JP2009001081A - Pneumatic tire for motorcycle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire for a motorcycle allowing improvement of grip at a camber angle (CA) 45° to 50°, in particular, when turning the motorcycle, while maintaining feeling of rigidity of the tire during the turning, and prevention of sudden lowering of grip force after wear is advanced. <P>SOLUTION: This pneumatic tire is provided with a tread part 12 formed into an annular shape. When a region of 50% of a tread extension width with a tire equatorial plane as a center is defined as a tread center part, and each region of 25% of a tread extension width on each of both the sides is defined as a tread side part, of the tread part 12, at least partial tread rubber of the tread side parts is divided into two layers in a thickness direction. A boundary surface of the two-layer tread rubber 12A and 12B is formed into waveforms changing in the thickness direction in one cross section parallel to the tire radial direction, and pitch of the waveforms is in the range of 15 to 40 mm. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a pneumatic tire for a motorcycle (hereinafter, also simply referred to as “tire”), and more particularly to a pneumatic tire for a motorcycle according to an improvement in a tread portion.

  Since motorcycles have the feature of turning with the vehicle body tilted, the portion of the tire that contacts the road surface moves due to the vehicle body inclination. In addition, due to such characteristics, the tire has a high speed when standing upright, and a force in the front-rear direction (the equator direction of the tire) is applied between the braking force and the driving force. Will be subject to a large lateral force.

  Therefore, the way the tire tread is used differs between the center portion and the shoulder portion. In particular, consumers of sports bikes and riders who are racing often have a chance to turn the bike down greatly, so in tires used in such bikes, it is important to exhibit a high grip at the tread shoulder. The shoulder portion of the tire may exhibit a grip force with respect to a lateral force. Furthermore, since the rear tire accelerates from a state in which the vehicle body is largely tilted, it is required to grip an input in the traction direction, that is, an input along the tire circumferential direction.

For this reason, in motorcycle tires, the type of tread rubber is often changed between the center portion of the tire and the shoulder portion of the tire (for example, Patent Documents 1 to 3).
. For example, in Patent Document 1, the turning stability on a wet road surface is improved and maintained until the end of tire use without reducing wear resistance, straight running stability, and grip when turning on a wet road surface. For this purpose, the tread part composed of two types of rubber, hard rubber and soft rubber, is divided into three parts, the center part including the tire equator and both shoulder parts, and the center part is composed of a single layer of hard rubber. The air for motorcycles has a cap-and-base structure with a shoulder part composed of a lower layer of hard rubber and an upper layer of soft rubber, and the thickness of the soft rubber center side is thicker than the tread end side. An inset tire is disclosed.

As described in Patent Document 1, generally, the tread rubber of the tire shoulder portion is generally softer than the tire center portion to ensure grip force during turning. In addition, when a tire for a motorcycle is cut in the cross section in the tire width direction, the tread surface of the tire is sufficiently round, and thus the ground contact shape tends to be rounded. It is easy to run even when. Therefore, some tires for motorcycles do not have so many grooves.
JP-A-11-189010 (Claims etc.) JP-A-7-108805 (Claims etc.) JP 2006-273240 A (Claims etc.)

  As described above, in a pneumatic tire for a two-wheeled vehicle, since the two-wheeled vehicle turns while tilting the vehicle body, the place where the tire tread portion is in contact with the road surface is different between straight traveling and turning. That is, the center part of the tread is used when going straight, and the end part of the tread is used when turning. Also, the performance required for tires is required to grip against the input (ie acceleration / deceleration) in the circumferential direction (equatorial direction) of the tire when going straight, and against the lateral direction (width direction) of the tire when turning. Gripping is required.

  In order to turn a two-wheeled vehicle quickly, it is necessary to tilt the vehicle body greatly in order to balance the centrifugal force that increases with the turning speed, and the tire must be able to grip the road surface by the same force as the centrifugal force. In other words, if the tire grip is insufficient when the vehicle body is greatly tilted, the vehicle cannot turn quickly, so the effect of the grip here on the turning performance is very large. Therefore, soft rubber may be mounted on the shoulder portion of the tire to generate a large grip.

