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Патент USA US2413028

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Dec. 24, 1946.
H. M. McCOY
2,413,028
ENGINE SYNGHRONIZEH
Filed March 11, 1944
2 Sheets-Sheet l
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INVENTOR
?o WAVQD M McCoy
BY
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ATTORNEY-V
Dec. 24, 1946.
H. M. MccoY
2,413,028
ENGINE SYNCHRONIZER
43
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Filed March 11, 1944
2 Sh
s-Sheet 2
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$5-2.
INVENTOR
3
BY
W L'A-
‘K
ATTORNEYJ
Patented Dec. 24, 1946
12,413,028
UNITED STATES PATENT OFFICE
2,413,028
ENGINE SYNCHRONIZER
Howard M. McCoy, Patterson Field, Ohio.
‘Application March 11, 1944, Serial No. 526,103
9 Claims.
(Cl. 172—293)
(Granted under the act of March 3, 1883, as
amended April 30, 1928; 370 0. G. 757)
-
1
The invention described herein may be manu
factured and used by or for the Government for
governmental purposes, without the payment to
me of any royalty thereon.
_
2 ,
erator large enough to operate a series of smaller .
synchronous motors, one on each of the remain
ing engines, whereby the respective engine gov
ernors each has a reference motorwith which
This invention relates to Synchronizers, the 5 to synchronize its engine. This arrangement,
adaptation shown being directed particularly to
however, requires an alternating current gen
maintaining the reference members of a plurality
erator of considerable size, depending, of course,
of differential governor mechanisms in synchro
on the number of engines to be synchronized.
It is therefore another object of this invention
In my copending application Serial No. 475,297, 10 to simplify a. mechanism of this character by
?led February 9, 1943, I show a differential gov
providing, in addition to a small direct current
ernor mechanism wherein a small reference
master motor which will remain constant at a
motor, which is adapted to remain constant vat
manually selected speed, a small direct current
any selected speed within its range, drives the
reference motor for each engine, synchronizing
reference member of the differential governor, 15 all of these direct current reference motors, as
the variable speed member being drivably con
nearly as may be, to the selected speed of the
nected to the power unit whose speed is to be
master motor by so regulating their ?eld strength
controlled, the differential governor also includy
that it will always be a function of the selected
ing servo mechanism operative by off-speed con-"
master motor speed, then correcting any remain
ditions of the power unit with respect to the 20 ing off-speed conditions in the several small direct
reference motor to actuate the speed changing
current motors by placing, on each direct current
controls of the power unit so as to bring it back
armature shaft, a small alternating current rotor
to speed.
with polyphase winding, and connecting the sev
The present invention as one object contem
eral windings in phase relationship.
.
plates the combining of a plurality of ‘differential 25 Other objects and advantages will appear as
governors of the kind above indicated, with a
the invention is described in greater detail and
novel means for maintaining the small reference 7 reference is made to the drawings, wherein—
motors of the several di?erential governors in
Figs. 1 and 2 are schematic views of two exem
nism.
perfect synchroni-sm to the end that the differen
tial governors may likewise maintain the power
units which are being controlled by the governors
in perfect synchronism.
Conventional aircraft
engine
Synchronizers ’
pli?cations of the invention.
-
Referring now to Fig. 1, a series of aircraft
engines 6 (two only being shown), each has a
propeller 8, the pitch of which is varied by a
servomotor ill or IOA, the rotation of the servo
motor being controlled by differential governor
usually comprise a reference motor in the cockpit,
to which the speeds of the several engines are 35 units I! or I2A.
‘
transmitted and diiferentiated, where necessary,
The differential governor as seen, at l2 or HA
with the reference speed, then different correc
is shown, described, and claimed in my copending
tive signalskeach appropriate to the off-speed
condition of a particular engine, must be trans
mitted back to the several engines to change the
propeller pitch thereby to bringthe speed of all
of theengines into synchronism with the refer
ence speed in the cockpit.
