depth when new in the tread is at least equal to 5 mm and at most equal at 8 mm, preferably at least equal to 6 mm and at most equal to 7 mm.

To optimize the rolling resistance, it is advantageous for the reinforcing elements of at least one working layer to be constituted by unitary metallic wires or monofilaments having a section of which the smallest dimension is at most equal to 0.40 mm, preferably at most equal to 0.30 mm. In fact, this type of reinforcing element makes it possible to reduce the thickness of the working reinforcement and therefore to limit the hysteresis of the materials which constitute it.

For a tire optimized for rolling resistance, it is advantageous that at least one rubber compound in contact with the reinforcing elements of the working layers has a dynamic tanô loss, measured according to the same standard ASTM D 5992 - 96, a temperature of 23 ° C and under a stress of 0.7 MPa at 10 Hz, at most equal to 0.20, preferably at most equal to 0.15.

It is advantageous that the transverse grooves axially external to the points located at an axial distance at most equal to 0.3 ^* LT from the equator plane P, have a width at most equal to 2 mm. In fact, in order to have effective grip on wet ground, it is preferable for the shoulder zone to include grooves and in particular transverse grooves for discharging water from the contact surface of the tire with the rolling ground. Usually the grooves have a width at least equal to 3 mm. This arrangement relaxes the tread and increases the rolling resistance. Another possibility is to increase the number of transverse grooves by limiting their width to 2 mm. During the crushing, the lateral surfaces of the grooves come to bear on one another thus limiting the flexibility of the tread and therefore its rolling resistance. By transverse groove is meant all the grooves making an angle with the axial direction of between -75 ° and 75 °.

It is advantageous that the carcass reinforcement consists of a single textile carcass layer, preferably of polyethylene terephthalate type, aliphatic polyamide, combination of aliphatic polyamide and aromatic polyamide, or combination of polyterephthalate d ethylene and aromatic polyamide. By limiting the number of carcass layers, the hysteresis of the materials in these layers is also limited, thereby limiting the rolling resistance of the tire.

A preferred solution is that the reinforcing elements of the hooping layer are textile reinforcing elements, preferably of the aliphatic polyamide, aromatic polyamide, combination of aliphatic polyamide and aromatic polyamide, polyethylene terephthalate or rayon type. .

BRIEF DESCRIPTION OF THE DRAWINGS The characteristics and other advantages of the invention will be better understood using Figures 1 to 4, said figures not being shown to scale but in a simplified manner, in order to facilitate understanding of the invention:

FIG. 1 is a part of a tire, in particular its architecture and its tread provided with transverse grooves and circumferential grooves.

• Figure 2 very schematically shows the widest working layer 41 and the hooping layer 5 unwound.

• Figure 3 shows a meridian section of the top of a tire according to the invention and illustrates the different radial distances, Rm, Re, d1 and the distance d2.

FIG. 4 represents a view of details of the shoulder zone of a meridian section of the summit to illustrate the distances d3, d4 and d5 and the rubbery stuffing compound 7.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 represents a perspective view of part of the crown of a tire. Each Cartesian plane is associated with a Cartesian coordinate system (XX ’, YY’, ZZ ’). The tire comprises a tread 2 intended to come into contact with a ground via a tread surface 21. In the tread 2, grooves 25 of width W are arranged possibly different from a groove with the other. These grooves 25 can be transverse grooves or circumferential grooves. The tire also comprises a carcass reinforcement 6 and a crown reinforcement 3 comprising a working reinforcement 4 and a hooping reinforcement 5. The working reinforcement comprises two working layers 41 and 42 each comprising parallel reinforcing elements between them.

Figure 2 very schematically shows the working layers 41 and 42 of respective width L41 and L42 and the hoop layer 5 "unrolled" to explain the principle of sizes, L41, L42, LF. The axial width LF is the overall width of the hooping layer between the most axially outer points of the hooping layer 512 and 51 1 which represent the beginnings or ends of laying the strip of reinforcing elements of the hooping layer 5. The width LB represents the width of the strip for applying the hooping layer. LB is easily measurable at the start or end points of the hooping layer. L41 represents the axial width of the working layer 41 and L42 represents the axial width of the working layer 42. These widths are substantially constant over the circumference of the tire to within the manufacturing variations and can be measured on a meridian cut.

