Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Background Of The Invention
.
The present invention comprises an improvement in the
subject matter described in Parker U.S. Patent No. 4,095,148
issued June 13, 1978, for "Direct Current Motors". The
Parker patent relates to a DC motor using silicon controlled
rectifiers in place of the brushes and commûtator which are
conventionally employed in such a motor, and includes a
mechanical commutator and associated brushes which are used
to connect a low voltage and current to activate the silicon
controlled rectifiers. The present invention replaces these
low current and voltage components of the Parker arrangement
by small rotating stacks of laminated iron and low power
electronic circuits, said circuits being so arranged that they
are capable of starting the motor from a standing position and
introduce commutation assistance during motor starting ar~d at
very low speeds thereby eliminating various special starting
circuits which are employed in the Parker arrangement to start
the motor.
The improved Direct Current motor of the present
invention is primarily intended for use in electric motor vehicles.
An object of the present invention is to eliminate the
mechanical brush-commutator SCR trigger means employed in the
aforementioned Parker patent by employing contactless electronic
circuit means in place thereof.
Another object of the present invention is to provide a
nonmechanical arrangement responsive to a particular rpm that
is adapted to advance or retard the magnetic position of the
rotor with respect to the stator, thereby to alter the time
at which the SCRs are triggered on in accordance with motor
speed.
An additional object of the present invention is to
provide an arrangement which insures that SCR triggers will be
available for motor starting at any rotor position.
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Yet another object of the present invention is to
provide an arrangement whereby a triggered assembly inhibits
si~ultaneous SCR trigger generation by a particular adjacent
trigger assembly.
A further object of the present invention is to provide
stator SCR commutation assistance during motor starting and
very low speed operation, which autcmatically ceases above a
particular speed.
Summary of The Invention
In accordance with the present invention, the motor
construction shown in Parker ~.S. Patent No. 4,095,148,is
modified in various respects to accomplish the foregoing
objects and advantages. As in the Parker patent, the motor
comprises a stator having a plurality of coils which, in the
preferred embodiment of the invention, are connected in series
with one another in a closed loop configuration, means being
provided to connect the junction between adjacent pairs of
the coils to diametrically opposed ones of said junctions
in said closed loop configuration. A plurality of pairs of
oppositely poled solid state gate controlled rectifiers,
preferaDly silicon controlled rectifiers (hereinafter referred
to as SCRs) are connected respectively to the junctions of
different adjacent pairs of the coils for selectively conduct-
ing current into and out of the stator coil junctions. A ~
current source is provided to energize each of the pairs of
silicon controlled rectifiers, and means including a distributor
driven by the motor rotor are provided for energizing the gate
electrodes of different ones of the silicon controlled rectifiers
in sequence thereby to produce a plurality of stator poles which
are angularly displaced from the rotor poles and which stator
poles shift in position about said closed loop stator coil
configuration with rotation of the rotor.
In accordance with the present invention, the brush-
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commutator arrangement which is used in the Parker patent
to effect energization of the gates of the several SCRs is
replaced by a plurality of trigger assemblies that are
connected respectively to different ones of the SCRs. Each
of said trigger assemblies includes a pick-up coil whose
inductance is selectively varied by an element of magnetic
material that moves past the pick-up coil in each trigger
assembly as the rotor rotates. The several pick-up coils
are mounted in spaced relation to one another along an
arcuate path which is concentric with the path of movement
of the magnetic element, and each pick-up coil is connected
to one or more impedance elements, preferably by capacitor
means, to form a frequency sensitive circuit in each trigger
assembly whose resonance condition varies as a function of
rotor position. Oscillator means are coupled to the frequency ;
sensitive elements in all of the trigger assemblies, the
oscillator means being operative to produce at least two
different output frequencies, and the actual output frequency
which is produced by the oscillator means at any given time
is controlled by an rpm responsive electronic switch so that
the output frequency produced by the oscillator means at any
given time is dependent upon the motor operating condition,
i.e., whether the motor is stopped or running.
As a result of this arrangement, the rotor position at
which a particular amplitude of the outpu-t signal is produced
by each of said frequency selective circuits is jointly depend-
ent upon the particular frequency of said oscillator and the
position of the magnetic element relative to each of the pick-
up coils in the several trigger assemblies as the rotor rotates.
This aspect of the arrangement non-mechanically advances or
retards the rotor's mechanical position at which said trigger
assemblies are activated. Circuit means, preferably comprising
a Schmitt trigger circuit whose input is connected to the
frequency selective circuit in each trigger assembly and whose
output is connected to a gate trigger amplifier in said assembly,
is responsive to a particular amplitude threshold of output
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signal which is produced by the frcquency selective circuit
in said trigger assembly to selectively energize the gate
electrodes of the SCRs that are associated with said trigger
assembly. The trigger assemblies are operative to trigger
on their associated SCRs in a predetermined sequence as the
rotor rotates.
In accordance with a further feature of the invention,
the several trigger assemblies are so arranged that each
trigger assembly, when rendered operative, provides a feedback
signal to an adjacent trigger assembly to inhibit the operation
of the previously operable adjacent trigger assembly, thereby
to assure that, at each rotor position where simultaneous SCR
triggers could otherwise be produced, SCR triggers are actually
produced by only a particular one of said adjacent trigger
assemblies.
In accordance with another feature of this invention, SCR
commutation assistance is automatically started or stopped at
a particular r~m by an arrangement that is synchronized by SCR
triggering and provides electronically delayed, forced commu-
tation near rotor positions of natural commutation. As a
result of this arrangement, a heavily loaded motor will reliably
start in any rotor position and produce very high torque at
very low speeds of, for example, tWG or three rpm as well as
at all higher speeds.
Brief Description of the Drawings
The foregoing construction and operation of the present
invention will become more readily apparent from the following
description and accompanying drawings in which:
Figure 1 illustrates in schematic form a motor constructed
in accordance with the present invention;
Fiyure 2 is an enlarged view of the portion of Figure 1
which shows the electromagnetic portion of the distributor
arranyement employed to activate the proper scRs;
Figure 3 is a schematic drawing of a typical one of the
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SC~ trigger assemblies employed in the arrangement of Figure l;
Figure 4 graphically depicts the signal amplitude varia-
tions which are produced at point A of the trigger assembly
shown in Figure 3 as the motor rotor rotates;
Figure 5 is a schematic drawing of a commutation assist-
ance circuit whose operation is commanded by particular action
of the trigger assemblies exemplified by Figure 3; and
Figure 6 is a schematic diagram of an rpm responsive circuit
that contactlessly switches the fre~uency of the oscillator at
predetermined motor speeds.
Description Of The Preferred Embodiments
Figure l depicts a motor arrangement which is generally
similar, both structurally and operationally, to the motor
arran~ement which is described in Parker ~.S. Patent No. 4,095,148. ~he
reference numerals employed in Figure 1 are the same as those
ut~lized in Figure 1 of the said Parker patent to the extent
that said reference numerals identify like components, and
additional components shown in Figure 1 of the instant
application are identified by reference numerals other than
those employed in Figure 1 of the Parker patent.
