Patent Description:
Transmission shafts are used in high lift actuation systems in commercial and military aircraft. Typically, they comprise a composite tube fitted with metallic flanged end fittings. The metallic flanged end fittings are connected to the rest of the system using bolted connections, and provide the necessary structural and mechanical properties for the transmission shaft, including the ability to transmit the required torsional loads without structural degradation or failure.

However, the metallic end fittings are relatively heavy and so add weight to the system, which is undesirable in an aircraft. In order to reduce the weight, transmission shafts have been proposed - for example in <CIT> - in which the flanged portion is also formed of a composite material. Then, to achieve the necessary mechanical properties, the flanged portion of the transmission shaft is formed in its final form integrally with the shaft portion by winding fibres about a mandrel with a flared part. The flared part of the mandrel includes eyelet forms for winding the fibres around to form holes in the flanged end fitting for connecting bolts. The wound fibre preform is then cured, and metal eyelets are then inserted into the holes. While this approach reduces the weight, it increases the complexity of manufacturing.

<CIT> discloses a method of manufacturing an all-composite torque tube formed using a pre-woven end sleeve at each end, and a fiber tow winding merging with each end sleeve.

<CIT> discloses a method of forming urethane composite articles comprising long fibres.

<CIT> discloses a rotary power transmission shaft comprising a tube with integrant flanges.

According to a first aspect of the invention there is provided a composite transmission shaft according to claim <NUM>.

In addition to the foregoing the reinforcement portion may be a first reinforcement portion and the flanged end fitting may comprise a second reinforcement portion fixed to the flared portion of the sleeve and disposed on an opposite side of the flared portion to the first reinforcement portion. The first and second reinforcement portions may be annular.

In addition or as an alternative to the foregoing the flared portion of the sleeve may comprise a plurality of holes punched through it, each one of which may be delimited by a plurality of fibre ends; wherein the reinforcement portion may comprise a plurality of holes formed in it, which holes may be delimited by portions of continuous fibres; and wherein the holes in the flared portion and the holes in the reinforcement portion may be aligned so that holes are formed in the flange of the flanged end fitting.

In addition or as an alternative to the foregoing the reinforcement portion may have been fixed to the flared portion of the sleeve by stitching prior to resin transfer moulding.

According to a second aspect of the invention there is provided a method of manufacturing a composite transmission shaft comprising a shaft portion, and a flanged end fitting as defined in claim <NUM>.

In addition to the foregoing, the method may comprise punching a plurality of holes in the flared portion of the sleeve prior to fixing the reinforcement portion thereto.

In addition or as an alternative to the foregoing the method may comprise forming the reinforcement portion with a plurality of holes therein.

In addition or as an alternative to the foregoing the method may comprise aligning the holes in the reinforcement portion with the holes in the flared portion of the sleeve before stitching the reinforcement portion to the flared portion.

In addition or as an alternative to the foregoing the method may comprise forming a transmission shaft as described with reference to the first aspect of the disclosure.

Embodiments of the invention will be described below by way of example only and with reference to the accompanying drawing in which:.

According to a first embodiment there is provided a composite transmission shaft <NUM>, comprising a shaft portion <NUM>, and a flanged end fitting <NUM>. The flanged end fitting <NUM> comprises a flared sleeve <NUM> comprising a tubular portion <NUM> and a flared portion <NUM>, and a reinforcement portion <NUM>, <NUM> fixed to the flared portion <NUM> of the sleeve <NUM>. The flanged end fitting <NUM> and shaft portion <NUM> have been resin transfer moulded together to form the transmission shaft <NUM>.

The transmission shaft <NUM> is therefore an all-composite transmission shaft <NUM>, formed entirely of composite material. The flared portion <NUM> of the sleeve <NUM> and the reinforcement portion <NUM>, <NUM> fixed to it together comprise the flange of the flanged end fitting <NUM>.

The transmission shaft <NUM> is formed by resin transfer moulding the flanged end fitting <NUM> together with the shaft portion <NUM>, though the preform versions of the flanged end fitting <NUM> and shaft portion <NUM> may also be connected by other means prior to resin transfer moulding, such as stitching.

The shaft portion <NUM> is composite and may be formed from a wound, braided, stitched or woven sheet of continuous fibre preform. The fibres may be carbon fibres comprising carbon filaments. The flanged end fitting <NUM> and/or flared sleeve <NUM> is also composite and may be formed from a wound, braided, stitched or woven sheet of continuous fibre preform. The fibres may be carbon fibres comprising carbon filaments.

The transmission shaft <NUM> may be made using only one resin transfer moulding process which joins together the preform of the shaft portion <NUM> and the preform of the flanged end fitting <NUM>.

