Pneumatic Tire Tread for a Heavy Duty Vehicle Comprising Stone-Expelling and Noise-Preventing Protuberances

Abstract

A tire tread (1) for a heavy construction plant vehicle, and aims to improve both its ability to not retain stones in its voids, during off-road use, and its ability to dampen the noise that it generates, during on-road use. At least one longitudinal groove (6) of the tread (1) has a longitudinal distribution of protuberances (7), and any protuberance (7) has a height H′ at least equal to 0.9 times the depth H of the groove (6) and has a first portion (71), having a height H1, a width W1 and a thickness T1, and a second portion (72), having a height H2, a width W2 and a thickness T2, satisfying the relationships: H′=H1+H2, 0.6*H′<=H2<=0.9*H′, W2>=0.25*W, T2<=min(3 mm; 1/3*T1), W1>=0.5*W, T1>=H1.

Claims

1. A tire tread for a heavy vehicle, which tread is intended to come into contact with the ground via a tread surface and comprises cuts delimiting rubber blocks that extend from a bottom surface in a radial direction (ZZ′), at least one cut being a longitudinal groove delimited by two opposite lateral walls that are connected to each other by a groove bottom and extending over the entire length L of the tread in a longitudinal direction (XX′), any longitudinal groove having a depth H, measured between the tread surface and the groove bottom in a radial direction (ZZ′), and a width W, measured between the two lateral walls in the tread surface in a transverse direction (YY′), at least one longitudinal groove comprising a longitudinal distribution of protuberances that bear against one or the other of the lateral walls two consecutive protuberances which do not necessarily bear against the same lateral wall being spaced apart by a pitch P, wherein any protuberance of the longitudinal groove extends radially outwards from the groove bottom over a height H′ at least equal to 0.9 times the depth H of the longitudinal groove and any protuberance of the longitudinal groove comprises a first portion, extending radially outwards from the groove bottom over a height H1, transversely towards the inside of the longitudinal groove from a lateral wall over a width W1 and longitudinally over a thickness T1, and a second portion, extending radially outwards from the first portion over a height H2, transversely towards the inside of the longitudinal groove from a lateral wall over a width W2 and longitudinally over a thickness T2, such that the following relationships are satisfied:
H′=H1+H2
0.6*H′<=H2<=0.9*H′
W2<=0.25*W
T2<=min(3 mm; 1/3*T1)
W1>=0.5*W
T1>=H1

2. The tread according to claim 1, wherein the protuberances of the longitudinal groove alternately bear against one or the other of the lateral walls.

3. The tread according to claim 1, wherein the protuberances of the longitudinal groove are spaced apart in pairs by a pitch P at most equal to 0.1 times the length L of the tread.

4. The tread according to any claim 1, wherein any protuberance of the longitudinal groove extends radially outwards from the groove bottom over a height H′ equal to the depth H of the groove.

5. The tread according to claim 1, wherein the second portion extends longitudinally over a thickness T2 at least equal to 1 mm.

6. The tread according to claim 1, wherein the second portion extends towards the inside of the longitudinal groove from a lateral wall over a width W2 at most equal to 0.75 times the width W of the longitudinal groove.

7. The tread according to claim 1, wherein the first portion extends longitudinally over a thickness T1 at most equal to 4 times the height H1.

8. The tread according to claim 1, wherein the first portion comprises lateral faces that form, with the transverse direction (YY′), an angle at most equal to 45°.

9. The tread according to claim 1, the longitudinal groove comprising at least one intersection with a transverse groove, wherein any intersection of the longitudinal groove and a transverse groove is provided with a protuberance.

10. The tread according to claim 9, wherein the first portion extends towards the inside of the longitudinal groove from a lateral wall over a width W1 at most equal to 2 times the width W of the longitudinal groove.

11. A tire for a heavy vehicle which tire comprises a tread according to claim 1.

Description

[0037] The features of the invention are illustrated by the schematic FIGS. 1, 2A, 2B, 2C and 3, which are not drawn to scale:

[0038] FIG. 1: View from above of a portion of a tread according to the invention,

[0039] FIG. 2A: Perspective view of a protuberance of a longitudinal groove of a tread according to the invention,

[0040] FIG. 2B: View in transverse cross section of a protuberance of a longitudinal groove of a tread according to the invention,

[0041] FIG. 2C: View from above of a protuberance of a longitudinal groove of a tread according to the invention,

[0042] FIG. 3: Perspective view of a protuberance positioned at the intersection of a longitudinal groove and a transverse void according to a preferred embodiment of the invention.

[0043] FIG. 1 is a view from above of a portion of a tread 1 according to the invention. The tire tread 1 for a heavy vehicle, which tread is intended to come into contact with the ground via a tread surface 2, comprises cuts 3 delimiting rubber blocks 4 that extend from a bottom surface 5 in a radial direction ZZ′. The cuts 3 in the tread 1 are either longitudinal grooves 6 or transverse voids 8. In the embodiment shown, of the four longitudinal grooves 6, each delimited by two opposite lateral walls 61 that are connected to each other by a groove bottom 62, and extending over the entire length L of the tread 1 in a longitudinal direction XX′, two of them, which are positioned in a central portion of the tread 1, each comprise a longitudinal distribution of protuberances 7 bearing alternately against one and the other of the lateral walls 61, two consecutive protuberances positioned respectively on two opposite lateral walls 61 being spaced apart by a pitch P. The pitch P is variable since said protuberances 7 are exclusively positioned, in the embodiment shown, at the intersection of a longitudinal groove 6 and a transverse void 8. Only the central longitudinal grooves are provided with protuberances 7, since the central portion is subjected to the highest contact pressures and is therefore the most sensitive to the retention of stones.

