Patent Application
20210080115
The present subject matter relates generally to electric coil heating elements for appliances.
Recent regulatory requirements mandate that electric coil heating elements on cooktop appliances be incapable of heating cooking oil to an oil ignition temperature. Thus, certain electric coil heating elements utilize a bimetallic thermostat to interrupt power to the coil when the thermostat reaches a tripping point. In some cooktops, the thermostat is remotely positioned from the cookware and infers the cookware temperature through correlation. In other cooktops, the thermostat contacts a bottom of the cookware to improve correlation. However, whether remotely positioned from the cookware or contacting the cookware, imperfect correlation requires conservative thermostat calibrations and thus results in reduced performance.
Known bimetallic thermostats have shortcomings. In particular, the flatness of the coil has a significant impact to system performance, as does the flatness of the bottom of the cookware. Poor contact between the cookware and the coil cause the portions of the coil that have poor conduction to the cookware to glow red hot and radiate heat. Radiative heat transfer from the coil to the thermostat can overcome the heat transfer from the cookware to the thermostat, causing the thermostat to trip early.
Aspects and advantages of the invention will be set forth in part in the following description, or may be apparent from the description, or may be learned through practice of the invention.
In an example embodiment, an electric resistance heating coil assembly includes a spiral wound sheathed heating element having a first coil section and a second coil section. A bimetallic thermostat is connected in series between the first and second coil sections of the spiral wound sheathed heating element. The bimetallic thermostat is spring loaded such that a distal end of the bimetallic thermostat is urged away from a top surface of the spiral wound sheathed heating element. A heat transfer disk is positioned on the bimetallic thermostat at the distal end of the bimetallic thermostat. The heat transfer disk is positioned concentrically with a center of the spiral wound sheathed heating element. A diameter of the heat transfer disk is greater than a diameter of the bimetallic thermostat, and the diameter of the heat transfer disk is less than a diameter of the center of the spiral wound sheathed heating element.
In another example embodiment, an electric resistance heating coil assembly includes a spiral wound sheathed heating element having a first coil section and a second coil section. A bimetallic thermostat is connected in series between the first and second coil sections of the spiral wound sheathed heating element. The bimetallic thermostat spring loaded such that a distal end of the bimetallic thermostat is urged away from a top surface of the spiral wound sheathed heating element. A heat transfer disk is positioned on the bimetallic thermostat at the distal end of the bimetallic thermostat. The heat transfer disk positioned at a center of the spiral wound sheathed heating element. A ratio of a diameter of the heat transfer disk to a thickness of the heat transfer disk being no less than twenty and no greater than seventy-five.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures.
Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.
A top panel 20 of range appliance 10 includes heating elements 30. Heating elements 30 may be, e.g., electrical resistive heating elements. Range appliance 10 may include only one type of heating element 30, or range appliance 10 may include a combination of different types of heating elements 30, such as a combination of electrical resistive heating elements and gas burners. Further, heating elements 30 may have any suitable shape and size, and a combination of heating elements 30 of different shapes and sizes may be used.
A cooking utensil, such as a pot, pan, or the like, may be placed on heating elements 30 to cook or heat food items placed in the cooking utensil. Range appliance 10 also includes a door 14 that permits access to a cooking chamber 16 of range appliance 10, e.g., for cooking or baking of food items therein. A control panel 18 having controls 19 permits a user to make selections for cooking of food items; although shown on a front panel of range appliance 10, control panel 18 may be positioned in any suitable location. Controls 19 may include buttons, knobs, and the like, as well as combinations thereof. As an example, a user may manipulate one or more controls 19 to select a temperature and/or a heat or power output for each heating element 30.
As shown in
Bimetallic thermostat 120 is connected in series between first and second coil sections 112, 114 of spiral wound sheathed heating element 110. Bimetallic thermostat 120 opens and closes in response to a temperature of bimetallic thermostat 120. For example, bimetallic thermostat 120 may be spring loaded such that a distal end 122 of bimetallic thermostat 120 is urged away from a top surface 118 of spiral wound sheathed heating element 110. Thus, distal end 122 of bimetallic thermostat 120 may be urged towards a utensil (not shown) positioned on top surface 118 of spiral wound sheathed heating element 110. Bimetallic thermostat 120 may measure the temperature of the utensil on top surface 118 of spiral wound sheathed heating element 110 due to heat transfer between the utensil and bimetallic thermostat 120. As discussed in greater detail below, electric resistance heating coil assembly 100 includes features for facilitating conductive heat transfer between the utensil on top surface 118 of spiral wound sheathed heating element 110 and bimetallic thermostat 120.
