MOTOR CYCLE TYRE

Abstract: A motor-cycle tyre improved in durability and steering stability under high speed running, which comprises bead cores one disposed in each bead region of the tyre a carcass extending between the bead regions and turned up at both edges around the bead cores the carcass having at least two plies of cords arranged at 20 to 28 degrees to the circumferential direction of the tyre, a tread disposed radially outwardly of the carcass and a breaker disposed between the tread and the carcass the breaker having two plies of cords arranged at 14 to 18 degrees to the circumferential direction of the tyre.

Description: The present invention relates to a pneumatic tyre for motor-cycles, which is improved in durability and steering stability under high speed running. In order to maintain stable running during cornering of motor-cycles which are tilted at a large bank angle, there has been employed a cross ply carcass in which at least two plies of parallel cords are arranged to intersect each other to provide a high lateral rigidity for the motor-cycle tyre. In such cross ply carcass tyres, however, a vibration of about 1 to 4 Hz, that is, the vibration of the weave mode is liable to occur during high speed running, causing deterioration of steering stability and manoeuvrability. This vibration of the weave mode is a small vibration of the rear wheel caused when the running speed is increased. In this phenomenon (hereinafter referred as "weave phenomenon") a vibration caused by an external disturbance from the road surface is not damped and grows into a continuous vibration due to the tyre damping capacity being decreased as a result of high speed running. In particular, racing tyres for use over 250 km/h are required to have characteristics to maintain stable running, and heretofore, in order to increase the lateral rigidity to improve the cornering performance and also to enhance the high speed durability, the tyre has been made with a carcass of cross ply construction in which carcass ply cords are laid at about 26 degrees to the circumferential direction of the tyre and also a breaker having cords laid at the same angle as that of the carcass cords. However, in such prior art tyres having the breaker ply cords arranged at the same angle as those of the carcass ply cords, sympathetic vibrations are liable to occur in the plies, and as a result, the amplitude of the vibration is increased, and the speed range within which such vibrations are caused is widened. On the other hand, there have been suggested tyres having a structure in which the breaker cords are arranged at more than 20 degrees and the carcass cords are arranged at about 30 degrees so that the angles of the breaker cords are different from those of the carcass ply cords. However, such a structure does not sufficiently increase the lateral rigidity of the tread region, and it is very difficult to maintain steering stability and durability under high speed running. Furthermore, if cords having a high rigidity such as aromatic polyamide fibre cords are employed in the breaker, breaker edge separation is liable to occur and such tyre a construction is also insufficient in high speed durability. A tyre according to the preamble of claim 1 is known, e.g. from US-A-4 614 215, which shows a motorcycle bias tyre having a belt whose cords are at an angle of 10°-20° to the circumferential direction of the tyre. It is therefore, a general object of the present invention to provide a motor-cycle tyre in which the above mentioned weave phenomenon is diminished and the high speed steering stability is improved, while the high speed durability is maintained. Another object of the present invention is to provide a motor-cycle tyre in which both durability and steering stability under high speed running are improved without using high rigidity cords, and the above mentioned weave phenomenon is effectively prevented. According to one aspect of the present invention, a motor-cycle tyre comprises bead cores one disposed in each bead region of the tyre, a carcass extending between the bead regions and turned up at both edges around the bead cores and a tread region, the carcass having at least two plies of cords arranged at 22 to 24 degrees to the circumferential direction of the tyre, and a breaker disposed between the tread and carcass having two plies of cords arranged at 14 to 16 degrees to the circumferential direction of the tyre. An embodiment of the present invention will now be described by way of example only with reference to the accompanying diagrammatic drawings in which:- Fig.1. is a sectional view of a left half of a motor-cycle tyre. A motor-cycle tyre 1 has a tread region 2, a pair of sidewall regions 3 extending radially inwardly one from each edge of the tread 2 and a pair of bead regions 4 positioned at the radially inward ends of the sidewall regions respectively. The tyre also comprises a pair of bead cores 5 disposed one in each bead region, a carcass 6 extending from one bead region to the other bead region through the sidewall regions 3 and tread region 2, a tread and a pair of sidewalls disposed on the carcass. A breaker 7 is disposed radially outwardly of the carcass 6 between the tread and the carcass 6. The carcass 6 comprises at least two plies 9 of cords laid at 20 to 28 degrees, more preferably 22 to 24 degrees with respect to the circumferential direction of the tyre. The carcass cords of one ply intersect with those of the other ply. The carcass 6 is turned up in both edge portions around the respective bead cores 5 from the inside to the outside thereof, and in this example, the two carcass ply turnups, an axially outer turnup 9A and an inner turnup 9B, are formed axially outwardly of each bead core 5. Preferably, the end of the outer turnup 9A is extended radially outwardly beyond the end of the inner turnup 9B to cover the inner turnup completely, thereby mitigating stress concentration on the end of the inner turnup 9A. Further, to reinforce the sidewall regions 3, the heights of the inner and outer turnups from the bead base 10 are respectively set in a range of 20 to 40% of and an angle of 25 to 80% of the height H of the tread edge from the bead base respectively. The cords of the carcass ply 9 are made of organic fibres such as nylon, polyester, rayon or aromatic polyamide. In addition to the above mentioned carcass structure in which the carcass 6 is turned up around the bead cores 5 from the inside to the outside, a structure in which the carcass 6 is turned up reversely from the outside to then inside or a combination structure of the former two may be applied to the carcass 6 in the present invention. The above mentioned breaker 7 comprises two plies 12 of cords laid at 14 to 18 degrees, more preferably 14 to 16 degrees with respect to the circumferential direction of the tyre so that the cords of one ply cross the cords of the other ply. The width of the breaker 7 is set in the range of 60 to 120 % and more preferably in the range of 80 to 100 % of the width of the tread region 2. The textile fabrics used for the breaker 7 are made of organic material cords such as nylon, polyester, rayon or aromatic polyamide (aramid). The breaker 7 increases the rigidity in the circumferential direction of the tyre, and restrains lifting of the tread crown which us caused by centrifugal force acting on the tyre during high speed running. Accordingly,, the stability in straight running is improved, and rubber separation in the tread region is prevented which improves the high speed endurance. As described above, in the breaker 7, the cords are laid at different angles from those of the carcass cords. Therefore, the small vibrations generated in the plies of the carcass and breaker during high speed running, interfere with each other, and as a result, the weave phenomenon is reduced compared with a conventional tyre to increase steering stability. Furthermore, a triangular bead apex 11 made of rubber having a JIS hardness of 45 to 95 degrees, is provided in each bead region. The bead apex 11 is extended radially outwardly tapering from the bead core 5 into the sidewall region 3 and in order to increase the transverse stiffness of the tyre, the height h of the outer end of the bead apex 11 from the bead base 10 is set in the range of 85 to 100% of the height H of the tread edge from the bead base. Note however, that the height h is set to be different from that of the carcass ply turnup 9A so that the two ends not at the same point, thereby avoiding stress concentration. Working Examples 140/80V17 motor-cycle tyres for a rear wheel were made including example tyres of the present invention and reference tyres. The test tyres have substantially same structure as the one shown in Figure 1. The detailed specifications thereof are set out in Table 1. Each test tyre was tested to evaluate the natural vibration generating speed and steering stability. The tests were feel tests by a skilled test rider done on a test circuit of an official course. The test results are shown in Table 2, wherein the higher the value the better the performance. Further, each tyre was tested using a drum tester to evaluate durability at high speed. The test results are shown in Table 2. As described above, in the motor-cycle tyre according to the present invention, the breaker cords are laid at such small angles as 14 to 18 degrees with respect to the circumferential direction whereby the lifting of the tread crown portion during high speed running is effectively restrained, and accordingly the steering stability in straight running together with durability at high speed running, are also improved. Further, in the present invention, the angles at which the breaker cords are arranged are different from those of the carcass cords. Accordingly, the speed at which the motor-cycle starts to vibrate, that is, the weave phenomenon generating speed is shifted to a higher speed than that of conventional tyres in which the carcass cord angles are almost the same as the breaker cord angles. As a result, the speed range for stable running is widened, and the amplitude of vibrations is decreased, whereby the high speed steering stability is improved.

