This and other aims are achieved, according to the invention, by a door-
locking device, the main characteristics of which are defined in general in appended Claim 1.
Further characteristics and advantages of the invention will become clear from the following detailed description, given purely by way of nonlimiting example, with reference to the appended drawings, in which:
Figure 1 is a perspective view of a door-locking device according to the invention, Figure 2 is a partial ly-exploded, perspective view of the device shown in Figure 1, Figure 3 is an exploded, perspective view of a portion of the device shown in the previous drawings, Figure 4 is a view sectioned on the line IV-IV of Figure 1, Figure 5 is a sectioned view similar to that of Figure 4 and shows the door-locking device in a different operative condition, and Figure 6 is a plan view of a portion of the device of the previous drawings, taken substantially along the arrow VI of Figure 4.
In Figure 1, a door-locking device according to the invention is generally indicated 1.
In the embodiment shown by way of example, the device comprises a body 2 of moulded plastics material at one end of which an opening 3 is formed for the insertion of an engagement member such as that shown in broken outline in Figure 5 and indicated 4 therein.
In known manner, the door-locking device 1 is intended to be fixed in the vicinity of an opening of an electric appliance and the engagement member 4 is intended to be connected to a movable door P associated with opening of the electric appliance.
A casing, generally indicated 5, is connected firmly to the body 2. As can best be seen in Figure 3, in the embodiment shown, the casing 5 is formed by two half-shells 5a and 5b, for example, made of moulded plastics material and snap-coupled with one another.
The body 2 has a plurality of resilient appendages 6 (Figures 1 and 2) the free ends of which form respective retaining teeth 6a (Figure 2) which can hold the casing 5 f irmly in the position in which it is coupled with the body 2.
A slide 7 is mounted so as to be axially translatable between the body 2 and the casing 5 (Figures 2, 4 and 5) The slide has a main opening 8 and two further openings 7a and 9. A helical spring 10 is housed in a seat 11 (Figure" 2 and 4) formed in the surface of the half-shell 5b which faces the body 2. The helical spring 10 is also engaged in the opening 9 of the slide 10, as can be seen in Figures 4 and 5.
The arrangement is such that the spring 10 tends to keep the slide 7 in the position shown in Figure 4, in which the opening 8 of the slide is aligned with the opening 3 of the body 2.
With reference to Figures 3 to 5 and 6, a metal plate 12 of known type is mounted inside the casing 5. In the embodiment shown, the plate 12 has an end 12a f ixed to a support projection 5c of the lower half-shell 5b of the casing 5. The opposite end 12b of the plate 12 carries an electrical contact member 13. An end appendage 12c having an opening 14 extends from the end 12b of the plate 12.
In the embodiment shown, the plate 12 has a substantially U-shaped slot 15 in its intermediate portion (Figure 3) This slot defines in the plate a central longitudinal portion 16 between two lateral portions 17. A substantially biconical spring 18 is interposed between the free end of the central portion 16 and the end portion 12b of the plate. The spring is loaded in compression and, in known manner, tends to confer on the metal plate 12 two different stable configurations in which, as can be seen in Figures 4 and 5, the central portion 16 of the plate extends below and above the general plane of the plate, respectively.
A bridge portion 19a of a shaped, electrically conductive element 19 bears on the fixed end 12a of the plate 12. The element 19 comprises a strip 19b (Figures 3 and 6) which connects its portion 19a to an end portion 19c shaped as a f lat pin. This portion 19c extends out of the casing 5 within a quadrangular shell 5d formed jointly by the two half- shells 5a and 5b (Figures 1, 2 and 6).
A further electrically conductive element, generally indicated 20, is fixed to the lower half-shell 5b, inside the casing 5. This element has an end portion 20a which extends below the end portion 12b of the plate 12 and which carries a fixed contact 20b which can cooperate (as described further below) with the movable contact member 13 carried by the plate.
The electrically conductive element 20 also has an end appendage shaped as a flat pin, indicated 20c, which extends out of the casing 5 within the shell 5d (Figures 1, 2 and 6).
A further electrically conductive element, fixed to the lower half-shell 5b of the casing 5, is generally indicated 21 in Figure 3. The conductive element 21 has an end portion 21a, an intermediate portion 21b, and a further end portion 21c shaped as a flat pin. The latter portion also extends out of the casing 5 in the quadrangular shell 5d, as can be seen in Figures 1, 2 and 6.
The terminal pins 19c, 20c and 21c enable the door-locking device 1 to be connected electrically to the electrical system and to the operation-control system of the electric appliance with which the device is associated.
An elongate bimetal element, indicated 22 in Figures 3 to 6, is disposed beneath the plate 12 and has one end which bears on a support 5e of the half-shell 5b (Figure 3), its other end bearing on the appendage 21a of the conductive element 21.
In its intermediate portion, the bimetal element 22 has an upwa rdl y-ext ending projection 22a (Figure 3).
A threaded opening 5f is formed in the lower half-shell 5b of the casing 5 and a calibration grub screw 23 is screwed therein (Figures 1, 2, 4 and 5).
The opening 5f of the casing 5 faces a corresponding opening 24 in the body 2.
A further elongate bimetal element 25 is disposed in the casing 5 and has one end which bears on the grub screw 23, its other end bearing on the projection 22a of the bimetal element 22 (Figures 4 and 5).
A resistive heating element 26 with a positive temperature coefficient is disposed on the intermediate portion of.the bimetal element 25. A bend 16a in the central portion 16 of the plate 12 bears permanently on the upper face of the heating element 26.
A locking member engaged on the end appendage 12c of the metal plate 12 is indicated 27 in Figures 3 to 5.
The locking member 27 extends through an opening 28 in the base of the lower half-shell 5b of the casing 5 (as can be seen in Figures 2, 4 and 5) . This opening 28 faces a corresponding opening 29 in the body 2.
The door-locking device described above operates in the following manner.
When the door of the electric appliance is open, the door-locking device adopts the rest configuration shown in Figure 4. No current flows through the heating element 26, and the plate 12 adopts the position shown in Figure 4, in which its movable contact 13 is spaced from the associated fixed contact 20b. The appendage 12c of the plate 12 keeps the locking member 27 in the retracted position shown in Figure 4, in which it does not project from the casing 5. The spring 10 keeps the slide 7 in the rest position, in which its opening 8 faces the opening 3 of the body 2.
If the user closes the door of the electric appliance, the engagement member 4 associated with the door passes through the opening 3 of the body 2 and engages in the opening 8 of the slide 7. In known manner, resilient biasing means associated with the engagement member 4 cause the latter, once it has passed through the opening 8 of the slide 7, to bring about translation of the slide 7 towards the retaining position shown in Figure 5, against the action of the spring 10, which is compressed.
If the electric appliance is now switched on, an electric current is caused to flow between the terminals 19c and 21c. This current flows through the bimetal element 22, the bimetal element 25, the resistive heating element 26, and the plate 12. The flow of current through the resistive heating element 26 brings about heating of the operating bimetal element 25 which, after a predetermined period of time, bends as shown in Figure 5, bringing about a curvature of the heating element 26. The heating element 26 acts on the central portion 16 of the plate 12 and brings about snap-switching thereof. The plate 12 thus adopts the configuration shown in Figure 5, in which its movable contact member 13 bears against the associated fixed contact 20b and the movable locking member 27 is disposed in the extended position in which it is engaged in the opening 7a of the slide 7, preventing the slide from returning to the rest position shown in Figure 4.
The door of the electric appliance is now effectively locked and can no longer be opened. This condition can be detected by the control unit of the electric appliance since the terminal 20c: is now live. The coupling of the contacts 13 and 20b can be used as a consent for the activation of the electric appliance.
The door of the appliance can subsequently be reopened only if the flow of current through the resistive or heating element 26 is interrupted, for example, upon completion of an operating cycle, or as a result of the interruption of the electrical energy supply to the appliance.
When the current ceases to flow in the resistive heating element 26, this element 26 and the bimetal operating element 25 start to cool. The bimetal element 25 tends to return to the rest configuration and, after a predetermined period of time, allows the plate 12 to snap back to the rest configuration shown in Figure 4. The movable locking member 27 is consequently returned to the retracted position in which it does not obstruct the return of the slide 7 to the rest position.
The door of the electric appliance can thus be opened.
The grub screw 23 is not affected by the flow of electric current and may therefore be made of insulating material. In particular, it permits calibration of the delay with which the plate 12 switches back to the rest configuration, returning the locking member to the retracted condition, when the current ceases to flow through the heating element 26. This delay corresponds basically to the time required, after the completion of an operating cycle of the electric appliance or after the interruption of its energy supply, before the user can open the door.
Since the grub screw 23 acts on one end of the bimetal element 25 at a point situated some distance from the resistive heating element 26, the calibration which can be achieved by the grub screw is very precise.
The bimetal element 22 has the function of compensating the delay with which the bimetal operating element 25 allows the plate and the locking member 27 to return to the rest position after an interruption of the flow of the above-mentioned current, for variations in ambient temperature.
In fact, as the ambient temperature increases, the bimetal element 25 tends to bend more markedly towards the plate 12. As a result of this more accentuated curvature, the time taken for the plate 12 to switch to the rest condition tends to increase. This effect is advantageously compensated by the bimetal element 22 which is formed and arranged in a manner such as to bend progressively downwards, as seen in Figures 4 and 5, as the ambient temperature increases. The increase in the curvature of the bimetal element 25 as the ambient temperature increases is thus counterbalanced.
The bimetal element 22 is advantageously disposed in a location remote from the heating element 26. It is thus sensitive substantially solely to the ambient temperature and is not in practice affected by the temperature of the heating element 26.
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 described and illustrated purely by way of non-limiting example, without thereby departing from the scope of the invention as defined in the appended claims.
CLAIMS 1. A door-locking device (1), particularly for an electric appliance, comprising:
support structure (2, 5), locking member (27) movable relative to the structure (2, 5) between a rest position and a working position, in which it permits and prevents opening of the door, respectively, and control means (12, 22, 25, 26) for controlling the position of the movable locking member (27), the control means comprising:
a metal plate (12) mounted in the structure (2, 5) and connected to the locking member (27), a heating element (26) the electrical resistance of which is variable in dependence on temperature, a bimetal operating element (25) which is arranged in thermal and electrical contact with the heating element (26) and can deform as a result of the passage of a current through the heating element (26) so as to bring about a movement of the plate (12) and of the associated locking member (27) from the rest position to the working position, a bimetal compensating element (22) cooperating with the bimetal operating element (25) and/or with the plate (12) in a manner such that, as the ambient temperature increases, the delay with which the bimetal operating element (25) allows the plate (12) and the locking member (27) to return to the rest position after the interruption of the flow of the current is reduced, and means for calibrating the value of the delay, the calibration means including a screw (23) for adjusting the position of the bimetal operating element (25), the device being characterized in that the bimetal operating element (25) has a first end cooperating with the adjustment screw (23) and a second end which is on the opposite side of the heating element (26) to the first end, and which is disposed adjacent the bimetal compensating element (22), the heating element (26) being disposed adjacent an intermediate portion of the bimetal operating member (25), between the adjustment screw (23) and the bimetal compensating element (22).