GB2183809A

GB2183809A - Heating control in a washing machine

Info

Publication number: GB2183809A
Application number: GB08627101A
Authority: GB
Inventors: Georg Kirmes
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-12-06
Filing date: 1986-11-13
Publication date: 1987-06-10
Also published as: IT8622587A0; FR2592406B3; IT1214573B; IT8623944V0; GB8627101D0; DE3543213A1; GB2183809B; FR2592406A1; DE3543213C2

Abstract

An automatic drum washing machine, equipped for washing and drying operation, comprises a motor safety device (11, 12) to switch off a drive motor (M) of the washing machine drum in the event of a fault affecting the motor. In order to protect the drum against overheating if the motor is switched off during a spin-drying operation, i.e. to avoid the drum being stationary in a heat flow, an electrical switching element (27) controls a protective switch (28) arranged in the current circuit of the drying heater is provided. An actuating signal for the switching element (27) is provided in dependence on a changed or changing operational magnitude of the drive motor (M) which results when the motor safety device (11) has responded or is responding. The signal is a change in the voltages at point 13 in the motor winding, the speed of rotation of the motor shaft or the magnetic field of the motor. <IMAGE>

Description

SPECIFICATION Heating control in a washing machine The present invention relates to a washing machine and has particular reference to protection against local overheating of the drum of an automatic washing machine by a heating element during a drying process and when, for example, the drum drive has been stopped because of motor overload or damage.

Drum washing machines usually have a motor protection device (cf. DE-PS 963 171) which is coupled with the drum drive motor and a protector switch of which is arranged in a series current circuit with the motor windings. This protection device protects the motor against thermal and/or electrical overloads.

In drum washing machines equipped for washing and drying, the heater serving for drying can be so arranged, for example a radiant heater as described in DE-OS 20 45 500 or an air heater blowing an air current onto the laundry, that when it is switched on it can lead to local overheating of the washing drum and/or its contents in the case of response of the motor protection device and consequent cessation of the drum rotation. In that case, the constituent material of the drum as well as the laundry can be damaged.

It would thus be desirable to arrange for such a drying heater to be switched off in the case of a motor standstill in consequence of response of a motor protection device.

According to the present invention there is provided a washing machine comprising a rotatable washing drum, an electric motor to drive the drum, a safety device responsive to a predetermined motor operating state to stop the motor, an electric heating element to provide heat in a drying phase of the machine, and switching means actuable to interrupt current supply to the heating element in response to change in an operational magnitude of the motor on or after response of the safety device.

In a preferred embodiment the switching means comprises a protective switch arranged in a current circuit of the heating element, an electrical protective switching signal for the switching means being initiated in dependence on a changed or changing operational magnitude of the drive motor when the motor safety device has responded or is responding.

Thus, when the drive motor is stopped notwithstanding a continuing requirement for drive of the drum, overheating damage to the drum or its content can be prevented. Little additional effort for this safety measure is necessary, since nothing need be changed in the customary functional components. In the case of an electromechanical program control device, it is merely necessary to insert a switch element, the inputs and outputs of which are connected into the circuit through simple modification of the outer line conduction present.

With suitable design of the motor safety device, even a short-circuit in the motor capacitor operates in the same desired manner.

The switching means can be a relay and the operational magnitude can be the voltage at the motor winding or windings for the drum drive at washing rotational speed. Alternatively, the switching means can be a relay and the operational magnitude can be the current through at least one of the motor windings not needed for the rotation of the drum at washing rotational speed. A construction according to either one of these alternatives is of advantage particularly in the case of an electromechanical program control device, because the switch contacts of a relay can be connected into such a circuit through simple modification of the line conduction present. In most cases it is merely necessary to release plug connections and to produce them again in a different order. This allows an existing automatic washing machine to be equipped with such a safety equipment.

For this purpose, the relay can be arranged in the parallel current circuit between an outer terminal of the windings of the drive motor which are switched on for spin-drying and an outer terminal of the motor safety device when the protective switch of the relay has a rest contact. This rest contact can then be inserted into the line conduction between the heating element and a program control device contact controlling this. In this circuit, the protective switching signal is the collapsing voltage at the motor windings for the drum drive at washing rotational speed. As long as this voltage is conducted by way of the safety device to the windings, the relay connected in parallel with the device has no voltage and the rest contact holds the heating element current circuit closed.Only when the safety device has responded and opened a switch thereof does the full voltage lie by way of the motor windings at the relay, which then opens its protective switch in the heating element circuit. This arrangement has the advantage that the relay is in operation only in the event of a fault.

In special circuits for electromechanical program control devices, the operating voltage for the drive motor may be supplied by way of a separate line during the drying process.

In this case, the relay can be connected in a series circuit between an outer terminal of the windings switched on for spin-drying and a program control device contact feeding the operating voltage during the drying operation, the switching of the switching means then having an operating contact. In such an arrangement, the relay is switched on constantly during normal drying operation and its operating contact closes the current circuit for the heating element. The current flowing through the relay also flows through the motor wind ings for spin-drying, to which no operating voltage is fed directly during the drying operation.Since all motor windings conduct the operating current away centrally by way of the motor safety device, when a switch of this device is opened then the current circuit for the relay is interrupted, which by its operating contact then interrupts the current circuit for the heating element.

If the relay in such a circuit has an operating contact which in operative setting connects the line conducting voltage during the drying operation with the outer terminal of a motor winding provided for the drive of the drum at washing rotational speed, a special program control device contact for the feed of operating voltage to the washing rotational speed motor winding during the drying process is redundant. At the same time, this prevents the relay from being supplied with operating voltage in program steps other than that of the drying process. It can thus be ensured that the current circuit for the heating element is closed by way of the operating.contact of the relay only during the drying operation.

In another arrangement, having the same advantages as the one mentioned above, the relay has an operating contact which in operative setting connects the line conducting voltage during the drying operation with a centre contact, which conducts voltage during the washing operation, of a reversing switch for the motor windings provided for washing operation. This gives the additional advantage that the drive motor can also be operated with reversing drive during the drying operation.

In cases where the monitoring of the voltage across the windings or of the current flow through the windings is not as simple as described above and where other types of motor, for example universal motors regulated in rotational speed, are used, the operational magnitude can be the rotational speed of the motor shaft and the switching means can comprise a tachogenerator which is coupled with the motor shaft and is effectively connected with the motor during the drying operation. Such tachogenerators are usual for motors regulated in rotational speed and provide a signal which is dependent on the rotational speed and which, together with a signal "drying operation running", offers a statement for the switching means about whether the drive motor is at standstill contrary to the requirements of the machine program.From this, the switching means can recognise the protective switching signal and by means of its switch interrupt the current circuit of the heating element.

Alternatively, the operational magnitude can be the magnetic flux within an iron core of the motor or in its environment and the switching means can comprise a Hall generator which is arranged in the magnetic flux and is effectively connected with the motor during the drying operation. This arrangement may also be used for kinds of drive motors in which the previously described arrangements cannot be readily used. Both of the last-mentioned alternatives are particularly suitable for cases in which electronic signal processing equipment is used in a washing machine, because the mains voltage is for this purpose converted into a low direct voltage for the operation of the electronic equipment.

Embodiments of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a schematic side view of a drum washing machine equipped for drying operation; Fig. 2 is a circuit diagram of a motor drive and associated safety equipment in a first washing machine embodying the invention; and Fig. 3 is a circuit diagram of a motor drive and associated safety equipment in a second washing machine embodying the invention.

Referring now to the drawings, there is shown in Fig. 1 a washing machine comprising a housing 1 with a liquor container 2 and a washing drum 3 mounted horizontally therein. This washing machine is equipped for drying in that, apart from a washing liquor heater (not shown), it includes a drying heater 4 which transmits its heat energy through radiation to the wall of the drum 3. The heat absorbed by the wall of the drum is transferred to laundry therein, the moisture of which thereby evaporates and precipitates externally of the drum at a cooling water film trickling down from a cooling water feed 5.

The cooling water and the condensate are conveyed out of the container 2 by a pump 6.

In departure from the illustrated embodiment, the washing machine can have a different arrangement of the drying heater or can be equipped with an air throughput drying system, the air heater of which is arranged externally of the container 2.

The motor circuits illustrated in Figs. 2 and 3 concern a two-phase induction motor, the rotational direction of which is determined by the arrangement of the field windings, switched on directly and displaced in phase, in the stator. The drive motor M is represented by all the parts framed by the dashed line.

These parts are windings 7 and 8 for spinning operation, windings 9 and 10 for operation of the drum at washing rotational speed and a motor protection device 11 with a protector switch 12. The windings 7 to 10 are connected at ends thereof to terminals 13 to 15 and the winding 10 also has a tap, which is connected to a terminal 16, for a phase-displaced field in spinning operation. Other ends of the windings 7, 9 and 10 are connected to a common coupling point 17, which is con nected by way of the motor protection device 11 and its switch 12 to a terminal 18, and the other end of the winding 8 is connected between the device 11 and the switch 12.

A series of program switches 21 and 22 and a reversing switch 23 are provided for the control of the drive motor M by way of the line 19 for the operating voltage during washing and drying and by way of the line 20 for the operating voltage during spinning. The centre contacts of the program switches 21 and 22 are connected together by way of a phase-shifting capacitor 24. The wiring of the lines and switches are evident from the drawings. The two program switches 21 and 22 are switched to the lefthand position for washing and for drying. The reversing switch 23 is driven alternately into the lefthand and the righthand position.As a result, the operating voltage of the line 19 is fed in alternation by way of the terminal 15 directly to the outer end of the winding 10 and by way of the program switch 21, the phase-shifting capacitor 24, the program switch 22 and the terminal 14 to the outer end of the winding 9.

The windings 9 and 10, which are thereby fed displaced in phase one relative to the other, impart a turning moment to the rotor of the drive motor in one rotational direction, for example anticlockwise rotation. When the reversing switch 23 is in its righthand position, the operating voltage of the line 19 is fed directly by way of the terminal 14 to the outer end of the winding 9 and by way of the program switch 22, the phase-shifting capacitor 24, the program switch 21 and the terminal 15 to the outer end of the winding 10. As a result, an opposite turning moment is imparted to the rotor so that the motor in this setting of the reversing switch rotates in, for example, the clockwise direction.

The drying heater 4 is arranged in a further circuit line 25 and is switched by a program contact 26 which is closed during drying operation.

In the embodiment illustrated in Fig. 2, a relay 27, the protective switch 28 of which contains a rest contact and is arranged in the current circuit of the heater 4, is connected to the terminal 13 which leads to the outer ends of the windings 7 and 8. Since the line 20 to the terminal 13 conducts voltage only during the spinning operation, the relay 27 according to operation remains free of voltage during washing and during drying, the voltage drop across the device 11 being too small to excite the relay 27. During the spinning operation, the line 20 conducts voltage and therefore excites the relay 27, so that its protective switch 28 opens the current circuit for the drying heater 4. This is not only harmless, but even confers advantages.

No voltage sufficient for excitation can be fed to the relay 27 during washing or during drying. If, however, the motor protection device 11 responds for any reason, for example excessive heat or current loading of the windings 9 and 10, in either of these modes of operation and opens the switch 12, then the full operating voltage is present by way of one of the windings 9 and 10 at the coupling point 17. Since the impedances of the windings 7 and 8 are very small compared with that of the relay 27, almost the full voltage also lies at the terminal 13 in this case and excites the relay 27, which now actuates its switch 28 and thus interrupts the current circuit for the heater 4. If this occurs in washing operation, then this interruption is harmless or useful.If the current circuit is interrupted in drying operation, then this is the desired effect, because the washing drum 3 is at standstill in front of the heater 4 (Fig. 1) due to the current supply circuit for the drive motor M having been interrupted by the device 11.

Since, however, the heater 4 is now switched off by the switch 28, the drum 3 is not subjected to local overheating. The drum and the laundry therein are thereby protected against damage.

In the embodiment of Fig. 3, a program switch 29, which is closed exclusively in washing operation, is shown in the line 19 to facilitate understanding. Connected to the terminal 13 of the motor M is the one line of the relay 30, which serves as a switching element and the other line of which is connected to the line 25 which is at operating voltage by way of the program contact 26 only during the drying operation. The relay 30 actuates the switch 31, which contains an operating contact and is arranged in the circuit for the heater 4. In this embodiment, the relay 30 is so arranged that it is always excited in drying operation, thus in the case of operating voltage on the line 25, by way of the windings 7 and 8 and the motor protection device 11 and its switch 12.It is thereby ensured that operation of the heater 4 is possible only when the relay 30 is excited and the switch 31 is conductive. The relay 30 remains unexcited in the operating modes "washing" and "spinning", so that the heater 4 cannot be switched on.

In order that the motor M can be operated in the operating mode "drying", the line 25 is furthermore connected to a line 32, which is led either by way of the transversely dashed branch line 33 to the terminal 14 when the motor is to rotate in only one direction during the drying operation or by way of the line 34, drawn in chain-dotted lines, to the centre contact of the reversing switch 23 when the motor is to be driven alternately for clockwise and anticlockwise rotation in drying operation.

A switch 35, containing an operating contact, of the relay 30 is inserted in the line 32 in order to prevent the relay 30 from receiving operating voltage and being excited in the operating modes "washing (clockwise rotation)" and "spinning". This voltage would otherwise pass by way of the switch 31 to the heater 4 and operate the heater at the wrong time.

In departure from the described embodiments, it is possible to use other kinds of switching elements which can recognise drive motor standstill contrary to required operation.

Such switching elements can process, instead of a static protective switching signal, a dynamic signal such as the transition from orderly to faulty operation of the motor.

Claims

1. A washing machine comprising a rotatable washing drum, an electric motor to drive the drum, a safety device responsive to a predetermined motor operating state to stop the motor, an electric heating element to provide heat in a drying phase of the machine, and switching means actuable to interrupt current supply to the heating element in response to change in an operational magnitude of the motor on or after response of the safety device.

2. A washing machine as claimed in claim 1, the switching means comprising a switch controlled by a relay and the magnitude being the voltage at a motor winding energised for drive of the drum in a washing phase of the machine.

3. A washing machine as claimed in claim 1, the switching means comprising a switch controlled by a relay and the magnitude being the voltage at a motor winding normally deenergised during drive of the drum in a washing phase of the machine.

4. A washing machine as claimed in claim 2, wherein the switch comprises a rest contact and the relay is arranged in a circuit branch parallel to a circuit branch containing a switch element of the safety device and a motor winding energised for drive of the drum in a spindrying phase of the machine.

5. A washing machine as claimed in claim 3, wherein the switch comprises a work contact and the relay is connected in series between a motor winding energised for drive of the drum in a spin-drying phase of the machine and voltage supply control means controlling the supply of voltage to that motor winding.

6. A washing machine as claimed in claim 5, the switching means comprising a further switch with a work contact arranged to connect an output terminal of the control means with a motor winding energised for drive of the drum in a washing phase of the machine.

7. A washing machine as claimed in claim 5, the switching means comprising a further switch with a work contact arranged to connect an output terminal of the control means with an input terminal of a reversing switch element controlling the supply of voltage alternately to said motor winding energised for drive of the drum in the washing phase and with a further such motor winding.

8. A washing machine as claimed in claim 1, the magnitude being the rotational speed of a drive shaft of the motor and the switching means comprising a tachogenerator coupled to the shaft and operatively connected to the motor during a drying phase of the machine.

9. A washing machine as claimed in claim 1, the magnitude being the magnetic flux within or in the region of an iron core of the motor and the switching means comprising a Hall generator arranged in the flux and operatively connected to the motor during a drying phase of the machine.

10. A washing machine substantially as hereinbefore described with reference to Figs.

1 and 2 of the accompanying drawings.

11. A washing machine substantially as hereinbefore described with reference to Fig. 3 of the accompanying drawings.