Abstract:
A range infinite switch including a ground fault circuit interrupter (GFCI) subsystem is provided. The GFCI subsystem operates a solenoid and plunger arrangement that activates a mechanical interlock within the switch permitting axial movement of a cam customarily used to bias temperature controlling contacts within the switch. Upon detection of a ground fault the latching mechanism is released and the cam moves to a position where the temperature controlling contacts are opened so as to disconnect power to a range heating element. In an appliance having more than one heating element, each heating element would be separately protected from ground fault conditions by use of the disclosed switch.

Description:
FIELD OF THE INVENTION 
     The present subject matter relates to home appliances. More particularly, the present subject matter relates to improvements in temperature control switches for cooktops, particularly those cooktops employing coil type heating elements. 
     BACKGROUND OF THE INVENTION 
     Electric range cooktops employing steel tube and magnesium oxide heaters have a propensity to degrade and short. Depending upon where a short may develop within the coil assembly, a shorting event can lead to excessive energy and molten metal being expelled. Incorporation of a ground fault circuit interrupter (GFCI) device within the cooktop can provide early detection of a short by monitoring for the presence of leakage currents thereby permitting disablement of the load, that is, the heating element, before a high power event occurs. 
     Advantages obtained through the inclusion of a GFCI device include reducing the risk of element shorting events as well as other undesirable occurrences including potential electric shock of a user or a fire within the cooktop. Often, the cooktop connector system, harnessing, and controls are damaged during occurrence of a high power event. Prior attempts to address these disadvantages have called for employing GFCI circuits utilizing relays in the cooktops which are separate from the traditional infinite control switches. This approach also has disadvantages due to the fact that simultaneous opening of both the power lines in a split-phase mains fed appliance is not assured. 
     Thus, a need exists for a protective approach that will ensure that both power lines to the heaters will open simultaneously. It would be particularly advantageous to simultaneously disconnect both power lines especially if the GFCI circuit becomes disconnected from only one power line becoming open thus loosing further protection. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention. 
     The present subject matter relates to a range infinite switch having a housing in which is mounted a shaft having a longitudinal axis which shaft is mounted at least partially within the housing for rotational and axial movement. A cam is secured to the shaft for rotational and axial movement therewith and a pair of terminals are provided and configured to be coupled to a source of alternating current (AC). The switch includes at least one pair of contacts positioned for movement between open and closed positions based on movements of the cam. There is also provided a ground fault circuit interrupter (GFCI) circuit board mounted within the housing and configured to monitor current flow through the pair of terminals. A solenoid operable in response to the GFCI is provided along with a plunger operable in response operation of the solenoid. A latching mechanism within the housing is configured to hold the cam in a first axial position until released by operation of said plunger so that release of the cam causes the at least one pair of contacts to separate. In this manner, any load coupled to the separated contacts will be disconnected from power applied to the pair of terminals upon detection of a ground fault. 
     The present subject matter also relates to a range infinite switch having a housing having a pair of side walls and a pair of end walls. In accordance with an exemplary embodiment, such range infinite switch incorporates a shaft extending through the pair of end walls and mounted within the housing for rotational and axial movement as well as a cam mounted within the housing and secured to the shaft for rotational and axial movement therewith. The range infinite switch also includes at least one pair of contacts positioned within the housing for activation by the cam. In accordance with this embodiment of the present subject matter, a fork is pivotally mounted at one end within a side wall of the housing and extends into the housing and is in contact with the cam for positioning the cam in a first position. A fork retainer is provided and configured to retain the fork in the first position. The range infinite switch further includes a ground fault circuit interrupter (GFCI) board mounted within the housing. The GFCI board including a solenoid energizeable upon detection of a ground fault and a plunger operable upon energization of the solenoid to move the fork retainer to release the fork. Release of the fork permits axial movement of the cam and opening of the at least one pair of contacts. 
     Embodiments of the preset subject matter further relates to a cooktop appliance. According to such embodiments there is provided a cooktop including at least one heating element and at least one range infinite switch configured to control application of electrical energy to the at least one heating element. In such embodiments the at least one range infinite switch comprises a housing, a shaft having a longitudinal axis mounted at least partially within the housing for rotational and axial movement, and a cam secured to the shaft for rotational and axial movement therewith. Further the at least one range infinite switch includes a pair of terminals configured to be coupled to a source of alternating current (AC) and at least one pair of contacts positioned for movement between open and closed positions based on movements of the cam. In such embodiments, there is also provided a ground fault circuit interrupter (GFCI) board mounted within the housing and configured to monitor current flow through the pair of terminals. The at least one range infinite switch also includes a solenoid operable in response to the GFCI, a plunger operable in response operation of the solenoid and a latching mechanism configured to hold the cam in a first axial position until released by operation of the plunger. In such embodiments release of the cam causes the at least one pair of contacts to separate thereby disconnecting power to the at least one heating element upon detection of a ground fault condition by the GFCI board. 
     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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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, in which: 
         FIG. 1  is a perspective view of a cooktop embodying coil-top cooktop useful in describing one form of the present invention; 
         FIG. 2  illustrates a schematic representation of a range infinite switch with integral GFCI subsystem in accordance with the present subject matter in an operating position; and 
         FIG. 3  illustrates a schematic representation of a range infinite switch with integral GFCI subsystem in accordance with the present subject matter in a tripped position. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     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. 
     Generally, the present subject matter is directed to home appliances and, more particularly, to improvements in temperature control switches for cooktops, particularly those cooktops employing coil type heating elements. 
     It should be appreciated that while the present disclosure is particularly directed to improvements in switches designed in general for use with cooktops, it is also envisioned that such switch may equally be employed with other appliances or devices where protection from ground fault currents in an electrical load is desirable. 
     Referring more particularly to the presently disclosed subject matter and with reference to  FIG. 1  there is shown a cooktop unit  10  comprising a conventional planar glass-ceramic cooktop surface  11  and a control panel  12 , the latter incorporating cooking temperature controls  13 , and indicator lights  14  to indicate the “on” condition of the cooking heaters. A plurality of steel sheathed coil assemblies  15   a - 15   d  adapted to orient and support cooking utensils during normal cooking operations are provided The cooktop unit  10  is shown in the form of a built-in unit mounted in the counter top  16  of a kitchen cabinet, however, it will be understood that a cook unit incorporating the present subject matter may be embodied in other arrangements such as the cooking surface atop the oven of a free standing range. 
     With reference to  FIGS. 2 and 3  there are illustrated representations of a range infinite switch  200 ,  300  with integral GFCI subsystem  202 ,  302  in accordance with the present subject matter.  FIG. 2  illustrates switch  200  in a normal position, that is, a position where electrical power is applied to a load.  FIG. 3  illustrates switch  300  in a tripped position, that is, in a position where electrical power is not applied to a load. 
     Switch  200 ,  300 , in accordance with the present subject matter, corresponds to an assembly which is a combination of a generally traditional “Infinite” switch used for electric range cooktop element level setting combined with a Ground Fault Circuit Interrupter (GFCI) detector and high current circuit deactivator. Examples of such traditional “Infinite” switches are well known in the art as exemplified by U.S. Pat. No. 4,052,591 to Sekera, Jr. et al. It is noted that the switch illustrated by Sekera, Jr. et al. corresponds to a voltage-mode type infinite switch as it includes a heater coil for the bi-metal element couple in parallel with the heating element to be controlled. Those of ordinary skill in the art will appreciate, however, that the present subject matter may also be employed in current-mode infinite switches wherein current flowing through the bi-metal is used as the bi-metal heat source. Likewise, GFCI circuits are also well known in the art as exemplified by U.S. Pat. No. 4,001,646 to Howell and assigned to the assignee of the present subject matter. The present subject matter, however, combines these known devices in a synergistic way along with a high current circuit deactivator mechanism to afford improved electrical fault protection for cooktops. 
     With further reference to  FIG. 2 , in “normal” operation of the cooktop, switch  200  functions as a traditional current-mode infinite switch where the arc, i.e., rotational, position of D-shaft  204  selects between OFF, FULL ON and infinitely variable duty cycle selection in between. If a ground fault is detected in load  250 , switch  200  cuts off the load current via operation of a mechanical interlocking arrangement between fork  206  and fork retainer  208  together with the axial movement of D-shaft  204 , fork  206 , and cam  224  in a direction opposite to arrow  240  causing separation of contact sets  226 ,  228  as will be described further later. Once tripped, manual intervention is required to restore normal operation. Generally a reset operation may be performed by pushing D-shaft  204  axially in the direction of arrow  240  so as to allow fork  206  to once again be latched in place by fork retainer  208  while at the same time moving cam  224  in the direction of arrow  240  so as to permit closure of contact sets  226 ,  228  when called for depending on the arc (rotational) position cam  224 . 
     With more specific reference to  FIG. 2 , it will be seen that switch  200  generally corresponds to a rectangular housing  234  having generally vertical parallel sidewall portions  242 ,  244  and horizontal end wall portions  246 ,  248 .  FIG. 2  illustrates switch  200  in an operating position, that is, in a position where electrical power is applied to load  250 , that, in this particular case, may correspond to a heating element for a cooktop. Further, switch  200  includes a D-shaft  204  that at least partially extends through end wall portions  246 ,  248 . D-shaft  204  is coupled to cam  224  in a manner such that both D-shaft  204  and cam  224  may rotate around the axial direction of D-shaft  204  represented by arrow  240  and to move axially together along the axis illustrated by arrow  240 . 
     Switch  200  further includes a GFCI circuit board  202  that, in certain embodiments, may correspond in part to end wall portion  246  of housing  234 . Alternative embodiments may provide a further wall portion configured to enclose GFCI circuit board  202  along with the remaining switch  200  components. In an exemplary configuration, GFCI circuit board  202  may correspond to a printed circuit board supporting various components including a current transformer  254  and solenoid  218  all of which are well known in the art and are exemplified by the &#39;646 patent to Howell previously noted. In accordance with the present subject matter, a high current circuit deactivator mechanism is provided by way of the cooperative operation of fork  206 , fork retainer  208 , cam  224  and contact sets  226 ,  228 , all activated by the operation of a solenoid  218  and plunger  220  associated with GFCI board  202 . 
     With continued reference to  FIG. 2 , there is illustrated a fork  208  that is pivotally mounted in housing  234  such that one end of fork  206  passes through an opening in side wall portion  242  to provide a fulcrum point  232  for fork  206 . A central length of fork  206  is configured to contact cam  224  and fork end  238  remote from fulcrum point  232  is engaged with fork retainer  208  to hold for  206  in contact with cam  224  against an a tension force produced by spring  222 . The central portion of fork  206  may be engaged by a securing device  236  to secure fork  206  to D-shaft  204  to maintain fork  206  in proper position and orientation for proper interaction at fulcrum point  232  and cooperative operation with fork retainer  208 . In this configuration, cam  224  may be rotated by way of rotational interaction with D-shaft  204  to operate as a traditional current-mode “Infinite” switch for electric range cooktop element control in cooperation with contact sets  226 ,  228  in a well-known manner. Generally, however, infinite switch operates based on rotation of cam  224  that causes contact set  226  to open and close based on “ON” and “OFF” positions of the switch. At the same time contact set  228  is variably biased so that heating of bimetal and heater arm  252  of the contact set must traverse variable distances in order to energize or deenergize load  250 , for example, a heating element. 
     In normal operation, household alternating current (AC) is applied to terminals  210 ,  212 , so that current flow through terminals  210 ,  212  is equal. If a path to ground develops in load  250  connected to terminals  214 ,  216 , the current flow through terminals  210 ,  212  becomes unequal. i.e., unbalanced. This unbalanced current flow is sensed by GFCI  202  in a well-known manner. When a current unbalance is sensed by GFCI  202  circuit, the circuit activates solenoid  218  whose plunger  220  displaces fork retainer  208  against a retaining force produced by spring  242 . Displacement of fork retainer  208  allows end portion  238  of fork  206  to become free and to move upwardly in a direction opposite to arrow  240  along with cam  224  due to the force produced by spring  222 . Movement of cam  224  in a direction opposite to arrow  240  causes contact sets  226 ,  228  to open thereby disconnecting any load connected to terminals  214 ,  216  from a power source connected to terminals  210 ,  212 . 
     With reference to  FIG. 3 , it will be seen that freed fork  306  relieves spring  322  pressure on cam  324 . When cam  324  is relieved, the contact sets  326 ,  328  it actuates are unloaded resulting in a spread between the contacts. When cam  324  and contact sets  326 ,  328  are no longer under spring  322  tension, contact sets  326 ,  328  cannot close to complete a circuit to the load. If the fault is removed or repaired, the mechanism can be reset to normal operating position by pressing on D-shaft  304  in an axial direction, i.e., in the direction of arrow  340 . D-shaft  304  is typically accessible from the front panel of the range as, for example, shown at  13  ( FIG. 1 ). 
     In accordance with the present subject matter, the synergistic placement of contacts  226 ,  228 ,  326 ,  328 , cam  224 ,  324 , fork  206 ,  306 , fork retainer  208 ,  308 , springs  222 ,  322 , solenoid  218 ,  318 , plunger  220 ,  320 , and D-shaft  204 ,  304  allows proper mechanical sequence for tripping and resetting. 
     As is common in GFCI circuits, a TEST terminal  230 ,  330  may be coupled to GFCI circuit  202 ,  302  to provide a means to simulate an unbalanced current. When test terminal  230 ,  330  is connected, switch  200 ,  300  will trip, i.e., disconnect the heating element after which switch  200 ,  300  can be manually reset as described above. 
     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.