  However, if soft rubber is installed, the rigidity of the tread at the tire shoulder will be reduced and the grip will be improved, but the tire will not feel firmly and the rider may feel dangerous. In addition, when the rubber is soft, wear may progress greatly. Therefore, it is conceivable to make the tread structure of the shoulder portion double. That is, it is possible to earn a grip while maintaining rigidity by arranging a hard rubber inside and arranging a rubber with a high grip outside.

  However, in this case, when the soft rubber on the surface is worn, the hard rubber is suddenly exposed, and the grip level is suddenly changed. When tire wear progresses and hard rubber is exposed, it is dangerous for the rider to make the same turn as before without noticing a decrease in grip.

  Accordingly, an object of the present invention is to solve the above-mentioned problems, maintain the tire rigidity during turning, improve the grip particularly at a camber angle (CA) of 45 to 50 degrees, and wear. An object of the present invention is to provide a pneumatic tire for a motorcycle that can prevent a sharp decrease in grip force after the travel of the vehicle.

  As a result of intensive studies, the present inventor has found that the above problem can be solved by adopting the following configuration, and has completed the present invention.

That is, the pneumatic tire for a motorcycle of the present invention is a pneumatic tire for a motorcycle including a tread portion formed in an annular shape.
When the region of 50% of the tread development width centered on the tire equatorial plane is the tread center portion and the region of 25% of each tread development width on both sides of the tread center portion is the tread side portion of the tread portion,
At least a part of the tread rubber on the side of the tread is divided into two layers in the thickness direction, and the boundary surface of the tread rubber of the two layers changes in the thickness direction within one cross section parallel to the tire radial direction. It has a shape, and the wave shape pitch is in the range of 15 to 40 mm.

  In the present invention, the boundary surface is parallel to the tire radial direction and does not change in the thickness direction in another cross section perpendicular to the one cross section, and the angle formed by the other cross section with respect to the tire circumferential direction is Preferably, the boundary surface is parallel to the tire radial direction and does not change in the thickness direction in another cross section orthogonal to the one cross section, and the other cross section is in the tire circumferential direction. It is also preferable that the angle formed with respect to is 30 to 90 degrees. The width of the corrugated convex portion is preferably 3 mm or more and 20 mm or less.

  Furthermore, in the present invention, the elastic modulus at 100% elongation of the inner tread rubber at 60 ° C. among the tread rubbers of the two layers is higher than the elastic modulus at 100% elongation of the outer tread rubber at 60 ° C. preferable. Furthermore, the wave shape can be preferably a trapezoidal wave, a rectangular wave, or a sine wave shape. Furthermore, with respect to the total thickness of the tread rubber divided into two layers in the thickness direction, the wavy shape based on the tread surface has a thickness to the upper end of 0 to 60% and a thickness to the lower end of 60 to 100. %, And the difference in thickness between the upper end and the lower end is preferably 20% or more.

  According to the present invention, the above configuration improves the grip at the time of turning, particularly at a camber angle (CA) of 45 to 50 degrees, while maintaining the tire rigidity while turning, and also reduces wear. It has become possible to realize a pneumatic tire for a motorcycle that can prevent a sharp decrease in grip force after traveling and has excellent steering stability performance during turning. In addition, since the boundary surface of the two-layer tread rubber according to the present invention changes in the thickness direction, it is possible to suppress the wear speed after the wear progresses to some extent and the inner tread rubber begins to be exposed.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a cross-sectional side view in a width direction of a pneumatic tire for a motorcycle according to a preferred embodiment of the present invention. As shown in the figure, the motorcycle tire of the present invention includes a pair of bead cores 1 embedded in a pair of left and right bead portions 11 and at least one extending from one bead portion to the other bead portion in a toroidal shape. A carcass (body ply) 2, at least one belt layer 3 disposed on the outer side in the tire radial direction, and a tread portion 12 formed in an annular shape and disposed on the outer side in the radial direction are provided.

