Axially fixed homokinetic transmission joint having a sleeve with centering lugs engaged with spherical wall surfaces of a driving barrel

An axially fixed homokinetic tripod joint for high-speed motor vehicle transmission has a tube (2) constituting a transmission shaft connected to a sleeve (26) in which extends a stem (6) provided at its end with a tripod element (10) cooperative with an adapted barrel (20) carried by a complementary transmission shaft. The sleeve (26) has at its free end three centering lugs (34A) which have an outer spherical surface and which cooperate with a spherical central cavity in the barrel (20) for providing an axially fixed and articulated assembly of the joint.

BACKGROUND OF THE INVENTION 
The present invention relates to an axially fixed articulated homokinetic 
transmission joint, in particular for a motor vehicle. 
The invention more particularly relates to an articulated homokinetic 
transmission joint of the type comprising a tripod element provided with 
three trunnions carrying rotative rollers and a driving barrel comprising 
three pairs of raceways spaced apart on the periphery of a central cavity 
of the driving barrel with respect to which the tripod element is capable 
of undergoing slight radial eccentricities due to the angular operation of 
the joint. The tripod element is carried by a stem connected to rotate 
with a driving or receiving shaft, the stem extending substantially 
axially in a sleeve which is connected to the shaft at a first end and has 
at its second end an outwardly spherical bell mouth provided with three 
recesses defining clearances for the three rollers of the tripod element. 
The recesses define on the outwardly spherical bell mouth three lugs for 
radially centering the sleeve in the central cavity of the driving barrel. 
Many axially fixed transmission joints are known in which a means for 
axially immobilizing a first shaft relative to a second shaft in the 
direction corresponding to their relative motions toward and away from 
each other is adapted for shafts rotating with large operating angles, on 
the order of 10.degree. to 12.degree., but at relatively low speeds, or 
rotating at high speeds, but with relatively small operating angles. 
The use of tripod joints as high-speed transmission joints is of interest 
in many applications owing to their high power transmitting capacity, 
their high efficiency, and their perfectly homokenetic character. However, 
their use has been limited to applications involving relatively small 
operating angles, since the tripod joint, by its very design, is subjected 
at high speed to cyclic radial excitations in the stem carrying the tripod 
element due to the eccentric rotation of the revolving masses connected to 
the tripod element. These cyclic radial excitations may give rise to 
unpleasant vibrations in the device in which the joint is mounted, for 
example the transmission of a motor vehicle. 
Document FR-A-1 440 784 discloses a homokinetic transmission joint of the 
aforementioned type which provides a solution to this problem of cyclic 
radial excitations. However, this homokenetic joint is of the sliding 
type, and only permits high-speed transmission of rotation at a relatively 
small angle between the two transmission shafts, owing to the sliding. 
Moreover, this joint becomes rapidly worn. 
Now, in practice, in particular in the design of a transmission for a motor 
vehicle, it is often necessary to employ an axially fixed homokinetic 
transmission joint. 
SUMMARY OF THE INVENTION 
An object of the invention is to provide an articulated homokinetic 
transmission joint which permits high-speed operation at large operating 
angles without giving rise to cyclic radial vibrations in the shaft 
connected to the tripod element and which is axially fixed. The invention 
therefore provides an axially fixed articulated homokinetic transmission 
joint of the aforementioned type, characterized in that the central cavity 
of the barrel comprises three spherical wall portions cooperative with the 
centering lugs of the sleeve for axially positioning, in a ball joint 
manner, the tripod element relative to the barrel. 
The invention may also have one of the following advantageous features: 
the barrel is open on a side remote from the shaft to permit placing the 
tripod element in position in the barrel when the lugs of the sleeve are 
engaged on the spherical wall portions of the cavity; 
the barrel carries a removable fluidtight cap, which may be for example set 
in position on the barrel and covers the opening of the barrel provided 
for inserting the tripod element in the barrel; 
the tripod element is carried by a splined end of the stem, the opposite 
end of the stem being connected to the shaft; 
the tripod is in one piece with the stem; 
the stem is provided at one of its ends with splines which are cooperative 
with complementary inner splines in the sleeve for their interconnection 
in rotation; 
the splines of the stem have a crowned profile permitting an angular 
movement of the stem relative to the sleeve; 
the joint comprises means for resiliently pressing the splined end of the 
stem against an inner shoulder of the sleeve; 
the cap has a pressure-applying region formed by an inwardly projecting 
deformation of the cap which resiliently acts on the unsplined end of the 
stem along the axis thereof; and 
a circular ring is interposed between the splined end of the stem and the 
shoulder of the sleeve.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
In a first embodiment shown in FIG. 1, a tube 2 forming a transmission 
shaft is axially welded to a cylindrical enlarged portion 4 which has the 
same diameter as the tube 2 and is in one piece with a stem 6. The stem 6 
extends along the same axis X--X' as the tube 2. The stem 6 has at its 
free end a splined portion 8 on which the hub of a tripod element 10 is 
mounted. 
In a conventional manner, the tripod element 10 comprises three radial 
trunnions 12 evenly spaced 120.degree. apart around the axis of rotation 
X--X' of the stem 6 carrying the tripod element. Each trunnion 12 has a 
cylindrical lateral outer surface whose axis intersects and is 
perpendicular to the axis of rotation X--X' of the tripod element. Each 
trunnion 12 receives a roller 14 which is rotatively and slidably mounted 
on a needle bearing 16. The rollers 14 have a spherical outer surface 18. 
A driving barrel 20, having the general shape of a thick disc and an axis 
Y--Y', is connected to a second transmission shaft (not shown in FIGS. 1 
and 2), and is the complementary part of the joint. The barrel 20 shown in 
FIG. 3 has an axial central cavity 22 around which there are provided, 
evenly spaced 120.degree. apart, three pairs of raceways 24A, 24B and 24C. 
These raceways are formed by three cylindrical bores opening onto the two 
end faces of the barrel 20 and communicating in the direction of the axis 
Y--Y' with the central cavity 22. The axes of these three bores are 
parallel to the axis Y--Y'. 
The raceways 24A, 24B, 24C constitute tracks for the rollers 14 of the 
tripod element 10. The latter is mainly contained within the barrel 20. 
The splined portion 8 of the stem 6 extends through the central cavity 22 
of the barrel 20. 
A sleeve 26 having an axis X--X' surrounds the stem 6 and is welded at one 
of its ends to the cylindrical enlargement 4 of the stem 6. The sleeve 26 
has in succession, starting at the enlarged portion 4, a section 27 of the 
same diameter as the enlarged portion 4, a section 28 of a smaller 
intermediate diameter, and then a narrowed section 29 extended by an 
outwardly spherical bell mouth 30 constituting the free end of the sleeve. 
As can be seen in FIG. 4, the spherical bell mouth 30 of the sleeve 26 has 
three longitudinal recesses 32 defining three centering lugs 34A, 34B and 
34C. The three centering lugs 34A, 34B and 34C therefore have outer 
surfaces consisting of portions of the same sphere. The recesses 32 
constitute clearances for the rollers 14 of the tripod element 10. 
As shown in FIG. 3, the centering lugs 34A, 34B, 34C cooperate with 
conjugate spherical wall portions 36A, 36B, 36C of the central cavity 22 
of the barrel 20. These spherical wall portions 36A, 36B, 36C of the 
central cavity 22 are delimited on each side by the raceways 24A, 24B, 24C 
for the rollers of the tripod element and are respectively opposite the 
latter relative to the center of the barrel 20. 
The guiding lugs 34A, 34B, 34C, having a spherical outer surface cooperate 
with the spherical wall portions 36A, 36B, 36C of the cavity 22 and 
constitute a ball joint which affords articulation and axial fixing of the 
sleeve 26 relative to the barrel 20, and therefore of the tube 2 relative 
to the complementary transmission shaft (not shown). 
The sleeve 26 has a high radial rigidity and constrains the tube 2 to 
rotate in a perfectly centered manner about the axis X--X' without 
sensitivity to the cyclic radial excitations transmitted through the 
tripod element 10 to the stem 6, which is less rigid as concerns bending 
than the sleeve 26. 
A fluidtight cap 38 set or formed over onto the periphery of the lateral 
wall 39 of the barrel 20 seals the joint by covering the face of the 
barrel remote from the tube 2. This cap defines, with a bellows 40 
extending from the lateral wall 39 of the barrel 20 to the portion 28 of 
intermediate diameter of the sleeve 26, a sealed space 41 in which a 
lubricant is retained for the moving parts of the joint. 
Tapped holes 42 are provided on the face of the barrel 20 remote from the 
tube 2 to permit axial fixing by means of screws of the complementary 
transmission shaft (not shown) of the joint. 
To assemble the joint, with the tripod element 10 not yet mounted on the 
stem 6, the free end of the sleeve 26 is placed in the barrel 20 by 
inserting with a large circumferential clearance the guiding lugs 34A, 
34B, 34C in the cylindrical bores delimiting the raceways 24A, 24B, 24C, 
as shown in dot-dash lines in FIG. 3. The sleeve is then turned relative 
to the barrel 20 about the axis X--X' so that the guiding lugs of the 
sleeve come into contact with the spherical wall portions 36A, 36B, 36C of 
the barrel 20, which have a complementary shape. The tripod element 10 is 
maintained on the stem 6 by a sliding it along the splines of the splined 
portion 8, the tripod element being received in the barrel 20. 
The tripod element 10 is maintained on the stem 6 by a circlip or by a 
setting or forming over (not shown) at the end of the stem 6. The sealing 
cap 38 is then set or formed over on the barrel 20. 
FIG. 2 shows a second embodiment of an axially fixed homokinetic tripod 
joint according to the invention. Elements of the joint which are 
identical or similar to those shown in FIG. 1 carry the same reference 
numerals, and only the differences relative to the first embodiment will 
be described. 
The tripod element 10 is in one piece with the stem 6, which is short, and 
has at its other end a splined portion 44. This splined portion, of 
limited length, cooperates with a corresponding splined portion 46 
provided on the inner surface of the narrowed section 29 of the sleeve 26. 
The splined portion 44 of the stem 6 bears at its free end, through a 
thrust O-ring 48 which also affords a seal, against a shoulder 50, which 
is an integral part of the inner wall of the sleeve 26 in the narrowed 
part 29 of the latter. 
The sealing cap 38, set on or formed over the lateral wall 39 of the barrel 
20, has at the center a pressure-applying region 52 which exerts a 
resilient axial pressure on the end of the stem 6 carrying the tripod 
element, along the axis of the latter. This pressure-applying region 52 is 
obtained by inwardly deforming the cap 38 which is made from a flexible 
sheet. It maintains the tripod element 10 in the barrel 20 and ensures 
that the stem 6 bears against the ring 48. 
As in the preceding embodiment, the tripod element 10 can undergo slight 
eccentricities relative to the barrel 20 while it transmits without 
vibration the rotation imparted thereto by the barrel 20 to the sleeve 26 
and therefore to the tube 2, through the splined portions 44 and 46. 
This joint is assembled in a manner similar to the manner of assembling the 
previously-described joint, the tripod element 10 and the stem 6 being 
inserted after the spherical end of the sleeve has been mounted in the 
barrel. 
It will be understood that the two described embodiments may have their 
features combined to provide desired technological alternative 
embodiments.