AU2003253386A1

AU2003253386A1 - Tyre for two-wheeled vehicles

Info

Publication number: AU2003253386A1
Application number: AU2003253386A
Authority: AU
Inventors: Bernard Guerinon; Pascal Prost; Alain Valle
Original assignee: Michelin Recherche et Technique SA Switzerland; Michelin Recherche et Technique SA France; Societe de Technologie Michelin SAS
Current assignee: Michelin Recherche et Technique SA Switzerland; Societe de Technologie Michelin SAS
Priority date: 2002-08-09
Filing date: 2003-08-06
Publication date: 2004-03-11
Also published as: KR20050033645A; ES2428626T3; EP1545910B1; WO2004018237A1; RU2334622C2; JP2005535505A; RU2005106241A; JP4522858B2; EP1545910A1; CN100375681C; CN1675078A; WO2004018237A8

Description

Certificate I, CHARLOTTE ELIZABETH ANNE COUCHMAN, B.A., Dip. Voc. Tech., MITI, of Lodestar Translations, 21 Queens Road, Harrogate, North Yorkshire, HG2 OHA, UK, do hereby certify that I am conversant with the English and French languages and am a competent translator thereof, and I further certify that to the best of my knowledge and belief the following translation is a true and correct translation made by me of PCT/EP/03/008708 as filed. Signed this 23rd day of February 2005 CHARLOTTE ELIZABETH ANNE COUCHMAN TYRE FOR TWO-WHEELED VEHICLE The present invention relates to a tyre intended to be fitted on a vehicle and more particularly intended to be 5 fitted on a two-wheeled vehicle such as a motorcycle. Although not limited to such an application, the invention will be more particularly described with reference to such a motorcycle, or motorbike, tyre. Tyre reinforcement armatures or tyre reinforcements, in 10 particular for motorcycle tyres, are currently - and most frequently - formed by stacking one or more plies conventionally designated "carcass plies", "crown plies", etc. This way of designating reinforcement armatures stems from the manufacturing process, which consists of making a 15 series of semi-finished products in the form of plies, provided with, often longitudinal, cord reinforcements, which are then assembled or stacked so as to build a tyre blank. The plies are made flat, with large dimensions, and are then cut as a function of the dimensions of a given product. The 20 plies are also assembled substantially flat in a first phase. The blank thus produced is then shaped into the toroidal profile typical of tyres. The semi-finished products known as "finishing products" are then applied to the blank, in order to obtain a product which is ready for vulcanisation. 25 Such a "conventional" type of process involves, in particular for the tyre blank manufacturing phase, the use of an anchoring element (generally a bead wire), used' to effect anchoring or retention of the carcass reinforcement in the tyre bead zone. Thus, for this type of process, a turn-up is 30 formed from a portion of all the plies constituting the -2 carcass reinforcement (or of only some) around -a bead wire disposed in the bead of the tyre. The carcass reinforcement is thereby anchored in the bead. The widespread use in the industry of this type of 5 conventional process, despite numerous variants in the manner of producing the plies and the assemblies, has led the person skilled in the art to use a vocabulary derived from the process; hence the terminology in general use, comprising in particular the terms "plies", "carcass", "bead wire", 10 "shaping" to designate transition from a flat profile to a toroidal profile, etc. Tyres now exist which do not strictly speaking comprise "plies" or "bead wires" which fit the above definitions. For example, document EP 0 582 196 describes tyres manufactured 15 without the aid of semi-finished products in the form of plies. For example, the reinforcement elements of the various reinforcement structures are applied directly onto the adjacent layers of rubber mixes, the whole being applied in successive layers onto a toroidal core whose shape allows the 20 direct obtainment of a profile resembling the final profile of the tyre in the process of being manufactured. Thus, in this case there are no longer "semi-finished products", or "plies" or "bead wires". The basic products such as the rubber mixes and the reinforcement elements in the form of 25 cords or filaments are applied directly to the core. Since this core is toroidal in shape, the blank no longer has to be shaped in order to be transformed from a flat profile to a profile in the form of a torus. Furthermore, the tyres described in this document do 30 not have the "traditional" carcass ply turn-up about a bead wire. This type of anchoring is replaced by an arrangement in -3 which circumferential cords are disposed adjacent to said sidewall reinforcing structure, the whole being immersed in an anchoring or bonding rubber mix. Assembly processes using a toroidal core also exist 5 which use semi-finished products specially adapted for rapid, effective and simple laying on a central core. Finally, it is also possible to use a composite comprising certain semi finished products to achieve certain architectural aspects (such as plies, bead wires, etc), while others are achieved 10 by the direct application of mixes and/or reinforcement elements. In the present document, so as to take account of recent technological developments both in the field of manufacture and in the design of products, the conventional 15 terms such as "plies", "bead wires" etc are advantageously replaced by neutral terms or terms which are independent of the type of process used. Thus, the term "reinforcement of carcass type" or "sidewall reinforcement" may be used to denote the reinforcement elements of a carcass ply in the 20 conventional process and the corresponding reinforcement elements, generally applied at the level of the sidewalls, of a ' tyre produced according to a process not using semi finished products. The term "anchoring zone", for its part, may denote both the "traditional" carcass ply turn-up about a 25 bead wire of a conventional process and the assembly formed by the circumferential reinforcement elements, the rubber mix and the adjacent sidewall reinforcement portions of a bottom zone produced using a process involving application on a toroidal core. 30 As in the case of all other tyres, we are witnessing the radialisation of motorcycle tyres, the architecture of such -4 tyres comprising a carcass reinforcement formed of one or two plies of reinforcement elements forming with the circumferential direction an angle which may be between 650 and 90', said carcass reinforcement being radially 5 surmounted by a crown reinforcement formed at least of generally textile reinforcement elements. Non-radial tyres do still exist, however, and the invention also relates to them. The invention also relates to partially radial tyres, that is to say whose reinforcement elements of the carcass 10 reinforcement are radial over at least part of said carcass reinforcement, for example in the part corresponding to the crown of the tyre. Numerous crown reinforcement architectUres have been proposed, depending on whether the tyre is intended to be 15 fitted at the front of the motorcycle or at the rear. A first structure consists, for said crown reinforcement, in using solely circumferential cables, and said structure is more particularly used for the rear position. A second structure, directly inspired by structures commonly used in passenger 20 vehicle tyres, has been used to improve wear resistance, and consists in using at least two crown plies of reinforcement elements which are parallel to each other within each ply but crossed from one ply to the next, forming acute angles with the circumferential direction, such tyres being more 25 particularly suitable for the front of motorcycles. Said two crown plies may be surmounted radially by at least one ply of circumferential elements, generally obtained by helical winding of a strip of at least one reinforcement element coated' with rubber. Patent no. FR 2 561 588 thus describes 30 such a crown reinforcement, having at least one ply whose reinforcement elements form with the circumferential -5 direction an angle which may vary between 00 and 8', the modulus of elasticity of such elements amounting to at least 6000 N/mm 2 , and, disposed between . the carcass reinforcement and the ply of circumferential elements, a 5 shock-absorption layer formed mainly of two plies of elements crossed from one ply to the next forming between them angles of between 600 and 900, said crossed plies being formed of textile reinforcement elements having a modulus of elasticity of at least 6000 N/mm 2 . 10 Document EP 0 456 933, with a view to providing a motorcycle tyre with excellent stability at high speed as well as. excellent contact with the ground, teaches for example that a crown reinforcement should be made with at least two plies: a first ply, radially the closest to the 15 carcass reinforcement, being composed of cables oriented at an angle of between 40' and 900 relative to the circumferential direction and the second ply, radially the closest to the tread, being composed of cables wound helically in the circumferential direction. 20 Patent no. US 5 301 730, with a view to enhancing the drive ability of a tyre designed for the rear of a motorcycle, proposes a crown reinforcement composed, proceeding from the radial carcass reinforcement to the tread, of at least one ply of substantially circumferential 25 elements and two plies of elements crossed from one ply to the next and forming with the circumferential direction an angle which may be between 350 and 5 5 9, elements of aromatic polyamide being suitable for use as the ply of elements parallel to the circumferential direction- and aliphatic 30 polyamide being suitable for the plies of crossed elements.