It is therefore another object of this invention,
to simplify conventional practice by providing a
relatively small reference motor at each engine,
and synchronizing the several small reference
motors, whereby there may be, close to each en
gine, a complete control unit comprising a small
reference motor, a differential governor, and the
necessary servo mechanism operated by the dif
ferential governor to control the engine speed.
Synchronizers are also known wherein one en
application Serial No. 475,297, ?led February v9,
1943. In this governor, a shaft H, which must
emanate from some constant speed source, as,
for instance, from a small motor I5 or ISA, carries
the elongated pinion i6, and, parallel to shaft H,
is another shaft l8 which carries the narrow
pinion 20, the pinions i6 and 20 being in mesh
one with the other. The shaft [8 is externally
threaded at 22 and the pinion 20 is internally
threaded to correspond. The differential between
the controlling shaft I 4 and the controlled shaft
7 I8 being evidenced by the movement of the pinion
20 on the screw 22, this type of differential is
known as a screw-and-pinion differential, as dis
tinguished from a gear differential, and may be
broadly referred to by numeral [1.
Reference motors I5‘ and I 5A are of the shunt
gine is selected as the reference engine, and that
engine provided with an alternating current gen 55 D. C. type. having a shunt ?eld II, and an arma
3
ture l3 which may be built directly on the shaft
l4, as shown, or on a separate shaft which is
drivably connected to the shaft l4.
A shaft 24 is placed end to end and in axial
alignment with the shaft l8. Shaft 24 may ema
nate from the propeller and rotate at propeller
speed, or at a speed which is a function of pro
4
engine, differential governor and reference motor
is not new in this application but is included as
a basis for showing how a plurality of similar ref erence units may be synchronized with a manu
ally variable speed master unit hereinafter de
scribed. The units IIIA, HA and ISA are dupli
cates of l6, l2 and I6 but are given the distin
peller speed.
guishing reference characters to facilitate subse
A gear differential 26 surrounds the adjacent
quent description of their operation.
ends of the shafts i8 and 24, one of the bevel 10
In the selector unit which may be broadly desig
differential gears 28 being fast on each shaft.
nated by the numeral 66, a small D. C. master
A differential pinion carrier 36 rotatably supports
motor 66 comprises an armature 62, which is fast
the bevel differential pinions 32 and keeps them
on a shaft 64, and a. field coil 66, one side of which
in'mesh with the differential gears 28. A spur
is connected to the armature winding, the other
side being grounded.
gear 34 is fast on the outside of the carrier 36.
A follow-up motor 36 carries a spur pinion 38
A spring loaded governor 66 has contact mem
which is in mesh with the gear 34, whereby rota
bers 10 and 12 which are carried on a disc 13,
tion may be imparted to the differential carrier
the disc being fast on the shaft 64 and the con
30. Obviously, as long as there is no rotation of
tact members being insulatedly secured thereto.
the carrier 30 by the motor 36, the shafts i 8 and 20 A slip ring 68 transmits current brought from the
24 will rotate oppositely and at the same speed.
battery 14 to the insulated contact 12. The con
It is equally obvious that as long as the shafts l6
tact members 16 and 12 are so formed and posi
and i4 rotate at exactly the same speed, the
tioned on the disc ‘II that their free ends tend
pinion 20 will remain in the position shown, but
to be separated by centrifugal force upon rotation
will move axially in one or the other direction
of the shaft 64. A spring 16 is biased to main
whenever the speed of the shaft I6 is greater than
tain the contact members in the closed position.
or less than that of the reference shaft l4.
