Note: Descriptions are shown in the official language in which they were submitted.
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HYBRID ALTERNATOR
Background Of The Invention
1. Field of the Invention
This invention relates to alternators of the type that are used in vehicles to
5 provide electrical power for running ~rcecschies and charging batteries. More
particularly, this invention relates to a high-efficiency hybrid alternator in which the
rotating magnetic field is provided by a rotor having permanent magnet poles andwound field poles operating in combination. The invention also relates to a
temperature monitoring voltage regulator specially designed to automatically
10 regulate bi-directional current flow in the rotor winding to control the output
voltage of hybrid alternators and to permit inaeased alternator output whenever
the alternator temperature is below a predetermined maximum operating
temperature.
2. Description of Related Art
The automotive industry has been attempting to increase the efficiency of
motorized vehicles, both at idle and at running speeds. The alternator design mos
commonly found in vehicles has been used for approximately twenty-five to thirtyyears and is inexpensive to produce, but exhibits very low efficiency levels, 2S low
as 4~50%. The problem is particularly acute at low RPMs where high excitation
20 levels in the rotor winding are required to produce the desired voltage, leading to
very low efficiency.
In conjunction with the desire for higher efficiency is the need to supply
alternators that have larger electrical ratings because modern vehicles have many
more motors and require much more electrical power. Moreover, fuel efficiency of25 vehicles is closely related to the weight of the vehicle ancl it is desirable to decrease
the weight of the alternator so as to minimize the total vehicle weight. These
objectives are achieved when the efficiency of the alternator is inaeased.
The increased power usage in vehicles has also led to an interest in using
components that operate at higher voltages than the standard 12 volts presently
30 used in automobiles. At the same time, it is foreseen that 12 volt power will be
required in such vehicles in addition to the higher voltage.
It is known to provide dual voltage alternators by providing two windings on
the stator. However, when a single winding is used on the rotor, it is difficult to
properly regulate the two different voltage outputs as different levels of rotor35 e~ccil~lion current may be required for the different circuits. Single and dual
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voltage alternators of the type represented by the present invention may also beused in various non-engine driven applications, such as wind or water driven
applications, for the efficient generation of electrical power.
Hybrid alternators significantly increase their efficiency by using permanent
magnets to produce a high level of magnetic flux immediately, while the alternator
is operating at low speed. Using the hybrid alternator disclosed herein, the
alternator will produce full rated alternator current and voltage output at engine
idling speed when installed in an automobile or other vehicle. This can be
co,-l,a~led with prior art alternators that are incapable of producing their full rated
10 output until they are turning at speeds far above their rotational speed at idle.
The full rated output of the hybrid alternator is achieved at low speed by
supplementing the magnetic flux produced by the permanent magnets. The
supplementing magnetic flux is produced by a rotor winding having a forward rotor
winding current induced therein by a forward polarity voltage applied across the15 winding. This is referred to as the boosting mode or the forward polarity mode in
which the wound field induced magnetic field is in the same direction as, and
supplements, the permanent magnet induced magnetic field.
As the alternator RPM increases, however, the magnetic flux from the
permanent magnets produces a greater output and the need for the supplementing
20 flux from the rotor winding decreases. Ultimately, at a sufficiently high speed, all
of the alternator's rated output is available solely from the permanent magnet
induced magnetic field, and no additional current is needed in the rotor windingGenerally, this transition occurs at a speed well below the maximum anticipated
operating speed of the alternator.
As the rotor speed exceeds this transition point, with the engine operating at
a high speed, the flux from the permanent magnets is too great and must be
reduced to avoid producing damaging overvoltages and overcurrents. This is
accomplished by operating the hybrid alternator in the bucking mode or the
reverse polarity mode in which a reverse polarity voltage is applied to the rotor
30 winding. The reverse polarity voltage produces a reverse current in the rotorwinding. The reverse current generates a magnetic flux which opposes the
magnetic flux from the permanent magnets, thereby reducing the output of the
alternator to maintain the desired output voltage.
The necessity for both forward and reverse rotor winding excitation current
35 imposes certain limitations and requirements on the voltage regulator for the hybrid
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alternator which are not required in the case of conventional alternators. Although
hybrid alternators of a low efficiency claw pole or Lundell type design are known,
the existence of these limitations and requirements has not heretofore been
recognized by the art even when producing voltage regulators for hybrid
5 alternators.
A first problem is related to the inductive effects of switching the highly
inductive rotor winding, particularly to transition between the forward and reverse
polarity excitation modes. The problem is most acute when the alternator is lightly
loaded and a battery is not connected to the alternator. In this condition, a net
10 instantaneous negative current may be introduced onto the main power bus.
Current induced in the field winding stores significant energy in the
magnetic field of the rotor winding. This energy can cause voltage spikes due to- sudden load changes or when switching the voltage to drive the rotor winding. To
reduce the output voltage of a hybrid alternator, the prior art has simply indicated
15 that the reverse polarity mode should be applied to reduce or reverse the current in
the field winding. However, before the current can be reversed, the previously
induced magnetic field must collapse. During this collapse, the forward current
originally induced in the forward polarity mode continues back up into the main
power bus leading to the battery and all of the automobile accessories.
In implementing the prior art system of regulation, a bridge circuit has been
used providing two state voltage pulse width modulation. This type of modulationresults in negative current steps into the main power bus with the negative stepamplitude equal to the magnitude of the field current. If the load current on the
main power bus is less than the magnitude of the field current, a net negative
current is applied to the bus. This current has no place to go because the alternator
diodes prevent negative current flow into the alternator and result in a destructive
voltage spike unless suppressed by the battery or a large bus capacitor.
If a battery is connected to the alternator as in the normal case, the battery
can be relied upon to absorb any net negative current after the battery's other
loads. Alternatively, a large capacitor can be used to absorb this energy. Ho~,vever,
the first method cannot be relied upon as a battery may not always be plresent
capable of absorbing the reverse current. Using a capacitor is extremely expensive,
particularly when capacitors adequate for handling all the energy stored in the rotor
winding are used that are temperature rated for use under the hood of an
automobile.
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If the battery were to be removed, without a capacitor there would be no
place for the net reverse current on the main power bus to go unless a large filter
capacitor is placed aaoss the circuit where the battery connection normally exists.
If moderate frequency pulse width modulation techniques are employed, this
5 capacitor can be of reasonable value. However, for lowest costs and small physical
size an aluminum electrolytic capacitor would be desirable. Aluminum electrolytic
capacitors, however, are not normally designed to tolerate temperatures in excess
in 105~C and thus, they could not be easily housed in the hot environment of thealternator in the vicinity of the vehicle engine.
Even if they were somewhat isolated from the hot alternator itself so as to
avoid temperatures above 105~C the life of capacitors is rapidly reduced with
inaeasing temperature. Thus, the under the hood environment would normally
not permit the use of aluminum electronics. Higher temperature tantalum
capacitors could be used but they are physically larger and much more expensive
15 and are thus less attractive for a cost sensitive high volume automotive application.
Also, even if capacitors are used to absorb the switching transients, there is
still a potential problem due to the large energy storage and long time constant of
the field coil. For example, if the alternator speed or load should abruptly change
so as to cause the alternator regulator to change the field voltage polarity from near
20 full voltage (e.g. boost in the forward polarity mode) in one direction to significant
voltage in the other direction (e.g. buck in the reverse polarity mode) a large
voltage transient would tend to occur if no battery were present and the system was
unloaded (except for field coil).
In this situation the initial energy in field coil would tend to go into the
25 capacitor and the voltage would be excessive unless the capacitor were extremely
large or the bus voltage were clamped.
Although only moderate sized capacitors would be required to handle the
ripple current from the pulse with modulation, the capacitor would have be
physically very large to be able handle the high energy in a field winding without
30 aeating an excessive voltage. Even if voltage clamps were employed to limit the
capacitor voltage, the costs would be excessive, there would be continuing
concerns over reliability due to the high temperature environment, and the size of
the components would aeate a problem in the aamped environment under the
hood.
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A solution allowing the use of pulse width modulation techniques, even if
the battery is not present, and one that does not require a large capacitor is needed.
A second, more subtle, problem is that precautions must be taken to prevent
the voltage regulator that is providing the reverse current in the reverse polarity
5 mode from being inactivated when the vehicle is turned off. At very high engine
and alternator speeds, the magnetic flux from the permanent magnet is almost
completely canceled by the oppositely directed magnetic flux in the hybrid rotorwinding. If the canceling flux were to be immediately turned off, e.g. by turning
off an ignition switch with the alternator operating at a high rotational speed, the
10 output voltage of the alternator would rapidly increase to damaging levels for the
electrical components in a typical automobile.
The present invention incorporates an automatic interlock which powers the
voltage regulator automatically and independently of the ignition system of the
vehicle to prevent it from inadvertently being deactivated. The design of the
15 automatic interlock is such that little or no current is drawn from the vehicle battery
when the vehicle is off, which might tend to discharge the vehicle battery.
The preferred embodiment of the voltage regulator also incorplorates
transient voltage suppression in a novel way that permits certain switches
(preferably FETs) needed for the purpose of switching the rotor winding between
20 forward and reverse polarity modes to perform a second function of suppressing
voltage transients that might damage the voltage regulator or other systems on the
battery bus.
A hybrid alternator constructed according to the desaiption above is
pre~rdL,ly designed to produce its full rated output at all engine speeds from idle to
25 the maximum engine speed at redline. Two limitations on the maximum power
output of the alternator are the maximum flux that the rotor windings, in
combination with the permanent rnagnets, can produce and the thermal capability
of the alternator to dissipate excess heat under continuous full output opera~tion in
high ambient temperature conditions. The first limitation usually dominates at low
30 speed operation and the second more often dominates at higher speeds.
Improving the alternator operation with respect to either limitation usually
~ results in inueased cost or undesirably inaeases the physical size of the alternator.
To produce greater magnetic flux requires inaeasing current flow through the rotor
windings (larger wire diameter and larger windings) or inaeasing the number or
35 ~I,e"~l, of the permanent magnets. Both options greatly affect the cost and size of
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the hybrid alternator. Improved thermal capability requires additional internal or
external fans, larger cooling fins on the alternator case, larger airflow p~çsa~s in
the interior of the rotor or special electronic components that can continuously operate at higher temperatures.
A hybrid alternator is preferably designed to safely produce its full rated
power output over its entire speed range under worst case expected ambient
temperatures. As a result, the cooling and magnetic flux limitations are balanced
during the alternator design process. This results in an alternator that has just
enough magnetic flux capacity to generate the desired full rated output power at10 engine idling speed and just enough cooling at all other speeds during worst case
high ambient temperatures to keep the alternator below a desired maximum
operating temperature.
However, this type of design results in excess power output capacity for the
alternator when the alternator is not operating in worst case conditions. Moreover,
15 even under worst case conditions, the alternator will not instantly reach themaximum operating temperature when producing full output. During the warm up
period, while the alternator temperature is below the maximum operating
temperature, it also has excess power output capacity that may be usefully
exploited.
In view of the problems with the prior art, one object of the present
invention is to provide an alternator which operates efficiently at low RPMs.
Another object of the invention is to provide an alternator which uses a
permanent magnet assembly in the rotor to provide a rotating permanent magnetic
field in combination with a rotating variable magnetic field generated by a rotor
winding.
Still another object of the invention is to provide an alternator which weighs
less than current alternators at the same output power or which produces a higher
output at the same weight.
Yet another object of the present invention is to provide an efficient dual
voltage alternator, preferably in which both voltages are well regulated under
varying loads.
Another object of the invention is to provide a voltage regulator for a hybrid
alternator that automatically interlocks to prevent the regulator from being
deactivated when the alternator is in the reverse polarity mode.
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Still another object of the invention is to provide a voltage regulatcr for a
hybrid alternator which provides voltage transient suppression.
A ~urther object of the invention is to provide a voltage regulator for a
hybrid alternator that allows the alternator to opffale without a battery attached
S and without requiring expensive capacitors or voltage clamps.
Yet another object of the invention is to provide a hybrid alternator which
provides the maximum rated output voltage and current when a vehicle in which
the alternator is installed is operating at idle speed.
A further object of the invention is to provide an alternator wllich is
10 maximally cooled through radial cooling slots located in the stator.
Still another object of the invention is to provide an alternator which can
safely exploit excess power output capacity in operating regimes limited by the
alternator's cooling capacity without risk of damaging the alternator from
overheating.
Summary of the Invention
The above, and other objects which will be apparent to those skilled in the
art, are accomplished in the presel-t invention in which, in a first aspect, is directed
to a hybrid alternator comprising a stator, and a rotor mounted for rotation within
the stator and separated therefrom by an air gap, said rotor having a rotor core20 defining a plurality of magnetic poles, adjacent ones of the magnetic poles having
alternating north and south magnetic fields, the plurality of magnetic poles
comprising at least one permanent magnetic pole defined by a permanent magnet,
and a plurality of electromagnetic poles, each of which is defned by a wound field.
