Abstract:
An electric cooker includes a base, a housing supported on the base and having an opening, and a power head configured to be removably attached to the housing at the opening. The power head includes a heating unit for generating and directing heat into the housing. At least one land piece is provided on the power head for securing the power head onto the housing, and at least one corresponding tab piece is provided on the housing and is configured to matingly engage the land piece for removably attaching the power head onto the housing. A locking device provided on the power head proximate the land piece prevents the land piece and the tab piece from disengaging from a temperature increase inside the housing.

Description:
FIELD OF THE INVENTION 
   This invention relates to electric cookers, and in particular to an electric cooker having a removable power head. 
   BACKGROUND OF THE INVENTION 
   In comparison to conventional ovens, counter-top electric ovens or cookers typically offer the advantage of being less bulky and having quicker cooking times. These counter-top cookers or ovens include a power head having a heating unit that is used to heat the cooking enclosure. To reduce the cooking time, counter-top electric ovens typically will rely on a hot air stream that is cycloned around the food by a high speed fan associated with the electric heating element, or by utilizing an infrared heating element in combination with a relatively low speed fan that generates sufficient air circulation in the oven to ensure a relatively uniform temperature distribution in the oven. 
   Typically, the power head is configured to be seated in the top opening of an oven housing and locked into place by engaging projections or tabs on the rim of the oven housing with corresponding grooves or slots on the power head. In this manner, the power head and the oven housing can be lifted off the base of the oven together as a unit for access to the inside of the cooking enclosure. Locking the power head and the oven housing together also prevents the power head from being lifted off the oven housing during cooking by the pressure built-up inside the cooking enclosure. 
   Very often the oven housing is made of heat resistant, transparent plastic or glass to enable the user to maintain visual progress of food item being cooked. As a result, known oven housings tend to expand with the temperature increase in the cooking enclosure, causing the locking mechanisms to disengage. Consequently, there is a risk that the power head will become detached from the oven housing during the cooking operation from the pressure inside the cooking enclosure. The oven housing could also slip off the power head as the user lifts the power head to gain access to the inside of the cooking enclosure. 
   SUMMARY OF THE INVENTION 
   An electric cooker includes a base, a housing supported on the base and having an opening, and a power head configured to be removably attached to the housing at the opening. The power head includes a heating unit for generating and directing heat into the housing. At least one land piece is provided on the power head for securing the power head onto the housing, and at least one corresponding tab piece is provided on the housing and is configured to matingly engage the land piece for removably attaching the power head onto the housing. A locking device provided on the power head proximate the land piece prevents the land piece and the tab piece from disengaging from a temperature increase inside the housing. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a counter-top electric oven or cooker in accordance with an embodiment of the invention; 
       FIG. 2  is an exploded view of the oven shown in  FIG. 1 ; 
       FIG. 3  is a diagrammatic section view of the oven shown in  FIG. 1 ; 
       FIG. 3A  is an enlarged view of the area indicated by lines  3 A— 3 A in  FIG. 3 ; 
       FIG. 4  is a perspective view of an oven pan of the oven shown in  FIG. 1 ; 
       FIG. 5  is an exploded view of a power head of the oven shown in  FIG. 1 ; 
       FIG. 6  is an enlarged view of the area indicated by lines  6 — 6  in  FIG. 3 ; 
       FIG. 7  is a diagrammatic representation of the operating components of the oven shown in  FIG. 1 ; 
       FIG. 8  is a flow chart illustrating selected operational features of the oven shown in  FIG. 1 ; 
       FIG. 9  is a diagram illustrating a land and a tab for attaching the power head to the oven housing; 
       FIG. 10  is diagram illustrating the expansion of the oven housing during a cooking operation; 
       FIG. 11  is a diagrammatic partial sectional view of the power head including locking brackets in accordance with an embodiment of the invention; and 
       FIG. 12  is a bottom view of the power head of  FIG. 11  including the locking brackets. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Broadly stated, an embodiment of the present invention is directed to a counter-top electric oven or cooker including a base, an oven housing supported on the base, and a power head for generating and directing heat into the oven housing. The power head also includes several brackets fixed along the bottom surface for preventing the power head from unexpectedly becoming detached from the oven housing. 