Still with reference to FIG. 2, the tire has axial distances D1, DT, D2, D2 'between the most axially outer points 51 1, 512 of the hooping layer 5 and the points 411, 412, 421 , 422 the most axially outermost of each working layer 41, 42 located on the same axial side of the equator plane P. In the present case:

the axial distance D1 separates the most axially external point 512 of the hooping layer 5 and the most axially external point 412 of the working layer 41 situated on the same left side of the equator plane P in FIG. 2,

the axial distance DT separates the most axially outward point 51 1 from the hooping layer 5 and the most axially outward point 41 1 from the working layer 41 situated on the same right side of the equator plane P in FIG. 2,

the axial distance D2 separates the most axially external point 512 of the hooping layer 5 and the most axially external point 422 of the working layer 42 situated on the same left side of the equator plane P in FIG. 2,

- the axial distance D1 ’separates the most axially outer point 511 of the hoop layer 5 and the most axially outer point 421 of the working layer 42 located on the same right side of the equator plane P in FIG. 2.

Here, we have D1 = DT and D2 = D2 ’.

FIG. 3 schematically represents the meridian half-section of the top of the tire according to the invention. FIG. 3 illustrates in particular the most axially exterior points of the working layers 41, 42, respectively the points 411 and 421, the most axially exterior point 51 1 of the hooping layer 5, the most axially exterior point 71 of the compound rubbery 7 for decoupling the carcass layer 6 and the hooping layer 5. The projection perpendicular to the running surface, on the running surface of point 421 is point 212. FIG. 2 also illustrates the following distances:

• Rm: radial distance from the axis of rotation of the tire to its most radially outer point 211, measured on the equator plane, the tire being mounted on a nominal rim and inflated to nominal pressure.

The distance d1: radial distance measured on the equator plane between the most radially exterior point of the tire 211 and the most radially exterior points of the most radially exterior working layer 42. • Re: radial distance from the axis of rotation of the tire at point 212 projected perpendicularly to the running surface, on the running surface of point 421 most axially outside of the most radially outside working layer 42.

The distance d2 between the most axially outer point 421 of the most radially outer working layer 42 and the point 212 projected perpendicularly to the rolling surface 21, on the rolling surface 21 of the most axially outer point 421 of the most radially outer working layer 42.

The depth of an HSC circumferential groove. In the case where several circumferential grooves are present, HSC represents the depth of the deepest groove. FIG. 4 represents a detail view of a meridian section of the shoulder zone to illustrate the distances d3, d4 and d5 and the rubbery stuffing compound 7:

D3 is the shortest distance from the most axially outer point 421 of the working layer 42 to the hooping layer 5,

D4 is the shortest distance from point 41 1 most axially outside of the working layer 41 to the hooping layer 5,

• d5 is the shortest distance from the most radially outside point of the hooping layer 5 overhanging from the most axially outside point 421 of the most radially outside working layer 42 to the most radially inside point of the cutouts 25, c that is to say at the bottom of the cutout 25 materialized by a dotted line in FIG. 4.

A meridian section of the tire is obtained by cutting the tire along two meridian planes. This section is used to determine the different radial distances, the center of the bottom faces of the transverse grooves and the circumferential grooves.

The invention was carried out on a tire A of size 205/55 R16 intended to equip a passenger vehicle. The depths of the carvings are between 5 mm at the shoulders and 7 mm at the equator. The crown reinforcement is composed of two working layers, the reinforcement elements of which form an angle of + or - 25 ° with the circumferential direction, and a textile hooping layer of which the reinforcement elements form an angle of + or - 3 ° with the circumferential direction. The invention A is compared with tires B and C. B according to the state of the art is identical to A but the hooping layer of the tire B is not of constant thickness and the width LF of the layer of hooping of tire B is weaker and has an additional turn on the shoulder area. The tire C is identical to the tire B but with a constant thickness of the hooping layer, namely without additional revolution of the hooping strip in the shoulder area and the same width LF of the hooping layer as the tire B.

