U.S. patent application number 13/122862 was filed with the patent office on 2011-08-11 for method for operating a dishwasher.
Invention is credited to Klaus-Martin Forst, Claudia Hofpeter, Uta Kreutzfeldt, Richard Schadt, Katerina Tzavella.
Application Number | 20110192426 13/122862 |
Document ID | / |
Family ID | 40427230 |
Filed Date | 2011-08-11 |
United States Patent
Application |
20110192426 |
Kind Code |
A1 |
Kreutzfeldt; Uta ; et
al. |
August 11, 2011 |
METHOD FOR OPERATING A DISHWASHER
Abstract
A method for operating a dishwasher comprising a washing tub for
accommodating articles to be cleaned and a circulation pump for
circulating a cleaning liquid within the washing tub, and wherein
there is provided for a plurality of washing programs selectable by
the user, said washing programs comprising a series of consecutive
steps selected from filling, pre-washing, washing, rinsing,
soaking, draining and drying steps. In the method suggested herein,
the washing programs comprise: (a) a first washing program in which
the circulation pump is operated at a nominal speed, and (b) a
second washing program in which, for at least part of the program,
the circulation pump is operated at a speed which is reduced with
respect to the nominal speed, and in which there is provided at
least one soaking step during which the circulation pump is
inactive.
Inventors: |
Kreutzfeldt; Uta;
(Freystadt, DE) ; Hofpeter; Claudia; (Furth,
DE) ; Forst; Klaus-Martin; (Wintersdorfer Strasse,
DE) ; Schadt; Richard; (Nurnberg, DE) ;
Tzavella; Katerina; (Furth, DE) |
Family ID: |
40427230 |
Appl. No.: |
13/122862 |
Filed: |
October 23, 2009 |
PCT Filed: |
October 23, 2009 |
PCT NO: |
PCT/EP09/07587 |
371 Date: |
April 6, 2011 |
Current U.S.
Class: |
134/25.2 ;
134/58D |
Current CPC
Class: |
A47L 2301/04 20130101;
A47L 15/0052 20130101; A47L 15/0002 20130101; A47L 15/4225
20130101; A47L 2501/05 20130101; A47L 2601/02 20130101 |
Class at
Publication: |
134/25.2 ;
134/58.D |
International
Class: |
A47L 15/42 20060101
A47L015/42 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 31, 2008 |
EP |
08019155.4 |
Claims
1. A method for operating a dishwasher comprising a washing tub for
accommodating articles to be cleaned and a circulation pump for
circulating a cleaning liquid within the washing tub, and wherein
there is provided for a plurality of washing programs selectable by
the user, said washing programs comprising a series of consecutive
steps selected from filling, pre-washing, washing, rinsing,
soaking, draining and drying steps, wherein said washing programs
comprise: (a) a first washing program in which the circulation pump
is operated at a nominal speed, and (b) a second washing program in
which, for at least part of the program, the circulation pump is
operated at a speed which is reduced with respect to the nominal
speed, and in which there is provided at least one soaking step
during which the circulation pump is inactive.
2. The method of claim 1, wherein in said second program the
circulation pump is operated at a speed which is in the range of
from 85 to 95 percent of the nominal speed.
3. The method of claim 1, wherein in said second program the
circulation pump is operated at a speed which is less than 90
percent of the nominal speed.
4. The method of claim 1, characterized in that wherein in said
second program there is provided a pre-washing step in which
non-heated water is circulated within the washing tub, and wherein
there is provided a soaking step following the pre-washing step
during which the circulation pump is inactive.
5. The method of claim 4, wherein said soaking step following the
pre-washing step has a duration of at least 15 min.
6. The method of claim 4, wherein the pre-washing step has a
duration of at least 10 min.
7. The method of claim 4, wherein during the pre-washing step a
detergent is dissolved in the water circulated within the washing
tub.
8. The method of claim 1, wherein in said second program there is
provided at least one washing step in which cleaning liquid is
circulated within the washing tub, wherein during at least a first
part of the washing step heat is provided to the cleaning liquid
and wherein during at least a second part of the washing step the
heated cleaning liquid is circulated within the washing tub without
providing additional heat to the cleaning liquid, wherein the
washing step comprises at least one soaking pause during which the
circulation pump is inactive.