A spring tensioning member ‘I8 is provided for
Servomotor ID has oppositely wound field coils
varying the stress of the spring 16. Member 18
40 and 42 while follow-up motor 36 has oppo
has a lever operated rack and pinion arrangement
sitely wound field coils 44 and 46, whereby either 30 86 whereby the tension of spring 16 may ‘be varied
motor may be made to rotate in either direction
manually. The circuit from the battery through
by connecting the proper ?eld coil in series with
the master motor 60 by way of the closed contacts
the armature. Both motors also have a brake to
‘III-‘l2 is of relatively low resistance. A parallel
arrest rotation, the brake being normally spring
circuit of higher resistance is provided, by way
engaged but being disengageable by solenoids‘ 48
of a resistance element 82, through which a lesser
and '56, whenever current is supplied to the motor
current will be supplied the master motor 86 ~
windings to cause rotation. Of the parts of these
when its rotative speed becomes high enough to
brake mechanisms, only the solenoids for releas
cause the contact members 16 and 12 to separate.
ing them are shown. Two switches 52 and 54
A condenser 84 is included to modify contact
are interposed in the path of the pinion 20 for 40 point arcing.
.
closing the electric circuits to the motors in
An arm 86 extends from the spring tensioning
and 36.
member 18 and carries the movable contact 86
If, looking in the direction of the arrow 66, the
of a rheostat 88 through which current from the
engine 6 rotates clockwise, the shaft 24 will rotate
battery 14 passes to the ?eld coils H of the shunt
clockwise and the shaft I8 anti-clockwise. If the
D. 'C. reference motors I6, I5A, etc. Operation
shaft I8 is rotating at exactly the speed of the
of the manual selector mechanism 18-46 one
reference shaft I4, the pinion will not move
way or the other will therefore raise or lower the
axially. If the engine 6 overspeeds, the thread
speed of the series D. C. master motor 66 through
22 being left-hand, the pinion 26 will move to
the governor 68, and will coincidentally raise or
close the switch 62 which will energize the coil 50 lower the speed of the shunt D. C. reference
46 of the servomotor III for pitch increase, the
motors l6, I6A, etc., by varying the field coil
coil 44 of the follow-up motor 36 being coinci
strength. By careful attention to' the design of
dentally energized for returning the pinion 20,
these parts, an entire series of shunt reference
by means of the differential 26, to the neutral
motors l5 may be maintained relatively close to
position shown. If the engine underspeeds, the
synchronism, one with the other, and the entire
pinion 26 will move to close the switch 54, which
series with the manually controlled series master
will energize the coil 42 of the servomotor l6 for
motor 60. However, since exact synchronism be
pitch decrease, the coil 46 of the follow-up motor
tween these motors is required, a relatively simple
36 being coincidentally energized for returning
additional mechanism is required. This addi
the pinion 20 to the neutral position. It will, of
tional mechanism, which will now be described,
course, be understood that, if the follow-up motor
constitutes a valuable feature of the invention.
36 and the differential gear 26 were eliminated,
Fast on the armature shaft 64 of the series D. C.
the governor l2 would still operate, but in that
master motor 66, is an A. C. rotor 92 having a
case the pinion 20, having, for instance, been
polyphase winding 94. An exact duplicate of the
moved by engine overspeed to close the switch 52,
wound rotor 82 is carried on each and every shaft
would not be moved back to the neutral position
l4 of the shunt D. C. motors I6, ISA, etc. That
except by an engine underspeed condition, with
one of the A. C. rotors 62, which is carried on the
the result that considerable hunting would be
shaft 64, is shown as being provided with a sep
experienced. Hereinafter when the term differ
arate field coil 96, but a suitable field may be
ential governor is used it is intended to refer to
provided for the rotor 92 by modifying the coil
the combination of parts comprising the refer
66 of the series motor 60, whereby the separate
ence shaft [4, the screW-and-pinion differential
?eld coil 96 may be omitted. The A. C. rotors 62
H, the gear differential 26, the servomotor ID, the
on the shafts l4 are energized by the field coils I I.
follow-up motor 36 and the controlled shaft 24.
