US3403244A

US3403244A - Low heat control system for infrared surface heating unit

Info

Publication number: US3403244A
Application number: US489242A
Authority: US
Inventors: Donald C Siegla
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1965-09-22
Filing date: 1965-09-22
Publication date: 1968-09-24
Anticipated expiration: 1985-09-24

Description

P 1968 D. c. SIEGLA 3,403,244

LOW HEAT CONTROL SYSTEM FOR INFRARED SURFACE HEATING UNIT Filed Sept. 22, 1965 2 Sheets-Sheet .l.

a q- I m m I K O i N 3 a w c N R N 2 INVENTOR.

BY QCm His Attorney Filed Sept. 22, 1965 p 1968 c. SIEGLA 3,403,244

LON HEAT CONTROL SYSTEM FOR INFRARED SURFACE HEATING UNIT 2 Sheets-Shet 2 INVENTOR. Donald G. .Sieg/a Qcgl/m His Af/omy United States Patent O 3,403,244 LOW HEAT CONTROL SYSTEM FOR INFRARED SURFACE HEATING UNIT Donald C. Siegla, Dayton, Ohio, assignor to General Motors Corporation, a corporation of Delaware Filed Sept. 22, 1965, Ser. No. 489,242 3 Claims. (Cl. 219-448) ABSTRACT OF THE DISCLOSURE A surface heating unit control for an unsheathed resistance element energizable to a temperature exceeding 1500 F. The control includes first switch means for selectively energizing equal parts of the resistance element in series and parallel electrical relationship to produce a first control of wattage output. Second switch means connect the series or parallel arranged parts of the resistance element across either a 115 voltage source or a 230 voltage source to produce another wattage control. A 'presettable infinite heat switch is included to vary the wattage output of part of the resistance for still further control.

This invention is directed to surface heating units of the infrared type.

In infrared surface heating units, it is desirable to include a high energy electrical resistance element that is self-heated substantially instantaneously into a high temperature, infrared emissive range when connected across a power source. Such units thereby act to immediately raise the temperature of a utensil supported thereon. To control the wattage output from such units, it is desirable to use a low-cost pulsing type controller. It has been found, however, that even at low temperature settings of such controllers, the instantaneous energy output from the unit can cause burning or scorching of foods because of fast self-heating response of the high energy resistance element in the infrared surface unit.

An object of the present invention, therefore, is to control the output wattage of an unsheathed high energy resistance element in an infrared surface heating unit in a manner to eliminate utensil scorching at low heat operation of the unit.

A further obiect of the present invention is to modulate the energy output from an infrared surface heater unit by an improved controller including an energy pulsing switch and means in association with the pulsing switch to prevent cycling an electrically energizable, high energy resistance element between full on and full off.

A further object of the present invention is to modulate the wattage output of an infrared type surface heater unit by means for pulsatingly controlling the power thereto and means for selectively maintaining a portion of the resistance element continuously energized to prevent cycling of the resistance element between full on and full off and wherein the continuously energized portion of the resistance element serves to illuminate the surface unit at all times.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein a preferred embodiment of the present invention is clearly shown.

In the drawings:

FIGURE 1 is a diagrammatic view of an electrical circuit for an infrared surface heating unit including the present invention;

FIGURE 2 is a schematic representation of the circuit in FIGURE 1 at a first control setting;

FIGURE 3 is a schematic representation of the circult in FIGURE 1 at a second control setting;

I 3,403,244 Patented Sept. 24, 1968 FIGURE 4 is a schematic representation of the circuit in FIGURE 1 at a third control setting; and

FIGURE 5 is a schematic representation of the circuit of FIGURE 1 at a fourth control setting.

Referring to FIGURE 1, an improved infared surface heating unit and control combination are set forth including a surface heating unit 10 having an upper utensil supporting plate 12 of infrared transmissive material 13 and a reflector plate 14 having an infrared reflective surface 16 thereon. The plates 12, 14 are spaced apart and have a high energy electrical resistance element 18 disposed therebetween out of direct heat transfer contact with the plates 12, 14. The resistance element 18 includes a first portion 20 and a second portion 22 which are both energizable into a high temperature infared emissive range. The radiation from the element 18 either passes directly through plate 12 or is reflected off the surface 16 and through plate 12 for heating utensils supported thereon.

