TUMBLER DRYERS

Abstract: A tumbler dryer incorporates a split phase induction motor with a conventional start winding for rotating the drum of the dryer. The motor (M) has a control circuit for periodically reversing the direction of rotation of the drum during a drying cycle. The circuit comprises switches (S2A, S2B) for reversing the sense of connection of the starting winding of the motor and means for example a further switch (S1) for de-energising the motor to allow it to come substantially to rest before restarting in a different direction of rotation. The switches are operated by cams of a timing mechanism used to time the duration of a drying cycle.

Description: "Tumbler Dryers" This invention relates to tumbler dryers and in particular to tumbler dryers having a dryer drum which during operation has periods of rotation in opposite directions so that the articles being dried do not tend to form into a roll or ball and the drying of the articles is more effective. Hitherto, in order to drive the drum of a tumbler dryer in opposite directions, it has been proposed to use capacitor-start and run induction motors in conjunction with a switch for reversing the supply to the start winding so that the motor can be started in either direction depending on the particular direction required by the motor control program at the time. Capacitor start and run motors are relatively expensive as compared with split-phase motors which are reversible motors capable of being started and run in either clockwise or anti-clockwise directions of rotation. However, it has been assumed that split phase motors cannot be run as reversing motors where reversals of direction of rotation are relatively frequent without reinforcing the start winding, i.e. by providing extra turns or by using heavier gauge wire, and if this is done, the cost of the motor increases and the benefit of low cost is lost. It is the object of. the present invention to enable a split phase induction motor to be used to drive the clothes drum of a tumbler dryer in opposite rotational directions in accordance with a required program. According to the present invention, there is provided a tumbler dryer including a rotatable drum which is driven in opposite rotational directions alternately for periods of time by a split phase induction motor having a main winding and a starting winding with a starting switch having contacts for connecting the starting winding in parallel with the main winding and disconnecting it when the motor approaches its running speed, and a timing mechanism for determining the said periods of time and including switching means for reversing the sense of connection of one of said windings relatively to the other, and means for de-energising the main winding between reversals of the direction of connection for a period of time sufficient for the motor to come substantially to rest The de-energising means may comprise an ON/OFF switch operable by the timing mechanism. In that case, the switching means may be operable to effect reversal of the sense of connection of the starting winding. Additionally, the timing mechanism may be such that the ON/OFF switch is operable to an "OFF" position while the motor is running, reversal of the sense of connection of the starting winding also occurring whilst the motor is running Alternatively, the switching means may be operable to reverse the sense of connection of the main winding and in this case the means comprises an arrangement for introducing a time delay between reversals of the direction of connection. In one embodiment of the invention, the timing mechanism includes a first switching means operable by the mechanism to permit energisation of the motor during the periods of time that the motor is required to run and to prevent energisation during intervals between those periods, the intervals being long enough to allow the motor to come substantially to rest, and second switching means operable by the mechanism to reverse the sense of connection of one of the windings relatively to the other in such manner that the motor is started in opposite directions alternately. In the embodiment just referred to, the timing mechanism may be operable to reverse the sense of connection of the starting winding and effects such reversal whilst the motor is running at full speed. In another embodiment, the first and second switching means comprises a multi-position switch having a first position in which the main winding is connected in one sense with the starting winding, a second position in which the main winding is connected in the reverse sense with the starting winding, and an intermediate position in which the main winding is disconnected form the starting winding and energisation of the main winding prevented. The timing mechanism may include cams for operating the first and second switching means. In order that the invention may be fully understood and readily carried into effect, embodiments thereof will now be described with reference to the accompanying drawings of which: Fig. 1 is a circuit diagram showing the connections of the induction motor to electricity supply terminals, Fig. 2 is a timing diagram to be used in explaining the operation of the circuit of Fig. 1, Fig. 3 is a circuit diagram showing an alterna tive method of connecting the induction motor to electricity supply terminals, and, Fig. 4 is a timing diagram to be used in explaining the operation of the circuit of Fig. 3. The tumbler dryer embodying the invention may take any one of a number of conventional designs and includes a drum into which articles to be dried are loaded at the commencement of a drying cycle and to which hot air is supplied. The drum is rotated during the drying cycle by a split phase reversing induction motor which also drives an impeller that supplies air via an air heater to the drum. The duration of a drying cycle may be controlled by a timer forming part of the timing mechanism and preset by a user before the commencement of a cycle to the required cycle time. Alternatively, some other form of control responsive to a condition of the article to be dried or to some other variable representative of that condition may be used. Referring now to Fig. 1, the split phase induction motor M has a main winding MW and a conventional, i.e. non-reinforced, starting winding SW. One end terminal of the winding ti is connected to one terminal of a timing mechanism shown enclosed within the dotted area TM and which controls the duration of the time periods during which the motor M runs in one direction or the other. The one terminal is connected via an ON/OFF switch Sl of the mechanism TM to an A.C. electrical power supply input terminal L. The other end terminal of the winding MW is connected through the solenoid coil of a starting relay SR to the other A.C. electrical power supply input terminals N. The starting winding SW of the motor M is connected to the moving contacts of a further switch S2A and via the contacts of the starting relay SR to the moving contact of a further switch S2B which also form part of the timing mechanism TM. The moving contacts of the switches S2A and S2B are operated together and have associated fixed contacts L and R. The fixed contact L of switch S2A and the contact R of switch S2B are connected together and to the terminal of the mechanism TM to which the first-mentioned end terminal of the main winding MW is connected. The fixed contact R of the switch S2A and the fixed contact L of the switch S2B are also connected together and to the terminal N of the supply. Consideration of Fig. 1 will reveal that the switch S1 controls the application of the A. C. supply to the motor M, and the switches S2A and S2B together serve to reverse the sense of connection of the starting winding SW with respect to the main winding MW. The starting relay SR serves to disconnect the supply to the starting winding SW when the current through the main winding MW falls as the motor M approaches its normal running speed. The timing mechanism TM includes two further switches S3 and S4 connected as shown to control, respectively, the energisation of the heater H which heats air supplied to the drum of the dryer and a motor P driving the timing mechanism. Motor P drives shafts carrying cams (not shown) that actuate the various switches. The movable contacts of switches Sl and S2A and B are operated by a fast rotating cam to give the changes of direction of rotation of the motor M at the requisite time intervals. Switches S3 and S4 are operated by a slowly rotating cam whose speed of rotation is related to the duration of a drying cycle. Switch S3 energises the heater H at the commencement of a drying cycle and de-energises it some 6-10 minutes before the end of the cycle to allow the contents of the drum to cool down before the drum stops rotating. Switch S4 controls the energisation of the timer motor of the timing mechanism which is switched on at the beginning of a drying cycle and switched off at the end of the cycle. Switch SI is also controlled by a slow cam but in a manner such that the slow cam over-rides the fast cam at the end of a drying cycle to ensure that the motor M is de-energised at the end of the drying cycle. The over-ride can be arranged in any one of a number of different ways, for example the slow cam may be so contoured as to disengage the moving contact of switch Sl from the fast cam at the instant of over-ride. A slight difference in the instant of operation of switches SI and S4 is required to ensure that at the end of a cycle switch S1 is turned off by the slow cam before S4 is turned off. The times of closure of the switches Sl, S2A, S2B, S3 and 54 are shown in Fig. 2 as heavy sections of respective lines labelled with the references used for the switches in Fig. 1. The time axis is horizonal in Fig. 2. As can be seen in Fig. 2, the switches S2A and S2B are operated in unison the movable contacts of which change from being connected to the contacts L to being connected to contacts R at substantially equal intervals of time. The operation of the switch S1 relative to that of switches S2A and B is such that the switch S1 closes whilst the moving contacts of switches S2A and S2B are in contact with fixed contacts L so that the motor starts to rotate to the left, say. When the motor has been running for about one minute, the switches S2A and B change over and shortly afterwards the switch S1 opens allowing the motor M to slow down. After a time delay sufficient to allow the motor to come to rest, or almost so, the switch S1 closes again but this time the motor M is started in the opposite direction because the starting winding is now energised in the opposite sense. This cycle of switch operations and starting and stopping of the motor continues for the duration oz the drying cycle, that is to say until the articles in the drum are considered to be sufficiently dry. In Fig. 2, actuations of switch S1 are shown twice, the breaks in the lower line being those caused by the first cam. To initiate a drying cycle, a user sets the timer (not shown) to a desired cycle duration and, in so doing, energises the timer motor P, switches Sl, S3 and S4 close and the heater and the motor M are energised. It is, of course, possible to employra "start" button operation of which has the same effect. The start button alternatIve may be used in tumbler dryers in which the duration of the drying cycle is contrclled automatically by temperature sensors responsive to the temperature of air leaving the drurr or in some other way. It will be appreciated fror a consideration of Fig. 2 that the precise instant of changeover of thE switches S2A and B is not critical because it can occur at any time that the motor is running at its full speed or close to it, energisation of the start ing winc ng at this time ben prevented by the starting relay SR of which the contacts are opened when the current through the main winding MW falls as the motor M approaches its norrel running speed. The variation in the speed of the motto M and the closing of the contacts cf the starting relay SR are also shown in Fig. 2. Instead of a starting relay the motor M way be provided with a centrifugal switch which becomes open circuit when the motor speed is, say 80% of its full running speed. With such a switch the contacts would be connected in the same way as the contacts of the relay SR, but of course there would be no solenoid coil to be connected in series with the main winding MW. The operation of the circuit with a centrifugal switch instead of the starting relay SR is as described above, except that the contacts of the centrifugal switch will close as soon as the motor speed falls below 80% of its running speed; this will have no effect because the switch SI is open at the time; and the starting winding will be energised when S1 is closed irrespective of whether there is a starting relay or a centrifugal switch. Further, it is possible to employ separate cams to operate the different switches referred to above. Fig. 3 is a circuit diagram of an alternative method of connecting the motor to an electricity supply. In Fig. 3 components identical with compon ents of the circuit shown in Fig. 1 have been given the same reference letters as in Fig 1. As in the case of the embodiment shown in Fig. 1, the starting winding SW is of conventional form. The timer motor P is not shown in Fig. 3 but it will be understood that it is similar to the motor P described above with reference to Fig 2. Energisation of the motor P in the Fig. 3 embodiment is controlled in a similar manner to that of the motor P in the Fig. 2 embodiment. Thus, the starting winding SW of the split phase induction motor M is connected via the contacts of the starting relay SR and a main control switch S6 between A.C. power supply terminals L and N. Connected across those terminals L and N in parallel with the start winding so is the heater H energisation of which is controlled by a switch S7. Reversal of the direction of rotation of the motor M is effected by reversing the sense of connec tion of the main winding MW. The main winding MW is connected, in series with the solenoid coil of the starting relay, between the moving contacts of switches S5A and S5B. Both of these switches have two fixed contacts L, R connected as shown, and a central unconnected position between the fixed contacts L, R. The switches S5A and S5B are actuated by the timing mechanism shown diagrammatically by the dotted rectangle TM. The motor of the timing mechanism has an output shaft on which is mounted a cam contoured to provide the operation of the moving contacts of the switches S5A and S5B to give the changes of direction of the motor M at the requisite time intervals. The contouring of the cam also ensures that the moving contacts rest in the intermediate position for a period of about 1-2 seconds long enough to allow the motor M to come substantially to rest. The cam just referred to is a fast rotating cam similar to those described above. Switch S6 is a main switch controlling energisation of the motor and is operated by a slowly rotating cam, operation being related to the duration of a drying cycle and this is set by a user. Switch S6 also controls energisation of the motor of the timing mechanism. Switch S7 controls energisation of the heater H and is catuated by another slowly rotating cam of the timign mechanism in a manner similar to that described above, i.e. the heater is energised at the commencement of a drying cycel and is de-energlsed some 6-10 minutes before the end of the cycle. As can be seen from Fig. 4, which shows the times of closure of the contacts of the switches of the embodiment shown in Fig. 3, the moving contacts of switches S5A and S5B are operated in unison. The moving contacts are connected to the fixed contacts L, R for equal periods of time whilst the dwell in the intermediate position is 1.5 seconds. When a user sets the timer at the commencement of a drying cycle, the timer motor is energised and the switches S6 and S7 close thereby energising both starting and run windings SW and MW (the contacts of the starting relay SR being closed at this time), and the heater H. When the motor M reaches about 80% of its full running speed, the solenoid coil of relay SR is de-energised as the current thrcugh the main winding MW falls and the starting winding is de-energised. At the appropriate time, the moving contacts of switches S5A and S5B move off fixed contacts L, pause for a period of about 1.5 seconds in the intermediate position to allow the motor M to slow down and come substantially to rest and then move to fixed contacts R. As the motor M comes to rest, the contacts of the starting relay close so allowing energisation of the starting winding but as now the sense of connection of the main winding relative to the starting winding has been reversed, the motor M will rotate in the opposite direction. The cycle of switch operations continues for the duration of the drying cycle. As explained above, it is possible to use a "start" button to initiate the drying cycel instead of setting the timing mechanism It will be appreciated that whilst the moving contacts of the switches SSA and S5B are in their intermediate positions, the current flow through the heater H increases and the air flow over the latter ceases but because of the short time that the contacts are in the intermediate positions this does not result in overheating. However, if a longer duration of stay in the intermediate position is required to ensure that the motor M comes substantially to rest, it may be necessary to de-energise the heater for that duration to avoid the risk of overheating. That can be achieved by another switch in series connection between switch S7 and heater H that is actuated synchronously with switches S5A and S5B being open circuited as the moving contacts of the latter switches move from contacts L to contacts R. As explained above, the embodiment of Fig. 3 may use a centrifugally operated switch in place of the starting relay SR. In addition, the duration of the drying cycle may be controlled in other ways than by means of a timer as is explained above.

Claims: Claims: 1. A tumbler dryer including a rotatable drum which is driven in opposite rotational directions alternately for periods of time by a split-phase induction motor having a main winding and a starting winding with a starting switch having contacts for connecting the starting winding in parallel with the main winding and disconnecting it only when the motor approaches its full running speed, a timing mechanism for determining the said periods of time and including switching means operable by the timing mechanism for reversing the sense of connection of one of said windings relatively to the other, and means operable by the timing mechanism for de-energising the main winding between reversals of the direction of connection for a period of time sufficient for the motor to come substantially to rest. 2. A tumbler dryer as claimed in claim 1 in which the de-energising means comprises an ON/OFF switch operable by the timing mechanism, and in which the switching means is operable to effect reversal of the sense of connection of the starting winding. 3. A tumbler dryer as claimed in claim 2 in which the timing mechanism is such that the ON/OFF switch is operable to an "OFF" position while the motOr is running and in which reversal of the sense of connection of the starting winding occurs whilst the motor is running. 4. A tumbler dryer as claimed in claim 1 in which the switching means is operable to reverse the sense of connection of the main winding and in which the means comprises an arrangement for introducing a time delay between reversals of the direction of connection. 5. A tumbler dryer including a rotatable drum which, in use, is driven in opposite directions alternately for periods of time by a split phase induction motor having a main winding and a starting winding with a starting switch having contacts for connecting the starting winding in parallel with the main winding and disconnecting it only when the motor approaches its full running speed, and a timing mechanism for determining the said periods of time, the timing mechanism including first switching means operable by the mechanism to permit energisation of the motor during the periods of time that the motor is required to run and to prevent energisation during intervals between those periods, the intervals being long enough to allow the motor to come substantially to rest, and second switching means operable by the mechanism to reverse the sense of connection of one of the windings relatively to the other in such manner that the motor is started in opposite directions alternately. 6. A tumbler dryer as claimed in claim 5 in which the second switching means is operable to reverse the sense of connection of the starting winding and effects such reversal whilst the motor is running at full speed. 7. A tumbler dryer as claimed in claim 1 in which the first and second switching means comprises a multi-position switch having a first position in which the main winding is connected in one sense with the starting winding, a second position in which the main winding is connected in the reverse sense with the starting winding, and an intermediate position in which the main winding is disconnected from the starting winding and energisation of the main winding prevented. 8. A tumbler dryer as claimed in claim 6 or 7 in which the timing mechanism includes cams for operating the first and second switching means. 9. A tumbler dryer as claimed in any one of claims 1-8 and which includes a heater for heating air prior to the air entering the drum and in which energisation and de-energisation of the motor is controlled by an ON/OFF switch operable by the timing mechanism to energise the heater at the commencement of a tumble drying operation and to de-energise the heater not later than the end of the operation. 10. A tumbler dryer as claimed in any one of the preceding claims and in which there is a further ON/OFF switch operable by the timing mechanism to permit energisation of the motor at the commencement of a tumble drying operation and to terminate energisation thereof at the end of that operation.

Inventors: DAVIES, JOHN GARFIELD
Applicants: T.I. DOMESTIC APPLIANCES LIMITED
Application year: 1982
Main classification: D06F58
IPC codes: D06F37, D06F58, H02P23