Aircraft tyre carcass reinforcements

Abstract

The present invention relates to a radial tyre for an aircraft, comprising at least one carcass ply (51) comprising reinforcing elements, each carcass ply (51) having a first main portion (52) which connects one bead wire to the other and is connected at the ends thereof to two other portions or turn-ups (53) each having a free end (531). The free ends (531) of the two turn-ups (53) of at least one carcass ply (52) are positioned axially so as to form an overlay (6) between the two axially outer walls (2112) of the two axially outermost grooves (211) of the tread, each overlay having an axial width (L) of less than one third of the axial width (L1) of the crown reinforcement.

Description

[0001] Description

[0002] Title: AIRCRAFT TIRE CARCASS REINFORCEMENTS

[0003]

[0001] The present invention relates to an aircraft tire with a radial carcass reinforcement.

[0004]

[0002] Aircraft tires are intended to carry heavy loads and to be inflated to relatively high pressures at least above 8 bars, preferably above 10 bars and up to 25 bars. The tires in question have rims having a diameter at least equal to 6 inches but preferably at least equal to 20 inches. Aircraft tires are also characterized by their high load and their deflection at nominal load and pressure which reaches 28% to 33% for civil aircraft and up to 50% for military aircraft. Airplanes are vehicles whose landing gear is not directional, the aircraft in flight or taxiing is steered by the manipulation of flaps on the wings or the rear stabilizer of the aircraft and not by the rotation of the tires like road vehicles.Aircraft tires are therefore very specific in their architecture both for their carcasses which must withstand a very high burst pressure and their crown reinforcements composed of two layers based on slit strips and devoid of free ends in their axial ends as shown in document EP 2499006 Bl.

[0005]

[0003] A tire having a geometry of revolution relative to an axis of rotation, the geometry of the tire is generally described in a meridian plane containing the axis of rotation of the tire. For a given meridian plane, the radial, axial and circumferential directions respectively designate the directions perpendicular to the axis of rotation of the tire, parallel to the axis of rotation of the tire and perpendicular to the meridian plane. The circumferential direction is tangent to the circumference.

[0006]

[0004] In the following, the expressions "radially inner", respectively "radially outer" mean "closer", respectively "further from the axis of rotation of the tire". By "axially inner", respectively "axially outer", is meant "closer", respectively "further from the equatorial plane of the tire", the equatorial plane of the tire being the plane passing through the middle of the rolling surface and perpendicular to the axis of rotation.

[0005] An aircraft tire according to the invention has a tread, comprising at least 2 longitudinal grooves, each groove having an axially inner wall and an axially outer wall, two grooves, the most axially outer, being located on either side of the equatorial plane.Usually, to avoid unnecessary stresses when mounting on the rim, a radially outermost groove is symmetrical to another radially outermost groove with respect to the equator plane. The grooves have the function of evacuating any water located on the track in order to ensure good grip for the tire.

[0006] An aircraft tire according to the invention also has a crown reinforcement comprising working layers comprising textile reinforcing elements, made of aliphatic polyamide or hybrid made of aliphatic polyamide and aromatic polyamide, coated with rubber compounds and making a variable angle with the longitudinal direction XX', the absolute value of which is between 0 and 45°.A working layer is most often obtained by a circumferential zigzag winding or by a circumferential winding in turns of a strip, on a cylindrical laying surface having as its axis of revolution the axis of rotation of the tire. The strip is generally made up of at least one continuous textile reinforcement coated in an elastomeric mixture and, most often, of a juxtaposition of continuous textile reinforcements, coated in an elastomeric mixture and parallel to each other. The advantage of having a circumferential zigzag winding or a circumferential winding in turns is to avoid, at the axial ends of the working layers, the presence of free reinforcement ends, likely to generate cracks in these areas and, consequently, to reduce the endurance of the working reinforcement and the service life of the tire.When a strip is wound in a zigzag circumferential direction, the working layers are laid in pairs, each pair of working layers constituting a working bilayer. Thus, a working bilayer is formed, apart from its axial ends, by two radially superimposed working layers. At its axial ends, a working bilayer generally comprises more than two radially superimposed working layers. The axial end allowance is the number of additional working layers, in the radial direction, compared to the two working layers in the current area of ​​the working bilayer. Thus, the number of bilayers is determined on a meridian section at the equator plane.

