Aircraft tire

The present invention provides an aircraft tire having a carcass structure capable of sufficiently satisfying recent demands for high pressure resistance without increase in tire weight. An aircraft tire 9 includes a pair of bead portions 2 and a carcass 4 made by stacking two or more carcass layers 3 composed of cords coated with rubber, which toroidally extend between the bead portions 2. Further, with respect to carcass layers 3 of the carcass 4 which are adjacent to each other, elongation at break of a widthwise outer carcass layer 3 is smaller than elongation at break of a widthwise inner carcass layer 3.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No. PCT/JP2010/002934 filed on Apr. 22, 2010, which claims priority from Japanese Patent Application No. 2009-103816, filed Apr. 22, 2009, the contents of all of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to an aircraft tire and more particularly to an aircraft tire which is intended to improve pressure resistance of the same.

RELATED ART

High-level safety has been demanded for aircraft tires and such tires are required to have pressure resistance for even four times the regular internal pressure.

In order to meet such demands, pressure resistance of aircraft tires is ensured with the use of a carcass as a framework; the carcass is formed by stacking two or more carcass layers composed of cords coated with rubber, which toroidally extend between a pair of bead portions.

As such an aircraft tire, WO2003/061991 proposes a tire including two or more carcass layers, the carcass layers having a tensile fracture strength of 6.3 cN/dtex or higher, an elongation percentage of 0.2% to 1.8% when 0.2 cN/dtex load is applied in an elongating direction, an elongation percentage of 1.4% to 6.4% when 1.9 cN/dtex load is applied in the elongating direction, and an elongation percentage of 2.1% to 8.6% when 2.9 cN/dtex load is applied in the elongating direction. Increase in the number of carcass layers is suppressed and the carcass layers are restrained from swelling in the widthwise direction of the tire accordingly.

However, in recent years, aircraft tires grow in size and are applied with higher internal pressure; therefore, it is not deniable that the tires with the structure of the above-mentioned technique lack strength. Thus, the number of carcass layers tends to be increased further than ever in order to restrain swelling in the tire width direction.

For example, when a new tire is developed with increase in the size of an aircraft tire, attempts have been made to increase the number of carcass layers having the same kind of cords in order to improve pressure resistance of the tire.

PRIOR ART DOCUMENT

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

Thus increased number of carcass layers provides resistance commensurate with increase in the number of carcass layers. On the other hand, increase in tire weight has been a new problem.

It is, therefore, an object of the present invention to propose a carcass structure capable of sufficiently satisfying recent demands for high pressure resistance without increase in tire weight.

Means for Solving the Problem

The inventor made a detailed study to achieve the above-mentioned object and newly found that, when a tire having a carcass composed of two or more layers is applied with high internal pressure, a carcass layer disposed on the widthwise inner side is elongated differently from a carcass layer disposed on the widthwise outer side and the above-mentioned object can be achieved by reducing such difference. That is to say, when a tire is applied with a high internal pressure, rubber of carcass layers is elongated in the width directions of the tire due to radial and widthwise expansion of the tire and the rubber gauge between the carcass layers is decreased accordingly. In particular, in a carcass, a region from a shoulder portion to a bead portion which is not tied with a belt significantly expands widthwise. The inventor found out that at the time of such expansion, cords constituting each carcass layer are differently elongated and carcass layers which have been greatly elongated are fractured early and that the above-mentioned object can be achieved by remediating this phenomenon. Note that the “widthwise inner carcass layer” and the “widthwise outer carcass layer” are referred to carcass layers corresponding to a “radially inner carcass layer” and a “radially outer carcass layer” viewed on the tire equatorial plane, respectively.

The above-mentioned phenomenon will be further explained in detail with reference to the drawings.FIG. 1is a view illustrating a tire before and after being applied with internal pressure, in which two carcass layers among the carcass layers of the tire are partially enlarged.

Assuming that, when the inside of a tire is not filled with air, the shortest distance from a tire equatorial plane to a line segment through the axis in the center of the carcass layer disposed on the widthwise inner side of the carcass, which is parallel to the tire equatorial plane is D1and the shortest distance from the tire equatorial plane to a line segment through the axis in the center of the carcass layer disposed on the widthwise outer side of the carcass, which is parallel to the equatorial plane is D2, the above-mentioned shortest distances are D1+Δ1and D2+Δ2, respectively when the inside of the tire is filled with air.