The flared portion <NUM> of the sleeve <NUM> may be substantially the same shape as the reinforcement portion <NUM>, <NUM>. The flared portion <NUM> may be substantially annular and the reinforcement portion <NUM>, <NUM> may be substantially annular. The flared portion <NUM> and the reinforcement portion <NUM>, <NUM> may be rings. Alternatively, the reinforcement portion <NUM>, <NUM> may be shaped differently to the flared portion <NUM> while still providing mechanical reinforcement. For example, the flared portion <NUM> may be annular and the reinforcement portion <NUM>, <NUM> may be substantially triangular, quadrilateral, polygonal etc..

The shaft portion <NUM> and the tubular portion <NUM> of the sleeve <NUM> may have substantially the same cross-sectional shape and corresponding dimensions (e.g. overlapping dimensions) so that at least a portion of one is disposed within at least a portion of the other so that those portions are fixed together by the resin transfer moulding process. They may be cylindrical and may have substantially the same diameter.

The reinforcement portion may be a first reinforcement portion <NUM> and the flanged end fitting <NUM> may comprise a second reinforcement portion <NUM> fixed to the flared portion <NUM> of the sleeve <NUM> and disposed on an opposite side of the flared portion <NUM> to the first reinforcement portion <NUM>. Both reinforcement portions <NUM>, <NUM> may have the same or complementary shapes and/or properties. The first and second reinforcement portions <NUM>, <NUM> may each be annular, or any suitable shape as described above. Then, the flared portion <NUM> of the sleeve <NUM> may be disposed between two reinforcement portions <NUM>, <NUM>, so that the flange of the flanged end fitting <NUM> comprises a sandwich of cured fibre preforms.

The reinforcement portion <NUM>, <NUM> comprises fibres oriented circumferentially and radially. The fibres of this and other parts of the transmission shaft may be arranged to improve and/or optimise the transmission of torsional loads through the flanged end fitting <NUM>.

The shaft portion <NUM> may be wound and may comprise fibres having multiple winding angles. The shaft portion <NUM> may be braided or woven. The fibres may be arranged to improve and/or optimise the transmission of torsional loads through the shaft portion <NUM>.

The fibres of any part of the transmission shaft may be arranged to improve torsional and/or axial stiffness, axial strength, and/or impact resistances. A plurality of different fibres and fibre orientations may be used to optimise the characteristics of the transmission shaft, and hence its performance.

The flared portion <NUM> of the sleeve <NUM> may comprise a plurality of holes punched through it, each one of which may be delimited by a plurality of fibre ends. The reinforcement portion <NUM>, <NUM> may comprise a plurality of holes formed in it, which holes are delimited by portions of continuous fibres. The holes in the flared portion <NUM> and the holes in the reinforcement portion <NUM>, <NUM> may be aligned so that holes are formed in the flange of the flanged end fitting <NUM>.

The holes in the flared portion <NUM> may be made by punching a hole in the flared portion <NUM> of the sleeve <NUM>, and hence may be surrounded by cut fibres delimiting the hole. The composite material of the flared portion <NUM> surrounding each hole may therefore be weaker as a consequence of the hole and the fibre ends. The reinforcement portion <NUM>, <NUM> may comprise holes punched therein, which holes would then be delimited by fibre ends like the holes in the flared portion <NUM> of the sleeve <NUM>. However, preferably the reinforcement portion <NUM>, <NUM> may be formed (e.g. stitched, woven, wound or braided) with holes in it, for example by winding or braiding about pegs, and therefore may not comprise fibre ends in the regions near the holes, or may primarily comprise continuous portions of fibre delimiting the holes. Thus, the holes in the reinforcement portion <NUM>, <NUM> may be stronger and serve to reinforce the flange of the flanged end fitting <NUM>.

Each hole of the flared portion <NUM> may be aligned with a corresponding hole in the reinforcement portion <NUM>, so that all holes in the flange of the flanged end fitting <NUM> are aligned. This may permit bolts or the like to be passed through the flange of the flanged end fitting <NUM> so as to allow fixing of the flange to another surface, thereby fixing the transmission shaft <NUM>. The holes may then be used to connect the transmission shaft <NUM> to other components as needed.

The reinforcement portion <NUM>, <NUM> may have been fixed to the flared portion <NUM> of the sleeve <NUM> by stitching prior to resin transfer moulding, e.g. as a preform. Where there are two reinforcement portions <NUM>, <NUM>, the second reinforcement portion <NUM> may comprise all the features of the first reinforcement portion <NUM>, including holes delimited by continuous composite fibres, which holes may be aligned with those of the flared portion <NUM>, and hence also with those of the first reinforcement portion <NUM>. The second reinforcement portion <NUM> may be fixed to the flared portion <NUM> by stitching, in the same manner as the first reinforcement portion <NUM>.

