TIRE WITH WORKING LAYERS COMPRISING AN OPTIMIZED ARCHITECTURE AND TREAD DESIGN

Abstract

A tire comprises, in the central part of its crown, at least one undulation (51) with a radial amplitude A of the radially outermost crown layer, circumferential furrows (24) and open grooves (25), some of these grooves being radially on the outside of the undulation (51). At least 50% of these grooves (25) are said to be adapted to the undulation. An open groove adapted to the undulation which it is radially on the outside of is such that the intersection points Ps of the bottom curve Cf of said groove and of the furrows (24) are at a distance from the radially outermost point Pext of said bottom curve Cf by a radial distance d2 at least equal to one third of the radial amplitude (A/3) of the undulation (51) and such that the curve Cf increases radially from the intersection points Ps to the point Pext.

Claims

1.-10. (canceled)

11. A tire comprising: a tread intended to come into contact with a ground via a tread surface having an axial width L and comprising a central part of the tread having a width equal to 0.8*L, the central part of the tread comprising at least two circumferential furrows, each circumferential furrow forming a space that opens onto the tread surface around an entire circumference of the tire and being delimited by two main lateral faces connected by a bottom face, and having a mean width Ws at least equal to 6 mm and a depth D at least equal to 4 mm, the central part of the tread comprising grooves forming a space that opens onto the tread surface, forming an angle at least equal to 15° with a circumferential axis, and being delimited by two main lateral faces connected by a bottom face, a groove having a width Wr defined by a mean distance between the two lateral faces, and having a width Wr at least equal to 0.5 mm, at least fifty percent of the grooves being open grooves that open into one or two circumferential furrows, and each open groove comprising a bottom curve Cf formed by all of the radially innermost points of the bottom surface of the groove, each bottom curve comprising at least one point Ps, and at most two, in common with the furrow or the two furrows into which the groove opens, and a radially outermost point Pext; a carcass layer and a crown reinforcement, radially on the inside of the tread, comprising at least one crown layer, the crown layer being a layer of reinforcing elements, the crown reinforcement comprising a working reinforcement comprising at least one working layer, each working layer comprising reinforcing elements which are at least partially made of metal coated in an elastomer material, are mutually parallel and form with the circumferential direction of the tire an oriented angle of which the absolute value is at least equal to 15° and at most equal to 50°, each crown layer extending radially from a radially inner surface to a radially outer surface, the radially outermost crown layer vertically beneath the central part of the tread comprising at least one central undulation with a radial amplitude A, the portion of the radially outer surface of the crown layer of the central undulation is radially on the outside of the points of the radially outermost crown layer vertically beneath the bottom face of the circumferential furrow closest to the central undulation, over at least 10% of the radially outer surface of the crown layer vertically beneath the central part of the tread, a radial distance between the radially outer surface of the radially outermost crown layer and the tread surface at the central undulation is at least 1 mm less than a radial distance between the radially outer surface of the radially outermost crown layer and the tread surface, this being the distance vertically beneath the bottom face of the circumferential furrow closest to the point in question on the surface, and the radial distance between the radially outer surface of the radially outermost crown layer and the bottom face of the circumferential furrows is at most equal to 4 mm, wherein at least 50% of the open grooves radially on the outside of the central undulation of the radially outermost layer of reinforcing elements are adapted to the central undulation, wherein an open groove that is adapted to the undulation which it is radially on the outside of being such that the intersection point Ps of the bottom curve Cf of the open groove adapted to the undulation and of the circumferential furrow into which the open groove adapted to the undulation opens are at a distance from the radially outermost point Pext of the bottom curve Cf by a radial distance at least equal to one third of the radial amplitude of the central undulation situated vertically beneath the open groove adapted to the undulation, and wherein the curve Cf increases radially from the intersection point Ps to the point Pext.

12. The tire according to claim 11, wherein an open groove adapted to the central undulation of the radially outermost crown layer which it is radially on the outside of is such that the radial distance between the intersection point Ps of the bottom curve Cf of the open groove and of the circumferential furrow into which the open groove opens and the radially outermost point Pext of the bottom curve Cf is at least equal to half the radial amplitude of the central undulation situated vertically beneath the open groove and at most equal to 1.5 times the radial amplitude of the central undulation situated vertically beneath the open groove.

13. The tire according to claim 11, wherein all the crown layers have central undulations, and the central undulations are substantially identical in terms of position and of radial amplitude in the portions situated vertically beneath the central part of the tread.

14. The tire according to claim 11, wherein at least 90% of the open grooves radially on the outside of a central undulation of the radially outermost crown layer are adapted to the central undulation, which they are respectively radially on the outside of, of the radially outermost crown layer.

