CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. provisional application 61/699,037 filed Sep. 10, 2012 and hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a latching mechanism for doors on household appliances and particularly to latching mechanisms that provide assistance in compressing a door gasket or the like. 
       BACKGROUND OF THE INVENTION 
       [0003]    Appliances such as dishwashers and front-loading washing machines may have an access door with a gasket that must be compressed to seal water within a washing chamber. Small area, highly compliant gaskets may be sealed by pressure from the user during the closing of the door. The gasket may then be held in a compressed state by a latch mechanism. 
         [0004]    Gaskets which require more force may be compressed by a latch mechanism having a lever operated by the user to engage a catch and draw the catch inward with a lever advantage to compress the gasket and hold the door shut. 
         [0005]    A closing lever may be avoided in latch mechanisms that provide a bi-stable spring mechanism. During initial stages of closing of the door, closing force on the door is used to energize a spring. When the door closes past a balance point, the spring releases its energy in a manner to pull the door fully closed. An example of an over-center spring mechanism is described in U.S. Pat. No. 4,497,513 to Sasaki. 
         [0006]    A variation on the bi-stable spring mechanism energizes the spring as the door is opened and holds that energy until the door is closed again. A balance point must still be crossed, and therefore a slight compression of the spring is required when the door is closed to release the energy. A latch of this kind is disclosed in U.S. Pat. No. 2,833,578 to Burke. 
         [0007]    U.S. Pat. No. 6,290,270 to Spiessl shows a variation on Burke in which the latch spring is energized when the door is opened and held in the energized state by the rotation of a hook cam. When the door is closed, the hook cam is rotated by a catch element to release the energized spring by moving a rim of the hook cam past a stop. This design reduces the force required to close the door by eliminating the need to compress a bi-stable spring past the balance point during door closure. In this design, the hook cam must be held on a lever, and the energized spring moves the lever and hook cam. 
         [0008]    U.S. Pat. No. 7,306,266 to Hapke, assigned to the same assignee as the present invention and hereby incorporated by reference, provides a latch that supports a rotating hook cam on a linear carriage rather than a lever, reducing the bending forces and permitting the carriage element to be manufactured of thermoplastic material. 
         [0009]    In these latter two designs, the rotating hook cam is held in its energetic state, before receipt of the catch element and closure of the door, by a stop abutting an outer surface of the hook cam. When the hook cam rotates with engagement of the catch element, the hook cam rotates so that a reduced diameter portion of the hook cam aligns with the stop allowing movement of the hook cam in retraction to compress the door gasket. 
         [0010]    The high forces between the hook cam and this stop can generate significant friction and accordingly it is known to use a rotating wheel for the stop to reduce sliding friction between the stop and hook cam. However reducing this friction increases the chance that the hook cam will accidentally shift in position independent of engagement of the catch element preventing proper operation in the future. 
       SUMMARY OF THE INVENTION 
       [0011]    The present invention provides a hook that is held in its energetic state by a pivoting lever that may lock in an over-center position rather than by a stop operating on a cam surface of the hook. The use of the lever element, rather than sliding contact between the cam surface and a stop, greatly reduces the friction that must be overcome to release the hook yet ensures a well-defined resistance to accidental dislodgment of the energized hook defined by the amount of over-center travel of the pivoting lever. 
         [0012]    The risk that a low activation force will prematurely trigger release of the hook is accommodated by using a floating pivot that allows the catch element to push the hook aside to engage the hook in such circumstances to reset the latch. 
         [0013]    Specifically then, the present invention provides an appliance latch for receiving a catch element along an axis in a receiving direction. The latch includes a latch frame attachable to a portion of the appliance and a floating pivot movable independently with respect to the latch frame along the axis and across the axis. A hook is supported to rotate about the floating pivot to capture a portion of the catch element in a capture position when the catch element enters a hook opening and to release the catch element in a release position when the catch element exits the hook opening. One or more springs urge the floating pivot in the receiving direction along the axis to move the hook. 
         [0014]    It is thus a feature of at least one embodiment of the invention to provide a mounting for the rotating hook that facilitates use of a low friction blocking element holding the hook in energized state and that accommodates the risk of accidental hook activation by allowing a resetting in which the catch element is reengaged with the hook after the hook is in the capture position. 
         [0015]    The one or more springs may also urge the floating pivot across the axis. 
         [0016]    It is thus a feature of at least one embodiment of the invention to provide spring-biased re-engagement of the hook and catch element during a reset operation. 
         [0017]    A single spring may urge the floating pivot in part along the axis and in part across the axis. 
         [0018]    It is thus a feature of at least one embodiment of the invention to reduce the number of springs required. 
         [0019]    The floating pivot may include a sliding element sliding across the axis with respect to the latch frame and a swing arm element pivotally attached to a sliding element to move the hook along the axis. 
         [0020]    It is thus a feature of at least one embodiment of the invention to implement at least one direction of “float” through the use of a simple swing arm structure. 
         [0021]    The swing arm may be pivotally attached to the latch frame by a pivot axle fitting within a slot extending across the axis and fixed with respect to the frame axis and a single spring may communicate between the latch frame and the swing arm to urge the hook along the axis in the receiving direction and across the axis. 
         [0022]    It is thus a feature of at least one embodiment of the invention to implement a floating pivot by a slotted pivot axle support. 
         [0023]    Alternatively, the swing arm may be pivotally attached to a sled sliding along a surface of the latch frame wherein a first spring communicates between the swing arm and the sled to urge the hook along the axis and wherein a second spring communicates between the latch frame and the sled to move the sled across the axis. 
         [0024]    The appliance latch may further include a toggle arm extending between the hook and the latch frame and pivotally attached to each of the hook and latch frame to brace the hook against movement in the receiving direction when the hook is in the release position and to release the hook for movement in the receiving direction with rotation of the hook from the release position to the capture position. 
         [0025]    It is thus a feature of at least one embodiment of the invention to eliminate a high friction stop holding the hook in an energized position. 
         [0026]    The pivotal attachment between the toggle arm and the hook may cross a line between the pivotal attachment between the toggle arm and the frame and the floating pivot point when the hook moves between the release position and the capture position. 
         [0027]    It is thus a feature of at least one embodiment of the invention to provide for a bi-stable element that promotes the hook being positioned stably in the capture position or release position. 
         [0028]    The appliance latch may further include an electrical switch indicating that the catch element has engaged the latch. 
         [0029]    It is thus a feature of at least one embodiment of the invention to provide a latch that may indicate proper closure of the door for the purpose of electrical interlocks on the appliance. 
         [0030]    The electrical switch may provide an operator triggered by the catch element independent of a position of the hook. 
         [0031]    It is thus a feature of at least one embodiment of the invention to provide a switching system that is not triggered by accidental release of the hook when the hook does not engage the catch element. 
         [0032]    The hook may provide a wedge surface extending diagonally to the axis when the hook is in the capture position to contact a catch element not engaged by the hook and, moving in the receiving direction, push the hook and floating pivot to move across the axis to allow the catch element to enter the hook opening when the hook is not in the receiving position. 
         [0033]    It is thus a feature of at least one embodiment of the invention to allow door closure and latch resetting in the event of accidental triggering, for example, caused by shocks during shipping or installation or the like. 
         [0034]    Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims and drawings in which like numerals are used to designate like features. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0035]      FIG. 1  is a simplified perspective view of a dishwasher that incorporates the latch of the present invention, showing a door having an upwardly extending catch element as may be received by a latch mechanism on a front edge of the dishwasher cabinet; 
           [0036]      FIG. 2  is a perspective cutaway of the appliance door and appliance housing showing positioning of a hook and toggle arm of the latch mechanism for receipt of the catch element; 
           [0037]      FIG. 3  is a top plan view of a latch mechanism with the hook attached to a floating pivot in the “capture position” as held by the toggle arm prior to receiving the catch element, the floating pivot point being provided by a sliding sled element and swing arm; 
           [0038]      FIG. 4  is a figure similar to that of  FIG. 3  showing an initial engagement of the hook and the catch element such as moves the toggle mechanism to an over-center position; 
           [0039]      FIG. 5  is a figure similar to that of  FIGS. 3 and 4  showing the hook in the capture position; 
           [0040]      FIG. 6  is a figure similar to that of  FIGS. 3-5  showing the hook in the capture position prior to engagement with the catch element, this position caused by inadvertent activation of the hook through a shock or the like and showing a wedge surface of the hook pushing the hook out of way to allow engagement of the hook with the catch element, the hook moving as supported on the floating pivot; 
           [0041]      FIG. 7  is a fragmentary figure similar to that of  FIGS. 3-6  with the hook, toggle arm and floating pivot removed for clarity showing a switch having an operator activated by movement of the catch element; and 
           [0042]      FIG. 8  is a top plan view of an alternative floating pivot employing a single spring and swing arm mounted to pivot in a slot. 
       
    
    
       [0043]    Before the embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including” and “comprising” and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items and equivalents thereof. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0044]    Referring now to  FIG. 1 , an appliance  10  such as a dishwasher or washing machine may provide for a housing  12  having a front opening  14  exposing one or more dish racks  16  for holding dishes or the like (in the case of a dishwasher) for washing within a housing volume  18 . A door  20  may be hingeably attached to the front of the housing  12  to seal thereagainst by compressing intervening peripheral gasket  22  encircling the front opening  14 . 
         [0045]    The door  20  may have a catch element  24 , for example, a pin, extending upward from an upper edge thereof which may be received by a latch mechanism  26  along a horizontal axis  25  in a receiving direction  23  (parallel to horizontal axis  25 ). Once so received, the catch element  24  is retained within the latch mechanism  26  to hold the door  20  in a closed position during the washing cycle with a sealing compression of the gasket  22 . 
         [0046]    Referring now to  FIGS. 2 and 3 , within the latch mechanism  26  the catch element  24  may pass into a downwardly and rearwardly opening slot  27  in a latch frame  29  to be received within a hook opening  30  of a rotatable hook  32 . The hook  32  may pivot about a floating pivot  34  at one end of a swing arm  36  extending generally perpendicular to axis  25 . This pivoting of the swing arm  36  provides a first direction  33  of motion of the floating pivot  34  being generally parallel to the receiving direction  23  and axis  25 . 
         [0047]    The other end of the swing arm  36  may attach to a pivot point  38  supported on a sled  40  slidable perpendicularly to axis  25  against a surface of the latch frame  29 . The sled  40  provides a second direction  35  of motion of floating pivot  34  generally across or perpendicular to the axis  25 . The sled  40  is biased in the direction of the hook  32  by a helical extension spring  42  connected between the latch frame  29  and a portion of the sled  40 . 
         [0048]    The two generally perpendicular directions  33  and  35  of the floating pivot  34  are independent before the floating pivot  34  is attached to the hook  32  and constrained thereby, meaning that motion in one direction  33  does not uniquely determine the position along direction  35 . 
         [0049]    The hook  32  may also be attached by means of pivot  44  near a periphery of the hook  32  away from the catch element  24  to one end of a toggle arm  46 . The toggle arm  46 , in turn, attaches via a pivot  48  to the latch frame  29 . As shown in  FIG. 3 , when the hook  32  is in a fully energized “receiving position” with floating pivot  34  fully toward the approaching catch element  24  on swing arm  36 , the swing arm  36  compresses a compression spring  50  operating to bias swing arm  36  and hook  32  away from the approaching catch element  24  along the receiving direction  23 . The compression spring  50  may be positioned between a portion of the sled  40  and the swing arm  36  so as to slide with motion of the sled  40 . The energy in the compression spring  50  provides sufficient force for the compression of the gasket  22  into a state of sealing. Generally, the force exerted by compression spring  50  on floating pivot  34  is along line of action  52  roughly parallel with axis  25 . 
         [0050]    Movement of the swing arm  36  and the hook  32  under the influence of compression spring  50  in this energized receiving position is prevented by a blocking action of the toggle arm  46  which is in an over-center position in which pivot  44  is to the right of a line of action  52  between pivot  48  and floating pivot  34 . This over-center position tends to rotate the toggle arm  46  in a counterclockwise direction as depicted but counterclockwise rotation is prevented by a range-limiting track (for example, a slot receiving a downwardly projecting tooth on the toggle arm  46 ) engaging the toggle arm  46 , or other blocking element. 
         [0051]    Referring now to  FIG. 4 , as the catch element  24  engages the hook opening  30  of the hook  32  it causes counterclockwise rotation of the hook  32  about the floating pivot  34 . This rotation in turn causes the toggle arm  46  to move in a clockwise direction about pivot  48  so that pivot  44  moves leftward across the line of action  52 . The over-center position (to the right of the line of action  52 ) of the toggle arm  46 , at a point where its rotation is stopped, and the spring force of spring  50 , together determine exactly how much force must be exerted on the hook  32  by the catch element  24  to move the toggle arm to the left of the line of action  52 . By tailoring this force, accidental displacement of the hook  32  is reduced and resistance to accidental displacement of the hook  32  does not rely on the varying influence of friction. 
