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

The Patent document <NUM> below discloses a motorcycle bias tyre. The tyre includes a bias carcass having carcass cords which are inclined with respect to the tyre circumferential direction and a band layer disposed on the carcass in the tread portion. The tyre has been expected to reduce the tyre weight and improve steering stability by the carcass ply and the band layer.

A motorcycle tyre in accordance with the preamble of claim <NUM> is known from <CIT>. Related tyres are known from <CIT>, <CIT> and <CIT>.

Motorcycle tyres including the carcass with a bias structure as described above tend to have a small camber thrust when turning at a relatively large camber angle. Thus, improvement in turning performance has been required.

The present invention has been made in view of the above circumstances and has a major object to provide a motorcycle tyre having a bias carcass capable of exhibiting superior turning performance. The object is achieved by a motorcycle tyre having the features of claim <NUM>. Sub-claims are directed to preferable embodiments.

In one aspect of the present invention, a motorcycle tyre includes a tread portion between a pair of tread edges, a pair of sidewall portions, a pair of bead portions, and a carcass having a bias structure and extending between the pair of bead portions. The tread portion, when a tread development width between the pair of tread edges of the tread portion is equally divided into five regions, includes a central crown region, a pair of shoulder regions including the pair of tread edges and a pair of middle regions located between the crown region and each of the shoulder regions. The carcass includes a plurality of carcass cords, and an angle θs with respect to a tyre circumferential direction of at least one of the plurality of carcass cords in the shoulder regions is greater than an angle θc with respect to the tyre circumferential direction of at least one of the plurality of carcass cords in the crown region. The tread portion is provided with a band layer extending in the crown region, the pair of middle regions and the pair of shoulder regions, wherein the band layer comprises a band ply having band cords oriented at an angle equal to or less than <NUM> degrees with respect to the tyre circumferential direction, and ends Em of the band cords in the middle regions is greater than ends Ec of the band cords in the crown region. Ends Es of the band cords of the band ply in each of the pair of shoulder regions are smaller than the ends Em.

According to a preferable embodiment of the present invention, in the crown region, the pair of middle regions and the pair of shoulder regions, an angle with respect to the tyre circumferential direction of the plurality of carcass cords is in a range of <NUM> to <NUM> degrees.

According to a preferable embodiment of the present invention, the angle θc is in a range of <NUM> to <NUM> times of the angle θs.

According to a preferable embodiment of the present invention, the ends Ec are in a range of from <NUM> to <NUM> times of the ends Em.

According to a preferable embodiment of the present invention, the ends Es are in a range of from <NUM> to <NUM> times of the ends Em.

According to a preferable embodiment of the present invention, a value θc*Ec/Em obtained by multiplying the angle θc by a ratio of the ends Ec to the ends Em is in a range of <NUM> to <NUM>.

According to a preferable embodiment of the present invention, a value θs*Es/Em obtained by multiplying the angle θs by a ratio of ends Es of the band cords of the band ply in each of the pair of shoulder regions to the ends Em is in a range of <NUM> to <NUM>.

According to a preferable embodiment of the present invention, the band ply comprises a jointless band ply having the band cords wound spirally.

<FIG> is a cross-sectional view including the tyre axis of a motorcycle tyre <NUM> (hereafter, simply referred to as "tyre") under a normal state in accordance with an embodiment of the present invention. The tyre <NUM> according to the present embodiment is a tyre for front wheel of motorcycle suitable for on-road sport driving. However, the tyre according to the present invention is not limited to a tyre for a front wheel of a motorcycle for on-road sport driving.

As used herein, when a motorcycle tyre is based on a standard, "normal state" is such that the tyre <NUM> is mounted onto a standard wheel rim with a standard pressure but loaded with no tyre load. As used herein, when a motorcycle tyre is not based on any standards, "normal state" means a standard usage state according to the purpose of use of the tyre, where the tyre is not mounted to a vehicle and loaded with no tyre load. As used herein, unless otherwise noted, dimensions of portions of the tyre <NUM> are values measured under the normal state.

As used herein, the "standard pressure" is a standard pressure officially approved for each tyre by standards organizations on which the tyre is based, wherein the standard pressure is the "maximum air pressure" in JATMA, the maximum pressure given in the "Tire Load Limits at Various Cold Inflation Pressures" table in TRA, and the "Inflation Pressure" in ETRTO, for example.

As illustrated in <FIG>, the tyre <NUM> according to the present embodiment includes a tread portion <NUM> between a pair of tread edges Te, a pair of sidewall portions <NUM>, and a pair of bead portions <NUM>. The tread portion <NUM> includes an outer surface <NUM> between the pair of tread edges Te. The outer surface <NUM> is curved in an arc-shaped manner protruding outwardly in the tyre radial direction so that a sufficient grounding area can be maintained even when turning with a large camber angle. Note that the pair of tread edges Te corresponds to the axially both edges of the ground contacting surface of the tread portion <NUM> when turning at the maximum camber angle.

The tread portion <NUM> includes a crown region Cr, a pair of shoulder regions Sh and a pair of middle regions Mi. The crown region Cr is the central region when the tread development width TWe between the pair of tread ends Te is equally divided into five regions in the tyre axial direction. The pair of shoulder regions Sh includes the pair of tread edges Te, and is the pair of regions on both sides of the tread portion <NUM> in the tyre axial direction when equally divided into the five regions. The pair of middle regions Mi is located between the crown region Cr and each of the shoulder regions Sh. The boundaries <NUM> of the regions extend so as to divide the tread development width TWe into five regions equally when the tread portion <NUM> is developed in a plane. On the other hand, in the tyre meridian cross-sectional view, the boundaries <NUM> extend in the normal direction of the tread portion <NUM> with respect to the outer surface <NUM>.

In addition, the tyre <NUM> according to the present embodiment includes a toroidal carcass <NUM>. The carcass <NUM> extends between the pair of bead portions <NUM> through the pair of sidewall portions <NUM> and the tread portion <NUM>. The carcass <NUM> includes at least one carcass ply having a plurality of carcass cords coated with a topping rubber. The carcass <NUM> according to the present invention has a bias structure in which the carcass cords are obliquely with respect to the tyre circumferential direction. The carcass cords, for example, are made of an organic fiber cord.

The carcass <NUM> according to the present embodiment, for example, includes a first carcass ply <NUM> and a second carcass ply <NUM> which are superimposed with each other. In the present embodiment, the first carcass ply <NUM> is located inwardly in the tyre radial direction with respect to the second carcass ply <NUM> in the tread portion <NUM>. In addition, the carcass <NUM> according to the present embodiment includes a main portion 6a and a pair of turn-up portions 6b. The main portion 6a extends between a pair of bead cores <NUM> of the pair of bead portions <NUM>, through the tread portion <NUM> and the sidewall portions <NUM>. Each of the turn-up portions 6b is connected to the main portion 6a and is turned up around a respective one of the bead cores <NUM> so as to extend outwardly in the tyre radial direction.

<FIG> illustrates a development view of the first carcass ply <NUM> and the second carcass ply <NUM>, and <FIG> illustrates a development view of the first carcass ply <NUM> to show an arrangement of the carcass cords <NUM>. As illustrated in <FIG> and <FIG>, in the present embodiment, the carcass cords <NUM> of the first carcass ply <NUM> are inclined in the first direction (upward to the right in each Figure of the embodiment) with respect to the tyre axial direction, and the carcass cords <NUM> of the second carcass ply <NUM> are inclined in the second direction opposite to the first direction (downward to the right in each Figure of the embodiment) with respect to the tyre axial direction. Thus, the first carcass ply <NUM> and the second carcass ply <NUM> are superimposed such that the carcass cords <NUM> cross with each other.

As illustrated in <FIG>, an angle θs with respect to the tyre circumferential direction of at least one of the plurality of carcass cords <NUM> in the shoulder regions Sh is greater than an angle θc with respect to the tyre circumferential direction of at least one of the plurality of carcass cords <NUM> in the crown region Cr. By adopting the above configuration, the tyre <NUM> according to the present invention can exhibit excellent turning performance. The reason for this is considered to be the following mechanism.

The arrangement of the above-mentioned the carcass cords <NUM> can enhance rigidity in the tyre axial direction of the shoulder regions Sh. Thus, in a process of grounding from the crown region Cr to either one of the shoulder regions Sh when turning, the camber thrust and cornering force can increase gradually and when either one of the shoulder regions Sh comes into contact with the ground, a sufficiently large camber thrust and cornering force can be obtained. On the other hand, the above-mentioned small angle of the carcass cords in the crown region Cr can enhance rigidity in the tyre circumferential direction of the crown region Cr, maintaining braking performance. In the present invention, it is considered that excellent turning performance can be exhibited by the above mechanism.

Hereinafter, a more detailed configuration of the present embodiment will be described. Note that each configuration described below shows a specific aspect of the present embodiment. Thus, the present invention can exert the above-mentioned effects even if the tyre does not include the configuration described below. Further, if any one of the configurations described below is applied independently to the tyre of the present invention having the above-mentioned characteristics, the performance improvement according to each additional configuration can be expected. Furthermore, when some of the configurations described below are applied in combination, it is expected that the performance of the additional configurations will be improved.

As illustrated in <FIG>, in the crown region Cr, the middle regions Mi and the shoulder regions Sh, an angle with respect to the tyre circumferential direction of the carcass cords <NUM> is preferably in a range of from <NUM> to <NUM> degrees.

In the crown region Cr, an angle θc with respect to the tyre circumferential direction of the carcass cords <NUM>, for example, is in a range of from <NUM> to <NUM> degrees, preferably <NUM> to <NUM> degrees. In addition, in the middle regions Mi, an angle θm with respect to the tyre circumferential direction of the carcass cords <NUM>, for example, is in a range of <NUM> to <NUM> degrees, preferably <NUM> to <NUM> degrees. In the shoulder regions Sh, an angle θs with respect to the tyre circumferential direction of the carcass cords <NUM>, for example, is in a range of <NUM> to <NUM> degrees, preferably <NUM> to <NUM> degrees. Note that the present invention is not limited to such angles.

Preferably, the angles with respect to the tyre circumferential direction of the carcass cords <NUM> in the respective regions satisfy the relation of the following equation (<NUM>).

In addition, it is preferable that an angle of the carcass cords <NUM> increases continuously from the crown region Cr side toward each shoulder region Sh side. As a result, the response when a motorcycle body is leaned becomes linear, and handling performance can be improved.

The angle θc of the carcass cords <NUM> in the crown region Cr is preferably equal to or more than <NUM> times of the angle θs of the carcass cords <NUM> in the shoulder regions Sh, more preferably equal to or more than <NUM> times, but preferably equal to or less than <NUM> times, more preferably equal to or less than <NUM> times. Such an arrangement of the carcass cords <NUM> can improve turning performance of the tyre while preventing the leaning response from becoming heavy.

The angle θm of the carcass cords <NUM> in the middle regions Mi is preferably equal to or more than <NUM> times of the angle θs of the carcass cords <NUM> in the shoulder regions Sh, more preferably equal to or more than <NUM> times, but preferably equal to or less than <NUM> times, more preferably equal to or less than <NUM> times. Such an arrangement of the carcass cords <NUM> can provide excellent handling performance when turning at a relatively large camber angle where one of the middle regions Mi and the shoulder region Sh adjacent thereto come into contact with the ground.

Note that the arrangements of the carcass cords <NUM> described above are applied not only to the carcass cords <NUM> of the first carcass ply <NUM> shown in <FIG> but also to the carcass cords of the second carcass ply <NUM>. Further, the angles of the carcass cords <NUM> in the above respective regions correspond to angles which are measured at the center position in the tyre axial direction of the respective regions.

As illustrated in <FIG>, the tread portion <NUM> according to the present embodiment further includes a band layer <NUM> extending in the crown region Cr, the pair of middle regions Mi and the pair of shoulder regions Sh. The band layer <NUM> includes a band ply <NUM> having band cords oriented at an angle equal to or less than <NUM> degrees with respect to the tyre circumferential direction. In some more preferred embodiment, the band ply <NUM> according to the present embodiment is configured as a jointless band ply that has one or more band cord wound spirally.

<FIG> is a development view of the band ply <NUM>. In the present embodiment, ends of the band cords <NUM> of the band ply <NUM> (the number of cords arranged per <NUM> of the ply width in a tyre cross-sectional view) are different for each region. This is expected to improve various performances.

Specifically, ends Ec of the band cords in the crown region Cr, for example, are in a range of from <NUM> to <NUM>, preferably <NUM> to <NUM>. Ends Em of the band cords in each middle region Mi, for example, are in a range of from <NUM> to <NUM>, preferably <NUM> to <NUM>. Ends Es of the band cords in each shoulder region Sh, for example, are in a range of from <NUM> to <NUM>, preferably <NUM> to <NUM>.

The ends Em of the band cords <NUM> in each middle region Mi are greater than the ends Ec of the band cords <NUM> in the crown region Cr. Specifically, the ends Ec in the crown region Cr are preferably equal to or more than <NUM> times the ends Em in the middle regions Mi, more preferably equal to or more than <NUM> times, but preferably equal to or less than <NUM> times, more preferably equal to or less than <NUM> times.

The ends Es of the band cords <NUM> in each shoulder regions Sh are smaller than the ends Em of the band cords <NUM> in each middle region Mi. Specifically, the ends Es in each shoulder region Sh are preferably equal to or more than <NUM> times the ends Em in the middle regions Mi, more preferably equal to or more than <NUM> times, but preferably equal to or less than <NUM> times, more preferably equal to or less than <NUM> times. Such an arrangement of the band cords <NUM> can relatively relax rigidity in the tyre circumferential direction of the shoulder regions Sh and increase an area of the contact patch of the shoulder regions Sh, so that grip performance of the tyre during turning can be improved.

As a result of various experiments, the inventor has found that the overall performance of the tyre, such as the response when leaning a motorcycle, steering stability and turning performance can be improved by associating an angle of the carcass cords <NUM> with respect to the ends of the band cords <NUM>.

Specifically, a value θc*Ec/Em obtained by multiplying the angle θc (shown in <FIG>) of the carcass cords <NUM> in the crown region Cr by a ratio of the ends Ec of the band cords <NUM> in the crown region to the ends Em of the band cords <NUM> in each middle region Mi is preferably equal to or more than <NUM>, more preferably equal to or more than <NUM>, but preferably equal to or less than <NUM>, more preferably equal to or less than <NUM>. Such an arrangement of the carcass cords <NUM> and the band cord <NUM> can improve wear resistance, grip performance and turning performance in a well-balanced manner while maintaining steering stability in a turning condition where the camber angle is relatively small.

From a similar point of view, a value θs*Es/Em obtained by multiplying the angle θs (shown in <FIG>) of the carcass cords <NUM> in each shoulder region Sh by a ratio of the ends Es of the band cords <NUM> in each shoulder region Sh to the ends Em of the band cords <NUM> in each middle region Mi is preferably equal to or more than <NUM>, more preferably equal to or more than <NUM>, but preferably equal to or less than <NUM>, more preferably equal to or less than <NUM>. Such an arrangement of the carcass cords <NUM> and the band cord <NUM> can improve wear resistance, grip performance and turning performance in a well-balanced manner while maintaining steering stability in a turning condition with a relatively large camber angle.

While the motorcycle tyre of an embodiment of the present invention has been described in detail above, the present invention is not limited to the above-mentioned specific embodiment, and can be embodied by modifying to various aspects within the scope of the appended claims.

Motorcycle tyres (for front wheel tyre) with a nominal width of <NUM>, an aspect ratio of <NUM>%, and a rim diameter of <NUM> inches, which have the basic structure of <FIG> were manufactured based on the specifications in Tables <NUM> to <NUM>. In addition, as a comparative example, a tyre was prototyped in which the angle of the carcass cords with respect to the tyre circumferential direction was constant over the crown region, the middle regions and the shoulder regions. Note that the comparative example tyre is practically the same as the tyres of the examples, except for the above structure. Then, turning performance, grip performance, steering stability and wear resistance of each test tyre were tested. The common specifications and test methods of each test tyre are as follows.

Turning performance, grip performance and steering stability test:
The above test motorcycle ran a test course on a dry asphalt road surface, and each performance was evaluated. "Turning performance" refers to the overall turning performance from upright to full bank. "Grip performance" refers to the overall grip performance over the entire driving range. "Steering stability" refers to overall steering stability, including handling performance over the entire driving range. The test results are shown with a maximum score of <NUM> points, and the larger the value, the better each evaluation performance.

After traveling <NUM>,<NUM> on a general road with the above test motorcycle, the remaining amount of tread rubber was measured. The test results are shown an index with the remaining amount of the comparative example as <NUM>, and the larger the value, the more the remaining amount of tread rubber, more excellent wear resistance.

The test results are shown in Tables <NUM> to <NUM>.

Claim 1:
A motorcycle tyre (<NUM>) comprising:
a tread portion (<NUM>) between a pair of tread edges;
a pair of sidewall portions (<NUM>);
a pair of bead portions (<NUM>); and
a carcass (<NUM>) having a bias structure and extending between the pair of bead portions (<NUM>), wherein
the tread portion (<NUM>), when a tread development width (TWe) between the pair of tread edges (Te) of the tread portion (<NUM>) is equally divided into five regions, comprises a central crown region (Cr), a pair of shoulder regions (Sh) including the pair of tread edges (Te) and a pair of middle regions (Mi) located between the crown region (Cr) and each of the shoulder regions (Sh), and
the carcass (<NUM>) comprises a plurality of carcass cords (<NUM>), and
an angle θs with respect to a tyre circumferential direction of at least one of the plurality of carcass cords (<NUM>) in the shoulder regions (Sh) is greater than an angle θc with respect to the tyre circumferential direction of at least one of the plurality of carcass cords (<NUM>) in the crown region (Cr),
characterized in that
the tread portion (<NUM>) is provided with a band layer (<NUM>) extending in the crown region (Cr), the pair of middle regions (Mi) and the pair of shoulder regions (Sh),
the band layer (<NUM>) comprises a band ply (<NUM>) having band cords (<NUM>) oriented at an angle equal to or less than <NUM> degrees with respect to the tyre circumferential direction,
ends Em of the band cords (<NUM>) in the middle regions (Mi) is greater than ends Ec of the band cords (<NUM>) in the crown region (Cr), and
ends Es of the band cords (<NUM>) of the band ply (<NUM>) in each of the pair of shoulder regions (Sh) are smaller than the ends Em.