Source: http://www.google.com/patents/US4999467?dq=6,163,776
Timestamp: 2016-05-06 07:56:05
Document Index: 705374106

Matched Legal Cases: ['Application No. 58', 'Application No. 56', 'art 7', 'art 7', 'art 9', 'art 7']

Patent US4999467 - Low-frequency electromagnetic induction heater - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inPatentsDisclosed is a low-frequency electromagnetic induction heater which comprises at least six induction coils each having a circular configuration and positioned in a circular and symmetrical configuration. The coils form three sets of coils such that each set of coils receives electrical power in a different...http://www.google.com/patents/US4999467?utm_source=gb-gplus-sharePatent US4999467 - Low-frequency electromagnetic induction heaterAdvanced Patent SearchPublication numberUS4999467 APublication typeGrantApplication numberUS 07/469,064Publication dateMar 12, 1991Filing dateJan 23, 1990Priority dateJan 23, 1989Fee statusLapsedAlso published asCA2008232A1, CA2008232CPublication number07469064, 469064, US 4999467 A, US 4999467A, US-A-4999467, US4999467 A, US4999467AInventorsAtushi IguchiOriginal AssigneeNikko Corporation Ltd.Export CitationBiBTeX, EndNote, RefManPatent Citations (10), Referenced by (7), Classifications (15), Legal Events (7) External Links: USPTO, USPTO Assignment, EspacenetLow-frequency electromagnetic induction heater
US 4999467 AAbstract
Disclosed is a low-frequency electromagnetic induction heater which comprises at least six induction coils each having a circular configuration and positioned in a circular and symmetrical configuration. The coils form three sets of coils such that each set of coils receives electrical power in a different phase from a three- phase electrical power source, such as a three-phase alternating current power source. The coils are interconnected such that the current flows from a first coil to a second other coil substantially opposed to the first coil. In a preferred embodiment, the heater consists of six coils connected in a three-phase double delta connection. This invention provides for heating of the heating element with continuous attraction to the induction coils, a substantial increase of electromagnetic flux density, prevention of noise due to electromagnetic vibration of the heating element, and high thermal efficiency.
1. A low-frequency electromagnetic induction heater comprising at least six induction coils electrically connected in a three-phase double delta connection, wherein each coil has a circular configuration, said coils being arranged in a circular symmetrical configuration, and wherein said coils form three sets of coils such that each set of coils receives electrical power of a different phase from a three-phase low-frequency electrical power source, and wherein the coils are enclosed in a resinous mold.
2. A low-frequency electromagnetic induction heater as set forth in claim 1, which operates with the three-phase alternating current power source in a commercial frequency range.
3. A low-frequency electromagnetic induction heater as set forth in claim 1, further comprising a heating element of an iron plate or a metal vessel.
4. A low-frequency electromagnetic induction heater as set forth in claim 3, wherein the center of the iron plate or the metal vessel substantially coincides with the center of a generated magnetic flux.
5. A low-frequency electromagnetic induction heater as set forth in claim 3, wherein the heating element is an iron cooking plate for meat.
6. A low-frequency electromagnetic induction heater as set forth in claim 1, which is a steam generator.
7. A low-frequency electromagnetic induction heater as set forth in claim 1, which is a rice-cooker.
8. A low-frequency electromagnetic induction heater as set forth in claim 1, wherein a good magnetic conductor, which absorbs escaping magnetic flux, surrounds the at least six induction coils and is attached to a heating element.
Griddles for use in the restaurant business, such as where steaks and Japanese style tacos (Okonomiyaki) are served, commonly employ fuel gases as a heat source. These griddles for use in the restaurant business have thick iron cooking plates. Gas is burnt under these plates so as to heat up these plates, and materials to be cooked, such as meat, are placed on the surface of the plate and heated with the conduction heat coming through these plates.
Other methods for heating iron cooking plates are known. One method is where an iron cooking plate is heated with the use of a nichrome resistance wire heater. Another method is where an iron cooking plate is indirectly heated by an induction heat source as disclosed in Japanese Examined Patent Application No. 58-39525 and Japanese Unexamined Utility Model Application No. 56-86789.
