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
Method of making the rotor of an external controller mounted BLDC motor
INVENTORS
Saple Chandrashekhar and Patil Vinod Padmakar, both Indian nationals and both of Crompton Greaves Ltd, Corporate R&D and Quality, Industrial Design Centre, Kanjur (E), Mumbai - 400042, Maharashtra, India
APPLICANTS
Name : CROMPTON GREAVES LIMITED
Nationality : Indian Company
Address : CG House, Dr Annie Besant Road, Prabhadevi, Mumbai 400025, Maharashtra, India
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 INVENTION
This invention relates to a method of making the rotor of an external controller mounted BLDC motor.
This invention also relates to the rotor of an external controller mounted BLDC motor made by the method and to an external controller mounted BLDC motor comprising the rotor made by the method.
BACKGROUND OF INVENTION
An external controller mounted BLDC (Brush Less Direct Current) motor comprises a rotor mounted on the motor shaft and comprising a rotor magnet ring located over a rotor core. The rotor is magnetized in a magnetization fixture and mounted on the shaft manually after marking the dividing line (centre line) between each pair of opposite magnetic poles of the rotor on the rotor using pole paper. During mounting, alignment of the dividing line between each pair of opposite magnetic poles of the rotor with the center line of a reference flat portion formed on the drive end or non-drive end of the shaft for mounting the sensor magnet of the motor externally of the motor, is carried out by trial and error and it is practically difficult manually to align precisely the dividing line between each pair of opposite magnetic poles of the rotor with the center line of the flat portion. Therefore,, mounting of the rotor on the shaft is time consuming and cumbersome and reduces productivity and increases labour and cost. It is also rather difficult to maintain accuracy and repeatability of mounting of the rotor on the motor shaft. The sensor magnet is magnetized separately and mounted on the motor shaft externally of the motor after marking the dividing line
2

(centre line) between each pair of opposite magnetic poles of the sensor magnet using pole paper. Due to angular displacement or misalignment of the dividing lines between each pair of opposite magnetic poles of the rotor magnets with the centre line of the flat portion, angular displacement or misalignment of the dividing lines between each pair of opposite magnetic poles of the rotor magnets and dividing lines between each pair of opposite magnetic poles of the sensor magnets also occurs and polarity of the sensor magnets as sensed by the hall sensors fixed to the drive end or non-drive end side end shield of the motor and output to the controller of the motor mounted on the respective end shield does not exactly match the polarity of the rotor magnets. Because of this mismatch of polarities, instances of switching on and off of the stator windings by the controller depending upon the polarity of the sensor magnets as sensed by the hall sensors are not accurate leading to lagging and reducing the torque and efficiency of the motor.
OBJECTS OF INVENTION
An object of the invention is to provide a method of making the rotor of an
external controller mounted BLDC motor, which method renders mounting
of the rotor on the motor shaft easy and convenient, reduces the mounting
time, labour and cost and increases productivity and enables accuracy and
repeatability of mounting of the rotor to be maintained. ,t
Another object of the invention is to provide a method of making the rotor of an external controller mounted BLDC motor, which method enables to, improve the torque and efficiency of the motor.
3

Another object of the invention is to provide the rotor of an external controller mounted BLDC motor made by the above method.
Another object of the invention is to provide a BLDC motor comprising the rotor made by the above method.
DETAILED DESCRIPTION OF INVENTION
According to the invention there is provided a method of making the rotor of an external controller mounted BLDC motor, the method comprising mounting the rotor on the motor shaft followed by magnetising the rotor mounted on the motor shaft in a magnetization fixture and marking the dividing lines between each pair of opposite magnetic poles of the rotor using pole paper in line with the center line of a reference flat portion provided at the drive end or non-drive end of the motor shaft for mounting the sensor magnet of the motor with the dividing line between each pair of opposite magnetic poles of the sensor magnets aligned with the center line of the flat portion.
According to the invention there is also provided the rotor of an external controller mounted BLDC motor made by the above method.
According to the invention there is also provided an external controller mounted BLDC motor comprising the rotor made by the above method.
The invention is described in detail with reference to the accompanying drawings, in which Figs 1 and 2 are, respectively, isometric view, and exploded view of the rotor of an external controller mounted BLDC motor
4