The tires have an overall width LT equal to 215 mm, measured on the tire inflated to 2.5 bars on a 6.5J16 rim. The axial width of the hooping layer is 174 mm for tires B and C and 190 mm for tire A according to the invention. The width LB of the application strip, measurable at the start and end points of application of the hooping layer is 10.2 mm for tires A, B and C so that the condition LB at most equal to 0.09 ^* LT is respected. The tire A according to the invention and the tire C have a thickness of the hooping layer constant and equal to 0.84 mm for a thickness of the reinforcing elements of the hooping layer equal to 0.66 mm. The tire B according to the state of the art has a thickness of the hooping layer varying from 1.7 mm at the shoulder, due to a dead turn of the hooping layer, for a thickness at the equatorial plane equal to 0.84 mm for reinforcing elements having a thickness equal to 0.66 mm. The axial widths of the working layers L41 and L42 are 178 mm and 164 mm respectively. Therefore for the tire A according to the invention, the axial width of the hooping layer is greater than each axial width of each working layer 41, 42. Each axial distance D1, DT, D2, D2 'between the points 511, 512 the most axially outermost of the hooping layer 5 on the circumference of the tire and the most axially outermost points 411, 412, 421, 422 of each working layer 41, 42 situated on the same axial side of the equator plane P as each point 51 1, 512 is at least equal to 0.38 ^* LB (4.56 mm) and at most equal to 1.25 ^* LB (15 mm) making it possible to comply with the related design conditions for the lower bound for uniformity and resistance to centrifugation at high speed and for the endurance of the shrinking layer. In this case, D1 = D1 '= 6 mm and D2 = D2' = 13 mm.

The absence of the excess thickness of the hooping layer in the tire according to solution C and the non-compliance with the conditions of the invention leads to a reduction in the speed limit of 20 km / h. Speed limit tests are well known to those of skill in the art and are required of automobile manufacturers. These tests consist of rolling the tire on a metal flywheel at a load and a pressure given by the manufacturer and making 20-minute steps at a speed given, increasing in stages, until the tire fails. Tires A and B achieve the same performance levels in speed limit and uniformity.

However, due to the presence of an additional turn on the shoulder area, the tire B has a mass greater than that of the tire A.

The absence of an additional thickness of the hooping layer in the shoulder area of the tire according to the invention also makes it possible to increase the rate of recess in this area to improve the grip on wet ground but also to raise the working layers. vis-à-vis the control tire which facilitates flattening and improves the rolling resistance of the tire.

Thus, one can consider modifying the tire A to manufacture a tire D having improved performance in rolling resistance. A, B and D have the same maximum radius Rm, equal to 316.8 mm and the same shoulder radius Re because the same mold profile at 309 mm and the same depth HSC of sculpture. The tires A and B have a distance d2 equal to 8 mm while the tire D has a distance d2 equal to 7 mm. The elimination of the excess thickness of the hooping layer in the shoulder area of the tire D relative to the tire B makes it possible to reduce the distance d2 for the tire D according to the invention to 7 mm as against 8 mm for the tire B while retaining the same tread thickness simply by removing a thickness of hooping layer whose thickness is 0.84 mm. In addition, tire D complies with the following conditions: d1 = 9.45 mm is at least equal to d2 + 0.2 (Rm-Re) = 8.7 mm when tire B does not comply with them: d1 = 9.45 mm and d2 + 0.2 (Rm-Re) = 9.68 mm.

The tire D thus achieves the same performance as the tires A and B in limit speed and uniformity but has an improved rolling resistance performance of 0.2 Kg / t.

Claims

1. Tire, intended to be mounted on a mounting rim of a wheel of a passenger vehicle, the tire having an overall axial width LT mounted on a nominal rim and inflated to a nominal pressure and comprising:

An axis of rotation (R), an equator plane (P) passing through the center of gravity of the tire and perpendicular to the axis of rotation (R),

• a crown (1) comprising a tread (2), intended to come into contact with the ground via a rolling surface (21) and a crown reinforcement (3), comprising three layers of elements reinforcement (41, 42, 5), the tread (2) being radially external to the crown reinforcement (3),

The crown reinforcement (3) comprising two working layers (41, 42) composed of reinforcing elements parallel to each other forming, with the circumferential direction, an angle between 15 ° and 50 °,

• the crown reinforcement (3) also comprising a hooping layer (5) composed of textile reinforcing elements forming, with the circumferential direction, an angle between 0 ° and 10 °, the hooping layer (5) being radially external to the working layers, and of an axial width LF equal to the axial distance between the two most axially external points of the hooping reinforcement,

A carcass reinforcement comprising at least one carcass layer (6), radially inner to the top and connecting the two beads,

