Patent Description:
Conventionally, bias tyres for two-wheel vehicle including a bias carcass structure are known. For example, <CIT> discloses a bias tyre for motorcycle that achieves both weight reduction and steering stability by specifying an inclination angle of the carcass line.

<CIT> discloses a motorcycle tire having a hybrid construction with different rubber compound zones. <CIT> discloses a tire for motorcycles having a wing rubber that forms a buttress surface and connects to a tread part of the tire. <CIT> discloses a motorcycle tire for uneven terrain having a tread and sidewalls formed from crosslinked rubber.

However, the bias tyre for motorcycle disclosed in <CIT> has room for further improvement in steering stability during turning because the tyre employs a single rubber component that extends between sidewall portions through the tread portion.

The present invention has been made in view of the above circumstances and has a major object to provide a bias tyre for two-wheel vehicle capable of improving steering stability during turning.

The problem is solved by a bias tyre having the features of claim <NUM>.

In the bias tyre for two-wheel vehicle, the tread rubber is connected to the sidewall rubber portions to form the boundary surfaces, and the outermost ends in the tyre axial direction of the boundary surfaces are located on an outer surface of the tyre and inwardly in the tyre radial direction of the respective tread edges. Such a bias tyre for two-wheel vehicle using the tread rubber and the sidewall rubber portions, can improve steering stability during turning.

An embodiment of the present invention will be explained below with reference to the accompanying drawings. <FIG> is a tyre meridian cross-sectional view of a bias tyre <NUM> for two-wheel vehicle (hereinafter, simply referred to as "tyre <NUM>") under a normal state according to the first embodiment.

As used herein, the "normal state" is such that the tyre <NUM> is mounted on a standard wheel rim with a standard pressure but 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.

Further, as used herein, the "standard wheel rim" is a wheel rim officially approved for each tyre <NUM> by standards organizations on which the tyre is based, wherein the standard wheel rim is the "standard rim" specified in JATMA, the "Design Rim" in TRA, and the "Measuring Rim" in ETRTO, for example.

Furthermore, as used herein, the "standard pressure" is a standard pressure officially approved for each tyre <NUM> 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 first embodiment includes a tread portion <NUM>, a pair of sidewall portions <NUM> extending inwardly in the tyre radial direction from both ends of the tread portion <NUM>, and a pair of bead portions <NUM> provided inwardly in the tyre radial direction of the pair of sidewall portions <NUM>. A pair of bead cores <NUM> is disposed in the pair of bead portions <NUM>, for example.

The tread surface <NUM> which is an outer surface of the tread portion <NUM>, for example, extends between tread edges Te through the tyre equator C in an arc shape that is convex outwardly in the tyre radial direction. Preferably, the tread width Wt which is a length in the tyre axial direction between the tread edges Te corresponds to the tyre maximum width.

Such a tyre <NUM> can turn with large camber angles. As used herein, the tread edges Te are outermost edges of the tread portion <NUM> in the tyre axial direction, and the tyre equator C is the center location between the tread edges Te in the tyre axial direction.

The tyre <NUM> according to the first embodiment further includes a carcass <NUM> having a bias structure that extends between the bead cores <NUM> of the bead portions <NUM> through the tread portion <NUM> and the sidewall portions <NUM>. The carcass <NUM> includes a main portion 6a extending between the pair of bead cores <NUM>, and a pair of turn-up portions 6b each turned up around a respective one of the pair of bead cores <NUM>.

The carcass <NUM> having a bias structure includes at least one carcass ply. In the first embodiment, the carcass <NUM> includes two carcass plies 6A and 6B. The carcass plies 6A and 6B, for example, include carcass cords that are oriented at an angle of from <NUM> to <NUM> degrees with respect to the tyre equator C. Preferably, the carcass plies 6A and 6B are superimposed such that the carcass cords cross with one another between the plies 6A and 6B.

