TIRE HAVING A REGROOVABLE TREAD

Abstract

The invention relates to a tire (1) that can be regrooved at least once, and the tread of which has at least one re-cuttable groove (3).

According to the invention, after regrooving, the height (H.sub.R) of said at least one re-cut groove (3) is greater than or equal to 70% of the groove height (H.sub.N3) of said at least one re-cuttable groove of the tire when new.

Claims

1.-9. (canceled)

10. A tire (1), that can be regrooved at least once, comprising a crown reinforcement (5), the crown reinforcement capped radially by a tread (6) made of at least one elastomer compound and connected to two beads via two sidewalls, the tread (6) having at least one re-cuttable groove (3) forming at least one tread-pattern element that constitutes a tread pattern of the tire, having a height (H.sub.N3) between a bottom of the at least one re-cuttable groove (3) and a tread surface when the tire is new, wherein, after regrooving, a height (H.sub.R) of the at least one re-cuttable groove (3) is greater than or equal to 70% of a groove height (H.sub.N) of the at least one re-cuttable groove (3) of the tire when new.

11. The tire (1) according to claim 10, wherein a height corresponding to a distance between the tread surface when new and the bottom of the at least one re-cuttable groove (3) after a regrooving operation is greater than or equal to 200% of the height (H.sub.N) between the bottom of the at least one re-cuttable groove (3) and the tread surface when the tire is new.

12. The tire (1) according to claim 10, wherein the at least one re-cuttable groove (3) is circumferential.

13. The tire (1) according to claim 10, wherein the at least one re-cuttable groove (3) is transverse.

14. The tire (1) according to claim 10, wherein the at least one re-cuttable groove (3) is oblique.

15. The tire (1) according to claim 10, wherein the at least one re-cuttable groove (3) can be re-cut at least twice.

16. The tire (1) according to claim 15, wherein an elastomer compound regrooved during a first regrooving operation is different from an elastomer compound regrooved during a second regrooving operation.

17. The tire (1) according to claim 10, wherein a regroovable elastomer compound is different from at least part of the at least one elastomer compound that constitutes the tread.

18. The tire (1) according to claim 10, wherein the tread comprises, at least locally, at least two layers of elastomer compounds radially superposed in the tread.

Description

[0053] Further details and advantageous features of the invention will become apparent hereinafter from the description of exemplary embodiments of the invention, with reference to FIGS. 1 to 3 in which:

[0054] FIG. 1 is a schematic meridian view of a tire according to a first exemplary embodiment of the invention,

[0055] FIG. 2 is a schematic meridian view of a tire according to a second exemplary embodiment of the invention,

[0056] FIG. 3 is a schematic depiction of the rolling resistance of a tire as it wears, for a reference tire and for two tires according to the invention.

[0057] In order to make them easier to understand, FIGS. 1 and 2 are not drawn to scale. FIGS. 1 and 2 show only a half-view of a tire, which extends symmetrically with respect to the axis XX, which represents the circumferential median plane, or equatorial plane, of a tire.

[0058] In FIGS. 1 and 2, the tire 1, of dimension 315/70R22.5, comprises a radial carcass reinforcement 2 anchored in two beads, around bead wires (not depicted). The carcass reinforcement 2 is formed of a single layer of metal cords. The carcass reinforcement 2 is hooped by a crown reinforcement 5, itself capped by a tread 6. The tread comprises three grooves 3 forming four ribs 4 and the two axially-central ribs are cut with oblique grooves that pass all the way through and are not depicted in FIGS. 1 and 2.

[0059] The lower sidewall regions and the beads of the tire 1 are in particular not depicted in the figures.

[0060] In FIGS. 1 and 2, the crown reinforcement 5 is formed radially from the inside to the outside: [0061] of a first working layer 51 formed of inextensible metal cords which are continuous across the entire width of the ply and oriented at an angle ?1, [0062] of a layer of circumferential reinforcing elements 53, which is formed of 21.23 elastic steel metal cords, with a pitch spacing of 2 mm, and [0063] of a second working layer 52 formed of inextensible metal cords which are continuous across the entire width of the ply, oriented at an angle ?2 and crossed with the metal cords of the first working layer.

[0064] The axial width L.sub.51 of the first working layer 51 is equal to 246 mm.

[0065] The axial width L.sub.52 of the second working layer 52 is equal to 228 mm.

[0066] The axial width L.sub.53 of the layer of circumferential reinforcing elements 53 is itself equal to 200 mm.

