GB2362927A

GB2362927A - A hub for a fan blade

Info

Publication number: GB2362927A
Application number: GB0005498A
Authority: GB
Inventors: Christopher Winston Lack; David Peter Fenner
Original assignee: Elta Fans Ltd
Current assignee: Elta Fans Ltd
Priority date: 2000-03-07
Filing date: 2000-03-07
Publication date: 2001-12-05
Also published as: GB0005498D0

Abstract

The hub may comprise two identical parts to be joined together, each part 12, having a plate 40 and a block 46 defining a seat for a cylindrical portion 28 and a collar 30 of a fan blade stub. A break 53, allows flexing of the seat, when the hub parts are joined together, to grip the blade stub. A plurality of seats may be provided for mounting a plurality of blades, and the blades may be twisted. The hub parts may be joined by nuts and bolts, the nuts and the heads of the bolts being hexagonal and received in corresponding recesses each having curved junction between the floor and a sidewall of the recess, and the sidewalls of each recess defining six convex portions joined at concave corners to define a substantially hexagonal profile (figure 11).

Description

2362927 1 0:\SPECS\BJND\E1t49.Iwp A HUB FOR A FAN BLADE The invention

relates to a hub for a fan blade.

A fan is known which comprises a plurality of blades mounted in a hub. The hub is in the form of a housing in two halves. Each half of the housing includes a plurality of semi-circular journal seats arranged around the edge of the housing. Each blade includes a cylindrical blade stub. To mount the blades, the blades are arranged with each blade stub received on a journal seat of one half of the hub. The other half of the hub is then bolted to the first half so that the semi-circularjournal seats grip the cylindrical blade stubs to hold the blades in position. The blades can be pivoted with respect to the hub about a radial axis with respect to the axis of rotation so that the angle of attack of the blades can be altered.

According to one aspect of the invention there is provided a hub for a fan blade having a mounting stub, the hub including a seat for part of the blade stub to mount the blade on the hub, part of the seat defining a break to allow flexing of the seat to grip the blade stub.

In this way, blades can be securely held in the hub irrespective of imperfections in the seat or hub.

Preferably the seat and stub are of complementary shapes. The hub may be arranged to hold each blade so that each blade is pivotable so that it can be held in the hub at a plurality of different angles, for example, about an axis extending radially from the hub. The contact surfaces of the seat are preferably part circular. In this way, the blades can be pivoted in the hub to any desired angle.

The hub may take any suitable form and may comprise a housing, each seat projecting, for example, inwardly, from the housing. The break may be of any desired size or shape. In one embodiment, the break extends through the seat to the housing. The break may be straight sided and in one embodiment is parallel sided.

2 According to another aspect of the invention there is provided the combination of a hub according to the preceding aspect of the invention and at least one blade.

Preferably the combination includes a plurality of blades.

Part of the blade stub which contacts the seat of the hub is preferably circular.

The blade may take any suitable form but in a preferred embodiment the blade has 8 to 12 degrees of twist, preferably of the order of 10 degrees of twist.

The blade may be made of any suitable material and may be made of aluminium, aluminium alloy, or plastics material. The blade may be made by any suitable technique and may be made by casting or moulding.

The hub may be made of any suitable material and may be made of aluminium or aluminium alloy for example. The hub may be made by any suitable technique and may be made by casting.

Where the hub and or blade are cast/moulded and in particular where either is gravity cast from metal, there may be imperfections in the surface or in the shape of the finished product. By means of the invention the blades can be securely clamped by the hub even so and no additional finishing step is required for either part.

Articles such as fan blade hubs undergo considerable stress in particular where they are used at high speeds or with long or heavy blades. The known hub described above has its two halves bolted together. In one known hub there is a cylindrical recess at the entrance to each bore. Socket spanners must then be used to tighten the nuts and bolts. For ease of assembly, in another known hub both of the halves include a hexagonal recess at the entrance to each bore so that a socket head bolt can be inserted through the bores in the two halves in the hub and a hexagonal nut can be received in one of the hexagonal recesses which will prevent it from turning while the socket head bolt is screwed in from the opposite end. The sharp corners of the hexagonal recess between the sidewalls at 120. and 3 between each wall and the floor at 90o act as stress raisers however so that under stress a crack can initiate at a comer of one of the hexagonal recesses.

According to a finiher aspect of the invention there is provided an article defining a recess to receive a nut or the head of a bolt, the recess being defined by a sidewall and a floor, the junction between the floor and the sidewall having a pronounced curve to substantially reduce the stress of the junction.