Electrical resistance heater are preferred as a heat source in particular industrial production processes where heating by burning petroleum, coal and/or natural gas is not the preferable method for heating. An example is the process of combining an axle with a wheel and an inner bearing race of an axle with a bearing for rolling stock or an electric car. In these cases, a round metal plate with a central round hole must be combined with an axle. This is done by heating the round metal plate with a central round hole so that the central round hole is thermally expanded. Then the axle is inserted into the central round hole, and the plate is cooled down to give a tightly combined assembly. Electric heating is the most suitable method for heating in these types of cases.
The most frequently used method of heating in the restaurant business is gas burning, as discussed above, which results in the problem of management of combustion gas evolved. The combustion gas should not be exhausted towards the customers. And, in cases where the combustion gas is exhausted in a direction other than toward the customers, for example, beneath or to the side of the cooking plate, the efficiency of heating is considerably decreased. Therefore, the combustion gas is currently exhausted towards the cook. When fuel gas is used, an exhaust duct must be provided, and this is constructed above the cook's head. Therefore, the cook has to breathe in the combustion gas and oily smoke, and is exposed to high temperature and high humidity, leading to a terrible working environment.
Additionally, in known methods of indirect heating with an induction heat source there exists a critical and unavoidable problem. Electromagnetic vibration of the plate occurs, resulting in loud noises, and sometimes destruction of the cooking apparatus itself.
It is the another object of this invention to provide a low-frequency electromagnetic induction heater with high thermal efficiency and easy temperature control, which is effective for prevention of over-heating, and consequently, prevention of formation of burnt material on a food material such as meat.
It is yet another object of this invention to provide a low-frequency electromagnetic induction heater wherein the heating element is conveniently attached and detached, and yet still operates in a steady and safe manner.
It is yet another object of this invention to provide a low-frequency electromagnetic induction heater which can operate without magnetically attracting iron cooking tools, such as knives, spatulas and trowels, by which a noisy sound may be generated due to vibration of these tools on a heating element, and without giving an undesirable magnetic effect to a precision instrument such as a wrist watch, by preventing escape of a magnetic flux from above and outside of the heating element.
FIG. 11 and FIG. 12 show another embodiment in this invention, which is equipped with a good magnetic conductor to absorb escaping magnetic flux.
A special feature of the low-frequency electromagnetic induction heater of this invention is that it comprises at least six induction coils, wherein each coil has a circular configuration, the coils are positioned in a circular and symmetrical configuration, and wherein the coils form three sets of coils such that each set of coils receives electrical power in a different phase from a three-phase electrical power source, and wherein the coils are interconnected such that the current flows from a first coil to a second coil substantially opposed to the first coil. The employment of this specific electric connection among induction coils achieves:
(1) heating of a heating element with continuous attraction to induction coils at all times during operation,
The low-frequency electromagnetic induction heater of this invention provides a very convenient heater having easy temperature control, prevention of formation of burnt material on cooked materials such as meat, and prevention of generation and scattering of oily smoke. Because an iron plate itself is the heat source in the case when an iron plate is used as a heating element, the usual large temperature difference between the heat source and the heating element is avoided in this invention.
FIG. 1 shows a typical connection diagram of a three-phase double delta connection which is the most important part of this invention. Six induction coils numbered from A1 to A6 are placed in a substantially circular configuration. The neighboring two coils A1 and A2 have been connected with the U phase of three-phase electric power, and the next neighboring two coils A3 and A4 have been connected with the V phase of three-phase electric power, and in the same manner, the last neighboring two coils A5 and A6 have been connected with the W phase of three-phase electric power. Then, each coil is connected to another substantially opposed coil in the circular and symmetrical configuration of the coils, so that the current flows from one coil to the opposing coil.
