GB2584888A

GB2584888A - Pneumatic aircraft tyre

Info

Publication number: GB2584888A
Application number: GB1908805.3A
Authority: GB
Inventors: Nair Abilash; Vieux-Pernon Celine
Original assignee: DUNLOP AIRCRAFT TYRES Ltd
Current assignee: DUNLOP AIRCRAFT TYRES Ltd
Priority date: 2019-06-19
Filing date: 2019-06-19
Publication date: 2020-12-23
Anticipated expiration: 2039-06-19
Also published as: GB2584888B; GB2584888A8; GB201908805D0

Abstract

A pneumatic aircraft tyre (100), comprising: a pair of sidewall portions (102a, 102b) connected by a crown portion (104), each sidewall portion (102a, 102b) comprising a bead region (106a, 106b) for mounting the tyre onto the rim (108) of a wheel, wherein each of the bead regions (106a, 106b) comprises a bead core (110a, 110b), each bead core (110a, 110b) comprising a toroidal member formed from a composite material. A method (200) of manufacturing the pneumatic tyre is also disclosed.

Description

Pneumatic aircraft tyre This application relates to a pneumatic aircraft tyre and a method of manufacturing a pneumatic aircraft tyre.

Aircraft tyres are generally formed from a pair of axially separated sidewall portions and a crown portion connected between them. The sidewall portions each comprise a bead region. The sidewall portions extend outward from the bead regions in a radial direction of the tyre and are linked by the crown portion at their radial outer ends. The bead regions are provided to hold the tyre securely on a rim of a wheel with which the tyre is attached for use.

The bead regions each comprise a bead core provided to anchor plies of a carcass forming the sidewalls and crown portion of the tyre. The bead cores also function to anchor the tyre to the wheel rim and provide structural strength.

There is a technical bias in the field of aircraft tyres to use bead cores formed from steel wires to act as reinforcing elements. The steel wires may be arranged side-byside or twisted into cables. It is also known to use aluminium to reduce weight, for example as disclosed in US20170057291. Aircraft tyres generally experience high levels of load, speed and pressure during use. These may be significantly greater than encountered in other types of tyre, such as automotive tyres. Aircraft tyres must meet strict safety requirements to ensure that they have adequate strength to reduce the risk of failure during use. For this reason, there is a strong technical bias to form aircraft tyre bead cores from bundles of high strength brass-coated steel cables as these have proven levels of strength and durability.

In a first aspect, the present application provides a pneumatic aircraft tyre, comprising a pair of sidewall portions connected by a crown portion, each sidewall portion comprising a bead region for mounting the tyre onto the rim of a wheel, wherein each of the bead regions comprises a bead core, each bead core comprising a toroidal member formed from a composite material.

By forming the bead core from a toroidal member made from a composite material the aircraft tyre may have a strong bead region to secure it to the rim of a wheel on which it is mounted, while still having a low overall weight. Weight reduction is of particular concern in the field of aircraft components such as aircraft tyres. The use of bead cores formed from a composite material therefore may be particularly advantageous. Although the use of composite materials for weight reduction may be known in other fields, they would not be considered for use in an aircraft tyre bead core where steel cables are trusted to provide adequate strength to meet design and safety requirements.

The composite material may be a carbon fibre reinforced plastics material. Preferably the composite material may be carbon fibre epoxy prepreg material. This has been found to provide an advantageous strength to weight ratio for use in an aircraft tyre.

Each bead core may be formed only from a composite material. Preferably each bead core may be formed only from a carbon fibre reinforced plastics material.

Each bead region may not include any tensile reinforcing elements in addition to the toroidal member forming the bead core. Preferably the bead core is formed from a single toroidal member. The use of the composite material may provide adequate strength without additional materials or components. This may provide an improved overall strength to weight ratio. Such a single toroidal bead core construction may specifically be combined with a radial tyre construction.

One or both of the toroidal members may have an at least partly roughened or textured outer surface. This may reduce de-bonding between the composite material and surround material of the bead regions of the tyre The bead regions of the side wall portions may each comprise a rubber material. One or both of the bead regions may further comprise a bonding structure adapted to provide a bond between the bead core and the rubber material. This may improve the bond between the composite material of the bead core and the surrounding material.

The rubber material to which the bead core is bonded may be a rubber coating on a casing of the tyre.

The bonding structure may comprise a rubber sheet material. The rubber sheet material may at least partly surround the bead core. The rubber sheet material may preferably be wrapped around the toroidal member forming the bead core. The use of a rubber sheet material may provide an improved bonding interface between the composite material and the surrounding rubber material.

The bonding structure may comprise a fabric sheet material. The fabric sheet material may at least partly surround the bead core. The fabric sheet material may preferably be wrapped around the toroidal member forming the bead core. The use of a fabric sheet material may provide an improved bonding interface between the composite material and the surrounding rubber material.

