Abstract:
An electrically operable door latch employs a permanent magnet for retaining an appliance door closed against the force of a resilient seal. An electromagnet bucks the magnetic attraction of the permanent magnet allowing the latch to be electronically releasable. A simple mechanism and inherent force limits are obtained by a direct magnetic attraction between a strike plate and the latch, one on the door and one on the housing.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application 60/641,536 filed Jan. 4, 2005, hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to appliances such as dishwashing machines and more specifically to a door latch for such appliances. 
     A residential dishwasher may provide a washing chamber holding racks into which soiled dishes may be placed. A door may close the chamber and may include a gasket sealing the door against the leakage of hot water sprayed on the dishes during the washing process. 
     In order to hold the gasket properly compressed, the door may have a latch assembly, for example, a hook interconnecting the housing and door and lever system for providing mechanical advantage to compress the gasket when the lever is moved. Such latch systems are complicated and can be expensive to manufacture and cumbersome to use. 
     BRIEF SUMMARY OF THE INVENTION 
     In a first embodiment, the present invention is an extremely simple magnetic latch for a dishwasher, holding the door of the dishwasher closed with the seal compressed. The magnetic latch includes a ferromagnetic strike plate attached to one of the housing and door, and a magnetic attractor having a pole piece communicating with a permanent magnet attached to the other of the housing and door in a form analogous to a “cabinet latch”. The magnet is sized to hold the door closed against a predetermined force of opening and the compression of the elastomeric seal. 
     Thus, it is one object of at least one embodiment of the invention to provide an extremely simple latch for a dishwasher having few or no moving parts which can nevertheless provide the force necessary to hold the elastomeric seal on a dishwasher door compressed against leakage. The elastic force of the gasket offsets a portion of the magnetic attraction of the latch, making manual opening of the latch practical. It is therefore another object of at least one embodiment of the invention to provide a latch that may be manually opened at any time, or during any part of the dishwashing cycle, by the simple and intuitive action of pulling on the door. 
     In a different embodiment, the latch further includes an electromagnet communicating with the pole face to counteract the permanent magnet and release the ferromagnetic strike from the pole face when the electromagnet is energized. 
     It is thus another object of at least one embodiment of the invention to provide a latch for an appliance allowing electronic release of the latch. 
     The latch may include a spring bias element biasing the door away from the housing so that the door moves away from the housing after the door is closed, retained, and then released. 
     Thus, it is another object of at least one embodiment of the invention to provide a latch that may be used to electronically open the door during a drying phase of a dishwasher cycle under the control of a cycle timer or manually operated switch. 
     The spring may be an elastomeric seal positioned between the door and housing. 
     Thus, it is another object of at least one embodiment of the invention to make dual use of the seal in providing a visible indication to the user when the door is unlatched as the seal pushes the door outward. 
     The latch may include latch control circuitry providing a pulse to the electromagnet or multiple pulses to release the door upon receipt by the latch control circuitry of a release signal. 
     Thus, it is another object of at least one embodiment of the invention to allow for electronic control of the latch that minimizes heating in the electromagnet, and thus the necessary size of the electromagnet while providing an extended unlatched period. 
     The latch may include a user operable handle for energizing the electromagnet upon activation of the handle by a user. 
     It is therefore one object of at least one embodiment of the invention to provide for a low force release of the latch. 
     The handle may be activated by movement of the handle to activate an electronic switch. 
     Thus, it is an object of at least one embodiment of the invention to provide a simple mechanism of incorporating the latch of the present invention into conventional dishwashers or other appliances having moving handles. 
     Alternatively, the handle may be activated by a grasping of the handle by a user and a sensing of the grasping. The sensing of the grasping may be, for example, capacitive or inductance detectors or those relying on a change of conductivity or light when the hand is in position to grasp the handle. 
     It is thus another object of at least one embodiment of the invention to provide an unlocking of the appliance door without the need to exert an unlatching force on the handle by a user. 
     The latch may include a motorized door closure mechanism attached to one of the housing in the door between the housing and the door and one of the ferromagnetic strike and pole face. The motorized door closure mechanism may receive a motor signal to move the door when the pole face is magnetically retained by the ferromagnetic strike against the pole face. 
