GB2583724A

GB2583724A - Gears

Info

Publication number: GB2583724A
Application number: GB1906316.3A
Authority: GB
Inventors: Dewhirst Michael; Lewis Paul
Original assignee: Lentus Composites Ltd
Current assignee: Lentus Composites Ltd
Priority date: 2019-05-03
Filing date: 2019-05-03
Publication date: 2020-11-11
Anticipated expiration: 2039-05-03
Also published as: GB2583724B; GB201906316D0

Abstract

A gear 10 comprises a metallic material component 12 of annular form, and a composite material component 14, wherein the composite material component 14 includes an outer layer or ply of reinforcing material bound with a resin material, the outer layer or ply being of relatively thick form. The reinforcing element may be reinforcing fibres, or a fibrous material and the outer layer of the composite material component may be relatively thick in relation to the diameter of the reinforcing material. The outer layer may be radially outer in relation to the composite material component. Also described are retainers (26 fig. 2) to reduce flexing of the metallic material component 12, and other gear structures

Description

GEARS

This invention relates to gears, and in particular to gears manufactured, at least in part, of composite materials.

Composite materials are in increasingly common use in a wide range of applications as they are typically of high strength and good load transmitting properties whilst being of low weight. Accordingly, in weight critical applications such as in aerospace applications or certain automotive applications where increased weight can lead to reduced fuel efficiency or reduced responsiveness to changing control inputs, the use of composite materials is thought to be advantageous.

Whilst composite materials may be of benefit in that they are of good strength and low weight, problems can be faced in attaching composite material components to other materials.

In the case of gears, it may be desired for the gear teeth to be of metallic form, for example provided on a metallic material annular component, and for the composite material to be used to provide a load or torque transmitting path between the metallic material component and, for example, a drive shaft or to another part of the gear, depending upon the application in which the gear is used. Providing a strong load transmitting connection between the composite material element and the metallic material component can be difficult to achieve.

Where the teeth are provided upon a metallic material component, in order to maximise the opportunity to make weight savings, it is desirable for the metallic component to be of thin form. However, components of such a form are relatively flexible and this may lead to undesirable movement between the gear teeth and the body of the gear.

It is an object of the invention to provide a gear manufactured or fabricated, at least in part, from a composite material in which at least some of the disadvantages associated with known gears of this type are overcome or are of reduced effect.

According to a first aspect of the invention there is provided a gear comprising a metallic material component of annular form, and a composite material component, wherein the composite material component includes an outer layer or ply of reinforcing material bound with a resin material, the outer layer or ply being of relatively thick form.

By way of example, the outer layer or ply may be of thickness in the region of at least 3 to 5 times the diameter of the reinforcing material. By providing an outer layer or ply of this form, increased bundling or bunching of the reinforcing material within the outer layer or ply may occur, at least some of the reinforcing material extending non-tangentially. A consequence of this is that the composite material component may be better able to withstand substantially radially directed loads, and as a result may be better able to support the metallic component against flexing. The risk of relative movement between the gear teeth and the body of the gear is thus reduced.

It will be appreciated that as a result, the use of metallic components of reduced wall thickness, and hence of lighter weight may be possible.

The metallic component is preferably a press fit with the composite material component. Preferably, the metallic component is provided, on a surface thereof which, in use, cooperates with the composite material component, with a series of spline teeth formations. The spline teeth are of small radial height, for example of less than 0.5mm and preferably of less than 0.25mm height. Such spline teeth are referred to herein as microsplines. During assembly, the microsplines dig into the outer surface of the composite material component, and it is thought that the interaction between the microsplines of the metallic component provides further resistance to bending or deformation of the metallic component. Again, this may permit reduced wall thickness metallic components to be used, leading to additional weight savings.

The composite material may be of electrically conductive form, and there is a risk, as a consequence, of galvanic corrosion occurring at the interface between the composite material component and the metallic component. In order to reduce this risk, a non-conductive material coating is preferably applied to the surface of the metallic component that, in use, engages with the composite material component. The coating should be of a material sufficiently resilient as to be able to withstand abrasion during the press fitting operation so as to maintain a sufficiently good level of electrical insulation between the components. By way of example, certain ceramic materials or polymers such as PEEK could be used for this purpose.

The composite material component may comprise layers of woven fibrous material, adjacent layers being orientated such that the threads or fibres of one of the layers are angularly offset relative to the threads or fibres of the adjacent layer. Each layer takes the form of an annular disc. The layers of fibrous material are impregnated with a suitable resin. Preferably, reinforcing fibres are stitched to the layers, or to individual ones of the layers. Some of the stitched reinforcing fibres are preferably arranged annularly adjacent the outer peripheries of the layers. Others of the stitched reinforcing fibres are preferably arranged annularly adjacent the inner peripheries of the layers. The stitched reinforcing fibres adjacent the outer periphery of the layers may form the aforementioned relatively thick outer layer.

Such an arrangement is advantageous in that it allows the formation of gears of relatively large diameters in a relatively simple and convenient fashion.

According to another aspect of the invention there is provided a gear comprising a metallic material component of annular form, and a composite material web component, and a composite material retainer to secure the metallic material component so the composite material web component to reduce or avoid relative movement therebetween.

The composite material retainer may comprise, for example, one or more annular components of a composite material that may be press fitted to the metallic material component to strengthen and/or compress at least part of the metallic material component, thereby reducing the risk of deformation of the metallic material component, in use.

Alternatively, the composite material retainer may take the form of fibres of a reinforcing material that are wound across a face of the gear between a first point on a periphery thereof and a second point on the periphery thereof spaced from the first point.

The first and second points may be located substantially diametrically opposite one another, in which case the composite material retainer may serve primarily to compress the metallic material component onto the composite material web component, reducing the risk of flexing thereof. Alternatively, the first and second points may be at a reduced angular spacing and the composite material retainer may further serve to transmit loads around the periphery of the gear.

According to a third aspect of the invention there is provided a gear comprising a metallic material component and a composite material component, wherein a peripheral surface of the component material component engaged by the metallic material component is of toothed form, and the metallic material component is of thin walled form.

In such an arrangement, the metallic material component serves as a wear surface, protecting the teeth of the composite material component from wear, whilst the composite material component provides the required load carrying capacity. The metallic material component may comprise a coating applied to the composite material component.

To provide the required level of strength, the composite material component preferably includes fibre ends exposed at the flanks of the teeth. The composite material component may be fabricated as an annular component that is subsequently machined to form the teeth thereon.

According to another aspect of the invention there is provided a gear comprising a metallic material component of annular form, and a composite material component, the composite material component comprising a laminate made up of a plurality of layers of woven fibrous material, at least some adjacent layers being orientated such that the threads or fibres of one of the layers are angularly offset relative to the threads or fibres of the adjacent layer, each layer having an outer periphery of circular shape.

Preferably, reinforcing fibres are stitched to the layers, or to individual ones of the layers. Some of the stitched reinforcing fibres are preferably extend annularly, being arranged adjacent the outer peripheries of the layers. Others of the stitched reinforcing fibres are preferably arranged adjacent the inner peripheries of the layers. The stitched reinforcing fibres adjacent the outer periphery of the layers may form a relatively thick outer layer for engagement with the metallic component, or may have such a layer provided thereon.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic view illustrating part of a gear in accordance with an embodiment of the invention; Figure 2 to 6 are diagrammatic views illustrating parts of gears in accordance with other embodiments of the invention.

Referring firstly to Figure 1, a gear 10 is illustrated comprising an outer metallic component 12 of annular form, and a composite material component 14. The metallic component 12 comprises a supporting ring 16 and a series of gear teeth 18 formed integrally with the ring 16. The ring 16 is of relatively thin walled form. Consequently, it is relatively flexible and there is a risk that the application of loadings to the teeth 18, in use, could cause undesired flexing of the ring 16. The composite material component 14 includes, adjacent its periphery, a composite material layer or ply 20 of relatively great thickness. By way of example, the thickness of this layer or ply 20 may be in the region of 3 to 5 times the diameter of the reinforcing fibres 22 contained therein. By containing the fibres 22 in a relatively thick layer or ply, it will be appreciated that increased bunching or bundling of the fibres 22 is permitted or encouraged and consequently in the layer 20 containing fibres 22 that extend in directions other than the tangential direction. Specifically, some of the fibres 22 may extend in a direction having a radial component. The effect of this is that the presence of the layer or ply 20 results in the composite material component 14 being of increased ability to withstand radially directed loads. The composite material component 14 is thus better able to support the metallic component 12, and in particular the ring 16 thereof, reducing the likelihood of flexing thereof.

It will be appreciated, therefore, that by providing the composite material component 14 with an outer layer or ply 20 of relatively great thickness, reduced thickness, and hence lighter metallic material components 12 may be used in the gear 10. Furthermore, in use, the outer layer 20 of the composite material component 14 may carry substantially all of the loads bourn by the composite material component 14, in use, and so the remainder of the component 14 may be designed in such a manner as to allow additional weight savings to be made.

The metallic component 12 and composite material component 14 are press fitted to one another and, as shown, the metallic component 12 is provided, on its inner periphery, with a series of spline teeth 24 that, during the assembly process, dig into the outer surface of the composite material component. The spline teeth 24 are of small radial height, preferably being of height less than 0.5mm, and more preferably being of height less than 0.25mm. Such formations are referred to herein as microsplines. It is thought that the interengagement between the spline teeth 24 and the composite material component 14 is such that flexing of the metallic component 12 is further reduced, as the spline teeth 24 would need to move relative to the surface of the composite material component 14 to permit such flexing, and the presence of the teeth 24 which are dug into the surface of the composite material component 14 resists such relative movement. Again, therefore, as the metallic component 12 is better supported, it is thought that the ring 16 may be of thinner wall thickness, and so the gear may be of reduced weight whilst maintaining a required level of strength.

As the composite material component 14 may be of an electrically conductive form, there is a risk of galvanic corrosion occurring at the interface between the composite material component 14 and the metallic material component 12. In order to reduce the risk of such corrosion, the surface of the metallic material component 12 that, in use, engages the composite material component 14 is preferably provided with a non-conductive material coating prior to assembly of the gear 10. The coating should be of a material capable of withstanding the abrasion and wear that will occur during the assembly process. By way of example, certain ceramic or polymer materials such as PEEK could be used.

Whilst the description hereinbefore relates to the outer periphery of a gear, and in particular to a planet gear, it will be appreciated that the features described may also or alternatively be applied at the inner periphery of a gear, for example if the gear takes the form of a ring gear. It will also be appreciated that the invention may be applied to other types of gear, for example to pinion gears, if desired.

Figure 2 illustrates an embodiment in which composite material reinforcing members 26 of annular, hoop wound form are provided. The members 26 are press fitted onto shoulders 16a of the support ring 16 and serve to provide an inwardly directed radial force, compressing the support ring 16 against the composite material component 14. In so doing, the risk of flexing of the metallic material component 12 as described hereinbefore is reduced, and so a gear of improved strength and load carrying ability is provided.

Figures 3 and 4 illustrate alternative forms of composite material reinforcing members 26. In each case, the reinforcing members 26 are of wound fibre form with the fibres wound in such a manner as to pass over a face of the gear between first and second locations on the periphery of the gear, over the periphery of the gear and across the reverse face of the gear. By appropriate angling of the windings, the fibres of the reinforcing members 26 may extend in a star-like configuration. In Figure 3, the first and second locations are spaced close to diametrically apart, and the reinforcing member 26 serves to apply a compressive load resisting lifting off and deflection or flexing of the metallic material component 12. In Figure 4, the first and second locations are more closely spaced, and the reinforcing member 26 serves, additionally, to transmit torque loads between the first and second locations. It will be appreciated that the positions of the first and second locations may be chosen depending upon the application in which the gear is to be used and the loads to be carried thereby.

If the first and second locations are truly diametrically opposite one another, then the reinforcing member 26 may extend across the axis of the gear. To allow the insertion of a hub or the like, the fibres may be pushed apart before curing, or machining after curing may be 10 undertaken.

Turning to Figure 5, part of an alternative design of gear 30 is illustrated. The gear 30, like the gear 10, comprises a metallic material component 32 and a composite material component 34. In this embodiment, the composite material component 34 is, at least in part of laminated form and comprises a series of layers 36, each of which comprises an annular disc of a woven fibre material. The layers 36 are arranged so that the fibres of each of the discs are angled relative to the fibres of an adjacent one of the discs. The layers 36 are impregnated with a suitable resin material which is cured to form the composite material.

Around the outer peripheries of the layers 36, prior to curing of the resin material, reinforcing fibres 38 are stitched to the layers 36. The reinforcing fibres 38 are stitched in such a fashion as to form a series of annular hoops extending around the layers 36, each of which is located at or close to the periphery of the composite material component 34. The reinforcing fibres 38 may form the fibres of a relatively thick outer layer or ply as described hereinbefore, or the laminated body may have the fibres of such a layer subsequently wound thereon. Another possibility is to use a braid rather than wound fibres to form the outer layer.

As before, whilst the description above is of the provision of the stitched reinforcing fibres 38 at or adjacent the outer periphery of the layers 36, reinforcing fibres may alternatively or additionally be located adjacent the inner periphery of layers 36, if desired.

The structure shown in Figure 5 is advantageous in that it permits the manufacture of a composite material component for a gear of relatively large diameter in a simple and convenient manner. It will be appreciated that where gears are required to be of a large diameter, the weight savings that can be made through the use of composite materials are significant.

