CA1121775A - Impeller for a variable pitch axial flow fan - Google Patents
Impeller for a variable pitch axial flow fanInfo
- Publication number
- CA1121775A CA1121775A CA000331478A CA331478A CA1121775A CA 1121775 A CA1121775 A CA 1121775A CA 000331478 A CA000331478 A CA 000331478A CA 331478 A CA331478 A CA 331478A CA 1121775 A CA1121775 A CA 1121775A
- Authority
- CA
- Canada
- Prior art keywords
- blades
- impeller
- pitch angle
- actuator
- hub
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Landscapes
- Structures Of Non-Positive Displacement Pumps (AREA)
Abstract
ABSTRACT
An impeller for a variable pitch axial flow fan in which the actuator is arranged to rotate the blades towards their maximum pitch angle, and the inherent blade turning moment of the blades when the impeller is rotating provides the restoring force for moving the blades towards their minimum pitch angle.
The impeller avoids the need for blade counterweights and a heavy return spring, and so enables a relatively smaller and lighter hub to be used compared with those employed in equivalent impellers with counterweighted blades.
An impeller for a variable pitch axial flow fan in which the actuator is arranged to rotate the blades towards their maximum pitch angle, and the inherent blade turning moment of the blades when the impeller is rotating provides the restoring force for moving the blades towards their minimum pitch angle.
The impeller avoids the need for blade counterweights and a heavy return spring, and so enables a relatively smaller and lighter hub to be used compared with those employed in equivalent impellers with counterweighted blades.
Description
'7~7S
~his in~ention relates to impellers for varlable pitch axial flow fans, that is to say impellers i~ which the pitch ~nKle of the blades can be varied while the impeller i8 rotating~
In such impellers the blades are commonly supported in bear~ngs carried by a hollow h~b, so as to be rotatable about respective axes extendi~g radially fro~ the axis of rotation of the impeller, the lnner ends of the blades carrying arms which extend outwardly with respect to the blade axes, and which are coupled to a~
actuator movable parallel to the impeller axis so as to effect a rotatisn of the blades w thin the respectiv~
bearings, and khereby vary their pitch angle~ The invention is concerned especially with impeller~ of this ki~d, which will hereinafter be referred to as of the kind specified.
It is well known that if a body~ rotatable about its own axis, i9 rotated about a perpendicular axis~
the centre of mass of the body will have a strong te~de~cy to align itself with the plane of rotation o~
the body axis.
- In a variable pitch axial flow fan this is maDife~ted by a turning force whiah tends to reduce the blade pitch a~gle, that i~ to say the angle measured between the chord line a~d said plane of rotatio~.
It i8 common to compensate for this turning moment i~ impellers of the kind specified by attachi~g cou~terweigh~s to the blade as~embly within the hub.
The actuator i8 then arranged to rotate the blades ~ i~ either directio~, a relatively strong retuxn spring being provided for rotating the blades in the opposike direction. However i~ such arrangeme~ts the hub has to.be ~uf~icientl~ wide to accommodate the cou~texweights, and moreover ~ince th~ co~nterweight~
~5 add con~idarably to th~ weight Or the blad~ assemblie~, it mu~t be made of suitably strong and heav~ material to with~tand the additio~al radial thru~t developed under :ll12~L~75 _ 3 _ centrifugal force.
An object of the invention is to provide a form of impel]er in which the use oE colmterweights can be avoided.
According to the invention there lS provided an impeller or a variable pitch axial flow fan incorporating a plurality of blades extending outwards from a hollow hub, and supported against radially ou~ward movement by respective thrust bearings located on the inner surface of the said hub so that the blades can be freely individually rotated about their axes with respect to the hub, the inner ends of which blades carry arms which extend outwardly with respect to the blade axes and are coupled to an actuator which is movable parallel to the axis of the impeller to rotate the blades within their bearings and so vary their pitch angle, wherein the actuator is operable to rotate the blades towards their maximum pitch angle and the blades are shaped to have an inherent turning movement due to centrifugal forces, which is greater than any opposing moment due to aerodynamic forces and which provides substantially the whole of the restoring force for moving the blades towards their minimum pitch angle.
