Range Temperature Protection

The invention relates in general to thermostatic controls, and in particular to means for protecting a temperature-sensitive electronic module associated with a domestic range employing electric resistance heating elements.

The continuing advance of microelectronics has made possible the computerized control of domestic appliances such as programmable microwave cooking ovens, automatic dishwashers, domestic ranges and the like. The associated integrated circuit containing electronic module for accomplishing such computerized microelectric control, while continuing to decrease in cost, still constitutes a high cost component of the controlled appliance, and thus must be fully protected from damaging high temperature conditions.

The problem of module temperature control is especially acute in a microcomputer-controlled domestic range having a horizontal cooking platform providing a plurality of resistance wire surface heating elements and a pyrolytic type self-cleaning oven located below the platform, the oven including radiant heating elements also formed of resistance wire.

In such a range, the electronic control module is typically contained within a boxlike control unit extending upwardly from and across the back edge of the cooking platform. Where the range is located in a confined area, it may be possible to overheat the module-containing control unit during a high-temperature self-cleaning cycle of the oven and/or during improper usage of surface heating units in an unloaded condition (i.e., without a cooking utensil placed on the energized surface heating element).

To protect the electronic module from damage by high temperatures, means must be provided to limit to a tolerable level an over-temperature condition of the module caused by the energization of one or more of the heating elements. Such a temperature limiting means must be durable and very reliable, due to the relatively long life expectancy of domestic appliances. Also, such a means must be low in cost due to the competitive nature of the domestic appliance business.

The present invention provides, in a domestic range having heating means temperature-regulated by a control unit including an electronic control module, an over-temperature protection means for the control module. The protection means includes a temperature-sensitive switch located generally at the site of the control module. The switch disables at least a portion of the heating means at a predetermined sensed temperature to preclude damage to the module caused by high temperatures generated by the heating means.

Preferably, the switch is constituted by a pair of bimetal snap-disc-actuated switches straddling the module, the bimetal switches and the module being mounted to a common heat sink member. The bimetal switches automatically reset when the sensed temperature reaches a tolerable level wherein normal operation of the range is resumed.

A fuller understanding of the invention may be had by referring to the following description and claims, taken in conjunction with the accompanying drawing.

FIG. 1 is a perspective view of a domestic range of the electric type incorporating the present invention, the range including an electronic module containing control unit extending upwardly from and across the back of the top horizontal cooking platform of the range;

FIG. 2 is a rearward view, with portions cut away, of the control unit illustrated in FIG. 1;

FIG. 3 is a plan view, with portions cut away, of the control unit illustrated in FIG. 2 as taken along line 3--3 of FIG. 4;

FIG. 4 is a side view cross section of the control unit illustrated in FIG. 2, taken along line 4--4 of FIG. 2; and

FIG. 5 is a schematic diagram of a typical range control circuit in accordance with the present invention.

With reference to FIG. 1, there is illustrated in accordance with the present invention a freestanding domestic range 10 of the electric type. The range includes a lower boxlike oven housing 12 typically formed of sheet metal panels. The housing 12 includes a windowed oven door 12A and a conventional utensil drawer 12B. The oven door 12A can be opened to pivot downwardly about a lower horizontal axis to provide access to an oven chamber 13, including an oven heating bake element 13A and one or more broiling elements (not shown). The element 13A and the non-illustrated broil elements are formed of shielded resistance wire that heats to a high degree when a predetermined amount of current flows through it. The oven chamber 13 can thus be highly heated by the heating elements contained therein so as to cause pyrolytic cleaning action of the oven walls, the oven door 12A being locked in a closed position during such pyrolytic cleaning, as is well known in the art.

A horizontal cooking platform 14 comprises the top of the boxlike oven housing 12, the horizontal cooking platform 14 including a plurality (e.g., four) of resistance wire surface heating elements 15 constituting burner locations upon which cooking utensils are placed for heating. The surface heating elements 15 are of a conventional nature and take the form of a pancake-shaped element of shielded resistance wire spirally wound as illustrated.

