FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
AND
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2005
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
A bidirectional fan with helical air flow for low noise of TEFC induction motors.
APPLICANTS :
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra/India, an Indian Company
INVENTOR (S):
Dhokane Prakash of Crompton Greaves Limited, LT Motors Division, A/6-2,
MIDC Industrial Area, Ahmednagar - 414111, Maharashtra, India; an Indian
National.
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:
The invention relates to the field of mechanical engineering and mechanical assemblies,
Particularly, this invention relates to the field of motors and associated cooling mechanisms and fan assemblies.
More particularly, this invention relates to Totally Enclosed Fan Cooled (TEFC) induction motors.
Specifically, this invention relates to a bidirectional fan with helical air flow for low noise of TEFC induction motors.
BACKGROUND OF THE INVENTION:
A motor for electrical purposes, i.e. an electric motor, is a device which converts electrical energy to mechanical energy. For industrial use, the ratings of motor may typically be very high. They may be placed in housings and are hence called totally enclosed motors.
Electricity, flowing through motor windings, develops heat due to the resistance of the windings. This heat is developed continuously and therefore the heat must also be removed / dissipated continuously or else the temperature of the windings would rise until the winding insulation is burned out.

Hence, the motor is constructed with a small fan on the rear shaft of the motor, usually covered by a housing. This fan draws air over the motor body, removing excess heat and cooling the motor.
Totally Enclosed, Fan Cooled (TEFC) motors are enclosure motors. This ordinarily means that the motor is dust tight, and has a moderate water seal as well.
TEFC motors have an externally mounted fan covered by a shroud blowing air across the surface of the motor enclosure. Heat developed in the windings moves by convection outward through the motor case then into the air moving along the surface of the motor case. The motor case is a heat sink drawing heat from the motor interior to the outside. TEFC motors may have fins on the motor case enhancing this heat transfer into the air.
Additionally, motors may have a clockwise rotational direction or an anticlockwise rotational direction. The fan assembly, according to the prior art, has to be selected according to the rotational direction. This results in inventory cost for a company manufacturing such motors and fans.
According to the prior art, the TEFC motor includes a fan which provides centrifugal air flow. This type of air flow generates more airborne noise in the range of 96dB(A)
Airborne noise is not acceptable by customers as it causes discomfort for
customers.

OBJECTS OF THE INVENTION:
An object of the invention is to provide improved cooling for a TEFC motor or for any appliance or electrical component which requires forced cooling.
Another object of the invention is to provide a fan, with noise level reduction, for a TEFC motor or for any appliance or electrical component which requires forced cooling.
Yet another object of the invention is to provide an improved air delivery of a fan for a TEFC motor or for any appliance or electrical component which requires forced cooling.
Still another object of the invention is to provide a fan for a TEFC motor or for any appliance or electrical component which requires forced cooling, which fan is suitable for both (anticlockwise and clockwise) directions of operations of motors.
SUMMARY OF THE INVENTION:
According to this invention, there is provided a bidirectional fan with helical air
flow, said fan comprises:
central hub on which blades project out, radially, characterised in that, said blades are helical blades positioned at a pre-defined angle in relation to lateral circumference of said hub.

According to this invention, there is also provided a low noise induction motors with bidirectional fan with helical air flow, said fan comprises:
a. central hub which is shaft mounted to provide angular displacement motion
to said fan;
b. blades project out from said hub, radially, characterised in that, said blades
are helical blades positioned at a pre-defined angle in relation to lateral
circumference of said hub.
Typically, said pre-defined angle of each of said blades is in correlation with the number of blades that are attached at said hub.
Typically, said blade is a substantially trapezoidal blade with parallel curvilinear edges with one internal edge adapted to join to said hub and one external edge forming an external circumference of said fan.
Typically, said blade includes an internal face and an external face such that said internal face and said external face are planar surfaces.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
The invention will now be described in relation to the accompanying drawings, in which:
Figure 1 illustrates an isometric view of the bidirectional fan with helical air flow;

