High performance tyre

Abstract

A tyre (100) for high performance or ultra high performance cars is described, which is particularly suitable for use on track. The tyre (100) has a tread band (1) extending across an equatorial plane (X-X) of the tyre and having a void-to-rubber ratio equal to or smaller than 0.06; said tread band (1) comprises a circumferential groove (2) and a plurality of longitudinal grooves (4) repeated along the circumferential development of the tyre; said longitudinal grooves (4) are oppositely located to said circumferential groove (2) relative to the equatorial plane (X-X); said longitudinal grooves (4) have a plan surface area, measured on the radially outer surface of the tyre, greater than or equal to 350 mm2.

Description

[0001] HIGH PERFORMANCE TYRE DESCRIPTION

[0002] Field of the invention

[0003] The present invention relates to a tyre for high or ultra high performance cars and racing cars, preferably intended for use on track.

[0004] Prior art

[0005] The following documents describe some examples of high or ultra high performance car tyres: WO2022208244, W02009 / 004408, US12064998 e US2022185022.

[0006] Summary of the invention

[0007] High or ultra high performance car wheel tyres, also intended for use on track, are required to provide performance, steering precision and excellent road grip, in order to be able to effectively transfer high driving and braking torque to the ground and withstand high lateral stresses, even at the high operating temperatures associated with use on track.

[0008] Better results in terms of performance and grip could be obtained with “slick” tyres, such as those used in racing, and / or with tyres characterized by a very low, substantially zero, void-to-rubber ratio.

[0009] Although excellent in terms of performance, this kind of tyres are not allowed by some racing regulations, according to which the provision of a minimum number of grooves is mandatory.

[0010] Generally, in order to comply with this kind of regulations, manufacturers provide such grooves in the tread band of the tyres, nevertheless minimizing the extension thereof so as not to deviate too much from the lowest possible void-to-rubber ratio.

[0011] The Applicant has observed that the presence of grooves having a limited extension, in the circumferential and / or transverse direction, incorporated into tread bands having a very low void-to-rubber ratio, locally and abruptly increases the stiffness variation, particularly in the axial direction, negatively affecting the localized wear of the tyre and potentially causing an early decay in its performance.

[0012] The Applicant has thus faced the problem of providing tyres for high or ultra high performance cars, in particular intended for use on track, capable of ensuring high performance levels, at the same time limiting problems of localized wear and early performance decay typical of tyres for use on tracks characterized by the presence of grooves having a limited extension, in the circumferential and / or transverse direction, incorporated into tread bands having a very low void-to-rubber ratio.

[0013] The Applicant has focused its efforts on achieving this improvement by creating a tyre provided with tread band having a low void-to-rubber ratio achieved with only two different kinds of grooves, suitably distributed, oppositely located relative to the equatorial plane, so as to obtain a controlled mix of rubber portions in contact with the ground and yielding portions in the tread as a whole, in order to achieve performance and readiness of response without generating excessive and abrupt stiffness variations, particularly in the axial direction.

[0014] In a first aspect thereof, the invention relates to a tyre for high or ultra high performance cars, suitable in particular also for use on track, having a tread band extending across an equatorial plane of the tyre, said tread band having a void-to-rubber ratio equal to or smaller than 0.06; wherein said tread band comprises a circumferential groove and a plurality of longitudinal grooves repeated along the circumferential development of the tyre; said longitudinal grooves are oppositely located to said circumferential groove relative to the equatorial plane; said longitudinal grooves have a plan surface area, measured on the radially outer surface of the tyre, greater than or equal to 350 mm2. Preferably, said plan surface area is greater than or equal to 400 mm2.

[0015] The Applicant has found that, thanks to these features, the tyre of the invention can achieve high performance levels, particularly on track, while still being able to ensure controlled stiffness variations, particularly in the axial direction.

[0016] Without wishing to be bound by any specific theory, the Applicant believes that the presence of a limited number of properly distributed grooves having a non-negligible size lends the tyre a controlled and progressive yielding in certain portions of the tread band which does not compromise its performance, but rather makes it easier to limit localized wear and, consequently, to prevent an early decay of performance levels.

[0017] The presence of such a combination of grooves and rubber portions in contact with the ground also controls axial stresses when rolling with zero drift (i.e., when the travel direction forms a null angle relative to the equatorial plane).

