EP0960231A2

EP0960231A2 - Laundry treating equipment with a driving motor mounted on the drum shaft

Info

Publication number: EP0960231A2
Application number: EP98906957A
Authority: EP
Inventors: Peter Rode; Frank Horstmann; Helmut Scheibner
Original assignee: Miele und Cie KG
Current assignee: Miele und Cie KG
Priority date: 1997-02-17
Filing date: 1998-02-17
Publication date: 1999-12-01
Anticipated expiration: 2018-02-17
Also published as: EP0960231B2; DE19806258A1; JP2001511674A; EP0960231B1; ES2176972T3; WO1998036123A2; US6341507B1; ATE217655T1; KR20000069295A; WO1998036123A3; KR100436152B1; DE59804137D1

Abstract

The invention relates to a laundry treatment apparatus like washing machines, laundry dryers or a washer-dryers with a rotatably mounted drum (6) with an at least approximately horizontal axle and with a drive motor (10) structured as a synchronous motor (10) energized by permanent magnets arranged on the drum (6) shaft, the stator (16) of the motor (10) being provided with a winding (18) which is energized by a converter. In order to optimize the motor in such machines in respect of energy consumption, noise development and costs it is proposed to design the winding (18) as a single pole winding, whereby the number of stator poles (27) and of the magnet poles (23) is different, and to utilize a frequency converter (104) as the converter the output voltage of which being set such the continuous currents are generated in all winding strands.

Description

description

Laundry treatment device with a drive motor arranged on the drum shaft

The invention relates to a laundry treatment device such as a washing machine, tumble dryer or washer dryer with a rotatably mounted drum with at least approximately a horizontal axis of rotation, and with a drive motor arranged on the drum shaft in the form of a permanent magnet-excited synchronous motor, the stator of which is provided with a winding which is supplied with current by a converter .

A washing machine is already known from DE 38 19 651 A1, in which the washing drum is driven directly without using the usual intermediate drive (drive belt, pulley). In these drives, the rotor forms the rotary motion transmission part to the drum of the washing machine. DE 38 19 651 A1 proposes to use an asynchronous motor with a squirrel-cage rotor. Such an engine is characterized by a relatively quiet running, but it has the disadvantage that under the given conditions such. B. large air gap and multi-pole design with asynchronous machines good efficiencies are not possible. Especially with a frequently operated household appliance, however, there is a desire for an environmentally friendly, ie. H. energy-saving mode of operation.

A motor according to the preamble of claim 1 is known from DE 43 41 832 A1. There, a motor that drives the drum is described, which is designed as an inverter-fed synchronous motor. No further details are given on the type of engine.

Washing machines with directly driving motors are also known which are constructed as external rotor motors (DE 44 14 768 A1, DE 43 35 966 A1, EP 413 915 A1, EP 629 735 A2). The rotor can be manufactured as a deep-drawn part, as a plastic bell or in a composite construction. The solution is advantageous as a deep-drawn part, since the iron forms the magnetic yoke at the same time. This design is, among other things, a typical version of fan motors.

In the above-mentioned direct drives for washing machines, collectorless DC motors are used. Their stator winding can either be designed as a conventional three-phase winding with a winding step over several stator teeth or as a single-pole winding with winding around a stator tooth. In this type of motor, the current is reversed using power semiconductors. The individual are dependent on the rotor position

CONFIRMATION COPY Strands of the stator winding are energized by an inverter so that the field of excitation rotates with the motor. In a three-phase excitation winding, this motor control only ever flows a current in two phases, which is used to generate moments, the third phase remaining de-energized. The current flow in the individual strings is block or trapezoidal. As a result, when the individual windings are switched on and off, high speeds of current change occur, which generate noise on the motor. Such noises are undesirable in laundry treatment devices, some of which are installed in living rooms (kitchen, bathroom).

In electronically commutated direct current motors, Hall sensors, magnetic sensors or optical sensors are used to sense the rotor position. The attachment of such sensors and the associated signal lines is associated with additional costs. In addition, sensors and cables are prone to failure. Another disadvantage is that operation with field weakening is not readily possible with such self-guided permanent magnet excited motors. The large torque and speed spreads between washing and spinning operations required in washing machines normally cause large spreads in the motor current. Therefore switchable or tapped windings must be installed or the motor winding and the power semiconductors must be dimensioned for the largest possible current.

