FIELD OF THE INVENTION
The present invention generally relates to electrical machines and in particular to a
stator core of an axial flux permanent magnet machine (PMM). The present
invention also relates to a method for making stator core of an axial flux permanent
magnet machine (PMM) using cold rolled non-grain oriented silicon (CRNGO Si)
laminated sheet and hardened glass laminated (HGL) rings.
BACKGROUND OF THE INVENTION
A stator core of an axial flux permanent magnet machine (PMM) generally
comprises teeth and a core back. The function of the teeth is to lead the magnetic
flux induced in the teeth by coils arranged round the teeth and thus the teeth
increases the efficiency of the interaction between the stator and a rotor compared
to stator having no teeth. The function of the core back is a provide a return path
for flux.
According to prior art, stator core is made of solid soft magnetic material. The
problem with this type of core is that eddy currents are induced in the stator core.
To reduce the problem of eddy currents, the stator core is made up of laminated
sheet and the laminations are electrically insulated from each other.
There are three different known types of methods available for making a stator core
of an axial flux permanent magnet machine (PMM). The first method is to wind the
cold rolled non-grain oriented silicon (CRNGO Si) steel sheet over a non magnetic
SS-316 ring 301 to a required diameter and placing another non magnetic SS-316
ring 302. The slots are made thereafter by machining or wire cutting as shown in
FIG.3. The second method is first to punch the slots over cold rolled non-grain
oriented silicon (CRNGO Si) steel sheet with variable distances between them and
to wind it into the form of a slotted toroidal core over a non magnetic SS-316 ring
to a required diameter and placing another non magnetic SS-316 ring. The third
technique to form the stator core is to use the trapezoidal segments as shown in
FIG.l with the stator core back as shown in FIG. 2 which is made up of cold rolled
non-grain oriented silicon (CRNGO Si) laminated sheets stacked together.
As the prior art stators use non magnetic SS-316 rings inside and outside the stator
core to reduce the eddy current losses, the weight of the stator core increases.
OBJECTS OF THE INVENTION:
It is therefore, an object of the invention to propose (d), which substantially
reduces weight of the stator core.
Another object of the invention is to propose (d), which reduces the eddy current
losses in the stator core.
A further object of the invention is to propose (d), which simplifies the fabrication
process of the stator core.
SUMMARY OF THE INVENTION
According, there is provided a method for making stator core of an axial flux
permanent magnet machine (PMM), comprising the steps of:
- winding cold rolled non grain oriented silicon (CRNGO - Si) laminated sheet
over a first hardened glass laminate (HGL) ring 401 to configure a required
diameter;
- placing a second hardened glass laminate (HGL) ring 402 over the assembly;
and
- forming slots by machining or wire cutting.
In the inventive process, (hardened glass laminate) HGL rings are used instead of
SS-316 rings inside and outside the stator core to hold the (cold rolled non grain
oriented silicon) CRNGO Si laminations.
It is easy to fabricate the stator core with standard (hardened glass laminate) HGL
rings to eliminate fabricating work which otherwise is unavoidable if SS-316 rings
were used.
Though the SS-316 rings used inside and outside the stator core are non magnetic
in nature, the eddy currents are still induced in it. The eddy currents are not
induced in the present invention because (hardened glass laminate) HGL rings,
which are insulators, are used inside and outside the stator core .
The reduction of weight in the stator core after manufacturing with (hardened glass
laminate) HGL rings is substantial in small stator cores when compared to the stator
core formed with SS-316 rings.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The advantages of the present invention will become apparent from the following
detailed description of embodiments with reference to the accompanying drawings,
in which:
FIG. 1 is a schematic view of a stator core segment formed from a lamination strip
according to the invention.
FIG. 2 is a schematic view of a stator core back.
FIG. 3 is a schematic view of a stator core with SS-316 rings according to prior art.