[0044] FIG. 2A is a perspective view of a protuberance 7 of a longitudinal groove 6 of a tread according to the invention. The protuberance 7 of the longitudinal groove 6 comprises a first portion 71, extending radially outwards from the groove bottom 62 positioned on the bottom surface 5, and bearing on the lateral wall 61, and a second portion 72, extending radially outwards from the first portion 71 and bearing on the lateral wall 61. The first, radially inner portion 71 ensures the stone ejector function, and the second, radially outer portion 72 ensures the anti-noise function.

[0045] FIG. 2B is a view in transverse cross section of a protuberance 7 of a longitudinal groove 6 of a tread according to the invention. The protuberance 7 of the longitudinal groove 6 extends radially, in the direction ZZ′, outwards from the groove bottom 62 over a height H′ at least equal to 0.9 times the depth H of the groove 6. The first portion 71 extends radially, in the direction ZZ′, outwards from the groove bottom 62 over a height H1, and transversely, in the direction YY′, towards the inside of the longitudinal groove 6 from a lateral wall 61 over a width W1. The second portion 72 extends radially, in the direction ZZ′, outwards from the first portion 71 over a height H2 and transversely, in the direction YY′, towards the inside of the longitudinal groove 6 from a lateral wall 61 over a width W2. According to the invention, the following relationships between the geometric characteristics described above are satisfied: H′=H1+H2, 0.6*H′<=H2<=0.9*H′, W2>=0.25*W and W1>=0.5*W.

[0046] FIG. 2C is a view from above of a protuberance 7 of a longitudinal groove 6 of a tread according to the invention. The first portion 71 extends transversely, in the direction YY′, towards the inside of the longitudinal groove 6 from a lateral wall 61 over a width W1 and longitudinally, in the direction XX′, over a thickness T1. The second portion 72 extends transversely, in the direction YY′, towards the inside of the longitudinal groove 6 from a lateral wall 61 over a width W2 and longitudinally, in the direction XX′, over a thickness T2. According to the invention, the following relationships between the geometric characteristics described above are satisfied: W2>=0.25*W, T2<=min (3 mm; 1/3*T1), W1>=0.5*W and T1>=H1.

[0047] FIG. 3 is a perspective view of a protuberance 7 positioned at the intersection of a longitudinal groove 6 and a transverse void 8 according to a preferred embodiment of the invention. The first portion 71 comprises lateral faces 711 that form, with the transverse direction YY′, an angle at most equal to 45° . The first portion 71 has a pyramid shape, of which the inclined lateral faces 711 make easier the mobility of the stones in the longitudinal groove, and therefore their ejection out of the tread, during running of the tire. The second, anti-noise portion 72 has the same characteristics as above.

[0048] The inventors have more particularly studied this invention for a tire of size 445/95R25 intended to be mounted on a mobile crane. According to the ETRTO standard, such a tire has to be capable of carrying a load equal to 6700 kg, when it is inflated to a pressure equal to 9 bar.

[0049] The inventors compared, in the 445/95R25 tire size, a tire comprising a tread having a tread pattern with anti-noise and stone ejector protuberances, in accordance with the invention, and a reference tire comprising a tread having a tread pattern identical to that of the invention but without anti-noise and stone ejector protuberances.

[0050] Table 1 below presents the characteristics of an anti-noise and stone ejector protuberance of the tread according to the invention:

TABLE-US-00001 TABLE 1 Characteristics of an anti-noise and stone ejector protuberance of the tread Values Depth H of the groove 21 mm Width W of the groove 18 mm Height H′ of the protuberance 21 mm Height H2 of the second (anti-noise) protuberance portion 13 mm Width W2 of the second (anti-noise) protuberance portion  6 mm Thickness T2 of the second (anti-noise) protuberance portion  1 mm Height H1 of the first (stone ejector) protuberance portion  8 mm Width W1 of the first (stone ejector) protuberance portion 18 mm Thickness T1 of the first (stone ejector) protuberance portion 24 mm

[0051] The tire of the example studied has an outside diameter equal to 1471 mm, and this corresponds to a developed tread length L equal to 4621 mm The tread comprises, in each of its two central longitudinal grooves and over its entire length L, 112 anti-noise and stone ejector protuberances alternately positioned on the opposite walls of the longitudinal groove, forming 56 pairs of protuberances forming 56 anti-noise barriers. When this tire is inflated to a pressure equal to 9 bar and subjected to a load equal to 6700 kg, the contact patch of its tread contains, for a given longitudinal groove, 3 pairs of protuberances, each forming an anti-noise barrier extending over almost the entire width of the longitudinal groove.

[0052] Compared with the reference tire, the tire in accordance with the invention generated an exterior noise that was 3 dB(A) lower, on a test of external noise of the “coast-by” type. Furthermore, a running test on ground covered with calibrated stones showed that the tread of a tire in accordance with the invention retained far fewer stones than that of the reference tire, without trapping of stones at the protuberances.

[0053] The tread according to the invention, which was developed for a conventional tire subjected to an inflation pressure, can also be used for a non-pneumatic tire, but also for a non-pneumatic rolling assembly intended to be fitted to an all-terrain vehicle, such as for example a caterpillar track.