Hooping Reinforcement for a Tire of a Heavy Duty Civil Engineering Vehicle

Abstract

Improve endurance of tire for heavy-duty vehicle of construction plant type. A hoop reinforcement has an axially continuous first hooping layer and axially discontinuous second hooping layer, first layer has an axial width LF1 at least equal to 25% and at most 75% of axial width LT of working reinforcement, the discontinuous second hooping layer consists of two hooping strips symmetrical with respect to equatorial plane (XZ) of tire, each extends axially from axially interior end as far as axially exterior end over an axial width LF2 which is at least equal to 10% and at most 35% of axial width LF1 of the first hooping layer, and the distributed tension at break TR of each hooping strip defined as the product of number D of reinforcers per mm times the force at break FR of each reinforcer expressed in daN, is at least equal to 100 daN/mm.

Claims

1. A tire for a heavy-duty vehicle of construction plant type, comprising: a crown reinforcement, radially on the inside of a tread and radially on the outside of a carcass reinforcement; the crown reinforcement comprising a protective reinforcement, a working reinforcement and a hoop reinforcement; the protective reinforcement, which is radially outermost in the crown reinforcement, comprising at least one protective layer, the protective layer comprising metal reinforcers that form an angle at least equal to 10° with a circumferential direction (XX′) tangential to the circumference of the tire; the working reinforcement comprising at least two working layers, each working layer comprising metal reinforcers that form an angle at least equal to 15° and at most equal to 45° with the circumferential direction (XX′) and are crossed from one working layer to the next; said working reinforcement having an axial width LT equal to the axial width of the widest working layer; the hoop reinforcement comprising at least two hooping layers, each made up of metal reinforcers that form an angle at most equal to 2.5° with the circumferential direction (XX), and are coated in an elastomeric compound; wherein the hoop reinforcement comprises an axially continuous first hooping layer and an axially discontinuous second hooping layer, in that the first hooping layer has an axial width LF1 at least equal to 25% and at most equal to 75% of the axial width LT of the working reinforcement, in that the discontinuous second hooping layer consists of two hooping strips that are symmetrical with respect to an equatorial plane (XZ) of the tire passing through the middle of the tread and perpendicular to the axis of rotation (YY′) of said tire, in that each hooping strip extends axially from an axially interior end as far as an axially exterior end over an axial width LF2 which is at least equal to 10% and at most equal to 35% of the axial width LF1 of the first hooping layer, and in that the distributed tension at break TR of each hooping strip, defined as being the product of the number D of reinforcers per mm times the force at break FR of each reinforcer expressed in daN, is at least equal to 100 daN/mm.

2. The tire according to claim 1, wherein the hoop reinforcement is positioned radially on the inside of the protective reinforcement.

3. The tire according to claim 1, wherein the first hooping layer is positioned radially on the outside of the radially innermost working layer.

4. The tire according to claim 3, wherein the second hooping layer is positioned radially on the outside of the first hooping layer and in contact therewith.

5. The tire according to claim 3, wherein the second hooping layer is positioned radially on the outside of the second working layer and in contact therewith.

6. The tire according to claim 3, wherein the second hooping layer is positioned radially on the outside of the carcass reinforcement and in contact therewith.

7. The tire according to claim 1, wherein the first hooping layer is made up of a circumferential winding of a ply of metal reinforcers.

8. The tire according to claim 1, wherein each hooping strip of the second hooping layer is made up of a circumferential winding of a ply of metal reinforcers.

9. The tire according to claim 1, wherein the first hooping layer is made up of an axial juxtaposition of contiguous turns of a thin strip, wound circumferentially, said thin strip comprising at least 8 and at most 30 consecutive metal reinforcers which are mutually parallel and coated in an elastomeric compound.

10. The tire according to claim 1, wherein each hooping strip of the second hooping layer is made up of an axial juxtaposition of contiguous turns of a thin strip, wound circumferentially, said thin strip comprising at least 8 and at most 30 consecutive metal reinforcers which are mutually parallel and coated in an elastomeric compound.

Description

[0085] The invention is illustrated in FIGS. 1 to 8, which are not shown to scale for the sake of understanding.

[0086] FIG. 1 shows a meridian section through the crown of a tire 1 according to the invention, comprising: [0087] A carcass reinforcement 40 made up of a single carcass layer, the reinforcers of which form an angle close to 90°, which is to say comprised between [85°, 95°] with the circumferential direction XX; [0088] A working reinforcement 60 radially on the outside of the carcass reinforcement 40 and comprising two working layers 61 and 62. The radially innermost working layer 61 has an axial width LT greater than that of the second working layer 62; [0089] A protective reinforcement 50 radially on the outside of the working reinforcement 60 and radially on the inside of the tread 20 and comprising two protective layers 51 and 52; [0090] A hoop reinforcement 70 comprising a continuous first layer 71 extending over an axial width LF1, and a discontinuous second layer formed of two strips 721 and 722, each having an axial width LF2. In the case depicted, the hoop reinforcement 70 is positioned radially between the two working layers (61, 62); [0091] A tread 20; [0092] The working 60, protective 50 and hoop 70 reinforcements constituting the crown reinforcement 30.

