GB2406154A - Composite shaft with metal sleeve - Google Patents

Abstract

A fibre reinforced composite shaft is provided with a thin walled metallic sleeve (S, figure 5) on its outer surface to provide surface protection. The metal tube is pulled over a tight (interference) fitting composite tubular core C before curing the polymer matrix resin. The shaft may be used as a high speed transmission shaft with improved impact and abrasion resistance. The outer fibre layer may be a filament wound helical layer, which can hold the rest of the preform in place during the sleeving process. The matrix resin forms a structural bond with the metal sleeve during curing. The metal sleeve can be machined to provide bearing elements.

Description

HYBRID COMPOSITE TRANSMISSION SHAFT

This invention relates to a means of producing a lightweight hybrid composite transmission shaft with surface protection which shields the load carrying structural composite from the adverse effects of impact damage and abrasive ware. Such shafts for use in torque carrying, power transmission applications are highly dynamic as in motor propshafts, marine shafts, helicopter drive shafts, industrial drive shafts, wind turbines and dynamometers. They are required to have good torsional, static and fatigue strength coupled with a high whirling resistance. To achieve the latter low shaft densities, large diameters, reduced length and high longitudinal modulus are all advantageous characteristics. However, for any specific design application the lengths and diameters of the shafts are fixed. A material combination with high specific axial modulus (high longitudinal modulus and low density) is required to produce a shaft with high resistance to whirling. To achieve this, composites reinforced axially with high modulus fibres and in particular high modulus carbon fibre reinforced plastics (CFRP) are the materials of choice. Shafts can then be designed in one piece reducing the system complexity and greatly reducing the mass of the system compared with two- piece shaft designs with centre bearings.

Fiber reinforced composite shafts exhibit advantages over metallic shafts, i.e., they are lighter in weight, more resistant to corrosion, stronger, and more inert. Fibre reinforced drive shafts comprising both glass fibers and carbon fibers in a resinous matrix have been disclosed in U.S. Pat. No. 4,089,190, "Carbon Fiber Drive Shaft" by Worgan and Reginald. This invention relates to fiber reinforced composite shafts and, more especially, to vehicle drive shafts comprising a fiber reinforced resinous shaft body with metallic coupling sleeves mounted at the ends.

Tubular fiber reinforced composites have been proposed, as demonstrated by U.S. Pat. Nos. 2,882,072 issued to Noland on Apr. 14, 1959, and 3,661, 670 issued to Pierpont on May 9, 1972, and in British Pat. No. 1,356,393 issued on June 12, 1974.

Vehicle drive shafts from tubular fiber reinforced composites, as demonstrated by U.S. - 2- Pat. No. 4,041,599 issued to Smith on Aug. 16, 1977, and to Rezin and Yates (Celanese Corporarion) in U.S. Pat No 4,171,626. Here the filaments bearing an uncured thermosetting resin are wound around a mandrel until the desired thickness has been established, whereupon the resinous material is cured. Zones or layers are positioned circumferentially within the wall of the shaft in the specific angular relationships there disclosed. The transmission of torque into the composite shaft through mechanical and adhesive joints is the subject of a series of further Celanese U.S. patents granted in 1980- 1981: 4185472, 4187135, 4214932, 4236386, 4238539, 4238540, 4259382 and 4265951.

Composite shafts can be manufactured in a variety of ways. Filament winding allows combinations of winding helix angles, ply thicknesses and fibre type to be used in optimised lay ups. The torque can be transmitted through the shafts via for example structurally bonded metallic end fittings. This type of shaft operates well in environments where the working shaft is shielded from the effects of stone impact or gravel abrasion, foreign bodies and others, however, such shielding is not always possible in practice. Limited surface protection can be added to the shaft through the use of a tough polymer or rubber jacket or by the use of sacrificial glass or aramid composite outer layer. In these cases the shaft surface is easily damaged and offers limited protection from abrasion and impact. Also the surface damage can cause the shaft to go out of balance and for sizable impact events the surface protection does not adequately protect the underlying structural composite from damage.

Our invention provides a structural composite shaft having a robust surface protection in the form of a continuous thin walled metallic sleeve firmly bonded to its outer diameter.

Metallic end flanges are bonded through a cylindrical torsional joint to the inside diameter of the composite shaft.

The shaft may be made from fibrous reinforcement in a polymeric matrix. The fibres may be based on carbon, glass, ceramic or high stiffness polymer filaments or from hybrid mixes of these fibrous forms. The matrix may be based on thermosetting polymers such as epoxy or for high temperature applications polyimide or bismaleimides.

