FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION (See section 10 and rule 13)
TITLE OF THE INVENTION An external rotor axial flow fan
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400
030, Maharashtra, India, an Indian Company
INVENTOR
Kamble Deepak Gajanana of Crompton Greaves Limited, Engineering Department,
Global R&D Centre, Kanjur Marg (E), Mumbai 400042, Maharashtra, India, an Indian
National
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed:

FIELD OF THE INVENTION
The present invention relates to axial flow fans, and more particularly to external rotor axial flow fans that require less components for their assembly.
BACKGROUND OF THE INVENTION
External rotor axial flow fans generally find application in cooling devices/machines such as air conditioners, air coolers, UPS, exhaust fans, and the like devices/machines. During operation of such axial flow fans, ambient air is axially sucked within the fans from a front side and axially thrown outside from the back side. Such fans are called as external rotor axial flow fans because the stators are positioned within the stators with the rotors rotatable around the stators.
An exploded view of one such external rotor fan 100 is shown in FIGS. 1 and 2. The external rotor axial flow fan 100 broadly includes components such as an impeller 102 having a rotor 104 and an impeller shaft 106 disposed therein, a wound stator 108, a shaft 110, a back end shield 112, a PCB 114, and a shroud 116. During assembly of the external rotor axial flow fan 100, the wound stators 108, the PCB 114 along with its holder 118, and the shaft 110 are mechanically coupled with the back end shield 112 with the help of fastening members 120 such as nuts, bolts, and screws, etc. As shown in FIG. 2, each of the wound stator 108, the PCB 114, the PCB holder 118 and the shaft 110 has corresponding holes 122 disposed therein, wherein each of these holes 122 matches corresponding fastening positions on the back end shield 112. The fastening members 120 are then used to connect these components together. Assembly of the wound stator

108, the PCB 114, and the shaft 110 with the back end shield 112 is shown in FIG. 3. Further, as shown in FIGS. 1-3, the back end shield 112 is then mechanically coupled with the shroud 116 by using another set of fastening members 126.
Last stage of the assembly includes rotatably coupling the impeller shaft 106 with the shaft 110. Generally, the impeller shaft 106 is fitted within the shaft 110 by the use of bearings 126 so that the impeller 102 rotates (due to rotation of the rotor) smoothly without being interfered by the shaft 110 that remains stationary due to its fixed attachment with the shroud 116. FIG. 4 shows a cross-sectional view of the fully assembled external rotor axial flow fan 100 illustrating mechanical connections between the various components, specifically, between the shaft 110 and the back end shield 112 and between the back end shield 122 and the shroud 116.
It is imperative for an efficient performance of the external rotor axial flow fans 100 that the shaft 110, the back end shield 112, and the shroud 116 are mechanically coupled with each other in such a manner that their axes are coaxial with each other. Specifically, during the axial flow fan operation, the shaft 110 should always be maintained in perpendicular orientation with respect to the back end shield 112 and the shroud 116. Further, mechanical engagement of these components should be extremely tight with respect to each other. However, maintaining the above conditions for such fans, in the long run, becomes extremely difficult as the fastening members 120, 126 such as nuts, bolts, screws, etc. are bound to become loose during prolonged operation. This results in various undesirable drawbacks which needs to addressed.

One of the drawbacks is that the shaft 110 may not remain in perpendicular orientation with respect to the back end shield 112 and/or the shroud 116 resulting in the impeller 102 and the fan blades (mounted on an outer surface of the impeller) to wobble within the shroud 116. This wobbling leads to the fan blade tips touching the internal surface of the shroud 116. Even a slight contact between the blade tips and the internal surface, during operation, creates a lot of noise which is very awkward and annoying. However, if the wobbling is significant then the blade (and the impeller) may not rotate as the inner surface of the shroud 116 would hamper rotation of the fan blades. Such a scenario, in any case, is unacceptable to the potential customers.
Another drawback is that the shaft 110, the back end shield 112, and the shroud 116 are manufactured separately adding up to additional manufacturing costs of these components. Thus, apart from the inconvenience of the fastening members 120, 126 required to couple these components being loosened up, the cost involved in manufacturing these components separately adds to the over all cost of the external rotor axial fans 100. Additionally, overall assembly of the external rotor motor fans 100 also consumes significant time.
Thus, there is a need to provide an external rotor axial flow fan that addresses at least some of the above problems yet maintaining the requisite standards of air flow generation.
SUMMARY OF THE INVENTION
Disclosed herein is an external rotor axial flow fan for generating airflow, the fan including a shroud having a back end and a hub at the back end, the hub having a

