Carcass reinforcement for aircraft tyre

Abstract

The invention relates to a radial tyre for an aircraft, comprising at least one carcass ply (51) containing reinforcing elements, each carcass ply (51) having a first main portion (52) connecting one bead wire and the other and connected at its ends to two other portions or curls (53), each other portion or hem has a free end (531). The free ends (531) of the two hems (53) of at least one carcass ply (52) are arranged axially such that overlays (6) are formed between the two axially outer walls (2112) of the two axially outermost grooves (211) of the tread, the axial width (L) of each overlay being less than one third of the axial width (L1) of the crown reinforcement.

Description

Technical Field

[0001] This invention relates to an aircraft tire with radial carcass reinforcement. Background Technology

[0002] Aircraft tires are designed to withstand heavy loads and be inflated to relatively high pressures, at least 8 bar, preferably 10 bar, and possibly up to 25 bar. The rim diameter of the tires in question is at least 6 inches, preferably at least 20 inches. Aircraft tires are also characterized by their high load capacity and their deflection under nominal pressure and load; the deflection of civil aircraft reaches 28% to 33%, and that of military aircraft reaches up to 50%. Aircraft are non-directional vehicles with landing gear; when flying or taxiing, aircraft are oriented by manipulating flaps on the wings or the rear vertical stabilizer, rather than by the rotation of the tires as is the case with road vehicles. Therefore, aircraft tires have a very specific structure for both the carcass and the crown reinforcement, the carcass needing to withstand very high burst pressures, and the crown reinforcement consisting of a double layer based on helical strips without free ends at the axial ends, as shown in document EP 2499006 B1.

[0003] Because tires have a geometry that rotates about an axis of rotation, their geometry is typically described in a meridional plane that contains the tire's axis of rotation. For a given meridional plane, the radial, axial, and circumferential directions represent the directions perpendicular to the tire's axis of rotation, parallel to the axis of rotation, and perpendicular to the meridional plane, respectively. The circumferential direction is tangent to the circumference of a circle.

[0004] In the following text, "radially inside / radially located inside" and "radially outside / radially located outside" refer to "closer to the tire's axis of rotation" and "farther from the tire's axis of rotation," respectively. "Axially inside / axially located inside" and "axially outside / axially located outside" refer to "closer to the tire's equatorial plane" and "farther from the tire's equatorial plane," respectively, where the tire's equatorial plane is a plane that passes through the middle of the tread surface and is perpendicular to the axis of rotation.

[0005] The aircraft tire according to the invention has a tread comprising at least two longitudinal grooves, each groove having an axial inner wall and an axial outer wall, with the two outermost axial grooves located on opposite sides of the equatorial plane. Typically, to avoid unnecessary stress during mounting on the rim, one outermost radial groove is symmetrical to the other with respect to the equatorial plane. The function of these grooves is to drain any water that may be present on the runway, ensuring the tire has adequate grip.

[0006] The aircraft tire according to the invention also has a crown reinforcement comprising a working layer with fabric reinforcement elements made of aliphatic polyamide or a mixture of aliphatic and aromatic polyamides, coated with a rubber compound and forming a variable angle with respect to the longitudinal direction XX', the absolute value of which is between 0° and 45°. The working layer is typically obtained by circumferentially winding strips in a zigzag pattern or in circumferential loops on a cylindrical lay-up surface with the tire's axis of rotation as its axis of rotation. The strips typically consist of at least one continuous fabric reinforcement coated with an elastomer compound, usually consisting of juxtaposed, parallel continuous fabric reinforcements coated with an elastomer compound. The advantage of zigzag or circumferential winding is that it avoids the presence of free ends of the reinforcement at the axial ends of the working layer, free ends that are prone to cracking in these areas and thus easily reduce the durability of the working reinforcement and the tire's life. When the strip is wound circumferentially in a zigzag pattern, the working layers are laid in pairs, each pair forming a working double layer. Therefore, away from its axial end, a working double layer consists of two radially stacked working layers. At its axial end, a working double layer typically includes more than two radially stacked working layers. The number of additional working layers in the radial direction compared to the two working layers in the main part of the working double layer is called axial end excess. Therefore, the number of double layers is determined on a meridional cross-section in the equatorial plane.