Synchronous motors with sinusoidal current and controlled via a converter are already known as servo drives. They are used where precise positioning is required. In known servo drives, the stator winding is designed as a classic three-phase winding, and the number of poles of the rotor and stator are identical. The three-phase winding is characterized by common and known winding techniques, but has the disadvantage that the copper volume is particularly large in the winding heads, which increases the manufacturing costs and increases the depth of the motor. The latter would reduce the drum volume in washing machines with a given housing depth. In addition, servo drives for controlled operation require very precise and expensive sensors to detect the rotor position

Another disadvantage of all of the aforementioned permanent magnet-excited motors is that they do not have any field weakening, since the magnetic flux of the motor depends essentially on the field of the permanent magnets and is therefore constant. Such motors are therefore rather unsuitable for washing machine drives, since a large torque and speed spread between the washing operation and the spin operation would result in a large spread of the motor current. The motor winding and the power semiconductors of the frequency converter should be therefore be dimensioned for the largest current and would be very expensive. As an alternative, a winding tap could be used, but additional lines must be run from the motor to the electronics. In addition, expensive changeover relays are necessary.

The invention thus presents the problem of optimizing the motor in terms of energy consumption, noise development and costs in a laundry treatment machine of the type mentioned at the outset. According to the invention, this problem is solved by a laundry treatment appliance with the features specified in claim 1. Advantageous refinements and developments of the invention result from the following subclaims.

In contrast to previously known direct drives for washing machines with collectorless DC motors, all three winding phases of the three-phase excitation winding are continuously energized in the drive concept described here, the frequency of the excitation field being predetermined by the electronics. In this case, the motor is operated as an externally operated synchronous motor. This procedure guarantees the lowest noise development in connection with a permanent magnet synchronous motor.

By using the single-pole winding, the copper insert is less than with a classic three-phase winding, in particular the copper volume of the winding heads is significantly lower. This makes the entire drive smaller and more compact. Due to the lower copper volume, higher efficiency can be achieved with the same motor size due to lower copper losses.

It is advantageous to design the rotor as an external rotor, as a result of which the most compact designs can be achieved because the torque-forming air gap radius is close to the outer radius.

It is also advantageous to use a control device which adjusts the output voltage of the frequency converter by regulating such that a minimal sinusoidal current is established as a function of the load torque. Sinusoidal currents make the motor run very quietly and reduce the losses caused by current harmonics. This is particularly the case if the output voltage is set in the form of a sinus-weighted pulse width modulation. Furthermore, the torque-dependent current control ensures optimum efficiency at every load point.

In the case of synchronous motors with a single-pole winding, the number of magnetic poles differs in a characteristic manner from the number of stator poles. With a three-strand design and one Continuous energization or a rotating flooding of the stator winding, a ratio of rotor poles to stator poles of 2 to 3 or 4 to 3 is favorable. Only in these two cases does the vectorial addition of the voltages of a phase induced in the individual pole windings result in a maximum and an optimum in efficiency.

With a pole ratio of 4 to 3, the use of about 30 stator poles is favorable in order to cover the required speed range from 0 to 2000 1 / min. The selected number of poles guarantees a safe start-up with externally controlled operation, a low torque ripple and a large speed spread.

In addition, it is advantageous if the control device for regulating the motor current is based on a mathematical model of the motor and if the current is applied to the winding strands without the use of rotary sensors. Since the motor current and the voltage on the motor can be recorded in the frequency converter itself, no sensors are required on the motor.

In an advantageous embodiment of a sensorless control system, the mathematical model can be calibrated as required or continuously. The motor-specific parameters such as winding resistance, motor inductance and constant of the induced voltage can be determined using the current sensors and the microprocessor control in the frequency converter and the mathematical model can be adapted based on the measured values.

