Title of Invention

A TYRE COMPRISING A TREAD COMPOSED OF TWO RADIAL LAYERS

Abstract

A tyre comprising a tread composed of two radial layers, the reinforcing charge of which is predominantly silica, the radially upper layer (8) being made conductive by means of at least one annular insert (11) perpendicular to the surface of said tread, a crown reinforcement (9) and a carcass reinforcement (1) made conductive by means of a mix or mixes for encasing cables which are conductive, said reinforcements being separated from each other by a section (6) made up of a rubber mix slightly charged with carbon black or based on silica, and a connection conducting electrical charges connecting the surface of the tread to the mounting rim, the connection between two conductive layers or layers made conductive (8, 9, 1) separated by a non-conductive layer (7, 6) being constituted by at least one band (12, 13) of rubber mix of low thickness, width and length, placed between the two faces of the splice of the non-conductive layer and in contact with the means making conductive the two layers connected by the connection.

Full Text

A TYRE HAVING SEVERAL NON-CONDUCTING MIXES The present invention has as its subject a tyre having several mixes comprising as major charge silica or mixes slightly charged in black, one of these mixes being the tread. It concerns more particularly a tyre intended to bear heavy loads, such as a tyre for a "heavyweight" vehicle. With environmental problems being increasingly crucial, savings with regard to fuel and the struggle against nuisance created by motor vehicles having become a priority, one of the aims of tyre manufacturers is to provide a tyre having both a very low resistance to rolling, an excellent adherence both on dry ground and on wet, snow-covered or icy ground, a very good resistance to wear and finally a reduced rolling noise. To reach this goal, in European Patent Application EP-A-501 227 a tyre was proposed having a tread comprising silica as main reinforcing charge. If this solution allows the best compromise to be obtained amongst all the very contradictory properties mentioned above, it has, however, been established that as a function of the vehicles, the tyres using a tread comprising silica as the main reinforcing charge display the disadvantage of accumulating static electricity, to a greater or lesser extent, which is formed by friction of the tyre on the road during the travelling of the vehicle, due to the absence of electrical conductivity of the silica. When certain particular conditions are combined, the thus accumulated static electricity in a tyre is liable to cause an unpleasant electric shock to the occupant of a vehicle, when he touches the bodywork of the vehicle. In addition, it is liable to hasten the ageing of the tyre owing to the ozone generated by the electric discharge. It can also be the origin, as a function of the nature of the ground and of the vehicle, of a poor functioning of the radio on board the vehicle, due to the interference which it generates. This problem of the accumulation of static electricity in a tyre and of the majority of the disadvantages linked therewith is of very long standing and was already posed when the reinforcing charge which was used was carbon black. Thus, in the patent US-A-2 329 332 it was proposed to arrange on the exterior of the carcass a ply of rubber mix based on acetylene carbon black, having a high electrical conductivity, extending from one tyre bead to the other, and to arrange a narrow band of this same mix circumferentially between the carcass and the tread. The patent GB-A-544 757 describes an improvement to the above solution, this improvement consisting in arranging one or more fine incisions of zero width through the entire thickness of the tread of the non-vulcanised tyre and injecting therein rubber of high electrical conductivity to join the conducting ply extending from bead to bead with the surface of the tread in contact with the ground. It has likewise been proposed in the patent US-A-2 339 546 to establish a connection between the chassis of the vehicle and the road by means of a ply of highly conductive rubber, based on acetylene carbon black, which is in contact with the wheel rim on which the tyre is mounted and which extends from the tyre bead up to the surface of the tread, either on the edges thereof or in the interior thereof. The application EP 0 658 452 Al describes the adaptation of the known principles to a so-called modern tyre, which adaptation allows the main problems to be solved relating to the solutions proposed in the documents cited above, and in particular the inauspicious heterogeneities introduced into the tyre structures. The proposed solution consists in inserting a band of conductive rubber mixture, extending preferably over the entire circumference of the tyre and connecting the surface of the tread either to one of the crown plies or to the carcass reinforcement, or to any other part of the tyre which is sufficiently conductive of electricity, the necessary electrical conductivity being given by the presence of a suitable carbon black. Such a solution is not optimized for a tyre comprising several layers of rubber mixes above the crown reinforcement and layers of rubber between the crown reinforcement and the carcass reinforcement, as is the case with any tyre capable of travelling with a high stabilised operating temperature. It is not optimized in its industrial realization nor in its structure both from the point of view of cost and of the performance which is obtained. If one of the aims of the invention is to dissipate in a tyre having several mixes which are non-conductive of electricity the electrostatic charges caused by the rolling of the tyre, without significantly affecting the level of the properties of the tyre, the other aim is to be able to obtain the simplest possible tyre and having the lowest cost, both from the point of view of material cost and manufacturing cost. In accordance with the invention, the tyre comprising a tread composed of two radial layers, the reinforcing charge of which is predominantly silica, the radially upper layer being made conductive by means of at least one annular insert perpendicular to the surface of said tread, a crown reinforcement and a carcass reinforcement made conductive by means of coating mix(es) of the cables which are conductive, said reinforcements being separated from each other by a section made up of a rubber mix based on silica, and a conductive connection of electric charges connecting the surface of the tread to the mounting rim, characterised in that, on the one hand, the electrical connection between the radially upper layer of the tread made conductive and the conductive crown reinforcement is realized by a band of rubberized mix, conductive and of small thickness, width and length, placed between the two faces of the splice S of the non-conductive radially lower layer of the tread, at the axial level of the layer insert, and on the other hand the electrical connection between the carcass reinforcement and the crown reinforcement, which are conductive, is realized by at least one band substantially of the same dimensions as the band, placed between the two faces of the splice S of the non-conductive layer, and in contact with the means making the two reinforcements conductive. The radially upper layer of the tyre tread is made conductive of electricity because of the presence of a rubber conductive insert, connecting the surface of the tread intended to come into contact with the ground to the radially interior face of said layer, this annular insert extending over the entire circumference of the surface of the tread and being perpendicular to the quasi-cylindrical crown reinforcement. The rubber composition constituting said insert and the electrical connection between two conductive layers can be a composition based on a special rubber which is conductive of electric current. However, according to a preferred variant, the rubber composition constituting the conductive connection of the electrostatic charges is based on a natural rubber and/or synthetic rubbers conventionally used in the manufacture of tyres and in particular treads having as reinforcing charge a conductive carbon black preferably generally used in the manufacture of tyres. The electrical connection with the mounting rim is preferably carried out by the carcass reinforcement which comes to wind around the bead wires, being in contact with the rubber mixture covering the beads of the tyre externally. The characteristics and advantages of the present invention will be better understood with the aid of the drawing attached to the following description, in which drawing: Figure 1 represents diagrammatically, viewed in meridian section, a tyre of the truck type according to the invention, Figure 2 represents, diagrammatically and partially, the same tyre viewed in section in a plane parallel to the equatorial plane, Figure 3 represents diagrammatically a variant of arrangement of the conductive band arranged at the splice of the radially lower layer of the tread. The tyre, of size 315/80R.22.5, designed to have a low resistance to rolling, comprises a carcass reinforcement (1), composed of a metallic ply formed of non-tensile metallic cables encased in a rubber calendering mix, made conductive of electrostatic charges by means of a carbon black currently used as reinforcing charge in mixes. Said carcass reinforcement (1) is, as is known, anchored to at least one bead wire (2) in each bead to form a turn-up (10). Between said turn-up (10) and the casing ply (1) there is arranged at least one reinforcement filler (3). Inside said carcass reinforcement (1) there are the usual reinforcement layers and the layers, designated interior layers, made up of mixes which are generally impermeable to the known inflation gases. The end(s) of said internal layer(s) is/are generally covered by the axially internal part of the protective layer (4) of the bead, a wear layer, the axially exterior part of which comes to rest on the mounting rim, said layer being generally highly charged with carbon black and hence highly conductive. The carcass reinforcement (1) is surmounted at its vertex by a crown reinforcement (9) composed, in the example described, of two half plies known as triangulation plies formed of non-tensile metallic cables oriented with respect to the circumferential direction at an angle being able to be comprised between 300 and 900; then radially above, of two plies known as working plies composed of non-tensile metallic cables crossed from one ply to the next, forming with the circumferential direction angles which are able to be equal or unequal and of absolute value comprised between 100 and 300; then generally, lastly, of at least one ply known as protective ply formed of elastic cables forming with the circumferential direction an angle equal in direction and value to the angle of the radially most exterior working ply. All the cables of this crown reinforcement (9) are encased in one or more rubber calendering mixes, conductive of electrostatic charges owing to a carbon black currently used as reinforcement charge in mixes. As the crown reinforcement (9) does not have the same transverse profile as that of the subjacent carcass reinforcement (1), it is separated from said carcass reinforcement (1) by a rubber assembly (6) of small thickness on the axial central part (61), where the two reinforcements are substantially parallel and, on either side of said axial part (61), of increasing thickness moving towards the exterior of the tyre to form wedges (62). For heating reasons, these wedges (62) of rubber and the connecting layer (61) are not produced from conductive rubber mixes, because they are charged very little with carbon black. Radially above the crown reinforcement the tread is arranged which is composed of the radially interior layer (7), designated the sub-layer, formed of a mix charged principally with silica, sub-layer (7) itself surmounted radially by the radially upper layer (8), the rolling layer, very highly charged with silica. The tread (7, 8) is connected to the beads by sidewall mixes (5), themselves very highly charged with silica. The rolling layer (8) is made conductive, as is known per se, by means of the rubber insert (11), present in the form of a circular ring over the entire height of the rolling layer (8), to connect the surface of the tread coming into contact with the ground with the radially upper face of the sub-layer (7). This insert (11) of very small axial width is, in the case shown, unique and decentred with respect to the equatorial plane XX1 of the tyre. It could be centred, in particular in the case of the absence of a central groove on the tread; there could be two inserts (11), placed for example symmetrically with respect to the equatorial plane, or more, but in any case placed axially so that the contact with the ground can be established whatever the level of wear of the tread. This insert or inserts (11), conductive of electrostatic charges, can be realized by any suitable means, both at the time of manufacture of the tyre in non-vulcanised state or after vulcanisation. The conductive insert or inserts (11) can be realized during the manufacture of the radially upper layer (8) of the tread in non-vulcanised state by coextrusion, or by injection, or by cutting the layer by any suitable means and application of the conductive rubber composition in the form of a rubber solution. In the case described, the insert or inserts (11) are realized in the form of a ring or rings by coextrusion during the manufacture of the upper layer of the tread. With the radially interior layer (7) being obtained in a separate manner by extrusion, the electrical connection between the rolling layer (8) and the radially exterior ply of the crown reinforcement (9), formed of metallic cables encased in a rubber mix charged with a conventional and conductive carbon black, is realized by the band of rubber (12), advantageously made up of an elastomer identical to one of those used in the formulation of a radially exterior layer (8) or to one of those used for the formulation of a radially interior layer (7), whether said layers are predominantly charged with silica or are normally charged with carbon black. As shown in Figure 1, said band (12) has an axial width el2, preferably greater than the very small axial width ell of the insert (11), which permits great ease and security in manufacture. In the case of the dimension described, the widths el2 and el 1 are respectively 20 and 0.4 mm. As regards the thickness of said band (12), it is, as shown in Figure 2, very small and equal to a few tenths of a mm, for example 0.6 mm. The length of the band can be subdivided into three parts: an upper part (120) arranged between the upper layer (8) of tread at the axial level of the insert (11) and the lower layer (7) of said tread, a median part (121) which is inserted between the two faces of the splice S of the layer (7), which faces are generally inclined with respect to the radial direction by an angle close to 45°, and a lower part (122) which ensures contact with the encasing rubber of the radially upper ply of the crown reinforcement (9), being placed on said ply. The upper and lower parts are small in length, and in the precise case are 10 mm, but can be comprised between 5mm and 25 mm according to the dimensions of tyres which are treated. The electrical connection between the crown reinforcement (9) and the carcass reinforcement (1) is realized by the same system, i.e. by the use of a band (13), of the same constitution and substantially of the same dimensions as the band (12), the axial width being in fact able to be less than the axial width of the band (12), the conformity between axial arrangements of the conductive means no longer being a problem. Said band (13) is placed on the carcass reinforcement (1), then between the two faces of splice S' of the section (6), then on the radially upper face of said section. The presence of two bands (13) can prove useful, particularly of two bands (13) arranged axially at the level of the wedges (62) and symmetrically with respect to the equatorial plane XX', as shown in dotted lines in Figure 1. With the splice S' of the section (6) not generally being localised circumferentially at the same place as the splice S, the circumferential position of the band (13) is staggered with respect to the circumferential position of the band (12), as shown on the right-hand part of Figure 2. In certain manufacturing configurations, the layers (7) and (8) are coextruded. It is then scarcely possible to insert the upper part (120) of a band (12) between the upper layer and the lower layer. It is sufficient to ensure the electrical connection to arrange, between the two faces of the splice S, the assembly of upper part - median part of the band (12) (Figure 3), the upper part (120) making contact with the insert (11) at the level of the faces of the splice S common to the two layers of tread. The complete connection is then ensured by the encasing mix of the carcass reinforcement cables, which, in the region of the beads, is in contact with the wear layer (4) surrounding the bead, this connection consequently permitting to be used as rubber mixes constituting the sidewalls of the tyre mixes also highly or completely charged with silica. The use in combination of mixes charged with silica for the constitution of the tread layers, sidewalls and layers between the crown reinforcement and carcass reinforcement of a truck tyre permits a considerable gain in resistance to rolling and consequently fuel consumption. CLAIMS 1. A tyre comprising a tread composed of two radial layers, the reinforcing charge of which is predominantly silica, the radially upper layer (8) being made conductive by means of at least one annular insert (11) perpendicular to the surface of said tread, a crown reinforcement (9) and a carcass reinforcement (1) made conductive by means of a cable encasing mix or mixes which are conductive, said reinforcements being separated from each other by a section (6) made up of a rubber mix based on silica, and a connection conductive of electrical charges connecting the surface of the tread to the mounting rim, characterised in that on the one hand the electrical connection between the radially upper layer (8) of the tread, made conductive, and the conductive crown reinforcement (9) is realized by a band (12) of rubberized mix, conductive and of small thickness, width and length, placed between the two faces of the splice S of the radially lower layer (7) of the tread, non conductive at the axial level of the insert (11) of the layer (8), and on the other hand the electrical connection between the conductive carcass reinforcement (1) and crown reinforcement (9) is realized by means of a band (13) substantially of the same dimensions as the band (12), placed between the two faces of the splice S1 of the non-conductive layer (6), and in contact with the means making the two reinforcements (1) and (9) conductive. 2. A tyre according to Claim 1, characterised in that the band or bands (12, 13) have axial widths el2 comprised between 0.4 and 20 mm and preferably greater than the very small axial widths el 1 of the insert or inserts (11) with which they are in contact. 3. A tyre according to one of Claims 1 or 2, characterised in that the band (12) comprises a central part (121) placed between the two faces of the splice (5) of the layer (7) of the tread, an upper part (120) placed between the upper layer (8) and the layer (7), and a lower part (122) ensuring contact with the encasing rubber of the crown reinforcement (9) by being placed on said reinforcement. 4. A tyre according to one of Claims 1 or 2, characterised in that the band (12) comprises an upper part (120) and a central part (121) placed between the two faces of the splice S of the layer (7) and a lower part (122) placed on the crown reinforcement (9). 5. A tyre comprising a tread composed of two radial layers, substantially as herein described, with reference to the accompanying drawings.

Documents:

360-mas-1998-abstract.pdf

360-mas-1998-claims duplicate.pdf

360-mas-1998-claims original.pdf

360-mas-1998-correspondence others.pdf

360-mas-1998-correspondence po.pdf

360-mas-1998-description complete duplicate.pdf

360-mas-1998-description complete original.pdf

360-mas-1998-form 1.pdf

360-mas-1998-form 26.pdf

360-mas-1998-form 3.pdf

360-mas-1998-form 4.pdf