Method for removing scum in a drum washing machine, and drum washing machine suitable for this purpose

1. A method for removing scum in a tub of an electronically controlled drum washing machine, the method comprising:

alternately rotating a drum following a main washing cycle and pumping liquid out of the drum;

pumping a liquid out of the drum for between 30 seconds to 15 minutes following the main washing cycle and pumping liquid out of the drum;

regulating a level of water following the main washing cycle and pumping liquid out of the drum by:

introducing a quantity of water into the drum which is sufficient to cover all water channels based on a pressure hysteresis measured by a pressure sensor used to determine a level of liquid in the tub such that a scum dilution results without renewed scum formation; and

rinsing over a short period of time t 2 , wherein the short period of time t 2 includes a range of 1 minute to 5 minutes; and

pumping liquid out of the drum while the drum is moved at a low rotational speed following the main washing cycle and pumping liquid out of the drum, wherein the low rotational speed includes a range of 20 to 60 revolutions per minute, wherein the electronically controlled drum washing machine includes a detergent-solution runoff system arranged on the base of the tub which has a detergent-solution pump and the pressure sensor for determining the level of liquid contained in the tub, the signal from this pressure sensor being recorded during operation of the detergent-solution pump, and the drum.

2. The method of claim 1 , wherein the pumping the liquid out of the drum following the main washing cycle and pumping liquid out of the drum includes:

pumping the liquid out of the drum for between 2 minutes to 10 minutes following the main washing cycle and pumping liquid out of the drum.

3. The method of claim 1 , wherein the pumping the liquid out of the drum following the main washing cycle and pumping liquid out of the drum includes:

pumping the liquid out of the drum for between 2.5 minutes to 4 minutes following the main washing cycle and pumping liquid out of the drum.

4. The method of claim 1 , wherein the low rotational speed includes a range of 30 to 50 revolutions per minute.

5. The method of claim 1 , wherein the alternately rotating the drum includes alternately rotating the drum in opposite directions following the main washing cycle and pumping liquid out of the drum.

6. The method of claim 1 , wherein the short period of time t 2 includes a range of 1 minute to 3 minutes.

7. The method of claim 1 , wherein the pressure sensor measures a pressure at an upper switching point for the water supply and a pressure at a lower switching point for the water supply and a pressure difference between the pressure at the upper switching point and the pressure at the lower switching point includes a range of 10 to 150 Pa.

8. The method of claim 1 , wherein the pressure sensor measures a pressure at an upper switching point for the water supply and a pressure at a lower switching point for the water supply and a pressure difference between the pressure at the upper switching point and the pressure at the lower switching point includes a range of 20 to 100 Pa.

9. The method of claim 1 , wherein the pressure sensor measures a pressure at an upper switching point for the water supply and a pressure at a lower switching point for the water supply and a pressure difference between the pressure at the upper switching point and the pressure at the lower switching point includes a range of 30 to 70 Pa.

10. The method of claim 1 , further comprising spinning the drum at a rotational speed below 500 revolutions/minute over a short period of time t 3 wherein the short period of time t 3 includes a range of 30 seconds to 5 minutes, after alternately rotating the drum and pumping a liquid out of the drum for between 30 seconds to 15 minutes and before regulating the level of water.

11. The method of claim 10 , further comprising:

alternately rotating the drum at the low rotational speed after spinning the drum at the rotational speed below 500 revolutions/minute over the short period of time t 3 ;

holding the drum still after spinning the drum at the rotational speed below 500 revolutions/minute over the short period of time t 3 ; and

pumping the liquid out between 30 seconds and 15 minutes after the spinning the drum at the rotational speed below 500 revolutions/minute over the short period of time t 3 .

12. The method of claim 10 , wherein the spinning the drum includes:

spinning the drum at a rotational speed below 400 revolutions/minute.

13. The method of claim 10 , wherein the spinning the drum includes:

spinning the drum at a rotational speed in a range of 100 to 200 revolutions/minute.

14. The method of claim 1 , further comprising performing a normal spin and rinse in which scum can be detected after the pumping liquid out of the drum while the drum is moved at the low rotational speed.

15. The method of claim 14 , further comprising:

detecting a scum;

aborting a spinning in response to the detecting the scum; and

in response to the detecting the scum, re-executing:

the alternately rotating the drum;

the pumping the liquid out of the drum for between 30 seconds to 15;

the regulating the level of water by introducing the quantity of water into the drum which is sufficient to cover all the water channels and rinsing over the short period of time t 2 ; and

the pumping the liquid out of the drum while the drum is moved at the low rotational speed.

16. A drum washing machine comprising:

a controller that controls a program execution;

a drum rotatably mounted in a tub;

a detergent-solution runoff system on a base of the tub, the detergent-solution runoff system including a detergent-solution pump;

a drive motor for the drum;

a heater;

a pressure sensor that determines a level of liquid contained in the tub based on a pressure hysteresis, a signal from the pressure sensor being recorded during operation of the detergent-solution pump; and

a switch responsive to a scum being detected,

wherein the controller is programmed to control the switch to:

alternately rotate the drum following a main washing cycle and pumping liquid out of the drum;

pump a liquid out of the drum for between 30 seconds to 15 minutes following the main washing cycle and pumping liquid out of the drum;

regulate a level of water following the main washing cycle and pumping liquid out of the drum by:

introducing a quantity of water into the drum which is sufficient to cover all water channels based on the pressure hysteresis measured by a pressure sensor used to determine a level of liquid in the tub such that a scum dilution results without renewed scum formation; and

rinse over a short period of time t 2 , wherein the short period of time t 2 includes a range of 1 minute to 5 minutes; and

pump liquid out of the drum while the drum is moved at a low rotational speed following the main washing cycle and pumping liquid out of the drum.