TECHNICAL FIELD

The present technology relates to a pneumatic tire.

BACKGROUND ART

A pneumatic tire is mounted on a rim wheel by fitting, to a rim of a rim wheel, a bead portion with a bead core corresponding to an annular member including a plurality of bead wires bundled. The bead portion is a portion that is actually mounted on the rim wheel in a case where the pneumatic tire is mounted on the rim wheel, and thus, in some known pneumatic tires, various improvements are made to the bead portions to achieve desired performance. For example, in the pneumatic tire described in Japan Patent No. 5629275, the bead cores are shaped to be wider in the tire width direction to reduce localized pressure, suppressing damage to the rim. Additionally, in the tire described in Patent Document 1, a bead heel portion of the bead base portion in a meridian cross-section has a round contour with a large radius of curvature, thus ensuring easiness of mounting on the rim.

Additionally, in a heavy duty pneumatic radial tire described in Japan Patent No. 4934241, a predetermined range is set for the ratio, to the volume of rubber chafer displaced and deformed by a rim bead sheet, of a space in which rubber chafer displaced and deformed due to mounting, is received, the space being located in a corner where the rim bead sheet is continuous with a rim flange. This configuration prevents separation of the rubber chafer. Additionally, a heavy duty radial tire described in Japan Unexamined Patent Publication No. 2010-188818 has a compression factor and a ratio of a bead core effective width to a bead core maximum width, which are each set to fall within a predetermined range to improve a rim slip resistance without causing weight increase. The compression factor is defined by dividing a compression allowance, which is a difference between a total thickness before mounting on a rim of only a rubber part on an inner side in a radial direction than a bead core and a total thickness after mounting on the rim, by the total thickness before mounting on the rim.

Here, pneumatic tires are mounted on various types of vehicles, and in construction vehicles, corresponding to a type of such vehicles, a large torque may be transmitted to the wheels during construction operations. For example, in a wheel loader, which is an example of a construction vehicle, in a case where a bucket provided at a front end of the vehicle is used to scoop up the earth and sand and the like, a large load acts on the front wheels, and thus traveling in this state causes the large torque to be transmitted to the front wheels. In recent years, in this type of wheel loader, high horsepower has been achieved, leading to a tendency toward an increase in torque transmitted to the wheels, and thus the wheels are often used under stringent conditions. Thus, in the wheels mounted on the construction vehicle such as a wheel loader, so-called rim slippage, corresponding to slippage between the rim and the bead portion, may occur due to the increased horsepower of the vehicle. In other words, the torque transmitted to the wheels is transmitted from the rim wheel to the pneumatic tire via the bead portion, and an excessively high torque transmitted from the rim wheel to the bead portion may cause slippage between the rim and the bead portion. The rim slippage thus occurring between the rim wheel and the pneumatic tire may wear rubber in a bead base portion corresponding to an inner circumferential surface of the bead portion and coming into contact with the rim, leading to damage to the bead base portion.

A possible cause of such rim slippage is an insufficient fastening force exerted on the rim by the bead portion. A possible method for increasing the fastening force of the bead portion is to reduce the inner diameter of the bead core of the bead portion or to reduce the circumferential length of the bead heel portion of the bead base portion. However, the reduced inner diameter of the bead core or the reduced circumferential length of the bead heel portion increases the fastening force of the bead portion, but may degrade mountability of the pneumatic tire on the rim in a case of mounting on the rim wheel. The degraded mountability on the rim may cause an eccentric fitting in which the bead portions are fitted eccentrically to the rim wheel, defective seating of the bead portion on the rim wheel, or the like, leading to a reduced fastening force. However, in a case where the inner diameter of the bead core or the circumferential length of the bead heel portion is set with the mountability on the rim emphasized, the fastening force exerted on the rim by the bead portion may be insufficient, leading to the likelihood of rim slippage. Thus, suppressing rim slippage without degrading the mountability on rims has been very difficult.

SUMMARY

The present technology provides a pneumatic tire that can suppress rim slippage while ensuring mountability on rims.

A pneumatic tire according to an embodiment of the present technology to be mounted on a 5°-tapered specified rim includes a pair of bead portions, a bead core, and a rim cushion rubber. The pair of bead portions are disposed on both sides of a tire equatorial plane in a tire width direction. The bead core is provided in each of the pair of bead portions. The rim cushion rubber is disposed on an inner side in a tire radial direction of the bead core in each of the pair of bead portions. The bead core has a hexagonal shape in a tire meridian cross-section. A bead core bottom as an inner circumferential surface of the bead core is inclined within a range of 0° or more and 5° or less with respect to a tire rotation axis in a direction in which the bead core bottom diverges toward an outer side in a tire radial direction as the bead core bottom extends from an inner side in the tire width direction toward an outer side in the tire width direction. Each of the pair of bead portions includes a bead base portion, a toe portion, and a heel portion. The bead base portion is an inner circumferential surface of each of the pair of bead portions. The toe portion is located on an inner side of the bead base portion in the tire width direction. The heel portion is located on an outer side of the bead base portion in the tire width direction. The bead base portion is linearly formed in the tire meridian cross-section. The bead base portion is inclined within a range of 8° or more and 12° or less with respect to the tire rotation axis in a direction in which the bead base portion diverges toward the outer side in the tire radial direction as the bead base portion extends from the inner side in the tire width direction toward the outer side in the tire width direction. The heel portion has a shape in the tire meridian cross-section formed in an arc shape having a radius of curvature within a range of 25 mm or more and 30 mm or less. The rim cushion rubber has a modulus at 100% elongation within a range of 5.0 MPa or more and 8.0 MPa or less. The toe portion has an amount of displacement in the tire radial direction between before and after mounting on the specified rim within a range of 9.0 mm or more and 13.5 mm or less.

In the pneumatic tire described above, preferably, when the pneumatic tire is mounted on the specified rim, a compression ratio of a rubber located on the inner side of the bead core in the tire radial direction is within a range of 45% or more and 55% or less at a position on an inner side in the tire radial direction of a center of the bead core bottom in the tire meridian cross-section.

Additionally, the pneumatic tire described above is preferably as follows. The pneumatic tire includes a carcass. The carcass is extended between the pair of the bead portions. The carcass runs through the inner side in the tire radial direction of the bead core and is folded back in the tire width direction in each of the pair of bead portions. The carcass has a radius of curvature R2in the tire meridian cross-section at a position on an inner side in the tire radial direction of the bead core bottom within a range of 50 mm or more and 70 mm or less. The radius of curvature R2has a relationship with a radius of curvature R1of the heel portion in the tire meridian cross-section of R1<R2.

Additionally, in the pneumatic tire described above, a relationship between a maximum width W1in the tire meridian cross-section of the bead core and a bead width W2as a distance in the tire width direction between an outer end portion of the bead core in the tire width direction and a leading edge portion of the toe portion is preferably within a range 0.65≤(W1/W2)≤0.75.

The pneumatic tire according to an embodiment of the present technology is effective in allowing suppression of rim slippage while ensuring mountability on rims.

