Note: Descriptions are shown in the official language in which they were submitted.
1~39785
This is a division of copending Canadian application
Serial l~o. 220,908 which was filed on 27 February 1975.
BACKGROUND AND SUr~l~lARY OF THE INVENTIOr~ ,
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This invention relates to a control system for frying
apparatus. More particular, this invention concerns a therm- ;
stat control system for regulating and li~iting the temperature
of heating elements during cooking and pyrolytic cleaning cycles.
In deep fat frying system the electric heating
elements often become coated with residues from the oil and
cooked products after prolonged cooking periods. Cleaning
the elements by hand is quite tedious and time consuming. Thus,
the practice of burning off the elements, called pyrolytic
cleaning, is sometimes employed. In pyrolytic cleaning the
heating elements are raised to relatively high temperatures,
usually between 600 and 900 F. Above about 1000 F. the
burner elements may discolor and oxidize, possibly resulting
in permanent damage to the elements. Moreover, pyrolytic
cleaning has been found to be safer and more effective if
the temperature of the elements is raised gradually to allow
2a slow burn-off to occur and decrease the possibility of damage
to the heating elements and associated apparatus.
During cooking, malfunctions of the operating thermo-
stat may cause overheating of the cooking fluid resulting in
burning of the product, premature deterioration of the cooking
fluid and even flash burning of the fluid. Thus, the cooking
; fluid temperature must be maintained below a safe temperature
limit, usually about 475 F. in order to insure a safe and
efficient cooking operation.
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In accordance with one aspect of the present
invention a control circuit for pyrolyticaly cleaning heating
elements is provided. The circuit is comprised of a power
supply; actuable relay means in the circuit for connecting
and disconnecting the heating elements to the power supply;
timing control means associated with the relay means for
cyclically actuating and deactuating the relay means to
gradually raise the temperature of the heating elements; and
switching means in thermal communication with the heating
elements for sensing the temperature of the elements and for ;:-
overriding the relay means to disconnect the heating elements : -
from the power supply when the elements reach a predetermined
temperature.
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BRIEF DESCRIPTION OF THE DRAWINGS
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The present invention taken in conjunction with the
invention described in copending Canadian patent.application
Serial No. 220,908 which was filed on 27 February 1975 will
be described in detail hereinbelow with the aid of the
accompanying drawings, in which:
FIGURE 1 is a top perspective view of a frying
apparatus incorporating a preferred embodiment of the present
invention;
FIGURE 2 is a top perspective view of the frying
apparatus of Figure 1 with the heater coils in raised position;
FIGURE 3 is a side elevational partial view of the
frying apparatus of Figure l;
FIGURE 4 is an enlarged fragmentary plan view of
the lower coil of the frying apparatus of Figure l;
FIGURE 5 is a sectional front view of the lower
coil of Figure 3 taken along line 5-5; and
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FIGURE 6 is a schematic diagram of the control
~, circuitry for the frying apparatus of Figure 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to Figures 1 and 2, a frying apparatus
~5 10 includes a rigid housing structure 12 supporting an upper
panel 14. A cooking basin 16 is provided in the top of housing
structure 12 behind front panel 14 for containing cooking fluid
normally used in deep fat frying. A back panel 18 extends
; ¦ vertically above the rear of cooking basin 16. A suspension
plate 20 is connected to extend horizontally across back panel
18 just above cooking basin 16. Plate 20 is positioned to
suspend wire mesh cooking baskets (not shown) over the cooking
fluid of basin 16.
A plurality of heating elements 22 are suspended
~15 horizontally near the bottom of cooking basin 16. Elements
~, 22 include two upper coils 24 and 26 and a lower coil 28.