9. The method of claim 8, wherein said soaking pause has a duration
of at least 15 min.
10. The method of claim 8, wherein said soaking pause is provided
at the conclusion of the washing step.
11. The method of claim 8, wherein a first soaking pause is
provided during said first part of the washing step and a second
soaking pause is provided during said second part of the washing
step.
12. The method of claim 11, wherein said first and/or second
soaking pause has a duration of 5 to 15 minutes.
13. The method of claim 8, wherein said soaking pause(s) is (are)
conducted at a temperature of 40 to 45.degree. C.
14. The method of claim 1, wherein in said second program there is
provided at least one washing step in which cleaning liquid is
circulated within the washing tub, wherein during at least a first
part of the washing step heat is provided to the cleaning liquid
and wherein during at least a second part of the washing step the
heated cleaning liquid is circulated within the washing tub without
providing additional heat to the cleaning liquid, wherein during a
third part of the washing step the temperature of the cleaning
liquid is kept constant.
15. The method of claim 14, wherein during said third part of the
washing step the temperature of the cleaning liquid is kept at a
temperature of between 40 to 45.degree. C.
16. The method of claim 1, wherein in said second program there is
provided at least one rinsing step in which fresh water is fed into
and circulated within the washing tub, and wherein there is
provided a soaking step which precedes the rinsing step and during
which the circulation pump is inactive.
17. The method of claim 16, wherein said soaking step preceding the
rinsing step has a duration of at least 20 min.
18. The method of claim 1, wherein the circulation pump, when
active, is operated in a pulsed mode.
19. The method of claim 1, wherein in said second washing program
the circulation pump, if and when active, is operated at a speed
which is reduced with respect to the nominal speed.
20. A dishwasher adapted for carrying out the method of claim 1.
Description
[0001] The present invention relates to a method for operating a
dishwasher comprising a washing tub for accommodating articles to
be cleaned and a circulation pump for circulating a cleaning liquid
within the washing tub, and wherein there is provided for a
plurality of washing programs selectable by the user, said washing
programs comprising a series of consecutive steps selected from
water intake, pre-washing, washing, rinsing, soaking, draining and
drying steps.
[0002] In modern dishwashers the user usually can select from a
plurality of washing programs which differ from each other by their
operation temperature, duration, amount of water used and selection
and sequence of consecutive steps.
[0003] Thus, a typical selection of washing programs in a
dishwasher comprises a standard program carried-out at a washing
temperature of for example 65.degree. C., an energy saving program
in which the washing step is carried-out at a lower temperature of
for example 50.degree. C., an intensive washing program in which
the washing step is carried out at a higher temperature of for
example 70.degree. C., and a quick cycle as it particularly can be
used for cleaning glasses in which a shorter washing cycle is used
and which is carried out at for example 40.degree. C. In each of
such washing programs the individual operation parameters such as
the amount of water fed into the dishwasher and the duration of the
individual steps can be fixed. Furthermore, the dishwasher may
comprise an automatic mode wherein a washing program is
automatically selected based on certain parameters which are
detected by sensors provided in the dishwasher, such as the washing
load (i.e. the amount and type of articles to be cleaned) and the
amount of soiling.
[0004] While the washing programs in today's dishwashers were more
and more optimized in terms of water and energy consumption, there
is a permanent desire in the art to provide for further
improvements as regards the performance and ease of use of the
dishwasher.
[0005] The present invention aims at providing a method for
operating a dishwasher, by which the generation of noise during
operation of the dishwasher is reduced. In particular, whereas in
modern dishwashers the noise level during operation as it is caused
by the cleaning fluid circulated through the machine and by the
operation of the circulation pump has been reduced by means of
acoustic insulation to a level which is below the regular noise
level experienced in a domestic household, it would be desirable to
be able to operate the dishwasher, particularly during night time,
in a silent mode in which the noise level created by the operation
of the dishwasher is further reduced. Thus, whereas in a domestic
household at daytime typically a sound pressure level of 40 to 41
dB is measured, conventional dishwashers typically operate at a
sound pressure level of 39 to 40 dB. While for daytime operation
this may be is sufficient because the operational noise of the
dishwasher blends into the background noise and hence is not
noticed, at night when there is less house and street noise the
noise caused by the operation of the dishwasher often is found to
be disturbing.
