EP0929991B1 - Kitchen range with container detection - Google Patents

Abstract

The invention concerns a kitchen range comprising a base (10), a heating element (12) arranged on the base (10) and at least an induction sensor (20) for detecting the presence of a conductive container, said induction sensor (20) comprising a coil including at least one spire. The invention is characterised in that the spire has a substantially elongate shape substantially long the range radial direction.

Description

The present invention relates to a cooking stove for example placed under an insulating plate, hearth for which it is desired to detect the presence of an electrically conductive container for example placed on the insulating plate. This detection can be used to start the fireplace only when it is partially or completely covered by a container. This technique is commonly used for radiant or halogen fires.

A known hearth is described in European patent EP 0490289. This hearth comprises, in its insulating edge, an inductive detection coil around the hearth. This fireplace is intended to be placed under an insulating plate, for example glass-ceramic. When an electrical conductive container, for example placed on the insulating plate, covers this coil, the value of its inductance is modified and the container can thus be detected. The main disadvantage of this type of focus is that the coil can detect only containers having a diameter at least equal to that of the coil. Indeed, it is found that the value of the inductance of such a coil increases substantially only when the coil is almost covered by the container. A container of smaller diameter than that of the coil can not be detected. Another disadvantage of this type of fireplace is that it is necessary to provide a coil size for a fireplace size. In general, in a range or in a cooktop for domestic use, there are several foci of different sizes, which makes it necessary to multiply the production tools of the different coils and consequently increases the cost of producing such sets with several foci. . When the container presence detection is used to start the fireplace, it is understood that such a fireplace can not be started when the container is of a diameter slightly smaller than that of the fireplace. More specifically, one can cite as an example a focus of diameter 220 mm, this fireplace having in its border a coil detection. It is noted that the coil does not detect the presence of a container of diameter less than or equal to 180 mm.

Another means used to detect the presence of a container and to know its diameter is described in US Pat. No. 4,319,109. The device describes a series of point sensors, for example inductive, placed radially on the hearth. Each sensor responds when covered by a container. When the sensor or sensors located near the center of the fireplace are covered, the presence of a small container is detected and when the sensors further from the center are covered, the presence of a larger container is detected. This device has the disadvantage of requiring a large number of sensors to accurately know the diameter of the container covering the home, which multiplies the electrical connections of these sensors and which complicates the processing of the various information from the sensors.

However, the knowledge of the diameter of the container is interesting, because it allows for example, to start the home, depending on the diameter of the container, to a power less than the maximum power of the home.

The present invention aims to overcome the disadvantages described above by using an inductive sensor placed on a radial direction of the focus, sensor sufficiently elongated to detect the presence and to know the diameter of a container covering it.

More specifically, the cooking chamber comprising a bottom, a heating element disposed on the bottom and at least one inductive sensor capable of detecting the presence of an electrically conductive container, the inductive sensor comprising a coil comprising at least one coil, is characterized in that the turn is elongated substantially in a radial direction of the hearth.

• la figure 1 représente schématiquement un exemple de conducteur électrique formant la bobine de détection, conducteur sensiblement enroulé dans un plan ;
• la figure 2 représente schématiquement un autre exemple de conducteur électrique formant la bobine de détection, conducteur enroulé autour d'un mandrin rectangulaire ;
• la figure 3 représente un foyer de cuisson en vue de dessus comportant un capteur inductif ;
• la figure 4 représente un foyer de cuisson en vue de dessus, plus petit que le foyer de cuisson représenté figure 3 et comportant un capteur inductif identique à celui représenté figure 3 ;
• la figure 5 représente en vue de dessus, un foyer de cuisson à deux circuits chauffants concentriques et séparés, comportant un capteur inductif ;
• la figure 6 représente en vue de dessus, un foyer de cuisson à deux circuits chauffants séparés, ce foyer étant prévu pour chauffer des récipients de forme oblongue ou ronde ;
• la figure 7 représente un foyer de cuisson en vue de dessus comportant deux capteurs inductifs ;
• la figure 8 représente un foyer de cuisson en vue de dessus comportant trois capteurs inductifs.

The invention will be better understood and other features will become apparent from the description below and the accompanying drawings in which:

• FIG. 1 schematically represents an example of an electrical conductor forming the detection coil, which conductor is substantially wound in a plane;
• FIG. 2 diagrammatically represents another example of an electrical conductor forming the detection coil, conductive wound around a rectangular mandrel;
• Figure 3 shows a cooking hearth in top view with an inductive sensor;
• Figure 4 shows a cooking hearth in top view, smaller than the cooking chamber shown in Figure 3 and having an inductive sensor identical to that shown in Figure 3;
• FIG. 5 represents a top view of a cooking zone with two concentric and separate heating circuits, comprising an inductive sensor;
• Figure 6 shows a top view, a cooking hearth with two separate heating circuits, the focus being provided for heating oblong or round shaped containers;
• Figure 7 shows a cooking hearth in top view with two inductive sensors;
• Figure 8 shows a cooking hearth in top view with three inductive sensors.

For simplicity, we will designate in the different figures the same elements by the same topological references.

The principle of the invention is based on the use of an elongated inductive sensor. A preferred example of winding shape of the electrical conductor forming a coil used to make the sensor is given in FIG. 1. In this example, the winding is in a plane, that of FIG. 1. From a first end 1, an electrical conductor 2 for example wraps around a rectangle 3 whose large side is significantly larger than the short side. This first turn forms a first elongated turn. An example of a rectangle with a large side of about 50 mm and a small side of 5 mm can be given. After a first turn of the rectangle 3 performed, the driver winds several times around himself while keeping sufficient electrical insulation, to a second end 4, thus forming several elongated turns, this as many times as necessary for obtain a desired inductance value. By way of example, it may be mentioned that a coil comprising 11 turns around the Rectangle 3 having the dimensions given above gives a value of no-load inductance of the order of 10 μH.

Several methods can be envisaged for producing such a form of coil. A first method is to cut such a metal chemically and immobilize between two thin layers of electrical insulation, such as mica, to form a sensor. Mica has been proposed here for its good temperature resistance. Indeed, such a sensor can be subjected to maximum temperatures of the order of 500 ° C. In order to electrically connect the sensor, it is possible for example to provide at each of the ends 1 and 4 a wider metal range than the driver. 2. In order to maintain the above-mentioned temperatures, the connection can be made by means of electrical wiring wires electrically welded to the metal surfaces. Moreover, the metal which constitutes the coil is chosen for example for its good temperature qualities so that the value of the inductance varies as little as possible with the temperature. By way of example, mention may be made of an alloy of aluminum and chromium.

This method has the advantage of providing a very thin sensor, for example of the order of 100 microns which can be subsequently pressed against the insulating plate under which is for example the cooking chamber.

A second method for producing this sensor consists of producing, for example by molding in a support, a groove which extends in the shape that is to be given to the electrical conductor 2. It is then sufficient to deposit in this groove an electric wire bare. The isolation between turns is here obtained by the distance separating two grooves. The support may for example be made of vermiculite.

A third method for producing this sensor consists in producing on a support a serigraphy of conductive ink. The pattern of this screen printing is that which is described in FIG. 1. The material of the support must be sufficiently smooth and not very porous, such as for example magnesium cement, to allow screen printing.

It is understood that the three methods described above are not limiting. The characteristic of this first example of form coil is to make all the turns of the coil substantially coplanar.

In the case where the fireplace is placed under an insulating plate, for example glass-ceramic, the shape of the coil, described in Figure 1, allows to press the sensor against the insulating plate. This has the advantage of a sensor as close as possible to the container to be detected. Which improves his sensitivity. Another advantage is that the sensor will monitor the temperature of the container through the insulating plate. However, it is known that the resistance of an electrical conductor varies as a function of its temperature. It is possible to use this property to know the temperature of the container by measuring the resistance of the sensor. The driver can choose a material whose resistance varies greatly depending on the temperature such as a low-alloy copper alloy. If on the contrary, we do not wish to take advantage of this advantage, we will choose for the driver a material whose resistance varies little depending on the temperature such as a particular alloy of copper and nickel called constantan.

Another example of the winding form of the electrical conductor of a coil is given in FIG. 2. In this example, which is more conventional for a coil, an insulated electrical conductor is wound on one or more layers around an elongated section mandrel. . The elongate section is for example a rectangle of length 60 mm and width 15 mm. In Figure 2 is shown in strong line an electrical conductor 2 wound on the mandrel cited above but not shown. Here, for example, four turns are represented on a single layer. The electrical conductor 2 extends beyond both ends 1 and 4 of the winding. The two extensions 5, each beyond one of the ends 1 and 4 can be used for the electrical connection of the sensor.

Conventional insulations of electrical conductors hardly withstand temperatures of the order of 500 ° C. To overcome this drawback, it is therefore possible to provide protection for the winding by means of a thermal insulating material.

