Alternating current generator

An alternating current generator for supplying the electrical loads on a motor vehicle. The generator has a stator core that carries a three-phase stator or output winding. The rotor of the generator has two claw pole members that are magnetically connected by a core. A field coil is disposed about the core. The pole fingers of the claw pole members are interleaved and a plurality of permanent magnets are secured to side surfaces of the pole fingers such that there is a permanent magnet between each pair of adjacent pole fingers. The generator is arranged such that flux developed by the permanent magnets can flow through a closed magnetic path that bypasses the air gap between the rotor and stator and such that energization of the field coil with unidirectional current cause permanent magnet flux to traverse the air gap between the rotor and stator and thereby provide a useful flux for generating voltage in the stator winding.

This invention relates to alternating current generators and more 
particularly to alternating current generators for supplying electrical 
power to the electrical loads on a motor vehicle including charging the 
vehicle storage battery. 
Because motor vehicles have ever increasing power demands, an alternator 
with greater electrical output, higher power to weight ratio and better 
conversion efficiency is needed. 
This invention proposes to increase the power output of an alternating 
current generator by utilizing a Lundell rotor for the generator that has 
a field coil and a plurality of permanent magnets that are interposed 
between adjacent pole fingers of claw tooth pole members. 
Alternating current generators that use permanent magnets and control 
windings are disclosed in the U.S. Pat. No. 3,411,027 to Rosenberg. In 
that patent, field flux diverted by the control windings is carried by the 
end frames and a tubular frame connecting the end frames and the control 
windings are stationary. This type of construction leads to large heavy 
machines. 
In contrast to the alternating current generator disclosed in the Rosenberg 
patent, the generator of this invention utilizes a Lundell rotor that is 
comprised of two claw-pole members having interleaved pole fingers and a 
field coil that is disposed about a magnetic core. The claw-pole members, 
core and field coil are supported and secured to a rotor shaft so that 
they all rotate together. The field coil is connected to slip rings which 
rotate with the shaft and which contact brushes. The rotor is provided 
with a plurality of permanent magnets with each permanent magnet being 
interposed between and in contact with side surfaces of adjacent pole 
fingers of the claw-pole members. Flux developed by the field coil crosses 
the air gap between the rotor and stator in a conventional fashion. 
However, the flux developed by the permanent magnets can bypass the air 
gap between the rotor and stator or can be caused to traverse the air gap 
between the rotor and stator by energization of the field coil with 
unidirectional current. 
More specifically, the flux developed by the permanent magnets can pass 
through a closed magnetic path that is comprised entirely of magnetic 
material. This path is comprised of the two claw-pole members and a core 
that engages the claw pole members. This closed magnetic path shunts or 
bypasses the air gap between the rotor and stator so that except for 
leakage flux, the flux developed by the permanent magnets does not link 
the stator winding. When the field coil is energized with unidirectional 
current, the magneto-motive force (mmf) developed by the field coil 
opposes the permanent magnet (mmf) in the closed magnet circuit and 
thereby causes the permanent magnet flux to cross the air gap between the 
rotor and stator and link the stator winding. 
It, accordingly, is an object of this invention to provide an alternating 
current generator of the type that has been described that can control 
both field flux and permanent magnet flux by controlling unidirectional 
field current. 
Another object of this invention is to provide a voltage regulated 
alternating current generator of the type described where field current is 
controlled by a conventional switching voltage regulator.

Referring now to the drawings and more particularly to FIG. 1, the 
alternating current generator of this invention comprises metallic end 
frames 10 and 12 that support a stator assembly 14. These end frames are 
typically formed of aluminum. A plurality of through-bolts (not 
illustrated) are used in a known manner to secure the end frames together. 
The stator assembly 14 is comprised of a slotted stator core 16 formed of 
a stack of steel laminations that carries a three-phase stator or output 
winding 18. Portions of the stator winding 18 are located in the slots of 
stator core 16 as is well known to those skilled in the art. 
The alternating current generator has a rotor generally designated by 
reference numeral 20. This rotor is comprised of a shaft 22 that is 
supported for rotation by bearings 24 and 26. A pulley 28 is connected to 
shaft 22 and a cooling fan 29 is secured to the shaft. 
The rotor 20 further comprises claw pole members 30 and 32 and an annular 
core 34, all of which are secured to shaft 22 to rotate therewith. The 
ends of core 34 respectively engage pole members 30 and 32. Pole members 
30 and 32 and core 34 are all formed of magnetic material such as steel. 
The core 34 supports a field coil 36 that is carried by a spool 38 that is 
formed of insulating material. The spool and field coil form parts of the 
rotor and rotate relative to the stator whenever the rotor is rotated. 
The rotor shaft 22 carries metallic slip rings 40 and 42 that are 
electrically insulated from each other and from shaft 22. The slip rings 
are engaged by brushes 44 and 46 that are supported by brush holder 48. 
The slip ring 40 is connected to one side of field coil 36 by a conductor 
52. The opposite side of field coil 36 is connected to slip ring 42 by a 
conductor 50. 
