Constant velocity control of the tripod type

A tripod joint has an outer joint part with three circumferentially distributed axis-parallel recesses which form circumferentially opposed tracks. An inner joint part with a star-shaped cross-section and three circumferentially distributed arms engages the recesses of the outer joint part. The arms hold roller assemblies. Each roller assembly includes a roller carrying means and a roller directly riding on the tracks. On each arm, a roller carrying element is held to be axially and angularly movable relative to the arm axis. Also, on each roller carrying element, the roller is axially secured and rotatably supported via a rolling contact bearing. A friction reducing mechanism is provided between the roller carrying elements and rollers. The friction reducing mechanism is effective with respect to the relative rotational movements taking place between the elements and rollers under axial forces.

BACKGROUND OF THE INVENTION 
The present invention relates to a tripod joint, and more specifically, to 
a tripod joint with an outer joint part having three circumferentially 
distributed axis-parallel recesses which form circumferentially opposed 
tracks. An inner joint part has a star-shaped cross-section and three 
circumferentially distributed arms which engage the recesses of the outer 
joint part. The arms hold roller assemblies which each include a roller 
carrying means and a roller directly riding on the tracks. On each arm, a 
roller carrying element is held so as to be axially and angularly movable 
relative to the arm axis. Also, on each roller carrying element, a roller 
is axially secured and rotatably supported via a rolling contact bearing. 
Known tripod joints are described in DE 28 31 044 (Honda), and DE 39 36 601 
(GKN) for example. In both cases, the roller, especially via a needle 
bearing, is rotatably supported on a roller carrier. The roller carriers 
are arranged to be axially movable on the arm and pivotable relative to 
the arm axis. 
In the first design, movability is achieved via an inner ring which, via a 
spherical outer face, engages an at least partially internally spherical 
inner face of the roller carrier. The inner ring is designed to be 
internally cylindrical and with a cylindrical arm being axially movable 
therein. 
In the second case, the roller carrier is provided with an internally 
cylindrical inner aperture, which is axially movably and pivotably engaged 
by an arm with a part-spherical outer end. 
Below, all parts of the "roller assembly" with the exception of the 
"roller" itself will be referred to as "roller carrying means". The 
expression "elements of the roller assembly" refers to the "roller 
carrier" and the "roller" itself, with the "roller carriers" being 
regarded as "non-rotating elements of the roller assembly". 
With a joint rotating in the articulated condition, there occurs, with 
reference to the inner joint part, radially oscillating movement of the 
rollers relative to the joint axis and pivoting movement of the rollers on 
the arms. At the same time, with reference to the outer joint part, there 
occurs longitudinally extending oscillating rolling movement of the 
rollers along the tracks. The first mentioned radial and pivoting 
movements are accompanied by sliding friction. The next mentioned rolling 
movement predominantly occurs in the form of rolling contact movement. As 
a result of the friction forces, the prior art tripod joints, with an 
increasing joint articulation angle, are characterised by an increase in 
the joint excitation forces, e.g. in the cyclic forces generated in the 
joint and transmitted to the driveline. If, as a result of the movements 
occurring when the joint rotates in an articulated condition, an arm, with 
reference to the outer joint part, is displaced radially inwardly, with 
the roller having to support itself radially inwardly relative to the 
outer joint part, the sliding friction forces are particularly high and 
disadvantageous. In particular, this applies to sliding friction forces 
caused by supporting forces resulting from tilting moments around axes at 
the roller assemblies assumed to be located transversely relative to the 
joint axis. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide a tripod joint which reduces 
the excitation forces which result from sliding friction in the joint. A 
first solution provides a rolling contact bearing between at least one end 
face of a roller and an opposed face of a holding means connected to the 
roller carrying element. A second solution provides each rolling member of 
the rolling contact bearing to be held by a cage. In both cases, between 
the roller carrying elements and rollers, friction reducing means is 
provided. The friction reducing means is effective irrespective of 
relative rotational movements taking place between the elements and 
rollers. This is particularly advantageous if relative axial forces occur 
between the two components. 
The friction reducing means, with reference to the rollers, is arranged at 
the roller carriers relative to the opposing holding means. Thus when the 
joint rotates in the articulated condition, the tumbling and diving 
movements of the arms relative to the rollers result in constantly 
changing axial forces between the roller carriers and rollers. The axial 
forces, upon relative rotational movements between the roller carriers and 
rollers, lead to increased friction forces. The friction forces are 
reduced as a result of the above. The reduction in friction forces 
smoothes and facilitates the movement of the rollers in the tracks in the 
axial direction, with reference to the outer joint part, so that the 
resulting joint excitation forces are reduced. 