[0007]

[0007] An aircraft tire according to the invention also has a radial carcass reinforcement, this radial carcass reinforcement comprising carcass layers comprising a plurality of textile reinforcing elements oriented substantially radially (i.e. making an angle of between 75° and 105° with the circumferential direction), this reinforcement being anchored to at least one circumferential reinforcing reinforcement in each bead, and most often to a single one called a bead wire. According to the state of the art, the reinforcing elements of said carcass layers are wound around said bead wire from the inside to the outside or vice versa, forming upturns whose respective ends are radially spaced relative to the axis of rotation of the tire. The reinforcing elements are coated in a rubber mixture called a calendering mixture.

[0008]

[0008] Each carcass layer has a first main part or forward strand, connecting one bead wire to the other and two parts or turn-ups each having a free end. By free end, it is meant that this end is not connected to another part of the carcass layer. Each end of the first part of each carcass layer is connected to one or other of the turn-ups having a free end, therefore neither of its ends is free. One of the ends of each turn-up is connected to the first so-called main part under the bead wire, the other end is free.

[0009]

[0009] For short turns, it is possible for the two turns, each having a free end, to be axially inside the first part of the carcass layer. The first main part of the carcass layer has the function of maintaining the internal pressure by taking up the tensions, in particular radial tensions, of the sidewall. The turn-ups have the essential role of preventing the carcass layer from unrolling by shearing of the calendering compounds between the reinforcement layers of the carcass layers. By unrolling, it is meant that the carcass layer separates under the effect of the internal pressure of the tire from the bead wire.

[0010]

[0010] The severe conditions under which aircraft tires are used are such that the endurance of the beads is an interesting avenue for improvement, particularly at the level of the carcass reinforcement overturning.

[0011]

[0011] The endurance of aircraft tire beads must however be improved, in fact said beads undergo heavy overloads with crushing of the order of 50% and more of the radial height of the tire. Furthermore, the necessary number of carcass layers, generally formed of reinforcing elements made of aliphatic or composite polyamide, that is to say formed of yarns of different moduli, is determined to withstand the tension due to the so-called test pressure which is equal to four times the service pressure. The large number of said carcass layers obviously leads to the multiplication of the free ends of reinforcing elements, the multiplication of interfaces between layers, greater hysteretic losses and therefore higher operating temperatures, all factors conducive to an increase in bead fatigue and a limitation of their endurance.

[0012]

[0012] Solutions with composite cables have notably been presented by patent EP1381525 and particularly composites formed from at least two yarns with a high modulus of elasticity and a single yarn with a low modulus of elasticity, more precisely two yarns made of aromatic or aramid polyamide, and one yarn made of aliphatic polyamide (more precisely Nylon).

[0013]

[0013] However, the architecture described in the state of the art is not an optimum, particularly for two essential performances of aircraft tires, namely endurance and mass. The inventors have set themselves the objective of improving these performances.

[0014]

[0014] This improvement is obtained by an aircraft tire, intended to be inflated to a pressure at least equal to 8 bars, having a crown comprising a tread and a crown reinforcement radially inside the tread, two beads capable of holding the tire on a mounting rim, two sidewalls between the beads and the crown and a radial carcass reinforcement ensuring the connection between the beads, the sidewalls and the crown,

[0015] • An equatorial plane of the tire being the plane passing through the middle of the rolling surface and perpendicular to the axis of rotation,

[0016] • the tread comprising at least 2 longitudinal grooves, two grooves, the most axially outer, being located on either side of the equatorial plane, each groove having an axially inner wall and an axially outer wall,

