Tire, the sidewall of which comprises ribs

Abstract

Tire (1) comprising a carcass reinforcement (2) surmounted by a crown reinforcement (3), itself capped by a tread (7), the said tread being connected to two beads (6) via two sidewalls (4) each having an exterior surface (40), at least one of the said sidewalls comprising at least two circumferential protrusions (5a, 5b, 5c), each sidewall (4) comprising an equator point (E) situated on the exterior surface of the sidewall radially at the same position as the axially outermost point (20) of the carcass reinforcement (2) in the unladen reference configuration, each circumferential protrusion (5a, 5b, 5c) being bounded by a radially upper wall (51), by a radially lower wall (52), and by a connecting wall (53) situated between the radially upper wall (51) and the radially lower wall (52) tire.

Claims

1. A tire comprising; a carcass reinforcement surmounted by a crown reinforcement, itself capped by a tread, the tread being connected to two beads via two sidewalls each having an exterior surface, at least one of the sidewalls comprising at least two circumferential protrusions, each sidewall comprising an equator point situated on the exterior surface of the sidewall radially at the same position as the axially outermost point of the carcass reinforcement in an unladen reference configuration, each circumferential protrusion being bounded by; a planar radially upper wall, a curved radially lower wall, and a connecting wall situated between the planar radially upper wall and the curved radially lower wall, wherein, for each circumferential protrusion: the connecting wall is substantially parallel to the carcass reinforcement considered axially facing the connecting wall, the planar radially upper wall is inclined relative to the radial direction, at least a portion of the curved radially lower wall is substantially parallel to the radial direction, the radially upper wall and curved radially lower wall are asymmetrically configured with respect to one another in the radial direction, the height (H) of each circumferential protrusion, measured in a direction substantially perpendicular to the carcass reinforcement from the exterior surface is greater than the smaller value of 0.8 times the total thickness (T) of the sidewall as measured at the equator (E) and 4 mm, and less than the greater value of 1.6 times the total thickness (T) and 8 mm, in the meridian plane at the center of the contact patch of the tire in a compressed configuration, an angle α formed by the planar radially upper wall with the radial direction is, in the case of the radially outermost protrusion, greater than 95°, and the radially innermost position of the connecting wall of the radially innermost protrusion is situated radially on the outside of the equator point (E).

2. The tire according to claim 1, wherein, for each protrusion, the curvilinear length of the connecting wall is greater than 50% of the height of the protrusion.

3. The tire according to claim 1, wherein, for each protrusion the curvilinear length of the connecting wall is greater than 1.5 times the height of the protrusion.

4. The tire according to claim 3, wherein, for each protrusion the curvilinear length of the connecting wall is greater than 2.5 times the height of the protrusion.

5. The tire according to claim 1, wherein each sidewall comprises at least three protrusions (5 a, 5 b, 5 c).

6. The tire according to claim 1, wherein the angle α is, for the radially outermost protrusion, greater than 105°.

7. The tire according to claim 1, wherein the angle α is decreasing in value when moving on from one protrusion to the next in the direction toward the equator.

8. The tire according to claim 1, wherein the smallest value for the angle (α), for all of the protrusions is greater than 90°.

9. The tire according to claim 1, wherein each protrusion is made up of the same rubber compound as the part of the sidewall that forms the exterior surface.

10. The tire according to claim 1, wherein each protrusion has sipes arranged substantially in a meridian plane, with a radial height of between 0.5 mm and 2 mm, spaced circumferentially by a spacing greater than twice the maximum of the depth of the sipes and the height (H) of the protrusion, and less than 10 mm, with an axial depth of between 25% and 50% of the height of the protrusion.

11. The tire according to claim 1, wherein each protrusion has, on its connecting wall, in the circumferential direction, a series of concave and convex surfaces, the peak-to-peak height of which is greater than 2 mm and less than 80% of the height of the protrusion.

12. The tire according to claim 1, wherein each protrusion comprises a rubber composition that contains at least 8 phr of anti-ozone wax.

