EP1906096B1 - Method for regulating the exhaust air volume flow from the cooking chamber of an oven - Google Patents

Description

The invention relates to a method for controlling the exhaust air volume flow from a cooking chamber of a baking oven, wherein the exhaust air volume flow is discharged through a blower to the environment whose speed is controlled in dependence of a gas concentration measured by a gas sensor in the cooking chamber of the oven.

It is known to equip ovens with cooling fans, on the one hand protect sensitive components, especially electronic controls and parts of the environment from overheating and on the other hand, free the cooking chamber of excessive steam. In addition, too high a vapor concentration in the cooking chamber and the escape of steam at leakage points should be prevented. Because due to different steam developments, caused by different baked goods, at comparable temperatures and because of the current state, in particular the oven wall dependent condensation of steam to cooler surfaces, the previously used control of the cooling fan due to the heating power of the furnace or its internal temperature is unsatisfactory.

A typ. Control method according to the prior art shows the font US-B1-6920874 ,

From the DE 38 04 678 A1 For example, a method for controlling the exhaust air flow from a cooking chamber is known. For this purpose, a suction fan is controlled as a function of a humidity measured during the cooking process in the vapor extraction channel.

Furthermore, it is from the DE 102 11 522 A1 It is known to set the speed of a fan for generating an air flow in the cooking chamber between zero and a maximum speed and thus to regulate the air extraction from the cooking chamber. To control the amount of exhaust air, the use of an oxygen sensor is proposed.

The DE 29 25 947 C2 moreover shows the general context that in a first time interval a measured value is determined and in a subsequent second time interval the manipulated variable determined therefrom is used.

In order to bring about, in particular, a regulation of the exhaust air volumetric flow which is coordinated with the cooking process and which takes place through the regulation of the rotational speed of the fan, is carried out according to EP 1 156 282 proposed to measure as control parameters at least one value with the pressure gradient between the interior of the furnace and its surroundings varying physical parameters. This ensures that the fan speed is adapted to the particular cooking process is regulated. In the embodiment of the prior art, for this purpose, the temperature is measured over a period of time, wherein a predetermined setpoint, when the temperature exceeds this setpoint, then the speed of the fan controls high, up to the point where the temperature falls below a predetermined setpoint again, until a change in temperature takes place, which is above the upper setpoint, in which case the control of the fan is increased again, etc.

In this known in the prior art control of the fan speed, this is dependent on the heating temperature in the oven, in particular by the blow-off or exhaust air volume flow according to the temperatures are controlled down, so that over the cooking process, a temperature profile is achieved, extending between a lower and an upper setpoint.

A disadvantage of this type of fan speed control, it is considered that a continuous speed control takes place, which binds particular computing capacity in the controller.

For optimal operation of a device, it is necessary that the fume extraction is operated on the cooking chamber so that Wrasen does not leave the cooking chamber by overpressure at unauthorized locations, supply air openings, leaks. Wrasen should leave the oven by means of a volumetric flow controllable suction only on the designated vent and there possibly located oxidation catalyst. For a minimum extraction is required. A sensor system, as described, gives the information on how much has to be extracted for this project. The less suctioned, the lower the energy losses of the cooking appliance. The required extraction capacity has hitherto generally been insufficiently adapted to the requirements. The realization that the fan speed is correlated with the oven temperature in the prior art according to the EP 1 156 282 described. It is assumed that at high temperature more vapors in the furnace chamber is formed than at lower, and therefore must be extracted more strongly. But there is no close link to the actual needs.

Thus, the problem arises for the invention to describe or provide an alternative method which has a close connection to the requirements and which manages without an additional opening in the cooking chamber.

The problem is solved by claim 1, advantageous developments emerge from the dependent claims.

According to the invention, a method is proposed, wherein the evaluation of the gas sensor signal and a special control of the Wrasenabsauggebläses on the pressure conditions in the cooking chamber can be closed to control the fan speed. Because during the cooking process, depending on the food to be cooked and the time of cooking, a certain amount of steam is produced. Vapors are gaseous or aerosol-like and are formed by the heat treatment or, more generally, by the energy input from the previously liquid and solid components of the food to be cooked. This extra. Gases try by the slight overpressure that they produce in the cooking chamber through all possible openings, eg. B. leaks to leave. A demand-adapted suction sucks just Wrasen through the exhaust opening just so strong that just no more vapors exits through all other intentional or random air openings of the oven, but dry kitchen room air is drawn into the oven. To determine how much to aspirate at a time, the strength of the suction is varied at intervals. If you start with low suction, the vapor signal does not change at first, as long as no dry kitchen room air is drawn through the supply air openings in the cooking chamber. For this purpose, first in a first time interval, the gas concentration is measured and determined in an electrical control of the oven from a speed for the fan. Only when it is extracted so strongly that dry kitchen room air is drawn into the cooking chamber, the concentration of fumes begins to decrease. The speed is then kept constant in a subsequent second time interval, wherein no gas concentration is measured in this time interval. Once the time interval has ended, another first time interval follows, in which, in particular, the gas concentration is measured, which then becomes significantly lower, so that the fan speed is then reduced in the subsequent second time interval, until a further gas concentration measurement during a renewed first time interval, which in turn then entails another second time interval which continues to be constant with the speed, for example, once again driven down.

The respective time intervals are repeated alternately during the cooking process, and the duration of the second interval is greater than that of the first, so that set via the cooking process, a fan control that generates an exhaust air volume flow, which generates or regulates a demand-adapted suction of Wrasengases. The degree of Wrasenabsaugung at the point at which just dry kitchen room air is drawn into the oven, is for this second time interval, z. B. of a few minutes, used as an orientation threshold. Depending on Desired in electronics an equation or a table is deposited, which realizes the actual fume extraction for the respective second time interval as a function of this threshold. This can z. On the recognized threshold, slightly below or above it. After the second time interval, the measurement and evaluation cycle is restarted for another first time interval to determine the required suction for the next second time interval, and so on.

If, for example, the exhaust air volume flow or the fan speed is plotted over time, the result is a minimum low threshold for the suction, for example, no suction, which is raised during the gas concentration measuring phase up to a fan speed sufficient to just kitchen room air in the oven to suck in, so that sets an upper threshold, then the fan speed is kept constant over the second time interval, which has a fixed period of time, until the first time interval begins, in which the gas concentration is measured again. This results in alternating threshold values, so that the demand-oriented extraction takes place over the time axis.

In principle, it is possible that during the first time interval, the entire speed range of the fan is traversed from low to maximum, but it is expedient to end the first time interval when the o.g. Threshold for the fan speed, so the orientation threshold for the second time interval has been reached.

In this case, the duration of the first time interval is selected to be so short that the gas concentration in the cooking chamber remains substantially constant for a constant exhaust air volume flow during the first time interval. In this case, the speed of the fan during the first time interval, starting from a low speed, in which only a part of the resulting Wrasens during cooking Wrasens is discharged by the fan to the environment, increases automatically or continuously in stages until the gas sensor measures a gas concentration , which is not equal to a measured at the beginning of the first time interval start-gas concentration, and which is automatically set depending on the last speed, the speed of the fan for the second time interval.

According to a particularly advantageous embodiment of the invention, the oxygen concentration in the cooking chamber is measured as a gas concentration by the gas sensor designed as an oxygen sensor. In a further development, the concentration of a gas generated by the cooking process in the cooking chamber as a gas concentration measured the gas sensor. If instead of Wrasens z. B. oxygen is measured in the cooking chamber, the concentration at low extraction also remains at a constant level, but then begins to rise at higher suction at the threshold, instead of sinking as in the case of vapor. The oxygen signal begins to increase in the moment in which due to the suction through the supply air vents no longer escape vapors, but oxygen is drawn from the kitchen room air. So the oxygen measurement is exactly the reverse, as with the vapor concentration or the moisture concentration.

Figur 1:

Eine erste Prinzipskizze zur erfindungsgemäßen Regelung des Abluftvolumenstroms aus einem Garraum eines Backofens;

Figur 2:

Eine nicht erfindungsgemäße Ausführung ähnlich der Figur 1 mit einer Klappensteuerung;

Figur 3:

Eine weitere nicht erfindungsgemäße Ausführung gemäß der Figur 2;

Figur 4:

Eine weitere erfindungsgemäße Ausführung gemäß der Figur 1 mit Anordnung des Sensors in der Abluftführung;

Figur 5:

Eine weitere Ausführung gemäß der Figur 4 mit Anordnung des Sensors hinter einem Abluftkatalysator;

Figur 6:

Beispiele für unterschiedliche Volumenstromverhältnisse aufgrund von Wrasenentstehung und Wrasenabsaugung und Zuluft;

Figur 7:

Zeigt den zeitlichen Verlauf der Feuchteanreicherung im Ofenraum bei einer Absaugung von 10 l/min und bei 20 l/min;

Figur 8:

Zeigt eine Grafik von Messzyklen über die Zeit zur Bestimmung der erforderlichen Gebläsedrehzahl.

An embodiment of the invention will become apparent from the following FIGS. 1 to 8 explained in more detail; show:

FIG. 1:

A first schematic diagram of the inventive regulation of the exhaust air volume flow from a cooking chamber of a baking oven;

FIG. 2:

A non-inventive embodiment similar to FIG. 1 with a flap control;

FIG. 3:

Another non-inventive embodiment according to the FIG. 2 ;

FIG. 4:

Another embodiment of the invention according to the FIG. 1 with arrangement of the sensor in the exhaust air duct;

FIG. 5:

Another embodiment according to the FIG. 4 with arrangement of the sensor behind an exhaust air catalyst;

FIG. 6:

Examples of different volume flow conditions due to vapor formation and vapor extraction and supply air;

FIG. 7:

Shows the time course of the moisture accumulation in the furnace chamber with a suction of 10 l / min and at 20 l / min;

FIG. 8:

Displays a graph of measurement cycles over time to determine the required fan speed.

The FIG. 1 shows in the schematic representation of the inventive control of an exhaust air volume flow 1 from a cooking chamber 2 of a baking oven 3 by a fan 4 to the environment. In this case, the rotational speed 5 is measured as a function of a gas sensor 6 Gas concentration in the cooking chamber 2 of the oven 3 controlled. For this purpose, an electronics 7 is provided between the blower 4 and the sensor 6, which processes the sensor signals for speed control. In this case, supply air 8 can enter the cooking chamber 2 due to leakage points.

The electronics 7 for changing the exhaust air volume flow 1 is prior art and can, for. B. the speed of the blower 4 or the control of the opening cross-section of a bypass damper 9 on the suction side of the fan 4, as shown in the FIG. 2 is shown, regulate. A supply air opening 8 may be a structurally provided opening, can be tightened by the dry kitchen room air into the cooking chamber 2 when it is sucked out of the cooking chamber 2. The supply air opening 8 may also be one or more air leaks 8 on the oven 3, which are almost always inevitable there, z. B. column in the door or lamp sealing area or on the bushings for radiators, Gargutthermometer or the like. This is especially true in the FIG. 3 shown.

Another variant shows the FIG. 4 in which the gas sensor 6 is arranged in particular in the exhaust air duct.

The FIG. 5 is different from the FIG. 4 only in that the gas sensor 6 is arranged in the flow direction behind an exhaust catalyst 10, or behind a heatable exhaust catalyst or a heated temperature-controlled exhaust catalyst.

In the method according to the invention is shown in FIG. 8 in a first time interval, such as in FIG. 6 is shown at low Wrasenanfall, the gas concentration (dashed line) and the rotational speed (solid line) measured for the fan 4 and automatically determined and set the fan speed for the subsequent second time interval in the electrical control 7 of the oven 3.

In the following second time interval, the thus determined speed of the fan 4 is kept substantially constant. Both time intervals, once with varying speed or at constant speed, repeat alternately during the cooking process, wherein the duration of the second time interval is greater than that of the first time interval. That's how it shows FIG. 8 a time course of Wrasenabgabe over time from the food (dashed line). This is about the same time course of the moisture delivery / time or the time course of (02-depletion) / time. The time course of the relevant fan speed in the graph is shown by a solid line. Two measuring cycles I and II are shown over the time axis, in which the blower speed required for the respective subsequent second time interval until the next measuring cycle is determined.

For the operation of the method, it is assumed that in each measuring cycle for determining the required fan speed, the time change of the vapor suction by changing the fan speed is (very) large, compared to the change in the Wrasens released from the food per time or the change in the time in Dependence of the generated vapor on decreasing oxygen concentration. This is usually true because cooking change processes typically are slow during cooking, while a fan speed can be driven relatively quickly through the first time interval.

Before the start of a measurement interval, ie a first time interval, a quantity of vapor / time from the food is now measured (one last time before the fan speed is changed). Now, as described above, it is assumed that this quantity of fume / time from the food and thus the gas concentration at a constant exhaust air volume flow remains constant with sufficient accuracy over the measuring cycle. The blower speed (solid line) is eg from min. after max. hazards. The fan speed, at which the vapor concentration or the moisture concentration begins to fall below the last measured value for the first time, or the oxygen concentration begins to rise above the last measured value before the measuring cycle for the first time, is a parameter for the required fan speed, represented in FIG FIG. 8 in measuring cycle I through the projection line. In order to recognize the first falling or rising safely, it makes sense to drive a little further on this point. This happens i. d .R. automatically when passing through the min.-max. Range for the fan speed and the exhaust air volume flow.

