JP5308732B2 - Aircraft radial tire - Google Patents

Description

  The present invention relates to a radial tire for an aircraft, and more particularly to a radial tire for an aircraft in which the weight of the tire is reduced and the durability of the bead portion of the tire is improved.

Radial tires for aircraft have a very high filling internal pressure exceeding 10 atm. According to official standards, they are subjected to large flexural deformation exceeding 30% in use, ensuring high reliability. Therefore, it is necessary to take a safety factor of four times or more of the normal internal pressure.
For this reason, in many cases, a radial carcass is configured by superposing a plurality of carcass plies made of organic fiber cords, thereby satisfying high pressure resistance and high durability requirements for the tire. .

By the way, in the bead portion of the aircraft radial tire used under the condition where the deflection exceeds 30%, the region in contact with the rim flange is repeatedly collapsed and restored every time the tire rotates. It is indispensable to adopt a material and a structure that can withstand deformation that is repeated every time in the radial carcass portion.
On the other hand, strict demands for reducing the weight of tires are imposed by aircraft manufacturers, and the compatibility of tire performance and weight reduction of tires is an important issue in tire design.

  For this reason, for example, Patent Document 1 discloses that the cord constituting the carcass ply is replaced with a conventional 6,6 nylon cord or the like for the purpose of improving the durability and reducing the weight of the tire. Pneumatic radial tires that use organic fiber cords with higher strength and higher modulus, such as polyketone fiber cords, reduce the number of carcass plies and reduce tire weight under excellent durability Has been proposed.

However, in such a conventional tire, the cord constituting the carcass ply is a cord having a high elastic modulus, and the cord may be fatigued due to repeated bending of the bead portion during traveling, and sometimes breaks. There was a concern that the durability as high as expected could not be realized.
JP 2007-190963 A

  As a result of intensive studies on this point, with respect to the durability of the bead portion, in the cord having a high modulus of elasticity, the cord constituting the carcass ply disposed on the outer side in the tire width direction is deformed by the deformation of the bead portion under load. It was found that this compressive force is the cause of fatigue and breakage of the cord.

  Accordingly, an object of the present invention is to provide a radial tire for aircraft in which the durability of the bead portion of the tire is improved while the weight of the tire is reduced.

The radial tire for aircraft according to the present invention includes a pair of bead cores and a plurality of organic fiber cords that extend in a toroid shape between the bead cores and extend at an angle in a range of 70 to 90 ° with respect to the tire equatorial plane. A radial carcass composed of at least two carcass plies, and this radial carcass has one or more turn-up plies wound around the bead core from the inner side to the outer side in the tire width direction; An organic fiber cord comprising at least one carcass ply, having one or more down plies extending inward in the radial direction so as to cover the winding portion of the turn-up ply and reaching around the bead core The tensile breaking strength of the steel is in the range of 10.0 to 20.0 cN / dtex and the tensile force action of 2.1 cN / dtex The tire bead is adjusted in the range of 1.0 to 5.0%, assembled to the applicable rim, filled with the normal internal pressure from the state where the internal pressure is 0 kPa, and applied with a load corresponding to the specified mass. The rim flange on the outer surface of the bead in the tire posture in which the deformation rate R _{F of the} outer surface of the bead part and the normal internal pressure are loaded and the normal load is applied until the outer surface is brought into close contact with the rim flange. Thickness L of the radial carcass at an internal pressure of 0 kPa at the position of the separation point from
2.0 <R _F /L<4.0
It is a polyketone fiber cord formed by satisfying this relationship.

Here, the “breaking strength” means a value calculated based on a result obtained by performing a tensile test according to JIS L 1017.
“Elongation” means a value calculated based on a result of a tensile test according to JIS L 1017.

“Applied rim” is an industrial standard that is valid for the region where tires are produced and used. .) A rim specified in YEAR BOOK, etc.
The “regular internal pressure” and “specified mass” refer to the air pressure and the maximum load capacity corresponding to the maximum load capacity in the applicable size described in TRA and the like, respectively.
In the radial tire for aircraft according to the present invention, normal or air with a changed oxygen partial pressure or an inert gas such as nitrogen can be used as the gas filled in the tire.

