WO2016074743A1

WO2016074743A1 - Kettle for induction hobs

Info

Publication number: WO2016074743A1
Application number: PCT/EP2014/074614
Authority: WO
Inventors: Johann Zita; Fredrik SJÖBERG
Original assignee: Aktiebolaget Electrolux
Priority date: 2014-11-14
Filing date: 2014-11-14
Publication date: 2016-05-19

Abstract

The present invention relates to a kettle (1; 10) for heating a fluid on an induction hob, said kettle comprising: a container (2; 11) made of a non ferromagnetic material, said container comprising an opening (3; 12), a fluid compartment and a bottom surface (5; 13); a container lid (4; 14) closing the container opening; a ferromagnetic plate lifting device (6; 30) comprising a shape memory material member (7; 32) arranged separated from the fluid compartment and an intermediate member (8; 31) extending between the shape memory material member and the ferromagnetic plate, the shape memory material member has a first and a second stable condition and, at a predetermined temperature, contracts or expands from the first to the second stable condition and lifts the ferromagnetic plate from the container bottom by the intermediate member.

Description

KETTLE FOR INDUCTION HOBS

Field of the invention

The present invention relates to a kettle for an induction hob. Background of the invention

Induction hobs are used in more and more households for preparation of food and beverages. The food or beverage is placed in a kettle, pot or pan formed of a ferromagnetic material, alternatively comprising a bottom area formed of a ferromagnetic material. A magnetic field, generated by an induction coil arranged in the hob, is applied on the ferromagnetic material in the kettle to heat the

ferromagnetic material as well as the food or beverage in the kettle, pot or pan.

In order to reduce the energy consumption and the risk that the kettle is boiling dry (no water or liquid remaining in container), it is desirable to have a kettle that is automatically shut-off when the water or fluid in the kettle is boiling.

One example of kettle for an induction hob that is automatically shut-off is disclosed in CN202051519U. The disclosed kettle is intended for boiling water and comprises an arrangement in the kettle lid for lifting a plate of ferromagnetic material movably arranged in the bottom of the container. When the water is boiling and the temperature in the kettle lid has reached a predetermined temperature a bi-metal locking element activates the arrangement in the kettle lid and the ferromagnetic plate is lifted from the container bottom. When the plate is lifted more than about 15mm the control device in the hob will detect that no ferromagnetic material is located on the hob and shut-off the induction coil. However, the disclosed kettle suffers from some drawbacks. First, the arrangement is rather complex and comprises several different components. Second, the shut-off arrangement must be correctly prepared by the user since the arrangement is loaded by movement of the kettle lid to reset the shut-off arrangement and consequently there is a risk that the user will not reset the shut-off arrangement properly which is devastating for the function of the kettle.

There is therefore a need for an improved kettle for boiling of water, or any other fluid, that ensures that the kettle is automatically shut-off without any involvement of the user.

Summary of the invention

The present invention, defined in the appended claims, relates to a kettle for heating fluid on an induction hob that reduces, or eliminates, at least the problems defined above.

The kettle comprises:

a container made of a non ferromagnetic material, said container comprising an opening, a fluid compartment and a bottom surface;

a container lid closing the container opening;

a ferromagnetic plate movably arranged in the container fluid compartment adjacent to the bottom surface; and

a ferromagnetic plate lifting device comprising a shape memory material member arranged separated from the fluid compartment and an intermediate member extending between the shape memory material member and the ferromagnetic plate, the shape memory material member has a first and a second stable condition and, at a predetermined temperature, contracts or expands from the first to the second stable condition and lifts the ferromagnetic plate from the container bottom by the intermediate member.

The kettle according to the invention solves the problems described above since the shape memory material will automatically contract or expand when it has been heated to the predetermined temeperature and thereby, via the intermediate member, lift the ferromagnetic plate from the bottom surface, away from the induction hob, to activate the shut- off function of the induction hob without any human involvement or additional control elements. After the fluid in the kettle has been heated and the hob is shut-off, the temperature within the enclosure will drop and when the temperature returns below the predetermined temperature the shape memory material member will expand or contract and return to its original size thereby returning the ferromagnetic plate to its initial position adjacent to the bottom surface whereby the kettle is once again ready for use without any involvement by the user.

