Traction roller transmission

In a planetary type traction roller transmission which comprises a sun, a traction ring and planetary traction rollers disposed in the space between, and in engagement with, the traction ring and the central sun all with somewhat conical traction surfaces so arranged that the tangential axial lines of the traction surfaces intersect in a point on the transmission axis there are provided engaging means for forcing the appropriate traction surfaces into firm engagement with one another but also means for limiting the engagement forces applied to the traction surfaces to a predetermined safe limit which is not exceeded no matter how strong the applied forces are.

BACKGROUND OF THE INVENTION 
The invention relates to fixed ratio planetary type traction roller 
transmissions whose traction surfaces are in engagement with each other 
for the transmission of motion therebetween. 
There are generally provided axial cam structures which generate axial 
forces dependent on the torque transmitted through the transmission and 
the axial forces so generated are applied to conical race rings or conical 
sun structures to provide the appropriate traction surface contact forces. 
An arrangement in which the traction ring consists of two slightly conical 
rings which are forced toward each other to engage the traction rollers 
therebetween is shown for example in U.S. Pat. No. 4,052,915. Applicant's 
published manuscript "Bearings and Rolling Traction, Analysis and Design" 
which is available from Excelermatic, Inc., Austin, Tex. 78731, describes 
and shows in FIG. 20-3a fixed ratio traction roller transmission in which 
the sun consists of two slightly conical sun sections which are forced 
toward each other to engage the traction rollers for firm torque-dependent 
engagement of the traction rollers with the traction ring and the sun 
structure. 
Australian Pat. No. 16,391, Italian Pat. No. 494,348 and U.S. Pat. No. 
3,375,739 show planetary type traction roller transmissions including sun 
rollers, traction rings and planetary traction rollers which are conical 
and so arranged that their axes and all tangential axial lines of the 
traction surfaces intersect on the axis of the transmission and means are 
provided for forcing the planetary rollers into engagement with the suns 
and the traction rings. 
The means providing the engagement forces are generally torque dependent so 
as to provide the appropriate engagement forces or they are structures 
which provide fixed forces especially if the torque to be transmitted 
through the transmission during its operation does not substantially vary. 
For generating torque-dependent engagement forces there are usually 
provided axial cam structures or there may be provided hydraulic 
engagement force generating means which require a pressurized fluid 
control structure in order to supply the appropriate engagement forces. 
Both arrangements are expensive. There are however certain applications, 
for example, in torpedo drives, where a traction roller transmission is 
advantageous because of its quiet operation but where costs should also be 
maintained as low as possible since the transmission is destroyed with the 
actual use of the torpedo. A preload corresponding to the maximum torque 
which can be achieved very inexpensively would also be quite adequate 
since a torpedo transmission is operated only for a short time and during 
all that time essentially at a predetermined torque. 
Torpedoes however are stored for long periods of time until they are 
actually used and keeping the transmission's traction surfaces under the 
preload as required for operation will, in time, cause denting and 
corrosion of the traction surfaces which results in noisy operation or 
even failure. 
Transmissions of the above type have relatively small cone angles in order 
to avoid the need for large axial engagement forces and therefore they 
require relatively large axial travel for the engagement member--when 
forced toward the other members, for example by a hydraulic piston--from a 
contact force-free position to a position in which the appropriate contact 
forces as needed for the transmission of the needed torque are generated. 
Also inappropriately large forces applied to the engagement member may 
damage the rollers' traction surfaces because the relatively small cone 
angles translate the engagement forces in large surface contact pressures. 
It is therefore the principal object of the present invention to provide a 
transmission whose traction rollers have relatively small cone angles in 
order to be able to be operated by only small axial engagement forces but 
which nevertheless can be operated by any available force generating 
structure without the danger of damage to the traction surfaces. It is 
also desirable that, in spite of the relatively small cone angles of the 
traction surfaces, only a relatively small amount of axial movement is 
required for the achievement of the required traction roller surface 
engagement. 
SUMMARY OF THE INVENTION 
This object is achieved wtih a planetary type traction roller transmission 
which comprises as traction elements a sun, a traction ring and planetary 
traction rollers disposed in the space between, and in engagement with, 
the traction ring and the central sun, all being so arranged that the 
tangential axial lines of the traction surfaces intersect in a point on 
the transmission axis; there are provided means for applying axial forces 
to the traction elements to cause their engagement with one another but 
there are also provided means to adjustably limit the application of such 
axial engagement forces to predetermined safe values in order to prevent 
traction surface loading beyond what is needed to transmit maximum torque. 
With this arrangement any available force generating means such as 
available pressurized fluid may be utilized to provide the engagement 
forces and the pressure does not need to be limited since the transmission 
includes means for limiting the application of such forces. 
In a preferred embodiment there are also provided means for limiting 
disengagement movement of the traction elements to avoid full 
disengagement, that is, to maintain certain engagement forces which 
however should be small enough so as to prevent damage to the traction 
element surfaces even if a transmission remains unused over a long period 
of time.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The traction roller transmission as shown in the FIGURE includes a housing 
1 having a cylindrical portion 2 with end walls 3 and 4 at opposite ends 
thereof. An input shaft 5 is rotatably supported in end wall 3 by a 
bearing 6 and has a sun roller section 7 with a slightly conical surface 
formed at its end within the housing 1. An output shaft 8 is rotatably 
supported in the end wall 4 by a bearing 9 and carries a traction ring 
structure 10 within the housing 1. The traction ring structure 10 includes 
a slightly conical traction ring 11 surrounding the sun roller section 7 
in spaced relationship. Slightly conical traction rollers 12 are supported 
in the annular space 13 between the traction ring 11 and the sun roller 
section 7 by a carrier 14 and are in motion transmitting engagement with 
both the sun roller section 7 and the traction ring 11 for the 
transmission of motion therebetween. 
The slightly conical surfaces have cone angles and are arranged such that 
the axial tangents to the slightly conical surfaces all coincide in a 
single point on the axis of the input and output shafts 5, 8 so that spin 
on the torque transmitting traction surfaces is avoided. 
The carrier 14 has support shafts 15 extending through the traction rollers 
12 and the support shafts 15 are interconnected by a support ring 16 
mounted to their free ends, the traction rollers 12 being supported on the 
support shafts 15 by needle bearings 17. Axial thrust bearings 18 are 
arranged between the carrier 14 and the traction rollers 12 in order to 
provide the axial engagement forces to the traction rollers 12 for forcing 
them into the space 13 between the ring 11 and the sun roller section 7. 
In order to provide the axial thrust forces the carrier 14 is provided with 
an annular cylinder 19 having an annular cylinder cavity 20 in which an 
annular piston 21 is disposed. The piston 21 is mounted to the end wall 3 
by bolts 22 and slide pins 23 are mounted into the carrier 14 and extend 
into bores 24 in the piston 21 such that the carrier 14 is axially movable 
but not rotatable relative to the piston 21. 
A hydraulic fluid supply passage 25 extends through the end wall 3 and 
through the piston 31 for supplying pressurized fluid to the annular 
cavity 20 for forcing the cylinder 19 toward the traction ring structure 
10 and the conical traction rollers 12 into the annular space 13 between 
the traction ring 11 and the sun roller section 7 for firm engagement 
therewith. 
Such engagement movement of the cylinder 19 however is adjustably limited 
by adjustment screws 26 which are adjusted to provide appropriate roller 
engagement forces for the maximum torque transmitted through the 
transmission no matter how large the pressure of the pressurized fluid 
supplied to the cylinder cavity 20 is. 
There is also provided in the end wall 3 an adjustment screw 27 which 
limits the disengagement movement of the planetary roller carrier 14 to an 
adjustable desired degree. 
With such an arrangement the traction rollers may be kept in a relatively 
low force engagement position as determined by the adjustment screw 27 in 
which no damage occurs to the traction surfaces even over long periods of 
time and full engagement forces are limited by the adjustment screws 26. 
The usually available high pressure fluid may then simply be admitted to 
the cylinder cavity when full engagement forces are needed for operation 
of the transmission but in spite of the high pressure of the fluid the 
traction surfaces are not overloaded but engagement pressures are limited 
to a preadjusted value. 
LISTING OF REFERENCE NUMERALS 
1 Housing 
2 Cylindrical portion 
3 End wall 
4 End wall 
5 Input shaft 
6 Bearing 
7 Sun roller section 
8 Output shaft 
9 Bearing 
10 Traction ring structure 
11 Traction ring 
12 Traction roller 
13 Annular space 
14 Carrier 
15 Shaft 
16 Traction ring 
17 Needle bearing 
18 Axial thrust bearing 
19 Annular cylinder 
20 Annular cylinder cavity 
21 Annular piston 
22 Bolt 
23 Sliding pin 
24 Bore 
25 Fluid supply passage 
26 Adjustment screw 
27 Adjustment screw