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I
Dec. 24, 1946.
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cRlSE
Q 2313i“)
THERKOSTATIC SWITCH
Filed May 27, 1943
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Patented Dec. ‘24, 1946
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2,413,100
UNITED STATES PATENT ' ‘OFFICE '
George W. Crise, Columbus, Ohio, asslgnor
to ‘Crise Electric Manufacturing Company,
Columbus, Ohio, a corporation of Ohio
Application May 27, 1943, Serial No. 488,706
7 Claims. (Cl, 200-138)
1 .
This invention relates to thermostatic switches,
having particular reference to switches of the
type causing automatic opening and closing of
electrical circuits in response to temperature vari
- ations.‘
In the construction of such switches, it is'a
common expedient to employ ?exible bimetallic
strips as the temperature-responsive motivating
element for moving the associated circuit closing
2
ture, magnetic attraction is created between the
magnet and the armature to such a degree as to
provide ?exing of the bimetallic element beyond
that which said element normally assumes at the
temperature when the attraction occurs, such at—
, traction being utilized to accelerate the movement
of the bimetallic element in effecting its circuit
completing and breaking operations.
Still, a further object of the invention resides in
or opening contact devices into and out of phys~ iii providing a switch of the character aforesaid in
ical engagement with each other. Due to the
which the bimetallic element is formed with one
relatively slow movement of such bimetallic ele
of the contact devices of the switch and the mag
ments, dii‘llculty has been encountered in provid
net armature is provided with a second contact
ing desired rapidity (snap action) in bringing the
contact devices into and out of engagement, in
order to avoid or minimize destructive arcing
eiiects produced as a result of electric current
device, the latter being adjustably carried by the
armature for effecting desired spacing of said con
tact device and regulate the temperature differen
tial required toeflect the separation of said de
discharges in the air space between the devices
vices. By temperature di?erential, I refer to the
when the same are but slightly spaced. Another
decrease in temperature from that required to
disadvantage present in conventional switches 29 bring the contact devices into relative engage
employing bimetallic elements is the difficulty in
ment with regard to that temperature at which
varying or controlling de?nitely the duration of
said devices are separated.
'
the periods in which the contact devices associAnother object is to provide a thermostatic
ated with such elements remain incircuit-com
switch characterized by its simplicity and rugged
pleting or interrupting relation.
ness in construction, its high contact emciency,
Accordingly, it is an object of the present in
ease of adjustment and the fact that all the avail
vention to provide a switch utilizing a bimetallic
able differential is utilized to produce the maxi
operating element for operating separable contact
mum speed in causing the contact devices to make
devices having embodied therein improved means
and break an associated circuit.
for effecting rapldlv executed relative movement
For a further understanding of the invention,
between said devices when the spacing of the lat
reference is to be had to the following description
ter is such as to be likely to produce damaging
and the accompanying drawing,_wherein:
electrical arcing therebetween.
It is another object of the invention to provide
a switch of the character set forth with improved
Fig. l is a vertical sectional view taken through
a thermostatic switch constructed in accordance
' with the present invention;
adjustable means for controlling the duration of
Fig. 2 is a top plan view thereof with the cover
the periods in which the contact devices are
plate or” the switch casing removed;
caused to remain in circuit-closing engagement.
Fig. 3 is a transverse cross sectional view taken
For example, the period measured by the time re
on the line II"—IIZ of Fig. 2.
quired to effect separation between the contact 40
Referring more particularly to the drawing,
devices when the switch responds to a decrease in
the numeral i designates the casing of my im
the temperature of the atmosphere surrounding
proved switch, said casing embodying a base sec
the bimetallic element with respect to that re
tion 2 and a removable cover or lid section 3. In
quired to effect closure of said devices, whereby to
the
particular form of the casing illustrated, the
enable the switch to maintain an associated elec
base section is formed with a depending bracket
trical circuit in a complete condition for de?nite
extension ii, to the lower portion of which is se
intervals of time.
cured, as by means of rivets 5, the fixed end of a
A further object of the invention is to provide a
?exible bimetallic element 6. This element, as
switch utilizing a bimetallic temperature-respon
usual, is composed of a pair of metallic strips with
sive element having the free or movable end there
one strip having a higher coeiiicient of expansion
of provided with a permanent magnet normally
than
the other, the strips being so mounted and
spaced from a longitudinally adjustable armature,
relatively united as to produce flexing movement
the latter being so disposed that when the bi
of the free end thereof in response to variations
metallic element is ?exed to bring the magnet into
in temperature of the surrounding atmosphere.
relatively close proximity to the end of the arma 65 As shown, the element 8 is provided with a U-bend
-
. asiaioo
.
3
-
‘l intermediately of its length in order to provide
an upwardly extending arm 3 which terminates
within the interior of the casing after passing
through an opening 9 provided in the bottom of
the base section 2.
