Energy transfer cooking appliance accessories, method for manufacturing energy transfer cooking appliance accessories and cooking appliance

Abstract

Energy transfer cooking appliance accessory (36) comprising a plastically deformed sheet (16) and a transformer-like power transfer unit (22) having a primary circuit (24) and a secondary circuit (26), wherein the plastically deformed sheet (16) has a deformation region (18) exhibiting a locally significantly increased magnetic permeability compared to the rest of the sheet (16) in the non-plastically deformed region, such that the plastically deformed sheet (16) allows a higher magnetic flux in the local deformation region (18) because the deformation region (18) is magnetically permeable, wherein the deformation region (18) is arranged between the primary circuit (24) and the secondary circuit (26) and forms a magnetically permeable coupling point (20) for the primary circuit (24) and the secondary circuit (26), such that a magnetic flux from the primary circuit (24) to the secondary circuit (26) is possible via the plastically deformed sheet (18). deformed sheet metal (16) is ensured.

Description

[0001] The invention relates to an energy transfer cooking appliance accessory, a method for manufacturing an energy transfer cooking appliance accessory, and a cooking appliance.

[0002] Professional and commercial kitchens use cooking appliances that have a cooking chamber in which food is cooked. Typically, heating elements and fans are used to create a homogeneous cooking environment to which the food is exposed.

[0003] Certain applications also require electrical power to be available within the cooking chamber itself, either to cook the food or to monitor the cooking process. One initial approach involves running a suitable cable into the cooking chamber to provide this power. However, this approach is problematic because it necessitates connectors within the cooking chamber to which removable cooking accessories, such as a contact heating plate, would need to be attached. These connectors would have to transmit high power levels, which would create further problems regarding electrical insulation, especially under the conditions prevailing within the cooking chamber.

[0004] Another problem is that, with an alternative cable routing, the oven wall must be thermally insulated to prevent both the oven's atmosphere from escaping and the temperature from rising too high in an adjacent electrical installation compartment housing the appliance's electronic components. However, thermal insulation is very complex, increasing the installation effort and, consequently, the manufacturing costs.

[0005] Therefore, the prior art provides for power transmission units in which electrical energy is transferred to the cooking chamber wirelessly. Resonant power transmission units, comprising a transmitter and a receiver, are typically used for this purpose. Both the transmitter and the receiver each have at least one free resonant circuit, which includes a corresponding transmitting and receiving coil, respectively.

[0006] Typically, a stainless steel wall separates the transmitter and receiver. This electrically conductive wall hinders efficient wireless power transmission, as high power can only be transmitted at high frequencies via resonant coupling. The frequencies commonly used for power transmission are above 10 kHz. Resonant circuits for lower frequencies would be unwieldy and large. The corresponding resonant frequencies of the respective coils are tuned to each other. Otherwise, poor efficiency results, making wireless power transmission impossible or at least severely limited. This is because electrical losses due to induced shielding currents increase quadratically with frequency, meaning that at typical transmission frequencies, most of the power remains in the wall.

[0007] Furthermore, non-resonant magnetic power transmission requires good magnetic coupling between the generating and load coils. In a transformer, this is achieved by placing both coils on a common, closed, high-permeability core. However, in a cooking appliance, this core is interrupted because the cooking chamber wall is not intended to be opened. The cooking chamber wall thus forms a gap at two points between the two halves of the core, which contains the non-magnetic material, namely the metal sheet of the cooking chamber wall. Such gaps significantly reduce the coupling between the coils. This increases losses, and larger coils are required to transmit the same power.

[0008] From DE 20 2009 000 990 U1, a device for mounting inductors for an induction cooktop is known. The device has a mounting frame made of a sheet steel with support elements made of a highly conductive material such as aluminium, which are intended to support and shield the inductors.

[0009] The JP 2008 - 110 168 A shows a steam cooking appliance comprising a plastic housing with a water reservoir in which a movable induction heating element for steam generation is arranged.

[0010] Furthermore, a method for applying an aluminum base to the bottom of a stainless steel pot is known from DE 32 32 480 A1.

[0011] DE 38 53 695 T2 shows an induction appliance for an oven.

[0012] Furthermore, a transformer-like power transmission unit is known from US 3 260 979 A.

