The present invention relates generally to a switch for a cooking appliance, and, more particularly, to a switch for electrically connecting and disconnecting a heating element of a cooking appliance with a power source.
Typically, heating elements of cooking appliances can reach operating temperatures of several hundred degrees in order to cook foodstuff in cookware. With this comes some inherent risk of burns and fire. For example, if foodstuff within cookware reaches a high enough temperature, the foodstuff can auto-ignite. As another example, if a cookware containing boiling water is heated for too long, the water will boil dry, at which point the cookware temperature will rapidly increase to temperatures that can cause serious burns. It is desirable to prevent cookware and foodstuff, and especially cooking or food oils, from reaching such dangerously high temperatures.
In accordance with a first aspect, a switch for electrically connecting a power source to a heating element of a cooking appliance is provided. The switch includes a first contact and a second contact, a bimetal strip configured to electrically connect and disconnect the first and second contacts, and a cam member. The cam member is rotatable about a rotational axis and has a cam surface for operative engagement with a cam follower. The cam surface has a profile dimension that varies about the rotational axis such that rotation of the cam member can cause displacement of the cam follower to thereby adjust an operating temperature of the heating element up to but not beyond a predetermined maximum temperature.
In accordance with a second aspect, a cooking appliance has a switch having a first contact that is electrically connected to the heating element, a second contact that is electrically connected to a power source, and a bimetal strip configured to electrically connect and disconnect the first and second contacts. A cam member is rotatable about a rotational axis and has a cam surface for operative engagement with a cam follower. The cam surface has a profile dimension that varies about the rotational axis such that rotation of the cam can cause displacement of the cam follower to thereby adjust an operating temperature of the heating element up to but not beyond a predetermined maximum temperature.
In accordance with a third aspect, a cooking appliance has a first switch assembly electrically coupled to a heating element and configured to selectively operate the heating element at a first operating temperature, and a second switch assembly electrically coupled to the heating element and configured to selectively operate the heating element at a second operating temperature that is greater than the first operating temperature.
The foregoing and other aspects will become apparent to those skilled in the art to which the present examples relate upon reading the following description with reference to the accompanying drawings, in which:
An example cooking appliance 10 is shown in
When the power circuit 18 is closed, power will be supplied to the heating element 14 from the power source 16, thereby causing the operating temperature of the heating element 14 to rise. (For the purposes of this disclosure, reference to the “operating temperature” of a heating element 14 can mean the temperature of the heating element 14 itself or the temperature of a target item heated by the heating element 14 such as, for example, a cookware disposed on or adjacent the heating element). If the power circuit 18 is later opened, the supply of power to the heating element 14 will cease, thereby causing the operating temperature of the heating element 14 to fall.
If the power circuit 18 is closed and power is supplied persistently for a sufficient amount of time, the operating temperature of the heating element 14 will eventually reach a maximum-operable-temperature of, for example, 700° C. or greater. (For the purposes of this disclosure, reference to the “maximum-operable-temperature” of a heating element 14 means the operating temperature of the heating element 14 during a steady state in which continued supply of power to the heating element 14 from an associated power source will no longer increase the operating temperature). However, it may be desirable to maintain the heating element 14 at an operating temperature below its maximum-operable-temperature. For instance, it has been found that foodstuff such as oils can auto-ignite at certain temperatures such as, for example, 424° C. for canola oil, 406° C. for vegetable oil, and 435° C. for olive oil. Thus, it may be desirable to maintain the heating element 14 at an operating temperature that is equal to or less than the auto-ignition temperature of a foodstuff, in order to ensure that a cookware heated by that element or that foodstuffs inside that cookware do not exceed the auto-ignition temperature.
As will be described in further detail below, the switch assembly 20 is designed to periodically open and close the power circuit 18 in a controlled manner to maintain the operating temperature of the heating element 14 about a desired temperature that is below its maximum-operable-temperature. Moreover, the switch assembly 20 is adjustable so that the operating temperature maintained by the switch assembly 20 can be adjusted. However, the switch assembly 20 is designed so that the operating temperature cannot be adjusted beyond a predetermined maximum temperature. For example, the switch assembly 20 can be designed so that the operating temperature cannot exceed a predetermined maximum temperature that is equal to or less than the auto-ignition temperature of a foodstuff such as, e.g. vegetable oil (406° C.), which should similarly limit the temperature of the foodstuff within an associated cookware being heated by the element 14. Thus, the switch assembly 20 can prevent fires that result from the auto-ignition of foodstuff by limiting the maximum operating temperature of the heating element 14 to a predetermined maximum temperature of, for example, 406° C. However, the predetermined maximum temperature can be any predetermined temperature above or below 406° C. in some examples.
