Infinitely variable traction roller transmission

An infinitely variable traction roller transmission having a housing, an input shaft and an output shaft rotatably and coaxially supported on the housing, an input toric disc and an output toric disc fitted on the input and output shafts, respectively, and engaged with the shafts for rotation therewith, the opposed surfaces of the toric discs cooperating with each other to form a toroidal cavity, a plurality of traction rollers disposed in the toroidal cavity symmetrically with the axes of the input and output shafts, trunnion devices rotatably supporting the traction rollers and supported by the housing for pivotal movement about a pivot axis perpendicular to the axis of rotation of the traction rollers, and pressing means for urging the input and output toric discs and the traction rollers against each other to bring them into engagement with each other and cause a traction force to be produced, is provided with a supporting device for mounting the trunnion devices on the housing for slight movement in the direction of the pivot axis, a screw device provided at the end of the pivot axis of the trunnion devices, and a speed change link mechanism provided on the screw device to rectilinearly move the trunnion devices in the direction of the pivot axis through the screw device.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an infinitely variable traction roller 
transmission in which the opposed surfaces of an input toric disc and an 
output toric disc provided on input and output shafts, respectively, 
disposed on the same axis cooperate with each other to form a toroidal 
cavity and traction rollers are disposed in the toroidal cavity and are 
engaged with the input and output toric discs so that a great torque is 
transmitted by a traction force created in the portion of engagement, and 
more particularly to an infinitely variable transmission which can 
continuously and smoothly accomplish the transmission ratio control of 
acceleration and deceleration by a small operating force and which is 
simple in structure and excellent in durability and moreover inexpensive. 
2. Description of the Prior Art 
Infinitely variable traction roller transmissions of the general type 
described above are known and various ones have been proposed. For 
example, the transmissions disclosed in U.S. Pat. Nos. 3,142,189 and 
3,810,398 are provided with a hydraulic cylinder and a servo valve. In 
these transmissions, a trunnion rotatably supporting the traction rollers 
is displaced in the direction of a pivot axis by the hydraulic cylinder 
and as a result, pivotal movement of the trunnion about the pivot shaft is 
induced to vary the radii of the engagement circles of the traction 
rollers with the input and output toric discs and effect self-transmission 
action and also move the servo valve backwardly by the variation in the 
angle of pivotal movement of the trunnion, thereby returning the 
displacement in the direction of the pivot axis to a neutral position. 
However, the hydraulic servo mechanism is very complicated in structure 
and adjustment and requires a hydraulic source and particularly, the use 
of a servo valve is liable to cause hunting and also, such transmissions 
have been expensive and it has been difficult to make them compact and 
light in weight. 
The transmission disclosed in U.S. Pat. No. 2,086,491 does not use a 
hydraulic pressure, but it uses a worm and a worm gear, a screw and a 
screw gear, a rack and a pinion, etc. to directly pivotally move the 
trunnion to thereby effect speed change. This transmission is not of the 
type in which the trunnion as previously mentioned is displaced in the 
direction of the pivot axis and thereby effects self speed change action, 
but is of the type in which the trunnion is forced to effect speed change 
and therefore, this transmission has required a great force for the speed 
changing operation and sudden speed change has been difficult with such 
device. 
Also, in the transmission disclosed in U.S. Pat. No. 2,907,220, a support 
member rotatably supporting the traction rollers is supported by a ball 
screw device for movement in the direction of the pivot axis, and a great 
thrust load exerted on the traction rollers is directly exerted as a 
radial load on the ball screw, and this has offered a problem in respect 
of the durability of the ball screw and also, it has been impossible to 
make the bearing rotatably supporting the traction rollers large in size 
and this has also led to a problem in respect of the durability of the 
bearing. 
