EP1611396B1 - Method for operating a baking oven - Google Patents

Abstract

A baking oven and a method of operating the baking oven. The baking oven including a thermally insulated muffle, a circulating fan arranged inside of a fan compartment in the muffle, a least one heating device outside of the fan compartment and adjacent the walls of the muffle. The baking oven further including a control device for switching the heating device and circulating fan off and on, in accordance with a pre-determined temperature/time profile during the operation of the baking oven. The operation of the baking oven compensates for the difference in temperature between a temperature sensor adjacent a wall of the baking oven and the center of the muffle.

Description

The invention relates to a method for operating a baking oven and to an oven for carrying out this method, provided with a closable, thermally insulated oven muffle, arranged with a circulating air blower disposed within a fan room of the oven muffle with at least one near the muffle walls outside the fan room thermal heating element and with a control device, with which the at least one heating element and the circulating air blower can be switched on and off in accordance with a predetermined temperature / time profile during the oven operation consisting of the heating phase and the heating phase.

An oven with arranged in a rear fan room of the oven muffle circulating air blower and arranged outside of this fan room thermal heating elements in the form of a top heat and a bottom heat is known ( DE 19640237A1 ).

There are different modes of such ovens are known in which for heating the oven from room temperature to a selectable cooking temperature, a so-called Anheizphase is performed, followed by reaching a selected target temperature approximate oven temperature by means of a control switch to a Fortheizphase. To shorten the total duration of the oven operation is often sought to keep the Anheizphase as short as possible. Thus, in a known method for cooking in a hot air device ( DE 3510680C2 ) a Fortheizphase with several Zwischenaufheizphasen leading heating phase carried out with constantly switched circulating air fan and with permanently switched heating elements to bring as much heat energy in the shortest possible time in the oven. Thereafter, in the period between the individual Zwischenaufheizphasen the circulating air blower is switched on cyclically with the heating off.

Similar methods are known from US-B-63882351 and the EP-A-0 981 961 known.

Experiments have now shown that it can be seen for the baking result, with a negative course in particular of heating element patterns, eg. B. on flat baked goods, also due to already taking place during the Anheizphase biochemical processes in the food is essential that at the time of switching from Anheizphase in the Fortheizphase in the treatment center of the oven, so in its central region one of the set temperature setpoint at least approximately treatment temperature (Fortheiztemperatur) is achieved. This is not optimal with the known ovens achievable, in particular due to the fact that due to increasingly good thermal insulation of ovens natural convection in the oven no longer takes place to any significant extent and that due to the usually eccentric arrangement of the temperature sensor of the controller a not insignificant temperature difference between the measured at the temperature sensor and the function of Control device formative temperature and the baking result formative temperature in the center of the oven is present. Especially in so-called conventional modes with heating of the circulating air exclusively by a top heat and / or a bottom heat, ie by heating elements outside the fan room, this temperature difference is so great that at the end of the heating phase and thus at the beginning of the actual control phase during the Fortheizphase very unfavorable conditions prevail for the beginning of the Fortheizphase.

The present invention is therefore the object of a method for operating a baking oven of the type mentioned in such a way that with simple tax technical means at the end of the heating phase, ie when switching off the heating elements or at the beginning of Fortheiz-control phase in the center of the oven muffle the set target temperature is maintained as close as possible to the cooking temperature.

This object is achieved according to the invention in a method of the type described above in that during the Anheizphase the at least one heating element is preferably continuously connected and that the circulating air fan according to one of the predetermined shutdown temperature of the heating element at the end of the heating phase at least partially dependent time profile temporarily turned on becomes. Preferably, this single or multiple connection of the circulating air blower is only briefly z. B. with a turn-on of about 30 seconds.

By the method according to the invention, a convection of the initially spatially only more or less unevenly distributed heated convection air is forced during the heating phase in the oven muffle, which leads to a more uniform heat distribution in the muffle room. This results in a, if any, then very small temperature difference between the measured at the temperature sensor, ie outside the muffle center temperature and the temperature in the center of the oven muffle, ie in the vicinity of the food to be treated. A commonly observed overshoot of the Temperature in consequence of the temperature sensor, which is usually not arranged in the direct radiation range of the heating elements (eg top heat, bottom heat), beyond the selected setpoint temperature is therefore substantially reduced or prevented. The consequence is that within the Fortheizphase takes place very quickly an adjustment of the current temperature in the muffle center to the ideal temperature profile.

According to an advantageous embodiment of the method according to the invention, the circulation fan is turned on at least once to one of the height of the shutdown temperature and / or the operating mode and arrangement of the at least one heating element and at least one more time to one by the temperature gradient of the respective Anheizprofils during the Anheizphase. Of course, there are also advantages in separate application of the aforementioned process characteristics. In particular, by the dependence of the time of the second or further temporary connection of the circulating air blower of the aforementioned temperature gradient is taken into account the fact that a temperature increase in the lower temperature range is faster than in a high temperature range. The time profile during the heating phase is advantageously brought into dependence on the operating mode of the oven, z. B. with one or more heating elements, and of the arrangement of the heating element or elements relative to the temperature sensor.

The invention will be explained with reference to an embodiment shown in the drawing below.

• Figur 1 die schematische Darstellung eines Backofens zur Durchführung des erfindungsgemäßen Verfahrens,
• Figur 2 ein Diagramm mit Darstellung des zeitlichen Temperaturverlaufs unterschiedlicher Betriebsabläufe des Backofens,
• Figur 3 ein Diagramm mit einem zeitlichen Temperaturverlauf gemäß dem erfindungsgemäßen Verfahren.

It shows:

• FIG. 1 the schematic representation of a baking oven for carrying out the method according to the invention,
• FIG. 2 a diagram showing the temporal temperature profile of different operations of the oven,
• FIG. 3 a diagram with a temporal temperature profile according to the inventive method.

FIG. 1 shows a schematic and perspective view of the cuboid oven muffle 5 of a baking oven, consisting of side muffle walls 6, 7, an upper muffle wall 8, a lower muffle wall 9 and a rear, vertical muffle 10. At the rear end of the Muffelraums 11 at a distance from the rear muffle wall 10th There is an intermediate wall 12 which forms a largely separate from the rest of the muffle blower chamber 13, in which a motor-driven circulating air blower 14 is arranged. This fan room communicates with the rest of the muffle space 11 via lateral exhaust openings (not shown) in FIG FIG. 1 represented by air flow arrows 15. Within the Muffelraums 11 and in the immediate vicinity of the upper muffle wall 8 is arranged as a radiator heating element 16, also called top heat, while below the lower muffle wall 9, a further heating element 17 is arranged as a so-called bottom heat. By air flow arrows 18 and 19 is in FIG. 1 indicated that from the circulating air fan 14, air flows in the direction of the aforementioned heating elements 16, 17 are heated there on the heating elements or on the adjacent muffle walls and sucked by the circulating air fan 14 via a central intake in the intermediate wall 12 of the fan chamber 13 again. In this case, an operation of heating elements within the fan chamber 13 is not provided. In Muffelraum 11 is further arranged a temperature sensor 20 which is spatially and functionally connected to a non-illustrated, conventional control device for the oven. This temperature sensor 20 is located in the vicinity of the upper muffle wall 8 and is for example attached to the rear muffle wall 10 and penetrates the intermediate wall 12 of the fan chamber 13. Thus, this temperature sensor 20 is - as usual - far outside the treatment center of the oven muffle 5, in which the food to be treated is located. The oven muffle 5 is surrounded by a thermal insulation, not shown, and is tightly closed by a furnace door, also not shown, during the oven operation.

The FIG. 2 illustrated by means of a set of curves, with which problem deals with the invention before lying. The diagram shows - as well FIG. 3 - The process sequence of the oven with the abscissa as the time axis and the ordinate as the temperature axis. The set of curves shows the curve 1, which shows the real temperature profile at the outside of the treatment center of the oven muffle 5 (FIG. FIG. 1 ) arranged temperature sensor 20 without, that during the heating phase 0 - t3, the circulating air blower 14 is turned on, so only the heating elements 16, 17 are continuously turned on. The time t3 is the point in the temperature / time profile in which the heating elements 16, 17 at Reaching the Aufheizspitze be switched off for the first time (shutdown), the Anheizphase is completed and the Fortheizphase t3 - tx begins with a known, cyclic control game of heating elements and circulating air blower, controlled by a conventional, not shown control device.

Curve 2 shows a desired, ideal course of the temperature profile at the temperature sensor with respect to a selected target temperature Tsoll in the treatment center, which is relatively far away from the real measured temperature at the temperature sensor at time t3, ie there is an overshoot of the temperature detected at the temperature sensor instead of the ideal temperature. The curves in FIG. 2 clearly show that relatively much time would pass during the heating phase t3-tx in order to achieve the ideal temperature profile of curve 2 in the region tx in the mode of operation according to curve 1.

The curve 3 is intended to illustrate the ideal temperature profile in the treatment center of the oven, in which treatment center there is no temperature sensor of the control device. At time t3, this ideal treatment temperature is at least substantially close to the setpoint temperature Tset, and there is only a minimal difference to the ideal temperature of the ideal curve 2 at this time t3.

With the curve 4 is to be clarified a corrected temperature / time profile according to the described invention, in which by preferably multiple entries of the circulating air blower 14 (FIG. FIG. 1 ) the temperature profile at the temperature sensor 20 at time t3 the ideal temperature profile according to curve 2 is approximated. As a consequence, in the reheating phase t3 - tx, the corrected temperature curve achieves the ideal temperature profile in a shorter time, such as FIG. 2 clearly shows.

Such a temperature / time profile is in FIG. 3 illustrated by the curve 5. During the heating phase 0 - t3, the circulation fan 14 (FIG. FIG. 1 ) at times t1 and t2 temporarily, z. For 30 seconds. FIG. 3 shows in contrast to this by the curve 6, a temperature / time profile, as would be without the inventive method, ie here the Anheizkurve would rise continuously and continuously until a shutdown when reaching a Anheizspitze at the end of the heating phase. Curve 5, on the other hand, illustrates the aforementioned activation of the circulating air blower at times t1 and t2. This results in the advantageous effect that the temperature rise at the outside of the treatment center of the oven arranged temperature sensor, which is responsible for the temperature control and ultimately for the baking result is slowed down for each t1 and t2 for a short time (curve 5) recognizable by the short-term interruption of the otherwise linear temperature rise (temperature gradient) , ie the partial loop-like course of the curve 5 at the time t1 and t2, so that the temperature in the treatment center has the opportunity to compensate for the prevailing temperature difference between the temperature sensor and treatment center due to the short-term forced Luftkonvektion.

In terms of control, the ideal time profile according to the invention is achieved in that the time profile is determined by the level of the switch-off temperature at t3 and / or by the operating mode and arrangement of the heating element or elements 16, 17 (FIG. FIG. 1 ). Preferably, this first switch-on time t1 in the time profile is a fixed percentage relative to the heating peak or the switch-off temperature at the end of the heating phase 0 - t3. The second switch-on time t2 is preferably determined by the temperature gradient of the respective heating profile which is dependent on the selected setpoint or switch-off temperature.

Of course, the advantages of the present invention arise equally both in a temporal advance of the temperature at the temperature sensor compared to the temperature in the treatment center and vice versa in the time lag of the temperature at the temperature sensor with respect to the temperature in the treatment center.

Claims (6)

1. Method of operating a baking oven, provided with a closable, thermally insulated oven muffle (5), with an air circulating fan (14) arranged within a fan space (13) of the oven muffle, with at least one thermal heating element (16, 17) arranged in the vicinity of the muffle walls (6 to 10) outside the fan space (13), and with the control device by which the at least one heating element (16, 17) and the air circulating fan (14) are switchable on and off in correspondence with a predetermined temperature/time profile during the baking oven operation consisting of a heating-up phase (0 - t3) and a continuing heating phase (t3 - tx), characterised in that during the heating-up phase (0 - t3) the at least one heating element (16, 17) is switched on preferably continuously and that the air circulating fan (14) is switched on temporarily in correspondence with a time profile at least partly dependent on the predetermined switch-off temperature of the heating element at the end of the heating-up phase.
2. Method according to claim 1, characterised in that the time profile is determined by the level of the switch-off temperature and/or the mode of operation and arrangement of the at least one heating element (16, 17).
3. Method according to any one of the preceding claims, characterised in that the time profile is determined by the temperature gradients of the respective heating-up profile dependent on the selected target or switch-off temperature.
4. Method according to one any of the preceding claims, characterised in that the air circulating fan (14) is briefly switched on at least twice during the heating-up phase (0 - t3).
5. Method according to claim 1 to 4, characterised in that during the heating-up phase (0 - t3) the air circulating fan (14) is switched on at least once at a point in time dependent on the level of the switch-off temperature and/or the mode of operation and arrangement of the at least one heating element (16, 17) and is switched on at least one further time at a point in time dependent on the temperature gradients of the respective heating-up profile.
6. Baking oven, particularly for performance of the method according to any one of the preceding claims, characterised in that a fan space (13) with an air circulating fan (14) is provided within a thermally insulated, closing oven muffle (5) and at least one thermal heating element (16, 17) is provided in the vicinity of the muffle walls (6 to 10) and preferably outside the fan space and that a control device, the temperature sensor (20) of which is disposed outside the treatment centre of the oven muffle (5), is constructed in such a manner that during a heating-up phase (0 - t3), which precedes a continuous heating phase (t3 - tx), of the oven muffle (5) the air circulating fan (14) is switched on temporarily in correspondence with a time profile at least partly dependent on the predetermined switch-off temperature of the heating element at the end of the heating-up phase (t3).

Images