GB2315819A - Fan with variable blade setting - Google Patents

Abstract

A coupling ring 20, mounted between a blade 11 and a hub (10)(fig. 1) for locking the blade on the hub at a selected pitch angle, comprises a plurality of groups A,B,C,D of five reference slots 21, adjacent slots of each group being spaced by 10{. The slots 21 are arranged to selectively engage a complementary reference formation 19 on the hub 10. Index ribs 22A, 22, 22C, 22D are associated with respective ones of the groups A,B,C,D of reference slots, the angle between each group and its respective rib being different. The blade 11 comprises a groove (17) which is arranged to selectively engage one of the index ribs 22A, 22, 22C, 22D. The coupling ring thus enables the blade 11 to be set to any angle at 2.5{ intervals between 10{ and 57.5{.

Description

An axial-flow fan impeller This invention relates to an impeller for an axial flow fan.

Axial flow fans generally comprise an impeller having a hub arranged on an axis of rotation and a plurality of impeller blades extending radially outwardly from the hub. It is preferable to form the blades separately from the hub, so that the pitch of the blades can be set during manufacture to provide the desired fan operating characteristics, thereby alleviating the need for fan manufacturers to stock a wide range of impellers for different applications.

Normally, the pitch of the impeller blades are set in a range from 10 to 600, with the flow rate and fan loading characteristics of the fan varying substantially across the range. Thus, during manufacture, great care has to be taken to set the blade angles accurately, otherwise the fan flow rate and loading will be out of tolerance.

British Patents Nos. 1 502 002 and 1 527 530 both disclose fan impellers having blades which can be accurately set at a number of predetermined angles. However, the intervals between the angles at which the blades can be set are large and thus it may not be possible to set the blades to have the desired fan characteristics.

We have now devised an impeller for an axial flow fan which alleviates the above-mentioned problems.

In accordance with this invention, there is provided an impeller for an axial flow fan, the impeller comprising a hub arranged for rotation about a first axis and at least one blade mounted to the hub and adjustable by turning about a second axis, the impeller further comprising a coupling element mounted between each blade and the hub for locking them together at a selected angle about said second axis, wherein the coupling element comprises a plurality of groups of reference formations angularly spaced around said second axis and arranged to selectively engage a complementary reference formation on one of said hub and said blade, the other of said hub and said blade being lockable to the coupling element at a plurality of positions angularly spaced relative to said coupling element around said second axis, said positions being associated with respective said groups of reference formations, and being angularly spaced from their respective groups of reference formations by different angles.

In use, the hub (or the blade) is coupled with one of the reference formations on the coupling element and the blade (or the hub) locked to the coupling element at the angular position which corresponds with the group to which that reference formation belongs. It will be appreciated that at each angular position of the blade (or hub) relative to the coupling element, the blade (or hub) is spaced by a different angle from its group of reference formations. Furthermore, it will be appreciated that in each group of reference formations, the different reference formations will have different angular spacings from the corresponding blade (or hub) position. In this manner, the blade (or hub) can be accurately set at any one of a large number of different angles about said second axis, relative to the hub (or blade), by selecting the appropriate reference formation to be engaged with the hub (or blade) and then locking the blade (or hub) to the coupling element at the angular position, relative to the coupling element which corresponds with the group of the selected reference formation.

Preferably the groups of reference formations lie in respective zones spaced around said second axis, and preferably the other of said hub and said blade are lockable to the coupling element at positions which are angularly spaced from their respective group of reference formations by angles which are in a first range, which is less than a second range of angles covered by each group. Thus, the angle between the blade and the hub can be set at any one of a large number of different angles over a small range.

Preferably each reference formation of each group is spaced from adjacent reference formations by the same angle.

Preferably the first range of angles is less than the angle between each reference formation.

Preferably the other of said hub and said blade are lockable to the coupling element at positions which are spaced apart by 360"/n, where n is the number of groups.

Preferably the coupling element comprises a disc for mounting normal to said second axis.

Preferably the reference formations comprise slots arranged around the periphery of said disc.

Preferably means for fastening the blade to the hub extends through an aperture formed axially in the disc.

Preferably the fastening means comprises a shaft which extends from the blade (or the hub) and which is engaged with the hub (or the blade).

An embodiment of this invention will now be described by way of example only and with reference to the accompanying drawings, in which: FIGURE 1 is an exploded perspective view of an impeller in accordance with this invention, for an axial flow fan; and FIGURE 2 is a plan view of a coupling ring of the impeller of Figure 1.

Referring to Figure 1 of the drawings, a fan impeller in accordance with this invention comprises a hub 10, mounted for rotation about an axis A-A, and a plurality of impeller blades e.g. 11 for engaging in respective sockets 12 arranged around the periphery of the hub 10.

The hub 10 has a part-spherical surface which is a solid of rotation about its rotational axis A-A. The interior of the hub 10 is hollow and each socket 12 comprises an aperture 13, which extends radially through the wall of the hub 10, and communicates with its hollow interior. The outer portion of each socket 12 comprises a circular recess 14 coaxial with the aperture 13 and having a bottom wall which lies parallel to the rotational axis A-A. A reference peg 19 on the side wall of the outer portion of each socket extends radially towards the respective socket aperture 13.

The root of each fan blade 11 comprises a shaft 15, which extends longitudinally of the vane 16 of the blade. The free end of the shaft 15 is formed with an external screw thread. The base of the shaft 15 is provided with a peripheral flange 18. The inner face of the flange 18 lies in a plane normal to the shaft axis B-B, and is provided with four radially extending index grooves 17, spaced at 900 intervals around the shaft 15.

An annular coupling ring 20 fits axially onto the shaft and is arranged to lock the blade 11 at a predetermined angle, about the axis B-B, to the hub 10, as will be described hereinafter in greater detail. The shaft 15 is received in one of the respective socket apertures 13 in the hub 10, and a nut (not shown) fits onto the free end of the shaft 15 inside the hub, in order to hold the blade 11 in engagement with the hub 10.

Referring to Figure 2, there is shown a coupling disc 20 which is fitted onto the shaft of each impeller blade e.g.

11 prior to engaging the blade with the impeller hub 11 as hereinbefore described. The coupling disc comprises four groups A,B,C,D of reference slots 21 formed around its periphery, with there being five slots 21 in each group.

Adjacent slots, 21 of each group are angularly spaced from each other by an angle a = 10 . Each group of slots, e.g. A comprises a triangular-section index rib 22A, which extends radially of the ring, and which is complementary in shape to the index grooves 17 on the flange 18 of the blade. The index rib 22A of group A is spaced from the group by an angle 0. The index ribs 22 of groups A,B,C,D are spaced at 900 intervals around the coupling ring 20.

The index grooves 17 on the flange 18 of the blade are arranged such that when the coupling ring 20 is engaged in one of the hub sockets 13, with the reference peg 19 on the socket extending into the most clockwise reference slot 21 of group A, the blade 11 has a pitch angle of 10 . Likewise, if the reference peg 19 extends into the next slot 21 in group A, then the blade will have a pitch angle of 200 and so on up to 500.

It will be noted that impeller blades are normally set between 100 and 600.

If it is desired to set the blade to an angle intermediate the angles that are available using group A, then it will be appreciated that the position of the corresponding slots in each successive group B,C,D are effectively transposed by successive 2.5 intervals from their respective index ribs 22. Thus, if the reference peg 19 extends into the most clockwise slot 21 of group C and the blade is rotated through 1800, then the angle of the blade will be 5 greater than it was at group A, owing to the increase in angular spacing between the index ridge 22C and group C.

The blade of an impeller in accordance with this invention can be set to any angle at 2-50 intervals between 100 and 57.50. Therefore, it is possible to accurately achieve the desired fan characteristics using only one type of blade and impeller.

Claims (11)

1) An impeller for an axial flow fan, the impeller comprising a hub arranged for rotation about a first axis and at least one blade mounted to the hub and adjustable by turning about a second axis, the impeller further comprising a coupling element mounted between each blade and the hub for locking them together at a selected angle about said second axis, wherein the coupling element comprises a plurality of groups of reference formations angularly spaced around said second axis and arranged to selectively engage a complementary reference formation on one of said hub and said blade, the other of said hub and said blade being lockable to the coupling element at a plurality of positions angularly spaced relative to said coupling element around said second axis, said positions being associated with respective said groups of reference formations, and being angularly spaced from their respective groups of reference formations by different angles.

2) An impeller as claimed in claim 1, in which the groups of reference formations lie in respective zones spaced around said second axis.

3) An impeller as claimed in claim 2, in which the other of said hub and said blade are lockable to the coupling element at positions which are angularly spaced from their respective group of reference formations by angles which are in a first range, which is less than a second range of angles covered by each group.

4) An impeller as claimed in claim 3, in which each reference formation of each group is spaced from adjacent reference formations by the same angle.

5) An impeller as claimed in claim 3, in which the first range of angles is less than the angle between each reference formation.

6) An impeller as claimed in any preceding claim, in which the other of said hub and said blade are lockable to the coupling element at positions which are spaced apart by 3600/n, where n is the number of groups.

7) An impeller as claimed in any preceding claim, in which the coupling element comprises a disc for mounting normal to said second axis.

8) An impeller as claimed in any preceding claim, in which the reference formations comprise slots arranged around the periphery of said disc.

9) An impeller as claimed in any preceding claim, in which means for fastening the blade to the hub extends through an aperture formed axially in the disc.

10) An impeller as claimed in any claim 9, in which the fastening means comprises a shaft which extends from the blade (or the hub) and which is engaged with the hub (or the blade).

11) An impeller substantially as herein described with reference to the accompanying drawings.