U.S. patent number 3,639,727 [Application Number 05/058,793] was granted by the patent office on 1972-02-01 for positive temperature control door lock system.
This patent grant is currently assigned to Westinghouse Electric Corporation. Invention is credited to James A. Leach.
United States Patent |
3,639,727 |
Leach |
February 1, 1972 |
POSITIVE TEMPERATURE CONTROL DOOR LOCK SYSTEM
Abstract
An oven upper temperature safety control is provided in the
instant invention by utilization of the door lock thermostat during
the cooking modes of the oven to prevent the temperature of the
oven reaching an unsafe level if failure of the temperature sensor
control system occurs. The operation of the door lock thermostat as
a temperature safety control is positively interrupted by actuation
of the door locking system for the oven.
Inventors: |
Leach; James A. (Shelby,
OH) |
Assignee: |
Westinghouse Electric
Corporation (Pittsburgh, PA)
|
Family
ID: |
22018966 |
Appl.
No.: |
05/058,793 |
Filed: |
July 28, 1970 |
Current U.S.
Class: |
219/491;
219/413 |
Current CPC
Class: |
G05D
23/24 (20130101); F24C 14/02 (20130101); G05D
23/1909 (20130101) |
Current International
Class: |
F24C
14/02 (20060101); F24C 14/00 (20060101); G05D
23/20 (20060101); G05D 23/24 (20060101); H01h
037/00 () |
Field of
Search: |
;219/412,413,491 |
References Cited
[Referenced By]
U.S. Patent Documents
|
|
|
3549862 |
December 1970 |
Holtkamp et al. |
3484858 |
December 1969 |
Jordan et al. |
|
Primary Examiner: Gilheany; Bernard A.
Assistant Examiner: Bell; F. E.
Claims
I claim as my invention:
1. An oven system having cooking and cleaning cycles including:
a. a cooking actuating circuit including a pair of relays actuated
by a temperature control means,
b. a clean actuating circuit including means for shorting out said
temperature control means,
c. a door lock thermostat means disposed in series relationship in
said cooking actuating circuit,
d. movable switch means for bypassing said door lock thermostat
means when said oven system is in said cleaning cycle,
e. a latch arrangement for said oven system, and
f. said movable switch means being moved to bypass condition by
said latch arrangement being moved to locked condition.
2. An oven system having cooking and cleaning cycles including:
a. a cooking actuating circuit including a pair of relays actuated
by a temperature control means,
b. a clean actuating circuit including means for shorting out said
temperature control means,
c. a door lock thermostat means disposed in series relationship in
said cooking actuating circuit,
d. movable switch means for bypassing said door lock thermostat
means when said oven system is in said cleaning cycle, and
e. said movable switch means includes
at least a pair of simultaneously actuated switches disposed in
series relationship.
3. The combination set out in claim 2 wherein said oven system
includes:
a. a three line supply, one of said lines being neutral and the
other of said lines having a potential,
b. said door lock thermostat means being disposed between one of
said lines having a potential and said cooking actuating
circuit.
4. The combination set out in claim 3 wherein:
a. one of said switches is in series circuit relationship with a
timer switch means.
5. The combination set out in claim 4 wherein:
a. the other of said switches is in series relationship with said
one of said switches.
6. The combination set out in claim 5 wherein:
a. the other of said switches in one position being in a noncurrent
carrying condition.
7. The combination set out in claim 6 wherein:
a. another thermostat means is provided for said oven system;
b. said thermostat means limits the top temperature of the oven
system in the clean cycle.
8. The combination set out in claim 6 wherein:
a. said door lock thermostat means limits the upper temperature of
the oven in the cooking cycle to a temperature below the flash
point of any residue present in the oven cavity.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to ovens and, more particularly, relates to
an oven upper temperature safety control system which provides a
safety control for too high oven temperatures during the cooking
modes of the oven.
2. Description of the Prior Art
Oven control relays used in self-cleaning ovens are normally of an
expanding wire thermal type and when these fail, they normally fail
in a power-on position, if defective as installed or if the defect
is developed during their operation. Failure of such a relay during
a cooking operation of the oven, denies temperature control to the
oven sensor permitting the oven to heat in an uncontrolled
manner.
If such a failure occurred during a cooling operation, the oven
temperature might well rise to a level well above the flash point
of any residue present in the oven cavity. Under such
circumstances, if the door to the oven was opened to thereby
provide a readily reachable oxygen supply, a flash fire could
result.
