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.

BACKGROUND OF THE INVENTION

Field of the Invention

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.

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.

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

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.

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.

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.

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.

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.

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.

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.

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.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the figures of the drawing in detail and first, particularly, toFIG. 1thereof, there is shown a raised-level, built-in cooking appliance, also referred to as a wall-mounted oven, with a housing1. The rear side of the housing1is mounted on a vertical wall3in the manner of a hanging cupboard. In the housing1a muffle5delimits a cooking space, which can be controlled by a viewing window set in the front face into the housing1. The muffle5is fitted with a non-illustrated heat-insulating sheathing, and it has a bottom muffle opening7. The muffle opening7can be closed with a lowerable bottom door9. InFIG. 1the bottom door9is shown in a lowered state, in which it lies with its underside on a work surface11, or sill plate, or countertop, of a kitchen appliance. A cooktop13is provided on a top side of the bottom door9facing the muffle opening7. The cooktop13is actuated via a control panel14, provided on the front side of the bottom door9.

As is evident fromFIG. 1, the housing1is connected via a bottom door guide mechanism15to the housing1. The bottom door guide mechanism is constructed in the manner of a telescopic guide mechanism, by means of which the bottom door9is guided over a lift path, which is limited by the housing1and the work surface11. For this the telescopic guide mechanism15has on both sides of the raised-level built-in cooking appliance a first guide rail17fixed to the housing1and a second guide rail23fixed on the bottom door9, as shown in FIG.2. The two guide rails17and23are connected to one another via a middle rail21to move longitudinally. According toFIG. 2the first guide rail17is mounted inside the housing1indicated by dashed lines via a screw connection19on the housing rear wall. The middle rail21can move longitudinally with the bottom door-side guide rail23in a sliding connection. InFIG. 2the topside of the bottom door9is shown partially raised. From this it is apparent that the guide rail23is designed as an L-shaped carrier, whereof the horizontal carrier leg31engages in the bottom door9in order to support the latter.

FIG. 3illustrates an enlarged sectional view along line II—II from FIG.2. Accordingly, the guide rails17,23and the middle rail21are designed as rigid, U-profile parts resistant to bending, which can be telescoped into one another. The bottom door-side guide rail23is guided in the middle rail21, while the middle rail21is mounted displaceably in the housing-side guide rail17. When the bottom door9is closed the housing-side guide rail17is thus arranged in the telescopic bottom door guide mechanism15. In this way the outermost guide rail17can 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.

The U-shaped rails17,21,23form a channel35according to FIG.3. Electric supply or signal lines37are laid in the channel35, for connecting the cooktop13and the control panel14in the bottom door9to control devices in the housing1. Arranged in the channel35also is a deflection sheave39swivel-mounted about a axis of rotation38. A pull rope41of 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 sheave39. The channel35open to the left is covered by grooved shutters43,47. When the bottom door9is lowered the operator cannot see into the channel35. The shutter43is assigned to the mobile guide rail23and is fastened detachably to its side walls. In similar fashion the shutter47is assigned to the middle rail23. The shutters43,47can be telescoped into one another corresponding to the rails21,23. When the bottom door9is closed the shutter43is thus arranged inside the shutter47. Provided on a front side of the shutter43is an infrared sensor45for non-contact temperature measuring of a cooking container arranged on the cooktop13.

FIG. 4illustrates a section fromFIG. 1, on an enlarged scale, taken along the line IV—IV. Accordingly, an electromotor49forming a drive mechanism is arranged in the interior of the housing1. The electromotor49is driven by the control panel14provided at the front on the bottom door9via current or signal lines37. The lines37run inside the conduit35configured in the guide and middle rails17;21,23. As apparent fromFIG. 5, the electromotor49is disposed in the region of the housing rear wall approximately in the middle between the two side walls of the housing1. The housing1is strongly outlined inFIG. 5with dashed lines.FIG. 5also demonstrates that the electromotor49is assigned tensile elements41a,41b. The tensile elements41are pull ropes in the present embodiment, which starting out from the electromotor49are first guided horizontally to laterally arranged housing-side deflection sheaves51, and are then guided in a vertical direction to a bottom door9indicated by dashed lines. The abovementioned deflection sheaves39are mounted in the bottom door-side guide elements23. The pull ropes41a,41bare guided in the manner of a lifting pulley around the bottom door-side deflection sheaves39and run once more in the housing1. The ends53of the pull ropes are fixed in place on switching elements55a,55bfastened on the housing side. According toFIG. 5the latter are arranged in the housing1at approximately the same height as the housing-side deflection sheaves51. Construction and operation of the switching elements55a,55bare described hereinbelow.

InFIGS. 6 and 7the electromotor49for the pull ropes41is shown in perspective in an exploded view and in the assembled state. The electromotor49has a driven shaft57, on which two winding drums59and61are mounted, as shown in the perspective view according to FIG.7. Depending on the direction of rotation of the driven shaft57each winding drum59,61winds the assigned pull rope41a,41bup or down. For this purpose the winding drums59,61are fitted with left-handed and right-handed rope grooves63and65. The ends67of the pull ropes41a,41bare held firmly on the winding drums59and61. InFIG. 7is a direction of rotation X of the driven shaft57in indicated in a clockwise direction. In this case both the pull ropes41a,41bare unwound from their assigned winding drums59,61. The bottom door9accordingly descends. With rotation of the driven shaft57in an anticlockwise direction each rope pull41a,41bis wound onto its assigned winding drum. As is further evident fromFIG. 6, a disc-like carrier67is attached to the driven shaft57. The carrier67has carrier teeth69on both its opposite front sides. With rotation of the driven shaft57flanks of these carrier teeth69press on corresponding front teeth71of the winding drums59,61. The carrier teeth69of the carrier67work as swing angle stops. Each of the winding drums59,61can be swiveled through a swing angle of approximately 90° between these swivel stops. Also, between the carrier67and each of the winding drums59,61acoil spring73a,73bis tensed. In terms of process technology both coil springs73a,73bare connected to one another at one spring end via a pin74, according to FIG.6. The coil springs73a,73bare supported by their common spring pin74on the one hand in a locking groove75of the carriers67. On the other hand the coil springs73a,73bare supported by their other spring ends in openings77of the winding drums59and61.

As evident fromFIG. 7, the winding drums59and61are mounted at the front and swivel mounted to one another. At the same time both winding drums59,61delimit a take-up space79. The carrier67, the radial teeth71of the winding drums and the springs73aand73bare housed economically in the take-up space79.

The assembly described with reference toFIGS. 6 and 7acts as a slack rope safety contrivance for the pull ropes41a,41b. The operation of the slack rope safety contrivance is described hereinbelow by means of FIGS.8A and8B: according toFIG. 8Athe pull rope41bis tensed by the weight FGof the bottom door9. A torque MGacts on the winding drum59in a clockwise direction. The torque MGpresses the radial teeth71of the winding drum59onto first flanks70of the carrier teeth69. Thus the winding drum59is held firmly with the carrier67. Depending on the direction of rotation of the driven shaft57the carrier67of the winding drums can rotate in a clockwise or in an anticlockwise direction. In the state according toFIG. 8Athe coil spring73asupported between the points75and77is pre-tensed. The coil spring73athus exerts on the winding drum59a tension torque MSpcountering the torque MG

InFIG. 8Bthere is illustrated a position which is reached when the bottom door9comes to rest, for example on the work surface11, as it descends. In such a case, as is described hereinbelow, switching elements55a,55bare first activated. These transmit corresponding switch signals to a control device103, which switches off the electromotor49. Due to the signal path between the switching elements55a,55band the electromotor49, and on account of mass reactance effects the electromotor49is switched off in time delay only after the switch signals are triggered. The consequence of the after-running of the electromotor49inside this time delay is that the weight of the bottom door9is taken up by the work surface11and the pull rope41bis relieved. Accordingly also the torque MGexerted on the winding drum59is reduced. Such pull relief is prevented by the tension torque MSp. The tension torque MSpacts in an anticlockwise direction on the radial teeth71of the winding drum59. The winding drum59is adjusted in relation to the driven shaft57in an anticlockwise direction and thus slackens the pull rope41b. A minimum value of the tensile force in the pull rope41bis maintained, such that slackening of the pull rope41bis prevented.

With reference toFIG. 9, the construction and operation of the above-mentioned switching elements55a,55bare described by way of example of the switching element55ashown to the right in FIG.5. The switching element55ahas a carrier plate81with a bore83, through which the pull rope end53is guided. Attached to the pull rope end53is a switch lug84, which protrudes through a switch window85placed on the front side of the carrier plate81. The switch lug84is guided displaceably inside the switch window85and supported by a spring87on a lower support89of the switch window85. By means of the switch lug84switches91,93arranged opposite one another on the carrier plate81are switched. For this purpose the switch lug83has two opposite switch ramps95,97, which are offset to one another in the pull rope longitudinal direction. Depending on the height position of the switch lug93the switch ramps95,97switch switch pins99,101of the switches91,3. The height position of the switch lug93depends on the magnitude of the tensile force FZa, with which the switch lug83presses on the spring87. With activation of the switch pins99,101switch signals Sa1, Sa2are generated in the switches91,93of the switching element55a, which are transmitted to a control device103according to the block diagram in FIG.10. The control device103controls the electromotor49in dependence on these switch signals.

InFIG. 9the left switch pin101of the switch93is activated by the switch ramp97. This is the case according to the present invention whenever the value of the tensile force Fzais 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 door9. In the event that a non-weight-loaded bottom door9goes against a lower stop, for example against the work surface11or against an object lying on the work surface, the pull rope41ais relieved. The tensile force FZain the pull rope41athus drops below the minimum value. In the process the switch ramp97, to the left according toFIG. 9, shifts up and disengages from the switch pin101. As shown inFIG. 10, the control device103thus receives a corresponding switch signal Sa1from the switch93to switch off the electromotor49.

The right switch pin99inFIG. 9is shown disengaged from the right switch ramp95. This is the case if the value of the tensile force FZais less than a maximum value of the tensile force FZa. This maximum value corresponds for example to a tensile force FZa, which is adjusted with preset maximum dead-weight loading of the bottom door9. The value of the tensile force FZacan exceed the maximum value, if the bottom door9is overloaded or if the bottom door9goes against an upper stop when the cooking space3is sealed off, for example against a bottom muffle flange of the muffle5. In such a case the tensile force rises. The switch lug84is pressed down against the spring87. This engages the right switch ramp95with the switch pin99. The control device103now receives a corresponding switch signal Sa2from the switching element55ato switch off the electromotor49. The operation described with respect to the switching element55aapplies identically for the switching element55b, inFIG. 5arranged on the right side of the housing1. According toFIG. 10the right switching element55bforwards corresponding switch signals Sb1and Sb2to the control device103.

The control device103according to the invention detects a time delay Δt between corresponding switch signals Sa1and Sa2and between Sb1and Sb2of the switching elements55a,55b. 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 door9. In such a case the bottom door9tilts out of its normally horizontal position into a slightly oblique position. Such an oblique position of the bottom door9is indicated in FIG.2. Accordingly the bottom door9is tilted at an angle of inclination α out of its horizontal position. The effect of the oblique position is that the pull ropes41a,41bare loaded by tensile forces FZa, FZbof varying magnitude. Here the tensile forces FZa, FZbdo not drop below the lower threshold value. As a consequence the switches99and101of the switching elements55a,55bare switched in time delay of Δt. Corresponding switch signals Sa1and Sb1are thus generated likewise in a time-delayed fashion. If the time delay between the switch signals Sa1and Sb1is greater than a value stored in the control device103, for example 0.2s, then the control device103reverses the electromotor49. The bottom door9is then raised to lessen the angle of inclination α.

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 electromotor49depending on the size of the angle of inclination α, in particular when the bottom door9descends.

The electric current recorded by the electromotor49is detected to determine a dead-weight loading of the bottom door9according to the present invention, by means of the control device103. Here the fact is employed that the current1recorded by the electromotor49behaves proportionally to a load torque, which acts on the driven shaft57of the electromotor49. This connection is illustrated in a loading diagram according to FIG.11.

At least two lift procedures are required to detect the weight of a cooking container set on the bottom door9. In the first lift procedure the control device103first detects a current value I1for a load torque M1as reference value. The load torque Mi is exerted on the driven shaft57and is necessary to raise the non-weight-loaded bottom door9. The current value I1is stored by the control device103. In the subsequent second lift procedure the current value I2is detected for a load torque M2, which is required for raising the weight-loaded bottom door9. Depending on the magnitude of the differential values (I2−I1) the control device103determines the dead-weight loading of the bottom door9.

The current requirement of the electromotor49is influenced by the level of the temperature in the electromotor49. In order to compensate for this influence it is advantageous to arrange a temperature sensor105in the electromotor49, as indicated in FIG.5. This is connected to the control device103. Depending on the temperature measured on the temperature sensor105the control device103selects corresponding corrective factors. By means of these corrective factors the temperature influence is equalized to the current consumption of the electromotor.

To avoid an influence of temperature on the weight detection the dead-weight loading of the bottom door9can be detected according to the tensile force sensor107indicated in FIG.5. The sensor107is in signal connection with the control device103and is assigned to the axis of rotation38of the deflection sheave39. In a lift procedure the pull rope41exerts a tensile force Fz, as shown inFIG. 5, on the tensile force sensor107. Depending on the magnitude of the tensile force Fzon the bottom door9the tensile force sensor107generates signals, which are transmitted to the control device103.

The signal of the tensile force sensor107can also be used, depending on the magnitude of the tensile force, to control the electromotor49. 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 device103, the electromotor49is then switched off. If the tensile force sensor107detects a value of the tensile force, which is above an upper threshold value of the tensile force, then the electromotor49is likewise switched off.

The tensile force sensor105can alternatively be replaced by a torque sensor, which detects a load torque, which is exerted on the driven shaft57of the electromotor49. 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.

In the exemplary figures, the work surface11acts as a lower end stop for the lowered bottom door9. Alternatively, the end stop can also be provided by selection limiters in the telescopic rails17,21,23. This enables any built-in height of the raised-level built-in cooking appliance on the vertical wall3. The maximum lift path is achieved when the telescopic parts17,21and23are fully extended from one another and the selection limiters prevent the rails from being separated.