Fixed ratio traction roller transmission

A traction roller transmission having a number of traction rollers arranged in an annular space between, and in engagement with, a sun roller structure and a traction ring structure for the transmission of motion therebetween includes sun roller and traction ring structures at least one of which has two concentric sleeves provided with complementary conical surfaces arranged opposite, and spaced from, one another and a plurality of bearing balls disposed in the space between the sleeves with an axial cam structure arranged axially adjacent one of the sleeves and adapted to force this sleeve into tighter engagement with the outer sleeve when a torque is transmitted through the transmission, thereby radially expanding the sleeves causing firm engagement of the traction rollers with the sun roller and traction ring structures.

BACKGROUND OF THE INVENTION 
The invention relates to planetary type, fixed ratio traction roller 
transmissions in which the contact forces applied to the traction surfaces 
of the transmission for the transmission of motion are dependent on the 
torque transmitted through the transmission. 
Basic traction roller transmissions are described, for example, by Harold 
A. Rothbart in "Mechanical Design and Systems" Handbook, pages 14`-8 and 
14-9, McGraw-Hill, New York, 1964. In the relatively simple arrangements 
of FIGS. 14.6 and 14.7 wherein the outer rings of planetary-type 
transmissions are slightly undersized to compress the roller arrangements 
therein, the surface pressure on the traction surfaces is always the same, 
that is, it is always at the highest value even if only a small torque is 
transmitted through the transmission. As a result, wear and losses are 
always relatively high. In the arrangements shown on page 14-8 of said 
handbook, means are provided for engaging the traction surfaces with each 
other with forces which are dependent on the torque transmitted through 
the transmission. 
It has been proposed to provide expandable sun roller structures provided 
with Belleville rings which, when axially compressed by torque-operated 
axial cams, were flattened to thereby grow radially and force the traction 
rollers into firm engagement with the traction ring (U.S. Ser. No. 281,983 
assigned to the assignee of the present invention). 
In another arrangement (descibed in U.S. Ser. No. 422,533, which is also 
assigned to the assignee of the present invention), a tapered ball screw 
structure is so associated with the sun roller or the traction ring that a 
torque transmitted through the transmission causes the tapered ball screw 
structure to expand radially for forcing the planetary traction rollers 
into firm engagement with the traction ring and the sun roller. However, 
while such an arrangement is quite simple, problems have arisen which 
limit the application of such transmissions. Especially, the transmission 
of larger torques is problematic as, in order to expand or compress the 
traction surface ring, the ball wedging angle must be relatively small so 
that the ring will remain locked under tension when the torque is reduced, 
especially if some torque is still applied. 
SUMMARY OF THE INVENTION 
In a traction roller transmission in which a number of traction rollers are 
arranged in an annular space between, and in engagement with, a sun roller 
structure and a traction ring structure for the transmission of motion 
therebetween, the sun roller or the traction ring structure includes two 
concentric sleeves provided with complementary conical surfaces arranged 
opposite, and spaced from, one another with a plurality of bearing balls 
disposed in the space between the sleeves which facilitate axial and 
rotational movement of one of the sleeves relative to the other. An axial 
cam structure is so arranged axially adjacent one of the sleeves that the 
sleeves are forced into tighter engagement with one another when a torque 
is transmitted through the transmission, thereby causing radial expansion 
of the sleeves and firm engagement of the traction rollers with the sun 
roller and traction ring structures. 
The cone angle is at least 5.degree. to prevent locking of the sleeves but 
preferably not more than 15.degree. to avoid excessive axial loads and 
uneven force distribution.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As shown in FIGS. 1 and 2, the traction roller transmission includes, in a 
housing 1, a traction ring structure 2, a sun roller 3 centrally disposed 
within the traction ring structure 2 and mounted on, or being part of, an 
input shaft 4. The sun roller 3 has an outer diameter substantially 
smaller than the inner diameter of the traction ring structure 2 such that 
an annular path 5 is formed between the traction ring structure 2 and the 
sun roller 3. Planetary traction rollers 6 are disposed in the annular 
path 5 between the traction ring structure 2 and the sun roller 3 and in 
engagement with the traction ring structure 2 and the sun roller 3. The 
planetary traction rollers 6 are rotatably supported by bearings 7 on 
shafts 8 extending between the flange 9 of an output shaft 10 and the 
opposite support plate 11 of a support cage 12 mounted on the output shaft 
flange 9 by bolts. The output shaft 10 is supported in the housing 1 by a 
bearing 13 and the input shaft 4 is supported in the housing 1 by a 
bearing and by the traction rollers 6, or alone by the traction rollers 6. 
The traction ring structure 2 consists of a back-up sleeve 14 mounted in 
the housing 1 and having a slightly conical inner surface 15 and a 
traction sleeve 16 having a conical outer surface 17 corresponding to the 
conical inner surface 15. Both conical inner and outer surfaces 15, 17 are 
spaced from one another. 
