Tire

Abstract

The present invention relates to a tyre (1) comprising: a carcass (5); at least one high elongation belt (1, 2, 3, 4), being applied as a single cord externally to said carcass (5); and an external tread portion (6), provided with two or more grooves (7) extending according to a circumferential direction (L) around said tread portion (6), wherein the axial width (Wg) of at least one of said grooves (7), measured according to an axial direction (A) parallel to an axis of rotation (R) of said tyre (10) and orthogonal to said circumferential direction (L), is at most equal to 2 millimeters.

Claims

1. A tire comprising: a carcass; a first belt, a second belt, a third belt, and a fourth belt radially superimposed to each other, wherein the first belt is at an innermost position and the fourth belt is at an outermost position with respect to the other belts, each of the first to fourth belts having a respective belt cord angle, wherein at least one of the first to fourth belts is a high elongation belt applied as a single cord strip radially externally to said carcass, said high elongation belt embedding a cord provided with a stiffness module variable between about 3,000 MPa for a strain value of said cord ranging from 0 to about 2% and 125,000 MPa for a strain value of said cord higher than about 2%; and an external tread portion provided with two or more grooves extending according to a circumferential direction around said tread portion, wherein an axial width of each of the two or more grooves, measured according to an axial direction parallel to an axis of rotation of said tire and orthogonal to said circumferential direction, is equal to or lower than 2 millimeters, wherein: the first belt cord angle equals from 35 to 40 measured counterclockwise from the circumferential direction; the second belt cord angle equals about 0 from the circumferential direction; the third belt cord angle equals from 20 to 28 measured clockwise from the circumferential direction; and the fourth belt cord angle equals from 40 to 60 measured counterclockwise from the circumferential direction.

2. The tire of claim 1, wherein said cord embedded in said high elongation belt has an elongation at break between 2.5% and 3.5%.

3. The tire of claim 1, wherein each of the two or more grooves have a depth in the radial direction and the axial width of each of the two or more grooves is substantially constant over a full depth of each of the two or more grooves.

4. The tire of claim 1, wherein: said first belt cord angle is equal to 40; said third belt cord angle is equal to 28; and said fourth belt cord angle (Q4) is equal to 52.

5. The tire of claim 1, which is a truck tire.

6. The tire of claim 1, wherein said first, second, third and fourth belts are radially superimposed to each other starting from said first belt to said fourth belt, wherein said first belt is at an innermost position and said fourth belt is at an outermost position with respect to the other belts.

7. The tire of claim 6, wherein said first belt is a high elongation belt applied as a single cord strip and having a belt cord angle equal to 0.

8. The tire of claim 1, wherein each of said first, second, third and fourth belt has a respective width, measured according said axial direction, which ranges from 100 to 300 millimeters.

9. The tire of claim 8, wherein a ratio between the widths of the second, third, and fourth belt with respect to said width of the first belt is defined as follows: the width of the second belt is from 85%-100% of the width of the first belt; the width of the third belt is from 95%-115% of the width of the first belt; and the width of the fourth belt is from 45%-60% of the width of the first belt.

10. The tire of claim 8, wherein each said respective width ranges from 130 to 250 millimeters.

11. The tire of claim 10, comprising: a first belt having a first width equal to 230 millimeters; a second belt having a second width equal to 215 millimeters, a third belt having a third width equal to 250 millimeters; and a fourth belt having a fourth width equal to 130 millimeters.

12. The tire of claim 1, wherein two of said two or more grooves are those grooves closest to a tire equatorial plane in a tire axial direction.

13. The tire of claim 12, wherein said two grooves are disposed one on each side of the tire equatorial plane in a tire axial direction.

14. The tire of claim 13, wherein more than one groove is disposed on each side of the equatorial plane in a tire axial direction.

15. The tire of claim 13, wherein between one and three grooves are disposed on each side of the equatorial plane in a tire axial direction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Reference will be made to the Figures of the enclosed drawings, wherein:

(2) FIG. 1 shows a schematic cross-sectional view of a preferred embodiment of a tire according to the present invention, of which, for greater clarity, only a section has been represented, some parts of which being exemplified;

(3) FIG. 1A is a simplified representation of a top view of the four belts comprised in the tire shown in FIG. 1;

(4) FIG. 2 is a diagram showing rolling resistance trend as function of Volume Void Ratio %;

(5) FIG. 3A shows a schematic cross-sectional view of a prior art tire provided with a closed pattern tread;

(6) FIG. 3B shows an enlarged detail of FIG. 3A, relating in particular to a standard groove of the tire tread pattern of this latter FIG. 3A, under loading conditions;

(7) FIG. 3C shows an enlarged detail of FIG. 3A, relating in particular to a closed pattern groove of the tire tread pattern of this latter FIG. 3A, subject to vertical load;

(8) FIG. 4 is a diagram showing the residual force Fy trend as a function of slip angle for standard pattern and closed pattern tread design, respectively;

(9) FIG. 5 shows exemplary values of the ply steer effect with reference to a standard pattern tire according to the prior art and a closed pattern tire according to the prior art;

(10) FIG. 6 shows exemplary values of wear energy with reference to standard wavy tire according to the prior art and a tire provided with a high elongation belt and a closed pattern tread, according to a preferred embodiment of the invention.