- 6 The production of motorcycle tyres results in large curvature values if such tyres are to be used on a camber. The invention is directed in particular at improving the properties of tyre grip and drive ability for' use on severe 5 camber. Studies carried out in this context have shown in particular that the presence of layers of reinforcement elements forming an angle with the longitudinal direction results in local circumferential and shearing rigidities 10 which diminish near the edges of said layers, the tension at the ends of the reinforcement elements being zero. A local tension of zero for the reinforcement elements results in reduced effectiveness of said reinforcement elements in this zone. The rigidities of the edges of the layers are 15 particularly important when the tyre is used on the most severe cambers, when cornering, the part of the tyre corresponding to said zones then facing the ground. The invention aims to improve further the quality of motorcycle tyres, without for all that impairing the other 20 properties required to satisfy the users. More specifically, the invention is directed at improving tyres comprising at% least one layer of reinforcement elements forming an angle with the longitudinal direction. This object has been achieved according to the invention 25 by a tyre comprising at least one carcass-type reinforcement structure, formed of reinforcement elements, anchored on either side of the tyre to a bead whose base is intended to be mounted on a rim seat, each bead being extended radially - towards the outside by a sidewall, the sidewalls meeting up, 30 radially towards the outside, with a tread, said tyre also comprising under the tread a crown reinforcement structure -7 consisting of at least one layer of reinforcement elements, known as a working layer, said layer consisting of at least one continuous reinforcing cord forming in the central zone of said layer portions forming identical angles, formed. with 5 the longitudinal direction, said angles being measured at the points of intersection with a circumferential plane, in such a way that two adjacent portions are linked by a loop or bend formed by said cord, and the portions forming an angle with the longitudinal direction of between 10 and 800. 10 Advantageously, in the case of a radial- structure, the reinforcement elements of the carcass-type reinforcement structure form an angle of between 65' and 900 with the circumferential direction. According to a preferred embodiment of the invention, in 15 the central zone of said working layer the portions are equidistant from one another over all circumferential planes. Variants according to other advantageous embodiments of the invention additionally provide for the portion patterns to be equidistant from one another over all circumferential 20 planes. Portion pattern should be understood to mean an assembly of several portions disposed in a given, repeated configuration. The longitudinal direction of the tyre, or circumferential direction, is the direction corresponding to 25 the periphery of the tyre and defined by the rolling direction of the tyre. A circumferential plane or circumferential section plane is a plane perpendicular to the axis of rotation of the tyre. The equatorial plane is the circumferential plane passing 30 through the centre or crown of the tread.

-8 The transverse or axial direction of the tyre is parallel to the axis of rotation of the tyre. The central zone of a working layer is a circumferential zone of said layer axially between two lateral zones, axially 5 outside said central zone. According to a preferred embodiment of the invention, this central zone is centred on the crown of the tyre tread. The term "cord" generally denotes any of monofilaments, multifilament fibres (possibly twisted around themselves) or 10 assemblies such as textile or metal cables, plied yarn or alternatively any type of equivalent assembly such as, for example, a hybrid cable, this being the case whatever the material(s) or the possible treatment of these cords, for example surface treatment or coating or pre-sizing to improve 15 adhesion to the rubber or any other material. According to the invention, the working layer is made with at least one cord, of which no free end is present at the edges of said layer. Preferably, the layer is made with a single cord and the layer is of the "monofilament" type. 20 However, industrial production of such layers results in discontinuities, in particular due to reel changes. A preferred embodiment of the invention consists therefore in using only a single or a small number of cords for a working layer and it is appropriate to arrange the beginnings and 25 ends of cords in the central zone of said layer. A tyre produced thus according to the invention comprises a reinforcement structure under the tread which does not exhibit any reinforcement element free end at the level of the edges axially outside the-working layers.

