JP6241936B2 - Motorcycle tire for rough terrain - Google Patents

Description

  The present invention relates to a tire suitable for a motorcycle traveling on rough terrain such as a forest or a wilderness.

  In rough terrain, the road surface is full of undulations. A motorcycle traveling on rough terrain repeats jumping and landing. When landing, a large load is applied to the tire. Motorcycle tires running on rough terrain absorb landing impacts with flexible sidewalls.

  In general, a tire having a so-called bias structure is used as a tire for a motorcycle for rough terrain. This tire is inferior in traction performance compared to a radial tire.

  Japanese Unexamined Patent Application Publication No. 2009-126408 discloses a motorcycle tire for rough terrain. This tire has a flexible sidewall. Japanese Unexamined Patent Application Publication No. 2008-279996 discloses a motorcycle tire for rough terrain. In this tire, the radius of curvature of the block tread that contacts the road surface is defined. In this tire, the traction performance is improved by the edge effect of the block tread.

JP 2009-126408 A JP 2008-279996 A

  The inventors have found that the traction performance can be improved by adopting a so-called JLB structure for the motorcycle tire for rough terrain. As for the motorcycle tire for rough terrain, the edge part of the shoulder block has projected greatly to the sidewall in the axial direction. When the band of the JLB structure is adopted up to the edge portion of the shoulder block, the side wall portion is covered with the band of the JLB structure.

  When the carcass is covered to the side wall portion with a band having a JLB structure, the side wall portion is difficult to bend. The impact absorption of the tire is impaired.

  An object of the present invention is to provide a motorcycle tire for rough terrain that has excellent traction performance and excellent shock absorption performance.

The motorcycle tire for rough terrain according to the present invention includes a tread having a large number of blocks including shoulder blocks on the outer surface thereof, a pair of sidewalls each extending substantially inward in the radial direction from the end of the tread, and A pair of beads positioned axially inward of the wall, a carcass extending between one bead and the other bead along the inside of the tread and the sidewall, and between the carcass and the tread And a band to be laminated.
This band includes a cord and a topping rubber. The cord extends substantially in the circumferential direction. The intersection point between the straight line passing through the axially inner wall surface of the shoulder block and the carcass is defined as a point Pa, and the intersection point between the straight line passing through the axially outer wall surface of the shoulder block and the virtual groove bottom is defined as a point Pb. When the intersection point between the straight line perpendicular to the bottom surface and the carcass is defined as a point Pc, the point Pd at the outer end in the axial direction of the band is located on the outer side in the axial direction from the point Pa. The ratio D2 / D1 of the distance D2 from the point Pa to the point Pd with respect to the distance D1 from the point Pa to the point Pc is 1/3 or more. This point Pd does not exceed the maximum width Pe of the carcass.

  Preferably, the ratio D2 / D1 is greater than ½. Preferably, the ratio D2 / D1 is 1 or less. Preferably, the inclination angle θ1 of the first side wall surface of the shoulder block is 0 ° or more and 5 ° or less. Preferably, the inclination angle θ2 of the rear wall surface of the shoulder block is 7 ° or more and 20 ° or less.

  The motorcycle tire for rough terrain according to the present invention is excellent in traction performance and also in shock absorption performance.

FIG. 1 is a cross-sectional view showing a part of a motorcycle tire for rough terrain according to an embodiment of the present invention. FIG. 2 is an explanatory view showing a shoulder block of the tire of FIG.

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

  FIG. 1 shows a motorcycle tire 2 for rough terrain. In FIG. 1, the vertical direction is the radial direction of the tire 2, the horizontal direction is the axial direction of the tire 2, and the direction perpendicular to the paper surface is the circumferential direction of the tire 2. In FIG. 1, an alternate long and short dash line CL represents the equator plane of the tire 2. The shape of the tire 2 is symmetrical with respect to the equator plane except for the tread pattern.

  The tire 2 includes a tread 4, a sidewall 6, a bead 8, a carcass 10, a band 12, an inner liner 14, and a chafer 16. The tire 2 is a tubeless type.

  The tread 4 includes a large number of blocks 18. These blocks 18 can be divided into a center block 20, a mid block 22 and a shoulder block 24. The center block 20 straddles the equator plane CL. The mid block 22 is located on the outer side in the axial direction than the center block 20. The shoulder block 24 is located on the outermost side in the axial direction. The shoulder block 24 is located on the outer side in the axial direction than the mid block 22. These blocks 18 form a block pattern on the tread 4. A plurality of mid blocks 22 may be arranged in the axial direction between the center block 20 and the shoulder block 24.

