GB2056200A - Device for accelerated heating of the washing liquid in a laundry washing machine with a rotary drum - Google Patents

Abstract

A washing machine has a single heating element (6) connected in series with the rectifier bridge (2, 3, 4, 5) for the supply voltage of the motor (1) which drives the drum. During each half cycle of the mains voltage, the heating element (6) is first connected in series with the rectifier bridge (2, 3, 4, 5) and subsequently connected by a triac (9) directly to the mains. Since the motor (1) is thus driven at a low speed with a substantial torque at the beginning of each half period, a current will flow in the heating element (6) which is substantially equal to that obtained when it is connected directly to the mains. The invention is used for obtaining simultaneous "stirring" and "heating" functions of the washing machine. <IMAGE>

Description

SPECIFICATION Device for accelerated heating of the washing liquid in a laundry washing machine with a rotary drum The present invention relates to a device for accelerated heating of the washing liquid in a laundry washing machine with a rotary drum, equipped with a single heating element and a rectifier bridge for the supply voltage of the motor which drives the drum, said bridge comprising at least two controlled rectifiers.

At present there are washing machines whose drum is driven by a d.c. motor whose speed of rotation is controlled by means of a power supply unit comprising a mixed bridge constituted by two diodes and two thyristors and an electronic circuit which responds to the e.m.f. of the motor (when said motor functions as dynamo) in order to control the induction current by modulating the conduction time during each quarterwave of the mains voltage. An immersion heater connected in series with the rectifier bridge limits the induction current of the motor when this motor is subject to a heavy load and serves to heat or to maintain the temperature of the washing liquid as said motqr rotates.

If heating at the maximum power of the immersion heater is required, the power supply bridge of the motor is short-circuited, so that, of course, the motor stops.

However, it is common knowledge that for a correct laundry washing process the washing liquid should be stirred while its temperature is being raised.

Current machines have two washing rhythms, a "normal" rhythm, for example 12 seconds on and 4 seconds off and a "slow" rhythm, which is the reverse of the first rhythm, i.e. 4 seconds on and 12 seconds off.

Under these conditions sitrring with the normal rhythm prohibits a sufficiently quick rise in temperature of the washing liquid, because the average current which flows in the immersion heater as the motor rotates is approximately half the maximum current during the stop periods in which the heating element is connected directly to the mains.

In order to avoid an excessively long heating time the slow rhythm is selected, but in certain cases this compromise may affect the quality of the washing process, whilst furthermore the heating time may become excessively long, for example in winter when the temperature of the water supplied to the machine is particularly low.

An easy solution is to employ a second immersion heater which is continuously energized by the mains, but this means that the advantages of simplicity, efficiency and reliability of the solution with one immersion heater are sacrificed.

One of the objects of the invention is to realize a washing machine with a single heating element whose power output during rotation of the motor very closely approximates the maximum power in the case of direct connection to the mains.

Another object of the invention is to realize a device for the accelerated heating, which operates fully electronically without any electromechanical component.

The invention is based on the recognition that the current consumed by the motor at a very low speed of rotation and at heavy loads very closely approximates that which flows in the immersion heater when this heater is connected directly to the mains.

According to the invention, the device for accelerated heating of the washing liquid in a laundry washing machine with rotary drum, equipped with a single heating element and a rectifier bridge for the supply voltage of the motor which drives the drum, said bridge comprising at least two controlled rectifiers, is characterized in that it comprises electronic switching means, which connect the heating element in series with the rectifier bridge during a first time interval which starts at the beginning of each quarter period of the mains voltage and subsequently connect said heating element directly to the mains during a second time interval which terminates at the end of said quarter period.

Suitably, the electronic switching means include the controlled rectifiers of the rectifier bridge.

During a fraction of each quarter period the drive motor of the drum is energized with a substantial resisting torque and as a result of this produces a current in the immersion heater which is substantially equal to that which flows during the rest of the time interval in which said immersion heater is connected directly to the mains.

