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 INVENTION
Skewed stator for an electric motor and method of making the same
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 025, Maharashtra, India, an Indian Company
INVENTOR
Kamble Deepak Gajanan, Crompton Greaves Ltd , Engineering Group,
CG Global R&D Centre, Kanjur (E), Mumbai 400042, Maharashtra, India, 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 INVENTION
This invention relates to a skewed stator for an electric motor and a method of making the
same.
BACKGROUND OF INVENTION
Electric motors comprising skewed stators are used in heavy duty applications in which high torques are to be delivered, typically electric vehicles. A skewed stator comprises a skewed stator core and conductor coils wound in the stator slots formed in the skewed stator core. A skewed stator is generally formed by stacking stator core laminations one above another concentrically, skewing the stack of laminations in a skewing fixture and casting the skewed stack of laminations with molten aluminium in a pressure die casting machine. The laminations will have punched therein motor shaft holes at the center and stator slots at the outer circumference thereof prior to stacking them together. The skewed stator core formed is removed from the skewing fixture and conductor coils are wound in the stator slots to form skewed stator. Pressure die casting is cumbersome to carry out and reduces productivity as it is time consuming. It consumes energy and is also expensive. It requires separate die and skewing fixture for each stack of laminations and aluminium for the die casting. During pressure die casting, variations occur in the properties of the molten aluminium due to variations in the atmospheric conditions at different times of the day. As a result of variations in the atmospheric conditions, parameters like die temperature, atmospheric temperature or molten aluminium temperature change at different times of the day. Due to variations in the properties of the molten aluminium, the magnetic properties of the skewed stator change thereby causing variations in the performance of the skewed motors comprising the same. Unless the variations in the magnetic properties are within permissible limits, the stator cores are
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liable to be rejected. Rejection rate of skewed stator cores formed by pressure die casting is normally high thereby incurring heavy losses and further reducing productivity. Besides, in case of damage to any stator laminations, there is no way it can be replaced as the laminations are cast together with aluminium.
US 2006/0267443 Al describes skewed stator and method of forming the same. Conductor coils are inserted in the stator slots at the inner circumference of the stator core formed by stacking core laminations one above another. The stator slots are skewed by rotating the core laminations by engaging a tool in the engaging grooves formed at the outer circumference of the stator core. The core laminations are fixed in position by welding them together. Method of making skewed stator as described above also reduces productivity as it is time consuming. It also consumes energy and is expensive because of the welding involved. As the stator is welded, replacement of damaged stator laminations is also not possible. Welding also makes the method cumbersome to carry out.
OBJECTS OF INVENTION
An object of the invention is to provide a skewed stator for an electric motor, which stator
is simple in construction and is cost effective.
Another object of the invention is to provide a skewed stator for an electric motor, which stator can be easily disassembled allowing easy replacement of damaged stator core laminations.
Another object of the invention is to provide a method of making a skewed stator for an electric motor, which method is simple and easy to carry out, reduces production time and
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increases productivity, does not consume energy, prevents variations in the magnetic properties of the stator and consequent rejection and allows the stator to be easily disassembled so as to facilitate easy replacement of damaged stator core laminations.
DETAILED DESCRIPTION OF INVENTION
According to the invention there is provided a skewed stator for an electric motor, the stator comprising a cylindrical hub with a motor shaft hole at the center thereof and a plurality of stator core laminations stacked one above another around the hub at a skewed angle, the core laminations each having punched therein a center hole corresponding to the outer diameter of the hub and a plurality of circumferentially spaced stator slots at the outer circumference thereof, the stator core laminations being tightly held together by mechanical means.
Preferably, the mechanical means is detachable.
According to an embodiment of the invention, the hub comprises a rim at one end thereof and a threading externally at the other end thereof, the hub further comprising a skewed keyslot externally extending along the length thereof and terminating in the rim and a key inserted in the skewed keyslot with its one end located in the keyslot terminating in the rim and the mechanical means comprises a tightening nut provided with threading at the inner circumference thereof and engaging grooves at the outer circumference thereof, the stator core laminations further comprising an engaging opening at the inner circumference thereof corresponding to the key and the laminations being stacked one above another with the engaging opening aligned with and engaged over the key, the laminations being
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tightly held on the hub by engaging the tightening nut around the other end of the hub and tightening the tightening nut against the stator core laminations.
According to the invention there is also provided a method of making a skewed stator for an electric motor, the method comprising stacking core laminations one above another around a cylindrical hub with a motor shaft hole at the center thereof, the core laminations being stacked at a skewed angle along the length of the hub, the core laminations each being punched with a center hole corresponding to the outer diameter of the hub and a plurality of circumferentially spaced stator slots at the outer circumference thereof; and mechanically holding the core laminations tightly together at the skewed angle.
Preferably, the core laminations are tightly held together at the skewed angle mechanically detachably.
The following is a detailed description of the invention with reference to the accompanying drawings, in which :
Fig 1 is an exploded view of a skewed stator for an electric motor according to an embodiment of the invention; and
Figs 2, 3 and 4 are isometric view, plan view and elevation of the skewed stator of Fig 1, respectively.