-9 In the central zone of the working layers, that is to say in the part of the working layers which does not include the loops linking the portions together, the portions display identical angles formed with the longitudinal direction, said 5 angles being measured at the points of intersection with a circumferential plane, whatever is said circumferential plane. In other words, for a given circumferential section plane, the portions all display the same angle formed with the longitudinal direction at the points of intersection with 10 said circumferential section plane. Furthermore, the above mentioned angle may vary depending on the circumferential section plane considered. According to a previously mentioned preferred embodiment, in the central zone of the working layers the portions are 15 equidistant from one another in circumferential section planes; the distance between adjacent portions being able itself to vary depending on the circumferential section plane considered, or more precisely, the distance between adjacent portions being capable of varying in the axial direction. 20 Such a tyre is advantageously made using a method of the hard or toroidal core type which allows in particular positioning of the reinforcement elements in the quasi-final position; in fact, since a shaping stage is not required with this type of process, the reinforcement elements are not 25 displaced any more after their positioning. If a method comprising a shaping stage, such as shaping or application of a flat ply on the profile of the tyre, is used, the curvature of a motorcycle tyre necessitates preparation of a special ply for allowing the obtainment of portions, displaying 30 identical angles and possibly equidistant from one another over all circumferential planes, linked by a loop; in - 10 particular at the ends of the ply and therefore at the level of the loops, shaping in accordance with the curvature of a motorcycle tyre results in variations in particular at the edges of the tyre which modify the position of the 5 reinforcement elements. This modification of the positions is additionally disrupted by the presence of the loops, which cause non-homogeneous modifications. For this reason, the various portions do not display angles, formed with the longitudinal direction, which are identical in the 10 circumferential section planes. Likewise, they are not equidistant from one another in circumferential section planes. In an advantageous variant of the invention, in particular in order to optimise the rigidities of the 15 reinforcement structure along the meridian of the tyre, and in particular at the edges of the working layers, the angles formed by said portions of the cord of the working layers with the longitudinal direction are variable in the transverse direction such that said angles are greater at the 20 edges axially outside the layers of reinforcement elements relative to the angles of said portions measured at the level of the equatorial plane of the tyre. Use of a method of the hard core type which in particular allows positioning of the reinforcement elements in the 25 quasi-final position without the need for a shaping stage exhibits further advantages. In fact, a method of the hard core type in particular allows simple angle variations distinctly greater than it is possible to obtain using processes comprising a shaping stage. Furthermore, said angle 30 variations, said angle tending towards 900 at the edges of the working layers, result in an increase in pitch and - 11 promote production of the loops, due to the reduction in bulk. The invention also proposes a tyre comprising at least one carcass-type reinforcement structure, formed of 5 reinforcement elements, anchored on either side of the tyre to a bead whose base is intended to be mounted on a rim seat, each bead being extended radially towards the outside by a sidewall, the sidewalls meeting up radially towards the outside with a tread, and comprising under the tread a crown 10 reinforcement structure consisting of at least one layer of reinforcement elements known as a working layer, said layer consisting of at least one continuous reinforcement cord forming portions in the central zone of said layer, such that two adjacent portions are linked by a loop, and such that 15 said portions form an angle with the longitudinal direction of between 10 and 800, said angles formed by said portions with the longitudinal direction being variable in the transverse direction in such a way that said angles are greater at the edges axially outside the layers of 20 reinforcement elements relative to the angles of said portions measured at the level of the equatorial plane of the tyre. Advantageously, in the case 'of a radial structure, the reinforcement elements of the carcass-type reinforcement 25 structure form an angle of between 65' and 900 with the circumferential direction. According to preferred embodiments of the invention, the portions form an angle with the longitudinal direction of between 20 and 75'. Preferably, the angle is less than 50' 30 and more preferably less than 40'. /1 - 12 According to a preferred embodiment of the invention, the crown reinforcement structure of the tyre comprises at least two layers of reinforcement elements such that from one layer to the next the portions form between them angles of between 5 20 and 1600 and.preferably between 40 and 1000. A first embodiment of the variant embodiment of the invention according to which the angles formed by said portions of the cord of the working layers with the longitudinal direction are variable in the transverse 10 direction consists in varying the angle of the portions in monotonic manner from the equatorial plane of the tyre as far as the edges of the working layer. A second embodiment of this variant consists in making the angle develop by stages from the equatorial plane of the 15 tyre as far as the edges of the working layer. A last embodiment of this variant consists in the angle developing such that given values are obtained for given axial positions. These various embodiments of the variant embodiment of 20 the invention according to which the angles formed by said portions of the cord of the working layers with the longitudinal direction are variable in the transverse direction allow in other words the obtainment of considerable circumferential rigidity of the crown reinforcement structure 25 due to the presence of closed, that is to say small, angles in the crown zone of the tyre, that is to say in the zone surrounding the equatorial plane. And, on the other hand, the presence of open angles, that is to say angles tending towards 450, or even towards 90', may be obtained at the 30 edges of the working layer or more precisely at the level of - 13 the shoulders of the tyre to improve the grip, drive ability, comfort, or indeed the operating temperature of the tyre; in fact, such variations in angle allow adjustment of the shearing rigidities of the working layers. 