Abstract
A composite tube comprising a region of greater diameter forming a bellow. The bellow has a first side and a second side spaced apart in the axial direction of the tube. Each side of the bellow comprises at least one hole and the at least one hole on the first side is offset in relation to the at least one hole on the second side. The holes in the bellow provide increased flexibility, thereby allowing a greater amount of bending or articulation in the shaft. The holes reduce the amount of material in the sides of the bellow, thereby reducing the material stiffness and thereby increasing the flexibility.
Claims
1. A composite tube, comprising: a region of greater diameter forming a bellow; wherein the bellow has a first side and a second side spaced apart in the axial direction of the tube; wherein each side of the bellow comprises at least one hole; wherein the at least one hole on the first side is offset in relation to the at least one hole on the second side.
2. A composite tube as claimed in claim 1, wherein the offset is an angular offset around the axis of the tube.
3. A composite tube as claimed in claim 1, wherein each side of the bellow comprises a plurality of holes.
4. A composite tube as claimed in claim 1, wherein the holes are evenly angularly distributed around each side of the bellow.
5. A composite tube as claimed in claim 1, wherein all the holes have the same radial extent.
6. A composite tube as claimed in claim 1, wherein all the holes have the same angular extent.
7. A composite tube as claimed in claim 1, wherein the holes on the first side have no overlap in the angular direction with the holes on the second side.
8. A composite tube as claimed in claim 1, wherein each hole has an associated region on the opposite side of the bellow; and when the tube bends about its axis, at least one such region of the bellow moves towards its associated hole.
9. A composite tube as claimed in claim 1, wherein the combined angular extent of holes on the first side and/or the second side is at least 90 degrees, optionally at least 120 degrees.
10. A composite tube as claimed in claim 1, wherein each of the first side and the second side of the bellow form an angle to a plane perpendicular to the axis of the shaft of no more than 30 degrees.
11. A composite tube as claimed in claim 1, wherein the composite tube is formed from fibre reinforced polymer.
12. A composite tube as claimed in claim 11, wherein the fibre reinforced polymer comprises a braided fibre structure.
13. A composite tube as claimed claim 11 wherein the fibre reinforced polymer comprises fibres oriented in the circumferential direction in the region of maximum diameter of the bellow.
14. A composite tube as claimed in claim 11, wherein at least some fibres of the fibre reinforced polymer are continuous throughout the tube.
15. A method of manufacturing a composite tube, the method comprising: providing a mandrel, the mandrel comprising a section of larger diameter; applying fibre over the mandrel; applying resin to the fibre; curing the resin; forming at least one hole in the section of larger diameter; and removing the mandrel.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0049] Certain examples of the present disclosure will now be described with reference to the accompanying drawings in which:
[0050] FIG. 1 is a perspective view of a drive shaft with bellows in accordance with an example of the present disclosure;
[0051] FIG. 2 is a perspective view of a bellow with holes in accordance with an example of the present disclosure;
[0052] FIGS. 3-5 are views of a bellow in accordance with various examples of the present disclosure illustrating possible arrangements of holes;
[0053] FIGS. 6A and 6B are views of a bellow in accordance with various examples of the present disclosure illustrating possible arrangements of holes;
[0054] FIGS. 7A and 7B are show comparative computer models of bellows with and without holes when the bellow is accommodating an angular misalignment;
[0055] FIGS. 7C and 7D are different views of FIGS. 7A and 7B;
[0056] FIG. 7E shows a shape comparison between FIGS. 7C and 7D;
[0057] FIG. 8 is a schematic view of the bellow and shaft showing the orientation of the fibres in accordance with an example of the present disclosure;
[0058] FIGS. 9A to 9D are cross-sectional views illustrating a method for manufacturing a composite tube in accordance with an example of the present disclosure.
DETAILED DESCRIPTION
[0059] FIG. 1 shows a perspective view of a drive shaft 2 according to an example of the present disclosure. The drive shaft 2 has a main shaft portion 3 and two bellows 4. Each bellow 4 has a larger diameter than the main shaft portion 3. In this particular example, the bellows 4 each have a diameter that is about two times that of the main shaft portion 3. The axis of the drive shaft 2 is shown as a dashed line A. the main shaft portion 3 is rotationally symmetric about the axis A. In this example, the bellows 4 are also rotationally symmetric about the axis A.
