Dual toroidal cavity type continuously variable transmission

A toroidal type continuously variable transmission includes first and second parallel toroidal transmission units which are both mounted on a common center transmission shaft. The center transmission shaft is axially movable, and the input cone disc of each transmission unit is mounted on the center transmission shaft through ball splines in such a manner as to enable both the torque transmission and relative axial motion therebetween. Therefore, the center transmission shaft transmits, from the input disc of the first unit to the input disc of the second unit, not only an input torque inputted to the input disc of first unit through a loding cam mechanism, but also the an axial thrust load produced by the loading cam mechanism.

REFERENCES TO RELATED U.S. APPLICATIONS 
The following, commonly assigned, U.S. Patent Applications relate to 
subject matter similar to that of the present invention. (1) Ser. No. 
7/313,418, filed Feb. 22, 1989. (2) Ser. No. 07/314,846; filed Feb. 24, 
1989. (3) Ser. No. 07/316,944; filed Feb. 28, 1989. (4) Ser. No. 
07/352,309; filed May 16, 1989. (5) Ser. No. 07/357,192; filed May 26, 
1989. (6) Ser. No. 07/450,303; filed Dec. 14, 1989. (7) Ser. No. 
07/448,194, filed Dec. 14, 1989. (8) Ser. No. 07/476,580, filed Dec. 414, 
1989. 
BACKGROUND OF THE INVENTION 
The present invention relates to a toroidal type continuously variable 
transmission (CVT), and more specifically to a toroidal transmission 
having two toroidal cavities around a common axis (often called a dual 
cavity type). 
Japanese Patent Provisional Publication No. 62-258255 discloses one 
conventional example. A toroidal transmission of this example has a first 
toroidal cavity formed between input and output discs of a first toroidal 
transmission unit, and a second toroidal cavity between input and output 
discs of a second unit. The first and second toroidal cavities are equal 
in size, coaxial with each other and axially spaced from each other. In 
this conventional example, the input discs of both units are mounted on a 
torque shaft, and drivingly connected with each other by the torque shaft. 
A loading cam mechanism for producing an axial thrust load in accordance 
with an input torque is provided at the side of the input disc of the 
first unit, and the thrust load is transmitted to the input disc of the 
second unit by an axially movable tension rod. The torque shaft is hollow, 
and the tension rod is arranged coaxially in the hollow torque shaft. 
The dual cavity type toroidal transmission of this conventional example 
requires two separate coaxial shafts, the torque shaft and tension rod for 
transmission of torque and transmission of thust load. This conventional 
transmission design, therefore, increases the number of required component 
parts, requires an additional machining process for forming coaxial 
shafts, and complicates the assembly process with the result of cost 
increase. 
A similar toroidal CVT is disclosed in Japanese Patent Provisional 
Publication No. 63-125852. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a dual 
toroidal cavity type continuously variable transmission which requires 
only a single shaft for both torque transmission and thrust load 
transmission, and which can eliminate a phase difference in rotation 
between two toroidal transmission units. 
According to the present invention, a toroidal type continuously variable 
transmission comprises a center transmission shaft, first and second 
outside discs, first and second inside discs, first and second rolling 
members, first loading means, and second loading means. The center 
transmission shaft is axially movable, and has first and second ends The 
first and second outside discs are mounted on and coupled with the center 
transmission shaft in such a manner as to permit the first and second 
outside discs to move axially relative to the center transmission shaft, 
and to prevent relative rotation between the center transmission shaft and 
each of the first and second outside discs. The first outside disc is near 
the first end of the center transmission shaft, and the second outside 
disc is near the second end. The first and the second inside discs are 
rotatably mounted on the center transmission shaft between the first and 
second outside discs. The first outside and inside discs form a first 
toroidal cavity therebetween, and the second outside and inside discs a 
second toroidal cavity. The first rolling member is installed in the first 
toroidal cavity, and serves as a medium for transmitting power from the 
first outside disc to the first inside disc or vice versa. The second 
rolling member is installed in the second toroidal cavity, and serves as a 
medium for transmitting power from the second outside disc to the second 
inside disc or vice versa. The first loading means is provided between the 
first outside disc and the center transmission shaft, and rotatably 
mounted on the center transmission shaft. The second loading means is 
provided between the second outside disc and the center transmission 
shaft. The first loading means is engaged with the center transmission 
shaft in such a manner that axial movement of said first loading means is 
limited by said center transmission shaft. The second loading means is 
also engaged with the center transmission shaft in such a manner that 
axial movement of the second loading means is the center transmission 
shaft.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 shows one embodiment of the present invention. A toroidal type 
continuously variable transmission (CVT) 10 of this embodiment includes a 
first toroidal transmission unit 12 and a second toroidal transmission 
unit 14, which are arranged side by side around a common axis C. 