For a more specific explanation of the operation of a surface heating unit including elements as set forth above, reference may be had to my copending United States application, Ser. No. 429,305, filed February 1, 1965, now U.S. Patent No. 3,345,489, issued Oct. 3, 1967, relating to an infrared surface heating unit wherein there is a detailed explanation of the compositions of the plates 12, 14 and the high temperature electrical resistance element 18 which, as noted, is energizable into a temperature range of from 1500 F. to 2000 F.

The high temperature resistance element 18, if desired, can be constructed of tungsten so long as the envelope formed by the utensil supporting plate and the reflector plate 14 are evacuated and sealed. High energy electrical resistance elements for purposes of the present discussion are characterized as electrically energizable resistance elements that are self-heated when connected across a power source without any appreciable time lag as is found in the case of sheathed resistance elements that are used in conventional surface heating units.

When such electrical resistance elements are energized full on and full off, there are large changes in the in: stantaneous wattage output therefrom that can cause burning or scorching of substances being heated within a utensil supported on the unit.

In accordance with certain principles of the present invention, to avoid this problem, the illustrated surface heating element 10 is associated with a controller 24 that includes a single-pole, double-throw selector switch 26 for selectively connecting the resistance element 18 across a high voltage and a low voltage power source. The unit further includes a double-throw, double-pole switch 28 that selectively connects the

portions

20, 22 of the re sistance element 18 in series or parallel relationship across either of the low or high voltage sources. Additionally, the controller 24 includes an infinite heat switch 30 of the energy pulsing type that pulsatingly energizes the portion 20 of the resistance element 18 at the various control settings.

More particularly, the controller 24 includes a manually rotatable knob portion 32 having suitable indicia thereon indicating varying temperature control points including a high, medium high, medium, low, and warm temperature settings. The controller knob 32 is shown in an off position with respect to a suitable indicator 34. In the illustrated arrangement the knob 32 is connected to a rotatable shaft 36 on which is connected an on-off cam 38, a cam 40 for controlling the position of selector switch 26, a cam 42 for controlling the position of the selector switch 28 and a cam 44 for conditioning the infinite heat switch 30.

When the control knob 32 is moved to a temperature setting between medium high and high, cam 38 positions a contact carrying arm 46 of a line switch 48 to close first pair of

contacts

50, 52 and a second pair of

contacts

54, 56 thereof. An indicator lamp circuit is thereby completed from wire L of a suitable alternating current power source through a conductor 58, the closed

contacts

50, 52, the conductive arm 46, the closed contacts 5456, a conductor 60 thence through a lamp 62 to a conductor 64 electrically connected to a wire N of the power source. In the illustrated arrangement wires L N constitute a low-voltage power source of 115 volts.

Additionally, the

surfaces

40a, 42a and 44a on

earns

40, 42, 44, respectively, are positioned to complete a high wattage output circuit through resistance element 18 which is generally set forth in FIGURE 2 as having the

resistance element portions

22, 20 each connected in parallel across wire L and a wire L of the power source that in the illustrated arrangement constitutes a high voltage source of 230 volts. Moreover, the resistance element portion 22 is continuously energized across the high voltage power source and the resistance element portion 20 is pulsatingly connected across the same power source through pulsating contacts of the infinite heat switch 30 to be described. When the

