Note: Descriptions are shown in the official language in which they were submitted.
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Description
Method for Operating a Steam Oven and Steam Oven
The invention relates to a method for operating a steam oven,
especially a domestic steam oven, wherein the steam oven has a
control unit and a water reservoir and wherein the steam oven is
equipped with a pyrolytic cleaning function. Furthermore, the
invention relates to a steam oven.
Steam ovens of this kind are well known in the art. It is also
known that a certain amount of water is necessary in the water
reservoir for properly carrying out the steam cooking process.
Thus, water level detection in the water reservoir (water tank)
is used at least in those cases in which a water reservoir is
employed which is manually filled with water by the user. As an
alternative the steam oven can directly be connected to a water
pipe.
In JP 2005273991 A a steam oven is disclosed. Here the start of
the cooking process is enabled only if enough water is present
in the water reservoir.
DE 100 38 136 Al discloses a steam oven comprising an emergency
overflow system.
In DE 10 2008 014 040 Al a steam oven is shown which comprises
an air bubble detection equipment in the water supply.
It has been found that the pyrolytic process - which is often
used in steam ovens for cleaning - is a quite high thermal load
to the whole oven system. Problematic elements are especially
the electronic components and the sensor element especially for
detecting the water level in the water reservoir.
Therefore, it is an object of the invention to propose a method
for operating a steam oven of the kind mentioned above which
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guarantees a better protection of the electronics and sensors of
the oven. Thus, it should be made sure that especially the pyro-
lytic cleaning process does not harm the oven system.
The solution of this object is achieved by the proposed method
in that the operation of the pyrolytic cleaning comprises the
following steps after the pyrolytic cleaning function is acti-
vated by the user:
a) detecting of the actual water level in the water reser-
voir by the control unit;
b) comparing of the detected actual water level with a de-
fined minimum pyrolytic water level by the control unit;
c) starting the pyrolytic cleaning function by the control
unit if the actual water level is equal or above the
minimum pyrolytic water level or
d) not starting the pyrolytic cleaning function but issuing
of an alarm to the user by the control unit if the actual
water level is below the minimum pyrolytic water level to
alert the user to fill up water into the water reservoir.
Thus, the water level in the water reservoir is detected by
suitable sensor elements; this is managed by the control unit.
Only if a certain and special water level is given in the water
reservoir (the defined minimum pyrolytic water level) the pyro-
lytic cleaning process is carried out; otherwise the user is
m alerted to fill up water into the water reservoir before the py-
rolytic process is done. By doing so enough water is in the res-
ervoir so that the thermal load to the components is reduced due
to an insulating property of the water.
The operation of the pyrolytic cleaning can furthermore com-
prises the steps after the pyrolytic cleaning function is acti-
vated by the user and before carrying out above mentioned step
c):
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b') after detecting of the actual water level in the water
reservoir according to step a): comparing of the detected
actual water level with a defined overfilled water level
by the control unit;
c') starting the pyrolytic cleaning function by the control
unit if the actual water level is below the overfilled
water level or
d') not starting the pyrolytic cleaning function but issuing
of an alarm to the user by the control unit if the actual
water level is above the overfilled water level to alert
the user to drain water from the water reservoir.
By doing so it is made sure that - on the other hand - not too
much water is in the water reservoir before the pyrolytic clean-
ing process is carried out.
The minimum pyrolytic water level can be a maximum water level
for normal steam cooking operation.
The minimum pyrolytic water level can also be a water level
which is between a maximum water level for normal steam cooking
operation and a defined overfilled water level.
An overfilling of the water reservoir can also be detected as
such. Therefore, a version of the proposed method proposes that
an alarm is issued to the user by the control unit if the actual
water level is above a defined overfilled water level to alert
the user to drain water from the water reservoir.
When it comes to the issuance of an alarm signal this signal can
be an optical signal (e. g. a respective message on a display of
the oven) or an acoustic signal.
The proposed steam oven with the pyrolytic cleaning function is
characterized by the invention in that the steam oven comprises
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at least one sensor element to detect the actual water level in
the reservoir, wherein the control unit comprises means for com-
paring the detected actual water level with a defined minimum
pyrolytic water level and wherein the control unit comprises
alarm means for issuing of an alarm to the user if the actual
water level is below the minimum pyrolytic water level and if a
pyrolytic cleaning operation is activated.
The at least one sensor element can be designed to detect an
W overfilled water level, wherein the control unit comprises means
for comparing the detected actual water level with the over-
filled water level and wherein the control unit comprises alarm
means for issuing of an alarm to the user if the actual water
level is above the overfilled water level.
The sensor element can comprise at least one floating magnet and
relay reeds. Also, it can be a capacitive element. Of course,
also other detection elements to measure the water level in the
water reservoir can be employed.
The control unit can be designed to calculate and output the wa-
ter volume necessary to reach a defined water level in accor-
dance with a detected water level by the sensor element. This
means that the invention does not only supplies the signal "too
less water in the water reservoir" or "too much water in the
reservoir" but can also inform the user how much water has to be
filled or drained into or from the tank.
Furthermore, the steam oven can comprise optical and/or acoustic
m alarm signal means.