[0018] For the purposes of the present invention, the following definitions apply:

[0019] By “tread pattern” it is meant the representation of all points of the tread band (including recesses) in a plane perpendicular to the equatorial plane of the tyre and tangential to the maximum diameter of the tyre.

[0020] The measurements of angles and / or linear quantities (distances, widths, lengths, etc.) and / or surface areas are to be intended as referring to the tread pattern as defined above. Furthermore, considering the angular arrangement of the grooves formed in the tread band relative to the equatorial plane of the tyre, such angular arrangement shall be understood, for each point of the groove, as referring to the acute angle (i.e., an angle comprised between 0° and 90° in absolute value) defined by a rotation starting from the equatorial plane to the direction tangent to the groove passing through that point.

[0021] By the term “equatorial plane” of the tyre it is meant a plane perpendicular to the rotation axis of the tyre and dividing the tyre into two substantially equal portions.

[0022] By “circumferential” direction it is meant a direction generally directed according to the rotation direction of the tyre, or slightly inclined (e.g., by at most about 20°) relative to the rotation direction of the tyre.

[0023] By “axial” direction it is meant a direction substantially parallel to the rotation axis of the tyre, or at most slightly inclined (e.g., by at most about 20°) relative to the rotation axis of the tyre. Generally, the axial direction is substantially perpendicular to the circumferential direction.

[0024] By “void-to-rubber ratio” it is meant the ratio between the total surface area of the recesses or grooves in a given portion of the tread band (possibly of the whole tread band) and the total surface area of the given portion of the tread band (possibly of the whole tread band).

[0025] The present invention, in one or more preferred aspects thereof, may comprise one or more of the features presented hereafter. Preferably, the longitudinal grooves may have a plan surface area, measured on the radially outer surface of the tyre, smaller than or equal to 2500 mm2.

[0026] Advantageously, the longitudinal grooves may have a maximum distance from the equatorial plane smaller than or equal to 7% of the circumferential development of the tyre.

[0027] Conveniently, the longitudinal grooves may have a maximum distance from the equatorial plane greater than or equal to 1% of the circumferential development of the tyre.

[0028] Conveniently, in order to ensure an as far as possible homogeneous behavior of the inner and outer sides of the tyre, the longitudinal grooves do not have intersection points with the equatorial plane.

[0029] Advantageously, the longitudinal grooves may have an extension greater than or equal to 10% of the circumferential development of the tyre.

[0030] Preferably, the longitudinal grooves may have an extension smaller than or equal to 20% of the circumferential development of the tyre.

[0031] Preferably, the longitudinal grooves may have a variable width along their extension. Conveniently, the longitudinal grooves may have maximum width 11 and a minimum width 12 such that the ratio of the maximum width 11 to the minimum width 12 is greater than or equal to 1.5.

[0032] Preferably, the ratio of the maximum width 11 to the minimum width 12 is smaller than or equal to 3.

[0033] Preferably, the longitudinal grooves may have a maximum width greater than or equal to about 3 mm. Preferably, the longitudinal grooves may have a maximum width smaller than about 15 mm.

[0034] Preferably, the longitudinal grooves may be mutually spaced apart in circumferential direction by a distance greater than or equal to 6% of the circumferential development of the tyre.

[0035] Conveniently, said distance is smaller than or equal to 12% of the circumferential development of the tyre.

[0036] Advantageously, the longitudinal grooves may have an extension direction relative to a circumferential direction so as to from an angle a smaller than or equal to 30° and greater than or equal to 4°.

[0037] Advantageously, due to the inclination thereof, the discontinuous longitudinal grooves generate a non-zero axial force while rolling, particularly when travelling in a straight line, such axial force compensating for the stress component generated by the structural part of the tyre.

[0038] Preferably, the longitudinal grooves may have a variable depth along their extension. Preferably, the longitudinal grooves may have a maximum depth smaller than or equal to 9 mm

[0039] Preferably, the longitudinal grooves may have a maximum distance from the equatorial plane smaller than the distance of the circumferential groove from the equatorial plane. Advantageously, the circumferential groove may have a distance from the equatorial plane smaller than or equal to 7% of the circumferential development of the tyre.

[0040] Preferably, said distance of the circumferential groove from the equatorial plane is greater than or equal to 1% of the circumferential development of the tyre.