[0060] The drive shaft 2 also has two connector portions 5 in the form of flanges for connecting the drive shaft 2 to other components in the system, e.g. via the illustrated bolt holes.
[0061] The drive shaft 2 is formed from continuous fibre-reinforced polymer, with the fibre extending continuously from one end of the drive shaft 2 to the other end of the drive shaft 2. Fibres thus extend continuously from one end of the drive shaft, across the first bellow 4 to the main shaft portion 3 and then across the second bellow 4 to other end of the drive shaft 2. Thus the bellows 4 are integrally formed with the main shaft portion 3. Forces can therefore be transmitted through the drive shaft 2 (including through both bellows 4) via continuous, unbroken fibres. It will be appreciated that FIG. 1 shows two bellows 4 as this is a common arrangement, but the drive shaft 2 could have only a single bellow 4 where that would provide sufficient articulation of the drive shaft 2.
[0062] FIG. 2 shows a perspective view of a drive shaft 2 according to another example of the present disclosure. Main shaft portions 3 extend on both sides of the bellow 4. The axis A of the main shaft portion 3 is shown as a dashed line as in FIG. 1. The bellow 4 has a first side 20 and a second side 21 that are spaced apart in the axial direction of the main shaft portion 3. These sides 20, 21 form an expanded region of the main shaft portion 3, i.e. a region of larger diameter than the main shaft portion 3. The two sides 20, 21 join together at their radially outer diameters. Each side 20, 21 joins the main shaft portion 3 at its radially inner diameter. The main shaft portion 3 and the bellow 4 (including its two sides 20, 21) are formed integrally as a single unit. In this example, the first side 20 has three holes 6 formed therein. The second side 21 also has three holes 7 formed therein (one of the holes 7 is not visible in FIG. 2). The configuration of the holes can be seen more clearly in FIG. 4.
[0063] FIG. 3 shows the first side 20 of the bellow 4 in order to demonstrate the angular and radial extent of the holes 6. The circumference of the main shaft portion 3 is shown as a dashed circle. Two radii are shown as dashed lines extending from the axis of the main shaft portion 3 in a plane perpendicular to the axis. The angular extent θ of the upper hole 6 in FIG. 3 is shown as the angle between these two radii. The radii are selected so that the contact the outermost edges of the hole 6, i.e. such that the entire hole 6 is located between the two radii. The radial extent r of another hole 6 (on the lower left of FIG. 3) is also illustrated and is defined as the radial distance between two circles which contact the radially innermost point of the hole 6 and the radially outermost point of the hole 6 and which thus completely contain the hole 6 between them. In this example of the present invention, the holes 6 all have the same angular extent and the same radial extent. The holes 6 also all have the same shape.
[0064] In this example, the holes 6 each have an angular extent θ of approximately 40°. As there are three holes, the combined angular extent is 120°.
[0065] FIG. 4 shows a view of the bellow 4 similar to that of FIG. 3, viewed along the axis of the main shaft portion 3. The circumference of the main shaft portion 3 is shown as a dashed circle. The holes 6 in the first side 20 of the bellow 4 are shown as solid lines, and the holes 7 in the second side 21 of the bellow 4 are shown as dashed lines to illustrate their position relative to the holes 6 of the first side 20, while indicating that they are not directly visible through the first side 20.
[0066] Each side of the bellow 4 has three holes 6, 7, all the holes 6, 7 having the same radial extent and the same angular extent. The holes 6, 7 are evenly angularly distributed around each side of the bellow 4, which will be discussed in more detail in relation to FIG. 5. The holes 6 on the first side 20 have no overlap in the angular direction with the holes 7 on the second side 21. This is beneficial because for each hole 6, 7, the associated region on the opposite side of the bellow 4 does not have any holes in the material. Therefore, in places where the hole 6, 7 reduces the material strength on one side 20, 21 of the bellow 4, the other side 21, 20 of the bellow 4 can compensate with a region of higher strength. This is illustrated best in FIG. 2 where a region of material 26 is located on the second side 21 opposite the hole 6 in the first side 20. Additionally, a region of material 27 is located on the first side 20 opposite the hole 7 in the second side 21.