In a related aspect, the present invention is directed to a hybrid alternator
25 comprising a stator having a stator winding, a rotor mounted for rotation within the
stator and separated therefrom by an air gap, the rotor including a rotor core
defining a plurality of rotor field poles, at least one permanent magnet, the imagnet
being attached to a co" esponding rotor field pole to define a permanent magnetic
pole, the magnet being attached in a manner such that it forms a portion of the
30 rotor perimeter, and a rotor winding associated with the remaining rotor field poles
~ to define a plurality of electromagnetic poles, the electromagnetic and permanent
magnet poles defining a plurality of magnetic poles, adjacent ones of the magnetic
poles having alternating north and south magnetic fields.
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ln another aspect, the present invention is directed to a hybrid alternator
comprising a stator having a stator winding, a rotor mounted for rotation within the
stator and separated therefrom by an air gap, the rotor including a rotor core
defining a plurality of rotor feld poles, at least one permanent magnet, the magnet
5 being positioned within the rotor perimeter and associated with a pair of adjacent
rotor field poles to form adjacent permanent magnetic poles, and a rotor winding;~csoci:~ted with the remaining rotor field poles to define a plurality of
electromagnetic poles, the electromagnetic and permanent magnetic poles defininga plurality of magnetic poles, adjacent ones of the magnetic poles having
10 alternating north and south magnetic fields.
In a related aspect, the present invention is directed to a hybrid alternator
comprising a stator having a stator winding, a rotor mounted for rotation within the
stator and separated therefrom by an air gap, the rotor including a rotor core
defining a plurality of rotor field poles, each of which having a pole shoe, at least
15 one permanent magnet, the magnet being mounted between the rotor core and
said pole shoe to form a permanent magnetic pole, and a rotor winding associatedwith the remaining rotor field poles to define a plurality of electromagnetic poles,
the electromagnetic and permanent magnetic poles defining a plurality of magnetic
poles, adjacent ones of the magnetic poles having alternating north and south
20 magnetic fields.
In another aspect, the present invention is directed to a hybrid alternator
comprising a stator having a stator winding, a rotor core mounted for rotation
within the stator and separated therefrom by an air gap, said core defining a
plurality of rotor field poles, each of which having a longitudinal axis substantially
25 parallel to the rotor core rotational axis, said rotor field pole including a body
portion radially extending from said core to an end surface and having a first
longitudinal length, and an end portion attached to said end surface and having a
second longitudinal length that is greater than said first longitudinal length.
In a further aspect, the present invention is directed to a hybrid alternator
30 comprising a rotor core mounted for rotation within the stator and separated
therefrom by a radial air gap, the rotor including a shaft mounted for rotation
within the stator, a wound field rotor portion mounted on the shaft for rotationwithin a first longitudinal region of the stator, the wound field rotor portion having
a rotor winding and multiple electromagnet poles wherein each electromagnetic
35 pole includes a rotor field pole having a longitudinal axis substantially parallel to
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said shaft and including a body portion radially extending from said rotor oDre to
an end surface and having a first longitudinal length and an end portion attached to
said end surface and having a second longitudinal length that is greater than said
first longitudinal length, and a permanent magnet rotor portion mounted on the
5 shaft in longitudinally spaced relation to the wound field rotor portion for rotation
within a second longitudinal region of the stator, the permanent magnet rotor
portion having multiple permanent magnetic poles.
In one embodiment, the hybrid alternator of the present invention comprises
a rotor excitation circuit connected to the rotor winding in the wound fieldl rotor
10 portion for producing a forward excitation current through the rotor winding to
increase output from the alternator in a boosting mode and a reverse excitation
current through the rotor winding to decrease output from the alternator in a
bucking mode.
In another embodiment, the hybrid alternator further includes a voltage
15 regulator for controlling bi-directional current flow through a winding of analternator to control an output voltage of the alternator, the voltage regulatorcomprising a voltage monitoring circuit connected to monitor the output voltage of
the alternator, the voltage monitoring circuit producing an error signal indicating
the output voltage of the alternator should be increased or decreased, a switching
20 circuit connected to the rotor winding and arranged to connect the windling in
multiple modes, including a forward polarity mode in which a forward polarity
voltage is applied to the rotor winding, a reverse polarity mode in which a reverse
polarity voltage is applied to the rotor winding, and a decay mode in which current
induced in the rotor winding when connected in the forward or reverse polarity
25 mode is permitted to decay without inducing damaging voltages in the voltage
regulator, and a control circuit connected to the switching circuit, responsive to the
error signal of the monitoring circuit, the control circuit controlling the switching
circuit to enter the forward polarity mode to inaease the output voltage of the
alternator, to enter the reverse polarity mode to decrease the output voltage of the
30 alternator and to enter the decay mode whenever switching away from the forward
or reverse polarity mode.
~ Another embodiment of the hybrid alternator of the present invention
comprises a stator, and a rotor mounted for rotation within the stator and separated
therefrom by an air gap. The rotor has a rotor core defining a plurality of magnetic
35 poles wherein adjacent ones of the magnetic poles having alternating north and
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south magnetic fields. The plurality of magnetic poles comprises a plurality of
permanent magnet poles and a plurality of electromagnetic poles. Each permanent
magnet pole is defined by a permanent magnet. The plurality of permanent magnet
poles comprises two (2) sets of diametrically positioned permanent magnet poles.Each permanent magnet is positioned within the rotor perimeter and associated
with a pair of adjacent magnetic poles to form adjacent permanent magnet poles.
A further embodiment of the hybrid alternator of the present invention
comprises a stator having a stator winding, a rotor mounted for rotation within the
stator and separated therefrom by an air gap. The rotor has a rotor core that defines
10 a plurality of rotor field poles and a plurality of permanent magnets. Each magnet
is positioned within the rotor perimeter and mounted between a pair of adjacent
rotor field poles to form adjacent permanent magnet poles. The plurality of
perrnanent magnet poles comprises two (2) diametrically positioned sets of
permanent magnet poles. A rotor winding is associated with the remaining rotor
lS field poles and defines a plurality of electromagnetic poles. The pluraiity of
electromagnetic poles comprises two (2) diametrically positioned sets of
electromagnetic poles. The electromagnetic and permanent magnet poles define a
pfurality of magnetlc potes. AdJacent ones of the magnetic poles have alternating
north and south magnetic fields.
Another embodiment of the hybrid alternator of the present invention is a
stator having a stator winding, and a rotor mounted for rotation within the stator
and separated therefrom by an air gap. The rotor includes a rotor core that defines
a plurality of rotor field poles asymmetrically positioned about the rotor core. Each
rotor field pole comprises a body radially extending from the rotor core to an end
surface. The rotor also includes a plurality of permanent magnets, each of whichbeing positioned within the rotor perimeter and mounted between a pair of
adjacent rotor field poles to form adjacent permanent magnet poles. The plurality
of permanent magnet poles comprises two (2) diametrically positioned sets of
permanent magnet poles wherein each set of permanent magnet poles comprises
four (4) adjacent permanent magnet poles. Each permanent magnet is arranged in amanner such that the direction of magnetization is oriented circumferentially
relative to the rotor core rotational axis. A rotor winding is associated with the
remaining rotor field poles to define a plurality of electromagnetic poles. The
plurality of electromagnetic poles comprises two (2) diametrically positioned sets of
35 electromagnetic poles. Each set of electromagnetic poles comprises two (2)
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adjacent electromagnetic poles. The electromagnetic and permanent magnet poles
define a plurality of magnetic poles wherein adjacent ones of the magnetic poleshave alternating north and south magnetic fields. The alternator further includes a
plurality of rotor field pole shoes. Each shoe is asymmetrically mounted to the end
S surface of a cc" es~onding one of the pole bodies such that the rotor field shoes are
equidistantly spaced from one another.
Another embodiment of the hybrid alternator uses a novel conn~ection
arrangement between the rotor winding and the stator winding. By using this
arrangement, a simplified voltage regulator may be used that significantly reduces
10 component costs. The voltage regulator alternately connects one end of the rotor
winding between the positive end of the battery and ground. The other end of therotor winding is connected to the neutral point of the stator (which operates atapp!oximately half the battery voltage). The switching circuit in the regulator needs
only two switches for alternately connecting the rotor to transition between the15 forward and reverse polarity modes.
The hybrid alternator is designed such that it produces the full rated output
voltage and current when the vehicle is operating at idle speed and continues toproduce that full rated output over its entire operating range of speeds.
Another aspect of the invention includes a temperature monitoring voltage
20 regulator for controlling bi-directional current flow through a winding of a hybrid
alternator that adjusts the output voltage of the hybrid alternator according to the
temperature of the alternator to limit power output when the alternator temperature
approaches a predetermined maximum operating temperature.
The temperature monitoring voltage regulator includes a voltage monitoring
25 circuit, a temperature sensor, a switching circuit and a control circuit. The voltage
monitoring circuit is connected to monitor the output voltage of the alternator and
produces an error signal indicating that the output voltage of the alternator should
be increased or decreased.
The temperature sensor is adapted to be mechanically mounted in thermal
30 conta~l with the hybrid alternator, preferably the heatsink of the output diode
bridge, to sense the alternator temperature. The temperature sensor is electrically
connected to the voltage monitoring circuit and modifies the error signal to reduce
the output voltage of the hybrid alternator as the temperature sensor senses an
alternator temperature approaching a predetermined maximum alternator
35 temperature.
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The switching circuit is connected to the rotor winding and can connect the
winding in either a forward polarity mode, in which a forward polarity voltage is
applied to the winding, or a reverse polarity mode in which a reverse polarity
voltage is applied to the rotor winding. The control circuit is responsive to the
error signal of the monitoring circuit and directs the switching circuit to enter the
forward polarity mode whenever necessary to increase the output voltage of the
alternator, and to enter the reverse polarity mode to decrease the output voltage of
the alternator. In the most highly preferred embodiment, the temperature sensor is
a thermistor, and the switching circuit also includes the decay mode.
Brief Des~ tion of the Drawings
Fig. 1 is a longitudinal aoss sectional view parallel to and through the shaft
of a hybrid alternator according to the present invention.
Fig. 2 is a aoss sectional view along the line 2-2 perpendicular to the rotor
shaft and through the wound field rotor portion of the alternator.
Fig. 3 is a cross sectional view along the line 3-3 perpendicular to the rotor
shaft and through the permanent magnet rotor portion of the alternator.
Fig. 4 is an electrical circuit diagram of the alternator of the present
invention with a rotor excitation circuit for voltage regulation and a voltage
converter circuit for producing a second output voltage.
Fig. 5 is a graph of field current versus engine RPM necessary to maintain a
constant voltage output in a typical embodiment of the present invention.
Fig. 6 is a aoss sectional view taken parallel to the rotor shaft of a first
alternative embodiment of the invention employing a solid disk-shaped permanent
magnet.
Fig. 7 is a side elevational view of a ten pole disk-shaped permanent magnet
used in the first alternative embodiment of the invention shown in Fig. 6.
Fig. 8 is a front elevational view of a segmented flux channeling element
used in the first alternative embodiment of the invention shown in Fig. 6.
Fig. 9 is a aoss sectional view of the segmented flux channeling element
along the line 9-9 shown in Fig. 8.
Fig. 10 is a aoss sectional view of a second alternative embodiment of the
invention using embedded permanent magnets.
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Fig. 1 1 is a aoss sectional view along the line 1 1-1 1 in Fig. 10 showing the
embedded permanent magnet portion of the rotor.
Fig. 12 is a block diagram of a voltage regulator for a bridge ~ircuit
controlledl rotor winding of a hybrid alternator.
Fig. 13 is a detailed circuit diagram of a circuit in accordance with the block
diagram ~f Fig. 12.
Fig. 13A is a detailed circuit diagram of a temperature monitoring voltage
regulator based on the circuit in Fig. 13 in which a temperature sensor is used to
adjust the alternator output voltage to permit higher than rated alternator output
whenever the alternator temperature is below a predetermined maximum operating
temperat~lre.
Fig. 14 is a wiring diagram of a novel arrangement for a hybrid alternator in
which the rotor winding is connected to the neutral point of the stator winding.Fig. 15 is a wiring diagram of a hysteresis modulator which provides
improved regulator dynamic performance, as compared to the corresponding
hysteresis inverter elements in Fig. 13.
Fig. 16 is a longitudinal aoss-sectional view parallel to and through the shaft
of an alternate embodiment of the hybrid alternator of the present invention.
Fig. 17 is a aoss-sectional view along line 17-17 perpendicular to th,e rotor
shaft of the alternator of Fig. 16.
Fig. 1 7A is a partial enlarged view of a permanent magnet pole shown in
Fig. 1 7.
Fig. 18 is a aoss-sectional view similar to Fig. 17, of an alternate
embodiment of the alternator of Fig. 16.
Fi~ 1 8A is a partial enlarged view of a permanent magnet pole sha,wn on
Fig. 1 8.
Fi~ 19 is a aoss-sectional view similar to Fig. 17, of a further embodiment
of the hybrid alternator of Fig. 16.
Fig. 1 9A is a cross-sectional view, similar to Fig. 1 7, of another embodiment
of the hybrid alternator of Fig. 16.
