NZ331564A

NZ331564A - Washing machine, direct drive motor uses dynamic and regenerative braking

Info

Publication number: NZ331564A
Application number: NZ331564A
Authority: NZ
Inventors: Matsumotu Satoru; Makino Yoshiyuki; Imamura Fumihiro; Ikeda Hiroshi
Original assignee: Toshiba Kk
Priority date: 1997-08-29
Filing date: 1998-08-26
Publication date: 2000-04-28
Also published as: KR19990086973A; CN1110594C; TW392015B; JP3225008B2; KR100315555B1; CN1211649A; JPH11128587A

Abstract

A washing machine bowl is driven by a direct drive three phase motor 20 powered by inverter 47. The motor circuitry is arranged so that the motor can be braked by a mix of dynamic, regenerative or short circuit braking. Dynamic braking is achieved by passing regenerated current through resistor 49. Short circuit braking is achieved by switching on switching elements 57b, 57d, 57f to short circuit the motor windings. In regenerative braking the regenerated current is passed into capacitors 42a and 42b in the DC power supply 43. The mix of braking modes is controlled by a microprocessor, and depends on the point in the washing or drying cycle the machine has reached.

Description

<div class="application article clearfix" id="description"> Patents Form No. 5 Our Ref: JT210864 INTELLECTUAL PROPERTY' OFFICE | OF NZ I | Patents Act 1953 2 6 AUG i938 COMPLETE SPECIFICATION RECEIVED j FTI—UL 7BTM—HTBWMTWm iT T—' IJ ill ■ Mi. i WASHING MACHINE WITH IMPROVED ELECTRIC BRAKING MEANS We, KABUSHIKI KAISHA TOSHIBA, a corporation of Japan of 72 Horikawa-cho, Saiwai-ku, Kawasaki, Kanagawa, Japan hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: PT05A66922 -1- (followed by page 1 a) la WASHING MACHINE WITH IMPROVED ELECTRIC BRAKING MEANS This invention relates generally to a washing machine including a rotatable tub for accommodating laundry with water, an agitator for agitating the water, and a brushless motor for driving the rotatable tub and the agitator, and more particularly to electric braking means provided in such a washing machine for braking the brushless motor. In washing machines of the type described above, a rotatable tub serving both as a wash tub and as a dehydration basket is rotatably provided in an outer tub as well known in the art. An agitator is rotatably mounted on the bottom of the rotatable tub. The rotatable tub and the agitator are rotated by a brushless motor. When a wash operation is executed, a rotational speed of the brushless motor is set at a wash speed and the agitator is rotated in normal and reverse directions alternately repeatedly by the brushless motor with the rotatable tub being stopped. In execution of a dehydration operation, the rotational speed of the brushless motor is set at a dehydration speed and both the rotatable tub and the agitator are rotated. Stopping rotation of the brushless motor by electric braking means has been proposed. The following points should be considered in this case. An operating state of the brushless motor differs with operating states of the washing machine such as wash and dehydration operations. Braking is required at an end or in the midst of each operation of the washing machine. Accordingly, provision of a single mode of electric braking means would reduce a braking effect and excessively increase a braking (followed by page 2) 2 time, resulting in vibration and noise. A direct drive mechanism is employed to rotate the rotatable tub and the agitator by the brushless motor for the purpose of reduction in the vibration and noise. When a mechanical braking 5 is used in this case, it would produce vibration and noise. As a result, the reduction in the vibration and noise by the direct drive mechanism would not be achieved. Conventional washing machines comprise a belt transmission mechanism, a clutch mechanism and a reduction gear mechanism 10 including a planetary gear. These mechanisms are provided between an electric motor and the rotatable tub and agitator for rotating them. These mechanisms increase the weight and the height of the washing machine. Furthermore, the reduction gear mechanism produces a loud noise during its operation. However, 15 the above-described direct drive mechanism can eliminate the belt transmission mechanism, the clutch mechanism and the reduction gear mechanism provided in the conventional washing machines. Furthermore, the direct drive mechanism reduces the weight and the height of the washing machine and noise produced by the 20 reduction gear mechanism. Therefore, an object of the present invention is to provide a washing machine wherein the arrangement for braking the brushless motor can be simplified by the provision of electric braking means as compared with the case where a mechanical braking 25 is employed, wherein a desired braking effect can be achieved, and wherein the vibration and noise can be reduced during the braking or to at least provide the public with a useful choice. The present invention provides a washing machine comprising 331564 a rotatable tub for accommodating laundry with water, an agitator for agitating the water, a brushless motor provided for driving the rotatable tub and the agitator and including a rotor and a stator having a winding, a DC power supply circuit, an inverter 5 main circuit to which a DC current is supplied from the DC power supply circuit, the inverter main circuit including switching elements bridge-connected to a plurality of phases of the motor so that the DC current from the DC power supply circuit is supplied via the switching elements to the brushless motor, regenerative 10 braking means returning a current due to an electromotive force of the brushless motor to the DC power supply circuit, dynamic braking means including a dynamic brake resistance element connected to a current path at an input side of the brushless motor so that the current due to the electromotive force of the brushless motor is supplied to the dynamic brake resistance element, and 15 short-circuit braking means short-circuiting the winding of the brushless motor. In the above-described washing machine, the electric braking means includes the regenerative braking means, the dynamic braking means and the short-circuit braking means. The 20 arrangement for the electric braking means can be simplified as compared with the mechanical braking means. These electric braking means differ from one another in the braking effect and a degree of production of vibration and noise depending upon the rotational speed of the motor at the time the motor is braked. 25 Furthermore, braking is required at an end or in the midst of each operation of the washing machine. These electric braking means are selectively effectuated so that the braking effect can be improved and the vibration and noise can be reduced during the INlclLtCijA t v-1 o, 331564 braking as compared with the case where a single electric braking means is employed. In a preferred form of the invention, rotation of the rotor of the brushless motor is transmitted directly to the rotatable 5 tub and the agitator. Since no reduction gear mechanism is provided, an amount of vibration and accordingly, the noise are small. In another preferred form, any one of, or a combination of two or more of the regenerative, dynamic ancj short-circuit 10 braking means is effectuated when the brushless motor is braked. In this regard, two or more braking means are selected in time sequence. The regenerative braking means returns an electromotive force of the brushless motor to the power supply circuit. The regenerative braking means is effective when the 15 motor speed is relatively high and can cope with emergency braking. The short-circuit braking means generates a short-circuit current in the winding short-circuited by an electromotive force induced in the brushless motor, convert-ing the resultant electrical energy to heat energy. This is a dynamic braking action. On the other hand, the dynamic braking means with the dynamic brake resistance causes the dynamic brake resistance to discharge the electrical energy due to the induced electromotive force of the motor, thereby converting the electrical energy to heat energy. In the dynamic braking means, the dynamic brake resistance element connected across both ends of an input side of the inverter main circuit consumes the electromotive force of the motor with the DC power supply circuit and the inverter main circuit being disconnected from each other. The dynamic braking means is also effective when the motor speed is high. The regenerative braking means is preferably switched to the dynamic braking means ! hviciLtcra,; 1 ^ ': I' Gr ^ : 1 S 1, tJ\l 11 4a w — „ ^ ,J particularly when a regenerative current is excessively large in execution of the regenerative braking means. However, the dynamic braking means accompanies a temperature increase. The short-circuit braking means is effective in a range of the motor speed from a high-speed rotation to a low speed rotation when continuously used g-^ate of the high-speed rotation. However, when suddenly li' id-L-uiiJ/,' G, 18 J. j 331564 used while the motor speed is low, the short-circuit braking means suddenly brakes the motor, resulting in the vibration and noise. Accordingly, when the brushless motor is electrically braked, a desired one or two or more of the braking means are selected 5 in time sequence to be combined. Consequently, the braking effect can be given priority, the temperature increase and breakage of circuit elements can be prevented and the reduction in the vibration and noise can be achieved with a desired braking effect. In further another preferred form, the combination of the 10 braking means differs depending upon contents of control for a washing operation. In this arrangement, too, the temperature increase and breakage of circuit elements can be prevented and the reduction in the vibration and noise can be achieved. In further another preferred form, the short-circuit braking 15 means is executed prior to the regenerative braking means when the regenerative braking means is to be executed. A high braking effect can be achieved from the regenerative braking means when the motor speed is high. However, the regenerative current becomes excessively large and may break circuit elements of the 20 DC power supply circuit or the inverter main circuit. In the above-described arrangement, the short-circuit braking means is executed before execution of the regenerative braking means. Accordingly, the motor winding is short-circuited without causing the current to flow through the circuit elements before execution 25 of the regenerative braking means, so that the motor speed is reduced to such an extent that the electromotive force of the motor becomes sufficiently low at the time of execution of the regenerative braking means. Consequently, the regenerative INitU-'.CiuA1-: i ■ .