EP0369270B1 - Method and device to optimise a spinning speed/time curve of washing machines - Google Patents

Description

The invention relates to a method and a device for optimizing the spin speed-time profile of household washing machines according to the preamble of claim 1. It relates in particular to a method for an optimal start-up of the laundry drum during spin drying, the last step of a washing machine program.

In known household washing machines, laundry-friendly drainage is achieved by spinning in several stages with increasing drum speed. The final spin speeds here are 850 or a maximum of 1200 revolutions per minute. (AEG brochure 1988 "Washing machines, dryers, spinners").

Furthermore, a "control circuit for different spin speeds of a washing machine" is known from DE-OS 36 15 712. Here too, the different spin speeds are increased to 1000 revolutions per minute in several, for example four, stages until the maximum speed is reached. The runtime per speed value is constant in each case one minute so that the maximum spin speed is reached after about three minutes.

With regard to the state of the art, the number of revolutions of equal to or greater than 1400 revolutions per minute and thus optimal dewatering of the laundry can only be achieved with the aid of separate spin dryers. However, such spin dryers are only a supplement to the known household washing machines. Although they can be set up as free-standing models, they require space and their own drainage system. (Except for the cumbersome transfer of laundry from the washing machine drum to the spin dryer).

The object of the invention is to effectively avoid the deficiencies and disadvantages inherent in the prior art by means of a suitable centrifugal process.

This object, according to the invention, is achieved by the characterizing features of claim 1. A further advantageous embodiment of the method according to the invention can be found in the subclaims.

The advantages which can be achieved by the method according to the invention consist in particular in that a final spin speed which is far above that in known washing machines is reliably reached and the laundry is consequently optimally dewatered or its residual moisture is reduced to a minimum. A re-spin in separate spin dryers is not necessary. The speed ramp-up profile of the laundry drum was chosen so that the load on the drive motor and laundry drum bearings remains minimal despite the increased spin speed. As a result, the bearings of conventional washing machines can advantageously be used for production purposes without their usual life would be reduced, ie expensive special high-performance bearings are not required.

An embodiment of the invention is illustrated by means of diagrams and is explained in more detail below.

• Fig. 1 das Drehzahlprofil eines End- oder Fertig-Schleudergangs (Trockenschleudern) mit der Wäschetrommelumdrehungszahl in Abhängigkeit von der Zeit,
• Fig. 2 die Restfeuchtigkeit der Wäsche in Abhängigkeit von der Schleuderzeit mit der Wäschetrommelumdrehungszahl als Parameter,
• Fig. 3 die effektive Lagerbelastung in Abhängigkeit von dem Schleuderzeit, mit der Wäschetrommelumdrehungszahl als Parameter.

Show it:

• 1 shows the speed profile of a final or finished spin cycle (dry spin) with the laundry drum speed as a function of time,
• 2 shows the residual moisture of the laundry as a function of the spin time with the laundry drum speed as a parameter,
• Fig. 3 shows the effective bearing load depending on the spin time, with the laundry drum speed as a parameter.

According to FIG. 1, the number of revolutions of the laundry drum during the final spin is increased in four stages at the end of the washing program:
In about 1.2 minutes in small steps, the so-called "soft start" to 850 revolutions per minute. These 850 revolutions per minute of the first stage are kept constant for 5 minutes, then in the
second stage: acceleration to 1000 revolutions per minute and keeping this speed constant for 1.7 minutes, then in the
third stage: acceleration to 1150 revolutions per minute and keeping this speed constant for 1.2 minutes, then in the
fourth stage: acceleration to 1350 revolutions per minute and keeping this speed constant for 0.5 Minutes, then brake the laundry drum to a standstill.

The laundry of a drum filling is optimally spun dry using this process. The moisture content or the residual moisture which is gradually withdrawn by the increase in the drum speed is illustrated in the diagram according to FIG. 2 according to the solid lines.

The increase in the effective bearing load on the device during the gradual increase in the number of revolutions of the laundry drum is illustrated by the solid lines in the diagram according to FIG. 3.

Practical investigations have shown that the above-mentioned graduated washing drum revolutions only have to be observed with an accuracy of + -10% of their nominal values and the respectively associated spin times with an accuracy of + -20% of their nominal values. Overall, within these tolerance ranges, approximately the same results are obtained in terms of minimum residual moisture and minimal bearing load.

The new spin cycle (last wash program section) or its spin speed-time profile is stored in terms of stepped speeds and associated spin times in an electronic module with a microprocessor or taken into account in the program switch of the washing machine.

Finally, it should be noted that a division into 5 or more drum speed stages would be conceivable and possible, but there are no noteworthy advantages.

Claims (4)

1. A method for optimising the spin speed-time-profile of domestic washing machines with a motor-driven washing drum, which can be accelerated in four stages during the last programme step to a maximum spin speed, whilst observing predetermined time periods, characterised in that, in the first stage, the washing drum maintains a rotational speed of 850 revolutions per minute for a period of five minutes, then in the second stage accelerates to 1000 revolutions per minute and maintains this speed for a period of 1.7 minutes, then in the third stage accelerates to 1150 revolutions per minute and maintains this speed for a period of 1.2 minutes, and finally in the fourth and last stage accelerates to 1350 revolutions per minute, which speed is maintained for 0.5 minutes.
2. A method according to claim 1, characterised in that the four-stage washing drum rotational speeds are observed with a degree of accuracy equal to or less than +-10% of their nominal value.
3. A method according to claim 1, characterised in that the four-stage washing drum rotational speeds are observed with a degree of accuracy equal to or less than +-20% of their nominal value.
4. A device for carrying out the method according to claim 1, characterised in that the predetermined, staged rotational speeds together with their respective spin times for the last wash programme step are stored or provided in an electronic module with a microprocessor or in a programme switching mechanism of the domestic washing machine.

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