15. The tire according to claim 11, wherein, for the part of the crown reinforcement vertically beneath the central part of the tread, over at least 20% of the radially outer surface of the radially outermost crown layer, the radial distance between the radially outer surface of the radially outermost crown layer and the tread surface is at least 1.5 mm less than the radial distance between the radially outer surface of the radially outermost crown layer and the tread surface, this being the distance measured vertically beneath the radially innermost point of the bottom face of the circumferential furrow closest to the central undulation at the point in question.

16. The tire according to claim 11, wherein the radial distance between the radially outer surface of the radially outermost crown layer and the bottom face of the circumferential furrow is at least equal to 0.5 mm and at most equal to 3 mm.

17. The tire according to claim 11, further comprising at least one wear indicator, wherein the minimum radial distance between the radially outer surface of the radially outermost crown layer of the crown reinforcement and the tread surface is at least equal to the radial distance between the tread surface and the radially outermost point of the wear indicator.

18. The tire according to claim 11, wherein the minimum radial distance between the radially outer surface of the radially outermost crown layer of the crown reinforcement and the tread surface is at most equal to the depth D of the closest circumferential furrow plus 2 mm and at least equal to the depth D of the closest circumferential furrow minus 2 mm.

19. The tire according to claim 11, wherein at least one filling material having a radial thickness at least equal to 0.3 mm is positioned vertically beneath each central undulation of the radially outermost crown layer.

20. The tire according to claim 19, the tread being made up of at least one rubber compound, wherein the filling material is a rubber compound having a dynamic loss tan δ1, measured at a temperature of 10° C. and under a stress of 0.7 MPa at 10 Hz, at most equal to the dynamic loss tan δ2 of the rubber material of which the tread is made, measured at a temperature of 10° C. and under a stress of 0.7 MPa at 10 Hz.

Description

[0067] The features and other advantages of the invention will be understood better with the aid of FIGS. 1 to 7, said figures not being drawn to scale but in a simplified manner so as to make it easier to understand the invention:

[0068] FIG. 1 shows a crown portion of the tyre, the crown layers and the tread thereof,

[0069] FIG. 2 shows a meridian half-section through the crown of a tyre according to the invention provided with open grooves (25) which are radially on the outside of undulations and the bottom profile Cf of which is adapted to the undulation. It illustrates the radial amplitude A of an undulation (51) of the radially outermost crown layer 5, the various radial distances do, d1, D, df, dc, and a filling material (6) suitable for creating an undulation in particular of the radially outermost crown layer,

[0070] FIG. 3 shows open grooves 25, the bottom surfaces and bottom curves, or talweg Cf, thereof, and the intersection points Ps with the circumferential furrows (24) and the radially outermost point Pext of the bottom curve Cf,

[0071] FIGS. 4, 5 and 6 show a portion of a meridian section through the central part 22 of the tread and the part of the crown vertically therebeneath. These figures show variants in the position of the filling material (6) in the crown layers (41, 42, 5) and variants of open grooves (25) adapted to the undulation (51) which they are radially on the outside of.

[0072] FIG. 7 shows a portion of a meridian section through the central part 22 of the tread and the part of the crown vertically therebeneath, in which there is located an undulation according to the invention A1 and according to the prior art B1 in the new state and in a worn state, A2 and B2, respectively, showing the effect of wear on the two variants.

[0073] A meridian section through the tyre is obtained by cutting the tyre on two meridian planes. This section is used to determine the various radial distances, the centre of the bottom faces of the grooves and of the furrows.

[0074] FIG. 1 shows a portion of the crown of a tyre. It shows a carcass layer 9, radially on the inside of the crown layer 3, comprising a working reinforcement 4 containing, in this instance, two working layers 41 and 42 made up of reinforcing elements 411 which are at least partially made of metal coated in an elastomer material, are mutually parallel and form with the circumferential direction (XX′) of the tyre an oriented angle of which the absolute value is at least equal to 15° and at most equal to 50°, and a hooping layer 5. The tyre also comprises a tread 2, which is delimited by the tread surface 21 and the outer lateral surfaces 26 and comprises cuts, in this instance two circumferential furrows 24 having widths Ws at least equal to 5 mm and grooves 25 having widths Wr at least equal to 0.5 mm. The circumferential furrows 24 comprise two lateral faces 241 and 242 and a bottom surface 243. FIG. 1 also shows a groove 25 opening into two circumferential furrows 24 and surrounded by two blind grooves 25 opening into one furrow. The grooves comprise lateral faces 251 and 252 and a bottom face 253 that is not shown in FIG. 1. The portions of the circumferential furrows shown in FIG. 1 in this case form a zero angle with the direction XX′; a circumferential furrow could be made up of a series of cuts that exhibit a non-zero angle with the direction XX′ and are connected to one another so as to form a continuous cut around the entire circumference of the tyre.

