Molded rotor assembly for an alternator and method for making the same

A molded rotor assembly (20) for a vehicle alternator and method for making the same are disclosed. The rotor assembly includes first and second pole pieces (24,26) aligned along a longitudinal axis (40), the pair of pole pieces (24,26) defining a region therebetween. A coil wire (46) is located in the region. The pole pieces (24,26) and a slip ring assembly (36) are mounted on a rotor shaft (38). The slip ring assembly (36) has a pair of slip rings (102,104) connected to a pair of terminals (96,98) which are attached to respective free ends of the coil wire (46) to form a pair of connections (126,128). A molded insert (22) is injection molded filling the region between the pole pieces (24,26) thereby encapsulating the connections (126,128) and the coil wire (96) and forming a smooth cylindrical periphery on the rotor assembly (20).

TECHNICAL FIELD 
This invention relates to rotor assemblies for vehicle alternators of a 
claw-pole type design. 
INCORPORATION BY REFERENCE 
The disclosures contained in patent applications entitled, "Rotor Assembly 
with Molded Fans And Method For Making The Same", U.S. Ser. No. 980,048, 
and "Automotive Alternator Slip Ring Assembly", U.S. Ser. No. 980,393, 
which are commonly owned by the Assignee of this application and which are 
simultaneously filed with this application, are hereby incorporated by 
reference. 
BACKGROUND ART 
Rotor assemblies for vehicle alternators are often of a claw-pole type 
design. These rotor assemblies typically include a pair of annular pole 
pieces aligned along a longitudinal axis and having bores at their 
centers. Each of the pole pieces has on its radial periphery a number of 
axially extending fingers giving that pole piece a claw-like appearance. A 
coil wire is wound about an annular bobbin forming a bobbin assembly. The 
bobbin assembly is placed in a region formed between the pole pieces. The 
pole pieces are mounted on a rotor shaft with the fingers of the 
respective pole pieces being interleaved with one another. The coil wire, 
bobbin and pole pieces are coated with a varnish and then baked to hold 
the coil wires in a fixed position relative to one another. 
A slip ring assembly is also mounted on the rotor shaft. The slip ring 
assembly has a pair of axially spaced slip rings which are adapted to mate 
with exterior brushes. The slip ring assembly includes a pair of terminals 
which are connected to respective slip rings. A pair of stamped metal fans 
is then attached to the axially outboard faces of each pole piece. 
The rotor assembly is mounted inside a stator and an alternator housing to 
form an alternator. When voltage is supplied to the slip ring assembly and 
the rotor assembly is rotated, the rotor assembly induces the flow of 
current in the windings of the stator. This current is output from the 
alternator. Heat generated by current flowing through the coil wire and 
windings is carried away by air currents, created by the rotation of the 
fans, through perforations in the alternator housing. 
Alternators, constructed as described above, have several shortcomings. 
First, the high speed rotation of the rotor assembly within the alternator 
housing creates a significant amount of noise. A portion of this noise is 
originated by air flowing between the pole pieces and the bobbin assembly 
during rotor assembly rotation. Likewise, during operation of the 
alternator, the fingers of the pole pieces may vibrate radially due to 
forces associated with changing magnetic fields, thereby creating 
additional noise. An annular support ring, made from a nonmagnetic 
material, is often placed within the interleaving fingers to provide 
radial support to the fingers thereby reducing vibration and noise. Also, 
separate spacer pieces, configured to fit between the interleaving 
fingers, are sometimes placed between the pieces to reduce air flow 
disturbance resulting from the nonuniform surface of the rotor. 
Second, connections formed between the terminals of the slip ring assembly 
and the respective ends of the coil wire are subject to failure. The high 
speed rotation of the rotor assembly, which may be on the order of 
18,000-23,000 RPM, subjects the connections to substantial acceleration 
forces. As these connections are generally isolated from and are not 
supported by the rest of the rotor assembly, fatigue failures of the 
connections may occur, with corresponding failure of the entire 
alternator. Consequently, the alternator must be disassembled, the 
connections repaired, and the alternator reassembled. Alternatively, the 
alternator must be completely replaced. In either case, the repair or 
replacement is expensive and time consuming. 