   An embodiment of a counter-top electric oven made according to one embodiment of the invention is described herein and is illustrated in the drawings in connection with an infrared counter-top oven. However, it should be understood that many features of the invention may find utility in other types of counter-top electric cooking ovens, including those using cyclonic air flow in combination with simple resistance electric heating elements. Accordingly, no limitation is intended to use in connection with an infrared heating element except insofar as expressly stated in the appended claims. 
   With reference to  FIGS. 1 and 2 , a counter-top electric oven  10  includes a base  12 , an oven pan  14  supported by the base  12 , a cooking rack  16  supported by the oven pan  14 , a generally cylindrical, a transparent oven housing  18  supported by the base  12 , and a power head  20  supported on the oven housing  18  and detachably connected to the oven housing  18 . Together, the oven pan and the oven housing  18  define a cooking enclosure  21  with the oven  10  in the assembled state shown in  FIG. 1 . 
   As best seen in  FIGS. 2 and 3 , the base  12  has an interior surface  22  defined by a generally cylindrical side wall  24  and a planar bottom  26 . A pair of handles  27  extend from the cylindrical side wall  24  to allow a user to move the oven  10  from one location to another. The interior surface  22  surrounds the oven pan  14  and is spaced from the oven pan  14  by an air gap. The base  12  further includes one or more supports  28  for the oven pan  14  and one or more thermal insulators  30  between the one or more supports  28  and the oven pan  14  to prevent overheating of the base  12  by the heat from the oven pan  14 . In the embodiment shown in  FIGS. 2 and 3 , the one or more supports  28  are provided in the form of three cylindrical pillars  28 A, and the one or more thermal insulating spacers  30  are provided in the form of three cylindrical spacers  30 A, each supported by one of the pillars  28 A. As seen in the section view of the spacer  30 A and pillar  28 A in  FIG. 3 , each of the spacers  30 A includes a cylindrical stub  32  that is engaged in a mating hole  36  in each pillar  28 A to retain each of the spacers  30 A to the respective pillar  28 A. While it is preferred that the cross-sections of the spacers  30 A and the pillars  28 A be generally circular, it should be understood that the invention contemplates non-circular cross-sections, such as, for example, triangular, oval, square, rectangular, trapezoidal, hexagonal, etc. The oven pan  14  is supported on the insulators  30  to maintain the air gap between the interior surface  22  and the cooking pan  14  and to prevent overheating of the base  12 , including the handles  27 . In one embodiment, the plastic base  12  is made from a suitable polycarbonate material and the thermal insulators  30  are made from a suitable silicone rubber insulating material. 
   The metallic oven pan  14  includes an interior surface and an exterior surface  38  defined by a cylindrical side wall  39  and a planar bottom  40 . The oven pan  14  is a one piece construction made of aluminum plate with a suitable nonstick PTFE coating on the interior surface  37 . A pair of retractable handles  41  are mounted to a lip  42  that defines an outer periphery of the oven pan  14 . The handles  41  are mounted to the lip  42  for movement between a first position, shown in  FIG. 2 , where the handles  41  are extended from the lip  42  so that a user may grasp the handles  41  to remove the pan  14  from the base  12 , and a second position, shown in  FIG. 4 , where the handles  41  are retracted toward lip  42  to allow the oven housing  18  to be positioned above the oven pan  14 , as shown in  FIG. 3 , without interfering with the handles  41 . As best seen in  FIG. 4 , each of the handles  41  has a pair of legs  43  extending from a grasping member  44 . Each of the legs  43  are received in a vertical guide hole  45  formed in the lip  42  to guide the handles  41  between the first and second positions. Each of the legs terminate in a tab  46  that engages the lip  42  with the handle  41  in the first position. The handles are made from a unitary piece of metallic wire that is bent to form the grasping member, the legs  43 , and the tabs  46 . 
   The cooking rack  16  includes a planar grid  47  for supporting food items that are being cooked, a first set of loop projections  48  extending in one direction from the plane of the  47  and a second set of loop projections  49  extending in the opposite direction from the plane of the grid  47 . The projections  48  can be used to support the grid to provide a first cooking height for food items supported by the grid  47 , while the projections  49  can be used to support the grid  47  to provide a second cooking height for the grid  47 . The cooking rack  16  is made from 304 stainless steel with a suitable non-stick PTFE coating in one embodiment. 
   As best seen in  FIG. 3 , the oven housing  18  includes an interior surface  50  defined by a generally cylindrical side wall  52  that blends into a generally conical shaped side wall  54  which in turn blends into a planar upper wall  56  which finally blends into a generally cylindrical ring portion  58 . An annular lip  59  is formed on the outer surface of the wall  52  and serves to support the oven housing  18  on the side wall  24  of the base  12 . A portion  60  of the wall  52  that extends below the lip  59  cooperates with the side wall  24  of the base  12  to restrict the leakage of hot gases, such as steam, from the cooking enclosure  21 . As best seen in  FIG. 3A , the portion  60  includes an annular lead-in chamfer or relief  61  that serves to guide the portion  60  into the base  12 , thereby easing the engagement of the oven housing  18  to the base  12  and preventing the mislocation of housing  18  relative to the base  12 , i.e., the housing  18  can be inserted into the base  12  while being tilted somewhat relative to vertical. In one embodiment, the oven housing  18  is formed from a suitable transparent polycarbonate material. However, other material such as glass, or even metal may be used. 
   As best seen in  FIGS. 3 and 5 , the power head  20  includes an exterior housing assembly  62 . The assembly  62  includes a domed shape upper housing  64  having a pair of handles  65  (best shown in  FIG. 5 ), and a lower housing  66  including a generally cylindrical wall portion  68  and an annular flange  70 . As seen in  FIG. 2 , four substantially equally spaced lands  72  (only one shown) are raised from the wall portion  68  to engage a plurality of corresponding ramped tabs  74  formed on the ring portion  58  of the housing  18  to detachably connect the power head  20  to the housing  18 . A illustration of the manner in which the tabs  74  engage the lands  72  are shown in  FIG. 9 . The land  72  engages the tab  74  when the power head  20  is rotated in the clockwise direction, thereby moving the land on the wall portion  68  in the direction indicated by arrow “A” towards the stationary tab projecting from the ring portion  58  of the housing  18 . 
   The power head  20  further includes a motor  76  for driving a cooling fan  78  and an oven fan  80  via a common shaft  82 , an infrared electric heating element  84 , a heater/fan housing  86 , a radiation plate  88  mounted to an interior surface of the heater housing  86 , a glass fiber thermal insulator  90  mounted between the heater housing  86  and the motor  76 , a mica sheet  92  mounted between the upper housing  64  and the lower housing  66 , a protective grid  94 , a thermistor  96 , a thermostat  98 , and a controller  100  including a pair of control boards  102  and  164  for controlling the heating element  84  and the motor  76  in response to signals from the thermistor  96  and command signals input into a control panel  106  by a user. 
   In one embodiment, the fan  78  is made of a suitable plastic material, while the fan  80  and the radiation plate  88  are made of aluminum plate in order to reflect the infrared energy from the heater  84  down toward the interior of the cooking enclosure  19 . The motor  76  drives the fans  78  and  80  at a speed in the range of about 2500 rpm, which should provide an adequate air flow from the fan  80  to create a relatively even temperature throughout the cooking enclosure  21  and to speed the cooking of food by convection to supplement the infrared cooking, without generating the high speed air motion associated with some cyclonic electric counter-top ovens. Another benefit of the relatively low speed air flow created by the fan  80  is that it helps to maintain the hot surfaces of the oven  10  in a temperature range that will tend to emit infrared radiation and limits the decrease in emissivity of the non-metal materials of the oven  10 . 
   Together, the cylindrical wall  68  of the lower housing  66 , the heater housing  86 , the radiation plate  88 , the fan  80 , and the heating element  84  define a heating unit  108  that extends into the cooking enclosure  21  through an opening  110  defined by the ring portion  58  of the housing  18 . Together, the upper housing  64  and the mica sheet  92  define a fan chamber  111  that is thermally insulated from the interior of the cooking enclosure  21  by the mica sheet  92 , the glass fiber insulator  90 , the heater housing  86 , the radiation plate  88 , and the lower housing  66 . As best seen in  FIGS. 3 and 5 , a plurality of cooling air outlets  112  are formed in the annular flange  70  of the lower housing  66 . Cut-outs  113  are provided in the mica sheet  92  to prevent interference between the outlets  112  and the mica sheet  92  and to allow a cooling air flow to pass through the mica sheet  92  to the outlets  112 . The outlets  112  are generally equally circumferentially spaced around the flange  70 . 
   Together the flange  70  and the outlets  112  define a cooling manifold  114  that surrounds the opening  110  of the housing  18  and faces the surface  56  outside of the cooking enclosure  21 . The cooling fan  78  actively cools the fan chamber  111  and the walls  52 ,  54 ,  56  and  58  of the housing  18  by drawing a cooling air flow through a plurality of inlet openings formed in the upper housing  64  and forcing the cooling air to exit through the outlets  112 , which direct the cooling air flow toward the surface  56  of the housing  18  to cool the housing  18 , as indicated by arrows A; 
   As best seen in  FIG. 6 , the wall  68  and the flange  70  are spaced from the ring portion  58  of the housing  18  by the tabs  74  to define a hot gas vent  118  that surrounds the heating unit  108  between the heating unit and the outlets  112  to vent hot gas, such as steam, from the inside of the cooking enclosure  21  for mixture with the cooling air flow from the air outlets  112 , as shown by the arrow “B”. 
   The control boards  102  and  104  are spaced from the interior surface of the upper housing  64  by a plurality of mount supports  120  to allow the cooling air flow to pass over both sides of the control boards  102  and  104  as it circulates around the fan chamber  111  before exiting through the outlets  112 , thereby enhancing the cooling of the electronics on the control boards  102  and  104 . 
   As best seen in  FIG. 7 , the controller  100  is connected to the motor  76  and the heating element  84  to control the flow of electric power to the motor  76  and the heating element  84  in response to signals from the thermistor  96  and command signals input by the control panel  106  by a user. The controller  100  is configured to selectively power the heating element  84  at a number of power levels P from a minimum power to a maximum power. At each power increment P, the controller  100  powers the heating element  84  when the thermistor  96  indicates that the temperature in the cooking enclosure  21  has fallen below a low temperature set point associated with the particular power level P. The controller  100  then terminates power to the heating element  84  when the temperature indicated by the thermistor  96  exceeds a high temperature set point associated with the particular power level P. The controller  100  provides power continuously to the motor  76  during the heating operations regardless of the power level selected. 
   As best seen in  FIG. 8 , the controller is configured to limit the cooking time at the maximum power setting to two hours to prevent overheating of the oven  100 . More specifically, after a user sets the power level P and enters the desired cook time t at block  130 , it is determined at  132  whether the power has been set to the maximum power level. If the power is set to maximum, it is determined at  134  whether the desired cooking time exceeds two hours. If the desired cooking time exceeds two hours, the cooking time is automatically limited to two hours by the controller  100  at  136 . If the desired cooking time is less than two hours, or if the power level P is not set to maximum, the controller is configured to run the heating element  84  and the motor  76  at the power level P and for the desired cooking time t, as shown at block  138 . 
   After the cooking time has expired, the controller  100  is configured to terminate power to the heating element  84  and to the motor  76 . However, as an optional feature, after the cooking time has expired, the controller  100  can be configured to terminate power to the heating element  84  while providing power to the motor  76  for a five minute cooling stage, for example, as shown at  140  and  142 . This may allow time for the hot gases in the cooking enclosure  21  to vent and to be cooled by the cooling air flow from the outlets  112 , thereby preventing hot gases, such as steam from accumulating in the cooking enclosure  21  and/or the fan chamber  111  and also preventing the handles  65  from overheating. 
