Motorcycle radial tyre

Abstract: A motorcycle radial tyre comprising a pair of bead cores (5) disposed one in each bead portion (4), a carcass (6) extending between the bead portions (4) and turned up around the bead cores (5), said carcass (6) having at least one ply of cords arranged radially at an angle of 70 to 90 degrees with respect to the tyre equator (C), a belt (7) disposed radially outside the carcass (6) and inside a tread (2), and a bead apex (9) disposed between each turned up portion (6b) and the main portion (6a) of the carcass and extending radially outwardly one from each bead core (5), characterised in that the height (Ht) of the carcass turned up portions (6b) from the bead base line is more than 0.2 times and less than 0.5 times the height (Hs) of the tread edges (E1,E2) from the bead base line, said belt comprises a plurality of axially divided pieces (7a,7b,7c,7d,7e,7f), each belt piece being a spiral winding of a ribbon (10) of rubber in which at least one cord (11) is embedded, with a small inclination angle with respect to the tyre equator (C) in the same winding direction as the other belt piece or pieces (7a-7f), the height (Ha) of the radially outer edge of the bead apex (9) from the bead base line is more than 0.2 times and not more than 0.5 times said tread edge height (Hs).

Description: The present invention relates to a pneumatic tyre, more particularly a belted radial ply tyre for motorcycle use. In general, although requirements for motorcycle tyres, especially during cornering, are quite different from those for four-wheeled vehicle tyres, motorcycle radial tyres are made according to a method similar to those for four-wheeled vehicle tyres. That is, as shown in Figures 7 and 8, a belt reinforcement (a) which is disposed radially outside the radial carcass to reinforce the tread portion, has been made as follows: a sheet of tyre fabric (d) usually unwoven fabric in which belt cords (b) are laid parallel with each other, is bias cut at a certain angle α into strips of fabric (e) having a width corresponding to the belt width; a strip of fabric (e) is wound around the carcass; and the bias cut ends (f) of the wound fabric are joined by overlapping a certain circumferential length. With such a conventional belt structure and belt making method, the recent severe requirements can not be achieved. Steering stability during straight running is inferior due to the bias cut joint, and also steering stability during cornering is inferior. These factors are especially notable during high speed running. Further, high speed durability is not satisfactory. To solve such problems, an endless belt has been proposed in Japanese Utility Model Publication No.58-160805, wherein the belt is, as shown in Figure 6, formed by spirally winding a belt cord (1) continuously from the axial edge p1 to the opposed axial edge p2 of the belt. Such a cord winding operation consumes much time and tyre production efficiency is low, and further uniformity of the belt is liable to be lost. A motorcycle tyre having the features of the preamble of claim 1 is known, for example, from DE-A-3535064. A motorcycle tyre wherein the height of the bead apex is 0.48 of the tread edge height is known from US-A-4773462. It is therefore, an object of the present invention to provide a motorcycle radial tyre, in which steering stability during high speed running and production efficiency are both improved. According to one aspect of the present invention, a motorcycle radial tyre comprising a pair of bead cores disposed one in each bead portion, a carcass extending between the bead portions and turned up around the bead cores, said carcass having at least one ply of cords arranged radially at an angle of 70 to 90 degrees with respect to the tyre equator, a belt disposed radially outside the carcass and inside a tread, and a bead apex disposed between each turned up portion and the main portion of the carcass and extending radially outwardly one from each bead core, the height of the carcass turned up portions from the bead base line being more than 0.2 times and less than 0.5 times the height of the tread edges from the bead base line, said belt comprises a plurality of axially divided pieces, each belt piece being a spiral winding of a ribbon of rubber in which at least one cord is embedded, with a small inclination angle with respect to the tyre equator in the same winding direction as the other belt piece or pieces, characterised in that there are four belt pieces two either side of the centre of the tyre, and the cords of all the belt pieces are wound in the same direction around the tyre and the height of the radially outer edge of the bead apex from the bead base line is more than 0.2 times and not more than 0.5 times said tread edge height. There may be two belt pieces each of which comprises substantially half the belt width or there may be four, two either side of the centre line of the tyre. Preferably the belt width is in the range 0.7 to 1.0 times the tread width. Another aspect of the invention provides a method of making a belt for a motorcycle tyre, said belt disposed radially outside a carcass and inside a tread and comprising a plurality of axially divided pieces, the Method being characterised by the steps of attaching one end of each of the ribbons of rubber to axially spaced positions on a rotatably mounted cylindrical tyre carcass each ribbon of rubber having therein at least one belt cord along the longitudinal direction thereof, said axially spaced positions of each ribbon being axially to the same side of the tyre, and rotating the carcass while supplying ribbons towards the cyclindrical tyre carcass and at the same time moving the supplied ribbons sideways of the carcass along the axis of the tyre face, so that all of the ribbons are wound in the same winding direction, and all the belt cords in the windings have small inclination angles of not more than 10 degrees with respect to the tyre equator. Embodiments of