The present invention addresses problems associated with the 
above-identified shortcomings. 
DISCLOSURE OF INVENTION 
The present invention includes an integrally molded rotor assembly and 
method for making the same. The rotor assembly includes a pair of pole 
pieces, a coil wire, a slip ring assembly, a rotor shaft, and a molded 
insert integrally molded to the pole pieces. 
The pole pieces are annular and are axially aligned along a longitudinal 
axis to define a region between the pole pieces. Each pole piece has a 
plurality of axially inboard-extending fingers located along the radial 
periphery of each pole piece. The fingers on each pole piece are 
preferably regularly spaced around the periphery and interleaved with the 
fingers on the other pole piece. 
The coil wire is wound in loops or turns and is located in the region 
between the pole pieces. Preferably, the coil wire is wound about an 
annular bobbin to form a bobbin assembly. The coil wire includes a pair of 
free ends. 
The slip ring assembly, preferably, includes a pair of slip rings, a 
central hub and a pair of terminals. The pair of pole pieces and the hub 
of the slip ring are mounted upon the rotor shaft. Each terminal is 
attached to a respective free end of the coil wire thereby forming a pair 
of connections. 
The molded insert is integrally molded to at least one of the pole pieces 
and fills at least partially the region between the pole pieces. 
Preferably, the molded insert provides radial support to the interleaving 
fingers of the pole pieces, resulting in reduced vibration in the fingers. 
The rotor assembly may further include a nonmagnetic annular support ring, 
encapsulated in the insert, which further radially supports the 
interleaving fingers. 
Ideally, the molded insert completely fills the region between axial 
outboard faces of the pole pieces such that the pole pieces and the molded 
insert cooperate to form a smooth cylindrical periphery on the rotor 
assembly. Air disturbance and noise created by air flowing between the 
pole pieces and bobbin assembly during rotor assembly rotation are thereby 
eliminated. 
Preferably, the molded insert also encapsulates and provides support for 
the connections between the free ends of the coil wire and the terminals 
of the slip ring assembly. This reduces the load and stresses experienced 
by the connections during rotor assembly rotation thus extending the 
fatigue life of the connections and increasing the rotational speeds at 
which the rotor assembly can be operated. 
The present invention further comprises a method for making an integrally 
molded rotor for an alternator. The method includes placing a coil wire, 
which has a pair of free ends and which preferably is wound about an 
annular bobbin to form a bobbin assembly, in a region defined between 
first and second annular pole pieces which are aligned along a 
longitudinal axis. Each pole piece has a plurality of axially inboard 
extending fingers which are interleaved, and preferably spaced apart, 
relative to the fingers of the other pole piece. 
A slip ring assembly and the pole pieces are mounted on a rotor shaft. The 
slip ring assembly includes a pair of slip rings connected to a respective 
pair of terminals. Each terminal is connected to a respective free end of 
the coil wire thereby forming a pair of connections. 
The above-identified components form a subassembly which is placed in a 
mold. A molded insert is then integrally molded to the pole pieces which 
at least partially fills the region between the pole pieces. Ideally, the 
molded insert completely fills the region between the pole pieces to form 
a generally smooth cylindrical periphery on the rotor assembly. 
Preferably, the molded insert encapsulates each of the connections. 
Further, this method may also include placing a support ring, prior to 
molding, within the interleaving fingers to provide additional radial 
support to the fingers. The rotor assembly may then be mounted inside a 
stator and an alternator housing to form a vehicle alternator. 
It is another object to provide a rotor assembly having an integrally 
molded insert which provides support to interleaving fingers on 
cooperating pole pieces to reduce vibrations of the fingers and noise 
created during rotation of the rotor assembly. 