[0006] Therefore it is an object of the present invention to devise
a method for operating a dishwasher which provides for a reduction
in operational noise.
[0007] In a method for operating a dishwasher comprising a washing
tub for accommodating articles to be cleaned and a circulation pump
for circulating a cleaning liquid within the washing tub, and
wherein there is provided for a plurality of washing programs
selectable by the user, said washing programs comprising a series
of consecutive steps selected from filling, pre-washing, washing,
rinsing, soaking, draining and drying steps, this object is solved
by the present invention in that the washing program further
comprises a first washing program in which the circulation pump is
operated at a nominal speed, and a second washing program in which,
for at least part of the program, the circulation pump is operated
at a speed which is reduced with respect to the nominal speed, and
in which there is provided at least one soaking step during which
the circulation pump is inactive.
[0008] The term "nominal speed" of the circulation pump, as used
herein, denotes the speed at which the circulation pump is operated
during regular operation of the dishwasher, i.e. during standard
washing programs as they are known as such in the art and in which
the speed of the circulation pump is selected primarily based on
the amount and pressure of cleaning liquid as required to achieve a
satisfactory cleaning result. In dishwashers in which during all
the regular washing programs the circulation pump is operated at a
single speed, the term "nominal speed" thus denotes such single
standard speed. Should the circulation pump be designed to operate,
during at least some of the regular washing programs, at more than
one speed, for example at a first speed which corresponds to the
afore-mentioned standard single speed and a second higher speed
that is used for intensive washing programs in which cleaning
liquid is passed at a higher rate onto the goods to be cleaned, the
term "nominal speed" denotes any one of such standard speeds which,
as was the case for a single speed pump, likewise are selected
primarily based on the amount and pressure of cleaning liquid
required to achieve a desired cleaning result.
[0009] Whereas in conventional dishwashers noise reduction was
achieved exclusively by mechanical means, such as providing for
better acoustic insulation, the present invention is based on the
concept of actually lowering the speed of the circulation pump,
which in conventional dishwashers is operated at a single speed and
hence is subject to an on/off-control only. Since the reduction in
operational speed of the circulation pump necessarily results in a
decrease in cleaning efficiency, measures have to be taken to
compensate for such decrease in cleaning efficiency. In accordance
with the present invention, the reduction in operational speed of
the circulation pump is made possible by including in the program
sequence at least one soaking step, i.e. a step during which the
articles to be cleaned within the dishwasher are first wetted with
cleaning liquid, whereupon operation of the dishwasher is paused,
i.e. the circulation pump is turned off for a certain period of
time and the washing liquid is allowed to soak into the soiling
that shall be removed from the articles to be cleaned.
[0010] Whereas in the prior art it was suggested to lower the sound
level of a dishwasher by prolonging the washing program, thus
making use of the fact that the sound level is measured based on
sound power, i.e. sonic energy per time, the present invention
provides for an operation mode for a dishwasher in which the peak
noise level experienced during operation of the dishwasher is
lowered. The present invention thus provides for a true "silent
mode" in which not only the sound level but also the sound pressure
created by the dishwasher is reduced. Measurements have shown that
by using the method suggested herein the operational noise of the
dishwasher could be reduced by about 2 to 3 dB. Thus, using the
method suggested herein dishwashers can be operated at noise levels
of about 36 to 38 dB.
[0011] Preferred embodiments of the present invention are defined
in the dependent claims.