[0017] • the radial carcass reinforcement comprising at least one carcass layer comprising reinforcing elements coated with rubber compounds and oriented substantially radially, i.e. making an angle of between 75° and 105° with the circumferential direction,

[0018] • each carcass layer being anchored to at least one circumferential reinforcement or bead wire in each bead, each carcass layer having a first main part connecting one bead wire to the other and connected at its ends to two other parts or turns each having a free end,

[0019] • the crown reinforcement comprising at least 1 pair of working layers comprising reinforcing elements coated with rubber compounds and making a variable angle with the longitudinal direction XX' whose absolute value is between 0 and 45°, having an axial width,

[0020] • the free ends of the two upturns of at least one carcass layer being positioned axially between the two axially outer walls of the two most axially outer grooves, one free end of one upturn being radially outer to the second free end of the other upturn of the carcass layer in question and being positioned axially relative to the radially inner free end so as to form an overlap of the two free ends of the two upturns of said carcass layer,

[0021] • each overlap of two turns of a carcass layer having an axial width less than one third of the axial width of the crown reinforcement.

[0022]

[0015] Indeed, bead optimization surprisingly does not only consist of searching for reinforcement elements with good fatigue resistance and presenting the highest possible breaking force for the lowest possible reinforcement mass. A surprising way of significantly reducing stresses in the lower zone and in particular the compression of certain carcass layers, is to eliminate the presence of the free ends of the carcass layers in the bead. It is even less relevant to place these free ends in the sidewall which is the zone of maximum flexion and deformation of the tire when rolling on level ground.An optimal area for arranging the ends of the carcass layer turns is under the tread in the area where the working layers take up a major part of the pressure, namely between the grooves and more precisely between the two axially outer walls of the two axially outermost grooves, these two grooves being located on either side of the equatorial plane. This arrangement, which makes it possible to eliminate one end of the carcass layer in each bead for at least one carcass layer, makes it possible to reduce the compression in the bead of the first parts of the carcass layers.

[0023]

[0016] To make it possible to lighten the tire by reducing the number of carcass layers, it is imperative to recouple the free ends of the carcass layers together so that this recoupled part, or overlap, prevents the carcass layers from unwinding by shearing of their calendering compounds. In the absence of recoupling, it is necessary to provide another recoupling layer with reinforcing elements close to the angles of the carcass layers, namely between 75 and 105°. The crown layers, due to their angles, do not have the capacity to absorb transverse forces.

[0017] Thus, for good endurance performance and for the optimal gain of the invention, it is necessary to have an overlap of the two upturns under the crown between the axially outermost grooves of the tread, and more precisely between their two axially outer walls.By overlapping is meant that a part of one turn is pressed against a part of the other turn, the radial distance between the two turns, between the centers of the reinforcing elements of the two turns, being less than the sum of the diameters of a reinforcing element of each turn, preferably less than 1.5 times the average of the diameters of a reinforcing element of each turn. The overlap allows the transfer of the forces applied on one of the turns to the other turn, namely the recoupling of the two turns.

[0024]

[0018] To allow an effective saving in mass, each overlap of two turns of a carcass layer has an axial width less than one third of the axial width of the crown reinforcement, advantageously has an axial width less than one quarter of the width of the crown reinforcement. The axial width of the turn or of the crown reinforcement can be measured for example on a meridian section of the tire.

[0025]

[0019] Each overlap of two turns of a carcass layer has an axial width at least equal to 30 mm and at most equal to 100 mm. From 30 mm, the overlap is already over a length which allows excellent recoupling. Beyond 100 mm, the overlap can be shortened to be optimal from a mass point of view.

[0020] Advantageously, the free ends of the two turns of each carcass layer are positioned axially between the two axially outer walls of the two most axially outer grooves. The advantage of arranging all the free ends of the carcass layers under the crown and not in the bead or the sidewalls, is to reduce the tension variations in the carcass layers at these ends. With their free ends thus positioned, it is possible to have all the carcass layers in tension at the bead which is extremely favorable for endurance.According to the usual design criteria, it is then possible to reduce the number of carcass layers in the tire for the same endurance and thus save mass, which is extremely interesting for aircraft tires.

[0026]

[0021] Preferably, each overlap of two turns of a carcass layer is positioned directly above a groove of the tread. The expression "directly above" means "radially inside at least within the limit of the axial coordinates delimited by". Thus "the overlap is directly above a groove" means that on each meridian section, the overlap is radially inside the groove at least on the axial coordinates delimited by the groove. The advantage of locating the overlap directly above a groove is to ensure better endurance of the overlap. Indeed, directly above the groove, the overlap benefits from greater pressure during curing of the tire as well as better curing, the supply of calories and pressure by the mold being higher at this point of the tire, under the raised element of the mold which creates the groove.

[0027]

[0022] Advantageously for a tire comprising at least 2 carcass layers, the carcass layers are different either in terms of nature, or properties of the reinforcing elements of the two carcass layers, or pitch between the reinforcing elements. In this type of architecture, it is possible to further optimize the mass or endurance, to destandardize the carcass layers either in terms of distance between the reinforcing elements, or in terms of properties by playing for example on the twist of the threads of the reinforcing elements, or in terms of nature of reinforcing elements with one carcass layer in hybrid textile or not and the other with another hybrid or nylon or aramid.Thus advantageously for a tire comprising at least 2 carcass layers, the carcass layers are different either in terms of hybrid or monomaterial nature of the reinforcing elements, or in terms of materials used, or properties of the reinforcing elements of the two carcass layers, or pitch between the reinforcing elements.

[0028]

[0023] Preferably for advantages of ease of manufacture, for a tire comprising at least 2 carcass layers, the carcass layers are standardized in all their characteristics, that is to say in terms of hybrid or monomaterial nature of the reinforcing elements, properties of the reinforcing elements of the two carcass layers and pitch between the reinforcing elements.

[0029]

[0024] Advantageously, for better absorption of transverse forces transmitted by the tread to the architecture of the tire, the crown reinforcement is radially external to the carcass reinforcement.

[0030]

[0025] Advantageously, the reinforcing elements of the carcass layers are textile reinforcing elements whose breaking force is at least equal to 35 daN. The breaking force is FR measured according to standard D885 / D885M - 10A (2014).

[0031]

[0026] A textile reinforcing element may be a textile elementary monofilament optionally coated with one or more layers of a coating based on a non-metallic adhesive composition. This textile elementary monofilament is obtained, for example, by melt spinning, solution spinning or gel spinning. Each textile elementary monofilament is made of an organic material, in particular polymeric, or inorganic, such as for example glass or carbon. The polymeric materials may be of the thermoplastic type, such as for example aliphatic polyamides, in particular polyamides 6-6, aliphatic polyamides (more precisely nylon) and polyesters, in particular polyethylene terephthalate. The polymeric materials may be of the non-thermoplastic type, such as for example aromatic polyamides, in particular aramid, and cellulose, both natural and artificial, in particular rayon.Each elementary textile monofilament has a substantially circular section with a diameter ranging, for example, from 2 pm to 100 pm.

[0032]

[0027] A textile reinforcing element may be an assembly of several elementary textile monofilaments as defined above, also called strand. A strand preferably comprises more than 10 elementary textile monofilaments, preferably more than 100 elementary textile monofilaments and more preferably more than 500 elementary textile monofilaments.

[0033]

[0028] A textile reinforcing element may also be an assembly of several strands as defined above. In one variant, the materials from which the elementary textile monofilaments of each strand are made are identical. In another variant, the materials from which the elementary textile monofilaments of each strand are made are different, the textile reinforcing element then being commonly called a hybrid textile reinforcing element.

[0034]

[0029] Advantageously, a tire according to the invention may comprise in the bead at least one inner tongue between the bead wire and the nearest carcass layer comprising textile reinforcing elements making an angle to the circumferential direction XX' of between 45° and 135°, the axially outermost free end of the tongue is radially less than the height of the nominal rim hook. A tongue differs from a carcass layer in that a tongue does not have a first main part connecting the two beads. It is generally positioned between the bead wire and the carcass layers. Its function may be to better distribute the shear forces between the bead wires and the carcass layers, to protect the carcass from impacts or other. In the invention, it is advantageous not to place the axially outermost end in the sidewall for the endurance thereof.The nominal rim dimensions of aircraft tires are set by the Aircraft Year Book published by the TRA Tire and Rim Association.

[0030] The characteristics of the invention are illustrated by schematic figures 1 and 2, not shown to scale, representing a meridian section of the tire according to the invention.

[0035]

[0031] In Figure 1, the aircraft tire (1) has a crown (2) comprising a tread (21) and a crown reinforcement (22) radially inside the tread, two beads (3) capable of holding the tire on a mounting rim, two sidewalls (4) between the beads (3) and the crown (2) and a radial carcass reinforcement (5) ensuring the connection between the beads (3), the sidewalls (4) and the crown (2). The equatorial plane (P) of the tire passes through the middle of the tread surface, perpendicular to the axis (YY') of rotation of the tire. The tread (22) comprises 4 longitudinal grooves (211). Two grooves, the most axially outside, are located on either side of the equatorial plane. Each groove (211) has an axially inner wall (2111) and an axially outer wall (2112).The radial carcass reinforcement (5) comprises a carcass layer (51) anchored to a bead wire (31) in each bead (3), the carcass layer (51) having a first main portion (52) connecting one bead wire to the other and connected at its ends to two upturns (53) each having a free end (531). The free ends (531) of the two upturns (53) are positioned axially between the two axially outer walls (2112) of the two grooves (211). One free end (531) of the upturns (53) is radially outer to the second free end (531) of the other upturn (53) and is positioned axially relative to the radially inner free end (531) so as to form an overlap (6) of axial length (L), positioned directly above a groove (211) of the tread (21).The crown reinforcement (22) comprising 3 pairs of working layers (221) comprising textile reinforcing elements making a variable angle with the longitudinal direction XX' of between 0 and 45°. The crown reinforcement has an axial width (L1) measured on the crown layer of greatest axial width. An inner tongue (32) is positioned between the bead wire (3) and the carcass layer (5) in order to better couple these two sub-elements of the tire. It comprises two free ends, neither of which is positioned in the sidewall (3), each of them being positioned below the rim hook (not shown here). Figure 1 includes a zoom on the overlap (6) which makes it possible to better distinguish at the level of the overlap 6, the two upturns 53a and 53b and their free ends 531a and 531b.

[0032] Figure 2 illustrates the invention with a carcass reinforcement (5) comprising 2 carcass layers whose free ends (531) of the upturns (53) are positioned under the crown (2) between the axially outermost walls (2112) of the two axially outermost grooves and have an axial length (L) of overlap (6). Each overlap being positioned directly above a different groove (211). This architecture can of course be extended to 3 or more carcass layers.

[0036]

[0033] The invention was tested on a tire of standardized dimension 790 x 275 R 15. The control tire has a carcass reinforcement comprising 6 layers of carcass whose ends are arranged regularly between the bottom and the top of the bead. The reinforcing elements are made of nylon with 3 twisted threads whose title is equal to 188 tex each.

[0034] A tire according to the invention was manufactured with 2 layers of carcass whose free ends of the turns are positioned under the crown by making an overlap of 40 mm of axial length; width less than 25% of the axial width of the crown reinforcement, and positioned under a groove of the tread. The absence of compression in the carcass layers made it possible to use hybrid reinforcement elements called A330 / A330 / N188, namely two aramid yarns of 330 tex each and a nylon thread of 188 tex each with a twist of between 220 and 280 turns.

[0037]

[0035] The crowns - tread and crown reinforcement - are identical between the control tires and the tires according to the invention.

[0038]

[0036] The invention has been successfully tested according to the TSO C62e standard, which tests in particular the endurance of the tire. The invention also passes the burst test or test at 4 times the nominal usage pressure with a result improved by 12.5% ​​compared to the control tire. The tire according to the invention makes it possible to reduce the mass by 2 kg compared to the control tire which meets these test criteria, i.e. a gain of almost 6% of the tire mass.

Claims

Claims 1. Aircraft tire (1) intended to be inflated to a pressure at least equal to 8 bars, having a crown (2) comprising a tread (21) and a crown reinforcement (22) radially inside the tread (21), two beads (3) capable of holding the tire on a mounting rim, two sidewalls (4) between the beads (3) and the crown (2) and a radial carcass reinforcement (5) ensuring the connection between the beads (3), the sidewalls (4) and the crown (2), • An equatorial plane (P) of the tire being the plane passing through the middle of the rolling surface and perpendicular to the axis of rotation, • the tread (22) comprising at least 2 longitudinal grooves (211), two grooves, the most axially outer, being located on either side of the equatorial plane, each groove (211) having an axially inner wall (2111) and an axially outer wall (2112), • the radial carcass reinforcement (5) comprising at least one carcass layer (51) comprising reinforcing elements coated with rubber compounds and oriented substantially radially, that is to say making an angle of between 75° and 105° with the circumferential direction, • each carcass layer being anchored to at least one circumferential reinforcement or bead wire (31) in each bead (3), each carcass layer (51) having a first main part (52) connecting one bead wire to the other and connected at its ends to two other parts or turns (53) each having a free end (531), • the crown reinforcement (22) comprising at least 1 pair of working layers (221) comprising reinforcing elements coated with rubber compounds and making a variable angle with the longitudinal direction XX' whose absolute value is between 0 and 45°, having an axial width (L 1 ), • characterized in that the free ends (531, 531a, 531b) of the two upturns (53, 53a, 53b) of at least one carcass layer (51) are positioned axially between the two axially outer walls (2112) of the two axially outermost grooves (211), a free end (531b) of one upturn (53b) being radially outer to the second free end (531a) of the other upturn (53a) of the carcass layer (51) in question and being positioned axially relative to the radially inner free end (531a) so as to form an overlap (6) of the two free ends (531, 531a, 531b) of the two upturns (53, 53a, 53b) of said carcass layer (51), • and in that each overlap (6) of two turns (53) of a carcass layer (51) has an axial width (L) less than one third of the axial width (L1) of the crown reinforcement, • and in that each overlap (6) of two turns (53) of a carcass layer (51) is positioned directly above a groove (211) of the tread (21) 2. Tire according to claim 1 wherein the free ends (531) of the two upturns (53) of each carcass layer (51) are positioned axially between the two axially outer walls (2112) of the two axially outermost grooves (211).

3. Tire according to any one of claims 1 or 2 wherein each overlap (6) of two turns (53) of a carcass layer (51) has an axial width (L) at least equal to 30 mm and at most equal to 100 mm.

4. A tire according to any preceding claim comprising at least two carcass layers (51) wherein the carcass layers (51) are different in terms of properties of the reinforcing elements of the two carcass layers, or pitch between the reinforcing elements.

5. Tire according to any one of claims 1 to 3 comprising at least two carcass layers (51) in which the carcass layers (51) are standardized in all their characteristics.

6. Tire according to any one of the preceding claims in which the crown reinforcement (22) is radially external to the carcass reinforcement (5).

7. Tire according to any one of the preceding claims in which the reinforcing elements of the carcass layers (51) are textile reinforcing elements whose breaking force is at least equal to 35 daN.

8. A tire according to any one of the preceding claims comprising in the bead (3) at least one inner tongue (32) between the bead wire (31) and the nearest carcass layer, comprising textile reinforcing elements making an angle to the circumferential direction XX' of between 45° and 135°, having two free ends in which the axially outermost free end of the tongue (32) is radially less than the height of the nominal rim hook.

9. Tire according to any one of the preceding claims, the nominal inflation pressure of which is at least equal to 10 bars.

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