Bearing balls 18 are arranged in the space 19 between the back-up sleeve 14 
and the traction sleeve 16, which bearing balls 18 facilitate axial 
translation of the traction sleeve 16 within the back-up sleeve 14. The 
traction sleeve 16 has a radially outwardly projecting lip 20 at its small 
outer diameter axial end and the back-up sleeve 14 has a radially inwardly 
projecting lip 21 at its larger inner diameter axial end adapted to retain 
the bearing balls 18 in the annular space 19 between the back-up sleeve 14 
and the traction sleeve 16. A radial fill hole 22 is provided in the 
back-up sleeve 14 for inserting the bearing balls 18, the fill hole 22 
being closed by a removable plug 23. 
Axially adjacent the larger diameter outer end of the traction sleeve 16 
there is provided a cam structure 24 consisting of axial cam lobes 25 
associated with the housing 1 and opposite axial cam lobes 26 associated 
with the traction sleeve 16 with rollers 27 disposed between the opposite 
axial cam lobes 25, 26. A plurality of such cam lobes are provided with 
lobe surfaces disposed at both sides adjacent each roller 27 so that 
relative rotation of the traction sleeve 16 in either direction will force 
the traction sleeve 16 axially into the back-up sleeve 14 for axial 
compression of the traction sleeve 16 into engagement with the traction 
rollers 6 therein and of the traction rollers 6 into engagement wth the 
sun roller 3. 
The sun roller 3, together with the input shaft 4, is supported at one end 
in the housing 1 by an anti-friction bearing 28 and, at the other end, has 
an axial projection 29 which is received in a cavity 30 in the output 
shaft 10 and is supported therein by an anti-friction bearing 31 so as to 
firmly support the input shaft 4 also when the sun roller 3 is not engaged 
by the traction rollers 6. 
The traction roller transmission provided hereby is quite simple and easy 
to manufacture. The balls filled into the space 19 between the back-up 
sleeve 14 and the traction sleeve 16 provide for friction-free axial and 
rotational movement of the traction sleeve within the back-up sleeve so 
that a torque transmitted through the transmission and generating a 
corresponding reaction torque on the traction sleeve 16 will cause the 
reaction sleeve to be forced by the cam structure 24 axially into the 
back-up sleeve for firm engagement of the traction rollers 6 with the sun 
roller 3 and the traction sleeve 16. 
Preferably, there are provided at least three traction rollers 6, all 
spaced equally around the sun roller, although only one is shown in the 
cross-sectional view of FIG. 1. 
In order to permit filling of the bearing balls 18 into the space 19 
between the back-up sleeve 14 and the traction sleeve 16 there may be 
provided a retaining ring 32 as shown in the lower part of FIG. 1--in 
place of the plugged fill hole 22. 
It is further noted the cone angle .alpha. of the inner surface of the 
back-up sleeve 14 and the outer surface of the traction sleeve 16 should 
be at least 5.degree. to avoid locking of the traction sleeve 16 within 
the back-up sleeve 14 and the angle .alpha. should be no greater than 
15.degree. to avoid uneven stress deflection and the need for large axial 
forces, that is, relatively flat axial cam lobes 25 and 26. 
In the arrangement as shown in FIGS. 1 and 2, the loading means is shown 
associated with the traction ring structure 52. However, if the sun roller 
is sufficiently large, the loading means may just as well be associated 
with the sun roller as shown in FIG. 3. Here, a housing 50 again encloses 
traction rollers 51 arranged between a traction sleeve 52 and mounted for 
rotation with an output shaft 53 by means of a flange member 66, while the 
input shaft 54 carries the sun roller structure 55. The sun roller 
structure 55 consists of an inner conical sleeve 56 mounted on the input 
shaft 54 and an outer sleeve 57 having a conical inner surface 58 arranged 
opposite of, and spaced from, the conical outer surface 59 of the inner 
sleeve 56, the space between the conical inner and outer surfaces being 
again filled with bearing balls 60. The bearing balls 60 are retained by 
the circumferential lip 61 on the inner sleeve 56 and the retaining ring 
62 mounted on the outer sleeve 57. A cam structure 63 is provided between 
a flange 64 mounted on the input shaft 54 and the axial end of the outer 
sleeve 57 having the smaller inner diameter so as to force the outer 
sleeve 57 onto the inner sleeve 56 when a torque is transmitted through 
the transmission. This causes expansion of the outer sleeve 57 thereby 
forcing the traction rollers 50 into firm engagement with the sun roller 
structure 55 and the traction ring 52 for transmitting motion from the sun 
roller structure 55 to the traction ring 52. Traction rollers 54 are 
supported on a drive bell 56 which is mounted on the output shaft 53. It 
is noted, however, that torque may be transmitted in either direction, 
that is, what is termed input shaft may be output shaft and vice versa. 
This arrangement is suitable for use where the sun roller structure may be 
relatively large. It is very simple and effectively prevents locking. The 
sun roller structure may be pre-assembled and readily mounted on the sun 
roller by means of a retaining bolt 65. 
Again, the cone angle at the interface between the inner and outer sleeves 
is preferably between 5.degree. and 15.degree..