With reference to both
The switch assembly 20 further includes a set of contacts 32 including a first contact 34 and a second contact 36 that are electrically connected or connectable to the power source 16 and the heating element 14, respectively. For example, as shown in
As shown in
The power circuit 18 can be closed by moving the free end portion 44 of the cam follower 38 in a direction Y toward the second contact 36 until the first and second contacts 34, 36 contact each other. To control the position of the free end portion 44 of the cam follower 38, the switch assembly 20 includes a cam assembly 50 configured for operative engagement with the cam follower 38. The cam assembly 50 includes a spindle 52 that can be mounted to the switch housing 22 such that the spindle 52 extends through the aperture 30 of the lid portion 26. On the outside of the housing 22 (e.g., above lid portion 26), a knob 54 (shown in
To operate the heating element 14, the knob 54 can be turned to a position corresponding to a desired operating temperature of the heating element 14. The cam 56 will rotate with the knob 54 and move the cam follower 38 in the direction Y toward the second contact 36 until the first and second contacts 34, 36 connect (i.e., close), thereby closing the power circuit 18 and allowing power to be supplied to the heating element 14 from the power source 16. The operating temperature of the heating element 14 will start rising. At the same time, current will pass through a resistive heat element 60 located approximate (e.g., attached to) the bimetal strip 40, causing the resistive heat element 60 to heat up. The bimetal strip 40 includes an expansion member 62 located proximate to the resistive heat element 60 that will in turn heat up and begin to expand. Eventually, expansion of the member 62 will cause the free end portion 48 of the bimetal strip 40 to deflect away from the first contact 34 such that the first and second contacts 34, 36 disconnect (i.e., open) and the power circuit 18 opens. The cam assembly 50 is designed such that this opening of the power circuit 18 will occur about the same time that the heating element 14 has reached the desired operating temperature, thereby preventing the operating temperature of the heating element 14 from further rising substantially above the desired operating temperature.
The power circuit 18 will remain open for a period of time, causing the operating temperature of the heating element 14 to stop rising and eventually, begin to fall. While the power circuit 18 is open, current will no longer pass through the resistive heat element 60 of the bimetal strip 40. With no current passing through the resistive heat element 60 to generate heat, the expansion member 62 of the bimetal strip 40 will begin to cool and shrink. As the member 62 shrinks, the free end portion 48 of the bimetal strip 40 will deflect back toward the first contact 34. Eventually, the first and second contacts 34, 36 will reconnect (i.e., close), thereby closing the power circuit 18 and allowing current flow to resume. The cam assembly 50 is designed such that this closing of the power circuit 18 will occur before the operating temperature of the heating element 14 drops significantly below the desired operating temperature. The power circuit 18 will then stay closed for a period of time until the free end portion 48 of the bimetal strip 40 again deflects away from the from the first contact 34, causing the first and second contacts 34, 36 to disconnect. In this manner, the switch assembly 20 can regulate the operating temperature of the heating element 14 by cycling the first and second contacts 34, 36 between open and closed states to intermittently provide power to the heating element 14 and maintain the heating element 14 about the desired operating temperature.
The desired operating temperature maintained by the switch assembly 20 can be adjusted by turning the knob 54 to adjust the rotational position of the cam 56. The rotational position of the cam 56 controls the position of the free end portion 44 of the cam follower 38, which in turn controls the operating temperature of the heating element 14 about which the first and second contacts 34, 36 will open and close. More specifically, as the free end portion 44 of the cam follower 38 is displaced in the direction Y toward the second contact 36, the first and second contacts 34, 36 will eventually connect with each other. If the free end portion 44 of the cam follower 38 is further displaced in the direction Y, this will cause the free end portion 48 of the bimetal strip 40 to also move in the direction Y away from its resting position. The further the free end portion 48 of the bimetal strip 40 is moved away from its resting position, the greater the operating temperature of the heating element 14 about which the first and second contacts 34, 36 will open and close because the bimetal strip will need to be deflected a greater degree in the Y direction (as a result of heating the resistor 60) for the contact 36 to escape contact with the contact 34. Conversely, the closer the free end portion 48 of the bimetal strip 40 is to its resting position, the lower the operating temperature of the heating element 14 about which the first and second contacts 34, 36 will open and close. Thus, the operating temperature maintained by the switch assembly 20 can be adjusted by turning the knob 54 to adjust the rotational position of the cam 56 and in turn, the amount of deflection of the free end portion 48 of the bimetal strip 40 from its resting position.