The skewed stator 1 as illustrated in Figs 1 to 4 of the accompanying drawings comprises a cylindrical hub 2 with a motor shaft hole 3 at the center thereof. 3a is a keyway in the
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motor shaft hole 3. 4 is a rim provided at one end of the hub. The other end of the hub is provided with a threading marked 5 externally. 6 is a skewed or inclined keyslot provided externally along the length of the hub and terminating in the rim. 7 is a key inserted in the keyslot with its one end located in the keyslot terminating in the rim. A plurality of stator core laminations marked 8 have each punched therein a center hole 9 corresponding to the outer diameter of the hub and a plurality of circumferentially spaced stator slots 10 at the outer circumference thereof. The laminations have also punched therein an engaging opening 11 at the inner circumference thereof corresponding to the key. The stator core laminations are stacked one above another around the hub with the engaging openings aligned with and engaged over the key. 12 is a tightening nut internally threaded corresponding to the threading at the other end of the hub. The stator core laminations are tightly held together by engaging the nut around the other end of the hub and rotating and tightening the nut 12 against the laminations. The engaging grooves 13 at the outer circumference of the nut provide a grip for a tool (not shown) used for rotating and tightening the tightening nut. After assembling the stator core, conductor coils (not shown) are wound in the stator slots to form the skewed stator.
The skewed stator of the invention is simple in construction in that the core laminations can be easily and conveniently stacked one above another at a skewed or inclined angle and tightly held together with the tightening nut. The invention eliminates the skewing fixture and pressure die casting and welding. It reduces production time and increases productivity, does not consume energy and is cost effective. As pressure die casting is eliminated, variations in the magnetic properties of the stator core due to variations in the atmospheric conditions and consequent rejection are eliminated and productivity is further increased. The tightening nut can be easily removed by rotating it in the opposite
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direction. Because of the tightening nut being detachable, replacement of damaged stator core laminations, if any, is very easily possible. The hub is made of material such as aluminium precasted and machined. The key is made of materials such as aluminium or steel. The tightening nut is made of materials such as aluminium or mild steel. Depending upon the skewing or inclination required for the coil conductors, the skewed or inclined angle of the keyslot and consequently that of the key and core laminations is selected.
The invention is in the stacking of the core laminations one above another at the skewed or inclined angle required and holding the stack of laminations tightly mechanically if desired removably. The mechanical means for rigidly holding the core laminations on the hub can be of a different construction and configuration. The mechanical means can be detachable or non-detachable. The method of the invention can be designed to hold the core laminations on the hub detachably or non-detachably. The keyway 3a in the motor shaft hole 3 is optional in that it may not be required in the case of low torque transmission motors. In the case of low torque transmission motors, the stator can be fitted on the motor shaft without key and keyway. Obvious variations in the construction and configuration of the skewed stator and in the method whereby the laminations are stacked one above another at a skewed angle and held tightly whether removably or non-removably are to be construed and understood to be within the scope of the invention.
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We claim:
1. A skewed stator for an electric motor, the stator comprising a cylindrical magnetic material hub with a motor shaft hole at the center thereof and a plurality of stator core laminations stacked one above another around the hub at a skewed angle, the core laminations each having punched therein a center hole corresponding to the outer diameter of the hub and a plurality of circumferentially spaced stator slots at the outer circumference thereof, the stator core laminations being tightly held together by mechanical means.
2. A skewed stator as claimed in claim 1, wherein the mechanical means is detachable.
3. A skewed stator as claimed in claim 1 or 2, wherein the motor shaft hole is provided with a keyway.
4. A skewed stator as claimed in anyone of the claims 1 to 3, wherein the hub comprises a rim at one end thereof and a threading externally at the other end thereof, the hub further comprising a skewed keyslot externally extending along the length thereof and terminating in the rim and a key inserted in the skewed keyslot with its one end located in the keyslot terminating in the rim and the mechanical means comprises a tightening nut provided with threading at the inner circumference thereof and engaging grooves at the outer circumference thereof, the stator core laminations further comprising an engaging opening at the inner circumference thereof corresponding to the key and the laminations being stacked one above another with the engaging opening aligned with and
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engaged over the key, the laminations being tightly held on the hub by engaging the tightening nut around the other end of the hub and tightening the tightening nut against the stator core laminations.
5. A skewed stator as claimed in any one of the claims 1 to 4, wherein the hub is made of aluminium precasted and machined.
6. A method of making a skewed stator for an electric motor, the method comprising stacking core laminations one above another around a cylindrical hub with a motor shaft hole at the center thereof, the core laminations being stacked at a skewed angle along the length of the hub, the core laminations each being punched with a center hole corresponding to the outer diameter of the hub and a plurality of circumferentially spaced stator slots at the outer circumference thereof; and mechanically holding the core laminations tightly together at the skewed angle.
7. A method as claimed in claim 6, wherein the motor shaft hole in the hub is provided with a keyway.
8. A method as claimed in claim 6 or 7, wherein the core laminations are tightly together at the skewed angle mechanically detachably.
Dated this 21st day of February 2007.
(Jose M A)
of Khaitan & Co Agent for the Applicants
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Abstract
A skewed stator (1) for an electric motor. The stator comprises a cylindrical hub (2) with a motor shaft hole (3) at the center thereof and a plurality of stator core laminations (8) stacked one above another around the hub at a skewed angle. The core laminations each have punched therein a center hole (9) corresponding to the outer diameter of the hub and a plurality of circumferentially spaced stator slots (10) at the outer circumference thereof. The stator core laminations are tightly held together by mechanical means (12). (Fig 1).