It is yet another object to provide a molded insert which encapsulates 
connections formed between terminals on a slip ring assembly and 
respective free ends of a coil wire of the rotor assembly such that the 
connections are fully supported thereby reducing failures at these 
connections and increasing the rotational speed at which the rotor 
assembly may be operated. 
Another object of the present invention is to provide an integrally molded 
insert which fills the region between the pair of pole pieces and 
cooperates with the pole pieces to produce a smooth cylindrical surface on 
the rotor assembly to reduce the amount of air disturbance and noise 
generated during the rotation of the rotor assembly. 
It is yet a further object to provide a method for making a molded rotor 
assembly for a vehicle alternator comprising the steps of interleaving and 
spacing axially inboard extending fingers of a pair of claw-pole pieces to 
form a region between the pole pieces with a coil wire being held in the 
region. A pair of slip rings, which are connected to a pair terminals, and 
the pole pieces are mounted to a rotor shaft. Connections are formed 
between respective free ends of the coil wire and the respective 
terminals. A molded insert is then integrally molded to at least one of 
the pole pieces such that the insert at least partially fills the region 
between the pole pieces. Preferably, the molded insert encapsulates the 
connections. Ideally the molded insert and the pole pieces cooperate to 
form a smooth, cylindrical surface on the rotor assembly. 
Other objects, features, and advantages will become more readily apparent 
from the following description and accompanying sheets of drawings.

BEST MODE FOR CARRYING OUT THE INVENTION 
With reference to the drawings, a molded rotor assembly made in accordance 
with a preferred first embodiment is generally indicated by the reference 
numeral 20. As seen in FIGS. 1 and 2, rotor assembly 20 includes a molded 
insert 22 sandwiched between first and second pole pieces 24 and 26. First 
and second molded fans 28 and 30 have a plurality of circumaxially spaced 
blades 32 and 34, respectively, which are integrally molded to first and 
second pole pieces 24 and 26. Prior to any molding, a slip ring assembly 
36, depicted in FIG. 3, as well as first and second pole pieces 24 and 26, 
are mounted to a rotor shaft 38 which is axially aligned along a 
longitudinal axis 40 of rotor shaft 38. 
FIG. 4 is an exploded view of components included in the rotor assembly 20. 
Stamped metal fans 328 and 330, used in place of molded fans 28 and 30 in 
an alternative embodiment of a rotor assembly, are also shown. The rotor 
assembly 20 comprises first and second pole pieces 24 and 26, slip ring 
assembly 36, rotor shaft 38, a bobbin assembly 42 including a bobbin 44 
which holds a coil wire 46, and a nonmagnetic annular support ring 48. 
Also shown is a collar 50 which mounts on rotor shaft 38 outboard of pole 
piece 26. 
First and second pole pieces 24 and 26 have respective central annular 
portions 54 and 56 and a plurality of circumaxially spaced and axially 
inboard-extending fingers 58 and 60 disposed along their respective radial 
peripheries. The annular portions 54 and 56 have hubs 62 and 64 with 
respective bores 66 and 68 therein. On the back or outboard axial face 69 
of pole piece 24 are annular recess 70 and a pair of radially extending 
channels 72 which are sized and configured to receive, in a flush manner, 
portions of slip ring assembly 36. Pole piece 26 has a front outboard face 
71 with an annular recess 73 formed therein which is adapted to receive 
collar 50. Pole pieces 24 and 26 are preferably made of steel. 
Rotor shaft 38, also preferably made of steel, has splined portion 74 onto 
which bores 66 and 68 of pole pieces 24 and 26 are press fit. An integral 
collar 76 is formed on rotor shaft 38 to provide a stop against which the 
slip ring assembly 36 may snugly fit. Rotor shaft 38 also has a reduced 
diameter end 78. Pairs of respective axial grooves 80 and radial grooves 
82 are formed in rotor shaft 38, with radial grooves 82 located within 
collar 76. 
