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
A dual stator radial flux motor
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTORS
Ekram Samsul and Patwardhan Vinay, both of Crompton Greaves Ltd, Advanced Motor Design & Technology Centre, CG Global R and D Centre, Kanjurmarg (East), Mumbai 400 042, 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 dual stator radial flux motor
This invention also relates to a method of making a dual stator radial flux motor.
PRIOR ART DESCRIPTION
JP 3139156 describes a twin stator brushless motor comprising an inner stator and an outer stator located in a casing in spaced apart relationship with each other. A motor shaft is axially disposed within the inner stator and rotatably mounted in the casing. A rotor mounted on a rotor shaft is rotatably disposed between the inner and outer stators. One end of the rotor shaft is fixed to the motor shaft. Due to the cantilever effect of the rotor at the unsupported other end thereof, the rotor will be prone to excessive vibrations and wobbling during operation of the motor, especially at high speeds. Wobbling will generate ripple torque and reduce the speed of operation, performance efficiency and power output of the motor. Besides, the air gap between the rotor and stators will become non-uniform and the motor will start malfunctioning. The rotor may also touch and rub against the stators and damage the stators. Except for the instability under dynamic conditions and consequent disadvantages as described above, the dual stator motor still has several benefits like high torque/weight ratio, high speed, high power output and high efficiency. It also has low L/D ratio and is compact and light weight. Material cost of such motor is also reduced. It is also ideal for driving low inertia loads like fans or pumps.
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OBJECTS OF THE INVENTION
An object of the invention is to provide a dual stator radial flux motor which is stable and prevents wobbling of the rotor thereof under dynamic conditions.
Another object of the invention is to provide a dual stator radial flux motor which has improved desirable benefits of a dual stator motor.
Another object of the invention is to provide a dual stator radial flux motor which is simple in construction and operation.
Another object of the invention is to provide a method of making a dual stator radial flux motor which is stable and prevents wobbling of the rotor thereof under dynamic conditions and gives improved desirable benefits of a dual stator motor.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention there is provided a dual stator radial flux motor comprising a housing mounted on a base plate, a drive end endshield and a non-drive end endshield fitted to the housing and base plate at the drive end and non-drive end of the motor, respectively, a cylindrical inner stator disposed in the housing axially and fitted to the non-drive end endshield, a cylindrical outer stator disposed over the inner stator in spaced apart relationship therewith and fitted in the base plate and housing, a motor shaft rotatably supported in the drive end endshield coaxially with the inner stator, the inner
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end of the motor shaft protruding into the housing and the outer end of the motor shaft protruding out of the housing and a cylindrical rotor mounted on a rotor shaft and rotatably disposed in the spacing between the inner stator and outer stator describing gaps with the outer circumference of the inner stator and inner circumference of the outer stator, one end of the rotor shaft being fitted to the inner end of the motor shaft and the other end of the rotor shaft being rotatably supported in the non-drive end endshield.
According to the invention there is also provided a method of making a dual stator radial flux motor, the method comprising disposing the cylindrical rotor of the motor rotatably between the cylindrical inner and outer stators of the motor describing air gaps with the outer circumference of the inner stator and inner circumference of the outer stator and supporting the rotor against cantilever effect at both ends thereof.
The following is a detailed description of the invention with reference to the accompanying drawings, in which the sole Fig 1 is a crossectional view of a dual stator radial flux motor according to an embodiment of the invention. The motor 1 as illustrated in Fig 1 comprises a housing 2 mounted on a base plate 3. 4 and 5 are a drive end endshield and a non-drive end endshiled fitted to the housing and base plate at the drive end and non-drive end of the motor respectively. 6 is a cylindrical inner stator mounted on a support rod 7 axially disposed in the housing and fitted to the non-drive end shield 5. The inner stator is further supported on the non-drive end shield by reinforcing ribs 8. 9 is a cylindrical outer stator disposed over the inner stator in spaced apart relationship therewith and fitted in the base plate and housing. 10 is a motor shaft rotatably supported in the drive end endshield using bearing 11. The inner end of the motor shaft protrudes
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into the housing and the outer end of the motor shaft protrudes out of the housing. 12 is a cylindrical rotor mounted on a U-shaped rotor shaft 13 and rotatably disposed in the spacing between the inner and outer stators describing gaps (not shown) with the outer circumference of the inner stator and inner circumference of the outer stator. One end of the rotor shaft is fixed to the inner end of the motor shaft and the other end of the rotor shaft is rotatably held in the non-drive end endshield using bearings 14. 15 is a support member disposed in the housing axially spaced apart from the drive end endshield and fitted to the base plate and the housing. Motor shaft is further rotatably held in the support member using bearing 16. The rotor is further supported at the inner end of the motor shaft by reinforcing ribs 17. The rotor is supported against cantilever effect at both ends thereof on the motor shaft and non-drive end shield. Therefore, the rotor is dynamically balanced and stable even at high speeds of operation of the motor. As the cantilever effect of the motor has been eliminated there will not be any wobbling of the rotor. The air gap between the rotor and stators is maintained and malfunctioning of the motor is prevented. Chances of the rotor touching and rubbing against the stators and damage to the stators are also prevented. The speed of operation, power output and performance efficiency of the motor are improved. The motor of the invention is also endowed with beneficial advantages like high torque/weight ratio and low L/D ratio. It is compact and light weight. Material cost of the motor is also reduced. It is ideal for driving low inertia loads like fans or pumps.