centrally disposed stationary shaft extending therefrom, a wound stator connected to an electronic controller, the wound stator and the electronic controller being fixedly mounted on the stationary shaft, a rotor rotatably disposed over the wound stator, and an impeller including a generally cylindrical body that has a plurality of blades disposed on an outer surface and the rotor fixed to an inner surface of the cylindrical body, the cylindrical body including an impeller shaft extending internally therefrom and coaxially aligned with the stationary shaft, the impeller shaft being rotatably held about the stationary shaft, wherein the shroud, the hub, and the stationary shaft being integrally formed as a single unit.
In some embodiments, the shroud, the hub, and the stationary shaft are molded together to form the single unit.
In some embodiments, the stationary shaft has an opening extending along a portion of a length of the stationary shaft, the opening receiving the rotatable impeller shaft therein.
In another embodiment, the impeller shaft has a groove formed on an outer surface thereof and adjacent to an outer end, the groove receiving a locking member disposed adjacent to the bearing within the opening to lock the impeller shaft against the stationary shaft.
In another aspect of the present invention, a shroud for an external rotor axial flow fan including a back end, a hub formed at the back end, and a stationary shaft centrally disposed on the hub and internally extending therefrom, the back end, the hub, and the stationary shaft are integrally formed as a single unit.

In yet another aspect of the present invention, an electrical machine requiring generation of airflow by an external rotor axial flow fan disposed therein, the machine including a shroud having a back end and a hub at the back end, the hub having a centrally disposed stationary shaft extending therefrom, a wound stator connected to an electronic controller, the wound stator and the electronic controller being fixedly mounted on the stationary shaft, a rotor rotatably disposed over the wound stator, and an impeller including a generally cylindrical body that has a plurality of blades disposed on an outer surface and the rotor fixed to an inner surface of the cylindrical body, the cylindrical body including an impeller shaft extending internally therefrom and coaxially aligned with the stationary shaft, the impeller shaft being rotatably held about the stationary shaft, wherein the shroud, the hub, and the stationary shaft being integrally formed as a single unit.
Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description of the present embodiments of the invention and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments of the invention and

together with the description serve to explain the principles and operation of the invention.
A BRIEF DESCRIPTION OF THE DRAWINGS
The above-mentioned and other features and advantages of the various embodiments of the invention, and the manner of attaining them, will become more apparent will be better understood by reference to the accompanying drawings, wherein:
FIG. 1 is an exploded view of a prior art external rotor axial flow fan;
FIG. 2 is another exploded view of the prior art external rotor axial flow fan of FIG. 1;
FIG. 3 is a partial exploded view of the prior art external rotor axial flow fan of FIG. 2;
FIG. 4 is a side cross-sectional view of a fully assembled prior art external rotor axial flow fan of FIGS. 1 and 2;
FIG. 5 is a perspective front end view of a shroud used in the external rotor axial flow fan according to an embodiment of the present invention;
FIG. 6 is a perspective back end view of the shroud of FIG. 5;
FIG. 7 is an exploded view of an external rotor axial flow fan having the shroud of FIG. 5 according to an embodiment of the present invention
FIG. 8 is a partial exploded view of the external rotor axial flow fan of FIG. 7;

