Abstract:
A transportation-robust bi-stable latch mechanism preserves low actuation forces by means of an auxiliary mechanism blocking the effects of shock forces during transportation.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
     BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to latching mechanisms for the door of a household appliance such as clothes washing machine, and, in particular, to an electrically actuated lock for such a latch.  
         [0002]     Appliances such as clothes washing machines and dishwashers may operate automatically through one or more cycles under the control of an automatic timer. During cycles when the consumer might be exposed to spraying water or hazardous moving parts, the door to the appliance may be locked by an electrical signal from the timer. The locking mechanism may, for example, insert a blocking member into a portion of the door latch to prevent it from being disengaged through the normal operation of the latch or may insert a blocking member directly into the door.  
         [0003]     The locking mechanism may be actuated by an electrical solenoid having an element that moves through a conductive coil when electrical power is applied to the coil. Alternatively, electrical actuators, such as wax motors and heated bimetallic strips, may be used.  
         [0004]     Each of the above mechanisms requires continuous power to remain actuated, typically for the duration of the locked cycle. In the case of a solenoid, this continuous duty requires increased size and expense of the coil windings which must be rated for continuous duty. A disadvantage of wax motors and bimetallic strips is that they rely on a heating process and thus cannot provide rapid locking and unlocking.  
         [0005]     These disadvantages can be overcome through the use of an electromagnetically driven bi-stable actuator. Such an actuator may include a bidirectional solenoid that may either push or pull an actuator element depending on polarity of applied electrical power or power being applied to one of two coils. An over-center spring mechanism holds the actuator element in its last position, either locked or unlocked, when power is not applied.  
         [0006]     During shipment of an appliance with a bi-stable lock, transportation shocks may cause the lock to move without the application of electrical power, for example, from the unlocked position to the locked position. This unintended locking of the appliance door can be inconvenient for the end user who may need access to the interior of the appliance before the appliance is installed and connected to electrical power, for example, to obtain parts or appliance manuals from the interior of the appliance.  
         [0007]     This inadvertent actuation of the bi-stable lock can be eliminated by increasing the force of the over-center spring or adding frictional elements to the latch. This approach, however, necessitates a larger electromagnetic actuator, defeating to some extent the motivation for using a bi-stable actuator. Frictional elements can be difficult to manufacture so that they provide a consistent friction over the life of the product.  
       BRIEF SUMMARY OF THE INVENTION  
       [0008]     The present invention provides a bi-stable lock for an appliance that preserves low actuation forces by using a separate, automatic mechanism that prevents actuation of the lock by transportation shock. In a principal embodiment of the invention, external shocks are sensed and sensed to block or oppose movement of the lock only during the duration of the shock. In a second embodiment of the invention, electrical power is used to un-block or allow movement of the lock only during the application of electrical power.  
         [0009]     Specifically then, the present invention provides a latch for a door of a household appliance that is subject to transportation shocks where the latch includes a latch body and a bi-stable actuator having an actuator element that is electrically moveable with respect to the latch body between a first and second position when electrical power is applied, and that is stable in the first and second position when electrical power is removed. A lock element may be attached to the bi-stable actuator for locking the latch when the actuator element is in one of the first and second positions and unlocking the latch when the actuator element is in the other of the first and second positions. The invention provides a restraining element communicating with the actuator element to selectively resist movement of the actuator element from the second position to the first position under the influence of an accelerated force alone but allowing the movement of the bi-stable actuator from the second position to the first position during the application of electrical power alone.  
         [0010]     Thus, it is a feature of at least one embodiment of the invention to provide a mechanism that distinguishes between forces caused by electrical actuation and forces caused by shocks, and to allow movement only in the absence of forces caused by shocks. It is another feature of at least one embodiment of the invention to provide a system that allows the bi-stable actuator to have low actuation thresholds for efficient operation and reliable operation.  
         [0011]     The restraining element may be sensitive to the acceleration of the latch body to prevent movement of the actuator element with respect to the latch body when acceleration is detected.  
         [0012]     Thus, it is one feature of at least one embodiment of the invention to provide a system that blocks shock movement of the lock by sensing the shock itself.  
         [0013]     The restraining element may sense acceleration using a weight movably attached to the latch body to move with respect to the latch body under the influence of acceleration of the latch body.  
         [0014]     It is thus a feature of at least one embodiment of the invention to provide a simple mechanical system for detecting acceleration and producing an actuation force.  
         [0015]     The weight may communicate with a lever having a portion engaging the actuator element when the weight moves with respect to the latch body.  
         [0016]     Thus, it is a feature of at least one embodiment of the invention to provide a mechanical system that may be easily tailored to a variety of applications.  
         [0017]     Alternatively, the mass may communicate with the actuator element to apply a countervailing force to the bi-stable actuator opposite and no less than the accelerative force during the acceleration.  
         [0018]     Thus, it is a feature of at least one embodiment of the invention to provide a mechanism that simply cancels out the forces of shock.  
         [0019]     In an alternative embodiment, the restraining element may be sensitive to the application of electrical power to the bi-stable actuator to block movement of the actuator element when electrical power is not applied to the bi-stable actuator.  
         [0020]     Thus, it is a feature of at least one embodiment of the invention to provide a mechanism that distinguishes between forces cause by electrical actuation and forces caused by shocks, and to allow movement only in the presence of forces caused by electrical actuation. It is again a feature of at least one embodiment of the invention to provide a system that allows the bi-stable actuator to have low actuation thresholds for efficient operation and reliable operation.  
         [0021]     The restraining element may be a magnetically attracted armature moved in response to electrical power flowing through a coil.  
         [0022]     Thus, it is a feature of at least one embodiment of the invention to provide a simple electrically actuated mechanism preventing inadvertent movement of the lock.  
         [0023]     The bi-stable actuator may include a solenoid moving the actuator element, and the coil moving the armature described above may be the solenoid.  
         [0024]     Thus, it is a feature of at least one embodiment of the invention to provide a simple mechanism that takes advantage of the solenoid already used as the bi-stable actuator.  
         [0025]     The armature may be attached with the actuator element and may include a portion engaging the housing when the power is not applied to the bi-stable actuator and disengaging from the housing and actuator when the power is applied to the bi-stable actuator.  
         [0026]     Thus, it is a feature of at least one embodiment of the invention to permit positioning of the free end of the armature near the solenoid coil as may be displaced from the actuator element.  
         [0027]     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  
       [0028]      FIG. 1  is a simplified perspective view of an appliance showing an orientation of a bi-stable lock before and after application of a lateral acceleration caused by transportation shock resulting in locking of the lock mechanism;  
         [0029]      FIG. 2  is a fragmentary front elevational view of the lock of  FIG. 1 , including a shock-sensitive blocking lever of the present invention, shown in a state when no shock is present;  
         [0030]      FIG. 3  is a figure similar to that of  FIG. 2 , showing movement of the lever to block sliding of the lock during a shock;  
         [0031]      FIG. 4  is a figure similar to that of  FIG. 2 , showing an alternative embodiment of the invention having a magnetically attractable armature blocking a sliding of the lock when electrical power is not present;  
         [0032]      FIG. 5  is a top plan view of the embodiment of  FIG. 4  showing the armature engaging blocking elements on the latch housing when electrical power is not present;  
         [0033]      FIG. 6  is a figure similar to that of  FIG. 5  showing attraction of the armature inward to allow a sliding of the lock when electrical power is present;  
         [0034]      FIG. 7  is a figure similar to that of  FIGS. 2 and 4 , showing an embodiment having a shock force compensation weight eliminating the effect of shock forces on the slide mechanism;  
         [0035]      FIG. 8  is a figure similar to that of  FIG. 2  showing an alternative embodiment where the blocking lever does not return to an unblocking state after the force of the shock; and  
         [0036]      FIG. 9  is a top plan view of  FIG. 9  showing a frictional element for holding the blocking lever and interaction between the blocking lever and a latching element for resetting the blocking lever. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0037]     Referring now to  FIG. 1 , an appliance  10 , such as a dishwasher or washing machine, may include a cabinet  12 , having a front door  14  that may be opened or closed to provide access to the interior of the cabinet.  
         [0038]     The door  14  or cabinet  12  may provide for a lockable latch  16  extending along an axis  18  and the latch  16  may include a slide  20  moving along axis  18  with respect to a latch housing  22 . One end of the slide  20  includes a locking element  24  that may engage a latching element  26 , for example, a rotating hook that may receive an interconnecting element on the opposite of the door  14  or cabinet  12  to hold the two closed. The engagement of the locking element  24  with the latching element  26  prevents release of the door or cabinet.  
         [0039]     The sliding mechanism may also attach to an over-center spring  28  that selectively urges the slide  20  to either extreme of its travel, such extremes representing the lowest energy state of the spring according to methods well known in the art. Slide  20  may be further attached to a bi-directional solenoid  30  having a magnetically attractable core  32  that may be driven in either direction along axis  18  according to one of two solenoid signals applied to a first solenoid coil  34  or to a second solenoid coil  36 . Alternatively, but not shown, the solenoid may provide for a magnetized core  32  driven by different polarities of electrical signal. In operation, a first signal to the solenoid  30  drives the locking element  24  into engagement with the latching element  26  and a second signal retracts the locking element  24  from the latching element  26 .  
         [0040]     Referring still to  FIG. 1 , the application of a sudden acceleration  40  to the cabinet  12 , may create a relative accelerative force  42  on the slide  20  causing the slide  20  to move from a state of non-engagement with the latching element  26  into engagement with the latching element  26  without application of power to the solenoid  30 . It will be understood that the term accelerative force  42  is intended to cover both actual forces from acceleration  40  and relative or reactive forces tending to move the slide  20  with respect to the appliance  10  absent of the application of electrical power.  
         [0041]     Referring now to  FIG. 2 , the slide  20  may rest in an unlocked state before application of any accelerative forces. In a first embodiment of the invention, a weight  48  is positioned near the slide  20  and held by an arm  53  pivoted about a pivot point  50  so that the weight  48  may move generally in a swinging radius  52  along axis  18 . A lever  56  is attached to the arm  53  joining the weight  48  to the pivot point  50  at a radius  54 , and, in the rest state, extending along axis  18  adjacent to the slide  20 . A torsion spring  58  biases the lever  56  in a counterclockwise direction (as shown) so that one end of the lever  56  abuts a stop  60  on a lock housing preventing further motion of the lever  56  in the counterclockwise direction. The end of the lever  56  provides a blocking surface  64  adjacent to an attachment tower  62  extending upward from the slide  20  to receive one end of the core  32  of the solenoid  30 .  
         [0042]     Referring now to  FIG. 3 , an acceleration  40  on the housing may apply an acceleration force on the weight  48  causing it to rotate along axis  18  as indicated by arrow  63 . This, in turn, causes the lever  56  to move away from the stop  60  such that a blocking surface  64  of the lever  56  moves into the path of the attachment tower  62  preventing further axial movement to the left of the slide  20 . Some motion of the slide  20  does occur, but is limited to an amount that would not flex the over-center spring  28  past a tipping point  68  where the over-center spring  28  would change state and, thus, the over-center spring  28  causes a return of the slide  20  to its rightmost position after the shock is complete.  
         [0043]     Referring again to  FIG. 2 , the radii  52  and  54  of arms  53  and  56  and the distance between a blocking surface  64  of the lever  56  and the attachment tower  62  may be adjusted so that the blocking surface  64  engages the attachment tower  62  before significant motion of the slide  20  occurs. The weight  48  and force of torsion spring  58  can also be adjusted for this purpose.  
         [0044]     Referring now to  FIGS. 4 and 5 , in an alternative embodiment, the slide  20  includes an upstanding tower  70  to which is attached a thin ferromagnetic armature  72  in cantilever extending the solenoid coil  34 . The free end of the armature  72  includes a crossbar  74  extending perpendicularly to the axis  18  and the general extent of the armature  72 . When the slide  20  is in the unlocked state (as shown in  FIG. 4 ), the crossbar  74  is positioned near the upper end of the solenoid coil  34  near where it abuts the lower end of solenoid coil  36 .  
         [0045]     While solenoid coil  34  is not energized (as shown in  FIG. 5 ), the armature  72  flexes away from the solenoid coil  34  against an inner edge of an upper surface of the latch housing  22  with the crossbar  74  engaging on its leftmost edge (as depicted) the rightmost edge of a pair of stops  76  extending downwardly from the latch housing  22 . In this state, axial movement by the slide  20  in direction  78  (to the left as depicted), under accelerative forces, is blocked by interengagement of the stop  76  and the crossbar  74 .  
         [0046]     Referring now to  FIG. 6 , when solenoid coil  34  is energized, such as would naturally move the slide  20  in the direction  78  to a locked position, leakage flux  80  from the solenoid coil  34  draws the armature  72  downward pulling the crossbar  74  from blocking engagement with the stop  76  and allowing motion of the slide  20  in the direction  78 . Thus, only during a period of energizing of solenoid coil  34  is the armature drawn downward so that the armature  72  and the slide  20  may move.  
         [0047]     Stop  76  may be ramped on its left side (as shown) to allow return of the armature  72  in the unflexed state, riding against the latch housing  22 , or the armature  72  may be configured to be drawn inward by the leakage flux is provided from solenoid coil  36 .  
         [0048]     Note that when the crossbar  74  is pulled downward, the latch  16  is susceptible to accelerative forces; however, normally that will not be problem as the accelerative forces occur only during shipment when the appliance is not commissioned for operation.  
         [0049]     Referring now to  FIG. 7 , in a third embodiment, the effective accelerative force  42  on slide  20  may be counteracted through the use of a compensator weight  90  pivoting about a pivot point  92  adjacent to the slide  20  so that the compensator weight  90  may rotate generally along axis  18 . Compensator weight  90  connects to the pivot point  92  by means of a short lever arm  94  and then continues past the pivot point  92  in a second lever arm  96  to a point over the center of the slide  20 . There, the end of the second lever arm  96  engages an upstanding peg  98  attached to the slide  20 . The engagement of the second lever arm  96  and the peg  98  is by means of a slotted fork connection  100  allowing relative lateral movement between the two.  
         [0050]     During a shock causing accelerative force  42  on the slide  20 , a corresponding accelerative force  42 ′ will act on the compensator weight  90  biasing the compensator weight  90  in a clockwise direction about pivot point  92 . This, in turn, causes the fork connection  100  to apply a rightward force against peg  98  canceling or overriding accelerative force  42 .  
         [0051]     In this embodiment, the total inertia of the slide  20  is effectively increased by the compensator weight  90  increasing the short term force that must be overcome by the solenoid  30 ; however, the long term force necessary for locking and unlocking of the latch  16  is not affected.  
         [0052]     It will be understood that this concept may be expanded, for example, to provide a slide  20  that integrates mass  90  and pivots about pivot point  92 , for example, in a rotating equivalent to slide  20 , to resist accelerative forces based on a general rotational symmetry of slide  20 .  
         [0053]     Referring now to  FIGS. 8 and 9 , in an alternative embodiment similar to that of the embodiment of  FIGS. 2 and 3 , a lever  102  may be attached to the housing  22  to rotate about an axis  104  perpendicular to axis  18  and perpendicular to axis  106  generally aligned with a line of action of an opening door  14  of the appliance  10 .  
         [0054]     The lever  102  pivots about a shaft  107  positioned behind a center of gravity  108  of the lever  102 , so that accelerative force  42  causes a generally clockwise motion of the lever  102  (according the orientation of  FIG. 9 ). This rotation causes a lever arm  110  of the lever  102  to engage a tooth  112  extending from the slide  20  preventing motion of the slide under the accelerative force  42  in a manner analogous to the engagement of blocking surface  64  with the attachment tower  62  described with respect to  FIG. 2 .  
         [0055]     Unlike the embodiment of  FIG. 2 , however, in this embodiment there is no torsion spring  58  and so after the clockwise rotation caused by the accelerative force  42 , the lever arm  110  remains engaged with the tooth  112 . Friction, resisting motion of the lever  102 , may be controlled and augmented by a leaf spring  114  pressing downward from the housing  22  on a surface of the lever  102 .  
         [0056]     A locking of the latching element  26  (preventing the door  14  from opening) requires engagement of a portion  116  of the slide  20  in front of the latching element  26  such as prevents movement of the latching element  26  along axis  106  beyond a certain point that would allow opening of the door  14 . Thus, the first accelerative force  42  blocks the slide  20 , locking the latching element  26  indefinitely. An advantage of this design is that there is reduced chance that multiple shocks will in some instance defeat the preventative action of the lever  102 .  
         [0057]     Referring to  FIG. 9 , the lever arm  110  may be disengaged with the tooth  112  so that the slide  20  is again free to move (and lock the latching element  26 ) upon the attempted opening of the door  14 . This opening serves to pull the latching element  26  along the axis  106  so that the latching element  26  engages a tooth  118  or other surface on the lever  102  rotating the lever  102  in a counterclockwise direction against the friction provided by the leaf spring  114 .  
         [0058]     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.