So, the invention allows to detect the exact level of water res-
ervoir of the steam oven which adds the functionality of over-
fill detection. Furthermore, the proposed concept tells the user
in an accurate manner how much water is missing in the water
reservoir or exactly how much water is too much in the reser-
voir.
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By the concept according to the invention electronic and sensor
elements which are employed to run the oven and to detect the
water level in a precise way are specifically protected against
overheating during the pyrolytic process; the pyrolytic cleaning
function of the oven is only enabled, if enough water is in the
water reservoir.
The present invention can be employed in the case that a remov-
able water tank is used within the steam oven. It can also be
the case that a build-in water reservoir is used which cannot be
removed. Especially if this water reservoir is not visible for
the user and thus that the water level cannot easily be moni-
tored by the user the present invention develops its full bene-
fits.
A removable water tank normally reduces the available space of
the cavity or of the front panel of the oven. An invisible res-
ervoir is sometimes better in this respect.
So, the concept according to the invention also defines at least
two water levels, i. e. a maximum water level for normal steam
cooking and an overfilled water level. By the proposed solution
it becomes redundant to equip the system with a drain pipe for
the case the too much water is in the water reservoir. Draining
of water via a drain pipe of course has significant disadvan-
tages which can be avoided by the invention.
A draining pipe can be arranged which is manually activated by
the user to remove water from the reservoir.
Due to the sufficient water level in the water reservoir during
the pyrolytic cleaning process it is made sure that the elec-
tronics and sensor element cannot be damaged due to too high
temperatures.
The sensors for detecting the water level can thus easier be de-
signed to detect a big range of filling degrees of the reser-
voir.
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Due to a visual and/or acoustical alert the user can be easily
informed concerning the filling or overfilling status of the
reservoir.
Via the display the user can also be specifically informed how
much water (i. e. how many millilitre) has to be refilled or
drained into or from the reservoir. This can be done in a quite
accurate manner due to the design of the sensor.
Consequently, the water reservoir does not need an automatic
draining pipe system for the case of overfilling.
In the case of gas cavity, where internal overfilling is not
recommended, the proposed oven avoids the leak of water in an
undesirable way.
Thus, the user of the oven is better guided to ensure the right
degree of filling of the water reservoir according to the actual
process which is running in the steam oven (normal cooking op-
eration or pyrolytic cleaning).
In the drawings an embodiment of the invention is depicted.
FIG 1 shows a schematic illustration of a steam oven in a sec-
tional side view and
FIG 2 shows an enlarged view of the water reservoir of the
steam oven according to the depiction of FIG 1.
In FIG 1 a steam oven 1 is shown schematically which has a cook-
ing cavity 5 closable by a door 6. The steam oven is equipped
with a well known arrangement to supply water steam into the
cavity 5. For doing so, the steam oven 1 comprises a water res-
ervoir 3 (water tank) in which water can be filled. Thus, the
water which is filled into the water reservoir 3 reaches up to
an actual water level L.
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In the water reservoir 3 a sensor element 4 is arranged which is
able to detect the actual water level L. The detected value for
the actual water level is forwarded to a control unit 2 of the
steam oven 1.
As can be seen in more detail in FIG 2 the water level L can
reach a maximum water level LmN for normal steam cooking. I. e.
this water level LmN is the maximum water level for the water in
the reservoir 3 when normal cooking operation is required.
Furthermore, the water level can reach an overfilled water level
LoF which is a bit above the level LmN, e. g. this level is
reached when 10% to 20% more water is filled in the reservoir as
in the case of the filling degree up to the level LMN.
Also the steam oven 1 is equipped with - not depicted - means
for carrying out a pyrolytic cleaning operation of the cavity 5.
When pyrolytic cleaning is carried out a minimum pyrolytic water
level LD,F, must be maintained.
In the present case the minimum pyrolytic water level LD,F, is
equal to the maximum water level 14,N for normal steam cooking;
but this needs not to be necessarily the case.
When a pyrolytic cleaning operation has to be carried out the
user selects the respective pyrolytic cleaning program by means
of an Input-Output-Device (not shown but connected with the con-
trol unit 2), i. e. the user activates the pyrolytic cleaning
program.
The pyrolytic cleaning program does not start immediately. At
first the actual water level L in the water reservoir 3 is de-
tected by the sensor element 4 and registered by the control
unit 2. Then a comparison takes place in the control unit 2 be-
tween the detected actual water level L and a stored value for
the minimum pyrolytic water level LD,p.
The pyrolytic cleaning function is started then by the control
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unit 2 if the actual water level L is equal or above the minimum
pyrolytic water level Lmp.
If this is not the case the pyrolytic cleaning function is not
started by the control unit 2 but an alarm is issued to the user
by the control unit 2 to alert him that water must be filled
into the water reservoir 3.
It is possible that a message is outputted to the user saying
W how much water has to be filled into the reservoir 3.
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Reference Numerals
1 Steam oven
2 Control unit
3 Water reservoir
4 Sensor element
5 Cooking cavity
6 Door
L Actual water level
Lylp Minimum pyrolytic water level
LOF Overfilled water level
LMN Maximum water level for normal steam cooking
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