The fabric sheet material and/or rubber sheet material may be wrapped helically around the respective bead core. This may improve bonding to the surrounding material.

The bonding structure may comprise an adhesive. The adhesive may preferably be provided on the outer surface of the toroidal member of the respective bead core. The adhesive may be applied before wrapping with the rubber sheet and/or fabric material. The adhesive may provide improved adhesion to the composite material and reduce de-bonding.

Each of the toroidal members may have an outside diameter of between 201.9 mm and 580.7 mm (i.e. 203.4+1.5 mm to 579.2+1.5 mm). Each of the toroidal members may have an inner diameter of between 181.5 mm to 535.5 mm (i.e. 183+1.5 mm to 534+1.5 mm). Each of the toroidal members may have a cross-section diameter or thickness of between 9.7 mm and 23.1 mm (i.e. 10.2+0.5 mm to 22.6+0.5 mm). This range of sizes may provide a sufficient level of strength and weight saving for a suitable sized tyrc for use in an aircraft.

More specifically, each of the toroidal members may have an outside diameter of between 444.80 and 446.60 mm, and a thickness (e.g. cross sectional diameter) of between 12.48 and 13.71 mm. This may provide a bead core with strength suitable for use in an aircraft tyre.

One or both of the toroidal members may be hollow. Preferably, one or both of the toroidal members may be formed by a pressurised tube. In such an embodiment. the toroidal members may have an annular cross section.

Alternatively, one or both of the toroidal members may be solid (i.e. having no internal cavities).

In a second aspect, the present application provides a method of manufacturing the pneumatic tyre of the first aspect, the method comprising any one or more of: assembling a casing structure comprising the bead cores; assembling an outer structure comprising the sidewall portions and crown portion; and applying heat and pressure to the casing structure and outer structure to form the tyre.

Assembling the casing structure may comprise carrying out one or more pre-processing steps on one or both of the bead cores. The pre-processing steps may comprise any one or more of: (a) a surface-roughening process arranged to form a roughened or textured finish on one or both of the toroidal members forming the bead cores; (b) applying an adhesive layer to some, or all, or the outer surface of the toroidal members forming the bead cores; (c) applying a layer of rubber sheet material around some or all of the surface of one or both of the bead cores; and (d) applying a layer of fabric sheet material around some or all of the surface of one or both of the bead cores.

Applying the layer of rubber sheet material and/or fabric sheet material may comprise helically wrapping the material around the bead cores.

Any of the features described in connection with the first aspect may be used in combination with the second aspect, and vice versa.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure la is a cross-section view through an aircraft tyre according to an embodiment; Figure lb shows a cross section through a bead core of the aircraft tyre shown in Figure I a; Figure 2 shows a cross-section view through a bead core portion of the aircraft tyre shown in Figure la; and Figure 3a shows a graphic representation of a typical universal load-speed-time test cycle (for tyres rated above 160 MPH (257.50 km/h)); Figure 3b shows a graphic representation of a typical rational load-speed-time test cycle; and Figure 4 shows a method of manufacturing an aircraft tyre.

A cross-sectional view through an aircraft tyre 100 is shown in Figure la. The tyre 100 comprises a pair of sidewall portions, a first sidewall portion 102a and a second sidewall portion 102b, connected by a crown portion 104. The sidewall portions may be axially opposed to one another as shown in Figure la. Each sidewall portion 102a, 102b comprises a bead region 106a, 106b located at its respective inner radial end. The first sidewall portion 102a comprises a first bead region 106a and the second sidewall portion 1026 comprises a second bead region 106b as illustrated in Figure la.

The sidewall portions 102a, 102b extend generally in a radial direction of the tyre 100, and are connected to the crown portion 104 at their respective radially outer ends. The crown portion 104 extends between the radially outer ends of the sidewall portions 102a, 102b in a generally axial direction of the tyre 100.

Each of the sidewall portions 102a, 102b and the crown portion 104 may be formed from a rubber compound. The rubber compound may comprise a mixture of natural and/or synthetic rubber, along with further additives to meet the specific requirements of each component as would be known to a skilled person in the field of the application.

The bead regions 106a, 106b are adapted to provide a mounting for mounting the tyre 100 onto the rim 108 of a wheel. The bead regions 106a, 106b each form a part of the respective sidewalls portions 102a. 102b that acts to anchor the tyre 100 to a respective flange 109a, 109b of the rim 108 when the tyre 100 is inflated.