Namely, the coils A1 and A4, the coils A2 and A5, and the coils A3 and A6, respectively, are connected to each other. With this specific electric connection among coils, a continuous force due to an electromagnetic force is generated between the induction coils and the heating element, for example an iron plate, and thus, they are continuously attracting each other. Therefore, even when a low-frequency alternating current electrical power source is employed, the heater does not produce noise due to electromagnetic vibration.
Point 0 in the FIG. 8 (A) indicates where no attractive forces is generated. FIG. 8 (B) shows current wave-form of the three-phase alternating current. The figure shows the time courses of each current wave-form of phases U, V, and W. The relationship between FIG. 8 (A) and FIG. 8 (B) will be explained in detail. The wave-form of attractive force in FIG. 8 (A) has been drawn on the same time scale as that of FIG. 8 (B) showing a current wave-form of the three-phase alternating current. The attractive force generated in this heater by the specific electric connection among induction coils is the result of synthesis of the attractive forces generated by each current phases, namely, both the waves in the minus part and that in the plus part generate the attractive forces.
FIG. 2 shows a principal mode of operation of this invention. The induction coil formed around the leg iron core 3 is positioned on the yoke iron 4. The figure depicts the case where an iron plate for an inner bearing race is used as a heating element. The lines of magnetic flux pass through the iron plate 1, and the eddy current is generated around these lines. The eddy current thus generated heats up the iron plate 1 from the central portion from the inside (FIG. 6). Even in the case where the iron plate has a hole in its central portion, the iron plate is heated from the periphery of the hole, because the magnetic flux passes through the metal periphery of the hole. More explanation about FIG. 6 will be presented in the Example.
FIG. 5 shows a cross sectional view along line A--A of the heater shown in FIG. 3. The induction coil formed around the leg iron core 3 is positioned on the yoke iron 4. The whole assembly is placed in a mold, then the mold is filled with molten resin to form a resinous mold having the coils and the irons inside. The reason why such resinous molding is performed is to protect the user from electrical shock and to maintain sight of the heater. Preferable molding resins are those having high thermal resistivities, for example, epoxy resins and silicone resins.
The iron plate 1, when employed as a heating element, may have any thickness as long as a magnetic flux can permeate through the plate. For example, the thickness ranges from 1 to 10 cm, but it is not restricted to this range. At least six of the induction coils 2 formed around the leg iron core 3 are placed under the iron plate 1. Although the number of the induction coils may be any number larger than six, for example, nine or twelve, six is preferable from the view point of achieving an easy electrical connection. The circular configuration of the six induction coils is preferable. However the configuration is not restricted to the above. Any configuration which allows the magnetic flux to pass through the iron plate 1 can be employed.
The heating element is placed closely to the induction coils 2 so that the magnetic flux can easily pass through the plate. A heat-resistant film such as a polyimide file or polyaromatic-amide film may be inserted as a buffer material between the iron plate 1 and the iron core 3, unless the film inhibits the permeation of the magnetic flux through the plate. The material of the iron core 3 or the yoke iron may be any material if it permits permeation of the magnetic flux. One preferable concrete example is a yoke iron of a coiled silicon steel plate. The thickness of the iron core or the iron yoke is such that the thickness maintains prevention of magnetic saturation. Preferably, the area of the cross section is sufficiently large so as to maintain a density of the magnetic flux below 20,000 gauss.
Next, in the case where prevention of escape of a magnetic flux from a heating element 1 to above and outside of the heating element 1 is necessary, a good magnetic conductor 14, which absorbs escaping magnetic flux, is attached around a conjunction of iron cores 3 and a heating element 1, as shown in FIG. 11 and FIG. 12. In the embodiment shown in FIG. 11 and FIG. 12, the good magnetic conductor 14 is fixed with bolts to the heating element 1, however, the method of fixation is not restricted to the above. A preferable good magnetic conductor 14 is one that has a ring like outer shape and is made of layers of silicon steel plates. The size of the good magnetic conductor is restricted to such sizes for which the thermal efficiency of the heating element 1 is not drastically decreased. An excessively large good magnetic conductor 14 decreases the thermal efficiency of the apparatus by reducing the density of the effective magnetic flux inside the heating element 1. For example, a preferable good magnetic conductor 14 is one that has a ring like outer shape of 400 mm in diameter, which is made of layers of silicon steel plates of 20 mm width and 15 mm thickness.