Extending across the back and upwardly from the horizontal cooking platform 14 is a control unit 16. The control unit 16 is boxlike and includes a front panel 20 providing, for example, six apertures through which extend the control shafts carrying four burner control knobs 22, 23 and two oven control knobs 25. The control panel 20 is typically formed of opaque glass and carries numerous indicia associated with the manual control knobs 22, 23, 25 to permit the user to regulate the temperature of the surface heating elements 15 and the temperature of the oven chamber 13. Located generally at the center or intermediate portion of the glass front panel 20 is a transparent window area 24 through which a time display mounted rearwardly of the panel 20 within the control unit 16 can be observed. To either side and below the display 24 is a plurality of touch pads 26 of the well-known capacitive switch type carried on the surface of the glass panel 20. The touch pads 26 are used to program an electronic control module to be subsequently illustrated and discussed, the module providing for the computerized time control of the oven chamber 13, the window area 24 being used to visually feed back to the user programmed information inputted via the touch pads 26, as well as conventional time of day information. While the control unit 16 illustrated in FIG. 1 only provides for computerized turning on and turning off of the oven chamber 13 (with temperature control of the oven chamber 13 being conventionally provided via the oven control knobs 25), it is to be recognized that a nonapertured glass panel 20, including touch pads or equivalents in place of the knobs 22, 23, 25, could be provided so as to provide full electronic touch control for the surface heating elements 15 and all oven heating elements.

If one or more of the surface heating elements 15 are energized to a high power condition, without a cooking utensil in place on the respective elements, heat radiated by the elements will impinge on the control unit 16 and, in particular, on the generally opaque glass front panel 20. Such a condition could cause the control unit 16 to be highly heated, wherein components within the control unit 16 would also be heated to a high extent. Further, pyrolytic cleaning of the oven chamber 13 at a temperature range of about 950.degree. F. for a time period of, for example, two or more hours could cause the entire oven housing 12 to heat up as well as the control unit 16, thereby exposing the components within the control unit 16 to a high temperature condition. The temperature problem noted above becomes particularly acute if the range 10 is located in a confined area wherein only a limited amount of cooling air can be circulated by convection through and about the domestic range 10.

With reference to FIG. 2, there is illustrated a rearward view of the control unit 16 with the burner control knobs 22, 23 (and associated electric power control elements 22a, 22b, 23a, 23b) being illustrated in phantom along with the oven control knobs 25 (and associated electric power control elements 25a, 25b). The rear of the control unit 16 is normally closed by a back panel or cover 17. In FIG. 2, a central portion of the back panel of the cover 17 has been cut away to reveal an electronic control module 30 which includes a power supply circuit board 30c (and other module boards to be subsequently illustrated) mounted on one side of a heat sink 40 in the form of a platelike metal bracket 42 having first and second side flanges 44, 46 fastened to an interior frame portion (to be subsequently illustrated) of the control unit 16. The control module 30 includes a plurality of temperature-sensitive, integrated circuit packages (e.g., a microprocessor, read-only-memory, etc.) of a known type which allow a range user to enter programmed material via the touch pad 26 (see FIG. 1) so as to determine when the oven chamber 13 (FIG. 1) will be heated on a time cycle basis.

To protect the module 30 from a damaging over-temperature condition, a temperature-sensitive switch means is located generally at the site of the control module. The switch means disables at least a portion of the range heating means (comprised of the oven heating element and surface heating element) at a predetermined sensed temperature to preclude damage to the module 30 caused by high temperature generated by the heating means of the range 10 (FIG. 1).

In a preferred form, the temperature-sensitive switch means is comprised of a pair of normally closed, bimetal snap disc thermostatic switches 47, 48 of a known type manufactured by Therm-O-Disc Incorporated of Mansfield, Ohio. The type of bimetal snap disc switch illustrated in FIG. 2 is of the general type shown in U.S. Pat. No. 2,954,447. However, the switch illustrated in the U.S. Pat. No. 2,945,447 patent is slightly more complex than the switches 47, 48 utilized in the preferred embodiment of the present invention. The bimetal snap disc switches 47, 48 have an open end exposing their respective snap discs. The open ends of the switches 47, 48 are fastened to and closed by a portion of the heat sink flanges 44, 46, wherein heating of the flanges of the heat sink 42 in turn causes generally radiant heating of the bimetal snap disc located within the switches 47, 48. Each switch 47, 48 is in series with a portion of the heating means of the range (surface and oven heating elements), wherein one or both of the switches 47, 48 can switch to an open condition to disable heating of the associated heating elements so as to maintain or lower the temperature of the module 30 to preclude its being damaged. The thermostatic switches 47, 48 will automatically reset to their normally closed electrically conducting condition to enable the disabled heating means portion upon a decrease from a predetermined temperature.

