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Патент USA US2042233

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May 26, 1936.
Filed Feb. 21, 1954
Fa’W/n H lock/wood
Patented May 26, 1936
Edwin H. Lockwood, Mans?eld, Ohio, assignor to
Westinghouse Electric & Manufacturing Com
pany, East Pittsburgh, Pa., a corporation of
Application February 21, 1934, Serial No. 712,342
2 Claims.
My invention relates to electric ranges and has
particular relation to the construction and con
trol of range heating units designed for energiza
tion by low-voltage currents supplied through
transformers from the usual residence-potential
power circuits.
Low-Voltage surface or exposed type heating
units for domestic and other electric ranges
possessa number of inherent advantages, a prop
er appreciation of which it now appears may
cause such units to supplement or even replace
the conventional line-voltage devices which at
the present time are so universally employed in
cooking-device applications. For example, by de
15 signing the unit for low-voltage energization,
little or no insulation is required on the heat
producing conductor and a correspondingly higher
e?iciency of thermal conductivity to receptacles
and materials may be realized. Likewise, the en
20 ergizing voltage may be reduced to a completely
non-dangerous value with an attending elimina
tion of all possibility of electrical shock to the
housewife or other user.
In addition, the body or cross-section of the
heavy-current heat-producing conductor may be
made sufficiently large to afford mechanical rug
gedness of an unbreakable order and to prevent
appreciable diminution due to a ?aking off of they
outer material at the high operating tempera
30 tures.
The life of such a unit is, therefore, prac
tically unlimited. Furthermore, the presence of
a transformer, the ratio of which may readily be
range structure which accommodates a step-down
transformer and a control switch;
Fig. 3 is a diagrammatic representation of ap Ul
paratus and circuits arranged to effect heat-in-'
tensity adjustment in accordance with my inven
Fig. 4 is a top or plan view of a second form of
parallel-path type of heating unit constructed in 10
accordance with my invention; and
Fig. 5 is a section view taken on line V-—V of
the device in Fig. 4.
Referring to the drawing, and particularly to
Figures 1 and 2 thereof, the improved heating
unit there represented comprises a plurality of
parallel-arranged heat-producing conductor sec
tions .lll connected between two terminal mem
bers l2 and 14 which are positioned on opposite
sides of a “heater-plate” area.
While as repre
sented this area is of the usual circular contour,
it‘ will be understood that the improved heating
unit of my invention may also be constructed in
square or rectangular form.
Energizing current is supplied from the usual 25
110 or 220 volt residence power circuit through
a suitable step-down transformer 20 conveniently
mounted beneath the range cooking-platform
30 through the top of which the heating unit pro
trudes. The voltage applied to the heating ele
ment may be as low as one or two volts.
shown, this transformer comprises a low-voltage
changed by Winding tap control, in the power
heavy-current secondary winding I8 connected
supply circuit makes practical a variation of en
by means of bus bars I6 to the heating unit ter
minal members l2 and I4, and a primary winding 35
22 arrange-dtoreceive energization from the power
source, which in the drawing is represented in
the form of circuit conductors 25 to 27, inclusive.
To control and adjust the intensity of heater
35 ergizing voltage in‘ a large number of steps and
thereby facilitates heat-intensity adjustments.
The present invention contemplates improve
ments which will make low-voltage heating sys
Fig. 2v is an end or side View, partially in sec
tion, showing the unit of Fig 1 installed in a
tems more practical.
One object of the invention is to provide im
energization, the'primary winding supply circuit 40
proved designs for low-voltage heavy-current
of the transformer includes a tap-selecting or
range heating units of the surface or exposed
ratio changing switch 24 the actuating knob 28 of
which protrudes through the front of the range
heat-producing-conductor type.
Another object of the invention is to provide
45 an improved heat-adjustment control scheme for
units or devices which are energized through a
trasformer from a multi-voltage supply circuit.
My invention itself, together with additional
objects and advantages thereof, will best be un
5 O derstoodthrough the. following description of
speci?c embodiments when taken in conjunc
tion with the accompanying drawing, in which:
Figure 1 is a top or plan view of one preferred
form of parallel-path type of heating unit con
55; structed in accordance with my invention}, ~
structure’ in the manner shown.
Insofar as the heating unit of my- invention is
concerned, it will be understood that the speci?c
details of the supply transformer 20 and its
mounting underneath the cooking platform 30 are
relatively immaterial, except that a device having 50
separate and electrically insulated primary and
secondary windings is preferable to a single wind
ing or auto-transformer since the former permits
the low voltage heater circuit to be completely
isolated from-the higher voltage supply circuit 55
and thereby effectively protects the user from all
possibility of electrical shock.
In addition, it is important that the resistance,
and hence the length, of the high-current sec
ondary leads or bus bars I6 be kept as low as
possible in order that the major portion of the
heat produced in the secondary circuit of the
transformer may be localized in the conductors
ll} of the surface heating unit. Hence, the bus
bars should be of generous cross-section to ac
bars desired may be obtained by varying their
cross-sections to change the distribution of cur
rent therethrough.
