Patent Description:
Conventionally, a motorcycle tire that includes a tread reinforcing layer in a tread portion thereof has been known. For example, <CIT> proposes a motorcycle tire that includes a tread reinforcing layer having two belt plies disposed outward of a carcass in a tire radial direction and one band ply disposed outward of the two belt plies in the tire radial direction.

However, regarding the motorcycle tire disclosed in <CIT>, further improvement for which an attempt to achieve both straight running stability during high-speed running and cornering performance is made has been desired.

The present invention has been made in view of the above circumstances, and a main object of the present invention is to provide a motorcycle tire capable of achieving both straight running stability during high-speed running and cornering performance.

The present invention is directed to a motorcycle tire including: a carcass extending from a tread portion through a pair of sidewall portions to a pair of bead portions; and a tread reinforcing layer disposed outward of the carcass in the tread portion in a tire radial direction. In the motorcycle tire, the tread reinforcing layer includes a belt layer and a band layer, the band layer includes at least one band ply in which band cords are arranged at an angle of <NUM>° or less relative to a tire circumferential direction, the belt layer includes a pair of inner belt plies disposed on both sides of the band ply in the tire axial direction so as not to overlap the band ply and at least one outer belt ply disposed outward of the band ply in the tire radial direction so as to overlap the band ply, the inner belt plies each have inner belt cords arranged at an angle different from the angle of the band cords relative to the tire circumferential direction, and the outer belt ply has outer belt cords arranged at an angle different from both of the angle of the band cords and the angle of the inner belt cords relative to the tire circumferential direction.

By having the above-described configuration, the motorcycle tire of the present invention can achieve both straight running stability during high-speed running and cornering performance.

An embodiment of the present invention will be described below in detail with reference to the drawings.

<FIG> is a tire meridian cross-sectional view of a motorcycle tire <NUM> (hereinafter, sometimes simply referred to as "tire <NUM>"), of the embodiment of the present invention, in a normal state.

The "normal state" refers to a state in which the tire <NUM> is fitted to a normal rim and is inflated to a normal internal pressure, and no load is applied to the tire <NUM>. Hereinafter, dimensions of parts of the tire <NUM> are values measured in the normal state, unless otherwise noted.

In a standard system including a standard on which the tire <NUM> is based, the "normal rim" is a rim that is defined for each tire by the standard, and is, for example, the "standard rim" in the JATMA standard, the "Design Rim" in the TRA standard, or the "Measuring Rim" in the ETRTO standard.

In a standard system including a standard on which the tire <NUM> is based, the "normal internal pressure" is an air pressure that is defined for each tire by the standard, and is the "maximum air pressure" in the JATMA standard, the maximum value indicated in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, or the "INFLATION PRESSURE" in the ETRTO standard.

As shown in <FIG>, the tire <NUM> of the embodiment of the present invention includes a tread portion <NUM>, a pair of sidewall portions <NUM> respectively extending inward in a tire radial direction from both ends of the tread portion <NUM>, and a pair of bead portions <NUM> each disposed inward of the sidewall portion <NUM> in the tire radial direction. In each of the pair of bead portions <NUM>, a bead core <NUM> is disposed, for example.

A tread surface <NUM> which is the outer surface of the tread portion <NUM>, for example, extends from a tire equator C to tread ends Te so as to be curved into an arc shape that protrudes outward in the tire radial direction. In the embodiment of the present invention, a position having a tire maximum width is determined by the positions of the tread ends Te. With such a tire <NUM>, cornering at a large camber angle is possible.

Here, the tread ends Te are the ends of the tread portion <NUM> in the tire axial direction. The tire equator C is the center between the tread ends Te in the tire axial direction. In addition, a length between the tread ends Te, measured along the tread surface <NUM>, is a tread development width TWe.

The tire <NUM> of the embodiment of the present invention includes a carcass <NUM> extending from the tread portion <NUM> through the pair of sidewall portions <NUM> to the pair of bead portions <NUM>. The carcass <NUM> includes, for example, a body portion 6a extending on and between a pair of the bead cores <NUM>, and turned-up portions 6b connected to the body portion 6a and turned up around the bead cores <NUM>. The tire <NUM> preferably includes a tread reinforcing layer <NUM> disposed outward of the carcass <NUM> in the tread portion <NUM> in the tire radial direction.

The carcass <NUM> includes at least one carcass ply in which carcass cords are arranged. In the embodiment of the present invention, the carcass <NUM> includes two carcass plies 6A, 6B. The carcass plies 6A, 6B, for example, include an inner carcass ply 6A disposed inward in the tire radial direction and an outer carcass ply 6B disposed outward of the inner carcass ply 6A in the tire radial direction, in the tread portion <NUM>.

