EP2319976A1 - Household device for cleaning items of laundry and method for operating a direct current motor fitted with brushes - Google Patents

Abstract

The household device comprises a brush-fitted direct current motor (1) for driving a washing drum. A stator is equipped with an excitation medium for generating an excitation field (7), where an armature is equipped with an armature winding (2). The armature winding of the excitation medium is electrically isolated to control the current flow independently of the excitation field. An independent claim is also included for a method for operating a direct current motor fitted with brushes.

Description

The invention relates to a household appliance for the care of laundry items. The domestic appliance comprises a laundry drum for receiving the laundry items, as well as a brushed DC motor for driving the laundry drum, which has a stator with excitation means for generating a field of excitation and an armature with an armature winding. Switching means are provided by means of which a current flow through the armature winding can be controlled. Due to this current flow, the armature can be moved in the excitation field. The domestic appliance also comprises a control device for controlling the switching means. The invention also relates to a method for operating a brushed DC motor in a domestic appliance for the care of laundry items.

It is state of the art to use universal motors as a drive for a washing drum of a washing machine. Such universal motors can be operated both with DC voltage and with AC voltage. The universal motors used today are series-wound motors - the armature winding of the armature and the field winding of the stator are connected in series, namely via a commutator. The current flowing through the field winding current also flows through the armature winding; the field current and the armature current are therefore the same. Such a universal motor of the series connection construction is for example from the document DE 10 2008 015 717 A1 known.

In order to achieve a predetermined spin speed in a universal motor, a field switch is to be made. As a rule, part of the exciter field is tapped, and the universal motor goes into subfield operation. This is, for example, the energization of only a portion of the field winding. In the subject matter in the publication DE 10 2008 007 401 A1 the field switching is made in dependence on a power reserve of the universal motor.

The armature winding is usually energized in the universal motors via the commutator and a brush system. If now the excitation field of the stator is weakened, then increases the current intensity of the field current and at the same time - the armature winding is connected in series with the field winding - the armature current flowing through the armature winding. The electric power delivered to the universal motor becomes higher, and the brush system as well as the commutator are loaded. The life and the life of the brush system are reduced. In addition, due to the field weakening increases the total power consumption of the household appliance. On the other hand, the weakening of the excitation field is required in order to achieve higher spin speeds can. This is especially true for a large load and associated high moment of inertia of the laundry drum. So the speed range of a universal motor is limited - it requires a weakening of the exciter field to allow a spin operation at high speeds. However, this success is associated with the above-mentioned disadvantages.

In addition, the control - and the control - the speed of today's universal motors is very expensive. To reduce the tax burden on universal motors to a minimum, is in the document DE 10 2005 007 759 B3 proposed to operate the universal motor optionally only at a first or a second speed value. The universal motor is thus operated optionally at two different power levels. This solution has the disadvantage that no further speed values can be set and the functionality of the universal motor is thus limited.

It is an object of the invention to provide a solution, as in a domestic appliance of the type mentioned in the brushed DC motor can be improved compared to the prior art.

This object is achieved by a domestic appliance with the features according to claim 1, as well as by a method having the features according to claim 12. Advantageous embodiments of the invention are the subject of the dependent patent claims and the description.

A household appliance according to the invention serves for the care of laundry items. The household appliance comprises a laundry drum into which items of laundry can be accommodated. It also includes a brushed DC motor for driving the laundry drum. The brushed DC motor has a stator with excitation means for generating a field of excitation and an armature with an armature winding. Switching means are provided by means of which a current flow through the armature winding can be controlled, wherein the armature can be moved in the exciter field due to the current flow through the armature winding. The domestic appliance also comprises a control device for controlling the switching means. The armature winding is electrically isolated from the exciter means and the current flow through the armature winding is controllable independently of the exciter field.

Thus, the strength of the anchor field generated by the armature winding can be adjusted independently of the strength of the exciter field by the controller. According to the invention, the armature winding is not connected in series with the excitation means - as is the case in the prior art in a series motor - switched, but the switching means are designed so that the armature winding can be energized independently of the excitation means or the control device through the current flow can control the armature winding independently of the excitation means.