Claims: A motor-cycle tyre comprising bead cores (5), one disposed in each bead region (4) of the tyre, a carcass (6) extending between said bead regions (4) and turned up at both edges around bead cores (5), a tread (2) disposed radially outward of said carcass (6) and a breaker (7) disposed between said tread (2) and carcass (6), the carcass (6) having at least two plies (9) of cords arranged at a first angle to the circumferential direction of the tyre and the breaker (7) having two plies (12) of cords arranged at a second angle to the circumferential direction of the tyre, characterised in that the first angle is within a range of 22 to 24 degrees and the second angle is within a range of 14 to 16 degrees. A motor-cycle tyre according to claim 1 characterised in that the heights of the inner and outer ply turnups (9B,9A) from the bead base (10) are in the range of 20 to 40% and 28 to 80% of the height of the tread edge respectively. A motor-cycle tyre according to claim 1 or 2 characterised in that the breaker (7) has a width in the range of 60 to 120% of the width of the tread (2). A motor-cycle tyre according to claim 1 or 2 characterised in that the breaker (7) has a width in the range of 80 to 100% of the width of the tread (2).

Inventors: SUZUKI, SHIGEHIKO
Applicants: SUMITOMO RUBBER INDUSTRIES LIMITED
Application year: 1988
Main classification: B60C9
IPC codes: B60C9