Although movement of the blades towards their minimum pitch angle position may be assisted by one or more springs, these can be relatively light compared with those employed in impellers having counterweighted blades for providing the restoring force.
Moreover the invention enables a relatively smaller and lighter hub to be used compared with those employed in counterweighted blade impellers.
In addition it has been found that thrust forces in the planes of the blade bearings on changing the pltch angle Oe the blades are signific~mtly reduced. Under these circumstances very simple axial thrust bearings can be utilised without recourse to the addition of journal bearings for the blades;
the line of action of the resultant forces on the bearing remaining within the ball tracks.
B
-3a-The actuator is preferakly arranged to be operatcd ky pneumatic pressure from a suitable source via a rotary seal.
B
'7S
~ he i~ention will be fu~ther described by reference to Figures 1 and 2 of the accompanying drawing9 in which Figure 1 illustrates an axial section through half of one impeller in accordance with the i~Yentio~ for an axial flow fan, and P~gure 2 show~ a tr~sverse section of a part of the împeller.
In the drawing 1 represents the impeller hub shown bolted to a hollow shaft 2 which is arra~ged to be secured to the shaft of an elec~ric motor ~not show~).
~round the periphery of the hub there are a ~umber of u~iformly spaced radially directed holes ~
into which are fitted the root poxtions 4 of respective aerofoil section blades 5 (show~ only in part).
~ ach blade 5 i~ held in position by means of a circular retaining plate 6 which is secured to the inner end of the blade root 4 by means o~ a nut 7, which is screwed on to the protruding end of a threaded insert 8 captive within khe blade root, a flange 10 at the outer end of the blade root being located in a recess around the outer end of the respective hoIe 3. A washer or pad 11 bei~g located betwèen the flange and the bottom o~ the reces~.
~ t~rust bearing 9 is clamped between the plate 6 and an inwardly fa¢ing surface of the hub 1 and, in use, when the imp~ller is rotating, the blades are urged outwardly under centrifugal force, the bearing 9 facilitating the rotation of the blade a~out its axis relative to the hub~ -2he ~hru~t bearing 9 comprises a number of 3 hardened steel balls 12 interposed betwee~ an annularinner race 13 adaace~t the plate 6 and an outer race 14 adaacent the hub ~ur~ace~ ~h~ balls are arra~ged to roll in shallow anntllar groo~ provided in the ~acin~
~urfa¢es o~ the races 13 and 14 a~d are equidi~tan~ly ~pa¢ed around t~e grooves by a~ ann~lar bearing cage 16 having a re~atively low mass, a~d foI~ed, for example, from a suitable plastics material such a~ acetal resin '75 or from nylon impregnated with graphite. r~he bearing cage 16 has a substantially channel shaped cross-section having in its base a plurality of uniformly spaced holes which accommodate the bearing balls 12, and is arranged so that in use either the base or the edges of its side walls bear again,st the surface of the outer race 14.
r~he bearing 9 contains a lubricant having a density substantially the same as the material of the bearing cage 16.
The bearing 9 is anclosed by an a~ular housing 20 which is of channel-shaped cross-section having its mouth directed radially inwards towards the impeller axis, the depth of the walls of the housi~g being such that the bearing is accommodated entirely within ths channel which thus serves to keep the balls a~d the cage of the bearing covered with lubrica~t despite the effect of centrifugal force when the impeller is in use. Clearances are provided between the sides of the housing 20 and the inner ball race 13 a~d plate 6 ~o permit the blade to rotate freely.
Adjustment of the pitch angle of the blades 5 is effected by means of an arm 21 extendi~g tran~versely from the plate 6 and supporting at its end a pin 22 carrying a roller 2~ which }ocates within a channel 24 in the periphery of a common actuator 25. ~he actuator 25 is in the form of a shell formed in two parts 29,~0 joined around their periphery~ the rear part 29 surroundinK the shaft 2 but being free to move axially along it on a bearing 26.
~ he shaft 2 carries coaxially at its end a circular plate 27 located within the actuator providing a backing for a diaph~agm 28 which is clamped around its peripher~
between the two parts 29~30 of the actuator 25 a~ shown.
~he plate 27 ~upports coaxially a stub shaft ~1 which provides a guide for the front part 30 of' the actuator which is free to slide axially along the ~haft 31 on a bearing 32. r~he inner edge of the diaphragm 28 is secured to the 77~
plate 27 around the stub shaft 31, by an annular clamping plate 50 and screws 510 ~ he actuator is made rotationally fast with the shaft, for exa~ple by means of studs 3~ secured to rear of the plate 27 and extending into respective guides 34 in the rear part 29 of the actuator 25.
In use of the impeller the inherent blade turning moment will tend to rotate the blades to their minimum pitch angle position as shown in ~igure 1 of the drawing.
In order to increase the pitch angle air under pressure is arranged to be admitted into the space betwee~ the front part 30 of the actuator and the diaphragm 28, via a rotatable coupling 35, and a duct formed by a gap or gaps (not shown) in the bearing 32~ '~his produces a forward move~ent of the actuator 25 and 50 increases the pitch angle of the blades by an amouL~ depending upon the admitted air pressure.
When the pressure is releasad the inherent blade turning moment, assisted if necessary by light springs around the studs 33 as at 37, causes the blades to be returned towards the minimum pitch angle position, which can be set by an adJustable stop 38~
~ o set the maximum pitch angle air pressure is admitted~ with the impeller stationary, to produce a forward moveme~t of the actuator 25 until a forwardl~
extending cylindrical pro~ection 39 on the rear part 29 of the actuator engages the rear surface of the plate 27.
With the nuts 7 securing the plates 6 to the blade roots slackened the blades 5 are manually set to the required maximum pit~h angle and the nuts are then tightened. The air pressure is fully released and the stop 38 adjusted to give the re~uired mlnimum pitch angle as aforesaid.
'~he impeller is completed by the attachment of a relatively thin-walled dome-shaped fairing 41 to the front of the hub 1 as ~hownO
~ he a~sembly of the impeller is facilitated by constructing the rear wall 42 of the actuator channel 24 in castellated form as shown more clearly in Figuxe 2, ~5 with the gaps 43 betwee~ the upstanding portions 44 of the wall of sufficient width to allo~ the passage of the rollers 23. ~fter the rollers 23 ha~e been located in the channel 24 the actuator is rotated relative to the ~b to bring the upstandinK portions opposite the rollers and i~ then secured against further rotation with respect to the hub by any co~enient mean~, for example the attachment of the plate 27 to the shaft 2 so that the studs 33 extend through the respecti~e guides 34.
~his in~ention relates to impellers for varlable pitch axial flow fans, that is to say impellers i~ which the pitch ~nKle of the blades can be varied while the impeller i8 rotating~
In such impellers the blades are commonly supported in bear~ngs carried by a hollow h~b, so as to be rotatable about respective axes extendi~g radially fro~ the axis of rotation of the impeller, the lnner ends of the blades carrying arms which extend outwardly with respect to the blade axes, and which are coupled to a~
actuator movable parallel to the impeller axis so as to effect a rotatisn of the blades w thin the respectiv~
bearings, and khereby vary their pitch angle~ The invention is concerned especially with impeller~ of this ki~d, which will hereinafter be referred to as of the kind specified.
It is well known that if a body~ rotatable about its own axis, i9 rotated about a perpendicular axis~
the centre of mass of the body will have a strong te~de~cy to align itself with the plane of rotation o~
the body axis.