5 A preferred embodiment of the invention provides for the tyre to consist in particular of a crown reinforcement structure which additionally comprises at least one layer of circumferential reinforcement elements; according to the invention, the layer of circumferential reinforcement 10 elements consists of at least one reinforcement element oriented according to an angle formed with the longitudinal direction of less than 5*. The presence of a layer of circumferential reinforcement elements is in particular preferable for the production of a 15 tyre intended to be used at the rear of a motorcycle. One advantageous embodiment of the invention provides for the layer of circumferential reinforcement -elements to be positioned at least in part on a working layer. When the layer of circumferential reinforcement elements is provided 20 on two working layers and placed directly under the tread, it may in particular contribute to the improvement of stability at high speed. The layer of circumferential reinforcement elements may thus be provided directly under the tread to form, in 25 addition to its primary function, a layer for protecting the carcass and the other layers of the crown reinforcement structure against any mechanical stresses which may occur. The layer of circumferential reinforcement elements may additionally be provided between the working layers, in - 14 particular for economic reasons, the quantity of material and laying time thus' being reduced. Another advantageous embodiment of the invention provides for the layer of circumferential reinforcement elements to be 5 positioned at least in part radially to the inside of the working layer radially furthest to the inside. According to this embodiment, the layer of circumferential reinforcement elements is provided radially to the inside- of the working layers and may in particular allow the grip and drive ability 10 of the tyre to be improved. Another variant of the invention provides for at least one layer of circumferential reinforcement elements to be positioned at least in part radially to the inside of the carcass-type reinforcement structure. This variant embodiment 15 may also repeat the various positioning arrangements mentioned above in relation to the working layers. The carcass may thus cover the complete crown reinforcement structure. Preferably, , the invention provides for at least one crown reinforcement layer to be positioned between the 20 carcass and the tread to ensure protection of the carcass. It should be noted that a tyre according to the invention, in particular when at least part of the crown reinforcement structure is provided radially to the inside of the carcass structure, is advantageously produced according 25 to a manufacturing method of the hard core or rigid form type. One advantageous embodiment of the invention provides for the carcass-type reinforcement structure to consist of two half-plies extending for example from the shoulders to the 30 beads. Depending on the nature, quantity and arrangement of - 15 the crown reinforcement elements, the invention effectively provides for the elimination of the carcass structure in at least a part of the zone of the tyre located under the tread. Such a carcass structure may be embodied as taught in 5 document EP-A-0 844 106. The above-mentioned relative positions of the various layers of the crown reinforcement structure are also compatible with such a carcass structure. According to a preferred embodiment of the invention, the reinforcement elements of the working layers are of textile 10 material. Preferably also, the reinforcement elements of the layer of circumferential reinforcement elements are metal and/or textile and/or glass. The invention in particular provides for the use of reinforcement elements of various types in one 15 and the same layer of circumferential reinforcement elements. Preferably also, the reinforcement elements of the layer of circumferential reinforcement elements have a modulus of elasticity greater than 6000 N/mm 2 . In an advantageous variant of the invention, a layer of 20 circumferential reinforcement elements may be provided in several parts positioned at various radial positions or different levels of the tyre. Such a tyre may in particular comprise a part of the layer of circumferential reinforcement elements radially to the outside of the other reinforcement 25 elements in the central. part of the tyre, that is to say under the central part of the tread. This part of the layer of circumferential reinforcement elements thus allows in particular protection of the carcass against any stresses which may affect the central part of the tread, considered as 30 the most exposed. Lateral parts of the layer of - 16 circumferential reinforcement elements, independent of the central part of said layer of circumferential reinforcement elements, may be positioned at any level, that is to say either radially to the inside of the working layers or 5 between them or indeed radially to the inside of the carcass layer, in particular with a view to reducing the quantity of reinforcement elements and the time required to produce such a layer of circumferential reinforcement elements. The invention additionally provides, in the case of a layer of 10 circumferential reinforcement elements made in several parts positioned in different radial positions, for the distribution of these various parts not to be symmetrical relative to the equatorial plane, or circumferential plane passing through the centre of the crown of the tyre. Such an 15 asymmetrical distribution may additionally be- associated with the selection of different materials from the circumferential reinforcement elements, as mentioned above. In accordance with this type of embodiment of a layer of circumferential reinforcement elements divided into several 20 parts, the invention advantageously provides covering of the axial ends of said parts between them. Other advantageous details and features of the invention will become clear below from the description of examples of embodiment of the invention made with reference to Figures 1 25 to 6, in which: - Figure 1 is a meridian view of a diagram of a tyre according to one embodiment of the invention, - Figure 2 is a diagrammatic representation of a working layer according to a first embodiment of the 30 invention, - 17 - Figure 3 is a diagrammatic representation of a working layer according to a second embodiment of the invention, - Figure 4 is a meridian view of a diagram of a tyre 5 according to a second embodiment of the, invention, - Figure 5 is a meridian view of a diagram of a tyre according to a third embodiment of the invention, - Figure 6 is a meridian view of a diagram of a tyre according to a fourth embodiment of the invention. 