     Thus, it is one object of at least one embodiment of the invention to provide a latch that is particularly well suited for a motorized door closure. The latch provides an extremely simple mechanism for holding the door to the motorized door closure mechanism, and yet one which releases under the force of an obstacle in the door or with a strong tug by a user in the event of a power failure. 
     The motorized door closure mechanism may include a force sensor and the electromagnet may be energized by the motorized door closure mechanism when a force of predetermined magnitude is sensed. 
     Thus, it is another object of at least one embodiment of the invention to provide an arbitrary threshold force at which the door will release as may be desired in an automatic door closing system. 
     At least one of the pole face and ferromagnetic strike may be attached by a gimbal to a respective door and housing. 
     Thus, it is another object of at least one embodiment of the invention to provide a latch that may accommodate manufacturing tolerance and wear of the dishwasher door. 
     The pole face may comprise at least one L-shaped pole having a first leg aligned with an axis of closing of the door to the housing and the second leg perpendicular thereto along which the permanent magnet and electromagnet are arrayed. 
     It is thus another object of at least one embodiment of the invention to provide a latch construction that may fit within the restricted axial depth of the housing and doors. It is another object of the invention to provide good magnetic linkage between the permanent magnet and electromagnet reducing the size of the electromagnet. 
     The present invention provides in one embodiment a dishwasher having an electronically controlled latch holding the door when the latch is in a first state and releasing the door when the latch is in a second state, and a motorized actuator communicating with the electronically controllable latch to move between a first position holding the door closed when the door is held by the electronically controllable latch, and a second position when the door is held partially open when the door is held by the electrically controllable latch. A door bias element may move the door from the second position to a third position further open than the second position when the electrically controllable latch is released. 
     Thus it is another object of at least one embodiment of the invention to provide a dishwasher whose door may be closed manually from a venting position to a point at which the latch may engage, and then be pulled in mechanically against the force of the seal. At least one of the first and second positions may provide for venting of the dishwasher. 
     Thus, it is another object of at least one embodiment of the invention to provide improved venting of a dishwasher. 
     These particular objects and advantages may apply to only some embodiments falling within the claims and thus do not define the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified perspective view of a dishwasher that may use the present invention showing a door opening about a washing chamber; 
         FIG. 2  is a cross-sectional fragmentary view of the upper edges of the door and washing chamber of  FIG. 1  taken along lines  2 - 2  showing a positioning of the magnetic latch between the door and housing of the dishwasher per one embodiment of the present invention when the door is in a sealed position; 
         FIG. 3  is a block diagram showing use of the latch of  FIG. 2  with a motorized door closing mechanism and the control thereof; 
         FIG. 4  is an exploded perspective view of the latch of  FIG. 2  showing the alignment of a permanent magnet and electromagnet along flanking pole pieces; 
         FIG. 5   a  is a figure similar to that of  FIG. 2  showing the door in a first venting position when a motorized door opener is used and the latch is retaining the door; and 
         FIG. 5   b  is a figure similar to that of  FIGS. 2 and 5   a  showing the door in a second venting position when a motorized door opener is used and the latch is released. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to  FIG. 1 , an appliance such as a dishwasher  10  includes a housing  12  having an opening  14  that may be closed by means of a door  16 . The door may hinge about a hinge axis  18  along its lower edge and may have a handle  20  on its front face. The handle, for example, may be a C-shaped bar of metal providing for a horizontal grasping surface  22 . 
     Referring to  FIGS. 1 and 2 , a latch  24  may be positioned between the door  16  and housing  12  to hold the door  16  against the housing  12  so as to seal the opening  14  by compression of interposed elastomeric seal  26  between the door  16  and the housing  12 . 
     An inner wall  28  of the door  16  may have a ferromagnetic strike plate  30  attached thereto. When the door is fully closed with the seal  26  compressed, the strike plate  30  may abut a pole face  32  of a magnetic attractor  34  of the present invention to be held there against the opening force of the compressed seal  26 . It will be understood that the positioning of the magnetic attractor  34  and strike plate  30  may be reversed. 