Adjacent to its free ?exible upper end, the arm
8 of the bimetallic element is apertured for
the reception of a contact device 50. Said device, ‘
a
the semicircular-1y headed end of the contact
device I ii, and a complemental wire 32 extends
from the strip 36 to the metallic bushing it of
the bearing block Id. The conductors 2i and 28
lead to trunk conductors 33 and 36, a lead 35
may extend to an electric motor 36 employed for
any suitable purpose, such as driving the fan or
blower of the furnace of a forced air heating
in this instance, partakes of the form of a rivet,
having a shank which is semicircularly headed
at one end and cylindrically- headed as at M at
its opposite end. Desirably, the contact device
I0 is formed from copper, silver or other good
conducting material for electric current. The
device ii] is carried by mica or other dielectric
disks i2 disposed on opposite sides of the arm
8, in order that the contact it may be elec
trically spaced or insulated from the bimetallic
element. Also, supported on the shank of the
contact device it is a permanent magnet i3, pref 20
erably of disk-like form and having north and
system, a lead 31 extending from the return side
of the motor, to the conductor 28, the circuit for
the motor thus being opened or closed by the
operation of the contact devices and their asso
ciated parts. When the switch isused in con»
nection with the forced air heating system, the
switch casing i may be mounted on the bonnet
or plenum housing of the furnace of such a sys
tem, so that the bimetallic element will extend
into the plenum chamber of the furnace, being
thereby responsive to the temperature of the air
south polarity regions. The magnet, the insu
the armature i 5 is adjusted longitudinally toward .
passing through said chamber.
From the foregoing, it will be evident that when
lating disk, and the contact device iii are uni
the magnet and the bimetallic strip to reduce‘
tarily carried by and secured to the free end of
the spacing between these parts, the switch will
the bimetallic element by the heads formed at 25 respond to a lower environmental temperature to
the opposite ends of said contact device.
bring the contacts iii and it into circuit~complet~
Arranged within the casing i is a stationary
ing engagement than when the armature is re;
bearing block it, preferably of an insulating ma
tracted to increase the spacing. When so re
terial. This bloci; is bored to receive a station
tracted, a higher environmental temperature is,
ary metallic bushing it, which is internally
of course, necessitated to cause the switch to com
threaded for‘the reception of the external threads
plete the associated circuit. In this manner, the
provided on a tubular steel armature it. By the
_ response of the switch to temperature is governed
rotation’ of the armature, it‘will be seen that the
solely by the spacing or relationship between the
same may be advanced or retracted longitudinally
armature and the magnet.
'
with respect to the magnet it in order to control 35
The time period produced by a decrease in_
the spacing therebetween and render the switch
temperature for breaking a completed circuit is
responsive in a circuit opening or closing sense
controlled by the positions of the differential
to varying temperatures affecting the bimetallic
screw iii and its associated contact 26. With the
element 5. A manipulating wheel if? is thread
armature in a given position of adjustment, it
edly mounted on the outer end of the armature 4.0 will be seen that by retracting the screw it and
and is held in secured engagement therewith by
its contact 29 relative to the end of the armature
a lock nut 58. The wheel i? may be formed from
facingthe magnet 53, a longer period of time or .
a molded plastic, if desired, ‘having dielectric
a greater drop in temperature will be required
properties. Preferably, the wheel has its outer
to produce sumcient tension of the free end of I
45
surface suitably graduated to indicate temper
the bimetallic strip to cause it to overcome the
ature in degrees Fahrenheit and this surface may
close attraction between the magnet and the
be adjusted relatively to a suitable indexing point
armature than when the screw it and its contact
to provide exterior indication of the temperature
is advanced to a more forward position. It will
adjustment of the armature.
be appreciated that the degree of attraction beThe armature is provided with an internally 50 tween the magnet '63 and the opposing end of
threaded bore which is adapted to receive the
external threads of a temperature di?’erential
controlling screw 99. The inner end of this screw
the armature increases or decreases with the dis
tance therebetween. Since the contact 28 is non
magnetic, it does not in?uence the magnet, this
latter function being assigned to the armature.
device 20 which, through the longitudinal adjust 55 ,Hence, the armature is used for temperature con
ment of the screw i9, may be brought into desired
trol and the screw is for differential regulation
relationship with the first-named contact device
By di?‘erential regulation, I refer to the duration
it. To facilitate adjustment of the screw t9,
of the operating cycle of ‘ the electrical apparatus
the outer end of the latter is equipped with a
in the circuit governed by the switch. The mag
60
knob 2| having its outer surface suitably cali
net and armature are in all their operative posi
brated, as at 22, for disclosing, exteriorly of the
tions spaced from each other, and their positions
casing, the adjustment of said screw. A coil
of relative approach are limited by the engage
spring 23 may be used to exert pressure on the
ment of the contacts H and 20.
