JP2008143319A - Tire for motorcycle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tire for a motorcycle with excellent performances. <P>SOLUTION: A tread 4 of the tire for the motorcycle comprises an under layer 36, a base layer 38 and a cap layer 40, all of which comprises cross-linked rubber. The foaming temperature of the base layer 38 is higher than that of the cap layer 40. The foaming temperature of the under layer 36 is set higher than that of the base layer 38. The under layer 36 is thin in a center region 24 and thick in shoulder regions 26. The cap layer 40 is thick in the center region 24 and thin in the shoulder regions 26. The thickness of the base layer 38 in the center region 24 is set equal to that of the base layer 38 in the shoulder regions 26. A ratio (Wc/Wt) is set to 0.3-0.7. A ratio (Ws/Wt) is also set to 0.3-0.7. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a pneumatic tire mounted on a motorcycle. In particular, the present invention relates to improvements in tire treads.

  For motorcycle tires, durability performance, stability performance, disturbance absorption performance, grip performance, etc. are extremely important. In the tread of a tire, various ideas intended to improve each performance have been made. JP-A-2-147410 discloses a tread having a three-layer structure. The outermost layer of this tread is in direct contact with the road surface. This outermost layer contributes to disturbance absorbing performance and grip performance.

Japanese Patent Application Laid-Open No. 2005-280406 discloses a tire in which a tread includes an under layer, a base layer, and a cap layer. In this tire, excellent durability performance is achieved by the under layer or base layer, and excellent disturbance absorbing performance and grip performance are achieved by the cap layer.
Japanese Patent Laid-Open No. 2-147410 JP-A-2005-280406

  In recent years, motorcycles are getting higher performance. This motorcycle can travel at high speed. In high-speed running, a great deal of frictional heat is generated. The tread temperature gradually rises as high-speed running continues. Since the tread is made of a crosslinked rubber, bubbles (that is, voids) are generated in the tread due to temperature rise. This phenomenon is called foaming. If bubbles are generated, the tread is severely damaged. There is a demand for a tread that is excellent in durability at high speeds.

  In the tread of a motorcycle tire, the center region protrudes outward from the shoulder region from the viewpoint of turning performance. In straight running, the center area of the tread is grounded, and in turning, the shoulder area of the tread is grounded. When the motorcycle travels straight for a long time, heat is generated mainly in the center region, and the shoulder region is damaged. When the motorcycle repeats turning, heat is generated mainly in the shoulder region, and the shoulder region is damaged.

  If the tread is formed from a material that does not easily generate bubbles, foaming is suppressed. However, it is difficult to obtain sufficient disturbance absorbing performance and grip performance with this tread.

  An object of the present invention is to provide a motorcycle tire excellent in various performances.

The motorcycle tire according to the present invention includes a tread including an under layer, a base layer located on the radially outer side of the under layer, and a cap layer located on the radially outer side of the base layer. In this tire, two or more of the following mathematical formulas (I) to (III) are satisfied.
Pcu (%) ≠ Psu (%) (I)
Pcb (%) ≠ Psb (%) (II)
Pcc (%) ≠ Psc (%) (III)
In the above formula,
Pcu represents the ratio of the thickness of the under layer to the thickness of the tread in the center region,
Pcb represents the ratio of the thickness of the base layer to the thickness of the tread in the center region,
Pcc represents the ratio of the thickness of the cap layer to the thickness of the tread in the center region,
Psu represents the ratio of the thickness of the under layer to the thickness of the tread in the shoulder region,
Psb represents the ratio of the thickness of the base layer to the thickness of the tread in the shoulder region, and
Psc represents the ratio of the thickness of the cap layer to the thickness of the tread in the shoulder region.

  Preferably, the ratio Pcc is greater than the ratio Psc. Preferably, the difference (Pcc-Psc) is 10 or more. Preferably, the ratio Pcu is smaller than the ratio Psu. Preferably, the difference (Pcu−Psu) is −10 or less. Preferably, the difference (Pcb−Psb) between the ratio Pcb and the ratio Psb is −10 or more and 10 or less.

  Preferably, the foaming temperature of the under layer or the foaming temperature of the base layer is higher than the foaming temperature of the cap layer. Preferably, both the foaming temperature of the under layer and the foaming temperature of the base layer are higher than the foaming temperature of the cap layer. Preferably, the foaming temperature of the base layer is higher than the foaming temperature of the cap layer, and the foaming temperature of the under layer is higher than the foaming temperature of the base layer. Preferably, the difference between the foaming temperature of the base layer and the foaming temperature of the cap layer is 10 ° C. or more, and the difference between the foaming temperature of the under layer and the foaming temperature of the base layer is 10 ° C. or more.

  In the present inventor, the thickness ratio of each layer constituting the tread is different between the center region and the shoulder region. With this tread, various performances can be achieved.

  Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

  FIG. 1 is a cross-sectional view showing a part of a motorcycle tire 2 according to an embodiment of the present invention. In FIG. 1, the vertical direction is the radial direction, the horizontal direction is the axial direction, and the direction perpendicular to the paper surface is the circumferential direction. The tire 2 has a substantially left-right symmetric shape centered on a one-dot chain line CL in FIG. This alternate long and short dash line CL represents the equator of the tire 2. The tire 2 includes a tread 4, a wing 6, a sidewall 8, a bead 10, a carcass 12, a belt 14, an inner liner 16, and a chafer 18.

  The tread 4 is made of a crosslinked rubber having excellent wear resistance. The tread 4 has a shape protruding outward in the radial direction. The tread 4 has a three-layer structure as will be described later. The tread 4 includes a tread surface 20. The tread surface 20 is in contact with the road surface. A groove 22 is carved in the tread surface 20. The groove 22 forms a tread pattern. The groove 22 may not be cut in the tread 4. The tread 4 can be divided into a center region 24 straddling the equator CL and a pair of shoulder regions 26 positioned outside the center region 24 in the axial direction.

  The sidewall 8 extends substantially inward in the radial direction from the end of the tread 4. The sidewall 8 is made of a crosslinked rubber. The sidewall 8 absorbs an impact from the road surface by bending. Further, the sidewall 8 prevents the carcass 12 from being damaged.

  The bead 10 is located substantially inward of the sidewall 8 in the radial direction. The bead 10 includes a core 28 and an apex 30 that extends radially outward from the core 28. The core 28 has a ring shape. The core 28 includes a plurality of non-stretchable wires (typically steel wires). The apex 30 is tapered outward in the radial direction. The apex 30 is made of a highly hard crosslinked rubber.

  The carcass 12 includes a carcass ply 32. The carcass ply 32 is spanned between the beads 10 on both sides, and extends along the inside of the tread 4 and the sidewall 8. The carcass ply 32 is wound around the core 28 from the inner side toward the outer side in the axial direction. Although not shown, the carcass ply 32 includes a large number of cords arranged in parallel and a topping rubber. The absolute value of the angle formed by each cord with respect to the equator plane is usually 70 ° to 90 °. In other words, the carcass 12 has a radial structure. The cord is usually made of organic fibers. Examples of preferable organic fibers include polyester fibers, nylon fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers. The carcass 12 may be composed of two or more carcass plies 32. A carcass having a bias structure may be employed.

  The belt 14 is located on the radially outer side of the carcass 12. The belt 14 is laminated with the carcass 12. The belt 14 reinforces the carcass 12. The belt 14 includes a belt ply 34. Although not shown, the belt ply 34 is made of a cord and a topping rubber. The cord extends in the circumferential direction and is wound spirally. The belt 14 has a so-called jointless structure. Preferred materials for the cord are aramid fiber and steel.

  FIG. 2 is an enlarged cross-sectional view showing a part of the tread 4 of the tire 2 of FIG. In FIG. 2, the illustration of the groove 22 is omitted. The tread 4 includes an under layer 36, a base layer 38, and a cap layer 40. The base layer 38 is located on the radially outer side of the under layer 36 and is laminated with the under layer 36. The cap layer 40 is located radially outside the base layer 38 and is laminated with the base layer 38. The under layer 36, the base layer 38, and the cap layer 40 are each made of a crosslinked rubber.