Further relative to the problem of regulating
heat distribution, it is important to note that the
heat produced by each of the parallel conductors
varies as the ?rst power of the resistance of that
conductor and as the square of the current
at the low voltages named may be of the order
of 1000 amperes or more. They may be joined
traversing it. Consequently, increasing the re
sistance, which proportionately reduces the cur 10
rent, causes the total heat dissipated by the con
ductor to .decrease. Assuming that the voltage
impressed upon all of the several parallel con
with the terminal portions I2 and [4 of the heat
ductors in a heating unit of my invention is
commodate the high heating-unit current, which
15 ing unit in any suitable satisfactory manner as by
One preferred manner of forming the heating
unit structure, which as illustrated in Figs. 1 and
2 is mounted to slightly protrude above the top
20 surface of the cooking platform 30‘ in order that
receptacles or materials to be heated may be set
directly thereupon, is to» cut from a plate of suit
able metal, such as nickel-chromium alloy or
other conducting material, having a high coeffi
25 cient of resistance in addition to being mechani
cally strong, parallel slots so spaced as to leave
the desired parallel conducting strips 10 through
which the heating current may pass. Because of
the exceedingly low voltage, no insulation what
ever is required on the unit assemblage which
further is so mechanically strong as to be com
pletely break-proof. High thermal e?iciency and
unlimited life are the respective advantageous
Distribution of current among the several par
allel heat-producing conductors l0 proper to
produce uniform or other predetermined heat
production among them may be effected by vary
ing their relative cross-sections in a manner to
40 be more fully described by a later portion of the
casting is in practice, found to be equally satis
The described heating unit may be supported
in the illustrated position in any suitable man
50 ner as through the utilization of angle piece or
clip members 23 attache-d to the underside of
the platform member 30 and disposed to engage
the edges of the terminal portions l2 and I4 as
shown. Preferably, sections of insulating ma
55 terial 29 are interposed between these support
ing members and the heater structure to prevent
a by-pass circuit from being established through
the platform or surface member material 30.
Another form of low voltage surface unit struc
60 ture of the parallel path type is illustrated in
Figs. 4 and 5. In this structure, I utilize a plu
rality of conducting material bars 34, the ends of
which are secured in cooperating holes made in
the solid and common terminal members 36 and
65 38, the necessary low resistance electrical con
nection being achieved by brazing the ends 40 to
the body portions of the terminal members or
by attaching in other suitable manner. These
terminal members 36 and 38 may be directly
70 connected with the heavy current low voltage out
put or secondary winding of the supply trans
(not shown)
ances equal, in which case the currents traversing
them will be equal.
The resistance of each conductor varies di
rectly with its length and inversely as its cross— 20
sectional area. Consequently, the several con
ductors in a heating unit may be made to pre
sent equal resistances by so adjusting their rela
tive areas that the quotient of the length of each
conductor divided by its area has the same value I
as does that of all the other conductors.
In the case of the plate type of heating unit
construction described in connection with Fig
ures 1 and 2, assuming that the plate material is
of uniform thickness, this means that to give the 30
uniformity of heat distribution mentioned, the
quotient of the effective length of each of the con—
ducting paths I0 divided by the width of that
path should be made equal to that of each of the
other conducting paths. For other constructions,
typi?ed by that shown in Figs. 4 and 5, the com
putation must take account of the coefficient of
resistance of the bar materials, in case all are
not alike, as well as their cross-sectional areas.
Considering now the improved heat-adjusting 40
or control system of my invention which is ap
Instead of forming the element from a ?at
sheet of metal as just described, an equivalent
structure may be produced in the form of a cast
45 ing of the desired conducting material. Such a
equal, the heat distribution thereamong may be
made uniform by making the conductor resist
or connected therewith
through the medium of bus bars of the general
form indicated at 42. As in the ?rst explained
75 constructions, any heat distribution among the
plicable to situations involving a transformer
and a multi-voltage power supply circuit, refer
ence may be had to the diagrammatic represen
tation of Figure 3, in which the several elements 45
of the complete range heating unit system previ
ously described in connection with Figs. 1 and 2
are identi?ed by corresponding reference numer
als. The particular arrangement illustrated is
capable, in combination with the 110-220 volt
power supply circuit represented by circuit con
ductors 25, 26 and 21, of effecting six different
adjustments in heat intensity through the utili
zation of but three tap connections, indicated at
a, b and c, on the primary winding 22 of the step 55
down transformer 20.
The tap selecting or control switch 24 requires
in effect, two blades, the ?rst of which, indicated
at 46, is joined with the central conductor 26 of
the power supply circuit and the second of which,
indicated at 48, is similarly joined with one of
the outer conductors as 25 of the power circuit.
To the remaining outer conductor 2'! of the power
circuit, the right-hand end of the transformer
winding 22 is joined by means of a conductor 50.