[0012] In particular, in the said second washing program the
circulation pump can be operated at a speed, which is the range of
from 85 to 95 percent of the nominal speed and preferably at a
speed which is less than 90 percent of the nominal speed. Thus, if
during the first washing program, which can be any one of the
regular washing programs, the circulation pump is operated at a
speed of for example 1800 rpm, in the said second washing program
the speed of the circulation pump can be reduced to 1600 rpm
without deteriorating the washing result. Similarly, if the
dishwasher during a first washing program that is designed as an
intensive care program in which the circulation pump is operated at
a speed of for example 2400 rpm, it was found that by providing for
soaking steps in the second washing program the speed of the
circulation pump can be reduced to 2200 rpm without deteriorating
the washing result.
[0013] In order to be able to reduce the speed of the circulation
pump without deteriorating the cleaning performance of the
dishwasher, periods of the washing cycle were identified during
which a soaking step or soaking pause effectively improves the
washing result and which thus enables to achieve at least similar,
if not even better washing results at a reduced speed of the
circulation pump.
[0014] It was found that in a washing cycle wherein there is
provided for a pre-washing step, in which non-heated water is
circulated within the washing tub, particularly good results are
obtained if there is provided for a soaking step following the
pre-washing step, during which soaking step the circulation pump is
inactive. Advantageously the soaking step which follows the
pre-washing step has a duration of at least 15 minutes, preferably
of at least 20 minutes, wherein the pre-washing step as such
preferably has a duration of at least 10 minutes, and more
preferred, of at least 15 minutes.
[0015] In order to facilitate the release of dirt particles from
the washing goods, a detergent can be dissolved in the water which
is circulated within the washing tub during the pre-washing step.
By providing for a soaking step with non-heated water after
conclusion of the pre-washing step, dirt particles are effectively
removed from the washing goods in a very energy-effective and hence
cost-effective manner.
[0016] In determining an optimum timing for the provision of
soaking steps it further was found that soaking step(s) can also
very effectively be included in the washing step, during which
heated cleaning liquid is sprayed onto the articles to be cleaned.
In such washing step usually heat is provided to the cleaning
liquid during a first part of the washing step, which warmed
cleaning liquid then is circulated within the washing tub without
providing additional heat to the cleaning liquid. It should be
understood that the washing step is not restricted to such
temperature profile but may comprises further parts before, after
or in between the said first and second part during which heated or
non-heated cleaning liquid is circulated within the washing
tub.
[0017] A very effective timing for a soaking step was found to be
in the last part of the washing step or after the washing step.
During the washing step usually most of the soil particles, which
during the pre-washing step were wetted and soaked, are dissolved
and removed from the washing goods. Some soiling types, such as
starch-containing soils or baked soil particles, require more time
for their removal in addition to the chemical and mechanical
cleaning effected during the washing step. Such additional time for
dissolving persistent soiling and thus achieve satisfactory washing
results can be provided for in a second soaking step following one
of the washing steps. Such soaking step following the washing step
preferably has a duration of at least 15 minutes, and more
preferred has a duration of at least 20 minutes. While such soaking
step following the washing step is referred to herein as "second
soaking step", it should be understood that such optional soaking
step can be employed either in addition or alternatively to the
soaking step following the pre-washing step.
[0018] Instead of a single soaking step following one of the
washing steps, the said second soaking step also can comprise a
first soaking pause which is provided during said first part of the
washing step, i.e. during warming of the cleaning liquid, as well
as a second soaking pause that is provided during the second part
of the washing step in which the cleaning liquid is circulated
within the washing tub without providing additional heat to the
cleaning liquid. In case that the soaking pause provided for in the
washing steps is split into a first and second soaking pause, such
soaking pauses preferably have a duration of 5 to 15 minutes, and
most preferred of at about 10 min.
[0019] Particularly when using in the washing liquid a cleaning
agent containing enzymes, it was found that a soaking pause
following the washing step or conducted following during the
washing step is most efficient if carried out at a temperature of
40 to 45.degree. C. and most preferably of about 42.degree. C.