The tyre <NUM> according to the first embodiment further includes a tread rubber <NUM> forming the tread portion <NUM>, and a pair of the sidewall rubber portions <NUM> forming the pair of sidewall portions <NUM>. In the first embodiment, the tread rubber <NUM> is connected to the sidewall rubber portions <NUM> to form boundary surfaces <NUM>. That is, the tread rubber <NUM> and the sidewall rubber portions <NUM> according to the first embodiment are made of different rubbers with one another. In the first embodiment, outer end portions 7a in the tyre axial direction of the tread rubber <NUM> are connected to the sidewall rubber portions <NUM> via the boundary surfaces <NUM>.

In such a tyre <NUM>, a rubber that has superior grip performance can be employed as the tread rubber <NUM>, and a rubber that has superior absorbing performance can be employed as the sidewall rubber portions <NUM>. Thus, the tyre <NUM> according to the first embodiment can improve steering stability during turning.

In the first embodiment, outermost ends 9a in the tyre axial direction of the boundary surfaces <NUM> are located on an outer surface of the tyre and inwardly in the tyre radial direction of the respective tread edges Te. When such a tyre <NUM> turns at large camber angles, the tread rubber <NUM> always comes into contact with the ground and there is no risk that the sidewall rubber portions <NUM> come into contact with the ground. Hence, in the tyre <NUM> according to the first embodiment, grip performance does not change suddenly since the sidewall rubber portions <NUM> do not come into contact with the ground during turning, and therefore steering stability performance can be improved.

Preferably, a distance L1 in the tyre radial direction between the outermost ends 9a of the pair of boundary surfaces <NUM> and the tread edges Te is equal to or less than <NUM>. When the distance L1 is <NUM> or less, the outermost ends 9a of the boundary surfaces <NUM> can be located on an outer surface of the tyre <NUM> with less distortion during turning, and thus durability performance of the tyre <NUM> can be improved. From this point of view, the distance L1 is more preferably <NUM> or less.

A height Ho in the tyre radial direction from a bead baseline BL to the outermost ends 9a of the pair of boundary surfaces <NUM> is preferably equal to or more than <NUM>%, more preferably equal to or more than <NUM>% of a height HS in the tyre radial direction from the bead baseline BL to the pair of tread edges Te. In such a tyre <NUM>, the outermost ends 9a of the boundary surfaces <NUM> can be located on a region where less distortion occurs during turning of the outer surface of the tyre <NUM>, and thus durability performance of the tyre <NUM> can be improved. Note that the bead baseline BL is an axial line that corresponds to a location of a rim diameter of the standard wheel rim on which the tyre <NUM> is to be mounted.

The height Ho of the outermost ends 9a of the boundary surfaces <NUM> is preferably equal to or less than <NUM>%, more preferably equal to or less than <NUM>% of the height HS of the tread edges Te. When such a tyre <NUM> turns at large camber angles, there is no risk that the sidewall rubber portions <NUM> come into contact with the ground, and therefore steering stability performance can be improved.

In the first embodiment, innermost ends 9b in the tyre axial direction of the boundary surfaces <NUM> are located outwardly in the tyre radial direction of the outermost ends 9a of the boundary surfaces <NUM>. In such a tyre <NUM>, even if repeated load is applied near the boundary surfaces <NUM>, the risk of cracking along the boundary surfaces <NUM> can be small, and thus durability can be improved.

Preferably, a distance L2 between the innermost end 9b and the outermost end 9a of each boundary surface <NUM> in the tyre radial direction is equal to or less than <NUM>. When the distance L2 is equal to or less than <NUM>, the outermost ends 9a of the boundary surfaces <NUM> can be located on a region where less distortion occurs during turning of the outer surface of the tyre <NUM>, and thus durability performance of the tyre <NUM> can be improved. From this point of view, the distance L2 is more preferably equal to or less than <NUM>.

In the first embodiment, the innermost ends 9b in the tyre axial direction of the boundary surfaces <NUM> are located outwardly in the tyre axial direction of the tread edges Te. In such a tyre <NUM>, even if repeated load is applied near the boundary surfaces <NUM>, the risk of cracking along the boundary surfaces <NUM> can be small, and thus durability can be improved.

The height Hi in the tyre radial direction of the innermost ends 9b of the boundary surfaces <NUM> from the bead baseline BL is preferably equal to or more than <NUM>%, more preferably equal to or more than <NUM>% of the height HS of the tread edges Te. Such a tyre <NUM> can reduce the risk that crack occurs along the boundary surfaces <NUM>, and thus durability of the tyre can be improved.

