EP2452541B1

EP2452541B1 - Induction oven

Info

Publication number: EP2452541B1
Application number: EP10711260.9A
Authority: EP
Inventors: Mark Baker; Denver Hewlett; Paul Taylor; Stuart Oxborough
Original assignee: Glen Dimplex Home Appliances Ltd
Current assignee: Glen Dimplex Home Appliances Ltd
Priority date: 2009-07-09
Filing date: 2010-03-25
Publication date: 2014-09-17
Anticipated expiration: 2030-03-25
Also published as: EP2452541A1; GB0911932D0; WO2011004168A1

Description

The present invention relates to an induction oven and in particular although not exclusively, to an oven in which an induction unit is capable of generating a sustained electromagnetic field within the oven cavity.
A variety of different types of oven find widespread use in both domestic and commercial kitchens. Such ovens include conventional heating element ovens that may use a fan to assist with thermal regulation. These convection ovens are generally regarded as alternatives to the more traditional gas ovens in which a gas fuelled flame provides the thermal driving force within the oven cavity.
However, the above types of oven have disadvantages including in particular the necessity for considerable amounts of insulation to surround the large oven cavity so as to i) attempt to isolate the high temperatures achieved within the oven from the immediate environment and ii) insulate the cavity to achieve high temperatures. Furthermore, these ovens are generally considered energy inefficient. This is largely due to heating of the entire oven cavity despite the need to heat only a relatively small region where the food is located. Also, these ovens generally take a reasonable amount of time to heat-up to the required temperature.
The microwave oven has emerged as an alternative to these more conventional ovens and is typically more energy efficient. This is due to the nature of the cooking mechanism which acts to heat fluids directly within the food via microwave radiation. However, microwave ovens, whilst being more energy efficient, require sophisticated shielding at the oven cavity so as to prevent external transmission of the harmful microwaves.
More recently, induction hobs have emerged as a possible alternative to existing hob types. Induction heating is a mechanism of heating an electrically conducting magnetic material. An induction unit is driven by a high frequency alternating current to generate an electromagnetic field in the region of the oven cavity. When a ferromagnetic cooking vessel is placed within the electromagnetic field, eddy currents are created in the vessel body which in turn generate heat to cook the food.
Furthermore, the concept of hob induction heating has been extended, in a primitive sense, to induction oven cooking. Such an induction oven is disclosed in GB 2325134 . The oven cavity is energised using a mantle of a ferromagnetic material positioned at a region of the cavity. According to the different embodiments, the ferromagnetic material may be positioned to surround the internal cavity or as pieces within it to create a non-uniform induction field that provide localised heating regions. Alternatively, removable ferromagnetic bodies may be disposed within the cavity to shape the field to the cooking vessel or the cooking vessel itself may comprise the pole pieces for attracting and receiving the field lines.
US 3,790,735 discloses an induction heating oven having an inner housing defining an internal oven cavity and an outer external housing spaced from the inner housing to create a cavity wall. According to one embodiment, induction units are positioned within the cavity wall to induce eddy currents within the internal housing which is formed from a magnetically susceptible metal material such as iron or stainless steel. Thermal shielding is positioned between the inner housing and the induction units to insulate the oven cavity in order to achieve the required cooking temperatures. Food positioned within the oven cavity is heated by the induction units indirectly via the eddy currents created within the oven cavity walls.
However, conventional induction ovens have a number of significant limitations. Typical induction units comprise a temperature restrictor which acts to regulate generation of the electromagnetic field so as to avoid overheating of the unit and surrounding components. This presents a practical problem when employed to generate elevated temperatures within the oven cavity. Additionally, for safety reasons, the maximum penetration depth of the electromagnetic field is restricted to avoid unintended induced heating in components such as cabling and other electric components in the region of the induction unit. This field depth restriction is problematic to induce effective high temperature heating within the oven cavity.