(11) The dimensions, as well as thicknesses and curvatures, shown in the Figures introduced above are to be understood as purely exemplary and are not necessarily shown in proportion. Moreover, as said, in said Figures some layers/components of the tire may have been omitted, for a clearer illustration of aspects of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(12) Hereinafter, several embodiments and variations of the invention will be described, with reference to the Figures introduced above.

(13) Moreover, the different embodiments and variants described in the following are possibly employed in combination, when they are compatible.

(14) An improved tire according to the present invention provides a new belt construction in combination with a closed pattern design of the tread, in order to balance ply-steer trade off and enhance rolling resistance RRc and wear performances, so to avoid the disadvantages of the prior art tire having a closed pattern design.

(15) As just said, the tire according to the present invention comprises an external tread portion provided with two or more grooves designed to realize a closed pattern. With reference to FIG. 1, a preferred embodiment of tire 10 comprises a tread portion 6 provided with two or more grooves 7, the grooves 7 extending according to a circumferential direction L around said tread portion 6.

(16) The axial width W.sub.g of at least one of said grooves 7, measured according to an axial direction A parallel to an axis of rotation R of the tire 10 and orthogonal to said circumferential direction L, ranges from 0.5 to 4 millimeters, in particular is lower than, or at least equal to, 2 millimeters.

(17) The axial width W.sub.g of said groove 7 is substantially constant over the full depth of the groove. By substantially it is meant that the groove walls might have a slight inclination of between 2 to 5 degrees with respect to the orthogonal plane in the point they intersect the tread rolling surface.

(18) The radial depth D.sub.g of at least one of said grooves 7, measured according to a radial direction of the tire 10, ranges from 7 to 14 millimeters, preferably 8 to 13 millimeters, more preferably from 9 to 12 millimeters.

(19) In a preferred embodiment at least one of said grooves 7 is the groove closest to the tire equatorial plane CL (or centerline CL) in a tire axial direction.

(20) The tire equatorial plane CL is the plane dividing the tread portion 6 into two equally wide portions.

(21) In another preferred embodiment two of said grooves 7 are the grooves closest to the tire equatorial plane CL (or centerline CL) in a tire axial direction.

(22) In another preferred embodiment two of said grooves 7 are the grooves closest to the tire equatorial plane CL (or centerline CL) in a tire axial direction, wherein the two grooves 7 are disposed on both sides, one on each side, of the tire equatorial plane CL (or centerline CL) in a tire axial direction.

(23) In another preferred embodiment one, two or three of said grooves 7 are disposed on both sides of the tire equatorial plane CL (or centerline CL) in a tire axial direction.

(24) The advantage of said grooves 7 being in the central area of the pattern, i.e. in an area closer to the equatorial plane CL, is that the stiffness of the tread pattern is thereby increased, resulting in an improved rolling resistance.

(25) In a preferred embodiment said grooves 7 are positioned within a maximum axial distance from the equatorial plane CL that corresponds to 30% of the axial width W.sub.1, W.sub.2, W.sub.3, W.sub.4 of the widest tread belt 1, 2, 3, 4.

(26) The tire 10 according to the invention further comprises a carcass 5 (which may include one or more inner body plies), and at least one high elongation belt. The at least one high elongation belt is applied radially, as a single cord strip, externally to the carcass 5.

(27) According to particular embodiments of the invention, the at least one high elongation belt is applied onto the most radially external side of an inner body ply of the tire. According to preferred embodiments of the invention, a tire comprising a plurality of belts radially superimposed to each other is provided, comprising one high elongation belt which corresponds to the second belt, starting from the carcass and going towards the tread portion.

(28) According to the preferred embodiment shown in FIG. 1, the tire 10 comprises four belts, in particular a first, a second, a third and a fourth belt, starting from the carcass 5 and going towards the tread portion 8, respectively denoted by the numerical references 1, 2, 3, 4.

(29) Preferably, each of the four belts 1, 2, 3, 4 is applied in such a manner to define a respective belt cord angle, denoted in FIG. 1A with the references .sub.1, .sub.2, .sub.3 and .sub.4 respectively, and more preferably each of said belt cord angle .sub.1, .sub.2, .sub.3, .sub.4 is different from the other ones.

