Tire With Greater Resistance To Unseating

Abstract

Resistance to unseating of a tire operating at low pressure is achieved by a tire comprising at least one bead having an axial width at the seat D comprising at least one main circumferential reinforcing element (22) of which the radially innermost point (222) is at a radial distance Z and at an axial distance Y from the radially innermost point (211) of the bead, and such that Y/D is at least equal to 0.5 and Z/D is at most equal to 0.4. This same bead comprises at least one bead layer (23) surrounding the bead filler rubber (21) and such that its axially outermost end (231) is radially on the outside of the end (311) of the carcass layer (31) and it also comprises at least one additional circumferential reinforcing element (24), radially on the inside of the radially outermost point (223) of the main circumferential reinforcing element (22).

Claims

1. A tire to be mounted on a mounting rim, comprising: two beads, which are adapted to come into contact with the mounting rim; each bead having a radially innermost point, an axial width at seat D, and an external face comprised of the surface of the tire in contact with the outside of the tire and belonging to the bead, and each bead comprising at least one bead filler comprised of at least one rubber composition and of at least one circumferential reinforcing element referred to as the main circumferential reinforcing element; the meridian section of the main circumferential reinforcing element having a radially innermost point, a radially outermost point and an axially innermost point, the radially innermost point being positioned at a radial distance Z and at an axial distance Y from the radially innermost point of the bead; the axial width at the seat D being measured between the radially innermost point of the bead and the point of intersection between a first straight line tangential to the external axial projection of the radially innermost point of the main circumferential reinforcing element and a second straight line tangential to the internal radial projection of the axially outermost point of the main circumferential reinforcing element; a carcass reinforcement connecting the two beads and comprising at least one carcass layer extending in each bead radially towards the inside as far as a carcass layer end; for at least one said bead, the carcass layer end is radially on the inside of the point of greatest axial width (SM) of the tire and axially on the outside of the axially innermost point of the main circumferential reinforcing element, wherein, for said bead, the ratio Y/D between the axial distance Y from the radially innermost point of the main circumferential reinforcing element to the radially innermost point of the bead, and the axial width of the bead at the seat D, is at least equal to 0.5, wherein, for said bead, the ratio Z/D between the radial distance Z from the radially innermost point of the main circumferential reinforcing element to the radially innermost point of the bead, and the axial width of the bead at the seat D, is at most equal to 0.4, wherein, said bead comprises a bead reinforcement, comprised of at least one bead layer, which surrounds the bead filler in such a way that the axially outermost end of the bead layer is radially on the outside of the radially innermost end of the carcass layer and such that the axially innermost end of the bead layer is at least radially on the outside of the radially innermost point of the main circumferential reinforcing element, wherein, for said bead, the points on the bead reinforcement which are positioned radially on the inside of the radially innermost point of the main circumferential reinforcing element are positioned, with respect to the external face of the bead, at a maximum distance that represents at most Z/2, half the radial distance Z between the radially innermost point of the bead and the radially innermost point of the main circumferential reinforcing element, and wherein, said bead comprises at least one additional circumferential reinforcing element, axially on the inside of the axially innermost point of the main circumferential reinforcing element, radially on the outside of a radially innermost part of the bead reinforcement and radially on the inside of the radially outermost point of the main circumferential reinforcing element.

2. The tire according to claim 1, wherein the ratio Y/D between the axial distance Y from the radially innermost point of the main circumferential reinforcing element to the radially innermost point of the bead, and the axial width of the bead at the seat D is at most equal to 0.75.

3. The tire according to claim 1, wherein the ratio Z/D between the radial distance Z from the radially innermost point of the main circumferential reinforcing element to the radially innermost point of the bead, and the axial width of the bead at the seat D is at least equal to 0.25.

4. The tire according to claim 1, wherein the axially outermost end of the bead layer is radially on the outside of the radially innermost end of the carcass layer by a difference in radius at least equal to 10 mm.

5. The tire according to claim 1, wherein the end of the carcass layer that is radially innermost is radially on the outside of the radially outermost point of the main circumferential reinforcing element.

6. The tire according to claim 1, wherein the end of the axially outermost bead layer is axially on the outside of the end of the radially innermost carcass layer.

7. The tire according to claim 1, wherein the end of the axially outermost bead layer is axially on the inside of the end of the radially innermost carcass layer.

8. The tire according to claim 1, wherein the reinforcing elements of a bead layer are comprised of textile, preferably of aliphatic polyamide, of aromatic polyamide, of a combination of aliphatic polyamide and of aromatic polyamide, of polyethylene terephthalate or of rayon.