         [0052]    Referring now to  FIG. 5 , when the toggle arm  46  moves clockwise so that the pivot  44  crosses the left of the line of action  52 , the track  56  no longer constrains rotation of the toggle arm  46 . Accordingly, the toggle arm  46  may move fully 90 degrees in a clockwise direction allowing full retraction of the hook  32  to a capture position as driven by the spring  50  to pull the catch element  24  inward releasing the force of spring  50  to compress the gasket  22 . 
         [0053]    It will be appreciated that all forces affecting motion of the hook  32  are concentrated on relatively small contact areas of pivots  44 ,  34  and  48  reducing the effective frictional resistance by the mechanical advantage of the levers that connect to the pivots. This is in contrast to the more substantial sliding friction between a hook cam and a stop in prior art designs. Generally spring  50  may be recompressed and the hook  32  returned to its receiving position by pulling outward on the door to withdraw the catch element  24  from the slot  27 . Generally, energy used in opening the door of the appliance is recycled to help close the door of the appliance through the agency of the spring  50   
         [0054]    Referring now to  FIG. 6 , it will be appreciated that if the hook  32  is inadvertently released to its de-energized state (capture state) while not engaging the catch element  24 , for example, as may be caused by shipping, tampering or installation shocks, the catch element  24  may nevertheless be pushed along axis  25  past a front lip  60  of the hook  32  to be then received by opening  30  in the hook  32 . In this regard, the front lip  60  has a slope  62  that is diagonal to the axis  25  (for example, at 45 degrees) to cause a leftward motion of the hook  32  when the catch element  24  is pressed against the front lip  60 . This movement of the hook  32  under pressure from the catch element  24  against front lip  60  is accommodated by the floating pivot  34  and results in movement of the sled  40  leftward against the influence of the helical spring  42 . Movement of the hook  32  allows the catch element  24  to be reengaged within the hook opening  30  to essentially reset the latch mechanism  26 . This leftward motion of the hook  32  does not require movement of the toggle arm  46  which remains in the position normally associated with the capture position of the hook  32 . 
         [0055]    Referring now to  FIG. 7 , the catch element  24  moving within the slot  27  may further move a switch operator  64 , for example, having a curved cam surface  66  extending over the slot  27  and causing the switch operator  64  to move counterclockwise about a pivot  68  attached to the frame  29  when the catch element  24  moves in receiving direction  23  into the slot  27 . The shape of the cam surface  66  is such as to promote sufficient rotation of the operator  64  to close a leaf spring contact  65  against a second contact  67  when the catch element  24  is fully received within the slot  27  (in a manner that would typically allow it to be fully engaged by the hook  32  as shown, for example, in  FIG. 6  in the capture position). The leaf spring contact  65  and second contact  67  together form an electrical switch. The switch formed by contact  65  and  67  may provide a signal to an appliance controller preventing operation of the appliance when the door  20  is not fully closed. The leaf spring contact  65  otherwise normally biases the operator  64  in a clockwise direction to partly occlude the slot  27 . 
         [0056]    Referring now to  FIG. 8 , it will be appreciated that the floating pivot  34  may be implemented alternatively as a pivot on one end of a lever  70 , the lever in turn pivoting about a fulcrum pin  72  fitting within a slot  74  in the latch frame  29 . The slot  74  extends generally perpendicularly to axis  25  and allows the lever  70  and hence the floating pivot  34  to move in the direction  35 . Pivoting action of the lever  70  about the pin  72  in the frame  29  provides motion of the floating pivot  34  in the direction  33  discussed above. 
         [0057]    A single compression spring  76  may have a line of force  78  generally diagonal to axis  25  to provide a component of bias along the direction  35  (as otherwise provided by spring  42  as shown in  FIG. 6 ) and a component of bias in the receiving direction  23  (otherwise provided by spring  50  as shown in  FIG. 6 ) where the degree of bias may be readily controlled by changing the line of force  78 . 
         [0058]    Various features of the invention are set forth in the following claims. It should be understood that the invention is not limited in its application to the details of construction and arrangements of the components set forth herein. The invention is capable of other embodiments and of being practiced or carried out in various ways. Variations and modifications of the foregoing are within the scope of the present invention. It also being understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention.
An appliance latch provides a hook that may be energized against a spring force to receive a catch element which releases the hook to pull the catch element into engagement. A toggle arm may be used to hold the hook in the energized state before receipt of the catch element to provide for a sensitive and predictable release of the spring force with rotation of the hook. The hook may be mounted on a floating pivot both to accommodate the toggle arm operation and to permit re-engagement of the catch element with the hook in the event that the hook is released from its energized state without engagement of the catch element, for example, by inertial forces.