Furthermore, such an oven, when set in a cooking mode and having
its relays fail (in a power on position), might well reach the
saturation temperature of approximately 1,280.degree.; and, at this
temperature, even without an opening of the oven door, provide an
outside temperature of the range surface which is at an unsafe
level.
Accordingly, it would be desirable to provide a positive safeguard
within any given oven system to prevent an unsafe temperature level
while the oven is in a cooking mode, in the event that the oven
control relays of the oven system failed in their power on
position.
SUMMARY OF THE INVENTION
An oven control system is provided in which a door lock thermostat
is placed in series with one of the main power leads, so that
excess temperatures within the oven cavity will cause the
thermostat to operate to open the circuit and prevent additional
power being supplied to the bake element. This thermostat is
bypassed by the action of latching the oven door so that control of
the oven in the clean phase is accomplished by a clean thermostat
which sets a high temperature limit for the oven cavity in this
mode. By this tandem thermostat arrangement, a positive control is
provided for the temperature in the oven cavity whether the oven
system is in the broil, bake or clean modes of operation.
Desirably, in the cooking modes of operation when the door is not
locked, the controlling thermostat opens between 560.degree. and
600.degree. F. to limit the top temperature to which the oven
cavity may be subjected.
DRAWING DESCRIPTION
For a better understanding of the invention, reference may be had
to the preferred embodiment, exemplary of the invention, shown in
the accompanying drawings, in which:
FIG. 1 is a schematic view of the oven system which embodies the
instant invention; and
FIG. 2 is a table which identifies which contacts of the selector
switch means are closed and in electrical contact for particular
settings of the selector switch means.
PREFERRED EMBODIMENT OF THE INVENTION
In FIG. 1, the control system for the oven of my invention is
generally indicated by the numeral 10. An oven selector switch 12
may be set from an off position (shown in FIG. 1) to a position
where a number of interrelated contacts within the selector switch
may be placed in contacting or noncontacting position. The external
terminals of the selector switch are identified by letter reference
in FIG. 1 which correspond to the letter references across the top
of the table of FIG. 2. FIG. 2 generally discloses the contacting
elements which are engaged and provide a flow of current by the
indication "X" for each mode in which the oven may be placed.
A temperature controller 14 for the oven is illustrated in the
bottom portion of FIG. 1 and is of the general bridge character and
includes an auxiliary relay 16 which is normally controlled in
accordance with operation of the temperature controller 14. The
auxiliary relay switch means 16 is normally disposed in a leg of
the temperature controlling means 14 and includes a pair of
switches 18 and 20 which conventionally controlled in accordance
with the operation of the temperature controller 14.
Since it is common practice in connection with heat cleaning ovens
to provide means to ensure that the oven door is latched shut
before a heat cleaning cycle is initiated and is in a condition to
permit locking of the door as the temperature in the oven rises
above the heat cleaning range a lock assembly is represented only
by the dash line rectangle 22 and its control, in part, by the
operation of a latch handle on the oven door is diagrammatically
illustrated. Such a latching arrangement is of the same general
character as disclosed in U.S. Pat. No. 3,387,874, owned by a
common assignee, so that no further description of such a door
locking arrangement is given in this application.
A source of electrical power for the oven and control system is
provided by a conventional three-line source in which a nominal
240-volt alternating potential exists between the power connections
denoted L1 and L2 and with 120 volts alternating potential between
these hot lines and the neutral designated N.
Temperature controller 14 is of the general type described in Baker
U.S. Pat. No. 2,962,575 and includes a hot wire which senses the
temperature in the oven and actuates the switches 18 and 20 to
close whenever the temperature sensed is below the temperature to
which the temperature controller is set. Upon deenergization, the
hot wire 24 cools and gradually permits these two switches to open.
Delay in opening of the switches after relay deenergization gives
time for a holding circuit to be established while the switch means
is closed.
The temperature controller 14 is connected in a temperature
controller circuit 26 which includes a secondary 28 of a
transformer 30 during the normal cooking operations (i.e., bake,
time bake, broil and auxiliary broil).
