TIRE WITH OPTIMIZED CROWN AND TREAD

Abstract

Tires comprising a hoop reinforcement (5) and 2 crossed working layers (41, 42) in which the breaking strength R.sub.C of each working layer (41, 42) is at least equal to 30 000 N/dm have improved endurance. The working layers comprise reinforcing elements made up of individual metal threads or monofilaments having a cross section at least equal to 0.20 mm and at most equal to 0.5 mm. The density of reinforcing elements in each working layer is at least equal to 100 threads per dm and at most equal to 200 threads per dm. The tire also comprises axially exterior cuts (25). At least one of the two axially exterior portions of the tread comprises a rubbery material having a Shore hardness at least equal to 48 and at most equal to 60.

Claims

1.-14. (canceled)

15. A tire for a passenger vehicle, the tire comprising: a tread intended to come into contact with the ground via a tread surface and having an axial width LT, the tread comprising two axially exterior portions, each having an axial width at most equal to 0.3 times the axial width LT, comprising at least one rubbery material intended to come into contact with the ground during running, at least one axially exterior portion comprising axially exterior cuts, an axially exterior cut forming a space opening onto the tread surface and being delimited by at least two main lateral faces connected by a bottom face, and the axially exterior cuts having a depth defined by the maximum radial distance between the tread surface and the bottom face; and a crown reinforcement radially on the inside of the tread, the crown reinforcement comprising a working reinforcement and a hoop reinforcement, the working reinforcement being made up of two working layers, each comprising reinforcing elements which are coated in an elastomeric material, mutually parallel and respectively form, with a circumferential direction of the tire, an oriented angle at least equal to 20 and at most equal to 50, in terms of absolute value, and of opposite sign from one layer to the next, the reinforcing elements in each ply being made up of individual metal threads or monofilaments having a cross-section the smallest dimension of which is at least equal to 0.20 mm and at most equal to 0.5 mm, and a breaking strength Rm, the density of reinforcing elements in each working layer being at least equal to 100 threads per dm and at most equal to 200 threads per dm, and the hoop reinforcement comprising at least one hooping layer comprising reinforcing elements which are mutually parallel and form, with the circumferential direction of the tire, an angle at most equal to 10, in terms of absolute value, wherein the breaking strength R.sub.C of each working layer is at least equal to 30,000 N/dm, Rc being defined by: Rc=Rm*S*d, where Rm is the tensile breaking strength of the monofilaments in MPa, S is the cross-sectional area of the monofilaments in mm.sup.2 and d is the density of monofilaments in the working layer considered, in number of monofilaments per dm, and wherein, in at least one of the two axially exterior portions, the at least one rubbery material intended to be in contact with the ground during running has a Shore hardness at least equal to 48 and at most equal to 60.

16. The tire according to claim 15, wherein the at least one rubbery material, in at least one of the two axially exterior portions and intended to be in contact with the ground during running, has a dynamic property tan(d)max measured at 23 C. at least equal to 0.12 and at most equal to 0.30.

17. The tire according to claim 15, wherein the depth of the axially exterior cuts is at least equal to 5 mm and are spaced apart, in the circumferential direction of the tire, by a circumferential spacing at least equal to 4 mm.

18. The tire according to claim 15, wherein the axially exterior cuts are spaced apart, in the circumferential direction of the tire, by a circumferential spacing at most equal to 50 mm.

19. The tire according to claim 15, wherein the depth of the axially exterior cuts is at most equal to 8 mm.

20. The tire according to claim 15, wherein a radial distance between the bottom face of the axially exterior cuts and the crown reinforcement is at least equal to 1 mm.

21. The tire according to claim 15, wherein a radial distance between the bottom face of the axially exterior cuts and the crown reinforcement is at most equal to 3.5 mm.

22. The tire according to any claim 15, wherein the axial width of each of the two axially exterior portions of the tread are at most equal to 0.2 times the axial width LT.

23. The tire according to claim 15, wherein each working layer comprises reinforcing elements made up of individual metal threads or monofilaments having a diameter at least equal to 0.3 mm and at most equal to 0.37 mm.

24. The tire according to claim 15, wherein each working layer comprises reinforcing elements which form, with the circumferential direction of the tire, an angle at least equal to 22 and at most equal to 35.

25. The tire according to claim 15, wherein the density of the reinforcing elements in each working layer is at least equal to 120 threads per dm and at most equal to 180 threads per dm.

26. The tire according to claim 15, wherein the reinforcing elements of the working layers are made of steel.

27. The tire according to claim 26, wherein the steel is carbon steel.

28. The tire according to claim 15, wherein the reinforcing elements of the at least one hooping layer are made of textile.

29. The tire according to claim 28, wherein the textile is selected from the group consisting of aliphatic polyamide, aromatic polyamide, combination of aliphatic polyamide and aromatic polyamide, polyethylene terephthalate and rayon type.

30. The tire according to claim 15, wherein the hoop reinforcement is radially on the outside of the working reinforcement.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0072] The features and other advantages of the invention will be understood better with the aid of FIGS. 1 to 3, the said figures being drawn not to scale but in a simplified manner so as to make it easier to understand the invention:

[0073] FIG. 1 is a perspective view depicting part of the tyre according to the invention, particularly its architecture and its tread.

[0074] FIG. 2 depicts the meridian section through the crown and illustrates the axially exterior parts 22 and 23 of the tread, and the width thereof.