Thus, it is possible to employ any washing rhythm demanded by the sort of laundry to be washed, whilst maintaining a substantially constant heating period.

Furthermore, power fluctuations during the heating cycle are substantially non-existent, so that pollution of the electric power mains is avoided.

Finally, the fully static operation of the device in accordance with the invention ensures a perfectly silent operation and its lower control power enables the device to be employed both in machines with electro-mechanical and hybrid program control and in machines controlled by a microprocessor.

The invention will now be described in more detail with reference to the accompanying drawings.

Figure 1 represents the circuit diagram of the device in accordance with the invention.

Figures 2, 3 and 4 represent diagrams of the currents in various points of the circuit diagram of Figure 1.

Figure 5 is a diagram showing the essential elements of the device in accordance with the invention.

Figures 6 and 7 are diagrams of the mains current in the device of Figure 5 during the "washing" and "heating/stirring" functions respectively.

Figure 8 is the simplified block diagram of a laundry washing machine incorporating the device in accordance with the invention.

Figure 9 is the circuit diagram of an embodiment of the device in accordance with the invention.

In Figure 1 a permanent-magnet induction motor is included between the commoned anodes of the two diodes 2 and 3 and the commoned cathodes of two thyristors 4 and 5.

The commoned cathode and anode of the diode 2 and of the thyristor 4 are connected to a mains terminal 7 via an immersion heater 6, the other mains terminal 8 being connected to the commoned cathode and anode of the diode 3 and of the thyristor 5.

The rectifier bridge, constituted by the diode 2, 3 and the thyristor 4, 5, is shunted by a triac 9.

The two contacts of an electronic switch 10 are respectively connected to the commoned gates of the thyristors 4 and 5 and to the gate of the triac 9, whilst the common contact of said switch 10 is connected to a source of 25 kHz trigger pulses.

The electronic switch 10 comprises an input which is controlled with twice the mains frequency (100 Hz).

Referring to Figures 2 and 3, the device of Figure 1 operates as follows: that the instant to of the quarter period the switch 10 is changed over to the right and the gates of the thyristors 4 and 5 receive trigger pulses; the current in the rectifier bridge (IP), Figure 2, increases till the instant t1 at which the switch 10 is changed over to the left; at this instant the triac 9 is fired, as a result of which the input of the bridge is short-circuited and the thyristors 4 and 5 are turned off, the current IP (Fig. 2) decreases to zero, whilst the current in the triac (IT, Fig. 3) which was zero till tr, flows till the instant t2 at which the switch 10 is again switched to the right, and the motor is again energized till the instant t3 at which the preceding process is repeated.

The motor is energized between to and t1 and is driven by inertia between t1 and t2, for it is completely disconnected from its power supply source because the thyristors 4 and 5 are turned off during said time interval.

From to to tithe current which flows in the heating element 6 is equal to the current IP (Fig.

2), whilst between the instants t, and t2 it is equal to the current IT (Fig. 3); assuming that the internal resistance of the motor 1 is negligible relative to that of the immersion heater 6, it follows that the current in said heater (IR, Fig. 4) is the sum of the currents IP and IT (Figs. 2 and 3) and that the immersion heater 6 receives its full power supply when the motor 1 is being driven.

It is evident that in practice there will be a loss of heating power in comparison with a power supply of the immersion heater directly from the mains; however, this loss remains very limited, of the order of 5%, which is substantially negligible with respect to the power variations which may be caused by mains voltage fluctuations within the normally permissible limits.

In Figure 5, in which the same references are used as in Figure 1, the first input of a comparator circuit 11 is coupled to the terminals of the motor 1 via an integration circuit which is constituted by a resistor 12 and a capacitor 13, whilst the second input is connected to a sawtooth generator 14 which is triggered by means of two zero-passage detection diodes connected in parallel with the power supply bridge of the motor 1.

The output of the comparator circuit 1 1 is connected to a complementary input of an ANDgate 17, whose second input is coupled to a 25 kHz trigger pulse generator 18, the output of said gate being connected to the commoned gate electrodes of the thyristors 4 and 5.

The output of the comparator 1 1 is also connected to an input of another AND-gate 1 9, whose second input is connected to an input terminal 21, on which a logic "1" is available, via a switch 20 for switching on the heating.

The output of the gate 1 9 is connected to a first input of a further AND-gate 22, whose second input is coupled to the generator 18, whilst the output is connected to the gate of the triac 9.

When the switch 20 for turning on the "heating" function is open, only the part of the circuit situated to the right of the dashed vertical line in the diagram is operative and constitutes a circuit for controlling the speed of the motor 1; the e.m.f. developed across the motor 1 when the bridge is not conductive is integrated and subsequently compared by the circuit 1 1 with a ramp of a sawtooth voltage produced by the generator 14, which is triggered by the diodes 15 and 16 upon each zero passage of the mains sinewave.

The comparator 11 produces a logic "0" level at its output when the e.m.f. is smaller than the voltage ramp, as a result of which the 25 kHz trigger pulses from the generator 1 8 are transferred by the gate 1 7 by means of its complementary input.

If the speed of the motor 1 tends to increase, the e.m.f. also increases, which delays the instant at which the comparator 11 is changed over and thus reduces the time during which the motor is energized, and vice versa.

Figure 6 represents the power supply current of the rectifier bridge during a controlled rotation mode corresponding for example to the "rinsing" or "washing" functions at a stabilized temperature of the washing liquid; the phase difference with the mains voltage is represented by dashed lines.

When the heating switch 20 is closed, the part which is situated to the left of the dashed line in the diagram is also rendered operative.

During starting, when the output of the comparator 11 is "0", the motor 1 is started as soon as the thyristors 4 and 5 can be turned on after the zero passage of the mains sinewave.

Since the motor is started at the zero passage of the mains voltage, the zero passage detection diodes 15 and 16 are inhibited and the generator 14 is not started; as a result of this, the negative input of the comparator 11 is fixed at a voltage level of +.07V which is determined by a diode (not shown) and comparison is then effected with the voltage ramp obtained by integration of the motor supply voltage on the positive input of the comparator.

At the instant at which said voltage ramp becomes 0.7 V, the output of the comparator 11 changes to "1", so that via the gate 22 the trigger pulses from the generator 18 are transferred to the gate of the triac 9; at this instant the voltage across the rectifier bridge drops to zero, so that the thyristors 4 and 5 are immediately turned off.

Consecutively, the voltage on the positive terminal of the comparator decreases again below 0.7 V, so that the comparator output is reset to "0", but the triac 9 remains operative until the instant at which the mains sinewave again passes through zero and the process is repeated.

In this mode of operation during the "heating" function, the operation of the part of the circuit situated to the right of the dashed line differs from that during the "washing" function in the following two respects: as the generator 14 is inhibited, the negative input of the comparator 11 is at a fixed, comparatively low, voltage level and comparison is effected with the integrated supply voltage at the motor 1; the low speed of rotation of the motor namely renders the e.m.f. developed during free rotation negligible.

Figure 7 represents the current which flows through the immersion heater 6 during the mode of operation just described. It is to be noted that upon each zero passage of the mains sinewave the supply current of the motor is slightly shifted in phase and that for the rest of the time the current which flows through the immersion heater 6 and the triac 9 is in phase.

Control of the speed of rotation during the "heating function" is not as good as that obtained during the "washing" function, but is amply sufficient for the stirring operation when the washing liquid is being heated.

In Figure 8, in which the reference numerals correspond to those in Figures 1 and 5, the washing machine comprises a power supply and control unit 23, which is connected to the motor 1 via a reversing switch 24.

A programming device 25 comprises inputs which are connected to a temperature detector 26 and to water level detectors 27a and 27b, an output which is connected to the device 28 for accelerated heating in accordance with the invention, "rhythm" and "speed" outputs connected to a power supply unit 23, control outputs for the electric valves 29a and 29b, a control output for the reversing switch 24, and a control output for a switch 30 which is connected in series with a motor 31 which drives the draining pump.

In the block diagram of Figure 8, which only shows the essential parts, the programmer 25 receives commands relating to the desired washing programmes and accordingly actuates the various functional elements of the machine in conformity with the information supplied by the detectors.

The device 28 in accordance with the invention receives the command for switching on the heating from the programmer 25, heating being discontinued when the detector 26 has detected that the programmed temperature of the washing liquid is reached.

Furthermore, the device 28 is coupled to the power supply and control unit 23, so as to receive signals necessary for its operation.

The programmer 25 may be of the customary manually operated electromechnical type or the automatically operated hybrid type or of the fully electronic type controlled by a microprocessor, the device for accelerated heating in accordance with the invention being readily adaptable to these different types of washing machine.

In Figure 9, in which the reference numerals corresponds to those used in Figures 1, 5 and 8, the commoned anodes of the diodes 2 and 3, constituting the negative pole of the rectified pulsating supply voltage for the motor 1, are connected to the common earth 32.

The switch 24 for reversing the direction of rotation of the motor 1 is controlled by means of the coil 33 or a relay which is energized by a reversing circuit (not shown).

The gates of the thrysitors, which are interconnected by two current limiting resistors 34 and 35, are connected to one end of the secondary of a transformer 37, whose other end is connected to the positive terminal of the rectifier bridge.

Between the junction of the resistors 34 and 35 and the positive terminal of the rectifier bridge an overvoltage-limiting diode 38 is included.

Via a resistor 39 the gate of the triac 9 is connected to one end of the secondary 40 of a transformer 41, the other end of said secondary being connected to the mains terminal 8.

Two interconnected ends of the primaries 42 and 43 of the transformers 37 and 41 are connected to the positive terminal 44 of a direct voltage source Vb, whose negative terminal 45 is connected to the earth terminal 32.

The two other ends of the primaries 42 and 43 are respectively connected to the collectors of two NPN transistors 46 and 47, whose emitters are connected to the earth terminal 32.

Between the commoned cathodes of the zeropassage detection diodes 15 and 16 and the earth terminal 32 a divider bridge constituted by two resistors 48 and 49 is included, the junction of said resistors being connected to the cathode of a threshold diode 52 via two cascaded NOR gates 50 and 51, the anode of said last-mentioned diode being connected to the negative input of the comparator 11; a relaxation network, comprisng a resistor 53 and a capacitor 54, which is connected to the earth terminal 32, is included between the negative input of the comparator 11 and the +Vb terminal 44.

The positive input of the comparator 22 is connected to the integration network 1 2, 13 via two resistors 55 and 56, the resistor 55 being decoupled by a capacitor 57. The junction of the resistors 55 and 56 is connected to a switchable voltage source (V.ESS), not shown, for the "spindry" function of the machine.

The positive input of the comparator 11 is provided with a temperature correction network constituted by a diode 58 in series with a resistor 59 which is connected to the earth terminal 32, the network being decoupled by means of a capacitor 60.

The output of the comparator 11 is connected to +Vb via a resistor 61 and to the first inputs of two NOR-gates 62 and 63, whose commoned second inputs are connected to the common contact of a switch 64, whose two other contacts are respectively connected to a normal-rhythm (CN) or a slow rhythm (CL) circuit, not shown.

The output of the gate 62 is connected to the first input of another NOR gate 65, whose second input is connected to +Byia a resistor 66 and to the heating switch 20, which is connected to the earth terminal 32.

The junction of the resistor 66 and the switch 20 is connected to another NOR gate 67, arranged as an inverter, whose output is coupled to the base of an NPN transistor 69 via a resistor 68, the emitter of said transistor being connected to earth and the collector being connected to the junction of the resistors 55 and 56 via a resistor 70; furthermore, a variable resistor 71 for adjusting the speed of rotation is included between said junction and the earth terminal 32.

Via another NOR gate 72, connected as an inverter, the output of the gate 65 is connected to the first input of another NOR gate 73, whose output is coupled to the base of the transistor 47 via a resistor 74, the base of said transistor being decoupled from earth by a capacitor 75.

Via a further NOR gate 76, connected as an inverter, the output of the gate 63 is connected to the first input of another NOR gate 77, whose output is connected to the base of the transistor 46 via a resistor 78.

The commoned second inputs of the gates 73 and 77 are connected to the triggerpulse generator 18, said generator comprising two NOR gates 79 and 80, connected as inverters, whose inputs and outputs are coupled via a network constituted by two resistors 81 and 82 and a capacitor 83.

The operation of the logic circuits in the diagram of Figure 9 has been chosen so that a "O" is obtained by connection to earth and a "1" by means of a pull-up resistor; this is in order to render the circuit insensitivie to spurious signals, which are always of a positive polarity, because they have been rectified by the power supply bridge of the motor 1. For this reason only NOR gates with two inputs have been used, for whose change-over it is necessary that the two inputs are "0", the logic operation in any case being the same as that of the simplified circuit of Figure 5.

When the heating switch 20 is open, the capacitor 54, which has been charged slowly via the resistor 53, discharges abruptly via the diode, the gates 50 and 51, and the resistor 49 of small value, when the mains voltage passes through zero, so that on the negative input of the comparator 11, a sawtooth voltage is obtained, which is compared with the e.m.f. voltage which has been integrated by means of R12, C13.

As long as the e.m.f. voltage is smaller than the sawtooth voltage the output of the comparator 11 will be "0"; the gate 63 conducts, if a rhythm signal "b" is applied to its second input, and the gate 77 is turned on via the gate 76 in the case of negative pulses from the generator 18.

During these pulses, the transistor 46 is bottomed and the pulses are transferred to the gates of the thrysitors 4 and 5.

As soon as the selected speed is reached, the output of the comparator will become "1 " and control is effected by phase ingression (Fig. 6), as a function of the comparison between the mean e.m.f. and the excursion of the sawtooth during each quarter period of the mains voltage.

When the switch 20 is open the triac 9 cannot be triggered by the presence of a "1" level on one of the inputs of the gate 65, which results in a "O" level at the output of the gate 73.

If the heating switch 20 is closed the triac 9 will be controlled in accordance with the information received from the comparator 11 via the gate 62.

If the output of the comparator as well as the rhythm signal from the inverter 64 are "0", the output of the gate 72 will be "1" and the gate 73 cannot transfer the trigger pulses of the "0" state, obtained from the generator 18, to the base of transistor 47; conversely, the motor 1 is energized as soon as the thyristors 4 and 5 can be turned on after the zero passage of the mains sinewave.

When the output of the comparator 11 becomes "1 ", the output of the gate 62 becomes "0" and the gate 73 is turned on so as to allow the transistor 47 to be bottomed for the duration of the negative trigger pulses from the generator 18.

As is described with reference to the diagram of Figure 5, starting of the motor 1 at the beginning of the quarter period of the mains voltage and conduction of the triac 9 for the rest of said period will inhibit the operation of the sawtooth generator R53, C54, and the negative input of the comparator 11 is fixed at a potential of 0.7 V determined by the diode 52.

The closure of the heating switch 20, via the inverting gate 67, also causes transistor 69 to be bottomed, so that the resistor 70 is switched in, thus providing compensation for the loss of speed of the drum of the machine as a result of the fact that the energizing time of the motor during each quarter period is then shorter than during the "washing without heating" or "rinsing" functions.

In the case of the "heating/stirring" function the speed of rotation of the drum is fixed at approximately 30 revolutions per minute instead of the normal 50 revolutions, so that the current in the immersion heater can increase and the control system cannot operate in accordance with the phase control process illustrated in Figure 6.

It is to be noted that the gate 62 receives the command for controlling the triac 9 as a function of the phase complement from the comparator 11 when the motor 1 is running or the signal "1" obtained from the rhythm inverter 64 during the stop periods of said motor, so that the triac 9 remains conductive for the full wave during these periods.

By means of the diode 58 and the resistor 59 a constant comparison level can be maintained on the positive terminal of the comparator 11 despite temperature variations to which the washing machine is subject.

By decoupling the base of the transistor 47 inadvertent triggering of the triac 9 by a spurious signal is avoided; owing to its presence trigger pulses with the repetition frequency of 25 kHz are not transferred without distortion, but this is not important because the triac 9 is triggered after the beginning of a quarter period and remains conductive until the mains sinewave passes again through zero.

Claims (13)

1. A device for accelerated heating of the washing liquid in a washing machine with a rotary drum, equipped with a single heating element and a rectifier bridge for the supply voltage of the motor which drives the drum, said bridge comprising at least two controlled rectifiers, characterized in that it comprises electronic switching means which connect the heating element in series with the rectifier bridge during a first time interval which starts at the beginning of each quarter period of the mains voltage and subsequenty connect said heating element directly to the mains during a second time interval which terminates at the end of said quarter period.

2. A device for accelerated heating as claimed in Claim 1, characterized in that said electronic switching means include the controlled rectifiers of the rectifier bridge.

3. A device for accelerated heating as claimed in Claim 1 or 2, characterized in that the control electrodes of the controlled rectifiers are coupled to the output terminal of a comparator circuit via a first chain of logic gates.

4. A device for accelerated heating as claimed in Claim 3, characterized in that it comprises a two-way static controlled switch which is included between an input terminal of the rectifier bridge, which is connected to the heating element, and the other input terminal, which is connected to the mains, the control electrode of said switch being coupled to the output terminal of the comparator circuit via a second chain of logic circuits.

5. A device for accelerated heating as claimed in Claim 4, characterized in that a first input of the comparator circuit is connected to one of the power supply terminals of the motor via an integration circuit.

6. A device for accelerated heating as claimed in Claim 5, characterized in that a second input of the comparator circuit is connected to a relaxation circuit which is triggered by means of two cascaded logic gates, whose input is connected to two diodes which are connected "head-to-tail" to the input of the rectifier bridge.

7. A device for accelerated heating as claimed in Claim 6, characterized in that a diode is included between the second input of the comparator circuit and the output of one of the logic gates which start the relaxation circuit.

8. A device for accelerated heating as claimed in Claim 4 and any one of the Claims 1, 2, 5, 6 and 7, characterized in that the output terminal of a pulse generator is connected to two commoned inputs of two gates belonging to each of the two logic networks.

9. A device for accelerated heating as claimed in Claim 4 and any one of the Claims 1, 2, 5, 6, 7 and 8, characterized in that the coupling between the first logic network and the control electrodes of the controlled rectifiers and between the second logic network and the control electrode of the two-way switch is realized by means of a transformer whose primary is included in the collector circuit of a transistor.

10. A device for accelerated heating as claimed in Claim 4, and any one of the Claims 1 to 3 and 5 to 9, characterized in that a heating control switch is included between one of the inputs of one of the gates of the second logic network and a common earth terminal.

11. A device for accelerated heating as claimed in Claim 10 and any one of the Claims 1 to 4 and 6 to 9, characterized in that the heating switch is also coupled to the base of a transistor whose collector resistor is connected to the first input of the comparator circuit.

12. A device for accelerated heating as claimed in Claim 4 and any one of the Claims 1,2 and 5 to 11, characterized in that the number of gates constituting the first and the second logic network is respectively odd and even and in that said gate are all of the NOR-gate type.

13. A laundry washing machine, characterized in that it is equipped with the device for accelerated heating as claimed in Claims 1 to 12.

1 4. A device for accelerated heating of the washing liquid in a washing machine with a rotary drum, substantially as hereinbefore described with reference to any one of the accompanying drawings.