  In the tire of the present invention, in the tread portion 12, a region of 50% of the tread development width centered on the tire equatorial plane is a tread center portion, and a region of 25% of each tread development width on both sides thereof is a tread side portion. Define. Here, expanding the tread means that the tread having a roundness in the width direction is flattened so that the length of the arc is a straight line. The tread center portion 50 was used as a tread center portion, and the other portions were used as tread side portions. That is, the tread side portion is 25 on each of the left and right sides.

  Thus, the basis for setting the tread center portion to 50 and the tread side portion to 25 depends on the ground contact position when the motorcycle is turned down with a CA (camber angle) of 45 to 55 degrees. When the motorcycle turns in such a CA, 25% of the tread width (25% from the end of the tread) is grounded. In the present invention, since the steering stability performance can be improved by improving the grip of the shoulder portion, attention is paid to this portion. In addition, since the safety of a motorcycle is most important when it is greatly tilted, it is important from the viewpoint of safety to prevent a sudden decrease in grip and the progress of wear during wear at this angle. Therefore, in the present invention, the tread side portion is defined as an area of 25% of the tread width, and the configuration is defined for this portion.

  In the present invention, at least a part or all of the tread side portion is divided into two layers in the thickness direction. This is a configuration called a cap-and-base structure, in which a cap rubber (outer tread rubber) 12A is arranged on the surface of the tread, and a base rubber (inner tread rubber) 12B is arranged inside the tread.

  The reason for adopting such a cap-and-base structure is that, as mentioned earlier, soft rubber is used on the tread surface to gain grip with the road surface, hard rubber is placed inside the tread, and the tread is subjected to lateral shearing. This is to increase the rigidity against the above. In rare cases, a very soft rubber is placed inside the tread, a hard rubber is placed on the tread surface, and the soft rubber appears when wear progresses, so as to ensure wet performance. In some cases. Grooves are arranged in ordinary motorcycle tires, but as wear progresses, the depth of the grooves becomes shallower, and drainage performance deteriorates. Therefore, an extremely soft rubber is exposed after wear, and the amount of deterioration in drainage performance is compensated by increasing the friction coefficient by contacting the soft rubber with the road surface. In these two cases, a cap and base structure is employed.

  Normally, the interface between the base rubber and the cap rubber forms a circular arc concentric with the tread surface in the tire cross section, that is, the base rubber and the cap rubber are uniformly the same thickness. The boundary surfaces of these two layers of tread rubbers 12A and 12B have a wave shape that changes in the thickness direction within one cross section parallel to the tire radial direction. In the illustrated example, an inner tread rubber 12B having a trapezoidal cross section is embedded in the tread side portion.

  The reason why the boundary surface has a wave shape in the cross section is that, as the wear progresses, the entire region does not suddenly become the inner tread rubber, but gradually the inner tread rubber 12B as the wear progresses. This is because there is a state in which the outer tread rubber 12A and the inner tread rubber 12B coexist in the middle of wear.

  In addition, the specific shape of the wave shape is not particularly limited as long as the boundary surface changes in the thickness direction within the cross section. In addition to the trapezoidal wave shown in the figure, a rectangular wave or sine wave shape It can be set as arbitrary shapes, such as. However, the corrugated pitch needs to be in the range of 15 to 40 mm. If the pitch of the wave shape is smaller than this range, the manufacture becomes difficult. On the other hand, if the pitch is larger than this range, the effect of gradually exposing the inner tread rubber 12B according to wear cannot be obtained sufficiently.