The height Hi of the innermost ends 9b of the boundary surfaces <NUM> is preferably equal to or less than <NUM>%, more preferably equal to or less than <NUM>% of the height HS of the tread edges Te. In such a tyre <NUM>, the outermost ends 9a of the boundary surfaces <NUM> can be located on a region where less distortion occurs during turning of the outer surface of the tyre <NUM>, and thus durability performance of the tyre <NUM> can be improved.

In the first embodiment, the boundary surfaces <NUM> are curved so as to be convex inwardly in the tyre radial direction. Since the ratio of the sidewall rubber portions <NUM> in the vicinity of the outer end portions 7a of the tread rubber <NUM> is small in such the boundary surfaces <NUM>, it is possible to improve steering stability of the tyre <NUM> when turning at large camber angles.

The bias tyre <NUM>, for example, may include a reinforcing layer <NUM> disposed outside in the tyre radial direction of the carcass <NUM> in the tread portion <NUM>. The reinforcing layer <NUM> include one or more reinforcing plies 10A. In the first embodiment, one reinforcing ply 10A is employed. In this case, the innermost ends 9b of the boundary surfaces <NUM> are located on the reinforcing layer <NUM>. Such a tyre <NUM> can suppress deformation during high-speed driving and improve high-speed durability performance.

In the first embodiment, loss tangent tan δS of the sidewall rubber portions <NUM> at <NUM> degrees C is smaller than loss tangent tan δT of the tread rubber <NUM> at <NUM> degrees C. Such sidewall rubber portions <NUM> have excellent absorption performance and can improve riding comfort of the tyre <NUM>. As used herein, loss tangent tan δ at <NUM> degrees C is measured using a "viscoelastic spectrometer" in accordance with JIS-K6394 under the following condition:.

The sidewall rubber portions <NUM> contain preferably <NUM> parts by mass or more, more preferably <NUM> parts by mass or more of natural rubber in <NUM> parts by mass of the rubber component thereof. Such sidewall rubber portions <NUM> can suppress the occurrence of cracks and improve durability performance of the tyre <NUM>.

<FIG> is a tyre meridian cross-sectional view of a bias tyre <NUM> for two-wheel vehicle (hereinafter, simply referred to as "tyre <NUM>") under the normal state according to the second embodiment. Note that elements having the same function as the above-described embodiment are denoted by the same reference numerals, and the description thereof may be omitted.

As illustrated in <FIG>, in the second embodiment, the bias tyre <NUM> includes the tread portion <NUM>, the pair of the sidewall portions <NUM> extending inwardly in the tyre radial direction from the both ends of the tread portion <NUM>, and the pair of bead portions <NUM> provided inwardly in the tyre radial direction of the pair of sidewall portions <NUM>. The pair of bead cores <NUM> is disposed in the pair of bead portions <NUM>, for example. The tyre <NUM>, the same as the above-mentioned tyre <NUM>, preferably includes the carcass <NUM> having a bias structure and the reinforcing layer <NUM> disposed outside in the tyre radial direction of the carcass <NUM> in the tread portion <NUM>.

In the second embodiment, the tyre <NUM> includes the tread rubber <NUM> forming the tread portion <NUM>, and the pair of sidewall rubber portions <NUM> forming the pair of sidewall portions <NUM>. In the second embodiment, the both end portions 7a of the tread rubber <NUM> are connected to the respective sidewall rubber portions <NUM> to form a pair of boundary surfaces <NUM> therebetween.

In the second embodiment, outermost ends 12a in the tyre axial direction of the boundary surfaces <NUM> are located on an outer surface of the tyre and inwardly in the tyre radial direction of the respective tread edges Te. When such a tyre <NUM> turns at large camber angles, the tread rubber <NUM> always comes into contact with the ground and there is no risk that the sidewall rubber portions <NUM> come into contact with the ground. Hence, in the tyre <NUM> according to the second embodiment, grip performance does not change suddenly since the sidewall rubber portions <NUM> do not come into contact with the ground during turning, and therefore steering stability performance can be improved.