As shown in FIG. 1, “deformation rate R _F ” is the separation point from the rim flange of the bead portion outer surface of the bead portion outer surface assembled to the applicable rim when the tire inner pressure is 0 kPa. As shown in FIG. 2, a radius of curvature R _t (connecting to a similar separation point C _t on the outer surface of the bead portion in a tire posture in which a normal internal pressure is filled and a load corresponding to a specified mass is applied. A to B _{t to} C _t (B _t is the midpoint of the A to C _t curve)) and the radius of curvature R _{r of the} rim flange that is the radius of curvature in the tire posture with normal internal pressure and a normal load applied. 1 / R _F = 1 / R _r −1 / R _t is determined based on A to B _{r to} C _r (B _r is the midpoint of the A to C _r curve)).
"The thickness of the radial carcass L" from separating point C _t, as shown in FIG. 1, it is assumed that means the thickness of the imaginary line pressure is orthogonal to the carcass ply in the state of 0 kPa.

This deformation rate R _F is obtained from the change in the curvature of the outer surface of the bead portion between the tire internal pressure of 0 kPa and the normal internal pressure when a load corresponding to the specified mass is applied. since the curvature 1 / R _r of the rim flange, when the bead outer surface is deformed such collapse under restriction by the rim flange, an approximate curvature. The radial carcass thickness L is the strain caused by the peripheral difference between the inner layer and the outer layer of the carcass ply, which is proportional to the radial carcass thickness L, when the radial carcass collapses due to the fall of the bead. Involved in the occurrence of differences.
That is, in order to suppress the compressive force in the longitudinal direction of the cord constituting the carcass ply disposed on the outer side in the tire width direction, it is effective to increase the deformation ratio R _F and reduce the radial carcass thickness L. The durability of the bead portion of the tire can be improved using the deformation rate R _F / L as an index.

More preferably, in such a tire, the heat shrinkage stress σ and the elastic modulus E of the organic fiber cord of one or more carcass plies have the following formulas (1) and (2):
σ ≧ −0.01E + 1.2 (1)
σ ≧ 0.02 (2)
[In the formula, σ is a heat shrinkage stress (cN / dtex) at 177 ° C., and E is an elastic modulus (cN / dtex) at a load of 49 cN at 25 ° C. ]
Satisfy the relationship.

  Here, the heat shrinkage stress σ means that a 25 cm long sample of a polyketone fiber cord before vulcanization subjected to a general dip treatment is heated at a heating rate of 5 ° C./min, and 2 at 177 ° C. The stress (cN / dtex) generated in the cord when heated for a minute is meant. The elastic modulus E refers to an elastic modulus (cN / dtex) calculated from a tangent at 49 cN of the SS curve according to a cord tension test of JIS L 1017 8.5.

  Preferably, the heat shrinkage stress of the polyketone fiber cord is 0.4 to 1.5 cN / dtex.

  The polyketone is a copolymer of carbon monoxide and at least one unsaturated hydrocarbon, and more preferably, the unsaturated hydrocarbon is ethylene.

  The radial tire for aircraft according to the present invention has a tensile breaking strength of an organic fiber cord constituting at least one carcass ply in a range of 10.0 to 20.0 cN / dtex and a tensile force action of 2.1 cN / dtex. By using a high strength and high elastic cord with a time elongation of 1.0 to 5.0%, an increase in tire weight can be suppressed based on a reduction in the cord diameter and the number of carcass plies.

  In other words, if the tensile breaking strength of the cord is less than 10.0 cN / dtex, in order to achieve the safety factor required for aircraft tires, a larger number of plies, a larger cord diameter, etc. are required, and the tire weight increases. On the other hand, if it exceeds 20.0 cN / dtex, the tire may rupture from the belt or bead wire, etc., when running under severe conditions such as puncture of the paired tires. There is.

  Also, if the elongation is less than 1.0%, the cord strength difference between the inner layer and the outer layer of the carcass ply becomes large when the bead portion collapses under load, which may cause separation at the end of the carcass ply. If it exceeds 5.0%, the amount of bulging in the radial direction and width direction of the tire during internal pressure filling increases, and the pressure resistance may be impaired.

And, it is assembled to the applicable rim, from the state where the internal pressure is 0 kPa, until the normal internal pressure is filled and the load corresponding to the specified mass is applied, until the tire bead part outer surface is brought into close contact with the rim flange. The deformation rate R _{F of the} outer surface of the bead part and the normal internal pressure are filled, and the internal pressure is 0 kPa at the separation point position from the rim flange on the outer surface of the bead part in a tire posture loaded with a normal load. The thickness L of the radial carcass
2.0 <R _F /L<4.0
By satisfying the above relationship, it is possible to effectively suppress the compressive force in the longitudinal direction of the cord constituting the carcass ply disposed on the outer side in the tire width direction due to the fall of the bead portion when a load is applied. it can.

