Patent Description:
Patent Document <NUM> below discloses a pneumatic tire of which bead portion is provided with a reinforcing rubber layer adjacent to the outside in the tire axial direction of a turned-up portion of a carcass ply in order to increase the stiffness of the bead portion and improve the durability. Patent Document <NUM>: <CIT>.

Similar pneumatic tires are disclosed in <CIT>, <CIT>, <CIT>, <CIT> and <CIT>.

In recent years, as the performance of vehicles has improved, there has been a demand for pneumatic tires further improved in steering stability.

On the other hand, in the pneumatic tires of which bead portions are provided with reinforcing rubber layers as described above, ride comfort is liable to deteriorate.

The present invention was made in view of the circumstances as described above, and a primary objective of the present invention is to provide a pneumatic tire capable of improving steering stability while maintaining ride comfort.

According to the present invention, a pneumatic tire comprises:.

The bead apex comprises a thermosetting resin.

In the pneumatic tire according to the present invention, therefore, as the above configuration is employed, steering stability can be improved while maintaining ride comfort.

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

<FIG> is a tire meridian cross section including the tire rotational axis, showing a pneumatic tire <NUM> as an embodiment of the present invention. The present invention is suitably applied to passenger car tires, and the tire <NUM> of the present embodiment is a pneumatic tire for passenger cars. In <FIG>, there is shown the tire <NUM> under its standard state.

Incidentally, in order to aid understanding of the present invention, the drawings may include expressions exaggerated or dimensionally differed from the actualities.

In the case that the tire <NUM> is a kind of pneumatic tires for which various standards have been established,
the "standard state" means a state of the tire when mounted on a standard wheel rim, and inflated to a standard tire pressure, but loaded with no tire load. The "standard wheel rim" is a wheel rim specified for the tire in a standard system including standards on which the tire is based, for example, the "Standard rim" in JATMA, "Design Rim" in TRA, "Measuring Rim" in ETRTO,
The "standard tire pressure" is the air pressure specified for the tire in a standard system including standards on which the tire is based, for example, the "maximum air pressure" in JATMA, "INFLATION PRESSURE" in ETRTO, and the maximum air pressure listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in TRA.

In the case that the tire <NUM> is a tire for which various standards are not yet established, the "standard state" means a standard usage state depending on the purpose of use of the tire and in a condition in which the tire is not attached to a vehicle and no tire load is applied.

In this application including specification and claims, dimensions and positions of each part or portion of the tire refer to those measured under the standard state unless otherwise noted.

As shown in <FIG>, the tire <NUM> of the present embodiment comprises a tread portion <NUM>, a pair of sidewall portions <NUM>, a pair of bead portions <NUM> and a carcass <NUM>. The sidewall portions <NUM> are respectively connected with the ends in the tire axial direction of the tread portion <NUM>. The bead portions <NUM> are respectively connected with the inner ends in the tire radial direction of the sidewall portions <NUM>. The carcass <NUM> extends between the bead portions <NUM> through the tread portion <NUM> and the sidewall portions <NUM> and has a toroidal shape.

The bead portions <NUM> are each provided with a bead core <NUM> and a bead apex <NUM>, the bead apex <NUM> extending radially outwardly from the bead core <NUM> in a tapered manner. The bead core <NUM> is a ring-shaped body formed by winding a high tensile modulus member, for example, a steel wire or filament (not shown) in multiple turns in the radial distortion and axial direction. The cross-sectional shape of the bead core <NUM> is, for example, a polygon, in the present embodiment, generally a rectangle. The bead apex <NUM> is made of hard rubber, for example, having a generally triangular cross sectional shape.

The carcass <NUM> comprises at least one carcass ply 6A. The carcass ply 6A extends between the bead portions <NUM> through the tread portion <NUM> and the sidewall portions <NUM> and is turned up around the bead core <NUM> in each bead portion from the axially inside to the axially outside so as to form a pair of turned-up portions 6b and a main portion 6a therebetween. The turned-up portions 6b extend radially outwardly from the bead cores on the axially outsides of the bead apexes <NUM>, respectively.

The carcass ply 6A is made of carcass cords covered with topping rubber (not shown). As the carcass cords, for example, organic fiber cords such as aramid or rayon can be used. The carcass cords are arranged at an angle in a range from <NUM> to <NUM> degrees with respect to the tire equator C, for example. Although the carcass <NUM> of the present embodiment is composed of only one carcass ply 6A, it may be composed of a plurality of carcass plies 6A.