Bobbin assembly 42 includes annular bobbin 44 which is U-shaped in 
cross-section and is designed to hold turns of coil wire 46. Coil wire 46 
is wound about bobbin 44 and has free ends 84 and 86. The turns of coil 
wire 46 are electrically insulated from one another by insulating coating 
88 which is applied to the outside of the coil wire 46 prior to winding 
coil wire 46 on to bobbin 44. In the preferred embodiment, this insulating 
coating is armored polythermaleze 2000 (APTZ) which is available, along 
with coil wire 46, from Phelps Dodge Magnet Wire Company of Fort Wayne, 
Indiana. 
Bobbin 44 preferably is made from a molded plastic and serves to assist in 
electrically insulating coil wire 46 from pole pieces 24 and 26. Along the 
radial periphery of bobbin 44 are a pair of forked guides 90 which retain 
free ends 84 and 86 of coil wire 46 as they leave bobbin 44. 
Slip ring assembly 36 comprises an annular metallic band 92, a hub 94, a 
pair of L-shaped terminals 96 and 98 and a circular mold shutoff ring 100. 
FIG. 6 shows a cross-sectional view of slip ring assembly 36 mounting on 
rotor shaft 38 and against pole piece 24. Metallic band 92 is preferably 
copper and has a pair of axially spaced slip rings 102 and 104 connected 
together by a reduced thickness bridge portion 106. After slip ring 
assembly 36 has been mounted on rotor shaft 38, the outer radial portion 
of band 92 is machined away to remove bridge portion 106 and thereby 
separate slip rings 102 and 104 from one another, as seen in FIG. 1. 
Terminals 96 and 98 are metallic, preferably copper, and are surrounded by 
insulating coverings 108 and 110, except at respective exposed ends 97 and 
99. Hub 94 has a bore 112 therein adapted to fit over reduced diameter end 
78 of rotor shaft 38 in a press-fit manner. Hub 94 serves to support and 
insulate slip rings 102 and 104 from each other and from rotor shaft 38. 
Mold shutoff ring 100 supports and provides structural rigidity to 
terminals 96 and 98. Terminals 96 and 98 pass through the axial length of 
mold shutoff ring 100. As best seen in FIG. 8, mold shutoff ring 100 has 
an inner radial surface 114, an outer radial surface 116, and planar 
inboard and outboard axial surfaces 118 and 120. Inboard axial surface 118 
mates flushly against annular recess 70 in outboard face 69 of pole piece 
24 as does collar 76 of rotor shaft 38. Inner radial surface 114 is 
flushly mounted over the outer diameter of collar 76 of shaft 38. 
Slip ring assembly 36 is constructed by soldering or welding first ends of 
terminals 96 and 98 to respective slip rings 104 and 102, as seen in FIG. 
6. Terminal 98 is configured to bypass slip ring 104. Terminals 96 and 98 
and slip rings 102 and 104 are then placed within an appropriately 
configured mold. The mold is filled with a molten plastic material to form 
hub 94, mold shutoff ring 100 and insulating coverings 108 and 110 of slip 
ring assembly 36. The preferred plastic material to be used in the 
construction of slip ring assembly 36 is a glass-filled polyphenylene 
sulfide sold under the trade name Ryton.RTM. by the Phillips 66 Company. 
Those skilled in the art will realize that alternative materials may also 
be used to mold slip ring assembly 36. 
Annular or circular support ring 48 has an outer diametrical periphery 
which is slightly larger than the inner diameters of interleaved first and 
second fingers 58 and 60 of respective pole pieces 24 and 26. Support ring 
48 is made of a nonmagnetic material such as aluminum. The support 
provided to fingers 58 and 60 by the support ring 48 reduces vibration 
during rotation of rotor assembly 20. 