[0020] Particularly, when using enzyme containing detergents in the
cleaning liquid, the cleaning action can be further improved, if
the washing step, in addition to a first part during which heat is
provided to the cleaning liquid and a second part during which the
cleaning liquid is circulated within the washing tub without
providing additional heat, i.e. during which the cleaning liquid is
circulated while cooling, comprises a third part during which the
temperature of the cleaning liquid is kept constant, preferably at
the enzyme temperature, which in most cases will be between 40 and
45.degree. C. and preferably is about 42.degree. C. Whereas during
the soaking pauses the circulation pump and hence the spray arms
within the dishwasher are inactive, during such heating pause in
which the temperature of the cleaning liquid is kept constant, the
circulation pump and hence the spraying arms may be active.
[0021] A third preferred time interval for providing for a soaking
pause is prior to the rinsing step, which usually constitutes the
last step in the washing cycle. During the rinsing step fresh water
is sprayed onto the washing goods so as to wash off loosened soil
particles and any remaining detergent. During the rinsing step the
washing goods furthermore are heated to a higher temperature, for
example, to 70.degree. C., so as to provide for a self drying
effect when the circulation of the cleaning liquid is terminated
and the washing tub is drained.
[0022] In a washing cycle wherein there is provided for an
intermediate rinsing step between the washing step and the final
rinsing step, the said soaking step can be effected during or at
the conclusion of the intermediate rinsing step. This final soaking
step also could be provided for after conclusion of an intermediate
rinsing step, i.e. after water, preferably cold fresh water, that
has been sprayed onto the washing goods has been drained from the
washing tub.
[0023] While said soaking step preceding the rinsing step
preferably has a duration of at least 20 minutes, best results were
achieved when such soaking step had a duration of about 30
minutes.
[0024] Whereas the above soaking steps could be used alternatively,
the best washing results were achieved when all three kinds of
soaking steps were employed, i.e. a soaking step during the
pre-washing step, a second soaking step during the washing step and
a third soaking step prior to the rinsing step.
[0025] The noise reduction, which can be achieved by being able to
operate the circulation pump at least during part of the washing
cycle at a lower speed than the nominal speed can be further
assisted by operating the circulation pump in a pulsed mode, i.e.
by continuously varying the speed of the pump, because it was found
that the operating noise created during operation of the
circulation pump in pulse mode creates a less disturbing sound
impression with the user. Furthermore, it should be understood that
although due to the soaking pauses the overall washing cycle has a
longer duration than without soaking pauses, such prolongation of
the washing cycle in many cases is not of disadvantage, because
dishwashers anyway often are operated at times when there is much
more time available than that required for the washing cycle, for
example, when the dishwasher is operated night time or at day time
when the user has left his home for work and will return long after
the washing program is terminated.
[0026] While actual noise reduction is achieved already when the
circulation pump only for part of its operation is operated at a
reduced speed, the circulation pump preferably is operated in the
entire second washing program at a speed which is reduced with
respect to the nominal speed.
[0027] Preferred embodiments of the method for operating a
dishwasher as suggested herein are described below by reference to
the attached drawings, in which:
[0028] FIG. 1 is a schematic representation of a washing program
for a dishwasher as it is used in prior art dishwashers;
[0029] FIG. 2 is a schematic representation similar to that shown
in FIG. 1, illustrating a program flow for a dishwasher which is
operated in accordance with the present invention; and
[0030] FIG. 3 is a schematic representation of an alternative
program flow for a dishwasher which is operated in accordance with
the present invention.
[0031] FIG. 1 shows an example of a washing program as it may be
used also in a conventional dishwasher. Such washing program
typically comprises a pre-wash step, in which the articles to be
cleaned are subject to an initial cleaning step for removing coarse
soil particles as well as dirt which easily can be removed from the
washing goods. Following such pre-wash step, a main wash step is
conducted, typically at a temperature that is higher than the
temperature employed in the pre-wash step, wherein during the main
wash step also the more persistent soil particles are loosened and
removed from the washing goods. After the main wash step, the
washing goods are exposed to a cold rinse step during which the
loosened dirt particles and detergent are washed-off from the
washing goods. In a final hot rinse step, heated fresh water is
sprayed onto the washing goods to fully clean the latter and at the
same time supply heat to the washing goods, which serves for drying
the washing goods.
