Pneumatic Tire with Optimized Crown-and-Tread-Pattern Architecture

Abstract

The invention is a tire comprising a crown comprising at least one layer of reinforcing elements. The radially outermost layer comprises at least one undulation (512). The undulations (512) in the radially outermost layer (5) are such that the points of the undulations are radially on the outside of the points of said layer (5) that are vertically beneath the centre of the bottom face (243) of the closest major groove (24) by at least a radial distance of 1.5 mm. The undulations (512) in the radially outermost crown layer make up at least 10% of the radially outer surface (ROS) of said crown layer (5). A rubber compound with a dynamic modulus G*, measured at 40° C. at 10% peak-to-peak strain at 10 Hz, that is at most equal to 3.25 MPa, makes up at least 30% of the rubber compounds vertically above said undulations.

Claims

1.-14. (canceled)

15. A tire for a passenger vehicle, comprising: a tread intended to come into contact with the ground via a tread surface comprising grooves, at least one of which forms a space that opens onto the tread surface and is delimited by two main lateral faces connected by a bottom face, having a width W defined by the mean distance between the two lateral faces and a depth D defined by the maximum radial distance between the tread surface and the bottom face), at least one groove, which is a major groove, having a width W at least equal to 1 mm and a depth D at least equal to 4 mm, the tire also comprising a crown reinforcement, radially on the inside of the tread, comprising at least one layer of reinforcing elements, denoted crown layer, the at least one layer of reinforcing elements extending radially from a radially inner surface (RIS) to a radially outer surface (ROS), wherein the radially outermost crown layer comprises at least one undulation, in that the at least one undulation in the radially outermost crown layer is such that the radially outermost crown layer portion of the undulation is radially on the outside of the points of said radially outermost crown layer that are vertically beneath the centre of the bottom face of the major groove closest to said undulation, in that the at least one undulation in the radially outermost crown layer is such that, over at least 10% of the radially outer surface (ROS) of said crown layer, the radial distance (du) between the radially outer surface (ROS) of the radially outermost crown layer and the tread surface is at least 1.5 mm less than the radial distance (dc) between the radially outer surface (ROS) of the radially outermost crown layer and the tread surface, which is the distance vertically beneath the center of the bottom face (243) of the major groove closest to said undulation, in that the minimum radial distance (du) between the radially outer surface (ROS) 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 major groove plus 2 mm and at least equal to the depth D of the closest major groove minus 2 mm, in that the part of the tread vertically above at least one undulation in the radially outermost crown layer comprises at least 30% of a rubber compound M, the dynamic shear modulus G* of which, measured at 40° C. at 10% peak-to-peak strain at 10 Hz, is at most equal to 3.25 MPa.

16. The tire according to claim 15, wherein the rubber compound M has a dynamic shear modulus G*, measured at 40° C. at 10% peak-to-peak strain at 10 Hz, that is at most equal to 3 MPa.

17. The tire according to claim 15, wherein the rubber compound M has a dynamic shear modulus G*, measured at 90° C. at 10 Hz and under a stress of 0.7 MPa, that is at most equal to 1 MPa.

18. The tire according to claim 15, wherein the rubber compound M has a tan δ0 value at least equal to 0.5, where tan δ0 denotes the tan δ value measured at a temperature of 0° C. at 10 Hz and under a stress of 0.7 MPa.

19. The tire according to claim 15, wherein, over at least 10%, and at most 85%, of the radially outer surface (ROS) of the radially outermost crown layer, the radial distance (du) between the radially outer surface (ROS) of the radially outermost crown layer and the tread surface is at least 1.5 mm less than the radial distance (dc) between the radially outer surface (ROS) of the radially outermost crown layer and the tread surface, which is the distance vertically beneath the center of the bottom face of the closest major groove.

20. The tire according to claim 15, wherein, over at least 10% and at most 85%, of the radially outer surface (ROS) of the radially outermost crown layer, the radial distance (du) between the radially outer surface (ROS) of the radially outermost crown layer and the tread surface is at most 5 mm less than the radial distance (dc) between the radially outer surface (ROS) of the radially outermost crown layer and the tread surface, which is the distance vertically beneath the center of the bottom face of the closest major groove.