Production methods can be based on laying combinations of low angle helical, higher angle helical and hoop layers distributed throughout the tube thickness to give combinations of controlled wall thickness, torsional and longitudinal stiffness and strengths commensurate with the design requirements. The lay-up methods may be based upon filament winding or fabric wrapping. For both fabric wrapping and filament winding the outer layer of the shaft is overwound with a helical angle layer running continuously over the conical mandrel ends. This outer layer ties down and holds the under lying structure in place during the subsequent process. At this stage the outer diameter of the winding is designed to be marginally larger than the internal diameter of a thin walled tubular metal sleeve. The mandrel containing the composite tube is accurately aligned axially with respect to the metallic tube such that it can be drawn into the sleeve. For a wet wound composite during this process excess matrix resin is extruded. At the same time the composite outer diameter and the sleeve inner diameter are deformed to coaxially align with the winding mandrel. For a dry preform configuration the insertion process is similar but this is followed by a vacuum impregnation of the composite with a suitable resin transfer mouldable matrix.

Alternatively a dry wind may also be prepared using prepreg tow or tape where the B staged matrix resin flows on heating prior to cure. In all cases as the composite cures, simultaneously a structural adhesive bond is formed between the outer surface of the composite and the inner surface of the metallic sleeve. After cure the mandrel is allowed to cool, the dome ends of the winding are cut offto allow the extraction of the hybrid shaft from the mandrel. The internal diameter of the shaft can be subsequently prepared for bonding of metallic or composite end fittings to transmit torque.

The metal sleeve can be tailored to meet the application and in particular the operating environment. Sleeves may be produced preferentially by seamless flow forming methods or by sheet wrapping and welding. The thickness required is a function of the specific stiffness, strength and hardness of the metal. Environmental factors such as resistance to corrosion from salt spray is also important. Although the preferred metal to give optimum mechanical performance and protection is a titanium alloy, aluminium alloy, steel, stainless steel or other metals can also be used. During a stone impact event the metal sleeve effectively spreads the stressed area and diffuses the high localised stresses - 4- which would otherwise have been transmitted into the composite walls causing mechanical damage.

Whilst the average density of the shaft is increased by the presence of the metallic sleeve causing a reduced whirl resistance, the sleeve has the advantageous effect of increasing the hoop modulus of the hybrid shaft. This both increases the resistance to transverse splitting during impact loading and also reduces the dynamic distortions in the form of out of round vibrations which are the major cause of boom noise in rotating shafts.

The presence of the metal sleeve also allows localised machining over a section length or lengths concentric with the tube axis. This region(s) can be used as a direct or indirect bearing surface to run as a plain bearing or to mount a rotating element or to run on another bearing element.

Embodiments of the invention will now be described with reference to the accompanying drawings.

Figure I is a view of a filament wound composite shaft on the conical ended mandrel.

Figure 2 is a is a view of a fabric wrapped composite shaft with an outer filament wound layer wound continuously on the conical ended mandrel.

Figure 3 shows the insertion process of the composite tube on the mandrel into the metallic sleeve.

Figure 4 shows the composite shaft with the sleeve fully in place prior t cure.

Figure 5 shows the cured and machined shaft.

Figure 6 shows a cross section of the shaft.

Figure 7 shows the vacuum impregnation of matrix resin into a dry perform.

Figure 8 shows the finished component with the bonded end fittings Figure 9 shows a shaft with a machined bearing region.

Figure l shows a conical ended cylindrical mandrel (M) of diameter di and cylindrical length L onto which has been filament wound a multiplicity of layers of reinforcement (C) at distinct winding angles (+ar, +a2, +ao). The fibre reinforcement in each layer may be of the same type or may vary between the layers to allow a wider range of tailorable c

- -

properties of the composite tube to be achieved. Figure I illustrates a three layer construction, however, any number of layers and winding angles may be used in practice such that the required outside diameter (dO) and total composite wall thickness (tc) is built up. Figure 2 illustrates a composite tube formed by fabric wrapping the inner structure (F) held down by a continuous outer helical layer (ao) running over the conical ends of the mandrel. A typical insertion process of the metallic outer sleeve tube (S) is illustrated in Figure 3. The inner surface of the tube is smooth so as not to damage the composite during the insertion process and degreased so as to form a good bond with the curing outer surface of the structural composite. The sleeve is aligned axially with the mandrel axis and the mandrel is pulled through the sleeve by force (P). During this process the outer helical layer holds the tube structure in place. In a wet wound or wet fabric wrapped construction the liquid resin acts as a lubricant and excess resin is extruded from the rear end of the mandrel. Figure 4 shows the composite shaft with the sleeve fully in place prior to cure and the excess resin (R). During this process the thin walled sleeve is automatically straightened to match the mandrel axis resulting in the composite tube and outer sleeve being concentrically aligned with the axis of the mandrel. Figure 5 shows the shielded tube once cured, extracted and machined to length.

A typical cross-section of the final tube is illustrated in Figure 6. This process may be carried out using dry fibre / fabric. A small amount of liquid resin may be applied to the outer helical tie down layer to act as a lubricant and minimise fbre damage during the sleeve insertion process. With the addition of end sealing caps, the metallic sleeve and the outer surface of the mandrel are used as the basis of the vacuum vessel and liquid matrix resin (R) is pulled through the perform using a vacuum (V). This process is illustrated in Figure 7.

