Patent Description:
The present invention relates to a motorcycle tire.

<CIT> describes a motorcycle pneumatic tire having a pair of bead cores and a carcass extending between a pair of bead portions. This motorcycle pneumatic tire includes hard rubber layers each arranged inside the carcass and outside a respective one of the bead cores in a tire radial direction. Related technologies are also known from <CIT>, <CIT>, <CIT>, and <CIT>.

A motorcycle turns by tilting the body and giving a camber angle to the tires. Tires are required to have improved sense of firmness, ground contacting feel, and absorbency during such cornering. The sense of firmness has a significant relationship to tread rigidity and affects stability during running. The ground contacting feel has a great relationship with the easiness of bending of the sidewall portions, and affects the easiness of steering. Further, the absorbency has a significant relationship to the ease of bending of the tread portion and the sidewall portions, and affects the easiness of suppressing vibration during running.

The present invention was made in view of the above, and a primary object thereof is to provide a motorcycle tire having improved sense of firmness, improved ground contacting feel, and improved absorbency during cornering.

The present invention is a motorcycle tire comprising:.

By adopting the above configuration, it is possible that the motorcycle tire of the present invention improves the sense of firmness, the ground contacting feel, and the absorbency.

An embodiment of the present invention will now be described below in conjunction with accompanying drawings.

<FIG> is a tire meridian section passing all through the tire rotation axis (not shown) of a motorcycle tire <NUM> (hereinafter may be simply referred to as "tire <NUM>") of the present embodiment in a standard state. The tire <NUM> of the present invention is suitably used for a tire intended for racing on a circuit, for example. However, the present invention is not limited to the tire <NUM> for racing.

The term "standard state" refers to a state in which the tire <NUM> is mounted on a standard rim (not shown), inflated to a standard inner pressure, and loaded with no tire load. In the present specification, unless otherwise noted, dimensions of various parts of the tire <NUM> are those measured in the standard state.

Further, the term "standard rim" refers to a wheel rim specified for the concerned tire by a standard included in a standardization system on which the tire is based, for example, the "normal wheel rim" in JATMA, "Design Rim" in TRA, and "Measuring Rim" in ETRTO.

Furthermore, the term "standard inner pressure" refers to air pressure specified for the concerned tire by a standard included in a standardization system on which the tire is based, for example, the maximum air pressure in JATMA, maximum value listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" table in TRA, and "INFLATION PRESSURE" in ETRTO.

As shown in <FIG>, the tire <NUM> of the present embodiment includes a tread portion <NUM>, a pair of sidewall portions <NUM>, a pair of bead portions <NUM>, and a carcass <NUM> extending toroidally from one bead portion <NUM> to the other bead portion <NUM>.

The tread portion <NUM> has a pair of tread edges (Te), a ground contacting surface (2a) that extends between the tread edges (Te) and is designed to contact road surfaces, and a tire inner cavity surface (2b). The ground contacting surface (2a) extends in an arc shape so as to be convex outward in a tire radial direction, for example. It is possible that the tire <NUM> configured as such turns with a large camber angle. The tread edges (Te) are outer edges in a tire axial direction of the tire that touch the ground when the camber angle is at its maximum.

Each of the sidewall portions <NUM> extends radially inward from a respective one of the tread edges (Te). Each of the sidewall portions <NUM> has a sidewall rubber <NUM> disposed axially outside the carcass <NUM>. In the present embodiment, each of the sidewall rubbers <NUM> forms an outer surface (3a) of a respective one of the sidewall portions <NUM>.

Each of the bead portions <NUM> is located radially inside a respective one of the sidewall portions <NUM>. In each of the bead portions <NUM> in the present embodiment, a bead core <NUM> is embedded therein.

<FIG> is an enlarged view of one of the sidewall portions <NUM> on one side in the tire axial direction of the tire <NUM> shown in <FIG>. As shown in <FIG>, each pf the sidewall portions <NUM> has a minimum thickness (Ts). The present invention was made by focusing on the fact that the ground contacting feel and the sense of firmness can be improved by specifying the minimum thickness (Ts) of each of the sidewall portions <NUM> and a minimum tire thickness (Ta) from each of the tread edges (Te) to the tire inner cavity surface (2b). That is, in the present invention, the minimum thickness (Ts) of each of the sidewall portions <NUM> is set to <NUM>% or less of the minimum tire thickness (Ta) from each of the tread edges (Te) to the tire inner cavity surface (2b). As a result, the sidewall portions <NUM> have a greater amount of deflection during cornering, thereby, the ground contacting feel is improved. Further, since the minimum tire thickness (Ta) is secured at each of the tread edges (Te), a high sense of firmness is exerted during cornering at a large camber angle. In order to effectively exert this effect, the minimum thickness (Ts) is preferably <NUM>% or more, more preferably <NUM>% or more and preferably <NUM>% or less, more preferably <NUM>% or less of the minimum tire thickness (Ta). The minimum tire thickness (Ta) in the present embodiment includes the sidewall rubber <NUM> and a later-described main body portion (6a) of the carcass <NUM>, but does not include a later-described turned up portion (6b) of the carcass <NUM> and a later-described tread reinforcement layer <NUM>.

