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1. WO2020156925 - JOINT ANTI-BASCULEMENT POUR ARBRE CREUX D'UN MOTEUR ÉLECTRIQUE

Note: Texte fondé sur des processus automatiques de reconnaissance optique de caractères. Seule la version PDF a une valeur juridique

[ EN ]

ANTI-TILTING SEAL FOR A HOLLOW SHAFT OF AN ELECTRIC MOTOR

DESCRIPTION

The present patent application for industrial invention relates to an anti tilting mechanical seal for a hollow shaft of an electric motor. Such a type of seal is especially suitable for being used for electric motors of electric vehicles with coolant circulation in order to isolate the coolant from the electric parts of the motor and from the bearings that support the rotary shaft of the motor. The field of reference is e-mobility. The term“e-mobility” refers to electric mobility, i.e. transportation means powered with alternative energy with a low environmental impact, namely electric energy. In particular, the present invention relates to the need to cool the mobile part of a motor (rotor) through the realization of a seal between a hollow shaft and the (static) lid of the motor.

Fig. 1 is a sectional view of an electric motor (M100) provided with a hollow shaft (A100) with an axis (X1 ) suitable for receiving a circulation of coolant of the motor. A mechanical seal (T100) is disposed between an ending section of the hollow shaft (A100) and a lid (C100) of the motor in order to prevent the coolant from reaching electric parts or mechanical bearings of the motor.

The hollow shaft (A100) comprises an internal duct (S100) disposed in coaxial position inside the hollow shaft in such a way to form an annular cavity (A101 ).

The arrows diagrammatically show the trajectory of the coolant inside the hollow shaft (A100). The coolant follows the following trajectory:

- it enters from a delivery hole (not shown in the appended figures) of the lid (C100);

- it flows inside the internal duct (S100);

- it passes from the duct (S100) to the annular cavity (A101 ) of the hollow shaft;

- it completely passes through the annular cavity (A101 );

- it flows inside the lid (C100) and comes out of the lid (C100) through a drain hole (not shown in the appended figures) provided on the lid (C).

Fig. 2 is a sectional view of the seal (T100). The seal (T100) comprises a fixed assembly (GF100) and a rotary assembly (GM100).

With reference to Fig. 1 , the fixed assembly (GF100) is positioned inside a seat provided on the lid (C100), whereas the rotary assembly (GM100) is positioned inside a seat (A102) provided in the ending section of the hollow shaft (A100).

The rotary assembly (GM100) comprises:

- a frame (100) fixed to the hollow shaft (A100);

- a rotary ring (400) integrally mounted to the frame (100);

- a seal (200) disposed between the frame (100) and the rotary ring

(400);

- a retaining ring (500) integral with the frame (100) and stopped against the seal (200).

The rotary ring has an axis (X2).

The fixed assembly (GF100) comprises:

- a fixed ring (600) in sliding contact with the rotary ring (400) of the rotary assembly (GM100);

- an external frame (1300) coupled with the lid (C);

- an internal frame (800) housed in the external frame (1300) and housing the fixed ring (600) at least partially;

- a seal (700) disposed between the internal frame (800) and the fixed ring (600);

- a retaining ring (1400) integral with said internal frame (800);

- a spring (1 100) disposed between the internal frame (800) and the external frame (1300);

- a spacer (900) and an O-ring seal (1200) disposed between the internal frame (800) and the external frame (1300) and retained by the fixed retaining ring (1400).

The fixed ring has an axis (X3).

With reference to Fig. 3, the rotary ring (400) has:

- an internal side (410) directed towards the axis (X1 ) of the hollow shaft (A100);

- an external side (420) directed outwards;

- a lower side (430) directed towards the hollow shaft (A100);

- a sliding side (440) directed towards the lid (C1 00);

The fixed ring (600) has:

- an internal side (610) directed towards the axis X1 of the hollow shaft (A100);

- an external side (620) directed outwards;

- a sliding side (630) directed towards the hollow shaft (A100);

- an upper side (640) directed towards the lid (C100).

The internal sides (610, 410) of the fixed ring and of the mobile ring are two operating sides, which are in direct contact with the coolant that comes out of the hollow shaft (A100).

The sliding sides (630; 440) of the fixed ring and of the rotary ring (400) guarantee a liquid seal, preventing the coolant from leaking out of the hollow shaft.

In order to guarantee a perfect seal, the axis (X2) of the rotary ring must coincide with the axis (X3) of the fixed ring.

The positioning of the rotary assembly (GM100) on the hollow shaft (A100) is performed by mounting by interference the frame (100) of the rotary assembly on the seat (A102) obtained on the ending section of the hollow shaft (A100). Any constructional defects of the seat (A102) of the hollow shaft (A100) or assembling errors of the components that form the rotary assembly (GM100) may generate an inclination of the axis (X2) of the rotary ring relative to the axis (X1 ) of the hollow shaft and consequently a misalignment between the axis (X2) of the rotary ring (400) and the axis (X3) of the fixed ring, i.e. the axis (X2) of the fixed ring is inclined relative to the axis (X3) of the rotary ring, generating a tilting between the two rings that results in an imperfect sliding of the sliding sides of the two seal rings with fluid leaks.

The rotation of the hollow shaft (A100) generates a centrifugal force on the fluid. Therefore, in correspondence of the seal (T100), the fluid tends to

push the internal sides of the rings and therefore tends to leak from the gap between the two sliding sides of the rings. This implies a risk of leaks.

In order to have a good seal, a predefined push of the fixed ring on the mobile ring, generated by the spring (1 100) is necessary. Therefore, the spring must be compressed perfectly. Because of the imperfections of the lid (C100), the spring compression may be too high or too low, involving an imperfect contact between the sliding sides of the two rings, with a risk of wear or leaks.

A last drawback refers to the fact that the seal (T100) comprises two separate assemblies (fixed assembly and rotary assembly). During the transportation and the handling of said assemblies, the sliding sides of the fixed ring and of the rotary ring are not covered, with the risk of being in contact and contaminated with external elements.

JP2004068982 discloses an electric motor for an electric vehicle provided with a first rotary hollow shaft connected to an internal rotor and a second rotary hollow shaft connected to an external rotor. The second hollow shaft is disposed inside the first hollow shaft in such a way to define an annular chamber where the coolant circulates. The second hollow shaft has a duct with a flow of lubricant oil. Obviously, the duct of the second hollow shaft is not in communication with the annular chamber to avoid mixing the coolant with the lubricant oil. A lid closes the stator of the motor. A mechanical seal is disposed between the first hollow shaft and the second hollow shaft. Therefore, the mechanical seal has two rotary rings in sliding contact. Such a mechanical seal does not have a fixed assembly fixed to the lid, to the stator or to the casing. A first seal ring is stressed by a spring. The first seal ring and the spring are disposed in a box fixed to the first rotary shaft. A second seal ring is fixed directly in a seat of the second hollow shaft. The second seal ring is disposed between the first seal ring and the lid, and the spring pushes the first seal ring towards the second seal ring away from the lid. Such an arrangement involves tilting problems between the two seal rings, as well as an uncontrolled compression of the spring.

The purpose of the present invention is to overcome the drawbacks of the prior art, by disclosing a motor assembly with hollow shaft and mechanical seal wherein a tilting of the rotary assembly relative to the fixed assembly, with consequent coolant leaks is eliminated.

Another purpose of the present invention is to disclose a motor assembly wherein the load between the sliding sides of the seal rings is not affected and altered by constructional tolerances of the motor or of the lid.

These purposes are achieved according to the invention with the characteristics of the appended independent claim 1 .

Advantageous embodiments appear from the dependent claims.

The assembly according to the invention is defined by claim 1.

For the sake of clarity, the description of the motor assembly according to the invention continues with reference to the attached drawings, which have a merely illustrative, not limiting value, wherein:

Fig. 1 is a sectional view of an electric motor with a hollow shaft with mechanical seal according to the prior art;

Fig. 2 is a sectional view of the mechanical seal according to the prior art;

Fig. 3 is a diagrammatic view of the mechanical seal according to the prior art;

Fig. 4 is an axial sectional view of the motor assembly according to the invention;

Fig. 5 is an axial sectional view of a mechanical seal of the motor assembly of Fig. 4;

Fig. 6 is a view of the mechanical seal of the motor assembly according to a second embodiment of the invention;

Fig. 6A is an enlargement of the detail enclosed in the circle R1 of Fig.

5;

Fig. 7 is a view of the mechanical seal of Fig. 6, wherein the coupling means are not in mutual contact;

Fig. 7A is an enlargement of the detail enclosed in the circle R2 of Fig.

Fig. 8 is a view of a portion of the mechanical seal of Fig. 6, mounted on a hollow shaft of a motor wherein the rotary ring is in direct contact with an end of the external duct of the hollow shaft;

Fig. 9 is the same view as Fig. 8 wherein the rotary ring is not in direct contact with the hollow shaft;

Fig. 10 is a diagrammatic sectional view of the mechanical seal according to the invention;

Figs. 1 1 and 12 are the same views as Fig. 4, except for they show some alternative embodiments of the invention;

Fig. 13 is an axonometric view of the mechanical seal of the motor assembly according to the invention.

With reference to Fig. 4, a motor assembly according to the invention is disclosed.

The motor assembly comprises a motor (M) comprising a casing (Z), a lid (C) fixed to the casing and a hollow shaft (A) with an axis (X). The hollow shaft is fixed to a rotor of the motor and is therefore a rotary shaft. The hollow shaft (A) comprises an axial duct (A2).

A stem (S) is fixed to the lid (C). The stem (S) is disposed inside the axial duct (A2) of the hollow shaft in such a way to define an annular chamber (A1 ) between the stem and the axial duct of the hollow shaft. The stem (S) has an axial duct that communicates in lower position with the annular chamber (A1 ). An end (A4) of the hollow shaft (A) is directed towards the lid (C).

The arrows diagrammatically show a trajectory of a coolant inside the assembly. The coolant follows the following trajectory:

- it enters from a delivery hole (not shown in the appended figures) provided on the lid (C);

- it is conveyed inside the duct (A3) of the stem;

- it passes from the duct (A3) of the stem to the annular chamber (A1 ) of the hollow shaft;

- it flows in the annular chamber (A1 ) towards the lid (C);

- it flows inside the lid (C) and comes out of the lid (C) through a drain hole (not shown in the appended figures) provided on the lid (C).

The motor assembly comprises a seal (T) disposed between the hollow shaft (A) and the lid (C).

With reference to Fig. 5, the seal (T) of the invention comprises a rotary assembly (GM) that is integrally mounted with the hollow case A), and a fixed assembly (GF) that is integrally mounted with the casing of the motor.

The fixed assembly (GF) comprises a fixed ring (6), whereas the rotary assembly (GM) comprises a rotary ring (4).

The two rings (4, 6) cooperate and are slidingly in contact in such a way to obtain a sliding seal.

The rotary assembly (GM) comprises a frame (1 ) fixed to the hollow shaft (A). The frame (1 ) comprises:

- a tubular portion (1 a)

- an annular portion (1 d) that protrudes radially outwards from the tubular portion.

With reference to Fig. 9 the tubular portion (1 a) of the frame is press-fitted by means of interference inside the axial duct (A2) of the hollow shaft, in such a way that a first section (1 b) is inside the hollow shaft (A) and a second section (1 c) protrudes from the end (A4) of the hollow shaft (A). Otherwise said, the annular portion (1 b) is spaced from the end (A4) of the hollow shaft.

The rotary ring (4) is disposed in the vicinity of the second section (1 c) and of the annular portion (1 d) of the mobile frame (1 ) in such a way that the rotary ring (4) is partially covered by the frame (1 ) and protrudes externally from the hollow shaft.

The rotary assembly (GM) also comprises a seal (2) disposed between the annular portion (1 d) and the rotary ring (4). The seal (2) comprises a cylindrical wall (21 ) disposed between the second section (1 c) of the tubular portion (1 a) of the frame (1 ) and the rotary ring (4), and an annular wall (22) that extends from a first end of the cylindrical wall (21 ) of the seal and is disposed between the rotary ring (4) and the annular portion (1 d) of the frame (1 ). The annular wall (22) of the seal (2) is axially compressed between the rotary ring and the annular portion (1 d) of the mobile frame (1 ). The cylindrical wall (21 ) of the seal is radially compressed between the rotary ring (4) and the second section (1 c) of the tubular portion (1 a) of the frame.

The fixed assembly (GF) also comprises an external frame (13) comprising an internal cylindrical wall (131 ), an external cylindrical wall (132) and a bottom wall (133) that joins the external cylindrical wall (132) with the internal cylindrical wall (131 ). The external cylindrical wall (132), the internal cylindrical wall (131 ) and the bottom wall (133) define an annular channel (E) provided with an opening that is directed towards the lid (C).

With reference to Fig. 5, the external frame (13) comprises an ending edge (130) with an annular portion (130a) that extends radially outwards from an end of the external cylindrical wall (132). The ending edge (130) may comprise a cylindrical wall (130b) that is axially folded relative to the annular portion (130a) (Fig. 6).

The fixed assembly (GF) comprises an internal frame (8) housed in the annular channel (E) of the external frame (13) in axially sliding mode. The internal frame (8) comprises a planar annular bottom wall (80) that faces the bottom wall (133) of the external frame (13), and a cylindrical wall (81 ) that extends axially from an external edge of the bottom wall (80) in such a way to enclose the fixed ring (6) of the fixed assembly (GF) at least partially.

The bottom wall (80) of the internal frame (8) has an internal curvilinear edge (82) that is axially folded towards the bottom wall (133) of the external frame (13).

The fixed assembly (GF) also comprises a seal (7) made of elastomeric material that is disposed between the fixed ring (6) and the internal frame (8). The seal (7) comprises a planar annular wall (70) disposed axially between the bottom wall (80) of the internal frame (8) and the fixed ring (6), and an external cylindrical wall (71 ) that extends axially from the annular wall (70) and is radially disposed between the cylindrical wall (81 ) of the internal frame (8) and the fixed ring (6).

The seal ring (6) is axially blocked inside the internal frame (8) by means of radial interference, i.e. by radially compressing the cylindrical wall (71 ) of the fixed seal (7). The annular wall (70) of the fixed seal is axially compressed between the bottom ball (80) of the internal frame (6) and the fixed ring (6).

The fixed seal (7) comprises a lip sealing portion (72) that extends from the annular wall (70) and is disposed between the internal curvilinear edge (82) of the bottom wall (80) of the internal frame (8) and the internal cylindrical wall (131 ) of the external frame (13). The lip seal portion (72) cooperates with the internal cylindrical wall (131 ) of the external frame (13), providing a static seal between the internal frame (8) and the internal cylindrical wall (131 ) of the external frame (13).

The fixed assembly (GF) also comprises a spring (1 1 ) disposed between the internal frame (8) and the external frame (13); the spring (1 1 ) is axially compressed between the bottom wall (80) of the internal frame (8) and the bottom wall (133) of the external frame (13), and constantly exerts an axial movement of the internal frame (8) away from the external frame (13). The spring (1 1 ) may comprise one or more torsional springs suitable for generating a suitable load between the rotary ring (4) and the fixed ring (6).

The rotary ring (4) and the fixed ring (6) can be made of ceramic material, such as for example silicon carbine with or without graphite, alumina, tungsten carbide or can be made of non-ceramic material, such as PTFE and carbon.

With reference to Fig. 10, the rotary ring (4) has:

an internal side (41 ) directed towards the axis (X) of the hollow shaft

(A);

an external side (42) directed outwards;

a sliding side (43) directed towards the hollow shaft (A); an upper side (44) directed towards the lid (C).

The fixed ring (6) has:

an internal side (61 ) directed towards the axis (X) of the hollow shaft

(A);

an external side (62) directed outwards;

a sliding side (63) directed towards the external frame (13);

a sliding side (64) directed towards the lid (C) and also directed towards the rotary ring (4).

The sliding side (43) of the rotary ring (4) comprises a sliding portion (43b) that protrudes externally from the hollow shaft (A) and a first portion (43a) in direct contact (see Fig. 8) or in indirect contact (see Fig. 9) with the end (A3) of the hollow shaft (A).

With reference to Fig. 8, the first portion (43a) of the sliding side (43) of the rotary ring (4) is in direct contact with the end (A3) of the hollow shaft (A).

With reference to Fig. 9, an annular spacer (49) is disposed between the first portion (43A) of the sliding side (43) of the rotary ring (4) and the end (A3) of the hollow shaft. The annular spacer (49) is suitable for protecting the rotary ring (4) against mechanical shocks during the assembly of the seal (T) or vibrational shocks caused by the hollow shaft (A) during rotation; the annular spacer (49) can be free, fastened to other elements of the seal (T), or made in one piece with said elements of the seal (T). In particular, as shown in Fig. 9, the annular spacer (49) is made in one piece with the seal (2) and extends externally from the cylindrical wall (21 ) of the seal (2). Preferably, the annular spacer (49) has a thickness lower than 1 mm.

The first portion (43A) and the portion (43b) of the sliding side can be coplanar (see Fig. 9) or joined by means of a connection section that is inclined or perpendicular to the two portions (43A, 43B) (see Fig. 9).

The sliding portion (43b) of the sliding side (43) of the rotary ring (4) is in sliding contact with the sliding side (64) of the fixed ring (6). The second sliding portion (43b) of the sliding side of the rotary ring (4) and the fourth sliding side (64) of the fixed ring are the two“sliding sides” of the rings.

The rotary assembly (GM) is constrained inside the hollow shaft (A) by means of the mobile frame (1 ) that, in addition to permitting a direct contact between rotary ring (4) and hollow shaft (A), reduced the radial volume and consequently the peripheral sliding speeds between the sliding sides (64 and 43B).

The external frame (13) comprises a coupling surface (139) that is press-fitted with the casing (Z) of the motor (M).

The casing (Z) of the motor comprises a seat obtained around the hollow shaft (A) that houses the external frame (13) of the fixed assembly (GF). The coupling surface (139) is in contact with said seat.

Such a coupling surface (139) is obtained on an external side of the external cylindrical wall (132). The diameter of the external cylindrical wall (132) of the external frame (13) is slightly higher than the diameter of the seat in such a way that the external frame (13) is splined by means of interference on the seat of the motor (M).

With reference to Figs. 1 1 and 12, the casing (Z) of the motor (M) comprises a flange (F) where the seat that houses the external frame (13) of the fixed assembly (GF) is obtained.

According to a different embodiment, shown in Fig. 12, an adapter (AD) that is connected to the flange (F). In such a case, the seat that houses the external frame (13) of the fixed assembly (GF) is obtained on the adapter (AD).

With reference to Fig. 13, the rotary assembly (GM) comprises a drive ring (5) joined to the rotary ring (4) and partially surrounding the rotary ring (4). The drive ring (5) comprises an annular wall (51 ) in contact with a portion of the fourth upper side (44) of the rotary ring (4), and a cylindrical wall (52) in contact with the external side (42) of the rotary ring (4). The drive ring (5) comprises perimetral projections (5a) that project in orthogonal direction from the annular wall (51 ).

The frame (1 ) of the rotary assembly comprises wings (1 e) that project radially from the annular portion (1 d) of the frame. Each wing (1 e) of the frame (1 ) is inserted in the space between two adjacent projections (5a) of the drive ring (5). In view of the above, during the rotation of the hollow shaft (A) and of the frame (1 ), the lateral edges of the wings are stopped against the lateral edges of the projections (5a) in such a way that the frame (1 ) drives the drive ring (5) and the rotary ring (4) in rotation. Such a driving movement prevents the rotary ring (4) and the mobile frame (1 ) from rotating at different speeds due to an excessive load between the sliding portion (43a) of the sliding side (43) of the rotary ring (4) and the sliding side (64) of the fixed ring (6) that will tend to slow the rotary ring (4) down because of friction.

The present solution may also provide for the simultaneous assembly of the fixed assembly (GF) and of the rotary assembly (GM) before the seal (T) is mounted on the motor (M). In view of the above the seal (T) comprises coupling means (MA) that are configured in such a way that the rotary assembly (GM) and the fixed assembly (GF) cannot be uncoupled when the seal (T) is not mounted on the hollow shaft (A).

With reference to Figs. 5 to 7, the coupling means (MA) comprise:

- a retaining ring (16) comprising a planar annular portion (161 ) disposed on the bottom wall (133) of the external frame (13) and fixed to the external frame (13) by interference, and a plurality of elements (162) that extend axially from said planar annular portion (161 ) above the fixed ring (6) and perimetrally surround the rotary ring (4) and the fixed ring (5); each element (162) comprises a section (162b) folded towards the internal cylindrical wall (131 ) of the external frame (13); and

- an annular stop shelf (17) being obtained in the cylindrical wall (52) of the drive ring (5) and protruding laterally outwards from said cylindrical wall (52) of the drive ring (5); said annular stop shelf (17) comprising a first side (17a) directed towards the bottom wall (133) of the external frame (13), and a second side (17b) opposite to said first side (17a) and suitable for being stopped against said section (162b) of the elements (162) of the retaining ring (16).

The engagement of the second side (17b) of the annular stop shelf (17) of the drive ring (5) against the side of the section of the elements (162) of the retaining ring (16) is due to the spring (1 1 ) that exerts a thrust on the internal frame (8) away from the external frame (13).

The spring (1 1 ) exerts an axial thrust on the internal frame (8), which partially houses the fixed ring (6) that is in contact with the rotary ring (4), pushing it. Being integral with the rotary ring (4), the drive ring (5) is pushed against the section (162b) of the elements (162) of the retaining ring (16), which opposes such a thrust and prevents the uncoupling of the fixed assembly (GF) relative to the rotary assembly (GM).

The seal (T) can be directly assembled outside the motor (M), as a single piece, where the rotary assembly (GM) and the fixed assembly (GF) are held

together by the coupling means (GA) that connect the rotary assembly (GM) with the fixed assembly (GF), guaranteeing the contact between the rotary ring (4) and the fixed ring (6).

The motor (M) also comprises a resolver (R) suitable for counting the revolutions of the hollow shaft (A). Preferably, said resolver (R) is disposed inside a lateral seat o obtained in lateral position in said adapter (AD). The adapter (AD) also comprises a set of radial openings which are used to discharge the leaks outside the motor (M).

The lid (C) comprises an annular edge that is provided with a free ending section (C1 ) towards the casing (Z) of the motor (M). The ending section (C1 ) comprises an internal surface (C1 1 ), an external surface (C12) and a heading surface directed towards the casing of the motor (M), which joins the internal surface (C1 1 ) and the external surface (C12). The assembly comprises a rubber ring (18), which is commonly defined as“O-ring”, disposed in said free ending section (C1 ) of the annular edge of the lid (C). Said rubber ring (18) provides a static seal between the lid (C) and the motor (M), stopping against the external frame (13) or the adapter (AD) or the flange (F).

With reference to Fig. 1 1 , the external diameter of the ending section (C1 ) of the annular edge is slightly lower than the diameter of the external cylindrical wall (132) of the external frame (13) in such a way that the ending section (C1 ) is inserted in the annular channel (E) defined by the external frame (13). In such a case, the rubber ring (18) is disposed on the external wall (C12) of the ending section (C1 ) of the annular edge of the lid (C) and is compressed between the external frame (13) and the lid (C) radially. In particular, it is compressed between the lid (C) and the external cylindrical wall (1 32) of the external frame (13).

With reference to Fig. 13, according to a different embodiment, the internal diameter of the ending section (C1 ) of the annular edge of the lid (C) is slightly higher than the diameter of the folded cylindrical wall (130b) of the ending edge (130). In such a case, the rubber ring (18) is disposed on the internal wall (C1 1 ) of the ending section of the annular edge of the lid (C) and is compressed between the folded cylindrical wall of the ending section and the lid (C) radially.

Alternatively, with reference to Fig. 13, the ending section (C1 ) of the annular edge of the lid (C) can be configured in such a way to be disposed outside the external frame (13) and coupled with the flange (F) or the adapter (AD).

Although it is not shown in the appended figures, the rubber ring (18) can be disposed in the heading wall of the ending section (C1 ) of the annular edge of the lid (C); in such a case, the rubber ring (18) will be in axial contact with the annular portion (130a) of the ending edge (130) of the external frame (13) of the seal (T) or in axial contact with the flange (F) or with the adapter (AD).

Preferably, the motor (M) may also comprise a flow deviator (DV) disposed on the cavity of the lid (C) around the stem (S). The flow deviator (DV) partially deviates the coolant flow in such a way to convey it inside the annular channel (E) and the coolant touches the rotary ring (4) and the fixed ring (6) in order to cool them down. The flow deviator (DV) comprises a set of axial holes (not shown in the appended figures) to control the quantity of coolant flow to be deviated.

In the inventive solution, the direct or indirect contact (with the interposition of the annular spacer (49)) between the rotary ring (4) and the ending section (A3) of the hollow shaft (A) guarantees that the axis of the rotary ring (4) always coincides with the axis of the fixed ring (6), preventing any tilting between the rotary ring and the fixed ring, and consequently any flow leaks.

Moreover, because of the special configuration of the seal (T), the operating sides of the rings are the external sides (42, 62) that are not subject to the centrifugal force of the fluid, preventing any leaks.

Furthermore, the provision of the seat that houses the external frame (13) of the fixed assembly (GF) in the casing of the motor, the compression of the spring (1 1 ) can be controlled easily and defined according to the relative positioning of the external frame (13) of the fixed assembly (GF) relative to the ending section (A3) of the hollow shaft (A).

More precisely, taking as reference the height of the ending edge (130) of the external frame (13) or the height of the bottom wall (133) relative to the height of the end (A3) of the hollow shaft (A), it is possible to know the compression of the spring (1 1 ), and consequently the load between the sliding sides of the two rings in advance.

The provision of the coupling means (MA) prevents the contamination of the sliding sides (64 and 43b) because the sliding sides (64 and 43b) are not uncoupled and therefore the sliding surfaces are not exposed in the environment. In addition to preventing the contamination of the sliding sides (64 and 43b), the provision of said coupling means (MA) facilitates the assembly and the relative positioning of the external frame (13) and consequently of the fixed assembly (GF) relative to the end (A3) of the hollow shaft (A).

Because of said coupling means and using a suitable device, the external frame (13) can be positioned in a correct manner relative to the end of the hollow shaft (A) in such a way that the spring (1 1 ) is disposed at an ideal working height. Said device has a stop side that is suitable for being stopped above the seal in order to push the seal (T) in working position until it is stopped by means of interference of the rotary assembly (GM) (frame (1 )) on the hollow shaft (A) and of the fixed assembly (GF) (external frame (13) on the relative seat obtained in the casing of the motor (M)); more precisely, said device comprises two stop surfaces, the first stop surfaces is stopped against the annular portion (1 d) of the mobile frame (1 ), whereas the second stop surface is stopped against the annular portion (130a) of the ending edge (130) of the external frame (13). Said device is designed according to the mutual axial position of the fixed assembly (GF) and of the rotary assembly (GM). More precisely, the two stop surfaces of the device are joined by a cylindrical wall with length equal to the axial distance between the annular portion (1 d) of the mobile frame (1 ) and the annular portion (130a) of the ending edge (130) of the external frame (13) until the spring (1 1 ) is disposed at an ideal working height.

Therefore, in order to mount the fixed assembly (GF) on the hollow shaft (A) and the rotary assembly (GM) on the seat obtained on the motor (M), the following steps are provided:

- positioning the circular surface of the first cylindrical body of the device in contact with the annular portion (1 d) of the frame (1 );

- positioning the circular surface of the second cylindrical body of the device in contact with the annular portion (130a) of the ending edge (130) of the external frame (13);

- pushing the seal (T) inside the seat until the first portion (43a) of the third surface (43) of the rotary ring (4) or the annular spacer (49) are not in contact with the end (A3) of the hollow shaft (A).

Because of the fact that the fixed assembly (GF) and the rotary assembly (GM) are both mounted on the casing (Z) of the motor (M), any constructional defects or errors of the lid (C) or of the casing will not alter the extension of the spring (1 1 ) after the seal (T) is mounted on the motor (M). After mounting the seal (T), the lid (C) is mounted and fixed to the casing (Z) of the motor (M). During such an operation, the extension of the spring (11 ) is not altered and the load between the sliding sides of the fixed ring and of the rotary ring (4) will always be the one that was set while positioning the seal (T).