9. The tire according to claim 1, wherein the reinforcing elements of a carcass layer are comprised of metal or of textile, preferably of aliphatic polyamide, of aromatic polyamide, of a combination of aliphatic polyamide and of aromatic polyamide, of polyethylene terephthalate or of rayon.

10. The tire according to claim 1, wherein the reinforcing elements of a carcass layer are parallel to one another and make with the circumferential direction an angle of between 65 and 115.

11. The tire according to claim 1, wherein the reinforcing elements of a bead layer are parallel to one another and make with the circumferential direction an angle of between 20 and 160.

12. The tire according to claim 1, wherein the at least one additional circumferential reinforcing element comprises at least one textile material, preferably an aliphatic polyamide, an aromatic polyamide, a polyester or a rayon.

13. The tire according to claim 1, wherein, for said bead, the bead filler portion, at least radially on the inside of the radially innermost point of the main circumferential reinforcing element, has an elastic modulus at 10% elongation E21 at least equal to 15 MPa.

14. The tire according to claim 1, wherein the bead filler portion radially on the outside of the radially outermost point of the main circumferential reinforcing element has an elastic modulus at 10% elongation E212 less than 0.5 times the elastic modulus at 10% elongation E21 of the bead filler portion at least radially on the inside of the radially innermost point of the main circumferential reinforcing element.

15. The tire according to claim 1, wherein the bead filler portion axially on the outside of the radially outermost point of the main circumferential reinforcing element has an elastic modulus at 10% elongation E213 less than 0.5 times the elastic modulus at 10% elongation E21 of the bead filler portion at least radially on the inside of the radially innermost point of the main circumferential reinforcing element.

16. A mounted assembly comprising a tire according to claim 1, and a wheel possessing at least one hump the height of which is at least equal to 1 mm.

17. The tire according to claim 1, wherein the axially outermost end of the bead layer is radially on the outside of the radially innermost end of the carcass layer by a difference in radius at least equal to 20 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0073] The features and other advantages of the invention will be better understood with the aid of FIGS. 1 to 12, the said figures not being drawn to scale but in simplified form, in order to make the invention easier to understand:

[0074] FIG. 1 depicts a tire according to the prior art.

[0075] FIG. 2 illustrates the terms inboard edge and outboard edge of a tread.

[0076] FIGS. 3 to 8 depict the movement of the sidewall of a tire as a function of the load applied to the tire sidewall during an unseating test.

[0077] FIG. 9 depicts a meridian section through the bead and sidewall according to the invention. FIG. 9 notably illustrates the distances Y and Z and the axial width of the bead at the seat D.

[0078] FIGS. 10 and 11 depict a meridian section of the bead and of the sidewall according to the invention, and preferred distributions of different bead filler rubbers.

[0079] FIG. 12 depicts the movements of the sidewall of a tire as a function of the load applied to the sidewall during an unseating test.

DETAILED DESCRIPTION OF THE DRAWINGS

[0080] FIG. 1 schematically depicts a tire 1 according to the prior art. The tire 1 comprises a crown 4 comprising a crown reinforcement (not visible in the figure) surmounted by a tread 7, two sidewalls 3 extending the crown radially inwards, and two beads 2 radially on the inside of the sidewalls 3.

[0081] FIG. 2 schematically depicts tires intended to be mounted on mounting rims of wheels of a vehicle 200 and having a set direction of mounting on the vehicle. It comprises an outboard axial edge 45 and an inboard axial edge 46, the inboard axial edge 46 being the edge intended to be mounted on the side of the body shell of the vehicle when the tire is mounted on the vehicle according to the said predetermined direction of mounting and the reverse in the case of the outboard axial edge 45. In the document the outboard side refers to the outboard axial edge 45.

[0082] The graph depicted in FIG. 5 shows the result of a numerical simulation of an unseating test in accordance with Chinese standard GB/T 4502-2009. A conical form is applied against the sidewall of the tire. This conical form advances at a set rate. The load ET required to make the conical form advance at this rate is plotted as a function of the movement DT of the conical form.

[0083] The initial situation of the tire 1 (only the bead and part of the sidewall of which have been depicted) on its mounting rim 5 is depicted in FIG. 3.

[0084] As the conical form moves, the resistance of the tire is manifested in the near-linear increase in the load ET. The bead begins to move up to the point at which it begins to tilt. This is the situation depicted in FIG. 4. This tilting causes a drop in the load required to cause the conical form to advance, until the bead has completely tilted, as is depicted in FIG. 8. The load then increases again because now the bead has to be made to rise over the hump 6 of the mounting rim 5, as illustrated in FIG. 7. It is only when the bead has overcome the hump 6 (situation depicted in FIG. 6) that unseating is complete.