- In a variable pitch axial flow fan this is maDife~ted by a turning force whiah tends to reduce the blade pitch a~gle, that i~ to say the angle measured between the chord line a~d said plane of rotatio~.
It i8 common to compensate for this turning moment i~ impellers of the kind specified by attachi~g cou~terweigh~s to the blade as~embly within the hub.
The actuator i8 then arranged to rotate the blades ~ i~ either directio~, a relatively strong retuxn spring being provided for rotating the blades in the opposike direction. However i~ such arrangeme~ts the hub has to.be ~uf~icientl~ wide to accommodate the cou~texweights, and moreover ~ince th~ co~nterweight~
~5 add con~idarably to th~ weight Or the blad~ assemblie~, it mu~t be made of suitably strong and heav~ material to with~tand the additio~al radial thru~t developed under :ll12~L~75 _ 3 _ centrifugal force.
An object of the invention is to provide a form of impel]er in which the use oE colmterweights can be avoided.
According to the invention there lS provided an impeller or a variable pitch axial flow fan incorporating a plurality of blades extending outwards from a hollow hub, and supported against radially ou~ward movement by respective thrust bearings located on the inner surface of the said hub so that the blades can be freely individually rotated about their axes with respect to the hub, the inner ends of which blades carry arms which extend outwardly with respect to the blade axes and are coupled to an actuator which is movable parallel to the axis of the impeller to rotate the blades within their bearings and so vary their pitch angle, wherein the actuator is operable to rotate the blades towards their maximum pitch angle and the blades are shaped to have an inherent turning movement due to centrifugal forces, which is greater than any opposing moment due to aerodynamic forces and which provides substantially the whole of the restoring force for moving the blades towards their minimum pitch angle.
Although movement of the blades towards their minimum pitch angle position may be assisted by one or more springs, these can be relatively light compared with those employed in impellers having counterweighted blades for providing the restoring force.
Moreover the invention enables a relatively smaller and lighter hub to be used compared with those employed in counterweighted blade impellers.
In addition it has been found that thrust forces in the planes of the blade bearings on changing the pltch angle Oe the blades are signific~mtly reduced. Under these circumstances very simple axial thrust bearings can be utilised without recourse to the addition of journal bearings for the blades;
the line of action of the resultant forces on the bearing remaining within the ball tracks.
B
-3a-The actuator is preferakly arranged to be operatcd ky pneumatic pressure from a suitable source via a rotary seal.
B
'7S
~ he i~ention will be fu~ther described by reference to Figures 1 and 2 of the accompanying drawing9 in which Figure 1 illustrates an axial section through half of one impeller in accordance with the i~Yentio~ for an axial flow fan, and P~gure 2 show~ a tr~sverse section of a part of the împeller.
In the drawing 1 represents the impeller hub shown bolted to a hollow shaft 2 which is arra~ged to be secured to the shaft of an elec~ric motor ~not show~).
~round the periphery of the hub there are a ~umber of u~iformly spaced radially directed holes ~
into which are fitted the root poxtions 4 of respective aerofoil section blades 5 (show~ only in part).
~ ach blade 5 i~ held in position by means of a circular retaining plate 6 which is secured to the inner end of the blade root 4 by means o~ a nut 7, which is screwed on to the protruding end of a threaded insert 8 captive within khe blade root, a flange 10 at the outer end of the blade root being located in a recess around the outer end of the respective hoIe 3. A washer or pad 11 bei~g located betwèen the flange and the bottom o~ the reces~.