That is, if R _F / L is less than 2.0, the bead portion collapses when a load is applied, and a compressive force is applied to the cords constituting the carcass ply disposed on the outer side in the tire width direction, so that the cord fatigue during running is reduced. As a result, if R _F / L exceeds 4.0, the contact pressure between the bead portion and the rim flange when a load is applied increases, and cracks may occur in the back surface of the bead during traveling.

The aircraft radial tire of the present invention will be described below in detail with reference to the drawings.
FIG. 3 is a cross-sectional view in the width direction showing one embodiment of the radial tire for aircraft of the present invention, and FIG. 4 shows the bead portion in more detail when the tire of FIG. 3 is assembled to an applied rim and the internal pressure is 0 kPa. It is a principal part expanded sectional view shown in FIG.
In the figure, 1 is a tread portion, 2 is a pair of sidewall portions that extend inward in the radial direction continuously to the side portions of the tread portion 1, and 3 is continuously provided on the inner peripheral side of each sidewall portion 2. Each bead portion is shown.

  The tire shown here is a plurality of bead cores 4 embedded in a pair of bead portions 3, and extends between the bead cores 4 in a toroid shape and extends at an angle in a range of 70 to 90 ° with respect to the tire equatorial plane. A radial carcass made of a carcass ply 5 made of an organic fiber cord is provided.

  Further, on the outer peripheral side of the crown region of the radial carcass, a belt 6 made of four cord crossing belt layers, a belt protective layer 7 made of a cord extending in a zigzag manner in the tire circumferential direction, and a tread rubber 8 are sequentially arranged, On the surface of the tread rubber 8, for example, a plurality of circumferential grooves extending in the tire circumferential direction are formed.

  The radial carcass here includes a turn-up ply 5a in which a side portion of the carcass ply 5 is wound around each bead core 4 from the inner side to the outer side in the tire width direction, and the bead core 4 of these turn-up plies 5a. A so-called up-down structure comprising a down ply 5b extending inward in the radial direction so as to cover the winding portion of the bead core 4 and extending to at least the radially inward portion of the bead core 4.

By adopting such an up-down structure, the carcass ply 5 is pulled out under the action of the mutual pull-out restraining force due to the cancellation of the tension around the bead core 4 acting on each of the turn-up ply 5a and the down ply 5b. Can be effectively prevented.
As a result, sufficient pressure resistance, load resistance and the like required for the radial tire for aircraft can be ensured.

In this aircraft radial tire, the tensile strength of the organic fiber cord constituting at least one carcass ply 5 is in the range of 10.0 to 20.0 cN / dtex, and the tensile force action is 2.1 cN / dtex. By setting the elongation at time in the range of 1.0 to 5.0%, assembling to the applicable rim, filling the normal internal pressure from the state where the internal pressure is 0 kPa, and applying a load corresponding to the specified mass, the tire The rim of the outer surface of the bead portion in a tire posture in which the deformation rate R _{F of the} outer surface of the bead portion and the normal internal pressure are loaded and the normal load is applied until the outer surface of the bead portion is brought into close contact with the rim flange. in separating point C _t position from the flange, and the thickness L of the radial carcass in a state where the internal pressure was 0 kPa,
2.0 <R _F /L<4.0
Satisfy the relationship.

  As a cord material constituting the carcass ply 5 that satisfies the above conditions, natural polymer fibers such as cotton, rayon, and cellulose, aliphatic polyamide, aromatic polyamide, polyester, polyvinyl alcohol, polybenzoazole, polyketone, and the like are synthesized. Polymer fibers are preferably used. These fibers can be used alone or as a mixture of a plurality of fibers.

More preferably, in the radial tire for aircraft, the heat shrinkage stress σ and the elastic modulus E of one or more organic fiber cords of the carcass ply 5 are expressed by the following formulas (1) and (2):
σ ≧ −0.01E + 1.2 (1)
σ ≧ 0.02 (2)
[In the formula, σ is a heat shrinkage stress (cN / dtex) at 177 ° C., and E is an elastic modulus (cN / dtex) at a load of 49 cN at 25 ° C. ]
Polyketone fiber cords satisfying the above relationship.
With this configuration, a high breaking strength is imparted to the radial carcass 5 to satisfy the pressure resistance required for the radial tire for aircraft, and the carcass ply is more than the case where the conventional nylon fiber cord is applied to the carcass ply 5. By reducing the number of 5, the tire weight can be significantly reduced.

The polyketone fiber cord exhibits heat shrinkage by shrinking with increasing temperature and exhibiting large heat shrinkage stress and elastic force, and has a reversibility that stretches and deforms with decreasing temperature, so the carcass ply 5 due to cord fatigue during running Can be prevented, and excellent tire durability can be secured.
Further, in addition to σ ≧ −0.01E + 1.2, by satisfying σ ≧ 0.02, the tread portion 1 radially outwards due to the action of centrifugal force during high speed running (high temperature) such as takeoff and landing The rubber distortion of the bead part 3 can be reduced while suppressing the protrusion to the surface.

  That is, in the case of σ <−0.01E + 1.2 and in the case of σ <0.02, there is no effect of suppressing the tread portion 1 from protruding outward in the radial direction when traveling at high speed (high temperature). It is sufficient and there is a tendency that improvement of internal pressure retention cannot be expected.

The polyketone fiber cord preferably has a heat shrinkage stress in the range of 0.4 to 1.5 cN / dtex, more preferably 0.6 to 1.0 cN / dtex.
If it is less than 0.4 cN / dtex, the alignment efficiency due to heating during tire production is reduced, and the strength as a tire tends to be insufficient. On the other hand, when it exceeds 1.5 cN / dtex, the shrinkage force of the organic fiber cord becomes too large at the time of vulcanization, resulting in the disorder of the cord inside the tire and the disorder of the rubber arrangement, resulting in deterioration of durability and uniformity. Tend to get worse.

ポリケトンは、一酸化炭素ＣＯと不飽和炭化水素との共重合体であり、例えば、高分子鎖中で各ＣＯ単位の隣に、エチレン単位等が一つずつ位置する交互共重合体である。また、ポリケトンは、一酸化炭素と特定の不飽和炭化水素の一種との共重合体であってもよく、一酸化炭素と不飽和炭化水素の二種以上との共重合体であってもよい。式中のＡを形成する不飽和炭化水素としては、エチレン、プロピレン、ブテン、ペンテン、シクロペンテン、ヘキセン、シクロヘキセン、ヘプテン、オクテン、ノネン、デセン、ドデセン、スチレン、アセチレン、アレン等の不飽和炭化水素化合物や、メチルアクリレート、メチルメタクリレート、ビニルアセテート、アクリルアミド、ヒドロキシエチルメタクリレート、ウンデセン酸、ウンデセノール、６−クロロヘキセン、Ｎ−ビニルピロリドン、スルニルホスホン酸のジエチルエステル、スチレンスルホン酸ナトリウム、アリルスルホン酸ナトリウム、ビニルピロリドン及び塩化ビニル等の不飽和結合を含む化合物等であってもよい。これらは単独で用いてもよく、二種以上を組み合わせて用いてもよい。
特にポリマーの力学特性や耐熱性等の点から、不飽和炭化水素としてエチレンを主体とするものを用いたポリケトンが好ましい。 The polyketone fiber cord is made of a polyketone fiber substantially composed of a repeating unit represented by Chemical Formula 1.

The polyketone is a copolymer of carbon monoxide CO and unsaturated hydrocarbon. For example, the polyketone is an alternating copolymer in which one ethylene unit is located next to each CO unit in the polymer chain. Further, the polyketone may be a copolymer of carbon monoxide and one kind of specific unsaturated hydrocarbon, or may be a copolymer of two or more kinds of carbon monoxide and unsaturated hydrocarbon. . The unsaturated hydrocarbon forming A in the formula includes unsaturated hydrocarbon compounds such as ethylene, propylene, butene, pentene, cyclopentene, hexene, cyclohexene, heptene, octene, nonene, decene, dodecene, styrene, acetylene, and allene. And methyl acrylate, methyl methacrylate, vinyl acetate, acrylamide, hydroxyethyl methacrylate, undecenoic acid, undecenol, 6-chlorohexene, N-vinylpyrrolidone, diethyl ester of sulphonylphosphonic acid, sodium styrenesulfonate, sodium allylsulfonate, It may be a compound containing an unsaturated bond such as vinyl pyrrolidone and vinyl chloride. These may be used alone or in combination of two or more.
In particular, from the viewpoint of the mechanical properties and heat resistance of the polymer, polyketone using unsaturated hydrocarbons mainly composed of ethylene is preferable.