   Turning now to  FIG. 10 , the power head  20  is shown attached to the oven housing  18  (partially shown), and locked together by the lands  72  (two shown) protruding from the wall portion  68  of the power head  20  to the corresponding tabs  74  projecting from the ring portion  58  of the oven housing. When the temperature inside the cooking enclosure  21  is relatively cool, the lands  72  and the tabs  74  remain locked to the housing  18 , as shown in solid lines. However, as the temperature rises in the cooking enclosure  21 , at least the ring portion  58  (shown in phantom) of the housing  18  may expand outwardly in the direction away from the wall portion  68  of the power head  20  (illustrated by arrows  144 ), causing the tabs  74  to be disengaged from the lands  72 . Consequently, the pressure inside the cooking enclosure  21  may force the power head  20  to be unseated from the housing  18 . Even if the power head  20  does not come off on its own, it likely will come off unexpectedly when an unsuspecting user lifts the power head  20 , thinking he/she is lifting the housing  18  along with the power head  20 . 
   Referring to  FIGS. 11 and 12 , and in accordance with an embodiment of the invention, several locking brackets  146  (two shown in  FIG. 10 ) are attached proximate the protruding lands  72  along the annular flange  70  (best shown in  FIG. 12 ). The locking brackets  146  are spaced from the wall portion  68  of the power head  20 , from which the lands  72  protrude. Gaps  148  between the locking brackets  146  and the wall portion  68  are substantially the thickness of the ring portion  58  of the housing  18 , so as to receive the ring portion substantially securely in the gap. 
   In one embodiment of the invention, the locking brackets  146  are formed from a substantially rigid, generally “L” shaped strip of material having a substantially straight horizontal portion  150  which is affixed to the annular flange  70 , and a substantially straight, vertical portion  152  which is generally parallel to the wall portion  68  of the power head  20 . In one embodiment of the invention, an end portion  154  extends from the vertical portion  152  at an angle (greater than zero to approximately 90 degrees) away from the wall portion  68  (best shown in  FIG. 11 ). The end portion  154  assist in guiding the ring portion  58  into the gap  148  between the locking brackets  146  and the wall portion  68  of the power head  20 . 
   It should be understood that the term “strip” as used in this application is not limited to a flat strip, but includes other cross-sectional shapes. The strip, for example, may be flat on the side facing the annular flange  70  but rounded on the opposite side, or a piece of wire with a diameter being sufficient to maintain a substantially rigid form, etc. The locking brackets  146  in one embodiment is metal, but other materials that remain substantially rigid after being formed into its generally “L” shape are also contemplated. 
   The horizontal portion  150  is affixed to the annular flange  70  by any known means such as welding, riveting, soldering, tightening by screws, etc., which may accommodate the cross-sectional shape of the horizontal portion. For example, screws or rivets might be more appropriate if the horizontal portion  150  is flat, but not, if a rigid piece of wire with a circular cross-section is used for the bracket  146 . 
   In operation, the locking brackets  146  are positioned along the annular flange  70  proximate the protruding lands  72  (best shown in  FIG. 12 ). When the power head  20  is inserted into the opening  110  of the oven housing  18  (best shown in  FIGS. 2 and 3 ), the ring portion  58  of the housing is guided between the locking brackets  146  and the wall portion  68  of the power head. In the locked position in which the tabs  74  and the lands  72  are engaged (best shown in  FIG. 9 ) to secure the power head  20  to the oven housing  18 , the locking brackets  146  abut, or are in very close proximity to the ring portion  58  of the housing  18  (best shown in  FIG. 11 ). Having this arrangement, the locking brackets  146  prevent the oven housing  18  from expanding in the direction away from the wall portion  68  of the power head  20  (as illustrated in  FIG. 10 ), at least in the area where the tabs  74  and the lands  72  are located. In this manner, the locking brackets  146  keep the tabs  74  and the lands  72  engaged or locked together, thereby securing the power head  20  to the oven housing  18  even when the temperature inside the cooking enclosure is high enough to cause the oven housing to expand. 
   While various embodiments of the present invention have been shown and described, it should be understood that other modifications, substitutions and alternatives are apparent to one of ordinary skill in the art. Such modifications, substitutions and alternatives can be made without departing from the spirit and scope of the invention, which should be determined from the appended claims.