FR2633351A1 - MULTI-COMPONENT SEAL FOR MECHANICAL SEAL WITH SEALING AROUND THE INPUT TREE - Google Patents

Abstract

Semi-rigid multi-element joint cover for mechanical seal; It comprises a hemispherical internal element 25 which is applied to the spherical surface 24 of the mechanical seal and a hemispherical external element 27 which surrounds the internal element 25, forming a spherical cavity between these elements which each have an opening 30, 52 for the passage of the input shaft of the mechanical seal; an intermediate element 35 comprises a spherical flange 36 which fits tightly in the cavity 31, as well as a cylindrical boss 37 which surrounds the input shaft 13. A shaft seal 40 bears on the input shaft 13 thanks to two ribs 45; 48 and locks onto the end of the boss 37, opposite the hemispherical flange 36, thanks to an internal protrusion 42 which clicks into an annular groove 41 of the boss; Application to articulated mechanical transmission joints, in particular for the driving wheels of a front-wheel drive vehicle.

Description

The subject of the present invention is a cover-cover or a cover

  protective seal for mechanical transmission of vehicles

  This seal has a substantially improved seal around the input shaft.

  The invention relates more particularly to the covers

  mechanical joint seals for torque transmission, over-

  everything in the case of joints subject to joint movement

  during their operation. More specifically, the invention

  The invention relates to a joint cover in which at least part of the cover is of the semi-rigid type. The invention relates to a seal for mechanical joints of the so-called constant speed type which is used in the transmission which drives the front wheels of a front-wheel drive motor vehicle,

  o part of the joint cover that surrounds the roadway

  The outer surface of the mechanical seal consists of concentric elements superimposed, each of these elements

  being made of semi-rigid material.

  Constant speed transmission seals are now widely used in automotive

  that means to transmit my torque between the trans-

  versaux of a front-wheel drive vehicle and the front-wheel drive of the vehicle. One or more of these transmission joints can be provided for each of the drive wheels. These transmission joints must be sealed to maintain the necessary lubrication inside the seal and to protect it against the ingress of sludge,

  dust and other external contaminants.

  Until now, the devices used to ensure

  watertightness and which is generally referred to by the expression

  "joint covers" or "protective sheath" are made

  made of flexible material, generally an elastomer, with a shape most often wavy or pleated accordion. This flexible structure, whatever the design, allows

  to the joint cover to adapt to the joint or movement

  angle of the input and output shafts (driving and driven) which are normally aligned with each other, in a

joint at constant speed.

  There has been extensive use of flexible joint covers for

  constant velocity transmission seals for

  -2-. However, these joint covers are relatively expensive and because of their flexibility must be put in place by manual operations. This precludes the use of more economical mechanical assembly techniques, which are based on the dimensional accuracy of the parts to be machined.

  be in place. In addition, flexible joint covers are

  made of elastomeric material and therefore they are ex-

  risk of tearing and puncturing, due to

  road accidents and other types of concentrated shocks.

  In addition, the physical properties of the elastomeric materials are subject to deterioration under the action of extreme temperatures, as encountered in the normal service life of an automobile. Finally, the internal free volume of

  these corrugated or wrinkled joint covers must be filled with

  in order to properly lubricate the seal it contains, and

  this requires the use of large amounts of fat.

  Moreover, there are many elastomeric materials used in the manufacture of these joint covers which undergo degradation when they are brought into contact with the grease,

  which limits the life of flexible joint covers.

  In the prior art, there is known a joint cover

  multiple seals, for mechanical seals, made of

  semi-rigid. An inner element of this joint cover has a

  I substantially spherical and sealingly carries, at its open end, against the spherical surface of the outer portion of the mechanical seal. The inner member has an inlet opening, axially disposed, for the passage of the input shaft. An outer member, hemispherical in shape, is concentrically disposed around the inner member and

  shape with the latter a cavity of substantially spherical shape

  than. An intermediate element is hermetically sealed against

  the mechanical seal inlet and has a flange for

  me spherical which is hermetically housed with possibility of displacement in a spherical cavity formed between the elements

internal and external.

  The problem with this type of joint cover is the

  sealing of the seal between the input or driving shaft and the intermediate element. This deficiency allows on the one hand

  the penetration of sludge, dust and water into the mechanical seal

-3-

  on the other hand, the leakage of the lubricant,

  premature deterioration of the mechanical seal. Different temptations

  are done to solve this problem by using

  O-rings or similar devices were inoperable

  rants or too expensive. The present invention consists in producing a protective seal provided with a new type of shaft seal which reliably ensures the seal between the input shaft or causing mechanical seal and

  the intermediate element of the joint cover.

  The subject of the present invention is therefore a gasket for sealing a mechanical transmission seal.

  of the kind comprising an input or driving shaft, an armature

  output or driven, and a coupling device

  binding the input shaft to the output shaft so that these

  two trees can articulate relative to each other.

  The coupling device comprises an outer race having an integral spherical outer surface

  from one of the input and output trees.

  The cover includes a semi-rigid hemispherical inner member having an open end which bears tightly against the outer spherical surface of the

  outer bearing ring. The internal element also has

  first opening at the opposite end

  posed at the aforementioned open end, this first opening

  surrounding the other shaft of the coupling. The joint cover

  additionally carries a semi-rigid external element of semi-

  spherical, concentric with the internal element and connected to this

  deny. The outer element has a second opening of

  gagement, concentric to the first clear opening of the inner member. At least one of these inner and outer members has a thinner portion that forms a cavity

  spherical between these elements. This spherical cavity is

  green at its end adjacent to said first and second clearance openings. An intermediate element, also semi-rigid, provided with a spherical-shaped flange, is housed

  hermetically and slidably in the spherical cavity

  cited and finally a cylindrical boss hermetically surrounds the other input or output shaft. The radius of this flange

  spherical, at its open end, is chosen so as to allow

-4-

  put some articulation movement of the element in-

  intermediate in said spherical cavity. The cylindrical boss

  that the intermediate element has an annular groove in its outer surface. The joint cover also includes a shaft seal provided with an annular rib which projects inwardly and fits into the annular cavity of the cylindrical boss to lock the shaft seal relative to the element. intermediate. The shaft seal also has at least one inwardly oriented rib that seals tightly into the outer surface of the other

input or output shaft.

  One of the aims of the present invention is to pre-

  see a joint cover to seal a mechanical joint

  than torque transmission, the tightness of this joint cover

  being substantially improved around the input shaft.

  In particular, one of the purposes of this

  This is to provide an improved joint cover for sealing a torque transmission in a joint.

  including the input and output devices, or

  nant and trained, undergo articulation movements

report to each other.

  Another object of the present invention is to provide

  a gasket for sealing a gasket

  at a constant speed, this cover being provided with a shaft seal of a new and improved type, capable of sealing at least one element of the cover-joint relative to

to the input shaft.

  On the other hand, the present invention aims to pre-

  see a joint cover providing improved sealing when

  that it is applied to a transmission seal of the type

  constant speed, used to operate the front wheels of a

front-wheel drive automobile.

  Finally, it is an object of the present invention to provide a gasket for sealing a constant velocity transmission joint of a front wheel drive vehicle, wherein the joint cover is composed of a plurality of substantially spherical members, each element being realized

  made of semi-rigid material. The elements of the joint cover are dis-

  placed centrally between them, the internal element applies

  -5- hermetically on the outer spherical surface of an element of the mechanical seal so as to allow the joint between the joint cover and that part of the mechanical joint which

  has a spherical outer surface.

  Other objects and advantages of the invention will emerge

  during the reading of the description which follows and relates

  FIG. 1 is a side elevational and sectional view of the accompanying drawing, in which:

  of a mechanical transmission joint at a constant speed

  aunt, provided with the waterproof seal and perfected according to a first embodiment of the present invention; FIGURE 2 is a partial view showing in section

  cross-section and on an enlarged scale the details of the cover

  shaft seal according to the invention, and FIGURE 3 is a partial view, similar to FIG.

  1, showing an alternative embodiment of the seal cover

  an alternative embodiment of the invention.

  Figure 1 shows a constant velocity mechanical seal

  te, the fixed type or without axial sliding, generally designated by the reference numeral 11. The mechanical seal 11 at constant speed receives at its input end 12 the

  torque to be transmitted applied to the shaft 13; this mechanical joint

  transmission of the torque to a trained organ (not

  sent) via an output shaft 14 which originates at the output end 15 of the transmission joint

  11 at constant speed. As is known from the prior art

  the torque is transmitted between the input shaft 13 and the output shaft 14 through a circumferential series of balls 16, for example six in number, housed in a cage 17. These balls 16 roll on a surface spherical 18 of an inner bearing ring 19 secured to the shaft

  13 by key, grooves or other known means, and the

  the 16 roll simultaneously on the inner surface 21 of gor

  Curved spokes 20 formed on an outer race 22. This outer race 22 is an extension of

  the output shaft 14. This output shaft and the outer ring

  22 are made integral with each other by

  forging or other suitable and known method.

  In use, the input shaft 13 and the output shaft 14 - 6 -

  are made to perform articulation movements at

  Figure 1. In the case of the torque transmission joint to the front wheels of a front-wheel drive automobile, this articulation may reach up to 45 in each direction, as a result of normal vibrations produced on the front wheel drive. road, by the bumps and valleys of the

  road, and also when taking turns at high speed.

  The constant velocity mechanical seal 11 is entirely suitable for

  it is possible to compensate for this considerable degree of articulation because the balls 16 roll in contact respectively with the spherical surface 18 of the inner race 19

  and the curved surface 21 of the outer roll ring

22.

  The transmission mechanical seal 11 at constant speed

  aunt, as stated above, consists of precisely machined parts moving relative to one another; therefore, these parts must be lubricated and free of mud, dust, water and other

  contaminants they may encounter in an environ-

  on the road. For this purpose, the transmission seal 11 is provided with a gasket or sealing sheath ,. referred to as a whole by reference number 23, in order to make

  hermetic space inside the mechanical seal 11. This cou-

  attached 23 must be able to withstand the degree of

  tion to which the transmission joint 11 to

  constant weight, without compromising its sealing properties

  during these articulation movements. In applications

  to the automobile, the sealing provided by the joint

  23 must be absolutely reliable and without

many years.

  As indicated above, the constant velocity mechanical seal 11 must be able to withstand a significant degree of inclination between the input shaft 13 and the output shaft 14. In the case of a seal for the front wheels of a front-wheel drive automobile, this joint can reach approximately 20 in each direction

  driving behavior, with occasional driving maxima

  in the extreme conditions of high-speed negotiated turns, for example. The joint - 7 -

  of the joint cover 23 can be obtained by realizing

  the outer bearing ring of the mechanical seal with

  an outer spherical surface 24 and making the cover

  sealing gasket 23 in the form of several superimposed elements

  posed. In the case of a forged outer race, the spherical outer surface 24 is preferably non-machined or rough forging, in order to reduce the cost thereof. The first element of the joint cover is an internal element

  which also has ribs 26 projecting radially

  inwardly and sealingly against the outer spherical surface 24 of the outer race 22. The inner diameter of the oriented ribs 26

  inward is less than the diameter of the spherical surface

  24 of the outer ring 22, so that the element

  the inner ring 25 is held against the inner race ring.

  by an elastic snap action by exceeding the cen-

  be, analogous to the knee effect. He is also

  since the hermetic seal cover according to this invention

  can be applied to existing universal joints

  using an outer race of cy-

  lindrical or other non-cylindrical shape. In this case, it is advisable to fix a frame of plastic or other material on the outer ring, this frame presenting

  necessarily a spherical outer surface to ensure

  touch the surface-to-surface contact with the ribs 26

  oriented towards the inside of the inner element. The cover

  hermetic seal 23 also includes an outer member 27 disposed concentrically with respect to the inner member 25

  and taking partial contact with this inner element.

  The inner member has a circumferential bead 28 located in the middle of its open end, an opening 30 through which the input shaft 13 passes, and a portion 31 of thickness

  partially reduced formed between the bead 28 and the

  30. The external element 27 also includes a

  52, concentric with the opening 30 of the inter-

  ne and that also crosses the input shaft 13.

  The front portion 32 of the outer member 27 has a thick

  growing and engages in the cavity formed in the

  25, between a radial flange 33 formed in its

  - 8 - open end 29 and the circumferential bead 28, in

  the purpose of locking the outer member 27 with respect to the

  25. This internal element-25 and the external element

  27 are flexible enough to allow them to lock each other by clicking when brought closer together

  with sufficient forces in the axial direction.

  The outer surface of the partial thickness part-

  of the inner element 25 and the inner surface of

  the outer member 27 together define a spherical cavity

  34 which extends between the opening 30 of the input shaft and the circumferential bead 28. An intermediate element also has a cylindrical boss 37 which surrounds

  the input shaft 13 so as to establish a closed contact

  only with this tree. To obtain the required seal between the inner member 25 and the intermediate member 35, it is possible to

  provide an inner bead 38 around the end or-

  green of the flange 36 with a substantially spherical shape, such as the

  shows more clearly Figure 3. Likewise, the inter-

  can not have an annular lip 39 which surrounds the

  30 and tightly against the inner surface

of the intermediate element 35.

  The seal between the input shaft 13 and the cylindrical boss 37 of the intermediate element 35 is formed by a shaft seal 40. Referring to FIG. 2, it can be seen that the cylindrical boss 37 opens into an annular locking cavity 42 formed on the portion of the shaft seal 40 which faces the mechanical seal. The end face of this cylindrical locking portion 42 has a

  beveled edge 43 intended to cooperate with a bevel edge

  corresponding tee 44 formed on the cylindrical boss 37 to lock the cylindrical portion 42 in the annular locking cavity 41 when a sufficient axial thrust is exerted on the shaft seal 40. Indeed, the projecting locking portion 42 of the seal of tree 40 and the cavity

  locking ring 41 formed in the cylindrical boss

  37 constitute an elastic snap fastening means

  which blocks the shaft seal 40 with respect to the element

  intermediate 35 of the joint cover. The end of the shaft seal which is opposed to said protruding portion of the verrina-42 has two inwardly facing sealing ribs 45 which seal tightly against the surface

  outside of the input shaft 13.

  Figure 3 shows an alternative embodiment of the shaft seal 40. In this construction, the cylindrical boss 37 of the intermediate member 35 of the joint cover has a

  annular locking groove 41, as in the case that

  be the Figure. In the alternative solution shown in FIG. 3, the shaft seal designated at 46 has a protrusion

  inner ring 47 as well as two inner ribs of

  48 which bear on the shaft 13 and correspond to the

  latching projecting portion 42 of the first embodiment

  FIG. 2. This shaft seal 46 further comprises a substantially hemispherical portion 49 forming a kind of shield concentric with the flange 36 of the intermediate member 35 as well as the outer surface of the outer member 27. shield 49 has an annular lip 50

  which bears tightly against the outer surface of the

  27. In order to further improve the sealing effect

  In that embodiment, an annular bead, such as that shown at 51, may be provided around the opening 52 on the input shaft side of the outer member 27. This bead 51 is hermetically sealed.

  against the inner surface of the shield 49.

  The articulation of the mechanical seal 11 at constant speed is partially absorbed by the articulation of the flange 36

  of the intermediate element 35 inside the spherical cavity

  34. The degree of articulation of the flange 36 in the cavity

  spherical tee 34 will preferably be sufficient to absorb

  shocks due to the road surface and vibrations

  curves and turns which the vehicle must normally

  meet during its operation. The depth of the spherical cavity 34 and the diameter of the flange 36 are

  chosen so that the flange 36 can move

  predetermined angular degree. For a transmission joint

  front-wheel drive vehicle, this predetermined angle is

  Viron 20 in each direction. The dimensions of the flange 36 and

  the depth of the spherical cavity 34 are also chosen

  so that the open end of the flange 36 carries

  be the bottom of the spherical cavity 34, 27 when the degree

- 10 -

  articulation exceeds this predetermined angle. In addition, the

  The articulation is then obtained by virtue of the rotational movement of the inner element 25 and the outer element 27 around the outer spherical surface 24 of the outer race 22. This articulation can absorb moreover up to a maximum 30 degrees of articulation in each direction, which is at least five degrees higher than what is normally required of a mechanical transmission joint for earlier drive wheels. However, this authorized articulation supplement only intervenes in exceptional circumstances, for example when negotiating turns.

  tight and / or when driving on a very rough surface.

  The inner member 25, the outer member 27, the intermediate member 35 and the shaft seal 40 will preferably be made of resistant, puncture-proof materials.

  and non-elastomers, or of semi-rigid elastomeric materials.

  It has been found that a polyurethane-based material is

  appropriate for the manufacture of each of these elements.

  ments. Preferably, the outer member 27 will be made of a material a little harder than the materials used to manufacture the inner member 25, to obtain a resistance

  the puncture and to improve the watertightness of the

  25. When manufactured with these materials,

  the joint cover 23 offers a substantially higher resistance

  punctures and tears, compared to the prior art flexible covers or sheaths for protecting mechanical transmission seals, while

  having dimensions which do not exceed the tolerances

  which makes the joint cover according to the present invention.

  able to lend itself to automatic mechanical manipulation

  robotics, and reduces the cost of

  lumber. Furthermore, the joint cover 23 will be more resistant

  under extreme temperature conditions as well as the

* normally against the service life of a transmission mechanical seal for front wheels of a traction vehicle

  before, while offering better resistance to the deterioration

  ration due to contact with the grease contained in the seal

  mechanical 11 at constant speed. According to another characteristic

  of the joint cover 23, the sliding movement of

- 11 -

  the flange 36 in the spherical cavity 34 will produce a self-lubricating effect because a portion of the inner surface of the flange 36 of the intermediate member 35 is in contact with the grease contained in the constant velocity mechanical seal. This self-lubricating effect is increased by the

  centrifugal forces acting on the fat during the

  tion of the mechanical seal at a constant speed and which tends to keep the grease in contact with the internal surfaces of the flange 36 during the hinge movements. Another

  characteristic of the joint cover 23 is that on the one hand the dia-

  meter of the opening formed by the bead 28 at the open end of the inner member 25 is smaller than the diameter of the outer spherical surface 24 of the outer race 22, and on the other hand the inner member 25, because of its non-elastomeric nature, is kept in place on

  the outer spherical surface 24 of the outer race

  by the elastic click, without being

  to use a collar or other means to contribute

  to this maintenance. This further reduces the cost price of

  these necessary for the manufacture of the mechanical seal with

  constant cost and the cost of assembling these

  rooms. Similarly, the intermediate element 35 is maintained

  metrically between the inner member 25 and the outer member 27 by the shaft seal 40, without having to use a clamping member or a groove to contribute to this restraint, which represents a further reduction of material and the

assembly cost.

  Various embodiments of the joint cover according to the present invention have been described with reference to their

  application to a transmission joint of the constant speed type

  aunt, since it is obvious that the invention has a very particular utility in this field. However, this type of seal or seal could also be applied to other types of transmission joints, for example those of the triangle type or ball contact, or even on

  transmission seals which are not of the constant speed type

  aunt, such as universal joints, from Hookes or Cardan.

  Although a preferred mode and a variant have been described

  embodiment of the invention, it is obvious for any

- 12 -

  in the art that modifications could be

  brought to the invention as it has been described without

  however, basic principles of the invention.

- 13 -

Claims (16)

  1. Cover or sheath for sealing a transmission mechanical seal (11) of the type comprising a shaft   input shaft (13), an output shaft (14) and an actuator   coupling for coupling the input shaft (13) to the   outlet (14), so that these shafts (13, 14) can be   to pull from one to the other, this coupling device   comprising in turn an outer race (22) having an outer spherical surface (24) integral with   of one of the input and output shafts (13, 14), this cover   joint being characterized in that it comprises: a) a semirigid inner member (25) of hemispherical shape, having an open end (29) which is hermetically applied against said outer spherical surface (24)   of the outer race (22) of the traction device   coupling and a first release opening (30)   at the opposite end to said opposite end (29) which   turns the other output or input shaft (14, 13);   b) a semi-rigid external element (27) of   shifting, concentric with the inner element (25) and   the latter so as to be in solidarity with it, that element ex-   dull (27) having a second release opening (52)   concentric with the first opening (30) of the element   at least one of these two inner and outer members (25, 27) having a reduced thickness portion which forms a spherical shaped cavity (34) between the inner member and the outer member, this cavity ( 34) opening at its end which is adjacent to said first and second clearance openings (30, 52); c) a semi-rigid intermediate element (35) provided with   a flange (36) of spherical shape which engages by sliding   in the spherical cavity (34) and a cylindrical boss (37) which hermetically surrounds the other shaft (14 or 13), the depth of the spherical cavity (34) and the radius of the spherical flange (36). ) at its open end being chosen so as to allow a certain degree of articulation of said intermediate element (35) in said spherical cavity   (34), the cylindrical boss (37) having an annular groove   locking wire (42) in its outer surface, and - 14 -   d) a shaft seal (40) having an inwardly projecting portion (42) which seats in   said annular locking groove (41) of the cylindrical boss   to lock the shaft seal (40) with respect to   port to the intermediate member (35), and at least one projecting rib (45) facing inwardly to seal against the outer surface of the other shaft input or output (13, 14).   2. The joint cover according to claim 1, characterized   in that the shaft seal (42) has two ribs (48)   which protrude inwards and bear against the over-   outer face of the other input or output shaft (13, 14). 3. The joint cover according to Claim 1, characterized in that the cylindrical boss (37) and the shaft seal (40) have bevelled surfaces (43, 44) which facilitate the axial movement of the intermediate element ( 35) and the shaft seal (40) relative to each other to engage the   projecting portion (42) of the shaft seal in the annular groove.   latch (41) of the cylindrical boss (37) which   rust the shaft seal (40) with respect to the inter- mediator (35).   4. The joint cover according to claim 1, characterized   in that said shaft seal (40) further comprises a   spherical cup (49) which tightly and slidably bears against said spherical outer surface (32) the outer member (27).   5. The joint cover according to claim 4, characterized in that said spherical shield (49) has a lip   ring (50) around its outer periphery, this   acting against the spherical outer surface (32) the outer member (37).   6. The joint cover according to claim 5, characterized   in that said outer member (27) has an annular bead   nular (51) bearing against the inner surface of said spherical clier (49).   7. The joint cover according to claim 1, characterized in that the inner member (25) has an annular cavity   (31) in its outer surface adjacent to its end or - 15 -   green and that the outer element (27) has an annular   (28) projecting inwards and retaining   in this inner annular cavity (31) in order to   rust the coupling between the outer element (27) and the   internally (25). 8. The joint cover according to claim 7, characterized in that the inner member (25) and the outer member (27) have   sufficient elasticity to enable that part to   inner lenient of the outer member (27) to resiliently lock into said annular cavity (31) when sufficient axial thrust is exerted on the inner member (25) and the outer member (27) for the bring one closer the other.   9. A joint cover (23) for sealing a radial joint   hinge type of the kind comprising an input shaft   (13), an output shaft (14), an inner race ring   (19) secured to one of these shafts (13, 14), an outer bearing ring (22) having an outer spherical surface integral with the other shaft (13 or 14), and a means   (16, 18) for coupling in rotation and articulation   inner bearing (19) to the outer race ring   (22), wherein the joint cover is characterized in that it comprises: a) an inner member (25) of spherical shape, having an open end which is hermetically applied to said outer spherical surface (24) of the ring outer race (22), a first relief opening (30) surrounding one of the input or output shafts (13, 14) and a peripheral cavity (34) formed in the outer surface (24) of the inner member (25) near said open end;   b) a spherical outer member (27) arranged   trestle over the inner member (25) and having a   an annular portion (28) projecting towards the interior   and fits into said peripheral cavity (34) in order to   lock the outer element (27) with respect to the element   dull (25) and secondly a second release opening   substantially concentric at the first clear opening   (30), at least one of the elements respectively internal - 16 -   (25) and outer (27) having a reduced thickness portion which forms a spherical shaped cavity having an end   open near the first and second openings   gagement; c) an intermediate member (35) having a flange   spherical (36) hermetically engaged and movable in the   said spherical cavity (34), and a cylindrical boss (37) which hermetically surrounds one of the input and output shafts (13, 14), said cylindrical boss (37) having   an annular locking groove (41) in its outer surface   and (d) a shaft seal (40) having a projecting portion   (42) facing inwards and which is housed in said housing   annular locking member (41) for locking the shaft seal (40) with respect to said intermediate member (35), said shaft seal (40) further comprising two sealing ribs (45) projecting towards inside and wear tightly against the outer surface of one of the trees input or output (13, 14).   O-ring according to Claim 9, characterized in that the radius of the spherical flange (36) is chosen so as to allow a certain amount of articulation of the intermediate element (35) in said spherical cavity (34). . 11. Joint cover according to Claim 10, characterized in that the shaft seal (46) comprises a spherical shield (49) which is slidably applied and sealed against the   outer spherical surface of the outer member (27).   12. Joint cover according to claim 9, characterized in that the cylindrical boss (37) and the shaft seal (46) have bevelled edges (44, 43) to facilitate the insertion of the annular portion. protruding (42) from the shaft seal (46) in the annular locking groove (41) by an elastic snap action when exerting axial thrust   to urge the cylindrical boss (37) and the gasket (46) towards each other.   13. Shaft seal (46) for the seal cover (23) of a mechanical seal (11) having an input shaft (13), an output shaft (14) and a coupling device for - 17 -   coupling the input shaft (13) to the output shaft (14), wherein the joint cover has at least one element (35)   provided with a cylindrical boss (37) which surrounds one of the   output shaft (13, 14), said shaft seal being characterized by comprising: a) an annular locking cavity (41) formed in the outer surface of said cylindrical boss (37), and b) a shaft seal (46) surrounding one of the shafts   in and out (13, 14) near said cyan boss.   lindrique (37), - said shaft seal (46) having on the one hand at least one rib (48) which projects inwards and is tight against one of the input and output shafts (13, 14), and on the other hand an annular portion (47) which projects inwardly and engages in the annular locking groove (41) to lock the seal   shaft (46) relative to the cylindrical boss (37).   A shaft seal as claimed in Claim 13, characterized in that the seal (46) has two inwardly projecting ribs (48) which bear tightly against each other.   input and output shafts (13, 14).   Shaft seal according to Claim 14, characterized in that the joint cover (23) has at least one element   an outer surface (27) provided with an outer surface of spherical   (32), this shaft seal further comprising a spherical shield (49) which slidably and movably bears against the spherical outer surface (32) of at least   the outer member (37) of the joint cover.   Shaft seal according to Claim 15, characterized in that said shield (49) has on its periphery an annular lip (50) facing inwards and which bears tightly against the spherical outer surface (32). the outer member (27).