The present invention relates to a method for manufacturing
a stator core of a vehicle rotary electric machine according to claim 1. Moreover,
the present invention also relates to a device for manufacturing a stator core of
a vehicle rotary electric machine according to claim 4. The vehicle rotary electric
machine can be comprised, for example, of an AC generator to be mounted in a passenger
car, a truck, etc.
In order to supply an inexpensive vehicle rotary machine,
a magnetic stator core is usually comprised of a spirally wound magnetic strip.
Such a stator core can provide a high yield percentage of magnetic material and
can be manufactured at a high manufacturing speed.
In order to meet a recent demand for a high power generator,
conductors are to be disposed in the slots of the stator core at as a high space
factor as possible.
As shown in JP-A11-299136, a pair long and thin magnetic
sheets is stamped out to form a pair of magnetic strips that has a plurality of
teeth and a core back in order to increase the yield percentage of the magnetic
strips, the teeth of one of the pair of magnetic strips are respectively formed
from portions inside slots of the other magnetic strip. Thereafter, each the magnetic
strip is spirally wound into a cylindrical stack with the slots of one layer being
aligned with those of another layer until the cylindrical stack has a prescribed
thickness. Then, the stack is welded or riveted. Because two or more magnetic strips
are formed at one time, the manpower and cost for manufacturing the stator cores
can be reduced.
In order to moderate stress of a magnetic strip when it
is spirally wound, JP-A-48-24204 discloses teeth whose tooth width becomes narrower
toward the core back. In other words, slot width is widened at the middle thereof.
This reduces strain of the strip when it is spirally wound and makes the size and
shape of a cylindrical stator core accurate.
Because the magnetic reluctance of the air gap between
the rotor and the stator is the largest in the magnetic circuit of a generator,
the tooth edge formed at the inner periphery of the stator has a wider cross-section
of a magnetic path than the rest of the tooth. In other words, each tooth has a
pair of circumferential projections to increase the width of the tooth.
As the space factor of the conductors increases, the slot
area is narrowed to thereby widen the cross-section of the tooth if the teeth of
one of the pair of magnetic strips are respectively formed from portions inside
slots of the other magnetic strip as disclosed in JP-A-299136, it is not possible
to provide such a circumferentially wide tooth.
If the tooth width is narrowed at the middle thereof as
shown in JP-A-48-24204, a widened tooth edge of one of a pair of magnetic strips
can be formed from the portion inside a widened slot of the other magnetic strip.
However, if the tooth is narrowed at the middle, the magnetic reluctance of the
teeth increases, and the magnetic flux flowing through the stator core decreases
significantly. This lowers the output power.
A stator core of a vehicle AC generator that has an outside
diameter between 90 mm and 140 mm is usually comprised of a laminated steel strip
of a thickness between 0.5 mm and 1.0 mm. It is necessary to have a margin (or clearance)
if teeth and slots are formed from a steel strip of the above thickness.
However, if the thickness is reduced to a thickness less
than 0.2 mm, the edge of the sheet may be drawn because of the low rigidity thereof.
As a result, the projections of the tooth edge cannot have proper length, and a
sufficient cross-section of the magnetic flux from the rotor cannot be provided.
It is an object of the present invention, to provide a
method and a device for manufacturing a stator core of a vehicle rotary electric
machine with which the stator core can be manufactured at a high yield percentage
and a high speed.
According to the inventive method this object is solved
by the features of claim 1. Improved embodiments of the inventive method result
from subclaims 2 and 3.
The inventive device for solving the above object results
from claim 4.
Other objects, features and characteristics of the present
invention as well as the functions of related parts of the present invention will
became clear from a study of the following detailed description, the appended claims
and the drawings. In the drawings:
- Fig. 1 is a fragmentary enlarged view of an axial end of a stator core of a
vehicle AC generator;
- Fig. 2 is an explanatory diagram showing a step of manufacturing a pair of magnetic
strips from a long and thin magnetic sheet;
- Fig. 3 is an explanatory diagram showing a step of manufacturing magnetic strips
according to a first embodiment of the invention;
- Fig. 4 is a fragmentary cross-sectional view of a stator core according to a
second embodiment of the invention;
- Fig. 5 is an explanatory diagram showing a step of manufacturing magnetic strips
according to a third embodiment of the invention; and
- Fig. 6 is an explanatory diagram showing a step of manufacturing magnetic strips
according to a variation of the third embodiment of the invention.