<FIG> is a schematic development of the tread reinforcing layer <NUM>. As shown in <FIG> and <FIG>, the tread reinforcing layer <NUM> of the embodiment of the present invention includes a belt layer <NUM> and a band layer <NUM>. The band layer <NUM> includes at least one band ply 9A in which band cords 9a are arranged at an angle θ1 of <NUM>° or less relative to a tire circumferential direction. In the embodiment of the present invention, the band layer <NUM> includes one band ply 9A. Here, in the present specification, the angle of each cord is measured as an angle less than or equal to a right angle relative to the tire circumferential direction.

The belt layer <NUM> includes a pair of inner belt plies 8A disposed on both sides of the band ply 9A in the tire axial direction and at least one outer belt ply 8B disposed outward of the band ply 9A in the tire radial direction. In the embodiment of the present invention, the belt layer <NUM> includes the pair of inner belt plies 8A and one outer belt ply 8B. The inner belt plies 8A are preferably disposed so as not to overlap the band ply 9A. The outer belt ply 8B is preferably disposed so as to overlap the band ply 9A.

The inner belt plies 8A of the embodiment of the present invention each have inner belt cords 8a arranged at an angle θ2 different from the angle θ1 of the band cords 9a relative to the tire circumferential direction. The outer belt ply 8B preferably has outer belt cords 8b arranged at an angle θ3 different from both the angle θ1 of the band cords 9a and the angle θ2 of the inner belt cords 8a relative to the tire circumferential direction.

Such a tread reinforcing layer <NUM> has the band ply 9A in an area that contacts with the ground during straight running, thereby restraining outer diameter growth during high-speed running and improving the straight running stability of the tire <NUM> during high-speed running. In addition, this tread reinforcing layer <NUM> has the inner belt plies 8A in an area that contacts with the ground during sharp cornering, thereby increasing cornering force during sharp cornering and improving the cornering performance of the tire <NUM> during sharp cornering.

In addition, in this tread reinforcing layer <NUM>, the outer belt ply 8B in which the outer belt cords 8b are arranged at the angle θ3 different from the angle θ1 in the band ply 9A and the angle θ2 in the inner belt ply 8A is disposed outward in the tire radial direction, thereby improving the transient characteristics during cornering. Accordingly, the tire <NUM> of the embodiment of the present invention can achieve both straight running stability during high-speed running and cornering performance.

In a more preferable mode, the angle θ3 of the outer belt cords 8b relative to the tire circumferential direction is larger than the angle θ2 of the inner belt cords 8a relative to the tire circumferential direction. Such a tread reinforcing layer <NUM> restrains shear force that acts on the tread surface <NUM> during cornering, and can improve the cornering performance of the tire <NUM>. In addition, the cornering force of the tire <NUM> can be adjusted by changing the angle difference between the angle θ3 of the outer belt cords 8b and the angle θ2 of the inner belt cords 8a in this tread reinforcing layer <NUM>.

The angle θ3 of the outer belt cords 8b relative to the tire circumferential direction is preferably <NUM> to <NUM>°. When the angle θ3 of the outer belt cords 8b is not less than <NUM>°, the shear force that acts on the tread surface <NUM> during cornering is restrained and the stiffness change due to the band ply 9A and the inner belt plies 8A is also restrained, thereby improving the cornering performance of the tire <NUM>. From such a viewpoint, the angle θ3 of the outer belt cords 8b is preferably not less than <NUM>°, and more preferably not less than <NUM>°.

Although not shown, when the angle θ3 of the outer belt cords 8b in the outer belt ply 8B is, for example, not less than <NUM>°, the outer belt cords 8b may be line-symmetrically arranged with respect to the tire equator C. Such a tread reinforcing layer <NUM> provides excellent balance performance between during left cornering and during right cornering, and can further improve the cornering performance of the tire <NUM>.

In this case, the outer belt cords 8b may be, for example, arranged in a V shape or a chevron shape centered on the tire equator C. Although the outer belt cords 8b may be arranged in an arc shape centered on the tire equator C, the maximum angle for the angle θ3 of the outer belt cords 8b is preferably not less than <NUM>°.

The angle θ2 of the inner belt cords 8a relative to the tire circumferential direction is preferably <NUM> to <NUM>°. Such inner belt plies 8A can achieve binding effect with the outer belt ply 8B, and serves to further increase the cornering force by promoting deformation of rubber in the tread surface <NUM>. Accordingly, the tread reinforcing layer <NUM> of the embodiment of the present invention can improve the cornering performance of the tire <NUM> during sharp cornering.

Each outer belt cord 8b and each inner belt cord 8a of the embodiment of the present invention are inclined in directions opposite to each other relative to the tire circumferential direction. Such a tread reinforcing layer <NUM> can achieve greater binding effect between the outer belt ply 8B and each inner belt ply 8A, and can further improve the cornering performance of the tire <NUM>.