[0075] FIGS. 3A and 3B depict two types of radially exterior meridian profile of the tread of a passenger vehicle tyre.

DETAILED DESCRIPTION OF THE DRAWINGS

[0076] FIG. 1 depicts part of the crown of a tyre. The tyre comprises a tread 2 which is intended to come into contact with the ground via a tread surface 21. In the axially exterior portions 22 and 23 of the tread, there are major grooves 26, axially exterior cuts including sipes 24 and grooves 25. The tyre further comprises a crown reinforcement 3 comprising a working reinforcement 4 and a hoop reinforcement 5, the working reinforcement comprising 2 working layers 41 and 42. FIG. 1 further depicts double-blind cuts, blind cuts, cuts that open axially externally or internally of simple and complex type, namely having parallel lateral faces or lateral faces with zigzag or sinusoidal portions in the main direction of the cut or in its depth, so as to block certain relative movements of the 2 lateral faces.

[0077] FIG. 1 depicts, in the axially exterior parts 22 and 23 of the tread, only axially exterior grooves that are axial, along the axial axis (YY). In actual fact, this depiction is purely for the sake of convenience for the readability of FIG. 1, it being possible, depending on the target performance, notably in terms of wet grip, for the axially exterior grooves in the treads of passenger vehicles to make an angle of between plus or minus 60 with the axial direction (YY).

[0078] FIG. 2 schematically depicts a meridian section through the crown of the tyre according to the invention. It illustrates in particular the widths LS1 and LS2 of the axially exterior portions 22 and 23 of the tread, and the total width of the tread of the tyre LT. The depth D of an axially exterior cut 24, 25, and the distance D1 between the bottom face 243 of an axially exterior cut 24 and the crown reinforcement 3, measured along a meridian section of the tyre, are also depicted. A meridian section through the tyre is obtained by cutting the tyre on two meridian planes. By way of example, a meridian section of tyre has a thickness in the circumferential direction of around 60 mm at the tread. The measurement is taken with the distance between the two beads being kept identical to that of the tyre mounted on its rim and lightly inflated.

[0079] In FIGS. 3A and 3B, the axial edges 7 of the tread, that make it possible to measure the tread width, are determined. In FIG. 3A, in which the tread surface 21 intersects the outer axial surface of the tyre 8, the axial edge 7 is determined trivially by a person skilled in the art. In FIG. 3B, in which the tread surface 21 is continuous with the outer axial surface of the tyre 8, the tangent to the tread surface at any point on said tread surface in the region of transition towards the sidewall is plotted on a meridian section of the tyre. The first axial edge 7 is the point for which the angle between the said tangent and an axial direction YY is equal to 30. When there are several points for which the angle J between the said tangent and an axial direction is equal to 30, it is the radially outermost point that is adopted. The same approach is used to determine the second axial edge of the tread.

[0080] The inventors have performed calculations on the basis of the invention for a tyre of size 205/55 R16, inflated to a pressure of 2 bar, comprising two working layers comprising steel monofilaments of diameter 0.3 mm, distributed at a density of 158 threads to the dm and forming, with the circumferential direction XX, angles respectively equal to 25 and 25. The monofilaments have a breaking strength R.sub.m equal to 3500 MPa and the working layers each have a breaking strength R.sub.c equal to 39 000 N/dm. The tyre comprises axially exterior cuts on the two axially exterior portions of the tread of the tyre that have an axial width equal to 0.21 times the axial width of the tread. The radial distance D1 between the bottom face of the axially exterior cuts and the crown reinforcement is at least equal to 2 mm.

[0081] Calculations were performed on various tyres. Tyre A, which does not conform to the invention, comprises grooves of a width equal to 5 mm and of a depth equal to 6.5 mm. The rubbery material of the two axially exterior portions of the tread of this tyre A, which does not conform to the invention, which is intended to be in contact with the ground during running is a material characterized by its high stiffness able to achieve a good compromise between wear and behaviour performance. The properties of this rubbery material are a Shore hardness equal to 67, and a tan () max equal to 0.35.

[0082] Tyre B, according to the invention, is in all respects identical to tyre A except that the rubbery material of the two exterior portions of the tread of this tyre B according to the invention, which material is intended to be in contact with the ground during running, is a material characterized by its low stiffness: The properties of this rubbery material are a Shore hardness equal to 52, and a tan () max equal to 0.17.

[0083] The conditions used for the calculation reproduce the running conditions of a front tyre on the outside of the bend, namely the tyre that is most heavily loaded in a passenger vehicle. Two situations were modelled, representing the conditions experienced by the tyre when the vehicle corners under the lateral acceleration of 0.3 g and of 0.7 g. At 0.3 g of transverse acceleration, the tyre experiences a lateral load (Fy) of 150 daN and a vertical load (Fz) of 568 daN, for a camber angle of 0.68. At 0.7 g of transverse acceleration, the tyre experiences a lateral load (Fy) of 424 daN and a vertical load (Fz) of 701 daN, for a camber angle of 3. The use, in tyre B according to the invention, of a rubbery material, in the two axially exterior portions of the tread, that is intended to come into contact with the ground, makes it possible to reduce the amplitude of the stresses calculated in the most heavily loaded monofilaments by 6.5% for both levels of stress loading as compared with these same stress loadings calculated under the same conditions of stress loading for tyre A.

[0084] Furthermore, the improvement in rolling resistance with the use of the material of the tread of tyre B compared with tyre A is at least equal to 15%.