Briefly, the motor comprises a stator consisting of
plurality of stator coils 21 through 36 connected in series
with one another in a closed loop configuration. Connections,
designated by the terminals A-H inclusive and A'-H' inclusive,
are brought out from the junction between each adjacent pair
of coils, the connections A-H being located on one half of
the stator coil array and the connections A'-H' being located
on the other half of the array. Junctions having the same
letters are interconnected to one another, i.e., junction A
is connected to A', etc., but these connections have not been
shown in Figure 1 in order to simplify the drawing. The
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positive terminal of a direct current power supply 38 is
connected to the opposite ends of a diameter of the coil
circle, and the negative terminal of the power supply 38 is
connected to the ends of a second diameter on the coil circle
which second diameter is located at right angles to the first
diameter, with the result that four poles are formed on the
stator which interact with four poles on an associated rotor
36, and which are angularly displaced therefrom, to create
a torque therebetween.
The rotor 36 comprises four coils 20 which are connected
in series with one another between slip rings 19 and 47, and
said slip rings are in turn interconnected to the power supply
via lines 40 and 99 to effect energization of the rotor coils
thereby to produce the rotor poles which coact with the stator
poles.
The circuit further includes a plurality of silicon
controlled rectifiers 61 - 76 grouped in oppositely poled pairs
and connected as shown to the aforementioned stator coil
junctions, to effect a current flow both into and out of each
coil junction at appropriate times in the manner and for the
purposes described in the aforementioned Parker patent. The
control electrodes of the 16 SCRs are operated respectively
by 16 separate secondary windings provided on eight transformers
90-97. One side of the primary windings of said transformers
are interconnected to one another, and the other sides of the
said primary windings of transformers 90-97 are individually
connected to SCR gate trigger assemblies 101 through 108 in
the manner shown in the drawings. Rotation of the rotor 36
operates to energize the gate electrodes of different ones
of the silicon controlled rectifiers in sequence thereby to
produce a plurality of stator poles which are angularly
displaced from the rotor poles, and which shift in position
about the closed loop coil configuration as the rotor rotates.
In the Parker patent, rotation of the rotor 36 effected
the aforementioned SCR gate control operation by means of a
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commutator that was driven by the rotor, and brushes that
rode on said commutator. In accordance with the present invention,
however, the commutator and associated brushes are replaced
by an armature 111 which rotates wlth rotor 36, and which
includes two stacks of laminations 109 fabricated of a
magnetic material and located 180 apart as shown in
Figures 1 and 2, and eight identical pick-up coils 110 are
mounted on centers spaced 22.5 apart concentrically around
the outer circumference of armature 111. Said coils 110 and
stacks 109, in eooperation with associated resistive and
capacitive elements, function as an electromagnetically
activated rotor position responsive arrangement which, in
further cooperation with low power electronie eireuits and
gate eontrolled solid state reetifiers, eomprise a novel
eontaetless input power distributor means whieh aeeomplishes the
purpose of the mechanieal brush/eommutator arrangement used
in the aforementioned Parker patent or other sueh arrangements
that have been used in the prior art for the energization
and eommutation of high power DC motors.
More partieularly, the eight piek-up eoils 110 are eon-
nected respeetively to eight identieal SCR trigger assemblies
101 through 108, eaeh of whieh eomprises a eireuit of the type
to be deseribed hereinafter in referenee to Figure 3; and
the several trigger assemblies 101 through 108 are assoeiated
with a variable frequeney sine wave oseillator 100 that is
adapted to provide either of two different output frequeneies
under the eontrol of an rpm responsive switehing eireuit 222
whieh is aetivated by a portion of eommutation eircuit 119. It
should be understood that the use of a two frequeney oseillator
and eight trigger assemblies is intended to be illustrative
only. The aetual number of frequeney steps between a higher
and lower frequeney provided by oscillator 100 may be more
than two, and the actual number of trigger assemblies employed
can be either higher or lower than eight.
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Inasmuch as the motor is described as it may be applied
to a moto, vehicle, the speed of the motor can he varied by
varying the magnitude of the voltage which is fed thereto,
e.g., by means such as a rheostat 115. Arm 115a is connected
in series with the positive side of the power supply 38, as
illustrated in Fig. 1, and an associated connector is provided
on the other side of said power supply 38 comprising a switch arm
116a which is ganged to arm 115a and movable along an arcuate
conductor 116. When the switch arms 115a, 116a are in their
extreme counterclockwise positions, in engagement with terminals
115b and 116b respectively, the motor is not energized and does
not rotate, but as the arms 115a, 116a are moved clockwise to the
successive positions indicated in the drawings, oscillator 100 and all
the control circuits connected thereto are energized and
increasing voltage levels are supplied to the motor to cause
the motor to run at increasing speeds. When the motor arrange-
ment of Figure 1 is used in an electric vehicle, which is one
of the applications for the motor system described in the
aforementioned Parker patent, the position of the ganged arms
115a, 116a can be controlled by a foot pedal in the vehicle.
However, it will be understood that the motor system can be
employed in other applications as well, and that the voltage
supplied to the motor can be controlled in other fashions.
In motor vehicle applications, the series motor as
described has the advantage of high torque at low and high
speeds. In other applications where constant speed is required,
shunt connection of the field windings is possible. In such
cases, an inductance coil may replace the series field as will
be described later.
Figure 3 is a schematic drawing of a typical one of the
SCR trigger assemblies 102, it being understood that the same
circuit is employed for each of the other assemblies 101
through 108, and depicts one of the induction pick-up coils
110 which is associated with said trigger assembly 102, as
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well as a portion of armature 111 and one of the sets of
laminations 109 which is mounted on said armature and which
moves past each of the induction coils 110 in sequence as the
motor rotor 36 is rotated. Trigger assembly 102 is, as shown
in each of Figures 1 and 3, employed to control the energization
of the primary winding of transformer 91, the secondary windings
of which in tuxn control the energization of the gate electrodes
of SCRs 64 and 71 to effect the stator current flows which are
described in the Parker patent when said two SCRs are rendered
conductive. Each of the other trigger assemblies shown in
Figure 1 is used to control an associated other one of said
transformer primary windings, to control in turn the conduction
of two other ones of said SCRs, all as described in the Parker
patent. The various primary windings are connected to the
power supply 38 as shown in each of Figures 1 and 3 and, in
addition, the sine wave oscillator 100 is coupled to each
of the trigger assemblies 101-108 via line 98, as also shown
in Figures 1 and 3.
Oscillator 100 is adapted to provide either of two output
frequencies. These frequencies are comparatively close to one
another, and may comprise for example the frequencies 10 Kc
and 13 Kc. The particular frequency which is provided by the
oscillator under any given operating condition is determined
by an rpm responsive circuit 222 shown schematically in
Figure 6, and in block form in Figùres 1 and 3.
