Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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r~ECH~NIC~J D GA tNG FOR ~L~CTRIC MOTORS
sAcKGRouND OF THE INVEMTION
This invention relates ~o direct current braking of
an alterna-ting current motor and, more par-ticularly, to a
mechanical degaussing arrangement for demagnetizing the motor
to allow it to return to its initial position from its braked
position.
In temperature controlling sys-tems, it is common to
use an electrlc motor or controlling valves -to supply a heat
exchange medium to one or more zones. All zones may be spaces
or one zone may be a space and another zone may be a source of
hot wa-ter, for example. In such a -two zone system the valve
will have three positions. In the first position, the heat
exchange medium, which may be water, is supplied to one zone
~ut blocked from the second zone; in a second position, the
heat exchange medium is supplied to both zones; and, in ~e
third position the heat exc~ancJe medium is supplied to the
second zone but blocked from the first zone. Thus, the motor
driven valve must be capable of assuming three different positions.
~ One motor control ~ystem for positioning a valve in
any of a number of positions is disclosed in Canadian patent
~89,935 issued May 25, L976. In the system described therein,
a spring returned alternating current motor has a de-energized
or initial posi-tion for supplyiny heated water to one zone, a
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; ~ second position for supplying heated~water to a second zone, and
an intermediate position for supplying water to both zones. When
the motor is to be driven to i~s intermediate position, the
source of alternating curren~ supplying the energizing current to
the motor i5/ disconnected and a direct current source 1~ sub-
stituted therefor for braking the motor and holding the motox
in its intermecliate positioil~ Because of the resiclual magnetism
of th motor due to -the dir~ct current/ the motor wi]l not return
to its de-energized position of its own accord when the direct
current source is taken awa~.~ fram it. A rel~ is included,
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therefore, for sensiny the mo~en-t at which the motor is to be
retu~ned to its i~itial or de-energized position for mom~ntarily
applying alternatiny current to the motor to demagnetize it.
Once demagnetized, the return spring wil] return the motor to
its de-energized position.
As an improvement over the systern disclosed in Canadian
patent 989,935, Canadian application 276/635 filed ~pril 21, 1977
discloses a systern for eliminating the relay shown in the
Canadian patent 989,935 by substituting a capacitor circuit
therefor. Thus, when the motor is to be returned to its initial
- position, the direct current to the motor is interrupted and the
capacitor is allowed to discharge through the motor. Since the
current discharges from the capacitor into an inductive motor,
it oscillates to provide an alternating current for demagnetizing
- the motor. Once demagnetized, the spring returns the motor to
its initial position.
SUMMARY OF T~E INVE~TION
; The present invention represents an improvement over
-the system disclosed in Canadian application 276,635, above
mentioned, in that a means is provided for limiting the direct
current used for braking and holding the motor in its mid-position
to a level ~:Jhich, when the direct current supplied to the motor
is interrupted, will allow the return spring to return the motor
to its initial position. Specifically, a motor contxol apparatus
is disclosed having a motor which is subject to residual mag-
netism resulting from the application of direct current braking
power to it, a source of alternating current, a source of direct
current, a return spring for returning the motor 'LO a de-energized
position when the motor is de-energized ana demagnetiæed, and a
circuit for conne~ting the source of alt~rnating current to the
motor to drive! the motor to at least a first ener~iæed position
i and responsLve to the motor reaching the first en-rgized posi-tion
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to disconnect the source of alternating curren-t from the motor
and to connect the source of direct current to the motor to
brake and hold the mo-tor at its first energized position, the
circuit having a current limiting element to compensate for any
residual magnetism produced in the motor by the direct current
by limiting the direct current below a level whereby the return
spring is capable of returning the motor to the de-energized
positi.on when the circuit interrupts the direct cur.rent to the
motor.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other features and advantages will become
more apparent from a detailed consideration o~ the invention
when taken in conjunction with the drawings in which;
Figure 1 a schematic diagram of the invenkion utilized
in a heating apparatus; and,
Figure 2 is a simplified circuit schematic of the
invention shown in Figure 1.