[0007] The aircraft tire according to the invention also has a radial carcass reinforcement comprising a carcass layer including a plurality of substantially radially oriented (i.e., forming an angle between 75° and 105° with respect to the circumferential direction) fabric reinforcement elements anchored to at least one circumferential reinforcement in each bead, typically anchored to a single circumferential reinforcement called a bead line. According to the prior art, the reinforcement elements of the carcass layer are wound around the bead line from the inside out or from the outside in, forming a rolled edge, with their respective ends radially spaced from the axis of rotation of the tire. The reinforcement elements are coated with a rubber compound called a surface compound.

[0008] Each carcass ply has a first main portion or outward strand connecting one bead line and another, and two portions or serrations, each having a free end. A free end is understood to refer only to that end that is not connected to other portions of the carcass ply. Each end of the first portion of each carcass ply is connected to one or the other serration with a free end, so neither end is free. One end of each serration is connected to the first portion below the bead line (called the main portion), and the other end is free.

[0009] For short crimps, the two crimps, each with a free end, can be axially located inside the first portion of the carcass ply. The function of the first major portion of the carcass ply is to maintain internal pressure by absorbing tension (especially radial tension) from the sidewall. The key function of the crimps is to prevent the carcass ply from unwinding due to shearing of the surface compound between the reinforcing layers. Unwinding refers to the separation of the carcass ply from the bead line under the pressure of the tire's internal structure.

[0010] The demanding conditions of using aircraft tires necessitate improvements in the durability of the tire bead, especially at the rolled edges of the carcass reinforcement.

[0011] However, the durability of aircraft tire beads needs improvement because they are subjected to considerable overload, with the tire's radial height compressing by approximately 50% or more. Furthermore, to withstand the tension caused by the so-called withstand pressure (which is equal to four times the operating pressure), the required number of carcass layers is determined. These carcass layers are typically formed of reinforcing elements made of aliphatic polyamides or composite materials (i.e., formed from filament yarns with different modulus values). The large number of carcass layers obviously leads to an increase in the number of free ends of the reinforcing elements, an increase in interlayer interfaces, greater hysteresis losses, and therefore higher operating temperatures—all of which tend to increase bead fatigue and limit bead durability.

[0012] Patent EP1381525 specifically proposes a solution using composite cords, particularly a composite material formed by at least two high-modulus filament yarns and one low-modulus filament yarn, more specifically a composite material formed by two filament yarns made of aramid or aramid and one filament yarn made of aliphatic polyamide (more specifically nylon).

[0013] However, the structures described in the prior art are not optimal, especially in two performance aspects crucial to aircraft tires: durability and mass. The inventors' goal is to improve these performance aspects. Summary of the Invention

[0014] This improvement has been achieved with an aircraft tire designed to inflate to a pressure of at least 8 bar. The aircraft tire has a crown, two beads, two sidewalls, and radial carcass reinforcements. The crown includes a tread and a crown reinforcement located radially inside the tread. The two beads hold the tire on a mounting rim. The two sidewalls are located between the beads and the crown. The radial carcass reinforcements provide connection between the beads, sidewalls, and crown.

[0015] The equatorial plane of the tire is a plane that passes through the middle of the tread and is perpendicular to the axis of rotation.

[0016] The tread includes at least two longitudinal grooves, with the two outermost axial grooves located on either side of the equatorial plane. Each groove has an inner axial wall and an outer axial wall.

[0017] The radial carcass reinforcement has at least one carcass layer, the carcass layer having a reinforcing element coated with a rubber compound and oriented substantially radially, i.e., forming an angle between 75° and 105° with the circumferential direction.