resistance element portions

20, 22 each has a maximum wattage output of 1000 watts when connected across a 230-volt source, by virtue of the circuit connection in FIGURE 2, the infrared surface heating unit 10, at a setting between medium high and high, will have a wattage output between 1000 watts and 2000 watts. The circuit of FIGURE 2 as described above is completed from line switch 48, the contact arm 46 thereof, a conductor 66 thence through a conductor 68 and resistance element portion 22 to a conductor 70 that electrically connects to a first contact 72 of the switch 28 that is in contact with a movable contact 74 carried by a movable electrically conductive contact carrying arm 76 of the switch 28 which in turn is connected by a conductor 78 through an electrically conductive movable contact carrying arm 80 of the switch 26. A continuous energization circuit for the resistance element portion 22 is then completed through a movable contact 82 and a fixed contact 84 of the switch 26 which is connected electrically by a conductor 86 to wire L The pulsating energization circuit for the resistance portion 20, as discussed with reference to FIGURE 2, is shown in FIGURE 1 as a parallel circuit to the energization circuit for resistance element portion 22 and as including a conductor 88 electrically connected to the conductor 66 thence through a heater 90 of the pulsing switch 30 that is located in heat transfer relationship with a polymetallic, movable contact carrying arm 92 that is biased to a greater or lesser degree by the cam surface 44a on cam 44 against a fixed contact 94 of the switch 30. When the pulsing switch 30 is on, a movable contact 96 on the polymetallic element 92 is in electrical contact with the fixed contact 94 to complete the energization circuit for resistance element portion 20 through a conductor '98 that is electrically connected to a movable contact 100 of the switch 28. The movable contact 100 at the high to medium high setting is positioned by the cam surface 42a to engage a fixed contact 102 that in turn is connected electrically by a conductor 104 to one side of the resistance element portion 20. The opposite side of the resistance element portion 20 is connected electrically to conductor 70 from whence the energization circuit eventually is connected to line L as described above.

Between the medium high and high positions on the control knob 32, the cam surface 44a will vary the bias of the polymetallic element 92 against the fixed contact 94 to vary the percentage on time of the filament 20,

the time required for the heater 90 to direct sufficient energy into the polymetallic arm 92 to cause it to deflect against the bias produced by the cam surface 44a sufficiently to open the

contacts

94, 96. The degree of bias varies the energy output of element portion 20 from zero to 1000 watts to produce a variable integrated output from unit between 1000 to 2000 watts.

The controller 32, when positioned between the medium high and medium low settings, is conditioned by

cam surfaces

40a, 42b and 44b to produce an energy output from the unit 10 reduced from that produced at the high to medium high settings. As shown in FIGURE 3, the

portions

20, 22 of the resistance element 18 of the surface heating unit 10 are connected serially across the wires L L of the power source and the resistance element portion 22 thereby serves a voltage dividing function so as to reduce the wattage output of the surface heater 10 when the pulser is in an off position to onefourth of the maximum wattage at the high to medium high setting. The pulsing switch 30 selectively shunts the resistance element portion 22 when in an on position and directly connects the resistance element portion 20 across the wires L L to produce a maximum wattage output from the medium high to medium low positions one-half of the maximum when the controller is at a high position.

More particularly, as seen in FIGURE 1, when the control knob 34 is moved to a temperature setting between medium high and medium low, the selector switch 26 is located by the cam surface 40a to electrically connect to wire L as was previously discussed. The cam 42 has a cam surface 42b thereof moved against the movable contact carrying arm 76 of the switch 28 to move the movable contacts 74, thereon respectively into electrical contact with fixed contacts 105, 106 of the switch 28. This repositioning of the contacts of the switch 28 arranges the

resistance element portions

20, 22 as shown in FIGURE 3 wherein the resistance element portion 22 is connected serially with the resistance wire portion 20 across wires L and L The series connection of the

resistance element portions

20, 22 is completed from wire L through the closed switch 48 thence through conductor 66, conductor 68, the

resistance portions

20, 22 thence through the conductor 104 and

closed contacts

74, 105 of switch 28 through conductor 78 and switch 26 back to conductor 86 and wire L The pulsing circuit in the medium high to medium low range is completed from wire L switch 48, conductor 66 thence through conductor 88, the heater 90,

closed contacts

94, 96 of the pulsing switch 30 thence through the conductor 98 and through closed contacts 100, 106 of the switch 28 through a conductor 108 and conductor 70 to one side of the resistance element portion 20. From the opposite side of resistance element portion 20 the pulsating energization circuit at the medium high to medium low setting is completed through conductor 104 thence through

closed contacts

74, 105 of switch 28 and conductor 78 and switch 26 back to conductor 86 and wire L During the operation of the controller at the medium high setting, the cam surface 44b biases the polymetallic arm 92 from a position where the contacts are just closed to a maximum biased position to vary the pulsating energization of the resistance wire portion 20 to produce a wattage output therefrom varying from zero to 1000 watts.