The windings 94 neither receive current from,
The foregoing described unit consisting of an
nor deliver current to, any outside line, but are
9,418,038v
5
connected only one tov the other. Slip rings 88‘
andbrushes 90 are provided for this purpose. A»
main switch I 00 is provided for ‘separating. the
battery 14 from the windings. The operation of
the device of Fig. 1 should be clear without much
additional. explanation. The operation is as fol
lows:
I
the thread being ?tted with a nut I20. A rod
I22, supported on the casing of the motor, ex
tends slidably through a hole in the nut I20 to
keep. it from turning. Rotation of the threaded
shaft’ I I8, in one or the other direction, therefore
moves the contact member III back or forth on
the resistance coil H6. Ashunt D, C. motor I5D,
The switch I00‘ is closed and the manually op
with an A. C. polyphase wound rotor, is identical
erable control 18-80 set for the desired master
with the» motors l5, I5A, I5B and I5C of Figs. 1
speed. The rheostat 90 will coincidentally ad 10 and 2 but is assigned a different reference char
just the strength of the ?eld coils II for pro
acter to distinguish it when describing its re
ducing the selected speed in the shunt D. C. ref
spective functions in the mechanism. To distin
erence motors I5, I-5A, etc. When the master
guish the motor I5D from the reference motors
motor 60 reaches the speed selected, the contacts
I5B and I5C, the motor I5D may be hereinafter
I ‘I0. and ‘I2 will separate, whereupon the battery 15 referred. to as the master reference motor. The
will momentarily supply current to the master
operation of the device of Fig. 2 is as follows:
motor 60 through the higher resistance path
The manually operable control I08 may be set
which includesthe resistance 82. This lowers the
for the_ desired speed and the switch I00 closed,
speed of the governor 68 which brings the con
whereby current from the battery ‘I4 flows
tacts ‘I0 and 12 back together again. This cycle 20 through the master motor I 04 and through the
is repeated as much as four hundred times per
rheostat I I0 to the shunt ?eld coils I I of all three‘
second, whereby the speed of the master motor
shunt D. C. motors I5B, I5C and I5D, the posi
60 remains substantially constant at the speed to
tion of the contact arm III on the rheostat I I 3
which it is set, and the shunt D. 0. reference
determining the instant strength of the several
motors I5, I5A, etc., take the same speed due to
shunt ?elds. the proper adjustment of their ?eld strength by
The switch .IOI is now closed, whereupon cur
the rheostat 90.
rent from the battery 14 will flow through the
Without the A. C. rotors 92, however, the shunt - armature I3 of the D. C. reference motors I 53,
D. C. motors I5, I5A, etc., would likely not remain
I5C and the master reference motor I5D. If the
closer to synchronism with each other and with 30 motor I5D rotates faster or slower than the mas
the master motor 60 than from ?ve to ten per
ter motor I04, the pinion 20 will move axially one
cent, but with the A. C. rotors 92 fast on the
or the other direction and close one or the other
several D. C. motors, and with the A. C. windings
of the switches 52 or 54. _
84 connected together as shown, it follows that
any out-of-phase condition of one of ‘the rotors
will be corrected by the other, and the entire
series of motors I 5, I5A, etc., will, for that reason,
rotate at exactly the same speed, and, since each
engine 6 thus has a constant speed reference mo
tor I5, I5A, etc., and a governor I2, I2A, etc.,
which synchronizes the engine with its reference
motor I5, it follows that all engines 6 will run in
Assume, for illustration, that the D. C. master
reference motor I5D, viewed in the direction of
the arrow 55, is rotating clockwise. The shaft
I8‘ will then rotate anti-clockwise and the shaft
I4 clockwise. If the master reference motor I5D
overspeeds, the thread 22 being left-hand, the
4-0 nut 20 will move right and close the switch 52. '
which will cause the coil 40 to be energized to
rotate the servomotor H0 in the direction of the
arrow 51.. The thread II8 being left-hand, the
nut I20 will move the arm III to increase the re
servomotor I 08 and IOC, the shunt D. C. ref 45 sistance to the‘ rheostat coil H6 and thereby
erence motors I5B and I 50, and the diil'erential
weaken the ?eld II andbring the master ref
governors I2B, I2C and -I2D are duplicates of
erence motor I5D back down to speed. Obviously‘
units I0, I2 andv I5 described with reference to
underspeeding of the motor I5D would be taken
Fig. l. Themechanism I02 by which a master
care' of by the closing of the switch 54 in a similar
speed is selected and impressed on the reference ’ manner.
