Tire For a Civil Engineering Vehicle, Comprising a Level-Wound Crown Reinforcement with Metal Reinforcements

Abstract

Reinforcers of crown layers (211, 212) of a civil engineering vehicle are made of metal and wound, in the form of a strip (5) of width W, along a circumferential zigzag trajectory following a periodic curve (7), extending over a number N of periods P distributed over a number T of circumferences 2ΠR and satisfying the two relations N*(W/sin A)=2ΠR*t, where 0.6⇐t⇐1, and N*P=2ΠR*T, so as to form a bilayer (21). Additionally, for at least 40% of the strip crossovers (53) axially positioned, relative to the circumferential direction (XX′), at an axial distance L1 equal to not more than 0.25 times the amplitude L of the periodic curve (7), the circular bilayer portion (213), centred on the strip crossover (53) and having a radius R1 equal to twice the width W of a strip (5), comprises Ne outer strip crossovers and Ni inner strip crossovers, such that |Ne-Ni|/(Ne+Ni)⇐0.3.

Claims

1. A tire for a civil engineering vehicle, comprising: a crown reinforcement radially on the inside of a tread and radially on the outside of a carcass reinforcement; the crown reinforcement comprising at least a crown bilayer made up at least partially of two radially superimposed crown layers, each made up of reinforcers coated in an elastomeric material; each crown bilayer being made up of a circumferential zigzag winding of a strip of width W, in a circumferential direction (XX′) of the tire and on a substantially cylindrical surface of revolution positioned at a radial distance R from the axis of rotation (YY′) of the tire; the trajectory of the circumferential zigzag winding being a periodic curve having a period P and an amplitude L; the periodic curve forming, with the circumferential direction (XX′), an angle A measured at the points on the curve positioned in an equatorial plane (XZ) passing through the centre of the tread and perpendicular to the axis of rotation (YY′), the periodic curve extending over a number N of periods P distributed over a number T of circumferences 2ΠR; the trajectory of the circumferential zigzag winding generating strip crossovers between a radially outer portion of strip and a radially inner portion of strip; a strip crossover being outer when the radially outer portion of strip forms a positive angle B with the circumferential direction (XX′) in an axial plane (XY); a strip crossover being inner when the radially outer portion of strip forms a negative angle B with the circumferential direction (XX′) in an axial plane (XY); wherein the crown layer reinforcers are made of metal, the periodic curve of the trajectory of the circumferential zigzag winding satisfies the following relations:
N*(W/sin A)=2ΠR*t, where 0.6⇐t⇐1,
N*P=2ΠR*T, and for at least 40% of the strip crossovers axially positioned, relative to the circumferential direction (XX′), at an axial distance L1 equal to not more than 0.25 times the amplitude L of the periodic curve, the circular bilayer portion centred on the strip crossover and having a radius R1 equal to twice the width W of a strip comprises Ne outer strip crossovers and Ni inner strip crossovers, such that |Ne-Ni|/(Ne+Ni)⇐0.3.

2. The tire according to claim 1, wherein any metal reinforcer has a circular cross section of diameter D, and wherein the width W of the strip is at least equal to D.

3. The tire according to claim 1, wherein the width W of the strip is equal to not more than 0.2 times the amplitude L of the periodic curve.

4. The tire according to claim 1, wherein the periodic curve has extrema and a radius of curvature R′ at its extrema, and wherein the radius of curvature R′ of the periodic curve is at least equal to the amplitude L of the periodic curve.

5. The tire according to claim 1, wherein the periodic curve has extrema and has a radius of curvature R′ at its extrema, and wherein the radius of curvature R′ of the periodic curve is at least equal to 7 times the amplitude L of the periodic curve.

6. The tire according to claim 1, wherein the ratio T/N is at least equal to 0.15 and at most equal to 1.3.

7. The tire according to claim 1, wherein N and T are whole numbers that are prime between each other.

8. The tire according to claim 1, wherein the metal reinforcers of the crown layers are elastic metal reinforcers having a structural elongation As at least equal to 0.5% and a tensile modulus of elasticity of not more than 150 GPa.

9. The tire according to claim 8, wherein the elastic metal reinforcers of the strip are multistrand ropes of structure 1×I comprising a single layer of I strands wound in a helix, each strand comprising an internal layer of J internal threads wound in a helix and an external layer of K external threads wound in a helix around the internal layer.

10. The tire according to claim 1, wherein the crown reinforcement comprises at least two crown bilayers.

Description

[0054] The features of the invention are illustrated by the schematic FIGS. 1 to 9, which are not drawn to scale:

[0055] FIG. 1: Meridian half-section of a crown of a tire for a civil engineering vehicle according to the invention.

[0056] FIG. 2: Perspective view of a circumferential zigzag winding of a strip along a periodic curve on to a cylindrical laying surface.

[0057] FIG. 3: Plan view of the trajectory of the strip at the end of T=1 one winding turn of the strip.