     Referring to  FIGS. 2 and 4 , the magnetic attractor  34  may include upper and lower pole pieces  36  and  38 , respectively, each being L-shaped with horizontally extending upper legs whose ends align to define the pole face  32  and with vertically extending lower legs passing downward within the housing  12 . 
     The vertically extending lower legs of the pole pieces  36  and  38  may sandwich a permanent magnet  40  with a vertically extending lower leg of pole piece  36  abutting rear (north pole) of the permanent magnet  40  and vertically extending lower legs of pole piece  38  abutting front (south pole) of the permanent magnet  40 . It will be understood from the following description that the polarities of the permanent magnet  40  may be reversed with appropriate changes in current flow through the electromagnet described below. 
     The permanent magnet  40  may be supported by plastic magnet frame  42  (not shown in  FIG. 2 ) supporting the edges of permanent magnet  40  while exposing its north and south poles to abut the pole pieces  36  and  38 . The magnet frame holds on its top surface a bobbin  44  wound with wire  50  to create an electromagnet  46 . The electromagnet  46  is vertically oriented having its coil wound around pole piece  36  above magnet  40 . Thus the electromagnet  46  when energized defines a vertically oriented magnetic axis passing between north and south poles in contrast to the permanent magnet  40  which has a horizontal magnetic axis. 
     The bobbin includes terminals  48  connected to wire  50  of the electromagnet  46  that may be energized with a DC current so as to create a north and south pole of the electromagnet  46  that counters the magnetism of the permanent magnet  40 . In this case, the electromagnet  46  will be energized so that its south pole will be at the top of the bobbin  44  near pole face  32 , and its north pole will be at the bottom of the bobbin  44  near permanent magnet  40 . 
     It will be understood that when the electromagnet  46  is properly energized, the field from the permanent magnet  40  may be counteracted causing a release of magnetic attraction between pole face  32  and strike plate  30 . 
     Referring still to  FIGS. 2 and 4 , the magnetic attractor  34  may be held on the housing  12  by means of a support bar  51  having outer ends  52  flanking a center section  54 . Ends  52  may attach to a face  59  of the housing  12  by means of screws (not shown) passing through holes  58 . The center section  54  may have an hourglass-shaped hole  56  extending vertically there through and may fit between the horizontally extending upper legs of pole pieces  36  and  38  near pole face  32  to be retained by a vertical drive pin  57  passing through horizontally extending upper legs of pole pieces  36  and  38 , and through the hourglass shaped hole  56  in the center section  54 . 
     The shape of the hourglass-shaped hole  56  allows gimbaling of the magnetic attractor  34  with respect to the housing  12  so that the pole face  32  may accurately align with the surface of the ferromagnetic strike plate  30  to provide maximum hold-in force when the two abut. The pole pieces  36  and  38  concentrate the magnetic flux of the permanent magnet  40  increasing its force of attraction on the ferromagnetic strike plate  30 . 
     Referring now to  FIG. 3 , the electromagnet  46  of the magnetic attractor  34  of the present invention may receive a release signal  60  in the form of a set of DC pulses from a latch drive circuit  62  such as are sized to momentarily release the magnetic attraction between the pole face  32  and strike plate  30 . The use of pulses over an extended time period limits the heating of the wire  50  of the electromagnet  46  and ensures release of the door  16  in the event that the door is momentarily retained against release, for example, by action of a user. 
     Optionally, it will be understood that control of the duty cycle of the pulses from latch drive circuit  62  allows moderation of the magnetic force of attraction only so as to create a second threshold of retention force in the event that that may be desired. 
     Latch drive circuit  62  may be activated by different sources. One source is a proximity sensor  64  that may be positioned on the grasping surface  22  of the handle  20  so that a user grasping the handle  20  may cause a releasing of the latch  24 . The proximity sensor  64  may be a simple switch activated by movement of the handle  20 , or a proximity sensor sensing the user&#39;s hand on the inner surface of the handle  20  such as indicates a desire by the user to pull the door  16  open. The proximity sensor  64  allows the door to be opened with very little force applied by the user despite the need for considerable hold-in force to retain the seal  26  in compression. 
     The proximity sensor  64  may be any of a variety of sensor types, for example, a capacitive sensor or one that relies on changes of conductivity, inductance, or light incident to the touching of the handle  20  on its inner surface. 