Figure 2 illustrates a top view of the bidirectional fan with helical air flow of Figure 1;
Figure 3 illustrates a blade profile of the bidirectional fan with helical air flow of Figure 1; and
Figure 4 illustrates a side view of the bidirectional fan with helical air flow of Figure 1.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
According to this invention, there is provided a bidirectional fan with helical air flow for low noise of TEFC induction motors.
Figure 1 illustrates an isometric view of the bidirectional fan (100) with helical air
flow.
Figure 2 illustrates a top view of the bidirectional fan (100) with helical air flow of Figure 1.
Figure 4 illustrates a side view of the bidirectional fan (100) with helical air flow of Figure 1.
In accordance with an embodiment of this invention, there is a central hub (14) on which blades (12) project out. The blades, in accordance with this invention, are helical blades. The helical blades are positioned at a pre-defined angle in relation

to lateral circumference of the hub. The angle of the blade is in correlation with the number of blades that are attached at the hub. The central hub is a circular hub which is shaft mounted to provide angular displacement motion to the fan.
Figure 3 illustrates a blade profile of the bidirectional fan with helical air flow of Figure 1.
In accordance with another embodiment of this invention, each blade (12) is a substantially trapezoidal blade with parallel curvilinear edges with one internal edge adapted to join to the hub and one external edge forming the external circumference of the fan. The blades include an internal face and an external face. The internal face and the external face are planar surfaces so that the fan can move in either direction without any operational prejudice.
Therefore, the bidirectional fan of this invention makes airflow helical. Also, the bidirectional nature of the fan renders the fan suitable for operation in both directions.
According to one non-limiting exemplary embodiment, it was observed that there was reduction in noise level from 96dB(A) to 86dB(A).
The technical advancement of this invention lies in provisioning a fan which has bidirectional operational capabilities. Further, the fan is adapted to provide helical airflow. Also, noise level reduction is possible. This is possible due to the nature of the fan blade as disclosed in the specification and due to is placement on the hub as disclosed in the specification.

While this detailed description has disclosed certain specific embodiments of the present invention for illustrative purposes, various modifications will be apparent to those skilled in the art which do not constitute departures from the spirit and scope of the invention as defined in the following claims, and it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

We claim,
1. A bidirectional fan with helical air flow, said fan comprising:
central hub on which blades project out, radially, characterised in that, said blades are helical blades positioned at a pre-defined angle in relation to lateral circumference of said hub.
2. A bidirectional fan as claimed in claim 1 wherein, said pre-defined angle of each of said blades is in correlation with the number of blades that are attached at said hub.
3. A bidirectional fan as claimed in claim I wherein, said blade is a substantially trapezoidal blade with parallel curvilinear edges with one internal edge adapted to join to said hub and one external edge forming an external circumference of said fan.
4. A bidirectional fan as claimed in claim 1 wherein, said blade includes an internal face and an external face such that said internal face and said external face are planar surfaces.
5. A low noise induction motors with bidirectional fan with helical air flow, said fan comprising:
a. central hub which is shaft mounted to provide angular displacement
motion to said fan;
b, blades project out from said hub, radially, characterised in that, said
blades are helical blades positioned at a pre-defined angle in relation to

lateral circumference of said hub.
6. A low noise induction motors with bidirectional fan as claimed in claim 5 wherein, said pre-defined angle of each of said blades is in correlation with the number of blades that are attached at said hub.
7. A low noise induction motors with bidirectional fan as claimed in claim 5 wherein, said blade is a substantially trapezoidal blade with parallel curvilinear edges with one internal edge adapted to join to said hub and one external edge forming an external circumference of said fan.
8. A low noise induction motors with bidirectional fan as claimed in claim 5 wherein, said blade includes an internal face and an external face such that said internal face and said external face are planar surfaces.