Looking back now to the exploded view of FIG. 3, pole pieces 24 and 26 are 
mounted upon rotor shaft 38 and are axially aligned along longitudinal 
axis 40. Fingers 58 and 60 of pole pieces 24 and 26 are interleaved and 
spaced apart with respect to one another. A region 122 is defined between 
pole pieces 24 and 26. Free ends 84 and 86 of coil wire 46 are shown 
extending axially outboard from region 122. 
Slip ring assembly 36 is also mounted on rotor shaft 38. Bore 112 of slip 
ring assembly 36 fits over reduced diameter end 78 in a press-fit manner. 
Axially extending portions of terminals 96 and 98 are received in axial 
grooves 80 of rotor shaft 38. Likewise, radially outward extending 
portions of terminals 96 and 98, located radially within mold shutoff ring 
100, are received in radial grooves 82 of collar 76. The portions of 
terminals 96 and 98 and of the portions of coverings 108 and 11 located 
radially outside mold shutoff ring 100 are received within radially 
extending channels 72 located in outboard face 69 of pole piece 24. 
Radially extending recesses 72 are deep enough to receive terminals 96 and 
98 and their coverings 108 and 110 beneath the planar surface of axial 
outboard face 69 of pole piece 24, as shown in FIG. 7. 
Referring again to FIG. 8, inboard axial surface 118 of mold shutoff ring 
100 is nested flush within annular recess 70 of pole piece 24. Likewise, 
collar 76 of rotor shaft 38 also rests flush in annular recess 70. Inner 
radial surface 114 of mold shutoff ring 100 fits snugly over and receives 
radial support from the cylindrical surface of collar 76. 
FIG. 5 shows a subassembly 124 including pole pieces 24 and 26, slip ring 
assembly 36, rotor shaft 38, bobbin assembly 42, and support ring 48 after 
these components have been assembled together. A pair of connections 126 
and 128 is formed between respective free ends 84 and 86 of coil wire 46 
and exposed ends 97 and 99 of terminals 96 and 98. 
To form connections 126 and 128, exposed ends 97 and 99 of terminals 96 and 
98 are first bent into a hook shape. Free ends 84 and 86 are then placed 
within the exposed ends 97 and 99 and an apparatus, not shown, crimps and 
heats ends 84 and 86 and exposed ends 97 and 99. In this operation, 
insulating coating 88 on each of ends 84 and 86 is melted away leaving 
respective welded connections 126 and 128 which are electrically 
connected, as shown in FIG. 6. 
Turning now to FIG. 9, rotor subassembly 124 is placed between a pair of 
mold halves 130 and 132 of a mold 134. Mold halves 130 and 132 have 
respective inner surfaces 136 and 138 which mate against mold shutoff ring 
100 and collar 50 and the outer radial periphery of pole pieces 24 and 26. 
Inner surface 136 has a cup-shaped recess 140 including a radial mating 
surface 142 and an outboard mating surface 144 which mate, respectively, 
with outer radial surface 116 and outboard surface 120 of mold shutoff 
ring 100. The mating of mold shutoff ring 100 between recess 70 on pole 
piece 24 and recess 140 of mold half 130 serves as a mold shutoff to 
prevent mold material from flowing onto rotor shaft 38 and band 92 during 
molding. Similarly, a cup-shaped annular recess 146 mates against the 
outboard and outer radial surfaces of collar 50 to provide a mold shutoff 
to prevent mold material from reaching rotor shaft 38 adjacent pole piece 
26. 
Rotor apertures 137 and 139 are formed in respective inner surfaces 136 and 
138 of mold 134 to accommodate rotor shaft 38. Sprue 152 is provided in 
mold half 130 to introduce mold material into mold 134. Blade recesses 148 
and 150 are also contoured into respective inner surfaces 136 and 138 to 
form blades 32 and 34 of molded fans 28 and 30 during molding. 
