This invention relates to a drive shaft, and in particular to a drive shaft of a composite material.

Composite materials, for example including glass fibre, carbon fibre or the like reinforcing materials are in increasingly wide spread use in a range of applications. At least in part, the use of composite materials can be advantageous in that they are typically of relatively low weight whilst being of good load bear and transmitting properties. Accordingly, in applications in which weight is a concern, such as in a number of aerospace applications, and in certain automotive applications, there is a desire to use composite materials as an alternative to the more traditionally used metallic materials.

One application in which it is desirable to be able to make use of composite materials is in the provision of drive shafts or the like intended for use in the transmission of torques or rotary loads.

Whilst the use of composite materials in drive shafts and similar applications may be beneficial in that weight savings may be made without significantly reducing the magnitudes of the loads that can be carried, one disadvantage with composite materials is that the attachment of fittings thereto, for example the attachment of gears and the like to the materials, is problematic. Where a gear or other fitting is to be attached to an end of a drive shaft, then it is known to use fittings provided with small spline features that are press or push fitted to the end of the shaft, the small spline features digging into the material of the shaft to provide a good load bearing capacity between the end fitting and the shaft. However, the use of such a technique in providing a fitting at a location spaced from an end of the shaft is inappropriate as the fitting would need to be pushed over an extended length of the shaft, and the interaction between the spline features and the outer surface of the shaft would result in an unacceptable level of damage to the outer surface of the shaft. It is an object of the invention to provide a drive shaft in which at least some of the disadvantages associated with known arrangements are overcome or are of reduced impact.

According to the present invention there is provided a drive shaft comprising a first drive shaft segment of a composite material, a second drive shaft segment of a composite material, and a fitting adapted to encircle an end part of the first drive shaft segment and an end part of the second drive shaft segment, wherein the fitting is push or press fitted onto the respective end parts to connect the first and second drive shaft segments to one another.

It will be appreciated that the invention permits the provision of a drive shaft in which a fitting is provided part way along the length of the drive shaft. The fitting may be provided with external gear teeth or other formations. It will be appreciated that in such an arrangement, a gear is provided part way along the length of the drive shaft, or a mount is provided whereby other components may be attached part way along the shaft.

The nature of the fitting and its cooperation with the first and second drive shaft segments may be such as to allow limited movement therebetween. Consequently, the first and second drive shaft segments may be arranged such that their axes are angled to one another, the limited relative movement accommodating such angling of the axes of the drive shaft segments and so, effectively, forming a drive shaft of enhanced flexibility. This may be advantageous in that it permits accommodation of slight axial misalignment between components with which the drive shaft cooperates, in use. The end parts of the first and second drive shaft segments conveniently include integral generally radially extending flanges to which the fitting is fitted. Such an arrangement may have enhanced flexibility through flexing of the flanges.

According to another aspect of the invention there is provided a drive shaft comprising a first drive shaft segment of a composite material, a second drive shaft segment of a composite material, the first and second drive shaft segments being formed integrally with one another, and a fitting adapted to encircle a part of the first drive shaft segment adjacent the second drive shaft segment, and a part of the second drive shaft segment adjacent the first drive shaft segment, wherein the fitting is push or press fitted onto the respective drive shaft segments to transmit loads therebetween.

A collar may be provided at the intersection between the first and second drive shaft segments, the collar reacting loads resulting from the presence of the fitting.

By way of example, the drive shaft segments may be of wound fibre reinforced form. During manufacture, the reinforcing fibre may be wound over the collar, causing the reinforcing fibre to splay radially outwards at the location of the intersection of the first and second drive shaft segments. The collar may be of composite material form, for example it may be of wound fibre reinforced form. The fibres thereof may be hoop wound, for example. Alternatively, it could comprise a prefabricated, for example metallic component.

During manufacture, the reinforcing fibres of the drive shaft segments may be machined, at the location of the intersection between the drive shaft segments, to form a generally cylindrical or conical surface for cooperation with the fitting, the fibres being exposed at the surface. In such an arrangement, it will be appreciated that the fitting may serve to transmit a significant part of the load, in use, between the drive shaft segments.

The collar conveniently serves to react compressive loads applied by the fitting, compressing parts of the drive shaft segments located between the collar and the fitting.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a diagrammatic view of a drive shaft in accordance with an embodiment of the invention; and Figure 2 is a diagrammatic view illustrating an alternative embodiment.

Referring firstly to Figure 1, an upper half of a portion of a drive shaft 10 is illustrated. The drive shaft 10 comprises a first drive shaft segment 12 of wound fibre reinforced, composite material form, and a second drive shaft segment 14, also of wound fibre reinforced composite material form. By way of example, the reinforcing fibre may be of carbon fibre form. However, the invention is not restricted to the use of this material.

