Belted radial tyre for motorcycle and belt making method

Abstract: A belted radial tyre (1) for motorcycles comprising a pair of bead cores (5) disposed one in each bead portion (4) of the tyre, a carcass (6) extending between the bead portions (4) through sidewall portions (3) and a tread portion (2) of the tyre (1), the carcass (6) having at least one ply of organic fibre cords arranged radially at an angle of 60 to 90 degrees to the tyre equator (C), a tread disposed radially outside the carcass to define the tread portion (2), and a belt (7) disposed radially outside the carcass (6) and inside the tread characterised in that the tread is curved so that the maximum cross section width of the tyre (1) lies between the tread edges (E1,E2), and the belt (7) comprises two ply pieces (7a,7b) each having an outer edge and an inner edge and each ply piece comprising at least one spirally wound cord having an elastic modulus of not less than 600 kgf/sq.mm and being formed by a wound ribbon (10) of rubber, in which said at least one thereof towards the tyre equator to the inner edge. The invention also provides a method of winding and arranging strips for the tyre. The resultant tyre provides improved straight running and cornering performance whilst preventing belt edge problems.

Description: The present invention relates to a belted radial tyre for motorcycles and method of making the belt. Recently, a radial ply carcass has come to be used for motorcycle tyres. Such a radial motorcycle tyre has been made based on techniques for four-wheeled vehicle tyres, e.g. passenger car tyres. That is, the tyre has been provided with a belt reinforcement formed as follows: a rubberised fabric (d) is cut at a small bias angle (α) to the cord direction as shown in Figure 14, which is usually 15 to 30 degrees, and the cut fabric (e) is wound around a carcass with the ends (f) connected as shown in Figure 13 to form an annular belt reinforcement (a). Accordingly, the laid angle of the belt cords (b) to the tyre equator becomes the same bias angle (α). In such a bias belt structure, however, steering stability during straight running and cornering, especially at high speed, is not good. Alternatively, a belt making method is known in which a belt cord is wound spirally and continuously from its one edge to the other edge at a generally zero angle to the circumferential direction of the tyre so as to form a jointless belt. When this is used in the motorcycle tyre instead of the conventional belt, high speed steering stability is improved, but belt edge separation failure and deterioration of tyre uniformity are often observed. Such a jointless belt is disclosed by DE-A-3535064 which also discloses a belted radial motorcycle tyre comprising a two-piece belt according to the preamble of claim 1. It is therefore an object of the present invention to provide a radial motorcycle tyre in which straight running performance and cornering performance during high speed running are improved, and at the same time belt edge separation failure and deterioration of tyre uniformity are effectively prevented. Accordingly, one aspect of the present invention provides a belted radial tyre for motorcycles comprising a pair of bead cores disposed one in each bead portion of the tyre, a carcass extending between the bead portions through sidewall portions and a tread portion of the tyre, the carcass having at least one ply of organic fibre cords arranged radially at an angle of 60 to 90 degrees to the tyre equator, a tread disposed radially outside the carcass to define the tread portion, and a belt disposed radially outside the carcass and inside the tread, wherein the tread is curved so that the maximum cross section width of the tyre lies between the tread edges, and the belt comprises two ply pieces each having an outer edge and an inner edge characterised by each ply piece comprising at least one spirally wound cord having an elastic modulus of not less than 600 kgf/mm² and being formed by a wound ribbon of rubber, in which said at least one cord is embedded, wrapped spirally around the carcass from the axially outer edge thereof towards the tyre equator to the inner edge, the inner edges being adjacent to one another and positioned an axial distance from the tyre equator which is 0.1 to 0.3 times the tread width measured between the tread edges along the tread face. Adjacent inner edges may be in edge-to-edge abutment but are more preferably in overlapping arrangement. The ribbons may have various shapes and sloping edges. When sloping edges are used it is preferably