When the controller 32 is positioned for operation between the medium low and low temperature settings on the knob 34, the resistance element 18 is connected by the selector switch 26 across the lower voltage power supply defined by wires L and N. The connection of the element 18 is accomplished by a surface 40b on the cam 40 that will locate the movable contact carrying arm 80 of the selector switch 26 to cause the movable contact 82 thereon to contact a fixed contact 108 electrically connected by a conductor 110 to conductor 64 to wire N.

At the temperature settings between medium low and low, the cam 42 is positioned by the knob 34 to cause a cam surface 42c thereon to locate the movable contact arm 76 to close contact pairs 72, 74 and 100, 102 of the selector switch 28.

Also at the temperature settings between medium low and low, a cam surface 440 on cam 44 positions the contact carrying polymetallic arm 92 to predetermined biased positions with respect to fixed contact 94 to establish a pulsating energization of the resistance Wire portion 20 forproducing a variable wattage output therefrom.

At the medium low to low settings, the resistance Wire portion 22 is continuously energized across the low voltage power source defined by wires L and N and the resistance wire portion 20 is pulsatingly energized across the same power source through the pulsing switch 30. This condition is illustrated in FIGURE 4 and since the voltage across wires L and N is one-half that across wires L and L the wattage output from the continuously energized resistance element portion 22 is one-fourth of the value across the energized resistance element portion 22 in FIGURE 2. Likewise, the maximum pulsating energy output from the resistance element portion 20 is one-fourth of the maximum wattage output of the resistance element portion 20 in the circuit arrangement of FIGURE 2.

The continuous energization circuit for the element portion 22 in FIGURE 4 is identical to the previously described circuit for resistance wire portion 22 in the circuit of FIGURE 2 except that the selector switch 26 is connected to wire N rather than wire L The pulsating energization circuit for wire portion 20 is identical to that described in the circuit of FIGURE 2 except that the selector switch 26 electrically connects the conductor 78 to wire N rather than wire L At the medium low to low settings, therefore, the resistance wire portion 18 operates at a considerably reduced wattage output as compared to the arrangements in FIGURES 2 and 3. Furthermore, since the resistance heater 9%) of the pulsing switch 30 is connected across a reduced voltage source, the polymetallic arm 92 will pulse at a reduced rate to reduce contact wear during the controlling operations between medium low and low and warm. Between medium low and low a cam surface 440 on 44 will vary the percentage on time of the pulsing switch 49 to cycle the unit between a wattage output of 250 watts as established by the continuously energized resistance element portion 22 and a maximum wattage output of 500 watts which includes the continuous 250 watts from the element portion 22 and a variable wattage output from the resistance portion 20 from zero to 250 watts depending upon the percentage on time of the switch 30 as established by the cam surface 441:.

When the controller is positioned between low and warm, the selector switch 26 also is positioned by the cam switch 40b of the cam 40 to close the

contacts

82, 108 to complete the electrical connection to the wire N through

conductors

110 and 64. At the low to warm settings the selector switch 28 is moved by a cam surface 42d on cam 42 into a position to connect the resistance element portions 2% 22 in series relationship as was the case shown in FIGURE 3 where the elements were connected across the high voltage supply defined by wires L and L During this phase of operation, a cam surface 44d on the cam 44 varies the bias on the polymetallic spring member 92 to vary the percentage on time of the pulser 30.

Accordingly, the

resistance element portions

20, 22 during this phase of operation, when the pulser switch 30 is opened, are serially connected through a circuit seen in FIGURE 5 as being identical to that described in FIGURE 3 except that the energization circuit is be tween wires L and N rather than wires L and L By the serial connection of the

resistance element portions

20, 22, the resistance element portion 22 serves as a voltage divider for establishing a base wattage output from the heating unit during the low to warm temperature settings.

The unit 10, during this phase of operation, has a high wattage output established by the percentage on time of the pulsing switch 30 which, when closed, will by-pass the resistance element portion 22 and electrically connect the resistance element portion 20' across the low-voltage supply L -N. Accordingly, the maximum wattage output is reduced by one-fourth from that shown in FIGURE 3.