1 Coils 24, 26 and 28 are conventional heating colls of the type
'-; used in frylng apparatus. Preferably the coils are made of
solid tubular heat conducting material. Alternately,
convention tubular sheath enclosed coils or any other
type of heat generating coils may be used. Each
,
coil is mounted on two cross bar pieces 30 and 32 by suitable
, ¦ straps 34. A pair of connecting rods 36 are integral with each
coil and extend vertically up the back of cooking basin 16 to ;
~5 ¦ attach to a pivot piece 38 at the base of back panel 18. A
i ¦ lever arm 40 extends vertically down the back of cooking basin
;1 l 16 and thence horizontally to pivotally connect to one of cross
` bar 32 at pivot point 42. A loop 44 is provided at the top
~, of lever arm 40 for pulling the arm 40 to tilt heating elements
;~, 30 22 upward out of basin 16 as shown in Fisure 2.
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As best seen in Figure 3, an operating thermostat 50
is mounted on a sloping inner wall 15 of upper panel 14 and
extends horizontally into the upper front portion~of cooking
basin 16. Thermostat 50 may be a differential expansion type
having a separate heater 51 mounted below thermostat 50 on wall
15. The structure and function of thermostat 50 and heater 51
are more fully shown and described in United States Patent No.
3,911,250 which issued on 7 October 1975.
A temperature selector dial 52 is mounted on the
front of upper panel 14 for selecting the desired temperature
for the operating thermostat 50. A heater light 54 is provided
at the center of selector dial 52 to indicate the on-off status
of the heating elements. A main on-off switch 56 is mounted
on the right side of selector dial 52 and is provided with
a main indicator light 58 therein. A high limit light 60 is
mounted on the left side of selector dial 52 to indicate shut
down of the heater elements because of excessive temperatures.
Figures 3, 4 and S disclose the heating elements 22
and associated thermostats in more detail. Coils 24, 26 and
g 20 28 are shown in cross-section as preferably of solid heat
~, conducting material. A first high limit thermostat 66 is
,~ connected above one side of lower coil 28 by a metal strap
68. A second high-limit thermostat 70 is further mounted
above the other side of coil 28 by a metal strap 72. Thermostats
66 and 70 are preferably pressure bulb thermostats being
fil~ed with a temperature sensitive liquid, such as mercury,
and having capillary tubes 67 and 71 running along lower coil
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', 28 and connecting rods 36 to back panel 18. Both thermo-
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stats have a "fail-safe" construction so that if the bulb or
capillary leaks the thermostat switch will open. A manual
reset switch (not shown) is provided in connection with thermo- -
stat 70 to prevent inadvertent automatic start-up after thermo-
stat 70 has opened the circuit. The reset switch includes a
_ hold-in relay which must be reset by hand before the circuit
will be reactivated. First high-limit thermostat 66 is spaced
further closer to lower coil 28 than second high-limit thermo-
stat 70. Thermostat 66 is in series with operating thermostat
50 and functions during the cooking process to turn off
` heater elements 22 if the temperature of the cooking fluid
exceeds a critical temperature, normally about 475 F, to
prevent danger to the operator and damage to the equipment.
Second high-limit thermostat 70 is positioned further away from
- 15 coil 28. Thermostat 70 operates as a back-up to thermostat
6~ to cut off the heaters if the safe operating temperature :
is exceeded. Furthermore, second high-limit thermostat 70
is used during pyrolytic cleaning of the coils of heating
elements 22 to turn off the elements after heating to a higher
temperature. When the heating elements 22 are tilted upward
out of the cooking fluid as shown in Figure 2, first high-
limit thermostat 66 is disconnected from the circuit and second
il high-limit thermostat 70 allows the coils of elements 22 to
J reach a much higher temperature, about 900 to 1000 F, before
~ 25 being shut off.
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As shown in Figure 5, the distance Dl between first
hiqh-limit thermostat 66 and low~r coil 28 is somewhat less than
the distance D2 between second high-limit ~hermostat 70 and lower
coil 28. The distance Dl is critical for proper shut-down of
the cooking circuitry at very low oil levels, especially when
the oil level drops below the coils, as required in safety
testing. Distance Dl must be accurately determined or fire
may result. Distance D2 is also critical during pyrolytic
cleaning. If D2 is too great, excessive element temperatures
!0 may damage the coils during burn-off. On the other hand, if
second high-limit thermostat 70 is placed too close to the
coils 28, premature shut-down of the heating elements 22 may
occur. Distances D1 and D2 are not as critical during cooking
;~because the cooking fluid conducts the heat more readily. Al-
though first high-limit thermostat 66 is closer to the coils, ¦
;it~has been found that second high-limit thermostat 70 will ¦
;shut off the coils at about the same time. Both thermostats
~66~and 70 are located above the heating elements in order to
obtain accurate readings because of convection currents of the
0 ~ cooking fluid and the atmosphere.