  The foaming temperature Fb of the base layer 38 is higher than the foaming temperature Fc of the cap layer 40. The foaming temperature Fu of the under layer 36 is higher than the foaming temperature Fb of the base layer 38. In other words, the tread 4 of the tire 2 uses a crosslinked rubber having a higher foaming temperature toward the inner side. When the high speed running is continued, the temperature of the tread 4 gradually increases. At this time, the tread 4 has a temperature distribution in the normal direction of the tread surface 20. Specifically, during traveling, the temperature of the base layer 38 is higher than the temperature of the cap layer 40, and the temperature of the under layer 36 is higher than the temperature of the base layer 38. By using rubber having a high foaming temperature for the under layer 36 and the base layer 38, foaming in the under layer 36 and the base layer 38 is suppressed. The tire 2 is not easily damaged. The base layer 38 whose foaming temperature Fb is lower than the foaming temperature Fu of the under layer 36 also contributes to grip performance.

  The cap layer 40 is made of a crosslinked rubber having a low foaming temperature. The cap layer 40 contributes to disturbance absorbing performance and grip performance. The tire 2 is excellent in durability performance, disturbance absorption performance, and grip performance. From the viewpoint of disturbance absorbing performance and grip performance, the hardness of the cap layer 40 is preferably 55 or greater and 70 or less. The hardness is measured by a JIS-A type spring type hardness tester. For the measurement, a slab having a thickness of 2 mm obtained by crosslinking the same rubber composition as that of the cap layer 40 at 160 ° C. for 10 minutes is used. Three slabs are stacked during measurement.

  From the viewpoint of suppression of foaming, disturbance absorbing performance, and grip performance, the difference (Fb−Fc) between the foaming temperature Fb of the base layer 38 and the foaming temperature Fc of the cap layer 40 is preferably 5 ° C. or higher, more preferably 10 ° C. or higher. preferable. This difference (Fb−Fc) is preferably 30 ° C. or less, and more preferably 15 ° C. or less. From the viewpoint of suppression of foaming and grip performance, the difference (Fu−Fb) between the foaming temperature Fu of the under layer 36 and the foaming temperature Fb of the base layer 38 is preferably 5 ° C. or more, and more preferably 10 ° C. or more. This difference (Fu−Fb) is preferably 30 ° C. or less, and more preferably 15 ° C. or less. The foaming temperature F of the under layer 36 is preferably 260 ° C. or higher and 290 ° C. or lower. The foaming temperature Fb of the base layer 38 is preferably 250 ° C. or higher and 280 ° C. or lower. The foaming temperature Fc of the cap layer 40 is preferably 240 ° C. or higher and 270 ° C. or lower.

  In the measurement of the foaming temperature Fu of the under layer 36, a large number of test pieces made of the same rubber composition as the under layer 36 are prepared. This test piece is a cube having a side of 1 cm. The first test piece is put in an oven at a predetermined temperature and held for 30 minutes. Then, the presence or absence of foaming is determined by visually observing the surface of the test piece. When foaming has not occurred, the second test piece is put into an oven having a temperature higher by 5 ° C. than this oven. Similarly, the presence or absence of foaming is determined. Such introduction into an oven having a temperature higher by 5 ° C. is sequentially performed. The oven temperature at which foaming is first confirmed is the foaming temperature Fu of the under layer 36. An oven set at a temperature where the position is “0” or “5” is used for the measurement. The test piece is cut out from a plate-like body having a thickness of 1 cm obtained by crosslinking at 160 ° C. for 15 minutes. The foaming temperature Fb of the base layer 38 and the foaming temperature Fc of the cap layer 40 are also measured by the same method.

  The foaming temperature Fu of the under layer 36 and the foaming temperature Fb of the base layer 38 may be the same. In this case, the foaming temperature Fu of the under layer 36 and the foaming temperature Fb of the base layer 38 are set higher than the foaming temperature Fc of the cap layer 40. Only one of the foaming temperature Fu of the under layer 36 and the foaming temperature Fb of the base layer 38 may be set higher than the foaming temperature Fc of the cap layer 40.

