High-speed heavy duty pneumatic radial tires

Abstract: A high-speed heavy duty pneumatic radial tire for use in airplanes comprises a radial carcass (3) extending between a pair of bead cores (2), in which a distance between outer surfaces (7) of bead portions (1) is equal to a rim width (RW) of a nominal rim and a bead base (5) of each bead portion has a profile between the bead heel (4) and bead toe (6) satisfying specified requirements. Specifically, (1) a defined point A is located inward from a defined point B and outward from a defined point C in the axial direction of the tire; (2) the inner diameter of the surface of the bead base (5) is gradually decreased from the bead heel (4) to the point A; (3) the inner diameter of the surface of the bead base (5) at the point A is substantially equal to or gradually and slightly larger than that at the point C; and (4) a distance (M) between the point A and the point C in the axial direction is 40-80% of a distance (N) between the point B and the point C in the axial direction.

Description: This invention relates to pneumatic tires and more particularly to a high-speed heavy duty pneumatic radial tire for use in airplanes and the like. In the airplane tire, it is required to reduce the tire weight as far as possible. For this purpose, as disclosed in JP-A-2-200504, which corresponds to the preamble of claim 1, it is known that a carcass ply is made into a radial structure and a bead core mooring such a carcass ply in a bead portion is made into a circular shape in section having a higher strength utilization as compared with a strand bead. In general, when a large braking force is applied to the tire, there is caused the slipping of the tire on the rim (deviation between tire and rim), whereby the braking distance may be prolonged or the tire and/or the rim may be damaged. Particularly, a large braking force is applied to the airplane tire in the landing, so that the rim slippage is apt to be caused. The occurrence of rim slippage becomes conspicuous in the pneumatic radial tire for airplanes having a bead core of a circular shape in section. It has been known that the rim slippage of the tire is prevented by simply making a tightening interference of the rim large over a full region of a bead base in the tire to increase a contact pressure of the tire onto the rim. In this case, however, it becomes difficult to conduct rim assembling operation and rim dissembling operation. And also, cracks are created on the surface of the bead base to lower the bead portion durability. For this end, as described in JP-A-2-200504, it is proposed to rationalize the tightening interference (or compression factor) of the rim by rendering the sectional shape of the bead base into such a two-step taper that the tapering in a portion of the bead base near to bead toe is larger than that near to bead heel. However, the difficulty of the rim assembling and dissembling operations is not yet solved completely. Furthermore, when a contact point of the two-step taper or an inflection point approaches under the bead core, cracks are created on the surface of the bead base. It is, therefore, an object of the invention to provide a high-speed heavy duty pneumatic tire comprising a radial carcass moored at a pair of bead cores having a circular shape in section which hardly occurs the rim slippage and troubles such as cracks on the surface of the bead base and the like, and is easy in the rim assembling and dissembling operations. According to the invention, there is the provision of a high-speed heavy duty pneumatic radial airplane tire comprising a radial carcass moored at a pair of bead cores having a circular shape in section, a distance from an outer surface of one of bead portion to an outer surface of the other bead portion is set to be the same as a rim width of a nominal standard rim, a point A is a point located at an outermost side in an axial direction of the tire among points indicating a minimum inner diameter of a surface of a bead base, and a point B is a point that a vertical line passing through a center of the bead core to a rotational axis of the tire contacts with the surface of the bead base, and a point C is a point of the surface of the bead base forming a tip of a bead toe, these points satisfy the following requirements: (1) the point A is located inward from the point B and outward from the point C in the axial direction of the tire; (2) the inner diameter of the surface of the bead base is gradually decreased from a bead heel to the point A; and (3) the inner diameter of the surface of the bead base in the point A is substantially equal to or gradually and slightly larger than that in the point C; characterized in that (4) a distance between the point A and the point C in the axial direction is 40-80% of a distance between the point B and the point C in the axial direction. In a preferable embodiment of the invention, the inner diameter of the surface of the bead base is gradually decreased at a one-step taper from the bead heel to the point A. The invention will be described with reference to the accompanying drawings, wherein: Fig. 1 is a partly sectional fragmentary schematic view of a bead portion in a pneumatic radial tire for an airplane according to the invention at a state of matching a distance between a pair of the bead portions in an axial direction of the tire with a rim width of a nominal rim without assembling onto the rim; Fig. 2 is a partly sectional meridional schematic view of a rim indicating a rim width (RW) of the rim; and