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
INVENTORS
Kamble Deepak and Shenoy Talachery Purushotham, Crompton Greaves Limited, Engineering & AMDTC, CG Global R&D, Kanjurmarg (East), Mumbai 400042, Maharashtra, India, both Indian Nationals
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:


FIELD OF THE INVENTION
This invention relates to an external rotor axial flow fan
BACKGROUND OF THE INVENTION
An external rotor axial flow fan is driven by an external rotor AC motor or external rotor brushless DC motor. During operation of the fan, air is axially sucked or drawn in from the front side of the fan and thrown out from the back side of the fan so as to create air circulation. An external rotor axial flow fan comprises a back endshield having a cupshaped body and a support portion inwardly extending from the center thereof. The fan also comprises an impeller having a recessed impeller body with a plurality of impeller blades on the outer surface thereof and an external rotor located at the inner surface thereof. The impeller further comprises an impeller shaft extending axially inwardly from the impeller body and rotatably held in the support portion with the edge of the impeller body disposed over the edge of the cupshaped body. It also comprises a support sleeve disposed over the impeller shaft and located against the support portion. A motor controller comprising a printed circuit board with hall sensor is located over the support sleeve. A wound stator pack is located over the support sleeve and disposed within the rotor describing a clearance or air gap with the rotor. The fan also comprises a shroud having support element at the back end of the shroud. The support element is fixed to the shroud by spaced apart reinforcing radial ribs. The back end shield is screw fitted to the support element of the shroud. Such an external rotor axial flow fan comprises a large number of components thereby increasing material cost and

manufacturing cost of the fan. Further the assembly time of the fan is increased thereby reducing productivity of the fan.
OBJECTS OF THE INVENTION
An object of the invention is to provide an external rotor axial flow fan which is simple in construction and comprises reduced number of components so as to reduce the material cost and manufacturing cost thereof.
Another object of the invention is to provide an external rotor axial flow fan which reduces the assembly time so as to increase productivity of the fan.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention there is provided an external rotor axial flow fan comprising a shroud having a cupshaped portion at the back end thereof, the cupshaped portion having an inwardly extending support portion at the center thereof, an impeller comprising a recessed impeller body having a plurality of impeller blades on the outer surface thereof and an external rotor located at the inner surface thereof and an axially inwardly extending impeller shaft, the impeller shaft being rotatably held in the support portion of the cupshaped portion with the edge of the recessed impeller body disposed over the edge of the cupshaped portion, a support sleeve disposed over the impeller shaft and located against the support portion of the cupshaped portion, a controller comprising a printed circuit board with a hall sensor located over the support sleeve and a wound stator pack located over the support sleeve and disposed within the rotor describing a clearance with the rotor.

The following is a detailed description of the invention with reference to the accompanying drawings, in which:
Figs 1 and 2 are front and back isometric views of the external rotor axial flow fan according to an embodiment of the invention;
Fig 3 is crosssectional view of the fan of Fig 1 or Fig 2;
Figs 4 and 5 are front and back isometric views of the shroud of the fan of Fig 1 or Fig 2; and
Fig 6 is an exploded view of the fan of Fig 1 or Fig 2,
The external rotor axial flow fan 1 as illustrated in Figs 1 to 6 of the accompanying drawings comprises a shroud 2 having a cupshaped portion 3 at the back thereof. The cupshaped portion has an inwardly extending support portion 4 at the centre thereof. The inwardly extending portion 4 is reinforced by radial ribs 4a. 5 is an impeller comprising a recessed impeller body 6 having a plurality of impeller blades 7 on the outer surface thereof and an external rotor 8 located at the inner surface thereof The impeller has an axially inwardly extending impeller shaft 9 at the center of the impeller body rotatably held against a collar 4b on the support portion 4 using spaced apart bearings 10 and 11. The impeller shaft is detachable from the impeller body and is adapted to be press or push fitted in a hole 9a in the impeller body. 12 is a spacer between the bearings so as to maintain the spacing between the bearings. The edge of the recessed impeller body is disposed over the edge of the cupshaped portion 3. 13 is a support sleeve disposed over

the impeller shaft and bearings and located against the support portion 4 over the collar 4b thereof. The support sleeve is provided with mounting lugs 13a with screw holes 13b and is fitted to the support portion 4 by screws 13c tightened in screw holes 13d in the support portion 4 and screw holes 13b in the lugs 13a of the support sleeve 13. A motor controller comprising a printed circuit board (PCB) 14 is located over the support sleeve and held to a PCB holder 15 by screws 16 passing through screw holes 17 in the PCB and corresponding screw holes 18 in flanges 18a of the PCB holder. 19 is a sensor holder fixed on the PCB in holes 19a in the PCB and 20 is a hall sensor held in the sensor holder. 21 is a wound stator located over the support sleeve against the flanges 18a of the PCB holder and disposed within the rotor describing a clearance or air gap (not marked) with the rotor. During assembly of the fan, the support sleeve 13 is fixed to the support portion 4 with screws 13c tightened in screw holes 13b in the mounting lugs 13a of the support sleeve and corresponding screw holes 13d in the support portion. The PCB 14 with the sensor holder 19 and hall sensor 20 is inserted over the support sleeve and fixed to the PCB holder 15 inserted over the support sleeve with screws 16 tightened in screw holes 17 in the PCB and screw holes 18 in the flanges 18a of the PCB holder. The wound stator pack is located over the support sleeve against the flanges 18a of the PCB holder. The impeller shaft 9 with the bearings 10 and 11 and spacer 12 is located in the support sleeve against the support portion 4. And finally the impeller body 6 with the impeller blades and rotor is push or press fitted over the impeller shaft through hole 9a in the impeller body. The cupshaped portion 3 of the shroud 2 provides a cover and shield for the inner parts of the fan and also prevents foreign particles like dust entering and getting accumulated within the fan. According to the invention, the fan construction is simplified. It eliminates the back endshield and reduces material cost and manufacturing cost of the fan. Further it reduces the assembly time of the fan and increases productivity.

The wound stator pack and rotor constituting the motor driving the fan is an external rotor AC motor or external rotor brushless DC motor.
The embodiment illustrated in the drawings is by way of example and should not be construed to be limiting the scope of the invention. The support portion of the cupshaped portion may be of a different construction / configuration. The support sleeve and PCB holder configurations can differ. Instead of two bearings the fan may comprise one or more than two bearings. The impeller shaft need not be detachable. Embodiments comprising such variations of the invention are obvious to those skilled in the art and are to be construed and understood to be within the scope of the invention.

We claim:
1. An external rotor axial flow fan comprising a shroud having a cupshaped portion at the back end thereof, the cupshaped portion having an inwardly extending support portion at the center thereof, an impeller comprising a recessed impeller body having a plurality of impeller blades on the outer surface thereof and an external rotor located at the inner surface thereof and an axially inwardly extending impeller shaft, the impeller shaft being rotatably held in the support portion of the cupshaped portion with the edge of the recessed impeller body disposed over the edge of the cupshaped portion, a support sleeve disposed over the impeller shaft and located against the support portion of the cupshaped portion, a controtter comprising a printed circuit board with a hall sensor located over the support sleeve and a wound stator pack located over the support sleeve and disposed within the rotor describing a clearance with the rotor.
2. The axial flow fan as claimed in claim 1, wherein the impeller shaft is rotatably held in the support portion of the cupshaped portion by a pair of spaced apart bearings.
3. The axial flow fan as claimed in claim 1 or 2, wherein the impeller shaft is detachable and is press or push fitted in the impeller body.
Dated this 15th day of January 2009.