Further, each of the sidewall rubbers <NUM> has a minimum thickness (Ds) of <NUM> or more and <NUM> or less. Since the minimum thickness (Ds) is <NUM> or less, the amount of deflection at each of the sidewall portions <NUM> is secured, therefore, the ground contacting feel is improved. Furthermore, since the minimum thickness (Ds) is <NUM> or more, excessive decrease in the rigidity of the sidewall portions <NUM> is suppressed, thereby, the absorbency during cornering is improved. In order to effectively exert such an effect, the minimum thickness (Ds) is preferably <NUM> or more, more preferably <NUM> or more and preferably <NUM> or less, more preferably <NUM> or less.

In each of the sidewall portions <NUM> (i.e., in each axial half of the tire <NUM>), it is preferred that a first distance H1 in the tire radial direction from the bead core <NUM> to a position P1, which is the position where the sidewall rubber <NUM> has the minimum thickness (Ds), is <NUM>% or less of a second distance H2 in the tire radial direction from the bead core <NUM> (more specifically, from an outermost end (5e) in the tire radial direction of the bead core <NUM>) to the tread edge (Te). If the first distance H1 exceeds <NUM>% of the second distance H2, the rigidity of the sidewall portions <NUM> becomes excessively small, and the minimum tire thickness (Ta) needs to be reduced, which may deteriorate the sense of firmness. In the present specification, the first distance H1 is specified by the distance in the tire radial direction from the position P1, which is the position on the outer surface (3a) of the sidewall portion <NUM> where the sidewall rubber <NUM> has the minimum thickness (Ds), to the outermost end (5e) of the bead core <NUM>. Further, the position P1 is determined excluding a portion within <NUM> radially outward from an innermost end (3i) in the tire radial direction of the sidewall rubber <NUM>. The second distance H2 is specified in the present specification as the distance in the tire radial direction from the outermost end (5e) of the bead core <NUM> to the tread edge (Te).

It is preferred that the first distance H1 is <NUM>% or more of the second distance H2. If the first distance H1 is less than <NUM>% of the second distance H2, the position P1, which is the position where the sidewall rubber <NUM> has the minimum thickness (Ds), will be close to the bead core <NUM>, and the amount of deflection of the sidewall portion <NUM> may be small. In order to deflect the sidewall portions <NUM> at the desired positions for the purpose of improving the ground contacting feel, the first distance H1 is more preferably <NUM>% or more and <NUM>% or less of the second distance H2. It should be noted that when the position P1 is formed at multiple locations, the first distance H1 from any of the positions P1 to the bead core <NUM> is preferably <NUM>% or more, more preferably <NUM>% or more and preferably <NUM>% or less, more preferably <NUM>% or less of the second distance H2.

A range T1 of <NUM>% or more and <NUM>% or less of the second distance H2 radially outward from the bead core <NUM> (i.e., the range T1 radially outward from the bead core <NUM> by <NUM>% or more and <NUM>% or less of the second distance H2) is a region in each of the sidewall portions <NUM> that greatly affects the ground contacting feel and the absorbency. Therefore, in the range T1, a difference (Dm-Ds) between a maximum thickness (Dm) (not shown) and the minimum thickness (Ds) of the sidewall rubber <NUM> is preferably <NUM> or less, and more preferably <NUM> or less. As a result, the deflection during cornering occurs uniformly in the range T1 in each of the sidewall portions <NUM>, thereby, the ground contacting feel is further improved.

Further, in the range T1, the thickness of the sidewall rubber <NUM> is preferably <NUM> or more, more preferably <NUM> or more, and preferably <NUM> or less, more preferably <NUM> or less. Since the thickness of the sidewall rubber <NUM> is <NUM> or more, it is possible that the absorbency is maintained high during cornering. Since the thickness of the sidewall rubber <NUM> is <NUM> or less, the flexibility of the sidewall portions <NUM> is secured and therefore the ground contacting feel can be maintained high.

