Pneumatic radial tire for aircraft

Abstract

Provided is a pneumatic radial tire for aircraft that includes a radial carcass constituting a backbone structure of the tire, a belt (6) disposed along an outer periphery of a crown region of the radial carcass, and at least one protective layer (7) disposed along an outer periphery of the belt (6) and formed by a plurality of cords (9). The cords (9) in the protective layer (7) are curved in a sinusoidal shape and disposed in parallel with equal phase. An acute inclination angle between an amplitude center line of each cord (9) relative to a tire circumferential direction, a half amplitude a of each cord (9), and a wavelength of each cord (9) satisfy the relationship: tan >2a/>0.4 (0<<90).

Claims

1. A pneumatic radial tire for aircraft comprising a radial carcass constituting a backbone structure of the tire, a belt disposed along an outer periphery of a crown region of the radial carcass, and at least one protective layer disposed along an outer periphery of the belt and formed by a plurality of cords, wherein: the cords in the protective layer are curved in a sinusoidal shape and disposed in parallel with equal phase; and an acute inclination angle of an amplitude center line of each cord relative to a tire circumferential direction, a half amplitude a of each cord, and a wavelength of each cord satisfy the relationship:
tan >2a/>0.4 (0<<90), and wherein
0.812a/>0.4.

2. The pneumatic radial tire for aircraft of claim 1, wherein cords of the belt are formed of nylon.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The present invention will be further described below with reference to the accompanying drawings, wherein:

(2) FIG. 1 is a cross-sectional view of an embodiment of a pneumatic radial tire for aircraft of the present invention, showing half of the tire along the meridional line;

(3) FIG. 2 is a partial developed plan view schematically showing the belt structure of the tire in FIG. 1;

(4) FIG. 3 is a partial plan view of a strip-shaped member schematically showing a cutting step to cut a sheet member with embedded wavy cords during formation of the material for the protective layer of the tire shown in FIG. 1;

(5) FIG. 4 is a plan view schematically showing steps for disposing the sheet member cut in the step shown in FIG. 3 along the outer periphery of a cylindrical tire structural member; and

(6) FIG. 5 is a partial developed plan view schematically showing the belt structure of a conventional pneumatic tire.

DESCRIPTION OF EMBODIMENTS

(7) The following describes the pneumatic radial tire for aircraft of the present invention in detail with reference to the drawings.

(8) In FIGS. 1 and 2, a tread portion is labeled 1, a pair of sidewalls extending continuously from the side of the tread portion 1 inwards in the radial direction is labeled 2, and a bead portion continuous with the inner circumference of each sidewall 2 is labeled 3.

(9) The tire shown here is provided with a bead core 4 embedded in each of the pair of bead portions 3 and a radial carcass formed by carcass plies 5 composed of a plurality of organic fiber cords extending toroidally between the bead cores 4 at an angle in a range from 70 to 90 with respect to the tire equatorial surface.

(10) Along the outer periphery of the crown region of the radial carcass, a plurality of nylon cords, for example, are aligned extending at an angle between 10 and 60, for example, with respect to the tire equatorial surface. A belt 6 composed of a cord cross belt layer, a protective layer 7 formed by disposing a plurality of cords curved in the shape of a sine wave, and a tread rubber 8 are disposed in this order. One protective layer 7 is show in the drawings. A plurality of circumferential grooves, for example, is formed on the surface of the tread rubber 8 extending in the circumferential direction of the tire.

(11) This radial carcass has a so-called up-down structure in which the carcass plies 5 include turn-up plies 5a that are wound around the lateral portion of each bead core 4 from the inside towards the outside in the direction of tire width and down plies 5b that cover the portion of the turnup plies 5a wound around the bead cores 4 and that extend inward in the radial direction at least to an inner portion of the bead cores 4 in the radial direction.

(12) This up-down structure offsets the tension around the bead cores 4 exerted on the turnup plies 5a and the down plies 5b, thus allowing mutual restraining forces to act in order to effectively prevent the carcass plies 5 from becoming dislodged.