Fig. 20 is a front elevational view of a rotor pole configuration that may be
utilized by the hybrid alternator of the present invention and the alternate
embodiments thereof.
Fig. 21 is a top plan view of the rotor pole of Fig. 20 taken along lines 21-
35 21.
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Fig. 22 is a ~erspe~live view of the rotor pole configuration of Fig. 20.
Fig. 23 is a front elevational view of an alternate embodiment of the rotor
pole configuration of Fig 20.
D~ )lion of the ~r~f~ J Embodiments
Referring to Fig. 1, the alternator of the invention includes a stator 10 havinga frst longitudinal stator region 12 and a second longitudinal stator region 14. A
three phase stator winding 16, as shown in Fig. 4, extends through slots 18 (shown
in Figs. 2 and 3) formed on the interior of the stator 10.
A rotor, generally indicated with arrow 20 is mounted for rotation within the
stator 10 on a shaft 22. The rotor includes a wound field rotor portion 24 whichrotates within the first stator region 12 and a permanent magnet rotor portion 38
which rotates within the second stator region 14.
The wound field rotor portion 24 has a rotor winding 28 which can be
ex~iled to produce a magnetic field whenever current is applied through slip rings
30, 32 on the shaft 22. Conventional brushes (not shown) would be mounted
within region 34 of case 36 to make contact with slip rings 30, 32 and allow
excitation current to be supplied to the rotor winding.
The permanent magnet rotor portion 38 is mounted on the shaft 22 in
longitudinally spaced relation from the wound field rotor portion 24. It includes a
plurality of permanent magnets 40 disposed about its perimeter mounted such thatthe direction of rnagnetization is radially oriented relative to the rotor shaft. The
magnets maintain a multiple pole permanent magnetic field which extends across
the air gap between the rotor and stator.
Fig. 2 is a aoss section through the first region 12 of the stator within which
the wound field rotor spins. The wound field rotor is conventionally formed frommultiple thin laminations having the aoss sectional shape seen in Fig. 2 stackedadjacently along the rotor shaft. Alternately, the wound field rotor poles may be
constructed using solid cast magnetic material. Each lamination on the rotor
includes a plurality of poles 42 around which the rotor windings 28 are arrangedwith alternate poles being wound in opposite directions to produce alternating
north and south magnetic fields.
Thus, the frst region 12 of the stator and the wound field rotor portion 24 of
the rotor act as a salient pole alternator to generate output from the stator windings
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16 through output leads 44, 46 and 48 (shown in Figs. 1 and 4) whenever an
eAcildlion current is supplied to the rotor windings 28.
Hybrid Alternator - Radially Ma~netized Permanent Magnets
Fig. 3 is a aoss section through the permanent magnet rotor portion of one
5 embodiment of the alternator. The permanent magnet rotor portion include~; eight
(8) permanent magnets 40 shaped as rectangular slabs and held in the permanent
magnet rotor laminations 38. Alternate designs may use more or less than eight
magnetic poles, but will always have the same number of poles as the wound fieldrotor. Shapes other than rectangular slabs may be used, for example the thickness
10 of the slab may be varied to match the curve of the rotor.
Each permanent magnet slab is magnetized through its thickness and
mounted such that the direction of magnetization extends radially, i.e., in a
direction which is perpendicular to the shaft 22 and normal to the large faces of the
slab 40.
The slabs are held in openings in the laminations 38 around the perimeter of
the permanent magnet rotor and alternate, with the north pole of one slab facingoutward and the north pole of the next slab facing inward. In this way, the
magnetic field generated by the wound rotor adds to the permanent magnetic fieldwhen a forward excitation current is applied to the rotor winding 28 and sul~tracts
from the permanent magnetic field when a reverse current is applied. The
permanent magnets in the design illustrated are formed of neodymium, however
other magnetic materials such as ceramic or samarium-cobalt magnets may also be
used andl may be preferred in particular applications. In production, the
neodymium magnets are nickel plated.
In addition to the openings which hold the magnets, the laminations 38
include multiple openings 50 to reduce weight and allow for cooling air flow
through the alternator.
Those familiar with electric machines in general and alternators in particular
will understand that the permanent magnets 40 provide a permanent magnetic fieldat the rotor which induces a voltage in the stator winding 16 whenever shaft 22 is
rotated. Rotation of the shaft is generally accomplished with a belt and pulley
drive, however a gear drive or other means may also be applied.
In the design shown in Fig. 1, the stator windings 16 extend from the first
stator region surrounding the wound field rotor portion continuously through thesecond stator region surrounding the permanent magnet portion. Thus, as shaft 22
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rotates, a voltage is induced in the stator winding 16 which is partially a result of
the magnetic field from the permanent magnets and partially a result of the
magnetic field generated by excitation current in the windings 28 of the wound
field rotor portion. It is also possible to use separate windings on the two stator
5 sections and combine their outputs electrically.
In the design shown in Figs. 1, 2 and 3, the stator portion of the alternator isthe same in region 14 as in region 12 and includes identical slots 18 and statorwindings 16. The slots 18 may, however, be skewed such that there is a twist
along its length. The purpose of the twist is to prevent magnetic cogging. In the
10 absence of such a twist, magnetic cogging and unwanted vibration is created due to
variable reluctance caused by slot openings in the air gap between the stator and
the rotor.
The stator is formed as a stack of thin laminations of electrical grade steel.
Each member of the stack is rotationally offset from its adjacent members
15 sufficiently to form the twist of one stator slot pitch along its length.
Although it is not shown in Fig. 3, the permanent magnet portion may
include a premanufactured cylindrical sleeve of a lightweight but strong material
such as a carbon fiber bonded in a resin. The sleeve has a thin wall thickness and a
diameter equal to the diameter of the permanent magnet rotor portion. It
20 surrounds the permanent magnet rotor portion and prevent the magnets 40 from
being thrown outward and damaging the stator under the centrifugal force
generated as a result of high speed operation.
In production versions of the invention, the preferred means of retaining the
permanent magnets on the rotor is to attach them with counter-sunk screws, as
25 shown in Fig. 24, to prevent the magnets from becoming dislodged from the rotor
pole during the rotation of the rotor. However, other means of retaining the
magnet to the rotor field poles may be used. For example, a pair circular endplates
mounted on the shaft on both sides of the rotor may be used wherein each
endplate has a lip portion projecting substantially parallel to the shaft that extends
30 about halfway aaoss the width of the rotor and above the magnet so as to form a
pole shoe. Alternatively, the endplates can be configured such that the lip portions
extend over a pole shoe mounted on top of the permanent magnet. Furthermore,
epoxy-type adhesives may also be used to secure the permanent magnets to the
rotor field poles. Other mechanical means for holding the permanent magnets to
35 the rotor will be apparent to those skilled in the art.
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As the alternator shaft 22 begins to spin, the magnet portion will inlduce a
voltage in the stator winding 16 which is be rectified to produce a desired output
voltage. Referring to Fig. 4, a typical stator winding 16 is composed of thnee legs
connected to a full wave voltage rectifier formed by six power diodes 60. The
5 power diodes 60 rectify the output and provide charging power to charge battery
62 and to supply a vehicle with power for accessories over output 64.
At low RPMs the output from the alternator due to the permanent magnets is
insufficient to provide the full voltage needed at output 64. Accordingly, a forward
e,ccilaLion polarity is applied to rotor winding 28. This increases the current in th
10 rotor, inaeases the strength of the magnetic field generated by the rotor winding,
and increases the output from the stator windings 16 to boost the output voltage to
the desired level. The forward polarity and forward current induced thereby is the
current and polarity which causes the magnetic field from the rotor winding to add
to the magnetic field from the permanent magnets in a boosting mode.
lS The necessity to boost the output by supplying a forward excitation current
to the rotor windings 28 occurs only at low engine RPMs. As the engine speed
inaeases, the output from the stator increases and a point is reached at which the
desiled output voltage is produced by the stator solely due to the perrnanent
magnet rotor portion. At this speed, no excitation current needs to be supplied to
20 the rotor winding 28. Above this speed, however, the permanent magnet rotor
portion would produce an over voltage in the stator windings.
To counteract the excess voltage at high RPMs, the rotor winding 28 is
supplied with a reverse excitation current which deaeases output from the
alternator in a bucking mode. Fig. 5 provides a graph of wound field current in
25 rotor winding 28 needed to maintain a constant output voltage at output 64 from
the stator windings 16 as a function of engine RPM. The graph is provided for
illustration of one possible implementation of the invention. Changes in gearing of
the alternator to the engine, the number of turns and resistance of windings on the
rotor and stator, and the relative strengths of the fields generated by the n-agnets
30 and rotor winding all will affeclt the actual curve for any specific application.
Referring to Fig. 5, it can be seen that the boost portion of the curve 66 in
which a forward excitation current is required occurs from idle at approximately600 RPM until 1200 RPM is reached. As the RPM increases from 600 RPM to
1200 RPM, the amount of forward excitation current needed to maintain the
35 cG,-sl~nl output voltage deaeases, reaching zero at point 70. At this point, all of
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the excitation is derived from the permanent magnet rotor portion. At speeds in
excess of 1200 RPM, the buck portion 68 of the curve is entered. In this section of
the curve, a reverse excitation, indicated by the negative current values on thevertical axis, is required to prevent the output voltage from exceeding the desired
level.
The crossing point 70 between the boosting mode and bucking mode will
vary with load and may be adjusted by varying the relative proportion of output
between the wound field rotor portion and the permanent magnet rotor portion.
Referring to Fig. 1, this can be accomplished by adjusting the strength of the
permanent magnets 40 or the field generated by the rotor winding. Alternatively, it
may be changed by varying the relative sizes of the permanent rotor portion 14 and
the wound field rotor portion 12. In Fig. 1, these have been illustrated as being of
approximately equal size, but the ratios may be varied as desired to adjust the
aossing point between the boost and buck regions of operation.
Dual Volta~e Hybrid Alternator
In the simplest form of the invention shown in Fig. 1, the stator winding 16
uses a conventional wiring layout shown in Fig. 4. However, other stator windingarrangements may be employed. For example, it is known to wire the stator with
two independent windings so as to produce two different output voltages. The
present invention conle"lplates this method of dual voltage generation where it is
desired to have a 12 volt output as well as a higher voltage output, typically 48
volts. A preferred method of dual voltage operation, however, is to use a voltage
converter circuit of the type desaibed in connection with Fig. 4.
Other variations of the invention are also contemplated. For example, in a
single voltage configuration, the stator winding may comprise two independent
stator windings, one found only within the first region 12 surrounding the woundfield rotor portion and one found within the second region 14 surrounding the
permanent magnet rotor portion. The outputs from these separate stator windings
are then combined electrically as needed to produce the desired output voltage.
Continuing to refer to Fig. 1, it can be seen that there is a gap 52 between
the two regions of the stator. The gap should be made of a relatively low magnetic
permeability material to isolate the magnetic regions of the stator 12 and 14. The
gap may be a simple air gap, or it may be partially or completely filled with a solid
material of low magnetic permeability such as plastic or the like. Where the stator
35 winding 16 extends from one region 12 completely through the gap to the second
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region 14, the gap may be filled with a material having the same aoss sectional
shape perpendicular to the rotor as the stator to provide a continuous slot 18 within
which the stator wires forming winding 16 may lie.
Hybri~ Alternator - Radial Cooling Slots Through Stator
In the ,urer~led embodiment, the air gap 52 between stator sections 112 and
14 is not solid, but is open to the outside air. Cooling air is permitted to enter the
interior of the alternator through air gap 52 between the stator sections where it is
then ducted out of the alternator at the ends. Typically this would be done by fans
located at one or both ends of the alternator (not shown).
The two section geometry for the stator iliustrated in Fig. 1 allows the
cooling air flow to be ducted into the center region of the alternator where thecooling is most needed. This construction enhances the dissipation of thermal
energy in the unit while at the same time maximizing the power output density.
The air gap is prererably provided with an axial spacer having a series of radially
oriented openings which open the air gap over approximately 85% of the surface
area of the spacer's circumferential section to allow cooling air into the warmest
part of the alternator. Arrow 53 indicates the entrance of cooling air into the
alternator interior radially flowing through the stator in contrast to the prior art
where the air flows only longitudinally in this section.
The air entering radially through the stator may flow through the gap
between the rotor and the stator. The wound field rotor section may also be
provided with air flow openings that are axially aligned and correspond to the air
flow p~csa~s 50 in the permanent magnet section. Air drawn into the center of
the alternator through the stator core flows aaoss critical sections of the stator coil,
sections of wound field coils and diodes as well as through the permanent rnagnet
section.
In addition to de~.easing the temperature of the alternator and increasing air
flow, by providing air flow openings in the stator core spacer and in the rotor
sections, the total weight of the alternator is significantly reduced. The air flow
openings in the regions referred to are located in sections of the alternator which
do not carry significant magnetic flux. Consequently adding these openings and air
flow holes does not diminish the electrical output of the alternator or affect its
efficiency.