When the tire is applied with internal pressure, a distance between carcass layers, that is, spacing between arrayed cords of the carcass layers is reduced and a distance δdefbetween cords when the tire is not applied with internal pressure and a distance δdefbetween cords when the tire is applied with internal pressure inFIG. 1satisfy the relationship δdef>δinf.

The distance δinfbetween cords when the tire is applied with internal pressure is shorter than δdefbecause the increases in the respective shortest distances are different, which results in Δ1>Δ2. As just described, Δ1becomes larger than Δ2; thus, cords constituting the carcass layer disposed on the widthwise inner side are differently elongated from cords constituting the carcass layer disposed on the widthwise outer side. As a result, the carcass layers are differently elongated. Specifically, the carcass layer disposed on the widthwise inner side is more elongated.

FIG. 2shows a relationship between tension and an elongation percentage of a conventional carcass layer at the timing when a tire is broken, that is, when any of the carcass layers constituting a carcass is broken. In the figure, CAindenotes a carcass layer disposed on the widthwise inner side and CAoutdenotes a carcass layer disposed on the widthwise outer side. Amax denotes an elongation pecentage when the carcass layer CAinis broken, namely elongation at break, and the tension at that time is Tmax. In addition, an elongation percentage of the carcass layer CAoutwhen the carcass layer CAinis broken is A and the tension at that time is T.

As shown inFIG. 2, as two carcass layers having the same specifications are compared, when the tire is broken, the carcass layer CAinis broken due to a limit of cord strength while the carcass layer CAoutdoes not reach a limit of cord strength. In other words, when the carcass layer CAinis broken, the carcass layer CAoutcan afford an extra elongation percentage and tension until the carcass layer CAoutis broken (ΔA and ΔT represent an extra elongation percentage and tension in the figure). Thus, the tire is broken while the carcass layer CAoutdoes not give the best performance. The above results show that the ability of the carcass layer CAoutis not utilized to the maximum.

Therefore, based on the above-mentioned knowledge, the inventor studied a method for bringing out each carcass layer constituting a carcass to the maximum and obtaining desired pressure resistance without increasing tire weight, and consequently found that it is effective for improving pressure resistance without increasing tire weight to appropriately adjust elongation at break of each carcass layer constituting a carcass from the widthwise inner side to the outer side. The present invention is predicated on the above-mentioned knowledge.

The subject matter of the present invention is as follows.

(1) An aircraft tire includes a pair of bead portions and a carcass made by stacking two or more carcass layers composed of cords coated with rubber. The carcass layers toroidally extend between the bead portions. With respect to carcass layers of the carcass which are adjacent to each other, elongation at break of a widthwise outer carcass layer is smaller than elongation at break of a widthwise inner carcass layer.

(2) In the aircraft tire according to (1) above, elongation at break Loutof a widthwise outermost carcass layer of the carcass and elongation at break Linof a widthwise innermost carcass layer satisfy 0.75<Lout/Lin<0.98.

(3) In the aircraft tire according to (1) or (2) above, elongation at break Minof cords constituting the widthwise innermost carcass layer of the carcass and elongation at break Moutof cords constituting the widthwise outermost carcass layer satisfy 0.75<Mout/Min<0.98.

(4) In the aircraft tire according to any one of (1) to (3) above, between two or more carcass layers composed of cords coated with rubber in the carcass, cords are stacked to intersect with each other. Further, with respect to adjacent carcass layers, an inclination angle of cords constituting a widthwise outer carcass layer with respect to a tire width direction is smaller than an inclination angle of cords constituting a widthwise inner carcass layer with respect to the tire width direction.

(5) The aircraft tire according to any one of (1) to (4) above, with respect to the adjacent carcass layers, twist turns of cords constituting the widthwise outer carcass layer is equal to or less than twist turns of cords constituting the widthwise inner carcass layer.

(6) In the aircraft tire according to any one of (1) to (5) above, the cords constituting the carcass layers are organic fiber cords.

(7) In the aircraft tire according to any one of (1) to (6) above, spacing distance between each of adjacent carcass layers in the carcass increases toward the widthwise outer side from the widthwise inner side.

(8) In the aircraft tire according to (7) above, the carcass layers are three or more carcass layers.

