Rotor for an automotive alternator

A rotor for an automotive alternator comprises a cylindrical bobbin having a cylindrical portion, a pair of first and second annular flange portions projecting perpendicularly from both ends of the cylindrical portion, a recessed groove disposed at an angle to the radial direction in the inner wall of the first flange portion, and an anchor portion disposed on an outer circumferential portion of the first flange portion in close proximity to the outer circumferential end of the recessed groove, the bobbin being fitted over the base portions of the pair of field cores; and a field winding wound a predetermined number of turns into multiple layers on the cylindrical portion of the bobbin, wherein the field winding has a flat shape, the starting end of the field winding being wound around the anchor portion and housed in the recessed groove, then drawn from the inner circumferential end of the recessed groove onto the outer circumferential surface of the cylindrical portion of the bobbin, and additionally taken across the outer circumferential surface of the cylindrical portion of the bobbin from the first flange portion to the second flange portion, and thereafter being wound onto the outer circumferential surface of the cylindrical portion of the bobbin at an angle relative to a plane which perpendicularly intersects the axial center of the bobbin.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a rotor for an automotive alternator, 
which has a Lundell-type core, for mounting on an automobile engine, and 
in particular, relates to a winding configuration for winding onto the 
Lundell-type field core. 
2. Description of the Related Art 
FIG. 2 is a cross-section of a conventional rotor for an automotive 
alternator and FIG. 3 is a cross-section of part of the rotor shown in 
FIG. 2. 
In FIGS. 2 and 3, a rotor 1 comprises a rotating shaft 11 rotatably 
supported by a pair of brackets (not shown), a pair of Lundell-type field 
cores 12a, 12b secured to the rotating shaft 11, a pair of fans 13a, 13b 
secured to both axial ends of the field cores 12a, 12b, slip rings 14 
secured to one end of the rotating shaft 11, and a field winding 15 wound 
onto the field cores 12a, 12b. 
The field cores 12a, 12b are made of iron, comprise cylindrical base 
portions 121a, 121b fitted over and secured to the rotating shaft 11 and 
claw-shaped magnetic poles 122a, 122b plurally projecting from the outer 
circumferential edges of the base portions 121a, 121b, and are secured to 
the rotating shaft 11 facing each other such that the end surfaces of the 
base portions 121a, 121b are in close contact with each other and the 
claw-shaped magnetic poles 122a, 122b intermesh alternately. The field 
winding 15 is a copper wire with a flat shape having a rectangular 
cross-section and is wound a predetermined number of times onto a bobbin 
16 fitted over the outer circumferences of the base portions 121a, 121b. A 
magnetic flux is generated when an electric current is supplied to the 
field winding 15 by means of the slip rings 14 and magnetic poles are 
formed in the field cores 12a, 12b by the magnetic flux. 
Inner circumferential tape 17a for protecting the winding is wound onto the 
cylindrical portion 16a of the bobbin 16. Outer circumferential tape 17c 
for protecting the winding is also wound onto the outer circumference of 
the field winding 15 wound onto the bobbin 16. In addition, side tape 17b 
is disposed between the lead portion of the field winding 15 and the 
multi-layered portion of the field winding 15. 
The construction of the field winding 15 will now be explained with 
reference to FIG. 4. 
The bobbin 16 is made of resin, and comprises a cylindrical portion 16a and 
a pair of first and second annular flange portions 16b projecting 
perpendicularly from both ends of the cylindrical portion 16a. A recessed 
groove 161 for housing a lead wire 15a at the start of the winding is 
disposed at an angle with respect to the radial direction in the inner 
surface of the first flange portion 16b so as to extend from the outer 
circumferential side thereof to the cylindrical portion 16a. An anchor 
portion 16c is disposed on an outer circumferential portion of the first 
flange portion 16b in close proximity to the upper end of the recessed 
groove 161. 
First, the inner circumferential tape 17a is wound onto the cylindrical 
portion 16a of the bobbin 16. Then, the starting portion of the field 
winding 15 is wound around the anchor portion 16c, inserted into the 
recessed groove 161, and drawn from the lower end (inner circumferential 
end) of the recessed groove 161 onto the cylindrical portion 16a. At this 
point, the side tape 17b is pasted onto the inner surface of the first 
flange portion 16b so as to cover the lead wire 15a at the start of the 
field winding 15 which is housed in the recessed groove 161. Then, the 
field winding 15 drawn out onto the cylindrical portion 16a is lined up in 
rows at an angle relative to a plane which perpendicularly intersects the 
axial center of the bobbin 16 as it is wound onto the cylindrical portion 
16a. Then, when the first layer of the winding is finished, a second layer 
is lined up in rows at an angle relative to the plane which 
perpendicularly intersects the axial center as it is wound onto the 
cylindrical portion 16a. In this way, the field winding 15 is wound up 
layer by layer in order from the bottom of the cylindrical portion 16a, 
and when a predetermined number of layers have been wound, the outer 
circumferential tape 17c is wound onto the outermost circumferential 
portion. In addition, the multi-layered portion of the field winding 15 is 
saturated with varnish. 