In the second embodiment, innermost ends 12b in the tyre axial direction of the boundary surfaces <NUM> are located outwardly in the tyre radial direction of the outermost ends 12a of the boundary surfaces <NUM>. In the second embodiment, the innermost ends 12b of the boundary surfaces <NUM> are located outwardly in the tyre radial direction of the tread edges Te. In such a tyre <NUM>, even if repeated load is applied near the boundary surfaces <NUM>, the risk of cracking along the boundary surfaces <NUM> can be small, and thus durability can be improved.

In the second embodiment, the boundary surfaces <NUM> are curved so as to be convex outwardly in the tyre radial direction. Since the ratio of the sidewall rubber portions <NUM> in the vicinity of the outer end portions 7a of the tread rubber <NUM> is large in such the boundary surfaces <NUM>, it is possible to improve steering stability of the tyre <NUM> when turning at large camber angles.

<FIG> is a tyre meridian cross-sectional view of a bias tyre <NUM> for two-wheel vehicle (hereinafter, simply referred to as "tyre <NUM>") under the normal state and not covered by the present invention. Note that elements having the same function as the above-described embodiment are denoted by the same reference numerals, and the description thereof may be omitted.

As illustrated in <FIG>, the tyre <NUM> includes the tread portion <NUM>, the pair of the sidewall portions <NUM> extending inwardly in the tyre radial direction from the both ends of the tread portion <NUM>, and the pair of bead portions <NUM> provided inwardly in the tyre radial direction of the pair of sidewall portions <NUM>. The pair of bead cores <NUM> is disposed in the pair of bead portions <NUM>, for example. The tyre <NUM>, the same as the above-mentioned tyre <NUM>, preferably includes the carcass <NUM> having a bias structure and the reinforcing layer <NUM> disposed outside in the tyre radial direction of the carcass <NUM> in the tread portion <NUM>.

The tyre <NUM> includes the tread rubber <NUM> forming the tread surface <NUM> of the tread portion <NUM>, and a toroidal rubber <NUM> disposed inwardly in the tyre radial direction of the tread rubber <NUM>. In <FIG>, the toroidal rubber <NUM> includes the pair of sidewall rubber portions 22a forming an outer surface of the pair of sidewall portions <NUM> and a connecting rubber portion 22b extending inward of the tread rubber <NUM> and connecting the pair of sidewall rubber portions 22a with each other. The tread rubber <NUM> is connected to the toroidal rubber to form a boundary surface <NUM> including a pair of axially outer boundary surfaces 23b. That is, the tread rubber <NUM> and the toroidal rubber <NUM> are made of different rubbers with one another.

In such a tyre <NUM>, a rubber that has superior grip performance can be employed as the tread rubber <NUM>, and a rubber that has superior absorbing performance can be employed as the toroidal rubber <NUM> including the sidewall rubber portions 22a. Thus, the tyre <NUM> can improve steering stability during turning.

In such a tyre <NUM>, heat generation due to distortion of the tread rubber <NUM> during high-speed running is suppressed by the presence of connecting rubber portion 22b between the tread rubber <NUM> and the carcass <NUM>, and durability performance during high-speed running can be improved. In addition, since energy loss of the tread portion <NUM> of the tyre <NUM> is reduced, rolling resistance can be reduced and fuel efficiency can be improved.

In <FIG>, outermost ends 23a in the tyre axial direction of the boundary surface <NUM> are located on an outer surface of the tyre and inwardly in the tyre radial direction of the respective tread edges Te. When such a tyre <NUM>, the same as the above-mentioned tyre <NUM>, turns at large camber angles, the tread rubber <NUM> always comes into contact with the ground and there is no risk that the sidewall rubber portions 22a come into contact with the ground. Hence, in the tyre <NUM>, grip performance does not change suddenly since the sidewall rubber portions 22a do not come into contact with the ground during turning, and therefore steering stability performance can be improved.

Preferably, a distance L3 in the tyre radial direction between the outermost ends 23a of the boundary surface <NUM> and the tread edges Te is equal to or less than <NUM>. When the distance L3 is <NUM> or less, the outermost ends 23a of the boundary surface <NUM> can be located on an outer surface of the tyre <NUM> with less distortion during turning, and thus durability performance of the tyre <NUM> can be improved. From this point of view, the distance L3 is more preferably <NUM> or less.