A temperature control bypass circuit 32 includes a pair of leads 34
and 36 which extend from the secondary 28 of the transformer 30 and
the oven temperature controller 14, respectively, and are in
electrical connection with a pair of contacts A and H formed in the
selector switch 12. Since the terminals A and H are not in
electrical carrying capacity during the aforementioned cooking
operations, the oven temperature controller 14 is energized through
the temperature controller circuit 26 that also includes a pair of
leads 38 and 40, with the lead 38 being connected to the secondary
28 of the transformer 30 and the lead 40 being connected to the
oven temperature controller 14. The temperature controller circuit
26 may normally be an 11-volt system, however, differing voltages
may be used even though an 11-volt system was utilized and to carry
out the invention.
An energizing circuit 42 for the transformer 30 includes a lead 44
which extends to and is an electrical connection with a contact of
an ambient thermostat switch 46 that has its other contact
connected through a lead 48 to neutral N. The ambient switch 46 is
normally in a closed position unless the ambient temperature
outwardly of the oven exceeds a certain value say, for example,
130.degree.. Thus, a closed circuit network is provided between
neutral and the primary winding 50 of the transformer 30. The
opposite side of the energizing circuit 42 for the transformer 30
is completed by a lead 52 which extends to the terminal X on the
selector switch 12. In the bake, latch, broil and auxiliary broil
modes of operation, a circuit is completed to terminal L3 (FIG. 2)
and from it to L2 voltage so as to energize the primary winding 50
of the transformer 30 and thereby energize the temperature
controller 14.
During the clean operation of the oven, the transformer 30 is
bypassed by a lead 54 which is electrically connected to the lead
52 on the L2 side of the primary winding 50, with this lead
extending to a timer switch 56 which is actuated to an open
condition by a timer motor 58 after a preset time of the oven in
the clean mode. When the timer switch 56 is in closed position and
the latch in latched position, a pair of solenoid-operated switches
60 and 62 are placed in one of their alternate positions indicated
by dotted lines in FIG. 1. In this position, (only attainable when
the latch handle is in the latch position), switch 60 provides for
a current flow from line L2 through a lead 64. Switch 62 in its
dotted line position obtains its current from a lead 66 that
extends to the L2 side of the supply. Since the contacts A and H
are placed in a current carrying capacity in the clean mode, the
oven temperature sensor 14 is bypassed by bypass circuit 32. This
shorts out the internal switch of the temperature controller 14
which normally opens and closes in accordance with the differential
between the sensed temperature of the temperature controller and
the oven temperature. Thus, a low voltage (11 volts) is applied
directly across the thermal delay element 24 so that the relay
switches 18 and 20 are maintained in their closed current carrying
condition.
Although the operation of the switches 60 and 62 has only been
detailed electrically it should be clear that they are physically
interrelated to the latching arrangement so that movement of this
arrangement into locked condition causes the switches to move from
their normally full line positions to the dotted position
illustrated in FIG. 1. Such could be accomplished easily, for
example, by placing these switches in a position where their switch
blades would be physically contacted and moved by a solenoid
plunger 63 of the operating latching arrangement.
The relay switch 20 is in circuit with a broil element 68 through a
lead 70, with the opposite side of the broil element 68 attached to
lead 72. Lead 72, in turn, is electrically connected to a lead 74
which extends through a pulse switch 76 that provides a pulsing
current flow to the broil element. Since the contacts L3 and S are
in a current carrying capacity during the clean mode of operation
of the oven, current is provided across L1 to L2 through the broil
element 68 to aid in cleaning of the oven. The pulsing of a switch
76 provides a cyclic energization of the broil element 68 to limit
the total time in which the broil element 68 is energized.
A clean thermostat 78 is also disposed in the circuitry just
described so as to limit the top temperature to which the interior
of the oven is subjected. This thermostat is normally set at about
1,050.degree. F. and thus ensures that all the combustibles that
are burnable within the oven enclosure are fully consumed. At the
upper temperature limit the thermostat 78, of course, opens so as
to remove any electrical energization from the broil element 78.
Interruption is accomplished because no circuit is then completed
between line L2 and L1 and the fact that the switches 60 and 62 are
in their dotted line positions has no effect in providing an energy
source for the broil element 68. The relay switches 18 and 20,
however, remain closed so that a reduction in temperature and a
consequent reclosing of thermostat 78 again provides current to
broil element 68. The cleaning cycle is permanently terminated by
the opening of timer switch 56 which removes current from primary
50, thereby opening-relay switches 18 and 20. A clean cycle then
may not be again initiated unless the selector-switch and latching
mechanism are moved through the latch and clean modes and after
oven temperature has fallen below door lock temperature.