The main advantage of the laundry treatment device designed according to the invention results from the possibility of dimensioning the number of turns of the stator windings in such a way that the amount of the induced voltage or the magnet wheel voltage for high speeds is greater than the maximum output voltage of the frequency converter. Such a winding design enables a field weakening operation of the synchronous motor in the higher speed range. The advantage of this winding design is a significant reduction in the motor current in washing mode. It can be chosen such that the motor can be operated with the same current in the washing and spinning mode. Because of the lower motor current, smaller and more cost-effective power semiconductors can therefore be used. In addition, the losses in the power semiconductors are reduced, which means that the overall efficiency of the motor and power electronics is higher than that of comparable ones

Drives with the same copper insert. To weaken a field even when using a control _. To enable rotor position sensors, it is advantageous to dispense with their evaluation at higher speeds. At higher speeds there are no washing machines large or short-term load fluctuations, so that regulation of the motor current is not absolutely necessary. In this case, the motor is operated externally, whereby the voltage and frequency are specified by the converter regardless of the position of the rotor field. The motor current then sets itself within limits depending on the load torque. In order to prevent the motor from overloading and falling out of step, it is sufficient to monitor the level of the motor current as a function of the rotating field frequency.

Furthermore, field weakening can also be used to achieve good efficiencies at high speeds even with multi-pole, permanently excited synchronous motors, since the magnetic loss as a result of the field weakening is reduced.

Collectorless DC motors can only be operated with extensive field weakening, since the position of the rotor position encoder would then have to be changed or the commutation times would have to be shifted computationally. A field weakening operation is not known for servo drives for the aforementioned reasons.

An embodiment of the invention is shown purely schematically in the drawings and is described in more detail below. It shows:

1 shows a section through a washing machine constructed according to the invention as

2 shows a partial section through the rear area of a tub (2), one

Drum (6) and its drive motor (10) Figure 3, the bearing cross (11) of a washing machine in a perspective view

FIG. 4 shows a single sheet of a stator (16) of the drive motor (10)

Figure 5 shows a permanent magnetic rotor (15) in perspective

FIG. 6 is a block diagram of the structure of the controlled drive with three-phase

Synchronous motor and rotor position sensors Figure 7 is a block diagram of the structure of the sensorless controlled drive with three-phase synchronous motor

The washing machine shown in Figure 1 has a housing (1) in which a tub (2) is suspended on springs (4) so that it can move. To dampen the vibrations, it is supported against the housing base (1a) by friction dampers (5). A drum (6) for holding laundry (not shown) is rotatably mounted in the tub (2) in a known manner. Drum (6), tub (2) and the housing front wall (1a) have corresponding openings through which the laundry can be filled into the drum (6). The openings can be opened through a front wall (1a) arranged door (7) are closed. The door (7) is locked by an electromagnetic locking device (8). The door lock is only shown schematically in the drawing. The structure and mode of operation of an electromagnetic closure device (8) itself is sufficiently known from the above-mentioned DE-OS 16 10 247 or from DE 34 23 083 C2 and is therefore not described in more detail. In the upper part of the front wall of the housing (1a) there is a control panel (not shown) in which a rotary selector switch (9) is used to select washing programs. As is known, the washing programs include a wash cycle and a subsequent rinse cycle, during which the laundry is spun several times. The washing speed for household washing machines is between 20 and 60 min-1, the spin speed should be as high as possible, especially during the last spin at the end of the wash cycle. It is limited by the resilience of the vibrating tub (2) - suspension (3; 4) - drive motor (10) - drum (6) system, the limits are currently around 1600 min-1.

Figure 2 shows a partial section through the rear area of a tub (2), a drum (6) and its drive motor (10). For the rotatable mounting of the drum (6), a four-armed bearing cross (11) shown in FIG. 3 is provided on an edge attachment (2a), which is formed by the jacket (2b) of the tub (2) and an edge of its base (2c) ) attached. In the center of this bearing cross (11) is a bearing hub (12) into which two radial roller bearings (13a, b) are inserted. These roller bearings (13a, b) in turn serve for rotatably receiving a drive shaft (14) which is connected to the drum base (6a) in a rotationally fixed manner. The rear end (14a) of the drive shaft (14) protrudes from the bearing hub (12). A permanent magnet rotor (15) designed as an external rotor is attached to it and thus drives the drum (6) directly. The stator (16) of the drive motor (10) is attached to the bearing cross (11).

The stator laminated core (17) with the stator windings (18) is essentially ring-shaped. FIG. 4 shows the sheet metal section of an individual stator sheet (17a). The individual sheets (17a) have attachment eyes for attaching the stator laminated core (17) to the bearing cross, which are arranged on the inner circumferential surface and are provided with through holes (19). Fastening screws (not shown) are guided through these bores (19) and screwed into threaded bores (26) on the bearing cross (11). The bores (26) are arranged concentrically with the bearing hub (12). Their free ends have contact surfaces (20) for an end face of the stator core (17). The stator lamination stack (17) is centered by means of radially designed stiffening ribs (21). The rotor (15) consists of a pot-shaped deep-drawn part or an aluminum injection molded part (15a) with a hollow cylinder section (15b), which contains an annular iron yoke (22) and the permanent magnets (23) attached to it as rotor poles (see also FIG. 5). Furthermore, the rotor (15) has a hub (24) which is positively connected to the free end (14a) of the drive shaft (14) by means of a screw bolt (25) and a serration (not shown) and thus non-rotatably.

The drive motor is designed as a permanent magnet three-phase synchronous motor. A three-strand single-pole winding (tooth winding) is accommodated in the stator (16), the strands being connected in a star connection (see FIGS. 5, 6). The windings of the teeth (27) of one strand are connected in series. The drive motor is thus constructed as a modular permanent magnet machine. The pole ratio of rotor poles (23) to stator poles (27) is 4 to 3 with a number of 30 stator poles (27).

Figure 5 shows a block diagram of the structure of the controlled drive with three-phase synchronous motor (10). The speed of the motor (10) is a function of the program set with the rotary selection switch (9, see FIG. 1)) as a setpoint by the program control

ST (101) of the washing machine. In order to influence the motor speed, both the frequency of voltage and current and the amount of voltage in the stator windings (18) must be adjusted. To regulate the motor (10), the motor current is also set as a function of the load torque. For this purpose, at least two phase currents and l _{2 are} measured with current sensors (103a, b).

The aforementioned variables are adjusted via the frequency converter (104). The mains voltage is first converted into a DC voltage using a rectifier (105) and smoothed using an intermediate circuit capacitor (106). The DC voltage is converted by a three-phase inverter (107) which is connected on the output side to the stator winding (18). Since the DC link voltage is constant, the voltage at the motor (10) is set using pulse width modulation. The effective value of the voltage can be changed over the pulse width. A pulse pattern is selected by means of which sinusoidal currents form in the stator winding (18) of the motor (10). One speaks therefore of a sinus-weighted pulse width modulation. The sinusoidal currents cause the motor (10) to run very quietly and reduce the losses caused by current harmonics. In order to influence the pulse pattern, the inverter (107) is assigned a microprocessor control MC (108) in which a control R (109) and a valve control V {1 0) are integrated. The control signals for the transistors of the inverter (107) are calculated on the basis of the respective rotor position in order to set the optimal orientation and strength of the rotating field at all times and thus to ensure a sufficient torque on the rotor (15). Because of the sinusoidal current supply to the synchronous motor (10) and the torque-dependent current control, continuous and accurate rotor position detection is required. Resolvers or analog Hall generators (111) can be used for this. Hall sensors (111) should be preferred because of their low cost. In both cases, these are absolute measuring systems which provide precise information about the absolute position of the rotor (15) in relation to the stator (16) immediately after switching on. If two analog Hall generators (111) are used, they will use the rotor magnets to generate two signals that are 90 ° out of phase with each other. With these two signals, the rotor angle can be determined using the mathematical function ß = arctan (a / b).

When using analog Hall generators (111), it makes sense to self-calibrate them, because B. sensitivity, offset, temperature drift, etc. the analog output signals of different Hall generators (111) are not necessarily identical in a constant magnetic field. The output signals must therefore be corrected for accurate rotor position detection. The aim of this correction is that the Hall generators (111) used deliver the same output signals in a constant magnetic field. Such a correction can be made by storing the analog output signals of both Hall generators (111) in a correction device K (112) integrated in the microprocessor control MC (108) during a rotor revolution and then the mean value as well as maximum and minimum from the stored values be determined. If the mean value is known, an offset can be corrected, while the sensitivity and the temperature drift can be corrected on the basis of maximum and minimum. A temperature influence on the remanent induction of the magnets (23) need not be taken into account, since in this case the output signals of both Hall generators (111) are changed in the same way and in the same size. If the rotor angle is calculated using the mathematical function ß = arctan (a / b), the quotient (a / b) remains as a function of the change in the magnetic field

Temperature constant. FIG. 6 shows a block diagram of the structure of a control system in which sensors for rotor position detection can be dispensed with. In the case of sensorless control of the synchronous motor (10) with continuous, in particular with sinusoidal current supply, the rotor position must be calculated by the microprocessor control MC (108). This is done on the basis of a mathematical model M (113) of the motor (10) stored in the control, in which the characteristic motor parameters such as winding resistance, motor inductance and induced voltage must be known. The motor currents (I1 2) and the motor voltage U_ _w are continuously measured vectorially, ie according to the magnitude and phase position, the currents being measured with the sensors and the voltage being known on the basis of the pulse pattern generated by the valve control V (110). The respective operating point of the motor (10) can thus be determined precisely and the motor (10) can be operated with the minimum current required for the load torque. Since the motor current and the voltage on the motor (10) can be recorded in the frequency converter (104) itself, no further sensors on the motor (10) are required.

In an advantageous embodiment of the sensorless control, the parameters of the mathematical model M (113) are adjusted either as required or continuously. Such a calibration may be necessary if the motor-specific parameters (winding resistance, motor inductance and induced voltage) change during operation as the motor (10) heats up. The winding resistance and induced voltage in particular are highly temperature-dependent variables. By briefly energizing the stator winding (18) with direct current through the frequency converter (104), advantageously during the reversing breaks in washing operation, both the instantaneous winding resistance (and thus also the temperature of the motor) and the motor inductance can be determined when the voltage at Motor (10) is known and the current is measured via the sensors (103a, b) in the frequency converter (104).

The winding resistance R results from the relationship R = U / l and the inductance L from the time constant T = L / R, the current having to be recorded continuously in order to determine the time constant T.

Since the machine is operated as an externally operated synchronous motor (10), it is important that the output frequency of the frequency converter (104) is low when the motor (10) starts up.

Switch-on frequencies of 0.1 to 1 Hz are typical. In conjunction with the high number of poles of the motor (10), this guarantees a safe and smooth start even under load. The number of turns of the stator winding (18) is dimensioned such that at higher speeds the magnet wheel voltage and the induced voltage of the synchronous motor (10) are higher than the output voltage or the intermediate circuit voltage of the frequency converter (104). This design enables operation with field weakening at higher speeds. The field weakening enables the motor (10) to operate at approximately the same motor current in two operating points with different speeds and different moments, such as washing and spinning operation.

In this case, field weakening is to be understood as a weakening of the field generated by the permanent magnets (23) of the rotor (15) in the air gap by a field generated in the stator (16) with a corresponding strength and phase position. In the case of field weakening, the magnet wheel voltage and motor current are not in phase, but the phase current leads the magnet wheel voltage. The angle between the stator flooding and the rotor field becomes greater than 90 ° (electrical) when the field is weakened. In addition to the force-generating component in the transverse axis, the current has a negative stator longitudinal current component which is opposite to the rotor field. The phase current can be broken down vectorially into a force-forming and a field-forming component, the force-forming component being in phase with the magnet wheel voltage and the field-forming component being directed towards the rotor field and weakening it.

In controlled operation, the torque-forming component of the current in the transverse axis and the stator longitudinal current component can be set separately from one another with the aid of the current sensors (103a, b), which detect the phase current in at least two phases. This means that the drive can also be operated in the field weakening area with minimal current and optimum efficiency. Sensing and regulating the motor current is advantageous in operation with field weakening, since if the longitudinal stator current component is too large, the magnets can be irreversibly weakened by the field generated by the stator flooding.

In the case of sensorless control, the rotor position or the position of the rotor field is calculated with the aid of the measured phase currents and with the mathematical model M (113) of the motor (10). The rotor position can therefore only be determined as long as the motor (10) is energized. In the case of sensorless control, it is therefore advantageous to energize the motor (10) from the washing speed or from the spin speed to a standstill even during the run-down phase. The frequency and amplitude of the rotating field specified by the frequency converter (104) is continuously reduced until standstill is reached. Are the winding strands of the motor (10) energized even at a standstill, at least partially, and the rotor (15) held in position, the next start-up can take place immediately and smoothly in the specified direction of rotation. When using rotor position sensors (111), the outlet can also be unguided or de-energized.

The drive described further enables reversing without or with only a slight reversing pause. In washing machines which have a drive belt as an intermediate drive, this is not readily possible. In these washing machines, universal motors are usually used as the drive, which run out uncontrolled or braked. After the engine has been switched off, the laundry drum will coast down or swing out. To avoid increased wear and noise from the drive belt, wait until the washing drum has come to a standstill after switching it off and then on again until the motor is switched on again. These downtimes for washing machines with drive belts are typically 2 to 4 seconds. The elimination of these hitherto usual and necessary breaks in reversing operation results in shorter washing times in the direct drive described here.

A further advantageous embodiment of a laundry treatment device has a device for evaluating the voltage induced by the rotor (15) during the runout. The current speed can be inferred from this voltage. As long as the motor (10) is rotating, a voltage is induced in the stator winding (18) of the motor (10). The height and frequency are proportional to the rotor speed. The induced voltage can be used to sense the drum rotation. In a washing machine with an electromagnetically or electromechanically locked door, the induced voltage can be used to operate the lock. As a result, a state-dependent, secure locking (8) of the door (7) is possible in a simple manner without the use of additional speed sensors. Such an application is generally possible in washing machines with permanent magnet excited rotors and is therefore not limited to the embodiment according to the invention.

Claims

claims

1. laundry treatment device such as washing machine, dryer or washer dryer with a rotatably mounted drum (6) with at least approximately horizontal axis of rotation, and with a drive motor (10) arranged on the drum shaft, in the form of a permanent magnet excited synchronous motor (10), the stator (16 ) is provided with a winding (18) which is supplied with current by a converter, characterized in that the winding (18) is designed as a single-pole winding, the number of stator poles (27) and the magnetic poles (23) being unequal, and that a frequency converter (104) is used as the converter, the output voltage of which is set in such a way that continuous currents form in all winding phases.

2. Laundry treatment device according to claim 1, characterized in that the rotor (15) is designed as an external rotor.

3. Laundry treatment device according to one of claims 1 or 2, characterized by a control device (108) which adjusts the output voltage of the frequency converter (104) by a controller (109) such that a minimal sinusoidal motor current is generated as a function of the load torque.

4. Laundry treatment device according to claim 3, characterized in that the output voltage is set in the form of a sinus-weighted pulse width modulation.

5. laundry treatment device according to claim 4, characterized in that the stator winding (18) is designed as a three-strand winding and that the ratio of magnetic poles (23) to stator poles (27) is 2/3 or 4/3.

6. laundry treatment machine according to claim 5, characterized in that the number of stator poles is approximately 30.

7. laundry treatment device according to one of claims 1 to 6, characterized in that the control device (108) for regulating the motor current is based on a mathematical model (113) of the motor (10) and that the energization of the winding strands (18) takes place without rotor position sensors .

8. laundry treatment device according to claim 7, characterized by sensors for determining variable motor-specific parameters such as winding resistance, motor inductance and constant of the induced voltage, the corresponding reference values of the mathematical model (113) in the control device (108) being correctable by the measured values.

9. laundry treatment device according to one of claims 7 or 8, characterized in that the rotor (15) can be positioned by a guided outlet in the washing operation such that an immediate start in the opposite direction is possible after it has come to a standstill.

10. Laundry treatment device according to one of claims 1 to 6, characterized in that the energization of the winding strands using the analog output signals from two Hall sensors (111), these output signals calibrated by a correction device (112) with respect to their time or state-dependent fluctuations become.

11. laundry treatment machine according to one of claims 1 to 10, characterized in that the number of turns of the stator windings (18) is dimensioned such that the amount of the induced voltage or the magnet wheel voltage is greater than the maximum output voltage of the frequency converter (104).

12. Laundry treatment machine according to one of claims 1 to 11, characterized in that the energization of the motor (10) at higher speeds with field weakening without evaluating any rotor position sensors (111).

13. laundry treatment machine, in particular according to one of claims 1 to 12, characterized by a device (8) for evaluating the voltage induced by the rotor (15).

14. laundry treatment machine according to claim 13 with an electromagnetically or electromechanically locked door (7), characterized in that the door (7) by the device (8) can be closed.