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

Abstract

Two crossed tire working layers (41, 42), comprise mutually parallel reinforcing elements forming, with the circumferential direction (XX) of the tire, an angle 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 at least equal to 0.20 mm and at most equal to 0.5 mm. The tire also comprises major grooves of a depth D at least equal to 5 mm and of a width W at least equal to 1 mm, axially exterior major grooves (26) opening inwardly into a circumferential groove (24) comprising at least one bridge of rubber (27) connecting the two main faces of the groove, the at least one bridge of rubber having a length LB at least equal to W and a height h at least equal to half the depth D of the groove.

Claims

1. A tire 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, at least one axially exterior portion comprising at least one circumferential groove, and 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 main lateral faces connected by a bottom face, of which grooves at least one opens internally, forming a space which likewise opens into the circumferential groove, at least one said axially exterior groove, referred to as major groove, having a width W, defined by the distance between their two main 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, 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 at least 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 reinforcing elements in each working layer being comprised 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 an axially exterior and inwardly opening major groove of the tread comprises at least one bridge of rubber connecting the two main faces of the groove, wherein the at least one bridge of rubber has a cumulative length LB at least equal to the width W of the groove and a radial height h at least equal to half the depth D of the groove, and wherein the breaking strength R.sub.C of each said 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 any axially exterior major groove has a width W at most equal to 10 mm.

3. The tire according to claim 1, wherein any said axially exterior major groove has a depth D at most equal to 8 mm.

4. The tire according to claim 1, wherein a said axially exterior major groove opens axially to the outside of the tread.

5. 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.

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 most equal to 50 mm.

7. The tire according to claim 1, wherein the bottom face of an inwardly-opening axially exterior major groove is positioned radially on the outside of the crown reinforcement at a radial distance D1 at least equal to 1.5 mm.

8. The tire according to claim 1, wherein the bottom face of an inwardly-opening axially exterior major groove is positioned radially on the outside of the crown reinforcement at a radial distance D1 at most equal to 3.5 mm.

9. The tire according to claim 1, wherein at least one bridge of rubber of an inwardly-opening axially exterior major groove, having a width Wmin at least equal to 1.5 mm, comprises at least one sipe having a width W1 most equal to 1 mm and a depth h1 at least equal to h/2 and at most equal to h, h being the radial height of the bridge of rubber.

10. The tire according to claim 1, a bridge of rubber of an inwardly-opening axially exterior groove having an axially exterior edge corner, wherein the axially exterior edge corner of the bridge of rubber is chamfered.

11. The tire according to claim 1, wherein at least an axially exterior portion, comprising axially exterior major grooves, comprises sipes having a width W2 at most equal to 1 mm.

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

13. The tire according to claim 1, wherein each said working layer comprises reinforcing elements comprised of individual metal threads or monofilaments having a diameter at least equal to 0.3 mm and at most equal to 0.37 mm.

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

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

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

17. 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.

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

19. The tire according to claim 16, wherein the steel is carbon steel.

20. The tire according to claim 17, wherein the textile is of aliphatic polyamide.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0066] The features and other advantages of the invention will be understood better with the aid of FIGS. 1 to 6, the said figures being drawn not to scale but in a simplified manner so as to make it easier to understand the invention:

[0067] FIG. 1 is a perspective view depicting part of the tire according to the invention, particularly its architecture and its tread.

[0068] FIG. 2 depicts a meridian section through the crown and illustrates the axially exterior parts 22 and 23 of the tread, and the width thereof.

[0069] FIGS. 3A and 3B depict two types of radially exterior meridian profile of the tread of a passenger vehicle tire.

[0070] FIGS. 4a, 4b illustrate various types of single or multiple bridges of rubber.

[0071] FIGS. 5a, 5b, 5c illustrate a method for determining the major grooves in the case of a network of grooves.

[0072] FIG. 6 illustrates the terms interior edge and exterior edge of a tread.

DETAILED DESCRIPTION OF THE DRAWINGS

[0073] FIG. 1 depicts of 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 circumferential grooves 24 and axially exterior major grooves 25 and 26 of width W and including one 26 which opens axially internally 26. That groove 26 comprises a bridge of rubber 27. The tread also comprises sipes 28 having a width W2 at most equal to 1 mm. 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 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.