10 To simplify understanding thereof, the Figures 1 to 6 are not to scale. Figure 1 shows a tyre 1 comprising a carcass reinforcement consisting of a single layer 2 comprising reinforcement elements of textile type. The layer 2 consists 15 of reinforcement elements disposed radially. The radial positioning of the reinforcement, elements is defined by the laying angle of said reinforcement elements; a radial arrangement corresponds to a laying angle of said elements relative to the longitudinal direction of the tyre of between 20 650 and 90'. -Said carcass layer 2 is anchored on either side of the tyre 1 in a bead 3 whose base is intended to be mounted on a rim seat. Each bead 3 is extended radially towards the outside by a 'sidewall 4, said sidewall 4 meeting up radially 25 towards the outside with the tread 5. The tyre 1 thus constituted has a value of curvature greater than 0.15 and preferably greater than 0.3. The value of curvature is defined by the Ht/Wt ratio, that is to say by the ratio of the height of the tread to the maximum width of the tread of 30 the tyre. The value of curvature will advantageously be - 18 between 0.25 and 0.5 for a tyre intended to be fitted at the frdnt of a motorcycle and it will advantageously be between 0.2 and 0.5 for a tyre intended to be fitted at the rear. Between the carcass and the tread there is positioned a 5 crown reinforcement consisting in the present case of two working layers 6, 7 and a layer of circumferential reinforcement elements 8. The layer of circumferential reinforcement elements is in Figure 1 the radially outer part of the crown reinforcement and the two working layers 6, 7 10 are interposed between the carcass layer 2 and the layer of circumferential reinforcement elements 8. The layer of circumferential reinforcement elements advantageously consists of a single cord wound to form an angle with the longitudinal direction substantially equal to 00. The layer 15 of circumferential reinforcement elements may also be produced by the simultaneous winding of several bare cords or cords in the form of strips when they are immersed in rubber. The working layers 6, 7 consist of textile reinforcements produced according to the invention with at least one 20 continuous reinforcing cord forming parallel portions in the central zone of said layer and the adjacent, portions being connected by loops. The arrangement of the cords is such that the portions are crossed from a layer 6 to the following layer 7. 25 Figure 2 illustrates an example of embodiment according to the invention of such a working layer 6 consisting of a single cord 9 positioned to form portions 10. Two adjacent portions are connected by loops 11. The portions 10 are so oriented that they form with the longitudinal direction L an 30 angle of between 10 and 800. In this illustration in Figure 2, the portions are formed with an angle which may vary in - 19 such a way that, at the edges of the working layer 6, said angle.becomes larger. Such a variant embodiment in particular allows considerable circumferential rigidity to be imparted around the equator, that is to say in the central part of the 5 tyre where the angles of said portions are smallest so as to resist centrifugation. On the other hand, the largest angles at the edge of the working layer 6 and advantageously at the level of the shoulders allow improvement of the grip and drive ability of the tyre at a camber by optimising the 10 shearing rigidity of the working layers when the angle is around 450 or alternatively improvement of comfort at a camber when the angle approaches 900. Figure 2 also shows two circumferential section planes XX' and YY' and the angles a and @ formed by the 15 reinforcement elements with the longitudinal direction at the various points of intersection with said circumferential planes XX' and YY'. The angles a on the one hand and B on the other hand are identical whichever reinforcement element is considered. Furthermore, the angles a and P are different 20 from one another. Figure 2 also shows that, when the layer 6 is centred on the crown or equator of the tyre, the equator forms a line 12 comprising the inflection points of the portions 10 formed by the cord 9. 25 Figure 3 illustrates another variant embodiment of the invention similar to that of Figure 2 according to which the length of the portions is not regular. In the case of Figure 3, the cord 9' is deposited so as to form portions 10', 10'' of two different lengths. Such a configuration allows the 30 obtainment of variations in density in the axial direction, the quantity of reinforcement elements varying in this same - 20 direction. Variations in density of this type are all the more significant in designing tyres for motorcycles with regard to optimising and adapting the different rigidities of the working layers required between the straight line 5 positions and the various inclined positions of the tyre due to the different parts of the tread and of the reinforcement structure which face the ground. In the case of Figure 3, two different portion lengths are provided, but the invention must not be interpreted as 10 limited to this scenario, it being possible for the number of different portion lengths to be greater. According to one or other of the embodiments illustrated in Figures 2 and 3, the layers 6 and 6' are preferably made with a single cord. However, for various reasons, deliberate 15 or otherwise, in the case where several cords are used to produce a working layer 6, 7, 6', 7', the ends of said cords are located in the central part of the tyre. More precisely, no free end appears at the edges of the working layers; all that is present at this level of'the working layers is the 20 loops 11, 11'. Furthermore, with regard to the production of such a tyre, this is advantageously obtained by manufacture of the hard core type. Thus, laying of the cords 9, 9' may be performed by a robot which deposits them precisely at the 25 desired angles in their quasi-final position. In fact, hard core type manufacture allows precise positioning of the cords because, since the hard core sets the required internal cavity shape, the profile of the tyre is "not subject to modification during building.