[0075] In FIGS. 2, 4, 5, 6 and 7, for reasons of ease of depiction, the grooves are shown as belonging to the meridian plane, but the grooves may have any of the forms known from the prior art, both in terms of angles and of shapes: simple, undulating, complex, with or without variations in thickness.

[0076] FIG. 2 schematically shows a meridian half-section through the crown of the tyre according to the invention. It illustrates in particular undulations of all the layers of the crown reinforcement (3), including the working layers (41, 42) and the radially outermost crown layer (5) with the aid of a filling material (6) positioned between the carcass layer (9) and the radially innermost working layer (42). This filling material causes all of the crown layers 41, 42, 5 to undulate and therefore creates an undulation 51 in the radially outermost hooping layer 5 of the crown layers.

[0077] FIG. 2 shows how the width L of the tread is determined. The width L of the tread is determined on a tyre mounted on a nominal rim and inflated to the nominal pressure. In the event of an obvious boundary between the tread surface and the rest of the tyre, the width of the tread is determined by a person skilled in the art in a trivial manner. If the tread surface 21 is continuous with the outer lateral surface 26 of the tyre, the axial limit of the tread passes through the point at which the angle between the tangent to the tread surface 21 and an axial direction YY′ is equal to 30°. When, in a meridian plane, there are several points for which said angle is equal to 30°, it is the radially outermost point that is adopted. The width of the tread is equal to the axial distance between the two axial limits of the tread surface on either side of the equatorial plane.

[0078] FIG. 2 also illustrates the following radial distances: [0079] D: the depth of a circumferential furrow (24), this being the maximum radial distance between the tread surface (21) and the bottom face (243) of the furrow (not including retreading wells), [0080] dc: the radial distance between the radially outer surface (ROS) of the radially outermost crown layer (5) and the tread surface (21), this being the distance vertically beneath the radially innermost point of the bottom face (243) of the circumferential furrow (24), [0081] do: the radial distance between the radially outer surface (ROS) of the radially outermost crown layer (5) and the tread surface (21) at the undulation (51), [0082] d1: the minimum radial distance (d1) between the radially outer surface (ROS) of the radially outermost crown layer (5) of the crown reinforcement (3) and the bottom face (243) of the circumferential furrows (24), [0083] df: the radial distance between the tread surface (21) and the radially outermost point of the wear indicator (11), [0084] A: the radial amplitude of the undulation measured for a given undulation between the radially outermost point of said undulation and the radially innermost point of said point situated vertically beneath the closest circumferential furrow 24.

[0085] FIG. 2 shows two undulations 51 of the radially outermost crown layer in the central part 22 of the tyre, which is centred on the equatorial plane and has a width equal to 0.8*L. Each of these undulations is radially on the inside of open grooves 25, the bottom curve Cf of the bottom surface 253 of which is adapted to the undulation. The bottom curve Cf is adapted inasmuch as the intersection points Ps of the bottom curve and of the lateral walls 241, 242 of the circumferential furrows 24 into which the grooves 25 open are radially on the inside of a point Pext, which is the radially outermost point of the bottom curve Cf, and such that the radial distance d2 between Pext and both of the points Ps is at least equal to one third of the radial amplitude of the undulation in question, the radial amplitudes of the undulations being able to vary from one rib to another. Moreover, the bottom curve increases radially from the points Ps to the point Pext.

[0086] FIG. 3 shows two grooves opening into two furrows 24. Of the first furrow in the foreground, all that is sketched is the lateral face 241. In Figure A′, there is a single bottom curve or talweg of the bottom surface 253, and it can be easily determined. The curve of intersection of the lateral face 241 of the circumferential furrow and of the bottom surface 253 of the groove is determined and its radially innermost point Ps, which is the starting point of the bottom curve, is determined. Similarly, the other end of the bottom curve Cf is determined either by following the same procedure with the other furrow or by finding the curve of intersection between the bottom surface 253 and the surface closing the groove in the case of a blind groove. Next, by intersection of the circumferential planes contained between the ends of the curve Cf with the bottom surface 253, the set of points forming the bottom curve Cf is determined. In FIG. 3 B′, there is not just one curve Cf and in this case a mean curve Cf made up of the most equidistant points from the lateral faces 251, 252 of the groove 25 in question from the possible intersection points PS with the circumferential furrow(s) is considered. Next, the same procedure is followed with the curves brought about by the intersection of the circumferential planes and the bottom surface 253 in order to determine the rest of Cf. A person skilled in the art knows how to determine the bottom curve of a groove without difficulty.

