The present invention relates to an adaptive method for drying heated dishes in a household dish washing machine by means of expulsion of damp air from the dish area.

The present invention also relates to a device which carries out said adaptive method.

Many households today use some kind of dishwasher. A dishwasher operates automatically according to a predefined control program which, inter alia, controls the opening and closing of one or several inlet valves for the supply of water, and which also controls the circulation of this water with a dose added by the user in advance of some sort of detergent which is dissolved in the dishwasher for flushing cleaning of dishes which have been placed in the dishwasher. The circulated water is either warm water which is supplied from a piping system, or alternatively, the supplied water is heated in the dishwasher. A number of flushing processes take place in which old water is pumped out, following which new water is supplied and circulated.

Many modern dishwashers are equipped with means for drying damp dishes, which immediately following the cleaning process are in a humidified atmosphere. The drying is most often done by means of a fan, which fan expels the humidified air out of the dishwasher and transfers it to the ambient atmosphere. In so doing, ambient atmosphere is supplied to the dishwasher so that an exchange of air takes place, which causes the humidity which in the form of liquid is in direct contact with the dishes to vaporize and be transferred to the ambient atmosphere.

US 5076306 describes a circulation system for the drying of an object in a dishwasher. A fan drives air from an air intake to an air outlet.

In many cases the drying time is controlled, that is the time that the fan is to be operational, by a predefined value which is independent of the amount of dishes and the success of the drying process. A fixed value of the time which the drying process is to be operational in most cases means that it is carried out during too long or too short a time. If it is carried out too short a time, the washed dishes will not be dry enough. If, on the other hand, the drying process is carried out during too long a time, there is an unnecessary energy consumption to operate said fan during a too protracted drying process. This also causes the total drying process to go on during an unnecessarily long time.

For this reason, dishwashers have been equipped with one or several sensors, preferably of the humidity sensor or temperature sensor kind. These sensors continuously detect the development of the process, and at a certain stage of this development the drying process is interrupted, that is the fan is turned off.

In many cases the ventilation process is combined with drying by means of heating of the air by means of heating elements.

JP 10-258014 describes how a humidity sensor is used inside of a dishwasher. The humidity content is detected as the time for a drying process elapses. The drying process is carried out by means of a fan. Either the drying process is interrupted when the humidity content has reached a certain predetermined value, or when the change in humidity content over time planes out.

EP-A2-1127532 describes a dishwasher including a fan which takes moist air out of the tank through a removal duct and mixes it with dry ambient air taken in through an opening before discharging it through an outlet.

EP-A1-0521815 describes a dishwasher with a washing compartment which can be closed by means of an appliance door, a vent or the like for the dishwasher container in the appliance door which vent connects the washing compartment to the ambient air, and a mixing chamber for removal of the moist air from the washing compartment when the dishes are being dried, a separate fresh air duct opens out into the mixing chamber.

A main purpose of the present invention is to provide a method and a device for controlling a drying process in a household dishwasher, with the humidity content of the ambience taken into consideration.

This object is obtained by means of an adaptive method according to the present invention, which comprises the steps of initiating the expulsion of the humid air, detecting the ambient humidity content which results in a first value, storing this first value of the humidity content, and that the humidity content of the expelled air is detected, which expelled air continuously will have a lower and lower value of its humidity content. The method finally comprises the step of interrupting the drying process when the value of the humidity content of the expelled air reaches a value which has a predetermined ratio to the stored first value of the ambient humidity content.

Said purpose is also obtained by means of a device according to appended claim 10.

In a preferred embodiment, said household machine is a dishwasher.

By means of this method and the corresponding device, an adaptive control of the drying process is obtained which in its design is simple, and thus reliable and cost efficient.

Other preferred embodiments of the present invention will become evident from the dependent claims.