FIG. 4 is a schematic view of a stator core with (hardened glass laminate) HGL
rings according to the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF
THE INVENTION:
To fabricate a stator core with SS-316 rings 301 and 302 inside and outside, SS-316
rings 301 and 302 have to be made either from solid piece by removing material or
SS-316 plates are to be bent and welded. In the case of smaller diameter stator
cores, bending of SS-316 rings 301 and 302 to the required diameter becomes even
more difficult. Another technique to form the stator core is to use the trapezoidal
segments as shown in FIG.l. The lamination strip 101 of constant thickness is
folded at different distances proportional to the radius. To make the folding 103
easy, the strip has transverse grooves 102 on opposite sides of the alternative
steps. The zigzag laminated segment 104 is finally compressed and fixed with the
stator coreback which is made up of cold rolled non-grain oriented silicon (CRNGO
Si) laminated sheets 202 stacked together as shown in the FIG. 2. With reference
to the above mentioned two methods, fabricating stator core of an axial flux
permanent magnet machine using (hardened glass laminate) HGL rings 401 and
402 is very easy as they are readily available in the market.
Inspite of non magnetic nature of SS-316 rings 301 and 302 used inside and
outside the stator core as shown in FIG. 3, the eddy currents are still induced in it
there by decreasing the efficiency of an axial flux permanent magnet machine. As
HGL rings 401 and 402 used inside and outside the stator core as shown in FIG. 4.
are insulators, the eddy currents are not induced and the efficiency of an axial flux
permanent magnet machine obtained will be more in this case compared to that in
the earlier case where SS-316 rings 301 and 302 are used.
The SS-316 rings 301 and 302 have high density compared to that of (hardened
glass laminate) HGL rings 401 and 402, so the weight of the stator core with SS-
316 rings 301 and 302 is less compared to that of the stator core with (hardened
glass laminate) HGL rings 401 and 402. The reduction of weight in the stator core
after manufacturing with (hardened glass laminate) HGL rings 401 and 402 is
substantial in small stator cores. Experiments show that a stator core with SS-316
rings 301 and 302 of thickness 3mm having ID 74mm, OD 126mm and length
50mm as shown in FIG. 3, having weight of the stator core of approximately 3140g.
A stator core with (hardened glass laminate) HGL rings 401 and 402 of thickness
3mm having ID 74mm, OD 126mm and length 50mm as shown in FIG. 4, is found
to have a weight of approximately 2560g. Thus a reduction in weight of the stator
core is 18.5%.The densities used in this calculation are as follows.
> Density of SS-316 is 7.9 g/cc.
> Density of (hardened glass laminate) HGL is 1.8 g/cc.
> Density of (cold rolled non-grain oriented silicon) CRNGO Si is 7.6 g/cc.
In the context of this invention, the inner and outer ring material is not limited to
HGL sheet only but to any insulation material like Bakelite (Cloth based epoxy or
Paper based epoxy) etc., which has more or less same mechanical strength as
(hardened glass laminate) HGL has. The present invention is very much useful in all
the applications where smaller axial flux permanent magnet machines are required
because percentage of reduction in the weight of the stator core increases as the
size of the stator core decreases.
WE CLAIM
1. A method for making stator core of an axial flux permanent magnet machine
(PMM), comprising the steps of :
- winding cold rolled non grain oriented silicon (CRNGO Si) laminated sheet
over a first hardened glass laminate (HGL) ring to configure a required
diameter;
- placing a second (hardened glass laminate) HGL ring over the assembly; and
- forming slots by machining or wire cutting.
2. The method as claimed in claim 1, wherein the weight of the stator core
formed is reduced by around 20% compared to prior art stator core formed
using other types of rings.
3. The method as claimed in claim 1, wherein the eddy current losses is
reduced compared to known processes.

ABSTRACT

The invention relates to a method for making the stator core of an axial flux
permanent magnet machine (PMM) is provided. The method includes the usage of
HGL (Hardened glass laminate) rings instead of (Stainless steel) SS-316 rings inside
and outside the stator core which is made up of CRNGO Si (Cold Rolled Non Grain
Oriented Silicon) laminated sheet. The method describes the ease of fabrication of
stator core of an axial flux permanent magnet machine (PMM). The method
includes the reduction of eddy current losses in the stator core of an axial flux
permanent magnet machine. The method also includes the reduction of weight of
stator core of an axial flux permanent magnet machine.