Tire for two-wheeled vehicles, comprising a tread having a circumferentially continuous groove

Abstract

A tire for a motorized two-wheeled vehicle comprising a reinforcing structure of the carcass type, made up of reinforcing elements, anchored on each side of the tire to a bead the base of which is intended to be mounted on a rim seat, each bead being extended radially outward by a sidewall, the sidewalls radially toward the outside joining to a tread. At least the central part of the tread comprises at least one circumferentially continuous cut, the cut being made up, for at least 80% of its length of at least one incision and at most 20% of at least one part having a width greater than that of an incision and the apparent area of the at least one incision is greater than the apparent area of the at least one part having a width greater than that of an incision.

Claims

1. A tire for a motorized two-wheeled vehicle comprising: a carcass reinforcing structure made up of reinforcing elements, anchored on each side of the tire to a bead the base of which is adapted to be mounted on a rim seat, each bead being extended radially outward by a sidewall, the sidewalls extending radially toward the outside joining to a tread, wherein at least the central part of the tread comprises at least one circumferentially continuous cut having opposed uninterrupted walls, wherein said circumferentially continuous cut is made up, for at least 80% of its length, of at least two incisions and, for at most 20% of its length, of at least two wells, each well having a width greater than that of an incision, wherein an apparent area of said at least two incisions is greater than an apparent area of said at least two wells, wherein each incision is located between two wells, wherein each incision is curved along a circumferential direction of the surface of the tread, wherein the width of each incision is uniform along its depth, and wherein the wells and the incisions have the same depth.

2. The tire according to claim 1, wherein the apparent area of said at least two wells is less than 75% of the apparent area of said at least two incisions.

3. The tire according to claim 1, wherein at least one well has a width greater than 2.5 mm.

4. The tire according to claim 1, wherein said at least one circumferentially continuous cut is formed, for at least 5% of its length, of at least two wells having a width greater than 2.5 mm.

5. The tire according to claim 1, further comprising: at least one circumferentially continuous groove spaced axially apart from the at least one circumferentially continuous cut, and at least one transverse groove coupled to the at least one circumferentially continuous groove so as to intersect the circumferentially continuous groove at an angle to the radial direction to give the tread a tread pattern direction.

6. The tire according to claim 1, wherein the tire has at least a W speed rating.

7. A tire for a motorized two-wheeled vehicle comprising: a carcass reinforcing structure made up of reinforcing elements, anchored on each side of the tire to a bead the base of which is adapted to be mounted on a rim seat, each bead being extended radially outward by a sidewall, the sidewalls extending radially toward the outside joining to a tread, wherein at least the central part of the tread comprises at least one circumferentially continuous cut forming two walls configured as opposed uninterrupted walls, wherein said circumferentially continuous cut is made up, for at least 80% of its length, of incisions and, for at most 20% if its length, of at least two wells, wherein distances between walls of the incisions are less than one third of distances between walls of the wells, wherein an apparent area of said incisions is greater than an apparent area of the wells, wherein each incision is located between two wells, wherein each incision is curved along a circumferential direction of the surface of the tread, wherein a width of each incision is uniform along its depth, and wherein the wells and the incisions have the same depth.

8. The tire according to claim 1 or 7, wherein said at least two incisions make an angle with the circumferential direction on the surface of the tread.

9. The tire according to claim 8, wherein the width of each of well is greater than 2.5 mm.

10. The tire according to claim 1 or 7, wherein the tread comprises at least one central part and two axially external parts, and wherein at least the surface of the tread consists of a first polymer compound extending over at least part of the central part and of at least one second polymer compound having physico-chemical properties different from those of said first polymer compound and covering at least part of the axially external parts of the tread.

11. The tire according to claim 1 or 7, wherein the reinforcing elements of the carcass-type reinforcing structure make with the circumferential direction an angle of between 65 and 90.

12. The tire according to claim 1 or 7, further comprising a crown reinforcing structure positioned radially inward of the tread and surmounting carcass reinforcing structure, the crown reinforcing structure comprising at least one working layer of reinforcing elements, wherein the reinforcing elements make with the circumferential direction angles of between 10 and 80.

13. The tire according to claim 12, wherein the angles made by the reinforcing elements of said at least one working layer with the longitudinal direction vary in a transverse direction.

14. The tire according to claim 1 or 7, further comprising a crown reinforcing structure positioned radially inward of the tread and surmounting carcass reinforcing structure, the crown reinforcing structure comprising at least one layer of circumferential reinforcing elements.

15. The tire according to claim 14, wherein the circumferential reinforcing elements are distributed in a transverse direction at a variable pitch.

16. The tire according to claim 1 or 7, wherein each well is circular.

17. The tire according to claim 1 or 7, wherein each well has a width greater than 2.5 mm and each incision has a width less than 1.5 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further details and advantageous features of the invention will become more clearly apparent hereinafter from the description of the embodiments of the invention given with reference to the following drawings:

(2) FIG. 1 is a partial perspective view of a diagram of a tire according to a first embodiment of the invention;

(3) FIG. 2 is a partial perspective view of a diagram of a tire according to a second embodiment of the invention;

(4) FIG. 3 is a partial perspective view of a diagram of a tire according to a third embodiment of the invention; and

(5) FIG. 4 is a partial view from above of a diagram of a tire according to the third embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

(6) In order to make them easier to understand, FIGS. 1 to 4 are not drawn to scale.

(7) FIG. 1 depicts a partial perspective view of a tire 1, and more specifically of the external surface 2 of the tread thereof, intended to be fitted to the front wheel of a motorbike. The tire 1 has a curvature in excess of 0.15 and preferably in excess of 0.3. The curvature is defined by the ratio Ht/Wt, which means the ratio of the height of the tread to the maximum width of the tread of the tire.