[0018] Each carcass ply is anchored to at least one circumferential reinforcement or bead line in each bead. Each carcass ply has a first major portion that connects one bead line and another bead line and connects at its ends to two other portions or crimps, each other portion or crimp having a free end.

[0019] The crown reinforcement includes at least one pair of working layers, each working layer having a reinforcing element coated with a rubber compound and forming a variable angle with respect to the longitudinal direction XX', the absolute value of which is between 0° and 45°. The crown reinforcement has an axial width.

[0020] • At least one carcass layer has two free ends of its two rolled edges axially disposed between the two outermost axial walls of two axial grooves, and one free end of one rolled edge is located radially outside the second free end of the other rolled edge of the carcass layer, and is axially configured relative to the radially inner free end such that the two free ends forming the two rolled edges of the carcass layer overlap.

[0021] • The axial width of each overlapping portion of the two rolled edges of the carcass layer is less than one-third of the axial width of the crown reinforcement.

[0022] Specifically, surprisingly, bead optimization doesn't involve finding reinforcing elements with good fatigue resistance and the highest possible fracture strength with the lowest possible reinforcing mass. An unexpected method to significantly reduce stress in the bottom region (especially compression of certain carcass layers) is to eliminate the presence of free ends of the carcass layers in the bead. Having these free ends in the sidewall is even less desirable, as it's the area where the tire deforms and bends most when driving on flat ground. The optimal placement of the rolled ends of the carcass layers is in the area below the tread where the working layers absorb most of the pressure, i.e., between the grooves, more specifically between the two outermost axial walls of the two outermost axial grooves located on opposite sides of the equatorial plane. This arrangement allows for the elimination of at least one carcass layer end in each bead, thereby reducing the compression of the first portion of the carcass layer in the bead.

[0023] To reduce tire weight by decreasing the number of carcass layers, it is important to reconnect the free ends of the carcass layers to each other so that the reconnected portion or overlay prevents the carcass layers from unwinding due to shearing of their surface compound. If reconnection is not performed, an additional layer is needed for reconnection, with its reinforcing elements positioned close to the angle of the carcass layers, between 75° and 105°. The crown layer, due to its angle, cannot absorb lateral forces.

[0024] Therefore, to achieve good durability and the optimal improvements of this invention, it is necessary to have an overlap of two curled edges below the tread between the outermost axial grooves (more specifically, between their two axial outer walls). The overlap is understood to mean that a portion of one curled edge presses against a portion of another curled edge, and the radial distance between the two curled edges (between the centers of the reinforcing elements of the two curled edges) is less than the sum of the diameters of the reinforcing elements of each curled edge, preferably less than 1.5 times the average diameter of the reinforcing elements of each curled edge. The overlap can transfer the force applied to one curled edge to the other, effectively reconnecting the two curled edges.

[0025] To effectively save weight, the axial width of each overlap of the two crimps of the carcass ply is less than one-third of the axial width of the crown reinforcement, and advantageously less than one-quarter of the width of the crown reinforcement. The axial width of the overlap or crown reinforcement can be measured, for example, on the meridional cross section of the tire.

[0026] Each overlapping portion of the two rolled edges of the carcass ply has an axial width of at least 30 mm and at most 100 mm. Starting from 30 mm, the length of the overlapping portion already allows for excellent rejoining. Beyond 100 mm, the overlapping portion can be shortened to achieve optimal quality.

[0027] Advantageously, the free ends of the two rolled edges of each carcass ply are positioned axially between the two outermost axial walls of the two outermost axial grooves. The advantage of arranging all the free ends of the carcass ply under the crown rather than in the bead or sidewall is that it reduces tension variations at these ends. By arranging their free ends in this way, all carcass ply can be under tension at the bead, which is extremely beneficial for durability. According to common design standards, the number of carcass ply in the tire can therefore be reduced while maintaining the same durability, thus saving mass, which is extremely advantageous for aircraft tires.

[0028] Preferably, each overlay of the two rolled edges of the carcass ply is configured to align with the grooves of the tread. The expression "aligned with" means "located radially inside, at least within the boundary of the axial coordinate defined by...". Therefore, "overlay aligned with groove" means that in each meridional cross-section, the overlay is radially inside the groove at least at the axial coordinate defined by the groove. Positioning the overlay aligned with the grooves has the advantage of ensuring better durability. This is because, when aligned with the grooves, the overlay benefits from higher pressure during tire curing, and thus also benefits from better curing, with higher heat and pressure supplied by the mold at that location on the tire below the raised element that creates the grooves in the mold.

[0029] Advantageously, for tires comprising at least two carcass layers, the carcass layers differ in properties, or in the performance of the reinforcing elements in the two carcass layers, or in the spacing between the reinforcing elements. In such a structure, to further optimize quality or durability, the carcass layers can be non-standardized in the following ways: in terms of the spacing between the reinforcing elements; or in terms of performance, for example, by changing the twist of the reinforcing element yarns; or in terms of the properties of the reinforcing elements, such that one carcass layer is or is not made of a blended fabric, while the other carcass layer is made of a different blended material or nylon or aramid. Therefore, it is advantageous for tires comprising at least two carcass layers to differ in the blended or single-material properties of the reinforcing elements, or in the materials used, or in the performance of the reinforcing elements in the two carcass layers, or in the spacing between the reinforcing elements.

[0030] Preferably, for the benefit of ease of manufacture, for tires comprising at least two carcass layers, the carcass layers are standardized in all their characteristics, namely, standardized in terms of the mixed or single material properties of the reinforcing elements, standardized in terms of the performance of the reinforcing elements in the two carcass layers, and standardized in terms of the spacing between the reinforcing elements.

[0031] Advantageously, in order to better absorb the lateral forces transmitted from the tread to the tire structure, the crown reinforcement is located radially outside the carcass reinforcement.

[0032] Advantageously, the reinforcing elements of the carcass layer are fabric reinforcing elements with a breaking force of at least 35 daN. The breaking force FR is measured according to standard D885 / D885M-10A (2014).

[0033] The fabric reinforcing element can be a basic fabric filament, optionally coated with one or more layers of a coating based on a non-metallic binder composition. This basic fabric filament is obtained, for example, by melt spinning, solution spinning, or gel spinning. Each basic fabric filament is made of an organic material (particularly a polymeric material) or an inorganic material (e.g., glass or carbon). The polymeric material can be thermoplastic, such as aliphatic polyamides (particularly polyamide 6,6), aliphatic polyamides (more specifically nylon), and polyesters (particularly polyethylene terephthalate). The polymeric material can be non-thermoplastic, such as aromatic polyamides (particularly aramid), and natural or synthetic cellulose (particularly rayon). Each basic fabric filament has a substantially circular cross-section with a diameter ranging, for example, from 2 micrometers to 100 micrometers.

[0034] The fabric reinforcing element may be an assembly of multiple basic fabric filaments as defined above, also known as a strand. The strand includes preferably more than 10 basic fabric filaments, preferably more than 100 basic fabric filaments, and more preferably more than 500 basic fabric filaments.

[0035] Fabric reinforcing elements can also be components of multiple strands as defined above. In one variation, the basic fabric filaments made of each strand are made of the same material. In another variation, the basic fabric filaments made of each strand are made of different materials; this type of fabric reinforcing element is often referred to as a hybrid fabric reinforcing element.

[0036] Advantageously, the tire according to the invention may include at least one internal tongue in the bead located between the bead line and the nearest carcass layer, the internal tongue comprising a fabric reinforcing element forming an angle between 45° and 135° with respect to the circumferential direction XX', the outermost axial free end of the tongue being radially lower than the height of the nominal rim flange. The tongue differs from the carcass layer in that it does not have a first major portion connecting the two bead layers. It is typically positioned between the bead line and the carcass layer. It can better distribute shear forces between the bead line and the carcass layer, protect the carcass from impacts, etc. In this invention, for the sake of sidewall durability, it is advantageous not to place the outermost axial end in the sidewall. The nominal rim size of aircraft tires is set by the Aircraft Yearbook edited by the Tire and Rim Association (TRA). Attached Figure Description