Each of the bead regions 106a, 106b comprises a bead core 110a, 110b. The first bead region 106a comprises a first bead core 110a and the second bead region 106b comprises a second bead core 110b. Each of the bead cores 110a, 110b comprise a toroidal member formed from a composite material. The toroidal member forms a continuous loop or ring structure extending in a circumferential direction around the tyre 100. In the described embodiment, each bead core 110a, 110b has a circular cross section. In other embodiments, the bead cores 110a, 110b may have other cross sectional shapes. They may, for example, be elliptical, square or rectangular in cross section, or other more complex shapes. By toroidal we therefore mean having a generally toroid shape formed by revolving a closed plane around an external axis that is parallel to it so it does not intersect. Where the cross section of the bead core is circular. the toroidal dement is a torus.

in some embodiments, the bead cores 110a, 110b may be hollow. In such embodiments, the bead cores 110a, 110b may be formed from hollow tubes filled with pressurised gas. Such bead cores are still considered to be toroidal in shape -for example, having a annular cross sectional shape, where the annuls is rotated around an external axis to form a hollow toroidal bead core. In other embodiments, the bead cores 110a, 110b may be solid (rather than hollow) and have circle, oval or square etc. cross sections.

By providing an aircraft tyre with a composite bead core 110a, 110b a strong and lightweight tyre 100 may be provided. This may be particularly important in the field of aircraft Lyres, where strength and weight are important.

The tyre 100 further comprises a casing 112 extending from the first bead region 106a to the second bead region 106b. The casing 112 is formed from a plurality of casing plies 114 (one of which is illustrated in Figure la). The casing plies 114 extend between the bead cores 1 I Oa, 110b of each bead portion 106a, 106b. The casing plies 114 may be wound around the bead cores 110a 110b to secure them in position and provide structural strength to the tyre 100. An end portion of each casing ply 114 may be wrapped around a respective one of the bead cores 110a, 110b to form a casing ply turn-up 116a, 116b. Other coupling methods may be used in other embodiments. Each bead region 116a, 116b also comprises a respective bead apex 1 1 la, 1 1 lb around which the casing ply turn-ups I I6a, 1166 are formed. The casing plies may include inner plies that are turned up around the bead cores 110a, 110b as shown in the Figures. Outer casing plies that are not turned up around the bead cores 110a, 110b may also be provided.

The casing plies 114 may be formed from one or more fabric cords (e.g. rayon, nylon, polyester and Kevlar) coated with one or more layers of rubber (e.g. a high modulus rubber). In other embodiments, any other suitable material may be used.

The casing plies 114 may be arranged so that the tyre 100 has a radial or a bias ply construction. The casing plies 114 may each run in a radial direction of the tyre (i.e. degrees to the direction of travel when the tyre is in use) to form a radial casing construction. in this embodiment, additional angled belt plies (not shown in the Figures) may also be provided. In an alternative embodiment, the casing plies may run diagonally from one bead core to the other, with successive plies laid at opposing angles forming a crisscross pattern. In this embodiment, a bias or cross ply tyre is formed.

The crown portion 104 may further comprise an outer tread layer 118. The tread layer may be formed integrally with the rubber material forming the crown portion 104, or may be applied to the surface of the crown portion 104. Where the tread layer 118 is applied to the surface of the crown portion 104, the tread portion 104 may form an inner tread layer. This may improve adhesion between the tread layer 118 and the casing 112, and may allow re-treading of the tyre 100. The tread layer 118 may be formed from a rubber compound. A series of circumferential grooves 120 may be provided in the tread layer 118 to disperse water and improve grip.

The tyre 100 may further comprise an inter-tread reinforcing fabric 121a and a belt package 121b disposed between the casing 112 and the tread layer 118 and extending circumferentially around the tyre. The inter tread reinforcing fabric 12Ia may be formed from a nylon fabric. The belt package may be formed from one or more fabric layers extending around the tyre. In some embodiments a hybrid belt package formed from nylon and aramid may be used. Other materials may be used for the inter tread reinforcing fabric 12Ia and the belt package 121b.

The tyre 100 may further comprise an inner liner 122 formed from an impervious material so that it can be inflated using air or other suitable fluid. The inner liner 122 may be disposed on the inner surface of the casing 112 to form a fluid resistant layer (e.g. an air and/or gas impermeable layer). In this embodiment, the tyre 100 is therefore tubeless. In other embodiments, the inner liner 122 may be formed from a separate tube that can be inflated with fluid.

The composite material from which the bead core 110a, 110b is formed may be a carbon fibre reinforced plastics material. The composite material may preferably be a carbon fibre epoxy prepreg material. This has been found to provide a strong and lightweight bead core suited for use in an aircraft tyre. The composite material may be formed using any suitable fibre geometry. It may, for example, be a unidirectional woven, unidirectional or cross ply woven carbon fibre reinforced plastics material. Other composite materials may also be used. The composite material may be a composite material that is toughened and/or may have a high glass transition temperature (Tg), for example sufficient to prevent dc-bonding during curing (e.g. heating of the tyre to about 150 degrees C).

