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
Totally enclosed fan cooled AC induction motor
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai - 400 030, Maharashtra, India, an Indian Company
INVENTORS
Desale Rajgopal and Dhokane Prakash, Technology Department, LT Motors, (M3) Crompton Greaves Ltd A6/2 MIDC Area, Ahmednagar, 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 a totally enclosed fan cooled AC induction motor.
BACKGROUND OF THE INVENTION
Totally enclosed fan cooled (TEFC) AC induction motors are heavy duty motors and are generally used in heavy duty applications. Typical application areas of TEFC AC induction motors include paper mills, steel mills or compressor units. A TEFC AC induction motor comprises a rotor mounted on a shaft and rotatably disposed within a stator which is located in a motor housing. The shaft is rotatably held in a pair of endshields fitted at the ends of the motor housing. A fan is mounted on the shaft at the non-drive end of the motor. The fan is enclosed in a fan cover fitted to the motor housing at the non-drive end thereof. Three segments of cooling fins are provided on the outer surface of the motor housing, one segment of fins at the top of the motor housing and two segments of cooling fins each at each opposite side of the motor housing. Each segment of fins extend along the length of the motor housing. During operation of the motor, the fan rotates with the shaft and air is swept and blown over the motor housing. Heat being generated in the motor housing and conducted to the outer surface of the housing and the fins is dissipated to the air being blown over the motor housing. The performance efficiency of the motor depends on its cooling efficiency. The higher the rate of dissipation of heat generated in the motor housing, the better the cooling efficiency of the motor. In case there is excess build up of temperature within the motor housing, the performance efficiency of the motor reduces. The stator and rotor windings and the insulation thereof also may get burnt and damaged thereby reducing the life of the stator and rotor windings. Since the air being blown over the motor housing is not properly

guided along the fins heat dissipation efficiency of the motor is reduced. In order to guide the air along the fins and improve the heat dissipation efficiency of the motor, air guides are known to be provided over the motor housing. The air guides generally extend only upto limited length of the segments of fins. Therefore, there is no significant improvement in the dissipation of heat by the fins. Noise level of operation of the motor is also high as the air flow along the motor housing is not smoothly guided. Further there is insufficient air flow over the bearing at the drive end of the motor. As a result, the bearing gets heated up and damaged.
OBJECTS OF THE INVENTION
An object of the invention is to provide a totally enclosed fan cooled AC induction motor having improved cooling efficiency and performance efficiency.
Another object of the invention is to provide a totally enclosed fan cooled AC induction motor which prevents damage to the stator and rotor windings and increases the life of the rotor and stator windings.
Another object of the invention is to provide a totally enclosed fan cooled AC induction motor which has reduced level of noise.
Another object of the invention is to provide, a totally enclosed fan cooled AC induction motor which is simple in construction and easy to assemble.

Another object of the invention is to provide a retrofit air guide assembly for a totally enclosed fan cooled AC induction motor so as to increase the cooling efficiency and performance efficiency of the motor.
Another object of the invention is to provide a retrofit air guide assembly for a totally enclosed fan cooled AC induction motor so as to prevent damage to the stator and rotor windings of the motor and increase the life of the windings.
Another object of the invention is to provide a retrofit air guide assembly for a totally enclosed fan cooled AC induction motor, which air guide assembly reduces the noise level during operation of the motor.
Another object of the invention is to provide a retrofit air guide assembly for a totally enclosed fan cooled AC induction motor, which is simple in construction and easy to assemble.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention there is provided a totally enclosed fan cooled AC induction motor comprising a rotor mounted on a shaft and rotatably disposed within a stator which is located in the motor housing, the shaft being rotatably fitted in a pair of endshields each fitted at each end of the motor housing, a fan mounted on the shaft at the non-drive end thereof and enclosed in a fan cover fitted at the non-drive end of the motor housing and three segments of cooling fins provided on the motor housing along the length of the motor housing, one segment of fins at the top of the housing and the remaining two