Figure 3 shows the mounting of a sensor in a radiant fire. It is understood that the radiant focus is given here by way of example: we can use such a sensor for any type of home, such as a halogen fireplace. The hearth described in FIG. 3 comprises a plate 10 shaped disk forming the bottom of the hearth. This plate 10 is usually made of thermal insulating material. The periphery of this plate 10 is raised by a border 11, edge also made of thermal insulating material. The upper part of this border 11 defines a plane which subsequently will preferably be in contact with the insulating plate which covers the hearth. On this plate 10 is disposed an electrical resistor 12 forming the heating element of the hearth. This resistor is connected to a power supply by means of two tongues 13. The hearth may also comprise, as is usual, a temperature limiter device 14 in order to prevent the internal temperature of the hearth from exceeding an upper limit. This limiter device comprises for example a rod 15 whose inner element expands with the increase in internal temperature of the hearth. When the expansion of this internal element reaches a given value, this entails the switching of a bimetallic switch located inside a cover 16 and, consequently, this makes it possible to cut off the power supply of the resistor 12. This switch can be connected in series between the resistor 12 and one of the terminals of the electric supply of the hearth.

According to the invention the hearth also comprises a mound 17 placed on the plate 10. This mound 17 has substantially a parallelepipedal shape, one end 18 is preferably located in the vicinity of the edge 11. The end 19 opposite 18 is substantially located in the center of the hearth, so that the mound 17 extends substantially in a radial direction of the hearth. This mound 17 serves to support a sensor 20 on which it is positioned so that the direction, in which the turns of the sensor 20 are elongate, is substantially coincidental with the radial direction of the focus on which the mound 17 is positioned. thickness of the mound 17 measured perpendicularly to the plate 10 is substantially equal to that of the edge 11 so that the surface of the sensor 20 opposite the surface with which it is in contact with the mound 17 is substantially in the same elevated plane of the border 11, so that the sensor 20 and the edge 11 are in contact with the insulating plate which preferably covers the fireplace in a range or a hob. It is possible to provide an imprint in the border to position the sensor 20. An end 21 of the sensor perpendicular to the radial direction is substantially positioned on the edge 11. The opposite end 22 is on a concentric circle 23 of the border 11. To facilitate the realization of the focus, the material of the mound 17 is advantageously the same as that of the border 11. auxiliary function of the mound 17 is to serve as support for the rod 15, this rod being then positioned between the mound 17 and the edge 11 for example in another radial direction than that on which the mound 17 extends.

When placing an electrically conductive container, for example metal, above the focus and concentrically with it, it may, depending on its diameter, partially or completely cover the sensor 20. A container of diameter greater than or equal to that of the focus will completely cover the sensor 20. A container of diameter between the diameter of the circle 23 and the diameter of the edge will partially cover the sensor 20 and a container of diameter less than the diameter of the circle 23 will not cover the sensor.

When an electric current is applied to the sensor, the frequency of which is for example 500 kHz, it is the presence of an electrically conductive container above the sensor 20 which makes the value of the inductance of the sensor 20 change. The use of such a frequency makes it possible to obtain a reduction in the value of the inductance of the sensor 20 for magnetic or non-magnetic containers. It will thus be possible to determine in the same way the presence of a container comprising an electrically conductive material such as, for example, aluminum alloy, stainless steel or ferritic steel. An example of expected value for the inductance of the sensor 20 is of the order of 8 μH when the sensor 20 is completely covered and of the order of 10 μH when it is not covered. A partial overlap gives a value of the intermediate inductance between the two extreme values mentioned above.

The knowledge of the diameter of a container covering the hearth can for example be used to modulate the electrical power delivered to the resistor 12. For example, it is possible to reduce the power when the diameter of the container is smaller than the diameter of the edge.

FIG. 4 shows the mounting of a sensor in a radiant heater where all the elements of the hearth described in FIG. 3 are found. On the other hand, the hearth described in FIG. 4 has a diameter smaller than that described in FIG. 3. As an example, a value of 220 mm can be given for the diameter of the hearth of figure 3 and 160 mm for the diameter of the hearth figure 4.

For example, it is possible to use on these two foci two identical sensors, one of the ends 21 of which is in the two FIGS. 3 and 4, positioned substantially on the edge 11. A container as shown in FIG. smaller than in a fireplace shown in Figure 3. This is well suited to a normal use of a cooking plate with several different sizes of fireplaces where we choose the size of the fireplace depending on the container that is to be heated. The use of the same sensor for households of different sizes makes it possible to standardize the sensor and an electronic processing device which is for example associated with it, which allows production cost savings.

As has been stated, the sensor 20 is formed of one or more elongated turns, that is to say of sufficient length to detect a container dimension in a range compatible with the dimensions of the focus. Advantageously, the length of the sensor 20 is at least three times greater than its width. For example, it is not desirable that the hearth shown in Figure 3, whose diameter is 220 mm, can heat a container whose diameter would be less than 160 mm. Thus, by using on this focal point a sensor 20 whose length is 50 mm, the sensor 20 will automatically detect any metallic container of diameter greater than 160 mm and the power control of the hearth can be done according to the information delivered by the sensor.

Figure 5 shows the mounting of a sensor in a radiant heater having two separate heating circuits. These two circuits are concentric. One, 30, is in the center: it is bounded at its periphery by a border 31. The other, 32, is concentric with the heating circuit 30 and is bounded at its periphery by a border 33. This fireplace also has tabs 13 power supply of the heating circuits and a temperature limiter device 14 itself comprising a cane 15 and a hood 16. This hearth further comprises a mound 34 carrying a sensor 20. This mound is, as for the foci shown in FIGS. 3 and 4, oriented on a substantially radial direction of the focus. One of its ends 19 is also located substantially in the center of the hearth. By against the other end 18 is, in Figure 5, located substantially between the borders 31 and 33. The sensor 20 is positioned on the mound 34, one of its ends 21 being disposed in the vicinity of the end 18 of the mound 34. The sensor 20 is thus substantially positioned astride the border 31; it makes it possible to know if a receptacle partially or completely covers the heating circuits 30 and 32. This makes it possible to electrically supply one and / or the other of the heating circuits 30 and 32 as a function of the dimension of the receptacle placed on the hearth .

Figure 6 shows, as in Figure 5, the mounting of a sensor in a radiant focus with two separate heating circuits. By cons, in Figure 6 the heating circuits are not concentric: one 40 is circular, limited by a border 41, the other 42 is positioned on one side of the heating circuit 40 so that the periphery of the grouping of two circuits 40 and 42 have an oblong shape. This type of fireplace is useful when you want to be able to heat on the same fireplace a circular container or an elongated container such as a fishmonger. In FIG. 6, as in FIG. 5, the sensor 20 is substantially positioned astride the edge 41 in its zone separating the heating circuits 40 and 42.

The foci shown in FIGS. 7 and 8 are similar to that shown in FIG. 3. On the other hand, two diametrically opposed sensors 20 have been placed on these foci in FIG. 7, and three sensors arranged at 120 ° in FIG. 8. In order to support the cane 15 of FIG. temperature limiter device, a small circular mound 50 was added to the center of the hearth. The advantage of these variants is to allow the measurement of the diameter of an off-center container. It is understood that these variants with two or three sensors can be transposed regardless of the size of the fireplace and regardless of the number of heating circuits.

Claims (13)

1. Cooker comprising a base (10), a heating element (12; 30, 32; 40, 42) disposed on the base (10) and at least one inductive sensor (20) capable of detecting the presence of an electrically conductive receptacle, the inductive sensor (20) having a coil comprising at least one turn, the cooker being characterised in that the turn is elongate in shape substantially in a radial direction of the cooker.
2. Cooker according to claim 1, characterised in that the turn is sufficiently elongate to detect a dimension of the said receptacle in a range of dimensions compatible with the dimensions of the cooker.
3. Cooker according to one of the preceding claims, characterised in that the length of the inductive sensor (20) is at a minimum three times greater than its width.
4. Cooker according to one of the preceding claims, characterised in that the turn forms a plane substantially parallel to the base (10) of the cooker.
5. Cooker according to one of the preceding claims, characterised in that all the turns of the coil are substantially coplanar.
6. Cooker according to claim 5, characterised in that it is placed under an insulating plate and in that the surface is pressed against the insulating plate.
7. Cooker according to any one of claims 4 to 6, characterised in that it comprises a rim (11; 31; 41) surrounding the cooker and in that the sensor (20) is placed on a hump (17, 34), the height of which is substantially close to that of the rim (11; 31; 41).
8. Cooker according to claim 7, characterised in that the material of the hump (17, 34) is the same as that of the rim (11; 31; 41).
9. Cooker according to one of the preceding claims, characterised in that the end of the sensor (20) perpendicular to the radial direction of the cooker is substantially positioned on a rim (11) surrounding the cooker.
10. Cooker according to one of the preceding claims, characterised in that the cooker comprises several heating circuits (30, 32; 40, 42) separated by a rim (31; 41) and in that the sensor (20) is situated straddling the rim (31; 41).
11. Cooker according to one of the preceding claims, characterised in that it comprises several sensors (20), to enable the diameter of an off-centre receptacle to be measured.
12. Cooker according to one of the preceding claims, characterised in that the winding of the sensor (20) is determined so as to obtain a value of the inductance offload of 10 µH.
13. Cooker according to one of the preceding claims, characterised in that it comprises means of measuring the electrical resistance of the sensor (20).

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