As shown in <FIG>, the carcass <NUM> is formed by at least one carcass ply, one carcass ply 6A in the present embodiment. The carcass ply 6A includes the main body portion (6a) extending from one bead core <NUM> to the other bead core <NUM> and a pair of the turned up portions (6b) connected to the main body portion (6a) and each turned up around a respective one of the bead cores <NUM>, for example. The carcass ply 6A is formed with a well-known structure. In each of the sidewall portions, the turned up portion (6b) has an outermost end (6e) in the tire radial direction located radially outside the range T1 (as shown in <FIG>). As a result, the rigidity is uniform within the range T1, therefore, it is expected to have the effect of maintaining a high ground contacting feel.

Further, the tread portion <NUM> of the present embodiment includes the tread reinforcement layer <NUM> adjacent to the carcass <NUM> on the radially outer side and a tread rubber <NUM> adj acent to the tread reinforcement layer <NUM> on the radially outer side to form the ground contacting surface (2a). The tread reinforcement layer <NUM> is formed with a well-known structure. The tread reinforcement layer <NUM> in the present embodiment has outermost edges (7e) in the tire axial direction each located axially inside and radially outside a respective one of the tread edges (Te). On each side in the tire axial direction, the tread rubber <NUM> and the sidewall rubber <NUM> are divided by a line segment connecting the outermost edge (7e) of the tread reinforcement layer <NUM> and the tread edge (Te), for example.

The tread rubber <NUM> and the sidewall rubber <NUM> contain an anti-aging agent (antioxidant). In addition, the tread rubber <NUM> and the sidewall rubber <NUM> contain wax in the present embodiment.

Compared to the tread rubber <NUM>, the sidewall rubber <NUM> is not subject to wear due to contact with the road surface. Therefore, the sidewall rubber <NUM>, which forms the outer surface (3a), is required to have excellent weather resistance in order to suppress cracking and chipping caused by continuous exposure to ultraviolet rays. Therefore, the blending amount of the anti-aging agent per unit mass of the sidewall rubber <NUM> is greater than the blending amount of the anti-aging agent per unit mass of the tread rubber <NUM>. It should be noted that if the amount of the anti-aging agent per unit mass of the sidewall rubber <NUM> is excessively large, the sidewall rubber <NUM> is prone to discoloration. For this reason, a difference (Ra-Rb) between a blending amount (Ra) (not shown) of the antioxidant contained in <NUM> parts by mass of the rubber component of the sidewall rubber <NUM> and a blending amount (Rb) of the antioxidant contained in <NUM> parts by mass of the rubber component of the tread rubber <NUM> is preferably <NUM> parts by mass or more, more preferably <NUM> parts by mass or more, and preferably <NUM> parts by mass or less, more preferably <NUM> parts by mass or less.

From the same perspective, it is preferred that the blending amount of the wax per unit mass of the sidewall rubber <NUM> is greater than the blending amount of the wax per unit mass of the tread rubber <NUM>. A difference (Wa-Wb) between a blending amount (Wa) of the wax contained in <NUM> mass parts of the rubber component of the sidewall rubber <NUM> and a blending amount (Wb) of the wax contained in <NUM> mass parts of the rubber component of the tread rubber <NUM> is preferably <NUM> parts by mass or more, more preferably <NUM> parts by mass or more, and preferably <NUM> parts by mass or less, and more preferably <NUM> parts by mass or less.

Examples of the anti-aging agents are, for example, as follows: naphthylamine antioxidants such as phenyl-α-naphthylamine; diphenylamine antioxidants such as octylated diphenylamine and <NUM>,<NUM>'-bis(α,α'-dimethylbenzyl)diphenylamine; p-Phenylenediamine antioxidants such as N-isopropyl-N'-phenyl-p-phenylenediamine, N-(<NUM>,<NUM>-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N,N'-di-<NUM>-naphthyl-p-phenylenediamine; quinoline antioxidants such as polymers of <NUM>,<NUM>,<NUM>-trimethyl-<NUM>,<NUM>-dihydroquinoline; monophenol-based antioxidants such as <NUM>,<NUM>-di-t-butyl-<NUM>-methylphenol and styrenated phenol; bis, tris, polyphenol antioxidants such as tetrakis-[methylene-<NUM>-(<NUM>',<NUM>'-di-t-butyl-<NUM>'-hydroxyphenyl)propionate]methane; and so on. As commercially available products, products of Seiko Chemical Co. , Sumitomo Chemical Co. , Ouchi Shinko Chemical Industrial Co. , FlexSys Inc. , and so forth are used. One of these may be used alone, or two or more may be used in combination. Among them, p-phenylenediamine antioxidants and quinoline antioxidants are preferred.

Further, the wax is not particularly limited, but the examples of the wax are petroleum-based waxes such as paraffin wax and microcrystalline wax; natural waxes such as vegetable waxes and animal waxes; synthetic waxes such as polymers of ethylene, propylene, and the like. As commercially available products, products of Ouchi Shinko Chemical Industrial Co. , Nippon Seiro Co. , Seiko Chemical Co. , and so on are used. One of these may be used alone, or two or more may be used in combination.