- 21 Variants of the embodiment of Figure 1 may provide a different stack of said layers constituting the crown reinforcement. In fact, in particular to reduce the costs in terms of material and also in terms of output or 5 manufacturing time, the invention provides for the layer of circumferential reinforcement elements to be provided between the two working layers or alternatively radially to the inside of the working layers. Figure 4 shows a variant embodiment of Figure 1. 10 According to this variant embodiment, the layer of circumferential reinforcement elements 8' is provided radially to the inside of the carcass layer 2 radially covered with two layers 6 and 7 similar to those of Figure 1. As mentioned above, an embodiment of this type allows 15 financial savings on two counts. Firstly, the quantity of material used to form a layer of circumferential reinforcement elements identical to that of Figure 1 is reduced due to the lower radial position of the layer 8' for one and the same tyre in terms of dimensions. And 20 consequently, the laying time for the reinforcement cord of said layer 8' is less than that necessary for provision of the layer of the tyre shown in Figure 1. Other variants of the same type may be provided with different positioning of the various layers constituting the 25 crown reinforcement. As for the variant embodiments envisaged in the case of Figure 1, the layer of circumferential reinforcement elements may be positioned between or radially to the outside of the working layers. Such embodiments result in embodiments according to which at least one of the working 30 layers is positioned radially to the inside of the carcass ply.