The first toroidal unit 12 has first input and output discs 16 and 18 which 
have opposite toroid surfaces confronting each other and forming a first 
toroidal cavity. Similarly, the second toroidal unit 14 has second input 
and output discs 20 and 22 forming a second toroidal cavity. Each toroidal 
unit has an intervening rolling member which comprises at least two power 
rollers 24 installed in the toroidal cavity. In each toroidal unit, the 
power rollers 24 are in frictional contact with the toroidal surfaces of 
the input and output discs 16 and 18 or 20 and 22. In this embodiment, 
each of the first and second toroidal units 12 and 14 has two power 
rollers 24 which are symmetrically arranged with respect to the axis C, as 
disclosed in the above-mentioned Japanese Patent Provisional Publication 
No. 62-258255. 
The power rollers 24 are inclined by one or more control valves and 
actuators (not shown) in accordance with an operating condition such as a 
vehicle operating condition, as disclosed in Japanese Utility Model 
Provisional Publication No. 63-92859. In each toroidal unit, the power 
rollers 24 transmit power from the input disc to the output disc by 
rolling, and continuously vary a transmission ratio between output and 
input speeds by inclining. FIG. 1 shows only one power roller 24. 
All the discs 16, 18, 20 and 22 are mounted on a single torque transmission 
center shaft 26. The axis of the center transmission shaft 26 is 
coincident with the above-mentioned common axis C. The center shaft 26 is 
hollow, and it is supported on a transmission housing 28 in such a manner 
that the center shaft 26 is axially movable, to a limited extent, with 
respect to the housing. 
The center shaft 26 has a first end which is a lefthand end as viewed in 
FIG. 1 and a second right hand end. The first toroidal unit 12 is mounted 
on the first lefthand half of the center shaft 26 between the first end 
and the middle of the center shaft. The second toroidal unit 14 is mounted 
on the second righthand half of the center shaft 26 between the second end 
and the middle of the center shaft 26. Among the discs 16, 18, 20 and 22, 
the first input disc 16 is closest to the first lefthand end of the center 
shaft 26, and the second input disc 20 is the closest to the second 
righthand end of the center shaft 26. The first and second output discs 18 
and 22 are disposed between the first and second input discs 16 and 20. 
Therefore, the input discs 16 and 20 of this embodiment are outside discs, 
and the output discs 18 and 22 are inside discs. 
The outside first input disc 16 is mounted on the center shaft 26 through a 
first ball spline coupling 30 so that the first input disc 16 is not 
rotatable relative to the center shaft 26, but it is axially slidable 
relative to the center shaft 26. Similarly, the outside second input disc 
20 is mounted on the center shaft 26 through a second ball spline coupling 
32 so that the second input disc 20 is not rotatable relative to the 
center shaft 26 but it is axially slidable. The first and second input 
discs 16 and 20 are engaged with the center shaft 26 through the ball 
spline couplings 30 and 32, respectively, so that the first and second 
input discs 16 and 20 rotate together with the center shaft 26. The first 
and second input discs 16 and 20 are axially movable on the center shaft 
26 to a limited extent. Each of the first and second ball spline couplings 
30 and 32 is a coupling means for coupling coaxial shafts for power 
transmission therebetween. In this embodiment, each coupling means 
comprises splines and balls for making the relative axial motion between 
the shafts smooth. Thus, the first ball spline coupling 30 serves as a 
first coupling means, and the balls of the first coupling 30 are provided 
between the first outside disc 16 and the center transmission shaft 26, 
for facilitating the relative axial motion between the fist outside disc 
16 and the center transmission shaft 26. The second ball spline coupling 
32 serves as a second coupling mean, and the balls of the second coupling 
32 are provided between the second outside disc 20 and the center 
transmission shaft 26, for facilitating the relative axial motion between 
the second outside disc 20 and the center transmission shaft 26. 