Figure 8 shows the finished component with a bonded end fitting (E). The structural bond (SB) is formed between the external diameter of the end fitting and the internal diameter of the composite tubular element. Torque is normally transmitted or applied through the end fitting flanges.

Figure 9 shows a transmission shaft with a machined bearing region (B) aligned concentrically with the shaft axis. This region can be used as a direct or indirect bearing - 6 surface to run as a plane bearing or to mount a rotating bearing element or to run on another bearing element. A multiplicity of such regions can be machined along the shaft length.

As an example of an embodiment of the invention the properties of a sleeved composite transmission shaft will now be illustrated based on sizes and ply orientations suitable for an autosport propshaft application. Here fatigue torques of up to 2kNm and rotation speeds of 8krpm are typical. The dimensions of a hybrid composite shaft would have an outside diameter of 61.05 mm with an ID of 55 mm and length of 1.4m. The filament winding would be based on a low angle (a) of +10 and higher helical angles (O) of +45 The lay up would be (+45 (0.6mm) / +10 (2. 05mm) / +45 (0.4mm). Standard grade carbon fibre is used for the high angle fibre and a high modulus pitch fibre is used for the low angle fibre. An epoxy bisphenol A resin with an anhydride curing agent would typically be used as the matrix resin. This is used to impregnate the fibre tows prior to laying down onto the mandrel. The longitudinal modulus ofthis construction is > 230 GPa and the composite density is <1700 kgm3. The metallic sleeve would typically be based on a 0.7mm thick thin walled titanium alloy with an internal diameter of 61mm of length 1. 4m. After heat curing the composite at 140 C and cooling the metallic sleeve is well bonded and coaxially aligned with the inner composite and its winding mandrel.

The shaft is cut to length, the mandrel extracted. Metallic end fittings designed from titanium alloy are aligned and coaxially bonded over an 80mm length to the internal diameter of the composite shaft using a structural epoxy adhesive. After curing the adhesive the shaft may be balanced by spinning at 5000rpm. The shaft tube mass is typically 2. lkg and with assembled titanium alloy end fittings is typically <4.5 kg. It supports torques of > 3.5 kN and has a life of >2 million cycles of 0- 2kNm. A prototype single piece shaft of this type has been made and successfully tested on aggressive world rally circuit with typical stone and gravel impact and sand abrasion during extreme driving conditions at rotation speeds up to 8krpm. It has survived over 6000 km without any change in drive properties or any adverse surface damage.

Although the invention has been described in connection with a preferred embodiment thereof, it will be appreciated by those skilled in the art that additions, modifications, - 7- substitutions and deletions not specifically described may be made without departing from the spirit and scope of the invention as defined in the appended claims. As such this invention is not restricted to the details of the foregoing example. -9 -

Claims (13)

1. l. A hybrid composite tubular artefact having a thin walled metallic sleeve (S) pulled over the outer surface (ad) of a composite tube (C), prior to cure of the polymer matrix resin, in such a manner that the matrix resin forms a structural bond with the inside surface of the metallic sleeve to form a single tubular shaft element.
2. 2. A structure according to Claim 1 where the metal sleeve is a thin walled titanium alloy tube.
3. 3. A structure according to Claim 1 where the metal sleeve is a thin walled aluminium alloy tube.
4. 4. A structure according to Claim 1 where the metal sleeve is a thin walled steel tube.
5. 5. A structure according to Claim I where the inner composite layers (C) are produced by wet filament winding with a resin matrix (R) onto a cylindrical mandrel (M) with conical ends such that the outer layer is a helical layer, the ends of which wrap and turn around on the conical mandrel ends in such a way as to hold the underlying composite structural layers in place whilst the tight fitting metallic sleeve (S) is pulled over the length of the composite tube.
6. 6. A structure according to Claim 5 where the inner composite layers (C) are produced using fabric reinforcement.
7. 7. A structure according to Claim 6 where the inner composite artefact (C) is dry wrapped and only the outer helical layer is impregnated with resin (R) so as to act as a lubricant whilst the metallic sleeve is pulled over the length of the composite tube prior to vacuum resin infusion into the inner composite preform (C) via an O-ring sealed (o) vacuum end cap arrangement.
8. 8. A structure according to the preceding claims where during the sleeving process the thin walled metallic sleeve is automatically straightened to match the mandrel axis resulting in the composite tube and outer sleeve being concentrically aligned with the mandrel axis.
9. 9. A tubular structure according to Claim 8 with bonded end fittings capable of transferring torsional stresses at high rotation speeds without whirling.

   File mmher n.12 l 7.iX.S q
10. 10. A structure according to Claim 9 able to resist surface impact and particulate abrasion to a greater extent than the underlying composite (C) alone.
11. 11. A structure according to preceding claims where the outer surface is machined to give a direct or indirect bearing surface to run as a plane bearing or to mount a rotating bearing element or to run on another bearing element.
12. 12. A tubular artefact substantially as described and/or as illustrated in the accompanying drawings.
13. 13. A method substantially as described.

    File m3mher ()121758