The arrangement of circuit 222 provides solid-state
switching that alters the output frequencies of oscillator 100
between the starting frequency (e.g., 13 Kc) and the second,
lower running frequency (e.g., 10 Kc) at predetermined rotor
speeds. More specifically, circuit 222 responds to rotation
derived signals coupled from commutation circuit 119 via line
113 (as shown on Figure 1) which ultimately cause a particular
transistor to switch on and off at predetermined rpms. In
other words, circuit 222 electronically performs speed-related
switching similar to that of mechan~cal centrifugal switch
means.
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Referring to Figure 5, it will be noted that line 113 connects to
the junction of zener diode 130 and resistor 129. The signals
coupled to this junction are described later in connection with
the operation of commutation circuit 119. It is sufficient here
to note that the first few pulses out of a group of pulses
generated by each SCR trigger assembly in response to rotor
rotation are coupled by zener diode 130 to line 113. The time
between said groups of pulses is inversely proportional to
rotor speed. In other words, as rotor speed increases, the
time between the start of succeeding trigger assembly pulse
groups decreases and vice-versa. Because each trigger assembly
is turned on twice during a 360 rotor revolution, line 113
couples 16 pulse groups per revolution to the input of circuit
222, the first pulse in said groups being respectively displaced
in time from one another in accordance with rotor rpm.
Figure 6 comprises a schematic diagram of circuit 222.
Some of the frequency determining components of oscillator 100, i.e.,
capacitors 250 and potentiometers 251 and 252, are also shown
in Figure 6. Circuit 222 consists of a transistor switch 244
that turns on and off in response to Schmitt trigger transistors
240 and 242 which respond to the integrated result of transistor
230 switching that is caused by said rpm related signals coupled
to the base electrode of transistor 230 by line 113.
When the motor is stopped, no signals appear on line 113
and transistor 230, having no other source of forward bias,
is off. Under this condition, capacitor 231, connected between
the collector of transistor 230 and ground charges to a positive
voltage determined by a resistor 233, the position of the
movable contact on an rpm operate adjust potentiometer 234,
and the base electrode input circuit of transistor 240. More
specifically, with the motor stopped and transistor 230 off,
positive voltage is coupled from t~le power supply via
potentiometer 234 and resistor 233 through resistor 232 and
diode 235 to the junction of resistors 238, 23g and capacitors
236, 237. When said junction voltage is approximately +.7v
or higher, forward bias is provided to transistor 240 through
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resiStor 239, and to transistor 244 through resistor 238. This
causes transistor 240 to conduct, which cuts off transistor
242 and allows additional forward bias to be coupled to the
base of transistor 244 from the positive side of the power
supply through resistor 243. This added bias assures more rapid
turn on and saturation of switch transistor 244. Line 114, shown
connected between the collector of transistor 244 and one end
of start frequency adjust potentiometer 251 of oscillator 100,
is thus switched to ground by collector-emitter conduction of
transistor 244. When transistor 244 is off and line 114 is
ungrounded, the operating frequency of oscillator 100 is
adjusted by the setting of run frequency potentiometer 252 alone.
However, when line 114 is grounded by conduction of transistor
244, the frequency of oscillator 100 shifts to a higher
frequency determined by the setting of start frequency po-
tentiometer 251. Thus, when the motor is stopped, circuit 222
establishes a condition whereby oscillator 100 is caused to
operate at the higher start frequency.
Assume now that the motor is running at 120 rpm and
potentiometer 234 is adjusted to activate circuit 222 during
acceleration at, for example, 200 rpm. The pulse groups on
line 113 would now be appearing at a rate of 32 groups per
second. The action of capacitor 228 and resistor 229 integrate
the few pulses in each group to a single continuous pulse.
Transistor 230 is thus caused to conduct for a single period
(of approximately 400 microseconds) each time an SCR trigger
assembly is first activated. During said conduction of
transistor 230, the junction of resistors 233, 232 and capacitor
231 is clamped to near ground potential and positive voltage
ceases to be coupled from the positive side of the power
supply to the input circuit of transistor 240. Under this
condition, the positive charge on capacitors 237 and 236 begins
discharging through resistors 238 and 239, thereby maintaining
conduction of transistor 240. When transistor 230 ceases
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conduction, capacitor 231 again charges through resistor 233
and ultimately positive voltage is again coupled through
resistor 232 and diode 235, whereby capacitors 236 and 237
cease di-~charging and begin charging toward a higher magnitude.
- It can now be seen that when the motor is running, the
peak voltage to which capacitor 231 can charge is also dependent
upon the rate at which transistor 230 is switched on and off
as well as the adjustment of potentiometer 234. Further, it
should be noted that variations in the voltage charge of
capacitors 236 and 237 are now dependent upon both the peak and
the average charge realized by capacitor 231. Under the present
assumed adjustment of potentiometer 234, the average charge of
capacitors 236 and 237 will continuously maintain transistor 240
conduction, and oscillator 100 will continue to operate at the
start frequency.
Assume now that the motor is caused to accelerate. The
average charge on capacitors 236 and 237 will begin decreasing
further in response to the decreased peak and average charge of
capacitor 231 resulting from the increased rate at which trans-
istor 230 is caused to switch by the signals on line 113. Ulti-
mately, capacitors 236 and 237 will discharge below the threshold
required to sustain the forward bias to transistors 240 and 244
as the motor continues to accelerate. For purposes of description,
it was previously assumed that the adjustment of potentiometer 234
causes said lack of forward bias to occur at 200 rpm.
At 200 rpm, therefore, transistor 240 ceases conduction,
which action allows forward bias to be supplied through resistor
241 to transistor 242 causing it to begin conducting. Collector-
emitter conduction of transistor 242 clamps the junction of
resistors 238, 243, capacitor 236 and the base electrode of
transistor 244 to near ground potential. The inter-connection
of capacitor 236 and resistor 238 between transistors 240 and
242 is of known Schmitt trigger form, and provides positive feedback
that accelerates the switching action of said transistors. Thus,
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when transistor 2~0 conduction begins to slowly decrease at 200
rpm, said Schmitt trigger arrangement accelerates this action
causing transistor 244 to be abruptly cut off by conduction of
transistor 242, and line 114, which had been grounded, is
thereby abruptly open-circuited. With line 114 ungrounded, the
frequency of oscillator 100 is dependent solely upon run frequency
adjust potentiometer 252 shown permanently grounded. Thus,
when the motor speed reaches 200 rpm, circuit 222 establishes
a condition whereby oscillator 100 is caused to operate at the
lower run frequency.
