Electric heating – Inductive heating – With heat exchange
Reexamination Certificate
1999-10-14
2001-10-16
Leung, Philip H. (Department: 3742)
Electric heating
Inductive heating
With heat exchange
C219S624000, C219S662000, C219S647000, C099SDIG014
Reexamination Certificate
active
06303912
ABSTRACT:
The invention relates to an induction heating appliance for heating kitchen utensils and the like.
Gas burners which may be put on any heat tolerant surface are well known as are electric cookplates which are available, not only when disposed directly in a cooktop but also singly, encased in a small cylindrical or boxlike container, either with controls on the front or simply switched on and off on the wall or by pulling the plug.
Induction heating elements are well known in the form of a component in a cooktop. They normally consist of a coil in a suitable fixture and optionally a set of ferrite rods disposed on the lower side. The connections to the coil are normally loose wires. In similarity with a motor for e.g. a dishwasher such a component is raw and unfit for immediate use by a consumer—it has to be installed properly first. In this way, the consumer is protected from direct access to parts which carry high voltages or have a high temperature.
With the increasing use of induction heating for the preparation of food there is a growing need for an induction heating element which takes the form of a kitchen appliance so that in can be moved around or placed in a closet when not in use. There is, however, presently no free-standing unit available, and the reason may be that the power convertor from mains voltage to ELF (i.e. 20 kHz-100 kHz) may be a bulky piece of apparatus which it is easier to accomodate inside a hob than inside a free-standing unit.
According to the invention there is provided an induction heating apparatus which not only is free-standing as a kitchen appliance but which also avoids the complex and bulky enclosure known from free-standing electric hotplates. This is obtained in that the coil of the appliance is disposed inside a dishshaped core structure, and that a heat tolerant electricaly insulating protective filler is cast around the coil, essentially filling all voids within the dish-shaped core structure. Thereby the core and coil constitute one solid and integrated structure. Such a unit is perfectly safe from a consumer viewpoint in that it provides no access to hot surfaces or dangerous voltages. This also means that such a unit may be built into any relevant cooktop without the need for review or approval by consumer protection authorities. Typically the core structure can be manufactured in a material such as densit (Trade Mark Aalborg Portland) with ferromagnetic particles or in an artificial resin having such particles. Similarly, the electrically protective filler can be made of densit, or alternatively in an artificial resin loaded with particles which contribute to heat conduction without providing electrical conductivity.
In an advantageous embodiment, a solid-state power converter is integrated into the coil and core structure by casting in the heat tolerant protective filler, having heat radiating fins facing downwards, the leads connecting the power converter to the mains being terminated in a mains socket of the appliance type. In this manner there is obtained a completely self-contained unit which a functionality which is similar to that of an electric hotplate. Similarly, the coil and core structure may be used to energize other kitchen utensils whereby the inductive energy is tapped and converted to a drive voltage for the kitchen appliance.
In a further advantageous embodiment the connections to the coil terminate in a plug which is fitted to the coil and core structure. In this manner no leads are left dangling.
In a use of the preceding embodiment, the terminating plug is supplied with ELF via a coaxial connection to a remote power supply converter. This provides for an installation where all protective circuitry, etc. is fitted inside the power supply converter, so that all that links the induction heating unit to said power supply unit is a coaxial cable fitted with suitable plugs.
In a further advantageous embodiment, the power supply converter is designed to provide ELF energy to a predetermined number of induction heating heating units via plugs and coaxial cables. This means that the house wiring system may provide not only wires carrying ordinary mains electricity, telephone wires and television signals, but similarly ELF power for particular outlets for use with induction heating units.
In a further advantageous embodiment, the controls for each individual induction heating unit are placed in the units themselves and communicate with the central power supply converter by means of signals carried simultaneously on the coaxial wire system. In this manner, the only connection between the individual induction heating units occurs via the coaxial cable.
In a further advantageous embodiment, the central power supply converter comprises means for determining the load condition for each individual induction heating unit and means for reducing or removing power from the unit in case the load condition indicates that the generated inductive field has a large stray field component. In this manner, the inductive heating units are intrinsically safe from incorrect use.
REFERENCES:
patent: 2415853 (1947-02-01), Shaw
patent: 3740513 (1973-06-01), Peters, Jr. et al.
patent: 4129767 (1978-12-01), Amagami et al.
patent: 4456807 (1984-06-01), Ogino et al.
patent: 4910372 (1990-03-01), Vukich
patent: 5580594 (1996-12-01), Matsumoto
patent: 1-189888 (1989-07-01), None
patent: 2-162680 (1990-06-01), None
patent: WO 94/05137 (1994-03-01), None
Aktiebolaget Electrolux
Leung Philip H.
Pearne & Gordon LLP
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