  As is apparent from FIG. 2, the under layer 36 is thin in the center region 24 and thick in the shoulder region 26. On the other hand, the cap layer 40 is thick in the center region 24 and thin in the shoulder region 26.

  In a motorcycle race, turning at high speed is repeated on a racing circuit. At the time of turning, the rider defeats the motorcycle, so that the shoulder region 26 is mainly grounded. In cornering, a large amount of frictional heat is generated in the shoulder region 26. The temperature of the shoulder region 26 is high. In the shoulder region 26, since the layer having a low foaming temperature (that is, the cap layer 40) is thin, foaming hardly occurs even when frictional heat is generated. Therefore, the shoulder region 26 is not damaged.

  In the straight traveling, the motorcycle is not brought down, so the center region 24 is mainly grounded. As described above, the cap layer 40 is thick in the center region 24. The cap layer 40 achieves excellent disturbance absorbing performance and grip performance. The tire 2 is excellent in all of durability performance at the time of turning, disturbance absorption performance at the time of straight traveling, and grip performance.

  As is clear from FIG. 2, the thickness of the base layer 38 in the center region 24 is equal to the thickness of the base layer 38 in the shoulder region 26. The thickness of the base layer 38 in the center region 24 may be different from the thickness of the base layer 38 in the shoulder region 26.

  FIG. 3 is an enlarged cross-sectional view taken along one-dot chain line CL in FIG. In FIG. 3, the center region 24 is shown. An arrow A in FIG. 3 represents the circumferential direction of the tire 2. In FIG. 3, what is indicated by the double arrow Tc is the thickness of the tread 4, what is indicated by the double arrow Tcu is the thickness of the under layer 36, and what is indicated by the double arrow Tcb It is the thickness of the base layer 38, and what is indicated by the double arrow Tcc is the thickness of the cap layer 40. The thicknesses Tc, Tcu, Tcb and Tcc are measured on a test piece obtained by cutting the tire 2. The thickness Tc is not less than 5 mm and not more than 10 mm.

  FIG. 4 is an enlarged cross-sectional view taken along line IV-IV in FIG. In FIG. 4, a shoulder region 26 is shown. An arrow A in FIG. 4 represents the circumferential direction of the tire 2. In FIG. 4, what is indicated by the double arrow Ts is the thickness of the tread 4, what is indicated by the double arrow Tsu is the thickness of the under layer 36, and what is indicated by the double arrow Tsb is It is the thickness of the base layer 38, and what is indicated by the double arrow Tsc is the thickness of the cap layer 40. The thicknesses Ts, Tsu, Tsb, and Tsc are measured on a test piece obtained by cutting the tire 2. The thickness Ts is substantially equal to the thickness Tc of the center region 24 (see FIG. 3). The thickness Ts is 5 mm or more and 10 mm or less. The thicknesses Ts, Tsu, Tsb, and Tsc are measured at the center of the shoulder region 26 in the axial direction.

In the present invention, the ratios Pcu, Pcb, Pcc, Psu, Psb, and Psc are calculated by the following mathematical formulas.
Pcu (%) = (Tcu / Tc) .100
Pcb (%) = (Tcb / Tc) .100
Pcc (%) = (Tcc / Tc) · 100
Psu (%) = (Tsu / Ts) .100
Psb (%) = (Tsb / Ts) .100
Psc (%) = (Tsc / Ts) · 100

  In the tire 2, the ratio Pcc is larger than the ratio Psc, and the ratio Pcu is smaller than the ratio Psu. In other words, the cap layer 40 is relatively thick in the center region 24, and the under layer 36 is relatively thick in the shoulder region 26. The center region 24 contributes to disturbance absorption performance and grip performance when traveling straight. In this respect, the difference (Pcc−Psc) is preferably 10 or more, and more preferably 20 or more. The difference (Pcc-Psc) is preferably 40 or less. The shoulder region 26 contributes to durability performance during turning. In this respect, the difference (Pcu−Psu) is preferably −10 or less, and more preferably −20 or less. The difference (Pcu−Psu) is preferably −40 or more.

  The difference (Pcb−Psb) between the ratio Pcb and the ratio Psb is preferably −10 or more and 10 or less. The base layer 38 exhibits appropriate rigidity from the center region 24 to the shoulder region 26. This base layer 38 provides excellent transient performance.

  The ratio Pcu is preferably 5% or more and 10% or less. The ratio Pcb is preferably 5% or more and 25% or less. The ratio Pcc is preferably 70% or more and 90% or less. The ratio Psu is preferably 10% or more and 30% or less. The ratio Psb is preferably 10% or more and 30% or less. The ratio Psc is preferably 60% or more and 80% or less.

  In FIG. 2, what is indicated by a double arrow Wt is a half width of the tread 4, and what is indicated by a double arrow Wc is a half width of the center region 24, which is indicated by a double arrow Ws. What is present is the width of the shoulder region 26. The ratio (Wc / Wt) is preferably 0.3 or more, and more preferably 0.4 or more, from the viewpoints of disturbance absorption performance and grip performance during straight travel. In light of durability performance during turning, the ratio (Wc / Wt) is preferably equal to or less than 0.7, and more preferably equal to or less than 0.6. From the viewpoint of durability performance during turning, the ratio (Ws / Wt) is preferably 0.3 or more, and more preferably 0.4 or more. The ratio (Ws / Wt) is preferably 0.7 or less, and more preferably 0.6 or less, from the viewpoint of disturbance absorption performance and grip performance during straight travel.

  The thickness of the under layer 36, the base layer 38, or the cap layer 40 may gradually change from the equator CL toward the end of the tread 4. In this case, there is no clear boundary between the center region 24 and the shoulder region 26. In this case, the thicknesses Tc, Tcu, Tcb, and Tcc are measured along the equator CL, and the thicknesses Ts, Tsu, Tsb, and Tsc are measured at a point away from the equator CL in the axial direction (0.75 Wt). .

  In applications where the center region 24 generates a lot of heat, the cap layer 40 is set to have a thin thickness in the center region 24 and thick in the shoulder region 26. Therefore, the ratio Pcc is smaller than the ratio Psc. In this case, the thickness of the under layer 36 is set to be thick in the center region 24 and thin in the shoulder region 26. Therefore, the ratio Pcu is larger than the ratio Psu. The thickness of the base layer 38 may be set thick in the center region 24 and thin in the shoulder region 26. In this case, the ratio Pcb is larger than the ratio Psb.

  Hereinafter, the effects of the present invention will be clarified by examples. However, the present invention should not be construed in a limited manner based on the description of the examples.

[Preparation of rubber composition]
The base rubber and various additives were kneaded with a kneader to obtain type A to C rubber compositions. Details of the formulation of the rubber composition are shown in Table 1 below.

[Example 1]
A motorcycle tire having the structure shown in FIGS. 1 to 4 was obtained. The tire tread includes an under layer, a base layer, and a cap layer. The under layer is made of a type C rubber composition, and its foaming temperature Fu is 280 ° C. The base layer is made of a type B rubber composition, and its foaming temperature Fb is 270 ° C. The cap layer is made of a type A rubber composition, and its foaming temperature Fc is 260 ° C. The ratio Pcu is 5%, the ratio Pcb is 15%, the ratio Pcc is 80%, the ratio Psu is 25%, the ratio Psb is 15%, and the ratio Psc is 60%. The size of this tire is “190 / 50ZR17”.

[Examples 2 to 8 and Comparative Example 1]
Tires of Examples 2 to 8 and Comparative Example 1 were obtained in the same manner as Example 1, except that the ratios Psu, Psb and Psc in the shoulder region were as shown in Tables 2 and 3 below.

[Example 9 and Comparative Example 2]
The tires of Example 9 and Comparative Example 2 were the same as Example 1 except that the ratios Pcu, Pcb and Pcc in the center region and the ratios Psu, Psb and Psc in the shoulder region were as shown in Table 3 below. Obtained.

[Examples 10 to 12]
Tires of Examples 10 to 12 were obtained in the same manner as in Example 1 except that the rubber composition constituting each layer was as shown in Table 3 below.

