GB2174140A - A device for locking the door of a washing-machine more particularly a clothes washing-machine - Google Patents

Abstract

The device comprises a PTC type resistive heating element (12) subjected to an electric voltage and thereby heated when a washing machine is actuated and a bimetallic actuating element (14) on one surface of the heating element (12), so that when the latter is heated, its temperature and that of the bimetallic actuating element have an initial period of rapid increase followed by a period of slower increase. The bimetallic actuating element (14) is deformable through heating so as to move (during said initial period) a locking means (18) for the machine door. One or more bimetallic control elements (10a, 10b, 10c) are connected to the other surface of the heating element (12) by an element (11) and when heated, become deformed in the opposite direction to the bimetallic actuating element. The element (11) has a shape and thermal capacity such that, the bimetallic control elements (10) are heated only after a preset delay which is substantially of the same order as the said initial period. <IMAGE>

Description

SPECIFICATION A device for locking the door of a washing-machine more particularly a clothes washing-machine.

The invention relates to a device for locking the door of a washing machine, more particularly a clotheswashing machine, comprising a holder or casing, a PTC type resistive heating element held in the casing and adapted to be subjected to an electric voltage and heated when the washing machine is actuated, a bimetallic actuating element disposed in contact with one surface of the heating element so that when the element is heated, its temperature and the temperature of the bimetallic element have an initial period of rapid growth followed by a period of slower growth, the bimetallic element being deformable by heating so as to move a locking means adapted to prevent opening the door, and one bimetallic control element electrically connected to the other surface of the heating element and deformable when heated in the opposite direction to the deformation of the bimetallic actuating element.

A device of this kind is known e.g. from Italian patent application 48663-A/76 of 18 March 1976. The device comprises an actuating bimetal and a compensating bimetal. The compensation bimetal is shaped and disposed so that it is in thermal contact mainly with the "ambient" air inside the container or casing of the device. Its temperature follows variations in the ambient temperature rather than variations in the temperature of the PTC pellet constituting the resistive heating element.

The known device has a serious disadvantage in that there are wide variations in the delay time between the instant when the washing machine is inactivated and the instant when the door can be subsequently opened. The time increases with the time between the instant when the locking device is operated and the instant when the device is inactivated. It may therefore happen that if the machine is inactivated after a rather long operating period it will be necessary to wait for several seconds or even minutes before opening the door.

The object of the invention is to construct a device for locking the door of a washing machine of the initially-specified type, the device being free from the previously-described disadvantage of the earlier devices.

The object of the invention is achieved by means of a locking device of the previously-described kind, characterised in that the intermediate conducting element is substantially indeformable within the operating temperature range of the heating element and has a shape and thermal capacity such that at least one bimetallic control element is heated, as a result of the heating of the heating element, after a preset delay reJative to the bimetallic actuating element and at a subsequent rate substantially equal to the slow rate of increase in the temperature of the actuating bimetal; the delay being substantially of the same order as the initial period of rapid increase in temperature of the resistive heating element.

As a result of this feature, the delay time between the instant when the washing machine is inactivated and the instant when the door can be opened is made substantially constant, more particularly independent of the time between operating the locking device and inactivating it.

Other features and advantages of the locking device according to the invention will be clear from the following detailed description with reference to the accompanying drawings, given by way of nonlimitative example only, in which: Figure 1 is a perspective view of an embodiment of a device according to the invention; Figure2 is a view in section along line Il-Il of Figure 1; Figures 3 and 4 are views corresponding to Figure 2, showing the device in two different operating states; Figure 5shows a larger-scale detail of Figure 2; Figure 6 is a top view along arrow VI in Figure 5, and Figure 7 is a set of Cartesian diagrams illustrating the operation of the device according to the invention.

In the embodiment shown in the drawings, the device according to the invention comprises an electrically insulating casing 1 made up of a container 2 and a cover element 3. Reference 4 denotes a component which moves relative to casing 1 and forms the bolt for opening and closing the door of a washing machine (not shown), e.g. a clotheswashing machine for domestic use.

Three electric contact strips 5, 6, 7 are secured inside container 2 and extend outwardly through slots formed in one side thereof, as shown in Figure 1. Contact 5 is adapted for connection to the electric circuits supplying the washing machine. Contact 6 is for connecting to one of the conductors in the electric supply line of the machine, and contact 7 is for conducting to the other conductor in the line.