In one embodiment of the kettle, the ferromagnetic plate lifting device lifts the centre of the ferromagnetic plate to an elevated position at least 10 mm above the container bottom surface. The elevated position 10mm above the container bottom surface ensures that the hob will detect the movement and shut-off the power to the induction coil. In one embodiment of the kettle, the intermediate member is elongated and extends between the shape memory material member and the ferromagnetic plate via the fluid compartment. This design of the intermediate member provides a reliable and robust kettle without reducing the volume of the fluid compartment. In one embodiment of the kettle, the ferromagnetic plate has an outer periphery and is movably secured to the container in one position around the outher periphery. This embodiment ensures that the plate remain in the position adjacent to the bottom surface in the container when the kettle is turned upside down to empty the heated fluid.

In one embodiment of the kettle, the intermediate member is attached to the ferromagnetic plate outer periphery opposite to the position where the ferromagnetic plate is movably secured in the container. This position of the intermediate member makes it possible to lift the ferromagnetic plate in a stable and controlled manner. The position furthermore requires a minimum force to lift the ferromagnetic plate from the position adjacent to the bottom surface. In one embodiment of the kettle, the outher periphery of the ferromagnetic plate is surrounded by an elastic material. This embodiment is favourable since bubbles and movements is generated in the boiling fluid and these movements will generate vibrations or movements of the ferromagnetic plate, which could lead to damages to the container alternatively generate unpleasant noise.

In one embodiment of the kettle, the shape memory material member is arranged within the lid or handle. These alternatives are favourable since both the lid and the handle could be designed to provide the required space to house the shape memory material member.

In one embodiment of the kettle, the shape memory material member is arranged within an enclosure with a passage connecting the enclosure with the container above the fluid compartment. In order not to lift the ferromagnetic plate until all fluid within the container is heated, the shape memory material member is arranged within an enclosure connected only by the passage to the container to avoid that the critical temperature where the shape memory material contracts or expands is reached to early. The area of the passage is selected to limit the amount of heated steam / vapour to reach the enclosure and thereby prevent that the shape memory material member is contracted or expanded too early.

In one embodiment of the kettle, the area of the passage is less than 900 mm² to prevent too early contraction or expansion of the shape memory material member. In one embodiment of the kettle, the enclosure is connected with the outside of the kettle via an air inlet with a total area not exceeding 900 mm². The air inlet ensures that the shape memory material member is cooled down below the predetermined temperature within a resonable time which is essential to prepare the kettle for use once again.

In one embodiment of the kettle, the shape memory material member is formed as a helical spring, curved or folded. The shape memory material member may be embodied in several different ways in order to adapt the characteristics of the member to specific needs following from the selected size and volume of the kettle, the required force to lift the ferromagnetic plate and the desired time to shut off the induction hob.

In one embodiment of the kettle, the ferromagnetic plate is made of material with a Curie temperature below 350°C. This is a favourable embodiment that improves the safety of the kettle further. In case there is no fluid in the container when the induction hob is activated, the ferromagnetic plate will be heated but since no fluid is present in the container, no vapour /steam is generated which would delay the required increase of the temperature in the shape memory material member and the desired lifting of the ferromagnetic plate to shut-off the induction hob. The ferromagnetic plate made of a material with a Curie temperature (Invar material) below 350°C will eliminate the described problem since the characteristics of the material, i.e. the material is no longer magnetic when the material reaches a specified Curie temperature, would activate the shut-off of the induction hob without requiring that the plate is lifted to the elevated position.

In one embodiment of the kettle, the container is made of a ceramic, wooden, stone, glas, paper or plastic material. Since the fluid in the kettle is heated by the

ferromagnetic plate the container could be made of any suitable material that is able to hold the fluid and withstand the heat generated by the ferromagnetic plate and the fluid. One embodiment of the kettle, comprises indication means connected to the shape memory material member to indicate that the shape memory material member has been heated above the predetermined temperature.

The different embodiments described above may of course be combined and modified in different ways without departing from the scope of the invention that will be described more in detail in the detailed description. Brief description of the drawings

In figure 1 shows a schematic illustration of the general idea behind the invention. Figure 2a and 2b illustrates an alternative embodiment of a kettle schematically. Figure 3a and 3b illustrates a further alternative embodiment of a kettle

schematically.

Figure 4 illustrates a cross-sectional view through a vertical plane in the centre of a first embodiment of a kettle.

Figure 5 illustrates an exploded view of the kettle in figure 3.

Figure 6 illustrates an exploded view of selected components arranged in the lid of the kettle.

Figure 7 illustrates a cross-sectional view of the lid through a vertical plane in the centre of the lid.

Detailed description

In figure 1 the general idea of the invention is illustrated. The figure illustrates a kettle 1 comprising a container 2 in which a fluid, normally water, is filled via an opening 3 in the upper part of the container. The opening is closed by a lid 4, only schematically illustrated. The lower part of the kettle comprises a substantially flat bottom surface 5 intended to rest on the induction hob. Within the container a substantially flat ferromagnetic plate is arranged adjacent to the bottom surface. In the kettle, a ferromagnetic plate lifting device 6 comprising a shape memory material member 7 is arranged. One end of the shape memory material member is secured in the kettle while the other end is connected to an elongated intermediate member 8 that extends via the container to the ferromagnetic plate in the lower part of the container.

When the induction hob is activated, the ferromagnetic plate is heated by induction power whereby the fluid in the container is heated simultaneously by the plate. When the temperature of the fluid rises, heated vapour / steam will move upwards towards the shape memory material member and when the shape memory material member is heated to a predetermined temperature the shape memory material member will contract and via the intermediate member lift the ferromagnetic plate to an elevated position above the bottom surface of the kettle. In figure 2a and 2b an alternative embodiment of the plate lifting device is illustrated. The illustrated embodiment comprises a shape memory material member 7b that expands when heated above the predetermined transition temperature. The shape memory material member 7b is arranged in the lid, extending substantially parallel to the intermediate member 8b, and will, when the shape memory material member is heated to the transition temperature, expand and lift the intermediate member and the ferromagnetic plate upwards. In order for this embodiment to work as intended, the intermediate member is formed as a rigid element supported by guiding elements 9b to ensure movement in the desired direction.

A further embodiment of the invention comprising an expanding shape memory material member 7c is illustrated in figure 3a and 3b. The intermediate member 8c is for example formed of an elastic wire or rope and is in one end secured to the ferromagnetic plate while the other end is secured in the upper part of the kettle or lid. The shape memory material member is arranged along the intermediate member 8c and extending in substantially horizontal direction perpendicular to the intermediate member 8c. One end of the shape memory material member 7c is permanently secured in the container while the other end is secured in the intermediate member between an upper and a lower intermediate support members 9c and will, when the transitional temperature is reached, force the central part of the intermediate member sideways thereby lifting the ferromagnetic plate in the container. This embodiment of the kettle is easily modified for use in combination with a contracting shape memory material member by arranging the shape memory material member on the opposite side of the intermediate member such that the intermediate member is drawn sideways by the contracting shape memory material member to lift the ferromagnetic plate from the bottom surface of the container.

A shape memory material is a type of material that has two different stable conditions depending on the temperature of the material. This means that the material, for example embodied as a helical spring, elongated rod, folded band etc, has a first length as long as the material temperature is below a predetermined transition temperature. The transitional temperature may be adjusted by modifications to the composition of the shape memory material. The shape memory material is either a polymer material or a metal material. When the temperature in the material is increased above the transition temperature, the shape memory material contracts or expands to a second stable condition, i.e. a second length shorter or longer than the first length. If the temperature of the shape memory material member is reduced below the transition temperature, the shape memory material member will expand or contract and return to the first stable condition, i.e. the first length.

In figure 4 a cross- sectional vertical view of a complete kettle 10 according to the invention is illustrated. The same kettle is furthermore illustrated in figures 5 to 7 and the same reference numerals will be used in all figures. The illustrated kettle works according to the principle illustrated in figure 1 and described above, i.e. that the shape memory material member contracts when the transition temperature is reached, and will be described more in detail to clarify further advantages.

The kettle comprises a container 11. The container is made of a non ferromagnetic material such as ceramic, wood, stone, glas, paper or plastic material depending on the desired apperarance and design of the kettle. The container comprises an opening 12 arranged in the upper part of the container in order to make it possible to fill the container with fluid, normally water, that should be heated. The volume of the fluid filled in the contaniner should not exeed a predetermined fluid fill level to avoid heated fluid from leaking from the container. The space defined by the inner walls of the container and the maximum fill level is refered to as the fluid fill compartment.