In the described embodiment, each bead core 110a, 110b is formed only from a composite material. Preferably, the bead cores 110a, 110b are formed only from a carbon fibre reinforced plastics material. The bead cores 110a, 110b therefore do not comprise additional materials such as metal wires or other reinforcing structures. This may provide a high overall strength to weight ratio that has been found to be suited to use in aircraft tyres. The beads used to reinforce the tyre are therefore formed from a single toroidal component or block of composite material, with no other components that would otherwise form a hybrid structure. Such a single component bead core design has been found by the inventors to provide an improved level of strength and weight saving compared to known aircraft tyres. The single toroidal component design of Figures la and 2 may be more suitable for use with a radial tyre.

Each bead region 106a, 106b may comprise a single bead core 110a, 110b formed from a single toroidal member. The bead regions 106a, 106b therefore do not include any tensile reinforcing elements in addition to the toroidal member forming the bead cores 110a, 110b. The composite material acts as the tensile reinforcing element of the tyre. The bead cores II0a, 110b are therefore formed from a single toroidal member, rather than having additional steel wires for strength. This may provide a suitable light weight arrangement. In other embodiments however, two or more toroidal members may be used in each bead portion 106a, 106b. This may provide improved strength, but at the expense of weight. This may be more suitable for a cross-ply (i.e. bias tyre) construction.

In yet other embodiments, additional strengthening members such as metal wires may be provided in addition to the composite bead cores. The strengthening members may be formed by metal wires wrapped around the composite bead cores so that the wires run around the circumference of the tyre.

Each bead region 106a, 106b may further comprise a chafer 124a, 1246. The chafers 124a, 124b are arranged to provide a point of contact between the tyre 100 and the flanges 109a, 109b of the rim 108 to which it is mounted. The chafers I24a, 124b may be formed from a rubberised nylon material and/or other suitable toughened material to protect the tyre 100 and flanges 109a, 109b from damage.

The size of the toroidal members used to form each of the bead cores 110a, 110b may be optimised to provide suitable strength to weight ratio for use in an aircraft tyre.

Each of the toroidal members may have an outside diameter (do) of between 201.9 mm and 580.7 mm (i.e. 203.4+1.5 mm to 579.2+1.5 mm). Each of the toroidal members may have an inner diameter (d1) of between 181.5 mm to 535.5 mm (i.c. 183+1.5 mm to 534+1.5 mm). Each of the toroidal members may have a cross-section diameter (or thickness if it has a non-circular cross section) (des) of between 9.7 mm and 23.1 mm (i.e. 10.2+0.5 mm to 22.6+0.5 mm). This range of sizes may provide a suitable sized tyre for use in an aircraft combined with the desired level of strength and weight saving. The definition of the outside diameter, inside diameter and cross section diameter are illustrated in Figure lb. This figure shows a cross-section through a plane normal to the axis of the bead core (and the tyre).

More preferably, each toroidal member may have an outside diameter of between 444.80 and 446.60 mm, and a thickness (i.e. a cross-sectional diameter) of between 12.48 and 13.71 mm. This has been found to provide an advantageous balance of strength and low weight. Other sizes are however possible.

A close-up sectional view of an embodiment of one of the bead regions of aircraft tyre 100 is shown in Figure 2. Reference numerals corresponding to those of Figure la have been used for corresponding features. The close-up view of Figure 2 shows an embodiment of the first bead region 106a. Anything described below in relation to the first bead portion 106a may apply equally to the second bead portion 106b.

In the embodiment shown in Figure 2, the bead core 110a has a roughened or textured outer surface 126. The roughened or textured surface may be formed using any suitable method, such as wet blasting. The roughened or textured surface 126 may improve the adhesion between the composite material of the bead core 110a and the surrounding layers of the bead region 106a. Preferably, all of the outer surface of the bead core 1 10a may be provided with a roughened or textured finish to aid adhesion. In some embodiments, only part of the bead core 110a may have a roughened or textured finish.

The bead region 106a may further comprise a bonding structure 128 adapted to provide a bond between the bead core 110a and the surrounding material of the bead region 106a. The bonding structure 128 may surround at least part of the outer surface of the bead core 110a. The bonding structure 128 may act as a joining interface between the bead core 110a and the casing 112 in which it is embedded. The bonding structure may provide a bonding interface between the composite material of the bead core and the rubber material (e.g. the rubber coating on the casing plies 114) of the bead region 106a.

