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 shaft dual radial gap electric motor
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTORS
Dr Ekram Samsul and Patwardhan Vinay, both of Crompton Greaves Ltd, Advanced Motor Design & Technology Centre, CG Global R&D Centre, Kanjur Marg (East), 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 dual shaft dual radial gap electric motor.
PRIOR ART DESCRIPTION
There are several electrical applications which require electric motors of different speeds and power outputs for their optimal and efficient operation. Typical examples are electric motors required for driving the blower and evaporator of an air conditioner, pumping two liquids of different viscosities into a mixing tank or pumping up a liquid like water to different heights. In order to avoid wastage of power and improve efficiency of operation and operational control, ideally two independent electric motors of appropriate ratings are to be used for such applications. However, two independent motors will require two separate controllers and will increase cost and space requirements for their occupation. The above problems can be partly addressed and overcome by using a dual shaft single radial gap electric motor which essentially comprises a rotor mounted on a shaft and rotatably held in a stator which is located in a housing of the motor. The shaft is rotatably held in a pair of endshields of the motor, each fitted at each end of the housing. The shaft ends protrude out of the endshields to form two shafts. In such a motor, both the shafts rotate at the same speed and give the same power output. Therefore, if a dual shaft single radial gap motor is used in electrical applications which require different speeds and power outputs, there will be wastage of power output. Efficiency and controllability of the motor also will be reduced. One of the shafts can be made to rotate at a lower speed by using a gearing arrangement which will, however, increase the cost and size of the motor. Dual shaft axial gap electric motors comprising two concentric shafts are known (US 5117141 and US 7256524B2). Axial gap electric motors differ from radial gap electric motors both in terms of construction and operating


principles. Radial gap electric motors are preferable to axial gap electric motors because of their advantages like simplicity of construction and cost benefit.
OBJECTS OF THE INVENTION
An object of the invention is to provide a dual shaft dual radial gap electric motor, in
which the shafts can rotate at the same speed or at variable speeds and give variable
power output because of which it can be ideally and optionally used in electrical
applications which require the same or different speeds of operation and different power
outputs.
Another object of the invention is to provide a dual shaft dual radial gap electric motor, which has improved efficiency and controllability.
Another object of the invention is to provide a dual shaft dual radial gap electric motor, which is compact, requires reduced space for its occupation and is cost effective.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention there is provided a dual shaft dual radial gap electric motor comprising a pair of shafts disposed in a motor housing end to end axially, each of the two shafts being rotatably held in an end shield fitted at each end of the motor housing, the inner ends of the shafts being mutually rotatably engaged to each other and the outer ends of the shafts protruding out of the respective end shields, a dual stator comprising a cylindrical shaped stator body disposed over the shafts spaced therefrom and mounted to one of the end shields at one end thereof, the other end of the stator body being mounted to a non-cantilever support member disposed over one of the shafts with the said one shaft


being rotatably held in the non-cantilever support member, the stator further comprising an inner stator winding located at the inner surface of the stator body and an outer stator winding located at the outer surface of the stator body, a dual rotor comprising a cup shaped rotor body disposed over the stator body spaced therefrom and mounted on said one shaft, the dual rotor further comprising a plurality of inner rotor magnets mounted on the other shaft describing a radial gap with the inner stator winding and a plurality of outer rotor magnets mounted on the inner surface of the rotor body describing a radial gap with the outer stator winding.
The following is a detailed description of the invention with reference to the accompanying drawings, in which :
Fig 1 is a crosssectional view of the dual shaft dual radial gap electric motor according to an embodiment of the invention; and
Fig 2 is side view of the dual stator of the electric motor of Fig 1,
The dual shaft dual radial gap electric motor 1 as illustrated in Figs 1 and 2 of the accompanying drawings comprises a pair of shafts 2 and 3 disposed in a motor housing 4 end to end axially. Shafts 2 and 3 are rotatably held in end shields 5 and 6 using bearings 7 and 8, respectively. The end shields are fitted at the ends of the housing and the inner ends of the shafts are mutually or independently rotatably engaged to each other using bearing 9. The outer ends of the shafts protrude out of the respective end shields. 10 is a dual stator comprising a cylindrical shaped stator body 11 disposed over the shafts spaced therefrom and mounted to endshield 5 at one end thereof with the help of brackets