In the above configuration of the apparatus, the magnetic flux is generated inside the iron cores 3, which, individually, are surrounded by the induction coils 2, and passes through the heating element 1 wherein Joule heat is evolved, and finally flow to reach the opposing iron cores 3. Here, it should be noted that the iron cores 3 are made of a good magnetic conducting material, and that the heating element 1 is made of a less magnetic conducting material than that used in the iron cores 3. Therefore, an escape of the magnetic flux from the heating element 1 occurs to some extent. Hence, the present invention employs a good magnetic conductor, which absorbs escaping magnetic flux, on the conjunction of iron cores 3 and the heating element 1.
The temperature of the heating element can be easily controlled by controlling the electrical current. Because the electrical current in ampere units and the temperature of the heating element has a simple and constant relation, the temperature of an iron cooking plate or a metal vessel is easily controlled to a suitable temperature for individual cooking conditions. For example, in the case of cooking a beef steak, the temperature of the iron cooking plate is automatically controllable in the range from 180� to 200� C. with the accuracy of �1� C. Thus, cooking by intuition or perception is not necessary, and a veteran cook is not required. The merit of this heater comes from employing an iron cooking plate or a metal vessel itself as the heating element. This aspect is completely different in principle from the prior art in which the temperature difference between the heat source and the heating element always exists. Because formation of burnt material or a generation of an oily smoke can be prevented with an extremely high probability, a duct may be unnecessary. Clean cooking provides an excellent working environment. The present three-phase alternating current induction heater dose not make noise, and is useful as a very quiet cooking apparatus. In addition, even after usage for a long period of time, the present three-phase alternating current induction heater does not suffer deformation of the iron plate.
(1) employment of a three-phase alternating current power source, and,
(2) An excellent working environment can be provided by clean cooking;
(4) The present three-phase alternating current induction heater is free from the disadvantage of deformation of the iron plate after usage for a long period of time, because the iron cooking plate of the metal vessel itself is the heating element, and because the iron plate of the vessel is not necessarily heated to such a high temperature that may cause overheating.
Further, in this invention, a good magnetic conductor, which absorbs escaping magnetic flux, is attached around iron cores and on a heating element of a low-frequency electromagnetic induction heater, which realizes;
(1) prevention of escape of a magnetic flux from a heating element to above and outside of the heating element, and consequently,
(2) prevention of noisy sound generation due to vibration of iron cooking tools, such as knives, spatulas and trowels, on a heating element, or of producing an undesirable magnetic effect to a precision instrument such as a wrist watch.
An iron cooking plate having 50 mm thickness, 50 cm length and 100 cm width is placed on induction coils as shown in FIG. 1 to 5 and 7 and, an electromagnetic induction griddle is constructed. The dimensions of the whole resinous molding part 7 including the induction coils, shown in a ground plan FIG. 5 are, about 270 mm in outer diameter and about 100 mm in inner diameter for the central hole. Each of the six induction coils is about 45 mm in diameter, and each of the central holes inside the induction coils has a diameter of about 15 mm. The height of the whole assembly shown in a front view FIG. 7, is about 160 mm. The resin used for molding is an epoxy heat-resistant resin.
The three-phase alternating current power of 60 Hz, 200 V, and 25 A is supplied to the induction coils to provide a current flow. It can be estimated from the electric power supplied to the primary induction coils that the current inside the iron cooking plate is of 0.5 V and 10,000 A. The temperature of the iron cooking plate of this apparatus could be raised to 200� C. in 15 minutes. After that, a beefsteak was put on the iron plate whose temperature was controlled at 200� C., a constant temperature. The beef steak was finely roasted without the formation of burnt material or generation of oily smoke. It was recognized that this cooking apparatus does not sound noisy and thus is quiet.