According to a second embodiment there is provided a method of manufacturing a composite transmission shaft <NUM> comprising a shaft portion <NUM>, and a flanged end fitting <NUM>. The method comprises: providing a sleeve <NUM> which is substantially tubular; deforming an end of the sleeve to form a flared portion <NUM>; fixing a reinforcement portion <NUM>, <NUM> to the flared portion <NUM> of the sleeve <NUM> to form a preform of the flanged end fitting <NUM> comprising a tubular portion <NUM> and a flange; positioning the tubular portion <NUM> of the flanged end fitting <NUM> in contact with the shaft portion <NUM>; and resin transfer moulding the shaft portion <NUM> and the flanged end fitting <NUM> together to form the transmission shaft <NUM>.

The resin transfer moulding process joins and fixes all of the components of the transmission shaft <NUM> together to form the final product. The flange of the flanged end fitting <NUM> is formed from the flared portion <NUM> of the sleeve <NUM> and the reinforcement portion <NUM>, <NUM> joined together. The tubular portion <NUM> of the flanged end fitting <NUM> is formed from the tubular portion <NUM> of the sleeve <NUM>, and is joined to the shaft portion <NUM> by the resin transfer moulding process. Prior to the resin transfer moulding process, the shaft portion <NUM>, the flared sleeve <NUM>, and the reinforcement portion <NUM>, <NUM> are preforms.

For the resin transfer moulding process, the assembled preforms of the shaft portion <NUM>, the flared sleeve <NUM>, and the reinforcement portion <NUM>, <NUM> may all be positioned in a suitable mould capable of applying pressure through the thickness of the assembly. A resin and/or a resin system may then be transferred into the mould and driven in the preforms as a result of the pressure applied on the preforms by the mould. A plurality of resins may be used, which may be thermoset and/or thermoplastic. The resin may be chosen to optimise the mechanical performance of the transmission shaft, for example for torsional strength, axial strength, impact resistance and/or thermal stability.

The step of deforming the end of the sleeve <NUM> to form the flared portion <NUM> may weaken the structure of the sleeve <NUM> by disrupting the arrangement of the fibres in the sleeve <NUM>. The reinforcement portion <NUM>, <NUM> may then be used to strengthen the weakened sleeve <NUM> and improve and/or optimise the transmission of torsional loads through the flange of the flanged end fitting <NUM> and reduce the risk of structural degradation or failure during use.

The method may comprise punching a plurality of holes in the flared portion <NUM> of the sleeve <NUM> prior to fixing the reinforcement portion <NUM>, <NUM> thereto. This step may further weaken the structure of the sleeve <NUM> by breaking fibres within the flared portion <NUM>. The resulting hole will be formed by breaking or cutting fibres and hence will be surrounded by fibre ends, as described above with reference to the first embodiment.

The method may comprise forming the reinforcement portion <NUM>, <NUM> with a plurality of holes therein. The method may comprise weaving, winding, stitching or braiding the reinforcement portion <NUM>, <NUM> to include holes therein. Then, the holes may be delimited by continuous portions of fibres as described with reference to the first embodiment and hence may allow the reinforcement portion <NUM>, <NUM> to be stronger than if holes were punched in it. However, the method may include punching holes in the reinforcement portion <NUM>, <NUM>, which will anyway serve to reinforce the flared portion <NUM> of the sleeve <NUM>. The method may comprise forming the holes so that fibre orientations thereabout improve and/or optimise the transmission of torsional loads.

The method may comprise aligning the holes in the reinforcement portion <NUM>, <NUM> with the holes in the flared portion <NUM> of the sleeve <NUM> before stitching the reinforcement portion <NUM>, <NUM> to the flared portion <NUM>. Other means of joining the reinforcement portion <NUM>, <NUM> to the flared portion <NUM> may be used prior to the resin transfer moulding process. Thus, the reinforcement portion <NUM>, <NUM> may further reinforce the flared portion <NUM> of the sleeve <NUM>.

The method may comprise stitching a second reinforcement portion <NUM> to the flared portion <NUM> of the sleeve <NUM> on a side of the flared portion <NUM> opposite the first reinforcement portion <NUM>. The second reinforcement portion <NUM> may be substantially the same as the first reinforcement portion <NUM>, and the method may comprise aligning holes of the second reinforcement portion <NUM> with the holes of the flared portion <NUM>.

The step of positioning the tubular portion <NUM> of the flanged end fitting <NUM> in contact with the shaft portion <NUM> may comprise aligning fibre orientations of the shaft portion <NUM> so as to improve or optimise the transmission of torsional loads therethrough.