In this way, the stress is reduced at the recess and the hub will have a longer life and/or can be used at higher stresses.

For an M8 bolt the radius of the curve is preferably at least 0.75nun, more preferably at 10 least lmm and most preferably at least 1.25mm. For bolts of other sizes the radius is geometrically scaled appropriately.

Each sidewall may display an inwards, convex curve. In this way, the nut, or head of the bolt, will tend to engage with its sidewall against the sidewall of the recess, rather than with its comer against or closely adjacent the comer of the recess. The sidewall curve radius is preferably between 4mm and 9mm and may be 5mm to 8mm being most preferably 6mm. to 7mm for an M8 bolt with other sizes geometrically scaled.

Preferably, the junction between each two adjacent sidewalls has a pronounced curve to substantially reduce the stress of the junction. The radius of the curve between two adjacent sidewalls is preferably at least Imm most preferably at least 1.7mm for an M8 bolt with other sizes geometrically scaled.

Preferably, the recess has no sharp comers or sharp ridges.

The article may be made of any suitable material and may be made of aluminium or aluminium alloy.

The article in a preferred embodiment is a fan hub or part of the fan hub.

4 The hub may be a hub according to the first or second aspects of the invention described herein.

Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which:

Figure 1 is a plan view of a fan hub of the embodiment of the invention; Figure 2A is an elevation of a fan blade of the embodiment; Figure 2B is a cross-section through the blade of Figure 2A at A-A; Figure 2C is a cross-section though the blade of Figure 2A at B-B; and Figure 2D is a cross-section through the blade of Figure 2A at CC; Figure 3 is an end elevation from the inner end of the blade of Figure 2; Figure 4 is an end elevation from the outer end of the blade of Figure 2; Figure 5 is an underneath plan view of the hub of Figure 1; Figure 6 is a perspective detail view at X in Figure 5; Figure 7 is the view of Figure 6 showing a fan blade mounted in the hub; Figure 8 is a cross-section at Y-Y in Figure 5 showing a fan blade in phantom; Figure 9 is a cross-section at Z-Z in Figure 5; Figure 10 is a detail elevation in cross-section through a hexagonal recess in the hub of Figure 1; and Figure 11 is a plan view of the recess of Figure 10; The fan 10 of the embodiment comprises a hub 12 and a plurality of blades 14.

The hub 12 is in two halves 16 as shown in Figs. 1 and 5. The halves 16 are identical and each half 16 has approximately hexagonal recesses 18.

Each hub half 16 is generally in the form of a circular tray having a floor 20 and a raised sidewall 22. The floor 20 includes a plurality of equally spaced bores 24 to receive bolts 56 to connect the two halves 16 of the hub 12 together.

Each hub half 16 may be cast from aluminium alloy. Each hub half 16 may be 350mm, 40Omm or 550mm in diameter or other hub sizes.

Each blade 14 has the profile and dimensions shown in Figures 2 to 4. The thickness of the blade 14 can be altered to take account of weight and force considerations.

The blade chord length is shown in Figure 2C as length "C", and proportions of this chord length are given in Figures 213 and 2D while the blade length is given as a multiple of that chord length in Figure 2A.

Each blade 14 has a stub 26 comprising a cylindrical main part 28 and a wider collar 30 at its inner end. The stub 26 blends with the wing section 32 of the blade 14 through a conical section 34 generally coaxial with the stub 26 and extending therefrom tapering into the wing section 32 from a base 36 which is of a similar diameter to the collar 30. The blade 14 shown is made of plastics material. The stub 26 and conical section 34 are hollow and the stub 26 and conical section 34 are strengthened by ribs 37 therewithin arranged in the form of a regular cross along the axis of the stub 26 and conical section 34.

In an alternative embodiment the blade 14 is made of aluminium alloy and the stub 26 and conical section 34 are solid.

Where the blades are made of aluminium alloy, they can be made by gravity casting or pressure die casting. Where the blades 14 are made of plastics material, they can be made by injection moulding.

As shown in particular in Figs. 6 to 9, each half 16 of the hub 12 includes semi-circular cut-outs 38 in the wall 22 from the free edge thereof equally spaced circumferentially around the hub 12 between the bores 24. Additional material is provided around each cut-out 38 in the form of two rectangular plates of material 40 arranged symmetrically with respect to the cut-out 38 and spaced apart slightly from one another, the plates 40 being of greater thickness than the wall 22. The front surfaces of the plates 40 are flush with the outer surface of the wall 22 so that the plates 40 protrude inwardly to the rear of the wall 6 22. The plates 40 have the same cut-out 41 as the wall 22 but to a slightly smaller radius. The plates 40 are not quite as tall as the wall 22.