In the tire <NUM> of the present embodiment, the tread portion <NUM> is provided with a belt <NUM> on the radially outside of the carcass <NUM>. The belt <NUM> in this example comprises two belt plies 7A and 7B of parallel belt cords arranged at an angle in a range from <NUM> to <NUM> degrees with respect to the tire circumferential direction. The belt cords of one belt ply 7A and the belt cords of the other belt ply 7B are inclined in opposite directions with respect to the tire circumferential direction to thereby effectively reinforce the tread portion <NUM>.

In the present invention, at least one of the bead portions <NUM> is provide with a bead reinforcing rubber <NUM> as shown in <FIG>. In the present embodiment, each of the bead portions <NUM> is provide with the bead reinforcing rubber <NUM>. The bead reinforcing rubber <NUM> is disposed axially outside the turned-up portion 6b.

The bead reinforcing rubber <NUM> comprises a plurality of reinforcing rubber layers arranged in the tire axial direction and each extending in a tire radial direction. In the present invention, the bead reinforcing rubber <NUM> comprises a first reinforcing rubber layer <NUM> and a second reinforcing rubber layer <NUM>, the second reinforcing rubber layer <NUM> disposed axially inside the first reinforcing rubber layer <NUM>. Although the bead reinforcing rubber <NUM> in the present embodiment is composed of only the first reinforcing rubber layer <NUM> and the second reinforcing rubber layer <NUM>, the bead reinforcing rubber <NUM> may include another rubber layer.

In the present invention, the complex elastic modulus E*<NUM> of the second reinforcing rubber layer <NUM> is smaller than the complex elastic modulus E*<NUM> of the first reinforcing rubber layer <NUM>.

In this application including specification and claims, the complex elastic modulus is measured according to Japanese Industrial standard (JIS) K6394 under the following conditions using a viscoelastic spectrometer:.

As the tire <NUM> of the present invention is provided with the above configurations, steering stability can be improved while maintaining ride comfort. The reason is considered as follows.

The bead reinforcing rubber <NUM> in the present invention can change the state of the turned-up portion 6b from a compressed state to a tensile state when the bead portion <NUM> is deformed outward in the tire axial direction. This improves the stiffness of the bead portion <NUM> and improves the steering stability.

Further, the first reinforcing rubber layer <NUM> having the complex elastic modulus E*<NUM> can prevent the bead portion <NUM> from falling outward in the tire axial direction, further improving the steering stability. Furthermore, in the present invention, since the second reinforcing rubber layer <NUM> having a relatively small complex elastic modulus E*<NUM> is disposed on the inner side in the tire axial direction, minute vibrations (especially high-frequency components of the vibrations) of the carcass <NUM>, bead apex <NUM> and bead core <NUM> cab be easily absorbed, without sacrificing the ride comfort.

Further, in the present invention, since the complex elastic modulus E*<NUM> of the second reinforcing rubber layer <NUM> is relatively small, embrittlement due to heat generation of the second reinforcing rubber layer <NUM> is prevented, and damages such as separation between the bead reinforcing rubber <NUM> and the turned-up portion 6b can be prevented. Therefore, according to the present invention, it is also expected to improve the durability of the bead portion <NUM>.

Hereinafter, a more detailed configuration of the present embodiment will be described.

The dimension Lb in the tire radial direction of the bead apex <NUM> is preferably set in a range from <NUM>% to <NUM>% of the total tire height h1 (for example, the dimension Lb is <NUM> or less) so that, with respect to positions in the tire radial direction, the radially outer end of the bead apex <NUM> approximates the radially outer end of the rim flange (not shown). As a result, when the bead portion <NUM> falls outward in the tire axial direction, strain in the bead portion <NUM> can be prevented from concentrating on the radially outer end portion of the bead apex <NUM>.

Here, the total tire height h1 means, as shown in <FIG>, the radial dimension from the bead base line BL to the radially outermost position on the tread surface which usually occurs at the tire equator C. The bead base line BL means a base line extending parallel to the tire axial direction at a radial position corresponding to the rim diameter of the standard wheel rim.

Preferably, the complex elastic modulus of the bead apex <NUM> is not less than <NUM> MPa, more preferably not less than <NUM> MPa, but not more than <NUM> MPa, more preferably not more than <NUM> MPa. Thereby, the stiffness of the bead portion <NUM> becomes appropriate for improving the steering stability and ride comfort in a well-balanced manner.

The bead apex <NUM> contains a thermosetting resin in order to improve strength so as to withstand large pressure and external forces that occur during running, and thereby improving the durability.

Each of the bead portions <NUM> is provided with a clinch rubber <NUM> disposed on the axially outer side of the bead reinforcing rubber <NUM> to form the outer surface of the bead portion <NUM>. The complex elastic modulus of the clinch rubber <NUM> is smaller than that of the bead apex <NUM>, and is set in a range from <NUM> to <NUM> MPa for example.