An inner bearing race for vehicles shown in FIG. 6, having an other diameter of 290 mm, an inner diameter of 130 mm and a thickness of 35 mm, and made of iron, was placed on the induction coils instead of the iron plate 1 in the FIG. 7. The temperature of the inner bearing race was raised from 25� C. to 100� C. By supplying a three-phase alternating current power of 200 V and 14 A to the apparatus, the temperature at the periphery of the central hole P1 was raised to 100� C. after 160 seconds as shown in FIG. 9. After 160 seconds the temperature curve became flat, which was caused by the action of the thermistor, by cutting the electrical connection to the electrical power source. The temperature at the middle part, P2, and at the periphery of the outer side of the inner-race, P3, reach 100� C. after about 200 seconds. The reason why the temperature at the periphery of the central hole, P1, is higher than the temperature at the middle part, P2, or at the periphery of the outer side of the inner-race, P3, is considered to be due to the density of the magnetic flux being higher in the central part than in the other parts. The thermal expansion coefficient for iron is α=1.2�10-5 K-1. Thus, the temperature difference of 75� C. makes the iron expansion of 0.117 mm. Consequently, an axle could be inserted into the thermally expanded race to yield a tightly combined assembly.
In the case where the above operation is performed by induction heating with a transformer as in the prior art, the operation takes more than 30 minutes. Therefore, it can be seen that this heating apparatus could perform the same job as the transformer in the prior art, in only about one tenth of the time required by the transformer.
FIG. 10 shows an example of a rice-cooker according to this invention. The rice-cooker comprises a pot 10 wherein the rice is boiled in the upper part, and a resinous molding part 7 including induction coils and a heating element 1 (an iron plate) in the lower part. The pot 10 has heat-pipes 8 at the inside of its side-wall part 9. In this example, the linear heat-pipes were set up with a standing configuration. Commercially available heat-pipes may be employed. The heat-pipes have the effect of enlarging the heating surface area so that the rice-cooker can provide heat from the side-wall.
The rice-cooker described is a type of a pressure cooker, so that it has a lid 11. The rice-cooker has props 12 and fulcrums 13 so that the cooked rice can be easily removed from the pot by rotating the pot. The structure of the resinous molding part 7 is shown in FIG. 1 to 5 and 7. The entire iron plate 1 serves as a heating plate, and therefore the heating surface is very large. Because of the large heating surface, the temperature of the heating element can be set within 30� C. higher than the cooking temperature of 100� to 110� C. without burning the materials inside.
In this example, the effect of a good magnetic conductor for decreasing the density of escaping magnetic flux will be explained by the data measured with a Gauss counter.
An iron cooking plate having 50 mm thickness, 50 cm length and 100 cm width is placed on induction coils as shown in FIG. 1 to 5, 11 and 12 and, an electromagnetic induction griddle is constructed. The three-phase alternating current power of 60 Hz, 200 V, and 25 A is supplied to the induction coils to allow current flow. It can be estimated from the electric power supplied to the primary induction coils that the current inside the iron cooking plate is of 0.5 V and 10,000 A. The temperature of the iron cooking plate of this apparatus could be raised to 185� C. during 15 minutes. After that, a beef steak was roasted on the iron plate at constant temperature of 185� C. The beef steak was finely roasted without a formation of burnt material or generation of an oily smoke. It has been recognized that this cooking apparatus does not sound noisy and, thus, is quiet.
In the case where a silicon steel ring of 400 mm in diameter, made of layers of silicon steel plates of 20 mm width and 15 mm thickness, is used as a good magnetic conductor 14, and where the three-phase alternating current power of 60 Hz, 200 V, and 25 A is supplied to the induction coils to heat up the iron cooking plate 1, the density of escaping magnetic flux has been measured and found to be in the range from 3 to 5 gauss by the use of Gauss counter.