21. The tire according to claim 15, wherein the radial distance (d1) between the radially outer surface (ROS) of the radially outermost crown layer and the bottom face of the major grooves is at least equal to 1 mm and at most equal to 5 mm and at most equal to 4 mm.

22. The tire according to claim 15, where at least one major groove of the tread comprises at least one wear indicator, wherein the minimum radial distance (du) between the radially outer surface (ROS) of the radially outermost crown layer of the crown reinforcement and the tread surface is at least equal to the radial distance (df) between the tread surface and the radially outermost point of the wear indicator.

23. The tire according to claim 15, wherein all parts of the tread and of the tread surface vertically above the undulations in the radially outermost crown layer comprise at least 50% of the rubber compound M, preferably 75%, preferably 100%.

24. The tire according to claim 15, and comprising at least one wear indicator, wherein the part of the tread radially on the outside of the wear indicators is made up 100% of the rubber compound M.

25. The tire according to claim 15, wherein the depth D of a major groove is at most equal to 10 mm.

26. The tire according to claim 15, wherein the void ratio of the tread is at least equal to 10%.

27. The tire according to claim 15, wherein the radially outermost crown layer of reinforcing elements of the crown reinforcement comprises reinforcing elements made of textile, preferably of the aliphatic polyamide or aromatic polyamide type, of a type involving a combination of aliphatic polyamide and aromatic polyamide, of polyethylene terephthalate type or of rayon type, which are mutually parallel and form an angle B at most equal to 10°, in terms of absolute value, with the circumferential direction (XX′) of the tire.

28. The tire according to claim 15, wherein at least one padding rubber compound having a radial thickness at least equal to 0.3 mm is positioned vertically beneath the undulation in the radially outermost crown layer.

29. The tire according to claim 15, wherein the padding rubber compound has a maximum dynamic loss tan δ1, measured at a temperature of 23° C. at 10 Hz, at most equal to and preferably 30% less than the maximum dynamic loss tan δ2 of the least hysteretic rubber compound of the tread (2) and radially on the outside of the bottom surfaces of the major grooves, measured at a temperature of 23° C. and under a stress of 0.7 MPa at 10 Hz.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0068] The features and other advantages of the invention will be understood better with the aid of FIGS. 1 to 4, said figures not being drawn to scale but in a simplified manner so as to make it easier to understand the invention:

[0069] FIG. 1 is a part of a tire, in particular the architecture and tread thereof.

[0070] FIG. 2 shows a meridian section through the crown of a tire according to the invention and illustrates the different radial distances, du, d1, D, df, dc and a padding rubber compound (6) suitable for creating an undulation in the radially outermost crown layer, working layer or hooping layer, this undulation comprising, vertically above it, a low-stiffness rubber compound M.

[0071] FIG. 3 shows a meridian section through the crown of a tire according to the invention and illustrates the different radial distances, du, d1, D, df, dc and a padding rubber compound (6) suitable for creating an undulation in the crown reinforcement, the working layers and the hooping layer, this undulation comprising, vertically above it, and in 100% of the part of the tread radially on the outside of the wear indicators, a low-stiffness rubber compound M.

[0072] FIG. 4 (a, b, c, d) shows a portion of the crown of the tire delimited circumferentially and axially by major grooves (24) that likewise delimit an undulation (512) in the radially outermost crown layer (5) for a tire having a hooping layer (5) and two working layers (41, 42). It illustrates the possibility of arranging, vertically beneath the undulation (512), one or more padding rubber compounds (6), which may have different properties depending on the specific needs associated with their respective radial, axial and circumferential positions and also various distributions of the low-stiffness rubber compound M in the tread.