As the axial supporting forces between the roller carrier and roller, with 
reference to their axis, constantly change their relative orientation when 
the joint rotates in the articulated condition. It is proposed that the 
friction reducing means in accordance with the invention, relative to the 
respective holding means, be provided opposite the two end faces of the 
rollers at the roller carriers. Further, the holding means at the roller 
carrier may either be an integral annular shoulder or a combination of a 
disc and securing ring held in an external groove. 
A rolling contact bearing may be provided between at least one end face of 
a roller and an opposed face of the holding means connected to the roller 
carrier. Thus, more sophisticated design measures achieve a maximum 
reduction in friction. The rolling contact bearing should preferably be 
provided at both axial end faces of the roller, e.g. on the radial inside 
and outside of the roller with reference to the joint axis. The rolling 
contact bearings are preferably provided with a cage. The rolling members 
of the rolling contact bearings may be designed as balls or needles. In 
the case of needles, outwardly increasing conical needles are preferred. 
Further, additional elements whose surfaces reduce sliding friction may be 
provided in each case between an end face of a roller and holding means 
connected to the roller carrier. Also, a holding element, which is 
connected to the roller carrier and whose surface reduces sliding 
friction, is positioned opposite at least one end face of the roller. 
It is advantageous to combine the two above-mentioned embodiments such that 
the former is provided to cooperate with a radially inner shoulder element 
at the roller carrier. The latter is arranged at the opposed end face of 
the roller on the radial outside of the roller carrier. 
The surfaces which reduce sliding friction may be provided in the form of 
phosphated surfaces, plastic-coated surfaces at the metallic elements or 
the surfaces of the components are made of a tribologically advantageous 
material. A steel-on-steel contact between the rollers and parts of the 
roller carrying means is thus advantageously avoided. 
In a preferred further development of the invention, the additional 
elements or holding means includes shoulder elements. With reference to 
the roller carrier, the shoulder elements are provided with an at least 
axially outwardly directed surface which reduces sliding friction and 
which embraces the end face of the roller carrying element. Such a design 
not only leads to a reduction in friction between the roller and roller 
carrier, but also between the roller carrier and the outer joint part in 
case the roller carriers, with reference to their axis, are directly 
axially supported relative to the outer joint part. Such a design is not 
required if the rollers themselves, with reference to their own axis, 
provide axial support by engaging the tracks. 
As far as the contents at the shoulder elements are concerned, the 
expression "friction reducing surfaces" applies the same as previously 
mentioned with reference to the additional elements and holding elements 
themselves to which the shoulder elements may preferably be integrally 
connected. 
In a preferred embodiment, the additional elements or holding elements are 
radially resilient annular elements. The elements are distributed around 
the circumference of, or through internal tension, secured to the roller 
carrier. However, the shoulder elements may also be provided separately 
from the additional elements or holding elements at the roller carrier and 
may be independently inserted or clamped on. 
From the following detailed description taken in conjunction with the 
accompanying drawings and subjoined claims, other objects and advantages 
of the present invention will become apparent to those skilled in the art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Below, FIGS. 1 through 3 will be described together to the extent that they 
include identical elements, which have been given the same reference 
numbers. 
FIGS. 1 through 3 each show a substantially annular inner joint part 11 
with circumferentially distributed radial cylindrical arms 12. An outer 
joint part 13 with circumferentially distributed recesses 14 engages the 
arms 12. Roller assemblies are provided on the arms 12. 
Each roller assembly includes an inner ring 15 with an internally 
cylindrical inner surface and an externally spherical outer surface. 
Relative to the arm 12, the inner ring 15 may oscillate axially relative 
to the arm axis. On the inner ring 15 a roller carrier 16 is held which, 
via an internally spherical recess, is pivotably positioned on the 
externally spherical outer surface of the inner ring 15. A roller 18 is 
rotatably held on the roller carrier 16 via bearing means 17a through c. 
The externally spherical roller 18 rides on one of the tracks 22 in the 
recess 14. In the radial interior of the roller assembly, the two halves 
of the track each include a shoulder 20 of which, on the radial inside, 
supports the roller carrier 16 via an annular shoulder 19. The roller 
carrier 16 may be supported on a supporting face 21 on the radial outside 
of the roller assembly. The bearing means 17a (FIG. 1) are described in 
greater detail in FIG. 7, the bearing means 17b (FIG. 2) in FIG. 8 and the 
bearing means 17c (FIG. 3) in FIG. 9. 
