Abstract:
A movable cooking appliance comprises a structure which is adapted to be placed on a kitchen worktop appliance or inside a cooking oven appliance and includes a heating element and releasable connector assembly for making electrical connection with power supply connectors. The heating element is an induction heating element and an electronic driving unit is mounted on the appliance. The releasable connector assembly comprising a plug connector having a plurality of terminals designed in order to provide a disconnection signal to the electronic unit before the power supply connectors are fully extracted.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to movable cooking appliances or cooking trays including structure which is adapted to be placed on a worktop of kitchen furniture or inside a cooking oven (collectively referred to as a cooking unit), and includes a heating element and releasable connector means for making electrical connection with power supply connector means. With the term “movable” we mean any kind of cooking and heating appliance which can be plugged or unplugged to a fixed support, whatever such support is. 
         [0003]    2. Description of the Related Art 
         [0004]    The above kind of cooking appliances or cooking accessories are well known in the art. An example is shown in U.S. Pat. No. 5,272,317. With the known appliances the heating element is an electrical resistance heater connected, for instance, to a shelf or tray adapted to be introduced into an oven cavity. The use of electrical resistance heaters has been replaced by more efficient induction heating elements which, despite a higher complexity and cost (mainly due to the complex electronic driving circuit), allow the induction heating elements to reach a desired temperature in a shorter time and with a lower energy consumption. One compromise would be to design an induction cooking appliance or accessory without a built-in electronic driving circuit, and integrating this in kitchen furniture or cooking appliance (such as a traditional oven or an induction oven). By adopting this solution it is important to assure a safe and reliable connection between the “fixed” electronic driving circuit and the movable induction cooking appliance or accessory. 
         [0005]    Prior art connectors that are in use generally have terminals with equal length. The design of these connectors doesn&#39;t implement any further safety feature that guarantees power supply cut-off when the user is extracting the removable tray with an induction heater while the tray is working. This abnormal procedure may happen during the use of the oven and this can cause a potential risk of electric arcing at the power terminals and potential breakdown of the insulated gate bipolar transistor (IGBT) associated with the electronic driving circuit of the heating element. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention is mainly focused on the problem of assuring safe and reliable insertion and extraction of a releasable connector means for connecting an induction tray, for instance, into an oven cavity. The present invention also addresses a tray including an induction element being plugged into or unplugged from the socket of a power supply connector means located inside an oven cavity in a safe manner. It is therefore an object of the present invention to provide a solution to the above concerns. 
         [0007]    The present invention is focused on the design of a connector that is to be used to connect an induction tray into a socket of an oven cavity or other type of support used for the tray. In a preferred embodiment of the invention, the connector has five male terminals, including two for the power connection (i.e., supplying an induction heating coil), two for the temperature sensor connection (that allows a reading of temperature sensor placed in the coil centre of the induction heating element for safety reasons) and one a ground connection (that guarantees electrical safety for the user). The design of the connector according to the invention enables a safer and more reliable insertion and extraction of the male plug of the induction heating tray whenever the user uses it as an accessory inside an oven or on a kitchen worktop. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Further advantages and features according to the present invention will be clear from the following detailed description, with reference to the attached drawings in which: 
           [0009]      FIG. 1  is a schematic view of an oven according to the present invention; 
           [0010]      FIG. 2  is a schematic view detailing the male and female terminals of a plug connector of the oven of  FIG. 1 , according to a first embodiment of the invention and in a first configuration of use; 
           [0011]      FIG. 3  is a schematic view similar to  FIG. 2 , showing the terminals in a second configuration of use; 
           [0012]      FIG. 4  is a schematic view similar to  FIG. 2 , showing the terminals in a third configuration; 
           [0013]      FIG. 5  is a schematic view similar to  FIG. 2 , showing the terminals in a fourth configuration; 
           [0014]      FIG. 6  is a schematic view detailing the male and female terminals of the plug connector an oven of  FIG. 1 , according to a second embodiment of the invention; 
           [0015]      FIG. 7  is a variant of the embodiment shown in  FIG. 6 ; 
           [0016]      FIG. 8  is a schematic view detailing the male and female terminals of a plug connector of the oven of  FIG. 1 , according to a third embodiment of the invention and in an unplugged configuration; 
           [0017]      FIG. 9  is a schematic view similar to  FIG. 8  in a plugged configuration; 
           [0018]      FIG. 10  is a schematic view detailing the male and female terminals of a plug connector according to a fourth embodiment of the present invention; 
           [0019]      FIG. 11  is a schematic view of the male terminals of a plug connector in accordance with a further embodiment of the present invention; 
           [0020]      FIG. 12  is a schematic view of the male terminals of a plug connector in accordance with yet a further embodiment of the present invention; 
           [0021]      FIG. 13  is a schematic view detailing the male and female terminals of a plug connector of the oven of  FIG. 1 , according to another embodiment of the invention, in a partially unplugged position; and 
           [0022]      FIG. 14  is a schematic view similar to  FIG. 13 , in a plugged position. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0023]    With reference to the drawings, an induction oven having a cabinet  10  is shown in  FIG. 1 , the oven cabinet  10  defining a cooking cavity  10   a  where an induction tray  12  can be inserted and pulled out. The tray  12  has a double layer main body structure made of non-ferromagnetic material, such as aluminium, and includes an embedded induction heating element or coil (indicated at  36  in  FIGS. 11 and 12 ) with a temperature sensor (depicted at  34  in  FIG. 11 ). On a rear side  12   a  of the tray  12  there is a plug connector  14  for the electrical connection of tray  12  with a socket connector  16  placed on a rear wall  11  of the oven cavity  10   a . In the following, we indicate with reference C the overall power connector assembly of the present invention, including the plug or male connector  14  supported by the tray  12  and the socket or female connector  16  supported by the oven. 
         [0024]    As noted previously, with known connectors, the design is not able to provide good safety as it doesn&#39;t implement any extra feature which lets the power board cut off the power before male plug extraction. Because of this, extraction of the induction tray  12  without cutting off the power supply to tray  12  may cause safety problems for the customer and reliability problems for the oven. 
         [0025]    According to a first embodiment of the present invention depicted in  FIG. 1 , the design of connector C presents assemblies of five male terminals and associated female terminals which make up a total of five connections. Two sets of the terminals  18  provide power connections, two sets of the terminals  20  are for the temperature sensor connection and one set including terminal  22  is for the ground connection. As shown in the embodiment of  FIG. 2 , the ground terminal  22  has the greatest length, the sensor terminals  20  (equal to each other in length) are the shortest ones and the power terminals  18  (equal to each other in length) have an intermediate length between the lengths of the ground terminal  22  and of the sensor terminals  20 . This design enables the ground terminal  22  to connect first during insertion of plug  14 , and to disconnect last during extraction of the plug  14 , guaranteeing safety electrical discharge through ground terminal  22  in case there might be a discharge between induction coil  36  (again depicted in  FIGS. 11 and 12 ) and aluminium plates of the tray  12 , thus eliminating the electrical risks for the user.  FIGS. 2 ,  3 ,  4  and  5  show different positions of the male-female connector C:  FIG. 2  shows a complete insertion of the plug  14  with all terminals having complete electrical contact;  FIG. 3  shows a partial extraction of male plug  14  with ground  22  and power terminals  18  yet in contact;  FIG. 4  shows a configuration in which only ground  22  remains in contact; and  FIG. 5  shows full extraction, i.e., all terminals are not in contact with socket connector  16 . As illustrated in  FIG. 3 , during extraction of the male plug  14 , the sensor terminals  20  lose electrical contact first since they have the shortest length. Once this happens, a power board indicated at P senses the connection as an open-circuit and automatically cuts off the power to the tray  12  before the power terminals are actually disconnected (as they are still in contact with the female sockets due to their longer terminals). 
