FR2633482A1 - Cooking vessel, method and device for thermal regulation of the heating of this vessel - Google Patents

Abstract

The cooking vessel comprises an electrical heating resistor 4, a sensor 7 for measuring the temperature of this vessel and means for thermal regulation of heating. It furthermore comprises plural heating functions having different maximum temperatures, means for selecting these functions, the thermal regulation means 14 being adapted to control the thermal regulation of heating for each of these functions. Use to allow the preparation of foods at various temperatures without the risk of exceeding the prescribed temperature.

Description

 The present invention relates to a cooking vessel having means for thermal regulation of the heating.

 The invention also relates to the thermal regulation method of this container, as well as the device for implementing this method.

 The cooking vessel may be a saucepan, a Dutch oven, a saute pan or the like.

 The various control devices commonly used in the industry implement a proportional, proportional derivative, proportional integral, derivative and self-adaptive control bearing only on a temperature band close to the maximum temperature or set temperature. Thus, the rise in temperature, from ambient temperature to the maximum temperature and maintenance at this temperature are performed according to predefined regimes. Thus, in the case of a cooking vessel such as an electric fryer, the heating is performed by supplying the heating resistors to full power. Therefore, the thermal load of the container is not taken into account, whether it contains a large quantity of liquid or a small quantity or is empty.

 No action has been taken to date to adapt the heating regime during the rise in temperature and maintaining it at the thermal load of the heater.

 Moreover, the known electric heating containers are generally adapted to a single function of food preparation.

 Thus, there are known heating containers which are specifically adapted for heating water to boiling, others which are adapted primarily for cooking or simmering food and still others for effecting food reheating.

 Therefore, users need a multiplicity of devices to perform all of the food preparations.

 The object of the present invention is to create a cooking vessel which is capable of producing most food preparations, which is easy to use and which ensures temperatures perfectly suited to each preparation without risk of exceeding them.

 According to the invention, this cooking vessel comprises several heating functions having different maximum temperatures, means for selecting these functions, the heating control means being adapted to control the thermal regulation of the heating for each of these functions.

 Thus, it suffices to select one of these functions and the thermal regulation will automatically be adapted to this function, which implies that the maximum temperature corresponding to this function will not be exceeded and will be maintained at this value for the designated duration.

In particular, the cooking vessel may include the following heating functions
- Bain-marie with a maximum temperature of about 650C and reduced heating power
- Warm up with a maximum temperature of about 850C
- Simmer with a maximum temperature of about 950C
- Boil with a maximum temperature of about loocc
- Fry with a maximum temperature of about 1700C.

 According to another aspect of the invention, the method of thermal regulation of the cooking vessel according to the invention is characterized in that the temperature is allowed to rise to a value substantially lower than a predetermined maximum temperature, then after stopping the heating, the temperature is allowed to rise by thermal inertia until the above-mentioned maximum temperature is substantially reached, the difference between this maximum temperature and the heating off temperature being determined as a function of the profile of the rise curve. temperature during the heating period.

 Thus, by calculating the difference between the heating off temperature and the maximum temperature, depending on the profile of the temperature rise curve, it is possible to stop the heating at a given temperature lower than the maximum temperature. whatever the thermal load of the device. After stopping the heating, the temperature rise continues with thermal inertia up to the maximum temperature. In other words, by analyzing the temperature rise curve, the method according to the invention makes it possible to predetermine the way in which the temperature rise curve will evolve by thermal inertia after stopping the heating.

 According to an advantageous version of the invention, the above-mentioned difference is determined as a function of the slope of the temperature rise curve and the heating is stopped when the measured temperature is slightly lower than the predetermined maximum temperature minus the aforementioned difference.

 The determination of this slope thus makes it possible to predict the deviation, that is to say how the temperature rise curve will evolve between the temperature at which the heating stops and the maximum temperature that it is desired to reach.

 According to a preferred version of the invention, during the rise in temperature, the temperature is measured at regular intervals and the average slope is calculated.

 For this purpose, the above-mentioned difference is continuously calculated as a function of the average slope.

 According to a third aspect of the invention, the device for carrying out the method according to the invention comprises a microprocessor programmed to record at regular intervals the temperature measured by the sensor, to calculate the slope and average of the curve of temperature rise, for calculating according to this slope the difference between the maximum temperature and the temperature at which the heating stops and for stopping the heating when the measured temperature is slightly lower than the maximum temperature minus the aforementioned difference .

 This microprocessor thus performs all the calculations and all the measurements defined in the aforementioned method.

 Other features and advantages of the invention will become apparent in the description below.

In the accompanying drawings given as non-limiting examples
FIG. 1 is a sectional view of a cooking vessel comprising a thermal regulation device according to the invention,
FIG. 2 is a diagram showing the evolution of the temperature of the heating resistor and the container as a function of time,
FIG. 3 is a diagram showing the evolution of the temperature of the container as well as that of the supply voltage of the heating resistor as a function of time,
FIG. 4 is a general flowchart of the operation of the device,
- Figure 5 is a diagram of the control panel of the container.

 In the embodiment of Figure 1, there is shown a cooking vessel 1 for containing a liquid or solid food to be heated, which rests removably on a heating base 2. The bottom 3 of the container 1 is in contact with a resistance of electric heater 4 supplied with electricity from a connector 5.

 The inner wall 6 of the base 2 adjacent to the bottom 3 of the reflector-shaped container.

 On the side of the base 2 is disposed a temperature sensor 7 bearing against the wall of the container 1 under the action of a spring 8. The rear of the sensor 7 is housed in a boftier 9 which contains various electronic components and in particular a power relay 10, a microswitch 11 detecting the presence of the container 1, function lights 12 and keys 13.

 The housing 9 also contains a microprocessor 14 of the 4-bit type, for example COP 422, programmed to perform the various functions that will be described later.

 FIG. 2 shows the evolution of the temperature T as a function of the time t of the heating element 4 (curve Ci) and of the wall of the container 1 (curve C :). Given the thermal inertia the temperature of the heating element 4 rises faster than that of the container 1.

 At the instant Tc of the cutoff of the electric supply current of the heating element 4, the temperature thereof drops rapidly, while that of the container 1 continues to progress from the cutoff temperature Tc. The temperature of the heating element 4 and the temperature of the container 1 tend towards an equal value TM.

 If Tx is the maximum or desired temperature that it is desired to achieve in the vessel 1, it will be seen that the heating of the heating element 4 must be stopped when the temperature of the vessel 1 reaches the value Tc. It is therefore necessary to predetermine the difference E between the temperatures Tx and Tc.

 Tests and calculations have shown that the difference E is even greater than the rate of rise in temperature of the container 1 is fast. The value of the difference E is a function of the slope Pt of the curve C2 of temperature rise of the container 1.

Indeed, at the temperature Tc heating cutoff, the equation of thermal equilibrium is written
the (4T - E) = Ic.E
where IR = inertia of the resistance
Ic = inertia of the IR container
either: E = tT. ~~~~~~ IR +1
The heat transfer condition is written
P = KS AT
where P is the heating power,
S the heat exchange surface and
K is a constant.

The heat balance equation is written
P = Pt. (IR + Ic)
1R
hence E = ~~~~~. Pt
KS
the, K and S being constants, the distance E is well proportional to the slope of the curve C: measured in temperature of the container 1. This linear law is valid for the first approach. However, to calculate E more precisely, it is better to use a parabolic law.

 According to the invention, the microprocessor 14 calculates, as a function of time and the temperature measured by the sensor 7, the slope Pt of the curve C2 and determines from this slope the value of the difference E.

 The microprocessor 14 controls the stopping of the heating, that is to say the interruption of the power supply of the resistor 4 when the temperature measured by the sensor 7 is slightly lower than the maximum temperature Tn predetermined minus the difference E According to the invention, it is indeed preferable to cut the heating to a temperature slightly lower than that theoretically necessary to avoid any risk of exceeding the temperature Tw.

 Preferably, after stabilization of the temperature measured by the sensor 7, the device according to the invention measures the temperature of the container regularly every four seconds (see Figure 3).

The temperature measured by the sensor 7 is corrected according to a relationship of the type A + B Pt, in which
Pt is the average slope calculated at the moment of the measurement, A is a correction coefficient taking into account the sensor / wall thermal brake of the container 1 and B is a correction coefficient taking into account the inertia of the system.

During the start of heating, the temperature rise curve is curved and often irregular. To compensate for this state of affairs, the slope Pt and the distance E are calculated for instants 0 - 1 then 2 - 0, then 3 - 0 and so on until 9 - 0. The average is then represented by the AB right (see Figure 3). To avoid being influenced by the first measurements, the following average is calculated on the moments 10 - 6, ie the right
CD, then on the instants he - 6; 12 - 6; 13 - 6 and so on.

Each temperature measurement is followed by the calculation of the slope Pt and the calculation of the difference E according to the formula
Ki Pt + h Pt
In this formula, and for the type of heating vessel previously described, R1 and Ko are the coefficients of the parabolic function. To be certain that the setpoint temperature TM is not exceeded, the calculation of the difference E is slightly increased. The comparison is established as follows: as soon as the corrected current temperature of the TC + E sensor is higher than the set temperature Tn, the supply of the heating element 4 is cut off. At the moment when the heating is cut off (point J on the diagram), the slope at the PtC cut-off is kept in memory. Taking into account the precautions taken (correction of the reading of the sensor + increase of the slope), the set temperature Tz does not will probably not be reached. One or more heat-up will be necessary. These warmups are made with the parameters kept in memory at the time of the first cut.

We will now explain how the temperature is maintained after the first cut of the power supply.

 The temperature measurements continue to be performed every 4 seconds as well as the slope and the difference E to be calculated. In this holding phase, the slope is calculated with the last 10 temperatures according to the relation e (TC) - 6 (TC - 10) / 9x4. The gap E itself is always calculated in the same way (see above). When the corrected current temperature of the TC + sensor the difference E is 10 ° lower than the set temperature TM, a certain amount of current is sent into the heating element 4.

The heating time (between points R and L of FIG. 3) is calculated according to the relation
TM - (TC + E). K
pTC
where TM is the predetermined maximum setpoint temperature,
TC is the heating cutoff temperature,
E is the calculated difference,
Ptc the slope at the cutoff of the heating,
K is a coefficient between 0.5 and 1 and
generally equal to 0.8.

 After expiry of the aforementioned heating period, the heating is switched off for a fixed duration equal to 15 seconds (delay between the points L and M of FIG. 3).

 This phase of maintaining the temperature near the TM value is illustrated by the flowchart of FIG. 4.

 The culinary heating vessel shown in FIG. 1 comprises several heating functions Fi, F2, F3, Fs, Fs having different maximum temperatures, means for selecting these functions, the microprocessor (14) being adapted to control the thermal regulation of the heating. for each of these functions.

In the example shown, this heating container comprises the following functions
- Bain-marie with a maximum temperature of about 650C and reduced power
- Warm up with a maximum temperature of about 850C
- Simmer with a maximum temperature of about 950C
- Boil with a maximum temperature of about 1000C
- Fry with a maximum temperature of about 1700C.

For this purpose, the control panel 15 (see FIG. 5) of the heating vessel comprises five keys F1, F2, F3,
F4, Fs intended to be actuated by the user and for selecting the various heating functions mentioned above.

 The control panel 15 also has two - and + keys for programming the operating times in the different heating functions.

 We will now detail each of these heating functions.

BOILING FUNCTION
In order to mount a liquid at the boiling temperature, it is necessary to provide the calories necessary for its rise in temperature (specific heat), to compensate for the thermal losses of the heating means (radiation and conduction of the heating element) and to compensate for thermal losses. of the container. Practice shows that the total heat loss is substantially constant regardless of the amount of liquid contained in the container.

 To maintain a boiling liquid, it suffices to compensate for the thermal losses of the system and to provide the necessary calories for a minimum evaporation. If there are excess calories, the bubbling is tumultuous and the evaporation important.

For the boiling function (whatever the nature of the liquid: water, soup, milk, cooking pasta or rice ... and its quantity) the virtual set temperature
TM is 970C. The difference E will be calculated to reach this temperature. But as soon as the temperature TC = 900C is reached, the supply of the heating element 4 is at 10% of its nominal power (3 seconds on a 30-second basis).

Two cases can then arise
a) a lid caps the container: the temperature curve curves slightly. The temperature curve substantially tangents the virtual temperature of 970C and is self-stabilizing at a temperature of about 1000C depending on the type of liquid (water, salt water, milk, etc.). Liquid evaporation stage feed continues at 10% of rated power (3 "live on a 30" timebase)
b) there is no lid: the temperature curve is curved frankly and falls because the losses are large; the temperature whose gap would reach 970C is not reached. The slope becomes negative, the power is taken to a value of 50% of the nominal power, which allows the liquid to reach its boiling point.

TIEDIR (OR BAIN-MARIE) FUNCTION
The energy requirement, according to "bain-marie" is
- a slow rise in temperature,
- regulation at 650C (maximum temperature set point TM).

 To do this, the power supplied to the resistor 4 is one-sixth of its nominal power (5 "under voltage on a time base of 30").

 If the container contains a certain amount of liquid, the temperature after one minute of heating, will have reached a value of 50C (called critical value). If this critical temperature is exceeded, it proves that the thermal transmission "resistance 4 + bottom of the container + product to be heated + container wall + sensor" is doing well: it is probably a small amount of liquid (a sauce for example). The regime at one-sixth of the nominal power is maintained.

 If the temperature is not reached, it is probably a large amount of liquid (soup to warm for example). The heating regime then changes to its nominal power.

 In both cases the target temperature TM is 650C.

SECURITY IN FUNCTION FRIRE
To fry a food supposes that the culinary preparation is very little watery, and that the container can reach the temperature of 1700C (cooking of meat, fries, confection of caramel, etc).

 However, it may happen that the frying function is inadvertently programmed for a liquid with a boiling point close to 1000 ° C.

 After one minute of heating, if it is dry cooking (grilled or sautéed meat, caramel ...), the temperature must have exceeded a critical temperature of 200C. If this is not the case, the heating mode automatically switches to "simmering" (maximum temperature 950C).

EVAPORATION SAFETY (DISCHARGE OF LOAD)
When using the "Boil" function, complete evaporation of the boiling liquid causes a rise in temperature of the container.

 When the temperature exceeds 1100C, the supply of the heating element 4 is cut off.

STABILIZATION OF THE TEMPERATURE SENSOR
A hot container may be placed on the heating resistor 4; conversely, the sensor 7, heated by the radiation emitted by the resistor, can be applied to a cold container. In all cases of use, the temperatures of the sensor and the container are not identical.

 The first phase of thermal regulation consists of calculating the successive slopes and putting the resistor under tension only if the instantaneous slope averaged according to the process described above is less than a certain value such as 0.1 for example.

 The various heating functions of the heating container according to the invention are thus entirely controlled by the microprocessor. The user only has to select one of the functions as well as the operating time.

 In all cases, the maximum temperature will not be exceeded regardless of the amount of product to be heated inside the container.

 In addition to the above, the method just described can also be adapted to diagnose that the target temperature is reached.

 For this purpose, it is necessary to locate the instant when the programmed setpoint temperature, using the selected function key, will be reached. This is the moment from which the hold time at the programmed temperature will be counted.

Two cases arise
A) "boil" function
In this case, from about 900C, the supply of the heating resistor is cycled to obtain an average power of 50 or 10% of the nominal power.

 Given the dispersion on the temperature measurement, the only knowledge of it does not allow to know precisely the instant of beginning of boiling.

 We use the physical definition of a boiling point, which is to have a perfectly stabilized temperature.

This is the next double test
- minimum temperature reached (970C for example)
- practically zero slope (<0,050C / s for example).

 When these two conditions are satisfied, the set temperature is deemed reached, and this time is stored for time management.

B) Other functions
In this case, the set temperature is deemed to be reached when the temperature TC is within a few degrees of the setpoint (to within 50 ° C, for example).

example: - Programmed F2 function (850C)
- at 800C, the deposit will be considered
reached, and this moment will be memorized.

 The programming of the cooking cycles is as indicated below depending on whether or not there is a warming provided for the programmed function.

A) With warm keeping
Once the target time has been reached, the temperature programmed by the selected function is maintained during a "dwell time".

 If a time has been programmed on a timer, the duration of this step is equal to this time.

Otherwise it is a default time that is taken into account. This time, preprogrammed by the chosen function, depends on it, for example selected function ........: default time in mn

<tb> Fl <SEP> F <SEP> 2F3F4F5 <SEP>
<tb> 60 <SEP> 6160 <SEP> 30 <SEP> 15 <SEP>
<Tb>
When the duration of this maintenance stage has elapsed, the cycle goes into warm keeping (which corresponds to the function F1) during a predetermined time, 90 min for example.

 This warming time having elapsed, the cooking cycle is finished.

B) without keeping warm
The process is identical to the previous one, but the end of the cooking cycle occurs as soon as the maintenance stage is finished.

 Of course, the invention is not limited to the embodiment that has just been described and can be made to it many modifications without departing from the scope of the invention.

Claims (21)

 1. Culinary vessel comprising an electric heating resistor (4), a sensor (7) for measuring the temperature of this receptacle and means for thermal regulation of the heating, characterized in that it comprises several functions (Fs, F2, Fs , F4, Fs) having different maximum temperatures, means for selecting these functions, the thermal control means (14) being adapted to control the thermal regulation of the heating for each of these functions.  2. Cooking vessel according to claim 1, characterized in that it comprises the following heating functions  - Bain-marie with a maximum temperature of about 650C and reduced heating power  - Warm up with a maximum temperature of about 850C  - Simmer with a maximum temperature of about 950C  - Boil with a maximum temperature of about 1000C  - Fry with a maximum temperature of about 1700C.  3. Cooking vessel according to one of claims 1 or 2, characterized in that it further comprises means for programming the operating times.  Container according to claim 3, characterized in that the means for selecting the different heating functions and for programming the operating times comprise keys (F 1, F 1, F 3, F4, Fs) to be operated by the user.  5. Container according to one of claims 2 to 4, characterized in that for the function "boil" means are provided to control a reduction of the heating power when a temperature of about 900C is reached.  6. Container according to claim 5, characterized in that it comprises means for controlling an increase in the heating power, when the container (1) is devoid of cover.  Container according to one of Claims 2 to 4, characterized in that for the water-bath function means are provided for maintaining the heating power at a reduced value if a set temperature is reached after a predetermined time and to control a higher heating power if this temperature is not reached after this period.  Container according to one of Claims 2 to 4, characterized in that for the function "frying" means are provided for automatically controlling the selection of the "simmering" function when a predetermined critical temperature is not reached. after a predetermined time.  9. Container according to one of claims 2 to 4, characterized in that for the function "boil" means are provided to automatically control the shutdown of the heater when the measured temperature exceeds 1100C.  Container according to one of claims 1 to 9, characterized in that the regulating device further comprises means for controlling the start of heating only when the calculated average slope is less than about 0.1.  11. A method of thermal regulation of the cooking vessel according to one of claims 1 to 10, characterized in that the temperature is allowed to rise to a value significantly lower than a predetermined maximum temperature (TM), then after stopping the heating, the temperature is allowed to rise by thermal inertia until the above-mentioned maximum temperature (TM) is substantially reached, the difference (E) between this maximum temperature and the temperature (TC) for stopping the heating being determined by depending on the profile of the temperature rise curve during the heating period.  12. Process according to claim 11, characterized in that the above-mentioned difference (E) is determined as a function of the slope of the temperature rise curve and the heating is stopped when the measured temperature is slightly lower than the temperature. predetermined maximum (TM) minus the difference (E) above.  13. The method of claim 12, characterized in that during the rise in temperature the temperature is measured at regular intervals and the average slope is calculated.  14. The method of claim 13, characterized in that continuously calculates the difference (E) above according to the average slope.  15. Method according to one of claims 12 to 14, characterized in that the difference (E) calculated is a function of the slope.  16. The method according to claim 15, characterized in that said function is determined experimentally.  17. Method according to one of claims 14 to 16, characterized in that to calculate the difference (E) only the average slope is taken into consideration.  18. A method according to one of claims 13 to 17, characterized in that after stopping the heating continues to determine at regular intervals the temperature, the slope and the gap (E) and is restarted on heating when the measured temperature plus the difference (E) is about 10C lower than the predetermined maximum temperature (TM).  19. Process according to claim 18, characterized in that the heating is restarted for a duration calculated according to the relation  TM - (TC + E). K  pTC  where TM is the predetermined maximum temperature,  TC the heating cutoff temperature,  E the calculated difference,  Ptc the slope at the heating cutoff, and  K is a coefficient of between 0.5 and 1,  which has been memorized after the first cut.  20. Process according to claim 19, characterized in that after expiry of the aforementioned heating period, the heating is cut off for a fixed period.  21. Device for implementing the thermal control method according to one of claims II to 20, comprising electric heating means (4), a sensor (7) for measuring the temperature and means for cutting the temperature. power supply, characterized in that it comprises a microprocessor (14) programmed to record at regular intervals the temperature measured by the sensor (7), to calculate the instantaneous and average slope of the temperature rise curve, to calculate in function of this slope the difference (E) between the maximum temperature (TM) and the temperature (TC) of heating stop and to control the stopping of the heating when the measured temperature is slightly lower than the maximum temperature (TM) less the difference (E) above.