Abstract:
The locking movement and/or the unlocking movement of a bimetallic drive of an electrothermally-controlled locking apparatus, for example for household-device doors, is or are driven by a separate bimetal member ( 10, 11 ) over only a first segment of its movement path. In the process, energy is supplied to the energy store ( 28 ) of a tipping over-center device until a dead-center position is attained, the energy being released as a moving drive for the remaining segment of the movement path when the dead-center position is exceeded, thereby cutting off the bimetal drive and stabilizing the locking member ( 2 ) in its end position.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a locking apparatus, for example for household-device doors, having a locking member that can be moved between an open and a closed position by a bimetallic drive. 
     Bimetal-controlled locking apparatuses for household-device doors are generally known. In a lock for a washing-machine door, in particular, which is known from DE 37 09 660 C2, a bimetallic snap disk is provided as the drive for a stopper that blocks the manually-operated locking member in the locked position. This bimetallic snap disk assures, on the one hand, a rapid blockage of the lock by the stopper when heating occurs. After such a blockage, the heating current for the bimetal snap disk is cut off. As it cools, the disk returns to its open position. The bimetallic heating of the snap disk serves solely to move a stopper for a blocking member, not directly for the locking member. 
     SUMMARY OF THE INVENTION 
     The present object is to ensure, with simple means, that a locked door cannot be opened, even with an interruption or breakdown of voltage. This is especially important for household devices that operate at very high temperatures. In these cases, the locked state must be maintained until cooling to non-dangerous levels has occurred, even if the current supply fails. 
     In addition to the high safety requirements, a particular object is to produce the locking apparatus simply, and therefore inexpensively. It should be compact so as not to limit the freedom in the designing of the device. Finally, the apparatus should operate in an energy-saving and environmentally-friendly manner, e.g., quietly. 
     These objects are accomplished or facilitated by a locking apparatus which is characterized in that the locking movement and the unlocking movement are respectively driven by separate bimetal members over only a first segment of their movement path, thereby supplying energy to the energy store of a tipping over-center device until a dead-center position has been attained, the energy being re-released when the dead-center position of the tipping over-center device has been exceeded, and used as a movement drive for the remaining segment of the movement path, and stabilizing the locking member in its end position at the end of the respective movement path. The bimetallic drives directly control the locking and unlocking movements, and not only a stopper that blocks the mobility of the locking member in the closed position. Power consumption only occurs during the switching process, and then only for controlling the first component of the locking or unlocking movement until the dead-center position of the tipping over-center device has been exceeded. Afterward, the tipping over-center device assumes control of not only the second component, that is, the completion, of the displacement movement or switching process, but preferably also the cutoff of the electrical bimetal heating. The functional system is therefore currentless once the dead-center position of the tipping over-center device has been exceeded; the locking or unlocking position is nevertheless stable. Both the locking and unlocking movements are preferably controlled in this manner. The attained end state—that is, the locked and unlocked positions—is stable. The entire system is bistable. 
     A further, special advantage lies in the structurally simple and, most importantly, compact construction that is attained particularly by a lowered positioning of the locking bar in comparison to the two bimetal members. Using a locking bar or a drive member that is inserted into or rests upon the moving ends of the two bimetal members permits an especially lowfriction drive of the locking bar, on which the bimetals act practically directly. The fact that the locking bar in the preferred embodiment is configured in two parts due to its position straddling a drive element that is disposed parallel to it and performs the same drive function has its basis in production and assembly considerations. The two parts could also be connected to one another to form a one-piece locking bar. This two-part embodiment offers a suspended retention and seating of the coupling-bridge drive member at the ends of the bimetals, without bearing forces that act on the locking bar acting on the coupling bridge, and thus the bimetals, thereby impairing the suspended seating of the coupling bridge, which is kept in contact with the bimetal ends by the energy store of the tipping over-center device. 
     Furthermore, the coupling bridge and the locking bar encapsulate the tipping over-center device between them, shielding it from the bimetal drive. All of the movements of the functional parts of the locking apparatus are completed in the longitudinal plane of the housing. This also facilitates an easy-to-assemble design. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded view of the locking apparatus with all of its individual parts that are necessary for functioning; 
     FIG. 2 is a plan view of the lower part of the housing with all of the essential functional parts of the locking apparatus inserted, and in the unlocked position of the locking bar; 
     FIG. 3 is a representation analogous to FIG. 2, with the locking bar in the locked position; 
     FIG. 4 is a representation of the driving connection between the moving ends of the bimetals and the coupling bridge; 
     FIG. 4 a  is a cutout IVa—IVa in FIG. 4 relating to the knife-edge seating of the coupling bridge on the bimetal ends; 
     FIGS. 5 and 7 are views showing the effect of the locking bar on structurally different door-locking systems in a respective unlocked position of a door; and 
     FIGS. 6 and 8 are representations analogous to FIGS. 5 and 7, in a respective locked position of the locking bar. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Inside the lower part  1  of the housing, which comprises an insulating material, a locking bar  2  is seated to be longitudinally displaced in the transverse direction  3  between its unlocked position (FIG. 2) and a locked position (FIG.  3 ). The bar has the outline of an upside-down down T; the two horizontal ends  4 ,  5  of the T crosspiece and the free vertical end  6  of the long piece project outwardly through housing openings  7  in the side walls of the lower part  1  of the housing. The ends  4 - 6  are the driving ends of the locking bar  2 , and act directly (FIGS. 5,  6 ) with door-side locking elements  8 , or indirectly via interposed transmission members  9 , for example in the form of a pivoting lever. The locking elements  8  are components of a device door to be locked, for example. 
     Two bimetal members  10 ,  11 , which will frequently be called simply “bimetals” hereafter, are disposed approximately perpendicular to the transverse direction  3  inside the lower part  1  of the housing. The bimetals are strip-shaped. The strip plane extends perpendicular to the drawing plane of FIGS. 1 through 4. The strip planes extend parallel to one another, and maintain a specific lateral spacing between themselves. The bimetals are fixed on the side of the housing by their foot ends  12 ,  13 . They are welded there to the reeds  14 ,  15 , which are fixedly positioned in slots  16  inside the housing side wall  17 ; the contact ends of the reeds project from the housing interior so as to be contacted externally (FIGS. 2,  3 ). 
     The moving ends  18 ,  19  of the bimetals  10 ,  11  indirectly engage the locking bar  2 , which is displaceable in the transverse direction  3 . This indirect engagement is only present as long as a coupling bridge  20  is interposed between the moving ends  18 ,  19  of the bimetals  10 ,  11  and the actual locking bar  2 ; the bridge, however, is viewed as a functional component of the locking bar  2  because of its form-fitting engagement  21  with the locking bar  2 , and its identical driving action, and its position parallel to the locking bar  2 . The two-part embodiment of the coupling bridge  20  and the locking bar  2  is based on production and assembly considerations. In the plan view, the two bimetals  10 ,  11  and the locking bar  2 , or its coupling bridge  20 , together form the two vertical legs and the horizontal leg mounted on them to form an overall shape corresponding to the Greek letter Π. In terms of assembly, the locking bar  2  or the coupling bridge  20  is respectively positioned on the moving ends  18 ,  19  of the two bimetals  10 ,  11 . The two bimetals  10 ,  11 , like the two support pillars of a bridge head, thus function as support elements for the coupling bridge  20 , which is guided longitudinally by the housing floor  22  and the housing lid  23  as lateral guides when the housing is in its final assembly state. This seating or retention of the coupling bridge  20  is especially low-friction, and therefore energy-saving. The bimetals  10 ,  11  project with their moving ends  18 ,  19  into recesses  24  at the flank of the coupling bridge  20  facing them. The recesses  24  function as a knife-edge bearing (FIG.  4 ). Their cross-section walls also provide displacement protection for the moving ends  18 ,  19  of the bimetals  10 ,  11 . The coupling bridge  20  is therefore suspended freely on the bimetal ends  18 ,  19 , and is guided in its movement solely by the bimetals  10 ,  11 . No additional guidance system is required for the displacement movement of the coupling bridge  20  within the housing  1 , although such a system should not be precluded by the housing floor  22  or housing lid  23 . The coupling bridge  20  is thus practically inserted onto the ends of the bimetals  10 ,  11 . 
     The coupling bridge  20  is connected to the locking bar  2  through a loose, form-fitting engagement  21 . This engagement transmits the drive movement of the bimetals  10 ,  11  onto the locking bar  2  without transmitting bearing pressures that act on the locking bar onto the coupling bridge  20 , and consequently indirectly onto the bimetals  10 ,  11 , thereby influencing and possibly impeding their functioning capability. 
     On the side facing the locking bar  2 , the coupling bridge  20  is hollowed out (trough  25 ) between the two recesses  24  for the moving ends  18 ,  19  of the bimetals  10 ,  11 , that is, between their pins, for a form-fitting engagement  21  at the locking bar  2 . The locking bar  2  has a countertrough  26  on the side facing the coupling bridge  20 , the countertrough corresponding to the trough  25 . The troughs  25 ,  26  encompass a hollow space, into which a housing projection  27  projects from the housing floor  22 . The housing projection  27  constitutes the housing-side support for the tipping spring  28 , whose lower end acts on the floor  29  of the trough  25  of the coupling bridge  20 . The screw heads  30 ,  31  of retaining screws that engage the spring winding serve to center the two ends of the tipping spring  28  at the coupling bridge  20  and the housing projection  27 , respectively. The tipping spring  28  constitutes the energy store of a tipping over-center device, which is shown in its two tipped positions in FIGS. 2 and 3, namely the locked position (FIG. 3) and the unlocked position (FIG.  2 ). In these positions, the tipping spring  28  acts on the coupling bridge  20  in the transverse direction  3  such that the bridge ends lie against either the left side wall  32  (FIG. 3) in the locked position or the right housing wall  33  (FIG. 2) in the unlocked position. This contact with the housing effects a stable positioning of the coupling bridge  20  or the locking bar  2  in the locked position (FIG. 3) and in the unlocked position (FIG.  2 ), regardless of the voltage. The housing projection  27  is simultaneously a component of the housing-side longitudinal guidance for the locking bar  2 , as can be seen clearly in FIGS. 1 through 3. Moreover, the tipping spring  28  holds the coupling bridge  20  securely on the moving ends  18 ,  19  of the bimetals  10 ,  11  in all of its positions. 
     The coupling bridge  20  is seated completely frictionless on the drive ends  18 ,  19  of the bimetals  10 ,  11 . The tipping spring  28  acting from above on the coupling bridge  20  between the two drive ends  18 ,  19  stabilizes this arrangement. The housing walls, which also form end stops for the two-sided displacement movements, can also effect the guidance of the locking bar  2  or the coupling bridge  20  inside the housing  1 . 
     The thermo-bimetals  10 ,  11  face one another with their active sides (FIG.  4 ). They are heated by PTC resistors  34 ,  35 . The PTCs  34 ,  35  are connected to voltage by way of reeds  14   a  and  39  and  15   a  and  39 , respectively. If the contacts  14   a ,  39  are connected to voltage in the unlocked position according to FIG. 2, the PTC resistor  34  is heated and the moving end  18  of the bimetal  10  pivots counterclockwise. The coupling bridge  20  transmits this pivoting movement with very low friction onto the locking bar  2 , which is moved to the left in the transverse direction  3  for locking. 
     The path of movement up to the stop of the coupling bridge  20  at the housing wide wall  32  is divided into two partial paths of approximately equal length. Traversing the first partial path requires the pivoting drive, which is initiated by the heating of the PTC  34  and effected by the outward bending of the bimetal  10 ; for this movement component, this drive also effects the compression of the tipping spring  28  until its longitudinal axis has reached the dead-center position, in which it is oriented at approximately a right angle to the transverse direction  3 , that is, vertically in FIGS. 2 and 3. Once the dead-center position has been passed through, the tipping spring  28  expands and effects the further displacement drive for the coupling bridge  20  or the locking bar  2 , independently of the heating of the PTC  34 . In contrast, in the second movement component, this displacement movement, which originates from the tipping spring  28  and acts on the locking bar  2  and is now based on a purely-mechanical drive, opens the contact  40  between the reeds  14  and  14   a , thereby interrupting the supply of current to the PTC  34 . The second movement component for the locking movement is therefore independent of the electrical drive. It is effected solely by the tipping spring  28 , and is not ended until the left end of the coupling bridge  20  impacts the inside housing wall  32 . In this stopped position, the locking bar  2  is stabilized in its locked position (FIG.  3 ). At the same time, the contact  41  is closed, so the locking apparatus is in an initial position, ready to be unlocked. 
     The unlocking from the locked position shown in FIG. 3 is effected in that the reed  15   a  and the compression spring  37  are connected to voltage via the reed  39  for the supply of current to the PTC  35 . The PTC  35  is heated, and the moving end  19  of the bimetal  11  pivots clockwise. The above-described tipping process effected by the tipping spring  28  is now completed in the opposite direction. After the dead-center position of the tipping spring  28  has been exceeded, the spring provides the further displacement drive for returning the coupling bridge  20  to the unlocked position (FIG.  2 ), which is likewise stabilized purely mechanically by the expansion of the tipping spring  28 . The opening of the contact  41  cuts off the current supply to the PTC  35 . Until the next switch, the system is again voltage-free. Because the transverse force of the tipping spring  28  is greater than the restoring force of the cooling bimetals  10 ,  11 , the system also remains voltage-free in the respective switching positions (FIGS. 2,  3 ), even in the event of a voltage breakdown. Even bimetal stresses caused by relatively-high, machine-stipulated ambient temperatures are compensated by the opposing arrangement or action of the two bimetals  10 ,  11 . 
     The coupling bridge  20  also effects the control of the signal contacts  42  of a signal device. Depending on the bridge&#39;s position, therefore, the status of the system can be ascertained externally at an arbitrary location. 
     The advantage of the locking apparatus lies in the extremely small dimensions of the unit. A stroke of, for example, 3 mm of the locking bar  2  suffices to lock the mechanism. The bistability of the two positions (locked and unlocked positions) is assured. The instantaneous position of the locking bar  2  is independent of any voltage breakdowns, and is maintained. The drive remains in its initial position if a voltage breakdown occurs during the switching process. Voltage is only applied to the bimetal or the PTC during the switching processes for locking and unlocking. The bimetals and PTCs are only slightly thermally stressed, so they assure a long service life. The system operates silently, in contrast to a magnet drive. The system automatically unlocks when it is connected to voltage. The energy requirement is very low, namely about 1 A over a maximum of 2 sec at 230 V. Lower voltages than the nominal voltage of 230 V can easily be employed to attain full functioning capability. The rod assembly necessary in other systems, such as a motor-driven drive, can be eliminated, because the locking lever  8  can be mounted directly to the device, for example.