the present invention will now be described in detail by way of example only,in conjunction with the accompanying drawings, in which: Figure 1 is a sectional view of a tyre of the present invention; Figure 2 is a developed plan view of the carcass and belt thereof; Figure 3 is an enlarged sketchy perspective view of a ribbon used to form the belt; Figure 4 is a cross sectional view showing a method of making the belt; Figure 5 is a cross sectional view showing a modification of the belt and a method of making the same; Figure 6 is a cross sectional view showing the belt and method according to a prior art; Figures 7 and 8 are plan views showing thy conventional belt and method. In Figures 1 to 4, a motorcycle radial tyre 1 has a tread portion 2, a pair of axially spaced bead portions 4, and a pair of sidewall portions 3 extending between the tread edges E1 and E2 and the bead portions. The tread portion 2 is curved with a single radius of curvature so that the maximum cross section width of the tyre lies between the tread edges E1 and E2. A pair of bead cores 5 is disposed one in each of the bead portions 4, a carcass 6 extends between the bead portions and is turned up around the bead cores 5 from the axially inside to outside thereof to form turned up portions 6b and a main portion 6a therebetween. A belt reinforcement 7 is disposed radially outside the carcass 6 and inside a rubber tread 2, and a bead apex 9 is disposed between each carcass turned up portion 6b and the carcass main portion 6a. The carcass 6 comprises at least one ply of cords arranged radially at an angle of 70 to 90 degrees with respect to the tyre equator C. The carcass has a profile such that the crown portion is curved substantially being generally parallel with the curved tread face. For the carcass cords, organic fibre cords, e.g. nylon, rayon, polyester, aromatic polyamide or the like may be used. The carcass turned up portion 6b has a radial height Ht of more than 0.2 times and less than 0.5 times the radial height Hs of the tread edges E1 and E2, both measured from the bead base line 15, whereby bending deformation of the bead portions is mitigated and bead durability is improved while maintaining the ride comfort. If the turnup height Ht is not more than 0.2 times the tread edge height Hs, the bead portions are decreased in rigidity and subjected to bending stress, and thereby the bead portions are liable to be cracked, and durability is lost. If the height Ht is more than 0.5 times the height Hs, the rigidity of the sidewall portions 3 and bead portions 4 is excessively increased and this deteriorates ride comfort. The belt 7 is disposed radially outside the carcass crown, and the belt has a curved profile similar to that of the carcass crown. The belt comprises a plurality of axially divided pieces. In this embodiment, the belt 7 is composed of two pieces 7a and 7b divided at the tyre equator C. Each of the belt pieces 7a and 7b is made of a spirally wound cord or spirally wound parallel cords. For the belt cord 11, organic fibre cords, e.g. Teflon (Trade Mark), aromatic polyamide, polyester or the like or steel cords, having a high elastic modulus of not less than 600 kgf/sq.mm are used. If the elastic modulus is less than 600kgf/sq.mm, the tread portion 2 is not provided with rigidity, and high speed straight running performance, high speed cornering performance, durability are impaired. Preferably, aromatic polyamide fibre cords are used for its light weight and high modulus nature. The cords of all the belt pieces are wound in the same winding direction. Further, in each belt piece, the windings of the belt cord or cords have a small inclination angle of not more than 10 degrees, more preferably not more than 5 degrees with respect to the tyre equator C. The belt width Wb measured along the curved belt 7 between its ends F1 and F2 is more than 0.7 times and less than 1.0 times the tread width Wt measured along the curved tread face between its edges E1 and E2. When the width Wb is not more than 0.7 times Wt, the rigidity in the tread shoulder region is decreased, and steering stability during abrupt cornering is lost. When the width Wb is not less than 1.0 times Wt, the rigidity of the sidewall portion is excessively increased, and ride comfort is deteriorated. The above-mentioned bead apex 9 is made of hard rubber and extends radially outwardly from the bead core 5 and tapering to provide a wedge-shaped cross section. The radial height Ha of the radially outer edge L of the bead apex measured from the bead base line 15 is more than 0.2 times and less than 0.5 times the above-mentioned tread edge height Hs, whereby durability is improved without sacrificing the ride comfort. If the height Ha is not more than 0.2 times the height Hs, the bending rigidity of the bead portion is decreased to lower the durability. If the height Ha is more than 0.5 times the height Hs, the rigidity of the sidewall portion 3 and bead portion 4 becomes too increased to lower ride comfort. Figure 4 shows a method of making the above-mentioned two-piece belt. Two ribbons of rubber, in which at least one belt cord 11 is embedded in coating rubber 12 along the length direction of the ribbon 10 as shown in Figure 3, are prepared. The carcass 6 is shaped into a toroidal shape in advance using a shaping drum, and the carcass is supported rotatably around its axis by a drum. The ends of two ribbons 10A and 10B are fastened to the outer surface of the carcass at positions F1 and G which are at the same side axial edges, in Figure 4 the left side edges, of the belt pieces 7a and 7b. The carcass 6 is rotated while supplying the ribbons 10A and 10B towards the carcass, and at the same time, moving the supplied ribbons in the axial direction of the carcass or drum from the above-mentioned starting positions F1 and G to stopping positions G and F2 corresponding to the other side axial edges, in Figure 4 the right side edges, of the belt pieces, so that all of the cords 11 in the ribbons 10A and 10B are wound in the same winding direction, and all of the windings of the belt cords have small inclination angles of not more than 10 degrees with respect to the tyre equator C. The ribbons are cut and the cut end of the ribbon 10A is joined to the ribbon 10B at a point J at the tyre equator C. The winding is thus finished and a strip of tread rubber is applied over and around the belt to complete the green tyre. Accordingly, the ribbon 10A is wound spirally from the position F1 near the left tread edge E1 to the position G near or at the tyre equator C to form the left belt piece 7a. On the other hand, to form the right belt piece 7b, the ribbon 10B is wound spirally from the position G to the position F2 near the right tread edge E2 in the same winding direction as the ribbon 10A. Therefore, the belt 7 can be formed in a shorter time. Figure 5 shows a modification of the belt 7. In this example, the belt is composed of four axially divided pieces 7c, 7d, 7e and 7f having the same widths, each of which is formed by spirally winding a ribbon 10 in the same manner as the above-explained former example. Thus, in the present invention, the belt is composed of a plurality of axially divided pieces. Accordingly, the time for winding the belt cord is reduced, and the production efficiency is improved. Tyres of size 170/60R17 were prepared. Each test tyre was mounted on its regular rim and inflated to its regular pressure and then tested for the following performance factors. The specifications of the test tyres are given in Table 1. 1) High speed straight running stability and High speed cornering stability The test tyre was installed on a motorcycle, and was run on a straight course at 260km/Hr. and a 400m radius course at 220km/Hr. to evaluate running stability by a test driver. The results are indicated by an index based on the assumption that the working example tyre 1 is 100. The larger the value, the better the stability. 2) High speed durability Using a drum tyre tester the running speed of the test tyre was increased every 20 minutes at steps of 10km/Hr. from an initial speed of 160km/Hr., and the speed at which the tread portion became cracked was measured as the durability. The test tyre load was the maximum load specified by JIS. The results are indicated by an index based on the assumption that the working example tyre 1 is 100. The larger the value, the better the durability. 3) Belt making time The total time to make each band inclusive of preparatory time was measured, and is indicated by an index based on the assumption that the reference tyre 1 is 100. In the motorcycle radial tyres according to the present invention, high speed running performance and high speed durability are improved. Further, according to the above-explained belt making method, the endless belt is made by a shorter time, and it becomes possible to make the tyre efficiently at a lower production cost.

Claims: A motorcycle radial tyre comprising a pair of bead cores (5) disposed one in each bead portion (4), a carcass (6) extending between the bead portions (4) and turned up around the bead cores (5), said carcass (6) having at least one ply of cords arranged radially at an angle of 70 to 90 degrees with respect to the tyre equator (C), a belt (7) disposed radially outside the carcass (6) and inside a tread (2), and a bead apex (9) disposed between each turned up portion (6b) and the main portion (6a) of the carcass and extending radially outwardly one from each bead core (5), the height (Ht) of the carcass turned up portions (6b) from the bead base line being more than 0.2 times and less than 0.5 times the height (Hs) of the tread edges (E1,E2) from the bead base line, said belt comprises a plurality of axially divided pieces (7a,7b,7c,7d,7e,7f), each belt piece being a spiral winding of a ribbon (10) of rubber in which at least one cord (11) is embedded, with a small inclination angle with respect to the tyre equator (C) in the same winding direction as the other belt piece or pieces (7a-7f), characterised in that there are four belt pieces (7c-7d) two either side of the centre of the tyre (C), and the cords of all the belt pieces (7a-7f) are wound in the same direction around the tyre and the height (Ha) of the radially outer edge of the bead apex (9) from the bead base line is more than 0.2 times and not more than 0.5 times said tread edge height (Hs). A tyre according to any of claims 1 characterised in that the belt width is more than 0.7 and legs than 1.0 times the tread width (Wt) measured along the curved surface of the tread between the edges (E1 & E2). A tyre according to claim 1 or 2 characterised in that the elastic modulus of the cords in the strip is greater than the 600Kg/square cm. A tyre according to any of claims 1 to 3 characterised in that the radial height of the bead apex (9) measured from the bead base line (15) is more than 0.2 and less than 0.5 times the tread edge height (Hs). A method of making a belt (7) for a motorcycle tyre, said belt (7) disposed radially outside a carcass (6) and inside a tread (2) and comprising a plurality of axially divided pieces (7a,7f), the method being characterised by the steps of attaching one end of each of the ribbons (10) of rubber to axially spaced positions on a rotatably mounted cylindrical tyre carcass each ribbon (10) of rubber having therein at least one belt cord (11) along the longitudinal direction thereof, said axially spaced positions of each ribbon (10) being axially to the same side of the tyre, and rotating the carcass while supplying ribbons (10) towards the cylindrical tyre carcass and at the same time moving the supplied ribbons sideways of the carcass along the axis of the tyre face, so that all of the ribbons (10) are wound in the same winding direction, and all the belt cords (11) in the windings have small inclination angles of not more than 10 degrees with respect to the tyre equator.

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