that they are arranged so that successive windings are complementary. This may be achieved by winding two strips at the same time. Another aspect of the invention provides a method of making a belt for a motorcycle radial tyre comprising a carcass having organic fibre cords arranged radially at an angle of 60 to 90 degrees to the tyre equator, a tread disposed radially outside the carcass ply and curved so that the maximum cross section width of the tyre is lying between the tread edges, and said belt disposed between the carcass and the tread, characterised by feeding two ribbons of rubber, in which said at least one cord is embedded towards a drum having an outer cylindrical face having a round profile, fixing the ends of said two ribbons one at each side edge of the cylindrical face, and moving both ribbons transversely of the cylindrical face towards the centre thereof while the drum is revolving and the ribbons are being fed so that each ribbon is wound around the drum spirally from the axially outer edge towards the equator of the tyre and stopping winding to form an axially inner edge for each of the belt pieces. A convenient method to provide closely fitting adjacent windings is to wind two strips at the same time having complementary edge shapes. This may be obtained from one strip cross sectional shape by inverting the second of the two strips to be wound and then bringing them together for winding. Embodiments of the present invention will now be 6 described in detail with reference to the accompanying drawings, in which: Figure 1 is a sectional view showing a tyre according to the present invention; Figure 2 is a perspective view showing a belt cord ribbon; Figures 3 and 4 are sectional views explaining a method of making the belt thereof; Figure 5 is a plan view showing an arrangement of the belt cords and the carcass cord; Figure 6 is a section view showing another method of making the belt; Figure 7 is a perspective view showing another example of the ribbon; Figures 8 and 9 are sectional views showing the operation thereof; Figure 10 is a sectional view showing another example of the ribbon; Figure 11 is a sectional view showing still another example of the ribbon; Figure 12 is a sectional view showing still another method of making the belt using the ribbon shown in Figure 11; Figure 13 and 14 are plan views showing a conventional belt and the making method. In the Figures, motorcycle tyre 1 has a tread portion 2, a pair of bead portions 4, and a pair of sidewall portions 3 extending radially inwardly of the tyre from the edges of the tread portion to the bead portions. The tread portion is curved so that the maximum cross sectional width of the tyre lies between the edges E1 and E2 of the tread, and the tread has an arched profile which is generally one third of a circle, and the tyre has an aspect ratio of not more than 60%. The tyre 1 comprises a pair of bead cores 5 disposed one in each bead portion 4, a carcass 6 extending between the bead portions 4 through the sidewall portions 3 and the tread portion 2, and having at least one ply of radially arranged cords turned up around the bead cores 5 from the axially inside to outside thereof to form two turned up portions 6b and a main portion 6a therebetween, a tread 2 disposed radially outside the carcass to define the tread portion, a belt 7 disposed radially outside the carcass 6 and inside the tread, and a bead apex 9 disposed between the carcass main portion 6a and each carcass turned up portion 6b and extending radially outwardly and taperingly from the bead core. The carcass 6 has one ply of cords arranged radially at an angle to 60 to 90 degrees, preferably 70 to 90 degrees, with respect to the tyre equator C. For the carcass cords, organic fibre cords, e.g. nylon, rayon, polyester, aromatic polyamide and the like can be used. Each turned up portion 6b is extended radially outwardly, and the radial height Ht of the radially outer edge of the turned up portion is 0.5 to 1.2 times the radial height Hs of the tread edge E1,E2, both measured from the bead base line 15. When the height Ht is less than 0.5 times the height Hs, the reinforcement becomes insufficient for the bead portion to endure bent deformation, and the durability deteriorates. When the height Ht is more than 1.2 times the height Hs, the rigidity of the sidewall portion as well as the bead portion becomes excessively increased, and ride comfort deteriorates. In this embodiment, each carcass turned up portion 6b is extended to a position in the tread portion to be sandwiched between the