- 22 Figure 5 shows an embodiment of the invention according to which the layer of circumferential reinforcement elements 13 is formed of several parts 13a, 13b, 13c positioned on the tyre at radially different levels. Such embodiments, for 5 example, allow the layer of circumferential reinforcement elements locally to maintain a protective role in particular with regard to the carcass ply and furthermore allow manufacturing costs to be reduced by forming said layer of circumferential reinforcement elements in part in radially 10 lower positions. This 'choice may also influence other properties of the tyre which are only required locally. In the case shown in Figure 5, the position of the axially outer parts 13b, 13c radially to the inside of the working layers 6, 7 in particular allows an improvement in stability at a 15 severe camber. Figure 6 shows, as in the case of Figure 5, an embodiment of the invention according to which the layer of circumferential reinforcement elements 14 is provided in a number of parts 14a, 14b, positioned on the tyre at radially 20 different levels. In contrast to Figure 5, the representation in Figure 6 does not exhibit symmetry relative to the equatorial plane 15. Such an embodiment may be particularly sought after when use of the tyre will itself not be symmetrical; for example, in the case of tyres designed for 25 use on specific circuits which subject the tyre to camber stress along substantially one side. In fact, the provision of such a tyre may be particularly relevant to use on a track where the majority of the curves or bends are in the same direction. 30 Such an embodiment of the layer of circumferential reinforcement elements in several parts may additionally be - 23 combined with the various variant embodiments of the invention presented above. It is possible in particular to provide a layer of circumferential reinforcement elements in part radially to the inside of or to the outside of or 5 between the working layers 6, 7. The various variant embodiments of the invention which have just been described allow the production of motorcycle tyres in which no free end of the reinforcement elements is present at the edges of the working layers. This feature of 10 the invention allows improvement of the quality and more particularly the grip, drive ability, comfort, or indeed the operating temperature of the tyres without impairing the various desired properties associated with the provision of said tyres.