(13) As a result, it is possible to guarantee sufficient pressure resistance, load bearing capabilities, and the like as required for radial tires for aircraft.

(14) In this pneumatic radial tire for aircraft, a plurality of cords 9 curved in a sinusoidal shape are disposed in parallel with equal phase in the protective layer 7. The acute inclination angle of the amplitude center line of each wavy cord 9 relative to the tire circumferential direction, and the half amplitude a and the wavelength of each wavy cord 9 satisfy the relationship tan >2a/>0.4 (0<<90).

(15) In such a tire, the protective layer 7 can absorb and bear stress in the tire radial direction produced by expansion during inflation to the internal pressure, thus reducing deformation and inhibiting the occurrence and growth of damage to the tread portion 1, while also inhibiting damage to the tread portion 1 from spreading in the circumferential direction of the tire. The protective layer 7 therefore increases the durability of the tire by dramatically improving cut resistance and preventing damage from reaching the belt 6 until the tread is nearly worn.

(16) In such a tire, the inclination angle is preferably in the following range: 40<<80. This range not only improves resistance to detachment of rubber, such as the tread rubber 8, but also decreases the size of any rubber fragment that does detach.

(17) The half amplitude a and the wavelength are preferably in the following ranges: 2 mm<a<20 mm, and 10 mm<<50 mm.

(18) In the above-described tire, the material for the protective layer 7 disposed along the outer periphery of the belt 6 may be formed as follows.

(19) First, as shown in FIG. 3, a plurality of wavy cords 9 curved in the sinusoidal shape are disposed in parallel with equal phase, coated with unvulcanized rubber, and formed into an elongated, wide strip-shaped member 12.

(20) Next, from the strip-shaped member 12 having the wavy cords 9 embedded therein, a sheet member 13a is cut out by cutting in the direction of length of the strip-shaped member 12, i.e. in a direction c that is inclined at a predetermined angle with respect to a straight line traversing the amplitude center of each wavy cord 9.

(21) Subsequently, as shown in FIG. 4(a), cylindrical protective layer material may be formed by, for example, attaching the sheet member 13a cut at the predetermined angle to the outer peripheral surface of a cylindrical tire structural member 11, such as belt material formed surrounding a cast drum. The sheet member 13a is attached with the cut direction c aligned with the circumferential direction of the tire structural member 11, so that the cut surface of the sheet member 13a faces outwards in the axial direction of the tire structural member 11.

(22) In a tire that is manufactured by vulcanization molding of a raw tire having such protective layer material, the inclination angle of the amplitude center line of each wavy cord in the protective layer relative to the circumferential direction of the tire matches the cut angle .

(23) Here, the waveform of the wavy cords 9 curved in the sinusoidal shape and embedded in the strip-shaped member 12 shown in FIG. 3 can generally be expressed as y=a.Math.sin(2/.Math.x)+y.sub.0, and the inclination of the tangent can be expressed as y=2a/.Math.cos(2/.Math.x). In particular, when x=, the inclination reaches the maximum value of 2a/.

(24) Furthermore, the inclination of the cut direction c when cutting the strip-shaped member 12 can be expressed as tan .

(25) For example, assuming the cut angle to be between 60 and 80, if the inclination tan of the tangent c and the maximum value 2a/ of this inclination satisfy the relationship tan >2a/ (0<<90), then the inclination of the cut direction c becomes larger than the maximum value of the inclination of the tangent to the wavy cords. As a result, when cutting the strip-shaped member 12, each wavy cord intersects the cut direction c at one point and is cut in one location, so that none of the wavy cords 9 aligned in the width direction of the strip-shaped member 12 is segmented within one sheet member 13a when the strip-shaped member 12 is cut.

(26) Therefore, since the relationship tan <2a/ is satisfied in the tire of this invention, the wavy cords are not segmented within the protective layer, thus allowing the cords in the protective layer to change shape in accordance with changes in form to the tire and preventing tension from being exerted on the cords.