[0037] Features of the present invention are shown in the illustration. Figure 1 and Figure 2 In these figures, which are not drawn to scale, the meridional cross-section of the tire according to the invention is shown. Detailed Implementation

[0038] exist Figure 1In this tire (1), there is a crown (2), two bead sections (3), two sidewalls (4), and a radial carcass reinforcement (5). The crown (2) includes a tread (21) and a crown reinforcement (22) located radially inside the tread. The two bead sections (3) are used to hold the tire on the mounting rim. The two sidewalls (4) are located between the bead sections (3) and the crown (2). The radial carcass reinforcement (5) provides connection between the bead sections (3), the sidewalls (4), and the crown (2). The equatorial plane (P) of the tire passes through the middle of the tread surface and is perpendicular to the axis of rotation (YY') of the tire. The tread (22) includes four longitudinal grooves (211). Two outermost axial grooves are located on either side of the equatorial plane. Each groove (211) has an inner axial wall (2111) and an outer axial wall (2112). The radial carcass reinforcement (5) has a carcass layer (51) anchored to a bead line (31) in each bead (3), the carcass layer (51) having a first main portion (52) connecting one bead line and another bead line and connecting at its end to two flanges (53), each flange having a free end (531). The free ends (531) of the two flanges (53) are axially positioned between two axial outer walls (2112) of two grooves (211). The free ends (531) of the flanges (53) are radially located outside the second free end (531) of the other flange (53) and axially positioned relative to the radially inner free end (531) to form an overlay (6) having an axial length (L), the overlay being aligned with the groove (211) of the tread (21). The crown reinforcement (22) comprises three pairs of working layers (221) having fabric reinforcement elements that form a variable angle between 0° and 45° with respect to the longitudinal direction XX'. The crown reinforcement has an axial length (L1) measured on the crown layer at its maximum axial width. An internal tongue (32) is disposed between the bead line (3) and the carcass layer (5) to better connect these two sub-elements of the tire. It comprises two free ends, neither of which is disposed in the sidewall (3) but rather each is disposed below the rim flange (not shown here). Figure 1 Including a close-up of the overlapping portion (6), which makes it easier to distinguish the two rolled edges 53a and 53b at the overlapping portion 6 and their free ends 531a and 531b.

[0039] Figure 2 The invention is illustrated, wherein the carcass reinforcement (5) comprises two carcass layers, wherein the free end (531) of the rolled edge (53) is disposed below the crown (2) and between the outermost axial walls (2112) of two outermost axial grooves, and has an axial overlap (6) of length (L). Each overlap is configured to align with a different groove (211). This structure can obviously be extended to three or more carcass layers.

[0040] This invention was tested on a standard-size 790x275R15 tire. The carcass reinforcement of the control tire comprises six carcass layers, the ends of which are regularly arranged between the bottom and top of the bead. The reinforcement element is made of nylon with three twisted filaments, each filament having a fineness of 188 tex.

[0041] The tire according to the invention is made of two carcass layers, wherein the free end of the rolled edge is disposed below the tread, forming an overlay with an axial length of 40 mm. The width of the overlay is less than 25% of the axial width of the tread reinforcement, and the overlay is disposed below the grooves of the tread. The absence of compression in the carcass layers allows the use of a hybrid reinforcement element called A330 / A330 / N188, consisting of two 330 tex aramid yarns and one 188 tex nylon yarn, with a twist count between 220 and 280 turns.

[0042] The crown (tread and crown reinforcement) of the comparison tire and the tire according to the present invention are the same.

[0043] The tire was tested according to the TSOC62e standard, which specifically tests tire durability, and the results were successful. The invention also passed burst tests or endurance tests at four times the nominal operating pressure, showing a 12.5% ​​improvement compared to the control. Compared to the control tire, the tire according to the invention can reduce weight by 2 kg, achieving a tire weight saving of nearly 6% under these test standards.

