EP0354151B1 - Induction cooking plate having an indication device showing the power effectively supplied to the utensil - Google Patents

Description

The present invention relates to a power display device for an induction hob.

The application of induction heating to cooking food contained in a kitchen utensil, such as a pan, is known.

In general, an induction cooking appliance is constructed according to the block diagram of FIG. 1 and mainly comprises, in a box (a), a support plate (b) in the form of a non-metallic plate, preferably made of vitro-material. ceramic, a heating inductor (c) mounted in the immediate vicinity of the support plate (b) and creating an alternating magnetic field closing in a utensil (h) placed on the support plate (b).

A set of electrical and electronic components constitutes a supply circuit (d), a control circuit (e), a power circuit (f) for supplying the coil (c).

In addition, as with all cooking appliances of the plate or enclosure type, the user has at his disposal a control member (g), for example a slider or an adjustment knob, for varying the power.

Devices of the above type are already described in patent applications FR 72 27 277 and FR 76 20 285.

In these devices, the adjustment knob acts on the current absorbed by the power circuit (f), therefore on the power delivered to the inductor.

• . le diamètre de l'ustensile,
• . l'excentration de l'ustensile par rapport au centre de la bobine inductrice,
• . la nature du matériau de l'ustensile.

Unfortunately, in an induction hob, the power actually transmitted to the cookware is not directly related to the power delivered to the inductor, nor to the position of the adjustment knob (g). For the same position of the adjustment knob and the same power delivered to the inductor, the power transmitted to the utensil varies greatly depending on:

• . the diameter of the utensil,
• . the eccentricity of the utensil relative to the center of the induction coil,
• . the nature of the cookware material.

By way of illustration of this phenomenon, the same position 7 of the control member (g) (see FIG. 1) can correspond to 1500 w actually transmitted to a cast iron pan and to 800 w transmitted to a stainless steel pan.

Furthermore, US-A-4 438 311 describes a induction cooking plate which comprises, in addition to a control member, a power display device.

Unfortunately, this device displays the power delivered to the inductor by direct detection of the current in the circuit of the inductor, and this displayed power is unrelated to the power actually transmitted by the utensil to the food to be cooked as already explained previously. In addition, current detection in this part of the installation is difficult to achieve due to the high values of the intensities and frequencies.

The user of an induction hob cannot therefore, as he would with another hob, rely on the indication of the control member or on a display device of the type described in the document US -A-4 438 311 to find out the power actually transmitted to the utensil, which is also called power actually transmitted to the load in the following text.

The user must learn by trial and error to correct the indication of the control member for each of his personal utensils, there is no suitable method or display device.

• . un organe de commande ;
• . un ensemble de composants électroniques formant un circuit d'alimentation, un circuit de commande, un circuit de puissance pour alimenter ;
• . une bobine inductrice de chauffage d'un ustensile ;
• . un dispositif de visualisation de puissance,

caractérisée en ce que le dispositif de visualisation de puissance comporte des moyens pour indiquer sur un affichage une grandeur en rapport direct avec la puissance absorbée par l'ustensile.To overcome this drawback, the induction hob according to the invention includes a power display device. actually transmitted to the load. More particularly, it is a cooking plate comprising at least:

• . a control member;
• . a set of electronic components forming a supply circuit, a control circuit, a power circuit for supplying;
• . an induction coil for heating a utensil;
• . a power display device,

characterized in that the power display device comprises means for indicating on a display a quantity directly related to the power absorbed by the utensil.

• . un bloc d'acquisition du courant dont le signal d'entrée est le courant alternatif consommé sur le secteur et dont le signal continu de sortie est une image directe du signal d'entrée ;
• . un dispositif de mise en forme attaqué par le signal de sortie du bloc précédent et transformant la valeur analogique de ce signal en un signal exploitable par un afficheur ;
• . un afficheur recevant les signaux du dispositif de mise en forme.

According to the preferred embodiment described below, the display device is composed of at least:

• . a current acquisition block whose input signal is the alternating current consumed on the mains and whose continuous output signal is a direct image of the input signal;
• . a shaping device attacked by the output signal of the previous block and transforming the analog value of this signal into a signal usable by a display;
• . a display receiving the signals from the shaping device.

More specifically, the acquisition unit comprises a current transformer whose primary is a current loop placed immediately before the input of the rectifier of the supply circuit.

In addition to the display device, the hob may include a servo block receiving the output signals from the acquisition block, to provide the control electronics with a signal enabling the power to be restored to the utensil. the order instruction.

• figure 1 : schéma de principe d'un appareil de type connu.
• figure 2 : synoptique d'un circuit électronique comportant un dispositif de visualisation conforme à l'invention.
• figure 3 : schéma électronique montrant les principaux composants du dispositif de visualisation de la figure 2.

The invention will be better understood with the aid of the description below and the following appended figures:

• Figure 1: block diagram of a known type of device.
• Figure 2: block diagram of an electronic circuit comprising a display device according to the invention.
• Figure 3: electronic diagram showing the main components of the display device in Figure 2.

Reference will first be made to FIG. 2 which shows in the form of a block diagram, the main functions of an electronic circuit for an induction hob comprising a display device according to the invention.

• un ensemble de composants électroniques (50) comportant un circuit d'alimentation (51), un circuit de commande (52), un circuit de puissance (53),
• un dispositif de chauffage (60) comportant au moins une bobine inductrice (61) placée immédiatement sous un support non métallique (63),
• un ustensile (62) placé sur le support (63),
• un organe de commande (40).

First of all, we find the classic arrangement of Figure 1 with:

• a set of electronic components (50) comprising a supply circuit (51), a control circuit (52), a power circuit (53),
• a heating device (60) comprising at least one induction coil (61) placed immediately under a non-metallic support (63),
• a utensil (62) placed on the support (63),
• a control member (40).

The originality of the circuit lies in the addition of a display device (10, 20, 30) composed of an acquisition block (10), a shaping block (20), a display (30); the function of the display device is to indicate on the display (30) a quantity directly related to the power absorbed by the utensil (62).

By way of nonlimiting example, the applicant proposes a preferred embodiment of the invention in FIG. 3 and described below.

The input of the acquisition block (10) is constituted by a current loop forming the primary of an intensity transformer (11) (see Figures 2 and 3). The input signal of the acquisition block (10) is therefore the current consumed on the sector.

The secondary of the current transformer (11) is followed by a calibration assembly (12) and a detection assembly (13) mainly consisting of a divider bridge (14), a diode (15) and a capacitor (16). The output signal (V) of the transformer is therefore calibrated and then detected to provide a continuous output signal (Vi) from the acquisition block (10).

The output signal (Vi) of the block (10) drives a shaping block (20) which has the function of transforming the analog value of the current into an exploitable value for the display (30).

In the case of a display by seven-segment displays, not shown, the block (20) can mainly comprise an analog-digital converter associated with a seven-segment converter.

In the case of a ramp display as in Figure 3, the block (20) may include a divider bridge associated with a network of comparators and drivers of LED (light emitting diode).

Preferably the integrated circuit ensuring the formatting is of logarithmic type (manufacturer reference LM 3915 for example) so that the number of lit points is a logarithmic function of the signal (Vi), because it is more useful to have a plus large number of display points in the low power range.

In all cases, the discrete components performing the formatting function can be replaced by a microprocessor.

In addition, the circuit may include a servo block (70) the function of which is to supply the control electronics with a signal (Va) making it possible to restore to the utensil a power corresponding to the set point supplied by the member. regardless of the position, diameter and nature of the cookware material, within the limits of the characteristics of the power components. When the servo cannot adjust the power in the cookware to the setpoint (for example diameter too small), the power components being at their limits, the power restored to the cookware is reduced. In this case, the presence of the display device (10, 20, 30), to display the power actually supplied to the utensil takes on its full meaning.

According to the preferred nonlimiting embodiment shown in FIG. 3, the block (70) is composed of a comparator (71), the two inputs of which are respectively attacked on the one hand by the continuous signal (Vi) output from the block d acquisition (10), image of the power in the utensil, and on the other hand by a setpoint signal (c) from the control member (40).

The output signal (Va) of the comparator (71) constitutes the input signal of the control electronics (52), the details of which have not been shown, since they do not have any particular construction.

The electronic power supply (51) and power (53) circuits are of conventional types, and the variations of the power can be obtained in a known manner by power cutting by wave train and / or by modulation of the conduction time. .

Of course, variants exist, they can relate for example to the choice of the components, the realization of the circuits of the various functional blocks (10, 20, ...), the place where the image is measured of the power supplied to the utensil.

According to the applicant, the best choice for detecting this current in the load consists in placing the input of the intensity transformer where the current constitutes the most faithful image of the power actually supplied to the utensil, therefore immediately upstream from the power supply (51), and downstream of an input filter (81) and from the low voltage power supply (82) of the device. Direct detection of the current in the device (60) would be more difficult to achieve due to the high values of the intensities and frequencies in this part of the circuit, and would not give the image of the power supplied to the utensil.

In addition, according to the preferred embodiment of FIG. 3, the output signal (Vi) from the acquisition block (10), intended to drive the shaping signal (20), is also used to perform the In this case, the acquisition block plays two roles: in the production of the display and in the production of the control.

As a variant, the input signal of the servo could be detected by a block distinct from the block (10).

Another variant would also consist in performing the functions of one or more of the functional blocks (10, 20, 70, 52, ...) by a microprocessor.

Similarly, protection is not limited to the LED display mode (light-emitting diode), any other display mode, for example LCD (liquid crystal display) or VFD (fluorescent display) can be used, and is not limited to induction hobs with a single hearth.

Claims (9)

1. Induction cooking plate comprising at least:

   - a control member (40);

   - an arrangement of electronic components (50) forming a supply circuit (51), a control circuit (52), a power circuit (53) for supply;

   - an induction coil (61) for heating a utensil;

   - a device for displaying the output power,

   characterized in that the device for displaying the output power comprises a display (30) which indicates a value of the output power in direct relation to the power absorbed by the utensil (62), and in that the device for displaying the output power is composed of an acquisition block arranged in derivation from the supply input of the cooking plate, a processing device (20) and the display (30) in series, the acquisition block (10) comprising a current transformer (11) whose primary is a loop of the mains current (i) placed immediately ahead of the input of the rectifier of a supply circuit (51), and whose secondary is followed by a calibration (12) and detection (13) arrangement transforming the output signal (V) of the transformer in a d.c. signal (Vi) supplied to the input of the processing device (20), in order to display the output power effectively absorbed by the utensil.
2. Induction cooking plate according to claim 1, characterized in that the calibration and detection arrangement is principally composed of a divider bridge (14), a diode (15) and a capacitor (16).
3. Induction cooking plate according to any one of the preceding claims, characterized in that it furthermore comprises a follow-up control device (70) for regulating the power effectively transmitted to the utensil to the command value of the control member (40)
4. Induction cooking plate according to claims 1, 2, 3, characterized in that the d.c. signal (Vi) furnished at the output of the acquisition block (10) is directly supplied to the follow-up control device (70).
5. Induction cooking plate according to claim 4, characterized in that the follow-up control device (70) is composed of a comparator to the inputs of which the signal (Vi) and the command value signal (c) of the control device are supplied, and whose output signal (Va) is supplied to the control electronics.
6. Induction cooking plate according to any one of the preceding claims, characterized in that the display (30) is a display of the type having light emitting diodes and in that the processing device (20) comprises a converter driver of the logarithmic type.
7. Induction cooking plate according to any one of claims 1 to 6, characterized in that the display (30) is a display of the liquid crystal type and in that the processing device (20) comprises a converter driver of the logarithmic type.
8. Induction cooking plate according to any one of claims 1 to 6, characterized in that the display (30) is a display of the fluorescent type and in that the processing device (20) comprises a converter driver of the logarithmic type.
9. Induction cooking plate according to any one of the preceding claims, characterized in that the function of at least one of the functional blocks (10, 20, 70, 52...) is realized by a microprocessor.

Images