Abstract:
Microwave pressure cooker including safety interlock mechanism. A blow vent is provided in cooker lid, and a lock bar is pivoted to cooker lid in a position to block blow vent when lock bar is resting under its own weight. Free end of lock bar includes a lock tab. Lock tab extends through a slot at periphery of lid. Cooker base includes handle with a cam section ending in a lock wall. Cooker lid is placed on base in a release position and rotated to a locking position. During rotation lock tab rides over cam section and then falls adjacent lock wall, thus sealing blow vent. After cooking cover is physically prevented from rotating back to release position by lock tab abutting lock wall. User must physically lift lock bar to unseal blow vent to ensure internal pressure is released. A spline may hold lock bar in raised position.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is related to co-pending Ser. No. 29/455,339, the contents of which are included herein by reference. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     The present invention relates in general to cooking implements, and pressure cookers for food. In particular, the present invention relates to an improved microwave pressure cooker having safety interlock features, and a guard against under-pressure locking. 
     Pressure cookers for use in microwave ovens are known in the literature, with U.S. Pat. No. 4,796,776 to Dalquist et al. being a good example. In practice, however, these devices must meet various regulations for safety including safety interlock features. The nature of these microwave pressure cookers do not lend themselves to existing interlock arrangements. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a microwave pressure cooker providing safety interlock features. 
     Another object of the present invention is to provide a microwave pressure cooker having a positive safety lock preventing opening of the cooker without release of internal pressure. 
     Yet another object of the present invention is to provide a pressure indicator which also functions to prevent negative pressure within the cooker during cooling. 
     These and other objects are achieved by a microwave pressure cooker. The pressure cooker includes safety interlock meeting current regulations. A blow vent is provided in the cooker lid, and a lock bar is pivoted to the cooker lid in a position to block the blow vent when the lock bar is resting under its own weight. The free end of the lock bar includes a lock tab with a spline projecting outward. The lock tab extends through a slot at the periphery of the lid. The cooker base include a handle with a cam section ending in a lock wall. The cooker lid is placed on the base in a release position and rotated to a locking position. During this rotation the lock tab rides over the cam section and then falls adjacent the lock wall, thus sealing the blow vent. After cooking the cover is physically prevented from rotating back to the release position by the lock tab abutting the lock wall. The user must physically lift the lock bar which in turn unseals the blow vent to ensure internal pressure is released. The spline may hold the lock bar in the raised position during rotation to the release position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects and features of the invention noted above are explained in more detail with reference to the drawings, in which like reference numerals denote like elements, and in which: 
         FIG. 1  is a top perspective view of a microwave pressure cooker according to the present invention in the locking position; 
         FIG. 2  is a top perspective exploded view thereof; 
         FIG. 3  is a bottom perspective view of the lid of the pressure cooker; 
         FIG. 4  is a top perspective view of the pressure cooker in the release position; 
         FIGS. 5 a -5 c    are detailed cross-sectional views generally along line  5 - 5  of  FIG. 1  illustrating the movements of the locking bar during locking and release; 
         FIG. 6  is a detail cross-sectional view along line A-A of  FIG. 1  illustrating the pressure relief valve; 
         FIG. 7  is a detail cross-sectional view along line A-A of  FIG. 1  illustrating the pressure indicator; and 
         FIG. 8  is a top perspective view of a pressure indicator stem according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIG. 1 , a microwave pressure cooker according to the present invention is generally designated by reference numeral  10 . The cooker  10  includes a base  12  in the form of a bowl with an upper peripheral edge, and a cover  14  which is generally concave with a downwardly extending lip  16  sized to fit over the edge of the base  12 . The cover and base are formed of a polymer suitable for the microwave. As seen in  FIG. 2 , the base  12  includes a set of spaced bayonet ledges  18  extending radially outward from, and spaced peripherally about, the upper peripheral edge. Similarly, the cover  14  includes a set of mating ledges  20  extending radially inward from, and spaced peripherally about, the lip  16 . As is known in the art, the mating ledges  20  may pass vertically between the bayonet ledges  18  only in a release position of the cover  14  with respect to the base  12 . By rotating the cover  14  with respect to the base from this release position the mating ledges  20  will pass below the bayonet ledges until the cover  14  reaches a locking position with respect to the base  12 . In this locking position the interference of the ledges  18  and  20  prevents the cover from rising with respect to the base, and this is the operating condition of the cooker  10 . 
     As is known in the art, an annular gasket  22  is provided to seal between the base  12  and cover  14 . The gasket  22  preferably will be loosely retained within the lip  16  of the cover  14  to ease assembly. The cooker  10  also includes a pair of base handles  24  extending radially outward from diametrically opposed positions on the base  12 , and a pair of cover handles  26  extending radially outward from diametrically opposed positions on the cover  14 . These are placed such that the cover handles  26  align with and overlie the base handles  24  when the cover  14  is in the locking position. This is shown in  FIG. 1 . 
     The cover  14  includes first and second valve apertures  28  and  30 , respectively, spaced from each other. The first aperture  28  will receive an elastomeric pressure relief valve  32  best illustrated in  FIG. 6 . The valve  32  takes the form of a disc sized for the first aperture  28  and having spaced peripheral flanges which will overly the top and bottom faces of the cover  14  to removably secure the valve  32  to the cover  14 . The valve includes a slit or slits  34  and the valve will deform under pressure within the cooker to open the slit  34  and allow steam to vent while maintaining a desired pressure. As may be seen, it is preferred that the valve  32  be formed symmetrical such that either face may be inserted facing out and still operate properly. 
     The second aperture  30  will receive a pressure indicator valve  36 . As best shown in  FIG. 7  the indicator valve includes an elastomeric indicator disc  38  secure similarly to that of relief valve  32 , but including a central aperture  40 . Received in central aperture  40  is an indicator stem  42  having an enlarged base  44  within the cooker  10 , a neck  46  slidingly received within aperture  40 , and a slightly enlarged head  48  to retain the stem  42  from falling through. As is known in the art, pressure within the cooker will cause the stem  42  to rise, providing a visual indication that the cooker is under pressure. 
     In the preferred embodiment, both apertures  28  and  30  are of the same diameter, as are valve  32  and disc  38 . This arrangement will allow the user to place the valves  32  and  36  in either aperture  28  or  30  and prevent any incorrect assembly. 
     During cooling after cooking the indicator stem will eventually fall to the position shown in  FIG. 7  due to a lack of internal pressure. While the neck  46  is smaller than the aperture  40 , the lower end of head  48  can plug aperture  40  in this rest position. With further cooling of the food, this can cause a negative pressure situation within the cooker  10 , causing it to be difficult to open. To avoid this, the lower end of head  48  includes at least one channel  50  providing fluid communication with atmosphere even in the rest position of  FIG. 7 . The channel  50  may be formed by two or more flanges  52  extending out from the lower end of the head  48 . Alternatively, the indicator disc  38  may include channels (not shown) formed by extending ribs (not shown) about aperture  40  to allow this fluid communication. Each of these arrangements is intended to be encompassed by the term means for permitting fluid communication to atmosphere while in the rest position. 
     The cooker  10  also include a safety interlock arrangement. The cover  14  includes a lock bar  54  having a first end  56  hinged to the cover  14  to define a free end  58 . The first end  56  may be hinged to the cover  14  via mating projections and depressions formed on the cover  14  and lock bar  54 . The lock bar may thus be rotated (oscillated) upward and downward with respect to the cover  14 . The free end  58  of the lock bar extends beyond lip  16  and above one of the cover handles  26 . This cover handle  26  includes a slot  60  extending therethrough. The free end  58  of the lock bar  54  includes a lock tab  62  extending downward therefrom and sized to be freely received through the slot  60 . As best shown in  FIG. 4 , when cover  14  is placed on base  10  in the release position the lock tab  62  will be adjacent a first edge of the base handle  24 . 
     This first edge of the base handle  24  includes an upwardly projecting cam section  64  to engage with a leading edge  66  of the lock tab  62  as the cover  14  (and thus the lock tab  62 ) is rotated from the release position toward the lock position. One or both of the lock tab  62  and cam section  64  are tapered to smoothly lift the lock tab (and thus rotate the entire lock bar  54 ) during this cover rotation. The cam section  64  also defines a lock wall  68  at its rear edge forming a vertical abutment. The length of the cam section  64  is chosen so that when the cover  14  is in the lock position with respect to the base  12 , the lock wall  68  is closely adjacent to a trailing edge  70  ( FIG. 2 ) of the lock tab  62 . 
     The locking operation will now be described. As noted, when the cover  14  is first placed on the base  12  in the release position the leading edge  66  of the lock tab  62  will be adjacent to the base handle  24  and the cam section  64  on that handle. This is best shown in  FIG. 4 . The user then manually rotates the cover toward the lock position (clockwise in the embodiment shown). This will cause the lock tab  62  to lift and ride over the cam section  64  (rotating the entire lock bar  54 ). This is best illustrated in  FIG. 5 a   . Upon continued rotation the cover  14  will reach the lock position, at which point the lock tab  62  will reach the end of the cam section  64  and will drop downward under its own weight (again rotating the entire lock bar  54 ). In this position the trailing edge  70  of the lock tab  62  will be adjacent to the lock wall  68  formed by the end of the cam section  64 . This is illustrated in  FIGS. 1 and 5   b.    