[0085] FIG. 9 schematically depicts the meridian cross section of a bead 2 and of part of the sidewall 3 according to the invention. The tire 1 comprises two beads 2 intended to come into contact with a mounting rim (not depicted). At least the bead 2 and the sidewall 3 positioned on the outboard side (cf. FIG. 2) comprise:

[0086] a main circumferential reinforcing element 22 of which the radially innermost point 222 is placed a radial distance Z away from the radially innermost point 211 of the tire and an axial distance Y away from this same point,

[0087] a carcass reinforcement comprising at least one carcass layer 31 of which the end 311 is situated, for this version of the invention, radially on the outside of the radially outermost point 223 of the main circumferential reinforcing element 22 and radially on the inside of the point 301 of greatest width of the tire. The end 311 of the carcass layer is also axially on the outside of the axially innermost point 224 of the main circumferential reinforcing element,

[0088] a bead reinforcement comprising at least one bead layer 23 of which the axially outermost end 231 is radially on the outside of the end 311 of the carcass layer 31 and of which the axially innermost end 232 is radially on the outside of the radially innermost point 222 of the main circumferential reinforcing element,

[0089] an additional circumferential reinforcing element 24 made up of several circumferentially wound threads of which at least one thread is axially on the inside of the axially innermost point 224 of the main circumferential reinforcing element 22, radially on the outside of a radially innermost part of the bead reinforcement and radially on the inside of the radially outermost point 223 of the main circumferential reinforcing element 22,

[0090] the axially outermost point 225 of the main circumferential reinforcing element 22 and its interior radial projection 226 onto the external face of the tire and the tangent T226 to the external face of the tire at this point 226 or seat of the bead,

[0091] the radially innermost point 222 of the main circumferential reinforcing element 22 and its external axial projection 227 onto the external face of the tire and the tangent T227 to the external face of the tire at this point 227 or side of the bead,

[0092] the intersection of these 2 tangents T226 and T227 at the point 228, the point at which the seat and the side of the bead meet,

[0093] the axial width of the bead at the seat D, equal to the axial distance between the radially innermost point 211 and the point 228 at which the seat and the side of the bead meet.

[0094] The bead 2 depicted in FIG. 9 further comprises a portion intended to come into contact with the mounting rim (not depicted).

[0095] FIGS. 10 and 11 illustrate the various preferred configurations of the portions of bead filler. In FIGS. 10 and 11, the bead filler portion 21 is at least radially on the inside of the radially innermost point 222 of the main circumferential reinforcing element 22. In FIG. 10, the bead filler portion 212 is radially on the outside of the radially outermost point 223 of the main circumferential reinforcing element. In FIG. 11, the bead filler portion 213 is axially on the outside of the radially outermost point 223 of the main circumferential reinforcing element 22. FIG. 11 also illustrates the possibility of the bead layer 23 being axially on the outside of the carcass layer 31 in the region of the zone of overlap, and at the end 311 of the carcass layer being radially on the inside of the radially innermost point 222 of the main circumferential reinforcing element 22. FIG. 11 also shows a few points 229 belonging to the external face of the bead. This figure also shows an example of a point 26 of the bead reinforcement, which points are positioned radially on the inside of the radially innermost point 222 of the main circumferential reinforcing element 22, positioned, with respect to the external face of the bead, at a maximum distance 25 at most equal to Z/2, half the radial distance Z between the radially innermost point of the bead 211 and the radially innermost point of the main circumferential reinforcing element 222.

[0096] FIG. 12 depicts the force ET, expressed in daN, required to cause the conical form of the unseating test in accordance with Chinese standard GB/T 4502-2009 to advance as a function of the displacement DT of the conical form, expressed in mm. The test results: [0097] of a tire A according to the prior art, inflated to a pressure of 0.7 bar, indicated by a continuous line; [0098] of a tire B, according to the invention, but without an additional circumferential reinforcing element, inflated to a pressure of 0.7 bar, indicated by a double continuous line; [0099] of a tire C according to the invention, comprising additional circumferential reinforcing elements made of polyethylene terephthalate (PET), inflated to a pressure of 0.7 bar, indicated by a discontinuous line; [0100] of a tire D according to the invention, comprising hybrid additional circumferential reinforcing elements made of aromatic polyamide (aramid) and of aliphatic polyamide (nylon), inflated to a pressure of 0.7 bar, indicated by a chain line made up of alternating dashes and dots; [0101] of a tire E according to the invention comprising hybrid additional circumferential reinforcing elements made of aromatic polyamide (aramid) and of aliphatic polyamide (nylon), inflated to a pressure of 0 bar, indicated by a dotted line;
are depicted.