'
motors I5Bv and I5C, however, is somewhat differ
Now since the shunt ?elds I I of all three shunt
ent, and comprises a master motor I04 which has
D. C. motors I58, I50 and I5D are controlled
a ?yball governor I06, controlled by manual
through the one rheostat II3, the governor I2D,
means I08, by which any desired speed may be
in synchronizing the motor I5D with the mas
substantially exact synchronism.
In the modi?cation Fig. 2, the engines 8, the
selected for the master motor. It also comprises
a servomotor IIO controlled by a differential gov
ernor I 2D. Governor I2D includes a shaft I4
ter motor I04, coincidentally synchronizes the
reference motors I5B and I5C ‘with the master
reference motor I5D. But since it is not safe
which may be an extension of the armature shaft to assume that the constant speed characteris
of the master motor I 04 or be attached; thereto,
tics
of the shunt D. C. motors is su?icient to
The diiferential governor I2D is exactly like the 60 maintain
exact synchronism between the three
governors I2B and I2C shown adjacent the en
D. C. motors, each motor is provided, as in Fig.
gines 6 but is assigned a different reference char1, with an A. C. wound rotor 92, the windings of
acter to avoid confusion in describing the oper
which are connected one to the other, whereby
ation of the mechanism, the differential gear-set
exact synchronism is had between the master
26 and the follow-up motor 38, as well as the
pinions I5 and 20 and switches 52 and 54 being
identical. The servomotor IIO, however, is dif
ferent from the servomotors I0, IOA, etc., in that
instead of being adapted to change the pitch of
a propeller it is adapted to change the position
of the movable contact III of a rheostat II3 with
respect to its resistance coil I I 5.
'
'
The mechanism for shifting the rheostat I I 3
comprises a prolongation of the armature shaft
of the servomotor IIO which is threaded at II8.
motor I04, the master reference motor I5D and
the reference motors I58 and I 50. From the
description relating to Fig. l, the manner in
which the differential governors I2B and I2C
synchronize the several engines 6 with the ref
erence motors I 5B and I5C will be readily un
V d’erstood.
Having described several embodiments of my
invention, I claim: '
l. Mechanism for synchronizing a series of di
rect current reference cnotors, which comprises,
2,418,028
7
8
in combination, a direct current master motor
for controlling the speed of said reference mo
supply, a centrifugal governor for controlling the
current ?owing from said source to said master
tors, a direct current source, a governor for con
motor, a manual means associated with said cen
trolling the current ?owing from said source to
said master motor, a manual means associated
with said governor for setting the speed at which
said governor holds said master motor, alternat
ing current rotors, one carried on the shaft of
said centrifugal governor holds said master mo
tor, polyphase wound alternating current rotors
one mounted for unitaiy rotation with each said
each reference motor and one on the shaft of
being connected each to the others and to no
trifugal governor for setting the speed at which
direct current armature, the polyphase windings
the master motor, said rotors having windings 10 other current source, an additional ?eld winding
each connected to the others, a rheostat for con
trolling the current ?owing from said source to
the ?eld coils of said reference motors, and op
erating means connecting said manual means
and said rheostat, whereby the speed at which
the manual means holds the master motor by
means of the centrifugal governor is a function
of the speed at which said rheostat holds the
reference motors by means of their ?eld coils.