(9) The aircraft tire according to (7) or (8) above, the spacing distance between the adjacent carcass layers progressively increases toward the widthwise outer side from the widthwise inner side.

According to the present invention, in a carcass composed of at least two carcass layers having a plurality of cords coated with rubber, elongation at break of the widthwise outermost carcass layer is made smaller than elongation at break of a widthwise innermost carcass layer, and the percentage of elongation at break of the both of the carcass layers is adjusted, to bring out the ability of each carcass layer to the maximum. Thus, a carcass structure capable of sufficiently satisfying recent demands for high pressure resistance without increase in tire weight can be provided. As a result, an aircraft tire obtaining desired pressure resistance can be provided.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be specifically explained.FIG. 3shows a widthwise sectional view of a pneumatic tire according to the present invention. The tire shown inFIG. 3includes an inner liner1, a pair of bead portions2which are engaged to rims when the tire is mounted on the rims, a carcass4composed of carcass layers3toroidally extending between the bead portions2(carcass layers3ato3cdenote carcass layers of the carcass4which are sequentially stacked on the widthwise outer side of the inner liner1). The tire further includes a belt6composed of belt layers5on the carcass4on the radially outer side of the tire (belt layers5ato5ddenote layers of the belt6which are sequentially stacked on the carcass4on the radially outer side of the tire). Furthermore, the tire includes a belt protecting layer7on the belt6on the radially outer side, and a tread portion8disposed on even the radially outer side than the belt protecting layer7. Reference numeral9denotes the whole tire.

The carcass4is made by stacking at least three layers of the carcass layers3composed of cords coated with rubber, three layers of the carcass layers3ato3cin the diagram. With respect to adjacent carcass layers, elongation at break of a widthwise outer carcass layer3is smaller than the elongation at break of a widthwise inner carcass layer3. Specifically, elongation at break of the carcass layer3bis smaller than the elongation at break of the carcass layer3a, and elongation at break of the carcass layer3cis smaller than the elongation at break of the carcass layer3b.

Here, elongation at break of the carcass layers3means an elongation percentage at break L of the carcass layers3and can be calculated from elongation at break M [%] of cords constituting the carcass layers3. Specifically, assuming that a is an inclination angle of cords with respect to the direction of the width of a tire, an elongation percentage at break L of the carcass layers3can be calculated from the following equation.
L=M×cos α  [Equation 1]

Elongation at break M of cords is measured by the tensile test compliant with JIS L 1017.

Thus, elongation at break of the carcass layers3can be increased or decreased by changing at least one of elongation at break M of cords and an inclination angle α of cords.

FIG. 4shows a relationship between an elongation percentage and tension of the carcass layers3when the tire9having a carcass structure in which elongation at break of the carcass layers3is appropriately adjusted according to the present invention is broken. As shown in this figure, although the carcass layer CAoutand the carcass layer CAineach have different limits of an elongation ratio and tension, it is found that the carcass layer CAoutand the carcass layer CAinare broken at the same time when the tire9is broken. Specifically, since elongation at break Amax2of the carcass layer CAoutis made smaller than elongation at break Amax1of the carcass layer elongation limit Amax1of the carcass layer CAinapplied with a higher pressure than the carcass layer CAoutis larger than the elongation limit Amax2of the carcass layer CAout. Therefore, the carcass layer CAinis not broken earlier but can be broken in synchronization with the carcass layer CAoutbeing broken. Therefore, the carcass layer CAincan afford a tension up to Tmax1and the carcass layer CAoutcan afford a tension up to Tmax2as well so that tension of the carcass layer CAout, which cannot be conventionally used up can be used up.

As a result, each of the carcass layers3ato3ccan be utilized to the maximum so that it is possible to improve pressure resistance without increasing the number of layers in the carcass4.

It is noted that the carcass structure and the number of the stacked carcass layers3shown in the widthwise sectional view of the tire9inFIG. 3are not limited in particular but can be appropriately adjusted as long as the advantageous effects of the present invention can be obtained. Further, the carcass4includes a carcass4having a bias structure and a carcass4having a radial structure. However, the carcass4having a radial structure generally has low durability in a region from sidewall portions to the bead portions; therefore, it should be noted that especially advantageous effects can be obtained by applying a structure according to the present invention to a tire including a carcass4having a radial structure.