Claims

1. An aircraft tire (1) designed to be inflated to a pressure of at least 8 bar, the aircraft tire having a crown (2), two bead sections (3), two sidewalls (4), and a radial carcass reinforcement (5), the crown (2) comprising a tread (21) and a crown reinforcement (22) radially located inside the tread (21), the two bead sections (3) capable of holding the tire on a mounting rim, the two sidewalls (4) located between the bead sections (3) and the crown (2), and the radial carcass reinforcement (5) providing connection between the bead sections (3), the sidewalls (4), and the crown (2). • The equatorial plane (P) of the tire is a plane that passes through the middle of the tread and is perpendicular to the axis of rotation. The tread (22) includes at least two longitudinal grooves (211), with the two outermost axial grooves located on either side of the equatorial plane. Each groove (211) has an axial inner wall (2111) and an axial outer wall (2112). The radial carcass reinforcement (5) has at least one carcass layer (51) having a reinforcing element coated with a rubber compound and oriented substantially radially, i.e., forming an angle between 75° and 105° with respect to the circumferential direction. • Each carcass ply is anchored to at least one circumferential reinforcement or bead line (31) in each bead (3), each carcass ply (51) having a first main portion (52) connecting one bead line and another bead line and being connected at its ends to two other portions or crimps (53), each other portion or crimp having a free end (531). The crown reinforcement (22) includes at least one pair of working layers (221), each working layer having a reinforcing element coated with a rubber compound and forming a variable angle with respect to the longitudinal direction XX', the absolute value of which is between 0° and 45°. The crown reinforcement (22) has an axial width (L1). Its features are as follows: At least one carcass layer (51) has two rolled edges (53, 53a, 53b) with free ends (531, 531a, 531b) arranged axially between two axial outer walls (2112) of two outermost axial grooves (211). The free end (531b) of one rolled edge (53b) is located radially outside the second free end (531a) of the other rolled edge (53a) of the carcass layer (51), and is axially arranged relative to the radially inner free end (531a) such that the two free ends (531, 531a, 531b) of the two rolled edges (53, 53a, 53b) of the carcass layer (51) overlap (6). • The axial width (L) of each overlapping portion (6) of the two rolled edges (53) of the carcass layer (51) is less than one-third of the axial width (L1) of the crown reinforcement; as well as • Each overlapping portion (6) of the two rolled edges (53) of the carcass layer (51) is configured to align with the groove (211) of the tread (21).

2. The tire according to claim 1, wherein, The free ends (531) of the two rolled edges (53) of each carcass layer (51) are axially positioned between the two axial outer walls (2112) of the two outermost axial grooves (211).

3. The tire according to any one of claims 1 and 2, wherein, The axial width (L) of each overlapping portion (6) of the two rolled edges (53) of the carcass layer (51) is at least 30 mm and at most 100 mm.

4. The tire according to any one of the preceding claims, comprising at least two carcass layers (51), wherein, The carcass layers (51) differ in the performance of the reinforcing elements of the two carcass layers or in the spacing between the reinforcing elements.

5. The tire according to any one of claims 1 to 3, comprising at least two carcass layers (51), wherein, All features of the fetal body layer (51) are standardized.

6. The tire according to any one of the preceding claims, wherein, The crown reinforcement (22) is located radially outside the carcass reinforcement (5).

7. The tire according to any one of the preceding claims, wherein, The reinforcing element of the carcass layer (51) is a fabric reinforcing element with a breaking force of at least 35 daN.

8. The tire according to any one of the preceding claims, comprising in the bead (3) at least one inner tongue (32) between the bead line (31) and the nearest carcass layer, the inner tongue comprising a fabric reinforcement element formed at an angle between 45° and 135° with respect to the circumferential direction XX', the inner tongue having two free ends, wherein, The outermost free end of the tongue (32) is radially lower than the height of the nominal rim flange.

9. The tire according to any one of the preceding claims, wherein the nominal inflation pressure is at least 10 bar.

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