A height H in the tyre radial direction from a bead baseline BL to the outermost ends 23a of the boundary surface <NUM> is preferably equal to or more than <NUM>%, more preferably equal to or more than <NUM>% of the height HS in the tyre radial direction from the bead baseline BL to the pair of tread edges Te. In such a tyre <NUM>, the outermost ends 23a of the boundary surface <NUM> can be located on a region where less distortion occurs during turning of the outer surface of the tyre <NUM>, and thus durability performance of the tyre <NUM> can be improved. Note that the bead baseline BL is an axial line that corresponds to a location of a rim diameter of the standard wheel rim on which the tyre <NUM> is to be mounted.

The height H of the outermost ends 23a of the boundary surface <NUM> is preferably equal to or less than <NUM>%, more preferably equal to or less than <NUM>% of the height HS of the tread edges Te. When such a tyre <NUM> turns at large camber angles, there is no risk that the sidewall rubber portions 22a come into contact with the ground, and therefore steering stability performance of the tyre <NUM> can be improved.

<FIG> is a development view of the tread portion <NUM> of the tyre <NUM> shown in <FIG> is a cross-sectional view taken along line A-A of <FIG>. As illustrated in <FIG> and <FIG>, the tread portion <NUM> is provided with a plurality of grooves <NUM>. The pattern and/or shape of the grooves <NUM> is not limited to those shown in <FIG> but can include one or more circumferential grooves extending continuously in the tyre circumferential direction, for example.

Some of the grooves <NUM> have a plurality of slip signs <NUM> for indicating wear condition of the tread portion <NUM>. Here, the slip signs <NUM> are portions protruding outward in the tyre radial direction from the groove bottoms of the grooves <NUM>. When the tread portion <NUM> is worn and one or more slip signs <NUM> are exposed on the tread surface <NUM>, users can know that it is time to replace the tyre.

As illustrated in <FIG>, the connecting rubber portion 22b is located inwardly in the tyre radial direction of an outer surface <NUM> of the slip sign <NUM> that is located nearest to the tyre equator C. Such a connecting rubber portion 22b is unlikely to be exposed to the tread surface <NUM> even if the area around the tyre equator C wears to the slip sign <NUM>. Thus, in the tyre <NUM>, grip performance does not change suddenly since the connecting rubber portion 22b do not come into contact with the ground even when the wear progresses. Therefore, steering stability of the tyre can be improved.

A thickness t of the connecting rubber portion 22b is preferably equal to or more than <NUM>, more preferably equal to or more than <NUM>. The thickness t of the connecting rubber portion 22b is preferably equal to or less than <NUM>, more preferably equal to or less than <NUM>. Such a connecting rubber portion 22b is suitable for suppressing heat generation due to distortion of the tread rubber <NUM> at high-speed driving.

The axially outer boundary surfaces 23b are curved so as to be convex inwardly in the tyre radial direction. Since the ratio of the sidewall rubber portions 22a in the vicinity of the outer boundary surfaces 23b is small in such the boundary surfaces 23b, it is possible to improve steering stability of the tyre <NUM> when turning at large camber angles.

Loss tangent tan δS of the sidewall rubber portions 22a and the connecting rubber portion 22b at <NUM> degrees C is smaller than loss tangent tan δT of the tread rubber <NUM> at <NUM> degrees C, same as the above-mentioned sidewall rubber portions <NUM>. Such sidewall rubber portions 22a have excellent absorption performance and can improve riding comfort of the tyre <NUM>.

The sidewall rubber portions 22a and the connecting rubber portion 22b contain preferably <NUM> parts by mass or more, more preferably <NUM> parts by mass or more of natural rubber in <NUM> parts by mass of the rubber component. Such rubbers 22a and 22b can suppress the occurrence of cracks and improve durability performance of the tyre <NUM>. In one aspect, the sidewall rubber portions 22a and the connecting rubber portion 22b may be formed integrally previously with one another. In another aspect, the sidewall rubber portions 22a and the connecting rubber portion 22b may be prepared separately and then be joined with one another to form the toroidal rubber <NUM>.