Assume now that the motor is caused to decelerate from a
speed of 200 rpm or greater for any reason, e.g., an increasing
load or a decrease in input voltage. The arrangement of circuit
222, by design, switches at a lower rpm when decelerating than
when accelerating. More particularly, the average charge on
capacitor 231 must be of a different magnitude to cause
transistor 240 to begin conducting than to cause transistor
240 to cease conduction. For this reason, the switching
action of circuit 222 is reliably positive during acceleration
or deceleration and is not subject to oscillation in the rpm
region of switching even when the motor slowly reaches or
leaves the specific rotor speed at which switching occurs.
The above described switching at different magnitudes --
of input threshold is typical of normal Schmitt trigger
operation and is further exaggerated in the specific arrange-
ment of circuit 222 by resistor 232 and capacitor 236. When,
for example, the motor is decelerating toward an rpm for
switching, conduction of transistor 242 e~fectively connects one
end of capacitor 236 and resistor 238 to ground through its
collector-emitter junction, and said components are thereby
effectively placed in parallel with capacitor 231 through
diode 235 and resistor 232. The voltage on capacitor 231 is
thus divided to a lower voltage by action of resistors 232
and 238 and the input charging time constant is increased by
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paralleling capacitor 237 with capacitor 236. The average
charge on capacitor 231 must, therefore, reach a different
magnitude to induce Schmitt trigger switching action during
deceleration than when resistor 238 and capacitor 236 are not
paralleled with capacitor 237 by conduction of transistor 242
(as is the case when the motor is accelerating toward an rpm
for switching). When the motor has slowed sufficiently to
raise the average voltage on capacitor 231 to the threshold
where Schmitt trigger action occurs, transistor 244 is driven
to saturation conduction by the combined forward bias previously
described when transistor 242 is cut off. This action again
grounds line 114 causing oscillator 100 to operate at the
higher start frequency where improved commutation of stator
SCRs is achieved at very low rotor rpm.
The above described switching of circuit 222 cooperates
with other portions of the present invention to advance the time at which
SCR pairs are triggered on during motor starting and in
accordance with a particular motor rpm when the motor is deceler-
ating from all higher speeds. In other words, the contactless
distributor arrangement of the present invention electronically
alters the rotor mechanical position where stator energization and
commutation occurs as a function of the output frequency of
oscillator 100, which frequency, in turn, is shifted by circuit
222 in dependence upon whether the motor is stopped or running and,
when running, in accordance with particular rpms.
Referring now to Figure 3, it will be noted that the pick~up
coil 110 which is associated with typical trigger assembly 102
is connected to a pair of capacitors 202 and 203 forming a
portion of the trigger assembly 102, to provide a frequency
selective network which is connected via resistor 200 to the
output of oscillator 100. Briefly, this arrangement provides
either little attenuation of the output signal frequencies of
oscillator 100, or substantial attenuation of a frequency spectrum
which includes said frequencies, in dependence upon the mechanical
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1 17~475
position of laminations 109. More particularly, the reactive
elements at the input to typieal trigger assembly 102 offer
little attenuation to the output signals from oscillator 100 when
laminations 109 are in proximity to the eoil 110 assoeiated
with said trigger assembly. Simultaneously, the same elements
of the other trigger assemblies provide substantial attenuation
of said signals beeause laminations 109 are, at that moment,
remote from their respeetive eoils 110.
The junetion of resistor 200 and capacitor 202 (point A in
Figure 3) is connected by means of a resistor 201 to the base
of a transistor 204, which is in turn connected to a transistor
207 and to the various resistors 205, 206 and 208 in a con-
figuration which constitutes a well-known Schmitt trigger
cireuit. In the partieular position of laminations 109 relative
to piek-up eoil 110 shown in Figure 3, transistor 204 is eaused
to eonduet by positive alternations of the s~ e wave signal coupled
from the output of oscillator 100 to the base of transistor 204
via resistors 200 and 201. The particular amplitude of the
signal which is supplied to the base of transistor 204 at any
given time is determined by the rotor position, resistor 200,
and the aforementioned frequency selective network consisting
of capaeitors 202, 203 and the induetance of coil 110.
Stacked laminations 109, more elearly shown in Figure 2,
rotate with the rotor and increase the Q and the inductance
of coil 110 when said laminations are in close proximity to the
coil. As a result, and in response to rotor movement, the
arrangement of resistors 200, 201 and the said frequency selective
network comprise an attenuator, variable in both bandwidth and
magnitude of attenuation, which is interposed between oscillator
100 and the input to transistor 204. More speeifieally, the
aformentioned resistance and capaeitanee elements eooperate
with the induetanee and Q of coil 110, which vary in dependenee
upon the mechanieal position of laminationslO9, to provide
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an AC signal attenuator of variable selectivity and variable
attenuation over a relatively broad frequency spectrum. The
signal pass to attenuate ratio is equal to the ratio between
the impedances realized by said reactive elements in a low Q
state of active series resonance and a higher Q state of active
parallel resonance in response to the posi-tion of laminations
109 and the continuous output signal from oscillator 100. Thus,
a substantially greater signal pass to attenuate ratio is realized
by the particular arrangement of resistlve and reactive elements
than may be achieved with the Q merit of said reactive elements
in a single state of resonance.
The above described electromagnetic portion of the contact-
less distributor employed in the present invention, i.e., said
frequency selective variable attenuator network, is substantially
immune to extraneous noise energy and achieves substantial immunity
to the variously coupled noise impulses that are generated by
the switching of adjacent high power SCRs. This is because the coil
elements 110 of all of said networks are maintained in a condition
of active (i.e., signal driven) resonance by every frequency output
of oscillator 100. In addition, said networks are caused to be
naturally immune to SCR trigger impulse noise because said
triggers are generated by the same output signal of oscillator 100,
and impulse noise therefore occurs at the particular frequency
to which all said netowrks are tuned at any given moment. In
other words, when no output is desired from particular ones of
said networks they are maintained in a signal driven state of
low impedance series resonance by the output signal of oscillator
100 at the same frequency at which SCR triggers are being
generated by the activated trigger assembly (whose frequency
selective network, at that moment, is actively parallel resonated
by said oscillator 100 output signal). Thus, the particular
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arrangement of each frequency selective network employed in
the system of the present invention (1) attenuates the output signal
from oscillator 100 and further employs said signal to improve
its noise immunity by a state of active, broadband series
resonance when laminations 109 are remote from coil 110, (2)
passes the output signal from oscillator 100 with noise rejecting
narrower bandwidth in a state of active parallel resonance when
laminations 109 are in proximity to coil 110, and (3) functions
ultimately as a variable impedance whose magnitude is a function
of the position of laminations 109 relative to coil 110. The
amplitude of the signal coupled from oscillator 100 to
transistor 204 is varied by the voltage divider action of resistor
200 and the said frequency selective network. Resistor 201 is
provided to raise the effective input impedance of transistor
204.
