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
Brushless DC motor driven ceiling fan
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTORS
Lohokare Yogesh and Kori Virendra, both of Crompton Greaves Limited, Advance Motor Design and Technology Centre, Global R&D Centre, 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 a brushless DC motor driven ceiling fan.
BACKGROUND OF THE INVENTION
Ceiling fans are conventionally driven by induction motors which have disadvantages like high power consumption. Modern version ceiling fans are advantageously driven by Brushless DC motors or BLDC motors or BL motors because of advantages like low power consumption associated with the Brushless DC motors. Brushless DC motors are also known as electronically commutated motors or EC motors or ECMs.
Brushless DC motors are functionally synchronous motors powered by AC source through an electronic communication system unlike DC motors with mechanical commutators and brushes. A BLDC motor mainly comprises a wound stator and a permanent magnet rotor. In the case of an external rotor BLDC motor, the rotor is disposed outside the stator defining a clearance or air gap therewith. In the case of an internal rotor BLDC motor, the rotor is disposed within the stator defining a clearance therewith.
A BLDC motor driven ceiling fan includes a motor having a housing formed of a top endshield and a bottom endshield fixed together. The top endshield is rotatably held about a fan shaft extending into the housing through a tubular projection projecting down inwardly from the centre of the top of the top endshield, using bearings housed in the tubular projection. The top end shield also comprises a cylindrical extension projecting down inwardly from the periphery of the top end shield concentric with the

tubular projection. A stator is disposed in the housing and mounted to the lower end of the fan shaft. A permanent magnet rotor is disposed in the housing around the stator defining a clearance with the stator and fixed to the inner surface of the cylindrical extension projecting down inwardly from the periphery of the top of the top endshield. A plurality of fan blades are mounted to the top endshield in a spaced apart manner.
During operation of the motor and ceiling fan, the stator windings are energised with a AC source to generate a stator magnetic field in the clearance or air gap between the rotor and stator. Due to interaction of the stator magnetic field and rotor magnetic field, a torque is generated causing the rotor to rotate. As a result, the top end shield rotates with the bottom endshield and the fan blades.
When the rotor rotates and transmits the drive to the top endshield via the cylindrical extension at the periphery of the top endshield, the top endshield rotates about the fan shaft at the centre of the top endshield alongwith the blades. Because of the transmission of the rotary motion from the rotor to the top endshield at the periphery of the top endshield, the top endshield experiences excessive vibration. Due to the excessive vibration of the top endshield, the operation of the fan becomes very noisy and the noise level may become intolerable.
SUMMARY OF THE INVENTION
According to the invention there is provided a brushless DC motor driven ceiling fan comprising a motor having a housing formed of a top endshield and a bottom endshield fixed together and a plurality of fan blades mounted to the top endshield in

a spaced apart relationship with one another, the top endshield being rotatably held about a fan shaft extending into the housing through a tubular projection projecting down inwardly from the centre of the top endshield using bearings housed in the tubular projection, the top endshield further having a cup shaped extension projecting down from the tubular projection concentric with the tubular projection, a wound stator disposed in the housing and mounted to the lower end of the fan shaft and a permanent magnet rotor disposed in the housing around the stator defining a clearance with the stator and mounted to the inner surface of the cup shaped extension.
DETAILED DESCRIPTION OF DRAWINGS
The following is a detailed description of the invention with reference to the accompanying drawings, in which the sole Fig 1 is a cross-sectional elevation of a Brushless DC motor driven ceiling fan according to an embodiment of the invention. The fan 1 comprises a motor 2 having a housing formed of a top endshield 3 and a bottom endshield 4 fixed together with screws 5. A plurality of fan blades 6 are mounted to the top endshield in a spaced apart relationship with one another. The top endshield is rotatably held about a fan shaft 7 extending into the top endshield through a tubular projection 8 projecting down inwardly from the centre of the top of the top endshield using bearings 9 housed in the tubular projection. The top endshield also comprises a cup shaped extension 10 projecting down from the tubular projection concentric with the tubular projection. A wound stator 11 is disposed in the housing and mounted to the lower end of the fan shaft. A permanent magnet rotor 12 is disposed in the housing around the stator defining a clearance or air gap 13 with the stator. The rotor is mounted to the inner surface of the cup shaped extension.

In the case of the brushless DC motor driven ceiling fan of (he invention, the cup shaped extension 10 is projecting down from the tubular projection 8 concentric with the tubular projection and rotor is mounted to the inner surface of the cup shaped extension. Therefore, during operation of the motor and fan, the rotor rotates and the rotary motion is transmitted directly to the tubular projection at the centre of the top endshield via the cup shaped extension. As the rotary motion is directly applied to the centre of the top endshield where the top endshield is rotatably held on the fan shaft, vibration of the top endshield is considerably reduced and the noise level of the motor is also considerably reduced. Further the noise is dampened within the cup shaped extension which has a reduced diameter and volume because of which the dampening effect is high. As a result of all this, the noise level of operation of the motor and fan is substantially reduced.

We claim:
1. A brushless DC motor driven ceiling fan comprising a motor having a housing formed of a top endshield and a bottom endshield fixed together and a plurality of fan blades mounted to the top endshield in a spaced apart relationship with one another, the top endshield being rotatably held about a fan shaft extending into the housing through a tubular projection projecting down inwardly from the centre of the top endshield using bearings housed in the tubular projection, the top endshield further having a cup shaped extension projecting down from the tubular projection concentric with the tubular projection, a wound stator disposed in the housing and mounted to the lower end of the fan shaft and a permanent magnet rotor disposed in the housing around the stator defining a clearance with the stator and mounted to the inner surface of the cup shaped extension.