Abstract:
A raised-level cooking appliance has a heating chamber with a lowerable trapdoor and a drive device. The drive device is configured to lower and lift the trapdoor. The drive mechanism is subject to a tension force, counteracting a weight of the trapdoor. The drive for moving the trapdoor may be switched off when the trapdoor comes into contact with an upper or lower stop in a simpler and more reliable manner. A control device controls the drive device in dependence on a magnitude of the tension force acting on the drive mechanism.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a continuation, under 35 U.S.C. § 120, of copending international application No. PCT/EP02/13456, filed Nov. 28, 2002, which designated the United States; this application also claims the priority, under 35 U.S.C. § 119, of German patent application No. 101 64 238.5, filed Dec. 27, 2001; the prior applications are herewith incorporated by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     Field of the Invention  
         [0003]     The present invention relates to a raised-level built-in cooking appliance, also referred to as a wall-mounted appliance, with a heating chamber, which has a floor-side chamber opening, which can be closed with a lowerable bottom door, and with a drive mechanism for lifting the bottom door, which has at least one tensile element, connected to the bottom door, which tensile element is stressed against a weight of the bottom door with a tensile force.  
         [0004]     A wall oven described in international PCT publication WO 98/04871 is to be considered as a generic raised-level built-in cooking appliance. The wall oven has a cooking space or an oven chamber, which is enclosed by side walls, a front, back and top wall, and has a bottom oven chamber opening. The wall oven is to be attached to a wall by its rear wall in the manner of a hanging cupboard. The bottom oven chamber opening can be closed by a lowerable bottom door. The bottom door is connected to the housing via a bottom door guide mechanism. By means of the bottom door guide the bottom door can be pivoted through a lift path.  
         [0005]     U.S. Pat. No. 2,944,540 discloses a raised-level built-in cooking appliance, in which the bottom door is connected to the cooking appliance housing via a telescopic guide mechanism. The lifting motion of the bottom door is executed by a housing-side drive motor, which is connected via pull ropes to the bottom door.  
       SUMMARY OF THE INVENTION  
       [0006]     It is accordingly an object of the invention to provide a raised-level built-in appliance, which provides improvements over the heretofore-known devices and methods of this general type and which, more particularly, provides a raised-level built-in cooking appliance in which a control for hoisting the bottom door is improved.  
         [0007]     With the foregoing and other objects in view there is provided, in accordance with the invention, a wall-mounted cooking appliance, comprising: 
    a housing defining a heating chamber and having a bottom muffle opening;     a lowerable bottom door for selectively closing the muffle opening;     a drive mechanism for hoisting the bottom door, the drive mechanism including at least one tensile element, connected to the bottom door and stressed against a weight of the bottom door with a given tensile force; and     a control device connected to and controlling the drive mechanism in dependence of a magnitude of the given tensile force.    
 
         [0012]     In other words, the objects are achieved with the raised-level built-in cooking appliance as described. Here, the raised-level built-in cooking appliance has at least one control device, which controls the drive mechanism in dependence on the magnitude of the tensile force occurring during a hoisting procedure. The drive mechanism can be switched on and off or the drive direction can be reversed as a result of a change in the magnitude of the tensile force.  
         [0013]     In an advantageous embodiment of the invention the lowering procedure of the bottom door can always be terminated by means of the control device, whenever the detected tensile force falls below a specific threshold value. This is the case when the bottom door comes into contact with a working plate or another object located under the bottom door. In addition, the control device can also interrupt the bottom door drive when an upper threshold value of the tensile force is exceeded. This is the case when the bottom door comes against an upper stop, for example against the floor-side muffle opening in the cooking appliance housing.  
         [0014]     To detect the tensile force the drive means, for example a pull rope, of the drive mechanism can be pre-tensed by a spring. With a change in the tensile force the spring moves over a spring path. Depending on the magnitude of the spring path the control device can determine the magnitude of the tensile force. Alternatively, a tensile force sensor can also be used, which detects the tensile forces engaging on a deflection sheave for the pull rope, for example.  
         [0015]     According to a particular embodiment of the invention the control device can detect an angle of inclination of the bottom door. Depending on the magnitude of the angle of inclination the control device can drive the drive mechanism in order to reduce the angle of inclination. This angle of inclination is set when the bottom door bears on an object during a lowering procedure, for example a cooking container arranged under the bottom door. In such a case the bottom door tilts out of its normally horizontal position into a slight oblique position.  
         [0016]     Angle sensors, which monitor the angle setting of the bottom door, can be employed to detect the angle of inclination. Alternatively, according to a preferred embodiment the magnitude of tensile forces can be detected by at least two tensile elements connected to the bottom door. Depending on a tensile force difference between the detected tensile forces the control device determines the angle of inclination of the bottom door.  
         [0017]     The abovementioned tensile force difference can be determined for example by means of at least a first and a second switch. These switches generate switch signals when there is a change in the tensile forces in the at least two tensile elements. The control device compares corresponding switch signals of both switches and deduces the tensile force difference.  
         [0018]     Other features which are considered as characteristic for the invention are set forth in the appended claims.  
         [0019]     Although the invention is illustrated and described herein as embodied in a raised-level built-in cooking device, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.  
         [0020]     The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]      FIG. 1  is a perspective view of a raised-level built-in cooking appliance mounted on a vertical wall, with lowered bottom door;  
         [0022]      FIG. 2  is a perspective schematic view, in which a bottom door guide mechanism of the raised-level built-in cooking appliance is raised;  
         [0023]      FIG. 3  is an enlarged view of a section taken along the line III-III of  FIG. 2 ;  
         [0024]      FIG. 4  is a side elevation enlarged in sections along the line IV-IV of  FIG. 1 ;  
         [0025]      FIG. 5  is a perspective schematic view, in which a drive mechanism of the raised-level built-in cooking appliance is raised;  
         [0026]      FIG. 6  is a perspective exploded view of an electromotor of the drive mechanism;  
         [0027]      FIG. 7  is a perspective illustration of the assembled electromotor;  
         [0028]      FIGS. 8A and 8B  are schematic sectional views taken along the line VIII-VIII of  FIG. 7 ;  
         [0029]      FIG. 9  is a detail Y of  FIG. 5  in an enlarged front elevation;  
         [0030]      FIG. 10  is a block diagram illustrating a signal sequence to a control device according to the invention; and  
         [0031]      FIG. 11  is a loading diagram of the electromotor of the drive mechanism.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0032]     Referring now to the figures of the drawing in detail and first, particularly, to  FIG. 1  thereof, there is shown a raised-level, built-in cooking appliance, also referred to as a wall-mounted oven, with a housing  1 . The rear side of the housing  1  is mounted on a vertical wall  3  in the manner of a hanging cupboard. In the housing  1  a muffle  5  delimits a cooking space, which can be controlled by a viewing window set in the front face into the housing  1 . The muffle  5  is fitted with a non-illustrated heat-insulating sheathing, and it has a bottom muffle opening  7 . The muffle opening  7  can be closed with a lowerable bottom door  9 . In  FIG. 1  the bottom door  9  is shown in a lowered state, in which it lies with its underside on a work surface  11 , or sill plate, or countertop, of a kitchen appliance. A cooktop  13  is provided on a top side of the bottom door  9  facing the muffle opening  7 . The cooktop  13  is actuated via a control panel  14 , provided on the front side of the bottom door  9 .  
         [0033]     As is evident from  FIG. 1 , the housing  1  is connected via a bottom door guide mechanism  15  to the housing  1 . The bottom door guide mechanism is constructed in the manner of a telescopic guide mechanism, by means of which the bottom door  9  is guided over a lift path, which is limited by the housing  1  and the work surface  11 . For this the telescopic guide mechanism  15  has on both sides of the raised-level built-in cooking appliance a first guide rail  17  fixed to the housing  1  and a second guide rail  23  fixed on the bottom door  9 , as shown in  FIG. 2 . The two guide rails  17  and  23  are connected to one another via a middle rail  21  to move longitudinally. According to  FIG. 2  the first guide rail  17  is mounted inside the housing  1  indicated by dashed lines via a screw connection  19  on the housing rear wall. The middle rail  21  can move longitudinally with the bottom door-side guide rail  23  in a sliding connection. In  FIG. 2  the topside of the bottom door  9  is shown partially raised. From this it is apparent that the guide rail  23  is designed as an L-shaped carrier, whereof the horizontal carrier leg  31  engages in the bottom door  9  in order to support the latter.  
         [0034]      FIG. 3  illustrates an enlarged sectional view along line II-II from  FIG. 2 . Accordingly, the guide rails  17 ,  23  and the middle rail  21  are designed as rigid, U-profile parts resistant to bending, which can be telescoped into one another. The bottom door-side guide rail  23  is guided in the middle rail  21 , while the middle rail  21  is mounted displaceably in the housing-side guide rail  17 . When the bottom door  9  is closed the housing-side guide rail  17  is thus arranged in the telescopic bottom door guide mechanism  15 . In this way the outermost guide rail  17  can be mounted simply on the housing rear wall. The rails are preferably mounted by way of bearings with balls, rollers, or cylinders. These are taken up in a known manner in non-illustrated bearing cages between the rails.  
         [0035]     The U-shaped rails  17 ,  21 ,  23  form a channel  35  according to  FIG. 3 . Electric supply or signal lines  37  are laid in the channel  35 , for connecting the cooktop  13  and the control panel  14  in the bottom door  9  to control devices in the housing  1 . Arranged in the channel  35  also is a deflection sheave  39  swivel-mounted about a axis of rotation  38 . A pull rope  41  of a drive mechanism, yet to be described, of the raised-level built-in cooking appliance is guided in the manner of a lifting pulley about this deflection sheave  39 . The channel  35  open to the left is covered by grooved shutters  43 ,  47 . When the bottom door  9  is lowered the operator cannot see into the channel  35 . The shutter  43  is assigned to the mobile guide rail  23  and is fastened detachably to its side walls. In similar fashion the shutter  47  is assigned to the middle rail  23 . The shutters  43 ,  47  can be telescoped into one another corresponding to the rails  21 ,  23 . When the bottom door  9  is closed the shutter  43  is thus arranged inside the shutter  47 . Provided on a front side of the shutter  43  is an infrared sensor  45  for non-contact temperature measuring of a cooking container arranged on the cooktop  13 .  
         [0036]      FIG. 4  illustrates a section from  FIG. 1 , on an enlarged scale, taken along the line IV-IV. Accordingly, an electromotor  49  forming a drive mechanism is arranged in the interior of the housing  1 . The electromotor  49  is driven by the control panel  14  provided at the front on the bottom door  9  via current or signal lines  37 . The lines  37  run inside the conduit  35  configured in the guide and middle rails  17 ;  21 ,  23 . As apparent from  FIG. 5 , the electromotor  49  is disposed in the region of the housing rear wall approximately in the middle between the two side walls of the housing  1 . The housing  1  is strongly outlined in  FIG. 5  with dashed lines.  FIG. 5  also demonstrates that the electromotor  49  is assigned tensile elements  41   a ,  41   b . The tensile elements  41  are pull ropes in the present embodiment, which starting out from the electromotor  49  are first guided horizontally to laterally arranged housing-side deflection sheaves  51 , and are then guided in a vertical direction to a bottom door  9  indicated by dashed lines. The abovementioned deflection sheaves  39  are mounted in the bottom door-side guide elements  23 . The pull ropes  41   a ,  41   b  are guided in the manner of a lifting pulley around the bottom door-side deflection sheaves  39  and run once more in the housing  1 . The ends  53  of the pull ropes are fixed in place on switching elements  55   a ,  55   b  fastened on the housing side. According to  FIG. 5  the latter are arranged in the housing  1  at approximately the same height as the housing-side deflection sheaves  51 . Construction and operation of the switching elements  55   a ,  55   b  are described hereinbelow.  
         [0037]     In  FIGS. 6 and 7  the electromotor  49  for the pull ropes  41  is shown in perspective in an exploded view and in the assembled state. The electromotor  49  has a driven shaft  57 , on which two winding drums  59  and  61  are mounted, as shown in the perspective view according to  FIG. 7 . Depending on the direction of rotation of the driven shaft  57  each winding drum  59 ,  61  winds the assigned pull rope  41   a ,  41   b  up or down. For this purpose the winding drums  59 ,  61  are fitted with left-handed and right-handed rope grooves  63  and  65 . The ends  67  of the pull ropes  41   a ,  41   b  are held firmly on the winding drums  59  and  61 . In  FIG. 7  is a direction of rotation X of the driven shaft  57  in indicated in a clockwise direction. In this case both the pull ropes  41   a ,  41   b  are unwound from their assigned winding drums  59 ,  61 . The bottom door  9  accordingly descends. With rotation of the driven shaft  57  in an anticlockwise direction each rope pull  41   a ,  41   b  is wound onto its assigned winding drum. As is further evident from  FIG. 6 , a disc-like carrier  67  is attached to the driven shaft  57 . The carrier  67  has carrier teeth  69  on both its opposite front sides. With rotation of the driven shaft  57  flanks of these carrier teeth  69  press on corresponding front teeth  71  of the winding drums  59 ,  61 . The carrier teeth  69  of the carrier  67  work as swing angle stops. Each of the winding drums  59 ,  61  can be swiveled through a swing angle of approximately 90° between these swivel stops. Also, between the carrier  67  and each of the winding drums  59 ,  61   a  coil spring  73   a ,  73   b  is tensed. In terms of process technology both coil springs  73   a ,  73   b  are connected to one another at one spring end via a pin  74 , according to  FIG. 6 . The coil springs  73   a ,  73   b  are supported by their common spring pin  74  on the one hand in a locking groove  75  of the carriers  67 . On the other hand the coil springs  73   a ,  73   b  are supported by their other spring ends in openings  77  of the winding drums  59  and  61 .  
         [0038]     As evident from  FIG. 7 , the winding drums  59  and  61  are mounted at the front and swivel mounted to one another. At the same time both winding drums  59 ,  61  delimit a take-up space  79 . The carrier  67 , the radial teeth  71  of the winding drums and the springs  73   a  and  73   b  are housed economically in the take-up space  79 .  
         [0039]     The assembly described with reference to  FIGS. 6 and 7  acts as a slack rope safety contrivance for the pull ropes  41   a ,  41   b . The operation of the slack rope safety contrivance is described hereinbelow by means of FIGS.  8 A and  8 B: according to  FIG. 8A  the pull rope  41   b  is tensed by the weight F G  of the bottom door  9 . A torque M G  acts on the winding drum  59  in a clockwise direction. The torque M G  presses the radial teeth  71  of the winding drum  59  onto first flanks  70  of the carrier teeth  69 . Thus the winding drum  59  is held firmly with the carrier  67 . Depending on the direction of rotation of the driven shaft  57  the carrier  67  of the winding drums can rotate in a clockwise or in an anticlockwise direction. In the state according to  FIG. 8A  the coil spring  73   a  supported between the points  75  and  77  is pre-tensed. The coil spring  73   a  thus exerts on the winding drum  59  a tension torque M Sp  countering the torque M G    
         [0040]     In  FIG. 8B  there is illustrated a position which is reached when the bottom door  9  comes to rest, for example on the work surface  11 , as it descends. In such a case, as is described hereinbelow, switching elements  55   a ,  55   b  are first activated. These transmit corresponding switch signals to a control device  103 , which switches off the electromotor  49 . Due to the signal path between the switching elements  55   a ,  55   b  and the electromotor  49 , and on account of mass reactance effects the electromotor  49  is switched off in time delay only after the switch signals are triggered. The consequence of the after-running of the electromotor  49  inside this time delay is that the weight of the bottom door  9  is taken up by the work surface  11  and the pull rope  41   b  is relieved. Accordingly also the torque M G  exerted on the winding drum  59  is reduced. Such pull relief is prevented by the tension torque M Sp . The tension torque M Sp  acts in an anticlockwise direction on the radial teeth  71  of the winding drum  59 . The winding drum  59  is adjusted in relation to the driven shaft  57  in an anticlockwise direction and thus slackens the pull rope  41   b . A minimum value of the tensile force in the pull rope  41   b  is maintained, such that slackening of the pull rope  41   b  is prevented.  
         [0041]     With reference to  FIG. 9 , the construction and operation of the above-mentioned switching elements  55   a ,  55   b  are described by way of example of the switching element  55   a  shown to the right in  FIG. 5 . The switching element  55   a  has a carrier plate  81  with a bore  83 , through which the pull rope end  53  is guided. Attached to the pull rope end  53  is a switch lug  84 , which protrudes through a switch window  85  placed on the front side of the carrier plate  81 . The switch lug  84  is guided displaceably inside the switch window  85  and supported by a spring  87  on a lower support  89  of the switch window  85 . By means of the switch lug  84  switches  91 ,  93  arranged opposite one another on the carrier plate  81  are switched. For this purpose the switch lug  83  has two opposite switch ramps  95 ,  97 , which are offset to one another in the pull rope longitudinal direction. Depending on the height position of the switch lug  93  the switch ramps  95 ,  97  switch switch pins  99 ,  101  of the switches  91 ,  3 . The height position of the switch lug  93  depends on the magnitude of the tensile force F Za , with which the switch lug  83  presses on the spring  87 . With activation of the switch pins  99 ,  101  switch signals S a1 , S a2  are generated in the switches  91 ,  93  of the switching element  55   a , which are transmitted to a control device  103  according to the block diagram in  FIG. 10 . The control device  103  controls the electromotor  49  in dependence on these switch signals.  
         [0042]     In  FIG. 9  the left switch pin  101  of the switch  93  is activated by the switch ramp  97 . This is the case according to the present invention whenever the value of the tensile force Fza is greater than or identical to a minimum value of the tensile force. This minimum value corresponds approximately to a value of the tensile force in a non-weight-loaded bottom door  9 . In the event that a non-weight-loaded bottom door  9  goes against a lower stop, for example against the work surface  11  or against an object lying on the work surface, the pull rope  41   a  is relieved. The tensile force F Za  in the pull rope  41   a  thus drops below the minimum value. In the process the switch ramp  97 , to the left according to  FIG. 9 , shifts up and disengages from the switch pin  101 . As shown in  FIG. 10 , the control device  103  thus receives a corresponding switch signal S a1  from the switch  93  to switch off the electromotor  49 .  
         [0043]     The right switch pin  99  in  FIG. 9  is shown disengaged from the right switch ramp  95 . This is the case if the value of the tensile force F Za  is less than a maximum value of the tensile force F Za . This maximum value corresponds for example to a tensile force F Za , which is adjusted with preset maximum dead-weight loading of the bottom door  9 . The value of the tensile force F Za  can exceed the maximum value, if the bottom door  9  is overloaded or if the bottom door  9  goes against an upper stop when the cooking space  3  is sealed off, for example against a bottom muffle flange of the muffle  5 . In such a case the tensile force rises. The switch lug  84  is pressed down against the spring  87 . This engages the right switch ramp  95  with the switch pin  99 . The control device  103  now receives a corresponding switch signal Sa 2  from the switching element  55   a  to switch off the electromotor  49 . The operation described with respect to the switching element  55   a  applies identically for the switching element  55   b , in  FIG. 5  arranged on the right side of the housing  1 . According to  FIG. 10  the right switching element  55   b  forwards corresponding switch signals S b1  and S b2  to the control device  103 .  
         [0044]     The control device  103  according to the invention detects a time delay Δt between corresponding switch signals S a1  and S a2  and between S bi  and S b2  of the switching elements  55   a ,  55   b . The time delay Δt results, for example, if the bottom door comes to bear on an object as it descends, for example a cooking container arranged underneath the bottom door  9 . In such a case the bottom door  9  tilts out of its normally horizontal position into a slightly oblique position. Such an oblique position of the bottom door  9  is indicated in  FIG. 2 . Accordingly the bottom door  9  is tilted at an angle of inclination α out of its horizontal position. The effect of the oblique position is that the pull ropes  41   a ,  41   b  are loaded by tensile forces F Za , F Zb  of varying magnitude. Here the tensile forces F Za , F Zb  do not drop below the lower threshold value. As a consequence the switches  99  and  101  of the switching elements  55   a ,  55   b  are switched in time delay of Δt. Corresponding switch signals S a1  and S b1  are thus generated likewise in a time-delayed fashion. If the time delay between the switch signals S a1  and S b1  is greater than a value stored in the control device  103 , for example 0.2s, then the control device  103  reverses the electromotor  49 . The bottom door  9  is then raised to lessen the angle of inclination α.  
         [0045]     Unintentional pinching of human body parts is prevented by the above-mentioned detection of the angle of inclination a of the bottom door and control of the electromotor  49  depending on the size of the angle of inclination α, in particular when the bottom door  9  descends.  
         [0046]     The electric current recorded by the electromotor  49  is detected to determine a dead-weight loading of the bottom door  9  according to the present invention, by means of the control device  103 . Here the fact is employed that the current  1  recorded by the electromotor  49  behaves proportionally to a load torque, which acts on the driven shaft  57  of the electromotor  49 . This connection is illustrated in a loading diagram according to  FIG. 11 .  
         [0047]     At least two lift procedures are required to detect the weight of a cooking container set on the bottom door  9 . In the first lift procedure the control device  103  first detects a current value I 1  for a load torque M 1  as reference value. The load torque Mi is exerted on the driven shaft  57  and is necessary to raise the non-weight-loaded bottom door  9 . The current value I 1  is stored by the control device  103 . In the subsequent second lift procedure the current value I 2  is detected for a load torque M 2 , which is required for raising the weight-loaded bottom door  9 . Depending on the magnitude of the differential values (I 2 -I 1 ) the control device  103  determines the dead-weight loading of the bottom door  9 .  
         [0048]     The current requirement of the electromotor  49  is influenced by the level of the temperature in the electromotor  49 . In order to compensate for this influence it is advantageous to arrange a temperature sensor  105  in the electromotor  49 , as indicated in  FIG. 5 . This is connected to the control device  103 . Depending on the temperature measured on the temperature sensor  105  the control device  103  selects corresponding corrective factors. By means of these corrective factors the temperature influence is equalized to the current consumption of the electromotor.  
         [0049]     To avoid an influence of temperature on the weight detection the dead-weight loading of the bottom door  9  can be detected according to the tensile force sensor  107  indicated in  FIG. 5 . The sensor  107  is in signal connection with the control device  103  and is assigned to the axis of rotation  38  of the deflection sheave  39 . In a lift procedure the pull rope  41  exerts a tensile force F z , as shown in  FIG. 5 , on the tensile force sensor  107 . Depending on the magnitude of the tensile force F z  on the bottom door  9  the tensile force sensor  107  generates signals, which are transmitted to the control device  103 .  
         [0050]     The signal of the tensile force sensor  107  can also be used, depending on the magnitude of the tensile force, to control the electromotor  49 . If the value of the tensile force measured by means of the tensile force sensor is below a lower threshold value stored in the control device  103 , the electromotor  49  is then switched off. If the tensile force sensor  107  detects a value of the tensile force, which is above an upper threshold value of the tensile force, then the electromotor  49  is likewise switched off.  
         [0051]     The tensile force sensor  105  can alternatively be replaced by a torque sensor, which detects a load torque, which is exerted on the driven shaft  57  of the electromotor  49 . Piezoelectric pressure sensors or deformation or tension sensors can also be employed as sensors for measuring the dead-weight loading, for example flexible stick-on strips or materials with tension-dependent optical properties and thus cooperating optical sensors.  
         [0052]     In the exemplary figures, the work surface  11  acts as a lower end stop for the lowered bottom door  9 . Alternatively, the end stop can also be provided by selection limiters in the telescopic rails  17 ,  21 ,  23 . This enables any built-in height of the raised-level built-in cooking appliance on the vertical wall  3 . The maximum lift path is achieved when the telescopic parts  17 ,  21  and  23  are fully extended from one another and the selection limiters prevent the rails from being separated.