2. The combination of a plurality of shunt con
nected direct current reference motors, a shunt
connected direct current master reference motor,
in the master motor for its said alternating cur
rent rotor, a rheostat for controlling the current
flowing from said source of direct current supply
to the shunt connected ?eld windings of the ref
erence motors and to the said additional ?eld
winding of the master motor, and operating
means connecting said manual means to said
rheostat, whereby the speed at which the man
rheostat, a governor for said master motor, man
ual means for adjusting said governor for ob
taining different master motor speeds, a diifer_
ual means holds the master motor, through reg
ulation of the centrifugal governor is a function
of the speed at which said rheostat holds the
reference motors through regulation of said
shunt ?eld windings.
5. In a system which includes a plurality of
reference motors to be synchronized, each with
the others, and a master motor with which the
ential governor for synchronizing the master
speed of the reference motors are synchronized,
a master motor, a source of direct current, a
the improvement in such a system which com
prises, a plurality of direct current armatures one
ing adapted to vary the resistance through said 30 for each reference motor and one for the master
reference motor with the master motor, the
servomotor of the said ‘differential governor be
rheostat to vary the ?eld strength of said ref
motor, direct current ?eld windings, one for each
erence motors and said master reference motor,
means for directing current from said source
reference motor and one for the master motor,
a source of direct current supply, a centrifugal
through said rheostat to the ?elds of the refer
governor for controlling the current ?owing from
ence motors and the master reference motor, '
means for directing current from said source di
said source to said master motor, a. manual means
associated with said centrifugal governor for
setting the speed at which said centrifugal gov
ernor holds said master motor, polyphase wound
rectly to the armatures of the reference motors
and the master reference motor, and polyphase
wound alternating current rotors, one carried on
alternating current rotors one mounted for uni
the shaft of each reference motor and one on the 40 tary rotation with each said direct current arma
shaft of the master reference motor, said poly
ture, the polyphase windings being connected
phase windings being connected only each to
each to the others and to no other current source, '
the others.
3. The combination of a plurality of reference
an additional field winding in the master motor
for its said alternating current rotor, a rheostat
motors, a master reference motor, a master mo
tor, a source of current, a rheostat, manual
for controlling the current ?owing from said
source of direct current supply to the ?eld wind
ings of the reference motors and to the said
additional ?eld winding of the master motor. and
means for setting said master motor at differ
ent speeds, a differential governor for synchro
nizing the master reference motor with the
master motor, the servomotor of the said differ
ential governor being adapted to vary the resist
ance through said rheostat to vary the ?eld
strength of said reference motors and said mas
ter reference motor, means for directing current
from said source through said rheostat to the
?elds of the reference motors and the master
reference motor, means for directing current
from said source directly to the armatures of the
operating means connecting said manual means
to said rheostat, whereby the speed at which the
manual means holds the master motor, through
regulation of the centrifugal governor is a func
tion of the speed at which said rheostat holds
the reference motors through regulation of said
shunt ?eld windings.
6. In a system which includes a plurality of
reference motors to ‘be synchronized each with
the other, and a master motor with which the
speed of the reference motors are synchronized,
reference motors and the master reference mo
tor, and polyphase wound alternating current 60 the improvement in such a system which com
prises, a plurality of direct current armatures
rotors, one carried on the shaft of each refer
ence motor and one on the shaft of the master
one for each reference motor and one for the
reference motor, said polyphase windings being
master motor, direct current ?eld windings, one
connected only each to the others.