Further, elongation at break Loutof the widthwise outermost carcass layer3of the carcass4and elongation at break Linof the widthwise innermost carcass layer3preferably satisfy 0.75<Lout/Lin<0.98. This is because when Lout/Linis smaller than 0.75, Loutis insufficient, so that the widthwise outermost carcass layer3is broken earlier than the widthwise innermost carcass layer3, which would make it impossible to utilize the ability of the whole carcass4to the maximum. On the other hand, when Lout/Linis larger than 0.98, as with a conventional carcass4, Loutis not small enough, so that the widthwise innermost carcass layer3is broken earlier than the widthwise outermost carcass layer3, which would make it impossible to utilize the ability of the whole carcass4to the maximum.

Furthermore, elongation at break Minof cords constituting the widthwise innermost carcass layer3of the carcass4and elongation at break Moutof cords constituting the widthwise outermost carcass layer3preferably satisfy 0.75<Mout/Min<0.98. This is because when Mout/Minis smaller than 0.75, Moutis insufficient, so that the cords constituting the widthwise outermost carcass layer3are broken earlier than the cords constituting the widthwise innermost carcass layer3, which would make it impossible to utilize the ability of the whole carcass4to the maximum. On the other hand, when Mout/Minis larger than 0.98, as with a conventional carcass4, Moutis not small enough, so that the cords constituting the widthwise innermost carcass layer3are broken earlier than the cords constituting the widthwise outermost carcass layer3, which would make it impossible to utilize the ability of the whole carcass4to the maximum.

In addition, with respect to the carcass4, it is preferable that cords are stacked to intersect with each other between two or more carcass layers composed of cords coated with rubber, and the inclination angle of the cords constituting the widthwise outer carcass layer3with respect to the tire width direction is not more than the inclination angle of the cords constituting the widthwise inner carcass layer3with respect to the tire width direction among respective radially adjacent carcass layers.

That is to say, the inclination angle of the cords constituting a widthwise outer carcass layer3with respect to the tire width direction is made less than the inclination angle of the cords constituting a widthwise inner carcass layer3with respect to the tire width direction, which allow elongation at break in the tire width direction to decrease from a widthwise inner carcass layer3to a widthwise outer carcass layer3. Further, the cords constituting the widthwise inner and outer carcass layers3can be broken at the same time when the tire9is broken by high internal pressure. Consequently, ability of the cords can be further utilized. On this occasion, it is preferable that the inclination angle of the cords with respect to the tire width direction is within a range of 0 degrees to 45 degrees. This is because if the angle exceeds 45 degrees, the carcass4is relatively reduced in stiffness in the width direction and cannot sufficiently serve as a member supporting water pressure in the water pressure test to be described below.

In addition, it is preferable that with respect to adjacent carcass layers, the number of twist turns of the cords constituting a widthwise outer carcass layer3is less than the number of twist turns of the cords constituting a widthwise inner carcass layer3. In general, as shown inFIG. 5, when the number of twist turns of cords is decreased (C3>C2>C1), as elongation at break of the cords is decreased (A3>A2>A1), tension of the cords tends to be increased (T3<T2<T1). That is to say, cords having the number of twist turns of less than that of cords constituting a widthwise inner carcass layer3are applied to a widthwise outer carcass layer3, which can increase cord tension and decrease elongation at break of the widthwise outermost carcass layer3. It is noted that the above-mentioned number of twist turns refers to the number of upper twist turns.

It is preferable to select appropriate organic fiber cords for cords constituting the carcass layers3depending on desired weight, stiffness, and the like. Flexibility and strength required for the cords vary depending on the kinds of aircrafts or tire structures. For example, rayon cords, aramid (aromatic polyamide) cords, or the like are preferably used for the organic fiber cord. The size of the cords can be naturally changed as appropriate depending on the kind of rubber forming the tire, and stiffness and cross-sectional shapes of bead cores10.

Further, spacing distance between adjacent carcass layers3in the carcass4is preferably larger toward the widthwise outer side from the widthwise inner side. This is because when spacing distance between adjacent carcass layers3on the widthwise outer side is large, the carcass4is larger in thickness on the widthwise outer side, and energy is required for deformation of a tire when the tire rotates with load applied thereto, which allows the elongation at break to decrease. On this occasion, in terms of further increasing the thickness of the carcass4and reducing elongation at break thereof, the carcass layers3are preferably three layers or more. Further, in terms of restraining change in spacing distance between each carcass layer3in the carcass4from causing excessive stiffness differences and improving durability of the tire; preferably, spacing distance between each adjacent carcass layer3is progressively longer toward the widthwise outer side from the widthwise inner side.

