EP3307132B1

EP3307132B1 - System to control the closing of a door of a household appliance, in particular for a washing machine, such as a dishwasher

Info

Publication number: EP3307132B1
Application number: EP16739562.3A
Authority: EP
Inventors: Marco Becchio; Paolo Da Pont; Paolo Ravedati
Original assignee: Elbi International SpA
Current assignee: Elbi International SpA
Priority date: 2015-06-10
Filing date: 2016-06-09
Publication date: 2019-03-13
Anticipated expiration: 2036-06-09
Also published as: EP3307132A1; TR201904841T4; PL3307132T3; WO2016199056A1

Description

Technical field

The present invention relates to a system to control the closing of a door of a household appliance, in particular for a washing machine, such as a dishwasher.

Technological background

In the field of household appliances, solutions have to be found, in order to allow an inner chamber obtained in a casing of said appliances to be closed. Typically, though not exclusively, these solutions need to be found in order to close a washing chamber of a washing machine, such as a dishwasher.
In particular, a door is used, which is movable relative to the casing so as to open and close an access opening, through which the inner chamber is able to communicate with the outside of the household appliance.
Generally speaking, these systems comprise an engagement element, intended to be fitted on one between the casing and the door, and a retaining element, which is intended to be fitted on the other one between the door and the casing. The retaining element is intended to hold the engagement element in a releasable manner, so as to constrain the door to the casing, when the household appliance is being used.
Typically, the coupling between the engagement element and the retaining element takes place by means of the action of a user, who brings them closer by manually pushing the door against the casing, so as to obtain a complete closing. The uncoupling between the engagement element and the retaining element usually takes place by means of the action of the user, who can act upon suitable control interfaces (for example, provided on the front wall of the door or on the front or upper face of the casing), which activate inner mechanisms of the retaining element, which release the engagement element from the retaining element.
EP 1 733 675 A2 discloses a dishwasher comprising a plate connected to the door latch which can be extended across the gap between the top of the open door and the body of the machine. It can take up two positions, in one of which the gap is wider than the other. It is extended by a motor controlled by a proximity switch. An independent claim is included for a method for operating a dishwasher program, in which the door is opened to produce the narrow gap and then moved to the position with the wider gap, according to the frying of the dishes in the machine.
EP 2 193 740 A1 discloses a machine which has a drive unit, i.e. electric motor, controlled by a control unit. A linear moving unit is driven by the drive unit for positioning a door. A locking device, i.e. U-shaped clamp, is arranged at the door and stays in effective connection with the linear moving unit for positioning and locking the door. Another drive unit, i.e. hub magnet, is arranged on the moving unit. A control rod is fixed on the latter drive unit in a linear movable manner such that the control rod is moved in and out for locking or unlocking the moving unit in the locking device. It is also disclosed a method for opening a door of a cleaning machine.
EP 0 711 528 A1 discloses a a method and a device for carrying out the method for drying crockery in a dishwasher with a rinse container closeable by means of a door. By means of two or three successive different method steps, the drying is improved. The method steps include a drainage phase, a drying phase with blower or condenser and an automatic, partial opening of the door.

Summary of the invention

An object of the present invention is to provide a system to close a door of a household appliance, which is improved and, at the same time, can be produced in a simple and economic fashion.
Another object of the present invention is to provide a system to close a door of a household appliance, which can enable a pre-opening of the door in an automatic and safe manner. For example, this opening can be used to establish a communication between the inner chamber and the outside, through the access opening.
The idea of enabling a pre-opening is particularly advantageous - by way of example, though not exclusively - in washing machines, such as dishwashers, since it allows the steam generated during the washing cycle to be let out, thus contributing to the at least partial drying of the articles contained in the washing chamber.
According to the present invention, these and other objects are reached by means of a system according to the appended independent claim.
The appended claims are an integral part of the technical teaches provided in the description with reference to the present invention.