4. In a system which includes a plurality of
reference motors to be synchronized, each with
the others, and a master motor with which the
speed of the reference motors are synchronized,
the improvement in such a system which com
prises. a plurality of direct current armatures
one for each reference motor and one for the
master motor, direct current shunt connected
?eld windings, one for each reference motor, a
direct current series connected ?eld winding for
the master motor, a source of direct current
for each reference motor and one for the master
motor, a source of direct current supply, a cen
trifugal governor for controlling the current
?owing from said source to said master motor,
a manual means associated with said centrifugal
governor for setting the speed at which said
centrifugal governor holds said master motor,
polyphase wound alternating current rotors one
mounted for unitary rotation with each said
direct current armature the polyphase windings
being connected each to the others and to no
other current source, a rheostat for controlling
9
2,418,098
the current ?owing from said source of direct
current supply to the ?eld windings of the ref
erence motors, and operating means connecting
said manual means to said rheostat, whereby
the speed at which the manual means holds the
master motor, through regulation of the centrif
ugal governor is a function of the speed at which
10
. current armatures one
for each reference motor
and one for the master reference motor, a plu
rality of direct current ?eld windings one for
each reference motor and one for the master
reference motor, a source of direct current sup
ply, a rheostat for controlling the flow of direct
current from said source of supply to the several
?eld windings of the reference motors and of the
7. In a system which includes a plurality of 10 master reference motor, a differential governor
mechanism interposed between the master motor
reference motors to be synchronized each with
and the master reference motor sensitive to an
the others, a master reference motor withwhich
underspeed or an overspeed condition of the
the reference motors are synchronized and a
master reference motor with respect to the
manually variable master motor with which the
master motor to move said rheostat in one or
master reference motor is synchronized, the im
the other direction to raise or lower the resist
provement which comprises, a plurality of direct
ance
therethrough, whereby the several reference
current armatures one for each reference motor
motors and the master reference motor are sub
and one for the master reference motor, a plu
stantially synchronized with each other and with
rality of direct current shunt connected ?eld
the master motor, and polyphase wound alter
windings one for each reference motor and one
nating current rotors one mounted on and for
for the master reference motor, a source of direct
unitary rotation with each said direct current
current supply, a rheostat for controlling the
armature, the polyphase windings being con
flow of direct current from said source of supply
nected each to the other and to no other current
to the several ?eld windings 0f the reference
source, whereby the speed of the several reference
motors and of the master reference motor, a
said rheostat holds the reference motors through
regulation of said shunt ?eld windings.
differential governor interposed between the
master motor and the master reference motor
sensitive to an underspeed or an overspeed con
motors will be exactly synchronized with the
speed of the master reference motor and with
each other.
9. In a system which includes a plurality of
dition of the master reference motor with re
spect to the master motor to close one or the 30 reference motors to be synchronized each with
the others, a master reference motor with which
other of two electric circuits, a servomotor oper
the reference motors are synchronized and a
ative in one or the other direction to raise or
master motor with which the master reference
lower the resistance through said rheostat,
whereby the several reference motors and the
motor is synchronized, the improvement which
master reference motor are substantially syn 35 comprises, a plurality of direct current arma
tures one for each reference motor and one for
chronized with each other and with the master
the master reference motor, a plurality of field
motor, and polyphase wound alternating current
windings one for each reference motor and one
rotors one mounted on and for unitary rotation
for the master reference motor, a source of cur_
with each said direct current armature, the
polyphase windings being connected each to the 40 rent supply, a rheostat for controlling the ?ow
of current from said source of supply to the
other and to no other current source, whereby
several ?eld windings of the reference motors
the speed of the several reference motors will be
and of the master reference motor, a differential
exactly synchronized with the speed of the master
governor interposed between the master motor
reference motor and with each other.
and the master reference motor sensitive to an
8. In a system which includes a plurality of
off speed condition of the master reference motor
reference motors to be synchronized each with
with respect to the master motor to adjust the
the others, a master reference motor with which
resistance through said rheostat, and polyphase
the reference motors are synchronized and a
Wound alternating current rotors one on each
manually variable master motor with which the
master reference motor is synchronized, the im 50 said direct current armature, the polyphase
windings being connected only each to the other.
provement which comprises, a. plurality of direct
HOWARD M. McCQY.
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