Contact strip 7 is secured to the inner surface of the bottom of container 2. An adjusting screw 8 is screwed in to contact 6, as shown in Figures 2 and 5, through a corresponding aperture formed in the bottom of container 2. Four parallel projections 9 extend from the inner surface of the bottom of container 2 at equal distances from the axis of screw 8.

References 10a, 10b and 10denote bimetallic control elements substantially in the form of rectangular strips having a widened central part (Figures 5 and 6) and bearing on the adjusting screw 8. As shown more particularly in Figure 5, the ends of the bimetallic elements extend between pairs of projections 9.

Reference 11 denotes a metal element bearing on the bimetallic control elements. Element 11 is substantially rectangular, with a widened central portion similar to the bimetallic control elements 10a, 1 Ob and 1 or. The ends of element 11 are formed, e.g. by stamping, with feet 11 a on which element 11 rests on the bimetallic control elements. The top surface of element 11 has a number of studs, indicated by 11 b in Figures 5 and 6.

Element 11 is made of a material such as steel which is electrically conductive and has an appreciable specific value and high thermal resistance.

A pellet 12 of positive temperature coefficient (PTC) resistive material is disposed on element 11.

The pellet diameter is such that it can move with a certain clearance relative to projections 9 (Figures 5 and 6). As will be shown hereinafter, the pellet is adapted to serve as a heating element when the washing machine is actuated and a voltage is applied to it.

Reference 14 denotes a bimetallic actuating element having one end gripped between the contact strip 7 and an inner shoulder of container 2. Element 14 extends above and beyond the heating element 12 and is preferably biased so as to press the heating element towards the adjusting screw 8.

Reference 15 denotes a metal strip having one end secured to contact 7 by a screw 16. Strip 15 is longer than the bimetallic element 14. It also has a central opening 15a through which the free end of element 14 can extend.

Reference 17 denotes a spring having one end secured to the free end of element 14 and the other end secured to strip 15. Strip 15 has a contact 15b adapted to co-operate with a corresponding contact 5a on terminal strip 5.

A pin 18 is slidable in an orifice 19 formed in container 2 in a direction perpendicular to the direction of motion of bolt 4. Pin 18 can occupy a retracted inoperative position shown in Figure 2, or an extended operating position shown in Figures 3 and 4, in which it is adapted to engage in an opening 4a formed in bolt 4 so as to prevent the bolt from moving.

Pin 18 has a notch 18a for engaging the free end of strip 15.

Figure 2 shows the device according to the invention in the inoperative state. The bimetallic control elements are substantially flat, strip 15 is not deformed and holds pin 18 in the retracted inoperative position, and contact 15b of strip 15 is at a distance from the corresponding fixed contact 5a on contact strip 5. The bimetallic actuating element 14 is curved upwards.

When the washing machine is actuated, i.e. is connected to the electric supply network, a current flows through contact strip 7, bimetallic element 14, pellet 12, the intermediate conducting element 11, the bimetallic control elements 10, the adjusting screw 8, and the contact strip 7. The temperature of element 12 increases rapidly at first and then more slowly and tends to stabilize. The temperature of element 14 increases substantially at the same rate, since it is in close thermal contactwith element 12.

In Figure 7, the Cartesian diagram at the top is a curve A substantially corresponding to the temperature of the bimetallic actuating element 14 in dependence on the time t, shown along the abscissa. to denotes the instant when the washing machine is actuated, i.e. the instant when current begins to flow between contacts 6 and 7. Between instant and instantt1, the temperature of element 14 increases very rapidly as shown by the ascending branch of curve A in Figure 7. Element 14 therefore becomes deformed from the shape shown in Figure 2 to the shape shown in Figure 3. Spring 17 pushes strip 15 upwards, contacts 15b and 5a meet, and pin 18 engages the opening 4a in bolt 4, which is therefore held in the position in which it locks the washingmachine door in the closed position.

Curve A in Figure 7 qualitatively indicates the progressive displacement undergone by the free end of element 14, since this displacement is substantially proportional to the temperature of element 14.

The constant level Si represents the position (the temperature of bimetal 14) at which, as a result of the release of spring 17, strip 15 moves from the inoperative position in Figure 2 to the operative position in Figure 3. The time tj between the instant to when the washing machine is actuated and the instantts when strip 15 is released in the "operating time" of the device according to the invention.

After the instant t1, the temperature of bimetal 14 would tend to increase more slowly towards a thermally stable condition as shown by the chainline curve A' in Figure 7. If element 14 continued to be progressively heated as shown in curve A', the delay time between inactivation of the washing machine and the instant when the locking device allowed the door to be opened, would increase with the time between actuation and inactivation of the washing-machine. If for example the washing machine was inactivated at instant t2, the temperature of bimetal 14, which was no longer energized, would decrease as per the chain-line curve B in Figure 7, strip 15 would return to the inoperative position and the door could be opened at instant t3.If on the other hand the machine was inactivated at an instant t'2 after t2, the door could not be opened until the instant t'3, i.e. after a delay t'r greater than the delay to = t3 - t2.

The bimetallic control elements 10a, b, c, are provided in order to obtain a substantially constant delay between switching off the washing machine and the instant when the door can be re-opened. The bimetals are electrically and thermally coupled to the heating element 12 via the intermediate conducting element 11. Element 11 has a shape and thermal capacity such that variations in the temperature of the control bimetals 10a, b, cfollowvariations in the temperature of the heating element and consequently in the actuating bimetal 14 after a delay substantially equal to t1 - to and at a similar rate.Further the control bimetals, as soon as their temperature tends to rise, become deformed (Figure 4) in a manner opposing the deformation undergone by bimetal 14 after pin 18 has stopped moving. In Figure 7, curve C qualitatively illustrates the variation with time tin the temperature of the control bimetals 10 and consequently in the deformation thereof. As already stated, when pin 18 stops moving the deformation of the control bimetals acts in the opposite direction to the deformation of the actuating bimetallic element.

In practice, therefore, the control bimetals alter the characteristic A-A' of bimetal 14 to the characteristic A-A" in Figure 7. After instant ta, the thermal characteristic A" of the sub-assembly formed by bimetals 14 and 10a, lOb is substantially parallel to the taxis and consequently the delay between inactivation of the washing machine and the instant when the door can be opened is made substantially constant.

This result is obtained by using bimetallic control elements disposed facing the heating element 12 and electrically and thermally coupled thereto via the intermediate conducting element 11. In thermal terms, element 11 substantially corresponds to a "series" resistance and a "parallel" capacitance, and therefore in electrical terms it substantially corresponds to an RC type delay group.

The bimetallic control elements are dimensioned and positioned so that, during the time when the washing machine is in operation and consequently current is flowing through them, they tend to stabilize at a temperature between that of the PTC pellet 12 and the temperature of container 2.

Although the drawings and the preceding specification refer to the use of three bimetallic control elements, it is obvious that a single control element could alternatively be used. It may be preferable to have two or more elements in order to obtain better "travel".

Of course, without altering the basic invention, the embodiments and constructional details can be widely varied from those described and illustrated by way of non-limitative example only, without thereby departing from the scope of the present invention.

Claims (5)

1. A device for locking the door of a washingmachine, comprising a holder or casing a PTC type resistive heating element held in the casing and adapted to be subjected to an electric voltage and heated when the washing machine is actuated, a bimetallic actuating element disposed in contact with one surface of the heating element so that when the element is heated, its temperature and the temperature of the bimetallic element have an initial period (tl - to) of rapid growth followed by a period (t > t1) of slower growth, the bimetallic element being deformable by heating so as to move a locking means adapted to prevent opening the door, and at least one bimetallic control element electrically connected to the other surface of the heating element by an intermediate conducting element and deformable when heated in the opposite direction to the deformation of the bimetallic actuating element characterised in that the intermediate conducting element (11) is substantially indeformable within the operating temperature range of the heating element and has a shape and thermal capacity such that at least one bimetallic control element is heated, as a result of the heating of the heating element after a preset delay relative to the bimetallic actuating element and at a subsequent rate (C) substantially equal to the slow rate of increase (A') in the temperature of the actuating bimetal the delay being substantially of the same order as the initial period (t1 - to) of rapid increase in temperature of the resistive heating element.

2. A device according to claim 1, characterised in that the intermediate conducting element comprises a metal strip having one surface formed with first projections for bearing against at least one bimetallic control element and the other surface formed with second projections against which the resistive heating element bears.

3. A device according to claim 2, characterised in that the intermediate conducting element is made of a material such as steel which is electrically conductive and has high specific heat and thermal resistance.

4. A device according to any of the preceding claims, characterised in that it comprises three adjacently disposed bimetallic control elements.

5. A device substantially as described and illustrated and for the specified purposes.