In the present case, a brush-type DC motor is understood as meaning such a drive motor which has both a smoothed and thus quasi-ideal DC voltage-for example, using pulse width modulation-as well as a voltage that is only rectified and thus still pulsating or time-varying-but mostly only positive can be operated. Thus, an externally excited brushed DC motor, which can only be operated with an ideal DC voltage, is included. The brushed DC motor is also referred to below as a universal motor, in the present case, the armature winding is not connected in series with the field winding, but the armature and field winding can be controlled independently.

The domestic appliance according to the invention has various advantages: It is the speed range of the universal motor both down - advantageous for a washing operation - as well as up - advantageous for a spin operation - increased. The excitation means comprise a field winding and a current flow through the field winding can be controlled by the control device independently of the current flow through the armature winding In the spin mode, a small current flow through the field winding (low strength of the exciter field) and a high current flow through the armature winding (high strength of the armature field) can be set. On the other hand, in a washing operation in which a high torque of the universal motor is required, a high current flow through the field winding (high strength of the excitation field) and a low current flow through the armature winding (low strength of the armature field) would be set. Thus, both very high spin speeds and very low speeds can be achieved in the wash mode. In the domestic appliance according to the invention, the current flow through the armature winding can also be controlled separately if a weakening of the exciter field is undertaken. Thus, a generally existing brush system is not thermally loaded, and the total power consumption of the domestic appliance can be reduced to a minimum. It also increases the life and the life of the brush system compared to universal motors according to the prior art. Another advantage is due to a reduced current flow through the armature winding in a low noise of the universal motor. The procedure according to the invention also enables a rapid acceleration of the universal motor, which in turn allows speed ranges of mechanical resonances to be passed quickly. Rapid acceleration of the universal motor is made possible by rapidly lowering the strength of the excitation field and simultaneously increasing the strength of the anchor field.

Another advantage of the domestic appliance according to the invention is the fact that active by the independent control of the current flow through the armature winding of the armature of the universal motor - controlled by the control device - can be braked. The control device can namely switch the switching means in a generator mode of the universal motor such that the armature winding is short-circuited, at least temporarily, against a reference potential. This shorting of the armature winding brakes the armature faster than in a natural spout. By quickly decelerating, time can be saved in performing an operating program of the domestic appliance.

Due to the separate armature winding, the exciter can also be designed and designed as desired. The armature current is namely completely independent of the Excitation means. It is thus possible to provide a wide variety of embodiments with regard to the excitation means-depending on the requirements of the speed setting range.

The exciter means have a field winding, by means of which then the excitation field can be generated. As a result, the excitation field can be adjusted freely, namely by the control device. The control device can control a current flow through the field winding, so that a total of two manipulated variables - the armature current and the field current - are available for controlling the speed of the universal motor and its power consumption. It thus eliminates the "tapping" of the excitation field used in the prior art and the associated disadvantages.

In one embodiment, the excitation means may additionally comprise permanent magnets that generate the exciter field. By means of the permanent magnets, the excitation field generated by the exciter windings is advantageously supported and a ground exciter field is provided. By using permanent magnets on the stator, the efficiency of the universal motor can be increased compared to the prior art. The use of permanent magnets also makes it possible to reduce the size of the universal motor, so that overall a compact universal motor and compact home appliance can be created.

In principle, a voltage that is constant over time-a DC voltage-can be applied to the field winding, resulting in a time-constant current flow through the field winding. Such a procedure is technically particularly simple - it must be generated only a DC voltage and applied to the field winding. Such DC voltage can be tapped for example from a voltage intermediate circuit. The amplitude of the DC voltage may be 12 V, for example. However, the benefits of field winding are fully realized when further switching means for controlling the flow of current through the field winding are provided and the controller can drive these switching means independently of the armature winding means.

