US3764822A

US3764822A - Arrangement for driving the drum of a washing machine

Info

Publication number: US3764822A
Authority: US
Inventors: W Ebbinge; Ruiter C De
Original assignee: US Philips Corp
Current assignee: US Philips Corp
Priority date: 1971-07-03
Filing date: 1972-06-29
Publication date: 1973-10-09
Anticipated expiration: 1990-10-09
Also published as: ES404450A1; CA954615A; FR2144747A1; IT958656B; GB1358494A; NL7109226A; DE2232041A1

Abstract

Arrangement including a self-commutating electric motor for driving the drum of a washing machine. The electric heating element of the washing machine is connected in the supply circuit in series with the motor. This supply circuit further contains a first rectifier which is connected in series with the motor and becomes conducting at the passages through zero of the supply voltage. Speed control of the motor is effected by means of a second rectifier which is of a bidirectional type and which shunts the series combination of the motor and the first rectifier and is set to the conductive condition by means of control pulses. The power dissipated by the heating element may also be regulated by means of this second rectifier.

Description

United States Patent [191 Ebbinge et a1.

Oct. 9, 1973 ARRANGEMENT FOR DRIVING THE DRUM OF A WASHING MACHINE [75] Inventors: Willem Ebbinge; Dirk Cornelis De Ruiter, both of Emmasingel, Eindhoven, Netherlands [73] Assignee: U.S. Philips Corporation, New

York, N.Y.

[22] Filed: June 29, 1972 [21] Appl. No.: 267,363

[30] Foreign Application Priority Data July 3, 1971 Netherlands 7109226 [52] US. Cl. 307/141, 318/345 [51] Int. Cl. H0lh 7/00 [58] Field of Search 307/141; 318/345 [56] References Cited UNITED STATES PATENTS 3,638,090 1/1972 Ebbinge et a1 318/345 Primary ExaminerRobert K. Schaefer Assistant ExaminerM. Ginsburg Attorney-Frank R. Trifari [57] ABSTRACT Arrangement including a self-commutating electric motor for driving the drum of a washing machine. The electric heating element of the washing machine is connected in the supply circuit in series with the motor. This supply circuit further contains a first rectifier which is connected in series with the motor and becomes conducting at the passages through zero of the supply voltage. Speed control of the motor is effected by means of a second rectifier which is of a bidirectional type and which shunts the series combination of the motor and the first rectifier and is set to the conductive condition by means of control pulses. The power dissipated by the heating element may also be regulated by means of this second rectifier.

10 Claims, 5 Drawing Figures ICD PAIENIEUUBT 91% 3,764,822

SHEET 10F 3 PAItNIEU 15 SHEET 3UF .3

ARRANGEMENT FOR DRIVING THE DRUM OF A WASHING MACHINE The invention relates to an arrangement including a self-commutating electric motor for driving the drum of a washing machine, which arrangement is provided with at least one electric heating element and has a supply circuit for the motor, which circuit includes the series combination of the heating element and a first rectifier, and a switch which is connected across the series combination of the motor and the first rectifier.

Such an arrangement is described, for example, in U.S. Pat. No. 3,638,090. The arrangement described in the said Patent is intended to provide a simple and cheap drum drive in which the heating element, which acts as a series resistor for the motor, is effectively utilized. Owing to this series resistor the motor acquires a kind of highly exaggerated series characteristic so that its load can be increased to an extent such that it can regularly run at a very low speed and may even be blocked without exceeding the permissible motor current. This is of particular importance in driving the drum of an automatic washing machine because the drum must be capable of rotating at one or a few low speeds during the washing cycle and at one or a few high speeds during the spinning cycle. In the arrangement described in the said Patent this is automatically achieved in that during the spinning cycle the load imposed on the motor is light with a consequent high speed, whereas during the washing cycle the motor load is heavy and hence owing to the exaggerated series characteristic the speed is very low. At the same time it is ensured that during the spinning cycle the power dissipated in the series resistor (heating element) is relatively low because the motor current is then small, whereas during the washing cycle this power is large because the motor current is large.

The exaggerated series characteristic of the motor further results in that the transition from washing speed to spinning speed is particularly smooth. During this transition the motor speed may be increased to the spinning speed before all the wash water has drained away, which, if the drum speed is appropriately chosen, may involve a very satisfactory distribution of the washing load.