1 -I Figure 6 discloses the electrical circuitry 78 employed
for automatically regulating and limiting the cooking and cleaning
Iproaesses using apparatus 10. Electrical inputs 80, 81 and 82
are connected to a contactor having contacts 84a, 84b,
84c, 84d and a reverse contact 84e. That contactor in turn is
`~connected through a contactor having contacts 86a, 86b and
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86c, to heating elements 22 comprising upper coils 24 a~d 26
and lower coil 28. A contactor coll 88 is positioned to activate
contacts 84a, 84b, 84c, 84d and 84e, and a contactor coil 90
activates contacts 86a, ~6b and 86c. A clrcuit breaker 92 lS
r~ connected between lnput llne 82 and circultry 78 to prevent -`
damage from overloading. The other side of circuit ~reaker 92
is connected in parallel to contact 84d and a reset switch
96. An on-off switch 56 is provlded at the output of contact
~` ~4d and switch 96. Main indicator light 58 is connected
between the on-off switch 56 and neutral. The second high-limit
thermostat 70 is also connected between reset switch 96 and
; neutral through contactor coil 88.
The other side of on-off switch 56 is connected to
~' a two-way function switch 98 having an upward position with
post 100 for a cooking function and a downward position in
~! contact with post 102 for a cleanin~ function. Connected to
post 100 in series are first high-limit thermostat 66 and operatin~
thermostat 50. On the other side of thermostat 50, connected in
- parallel, are a biasing heater 104 for use in conjunction with
operating thermostat 50, heater light 54, and contactor coil
90. Connected to post 102 of function switch 98 is a two-
`i way percentage relay switch 106 having an upward burn-off
~, position when in contact with a post 108 and a downward delay
position when in contact with post 110. Connected to post
110 is a heater resistor 112 which operates in association
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1~39785
with cielay relay switch 106. Heater resistor 112 lS in turn
connected to neutral. Reverse contact 84e is connected between
circuit breaker 92 and neutral through high-limit light 60
and closes whenever thermostats 6~ and 70 open contacts 84a,
84b, 84c and 84d because of a high temperature condition.
In operation, power, usually 120 volts, is impressed
on control circuit 78 through inputs 80, 81 and 82. Circuit
breaker 92 is normally closed. When reset switch 96 is depressed,
contactor coil 88 is activated to close contacts 84a, 84b,
84c, 84d and to open reverse contact 84e. A cir-
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cuit is maintained through second high-limit thermostat 70 by ~
; contact 84d which will continue to hold until interrupted by a ~;
- ~ower loss or a high temperature condition opening thermostat
70. The frying apparatus 10 is placed in operation by closing
on-off switch 56. When heating elements 22 are positioned in
cooking basin 16, switch 98 is in the upward cooking position
in contact with post 100. Activatinq switch 56 therefore energizeS
contactor coil 90 closing contacts 86a,86b and 86c and supplying power
to heating elements 22. Thermostats 66 and 50 are also actuated
as well as biasing heater 104. ~he selected cooking temperature
on selector dial 52 is maintained by ~operating thermostat 50
which turns heating elements 22 off and on.