With reference now to
For instance, in the example cam surface 58 shown in
As configured in
Turning now to
In the example cam surface 58 shown in
When configured as shown in
The switch assembly 20 and power circuit 18 described above are designed to prevent fires that result from the auto-ignition of foodstuff by prohibiting the heating element 14 from reaching its maximum-operable-temperature, which can be several hundreds of degrees Celsius higher than the auto-ignition temperature of a foodstuff. In particular, the switch assembly 20 and power circuit 18 are designed so that the operating temperature of the heating element 14 can be adjusted up to but not beyond a predetermined maximum temperature that is equal to or less than, for example, 400° C. However, limiting the maximum operating temperature of the heating element 14 as such can negatively affect certain cooking operations. For example, the time required to boil water in a cooking vessel will be considerably longer when operating a heating element at 400° C. compared to 700° C. Thus, another example power circuit is described below that will normally limit the maximum operating temperature of the heating element 14 to a predetermined temperature (e.g., 400° C.). But in select circumstances such circuit can be temporarily operated to permit higher heating-element temperatures to improve cooking performance.
Turning to
As will be described in further detail below, the first switch assembly 120 is configured to selectively operate the heating element 14 at a first operating temperature and the second switch assembly 122 is configured to selectively operate the heating element 14 at a second operating temperature that is greater than the first operating temperature. In particular, the first switch assembly 120 can be engaged to operate the heating element 14 at a first temperature that is, for example, below the maximum-operable-temperature of the heating element 14 and preferably, equal to or less than 400° C. Meanwhile, the second switch assembly 122 can be engaged during other operations when it is desirable to operate the heating element 14 at a second temperature higher than the first temperature maintained by the first switch assembly 120. (For the purposes of this disclosure, a switch assembly is “engaged” when its operative contacts are closed and/or automatically cycling between open and closed states, thereby allowing current to continuously or periodically pass through the contacts. Moreover, a switch assembly is “disengaged” when its operative contacts are open and are not automatically cycling between open and closed states, thereby persistently prohibiting current from passing through the contacts).
More specifically, the first switch assembly 120 includes a set of contacts 132 having two contacts 134, 136 that are connected in series between the heating element 14 and the switch assembly's associated power source. The second switch assembly 122 includes a set of contacts 142 having two contacts 144, 146 that are also connected in series between the heating element 14 and the switch assembly's associated power source. For example, the two contacts 134, 136 of the first switch assembly 120 can be respectively connected to the terminal L2 of the power source 16 and the terminal 112 of the heating element 14, or vice versa. Meanwhile, the two contacts 144, 146 of the second switch assembly 122 can also be respectively connected to the terminal L2 of the power source 16 and the terminal 112 of the heating element 14, or vice versa. Thus, the sets of contacts 132, 142 of the first and second switch assemblies 120, 122 can be electrically connected in parallel between the terminal L2 of the power source 16 and the terminal 112 of the heating element 14. In an alternative example, the two contacts 134, 136 of the first switch assembly 120 can be respectively connected to the terminal L1 of the power source 16 and the terminal H1 of the heating element 14, or vice versa. Meanwhile, the two contacts 144, 146 of the second switch assembly 122 can also be respectively connected to the terminal L1 of the power source 16 and the terminal H1 of the heating element 14, or vice versa. Thus, the sets of contacts 132, 142 of the first and second switch assemblies 120, 122 can be electrically connected in parallel between the terminal L1 of the power source 16 and the terminal H1 of the heating element 14. However, the sets of contacts 132, 142 of the first and second switch assemblies 120, 122 can be arranged differently in other examples to electrically connect the same or different power sources to the same or different terminals of the heating element 14.
Normally, the second switch assembly 122 will be disengaged such that its contacts 144, 146 are disconnected and non-cycling, thereby maintaining the bypass circuit 152 in a persistently open state. With the second switch assembly 122 disengaged and the bypass circuit 152 open, the first switch assembly 120 can be selectively engaged to operate the heating element 14 at a predetermined temperature. For instance, the first switch assembly 120 can be configured similarly or identically to the switch assembly 20 described above such that rotation of a cam will cause the two contacts 134, 136 of the first switch assembly 120 to connect, thereby closing the primary circuit 150 and allowing power to be delivered to the heating element 14 from the power source 16 via the primary circuit 150. The first and second contacts 134, 136 can then be cycled between open and closed states using a bimetal strip and resistive heat element as described above, thereby cycling power from the power source 16 to the heating element 14 through the primary circuit 150 in a manner that maintains the heating element 14 at a desired operating temperature. However, other structure can be provided to initially connect the two contacts 134, 136 of the first switch assembly 120 and then cycle the contacts 134, 136 between open and closed states such as, for example, a programmable logic controller.
The operating temperature maintained by the first switch assembly 120 can be fixed or adjustable. For example, the first switch assembly 120 can be similarly or identically configured to the switch assembly 20 described above such that rotation of a cam will adjust the operating temperature maintained by the first switch assembly 120. In particular, a cam surface of the cam can be designed as described above so that the desired operating temperature can be adjusted up to but not beyond a predetermined maximum temperature. Preferably, the predetermined maximum temperature is less than a maximum-operable-temperature of the heating element and in particular, less than or equal to about 400° C. However, other temperatures and temperature ranges are possible in other embodiments. Moreover, the operating temperature maintained by the first switch assembly 120 can be adjustable using other structure such as, for example, a user interface for a programmable logic controller. Furthermore, in some examples, the first switch assembly 120 may be non-adjustable and will maintain the heating element 14 at a fixed operating temperature that is, for example, equal to or less than about 400° C.
When operating the heating element 14, the first switch assembly 120 can prevent fires that result from the auto-ignition of foodstuff by limiting the maximum operating temperature of the heating element 14 to a predetermined maximum temperature of, for example, 400° C. However, it may be desirable to temporarily operate the heating element 14 at a higher temperature for certain cooking operations. Accordingly, in such cases, the second switch assembly 122 can be selectively engaged to bypass the first switch assembly 120 and to persistently energize the heating element 14 so as to operate the heating element 14 at a higher temperature.
More specifically, the second switch assembly 122 can be selectively engaged to connect its contacts 144, 146, thereby closing the bypass circuit 152 and allowing power to be delivered to the heating element 14 from the power source 16 via the bypass circuit 152 regardless of the state of the switch assembly 120. For instance, the second switch assembly 122 can be configured similarly or identically to the switch assembly 20 described above such that rotation of a cam will cause the two contacts 144, 146 of the second switch assembly 122 to connect. Alternatively, the second switch assembly 122 can include a toggle switch that can be manually switched to connect the two contacts 144, 146. The second switch assembly 122 can include various types of structure for selectively connecting the two contacts 144, 146.
When engaged, the second switch assembly 122 is configured to provide either cycled or non-cycled power to the heating element 14 via the bypass circuit 152. For instance, in the present example, the second switch assembly 122 is configured such that when engaged, the contacts 144, 146 will remain persistently closed, thereby allowing non-cycled power to be delivered from the power source 16 to the heating element 14 via the bypass circuit 152. If power is supplied persistently via the bypass circuit 152 for a sufficient amount of time, the operating temperature of the heating element 14 will eventually reach its maximum-operable-temperature. Thus, the second switch assembly 122 can be selectively engaged to operate the heating element 14 at its maximum-operable-temperature.
In other examples, the second switch assembly 122 can be configured such that when engaged, its contacts 144, 146 will cycle between open and closed states to provide a cycled power through the bypass circuit 152 that maintains the heating element 14 at a desired operating temperature. For instance, the contacts 144, 146 can be cycled using a bimetal strip and resistive heat element as described above or the contacts 144, 146 can be cycled using other structure such as, for example, a programmable logic controller. In such examples, the operating temperature maintained by the second switch assembly 122 can be fixed or adjustable. Whether the operating temperature is fixed or adjustable, the second switch assembly 122 is preferably configured such that when engaged, the second switch assembly 122 will operate the heating element 14 at a temperature greater than the maximum operating temperature maintained by the first switch assembly 120.
In the example configuration shown in
When it is desired to operate the heating element 14 at a temperature beyond the maximum operating temperature permitted by the first switch assembly 120, the second switch assembly 122 can be engaged to deliver non-cycled power from the power source 16 to the heating element 14 via the bypass circuit 152. In this state (i.e., boost mode), power will be continuously supplied to the heating element 14 via the bypass circuit 152, causing its operating temperature to rise and exceed the maximum operating temperature permitted by the first switch assembly 120. If power is supplied persistently for a sufficient amount of time, the operating temperature of the heating element 14 will eventually reach its maximum-operable-temperature (e.g., 700° C.). Thus, the second switch assembly 122 can be selectively engaged to operate the heating element 14 at its maximum-operable-temperature.
When it is no longer desired to operate the heating element 14 at a temperature beyond the maximum operating temperature permitted by the first switch assembly 120, the second switch assembly 122 can be disengaged to open the bypass circuit 152. The first switch assembly 120 will then control the operating temperature of the heating element 14 in safe mode until the second switch assembly 122 is re-engaged or the first switch assembly 120 is disengaged.
In some cases, it may be desirable to limit the time that the heating element 14 is permitted to be operated in boost mode. Thus, in some examples, the power circuit 118 can include a timer 160, as shown in
In some cases, it may be desirable to prevent or discontinue operation of the heating element 14 in boost mode if a user is not near the appliance 10. Thus, as further shown in
In other example configurations of the power circuit 118, the first switch assembly 120 will have another set of contacts 172 that includes two contacts 174, 176, as shown in
In the example configuration shown in
The invention has been described with reference to example embodiments described above. Modifications and alterations will occur to others upon a reading and understanding of this specification. Example embodiments incorporating one or more aspects described above are intended to include all such modifications and alterations insofar as they come within the scope of the appended claims.
This application claims the benefit of U.S. Provisional Application No. 62/232,101, filed Sep. 24, 2015, which is incorporated in its entirety herein by reference.
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