[Durability during turning]
The tire was mounted on a drum-type running test machine in a state where it was inclined by 40 °. The shoulder area touched the drum. The test machine was operated for 10 minutes under the condition of a speed of 180 km / h. Thereafter, the test machine was operated for 10 minutes under conditions where the speed was 10 km / h faster. Thereafter, similarly, the speed was increased by 10 km / h for 10 minutes. The speed at which damage occurs is shown in Tables 2 and 3 below.

[sensory evaluation]
The tire was assembled in a rim of “MT6.00 × 17”, and the tire was filled with air so that the internal pressure was 290 kPa. This tire was mounted on a motorcycle having a displacement of 1000 cm ³ . The motorcycle was run on a circuit, and the rider was evaluated for stability during turning and disturbance absorption performance when going straight. The results are shown in Tables 2 and 3 below. The larger the value, the better the evaluation.

  As shown in Tables 2 and 3, the tires of the examples are excellent in various performances. From this evaluation result, the superiority of the present invention is clear.

The tire according to the present invention can be mounted on various motorcycles. This tire is particularly suitable for a motorcycle having a displacement of 1000 cm ³ or more.

FIG. 1 is a cross-sectional view showing a part of a motorcycle tire according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view showing a part of the tread of the tire of FIG. 1. FIG. 3 is an enlarged cross-sectional view taken along one-dot chain line CL in FIG. FIG. 4 is an enlarged cross-sectional view taken along line IV-IV in FIG.

Explanation of symbols

2 ... Tires for motorcycles 4 ... Treads 8 ... Side walls 10 ... Beads 12 ... Carcass 14 ... Belts 24 ... Center region 26 ... Shoulder region 36 ... Under layer 38 ... Base layer 40 ... Cap layer

Claims (10)

A tread including an under layer, a base layer positioned radially outward of the under layer, and a cap layer positioned radially outward of the base layer;
A motorcycle tire satisfying two or more of the following formulas (I) to (III).
Pcu (%) ≠ Psu (%) (I)
Pcb (%) ≠ Psb (%) (II)
Pcc (%) ≠ Psc (%) (III)
(Pcu represents the ratio of the thickness of the under layer to the thickness of the tread in the center region,
Pcb represents the ratio of the thickness of the base layer to the thickness of the tread in the center region,
Pcc represents the ratio of the thickness of the cap layer to the thickness of the tread in the center region,
Psu represents the ratio of the thickness of the under layer to the thickness of the tread in the shoulder region,
Psb represents the ratio of the thickness of the base layer to the thickness of the tread in the shoulder region, and
Psc represents the ratio of the thickness of the cap layer to the thickness of the tread in the shoulder region. )   The tire according to claim 1, wherein the ratio Pcc is larger than the ratio Psc.   The tire according to claim 2, wherein a difference (Pcc-Psc) between the ratio Pcc and the ratio Psc is 10 or more.   The tire according to any one of claims 1 to 3, wherein the ratio Pcu is smaller than the ratio Psu.   The tire according to claim 4, wherein a difference (Pcu-Psu) between the ratio Pcu and the ratio Psu is -10 or less.   The tire according to any one of claims 1 to 5, wherein a difference (Pcb-Psb) between the ratio Pcb and the ratio Psb is -10 or more and 10 or less.   The tire according to any one of claims 1 to 6, wherein a foaming temperature of the under layer or a foaming temperature of the base layer is higher than a foaming temperature of the cap layer.   The tire according to claim 7, wherein both the foaming temperature of the under layer and the foaming temperature of the base layer are higher than the foaming temperature of the cap layer.   The tire according to claim 8, wherein the foaming temperature of the base layer is higher than the foaming temperature of the cap layer, and the foaming temperature of the under layer is higher than the foaming temperature of the base layer.   The tire according to claim 9, wherein the difference between the foaming temperature of the base layer and the foaming temperature of the cap layer is 10 ° C or more, and the difference between the foaming temperature of the under layer and the foaming temperature of the base layer is 10 ° C or more.

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