In operation, mold halves 130 and 132 are pressed against pole pieces 24 
and 26 of rotor subassembly 124. Recesses 140 and 146 mate against mold 
shutoff ring 100 and collar 50 to prevent mold material from reaching 
rotor shaft 38 and band 92 during the molding operation. As mold shutoff 
ring 100 is radially supported by collar 76 on rotor shaft 38 and axially 
supported against recess 70, large compressive forces can be applied 
across mold half 130, mold shutoff ring 100 and pole piece 24 to ensure 
proper mold shutoff without damaging mold shutoff ring 100. Similarly, a 
counterbalancing compressive force can be applied across mold half 132, 
collar 50 and pole piece 26. As mold material is injected at high 
temperatures and under high pressure, a large rather than small 
compressive load holding mold 134 about rotor assembly 124 is preferred. 
Prior to molding, subassembly 124 is preheated. The mold material forming 
molded fans 28 and 30 and molded insert 122 is Ryton.TM., the same 
material as is used to make slip ring assembly 36. The mold material is 
heated to a molten state of approximately 316.degree. C. 
Mold material is then injection molded at high pressures through sprue 152 
into the open spaces between mold 134 and pole pieces 24 and 26 to form 
molded rotor assembly 20. The mold material travels radially outwardly 
forming fan 28 having blades 32. The mold material then passe through the 
circumaxially spaced gaps in outboard face 69 formed between fingers 58 
and fills region 122 located between pole pieces 24 and 26 to form molded 
insert 22. Finally the mold material passes through circumaxially spaced 
gaps in outboard face 71 between fingers 60, to form fan 30 having blades 
34. 
The molten mold material cools and solidifies before melting either 
coverings 108 and 110 or mold shutoff ring 100 of slip ring assembly 36. 
The armored polythermaleze 2000 coating 88 on coil wire 40 has a flow 
temperature of between 325.degree.-350.degree. C. Therefore, no flow or 
disruption of coating 88 on coil wire 46 occurs during molding. 
Consequently, coil wire 46 and terminals 96 and 98 remain electrically 
insulated from pole pieces 24 and 2 after the molding operation has been 
completed. 
The resulting molded rotor assembly 20 is shown in FIGS. 1 and 2. The 
outboard axial faces 69 and 71 of pole pieces 24 and 26 include thin 
coverings 154 and 156 of molded material. Coverings 154 and 156 and the 
blades 32 and 34 combine to form fans 28 and 30. Connections 126 and 128, 
as well as support ring 48 and bobbin assembly 42, are encapsulated by 
molded insert 22. Molded insert 22 fills region 122 between pole pieces 24 
and 26 and is integral to fans 32 and 34, thereby retaining fans 32 and 34 
to pole pieces 24 and 26. 
The radially outer periphery of molded rotor 20, if not sufficiently 
smooth, is then machined. This produces a smooth cylindrical periphery 
with radially outer surfaces on the fingers 58 and 60 being exposed. Band 
92 of slip ring assembly 36 is machined to produce a clean conductive 
surface and to electrically separate slip rings 102 and 104 from one 
another. 
The smooth outer cylindrical periphery of molded rotor assembly 20 produces 
less air disturbance than a similar rotor without a smooth periphery. 
Also, less noise is generated by vibrating fingers 58 and 60 on pole 
pieces 24 and 26, which are supported by molded insert 22, as compared to 
a rotor assembly wherein the fingers are not supported. 
Rotor assembly 20 is then balanced. Appropriate portions of material are 
removed from pole pieces 24 and 26 in a standard balancing procedure. 
Alternatively, material could be added to rotor assembly for the purpose 
of balancing. With molded insert 22 and molded fans 32 and 34 being 
accurately molded to pole pieces 24 and 26, rotor assembly 20 has been 
found to be better balanced and require less rework to achieve a balance 
condition than a corresponding rotor assembly which has metal fans welded 
to pole pieces. 
FIG. 14 demonstrates how rotor assembly 20 is combined with other 
components to form a vehicle alternator 160. Bearings 162 and 164 are 
mounted on either side of molded rotor assembly 20 on rotor shaft 38. 