FIGS. 4 through 6 will be described together to the extent that they 
include identical elements, which have been given the same reference 
numbers. 
FIGS. 4 through 6 show a substantially annular inner joint part 31 which 
includes radially adjoining circumferentially distributed externally 
spherical arms 32. The arms 32 are inserted into circumferentially 
distributed recesses 34 of an outer joint part 33. Roller assemblies are 
positioned between the arms and recesses. 
The roller assemblies each include a roller carrier 36 with an internally 
cylindrical inner aperture. The carrier 36 is held to be pivotable and 
axially movable on the arm 32 with reference to the arm axis. A roller 38 
is held on the roller carrier 36 via bearing means 37a through c. The 
externally spherical roller 38 rides on one of the tracks 42 in the recess 
34. On the radial inside of the roller assembly, both halves of the track 
each include a shoulder 40 which, on the radial inside, supports the 
roller carrier 36 via an annular shoulder 39. Also, the roller carrier 36 
may be supported on a supporting face 41 on the radial outside of the 
roller assembly. The bearing means 37a (FIG. 4) are described in greater 
detail in FIG. 7, the bearing means 37 (FIG. 5) in FIG. 8 and the bearing 
means 37c (FIG. 6) in FIG. 9. 
FIG. 7 shows an inner joint part 131 with one of the spherical arms 132. 
Teeth 133 and a securing ring 134 hold the inner joint part on shaft 
journal 135. The securing ring 134 rests against the inner joint part and 
engages an annular groove 136 in the arm 132. 
The roller assembly in accordance with the invention includes a roller 
carrier 137 in whose internally cylindrical recess 138 the spherical arm 
is positioned so as to be axially and, angularly movable. A first annular 
insert 149 in the recess 138 forms an upper stop and a lower annular 
insert 150 forms a pivot stop for the arm 132. 
A roller 140 is rotatably supported on the roller carrier 137 via a needle 
bearing 139. With reference to the common axis, the roller 140 is axially 
supported on the roller carrier 137 on an annular shoulder 141 on the one 
hand and on a disc 142 on the other hand. The disc 142 is held by a 
securing ring 143 engaging an annular groove 144 on the outside of the 
roller carrier 137. Direct contact between the holding means is 
established via the annular shoulder 141, ball bearing 146 with cage 148, 
on the one hand and the disc 142 and securing ring 143 in connection with 
the annular groove 144 and ball bearing 145 with cage 147 on the other 
hand. The annular shoulder 141 and the disc 142 as well as the axial end 
faces of the roller 140 are provided with grooves for guiding the ball 
bearings 145, 146. 
In FIG. 8, any details corresponding to those in FIG. 7 have been given 
reference numbers increased by 20. The difference between the two figures 
is that needle bearings 165, 166 are provided instead of ball bearings. 
The needle bearings 165 may have a cylindrical or conical shape. 
In FIG. 5, any details corresponding to those in FIG. 7 have been given 
reference numbers increased by 40. FIG. 9 deviates from FIG. 7 in that 
instead of a first rolling contact bearing a holding element 185 is 
provided which directly engages the annular groove 184. The holding 
element 185 includes a friction reducing material. The holding element 185 
may be formed of a plate metal, have a non-steel bright surface, or be a 
self supporting holding element. Further, in FIG. 9, instead of a second 
rolling contact bearing between the annular shoulder 181 and the roller 
180, an additional element 186 with a friction reducing surface is 
provided. Both elements 185, 186 may have friction reduction surface such 
as phosphated surfaces or plastic coated surfaces. At the roller carrier 
177, with reference to the joint axis, an externally positioned shoulder 
element 187 is provided. The shoulder 187 is of a friction reducing 
material. Also positioned on the opposite side is a shoulder element 188 
of a friction reducing material. The shoulder element 187 is integrally 
connected to the holding element 185 and the latter 188 is integrally 
connected to the additional element 186. The components may be clamped on 
to the roller carrier 177 if, in some region of its circumference, it is 
provided with slots. 
While the above detailed description describes the preferred embodiment of 
the present invention, the invention is susceptible to modification, 
variation, and alteration without deviating from the scope and fair 
meaning of the subjoined claims.