DETAILED DESCRIPTION OF THE INVENTION
In Figure 1 J a mator control apparatus 10 has a
conv~ntional synchronous alternating current electric motor 11
for driving valve operator 12 of valve 13 through reduction
gear train or apparatus 14 and shaft 15. Valve 13 is a three
position motor valve as shown. Connected to shaft 15 is coiled
return spring 20 adapted to bias shaft 15 and motor 11 in a
clockwise direction ~opposite to the directi.on shown by the arrow)
to hold valve member 21 in a valve end, de-energized or initial
position against valve seat 22. Upon energization of motor 11
from alternat:Lng current source 16, shaft 15 is rotated counter-
clockwise (in the direction of the arrow~ to move valve member 21
from the de-energized position against valve seat 22 to a first
energized position or mid-position 25 or -to a second energ:ized or
opposite end position against valve seat 24. The first and second
energized positions are shown as dotted lines in Figure 1.
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Valve member 21 assumes -the first energized position ~5
by holding or braking motor 11 in a predetermined position inter~
mediate the de-energized position and the second energized pos-tition
by the application of direct current whlch is supplied by diode
17. The direct current magnetizes the motor poles and the motor
is held in position. Unless -the motor is demagnetized, it will
remain in the mid-position even after the direct current i5 ter-
minated. The solutions of the above mentioned Canadian patent
and Canadian application are to momentarily apply alternating
current to demagnetize or degauss the motor and allow the spring
to return it to its initial position. In the present invention,
momentary alternating current is not applied to th~-motor but
rather spring 20 is relied upon to degauss the m~tor. However,
if the residual magnetism produced by the direct current remains
uncompensated, spring 20 may not be sufficient of itself to de-
gauss motor 11. Therefore, this residual magnetism is compensated
for by providing resistor 18 connected in series with diode 17
to limit the braking direct current supplied motor 11 to a level
at which spring 20 can of its own power degauss or demagnetize
motor 11.
~ Valve 13 is connected to a conventional water heater
¦ ~ system supplying hea~ to ZONES 1 and 2. Specifically, the water
is heated by heating apparatus 30 connected to supply line 31
containing pump 32 to supply heated water to inlet 33 o~ valve
13. Wlth the valve in the posi~ion shown, the water will be
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supplied through line 41 anid to the radiator 3S located within
ZONE 2 and then back through line 55 to heating apparatus 30.
,
~ When the valve is ayalnst valve seat 24 in the second energized
¦~ ~ position, water will bè supplied through valve 13, line 40,
to radiator 3h in ZONE 1 and back through line 55 to heating
apparatus 30. If both zones are to be heated, valve operator
~ ~1 will assume its intermediary or first energized position 25
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in which case water is supplied through valve 13, bo-th of lines
~0 and 41, to both radiators 34 and 35, and back through line
55 to heating apparatus 30.
Located within ZONE 1 i5 thermos-tat 42 having bi~
metallic contact 23 for sensing the tempera-ture within ZONE 1.
When the temperature within ZONE 1 is suficient, bimetallic
contact ~3 will contact its OFF contact. Bimetallic contact 23
is connected by line 26 to terminal Ll of alternating current
source 16. When the temperature within ZONE 1 drops sufficiently,
bimetallic contact 23 will move against its ON contact which is
connected by line 27 to the normally closed contact of switch 51
and the movable contact of switch 52. An anticipation resistor
36, associated with thermostat 42, is connected between line 27
and terminal L2 oE alternating current source 16.
Located within ZONE 2 is thermostat 43 having a bi-
metallic elemen-t or contact 37 for sensing the temperature within
ZONE 2. When the temperature in ZONE 2 is sufficiently hi~h,
bimetallic contact 37 will contact its OFF contact. Bimetallic
contact 37 is connected to terminal Ll~ by line 26 and the OFF
contact is connected to the normally open contact of switch 1.
When the temperature in ZONE 2 has~dropped su~ficiently, contact
L 37 will move against its ON contact. This ON contac-t is con-
nected by line 38 to the normally open contact of switch 52
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and to one side o pump 32 the other side of which is connected
to terminal L2 of al-ternating current souce 16.
Switches 51 and 52 operated by cam 53 driven by shaft
15 sense the position of valve operator 21. Switch 51 has a
movable contart connected to terminal 29 of motor 11 and to one
side of the series combination of diode 17 and resistor 18 the
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other side of which is connected to the normally closed contact
of switch 52. A resistor 44~is connected between the normally
~ open contacts of switch 51 and switch 52. It has been found
; that after a predetermlned number of cycles of operation, which
varies with the motor, motor friction increases to a point: ~here
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mechanical degaussing does not work all the time. Therefore,
resistor 44 is included and has a sufficiently larye value
to allow a trickle curren-t to the mo-tor which wipes out a portion
of the residual magnetism electrically so that the re-turn spring
is allowed to finish demagnetizing or degaussing the motor. In
those systems which require a gas valve connected in ~arallel
to the pump, the amount of current which can be allowed for de-
gaussing through resistor 4~ is limited by the yas valve coil
which sees this current when thermostat 43 is in the OFF position.