With reference to FIG. 3, the control module 30 is further illustrated as including a logic control circuit board 30a and a digital-type timer display circuit board 30b in addition to the power supply circuit board 30c. The integrated circuit containing boards 30a, 30b, 30c constitute the electronic control module 30, the boards 30a, 30b, 30c being fastened in position on the heat sink 40 (FIG. 2) having its flange portion 44, 46 fastened to an internal frame member 41 of the control unit 16. A display face 31 of the timer board 30b can be observed by the user through the transparent window area 24 (see FIG. 1) of the glass front panel 20, the timer display face 31 being spaced slightly inwardly away from the inner surface of the glass panel 20 to preclude conduction heating of the display face 31 by the panel 20.

The bimetal snap disc switches 47,48 are more clearly illustrated in FIG. 3 as having open-ended nose portions 49 in contiguous relationship against the heat sink flanges 44, 46, the portions 49 of the switches containing the bimetallic discs which are directly exposed to radiant heating by the flanges 44, 46. In a preferred manner, the switches 47, 48 straddle the module 30 so as to fully protect it from a high temperature condition generated at either end of the control unit 16 (see FIG. 1). Further, the use of an open-nose switch permits a very fast switch response time to a sensed over-temperature condition.

With reference to FIG. 4, the bimetallic snap disc switch 47 (which is identical to the snap disc switch 48) is further illustrated as including, in addition to the nose portion 49, a mounting bracket 49b which secures, by appropriae screws 49c, the switch 47 in position against the heat sink flange 44. A pair of contacts 49a (only one shown) has connected between them a single pole switch which is in a normally closed position until a high temperature condition is reached wherein a bimetallic snap disc in the nose portion 49 actuates the switch to an open condition in a well known manner.

Turning to FIG. 5, there is illustrated in schematic fashion a typical control circuit for a domestic range of the type illustrated in FIGS. 1 through 4. The electric power control elements 22a, 22b, 23a, 23b for the surface heating elements 15 are schematically illustrated as being energized by a pair of power lines L.sub.1, L.sub.2 in a typical fashion. Power to the elements 15 energized via control elements 22a, 22b, and 23a is provided via the snap disc switch 48. The snap disc switch 47 provides power to control element 23b as well as to the oven control circuitry 60 via a power control line 65. The oven control circuitry 60 is of a conventional nature and energizes, in a known fashion, the oven heating elements 13a along with, for example, a broil element 63 and its associated speed broil element 61. It can be seen that opening of the thermostatic switches 47, 48 will disable the powering of the respective portions of the heating elements contolled so as to preclude overheating of the control module 30 as discussed above.

While the present invention has been illustrated in the environment of a domestic range of the electric resistance heating type, it is to be understood that the invention has equal applicability to a gas range wherein over-temperature protection of an electronic control module of the type illustrated is desired. Also as noted earlier, the present invention applies to a fully electronically controlled range, although FIGS. 1 through 4 illustrate the range having conventional knob-type mechanical controls for the heating elements, both of the surface heating type and the oven heating type.

The switches 47, 48 in conjunction with the heat sink 40 advantageously preclude overheating of the associated control module 30. The switches 47, 48 are relatively low in cost and easily handle high current loads over many switch cycles. The relative simplicity of the heat sink in combination with the switches 47, 48 provides a very rugged and reliable over-temperature protection means for the electronic control module 30.

Although the preferred embodiment of this invention has been shown and described, it should be understood that various modifications and rearrangements of the parts may be resorted to without departing from the scope of the invention as disclosed and claimed herein.