(27) On the other hand, if the strip-shaped member 12 is cut at a cut angle that is too small to satisfy the above conditions, for example between 20 and 40, then in particular in the wide strip-shaped member 12 with a large number of cords, each wavy cord intersects the cut direction d at two or more points and is cut in two or more locations, as shown in FIG. 3. In this case, segmented cords 19a, 19b and 19c exist within one sheet member 13b. Therefore, segmented wavy cords also exist in the protective layer of a tire manufactured using protective layer material formed as shown in FIG. 4(b), resulting in the cords within the protective layer not being able to change in accordance with changes in form to the tire.

EXAMPLES

(28) Next, prototype tires of size 5020.0R22 32PR were produced to have the structure shown in FIGS. 1 and 2. As shown in Table 1, specifications were changed among Example Tires 1-3 and Comparative Tires 1-3, and the resistance to detachment of the tread portion as well as the size of detached rubber were measured for each tire.

(29) Note that the Comparative Tires required no structural alterations apart from the protective layer and therefore were produced in accordance with the Example Tires.

(30) TABLE-US-00001 TABLE 1 Example Example Example Comparative Comparative Comparative Tire 1 Tire 2 Tire 3 Tire 1 Tire 2 Tire 3 Cord angle 40 60 80 0 20 90 (deg.) tan 0.84 1.73 5.67 0 0.36 Wavelength 31 15 12 28 45 27 (mm) Half 4 4 10 3 2.5 4 amplitude a (mm) 2a/ 0.81 1.68 5.24 0.67 0.35 0.93

(31) Resistance to Detachment of Tread Portion

(32) Each of the Example Tires 1-3 and Comparative Tires 1-3 was attached to a size 5020 OR22 rim and inflated to an internal pressure of 1520 kPa. A cut the width of the center rib was made in each tire from the tread surface to the top of the cords in the protective layer. Test liftoff was then repeatedly performed at 120% tire load, and the number of runs until the tread portion detached was measured to assess the resistance to detachment of the tread. Table 2 shows the results of assessment.

(33) Note that the indices in Table 2 were calculated using the value for Comparative Example Tire 1 as a control. A larger index indicates superior resistance to detachment of the tread portion.

(34) Size of Detached Rubber

(35) For each of the Example Tires 1-3 and Comparative Tires 1-3, the size of the rubber that detached during the test of resistance to detachment of the tread portion was measured. Table 2 lists the results.

(36) Note that the indices in Table 2 were calculated using the value for Comparative Tire 1 as a control. A smaller index indicates a smaller fragment of detached rubber.

(37) TABLE-US-00002 TABLE 2 Example Example Example Comparative Comparative Comparative Tire 1 Tire 2 Tire 3 Tire 1 Tire 2 Tire 3 Resistance to 100 130 100 100 80 80 detachment of tread Size of detached tread 70 50 40 100 80 30

(38) The results in Table 2 show that as compared to the Comparative Tire 1, the Example Tire 1 had equivalent resistance to detachment of the tread portion yet yielded smaller detached rubber. The Example Tire 2 dramatically improved on both the resistance to detachment of the tread portion and the size of the detached rubber as compared to the Comparative Tire 1. The Example Tire 3 had equivalent resistance to detachment of the tread portion yet dramatically improved on the size of the detached rubber as compared to the Comparative Tire 1.

(39) The Comparative Tire 2 had worse resistance to detachment of the tread portion yet yielded a smaller detached tread than the Comparative Tire 1. The Comparative Tire 3 did not achieve the effect of change in the wavy cords whatsoever and thus had worse resistance to detachment of the tread portion than the Comparative Tire 1.

REFERENCE SIGNS LIST

(40) 1: Tread portion

(41) 2: Sidewall

(42) 3: Bead portion

(43) 4: Bead core

(44) 5: Carcass plies

(45) 5a: Turn-up ply

(46) 5b: Down ply

(47) 6: Belt

(48) 7: Protective layer

(49) 8: Tread rubber

(50) 9: Wavy cord

(51) 11: Tire structural member

(52) 12: Strip-shaped member

(53) 13a, 13b: Sheet member

(54) 19a, 19b, 19c: Segmented cord

(55) c, d: Cut direction

(56) , : Cut angle

(57) : Inclination angle