     By deploying the proximity sensor  64  only on the inner surface of the handle  20 , release of the latch  24  will not be caused by a pressing on the outer surface of the handle  20  such as may be used to close the door  16 , but the user&#39;s intent to open the door may be distinguished. 
     Alternatively, the signal from the proximity sensor  64  may be gated by latch drive circuit  62  to be informed by the last state of the door  16  as opened or closed. Thus, if the door were previously in an open state, the proximity sensor  64  could be ignored until the door was in a closed state, and then a signal from proximity sensor  64  would cause an opening of the door by releasing of the latch  24 . 
     It will be understood that the proximity sensor  64  may form the entire handle  20  properly isolated from other electrical sources or may be a separate component on the handle. 
     Referring still to  FIG. 3 , the magnetic attractor  34  need not be directly attached to the housing  12  (or door  16 ), but may be indirectly connected to the housing  12  (or door  16 ) through a motorized actuator  66  such as are described generally in U.S. Patent Application 20040163684 entitled: “Automatic Door For Dishwasher” and assigned to the assignee of the present invention, and hereby incorporated by reference. The motorized actuator  66  generally permits movement of the magnetic attractor  34  inward and outward. 
     When the motorized actuator  66  is fully extended from the housing  12  and latch  24  is closed (i.e., with magnetic attractor  34  attached to the strike plate  30 ), the motorized actuator  66  may pull the door  16  further closed against the force of the seal  26 . During this pull-in, the motorized actuator  66  may sense a resisting force greater that the force of the seal  26  such as may indicate jamming or a utensil trapped between the door  16  and the housing  12 . In this case, the motorized actuator  66  may produce a jam signal  70  causing a release of the magnetic attractor  34  by the latch drive circuit  62 . In this context, the motorized actuator  66  may control the latch drive circuit  62  to vary the magnetic force of the latch  24 , for example, as a function of how far the door  16  has been closed to increase the pull-in force after the risk of entrapped obstacles is low. 
     Note that the release of the latch  24  by the latch drive circuit  62  in the event of a jam or obstruction is backstopped by the limited force of attraction between the permanent magnet  40  in attracting strike plate  30 . This force, which may be overcome by the user pulling sharply on the handle  20 , allows the door to be opened at anytime including during a power failure, and effectively creates a force limit to a closing of the door such as provides for additional safety considerations. 
     As has been described in the co-pending applications cited above, the motorized actuator  66  may be controlled by a cycle timer  72  for controlling timing of the washing cycle. Cycle timer  72  may receive user commands from a control panel  76  of a type well known in the art. 
     Referring now to  FIGS. 3 and 5   a , upon reaching a drying stage, the cycle timer  72  may produce a door venting signal  73  causing an extension of the motorized actuator  66  to create a gap  78  between the door  16  and housing  12  and around seal  26  that will allow venting of vapor from inside the housing  12 . Venting of this type, described in the above-described co-applications, can improve the drying time of the dishes contained in the dishwasher  10 . 
     This venting position may also be used prior to starting of the dishwasher  10  to allow ongoing venting of the chamber of the dishwasher  10  and optionally to tip the door to provide access to the top of door  16  from beneath a counter or the like in cases where the top of the door  16  includes the control panel  76  shown in  FIG. 3 . 
     Referring to  FIGS. 3 and 5   b , an increased drying effect may be obtained after the motorized actuator  66  is in full extension as shown in  FIG. 5   a , by releasing magnetic attractor  34  and allowing door  16  to open to second gap  78 ′ being greater than gap  78  as driven by a bias spring  80  as shown in  FIG. 5   b . The bias spring  80  urges the door  16  to an open position where it is releasably restrained by detent  82 . Detent  82  stops increased opening of the door  16  beyond gap  78 ′ absent additional manual force by the user. 
     After drying is complete, the user may pull on the handle  20  to fully open the door  16  for removal and insertion of soiled dishes, then return the door to the position shown in  FIG. 5   a  with the motorized actuator  66  used to fully close the door against the seal  26 . 
     It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims. For example, pole pieces  36  and  38  need not be ‘L’ shaped unless required by the physical constraints of the surrounding enclosure.