[0067] In FIG. 1, according to the invention, the grooves 3 are of re-cuttable type. As illustrated in FIG. 1, the grooves 3 consist of a single layer A forming the bottom of the grooves when new and corresponding to a single regrooving operation.

[0068] The height H.sub.N3 of the grooves 3 when the tire is new, is equal to 7.5 mm.

[0069] The height H.sub.R of the grooves 3 after regrooving is equal to 9.5 mm and therefore represents 127% of H.sub.N3.

[0070] This height H.sub.R corresponds to a regrooving by 7.5 mm while there still remains 2 mm of the initial groove height, which value is close to the legal limit generally permitted, corresponding to the minimum height and to the height of the tread-wear indicators. This limit is indicated by the line 7 in FIG. 1.

[0071] The height, that cannot be measured before this regrooving and that corresponds to the distance between the tread surface when new and the bottom of a groove 3 after regrooving, is thus equal to 15 mm. The ratio of this non-measurable height equal to 15 mm to the height H.sub.N3 is equal to 2 and therefore is indeed greater than or equal to 200%.

[0072] The height H.sub.R, measured after regrooving, and the height, that cannot be measured before regrooving and that corresponds to the distance between the tread surface when new and the bottom of a groove 3 after regrooving, can also be determined on a new tire from the regrooving diagrams supplied by the manufacturer as explained earlier.

[0073] FIG. 2 illustrates a tire the grooves 23 of which can be re-cut twice. The grooves 23 when new consist of two layers B and C forming the bottom of the grooves when new and corresponding to these two regrooving operations.

[0074] The height H.sub.N23 of the grooves 23 when the tire is new, is equal to 6 mm.

[0075] The height H.sub.R1 of the grooves 23 after the first regrooving operation is equal to 7 mm and therefore represents 117% of H.sub.N23.

[0076] This height H.sub.R1 corresponds to a regrooving by 5 mm while there still remains 2 mm of the initial groove height, which value is close to the legal limit generally permitted, corresponding to the minimum height and to the tread-wear indicators. This limit is indicated by the line 71 in FIG. 2.

[0077] The height, that cannot be measured before a first regrooving operation and that corresponds to the distance between the tread surface when new and the bottom of the groove after the first regrooving operation, is thus equal to 11 mm.

[0078] The height H.sub.R1, measured after the first regrooving operation, and the height, that cannot be measured before a first regrooving operation and that corresponds to the distance between the tread surface when new and the bottom of the groove after the first regrooving operation, can also be determined on a new tire from the regrooving diagram supplied by the manufacturer as explained earlier.

[0079] The height H.sub.R2 of the grooves 23 after the second regrooving operation is equal to 6 mm and therefore represents 100% of H.sub.N23. And the height H.sub.R2 of the grooves 23 after the second regrooving operation represents 86% of H.sub.R1.

[0080] This height H.sub.R2 corresponds to a regrooving by 4 mm while there still remains 2 mm of the initial groove height, which value is close to the legal limit generally permitted, corresponding to the minimum height. This limit is indicated by the line 72 in FIG. 2.

[0081] The height, that cannot be measured before the two regrooving operations and that corresponds to the distance between the tread surface when new and the bottom of the grooves 23 after the second regrooving operation, is thus equal to 15 mm. The ratio of this non-measurable height equal to 15 mm to the height H.sub.N23 is equal to 2.5 and therefore is indeed greater than or equal to 200%.

[0082] The height H.sub.R2, measured after the second regrooving operation, and the height, that cannot be measured before the two regrooving operations and that corresponds to the distance between the tread surface when new and the bottom of the grooves after the second regrooving operation, can also be determined on a new tire from the regrooving diagram supplied by the manufacturer as explained earlier.

[0083] The tire thus depicted in FIG. 2 is anticipating two regrooving operations at various stages in the wearing of the tire. Advantageously according to the invention, the grooves are re-cut simultaneously in each regrooving step.

[0084] According to other variant embodiments of the invention, the re-cutting of the various grooves of a tire may be scheduled to be performed in a manner that is spread over time. According to these variant embodiments, the tire may comprise a proportion of grooves that can be re-cut just once, and of other grooves that can be re-cut a plurality of times. A tire could thus comprise a combination of grooves such as those illustrated in FIG. 1 and of grooves such as those illustrated in FIG. 2.

[0085] Tires were produced based on the elastomeric compound described hereinbelow by way of the compound of which the tread is formed.