Considering now the general operation of the typical frequency
selective netowrk shown in Figure 3, the value of capacitor 202
is selected to be such that, when laminations 109 are remote
from coil 110, capacitor 202 and coil 110 are near series
resonance at either of the aforementioned two output frequencies
of oscillator 100. This is possible only because the bandpass
of series resonating coil 110 and capacitor 202 is broadened
by the de-Qing effect of series resistor 200 and is further
broadened by the fact that, when laminations 109 are remote
from coil 110, the Q of coil 110 is lower than when it is in
proximity thereto. For example, the frequency selective networks
of a contactless distributor constructed in accordance with
the present invention, exhibited a typical 6 DB bandpass of
approximately 10 Khz at series resonance when the laminations 109
were remote from coil 110, and a 6 DB bandpass of 2.5
Khz at parallel resonance when the laminations 109
were in proximity to coil 110. Under the condition of operation
when laminations 109 are remote from coil 110, the bandpass of
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the resonant circuit is broad, its impedance is low, and the
attenuation of the variable impedance network, therefore, is
high. As a result, the amplitude of the signal coupled from
point A by resistor 201 at any frequency of oscillator 100 is
less than the +0.7v conduction threshold of transistor 204.
Since transistor 204 has no other source of forward bias, it
does not conduct under this condition of operation and no SCR
triggers are produced by the trigger assembly 102.
The value of capacitor 203 is selected to be such that,
as laminations 109 are moved by rotation of the rotor to a
position wherein said laminations partially overlap coil 110,
capacitor 203 and the increased inductance and Q of coil 110
achieves parallel resonance with substantially narrower bandpass
at the higher of the two frequencies from oscillator 100. When
the laminations 109 completely overlap coil 110 due to continued
rotation of the rotor (this being the particular relative positions
of the components shown in Figure 3) resonance and said Q
increase occurs at the lower of the two output frequencies from
oscillator 100. This operation will be described in greater
detail subsequently in reference to Figure 4. When the frequency
selective circuit is near parallel resonance, its impedance
increases and there is a decrease in the attenuation by said
voltage divider action of the output signal from oscillator 100.
Consequently, the amplitude of the signal coupled to transistor
204 by resistor 201 rises above +0.7v causing transistor 204
to conduct. Conduction of transistor 204 is a prerequisite to
the production of SCR triggers by trigger assembly 102, and therefore
SCR triggers may be produced only when the armature 111 connected
to rotor 36 is in a physical position such that laminations 109
induce parallel or near parallel resonance of coil 110 and its
associated capacitor 203.
~ - f
1 1~5475
As mentioned previously, transistor 204, in association
with transistor 207 and resistors 205, 206 and 208, form a
Schmitt trigger circuit the operation of which is well known
in the art. One aspect of the operation of such a trigger
circuit is that, because of the positive feedback between the
output and input of the circuit, a Schmitt trigger is caused
to exhibit a minimum output pulse width when a sine wave of
varying amplitude is coupled to its input. Said positive
feedback causes the first transistor to turn off at a lower
input voltage level than is required to turn said transistor
on. The parameter values of the various circuit components
employed in each typical trigger assembly of the present
invention are so selected that the minimu!n output pulse width
at the collector of transistor 207 exceeds the minimum require-
ment for reliable SCR triggering any time transistor 204 is
brought to even momentary conduction. This insures reliable
SCR tur~ on even though the sine wave amplitude coupled to
the input of transistor 204 varies widely and rapidly in response
to rotor movement, and may therefore exceed a conduction thresh-
old for less than, for example, two microseconds.
The collector of transistor 207 is connected to the
base of transistor 209 which serves as an SCR gate trigger
amplifier. As a result, the voltage pulses produced at the
collector of transistor 207 in response to rotor position are
converted to current pulses suitable for SCR turn on by action
of transistor 209 and transformer 91 the primary of which, as
shown in Figure 3, is connected between power supply 38 and
said transistor 209.
As noted previously, the improvement of the present
19
175~715
invention electronically advances or retards -the apparent
mechanical position of the rotor relative to the stator at
which SCR triggers are first produced. This aspect of the
invention will become most readily apparent by conslderation
of Figure 4 which graphically illustrates the signal amplitude
variations at point A of Figure 3 in tcrms of rotor position,
and the particular frequency which is being produced by
oscillator 100 in dependence upon the operating condition of
the motor. As mentioned previously, oscillator 100 is caused
to operate at a first frequency, e.g., 13 Kc when the motor
is in its starting mode of operation (this condition being
designated by the curve 224 "start frequency" in Figure 4),
and is switched by rpm responsive circuit 222 to produce
a lower frequency output when the motor is in its running
mode of operation (to produce the condition depicted by
curve 226 designated "run frequency" in Figure 4). The
graphical representations in Figure 4 illustrate the signal
amplitude variations at point A of Figure 3 for these start
and run frequencies as a lamination stack 109 approaches,
partially overlaps, fully overlaps, and then partially overlaps
and moves away from a given pick-up coil 110. The line 225
represents the signal level constituting the turn-on threshold
for transistor 204, i.e., the minimum signal amplitude which
must be present at point A before SCR triggers may be produced
by operation of the trigger assembly 102.
In the particular example of the present invention
and 2,
illustrated in Figures-l~the several coils 110 are located on
centers spaced 22.5 apart, and the angular designations shown
in Figure 4 are based on this assumed spacing. In addition,
inasmuch as the several coils 110 extend over an arc of 180,
and the armature 111 has two diametrically opposed segments 109
of magnetic material, and, as shown in each of Figures 1 and 2,
each segment 109 extends over an arc which is greater than the
arcuate extent of any individual coil 110, a segment 109 will
necessarily be in at least partially overlapping relaticn to
~ 17547~
at least one of thc coils 110 when the motor is stopped,
regardless of the angular position of the rotor at that time.
The curves 224 and 226 of Figure 4 dcpict the signaL amplitude
which may be present at point A in the trigger assembly
associated with that one of coils 110. The region between
points B and C in Figure 4 represents that portion of the
rotation wherein the coil 110 in question exhibits maximum
inductance due to full overlap of the segment 109 with said
coil 110.
With the motor in its stopped condition, or in its starting
mode, the oscillator 100 produces the aforementioned start
frequency, and the amplitude of the signal 224 at point A rises
above the transistor 204 conduction threshold (line 225) for
approximately 30 of the rotation of the segment 109 past coil
110 inasmuch as resonance occurs before a given set of
laminations 109 increases the inductance of coil 110 to
a maximum level. In other words, the effect of laminations 109
overlapsadjacent coils 110. This eliminates the possibility
of the motor not starting because segment 109 was stopped
between two coils 110.
When the run frequency of oscil'ator 100 is selected by rpm
responsive circuit 222, however, parallel resonance is achieved
only when laminations 109 increase the inductance of coil 110
to its maximum value and, as a result, and as depicted by curve
226 in Figure 4, for this running mode of operation the signal
at point A rises above the conduction threshold (line 225) for
transistor 204 for substantially less than 30 rotation. At
run frequency, the resonance effect of laminations 109 cannot
overlap adjacent coils 110 at any rotor position.