carcass and each belt edge portion. The bead apex 9 is made of hard rubber having a JIS A hardness of not less than 60. The radial height Ha of the radially outer edge thereof from the bead base line 15 is 0.5 to 1.2 times the radial height Hs of the tread edge from the bead base line 15, and the height Ha is lower than the height Ht. When the height Ha is less than 0.5 times the height Hs, the rigidity of the bead portion against bending deformation is low, and the bead durability is reduced. When the height Ha is more than 1.2 times the height Hs, the rigidity of the sidewall portion and the bead portion is increased excessively so that ride comfort deteriorates. The belt 7 is composed of spirally wound cords, and the belt width Wb measured along the curved belt is 0.7 to 1.0 times the tread width WT measured between the tread edges E1 and E2 along the tread face. When the width Wb is less than 0.7 times the tread width WT, the rigidity of tread shoulder regions is decreased, and stability in rapid cornering is lost. When the width Wb is more than 1.0 times the tread width WT ride comfort deteriorates due to the excessively increased sidewall rigidity. For the belt cord 11, organic fibre cords, for example polyfluoroethylene, aromatic polyamide, polyester and the like, or steel cords, having a high modulus of elasticity of not less than 600 kgf/mm² are used. When the elastic modulus is less than 600 kgf/mm², the tread portion has an insufficient rigidity, and the directional stability and cornering performance at high speed and the durability deteriorates. Preferably, aromatic polyamide fibre cords having a high modulus of the same level as steel are used. In the embodiment shown in Figure 1 the belt 7 is composed of a two-piece ply made up of pieces 7a and 7b, each of which extend respectively from positions F1,F2 near the tread edge E1,E2 to positions G1,G2 near the tyre equator C. In each ply piece, at least one belt cord 11 is wound spirally and continuously from its axially outer edge to inner edge at zero angle or a small angle with respect to the tyre equator C. In Figure 1, the left piece 7a is extended over the tyre equator C and terminated at the position G1 located right side of the equator and the right piece 7b is extended to the substantially same position G2 and terminated thereat. The distance WL measured along the belt 7 from the tyre equator C to the position G1 is 0.1 to 0.3 times the above-mentioned tread width WT. When the distance WL is less than 0.1 times WT, the joint part between the axially inner edges G1 and G2 of the pieces 7a and 7b is liable to be fatigued by the repeated deformation during straight running, which will finally cause cord separation. When the distance WL is more than 0.3 times WT, the tyre uniformity is liable to be disturbed. The belt 7 is formed by winding a ribbon 10 around the circumference of the carcass 6. The ribbon is a strip of rubber 12 in which a cord or a plurality of parallel cords 11 are embedded. Figure 2 shows an example of the ribbon 10, wherein the cross sectional shape thereof is a flat rectangle, and two parallel belt cords 11 are embedded therein at a pitch P, and the distance N measured from the edge 10a of the ribbon to the centre of the outermost cord is set to be not more than 1/2 of the cord pitch P. In order to make the above-mentioned belt 7, as shown in Fig.3 and 4, two ribbons are used. The ribbons to be wound are supplied from two different or opposite directions as indicated by a chain lime in Fig.3, and they are simultaneously wound spirally around a profiled cylindrical face F, which is revolved around its axis, towards the tyre equator C starting from the respective axially outer edges F1 and F2 to the inner edges G1 and G2 so that the ribbon in the ply piece 7a and the ribbon in the ply piece 7b are inclined in the same direction at the same small angle to the tyre equator. As mentioned above, the tread profile is approximately one third of a circle, and the carcass in the tread portion and the belt profile are each provided with a round profile similar to the tread profile. The above mentioned profiled cylindrical face F is generally the radially outer face of the unvulcanised carcass applied to a profile drum of which outer surface is formed in a round profile to give the designed profile to the carcass. That is, generally the ribbon is wound directly on the carcass. However, the profiled face F may be the outer surface of a belt shaping drum which has the same profile as the carcass. The terminal ends G1 and G2 of the ribbon are butt jointed as