Electric resistance heating coil assembly 100 may also include a shroud 102 and coil support arms 104. Coil support arms 104 extend, e.g., radially, from shroud 102, and spiral wound sheathed heating element 110 is positioned on and supported by coil support arms 104. Coil support arms 104 may rest on top panel 20 to support electric resistance heating coil assembly 100 on top panel 20. Bimetallic thermostat 120 may be mounted to a shroud cover 106, e.g., on a top wall 107 of shroud cover 106. Shroud cover 106 extends over shroud 102. In particular, a top of shroud 102 may be nested in shroud cover 106. A spring 108 biases shroud cover 106 and bimetallic thermostat 120 thereon upwardly.
As shown in
Heat transfer disk 130 may be formed of aluminum, copper, a copper alloy, or an aluminum alloy. Such materials advantageously facilitate conductive heat transfer between the utensil on top surface 118 of spiral wound sheathed heating element 110 and heat transfer disk 130. In certain example embodiments, a casing 124 (
Heat transfer disk 130 and/or bimetallic thermostat 120 may be positioned concentrically with a center 119 of spiral wound sheathed heating element 110. Center 119 of spiral wound sheathed heating element 110 may be open, and spiral wound sheathed heating element may extend circumferentially around heat transfer disk 130 and/or bimetallic thermostat 120 at center 119. Heat transfer disk 130 may also cover distal end 122 of bimetallic thermostat 120. Thus, heat transfer disk 130 may be positioned between bimetallic thermostat 120 and a utensil on top surface 118 of spiral wound sheathed heating element 110, and heat transfer disk 130 may contact the utensil. Heat transfer disk 130 may also include a flange 132 that extends downwardly towards shroud cover 106 towards shroud cover 106.
In certain example embodiments, the diameter DH of heat transfer disk 130 may be no less than one inch (1″) and no greater than one and a half inches (1.5″). Conversely, a thickness TH of heat transfer disk 130, e.g., that is perpendicular to the diameter DH of heat transfer disk 130, may be no less than two hundredths of an inch (0.02″) and no greater than five hundredths of an inch (0.05″). In addition, a ratio of the diameter DH of heat transfer disk 130 to the thickness TH of heat transfer disk 130 may be no less than twenty (20) and no greater than seventy-five (75) Such sizing of heat transfer disk 130 advantageously assists conductive heat transfer from the utensil on top surface 118 of spiral wound sheathed heating element 110 to bimetallic thermostat 120.
As noted above, heat transfer disk 130 may be in direct thermal conductive communication with bimetallic thermostat 120. To provide direct thermal conductive communication between bimetallic thermostat 120 and heat transfer disk 130, heat transfer disk 130 may be spot welded, seam welded, ultrasonic welded or resistance welded to bimetallic thermostat 120. It will be understood that other connections between bimetallic thermostat 120 and heat transfer disk 130 also provide direct thermal conductive communication. For example, with reference to
As may be seen from the above, heat transfer disk 130 advantageously has increased conductive heat transfer from a utensil on top surface 118 of spiral wound sheathed heating element 110 to bimetallic thermostat 120 relative to known heating elements without heat transfer disk 130. Known heating elements without heat transfer disk 130 have limited ability to transfer heat between a cooking utensil and an associated bimetallic thermostat due to limited contact area between such components, along with varying degrees of contact resistance between the cooking utensil and bimetallic thermostat. Testing has shown that heat transfer disk 130 mounted to bimetallic thermostat 120 at distal end 122 of bimetallic thermostat 120 increases conduction between bimetallic thermostat 120 and cookware on spiral wound sheathed heating element 110. Even under conditions that cause known heating elements to trip before water can boil, electric resistance heating coil assembly 100 runs continuously and without interrupted power. Thus, electric resistance heating coil assembly 100 is advantageously robust to warped coils and bowed bottom pans, and better tracks the temperature of cookware despite excessive heat transfer from spiral wound sheathed heating element 110.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