DETAILED DESCRIPTION OF THE DRAWINGS

[0073] FIG. 1 shows a perspective view of a part of the crown of a tire. A Cartesian frame of reference (XX′, YY′, ZZ′) is associated with each meridian plane. The tire has a tread 2 intended to come into contact with the ground via a tread surface 21. Arranged in the tread are grooves 24 with a width W that possibly differs from one groove to another. The tire also comprises a crown reinforcement 3 comprising a working reinforcement 4 and in this case, for example, a hoop reinforcement 5. The working reinforcement comprises at least one working layer and in this case, for example, two working layers 41 and 42, each comprising mutually parallel reinforcing elements (411 for the crown layer 41). The radially outer surface (ROS) of the radially outermost working layer (41) is also shown.

[0074] FIG. 2 schematically shows the meridian section through the crown of the tire according to the invention. It illustrates in particular the carcass layer 1, an undulation (512) of the radially outermost crown layer (5) and a padding rubber compound (6) positioned vertically therebeneath. FIG. 2 also illustrates the following radial distances: [0075] D: the depth of a groove, which is the maximum radial distance between the tread surface (21) and the bottom face (243) of the groove, [0076] dc: the radial distance between the radially outer surface (ROS) of the radially outermost crown layer (5) and the tread surface (21), which is the distance measured vertically beneath the radially innermost point of the bottom face (243) of the major groove (24) closest to said undulation (512), [0077] du: the minimum radial distance (du) between the radially outer surface (ROS) of the radially outermost crown layer (5) of the reinforcement and the tread surface (21), [0078] df: the radial distance between the tread surface (21) and the radially outermost point of the wear indicator (7), [0079] d1: the minimum distance between the radially outer surface (ROS) of the radially outermost crown layer (5) and the bottom face (243) of the major grooves (24).

[0080] FIG. 3 schematically shows the meridian section through the crown of the tire according to the invention. It illustrates in particular an undulation in the crown reinforcement made up of two working layers (41 and 42) and the hooping layer (5), the radially outermost crown layer, and a padding rubber compound (6) disposed vertically beneath the undulation under the radially innermost working layer (42).

[0081] A meridian section through the tire is obtained by cutting the tire 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.

[0082] FIG. 4a shows an undulation 512 in the crown reinforcement, the two working layers (41 and 42) and the hooping layer (5). The undulations are limited axially and circumferentially, at a tread pattern element. These tread pattern elements may repeat in the tread pattern of the tire with or without undulations vertically beneath them. The sum of the areas of the surfaces of the undulations has to at least represent 10% of the total surface area of the radially outermost crown layer in order for the effect to be advantageous. FIG. 4 abcd also shows how it is possible to obtain an undulation by laying a padding rubber compound 6 radially on the inside of the various layers of reinforcing elements of the crown reinforcement. In these tread pattern elements, the rubber compound M may be the only rubber compound of the tread, or of the tread pattern element or one of the rubber compounds. M2 in FIGS. 4b, 4c, 4d represents a second rubber compound, different from M, of the tread.

[0083] The invention was implemented on a tire A of size 305/30 ZR20 intended to equip a passenger vehicle. The depths D of the grooves in the tread pattern are between 5 mm at the shoulders and 7 mm at the equator, for widths W that vary between 4 and 15 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 textile hooping layer, the reinforcing elements of which make an angle of + or −3 with the circumferential direction. The radially outermost crown layer, the hooping layer 5, is undulated over 50% of its surface area. The undulations are made with the aid of padding rubber compounds radially on the inside of the radially innermost working layer, said padding rubber compounds being situated more specifically between the carcass layer and the radially innermost crown layer. The undulations have amplitudes of 2 mm, meaning that the radial distances (du) between the radially outer surface (ROS) of the radially outermost crown layer (5) and the tread surface at the undulations (512) are 2 mm less than the radial distances (dc) between the radially outer surface (ROS) of the radially outermost crown layer (5) and the tread surface (21), these being the distances vertically beneath the radially innermost point of the bottom face of the major grooves (24) closest to said undulations (512). The radial distance (d1) between the radially outer surface (ROS) of the radially outermost crown layer (5) and the bottom face (243) of the major grooves (24) is equal to 1.5 mm. The tread is made up of a single rubber compound CC1 having the following features: [0084] G*, measured at 40° C. at 10% peak-to-peak strain at 10 Hz, is equal to 2.3 MPa, [0085] a dynamic shear modulus G*, measured at 90° C. at 10 Hz and under a stress of 0.7 MPa, equal to 0.45 MPa, [0086] tan δ, measured at a temperature of 0° C. at 10 Hz and under a stress of 0.7 MPa, is equal to 0.58.