shown in Fig.5. and fixed by means of adhesive tape or adhesive agent if needed. Accordingly, the ribbon is wound radially outwardly, while pressing the previously wound part thereof by its edge, thereby preventing the wound ribbon from-being loosened. If the above mentioned distance WL is more than 0.3 times the tread width WT, when the ribbon exceeds such distance, the ribbon should be wound radially inwardly while decreasing its winding diameter, and accordingly the ribbon is easily loosened. As a result, accuracy in winding pitches is liable to be lost. Alternatively, the tyre can be made as follows: a raws carcass is applied to the outer face of the profile drum; the edge portions of the carcass are folded back around the bead cores to sandwich a raw rubber bead apex between the carcass main portion and each folded edge; raw belt ribbons are wound as explained above; a raw rubber tread, sidewalls and so on are applied to the outer side of the belt and carcass; the assembly is inserted into a vulcanising mould, an inflating tube is disposed inside the assembly; the tube is inflated to press the assembly against the negative impression of the mould; and the assembly is vulcanised. Fig.6. shows an expedient to further prevent the looseness of the wound ribbon during the winding operation. The ribbon 10 is wound so that the edge 10a thereof overlaps with the adjacent edge 10a of the previously wound part thereof to press it into the face F. Accordingly, the wound ribbon is prevented from being loosened, and as a result belt edge separation during running is prevented. By winding in this way, as shown in Fig.5, the belt 7 has an asymmetrical structure with respect to the tyre equator C, in which the inclination and the winding direction of the cords in one belt ply piece is same as those in the other piece. However, the belt can be provided with a symmetrical structure by supplying the ribbons from the same direction contrary to the figure 3. Thus, the winding direction of the cords in one belt ply piece is then different from that in the other piece. In order to make a smooth overlap of the ribbon edges, the cross sectional shape of the ribbon 10 can be modified as shown in Figures 7, 10 and 11. In each example, the edges of the ribbon 10 are tapered. In Figure 7, the cross sectional shape of the ribbon 10 is a flat hexagon in which the upper side and lower side of each tapered portion are formed in the same length, and two parallel cords 11 are embedded in its main portion 15 along the longitudinal direction of the ribbon. This hexagonal ribbon is wound as shown in Figures 8 and 9. A previously wound portion 10S is set on the profiled face F with its one side 10c contacting with the face F. As the drum revolves, the portion 10T to be wound approaches to the wound portion 10S, and its tapered edge 13B contacts with the tapered edge 13A of the previously wound portion thereto. As the result, the tapered edges 13A and 13B are deformed as shown in Figure 9. In Figure 10, the cross sectional shape of the ribbon 10 is a rhombus, and one cord 11 is embedded therein. In this case, the cord inclination can be made smaller than the above mentioned ribbons in which plural cords are embedded. In Figure 11, the cross sectional shape of the ribbon 10 is a flat trapezoid, and three parallel cords 11 are embedded in its main portion 15 along the longitudinal direction of the ribbon. In this case, contrary to the previous case, the cord inclination can be largely increased. As shown in Figure 12, two adjoining ribbons 10A and 10B, one of which is reversed, are simultaneously fed toward the drum and wound. The ribbons 10A and 10B when not wound are separated, but the wound ribbons 10A and 10B on the profiled face F contact with each other. Incidentally, the sectional shape, section width, the number of the embedded cords, the cord material, the rubber hardness and the like can be changed between the ribbon 10A and the ribbon 10B. However, as the profiled face F is curved in the lateral regions thereof the angle between the face F and the widthwise direction of the ribbon to be wound becomes very large, for example over 45 degrees. Therefore, when the ribbon has a rectangular section as shown in Figure 2, the ribbon sometimes makes contact with the face F only at its side face 10a, which makes a twisted part and disturbs the cord pitches. However, by making the tapered portions 13 as explained above, such problems can be solved. Incidentally, in each of the pieces and/or between the pieces, the inclination of the ribbon or cords can be changed.

Claims: A belted radial tyre (1) for motorcycles comprising a pair of bead cores ( 5) disposed one in each bead portion (4) of the tyre, a carcass (6) extending between the bead portions (4) through sidewall portions (3) and a tread portion (2) of the tyre (1), the carcass (6) having at least one ply of organic fibre cords arranged radially at an angle of 60 to 90 degrees to the tyre equator (C), a tread disposed radially outside the carcass (6) to define the tread portion (2), and a belt (7) disposed radially outside the carcass (6) and inside the tread, wherein the tread is curved so that the maximum cross section width of the tyre (1) lies between the tread edges (E1,E2), and the belt (7) comprises two ply pieces (7a,7b) each having an outer edge and an inner edge characterised by each ply piece (7a,7b) comprising at least one spirally wound cord (11) having an elastic modulus of not less than 600 kgf/mm² and being formed by a wound ribbon (10) of rubber, in which said at least one cord (11) is embedded, wrapped spirally around the carcass from the axially outer edge thereof towards the tyre equator (C) to the inner edge, the inner edges being adjacent to one another and positioned an axial distance (WL) from the tyre equator (C) which is 0.1 to 0.3 times the tread width (WT) measured between the tread edges (E1,E2) along the tread face. A tyre according to claim 1 characterised in that the adjacent inner edges of each ply piece (7a,7b) are overlapped. A tyre according to either of claims 1 or 2 characterised in that the cross sectional shape of the ribbon (10) is a flat rectangle. A tyre according to either of claims 1 or 2 characterised in that the edges of the ribbon (10) are tapered. A tyre according to either of claims 1 to 2 characterised in that the cross sectional shape of the ribbon (10) is a flattened hexagon. A tyre according to either of claims 1 or 2 characterised in that the cross sectional shape of the ribbon (10) is a rhombus. A tyre according to either of claims 1 or 2 characterised in that the cross sectional shape of the ribbon (10) is a flat trapezoid. A tyre according to any of claims 4, 5, 6 or 7 characterised in that the edge of adjacent windings of ribbon (10) are in overlapping arrangement. A method of making a belt (7) for a motorcycle radial tyre (1) comprising a carcass (6) having organic fibre cords arranged radially at an angle of 60 to 90 degrees to the tyre equator, a tread disposed radially outside the carcass ply and curved so that the maximum cross section width of the tyre is lying between the tread edges (E1,E2), and said belt (7) disposed between the carcass (6) and the tread, characterised by feeding two ribbons (10) of rubber, in which said at least one cord (11) is embedded towards a drum having an outer cylindrical face (F) having a round profile, fixing the ends of said two ribbons (10) one at each side edge of the cylindrical face (F), and moving both ribbons (10) transversely of the cylindrical face (F) towards the centre thereof while the drum is revolving and the ribbons (10) are being fed so that each ribbon (10) is wound around the drum spirally from the axially outer edge towards the equator (C) of the tyre (1) and stopping winding to form an axially inner edge for each of the belt pieces (7a,7b). A method according to claim 9 characterised in that the adjacent edges of each successive winding of the ribbons (10) are overlapped with each other. A method according to claims 9 and 10 characterised in that the ribbon (10) is formed as a flat rectangle. A method according to claim 9 or 10 characterised in that the edges of each ribbon (10) are tapered. A method according to claim 9 or 10 characterised in that the ribbon (10) is formed as a flat hexagon. A method according to claim 9 or 10 characterised in that the ribbon (10) is formed as a rhombus. A method according to any one of claims 9 to 14 characterised in that two ribbons (10A,10B) are brought together to form a pair for each of the two ribbons at the edges of the cylindrical surface (F) of round profile, and the two said pairs of ribbons (10A,10B) are both wound spirally inwards of the drum. A method according to claim 15 characterised in that adjacent edges of both the ribbons (10A,10B) being paired together are brought into abutment on winding onto the cylindrical face (F). A method according to claim 15 characterised in that the two paired ribbons (10A,10B) are each formed to give a pair of mutually complementary edge-to-edge profiles. A method according to claim 17 wherein both ribbons (10A,10B) of the pair are formed with the same shape and one ribbon is turned over with respect to the other so that adjacent edges are fitted together. A method according to claim 18 wherein the shape of both ribbons (10A,10B) is a flat trapezoid.

Inventors: NAITO SADAAKI, SUZUKI SHIGEHIKO, YASUI ITSUO, NAITO, SADAAKI, SUZUKI, SHIGEHIKO, YASUI, ITSUO
Applicants: SUMITOMO RUBBER IND, SUMITOMO RUBBER INDUSTRIES LIMITED
Application year: 1991
Main classification: B60C9
IPC codes: B60C9, B60C15