[0102] The improvement afforded by an embodiment of the invention for causing unseating, is measured in terms of force between the maximum on the ordinate axis of the curve corresponding to the tire according to the prior art and the maximum on the curve corresponding to an embodiment of the invention considered. The improvement afforded is measured in terms of the displacement between the abscissa values for these two maxima.

[0103] The inventors carried out the invention for a tire of size 335/30_ZR_18, having a carcass reinforcement made up of two carcass layers of polyester making an angle of +/85 with the circumferential direction, a bead layer made of aramid making an angle of 55 with the circumferential direction, a main circumferential reinforcing element made up of braided metal cords with a cross section of 17 mm.sup.2, the elastic modulus at 10% elongation of the bead filler 21 is equal to 54 MPa and that of the bead filler 213 to 23 MPa. The positioning of the main circumferential reinforcing element is such that Y=10 mm, Z=6.7 mm, D=17.7 mm, Y/D=0.56, Z/D=0.38. The length of overlap between the carcass layer and the bead layer varies from 20 to 25 mm; the radial position of the end 311 of the radially innermost carcass layer is equal to the radial position of the radially outermost point 223 of the main circumferential reinforcing element 22, the mean thickness of the protective rubber of the bead toe is 1.5 mm. The inventors carried out two alternative forms of the invention, using this geometry to which they added an additional circumferential reinforcing element made up of:

[0104] either 40 turns of a reinforcer consisting of two strands of polyethylene terephthalate with a thread count of 140 dTex, laid in such a way that the diameter of the radially innermost turn of the reinforcer of the tire mounted on the rim was at least 4% greater than its laying diameter during manufacture, the purpose of this being to create an additional clamping force clamping the tire on to the rim,

[0105] or 40 turns of a hybrid reinforcer consisting of two strands of aromatic polyamide (aramid) with a thread count of 167 dTex, and of one strand of aliphatic polyamide (nylon) with a thread count of 140 dTex laid in such a way that the diameter of the radially innermost turn of the reinforcer of the tire mounted on the rim was at least 2% greater than its laying diameter during manufacture, the purpose of this being to create an additional clamping force clamping the tire on to the rim.

[0106] These solutions are compared against a tire according to the prior art, of size 335/30_ZR_18, having a carcass reinforcement made up of two polyester carcass layers making an angle of +/85 with the circumferential direction, a circumferential reinforcing element of braided metal cords of cross section 17 mm2, a bead filler the elastic modulus of which is equal to 23 MPa, and a bead toe of which the elastic modulus at 10% elongation is equal to 23 MPa; the positioning of the main circumferential reinforcing element being such that Y=7 mm, Z=8 mm, D16 mm, Y/D=0.43, Z/D=0.5.

[0107] In order to measure the impact that the presence of the additional circumferential reinforcing element has, the inventors created a tire according to the invention but without the additional circumferential reinforcing element. In this manufacture, the positioning of the main circumferential reinforcing element is such that Y=7.8 mm, Z=4.5 mm, D14.6 mm, Y/D=0.53, Z/D=0.31.

[0108] The test method is similar to the one recommended in Chinese standard GB/T 4502-2009. The test is carried out under a pressure of 0.7 bar. The wheel used is a wheel in accordance with the ETRTO standard, with a hump measuring 1.5 mm in height.

[0109] The tire, depicted by curve B in FIG. 12, according to the invention but without the presence of an additional circumferential reinforcing element allows an 18% improvement on the displacement and a 19% improvement on the unseating force needed for a tire according to the prior art, represented by curve A in FIG. 12, when the pressure needed to overcome the hump of the rim during fitting is reduced by 50%, thus demonstrating that the ease of fitting is not only maintained but also improved.

[0110] The two productions of tire according to the invention, represented by curves C and D in FIG. 12, do not unseat at the limits of the test machine used, and this represents an at least 50% improvement on the displacement and an at least 100% improvement on the force as compared with a tire of the prior art (curve A in FIG. 12) when the pressure needed to overcome the rim hump during fitting is reduced by 30 to 20%, thus demonstrating that the ease of fitting is not only maintained but also improved.

[0111] The tire according to the invention, comprising an additional circumferential reinforcing element made up of 40 hybrid threads containing an aromatic polyamide (aramid) and an aliphatic polyamide (nylon) was also tested at a pressure of 0 bar (curve E depicted by dotted line in FIG. 12). The test went to the limit of displacement of the machine without the tire unseating from the wheel. This last test demonstrates the unseating improvements afforded by the invention not only at low pressure but also for a tire at zero pressure.