An output gear (terminal member) 34 is rotatably mounted on the center 
shaft 26 through appropriate bearing means, 26a the first and second 
output discs 18 and 22 are splined to the output gear 34. Torque 
transmitted from the first input disc 16 to the first output disc 18, and 
torque transmitted from the second input disc 20 to the second output disc 
22 are both transmitted to the output gear 34, and power is taken out 
through the output gear 34. The output gear 34 is rotatably supported by 
an inwardly projection portion of the housing 28 through ball bearings 38 
and 40. The output gear 34 (second terminal member) is disposed between 
the first and second inside discs 18 and 22, and the inwardly projecting 
portion of the housing 28 projects inwardly toward the center transmission 
shaft 26 between the first and second inside discs 18 and 22, as shown in 
FIG. 1. 
The toroidal transmission 10 further includes a loading cam mechanism 42 
serving as a first loading means. The loading cam mechanism 42 is disposed 
next to the first input disc 16 around the first lefthand end of the 
center shaft 26. The loading cam mechanism 42 is designed to produce an 
axial pushing force (thrust load) in accordance with an input torque. The 
loading cam mechanism 42 has a loading cam disc 44 shaped like a flange, 
and loading rollers 46 which are confined between a cam surface 44a of the 
loading cam member 44 and an outside surface of the first input disc 16. 
The loading rollers 46 are supported by a support plate 46a disposed 
between the loading cam member 44 and the first input disc 16. 
The loading cam member 44 is rotatably mounted on the center shaft 26 so 
that a relative rotation therebetween is possible, and engaged through a 
thrust bearing 48 with a flange 26a formed in the first lefthand end of 
the center shaft 26. A leftward pusing force applied on the loading cam 
member 44 is transmitted through the thrust bearing 48 and the flange 26a 
to the center shaft 26. 
The loading cam mechanism 42 of this embodiment has at least one pin hole 
47 which extends axially through the loading cam member 44, and the 
support plate 46a, into the first input disc 16. When the loading cam 
mechanism 42 is assembled, a knock pin (not shown) is inserted in the pin 
hole 47. 
A torque input shaft 50 (terminal member) is rotatably received through a 
needle bearing 52 in the first lefthand end of the hollow center shaft 26. 
The input shaft 50 is coaxial with the center shaft 26. The input shaft 50 
has a flange 54 which rotates with the input shaft 50 as a unit. The 
flange 54 is connected with the loading cam member 44 through a coupling 
means 56 shaped like splines. 
A first disc spring 58 is disposed through a spacer 60 and a needle bearing 
62 between the first input disc 16 and the loading cam member 44. The 
first disc spring 58 of this embodiment is a combination of Belleville 
springs (initially coned disc springs). A biasing force of the first disc 
spring 58 is parallel to the pushing force produced by the loading cam 
mechanism 42. 
A second disc spring 68 for preloading is mounted on the second righthand 
end of the center transmission shaft 26. The second disc spring 68 is also 
a combination of Belleville springs, and serves as a second loading means. 
A loading nut 64 and a lock nut 66 are screwed firmly on the second right 
hand end of the center transmission shaft 26. The loading nut 64 prevents 
the first toroidal unit 12 and the second toroidal unit 14 from being 
axially extracted from the center shaft 26. The second disc spring 68 is 
disposed between a flange 64a of the loading nut 64 and the second input 
disc 20. A spacer 70 is interposed between the second input disc and the 
second disc spring 68. The second disc spring 68 applies a biasing force 
on the second input disc 20, and a reaction force due to this biasing 
force is applied through the loading nut 64 to the center transmission 
shaft 26. 