In contrast, the current state of the art Lundell or claw pole geometry
alternators do not allow anything more than double end ventilation. It is not
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possib!e to ventilate through the mid section of the stator core nor is there anopportunity to ventilate through the rotor area because the Lundell and claw pole
construction is a relatively solid mass construction with no voids or areas that could
be devoted to the air flow.
By providing additional parallel air flow paths, cooling fans in the alternator
do not need to develop as much of a pressure differential to cause a given volume
of air to flow. This reduces overall alternator noise and/or permits fan blade
diameter and blade design to be altered to reduce the total size of the alternator.
The air flow is particularly valuable in keeping the temperature of the
permanent magnets as low as possible under all conditions of operation. This
enhances the output of the alternator and minimizes the risk of demagnetization at
high temperatures. This allows the alternator to be rated at the highest possible
output in the high temperature conditions that exist under the hood of modern
automobiles.
Voltage Regulation - Basic Two State PWM Regulator
In order to maintain a desired constant output voltage from the alternator, it
is necessd. y to feed a forward or reverse excitation current into the rotor winding
28 which varies in a manner similar to that shown in Fig. 5. Fig. 4 illustrates a
rotor excitation circuit appropriate for achieving this objective. The rectified output
64 from the stator is compared to a reference voltage 80 in a summing circuit 82which subtracts the reference voltage 80 from the output voltage 64 and providesan error signal on line 84 to function generator 86.
The function generator controls modulator 88 which provides a forward
excitation current to field winding 28 through the slip rings 30, 32 whenever the
output voltage 64 is below the reference voltage 80. Typically, the reference
voltage is set to the desired charging voltage for battery 62. The function generator
provides a reverse excitation current to field winding 28 whenever the output
voltage 64 rises above the reference voltage 80.
Function generator 86 acts as an amplifier compensation block to control
modulator 88 as needed to supply the desired forward or reverse field current and
produce the desired output voltage. The amplification and compensation
produced is dependent upon the error signal on line 84 determined as the error
between the output voltage at 64 and the reference voltage 80.
Function generator 86 and modulator 88 may be arranged to simply provide
a steady, i.e., unswitched and unpulsed continuously linearly variable, forward or
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reverse excitation current in the amount needed to produce the desired OUtpUlt and
to thereby linearly reduce the error signal 84 to zero. This produces a linear
regulation scheme in which the linear output of the modulator 88 is the same as
the average current needed to produce the desired output voltage. However~ it isS only necesw~ for the average current to approximate the desired levels, and so a
preferred method of regulation is to arrange the function generator 86 and
modulator 88 to use pulses to adjust the average current through rotor winding 28.
Pulses of a positive polarity cause a forward voltage to be applied to the fieldwinding and pulses of a reverse polarity cause a reverse voltage to be applied. The
10 width of the pulses is varied to vary the average current through the field winding.
This provides an electrically efficient circuit design to control the magnitude and
direction of the average field current. This constitutes the basic two state pulse
width modulation (PWM) voltage regulator circuit that alternately switches directly
bet~,veen the forward and reverse polarity modes.
1 S Volta~e Re~ulation - Dual Volta~e Alternator
The rotor excitation circuit comprising elements 80-88 provides a constant
output voltage at 64 to supply electrical circuits and charge battery 62. If thealternator is to be a single voltage alternator, this is sufficient. If the alternator is to
be a dual output voltage alternator, then typically one of two alternative designs
20 will be used. In the simplest design, the stator will be provided with a second
winding as previously mentioned. The error signal 84 may be based upon the
output from only one of the two stator windings, with the second output perrnitted
to seek its own level as the first is regulated.
Alternatively, an error signal which is a function of the output voltage from
25 both windings may be used so that neither output is fully regulated, but both are
held approximately to the desired level set by the composite error signal.
However, Fig. 4 illustrates a preferred alternative design for a dual output
voltage alternator according to the invention. In this design, the alternator isprincipally a single output voltage alternator producing a constant voltage at output
30 64 for battery 62 which is the higher voltage battery.
Instead of producing the second voltage from a second winding, it is
provided by a voltage converter circuit 90. In a manner similar to that described
for the excitation circuit above, a reference voltage 94 is summed with an output
voltage 96 connected to the second battery 92 in a summing circuit 98 to produce35 an error signal on line 100.
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A function generator 102 controls a modulator 104. Modulator 104
generates a series of pulses to turn switch 106 on and off in a switching power
supply design. The switching power supply is conventional and produces a voltagereg~ tecl output which is filtered with capacitor 108 and coil 110.
5The voltage source for the switching regulator must be higher than its output
voltage and may be connected either to output 64 over line 1 14 or directly to the
stator windings 16 over dashed line 116.
Generally, one source or the other would be selected and the connection
would be made permanently over line 114 or 116 instead of through a switch 118.
10Hybrid Alternator - Axially Magnetized Permanent Magnet
Fig. 6 shows a first alternative embodiment of the alternator generally
indicated at 200, employing a pair of solid disk-shaped permanent magnets 210,
212 magnetized with multiple poles. The disk may be made of a bonded
permanent magnet material. The stator 214 is essentially similar to the stator 14
15desaibed in connection with the previous embodiment, and, accordingly, is shown
only in outline form. It generally will include a three phase winding wound intothe slots in a laminated or cast stator made of a good grade of electrical steel. Dual
windings may be used in dual voltage output designs, if desired.
Stator air gaps co" esponding to stator air gap 52, described previously, may
20be introduced on either side of the wound field rotor portion to isolate the
permanent magnet portion of the stator from the wound field portion. A single
permanent magnet portion may be used similar to the design des~ibed in
connection with Figs. 1-3 or two permanent magnet portions longitudinally
separated on opposite sides of the wound field rotor portion may be used as shown
25in the embodiment of Fig. 6.
The solid disk permanent magnet element is shown separately in Fig. 7. It
could be made of separate permanent magnet elements, but is preferably made as asingle piece, magnetized through its thickness, in a longitudinal direction, parallel
to the shaft when assembled. This is 90~ (ninety degrees) to the direction of
30magnetization of the permanent magnets shown in Figs. 1 and 3 where the
magnetization is radially oriented instead of longitudinally.
In order to generate electricity, the field lines of the rotor must penetrate the
air gap 216 between the rotor and the stator and cut the stator windings. With the
magnetic field turned longitudinally, the magnetic flux must be turned and directed
35up to the air gap. This is accomplished with a flux channeling element generally
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indicated with reference numeral 218 made up of multiple pole segments 220 as
shown in Figs. 8 and 9. Individual pole segments 220 carry the flux from the
permanent magnet disk 210 up to the air gap 216 to penetrate the stator windings.
A second flux channeling element comprises a flux return plate 222. Two flux
return plates are used, located at the end faces of the rotor, one for each magnetic
disk.
By forming the permanent magnet in a solid disk and rotating the direction
of magnetization, improved mechanical strength is achieved and ~eater magnet
size and surface areas results. This provides for an inherently strong design and
allows the magnetic flux exiting the large face areas of the disk to be conc~"llaled
as it is channeled up to the air gap by the pole segments 220.
In the preferred configuration of this embodiment, the pole segment pieces
220 are shaped with openings 224 which wrap around the winding extensions in
the wound rotor. This shape give added strength to the windings and allows very
high rotational speeds to be achieved without damage to the rotor.
The end pieces 222, permanent magnet disks 210, pole segment pieces 220
and the wound rotor section are held together by rivets 226 extending through
holes 228 and 230 in the segment pieces and magnetic disk respectively.
The rotor components of Fig. 6 are mounted on shaft 22 in a manner
identical to that shown in Fig. 1. Shaft 22 will be journaled in a housing and have
slip rings contacted by brushes for supplying current to the wound field rotor
section. Voltage output and regulation is identical to that described previously.
Hybrid Alternator - Circumferentially Magnetized Permanent Ma~net
Yet another embodiment of the invention is shown in Figs. 10 and 1 1 and
generally indicated with reference numeral 300. In this embodiment, permanent
magnets 302 are embedded in a retainer 304, formed of a non-magnetic material
such as aluminum, which forms a hub around the rotor shaft 22. The retainer
isolates the magnets magnetically from the hub and holds them securely.
As in each of the previous two designs, the permanent magnets 302 are
magnetized through their thickness. However, they are mounted with the directionof magnetization oriented in yet a third direction, in this case circumferentially
6 relative to the shaft. The embedded magnets in Fig. 11 are inserted into the non-
magnetic retainer with alternate orientations between flux channeling elemen~s 306
located circumferentially adiacent to and between the magnets 302. Th~ flux
channeling elements 306 are made of a material that has high magnetic
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pe"~eability. They direct the magnetic flux, as indicated by arrows 308 from themagnets to the air gap between the rotor and stator.
This design like the design desaibed in connection with Figs. 6-9 permits a
relatively large amount of permanent magnet material to be used in a small space,
S with the flux being conce~ aled at the rotor perimeter. In some applications, this
allows the use of less expensive permanent magnets which reduces cost. in other
applications using high energy magnets, the design in Figs.1-3 may be preferred.The stator 310 will be substantially identical to the stator desaibed in
connection with Figs. 1-3. A non-magnetic end cap 312 provides support for the
10 wound field rotor extensions in the wound field portion 314. A similar end cap for
the rotor windings may be incorporated into the magnet retainer as shown, or maybe formed as a separate piece. It should be noted that while this end cap piece is
similar in appearance to the magnetic material piece 220, in Fig. 6, it is formed of a
non-magnetic material in this design and of a magnetically permeable material in15 Fig. 6.
Voltage Regulator - Three State Desi~n
Fig. 12 illustrates a block diagram of a first preferred embodiment of a
bridge circuit type of three state voltage regulator. The voltage regulator controls
bi-directional current flow through a winding 400 on the rotor of a hybrid
20 alternator of a type previously described. The regulator may also be used with
other types of alternators or devices requiring three state control. The rotor
winding 400 in combination with the permanent magnet portion of the rotor
induces a flux in the stator winding 402, 404, 406 of the hybrid alternator.
Bi-directional current flow is achieved through the use of four switches 408,
25 410, 412 and 414 arranged in a bridge configuration to form a switching circuit. A
first upper switch 408 is connected to a first end of the winding 400 and forms with
a first lower switch 414 a first pair of switches. When these switches are ciosed,
the first end of the rotor winding 400 is connected to the positive end of the battery
416 over the positive bus 418 and the second end of the rotor winding 400 is
30 connected to the negative end of the battery 416 over the ground 420. When the
first pair of switches 408, 414 are closed, the voltage regulator said to be in the
forward polarity mode or in the boosting mode, and forward current flows from the
first end of the rotor winding 400, connected to switch 408, to the second end of
the rotor winding 100, connected to switch 414.
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A second upper switch 410 forms with a second lower switch 412 a second
pair of switches. When the second pair of switches is closed, a second end of the
rotor winding 400 is connected to the positive bus 418 and the first end is
connected to the ground 420. In this configuration the voltage regulator is said to
5 be in the reverse polarity mode or the bucking mode. Control logic is provided to
make these modes mutually exclusive. Winding 400 is wound onto the rol:or so
that in the forward polarity mode the magnetic flux produced by forward current
flow is added to the magnetic flux provided by the permanent magnet section of
the rotor.
Conversely in the reverse polarity mode, a reverse current flow through the
rotor winding 400 will generate magnetic flux of the opposite polarity which is
subtractively combined with the magnetic flux from the permanent magnets.
In order to regulate the output of the hybrid alternator, the prior ar~ has
simply switched the rotor winding 400 between forward and reverse polarity
modes as desaibed in the basic PWM regulator above. A voltage regulator which
operates in only these two modes may be referred to as a two state PWM voltage
regulator. The voltage regulator is switched into the forward polarity mode
whenever it desired to inaease the output and is switched into the reverse polarity
mode whenever it is desired to decrease the output.
As discussed above, however, when a forward current has been induced
into the rotor winding 400 through switches 408 and 414, considerable energy is
stored in the magnetic field produced by coil 400. If the first pair of switches 408
and 414 are immediately opened and the second pair of switches 410, 4112 are
immediately closed, the forward current induced in the forward polarity mode will
continue to flow as the magnetic field from rotor winding 400 slowly collapses.
Under certain conditions, this forward field current will continue to flow as reverse
current through the second upper switch 410 and in lower switch 412. It will also
appear as a reverse current on the positive bus 418. If the net loads on the bus are
low, and provided that battery 416 is connected, this reverse current normally
enters the battery and charges it slightly. However, in the absence of a batltery or
other conditions likely to occur, a large voltage spike will be produced which may
damage the vehicle components.
These spikes and other spikes produced as a result of changing loads on the
~ electrical system of the vehicle could be handled by placing a capacitor aaoss the
35 terminals of the battery 416 from the positive bus 418 to ground 420. However, a
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l alJ~ or of sufficient size with a temperature rating suitable for operation under
the hood of a vehicle would be expensive.