[0074] FIG. 1 depicts in the axially exterior parts 22 and 23 of the tread, only axially exterior grooves that are axial, following 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.

[0075] Furthermore, the sensitivity of the monofilaments of the working layers to buckling is dependent on the relative angles between the axially exterior grooves and the monofilaments. The relative angles between the axially exterior grooves and the monofilaments which are most penalising for this performance aspect are equal to 90. Knowing that the angles made by the monofilaments with the circumferential axis is comprised between 20 and 50, the angles made by the axially exterior grooves with respect to the transverse axis (YY) for which the invention is most effective, is comprised between 20 and 50 modulo pi. However, the invention also makes it possible to improve the performance in terms of the endurance of the monofilaments to buckling, when the grooves are axial.

[0076] 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 portions 22 and 23 of the tread, and the total width of the tire LT. The longitudinal groove 24, the depth D of an axially exterior groove 25, 26, and the distance D1 between the bottom face 253 of any groove 25, 26 and the crown reinforcement 3, measured along a meridian section of the tire, are also depicted. FIG. 2 also illustrates a bridge of rubber 27 as well as the crown reinforcement 3. 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.

[0077] 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 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. In FIG. 3B, in which the tread surface 21 is continuous with the exterior axial surface of the tire 8, 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 meridian section of the tire. The first axial edge 7 is the point for which the angle between the said tangent and an axial direction is equal to 30. When there are several points for which the angle between the said tangent YY and an axial direction YY 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.

[0078] FIGS. 4a and 4b schematically depict inwardly-opening axially exterior major grooves 26 of a tread 2 which grooves are equipped with bridges of rubber. FIG. 4a illustrates the case of a chamfered single bridge of rubber with radial height h and mean length LB. FIG. 4b illustrates the case of multiple bridges of rubber, with radial heights h1 and h2 at least equal to half the depth D and with cumulative mean length LB equal to the sum of the mean lengths of the various bridges of rubber.

[0079] 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 251 and 252. 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 26_1 (FIG. 5b) made up of the lateral face of the network 251 and the opposite lateral face directly adjacent to 251, 252, over a first section leading from point A to point B, and of the lateral face of the network 251 and the opposite lateral face 252 directly adjacent to 251, over a second portion leading from point B to point C. Next, consider the groove 26_2 (FIG. 5c) made up of the lateral face of the network 252 and the opposite lateral face 251 directly adjacent to 252, over a first section leading from point A to point B, and the opposite lateral face 251 directly adjacent to 252, 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.

[0080] FIG. 6 schematically depicts tires 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 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.

[0081] 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 comprising steel monofilaments of diameter 0.3 mm, distributed at a density of 158 threads to the dm and forming, with the circumferential direction, angles A1 and A2 equal respectively to 27 and 27. 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 tire comprises a circumferential groove 45 mm from the edge of the contact patch and inwardly-opening and outwardly-opening axially exterior major grooves of depth D equal to 7 mm and of width W equal to 5 mm, with a circumferential spacing of 30 mm. The radial distance D1 between the bottom face of the axially exterior grooves and the crown reinforcement is at least equal to 2 mm.

[0082] Two tires were calculated, a first A without a bridge of rubber and a second B equipped with a bridge of rubber of radial height h of 5.5 mm and of a mean length of 7 mm. 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 710 daN, a lateral load (Fy) of 505 daN and a camber angle of 3.0. The presence of the bridge of rubber makes it possible to reduce the bending stresses in the monofilaments of the working reinforcement by 17%, which stresses are what cause them to break through fatigue loading.

[0083] The inventors produced two tires A and B of the size 205/55 R16, corresponding to the tires evaluated in the calculation. These two tires, inflated to a pressure of 2 bar, subjected to a load (Fz) of 749 daN, a lateral load (Fy) of 509 daN and a camber angle of 3.12, were tested in rolling-road running, on an 8.5 m drum. Running was paused regularly for nondestructive measurement in order to check for breakage of the reinforcing elements in the working layers. In line with the calculation, breakages in the working layers of tire A appear after a distance 18% lower than for tire B.