12. The other end of the stator body is mounted to a non-cantilever support member 13 disposed over shaft 3 with the shaft 3 rotatably held in the non-cantilever support member using bearing 14. The stator also comprises an inner stator winding 15 located at the inner surface of the stator body and an outer stator winding 16 located at the outer surface of the stator body. 17 is a dual rotor comprising a cupshaped body 18 disposed over the stator body spaced therefrom and mounted on shaft 3. The dual rotor also comprises a plurality of inner rotor magnets 19 mounted on the shaft 3 describing a radial gap 20 with the inner stator winding and a plurality of outer rotor magnets 21 mounted on the inner surface of the rotor body describing a radial gap 22 with the outer stator winding.
The inner stator coil is energized to drive shaft 2 and the outer stator coil is energized to drive shaft 3. Energisation of the stator coils is carried out by a common motor controller or two impendent motor controllers as required so as to control the speed of rotation of both the shafts independently. The shafts may be made to rotate at the same speed or at two different speeds as required by appropriately energising the inner and outer stator windings by the common controller or respective controllers as the case may be. The power outputs of the shafts will be different depending upon the LD ratio, where L is the length of the stator winding and D is the diameter of the gap around the inner stator winding or the gap around the outer stator winding. Drives are taken from the two shafts to drive two loads (not shown).
The electric motor of the invention is compact in that it integrates twin motors to give two drives of the same speeds or variable speeds and two power outputs. It requires reduced space for its occupation and is ideal for use in electrical applications which require two


drives and two power outputs, where the operational speed of the two drives may be the same or different. It enables to make optimal and efficient use of the speed and power outputs of the motor in a given electrical application. The integrated construction of the motor eliminates the gearing arrangement. It also reduces the overall cost besides improving the controllability of the motor.
The shaft 2 can be extended over the shaft 3 and the non-cantilever support member can be disposed over shaft 2 instead of shaft 3. The configuration / geometry of brackets 12 can vary. Such variations in the construction of the motor are obvious to those skilled in the art and are to be construed and understood to be within the scope and spirit of the invention.


We claim:

1. A dual shaft dual radial gap electric motor comprising a pair of shafts disposed in a motor housing end to end axially, each of the two shafts being rotatably held in an end shield fitted at each end of the motor housing, the inner ends of the shafts being mutually rotatably engaged to each other and the outer ends of the shafts protruding out of the respective end shields, a dual stator comprising a cylindrical shaped stator body disposed over the shafts spaced therefrom and mounted to one of the end shields at one end thereof, the other end of the stator body being mounted to a non-cantilever support member disposed over one of the shafts with the said one shaft being rotatably held in the non-cantilever support member, the stator further comprising an inner stator winding located at the inner surface of the stator body and an outer stator winding located at the outer surface of the stator body, a dual rotor comprising a cup shaped rotor body disposed over the stator body spaced therefrom and mounted on said one shaft, the dual rotor further comprising a plurality of inner rotor magnets mounted on the other shaft describing a radial gap with the inner stator winding and a plurality of outer rotor magnets mounted on the inner surface of the rotor body describing a radial gap with the outer stator winding.
2. The electric motor as claimed in claim 1, wherein each of the two shafts is rotatably held in each of the end shields using a bearing and the inner ends of the shafts are mutually or independently rotatably engaged to each other using a bearing and the said one shaft is rotatably held in the non-cantilever support member using a bearing.




Abstract
A dual shaft dual radial gap electric motor (1) comprising a pair of shafts (2 and 3) disposed in a motor housing (4) end to end axially. Each of the two shafts is rotatably held in an end shield fitted at each end of the motor housing. The inner ends of the shafts are mutually rotatably engaged to each other and the outer ends of the shafts protruding out of the respective end shields (10) is a dual stator comprising a cylindrical shaped stator body (11) disposed over the shafts spaced therefrom and mounted to one of the end shields at one end thereof. The other end of the stator body is mounted to a non-cantilever support member (13) disposed over one of the shafts with the said one shaft rotatably held in the non-cantilever support member. The stator further comprises an inner stator winding (15) located at the inner surface of the stator body and an outer stator winding (16) located at the outer surface of the stator body. (17) is a dual rotor comprising a cup shaped rotor body (18) disposed over the stator body spaced therefrom and mounted on said one shaft. The dual rotor further comprises a plurality of inner rotor magnets (19) mounted on the other shaft describing a radial gap (20) with the inner stator winding and a plurality of outer rotor magnets (21) mounted on the inner surface of the rotor body describing a radial gap (22) with the outer stator winding (Fig 1).