[0058] FIG. 4: Plan view of the trajectory of the strip at the end of T=2 winding turns of the strip.

[0059] FIG. 5: Plan view of the trajectory of the strip at the end of T=28 winding turns of the strip, corresponding to the crown bilayer in its final state.

[0060] FIG. 6: Plan view of the trajectory of the strip at the end of T=28 winding turns of the strip with location of the strip crossovers in a median part.

[0061] FIG. 7: Diagram of an outer strip crossover.

[0062] FIG. 8: Diagram of an inner strip crossover.

[0063] FIG. 9: Principle of counting the inner and outer strip crossovers in the vicinity of a strip crossover.

[0064] FIG. 1 shows a meridian half-section, on a meridian plane YZ, passing through the axis of rotation YY′ of the tire, of a tire 1 for a civil engineering vehicle, comprising a crown reinforcement 2 radially on the inside of a tread 3 and radially on the outside of a carcass reinforcement 4. The crown reinforcement 2 comprises a crown bilayer 21 made up at least partially of two radially superposed crown layers (211, 212) and produced by the circumferential zigzag winding of a strip of width W onto a cylindrical laying surface of radius R (not shown), having as its axis of revolution the axis of rotation YY′ of the tire. In the embodiment shown, the crown bilayer 21 is a working bilayer, radially on the inside of a protective reinforcement 22 consisting of two protection layers. In the meridian plane YZ, each crown layer (211, 212) is made up of an axial juxtaposition of strip portions 5 of width W/cos A, where W is the width (not shown) of the strip 5, measured perpendicularly to the mid-line of the strip 5, and A is the angle (not shown) formed by the mid-line of the strip 5 with the circumferential direction XX′ in the equatorial plane XZ.

[0065] FIG. 2 is a perspective view of a circumferential zigzag winding of a strip 5 of width W, along a periodic curve 7, on to a cylindrical laying surface 6 which is a surface of revolution about the axis of rotation YY′ of the tire and has a radius R. This circumferential zigzag winding of a strip 5 forms a crown bilayer.

[0066] FIG. 3 is a plan view of the trajectory of the strip at the end of T=1 one winding turn of the strip, or, more precisely, of the middle fibre of the strip, the width of the strip not being shown, in order to improve the readability of the figure. This plan view, in a plane XY, corresponds to the developed surface of the cylindrical laying surface, having a length equal to the circumference C=2ΠR, where R is the radius of the cylindrical laying surface, and a width equal to the amplitude L of the periodic curve 7. The trajectory of the circumferential zigzag winding is a periodic curve 7 having a period P and an amplitude L. The periodic curve 7 forms, with the circumferential direction XX′, an angle A measured at the points on the curve positioned in an equatorial plane XZ passing through the centre of the tread and perpendicular to the axis of rotation YY′. The periodic curve 7 has extrema (71, 72) and has a radius of curvature R′ at its extrema (71, 72). In the embodiment shown, when the choices of the angle A and the radius of curvature R′ have been made, the period of the periodic curve 7 extends over 2.2 periods P, over one winding turn.

[0067] FIG. 4 is a plan view of the trajectory of the strip at the end of T=2 winding turns of the strip. In the embodiment shown, the periodic curve 7, in the second winding turn, crosses the trajectory of the 1.sup.st winding turn at 5 points, thus creating 5 strip crossovers 53.

[0068] FIG. 5 is a plan view of the trajectory of the strip at the end of T=28 winding turns of the strip, corresponding to the crown bilayer in its final state. In the embodiment shown, the crown bilayer is in its final state when the curve 7 extends over a number N=61 of periods P distributed over a number T=28 of circumferences 2ΠR.

[0069] FIG. 6 is a plan view of the trajectory of the strip at the end of T=28 winding turns of the strip, corresponding to the crown bilayer in its final state, showing an example of a circular portion of bilayer 213, centred on a strip crossover 53, positioned at the axial distance L1, and having a radius R1 equal to twice the strip width W. This circular portion of bilayer 213 is a reference element on which are determined the number Ne of outer strip crossovers and the number Ni of inner strip crossovers in the vicinity of the strip crossover 53.

[0070] FIG. 7 is a diagram of an outer strip crossover 53 between a radially outer strip 51 and a radially inner strip 52. In the case of an outer strip crossover, the radially outer portion of strip 51 forms a positive angle B with the circumferential direction XX′ in an axial plane XY. An axial plane XY is an oriented plane, defined by a first circumferential direction XX′, tangential to the surface of revolution and oriented in the running direction of the tire, and a second axial direction YY′, parallel to the axis of rotation of the tire: it is therefore a plane tangential to the surface of revolution.

[0071] FIG. 8 is a diagram of an inner strip crossover 53 between a radially outer strip 51 and a radially inner strip 52. In the case of an inner strip crossover, the radially outer portion of strip 51 forms a negative angle B with the circumferential direction XX′ in an axial plane XY.