Accordingly, the preferred embodiment of the voltage regulator employs a
configuration which may be ler~-ed a three state voltage regulator design. In this
5 construction, the voltage regulator employs a normal forward polarity mode forstarting the flow of a forward current in winding 400 or for inaeasing an existing
forward current flow. The reverse polarity mode is used for starting a reverse
current flow or increasing the magnitude of the reverse current flow. The third
mode, rer~led to here as a decay mode, is entered after the voltage regulator
10 leaves the forward or reverse polarity mode.
în the decay mode (which might also be considered a zero voltage or zero
polarity mode), current induced in either of the two other modes is permitted tocircu!ate through the rotor winding and decay towards zero without inducing any
damaging voltages in the remainder of the circuit. The decay is entered after either
15 of the other two modes whenever the decay current is present to prevent a direct
transition from the forward polarity mode to the reverse polarity mode, or the
opposile transition which would result in reverse current being applied to the main
power bus.
Those familiar with four element bridge circuits, for example full wave,
20 bridge rectifiers and the like, will recognize that in the conventional use of bridge
circuits opposite pairs of elements are intended to conduct simultaneously. Thus,
the first pair of switches conduct in one state and the second pair of switches
conduct in the second state. In this three state design, two elements that are
directly opposite to one another (instead of diagonally opposite to one another) are
25 opened simultaneously and current is allowed to flow through the remaining two
elements in a circulating decay current pattern.
For example, in the forward polarity mode, switches 408 and 414 are
closed. In the decay mode, switch 408 iS opened while switch 414 remains closed.In some implementations of the invention, switch 412 would be closed at this time
30 to provide a conducting path in the forward direction down through the first lower
switch 414 and back up in a reverse direction through second lower switch 412.
As discussed more fully below, however, switches 412 and 414 are semiconductor
switches, preferably field effect transistors which have the property that they can
conduct in the reverse mode through an internal diode without applying a control35 signal to close the switch. This internal diode generates a voltage drop when
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reverse current flow is occurring which is used to detect the presence of decay
current.
The decay mode may also be implemented by allowing the decay current to
flow through upper switches 408 and 410.
Continuing to refer to Fig. 12, the voltage produced by the combin~ed effect
of the magnetic flux from the rotor 400 and the permanent magnets on the rotor is
generated by the stator windings 402, 404 and 406 and is rectified in a
conventional three phase full wave bridge rectifier composed of six diodes 422,
424, 426, 428, 430 and 432. These six diodes correspond to diodes 60 in Fig. 4.
10 The rectified output is fed to the battery 416 over the positive power bus 418 and
also feeds the electrical load of the vehicle over a connection (not shown) to the
power bus 418.
The output voltage of the alternator is monitored over wire 434 by a voltage
monitoring circuit 436. The voltage monitoring circuit compares the output
15 voltage of the alternator to a reference voltage from the voltage reference circuit
438 and produces an error signal on line 440.
The error signal 440 is applied to the input of control circuit 442. The
control circuit 442 includes a primary circuit 444, a decay current detecting circuit
446 and logic circuit 448. The primary circuit is directly responsive to the error
20 signal of the monitoring circuit over line 440 and produces one or more primary
control signals that signal the logic circuit 448 to increase or deaease the output of
the alternator.
In the basic two state PWM regulator, the primary control signal would have
been used to turn on the first pair of switches when an increased output was
25 desired and to turn on the second pair of switches when a decreased output was
desired.
In the present invention however, the primary control signals are rnodified
in the logic circuit 448 with information obtained from the decay current detecting
circuit 446 before secondary control signals are produced. The secondary control30 signals control the states of the switches 408, 410, 412 and 414 individually over
control lines 450, 452, 454 and 456.
The decay current detecting circuit 446 is connected to monitor the decay
current in rotor winding 400. In the preferred design this monitoring is
conveniently done by connections 458 and 460 between the decay current
35 detecting circuit 446 and the first and seconds ends of the winding 400. The decay
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circuit detecting circuit 446 produces one or more inhibiting signals which are
applied to inputs of the logic circuit 448 over lines 462, and 464. Those familiar
with the art will recognize that there are other ways to monitor the decay current in
winding 400.
5 Automatic Interlock and Internal Voltage Re~ulator Power Supply
Three additional diodes 466, 468 and 470 provide independent power to an
internal power supply 472 producing Vcc power. The internal power supply 472
supplies power for operating the voltage regulator circuitry. This voltage is
regulated to provide the control voltage power supply for the regulator. Since the
10 hybrid alternator contains both a permanent magnet and wound field, the
alternator begins to generate a voltage as soon as it begins turning. As the voltage
becomes larger it generates enough voltage to power the electronics so that
additional boost field can be generated. All of this occurs even before the vehicle
reaches idling speed, so that at idle, the voltage regulator is functioning properly.
Operating the system in this manner provides an automatic interlock so that
the voltage regulator loop is disconnected and draws almost zero field and control
current when the alternator is not turning, but automatically connects the voltage
regulator electronics as the alternator speeds up.
An automatic interlock is very important in a hybrid alternator because the
20 field current should never be shut down when the system is operating at high
speeds as severe overvoltages and overcurrents will occur. This is in distinct
cor,l~a~l to present alternators which allow the ignition switch to turn off thevoltage regulator field. It is important that the alternator field current be zero when
the vehicle is not operating and the engine is off to avoid battery drain, but this
25 should not be done with the ignition key alone. This is because the ignition could
accidentally be turned off when the alternator is operating at high speed.
Fig. 13 is a detailed schematic circuit diagram corresponding to the block
diagram of Fig. 12. Battery 416 is connected to the six (6) bridge rectifier output
diodes 422-432 which are connected in turn to the stator windings 402,404 and
30 406 in the manner illustrated in Fig. 12. The stator windings 402,404 and 406 are
not shown in Fig. 13, but their connection is entirely conventional.
The internal power supply 472 comprises a zener diode 500 regulating the
output voltage Vcc of an NPN transistor 502. Three terminal voltage regulating
devices and other voltage regulating circuits would also be suitable.
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The voltage monitoring circuit 436 monitors the battery voltage 416 over
wire 434 which produces a voltage drop aaoss the resistor bridge 504,506 and
508. Resistor 506 is made adjustable to adjust the output voltage of the regulator.
The scaled output voltage of the alternator is compared in error amplifier 510 with
5 the reference voltage from the voltage reference circuit 438.
The voltage monitoring circuit performs error amplification and loop
compensation. The reference voltage from reference voltage source 438 is appliedto one input of error amplifier 510 and the other input is connected to a voltage
divider from the battery. Integral compensation is provided by the capacitive
10 nature of the feedback network between the inverting input of the error amplifier
510 and the output. The compensating network is generally indicated with
r~r~ence arrow 512. This network eliminates DC error in the regulator voltage
over the complete range of speed and load on the alternator.
The output of the error amplifier is an amplified error signal on line 440
15 which is provided to the primary circuit section 444 of the control circuit 442. The
error signal is applied to the input of a simple hysteresis block formed by a
hysteresis inverter 516 which acts as a two state modulator. When the alternatoroutput is too high, the error signal 440 will be lower and the output of the
hysteresis inverter 516 will switch high. This high signal always causes the net field
20 in the alternator to be deaeasing. Alternately, when 516 is low the net field in the
alternator is inaeasing.
The primary circuit 444 produces four primary control signals on lines 518,
520,522 and 524. The primary control signal on line 518 is taken directly from
the output of the two state modulator 516 and the primary control signal on line25 520 is the inverted opposite of that signal. Primary control signal 520 is produced
by the inverter 526. The control signals on lines 518 and 520 could be used to
drive the diagonally opposite switch pairs of the switching bridge in a two state
basic PWM regulator design. They serve as the starting point for the modified
control shown here that results in the secondary control signals that actually
30 perform the desired switching.
The hysteresis in the inverter 516 in combination with the gain and
dynamics of the error amplifier block 436 controls the voltage error and sets the
natural oscillation frequency of the loop. The function of the primary inverter 516
could also be performed by a pulse width modulator with a ramp oscillator and
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cc, -es~onding components, however such a design wouid be more complex and
more expensive than the simple digital circuitry shown in Fig.13.
The hysteresis inverter formed by 516 and the positive feedback resistors as
shown in Fig. 13 may be replaced by the improved circuit of Fig. 15 which
5 discloses a hysteresis modulator formed by 516 and the resistor capacitor feedback
network surrounding it. In this improved circuit, the comparator/operational
amplifier element 516 includes feedback to the positive terminal and a first order
filter to the negative feedback side providing a hysteresis modulator. This circuit
provides improved regulator dynamic performance, as compared to the
10 corresponding elements in Fig. 13, by allowing the modulator frequency to be set
well above the loop crossover frequency.
The primary control signals on lines 518 and 520 are accompanied by
delayed copies of the primary control signals on lines 522 and 524 which are
generated by inverters 528 and 530. The output from hysteresis inverter 516 is
15 delayed in a simple resistor capacitor delay generally indicated with reference
arrow 532. Thus, primary control line 522 carries a delayed version of the primary
control signal of line 520. Line 524 carries a delayed version of the primary
control signal on line 518. The primary control signals on lines 518 and 520 areused to provide inputs to the logic circuit 448 which ultimately produces the
20 secondary control signals for switching the switches directing current through the
winding 400.
Switching elements 408, 410, 412 and 414 in Fig. 12 correspond to field
effect transistors (FETs) 534, 536 and 538 and 540 with their associated drive
electronics in Fig. 13. When FET 534, corresponding to the first upper switch, and
25 FET 540, co., e~onding to the first lower switch, are on, the alternator is said to be
in the forward polarity mode. When FETs 536 and 538 are on, the alternator is
said to be in the reverse polarity mode. The alternator may be said to be in thedecay mode whenever both of the upper FETs are off or both of the lower FETs areoff indicating that no voltage is being applied to the winding 400 from the battery
30 or alternator output.
Different implementations of the invention may turn off both upper switches
to disconnect the winding 400 from the battery or both lower switches may be
turned off. With additional components other configurations for applying zero
voltage to the winding 400 may be employed.
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In addition to disconnecting the winding 400 from the battery, the ~vinding
must be connected so that the current can decay without inducing damaging
voltages in the remaining circuitry of the voltage regulator or elsewhere in theautomobile. This is accomplished by allowing the decay current to recirculate
5 through h,vo of the switches connected to opposite ends of winding 400. In thepr~r~et3 design shown in Fig. 13, the recirculating circuit is carried through the
lower two FETs. However, the recirculating current could alternatively be carried
in the upper two FETs or through other components.
Both FETs 538 and 540 could be turned on to carry the recirculating circuit
10 however the FETs have an internal diode which will permit them to carry a reverse
current even when they are not biased on. When left off, the recirculating decaycurrent induces a voltage aaoss the internal diode of the lower FET which is sensed
by the decay current detecting circuit 446 over lines 458 and 460 connected to the
first and second ends of the winding 400.
Diodes 542 and 544 isolate comparators 546 and 548 from the FETs
whenever the drain of the FET is high during the forward or reverse polarity mode.
One side of the comparators 546 and 548 has a voltage reference obtained from a
voltage divider and the voltage reference source 438 Vref and the other side has a
filtered version of a voltage which is one diode drop above the FET drain voltage
20 when it is near ground. Diode 542 and 544 raise the voltage level by one diode
voltage drop so that no negative voltages are needed on the inputs of comparators
546 and 548.
The logic circuit 448 is implemented in Fig. 13 with logic gates 550, 552,
554, 556, 558, 560 and 562. The logic circuit implemented in these gates accepts25 the primary control signals and inhibiting signals over lines 462 and 464 from the
decay current detecting circuit 446 to produce the secondary control signals on
lines 450, 452, 454, 456.
When a secondary control signal such as the secondary control signal 454
switches high, its associated FET, e.g. FET 534 turns on. The logic function
30 p~ ro,-"ed by gates 550, 552 and 554 is identical to the logic function performed
by gates 556, 558, 560, and 562. Different logic elements are used to impllementthe same logic function in order to reduce component count which can be
implemented on only two logic chips. Logic gates 550 and 562 control the upper
FETs 534 and 536 respectively.
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Logic gate 550 is a triple input AND gate. Its output is high and the
cc. ,e~,uonding FET 534 is on only when all three inputs to the triple input ANDgate are high. These three inputs are the primary undelayed PWM control signal
on line 518, the delayed primary control signal PWM on line 524 and the
5 inhibiting signal on line 464 from the decay current monitoring circuit monitoring
reverse current in FET 540.
The presence of the inhibiting signal on line 464 indicates the presence of
reverse decay current in the winding 400 as a result of a decaying current originally
induced in the reverse polarity mode. The inhibiting signal on 464 is holding the
10 second lower FET 538 on and inhibiting FET 534 immediately above it from being
switched on at the same time. Once the current induced in the reverse polarity
mode decays to a sufficiently small value, the inhibiting signal on 464 switchesstate allowing the circuit to change modes.
Although the voltage exciting the field winding has three modes namely the
15 forward polarity mode, the reverse polarity mode and the decay mode, the FETsactually have four different states. In the forward polarity mode FET 534 and 540
conduct. In the reverse polarity mode FETs 536 and 538 conduct. In the decay
mode (two states), both FETs 534 and 536 are off.