TABLE-US-00001 Compound NR 80 BR 20 N234 48 6PPD - 1.3DIMETHYL 3 BUTYL PHENYL PARAPHENYLENE- DIAMINE ZnO 3 SULFUR 1.5 Accelerator (CBS) 0.9

[0086] The values of the constituent ingredients are expressed in phr (parts by weight per hundred parts of rubber/elastomer).

[0087] A reference tire R similar to the one in the figures was produced to a configuration corresponding to the traditional embodiments for regrooving. It comprises a single regrooving layer at the bottom of the grooves, such that the height of the grooves after regrooving is equal to 5 mm and represents 42% of the height of the grooves when new, which is itself equal to 12 mm. This height after regrooving, which is equal to 5 mm, corresponds to a regrooving by 3 mm while there still remains 2 mm of the initial groove height, which value is close to the legal limit generally permitted, corresponding to the minimum height. The height, that cannot be measured before regrooving and that corresponds to the distance between the tread surface when new and the bottom of the grooves after regrooving, is thus equal to 15 mm.

[0088] As in the case of the tires according to the invention and as explained hereinabove, the height, measured after a first regrooving operation, and the height, that cannot be measured before regrooving and that corresponds to the distance between the tread surface when new and the bottom of the grooves afterwards, can also be determined on a new tire from the regrooving diagrams supplied by the manufacturer.

[0089] Tires T1 and T2 conforming to the invention were produced.

[0090] Tire T1 conforms to that depicted in FIG. 1.

[0091] Tire T2 conforms to that depicted in FIG. 2.

[0092] Measurements of grip on wet ground were taken on each of the tires under identical running conditions in accordance with the ISO 15222 standard. The results of the measurements are given in the following table; a value of 100 being assigned to the tire R when new. Values higher than 100 express superior grip performance.

TABLE-US-00002 After After New regrooving once regrooving twice Tire R 100 96 Tire T1 100 100 Tire T2 98 100 100

[0093] These values show that at all stages in the wearing of the tire the wet-grip properties are maintained.

[0094] Moreover, wearing tests were conducted to demonstrate substantially identical performance between the tires T1 and T2 according to the invention and the reference tire R. Specifically, the volume of elastomer compounds constituting the tread and that can be worn away during the course of the life of the tire and of the regrooving operation or operations is substantially the same for all three tires, leading to very similar tire lifespans. Tire life may be slightly superior for tires T1 and T2 in harsh-wear scenarios, and slightly inferior in what might be termed mild-wear scenarios, the difference in ranking being associated with the difference in tread stiffness, the depth of the grooves being of order one with reference to tread stiffness.

[0095] Rolling resistance measurements were also carried out on each of the tires under identical running conditions according to Regulation No 117 of the United Nations Economic Commission for Europe (UNECE). The results of the measurements are given in the following table, a value of 100 being assigned to the tire R when new. A value of 90 signifies that the coefficient of rolling resistance is reduced by 10% and corresponds to superior performance in terms of rolling resistance. Measurements were performed on a new tire and on a tire planed down to the level of the usual wear limit of around 2 mm on each of the tires R, T1 and T2. A measurement was performed again after each of the tires R, T1 and T2 had been regrooved, and then another measurement was performed on each of the tires R, T1 and T2 when they had been again planed down to the level of the usual wear limit of around 2 mm. Tire T2 was then measured once again after the second regrooving operation and then a final measurement was performed on this tire T2 after it had been planed down to the level of the usual wear limit of around 2 mm.

TABLE-US-00003 After After Wear regrooving Wear regrooving Wear New limit once limit twice limit Tire R 100 68 72 62 Tire T1 94 77 86 62 Tire T2 92 80 86 70 75 62

[0096] FIG. 3 schematically illustrates how the rolling resistance of each of the tires R, T1 and T2 evolves from the as-new state to the end-of-life, namely over the 13 mm of wear of the tread. In FIG. 3, the ordinate axis represents the measured or estimated value of the rolling resistance of the tire, as a function of the height of tread pattern worn away, and the abscissa axis represents this height starting from 0 and ending at 13 mm. The 13 mm correspond to the 15 mm of tread provided on each of the tires R, T1 and T2, accounting for the 2 mm kept at the end-of-life of the tires, which value is close to the legal limit generally permitted.

[0097] The three lines plotted in this FIG. 3 correspond to each of the tires R, T1 and T2. Calculating the areas bounded by these three plotted lines makes it possible to estimate the mean rolling resistance of each of these tires over the use thereof. The results showed that tire T1 yields an improvement of 7% relative to tire R, and that tire T2 yields an improvement of 14% relative to tire R.