Each inner belt cord 8a of the embodiment of the present invention is an organic fiber cord. Examples of the material of the inner belt cords 8a include aramid, cellulose fibers, polyester, and nylon. Since the inner belt cords 8a in such an inner belt ply 8A are easily bent, the inner belt ply 8A promotes deformation of the tread surface <NUM> during sharp cornering, and serves to improve the cornering performance of the tire <NUM> during sharp cornering.

Each outer belt cord 8b is preferably an organic fiber cord, similar to the inner belt cord 8a. Examples of the material of the outer belt cords 8b include aramid, cellulose fibers, polyester, and nylon. Such an outer belt ply 8B promotes deformation of the tread surface <NUM> during sharp cornering in cooperation with the inner belt plies 8A, and can improve the cornering performance of the tire <NUM> during sharp cornering.

A development width W1 of the outer belt ply 8B is preferably not larger than the tread development width TWe. Such an outer belt ply 8B is restrained from becoming large, and serves to reduce the weight of the tire <NUM>.

The development width W1 of the outer belt ply 8B of the embodiment of the present invention is larger than a development distance L1 between the outer edges, in the tire axial direction, of the pair of inner belt plies 8A. Such an outer belt ply 8B restrains stiffness change at the outer edges, in the tire axial direction, of the inner belt plies 8A, and thus can improve the cornering performance of the tire <NUM> during sharp cornering.

A development width W2 of each inner belt ply 8A is preferably <NUM>% to <NUM>% of the tread development width TWe. Such inner belt plies 8A serve to increase cornering force during sharp cornering.

A development width W3 of the band ply 9A of the embodiment of the present invention is smaller than the development width W1 of the outer belt ply 8B. Such a band ply 9A restrains outer diameter growth during high-speed running, and can improve the straight running stability of the tire <NUM> during high-speed running. In addition, this tread reinforcing layer <NUM> restrains stiffness change in the end portions of the band ply 9A, and can improve the cornering performance of the tire <NUM>.

The development width W3 of the band ply 9A is preferably <NUM>% to <NUM>% of the tread development width TWe. When the development width W3 of the band ply 9A is <NUM>% or more of the tread development width TWe, the band ply 9A can be reliably positioned in an area that contacts with the ground during straight running, thereby improving the straight running stability of the tire <NUM> during high-speed running.

When the development width W3 of the band ply 9A is <NUM>% or less of the tread development width TWe, deformation of the tread surface <NUM> during cornering is promoted and force due to the outer diameter difference between the inner side and the outer side of a ground-contact surface can be generated, thereby improving the cornering performance of the tire <NUM>. Such a band ply 9A increases a camber thrust due to deformation of the tread surface <NUM>, and serves to improve the cornering performance of the tire <NUM> during sharp cornering.

A distance L2 between the band ply 9A and each inner belt ply 8A is preferably <NUM> to <NUM>. Such a tread reinforcing layer <NUM> reduces stiffness change between the band ply 9A and each inner belt ply 8A, and serves to improve the cornering performance of the tire <NUM>.

Motorcycle tires each having the basic structure shown in <FIG> were produced as samples according to the specifications in Table <NUM>. The tires produced as samples were mounted to the front and rear wheels of a motorcycle for tests, and sensory evaluation was made by the test driver for straight running stability during high-speed running and cornering performance during sharp cornering. The results are represented by indexes with the result of Comparative Example <NUM> being regarded as <NUM>. A higher numerical value indicates that each of the straight running stability and the cornering performance is better. The common items are as follows.

The results of the tests are shown in Table <NUM>.

Claim 1:
A motorcycle tire (<NUM>) comprising: a carcass (<NUM>) extending from a tread portion (<NUM>) through a pair of sidewall portions (<NUM>) to a pair of bead portions (<NUM>); and a tread reinforcing layer (<NUM>) disposed outward of the carcass (<NUM>) in the tread portion (<NUM>) in a tire radial direction, wherein
the tread reinforcing layer (<NUM>) includes a belt layer (<NUM>) and a band layer (<NUM>),
the band layer (<NUM>) includes at least one band ply (9A) in which band cords (9a) are arranged at an angle (θ1) of <NUM>° or less relative to a tire circumferential direction,
characterized in that
the belt layer (<NUM>) includes a pair of inner belt plies (8A) disposed on both sides of the band ply (9A) in the tire axial direction so as not to overlap the band ply (9A) and at least one outer belt ply (8B) disposed outward of the band ply (9A) in the tire radial direction so as to overlap the band ply (9A),
the inner belt plies (8A) each have inner belt cords (8a) arranged at an angle (θ2) different from the angle (θ1) of the band cords (9a) relative to the tire circumferential direction, and
the outer belt ply (8B) has outer belt cords (8b) arranged at an angle (θ3) different from both the angle (θ1) of the band cords (9a) and the angle (θ2) of the inner belt cords (8a) relative to the tire circumferential direction.