In this known arrangement, in order to enable the motor speed to be regulated at least at one washing speed, in one embodiment a controlled rectifier is connected in series with the motor. In known manner phase control of the supply voltage is achieved, i.e., the controlled rectifier is rendered conductive for one halfcycle of the supply voltage by the application of a triggering signal to its control electrode and remains conductive for the remainder of this half-cycle. This control of the triggering instant enables the motor current and hence the motor speed to be controlled.

The arrangement described hereinbefore suffers from some limitations and disadvantages. Firstly the amount of heat generated by the heating element is entirely dependent on the operating condition of the motor, because the value of the series resistor is completely determined by the desired spinning speed. This desired spinning speed also determines the back E.M.F. of the motor at the washing speed and hence the current flowing through the motor and the series resistor at a given desired power. This means that the power dissipated in the series resistor and hence the heat emission during the washing cycle are entirely determined by the desired spinning and washing speeds, which may prevent the generation of heat from reaching a desired high value during the washing cycle. Furthermore the current flowing through the series resistor depends upon the motor control, i.e., upon the triggering instant of the controlled rectifier, and hence the generation of heat will also vary with this control.

To enable the wash water to be heated more rapidly at the beginning of the washing program an additional heating element may obviously be provided. However, this additional heating element requires the provision of an additional power switch which must be switched by the program device. A second possibility of increasing the generation of heat consists in the provision of an additional switch which is capable of directly connecting the heating element to the supply voltage, as is described in the said Patent. This switch may be closed in the stationary condition of the motor so that the heating element delivers its maximum power. However, in this method the power delivered by the heating element is entirely dependent upon the washing rhythm, i.e., upon the durations of the times during which the drum must rotate and be stationary. These times may be widely different, forexample, for a given washing program the drum may be required to rotate for periods of 12 seconds each with stationary intervals of 3 seconds, whereas for another washing program the drum may be required to rotate for periods of 3 seconds separated by stationary periods of 12 seconds. Obviously the amounts of power dissipated by the heating element will be widely different in these cases. Moreover, the additional power switch will be subject to intense wear.

A second disadvantage of the known arrangement is the risk of radio-frequency interference owing to the phase control by means of the controlled rectifier. This risk of radio-frequency interference is due to the fact that the rectifier is triggered, and hence the motor current is switched on, at an instant at which the supply voltage has reached a value different from zero, possibly even its maximum value, which gives rise to large current variations.

Another disadvantage of the known arrangement is that owing to the control used considerable variations in the line load occur. These variations may be particularly annoying if their repetition frequency is low, for example, 10 Hz, which may even cause the lights connected to the same line supply to flicker, which obviously is inadmissible.

It is an object of the present invention to provide a driving arrangement in which, although it is based on the principle of the described known arrangement and has the advantages thereof, the disadvantages attendant on this known arrangement are largely avoided and which provides, in addition to simple motor control, simple control of the power dissipated by the heating element without the need for additional power switches and for appreciable extension of the programming device.

The arrangement according to the invention is characterized in that the switch consists of a second rectifier which is of a bidirectional conductivity type and has a control electrode to which a control signal may be applied which controls the conduction period of the rectifier.

A first advantage of the arrangement according to the invention is that the power supplied to, and dissipated by, the heating element is approximately independent of the operating condition of the motor. This is directly due to the provision of the second controlled bidirectional rectifier and to the fact that the speed of the motor is controlled by means of this rectifier. The presence of this controlled rectifier permits the use of a motor control method different from the conductionangle phase control employed in the known arrangement.

Assuming the motor to be fed during a half-cycle of the supply voltage, this supply may be terminated at any desired instant by triggering the second controlled rectifier, for this rectifier shunts the series combination of the motor and the first rectifier, so that rendering this second rectifier conductive causes the said series combination to be short-circuited with the result that no current is supplied to the motor. Triggering this sec ond rectifier entails only a limited variation of the current flowing through the series resistor. Before the triggering instant this current is equal to the motor current and after the triggering instant the series resistor is directly fed with the supply voltage. Furthermore, retriggering the second rectifier at an appropriate instant, that is the instant at which the current flowing through this rectifier becomes zero, permits of ensuring that the series resistor is supplied during the other half-cycle of the supply voltage also. Thus, in this case the heating element is fed during the entire cycle of the supply voltage and hence dissipates maximum power. When the second rectifier is not re-triggered at the aforementioned instant, the heating element is energized during only one half-cycle of the supply voltage so that it dissipates only one half of its maximum power. Triggering this second rectifier consequently ensures, in addition to the motor control, control of the heating effected by the heating element.