[0032] In the illustrative example of such washing program as it is
depicted in FIG. 1, the pre-wash step begins with a drain sub-step,
during which the drain pump is activated, so as to remove any
liquid that has accumulated in the sump of the dishwasher during a
previous cleaning cycle. Upon having activated the drain pump for a
certain amount of time or until no further liquid is withdrawn from
the sump of the dishwasher, fresh water is fed into the dishwasher
and a circulation pump is activated so as to feed such water to
rotatable spray arms and thus to spray it onto the articles to be
cleaned, which typically are arranged on dish racks, such as a
lower and an upper dish rack, provided within the washing chamber
of the dishwasher. The pre-wash step can be carried out either with
cold water, i.e. with water at a temperature as it has when coming
from the tap to which the dishwasher is connected, or with heated
water, that is with water which during being fed into the washing
compartment or during being recycled within the washing compartment
is heated, or by using in sequence both cold and heated water.
Preferably, the pre-wash step is carried out at a temperature of
between 15 and 55.degree. C.
[0033] During the pre-wash step a detergent can be added to the
water circulated within the dishwasher, which detergent can be
added to the cleaning liquid either by a detergent dispenser, a
detergent compartment that is flushed with cleaning liquid, or by
using multi-component detergents which are provided in the form of
tablets containing a plurality of active agents that are dissolved
into the cleaning liquid at different times during the cleaning
cycle. At the end of the pre-wash step the drain pump is activated,
so as to remove the cleaning liquid and any dirt particles that
were dissolved from the washing goods.
[0034] Following the pre-wash step there is carried-out a main wash
step during which warmed cleaning liquid is circulated within the
dishwasher, i.e. first fresh water is fed into the washing tub and
then the circulation pump is activated, so as to feed water which
collects within the sump of the dishwasher to the spray arms that
are located below or above the dish racks, on which the articles to
be cleaned are arranged, so as to spray the cleaning liquid onto
the washing goods. During the main wash step the cleaning liquid
typically is heated to a temperature in the range of from 30 to
70.degree. C.
[0035] Upon having sprayed cleaning liquid onto the washing goods
for a certain amount of time, the circulation pump is deactivated
and the cleaning liquid, now containing dissolved detergent as well
as soil and dirt particles that have been washed-off from the
washing goods, is drained from the sump of the dishwasher by
activation of the drain pump.
[0036] Following the main wash step, the washing cycle comprises a
number of rinsing steps during which water is fed into the
dishwasher and the circulation pump is operated so as to rinse
remaining dirt particles and detergent from the goods to be
cleaned. Although during the rinsing steps typically no detergent
is added to the water fed into the dishwasher, particularly in the
initial rinsing steps some detergent may be present in the cleaning
liquid, for example, when multi-component cleaning tabs are used
that may not have fully dissolved during the pre-wash and main wash
steps. Furthermore, certain further treating agents may be added to
the cleaning liquid, possibly also by the use of multi-component
cleaning tabs, such as specific glass treating agents or the
like.
[0037] While the initial rinsing step typically is carried-out at a
lower temperature of, for example, 30 to 40.degree. C., during the
terminal rinsing step a higher temperature of, for example, 35 to
70.degree. C. is used, so as to heat the rinsed washing goods to
thus facilitate drying of the washing goods. At the end of each
rinsing step, the sump may be emptied by activating the drain
pump.
[0038] It should be noted that any of the individual steps of the
washing program may comprise several sub-steps, such as the main
wash step being divided into plural washing phases which are
carried-out at different temperatures. In this case the cleaning
liquid used within the washing compartment can be exchanged between
such sub-phases by activating the drain pump upon termination of
the first phase and feeding fresh water into the washing
compartment at the beginning of the second phase.
[0039] During all the steps described above, the circulation pump
can be operated at a single speed so as to provide for a certain
water pressure with which the cleaning liquid is sprayed onto the
articles to be cleaned. Should, however, a higher water pressure be
desired, as it could be employed for the cleaning of heavily soiled
articles such as pans having baked soils adhering thereon, the
dishwasher may be designed to operate the circulation pump at a
higher speed. Since, however, a higher water pressure may cause
damages of certain articles, such as fine glass ware or the like,
the use of a higher speed of the circulation pump and
correspondingly of a higher water pressure during any of the
washing cycles should be activated only on specific request by the
user, such as by selecting an "intensive care" program or the
like.