[0013] The object of the invention is to provide a simple, wireless energy transmission system for a cooking appliance using simple and cost-effective means.

[0014] The object is achieved according to the invention by an energy transfer cooking appliance accessory comprising a plastically deformed sheet metal and a transformer-like power transfer unit having a primary circuit and a secondary circuit, wherein the plastically deformed sheet metal has a deformation area that exhibits a locally significantly increased magnetic permeability compared to the rest of the sheet metal in the non-plastically deformed area, so that the plastically deformed sheet metal enables a higher magnetic flux in the local deformation area, since the deformation area is magnetically permeable, wherein the deformation area is arranged between the primary circuit and the secondary circuit and forms a magnetically permeable coupling point for the primary circuit and the secondary circuit, so that a magnetic flux from the primary circuit to the secondary circuit via the plastically deformed sheet metal is ensured.

[0015] The basic idea of ​​the invention is to provide a non-resonant, inductive power transmission unit based on the transformer principle, in which a free-space path between the primary and secondary circuits is avoided. This is possible because the plastically deformed sheet metal has a deformation zone that exhibits a significantly increased local magnetic permeability compared to the rest of the sheet metal in the non-plastically deformed area. This ensures that the sheet metal allows for a higher magnetic flux in the local deformation zone, since the deformation zone is magnetically permeable. Furthermore, the sheet metal is formed entirely from the same material, as no additional or different material, such as one with a higher magnetic permeability, has been incorporated into the sheet metal and arranged between the primary and secondary circuits.The single-piece sheet metal has only been locally processed to create a local magnetically permeable coupling point.

[0016] Furthermore, due to the high permeability of the plastically deformed sheet metal in the deformation zone, less coil and iron core material is required in the primary and secondary circuits to achieve the desired efficiency of the power transmission unit. The deformation zone of the sheet metal is specifically designed to be localized, so that this local deformation zone forms the magnetically permeable coupling point for the primary and secondary circuits.

[0017] In general, the plastic deformation of the sheet metal is recognizable when cutting through the sheet metal due to the changed grain size in the deformation area, i.e., at a microscopic level.

[0018] One requirement is that the sheet metal be made of stainless steel. This could be the non-magnetic stainless steel 1.4301, which inherently has no magnetic conductivity or permeability. Therefore, a magnetic flux between the primary and secondary circuits is significantly reduced or even impossible in an area of ​​the stainless steel sheet that is not plastically deformed, thus severely limiting the efficiency of the wireless power transmission. With a non-plastically deformed stainless steel sheet, a path length of 40 cm, a core magnetic permeability of 2000, two 1 mm gaps, and a cooking chamber wall magnetic permeability of 1 would result in an effective magnetic permeability of 181, which is too low for efficient power transmission.

[0019] In particular, the sheet metal has a smooth surface. This improves the hygienic properties of the sheet, as its surface is easier to clean. Furthermore, this allows for better control of the magnetic flux through the sheet, since the saturation magnetization is not locally exceeded, as would be the case with an irregular surface. The smooth surface applies specifically to both opposite sides of the sheet.

[0020] According to another aspect, the sheet metal was pressed, specifically with a press die designed as a matrix. This resulted in local plastic cold forming of the sheet metal in the deformation area. Due to this plastic cold forming, only a slight reduction in thickness occurs in the deformed sheet metal in the deformation area. The stability of the sheet metal is therefore maintained.

[0021] The object is further achieved according to the invention by a method for manufacturing an energy transfer cooking appliance accessory of the aforementioned type, in which a sheet and a transformer-like power transfer unit with a primary circuit and a secondary circuit are provided, wherein the sheet is plastically deformed such that the plastically deformed sheet has a deformation area which has a locally significantly increased magnetic permeability compared to the rest of the sheet in the non-plastically deformed area, so that the plastically deformed sheet enables a higher magnetic flux in the local deformation area, since the deformation area is magnetically permeable, wherein the sheet forms a magnetically permeable coupling point for the primary circuit and the secondary circuit of the transformer-like power transfer unit.wherein the primary circuit is arranged on one side of the plastically deformed sheet and the secondary circuit on the opposite side of the plastically deformed sheet. The primary and the secondary circuits are each arranged at the magnetically permeable coupling point, which is formed by the local deformation area of ​​the sheet that exhibits a locally increased magnetic permeability.

[0022] Furthermore, the sheet metal can be pressed, particularly with a press die designed as a matrix. Pressing the sheet metal is a cost-effective process step for easily creating the local deformation area with increased magnetic permeability.

[0023] According to another aspect, the sheet metal is pressed at least twice. In the first pressing, it is pressed with a die designed as a press punch, specifically one that has a surface capable of high material deformation. For example, a die with a knurled surface can be used. The subsequent second pressing ensures that the sheet metal has the smoothest possible surface in the local deformation zone. This results in a defined surface and thus a controllable saturation magnetization due to the essentially uniform thickness of the sheet metal in the local deformation zone. Consequently, essentially identical magnetic flux paths are formed in the local deformation zone or at the magnetically permeable coupling point.

[0024] If more than two pressing operations are planned, the sheet metal is pressed with a die designed as a press punch in all but the last pressing operation. This ensures that the surface of the sheet metal is smooth and flat after forming.

[0025] If more than two pressing operations are planned, complementary press dies can be used, particularly in succession. The complementary press dies cause opposite deformations of the sheet metal, thereby achieving the desired high degree of material deformation quickly.

[0026] Furthermore, the sheet metal can be heated, in particular tempered, or heated and slowly cooled. This creates an additional ferritic phase, which increases the magnetic permeability in the local deformation zone of the plastically deformed sheet metal. Additionally, residual stresses in the deformed sheet metal, especially in the deformation zone, can be reduced due to the temperature increase. This is particularly effective through moderate temperature increases (tempering), which eliminate any remaining springback effect that may have arisen as a result of the forming process.

[0027] Another aspect involves plastically deforming the sheet metal across its entire thickness, creating a continuous, formed section. Accordingly, all available material within the local deformation zone is reshaped. This forming process differs from embossing the sheet metal surface in that embossing only compresses the material in a specific area of ​​the surface.

[0028] Furthermore, the object of the invention is achieved by a cooking appliance comprising a cooking chamber and a cooking chamber wall, wherein at least a part of the cooking chamber wall forms the plastically deformed sheet metal of the energy transfer cooking appliance accessory of the aforementioned type, such that this part of the cooking chamber wall forms a magnetically permeable coupling point for the primary circuit and the secondary circuit of the transformer-like power transfer unit. The plastically deformed sheet metal can accordingly be the cooking chamber wall, so that the part of the energy transfer cooking appliance accessory is already provided during the manufacture of the cooking appliance. Subsequently, only the transformer-like power transfer unit needs to be arranged on both sides of the cooking chamber wall to form the wireless energy transfer cooking appliance accessory. Accordingly, a cooking appliance with an energy transfer cooking appliance accessory of the aforementioned type can be easily realized.

[0029] In particular, a cooking appliance is thus provided which includes an energy transfer cooking appliance accessory of the aforementioned type.

[0030] Further advantages and features of the invention will become apparent from the following description and the drawing, to which reference is made. The single figure shows a schematic representation of a cooking appliance according to the invention with an energy transfer cooking appliance accessory according to the invention.

[0031] In Fig. Figure 1 is a cooking appliance 10 partially shown in a schematic way, since the cooking chamber 12 is only shown in part.

[0032] The cooking chamber 12 is, in the section shown, bounded among other things by a cooking chamber wall 14, which is formed by a sheet metal 16, in particular by a stainless steel sheet (material 1.4301).

[0033] The cooking chamber wall 14 or the sheet metal 16 was locally plastically deformed during manufacturing, resulting in a local deformation zone 18. The deformation zone 18 exhibits a higher magnetic permeability than the rest of the cooking chamber wall 14 or the sheet metal 16, even though the rest of the cooking chamber wall 14 and the deformation zone 18 are made of the same material.

[0034] This is because, due to the plastic deformation of the sheet 16 in the local deformation area 18, the grain structure in the material of the sheet 16 has changed compared to a flat sheet. Accordingly, the deformation area 18 forms a magnetically permeable coupling point 20, which allows a magnetic flux through the otherwise magnetically non-conductive cooking chamber wall 14.

[0035] The magnetic conductivity was thus achieved by a forming process of the cooking chamber wall 14 or the sheet metal 16, since no other material was used to form the magnetically permeable coupling point 20.

[0036] The cooking appliance 10 also includes a transformer-like power transmission unit 22, which is connected at the coupling point 20. The transformer-like power transmission unit 22 serves for wired or wireless power transmission from one side of the cooking chamber wall 14 to the other side of the cooking chamber wall 14, thus enabling, for example, wireless power transmission into the cooking chamber 12. A cable gland or similar is therefore not required.

[0037] The transformer-like power transmission unit 22 has a primary circuit 24 and a secondary circuit 26, wherein, in the illustrated embodiment, the primary circuit 24 is arranged outside the cooking chamber 12 and the secondary circuit 26 is arranged inside the cooking chamber 12. The primary and the secondary circuits 24, 26 each have a primary and secondary coil 28, 30 respectively, the number of turns of which can differ.

[0038] Furthermore, it is evident from the Fig.Figure 1 shows that the transformer-like power transmission unit 22 includes an attached heating area 32, which is, for example, assigned to a cooking tray 34, shown as a dashed line. Accordingly, the energy wirelessly transmitted to the cooking chamber 12 via the transformer-like power transmission unit 22 can be used to heat the cooking tray 34, thus enabling an electrically heated cooking surface to be arranged in the cooking chamber 12 without requiring an insulated cable penetration through a cooking chamber wall 14.

[0039] The transformer-like power transmission unit 22 and the deformation area 18 of the sheet metal 16 or the cooking chamber wall 14, i.e. a plastically deformed sheet metal section, together form an energy transmission cooking appliance accessory 36.

[0040] The energy transfer cooking appliance accessory 36 can also form a cooking accessory 38 together with the heating area 32 and / or the tray 34.

[0041] As an alternative to the cooking tray 34 with the heating area 32, another cooking accessory can also be provided which requires electrical power and can be coupled with the energy transfer cooking appliance accessory 36, for example a temperature sensor, in particular a core temperature probe.

[0042] In general, the power transmission unit 22 is designed in a transformer-like manner, since a free space, i.e., a magnetically non-conductive path, between the primary and secondary circuits 24, 26 is prevented. This is because the local deformation area 18 is magnetically permeable, particularly in a similar way to the ferrite or iron material that at least partially forms the primary or secondary circuit 24, 26.

[0043] The ferrite or iron material of the primary and secondary circuits 24, 26 thus forms together with the magnetically permeable deformation area 18 or the coupling point 20 formed thereby a multi-part core 40 of the transformer-like power transmission unit 22, as is usual in a transformer.

[0044] Gaps or magnetically non-permeable materials between the respective coils 28, 30 of the primary and secondary circuits 24, 26 are therefore avoided, which is why a transformer-like power transmission unit 22 is mentioned, which wirelessly transmits the energy from one side of the cooking chamber wall 14 to the other side of the cooking chamber wall 14, in particular into the cooking chamber 12.

[0045] This is a non-resonant power or energy transfer system, which is why coils 28 and 30 do not need to be tuned to each other with respect to their resonant frequencies. This significantly reduces the manufacturing effort.

[0046] The local deformation zone 18 can be produced in particular by a pressing process in which the sheet metal 16 is formed. This ensures that the material thickness of the sheet metal 16 changes only slightly in the local deformation zone 18.

[0047] Furthermore, it may be provided that the sheet 16 is subsequently thermally treated, for example by being subjected to a moderate temperature increase (tempering) in order to reduce stresses in the sheet 16 that have been introduced due to the deformation process.

[0048] Alternatively or additionally, the sheet 16 can be strongly heated and then slowly cooled in order to introduce an additional ferritic phase into the austenitic material, which results in an additional increase in the magnetic permeability of the sheet 16 in the local deformation area 18.

[0049] The sheet metal 16 is plastically deformed over its entire thickness, particularly in the deformation area 18, so that a continuously deformed sheet metal section is formed, which represents the local deformation area 18. Accordingly, the deformation process is not an embossing process in which the material is merely compressed in a specific area, particularly at the corresponding surface.

[0050] During the forming of sheet 16, the sheet is deformed in such a way that the resulting surface of sheet 16 is flat and smooth after the final forming step. A rough surface of sheet 16 in the deformation area 18 would result in a partially strong concentration of the magnetic field lines during energy transfer, which could locally exceed the saturation magnetization and negatively affect power transfer. Furthermore, such a surface is also more hygienic, as it is easier to clean.

[0051] In general, the sheet metal 16 can be pressed during forming, for example using a press punch designed as a matrix.

[0052] In particular, it is provided that the sheet 16 is pressed twice, whereby the sheet 16 is first pressed with a press die that has a surface which results in a high degree of material deformation. This allows the magnetic permeability of the sheet 16 in the local deformation area 18 to be greatly increased.

[0053] Due to the high degree of material deformation, the sheet 16 exhibits an uneven or rough surface in the deformation area 18, which is disadvantageous with regard to both cleaning and wireless energy transmission, as already described. Therefore, the sheet 16, pressed with such a press die, is pressed again to obtain the smoothest possible surface.

[0054] Accordingly, a wireless energy transmission is created using simple means, which is non-resonant and inductive, whereby the transmitted energy can be easily used by a cooking accessory.

Claims

[1] Energy transfer cooking appliance accessory (36) comprising a plastically deformed sheet (16) and a transformer-like power transfer unit (22) having a primary circuit (24) and a secondary circuit (26), wherein the plastically deformed sheet (16) has a deformation area (18) exhibiting a locally significantly increased magnetic permeability compared to the rest of the sheet (16) in the non-plastically deformed area, such that the plastically deformed sheet (16) allows a higher magnetic flux in the local deformation area (18) because the deformation area (18) is magnetically permeable, wherein the deformation area (18) is arranged between the primary circuit (24) and the secondary circuit (26) and forms a magnetically permeable coupling point (20) for the primary circuit (24) and the secondary circuit (26), such that a magnetic flux from the primary circuit (24) to the secondary circuit (26) is possible via the plastically deformed sheet metal (16) is ensured. [2] Cooking appliance accessories (36) according to claim 1, characterized by , that the sheet (16) is a stainless steel sheet. [3] Cooking appliance accessories (36) according to claim 1 or 2, characterized by , that the sheet (16) has a smooth surface. [4] Cooking appliance accessories (36) according to any one of the preceding claims, characterized by , that the sheet (16) has been pressed, in particular with a press die designed as a matrix. [5] A method for manufacturing an energy transfer cooking appliance accessory (36) according to one of the preceding claims, wherein a sheet (16) and a transformer-like power transfer unit (22) with a primary circuit (24) and a secondary circuit (26) are provided, wherein the sheet (16) is plastically deformed such that the plastically deformed sheet (16) has a deformation area (18) which has a locally significantly increased magnetic permeability compared to the rest of the sheet (16) in the non-plastically deformed area, so that the plastically deformed sheet (16) allows a higher magnetic flux in the local deformation area (18) because the deformation area (18) is magnetically permeable, wherein the deformation area (18) forms a magnetically permeable coupling point (20) for the primary circuit (24) and the secondary circuit (26) of the transformer-like power transfer unit (22),wherein the primary circuit (24) is arranged on one side of the plastically deformed sheet (16) and the secondary circuit (26) is arranged on the opposite side of the plastically deformed sheet (16). [6] Method according to claim 5, characterized by , that the sheet (16) is pressed, in particular with a press die designed as a matrix. [7] Method according to claim 5 or 6, characterized by that the sheet (16) is pressed at least twice, wherein the sheet (16) is pressed at least in the first pressing operation with a matrix designed as a press punch, in particular wherein the press punch has a surface which results in a high material deformation. [8] Method according to any one of claims 5 to 7, characterized by , that the sheet (16) is heated, in particular tempered or heated and then slowly cooled. [9] Method according to any one of claims 5 to 8, characterized by, that the sheet (16) is plastically deformed over its entire thickness, so that a continuously formed sheet section is formed. [10] Cooking appliance (10) with a cooking chamber (12) and a cooking chamber wall (14), wherein at least a part of the cooking chamber wall (14) forms the plastically deformed sheet metal (16) of the energy transfer cooking appliance accessory (36) according to one of claims 1 to 4, such that the part of the cooking chamber wall (14) forms a magnetically permeable coupling point (20) for the primary circuit (24) and the secondary circuit (26) of the transformer-like power transfer unit (22).

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