` Should operating thermostat S0 fail for any reason,
first hiqh~limit thermostat 66 will cut off contactor coil 90
and open contacts 86a, ~6b, and 86c shutting down heatlng elements
2~ as soon as a
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¦~preselec ed ~emperature has been reached. As previously men- l
¦tioned, the critical temperature is nor~ally considered to ~
¦be around 475 F. above which danger or damage may occur. If
¦contactor coil 90 welds or sticks shut, second high-limit
thermostat 70 ~ill open, dropping out contactor coil 88 and
¦open contacts 84a, 84b, 84c and 84d to turn off heater elements
¦22 an.l prevent fire or damage. ~
¦ When it is desired to clean the coils, the end loop ;
44 of lever arm 40 is grasped and pulled upward to tilt heating
¦elements 22 out of the cooking fluid to a vertical position
¦as shown in Figure 2. This action automatically throws functiQn
¦switch 98 do~mward to contact post 102 in the cleaning position.
Percentage relay switch 106 is normally downward against post
110 in the delay position. A closed circuit is thus formed by-
passing operating thermostat 50 and first high-limit thermostat
66. The temperature of heating elements 22 is allowed to rise
~ to a pyrolytic burn-off level o'f about 600Dto 900 F. During this
A rise in temperature, percentage relay switch 106 cycles between
its burn-off position in contact with post 108 and its delay
position in contact with post 110. After remaining ~n the
delay position for about 20 seconds, heater resistor 112 reaches
a temperature sufficient to throw the contacts of switch 106 to
`~, post 108 thereby energizing contactor coil 90 and heating elements
22. After cooling off, delay relay switch 106 again drops to
, 25 make contact with lowex post 110 in the delay position, turning
off heating elements 22 and reactivating heater resistor 112.
This cycling a~tion provides for an approximate on time of 40%
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for the heater elemerlts 22 and biasing heatcr 104 thereby
slowing the rate of temperaturc rise of the heater elements
` 22.
In this manncr, the pyrolytic burn-off of accumulated
dirt, food and other debris on heater elements 22 is accom-
plished gradually and no risk is ta~en that damaging temperatures
may be inadvertently reached. After several minutes of pyro-
lytic burn-off, the heater elements 22 will reach a temperature
sufficient to open second high-limit thermostat 70 and deactivate
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L0 contactor coil 88. Contacts 84a, 84b, 84c and 84d are
thereby opened, turning off heating elements 22. As previously
mentioned, thermostat 70 is provided with a reset switch which
cannot automatically restart the circuit but must be manually
reset. Ncrmally sufficient burn-off has occurred by the time
l~ thermostat 70 opens the circuit that the cooking process may
; be resumed. Heating elements 22 are allowed to cool and then
~ are returned to the cooking fluid by pushlng lever arm 40 down.
`~ Reset switch 96 is then depressed to again begin the normal
q cooking operation.
depressed to again begin the normal cooking operation.
It is understood from the foregoing description that
the control system of the present invention provides several
important advantages over other systems. By providing for
l pyrolytic cleaning of the heating coils, considerable delay,
'~ 5 time and effort are eliminated. The coils need not be cooled
down in order to clean the coils. The high-limit thermostats
connected directly to the heating coils provide a simple means
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for protecting the coils during the cooking and cleaning pro-
cesses. As previously indicated, the same type thermostats may
be used for both applications by simply placing~them different
distanccs from the heating coils and setting them to cut off ~-
at different te~peratures. By using these two therm~stats, the
possibility of dama~e to the coils or other equipment is avoided.
Moreovcr, the automatic operation of the thermostats
eliminates any need for the operator to reach across the cooking
fluid during cooking or near the heating coils during the pyro- ;
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lytic cleaning to adjust or turn off controls thereby risking
injury~ The use of the thermal percentage delay relay insures
that the temperature of the heating elements will not rise too
` rapidly during the pyrolytic cleaning phase but will gradually ~
burn off the accumulated debris from the coils before being `
~ turned off by the second high limit thermostat. The manual
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reset circuit for the high-limit thermostats provides a fail-
safe feature to prevent automatic restart when not desired.
Moreover, the automatic operation of the function switch in
response to movement of heating coils out of or into the
cooklng basin eliminates the need for further operator action.
Although a particular embodiment of the invention has
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been illustrated in the accompanying drawings and described in
the foregoing detailed description, it wiil be understood that
the invention is not limited to the embodiment disclosed but is
capable of rearrangement, modification and substitution without
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departing from the spirit of the invention.
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