Then, as already explained, two manipulated variables, in particular open-loop or closed-loop control variables, are available, which can be set separately from one another, namely on the one hand the armature current or one applied to the armature winding Armature voltage and on the other hand, the field current (excitation current) or applied to the field winding field voltage (excitation voltage). The switching means for the armature winding and the switching means for the field winding may each have an active and controllable by the control device rectifier; then an active rectifier is assigned to the armature winding and an active rectifier is assigned to the field winding. The rectifiers can be coupled to a grid connection and thus directly pick up an AC supply voltage of a supply network and rectify the same AC supply voltage. The separate rectifiers can be bridge rectifiers, each with four thyristors, which can be controlled by the control device. Then a rectified supply voltage can be applied to both the armature winding and the field winding, and the respective (average) amplitudes of the supply voltages applied to the armature winding and the field winding can be adjusted by the control device, namely by outputting corresponding control signals to the respective rectifiers , In this embodiment, a so-called phase section or phase control is performed. In an alternative embodiment, a common - in particular passive - rectifier rectify the AC supply voltage of the electrical supply network, and it can be provided with a common DC link capacitor, a voltage intermediate circuit. Then, the armature winding and the field winding current from the voltage intermediate circuit in each case via an electronic switch - in particular a transistor - are supplied. Both electronic switches can be coupled to the voltage link. The controller may, in this embodiment, control the respective (average) amplitudes of the armature voltage and the field voltage using pulse width modulation. By using a voltage intermediate circuit and when using the pulse width modulation is achieved that the armature current and the field current are each direct currents with very low - almost negligible - harmonic components. This leads to a lower noise and a lower heating and a longer life of the universal motor.

wobei U_a die Ankerspannung, R_a einen Ohmschen Widerstand der Ankerwicklung, I_a den Ankerstrom, L_a eine Induktivität der Ankerwicklung, c die Maschinenkonstante, M ein Drehmoment des Universalmotors, n die Drehzahl und Φ_B einen durch die Erregermittel erzeugten magnetischen Fluss bezeichnen.If the amplitudes of the armature voltage and of the field voltage are controlled separately or independently of one another, then the following equations apply to the universal motor or the DC motor: $${\mathrm{U}}_{\mathrm{a}}\mathrm{=}{\mathrm{R}}_{\mathrm{a}}{\mathrm{l}}_{\mathrm{a}}\mathrm{+}{\mathrm{L}}_{\mathrm{a}}\frac{\mathrm{d}{\mathrm{l}}_{\mathrm{a}}}{\mathrm{dt}}\mathrm{+}\mathrm{c}{\mathrm{\Phi }}_{\mathrm{B}}\mathrm{n\; and\; M}\mathrm{=}\frac{\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="imgf0001.png"\; state="\{\{state\}\}">c</figure-callout>}}{\mathrm{2}\mathrm{\pi }}\mathrm{\cdot }{\mathrm{\Phi }}_{\mathrm{B}}{\mathrm{l}}_{\mathrm{a}}\mathrm{.}$$

where U _a is the armature voltage, _Ra an ohmic resistance of the armature winding, I _{a is} the armature current, L _a is an inductance of the armature winding, c is the machine constant, M, a torque of the universal motor n, the rotational speed and Φ _B denote a magnetic flux generated by the excitation means ,

wobei k_Φ eine Konstante und R_f einen Ohmschen Widerstand der Feldwicklung bezeichnen. Die statische Drehzahl-Drehmoment-Kennlinie ergibt sich aus den beiden erstgenannten Gleichungen: $$\mathrm{n}\mathrm{=}\frac{{\mathrm{U}}_{\mathrm{a}}}{\mathrm{c}{\mathrm{\Phi }}_{\mathrm{B}}}\mathrm{-}\frac{{\mathrm{R}}_{\mathrm{a}}}{\mathrm{2}\mathrm{\pi }{\left(\mathrm{c}{\mathrm{\Phi }}_{\mathrm{B}}\right)}^{\mathrm{2}}}\mathrm{\cdot }\mathrm{M}\mathrm{.}$$