EXAMPLE

Aircraft tires having a size of 46×17820 (30PR) were produced under various specifications shown in Table 1. Each tire was mounted on a normal rim based on a “Year Book” of TRA (The Tire And Rim Association, inc.) in the United States of America to obtain tire wheels, and weight and pressure resistance of each tire wheel were examined. Pressure resistance of the tire was examined as a factor of safety (pressure at break). The results are shown in Table 1.

Pressure resistance of each tire was evaluated by examining a factor of safety (pressure at break). The factor of safety (pressure at break) was surveyed by the water pressure test, in which the inside of a tire was filled with water and its water pressure was gradually increased up to the timing when the tire was broken. The measured value shows the ratio of the water pressure at the time of tire breakage to the specified internal pressure. The higher the value is, the tire pressure resistance is more excellent. It is defined in TSO-c62e of “TSO (Technical Standard Order)” which is an official standard of FAA (Federal Aviation Administration) in the United States of America that a practical tire must successfully withstand for 3 seconds without bursting in a state where the tire is filled with air having a pressure of four times the regular internal pressure.

TABLE 1ConventionalConventionalExampleExampleExampleExampleExampleExampleExampleExampleTire 1Tire 2Tire 1Tire 2Tire 3Tire 4Tire 5Tire 6CarcassMaterialNylonNylonNylonNylonNylonNylonNylonNylonCords1400dtex1400dtex1400dtex1400dtex1400dtex1400dtex1400dtex1400dtex/2//2/2//2/2//2/2//2/2//2/2//2/2//2/2//2Layer number6 layers5 layers5 layers5 layers5 layers5 layers5 layers5 layersCarcass No.*11-61-51-34, 51-34, 51-34, 51-34, 51-34, 51-34, 5Angle (degrees)*4000000000000010Twist turns (index)100100100631007710080100901009510080Cord strength100100100125100121100114100105100102100114(index)Elongation at break20.420.420.415.120.416.120.417.220.419.320.42020.417.2of cords (%)Elongation at break202020152016201720192019.62017of carcass layer (%)Lout20201516171919.617Lin2020202020202020Lout/Lin110.750.80.850.950.980.85Mout20.420.415.216.317.219.319.917.2Min20.420.420.420.420.420.420.420.4Mout/Min110.750.80.840.940.980.85PerformanceWeight (index)*510096969696969696Factor of safety4.63.83.94.34.44.23.94.4(pressure at break)*6*1The first carcass, the second carcass.,,, sequentially from the radially inner side of the carcass.*2Inclination angle of cords with respect to the tire width direction.*3The upper twist multiplier of the cords of Conventional Example Tire 1 is defined as 100.*4The cord strength (index) of the cords of Conventional Example Tire 1 is defined as 100.*5The tire weight (index) of Example Tire 2 is defined as 100.*6The tire is mounted on a rim and the inside of the tire is filled with water to increase the pressure therein.The ratio of the water pressure at the time of tire breakage to the regular internal pressure.The ratio is at least 4 in the official standard.

As apparent from the results in Table 1, with respect to Conventional Example Tire 1, the factor of safety was effectively ensured; however, the weight was not sufficiently reduced. Further, with respect to Conventional Example Tire 2, although the weight was reduced sufficiently, the factor of safety was not effectively ensured. Meanwhile, with respect to Example Tires 1 to 6, the factor of safety (pressure at break) was effectively ensured as with Conventional Example Tire 1; the effect is particularly significant in Examples 2 to 4 and 6 in which Mout/Minwas in the range of 0.80 to 0.95. On this occasion, the conditions of TSO-c62e were achieved in each of Conventional Example tire 1, Example Tires 2 to 4, and 6. Further, the weight of each of Example Tires 1 to 6 was effectively reduced as with Conventional Tire 2.

INDUSTRIAL APPLICABILITY

As clearly understood from the above description, the present invention can provide an aircraft tire with improved pressure resistance by optimizing a carcass structure which can effectively restrain increase in tire weight.