Surface texture for a tire tread

Abstract

The surface state of the treads of tires cured in a vulcanization mold manufactured by 3D printing represents an optimal compromise between cost, appearance, and grip performance of the tire. The texture is formed by an arrangement of contiguous elements of pyramidal shape, each element of pyramidal shape having a base of parallelogram type positioned on the tread surface, and an apex situated at a normal distance H from the base in the range 0.15 mm to 0.5 mm.

Claims

1. A tire provided with a tread of which portions of a tread surface that are intended to be in contact with a ground comprise a texture formed by an arrangement of contiguous elements of pyramidal shape, each element of pyramidal shape having a base of parallelogram type positioned on the tread surface, and an apex situated at a radial distance H from the base, the base being defined by: a first pair of mutually parallel sides spaced apart from one another by a first pitch P1, and forming an angle alpha with a circumferential direction of the tire; and a second pair of mutually parallel sides spaced apart from one another by a second pitch P2, and forming an angle beta with the circumferential direction, a side of the second pair of mutually parallel sides meeting a side of the first pair of mutually parallel sides to form an acute angle, wherein the first pair of parallel sides and the second pair of parallel sides form, at an intersection, vertices of the bases of parallelogram type, constituting a mesh of the portions of the tread surface, wherein the angle alpha is in a range from 15 to 75, wherein the angle beta is in a range from 75 to 15, and wherein a normal distance from the apex to the base is in a range from 0.15 mm to 0.5 mm.

2. The tire according to claim 1, wherein the first pitch P1 or the second pitch P2 is constant.

3. The tire according to claim 1, wherein the angle beta is equal in terms of absolute value to the angle alpha.

4. The tire according to claim 1, wherein the first pitch P1 of the first pair of sides is less than or equal to 2*H/Tan (alpha).

5. The tire according to claim 1, wherein the first pitch P2 of the first pair of sides is less than or equal to 2*H/Tan (beta).

6. The tire according to claim 1, wherein the texture of the portions of the tread surface has a density of elements of pyramidal shape that is greater than or equal to 10 elements per square centimeter.

Description

DESCRIPTION OF THE FIGURES

(1) The invention will be understood better from reading the following description, which is given solely by way of example and with reference to the drawings, in which:

(2) FIG. 1-A is an extract of the tread obtained after vulcanization of the tyre, depicting the texture proposed by the invention. FIG. 1-B is the same depiction as FIG. 1-A but seen from the computer-aided design (CAD) side. View 1-C is an enlargement of FIG. 1-B that highlights the construction of the texture of the invention.

(3) FIGS. 2-A to 2-E illustrate the terminology of moulds that is commonly used. FIG. 1-A is a perspective view of a mould lining, FIG. 2-B is a perspective view of a mould sector comprising a support block and the lining shown in FIG. 2-A fastened to said support block; FIG. 2-C is a top view of the sector in FIG. 2-B, FIG. 2-D is a cross-sectional view of the sector in FIG. 2-B; finally FIG. 2-E is an example of a mould with its sectors comprising the linings that are attached thereto.

(4) FIGS. 3-A, 3-B, and 3-C depict partial views of mould linings obtained by 3D printing. Graph 3-B is an enlargement of view 3-A to highlight the texture proposed by the invention, in comparison with conventional textures depicted in FIG. 3-C that are formed of patterns in the form of concentric circles. FIG. 3-D is an enlargement of FIG. 3-B with the texture pattern of the invention showing the texture with elements of pyramidal shape.

(5) FIG. 4 depicts a mould of which the lining is manufactured by 3D printing.

(6) FIG. 5 depicts the diagram of the principle of operation of the manufacturing by 3D printing. The lining with its components, skin, protruding elements and recessed elements are made in one piece by 3D printing.

DETAILED DESCRIPTION OF THE INVENTION

(7) FIG. 1-C shows the details of the construction of the pattern of the tread of the tyre with the general reference 1. The pattern of pyramidal shape (ABCDE), represented by the reference 2, of which the base is the parallelogram (ABCD), can be seen. The sides AB and DC are parallel and form an angle Alpha with a circumferential direction (XX); as for the sides DA and CD, they are also parallel and form an angle Beta with this same circumferential direction. The apex E is positioned radially on the outside of the tread surface. FIG. 1-B is the computer-aided design model of the surface of the tread from the pattern shown in FIG. 1-C, and finally FIG. 1-A is an extract of the tread surface after vulcanization of the tyre.

(8) FIG. 2-A depicts a portion of lining 14 limited to the sector shown in FIG. 2-B. More specifically, a lining 14 as used in the invention is characterized in that it comprises: a skin 18 comprising opposing first 20 and second 22 surfaces, the first surface being intended to be in contact with a support block 12 of a mould for a tyre, the thickness of the skin 18 being between 0.25 and 3 millimetres for a mould for vulcanizing a passenger-vehicle tyre, and a plurality of protruding and recessed lining elements 24 of the second surface 22 of the skin, the lining elements 24 being intended to form tread patterns of a part of a radially external surface of a tyre.

(9) FIG. 2-B depicts a sector, denoted by the general reference 10, of a sectored mould for vulcanization of a tyre. The sector 10 comprises a support block 12 and a lining 14 attached to the support block 12.

(10) The support block 12 is formed by a solid steel block comprising in particular a support surface 16 intended to receive the lining 14. The support surface 16 is substantially smooth and has a shape that substantially matches the overall curvature of the tread of the tyre to be moulded.

(11) The lining 14 comprises a skin 18 containing opposing first 20 and second 22 surfaces, the first surface 20 being intended to be in contact with the support surface 16 of the support block 12.