The invention will in the following be described in connection to examples of preferred embodiments and the appended drawings, in which

Fig. 1

is a partially cut schematic front view of a dishwasher according to the present invention;

Fig. 2

is a partially opened schematic side view of a dishwasher according to the present invention; and

Fig. 3

is a schematic description of the drying process according to the present invention.

In the following, a preferred embodiment will be described. It will relate to a dishwasher for household purposes.

With reference to Fig. 1 and Fig. 2, a dishwasher 1 according to this example of an embodiment is equipped with means for drying the damp dishes in the washing area 2, which dishes immediately following the cleaning process are in a humid atmosphere. The drying is, in brief, done by means of a fan 3 starting, which fan 3 expels the humid atmosphere out of the washing area 2, and transfers it to the ambient atmosphere via an air outlet 4. In so doing, ambient atmosphere is transferred to the washing area 2 via another opening (not shown), so that an exchange of air takes place which causes the humidity, which in the form of liquid is in contact with the dishes to evaporate, and be transferred to the ambient atmosphere.

According to the present invention, there is arranged, inter alia, a number of canals, and said fan 3 in a door 5 belonging to the dishwasher 1. A first canal 6 leads from the ambient atmosphere to the fan 3, a second canal 7 (see Fig. 1) leads from the washing area 2 of the dishwasher to the fan 3, and a third canal 8 leads from the fan 3 to the ambient atmosphere via the air outlet 4. A valve 9, the design of which will be described in more detail later, during the washing process blocks the passage between the second canal 7 and the fan 3, and thus also between the second canal 7 and the other two canals 6, 8. The other canal 7 is in connection with the washing area 2 via an opening 10.

With special reference to Fig. 1, the valve function will now be described. The valve 9 consists of a moveable element 11, which in its closed end position is biased by a spring 12 and blocks the passage of air between the second canal 7 and the fan 3. The moveable element 11 is connected to a so-called wax engine 13, which is arranged to move the moveable element 11 from the closed end position against the spring force when it is biased with a suitable tension. The voltage supply to the wax engine 13 is symbolized by a connection 14 which leads to a power supply 15 which in turn is connected to a control unit 16. The connections between the power supply 15 and the control unit 16 are in the figures symbolized by a connection 17.

The function of the wax engine 13 is previously known, and is only described here summarily for the sake of clarity. A resistor (not shown) comprised in the wax engine 13 develops heat when it is exposed to a voltage. A certain amount of wax (not shown), partially enclosed in a container 18, then expands, and said amount of wax is so arranged that it then via a power transferring organ 19 presses on the previously mentioned moveable element 11 towards the biasing spring force, so that the valve 9 is opened. The open position remains as long as the wax is heated and thus is in an expanded state. When the voltage is removed from the resistor, the resistor cools off, causing the amount of wax to return to its earlier contracted shape. Said power transferring organ 19 then also returns, with the spring force causing also the moveable element 11 to return, causing the valve 9 to be closed. An important detail in this context is that there is a certain time delay from the moment when the voltage is applied to the resistor until the wax has been heated and expanded so much that the valve 9 has been opened. In a corresponding manner, there is a delay from the removal of the voltage from the resistor until the wax has cooled off and contracted to a degree where the valve 9 is closed. In a preferred embodiment, this time delay is approximately 30 seconds.

We will now return in the description both to Fig. 1 and Fig. 2, in a state where the cleaning process is finished and the drying process is just about to begin. All of the program steps for these processes are controlled by the earlier mentioned control unit 16 arranged in the dishwasher 1. Voltage is now applied to the fan 3, the voltage feeding to the fan 3 symbolized by means of a connection 20 which leads to the power supply 15. The fan 3 starts at the same time as voltage is applied to the wax engine 13 (not shown in Fig. 2), whose valve opening process starts. At this stage, air will be transported into the first canal 6 at the area A from the ambient atmosphere via an air intake 21 through the first canal 6 to the fan 3 and further along through the third canal 8 and back out into the ambient atmosphere at point B via the air outlet 4. In Figs. 1 and 2, said air intake 21 is shown to be arranged at the upper edge of the door 5, but this is merely an example of the placement of such an air intake and should not be seen as a limitation. Downstream from the fan 3 but upstream from the air outlet 4, there is in the third canal 8 a humidity sensor 22 arranged, which humidity sensor 22 preferably is of the capacitive kind, and which as such is previously known.