[0072] FIG. 9 shows schematically the principle of counting the inner and outer strip crossovers in the vicinity of a strip crossover, the latter being inner in the case shown. For each strip crossover 53 axially positioned, relative to the circumferential direction XX′, at an axial distance L1 equal to not more than 0.25 times the amplitude L of the periodic curve 7 (see FIG. 6), a circular bilayer portion 213, centred on the strip crossover 53 and having a radius equal to twice the width W of a strip 5, is defined. The respective numbers of outer strip crossovers Ne and inner strip crossovers Ni contained in said circular portion are then counted. It should be noted that the strip crossover 53, being inner in the case shown, is included in Ni. The parameters of the periodic zigzag winding are then optimized so that, for at least 40% of the selected strip crossovers, regardless of whether they are inner or outer, the following condition is satisfied: |Ne-Ni|/(Ne+Ni)⇐0.3. This condition ensures that the numbers of outer strip crossovers Ne and inner strip crossovers Ni, respectively, are similar, this criterion being, according to the inventors, characteristic of a uniform distribution of the inner and outer strip crossovers, resulting in uniform mechanical functioning of the crown bilayer.

[0073] The inventors have defined an optimized crown bilayer with level winding, as defined in the invention, for a tire for a civil engineering vehicle of the 24.00R35 size.

[0074] The tire under examination comprises a crown reinforcement made up of two crown bilayers, for which each of the crown layers is made up of elastic metal reinforcers of the multistrand rope type.

[0075] The structure of these multistrand ropes is of the 1×I type, comprising a single layer of I strands wound in a helix, each strand comprising an internal layer of J internal threads wound in a helix and an external layer of K external threads wound in a helix around the internal layer. In the example examined, the multistrand ropes used have a structure of 52.26=4*(5+8)*26; that is to say they are made up of I=4 strands, each strand comprising an internal layer of J=5 internal threads and an external layer of K=8 external threads wound in a helix around the internal layer, the threads having a cross section with a diameter d=0.26 mm. These reinforcers have a diameter D equal to 3.1 mm, a tensile elastic modulus E equal to 70 GPa, and a structural elongation As equal to 0.7%, and are distributed axially with an axial interval of 5 mm.

[0076] Table 1 below summarizes the properties of the multistrand elastic ropes tested:

TABLE-US-00001 TABLE 1 Type of reinforcer Rope 52.26 Diameter D of the reinforcer 3.1 mm Number I of strands 4 Number J of internal layer threads 4 Number K of external layer threads 9 Tensile modulus of elasticity 70 GPa Structural elongation As 0.7%

[0077] The crown bilayer is made up of a circumferential zigzag winding of a strip of width W equal to 35 mm, in a circumferential direction XX′ of the tire and on a substantially cylindrical surface of revolution positioned at a radial distance R equal to 985 mm from the axis of rotation YY′ of the tire, this radial distance R being measured in an equatorial plane XZ passing through the middle of the tread and perpendicular to the axis of rotation YY′. The trajectory of the circumferential zigzag winding is a periodic curve having a period P equal to 2841 mm and an amplitude L equal to 400 mm. The periodic curve forms, with the circumferential direction XX′, an angle A equal to 24°, measured at the points on the curve positioned in the equatorial plane XZ. The periodic curve extends over a number N, equal to 61, of periods P distributed over a number T, equal to 28, of circumferences 2ΠR. The periodic curve of the trajectory of the circumferential zigzag winding satisfies the following relations: N*(W/sin A)=2ΠR*t=5.3 m where t=0.85, and N*P=2ΠR*T=173.3 m.

[0078] Table 2 below summarizes the properties of the periodic curve of the circumferential zigzag winding of the strip forming the crown bilayer:

TABLE-US-00002 TABLE 2 Size 24.00R35 Radius R of the cylindrical surface at the centre 985 mm Width W of strip 35 mm Angle at the centre A of the periodic curve 24° Radius of curvature R′ at the extrema 995 mm Period P of the periodic curve 2841 mm Amplitude L of the periodic curve 400 mm Number N of periods P 61 Number T of winding turns 28 Ratio T/N 0.46 Rate of overlap t of the level winding 0.85

[0079] The inventors have found that, for 58% of the strip crossovers axially positioned, relative to the circumferential direction XX′, at an axial distance L1 equal to not more than 100 mm (=0.25*L), the circular bilayer portion centred on the strip crossover and having a radius R1 equal to 70 mm (=2*W) comprises Ne outer strip crossovers and Ni inner strip crossovers, such that |Ne-Ni|/(Ne+Ni)⇐0.3.

[0080] This invention, devised in the field of tires for civil engineering vehicles, may be applied to any tire comprising a crown reinforcement comprising at least two metallic crown layers, such as a tire for a heavy goods vehicle, for example.