A second advantage is that the risk of radiofrequency interference can be appreciably reduced, for the motor current may be switched on at an instant at which the voltage across the first rectifier is zero, which instant is determined by the variation of the supply voltage and the value of the back E.M.F. The ensuing transient phenomena and hence the resulting radiofrequency interference will be a minimum so that the anti-interference means required may be reduced to a minimum.

A third advantage is that the variations of the line load are appreciably smaller than in the known arrangement. In the maximum setting of the heating the heating element is not continually switched on each time the motor is stopped, but owing to the triggering of the second rectifier it is fed during the entire cycle of the supply voltage, so that the variations in the line load are negligible.

Finally no additional power switches are required and a simple programming device may be used.

A first embodiment of the arrangement according to the invention furthermore enables the direction of the motor to be electronically reversed. In this embodiment the first rectifier element connected in series with the motor is a controlled bidirectional rectifier element. Changing the triggering instants of the first and second rectifier elements permits of reversing the direction of flow of the motor current.

A second embodiment of the arrangement according to the invention is characterized in that the first rectifier is a diode. The use of such an uncontrolled rectifier is possible in the arrangement according to the invention because this rectifier need not be used for the speed control.

Obviously various types of self-commutating motors may be used, for example, motors with permanentmagnet energization, collector motors with series, shunt or compound energisation, motors having rotating permanent magnets, and so on.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which: 7

FIG. 1 is a schematic circuit diagram of an embodiment of the known arrangement,

FIGS. 2 and 3 are schematic circuit diagrams of two embodiments of the arrangement according to the invention,

FIG. 4 shows the waveforms of the various currents flowing in an arrangement according to the invention, and

' FIG. 5 shows, by way of example, a circuit diagram of an arrangement according to the invention including control circuits.

Referring now to FIG. 1, the embodiment shown of the known arrangement includes a self-commutating electric motor 1, for example, a motor provided with permanent-magnet energisation. The motor 1 is connected in series with a heating element 2, which serves as a series resistor for the motor and the resistance of which is chosen so that the motor has a highly exaggerated series characteristic. The motor is also connected in series with a controlled rectifier (thyristor) 3 the control electrode, or gate, of which is connected to a terminal 4. A supply voltage V- is applied to this series combination of the heating element 2, the motor 1 and the thyristor 3 via

terminals

6 and 6.

The speed of the motor is controlled by controlling the firing instant of the thyristor 3, i.e., by applying a trigger pulse to the terminal 41 at a desired instant. This has the disadvantage that the likelihood of radiofrequency interference is great, for the thyristor current is switched on at an instant at which the voltage across this element has a positive value, which may give rise to considerable current variations.

It will further be clear that the current through the heating element 2 is entirely determined by the motor current. Current is only supplied to the heating element during the part of the positive half-cycle of the supply voltage V- in which the thyristor is conductive, so that the generation of heat depends entirely on the motor conditions.

To permit the generation of heat to be increased at a desired instant a switch 5 is provided which enables the heating element 2 to be directly connected to the supply voltage during the stationary periods of the motor. Heat dissipation naturally is entirely dependent on the duration of these stationary periods which may widely differ in the various washing programs.

FIG. 2 shows a first embodiment of the arrangement according to the invention. Similarly to the known arrangement the arrangement shown in FIG. 2 include the series combination of a heating element 2, a motor 1 and a controlled rectifier 3", the supply voltage V- being applied to this series combination via

terminals

6 and 6. The rectifier 3" used in this case is a controlled bidirectional rectifier (triac), however, it may alternatively be a thyristor. The series combination of the motor 1 and the first rectifier 3 in this embodiment is shunted by a second bidirectional rectifier 7. The triggering signals for both rectifiers are supplied by a control device 8.

The use of the second rectifier 7 provides a speed control for the motor I which is quite different from that used in the known arrangement, as will be explained with reference to the waveforms of the various currents shown in FIG. 4. At the beginning of a halfcycle of the supply voltage V-, for example, at the beginning of the positive half-cycle (instant t a control pulse is applied to the rectifier 3. Hence at this instant a motor current I will start flowing, and the current I flowing through the heating element is equal to the current I,. At a given instant t, during the positive halfcycle of the supply voltage V- there is applied to the second rectifier 7 a control pulse which renders it conductive, so that the series combination of the motor 1 and the rectifier 3 is short-circuited and hence current is no longer supplied to the motor. Owing to the inductive nature of the motor a motor current I will remain flowing for a certain period (t,t This motor current flows through the first rectifier 3 and through the second rectifier 7. Thus the second rectifier 7 also serves as a freewheel diode for the motor.

At the instant t, the heating element 2 is directly connected to the supply voltage via the second rectifier 7, so that the current I flowing through this element will show an abrupt variation. The current I, flowing through the second rectifier 7 is equal to the difference between the currents I and I,.

At the instant at which the current I, flowing through the second rectifier 7 becomes zero, i.e., at the instant at which the motor current I and the current flowing through the heating element 2 are equal, which instant precedes the instant t, as the supply voltage V- passes through zero, the second rectifier may or may not be triggered again. If at this instant t, a new trigger pulse is supplied to the second rectifier, this rectifier will remain conducting and the sign of the current direction will be reversed. In this case there will continue flowing through the heating element 2 a current the direction of which is reversed at the instant t At the instant t, at which the motor current I becomes zero, the current I flowing through the heating element 2 and the current I, flowing through the second rectifier 7 become equal to one another and remain so during the remainder (1 -1 of the negative half-cycle of the supply voltage V-. If the second rectifier is not re-triggered at the instant 1,, the currents I and I, will be zero from this instant. If desired, the second rectifier may be retriggered at an instant later than t,, which permits regulation of the heat dissipation.

A first advantage of the aforedescribed motor speed control permitted by the arrangement according to the invention is that the power supplied to the heating element 2 is substantially independent of this speed control. FIG. 4 shows that the waveform of the current I flowing through the heating element is substantially sinusoidal. When the instant r, is varied, the sudden change of this waveform will follow this variation, the overall power supplied to the heating element will be substantially constant. Hence, substantially maximum power is supplied to the heating element irrespective of the motor conditions. If the second rectifier 7 is not retriggered at the instant t the power supplied to the heating element is halved. Thus, triggering of this second rectifier 7 not only provides a motor speed control but also enables the power supplied to the heating element to be controlled and to be substantially independent of the motor conditions. Triggering the second rectifier 7 alone at the passages through zero of the supply voltage V- provides maximum heating in the stationary condition of the motor.

The invention also enables the first rectifier to be triggered at the instant at which the voltage across it is zero, i.e., at the instant at which the supply voltage V- is equal to the back E.M.F. of the motor I. This method of triggering greatly reduces the risk of radio-frequency interference.

Also, the variations of the line load will be small because when the heating element is switched to full power, current is supplied to it continuously and not, as in the known circuit arrangement, at intervals.

The fact that the first rectifier 3 is a bidirectional rectifier has the advantage of permitting the direction of rotation of the motor to be reversed by fully electronic means, for triggering this rectifier at the instant t instead of at the instant t, causes the direction of the current flowing through the motor to be reversed. In this case the speed control is effected by triggering the second rectifier 7 during the negative half-cycle of the supply voltage.

FIG. 3 shows a second simple embodiment of the arrangement according to the invention. In this arrangement the first rectifier 3' connected in series with the motor is a diode. As a result, the motor current is automatically switched on at the instant at which the voltage across this diode exceeds the threshold value thereof. To enable the direction of rotation of the motor to be reversed a second diode 3 having a pass direction opposite to that of the first diode and a switch 9 are provided. The direction of current flow through the motor can be reversed by changing over the switch 9 by means of the control device 8. Speed control and regulation of the power supplied to the heating element 2 are again effected by means of the second rectifier 7 which is triggered by the control device 8.

FIG. 5 shows, by way of example, an arrangement according to the invention which includes control circuits. The motor circuit diagram is enclosed in a block M. The trigger pulses for the gates of the

rectifiers

3 and 7 are obtained by means of a trigger circuit TR and a control device D. A square-wave voltage corresponding to a half-cycle of the supply voltage V- is derived from the supply voltage V- by means of the trigger circuit TR. This square-wave voltage is applied to the control device D, in this case to the base of a transistor Tr The collector of this transistor Tr is connected to the base of a transistor Tr Two further transistors Tr and Tr, are driven by means of these two transistors. The collector voltages of the transistors 'Ir, and Tr, determine the voltages at the gates of the

rectifiers

3 and 7 and hence their conducting or non-conducting conditions. When the positive square-wave voltage is applied to the base of the transistor Tr, the collector of the transistor Tr, will assume a negative potential, permitting the rectifier 3 to become conducting, so that current is supplied to the motor, for example, during the positive half cycle of the supply voltage V- When the square-wave voltage collapses the collector voltage of the transistor Tr, becomes negative and the rectifier element 7 becomes conducting, so that current is supplied to the heating element 2 during the negative halfcycle of the supply voltage V-'also.

The speed control is effected by means of a tachogenerator device S. When the first rectifier is conducting, the transistor Tr: is non-conducting, so that its collector voltage is high. This collector voltage is applied to the emitter of the transistor Tr The collector current of this transistor Tr is determined by the voltage applied to its base by the tachogenerator and is used to charge a capacitor C connected between the collector of the transistor Tr, and the base of the transistor Tr,. When the voltage across this capacitor has risen to about 0.7 volts, the transistor Tr becomes conducting and the rectifier 7 is triggered. Consequently this triggering instant is determined by the voltage from the tachogenerator and hence by the motor speed. Obviously, the back E.M.F. of the motor may also be used as an indication of the speed.

A capacitor C is included in the connection between the collector of the transistor Tr and the base of the transistor Tr-,. The capacitors C and C serve'to limit the durations of the trigger pulses. Should a trigger pulse be applied to the series rectifier 3 during an entire half-cycle of the supply voltage, the motor may be short-circuited, since at the instant at which the motor current becomes zero this trigger pulse would still be present and at the same time the second rectifier 7 would be conducting, so that the direction of the current flow through the motor may be reversed. This condition persists until the back E.M.F. is zero and hence the motor is stationary. The capacitors C and C limit the durations of the trigger pulses, because they are charged via the resistors used. Further capacitors (C and C are provided to suppress the influence of interference signals.

To enable the motor to be stopped and a choice to be made between maximum and minimum energy supplied to the heating element the control device D includes four transistors Tr Tr Tr and Tr The collector emitter path of the transistor Tr shunts the base emitter path of the transistor Tr When a positive voltage is applied to the base of the transistor Tr, the base emitter path of the transistor Tr is substantially shortcircuited, so that the collector voltage of this transistor always is high and the first rectifier 3 is not triggered,

causing the motor to stop. The transistor Tr is connected in series with a base resistor R u of the transistor Tr.,. When this transistor is conducting owing to a positive voltage being applied to its base, the second rectifier 7 can be triggered. When the transistor Tr is cut off, the rectifier 7 cannot be triggered, so that power can only be supplied to the heating element via the motor current.

In the stationary condition of the motor maximum power may be supplied to the heating element by means of transistors Tr and Tr If, during the washing program, the motor is in a stationary condition, a positive voltage is applied to the base of the transistor Tr If maximum heat dissipation is desired, a positive voltage is also applied to a terminal Q and hence to the base of the transistor Tr As a result, during the entire cycle of the supply voltage a trigger pulse is applied to the rectifier 7 and hence maximum power is supplied to the heating element.

The cycle of operation of the motor, i.e., the periods during which the motor is required to run and to be stationary, and the reversal of its direction of rotation are effected by means of an astable multivibrator A and a bistable multivibrator B. The cycle periods of the astable multivibrator A may be interchanged by an inverter comprising transistors Tr and Tr Depending upon the voltage at a terminal P (base of the transistor Tr either an end 10 or an end 11 of a resistor R is connected to the supply via a diode D or a diode D respectively. Thus a choice may be made between a quick operating rhythm of the motor (short stationary periods and long running period) and a slow operating rhythm (long stationary periods and short running periods).

The output voltage of this astable multivibrator A, which voltage corresponds to the desired running period, is applied to the bistable multivibrator B. This ensures reversal of the direction of rotation of the motor. The output voltages of this bistable multivibrator are applied via diodes D and D-, to the trigger circuit and determine during which half-cycle of the supply voltage V- this trigger circuit applies a square-wave voltage to the control device (base of the transistor Tr The input of the astable multivibrator A is also connected to the transistor Tr so that during the stationary period of the motor the series rectifier 3 is not triggered, and to the transistor Tr so that during this stationary period the application or non-application of a positive voltage to the terminal Q (base of the transistor Tr permits a choice to be made between maximum and minimum dissipation.

What is claimed is:

l. A control circuit for a self-commutating electric motor comprising, a pair of input terminals adapted for connection to a source of supply voltage, an electric heating element, a first rectifier, means connecting the heating element, the motor and the first rectifier in a series circuit across said input terminals, a bidirectional controlled rectifier connected across the series combination of the motor and the first rectifier and in series with the heating element across the input terminals,

and first means for selectively applying a first control signal to the control electrode of said bidirectional rectifier to control the conduction period thereof in a manner to regulate the motor current and thereby control the motor speed.

2. A control circuit as claimed in claim 1 wherein the first rectifier comprises a bidirectional controlled rectifier having a control electrode connected to a control device for selectively supplying control signals to said control electrode to control the conduction of said first rectifier.

3. A control circuit as claimed in claim 1, characterized in that the first rectifier comprises a diode.

4. A control circuit as claimed in claim 3 further comprising, a second diode connected to the motor with opposite polarity to that of the first diode, and a switching element having first and second positions for selectively connecting said first and second diodes, respectively, in series with the motor and the heating element across said input terminals.

5. A control circuit as claimed in claim 1 wherein said supply voltage is an AC voltage and said first rectifier comprises a controlled rectifier having a control electrode for initiating conduction therein, second means for applying a second control signal to the control electrode of said first rectifier at the time the supply voltage across the first rectifier is approximately zero voltage, said first control signal applying means being arranged to supply said first control signal to the control electrode of the bidirectional rectifier during the half cycle of the supply voltage following said second control signal and at an instant of time which determines the motor speed.

6. A control circuit as claimed in claim wherein said first control signal applying means includes means for selectively applying a third control signal to the control electrode of the bidirectional rectifier at the start of the next half cycle of the supply voltage.

7. A control circuit as claimed in claim 5 wherein said first controlled rectifier comprises a second bidirectional rectifier and said second control signal applying means is arranged to selectively apply said second control signal at the positive or negative going zero voltage crossover of the supply voltage thereby to control the direction of rotation of the motor.

8. A control circuit as claimed in claim 7 wherein said first control signal applying means includes means for selectively applying a third control signal to the control electrode of the first bidirectional rectifier during alternate half cycles of the AC supply voltage that follow the half cycles during which the first control signal is applied to the control electrode of the first bidirectional rectifier.

9. A control circuit as claimed in claim 1 wherein said supply voltage is an AC voltage and said first rectifier comprises a controlled rectifier having a control electrode for initiating conduction therein, and second means for applying a second control signal to the control electrode of said first rectifier whereby the motor speed is controlled jointly by said first controlled rectifier and said bidirectional rectifier.

10. A control circuit as claimed in claim 9 wherein said first controlled rectifier comprises a bidirectional rectifier.

Claims

1. A control circuit for a self-commutating electric motor comprising, a pair of input terminals adapted for connection to a source of supply voltage, an electric heating element, a first rectifier, means connecting the heating element, the motor and the first rectifier in a series circuit across said input terminals, a bidirectional controlled rectifier connected across the series combination of the motor and the first rectifier and in series with the heating element across the input terminals, and first means for selectively applying a first control signal to the control electrode of said bidirectional rectifier to control the conduction period thereof in a manner to regulate the motor current and thereby control the motor speed.

6. A control circuit as claimed in claim 5 wherein said first control signal applying means includes means for selectively applying a third control signal to the control electrode of the bidirectional rectifier at the start of the next half cycle of the supply voltage.