Additionally, induction ovens that utilise magnetically susceptible materials for the oven cavity walls are not capable of generating sufficiently high temperatures within the oven cavity to provide a full range of cooking temperatures required for roasting for example. Furthermore, the magnetic cavity walls are susceptible to damage, following prolonged use and typically require coating treatment on their inner facing surface so as to enable ease of cleaning. Moreover, considerable thermal insulation is required around the internal walls so as to sufficiently protect the various electronic components within the oven cavity walls from the very hot ferromagnetic walls.
Accordingly, the inventors provide an induction oven that is configured for the sustained generation of an electromagnetic field within the oven cavity region so as to provide temperatures within at least a region of the cavity of greater than 160°C. Typically, the present induction oven is configured to provide heating temperatures of between 60°C to 350°C according to specific modes of cooking. This may be achieved firstly by specifically configuring the induction unit to be 'desensitised' to the feedback temperature resultant from the heated cavity. Also, the inventors have optimised the relative position of the induction unit at the oven cavity so as to create an electromagnetic field effective to induce heating of a cooking vessel/object positioned at a convenient region with the cavity. In particular, the present induction oven comprises cavity walls formed from a non-ferromagnetic material so as to be effectively transparent to the electromagnetic field generated by the induction units and allow the field to project into the inner cavity without any appreciable loss in field strength.
According to a first aspect of the present invention there is provided an induction oven comprising: sidewalls, a top, a bottom and a door to define an internal cavity; an induction unit mounted external of the cavity and in close proximity to at least one of the sidewalls, the top and/or bottom of the cavity, the induction unit configured to create an electromagnetic field within the cavity; the induction unit mounted external of the cavity; the at least one of the side walls, top and/or bottom of the cavity positioned in close proximity to the induction unit comprises a material not susceptible to magnetic induction; characterised in that the induction unit comprises a temperature regulator and thermal shielding positioned about the temperature regulator and between the temperature regulator and the internal cavity; the oven further comprises cavity thermal shielding positioned externally around the oven cavity, the cavity thermal shielding being additional to the thermal shielding positioned about the temperature regulator; wherein the induction unit is mounted at a distance of less than 45 mm from the oven cavity;.
Preferably, a portion of at least one of the sidewalls, top and/or bottom of the cavity comprises an aluminium, glass, ceramic or glass-ceramic material, preferably in the form of a sheet or plate. In particular, the induction unit may be positioned immediately behind/adjacent the non-magnetic material at an external side of the cavity.
Preferably, at least one of the sidewalls, top and/or bottom comprises a hollow region, the induction unit being housed at least partially within the hollow region so as to be effectively recessed in the sidewalls, top and/or bottom of the oven. Optionally, the hollow region extends from the cavity through the sidewalls, top and/or bottom to an external side of the oven, the non-magnetic material being positioned at the cavity end of the hollow region. Preferably, the induction unit is positioned at least partially within the hollow region within the sidewalls, top and/or bottom between the internal cavity facing side of the hollow region and the external facing side of the oven.
Preferably, the oven further comprises control means electrically coupled to the induction unit to determine and regulate the temperature in the cavity by control of the electromagnetic field strength generated by the induction oven.
Optionally, the oven may further comprise a grill unit mounted within the cavity. Alternatively or in addition, the oven may further comprise a resistance heating element mounted at the region of the cavity. Optionally, the oven may further comprise a fan unit mounted at the cavity such that the oven is configured as a convention oven.