The lower part of the the container 11 comprises a substantially flat bottom surface 13 intended to rest on the surface of the induction hob (not illustrated). In the upper part of the kettle, a container lid 14 is attached to the container by a hinge 15 to be movable between a container closing position and an open position that makes it possible to fill the container under for example a water tap. The lid has a shape corresponding to the opening in the container. The opening and the lid could be modified in a number of ways depending on the desired design of the kettle as long as they fit together. The kettle furthermore comprises a handle 16 extending from the container and a spout 17 to facilitate the pouring of heated fluid from the container.

Adjacent to the bottom surface 13 a ferromagnetic plate 20 movably arranged in the container fluid compartment. The ferromagnetic plate has an outer periphery 21 enclosed by an an elastic material 22, and shape correpsonding to the size and shape of the bottom surface 13. The ferromagnetic plate is movably secured to the container in one position 23 around the outher periphery 21 by a hinge device 24 to be maintained in the intended position within the container if the kettle is turned up side down during filling or emptying of the container.

The kettle furthermore comprises a ferromagnetic plate lifting device 30. The different components of the ferromagnetic plate lifting device 30 are illustrated in figures 4 to 7 but the ferromagnetic plate lifting device could be embodied in several different ways without departing from the scope of the invention defined by the claims. The ferromagnetic plate lifting device 30 comprises an intermediate member 31 extending in the container via the fluid compartment between the ferromagnetic plate and a shape memory material member 32 arranged separated from the fluid compartment in the lid. The intermediate member is 31 attached to the ferromagnetic plate outer periphery 21 opposite to the position of the hinged securing 23 of the ferromagnetic plate 20 by attachment means 33. In the illustrated embodiment the ferromagnetic plate lifting device 30 furthermore comprises a transfer mechanism 34 arranged in the lid, between the shape memory material member 32 and the intermediate member 31 to redirect the movement generated by the shape memory material member contraction to a plate lifting movement in the intermediate member 31 and make it possible to lift the centre of the ferromagnetic plate to an elevated position at least 10 mm above the container bottom surface. The different components of the mechanism 34 is illustrated in the exploded view in figure 4 and 5a to 5d. The lid comprises a lid housing 35 formed by an upper part 36 and two lower parts 37a and 37b that enclose the transfer mechanism 34 and the shape memory material member 32. Between the two lower parts 37a and 37b a small gap 45 is formed. The gap directs heated vapour, air or steam from the container to the shape memory material member 32.

The the shape memory material member 32 is embodied as a helical spring extending substantially horisontal withn an enclosure 38 in the lid. The enclosure 38 forms a protective casing around the shape memory material member 32 to avoid to rapid heating of the shape memory material member 32 when the indution hob is activated and the ferromagnetic plate heated in the kettle. However, the shape memory material member 32 must evantually be heated and heated vapour, air or steam from the container is led via the gap 45 and at least one passage 39 in the lower part of the lid 37b into the enclosure 38 and the shape memory material member 32. The passages 39 are arranged to connect the enclosure 38 with the container above the fluid compartment. The total area of the passages 39 is used as one parameter to adjust the time for the shape memory material member to contract and ensur that the fluid is heated to the desired temperature before the the shape memory material member 32 contracts. Preferably the total area of the passages is less than 900 mm².

The upper part of the enclosure 38 comprises an air inlet 40 with access via a lid air inlet 41 to surrounding air to ensure tha the shape memory material member 32 is cooled down once the induction hob is shut-off in order to reset the kettle and make it ready to be used once again.

The shape memory material member 32 has a first 42 and a second end 43. The first end is stationary secured in the lid. The second end 43 is secured in a first transfer mechanism arm 44. The first transfer mechanism arm is substantially straight with a first 45 and a second end 46. The second end 43 of the shape memory material member 32 is secured in the first end 45 of the first transfer mechanism arm in order to move the first end 45 of the first transfer mechanism between a first and a second horisontal position depending on the condition of the shape memory material member. In figure 5 the shape memory material member is in the contracted condition, i.e. the temperature of the shape memory material member is above the predetermined temperature.