The bonding structure 128 may comprise a rubber sheet material 130 at least partly surrounding the bead core 110a. The rubber sheet material 130 may be wrapped around the toroidal element forming the bead core 110a to form a first layer of the bonding structure 128. The rubber sheet material 130 may be wrapped completely around the bead core 110a or disposed over only part of its outer surface.

The rubber sheet material 130 may be formed from a rubber compound with appropriate modulus to meet the design requirements. Natural rubber (NR) and Styrene Butadiene Rubber (SBR) and its blends can be used, however, other blend compositions may be used in other embodiments. The rubber sheet material may be formed from a same or different rubber compound to the rest of the tyre with improved adhesion characteristics to the surrounding bead regions of the tyre. The rubber type(s), grade(s) and other compounding ingredients such as adhesion promoters for the rubber sheet material may be chosen so that it provides an improved bond to the composite material compared to the rubber material of the sidewall regions. The rubber sheet material may have a calendered surface to improve adhesion. In other embodiments, other material may be used to form the rubber sheet material, such as resorcinol-free or similar compounds that can contribute improved adhesion.

The bonding structure 128 may further comprise a fabric sheet material 132, the fabric sheet material 132 at least partly surrounding the bead core 110a. Similarly to the rubber sheet material 130, the fabric sheet material 132 may be wrapped around the toroidal element forming the bead core 110a to form a second layer of the bonding structure 128. The fabric sheet material 132 may be wrapped completely around the bead core 110a or disposed over only part of its outer surface.

The fabric sheet material 132 may be formed from any suitable fibres such as nylon and aramid. The fibres may be dipped in Resorcinol-Formaldehyde-Latex (RFL) or any suitable Resorcinol-free latex dips and/or may be rubberised. In other embodiments, any other suitable material may be used for the fabric sheet such as a hybrid material e.g. a combination of nylon and aramid.

Either or both of the fabric sheet material 132 and/or rubber sheet material 130 may be wrapped helically around the toroidal element forming the bead core 110a In other embodiments, other wrapping patterns may be used.

The bonding structure 128 may further comprise an adhesive. The adhesive may be provided on the outer surface of the toroidal member forming the bead core 110a to aid bonding to the other layers of the bonding structure 128 (or other surrounding material). In other embodiments, adhesive may additionally or alternatively be used to bond other layers or materials forming the bonding structure 128, or may be applied to the outer surface of the bonding structure 128 so that it adheres to the surrounding material or rubber compound in which it is embedded.

The adhesive may preferably be a NR-based rubber solution. it may be a solution specifically prepared for aircraft tyre application. This has been found to provide a suitable bond between the bead core 110a and surrounding rubber sheet material 130. Other adhesives may be used, and may be tailored to the type of material surrounding the bead core 110a.

In the embodiment shown in Figure 2, the bonding structure comprises both the rubber sheet material 130 and the fabric sheet material 132. In this embodiment, the rubber sheet material 130 is closest to the bead core 110a, with the fabric sheet material 132 wrapped around it. This structure may provide an improved interface between the composite material of the bead core 110a and the surrounding rubber compound included in the bead region 106a. In other embodiments, the arrangement of fabric sheet material 132 and rubber sheet material 130 may be reversed so that the rubber sheet material 130 surrounds the fabric sheet material 132. In vet other embodiments, the bonding structure 128 may comprise other layers, materials or adhesives. In yet further embodiments, the bonding structure may be omitted.

Referring again to Figure la, in the described embodiment, the tyre 100 is symmetric about a plane X orthogonal to the axis of rotation of the tyre 100. The bead cores 110a, 110b provided in each bead region 106a, 1066 are therefore the same. In other embodiments, the tyre 100 may not have such symmetry. The bead cores 110a, 110b may therefore be different from each other, as may the structure of the respective bead regions 106a, 106b in which they arc embedded. Any of the features described above in connection with the bead core 110a shown in Figure 2 may also apply to the other bead core 1106 of the tyre 100. In one embodiment, both bead cores 110a, 1106 are formed from a single composite toroidal member. This may provide an advantageous lightweight and strong aircraft tyre. In other embodiments, a first composite bead core may be provided along with a bead core of a different type (e.g. formed from metal wires or a different number of toroidal members).

Tests have been carried out by the inventors on six sample aircraft tyres. The results of the tests are summarised in table 1 below.

Tyre Tyre composition Test Test Comments Sample applied cycles No completed 1 -Carbon fibre composite bead core pair, no surface roughening; -adhesive coating; -rubber sheet material spiral wrap; Burst n/a Passed. Burst pressure -fabric sheet material spiral wrap. 40.33 Bar (585 psi) compared to required level of 38.61 Bar (560 psi).

2 -Carbon fibre composite bead core pair, no surface roughening; -adhesive coating; -rubber sheet material spiral wrap; ETSO 26/61 Test stopped due to -fabric sheet material spiral wrap. split found in lower sidcwall near chafer.