--".I. Cr .V- 331564 current can be prevented from being excessively large and the circuit elements of the DC power supply circuit or the inverter main circuit can be prevented from being broken. In a further another preferred form, the washing machine 5 further comprises switching means for switching between a regenerative braking means connected state wherein the inverter main circuit is connected to the DC power supply circuit and is open to the dynamic brake resistance element, and a dynamic braking means connected state wherein the inverter main circuit is open to the DC power supply circuit and is connected to the dynamic brake ■0 resistance element. In this arrangement, when the regenerative braking means is to be executed, the short-circuit braking means and the dynamic braking means are executed in turn prior to the regenerative braking means, and the switching means is switched to the dynamic braking means connected state during execution of the short-circuit braking means. In this arrangement, too, breakage ofi the circuit elements can be prevented since the short-circuit and 5 dynamic braking means are executed in turn before execution of the regenerative braking means. Furthermore, the motor 20 electromotive force sometimes results in a potential difference between the inverter main circuit and the DC power supply circuit while the regenerative braking means is being executed. Sparks or contact welding occurs when the switching means is switched with the potential difference occurring between the inverter main 25 circuit and the DC power supply circuit. In the above-described arrangement, however, the switching means is switched during execution of the short-circuit braking means which does not result in the potential difference between the inv-er-ternmain .circuit and flNTtLLtClUAL P.fV*." - - I Or" W t- 1 4 © 1 " M ^ 7 331564 the DC power supply circuit. Consequently, the sparks and the contact welding can be prevented. In further another preferred form, the combination of the braking means for a wash operation differs from the combination 5 of the braking means for a dehydration operation. In this arrangement, a desired braking effect can be achieved in each of the wash and dehydration operations. Furthermore, a temperature increase and breakage of circuit elements due to the braking can be prevented and the vibration and noise can be reduced. 10 In further another preferred form, the combination of the braking means differs depending upon whether braking the brushless motor is with or without emergency. The motor is braked with or without emergency. A combination of the braking means with high braking effects is preferred when the motor is braked 15 with emergency, whereas a combination of the braking means giving the priority to prevention of temperature increase or of vibration and noise is suitable when the motor is braked without emergency. Since the combined braking means differ depending upon the braking is with or without emergency in the above-described arrangement, 20 the motor can be braked in a short time in a case of emergency. On the other hand, the motor can moderately be braked without emergency with prevention of the temperature increase and the vibration and noise being given priority. In a further another preferred form, the washing machine 25 further comprises a discharge circuit including the discharge element, a discharge switching element connected in series to the dynamic brake resistance element so as to be operated according to a motor induced voltage appearing at the inverter main circuit, and ' ! u/ I O > 1 8 . llM 1 tlljj.o I d a capacitor i,. x - - ^ 331564 connected in parallel to a series circuit of the dynamic brake resistance element and the discharge switching element, and switching means for selectively switching between a first state wherein the DC power supply circuit is electrically connected to the input side of the 5 inverter main circuit and the discharge circuit is electrically disconnected from the input side of the inverter main circuit, and a second state wherein the DC power supply circuit is electrically disconnected from the input side of the inverter main circuit and the discharge circuit is electrically connected to 10 the input side of the DC power supply circuit. In this arrangement, the switching means is switched to the second state when the dynamic braking means is to be executed. From the point of view of preventing vibration, the motor is preferably deenergized at a first stage into a free rotation 15 when braked during its high-speed rotation. In this case, the deenergization results in an induced voltage in the motor. The inverter main circuit and the DC power supply circuit are sometimes adversely affected when the induced voltage is high. In such a case, the dynamic braking means should be executed. 20 In the above-described arrangement, the switching means is switched to the second state when the dynamic braking means is to be executed. Then, the discharge switching element is turned on and off according to the induced voltage, so that the motor electromotive force is consumed through the dynamic brake 25 resistance element such that the motor is braked. The discharge switching element turns on and off at a relatively high frequency. However, since the capacitor is ' I.vicLLLCIUAL . . connected in parallel to the series circuit of t!he dynamic brake resistance t "At vJ ' 9 element and the discharge switching element in the above-described arrangement, the occurrence of electrical noise can be restricted. If the capacitor should fixedly be connected across input terminals of the inverter main circuit, the occurrence of 5 electrical noise would be restricted. In this case, however, large charge and discharge currents would flow through the capacitor. Accordingly, a capacitor with a current capacity larger than that required as a noise filter is necessitated. In the above-described arrangement, however, the capacitor is used 10 as the noise filter only when the switching means is switched to the second state or when the discharge element is used. Consequently, a large capacity is not required of the capacitor. In further another preferred form, the washing machine further comprises a discharge resistance connected in series to 15 the capacitor so that the capacitor is charged from the DC power supply circuit when the switching means is in the first state. When the switching means is in the first state, the DC power supply circuit is supplying the DC power to the inverter main circuit so that the motor is being rotated according to the operation mode 20 of the washing machine. The switching means is switched to the second state when the motor is braked upon completion of the operation mode. The capacitor is charged via the discharge resistance when the switching means is in the first state, so that the discharge circuit is at the same potential as a positive side 25 output terminal of the DC power supply circuit. Accordingly, even if the switching means were switched to the second state, sparks or contact welding would not occur. In further another preferred form, the washing machine 10 further comprises a diode connected in parallel to the discharge resistance so that an electric charge is discharged to the DC power supply circuit side. The output voltage of the DC power supply circuit gradually drops when a power failure occurs or a plug of 5 the washing machine is withdrawn during rotation of the motor with the switching means being in the first state. Since the capacitor is then charged with electric charge, the terminal voltage thereof is raised above the output voltage of the DC power supply circuit, thereby turning on the diode. The electric charge of the 10 capacitor is discharged via the diode to the DC power supply circuit. At this time, the DC power supply circuit side is at the same potential as the discharge circuit side. Accordingly, even if the switching means were switched to the second state, sparks or contact welding would not occur. In this regard, the 15 switching means may be composed into a relay switch which is switched to and held at the first state at a predetermined operating voltage and is switched to the second state below the predetermined operating voltage (including deenergization). In further another preferred form, an ON time of each 20 switching element taking place in synchronization with accordance of a phase current amplitude of the brushless motor between different phases is displaced between the different phases. The ON times of the switching elements corresponding to the respective phases of the inverter main circuit sometimes takes place 25 simultaneously in synchronization with the accord of the phase current amplitude of the brushless motor. In this case, a large spike current flows into the inverter main circuit, producing noise. In the above-described arrangement, however, the ON times 11 of the switching elements taking place in synchronization with the accordance of the phase current amplitude of the motor are displaced, a large spike current and accordingly noise can be prevented. 