~ t~rust bearing 9 is clamped between the plate 6 and an inwardly fa¢ing surface of the hub 1 and, in use, when the imp~ller is rotating, the blades are urged outwardly under centrifugal force, the bearing 9 facilitating the rotation of the blade a~out its axis relative to the hub~ -2he ~hru~t bearing 9 comprises a number of 3 hardened steel balls 12 interposed betwee~ an annularinner race 13 adaace~t the plate 6 and an outer race 14 adaacent the hub ~ur~ace~ ~h~ balls are arra~ged to roll in shallow anntllar groo~ provided in the ~acin~
~urfa¢es o~ the races 13 and 14 a~d are equidi~tan~ly ~pa¢ed around t~e grooves by a~ ann~lar bearing cage 16 having a re~atively low mass, a~d foI~ed, for example, from a suitable plastics material such a~ acetal resin '75 or from nylon impregnated with graphite. r~he bearing cage 16 has a substantially channel shaped cross-section having in its base a plurality of uniformly spaced holes which accommodate the bearing balls 12, and is arranged so that in use either the base or the edges of its side walls bear again,st the surface of the outer race 14.
r~he bearing 9 contains a lubricant having a density substantially the same as the material of the bearing cage 16.
The bearing 9 is anclosed by an a~ular housing 20 which is of channel-shaped cross-section having its mouth directed radially inwards towards the impeller axis, the depth of the walls of the housi~g being such that the bearing is accommodated entirely within ths channel which thus serves to keep the balls a~d the cage of the bearing covered with lubrica~t despite the effect of centrifugal force when the impeller is in use. Clearances are provided between the sides of the housing 20 and the inner ball race 13 a~d plate 6 ~o permit the blade to rotate freely.
Adjustment of the pitch angle of the blades 5 is effected by means of an arm 21 extendi~g tran~versely from the plate 6 and supporting at its end a pin 22 carrying a roller 2~ which }ocates within a channel 24 in the periphery of a common actuator 25. ~he actuator 25 is in the form of a shell formed in two parts 29,~0 joined around their periphery~ the rear part 29 surroundinK the shaft 2 but being free to move axially along it on a bearing 26.
~ he shaft 2 carries coaxially at its end a circular plate 27 located within the actuator providing a backing for a diaph~agm 28 which is clamped around its peripher~
between the two parts 29~30 of the actuator 25 a~ shown.
~he plate 27 ~upports coaxially a stub shaft ~1 which provides a guide for the front part 30 of' the actuator which is free to slide axially along the ~haft 31 on a bearing 32. r~he inner edge of the diaphragm 28 is secured to the 77~
plate 27 around the stub shaft 31, by an annular clamping plate 50 and screws 510 ~ he actuator is made rotationally fast with the shaft, for exa~ple by means of studs 3~ secured to rear of the plate 27 and extending into respective guides 34 in the rear part 29 of the actuator 25.
In use of the impeller the inherent blade turning moment will tend to rotate the blades to their minimum pitch angle position as shown in ~igure 1 of the drawing.
In order to increase the pitch angle air under pressure is arranged to be admitted into the space betwee~ the front part 30 of the actuator and the diaphragm 28, via a rotatable coupling 35, and a duct formed by a gap or gaps (not shown) in the bearing 32~ '~his produces a forward move~ent of the actuator 25 and 50 increases the pitch angle of the blades by an amouL~ depending upon the admitted air pressure.
When the pressure is releasad the inherent blade turning moment, assisted if necessary by light springs around the studs 33 as at 37, causes the blades to be returned towards the minimum pitch angle position, which can be set by an adJustable stop 38~
~ o set the maximum pitch angle air pressure is admitted~ with the impeller stationary, to produce a forward moveme~t of the actuator 25 until a forwardl~
extending cylindrical pro~ection 39 on the rear part 29 of the actuator engages the rear surface of the plate 27.
With the nuts 7 securing the plates 6 to the blade roots slackened the blades 5 are manually set to the required maximum pit~h angle and the nuts are then tightened. The air pressure is fully released and the stop 38 adjusted to give the re~uired mlnimum pitch angle as aforesaid.