  The polyketone used as the raw material for the polyketone fiber cord may have partially bonded ketone groups and unsaturated hydrocarbon-derived portions, but the unsaturated hydrocarbon-derived portions and ketone groups are alternately arranged. It is preferable that the proportion of the portion is 97% by mass or more.

（式中、ｔ及びＴは、純度９８％以上のヘキサフルオロイソプロパノール及びヘキサフルオロイソプロパノールに溶解したポリケトンの希釈溶液の２５℃での粘度管の流過時間であり；Ｃは、上記希釈溶液１００ｍＬ中の溶質の質量（ｇ）である）で定義される極限粘度［η］が１〜２０ｄＬ／ｇの範囲にあることが好ましく、２〜１０ｄＬ／ｇの範囲にあることが更に好ましく、３〜８の範囲にあることがより一層好ましい。極限粘度が１ｄＬ／ｇ未満では、分子量が小さ過ぎて、高強度のポリケトン繊維コードを得ることが難しくなる上、紡糸時、乾燥時及び延伸時に毛羽や糸切れ等の工程上のトラブルが多発することがあり、一方、極限粘度が２０ｄＬ／ｇを超えると、ポリマーの合成に時間及びコストがかかる上、ポリマーを均一に溶解させることが難しくなり、紡糸性及び物性に悪影響が出ることがある。 Furthermore, as a polymerization degree of polyketone, the following formula:

(In the formula, t and T are hexafluoroisopropanol having a purity of 98% or more and a polyketone diluted solution dissolved in hexafluoroisopropanol at a flow rate of 25 ° C. in a viscosity tube; C is in 100 mL of the diluted solution) The intrinsic viscosity [η] defined by the mass (g) of the solute is preferably in the range of 1 to 20 dL / g, more preferably in the range of 2 to 10 dL / g, and 3 to 8 It is still more preferable that it exists in the range. If the intrinsic viscosity is less than 1 dL / g, the molecular weight is too small to obtain a high-strength polyketone fiber cord, and troubles such as fluff and yarn breakage occur frequently during spinning, drying and stretching. On the other hand, if the intrinsic viscosity exceeds 20 dL / g, it takes time and cost to synthesize the polymer, and it becomes difficult to uniformly dissolve the polymer, which may adversely affect the spinnability and physical properties.

  Here, as a spinning method of the unstretched yarn of polyketone, a known method can be employed, and specifically, JP-A-2-112413, JP-A-4-228613, and JP-T-4-505344. A wet spinning method using an organic solvent such as hexafluoroisopropanol and m-cresol, as described in WO 99/18143, WO 00/09611, JP 2001-164422, JP 2004-218189. And a wet spinning method using an aqueous solution of zinc salt, calcium salt, thiocyanate, iron salt and the like as described in JP-A No. 2004-285221.

  For example, in a wet spinning method using an organic solvent, a polyketone polymer is dissolved in hexafluoroisopropanol, m-cresol, or the like at a concentration of 0.25 to 20% by mass, extruded from a spinning nozzle to be fiberized, and then toluene, ethanol, isopropanol The unstretched yarn of polyketone can be obtained by removing and washing the solvent in a non-solvent bath such as n-hexane, isooctane, acetone or methyl ethyl ketone.

  On the other hand, in the wet spinning method using an aqueous solution, for example, a polyketone polymer is dissolved in an aqueous solution of zinc salt, calcium salt, thiocyanate, iron salt or the like at a concentration of 2 to 30% by mass, and a spinning nozzle is formed at 50 to 130 ° C. Then, it is extruded into a coagulation bath and subjected to gel spinning, followed by desalting and drying to obtain an undrawn polyketone yarn.

