Tire comprising working layers including monofilaments for preventing cracking

Abstract

Technique to increase the endurance of tires comprising two crossed working layers (41, 42), comprising mutually parallel reinforcing elements (411, 421) forming, with the circumferential direction (XX′) of the tire, an angle at least equal to 20° and at most equal to 50°, the reinforcing elements being made up of individual metal threads or monofilaments having a cross section at least equal to 0.20 mm and at most equal to 0.6 mm. The end of the monofilaments comprises flats such that they reduce the shear forces in the rubber compounds of the tire under compressive loading.

Claims

1. A tire comprising: a tread, adapted to come into contact with the ground via a tread surface, and a crown reinforcement, radially on the inside of the tread, the crown reinforcement comprising a working reinforcement, the working reinforcement comprising at least two working layers, each working layer comprising reinforcing elements which are coated in an elastomeric material, mutually parallel and respectively form, with a circumferential direction of the tire, an angle A at least equal to 20° and at most equal to 50°, in terms of absolute value, and of opposite sign from one layer to the next, each said reinforcing element of a respective working layer being comprised of an individual metal thread or monofilament, and comprising a cylindrical portion extended on each side by two end portions, each said working layer comprising at least 100 and at most 200 reinforcing elements per 10-cm unit width of working layer measured perpendicular to the monofilaments, the cylindrical portion of each said reinforcing element having an axis and being delimited by a lateral surface, parallel to the axis, and two base surfaces, perpendicular to the axis, each said base surface having a smallest characteristic dimension at least equal to 0.20 mm and at most equal to 0.60 mm, each said end portion comprising an end surface, that is not planar and not perpendicular to the axis, having an endpoint, positioned at the greatest possible distance, from the base surface, wherein at least 80% of the reinforcing elements of each working layer have end portions cut along a line so as to comprise an end surface of which all points on the end surface which are distant from the endpoint by at most d/10, where d is the smallest characteristic dimension of the base surface of the cylindrical portion, are distant from the endpoint by at most d/25, and wherein the monofilament endpoints which are situated on the same side of a circumferential median plane belong to the same circumferential plane.

2. The tire according to claim 1, wherein the base surface of the cylindrical portion of any said reinforcing element is a circular surface.

3. The tire according to claim 1, wherein the base surface of the cylindrical portion of any said reinforcing element is a circular surface having a diameter at least equal to 0.30 mm and at most equal to 0.37 mm.

4. The tire according to claim 1, wherein each said working layer comprises reinforcing elements which form, with the circumferential direction of the tire, an angle A at least equal to 22° and at most equal to 35° in terms of absolute value.

5. The tire according to claim 1, wherein each said working layer comprises at least 120 and at most 180 reinforcing elements per 10-cm unit width of working layer, measured perpendicular to the monofilaments.

6. The tire according to claim 1, wherein the reinforcing elements of the working layers are comprised of steel.

7. The tire according to claim 1, wherein the reinforcing elements of the working layers are comprised of carbon steel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The features and other advantages of the invention will be understood better with the aid of FIGS. 1 to 7, the said figures being drawn not to scale but in a simplified manner so as to make it easier to understand the invention:

(2) FIG. 1 is a perspective view depicting part of the tire according to an embodiment of the invention, particularly its architecture and its tread.

(3) FIG. 2 depicts a sectioned working layer, one monofilament resulting from the operation and one monofilament according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

(4) FIG. 1 depicts a perspective view of a part of the crown of a tire. The tire comprises a tread 2 which is intended to come into contact with the ground via a tread surface 21. The tire further comprises a crown reinforcement 3 comprising a working reinforcement 4. The working reinforcement comprises two working layers 41 and 42 each comprising reinforcing elements (5) which are mutually parallel and respectively form, with a circumferential direction (XX′) of the tire, an oriented angle at least equal to 20° and at most equal to 50°, in terms of absolute value, and of opposite sign from one layer to the next.

(5) FIG. 2 schematically depicts a working layer cut, during manufacture, at an angle A, which is found at the end surface of the monofilament M1 causing the rubber compounds of the tire to be penetrated and to crack. The figure illustrates the cylindrical portion 51 and one of the end portions 52 of the monofilament, the axis of the monofilaments WW′, the lateral surface, S.sub.L, a base surface S.sub.B, an end surface S.sub.E, the endpoint E at the longest distance d.sub.E away from the base surface S.sub.B. The monofilament M2 according to the invention is cut with the working layer along a line such that the points on the surface S.sub.E which are distant by at most d/10, namely one tenth of the smallest dimension of the cross section S of the monofilament, is distant axially by at most d/25, one twenty-fifth of the smallest dimension D of the cross section S, creating a flat m which, according to our calculations, decreases the penetration pressure of the end of the monofilament on the rubber compounds of the tire by at least a factor of 10.

(6) 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.