When the blades of switch 24 occupy the ex
treme upper or “off” position in which they are
illustrated, the transformer energizing circuit is
interrupted. As the switch blades are moved
downwardly to active position No. 1, there is com 70
pleted an energizing circuit for winding 22 which
extends from power source conductor 26 through
conductor 52, the switch blade 46, conductor 54,
winding tap a, the winding 22, and conductor 50
back to power source conductor 21. This applies 75
the potential appearing between conductors 26
and 2'! of the supply circuit, designated in the
drawing as 110 volts, to the complete winding and
produces a minimum value of voltage in the heat
er supply secondary winding [8.
Actuation of the switch blades to position No. 2
transfers the energizing connection just described
from winding tap a to winding tap b, thereby
causing the same supply potential to act upon a
As a
10 smaller number of primary winding turns.
result, the heater energizing voltage induced in
secondary winding I8 is correspondingly raised.
Further downward movement of the switch blades
to active position No. 3 transfers the described
energizing connection to tap c of winding 22 and
still further raises the voltage induced in the
Winding I8.
As the blades of switch 24 are advanced down
wardly to active position No. 4, the transformer
2-0 energizing circuit is transferred from blade 46,
connected with the 110-volt supply, to blade 48
which is connected with the 220-volt supply con
ductor 25. In this new position, the transformer
energizing circuit may be traced from power
source conductor 25 through conductor 58, switch
blade 48, conductor 60, tap connection a, the
winding 22, and conductor 5!! back to power source
conductor 21. Under these conditions, the 220
volts are impressed across the complete winding
30 22. The number of turns and tap connecting
points of this winding are so proportioned that
there is now produced in the secondary winding l8
a voltage somewhat higher than resulted when
the 110 volts were applied to winding tap 0.
Further downward movement of the switch
blades to active position No. 5 transfers the en
ergizing connection just described from tap a
to tap b and thereby further increases the voltage
induced in secondary winding l8. Additional ad
40 vancement of the blades to active position No. 6
further transfers the 220-volt energizing connec
tion to tap c of winding 22 to produce the maxi
mum value of heater voltage in winding l8. In
the illustrated connection, active position No. 6
45 constitutes the extreme limit of travel of the
blades of switch 24 in the downwardly or voltage
increasing direction.
To summarize the manner of operation of the
improved control system of my invention, I have
consolidated the descriptive information just
given in the form of the following table:
Swltch settmg
Oil (upper limit) ___________ __
__________ __
0. 00
Active No. l..."
0. 50
Active No. 2,. . .i
Active No. 3"
Active No. 4 _______________ __
Active No. 5 ............... __
Active No. 6 _______________ __
l. 00
l. 50
The heater voltage values presented by this
table apply to the 1% volt maximum parallel path
type of heating unit described in connection with
Figs. 1 and 2. Since these speci?c values of volt
age induced in the secondary winding [8 of the
step-down transformer are for illustrative pur
poses only, it will be understood that in case heat
ing units of other maximum voltage ratings are to
be controlled, the values stated will all be modi?ed
accordingly. A similar comment applies to the
values listed in the supply voltage column. In 10
stead of the 110-220 volt combination, it will be
apparent that other potentials differing not only
in absolute magnitude but also in relative values
lend themselves to utilization by my improved
control system.
It is, in this connection, further signi?cant to
note that supply voltage circuits providing more
than two different values of voltage may also be
adapted to the control system of my invention.
Nor is the system restricted to the six di?erent 20
heat adjustments shown and described, since,
practically any number desired may be incorpo
rated by increasing the number of transformer
winding taps and active control switch position.
The important feature resulting from its use is 25
the reduction of the required number of trans
former taps for a given number of heat adjust
merits. Thus, in the illustrated two voltage sup
ply circuit combination, six different values of
heater voltage are obtained through the use of '
only three winding taps. If a three voltage supply
circuit were available, the same three taps could
be caused to produce nine heat adjustments, and
so on.
Although I have shown and described certain 35
speci?c embodiments of my invention, I am fully
aware that many modi?cations thereof are possi
ble. My invention, therefore, is not to be restrict
ed except insofar as is necessitated by the prior
art and by the scope of the appended claims.
I claim as my invention:
1. An electric range low-voltage heating unit
comprising a pair of spaced terminal members,
and a plurality of conductors of dissimilar lengths,
parallel-positioned in a common horizontal plane, 45
interconnecting said members, the cross-section
of each of said conductors being so related to its
length that the resistance of that conductor is
the same as is that of each of the others.
2. An electric range low-voltage heating unit
comprising a ?at metal plate having parallel slots
which provide within a substantially circular area
a plurality of parallel-positioned heat-producing
conductor strips of dissimilar lengths through
which current may be caused to flow in parallel
from the plate material on one side of said area
to the material on the opposite side, the width of
each of said strips being so related to its length
that the resistance of that strip is the same as
is that of each of the others.
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