GB2273973A

GB2273973A - A control device for a tumble drier

Info

Publication number: GB2273973A
Application number: GB9325194A
Authority: GB
Inventors: Pont Paolo Da
Original assignee: Elbi International SpA
Current assignee: Elbi International SpA
Priority date: 1992-12-29
Filing date: 1993-12-08
Publication date: 1994-07-06
Anticipated expiration: 2013-12-08
Also published as: GB2273973B; IT1257959B; ITTO921052A0; DE4344806A1; ITTO921052A1; GB9325194D0

Description

2273973

DESCRIPTION

The subject of the present invention is a control device for a tumble drier.

In the present description and the claims which follow, the term tumble drier means, in general, a machine which is intended solely for drying laundry and/or a washing machine which is arranged also to perform a laundry-drying function.

In particular, the subject of the invention is a control device comprising:

- a programmer, including:

a support frame, an alternating-current electric motor carried by the frame for connnection to alternating-voltage supply terminals, a main cam mounted rotatably in the support frame for rotating in steps in order to control the 'various stages of the operating cycle of the drier, a stepping pawl which cooperates with a toothed wheel of the main cam and is coupled kInematically to the motor in order to perform a movement similar to that of a connecting rod at intervals in order to rotate the main cam in steps, a stop member movable in the frame between first and second working positions, that is, a release position and a locking position, respectively, in which it can 2 enable and p revent the rotation qt 49 Fiolfi gifl by 49 stepping pawl, respectively, control means for controlling the. pos4.ti&n of the -s+op member, including an electromagnetic device comprising a coil carried by the frame, a f ixed core f ixed to the coil, and a movable core which cooperates with the stop member in a manner such that, when the coil is energized, the stop member can be held in one of the working positions; - an electrical, humidity sensor associated with the operating chamber of the drier, - a step-down transformer, the input side of which is connected to the supply terminals, and - a control circuit which is connected to the secondary or output side of the transformer by means of a rectifier circuit and which comprises comparator circuit means connected to the humidity sensor, the control circuit being adapted to control the energizing and/or de-energizing of the coil in dependence on the signal of the humidity sensor so that, during a laundry-drying stage, the stop member remains in the locking position as long as the signal supplied by the sensor is indicative of a degree of humidity greater than a predetermined reference value.

A control device of this type according to the prior art -is diagraamtically illustrated in fig= 1 of the appended drawings.

In this drawing, the electric motor of the programmer is indicated M The motor is connected to two 3 alternating-voltage supply terminals 1, 2. These terminals are also connected to the primary. winding Wl of a step-down transformer TR. A full-wave rectifier R connected to the secondary winding W2 of the transformer has a smoothing capacitor C connected in parallel with its output.

A circuit branch connected downstream of the capacitor includes a resistor Rl, the collector-emittor path of a transistor T1, and the excitation winding W of a relay, the movable contact A of which is normally open and is connected in parallel with the primary winding WI of the transformer TR, in series with the coil B of a control electromagnet E.

The electromagnet comprises a fixed core F and an associated movable core M which, when the coil B is in the de-energized condition, is kept att, a certain distance from the fixed core F by known biasing means, not shown.

A stop member L mounted movably in the frame of the programmer (in known manner) is connected to one end of the movable core M of the electromagnet E. The arrangement is such that, when the coil B is energized, the displacement of the movable core M towards the f ixed core F brings the stop member L to a working position in which it can prevent the stepping pawl of the programmer from rotating the main cam thereof. This in fact stops the main cam of the programmer temporarily.

The output of a comparator COMP is connected to the base of the transistor Tl by means of a resistor R2. One input of the comparator is connected to the central 4 tap of a vo ltage- divider formed by two resistors R.' and R4 which are connected downstream of the capacitor C so as to define a direct-current reference voltage. The other input of the comparator COMP is connected to an electrical, humidity sensor S associated with the operating chamber of the tumble drier.

This sensor is represented by a variable resistor and with an associated resistor RS, it forms a voltage divider with a variable division ratio.

In operation, when the programmer of the tumble drier starts a drying stage, the signal supplied by the sensor S is indicative of a degree of humidity greater than a predetermined value corresponding to - the reference voltage defined by the resistors R3, R4. The comparator COMP accordingly makes the transistor Tl conductive. This causes current to flow in the relay coil W and closes the associated contact A.

Current flows through the coil B of the electromagnet E and the magnetic field consequently generated moves the movable core M towards the fixed core F. This moves the stop member L to its working position, in which it prevents further rotation of the main cam of the programmer.

The device remains in this condition until the signal supplied by the sensor S indicates that the degree of humidity in the operating chamber of the drier has fallen below the predetermined threshold.

In this situation, the comparator COMP cuts off the transistor T1, the relay coil W is de-energized, and the associated contact A opens, deenergizing the electromagnet E. The stop member L leaves its preventing position and the pawl can engage the toothed wheel of the main cam again in order to move it in steps.

The known control device described above has the disadvantage that, in order to stop the main cam of the programmer during the drying stage, it requires the use of a relay A and of an electromagnet E of considerable power.

The electromagnet is in fact connected to the high-tension side of the transformer TR and is supplied with the mains alternating voltage. Moreover, the coil of the electromagnet is dimensioned for causing the movable core M to perform the necessary travel to bring the preventing member L to the position in which it can prevent engagement between the pawl and the main cam.

The coil B is therefore a fairly high-powered coil.

An object of the present invention is to provide a control device of the type specified above which enables the main cam to be stopped during the drying stage with the use of a low-powered electromagnet and without the need for a further relay for controlling the energizing thereof.

Claims

This object is achieved, according to the invention, by a control device

of the aforesaid type having the characteristics defined, in particular, in Claim 1.

In the control device according to the invention, when a drying stage commences, the movable core of the 6 electromagnet is moved close to the f -1xed core of the coils mechanically.

This may take place slightly before the coil is energized (and, in this case, the movable core must be kept near the fixed core at least until the coil is energized), or slightly after it is energized.

The coil may thus be dimensioned for generating an attractive force sufficient to hold the movable core against the fixed core. A decidedly lower-powered coil suffices for this purpose since it is not intended to cause the movable core to perform any closure travel.

The coil is thus conveniently disposed downstream of the secondary or output side of the transformer and is energized at low tension.

The invention thus affords the dual advantage that it uses a lowerpowered and smaller coil and that it avoids the use of a relay for controlling the energizing thereof.

Further ch ' aracteristics and advantages of the invention will become clear from the detailed description which follows with reference to the appended drawings and provided purely by way of non-limiting example.

In the drawings:

Figure 1, which has already been described, is a circuit diagram of a control device according to the prior art, Figure
2 is a circuit dlagram of a control device according to the invention, and Figures 3 and 4 are two partially-sectioned front views of a programmer for a control device according to the invention in two different operative conditions.

Figure 2 is a diagram of the circuit portion of a control device according to the invention. in this drawing, parts and elements already described with reference to Figure 1 have again been given the same alphanumeric references.

In comparison with the diagram of Figure 1, it can be noted that the coil B of the electromagnet E is disposed in series with the collector-emitter path of the transistor T1, downstream of the secondary side W2 of the step-down transformer TR. A freewheeling diode D1 is connected in parallel with the coil in the usual manner.

In operation, the coil B is energized simply as a result of the transistor T1 becoming conductive.

The coil is conveniently fixed to the frame of the programmer of the machine, as shown in Figures 3 and 4, and, by virtue of a device an embodiment of which will now be described with reference to these drawings, is a low-powered coil.

Figures 3 and 4 show an embodiment of a programmer P included in a control device according to the invention.

The programmer comprises a support frame 10 in which a.

8 control electric motor qDamdnd by alternating current is mounted in known manner.

The output shaft of the motor is shown in broken outline in Figures 3 and 4 and has been indicated M A main cam CP mounted f or rotating about an axis X in the frame 10 of the programmer is intended to rotate in steps and to cooperate in known manner with electrical contacts (not shown) associated therewith, in order to control the various stages of the operating cycle of the machine.

A stepping pawl N, associated with the main cam CP, is mounted for pivoting about an eccentric pin 11 carried by a gear 12 which can be rotated by the motor shaft TM in the sense indicated by the arrow F, by means of a gear train generally indicated GT.

One end of a biasing spring 13 is connected to the frame of the programmer at 14 and its other end is connected to an appendage 15 of the stepping pawl N.

The spring 13 urges a hooked appendage 16 of the pawl into engagement with a toothed wheel 17 of the main cam CP.

The stepping pawl N has a projection 18 one surface 18a of which slides in contact with a stationary abutment member 19 fixed to the frame 10 of the programmer.

The upper end of a lever, indicated L, is articulated for pivoting relative to the frame 10 of the programmer about an axis indicated Y. The lower end of the lever L is articulated at 20 to an end of the movable core M 9 of the electromagnet E.

A helical spring 21 is interposed between a stationary reaction surface 22 fixed to the frame 10 of the programmer and the lower end of the lever L which is articulated on the movable core M of the electromagnet.

The lever L forms a heel Q which is in contact with the end of the hooked appendage 16 of the stepping pawl N.

The helical spring 21 urges the movable core M of the electromagnet towards the fixed core F and urges the lever L towards the stepping pawl N.

The springs 13 and 21 are dimensioned in a manner such that, when the coil B of the electromagnet E is de-energized, the force exerted by the spring 13 on the stepping pawl N is such as to allow the hooked appendage 16 of the pawl to engage the toothed wheel of the main cam CP during a stage of the rotation of the eccentric pin 11, overcoming the opposing force of the spring 21 and of the lever L, as shown in Figure 3.

When the electromagnet E is de-energized, as a result of the rotation of the motor TM of the programmer, of the engagement of the shaped projection 18 with the stationary abutment member 19, and of the action of the helical spring 13, the stepping pawl N performs a movement similar to that of a connecting rod at intervals in order to cause the main cam CP of the programmer to perform a stepped rotary movement.

The lever L correspondingly oscillates about the axis Y following the movements of the hooked appendage 16 of the stepping pawl, by virtue of the spring 21.

Figure 4 shows, in particular, that when the stepping pawl N is disengaged from the toothed wheel of the main cam CP, the movable core M of the electromagnet is adjacent the associated fixed core F.

if the laundry-drying stage is started whilst the programmer is in the configuration shown in Figure 4, the energizing of the coil B of the electromagnet results in a attractive force on the movable core M which, in cooperation with the thrust exerted by the spring 21, can hold the movable core M against the associated fixed core F, also holding the lever L in the position of Figure 4 in which its heel Q prevents the stepping pawl N from returning into engagement with the main cam CP of the programmer in order to advance it by one step.

Until the humidity detected by the sensor S in the operating chamber of the drier falls below a predetermined value, the stepping pawl N is thus prevented from causing further stepped rotation of the main cam. The latter remains stationary.

Upon completion of the drying stage, the electromagnet E is de-energized and thus ceases to exert the attractive magnetic force on the movable core M.

The helical spring 13 associated with the stepping pawl can then return the pawl into engagement with the main cam CP of the programmer.

For the electromagnet E, a low-powered coil B with a low-tension supply suffices to develop the magnetic force necessary simply to hold the movable core M against the fixed core F during the drying stage. The 11 coil B must suffice simply to hold the movable core against the fixed core, since it is not required to cause the movable core to perform any travel.

If a drying stage is started whilst the programmer is in the condition shown in Figure 3, the attractive force developed as a result of the magnetic field generated by the coil B may be insufficient to attract the movable core M against the fixed core F. However, as soon as the stepping pawl N is disengaged from the main cam CP as a result of the further rotation of the programmer motor and of the engagement of the projection 18 with the abutment member -19, the spring 21 urges the movable core M against the fixed core F bringing the core and the lever L to the respective positions shown in Figure 4. in this condition, the magnetic field developed by the coil B is then sufficient to keep the movable core and the lever L in the condition of Figure 4, preventing the stepping pawl from re-engaging the main cam until the drying operation is completed.

An electromagnet E with a low-powered coil B can thus nevertheless prevent the main cam CP of the programmer from advancing throughout the duration of the drying operation.

The solution described above with reference to Figures 3 and 4 is purely an example and further variants may easily be devised by experts in the field.

In particular, it should be noted that, in the solution of Figures 3 and 4, the electromagnetic device is associated with the stop lever L in a manner such as to restrain it in the condition in which the stepping pawl N 19 gtOPP@G WhOn thg 0011 19 in thg gngrg!29d condition. In this solution, the coil B is kept energized (at least) throughout the duration of a laundry-drying stage.

However, it will be clear to an expert in the art, that solutions in which the electromagnetic device E is associated with the stop lever L in a manner such that, when the coil b is energized, the lever is restrained in the condition in which the pawl L is released, are also possible. In these conditions, the coil B is de-energized during the laundry-drying stage or stages.

The usual programmers for washing machines and tumble driers typically also comprise a so-called fast cam or reversing cam which is mounted rotatably in the support frame of the programmer and cooperates with electrical contacts to reverse the sense of rotation of the laundry drum of the machine periodically.

A further alternative solution to that described above with reference to Figures 3 and 4 may then consist of the formation of a projection on the fast cam or reversing cam of the programmer for cooperating with the lever member L or the movable core M so as to position the movable core M of the electromagnet E near the associated fixed core F slightly before or during the energizing of the coil B so that the coil of the electromagnet in this embodiment is also called upon to develop only the force necessary to hold the movable core against the fixed core.

Naturally, the principle of the invention remaining the same, the forms of embodiment and details of construction may be varied widely with respect to those 1 -2 described and illustrated purely by way of non-limiting example, without thereby departing from the scope of the present invention.

14 CLAIMS 1. A control device for a tumble drier, comprising: - a programmer (P), including: a support frame (10), an alternating-current electric motor (TM) carried by the frame (10) for connnection to alternating-voltage supply terminals (1, 2), a main cam (CP) mounted rotatably in the support frame (10) for rotating in steps in order to control the various stages of the operating cycle of the drier, a stepping pawl (N) which cooperates with a toothed wheel (17) of the main cam (CP) and is coupled kinematically to the motor (TM) in order to perform. a movement similar to that of a connecting rod at intervals in order to rotate the main cam (CP) in steps.

a stop member (L) movable in the frame (10) between first and second working positions, that is, a release position and a locking position, respectively, in which it can respectively enable and prevent the rotation of the main cam (CP) by the stepping pawl (N).

control means for controlling the position of the stop member (L), including an electromagnetic control device (E) comprising a coil (B) carried by the frame (10), a fixed core (F) fixed to the coil (B), and a movable core (M) which cooperates with the stop member (L) in a manner such that, when the coil (B) is energized, the stop member (L) can be held in one of the working positions; - an electrical,humidity sensor (S) associated with the operating chamber of the drier, - a step-down transformer (TR), the input side (W1) of which is connected to the supply terminals (1, 2), and - a control circuit (T1, COMP, R3, R4) which is connected to the secondary or output side (W2) of the transformer (TR) by means of a rectifier circuit (R) and which comprises comparator circuitry (COMP) connected to the humidity sensor (S), the control circuit being adapted to control the energizing and/or de-energizing of the coil (B) in dependence on the signal of the humidity sensor (S) so that, during a laundry-drying stage, the stop member (L) remains in the locking position as long as the signal supplied by the sensor (S) is indicative of a degree of humidity greater than a predetermined reference value, the control device being characterized in that the control means (21) of the programmer (P) comprise displacement means (21; 18, 19) for positioning the movable core (M) of the electromagnetic device (E) near the associated fixed core (F) when the associated coil (B) is in an energized condition, and in that the coil (B) is dimensioned so as to produce an attractive force which suffices to hold the movable core (M) near the fixed core (F) when the core is in the energized condition, and is connected to the secondary or output side (W2) of the transformer (TR) so that it is energized at low tension in operation.

16 2. A device according to Claim 1, characterized in that the programmer (P; 21; 18, 19) is arranged to position the movable core (M) near the associated fixed core (F) before the coil (B) is energized and to keep the movable core (M) near the fixed core (F) until the coil (B) is energized.
3. A device according to Claim 1, cheracterized in that the programmer (P; 21; 12, 19) is arranged to position the movable core (M) near the associated fixed core (F) whilst the coil (B) is energized.
4. A control device according to one of the preceding claims in which the stepping pawl (N) is operated by the motor (TY.) of the programmer (P) by means of an eccentric (11) which is rotatable in the support frame (10) and is connected to a first resilient means (13) which urges it into engagement with the main cam (CP), the pawl (N) having a shaped surface (18a) which can cooperate with an abutment member (19) fixed to the frame (10) of the programmer in order to disengage. the pawl (N) from the main cam (C) during a stage of the rotation of the eccentric (11), against the action ofthe first resilient means (13), and in which the stop member is a lever member (L) which is mounted pivotably in the frame (10) and has one end coupled to the movable core (M) of the coil (B), the operating means comprising a second resilient means (21) which is associated with the movable core (M) andlor with the lever member (L) and which urges the movable core (M) towards the fixed core (F) and urges the lever member (L) into the stopping position in which it can prevent the stepping pawl (N) from engaging the main cam (CP), opposing the action of the first resilient means (13)r 17 the arrangement being such that when the coil (B) is in the de- energized condition, t-he first resilient means (13) can cause the stepping pawl (N) to engage the main cam (CP), overcoming the 3pposing action exerted by the second resilient means (21) whereas, when the coil (B) is in the energized condition, the simultaneous effects of the second resilient means (21) and of the magnetic field developed by the coil (B) are such as to keep the movable core (M) near the f ixed core (F) and the lever member (L) in the locking position in which it prevents the stepping pawl (N) from engaging the main cam (CP).
5. A control device according to one of Claims 1 to 3, in which the programmer (P) also comprises a f ast or reversing cam which is mounted rotatably in the support frame (10) for periodically reversing the sense of rotation of the laundry drum of the drier, and in which the control means comprise a projection of the fast cam for cooperating with the stop member (L) so as to position the movable core (M) of the coil (B) near the associated fixed core (F) when the coil (B) of the electromagnetic device (E) - is in an energized condition.
6. A control device as claimed in Claim 1 and substantially as hereinbefore described with reference to, and as shown in the accompanying drawings.