Turning to Figure 6, an arrangement is illustrated in which a composite material component 40 is provided, an outer periphery thereof being formed with gear teeth formations 42. An outer layer 44 of a metallic material is applied over the outer periphery of the component material component 40. The outer layer 44 could take the form of a component pre-formed to the required shape that is press-fitted or the like to the composite material component. Alternatively, it could comprise a foil or the like applied to the composite material component 40, or it could comprise a coating applied thereto. In such an arrangement, the composite material component 40 provides the gear with the required load bearing and transmitting capacity, the metallic material layer 44 providing the required level of hardness and wear resistance.

The composite material component 40 may take the form of an annular element of wound fibre reinforced composite material which has been cured and, after cured, is machined to form the teeth formations 42 in the outer periphery thereof. Such a manufacturing technique has the advantage that the reinforcing fibres are exposed at the flanks of the gear teeth formations 42, aiding in achieving the required load bearing characteristics in the gear. However, other manufacturing techniques may be used. By way of example, the composite material may be wound in such a fashion as to take substantially the required shape, no subsequent machining (other than minor finishing) being required to form the gear teeth formations. The fibres within the composite material component 40 are preferably arranged at a range of winding angles to achieve the required level of strength and load bearing capacity.

It will be understood, as described hereinbefore, that gears incorporating composite materials in this manner are advantageous in that significant weight savings can be made without significantly reducing the strength or other characteristics of the gear, and the weight savings can lead to operating efficiencies, in use. Another benefit of such gears is that they are inherently more flexible than many metallic material gears, and so can provide additional damping, improving the fatigue life of the gears.

Whilst specific embodiments of the invention have been described hereinbefore, it will be appreciated that a number of modifications and alterations to the invention may be made without departing from the scope of the invention.

Claims

CLAIMS: 1. A gear comprising a metallic material component of annular form, and a composite material component, wherein the composite material component includes an outer layer or ply of reinforcing material bound with a resin material, the outer layer or ply being of relatively thick form.
2. A gear according to Claim 1, wherein the outer layer or ply is of thickness in the region of at least 3 to 5 times the diameter of the reinforcing material.
3. A gear according to Claim 1 or Claim 2, wherein the metallic component is a press fit with the composite material component.
4. A gear according to Claim 3, wherein the metallic component is provided, on a surface thereof which, in use, cooperates with the composite material component, with a series of spline teeth formations.
5. A gear according to Claim 4, wherein the spline teeth are of small radial height, preferably of less than 0.25mm height.
6. A gear according to any of the preceding claims, wherein the composite material is of electrically conductive form, and a non-conductive material coating is applied to the surface of the metallic component that, in use, engages with the composite material component.
7. A gear according to any of the preceding claims, wherein the composite material component comprises layers of woven fibrous material, adjacent layers being orientated such that the threads or fibres of one of the layers are angularly offset relative to the threads or fibres of the adjacent layer.
8. A gear according to any of the preceding claims, further comprising a composite material retainer to secure the metallic material component so the composite material web component to reduce or avoid relative movement therebetween.
9. A gear according to Claim 8, wherein the retainer comprises one or more annular components of a composite material that may be press fitted to the metallic material component.
10. A gear according to Claim 8 or Claim 9, wherein the composite material retainer comprises fibres of a reinforcing material that are wound across a face of the gear between a first point on a periphery thereof and a second point on the periphery thereof spaced from the first point.
11. A gear according to Claim 10, wherein the first and second points are located substantially diametrically opposite one another.
12. A gear according to Claim 10, wherein the first and second points are angularly spaced apart by less than 150°.
13. A gear comprising a metallic material component of annular form, and a composite material web component, and a composite material retainer to secure the metallic material component so the composite material web component to reduce or avoid relative movement therebetween.
14. A gear according to Claim 13, wherein the retainer comprises one or more annular components of a composite material that may be press fitted to the metallic material component.
15. A gear according to Claim 13 or Claim 14, wherein the composite material retainer comprises fibres of a reinforcing material that are wound across a face of the gear between a first point on a periphery thereof and a second point on the periphery thereof spaced from the first point.
16. A gear comprising a metallic material component and a composite material component, wherein a peripheral surface of the component material component engaged by the metallic material component is of toothed form, and the metallic material component is of thin walled 10 form.
17. A gear comprising a metallic material component of annular form, and a composite material component, the composite material component comprising a laminate made up of a plurality of layers of woven fibrous material, at least some adjacent layers being orientated such that the threads or fibres of one of the layers are angularly offset relative to the threads or fibres of the adjacent layer, each layer having an outer periphery of circular shape.