The desired blower speed is now determined with respect to the suction power found after the measuring cycle I for a follow-up time until a new value in a further measurement cycle, here II, is determined.

Depending on the project, the desired blower speed can be exactly at the point where the measured value of the vapor delivery / time first begins to drop below the value before the measuring cycle (desired extraction speed = parameter). But it can also be intentionally slightly higher (desired extraction speed> characteristic) or lower (desired extraction speed <characteristic), e.g. a stored percentage of the characteristic (for example + 10% or - 10%).

Due to this design, in particular computing capacity is saved, because only in the shorter first time interval, here measuring cycle I and II, the gas concentration is measured.

In this case, the duration of the first time interval is selected to be so short that the gas concentration in the cooking chamber 2 remains substantially constant for a constant exhaust air volume flow during the first time interval. The speed of the blower 4 is automatically increased continuously or in stages during the first time interval, starting from a low speed, low threshold at which only a portion of the steam generated during the cooking process is delivered by the blower 4 to the environment in the FIG. 8 2, until the gas sensor 6 measures a gas concentration which is not equal to a starting gas concentration measured at the beginning of the first time interval. Depending on the last speed, the speed of the fan 4 is automatically set for the second time interval, and kept constant over the second time interval. If the second time interval has expired, the measurement begins again with the first time interval in which, in particular, the gas concentration is measured.

It goes without saying that when the oxygen concentration in the cooking chamber 2 is measured by the gas sensor 6 formed as an oxygen sensor as a gas concentration, the curve is correspondingly different, because with increasing cooking time, the oxygen concentration in the furnace chamber 3 is lower. The oxygen signal begins to increase in the moment in which due to the suction through the supply air openings 8 no longer vapors escapes, but oxygen is drawn from the kitchen air. Then again starts the first time interval, in which in particular the oxygen concentration is measured. In an advantageous embodiment, the gas concentration of a gas generated by the cooking process in the cooking chamber 2 is measured by the gas sensor 6.

Examples of different volume flow conditions due to vapor formation and vapor extraction and supply air are in the FIG. 6 shown here, where the Figures 6a and 6b shows no dilution of the Wrasens by supply air 8, and in both cases, the same Wrasenkonzentration is measured. The FIG. 6c shows, however, a dilution of Wrasens by supply air 8, so that sets a lower Wrasenkonzentration or moisture concentration or a higher oxygen concentration in the cooking chamber 2.

The FIG. 7 shows the time course of the moisture accumulation in the furnace chamber with a suction of 10 l / min and at 20 l / min.

Claims (3)

1. Method for regulating the exhaust air volume flow (1) from a cooking chamber (2) of an oven (3), the exhaust air volume flow (1) being discharged to the surroundings by a fan (4), the speed (5) of which is controlled depending on a gas concentration in the cooking chamber (2) of the oven (3) measured by a gas sensor (6), characterised in that, in a first time interval, the gas concentration is measured and the speed (5) of the fan (4) is increased continuously or in stages during the first time interval, starting from a low speed at which only some of the fumes arising during cooking are discharged to the surroundings by the fan (4), until the gas sensor (6) measures a gas concentration that is different to a starting gas concentration measured at the beginning of the first time interval, and in that, depending on the final speed (5), the speed (5) of the fan (4) is automatically set in an electrical control means (7) for a second time interval hollowing the first time interval, the speed (5) of the fan (2) thus determined being kept substantially constant, the two time intervals being alternately repeated during the cooking process and the second time interval being longer than the first time interval, and the first time interval being selected to be short such that, in the event of a constant exhaust air volume flow (1), the gas concentration in the cooking chamber (2) remains substantially constant during the first time interval.
2. Method according to claim 1,
   characterised in that
   the oxygen concentration in the cooking chamber (2) is measured as the gas concentration by the gas sensor (6) configured as an oxygen sensor.
3. Method according to claim 1,
   characterised in that
   the concentration of a gas, produced by the cooking process, in the cooking chamber (2) is measured as the gas concentration by the gas sensor (6).

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