5 Other objects, features and advantages of the present invention will become clear upon reviewing the following description of the preferred embodiment thereof, made with reference to the accompanying drawings, in which: FIGS. 1A and IB are circuit diagrams showing the electrical 10 arrangement of a full-automatic washing machine of one embodiment in accordance with the present invention; FIG. 2 is a longitudinally sectional side view of the washing machine; FIG. 3 is a longitudinally sectional side view of the driving 15 mechanism section for the rotatable tub and the agitator; FIG. 4 is an exploded perspective view of the stator of the brushless motor; FIG. 5 is an exploded perspective view of the brushless motor and the clutch; 20 FIG. 6 is a perspective view of the clutch and a control lever; FIG. 7 is a view similar to FIG. 3, showing the state of the clutch differing from that in FIG. 3; FIGS. 8A to 8F are time charts showing the case where the brushless motor is energized with sinusoidal power; 25 FIG. 9 is a graph showing the variations in the motor speed in the wash operation; FIG. 10 is a graph showing the variations in the motor speed in the braking modes in the dehydration operation; 12 FIG. 11 is a graph showing the variations in the motor speed in another braking mode in the dehydration operation; FIG. 12 illustrates portions of energization signals of phases U and V in the embodiment; 5 FIG. 13 also illustrates portions of the energization signals of phases U and V; FIGS. 14A to 14D are graphs showing ON-OFF action of the switching elements and the variations in the DC line current; FIG. 15 illustrates portions of the energization signals of 10 phases U and V in a compared case; FIG. 16 is a view similar to FIG. 13, showing the compared case; FIGS. 17A to 17D are views similar to FIGS. 14A to 14D respectively; 15 FIG. 18 illustrates current flow upon ON-OFF action of the switching elements; FIG. 19 shows brake modes and combinations of braking means used in the wash and dehydration operations; and FIG. 20 shows the relationship between the rotational speed 20 of the rotatable tub and the brake mode to be used. One embodiment of the present invention will now be described with reference to the accompanying drawings. The invention is applied to a full-automatic washing machine in the embodiment. Referring first to FIG. 2, the overall construction of the 25 full-automatic washing machine is shown. The washing machine comprises an outer cabinet 1 enclosing an outer or water-receiving tub 2 receiving water discharged in a dehydration operation. The water-receiving tub 2 is suspended on a plurality of elastic 331564 suspension mechanisms 3 one of which is shown. A rotatable tub 4 serving both as a wash tub and as a dehydration basket is rotatably mounted in the water-receiving tub 2. An agitator 5 is rotatably mounted on the bottom of the rotatable tub 4. 5 The rotatable tub 4 includes a generally cylindrical tub body 4a, an inner cylinder 4b provided inside the tub body 4a to define a water passing space, and a balancing ring 4c mounted on an upper end of the tub body 4a. Upon rotation of the rotatable tub 4, a resultant centrifugal force raises water therein, which is then 10 discharged into the water-receiving tub 2 through dehydration holes (not shown) formed in the upper portion of the tub body 4a. A drain hole 6 is formed in the right-hand bottom of the water-receiving tub 2, as viewed in FIG. 2. A drain valve 7 is provided in the drain hole 6. A drain hose 8 is connected to the 15 drain hole 6. The drain valve 7 is a motor operated valve closed and opened by a drain valve motor 9 (see FIG. IB) serving as drain valve driving means which will be described later. The drain valve motor 9 comprises a geared motor, for example. An auxiliary drain hole 6a is formed in the left-hand bottom of the water-20 receiving tub 2, as viewed in FIG. 2. The auxiliary drain hole 6a is connected through a connecting hose (not shown) to the drain hose 8. The auxiliary drain hole 6a is provided for discharging water which has been discharged through the dehydration holes in the upper portion of the rotatable tub 4 into the water-receiving 25 tub 2 upon rotation of the rotatable tub 4 for the dehydration operation. Referring to FIGS. 2 and 3, a mechanism base 10 is mounted on an outer bottom of the water-receiving tub 2. The mechanism ! IKillLlcOIU.M An^'ViiiY L.vi - i! Or L 14 base 10 is formed in its central portion with a vertically-extending shaft support cylinder 11. A hollow tub shaft 12 is inserted in the shaft support cylinder 11 to be supported on bearings 13 for rotation. An agitator shaft 14 is inserted in 5 the tub shaft 12 to be supported on bearings 15 for rotation. Upper and lower ends of the agitator shaft 14 extend out of the tub shaft 12. An upper end of the shaft support cylinder 11 is fitted into a through hole 2a formed in the central bottom of the water-10 receiving tub 2 with a seal 16 being interposed therebetween for watertight seal. Another seal 16 is provided between an outer circumferential surface of the tub shaft 12 and the upper end of the shaft support cylinder 11 for watertight seal therebetween. A sleeve 12b with a flange 12a is connected to the upper end of 15 the tub shaft 12. The rotatable tub 4 is mounted on a tub support plate 17 further fixed to the flange 12a so that the rotatable tub 4 is coupled via the sleeve 12b with the tub shaft 12 to thereby be rotated with the latter. The upper end of the agitator shaft 14 is fitted into the agitator 5 so that the agitator 5 is fixed 20 by a screw to the agitator shaft 14, whereby the agitator 5 is rotated with the agitator shaft 14, as shown in FIGS. 2 and 3. A drain cover 18 extends between the central inner bottom of the water-receiving tub 2 and the drain hole 6 to define a draining passage 19 extending from a through hole 4d formed in 25 the bottom of the rotatable tub 4 to the drain hole 6, as shown in FIGS. 2 and 3. In this construction, water is stored in the rotatable tub 4 and the draining passage 19 when supplied into the tub 4 with the drain valve 7 being closed. The water in the 15 rotatable tub 4 is discharged through the hole 4d, the draining passage 19, the drain hole 6, the drain valve 7, and the drain hose 8 sequentially when the drain valve 7 is opened. An outer rotor type brushless motor 20, for example, is 5 mounted on the mechanism base 10 further mounted on the outer bottom of the water-receiving tub 2 . More specifically, a stator 21 of the motor 20 is mounted on the mechanism base 10 by stepped screws 22 to be concentric with the agitator shaft 14, as shown in FIG. 3 . The stator 21 comprises a laminated iron core 23, upper 10 and lower bobbins 24 and 25, and a winding 26, as shown in FIG. 3. The laminated core 23 comprises three generally circular arcuate unit iron cores 23a connected to one another into an annular shape, as shown in FIG. 4. The upper and lower bobbins 24 and 25 are each made of a plastic and adapted to be fitted to 15 upper and lower teeth of the laminated core 23 respectively. The winding 26 is wound around the outer peripheries of the bobbins 24 and 25. The winding 26 is composed of three-phase windings 26U, 26V and 26W as shown in FIG. 1A. A rotor 27 of the brushless motor 20 is mounted on the lower 20 end of the agitator shaft 14 to be rotated therewith, as shown in FIGS. 3 and 5. The rotor 27 comprises a rotor housing 28, a rotor yoke 29, and a plurality of rotor magnets 30. The rotor housing 28 is made of aluminum by die-casting and has a central boss portion 28a and an outer peripheral magnet mounting portion 25 28b. The lower end of the agitator shaft 14 is fitted into the boss portion 28a to be fixed in position. The magnet mounting portion 28b of the rotor housing 28 includes a horizontal portion and a vertical portion. The rotor 16 yoke 29 is abutted against an inner surface of the vertical portion of the magnet mounting portion 28b and further fixed by screws to the horizontal portion of the magnet mounting portion 28b. The rotor magnets 30 are bonded to an inner surface of the rotor yoke 5 29, for example. The rotor housing 28 has a number of radially extending ribs 28c formed on an upper circumferential surface thereof opposed to the winding 26 of the stator 21, as shown in FIGS. 3 and 5. The rotor housing 28 further has a plurality of convex portions 28d formed on the central bottom thereof to 10 radially protrude about its axis. These convex portions 2 8d constitute an engaged portion. Three Hall ICs 31a, 31b and 31c are mounted on respective fixtures 32 which are further fixed to the outer periphery of the mechanism base 10, as shown in FIGS. 1 and 3. FIG. 3 shows one 15 31a of the Hall ICs. The Hall ICs serve as rotor position detecting means for detecting a rotational position of the rotor magnets 30 of the rotor 27. The Hall ICs 31a, 31b and 31c are disposed so that position signals Ha, Hb and He delivered from them respectively are 120 degrees out of phase, as shown in FIG. 20 8B. Furthermore, the Hall ICs 31a, 31b and 31c are positioned so as to deliver high-level and low-level digital signals in synchronization with a phase of an induced voltage of each phase. A clutch 32 is provided on the lower end of the tub shaft 12, as shown in FIGS. 3 and 5. The clutch 32 has a function of 25 switching between a first mode in which the tub shaft 12 is operatively coupled to the agitator shaft 14 in a dehydration operation so that the rotor 27, the agitator shaft 14 and the tub shaft 12 are rotated together, and a second mode in which the tub 17 shaft 12 is decoupled from the agitator shaft 14 in a wash operation so that the tub shaft 12 is prevented from being rotated with the rotor 27 and the agitator shaft 14. The clutch 32 will be described in detail. Referring to FIG. 5 6, the clutch 30 comprises a generally rectangular frame-shaped change-over lever 33 and a holder 34 provided inside the lever 33. The holder 34 is mounted on the lower end of the tub shaft 12 to be rotated together. More specifically, the tub shaft 12 has a pair of flat faces 12b formed on a lower outer circumferential 10 surface thereof to be opposed to each other, as shown in FIG. 5. The holder 34 has a central fitting hole 34a having flat inner surfaces against which the flat faces 12b of the tub shaft 12 are abutted. The holder 34 further has a pivot concave portion 34b formed in the left-hand outer surface thereof to have an 15 approximately semicircular section, as viewed in FIG. 5. The lower end of the tub shaft 12 is fitted into the fitting hole 34a of the holder 34 and then fixed by screws (not shown) so that the holder 34 is fixed to the tub shaft 12. Furthermore, a corrugated washer 3 5 is provided between the holder 34 and the lower bearing 20 13, for example. The corrugated washer 35 is adapted to press the lower bearing 13 upward. The change-over lever 33 is fitted into the holder 34 so as to be rotated with the holder 34 and the tub shaft 12, as shown in FIGS. 5 and 6. The change-over lever 33 has in the inside of 25 one end 33a thereof (a left-hand end in FIG. 5) a pivot convex portion 33b (see FIG. 3) having an approximately semicircular section. The pivot convex portion 33b is fitted into the pivot concave portion 34b of the holder 34 so that the change-over lever 18 33 is pivotable or rotatable upward and downward about the portion 33b. Furthermore, two toggle type springs 36 each comprising a compression coil spring are provided between the change-over lever 33 and the holder 34, as shown in FIGS. 5 and 6. The toggle 5 type springs 36 hold the change-over lever 33 at an upper position (see FIG. 4) when the same is rotated upward and at a lower position (see FIG. 7) when the same is rotated downward. The change-over lever 33 has convex portions 33d and 33e formed on the upper and lower portions of an end 33c thereof and an operated portion 33f 10 protruding from an outside surface of the end 33c. A recess 37 is formed in the underside of the mechanism base 10 serving as a stationary portion so as to be opposed to the upper convex portion 33d of the change-over lever 33, as shown in FIGS. 3 and 5. On one hand, the upper convex portion 33d of the 15 change-over lever 33 is fitted into the recess 37 when the change-over lever 33 is rotated upward, as shown in FIG. 3 showing the condition in the wash operation. Consequently, the tub shaft 12 and accordingly, the rotatable tub 4 are fixed to the mechanism base 10 serving as the stationary portion. The tub shaft 12 is 20 thus decoupled from the agitator shaft 14 so as not to be co-rotated with the latter and the motor rotor 2 7 when the upper convex portion 33d has been fitted in the recess 37. The agitator shaft 14 and the motor rotor 27 are originally coupled to each other to be rotated together. 