Pneumatic Tire, Having Working Layers Comprising Monofilaments And A Tire Tread With Grooves

Abstract

Technique to increase the endurance of tires comprising two crossed working layers (41, 42), comprising mutually parallel reinforcing elements forming, with the circumferential direction (XX) of the tire, an angle which is at least equal to 20 and at most equal to 50. The reinforcing elements are made up of individual metal threads or monofilaments having a cross section which is at least equal to 0.20 mm and at most equal to 0.5 mm. The tire also comprises grooves comprising a radially inferior zone Z1 having a radial height h1 equal to D/3, and a radially superior zone Z2 having a radial height h2 equal to 2D/3. These grooves have a mean width W at least equal to 1 mm and a depth D at least equal to 5 mm, and a maximum width W1 of zone 1, at least equal to 2 mm and a width of zone 2 at most equal to 1 mm.

Claims

1. A fire for a passenger vehicle, comprising: a tread adapted 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 and each delimited axially on the inside by a circumferential groove, at least one axially exterior portion comprising axially exterior grooves, an axially exterior groove forming a space opening onto the tread surface and being delimited by at least two faces referred to as main lateral faces connected by a bottom face, at least one axially exterior groove, referred to as major groove, having a mean width W, defined by the mean distance between the two lateral faces, at least equal to 1 mm, a depth D, defined by the maximum radial distance between the tread surface and the bottom face, at least equal to 5 mm, and a curvilinear length L, the axially exterior major grooves each comprising, over a portion of the curvilinear length L, a radially interior zone Z1 having a radial height h1 equal to D/3 and a maximum width W1 that is substantially constant, and a radially exterior zone Z2 having a radial height h2 equal to 2D/3 and a width W2, the tire further comprising a crown reinforcement radially on the inside of the tread, the crown reinforcement comprising a working reinforcement and a hoop reinforcement, the working reinforcement comprising 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, said working layer reinforcing elements being comprised 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, 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 B at most equal to 10, in terms of absolute value, wherein the the axially exterior major grooves of the tread, of depth D, comprise, over at least 30% of their curvilinear length L, a radially interior zone Z1 having a maximum width W1 at least equal to 2 mm and a radially exterior zone Z2 having a width W2 at most equal to 1 mm over a radial height h3 at least equal to D/3, and 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.

2. The tire according to claim 1, wherein the axially exterior major grooves of the tread comprise a radially interior zone Z1 having a width W1 at most equal to 8 mm.

3. The tire according to claim 1, wherein the axially exterior major grooves of the tread comprise a radially exterior zone Z2 having a width W2 at least equal to 0.4 mm.

4. The tire according to claim 1, wherein at least one axially exterior groove opens axially on the outside of the tread.

5. The tire according to claim 1, wherein at least one axially exterior groove opens axially on the inside of a circumferential groove of the tread.

6. The tire according to claim 1, wherein the axially exterior major grooves are spaced apart, in the circumferential direction of the tire, by a circumferential spacing P at least equal to 8 mm.

7. The tire according to claim 1, wherein the axially exterior major grooves are spaced apart, in the circumferential direction of the tire, by a circumferential spacing P at most equal to 50 mm.

8. The tire according to claim 1, wherein the radial distance D1 between the bottom face of the axially exterior grooves and the radially outermost reinforcing elements of the crown reinforcement is at least equal to 1.5 mm.

9. The tire according to claim 1, wherein the radial distance D1 between the bottom face of the axially exterior grooves and the radially outermost reinforcing elements of the crown reinforcement is at most equal to 3.5 mm.

10. The tire according to claim 1, wherein at least an axially exterior portion of the tread comprises sipes having a mean width w at most equal to 1 mm.

11. The tire according to claim 1, wherein the two axially exterior portions of the tread each have an axial width at most equal to 0.2 times the axial width LT.

12. The tire according to claim 1, 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.

13. The tire according to claim 1, wherein each working layer comprises reinforcing elements which form, with a circumferential direction of the tire, an angle the absolute value of which is at least equal to 22 and at most equal to 35.

14. The tire according to claim 1, wherein the density of reinforcing elements in each working layer is at least equal to 120 threads per dm and at most equal to 180 threads per dm.

15. The tire according to claim 1, wherein the reinforcing elements of the working layers are made of steel.

16. The tire according to claim 1, wherein the reinforcing elements of the at least one hooping layer are made of textile, aromatic polyamide or combination of aliphatic polyamide and of aromatic polyamide, polyethylene terephthalate or rayon type.