As shown in <FIG>, the radially outer end 6bo of the turned-up portion 6b of the carcass ply 6A is positioned at a distance L3 in the tire radial direction from the above-mentioned bead base line BL which is, for example, in a range from <NUM>% to <NUM>% of the above-mentioned total tire height h1.

It is preferable that the radially outer end 6bo of the turned-up portion 6b is spaced apart at least <NUM> in the tire radial direction from both of the radially outer end of the first reinforcing rubber layer <NUM> and the radially outer end of the second reinforcing rubber layer <NUM>. Thereby, failures at the radially outer ends of the turned-up portion 6b and the rubber layers <NUM> and <NUM> are suppressed and the bead portion <NUM> is improved in durability.

As shown in <FIG>, the bead reinforcing rubber <NUM> is disposed radially outside the bead core <NUM>. The bead reinforcing rubber <NUM> is spaced apart at least <NUM> from the outer end 7o in the tire axial direction of the belt <NUM>. The bead reinforcing rubber <NUM> is preferably arranged on the radially inside than a tire maximum width position <NUM> in the sidewall portion <NUM>. The bead reinforcing rubber <NUM> is arranged so as to contact with an axially outer side of the turned-up portion 6b of the carcass ply 6A and an axially outer side of the main portion 6a of the carcass ply 6A as shown in <FIG>.

It is preferable that the complex elastic modulus E*<NUM> of the first reinforcing rubber layer <NUM> and the complex elastic modulus E*<NUM> of the second reinforcing rubber layer <NUM> are both larger than the complex elastic modulus of the clinch rubber <NUM>. The complex elastic modulus E*<NUM> of the first reinforcing rubber layer <NUM> is preferably not less than <NUM> MPa, more preferably not less than <NUM> MPa, but preferably not more than <NUM> MPa, more preferably not more than <NUM> MPa. The complex elastic modulus E*<NUM> of the second reinforcing rubber layer <NUM> is preferably not less than <NUM> MPa, more preferably not less than <NUM>, but preferably not more than <NUM> MPa, more preferably not more than <NUM> MPa.

The ratio E*<NUM>/E*<NUM> of the complex elastic modulus E*<NUM> to the complex elastic modulus E*<NUM> is preferably larger than <NUM>, more preferably not less than <NUM>, but preferably smaller than <NUM>, more preferably not more than <NUM> from the viewpoint of improving the steering stability and ride comfort in a well-balanced manner.

<FIG> is a cross-sectional view showing only the first reinforcing rubber layer <NUM> and the second reinforcing rubber layer <NUM>. As shown, each of the first reinforcing rubber layer <NUM> and the second reinforcing rubber layer <NUM> has a tapered radially inner end portion and a tapered radially outer end portion. Accordingly, each of the first reinforcing rubber layer <NUM> and the second reinforcing rubber layer <NUM> has a portion having a maximum thickness located between the tapered radially inner end portion and tapered radially outer end portion thereof.

The first reinforcing rubber layer <NUM> has an axially outer surface <NUM> and an axially inner surface <NUM>, and in this example, as shown in <FIG>, the entire outer surface <NUM> is in contact with the clinch rubber <NUM>, and the entire inner surface <NUM> is in contact with the second reinforcing rubber layer <NUM>. Preferably, the radially outer end 11o of the first reinforcing rubber layer <NUM> is located radially outside the radially outer end 6bo of the turned-up portion 6b. The dimension L1 in the tire radial direction of the first reinforcing rubber layer <NUM> is preferably not less than <NUM>%, but not more than <NUM>% of the above-mentioned distance L3 in the tire radial direction from the bead base line BL to the radially outer end 6bo of the turned-up portion 6b, for reliably improving the steering stability.

The second reinforcing rubber layer <NUM> has an axially outer surface <NUM> and an axially inner surface <NUM>.

In this example, as shown in <FIG>, a part of the axially outer surface <NUM> is in contact with the first reinforcing rubber layer <NUM>, and the remaining part of the axially outer surface <NUM> is in contact with the clinch rubber <NUM>. In the cross section as shown in <FIG>, the length along the above-mentioned part of the axially outer surface <NUM> contacting with the first reinforcing rubber layer <NUM> is larger than the length along the above-mentioned part of the axially outer surface <NUM> contacting with the clinch rubber <NUM>, and is in a range from <NUM>% to <NUM>% of the length along the entire axially outer surface <NUM>. Thereby, ride comfort can be reliably maintained.

In this example, as shown in <FIG>, a part of the axially inner surface <NUM> is in contact with the turned-up portion 6b, and the remaining part of the axially inner surface <NUM> is in contact with the main portion 6a. In the cross section as shown in <FIG>, the length along the above-mentioned part of the axially inner surface <NUM> contacting with the main portion 6a is in a range from <NUM>% to <NUM>% of the length along the entire axially inner surface <NUM>. Thereby, slight vibrations of the main portion 6a becomes easily absorbed by the second reinforcing rubber layer <NUM>, and riding comfort can be improved.

Preferably, the dimension L2 in the tire radial direction of the second reinforcing rubber layer <NUM> is larger than the dimension L1 in the tire radial direction of the first reinforcing rubber layer <NUM>. For example, the dimension L2 is not less than <NUM>%, but not more than <NUM>% of the dimension L1. such second reinforcing rubber layer <NUM> helps to improve the ride comfort and steering stability in a well-balanced manner.

Preferably, the radially outer end 11o of the first reinforcing rubber layer <NUM> is spaced apart at least <NUM> in the tire radial direction from the radially outer end 12o of the second reinforcing rubber layer <NUM> from the view point of suppressing separation between the first reinforcing rubber layer <NUM> and the second reinforcing rubber layer <NUM>,
Further, it is preferable that, as shown in <FIG>, the sum of a maximum thickness tc of the clinch rubber <NUM> and a thickness t1 of the first reinforcing rubber layer <NUM> measured at a position on the axially inner surface of the clinch rubber at which the maximum thickness tc of the clinch rubber <NUM> occurs, is not less than <NUM>% of the overall thickness Bt of the bead portion <NUM> measured at the above-mentioned position. Thereby, the first reinforcing rubber layer <NUM> and the clinch rubber <NUM> can effectively prevent the bead portion <NUM> from falling axially outward, and the durability of the bead portion <NUM> and the steering stability are further improved.

while detailed description has been made of a preferable embodiment of the present invention, the present invention can be embodied in various forms without being limited to the illustrated embodiment.

Based on the structure shown in <FIG>, pneumatic tires of size <NUM>/70R15 for passenger cars were experimentally manufactured as test tires (working example tire and comparative example tire). The test tires had the same structure except for the values of the complex elastic moduli E*<NUM> and E*<NUM>. In the comparative example tire, the value of E*<NUM> was larger than the value of E*<NUM> as shown in Table <NUM>.

The test tires mounted on a wheel rim of size 15x6.5J and inflated to <NUM> kPa were attached to a test vehicle (<NUM> cc minivan). Then, using the test vehicle, the tires were tested for steering stability and ride comfort as follows.

The steering stability of the test vehicle when running on a test course was evaluated by a test driver. The test results are indicated in Table <NUM> by an index based on the comparative example being <NUM>, wherein the larger the value, the better the steering stability.

The ride comfort when the test vehicle was running on an uneven tire test course, was evaluated by a test driver. The test results are indicated in Table <NUM> by an index based on the comparative example being <NUM>, wherein the larger the value, the better the ride comfort.

Claim 1:
A pneumatic tire (<NUM>) comprising:
a pair of bead portions (<NUM>) each provided with a bead core (<NUM>) and a bead apex (<NUM>) which extends radially outwardly from the bead core (<NUM>) in a tapered manner, and
a toroidal carcass (<NUM>) comprising a carcass ply (6A) extending between the bead portions (<NUM>) and turned up around the bead core (<NUM>) in each bead portion from the axially inside to the axially outside so as to form a pair of turned-up portions (6b) and a main portion (6a) therebetween,
the turned-up portions (6b) extending radially outwardly on the axially outer sides of the bead apexes (<NUM>), respectively, wherein
at least one of the bead portions (<NUM>) is provided with a bead reinforcing rubber (<NUM>) disposed on the axially outer side of the turned-up portion,
the bead reinforcing rubber (<NUM>) comprises a first reinforcing rubber layer (<NUM>) and a second reinforcing rubber layer (<NUM>) disposed axially inside the first reinforcing rubber layer (<NUM>), and
a complex elastic modulus E*<NUM> of the second reinforcing rubber layer (<NUM>) is smaller than a complex elastic modulus E*<NUM> of the first reinforcing rubber layer (<NUM>),
wherein the complex elastic modulus is measured according to JIS K6394 under the following conditions using a viscoelastic spectrometer:
Initial strain: <NUM>%,
Strain amplitude: +/-<NUM>%,
Frequency: <NUM>,
Deformation mode: tension,
Measuring temperature: <NUM> degrees C,
and characterized in that
the bead apex (<NUM>) comprises a thermosetting resin.