The oven of the present invention utilises an electrically conducting, magnetic material and in particular a ferromagnetic material positioned within the cavity as a means of radiating heat. In particular, a ferromagnetic cooking vessel or object (such as a griddle or hotplate) is preferred. The vessel is removable houseable within the oven cavity and when subjected to the electromagnetic field provides cooking temperatures of between 60°C to 350°C within regions of the cavity. Where the cooking vessel is a pot having a removable lid, induced cooking temperatures within the pot of 160°C to 350°C are achievable. Induced cooking temperatures within the oven cavity as a whole, external of the cooking vessel, may be in the range of 60°C to 160°C. The present induction oven is therefore configured to provide a multi-zone heating environment. Also, by enclosing discrete regions of the cavity, the different cooking zones may be configured to cook the food according to different mechanisms such as grilling, induction heating, slow cooking (using regulated temperatures typically below 100°C), frying, roasting, steaming and/or fan assisted heating element cooking.
Optionally, the cooking vessel comprises a removable insert comprising any one or a combination of the following group of: a roasting trivet comprising a solid base and a side lip extending from the base, the trivet configured to be removeably housed within the cooking pot; a steam trivet comprising a perforated base and a side lip extending from the base and configured to be removable housed within the cooking pot; wherein the solid and perforated base are configured to sit above an internal base of the pot.
According to a second aspect of the present invention there is provided a method of cooking using an induction oven having sidewalls, a top, a bottom and a door to define an internal cavity, the method comprising: generating an electromagnetic field using an induction unit mounted in close proximity to at least one of the sidewalls, top and/or bottom of the cavity and externally of the cavity; operating the induction unit to provide a sustained electromagnetic field directed within the cavity; wherein the induction unit is mounted external of the cavity; wherein the at least one of the side walls, top and/or bottom of the cavity positioned in close proximity to the induction unit comprises a material not susceptible to magnetic induction; characterise in that: the induction unit comprises a temperature regulator and thermal shielding positioned about the temperature regulator and between the temperature regulator and the internal cavity; the oven further comprises cavity thermal shielding positioned externally around the oven cavity, the cavity thermal shielding being additional to the thermal shielding positioned about the temperature regulator; wherein the induction unit is mounted at a distance of less than 45 mm from the oven cavity.
Within this specification, reference to a material not susceptible to magnetic induction includes materials that are not diamagnetic, paramagnetic or ferromagnetic. The material of the sidewalls, top, bottom or door of the oven cavity positioned adjacent to the induction unit does not therefore interfere with the electromagnetic field generated by the induction unit such that this field may act directly upon an object (cooking vessel) positioned within the cavity. The present invention therefore provides for the generation of high temperatures within regions of the oven by inducing eddy currents directly in the cooking vessels placed within the cavity and not by heating the walls of the oven cavity.
Preferably, an induction unit is located at the floor or base part of the oven and an aluminium, glass, ceramic and/or glass-ceramic plate is positioned directly above the induction unit so as to form the bottom surface of the oven cavity upon which a cooking vessel may be placed.
According to one aspect of the subject invention, the oven comprises specific thermal shielding/insulation around at least a portion of the induction unit so as to shield the induction unit from the heat generated within the oven cavity. Additionally, the oven comprises additional thermal insulation around the oven cavity being of the same or different material to that thermal shielding positioned around the induction unit. Therefore, in the region of the induction unit there may be at least two layers and/or types of thermal insulation between the oven cavity wall (glass, ceramic and/or glass-ceramic plate) and the induction unit.
A specific implementation of the present invention will now be described by way of example only and with reference to the accompanying drawings in which:

figure 1 is an exploded perspective view of the induction oven having an induction unit mounted at a base region of the oven according to a specific implementation of the present invention;
figure 2 is a front elevation view of the oven of figure 1 having a roasting pot seated on a base of the cavity within the oven of figure 1;
figure 3 illustrates a cross-sectional side elevation view through the oven of figure 2.

Referring to figure 1 the induction oven 115 comprises a cavity 100 formed internally within the oven body. Internal cavity 100 is defined by base surface 101, three sidewalls 102 and a door 124. A hollow region 105 extends through a base wall 304 between base surface 101 and an external facing side 120 of oven 115. A recessed border 107 surrounds hollow portion 105 and is formed on base surface 101. A glass-ceramic sheet 106 is accommodated within the recessed border 107 so as to sit flush with base surface 101. Suitable means are provided (not shown) to secure sheet 106 in position at surface 101. Sheet 106 therefore partially defines internal cavity 100 at the region of the cavity base 101. A thermal insulation material 305 is positioned around the base surface 101, three side walls 102 and door 124 so as to insulate the oven cavity and facilitate heating to high temperatures above 110°C.
Referring to figure 1 and 3, an induction unit 108 is mounted within hollow region 105 defined by sidewalls 104 extending between base surface 101 of cavity 100 and the external facing side 120 of oven 115. Induction unit 108 is secured in position via an outer mounting plate 109 and an inner mounting plate 123 which effectively closes the external facing end of hollow region 105.
Accordingly, induction unit 108 is mounted in close proximity to internal cavity 100 and immediately below the glass-ceramic sheet 106. Due to the electromagnetic field depth of the induction unit, the unit is mounted within a distance of 30 mm of the oven cavity such that the electromagnetic field generated in the cavity is sufficient to induce heating in a cooking vessel positioned within the cavity. By recessing the induction unit within the bottom wall of the oven the generated magnetic field penetrates into the oven cavity to a greater extent so as to enable the elevated and sustained cooking temperatures and to induce heating within a larger volume of the oven cavity.
According to the specific implementation, induction unit 108 comprises a temperature regulator (not shown). In addition to thermal insulation 305 surrounding the oven cavity, the oven comprises thermal shielding 306 positioned above the region of the induction unit 108. In particular, thermal shielding 306 is positioned between the induction unit 108 and the glass-ceramic sheet 106 and is configured to further thermally isolate the induction unit from the heat generated within the oven cavity 100. In particular, the thermal shielding 306 is positioned between the temperature regulator (not shown) and internal cavity 100 so as to thermally shield the temperature regulator (not shown).
According to further specific implementations, induction unit 108 may comprise a mechanically and/or electrically disabled temperature regulator (not shown). According to a further embodiment induction unit 108 may be devoid of a temperature regulator.
Oven 115 also comprises a conventional grill resistance heating element 202 and an oven resistance heating element 300 mounted within cavity 100. A fan unit 200 is also mounted at cavity 100 and assists with circulation and regulation of the cooking temperature within the cavity 100. Grill heating element 202 is configured to provide 'browning' of food within cavity 100. Oven 115 also comprises suitable shelving 201 and control means 118, 119 coupled to the induction unit 108, heating elements 202, 300 and fan unit 200 to allow a user to adjust the operating temperature within the cavity 100 and to select the cooking/heating mode. Accordingly, the present oven is configurable for use as an induction oven, a fan assisted resistance heating element based oven and/or a grill-oven combination.
Oven 115 is designed for use with a ferromagnetic cooking device such as a hotplate griddle or vessel 110. Vessel 110 comprises a base 121 and sidewalls 122 to define an internal cooking chamber 301. A lid 116 is removeably positioned at the upper rim of walls 122 to enclose the cooking chamber 301. A plurality of different vessel inserts are mountable within cooking chamber 301. A first insert 112, suitable for 'roasting' food comprises a base 113 and a side lip 114 outwardly extending from base 113. An alternative or additional insert 111 is designed for 'steaming' food and comprises a plurality of perforations 117 formed in base 113. Inserts 112, 111 are designed to be seated at a lower region of vessel 110 in close proximity to vessel base 121. Suitable spacers, optionally in the form of legs, may extend from the underside of each base 113 of inserts 112, 111 to provide means by which each insert 112, 111 may stand upon the internal facing surface of base 121 within cooking chamber 301. Inserts 112, 111 act to suspend food (placed upon each base section 113) away from the internal facing surface of vessel base 121. This prevents the food burning which would otherwise occur if placed in direct contact upon vessel base 121.
In use, with induction unit 108 energised, an induction field 302 is generated through glass-ceramic sheet 106 and into oven cavity 100. The depth of the induction field 302 is sufficient to extend into cavity 100 so as to capture at least a portion of vessel 110 and in particular vessel base 121 so as to induce eddy currents within the vessel body 110. The penetration depth of field 302 within cavity 100 is achieved by positioning induction unit 108 within oven base wall 304 between the external facing side 120 and internal facing side 101.
Induced heating of vessel 110 by induction field 302 in turn heats the cavity oven 100 and also the cooking chamber 301 within vessel 110. According to the specific implementation, the region within cavity 100, external of the vessel cooking chamber 301, may reach temperatures of 110°C to 160°C. Oven 115 is configured to generate temperatures of up to 350°C within the vessel cooking chamber 301. Accordingly, the temperature within cavity 100 surrounding vessel 110 is suitable for cooking foodstuffs that require modest temperatures whilst the elevated temperature (200°C to 350°C) within vessel 110 is suitable for roasting and other high temperature cooking techniques. As vessel 110 is heated by induction, the present oven is capable of achieving a cooking temperature of around 250°C in approximately two minutes. In contrast, a conventional resistance heating element oven would typically take 7 to 10 minutes to achieve this cooking temperature.

Experimental investigations have also established that the present induction oven provides a 50% or higher energy saving when compared to a conventional fanned oven as detailed in tables 1 and 2.

Table 1. Experimental results for roasting cooking

Oven Used	Conventional Fanned Oven	Induction Oven
Food Cooked	Pot Roast Chicken
Temperature/Setting	180°C	9-5
Preheat Time	15 mins	15 mins
Cook Time	60 mins	60 mins
Energy Used	1.43 kW/h	0.66 kW/H
Comments	No discernable difference was identified between pre-browned chickens placed in identical cooking vessels, the first being cooked in the fan oven and the second in the induction oven.

Table 2. Experimental results for general cooking

Oven Used	Conventional Fanned Oven	Induction Oven
Food Cooked	Frozen Ready Meal
Temperature/Setting	190°C	9-6
Preheat Time	15 mins	15 mins
Cook Time	45 mins	45 mins
Energy Used	1.07 kW/h	0.69 kW/h
Comments	The temperatures observed in the cooking vessels placed within each oven was 80°C for the fan oven 83°C for the induction oven. Whilst the temperatures were comparable between the two oven type, the energy saving was significant for the induction oven.

The inventors have found that when the induction oven is used for slow cooking (at temperatures of lower than 100°C within cooking chamber 301) the energy saving over a conventional slow cooking oven (non-induction oven) was approximately 80%.
The present multifunction oven is suitable for cooking according to a variety of different modes including in particular:

1. induction roasting;
2. induction steam cooking;
3. induction slow cooking;
4. fan assisted grill cooking; and
5. fan assisted heating element cooking.

In one mode of operation, the induction unit is configured to generate an electromagnetic field within the oven cavity so as to provide a cooking temperature in the range of 60°C to 160°C. This cooking temperature, within the oven cavity and/or within a cooking vessel within the oven cavity, is suitable for slow cooking, casserole cooking or steam cooking. According to a different mode of operation, the multifunction oven is capable of sustaining generated temperatures within the oven cavity in the range 160°C to 350°C. Such cooking temperatures are possible in segmented zoned region within the oven cavity, typically defined by a cooking vessel having a top, sidewalls and a bottom (such as a roasting pot). Such cooking temperatures are suitable for roasting and other high temperature cooking methods.
As will be appreciated, the present oven is suitable for use with a variety of different cooking vessels such as multi-environment/zone roasting trays, steamers, griddles etc. In particular, a cooking vessel may be provided in which the internal cooking chamber 301 is divided into a plurality of different cooking zones, each zone offering a different cooking type, e.g. roasting or steaming and configured to cook food at different temperatures. The cooking chamber 301 may be divided by removable inserts or may be permanently divided into different zones.