The toroidal transmission 10 of this embodiment is operated as follows: 
Torque from a prime mover such as an engine of a motor vehicle is first 
inputted to the torque input shaft 50. This input torque is transmitted 
from the input shaft 50 through the coupling means 56 to the loading cam 
member 44, so that the loading cam member 44 and the first input disc 16 
rotate relative to each other. This relative rotation between the cam 
member 44 and the first input disc 16 causes the loading rollers 46 to be 
compressed between the loading cam member 44 and the first input disc 16 
by the action of the cam mechanism 42. In this way, the loading rollers 46 
are compressed between the cam member 44 and the first input disc 16, and 
the torque is transmitted from the cam member 44 to the first input disc 
16. The force pressing the loading rollers 46 between the cam member 44 
and the first input disc 16 is increased in proportion to the input 
torque, and this force acts also as a force (thrust load) pushing the 
first input disc 16 rightwardly toward the second end of the center 
transmission shaft 26. 
The torque of the first input disc 16 is transmitted through the first ball 
spline coupling 30 to the center transmission shaft 26, and further 
transmitted from the center transmission shaft 26 through the second ball 
spline coupling 32 to the second input disc 20. The torque transmitted to 
the first input disc 16 is transmitted through the power rollers 24 to the 
first output disc 18. At the same time, the torque transmitted to the 
second input disc 20 is transmitted through the power rollers 24 to the 
second output diSc 22. In each Of the first and second toroidal units 12 
and 14, power is transmitted from the input disc to the output disc 
through the power rollers 24 which are rolling about an inclinable axis. 
The axial thrust force produced by the loading cam mechanism 42 pushes the 
first input disc 16 rightwardly toward the first output disc 18. At the 
same time, the reaction force of the this axial thrust force is 
transmitted through the thrust bearing 48 to the transmission shaft 26. 
Therefore, the transmission shaft 26 is axially moved, and applies a 
leftward axial force to the second input disc 20 through the loading nut 
64 and the second disc spring 68. 
In the toroidal transmission 10 of this embodiment, the single transmission 
shaft 26 alone is used for transmitting a torque between the first and 
second input discs 16 and 20, and transmitting a thrust load produced by 
the loading cam mechanism 42. The single transmission shaft 26 can perform 
the functions of both the torque shaft and tension rod of the conventional 
design. The toroidal transmission 10 of this embodiment can reduce the 
number of required component parts, simplify the structure, and facilitate 
the forming and assembly processes. 
The first and second input discs 16 and 20 are engaged with the 
transmission shaft 26 through the ball splines 30 and 32 in such a manner 
that the first and second input discs 16 and 20 and the transmission shaft 
26 all rotate together. Therefore, the toroidal transmission 10 of this 
embodiment can transmit torque efficiently with no phase difference in the 
rotational direction between the first and second input discs 16 and 20. 
The ball splines 30 and 32 enable the first and second input discs 16 and 
20 to move smoothly in the axial direction with respect to the 
transmission shaft 26, so that the thrust load of the loading cam 
mechanism 42 is transmitted smoothly. 
In each of the toroidal units 12 and 14, the thrust load produced by the 
loading cam mechanism 42 acts to push the input disc 16 or 20 toward the 
output disc 18 or 22, and enables the power rollers 24 to transmit power 
without slippage. 
The second disc spring 68 is interposed between the center transmission 
shaft 26 and the second input disc 20 which are so engaged by the ball 
spline coupling 32 as to prevent a relative rotation therebetween. 
Therefore, the second disc spring 68 rotates together with the center 
transmission shaft 26 and the second input disc 20, and the friction 
surfaces of these members are made immune from wear. 
When the loading cam mechanism 42 is assembled, a knock pin is inserted in 
the pin hole 47 to effect an initial alignment of the loading cam 
mechanism 42, which helps prevention of the preload of the second disc 
spring 68 from being decreased when the loading cam mechanism 42 is 
displaced. The knock pin is extracted from the hole 47 after the assembly 
process. 
In the toroidal transmission of this embodiment, torque is inputted to the 
outside discs 16 and 20, and taken out from the inside discs 18 and 22 
through the output gear 34. However, the opposite arrangement is possible 
in which torque is inputted through the output gear 34 to the inside discs 
18 and 22, and taken out from the outside discs 16 and 20.