[0087] FIGS. 4, 5 and 6 show variants of possible positions of the filling material 6 in the crown 3: [0088] Between the carcass layer 9 and the radially innermost working layer, as illustrated in FIG. 6, [0089] Between the working layers 41 and 42, as illustrated in FIG. 4, [0090] Between the radially outermost working layer 41 and the radially outermost crown layer 5, as illustrated in FIG. 5. [0091] It is possible to conceive of several filling materials positioned in the different positions illustrated here, with suitable thicknesses for obtaining undulations with a desired radial amplitude.

[0092] FIG. 4 shows a blind groove 25, which thus opens into a single circumferential furrow (24).

[0093] FIG. 5 shows that the grooves 25 can have a shallow depth, less than 2 mm.

[0094] FIG. 6 shows a bottom curve with several levels of curves. It is possible to have rectilinear bottom curves or bottom curves that are rectilinear in a piecewise manner.

[0095] FIG. 7 shows a rib of the tread radially on the outside of an undulation 6, comprising a groove 25 opening into two circumferential furrows 24 on either side of the rib and the bottom curve Cf of said groove. For Figure A1, according to the invention, Cf is adapted to the undulation. For Figure B1, according to the prior art, Cf is not adapted to the undulation of the radially outermost crown layer vertically beneath the rib. Figures A2 and B2 show the ribs A1 and B1, respectively, after wearing down. On account of the undulation, the ribs will exhibit more pronounced wear at the cliffs of the circumferential furrows. Under the effect of the pressure, the working layers will become taut and the undulation will lose radial amplitude A and the centre of the rib will hollow out with respect to the cliffs of the furrows, creating a wear pattern that is more accentuated at this location. For a bottom curve Cf that is not adapted, the groove will disappear at the cliffs of the ribs, as in diagram B2. In the contact patch, this groove, which is not disposed over the entire width of the rib, will trap air, generating noise on leaving the contact patch. With an adapted bottom curve, the groove remains open and the level of noise does not worsen.

[0096] The invention was implemented on a tyre A of size 295/35 ZR20 intended to equip a passenger vehicle. The depths D of the circumferential furrows in the tread pattern are equal to 7.5 mm, for widths Ws that vary in the vicinity of 4 mm. The crown reinforcement is made up of two working layers, the reinforcing elements of which make an angle of + or −38 with the circumferential direction, and of a hooping layer, the reinforcing elements of which make an angle of + or −3 with the circumferential direction. The reinforcing elements of the working layer are continuous metal cords. The radially outermost crown layer is undulating such that 50% of its radially outer surface (ROS) is at least 1 mm radially further out compared with this same surface vertically beneath the closest circumferential furrows. The undulations have radial amplitudes of 2 mm. The radial distance (d1) between the radially outer surface (ROS) of the radially outermost working layer (41) and the bottom face (243) of the circumferential furrows (24) is equal to 1.6 mm. The tread pattern has 4 circumferential furrows and 4 ribs in the central part 22 of the tread. Each rib of the central part 22 is radially on the outside of an undulation 51 of the crown layers 41, 42, 5. The ribs comprise grooves 25 that open into the circumferential furrows 24 with a depth of 3 mm and are spaced apart from one another by a mean spacing equal to 30 mm. The bottom curves of the grooves are all adapted to the undulations of the crown layers 5, 41, 42. The distance d2 between the intersection points Ps of the bottom curve and of the circumferential furrows and the radially outermost point Pext of the bottom curve of the grooves is at least equal to 0.7 mm. The bottom curves increase radially from the points Ps and Pext.

[0097] The tyres A were compared with tyres B of the same size, having the same characteristics except that the bottom curves of the grooves in the central ribs are not adapted to the undulations of the crown layers, the bottom curves of the grooves being on one and the same radius, from one furrow to another.

[0098] The tyres were tested for noise in the new state in accordance with the European standard in force. No difference in performance was measured. The tyres were then worn down on the open road under the same running conditions, using the same types of vehicles, at the same speeds. After 1.7 mm of wear, the majority of the grooves for the tyre A according to the invention and the tyre B according to the prior art exhibit greater wear at the cliffs of the ribs than at their centres. In the tyre A according to the invention, the majority of the grooves, on account of the bottom curve Cf being adapted to the presence of the undulations of the crown layers, remain open. For the tyre B, the grooves were worn down at the cliffs such that the ends of the grooves, in their worn form, are located at the top of the rib. A coast-by noise test of these two tyres shows that the performance of the tyre A is better than the performance of the tyre B by around 0.7 dB under a test protocol according to the European directive 2001_43_CE in force.