knob 2! for the purpose of maintaining the screw
The operation of the thermostatic switch when
65
l9 in set positions of adjustment.
used in a furnace system may be explained as
Many di?erent devices may be provided for
follows: Assuming that the asociated furnace has
conducting electrical current to the contact de
been cold and is in process of warming up, the
vices lU and 20. By way of illustration, the eas
increased temperature in the plenum chamber
ing, in this instance, has been shown as provided
will cause the bimetallic element to ?ex in order
70
with a block 26 of an insulating material. This
to advance the contact device it and the mag
block carries a pair of, spaced upstanding threaded
net iii gradually toward the inner end of the
posts 25.carrying nuts 26. Conductors 2'? and 2d
armature it. This movement is continued with
are shown as electrically connected with these
temperature increase until the attraction of the
posts and with copper strips 29 and 30 carried
magnet it‘ with respect to the armature is sum
thereby. A wire 3i extends from the strip 29% i0 75 ciently great to overcome normal rigidity of the
carries in ?xed engagement therewith a contact
asiaioo
‘n
w
bimetallic element 8. at this time, the magnetic
elated therewith, such as a furnace fan, fuel
feeding atelier, incl control valve or the like.
attraction is such that the contact devices will
snap together and the circuit of ‘the switch will
I claim:
,
be complete, causing the fan, motor or other
1.
In
thermostatic
switch,
a
bimetallic
strip
apparatus in the circuit to be energized.
5 anchor at one end and adapated to have its
When, in the course of time, the furnace has
free end de?ected by temperature variations, a
cooled so that the bimetallic element, which for
magnet carried by the free end of said strip, a
this application has its high expanding metal
contact movable in unison with the deflectable
strip on the inside of its bend, has generated su?i
end
of said strip and said magnet, atemperature
cient tension to overcome the magnetic attraction 10
controlling armature adjustably mounted to vary
between the magnet and the armature, thus pull~
the spacing between one end thereof and said
ing the magnet away from the armature so that
magnet,
differential varying element movable
engagement between the contact devices will be
bodily with said armature and adjustable longi
broken suddenly with spring action on the part
’ of the free end of the bimetallic element.
tudinally and independently with respect to the
Be
sult as had the contacts separated at a much
faster rate and to a greater distance than their
actual mechanical movement.
armature, and a second contact carried by said
element adapted to be brought into and out of
engagei'nent with said ?rst contact upon deflection
of nail strip.
‘9 In thermostatic switch, a supporting base,
bimetallic strip anchored at one end to said
base and having its free end de?ectable in re
adjusting screw is, which can be adjusted or r =
naliy threaded bore provided longitudinally and
cause of the strong magnetic ?eld across the path
of the ensuing arc, the flame will be thrown
laterally out of the natural shortest path and
rapidly extinguished, with the same e?ect and re
sa
sponse to temperature variations, a contact mem
Since appreciable power is required to separate
ber carried by the free end of said strip, a perma
the contact elements against the attraction of the
magnet, a temperature differential results, de~ 25 nent magnet surrounding said member and mov
able in unison therewith upon deflection of the
pending upon the strength of the magnet and its
free end of said strip, a temperature regulating
proximity to the armature. As the strength of
and armature-forming screw, mounting means
the magnet is a fixed quantity, the only remain
for said screw carried by said base, said means
ing variable is the resistance between the magnet
and the armature when the contact devices ill 30 admittinf7 oi’ adjustment of said screw toward
and away from said magnet, a differential ad
and 2c are in physical engagement. Thus, the
justing
screw having engagement with an inter
contact device 20 is mounted on the differential
axially in said temperature-regulating screw,
tracted with respect to the inner end of the
and
a second contact member carried by the
armature it by turning the knob 2!. Therefore, 35
differential regulating screw in registration with
the closed contact position of the magnet 93 with
said ?rst contact member.
relation to the armature I6 is under complete
3. In a thermostatic switch, a supporting base,
manual control. The difference between the cir==
a bimetallic strip ?xed at one end to said base
(‘nit-making and interrupting temperatures of ‘the
and having its free end disposed for flexing move
ment in response to temperature variations, a
magnet and a contact member carried by and
bodily movable with the free end of said strip, a
thermostat switch are fully adjustable by the op~
eration of the knob 2i.