Contrary to the above, in the case where a good magnetic conductor 14 is not used, the density of the escaping magnetic flux has been measured and found to be in the range from 180 to 200 gauss by the use of Gauss counter.
Patent CitationsCited PatentFiling datePublication dateApplicantTitleUS3906181 *Jun 22, 1973Sep 16, 1975Mitsubishi Electric CorpInduction heating apparatus for minimizing vibration and noiseUS3980858 *Aug 22, 1974Sep 14, 1976Mitsubishi Denki Kabushiki KaishaExciter for induction heating apparatusUS4029926 *Oct 29, 1974Jun 14, 1977Roper CorporationWork coil for use in an induction cooking applianceUS4348571 *Mar 18, 1981Sep 7, 1982General Electric CompanyFlux shaping arrangement for induction surface unitUS4647744 *Jul 10, 1985Mar 3, 1987Tokuden Co., Ltd.Rotating heating roller of the type having a three phase circumferentially laminated leg coreUS4675487 *Oct 2, 1984Jun 23, 1987Valmet OyApparatus and method for electromagnetic heating of a rollUS4792652 *Feb 4, 1987Dec 20, 1988Electricite De France - Service NationalElectric induction cooking appliance with reduced harmonic emissionUS4874916 *Nov 30, 1987Oct 17, 1989Guthrie Canadian Investments LimitedInduction heating and melting systems having improved induction coilsJPS5686789A * Title not availableJPS5839525A * Title not available* Cited by examinerReferenced byCiting PatentFiling datePublication dateApplicantTitleUS5237144 *Jun 17, 1991Aug 17, 1993Nikko Co., Ltd.Electromagnetic induction heaterUS5347107 *Aug 5, 1993Sep 13, 1994Nikko Corporation Ltd.Low frequency electromagnetic induction heater with magnetic flux diffusing membersUS5401939 *May 27, 1994Mar 28, 1995Hidec Corporation Ltd.Electromagnetic induction heater with magnetic flux diffusing membersUS20090020526 *Dec 27, 2006Jan 22, 2009Fagorbrandt SasInduction device comprising multiple individual coils for induction heating platesDE19814949C2 *Apr 3, 1998Apr 18, 2002Aeg Hausgeraete GmbhGareinrichtung mit Induktionsbeheizung und WiderstandsbeheizungEP0585629A1 *Aug 2, 1993Mar 9, 1994Hidec Corporation Ltd.Electromagnetic induction heaterWO2000035248A1 *Nov 26, 1999Jun 15, 2000Linlan Induction AbDevice for induction heating and method for controlling the same* Cited by examinerClassifications U.S. Classification219/624, 219/671, 219/674, 219/669International ClassificationH05B6/12, H05B6/02, H05B6/44, H05B6/36Cooperative ClassificationH05B6/1272, Y02B40/126, H05B6/1254, H05B6/105European ClassificationH05B6/10S, H05B6/12A4A, H05B6/12A4CLegal EventsDateCodeEventDescriptionJan 23, 1990ASAssignmentOwner name: NIKKO CORPORATION LTD., JAPANFree format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:IGUCHI, ATUSHI;REEL/FRAME:005225/0511Effective date: 19900113Jun 15, 1993CCCertificate of correctionJun 30, 1994FPAYFee paymentYear of fee payment: 4Sep 15, 1997ASAssignmentOwner name: HIDEC CORPORATION LTD., JAPANFree format text: MERGER AND CHANGE OF NAME;ASSIGNORS:NIKKO CORPORATION LTD.;SENKO DENKI CORPORATION LTD.;REEL/FRAME:008715/0498Effective date: 19930710Oct 6, 1998REMIMaintenance fee reminder mailedMar 14, 1999LAPSLapse for failure to pay maintenance feesMay 25, 1999FPExpired due to failure to pay maintenance feeEffective date: 19990312RotateOriginal ImageGoogle Home - Sitemap - USPTO Bulk Downloads - Privacy Policy - Terms of Service - About Google Patents - Send FeedbackData provided by IFI CLAIMS Patent Services