17. The tire according to claim 1, wherein the hoop reinforcement is radially on the outside of the working reinforcement.

18. The tire according to claim 15, wherein the steel is carbon steel.

19. The tire according to claim 16, wherein the textile is of aliphatic polyamide.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0071] The features and other advantages of the invention will be understood better with the aid of FIGS. 1 to 7, the said figures being drawn not to scale but in a simplified manner so as to make it easier to understand the invention:

[0072] FIG. 1 is a perspective view depicting part of the tire according to the invention, particularly its architecture and its tread.

[0073] FIG. 2 depicts a meridian section through the crown of a tire according to the invention and illustrates the axially exterior parts of the tread.

[0074] FIGS. 3A and 3B depict two types of radially exterior meridian profile of the tread of a passenger vehicle tire.

[0075] FIG. 4 illustrates various embodiments of axially exterior grooves according to the invention.

[0076] FIG. 5A, 5B, 5C illustrate a method for determining the major grooves in the case of a network of grooves.

[0077] FIG. 6 illustrates two types of siping for two examples of the tires A and B described hereinafter.

[0078] FIG. 7 illustrates the respective exterior and interior edges of a tread.

DETAILED DESCRIPTION OF THE DRAWINGS

[0079] FIG. 1 is a perspective view depicting a part of the crown of a tire. The tire comprises a tread 2 which is intended to come into contact with the ground via a tread surface 21. In the axially exterior parts 22 and 23 of the tread there are axially exterior grooves 24. The tire further comprises a crown reinforcement 3 comprising a working reinforcement 4 and a hoop reinforcement 5. The working reinforcement comprises two working layers 41 and 42 each comprising reinforcing elements which are mutually parallel and respectively form, with a circumferential direction (XX) 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.

[0080] FIG. 1 depicts in the axially exterior parts 22 and 23 of the tread, only axially exterior grooves, running along the axial axis (YY). In reality, this depiction is pure convenience for the sake of the readability of FIG. 1, it being possible, depending on the performance aims, particularly in terms of wet grip, for the axially exterior grooves in the treads of passenger vehicles to make with the axial direction (YY) an angle of between plus and minus 60.

[0081] FIG. 2 is a schematic meridian section through the crown of the tire according to the invention. It illustrates in particular the widths LS1 and LS2 of the axially exterior parts 23 and 24 of the tread, and the total width of the tire LT. The depth D of an axially exterior groove 24, and the distance D1 between the bottom face 243 of any groove 24 and the crown reinforcement 3, measured along a meridian section of the tire, are also depicted. A meridian section of the tire is obtained by cutting the tire on two meridian planes. By way of example, a meridian section of tire 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 tire mounted on its rim and lightly inflated.

[0082] FIGS. 3A and 3B, depict the method for determining the axial edges 7 of the tread, that make it possible to measure the tread width. In FIG. 3A, in which the tread surface 21 is secant with the exterior axial surface of the tire 8, the axial edge 7 is determined by a person skilled in the art in a trivial way as being the point of intersection between the two surfaces. In FIG. 3B, in which the tread surface 21 extends the exterior axial surface of the tire 8 in a manner which, mathematically speaking, is continuous and differentiable, the tangent to the tread surface at any point on the said tread surface in the region of transition towards the sidewall is plotted on a radial section of the tire. The first axial edge 7 is the point for which the angle p between the said tangent and an axial direction is equal to 30. When there are several points for which the angle p 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 which is symmetrical with respect to the equatorial plane of the tire.

[0083] FIG. 4 schematically depicts cross sections, substantially perpendicular to the main lateral faces (241, 242) of the axially exterior grooves 24 in a tread 2 according to four different embodiments. The axially exterior grooves 24 comprises a radially interior zone Z1 having a radial height h1 equal to D/3 and a maximum width W1, and a radially exterior zone Z2 having a radial height h2 equal to 2D/3 and a width W2. FIG. 4a illustrates a first embodiment of a groove for which the width W2 of zone 2 is at most equal to 1 mm over a height at least equal to 0.33 D and the width W1 of zone 1 is at least equal to 2 mm. FIG. 4b illustrates a second embodiment of a groove for which the main lateral faces have special shapes intended to block their relative movements when they come into contact in the contact patch. These technologies of what is referred to as self-locking siping, whether they be self-locking in the radial direction as illustrated in FIG. 4b, in the overall direction of the groove as illustrated in FIG. 1 by the siping 24 on the axially exterior part 22, or in both of these two directions, are well known to those skilled in the art. The benefit of such solutions is that relative movements of the main lateral faces are blocked and specific wear forms detrimental to the performance of the tire are avoided. FIGS. 4c and 4d illustrate two other possible embodiments of axially exterior grooves 24.

[0084] FIGS. 5A, 5B, 5C illustrate a method for determining the major grooves in the case of a network of grooves. For certain tread patterns, grooves open into other grooves as illustrated in FIG. 5A. In that case, the lateral faces of the network which are the continuous lateral faces most circumferentially distant from one another in the network of grooves will be determined, which in the present case are the lateral faces 241 and 242. The invention will be applied to all the grooves which, as their lateral faces, have one of the lateral faces of the network and the directly adjacent opposite lateral face. Let us therefore consider here the groove 24_1 (FIG. 5B), of mean linear profile L_1, made up of the lateral face of the network 241 and the opposite lateral face directly adjacent to (241, 242), over a first portion leading from point A to point B, and of the lateral face of the network 241 and the opposite lateral face 242 directly adjacent to 241, over a second portion leading from point B to point C. Next, consider the groove 24_2 (FIG. 5C), of mean linear profile L_2, made up of the lateral face of the network 242 and the opposite lateral face 241 directly adjacent to 242, over a first portion leading from point A to point B, and of the lateral face of the network 242 and the opposite lateral face 241 directly adjacent to 242, over a second portion leading from point B to point C. For more complex networks, this rule will be generalized so that all of the possible major grooves of the network substantially following the orientation of the lateral faces of the network satisfy the characteristics of the invention.

[0085] FIG. 7 schematically depicts tires which are intended to be mounted on mounting rims of wheels of a vehicle 200 and having a predetermined direction of mounting on the vehicle. Each tire comprises an exterior axial edge 45 and an interior axial edge 46, the interior axial edge 46 being the edge which is intended to be mounted on the bodyshell side of the vehicle when the tire is mounted on the vehicle in the said predetermined direction of mounting, and the exterior axial edge 45 being the opposite of that. In the document, outboard side of the vehicle denotes the exterior axial edge 45.

[0086] The inventors have performed calculations on the basis of the invention for a tire of size 205/55 R16, inflated to a pressure of 2 bar, comprising two working layers of steel monofilaments of diameter 0.3 mm and distributed at a density of 158 threads to the dm and forming, with the circumferential direction, angles respectively equal to 27 and 27. The monofilaments have a breaking strength R.sub.v equal to 3500 MPa and the working layers each have a breaking strength R.sub.c equal to 39 000 N/dm. The tire comprises axially exterior grooves of the blind type of a depth of 6.5 mm, on the two axially exterior portions of the tread of the tire having a width 0.2 times the width of the tread, distributed at a circumferential spacing of 27 mm. The radial distance D1 between the bottom face of the axially exterior major grooves and the crown reinforcement is at least equal to 2 mm.

[0087] Tire A comprises grooves of rectangular section, having a depth equal to 6 mm, a width 3.5 mm and a cross section equal to 21 mm2, as illustrated in FIG. 6A. Tire B comprises grooves having a depth equal to 6 mm, which are rectangular in segments. The radially innermost zone 1 of the grooves of tire B has a maximum width W1 equal to 5 mm and a depth equal to 4 mm. The radially outermost zone 2 of the grooves of tire B has a width equal to 0.6 mm and a height equal to 2 mm. These grooves are illustrated in FIG. 6B. They satisfy the features of the invention. The cross section of these two types of grooves is equal to 21 mm2. The tires are calculated with a distance between each adjacent groove. The circumferential distance between two consecutive grooves is equal to 27 mm. The overall direction of the grooves is substantially axial.

[0088] The conditions used for the calculation reproduce the running conditions of a front tire on the outside of the bend, namely the tire that is most heavily loaded in a passenger vehicle. These loadings, for a lateral acceleration of 0.7 g, are as follows: a load (Fz) of 749 daN, a lateral load (Fy) of 509 daN and a camber angle of 3.12. The shape of the grooves of tire B makes it possible to reduce the bending stresses in the monofilaments of the working reinforcement by 37% with respect to tire A comprising the type A grooves, these bending stresses being what causes them to rupture through fatigue. The shape of the major grooves of tire B therefore makes it possible to guarantee the monofilaments' superior endurance in relation to the major-grooves shape of tire A, while at the same time maintaining the same void volume ratio.