This gas valve is used for supp]ying heat to water heating ap-
paratus 30. If a larger current is allowed to flow through motor
11 for entirely degaussing the motor electrically, the gas valve
will be maintained permanently energized. Therefore, resistor
44 must be sufficiently large to reduce this current below the
level which will energize the gas valve and pump but at the same
time have a value to allow it to aid spring 20 in degaussing
motor 11. Resistor 44 is not needed in all cases but is needed
where motor 11 is of such a nature that after a predetermined
number of cycles of operation, its friction is sufficiently
large to prevent it from being degaussed strictly mechanically.
Switch 51 is arranged to operate its movable contact
from its normally closed contact to its normally open contact
when the motor has traveled far enough to drive valve member 21
to its mid~position; i.e. 50% of valve member 21 travel. Switch
52 may be arranged to operate its movable contact from its nor-
mally closed contact to its normally open contact at 60% of
valve member 21 travel from valve seat 22 to valve seat 24
In operation, if ZONE 2 requires heating, contact 37
of thermostat 43 will move against its ON contact establishing
a circuit from terminal Ll through thermostat 43 and line 38
to pump 32 ancl back to terminal L2. Pump 32 will, therefore,
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be energized to supply wa-ter thLouyh valve 13, line 41,
radiator 35 and return line 55 to water heatiny apparatus 30
and then to the inslde of pump 32. The hot water circulating
in radia-tor will begin heating ZONE 2 and, when the temperature
within ZONE 2 has risen sufficiently, contact 37 of thermostat
43 will move away ~rom the ON contact to the OFE contact de-
energizing pump 32.
If both ZONES 1 and 2 require heating, bimetal con-
tacts 23 and 37 move against their respec-tive ON contacts.
Pump 32 is energized through the ON contact of thermostat 43
and motor 11 is energized from terminal L1, thermostat 42, line
27, switch 51 and then back to terminal L2 through motor 11.
Thus, motor 11 is energized to drive valve opera-tor 21 in a
counterclockwise direction. Cam 53 is also driven in the coun-
terclockwise direction and, when operator 21 is approximately
half way between valve seat 22 and valve seat 24~ switch 51
operates against its normally open contact to break the al-
ternating current path through switch 42 and line 27 to motor
11. Thus, motor 11 is supplied with direct current from line
~6, thermostat 42, swi-tch 52, resistance 18, diode 17, motor 11
and back to terminal L2. This direct current brakes motor 11
and holds it in the mid-position. Since pump 32 is energized,
it will supply water through valve 13 to both radiators 34 and
35 to heat both ZONES 1 and 2. At this point, one of three
actions can occur.
~¦~ First, the temperature within ZONE 1 may rise suf-
ficiently to satisfy thermostat 42. With thermostat 42 against
its ON contact, motor 11 receives direct current through resis-
tor 18 and diode 17. Resistor 18 has a value to limit the cur-
rent through motor 11 in order to maintain the residual magnetism
in motor 11 caused by the direct current flowing therethrough to
a level which will allow spring 20 to return motor 11 to its
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ini~ial position when desired Fur-thermore, with thermostat
43 a~ainst its ON contact, a small amount of alternating cur-
ren-t is supplied through resistor 44 and switch 51 to motor 11
so that when thermostat 42 switches to its OFF position, the
combination of the al-ternating current flowing through motor
11 and the mechanical degaussing spring 20 will drive motor
11 back to its initial position. Thus, when the thermostat in
ZONE 1 is satisfied, thermostat 42 switches to its OFF position
which interrupts the flow of direct current to motor 11. Motor
11 is degaussed both by spring 20 and the alternatiny current
flowing through resistor 44 and switch 41, and is all.owed,
therefore, to return to its de-energized position where valve
member 21 seats against valve seat 22. Since thermostat 43 is
still on, pump 3~ is still energized for supplying water through
line 41 to radiator 35 in ZONE 2 and back to water heating ap-
paratus 30.