'~he impeller is completed by the attachment of a relatively thin-walled dome-shaped fairing 41 to the front of the hub 1 as ~hownO
~ he a~sembly of the impeller is facilitated by constructing the rear wall 42 of the actuator channel 24 in castellated form as shown more clearly in Figuxe 2, ~5 with the gaps 43 betwee~ the upstanding portions 44 of the wall of sufficient width to allo~ the passage of the rollers 23. ~fter the rollers 23 ha~e been located in the channel 24 the actuator is rotated relative to the ~b to bring the upstandinK portions opposite the rollers and i~ then secured against further rotation with respect to the hub by any co~enient mean~, for example the attachment of the plate 27 to the shaft 2 so that the studs 33 extend through the respecti~e guides 34.
Claims (3)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An impeller for a variable pitch axial flow fan incorporating a plurality of blades extending outwards from a hollow hub, and supported against radially outward movement by respective thrust bearings located on the inner surface of the said hub so that the blades can be freely individually rotated about their axes with respect to the hub, the inner ends of which blades carry arms which extend outwardly with respect to the blade axes and are coupled to an actuator which is movable parallel to the axis of the impeller to rotate the blades within their hearings and so vary their pitch angle, wherein the actuator is operable to rotate the blades towards their maximum pitch angle and the blades are shaped to have an inherent turning movement due to centrifugal forces, which is greater than any opposing moment due to aerodynamic forces and which provides substantially the whole of the restoring force for moving the blades towards their minimum pitch angle.
2 An impeller according to Claim 1 having an adjustable stop which limits the movement of the actuator towards the minimum pitch angle position, adjust-ment of the stop enabling the minimum pitch angle of the blades to be set to a predetermined value.
3. An impeller according to Claim 1 or Claim 2 wherein the arms terminate in rollers which engage in a peripheral channel in the actuator, and one wall of the channel is formed with uniformly spaced gaps corresponding in number to the number of rollers and each having a width greater than the diameter of the rollers, the rollers being circumferentially displaced from the gaps during normal operation of the impeller.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB7917849 | 1979-05-22 | ||
| GB7917849 | 1979-05-22 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1121775A true CA1121775A (en) | 1982-04-13 |
Family
ID=10505355
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000331478A Expired CA1121775A (en) | 1979-05-22 | 1979-07-10 | Impeller for a variable pitch axial flow fan |
Country Status (6)
| Country | Link |
|---|---|
| JP (1) | JPS5627099A (en) |
| CA (1) | CA1121775A (en) |
| HK (1) | HK52683A (en) |
| MY (1) | MY8400202A (en) |
| SG (1) | SG22083G (en) |
| ZA (1) | ZA793464B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5022821A (en) * | 1988-10-03 | 1991-06-11 | Flexxaire Manufacturing Inc. | Variable pitch fan |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS60222597A (en) * | 1984-04-20 | 1985-11-07 | Matsushita Seiko Co Ltd | Variable node type movable-vane fixing apparatus for axial-flow blower |
-
1979
- 1979-07-10 CA CA000331478A patent/CA1121775A/en not_active Expired
- 1979-07-10 ZA ZA00793464A patent/ZA793464B/en unknown
-
1980
- 1980-05-15 JP JP6467280A patent/JPS5627099A/en active Pending
-
1983
- 1983-04-28 SG SG22083A patent/SG22083G/en unknown
- 1983-11-10 HK HK52683A patent/HK52683A/en unknown
-
1984
- 1984-12-30 MY MY8400202A patent/MY8400202A/en unknown
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5022821A (en) * | 1988-10-03 | 1991-06-11 | Flexxaire Manufacturing Inc. | Variable pitch fan |
Also Published As
| Publication number | Publication date |
|---|---|
| MY8400202A (en) | 1984-12-31 |
| ZA793464B (en) | 1980-06-25 |
| HK52683A (en) | 1983-11-18 |
| JPS5627099A (en) | 1981-03-16 |
| SG22083G (en) | 1983-12-16 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |