EP0743805A1

EP0743805A1 - Shielding sheet for induction heating device

Info

Publication number: EP0743805A1
Application number: EP95500077A
Authority: EP
Inventors: Jesus Balay S.A. Ferrer Salillas; Jose Andres Balay S.A. Garcia Martinez
Original assignee: Balay SA
Current assignee: BSH Balay SA
Priority date: 1995-05-19
Filing date: 1995-05-19
Publication date: 1996-11-20

Abstract

THE SHIELDING SHEET FOR INDUCTION HEATING DEVICE, to be used for the cooking of food, is located on the ceramic glass in contact with the inductor element, and is distinguished because on the inductor element (7) there is a shielding sheet (1), with a thickness, material and form that allow the discharge of the capacitive coupling of the inductor element and the recipient, and do no interfere in the magnetic field; being formed by a central body (8) with the shape of an open circular corona, provided with a pair of external radial prolongations (9) opposite one another, joined to their corresponding concentric branches (10), defined according to an angle lightly lower than 180 degrees, one of those branches (10) having an external arm (3) which is bent on the lateral surface of the base support for its fastening through the corresponding bolt (5) and joint to ground, in such a way that the loops forming the shielding sheet (1) remain all open in order to avoid the induced currents.

Description

PURPOSE OF THE INVENTION

The following invention, as stated in the heading of this descriptive memory, refers to some improvements introduced in the object of the Invention Patent no. EP93.200.976 on: Device for induction heating, to be used for the cooking of food, in such a way that with the induction cooking plate, the calorific energy is generated in the same recipient of ferromagnetic material, located on the ceramic glass, under which remains the coil generating the induced currents.
The improvements refer to the incorporation of an shielding sheet, located on the upper side of the inductor coil under the ceramic glass, avoiding the electrostatic load of the recipient, which is generated as a consequence of the capacitive coupling existing between the inductor element and the ferromagnetic recipient.

BACKGROUND OF THE INVENTION

In the section referring to "background of the invention" of the main patent no. EP93.200.976, there is a reference to the conventional means used for the cooking of food, based in the generation of heat by thermal conductivity, being in that case necessary the presence of calorific flame or source.
In this case, one of the greatest disadvantages is the cleaning of the surface on which you cook because, due to the high temperatures, when there is an overflow of the contents of the recipient, it sticks and incrusts to the plate making its cleaning more difficult.
On the other hand, in the induction cooking, the ferromagnetic recipient is loaded electrostatically as a consequence of the capacitive coupling existing between the inductor element (coil) and the recipient ferromagnetic, in such a way that when the user touches the recipient, there may be a small discharge that, though innocuous, may be annoying for the user.

DESCRIPTION OF THE INVENTION

The improvements described in this memory are based on the incorporation of an shielding sheet to the inductor element used for the cooking of food, in order to avoid that the ferromagnetic recipient is loaded electrostatically, and may cause a small discharge whenever it is touched by the user.
The shielding sheet, located on the inductor coil, due to its typical form, thickness and material, is transparent to the magnetic field, and its shape is defined by a number of curve sections, like open loops, thus avoiding the closing of the generated currents.
The shielding sheet ends in an arm that allows its adaptation to the different diameters of the coils, and its bending on the lateral surface of the coil support, for its fastening to it through the corresponding bolt. Besides, the fastening of the sheet can be carried out with the help of some adhesive, though it is not necessary since its shape allows the fixing in the transportation, and it is perfectly located in its installation by having the ceramic glass on it.
As stated previously, in the Main Patent no. EP93.200.976, it is requested a device for induction heating, based on a support with some slots on its upper side, where it is adjusted the coil of stiff wire with a diameter between 1 and 1,3 mm. preferably, being the stiff wire fixed in different points to allow its fastening to the support, in such a way that under the coil defined there are four orthogonal ferrites, two by two.
Also it is requested in this dossier some improvements based on the replacement of the stiff wire by a rolled iron plate of a thickness between 0,25 and 0,45 mm. preferably, and a height between 5 and 10 mm. preferably, being in a vertical position on the upper side of a base support through a micron sheet, leaving the turns of the coil as desired.
In this way, the shielding sheet is on that coil fixed to the base support and joined to ground, adapting its best shape to the power circuit, that is, the voltage and the intensity, and so the sheet is defined by a central passage with the shape of an open circular corona, and with some prolongations opposite one another in radial position, those prolongations having both some branches concentric to the open central section, defined according to an angle slightly lower than 180 degrees, with its sides closely finished, in such a way that one of them has a radial prolongation, forming the arm through which it is joined to the base support and connected to ground.
In order to complete the description that follows, and with the purpose of helping to a better understanding of its features, this descriptive memory comes together with a plan, where the figures, in an illustrative and no restrictive way, shows the most significant details of the invention described in this memory.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1. Shows a general view of the inductor coil, where you can notice how the shielding sheet remains on the upper side, joined to ground, thus avoiding the recipient is loaded electrostatically.
Figure 2. Shows a sectioned view of the inductive element, where you can notice the rolled iron plate with its equidistant turns, with the shielding sheet on it, and above this the ceramic glass for its assembly.

DESCRIPTION OF A PREFERRED EMBODIMENT

Considering the above mentioned figures and following the numbering adopted, we can see how the shielding sheet 1 is located on the rolled iron plate 2, being its external arm 3 bent on the side surface of the base support 4 and fastened by the corresponding screw 5.
The arm 3 has some slots 6 that define a number of sections allowing their bending and adaptation to the coils 7 of different diameters, so that the shielding sheet 1 is perfectly centered, regardless of the diameter of the coil.
The shielding sheet 1 is adapted, due to its shape, to the power circuit, that is, to the voltage and the intensity, being defined by a central section 8, with the shape of an open circular corona, having that central section 8 a pair of external radial prolongations 9 opposite one another, to which are joined their corresponding concentric branches 10 with the central section 8, with their lateral sides located next to each other, being defined these curve branches according to an angle slightly lower than 180 degrees, and having one of those branches 10 the arm 3 as a prolongation of section 9, in such a way that all loops remain open in order to avoid the closing of the induced currents that are generated in the various curve sections.
By locating the shielding sheet 1 between the inductor element and the ferromagnetic recipient we avoid that it is loaded electrostatically since, as it is known, a capacitive coupling between the inductive element and the recipient exists, which makes the recipient be loaded electrostatically.
If the recipient is loaded electrostatically, as it happens without the presence of the shielding sheet 1, whenever the user is cooking and touches the recipient, there may be a small discharge that, though innocuous, may be annoying.
The shielding sheet 1 is made of stainless steel and has a minimum thickness, being transparent to the magnetic field, and given that it has no closed loops, no induced currents are created, thus reducing the capacitive coupling and avoiding the electrostatic load of the recipient.
To sum up, in the induction cooking, with the incorporation of the shielding sheet 1 on the inductor element 7, we avoid that the ferromagnetic element used for the cooking of food is loaded electrostatically and its discharge takes place whenever the user touches it, with the disturbances it means.
Therefore, the incorporation of the shielding sheet 1 increases the protection of the device for induction cooking, keeping its total performance and with no additional work, both in its fastening and its assembly by the operator installing that device.

Claims

SHIELDING SHEET. IMPROVEMENT ON THE PATENT EP93.200.976 BY INDUCTION HEATING DEVICE, to be used for the cooking of food, in such a way that the calorific energy is generated in the same ferromagnetic recipient, being located on the ceramic glass in connection with the inductor element, mainly distinguished because on the inductor element (7) there is an shielding sheet (1), with a thickness, material and form that allow the discharge of the capacitive coupling existing between the inductor element and the recipient, and do not interfere in the magnetic field, being formed by a central body (8) with the shape of an open circular corona, provided with a pair of external radial prolongations (9) opposite one another, to which are joined their corresponding concentric branches (10) with the central body (8), and defined according to an angle slightly lower than 180 degrees each one, in such a way that one of those branches (10) has an external arm (3) that is bent on the lateral surface of the base support for its fastening through the corresponding screw (5) and joint to ground, having foreseeing that the loops forming the shielding sheet (1) remain all open in order to avoid the closing of the induced currents circulating around, with the special feature that the arm (3) has some slots (6) that allow its adaptation to the different diameters of the coil, so that the shielding sheet (1) is perfectly centered, regardless of the diameter of the coil.