Fig. 3 is a partly sectional fragmentary schematic view of the conventional bead portion having a two-step taper. In the tire according to the invention, the bead base ranging from the bead heel to the bead toe has the sectional shape satisfying the requirements (1) - (4) as mentioned above, so that the rim assembling and dissembling operations are considerably improved. When the distance between the point A and the point C exceeds 80% of the distance between the point B and the point C in the axial direction of the tire, the point A extremely approaches to the point B and hence stress concentration occurs in an inflection point between a tapered part and a flat part of the bead base to cause cracking. On the other hand, when the distance between the point A and the point C is less than 40% of the distance between the point B and the point C in the axial direction of the tire, the point A extremely approaches to the point C and hence the abrasion is apt to be caused by rubbing rubber of the bead base surface located at the side of the bead toe on the rim and it tends to make the rim assembling and dissembling operations difficult. In this type of the tire according to the invention, the distribution of contact pressure between the bead base and the wheel rim indicates a peak in the vicinity of a position just beneath the bead core (point B). According to the invention, therefore, it has been found that the rim slippage can be prevented by imparting an adequate tightening interference to the bead base having the above sectional shape in the vicinity of the point B (located just beneath the bead core). Moreover, if the inflection point is existent on the surface of the bead base in the vicinity of the point B (located just beneath the bead core), the stress concentration is apt to be caused to create cracking. In order to avoid such cracking trouble, it is favorable that the inner diameter of the bead base surface is gradually decreased at a one-step taper from the bead heel to the point A in the pneumatic tire according to the invention. A tire of Example 1 according to the invention will be described with reference to Fig. 1. In Fig. 1 is partly shown a schematic section of a bead portion 1 in a pneumatic radial tire for an airplane according to the invention at a state of matching a distance between a pair of the bead portions in an axial direction of the tire with a rim width (RW) of a nominal rim without assembling onto the rim. The tire has a tire size of H46x18.0 R20 and the nominal rim has a size of H45x17.0-20 and a rim width (RW) of 11 inches (279.4 mm). The term "distance between a pair of the bead portions in an axial direction of the tire" used herein means a distance ranging from an outer surface 7 of one of the bead portions to an outer surface 7 of the other bead portion, while the term "rim width (RW)" used herein means a distance ranging from an inner surface of one of the rim flange to an inner surface of the other rim flange as shown in Fig. 2. In the tire of the illustrated embodiment, the bead portion 1 is provided with a bead core 2 having a circular shape in section, and a carcass 3 comprised of 6 rubberized plies each containing 6,6-nylon cords of 1890 d/3 arranged in a radial direction is moored at the bead core 2. That is, the carcass 3 has so-called up-down structure that 4 plies among the above 6 plies are wound around the bead core 2 from inside toward outside and the remaining 2 plies are wound along the outermost turnup portion from outside toward inside. Moreover, the other structural members such as flipper, chafer and the like are omitted without illustration. The bead core 2 is a cable bead having a circular shape in section as shown in Fig. 1, which is an annular spiral wire bundle having a twisting structure of 1x5 mm + (10+16+22+28) x 2.2 mm in which four sheath layers are spirally wound around a circular core strand at 10, 16, 22 and 28 turns so as to butt both free ends to each other. When the distance from the outer surface 7 of one of bead portion to the outer surface 7 of the other bead portion is set to be the same as the rim width (RW) of the nominal rim, the point A located at an outermost side in an axial direction of the tire among points indicating a minimum inner diameter of a surface of a bead base 5, the point B contacting a vertical line passing through a center of the bead core 2 to a rotational axis of the tire with the surface of the bead base 5, and the point C of the surface of the bead base 5 forming a top of a bead toe 6 satisfy the following requirements: (1) the point A is located inward from the point B and outward from the point C in the axial direction of the tire; (2) a downward straight line starting from a bead heel 4 of a convex curved face is extended through the point B to the point A at a one-step taper having an inclination angle of 9° with respect to the axial direction of the tire, while the inner diameter of the surface of the bead base is gradually decreased from the bead heel to the point A; (3) the inner diameter of the surface of the bead base in the point A is equal to that in the point C to form a flat face of the bead base; and (4) the distance M between the point A and the point C in the axial direction is 40% of the distance N between the point B and the point C in the axial direction. A tire of Example 2 is substantially the same as in Example 1 except that the distance M between the point A and the point C in the axial direction is 60% of the distance N between the point B and the point C in the axial