For the bead cores <NUM>, a tape bead structure or a single wind structure (not shown) can be appropriately adopted, for example. The tape bead structure and the single-wind structure create high mating pressure with the rim (not shown) and help increase the sense of firmness. In the tape bead structure, the bead core <NUM> is formed by spirally winding a belt-shaped body from the inside to the outside in the radial direction. The belt-shaped body is formed by an array of bead wires arranged parallel to each other and topped with a rubber or resin material. In the single-wind structure, a single bead wire is continuously wound in a spiral and multi-row, multi-stage configuration to form the bead core <NUM>. Steel cords are suitably used as the bead wires, but organic fiber cords can also be used.

<FIG> is an enlarged view of one of the bead portions <NUM>. As shown in <FIG>, each of the bead portions <NUM> is provided with a chafer <NUM> formed by monofilament cords and a clinch rubber <NUM> adjacent to the chafer <NUM>, for example. The chafer <NUM> increases the mating pressure with the rim to help maintain the sense of firmness high.

The chafer <NUM> is arranged axially inside the bead core <NUM> and includes an inner portion (8a) arranged axially inside the bead core <NUM> to partially form the tire inner cavity surface (2b), an outer portion (8b) arranged axially outside the turned up portion (6b) of the carcass, and an middle portion (8c) connecting the inner portion (8a) and the outer portion (8b), for example. The outer portion (8b) has an outermost end (8e) in the tire radial direction of the chafer <NUM>, for example. The outer portion (8b) separates the sidewall rubber <NUM> and the clinch rubber <NUM> in the present embodiment.

The outermost end (8e) of the chafer <NUM> is located radially outside the outermost end (5e) of the bead core <NUM> in the present embodiment. The outermost end (8e) of the chafer <NUM> is located radially inside the outermost end (6e) of the turned up portion (6b), for example. The outermost end (8e) of the chafer <NUM> is located within the range T1 in the present embodiment. Thereby, the mating pressure with the rim is maintained high.

The clinch rubber <NUM> is located between the carcass <NUM> and the chafer <NUM>, for example. The clinch rubber <NUM> includes a first portion (11a) arranged between the main body portion (6a) of the carcass <NUM> and the inner portion (8a), a second portion (11b) arranged between the turned up portion (6b) of the carcass <NUM> and the outer portion (8b), and a third portion (11c) connecting the first portion (11a) and the second portion (11b). The clinch rubber <NUM> has an outermost end (11e) in the tire radial direction located in the second portion (11b), for example. The outermost end (11e) of the clinch rubber <NUM> is located in the range T1 (shown in <FIG>) in the present embodiment.

While detailed description has been made of an especially preferred embodiment of the present invention, the present invention can be embodied in various forms as claimed.

Motorcycle tires having the basic structure shown in <FIG> were made by way of test according to the specification listed in table <NUM>. The test tires were mounted on the front wheel of a motorcycle and a test driver drove the motorcycle. The sense of firmness, the ground contacting feel, and the absorbency during driving were evaluated by the sensory perception of the test driver. The specifications of the rear tires are common. The test results are indicated by an evaluation point based on Reference <NUM> being <NUM>, wherein a larger number is better. The main common items are as follows.

Claim 1:
A motorcycle tire (<NUM>) comprising:
a tread portion (<NUM>) having a pair of tread edges (Te);
a pair of sidewall portions (<NUM>) each extending inward in a tire radial direction from a respective one of the tread edges (Te);
a pair of bead portions (<NUM>) each arranged radially inside a respective one of the sidewall portions (<NUM>); and
a carcass (<NUM>) extending from one bead portion (<NUM>) to the other bead portion (<NUM>) in a toroidal manner, wherein
each of the sidewall portions (<NUM>) has a sidewall rubber (<NUM>) arranged outside the carcass in a tire axial direction,
characterized in that
a minimum thickness (Ts) of each of the sidewall portions (<NUM>) is <NUM>% or less of a minimum tire thickness (Ta) from a respective one of the tread edges (Te) to a tire inner cavity surface (2b), and
a minimum thickness (Ds) of the sidewall rubber (<NUM>) is from <NUM> to <NUM>,
the tread portion (<NUM>) includes a tread rubber (<NUM>) forming a ground contacting surface (2a),
each of the sidewall rubber (<NUM>) and the tread rubber (<NUM>) contains an anti-aging agent, and
a blending amount of the anti-aging agent per unit mass of the sidewall rubber (<NUM>) is greater than a blending amount of the anti-aging agent per unit mass of the tread rubber (<NUM>).