FIG. 9 is a partial exploded view of an impeller that is coupled with the shroud of FIGS. 5 and 6;
FIG. 10 is a side cross-sectional view of the fully assembled external rotor axial flow fan of FIGS .7 and 8;
FIG. 11 is a perspective front view of a fully assembled external rotor axial flow fan of FIGS 7 and 8; and
FIG. 12 is a back end perspective view of a fully assembled external rotor axial flow fan of FIG. 11.
DETAILED DESCRIPTION OF THE PREFFERED EMBODIMENTS
Reference will now be made in detail to the exemplary embodiment(s) of the invention, as illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts.
FIGS. 5 and 6 illustrate a front perspective view and a back perspective view, respectively, of a shroud 200 according to an embodiment of the present invention. The shroud 200 is defined by a front end 202, a back end 204, and a hollow portion 206 extending between the front end 202 and the back end 204. Each of the front end 202 and the back end 204 has an opening 208 to correspond the hollow portion 206. Preferably, as shown in FIGS. 5 and 6, the hollow portion 206 and the openings 208 in the front end 202 and the back end 204, respectively, are generally circular in shape. However, in another embodiment of the present invention, the hollow portion 206 and the openings

208 may have an oval shape. Alternatively, the hollow portion 206 and the openings 208 may also have other shapes as well and be within the scope of the present invention.
As shown in FIG. 6, the back end 204 of the shroud 200 includes a centrally formed hub 210 with centre of the hub 210 being concentric with the back end 204. The hub 210, which is preferably circular in shape, has a front surface 212, a back surface 214, and a central portion 216 extending between the front surface 212 and the back surface 214. The back surface 214 of the hub 210 forms a portion of the back end 204 of the shroud 200 whereas the front surface 212 and the central portion 216 extends up to a certain length of the hollow portion 206 of shroud 200. However, in another embodiment of the present invention, the central portion 216 may also extend up to the entire length of the hollow portion 206 of the shroud 200 and be within the scope of the present invention.
Preferably, the back end 204 of the shroud 200 has a plurality of ribs 218 that connects the hub 210 with a plurality of edges 220 of the opening 208 provided on the back end 204. Alternatively, the back end 204 of the shroud 200 may also be connected with the back surface 214 of the hub 210 by other known methods and mechanisms.
Further, as shown in FIG. 5, a stationary shaft 222 is disposed at the centre of the hub 210 with the centre of the stationary shaft 222 being concentric with the hub 210. Thus, the back end 204 of the shroud 200, the hub 210, and the stationary shaft 222 are concentric to each other. Further, the stationary shaft 222 extends from the back surface 214 of the hub 210 inwardly towards the front surface 212 of the hub 210. Preferably, the stationary shaft 222 extends beyond the front surface 212 of the hub 210 and up to a

certain length of the hollow portion 206 of the shroud 200. Alternatively, in one embodiment of the present invention, the stationary shaft 222 may extend only up to the front surface 212 of the hub 210.
In one embodiment of the present invention, the stationary shaft 222 has a central opening 224 provided at an outer end 226 thereof with the central opening 224 extending up to a distance towards the centre of the hub 210. In another embodiment, the central opening 224 may extend throughout the stationary shaft 222 and the centre of the hub 210. Thus, this central opening 224 allows the stationary shaft 222 to have an outer surface 228 and an inner surface 230. The inner surface 230 and the outer surface 228 of the stationary shaft 222 securely retain various mechanical and electrical components forming an external rotor axial flow fan 232.
It is to be noted that in all of the above and the foregoing embodiments, the shroud 200, the hub 210, and the stationary shaft 222 are integrally formed as a single unit. Preferably, the shroud 200, the hub 210, and the stationary shaft 222 are formed into the single unit by molding process. However, in other embodiments, the above components forming the shroud 200 as a single unit may also be manufactured by other known methods in the art and be within the scope of the present invention.
As explained above in the background art in the prior art external rotor ax'tal flow fans 100, all these components were manufactured separately and then assembled together. However, in the various embodiments of the present invention described herein the stationary shaft 222, the hub 210 (corresponding to the back end shield 112 of the prior art fans), and the shroud 200 are formed as a single unit. Thus, a skilled person in