  Further, for example, according to the method described in JP-A-2-112413, the polymer is dissolved in, for example, hexafluoroisopropanol, m-cresol, etc. at a concentration of 0.25 to 20% by mass, preferably 0.5 to 10% by mass. The fiber is extruded from a spinning nozzle, and then the solvent is removed and washed in a non-solvent bath such as toluene, ethanol, isopropanol, n-hexane, isooctane, acetone, methyl ethyl ketone, and preferably in an acetone bath to obtain a spinning yarn. Further, a solution spinning method in which stretching treatment is performed at a temperature in the range of (melting point−100 ° C.) to (melting point + 10 ° C.), preferably (melting point−50 ° C.) to (melting point) can be employed.

  The unstretched yarn of the resulting polyketone can be obtained by (i) performing multi-stage hot drawing and drawing at a specific temperature and magnification in the final drawing step of the multi-stage hot drawing, or (ii) after hot drawing and completion of hot drawing. A method of rapid cooling while applying high tension to the fibers is preferred. A desired filament suitable for production of a polyketone fiber cord can be obtained by fiberizing the polyketone by the method (i) or (ii).

  As a drawing method of the obtained undrawn yarn, a hot drawing method in which the undrawn yarn is heated and drawn to a temperature higher than the glass transition temperature of the undrawn yarn is preferable. ) May be carried out in one stage, but it is preferably carried out in multiple stages. There is no restriction | limiting in particular as a method of heat drawing, For example, the method etc. which run a thread | yarn on a heating roll or a heating plate are employable. Here, the heat stretching temperature is preferably in the range of 110 ° C. to (the melting point of the polyketone), and the total stretching ratio is preferably 10 times or more.

  When polyketone fiberization is carried out by the above method (i), the temperature in the final stretching step of the multistage thermal stretching is preferably in the range of 110 ° C. to (the stretching temperature of the stretching step one step before the final stretching step). Moreover, the draw ratio in the final drawing step of multistage heat drawing is preferably in the range of 1.01 to 1.5 times. On the other hand, when polyketone fiberization is carried out by the above method (ii), the tension applied to the fiber after completion of the hot drawing is preferably in the range of 0.5 to 4 cN / dtex, and the cooling rate in rapid cooling is 30 The cooling end temperature in the rapid cooling is preferably 50 ° C. or less. Here, there is no restriction | limiting in particular as a rapid cooling method of the heat-stretched polyketone fiber, A conventionally well-known method can be employ | adopted, Specifically, the cooling method using a roll is preferable. In addition, since the polyketone fiber obtained in this way has a large residual elastic strain, it is usually preferable to perform relaxation heat treatment so that the fiber length is shorter than the fiber length after hot drawing. Here, the temperature of the relaxation heat treatment is preferably in the range of 50 to 100 ° C., and the relaxation ratio is preferably in the range of 0.980 to 0.999 times.

  The organic fiber cord is formed by, for example, twisting a plurality of filament bundles made of polyketone, preferably two or three strands. For example, a filament bundle made of polyketone is twisted, and then a plurality of filament bundles are joined together. Thus, by twisting in the opposite direction, a twisted cord having a double twist structure can be obtained.

Next, a radial tire having a structure as shown in FIG. 3 and a size of 46 × 17R20 30PR was prototyped, and as shown in Tables 1 and 2, Example Tire 1 and Comparative Example in which the respective specifications were changed were shown. For each of the tire 1 to the comparative example tire 5, the weight, the safety factor, and the remaining strength of the outermost carcass ply cord were evaluated.
The polyketone, which is a material used for the organic fiber cord of the carcass ply, is composed of almost 100% of the repeating unit represented by the above (Chemical Formula 1), and 97 mol% or more thereof is 1-oxotrimethylene.

(Tire weight)
The tire weight of each of Example Tire 1 and Comparative Example Tire 1 to Comparative Example Tire 5 was measured. The results are shown in Table 3 as index values.
In addition, the index value in a table | surface was calculated | required using the value of the comparative example tire 1 as control, and the weight was so small that the numerical value was small.

(safety ratio)
For each of Example Tire 1 and Comparative Example Tire 1 to Comparative Example Tire 5, when the tire is mounted on a rim having a rim size of 46 × 17R20 and the inside of the tire is filled with water and the internal pressure is increased, The ratio to the specified internal pressure determined by TRA (pressure at which the tire breaks / normal internal pressure determined by TRA) was measured. The evaluation results are shown in Table 3.
The TSO defined by FAA stipulates that the safety factor for aircraft tires is four times or more. The larger the value, the better the pressure resistance.

