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

Abstract

Technique to increase the endurance of tires comprising two working layers (41, 42), comprising mutually parallel reinforcing elements (411, 421) each forming, with the circumferential direction (XX) of the tire, an oriented angle (A1, A2) the absolute value of which is at least equal to 20 and at most equal to 50, such that these respective angles are of opposite sign. The reinforcing elements of each ply are 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. The tire also comprises axially exterior major grooves (24) in the tread (2). The mean linear profile L of the axially exterior major grooves (24) of a width W at least equal to 1 mm and of a depth D at least equal to 5 mm forms, with the circumferential direction (XX), an angle C belonging to the interval [min(A1,A2)+100, max(A1, A2)+80].

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 axially exterior grooves, an axially exterior groove forming a space opening onto the tread surface and being delimited by at least two main lateral faces connected by a bottom face, at least one axially exterior groove, referred to as major groove, having a width W, defined by the 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 mean linear profile L, 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 the mean linear profile L of any axially exterior major groove of at least one axially exterior portion of the tread forms, with the circumferential direction of the tire, an angle C belonging to the interval [min(A1,A2)+100, max(A1, A2)+80], 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 angle C of the mean linear profile L of any axially exterior major groove of at least one axially exterior portion of the tread belongs to the interval [min(A1,A2)+105, max(A1, A2)+75].

3. The tire according to claim 1, wherein the angle C of the mean linear profile L of any axially exterior major groove of at least one axially exterior portion of the tread belongs to the interval [(A1+A2)/2+80, (A1+A2)/2+100].

4. The tire according to claim 1, wherein any axially exterior major groove has a width W at most equal to 10 mm.

5. The tire according to claim 1, wherein any axially exterior major groove has a depth D at most 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 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 bottom face of an 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.

9. The tire according to claim 1, wherein the bottom face of an 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.

10. The tire according to claim 1, wherein at least an axially exterior portion, comprising axially exterior major grooves, comprises sipes having a width W1 at most equal to 1 mm.

11. 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 of the tread.

12. The tire according to claim 1, wherein the angles of the respective reinforcing elements of the working layers are equal in terms of absolute value.

13. The tire according to claim 1, 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.

14. 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.

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 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.

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 15, 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

[0070] The features and other advantages of the invention will be understood better with the aid of FIGS. 1 to 8, the said figures being drawn not to scale but in a simplified manner so as to make it easier to understand the invention:

[0071] FIG. 1 is a perspective view depicting part of the tire according to the invention, particularly its architecture and its tread.

[0072] FIG. 2 depicts a meridian section through the crown of a tire according to the invention and illustrates the axially exterior parts 22 and 23 of the tread, and the width thereof.

[0073] FIGS. 3A and 3B depict two types of radially exterior meridian profile of the tread of a passenger vehicle tire.

[0074] FIG. 4 illustrates various possible types of axially exterior groove 24.

[0075] FIG. 5 illustrates the angle characteristic for the angle C of the mean linear profile L of any axially exterior major groove belonging to the interval [min(A1,A2)+100, max(A1, A2)+80].

[0076] FIG. 6 illustrates the angle characteristic for the angle C of the mean linear profile L of any axially exterior major groove belonging to the interval [(A1+A2)/2+80, (A1+A2)/2+100].

[0077] FIGS. 7A, 7B, 7C illustrate a method for determining the major grooves in the case of a network of grooves.

[0078] FIG. 8 illustrates the terms interior edge and exterior edge of a tread.

DETAILED DESCRIPTION OF THE DRAWINGS

[0079] FIG. 1 is a perspective view of 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 portions 22 and 23 of the tread there are axially exterior grooves 24 of width W and of mean linear profile L forming an angle C with the circumferential direction XX of the tire. 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 (411, 421) which are mutually parallel and respectively form, with a circumferential direction (XX) of the tire, an oriented angle (A1, A2) 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. 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 tread of the tire LT. The depth D of an axially exterior groove 24, and the distance D1 between the bottom face 243 of an axially exterior 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.

[0081] 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 (beta) between the said tangent and an axial direction YY is equal to 30. When there are several points for which the angle between the said tangent 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.

[0082] FIG. 4 schematically depicts axially exterior grooves 24 in a tread 2. A person skilled in the art determines the main profiles 241 and 242 of the grooves, which are distant from one another by a distance W. These profiles are linearized into a mean linear profile L by linear interpolation of the profiles in the axial direction YY. The axially innermost point a and the axially outermost point b of the mean linear profile L respectively define the origin and the end of the vector used to define the oriented angle C of the mean linear profile of a groove formed with the circumferential direction XX. The grooves may be open-ended like the groove 24A, blind like the groove 24C or double-blind like the groove 24B.

[0083] FIG. 5 depicts the angle characteristic for the angle C of the mean linear profile L of any axially exterior major groove belonging to the interval [min(A1,A2)+100, max(A1, A2)+80]. In order to avoid any buckling, the mean linear profile L must not be perpendicular to the monofilaments of the two working layers, to within plus or minus 10. Hence, the angle C of the mean linear profile L belongs neither to the interval [A1+9010, A1+90+10], namely [A1+80, A1+100], nor to the interval [A2+80, A2+100]. For reasons associated with wet grip, the angle C of the mean linear profile cannot belong to the zones Z3 close to the circumferential direction XX. Hence, the angle C belongs to the interval [A2+100, A1+80] when A2 is negative, or conversely to the interval [A1+100, A2+80] when A1 is negative: this is expressed mathematically by writing that the angle C belongs to the interval [min(A1, A2)+100, max(A1, A2)+80], to within plus or minus 180.

[0084] FIG. 6 depicts the angle characteristic for the angle C of the mean linear profile L of any axially exterior major groove belonging to the interval [(A1+A2)/2+80, (A1+A2)/2+100]. This feature means that the mean linear profile L of any axially exterior major groove is substantially perpendicular, to within + or 10 at most, to the bisector of the angle (A1+A2)/2, formed by the respective directions of the monofilaments of the two working layers.

[0085] FIGS. 7A, 7B, 7C 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. 7A. 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. 7B), 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. 7C), 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.

[0086] FIG. 8 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, the outboard side of the vehicle denotes the exterior axial edge 45.

[0087] 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, the angles A1 and A2 respectively equal 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 axially exterior major 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 an axial width equal to 0.21 times the axial width of the tread, distributed at a circumferential spacing of 30 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.

[0088] Various tires were calculated, varying the angle C of the mean linear profile of the axially exterior major grooves with respect to the circumferential direction from 60 to 120, in steps of 15. The widths of the axially exterior major grooves are at least equal to 2 mm, which means that the volume void ratio of the tire tread remains the same whatever the angle of the mean linear profile of the axially exterior major grooves. 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 following table gives the maximum of the bending stress loadings in the monofilaments as a function of the angle C made by the mean linear profile of the axially exterior major grooves with the circumferential direction. These maximum values are standardized to the value determined for the 120 value for the angle C made by the axially exterior major grooves as base 100.

TABLE-US-00001 Angle C 60 75 90 105 120 Maximum 92 71 58 75 100 bending stress (base 100)
The minimum bending stress is achieved for a mean linear profile of the axially exterior major grooves close to the perpendicular to the bisector of the directions of the monofilaments, namely 90. In the interval [min(A1,A2)+100, max(A1, A2)+80], which, in the example studied, equates to [73, 107], the maximum bending stress is at least 25% lower than the maximum bending stress calculated for an angle C of a mean profile close to the perpendicular to the direction of the monofilaments of the second layer A2 of the working reinforcement, namely 120.

[0089] The inventors produced two tires A and B of the size 205/55 R16, corresponding to the tires evaluated in the calculation, tire A, characterized by an angle C made by the mean linear profile of the axially exterior major grooves with the circumferential direction equal to 90, and tire B, characterized by an angle C equal to 120. These two tires, inflated to a pressure of 2 bar and subjected to a load (Fz) of 749 daN, a lateral load (Fy) of 509 daN and a camber angle of 3.12, were subjected to a rolling-road running test on an 8.5 m drum. Running was paused regularly for nondestructive measurement so as to check for breakages of the reinforcing elements in the working layers. In line with the calculation, breakages in the working layers of tire B appear after a distance lower than for tire A by a factor of two.