[0087] Tires A were compared with tires B and C of the same size, having the same characteristics except that: [0088] Tire B is such that its crown layers are not undulated and its tread consists of a single rubber compound CC2. [0089] Tire C is such that its crown layers are not undulated and the tread consists of a single rubber compound CC1 similar to tire A.

[0090] The rubber compound CC2, which does not correspond to the invention, is a rubber compound suitable for use in the tread and has the following properties: [0091] G*, measured at 40° C. at 10% peak-to-peak strain at 10 Hz, is equal to 3.3 MPa, [0092] a dynamic shear modulus G*, measured at 90° C. at 10 Hz and under a stress of 0.7 MPa, equal to 1.05 MPa, [0093] tan δ, measured at a temperature of 0° C. at 10 Hz and under a stress of 0.7 MPa, is equal to 0.48.

[0094] The padding rubber compound used to create the undulations in tire A has a dynamic loss tan δ1, measured at a temperature of 23° C. and under a stress of 0.7 MPa at 10 Hz, that is 60% less than that of the rubber compound CC1 of which the tread of A is made.

[0095] The performance aspects of the tire according to the invention can be seen in the following table in base 100. An evaluation above 100 means that the performance of the tire is better than that of the control. A better performance in terms of rolling resistance, and thus above 100, means that the rolling resistance of the tire is less than that of the control. Dry grip above 100 means that the time taken for a lap of the test circuit is less than that of the control tire.

TABLE-US-00001 TABLE I performance of the invention Rolling Dry resistance grip Wear Behaviour A—invention 100 102 100 100 B 100 100 100 100 C 92 101.5 90 90

[0096] The objective of the invention is to allow the use of “soft” or low-stiffness rubber compound in the tread. The prior art tires B, which do not have undulated crown layers or low-stiffness rubber compound in the tread, serve as control.

[0097] The use of low-stiffness rubber compound, as defined, in the tread on an architecture without undulation, visible in tire C, causes unacceptable degradations in all of the performance aspects of rolling resistance, wear and behaviour and only an improvement in dry grip, compared with the control tire B. Given the sporting use of the size and its high rolling resistance value, the deterioration in rolling resistance is such that the tire C is no longer acceptable in respect of environmental standards.

[0098] The invention, visible on tire A, not only makes it possible to remedy all of the deteriorations caused by the use of the low-stiffness rubber compound CC1 but surprisingly makes it possible to improve dry grip brought about a priori by the rubber compound CC1 by an additional 25% through the coupling between the architecture and the low-stiffness rubber compound.

[0099] The improvement of the invention in terms of rolling resistance was evaluated on a standard machine for measurements standardized in accordance with ISO 2850:2009.

[0100] The behaviour was evaluated by a measurement of the characteristic Dz of the Pacejka tire behaviour model well known to a person skilled in the art, at a pressure of 3 b, hot.

[0101] The tires were also fitted to a sports-type vehicle and tested on a winding circuit capable of generating significant transverse loadings. A professional driver, trained in assessing tires, compared tires A according to the invention with tires B and tires C according to the prior art and according to a rigorous testing process, under the same temperature conditions and ground running conditions, without knowing the characteristics of the tires being tested, repeating the measurement. The driver assigned scores to the tires. In all the tests performed, tires A according to the invention outclassed tires B and C in terms of vehicle behaviour, roadholding, on dry ground and in terms of grip.

[0102] Wear was evaluated in tests in which vehicles of the same type follow one another on a given circuit representing usage by customers. The vehicles were driven by professional drivers, trained in assessing tires and with the same type of driving style, according to a rigorous testing process, under the same temperature conditions and ground running conditions, without knowing the characteristics of the tires being tested, repeating the measurement. After each test day, the remaining tread pattern heights were measured. The wear given here corresponds to an improvement in wear after rolling that corresponds to 30% of the life of the tire.