Bearing 164 is supported by a retainer 166 which is bolted to a front 
housing piece 168. A stator 170 with windings 172, is placed radially 
about rotor assembly 20. A back housing piece 174 is joined to front 
housing piece 168 to support stator 170 and bearings 162 and 164. A brush 
holder and regulator 176, rectifier 178 and cover 180 are also included in 
vehicle alternator 160. 
Method steps used in constructing rotor assembly 20 are as follows. First, 
coil wire 46, having coating 88 thereon, is wound about bobbin 44 to form 
the bobbin assembly 42. First and second pole pieces 24 and 26 are then 
placed together on rotor shaft 38 capturing the bobbin assembly 44 in the 
region 122. Hubs 46 and 48 are placed to abut one another such that the 
axially extending fingers 58 and 60 are interleaved and spaced apart 
relative to one another. Slip ring assembly 36 is then press fit onto 
rotor shaft 38 with mold shutoff ring 100 being flush against recess 70 of 
pole piece 24 and rotor shaft 38. Connections 126 and 128 are made between 
each of free ends 84 and 86 of coil wire 46 and the respective exposed 
ends 97 and 99 of terminals 96 and 98 of slip ring assembly 36. Finally, 
rotor subassembly 124 is compressively held in place between mold halves 
130 and 132 of a mold assembly 134 with mold shutoff ring 100 sealing 
rotor shaft 38 and slip rings 102 and 104 from mold 134. 
Mold material is then injunction molded into the mold 134 forming molded 
insert 22 which is molded integrally to pole pieces 24 and 26 and fills 
region 122 between pole pieces 24 and 26. Also, fans 28 and 30 are formed. 
Molded insert 22 partially encapsulates fingers 58 and 60 thereby 
providing radial support to fingers 58 and 60. Further, a smooth 
cylindrical surface on the rotor assembly 20 is formed. Optionally, the 
method includes placing a support ring 48 within fingers 58 and 60 prior 
to the molding step. 
A second embodiment of a rotor assembly 220 is shown in FIG. 10 and is 
similar to rotor assembly 20 described above, however,.no molded insert is 
created. Rotor assembly 220 has pole pieces 224 and 226 with molded fans 
228 and 230 being molded thereon. Fans 228 and 230 include respective fan 
blades 232 and 234. Slip ring assembly 36 mounts on rotor shaft 38 with 
mold shutoff ring 100 again serving as a shutoff providing a radial seal 
between a mold assembly (not shown) and rotor shaft 38 during injection 
molding of fans 228 and 230. 
Radially inner and outer anchor recesses 241 and 243 are provided on the 
outboard axial face of pole pieces 224. Similarly, radially inner and 
outer anchor recesses 245 and 247 are formed in pole pieces 226. 
Preferably, the anchor recesses 241, 243, 245 and 247 are dovetailed in 
cross-section. Radially inner anchor recesses 241 and 245 may extend 
continuously circumferentially or else be circumaxially spaced. Anchor 
recesses 243 and 247 are circumaxially spaced on the outboard axial faces 
adjacent fingers 258 and 260. 
The mold assembly used to form fans 228 and 230 seals against the outboard 
axial faces of pole pieces 224 and 226. This prevents leaking of mold 
material between the circumaxially spaced gaps formed between fingers 258 
and 260 and into the region formed between pole pieces 224 and 226 during 
molding. Fans 228 and 230 have respective anchors 249 and 251 and 253 and 
255 which are cooperatively held within respective anchoring recesses 241, 
243, 245 and 247. This anchoring prevents fans 228 and 230 from separating 
from pole pieces 224 and 226 and eliminates the need to have a molded 
insert between pole pieces 224 and 226. 
A third embodiment of a rotor assembly 320, also similar in construction to 
that of rotor assembly 20, is shown in FIG. 13. Rotor assembly 320 has a 
molded insert 322 formed between pole pieces 24 and 26. However, rather 
than using molded fans, rotor assembly 320 uses stamped metal fans 328 and 
330, which are shown in FIG. 4. 
FIGS. 11 and 12 show pole pieces 24 and 26 prior to attachment of fans 328 
and 330. Axially outboard faces 69 and 71 of pole pieces 24 and 26 remain 
free of mold material, with the exception of radially extending channels 
72 which are again filled with mold material during the molding operation. 
Connection 126, shown cutaway in FIG. 13, and connection 128, not shown, 
are again encapsulated in mold material. A lower portion of molded rotor 
assembly 320 in FIG. 12 is shown without mold material to illustrate the 
space available in region 122 between pole pieces 24 and 26. Without 
molded insert 322, air passing through region 122 would cause noise during 
the rotation of rotor assembly 320. 
The mold used to form molded rotor assembly 320, not shown, mates flushly 
against the outboard axial faces 69 and 71 of pole pieces 24 and 26 to 
keep these faces free of mold material, except for the axially extending 
channels 72 which are filled with mold material in the molding step. 
Stamped metal fans 328 and 330, having respective axially outboard 
extending fan blades 332 and 334, as shown in FIGS. 4 and 13, are welded 
to outboard axial faces 69 and 71 of pole pieces 24 and 26. 
As described above, the use of molded insert 22, molded fans 28 and 30 and 
slip ring assembly 36 in molded rotor assembly 20 has advantages over 
prior art rotor assemblies. 
Molded insert 22 fills the region 122 eliminating any empty air space 
located between the pole pieces 24 and 26. The exterior cylindrical 
surface of the rotor assembly 20 may be made smooth. Therefore, there is 
significantly less air disturbance in the region between pole pieces 24 
and 26 in the present design than in a rotor assembly design having no 
molded insert 22. Accordingly, noise produced by the rotating rotor 
assembly 20 is less than the noise of rotor assemblies of a conventional 
design. 
A second advantage is that the molded insert 22 provides radial and 
circumferential support to the fingers 58 and 60 of the pole pieces 24 and 
26, respectively. The molded insert 22 provides sufficient support such 
that the support ring 48 may be eliminated. However, the combination of 
the support ring 48 and molded insert 22 provides more support, and 
consequently allows less vibration by the fingers 58 and 60, than is 
allowed by using molded insert 22 alone. Molded insert 22 also appears to 
serve a noise dampening function due to its material characteristics. 
A third advantage of using the molded insert 22 is that connections 126 and 
128 are completely encapsulated and supported. This support reduces the 
loads and corresponding stresses carried by the connections 126 and 128 
during alternator operation, and therefore, extends the fatigue life of 
connections 126 and 128. Accordingly, the operational lives of the rotor 
assembly 20, and its corresponding alternator 160, are extended. 
Use of molded fans 28 and 30 in rotor assembly 20 obviates the need to 
affix fans to pole pieces 24 and 26. Additionally, configurations of blade 
shapes which are not possible with stamped metal fans are available with 
molded fans. Further, molded fans 28 and 30 can be accurately incorporated 
into rotor assembly 20 to provide a rotor assembly which is relatively 
well balanced and requires less rework to achieve a proper balance than do 
conventional rotor assemblies using stamped metal fans. 
Mold shutoff ring 100 provides significant structural support and rigidity 
to terminals 9 and 98. Further, mold shutoff ring 100 provides a ready 
mold shutoff mechanism when captured between a mold and a pole piece to 
prevent molten mold material from overflowing onto a rotor shaft and 
associated slip rings. The mating of mold shutoff ring 1 between pole 
piece 24 and mold half 132 allows substantial compressive forces to be 
applied across rotor subassembly 124 without damaging mold shutoff ring 
100 or adversely affecting its sealing function. 
While this invention has been described in the foregoing specification in 
relation to certain preferred embodiments thereof, and many details have 
been set forth for the purposes of illustration, it will be apparent to 
those skilled in the art that the invention is susceptible to additional 
embodiments and that certain details described herein can be varied 
considerably without departing from the basic principles of the invention.