It will be further noted from Figure 4 that the rotor
position at which the signal amplitude at point A first rises
above the thrcshold line 225 when the oscillator 100 is pro-
duciny the motor start frequency (line 224) occurs approximately
5 earlier in the rotation than when the oscillator 100 is
opera~iny to produce the motor run frequency (line 226). As
r ~ 175475
a result, the particular physical position of the rotor with
respect to the stator at which transistor 204 first conducts
is jointly dependent upon both the rotor position and the
particular output frequency of the oscillator, said ~requency
being dctermined by the speed of rotation of the rotor. Thus,
by appropriate choice of the start and run frequencies, the
rotor/stator mechanical positions at which particular stator
coils are energized by SCR conduction may first be optimized
for a motor starting condition, and then shifted electronically
for optimum motor running conditions, without any actual
movement of pick-up coils 110.
Inasmuch as the angular extent of a given set of lamina-
tions 109 is sufficiently large to overlap more than one of
the pick-up coils llO, it is necessary to provide means which
will assure that, regardless of rotor position, and regardless
of the fact that the frequency sensitive circuits in more than
one of the trigger assemblies 101-108 may be near parallel
resonance due to the fact that their respective coils 110 are
in joint proximity to laminations lO9 when the motor is
stopped or in its starting mode, only one of the trigger
assemblies will operate to produce SCR triggers to only one
pair of SCRs in the starting mode. This is accomplished in
the present invention by the provision of the transistors 215
and 217, and their associated components, in each trigger
assembly.
Transistor 217 comprises a trigger amplifier inhibit
switch, and has its collector connected to the base of
transistor 209 and its emitter connected to ground. When
a voltage equal to or greater than +0.7v is coupled to the
base of transistor 217 by resistor 218, transistor 217 will
conduct thereby to effectively connect the base of transistor
209 to yround, and this effectively inhibits SCR trigger outputs
from transformer 91 even though transistor 204 is caused to
conduct by the frequency selcctive attenuator and rotor action
described previously. Transistor 215, operating as an inhibit
1 17~475
command switch, has its emitter connected to the positive side
of power supply 38 through a resistor 212, its base connected
through resistor 21~ to the collector of transistor 209, and
its collector connected via line 102a to the trigger assembly
inhibit switch (corresponding to transistor 217) in the
adjacent trigger assembly 101.
The input to trigger amplifier inhibit switch 217 in SCR
trigger assembly 102 is connected to the inhibit command
switch (corresponding to transistor 215) in the other adjacent
trigger assembly 103 via line 103a. Thus, when SCR gate trigger
pulses are induced in trigger assembly 103, the inhibit command
switch transistor (corresponding to transistor 215) in said
adjacent assembly 103 couples corresponding positive voltage
pulses to asse~bly 102 via line 103a. These pulses charge a
capacitor 220 and are coupled to the base of transistor 217 by
resistor 218. When said pulses are present, transistor 217
conducts to inhibit operation of gate trigger amplifier
transistor 209. During the interval between pulses on line
103a, capacitor 220 slowly discharges to ground through resistor
219, and through resistor 218 and the base-emitter junction of
transistor 217. Capacitor 220 holds transistor 217 at conduc-
tion until its charge falls below approximately +0.8 volts. The
discharge time constant is designed to be longer than the
interval between pulses.
By reason of the foregoing circuit configuration, when
SCR gate trigger pulses are developed by assembly 103, assembly
102 SCR gate triggers are inhibited by reason of the conduction
of transistor 217 in assembly 102 in response to the pulses
which are fed from assembly 103 to assembly 102 on line 103a,
i.e., when assembly 103 is actively producing SCR gate trigger
pulses, assembly 102 is inhibited from producinq SCR trigger
pulses by reason of the feedback from assembly 103 to assembly
102. Likewise, when assembly 102 (shown in ~igure ~) is
producing SCR trigger pulses, its inhibit command switch
transistor 215 couples corresponding positive pulses via line
1175475
102a to the trigger amplifier inhibit switch in assembly
101, thereby inhibiting SCR trigger pulses from trigger
assembly 101.
The foregoing feedback arrangement between adjacent
trigger assemblies is present throughout all of the SCR
trigger assemblies 101 through 108. Therefore, when oscillator
100 is operating to produce the start frequency, and the rotor
position of the motor is such that parallel resonance is induced
on adjacent assemblies by overlapping pr~ximity of laminations
109 to the coils 110 of said adjacent assemblies, one pair of
SCRs will always receive gate triggers regardless of rotor
position, and only said one pair of SCRs will receive such
gate triggers until the rotor position has been changed
sufficiently to effect operation of the next adjacent trigger
assembly which operation, in turn, will inhibit production of
gate trigger pulses from the trigger assembly that had previously
produced such pulses.
For reasons previously explained, the motor will commence
rotation in any rotor position. However, because self-commuta-
tion of stator SCRs does not occur below particular rotor speeds,
commutation assistance is provided during motor starting and
below said particular rotor speeds. Said particular speeds
have been determined to be proportional to the mechanical load
of the moment imposed upon the motor. More specifically, the
greater the magnitude of motor load, the faster the rotor
must rotate to provide reliable self-commutation. It has been
determined, for example, that with a stator winding constructed
in accordance with Parker U.S. Patent No. 4,095,148 a rotor speed of 50 rFm or
greater must be maintained for reliable self-commutation with
a load of 100 ft.lbs.
Briefly, the method employed in commutation assistance
uses a charged capacitor that is switched in reverse polarity
across the stator assembly when the rotor is near a position
where commutation naturally OCCurs. This reverse volt~ge turns
off all stator SCRs,but those receiving trigger pulses immediately
24
~ 17~75
turn back on when the commutating capacitor has discharged
through the rotor winding, which action restorcs a substantial
portion of the energy employed for commutation back to battery
38. This aspect of the operation is achieved by synchronized
commutation circuit 119 shown in Figures 1 and 5, which
provides or assists commutation during motor starting and
during operation at relatively low rotor speeds. Circuit 119
automatically ceases said assistance at speeds above approximately
60 rpm.
Referring to Figure 1, it will be noted that one input to
commutation circuit 119 is a bus 128 which is common to all of
trigger assemblies lOl through 108. Another input to circuit
119 is provided by line 126 from the positive voltage terminal
of a DC-to-DC power supply 125. One output of circuit 119 is
connected to the ungrounded side of rotor 20 at line 99, and another
output from said circuit is connected to stator power input line 39.
As shown in Figure 3, bus 128 connects to the cathode of a
diode 223 whose anode is connected to the collector of transistor
215 in typical trigger assembly 102. As described previously,
trigger assemblies 101 through 108 are identical. The outputs of
the transistors 215 in the several trigger assemblies are
coupled to bus 128 by the diodes 223 in said assemblies, and
successively command operation of commutation circuit 119 only
at the beginning of conduction of each successive pair of stator
SCRs for reasons which will be discussed hereinafter.