Claims

1. A tyre comprising at least one carcass-type reinforcement structure, formed of reinforcement elements, 5 anchored on either side of the tyre to a bead whose base. is intended to be mounted on a rim seat, each bead being extended radially towards the outside by a sidewall, the sidewalls meeting up radially towards the outside with a tread, and comprising under the tread a crown reinforcement 10 structure consisting of at least one layer of reinforcement elements known as a working layer, characterised in that said layer consists of at least one continuous reinforcement cord forming portions in the central zone of said layer, said portions displaying identical angles formed with the 15 longitudinal direction, said angles being measured at the points of intersection with a circumferential plane, in that two adjacent portions are linked by a loop, and in that the portions form an angle with the longitudinal direction of between 10 and 800. 20

2. A tyre according to Claim 1, characterised in that, in the central zone of said layer, the portions are equidistant from one another along all circumferential planes.

3. A tyre according to Claim 1 or 2, characterised in that the angles formed by said portions with the longitudinal 25 direction are variable in the transverse direction and in that said angles are greater at the axially outer edges of the layers of reinforcement elements relative to the angles of said portions measured at the level of the equatorial plane of the tyre. - 25

4. A tyre comprising at least one carcass-type reinforcement structure, formed of reinforcement elements, anchored on either side of the tyre to a bead whose base is intended to be mounted on a rim seat, each bead being 5 extended radially towards the outside by a sidewall, the sidewalls meeting up radially towards the 'outside with a tread, and comprising under the tread a crown reinforcement structure consisting of at least one layer of reinforcement elements known as a working layer, characterised in that said 10 layer consists of at least one continuous reinforcement cord forming portions in the central zone of said layer, in that two adjacent portions are linked by a loop, in that said portions form an angle with the longitudinal direction of between 10 and 800, in that the angles formed by said 15 portions with the longitudinal direction are variable in the transverse direction and in that said angles are greater at the edges axially to the outside of the layers of reinforcement elements relative to the angles of said portions measured at the level of the equatorial plane of the 20 tyre.

5. A tyre according to Claims 1 to 4, characterised in that the crown reinforcement structure comprises at least two layers of reinforcement elements and in that from one layer to the next the portions form between them angles of between 25 20 and 1600.

6. A tyre according to Claim 3, 4 or 5, characterised in that the angles of the portions vary in monotonic manner from the equatorial plane of the tyre as far as the edges of the working layer. 30

7. A tyre according to Claim 3, 4 or 5, characterised in that the angles of the portions vary by stages from the - 26 equatorial plane of the tyre as far as the edges of the working layer.

8. A tyre according to one of Claims 1 to 7, characterised in that the reinforcement elements of the carcass-type 5 reinforcement structure form an angle of between 650 and 900 with the circumferential direction.

9. A tyre according to one of Claims 1 to 8, characterised in that the crown reinforcement structure comprises at least one layer of circumferential reinforcement elements.

10 10. A tyre according to Claim-9, characterised in that the layer of circumferential reinforcement elements is positioned at least in part radially to the outside of a working layer.

11. A tyre according to Claim 9 or 10, characterised in that the layer of circumferential reinforcement elements is 15 positioned at least in part radially to the inside of the working layer radially furthest to the inside.

12. A tyre according to one of Claims 9 to 11, characterised in that the layer of circumferential reinforcement elements is positioned at least in part radially to the inside of the 20 carcass-type reinforcement structure.

13. A tyre according to one of Claims 1 to 12, characterised in that the carcass-type reinforcement structure is made of two half-plies extending from the shoulders to the beads.

14. A tyre according to one of Claims 1 to 13, characterised 25 in that the working layer reinforcement elements are of textile material.

15. A tyre according to one of Claims 9 to 14, characterised in that the reinforcement elements of the layer of - 27 circumferential reinforcement elements are metal and/or textile and/or glass.

16. A tyre according to Claim 15, characterised in that the reinforcement elements of the layer of circumferential 5 reinforcement elements exhibit a modulus of elasticity greater than 6000 N/mm 2 .

17. Use of a tyre as described according to one of Claims 1 to 16 for a two-wheeled motorised vehicle such as a motorcycle.