according to an exemplary embodiment of the invention. The rotor 1 as illustrated in the accompanying drawings comprises a rotor magnet ring 2 located over a rotor core 3 and mounted on the motor shaft 4 manually. 5 is a flat portion formed on the motor shaft at the drive end or non-drive end thereof. The rotor mounted on the motor shaft is magnetized into four poles (two pairs of opposite magnetic poles) in a magnetization fixture (not shown) and the dividing lines between each pair of opposite magnetic poles of the rotor are marked using pole paper with the dividing lines aligned with the center line of the flat portion. The dividing lines passing through the each pair of opposite magnetic poles of the rotor magnet and the center of the flat portion are marked 6 and 7. 8 is a hole in the rotor for mounting it on the motor shaft. The sensor magnet (not shown) after magnetization and marking of the dividing lines between each pair of opposite magnetic poles thereof is manually mounted over the flat portion at the drive end or non-drive end of the motor shaft with the dividing lines between each pair of opposite magnetic poles of the sensor magnet aligned with the center line of the flat portion.
According to the invention the rotor is magnetized and the dividing lines between each pair of opposite magnetic poles are marked and aligned precisely with the centre line of the flat portion after it is mounted on the motor shaft. Therefore, alignment of dividing lines between each pair of opposite magnetic poles of the rotor mounted on the motor shaft with the center line of the flat portion can be carried out easily and conveniently and within reduced time. Also labour and effort required for the alignment are reduced, productivity is increased and cost of production is reduced. Accuracy and repeatability of mounting of the rotor also can be maintained.
5

As the dividing lines between each pair of opposite magnetic poles of the rotor are precisely aligned with the center line of the flat portion, angular displacement or misalignment of the dividing lines between each pair of opposite magnetic poles of the rotor magnets and the polarities of the magnets is also reduced. As a result, during operation of the motor depending upon the polarity of the sensor magnets as sensed by the hall sensors and output to the controller, the controller switches on and off the respective stator coils in the stator accurately so as to prevent lagging and improve the torque and efficiency of the motor.
The flat portion is only a reference for aligning the sensor magnets with rotor magnets and can be any other reference or can be a symbol or marking, The rotor need not be four pole. There can be more number of pairs of opposite magnetic poles for the rotor and corresponding number of poles for the sensor magnet. Such variations in the construction of the rotor are obvious to those skilled in the art and the scope of the invention should be construed and understood accordingly.
6

We claim :
1) A method of making the rotor of an external controller mounted BLDC motor, the method comprising mounting the rotor on the motor shaft followed by magnetising the rotor mounted on the motor shaft in a magnetization fixture and marking the dividing lines between each pair of opposite magnetic poles of the rotor using pole paper in line with the center line of a reference flat portion provided at the drive end or non-drive end of the motor shaft for mounting the sensor magnet of the motor with the dividing line between each pair of opposite magnetic poles of the sensor magnets aligned with the center line of the flat portion.
2) Rotor of an external controller mounted BLDC motor made by the method as claimed in claim 1.
3) An external controller mounted BLDC motor comprising the rotor made by the method as claimed in claim 1.
Dated this 31st day of August 2006

(Jose M A)
of Khaitan& Co
Agent for the Applicants
7

ABSTRACT
A method of making the rotor of an external controller mounted BLDC motor. The method comprises mounting the rotor on the motor shaft followed by magnetising the rotor mounted on the motor shaft in a magnetization fixture and marking the dividing lines between each pair of opposite magnetic poles of the rotor using pole paper in line with the center line of a reference flat portion provided at the drive end or non-drive end of the motor shaft for mounting the sensor magnet of the motor.