GB2199897A

GB2199897A - An extractor fan

Info

Publication number: GB2199897A
Application number: GB08800563A
Authority: GB
Inventors: Haydn John Whiddington; Peter James Heywood
Original assignee: Airflow Developments Ltd
Current assignee: Airflow Developments Ltd
Priority date: 1987-01-15
Filing date: 1988-01-12
Publication date: 1988-07-20
Also published as: GB8800563D0

Abstract

The fan has automatic backdraught flap control obtained by arranging a rotatable actuator element 5 for the flaps 4 to be operable in dependence on the forces generated by the impeller fan drive motor 3. Thus the reaction on the motor stator at impeller drive start up is used to effect engagement between a rack on the actuator element and a pinion on the shaft of the motor to open the flaps by rotation of the element in one direction and impeller drive inertial forces at turn-off to close the flaps by rotation of the element in the other direction. Between these positions the pinion is held in a run-oil area on the actuator element. In the embodiment shown the pinion 14 on motor shaft 2 engages a rack 11 to open the flaps and engages a rack 10 to close the flaps, the racks each having a respective run-off area 12 and 13. In other embodiments the racks are defined by teeth on the periphery of a gear wheel, and the run off areas are defined by tooth-free regions on that periphery. <IMAGE>

Description

"An Extractor Fan" FIELD OF THE INVENTION The present invention relates to an extractor fan and particularly to an extractor fan provided with automatic backdraught flap control.

BACKGROUND ART Known backdraught flap mechanisms employed in extractor fans in present day use, include an air actuated system wherein a flap valve is opened by the air being expelled by the fan impeller. With this type there is no control over movement of the flaps when the valve is closed and the flaps therefore rattle in the wind. This design also reduces air flow through the system.

Another known backdraught mechanism is the ordinary manually operated pull cord. While being simple and effective che main disadvantage of this design is that it cannot be actuated from a remote position.

The use of a solenoid which permits remote operation to control the flaps, is employed in other systems but such is not cost efficient, and there is a problem with mains hum.

A backdraught mechanism, operable under centrifugal force principles, is in use, but the design tends to be complicated and costly and unacceptable noise can be produced by rubbing contact of the rotating components and the load on the drive motor.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an extractor fan with automatic backdraught flap control free of the disadvantages of the prior art.

According to the invention there is provided an extracter fan assembly comprising a fan aperture, an impeller drive for moving air through said aperture, one or more shutters for said aperture, an actuating element for opening and closing the shutters, and impeller drive take-off means cooperating with said actuating element to control the or each shutter in dependence on the operation of said impeller drive.

Preferably the impeller drive take-off means cooperates with said actuating element by means of a pinion on a rotating shaft of the impeller drive engaging a rack on the actuating element.

In a preferred arrangement, the rack has two spaced rack guides, each being selectively engageable by the pinion to drive the actuating element in opposite directions thereby to open and close the shutters.

The first rack guide is engaged by the pinion as the drive shaft rotates thereby to open the shutters.

At switch-off the pinion is moved into engagement with the second rack guide to drive Lhe actuating element in the return directloll thereby to close the shutters.

At the end of each rac guide is a rack run-off area wherein to allow the drive shaft to disengage from the respective ends of rack guides and move into free space.

The rack and pinion drive acts against an over-centre spring controlling movement of the shutters. Both overcentre positions correspond to the position of the drive shaft in one of the run-off positions of the rack, so that the shutters are maintained in either the open or closed positions as the case may be.

Selective rack guide engagement is effected by an actuating pin cooperating with the actuating element, the pin being provided on the normally stationary carcase or stator of the impeller drive.

The carcase or stator of the impeller drive has a limited freedom of rotational movement. Therefore when the drive is under load the normal reaction forces actto rotate the carcase in the opposite direction to that of the drive shaft. In response to this condition the pin on the carcase or stator of the impeller drive moves the actuating element such that the rotating shaft moves out of one of the run-off areas on the rack and the pinion engages a rack guide thereby to drive the actuating element to open the shutters, thereafter to move into the other run-off area when the shutters are completely open.

When the load is removed, the spring and the reaction and other inertia forces, applied to the impeller drive, act to rotate the carcase or stator in the opposite direction which has the effect of causing the pinion to move from one run-off area into engagement with the other rack guide thereby to close the shutters.

Further features and advantages of the present invention will now be set forth by describing particular embodiments of the invention by way of example with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: Figure 1 is an exploded schematic view of the extractor fan assembly according to an embodiment of the invention, and Figure 2 is a modification of the assembly of Figure 1 according to another embodiment of the invention.

BEST MODES OF CARRYING OUT THE INVENTION The extractor fan assembly shown in Figure 1 of the drawings comprises an impeller 1 mounted on the shaft 2 of an a.c. motor 3.

The extractor fan assembly, is provided with closure shutters or flaps 4 over the fan outlet and/or inlet (not shown). Control of the flaps 4 is effected by means of a triangular shaped actuating element 5 rotatably mounted via an oval slot 5' on an actuating arm 6. The actuating arm G engages a linkage L joining each of the flaps 4 whereby rotation of the arm 6 opens and closes the flaps 4 against the action of an over-centre spring 7, the two over-entre positions of the spring 7 corresponding to complete ciosure and opening of the flaps 4.

The triangular actuating element 5 has an arcuate slot 8, the edges of which have rack teeth 9 forming two rack guides 10 and 11. At the end of the arcuate slot are two wider slot portions 12 and 13 providing rack run-off areas, the purpose for which will be described.

The shaft 2 of the motor 3 passes through the arcuate slot 8 and is provided with a pinion 14 for selective engagement with the rack guides 10 and 11. The carcase or stator of the motor drive 3 is provided with a projecting pin 15 which engages a second arcuate slot 16 on the actuating element 5. The pin 15 is loaded by means of a spring 174 The carcase or stator of the motor 3 is mounted in a secondary motor bearing 18 which allows limited rotational freedom of movement thereof.

The above described embodiment of the invention operates as follows.

It will be assumed that the flaps 4 are shut and the shaft 2 occupies the run-off area 13.

When the motor 3 is switched on, the pin 15 is actuated by an opposite rotational movement of the stator or carcase of the motor 3 to that of the shaft 2 which in turn loads the sprint 17, shifts the element 5 on the end of arm 6, so that the pinicn 14 engages the lower rack guise 11.

The ectaatillg element 5 is then driven in a clock wise direction to rotate the arm 6 which in turn opens the flaps 4. When the flaps 4 are fully open the shaft 2 occupies the run-off area 12.

The flaps 4 are maintained firmly and positively in the open position by means of the over-centre spring 7, and the shaft 2 rotates freely in the run-off area 12 causing the impeller 1 to expel air through the open flaps 4.

When the motor 3 is switched off, the forces applied by the loaded spring 17, the induction braking of the motor 3 plus bearing drag, act to rotate the carcase of the motor in the opposite direction and the pin 15 to shift the element 5, which has the effect of moving the shaft 2 out of the run-off area 12 to move the pinion 14 into engagement with the upper rack guide 10 thereby to reverse rotate (anti-clockwise) the element 5 and close the shutters 4 through the arm 6 and link 5.

When the flaps 4 are fully closed the shaft 2 enters the run-off area 13, the flaps then being firmly held in the closed position by means of over-centre spring 7.

During both open and closing movements the actuating element 5 acts first against the over-centre spring 7 and is then assisted by it.

In Figure 2 there is shown an alternative impellerdrive take-off arrangement for operating the fan shutter actuating element of the Figure 1 embodiment.

It comprises an inertial lag device having a flywheel 19 attached for axial movement to the shaft S of the impeller (not shown).

The flywheel 19 is provided with an internal helical groove which is engaged by a pin 20 on the shaft of an impeller-drive motor 21.

The actuating element A for the fan shutters in Figure 2 is provided with axially (with respect to the axis of the shaft S) offset arcuate racks R1 and RA each comprising a series of gear segments 22 delimited at each end by run-off areas 23. A pinion 24 on the impeller shaft S is provided to engage the gear segments 22 in the racks R1 and Rto rotate the actuating element A either clockwise or anticlockwise about fixed pivot point P.

Thus at switch-on and switch-off of the motor 21, and due to the inertia of the impeller, the pin 20 moves in the internal helical groove of flywheel 19 axially to displace the flywheel 19 respectively in opposite directions and with contra-wise rotation, to transfer, as the case may be, the pinion 19 out of one of the runoff areas 23 into engagement with the gear segments22 of either one of the racks R and R2, thereby to rotate the actuating element A and effect opening and closing of the fan shutters.

A further embodiment of the invention is shown in fragmentary form in Figure 3.

As in the previously described embodiments, the motor 3 is mounted on a secondary bearing 18 so that it may rotate part of a revolution.

A pinion 25, similar to pinions 14 and 24 in the Figure 1 and 2 embodiments, is provided on the shaft 2 of the motor 3.

The pinion 25 engages a a gear wheel 26. The gear wheel 26 has a number of missing gear segments located at the ends of a diameter of the wheel 26, these missing segments providing run-off areas 27 and 28 for the pinion 25 for a purpose to be described.

A pin 29 on the carcase of the motor 3 engages an annular groove 30 in a face of the gear wheel 26, the pin 29 being located off-axis with respect to the axis of the shaft 2.

The groove 30 is divided into two sections of differing radii providing abutments 31, 32 in the run of the groove 30, to arrest movement of the pin 29 therein during rotation of the wheel 26 as will be described.

The gear wheel 26 is provided with a projecting pin 33 on the other of its faces, the axis of which is off-set from the central axis of the wheel 26. The pin 33 engages a rectilinear slot 34 provided on a lever arm 35. The arm 35 engages a linkage L (as in the Figure 1 embodiment) whereby rotation of the arm 35 opens and closes the flaps 4 against the action of the over-centre spring 7.

A bilobular cam 36 is attached at the centre of the wheel, to that face of the gear wheel 25 in which is formed the groove 30.

A spring loaded lever 37 engages the bilobular cam 36.

At switch-on, with the pinion 25 in run-off area 27, the casing of the motor 3, under inertial forces, will rotate in the opposite direction to the rotation of the drive shaft 2, so causing the pin 29 to move off the abutment 31 in the groove 30 and allowing the gear wheel 26, under the action of lever 37, on the bilobular cam 36, to advance into mesh with the pinion 25.

The gear wheel 26 is then driven through half a revolution until the pin 29 meets the abutment 32.

The motor 2 and impeller 1 can then rotate freely because the pinion 25 is in the run-off area 28. The shutters 4 will then have been opened through action of the pin 33 on the lever arm 35 on the linkage mechanism L.

At switch-off, induction braking of the motor 3 and bearing drag, acts to rotate the casing of the motor 3 in the same direction as the shaft 2 and pinion 25.

The pin 29 will move off the abutment 32 allowing the gear wheel 26 to advance into mesh with the pinion 25.

The shutters 4 will then close and the motor 3 and impeller 1 are able to run down with gear 25 in the runoff area 27.

Another embodiment of the invention, being a refinement of the Figure 3 embodiment, is shown in Figures 4a and 4b so that similar features as between the two embodiments will be assigned the same reference number.

In this arrangement, the drive and control functions of gear wheel 26 in the Figure 3 embodiment, is split between a drive gear 38 and control gear 39. The ratio between drIve gear 38 and control gear 39 may be any multiple of two in the preferred example.

The control gear 39 is provided with an annular groove 40, identical to the groove 30 in wheel 26 of the Figure 3 embodiment, the pin 29 on the face of the motor 3 engaging this groove 40 to perform a similar function.

A further distinct variant, compared with th Figure 3 embcdiment, is that the drive gear 38 has only a single run-off area 41, shown more particularly in the detail view in Figure 4b, so that opening and closing of the shutters is effected by a 3600 rotation of the gear 38 instead of a half revolution as before.

This is possible by virtue of the 2:1 ratio between the gears 38 and 39.

To assist quieter meshing as between the pinion 25 and drive gear 38, the run-off area 41 has a synchronising feature 42 as shown in the detail view in Figure 4b This depends to a large extent on the flexibility of the material from which drive gear 38 is constructed.

In view of the full rotation of the drive gear 38, the bilobular element and co-acting spring loaded lever arrangement of the Figure 3 embodiment, is replaced by a hair spring 43 and single lobed cam 44.

As additional variants, the arrangement of Figure 4 incorporates an over centre spring 45 for the shutters intergral with the shutter link L.

Also shown in Figure 4a, for purposes of illustration, is the body 46 of the fan unit.

As compared with the Figures 1 and 2 embodiment, the arrangements of Figures 3 and 4, are designed to bring the respective gear elements into mesh tangentially rather than radially. In addition 2. lower effective ratio has been achieved in the permitted space available.

Moreover since the drive elements rotate about fixed centres, there is now no slippage and less wear.

While the motor 3 still rotates against the reaction torque, it does not have tQ move the actuator 5 as in the Figure 1 and 2 embodiments, and therefore a motor return spring is not now necessary and this permits wider speed control.

Claims

1. An extractor fan assembly comprising a fan aperture, an impeller drive for moving air through said aperture, one or more shutters for said aperture, an actuating element for opening and closing the or each shutter, and impeller drive take-off means cooperating with said actuating element to control the or each shutter in dependence on the operation of said impeller drive.

2. A fan assembly as claimed in claim 1 wherein the impeller drive take-off means cooperates with said actuating element by means of a pinion on the shaft of the impeller drive engaging a rack on the said actuating element.

3. A fan assembly as claimed in claim 2 wherein said rack comprises a first and second rack guide, said first and second rack guides being selectively engageable by the pinion to open and close the shutters respectively.

4. A fan assembly as claimed in claim 3 wherein said rack comprises run-off areas for said impeller drive shaft at the end of said first and second rack guides.

5. A fan assembly as claimed in claim 4 wherein said rack and pinion drive acts against an over-centre spring arranged to control movement of the shutters, each over-centre position of said spring corresponding to a fully closed and fully open position of the shutters, with said drive shaft in one of said run off areas respectively.

6. A fan assembly as claimed in claim 5 wherein said stator is mounted for limited freedom of rotational movement, a pin on the stator engaging said actuating element thereby to cause the pinion selectively to engage said first and second rack guides in dependence on the rotational movement of the strator.

7. A fan assembly as claimed in claim 6 wherein said actuating element is a rotatably mounted arcuate member, an arcuate slot in the body of said arcuate member providing said rack guides along opposing edges of said slot, which edges are on differing radii w.th respect to the axis of rotation of said arcuate member.

8. A fan assembly as claimed in claim 4 wherein said actuating element is a gear wheel, said rack guides being on a periphery of the gear wheel between a said run-off area at each end of a diameter thereof.

9. A fan assembly as claimed in claim 8 wherein said gear wheel is provided with an annular groove, a pin on the body of said motor engaging said groove, said groove being provided with stop abutments for the pin on a diameter of the gear wheel whereby to control the rotational movement of said body of the motor to 180' in each direction.

0. A fan assembly as claimed in claim 8 wherein the position of said pin when on each abutment corresponds to a respective position of said pinion in a said run-off area.

11. A fan assembly as claimed in claim 10 wherein a projection on said gear wheel engages a rectangular slot in a control arm for operating said shutters, whereby rotation of the gear wheel by said pinion causes said projection to move in said rectangular slot to open and close the shutters as the pinion moves between said run-off areas.

12. A far. assembly as claimed in claim 11 wherein said gear wheel rotates against the bias of a spring controlled lever whereby to move said pin off a respective stop abutment and said pinion into engagement with a respective rack guide.

13. A fan assembly as claimed in claim 12 wherein said lever bears against a bilobular cam attached at the centre of said gear wheel to effect meshing of said pinion with a respective rack guide.

14. A fan assembly as claimed in claim 2 wherein said actuating element comprises a shutter control gear wheel, control and drive gear wheels for said shutter control gear wheel with the drive gear wheel in engagement with said shutter control gear wheel, and wherein said rack is provided on the periphery of said control gear wheel for engagement with said pilon to open and close the shutters respectively depending on the rotational direction of said shutter control gear wheel.

15. A fan assembly as claimed in claim 14 wherein said rack includes a run-off area for the pinion of said impellor drive shaft in the open and closed position of said shutters.

16. A fan assembly as claimed in claim 15 wherein said shutter control gear wheel is provided with an annular groove, a pin on the body of said motor engaging said groove, said groove being provided with stop abutments for the pin on a diameter of the shutter control gear wheel whereby to control rotational movement of said motor body to 1800 in each rotational direction.

17. A fan assembly as claimed in claim 16 wherein the position of said pin when on each abutment in the annular groove of the shutter control gear wheel corresponds to the position of said pin in said run-off area on said drive gear wheel.

18. A fan assembly as claimed in claim 17 wherein a projection on said shutter control gear wheel engages a rectangular slot in a control arm for operating said shutters whereby rotation of the drive gear wheel causes the projection to move in said slot to open and close the shutters as the pinion moves on the periphery of said control gear wheel during a 360 rotation of said drive gear wheel in engagement with said shutter control gear wheel.

19. An extractor fan assembly as claimed in any one of claims 14 to 18 wherein the drive ratio of said control and drive gear wheels is any multiple of two.

20. An extractor fan assembly substantially as here inbefore described with reference to the accompanying drawings.