EP4689332A1

EP4689332A1 - Opening device for a wing or a drawer

Info

Publication number: EP4689332A1
Application number: EP24720566.9A
Authority: EP
Inventors: Bostjan UDOVIC
Original assignee: Car Srl; Metalimpex d o o
Current assignee: Car Srl; Metalimpex d o o
Priority date: 2023-03-27
Filing date: 2024-03-25
Publication date: 2026-02-11
Also published as: WO2024201270A1

Abstract

An opening device for a wing or drawer, comprising a containment body (2), a piston (3) slidingly inserted into the containment body (2), retaining means (4) associated with the piston (3) and the containment body (2), and a movement mechanism (5) operatively interposed between the containment body (2) and the piston (3) and configured to move the piston (3) between a first axial position in which the piston (3) is predominantly extracted from the containment body (2), and a second axial position, in which the piston (3) is predominantly housed within the containment body (2). The movement mechanism (5) comprises an elastic element (6) and a switching unit (7) configured to cooperate with the elastic element (6) to position the piston (3) in the first or second axial position by passing through a transition position, wherein the switching unit (7) comprises a retention body (11) and a guide element (12) constrained to said bottom portion (2c) of the containment body (2) and provided with a guide path (13) selectively engageable by the terminal hook (11b) of the retention body (11). The guide path (13) comprises a proximal zone (15) at the bottom (2c) of the containment body (2) provided with at least one axial gap (15a, 15b) placed at least in part through the bottom portion (2c) in order to temporarily accommodate the terminal hook (11b) when the piston (3) is in the transition position, at least with the first (9) and second component (10) in the extended configuration.

Description

OPENING DEVICE FOR A WING OR A DRAWER

The present invention relates to an opening device for a wing or a drawer.

In the field of manufacturing furniture, and more generally furnishing or architectural elements, the use of devices adapted to facilitate the opening of wings or drawers by means of a simple pressure exerted by the user on the external panel is known.

Such systems, known in the market as push-open or push-to-open, have become increasingly important in the furniture market, as they perfectly complement the trends of minimising and simplifying visible surfaces, which today are mostly devoid of handles or grasping portions.

In fact, such a solution makes it possible to give the edge of the wing or drawer itself the role of a handle by means of a partial extraction thereof, generally operated by pressure devices provided with a piston or pusher.

There are numerous examples in the prior art of push-open devices which have the most varied movement mechanisms.

One of the most commonly used solutions involves exploiting the collaboration between an elastic element, typically a coil spring, and a hookcardioid assembly, in which the hook alternately engages and disengages from the cardioid guide with each axial thrust, of sufficient magnitude, undergone by the piston.

Usually, as shown in the prior art documents EP2951373 and IT102015000040440, such devices are provided with a hook pivoted to the bottom of a cylindrical containment body which is selectively engageable with a slider, axially constrained to the piston and on which a cardioidshaped guide path is made.

The cardioid shape allows the hook to enter the path along an inlet portion, placing it stably in a cavity which allows the hook to retain the piston in a retracted position.

Following a thrust capable of overcoming the elastic resistance of the spring, the hook enters an outlet portion of the guide path which allows the piston to disengage, thus allowing it to return to the maximum extraction position.

It should be noted, however, that in most of the devices currently on the market, the installer is provided with a possibility to adjust both the stroke and the axial load to which the piston is subjected.

In particular, the most recent embodiments involve the presence of a threaded axial coupling between the piston and the slider which carries the cardioid guide, which allows the point of contact between the spring and the slider to be retracted, effectively increasing the resistance opposed by the piston and at the same time reducing the stroke thereof between the maximum extraction position and the retracted one.

This makes it possible, on the one hand, to adapt the spring preload to the weight of the wing to be opened and, on the other hand, to compensate for differences in height between the wing and its stopper.

Disadvantageously, however, such a functionality brings certain drawbacks therewith which the prior art has not yet managed to overcome.

For example, the known devices have a guide profile which, being obtained on the movable slider, has considerable dimensional constraints, which are not always compatible with the need to provide full operability of the pushopen movement in all the relative positions which the piston can assume with respect to the slider.

In fact, it is not uncommon that a perfect functionality in the maximum extension position (i.e., maximum distance between piston and slider) is not matched by the same level of efficiency in the minimum extension position, or vice versa.

Therefore, the aim of the present invention is to provide an opening device for a wing or a drawer with increased operating efficiency, which is reliable in any configuration (extended or contracted) of the piston.

Said aims are achieved by an opening device for a wing or a drawer having the characteristics of one or more of the following claims.

In particular, said aims are achieved by an opening device for a wing or a drawer which has a containment body, a piston and a movement mechanism.

Preferably, the containment body develops at least in part along its own longitudinal axis between a bottom portion and an end opening.

Preferably, the piston is slidingly inserted into said containment body and provided with a free end projecting outward from said end opening.

Preferably, retaining means are associated with said piston and said containment body.

Preferably, the retaining means are configured to prevent the piston from escaping from the containment body through said end opening.

Preferably, the movement mechanism is operatively interposed between the containment body and the piston.

Preferably, the movement mechanism is configured to shift the piston between a first axial position, in which the piston is predominantly extracted from the containment body, and a second axial position, in which the piston is predominantly housed within the containment body.

Preferably, the movement mechanism comprises an elastic element and a switching unit.

Preferably, the elastic element is operatively interposed between said piston and said bottom portion of the containment body.

Preferably, the elastic element is configured to generate at least one axial thrust on said piston, oriented so as to push the piston out of said end opening of the containment body.

Preferably, the switching unit is configured to collaborate with said elastic element to position the piston in the first or second axial position by passing through a transition position, of maximum retraction of the piston within the containment body.

Preferably, the piston comprises a first component and a second component arranged in axial succession, with said elastic element acting with thrust on the first component and the retaining means associated with the second component. Preferably, the first and second components are axially constrained in an adjustable manner between a compact configuration and an extended configuration to vary a preload of said elastic element.

Preferably, the switching unit comprises a retention body and a guide element.

Preferably, the retention body develops starting from said first component of the piston and away from said end opening of the containment body as far as a terminal hook.

Preferably, the guide element is constrained to said bottom portion of the containment body and provided with a guide path selectively engageable by the terminal hook of the retention body.

Preferably, the guide path comprises a distal zone which is distal from the bottom portion and a proximal zone which is proximal to the bottom portion. Preferably, the distal zone comprises a lead-in section that is open away from the bottom portion so as to facilitate coupling and uncoupling of the terminal hook of the retention body with the guide path.

Preferably, the proximal zone comprises at least one axial gap placed at least in part through the bottom portion in order to temporarily accommodate the terminal hook when the piston is in the transition position, at least with the first and second component in the extended configuration.

Advantageously, this allows the arrangement of a guide path provided with axial gaps capable of compensating for the different stroke of the terminal hook in the different piston configurations, thus allowing to ensure maximum efficiency of the device, without negatively impacting either the size or complexity thereof.

These and other characteristics, together with their relative advantages, will be become clearer from the following non-limiting exemplary description of a preferred, and therefore non-exclusive, embodiment of an opening device for a wing or a drawer of a piece of furniture having the characteristics illustrated in the attached drawing tables, in which:

- figure 1 shows a front perspective view of an opening device for a wing or a drawer of a piece of furniture according to the present invention;

- figure 2 shows a longitudinal section of the opening device of figure 1 ;

- figure 3 shows an exploded view of the device of figure 1 ;

- figures 4 and 5 schematically show the operation of the movement mechanism of the opening device of figure 1 ;

- figures 6a-6d show a detail of the section of figure 2 in different operating configurations;

- figure 7 schematically shows a piece of furniture comprising the opening device for a wing or a drawer according to the present invention.

With reference to the appended figures, the number 1 denotes an opening device for a wing or a drawer of a piece of furniture according to the present invention.

An opening device is thus understood as a device whose actuation results in the opening, even partially, of a closing element 101 (wing or drawer) with which it is operatively associated, making it possible for a user to grasp it. Therefore, the opening device 1 is preferably couplable with a frame 102 of a piece of furniture 100 or other furnishing or architectural element, in a position such that it faces and interacts with an unexposed face of the closing element 101.

In the preferred embodiment, the opening device 1 is insertable in a cavity made in a sidewall of the frame 101 but could alternatively be anchored thereto in another manner.

For example, the opening device 1 could be constrained to the furniture by means of a bracket attached to the sidewall of the furniture or by means of some other known system.

Preferably, the device 1 comprises a containment body 2 within which a piston 3 slides.

The containment body 2 develops at least in part along its own longitudinal axis 'A' between two ends.

At one end there is a bottom portion (or wall) 2c, while at the other end there is an end opening 2a. More precisely, therefore, the containment body 2 comprises at least one tubular portion 2b developing along the longitudinal axis from a bottom wall 2c to said end opening 2a.

At the end opening 2a there is preferably a stopper shoulder 2d, developing in a radially external direction with respect to an external surface of the containment body 2; such a stopper shoulder 2d has the function of stopping the sliding of the containment body 2 inside the wing (or bracket), guaranteeing the alignment between the end opening 2a and the sidewall of the wing.

The containment body 2 is preferably made of plastic, but in some alternative embodiments it could be made of other materials (e.g., metal). As mentioned, a piston 3 is sliding within the containment body 2.

Such a piston 3 is movable along the longitudinal axis 'A' and is provided with at least one free end 3a which, in use, projects outside said end opening 2a of the containment body 2.

Preferably, therefore, the piston 3 develops between a first end, housed inside the containment body 2 (in particular at the tubular portion 2b) and a second end, which in at least one operating condition of the opening device 1 is arranged outside the end opening 2a of the containment body 2.

Such a second end corresponds to the free end 3a of the piston 3.

It should be noted that the expression 'free end' is not intended in the present text to mean that the end is free of all constraints with other elements, but only that such an end is free from direct interaction with movement systems inside the containment body 2.

In the preferred embodiment, the containment body 2 and the piston 3 have a cross-section (at the longitudinal axis A) of circular shape; however, other shapes could be used without deviating from the spirit of the present invention.

It should be noted that, preferably, retaining means 4 associated with said piston 3 and said containment body 2 and configured to prevent he piston 3 from escaping from said containment body 2 through said end opening 2a are provided.

Preferably, the retaining means 4 are defined by an active stopper or catch on the piston 3 when a maximum extraction position is reached.

In the preferred embodiment, the retaining means 4 comprise a radial shoulder 4a of the piston 3, placed near the first end, configured to abut a radially internal projection 4b (preferably annular) of the containment body 2. Such a radially internal projection 4b is preferably made at the end opening 2a.

Preferably, the opening device 1 comprises a movement mechanism 5 operatively interposed between the containment body 2 and the piston 3. Such a movement mechanism 5 is configured to shift the piston 3 between a first axial position, in which piston 3 is predominantly extracted from the containment body 2, and a second axial position, in which the piston 3 is predominantly housed within the containment body 2.

In the first axial position, the piston 3 is sufficiently extracted to move the closing element 101 away from the frame 102 by a space such as to allow it to be gripped by the user.

In this regard, preferably the retaining means 4 are configured to come into action when the piston 3 is in the first axial position.

In other words, the radial shoulder 4a and the radially internal projection 4b are dimensioned to come into contact when the piston 3 is in the first axial position.

Preferably, the movement mechanism 5 is configured to generate at least one axial thrust on said piston 3 oriented so as to push the piston 3 out of said end opening 2a of the containment body 2.

The movement mechanism 5 is thus configured to exert at least one thrust on the piston 3, preferably on its first end, oriented parallel to the longitudinal axis 'A' (hence axial thrust) and exiting from the end opening 2a of the containment body 2.

In this regard, preferably the first and second axial positions are respectively a retracted and an extracted position of the piston 3, where 'retracted' and 'extracted' are relative definitions and mutually referring to each other.

Therefore, the first axial position is a position in which the piston 3 is more extracted from the containment body with respect to the second axial position, and vice versa.

Advantageously, in the use condition a user only needs to apply an adequate pressure on the zone of the closing element 101 proximal to the opening device 1 to bring the piston from the first to the second axial position or vice versa.

In the preferred embodiment, the movement mechanism 5 is configured to sequentially arrange the piston 3 in the first and second axial positions in response to a corresponding sequence of axial pressures exerted on the free end 3a, with opposite direction and greater force with respect to said axial thrust, such as to allow the piston 3 to reach a transition (axial) position, more retracted with respect to the first and second axial positions.

In other words, each pressure exerted on the free end 3a with sufficient force and duration to bring the piston 3 into the transition position corresponds to an effective shift of the piston 3 from the first to the second position, or vice versa.

Therefore, the movement mechanism 5 is configured so that, following the aforementioned pressure action on the free end 3a, the piston 3 retracts from the first or second axial position to the transition position and then returns to the second or first axial position, respectively.

Preferably, the movement mechanism comprises an elastic element 6 and a switching unit 7.

The elastic element 6 is operatively interposed between the piston 3 and the bottom portion 2c of the containment body 2 and is configured to generate at least one axial thrust on said piston 3, oriented so as to push the piston 3 out of said end opening 2a of the containment body 2.

Preferably, the elastic element 6 is defined by a coil spring 8 housed in the containment body 2 and developing along the longitudinal axis 'A' between a first end 8a and a second end 8b. The first end 8a abuts the bottom portion 2c of the containment body 2, preferably in a position which, independent of the position of the piston 3, remains unaffected.

The second end 8b instead preferably abuts (with thrust) on the piston 3, in particular on the first end thereof; preferably, therefore, as the axial position of the piston 3 varies, the position of the second end 8b of the coil spring 8 (or, more generally, of the elastic element 6) within the containment body 2 varies.

In accordance with this, the load (i.e., the thrust action) generated by the elastic element 6 itself on the piston 3 is also varied.

In order to allow an adjustment of such a load, preferably, the piston 3 comprises a first component 9 (or slider) and a second component 10 (or rod) arranged in axial succession within the containment body 2 and constrained to each other.

The elastic element 6 acts with thrust on the first component 9, while the retaining means 4 are associated with the second component 10.

The first 9 and the second component 10 of piston 3 are axially constrained to each other in an adjustable manner between a compact configuration and an extended configuration, so as to vary a preload of said elastic element 6.

When the first 9 and the second component 10 are in the compact configuration and the piston 3 is in the first axial position (extracted), the retaining means 4 come into action to prevent the second component 10 from completely slipping out of the containment body 2, while the first component 9 remains housed in the containment body 2 itself adjacent to the second component 10, with the elastic element 6 in its maximum extension configuration (for application).

On the contrary, when the first 9 and the second component 10 are in the extended configuration and the piston 3 is in the first axial position (extracted), the retaining means 4 come into action to prevent the second component 10 from completely slipping out of the containment body 2, while the first component 9 remains housed in the containment body 2 itself at a distance from the second component 10 which causes a compression of the elastic element 6 with respect to its maximum extension configuration.

This advantageously allows to vary both the position of the free end 3a of the piston 3 in the second axial position and the preload of the elastic element 6, i.e., the level of thrust required to activate movement, in the first axial position.

In the preferred embodiment, the first 9 and the second component 10 are constrained by means of a threaded coupling between an external thread 9e of the first component 9 and an internal thread of the second component 10.

Advantageously, it is thereby possible to adjust the relative position between the two components continuously and precisely.

Preferably, in each case, the first component 9 comprises one or more locking elements 9a configured to prevent complete decoupling with the second component 10; in the embodiment, such locking elements 9a are defined by a pair of radial teeth which grasp to the internal surface of the second component 10 (in particular to the projections of the thread) to prevent the complete separation of the two components.

This advantageously prevents the second component (or rod) 10 from moving freely in the containment body with the first component in the first axial position of the piston 3 and, at the same time, ensures that there is always a sufficient coupling area between the two components, which is useful to avoid problems with jamming.

Returning to the shape of the movement mechanism 5, as mentioned above, it comprises a switching unit 7 which cooperates with the elastic element 6 to alternately arrange the piston 3 in the first or second axial position.

More precisely, such a switching unit 7 is configured to collaborate with said elastic element 6 to position the piston 3 in the first or second axial position by passing through the transition position, corresponding as discussed above to a maximum retraction position of the piston 3 within the containment body 2.

Preferably, the switching unit 7 comprises a retention body 1 1 which is selectively engageable with a guide element 12.

The retention body 11 develops starting from the piston 3, in particular from the first component 9 of the piston 3, and is oriented approaching the bottom portion 2c (i.e., away from said end opening 2a) of the containment body 2. The guide element 2 of switching unit 7 is instead constrained to the bottom portion 2c of the containment body 2.

More precisely, the retention body 11 develops along the main axis 'A' between a constrained portion 1 1 a, as mentioned connected to the piston 3, and a free portion, defined by a terminal hook 1 1 b.

Preferably, the retention body 1 1 is pivoted to the piston 3 at the constrained portion 1 1 thereof, with the possibility of oscillating with respect to said piston 3 within a predetermined angular range about a pivot axis 'B' orthogonal to said longitudinal axis 'A'.

In the preferred embodiment, the retention body 1 1 is defined by a metal wire folded at the ends, one defining the pivot axis and engaged in the piston 3, in particular in the first component 9, and the other defining the terminal hook 1 1 b.

In this regard, therefore, the first component 9 comprises a retaining portion 9b and an adjustment portion 9c arranged in axial succession with each other and between which is interposed an annular thrust portion 9d.

In other words, the retaining portion 9b is oriented towards the bottom portion 2c of the containment body 2 and comprises a receiving element of the constrained portion 1 1 a of the retention body 1 1 .

Adjacent to the retaining portion 9b is the annular thrust portion 9d; such a portion defines an annular shoulder on which the second end 8b of the coil spring 8 (i.e., the elastic element 6) abuts (and with thrust).

The coil spring 8 is therefore fitted around the retaining portion 9b and abuts, with the second end 8b thereof, the annular thrust portion 9d. Starting from the annular thrust portion 9d, moving away from the retaining portion 9b, the adjustment portion 9c then develops.

Such an adjustment portion 9c is preferably defined by a threaded shaft, which can be coupled by screwing with the second component 10 of the piston 3; the locking elements 9a are preferably made on the adjustment portion 9c.

In order to allow the adjustment and alignment of the movement mechanism, the annular thrust portion 9d is preferably provided with a guide notch 22 slidingly engaged in a longitudinal groove 21 made on an internal surface of the tubular portion 2c of the containment body 2.

Returning to the guide element 12, it is preferably provided with a guide path 13 which is selectively engageable by the terminal hook 1 1 b of the retention body 1 1 to determine the location of the piston 3 in the first or second axial position.

During the movement of the piston 3 between the first and second axial positions, the terminal hook 1 1 b engages with the guide path 13, following the profile thereof, preferably thanks to its ability to tilt.

The guide path 13 is preferably shaped like a cardioid, i.e., a path which resembles the shape of a heart due to the presence of two divergent sections starting from a common inlet area which come together to form a sort of cusp.

The guide path 13 preferably lies in a plane substantially orthogonal to the pivot axis of the retention body 1 1 .

In more detail, the guide path 13 preferably comprises a distal zone 14 which is distal from the bottom portion 2c of containment body 2 and a proximal zone 15 which is proximal to the bottom portion 2c.

The distal zone 14, clearly illustrated in figures 4 and 5, comprises a lead- in section 14a which is open away from the bottom portion 2c so as to facilitate coupling and uncoupling of the terminal hook 11 c of the retention body 1 1 with the guide path 13.

The proximal zone 15 instead comprises at least one axial gap 15a, 15b placed at least in part through the bottom portion 2c of the containment body 2.

It should be noted that the expression 'axial gap' is intended in the present text to define a kind of extra-stroke which allows the terminal hook 1 1 c to be accommodated when the piston 3 is in the transition position, ensuring the precise operation of the device in all the extended to retracted configurations of the first 9 and second component 10.

Preferably, the axial gap 15a, 15b is oriented parallel to the longitudinal axis 'A'.

The axial gap 15a, 15b is therefore configured to temporarily accommodate the terminal hook 1 1 c when the piston 3 is in the transition position, at least with the first 9 and the second component 10 in the extended configuration. Preferably, the axial gap 15a, 15b is defined by at least one through notch 19 made in the bottom portion 2c of the containment body 2.

Advantageously, the presence of the axial gap 15a, 15b provides the guide path 13 with a tolerance zone which allows optimised operation under all operating conditions assumed by the first 9 and second component 10. This allows the size of device 1 to be kept compact, without losing effectiveness and efficiency.

Preferably, the guide path 13 comprises an inlet portion 13a and an outlet portion 13b along which the terminal hook 11 b slides in the translation of the piston 3 from the first axial position to the transition position and from the transition position to the first axial position.

The inlet portion 13a therefore develops from the lead-in section 14a to the first axial gap 15a and, in use, is crossed by the terminal hook 1 1 b in a retraction movement of the piston 3 from the first axial position to the transition position.

The outlet portion 13b develops from the second axial gap 15b to the lead- in section 14a and, in use, is crossed by the terminal hook 1 1 b in an extraction movement of the piston 3 from the transition position to the first axial position. Preferably, the guide path 13 further comprises a retaining portion 13c operatively interposed between the inlet portion 13a and the outlet portion 13b.

The retaining portion 13c develops between the first 15a and the second axial gap 15b passing through a cavity zone 13d adapted to stably accommodate the terminal hook 1 1 b in the second axial position of the piston 3.

In other words, the retaining portion 13c preferably develops along a 'V- shaped path, with apex defined by said cavity zone 13d and oriented in the direction of the end opening 2a of the containment body.

It should be noted that the guide path 13 preferably develops from the bottom portion 2c in the direction of the end opening 2a, occupying a narrow radial footprint in order to determine, on the bottom portion 2c, an annular thrust zone homologous to that of the annular thrust zone 9c of the first component 9 of the piston 3.

The first end 8a of the coil spring 8 (i.e., the elastic element 6) acts on such an annular thrust zone.

Preferably, it should be noted that the bottom portion 2c is defined by a removable plug 16 which is couplable to the tubular portion 2b of the containment body 2.

The plug 16 preferably comprises a base portion 17 and an operative portion 18.

The base portion 17 is removably connected to the tubular portion 2b of the containment body 2.

It should be noted that, preferably, the base portion 17 comprises the through notch 19 described above and defining one of said axial gaps 15a, 15b.

More preferably, the base portion 17 comprises two half-parts 17a which are spaced apart from each other and elastically movable in reciprocal approach and distancing.

Preferably, the two half-parts 17a are separated from each other by the through notch 19 mentioned above, thus they are separated by one of said axial gaps 15a, 15b (preferably the first axial gap 15a).

In the preferred embodiment, one of said half-parts 17a, in particular the one adjacent to the outlet portion 13b of the guide path 13, is crossed by a through slit 20 defining the second axial gap 15b.

Such a through slit 20 is of such a size that it can accommodate, when sliding, the terminal hook 1 1 b, being able to be completely crossed by it in use.

Preferably, moreover, the half-parts 17a each have an outer surface with at least one fixing tooth 17b.

Each fixing tooth 17b is constrainable by snap-fit coupling to the containment body 2, in particular to the tubular portion of the containment body 2.

The invention achieves its intended purposes and obtains important advantages.

In fact, the arrangement of a guide path provided with axial gaps capable of compensating for the different stroke of the terminal hook in the different piston configurations, thus allowing to ensure maximum efficiency of the device, without negatively impacting either the size or complexity thereof.

Moreover, such a combination of characteristics, with the retention body anchored to the piston and the guide element connected to the bottom portion, greatly facilitates the in-line assembly of the device, as the most delicate step, i.e., the insertion of the retention body into the coil spring, is carried out prior to the introduction of the piston into the containment body.

Claims

1 . Opening device for a wing or a drawer, comprising:

- a containment body (2) developing at least in part along its own longitudinal axis (A) between a bottom portion (2c) and an end opening (2a);

- a piston (3) slidingly inserted into said containment body (2) and provided with a free end (3a) projecting outward from said end opening (2a);

- retaining means (4) associated with said piston (3) and said containment body (2) and configured to prevent the piston (3) from escaping from the containment body (2) through said end opening (2a);

- a movement mechanism (5) operatively interposed between the containment body (2) and the piston (3) and configured to shift the piston (3) between a first axial position, in which the piston (3) is predominantly extracted from the containment body (2), and a second axial position, in which the piston (3) is predominantly housed within the containment body (2); said movement mechanism (5) comprising: an elastic element (6) operatively interposed between said piston (3) and said bottom portion (2c) of the containment body (2) and configured to generate at least one axial thrust on said piston (3), oriented so as to push the piston (3) out of said end opening (2a) of the containment body (2), a switching unit (7) configured to collaborate with said elastic element (6) to position the piston (3) in the first or second axial position by passing through a transition position, of maximum retraction of the piston (3) within the containment body (2); wherein said piston (3) comprises a first component (9) and a second component (10) arranged in axial succession, with said elastic element (6) acting with thrust on the first component (9) and the retaining means (4) associated with the second component (10); said first (9) and said second component (10) being axially constrained in an adjustable manner between a compact configuration and an extended configuration to vary a preload of said elastic element (6); characterized in that said switching unit (7) comprises:

- a retention body (1 1 ) developing starting from said first component (9) of the piston (3) and away from said end opening (2a) of the containment body (2) as far as a terminal hook (1 1 b);

- a guide element (12) constrained to said bottom portion (2c) of the containment body (2) and provided with a guide path (13) selectively engageable by the terminal hook (1 1 b) of the retention body (1 1 ), wherein said guide path (13) comprises a zone distal (14) from the bottom portion (2c) and a zone proximal (15) to the bottom portion (2c), wherein:

- the distal zone (14) comprises a lead-in section (14a) that is open away from the bottom portion (2c) so as to facilitate the coupling and uncoupling of the terminal hook (1 1 b) of the retention body (1 1 ) with the guide path (13);

- the proximal zone (15) comprises at least one axial gap (15a, 15b) placed at least in part through the bottom portion (2c) in order to temporarily accommodate the terminal hook (1 1 b) when the piston (3) is in the transition position, at least with the first (9) and second component (10) in the extended configuration, wherein the bottom portion (2c) comprises a through notch (19) defining said at least one axial gap (15a).

2. Opening device according to claim 1 , wherein the proximal zone (15) comprises a first axial gap (15a) and a second axial gap (15b) substantially parallel to each other.

3. Opening device according to claim 2, wherein the guide path (13) comprises:

- an inlet portion (13a), developing from the lead-in section (14a) to the first axial gap (15a), crossed by the terminal hook (1 1 b) in a movement of retraction of the piston (3) from the first axial position to the transition position;

- an outlet portion (13b), developing from the second axial gap (15b) to the lead-in section (14a), crossed by the terminal hook (1 1 b) in a movement of extraction of the piston (3) from the transition position to the first axial position.

4. Opening device according to claim 2 or 3, wherein the guide path (13) comprises a retaining portion (13c) developing between the first (15a) and second axial gap (15b) passing through a cavity zone adapted to stably accommodate the terminal hook (1 1 b) in the second axial position of the piston (3).

5. Opening device according to any one of the preceding claims, wherein the bottom portion (2c) is defined by a plug (16) comprising:

- a base portion (17) removably connected to said containment body (2);

- an operative portion (18) protruding from said base portion (17) inside the containment body (2) and on which said guide path (13) is made.

6. Opening device according to claim 5, wherein said through notch (19) is made in said base portion (17).

7. Opening device according to claim 6, wherein said base portion (17) comprises two half-parts (17a) spaced apart from each other by said through notch (19), which are elastically movable in reciprocal approach and distancing.

8. Opening device according to claim 7, wherein said half-parts (17a) are each provided with an outer surface provided with at least one fixing tooth (17b) and constrainable by snap-fit coupling to the containment body (2).

9. Opening device according to claim 6 or 7, wherein one of said half-parts (17a) is crossed by a through slit (20) defining a second axial gap (15b).