Inasmuch as the armature, the ‘screw iii and
the contact device to rotate as a unit by turning
the wheel ii and thereby approach or recede from
the bimetallic element, any working range of tem
perature to which the switch is responsive may
be obtained through the manual adjustment of
temperature-regulating and armature-forming
45
screw, a threaded bearing carried by said base
for the reception of said screw, a manually op
erated control carried by one end of said screw
1
for effecting its rotation, whereby to govern the
It is important to note that the temperature at
spacing between the opposite end of said screw
which the switch makes circuit-completing con
and said magnet, and a manually adjustable dif
tact is determined by the position of the armature
ferential regulating screw mounted in a threaded
i6 and not by the position of the contact 20. This
bore formed longitudinally and axially in the
is because of the fact that the attraction of the
temperature-regulating screw, one end of said
magnet it causes the contacts ill and 20 to snap
differential regulating screw being formed to pro
together whenever they come within a ?xed dis 55 vide a second contact member arranged for co
tance of separation, which on a standard ‘as-i
action with said iirst=named contact member.
the wheel ll.
sembly may be 33; of an inch.
This is a very
' a. In a thermostatic switch, a supporting base,
a bimetallic strip ?xed at one end to said base
Code specifies certain limits at which fan switches
and having its free end disposed for flexing move
must contact, a condition with which the present (iii ment in response to temperature variations, a
construction complies. Furthermore, the con
magnet and a contact member carried by and
struction permits accurate calibration of the
bodily movable with the. free end of said strip, a
thermostatic switch by means of the locking nut
temperature-regulating and armature-forming
is on the armature l6, and this calibration of the
screw, a threaded bearing carried by said base
armature is unaffected by the adjustment of the
for the reception of said screw, a manually oper
differential knob 2i. Another feature of impor
ated control carried by one end of said screw for
practical feature, since a standard Underwriters
tance is that by increasing the magnetic action to
absorb all the available power of the allowable
differential, maximum advantage is obtained for
the contact points and a greater current can be _
handled than would be possible with prior art
designs. A further advantage is that the switch
here disclosed admits of large variations in di?er
, ential in order to regulate the operating cycle of
the motor driven equipment which may be asso
effecting its rotation, whereby to govern the spac
ing between the opposite end 01' said screw and
said magnet, a manually adjustable differential
regulating screw mounted in a threaded bore
formed longitudinally and axially in the tempera
tum-regulating screw, one end of said differential
regulating screw being formed to provide a sec
ond contact member arranged for coaction with
said first-named contact member, and circuit
2,418,100
7
forming conductors joined in current-transmit
axially threaded therein for adjustment a: the
ting union with said contact members.
contact on the end thereof toward and away from '
, 5. In a thermostatic switch, a'supporting base,
the contact element on said bimetallic strip, and
a threaded bearing carried by said base,-a tem~
concentrically disposed calibrated manipulating
perature-regulating armature screw supported by 5 devices accessible from the exterior of said casing:
'for e?ecting adjustment of said armature and
said bearing for longitudinal movement, said
screw having an internally threaded bore, a dif
regulator.
i'erentiai-adjusting screw adjustably mounted ‘in
the threaded bore of said temperature-regulating
screw, independently movable means, carried by
'
"
a
_
I
7. A thermostatic switchcomprising acasing;
, ‘ tension‘and
body
having
strip
having
ofits
said
bottom
onean
stripadjacent
end
formed
projecting
?xed with
opening,
to said
upwardly
a depending-ex;
extension,
a bimetallic
through
the
the outer ends of said screws for manually ro
tating and adjusting their operating positions, a
contact member formed on the inner end vof the
di?erential-regulating screw, a bimetallic strip
said opening for unrestricted movement therein,v
the upper de?ectable end of said strip being dis
having a ?xed end and a free end de?ectable’in 15 posed within the con?nes of said casing, a contact ‘
response to temperature variations, and a second
element and a permanent magnet carried by and
contact member and a permanent magnet mount
movable bodily in unison with the upper de?ect
ed on, and bodily movable in unison with the
able end of said strip, a bearing in said casing,
de?ectable end of said strip.
,
6. In a thermostatic switch, a casing, a bi
a, temperature-regulating
armature threadedly ' -
20 mounted in said bearing for adjusting 'r'novement -
metallic strip ?xed at one end to said casing and
having its'oppiosite end free for ?exing move
ment in response to environmental temperature
longitudinally toward and away from said arma
ture, a di?erential regulator having a contact
formed on one end thereof, said regulator being
variations, a contact element and a surrounding
coaxially threaded in said armature for adjusting permanent magnet carried by and movable bodily 25 movement of its contact toward and away fromv
with the free de?ectable end of sai'dstrip, a tem
the contact element of said bimetallic strip, and
perature-regulating armature threadedly mount- I
concentrically disposed calibrated manipulating
ed in said casing for adjusting movement'toward
‘devices accessible exteriorly of said casing for
and away from said magnet, a di?erential resu
facilitating manual adjustment of said armature,
lator having a contact at one end thereof, said‘ 30 and regulator.
regulator being carried by‘ said armature and oo
GEORGE W. CRISE.
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