Brief description of the drawings

Further features and advantages of the present invention will be best understood upon perusal of the following detailed description, provided by way of example and is not limiting, with reference to the accompanying drawings, wherein:

figure 1 is a perspective view of a dishwasher comprising a system to control the closing of a door of a household appliance according to an explanatory embodiment of the present invention;
figure 2 is a partial perspective view of the system shown in figure 1, with some inner components visible;
figure 3 is an exploded perspective view of the system shown in the previous figures;
figures 4 and 5 are plan views, from above and from below, of an assembly of components of the system shown on figure 3;
figures 6 and 7 are views that are similar to the ones of figures 4 and 5, but with the assembly of components in a different operating configuration;
figure 8 is a partial perspective view of a system according to a further explanatory embodiment of the present invention.
figure 9 is an exploded perspective view of the system shown in figure 8;
figures 10 to 13 are views, in different perspectives, of operating details of the embodiment shown in figures 8 and 9; and
figures 14 to 18 are views, in different perspectives, of a variant of the operating details shown in figures 10 to 13.

Detailed description of the invention

With reference, in particular, to figure 1, W indicates, as a whole, an example of a washing machine, on which a first and, respectively, a second explanatory embodiment of a system 10, 110 according to the present invention is suited to be installed. The washing machine is a dishwasher W, though, as confirmed by the following description, system 10, 110 can also be applied to different washing machines or to other household appliances.
With reference, in particular, to figure 1, dishwasher W has a casing C, in which a washing tank or chamber WT is defined, for receiving the dishes to be washed. Washing tank WT has an access opening O, through which the same communicates with the outside and which, therefore, is able to house the dishes. Furthermore, dishwasher W has a door D, for opening and closing access opening O (figure 1).
Access opening O is arranged on a front face of casing C and, preferably, door D is pivotable relative to casing C, for example it is hinged along a horizontal axis that is arranged in the lower part of the latter. In the embodiments shown, access opening O is peripherally provided with a sealing gasket SG, so as to allow washing tank WT to be closed in a fluid-tight manner, when door D is in a completely closed condition.
In the embodiments shown, casing C has a lid L, which is advantageously arranged on the top of said casing C.
With reference, in particular, to figures 2 to 7, it is shown the first embodiment of system 10 according to the present invention.
The system is designed to allow door D of dishwasher W to be closed and comprises an engagement element 11, for being fitted in correspondence to casing C, for example on the cross bar CB arranged between casing C and lid L. Engagement element 11 is suited to be held in a releasable manner by a retaining element 16, for being fitted on door D, for example on its rear face facing access opening O.
Retaining element 16 is suited to hold engagement element 11 in a releasable manner, so as to constrain door D to casing C, when washing machine W is being used. In the embodiments shown, engagement element 11 is fitted on casing C and retaining element 16 is fitted on door D.
Engagement element 11 comprises a support element 12, which, in the embodiments shown, is fixed to casing C.
Engagement element 11 comprises, furthermore, a striker 14, for being coupled, in a releasable manner, to retaining element 16 and is movable, relative to support body 12, between a retracted position (figures 4 and 5) and an extracted position (figures 6 and 7).
In particular, the releasable connection occurring between striker 14 and retaining element 16 (which is fitted on door D) is such as to constrain door D to casing C, when dishwasher W is being used. In the embodiment shown, support body 12 is manufactured as an internally hollow case, for example comprising a pair of half-shells or cups 12a, 12b, which are coupled to one another - in particular in an interlocking manner - in the area of their periphery.
In the embodiment shown, half- shells 12a, 12b of support body 12 are manufactured with a plastic material, for example by means of injection molding. Preferably, support body 12 is screwed to casing C of household appliance W.
Advantageously, striker 14 is movable in such a way that it is guided by support body 12, in particular by inner walls thereof. Preferably, striker 14 can slide relative to support body 12. In particular, striker 14 is manufactured with a plastic material, for example by means of injection molding.
In the embodiment shown, striker 14 can translate between the retracted position and the extracted position.
In the embodiment shown, in the retracted position, striker 14 partially projects from support body 12 with a section, whereas, in the extracted position, striker 14 further projects with an additional section. Preferably, striker 14 projects through a slit (without reference number), which is obtained on the front face of casing C of dishwasher W, on which engagement element 11, as a whole, is mounted.
In particular, when striker 14 is coupled to retaining element 16 and moves to the extracted position, retaining element 16 moves away relative to support body 12, which consequently causes door D to be moved away, remaining at the same time constrained to casing C, though without being closed in a fluid-tight manner in the area of access opening O.
Retaining element 16 is substantially of a known type and has, for example, a containing body, which is provided with a slit and houses a coupling mechanism, which can be accessed by striker 14 through said slid, so as to allow the striker 14 itself to be coupled in a releasable manner to said coupling mechanism. Generally speaking, said coupling mechanism is pivotable between an operating position and a rest position and comprises a rotary member, whose movement is opposed by an elastic member and which is suited be engaged in a releasable manner by striker 14. In the operating position, the rotary member of the coupling mechanism holds striker 14 when door D is closed. On the other hand, in the rest position, the rotary member of the coupling mechanism releases striker 14 when the user operates a suitable release mechanism (not shown), for example including a push-button, a lever or a knob, which is arranged on door D.
Examples of a retaining element 16 of the type described above are widely known in the technical field and are described in detail in many prior art documents. In order to provide complete information, Italian patent applications no. TO97A1120 , TO2000A000383 and TO2001A01003 are mentioned, whose content is to be considered as included herein by mere way of example. Therefore, for sake of brevity, retaining element 16 will not be further disclosed in the description below.
When striker 14 is coupled to retaining element 16 and is arranged in its retracted position, and door D is in a complete closing condition, thus closing access opening O of washing chamber WT in a fluid-tight manner. On the other hand, when striker 14 is coupled to retaining element 16, but is arranged in its extracted position, door D assumes a pre-opening condition, thus being slightly spaced apart from access opening O of casing C, so as to establish a fluid communication between washing chamber WT and the outside of casing C. In particular, in the pre-opening condition, the steam contained in washing tank WT (which, for example, is generated during a washing cycle of dishwasher W) is allowed to flow out of dishwasher W, so as to allow the dishes contained therein to be at least partially dried.
In other words, when striker 14 is coupled to retaining element 16 and moves to the extracted position, it allows retaining element 16 to be moved away from support body 12, which consequently causes door D to be moved away from casing C. However, due to the coupling between striker 14 and retaining element 16, door D remains in any case constrained to casing C, though without closing access opening O in a fluid-tight manner.
With reference, in particular, to figures 4 and 5, engagement element 11 preferably comprises a stop assembly, which is indicated, as a whole, with number 18. In the embodiment shown, stop assembly 18 is fitted on support body 12; in particular, it is contained in the cavity defined the support body 12 itself.
Stop assembly 18 moves between:

a release condition (figure 6 and 7), in which it is suited to allow striker 14 to be released, thus allowing the latter to move from the retracted position to the extracted position, and
a locking condition (figures 4 and 5), in which it is suited to prevent striker 14 from moving from the retracted position to the extracted position.

Furthermore, engagement element 11 comprises moving means 20, in particular electrically operated ones, comprising a bidirectional motor 22 (for example, an AC one) and a transmission mechanism 24, which is operated by motor 22 and cooperating with striker 14. As explained more in detail below, motor 22 is designed to selectively deliver to transmission mechanism 24:

a pre-opening torque, oriented in a direction of rotation that allows striker 14 to be brought from the retracted position to the extracted position, and, respectively,
a return torque, oriented in an opposite direction of rotation that allows said striker 14 to be brought from the extracted position to the retracted position.

In the embodiment shown, moving means 20 are configured to:

control the movement of stop assembly 18 from the locking condition to the release condition, at the same time keeping striker 14 in the retracted position; and
control the movement of striker 14 from the retracted position to the extracted position, at the same time keeping stop assembly 18 in the release condition.

In the embodiment shown, moving means 20 are connected to a control device 21, for controlling moving means 20 according to predetermined use conditions.
In the embodiment shown, moving means 20 are mounted on support body 12, for example they are housed in the cavity defined therein.
In the embodiment shown, motor 22 and transmission mechanism 24 are located in support body 12, in particular in lower half-shell 12b.
The operation of motor 22 controls the movement of striker 14 and of stop element 18 through transmission mechanism 24.
As already mentioned above, motor 22 is a bidirectional one, which means that it can selectively deliver, as an output, a torque oriented in a direction of rotation and also in the opposite direction of rotation.
Preferably, as you can see in figure 2, transmission mechanism 24 comprises a gear 26 driven by motor 22 and cooperating with striker 14, in particular through a rack coupling (for example, by means of a linear toothing 27 carried by striker 14 and shown in figures 5 and 7). In particular, gear 26 simultaneously cooperates with stop assembly 18 in the ways that are described more in detail below.
In the embodiment shown in particular in figure 3, gear 26 comprises a plurality of toothed wheels 26a-d, which cooperate with one another and are supported in their rotation by support body 12, for example by pins (with no reference numbers) projecting from lower half-shell 12b.
Preferably, stop assembly 18 comprises a cam 28, which can be moved to operate motor 22, and a cam follower 30, for cooperating with cam 28 in an elastically countered manner (for example countered by an elastic member, such as a spring 32). For example, cam follower 30 is adapted to be subjected to a stress through a push of cam 28; alternatively, cam follower 30 can be subjected to a stress through a pull of cam 28. In particular, cam 28 can be adapted to stress cam follower 30 through push and pull, thus creating between the two of them a desmodromic cooperation or configuration.
More preferably, stop assembly 18 comprises, furthermore, a lock bolt 34, which is movable relative to support body 12 under the control of cam follower 30, in particular relative to lower half-shell 12b, and is designed to:

be coupled to striker 14, thus preventing it from moving, when stop assembly 18 is in the locking condition, and
be uncoupled from striker 14, thus allowing it to move under the control of moving means 20, when stop assembly 18 is in the release condition.

In the embodiment shown, the movement of cam 28 is controlled by moving means 20. In particular, the movement of cam 28 takes place through transmission mechanism 24. More in particular, the rotation of cam 28 is controlled by gear 26, for example cam 28 being carried by one of toothed wheels 26a-d. In the embodiment shown, cam 28 is carried by the toothed wheel indicated with 26c.
In the embodiment shown, cam follower 30 comprises a stem 30a, for cooperating with the profile of cam 28 (for example being pushed by the latter), and a head 30b, which is advantageously wider and is designed to cooperate, in turn, with lock bolt 34 (for example pushing the latter) so as to move stop assembly 18 to the locking condition and to the release condition.
Preferably, lock bolt 34 is movable so as to be coupled to a recess 36 made in striker 14 when stop assembly 18 is in the locking condition. Accordingly, when stop assembly 18 is in the release condition, lock bolt 34 is uncoupled from recess 36.
In the embodiment shown, lock bolt 34 is rotary relative to support body 12, in particular it being coupled to cam follower 30 with a clearance. Advantageously, though not necessarily, head 30b is coupled to lock bolt 34 with a clearance, so that the push of cam follower 30 causes an oscillation movement of lock bolt 34, in particular in such a way that it engages and disengages recess 36.
In particular, spring 32 is mounted so as to cooperate with cam follower 30 (for example pushing the latter), tending to hold it in the locking condition of stop assembly 18, i.e. in a coupling with striker 14, for example in recess 36. In other words, the action of spring 32 is used to counter the push exerted by cam 28 upon the cam follower 34.
Preferably, control device 21 comprises a sensor assembly, for detecting at least one between the position taken on by striker 14 and the condition assumed by stop assembly 18. More in particular, the sensor assembly is designed to detect at least one between:

the reaching of the two extreme positions (or limit stop positions) taken on by striker 14, in particular the retracted position and the extracted position, and
the reaching of the locking condition and of the release condition of stop assembly 18.

In the embodiment shown, the sensor assembly comprises at least one position sensor, for example a pair of limit stop switches 38a, 38b (such as micro-switches), and for detecting at least one between the position taken on by striker 14 and the condition assumed by stop assembly 18. Preferably, each limit stop switch 38a, 38b detects a respective parameter between the position taken on by striker 14 and the condition assumed by stop assembly 18.
In particular, control device 21 further comprises a control unit 40, for example obtained on a printed circuit board. In the embodiment shown, control unit 40 is adapted to control motor 22 based on the detections of the sensor assembly (in particular, of limit stop switches 38a, 38b), so as to allow striker 14 to move between the retracted position and the extracted position according to some predetermined criteria. Let's assume, for example, that, during the movement of striker 14 from the retracted position to the extracted position, there is an external obstacle to door D, which forcedly stops the movement of striker 14. In this case, device 21 can be programmed in such a way that the limit stop switches 38a, 38b provide detections that cause control unit 40 to have motor 22 reach its maximum torque and invert its direction of rotation. In this way, striker 14 returns to the retracted position, thus preventing moving means 20 - in particular transmission mechanism 24 - from being subjected to abnormal mechanical stresses.
As described more in detail below, in the embodiment shown, moving means 20 are adapted to create an intermittent rotation motion to move striker 14 between the retracted position and the extracted position. Preferably, striker 14 remains still in its position (in particular, in the retracted position) when stop mechanism 18 moves between the release condition and the locking condition.
In the embodiment shown, transmission mechanism 24 has a main toothed wheel 26c, which has an interruption 42 in its outer toothing, so that said main toothed wheel 26c is not capable of meshing with the following toothed wheel 26d. In other words, along the section of the toothing showing interruption 42, main toothed wheel 26c is not capable of provoking the rotation of the toothing of following toothed wheel 26d and, therefore, striker 14 is not caused to move between the retracted position and the extracted position (thus remaining still in its position).
Therefore, transmission mechanism 24 operates like a Geneva stop wheel or, more in general, similarly to further kinematic mechanisms that can provide an intermittent rotation motion for the control of the movement of striker 14.
With reference to the embodiment shown, by way of example, in figures from 4 to 7, we will now describe - in a non limiting manner - the operation of engagement element 11. The aforesaid figures show some components of engagement element 11, such as striker 14, stop assembly 18 and transmission mechanism 24. These components are shown in a plan view from below (figures 4 and 6) and, respectively, in a plan view from above (figures 5 and 7) for an observer watching engagement element 11 shown in figure 2.
In figures 4 and 5, striker 14 is shown in the retracted position and stop assembly 18 is in the locking condition. In this configuration, in use, it is desired to do is to release striker 14 from the connection with stop assembly 18, in order to then move striker 14 from the retracted position to the extracted position in a following step.
In this case, control device 21 causes a rotation of gear 26, so that main toothed wheel 26c is driven in a rotation R1 in a clockwise direction for those observing figure 4. During this rotation, cam 28, which rotates together with main toothed wheel 26c, has its increasing bending radius and cooperates with cam follower 30 (for example pushing it in the direction of arrow F1). In this way, lock bolt 34 is oscillated in such a way that it gets uncoupled from recess 36 carried by striker 14, thus causing stop assembly 18 to assume the release condition.
At the same time, main toothed wheel 26c has its interruption 42 facing the toothing or pinion of the following toothed wheel 26d. Therefore, in this step, main toothed wheel 26c is not capable of transmitting any rotation to following toothed wheel 26d. Hence, gear 26 cannot control the movement of striker 14 from its retracted position, where the latter remains still.
In figures 6 and 7, striker 14 is shown in the extracted position and stop assembly 18 is in the release condition. In the configuration shown therein, the movement of striker 14 from the retracted position to the extracted position has already occurred.
Starting from the position shown in figures 4 and 5, in order to reach the configuration shown in figures 6 and 7, control device 21 causes a further rotation of gear 24, so that the main toothed wheel 26c is driven in a further rotation R2 in a clockwise direction for those observing figure 6. During this rotation, cam 28, which rotates together with main toothed wheel 26c, has its constant bending radius and keeps cam follower 30 still in its position. In this way, lock bolt 34 remains uncoupled from recess 36 carried by striker 14, in the release condition of stop assembly 18.
At the same time, main toothed wheel 26c has its toothing facing and meshing with the toothing or pinion of the following toothed wheel 26d. Therefore, in this step, main toothed wheel 26c is capable of transmitting a rotation to the following toothed wheel 26d. Hence, gear 26 controls the movement, in the direction of arrow F2, of striker 14 from its retracted position to its extracted position, thus bringing it to the arrangement shown in figures 6 and 7.
To sum up, in this last configuration, stop assembly 18 is in the release condition, whereas striker 14 is in the extracted position. In the embodiment shown, limit stop switches 38a, 38b are adapted to detect the condition of stop assembly 18 and position of the striker 14, so that the rotation of motor 20 is inverted by control device 21 in case striker 14 needs to be moved back to the retracted position. To this regard, in order to move striker 14 back to the arrangement shown in figures 4 and 5, the operating steps described herein must be carried out in reverse order and with opposite directions of movement compared to the ones described above.
Figures 8 to 13 show a system 110, manufactured according to a second embodiment of the present invention.
Said system 110 is substantially similar to system 10 manufactured according to the first embodiment of the present invention. Therefore, details and elements that are similar to those of the embodiment described above or fulfill a similar function are associated with the same alphanumeric references. For the sake of brevity, the description of these details and elements will not be repeated below, but reference is made to what was previously explained in the description of the first embodiment.
For example, the second embodiment of system 110 differs from the first embodiment of system 10 because stop assembly 18 is not provided. This solution ensures a quicker opening and closing operation compared to the first embodiment of system 10. To this regard, we would like to highlight the simpler configuration of the transmission mechanism indicated with 124 (in particular as far as gear 126 is concerned), which is not designed any longer to deliver an intermittent rotation motion to be transferred to striker 14.
In this second embodiment, motor 22 (for example a CC motor) is coupled to transmission mechanism 124 through a worm screw (with no reference number).
In the embodiment shown, on the other hand, transmission mechanism 124 being provided with a safety clutch 142, which is capable of uncoupling it from motor 22 in case there are abnormal torques running through gear 26. In particular, transmission mechanism 124 comprises a main toothed wheel 124b, on which there is mounted safety clutch 142, which disconnects said main toothed wheel 126b from the following toothed wheel 126c (which, in turn, meshes with a linear toothing shown by striker 14, thus creating a rack coupling).
Safety clutch 142 can be designed, by mere way of example, with an unadjustable disengagement torque (figures 10-13) or with an adjustable disengagement torque (figures 14-18) .
In the version with an unadjustable disengagement torque, the safety clutch comprises a meshing system for at least one pin 144 with at least one respective striker spring 146, for cooperating with the pin 144, engaging it, thus causing main toothed wheel 126b to be constrained, in its rotation, to the following toothed wheel 126c. In the embodiment shown, there are provided a pair of pins 144 and a respective pair of striker springs 146.
When the torque transmitted through the safety clutch 142 exceeds a predetermined threshold value, pins 144 are subjected to a stress that is such as to overcome the action of the respective striker springs 146, thus disconnecting the main toothed wheel 126b from the following toothed wheel 126c. In this way, the kinematic connection between the main toothed wheel 126b and the following toothed wheel 126c becomes "idle", thus making them independent in their rotation for transmitted torques that are too high.
In the version with an adjustable disengagement torque, the safety clutch comprises a plate 244 cooperating with a spring 246, which, in turn, is pre-loaded (for example through compression) and can be moved relative to plate 244 by a dowel 248, thus constraining, in their rotation, main toothed wheel 126b and the following toothed wheel 126c.
When the torque transmitted through safety clutch 242 exceeds a threshold value, which can be determined by positioning dowel 248 and compressing spring 146, plate 244 can be subjected to a stress that is such as to cause it to be lifted and disengaged, thus overcoming the action of striker spring 246. In this way, the kinematic connection between main toothed wheel 126b and the following toothed wheel 126c becomes "idle", thus making them independent in their rotation for transmitted torques that are too high.
The use of safety clutch 142, 242 ensures a safe operation of engagement element 11, since the generation of excessively high torques typically corresponds to an operating fault of the system, which can jeopardize the operation thereof. Therefore, safety clutch 142, 242 makes sure that there is a proper disengagement when torque predefined values are reached or exceeded, which are predetermined based on designing and building needs.
Naturally, the principle of the present invention being set forth, embodiments and implementation details can be widely changed relative to what described above and shown in the drawings as a mere way of non-limiting example, without in this way going beyond the scope of invention provided by the accompanying claims.
The technical features characterizing the different variants and embodiments described and illustrated above can freely be exchanged or combined with one another, provided that they are compatible. To this regard, as a person skilled in the art can clearly understand, in the first embodiment shown in figures 1-7, the transmission mechanism indicated with 24 can integrate a safety clutch so as to fulfill the functions described above, which, for the sake of brevity, will not be further discussed herein. For example, said safety clutch can be the one indicated with 142 in figures 10-13 or the one indicated with 242 in figures 14-18.

Claims

System (10; 110) for controlling the closing of a door of a household appliance, in particular for a washing machine, such as a dishwasher; said door (D) being designed to close an inner chamber (WT), which is obtained in a casing (C) of said household appliance (W) and communicates with the outside through an access opening (O); said system (10; 110) comprising an engagement element (11), to be fitted on one between said casing (C) and said door (D) and to be held, in a releasable manner, by a retaining element (16), for being fitted on the other one between said door (D) and said casing (C), so as to constrain said door (D) to said casing (C), when using said household appliance (W) ;
said engagement element (11) comprises:
- a support body (12), for being fitted on one between said casing (C) and said door (D);

- a striker (14), for being coupled, in a releasable manner, to said retaining element (16), and is mounted so as to move, relative to said support body (12), between a retracted position and an extracted position; when said striker (14) is coupled to said retaining element (16) and takes on said retracted position and, respectively, said extracted position, said door (D) being suited to end up in a complete closing condition, thus closing said access opening (O) in a fluid-tight manner, and, respectively, in a pre-opening condition, thus being arranged at a distance from said access opening (O), so as to establish a fluid communication between said inner chamber (WT) and the outside of said casing (C);

- moving means (20) comprising a bidirectional motor (22) and a transmission mechanism (24; 124), operated by said motor (22) and cooperates with said striker (14); said motor (22) for selectively delivering to said transmission mechanism (24; 124)
a pre-opening torque, which is oriented in a direction of rotation (R1) that allows said striker (14) to be brought from the retracted position to the extracted position, and, respectively,

a return torque, which is oriented in an opposite direction of rotation that allows said striker (14) to be brought from the extracted position to the retracted position;

characterized in that said engagement element (11) comprises a stop assembly (18), tending to move between:
- a release condition, in which said stop assembly (18) is capable to allow said striker (14) to be released, thus allowing said striker (14) to move from said retracted position to said extracted position under the control of said transmission mechanism (24), and

- a locking condition, in which said stop assembly (18) is for preventing said striker (14) from moving from said retracted position to said extracted position; and
in that said transmission mechanism (24) cooperates with said stop assembly (18) and said striker (14) and is adapted to:
- control the movement of the stop assembly (18) from the locking condition to the release condition, at the same time keeping the striker (14) in the retracted position; and

- control the movement of the striker (14) from the retracted position to the extracted position, and at the same time keeping said stop assembly (18) in the release condition.
System (10; 110) according to claim 1, wherein said transmission mechanism (24; 124) comprises a gear (26; 126) .
System (10) according to any of the previous claims, wherein said stop assembly (18) comprises:
- a cam (28), operated by said transmission mechanism (24),

- a cam follower (30), for cooperating with the cam (28) in an elastically countered manner and for permitting and, respectively, avoiding the movement of the striker (14), when said stop assembly (18) is in the release condition and, respectively, in the locking condition.
System (10) according to claim 3, wherein said stop assembly (18) comprises, furthermore, a mobile lock bolt (34), which is controlled by said cam follower (30) so as to:
- be coupled to the striker (14), thus preventing it from moving, when the stop assembly (18) is in the locking condition, and

- be uncoupled from the striker (14), thus allowing it to move, when the stop assembly (18) is in the release condition.
System (10) according to claim 3 or 4, wherein said cam (28) is carried by said transmission mechanism (24).
System (10) according to any of the previous claims, wherein said transmission mechanism (24) is capable of generating an intermittent motion to move said striker (14) between the retracted position and the retracted position, wherein said striker (14) remains still in its position when the stop mechanism (18) moves between the release condition and the locking condition.
System (110) according to any of the previous claims, wherein the transmission mechanism (124) comprises a safety clutch (142, 242), for stopping torque transmission through said transmission mechanism (124), when said torque reaches a threshold value that is predetermined or can be predetermined.
System (10; 110) according to any of the previous claims, wherein said engagement element (11) comprises a control device (21), capable of controlling the moving means (20) according to predetermined criteria.
System (10; 110) according to claim 8, wherein said control device (21) comprises, furthermore, a sensor assembly (38a, 38b), configured to detect at least one between the following parameters:
- the position taken on by the striker (14), and

- the condition taken on by the stop assembly (18).
Household appliance (W) comprising:
- a casing (C) having an inner chamber (WT), which has an access opening (O), through which said inner chamber (WT) can communicate with the outside of said casing (C);

- a door (D), for closing said access opening (O); and

- a device (10; 110) according to any of the previous claims.