The decay mode has two different states, a forward decay mode and a
20 reverse decay mode. In the forward decay mode, the current induced in the
forward polarity mode is allowed to decay and FET 540 is held on with FET 538
remaining off, but conducting through its internal diode. In the forward decay
mode, the decay current continues to flow through the winding 400 in the same
direction as its flows when in the forward polarity mode. In the reverse decay
25 mode, FET 538 is on and FET 540 is off, but conducting through its internal diode
with reverse current circulating through the winding 400 down through FET 538
and back up through FET 540.
The present invention utilizes a bridge circuit arrangement to provide
bilateral voltage excitation of the winding 400. The voltage monitoring circuit 436
30 provides basic error amplification to produce the error signal on line 440. The
voltage regulation loop contains a compensation block to shape the loop frequency
response to provide for tight control of the average battery voltage. The
compensated amplifier output error signal on line 440 drives a pulse width
modulator, or other two state modulator, which indirectly drives a full bridge
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output stage to provide the bi-directional current through winding 400 which is
connected across the center taps of the bridge.
Logic circuit 448 modifies the output of primary circuit 444 to allow a third
state of voltage excitation of near zero voltage applied to the winding 400
5 whenever the field current magnitude is being decreased. Primary control signals
from primary circuit 444 act to directly turn on the diagonally located pair of
bridge switches. However a zero voltage excitation is employed whenever the
magnitude of the field current is to decrease.
When the field current's instantaneous magnitude is being commanded to
10 increase by the primary control signals from 444, full bus voltage of appropriate
polarity is applied to the field coil by exciting the appropriate diagonal pair of
bridge elements. However, when the field current magnitude is being reduced,
only the upper switch in the previously conducting diagonal pair of swi~Fhes is
turned off. By utilizing a delay in the turn off of the lower diagonal switch and turn
15 on delays in the opposite diagonal switches, the inductive field current that was
flowing in the upper switch transfers to negative current in the switch element
immediately below the one being turned off.
Current flow in the lower diagonal switch continues due to the previously
described delay in its turn off. Its lower diagonal switch is then commanded to
20 remain on by the presence of reverse current in the other lower switch. When the
reverse conducting power switch is an FET, as shown in the preferred embodiment
of Fig. 13, and when that switch has a delayed turn on, the reverse current first
flows through the FET's intrinsic diode generating a voltage drop of about -0.6
voltages. If the lower reverse conducting FET were turned on, the reverse
25 circulating current would also flow through FET on resistance leading to a lower
voltage drop.
As described above in the preferred implementation of this invention this
FET is kept off during the decaying current in order to allow the voltage across the
FET's intrinsic diode to provide a simple indicator of the presence of decaying field
30 current. The nonlinear diode characteristic provides a reasonable voltage level
even for small currents. This allows the use of a simple voltage comparator in the
form of comparators 546 and 548, to indicate the presence of field current. Whenthe intrinsic diode voltage is more negative than a threshold set by reference
voltage source 438 and the resistor divider below that point, the presence of
35 rever~ current is indicated.
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When the comparator indicates the presence of field current in the reverse
conducting switch, the drives to the opposite diagonal elements are inhibited bythe comparator signal and drive to the lower FET which is conducting the decaying
field current is kept on. After the comparator indicates near zero field current, it is
safe to excite the opposite diagonal bridge elements as commanded by the primarycontrol signals of the primary circuit 444. Switching the new diagonal pair on at
zero field current will not introduce any negative current into the bus and therefore
causes no harmful voltage spikes if the battery becomes disconnected when the
system is lightly loaded.
Control Logic and Method of Three State Regulation
The primary control loop contains the voltage monitoring circuit 436
monitoring the output on line 434 and includes an error amplifier operating on the
difference between the battery voltage and the reference 438. The amplified error
signal drives a pulse width modulator, or other two state modulator, incorporated
15 in primary circuit 444 to produce the primary control signals, which include the
PWM signal at the output of the two state modulator, the inverted PWM signal anddelayed copies of those two signals. The primary PWM control signal switches
between the on state and the off state. During the on state it is set to turn on one
diagonal pair and the opposite diagonal pair during the off state and vice versa.
20 Because of the two state basic step up, digital logic is preferred for implementing
the control system.
The actual switch commands are modified by delays, inhibits and other
signals to produce a more complex switching structure and avoid negative bus
current as described below.
When increasing the instantaneous magnitude of field current through the
winding 400, the appropriate diagonal bridge pair is fully on. However, to avoidnegative current steps into the bus, the bridge operates to let the field current decay
naturally in a circulating current loop containing only the lower switches rather
than forcing a more rapid decay with reverse excitation from the bus. To set up
30 this natural decay, both the upper bridge elements are off and the decaying field
current circulates in the lower bridge elements. One lower bridge element
conducts in a forward direction while the other conducts in reverse. This natural
decay continues until the two state modulator, corresponding to hysteresis inverter
516, changes state again or the field current goes to zero.
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ln the first case, the originally conducting pair comes on again. In l:he lattercase, when the field current reaches zero, the opposite diagonal pair ca~mes on.The natural decay feature is performed by inhibiting the turn on of Ithe new
diagonal pair until the decay current has approximately reached zero. Overall
S operation in the preferred design is thus multiple state with four states of operation
of the output switches taking place or three states of instantaneous voltage across
the field winding if the switch device drops are neglected. The three states of
instantaneous field winding voltage are plus battery voltage, zero voltage and
minus battery voltage.
The preferred method of operation of the invention employs the following
steps:
(1) the on upper device turns off immediately in response to an undelayed PWM off
command,
(2) the turn off of the lower elements is delayed and all bridge element turn ons are
delayed an equal or longer time allowing circulating current in the lower bridgeelements to automatically take place when the upper device turns off,
(3) threshold comparators on each lower switch indicate the presence of reverse
current (decaying field current) in that device and that logic signal is used tc,
p~ rO~ ~n the following steps:
a) The FET drive on the reverse conducting switch is inhibited to avoid
i,.l~ r~ ing with the threshold voltage measurement;
b) The turn off drive on the new upper diagonal switch is inhibited because
the switch below it will be on for the circulating decay current;
c) The drive on the other lower FET will be forced to remain on to carry the
decaying circulating current;
d) If the primary control signals return to their original state before the field
current goes to zero, the original diagonal pair of output devices will come back on
and the magnitude of field current begins to inaease again. This is the normal
mode of operation when operating at constant speed and fixed loads. The system
30 will operate between driving the field winding with the bus voltage in one state
and having the field decay with circulating currents in the lower FETs for the other
~ state. This full drive voltage followed by zero drive voltage operates in the same
manner independent of the direction of the average field current. Thus, in normal
~ operation at relatively low alternator speeds, with a fixed load, the alternator will
35 cycle between the forward polarity mode and the decay mode (more specifically,
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between the forward polarity mode and the forward decay mode). When the
alternator is operating at relatively high speeds, the alternator will cycle between
the revffse polarity mode and the decay mode (more specifically, between the
reverse polarity mode and the reverse decay mode). During these normal cycles
5 between the forward or reverse polarity mode and the decay mode, the primary
control signal on line 518 will be alternating between the on and off states.
e) Only when the field current goes to zero before the primary signal on
line 518 returns to its original state does the opposite bridge pair come on and the
current in the rotor winding 400 change direction. This type of operation will
10 occur if the average field current is near zero or if the alternator speed or load
changes abruptly.
Temperature Monitoring Voltage Regulator
Fig. 1 3A provides a circuit diagram of the preferred embodiment of a
temperature monitoring voltage regulator in accordance with the present invention.
15 The circuit illustrated substantially corresponds to the circuit diagram of the three-
state voltage regulator shown in Fig. 13, except that the voltage monitoring circuit
436 has been modified to replace resistor 508 with temperature sensor 509.
Temperature sensor 509 is mounted in thermal contact with the hybrid
alternator so that it can monitor the alternator temperature, and has a variable20 resistance that is a function of temperature. A preferred location for mounting
temperature sensor 509 is on a common heatsink with the output diodes 422~32.
Other mounting locations are also suitable. Generally, a mounting location near
the most heat sensitive components of the alternator or near the location where the
most heat is produced by the alternator is preferred.
The function of the temperature sensor 509 is to adjust the error signal at the
output of the voltage monitoring circuit (on line 440) whenever the alternator
approaches or exceeds a preset alternator temperature. In the embodiment shown
in Fig. 13A, the temperature sensor 509 is preferably a thermistor with a positive
temperature coefficient (PTC). This type of PTC thermistor sensor has a resistance
that is a nonlinear function of temperature. At temperatures below a critical
temperature, the PTC thermistor has a relatively constant resistance.
This constant resistance appears in the resistive voltage divider formed by
resistors 504, 506 and the sensor 509, and the voltage regulator acts in exactly the
manner described in connection with Fig. 13 incorporating resistor 508. This
produces a voltage at the input of the error amplifier 510 that is directly
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proportional to the output voltage of the alternator. If the alternator outpult voltage
rises or falls in response to a changing load, the rise or fall is sensed by the error
amplifier relative to the reference voltage from 438 and the alternator output is
adjusted, as previously desaibed, to hold the desired output voltage constant.
As the alternator heats up and approaches the aitical temperature of the
thermistor, however, the thermistor's resistance begins to increase dramatically.
The portion of the output voltage that appears a~oss temperature sensor S09 in the
resistive divider increases correspondingly. The error amplifier 510 sees this
voltage increase as an apparent increase in the output voltage of the alternator, and
begins to decrease the output voltage in response. As the output voltage drops, the
output power of the alternator decreases and the alternator temperature being
sensed decreases. The result is that the alternator can produce significantly more
power than its rated output for as long as the thermistor temperature remains below
its critical temperature.
With the proper selection of thermistor, having a desired variable resistance
as a function of temperature, any desired maximum operating temperature for the
hybrid alternator may be set. An appropriately designed hybrid alternator
constructed with a temperature monitoring regulator of the type described will be
able to continuously provide its full rated power output at any engine speed and at
any ambient temperature. It will be able to provide this power from the instant the
engine first begins to turn the alternator.
At speeds above idling speed, the hybrid alternator will be able to provide
significantly more than its full rated power output. Even under worst case high
ambient temperatures extra output is available for a short time until the alternator
reaches its maximum operating temperature set by the temperature sensor and the
design of the voltage regulator. Thereafter it will be limited by the design cooling
of the alt0nator and will be able to continuously produce its full rated output.Under cooler ambient temperatures than the worst case conditions, the
alternator will be able to continuously produce greater than its rated output. This
assumes that the engine is turning sufficiently fast that the alternator output is not
limited by the magnetic flux the rotor windings can produce in combination with
- the perrnanent magnets.
If the load on the alternator is so great that the alternator's cooling capacityis exceeded, the temperature monitoring voltage regulator will redJuce the
alternator voltage output. The alternator's power output is reduced just enough ta,
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continuously hold the alternator at or near the aitical temperature of the
thermistor, i.e. at the maximum safe operating temperature of the alternator. In this
way the alternator is protected against damage from overheating when its rated
output is exceeded.
Those familiar with the art will recognize that a negative temperature
coefficient (NTC) resistive device or equivalent circuit could also be used instead of
the PTC thermistor 509, by replacing resistor 504 in the upper branch of the
resistive divider with the NTC element and by reinserting resistor 508 in the lower
branch. Alternatively, the variable resistance of a temperature sensor may be used
10 to modify the reference voltage seen by the error amplifier at the other input to
error amplifier 510. This could be accomplished by using a resistive bridge similar
to the resistive bridge shown in Fig. 13A, except placing that bridge at the non-
inverting input of the error amplifier and applying the reference voltage across the
bridge. The variable resistance due to temperature would then vary the reference15 voltage and thereby modify the error signal to control the output voltage and output power.
Other types of temperature sensors, such as thermocouples, temperature
sensitive diodes, etc. along with additional circuitry, as needed, may also be used.
Further, although the preferred embodiment is based upon the three state voltage20 regulator design, a two state voltage regulator design as shown in Fig. 4 may also
be used. The modification nece~sd~y to implement the invention in a two state
voltage regulator design corresponds exactly to the modification desaibed above
for the three state design. Preferably a resistive bridge is formed with a sensor
having a nonlinear variable resistance as a function of temperature, and the bridge
25 is used at one of the inputs to the summing circuit 82 either to modify the sensed
alternator output voltage or to modify the reference voltage. In either case theresistive bridge is arranged to deaease the output voltage of the alternator as the
maximum desired operating temperature is reached.
Transient Suppres~ on
The voltage regulator illustrated in Fig. 13 incorporates a unique method of
suppressing voltage transients, such as those generated in a classic "load dump"situation well known in the automotive industry. Load dump is a situation where a
heavy battery load is suddenly switched off or when the battery itself is
disconnected while drawing heavy current. In this situation a suppresser device is
35 required to handle the inductive energy stored in the alternator windings. The
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pres~nl voltage regulator uses a signal level zener diode 580 with directing diodes
582, 584, 586 and 588 that turn on the bridge FET diodes so that the bridge FETscan absorb the transient. FET devices are able to handle large power impulses
effectively and thus the bridge arrangement when properly controlled in a transient
5 voltage situation allows these devices to perform a dual function.