The basic invention is in the elimination of the cantilever effect of the rotor of the motor. The non-cantilever support for the rotor for eliminating the cantilever effect as illustrated in the drawings may be different. Instead of reinforcing ribs 8 and reinforcing ribs 17 other support means may be used for supporting the stator and rotor. Support member 15
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and the bearing 16 are optional. The rotor shaft shape and configuration may be different. Variations in the construction of the motor for achieving the objects of the invention which are obvious to those who skilled in the art, are to be construed and understood to be within the scope of the invention.
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We Claim:
1. A dual stator radial flux motor comprising a housing mounted on a base plate, a drive end endshield and a non-drive end endshield fitted to the housing and base plate at the drive end and non-drive end of the motor, respectively, a cylindrical inner stator disposed in the housing axially and fitted to the non-drive end endshield, a cylindrical outer stator disposed over the inner stator in spaced apart relationship therewith and fitted in the base plate and housing, a motor shaft rotatably supported in the drive end endshield coaxially with the inner stator, the inner end of the motor shaft protruding into the housing and the outer end of the motor shaft protruding out of the housing and a cylindrical rotor mounted on a rotor shaft and rotatably disposed in the spacing between the inner stator and outer stator describing gaps with the outer circumference of the inner stator and inner circumference of the outer stator, one end of the rotor shaft being fitted to the inner end of the motor shaft and the other end of the rotor shaft being rotatably supported in the non-drive end endshield.
2. The motor as claimed in claim 1, wherein the rotor shaft is U-shaped, the motor shaft is further rotatably supported in a support member disposed in the housing axially spaced apart from the drive end endshield and fitted to the base plate and the housing, the inner stator is mounted on a support rod disposed in the housing coaxially with the motor shaft and fitted to the non-drive end endshield, the motor shaft side of the rotor is further supported on the inner end of the motor shaft and the non-drive end endshield side of the inner stator is further supported on the non-drive end endshield.
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3. A method of making a dual stator radial flux motor, the method comprising disposing the cylindrical rotor of the motor rotatably between the cylindrical inner and outer stators of the motor describing air gaps with the outer circumference of the inner stator and inner circumference of the outer stator and supporting the rotor against cantilever effect at both ends thereof.
Dated this 6th day of September 2007.
Crompton Greaves Limited By their Agent & Attorney

(Jose Madan)
of Khaitan &Co
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ABSTRACT
There is provided a dual stator radial flux motor (1) comprising a housing (2) mounted on a base plate (3). A drive end endshield (4) and a non-drive end endshield (5) are fitted to the housing and base plate at the drive end and non-drive end of the motor, respectively. A cylindrical inner stator (6) is disposed in the housing axially and fitted to the non-drive end endshield. A cylindrical outer stator (9) is disposed over the inner stator in spaced apart relationship therewith and fitted in the base plate and housing. A motor shaft (10) is rotatably supported in the drive end endshield coaxially with the inner stator. The inner end of the motor shaft protrudes into the housing and the outer end of the motor shaft protrudes out of the housing. A cylindrical rotor (12) is mounted on a rotor shaft (13) and rotatably disposed in the spacing between the inner stator and outer stator describing gaps with the outer circumference of the inner stator and inner circumference of the outer stator. One end of the rotor shaft is fitted to the inner end of the motor shaft and the other end of the rotor shaft is rotatably supported in the non-drive end endshield using bearings (14) (Fig 1). Also a method of making a dual stator radial flux motor. The method comprises disposing the cylindrical rotor of the motor rotatably between the cylindrical inner and outer stators of the motor describing air gaps with the outer circumference of the inner stator and inner circumference of the outer stator and supporting the rotor against cantilever effect at both ends thereof.