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 (AA, AB), such that these respective angles are of opposite sign, the reinforcing elements being comprised of individual metal threads, by combining a manufacturer-recommended direction of rotation (SR) and an optimized design of tread pattern. The tire also comprises axially exterior major grooves (24) in the tread (2) having a mean linear profile L of a width W at least equal to 1 mm and of a depth D at least equal to 5 mm. Different conditions governing the angular orientations of the mean linear profiles L of the axially exterior major grooves (24) apply to the left-hand axially exterior portion (22) and to the right-hand axially exterior portion (23) of the tread (2).

Claims

1. A tire for a passenger vehicle, adapted to be mounted on a rim in a recommended direction of rotation orientating a circumferential direction, comprising: with respect to the circumferential direction oriented in the recommended direction of rotation, a left-hand part and a right-hand part extending axially and symmetrically from a circumferential median plane, passing through the middle of a tread of the tire, intended to come into contact with the ground via a tread surface, and perpendicular to an axis of rotation of the tire, the tread comprising two axially exterior portions, belonging respectively to the left-hand part and to the right-hand part of the tire, each respectively having an axial width at most equal to 0.3 times the axial width LT, at least one axially exterior portion of the tread 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 open, referred to as major groove, having a width W, defined by the distance between the 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, and a mean linear profile, having an axially innermost point and an axially outermost point which define the vector of the mean linear profile, the tire radially on the inside of the tread, and 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, two oriented angles AA and AB in the counterclockwise direction 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 said working layer being comprised of individual metal threads or monofilaments having a cross section S 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 d of monofilaments 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 at most equal to 10, in terms of absolute value, wherein the vector of any mean linear profile of any axially exterior major groove of the left-hand axially exterior portion of the tread forms, with the circumferential direction of the tire, an oriented angle C at least equal to (85+(AA+AB)/2), wherein the vector of any mean linear profile of any axially exterior major groove of the right-hand axially exterior portion of the tread forms, with the circumferential direction of the tire, an oriented angle C at most equal to (85+(AA+AB)/2)), 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 the vector of any mean linear profile L of any axially exterior major groove of the left-hand axially exterior portion of the tread forms, with the circumferential direction of the tire, an oriented angle C at least equal to (90+(AA+AB)/2), and at most equal to (120+(AA+AB)/2), and the vector of any mean linear profile of any axially exterior major groove of the right-hand axially exterior portion of the tread forms, with the circumferential direction of the tire, an oriented angle C at most equal to (90+(AA+AB)/2), and at least equal to (120+(AA+AB)/2).

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

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

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 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 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 axially exterior portion, comprising axially exterior major grooves, comprises sipes having a width W1 at most equal to 1 mm.

10. 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.

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

12. 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 at least equal to 22 and at most equal to 35 in terms of absolute value.

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 the reinforcing elements of the working layers are made of steel.

15. 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.

16. The tire according to claim 1, wherein the reinforcing elements of the at least one hooping layer are made of textile.

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 1, wherein the reinforcing elements of the working layers are made of carbon steel.

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

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0077] The features and other advantages of the invention will be understood better with the aid of FIGS. 1 to 9, the said figures being drawn not to scale but in a simplified manner so as to make it easier to understand the invention:

[0078] FIG. 1 is a perspective view depicting a tire that has a recommended direction of rotation (SR).

[0079] FIG. 2 depicts part of a tire according to the invention, particularly its architecture and its tread.

[0080] FIG. 3 depicts a meridian section through the crown of a tire according to the invention and illustrates the axially exterior portions 22 and 23 of the tread, and the respective axial widths LG and LD thereof.

[0081] FIGS. 4A and 4B depict two types of radially exterior meridian profile of the tread of a passenger vehicle tire.

[0082] FIG. 5 illustrates various possible types of axially exterior groove 24.

[0083] FIG. 6A illustrates the optimum intervals I for the angle C between the circumferential direction XX and the direction of the mean linear profile L of any axially exterior major groove, [90+(AA+AB)/230; 90+(AA+AB)/2+30] mod(180), for a tire without a recommended direction of rotation. FIG. 6B illustrates the optimum respective intervals IG and ID for the angles C and C between the circumferential direction XX and the direction of the mean linear profiles L of any axially exterior major groove of the left-hand portion PG and of the right-hand portion PD of the tire, respectively.

[0084] FIG. 7A illustrates the effect of a left-hand bend on a reinforcing element of a right-handed working layer in the contact patch, and FIG. 7B illustrates the effect of a left-hand bend on a reinforcing element of a left-handed working layer in the contact patch.

[0085] FIG. 8A illustrates a type of tread pattern that is not optimized by the invention, and FIG. 8B illustrates a type of tread pattern that is optimized by the invention with a recommended direction of rotation.

[0086] FIGS. 9A, 9B, 9C illustrate a method for determining the profiles of the grooves in the case of a network of grooves.

DETAILED DESCRIPTION OF THE DRAWINGS

[0087] FIG. 1 depicts a perspective view of a tire (1) having a tread (2) and a direction of rotation (SR) recommended by the manufacturer and usually indicated by an arrow on a sidewall. When rotating about its axis YY, in the direction of rotation (SR), the tire moves in the direction of forward travel (DA). The anticlockwise cylindrical frame of reference (O, XX, YY, ZZ) is chosen such that the direction vector for the circumferential direction XX is always oriented in the recommended direction of rotation (SR). The circumferential median plane of the tire (XX, ZZ), which passes through the middle of the tread and is perpendicular to the axis of rotation YY, and the direction vector for the circumferential direction XX, oriented in the direction of rotation (SR) that gives the direction of forward travel (DA), make it possible to determine two half-torus shapes, respectively referred to as the left-hand portion (PG), the points of which have positive coordinates in the axial direction YY, and the right-hand portion (PD) of the tire, the points of which have negative coordinates in the axial direction YY. The tread comprises a tread surface (21) intended to come into contact with the ground. Also depicted are frames of reference (O, XX, YY, ZZ) associated with meridian planes having different angular positions about the axis of rotation YY.

[0088] FIG. 2 depicts a perspective view of a part of the crown of a tire. A plane of reference (O, XX, YY, ZZ) is associated with each meridian plane. The tire comprises a tread 2 which is intended to come into contact with the ground via a tread surface 21. Arranged in the respectively left-hand 22 and right-hand 23 axially exterior portions of the tread are axially exterior grooves 24 of width W each having main profiles 241 and 242 and a bottom face 243 and having a mean linear profile L. The tire further comprises a crown reinforcement 3 comprising a working reinforcement 4 and a reinforcement 5. The working reinforcement comprises two working layers 41 and 42 each comprising mutually parallel reinforcing elements, one of them being a right-handed working layer and the other a left-handed working layer.

[0089] FIG. 3 is a schematic meridian section through the crown of the tire according to the invention. It illustrates in particular the axial widths LG and LD of the left-hand 22 and right-hand 23 axially exterior portions of the tread, and the total axial 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.

[0090] In FIGS. 4A and 4B, the axial edges 7 of the tread, that make it possible to measure the axial width of the tread, are determined. In FIG. 4A, 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. 4B, 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.

[0091] FIG. 5 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 ab. These vectors make it possible to define the oriented angles C (XX; ab) of the mean linear profiles that the grooves 24 make with the circumferential direction XX in the left-hand 22 and right-hand 23 axially exterior portions of the tread. The grooves may be open-ended like the groove 24A, blind like the groove 24C or double-blind like the groove 24B.

[0092] FIG. 6A illustrates, for a tire with no recommended direction of rotation, the cones I of the optimum directions of the mean linear profile L of any axially exterior major groove: an optimal angle C, between the circumferential axis and the direction of the mean linear profile L, belongs to the interval [90+(AA+AB)/230; 90+(AA+AB)/2+30] mod (180). A reinforcing element of a right-handed working layer 411 is depicted with its ends ED making an oriented angle AA with the circumferential axis XX, and a reinforcing element of a left-handed working layer 421 making an oriented angle AB with the circumferential axis XX. The mediator of these two angles (AA+AB)/2 makes it possible to define the interval for the optimal angles for the directions of the mean linear profiles of the major exterior grooves about its perpendicular (AA+AB)/2+90, to plus or minus 30. Rotating FIG. 6A through 180 has no impact on how it is depicted because the direction of rotation of the tire has no influence.