The starting portion of the field winding 15 will now be explained. 
The broad surface of the flatly shaped lead wire 15a is housed in the 
recessed groove 161 so as to closely contact the bottom of the recessed 
groove 161. In other words, the broad surface of the lead wire 15a lies on 
a plane which intersects the axial center of the bobbin 16 
perpendicularly. The outer circumferential surface of the cylindrical 
portion 16a of the bobbin 16, on the other hand, is parallel to the axial 
center of the bobbin 16. 
Thus, the field winding 15, whose broad surface lies on a plane which 
intersects the axial center of the bobbin 16 perpendicularly, is bent at a 
right angle towards the cylindrical portion 16a at the inner 
circumferential end of the recessed groove 161, and is drawn out onto the 
outer circumferential surface of the cylindrical portion 16a. In addition, 
the field winding 15 drawn out onto the outer circumferential surface of 
the cylindrical portion 16a is twisted at approximately 90 degrees on the 
outer circumferential surface of the cylindrical portion 16a such that the 
longitudinal direction of the field winding 15 is at an angle relative to 
a plane which intersects the axial center of the bobbin 16 
perpendicularly, and winding of the first layer is started. 
In the conventional rotor 1 for an automotive alternator constructed in 
this manner, in the starting portion of the fieldwinding 15, the field 
winding 15 is bent at a right angle towards the cylindrical portion 16a at 
the inner circumferential end of the recessed groove 161, and is drawn out 
onto the outer circumferential surface of the cylindrical portion 16a, and 
in addition is twisted at approximately 90 degrees on the outer 
circumferential surface of the cylindrical portion 16a such that the 
longitudinal direction thereof is at an angle relative to a plane which 
intersects the axial center of the bobbin 16 perpendicularly. However, the 
field winding has a flat shape and therefore cannot completely absorb the 
kinks caused by bending and twisting, and kinks arise in the starting 
portion of the field winding 15. 
Thus, one problem is that the second and subsequent layers of the field 
winding 15 are wound over the kinks, leading to damage in the starting 
portion of the field winding 15. Furthermore, the starting portion of the 
field winding 15 is the bottommost layer in the multi-layer portion and 
damage to the wire is difficult to detect there, leading to quality 
control problems. 
Another problem is that the angle of the bending and twisting of the field 
winding 15 at the inner circumferential end of the recessed groove 161 is 
great, reducing workability as well as giving rise to wire breakages. 
SUMMARY OF THE INVENTION 
The present invention aims to solve the above problems and an object of the 
present invention is to provide a rotor for an automotive alternator which 
enables quality to be stabilized as well as improving workability by 
suppressing the occurrence of damage to wire caused by winding successive 
layers of a field winding and suppressing the occurrence of breakages by 
reducing the angle of bending and twisting and minimizing kinks in the 
starting portion of the flatly shaped field winding. 
In order to achieve the above object, according to one aspect of the 
present invention, there is provided a rotor for an automotive alternator 
comprising a pair of field cores each having a cylindrical base portion 
and a plurality of claw-shaped magnetic poles projecting from the outer 
circumferential edges of the base portions, the field cores being secured 
to a rotating shaft facing each other such that the end surfaces of the 
base portions are in close contact with each other and the claw-shaped 
magnetic poles intermesh with each other, a cylindrical bobbin having a 
cylindrical portion, a pair of first and second annular flange portions 
projecting perpendicularly from both ends of the cylindrical portion, a 
recessed groove disposed at an angle to the radial direction in the inner 
wall of the first flange portion, and an anchor portion disposed on an 
outer circumferential portion of the first flange portion in close 
proximity to the outer circumferential end of the recessed groove, the 
bobbin being fitted over the base portions of the pair of field cores, and 
a field winding wound a predetermined number of turns into multiple layers 
on the cylindrical portion of the bobbin, wherein the field winding has a 
flat shape, the starting end of the field winding being wound around the 
anchor portion and housed in the recessed groove, then drawn from the 
inner circumferential end of the recessed groove onto the outer 
circumferential surface of the cylindrical portion of the bobbin, and 
additionally taken across the outer circumferential surface of the 
cylindrical portion of the bobbin from the first flange portion to the 
second flange portion, and thereafter being wound onto the outer 
circumferential surface of the cylindrical portion of the bobbin at an 
angle relative to a plane which perpendicularly intersects the axial 
center of the bobbin.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The preferred embodiment of the present invention will now be explained 
with reference to the drawings. 
