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
Stator pack of an external rotor motor
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai - 400 030, Maharashtra, India, an Indian Company
INVENTOR
Kamble Deepak Gajanan, Crompton Greaves Limited, Engineering R&D, Kanjurmarg (East), Mumbai 400042, Maharashtra, India, an 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 THE INVENTION
This invention relates to a stator pack of an external rotor motor.
BACKGROUND OF THE INVENTION
Stator pack of an external rotor motor like external rotor AC motor or external rotor brushless DC motor comprises a plurality of laminations stacked to the required core length and riveted together. Each of the laminations comprises a ring and a shaft mounting portion with a shaft hole at the center of the ring in spaced apart relationship. The ring and shaft mounting portion are held together by integrally formed radially spaced nibs or ribs. The ring comprises a plurality of stator slots around the circumference thereof in radially spaced apart relationship and a plurality of rivet holes in radially spaced apart relationship. Because of the ribs and shaft mounting portion, each of the laminations comprises a large quantity of material and increases the material cost of the stator pack. Stacking of the laminations aligned with the rivet holes and riveting the laminations together is time consuming and inconvenient and cumbersome to carry out. As a result, productivity of the stator pack is reduced. As the laminations are held together only by the rivets, the stator pack is not mechanically very strong and rigid. There are also chances for the outer laminations to be damaged while being handled.
OBJECTS OF THE INVENTION
An object of the invention is to provide a stator pack of an external rotor motor, which stator pack comprises reduced material and reduces the material cost.

Another object of the invention is to provide a stator pack of an external rotor motor, which stator pack renders its assembly easy and convenient and increases the productivity.
Another object of the invention is to provide a stator pack of an external rotor motor, which stator pack is mechanically strong and rigid and is not prone to be damaged during handling.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention there is provided a stator pack of an external rotor motor, the
stator pack comprising a plurality of laminations sandwiched between a pair of stator
holders riveted together, the stator holders each being made of a magnetic material and
having a shaft hole at the center thereof fitted with a bush and a shaft fitted within the
bush.
The following is a detailed description of the invention with reference to the accompanying drawings, in which :
Fig 1 is an isometric view of the stator pack according to an embodiment of the invention;
Fig 2 is a crosssectional view of the stator pack of Fig 1;
Fig 3 is an isometric view of a lamination of the stator pack of Fig 1;

Fig 4 is an isometric view of a stator holder of the stator pack of Fig 1;
Fig 5 is a crosssectional view of the stator holder of Fig 4; and
Fig 6 is an exploded of the stator pack of Fig 1.
The stator pack 1 as illustrated in Figs 1 to 6 of the accompanying drawings comprises a
pair of stator holders 2 made of magnetic material selected from mild steel, .
Preferably, the stator holder is made of mild steel. Each of the stator holders comprises a rim 3 having a radially extending portion 3a, a laterally extending portion 3b and an upwardly extending portion 3c. The stator holder further comprises a shaft mounting portion 4 at the center thereof in spaced apart relationship with the rim. The shaft mounting portion comprises a shaft hole 5 and a collar 6 extending from the outer surface of the shaft mounting portion. The rim and the shaft mounting portion of the stator holder are held together by integrally formed radially spaced apart ribs 7. The stator holder is also provided with a plurality of rivet holes 8a and 8b in the radially extending portion 3a of the rim and the shaft mounting portion thereof, respectively. 9 represents reinforcing lugs for some of the rivet holes 8a. The stator pack also comprises a plurality of laminations 10 (only two laminations have been shown in Fig 6 for brevity and clarity) sandwiched between the stator holders. Each of the laminations comprises a ring 11 having a plurality of stator slots 12 around the circumference thereof in radially spaced apart relationship. Part of the laminations 10 are assembled on the laterally extending portion 3b of one stator holder 2 and the remaining laminations are assembled on the laterally extending portion 3b of the other stator holder 2. The stator holders are riveted together with rivets 13 with a bush 14 located in the shaft holes in the stator holders and

respective collars of the stator holders. A shaft 15 is inserted in the bush and rigidly located in the bush by a shaft key 16 engaged in matching key ways 17 and 18 provided in the bush and in the shaft, respectively. The invention eliminates shaft mounting portion and ribs of individual laminations and the material and material cost of the laminations is thus reduced besides simplying the construction of the laminations. The stator pack can be easily and conveniently assembled by simply locating the laminations on the stator holders and riveting the stator holders together. Therefore, assembly time of the stator pack is reduced and productivity of the stator pack is increased besides rendering the assembly easy and convenient. Because of the stator holders, rigidity and mechanical strength of the stator pack is increased. Damage to the outer laminations during handling is also reduced.
The above embodiment is by way of example of the invention and should not be construed and understood to be limiting the scope of the invention. The stator holder configuration and construction can be different. Embodiments comprising such variations are obvious to those skilled in the art and the scope of the invention should be construed and understood to include such variations.

We claim :
1) A stator pack of an external rotor motor, the stator pack comprising a plurality of laminations sandwiched between a pair of stator holders riveted together, the stator holders each being made of a magnetic material and having a shaft hole at the center thereof fitted with a bush and a shaft fitted within the bush.
2) The stator pack as claimed in claim 1, wherein the stator holders each comprises a rim comprising a radially extending portion, a laterally extending portion and an upwardly extending portion, a shaft mounting portion at the center of the rim provided with a shaft hole and a collar extending from the outer face of the shaft mounting portion, the rim and the shaft mounting portion being held together by integrally formed radially spaced apart ribs, the upwardly extending portion of the rim and the shaft mounting portion being provided with rivet holes, each of the laminations comprises a ring having a plurality of stator slots around the circumference thereof in radially spaced apart relationship, the laminations being disposed over the laterally extending portions of the stator holders and being held together by riveting the stator holders together with a bush inserted in the shaft holes in the stator holders and the respective collars and a shaft located in the bush.
3) The stator pack as claimed in claiml or 2, wherein the stator holders each comprises mild steel.
Dated this 19 day of January 2009