[0093] FIG. 6A illustrates the meaning of the cone I. For a profile L, of interior axial end a, the angle at a of the cone is equal to 60, the mediator of the cone makes, with the circumferential axis, an angle of (AA+AB)/2+90 for the left-hand portion of the tire, and an angle of (AA+AB)/290 for the right-hand portion. If the exterior axial end of the mean linear profile of the groove, c1 or c2, is such that the direction ac1 or ac2 does not lie inside the cone, then the groove does not meet the groove optimization conditions. If the exterior axial end of the mean linear profile of the groove, b1 or b2, is such that the direction ab1 or ab2 lies inside the cone, then the groove meets the groove optimization conditions, not within the sense of the invention but for the case of a tire that has no recommended direction of rotation.

[0094] By adopting a recommended direction of rotation SR of the tire, it is possible to optimize endurance still further, and FIG. 6B illustrates the optimum cones IG and ID for the directions of the mean linear profiles L of any axially exterior major groove. The angles of the mean linear profiles L of any axially exterior major groove in the left-hand portion (PG) of the tire with the circumferential axis XX, are at least equal to 90+(AA+AB)/2, and at most equal to 90+(AA+AB)/2+30. The angles of the mean linear profiles L of any axially exterior major groove in the right-hand portion of the tire with the circumferential axis XX, are at most equal to 90+(AA+AB)/2, and at least equal to 90+(AA+AB)/230. In this case, with a recommended direction of rotation and following this recommendation, the end E1G of the left-handed reinforcing element 421 is always first, in forwards running, in bends with a high transverse acceleration, to enter the contact patch as compared with the end E2G, and likewise the end E1D of the right-handed reinforcing element is first to enter the contact patch as compared with the end E2D. Rotating FIG. 6B by 180 influences the positions of the optimal intervals IG and ID, and therefore of the grooves with regard to entering the contact patch.

[0095] FIG. 7A illustrates, viewed from the axis of rotation, the effect of a left-hand bend on a reinforcing element 411 of a right-handed working layer in the contact patch. The entry to the contact patch is denoted by E, the exit by S and the direction of forward travel is DA. The tire, subjected to transverse loading, is placed in bending. The zone of maximum compression ZCM in the direction XX is at the exit from the contact patch in the right-hand portion. The end E1D of the reinforcing element 411 that is first to enter the contact patch and therefore near the exit, is significantly to the right of the end 2ED. This latter end, which enters later, is near the entry of the contact patch.

[0096] The reinforcing element under consideration is subjected to a force FY from the ground onto the tire, which is zero at the entry to the contact patch and that increases as the tread becomes progressively sheared until it reaches a maximum after which it decreases because of the slippage on exiting the contact patch. This force deforms the reinforcing element 411 to 411D, giving it a direction closer to XX, and generating a return force FYR that increases from the entry to the contact patch as far as the slip zone at the exit from the contact patch. At the exit of the contact patch, the force FY of the ground on the tire decreases because of the slippage when the return force FYR caused by deformation of the crown and of the reinforcing elements is at a maximum, and so the reinforcing element returns as quickly as possible to a position in a direction DS that is near-perpendicular to the direction XX, which is the direction of the bending compression. Therefore, the reinforcing element absorbs only a very small amount of compression and, at this working layer, the compression forces are absorbed by the rubbery compound of the matrix. It is therefore not for the benefit of the reinforcing elements of the right-handed layers that the tread pattern needs to be optimized in a left-hand bend.

[0097] Conversely, FIG. 7B illustrates, viewed from the axis of rotation, the effect of that same left-hand bend on a reinforcing element 421 of a left-handed working layer in the contact patch. The end E1G of the reinforcing element 421 that is first to enter the contact patch has left the contact patch. It is well to the right of the end E2D that entered later and is still in the contact patch. This reinforcing element is subjected to the force FY from the ground onto the tire, which is zero at the entry to the contact patch and that increases as the tread becomes progressively sheared until it reaches a maximum and then decreases because of the slippage on exiting the contact patch. This force deforms the reinforcing element 421 at 421D, giving it a direction closer to YY, and generating a return force FYR that increases from the entry to the contact patch as far as the slip zone at the exit from the contact patch. On leaving the contact patch, the force FY of the ground on the tire decreases when the return force FYR is at a maximum, and so the reinforcing element therefore quickly returns to a position that makes a direction DS near-parallel to the direction XX, which is the direction of maximum compression caused by the flexing of the crown under the effect of the transverse force. The reinforcing element therefore absorbs all of the compression. In order to avoid the axially exterior major grooves of the right-hand part PD being perpendicular to the deformed form of the deformed reinforcing element, thus encouraging it to buckle, it is necessary that the perpendicular P411D to the deformed form 411D at the zone of maximum compression should not belong to the cone ID allowed for the vectors ab of the mean linear profiles of the axially exterior grooves. Therefore, in order to avoid buckling of the reinforcing elements of this working layer, in the right-hand portion of the tire, the vectors ab of the mean linear profiles of the axially exterior grooves need to make, with the circumferential axis XX, an oriented angle C at most equal to 90+(AA+AB)/2, and at least equal to (90+(AA+AB)/2)30, namely 120+(AA+AB/2).