The method may comprise determining a stress analysis of the transmission shaft in intended use and preparing the preforms such that fibres of the respective preforms are aligned with predetermined directions to optimise certain performance characteristics of the final product, e.g. ultimate torsional strength.

The method may comprise forming a transmission shaft as described above with reference to the first embodiment.

A preform for a flanged end fitting <NUM>, comprises a flared sleeve <NUM> comprising a tubular portion <NUM> and a flared portion <NUM>, and a reinforcement portion <NUM>, <NUM> attached to the flared portion <NUM> of the sleeve <NUM>.

The reinforcement portion of the preform for a flanged end fitting <NUM> may be a first reinforcement portion <NUM> and preform may comprise a second reinforcement portion <NUM> fixed to the flared portion <NUM> of the sleeve <NUM> and disposed on an opposite side of the flared portion <NUM> to the first reinforcement portion <NUM>.

The preform may be suitable for use in the method described above in relation to the second aspect of the invention, and - once cured - may provide a flanged end fitting <NUM> comprising any and all of the features of the flanged end fitting <NUM> described above with reference to the first aspect of the invention.

In more detail, a transmission shaft <NUM> is shown in <FIG>, comprising a shaft portion <NUM> and a flanged end fitting <NUM>. Although shown in cross-section, the transmission shaft <NUM> is circularly symmetric about an axis A. The flanged end fitting <NUM> comprises a sleeve <NUM> comprising a tubular portion <NUM> and a flared portion <NUM>. The flanged end fitting <NUM> further comprises a first reinforcement portion <NUM> and a second reinforcement portion <NUM> stitched and resin transfer moulded to the flared portion <NUM> of the sleeve <NUM>.

The shaft portion <NUM> is formed of a wound or braided carbon fibre sock. The sleeve <NUM> is formed of a wound or braided carbon fibre sock. The tubular portion <NUM> of the sleeve <NUM> is substantially the same diameter as the shaft portion <NUM>. The flared portion <NUM> of the sleeve gradually flares outwards. The first reinforcement portion <NUM> is a stitched carbon fibre preform with holes and fibre directions which enable and improve the transmission of torsional loads. Some of the fibres in the reinforcement portions <NUM> and <NUM> are arranged in circumferential directions, and others are arranged in radial directions. The second reinforcement portion <NUM> is substantially the same as the first, and is disposed on an opposite side of the flared portion <NUM> of the sleeve <NUM> to the first reinforcement portion <NUM>.

<FIG> shows a flowchart of a method <NUM> of manufacturing a composite transmission shaft. During manufacture, the sleeve <NUM> is provided at step <NUM>. The sleeve <NUM> starts as a tubular shape of substantially constant diameter along its length. Then, one end of the sleeve <NUM> is folded or deformed radially outwards at step <NUM> so as to form the flared portion <NUM> with a short shank. The tubular portion <NUM> is then formed of the part of the sleeve <NUM> that has not been deformed.

Holes (not shown) are then punched through the flared portion <NUM> of the sleeve <NUM> to allow the connection of bolts for mounting the transmission shaft <NUM> for use. The reinforcement portions <NUM> and <NUM> in the form of stitched preforms are aligned with the flared portion <NUM> so that holes in the reinforcement portions <NUM> and <NUM> align with the holes in the flared portion <NUM>. At step <NUM> the reinforcement portions are stitched directly on the flared portion <NUM> of the sleeve <NUM>.

At step <NUM> the flanged end fitting <NUM> is laid up together with the shaft portion <NUM> so that the shaft portion <NUM> is inserted partially within the tubular portion <NUM> of the flanged end fitting <NUM>. Finally at step <NUM> the entire lay-up is resin transfer moulded to form the final transmission shaft. The process of resin transfer moulding joins the shaft portion <NUM> to the tubular portion <NUM> of the sleeve <NUM>. It also secures the reinforcement portions <NUM> and <NUM> to the flared portion <NUM> of the sleeve <NUM>.

Claim 1:
A composite transmission shaft (<NUM>), comprising a shaft portion (<NUM>), and a flanged end fitting (<NUM>);
wherein the flanged end fitting comprises a flared sleeve (<NUM>) comprising a tubular portion (<NUM>) and a flared portion (<NUM>); and
wherein the flanged end fitting and shaft portion have been resin transfer moulded together to form the transmission shaft;
characterised in that:
the flanged end fitting comprises a reinforcement portion (<NUM>, <NUM>);
wherein the reinforcement portion comprises fibres oriented circumferentially and radially; and
wherein the reinforcement portion (<NUM>, <NUM>) is fixed to the flared portion of the sleeve.