  Furthermore, the relative thickness of the two-layer tread rubber forming the corrugated shape is up to the upper end of the corrugated shape based on the tread surface with respect to the total thickness of the tread rubber divided into two layers in the thickness direction. The thickness is preferably 0 to 60%, the thickness to the lower end is 60 to 100%, and the difference in thickness between the upper end and the lower end is preferably 20% or more. Here, the upper end of the wave shape means the upper end of the inner tread rubber, and the lower end of the wave shape means the lower end of the outer tread rubber. Accordingly, the upper end of the inner tread rubber 12B may be exposed on the tread surface from the beginning as shown in FIG. 2, but if it is at a very deep position, the amount of inner tread rubber (arrangement thickness) is reduced, If the wear does not progress considerably, it will not be exposed, and it is not preferable to dispose the inner tread rubber. Further, if the lower end of the outer tread rubber 12A is at a very shallow position, the amount of the outer tread rubber is small, wears out early, and the effect of arranging two layers is less preferable. Note that the lower end of the outer tread rubber 12A may reach the lower end of the entire tread rubber (a state where the lower ends of the inner tread rubber and the outer tread rubber are in the same position). If the difference in thickness is too small, it is difficult to change the outer tread rubber to the inner tread rubber step by step, and the change accompanying wear tends to be abrupt.

  In addition, as shown in FIG. 2, by changing the height (thickness in the depth direction) for each convex portion constituting the wave shape, the base rubber gradually appears as wear progresses. Thus, it is possible to prevent a sudden change in grip more effectively, which is preferable.

  The range divided into two layers may be at least a part of the tread side portion, but preferably, 50% or more of the tread side portion, more preferably the whole is divided into two layers. To do. The larger the range divided into two layers, the more preferable is that the inner tread rubber is gradually exposed as wear progresses. On the other hand, if this range is too small, the desired effect of the present invention cannot be obtained.

  FIG. 2B shows only the inner tread rubber 12B and shows the shape of the boundary surface between the two layers of tread rubber. As shown in the drawing, in the present invention, the boundary surface of the two-layered tread rubber has a wave shape that changes in the thickness direction within one cross section (X direction) parallel to the tire radial direction R. In another cross section (Y direction) parallel to the radial direction R and orthogonal to the one cross section, the thickness direction does not change.

  In the present invention, the desired effect can be obtained regardless of the angles of the X and Y directions with respect to the tire circumferential direction. Preferably, for example, the Y direction, that is, the boundary surface is An angle formed by a cross section in which convex portions continue without changing in the thickness direction with respect to the tire circumferential direction is 0 degree. In this case, the X direction coincides with the tire width direction, and when the tire is manufactured by winding the tread rubber in the tire circumferential direction, the tread can be easily wound and the tire can be easily manufactured. preferable.

  Moreover, it is also preferable that the angle which the cross section (Y direction) where a convex part continues makes with respect to a tire peripheral direction shall be 30 degree | times-90 degree | times. When a direction (longitudinal direction) in which convex portions are continuous at a certain angle with respect to the tire circumferential direction is set, there is an advantage that the rigidity of the tread in this direction can be increased. For example, when the longitudinal direction of the convex portion is arranged perpendicular to the tire circumferential direction, the tread behaves strongly in the tire width direction. Further, when the base rubber is partially exposed, uneven wear does not occur if the longitudinal direction of the convex portion exists along the tire input direction.

  Here, when the tire is turned sideways, a lateral input is made from an angle of 90 degrees with respect to the tire circumferential direction, so from this point of view, the longitudinal direction of the convex portion is relative to the tire circumferential direction. It is preferable to make an angle of 90 degrees. However, in the case of a rear tire, traction is applied to further accelerate the vehicle while tilting the vehicle body, so that both forces in the tire width direction and the circumferential direction are applied. Therefore, a resultant force acts in an oblique direction, and an oblique force is applied to the tread. On the other hand, since the brake acts on the front tire, a force in an oblique direction is applied in the same manner. From the above, by appropriately setting the angle formed with respect to the tire circumferential direction in the range of 30 to 90 degrees in relation to the tire rotation direction, the effect of improving rigidity and the effect of suppressing uneven wear can be obtained in any direction. ,preferable. In general, since the force in the tire width direction is larger, the angle is more preferably 45 degrees to 90 degrees with respect to the tire circumferential direction.

  FIG. 3 shows (a) BB ′ sectional view when the longitudinal direction (Y direction) of the convex portion is inclined at an angle α = 45 degrees with respect to the tire circumferential direction, and (b) a schematic perspective view of the entire tire. A figure and (c) AA 'sectional drawing are shown, respectively. The arrow in FIG.3 (b) shows the rotation direction of a tire. In this case, the wave shape of the boundary surface is a sine wave shape. The B-B ′ cross section shows the cross section of the tire in the width direction, and the boundary surface has a wave shape. Further, the A-A ′ cross section shows a cross section in the tire circumferential direction, and the boundary surface has a wave shape also in this direction. If the convex portion is formed with an angle in the longitudinal direction in this way, the rigidity of the tread is increased with respect to both the input from the tire width direction and the input from the traction direction (vertical direction = circumferential direction). It is possible.

  Furthermore, the width of the corrugated convex portion is preferably 3 mm or more and 20 mm or less. If the width of the convex portion is narrower than 3 mm, the convex portion constituted by the hard inner tread rubber is difficult to have rigidity. On the other hand, if it exceeds 20 mm, there may be a case where only one convex portion is included in the ground contact area of the tire, and the change in rigidity is large at the portion corresponding to the convex portion in the ground contact surface, and the rider feels uncomfortable. There is a fear. Further, when the longitudinal direction of the convex portion is 90 degrees with respect to the tire circumferential direction, when the width of the convex portion exceeds 30 mm, the convex portion forms a polygon in the 360-degree circumferential direction of the tire. When rotating, the vibration is generated every time it gets over the convex portion, which is not preferable. The width of the convex portion is preferably 3 to 20 mm in consideration of appropriate rigidity, roundness of the tire, and continuity of the grip in the process of attaching CA, and more preferably, the rigidity of the tread and the tire From the viewpoint of roundness, the thickness is 5 to 20 mm. In the present invention, the width of the convex portion refers to a width at a portion between the outermost height of the convex portion and the bottom surface of the convex portion (a height that is ½ of the height from the bottom surface to the outermost side). For example, in the case of a sine wave-shaped convex portion, the width is a height at the middle of the vertical amplitude. Specifically, when the amplitude is 6 mm / 2 = 3 mm and the period is 7 mm, the width of the convex portion is 3.5 mm. It becomes. In the case of a trapezoidal wave shape, in the case of an upper base of 3 mm and a lower base of 6 mm, the width of the convex portion is 4.5 mm regardless of the interval between adjacent convex portions.

  Preferably, in the present invention, among the tread rubbers of the two tail layers, the elastic modulus at 100% elongation of the inner tread rubber at 60 ° C. is more than the elastic modulus at 100% elongation of the outer tread rubber at 60 ° C. Also make it high. That is, by making the rubber inside the tread harder than the rubber on the tread surface, the outer tread rubber on the surface gains grip, that is, it can be gripped using the high friction coefficient of soft rubber, The inner tread rubber can secure the rigidity of the tread.

  In the tire of the present invention, it is important to satisfy the above conditions for the tread rubber constituting the tread portion, whereby the desired effect of the present invention can be obtained, and other tire structures, materials, etc. The conditions are not particularly limited. For example, the tread rubber at the tread center portion is not particularly limited in the present invention, and may be the same as or different from any of the rubbers constituting the tread side portion.

  In the illustrated example, a spiral belt made of a reinforcing element having an angle of 0 degrees to 5 degrees with respect to the tire circumferential direction is disposed as the belt layer 3. The spiral belt 4 can be formed by covering one or a plurality of cords with rubber and winding the cord around the tread so as to be spirally wound around the tread in the tire manufacturing process. . By providing such a spiral belt 4, it is possible to prevent expansion due to centrifugal force during high-speed traveling, and it is possible to further increase steering stability at high speed. The spiral belt may be formed of a steel cord in addition to an organic fiber cord such as aromatic polyamide.

  The belt layer is only the spiral belt 3 in the illustrated example, but is not limited to this in the present invention, and the spiral belt 3 and the crossing belt layer may be provided in combination, or only the crossing belt layer alone. You may comprise. The crossing belt layer can be provided by, for example, crossing reinforcing cords made of aromatic polyamide or the like at ± 20 degrees to 80 degrees with respect to the tire circumferential direction. Further, the spiral belt may be arranged in a double manner, and a belt having an angle of 90 degrees with respect to the tire circumferential direction may be added in addition to the spiral belt to form a spiral belt and a mesh to strengthen the belt. Further, the crossing belt layer is not limited to two layers, and may be provided by three or more layers, and there is no particular limitation.

  Further, for example, the tire of the present invention includes a pair of bead portions 11, a pair of sidewall portions 13 that are continuous with the bead portions 11, and a tread portion 12 that is continuous in a toroidal shape between the sidewall portions 13. The carcass 2 that reinforces each part between the bead parts includes at least one carcass ply formed by arranging relatively highly elastic textile cords in parallel with each other. The number of carcass plies may be one or two, or three or more. In the illustrated example, both end portions of the carcass 2 are locked by sandwiching the end portions of the carcass 2 from both sides with bead wires. However, the carcass 2 may be bent and locked to the bead core 1 from the tire inner side to the outer side. . Further, an inner liner is disposed on the innermost layer of the tire (not shown), and a tread pattern is appropriately formed on the surface of the tread portion 12 (not shown). The present invention is applicable not only to radial tires but also to bias tires.

Hereinafter, the present invention will be specifically described with reference to examples.
In accordance with the following conditions, a pneumatic tire for a motorcycle was manufactured with a tire size of 190 / 50ZR17. Each test tire includes a carcass made of two carcass plies extending across a toroid between a pair of bead cores, and a nylon cord is used for the carcass ply (carcass 2 in FIGS. 1 and 2). Is indicated by a single line, both of which are overlapped). The two carcasses may be in the radial direction (angle with respect to the tire circumferential direction is 90 degrees), but in this embodiment, those having an angle with respect to the tire circumferential direction of ± 70 degrees are used in a mutually intersecting manner. Further, the end portion of the carcass 2 is sandwiched and locked between the bead wires from both sides in the bead portion.

  Further, the spiral belt 3 was disposed outside the carcass in the radial direction. The spiral belt 3 is formed by winding a steel cord twisted by a 1 × 3 type steel single wire having a diameter of 0.21 mm and winding it in a spiral shape in the tire circumferential direction at an interval of 50/50 mm. A belt-like body (strip) in which the parallel cords were embedded in the coated rubber was manufactured by a method of winding the tire in the tire rotation axis direction in a spiral manner substantially along the tire circumferential direction. A tread portion was provided outside the spiral belt, and the thickness thereof was 9 mm. In the tire of this example, no groove was disposed on the tread surface.

  Based on the above structure, in the tread portion, a region of 50% of the tread deployment width centered on the tire equator plane is a tread center portion, and a region of 25% of each tread development width on both sides thereof is a tread side portion. Of these, the tread rubbers on the tread side portions were respectively changed in accordance with the following, and test tires of respective conventional examples, examples, and comparative examples were manufactured.

<Conventional example 1>
The entire region of the tread portion consisting of the tread center portion and the tread side portion was made of a single type of rubber. The elastic modulus at 100% elongation at 60 ° C. of the tread rubber of Conventional Example 1 is defined as 100. Hereinafter, the elastic modulus of each rubber is indicated by an index.

<Conventional example 2>
The entire region of the tread portion consisting of the tread center portion and the tread side portion was made of a single type of rubber. The elastic modulus at 100% elongation of the tread rubber of Conventional Example 2 at 60 ° C. was 70.

<Example 1>
As shown in FIG. 1, the entire tread rubber on the side of the tread is divided into two layers in the thickness direction, and the boundary surface between the two layers of tread rubber is changed in the thickness direction within a cross section parallel to the tire radial direction. A trapezoidal wave shape was assumed. Further, the longitudinal direction of the convex portion was set to 0 degree with respect to the tire circumferential direction. As shown in the figure, there are three convex portions per one tread side portion. Further, the upper base of the convex portion was 6 mm, the lower base was 12 mm, the width of the convex portion was 9 mm, and the wave-shaped pitch was 18 mm. Furthermore, the upper end of the trapezoidal wave exists at a position 2 mm from the tire surface (that is, the surface of the convex portion is visible when the tire wears 2 mm), and the lower end exists at a position 7 mm from the tire surface (that is, the tire 7 mm). When worn, the outer tread rubber is completely removed, leaving only the inner tread rubber).