[0098] Similar reasoning makes it possible, for a right-hand bend, to determine the optimum angle for the axially exterior grooves of the left-hand portion of the tire in order to preserve the reinforcing elements of the right-handed working layer from buckling. Therefore, in the left-hand portion of the tire, the vectors ab of the mean linear profiles of the axially exterior grooves need to make, with the circumferential axis XX, an oriented angle C belonging to IG, namely at least equal to 90+(AA+AB)/2, and at most equal to 90+(AA+AB)/2+30, namely 120+(AA+AB/2).

[0099] FIGS. 9A, 9B, 9C 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. 9A. 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. 9B), 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. 9C), 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.

[0100] 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 monofilaments 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.

[0101] Various tires were calculated and tested, varying the angles C and C of the mean linear profile of the axially exterior major grooves with respect to the circumferential direction in the left-hand and right-hand portions of the tire respectively: [0102] Tire A, according to the invention, characterized by having angles C and C of the mean linear profile of the axially exterior major grooves with respect to the circumferential direction XX, in the left-hand and right-hand portions of the tire, of 90 and 90 respectively [0103] Tire B, according to the invention, characterized by having angles C and C of 120 and 120 respectively. [0104] Tire C, excluded from the invention, characterized by having angles C and C of 60 and 60 respectively.

[0105] 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, corresponding to a left-hand bend. The following table gives the maximum of the bending stress loadings in the monofilaments as a function of the tire in the left-handed working layer which is the working layer most heavily loaded in a left-hand bend. These maximum values are referenced with respect to the value determined for tire A according to the invention. The tires calculated were run on an 8.5 m rolling road under the same conditions and running was interrupted at regular intervals to take nondestructive measurements in order to check for the presence of breakages in the reinforcing elements of the working layers. The distance covered before the monofilaments in a working layer, in this instance the left-handed working layer, broke is given in Table I below.

TABLE-US-00001 TABLE I Tire A (according B C to the (according to the (excluded from invention) invention) the invention) Angles C and C 90 C. and 120 C. and 120 C. 60 and 60 90 C. Maximum bending 100 98 166 stress (base 100) by calculation Distance covered 100 100 65 before breaking (base 100) by calculation

[0106] By calculation, the minimum bending stress is reached in tires A and B according to the invention. In testing on tires, the maximum distance covered before the monofilaments in the left-handed working layer broke is also reached in tires A and B according to the invention. Tire C, excluded from the invention, has a significantly lower distance covered before breakage.

[0107] Two tires A and B, of the same size 205/55 R16, with the same architecture as tires A and B and with tread patterns that were mutually identical apart from the angles C and C, were also tested using the same procedure, simulating a left-hand bend and a right-hand bend as the case may be. [0108] A, according to the invention, is such that the vectors ab of any mean linear profile L of any axially exterior major groove of, respectively the left-hand and the right-hand axially exterior portion of the tread form, with the circumferential direction (XX) of the tire, oriented angles C and C equal respectively to 102 and 102 [0109] B, excluded from the invention, is such that the vectors ab of any mean linear profile L of any axially exterior major groove of, respectively the left-hand and the right-hand axially exterior portion of the tread form, with the circumferential direction (XX) of the tire, oriented angles C and C equal respectively to 78 and 78

[0110] The rolling-road running was interrupted at regular intervals to take nondestructive measurements in order to check for the presence of breakages in the reinforcing elements of the most heavily loaded working layer of the tire, according to the direction of the bend. The distance covered before monofilament breakage started to appear is given in the following Table II, to base 100 with respect to the distance covered by tire A according to the invention, the endurance performance of which is, in both instances, superior, regardless of the direction of the bend.

TABLE-US-00002 TABLE II Distance covered before monofilament breakages A B started to appear, to base (according to (excluded from 100 the invention) the invention) Right-hand bend 100 65 Left-hand bend 100 50