Patent Description:
Mechanical seals are devices that can be applied to rotating shafts to prevent fluid leakage and can withstand high pressure and mechanical stress.

Mechanical seals are used, for example, in centrifugal pumps and in motor boats in which a shaft transmits rotational motion from an engine, located inside a boat, to a propeller, which is completely submerged in water, to prevent liquid from entering the boat through the shaft.

Nowadays, a mechanical seal is realised by a pair of annular bodies, one stationary and one rotating sealing body, placed around a drive shaft and in relative motion with respect to each other when the drive shaft is driven; the two annular bodies are coaxial and coupled frontally so that a circular crown face of one is in contact with that of the adjacent annular body.

The rotating annular body is kept in contact with the stationary one by elastic means that push it axially against the stationary body. Preferably, such elastic means consist of a wave spring with a substantially annular profile.

During rotation, a minimal amount of fluid, sufficient to lubricate and prevent overheating, seeps through the two annular bodies without, however, escaping into the environment to be insulated.

With particular reference to the rotating part, it generally comprises a sealing element, presenting the sealing surface, and an annular body integrally connectable to a rotating shaft in such a way as to ensure a seal thereon.

In order to allow for mutual flotation of the sealing element and the annular body, they are coupled with clearance along the rotation axis of the shaft, so that they are free to make a limited and controlled translation in the axial direction. The wave spring, having a substantially annular profile, is placed between the sealing element and the annular body to absorb such axial movements and maintain mutual pressure between the coupling surfaces.

In order to enable the transfer of rotational motion from the annular body to the sealing element, it is known to make a shape coupling between the two. In particular, two teeth are made on the annular body at the level of the annular head surface and away from it. These teeth have an axial extension equal to the axial extension of the sealing element and are diametrically opposed. Corresponding counter-seats for such teeth are formed on the sealing element in order to transfer rotational motion from the annular body to the sealing element by means of a rotational shape coupling between such teeth formed on the annular body and such counter-seats formed on the sealing element.

Disadvantageously, the teeth have a large extension, so this solution is excessively costly due to the process of obtaining these teeth on the annular body, which are in fact obtained by removal of material, generating considerable waste of the material removed, and therefore considerable costs.

Even more disadvantageously, these teeth, being subject to considerable mechanical stress, must undergo a process of ion nitriding or hardening in order to make them stronger. Unfortunately, this process is expensive and, together with the costs related to the manufacturing process by material removal, results in an uneconomical product.

In order to obviate the costs of the material removal procedure for obtaining teeth at the level of the annular body, it is known to transfer the rotational motion from the annular body to the sealing element by means of the elastic means between them, as described in <CIT> and in <CIT>. In particular, such elastic means comprise a wave spring, interposed between the annular body and the sealing element, having a substantially annular profile and presenting a plurality of teeth, one for each wave of the spring, diametrically opposed and extending on the surface in which the spring itself lies, alternating teeth projecting inwards and outwards from the annular profile defined by the spring. In <CIT> there are two and diametrically opposite teeth protruding inwards and two and diametrically opposite teeth protruding outwards.

In more detail, the teeth protruding inwards from the annular profile defined by the spring are configured to engage respective radially through recesses made in the annular body, while the teeth protruding outwards from the annular profile defined by the spring are configured to engage respective recesses made in the sealing element.

Disadvantageously, the creation of recesses radially passing through the side wall of the annular body requires the removal of material, which, although limited, generates production costs, imposes a high overall size of the mechanical seal, and requires the presence of teeth protruding towards the inside of the annular profile defined by the spring, which can be dangerous during assembly/disassembly.

In addition, during assembly of the seal, the annular body and the sealing element can become axially detached, creating problems and forcing the assembly actions to be repeated several times before the correct configuration is achieved.

Furthermore, disadvantageously, the teeth protruding towards the outside of the annular profile defined by the spring rest in the respective recesses made in the sealing element, thus generating a distribution of the forces generated by the wave spring that is not uniform, but rather concentrated in the limited support areas. In addition to the above, the inner and outer teeth of the wave spring have sharp edges, which can disadvantageously cause potential injuries during assembly and disassembly of the mechanical seal.

Finally, known mechanical seals are generally made of AISI <NUM> steel, which is particularly resistant to corrosion. In this case, the stationary body is generally made of silicon carbide and it is necessary to place an insert of sacrificial material, usually graphite, between the stationary and the rotating sealing body. However, this solution is not very environmentally friendly as the graphite insert must be sealed on a circular crown surface of the sealing element using a polluting agent. In addition, graphite, which is also a polluting agent, being porous, needs to be impregnated with antimony, a material that is toxic and polluting even though it withstands high temperatures. Even more disadvantageously, the rotating part, comprising a graphite insert sealed to it, requires a separation of the graphitic portion from the metal portion during disposal.

In this context, the technical task underlying the present invention is to propose a mechanical seal that overcomes at least some of the drawbacks of the prior art mentioned above.

In particular, it is the purpose of the present invention to provide a mechanical seal that ensures versatile and safe assembly for the operator. A further aim of the present invention is to propose a mechanical seal that can be realised through an economical production process and that minimises material waste.

The defined technical task and the specified aims are substantially achieved by a mechanical seal comprising the technical characteristics set forth in one or more of the appended claims.

In particular, the first shape coupling comprises at least one recess axially passing through the wave spring, preferably one recess for each wave defined by the wave spring, and at least one tooth, preferably one tooth for each wave defined by the wave spring, extending axially away from an annular head surface of the annular body. The tooth is configured to fit axially into the recess in order to rotationally constrain the wave spring to the annular body.

This makes it possible to limit the production costs and overall size of the mechanical seal, which is also safer due to the lack of radially projecting parts towards the rotation axis.

The dependent claims correspond to possible embodiments of the invention and are incorporated herein by reference.

Preferably, an axially-shaped coupling is provided configured to axially constrain the wave spring and the annular body in such a way as to prevent them from detaching from each other along the rotation axis. The axially-shaped coupling is configured to be reversibly activated upon relative rotation between the wave spring and the annular body.

In this way, the annular body and the sealing element are not only rotationally but also axially constrained, improving versatility when installing the seal.

Preferably, the sealing element has at least one outer recess, preferably one for each wave of the wave spring, and the wave spring has at least one outer tooth, preferably one for each wave of the wave spring, protruding away from the rotation axis and configured to engage the outer recess to define the second rotationally-shaped coupling. Even more preferably, the outer recess has a depth greater than the radial extension of the outer tooth so that an area of the wave spring adjacent to the outer tooth defines an extended support surface between the wave spring and the sealing element in the deformed condition of the wave spring itself. Therefore, the outer tooth is free to move within the outer recess, resulting in a uniform and extended distribution of the forces generated by the wave spring over a section of the wave spring itself. Preferably the annular body is made of AISI <NUM>, while the sealing element when integral, i.e. without the graphite or silicon insert, is preferably made of chromium steel.

This makes it possible to realise an environmentally friendly mechanical seal that avoids the pollution caused by the use of the graphitic insert between the rotating part and the stationary body.

Further features and advantages of the present invention will become more apparent from the approximate and thus non-limiting description of a preferred, but non-exclusive, embodiment of a mechanical seal.

Such description will be set forth herein below with reference to the accompanying drawings, provided for merely indicative and therefore non-limiting purposes, wherein:.

With reference to <FIG>, a mechanical seal is referred to generically with the numerical reference <NUM> and will be referred to hereafter with the notation "mechanical seal <NUM>".

The mechanical seal <NUM> is applicable to a fixed wall "P" and a non-illustrated rotatable shaft passing through an opening in the wall "P", so as to generate a fluid seal through that opening, in particular to isolate a first side of the wall "P" from a fluid present at an opposite second side thereof. The wall "P" forms, for example, part of the hull of a boat and the rotating shaft passes through an opening in it to transmit motion from the engine, located on board the boat, to the propeller, located outside the hull. In this type of application, the mechanical seal <NUM> isolates the inside of the hull from the water on the outside of the hull.

In the context of this description, the outer side "E" is indicated as the side of the mechanical seal <NUM> exposed to the fluid to be contained, and the inner side "I" as the side opposite the outer side "E".

The mechanical seal <NUM> comprises a rotating part <NUM> and a fixed part <NUM>. The rotating part <NUM> is connected integrally to the rotating shaft via a first fluid-tight coupling and the fixed part <NUM> is integrally connectable to the wall "P" via a second fluid-tight coupling.

The rotating part <NUM> and the fixed part <NUM> have respective coupling surfaces, in particular a rotating coupling surface <NUM> and a fixed coupling surface <NUM>, which are arranged in abutment and pressed against each other so as to slide mutually during the rotation of the rotating shaft and generate a fluid seal.

The rotating part <NUM> comprises an annular body <NUM> and a sealing element <NUM> essentially coaxial to the annular body <NUM>.

The annular body <NUM> can be integrally connected to the rotating shaft and rotates together with it around a rotation axis "R".

The annular body <NUM>, illustrated in <FIG>, <FIG>, is preferably a substantially bushed body extending around the rotation axis "R".

The annular body has a side surface "SP" proximal to the rotation axis "R", a side surface "SD" distal to the rotation axis "R" and two annular head surfaces "ST", one external, exposed to the fluid to be contained, and one internal, its opposite. In particular, the head surfaces ST extend around the rotation axis R.

The annular body <NUM> has at least one tooth <NUM>, preferably two and diametrically opposed. In particular, the tooth <NUM> extends axially and away from the respective annular head surface "ST" of the annular body <NUM>.

Preferably, the tooth <NUM> has a radial thickness less than a radial thickness of the annular head surface "ST" from which it extends. Even more preferably, the tooth <NUM> is arranged proximal to the rotation axis "R".

Advantageously, the tooth <NUM> has at least one appendage 115a extending in a circumferential direction with respect to the rotation axis "R", defining a circumferential housing 115b. More specifically, the appendage 115b appears to be positioned distally with respect to an annular head surface "ST".

Conveniently, the tooth <NUM> has a lower axial extension than the axial extension of the sealing element <NUM>.

In addition, the annular body <NUM> preferably has an abutment shoulder <NUM> formed on its distal side surface "SD" and adjacent to the outer portion of the mechanical seal.

The sealing element <NUM>, illustrated in <FIG>, <FIG>, <FIG>, has a central cavity "C" adapted to accommodate the rotating shaft and the annular body <NUM> integral with it.

The sealing element <NUM> comprises the rotating coupling surface <NUM> described above and is coupled to the annular body <NUM> so as to be movable with respect to it (and with respect to the rotating shaft) along the rotation axis "R". It is thus possible to maintain contact of the rotating coupling surfaces <NUM> and static coupling surfaces <NUM> following a translation of the rotating shaft and the annular body <NUM> connected thereto.

Preferably, the sealing element <NUM> has a cylindrical mouth <NUM> for access to the central cavity "C" and the side surface "SD" distal to the rotation axis R of the annular body <NUM> is slidably inserted into this mouth <NUM>. The annular body <NUM> is free to slide within the sealing element <NUM> until it abuts against the latter at the abutment shoulder <NUM>.

Moreover, the sealing element <NUM> preferably has a channel <NUM>, in communication with the mouth <NUM>, defining a portion of the cavity "C" having a smaller diameter than the mouth <NUM> and preferably dimensioned so as to allow a fluid-tight coupling with the rotating shaft.

Preferably, the sealing element <NUM> has an inner annular groove <NUM> facing the rotation axis "R" and preferably interposed between the mouth <NUM> and the channel <NUM>.

Preferably, the annular groove <NUM> has a larger diameter than the mouth <NUM> and the channel <NUM>, so as to define an annular surface <NUM> extending around the rotation axis "R", a hitting shoulder <NUM> extending normal to the rotation axis "R" and arranged between the annular surface <NUM> and the channel <NUM> and, preferably, a containment shoulder <NUM> arranged between the annular surface <NUM> and the mouth <NUM>.

The sealing element <NUM> also has at least one external recess <NUM>, preferably two and diametrically opposed.

In the preferred embodiment, illustrated in <FIG> and <FIG>, the outer recesses <NUM> are partially obtained at the hitting shoulder <NUM> and the annular surface <NUM>, these recesses are also inclined in relation to the hitting shoulder <NUM>.

The mechanical seal <NUM> further comprises elastic means active between the annular body <NUM> and the sealing element <NUM> to keep the rotating coupling surface <NUM> pressed against the static coupling surface <NUM>.

These elastic means are also configured to allow a mutual position adjustment along the rotation axis "R" between the annular body <NUM> and the sealing element <NUM>, for example as a result of translational movements of the rotatable shaft along the rotation axis "R" with respect to the wall "P".

Advantageously, the elastic means comprise a wave spring <NUM> illustrated in <FIG> with a substantially annular, preferably two-wave, closed annular shape.

The wave spring <NUM> is preferably housed in the sealing element <NUM>, even more preferably in the annular groove <NUM>, and has an outer profile, thus distal from the rotation axis "R", substantially countershaped to the annular surface <NUM>. Preferably, the wave spring <NUM> has an inner diameter at least coincident with the diameter of the containment shoulder <NUM> and the mouth <NUM> so as to protrude with respect to them towards the rotation axis "R".

Preferably, the containment shoulders <NUM> and hitting shoulders <NUM> are configured to engage the wave spring <NUM> in a fully extended configuration to define a maximum, or limit stop, extension along the rotation axis "R" coincident with the width of the annular groove <NUM>. In the preferred embodiment, the width of the annular groove <NUM> is less than the axial extension of the wave spring <NUM> in the unloaded configuration, resulting in pre-compression.

In addition, in the preferred embodiment shown in <FIG>, the hitting shoulder <NUM> has an inclination of less than <NUM>°, preferably equal to <NUM>°, to the rotation axis "R", as can be seen in figure 9b. In other words, the hitting shoulder <NUM> is inclined with respect to a plane X, orthogonal to the rotation axis "R", by an angle α comprised between <NUM>° and <NUM>°, preferably <NUM>°.

Advantageously, the aforementioned technical feature promotes lower stress on the wave spring <NUM>, thus allowing for a longer service life thereof.

Even more advantageously, the aforementioned inclination of the hitting shoulder <NUM> avoids edge contact between the spring <NUM> and the shoulder <NUM> itself, thus limiting possible notching and wear of the sealing element <NUM>.

The wave spring <NUM> has at least one axially pass-through recess <NUM> formed in a portion of the wave spring <NUM> facing the rotation axis "R", the recess <NUM> also being open towards the rotation axis "R". Preferably, the wave spring <NUM> has a recess <NUM> for each of its waves; even more preferably, there are two such recesses, square in shape and diametrically opposed. Advantageously, each recess <NUM> is obtained along an inner perimeter edge of the wave spring <NUM>.

The wave spring <NUM> also has at least one outer tooth <NUM>, preferably one for each wave of the wave spring <NUM>, protruding away from the rotation axis "R". Preferably, this outer tooth <NUM> has a curvilinear profile.

Advantageously, each outer tooth <NUM> is made along an outer perimeter edge of the wave spring <NUM>.

In the preferred embodiment illustrated in <FIG>, the wave spring <NUM> has two inner recesses <NUM>, diametrically opposite the centre of extension of the wave spring <NUM>, and two outer teeth <NUM>, also diametrically opposite the centre of extension of the wave spring <NUM> and angularly spaced <NUM>° apart from the inner recesses <NUM>.

Considering the rotating part <NUM> in its entirety, the wave spring <NUM> has respective and opposite ends, coinciding with ridges and depressions of its wave profile, arranged in abutment against an annular head surface "ST" of the annular body <NUM> and the hitting shoulder <NUM> of the sealing element <NUM>. In other words, the wave spring <NUM> is interposed between an annular head surface "ST" of the annular body <NUM> and the hitting shoulder <NUM> of the sealing element <NUM>: the wave spring <NUM> is therefore arranged to be pressed against them to be compressed during a mutual approach of the annular body <NUM> and the sealing element <NUM> along the rotation axis "R".

Even more preferably, as shown in <FIG>, the annular body <NUM> is coupled to the sealing element <NUM> so that the distal side surface "SD" faces the annular groove <NUM> to define, in cooperation therewith, an at least partially closed housing volume "V" for the wave spring <NUM>. Advantageously, the rotating part <NUM> comprises sealing means <NUM>, e.g. one or more O-rings, interposed between the annular body <NUM> and the sealing element <NUM> to seal the housing volume "V" of the wave spring <NUM> at least with respect to the fluid present on the outer side "E" to the mechanical seal <NUM>.

Advantageously, the wave spring <NUM> has a first rotationally-shaped coupling with the annular body <NUM> configured to rotationally constrain the wave spring <NUM> to the annular body <NUM> around the rotation axis "R". Specifically, this coupling is achieved by axially inserting a tooth <NUM> of the annular body <NUM> into a recess <NUM> of the wave spring <NUM>. In other words, a tooth <NUM> is configured to fit axially into a recess <NUM> in order to define this first rotationally-shaped coupling.

This first rotationally-shaped coupling is capable of transferring the rotation of the annular body <NUM>, imposed by the rotating shaft, to the sealing element <NUM>. In other words, the sealing element <NUM> is only rotationally constrained to the annular body <NUM> by the wave spring <NUM>.

Advantageously, the wave spring <NUM> has a second rotationally-shaped coupling with the sealing element <NUM> configured to rotationally constrain the sealing element <NUM> to the wave spring <NUM> around the rotation axis "R". Specifically, such a second rotationally-shaped coupling results in the insertion of an outer tooth <NUM> of the wave spring <NUM> into an outer recess <NUM> of the sealing element <NUM>. In other words, an outer tooth <NUM> is configured to engage an outer recess <NUM> in order to define such a second rotationally-shaped coupling.

Even more advantageously, an outer recess <NUM> has a greater depth than the radial extension of an outer tooth <NUM>. In other words, the wave spring <NUM>, instead of resting with one end of the outer tooth <NUM> inside the cavity defined by the outer recesses <NUM>, rests at the level of the hitting shoulder <NUM>. Consequently, the wave spring <NUM> rests on the hitting shoulder <NUM> with an area adjacent to at least one outer tooth <NUM>, the latter thus remaining free from mechanical stress. When the spring <NUM> is in a deformed configuration, i.e. when the annular body <NUM> and the sealing element <NUM> are in close proximity along the rotation axis "R", this feature is convenient allowing the definition of a support surface between the wave spring <NUM> and the sealing element <NUM> coinciding with an area of the wave spring <NUM> adjacent to an outer tooth <NUM> and varying with the degree of compression of the wave spring <NUM>. In this way, it is possible to achieve a distribution of the forces generated by the wave spring <NUM> that is uniform and promotes homogeneous wear at the rotating coupling surface <NUM> between the rotating and stationary parts.

Advantageously, the first rotationally-shaped coupling results in a rotational constraint between the annular body <NUM> and the spring <NUM> which, being constrained to the sealing element <NUM> by the second rotationally-shaped coupling, results in a rotational constraint between the annular body <NUM> and the sealing element <NUM>. In other words, thanks to the interposition of the wave spring <NUM> between the annular body <NUM> and the sealing element <NUM>, these are both constrained to rotate about the rotation axis "R" integrally with the rotating shaft.

Furthermore, thanks to the interposition of the wave spring <NUM> between the annular body <NUM> and the sealing element <NUM>, they can move mutually along the rotation axis "R", however counteracted by the axial action of the wave spring <NUM>.

The wave spring <NUM> also has an axially-shaped coupling with the annular body <NUM>, which is configured to axially constrain the wave spring <NUM> and the annular body <NUM> so as to prevent them from detaching from each other along the rotation axis "R". More specifically, this axially-shaped coupling is configured to be reversibly activated upon relative rotation between the wave spring <NUM> and the annular body <NUM>. For explanatory purposes, <FIG> show the sequence whereby, in a possible embodiment, the axial constraint between wave spring <NUM> and annular body <NUM> is achieved by keeping the annular body <NUM> stationary and rotating the sealing element, in which the spring is inserted, clockwise, or vice versa. The housing 115b is configured to engage the wave spring <NUM> in a portion thereof adjacent to a recess <NUM> as a result of relative rotation between the wave spring <NUM> and the annular body <NUM>. More specifically, following a relative rotation between the wave spring <NUM> and the annular body <NUM>, the appendage 115a is able to oppose the mutual axial detachment between the wave spring <NUM> and the annular body <NUM>. In other words, the housing 115b is configured to define a bayonet coupling with the area adjacent to the recesses <NUM> formed in the wave spring <NUM>. In a further embodiment not illustrated, the annular body <NUM> has at least one internal recess, preferably two, running through one of its cylindrical walls in a radial direction with respect to the rotation axis "R". Preferably, an inner recess extends parallel to the rotation axis "R". This inner recess has at least one appendage proximal to the median portion of the annular body <NUM> and defining a circumferential housing.

In such a configuration, the wave spring <NUM> has at least one internal tooth, preferably one for each wave defined by the wave spring <NUM>, protruding towards the rotation axis "R" and configured to engage a respective internal recess of the annular body <NUM> to define the first rotationally-shaped coupling between the wave spring <NUM> and the annular body <NUM>. At the same time, the appendage is configured to realise the axially-shaped coupling between wave spring <NUM> and annular body <NUM> as a result of relative rotation between wave spring <NUM> and annular body <NUM>. In other words, an appendage formed in a recess of the annular body <NUM> is adapted to oppose the mutual detachment between the wave spring <NUM> and the annular body <NUM>.

In terms of construction materials, a first traditional embodiment, shown in <FIG>, includes an annular body <NUM> and a sealing element <NUM> both made of AISI <NUM>, a particularly corrosion-resistant steel, while the stationary body is made of silicon carbide. This first traditional embodiment also includes a sealed graphite insert <NUM> on the sealing element <NUM> of the rotating part <NUM> to accommodate the front coupling between the rotating part <NUM> and the stationary part <NUM>. In other words, the front coupling between the rotating part <NUM> and the stationary body <NUM> occurs between the graphite insert <NUM> of the sealing element <NUM> and the silicon carbide of the stationary body <NUM>.

A second innovative embodiment implemented through the configuration of the mechanical seal <NUM> described herein is shown in <FIG>. This second innovative embodiment includes an annular body <NUM> and a sealing element <NUM> made entirely of chromium steel (Y1), while the stationary body is made of graphite. This would result in an integral sealing element <NUM> as shown in <FIG>. An integral sealing element is defined as a sealing element without a graphite or silicon insert and preferably made of chromium steel. This type of sealing element, being composed of only one piece, is environmentally friendly.

The present invention achieves the proposed aim, overcoming the drawbacks complained of in the prior art.

Advantageously, the shape of the wave spring <NUM> and its coupling, with the annular body <NUM> and the sealing element <NUM>, in particular the first and second rotationally-shaped couplings described here allow for mutual rotational drive between the two elements.

In addition, the reversible axial constraint between annular body <NUM> and wave spring <NUM> ensures versatile mounting for the operator. Even more advantageously, the curved profile of the outer teeth <NUM> of the spring <NUM> aids the operator during assembly, preventing any injuries caused by sharp edges.

Conveniently, the conformation of the coupling between the outer recesses <NUM> in the sealing element <NUM> and the outer teeth <NUM> of the wave spring <NUM> allows an even distribution of the forces generated by the wave spring <NUM> and transmitted to the frontal coupling area between the rotating and stationary bodies. More specifically, the spring <NUM>, resting on the hitting shoulder <NUM> in an area adjacent to its outer teeth <NUM>, generates a uniform distribution of forces that promotes homogeneous wear at the front coupling surface between the rotating and stationary parts. In addition, this allows the support surface of the wave spring <NUM> to vary consistently with the compression of the wave spring <NUM>.

The main purpose achieved by means of the mechanical seal <NUM> described herein relates to the cost-effectiveness of the product as this mechanical seal <NUM> can be realised by means of a production process capable of minimising material waste, in particular by introducing teeth <NUM> at the level of the annular body <NUM>. These teeth have a limited axial extension and less than the axial extension of the sealing element <NUM>. In addition, the mechanical seal <NUM> described here brings cost-effectiveness to the production process by not requiring an ion nitriding step to make its components stronger.

Claim 1:
Mechanical seal (<NUM>), comprising a rotating part (<NUM>) connectable to a rotating shaft and a fixed part (<NUM>) connectable to a fixed wall (P); said rotating part (<NUM>) comprising:
- an annular body (<NUM>) integrally connectable to a rotating shaft (A) about a rotation axis (R);
- a sealing element (<NUM>) substantially coaxial with said annular body (<NUM>) and having a rotating coupling surface (<NUM>) configured to abut against a respective static coupling surface (<NUM>) of said fixed part (<NUM>); and
- elastic means comprising a wave spring (<NUM>) having a substantially annular profile, said elastic means being active between said annular body (<NUM>) and said sealing element (<NUM>) to maintain said rotating coupling surface (<NUM>) pressed against said static coupling surface (<NUM>) and to allow a mutual position adjustment along said rotation axis (R) between the annular body (<NUM>) and the sealing element (<NUM>);
- a first rotationally-shaped coupling configured to rotationally constrain said wave spring (<NUM>) to said annular body (<NUM>) about said rotation axis (R) and a second rotationally-shaped coupling configured to rotationally constrain said sealing element (<NUM>) to said wave spring (<NUM>) about said rotation axis (R),
characterized in that
said wave spring (<NUM>) has at least one axially pass-through recess (<NUM>), preferably one for each wave defined by said wave spring (<NUM>), and in that said annular body (<NUM>) has at least one tooth (<NUM>), preferably one for each wave defined by said wave spring (<NUM>), wherein said tooth (<NUM>) extends axially away from an annular head surface (ST) of said annular body (<NUM>) developed about said rotation axis (R), said tooth (<NUM>) being configured to axially fit into said recess (<NUM>) so as to define said first rotationally-shaped coupling.