(30) At least one of said first, second, third and fourth belt 1, 2, 3, 4 is a high elongation belt, applied as a single cord strip and having a belt cord angle equal to 0. That is, the high elongation belt is configured as a longitudinal belt.

(31) In particular, the single cord strip is spirally applied, and thanks to such a kind of application the obtainment of a belt cord angle equal to 0 is facilitated.

(32) Preferably, the value of each belt cord angle .sub.1, .sub.2, .sub.3, .sub.4 ranges from 0 to 80, measured with respect to the circumferential axis L.

(33) More specifically, the belt cord angle is the lowest angle (having a positive or negative value of amplitude, wherein a positive amplitude is measured according to a clockwise direction, and a negative amplitude is measured according to a counterclockwise direction) comprised between the circumferential axis L and the cords main extension axis. As way of example, in FIG. 1A belt cord angles .sub.1 and .sub.4 are shown having an amplitude equal to about 45, according to a counterclockwise direction.

(34) According to the preferred embodiment of the invention shown in FIGS. 1 ad 1A, the second belt 2 is provided as a high elongation belt, applied as a single cord strip and being configured to define, as already said, a second belt cord angle .sub.2 equal to 0.

(35) In particular, the tire 10 comprises a first belt 1, defining a first belt cord angle .sub.1 ranging from 35 to 60; a second high elongation belt 2, defining a second belt cord angle .sub.2 equal to 0; a third belt 3, defining a third belt cord angle .sub.3 ranging from 20 to 40; and a fourth belt 4, defining a fourth belt cord angle .sub.4 ranging from 40 to 60.

(36) According to a preferred embodiment of the invention, the ratio between the angles of the belts with respect to the first belt cord angle .sub.1 is defined as follows: The second belt cord angle .sub.2 equals to 0; The third belt cord angle .sub.3 equals to 60%-80%, preferably to 70% of the first belt cord angle .sub.1 and the fourth belt cord angle .sub.4 equals to 120%-140%, preferably to 130% of the first belt cord angle .sub.1.

(37) According to a more preferred embodiment of the invention, the first belt 1 defines a first belt cord angle .sub.1 equal to 40, the second belt 2 defines a second belt cord angle .sub.2 equal to 0, the third belt 3 defines a third belt cord angle .sub.3 equal to 28, and the fourth belt 4 defines a belt cord angle .sub.4 equal to 52.

(38) Instead, according to an alternative embodiment of the invention, only the first belt 1 is a high elongation belt, being applied as a single cord strip and defining, according to such an embodiment, a first belt cord angle .sub.1 equal to 0.

(39) According to still another embodiment of the invention, both the first and the second belts 1, 2 are high elongation belts, being applied as a single cord strip and defining, respectively, a first .sub.1 and a second .sub.2 belt cord angle equal to 0.

(40) Referring again to the preferred embodiment of tire 10 shown in FIGS. 1 and 1A, each of said first, second, third and fourth belt 1, 2, 3, 4 has a respective width W.sub.1, W.sub.2, W.sub.3, W.sub.4, measured according said axial direction A, which ranges from 100 to 300 millimeters. According to a preferred embodiment of the invention, said width could range from 130 to 250 millimeters.

(41) According to a preferred embodiment of the invention, the ratio between said width W.sub.2, W.sub.3, W.sub.4 of the second, third and fourth belt 2, 3, 4 with respect to said width W.sub.1 of the first belt 1 is defined as follows: The width W.sub.2 of the second belt 2 equals to 85%-100%, preferably to 92% 94% of the width W.sub.1 of first belt 1, the width W.sub.3 of the third belt equals to 95%-115%, preferably to 107%-109% of the width W.sub.1 of first belt 1 and the width W.sub.4 of the fourth belt 4 equals to 45%-60%, preferably to 55%-57% of the width W.sub.1 of the first belt 1.

(42) In particular, the first belt 1 has a first width W.sub.1 equal to 230 millimeters, the second belt 2 has a second width W.sub.2 equal to 215 millimeters, the third belt 3 has a third width W.sub.3 equal to 250 millimeters, and the fourth belt 4 has a fourth width W.sub.4 equal to 130 millimeters.

(43) As visible in FIG. 1, the four belts 1, 2, 3, 4 are radially superimposed to each other in such a manner to realize a sandwich structure or belt system. In particular, the first belt 1 is at an innermost position and the fourth belt 4 is at an outermost position with respect to the other belts 2, 3. According to such an embodiment, the second belt 2 is interposed between the first 1 and the third belt 3, whereas the third belt 3 is interposed between the second belt 2 and the fourth belt 4.

(44) The tire according to the embodiments above disclosed is particularly intended to be a truck or bus tire.

(45) The present invention has been up to here described with reference to preferred embodiments. It is to be intended that other embodiments are possible within the same inventive core, as defined by the scope of protection of the following claims.