(12) The skin 18 further comprises a plurality of lining elements 24 protruding from the second surface 22, the lining elements 24 being intended to form the tread patterns of a part of the tread of the tyre to be moulded.

(13) Among the lining elements 24, there are distinguished in particular lamellae 26 intended to form circumferential slots in the tread of the tyre, and circumferential ridges 28 intended to form a longitudinal groove on the tread of the tyre.

(14) The various ridges 28 are connected by axial lamellae 30 so as to form a network of lining elements 24.

(15) FIG. 2-E depicts the mould of general reference 3 in the open position. The shells that are intended to mould the sidewalls of the tyre are not shown. Each sector is generally made of steel or cast iron. The moulding lining 14 is generally made of an aluminium alloy. In a known manner, a plurality of sectors 10 are arranged side by side circumferentially around the axis of symmetry V-V of the mould and form an annulus, the sectors being able to move radially by virtue of a device comprising a ring (4) that encompasses the sectors. The ring 4 is shown in FIG. 4.

(16) FIGS. 3-A, 3-B, 3-C and 3-D relate to the mould obtained by 3D printing. FIG. 3-A is a portion of the lining 14 having the skin 18 with the texture of the invention but on the mould side, i.e. it is the reverse pattern of that of the tread of the tyre. References 100 and 120 are examples of protruding and recessed elements that will imprint the tread after moulding.

(17) FIG. 3-B is an enlargement of the lining portion in FIG. 3-A, which more clearly shows the pattern of the invention 110 borne by the skin 18 of the lining 14.

(18) FIG. 3-C depicts the conventional surface state obtained by 3D printing with concentric circles revealing ridges 115 that imprints the tyre after vulcanization. FIG. 3-A is precisely the improvement of this surface state 3-C.

(19) FIG. 4 illustrates a partial cross-sectional view of a vulcanization mould sector 10 in which the main parts of the mould can be seen. The lining 14 is fastened to a support 12, generally made of steel or cast iron. The lining 14 is generally made of an aluminium alloy and bears the negative of the tread pattern of the tread of the tyre. A ring 4 encircles the sectors 10 so as to allow the operations of opening and closing the mould. The shell 5 ensures the moulding of the sidewalls and comprises an interface 7 with the lining 14. The shell 5 and the ring 4 are borne by a plate 6. The ring 4 has a radially inner surface of frustoconical shape that cooperates with the radially outer surface of frustoconical shape of the sectors 10.

(20) The lining 14 is manufactured by 3D printing. The pattern in FIG. 3-D formed around a pyramidal shape 2 is reproduced on the surface 22 of the skin 18 between the protruding and recessed lining elements 24.

(21) FIG. 5 shows the schematic diagram of the manufacturing by 3D printing.

(22) Prior to manufacturing by 3D printing, a first step consists in modelling the part to be manufactured using computer-aided design (CAD) software that defines the morphological constraints of the part to be produced. The next step is importing the previous data into software making it possible to define the strategy for development of the object, and the parameters of the method, then instructions are transmitted to the machine for manufacturing by 3D printing for the production of the object in its physical form.

(23) Thus, in FIG. 5, the part to be produced is manufactured gradually on a removable plate 230 of which the location is identified by a local axis system (X1, X2, X3). The plane (X1, X2) is parallel to the plane of the plate 230, and the direction X3 is orthogonal to this same plane. The plate 230 is fed with powder via the feed channel 220; a system for equalizing the powder layer 250 spreads the powder over a uniform thickness. The laser generator 270 directs the laser beam onto an optical system 210. The laser is moved over the plate 230 using an optical chain 210 that is in fact a system of oscillating mirrors driven by the data from the CAD. The manufactured part 260 is welded to the support 240.

(24) In order to produce the lining of the mould, which generates the texture of the tread surface of the tyre, the laser of the method for manufacturing by 3D printing traces, on the skin of the lining, a first set of mutually parallel segments forming an angle Alpha with the circumferential direction of between [15; 75 ], and a second set of pairwise parallel segments forming an angle Beta with the circumferential direction of between [75; 15 ]. The points at the intersection of the segments are the nodes of the mesh and correspond to the vertices of the parallelograms. Each parallelogram is hollowed out at its centre by the laser so as to form an inverted pyramid.

(25) The main parameters of the method for manufacturing by 3D printing that are used for the invention are: the power of the laser [100-1000 W], the scanning speed of the laser [0.1-5 mm.Math.s1], the diameter of the laser spot [50-200 m], which can be adjusted by adjusting the distance between the surface of the powder layer and the focal point of the laser, the thickness of the powder layer [20-200 m], and the lasering spacing [25-200 m], which corresponds to the spacing between two lines of passage of the laser, which are adjacent and parallel. It is generally less than the diameter of the laser spot in order to obtain an overlap zone.

(26) The invention has been described in relation to a mould of the sectored type. It can also be implemented in relation to a mould of another type.

(27) Tests

(28) In order to validate the invention, the test was carried out on a tyre of standardized size according to ETRTO (ETRTO: European Tyre and Rim Technical Organisation): 13R22.5 TL 156/151 K. The inflation pressure is 875 kilopascals for a load to be carried in individual mounting of 3450 kilos.

(29) The tyre has been tested according to regulation UN/ECE/R117, which relates to the mandatory performance thresholds before marketing of tyres in Europe, issued by the United Nations Economic Commission for Europe (UN/ECE).

(30) The results of the tests carried out relate in this case to grip on wet and snowy ground.

(31) Compared to the control provided by the regulations (SRTT), the tyre of the invention has improved grip performance on wet ground of 120%, and on snow an improvement of 185%.

(32) The invention has been presented for passenger-vehicle and heavy-duty-vehicle tyres, but it can actually be applied to any type of tyre.