direction. A tire of Example 3 is substantially the same as in Example 1 except that the distance M between the point A and the point C in the axial direction is 80% of the distance N between the point B and the point C in the axial direction. A tire of Comparative Example 1 is substantially the same as in Example 1 except that the distance M between the point A and the point C in the axial direction is 30% of the distance N between the point B and the point C in the axial direction. A tire of Comparative Example 2 is substantially the same as in Example 1 except that the distance M between the point A and the point C in the axial direction is 90% of the distance N between the point B and the point C in the axial direction. A tire of Comparative Example 3 is a tire having a bead base of two-step taper as shown in Fig. 3. That is, the surface of the bead base is extended at a taper of 9° from the bead heel and at a taper of 14° from the way and finally becomes flat. Further, the distance of the flat part in the axial direction of the tire is 30% of a distance between a point contacting a vertical line passing through a center of the bead core to a rotational axis of the tire with the surface of the bead base, and a point of the surface of the bead base forming a top of a bead toe (point C). The tire performances are measured with respect to Examples 1-3 and Comparative Examples 1-3 to obtain results as shown in Table 1. The rim dissembling property is evaluated by assembling the tire onto the nominal rim, inflating under an internal pressure of 14.0 kgf/cm 2 , releasing the internal pressure after 12 hours, and then pushing the sidewall portion of the tire inward by hydraulic means at a state of fastening the rim to measure a pressure required for dissembling the bead portion of the tire from the rim and represented by an index on the basis that Example 2 is 100. The smaller the index value, the easier the rim dissembling operation. The take-off test on an indoor drum for durability is carried out 50 times under conditions defined in TSO-C62d as a standard for civil airplanes in USA that an internal pressure is 15.3 kgf/cm 2 , a load is 20 ton and a nominal speed is 225 mph, whereby the occurrence of troubles is measured. Rim dissempling property Result of durability test Example 1 115 no trouble Example 2 100 no trouble Example 3 88 no trouble Comparative Example 1 145 no trouble Comparative Example 2 75 trouble occurred Comparative Example 3 155 no trouble As seen from the results of Table 1, the tires of Examples 1-3 are excellent in the rim dissembling property and durability as compared with the tires of Comparative Examples 1-3 As mentioned above, according to the invention, there are provided high-speed heavy duty pneumatic tires, particularly airplane tires comprising a radial carcass moored at a pair of bead cores each having a circular shape in section, which hardly create the slipping of the tire on the rim and troubles such as cracking on the surface of the bead base and are easy in the rim assembling and dissembling operations.

Claims: A high-speed heavy duty pneumatic radial airplane tire comprising a radial carcass (3) extending between a pair of bead cores (2) having a circular shape in section, a distance from an outer surface (7) of one bead portion (1) to an outer surface of the other bead portion is set to be the same as a rim width (RW) of a nominal standard rim, a point A is a point located at an outermost side in an axial direction of the tire among points indicating a minimum inner diameter of a surface of a bead base (5), and a point B is a point where a vertical line passing through the center of the bead core (2) to a rotational axis of the tire contacts with the surface of the bead base (5), and a point C is a point of the surface of the bead base (5) forming a tip of a bead toe (6), these points satisfy the following requirements: (1) the point A is located inward from the point B and outward from the point C in the axial direction of the tire; (2) the inner diameter of the surface of the bead base (5) is gradually decreased from a bead heel (4) to the point A; and (3) the inner diameter of the surface of the bead base (5) at the point A is substantially equal to or gradually and slightly larger than that at the point C; characterized in that (4) a distance (M) between the point A and the point C in the axial direction is 40-80% of a distance (N) between the point B and the point C in the axial direction. A pneumatic radial tire as claimed in claim 1, characterized in that the inner diameter of the surface of the bead base (5) is gradually decreased at a one-step taper from the bead heel (4) to the point A. A pneumatic radial tire as claimed in claim 1 or 2, characterized in that each of said bead cores (2) is a cable bead having a circular shape formed by a wire bundle having a twisting structure of 1 x 5 mm + (10 + 16 + 22 + 28) x 2.2 mm. A pneumatic radial tire as claimed in any of claims 1 to 3, characterized in that said carcass (3) comprises six rubberized plies each containing 6,6-nylon cords of 1890 d/3. A pneumatic radial tire as claimed in any of claims 1 to 4, characterized in that a downward straight line beginning from a bead heel (4) and extending through point B to point A defines a one-step taper having an inclination angle of 9° with respect to the axial direction of the tire.

Inventors: WATANABE JUN, WATANABE, JUN
Applicants: BRIDGESTONE CORP, BRIDGESTONE CORPORATION
Application year: 1995
Main classification: B60C15
IPC codes: B60C9, B60C15