A further wall 42 is positioned radially inwards of the wall 22. The wall 42 is interrupted by the bores 24 and allows a clear area around them. Each section 44 of the wall 42 is 5 tangential with respect to a radius of the hub half 16 along the axis of the cut-out 38 Each tangential section 44 of the wall 42 is interrupted by two rectangular blocks 46 of material which are cut away to form a seat for the collar 30 of the stub 26. Thus, the spaced apart blocks 46 provide a semi-circular surface 48 which leads through a part frusto-conical section 50 to a large diameter semi-cyclindrical bearing seat surface 52. The surfaces 48, 50, 52 are interrupted by the spacing between the blocks 46 which provides a parallel sided break 53 in the bearing seat represented by the surfaces 48, 50, 52, the break 53 extending down to the housing of the hub 12 constituted by the floor 20 (and outer wall 22). Two radial strengthening ribs 54 extend radially inwardly from the blocks 46.

The halves 16 of the hub 12 are connected together by M8 socket head bolts 56 through the bores 24. The head of each bolt 56 is rotatably received in one of the approximately hexagonal recesses 18. A hexagonal nut 58 is received in each opposite hexagonal recess 18 of the other half 16. Each nut 58 is in the shape of a regular hexagon. In cross-section radially of the hub 12 as shown in Figure 10, the sidewalls 60 of the recess 18 are tapered. This aids removal from the casting mould. At the junction between the sidewall 60 and the floor 62 of each recess 18 there is a pronounced curve 64 of 1.5mm radius. The hexagonal recess 18 is 13.Omm across at its minimum diameter. Each sidewall 60 consists of concave radiussed to comer sections 66 and convex radiussed wall 68 as shown in Fig. 11. The radius of the comer sections 66 is 2mm and the radius of the wall sections 68 is 6.5mm.

In use, one hub half 16 is laid on its outer surface. A blade 14 is then placed so that the cylindrical section 28 of the stub 26 is received in the bearing journal surface 41, and the collar 30 is received by the bearing surface 52 as shown in Fig. 7. The inner edge 70 of the blade 14 together with the base 36 of the conical section 34 abut or lie closely adjacent the 7 outer surface of the wall 22 of the hub half 16 while the outwardly facing surface 72 of the collar 30 abuts or lies closely adjacent the surface 50 of the blocks 46.

When as many blades 14 as desired have been arranged on the hub half 16, the other hub half 16 is placed on top of the first hub half 16 and the stub 26 of each blade 14 is received by the second hub half 16 in the same manner as the first hub half 16. Nuts 58 are then inserted into the approximately hexagonal recesses 18 to be rotationally held thereby. Bolts 56 are screwed into the nuts 58 and their heads advance into the hexagonal recesses 18 in the opposite hub half 16. As each bolt 56 is tightened on its respective nut 58, the nut 58 will be turned and will contact the wall 60 of the recess 18. In the case of a regular hexagonal recess, each comer 74 of the nut 58 would contact a flat sidewall of the recess and pressure would be applied along the line of contact only providing substantial localised stress. By means of the invention however, as shown in Figure 11, the radius on the comer section 66 is such that the comer 74 of the nut 58 does not contact the sidewall 60, but instead the planar wall surface 76 between comers 74 contacts the convex wall section 68 of the approximately hexagonal recess 18 so that the applied load is distributed over a wider contact area. Furthermore, as the comer sections 66 are radiussed and the junction between the sidewall 60 and floor 62 of the recess 18 radius is curved 64 there is no sharp comer or ridge close to the position of the applied stress to concentrate the stress and so this structure is very strong.

As the bolts 56 are tightened each half 16 of the hub 12 will start to flex. The walls 22 and 42 strengthen the floor 20 of the hub 12 to resist flexing, but the break 56 between the blocks 46 means that the surface 52 can flex around the stub 26 of each blade 14 to grip the blade stub 26. This not only means that the blade stub 26 is held securely, but also means that finishing processes to provide closely toleranced fit between the blade stub 26 and hub 12 are not required as flexing of the hub 12 will ensure a close fit irrespective of minor surface imperfections resulting from the manufacturing method.

The design of hub and blade described form a coherent and integrated design which is eminently suitable for application to a range of hub sizes, each hub being able to accept different numbers of blades, such as 3, 6, 9 or 12 blades and blades of different lengths, 8 each blade having the proportions of that shown in Figures 2 to 4 and 10 to. 12 cropped or extended to the desired length and geometrically scaled as desired. This provides tremendous flexibility in manufacture. For particular performance characteristics, it is possible to select the most appropriate hub and fit it with the most appropriate number of blades at the most appropriate length, but a limited number of hubs and ultimate blade lengths are required in view of the ability to fit the hubs with fewer than the maximum of blades, and the ability to crop the blades to have a plurality of different lengths.

1 9

Claims

Claims

Claims 1. A hub for a fan blade having a mounting stub, the hub including a seat for part of the blade stub to mount the blade on the hub, part of the seat defining a break to allow flexing of the seat to grip the blade stub.
2.

shapes.

A hub as claimed in claim 1, wherein the seat and stub are of complementary
3. A hub as claimed in claim 1 or claim 2, wherein the hub is arranged to hold each blade so that each blade is pivotable to be held in the hub at a plurality of different angles.
4. A hub as claimed in claim 1, 2 or 3, wherein the contact surfaces of the seat are part circular.
5.

A hub as claimed in any preceding claim, wherein the hub comprises a housing.
6. A hub as claimed in claim 5, wherein each seat projects inwardly away from the housing.
7. A hub as claimed in claim 5 or claim 6, wherein the break extends through the seat to the housing.
8. A hub as claimed in any preceding claim, wherein the break is straight sided.

3, 0
9.

A hub as claimed in any preceding claim, wherein the break is parallel sided.

t
10. A hub substantially as described herein with reference to the accompanying drawinas.
11. The combination of a hub according to any of the preceding claims and at least 5 one blade.
12. The combination of claim 11, wherein the combination includes a plurality of blades.
1 n.

J The combination of claim 11 or claim 12, wherein the part of the blade stub which contacts the seat of the hub is circular.
14. The combination of claim 11, 12 or 1 3), wherein the blade has 8 to 12 degrees of twist.
15. The combination of claim 14, wherein the blade has of the order of 10 degrees of twist.
16. The combination as claimed in any of claims 11 to 15, wherein the blade is 20 made by casting or moulding.
17. The combination of any of claims 11 to 16, wherein the hub is made by casting.
18. The combination of claim 16 or claim 17, wherein the casting from metal.

is gravity casting
19. The combination of a hub and at least one blade substantially as described herein with reference to the drawings.
20. An article defining a recess to receive a nut or the head of a bolt, the recess being defined by a sidewall or a plurality of sidewalls and a floor, the junction between 1 11 the floor and the sidewall having a pronounced curve to substantially reduce the stress of the junction.
21. An article as claimed in claim 20, wherein the radius of the curve is at least 5 0.75mm.
22. An article as claimed in claim 20, wherein the radius of the curve is at least 1 nim.
23. An article as claimed in claim 20, wherein the radius of the curve is at least 1.25=
24. An article as claimed in any of claims 20 to 23, wherein the article is arranged to receive the head of an M8 bolt in the recess.
25. An article as claimed in any of claims 20 to 24, wherein each sidewall displays an inwards, convex curve.
26. An article as claimed in claim 25, wherein the sidewall curve radius is between 20 4= and 9mm.
27. An article as claimed in claim 25, wherein the sidewall curve is between 5mm and 8mm.
28. An article as claimed in claim 25, wherein the sidewall curve is between 6mm and 7mm.
29. An article as claimed in any of claims 20 to 28, wherein the junction between each two adjacent sidewalls has a pronounced curve to substantially reduce the stress of JM the junction.
12 An article as claimed in claim 29, wherein the radius of the curve between two adjacent sidewalls is at least 1=.
31. An article as claimed in claim 29, wherein the radius of the curve between two adjacent sidewalls is at least 1.7mm.

3
32. An article as claimed in any of claims 20 to 3 1, wherein the recess has no sharp corners or sharp ridges.
1 An article as claimed in any of claims 20 to.')2, wherein the article is made of aluminium or aluminium alloy.
34. An article as claimed in any of claims 20 to 33, wherein the article is a fan hub or part of a fan hub.
35. A hub as claimed in claim 34 and also as claimed in any of claims 1 to 10.