25 On the other hand, the lower convex portion 33e of the change-over lever 33 engages two of the convex portions 28d on the upper face of the rotor housing 28 when the change-over lever 33 is rotated downward, as shown in FIG. 7 showing the condition 19 in the dehydration operation. Consequently, the tub shaft 12 is co-rotated with the motor rotor 27 and the agitator shaft 14. In this condition, the tub shaft 12, the rotatable tub 4, the agitator shaft 14 and the agitator 5 are directly driven by the brushless 5 motor 20. Thus, the brushless motor 20 directly drives only the agitator 5 or both of the agitator 5 and the rotatable tub 4 together. A control lever 38 is mounted at its one end on the right-hand end of the mechanism base 10 to be pivotable, as viewed in FIG. 10 3. The control lever 38 has bifurcated portions at the other end thereof as shown in FIG. 6. One of the bifurcated portions of the lever 38, which is a right-hand one in FIG. 6, has a downwardly inclined surface 38a on its distal end, whereas the other bifurcated portion thereof, which is a left-hand one in FIG. 6, 15 has an upwardly inclined surface 38b on its distal end. The operated portion 33f of the change-over lever 33 of the clutch 32 is pushed downward by the downwardly inclined surface 3 8a of the control lever 38 when the drain valve motor 9 driving the drain valve 7 causes the control lever 38 to pivot in a direction. 20 Consequently, the change-over lever 33 is rotated downward into the condition of FIG. 7 during the dehydration operation with the drain valve 7 being opened. A return spring (not shown) of the drain valve 7 causes the control lever 38 to pivot in the opposite direction when the drain 25 valve motor 9 is deenergized under the condition as shown in FIG. 7. Consequently, the operated portion 33f of the change-over lever 33 is upwardly pushed by the upwardly inclined surface 38b of the control lever 38 such that the change-over lever 33 is 20 rotated upward into the condition of FIG. 3 during the wash operation with the drain valve 7 being closed. An electrical arrangement of the full-automatic washing machine will now be described with reference to FIGS. 1A and IB. 5 One of two terminals of a commercial AC power supply 3 9 is connected through a reactor 40 to an input terminal of a full-wave rectifier circuit 41. The other terminal of the power supply 39 is connected directly to another input terminal of the full-wave rectifier circuit 41. Smoothing capacitors 42a and 42b are connected 10 between output terminals of the full-wave rectifier circuit 41. A DC power supply circuit 43 is composed of the full-wave rectifier circuit 41 and the smoothing capacitors 42a and 42b. The DC power supply circuit 43 supplies a DC voltage of 280 V, for example. A voltage regulator circuit 45 is connected between positive 15 and negative side power supply lines 44a and 44b serving as output lines of the DC power supply circuit 43. The voltage regulator circuit 45 supplies a constant DC voltage to a microcomputer 63 etc. as will be described later. An output terminal 44A of the positive side power supply line 44a of the DC power supply circuit 20 43 is connected via a normally open terminal (NO terminal) and a common terminal (COM terminal) of a relay switch 46 serving as switching means to an input terminal 47A of one DC line 47a of the inverter main circuit 47. The other output terminal 44B is connected to an input terminal 47B of the other DC line 47b of 25 the inverter main circuit 47. The relay switch 46 has the above-described NO and COM terminals and a normally closed terminal (NC terminal). The relay switch 46 is switched by a relay drive circuit 4 6a. A circuit 3315 6 A between the COM and NO terminals is closed (a first state) when a relay coil (not shown) is energized from the relay drive circuit 46a. A circuit between the COM and NC terminals is automatically closed (a second state) when the relay coil is deenergized. The 5 relay drive circuit 46a holds the first state until the output voltage of the DC power supply circuit 43 drops below 50 V. In the first state, the relay switch 46 closes a circuit between the positive side output terminal 44A of the DC power supply circuit 43 and the positive side input terminal 47A of the inverter main 10 circuit 47. Furthermore, the relay switch 46 opens a circuit between the positive side input terminal 47A of the inverter main circuit 47 and one end of a discharge circuit 48 which will be described later. In the second state, the relay switch 46 opens the circuit between positive side output terminal 44A of the DC 15 power supply circuit 43 and the positive side input terminal 47A of the inverter main circuit 47. Furthermore, the relay switch 46 closes the circuit between the positive side input terminal 47A of the inverter main circuit and the end of the discharge circuit 48. 20 The dynamic braking circuit 48 serving as braking current dynamic braking means is connected between the NC terminal of the relay switch 46 and the negative side input terminal 47B of the inverter main circuit 47. The dynamic braking circuit 48 comprises a series circuit of a dynamic brake resistance 49 serving as a dynamic brake resistance element and a discharge switching element 50 comprising a transistor. A capacitor 51 is connected in parallel to the 25 series circuit of the discharge resistance 49 and the discharge switching element 50. A control terminal or gate of the switching element 50 is connected to a r IkltLLuClu.V ■ ' i! 0.- i\, 22 drive circuit 52 comprising a photocoupler, for example. A charge resistance 53 connected in series to the capacitor 51 is connected between the positive side input terminal 47A of the inverter main circuit 4 7 and the discharge circuit 4 8. A diode 5 54 is connected in parallel to the charge resistance 53. A regenerative diode 55 is connected between the COM and NO terminals of the relay switch 46 between the output terminal 44A of the DC power supply circuit 43 and the input terminal 47A of the inverter main circuit 47. A voltage divider circuit 56 10 serving as voltage detecting means is provided for detecting a voltage at the DC line 47a of the inverter main circuit 47. The voltage detected by the voltage divider circuit 56 is supplied to a microcomputer 63 which will be described later. The inverter main circuit 47 comprises three-phase 15 bridge-connected switching elements 57a to 57f comprising respective IGBTs and free-wheel diodes 58a to 58f connected in parallel to the respective switching elements 57a to 57f. The inverter main circuit 47 has output terminals 59u, 59v and 59w connected to the three-phase windings 26u, 26v and 26w of the 20 brushless motor 20 respectively. The switching elements 57a to 57f of the inverter main circuit 47 include control terminals or gates connected to drive circuitry 60 composed of photocouplers, for example. The drive circuitry 60 is controlled by signals delivered from a PWM circuit 61 to thereby on-off control the 25 switching elements 57a to 57f. The DC power supply circuit 43, the inverter main circuit 47, the drive circuitry 60, and the PWM circuit 61 constitute driving means in the invention. The PWM circuit 61 is provided with means for generating a 23 triangular wave signal having a predetermined frequency. Based on energization signals Du, Dv and Dw supplied from a microcomputer 63 which will be described later, the PWM circuit 61 forms drive signals Vup, Vun and Vvp, Vvn, Vwp, and Vwn to 5 form sinusoidal winding currents, which drive signals are delivered to the drive circuitry 60. FIG. 8D shows the drive signals Vup and Vun. The position sensor signals Ha, Hb and He delivered from the respective Hall ICs 31a, 31b and 31c of the brushless motor 20 10 are supplied to the microcomputer 63. Furthermore, the microcomputer 63 controls the drain valve motor 9 for opening and closing the drain valve 7 and a water-supply valve 64 for supplying water into the rotatable tub 4. Additionally, the microcomputer 63 is supplied with a power failure signal from a power failure 15 detecting circuit 65 for detecting power failure on the basis of the voltage of the AC power supply 39. The microcomputer 63 is also supplied with a water level signal from a water level sensor for detecting the water level in the rotatable tub 4 and a lid signal from a lid switch 68 for detecting an open or closed state 20 of a lid 67 (see FIG. 2) provided on the top of the outer cabinet 1. The microcomputer 63 is further supplied with switch signals from various switches 69 provided on an operation panel (not shown). The microcomputer 63 has a function of drive control means 25 for controlling the brushless motor 20, a function of controlling the overall operation of the automatic washing machine, and a function of generating electric braking for the motor 20. The microcomputer 63 is provided with a ROM for storing control 24 3315 programs for accomplishment of the above-described functions and data required for execution of these control programs. The microcomputer 63 controls the switching elements 57a to 57f of the inverter main circuit 47, the discharge switching element 50 5 and the relay switch 46 to thereby generate soft braking as well as the regenerative braking, the dynamic braking and the short-circuit braking. The above-described electric brakings will be described. Regenerative braking 10 The switching elements 57a to 57f are on-off controlled by an energization pattern in which the phase currents lag voltages induced at the respective windings 26u, 26v and 26w of the motor 20. As a result, motor energy is returned via the regenerative diode 55 to the side of the DC power supply circuit 43. 15 Accordingly, the switching element on-off controlling function of the microcomputer 63 and the regenerative diode 55 constitute regenerative braking means in the invention. The regenerative braking is effective when the rotational speed of the motor 20 is relatively high. Thus, the regenerative 20 braking can cope with the case where the braking is urgently required. However, the regenerative braking is not suitable to the case where the braking is required during rotation of the motor 20 at low speeds, since the regenerative power is rendered low. Furthermore, the motor electromotive force is rendered 25 excessively large during rotation of the motor at high speeds, thereby breaking the circuit components of the inverter main circuit 47 or the DC power supply circuit 43. Dynamic brakinq I, ''^LLLuiu/'.L; nfVcun I- : y ij Or i\ ! 1 § :.\,i; I1 25 3315 The switching elements 57a to 57f are on-off controlled by an energization pattern in which the phase currents lag voltages induced at the respective windings 26u, 26v and 26w of the motor 20. The relay switch 46 is switched so that the circuit between 5 the COM and NC terminals is closed. When the detection voltage detected by the voltage divider circuit 56 is at or above a predetermined upper limit value indicating that the voltage at the DC line 47a rises to 400 V, the discharge switching element 50 is turned on so that the motor energy is consumed by the 10 discharge resistance 49, whereby braking is generated. The discharge switching element 50 is turned off when the detection voltage drops to or below a predetermined lower limit value indicating that the voltage at the DC line 47a drops to 350 V. Accordingly, dynamic braking means in the invention is 15 constituted by the on-off controlling function of the microcomputer 63 for the switching elements 57a to 57f and the discharge switching element 50, the relay switch 40, the voltage divider circuit 56 and the discharge circuit 48. The dynamic braking means is operated according to the induced voltage of the 20 motor 2 0 during execution of the regenerative braking means. The dynamic braking means is effective when the motor speed is high. Particularly when the regenerative current is rendered excessively large during the execution of the regenerative braking means, the braking is often switched to the dynamic 25 braking means. In this case, however, the dynamic braking is accompanied by a temperature increase. Short-circuit braking The lower three switching elements 5 7K'V' tS-V'cl5u7'f' of'those iTfvo*k 26 57a to 57f of the inverter main circuit 47 are simultaneously turned on so that all the windings 26u, 26v and 26w of the motor 20 are short-circuited, whereby the motor 20 is braked. Accordingly, the on-off controlling function of the microcomputer 5 63 constitutes short-circuit braking means in the invention. The short-circuit braking is effective until the low-speed rotation state when continuously used in the high-speed rotation state of the motor 20. However, when the short-circuit braking is effected during the low-speed rotation of the motor 20, the 10 motor is suddenly braked, whereupon vibration and/or noise due to the vibration is produced. Soft braking ON duty ratios of the switching elements of the inverter main circuit 47 are lowered to zero, whereby the motor 20 is braked. 15 Accordingly, the microcomputer's function of on-off controlling the switching elements 57a to 57f constitutes soft braking means controlling the duty ratios in the invention. The soft braking is moderate in its braking effect and produces low vibration and noise. The soft braking is suitable particularly to the case 20 where the motor 20 is rotated at low speeds. The washing machine is further provided with initial idle running means, normal idle running means and positioning means as control means regarding the braking in addition to the above-described braking means . In the initial idle running means, 25 all the switching elements 57a to 57f of the inverter main circuit 47 are turned off by the microcomputer 63 so that the motor 20 is rotated by inertia. At this time, the rotational speed of the motor 20 is detected on the basis of the position sensor signals 27 Ha, Hb and He delivered from the respective Hall ICs 31a, 31b and 31c. In the normal idle running means, all the switching elements 5 7a to 57f are turned off by the microcomputer 63 so that the motor 5 20 is rotated by inertia. At this time, however, the motor speed is not detected. In the positioning means, the switching elements 5 7a to 57f are controlled so that the motor 20 is rotated at very low speeds. The positioning means is executed for an exceedingly short period of time (0.5 sec) such that the motor 20 is 10 substantially stationary, whereby the rotor is regarded as positioned at the rotation angle. FIG. 19 shows braking modes used in the dehydration and wash operations and combinations of the braking modes. FIG. 20 shows the relationship between the rotational speed of the rotatable 15 tub and the braking mode to be used. The microcomputer 63 combines the above-described braking means in a time-sequence manner when brake is to be effected. As shown in FIG. 19, the combinations of braking means include a low braking mode, a normal braking mode, a high braking mode, an emergency braking mode, and a wash braking 20 mode. The wash braking mode is used in the wash operation and executed after every normal rotation and after every reverse rotation. In the wash braking mode, as shown in FIG. 19, the soft braking means is first executed for a predetermined time and the 25 short-circuit braking means is then executed until rotation of the motor 20 is stopped. Thereafter, the positioning means is executed for the predetermined time (0.5 sec). The low braking mode is used when the dehydration operation 28 is normally finished with the set dehydrating time having expired, when a power-off switch or an interrupt switch of the operation switches 69 is operated, or when the lid 67 is opened (this is detected by the lid switch 68). The low braking mode is effected 5 when any one of the above-described conditions is met and the initial idle running including detection of rotational speed is executed for 40 ms and the speed of the motor 20 detected during 4 0 ms is below 3 00 rpm. In the low braking mode, following the initial idle running means, the normal idle running means is 10 executed until 400 ms expire from the start of the initial idle running means. Thereafter, the soft braking means is executed for the predetermined time and the short-circuit braking means then executed until rotation of the motor is stopped. The normal braking mode is used when the dehydration 15 operation is normally finished with the set dehydrating time having expired and the speed of the motor 2 0 detected during execution of the initial idle running means is at or above 3 00 rpm. Furthermore, the normal braking means is executed when the power-off switch or the interrupt switch of the operation switches 20 69 is operated or when the lid 67 is opened and when the speed of the motor 20 detected during the initial idle running means is at or above 300 rpm and below 600 rpm. In the normal braking mode, the initial idle running means is executed for 40 ms and thereafter, the short-circuit braking means is executed until the 25 motor 20 is stopped. The high braking mode is used when the power-off switch or the i.nterrupt switch is operated or when the lid 67 is opened and the speed of the motor 20 detected during the initial idle running 331564 means is at or above 600 rpm and below 1000 rpm. A maximum speed of the motor 20 during the dehydration operation is 900 rpm and accordingly, the motor speed does not usually exceed 900 rpm to a large extent. 5 In the high braking mode, the short-circuit braking means is executed for 400 ms after execution of the initial idle running means. The regenerative braking means including the dynamic braking means is then executed until the motor speed is decreased to 480 rpm. Thereafter, the short-circuit braking means is 10 executed until the motor speed is decreased to zero (stop of rotation). The emergency braking mode is used irrespective of the motor speed when power failure occurs during the dehydration operation. In the emergency braking mode, the short-circuit braking means 15 is executed for 400 ms after execution of the initial idle running means. The regenerative braking means including the dynamic braking means is then executed until the motor speed is decreased to 100 rpm. Thereafter, the short-circuit braking means is executed until the motor speed is decreased to zero (stop of 20 rotation). In execution of the regenerative braking means including the dynamic braking means in each of the high and emergency braking means, only the regenerative braking means is executed or the regenerative braking means and the dynamic braking means are 25 executed alternately. The operation of the washing machine will now be described together with the control manner of the microcomputer 63. The motor 20 is driven to rotate the agitator 5 or the rotatable tub I IN'IcLLLCIuAl | Or .Vi II 18 / ■ * : 30 4 in the wash and dehydration operations. Based on the position sensor signals Ha, Hb and He, the microcomputer 63 forms the energization signals Du, Dv and Dw (see FIG. 8C) represented by 8-bit data values to obtain a predetermined speed for rotation 5 of the motor 20. The PWM circuit 61 forms the drive signals Vup, Vun, Vvp, Vvn, Vwp, and Vwn on the basis of the energization signals. FIG. 8D shows the drive signals Vup and Vun. FIG. 8E shows a phase U output voltage and FIG. 8F shows a sinusoidal phase U winding current. A sinusoidal current is also supplied to each of the 10 other phase V and W windings. The energization signals Du, Dv and Dw are shifted from one another by an electrical angle of 121 degrees. The microcomputer 63 further supplies a signal Do for permission and stop of output to the PWM circuit 61 as well as the above-mentioned energization signals Du, Dv and Dw. When the 15 signal Do is 0, each of the drive signals Vup, Vun, Vvp, Vvn, Vwp and Vwn is turned to the low level so that all the switching elements 57a to 57f are turned off, whereby the motor 20 is deenergized. In the wash operation including that with detergent being 20 used or that accompanied by rinsing, the agitator 5 is rotated repeatedly alternately in the normal and reverse directions. For this purpose, as shown in FIG. 9, the microcomputer 63 rotates the motor 20 in the normal direction and thereafter brakes the motor 20 in the wash braking mode. The microcomputer 63 then 25 rotates the motor 20 in the reverse direction and thereafter brakes the motor 20 in the wash braking mode. This control manner is repeated. In the wash braking mode, as described above, the soft braking means is first executed for the predetermined time 31 331564 and the short-circuit braking means is then executed until rotation of the motor 20 is stopped. Thereafter, the positioning means is executed for the predetermined time (0.5 sec). The wash braking mode is used during the wash operation. When the 5 dynamic braking means is first used to brake the agitator 5, it is suddenly braked such that sound due to the splash of water is increased. In the embodiment, however, the soft braking means is executed before execution of the dynamic braking means. As a result, occurrence of an offensive sound due to the splashing 10 of water can be prevented. In the dehydration operation, the microcomputer 63 drives the motor 20 to rotate the rotatable tub 4. When the dehydration operation is normally finished with expiration of the set dehydrating time, the microcomputer 63 brakes the rotatable tub 15 4 in the following manner. The low braking mode is used when the motor speed detected during the initial idle running means is below 300 rpm. In the low braking mode, the normal idle running means in which all the switching elements 57a to 57f are turned off is executed after execution of the initial idle running means 20 in which all the switching elements are also turned off. During execution of the normal idle running means, the microcomputer 63 controls the relay drive circuit 46a to deenergize the relay coil, thereby switching the relay switch 46 so that the circuit between the COM and NC terminals thereof is closed. Consequently, supply 25 of the DC power to the inverter main circuit 47 is interrupted. Thereafter, the microcomputer 63 executes the soft braking means in which the ON duty ratios of the switching elements 57a to 5 7f are gradually rendered zero. Experiments conducted by the ' n a . 1 ft ' 'i 32 inventors show that the motor speed immediately before execution of the soft braking means takes a certain value. Accordingly, the ON duty ratio is gradually decreased from an experimentally determined value to zero. Execution of the soft braking means 5 is stopped when the ON duty ratio has become zero. The short-circuit braking means in which the switching elements 57b, 57d and 57f are turned on is then executed. At this time, the motor speed is reduced approximately to 100 rpm. As a result, even when the short-circuit braking means is executed, the motor 10 speed is not suddenly reduced. Thus, the motor 20 is smoothly braked and accordingly, vibration and noise can be prevented. The low braking mode is used when the power-off switch or the interrupt switch is operated in the dehydration operation or when the lid 67 is opened and the speed of the motor 20 detected 15 during execution of the initial idle running means is below 300 rpm, as described above. In this case, too, the vibration and noise can be prevented. FIG. 11 shows the variation in the motor speed when the motor 20 is braked in the low braking mode. The normal braking mode is used when the dehydration 20 operation is normally finished with the motor speed being at or above 300 rpm, as shown in FIG. 19. Following execution of the initial idle running means for 4 0 ms, the short-circuit braking means is executed. The short-circuit braking means is started until expiration of 400 ms from the start of the initial idle 25 running means. More specifically, the relay drive circuit 46a deenergizes the relay coil within 400 ms from the start of the initial idle running means so that the circuit between the COM and NC terminals is closed, whereby the supply of DC power to the 33 inverter main circuit 47 is stopped. The short-circuit braking means is executed until rotation of the motor is stopped. In this case, motor rotation is stopped in about 2 0 seconds after start of braking. Since execution of the short-circuit braking means 5 is initiated when the motor speed is high, the braking effect is lower than the regenerative braking means. However, the vibration and noise can be reduced. Thus, the braking is not required urgently when the dehydration operation is normally finished. Accordingly, prevention of vibration and noise can be 10 preferentially considered when the motor 20 is braked. The normal braking mode is used when the power-off switch or the interrupt switch is operated in the dehydration operation or when the lid 67 is closed and the motor speed is at or above 300 rpm and below 600 rpm. In this case, the braking is required rather urgently. 15 However, since the motor speed is below 600 rpm at its upper limit, it does not take so much time for the motor 20 to be stopped even when the normal braking mode is used. Consequently, the occurrence of vibration and noise can be reduced. The high braking mode is used when the power-off switch or 20 the interrupt switch is operated in the dehydration operation or when the lid 67 is opened and the motor speed is at or above 600 rpm and below 1000 rpm. In this case, the braking is required rather urgently. If the above-described normal braking mode should be used in this case, it would take much time until the 25 rotation of the motor is stopped since the motor speed is high. In the high braking mode, the initial idle running means is executed and thereafter, the relay drive circuit 46a deenergizes the relay coil so that the circuit between the COM and NC terminals 34 is closed, whereby the short-circuit braking means is executed within 400 ms. That is, the inverter main circuit 47 is disconnected from the DC power-supply circuit 43 and the discharge circuit 48 is then connected. Thereafter, the regenerative 5 braking means is executed. In the regenerative braking means, as described above, the switching elements 57a to 57f are on-off controlled by the energization pattern in which the phase currents lag voltages induced at the respective windings 26u, 2 6v and 26w of the motor 10 20. As a result, motor energy is returned via the regenerative diode 55 to the side of the DC power supply circuit 43. In this case, when the speed of the motor 20 is high, the electromotive force thereof is large, so that the induced voltage rises about to 600 V. When the motor induced voltage appearing on the DC line 15 47a exceeds 400 V, this is detected by the voltage divider circuit 56. As a result, the microcomputer 63 turns on the discharge switching element 50 via the drive circuit 52, whereby the motor energy is consumed by the discharge resistance 49. This causes the line voltage of the DC line 47a to drop. When the line voltage 20 drops to or below 350 V, the discharge switching element 50 is turned off. However, the motor 20 is still running. Accordingly, the discharge switching element 50 is turned on and off repeatedly while the induced voltage is higher than 400 V. The discharge switching element 50 is finally turned off when 25 the motor induced voltage is less than 400 V, whereupon the motor energy is returned via the regenerative diode 55 to the DC power-supply circuit 43 side. The regenerative braking means is thus executed. The regenerative braking means is executed until 35 331564 the motor speed is decreased to 480 rpm. When the motor speed reaches 480 rpm, the on-off switching pattern of the switching elements 57a to 57f in the dynamic and regenerative braking means is switched to the pattern in which the lower three switching 5 elements 57b, 57d and 57f are simultaneously turned on, whereby the short-circuit braking means is executed. The short-circuit braking means is executed until the rotation of the motor is stopped. When the speed of the motor 20 is high and the braking is required rather urgently, the high braking mode can provide 10 for a higher braking effect than the normal braking mode and reduce the braking time. The emergency braking mode is used irrespective of the rotational speed of the motor 20 when a power failure occurs during the dehydration operation. The emergency braking mode differs 15 from the high braking mode in that the regenerative braking means with the dynamic braking means is executed until the motor speed is reduced to 100 rpm, as described above. In this case, the braking force is increased since the regenerative braking means is executed until the motor speed is reduced to 100 rpm. 20 Furthermore, the braking time is shorter in the regenerative braking means. The emergency braking mode is thus suited for the case where the braking is urgently required. FIG. 10 shows the changes in the motor speeds in the braking modes when the motor 20 being rotated at or above 600 rpm and below 1000 rpm in the 25 dehydration operation is braked. As obvious from FIG. 10, the braking time is shorter in the emergency braking mode than in the high braking mode and in the high braking modq .than, in the normal If' ILL L j I J,11 ! , i" _ , 1 braking mode. <■ 0 '' i§:v:rj 36 331564 The short-circuit braking means is executed prior to execution of the regenerative braking means in the high and emergency braking modes. Consequently, the circuit elements of the DC power-supply circuit 43 and the inverter main circuit 47 5 can be prevented from being broken. More specifically, the regenerative braking means achieves a high braking effect when the motor speed is high. However, the regenerative current is rendered excessively large and may break the circuit elements of the DC power-supply circuit 43 and the inverter main circuit 47. 10 In the embodiment, however, the short-circuit braking means is executed prior to the regenerative braking means. The motor energy is consumed by the short-circuiting of the motor windings. The regenerative current is prevented from being excessively large in execution of the regenerative braking means following 15 the short-circuit braking means. Consequently, the breakage of the circuit elements can be prevented. The dynamic braking means is executed when the potential at the side of the inverter main circuit 47 is rendered higher by the motor electromotive force than the potential at the DC 20 power-supply circuit 43 . Spark occurs in the portion of the relay switch 46 or switch contacts are welded when the relay switch 46 is switched, for execution of the dynamic braking means, from a first state in which the inverter main circuit 47 is connected to the DC power-supply circuit 43 and is open to the discharge 25 resistance 4 9 to a second state in which the inverter main circuit 47 is open to the DC power-supply circuit 43 and connected to the discharge resistance 49. In the embodiment, however, the short-circuit braking means resulting in no potential difference li C " I is:"" : 331564 between the DC power-supply circuit 43 and the inverter main circuit 47 is executed prior to the regenerative braking means with the dynamic braking means, as shown in FIG. 19. The relay switch 46 is switched during execution of the short-circuit 5 braking means. Consequently, the above-mentioned spark and contact welding can be prevented. In the high braking and emergency braking modes, the discharge switching element 50 is turned on so that the dynamic braking means is executed. The discharge switching element 50 10 is turned on and off at a relatively higher frequency until the motor induced voltage drops below 400 V. This on-off operation may result in occurrence of noise. In the embodiment, however, the capacitor 51 is connected in parallel to a series circuit of the discharge resistance 49 and the discharge switching element 15 50. Consequently, occurrence of the above-mentioned noise can be prevented. If the capacitor 51 should fixedly connected between both input terminals 47A and 47B of the inverter main circuit 47, the noise would be suppressed. In this case, however, large charge and discharge currents normally flows into the 20 capacitor 51, so that a capacitor having a larger capacity than required as a noise filter is required. In the embodiment, however, the capacitor 51 is used as the noise filter only when the relay switch 46 is switched to the second state, namely, only when the discharge resistance 49 is used. Consequently, the 25 capacitor 51 need not have a large capacity. The DC power is supplied to the inverter main circuit 47 from the DC power-supply circuit 43 when the relay switch 46 is in the first state (in which the circuit between the C,OM and NC terminals I IT' I —L olu r I; o ,• !! 1 a 38 is closed) in the wash and dehydration operations, so that the motor 20 is under rotation according to the control mode. The relay switch 46 is switched to the second state (in which the circuit between the COM and NC terminals is opened) when the motor 5 is braked upon completion of the wash or dehydration operation. In this case, the capacitor 51 is charged via the charge resistance 53 when the relay switch 46 is in the first state such that the discharge circuit 48 is at the same potential as the positive side output terminal 44A of the DC power-supply circuit 43. 10 Consequently, spark and contact welding can be prevented when the relay switch 46 is switched to the second state. The motor 20 is braked in the emergency braking mode when power failure occurs or a plug of the washing machine is withdrawn during rotation of the motor with the relay switch 46 in the first 15 state. In this case, the output voltage of the DC power supply circuit 43 gradually drops. Since the capacitor 51 is then charged with electric charge, the terminal voltage thereof is raised above the output voltage of the DC power supply circuit 43, thereby turning on the diode 54. The electric charge of the 20 capacitor is discharged via the diode 54 to the DC power supply circuit 43. At this time, the DC power supply circuit 43 side is substantially at the same potential as the discharge circuit 48 side. Accordingly, even if the relay switch 46 is switched to the second state during the braking in the emergency braking 25 mode , sparks or contact welding can be prevented. Furthermore, the relay switch 4 6 is automatically switched to the second state when the operating voltage is at or below the predetermined value (50 V) in the embodiment. Accordingly, the sparks or the contact 39 welding in the relay switch 46 can also be prevented even in the case where the relay switch is switched when the power failure occurs or the plug of the washing machine is withdrawn in the occasions other than under actuation of the braking. The 5 energization signals Du, Dv and Dw are formed so that the electrical angles thereof are shifted, for example, by one degree from one another when the energization signals have the same amplitude (the same data value). More specifically, the energization signal Dv is generated with a phase shift of 121 10 degrees (electrical angle) relative to the energization signal Du. The energization signal Dw is generated with a phase shift of 121 degrees relative to the energization signal Dv. This will be described in detail with respect to the phases U and W, for example. FIG. 12 shows the phase U and V energization signals 15 Du and Dv. Each signal is shown in the form of sinusoidal data represented by electrical angle data obtained by dividing one period electrical angle by 3 60 and numeric data representative of the voltage magnitude in the quantum of "256". The amplitude of the sinusoidal winding current of the corresponding phase 20 depends upon the magnitude of the numeric data. The amplitude (current value) of the winding current depends upon a time period for which the switching element (any one of the switching elements 57a to 57f) energizing the phase winding is energized. Furthermore, the electrical angle determines the timing of 25 energization. The phase U and V energization signa.1 waveforms are usually shifted by an electrical angle of 120 degrees from each other. FIG. 15 shows such waveforms as examples. As shown in FIG. 15, 40 the portion where the amplitudes of the phase U and V winding currents become equal to each other or the current waveforms cross each other, which portion is shown as portion P in FIG. 8F, occurs in the portion Pk where the phase u and V energization signals 5 Du and Dv cross each other. When the energization signals Du and Dv overlap each other at an electrical angle K as the same numeric data, a large spike current occurs, resulting in noise. Regarding phase U, the reference symbol il in FIG. 18 designates the current flowing into the DC line 47a of the inverter 10 main circuit 47 when the switching elements 57a and 57f are turned on and the amplitude of the current flowing into the phase U winding 26u is 2 A. In this state, when the switching element 57a is switched from the ON state to the OFF state, the winding current flows through the motor windings 2 6u and 26w, the circuit between 15 collector and emitter of the switching element 57f, the freewheel diode 58b, and the motor windings 26u and 26w, as shown by reference symbol i2 in FIG. 18. When the switching element 57a is turned on again, the electric charge due to the current having flown until then delays recovery of the free-wheel diode 58b to 20 the shut-off state. As a result, a short-circuit current of about 7 A flowing through the switching element 57a and the diode 58b further flows into the DC line 47a, as shown in FIG. 17. A short-circuit current of 9 A flows when the switching element 57c is turned to the ON state. 25 The switching elements are switched with the energization periods slightly differing at the respective electrical angles when the sinusoidal currents are caused to flow through the windings 26u, 26v and 26w. For example, when the current flows 33 1 5 6 4 through the phases U and V, the switching elements 57a, 5 7c and 57f are turned on. A short-circuit current flows into the DC line 47a in synchronization with the switching of the element 57a from the Off state to the ON state and the switching of the element 5 57c from the OFF state to the ON state. In the case where the current amplitudes of the phases U and V agree with each other (the current waveforms cross each other), the drive signals Vup and Vvp processed by means of PWM completely correspond with each other when the energization signals Du and Dv at the electrical angle at that time agree with each other, as shown in FIG. 16. 10 Consequently, the ON timing of the switching element 57a becomes completely the same as that of the switching element 57c {see reference symbols x and y in FIG. 17). Then, the short-circuit current simultaneously flows into both of the free-wheel diodes 58b and 15 58d such that a spike current of 15 A about twice as large as in the normal case. The spike current adversely affects the operation of household electric equipment other than the washing machine as well as the entire operation of the control circuit. In particular, when the rotational speed of the motor 20 is reduced 20 and more particularly, while the positioning means is being executed in the wash operation, the period of one degree of electrical angle is longer so that the time for which the short-circuit currents overlap each other is longer, whereupon the noise is further intensified. 25 In the embodiment, however, the energization signals Du, Dv and Dw are shifted from one another by the electrical angle of 121 degrees, as shown in FIGS. 12 and 13. As a result, the energization signals do not take the same numeric data at the same 42 electrical angle as shown in FIG. 14. Thus, since the ON times of the switching elements are shifted in synchronism with agreement of the amplitudes of the phase currents of the motor 20, the short-circuit currents are prevented from overlapping. 5 Consequently, generation of a large spike current can be prevented and accordingly, the noise can be prevented. The noise is effectively prevented particularly in the execution of the positioning means. Although the direct drive mechanism is employed for driving the rotatable tub and the agitator by the 10 brushless motor in the foregoing embodiment, a belt transmission mechanism may be used, instead. The foregoing description and drawings are merely illustrative of the principles of the present invention and are not to be construed in a limiting sense. Various changes and 15 modifications will become apparent to those of ordinary skill in the art. All such changes and modifications are seen to fall within the scope of the invention as defined by the appended claims. </div>

Claims

<div class="application article clearfix printTableText" id="claims"> 43 WE CLAIM:

1. A washing machine comprising: a rotatable tub for accommodating laundry with water; 5 an agitator for agitating the water; a brushless motor provided for driving the rotatable tub and the agitator and including a rotor and a stator having a winding; a DC power supply circuit; an inverter main circuit to which a DC current is supplied 10 from the DC power supply circuit, the inverter main circuit including switching elements bridge-connected to a plurality of phases of the motor so that the DC current from the DC power supply circuit is supplied via the switching elements to the brushless motor; 15 regenerative braking means returning a current due to an electromotive force of the brushless motor to the DC power supply circuit; dynamic braking means including a dynamic brake resistance element connected to a current path at an input side of the brushless motor so that the current due to the electromotive force of the brushless motor is supplied to the dynamic brake resistance element; and short-circuit braking means short-circuiting the winding of the brushless motor. 25

2. A washing machine according to claim 1, wherein the regenerative braking means returns the current via the inverter main circuit to the power supply circuit side, the dynamic brake resistance element of the dynamic braking means is connected to an input 44 ^1564 side of the inverter main circuit, and the short-circuit braking means short-circuits the motor winding through the switching elements of the inverter main circuit. 5

3. A washing machine according to claim 1, wherein rotation of the rotor of the brushless motor is transmitted directly to the rotatable tub and the agitator.

4. A washing machine according to claim 2, wherein rotation 10 of the rotor of the brushless motor is transmitted directly to the rotatable tub and the agitator.

5. A washing machine according to claim 1, wherein any one of, or a combination of two or more of the regenerative, dynamic 15 and short-circuit braking means is effectuated when the brushless motor is braked.

6. A washing machine according to claim 2, wherein any one of, or a combination of two or more of the regenerative, dynamic 20 and short-circuit braking means is effectuated when the brushless motor is braked.

7. A washing machine according to claim 5, wherein the rotatable tub can be driven according to a plurality of control operations, such as a wash operation or a dehydration operation, and wherein the combination of the braking means differs 25 depending upon the control operation. .

8. A washing machine according to claim 6, wherei driven according to a plurality of control operations, ,rotat|iliNe!M&T0ALnPtePERTY OFFIC OF NZ. ^s-'a wa§h Operation or a 2 3 FEB 2000 2 3' JAN 2000 DECEIVED dehydration operation, and wherein the combination of the braking means differs depending upon the control operation.

9. A washing machine according to claim 5, wherein the short-circuit braking means is executed prior to the regenerative braking means when the regenerative braking means is to be executed.

10. A washing machine according to claim 6, wherein the short-circuit braking means is executed prior to the regenerative braking means when the regenerative braking means is to be executed.

11. A washing machine according to claim 2, which further comprises switching means for switching between a regenerative braking means connected state wherein the inverter main circuit is connected to the DC power supply circuit and is open to the dynamic brake resistance element, and a dynamic braking means connected state wherein the inverter main circuit is open to the DC power supply circuit and is connected to the dynamic brake resistance element, and wherein when the regenerative braking means is to be executed, the short-circuit braking means and the dynamic braking means are executed in turn prior to the regenerative braking means, and the switching means is switched to the dynamic braking means connected state during execution of the short-circuit braking means.

12. A washing machine according to claim 7, wherein the combination if or a wash operatd.©ffdlf fers from 0F NZ " * o q —n L. J t htCEIVED INTELLECT iWHRTY OFFICE 2000 RECEIVED 44 side of the inverter main circuit, and the short-circuit braking means short-circuits the motor winding through the switching elements of the inverter main circuit. 5 3 . A washing machine according to claim 1, wherein rotation of the rotor of the brushless motor is transmitted directly to the rotatable tub and the agitator.

4. A washing machine according to claim 2, wherein rotation 10 of the rotor of the brushless motor is transmitted directly to the rotatable tub and the agitator. 15

5. A washing machine according to claim 1, wherein any one of, or a combination of two or more of the regenerative, dynamic and short-circuit braking means is effectuated when the brushless motor is braked. 20

6. A washing machine according to claim 2, wherein any one of, or a combination of two or more of the regenerative, dynamic and short-circuit braking means is effectuated when the brushless motor is braked.

7. A washing machine according to claim 5, wherein the rotatable tub can be driven according to a plurality of control operations, such as a wash operation or a dehydration operation, and wherein the combination of the braking means differs 25 depending upon the control operation. 8 A washing machine according to claim 6, whereinJh tatable tub can be driven according to a plurality of control operations, <JBi®ti6CTI!JAiof>f^)pEflTY OFFICE | OF NZ 2 3 FEB 2000 ! i RECEIVED 45 dehydration operation, and wherein the combination of the braking means differs depending upon the control operation.

11. A washing machine according to claim 2, which further comprises switching means for switching between a regenerative braking means connected state wherein the inverter main circuit is connected to the DC power supply circuit and is open to the dynamic( brake resistance element, and a dynamic braking means connected state wherein the inverter main circuit is open to the DC power supply circuit and is connected to the dynamic brake resistance element, and wherein when the regenerative braking means is to be executed, the short-circuit braking means and the dynamic braking means are executed in turn prior to the regenerative braking means, and the switching means is switched to the dynamic braking means connected state during execution of the short-circuit braking means.

12. A washing machine according to claim 7, wherein the combination of the braking mear ~ ^on differs from INTELLECTUAL PROPERTY OFF! OF N.Z 2 3 FEB 2000 RECEIVED 33156 A the combination of the braking means for a dehydration operation.

13. A washing machine according to claim 8, wherein the combination of the braking means for a wash operation differs from the combination of the braking means for a dehydration operation.

14. A washing machine according to claim 5, wherein the combination of the braking means differs depending upon whether the brushless motor is in an emergency braking mode.

15. A washing machine according to claim 6, wherein the combination of the braking means differs depending upon whether the brushless motor is in an emergency braking mode.

16. A washing machine according to claim 2, which further comprises a discharge circuit including the dynamic brake resistance element, a discharge switching element connected in series to the discharge element so as to be operated according to a motor induced voltage appearing at the inverter main circuit, and a capacitor connected in parallel to a series circuit of the dynamic brake resistance element and the discharge switching element, and switching means for selectively switching between a first state wherein the DC power supply circuit is electrically connected to the input side of the inverter main circuit and the discharge circuit is electrically disconnected from the input side of the inverter main circuit, and a second state wherein the DC power supply circuit is electrically disconnected from the input side of the inverter main circuit and the discharge circuit is electrically connected NOW AMENDED " 331564 to the input side of the DC power supply circuit, and wherein the switching means is switched to the second state when the dynamic braking means is to be executed. 5 17. A washing machine according to claim qLO/ further comprising a discharge resistance connected in series to the capacitor so that the capacitor is charged from the DC power supply circuit when the switching means is in the first state. 10 18. A washing machine according to claim 17, further comprising a diode connected in parallel to the discharge resistance so that an electric charge of the capacitor is discharged to the DC power supply circuit side. 15 19. A washing machine according to claim 1, wherein an ON time of each switching element in synchronization with accordance of a phase current amplitude of the brushless motor between different phases is displaced between the different phases. 20 20. A washing machine according to claim 2, wherein an ON time of each switching element in synchronization with accordance of a phase current amplitude of the brushless motor between different phases is displaced between the different phases. 25 21. A washing machine substantially as herein described with reference to the accompanying drawings. Kabushxki Kaisha Toshiba m, By Its Attorneys BAIIMN SHELSIUN WATERS 47 AS AMENDED to the input side of the DC power supply circuit, and wherein the switching means is switched to the second state when the dynamic braking means is to be executed. 5

17. A washing machine according to claim 16, further comprising a discharge resistance connected in series to the capacitor so that the capacitor is charged from the DC power supply circuit when the switching means is in the first state. 10

18. A washing machine according to claim 17, further comprising a diode connected in parallel to the discharge resistance so that an electric charge of the capacitor is discharged to the DC power supply circuit side. 15

19. A washing machine according to claim 1, wherein an ON time of each switching element in one phase is shifted from an ON time of another switching element in another phase in synchronization with when the phase current amplitudes between the different phases intersect with each other. 20

20. A washing machine according to claim 2, wherein an ON time of each switching element in one phase is shifted from an ON time of another switching element in another phase in synchronization with when the phase current amplitudes between the 25 different phases intersect with each other.

21. A washing machine substantially as herein described with reference to the accompanying drawings. 30 Kabushiki Kaisha Toshiba 35 INTELLECTUAL PROPERTY OFFICE OF NZ. .1 6 MAR 2001 RECEIVED By Its Attorney BALDWIN SHELSTON WATERS </div>