(Remaining strength of outermost ply cord)
For each of Example Tire 1 and Comparative Example Tire 1 to Comparative Example Tire 5, the tire was mounted on a rim having a rim size of 46 × 17R20, the internal pressure was 1530 kPa, the load mass was 20870 kg, and the speed was measured on the drum tester. A taxing test of running at 64 km / h for 10 minutes and cooling for 110 minutes was repeated for 100 cycles, and then the outermost ply cord of the bead portion was collected by dissection, and the residual strength was measured with a cord tension tester. The evaluation results are shown in Table 3.
The cord strength of the comparative example tire 1 was obtained as a control, and the larger the value, the better.

  From the results of Table 3, the example tire was able to achieve an improvement in safety factor and ply cord fatigue of the bead portion while suppressing an increase in the tire weight with respect to the comparative example tire 1 to the comparative example tire 5. .

1 is an enlarged cross-sectional view of a main part of a bead part when an embodiment of a radial tire for aircraft according to the present invention is assembled to an applied rim and an internal pressure is 0 kPa. 1 is an enlarged cross-sectional view of a main portion of a bead portion when a normal internal pressure is charged and a load corresponding to a specified mass is applied to an embodiment of a radial tire for aircraft according to the present invention. 1 is a widthwise step view showing an embodiment of an aircraft radial tire of the present invention. FIG. 4 is an enlarged cross-sectional view of a main part showing the bead portion in more detail when the tire of FIG. 3 is assembled to an applied rim and the internal pressure is 0 kPa. It is a principal part expanded sectional view of the bead part when the conventional radial tire for airplanes is assembled | attached to an application rim, and an internal pressure is 0 kPa. It is a principal part expanded sectional view of the bead part when the conventional radial tire for airplanes is assembled | attached to an application rim, and an internal pressure is 0 kPa. It is a principal part expanded sectional view of the bead part when the conventional radial tire for airplanes is assembled | attached to an application rim, and an internal pressure is 0 kPa. It is a principal part expanded sectional view of the bead part when the conventional radial tire for airplanes is assembled | attached to an application rim, and an internal pressure is 0 kPa.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 4 Bead core 5 Carcass ply 5a Turn-up ply 5b Down ply 6 Belt 7 Belt protective layer 8 Tread rubber

Claims (5)

A pair of bead cores and at least two carcass plies formed of a plurality of organic fiber cords extending in a toroidal shape between these bead cores and extending at an angle in a range of 70 to 90 ° with respect to the tire equatorial plane. A radial carcass, and the radial carcass covers one or more turn-up plies with side portions wound around each bead core from the inside to the outside in the tire width direction, and covers the turn-up ply of the turn-up ply. In an aircraft radial tire having one or more down plies extending radially inward and reaching around a bead core,
The tensile strength at break of the organic fiber cord constituting at least one carcass ply is in the range of 10.0 to 20.0 cN / dtex, and the elongation at the time of the tensile force of 2.1 cN / dtex is 1.0 to 5.0% range,
From the state where the internal pressure is 0 kPa after being assembled to the applied rim, by filling the regular internal pressure and applying a load corresponding to the specified mass, the outer surface of the tire bead part is brought into close contact with the rim flange. Radial in a state in which the internal pressure is 0 kPa at the separation point position from the rim flange on the outer surface of the bead part in the tire posture in which the deformation ratio R _{F of the} outer surface of the bead part and the normal internal pressure is filled and a normal load is applied. The carcass thickness L is
2.0 <R _F /L<4.0
An aircraft radial tire characterized by satisfying the above relationship. The thermal contraction stress σ and the elastic modulus E of the organic fiber cord of one or more carcass plies have the following formulas (1) and (2):
σ ≧ −0.01E + 1.2 (1)
σ ≧ 0.02 (2)
[In the formula, σ is a heat shrinkage stress (cN / dtex) at 177 ° C., and E is an elastic modulus (cN / dtex) at a load of 49 cN at 25 ° C. ]
The radial tire for aircraft according to claim 1, wherein the cord is a polyketone fiber cord satisfying the following relationship. The radial tire for aircraft according to claim 2 , wherein the heat shrinkage stress of the polyketone fiber cord is 0.4 to 1.5 cN / dtex.   The radial tire for aircraft according to claim 2 or 3, wherein the polyketone is a copolymer of carbon monoxide and at least one unsaturated hydrocarbon.   The radial tire for aircraft according to claim 4, wherein the unsaturated hydrocarbon is ethylene.

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