Figure 5 is a schematic diagram of synchronized commutation
circuit 119. Functionally speaking, circuit 119 comprises a
commutation command switch generally designated 150, a mono-
staDle multivibrator (generally designated 151) which serves
to cenerate an intentionally delayed commutation trigger below
a particular rotor rpm and no commutation trigger above said
particular rpm, an SCR gate trigger amplifier generally designated
1 17 54~ ~
152, and stator SCR commutation means, generally designated
153, which is selectively triggered by action of monostable
multivibrator 151.
Familiaxization with the specific nature of the signals
present at the collector of transistor 215 in its capacity as
an inhibit command switch will aid in understanding the rpm responsive
operation OL commutation circuit 119 which, as stated above, is
also connected to the collector of transistor 215 by diode 223~
Referring again to Figure 3, the components connected
to the emitter of transistor 215 comprise resistor 212 which is
connected in series between the positive side of power supply 38
and said emitter electrode, and a resistor 214 and capacitor 213
connected in parallel with one another from said emitter to
ground. When transistor 215 is nonconducting, capacitor 213
charges to a peak value determined by voltage divider action of
resistors 212 and 214. Assume now that the power supply voltage is,
for example, 50 vdc and that all resistors in trigger assembly 102
are of the same value. Under this condition, capacitor 213
will charge to 25 vdc. As discussed previously, the collector
of transistor 215 connects via line 102a to the input of a trigger
amplifier inhibit switch (exemplified by transistor 217 on
Figure 3), and there is a resistor 219 which connects to ground
and a resistor 218 which may conduct positive voltage to
ground through the base emitter junction of transistor 217.
Since the junction of resistors 218 and 219 is connected
to the collector of transistor 215 via line 102a, let us now
consider the nature of the signals that will appear at the
collector of transistor 215 when assembly 102 generates SCR triggers.
As discussed previously, transistor 215 responds to pulses coupled
to its base electrode from transistor 209 by resistor 216, and trans-
istGr 20~ develops an SCR trigger pulse ~ith each positive alternation
of oscillator 100 throughout the period of ti~.e that parallel resonance
is induced by la~inations 109 in coil 110. This SCR pulse production
by each trigyer asse~lbly occurs for approximately 22.5 of rotor
rotation.
26
- ~t~5~75
When the first SCR trigyer pulse appears at the collector
of transistor 209 at the beginning of this 22.5 arc, transistor
215 is switched on and the junction of reslstors 212 and 214
and capacitor 213 will be connected through the emitter collector
junction of transistor 215 to the junction of resistors 218 and
219 and capacitor 220. One end of each of resistors 214
and 219 is connected to ground and resistor 218 is grounded
through the base emitter junction of transistor 217. When
transistor 215 conducts, the other end of resistor 214 becomes
connected to line 102a which, in turn, connects through interconnecting
line 224 and line 103a to the other ends of resistors 219 and
218 resulting in the parallel connection of these resistors. Line
224 is shown as a broken line since it actually represents a connection
between adjacent trigger amplifiers 102 and 101,and is shown
in this manner for descriptive purposes only. Thus, at the
moment of turn on, capacitor 213 begins discharging from the
(previously assumed) 25v peak toward a divided lower voltage
which results from paralleling resistors 218 and 219 with 214.
By design choice, the RC time constants of capacitor 213 and
the associated resistors are such that during the short SCR
pulse duration (approximately 25 microseconds), capacitor 213
can not completely discharge to this new lower voltage before
transistor 215 is again cut off. Thus, several SCR trigger
pulses must occur in succession before the voltage charge of
capacitor 213 is reduced to the lower voltage caused by the
additional voltage dividing action of resistors 218 and 219.
The specific nature of the signals appearin~ at the
collector of transistor 215 when assembly 102 is activated by
the passage of laminations 109 may now be summarized. Said
signals consist of a series of pulses, the first of which
equals the initial charge of capacitor 213, with each succeeding
pulse being of lesser amplitudc until the peak voltage on
capacitor 213 becomes equal to the increased voltage dividing
action introduced during moments of transistor 215 conduction.
In other words, the amplitude of the pulse train decays
-- - 1 17S475
exponentially during the first several pulses and then remains
at a new lower level for the remainder of the 22.5 rotation.
Since assembly 102 is inoperative for the next 157.5 capacitor
213 has time to recharge to its original peak voltage and,
therefore, to duplicate this behavior each time assembly 102
is made operative. As the rotor rotates, the signal Oll bus 128
consists of a series of groups of pulses identical tc, those just
described for assembly 102, that is, one group for each trigger
assembly.
Referring again to Figure 5, bus 128 is con~lected to the
cathode of zener diode 130, the anode of which conne.ts through
resistor 129 to the junction of resistor 132, capa;itor 131
and the base of transistor 133. The zener (conduction) voltage of
diode 130 is selected to reject the lower amplitude pulses present
during each 22.5 output from trigger ass~mblies 101 through 108.
Thus, only the first two or three pulses at the beginning of
said 22.5 of rotor rotation are coupled by diode 130 to the base
of transistor 133. Resistor 132, one side of which is grounded,
holds transistor 133 cut off in the absence of said higher
amplitude pulses coupled by zener diode 130.
The action of capacitor 131 and transistor 133 will be explained
in connection with the operation of multivibrator 151, which
comprises transistors 136 and 143 interconnected with a plurality
of resistors and capacitors in a known monostable multivibrator
configuration. In the absence o other controlling signals ,
the monostable multivibrator 151 assumes the following condition:
transistor 136 conducts due to forward bias coupled ~rom the
power supply to its base by resistor 138. The junction of resistors
137, 139 and capacitor 131 at transistor 136's collector are,
therefore, near ground potential. The base of transistor 143 is
coupled through resistor 139 to the collector of transistor 13G.
Thus, when transistor 136 is conducting, transistor 143 is held
in cutoff by resistor 139.
28
~ 175~75
COnsider now the action of multivibrator 151 when the
signals appearing on bus 128 exceed the zener voltage of diode
130. Whcn diode 130 couples a signal of more than approximately
.6 vdc to the base of transistor 133, transistor 133 conducts
and its collector, which is connected to the base of transistor
136, is clamped to near ground potential. Transistor 136, there-
fore, ceases conduction at that moment and its collector rapidly
rises toward the positive potential of the power supply. This
positive going voltage at the collector of transistor 136 is
coupled by capacitor 131 to the base of transistor 133 and, being
in the nature of positive feedback, accelerates the switching
action of both transistor 133 and 136. At the same time, transistor
143 is rapidly driven into saturation by the forward bias coupled
from power supply positive through resistors 137 and 139, while
capacitor 134 is discharged to ground potential through the
collector-emitter junction of transistor 133.
As previouly mentioned, zener diode 130 couples only the
first two or three pulses at the beginning of each trigger assembly's
22.5 conduction period to the base of transistor 133. Thus, within
a few hundred microseconds after the first pulse, transistor 133,
receiving no other pulses from diode 130, ceases conduction. When
transistor 133 cuts off, capacitor 134 connected to the base of
transistor 136 and to the positive side of the power supply by
resistor 138 begins charging towards a positive voltage established
by voltage divider action of resistors 138 and 135. Ultimately,
the voltage across capacitor 134 reaches appro~imately .6 vdc
at which moment transistor 136 again begins conduction, thereby
removing the forward bias to transistor 143. As transistor 143
decreases conduction, its collector voltage begins rising towards
the power supply positive potential due to resistor 141. The
positive feedback of capacitor 140 accelerates the switching
process with result that the positive voltage at the collector
of transistor 143 increases rapidly. This positive going voltage
pulse is coupled by capacitor 142 to transistor 145 in gate trig-
ger amplifier 152 and serves as a commutation command trigger
~ ~75~7~
of a few (approximately 50) microseconds duration for SCR 121.
This action of commutation command switch 150 and commutation
delay monostable 151 is repeated as each trigger assembly is
activated by rotor rotation only when the time it takes the
rotor to travel 22.5 is longer than the delay time of monostable
151. As the motor accelerates, a speed is ultimately reached
where capacitor 134 is discharged by conduction of transistor
133 before transistor 136 can turn on. From this speed upward,
monostable 151 is inoperative because transistor 136 is thus
prevented from ever conducting while transistor 143 remains
conducting and commutation assistance automatically stops~
The operation of monostable multivibrator i51 serves two
purposes:
(1) The automatic stopping of commutation trigger
generation above a particular rpm eliminates
the need for special rpm responsive means to
stop commutation assistance above a particular
speed ; and
(2) The delayed generation of commutation command
triggers after turn on of an SCR trigger assembly
provides commutation assistance near rotor
positions where self-commutation of stator SCR
pairs naturally occurs.
More particularly, in regard to the rotor position of
self-commutation, it has been determined that self-commutation
naturally occurs when the rotor has travelled approximately 5.5
after a succeeding pair of SCRs has been triggered into conduction.
Forced commutation by circuit means 153 is more efficiently .
accomplished at speeds below 50 rpm when activated near a natural
rotor position of self-commutation than, for example, at the
rotor position where a succeeding SCR pair is first triggered on.
Further, it has been determined that selecting a delay time
for operation of monostable multivibrator 151 that corresponds
to a rotor movement of 5.5 at 15 rpm provides reliable motor
starting and efficient low speed operation at maximum rated
5 4 ~ ~
motor loads. Thus, the natural action of monostable multivibrator
151 activates commutation by circuit 153 below a particular
(selectable) rpm, and the generation of commutation command
triggers which are delayed a particular time after a succeeding
pair of stator SCRs has been turned on. The foregoing actions
provide automatic turn on and off of commutation assistance
with efficient very low speed motor operation and reliable
starting at any rotor position and under any load condition.
SCR gate trigger amplifier 152 converts its voltage pulse
input, received from multivibrator 151, to a current pulse
suitable for triggering SCR 121 of commmutation circuit 153.
Commutation circuit 153 consists of SCR 121, resistor 123 and
capacitor 122. Capacitor 122 has one terminal connected to line 39,
the main power input to the stator, and its other terminal
connects to the junction of resistor 123 (the other side of
which connects to line 126, the high voltage terminal of power
supply 125) and the anode of SCR 121 whose cathode connects to
line 99 (the junction between the stator and rotor windings).
Assume SCR 121 is nonconducting and motor starting power
is applied to line 39 via rheostat 115. Capacitor 122 charges
through resistor 123 with the result that the voltage at its
terminal, which is connected to the junction of resistor 123
and the anode of SCR 121, becomes substantially more positive
than the voltage input to the stator on line 39. The motor
starting power applied to line 39 causes the rotor to begin
to rotate, which action leads to a next trigger assembly being
activated by laminations 109. When this next trigger assembly first
begins producing stator SCR triggers, operation of synchronized
commutation means 119 is initiated as described above. After the
selected time delay of monostable multivibrator 151, a suitable
SCR current trigger pulse is couplcd to the gate electrode of
SCR 121 via line 124, the ou-tput of trigger amplifier 152. Upon
receipt of said trigger pulse, SCR 121 turns on and the
- ~175~7~
substantially hlgh positive voltage side of capacitor 122 is
connected to line 99, the junction of the rotor and stator
windings. By this action, the voltage across the stator SCRs is
reversed, that is, the cathodes of the still conducting SCR pair
which are no longer receiving triggers, as well as the pair being
triggered, are raised to a high positive voltage with respect to
their anodes. This condition continues until the charge on capacitor
122 is equalized by discharge through rotor winding 20 to ground,
rheostat 115 and battery 38 in a charging direction. Under this
reverse voltage condition, the stator SCRs are commutated off;
however, the SCR pair receiving triggers immediately turn back on
while the previous pair, no longer receiving triggers, remain off.
The rotor thus continues to rotate, SCR 121 self-commutates when
capacitor 122 has discharged and, with SCR 121 off, capacitor 122
again charges toward the high voltage present on line 126. This
commutation action cycle is repeated as each succeeding trigger
assembly is activated until the rotor accelerates to a speed of
approximately 60 rpm at which time commutation command triggers cease
being generated by block 151 for the reason previously explained.
Thus, during motor start, or any time rotor speed decreases below
60 rpm, commutation assistance is automatically provided by
synchroniæed commutation circuit 119.
As discussed in Parker U.S. Patent NO. 4,095,148, rotor 36 may
be constructed using permanent magnets instead of electromagnets as
shown on Figure 1. If rotor 36 is of permanent magnet construction--,
an inductor 129 should preferably be connected between line-40 and
line 99 as shown by broken line 99a in Figure 1. Optional inductor
129 would then serve as a suitable impedance,in place of electro-
magnetic rotor winding 20,which has sufficient inductance for
operation of commutation circuit 119 described previously. For
purposes of standardization, inductor 129 can be provided in line
40 as shown, but with a jumper 40a across said inductor, to render
it inoperative when the rotor 20 has adequate inductance. The
same optional inductor may also be employed if the impedance of
a wound rotor is found insufficient to assist commutation, in which
case dotted jumper 40a wo~a be omitted.
~ 175~7~i
While we have thus described preferred embodiments of the
present invention, many variations will be apparent to those
skilled in the art. It must, therefore, be understood that the
foregoing description is intended to be illustrative only and is
not limitative of the present invention, and all such variations
and modifications as are in accord with the principles described
are meant to fall within the scope of the appended claims.
Having thus described our invention, we claim:
