Extended life infinitely variable traction roller transmission with different toric traction roller disks

In an infinitely variable traction roller transmission, wherein two toric traction disks are rotatably supported opposite one another and define a toric cavity in which at least two motion transmitting traction rollers are disposed in engagement with the two toric disks and supported by trunnions, the trunnions being pivotally supported to permit changing the ratio of motion transmission between the toric disks, the toric disks each have a different cavity radius, thus causing the circles of contact of the traction rollers with the toric disk to change as the trunnions pivot to various transmission ratio positions, thereby distributing the loads on the traction rollers over a relatively large surface area thus extending the fatigue life of the traction rollers, and consequently, of the transmission.

BACKGROUND OF THE INVENTION 
The invention relates to an infinitely variable traction roller 
transmission in which power is transmitted through traction rollers 
pivotally supported between toric input and output disks. 
To enable such toroidal traction roller motion transmissions to transmit 
large torques at high speeds over a long period of time, the traction 
rollers are positioned inwardly of the center of the toroidal cavity 
between the toric disks and are engaged with the toric disks with 
considerable forces causing large surface loads on the traction rollers. 
For transmissions of toric design, the fatigue life of the drive system is 
controlled by the traction roller element since the rolling contact track 
of the roller is in continual contact whereas the circle of rolling 
contact on the toric disks is continually moving across the entire surface 
of the disks as the motion transmission ratio is varied. 
It is the object of this invention to provide a design in which the life of 
the power transmitting traction rollers which determine the life of the 
transmission, is substantially increased. 
SUMMARY OF THE INVENTION 
This is achieved in an infinitely variable traction roller transmission, 
wherein two toric traction disks are rotatably supported opposite one 
another on co-axial input and output shafts and define a toric cavity in 
which at least two motion transmitting traction rollers are supported by 
trunnions and disposed in engagement with the two toric disks along a 
circle of contact. The trunnions are pivotally supported to permit 
changing the ratio of motion transmission between the toric disks wherein 
the toric disks are dimensioned such that each has a different cavity 
radius, thus causing the circles of contact of each traction roller with 
the toric disks to move as the traction rollers pivot to different 
transmission ratio positions so as to distribute the surface loads over a 
relatively large roller surface area. This greatly extends the fatigue 
life of the traction roller and, consequently, of the transmission.

DESCRIPTION OF A PREFERRED EMBODIMENT 
A simple traction roller power transmission arrangement as shown in FIG. 1 
consists of a housing 10 having coaxial input and output shafts 12, 14 
rotatably supported therein by bearings 16 and 18. Associated with the 
input and output shafts 12, 14 are toric disks 20, 22, which are disposed 
opposite one another and are shaped so as to define therebetween a toric 
cavity 24 of essentially circular cross-section. The toric disks 20, 22 
however have two slightly different cavity radii. Within the toric cavity 
24, traction rollers 26, 28 are rotatably supported in engagement with the 
toric traction disks 20, 22. 
The traction rollers 26, 28 are supported in the housing 10 by pivot 
trunnions 30, 32 which are pivotally supported by way of trunnion support 
rollers 34, 36 running on hard metal track members 38, 40 received in 
track cavities 42, 44 formed in the housing 10. Each of the pivot 
trunnions 30, 32 carries a traction roller bearing 46 for rotatably 
supporting the associated traction rollers 26, 28 which are forced into 
firm engagement with the traction disks 20 and 22 by way of the trunnion 
support rollers 34, 36. The traction disks 20, 22 are supported in the 
housing 10 by axial thrust bearings 48 and 50, respectively. 
As shown in FIGS. 2-4, each of the pivot trunnions 30, 32 includes a 
cylinder 52 with a hydraulic trunnion piston 54 disposed therein. The 
pivot trunnion piston 54 carries the support roller 34. A post 56 extends 
from the trunnion piston 54 through an opening 58 in the trunnion cylinder 
52 and is pivotally received within the traction roller 26 and engaged 
therein by a pivot bearing structure 59, which allows the pivot trunnion 
30 to tilt slightly relative to the trunnion piston 54. This makes it 
possible for the traction roller to adapt to the different curvatures of 
the toric surfaces of the traction disks 20 and 22 in the various pivot 
positions of the trunnion. 
The piston 54 has a relatively large play in the cylinder 52 and is 
provided with relatively wide seal rings 60 which are seated in deep 
grooves. Also the seal rings 62 in the opening 58 are relatively wide and 
the opening 58 is relatively large to permit the tilting of the piston 54 
in the cylinder 52. Furthermore, the edges of the piston 54 may be rounded 
to accommodate the tilting of the piston 54 in the cylinder 52. 
Hydraulic operating fluid is supplied to the cylinder 52 to force the 
traction roller 26, 28 into engagement with the toric disks 20, 22. The 
engagement forces of the traction rollers 26, 28 with the toric traction 
disks 20 22 depend on the loading applied by the hydraulic operating 
fluid. 
FIGS. 2, 3, and 4 show the traction roller 26 in various engagement 
positions for different transmission ratios. 
FIG. 2 shows the traction roller 26 in its 1:1 transmission ratio position. 
At this point, forces are distributed evenly, contact force left cf.sub.L 
and contact force right cf.sub.R being effective at the same radial 
location on both of the toric disks 20, 22 and the line of contact of the 
traction roller with the toric disks also being the same for both toric 
disks. 
As the roller 26 pivots clockwise from the 1:1 position as shown in FIG. 2 
to the position shown in FIG. 3, the circle of contact moves outwardly on 
the traction roller 26. However, the circle of contact 64a with the left 
toric disk 20 moves at a rate different from that with which the circle of 
contact 64b with the right toric disk 22 moves, thereby providing for two 
different circles of contact of the traction roller 26, one 62a with the 
left toric disk 20 and the other 64b with the right toric disk 22. Since 
forces are no longer equally distributed, a moment is generated. The 
tilting of the trunnion piston 31 within the cylinder 30 helps to minimize 
the moment created by the two different circles of contact 64a and 64b. 
The circles of contact 64a and 64b move on the traction roller 26 because 
the toric disks 20, 22 each have a different cavity radius. The movement 
of the circles of contact provide for a distribution of wear over a 
relatively large surface area of the traction rollers 26, 28, thereby 
increasing the life of the traction rollers and thus the life of the 
transmission. 
Likewise, pivoting the rollers counterclockwise from the 1:1 position, as 
shown in FIG. 4, creates the same effect, however, in opposite sense from 
the clockwise movement. Here, the traction roller 26 is in engagement with 
the left toric disk 20 along a circle of contact 64c and with the right 
toric disk 22 along a circle of contact 64d. 
FIG. 5 shows the traction roller supported on a trunnion corresponding to 
FIG. 2 but turned by 90.degree.. It can be seen that the trunnion 30 has 
piston end portions 66, 68 received in housing cylinders 70,72 to which 
hydraulic operating fluid (oil) under pressure is supplied through 
passages 74, 76. Depending on the fluid applied to the opposite piston 
ends 66 and 68, the trunnion is moved or tilted slightly sidewardly to 
initiate a change of the transmission ratio as described in U.S. Pat. Nos. 
4,858,484 and 4,964,312, which are both assigned to the assignee of the 
present invention. From the cylinders 74, 76 the oil under pressure is fed 
to the hydraulic cylinder 52 through passages 78, 80 each of which 
includes a check valve 82. 
FIGS. 6-9 illustrate another embodiment of the invention. In this 
embodiment the traction roller 26 is again supported in the housing 10 by 
a pivot trunnion 30 which is pivotally supported by way of a trunnion 
support roller 34. Track cavities 42 formed in the housing 10 receive the 
hard metal track members 38 on which the support rollers 34 run. However, 
the pivot trunnion 30' includes a hydraulic cylinder portion 84. Disposed 
within the cylinder portion 84 of the trunnion 30' is a hydraulic load 
piston 86. Preferably, the outer side of the piston is axially curved. A 
swivel post 56' extends from the trunnion 30' through an opening 58' in 
the center of the hydraulic load piston 86 ending in the center of the 
traction roller 26 where it is provided with a bearing support structure 
59' engaging the traction roller 26. Although the post 56' engages the 
traction roller 26, it allows the traction roller 26 and the load piston 
86 to swivel slightly with respect to the trunnion 30 so as to permit the 
traction roller 26 to adapt to the differently curved traction disks 
20,22. 
FIGS. 7 and 8 further illustrate the traction roller in different positions 
similar to those shown in FIGS. 3 and 4. FIG. 9 is comparable to FIG. 5, 
showing hydraulic oil passages 78', 80' with check valves 82 and trunnion 
piston ends 66', 68' disposed in housing cylinders 70', 72'. 
With the arrangement according to the invention wear of the traction 
rollers is substantially reduced and the life span of the traction rollers 
and, consequently, of the transmission is substantially increased as the 
traction rollers are loaded not only along one particular line of contact. 
As explained, the lines of contact of the traction rollers with the 
traction disks change with the transmission ratio so that the traction 
roller surface load is distributed over most of the traction roller 
surface. Preferably, the toric disk with the smaller curvature radius, in 
the figures toric disk 20, is mounted on the input shaft since, generally, 
the transmission is used in an over-all speed reducing arrangement.