Each of the drive shaft segments 12, 14 includes an integral end part 12a, 14a shaped to define respective integral radially outwardly extending flanges 16.

The drive shaft 10 further comprises a fitting 18 of metallic form. In this embodiment, the fitting 18 takes the form of a short cylindrical shaft that is provided, on its inner surface, with a series of small spline or rib formations. The inner diameter of the fitting 18 is selected to match the outer diameters of the flanges 16, such that the flanges 16 can be push or press fitted into the fitting 18 to connect the shaft segments 12, 14 to one another. During the push or press fitting operation, the ribs or splines dig into the outer surface of the flanges 16, enhancing the quality of the connection between the fitting 18 and the drive shaft segments 12, 14, and thereby enhancing the transmission of loads along the drive shaft 10.

The arrangement shown in Figure 1 is advantageous in that flexing of the flanges 16 may occur, in use, with the result that the drive shaft 10 may be of relatively flexible form, allowing it to accommodate slight axial misalignment or movement between components or fittings with which it is used, whilst still being of good load or torque transmitting form. Furthermore, limited relative movement between the flanges 16 and the fitting 18 may also increase flexibility of the drive shaft 10. In a modification to the arrangement shown in Figure 1, the outer surface of the fitting 18 may be provided with gear teeth that, in use, may cooperate with other gears or the like. It will be appreciated that, in such an arrangement, the invention permits the mounting or attachment of a gear or other mount part way along the length of a drive shaft. The gear teeth may serve to allow the input of torque loadings to the drive shaft 10, or may serve as a take-off point, being used to drive other pieces of equipment for rotation.

Where used as a gear, if there is no requirement for the drive shaft to be of flexible form then the flanges 16 may be omitted and the fitting 18 mounted directly to the main parts of the drive shaft segments 12, 14.

Figure 2 illustrates a modification to the arrangement of Figure 1, manufactured in a different manner. In the arrangement of Figure 2, a drive shaft 20 is provided (only an upper portion of a portion of a drive shaft being diagrammatically illustrated), comprising a first drive shaft segment 22 and a second drive shaft segment 24. The drive shaft segments 22, 24 are formed integrally with one another as a single wound fibre reinforced composite material shaft. During the manufacturing process, the reinforcing fibre is wound over a collar 26 located upon a mandrel, the effect of which is to cause the reinforcing fibres to splay radially outwards at the location of the collar 26. The collar 26 may be of a wound fibre reinforced composite material form, for example with the reinforcing fibres thereof of generally hoop wound form, and could be formed as an initial stage of the winding process, if desired. Alternatively, it could be a preformed component. By way of example, it could be of metallic form, fitted to the mandrel before winding commences, or it may be a prefabricated composite material part.

After winding of the reinforcing fibre material over the collar 26, and curing of the composite material to form a rigid shaft, a machining operation is undertaken to machine away part of the composite material in the region of the collar 26, exposing at least some of the reinforcing fibre in this location. Subsequently, a fitting 28 is introduced onto the shaft and is press or push fitted onto the machined section. As with the arrangement of Figure 1, the fitting 28 is preferably of tubular form having an inner diameter that is larger than the outer diameter of the majority of the shaft (and so allowing free movement of the fitting 28 along the shaft) and that matches the outer diameter of the machined part so as to allow press or push fitting of the fitting 28 thereto. The inner surface of the fitting 28 is preferably provided with a series of small spline or rib features that, upon press or push fitting, dig into the material of the shaft, cooperating with the reinforcing fibres to provide a load or torque transmission path between the first and second drive shaft segments 22, 24.

The presence of the collar 26 serves to react compressive loads applied to the drive shaft segments 22, 24 by the fitting 28, effectively resulting in parts of the drive shaft segments 22, 24 being compressed between the collar 26 and the fitting 28.

As illustrated, the fitting 28 is conveniently provided with gear teeth 30, allowing the provision of a gear part way along the shaft 20. It will be appreciated, however, that the fitting could take other forms, for example it may include projections provided with openings to allow the fitting to be bolted or otherwise secured to other components.

As with the arrangement of Figure 1, the drive shaft 20 of Figure 2 may be of enhanced flexibility.

It will be appreciated that the drive shaft of the invention is advantageous in that gears or other fittings may be located part way along a shaft, for example for the purposes of load or torque introduction or transmission, and that the shaft may be of enhanced flexibility.

Whilst specific embodiments of the invention are described herein, it will be appreciated that a wide range of modifications or alterations may be made thereto without departing from the scope of the invention as defined by the appended claims.