[0040] FIG. 2 shows a washing program, which comprises similar
program steps as the ones shown in FIG. 1, but wherein there are
provided several soaking pauses, during which the circulation pump
is inactive and which serve for providing additional time for the
cleaning liquid and any active agents added thereto to soak into
the dirt particles adhering to the articles to be cleaned.
[0041] While in the example shown in FIG. 2 soaking pauses are
inserted at the end of the pre-wash step, the main wash step and
the cold rinse step, in each such step after the sub-step of
draining the washing tub, the soaking pauses also could be employed
before draining the dishwasher. In any event, the soaking step or
soaking pause should have a duration of several minutes, that is
preferably of between 5 and 30 minutes, so as to allow for
sufficient time to provide for sufficient soaking. By the use of
soaking pauses, the cleaning efficiency is improved to such an
extent that the circulation pump can be operated at a lower speed,
which correspondingly provides for a lower pressure at which the
cleaning liquid is sprayed onto the articles arranged within the
dishwasher. In this manner, not only the average noise level, but
indeed the actual and instantaneous noise level caused by operation
of the dishwasher is lowered. While evidently the use of soaking
steps causes a prolongation of the overall washing program, such
prolongation is of little or no concern when the dishwasher is
operated overnight, i.e. when the dishwasher is filled and started
in the evening and is unloaded not until the next morning.
[0042] In a dishwasher as is suggested herein, the user of the
dishwasher thus can select between a number or "regular" washing
programs, such as an automatic program or standard programs that
are carried out at different temperatures, such as at 40.degree.
C., 50.degree. C. or 65.degree. C., an intensive washing program
carried out at a higher temperature of for example 70.degree. C.,
or a quick cleaning program having a shortened program duration.
Common to all these programs is that the circulation pump is
operated at a nominal speed that is optimized in terms of the
cleaning efficiency and which may be the same in all washing
programs. In addition to the these programs, the user can also
select a silent mode, in which, for at least part of the respective
program and preferably for the entire program, the circulation pump
is operated at a speed which is reduced with respect to said
nominal speed, and in which there is provided at least one soaking
step during which the circulation pump is inactive.
[0043] FIG. 3 shows a portion of a modified main wash step as it
could be employed in an overall washing program as it is shown in
FIG. 2. In particular, FIG. 3 shows a main wash step which
comprises several sub-phases, namely a first main wash phase during
which a'mildly warmed cleaning liquid having a temperature of about
30 to 45.degree. C. is sprayed onto the articles to be cleaned and
in which during a second main wash phase the cleaning liquid is
warmed to a higher temperature of generally 40 to 70.degree. C.
[0044] In the example shown in FIG. 3 there are provided two
soaking pauses in such main wash step, namely a first soaking step
following the first washing phase, and a second soaking pause in
the terminal phase of the main wash step. In the embodiment shown,
the cleaning liquid is not drained from the washing tub between the
first and second main wash phases, but rather upon termination of
the lower temperature first main wash phase only the circulation
pump is deactivated, and upon termination of the first soaking
pause heat is provided to the washing tub and hence to the cleaning
liquid present therein when the circulation pump is again activated
to carry out the second main wash phase. While FIG. 3 thus shows an
embodiment in which the sump of the dishwasher is drained upon
deactivation of the circulation pump upon conclusion of the second
main wash phase but before the soaking pause of the second main
wash phase, if preferred the cleaning liquid could also be
partially or fully exchanged during the first and second main wash
phases.
[0045] Particularly when using enzymes-containing cleaning agents,
it was found that the cleaning result is most efficient, when the
first and or the second soaking pause in the main wash step is
carried-out at a temperature of 40 to 45.degree. C. and most
preferably of about 42.degree. C. In this manner, particularly
advantageous conditions are realized in the washing compartment for
the cleaning agent to perform its cleaning activity.
* * * * *