The remaining transistors and inverters 590 and 592 are drive circuitry
which drives the various FETs in the bridge circuit. The upper power FETs 534 and
536 are directly driven with conventional NPNIPNP level translation circuitry. The
PNP transistors 594 and 596 nearest the FET gates provide active gate pull down.10 The FETs are turned on and off relatively slowly with the circuitry shown to
minimize interference. The field current modulation can produce current steps inthe alternator output ranging between full alternating field current and zero. Since
the alternator has a finite output inductance, it cannot change its current instantly.
Slower rise and fall times on the power FETs partially alleviate this problem and the
15 voltage clamp arrangement provided by zener diode 580 and its associated diodes
582-58B protects the FETs from reaching their breakdown voltage should be short
voltage excursions exceed the clamp voltage. A clamp voltage of about 27 volts is
used.
Inverters 590 and 592 are arranged as two charge pump oscillators. The
20 oscillators, with the rectifying and related circuitry generally indicated with arrows
591 and 593 provide a voltage higher than the battery voltage on line 595 for
driving the upper power FETs to switch the battery voltage.
Neutral Point Connected Alternator
Fig. 14 illustrates a novel wiring arrangement for a hybrid alternator in
25 which the rotor winding 600 is connected to the neutral point connection of the
stator windings 602, 604 and 606.
As discussed above, the rotor winding 600 of a hybrid alternator must be
supplied with a forward polarity voltage to inaease the alternator output voltage
and a reverse polarity voltage to decrease the alternator output. This polarity
30 reversal is achieved in the three state voltage regulator shown in Fig. 12 with a
bridge circuit which alternately turns on opposite diagonal pairs of switches in a
four element bridge circuit. One pair connects the rotor winding between full
battery voltage and ground to produce the forward current, and the diagonally
opposite pair connects the rotor winding between full battery voltage and ground35 with the opposite polarity to induce reverse current flow through the winding.
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The bridge circuit requires at least four switching elements to accomplishthis polarity reversal. In the circuit shown in Fig. 14, however, only two switches
are needed. A first end of the rotor winding 600 is connected to the neutral point
608 of the stator winding and the second end is connected to a switching circuit5 624 in a voltage regulator 642. The neutral point 608 of the alternator of Fig. 14 is
at the center point of the three individual stator windings 602, 604 and 606.
Multiphase windings composed of different numbers of individual stator windings
connected together at one end to form a star may also be used. The multiphase
stator winding is conventionally rectified in a multiphase bridge rectifier composed
10 of diodes 612-622.
Because the neutral point of a star configured stator winding operates at
approximately one half the output voltage applied to the battery 610, a forward
current can be induced in the rotor winding 600 simply by connecting the opposite
end of the rotor winding to the positive end of the battery 610. Alternatively, to
15 induce a negative current in the rotor winding, the opposite end can be connected
to ground.
Although the voltage applied to the rotor winding in this configuration is
less than the voltage applied in a bridge configuration, the current may be madecomparable by adjusting the number of turns and the impedance of the rotor
20 winding to produce the desired magnetic flux.
The switching of the second end of the rotor winding between battery and
ground is accomplished with a switching circuit 624 that needs only two switches626 and 628. The operation of switches 626 and 628 is controlled by a control
circuit 630 over primary control lines 632 and 634. Control circuit 630 closes
25 switch 626 and opens switch 628 to apply a forward polarity voltage to the rotor
winding 600. Switch 626 is opened and switch 628 is closed to apply a reverse
polarity voltage to the rotor winding 600. By driving the switches in
complementary fashion and by using a varying duty cycle from 0 to 100 percent,
the average voltage across the field coil can be controlled to range between full
30 boost and full buck to account for various speeds and loads.
During the forward polarity mode, current flows from the battery, through
switch 626, through the rotor winding 600 to the neutral point 608 and from there
out the individual stator windings 602-606 and bridge diodes 612-622. The
specific amounts of current flowing through the specific stator windings and bridge
35 diodes depends on the phase of the alternator and varies as the alternator rotates.
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A monitoring circuit 636 monitors the output voltage over line 638 by
comparing the output voltage to a reference voltage 640. The voltage rlegulator
642 is essentially a two state PWM voltage regulator of the basic type previously
described. However, instead of using the primary control signals to turn on and off
diagonal pairs of switches in a bridge circuit, the primary control signals are used to
turn on and off only two individual switches 626 and 628.
In applications where the basic two (2) state PWM control scheme for the
voltage regulator is suitable, the reduction in voltage regulator cost due ~o using
only two switches when used with a neutral point connected hybrid alternator will
be significant.
The neutral point connected hybrid alternator has a further advantage that
the alternator field current automatically goes to zero at zero speed. Tlhus, the
alternator drive does not have to be disabled to turn off alternator current vvhen the
ignition is turned off. The control electronics may be designed to consurne verylittle power, and thus may be left continuously on without risk of discharging the
battery. In this manner, the neutral point connected hybrid alternator achi~eves the
automatic interlock function previously described in which the regulator is
automatically powered when the alternator begins to rotate and automatically
unpowered when the alternator stops rotating.
The control circuit 630 may be a simple two state hysteresis amplifier, a
simple inverter with hysteresis, a comparator or operational amplifier with fieedback
to produce hysteresis, a standard pulse width modulator, etc. The neutral point
connected rotor winding may also be driven with a linear drive in which the
current is smoothly varied between a forward maximum and a reverse maximum
using alternative control systems.
Because the rotor winding is rotating and the stator windings are fixed, the
field winding to the connection to the neutral point and the switching circuit will
be made through slip rings in a conventional way.
Hybrid Alternator-With Single Rotor Having Poles Fitted With Permanent
Magnets And Field Windings
Figs. 16 and 17 show an alternate embodiment of the hybrid alternator of
the present invention. Hybrid alternator 700 includes a stator 702 having a
longitudinal stator region 704. A three phase stator winding 706 (also the same as
winding 706 shown in Fig. 4) extends through slots 708 formed on the interior of35 stator 700. A rotor 710 is mounted for rotation within stator 702 on shaft 712.
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Rotor 710 comprises core 714 (indicated by the area within the circular dotted linein Fig. 17) and defines a plurality of magnetic rotor field poles 716. Poles 716 are
configured to have alternating north and south magnetic fields. The rotor 710 may
be conventionally formed from multiple thin laminations having the cross-sectional
5 shape seen in Fig. 17 stacked adjacently along rotor shaft 712. Alternately, the
rotor field poles may be constructed using solid cast magnetic material.
Fig. 17 is a cross-section through stator region 704 of stator 702 within
which rotor 710 rotates. Two (2) of the magnetic poles 716 include permanent
magnet 718 mounted on the end thereof to define permanent magnetic poles 716a
10 and 716b. The remaining magnetic poles are wound field rotor poles and have
rotor windings 720 wherein alternate poles positioned between poles 716a and
716b are wound in opposite directions to produce alternating north and south
magnetic fields.
Permanent magnets 718 have a "bread-loaf" shape that matches the curve or
15 perimeter of rotor 710. The rotor field pole bodies that are part of the permanent
magnetic poles are preferably tapered as shown in Fig. 17. The pole bodies may
aiso be configured to have a uniform width, or other geometric shapes may be
used. Furthermore, although Fig. 17 shows rotor 710 having ten (poles) 716
wherein two (2) poles are permanent magnetic poles diametrically positioned,
20 alternate configurations may also be used. For example, alternate designs mayutilize more or less than two (2) permanent magnetic poles. Furthermore, if morethan two (2) permanent magnetic poles are used, the position of these poles withrespect to one another may be varied.
Each magnet 718 is magnetized through its thickness and mounted such that
25 the direction of magnetization extends radially as indicated by arrow 721, i.e., in a
direction which is perpendicular or radial to shaft 712 and normal to the large faces
of magnets 718. The magnets are held in openings in rotor laminations 715
around the perimeter of rotor 710. Referring to Fig. 17A, it is preferred that
magnets 718 are secured to rotor field pole body 717 via screw 719 that is counter-
30 sunk to be flush with the top surface of magnet 719.
If permanent magnets are to placed adjacent one another, then the northpole of one magnet must face outward and the north pole of the next magnet must
face inward or vice-versa, in order to effect alternating north and south magnetic
poles throughout the entire rotor perimeter. The permanent magnets 716a, 716b
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are fabricated from the same materials discussed above for the other embocliments
shown in Figs. 1-3.
Laminations 715 include multipie openings 722 to reduce weight and allow
for cooling air flow through the alternator.
Fig. 18 is a view similar to Fig. 17 of a further alternator embodiment.
Alternator 750 is similar to alternator 700 and includes stator 702 having a
longitudinal stator region and rotor 752. Rotor 752 comprises core 754 (indicated
by the area within the dotted line in Fig. 18) and defines a plurality of ro~or field
poles 756. Poles 756 are configured to have alternating north and south magnetic10 fields. Rotor 754 may be conventionally formed from multiple, thin laminations
having tlhe ~oss-sectional shape seen in Fig. 18 stacked adjacently along rol:or shaft
712. Alternately, the rotor field poles may be constructed using solid cast magnetic
material. The laminations include multiple openings 755 to reduce weight and
allow for cooling air flow through the alternator.
Magnetic poles 756a and 756b are permanent magnet poles and include
permanent magnets 758a and 758b, respectively. Permanent magnet 758a is
mounted between body portion 760a and pole shoe 762a. Similarly, permanent
rnagnet 758b is mounted between body portion 760b and pole shoe 762b. The
placement of the permanent magnets between the pole body and the pole shoe
improves the mechanical integrity of rotor 7S2 and reduces vibrations during
rotation of the rotor. Similar to rotor 710, the remaining magnetic poles of rotor
752 are wound field rotor poles and have rotor windings 764 wherein alternate
poles positioned between poles 756a and 756b are wound in opposite directions
to produce alternating north and south magnetic fields.
Permanent magnets 758a and 758b have a substantially rectangular shape.
Pole shoes 762a, 762b have a "bread-loaf" shape that matches the curve or
perimeter of rotor 710. However, other pole shoe and magnet shapes may be
used. Although Fig. 18 shows rotor 752 having ten (10) poles wherein two (2) of
the poles are permanent magnetic poles diametrically positioned, alternate
configurations may be used. For example, alternate designs may utilize more or
less than two (2) permanent magnets. Furthermore, if more than two (2) permanentmagnets are used, the position of the magnets with respect to one another may bevaried. As des~ibed above for permanent magnets 718 of rotor 710, permanent
- magnet 758a and 758b are magnetized through its thickness and mounted such
that the direction of magnetization extends radially as indicated by arrow i'21, i.e.,
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in a direction which is perpendicular to shaft 71 2 and normal to the large faces of
the magnets. Referring to Fig. 1 8A, it is preferred that pole shoe 762a and magnet
758a are secured to rotor pole body 760a via saew 71 9 that is counter-sunk to be
flush with the top surface of pole 762a. Pole shoe 762b and magnet 758b are
5 secured to pole body 760b in the same manner.
Referring to Fig. 19, a further embodiment of the alternator of the present
invention is shown. Alternator 800 includes stator 802 which has a longitudinal
stator region and a rotor 808 which is mounted for rotation within stator 802 on a
shaft. A three phase stator winding 804 extends through slots 806 formed on the
10 interior of stator 802. Rotor field poles 810 radially extend form rotor core 812
which is defined as the area within the dotted line. Poles 810 are magnetic poles
wherein adjacent ones of the poles 81 0 produce alternating north and south
magnetic fields. Poles 810a-d are permanent magnet poles and are formed by
magnets 814a and 814b. Magnet 814a is contiguous to and mounted between
15 poles 810a and 810b. The permanent magnets 814a and 814b effect a magnetic
field that is oriented circumferentially relative to the rotor core rotational axis. The
magnetic field is indicated by arrow 81 5 in Fig. 1 9.
Magnet 814a is mounted between poles 810a and 810b in a manner such
that magnet 81 4a is within the rotor perimeter. Non-magnetic spacer 81 6a
20 magnetically isolates permanent magnet 814a from rotor core 812. Spacer 816a
can be fabricated from non-magnetic material such as aluminum. However, an air
gap or space may also be used without any non-magnetic material. Similarly,
magnet 81 4b is contiguous to and mounted between poles 81 Oc and 81 Od.
Magnet 814b is mounted between poles 810c and 810d in a manner such that
25 magnet 814b is within the rotor perimeter. Non-magnetic spacer 816b isolates
permanent magnet 814b from rotor core 812. As stated above, an air gap or space
may be used in place of a non-magnetic material. Thus, magnets 814a and 814b
effect two (2) pairs of adjacent permanent magnet poles. The remaining rotor poles
have rotor windings 81 8 arranged such that alternate poles are wound in opposite
30 directions to produce alternating north and south magnetic fields.