13. The tire according to claim 1, wherein each protrusion comprises a rubber compound containing an amide of formula (I): ##STR00004## where R.sub.1 represents: a linear or branched alkylene radical containing 1 to 6 carbon atoms substituted with an amide radical of formula (II), ##STR00005## in which: R.sub.2′ represents a linear or branched hydrocarbon radical comprising from 12 to 24 carbon atoms, and the arrow (.fwdarw.) represents the point of attachment of the amide radical of formula (II); a linear or branched alkyl radical comprising from 1 to 6 carbon atoms, or a hydrogen atom: where R.sub.2 represents a linear or branched hydrocarbon radical comprising from 12 to 24 carbon atoms.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further details and advantageous features of the invention will become apparent hereinafter from the description of exemplary embodiments of the invention, in particular with reference to the following figures in which:

(2) FIG. 1 is a partial meridian view of one particular embodiment of the invention;

(3) FIG. 2 is a partial meridian view of the embodiment of FIG. 1, with the tire subjected to load;

(4) FIG. 3 is an enlargement of zone III indicated in FIG. 2;

(5) FIG. 4 is a first variant embodiment of the invention;

(6) FIG. 5 is a second variant embodiment of the invention;

DETAILED DESCRIPTION OF THE DRAWINGS

(7) In order to make them easier to understand, the figures are not shown to scale. The invention is illustrated in an application to a tire.

(8) FIG. 1 partially shows a tire 1 mounted on its reference rim J and inflated to its nominal pressure, comprising a carcass reinforcement 2 surmounted by a crown reinforcement 3; also visible are a tread 7, a bead 6 and a sidewall 4; the sidewall 4 has an exterior surface 40 on which may be seen three circumferential protrusions 5a, 5b and 5c; let it be emphasized that because the protrusions are circumferential, any meridian section through the tire, taken at any azimuth, will exhibit an identical profile. An equator point E is marked on the sidewall 4 opposite the axially outermost point 20 of the carcass reinforcement, and radially at the same height as the point 20.

(9) With reference more particularly to the protrusion 5a, a radially upper wall 51, a radially lower wall 52, and a connecting wall 53 situated between the radially upper wall 51 and the radially lower wall 52 may be identified on each circumferential protrusion; of course, each protrusion comprises such upper, lower and connecting walls, FIG. 1 having been deliberately spared some of the multiple references that are not required for an understanding of the invention.

(10) FIG. 2 partially shows the profile of the same tire 1 mounted on its reference rim, inflated to its nominal pressure, and this time compressed under the effect of a nominal load. This profile considered in the centre of the contact patch in which the tire is in contact with the ground, commonly is referred to as “compressed profile”. FIG. 3 more specifically illustrates the configuration of the radially upper wall, more specifically the zone identified by the circle III in FIG. 2. Let it be recalled that FIG. 2 is a cross section (partial view) on a meridian plane in the middle of the contact patch of the tire in the compressed configuration, namely considered mounted on the reference rim and inflated to the nominal pressure and compressed under its nominal load (reference may be made to the standards, for example the ETRTO standard). The angle α is the angle that the radially exterior wall 51 makes with the radial direction. Because this wall can be slightly curved, by convention and as may be seen in FIG. 3, the angle to be considered is the angle bounded by the tangent mid-way up the height of the wall.

(11) In the embodiment of the invention that is illustrated in FIG. 1, the protrusion has a substantially planar radially upper wall 51. The connecting wall 53 is substantially parallel to the cord 21 of the carcass reinforcement 2. Let it be emphasized that there may be a great deal of variability in the shape of the radially inner wall 52: with a reasonable degree of inconsequentiality regarding the performance of a tire according to the invention, it may be frustoconical, it may have a break in gradient as in FIG. 1, or else it may leave an arc-shaped line in its cross section on a meridian plane. Naturally there are fillet radii. At the junction with the exterior surface 40 of the sidewall 4, each protrusion, viewed in section on a meridian plane, ends in a line that is preferably parallel to the line of the carcass reinforcement 2. By way of example, for a tire of size 12 R 22.5, each protrusion 5 (when the reference 5 or 51, 52, 53 is not followed by a suffix it refers to a generic feature that is valid for all of the protrusions whatever their position) has a base measuring approximately 15 mm, a height H of 5.5 mm, and a connecting wall 53 measuring 3.5 mm.

(12) Let us now move on to the material of which the protrusions 5 are made. The results show a very large decrease in the coefficient of friction p of the compositions in accordance with the invention that contain an amide of formula (I). Thus, the present invention makes it possible to significantly improve the life of tires, since these tires become much less sensitive to external attack. In the exemplary embodiment of the invention, use is made of a compound containing 10 phr of wax, for the first part 55 (see FIG. 3), radially and axially on the outside, of each protrusion 5; this compound with wax lies flush with and forms the entirety of the radially upper wall 51 and part of the connecting wall 53. The rubber compound constituting the sidewalls 4 is also present in the second part, radially and axially on the inside, of each protrusion 5 over a thickness greater than 0.8 mm. A person skilled in the art will readily appreciate that all that is required is for a rubber compound with a low coefficient of friction, namely one that is slippery, to be positioned so that it partially envelops the protrusion, in order to obtain the advantages specific to this preferred embodiment of the invention.

(13) Other aspects of the particular embodiment of the invention may be adopted. For example, on the connecting wall 53 of the protrusions, it is possible to provide, as shown in FIG. 4, sipes 5e, arranged substantially in a meridian plane, with a radial height of between 0.5 mm and 2 mm, spaced circumferentially by a spacing greater than twice the maximum of the depth of the sipes and the height (H) of the protrusion, and less than 10 mm, preferably of from 1.5 to 3 mm, with an axial depth of between 25% and 50% of the height of the protrusion. This allows better resistance to abrasion when the tire rubs against a kerb. Just some protrusions may thus be provided with sipes, and in that case it is preferably those that are close to the equator that are provided with sipes.

(14) As a variant, it is possible to provide on the connecting wall 53 of the protrusions, as shown in FIG. 5, a series, in the circumferential direction, of concave and convex surfaces 5d, the peak-to-peak height of which is greater than 2 mm and less than 80% of the height of the protrusion. The concave or convex nature is assessed from the inside of the tire cavity. In FIG. 5, the concave and convex surfaces are half-cylinders with identical radii, but the generatrix may be made up of a series of ellipses or other shapes such as splines. The concave and convex parts may be of different shapes, in which case the convex part preferably has a greater height than the concave part. The actual shape is given by the intersection of the meridian profile of the protrusions and by the circumferential series of concave and convex surfaces 5d. That too makes it possible to better withstand abrasion.

(15) Four variants of tires are tested under the following conditions: A reference conventional tire (MICHELIN® 12R22.5 XZE2+) denoted T1; The same conventional tire, except with the sidewall thickness reduced by 2 mm, therefore lighter than T1 by 1.3 kg, denoted T2; The same conventional tire, except for a sidewall compound doped to 10 phr with wax, denoted T3; A tire according to the invention, with the thickness reduced by 2 mm (see T2) and comprising three cordons as described in FIGS. 1 and 2, lighter than T1 by 1.1 kg, denoted T4. A tire with the thickness reduced by 2 mm and with three cordons as described in FIGS. 1 and 2, and a sidewall compound containing 10 phr of wax, denoted T5.

(16) All the tires are inflated to 9 bar and loaded with 3500 kg. Rail-guided running is performed, using by way of element aggressive towards the tire a cylindrical rod of which the end that comes into contact with the tire is a hemisphere, of radius 15 mm, oriented perpendicular to the direction of forward travel of the tire, and making an angle of 50° with respect to the vertical, and positioned to the side of the edge of the tread. The rod is raised progressively and the rod height beyond which the sidewall is pierced is observed. The measurement is repeated on three exemplars of each of the tires T1, T2, T3, T4 and T5, and the mean value is adopted.

(17) The results are given in the following table:

(18) TABLE-US-00001 Tire Height T1 125 T2 115 T3 125 T4 125 T5 130
It is therefore found that the presence of the cordons makes it possible to maintain the performance of the control tire with a 1 kg drop in mass and that the addition of a slippery compound on the exterior edges of the cordons improves the performance whereas on a conventional tire, this compound is neutral.

(19) The scope of protection of the invention is not limited to the examples given hereinabove. The invention is embodied in each novel characteristic and each combination of characteristics, which includes every combination of any features which are stated in the claims, even if this feature or combination of features is not explicitly stated in the examples.