Second, the thermostat within ZONE 2 may have risen
sufficiently -to satisfy thermostat 43. In this case/ the bi-
metal contact 37 of thermostat 43 moves against its OFF contact
to supply alternating current.from terminal Ll, through line 26,
thermostat 43, the.normally open contact of switch 51~ through
motor ll and back to terminal L2 driving motor-ll to its second
energi~ed position in which valve member 21 rests against valve
seat 24. Switch 52 is now operated against its normally open
contact so that current flows from terminal Ll, through line
26, thermostat ~2, switch 52, line 38, pump 32 and terminal L2
to energize pump 32. Pump 32 circulates hot water through ~alve
13, line 40, radiator 34 in ZONE 1 and back to water heating
apparatus 30. Even after thermostat 42 is satisfied and switches
to its OFF contact, motor 11 will still receive alternating cur-
rent through the OFF contact of thermostat 43 and the normally
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open contac-t of switch 51 to malntain valve operator 21 now rest-
ing against valve seat 24. However, since thermostat 42 is now
switched to its OFF position, pump 32 is de-energized and
wa-ter is no longer circulated through the system. Thus, un-
like the systems disclosed in the abovemsntioned Canadian
patent or abovementioned Canadian application, valve 32 will
remain in either its de-energized position or second energized
position of last call and is only returned to i~s de-energized
position from mid-position.
Third, it is possible that the temperature within
ZONES 1 and 2 may have risen sufficiently to satisfy both ther-
mostats 42 and 43 simultaneously. In this case, swiich 51 still
bridges its normally open contact so that when switch 42 switches
against its OFF contact, pump 32 is de-energized and when switch
43 returns to its OFF contact, alternating current is supplied
through the normally open con-tact of switch 51 to motor 11 to
drive motor 11 to its second energized position. If at this
point ZONE 1 requires additional heating, thermostat 42 switches
against its ON contact and will energize pump 32 through switch
5~. On the other hand, if ZONE 2 requires heatingr ~hermostat
43 will switch against its ON contact which will break the al-
ternating~current circuit to motor 11 allowing it to return to
its de-energized position for supplying water to radiator 35.
If both ZONES 1 and 2 require heat, both thermostats 42 and 43
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will switch to their ON contacts Which breaks the alternating
current path to motor 11 allowing motor 11 to begin returning
to its de-energized position. However, when it reaches the
point where switch 52 switches against its normally closed con-
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~ ~ tact, a current~path will be established through resis-tor 18
¦~ and diode 17 to-brakff motor 11 at its mid-position~
l ~ ~ With valve operator 21 against valve seat 22, motor
¦ ~ 11 is in its de-energized position. If only ZONE 1 requires
heating/ bimetal 23 will move against its ON contact. Motor 11
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is firs-t driven through thermostat 42 and switch 51 until it
reaches mid-posi-tion where switch 51 switches ayainst i-ts
normally open contact where alternating current will now be
supplied through thermostat 43, and the normally open contact
of switch 51. Thus, valve operatcr 21 is driven all the way
against valve seat 24 and pump 32 is energized through thermo-
stat 42 and switch 52 to supply water through valve 13, line 40,
to radiator 34 and back through return line 55 to water heating
apparatus 30. When thermostat 42 is satisfied, motor ll will
remain in its second energized position because it is supplied
with alternating current through the O~'F conkact of thermostat
43 and the normally open contact of switch 51. Motor ll can
be returned to its de-energized position or first energized
mid-position, when either thermostat 43 or a combination of
thermostats 42 and 43 are energized.
As discussed above, in many cases, resistance 18
which is included for limiting the current to motor ll is suf-
ficient -to allow mechanical degaussing of the motor~ However,
in those cases where the ~riction o~ motor ll is too high,
resistor 44 may be added to add electrical degaussing to the
mechanlcal degaussing of the spring. Furthermore, resistor 4~
must be selected sufficiently large enough -to limit the current
through pump 32 and any gas valve whi~h may be included in the
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circuit for supplying heat to the water hea~ing apparatus 30
below the level which will energize either pump 32 or the gas
valve. Moreover, where ZONE 2 is a hot water heater, thermostat
42 ma~ be included in ZONE l and thermostat 43 may sense the
temperature of the water in the water heater. In such a ca~e,
the heat generated by water heating apparatus 30 is diviAed be-
tween ZONE l a.nd the hot water heater to heat the air in ZONE 1
or the hot water in hot water heater.
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