The second end 46 of the the first transfer mechanism arm 44 is turnably secured in a second transfer mechanism arm 47 between a first 48 and a second end 49 of the second transfer mechanism arm 47. The first end 48 of the second transfer mechanism arm 47 is turnably secured in the lid close to the first end 42 of the shape memory material member 32 around an axis Al, and the second end 49 of the second transfer mechanism arm 47 is connected to the upper end of the elongated intermediate member 31. The first 44 and second transfer mechanism arm 47 are both movable within the same vertical plane perpendicular to the axis Al. In other words, when the shape memory material member 37 contracts, the first end of the first transfer mechanism arm 44 is moved in horisontal direction H from an intitial position, i.e. to the right in the illustration in figure 5. This horisontal movement H is transferred via the first transfer mechanism arm 44 to the second transfer mechanism arm 47 and transformed to a vertical movement V in the second end 49 of the second transfer mechanism arm 47 thereby moving the elongated intermediate member 31 connected to the second end 49 of the second transfer mechanism arm 47 and the ferromagnetic plate the same distance in vertical direction V. Once the temperature in the shape memory material member falls below the predetermined temperature, the shape memory material member will expand and the first 44 and second transfer mechanism arm 47 return to their initial position.

The lid furthermore comprises heating indication means 50 arranged in the upper part of the lid. The heat indication means 50 are movable in vertical direction together with the second transfer mechanism arm 47 from a first position to a second position. In the first position, the heat indication means are retracted into the lid and not visible from the outside of the kettle. The heat indication means 50 are arranged in this first position as long as the ferromagnetic plate is arranged adjacent to the bottom surface of the kettle, i.e. heating of the fluid in the container takes place. When the transition temperature is reached in the shape memory material member, the heating indication means are lifted together with the second transfer mechanism arm 47 to an elevated position in which at least a section of the heat indication means 50 are visibly arranged above the lid to indicate that the heating of the fluid in the kettle is completed. The heating indication means 50 are retracted together with the second transfer mechanism arm when the ferromagnetic plate lifting device is reset.

The embodiments described above may be combined and modified in different ways without departing from the scope of the invention that is defined by the appended claims.

Claims

1. Kettle (1; 10) for heating a fluid on an induction hob, said kettle comprising:

a container (2; 11) made of a non ferromagnetic material, said container comprising an opening (3; 12), a fluid compartment and a bottom surface (5; 13);

a container lid (4; 14) closing the container opening;

a ferromagnetic plate (6; 20) movably arranged in the container fluid compartment adjacent to the bottom surface; and

a ferromagnetic plate lifting device (6; 30) comprising a shape memory material member (7; 32) arranged separated from the the fluid compartment and an intermediate member (8; 31) extending between the shape memory material member and the ferromagnetic plate, the shape memory material member has a first and a second stable condition and, at a predetermined temperature, contracts or expands from the first to the second stable condition and lifts the ferromagnetic plate from the container bottom by the intermediate member.

2. Kettle according to claim 1, wherein the ferromagnetic plate lifting device lifts the centre of the ferromagnetic to an elevated position at least 10 mm above the container bottom surface.

3. Kettle according to claim 1 or 2, wherein the intermediate member is elongated and extends between the shape memory material member and the ferromagnetic plate via the fluid compartment.

Kettle according to anyone of the previous claims, wherein the ferromagnetic plate has an outer periphery (21) and is movably secured to the container in one position (23) around the outher periphery.

Kettle according to claim 4, wherein the intermediate member is attached to the ferromagnetic plate outer periphery opposite to the position where the ferromagnetic plate is movably secured in the container.

Kettle according to claim 4 or 5, wherein the outher periphery of the ferromagnetic plate is surrounded by an elastic material (22).

Kettle according to anyone of the previous claims, wherein the kettle furthermore comprises a handle (16) and the shape memory material member is arrangend within the lid or handle.

Kettle according to anyone of the previous claims, wherein the shape memory material member is arranged within an enclosure (38) with at least one passage (39) connecting the enclosure with the container above the fluid compartment.

9. Kettle according to claim 8, wherein the area of the passage is less than 900

10. Kettle according to claim 8, wherein the enclosure is connected with the

surrounding air via an air inlet (40) with a total area not exceeding 900 mm².

11. Kettle according to anyone of the previous claims, wherein the shape memory material member is formed as a rod, a helical spring, curved or folded.

12. Kettle according to anyone of the previous claims, wherein the ferromagnetic plate is made of material with a Curie temperature below 350°C.

13. Kettle according to anyone of the previous claims, wherein the container is made of a ceramic, wooden, stone, glas, paper or plastic material.

14. Kettle according to anyone of the previous claims, comprising indication means (50) connected to the shape memory material member to indicate that the shape memory material member has been heated above the predetermined temperature