Embodiment 1 
FIG. 1 is a perspective view explaining the winding configuration of a 
field winding in a rotor for an automotive alternator according to 
Embodiment 1 of the present invention. 
In FIG. 1, the field winding 15 is a flatly shaped copper wire which has a 
rectangular cross-section. Furthermore, the bobbin 16 is made of resin, 
and comprises a cylindrical portion 16a and a pair of first and second 
annular flange portions 16b projecting perpendicularly from both ends of 
the cylindrical portion 16a. A recessed groove 161 for housing a lead wire 
15a at the start of the winding is disposed at an angle with respect to 
the radial direction in the inner surface of the first flange portion 16b 
so as to extend from the outer circumferential side to the cylindrical 
portion 16a. An anchor portion 16c is disposed on an outer circumferential 
portion of the first flange portion 16b in close proximity to the outer 
circumferential end of the recessed groove 161. 
The winding configuration of the field winding 15 according to Embodiment 1 
will now be explained. 
First, the inner circumferential tape 17a is wound onto the cylindrical 
portion 16a of the bobbin 16. Then, the starting portion of the field 
winding 15 is wound around the anchor portion 16c, inserted into the 
recessed groove 161, and drawn from the inner circumferential end of the 
recessed groove 161 onto the cylindrical portion 16a. At this point, the 
side tape 17b is pasted onto the inner surface of the first flange portion 
16b so as to cover the lead wire 15a at the start of the field winding 15 
which is housed in the recessed groove 161. The field winding 15 drawn out 
onto the cylindrical portion 16a is taken across the outer circumferential 
surface of the cylindrical portion 16a from the first flange portion 16b 
to the second flange portion 16b at a predetermined angle relative to a 
plane which perpendicularly intersects the axial center of the cylindrical 
portion 16a. Then, the field winding 15 taken across to the root portion 
of the second flange portion 16b is lined up in rows at an angle relative 
to a plane which perpendicularly intersects the axial center of the bobbin 
16 as it is wound onto the cylindrical portion 16a. When the first layer 
of the winding is finished, a second layer is lined up in rows at an angle 
relative to the plane which perpendicularly intersects the axial center as 
it is wound onto the cylindrical portion 16a. In this way, the field 
winding 15 is wound up layer by layer in order from the bottom of the 
cylindrical portion 16a, and when a predetermined number of layers have 
been wound, the outer circumferential tape 17c is wound onto the outermost 
circumferential portion. In addition, the multi-layered portion of the 
field winding 15 is saturated with varnish. 
The starting portion of the field winding 15 according to Embodiment 1 will 
now be explained. 
The broad surface of the flatly shaped lead wire 15a is housed in the 
recessed groove 161 so as to closely contact the bottom of the recessed 
groove 161. 
In other words, the broad surface of the lead wire 15a lies on a plane 
which intersects the axial center of the bobbin 16 perpendicularly. The 
outer circumferential surface of the cylindrical portion 16a of the bobbin 
16, on the other hand, is parallel to the axial center of the bobbin 16. 
Thus, the field winding 15, whose broad surface lies on a plane which 
intersects the axial center of the bobbin 16 perpendicularly, is bent at a 
right angle towards the cylindrical portion 16a at the inner 
circumferential end of the recessed groove 161, and is drawn out onto the 
outer circumferential surface of the cylindrical portion 16a. In addition, 
the field winding 15 drawn out onto the outer circumferential surface of 
the cylindrical portion 16a is twisted on the outer circumferential 
surface of the cylindrical portion 16a and taken across the outer 
circumferential surface of the cylindrical portion 16a from the first 
flange portion 16b to the second flange portion 16b. Then, the field 
winding 15 taken across to the root portion of the second flange portion 
16b is twisted on the outer circumferential surface of the cylindrical 
portion 16a such that the longitudinal direction of the field winding 15 
is at an angle relative to a plane which intersects the axial center of 
the bobbin 16 perpendicularly, and winding of the first layer is started. 
Moreover, the rest of the construction is the same as for the conventional 
rotor shown in FIGS. 2 and 3. 
In a rotor constructed in this manner, the end of the portion of the field 
winding 15 taken across is positioned in front of the inner 
circumferential end of the recessed groove 161 in the direction of 
winding. Furthermore, the direction which the field winding is twisted in 
at the portion where the field winding 15 is drawn out from the inner 
circumferential end of the recessed groove 161 onto the cylindrical 
portion 16a is the same as the direction which the field winding is 
twisted in at the end of the portion of the field winding 15 taken across. 
Thus, the bending and twisting of the wire in the starting portion of the 
field winding 15 is distributed to two positions, the portion where the 
field winding 15 is drawn out from the inner circumferential end of the 
recessed groove 161 onto the cylindrical portion 16a and the end of the 
portion of the field winding 15 taken across, enabling the angle of 
bending and twisting of the wire to be reduced at each position. 
As a result, kinks in the wire resulting from bending and twisting are 
reduced significantly compared to the conventional technique, providing a 
rotor with stable quality in which the second and subsequent layers of the 
field winding can be wound on top of the kinked portions without giving 
rise to damage in the starting portion of the field winding 15. 
Furthermore, stresses generated in the bent and twisted portions of the 
wire as a result of the bending and twisting are reduced, minimizing the 
occurrence of breakages in the wire. 
In addition, the bending and twisting work is facilitated, improving the 
winding operation. 
Furthermore, since a flatly shaped field winding 15 is used, spacing 
between portions of the field winding 15 in the radial direction is 
practically reduced to zero, increasing rigidity, improving resistance to 
vibrations, and enabling the occurrence of disarray in the winding to be 
suppressed. Similarly, thermal conductivity between portions of the field 
winding 15 is improved and radiation of heat increases, enabling 
high-output to be attained. In addition, the thickness of the field 
winding 15 is reduced and the field winding 15 can be wound to a high 
density, attaining reduced size and increased output. 
Now, after the field winding 15 has been drawn out from the inner 
circumferential end of the recessed groove 161 onto the outer 
circumferential surface of the cylindrical portion 16a and taken across 
the outer circumferential surface of the cylindrical portion 16a from the 
first flange portion 16b to the second flange portion 16b, winding of the 
first layer is started. At that time, the field winding 15 is wound on top 
of the portion of the field winding 15 taken across, giving rise to 
irregularities in the outer circumference of the multi-layered portion. 
Moreover, if more than one lap is required to take the field winding 15 
across the outer circumferential surface of the cylindrical portion 16a 
from the first flange portion 16b to the second flange portion 16b after 
the field winding 15 has been drawn out from the inner circumferential end 
of the recessed groove 161 onto the outer circumferential surface of the 
cylindrical portion 16a, the field winding 15 will be wound on top of the 
portion of the field winding 15 taken across at two or more places in the 
circumferential direction, increasing the number of irregularities arising 
in the outer circumference of the multi-layered portion. In other words, 
the outer circumference of the multi-layered portion of the field winding 
15 will be less uniform in the axial direction, leading to eccentricities 
in the multi-layered portion. When the eccentricities in the multi-layered 
portion are large, there is a risk that vibrations will be induced in the 
rotor during high-speed rotation. From this, it is desirable that the 
field winding 15 is taken across the outer circumferential surface of the 
cylindrical portion 16a from the first flange portion 16b to the second 
flange portion 16b within one lap. 
The present invention is constructed in the above manner and exhibits the 
effects described below. 
According to one aspect of the present invention, there is provided a rotor 
for an automotive alternator comprising a pair of field cores each having 
a cylindrical base portion and a plurality of claw-shaped magnetic poles 
projecting from the outer circumferential edges of the base portions, the 
field cores being secured to a rotating shaft facing each other such that 
the end surfaces of the base portions are in close contact with each other 
and the claw-shaped magnetic poles intermesh with each other, a 
cylindrical bobbin having a cylindrical portion, a pair of first and 
second annular flange portions projecting perpendicularly from both ends 
of the cylindrical portion, a recessed groove disposed at an angle to the 
radial direction in the inner wall of the first flange portion, and an 
anchor portion disposed on an outer circumferential portion of the first 
flange portion in close proximity to the outer circumferential end of the 
recessed groove, the bobbin being fitted over the base portions of the 
pair of field cores, and a field winding wound a predetermined number of 
turns into multiple layers on the cylindrical portion of the bobbin, 
wherein the field winding has a flat shape, the starting end of the field 
winding being wound around the anchor portion and housed in the recessed 
groove, then drawn from the inner circumferential end of the recessed 
groove onto the outer circumferential surface of the cylindrical portion 
of the bobbin, and additionally taken across the outer circumferential 
surface of the cylindrical portion of the bobbin from the first flange 
portion to the second flange portion, and thereafter being wound onto the 
outer circumferential surface of the cylindrical portion of the bobbin at 
an angle relative to a plane which perpendicularly intersects the axial 
center of the bobbin, reducing the angle of bending and twisting and 
minimizing kinks in the starting portion of the field winding, thereby 
suppressing the occurrence of damage to the wire caused by winding 
successive layers of a field winding and suppressing the occurrence of 
breakages, and thus providing a rotor for an automotive alternator which 
enables quality to be stabilized as well as improving workability. 
The field winding is taken across the outer circumferential surface of the 
cylindrical portion from the first flange portion to the second flange 
portion within one lap after being been drawn out from the inner 
circumferential end of the recessed groove onto the outer circumferential 
surface of the cylindrical portion of the bobbin, enabling the multi-layer 
portion of the field winding to be formed with a uniform outer 
circumference.