(8) In a way which has not been depicted in the figures, the tire 1 comprises a carcass reinforcement consisting of a layer comprising reinforcing elements of textile type. The layer consists of reinforcing elements laid radially. The radial positioning of the reinforcing elements is defined by the angle at which the said reinforcing elements are laid; a radial arrangement corresponds to the said elements being laid with respect to the longitudinal direction of the tire at an angle of between 65 and 90.

(9) The carcass reinforcement is anchored on each side of the tire 1 in a bead the base of which is intended to be mounted on a rim seat. Each bead is extended radially outwards by a side wall, the side wall radially towards the outside joining to the tread.

(10) The tire 1 further comprises a crown reinforcement consisting for example of two layers of reinforcing elements making angles with the circumferential direction, the said reinforcing elements being crossed from one layer to the next making between them angles for example of 50 in the region of the equatorial plane, the reinforcing elements of each of the layers making an angle of, for example, 25, with the circumferential direction.

(11) The crown reinforcement may even consist of a layer of circumferential reinforcing elements instead of the layers of reinforcing elements that make angles with the circumferential direction or alternately in combination therewith.

(12) The tread 2 of the tire 1 comprises a tread pattern consisting of circumferentially directed continuous grooves 3 and transverse grooves 4, the main direction of the latter being at a slight angle to the radial direction in order to give the said tread pattern a direction.

(13) According to the invention, the tread has a circumferential cut consisting of incisions or slits 5, the non-zero widths of which are very much smaller than those of the abovementioned grooves 3 and 4. These incisions 5 are joined together by regions of greater width that can be qualified as wells 6.

(14) In the case of FIG. 1, the circumferentially continuous cut consisting of the incisions 5 and of the wells 6 more or less coincides with a circumferential plane and, in this particular instance, with the equatorial plane.

(15) The presence of the incisions 5 makes it possible during running to increase the flattening-out of the tread in order to optimize the area of the contact patch. The presence of the incision also makes it possible to reduce the compressive loading on the rubber compounds of which the tread is made. Further, the short distance between the walls of the incision makes it possible to avoid an absence of material that would reduce the area of the contact patch.

(16) This area is, however, slightly reduced by the presence of the wells which do not themselves close up completely at the surface of the tread as the tire is squashed down onto the ground. This is why these do not represent any more than 20% of the length of the circumferentially continuous cut; torque transfer is almost undisturbed by their presence in the contact patch.

(17) As explained earlier, the wells are advantageously located at the junctions between mold segments in order to avoid the risk of cracking. Depending on the number of segments that make up the mold, it is possible to provide additional wells in order to give the surface of the tread a more uniform appearance as the wheel turns.

(18) The apparent area of all of the incisions 5 of the tire is equal to 920 mm.sup.2.

(19) The apparent area of all of the wells 6 of the tire is equal to 585 mm.sup.2.

(20) According to the invention, the apparent area of all of the incisions 5 is greater than the apparent area of all of the wells 6.

(21) FIG. 2 depicts a partial perspective view of a tire 21 similar to that of FIG. 1 and which differs therefrom by a circumferentially continuous cut which on the surface of the tread 22 is Z-shaped or, more precisely, consists of a succession of incisions 25 the orientation of which makes an angle with the circumferential direction and which are connected to one another by wells 26.

(22) This orientation of the incisions means that in addition to their contribution towards the flattening of the tire in the torque-transfer contact patch, they can also contribute directly to improving grip, particularly on wet surfaces.

(23) The presence of the wells 26 advantageously coincides according to the invention with the regions where the mold segments meet. They are also present at the end of each of the incisions to join two incisions together and avoid there being any direct connection between two incisions as this might be a potential source of crack initiators.

(24) The apparent area of all the incisions 25 of the tire is equal to 1140 mm.sup.2.

(25) The apparent area of all of the wells 26 of the tire is equal to 585 mm.sup.2.

(26) According to the invention, the apparent area of all of the incisions 25 is greater than the apparent area of all of the wells 26.

(27) FIGS. 3 and 4 respectively depict a partial perspective view and a partial view from above of a tire 31 differing from that of FIG. 2 by incisions 35 of which the line on the surface of the tread 32 is no longer straight but curved.

(28) This curved profile of the incisions 35 encourages even better grip, notably on wet surfaces.

(29) The apparent area of all of the incisions 35 of the tire is equal to 1180 mm.sup.2.

(30) The apparent area of all of the wells 36 of the tire is equal to 585 mm.sup.2.

(31) According to the invention, the apparent area of all of the incisions 35 is greater than the apparent area of all of the wells 36.

(32) Contact patch area measurements were taken firstly on a tire according to the invention as depicted in FIG. 1 and secondly on a first reference tire R1 of the same size but with no continuous circumferential cut and on a second reference tire R2 having a circumferential groove with a width of 6.5 mm.

(33) The tire measured is a tire of size 180/55 ZR 17, inflated to 2.5 bar and compressed under a load of 180 daN.

(34) The measured relative values were 100 for the reference tire R1, 95 for the reference tire R2 and 110 for the tire according to the invention.

(35) The circumferentially continuous cut according to the invention does therefore allow an increase in the surface area of the contact patch and therefore promotes better transmission of driving or braking torque.

(36) The value obtained with reference tire R2 also confirms that a circumferential groove limits the compressive loading on the tread and therefore limits energy losses but that the absence of rubber compound corresponding to the groove reduces the surface area of the tire in contact with the ground in the contact patch.

(37) The invention must not be considered to be limited to the description of the examples above. In particular, the invention must not be considered to be limited to the case of a tire intended to be fitted to the rear wheel of a motorized two-wheeled vehicle as it is also of benefit for a front wheel.