The bake cycle for the oven is initiated by current flow from line
L2 through the relay switch 18 and from thence into a lead 80 which
extends to and is in electrical connection with a bake element 82.
Since the contacts B and L1 in the selector switch 12 are in a
current carrying condition in this mode of operation, L1 is
connected to the other side of the bake element 82 by means of a
lead 84 extending to the L1 side through relay 20.
A control clock 86 is also provided to control a bake cycle of a
set duration of time. This clock operates in a conventional manner
and is connected across line L2 to neutral N, when a pair of
contacts 88 and 90 within the clock are in engaged position. With
these contacts closed, the primary 50 of the transformer 30 is also
provided with current so as to actuate the temperature controller
14. With the contacts 88 and 90 in a nonelectrical carrying
capacity, (at the end of the time period set) the primary winding
50 also has no current maintained in it so that the temperature
control sensor is disabled. With the primary coil 50 disabled and
the temperature sensor 14 in an unenergized state, both the relay
switches 18 and 20 move to open position so that no current is
provided to the bake element 82 thereby terminating a time bake
cycle.
In the auxiliary broil mode of operation (FIG. 2) the contacts L3
and T are in electrical carrying capacity, placing the broil
element 68 across the lines L1 and L2 and at the same time, the
contacts L1 and M are in electrical current carrying capacity
placing the auxiliary broil element 92 in an energized condition so
that the elements 68 and 92 both contribute to the cooking of the
food contained in the oven.
An oven pilot light 94 is also provided to indicate operation of
the oven, with this pilot light in an energized condition for all
modes of operation of the oven other than the latch and the off
position. This pilot light is simply connected across neutral N and
the supply line L2 through a lead 96 and the contacts P and L2,
with the contact L2 having a lead 98 extending to neutral N.
Insofar as related, except for the solenoid-operated switches 60
and 62, the oven circuit 10 is substantially conventional and
operates to provide fairly satisfactory temperature control
operation. However, the switches 18 and 20 are subject to failure
and normally would fail in an ON position so that the temperature
sensor 14 would be unable to actuate these switches to open
condition. In order to provide an upper temperature safety feature
for the foregoing oven circuitry 10, a door lock thermostat 100 is
placed in series with the supply line L2 and is connected to a lead
102 that extends to and is in contact with the switch 62 when it is
in its full line position. By this arrangement, then, current flow
from supply L2 may not pass inwardly into the oven system 10 unless
the thermostat 100 is in a closed condition or unless the switch 62
is in latching position (clean mode). This thermostat is provided
to open at a temperature of 560.degree. to 600.degree. F. For the
bake, broil auxiliary broil and time bake modes of operation of the
oven, then, the thermostat 100 provides a safety feature to prevent
any of these modes from attaining a temperature which would tend to
combust any flammable products within the oven. Of course, in the
clean or latch mode of operation, of the oven system 10, the door
lock thermostat 100 is bypassed and clean thermostat 78 provides,
the upper temperature limit of 1,050.degree. F. Since the switch 62
is in its dotted line position and lead 66 bypasses thermostat
100.
In review, it should be emphasized that the door lock thermostat
100, because of its position in the described circuitry, provide a
safety temperature control for limiting the upper temperature of
the oven 10 for all the cooking modes of it and that this
thermostat is bypassed by the lead 66 and switch 62 only when the
solenoid plunger 63 is actuated to the latch and then clean mode.
With the oven 10 in the clean mode, the clean thermostat 78 still
provides an upper temperature limit for the oven 10, but one which
is significantly higher than that afforded to the oven 10 in the
cooking modes. Further, when the oven 10 is in the clean mode of
operation, door lock thermostat 100 still provides for positive
locking of the latching arrangement 22 since opening of its
contacts prevents removal of the solenoid plunger 63 from blocking
interference with the unlatching functioning of the latching
assembly 22.
It should be obvious from the foregoing description that an oven
system has been provided which provides a safety feature not found
in the prior art and that such is extremely important from a safety
standpoint. Further although only a single embodiment of the
invention has been described, it would be clear to one skilled in
the art that many minor modifications could be made therein without
departing from the spirit of the invention as disclosed in the
foregoing specification.
* * * * *