GB2390647A - Mounting blades in axial flow fan impeller - Google Patents

Abstract

An axial flow impeller comprises blades 27 with stubs 29 at the blade roots. The stubs are fixed to the hub by laminations or plates 21, 22, 23 which have shaped slots 34, that together form spaces for the stubs. The impeller may allow adjustment of the pitch angle of the blades, through loosening clamping plates and turning the blades about radial axes as desired. Further positive pitch location of the blades may be provided through serrations or roughening of the blade stub, or an array of holes (17, Fig 4) able to register with a peg (18, Fig 4). Slots (9, Fig 1) on the clamping plates (7, Fig 1) may engage with flanges on the stubs(13, Fig 1). Spring tags (41, Fig 8) may be incorporated to improve radial location of the blades with respect to the hub.

Description

AXIAL FLOW IMPELLER

This Invention relates to an axial flow Impeller, more particularly but not exclusively, an mpellemn which the pitch angle of the Impeller blades can be adjusted manually An axial flow impeller comprises a hub and a plurality of radially extending blades, each blade being at an angle to the plane of the impeller, e at an angle to the plane perpendicular to the hub axis The angle between the blade and the Impeller plane is called the pitch angle.

Impellers are used for applications such as heating and ventilation systems, air-

conditioning and smoke extraction equipment and cooling fans for Internal combustion engines The term Impeller also includes the propeller of a propeller driven aeroplane As Is known, aircraft propellers have blades with controllable variable pitch, e variable while actually in use various quite complex mechanisms for providing this are known Controllable pitch might be useful for other applications. However, it Is also useful sometimes for the pitch to be manually adjustable, i e while the Impeller is stopped, for example, so that experiments can be made to achieve the optimum Impeller charactenstcs for a particular situation or so that a standard Impeller can be supplied for use In a range of applications requiring different pitch angles It Is known to provide a manually adjustable axial flow Impeller comprising blades with blade roots (the radially Inward part by which the blade Is secured to the hub) In the form of short cylindrical stubs These stubs are then clamped between two apertured plates forming the Impeller hub, sometimes also with spacers between the two plates.

Patent specification GO 2231924A shows an Impeller with a sheet metal hub and a

clamping arrangement, e an annular clamping ring or respective separate clamping

plates, press-formed to define radial recesses for receiving the stubs The stubs can have flanges to give positive location of the blades In the radial direction Meanwhile, patent specification US 4634341 discloses an impeller with a hub formed of two sheet

metal plates with, for each blade stub, respective split clamps Each clamp comprises a pair of spaced blocks having matching partly cylindrical recesses for the pair to fit round the stub with a gap therebetween The "open" construction of some Impellers, especially adjustable pitch Impellers, may result In undesirable noise generation whilst others may be expensive to manufacture.

One object of this Invention Is to reduce noise. Another is to provide reduced noise In.

an adjustable pitch Impeller whilst still providing effective low-cost adjustment means À *.

À. According to one aspect of the invention, there Is provided an axial flow impeller...

À. including a plurality of blades with respective blade roots fixed to a hub by fixing À means, charactersed in that the fixing means comprises a plurality of sheets having À À respective apertures therein and regstenng one with another to define spaces In which the respective blade roots are enclosed According to a second aspect of the invention, there Is provided an adjustable pitch axial flow Impeller Including a plurality of blades with respective cylndncal stubs fixed to a hub by fixing means, characterized In that the fixing means comprises a plurality of plates having respective apertures therein and regstenng one with another to define spaces In which the respective stubs are enclosed and clamped Preferably, the Impeller is adapted to give positive location of the pitch angle of the blades

The hub can comprise at least one spider and plates fixed each side of the spider or two spiders and plates between the two spiders The hub Itself may comprise a plurality of plates having respective apertures therein and registering one with another to define spaces in which the respective stubs are enclosed and clamped Advantageously, the hub then comprises two circular outer plates and an annular plate between the two outer plates.

Preferably, the impeller comprises spring means operable to urge the Impeller blades..

radially outwards with respect to the fixing means À.

Reference will now be made, by way of example, to the accompanying drawings in.

which. Figure 1 is a perspective view of part of a first adjustable pitch axial flow Impeller composing a hub and blades, only one of which Is shown; figure 2 Is a sectional side view of the impeller of figure 1, figure 3 Is a section on line lil lil in Figure 2, Figure 4 Is a partlydsassembled perspective view of part of a modification of the first impeller, Figure 5 Is a front view of a second adjustable pitch axial flow impeller comprising a hub and blades, figure 6 Is a section on VI-VI In figure 5,

Figure 7 Is a perspective view of the hub of the second Impeller with the blades removed, and Figure 8 is a perspective view of an annular member forming part of the Figure 7 hub of the second impeller Both impellers described herein are Intended for use as cooling fans for internal combustion engines However, they could be used as they are or they could be adapted for other air-moving applications.

The first Impeller shown comprises a hub 1 made up of two spider plates 2 The spider '''.

plates 2 are generally octagonal but with each side 3 of the octagon having a radially projecting extension 4 The extensions 4 have radially extending central slots 5 which.

are open at the periphery of the hub At the radially inner end of each slot, it widest À::::e out transversely to define the shape of a letter T albeit with a relatively wide downward limb The spider plates 2 do not have to be octagonal -they could be mult'-sided but with a different number of sides or they could be generally round or any other suitable shape By way of example, the plates 2 could be made from sheet metal by pressing, stamping or machining, preferably laser machining At each side of each extension 4, there are two rectangular plates 6 and 7. Each Inner plate 6 Is formed with a radially extending slot 8 similar to slot 5 but narrower However slot 8 still widens out transversely to form a T-shape Each outer plate 7 only has a

s transverse slot 9 corresponding to the top-lmb of the T-shape defined by slots 5 and 8 as described Like the plates 2, the plates 6 and 7 are made from sheet metal by a suitable process such as pressing, stamping or machining, preferably laser machining The blades 10 of the impeller are fixed to the hub 1 by stubs 11 Each stub Is made as a one-piece forging and has a cylindrical part 12 with a flange 13 at its radially Inner end and, at its other, e its radially outward end, it merges to a blade fixing plate 14 to which the respective blade 10 is fixed by rivets 15 Instead of rivets, the blades 10...

could be fixed to the stubs 11 by bolts or another suitable means Instead of being lo.: À. forged the stubs 11 could be machined, press formed, or fabricated by any other :' suitable method.

À:::: The plates 2, 6 and 7 are bolted together so that slots 5 and 8 defne radially extendng. * À À- apertures for receiving the cylindrical portions 11 of respective impeller blades 10. The flanges 13 of the stub portions 11 engage slots 9 In the outer plates 7.

Instead of two plates each side of the two spider plates, there could be three or four or more. Before the plates are bolted tight together with the blade stubs held therein, each blade is adjusted In pitch and the plates are tightened so as to clamp the blades to the hubs The engagement of flanges 13 In the widened portions of the slots 5 and 8 and In slots 9 gives positive radial location of each blade

To give additional locking or clamping of the pitch angle of each blade, the blade stub could be serrated or roughened, e.g. by grit blasting Alternatively, the internal surfaces of the stub receiving space could be roughened by grit blasting Another possibility is for the cylndncal part of the stub to be provided with an array of holes able to register with a peg or like projection provided In, say, one of the outer plates As shown In figure 4, to Increase the resolution of adjustment, there could be a line of holes 16 in one of the outer plates and several lines of holes 17 in the stub crossing the line of holes in the plate and at overlapping positions with respect to one another Then a peg 18 Is fitted in one of the holes In the stub so as to register in a,.

hole In the plateÀ.2 À:e Instead of the plates 6 and 7 fixed each side of spider plates 2, there could be two....

À - spider plates with plates such as 6 and 7 fixed between them to form a boxlike À.e construction of the hub....

À À As may be seen, the stub portions 10 are enclosed and clamped In the housings defined by the laminated plates 2, 6 and 7 There are no noise Inducing gaps between the plates Refernng now to Figure 5 to 8, the second Impeller comprises a hub 20 made up of two coaxial circular plates 21 and 22 and a coaxial annular plate 23 positioned between the plates 21 and 22 The hub 20 Is fixed by bolts flanged to a boss 24 which Is keyed to a shaft 25. The Impeller further comprises nine blades 27 arrayed around the axis of the Impeller and each fixed to the hub by way of a stub 28 composing a cylndocal portion 29 with a

flange 19 at its radially Inner end and a fixing plate 31 at the other end. Thus, each stub 28 is similar to the stubs 11 of the first impeller As shown In Figure 5, each blade 27 Is curved and has a shape which at first widens out going In the radial direction from the Impeller axis and then, from about twenty percent out from the Inner end of the blade, becomes gradually narrower again The shape and curvature of the blade Is of course adapted to the application intended for the particuiammpeller.

Each blade 27 Is stiffened by backing plates 32 and 33, the plate 32 being smaller than the blade 27 and the plate 32 being smaller than the plate 33 as shown The backing plates 32 and 33 are curved to match the blade 27 and are fixed snugly to the blade by rivets (not shown) and/or by rivets 33 that fix the blades 27 to the fixing plates 31 The plates 21, 22 and 23 have respective crcumferentally arrayed slots 34 which extend from the periphery of the respective plate radially Inwards towards the hub axis The slots 34 in the plates match up to form, in the hub 20, spaces 32 for receiving respective ones of the stub cylindrical portions 29, each slot 34 having a matching relieved portion 35 to form cross- slots 36 for receiving the flanges 30 The cylindrical portions 29 are retained in the slots 34 by clamping plates 37 positioned each side of the hub 20 and having respective curved central portions 38 for engaging the sides of the cylndncal portions 29 of the stubs 28. The clamping members 36 are fixed to the hubs by bolts 38 extending through the members 36 and the hub, and by spring washers 39 and nuts 40 engaged with the bolts 38. Each two corresponding

clamping members 36 could be fixed by two bolts as shown at A in figure 8 or by four bolts as shown at B in figure 8. The use of four bolts Is Just a possible design alternative - it Is not shown In figures 5 and 8.

As shown in figure 8, in the annular plate 23, each slot 34 extends inwardly a short way beyond the respective slot 36 In these extensions of the slots 34, Just inward of the flange receiving slots 36, there are respective spring tags 40. Each tag 40 extends from one side of the respective slot 34 towards the other side of the slot and when the stub Is not fitted, Is angled radially outwardly so as to encroach into the respective slot 36. Thus, when the stubs are fitted, the spring tags 40 engage the ends of the respective portions 28 and urge the stubs 27 radially outwards against the radially.....

outward sides of the slots 34. This gives even better radial location of the blades with À.'..

respect to the hubs.

:' . The plates 21, 22 and 23 could be made by laser machining as could the blades 27....

. and backing the curved shapes of the blades and backing plates could be done by..

ÀÀ. press-formng plates 32 and 33 As before, the stubs 28 could be made by forging, machining, or press-forming, or they could be fabricated by fixing several component parts together.

In use, to adjust the pitch of the blades 27, the nuts 40 are loosened and the blades turned to the required pitch The nuts 40 are then re- tightened on the bolts 38 to hold the stubs In position

Claims (4)

1 An axial flow Impeller including a plurality of blades with respective blade roots fixed to a hub by fixing means, charactensed In that the fixing means comprises a plurality of laminated sheets having respective apertures therein and registering one with another to define spaces In which the respective blade roots are enclosed

2 An adjustable pitch axial flow impeller including a plurality of blades with respective cylindrical stubs fixed to a hub by fixing means charactensed In that the fixing means comprises a plurality of plates having respective apertures therein and registering one with another together to define spaces in which the respective stubs are enclosed and clamped.

À -

3 An impeller according to Claim 1 or 2, adapted to give positive location of the..

pitch angle of the blades.

4 An impeller according to Claim 1, 2 or 3, comprising a hub formed by at least one spider and plates fixed each side of the spider 5 An shapelier according to Claim 1, 2 or 3, composing a hub formed by two spiders and plates between the two spiders 6 An Impeller according to Claim 1, 2 or 3, wherein the hub comprises a plurality of plates having respective apertures therein and registering one with another to define spaces In which the respective stubs are enclosed and clamped.

. 7 An Impeller according to Claim 6, wherein the hub comprises two circular outer plates and an annular plate between the two outer plates 8. An impeller according to any preceding Claim, Including spring means operable for urging the impeller blades radially outwards with respect to the fixing means 9. An adjustable pitch axial flow impeller comprising first and second outer metal plates and at least one further metal plate positioned between the first and second plate said plates being coaxial and having matching radially extending slots extending Into the plates from the....

peripheries thereof to bound a crcumferentially distributed plurality of À radially extending spaces in the assembly, a plurality of Impeller blades with fixing stubs at the blade roots, said stubs.

being engaged In respective ones of said spaces; and....

clamping means for clamping said plates and said stubs together 10 An Impeller according to claim 9, wherein said stubs comprise flanges engaged In slots in said plates for retaining the blades against radially outward movement of the blades and spring tag means In each said paces and operable for engaging said stubs and urging said blades radially outward to the extent permitted by the engagement of said flanges In said slots