SPLINED END FITTINGS

Abstract

A metallic end fitting for a given tubular component made of fibre reinforced polymer matrix composite material includes first and second concentric surfaces extending longitudinally along a central axis to form a socket for receiving an end of the tubular component. The socket has an outer diameter defined by the first surface, and an inner diameter defined by the second surface, wherein the outer diameter and inner diameter are chosen to provide an interference fit with respective outer and inner of the given tubular component when the component is press fitted into the socket. Each of the first and second concentric surfaces comprises one or more longitudinal cutting teeth. When the given tubular component is press fitted into the socket, the one or more longitudinal cutting teeth are designed to cut one or more longitudinal grooves into respective outer and inner surfaces of the composite material tubular component.

Claims

1. A metallic end fitting for a given tubular component made of fibre reinforced polymer matrix composite material, the end fitting comprising: first and second concentric surfaces extending longitudinally along a central axis to form a socket for receiving an end of the tubular component, wherein the socket has an outer diameter defined by the first surface, and an inner diameter defined by the second surface, wherein the outer diameter and inner diameter are chosen to provide an interference fit with respective outer and inner surfaces of the given tubular component when the component is press fitted into the socket; wherein each of the first and second concentric surfaces comprises one or more longitudinal cutting teeth.

2. The metallic end fitting of claim 1, wherein the one or more cutting teeth comprise a plurality of axial or helical splines.

3. The metallic end fitting of claim 1, wherein the end fitting comprises: the first surface facing radially inwardly and comprising a plurality of splines extending along the central axis, each spline flanked by a pair of troughs extending along either side of the spline and projecting radially outwardly to a diameter greater than the outer diameter, and each spline projecting radially inwardly from the outer diameter, to form a corresponding plurality of longitudinal cutting teeth, adjacent cutting teeth being spaced apart by lands extending circumferentially at the outer diameter; or the second surface facing radially outwardly and comprising a plurality of splines extending along the central axis, each spline flanked by a pair of troughs extending along either side of the spline and projecting radially inwardly to a diameter less than the inner diameter, and each spline projecting radially outwardly from the inner diameter, to form a corresponding plurality of longitudinal cutting teeth, adjacent cutting teeth being spaced apart by lands extending circumferentially at the inner diameter.

4. The metallic end fitting of claim 1, at least one of the first and second concentric surfaces is angled relative to the central axis.

5. The metallic end fitting of claim 4, wherein the first and second surfaces are angled to converge towards the central axis from an open end of the socket that receives the end of the tubular component.

6. The metallic end fitting of claim 1, wherein the first and second concentric surfaces are parallel to the central axis.

7. The metallic end fitting of claim 1, wherein the socket comprises an open end arranged to receive an end of the given tubular component, an end portion providing the open end, and splined surface portions providing the first and second concentric surfaces, wherein the end portion comprises further first and second lead-in surfaces that are angled to extend radially away from the outer and inner diameters.

8. The metallic end fitting of claim 1, wherein the socket comprises an open end arranged to receive an end of the given tubular component and a base at an opposite end of the socket, wherein the base comprises an undercut having a diameter different to the outer and/or inner diameter.

9. The metallic end fitting of claim 1, wherein the end fitting is a one-piece component.

10. An end fitting assembly comprising: a tubular component made of fibre reinforced polymer matrix material inserted into the socket of an end fitting according to claim 1.

11. The end fitting assembly of claim 10, wherein the socket is tapered on at least one of the first and second concentric surfaces and the tubular component comprises tapered outer and/or inner surfaces inserted into the tapered socket.

12. The end fitting assembly of claim 11, wherein the end fitting assembly comprises an adhesive bond between the first surface of the socket and an outer surface of the tubular component, and/or an adhesive bond between the second surface of the socket and an inner surface of the tubular component.

13. A method of assembling a torque transmission/drive shaft, comprising: providing a tubular component made of fibre reinforced polymer matrix material; and press fitting a metallic end fitting according to claim 1 onto each end of the tubular component.

14. A method of making a metallic end fitting for a given tubular component, the end fitting comprising: first and second concentric surfaces extending longitudinally along a central axis to form a socket for receiving an end of the tubular component; the socket having an outer diameter defined by the first surface, and an inner diameter defined by the second surface, wherein the outer diameter and inner diameter are chosen to provide an interference fit with respective outer and inner surfaces of the given tubular component when the component is press fitted into the socket; wherein each of the first and second concentric surfaces comprise one or more longitudinal cutting teeth.

Description

DETAILED DESCRIPTION

[0037] One or more non-limiting examples will now be described, by way of example only, and with reference to the accompanying figures, in which:

[0038] FIG. 1a is an isometric view, FIG. 1b is an enlarged view, and FIG. 1c is a cross-sectional view, of a double splined end fitting comprising a socket according to an example;

[0039] FIG. 2 is a cut-through sectional view of an end fitting assembly with a composite tube inserted into the socket of the end fitting of FIG. 1;

[0040] FIG. 3 is a cross-sectional view of a double splined end fitting according to another example;

[0041] FIG. 4a is a cross sectional view of another end fitting assembly with a composite tube inserted into a socket having an undercut;

[0042] FIG. 4b is a cross sectional view of another end fitting assembly with a composite tube inserted into a socket having an alternative undercut shape;

[0043] FIG. 5 is a close up view of a splined surface; and

[0044] FIG. 6 is a cross sectional view of a composite tube with end fitting assemblies press fitted onto both ends.

[0045] There is seen in FIGS. 1a, 1b and 1c an example of a double splined end fitting 2. The metallic end fitting 2 comprises a base portion 4 and a socket portion 6. The socket portion 6 comprises concentrically spaced outer and inner portions 8, 10 which each comprise a cylindrical shell that extends from the base portion 4 in a longitudinal direction parallel to a central axis C. The inner portion 10 is located radially inward of the outer portion 8 such that a socket 13 with an annular cross section is formed, defined by an outer surface 12 of the inner portion 10 that is facing radially outwardly and an inner surface 14 of the outer portion 8 that is facing radially inwardly. The socket 13 has an outer diameter defined by the inner surface 14, an inner diameter defined by the outer surface 12, and a base proximal to the base portion 4. In this example the outer and inner surfaces 12, 14 are parallel to the central axis C, such that the cross section of the socket 13 is consistent along its depth.

[0046] The outer surface 12 is splined, wherein it comprises a plurality of radially and longitudinally extending cutting teeth spaced by longitudinally and circumferentially extending lands. The inner surface 14 is similarly splined. The cutting teeth are shown in in more detail in FIG. 5 and described below. FIG. 1c shows that the plurality of teeth do not extend the entire depth of the outer and inner portions 8, 10 but instead an undercut 18 is formed at the base of the socket 13 which will also be explained in further detail below.

[0047] As is seen most clearly from FIG. 1C, the splined surface portions 12, 14 of the socket 13 do not extend all the way along the length of the socket 13. The socket 13 has an open end 11 arranged to receive a tubular component. The open end 11 is provided by an end portion 13a of the socket 13. In the end portion 13a, inner and outer lead-in surfaces 11a, 11b are angled to extend radially away from the outer and inner diameters defined by the splined surface portions 12, 14. The flared lead-in surfaces 11a, 11b can assist with insertion of a tubular component into the socket 13.

[0048] The base portion 4 further comprises connecting holes 20, so that the end fitting 2 may be connected to another component (not shown). The end fitting 2 is formed of a metallic material as a one-piece component.

[0049] The splines shown in this figure extend longitudinally, which gives a connection with a tubular component the best torsional strength, although the splines may extend helically (akin to a screw thread) to give improved axial load transmission. Helically extending splines may extend at an angle to the longitudinal direction of less than or equal to 15 although angles up to 89 may be beneficial in some examples.

[0050] As shown in FIG. 2, a fibre reinforced polymer matrix composite material tube 22 may be inserted into the socket 13 to connect the tube 22 to the end fitting 2. The tube 22 comprises an internal cylindrical surface 24 and an external cylindrical surface 26 which have diameters such that an interference fit is formed between the composite tube 22 and the outer and inner surfaces 12, 14 of the socket 13, preventing accidental separation of the tube 22 and the end fitting 2 during use. During assembly, the composite tube 22 is press fitted into the socket 13 by applying force in a longitudinal direction (i.e. along the central axis C), and as the tube 22 enters the socket 13, the cutting teeth of the outer and inner surfaces 12, 14 cut longitudinal grooves into the internal and external surfaces 24, 26 of the tube 22. This forms a mechanical locking interface, such that relative rotation of the end fitting 2 and the composite material tube 22 is prevented.

[0051] The undercut 18 shown in FIG. 1c at the base of the socket 13 serves to collect debris created by the cutting teeth as the composite material tube 22 is inserted into the socket 13. The undercut 18 also serves to reduce stress in the end fitting 2 caused by the interference fit with the composite material tube 22 and prevents any load from being applied to the end of the composite material tube 22, which is often undesirable.

[0052] Adhesive may be disposed in the socket 13 before the composite material tube 22 is inserted to increase the strength of the mechanical locking interface. In this case the undercut 18 also serves to collect excess adhesive that may be displaced as the tube 22 is inserted.

[0053] In another example, illustrated in FIG. 3, an end fitting 102 comprises a base portion 104 and a socket portion 106. The socket portion 106 comprises concentrically spaced outer and inner portions 108, 110 which each comprise a generally cylindrical shell that extends from the base portion 102 in a longitudinal direction parallel to a central axis C to an open end 111. The inner portion 110 is located radially inward of the outer portion 108 such that a socket 113 with an annular cross section is formed, defined by an outer surface 112 of the inner portion 110, an inner surface 114 of the outer portion 108. The socket 113 has an outer diameter defined by the inner surface 114, an inner diameter defined by the outer surface 112 and a base proximal to the base portion 104. In this example the outer surface 112 (facing radially outwardly) and the inner surface 114 (facing radially inwardly) are both angled relative to the central axis C, such that the socket 113 tapers inwardly to a narrowest point at its base. It can be seen in FIG. 3 that the surfaces 112, 114 are angled to converge towards the central axis C from the open end 111 of the socket 113 that receives the tube 122. The outer surface 108 and the inner surface 106 are splined, and the end fitting 102 comprises an undercut 118 at the base of the socket 113, as generally seen in the previous example but enlarged in this example.

[0054] A wall of a fibre reinforced polymer matrix composite material tube 122 is also shown in FIG. 3. The composite material tube 122 comprises fibres 123 that run longitudinally within its walls, and the tubular walls are tapered to match the taper of the socket 113 such that the ends of some of the fibres 123 are exposed at tapered internal and external surfaces 124, 126 of the tube 122. Tapering of the tube walls may be achieved by grinding away material from a composite material tube with straight walls.

[0055] During assembly, the composite material tube 122 is inserted into the socket 113. As the tapered surfaces 124, 126 match the socket 113, the composite material tube 122 is press fitted into an interference fit with the outer and inner surfaces 112, 114. The cutting teeth of the outer and inner surfaces 112, 114 cut longitudinal grooves into the tube 122 to form a mechanical locking interface which prevents relative rotation of the end fitting 102 and the composite tube 122.

[0056] As in the previous example, the undercut 118 at the base of the socket 113 serves to reduce stress in the end fitting 102 and to collect debris created by the cutting teeth as the composite material tube 122 is inserted into the socket 113. Also as in the previous example, adhesive may be disposed in the socket 113 before the composite tube 122 is inserted and the undercut 118 may serve to collect any excess adhesive.

[0057] FIG. 4a is a cross section of an entire metallic end fitting 202 when assembled with a composite material tube 222. In this example the tube 222 comprises an external surface 226 that is tapered and an internal surface 224 that is straight, i.e. a tube 222 with a single taper rather than the double taper seen in FIG. 3. The end fitting 202 comprises a socket 213 with matching concentric surfaces, one being straight and the other tapered. Of course the surfaces could be reversed. The end fitting 202 also comprises a large undercut 218. Otherwise the end fitting 202 is substantially the same as previously described and the tube 222 is press fitted into the socket 213 in the same way.

[0058] FIG. 4b illustrates an alternative example of a metallic end fitting 302 comprising a socket 313 with a smaller undercut 318 at its base, wherein the undercut 318 comprises a semi-circular void. This profile of this undercut 318 may be easier to manufacture than alternatives, while still providing room for debris and/or adhesive when a composite material tube 322 is press fitted into the socket 313.

[0059] As described above, in examples of the present disclosure the concentric surfaces of the socket provided by the end fitting are splined. FIG. 5 is a close up cross section of a splined surface 402 according to the present disclosure. The surface 402 extends generally along a surface plane S and comprises a repeating pattern of splines 404, troughs 406 and flats 408, each of which extends in a longitudinal direction L (e.g. corresponding to the central axis C in FIG. 1a). Within the repeating pattern, each spline 404 projects out from the surface plane S and is flanked by a pair of troughs 406 which are recessed into the surface plane S. Each spline 404 and its flanking troughs 406 form a longitudinal cutting tooth 410, and adjacent cutting teeth 410 are separated by a flat 408, which does not project from the surface plane S. The cutting teeth 410 typically comprise a cutting angle of between 5 and 85. Although the surface plane S is schematically shown as a straight plane in FIG. 5, it is of course an arcuate plane when the splined surface 402 is a concentric surface of a socket in one of the end fitting disclosed herein. The longitudinal direction L then extends along the central axis C, in a parallel direction for a straight surface or an angled direction for a tapered surface.

[0060] FIG. 6 shows a fully assembled composite material torque transmission/drive shaft 524 comprising a fibre reinforced polymer matrix material tube 522 with metallic end fittings 502 press fitted onto both ends. The end fittings 502 are connected to the composite tube 522 as described herein, with the composite material tube 522 being press fitted into a splined socket formed in each end fitting 502.

[0061] In the illustrated example, the end fittings 502 are identical, but in similar examples where connections are required on both ends of a composite material tube 522, dissimilar end fittings may be employed, or one metallic end fitting according to the present disclosure may be used on a first end of the composite tube, with a different connection means used at the other end.