the art will appreciate that benefits of having the shroud 200 integrally formed with the hub 210 and the stationary shaft 222 are numerous, First, the major drawback of the stationary shaft 222 loosing its perpendicularity with respect to the back end 204 of the shroud 200 is completely eliminated as there are no separate fastening means are involved. Thus, wobbling of the blades within the hollow portion 206 of the shroud 200 is avoided. Second, hassles of having the stationary shaft 222, the hub 210, and the shroud 200 manufactured separately are completely avoided thereby resulting in significant cost being saved during manufacturing of the shroud 200. Third, noise and vibration levels are reduced very significantly. Finally, assembly time for external rotor flow fans 232 is also reduced.
FIG. 7 shows an exploded view of the external rotor axial flow fan 232 in which various electrical and mechanical components used in construction of the axial flow fan 232 may be coupled with the shroud 200, according to an embodiment of the present invention. The components may include a plurality of bearings 234, a spacer 236, a wound stator 238, an electronic controller 240, an electronic controller holder 242, a sensor 248 and a sensor holder, and an impeller 244 having a rotor 246 disposed therein. Other components that may be used in the construction of the external rotor axial flow fan 232 are not shown FIG. 7 as well as in the foregoing figures for the simplicity of the description of the various embodiments. FIG. 8 shows a partial assembly of the components shown in FIG. 7 with the shroud 200.
Reference will now be given to FIGS. 7 and 8 to describe the partial assembly of the external rotor axial flow fan 232. Diameter of the plurality of bearings 234 and the spacer 236 are smaller than an inner diameter of the stationary shaft 222. As a result of

this, the plurality of bearings 234 and the spacer 236 are inserted within the stationary shaft 222. The bearings 234 and the spacer 236 are fixedly attached to the inner surface 230 of the stationary shaft 222 with the spacer 236 disposed in between the two bearings
234.
Preferably, as shown in FIG. 8, a wound stator 238 known in the art is fixedly attached on the outer surface 228 of the stationary shaft 222. The wound stator 238 has a central opening 224 that is greater than the outer diameter of the stationary shaft 222 and because of this the wound stator 238 is comfortably fitted over the stationary shaft 222. The electronic controller 240 secured by the electronic controller holder 242 is also disposed over the stationary shaft 222 and positioned adjacent to the wound stator 238. The electronic controller 240, which is preferably a PCB (printed circuitry board), has a sensor 248 disposed therein that senses magnetic polarity of the rotor 246 facing the sensor 248 and to send signal to the electronic controller 240. The electronic controller 240 is electrically connected to the wound stator 238 to provide selective magnetic polarity thereto in response to the signals received from the sensor 248. The electronic controller 240 derives power from an external power source (not shown).
Preferably, the various components connected to the inner surface 230 as well as the outer surface 228 of the stationary shaft 222 are pressure fitted. This is to ensure that while the axial flow fan 232 is in operation, these components do not move from their respective places to hamper efficient operation of axial flow fan 232. However, other variants of fixedly attaching these components to the stationary shaft 222 may also be envisaged in alternative embodiments and be within the scope of the present invention. Assembly of the electronic controller 240 and the wound stator 238 on the outer surface

228 of the stationary shaft 222 is shown in FIG. 8. Assembly of the plurality of bearings 234 and the spacer 236 with the inner surface 230 of the stationary shaft 222 is shown in FIG. 12 illustrating cross-sectional view of the fully assembled external rotor axial flow fan 232.
FIG. 9 shows a partial exploded view of the impeller 244. The impeller 244 has an inner surface 250, an outer surface 252, and an annular portion that has a generally cylindrical shaped body 254. A plurality of blades 256 is disposed on the outer surface 252 of the impeller 244 whereas the inner surface 250 of the impeller 244 has the rotor 246 fixedly attached thereto. The rotor 246 is preferably a magnetic ring and has a plurality of equal opposite (North-South) poles therein. The inner diameter of the rotor 246 is constructed to have a larger value than an outer diameter of wound stator 238 (See FIG. 10). This is to ensure that when the impeller 244 is coupled with the shroud 200, there is sufficient gap between the two to allow the rotor 246 to rotate under the influence of variable magnetic flux between the rotor 246 and the wound stator 238.
Further, as shown in FIG. 9, the impeller 244 also has a front end 260 and a back end 262. An impeller shaft 264 connected to the back end 262 and extends internally towards the front end 260 of the impeller 244. The impeller shaft 264 is an elongated shaft that is connected centrally to the back end 262 of the impeller 244. Furthermore, the impeller shaft 264 has grooves 266 formed on its outer surface adjacent to an outer end of the impeller shaft 264. As shown in FIGS. 6 and 7, the back end 204 of the shroud 200 also has an opening 268. When the impeller 244 is received within the shroud 200, a locking member 270, which is preferably a circlip, engages the grooves 266 to lock the impeller shaft 264 against the stationary shaft 222 and the shroud 200. This locking

ensures a tight fitting between the impeller 244 and the shroud 200. Locking engagement of the impeller 244 with the shroud 200 is shown in FIG. 12.
FIG. 10 shows a cross-sectional view of the fully assembled external rotor axial flow fan 232. The impeller shaft 264 is received within the central opening 224 of the stationary shaft 222 of the shroud 200. Prior to inserting the impeller shaft 264 within the stationary shaft 222, the impeller shaft 264 is aligned with the stationary shaft 222 of the shroud 200 in an orientation that has axis of both the impeller shaft 264 and the stationary shaft 222 aligned coaxially to each other. It is to be noted that length of the impeller shaft 264 is such that it is easily received within the central opening 224 provided in the stationary shaft 222. Further, it is also to be understood that the constructional design of the impeller 244 is such that when the impeller shaft 264 is coupled with the stationary shaft 222, the impeller 244 is securely positioned within the shroud 200 (See FIGS. 10-12).
When the impeller shaft 264 is received in the stationary shaft 222, the plurality of bearings 234 along with the spacer 236 is sandwiched between the inner surface 230 of the stationary shaft 222 and the outer surface of the impeller shaft 264. The plurality of bearings 234 ensures that rotation of the impeller shaft 264 is not transferred to the stationary shaft 222. Further, the outer end of the impeller shaft 264 is arranged within the stationary shaft 222 in such a manner that the grooves 266 provided adjacent to the outer end of the impeller shaft 264 extends beyond the plurality of bearings 234. Due to this arrangement, the grooves 266 easily receive the circlip, which is pushed from the back surface 214 of the hub 210 to engage the grooves 266,

FIG. 10 also shows that when the impeller shaft 264 is fully received within the stationary shaft 222, the annular portion of the impeller 244 engages the central portion 216 of the hub 210. Further, the rotor 246 of the impeller 244 is positioned adjacent to the wound stator 238 and aligned therewith with a constant predetermined gap therebetween. FIGS. 11 and 12 show the perspective front side and back side views of the fully assembled external rotor axial flow fan 232.
During operation of the external rotor axial flow fan 232, the sensor 248 senses the current polarity of the rotor 246 positioned in front of the rotor 246 and sends the signal representative of the polarity to the electronic controller 240. The electronic controller 240, as it is well known in the art, has a preprogrammed chip that primarily performs two critical functions. First, it senses the current polarity of the rotor 246 and then accordingly creates a similar polarity on the wound rotor 246 facing the rotor 246 and second, it also calculates and maintains the RPM at which the rotor 246 rotates.
Due to creation of similar poles at the wound stator 238, a repulsive force between the wound stator 238 and the rotor 246 is generated that results in a torque being created. Since the wound stator 238 is fixedly attached to the stationary shaft 222, in order to compensate for the torque, the rotor 246 starts moving. As the rotor 246 is fixedly attached to the inner surface 250 of the impeller 244, rotational motion of the rotor 246 gets transferred to the impeller 244 thereby allowing the blades 256 to rotate and generate airflow. Moreover, due to the presence of bearings 234 between the impeller shaft 264 and the stationary shaft 222, the impeller shaft 264 conveniently rotates within the stationary shaft 222. Further, as the rotor 246 starts rotating, the magnetic polarity facing the sensor 248 varies. Accordingly, the sensor 248 sends signals to the electronic

controller 240 which in turn changes the polarity of the wound stator 238 to become similar to that of the rotor 246. This leads to generation of a continuous torque, which helps in moving the rotor 246 against the wound stator.
The external rotor axial flow fans 232 can be easily used within air conditioners, refrigerators, air coolers, UPS, exhaust fans, and the like machines.
It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Thus it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

We claim:
1. An external rotor axial flow fan for generating airflow, the fan comprising:
a shroud having a back end and a hub at the back end, the hub having a centrally disposed stationary shaft extending therefrom;
a wound stator connected to an electronic controller, the wound stator and the electronic controller being fixedly mounted on the stationary shaft;
a rotor rotatably disposed over the wound stator; and
an impeller including a generally cylindrical body that has a plurality of blades disposed on an outer surface and the rotor fixed to an inner surface of the cylindrical body, the cylindrical body including an impeller shaft extending internally therefrom and coaxially aligned with the stationary shaft, the impeller shaft being rotatably held about the stationary shaft, wherein
the shroud, the hub, and the stationary shaft being integrally formed as a single unit.
2. The external rotor axial flow fan according to claim 1, wherein the shroud, the hub, and the stationary shaft are molded together to form the single unit.
3. The external rotor axial flow fan according to claim 1, wherein the stationary shaft has an opening extending along a portion of a length of the stationary shaft, the opening receiving the rotatable impeller shaft therein.

4. The external rotor axial flow fan according to claim 3, wherein the opening has a bearing fixedly attached thereto, the bearing sandwiched between the impeller shaft and the stationary shaft.
5. The external rotor axial flow fan according to claim 4, wherein the impeller shaft has a groove formed on an outer surface thereof and adjacent to an outer end, the groove receiving a locking member disposed adjacent to the bearing within the opening to lock the impeller shaft against the stationary shaft.
6. A shroud for an external rotor axial flow fan comprising:
a back end;
a hub formed at the back end; and
a stationary shaft centrally disposed on the hub and internally extending therefrom, the back end, the hub, and the stationary shaft are integrally formed as a single unit.
7. The shroud according to claim 6, wherein the shroud, the hub, and the stationary shaft are molded together to form the single unit.
8. The shroud according to claim 1, wherein the stationary shaft has an opening extending along a portion of a length of the stationary shaft, the opening capable of receiving a rotatable impeller shaft of an impeller therein.

9. An electrical machine requiring generation of airflow by an external rotor axial flow
fan disposed therein, the machine comprising:
a shroud having a back end and a hub at the back end, the hub having a centrally disposed stationary shaft extending therefrom;
a wound stator connected to an electronic controller, the wound stator and the electronic controller being fixedly mounted on the stationary shaft;
a rotor rotatabfy disposed over the wound stator; and
an impeller including a generally cylindrical body that has a plurality of blades disposed on an outer surface and the rotor fixed to an inner surface of the cylindrical body, the cylindrical body including an impeller shaft extending internally therefrom and coaxially aligned with the stationary shaft, the impeller shaft being rotatably held about the stationary shaft, wherein
the shroud, the hub, and the stationary shaft being integrally formed as a single unit.
10. The electrical machine according to claim 9, wherein the electrical machine is an air
conditioner and refrigerator, or an air cooler, or a UPS, or an exhaust fan, or the like
machines