segments of fins each at each opposite side of the housing and an air guide assembly extending over the entire length of the segments of cooling fins.
According to the invention there is also provided a retrofit air guide assembly for a totally enclosed fan cooled AC induction motor having three segments of cooling fins provided on the motor housing along the length of the motor housing, one segment of fins at the top of the housing and the remaining two segments of fins each at each opposite side of the housing, the air guide assembly comprising a top air guide cover extending along the entire length of the segment of cooling fins at the top of the motor housing and a pair of side air guide covers each extending along the entire length of each segment of fins at each side of the motor housing, the top air guide cover being adapted to be mounted at the top of the motor housing and the side air guide covers being mounted to the top air guide cover.
The following is a detailed description of the invention with reference to the accompanying drawings, in which :
Fig 1 is a partly crosssectional view of a totally enclosed fan cooled AC induction motor according to an embodiment of the invention along the length thereof;
Fig 2 is a crosssectional view of the motor of Fig 1; and
Fig 3 is a partly exploded view of the motor of Fig 1.

The totally enclosed fan cooled (TEFC) AC induction motor 1 as illustrated in Figs 1 to 3 of the accompanying drawings comprises a rotor 2 mounted on a shaft 3 and rotatably disposed in a stator 4 which is located within the motor housing 5. The shaft is rotatably held in a pair of endshields 6,6 using bearings 7,7 and the endshield are fitted at opposite ends of the motor housing. 8 is a cooling fan mounted on the shaft at the non-drive end 9 of the motor and enclosed in a fan cover 10 fitted to the non-drive end of the motor housing. Three segments of cooling fins are provided on the motor housing along the entire length thereof namely one segment of fins 11 at the top of the housing and the remaining two segments of fins 12, 12 each at each side of the motor housing. Eye bolts of the motor for lifting or otherwise handling the motor are marked 13. Mounting holes 14 for the eye bolts are formed in bosses 15 on the motor housing. 16 is a top air guide cover having mounting holes 17 matching with the mounting holes 14 for the eye bolts on the motor housing in the bosses. The top air guide cover comprises an overhanging portion 18 extending over the bearing at the drive end 19 of the motor. The overhanging portion of the top air guide cover is fitted to the top air guide cover by tightening screws (not shown) in mounting holes 20 in the overhanging portion and corresponding mounting holes 21 in the top air guide cover. The top air guide cover is fitted at the top of the motor housing over the top segment of fins by tightening the eye bolts in the mounting holes 17 in the top air guide cover and matching holes 14 in the bosses. A pair of tie bands 22 are provided at opposite sides of the top air guide cover. 23, 23 are pair of side air guide covers each disposed at each side of the motor housing over the respective side segment of fins. The side air guide covers are fixed to the tie bands by tightening bolts 24 in fixing holes 25 provided at the free ends of the tie bands and corresponding fixing holes 26 in the side air guide covers. Bolts fixing the tie bands to the top air guide cover are marked 27. The foot of the motor is marked 28.

During operation of the motor air being swept and blown by the fan over the motor housing are guided along the fins at the top and sides of the motor housing by the respective air guide covers. Air is also guided onto the bearing at the drive end of the motor. As the air is guided along the entire length of the motor housing heat dissipation efficiency of the fins is improved. The cooling efficiency and performance efficiency of the motor are increased. The bearing at the drive end of the motor is also kept cooled. Therefore, overheating of the bearing and damage to the bearing is prevented. As the cooling efficiency of the motor is improved excess heat development within the motor housing is reduced. Damage to the stator and rotor windings is reduced and life of the windings is increased. The air guide assembly is simple in construction and can be easily assembled and fitted on the motor housing using the eye bolts. No additional fixing arrangement or fixing bolts are required for fixing the top air guide cover on the motor housing. The side air guide covers remain in position because of their being fixed to the top air guide cover and under their own weight. The air guide assembly also can be easily fitted onto existing motors and serves as a retrofit. The inner surface of the air guide covers are coated with a noise dampening coating 29 like polyurethane coating. Because of this coating, friction between the cooling air and the inner surface of the air guide covers during operation of the motor is reduced and noise level due to the friction effect is reduced. In the case of a retrofit air guide assembly, the mounting hoies J 7 in the top air guide cover may be made as knock down holes and the holes 17 may be fully opened at the time of assembly of the air guide assembly on the induction motor.
The basic invention is in the air guide assembly which extends over the entire length of the segments of cooling fins and also over the bearing at; the drive end of the motor so as

to cool the motor uniformly along the length of the motor and also to cool down the bearing at the drive end of the motor. The air guide assembly can be of a different construction or configuration so as to achieve this objective. However, the overhanging portion of the top air guide cover is optional. The number of segments of fins may vary and the construction and configuration of the air guide assembly also may vary accordingly. Variations in the construction and configuration of the air guide assembly which are obvious to a person skilled in the art are to be construed and understood to be within the scope of the invention.

We claim :
1. A totally enclosed fan cooled AC induction motor comprising a rotor mounted on a shaft and rotatably disposed within a stator which is located in the motor housing, the shaft being rotatably fitted in a pair of endshields each fitted at each end of the motor housing, a fan mounted on the shaft at the non-drive end thereof and enclosed in a fan cover fitted at the non-drive end of the motor housing and three segments of cooling fins provided on the motor housing along the length of the motor housing, one segment of fins at the top of the housing and the remaining two segments of fins each at each opposite side of the housing and an air guide assembly extending over the entire length of the segments of cooling fins.
2. The AC induction motor as claimed in claim 1, wherein the air guide assembly comprises a top air guide cover extending along the entire length of the segment of cooling fins at the top of the motor housing and a pair of side air guide covers each extending along the entire length of each segment of fins at each side of the motor housing, the top air guide cover being adapted to be mounted at the top of the motor housing and the side air guide covers being mounted to the top air guide cover.
3. The AC induction motor as claimed in claim 3, wherein the top air guide cover comprises a pair of mounting holes matching with mounting holes for the eye bolts of the motor at the top thereof and a pair of tie bands at each side thereof, the distal ends of the tie bands being formed with fixing holes, the side air guide covers having fixing holes matching with the fixing holes at the distal ends of the tie bands and being fixed to the tie

bands at each side of the top air guide cover with screws tightened in the fixing holes in the tie bands and in the side air guide covers.
4. The AC induction motor as claimed in anyone of claims 1 to 3, wherein the top air guide cover comprises an overhanging portion extending over the bearing at the drive end of the motor.
5. The AC induction motor as claimed in any one of claims 2 to 4, wherein the inner surface of each of the three air guide covers is coated with a noise dampening coating.
6. The AC induction motor as claimed in claim 5, wherein the noise dampening coating comprises polyurethane.
7. A retrofit air guide assembly for a totally enclosed fan cooled AC induction motor having three segments of cooling fins provided on the motor housing along the length of the motor housing, one segment of fins at the top of the housing and the remaining two segments of fins each at each opposite side of the housing, the air guide assembly comprising a top air guide cover extending along the entire length of the segment of cooling fins at the top of the motor housing and a pair of side air guide covers each extending along the entire length of each segment of fins at each side of the motor housing, the top air guide cover being adapted to be mounted at the top of the motor housing and the side; air guide covers being mounted to the top air guide cover.

8. The retrofit air guide assembly as claimed in claim 7, wherein the top air guide cover comprises a pair of mounting holes matching with the mounting holes for the eye bolts of the motor at the top thereof and a pair of tie bands at each side thereof, the distal ends of the tie bands being formed with fixing holes, the side air guide covers having fixing holes matching with the fixing holes at the distal ends of the tie bands and being fixed to the tie bands at each side of the top air guide cover with screws tightened in the fixing holes in the tie bands and in the side air guide covers.
9. The retrofit air guide assembly as claimed in claim 7 or 8, wherein the top air guide cover comprises an overhanging portion extending over the bearing at the drive end of the motor.
10. The retrofit air guide assembly as claimed in any one of claims 7 to 9, wherein the inner surface of each of the three air guide covers is coated with a noise dampening coating.
11. The retrofit air guide assembly as claimed in claim 10, wherein the noise dampening coating comprises polyurethane.