  The sidewall 6 extends substantially inward in the radial direction from the end of the tread 4. The sidewall 6 is made of a crosslinked rubber having excellent vibration absorption, cut resistance and weather resistance.

  The bead 8 is located inside the sidewall 6 in the axial direction. The bead 8 includes a core 26 and an apex 28 extending outward from the core 26 in the radial direction. The core 26 has a ring shape and includes a wound non-stretchable wire. A typical material for the wire is steel. The apex 28 is tapered outward in the radial direction. The apex 28 is made of a highly hard crosslinked rubber.

  The carcass 10 includes a first ply 30 and a second ply 32. The first ply 30 and the second ply 32 are bridged between the beads 8 on both sides, and extend along the tread 4 and the sidewall 6. The first ply 30 is folded around the core 26 from the inner side to the outer side in the axial direction. By this folding, the main portion 30a and the folding portion 30b are formed in the first ply 30. The second ply 32 is folded around the core 26 from the inner side to the outer side in the axial direction. By this folding, the main portion 32a and the folding portion 32b are formed in the second ply 32. The end 34 of the folded portion 30b of the first ply 30 is located outside the end 36 of the folded portion 32b of the second ply 32 in the radial direction.

  The first ply 30 and the second ply 32 are composed of 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 30 ° to 90 °. The direction of inclination of the cord of the second ply 32 with respect to the equator plane is opposite to the direction of inclination of the cord of the first ply 30 with respect to the equator plane. In the tire 2, the carcass 10 has a bias structure. The cord is made of organic fiber. Examples of preferable organic fibers include nylon fibers, polyester fibers, aramid fibers, rayon fibers, and polyethylene naphthalate fibers. The carcass 10 may be formed from one or three or more plies. The carcass 10 may have a radial structure.

  The band 12 is located outside the carcass 10 in the radial direction. The band 12 is located between the tread 4 and the carcass 10. The band 12 extends from the inside of one shoulder block 24 to the inside of the other shoulder block 24 (not shown) in the axial direction. Although not shown, the band 12 is composed of a cord and a topping rubber. The cord is wound in a spiral. This band has a so-called JLB structure (jointless structure). The cord extends substantially in the circumferential direction. The angle of the cord with respect to the circumferential direction is 5 ° or less, and further 2 ° or less. The cord is made of organic fiber. Examples of preferable organic fibers include nylon fibers, polyester fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

  The chafer 16 is located in the vicinity of the bead 8. When the tire 2 is incorporated into the rim, the chafer 16 comes into contact with the rim. By this contact, the vicinity of the bead 8 is protected. The chafer 16 is made of cloth and rubber impregnated in the cloth.

  A two-dot chain line La in FIG. 1 is a straight line passing through the axially inner wall surface 24 a of the shoulder block 24. The straight line passing through the wall surface 24a means a straight line parallel to the wall surface 24a and passing through the wall surface 24a. A two-dot chain line Lb is a straight line passing through the axially outer wall surface 24b of the shoulder block 24. The straight line passing through the wall surface 24b means a straight line parallel to the wall surface 24b and passing through the wall surface 24b. A point Pa is an intersection of the outer surface of the carcass 10 and the straight line La. Point Pb is the intersection of the virtual groove bottom surface and straight line Lb. This virtual groove bottom surface is a virtual surface when the portion where the shoulder block 24 is formed is the groove bottom surface where the shoulder block 24 is not formed. The two-dot chain line Lc is a straight line that passes through the point Pb and intersects the imaginary groove bottom surface perpendicularly. Point Pc is the intersection of the outer surface of carcass 10 and straight line Lc. The point Pd is the outer end of the band 12 in the axial direction. The point Pe is a point indicating the maximum axial width of the carcass 10.

  A double-headed arrow D1 indicates the distance from the point Pa to the point Pc. A double-headed arrow D2 indicates the distance from the point Pa to the point Pd. These points Pa, Pb, Pc, and distances D1 and D2 are measured along the outer surface of the carcass 10. The distances D1 and D2 are measured in a cross section cut out from the tire 2.

  An arrow R in FIG. 2 indicates the normal rotation direction of the tire 2. The shoulder block 24 includes a forward-facing first side wall surface 24c and a rear side wall surface 24d. A point Pv indicates an intersection of the installation surface 38 and the wall surface 24c. An alternate long and two short dashes line Lv indicates a straight line that passes through the point Pv and is orthogonal to the installation surface 38. A point Pw indicates an intersection with the installation surface 38 and the wall surface 24d. An alternate long and two short dashes line Lw indicates a straight line that passes through the point Pw and is orthogonal to the installation surface 38.