It can be noted that such a capacitive humidity sensor is fed by means of direct current, and delivers an output signal within a certain frequency interval, where the frequency is proportional to the relative humidity content. The humidity sensor 22 detects, preferably but not exclusively, a relative humidity content in the interval of 10%-95%. The rest of the function of the humidity sensor will not be described here.

The connection to the humidity sensor 22 is symbolized by a connection 23 which leads to the control unit 16. This humidity sensor 22 at this stage detects the humidity content which results in a humidity value, for example by means of a number of measured values being sampled and filtered. This value in principle corresponds to the humidity content of the ambient atmosphere, since the humid air in the washing area 2 has not yet had access since the valve 9 is closed. This first value is stored. The wax engine 13 opens the valve 9 after said time delay, and the humid air in the washing area 2, led into the second canal 7 by means of the opening 10, is led further on through the second canal 7 to the fan 3 where it is mixed with the ambient atmosphere which is led to the fan 3 via the first canal 6. The mixture of the humid air with the ambient atmosphere causes the amount of vapour of the humid air to decrease, which is desirable from a user's point of view. The mixture is led further down through the third canal 8. The third canal 8 opens into the air outlet 4, which preferably is placed at the lower edge of the door 5 where the mixed air which is blown out will not be noticed very much by the user. There, the blown-out air mixture is led out in such a manner that the exhaust is primarily horizontal (see in particular Fig. 2). Another advantage of leading the expelled air mixture to the lower edge of the door 5 is that when said air mixture travels through the third canal 8, said air mixture is cooled, which further reduces the amount of steam. After the detection by the humidity sensor 22 of the humidity content of the ambient atmosphere, it takes a certain time before it again starts to detect the humidity content, which will be described in more detail below. After a predetermined time, the humidity sensor 22 again begins to detect the humidity content. When the humidity content after a certain amount of time reaches a detected value which has a certain predetermined relationship to the first stored value, the drying process is interrupted. The drying process, as described above, functions in an adaptive manner since it is adapted to the current surrounding humidity content at the time in question.

The drying process is schematically shown in Fig. 3. At the time to a value is obtained of the humidity content of the ambient atmosphere F₀. After a predetermined time t₁ the humidity sensor again begins to detect the humidity content. When the humidity content after a certain amount of time t₂ reaches a detected value F₂ which has a certain predetermined relationship to the first stored value F₀, the drying process is interrupted.

This relationship can for example be such that the first stored value F₀ is divided by a predetermined factor. This factor is in a particularly preferred embodiment 0,97 but can of course be chosen to another value if this is deemed to be advantageous. It is in this context important that the earlier mentioned predetermined time t₁ when the humidity sensor again begins to determine the humidity content after the first value having been detected and stored is chosen so that the time t₂ when the humidity content reaches the detected value F₂ is not mistaken for the time t₃ at the beginning of the drying process, when the value F₂ of the humidity content is passed. The value F₂ of the humidity content can, in the beginning of the drying process, be passed a number a times since the humidity content can fluctuate somewhat (not shown).

In a preferred embodiment the drying process is carried out by means of a time control which guarantees a certain minimal drying time. This time control in addition controls the drying process so that it does not go on longer than a certain predefined amount of time.

The invention is not limited to the above described examples of embodiments which have also been shown in the drawings but can be varied within the scope of the appended claims. For example, the valve is not necessary for the invention. Also the humidity sensor 22 does not need to be of the capacitive kind but other kinds of humidity sensors can also be used. Furthermore the invention is not limited to the application of dishwashers but can generally be applied to household machines where dishes are dried.