  The elastic modulus at 100% elongation at 60 ° C. of the outer tread rubber of Example 1 was 70, the elastic modulus of the inner tread rubber was 130, and the average elastic modulus was 100. The tread center portion was formed of the same rubber as that of Conventional Example 1 having an elastic modulus of 100.

<Example 2>
As shown in FIG. 3, the entire tread rubber on the tread side is divided into two layers in the thickness direction, and the boundary surface of the two layers of tread rubber is changed in the thickness direction within a cross section parallel to the tire radial direction. Sine wave shape was assumed. In addition, the longitudinal direction of the convex portion was inclined by 45 degrees with respect to the tire circumferential direction. The amplitude of the wave was 7 mm / 2 = 3.5 mm. The width of the convex portion was 7 mm, and the period (pitch) of the sine wave was 14 mm. The upper end of the sine wave exists at a position 1 mm from the tire surface (that is, the surface of the convex portion is visible when the tire wears 1 mm), and the lower end exists at a position 8 mm from the tire surface (that is, when the tire wears 8 mm) The outer tread rubber is completely gone, and only the inner tread rubber is left). Therefore, only the inner tread rubber exists in the last 1 mm (depth 8 mm to 9 mm).

  The elastic modulus at 100% elongation at 60 ° C. of the outer tread rubber of Example 2 was 70, the elastic modulus of the inner tread rubber was 130, and the average elastic modulus was 100. The tread center portion was formed of the same rubber as that of Conventional Example 1 having an elastic modulus of 100.

  In addition, the rotation direction of the tire of Example 2 is as shown in FIG. 3, and is a direction in which the tire center side of the convex portion inclined by 45 degrees first contacts the road surface. When turning at a CA of 45 degrees or more, the lateral force acts on the tread of the tire from the center side of the tire to the tread end side. On the other hand, traction acts in the opposite direction to the tire rotation direction. The direction of the resultant force of traction and lateral force coincides with the longitudinal direction of the convex portion shown in FIG.

<Example 3>
The configuration was the same as in Example 2 except that the longitudinal direction of the convex portion was inclined by 70 degrees with respect to the tire circumferential direction.

<Example 4>
The configuration was the same as in Example 2 except that the longitudinal direction of the convex portion was inclined by 90 degrees with respect to the tire circumferential direction.

<Comparative example>
The configuration was the same as that of Example 1 except that the boundary surface of the two-layered tread rubber did not change in the thickness direction and had a conventional general cap and base structure. That is, the tire side part of the comparative example is formed of two layers of rubber, and the boundary surface exists at a position 4.5 mm from the tire surface. The elastic modulus at 100% elongation at 60 ° C. of the rubber from the tread surface to a depth of 4.5 mm is 70, and the same elastic modulus of the internal rubber (rubber from the tread surface to a depth of 4.5 mm to 9 mm) is 130.

  In order to confirm the performance improvement effect of the tire for motorcycles of the present invention, a comparative test of steering performance using an actual vehicle was performed. Since each test tire was a rear tire, only the rear tire was replaced and an actual vehicle test was performed. The front tire was always fixed with a conventional one. The evaluation method is shown below.

  Each test tire is mounted on a 1000cc sports-type motorcycle, run on the test track, evaluated with a focus on steering stability performance (cornering performance) when the vehicle is largely defeated, and according to the feeling of the test rider Overall evaluation was performed by a 10-point method.

Also, for each tire, we prepared tires that were uniformly trimmed 2.5 mm and 5 mm from one tread edge to the other tread edge, and compared to those that were not shaved. A stability performance test was performed.
In each case, the test course of one lap about 80 seconds was evaluated by running five laps. These results are shown in Table 1 below, along with evaluation comments from test drivers.

  As shown in Table 1 above, as compared with Conventional Example 1, all of the Examples have higher steering stability performance when new. This is because the friction coefficient is improved by using rubber having a low elastic modulus on the surface of the shoulder portion. In Conventional Example 2, the entire tread portion is formed of rubber having a low elastic modulus and a high grip. However, since the tread is too soft when it is new, the tire has a lack of rigidity and the driving stability performance score is not high. The rider also pointed out that the tread wears quickly.

  Although Example 1 and Example 2 showed the same characteristic, in Example 2, it was pointed out that the rigidity of a tire was high especially when traction was added. This is considered to be because the longitudinal direction of the convex portion exists in the resultant force direction with the lateral force when traction is applied. Moreover, although Example 3 and Example 4 are substantially the same feeling, especially the side grip at the time of turning of Example 4 is high. This is because the longitudinal direction of the convex portion is the lateral direction, and the rigidity of the tread is high in the direction along the lateral input.

  In the comparative example, the initial grip is high. However, since the boundary surface is not three-dimensional, the rigidity of the tread is slightly insufficient, and the initial steering stability performance is lower than in Examples 2 to 4. In addition, the grip of the tread cut 5 mm suddenly decreased. This is because the tread is formed only from hard rubber.

  As a result of the above, the tires of the respective examples according to the present invention all had better initial steering stability performance than the conventional tires, and there was little change in steering stability performance even as wear progressed. . Furthermore, it was confirmed that there was no sudden change in grip force in the process of wear as shown by the tire of the comparative example.

1 is a cross-sectional view in a width direction showing a pneumatic tire for a motorcycle according to a preferred example of the present invention. It is a width direction sectional view showing a pneumatic tire for two-wheeled vehicles concerning other suitable examples of the present invention. (A) BB ′ sectional view, (b) schematic perspective view of entire tire, and (c) AA ′ sectional view when the longitudinal direction of the convex portion is inclined at an angle of 45 degrees with respect to the tire circumferential direction FIG.

Explanation of symbols

1 Bead core 2 Carcass 3 Belt layer (spiral belt)
11 Bead part 12 Tread part 12A Outer tread rubber 12B Inner tread rubber 13 Side wall part

Claims (7)

In a pneumatic tire for a motorcycle including a tread portion formed in an annular shape,
When the region of 50% of the tread development width centered on the tire equatorial plane is the tread center portion and the region of 25% of each tread development width on both sides of the tread center portion is the tread side portion of the tread portion,
At least a part of the tread rubber on the side of the tread is divided into two layers in the thickness direction, and the boundary surface of the tread rubber of the two layers changes in the thickness direction within one cross section parallel to the tire radial direction. A pneumatic tire for a two-wheeled vehicle characterized by having a shape and a pitch of the corrugated shape in a range of 15 to 40 mm.   The boundary surface is parallel to the tire radial direction and does not change in the thickness direction in another cross section orthogonal to the one cross section, and an angle formed by the other cross section with respect to the tire circumferential direction is 0 degree. Item 2. A pneumatic tire for a motorcycle according to item 1.   The boundary surface is parallel to the tire radial direction and does not change in the thickness direction in another cross section perpendicular to the one cross section, and the angle formed by the other cross section with respect to the tire circumferential direction is 30 degrees to 90 degrees. The pneumatic tire for a motorcycle according to claim 1.   The pneumatic tire for a motorcycle according to any one of claims 1 to 3, wherein a width of the corrugated convex portion is 3 mm or more and 20 mm or less.   The elastic modulus at 100% elongation at 60 ° C of the inner tread rubber among the tread rubbers of the two layers is higher than the elastic modulus at 100% elongation of the outer tread rubber at 60 ° C. The pneumatic tire for a motorcycle according to one item.   The pneumatic tire for a motorcycle according to any one of claims 1 to 5, wherein the wave shape is a trapezoidal wave, a rectangular wave, or a sine wave shape. The total thickness of the tread rubber divided into two layers in the thickness direction is 0-60% in thickness to the upper end and 60-100% in thickness to the lower end of the corrugated shape based on the tread surface. And the difference of the thickness of an upper end and a lower end is 20% or more, The pneumatic tire for two-wheeled vehicles as described in any one of Claims 1-6.

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