초록 ▼

In an electromagnetic induction heating apparatus, a cooking vessel made of a nonmagnetic metal, which has conventionally been incapable of magnetic inducting heating, is provided adjacent a heating coil which applies an alternating field with a high-frequency of at least 50 kHz. An inverter circuit

In an electromagnetic induction heating apparatus, a cooking vessel made of a nonmagnetic metal, which has conventionally been incapable of magnetic inducting heating, is provided adjacent a heating coil which applies an alternating field with a high-frequency of at least 50 kHz. An inverter circuit for supplying the heating coil with a high-frequency current operates in response to an output signal from a detector which automatically detects the magnetic characteristics of the metallic material of the cooking vessel. As the high-frequency magnetic field is applied, a skin effect is produced within the metallic material of the vessel, so that the impedance for the magnetic field of the vessel is substantially fixed without regard to the wall thickness of the vessel.

대표청구항 ▼

1. In a cooking apparatus for the induction heating of cooking utensils or vessels, comprised of solely nonmagnetic metal of at least a predetermined thickness, so as to cook food contained therein, said cooking apparatus comprising: plate means for stably supporting one of said nonmagnetic cooki

1. In a cooking apparatus for the induction heating of cooking utensils or vessels, comprised of solely nonmagnetic metal of at least a predetermined thickness, so as to cook food contained therein, said cooking apparatus comprising: plate means for stably supporting one of said nonmagnetic cooking vessels; and magnetic heating means, positioned under said plate means, for directly applying to said one vessel an alternating magnetic field with a frequency higher than 50 kHz to produce a skin effect inside said nonmagnetic-metal of said one vessel to inductively heat said one vessel, which skin effect causes the impedance for the magnetic field of said vessel to be substantially constant without regard to the thickness of said vessel, said magnetic heating means comprising a plurality of coil means stacked together for decreasing the primary impedance of said magnetic heating means while increasing the impedance of said one vessel toward that of a ferromagnetic cooking vessel, thereby improving the heating efficiency of said cooking apparatus while inductively heating said nonmagnetic-metal vessel. 2. An apparatus according to claim 1, wherein said predetermined thickness substantially corresponds to 0.5 mm, and said alternating magnetic field frequency is higher than 100 kHz. 3. An apparatus according to claim 2, wherein said magnetic heating means comprises inverter means for producing a high-frequency current of a frequency the same as said magnetic field frequency, said inverter means including semiconductor switching elements. 4. An apparatus according to claim 3, wherein each of said coil means comprises: a wire body spirally wound within a diameter and defining a spiral gap space, said body being formed of a plurality of conductive wires insulated from one another; and an electrical insulative wire wound spirally in said spiral gap space of said wire body so as to fill said spiral gap space and thereby enlarge the diameter of said conductive wire body to prevent partial concentration of said high-frequency magnetic field on said nonmagnetic cooking vessel, thereby improving uniformity of the application of said magnetic field to said vessel. 5. An apparatus according to claim 4, wherein said electrical insulative wire has lateral faces in contact with said conductive wire body, said lateral faces having a plurality of recesses formed therein to thereby improve the air-ventilating efficiency of said conductive wire body. 6. A cooking apparatus for the induction heating of food contained in a metallic cooking vessel made of a ferromagnetic metallic material or a nonmagnetic metallic material, said cooking apparatus comprising: plate means for stably supporting one of the ferromagnetic and nonmagnetic cooking vessels; (b) detector means for detecting whether said one supported vessel is ferromagnetic or nonmagnetic and for outputting signals indicative thereof; and (c) magnetic heating means, positioned under said plate means and responsive to said output signals of said detector means, for generating a first alternating magnetic field with a frequency lower than 50 kHz for application to a detected ferromagnetic vessel, and for generating a second alternating magnetic field with a frequency higher than at least 100 kHz for directly applying said second magnetic field to a detected nonmagnetic cooking vessel to produce a skin effect inside the nonmagnetic material constituting said nonmagnetic vessel, thereby making the impedance for the magnetic field of said nonmagnetic vessel substantially constant without regard to its thickness, wherein said magnetic heating means includes a plurality of coil means, stacked together and operative to emanate said generated magnetic fields, for causing the primary impedance of said magnetic heating means during application of said second magnetic field to said nonmagnetic vessel to be decreased while causing the impedance of said nonmagnetic vessel to increase so as to approach that of the ferromagnetic cooking vessel, thereby improving the heating efficiency of said cooking apparatus while heating said nonmagnetic vessel. 7. The apparatus according to claim 6, wherein when said supported vessel is made of a material from among a group of nonmagnetic metals including aluminum, said magnetic heating means applies said second alternating field to said supported vessel and produces a skin effect within the nonmagnetic metal so that the magnetic flux of said second alternating field concentrates on an internal region of said nonmagnetic metal at a given depth from the surface thereof, thereby substantially fixing the impedance for said magnetic field of said supported vessel without regard to the thickness of said supported vessel. 8. The apparatus according to claim 7, wherein said magnetic heating means generates said second alternating field so that said alternating field has a frequency of more than 100 kHz. 9. The apparatus according to claim 7, wherein said magnetic heating means comprises: inverter means, connected to said detector means, for selectively generating a first high-frequency current and a second high-frequency current with a frequency higher than that of said first high-frequency current in response to said output signal from said detector means; and wherein said plurality of coil means are operatively connected to said inverter means and selectively receive said first and second high-frequency currents to selectively generate said first and second alternating magnetic fields and thereby apply said fields uniformly to at least a bottom portion of said supported vessel. 10. The apparatus according to claim 9, wherein said plurality of coil means includes: a first coil having a first number of turns and receiving said first high-frequency current; and a second coil having a second number of turns greater than said first number of turns and receiving said second high-frequency current alternately with respect to said first coil. 11. The apparatus according to claim 10, wherein said second coil includes: a conductive wire wound spirally to define a spiral gap space therebetween; and an electrical insulative wire wound spirally in the spiral gap space of said conductive wire so as to fill said spiral gap space, said insulative wire having lateral faces in contact with said conductive wire and a plurality of recesses formed in said lateral faces, thereby allowing for ventilation to accelerate air cooling of said conductive wire. 12. The apparatus according to claim 9, wherein said plurality of coil means includes: a plurality of coils each having a predetermined number of turns; and coil connection changing means for changing the connections between said coils, thereby selectively changing the gross number of turns of said coils between first and second number of turns corresponding to said first and second high-frequency currents, respectively.