The rotor pole members 30 and 32 are identical. Pole member 30 has a disk 
portion 30A and six circumferentially spaced and axially extending pole 
fingers 30B. Pole member 32 has a disk portion 32A and six 
circumferentially spaced and axially extending pole fingers 32B. It can be 
seen that the pole fingers 30B and 32B are interleaved, that is, pole 
fingers 30B are located in spaces between pole fingers 32B and vice-versa. 
The rotor has twelve permanent magnets each of which is designated as 54. 
Each permanent magnet 54 has opposed end faces 54A and 54B that engage 
respective side surfaces on pole fingers 30B and 32B. The sides of 
permanent magnets 54 fit into slots or grooves 30C and 32C formed in pole 
fingers 30B and 32B shown in FIG. 2. The permanent magnets are 
press-fitted into the grooves or slots and may be secured to the pole 
fingers by a suitable adhesive. The faces 54A and 54B have opposite 
magnetic polarities. Thus, it will be assumed in the further description 
of this invention that faces 54A have a south magnetic polarity and that 
faces 54B have a north magnetic polarity. 
Although only two permanent magnets 54 have been shown in FIG. 1, it is to 
be understood that 12 magnets are used, and that there is a permanent 
magnet 54 between each pair of opposed side surfaces of pole fingers 30B 
and 32B. Further, the permanent magnets are arranged such that the opposed 
sides of pole fingers 32B are respectively engaged by magnet surfaces 54B 
of a north magnetic polarity and opposed sides of pole fingers 30B are 
engaged by magnetic surfaces 54A of a south magnetic polarity. This 
arrangement causes all the pole fingers 32B to have a north magnetic 
polarity and all the pole fingers 30B to have a south magnetic polarity. 
The field coil 36 of the generator, shown in FIG. 1, is energized with 
unidirectional current by a voltage regulating arrangement that is shown 
in FIG. 4. In FIG. 4, output winding 18 is shown as being Delta-connected 
but it could be Y-connected if so desired. The stator or output winding 18 
is connected to a three-phase, full-wave bridge rectifier 60 having a 
positive direct voltage output terminal 62 and a grounded negative direct 
voltage output terminal 64. The positive terminal 62 is connected to the 
positive terminal of storage battery 66 by line 68. 
Unidirectional current is supplied to field winding 36 by line 70 and a 
field effect transistor 72 which forms a part of a conventional generator 
voltage regulator. The drain of transistor 72 is connected to line 70 and 
its source is connected to one side of field coil 36 through slip ring 42. 
The opposite side of field winding 36 is grounded through slip ring 40 and 
a field discharge diode 74 is connected across field winding 36. The gate 
of transistor 72 is connected to a voltage sensing circuit identified as 
VS. The voltage sensing circuit is connected between the positive side of 
battery 66 and ground and it accordingly senses the voltage across battery 
66. The voltage regulator is of the type disclosed in the U.S. Pat. No. 
4,636,706 to Bowman et al. When the voltage between line 68 and ground is 
above the desired regulated value, the voltage sensing circuit VS causes 
transistor 72 to be shut-off or nonconductive to cut-off field current to 
field winding 36. When the voltage between line 68 and ground is below the 
desired regulated value, the transistor 72 is pulse-width modulated on and 
off that provides a field current that tends to increase the voltage on 
line 68 toward the desired regulated value. When the voltage on line 68 
increases to a level where it exceeds the desired regulated value, 
transistor 72 shuts off. The pulse-width modulated control of field 
current is explained in above-referenced patent 4,636,706. 
The field coil 36 is so wound and the direction of the current flow 
therethrough is such that disk portion 32 and pole fingers 32B have a 
north magnetic polarity and the disk portion 30A and pole fingers 30B have 
a south magnetic polarity. This is under the assumption that permanent 
magnets 54 have the magnetic polarities described above. 
When no current is supplied to field coil 36, the flux developed by each 
permanent magnet 54 will flow from its north pole (face 54B) to its south 
pole (face 54A) in a path that is made up entirely of steel or iron with 
no air gaps in this path. The path is from a face 54B of a magnet 54 to a 
pole finger 32B, through disk portion 32A to pole core 34 and then through 
pole core 34, disk portion 30A and a pole finger 30B to a face 54A of a 
magnet 54. The flux path has been described for only one magnet 54 and it 
will be apparent that the flux path is the same for all twelve magnets. 
The flux developed by the permanent magnets 54 is retained within the 
rotor and does not link the output winding 18 except for a small quantity 
of magnetic leakage flux. Accordingly, the voltage induced in stator 
winding 18 is small. The flux path that has been described can be 
considered as diverting or shunting the permanent magnet flux away from 
the air gap between the rotor and stator core 16. Since pole fingers 30B 
and 32B form a shunt magnetic path, their cross-sectional areas are sized 
such that they are large enough to carry the permanent magnet flux. 
Assume now that field coil 36 is energized. With the polarities of the 
permanent magnets and field coil, as has been described, the flow of 
permanent magnet flux through pole fingers 30B and 32B and core 34 is 
determined by the mmf developed by field coil 36. The mmf developed by 
field coil 36 opposes the mmf developed by the permanent magnets in the 
closed magnetic circuit comprised of pole members 30 and 32 and core 34. 
In regard to the development cf an mmf by field coil 36, it will be 
appreciated that the mmf between pole fingers 30B and 32B varies as field 
current is varied and is zero with no field current. This said mmf 
determines the flux that flows through a path that includes pole fingers 
32B through the air gap to stator core 16 through the air gap between 
stator core 16 and pole fingers 30B and then from pole fingers 30B through 
disk portion 30A and pole core 34. Permanent magnet flux can flow in two 
paths: one path, which diverts flux from the air gap between the rotor and 
stator is through pole fingers 30B and 32B and through core 34. The other 
path is from pole fingers 32B to stator core 16 and through stator core 16 
to pole fingers 30B. From what has been described, it will be apparent 
that fluxes developed by the permanent magnet and by the field coil both 
link stator output winding 18 so that both fluxes now serve to cause a 
voltage to be induced in winding 18. The amount of permanent magnet flux 
that is diverted away from the stator core 16 depends on the amount of mmf 
developed by field coil 36. When there is no current supplied to field 
coil 36, all of the permanent magnet flux except for leakage is diverted 
away from stator core 16 because it flows through the previously described 
closed iron path, including pole fingers 30B and 32B and core 34. As field 
coil 36 is energized, less permanent magnet flux is diverted away from 
stator core 16. The amount of permanent magnet flux that is diverted away 
from stator core 16 will depend upon the magnitude of the mmf developed by 
field coil 36 which, in turn, depends upon the magnitude of field current 
supplied to field coil 36. At some intermediate level of field coil mmf, 
none of the flux developed by permanent magnets 54 is diverted away from 
stator core 16. As field coil mmf is further increased, all the permanent 
magnet flux plus field coil flux, less leakage, is delivered to stator 
core 16. Thus, the total air gap flux can be controlled from some near 
zero minimum to some maximum design value. In a practical application, the 
system may be configured such that at maximum field current, the total 
useful flux that links output winding 18 can be made up of 40% permanent 
magnet flux and 60% field coil flux. 
It will be appreciated that the output voltage of output winding 18 can be 
maintained at a desired regulated value by the simple voltage regulating 
arrangement shown in FIG. 4 which supplies unidirectional current to field 
coil 36. Thus, when the output voltage of output winding 18 is below the 
desired regulated value, field current is increased. A field current 
increase has a two-fold effect in increasing generator output voltage; 
that is, it causes less permanent flux to be diverted away from stator 
core 16 and it causes an increased field coil flux to link output winding 
18 due to increased field current. When the output voltage of output 
winding 18 exceeds the desired regulated value, field current is reduced 
which reduces air gap flux. By using the generator structure in FIG. 1, 
which is capable of variably diverting permanent flux away from stator 
core 16 the simple voltage regulating arrangement shown in FIG. 4, can 
regulate the output voltage of the generator. There is no need to reverse 
the direction of current flow through field coil 36 to regulate the output 
voltage of the generator. Regulation is accomplished by supplying a 
variable unidirectional current to field coil 36. 
The concept disclosed above can be extended to alternators having twin 
rotor sections consisting of two back to back Lundell rotors on a common 
shaft. FIG. 3 illustrates such a rotor construction that can be 
substituted for the rotor of FIG. 1. The rotor of FIG. 3 uses two rotors 
supported by a common shaft 78 where each rotor is like the rotor shown in 
FIG. 1. One of the rotors is comprised of pole fingers 80 and 82 with 
permanent magnets 84 interposed therebetween. This rotor has a field coil 
and core like FIG. 1 which is not illustrated. The other rotor is 
comprised of pole fingers 86 and 88 with permanent magnets 90 interposed 
therebetween. This rotor also has a field coil and core like FIG. 1 which 
is not illustrated. The FIG. 3 rotor is constructed like the rotor shown 
in FIGS. 8 and 9 of patent application Ser. No. 263,850 filed on Oct. 28, 
1988, now U.S. Pat. No. 4,882,515 which is incorporated herein by 
reference. The rotor shown in FIGS. 8 and 9 of application Ser. No. 
263,850, now U.S. Pat. No. 4,882,515 is modified to the extent of 
replacing permanent magnet 94 with a field coil like field coil 90. Each 
rotor that has been described operates like the rotor shown in FIG. 1. 
The two field coils of the rotor shown in FIG. 3 can be regulated by the 
system shown in FIG. 4. That is, the two field coils can be connected in 
series or in parallel and, thus, powered via transistor 72. The manner of 
connecting the field coils in series or in parallel is shown in FIGS. 6 
and 7 of the above referenced patent application Ser. No. 263,850 now U.S. 
Pat. No. 4,882,515. 
It will be appreciated that when the dual rotor of FIG. 3 is used as a 
component of an alternating current generator the length of the stator 
core 16 must be increased to accommodate the two rotors. The advantage of 
the construction shown in FIG. 3 is that greater output power can be 
obtained for a given rotor diameter.