The hooping layer (5) being constituted by the helical winding of a strip of reinforcing elements whose width LB measured perpendicular to the reinforcing elements is at most equal to 0.09 ^* LT,

characterized in that each axial distance (D1, DT, D2, D2 ') between the most axially outermost points (51 1, 512) of the hooping layer (5) and the points (41 1, 412, 421, 422 ) the most axially outermost of each working layer located on the same axial side of the equator plane is at least equal to 0.38 ^* LB and at most equal to 1 25 ^* LB • in that the hooping layer (5) is of constant thickness and the axial width LF of the hooping layer (5) is greater than the axial widths (L41, L42) of the working layers (41, 42).

2. A tire according to claim 1, in which

- the most radially outer point (211) of the tire being distant from the axis of rotation (R) by a radial distance Rm, measured on the equatorial plane, the tire being mounted on a nominal rim and inflated to a nominal pressure ,

- the most radially external working layer (42) having an most axially external point (421), the projection (212) of which is perpendicular to the running surface on the running surface, is at a radial distance Re from the axis of rotation R, Re being measured, the tire being mounted on a nominal rim and inflated to a nominal pressure, and said spray (212) being at a distance d2 from the most axially outer point (421) of the working layer (42 ) the most radially outer,

the radial distance d1 from the most radially outer working layer (42) to the most radially outer point (211) of the tire measured on the equatorial plane (P) is at least equal to d2 +0.2 ^* (Rm- Re).

3. A tire according to any one of the preceding claims, in which a rubber compound, known as a decoupling compound (7) of the carcass (6) of the crown (1), is radially external to the carcass reinforcement (6), is radially inner to the most radially inner working layer (41), the most axially inner point of which is axially inner to the most axially outer point (411) of the most radially inner working layer (41) and the the most axially external point (71) of said decoupling compound (7) of the carcass (6) of the crown (1), is axially external to the most axially external point (51) of the hooping reinforcement (5).

4. Tire according to any one of the preceding claims, in which the shortest distance (d3) from the most axially external point (421) of the most radially external working layer (42) to the hooping layer (5 ) is at least equal to 0.75 times the shortest distance (d4) from the most axially outer point (411) of the most radially inner working layer (41) to the hooping layer (5) and at most equal to 1.25 times the shortest distance (d4) from the most axially outer point (41 1) of the most radially inner working layer (41) to the hooping layer (5).

5. A tire according to any one of the preceding claims, comprising cutouts (25) in the tread overhanging the most axially outer points (421) of the most radially outer working layer (42), tire in which the shortest distance (d5) from the most radially outer point (621) of the hooping layer (5) overhanging the most axially outer point (421) of the most radially outer working layer (42) at the bottom of the cutout (25) overhanging, is at least equal to 1.5 mm and at most equal to 3 mm, preferably at least equal to 2 mm and at most equal to 2.5 mm.

6. Tire according to any one of the preceding claims, in which at least one radially exterior rubber compound at the most radially interior points of the cutouts (25) has a dynamic tanô loss, measured according to the same standard ASTM D 5992-96, a temperature of 23 ° C and under a stress of 0.7 MPa at 10 Hz, at most equal to 0.30, preferably at most equal to 0.25.

7. A tire according to any one of the preceding claims, comprising cutouts (25) in the tread and in which the maximum depth of the cutouts (25) in the tread is at least equal to 5 mm and at most equal at 8 mm, preferably at least equal to 6 mm and at most equal to 7 mm.

8. Tire according to any one of the preceding claims, in which the reinforcing elements of at least one working layer (41, 42) are constituted by unitary metallic wires or monofilaments having a section the smallest dimension of which is at more equal to 0.40 mm, preferably at most equal to 0.30 mm.

9. Tire according to any one of the preceding claims, in which at least one rubbery compound in contact with the reinforcing elements of the working layers (41, 42) has a dynamic tanô loss, measured according to the same standard ASTM D 5992 - 96 , at a temperature of 23 ° C and under a stress of 0.7 MPa at 10 Hz, at most equal to 0.20, preferably at most equal to 0.15.

10. A tire according to any one of the preceding claims, comprising cutouts (25) comprising transverse grooves axially external to the points (423) located at an axial distance at most equal to 0.3 x LT from the equator plane (P), have a width at most equal to 2 mm.