         [0026]    According to a second embodiment of the invention depicted in  FIG. 6 , inside the female plug  16  there is a switch  24  that is electrically closed by the ground plug  22  when inserting the male plug  14 . This circuit is connected to power board P of the oven. The switch  24  can be of any kind. For instance, it can be a mechanical switch (that is in physical contact with the terminals) or it can be a proximity switch (that doesn&#39;t need a physical contact), such as a reed switch  40  shown in  FIGS. 13 and 14 . This switch mechanism  24  can be short-circuited and open-circuited, distinguishing the cases between complete male plug insertion and not complete insertion, respectively. As can be seen in  FIG. 6 , the extraction of the male plug  14  from the female socket  16  including mechanical switch  24  causes the opening of the circuit, sending therefore a signal to the power board P to interrupt the power supply to the tray  12  before the power terminals  18  are disconnected. 
         [0027]    It is clear that the position of the mechanical switch  24  (in  FIG. 6  it is positioned close to the ground terminal  22 ) can vary and can be applied to any other terminal. However, it must be placed in a way that the mechanical switch  24  opens before the power terminals  18  are completely extracted, in order to allow the power board P to cut off the power before the connector  14  is fully extracted from female plug  16  (safety power cut-off). 
         [0028]      FIG. 7  shows a connector C which is slightly different from the one shown in  FIG. 6 , and where the length of the terminals  18 ,  20  and  22  are similar to the one shown in  FIG. 2 . In this embodiment, the ground terminal  22  remains the longest for safety precaution as already explained. If the switch  24  is a reed switch, the terminal involved has to be made of permanent magnetic material. 
         [0029]    A further embodiment of the present invention is shown in  FIGS. 8 and 9 , where the male plug  14  has terminals of identical lengths and a female socket  16  with a mechanical switch mechanism  26 . This mechanism  26  comprises a metal piece  26   a  hinged to one of the temperature sensor female terminals  20  via a spring  26   b . When the male plug  14  is not inserted ( FIG. 8 ), the metal piece  26   a  contacts both terminals  20  of sensor  34 , short-circuiting them. The power board P senses that temperature sensor terminals  20  are short circuited and it doesn&#39;t supply power to induction tray  12 . Otherwise, when the male plug  14  is inserted ( FIG. 9 ), the metal piece  26   a  doesn&#39;t contact both terminals  20  and therefore the power board P supplies power to the induction tray  12  as it senses that the male plug  14  is fully inserted and there is no safety issue. 
         [0030]    The embodiment shown in  FIG. 10  has all five terminals  18 ,  20 ,  22  mentioned above at equal length, and it presents in addition a sixth terminal  30   b  (associated with an additional plug  30   a ) which is made of another material such as ceramic or plastic and which has a greater length than other terminals. This sixth terminal  30   b  turns on and off the electrical connection by a mechanical switch  32  during insertion and extraction, respectively. 
         [0031]    The embodiment shown in  FIG. 11  has the aim of reducing the number of terminals or to avoid the need of adding extra sensor terminals. Reducing the number of terminals would provide a cost saving and easier connection in addition to space saving inside the oven. More specifically, the male plug  14  in this embodiment has four terminals consisting of one ground terminal  22 , two power terminals  18  and one single terminal  20  for a temperature sensor indicated with reference  34  in  FIG. 11 , while the induction coil is schematically indicated with reference  36 . According to this embodiment, in order to save material and space, it is possible to use the ground terminal  22  as the second sensor terminal. This embodiment has the ground terminal  22  with the greatest length, the sensor single terminal  20  with the shortest length and the power terminals  18  in between these two lengths as in the first above embodiment. The power board P should be designed for reading the sensor signal with an isolated signal-conditioning circuit, as it is referenced with the oven ground which is isolated with respect to the power supplier in any appliance by default. 
         [0032]    In the further embodiment shown in  FIG. 12 , the five terminals of the previous embodiment  18 ,  20  and  22  are maintained and an extra temperature sensor  38  is added that will still use the ground as a reference level. This can also be extended to three readings using three terminals and a ground terminal, and so on. Increasing the number of temperature readings enables a better control of the induction heater temperature, and using the ground terminal provides a savings from the number of terminals needed. The power board P should be designed for reading the sensor signal with an isolated signal-conditioning circuit in this embodiment, as well. 
         [0033]    Even if in the above embodiments the plug connector  14  is shown as supported by the induction tray  12 , it is clear that such a plug connector can be supported by the rear oven wall  11  and the socket connector  16  can be supported by the tray  12  as well.