With the first example, bias tyres for two-wheel vehicle having a structure shown in <FIG> and <FIG> were prototyped based on the specification of Table <NUM>. Further, as a comparative example, a bias tyre for two-wheel vehicle in which the tread rubber and the sidewall rubber portions are formed integrally was prototyped. Then, using these prototype tyres, steering stability, ride comfort and durability were tested. The common specifications and test methods for each prototype tyre are as follows.

A test rider drove a medium-sized scooter with each prototype tyre mounted on the rear wheel on a test course, and evaluated steering stability during turning in view of grip performance, feeling of ground contact, and the transient characteristics when turning by the rider's feeling. The test results are shown in Table <NUM> using an index with the comparative example as <NUM>, wherein the larger the value, the better the steering stability.

A test rider drove the medium-sized scooter with each prototype tyre mounted on the rear wheel on a test course, and evaluated ride comfort by the rider's feeling. The test results are shown in Table <NUM> using an index with the comparative example as <NUM>, wherein the larger the value, the better the ride comfort.

The prototype tyres were put into an ozone chamber having a concentration of <NUM> pphm for <NUM> weeks to be subjected to ozone deterioration treatment. Then, these tyres were made to run <NUM>,<NUM> on a drum tester under a load of <NUM> kN. After that, durability performance of each tyre was evaluated based on the crack occurrence rate of the sidewall portions. The test results are shown in Table <NUM> using an index with the comparative example as <NUM>, wherein the larger the value, the better the durability.

Next, with the second example, bias tyres for two-wheel vehicle having a structure shown in <FIG> were prototyped based on the specification of Table <NUM>. Further, as a comparative example, a bias tyre for two-wheel vehicle in which the tread rubber and the sidewall rubber portions are formed integrally was prototyped same as the first example. Then, using these prototype tyres, high-speed durability, steering stability, ride comfort and durability were tested. The common specifications and test methods for each prototype tyre are as follows.

Each prototype tyre was made to run on a drum tester at a speed of <NUM>/h for two hours under a load of <NUM> kN. After that, the tyre was cooled to room temperature, and then the running speed was gradually increased every <NUM> minutes. Then, the running time until the tyre was damaged was measured. The test results are shown in Table <NUM> using an index with the comparative example as <NUM>, wherein the larger the value, the better the high-speed durability.

The test was conducted in the same way as the first example. The test results are shown in Table <NUM> using an index with the comparative example as <NUM>, wherein the larger the value, the better the steering stability.

The test was conducted in the same way as the first example. The test results are shown in Table <NUM> using an index with the comparative example as <NUM>, wherein the larger the value, the better the ride comfort.

The test was conducted in the same way as the first example. The test results are shown in Table <NUM> using an index with the comparative example as <NUM>, wherein the larger the value, the better the durability.

Claim 1:
A bias tyre (<NUM>, <NUM>) for a two-wheel vehicle , the tyre comprising:
a tread portion (<NUM>) defining a pair of tread edges (Te), the tread edges (Te) being outermost edges of the tread portion (<NUM>) in the tyre axial direction;
a pair of sidewall portions (<NUM>);
a carcass (<NUM>) having a bias structure;
a pair of sidewall rubber portions (<NUM>) forming an outer surface of the pair of sidewall portion (<NUM>); and
a tread rubber (<NUM>) forming an outer surface of the tread portion (<NUM>) and connected to the pair of sidewall rubber portions (<NUM>) to form a pair of boundary surfaces (<NUM>, <NUM>) therebetween, outer end portions (7a) in the tyre axial direction of the tread rubber (<NUM>) being connected to the sidewall rubber portions (<NUM>) via the boundary surfaces (<NUM>, <NUM>), wherein
outermost ends (9a, 12a) in a tyre axial direction of the pair of boundary surfaces (<NUM>, <NUM>) are located on an outer surface of the tyre and inwardly in a tyre radial direction of the respective tread edges (Te),
characterized in that innermost ends (9b, 12b) in the tyre axial direction of the boundary surfaces (<NUM>, <NUM>) are located outwardly in the tyre radial direction of the tread edges (Te).