3 -One carbon fibre Structural 64/100 Casing failure on both sides of the tyre composite bead core, one steel wire bead core; -adhesive coating; -rubber sheet material spiral wrap; -fabric sheet material spiral wrap.

4 -Carbon fibre composite bead core pair, with surface roughening; -adhesive coating; ETSO 61/61 Completed test successfully -rubber sheet material spiral wrap; -fabric sheet material spiral wrap.

-Carbon fibre composite bead core pair, with surface roughening; -adhesive coating; -rubber sheet material spiral wrap; ETSO 61/61 Completed test -fabric sheet material spiral wrap. successfully 6 -Carbon fibre composite bead core pair, with surface roughening; -adhesive coating; -rubber sheet material spiral wrap; ETSO - 6/6 Completed test -fabric sheet material spiral wrap. double successfully overload take-off Table 1. Test results The six aircraft tyrcs tested had the following construction: Tyres 1 and 2: each of tyres 1 and 2 comprised a pair of carbon fibre composite bead cores each coated in a rubber-based joining adhesive. The joining adhesive was applied uniformly to the outer surface of the composite material. The bead cores were also each spirally wrapped with a rubber sheet material and a fabric sheet material. The fabric sheet material was wrapped around the rubber sheet material.

Tyre 3: comprised a first bead region comprising a bead core formed from a carbon fibre composite material and a second bead region comprising a plurality of brass-coated steel cables arranged side by side. Both bead regions were also provided with adhesive coating, rubber sheet material and fabric sheet material as for tyres I and 2.

Tyres 4, 5 and 6: each comprised a pair of carbon fibre composite bead cores having a roughened outer surface. The surface roughening was provided using a wet blasting surface roughening technique. Each of the bead regions were also provided with an adhesive coating, a rubber sheet material wrap and a fabric sheet material wrap. For tyre 4 the rubber sheet material wrap was formed from NR-based rubber compound.

For tyres 5 and 6 the rubber sheet material wrap was formed from NR/SBR-based rubber compound. The fabric sheet material was formed from RFL-dipped and rubberised nylon in each of the tyres being tested.

Each of the carbon fibre composite bead cores used in the test were formed from a torus shaped element having a circular cross section of diameter in a range between 12.48 and 13.71 mm. The inside diameter of each of the torus elements was in a range between 419.3 and 419.4 mm and the outside diameter was in a range between 444.8 and 446.6 mm.

The tests applied to the each of sample tyres 1 to 6 were as follows: Burst test: this test was performed by inflating the tyre with pressurised air and water until a burst failure occurred.

Two types of dynamometer tests were carried out on the test tyres: a) ETSO test (European Technical Standard Order ETSO-C62d): This standard gives the requirements which aircraft tyres (excluding tailwheel tyres) must meet in order to be identified with the applicable ETSO marking. This is the minimum performance standard for a tyre to be considered airworthy by the European Aviation Safety Agency (EASA). The standard requires materials used in the tyre to be suitable for the purpose intended and that the suitability of the materials must be determined on the basis of satisfactory service experience or substantiating dynamometer tests. Dynamometer testing on tyres having a bead core according to the present application were carried out to this standard.

The tested tyre must withstand 50 take-off cycles, 1 overload take-off cycle, and 10 taxi cycles as described below. The sequence of the cycles is optional.

Number of test cycles Minimum Load, lbs Minimum speed, mph Minimum Roll Distance, ft 8 Rated load 40 (64.37 kmph) 40 (64.37 kmph) 35,000 (10.67 km) 35,000 (10.67 km) 2 1.2 times rated load in the case of the take-off cycles the loads, speeds, and distance must conform to either Figures 3a or Figure 3b. Figure 3a defines a test cycle that is generally applicable to any aircraft. in Figure 3a, the Test Load at L0 must be equal to or greater than rated load of the tyre. The Test Speed at S2 must be equal to or greater than the rated speed of the tyre. If Figure 3b is used to define the test cycle, the loads, speeds, and distance must be selected based on the most critical take-off conditions. In Figure 3b, the operational load is for most critical take off conditions. The Test Load Lo must be equal to or greater than the rated load of the tyre. Test Speed S, must be equal to or greater than the rated speed of the tyre. Between To and T2 the Test Load at any speed must be equal to or greater than the Operational Load by the ratio Lof L01. The Roll Distance must be determined for each application.

I5 b) Structural testing: A structural test was carried out to test the structural integrity of the casing of the main components of the tyre. This test can be used as an indicator of the number of retread lives the tyre casing would withstand. The tread rubber is removed so that the heat generated in this part of the tyre does not cause an early failure. The test tyre is run at taxi-speed (depending upon the outside diameter of the tyre), at 1.3 times rated load for 600 seconds in each cycle and allowed to cool between cycles The total number of cycles completed and the cause of failure is recorded.

Test results: Tyre 1 was tested for burst pressure. The test was passed -tyre I achieved a burst pressure of 40.33 Bar (585 psi) against the minimum specification requirements of 38.61 Bar (560 psi). The failure was due to a burst at the sidewall region.

Tyre 2 was tested for ETSO. The tyre completed 26 test cycles. The test was stopped when a split was observed in a lower part of the sidewall portion near the chafer of the tyre. From shearography measurements, it was found that the tyre failure was not directly related to the carbon composite bead cores, but rather signs were observed of de-bonding with the rubber compound sheet material that was wrapped around the bead cores. The carbon composite material maintained its structural integrity.

Tyre 3 was made with a carbon fibre composite bead core and standard cable bead core side by side. Tyre 3 survived 64 cycles on the structural test apparatus. The failure was due to casing delamination in the sidewall portion on both sides of the tyre rather than being due to the carbon composite bead core. The carbon fibre bead core maintained its structural integrity, but signs of de-bonding were observed. The bead core used in this test was not surface-treated.

Tyres 4, 5 and 6 were made using surface-roughened bead cores and were tested for ETSO including a double overload take-off. All three tyres passed the ETSO tests.

Summary of test results:

The structural test carried out on a tyre with both a carbon composite bead core and cable bead core showed that the carbon composite material did not suffer any loss of structural integrity and did not cause the tyre to fail. While not essential to provide an aircraft tyre, the use of surface roughening to provide a roughened or textured finish on the composite material was found to improve performance by reducing de-bonding. Overall, the combined use of surface roughening, adhesive coating, rubber sheet wrapping and fabric sheet wrapping was found to provide advantageous performance. These features should however be understood as advantageous rather than essential, with strength and weight saving provided by the use of composite bead cores. Each of the features of the tyre described above may be used separately or in any combination to provide improved bonding and adhesion between the bead core and surrounding material.

A method 200 of manufacturing the aircraft tyre 100 is shown schematically in Figure 4. The method 200 comprises assembling 202 a casing structure comprising the bead cores 110a, 110b and the inner liner 122 and casing 112 where provided. The method 200 further comprises assembling 204 an outer structure formed from the sidewall portions 102a, 102b, crown portion 104 and outer tread layer 118. Once assembled, heat and pressure may be applied 206 to the combined casing structure and outer structure to form the tyre 100. The casing and outer structure may be formed separately and then combined in a separate coupling step, or the outer structure may be formed directly onto the casing structure.

The casing structure may be assembled on a suitably shaped drum or former by first applying 208 the inner liner 122 onto the drum surface (if the inner liner is not used this step may be omitted). Assembling the casing structure further comprises applying 210 one or more casing plies 114 onto the drum to form the casing 112. Following this, the toroidal members forming the bead cores 110a, 110b are positioned 212 onto the drum over the casing plies 114 with the desired axial separation between each bead core along the drum. The ends of the casing plies may then be coupled 214 to the bead cores 110a, 110b, e.g. by wrapping their ends around the bead cores 110a, 110b to form the casing ply turn-ups 116a, 116b described above. The outer casing plies 114 may turn down around the bead cores 110a and 110b. Other coupling methods may be used.

Before being positioned around the casing plies 112 one of more pre-processing steps may be carried on one of both of the bead cores 110a, 110b. A surface roughening process 216 may be carried out to form a roughened finish 126 on some, or all, of the outer surface of the toroidal members forming the bead cores 110a, 110b. The surface roughening 126 may be carried out using a wet blasting technique or other suitable method. The pre-processing may also comprise applying 218 an adhesive layer to some, or all, or the outer surface of the toroidal members. The pre-processing may further comprise applying 220 a layer of rubber sheet material 130 and applying 222 a layer of fabric sheet material 132 around some or all of the surface of the bead cores 110a, I lob. Applying the layer of rubber sheet material and/or fabric sheet material may comprise wrapping the material around the bead cores 110a, 110b. The wrapping may be spiral or helical wrapping.

The pre-processing steps may therefore form the bonding structure 128 described above. The order of the method steps may be altered according to the desired composition of the bonding structure, with steps added or omitted where required according to the desired construction of the tyre. Some of the steps, e.g. the surface roughening, may be carried out in a separate manufacturing process.