[0093] FIG. 2 depicts a perspective view of the hoop reinforcement 70 that forms the subject of the invention, with a continuous first hooping layer 71, and a discontinuous second hooping layer made up of two strips 721, 722 which are symmetrical about an equatorial plane passing through the centre of the tire.

[0094] FIG. 3 shows a meridian section through the crown of a tire according to the invention, marking the characteristic dimensions of the invention: [0095] The axial width LF1 is the measurement of the axial width of the first hooping layer. Said axial width is expressed as a proportion of that of the first working layer LT (not depicted); [0096] The second hooping layer comprising two hooping strips 721 and 722 which are symmetrical about the equatorial plane, the strip 721 (and respectively 722) having an axially exterior first end E721 (and respectively E722) and an axially interior second end I721 (and respectively I722), the axial width of the hooping strip LF2 is the axial distance between the ends E721 and I721. The axial width DF2 measures the distance between the respective axially interior ends I721 and I722 of the two hooping strips 71 and 72 and therefore the axial width of the discontinuity.

[0097] FIG. 4 depicts a meridian section through the crown of a tire according to the invention according to one embodiment of the invention in which the first hooping layer 71 is radially on the outside of the first working layer 61. The two hooping strips (721; 722) that form the layer 72 are radially on the outside of the second working layer 62.

[0098] FIG. 5 depicts a meridian section through the crown of a tire according to the invention according to another embodiment of the invention in which the two hooping strips (721; 722) are radially on the outside of the carcass reinforcement 40. The hooping layer 71, for its part, is radially on the outside of the first working layer 61.

[0099] FIG. 6 depicts a hooping layer with reinforcers having a diameter Φ, that can vary between 1.9 mm and 3.8 mm, distributed at a spacing P and coated in a coating rubber of thickness h on the back of the upper reinforcer or equal to 0.6 mm.

[0100] A hooping layer of the crown reinforcement of the tire is obtained either by the circumferential winding of a ply as depicted in FIG. 6, or as an axial juxtaposition of contiguous turns of a thin strip, wound circumferentially, said thin strip comprising at least 8 and at most 30 consecutive metal reinforcers which are mutually parallel and coated in an elastomeric compound.

[0101] FIG. 7 depicts a thin strip 8 as described previously, comprising 8 consecutive metal reinforcers that are mutually parallel and coated in an elastomeric compound.

[0102] The width L8 of the thin strip depends on the diameter Φ of a reinforcer and on the spacing P between two consecutive reinforcers. Typically, the width L8 is defined for a number of reinforcers ranging from 8 to 30, with a spacing P that can range from 2.5 mm to 4.4 mm. The width L8 of the thin strip can range from 35 to 252 mm.

[0103] FIG. 8 depicts one reinforcer of the hooping layer. Said reinforcer is a collection of 4 strands 100, each one made up of an internal layer 110 of 3 threads and of an external layer 120 of 8 threads.

[0104] The invention was implemented on a 59/80R63 sized tire for a heavy-duty vehicle of construction plant type. The tire according to the invention differs from the reference tire in terms of the hoop reinforcement. For the reference tire, the hoop reinforcement is obtained by the circumferential winding of a ply radially on the outside of the first working layer 61, extending from a circumferential first end as far as a circumferential second end, so as to form a radial stack of at least two hooping layers. For the invention, the tire is manufactured in accordance with FIG. 1, in which the second hooping layer is formed of the two hooping strips 721 and 722, as depicted in FIG. 2. The axially interior ends of the two hooping strips are distant by a length DF2.

[0105] For the tire size 59/80R63 being studied, the geometric features of the hoop reinforcement are given in Table 1 below:

TABLE-US-00001 TABLE 1 Axial distance Axial width DF2 between LF2 of each the two hooping Axial width LT Axial width LF1 hooping strip of strips of the 2.sup.nd of the 1.sup.st working of the 1.sup.st hooping the 2.sup.nd hooping hooping layer layer (mm) layer (mm) layer (mm) (mm) 1034 520 65 390

[0106] The calculations simulating running of the tire were conducted on the tire size 59/80R63 for a supported load of 104 tonnes, with an inflation pressure of 7 bar. Furthermore, the tire was subjected to a cornering force of 26 tonnes.

[0107] The results of the finite-element calculations show that the shear deformations in the meridian and circumferential planes are of the same order of magnitude for the reference tire and the tire of the invention:

TABLE-US-00002 TABLE 2 Maximum Maximum amplitude of amplitude of shear in the shear in the meridian circumferential plane plane Reference: Tire 0.8 0.27 with both of the two hooping layers continuous across the entire width of the crown Tire of the 0.81 0.27 invention: second hooping layer discontinuous
This result confirms that the absence of hooping at the centre of the tread does not adversely affect the endurance of the tire.

[0108] The tire produced in accordance with the invention has a mass lower than that of the reference tire, as illustrated in the following table:

TABLE-US-00003 TABLE 3 Mass in base 100 Reference: Tire with both 100 of the two hooping layers continuous across the entire width of the crown Tire of the invention: 155 second hooping layer discontinuous

[0109] The mass of the hoop reinforcement is 55% lower than that of the reference tire.

[0110] Eliminating the hooping layer over a distance DF2 of 390 mm has also improved the thermodynamics of the tire. In the equatorial plane that passes through the centre of the tire, above the second protective layer, the temperature has dropped by 5°.