There is generally a non-linear relationship between the field current I _f or the field voltage U _f and the magnetic flux Φ _B. With a relatively small strength of the excitation field - that is, if the exciter field is not yet saturated - but one has a linear relationship: $$\mathrm{c}{\mathrm{\Phi }}_{\mathrm{B}}\mathrm{=}{\mathrm{k}}_{\mathrm{\Phi }}\mathrm{\cdot }{\mathrm{l}}_{\mathrm{f}}\mathrm{=}{\mathrm{k}}_{\mathrm{\Phi }}\frac{{\mathrm{U}}_{\mathrm{f}}}{{\mathrm{R}}_{\mathrm{f}}}\mathrm{.}$$

where k _Φ denotes a constant and R _f an ohmic resistance of the field winding. The static speed-torque characteristic results from the first two equations: $$\mathrm{n}\mathrm{=}\frac{{\mathrm{U}}_{\mathrm{a}}}{\mathrm{c}{\mathrm{\Phi }}_{\mathrm{B}}}\mathrm{-}\frac{{\mathrm{R}}_{\mathrm{a}}}{\mathrm{2}\mathrm{\pi }{\left(\mathrm{c}{\mathrm{<figure-callout\; id="2"\; label="\Phi \; B"\; filenames="imgf0001.png"\; state="\{\{state\}\}">\Phi \; </figure-callout>}}_{\mathrm{B}}\right)}^{\mathrm{2}}}\mathrm{\cdot }\mathrm{M}\mathrm{,}$$

The idle speed is: $${\mathrm{n}}_0\mathrm{=}\frac{{\mathrm{U}}_{\mathrm{a}}}{\mathrm{c}{\mathrm{\Phi }}_{\mathrm{B}}}\mathrm{,}$$

The idle speed can be controlled by the armature voltage and the field voltage (exciter voltage), in particular regulate. For a low idling speed - for example in a washing operation - one would set a small armature voltage and a high field voltage. By contrast, a high armature voltage and a low field voltage can be set by the control device for high rotational speeds, for example in a centrifugal operation. For a given strength of the exciter field, that is at given excitation, the torque is determined by the armature current. With a high strength of the exciter field and thus lower speeds relatively high torques are possible for washing. In spin mode, however, lower torques are required, so that the smaller excitation does not lead to excessive armature currents. In other words, in a centrifugal operation of the domestic appliance, the control device can set the average current intensity of the armature current higher than the average current intensity of the field current. By contrast, in a washing operation of the domestic appliance, the control device can set the average current intensity of the armature current smaller than the average current intensity of the field current.

In one embodiment, it is also provided that when changing from a washing operation to a centrifuging operation of the domestic appliance, the control device increases the average current intensity of the armature current and reduces the average current intensity of the field current. In contrast to the prior art, therefore, no intervention in the field winding is required for the reduction of the exciter field, and the universal motor can still be operated at very high spin speeds.

The control device can - at least temporarily short-circuit the armature winding against a reference potential, under appropriate control of the switching means, in order to actively decelerate the armature of the universal motor. Thus, the time required to complete an operating program of the domestic appliance can be reduced to a minimum.

If the switching means for the armature winding are coupled to a voltage source, for example to an intermediate circuit capacitor, then the control device can recuperate in a generator operation of the universal motor. Namely, in the generator operation, the control device can control the switching means in such a way that an armature voltage induced in the armature winding in generator operation is supplied to the voltage source. Then, an electric power supplied in the generator operation by the universal motor is stored in the power source and can be reused at a later time, namely, to re-accelerate the universal motor. Thus, the energy efficiency of the household appliance is increased.

It has been found to be particularly advantageous if - in particular when using the pulse width modulation for controlling the switching means for the armature winding - the control means controls this switching means synchronously with a commutator frequency of the armature. The commutator frequency denotes the frequency with which a brush (carbon brush) of the brush system jumps from a commutator to a next Kommutatorlamelle. This commutator frequency is thus dependent on the one hand on the number of commutator and on the other hand on the instantaneous speed of the armature. The instantaneous speed can be measured, for example, by means of a speedometer device. By driving the switching means time synchronous with the commutator can be achieved that the armature voltage is applied by means of the switching means directly to the armature winding only when the brush is in contact with a commutator. When a lamella change, the armature voltage can be removed from the armature winding again. Such a synchronization can be achieved in particular in the pulse width modulation of the armature voltage without much effort. It is avoided by this embodiment, the sparking between the brush system and the Kommutatorlamellen - a so-called brush fire. It thus increases the life and the life of the brush system and thus the entire universal motor and the household appliance.

In one embodiment, the controller may detect the armature current flowing across the armature winding. Depending on the current strength of the armature current, the control device can control the armature voltage or the armature current and / or the field voltage or the field current. For example, the control device may regulate the current strength of the armature current to a constant or a speed-dependent value. The monitoring of the armature current allows on the one hand a lower heating of the brush system - namely, the current strength of the armature current can be set correspondingly low - and thus an increase in the life of the universal motor; On the other hand, with the aid of the measured values of the armature current, an omission of the field current can be detected, and corresponding safety measures can be taken. In fact, when the field current ceases, there is the danger of a "runaway" of the universal motor, that is to say the rotational speed and the current intensity of the armature current increase sharply. Such a "runaway" of the universal motor can now by the controller on the basis of Amount of current of the armature current can be detected, and the controller can separate the armature winding from a voltage source. By detecting the armature current, moreover, belt cracks can be detected. In the event of a belt break, the engine speed increases, while the armature current decreases. The control device can detect such a false state and, for example, output an information signal to an operator of the domestic appliance.

In a method according to the invention for operating a universal motor, a laundry drum is driven in a household appliance for the care of laundry by selbigen universal motor. A field of excitation is generated by energizing means of a stator of the universal motor, and current flow through an armature winding of an armature of the universal motor is controlled by means of a controller. Due to the current flow through the armature winding of the armature is moved in the exciter field. The current flow through the armature winding is controlled independently of the exciter field. The preferred embodiments presented with reference to the domestic appliance according to the invention and their advantages apply correspondingly to the domestic appliance according to the invention.

Further advantages of the invention will become apparent from the claims, the figures and the description of the figures. All the features and feature combinations mentioned above in the description as well as the features and feature combinations mentioned below in the description of the figures and / or shown alone in the figures can be used not only in the respectively specified combination but also in other combinations or in isolation.

• Fig. 1 in schematischer Darstellung ein Ersatzschaltbild eines bürstenlbehafteten Gleichstrommotors zum Antreiben einer Wäschetrommel eines Hausgeräts gemäß einer Ausführungsform der Erfindung, wobei Schaltmittel für eine Ankerwicklung sowie Schaltmittel für eine Feldwicklung des Gleichstrommotors bereitgestellt sind;
• Fig. 2 einen Verlauf der Stromstärke eines Ankerstroms sowie einen Verlauf einer Ankerleistung bei einer konstanten Schleuderdrehzahl jeweils in Abhängigkeit von der Stromstärke eines Feldstromes (Erregerstromes); und
• Fig. 3 in schematischer Darstellung eine Antriebsvorrichtung zum Antreiben einer Wäschetrommel eines Hausgeräts gemäß einer weiteren Ausführungsform der Erfindung.

The invention will now be explained in more detail with reference to individual preferred embodiments, as well as with reference to the accompanying drawings. Show it:

• Fig. 1 schematically an equivalent circuit diagram of a brushless DC motor for driving a laundry drum of a domestic appliance according to an embodiment of the invention, wherein switching means for an armature winding and switching means for a field winding of the DC motor are provided;
• Fig. 2 a profile of the current strength of an armature current and a profile of an armature power at a constant spin speed in each case as a function of the current intensity of a field current (exciter current); and
• Fig. 3 a schematic representation of a drive device for driving a laundry drum of a domestic appliance according to another embodiment of the invention.

In the figures, identical and functionally identical elements are provided with the same reference numerals.

Fig. 1 shows a schematic representation in its upper part of an equivalent circuit diagram of a universal motor 1 and a third-party brushed DC motor, which is installed in the embodiment in a washing machine. The universal motor 1 is used to drive a laundry drum not shown in the figures for receiving laundry items. The universal motor 1 comprises a stator to which an armature (also known by the name "rotor") is rotatably mounted. The armature comprises an armature winding 2, which in the equivalent circuit diagram according to FIG Fig. 1 is shown on the left side. The armature winding 2 is energized via a commutator and a brush system.

If one now considers the armature winding 2 from two connection terminals 3, 4, one sees an ohmic resistance R _a , an inductance L _a and a voltage source 5, which represents a voltage U _i induced in the armature winding 2. Between the terminals 3, 4 is an armature voltage U _a . Through the armature winding 2, an armature current I _{a flows} .

The stator comprises excitation means, which in the exemplary embodiment comprise a field winding 6, the equivalent circuit diagram in FIG Fig. 1 is shown on the right. The excitation means may also comprise permanent magnets. In the operation of the universal motor 1, the field winding 6 generates an exciting field 7, in which the armature is rotated with respect to the stator.

Looking at the field winding 6 of two terminals 8, 9, so you can see an ohmic resistance R _f and an inductance connected in series L _f . Between the terminals 8, 9 is applied to a field voltage U _f (excitation voltage). Through the field winding 6, a field current I _f (excitation current) flows.

Both for the armature winding 2 and for the field winding 6 switching means 10, 11 are provided, via which the armature winding 2 and the field winding 6 are energized. Namely, the switching means 10, 11 each comprise an active bridge rectifier with four thyristors 12 each. The bridge rectifiers are therefore full-wave rectifiers. The thyristors 12 of the switching means 10 for the armature winding 2 are driven by a control device 13a - for example a microcontroller -, and the thyristors 12 of the switching means 11 for the field winding 6 are also driven by a control device 13b, which may be a microcontroller. The control devices 13a, 13b are shown only schematically, and a common control device 13 for the switching means 10, 11 can also be provided.

It is a relay system 14 between the switching means 10 and the terminals 3, 4 of the armature winding 2 is provided. By means of the relay system 14, which can be controlled by the control device 13a, the armature voltage U _{a can be} reversed, and the direction of rotation of the armature can be changed.

The two bridge rectifiers pick up a supply AC voltage U _{V of} a supply network, which is applied between two input terminals 15, 16.

In the in Fig. 1 illustrated embodiment, therefore, two separate active bridge rectifier are used in order to energize the armature winding 2 and the field winding 6 independently. Between the terminals 3, 4 and 8, 9, that is, to the armature winding 2 and the field winding 6, thus in each case a rectified and thus positive voltage is applied. The control devices 13a, 13b can use phase-angle control or phase-angle control in the control of the thyristors 12 and thus in the control of the respective amplitudes of the armature voltage U _a and the field voltage U _f . Thus, the control devices 13a, 13b to the armature winding 2 and the field winding. 6 separately control outputs delivered or set the respective average currents of the armature current I _a and the field current I _f separately.

Fig. 2 shows a principal course 17 (dashed line) of the armature current I _a and a course 18 (solid line) of an armature power P _a respectively as a function of the current intensity of the field current I _f . The curves 17, 18 are shown for a constant spin speed of the washing machine. As from the graph according to Fig. 2 can be seen, the current strength of the armature current I _a decreases with increasing current intensity of the field current I _f . The course 18 of the armature power P _a , however _, has a minimum 19, which is speed and load-dependent. The recorded armature power P _a can thus be reduced to a minimum, as well as the total energy consumption of the washing machine. Namely, the universal motor 1 can be operated at such an operating point at which the minimum 19 of the armature power P _{a is} given. In other words, the current intensity of the field current I _f can be adjusted so that the minimum 19 of the armature power P _{a is} reached. At this operating point, the current intensity of the armature current I _{a is} relatively low, so that the brush system of the universal motor 1 is spared.

In Fig. 3 is another example of the control of the universal motor 1 and for the energization of the armature winding 2 and the field winding 6 shown. On the right is in Fig. 3 the universal motor 1 with the field winding 6 and the armature winding 2 shown schematically. In the embodiment according to Fig. 3 is from the supply AC voltage U _V (in Fig. 3 not shown) of the electrical supply network generates a DC link voltage U _z , namely, for example by means of a rectifier. The DC link voltage U _z is between two DC link connections 20, 21. At the DC link 21, a reference potential B is provided. Between the DC link 20, 21, an intermediate circuit capacitor 22 is connected to which the DC link voltage U _z is applied.

Optionally, a voltage boost converter 23 can also be connected between the DC link connections 20, 21, by means of which the amplitude of the DC link voltage U _z can be set _as desired. In this way, the washing machine can then be operated on different supply networks become. Instead of the voltage step-up converter 23 or in addition to a voltage doubler can be used, which may have a connectable to the intermediate circuit capacitor 22 as needed in series connectable capacitor.

As in the embodiment according to Fig. 1 , The armature winding 2 and the field winding 6 are also in the embodiment according to Fig. 3 energized by means of switching means 10, 11. The armature winding 2 is connected on the one hand to the intermediate circuit terminal 20 and on the other hand to the collector terminal 24 of a bipolar transistor 25. The emitter terminal 26 of the bipolar transistor 25 is coupled to the reference potential B via a current sensing resistor 27 (shunt). The base terminal 28 of the bipolar transistor 25 is connected to a control device 13 (for example a microcontroller). The control device 13 can thus drive the bipolar transistor 25 and thus control the current flow through the armature winding 2, namely, for example, using the pulse width modulation.

The field winding 6 is also energized by a bipolar transistor 29. In the embodiment according to Fig. 3 the field winding 6 is also energized via the relay system 14, by means of which the direction of rotation of the universal motor 1 can be changed. In the in Fig. 3 illustrated state of the relay system 14, the field winding 6 on the one hand to the DC link 20 and on the other hand connected to the collector terminal 30 of the bipolar transistor 29. The emitter terminal 31 of the bipolar transistor 29 is coupled to the reference potential B via a current sensing resistor 32. The base terminal 33 of the bipolar transistor 29 is connected to the control device 13. Thus, the control device 13 can control the flow of current through the bipolar transistor 29 and thus through the field winding 6.

The control device 13 can also detect the armature current I _a as well as the field current I _f , namely via lines 34, 35.

Thus, the controller 13 in the embodiment according to Fig. 3 - As in the embodiment according to Fig. 1 - Control the current flow through the armature winding 2 and the current flow through the field winding 6 independently. In the embodiment according to Fig. 1 the phase section control or Phase control. In the embodiment according to Fig. 3 The control of the current flows using the pulse width modulation, this for both the bipolar transistor 25, as well as for the bipolar transistor 29. The controller 13 can thus both in the embodiment according to Fig. 1 as well as in the according Fig. 3 the average amplitudes of the armature voltage U _a and the field voltage U _f , as well as the average currents of the armature current I _a and the field current I _f control.

In a washing operation of the washing machine, in which the universal motor 1 is operated at lower speeds, the control device 13 sets a low armature voltage U _a and a high field voltage U _f . In a spin operation of the washing machine, in which the universal motor 1 is operated at high speeds, the control device 13, however, sets a high armature voltage U _a and a low field voltage U _n .

In Fig. 3 In addition, a speedometer device 36 is shown, which can detect the speed of the universal motor 1. The tachometer 36 transmits signals with information about the respective instantaneous speed of the universal motor 1 to the control device 13. The control device 13 can thus control or regulate the speed of the universal motor 1.

The control device 13 can control the same current intensity and / or the current intensity of the field current I _{f as a} function of the measured current intensity of the armature current I _a . It is also possible to regulate the current intensity of the armature current I _a . Thus, an excessive power consumption can be avoided, so that the total power consumption of the washing machine can be reduced to a minimum. It can thus be avoided a burden on the brush system, and the life and the service life of the universal motor 1 can be increased. The regulation of the current intensity of the armature current I _a can, for example, be such that the minimum 19 of the armature power P _{a in} accordance with Fig. 3 is reached.

Overall, therefore, a domestic appliance is created in which an improved compared to the prior art universal motor 1 is used for driving the laundry drum. Instead of a universal motor of the series connection construction, a universal motor 1 is used, the armature winding 2 is energized independently of the field winding 6 can be. It thus eliminates the "field tap", as is done in the prior art at high speeds of the universal motor. By a separate control of the current flow through the armature winding 2 and the field winding 6 a total of a larger speed control range of the universal motor 1 can be achieved.

LIST OF REFERENCE NUMBERS

1

brushed DC motor

2

armature winding

3, 4

terminals

5

voltage source

6

field winding

7

exciting field

8, 9

terminals

10, 11

Bridge rectifier

12

thyristors

13, 13a, 13b

control device

14

relay system

15, 16

input terminals

17, 18

courses

19

minimum

20.21

DC link connections

22

Link capacitor

23

Voltage step-up converter

24

Collector terminal

25

bipolar transistor

26

Emitter terminal

27

Current sensing resistor

28

Base terminal

29

bipolar transistor

30

Collector terminal

31

Emitter terminal

32

Current sensing resistor

33

Base terminal

34, 35

cables

36

Tacho facility

I _a

armature current

I _f

field current

U _a

armature voltage

U _f

field voltage

R _a

Ohmic resistance of the armature winding 2

L _A

Inductance of the armature winding 2

U _i

induced voltage

R _f

Ohmic resistance of the field winding 6

L _f

Inductance of the field winding 6

U _V

AC supply voltage

U _z

Intermediate circuit voltage

P _A

anchor performance

Claims (12)

Domestic appliance for the care of laundry, with: a laundry drum for picking up the laundry items, - A brushed DC motor (1) for driving the laundry drum, which has a stator with excitation means (6) for generating a field of excitation (7) and an armature with an armature winding (2), - Switching means (10), by means of which a current flow (I _a ) through the armature winding (2) is controllable, wherein due to the current flow (I _a ) through the armature winding (2) of the armature in the excitation field (7) is movable, and a control device (13, 13a, 13b) for activating the switching means (10),
characterized in that
the armature winding (2) is electrically isolated from the exciter means (6) and thereby the current flow (I _a ) is controllable by the armature winding (2) independently of the excitation field (7). Domestic appliance according to claim 1, characterized in that the excitation means (6) permanent magnets for generating the exciter field (7). Domestic appliance according to claim 1 or 2, characterized in that the exciter means (6) comprise a field winding (6) for generating the exciter field (7). Domestic appliance according to claim 3, characterized by further switching means (11) for controlling a current flow (I _f ) through the field winding (6), wherein the control device (13, 13a, 13b) is adapted to the further switching means (11) independently of the To control switching means (10) for the armature winding (2). Domestic appliance according to claim 3 or 4, characterized in that the control device (13, 13a, 13b) is adapted to, at a change from a washing operation in a centrifugal operation of the domestic appliance, the average current intensity to increase an armature current (I _a ) flowing through the armature winding (2) and to reduce the average current intensity of a field current (I _f ) flowing through the field winding (6). Domestic appliance according to one of claims 3 to 5, characterized in that the control device (13, 13a, 13b) is adapted to, in a centrifugal operation of the domestic appliance, the average current intensity of an armature winding (2) flowing armature current (I _a ) higher than that average current intensity of a field current (I _f ) flowing through the field winding (6). Domestic appliance according to one of claims 3 to 6, characterized in that the control device (13, 13a, 13b) is adapted to, in a washing operation of the domestic appliance, the average current intensity of an armature winding (2) flowing armature current (I _a ) less than that average current intensity of a field current (I _f ) flowing through the field winding (6). Domestic appliance according to one of the preceding claims, characterized in that the control device (13, 13a, 13b) is designed to short-circuit the armature winding (2) at least temporarily against a reference potential (B) for active braking of the armature. Domestic appliance according to one of the preceding claims, characterized in that the switching means (10) for the armature winding (2) are coupled to a voltage source (22) and the control device (13, 13a, 13b) is designed to operate in a generator mode of the DC motor ( 1) to control the switching means (10) such that in the armature winding (2) induced in generator operation armature voltage (U _a ) of the voltage source (22) can be fed. Domestic appliance according to one of the preceding claims, characterized in that the control device (13, 13a, 13b) is adapted to control the switching means (10) for the armature winding (2) synchronously with a commutator frequency. The domestic appliance according to any one of the preceding claims, characterized in that the control device (13, 13a, 13b) is adapted to the current flowing through the armature winding (2) armature current (I _a) to be detected. Method for operating a brushed DC motor (1), by which a laundry drum is driven in a domestic appliance for the care of laundry, with the steps: - Generating an excitation field (7) by excitation means (6) of a stator of the DC motor (1), and - Controlling a current flow (I _a ) by an armature winding (2) of an armature of the DC motor (1) by means of a control device (13, 13 a, 13 b), wherein due to the current flow (I _a ) through the armature winding (2) of the armature in the Excitation field (7) is moved,
characterized in that
the current flow (I _a ) is controlled by the armature winding (2) independently of the excitation field (7).

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