[0041] Conveniently, the circumferential groove has a width smaller than or equal to 15 mm. Preferably, the circumferential groove has a width greater than or equal to 6.5 mm.

[0042] Advantageously, the circumferential groove may have a constant width along its extension.

[0043] Preferably, the circumferential groove may have a depth greater than o equal to 3 mm. Advantageously, the circumferential groove may have a constant depth along its extension.

[0044] Conveniently, the void-to-rubber ratio of said tread band is achieved through the circumferential groove and the plurality of longitudinal grooves relative to the whole tread band.

[0045] Further features and advantages of the invention shall become more apparent from the detailed description of some preferred, although not exclusive, embodiments of a tyre for high or ultra high performance cars, preferably intended for use on track, according to the present invention.

[0046] Brief description of the drawings Such description shall be made hereafter with reference to the accompanying drawings, provided only for indicating, and thus non-limiting, purposes, wherein: figure 1 shows a view of a first example of a tyre according to the invention; figure 2 is an enlarged view of a cross-section of the tyre of figure 1; and figure 3 is a schematic plan view of a tread band portion of the tyre of figure 1.

[0047] Detailed description of embodiments of the invention

[0048] With reference to the attached figures, a tyre for wheels of high or ultra high performance cars, also intended for use on track, is generally indicated at 100.

[0049] The structure of the tyre 100 is in itself of a conventional type and comprises a carcass, a tread band 1 placed in crown to the carcass, a pair of axially opposed sidewalls, ending in beads reinforced by bead cores and associated bead fillers. The tyre preferably also comprises a belt structure interposed between the carcass and the tread band. The carcass comprises one or more carcass plies anchored to the bead cores, whereas the belt structure comprises two radially superimposed belt strips. The belt strips are made up of pieces of a rubberized fabric incorporating metal cords parallel to one another in each strip and having a crossed orientation, preferably with a symmetrical inclination relative to the equatorial plane, relative to the cords of adjacent strips. Preferably, the belt structure also comprises, in a radially outer position, a third belt layer provided with cords oriented substantially parallel to the equatorial plane. Preferably, although not necessarily, the tyre according to the invention has a nominal section width equal to at least about 205, more preferably to at least about 225. For example, the tyre may have a nominal section width equal to 225, 245, 275, 295, 355. Preferably, the tyre according to the invention has a reduced section height. For example, the section height may be smaller than or equal to 60%, more preferably smaller than or equal to 50%, of the nominal section width.

[0050] The tread band 1 has overall a low void-to-rubber ratio, preferably smaller than 0.06. Preferably, the overall void-to-rubber ratio of the tread 1 is greater than 0.03.

[0051] Preferably, although not necessarily, the tyre according to the invention is of the asymmetrical type, i.e., the tread band pattern of the tyre on the right of the equatorial plane X-X is substantially different from that on the left. Therefore, the tyre 100 and / or the tread band 1 have an inner side to be preferably arranged, when fitted, towards the inside of the vehicle (on the right in the examples shown in the figures) and an outer side to be preferably arranged towards the outside of the vehicle (on the left in the examples shown in the figures).

[0052] Referring to the exemplary embodiment shown in the figures, the tread band 1 comprises a circumferential groove 2 and a plurality of longitudinal grooves 4 oppositely located relative to the equatorial plane X-X.

[0053] In other words, the plurality of longitudinal grooves 4 is located on one portion or side, of the two defined by the equatorial plane X-X, of the tread band 1 of the tyre, whereas the circumferential groove 2 is located on the remaining portion or side of the tread band 1. Preferably, the plurality of longitudinal grooves is located on the outer side of the tread band 1; preferably, the circumferential groove 2 is located on the inner side of the tread band 1.

[0054] The circumferential groove 2 has a substantially straight course in the circumferential direction, preferably over the whole circumferential development of the tyre.

[0055] For example, the circumferential groove 2 may have a width smaller than or equal to about 15 mm, more preferably smaller than or equal to about 12 mm, in any case greater than or equal to about 6.5 mm.

[0056] Preferably, the circumferential groove 2 has a width comparable to or slightly greater than the maximum width of the longitudinal grooves 4. For example, the circumferential groove 2 may have, at most, a width greater than about 10% of the maximum width of the longitudinal grooves 4.

[0057] The circumferential groove 2 may have a depth smaller than or equal to about 9 mm, more preferably smaller than or equal to about 8 mm, in any case greater than or equal to about 3 mm.

[0058] Still referring to the embodiments shown in figures 1-3, the circumferential groove 2 is formed so as to have a straight section of substantially trapezoidal shape.

[0059] The circumferential groove 2 is located at a distance D2 from the equatorial plane X-X smaller than or equal to 7% of the circumferential development of the tyre.

[0060] For example, the distance D2 from the equatorial plane X-X may be smaller than or equal to 100 mm.

[0061] Preferably, the circumferential groove 2 is located at a distance D2 from the equatorial plane greater than or equal to 1% of the circumferential development of the tyre.

[0062] For example, the distance D2 from the equatorial plane X-X may be greater than or equal to 40 mm.

[0063] The tread band 1 does not have any further kind of grooves or recesses in the portion identified by the equatorial plane X-X where the circumferential groove 2 is located. The plurality of longitudinal grooves 4 is instead located in the remaining portion relative to the equatorial plane X-X.

[0064] The longitudinal grooves 4 of the aforementioned plurality are cyclically repeated along the circumferential development of the tyre.

[0065] The longitudinal grooves 4 have a plan surface area, measured on the radially outer surface of the tyre, greater than or equal to 350 mm2.

[0066] The longitudinal grooves 4 have a plan surface area, measured on the radially outer surface of the tyre, smaller than or equal to 2500 mm2.

[0067] Preferably, the longitudinal grooves 4 have a substantially straight course.

[0068] The longitudinal grooves 4 have an extension greater than or equal to 10% of the circumferential development of the tyre 100.

[0069] Preferably, the longitudinal grooves have an extension smaller than or equal to 20% of the circumferential development of the tyre 100.

[0070] The longitudinal grooves 4 have a maximum width greater than or equal to about 3 mm. Preferably, the longitudinal grooves 4 have a maximum width smaller than about 15 mm. For example, they may have a maximum width of between about 6 and about 9 mm.

[0071] The longitudinal grooves 4 may have, as in the examples shown in figures 1-3, a width varying along their extension between a maximum width 11 and a minimum width 12. The difference between the maximum width 11 and the minimum width 12 is quite small and such that the ratio of the maximum width 11 to the minimum width 12 is greater than or equal to 1.5.

[0072] Preferably, the ratio of the maximum width 11 and the minimum width 12 is smaller than or equal to 3.

[0073] Preferably, although not necessarily, the longitudinal grooves 4 extend in a direction forming an inclination angle a relative to a direction parallel to the equatorial plane X- X smaller than or equal to 30°, preferably smaller than or equal to 20°.

[0074] Preferably, the longitudinal grooves 4 extend in a direction forming an inclination angle a relative to a direction parallel to the equatorial plane X-X greater than or equal to 4°. In a different embodiment, not shown in the figures, the longitudinal grooves 4 extend in a direction substantially parallel to the equatorial plane X-X.

[0075] The longitudinal grooves 4 do not have intersection points with the equatorial plane X- X, being instead located at a certain distance therefrom.

[0076] The longitudinal grooves 4 have a maximum distance DI from the equatorial plane X- X smaller than the distance D2 from the equatorial plane X-X of the circumferential groove 2.

[0077] According to another embodiment not shown in the figures, the longitudinal grooves 4 have a maximum distance DI from the equatorial plane X-X substantially equal to the distance D2 from the equatorial plane X-X of the circumferential groove 2.

[0078] Preferably, the longitudinal grooves 4 have a maximum distance DI from the equatorial plane X-X smaller than 6% of the circumferential development of the tyre. Even more preferably, the longitudinal grooves 4 have a maximum distance DI from the equatorial plane X-X smaller than 5% of the circumferential development of the tyre.

[0079] Preferably, the longitudinal grooves 4 have a maximum distance DI from the equatorial plane X-X greater than 1% of the circumferential development of the tyre.

[0080] For example, the longitudinal grooves 4 have a maximum distance DI from the equatorial plane X-X smaller than or equal to 70 mm.

[0081] However, the longitudinal grooves 4 may be located at a maximum distance DI from the equatorial plane X-X for example greater than or equal to 30 mm.

[0082] The longitudinal grooves 4 also have no points of mutual intersection, being in fact spaced apart from each other in the circumferential direction by a distance D3 greater than or equal to 6% of the circumferential development of the tyre.

[0083] Preferably, the distance D3 is smaller than or equal to 12% of the circumferential development of the tyre.

[0084] For example, the distance D3 may be greater than or equal to 100 mm.

[0085] For example, the distance D3 may be smaller than or equal to 200 mm.

[0086] In the embodiment shown in the figures, the longitudinal grooves 4 do not have a constant depth along their extension.

[0087] Preferably, the longitudinal grooves 4 have a decreasing depth moving away from the end having a greater width.

[0088] The longitudinal grooves 4 may have a maximum depth of smaller than 9 mm, more preferably smaller than or equal to about 8 mm, in any case greater than or equal to about 3 mm. Still referring to the embodiments shown in figures 1-3, the longitudinal grooves 4 are formed so as to have a straight section of substantially trapezoidal shape. Various modifications may be made to the embodiments described herein in detail, while still remaining within the scope of protection of the invention, as defined by the following claims.

Claims

CLAIMS1. Tyre (100) for high or ultra high performance cars, suitable in particular also for use on track, having a tread band (1) extending across an equatorial plane (X-X) of the tyre, said tread band (1) having a void-to-rubber ratio equal to or smaller than 0.06; wherein said tread band (1) comprises a circumferential groove (2) and a plurality of longitudinal grooves (4) repeated along the circumferential development of the tyre; said longitudinal grooves (4) are oppositely located to said circumferential groove (2) relative to the equatorial plane (X-X); said longitudinal grooves (4) have a plan surface area, measured on the radially outer surface of the tyre, greater than or equal to 350 mm2.

2. Tyre (100) according to claim 1, characterized in that said longitudinal grooves (4) have a plan surface area, measured on the radially outer surface of the tyre, smaller than or equal to 2500 mm2.

3. Tyre (100) according to claim 1 or 2, characterized in that said longitudinal grooves (4) have a maximum distance DI from the equatorial plane (X-X) smaller than or equal to 7% of the circumferential development of the tyre.

4. Tyre (100) according to any one of claims 1 to 3, characterized in that said circumferential groove (2) has a distance D2 from said equatorial plane (X-X) smaller than or equal to 7% of the circumferential development of the tyre.

5. Tyre (100) according to claim 4, characterized in that said distance D2 is greater than or equal to 1% of the circumferential development of the tyre.

6. Tyre (100) according to any one of claims 1 to 5, characterized in that said longitudinal grooves (4) have an extension greater than or equal to 10% of the circumferential development of the tyre (100).

7. Tyre (100) according to any one of the previous claims 1 to 6, characterized in that said longitudinal grooves (4) have an extension smaller than or equal to 20% of the circumferential development of the tyre (100).

8. Tyre (100) according to any one of claims 1 to 7, characterized in that saidlongitudinal grooves (4) have a variable width along their extension.

9. Tyre (100) according to any one of the previous claims 1 to 8, characterized in that said longitudinal grooves (4) have maximum width 11 and a minimum width 12 such that the ratio of the maximum width 11 to the minimum width 12 is greater than or equal toI.5.10 Tyre (100) according to any one of the previous claims 1 to 9, characterized in that said longitudinal grooves (4) have maximum width 11 and a minimum width 12 such that the ratio of the maximum width 11 to the minimum width 12 is smaller than or equal to 3.I I . Tyre (100) according to any one of the previous claims 1 to 10, characterized in that said longitudinal grooves (4) are mutually spaced apart in circumferential direction by a distance D3 greater than or equal to 6% of the circumferential development of the tyre.

12. Tyre (100) according to claim 11, characterized in that said distance is smaller than or equal to 12% of the circumferential development of the tyre.

13. Tyre (100) according to any one of claims 1 to 12, characterized in that said longitudinal grooves (4) have an extension direction relative to a circumferential direction so as to from an angle a smaller than or equal to 30° and greater than or equal to 4°.

14. Tyre (100) according to any one of claims 1 to 13, characterized in that said longitudinal grooves (4) have a variable depth along their extension.

15. Tyre (100) according to any one of claims 1 to 14, characterized in that said circumferential groove (2) has a constant width along its extension.

16. Tyre (100) according to any one of claims 1 to 15, characterized in that said circumferential groove (2) has a constant depth along its extension.

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