By virtue of the illustrated arrangement a resistance element controller is provided which has a wide range of wattage output varying in accordance with the following schedule of percentages of the maximum wattage output of resistance element:

Percent High Medium high 50 Medium low 25 Low 12 /2 Warm 6% Furthermore, the infrared surface heating unit arrangement described above is characterized by the fact that the resistance element is never pulsed full on or full off and at least one portion of the resistance element is continuously energized at all times to produce a constant illumination of an upper utensil supporting plate 12 thereof.

Furthermore, by a progressive reduction of the maximum wattage output as shown in the above schedule, the energy output of the unit 10 at low settings is reduced to a point where a supported utensil will be heated gradually by a low-wattage output during low and warm settings to prevent burning or scorching of substances in a utensil receiving energy from the unit.

A still further feature of the present invention is that at the low-energy output operation of the infrared surface heating unit 10, the pulsing switch 30 has a reduced pulse rate whereby the contacts thereof remain closed a greater percentage of the time to produce a variation in the energy output between the medium low and warm settings whereby contact wear is substantially reduced.

While the embodiment of the present invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. In an infrared surface heater assembly, the combination of, an upper utensil supporting plate of infrared transmissive material, a reflector plate in spaced relationship to said upper plate having an infrared reflective surface, a high temperature electrical resistance element having a first and second portion supported between said plates out of direct heat transfer contact therewith, said resistance element being unshielded and energizable above 1500 F., circuit means including an infinite heat switch means for pulsatingly energizing said first portion of said resistance element to produce a visually observable light pulsation beneath said upper plate, said infinite heat switch means including a presettable controller to control the energy output of the assembly through a plurality of settings by varying the on time of said infinite heat switch means, circuit means energizing said resistance element during the variable pulsating energization of said first portion for maintaining a partial energization of the resistance element at all times to produce background illumination of said upper plate during operation of the heater assembly, said first and second portions having substantially equal maximum wattage outputs, said circuit means including means for selectively connecting said second portion of said electrical resistance element in voltage dividing relationship with said first resistance element portion for halving the wattage output of said resistance element when said infinite heat switch is pulsed to an open position.

2. In the combination of claim 1, means for selectively connecting said resistance element portions across first and second voltage sources to further control the wattage output of said resistance element, said last mentioned means -conditioning said infinite heat switch means to have a lesser pulse rate when said resistance element is connected across one of said voltage sources.

3. In an infrared surface heating assembly, the combination of, an upper plate of infrared transmissive material, a reflector plate in spaced relationship to said upper plate including an infrared reflective surface, a high temperature electrical resistance element disposed between said plates out of direct heat transfer contact therewith energizable above 1500 F., a first source of power, a second source of power, said resistance element including a first portion and a second portion of substantially equal maximum wattage outputs, infinite heat switch means for pulsatingly connecting said first resistance element portion across at least one of said power sources to produce a first variable wattage output from said resistance element, first selector switch means for selectively connecting said second resistance element portion in both parallel and in series relationship with said first resistance element portion to produce a second variable wattage output from said resistance element, said second of said resistance element portions serving as a voltage divider for reducing the wattage output of said resistance element when in series relationship with said first portion of said resistance element, second selector switch means for selectively connecting said resistance element across said first and second sources of power, said first selector switch means for connecting said first and second portions in serial and parallel relationship serving to vary the maximum wattage output from said resistance element when said resistance element is connected across either of said voltage sources.

References Cited UNITED STATES PATENTS 2,790,057 4/1957 Schauer 219452 X 2,799,765 7/1957 Jenkins et a1. 219464 X 2,824,941 12/1958 Fry 219492 X 2,870,316 1/1959 Ferguson 219-464 X 3,345,498 10/1967 Siegla 219-464 RICHARD M. WOOD, Primary Examiner.

L. H. BENDER, Assistant Examiner.

U.S. DEPARTMENT OF COMMERCE PATENT OFFICE Washington, 0.6. 20231 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,403,244 September 24 1968 Donald C. Siegla It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 23, "3,345,489" should read 3,345,498

Signed and sealed this 17th day of March 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer