Note: Descriptions are shown in the official language in which they were submitted.
11453975
1 Case 2572
PERMANENT MAGNET A~TERNATOR WITH CLAW TYPE ROTO~
AND MEANS TO ADJUST THE EXCITATION MODULE
This invention relates to claw type dynamoelec-
tric machines, and in particular it relates to claw
type alternators having a field provided by permanent
magnets with means to control the field.
Claw type alternators having permanent magnets
to generate the active field are known. For example,
Canadian Patent No. 773 214 - Tiltins, issued December
5, 1972, describes a claw type alternator structure
which may have either a permanent magnet arrangement
or a fiéld winding to provide the alternator field.
It is also known to control the flux from a permanent
magnet in an alternator. In Canadian Patent No.
793 961 - Rosenberg, issued September 3, 1968, there
i~ described, for example, a claw type alternator
having permanent magnets mounted on the rotor to
generate flux for the alkernator, and a control
winding on the stator which is able to adjust or
control the flux in the main air gap.
None of the known prior art alternators seem
to include a structural arrangement which simplifies
adju~tment as well as as~embly and disassembly.
To provide higher efficiencies in alternators
which use permanent magnets, it is of course desirable
to use magnets with a high field strength. The large
magnetic attraction forces associated with the
permanent magnets create problems during assembly and
disassembly as well as with adjustment of the air gap.
'--~
li4~975
Case 2572
The present invention reduces or eIiminates these
problems.
In the present invention the permanent magnets
are mounted on a radially extending surface of a
stationary module. The magnetic attractive forces are
axially directed. The module may be moved axially
using jack screws to adjust the air gap. Assembly
and disassembly can be carried out using screw
adjustment means to move the module inwardly the final
part of the distance during assem~ly and to move the
module initially outwards during disassembly until the
attractive forces diminish to manageable levels.
The present invention also provides a field
winding or control winding on the stationary module.
lS The module thus includes the permanent magnets which
provide the "normal" excitation and the field coil
which provides regulatory excitation, and the module
is axially movable as a unit for assembly and
disassembly as well as for adjustment of the air gap.
The arrangement of the magnets and the field coil is
such that the field coil may be energized during
as3embly or disassembly, and the field it generates
will reduce the magnetic flux at the poles, due to
the permanent magnets, substantially to zero if
desired. Thus the magnetic forces may be reduced to
manageable levels during assembly and disassembly if
desired.
The present invention i9 particularly suited
for use with a low speed wind turbine where a substan-
tially constant output is desired over a speed rangeof perhaps 70 - 200 RPM. However, it will be apparent
that the alternator of the present invention is not
restricted to any particular use. The structure which
permits easy assembly and disassembly, and also
adjustment, may be used in any alternator having
114~)975
Case 2572
permanent magnets and a fieId winding or control
winding. The present invention is, in addition,
suitable for use in motors as will be apparent to those
skilled in the art. In fact, if the invention is
incorporated in a synchronous motor, the ~ield winding
may be energized for a short time during the starting
cycle to assist the motor to accelerate under load.
It is a feature of the present invention to
provide a structure for a claw type dynamoeIectric
machine having permanent magnets which permits easier
assembly, disassembly and adjustment.
It is another feature of the present invention
to provide in a claw type dynamoelectric machine, a
stationary module which includes both the permanent
magnets for providing the main excitation flux and a
field winding for regulating the flux in the air gap
and which is adjustable and removable as a unit.
It is also a feature of the invention to provide
a claw type alternator with a module that is readily
assembled and disa9sembled and which includes means to
provide a controllable flux.
~ ccordingly in one form of the invention there
is provided a dynamoelectric machine comprising, a
stator with a stator winding, a claw type rotor having
a spider of magnetic material mounted to a shaft for
rotation within said stator, said spider having a
plurality of first claws spaced around the periphery
forming a first set of poles, an annular disc of
magnetic material spaced axially from said spider by
a non-magnetic material, said annular disc having a
plurality of second claws spaced around the periphery
and interleaved with said first claws forming a second
set of poles, an excitation module having a core of
magnetic material with a first radially extending
planar surface and a second radially extending planar
Case 2572
surface spaced axially from and outwardly with respect
to said first surface, and a plurality of permanent
magnets on said second surface, said module when in
an operating position having said first surface in
juxtaposition with said spider forming a first air gap
therewith and said permanent magnets in juxtaposition
, with said annular disc forming a second air gap
therewith, said permanent magnets providing flux to
said first claws of one polarity and to said second
claws of opposite polarity.
According to another form of the invention
there is provided an alternator comprising a casing
having a first and second endshield and an intermediate
stator shell, a stator core mounted within said
stator shell, a stator winding on said stator core, a
claw type rotor mounted to a shaft supported by
bearings in at least one endshield for rotation within
said stator core, said rotor including a spider of
magnetic material mounted to said shaft and having a
plurality of first claws spaced around the periphery
thereof forming a first set of poles, an annular disc
of magnetic material spaced axially from said spider
by a non-magnetic material, and means mounting said
. annular disc to said spider, said annular disc having
a plurality of second claws, equal in number to said
first claws, spaced around the periphery thereof
forming a second set of poles and interleaved with said
first claws, a stationary excitation module having a
core of magnetic material,with first and second
parallel and radially extending surfaces, the second
surface being spaced axially from the first surface
and being positioned outwardly with respect to said
first surface, a plurality of permanent magnets
mounted on said second surface, said first surface
forming with said spider a first air gap and the
1140975
Case 2572
magnets on said second surface forming with said
annular disc a second air gap, said permanent magnets
inducing north magnetic poles in one of said first
set of poles or said second set of poles and south
magnetic poles in the other.
According to yet another form of the invention
there is provided in a dynamoelectric machine having
a stator and a stator winding, a claw type rotor having
a spider secured to a rotor with first spaced peripheral
claws, and an annular disc spaced axially from said
spider and fixed thereto with second spaced peripheral
claws interleaved with said first claws, said spider
and said disc being of magnetic material, an excitation
module having a first planar surface facing said spider
and a second planar surface facing said annular disc,
a plurality of permanent magnets mounted on one of
said first or second surfaces, and, means to move said
excitation module axially for assembly, disassembly
and adjuqtment of the air gap between said magnets
and the opposing one of said spider or disc.
The invention will be described in more detail
with reference to the accompanying drawings in which
Figure 1 is a cross-sectional view of a
dynamoelectric machine according to the invention,
showing only one half of the machine, and
Figure 2 is an isometric overall view of the
machine of Figure 1.
Referring now to the drawings an alternator
10 has a casing 11 which includes a stator shell 12
with an upper endshield 14 and a lower endshield lS.
The endshields 14 and 15 are secured to shell 12 with
bolts 16 and 17 respectively, spaced around the
periphery of the casing. A bearing assembly 18 is
mounted inside collar 20 of endshield 14 and supports
a shaft 21 for rotation therein. The bearing assembly
11~0975
Case 2572
comprises deep groove ball bearing sets 22 and 23
separated by a spacer 24. A locknut 25 on shaft 21
- retains the bearing assembly 18. Bearing caps 26 and
27 are mounted to collar 20 above and below the
bearing assembly 18 with bolts 31. A flinger 28 is
mounted to shaft 21 and has a portion extending into
a groove or well 30 in bearing cap 27 to fling oil
lubricant upwards and outwards away from the shaft.
It is preferred to locate the bearings on one
side of the rotor as will become apparent. This not
only places the bearings in a region where they will
not be subjected to magnetic flux, but it simplifies
assembly and disassembly of the flux providing module
also as will become apparent subsequently.
Mounted within the stator shell 12 is stator
core 32 with stator winding 33. Preferably a series
of grooves 34 behind core 32 in shell 12, are provided
to form passages for circulating air. The outer surface
of shell 12 has radiating fins 35 to assist in radiating
or dissipating heat. The cooling of the alternator
will be discussed subsequently.
A rotor 36 is mounted to shaft 21. The rotor
36 may be keyed to shaft 21 with a key 37 and retained
by a lock ring 38. Other suitable Eastening means
may be used.
The rotor 36 comprises a spider 40 of magnetic
material having at the outer periphery a plurality of
more or less L-shaped claws 41. The claws 41 are
spaced apart and form one set of poles. The claws 41
are conveniently integrally formed with spider 40.
An annular disc 42 of magnetic material has at the
outer periphery a plurality of more or less L-shaped
claws 43. The claws 43 are spaced apart and
interleaved with claws 41. The claws 43 are
conveniently integrally formed with disc 42 and form
11~0975
Case 2572
the other set of poles. The disc 42 is spaced from
spider 40 by a ring 44 of non-magnetic material.
Machine screws or bolts 45 spaced around the spider 40
extend through spider 40 and through ring 44 into disc
42 to mount the disc 42 and ring 44 to spider 40
forming the rotor assembly.
A stationary excitation module 46 comprises
a core 47 of magnetic material mounted to end shield
15 by a plurality of bolts 48. The core 47 has a
radially extending planar surface 50 on which are
mounted a plurality of permanent magnets 51 extending
around the planar surface 50 and forming with the
adjacent surface of annular disc 42 an air gap 52.
This is the air gap that is adjustable. Core 47 has
a recess or well 53 extending around it, the bottom
surface of well 53 forming a cylindrical surface at
right angles to planar surface 50. A field winding
or control winding 54, in the form of a doughnut
shaped coil, is mounted in well 53. Field winding
54 may have applied to it a dc current, and the
strength and direction of the current determines the
strength and direction of the field in core 47. Thus
the field coil may provide a flux which aids or
opposes the flux from the permanent magnets 51. An
opposing flux may be of a strength to substantially
prevent magnets 51 from providing excitation flux.
It will be apparent that the magnets could be
mounted to the surface of core 47 which faces spider
36. While this alternative is satisfactory, it is not
preferred because the area of the air gap surfaces at
this location is smaller than the available area at
the gap facing the surface of rotor disc 42 since the
air gap at rotor disc 42 is at a larger radius or
distance from the axis of rotation.
3S When the alternator 10 is operating, the
114~)97S
Case 2572
permanent magnets 51 provide the operating flux to
the rotor. Assuming for convenience of description that
the permanent magnets have a north pole facing air gap
- 52, flux will cross air gap 52, disc 42, and the claws
43 will be north poles. Similarly, there will be a
flux path through core 47, across an air gap 55,
through spider 40, and the claws ~l will be south
poles. As the claws 41 and 43 are interleaved there
will be a succession of alternating north and south
poles around rotor 36, and as rotor 36 rotates there
will be an alternating current generated in stator
winding 33.
It should be noted that the permanent magnets
51 are located where they are magnetically shielded
from armature reaction effects even up to a condition
where a short circuit might occur in the armature
winding .
As the speed increase~ over the working speed
range of the alternator, the current in field winding
54 is controlled to maintain the output voltage of the
alternator substantially constant. When the alternator
is used with a wind turbine, it is normally used to
charge a battery and it is therefore necessary that
the output voltage be kept within preset limits, i.e.
substantially constant over the working range.
Referring for a moment to heat dissipation
during operation, heat generated by field winding 54
tends to flow through the heavy magnetic core 47 to
casing 11 where it is radiated or removed by air flow
over the surface of the casing. Because of its
considerable mass, core 47 provides a good heat flow
path. The moving rotor 36 causes internal circulation
of air generally as indicated by arrows 56. This air
flow passes over the end heads of the stator winding,
through rotor 36 and through the passage formed by
114~)975
Case 2572
grooves 34. Heat tends to be transferred to shell 12
where it is removed by radiation or by air flow over
fins 35. Air can be circulated over shell 12 by an
air duct and a fan if desired.
In the assembling of alternator 10, very
briefly, the shaft 21 and bearing assembly 18 are
positioned in endshield 14 and locknut 25 mounted.
Flinger 28 is installed. Bearing caps 26 and 27 are
installed using bolts 31. The rotor 36 including disc
42, ring 44 and both sets of claws is placed on shaft
28, key 37 is positioned and lock ring 38 installed.
The stator shell 12 with core 32 and winding 33 is
mounted to endshield 14 using bolts 15. Now the
portion so far assembled is fixed with respect to a
reference surface by using mounting bracket 57 and
bolts 58 indicated in broken lines. The distance is
measured from spider 37 and disc 42 to the reference
surface. The distance is measured from the exposed
end surface of shell 12 i.e. from the outer surface
of flanged portion 60 on shell 12 to the reference
surface. With these measurements and knowing the
dimensions of core 47, magnets 51 and endshield 15,
a required measurement for shims 59 to be placed
between core 47 and endshield 15 can be determined
to provide the required air gaps 52 and 55. When the
necessary shimming has been determined, core 47, with
field winding 54 and magnets 51 installed, is mounted
to endshield 15 with shims 59 in place, using bolts
48. The endshield 15 with the excitation, module 46
(core 47, winding 54 and magnets 51) is now ready to
mount.
Referring for the moment to Figure 2, the
flanged portions 60 and 61 on the stator shell 12
and the lower endshield 15 respectively, and which
are secured by bolts 17 to hold the lower endshield 15
114U975
Case 2572
to shell 12~ are also provided with jack screws 62.
There are four jack screws 62, distributed around the
flanged portions 60 and 61. Any number of jack screws
62 may of course be used as long as they are sufficient
to move the endshield 15 slowly towards shell 12. The
jack screws may be threaded into flanged portion 61
and project to engage flanged portion 62.
To continue with the assembly, the jack screws
62 are extended and guide pins placed in at least some
of the holes which accommodate bolts 17 to align the
bolt holes. It will be recalled that the attractive
force caused by the permanent magnets is axial in
direction. Now the lower endshield 15 with the
excitation module 46 is positioned with the holes for
bolts 17 aligned and the jack screws 62 engaging
flanged portion 60. The jack screws 62 are then
progressively retracted to permit the flanged portion
61 to engage the flanged portion 60. The guide pins
are removed and bolts 17 tightened to secure the
casing.
In a typical alternator designed, for example,
to provide 720 W when rotating at a rated speed of
200 RPM, the magnetic force with the alternator
assembled might be of the order of 2000 lb. The
working air gap 52 might be of the order of 0.030
inch (0.7620 mm). When this air gap has been enlarged
to say 14 times the working air gap, that is to about
0.42 inch (10.668 mm), the magnetic force will have
decreased to about 1/200 of the assembled force or
about 10 lb. Thus, the jack screws 62 need anly be
capable, under these conditions, of operating through
a movement of about 0.5 inch (13 mm).
The field winding 54, it will be recalled, is
a doughnut shaped coil and it will produce in core 47
a flux which is substantially in either the same
. ,
1~4~975
Case 2572
11
direction or in the opposite direction to the flux
from the permanent magnets 51. Thus, if preferred,
the field winding 54 can be energized to reduce the
resultant flux to substantially zero prior to assembling
the endshield 15 with excitation module 46 to the
remainder of the alternator. The same technique, in
reverse, can be used for disassembly. This makes
assembly and disassembly much easier provided the
permanent magnets 51 can withstand the reverse
excitation. This will depend on the material of the
permanent magnets. A cobalt rare earth magnet is able
to withstand such reverse excitation.
It was previously mentioned that the present
invention could be used in a motor and this will now
be apparent. When the machine described is used as
a motor, the field winding 54 is obviously used for
a different purpose as there is no output voltage
to regulate. The invention is directed primarily to a
structure which provides a simpler assembly and
disassembly and thiC is available in a dynamoelectric
machine of the type described uRed either as an
alternator or as a motor. The field winding may be
used to aid assembly and disassembly whether in an
alternator or motor. Also, in an alternator, the
field winding can regulate voltage and in a motor it
can be used to assist starting.
Other advantages and uses may be apparent to
those Rkilled in the art.