     As may be envisioned, any attempt to manually rotate the cover  14  from the lock position toward the release position will be physically blocked by the lock tab  62  abutting against the lock wall  68 . To open the cooker  10  the user must manually lift the lock bar  54  to move the lock tab  62  above the height of the lock wall  68 . While not required, it is preferred to provide the lock tab  62  with a projecting spline  72  positioned to hold the lock tab in such a raised position by abutment with the slot  60  (with the lock tab  54  elastically deforming to allow the spline to ride over the slot  60 ). This is illustrated in  FIG. 5 c   . With this arrangement the user need not hold the lock bar in the raised position of  FIG. 5 c    and may instead grasp the various handles to rotate the cover  14 . Finally, the free end of the lock tab  62  may include an undercut  74  intended to abut against slot  60  to prevent the lock tab  62  from falling out of the slot  60  when the user inverts the cover  14  during use. 
     While not required it is preferred that the cover  14  also include a blow vent  76  extending therethrough at a position beneath the lock bar  54 . The lock bar  54  will then include a mating plug  78  on its lower face positioned to block the blow vent when the lock bar  54  is in the rest position. To provide an appropriate seal to ensure pressure within the cooker  10  the plug  78  may be formed as an elastomer button (as shown), or the blow vent  76  may have an elastomeric ring (not shown). Finally, the lip  16  of cover  14  may include a ring aperture  80  extending therethrough at a position adjacent the gasket  22 . As best illustrated in  FIGS. 5 a - c   , the ring aperture is sized to be blocked by the gasket  22  during normal use. 
     The operation and full safety features will now be described. When the cover  14  is first placed upon the base  12  in the release position the ledges  18  and  20  are not yet engaged. As such, the cover  14  may freely lift with respect to the base  12  and no pressure may be achieved in the cooker. Once the user begins to rotate the cover  14  toward the lock position then the lock tab  62  will ride up over the cam section  64 . This will rotate the entire lock bar  54 , thus lifting the plug  78  to open the blow vent  76 . This again prevents pressure from being achieved in the cooker  10 . Once the cover  14  has been rotated to the lock position the lock bar  54  will rotate downward with the lock tab  62  falling down the lock wall  68  of the cam section  64 . This will cause the plug  78  to block the blow vent  76 . At this point, with the ledges  18  and  20  fully engaged in the lock position, pressure may be achieved in the cooker  10  with a rise in internal temperature due to cooking. 
     The microwaves will pass through the cooker  10  to heat the food and thereby raising the internal pressure within the cooker  10 . As the internal pressure rises, the indicator stem  42  will rise to provide a visual indication of proper operation to the user. The relief valve  32  is designed to deform and open the slit  34  upon reaching the desired operating pressure, to thus vent the cooker  10  and prevent any further pressure increase above operating pressure. However, should the indicator valve  36  become blocked and the pressure rise appreciably above operating pressure, then the indicator disc  38  is designed to deform and be blown from its aperture  30  to vent the cooker  10 . Similarly, should the indicator disc  38  fail to unseat, and the pressure rise even further then the relief valve  32  is similarly designed to deform and be blown from the aperture  28 . This would again vent the cooker  10 . Should all these measures fail, and the pressure rise yet more, then the seal aperture  80  has been designed and sized to allow the gasket  22  to deform under pressure through the seal aperture  80  to again vent the cooker  10 . Finally, should all previous measure fail and the pressure rise yet more, then the plug  78  will be lifted by the pressure (rotating the lock bar  54  upward against its own weight) to again vent the cooker  10 . It is again noted that the lock bar  54  is not held in the rest position of  FIG. 5 b   , but simply rests there under its own weight and is freely lifted by the user (or the internal pressure as described). 
     After the food has been cooked the proper time, microwaves are no longer applied. The food within the cooker  10  begins to cool and the internal pressure begins to reduce. The indicator stem  42  will fall when the pressure is reduced. The cooker  10  may still contain pressure, however. As noted above, rotation of the cover  14  from the lock position to the release position is blocked by the trailing edge  70  of the lock tab  62  butting against the lock wall  68 . The user must first manually lift the lock tab  62 , thus rotating the lock bar  54  to a position as illustrated in  FIG. 5 c   . As shown there, this will move the plug  78  from blocking the blow vent  76 . In this manner, the cooker  10  is automatically vented by the same operation which unlocks the cover for opening. This venting occurs while the cover is still in the lock position and the ledges  18  and  20  are still engaged. As such, it is ensured that the cooker is vented before the cover  14  reaches the release position. 
     From the foregoing it will be seen that this invention is one well adapted to attain all ends and objects set forth above together with the other advantages which are inherent within its structure. 
     It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims. 
     Since many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth of shown in the accompanying drawings is to be interpreted as illustrative, and not in a limiting sense.