The design configuration of rotor 808 offers significant advantages. One
advantage is that since magnets 814a and 814b are directly in series with the near
half of the steel rotor poles 81 Oa and 81 Ob, and the far half of poles 81 Oa and 81 Ob
may be utilized with the adjacent wound field poles on either side of the
35 permanent magnet pole pair. Thus, the permanent magnet poles 810a and 810b
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do not magnetically present a high reluctance to the adjacent wound fields.
Another advantage is that permanent magnets 814a and 814b may be realized by
low cost ferrite magnets. The aforementioned ad~,d"ldges also apply to the
permanent magnet pole pair comprised of poles 810c, 81 Od and permanent
magnet 814b.
Although two (2) diametrically positioned permanent magnet poles are
shown, other configurations may also be used. For example, only one (1)
permanent magnet pole pair maybe used. Another example is two (2) permanent
magnet poie pairs that are not diametrically positioned on rotor 808.
Designs utilizing different proportions of permanent magnet poles to
electromagnetic poles may be used. Furthermore, although Figs. 17, 18 and 19
show rotors 710, 752 and 808, respectively, using ten (10) rotor field poles, the
~ rotors may be configured to define more or less than ten (10) rotor field poles.
The alternator hybrid alternator embodiments of Figs. 17-19 may be
ope(ated with a field regulator that can be operated in bucking and boosting modes
described above. Furthermore, the alternate hybrid alternator embodiments of Fig.
17-19 may be used with the two (2) and three (3) state voltage regulators described
above. Additionally, the hybrid alternators of Fig. 17-19 may be configured as
neutral point connected alternators as described above.
Referring to Fig. 19a, a further embodiment of the alternator of the present
invention is shown. Alternator 900 includes stator 902 which has a longitudinal
stator region and a rotor 908 which is mounted for rotation within stàtor 902 on a
shaft. A three phase stator winding 904 extends through slots 906 formed on the
interior of stator 902. Twelve (12) rotor field poles 910 radially extend from rotor
core 912. It is highly preferred that core 912 be non-magnetic in order to
magnetically isolate permanent magnets 914a-f from rotor core 912. Such
magnetic isolation prevents flux from flowing from a portion of a magne~ having
one polarity, through rotor core 912 and to a portion of another magnet having an
opposite polarity. For example, non-magnetic core 912 prevents flux from flowingthrough core 912 and between the S-pole of magnet 914a and the N~pole of
magnet 914c. Thus, such magnetic isolation eliminates an unusable flux path at
~ the point of isolation and forces the flux to be focused toward active air ~ap 913
which is between rotor 908 and stator 902. In a preferred embodiment, core 912
- is fabricated from a non-magnetic material such as aluminum, copper, brass, plastic
35 and ceramic. As shown in Fig. 19A, non-magnetic core 912 has a pair of
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diametrically positioned substantially dovetail shaped male formations 913 and
915 which are disposed in corresponding substantially dovetail shaped female
formations 917 and 919, respectively, formed in rotor 908. Such a configuration
prevents core 912 from rotating with respect to the remaining portion of rotor 908.
S It is highly preferred that the number of slots 906 be equal to 3 times the
number of poles. Thus, as shown in Fig.19A, there are 36 slots 906 formed on theinterior of stator 902. Poles 910 are magnetic poles wherein adjacent ones of the
magnetic poles 910 produce alternating north and south magnetic fields. Poles
910a-h are permanent magnet poles and are formed by magnets 914a-f. Magnet
914a is contiguous to and mounted between poles 910a and 910b. Magnet 914 b
is contiguous to and mounted between poles 910b and 910c and magnet 914c is
contiguous to and mounted between poles 910c and 910d. Similarly, magnet
914d is contiguous to and mounted between poies 910e and 910f. Magnet 914e is
contiguous to and mounted between poles 910f and 910g, and magnet 914f is
contiguous to and mounted between poles 910g and 91 Oh.
Magnets 914a-c effect four (4) adjacent and contiguous permanent magnet
poles. Similarly, magnets 914d-f effect four (4) adjacent and contiguous permanent
magnet poles that are diametrically position in relation to the permanent magnetpoles produced by magnets 914a-c. The remaining four (4) rotor poles comprise
electromagnetic poles 910i-l. Poles 910i and 910j are diametrically positioned in
relation to poles 9101 and 910k, respectively. Poles 910i-l have rotor windings 918
arranged such that alternate poles are wound in opposite directions to produce
alternating north and south magnetic fields.
Magnets 914a-f are mounted between the poles in a manner such that
magnets 914a-f are within the rotor perimeter. Permanent magnets 914a-f effect amagnetic field that is oriented circumferentially relative to the rotor core rotational
axis. Thus, magnets 914a-f are magnetized transversely aaoss the narrow, but
variable, dimension thereof (see arrow 915 in Fig. 19a). Such a magnet
configuration is referred to herein as the "focused flux configuration."
Alternator 900 offers significant advantages. One advantage is that because
magnets 914a and 914c are directly in series with the near half of the steel rotor
poles 910a and 910d, respectively, the far half of poles 910a and 910d may be
utilized with adjacent wound field poles 91 Ok and 910i, respectively.
Furthermore, the permanent magnet poles 910a and 910d do not magnetically
present a high reluctance to the adjacent wound fields. Similarly, magnets 914d
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and 914f are directly in series with the near half of the steel rotor poles 910e and
910h, respe~lively. Thus, the far half of poles 910e and 910h may be utilized with
adjacent wound field poles 9101 and 910j, respectively. Permanent magnet poles
910e and 910h also do not magnetically present a high reluctance to the adjacent5 wound fields. Another advantage of such a configuration as des~ibed above is that
magnets 914a-f do not interfere with the wound field flux. A further advantage of
alternator 900 is that twelve (12) rotor poles provide an output frequency Ithat can
be used to implement a variety of electronic functions associated with the
operation of motor vehicles such as an automobile.
In a preferred embodiment, permanent magnets 914a-f may be realized by
low cost ferrite magnets such as sintered ferrite. However, other types of rnagnets
also may be utilized such as bonded neodymium, bonded ferrite or samarium
cobalt.
As shown in Fig. l9a, the wound field pole bodies of poles 910i-i are
circumferentially positioned on rotor core 912 by a predetermined distance and
pole shoes 920a-d are positioned on the wound field pole bodies in a manner suc
that all twelve (12) pole shoes are equidistantly spaced, relative to one another,
around the rotor circumference. Such a configuration provides significantly morefield winding space for the two (2) pairs of adjacent wound field poles 910i, 910j
and 910k, 9101, thereby increasing the available excitation ampere-turns and thepower density of the alternator. All twelve (12) pole bodies are asymmetrically
spaced so as to inaease the space available for receiving windings and inaease air
flow in the areas between adjacent wound field coils (poles 910i, 910j and 910k,9101) thus reducing the operating temperature of the alternator.
In a preferred embodiment, the pole bodies of the rotor field poles
positioned between a magnet and a wound field pole, such as poles 910a, 910d,
910e and 910h, have a geometric shape (length and width) that corresponds to th
resultant summation of flux contributed by the magnet on one side, and the woundfield pole on the other side. Thus, poles 910a, 910d, 910e, and 910h are referred
to as contribution poles.
The geometrical shape of the pole bodies of poles 910a, 910d, 910h and
910e are chosen so as to allow the poles to carry a predetermined pole flux. Thus,
the geometrical shape of the pole body of poles 910a, 910d, 910e and 910h may
- be different than the pole bodies of the poles positioned between the magnets or
the pole bodies of the wound field poles. For example, as shown in Fig. 1 9a, the
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geometrically shape, e.g. width, of poles 910a, 910d, 910e and 910h is differentthan the pole body width used for the poles positioned between magnets since thebody of poles 910a, 901d, 910e and 910h do not taper as does the pole body of
pole 910c.
Thus, the single-stack hybrid alternator embodiments shown in Fig. 19a
offers the following significant advantages:
a) reduced complexity of design. For example, the design configuration
of Fig. 1 9a eliminates stator insulating spacer 52 as shown in Fig. 1;
b) overall reduction in size of the alternator;
c) improved cooling and ventilation of the alternator thereby reducing
the probability of overheating;
d) reduced manufacturingcosts;
e) a power density that is substantially the same as the double-stacked
configuration shown in Fig. 1;
f) outputs a frequency that can be used to implement electronic
functions necessary for the operation of a motor vehicle;
E~) can utilize low cost ferrite magnets; and
h) prevents unusable flux from flowing through the rotor core.
Although eight (8) permanent magnet poles (two diametrically positioned
sets of four (4) permanent magnet poles) are shown, other configurations may also
be used. For example, different proportions of permanent magnet poles to
electromagnetic poles may be used. Furthermore, the rotor may be configured to
define more or less than twelve (12) rotor field poles. For example, the rotor may b
configured to define 8,10 or 14 rotor field poles. The aforementioned advantageswould also be realized with the aforementioned variations.
The hybrid alternator embodiment of Fig. 1 9a may be operated with a field
regulator that can be operated in bucking and boosting modes described above.
Furthermore, the hybrid alternator Fig. 1 9a may be used with the two (2) and three
(3) state voltage regulators desaibed above. Additionally, the hybrid alternator of
Fig. 19a may be configured as a neutral point connected alternator as described
above.
Indented Rotor Field Poles
Referring to Figs. 20-22, rotor field pole 850 comprises body portion 852
35 and pole shoe portion 854. Body portion 852, radially extends from rotor core 856
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to and end surface 858. Body portion 852 has a longitudinal axis substantially
parallel to shaft 860, a longitudinal length L1 and a width W1. Pole shoe portion
854 is attached to end surface 858, has a longitudinal length L2 that is gre;~ter than
body portion length L1, and a width W2. Thus, body portion 852 is indented
5 along its entire perimeter from pole shoe portion 854 by a distance A. Dctted line
853 in Figs. 21 and 22 re,l~resenls the perimeter of body portion 852. Since
indenting the pole body 852 would reduce the pole body longitudinal length to L1,
the pole body width is increased by a proportional amount to width W1 so as to
maintain the necessary pole body aoss-sectional area.
Rotor field pole 850 may be fabricated from a cast, high permeability steel
piece wherein the indentations are directly formed by casting or by machining. An
alternate indented rotor field pole configuration is shown in Fig. 23. Rotor field
pole 862 is comprised of end caps 864a, 864b and central body portion 866. Caps
864a, 864b are rigidly attached to central body portion 866. The cenl~er body
15 portion has a longitudinal length L3 and each cap has a longitudinal length of L4.
The overall longitudinal length of central body portion 862 is L1, which is lhe same
as pole 850, and is the sum of L3 + 2xL4. Cap 864a comprises an end portion
865a and a body portion 867a. Body portion 867a and end portion 865a have
lengths L4 and L5, respectively. The difference in length between L5 and L4 is
20 represented by the letter A. Thus, body portion 867a is indented from end portion
865a by a distance A. Similarly, cap 864b comprises end portion 865b and a body
portion 867b. Body portion 867b and end portion 865b have lengths L4 and L5,
respectively. The difference in length between L5 and L4 is represented by the
letter A. Thus, body portion 867b is indented from end portion 865b by a distance
25 A for the entire perimeter of body portion 866.
The indentation distance A can be varied according to the number of
required turns of the rotor field windings and/or whether it is desired to have the
windin~s extend beyond the stator wound field stack section. The indentation on
both ends of the rotor field provide a natural winding support on either end of the
30 rotor pole thus making unnecessary the use of round, pole shoe support pins.
Furthermore, an increase in the number of rotor field poles can be realized since
the rotor field poles can be wound such that the windings do not extendl beyond
edges 854a, 854b and 854c of rotor field pole 852, or edges 869a, 869b and 869c
of pole 862, thereby allowing the rotor field poles to be spaced closer togetherr
35 This feature also allows wound field portion 24 to be positioned closer to
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permanent magnet rotor portion 38 of the alternator of Fig. 1. Since the perimeter
of the pole body is reduced, the net mean turn of the rotor windings is reduced.Therefore, less wire is required than conventional pole bodies. A reduction in the
amount of wire also effects a deaease in resistance to current flowing through the
5 windings thereby reducing power consumption. Additionally, the reduction in the
amount of wire also reduces weight and cost to manufacture the rotor.
Furthermore, the reduction in the amount of wire reduces the wound field windingthickness thereby facilitating heat transfer from the winding. This improves heat
conduction and reduces the probability of over heating.
It will thus be seen that the objects set forth above, among those made
apparent from the preceding description, are efficiently attained and, since certain
changes may be made in the above constructions without departing from the spiritand scope of the invention, it is intended that all matter contained in the above
desaiption or shown in the accompanying drawings shall be interpreted as
illustrative and not in a limiting sense.
While the invention has been illustrated and described in what are
considered to be the most practical and preferred embodiments, it will be
recognized that many variations are possible and come within the scope thereof,
the appended claims therefore being entitled to a full range of equivalents.
Thus, having desaibed the invention, what is claimed is:
