Patent Application
20090289054
The present invention relates to induction stoves. More particularly, the present invention relates to induction stove assemblies having improved safety and convenience and devices for improving the safety and convenience of an induction stove.
Induction stoves have been known for decades but have gained popularity in recent years due to their many advantages over other types of stoves. Like a traditional electric stove, an induction stove uses electricity to generate heat. However, instead of heating a resistive element (such as a coil of metal) by passing electric current through it, an induction stove generates an oscillating magnetic field that causes the cooking vessel itself to be heated. The term “cooking vessel,” as used throughout this specification, refers to any pot, pan, skillet or other article in which food or other material is placed to be heated on a stove.
In an induction stove, a wire coil located beneath the cook-top receives an alternating electrical current, and thereby creates an oscillating magnetic field. When a cooking vessel made from a ferromagnetic material is placed on the cook-top, the oscillating magnetic field causes the ferromagnetic material to heat up. The ferromagnetic material is heated by means of magnetic hysteresis loss in the ferromagnetic material as well as by eddy currents created in the ferromagnetic material (which generate heat due to the electrical resistance of the material). The mechanisms by which an induction stove generates heat in a cooking vessel are well known to those of skill in the art. Typically, no portion of the cook-top itself is directly heated by the induction heating element, unlike in a traditional electric stove, where a circular heating element is heated in order to heat a cooking vessel that is placed thereon.
One advantage of induction stoves is that the cook-top surface is often formed of a smooth, ceramic glass material that is easy to clean and has a pleasing appearance. Gas stoves are often much more difficult to clean because of the need to have deep recesses for the grates on which cooking vessels are placed and protrusions for the gas outlets.
Additionally, the fact that no portion of an induction cook-top itself is directly heated provides a safety benefit over a traditional electric stove. As is well known, the heating element of a traditional electric stove remains dangerously hot for a long period after the stove is turned off. This residual and unwanted heat poses a clear safety hazard, which can be largely overcome by induction stoves.
Unfortunately, prior art induction stoves, while possessing many advantages over traditional gas and electric stoves, still suffer from notable drawbacks. In many prior art induction stoves, the ceramic glass cook-top surface, while pleasing to look at, is sometimes susceptible to scratches in the areas of the cook-top in which cooking vessels are placed during use. Cooking vessels used for induction cooking include those constructed from cast iron, carbon steel, and some stainless steels—which materials can sometimes have rough surfaces and/or corners that can scratch ceramic glass. Also, very heavy cooking vessels (such as those made from cast iron) may crack or break the cook-top if they are mishandled or dropped on the cook-top.
Additionally, it is sometimes undesirable to clean the cook-top itself. For example, the cook-top may retain some residual heat from the cooking, or the cook-top may be susceptible to damage from a particularly abrasive cleaning product. Or, if a plurality of induction stoves are installed in a hotel or dormitory, cleaning all of the cook-tops by hand may be an inefficient use of time. In such circumstances, it may not be desirable to clean the cook-top.
Further, the benefit of not directly heating any part of the cook-top can be noticeably reduced as a result of the transfer of heat from the cooking vessel (which was directly heated by the induction coil) to the cook-top surface. While the induction stove cook-top will not pose as serious a safety hazard as a traditional electric stove, the residual heating of an induction stove cook-top can be annoying and can, in some cases, cause minor burns.
Some prior art induction stoves have included features intended to improve the safety and performance of the stoves. For example, U.S. Pat. No. 7,173,224 to Kataoka et al. discloses an induction stove that includes an electrostatic shielding member formed on the top surface of the cook-top. The electrostatic shielding member also includes an insulating layer that is intended to prevent leakage current from harming a user of the stove. However, both the shielding member and the insulating layer protrude above the cook-top and are not removable from the cook-top. These features of the Kataoka stove impede cleaning of the cook-top and are vulnerable to breakage. Also, there is no disclosure of any means to handle or mitigate the heat retained in the cook-top from the cooking vessel. There is also no protection provided against scratching or cracking of the insulating layer or the electrostatic shielding member.
U.S. Pat. No. 7,081,603 to Hoh et al. discloses an induction stove that includes, as an additional heating mechanism, a conventional electrical resistive heating unit. The cook-top includes heat resisting plates in the induction cooking zones, and each plate has planar heating element attached in a groove on the bottom of the plate. There is no disclosure of a means to prevent or mitigate the unsafe indirect heating of the cook-top via the cooking vessel.
What is desired therefore, is an assembly and/or device that will protect the cook-top of an induction stove and that will improve the ease of cleaning of the stove. It is also desired that such an assembly and/or device alleviate the problems associated with the indirect heating of an induction stove cook-top.
In this regard, the present invention provides induction stove assemblies and devices for use with induction stove assemblies that improve the convenience and safety of cooking with induction heat.
In a first embodiment of the present invention, a cook-top assembly for use with an induction stove is provided. The assembly utilizes a coil to create an oscillating magnetic field that interacts with and generates an amount of heat in a cooking vessel located in an induction cooking zone of the stove. The assembly comprises a cook-top, comprising a substantially horizontal surface and at least one recess formed in the surface, and a pad, placed on the cook-top with at least a portion of the pad disposed in the recess. The portion of the pad disposed in the recess substantially prevents horizontal movement of the pad relative to the cook-top but does not impede removal of the pad from the cook-top.
In some embodiments, the pad causes no more than about a 40% reduction in the amount of heat generated in the cooking vessel by the oscillating magnetic field. In some embodiments, the pad causes no more than about a 20% reduction in the amount of heat generated in the cooking vessel by the oscillating magnetic field. In some embodiments, the pad causes substantially no reduction in the amount of heat generated in the cooking vessel by the oscillating magnetic field.
In some embodiments, the pad exhibits substantially no deformation of shape when exposed to temperatures between 150° F. and 500° F. In some embodiments, the magnetic permeability of the pad is less than 5×10−6 μH/m.
In some embodiments, the pad is sized to correspond to the size of the induction cooking zone. In some embodiments, the pad is sized to cover a majority of the surface area of the cook-top. In some embodiments, the pad is formed of a flexible, shock-absorbing material.
In some embodiments, the cook-top further comprises: a top plate, having an opening, and a bottom plate, having an upper surface that is fixed to a lower surface of the top plate and substantially covers the opening. The recess is defined by the space bound by the upper surface of the bottom plate and the opening in the top plate.
In some embodiments, the pad is sized to fit within the recess and rests upon the upper surface of the bottom plate. In some embodiments, the pad includes a protrusion sized to fit within the recess. In some embodiments, the pad is comprised of silicone rubber. In some embodiments, any portions of the pad and the cook-top that are located between the coil and the cooking vessel have a combined thickness of about 10 millimeters or less.
According to another embodiment of the present invention, a pad for use with an induction stove is provided. The induction stove includes a cook-top and a coil for generating an oscillating magnetic field that interacts with and generates an amount of heat in a cooking vessel located in an induction cooking zone. The pad comprises a bottom surface for contacting the cook-top and a top surface for supporting a cooking vessel to be heated. The pad is made of a flexible, shock-absorbing material.
In some embodiments, the pad includes a protrusion for fitting within a recess formed on the cook-top. In some embodiments, the pad is comprised of silicone rubber. In some embodiments,
In some embodiments, the pad is sized to substantially correspond to an induction cooking zone of the induction stove and shaped so that when the protrusion is fitted within the recess, the pad is located above the coil. In some embodiments, the pad is sized to substantially correspond to the surface area of the cook-top.
According to yet another embodiment of the present invention, a method of maintaining a plurality of induction stoves, each of which comprises a cook-top, is provided. The method comprises the steps of: providing a set of pads, each of which is adapted to rest on a cook-top; placing a first subset of pads from the set of pads on the cook-tops of the plurality of induction stoves so that users may use the plurality of induction stoves; removing a first pad of the first subset of pads after use of a first induction stove by a first user; placing a second pad taken from a second subset of pads from the set of pads on the cook-top of the first induction stove to replace the first pad so a second user may use the first induction stove; and cleaning the first pad and transferring it to the second subset for subsequent use.
As used in this specification, the term “induction cooking zone” refers to the volume of space in which a ferromagnetic cooking vessel can be heated by the induction coil of an induction stove.
The invention and its particular features and advantages will become more apparent from the following detailed description considered with reference to the accompanying drawings.
Referring first to
The induction cooking zones have different sizes—zone 13 is a larger cooking zone than zone 14. The zone 13 has a larger horizontal extent than the zone 14. A larger induction cooking zone is able to heat a large cooking vessel quicker and more evenly than a smaller induction cooking zone would heat that same vessel. Each induction cooking zone has associated with it a recess formed in the cook-top 11. In
The pads 17 and 18, and those described elsewhere in this specification, are designed to receive cooking vessels used with the induction stove assemblies to heat and cook food. The pads of the present invention are designed in a variety of ways to have beneficial features. As shown in
The shape of the pads is varied according to the design of the cook-top, induction stove, and the preferences of the manufacturer and/or end user. The pads 17 and 18 shown in
The pads 17 and 18 are designed so that the center portions of the pads, i.e., in the area of the ridges 20, are mostly contained within the circular recesses in the cook-top, while only the raised rings 19 protrude above the cook-top. In other embodiments, such as that shown in
The pads for use according to the present invention are constructed from a variety of materials. A primary consideration in selection of a material for a pad is that the pad will not interact with the oscillating magnetic field of the induction cooking zones and interfere with the heating of the cooking vessels. Thus, materials having a high magnetic permeability, such as ferrites, nickel, cobalt, etc., are to be avoided. Such materials are also to be avoided for use in the cook-top. It is generally preferred to select materials for the pads having a relatively low magnetic permeability, for example, around 5×10−6 μH/m or less. Suitable pads for use in the present invention will, ideally, have a minimal negative impact on the effectiveness of the induction stove in heating a cooking vessel. A suitable pad will reduce the amount of heat generated in a cooking vessel by the oscillating magnetic field of the induction coil by no more than about 40% or less, as compared to the performance of the stove in the absence of the pad. More preferably, the pad will reduce the amount of heat generated in the cooking vessel by the oscillating magnetic field by no more than about 20%. Most preferably, of course, the pad will cause substantially no reduction in the amount of heat generated in the cooking vessel by the oscillating magnetic field.
It is also desirable to design the pad to not deform due to the heat of the cooking vessel. In some embodiments, the pad does not deform when exposed to temperatures between 150° F. and 500° F. In some embodiments, of course, the pad exhibits no deformation when exposed to much higher temperatures. Most induction stoves include a temperature sensor for preventing the stove from heating a pan above a chosen temperature. By careful selection of the material or materials for use in the pad, a pad according to the present invention can be designed to be used with stoves of virtually any power capability. Pads that do not deform when exposed to temperatures up to 600° F., 700° F., 800° F., 900° F., 1000° F., and above may be used in accordance with the present invention.
In addition to resisting deformation due to high temperatures, some pads used in embodiments of the present invention are used to insulate the cook-top from the heat generated in the cooking vessel. The heat insulating character of such pads helps to prevent the cook-top 11 from becoming undesirably hot. After use of an induction stove with a pad between the cook-top and the cooking vessel, the pads can be removed from the cook-top (using tongs if necessary) and immediately cooled using cold water or stored in a secure place. In some embodiments, depending on the material used to form the pad, removal of the pad may not be necessary because of the rapidity with which the pad cools after the cooking vessel is lifted off of it. In this way, the pads improve the safety of the induction stove.
Another design consideration for a pad according to the present invention is the ability of the pad to absorb impact and protect the stove cook-top. For example, a material that is soft and resilient will help absorb the impact of a dropped cooking vessel—thereby reducing the likelihood that the cooking vessel will damage the cook-top. Materials that exhibit good impact absorption typically are soft and elastic, even at high temperatures. Such materials are also resilient, in that they will return to shape automatically after being deformed by an external weight.
A material that has a relatively high “surface tack” has also been found to be useful in pads according to the present invention. “Surface tack” helps to prevent a cooking vessel from sliding off of the stove while in use. “Surface tack” refers to the surface of the material having a high coefficient of friction, particularly static friction. Using pads with high surface tack is particularly important with stoves that are to be used in a boat or mobile home.
Finally, it has also been found to be beneficial to make the pads from materials that are resistant to damage that could be caused by cleaning products and/or automatic dishwashers. This enables spills cooking vessels in use to be cleaned up very efficiently, since most spills will be contained on the pad. The pad can simply be lifted off of the cook-top and either cleaned in the sink or placed in a dishwasher for later cleaning. A material that is inert, i.e., non-reactive with most chemicals, is desirable.
While in some embodiments, a pad will possess all of the foregoing desirable traits, it is not necessary for every embodiment. The pads are custom designed for particular applications. For example, an aluminum pad will exhibit very poor impact absorption and surface tack, but will be very resistant to high temperatures and durable. Also, if impact absorption is not a critical design factor and inexpensive production is important, paper specially treated to be resistant to damage from high temperature could be used as a pad. There are uncountable possibilities for pad design. Of course, other materials with varying degrees of suitability in the above-described categories are advantageously employed in embodiments of the present invention.
The inventors have found that heat-insulating silicone rubber is a highly advantageous material for use as a pad in the present invention. Pads made from silicone rubber are relatively easy and inexpensive to fabricate. The material does not interfere significantly with the oscillating magnetic field of the induction stove. The material is soft and flexible but non-reactive with most cleaning agents. It is also a good heat insulator and can be designed not to deform at high temperatures. Silicone rubber can be created in numerous colors, so that the pads can be made to match any kitchen or home décor.
In order to create the recesses in the cook-top 11, the bottom panel 20 is secured to the underside of the top panel 21. Generally, the bottom panel 20 is made of the same material used for the top panel 21, but the panels may be of different materials so long as they are suitable for use as an induction stove cook-top. The bottom panel 20 is secured in a permanent or semi-permanent fashion to the top panel 21, by use of adhesives or any other means for joining ceramics, glasses, or other suitable materials. The recesses are thus formed as the space created by the circular openings 22 and 23 and the top surface of the bottom panel 20. This arrangement is also shown in
The recesses are formed in other ways in other embodiments. For example, as shown in
The function of the electronic components of the induction stove to generate heat in an appropriate cooking vessel is well known in the art. When one desires to heat food in a cooking vessel, the vessel is placed on one of the pads 29 or 30, depending on the size of the cooking vessel and the desired heating power. The user then powers the system and selects a temperature setting using the controls 16. If, for example, the user is using cooking zone 14, alternating current in sent through the coil 32 via the electronics assemblies 37. This causes the coil 32 to produce an oscillating magnetic field that interacts with the cooking vessel 40 placed on the pad 30. If the cooking vessel is ferromagnetic, it will heat up in accordance with the selected temperature setting. Shown in
In order for any induction stove assembly to function effectively, the separation between the bottom of a cooking vessel and the induction coils must be maintained within the limits of that particular assembly. In the embodiments shown in the FIGs., the induction coils function most effectively when the bottom of the cooking vessel is less than 10 millimeters away. Thus, the combined thicknesses of the portions of the cook-top and the pad that are between the coil and the cooking vessel must be carefully chosen. In other embodiments which utilize differently designed and/or more powerful coils, this distance can be increased. Induction coils capable of heating cooking vessels at much greater distances are known in the art and are used in other embodiments of the present invention.
Instead of two circular pads that are roughly the same size as the induction cooking zones, the embodiment shown in
The use of the large pad 101 with the second embodiment, has the advantage of providing the entire cook-top surface with protection while the stove is in use. Clearly, a dropped cast iron cooking vessel could damage the ceramic glass cook-top even if the vessel was dropped somewhere other than in the induction cooking zones. The large pad 101 helps prevent such damage since it covers substantially the entire cook-top 102 when it is in position.
The unique induction stove assemblies according to the present invention clearly provide many advantages to residential users who cook for themselves and their families at home. However, the present invention also brings numerous advantages in other contexts as well, such as in a hotel or dormitory setting. In a hotel, for example, many substantially similar stoves will be installed in the guest rooms. These stoves will most often need to be cleaned on a daily basis. By utilizing the pads of the present invention, the daily cleaning of the stoves in these rooms can be accomplished in a much more efficient manner.
For example, for a hotel with 100 rooms, each with an induction stove having a single induction cooking zone, the hotel purchases 200 pads. 100 of these pads are placed on the cook-tops of the stoves and form a first subset of the set of 200 pads. When each room is cleaned after use by a guest in the hotel, the pad is removed from the induction stove in that room and replaced with a pad from the 100 reserve pads that form a second subset of the set of 200 pads. (In some embodiments, the pad is only be removed if the stove was actually used). The used pad is then cleaned (along with all other used pads from the first subset) by the hotel staff by hand or using a dish-washing machine. The cleaned pads then become part of the second subset of pads for subsequent use in the hotel rooms. Significant cleaning time is saved because the hotel cleaning staff does not need to scrub each individual stove cook-top that was used. This method is also effective in dormitories or apartment buildings that utilize a central cleaning service.
It should be appreciated by those skilled in the art that various changes and modifications can be made to the illustrated embodiments without departing from the spirit of the present invention. All such modifications and changes are intended to be covered within the scope of the present invention disclosure.
This application claims the benefit of U.S. Provisional Application No. 61/054,693, entitled Cooking Pad for Induction Appliance, filed on May 20, 2008 and U.S. Provisional Application No. 61/080,858, entitled Cut-Out Induction Cook Top, filed on Jul. 15, 2008. The disclosures of both of these applications are hereby incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 61054693 | May 2008 | US | |
| 61080858 | Jul 2008 | US |