  A double arrow θ1 indicates an angle formed by the straight line Lv and the wall surface 24c. This angle θ1 indicates the inclination angle of the first side wall surface 24c. A double arrow θ2 indicates an angle formed by the straight line Lw and the wall surface 24d. This angle θ2 indicates the inclination angle of the rear side wall surface 24d.

  In the tire 2, since the cord of the band 12 extends substantially in the circumferential direction, the movement of the block 18 in the circumferential direction is suppressed. The band 12 contributes to improvement of the traction performance of the tire 2.

  In the tire 2, the axially outer end Pd of the band 12 is positioned on the axially outer side from the point Pa. In this tire, the ratio D2 / D1 of the distance D2 to the distance D1 is set to 1/3 or more. Thereby, also in the shoulder block 24, the improvement effect of the traction performance by the JLB structure is acquired. From this viewpoint, the ratio D2 / D1 is preferably set to 1/2 or more. By setting the ratio D2 / D1 to be equal to or greater than 1/2, the shoulder block 24 can obtain a greater effect of improving the traction performance.

  In a motorcycle that runs on rough terrain, the sidewall 6 is greatly bent when landing on a jump. A large load at the time of landing is absorbed by the side wall 6 being greatly bent. When the outer end Pd of the band 12 goes around the sidewall 6 deeply, the deformation of the sidewall 6 in the axially outer side is suppressed. The impact absorbability of the tire 2 is impaired. From this point of view, the outer end Pd of the band 12 is in a range that does not exceed the point Pe. More preferably, the ratio D2 / D1 is set to 1 or less.

  Since the tire 2 has excellent traction performance due to the band 12, sufficient traction performance can be obtained even if the inclination angle of the wall surface of the block 18 (20, 22, 24) is made smaller than that of the conventional tire. Generally, in the tire for motorcycles on rough terrain, the inclination angle of the wall surface of the block is 7 ° to 15 °. In the tire 2, the inclination angle of the wall surface is reduced, and sufficient traction performance can be obtained.

  In the tire 2, a high traction performance can be obtained by reducing the inclination angle θ1 of the first sidewall surface 24c. From this viewpoint, the inclination angle θ1 is preferably 5 ° or less, and more preferably 4 ° or less. On the other hand, in the tire 2 having the large inclination angle θ1, high rigidity of the shoulder block 24 is obtained. From this viewpoint, the inclination angle θ1 is preferably 0 ° or more, and more preferably 1 ° or more. In the tire 2, sufficient rigidity is obtained for the shoulder block 24 even if the inclination angle θ <b> 1 is reduced. In the tire 2, occurrence of groove bottom cracks is suppressed.

  In the tire 2 in which the inclination angle θ2 of the rear landing side wall surface 24b is small, a high braking effect can be obtained during braking. In this respect, the inclination angle θ2 is preferably 20 ° or less, and more preferably 15 ° or less. On the other hand, in the tire 2 having a large inclination angle θ2, high rigidity of the shoulder block 24 is obtained. From this viewpoint, the inclination angle θ2 is preferably 7 ° or more, and more preferably 9 ° or more.

  Here, the inclination angle θ1 of the first side wall surface 24c of the shoulder block 24 and the inclination angle θ2 of the rear side wall surface 24d have been described as examples. The same effects as those of the shoulder block 24 can be obtained with respect to the inclination angle of the first and second sidewall surfaces of the center block 20 and the mid block 22.

  In the present invention, unless otherwise specified, the size and angle of each member of the tire 2 are measured in a state where the tire 2 is incorporated in a normal rim and the tire 2 is filled with air so as to have a normal internal pressure. During the measurement, no load is applied to the tire. In the present specification, the normal rim means a rim defined in a standard on which the tire 2 depends. “Standard rim” in the JATMA standard, “Design Rim” in the TRA standard, and “Measuring Rim” in the ETRTO standard are regular rims. In the present specification, the normal internal pressure means an internal pressure defined in a standard on which the tire 2 relies. “Maximum air pressure” in JATMA standard, “Maximum value” published in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in TRA standard, and “INFLATION PRESSURE” in ETRTO standard are normal internal pressures.

  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.

[Example 1]
A tire having the structure shown in FIG. 1 was obtained. The tire size is also “120 / 80-19”. In this tire, the inclination angles θ1 and θ2 of the wall surface of the shoulder block are as shown in Table 1. The position of the outer edge of the band of this tire was as shown in Table 1.

  In Tables 1 to 3, symbols A and B at the positions of the outer ends of the bands mean the following position ranges, respectively. The symbol A is located in a range where the outer end of the band does not exceed the maximum width of the carcass. Symbol B is located in a range where the outer end of the band exceeds the maximum width of the carcass.

[Comparative Example 1]
A tire was obtained in the same manner as in Example 1 except that no band was provided.

[Example 2-3 and Comparative example 2-3]
A tire was obtained in the same manner as in Example 1 except that the ratio D2 / D1 was as shown in Table 1.

[Example 4-7]
A tire was obtained in the same manner as in Example 1 except that the inclination angle θ2 of the wall surface on the rear landing side was as shown in Table 2.

[Examples 9-12]
A tire was obtained in the same manner as in Example 1 except that the inclination angle θ1 of the wall surface on the first arrival side was as shown in Table 3. In addition, -1 degree of inclination | tilt angle (theta) 1 of Example 10 has shown that the wall surface of the arrival side inclines in the reverse direction of Example 1 with respect to the straight line Lv.

[Traction performance and braking performance]
A tire was incorporated into a regular rim, and the tire was filled with air to adjust the internal pressure to 80 kPa. This tire was mounted on a 450cc motocross bike. This motocross bike was run on the motocross course, and the motocross professional riders evaluated the traction performance. Further, the braking performance of the tires of Example 1 and Examples 4 to 8 was sensory evaluated. The evaluation results are shown in Tables 1 to 3. In this evaluation, the greater the number, the better.

[Shock absorption]
In addition to traction performance, sensory evaluation of impact absorption was performed. The evaluation results are shown in Tables 1 to 3. In this evaluation, the greater the number, the better.

[Crack resistance]
A motocross course on a hard road was run for 1 hour under the same conditions. After running, the presence or absence of cracks at the groove bottom of the tire, the size of the cracks that occurred, and the number of cracks that occurred were confirmed. In this evaluation, the acceptable level of the commercial product was set to 5 points. Relative evaluation was made with a score of 10 out of 5 points. The evaluation results are shown in Tables 1 to 3. In this evaluation, the larger the number, the better.

  As shown in Tables 1 to 3, the tires of the examples have higher evaluation than the tires of the comparative examples. From this evaluation result, the superiority of the present invention is clear.

  The pneumatic tire described above is particularly suitable for motorcycle tires for rough terrain.

2 ... tyre 4 ... tread 6 ... side wall 8 ... bead 10 ... carcass 12 ... band 14 ... inner liner 16 ... chafer 18 ... block 20 ... .. Center block 22 ... Mid block 24 ... Shoulder block 26 ... Core 28 ... Apex 30 ... First ply 32 ... Second ply 34, 36 ... End 38 ··contact area

Claims (4)

A tread having a large number of blocks including shoulder blocks on its outer surface, a pair of sidewalls each extending substantially inward in the radial direction from the end of the tread, and a pair of beads positioned axially inward from the sidewalls And a carcass spanned between one bead and the other bead along the inside of the tread and the sidewall, and a band laminated between the carcass and the tread,
This band has a cord and topping rubber,
This cord extends substantially in the circumferential direction,
The point of intersection of the straight line passing through the axially inner wall surface of the shoulder block and the carcass is a point Pa, the point of intersection of the straight line passing through the axially outer wall surface of the shoulder block and the bottom surface of the virtual groove is a point Pb, and the virtual groove passes through the point Pb. When the intersection point of the straight line perpendicular to the bottom surface and the carcass is defined as a point Pc, the point Pd at the axially outer end of this band is located on the axially outer side from this point Pa,
The ratio D2 / D1 of the distance D2 from the point Pa to the point Pd with respect to the distance D1 from the point Pa to the point Pc is 1/2 or more ,
This point Pd does not exceed the maximum width Pe of the carcass ,
A motorcycle tire for rough terrain in which a position of an intersection of a groove bottom surface and a straight line Lb in a cross section perpendicular to the circumferential direction coincides with a position of the point Pb in a cross section perpendicular to the circumferential direction . The tire according to claim 1, wherein the ratio D2 / D1 is 1 or less. The tire according to claim 1 or 2, wherein an inclination angle θ1 of the first side wall surface of the shoulder block is not less than 0 ° and not more than 5 °. The tire according to any one of claims 1 to 3, wherein an inclination angle θ2 of a rear side wall surface of the shoulder block is 7 ° or more and 20 ° or less.

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