Kitchen Workplate With Integrated Cooking Field

1. Field of the Invention

The invention relates to the area of kitchen technology. In particular, the invention refers to the construction of a kitchen workplate as a cooking field, which combines the functions of a cooking stove and of a workplate in a novel fashion.

2. Brief Description of the Background of the Invention Including Prior Art

For a long time the open flame has been the most important source for the feeding of heat required during cooking.

The reason for this, with the exception of grilling (radiation heat), is associated less with the flame itself, but is connected with the purely technical fact that a change of the feeding of heat can be induced very quickly. Here, the most important reason is to be found why the top gastronomical chefs still cook with gas. For example, if one switches the gas flame off during cooking, then the feeding of heat is instantly interrupted. This is not possible in connection with a conventional electric plate cooking field or with a conventional glass ceramic cook field based on the after-heating effect of the heated electric spirals. The automatic control of the feeding of heat with gas occurs substantially more spontaneous. A quick regulation and automatic control of the fed heat, however, is of a decisive interest in connection with the use of temperature-sensitive ingredients, which obtain the desired consistency only in case of a well-metered heat treatment, such as for example in the preparation of sauces with a high fat content.

Despite the indispensability in connection with cooking, gas stoves are associated with the disadvantage that a substantially mechanical expenditure has to be provided for the generation of the flame on the cooking field in order to be able to furnish an accident-proof gas flame.

Organic materials, such as splashes of fat and food residues, deposit on these mechanical parts during cooking operations, which are then burnt into the gas burners on the cooking field by the flame. Overall, the gas cooking field (burner, recess) and the grate required for positioning the pots on the flame are cleaned only with difficulty and are accompanied by substantial time expenditures.

The sticking of burnt-on food residues and fats occurs also in connection with the electric stove, as well as in case of glass-ceramic cooking fields, which react with sensitivity to the burnt-on organic materials upon a long-term use and which are therefore more and more difficult to clean with increasing age based on the damaging of the surface. Glass-ceramic cooking fields are further exhibiting the property that they are sensitive to breakage upon occurrences of strokes and jolts.

Based on the method of magnetic induction it is possible to transfer energy through a suitable medium such as, for example, glass ceramics. This method is used in connection with modern inductive cooking fields, where a magnetic flux is generated in a suitable pot material through a glass-ceramic plate, where the magnetic flux directly heats the pot and where the heat is no longer transferred from the cooking field to the pot but, to the contrary, the heat is generated in the pot itself and only subsequently the residual heat is radiated back to the cooking field. This method achieves as a positive side effect, on the one hand, a clear reduction of the heat loss overall generated during the cooking process. However, on the other hand, much more important for the cooking itself is the fact that a change of the inducing flux has a spontaneous effect on the change of the fed-in energy just as occurs during the cooking with gas.

The magnetic flux is generated by a simple coil in connection with an inductive stove, wherein the coil is passed through by a high-frequency alternating current. The feed-in of energy can be controlled very finely metered and based on a suitable, commercially available electronic circuit.

Since in this context primarily the pot is heated, the time-dependent behavior of the change of the energy feed to the cooked materials is similarly direct as in the case of cooking with gas and, in general, even better.

An important step in connection with the development of modern kitchen technology was the introduction of kitchen workplates, which are today already employed as standard, which provide a homogeneous surface for the free operating continuously above the various bases such as cabinets, refrigerators, washing machines or dish washing machines and which are simple to clean based on the lack of interfering corners, edges, and open seams. In addition, an easily surveillable and flexibly organizable kitchen operation becomes possible.

In most recent times, stone, in particular granite, has proven to be an indestructible material for such workplaces. For example, one can cut with knives on the stone without leaving a scratch. The cleaning of granite is very simple based on the smooth and hard surface, since dirt and residues cannot really adhere even in case of an intensive use and a strong drying. Should this nevertheless happen, then these residues can be removed with hard objects without damaging the surface of the granite plate.

Such kitchen workplates are however still interrupted today by the cooking field, recessed in the plate, which still creates transitions in the region of the stove which are difficult to clean completely, and in particular prevents the user, based on the relatively sensitive surfaces of glass ceramics, from using the cooking field itself as a working field with the above recited advantages.

1. Purposes of the Invention

It is presented the task to integrate the cooking field as completely as possible into the workplate such that a homogeneous and easy-care surface is generated, wherein the surface is capable to connect the workplate regions to the right and to the left of the cooking field together with the cooking field proper to a continuous workplate based on the additional usability of the cooking field as a workplate.

An additional purpose is presented for the improvement of the wearability and the lifetime of cooking-field surfaces as well as a reduction of the surface temperature of induction cooking fields. Based on a decrease of the surface temperature, on the one hand, there are generated new possibilities of the use of temperature measurement equipment on the cooking field, which new possibilities of employing temperature measurement devices in turn represent new tasks for the temperature control of cooking processes on the cooking field, and which new possibilities of employing temperature measurement devices are already today employed in modern baking tubes and microwave ovens.

These and other objects and advantages of the present invention will become evident from the description which follows.

2. Brief Description of the Invention

This object is achieved by the combination of a stone plate (granite plate) having an intact surface and of one or several induction coils disposed underneath the stone, where the induction coils are placed at a sufficiently small distance relative to the surface in order to generate the magnetic flux density in the pot necessary for a transfer of the electric power. The pot in this case is simply placed onto the granite plate for cooking. This position can be marked on the plate with a suitable marking such as, for example, a limited number of small metallic distance spacers, which are entered into the granite surface and which provide a thermal insulation with the aid of the medium air. Removable distance spacers can also be employed as an alternative relative to the previous method. It is possible to dispense with such distance spacer if permitted by the thermal loadability of the respectively employed granite. In order to protect the granite in this context from the crack formation resulting from the effect of heat, which is typical for stone, the mechanical stabilization is provided by a suitable reinforcement. The slight heat generation on the cooking field surface, caused by the induction cooking field, allows for the employment of temperature measurement devices on the cooking field without danger, i.e. in the cooked material itself, and thus allows a program-controlled cooking based on computer-controlled heat feed or, respectively, automatically controlled heat feed.

A continuous workplate remains after the cooking and after the removal of the pots, wherein the continuous workplate is easy to clean based on its insensitivity to soiling and based on the seamless surface. In the following, the cooking field proper can be used as work field while benefiting from all the advantages of the stone material.

Damages of the surface from a burning in, scratching, and in particular jolts and strokes do not occur in contrast to the up to now employed glass-ceramic surfaces in connection with induction cooking fields based on the hardness of the granite.

One of the essential effects of the invention results in addition from the geometric form of the granite, surrounding the induction coil, in connection with the weakly ferromagnetic properties of granite materials, which thus effects a shielding of the spreading of electromagnetic waves.

Based on the geometry of the arrangement of the granite, in particular the thin granite web above the induction coil (about 7 mm) and the residual granite plate which is relatively thick relative to the thin granite web, where the residual granite plate surrounds the coil at the edge of the coil over a large surface, the magnetic field lines (H field) experience a substantially higher electromagnetic resistance at the edge of the coil than above the coil toward the pot material.

According to the Maxwell equations (in particular according to the fourth Maxwell equation div. B=0), according to which the magnetic field lines have to be closed, this effects a strong bundling of the H field in the center of the arrangement perpendicular to the thin granite web above the coil, and thus a substantial weakening of the relatively energy-rich stray fields, which occur in connection with conventional unshielded induction cooking fields, and where the stray fields cause the high energetic "electrosmog." Depending on the relation between the thickness of the web above the coil and the thickness of the remaining granite plate, the stray fields can be reduced in comparison to unshielded arrangements of induction coils to one tenth up to a hundredth, depending on the distance from the stove.

A further advantage is the better heat distribution, since the heat, in contrast to thin glass ceramic fields, in the stone with a typical thickness of 4 centimeters is conducted not only in a horizontal direction but also in a vertical direction, which as a consequence is associated with a reduction of the temperature at the surface. The reduction of the surface temperature can be further supported by the placing of the above-recited distance spacers. Thereby, the zones immediately around the pot remain hand warm.

These comparatively low temperatures on the cooking field allow the use of temperature measurement devices on the cooking field without damaging the heat lines required for the measurement by way of temperature sensors based on thermal overloading. This temperature measurement signal can be led to an automatic control circuit, which allows an automatic temperature surveillance or automatic temperature control by a computer. In case of using a freely programmable computer control, it becomes thereby possible to pass through cooking processes automatically and to store the temperature changes to be performed in suitable electronic media and, if desired, to reproduce these temperature changes to be performed in an identical way.

The thus generated kitchen workplate stove made of stone (stone stove) combines two essential advantages of the state of modern kitchen technology and generates a new third one:

1. the advantage of the immediate and direct energy transfer onto the material to be cooked material and thus the functionality of the fast heat-input change with the aid of the magnetic induction.

2. the advantage of the high loadability and ease of care of a continuous kitchen workplate of granite, which is not interrupted by the conventional transitions to the cooking field; and

3. the advantage of the employment of feed-back temperature measurement now, just as in baking ovens, on the cooking field, and thus to perform an automatic control of the cooking processes.

4. the advantage of the reduction of the stray fields which are common in connection with induction cooking fields.

The result is a stove which can be universally employed with additional functions with the novel feature of the complete integration into the kitchen workplate. The expenditure for care and keeping clean is reduced and additional work space is obtained while simultaneously increasing the lifetime of the surface.

The use of temperature measurement sensors with the very temperature-sensitive feed lines is now also possible on the cooking field without danger based on a temperature reduction, which allows the automatic controllability of cooking processes and thus furnishes a new dimension in the functionality of cooking fields.

The novel features which are considered as characteristic for the invention are set forth in the appended claims. The invention itself, however, both as to its construction and its method of operation, 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.

In the accompanying drawings, in which are shown several of the various possible embodiments of the present invention:

FIG. 1 is a schematic view of a workplate;

FIG. 2 is a sectional view of an optional reinforcement along line 2--2 shown in FIG. 1;

FIG. 3 is a schematic view of a granite plate; and

FIG. 4 is a sectional view of an inserted mechanical armatures along line 4--4 shown in FIG. 1.

Milled cavities (o) are furnished in the stone plate (1) at the predetermined positions for performing the invention, where the diameters of the milled cavities are adapted to the diameter of the induction coils (2) to be employed. The remaining wall thickness of the workplate relative to the surface is selected such that, on the one hand, an energy transfer as high as possible onto the metal pot is present and, on the other hand, a sufficient mechanical stability of the stone is assured in the region of the milled cavity. In order still to assure this stability in the working material granite, the wall thickness should not be below a certain value (which is 7 mm in connection with most kinds of granite). In order to support a favorable pressure distribution and tensile stress distribution in the heated state of the stone, the milled cavities should have rounded edges in order to avoid a wedge effect. The rounding radius r of the chamfer is in this case dependent on the thickness of the granite plate employed and on the respective individual shape of the granite plate. The calculation of an optimum voltage distribution dependent on the rounding radius r of the chamfer and on the other geometric dimensions is performed with the aid of numerical computer simulation programs based on the method of finite elements (for example, the program package MARC). This calculation is under certain circumstances decisive for the respective individual construction of the invention while taking into consideration the mechanical stability of the workplate under heat impact.

Furthermore, it is required that the stone plate be mechanically stabilized in the region of the cooking field in order to avoid the formation of cracks based on thermal tension in the stone. Based on the mounting of armatures such as, for example, winding rods (6), the stone is mechanically pretensioned in order to compensate the thermal tensions in the granite plate occurring during operation. The winding rods are embedded into milled cavities (10) furnished for this purpose and the winding rods are pretensioned with nuts (11) and support washers (12).

A sandwich construction is an alternative to counteract the high mechanical load of the stone under heat impact and thus to avoid crack formation, where, as an armature, for example, a continuous carbon fiber plastic plate (17), about 3 mm strong, is glued between two granite plates of the same thickness. Carbon fiber compound materials are associated with the advantage that they exhibit similar expansion coefficients and the same expansion behavior as granite, however, they are associated with a high tensile strength in contrast to granite. Since the crack formation typically runs radially to the center of the cooking field, the direction of the carbon fiber course should therefore be, if possible, perpendicular to the radius of the cooking field and thus perpendicular to the possible course of a crack in order to compensate the expansion forces of the stone.

It is a cost question which method is preferred in the end for the stabilization of the stone and this depends on the individual geometry of the kitchen workplate. Carbon fiber laminates are at this time still materials which are processed at a relatively high cost.

The coil (2) itself is glued in place together with the thin mica plate (3) with a temperature-stable casting agent (9), for example, epoxy resin with carbon fiber content. The carbon fiber serves in this context for the mechanical stabilization of the thin stone web in the region of the milled cavity and the mica plate serves for the protection of the coil against overheating. In the following, a suitably adapted and cut inlet (5) of the same stone material as the working plate proper is inserted in the remaining hollow space for the mechanical end stabilization of the stone plate. All separating open seams are filled with the casting agent and the carbon fiber (9), which mechanically stabilizes after hardening has occurred and which protects the stone against breakage based on temperature tensions and stroke impact. Distance spacers (7) can be inserted optionally into the stone plate, in order, if necessary, to provide an additional thermal insulation based on an air gap between the stone plate and the pot.

The connections (4) of the induction coil as well as the possibly required further electrical lines for the connection of a temperature measurement sensor for preventing an excessive temperature in the stone, are led out either through the separating open seam between the workplate and the inlet or through a borehole 18 in the inlet, and are fed to a control electronics. For shielding the induction field in a downward direction, the coil is furnished on the bottom side with ferrite cores (8). The commercially available control apparatus of the induction coil is disposed independent of the location of the stove, and because of the heat generation, if possible, the control apparatus is disposed even remote from the stove, at a desired location in a space-saving way, and is automatically controlled by a commercially available personal computer (PC) employable as a board computer (15). The automatic control value is in this case the signal delivered by a temperature sensor (13) placed in the cooked material, where the signal is fed to the PC with the aid of a conventional analogue/digital converter (16). The operating field of the cooking stove with the automatic temperature controllers, furnished for the manual operation, is in turn installed independent of the location of the control electronics at a suitable location in the kitchen, preferably in the exhaust hood disposed above the cooking field. In order not to interfere with the usability of the stone surface as a work surface based on armatures, an optional child safety bow-shaped guard (14) is attached at the support washers (12) underneath the kitchen workplate, and where the child safety bow-shaped guard is removable and formed as shown in FIG. 3.

A preferred embodiment of the invention is illustrated schematically in FIGS. 1 and 2. There are shown the stone workplate 1 with milled cavity (0), the induction coil 2 with mica plate (3) and with electrical connections (4); the stabilizing stone inlet (5) and the metallic armatures (6), (11) and (12) embedded in the granite plate (1).

FIG. 2 shows also the optional reinforcement with a carbon fiber insert (17) as a dashed line.

FIG. 3 shows the granite plate with the distance spacers (7) and the child safety bow-shaped guard (14) from above. FIG. 4 shows the inserted mechanical armatures for stabilizing the stone in a sectional view from the side with the attachment of the child safety bow-shaped guard underneath the granite plate.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of kitchen workplate differing from the types described above.

While the invention has been illustrated and described as embodied in the context of a kitchen workplate with an integrated cooking field, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.

What is desired to be protected by Letters Patent is set forth in the appended claims.