The present invention will be explained, based on exemplary embodiments, in more detail with reference to the following
The present invention proposes a method in which, in order to control the fan speed, the pressure conditions in the cooking chamber can be inferred from analysis of a gas sensor signal and a special control of the cooking vapor exhaust fan. This is possible because cooking vapors are produced in different specific quantities, depending on the food to be cooked and on the point in time in the cooking process. Cooking vapors are in the form of a gas or aerosol and are produced by heat treatment, or more generally, by energy supply from the previously liquid and solid components of the food being cooked. These additional gases produce a slight positive pressure in the cooking chamber, as a result of which they tend to exit through any openings that may be available, such as leaks. If the extraction is adjusted to demand, the cooking vapors are extracted through the exhaust air port at a rate which, on the one hand, is just sufficient to prevent cooking vapors from exiting through any other desired or unintended air openings of the oven, and which, on the other hand, causes dry ambient kitchen air to be drawn into the cooking chamber. In order to determine the extraction rate required at a particular point in time, the extraction rate is varied in intervals. When starting at a low extraction rate, the cooking vapor signal does not change as long as no dry ambient kitchen air is drawn into the cooking chamber through the air intake openings. To this end, initially, the gas concentration is measured in a first time interval, whereupon a speed for the fan is determined therefrom in an electrical controller of the baking oven. The concentration of cooking vapors does not begin to decrease until extraction takes place at a rate sufficient to cause dry ambient kitchen air to be drawn into the cooking chamber. Then, the speed is maintained constant during a subsequent second time interval, in which no gas concentration is measured. When said time interval ends, a further first time interval follows in which the gas concentration is measured. It may then be significantly lower, so that the fan speed will be reduced in the following second time interval, until a further gas concentration measurement is made during a new first time interval. Subsequently this new first time interval will be followed by a further second time interval during which the fan will proceed at a constant, possibly further reduced speed.
The respective time intervals are alternatingly repeated during the cooking process, the second time interval being longer than the first one, so that the fan control occurring during the cooking process produces an exhaust flow which causes the cooking vapors to be extracted in a manner that is adjusted to demand. The degree of vapor extraction at a point which is just sufficient to cause dry ambient kitchen air to be drawn into the cooking chamber is used as an orientation threshold for this second time interval, which may have a duration of several minutes. Optionally, the electronics may have stored therein an equation or a table which implements the actual cooking vapor extraction for the respective second time interval as a function of said threshold. This may be, for example, at the identified threshold, or slightly below or above it. After the second time interval, the measurement and analysis cycle is restarted for a further first time interval in order to determine the extraction rate required for the next second time interval, and so on.
When plotting, for example, the exhaust flow rate and/or the fan speed, against time, then a minimum low threshold value is obtained for the extraction, zero extraction also being possible, which is raised during the gas concentration measurement phase until a fan speed is reached which is just sufficient to cause ambient kitchen air to be drawn into the cooking chamber, which results in an upper threshold at which the fan speed is then maintained constant during the second time interval, said second time interval having a defined duration, until a new first time interval begins in which the gas concentration is measured. This results in alternating threshold values, so that the extraction takes place over time in a manner that is adjusted to demand.
In principle, it is possible to vary the fan speed through the entire fan speed range from low to maximum during the first time interval. However, it is convenient to terminate the first time interval when the above-mentioned threshold value for the fan speed, i.e., the orientation threshold for the second time interval, is reached.
The duration of the first time interval is selected to be so short that the gas concentration in the cooking chamber remains substantially constant during the first time interval, given a constant exhaust flow rate. During the first time interval, the fan speed is automatically increased in a continuous or stepwise manner, starting from a low speed at which only part of the vapors produced during the cooking process is discharged by the fan to the environment, until the gas sensor measures a gas concentration which is different from an initial gas concentration measured at the beginning of the first time interval, and the fan speed is automatically set for the second time interval as a function of the last speed.
In one embodiment of the present invention, the gas sensor is in the form of an oxygen sensor which measures, as a gas concentration, the oxygen concentration in the cooking chamber. In a refinement, the gas sensor measures, as a gas concentration, the concentration of a gas produced by the cooking process in the cooking chamber. If, for example, oxygen is measured in the cooking chamber in place of the cooking vapors, the concentration will also initially remain at a constant level, given a low extraction rate. However, at a higher extraction rate at the threshold, it will begin to increase and not decrease as would be the case with cooking vapors. The oxygen signal begins to increase once a point is reached where, due to the extraction, there are no more cooking vapors escaping through the air intake openings, but oxygen is drawn in from the ambient kitchen air. That is, what happens during oxygen measurement is just the opposite of what occurs when measuring the concentration of cooking vapors or of humidity.
Electronics 7 for varying the rate of exhaust flow 1 may be used, for example, to control the speed of fan 4 or the cross sectional area of the opening of a bypass damper 9 on the intake side of fan 4, as is shown in
Another variant is shown in
In accordance with the method of the present invention illustrated in
In the subsequent second time interval, the so-determined speed of fan 4 is maintained substantially constant. Both time intervals, one with varying speed and one with constant speed, are alternatingly repeated during the cooking process, the second time interval being longer than the first time interval. Thus,
For the functioning of the method, it is assumed that in each measurement cycle for determining the required fan speed, the variation with time of the vapor extraction rate caused by the change in the fan speed is large compared to the variation in the amount of cooking vapors emitted from the food per unit time, or compared to the variation in the oxygen concentration which decreases per unit time as a function of the cooking vapors produced. This assumption is generally satisfied since processes of alteration in the food during cooking typically occur slowly, while the fan speed can be changed relatively rapidly during the first time interval.
Before a measurement interval, i.e., a first time interval, starts, an amount per unit time of cooking vapors released from the food is measured (for the last time before the fan speed is changed). As described above, it is assumed that this amount per unit time of cooking vapors from the food, and thus the gas concentration, remains sufficiently constant during the measurement cycle, given a constant exhaust flow rate. The fan speed (solid line) is changed, for example, from minimum to maximum. The fan speed at which, for the first time, the concentration of cooking vapors, or the concentration of humidity, begins to decrease below the last measured value, or at which, for the first time, the oxygen concentration begins to increase above the last measured value before the measurement cycle, is a reference value for the required fan speed, illustrated in
After measurement cycle I, the desired fan speed is then fixed for a subsequent period with respect to the so-determined extraction power until a new value is determined in a further measurement cycle, here measurement cycle II.
Depending on the purpose, the desired fan speed may be exactly at the point where, for the first time, the measured value of the emission of cooking vapors per unit time begins to decrease below the value before the measurement cycle (desired fan speed=reference value). However, it may also be selected to be slightly higher (desired fan speed>reference value) or lower (desired fan speed<reference value), such difference being, for example, a stored percentage of the reference value (for example, +10% or −10%).
This design especially saves computing power because the gas concentration is only measured in the shorter first time interval, here measurement cycles I and II.
The duration of the first time interval is selected to be so short that the gas concentration in cooking chamber 2 remains substantially constant during the first time interval, given a constant exhaust flow rate. As can be appreciated in
It is understood that when gas sensor 6 is in the form of an oxygen sensor which measures, as a gas concentration, the oxygen concentration in cooking chamber 2, a different curve will be obtained because the oxygen concentration in oven chamber 3 decreases as the cooking process proceeds. The oxygen signal begins to increase once a point is reached where, due to the extraction, there are no more cooking vapors escaping through air intake openings 8, but oxygen is drawn in from the ambient kitchen air. Then, a new first time interval begins in which, in particular, the gas concentration is measured. In an advantageous refinement, gas sensor 6 measures the gas concentration of a gas produced by the cooking process in cooking chamber 2.
Number | Date | Country | Kind |
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10 2006 043 933.3 | Sep 2006 | DE | national |