The outer structure of the tyre 100 may be formed by assembling 224 the sidewall portions 102a, 102b and crown portion 104 onto the casings structure or a separate assembly drum. Once the sidewall portions 102a, 102b and crown portion have been assembled, the belt package 121b, inter-tread fabric (ITF) 121a and/or foreign object damage (FOD) resistant layers (e.g. cut and puncture resistant material) may be applied if being used before the outer tread layer 118 may be applied 226 around the periphery of the tyre 100. Where the outer tread layer 118 is integral with the tread portion 104 step 226 may be omitted. The chafers may also be added to the outer structure assembly where necessary. I0

Once the outer structure and casing structure have been formed and brought together a step of applying 206 heat and pressure is carried out to form the tyre. During this step, the tyre may be inflated with a suitable fluid so that it is expanded into a mould to form the final desired shape.

Various modifications will be apparent to the skilled person without departing form the scope of the claims. Any feature of any of the aspects or embodiments of the disclosure may be employed separately or in combination with any other feature of the same or different aspect or embodiment of the disclosure and the disclosure includes any feature or combination of features disclosed herein.

Claims

CLAIMS7. A pneumatic aircraft tyre, comprising: a pair of sidewall portions connected by a crown portion, each sidewall portion comprising a bead region for mounting the tyre onto the rim of a wheel, wherein each of the bead regions comprises a bead core, each bead core comprising a toroidal member formed from a composite material.
2. A pneumatic aircraft tyre according to claim 1 or claim 2, wherein the composite material is a carbon fibre reinforced plastics material, and is preferably carbon fibre epoxy prepreg material.
3. A pneumatic aircraft tyre according to claim 2, wherein each bead core is formed only from a composite material, and preferably is formed only from a carbon fibre reinforced plastics material.
4. A pneumatic aircraft tyre according to any preceding claim, wherein each bead region does not include any tensile reinforcing elements in addition to the toroidal member forming the bead core, wherein preferably the bead core is formed from a single toroidal member.
5. A pneumatic aircraft tyre according to any preceding claim, wherein one or both of the toroidal members have an at least partly roughened or textured outer surface.
6. A pneumatic aircraft tyre according to any preceding claim, wherein the bead regions of the side walls each comprise a rubber material, and wherein one or both of the bead regions further comprises a bonding structure adapted to provide a bond between the bead core and the rubber material
7. A pneumatic aircraft tyre according to claim 6, wherein the bonding structure comprises a rubber sheet material, the rubber sheet material at least partly surrounding the bead core, wherein the rubber sheet material is preferably wrapped around the toroidal member forming the bead core.
8. A pneumatic aircraft tyre according to claim 6 or claim 7, wherein the bonding structure comprises a fabric sheet material, the fabric sheet material at least partly surrounding the bead core, wherein the fabric sheet material is preferably wrapped around the toroidal member forming the bead core.
9. A pneumatic aircraft tyre according to claim 7 or claim 8, wherein the fabric sheet material and/or rubber sheet material is wrapped helically around the respective bead core.
10. A pneumatic aircraft tyre according to any of claims 6 to 9, wherein the bonding structure comprises an adhesive, the adhesive preferable being provided on the outer surface of the toroidal member of the respective bead core.
11. A pneumatic aircraft tyre according to any preceding claim, wherein each of the toroidal members has: a cross-sectional diameter or thickness of between 9.7 mm and 23.1 mm.
12. A pneumatic aircraft tyre according to any preceding claim, wherein each of the toroidal members has: an outside diameter of between 201.9 mm and 580.7 mm; and an inner diameter of between 181.5 mm to 535.5 mm.
13. A pneumatic aircraft tyre according to claim 11 or claim 12, wherein each of the toroidal members have an outside diameter of between 444.80 and 446.60 mm, and a has a cross-sectional diameter or thickness of between 12.48 and 13.71 mm.
14. A pneumatic aircraft tyre according to any preceding claim, wherein one or both of the toroidal members is hollow, and preferably are formed by a pressurised tube.
15. A pneumatic aircraft tyre according to any of claims I to 13, wherein one or both of the toroidal members are solid.
16. A method of manufacturing the pneumatic tyre of any preceding claim, the method comprising: assembling a casing structure comprising the bead cores; assembling an outer structure comprising the sidewall portions and crown portion; and applying heat and pressure to the casing structure and outer structure to form the tyre.
17. A method according to claim 16, wherein assembling the casing structure comprises carrying out one or more pre-processing steps on one or both of the bead cores, the pre-processing steps comprising any one or more of: (a) a surface roughening process arranged to form a roughened or textured finish one or both of the toroidal members forming the bead cores; (b) applying an adhesive layer to some, or all, or the outer surface of the toroidal members forming the bead cores; (c) applying a layer of rubber sheet material around some or all of the surface of one or both of the bead cores; and (d) applying a layer of fabric sheet material around some or all of the surface of one or both of the bead cores.
18. A method according to claim 17, wherein applying the layer of rubber sheet material and/or fabric sheet material comprises helically wrapping the material around the bead cores.