[0067] FIG. 5 illustrates various examples of the first side 20 of the bellow 4 when there are three, four, and five holes respectively, in each case evenly angularly distributed around the first side 20 of the bellow 4. Thus, in the examples given in FIG. 5, three holes are positioned at 120° intervals, four holes are positioned at 90° intervals, and five holes are positioned at 72° intervals. These arrangements are advantageous because the drive shaft 2 rotates in use. Any angular or lateral misalignment of the main shaft portions 3 on either side of the bellow 4 will thus cause a periodic force to be applied to a given portion of the bellow as it rotates around the axis. The response of the bellow 4 will vary with the presence/absence/location of the holes 6, 7 which will lead to a vibration or oscillation in the drive shaft 2. An even angular distribution of the holes 6, 7 as shown in the examples of FIG. 5 means that the response of the shaft is more uniform as it goes through an entire rotation, thereby keeping the amplitude of vibration to a minimum and thus maintaining a high critical speed for the drive shaft 2.
[0068] FIGS. 6A and 6B shows views of the first side 20 of the bellow 4 in various examples of the present disclosure. The holes 6 in the first side 20 of the bellow 4 are shown as solid lines, and the holes 7 in the second side 21 of the bellow 4 are shown as dashed lines. It will be appreciated that dashed lines have been used for the entirety of the holes 7, even though in FIG. 6A parts of those holes would actually be visible through the holes 6 in the first side 20. This is for clarity of illustration.
[0069] FIG. 6A shows an example in which the holes 6 on the first side 20 are offset in relation to the holes 7 on the second side 21, and there is an overlap in the angular and radial extent of the holes 6, 7. This is in contrast to FIG. 4 in which the holes 6 on the first side 20 are angularly offset from the holes 7 on the second side 21 with no overlap.
[0070] FIG. 6B shows an example in which the holes 6 on the first side 20 are offset in relation to the holes 7 on the second side 21, and there is an overlap in the angular extent of the holes 6, 7 but no overlap in the radial extent of the holes 6, 7.
[0071] The examples shown in FIGS. 6A and 6B are not intended to be limiting. There are many configurations that are possible with different relative positioning of the holes 6, 7 which achieve differing amounts of overlap between the angular and/or radial extents of the holes 6, 7.
[0072] FIGS. 7A and 7B show a computer model of one side of the drive shaft 2 when the main shaft sections 3 on either side of the bellow 4 are angularly misaligned (i.e. the two main shaft sections 3 are not parallel). Although only one side of the bellow 4 is shown, the model is based on a full bellow 4 (i.e. with both first side 20 and second side 21). Only one side is shown so as to better illustrate the effect of the holes on the shape of the bellow 4.
[0073] In FIG. 7A the bellow 4 has holes 6, 7 as shown in FIG. 2 and in FIG. 7B the bellow 4 has no holes in the sides 20, 21. In both cases, the angular articulation between the main shaft portions 3 (and thus accommodated by the bellow 4) is 1°. In FIG. 7B, it can be seen that the edge of the bellow 4 on the right hand side of the figure (which represents the midline of the bellow 4 around the region 8 of maximum diameter when it is in an unarticulated state) is flat (i.e. planar). This shows that a bellow 4 without holes bends symmetrically on each side 20, 21 of the bellow 4 so that the midline of the bellow 4 around its region 8 of maximum diameter remains planar, but merely deflected relative to the axes of the main shaft portions 3.
[0074] However, in FIG. 7A it can be seen that the bellow 4 has deformed such that the region of maximum diameter 8 has become deformed to a non planar shape. In particular, the holes 6, 7 enable the bellow 4 to bend out of the plane perpendicular to the axis of the main shaft portion 3 in a different way to regions with no holes 6, 7 in response to the articulation. Thus the deformation of the bellow 4 varies angularly around the axis of the main shaft portion 3, i.e. same angular regions experience more deformation than others. This is because each hole 6, 7 has an associated region 26, 27 on the opposite side of the bellow 4 and when the shaft bends about its axis, the region 26, 27 of the bellow 4 is able to move towards its associated hole 6, 7. As the holes are alternately on each side 20, 21 of the bellow, deformation of the bellow 4 alternates thereby causing the midline of the bellow 4 at the region of maximum diameter 8 to become non-planar. This gives the bellow 4 with holes 6, 7 more flexibility than a bellow without holes.
[0075] In the particular example shown and modelled in FIGS. 7A and 7B, the reaction force of the shaft to the 1 degree articulation was around 55 Nm in the FIG. 7A arrangement with holes 6, 7, while the reaction force of the shaft to the 1 degree articulation was around 101 Nm in the FIG. 7B arrangement with no holes. Thus the bellow 4 with holes is less stiff than the bellow 4 with no holes.
[0076] FIGS. 7C, 7D and 7E illustrate this effect further. FIG. 7C correspond to the model of FIG. 7A, but is viewed in the direction of arrow C in FIG. 7A. FIG. 7D corresponds to the model of FIG. 7B, but is viewed in the direction of arrow D in FIG. 7B. On each of FIGS. 7C and 7D, a dashed line 31, 32 has been superimposed on the model indicating the curvature of the first side 20 of the bellow 4. In FIG. 7E, these two lines 31, 32 have been duplicated and placed next to each other (in solid form rather than dashed form) to highlight the difference in shape. In FIG. 7E it can clearly be seen how the bellow 4 with holes 6, 7 (as modelled in FIGS. 7A and 7C has a more pronounced curvature (tighter curve) in line 31 at the top and bottom of FIG. 7E, with a concave deflection towards the right in the middle of line 31 of FIG. 7E. By contrast line 32 (corresponding to the model of FIGS. 7B and 7D) is a more uniform convex curve throughout.
[0077] FIG. 8 is a schematic view of the drive shaft 2 showing the orientation of fibres 9 in accordance with an example of the present disclosure. A portion of the fibres 9 are oriented substantially in the circumferential or “hoop” direction in the region of maximum diameter 8 of the bellow 4. This fibre arrangement is beneficial for transmission of torque from one side of the bellow to the other, but is also particularly advantageous for reducing the stiffness of the bellow 4 against angular articulation. Axially oriented fibre across this region provides high axial tensile strength and thus resists articulation, making the bellow 4 stiffer rather than compliant. On the other hand, the hoop fibre 9 is less stiff against articulation and therefore allows a more flexible bellow 4 to be formed. It may be noted that this advantage applies whether there are hole 6, 7 or no holes. Any fibre placement technique may be used to lay the fibres 9 in the hoop direction (or close to it) in order to achieve this benefit. However, advantageously, using a braiding technique to deposit the fibre has a natural tendency to orientate the fibres more towards the hoop direction as the diameter increases from a small diameter (i.e. on the main shaft section 3) to a larger diameter (i.e. the region 8 of maximum diameter of the bellow 4). Therefore a braided fibre bellow 4 is particularly flexible.
[0078] FIGS. 9A to 9D illustrate a method for manufacturing a composite tube in accordance with an example of the present disclosure. FIGS. 9A to 9D each show a cross-sectional view of the drive shaft 2 at various stages during its method for manufacture.
[0079] FIG. 9A shows a fibre and resin layer 10 applied over a mandrel 11, 12. The mandrel comprises two sections. The first section 11 is a cylinder that is used to form the main shaft portion 3. The second section 12 has a larger diameter than the first section 11 and is used to form the bellow 4. The second section 12 is a removable section. In some examples it is a sacrificial section.
[0080] The resin and fibre layer 10 is applied by any of a number of techniques, including filament winding, braiding, automated fibre placement or fibre sheet layup. The resin may be applied before, during or after the fibre. In some examples a fibre sock is braided over the mandrel parts 11, 12 and then fibre sock is impregnated with resin. The resin and fibre layer 10 is then cured with the mandrel 11, 12 in place. FIG. 9B shows the first step in removing the mandrel 11, 12 after the resin and fibre layer is cured. The first section 11 is removed by sliding it out of one end of the main shaft portion 3. The second section 12 remains in place as shown in FIG. 9C. The second section 12 is then removed. In one example of the present invention, the second section 12 is a wash-out section that can be removed by flushing with water.
[0081] FIG. 9D shows the drive shaft 2 after both the first and second mandrel parts 11, 12 have been removed. It will be appreciated that the thickness of the fibre and resin layer 10 and the height and shape of the bellow 4 in this figure are not necessarily shown to scale.
[0082] It will be appreciated that this is just one example of a method for manufacturing the drive shaft 2. In other examples of the present disclosure, the entire mandrel 11, 12 may be formed in one section which may be collapsible, deformable, sacrificial or capable of being dismantled. In other examples, one or both parts of the mandrel 11, 12 may be collapsible, deformable, sacrificial or capable of being dismantled for removal from the drive shaft 2.
[0083] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, element components, and/or groups thereof.
[0084] While the present disclosure has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this present disclosure, but that the present disclosure will include all embodiments falling within the scope of the claims.