Claims

An induction oven (115) comprising:
sidewalls (102), a top, a bottom (101) and a door (124) to define an internal cavity (100);

an induction unit (108) mounted in close proximity to at least one of the sidewalls (102), the top and/or bottom (101) of the cavity (100), the induction unit (108) configured to create an electromagnetic field within the cavity (100);

the induction unit (108) mounted external of the cavity (100);the at least one of the side walls (102), top and/or bottom (101) of the cavity (100) positioned in close proximity to the induction unit (108) comprises a material not susceptible to magnetic induction;

characterised in that:
the induction unit (108) comprises a temperature regulator and thermal shielding (306) positioned about the temperature regulator and between the temperature regulator and the internal cavity (100);

the oven further comprises cavity thermal shielding (305) positioned externally around the oven cavity (100), the cavity thermal shielding (305) being additional to the thermal shielding (306) positioned about the temperature regulator;

wherein the induction unit (108) is mounted at a distance of less than 45 mm from the oven cavity (100).
The oven (115) as claimed in claim 1 wherein the at least one side walls (102), top and/or bottom (101) of the cavity (100) positioned in close proximity to the induction unit (108) comprises an aluminium, glass, ceramic or glass-ceramic materials; and the induction unit (108) is positioned immediately behind the aluminium, glass, ceramic or glass-ceramic material at an external side of the cavity (100).
The oven (115) as claimed in claim 2 wherein at least one of the sidewalls (102), top and/or bottom (101) comprises a hollow region (105), the induction unit (108) being housed at least partially within the hollow region (105) so as to be effectively recessed in the sidewalls (102), top and/or bottom (101) of the oven (115).
The oven (115) as claimed in claim 3 wherein the hollow region (105) extends from the cavity (100) through the sidewalls (102), top and/or bottom (101) to an external side of the oven (115), the aluminium, glass, ceramic or glass-ceramic sheet (106) being positioned at the cavity (100) end of the hollow region (105).
The oven (115) as claimed in claim 4 wherein the induction unit (108) is positioned at least partially within the hollow region (105) within the sidewalls (102), top and/or bottom (101) between the internal cavity facing side of the hollow region (105) and the external facing side of the oven (115).
The oven (115) as claimed in any preceding claim further comprising control means electrically coupled to the induction unit (108) to determine and regulate the temperature in the cavity (100) by control of the electromagnetic field strength generated by the induction unit (108).
The oven (115) as claimed in any preceding claim further comprising a cooking vessel (110) removeably accommodated in the cavity (100).
The oven (115) as claimed in claim 7 configured such that the electromagnetic field generated by the induction unit (108) penetrates at least a region of the cooking vessel (110) housed within the cavity (100).
The oven (115) as claimed in claims 7 or 8 wherein the cooking vessel (110) comprises a removable insert (111) selected from any one or a combination of the group of:
a roasting trivet comprising a solid base and a side lip extending from the base, the trivet configured to be removeably housed within the vessel (110);

a steaming trivet comprising a perforated base and a side lip extending from the base and configured to be removeably housed within the vessel (110);

wherein the solid and perforated base are configured to sit above an internal base of the vessel (110).
The oven (115) as claimed in any preceding claim wherein the induction unit (108) is configured to generate the electromagnetic field within the cavity (100) such that the temperature within at least a region of the cavity (100) is in the range 160°C to 350°C.
A method of cooking using an induction oven (115) having sidewalls (102), a top, a bottom (101) and a door (124) to define an internal cavity (100), the method comprising:
generating an electromagnetic field using an induction unit (108) mounted in close proximity to at least one of the sidewalls (102), top and/or bottom (101) of the cavity (100);

operating the induction unit (108) to provide a sustained electromagnetic field directed within the cavity (100);

wherein the induction unit (108) is mounted external of the cavity (100);

wherein the at least one of the side walls (102), top and/or bottom (101) of the cavity (100) positioned in close proximity to the induction unit (108) comprises a material not susceptible to magnetic induction;

characterised in that:
the induction unit (108) comprises a temperature regulator and thermal shielding (306) positioned about the temperature regulator and between the temperature regulator and the internal cavity (100);

the oven further comprises cavity thermal shielding (305) positioned externally around the oven cavity (100), the cavity thermal shielding (305) being additional to the thermal shielding (306) positioned about the temperature regulator;

wherein the induction unit (108) is mounted at a distance of less than 45 mm from the oven cavity (100).
The method as claimed in claim 11 comprising:
generating an electromagnetic field within the cavity (100) so as to provide a sustained and controlled temperature within at least part of the oven (115) being greater than 160°C.