The invention can be applied to a vehicle rotary electric
machine such as a generator or a motor. For example, it is mounted in an engine
and driven by the engine as an AC generator. It is also mounted in an engine as
A stator core of a vehicle AC generator is described with
reference to Figs. 1 - 5 .
A cylindrical stator core 1 is comprised of a spirally
wound and laminated magnetic strip 10 that is as thick as 0.35 mm. The magnetic
strip 10 has a plurality of teeth 2 and a core back 3 from which the plurality of
teeth 2 extends. When wound and laminated, tooth edges 20 of teeth 2 are disposed
A pair of circumferential notches 21 is formed at opposite
sides of a base portion of each tooth 2 adjacent to the core back 3. A width B of
the base between the notches 21 is set larger than a minimum width A between a pair
of circumferential projections 201 formed at the tooth edge 20. Each slot 6 has
a pair of walls 23 and 24 facing each other in the circumferential direction. The
pair of walls 23 and 24 becomes parallel after the magnetic strip 10 is wound up.
The pair of projections 201 is almost the same in shape
as a slot bottom 210 that includes the pair of notches 21 . When a pair of magnetic
strips 10 is formed from a long and thin magnetic sheet 100 such as a hoop of a
steel sheet, the tooth edges 20 of one magnetic. strip 10 and the slot bottom 210
of the other magnetic strip 10 is sheared and separated without any clearance or
margin except for clearances or marginal portions 200 at opposite sides of each
tooth 2, as shown in Fig. 2. This increases the yield percentage of the magnetic
strip. Because the thickness of the magnetic strip 10 is 0.35 mm, the projections
201 do not deform and keep the magnetic reluctance at a low level.
Thus, the magnetic cross-section of the teeth 2 is the
smallest at the base of the projections 201, i.e. at the tooth edge 20 from which
the projections 201 extend. In other words, the cross-section of middle portion
of the teeth 2 between the base of the projections 201 and the core back 3 is not
smaller than the magnetic cross-section at the base of the projections 201. The
radial width of each notch 21 is narrowed when the magnetic strip 10 is spirally
wound. Accordingly, the magnetic reluctance around the notches 21 is reduced when
the stator core 1 is completed.
In addition, a plurality of magnetic strips 10 can be formed
from a single long and thin magnetic sheet 100, and the notches 21 make the winding
step of the magnetic strip 10 easier.
As a method of manufacturing the stator core according
to a first embodiment of the invention, a long magnetic sheet can be loaded between
a pair of parallel rollers having a punch and a die to stamp out the magnetic strip
10 continuously, as shown in Fig. 3. Because the magnetic strip 10 can be formed
continuously, the production time and cost can be reduced.
The thickness of the magnetic sheets can be changed from
0.35 mm to a thickness between 0.2 mm and 0.5 mm.
A stator core according to a second embodiment of the invention
is described with reference to Fig. 4. A unit of the conductor coils 5 can be divided
into two groups, and each output power is added to each other. The number of the
slots per each unit length of the magnetic sheet becomes twice as many as the number
of the slots of the magnetic sheet according to the first embodiment. On the other
hand the width of the slots becomes a half the width of the slot of the magnetic
sheet according to the first embodiment. Thus, the number of the notches increases
so that the magnetic strip can be wound into a more accurate cylindrical shape at
a low cost.
As a method of manufacturing the stator core according
to a third embodiment of the invention, the clearance 200a for stamping out can
be formed at a side of each tooth 2, as shown in Fig. 5. Because the width of the
clearance can be increased, the magnetic strips can be stamped out more easily.
The pair of magnetic strips can be formed by the pair of parallel rollers, as shown
in Fig. 3.
As a variation, a clearance 200b can be increased until
the notches at the base of the teeth 2 are removed. This makes the manufacturing
steps easier and the manufacturing cost lower.
In the foregoing description of the present invention,
the invention has been disclosed with reference to specific embodiments thereof.
It will, however, be evident that various modifications and changes may be made
to the specific embodiments of the present invention without departing from the
scope of the invention as set forth in the appended claims. Accordingly, the description
of the present invention is to be regarded in an illustrative, rather than a restrictive,