SUMMARY OF THE INVENTION 
The present invention eliminates all of the above-noted problems peculiar 
to the prior art. According to the present invention, a screw device is 
provided at the end of the pivot axis of trunnion devices and the screw 
device may be rotated to thereby move the trunnions slightly in the 
direction of the pivot axis and the automatic speed change action in which 
traction rollers rotate is induced in accordance with the amount of 
displacement of the trunnions, and by the rotation of the traction 
rollers, the trunnions are pivotally moved and the screw is rotated in 
reverse direction, whereby the displacement is returned to the original 
neutral position and thus, a speed change to a desired transmission ratio 
can be obtained. 
The invention will hereinafter be described in detail with respect to 
embodiments thereof shown in the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1 which is a transverse cross-sectional view of an 
infinitely variable traction roller transmission of the present invention, 
an input toric disc 2 is fitted on an input shaft 1 shown as an end 
surface and is engaged by an engaging member, not shown, in a well-known 
manner so that they rotate together. Although not shown, an output shaft 
and an output toric disc are similarly provided on this side of FIG. 1. 
Between the input toric disc 2 and the output toric disc, two left and 
right traction rollers 3 are rotatably supported on trunnions 4 and are 
engaged with the input and output toric discs while being urged against 
each other. The upper and lower ends of the trunnions 4 are held by 
tension members 5 through spherically outer-surfaced bearings 6, each of 
the tension members 5 having its central portion supported by a housing 15 
through a spherical pole 10. Thus, the tension members are each rotatable 
about a pivot axis Z--Z and slightly movable in the direction of the axis 
Z--Z. 
The screw shaft 7 of a ball screw is formed on each shaft end of the 
trunnion 4 and a ball nut 8 is threadably engaged with the screw shaft 7 
through balls. The ball nut 8 is rotatably and axially stationarily 
supported on the housing 15 by a bearing 9, and left and right opposed 
speed change levers 11 and 11 are mounted on the upper end of the ball 
nuts as shown in FIG. 2, one end of each of connecting levers 12 being 
pivotally supported on the end of each of the speed change levers 11 and 
11. The other ends of the connecting levers 12 are connected together by a 
balance lever 13, and a speed change rod 14 is pivotally supported on the 
central portion of the balance lever 13, as shown. The angle of pivotal 
movement is limited by the balance lever 13 contacting the bifurcated 
shoulder 141 of the speed change rod 14. 
In the embodiment of the present invention having such a construction, when 
the input shaft 1 is rotating as indicated by arrow A in FIG. 1, a 
traction force Ft and a thrust load Fa resulting from the engagement of 
the traction rollers 3 with the input toric disc 2 and the output toric 
disc (not shown) are exerted on the traction rollers 3, as shown, and the 
thrust load Fa is borne by the tension members 5 and, since the tension 
members 5 are supported by the spherical portions of the spherically 
outer-surfaced bearings 6 and the spherical pole 10, the left and right 
trunnions 4 can each move slightly in the direction of the pivot axis Z--Z 
while involving pivotal movement of the tension members. Accordingly, the 
thrust load Fa is not exerted on the screw shafts 7 of the screw device, 
the ball nuts 8 and the bearings 9, but only the traction force Ft acts on 
them. The direction of action of this traction force Ft is opposite at 
left and right and, when the rotation of the input shaft 1 is in the 
direction of arrow A as previously described, it produces a torque for 
rotating the right speed change lever 11 and the connecting lever 12 in 
the direction of arrow B and rotating the left speed change lever 11 and 
the connecting lever 12 in the direction of arrow B'. These left and right 
torques are balanced by the balance lever 13, that is, the left and right 
traction forces become equal to each other in magnitude. Also, the balance 
lever 13 can only pivotally move in the range of angle limited by the 
bifurcated shoulder 141 thereof, relative to the transmission rod 14, as 
previously described, the angles of rotation of the left and right speed 
change levers 11 do not become remarkably different and the balance 
between the left and right portions can be maintained by the left and 
right speed change levers. 
Now, when the speed change rod 14 is vertically moved in FIG. 2, the speed 
change levers 11 and 11 rotate in opposite directions to move the left and 
right ball nuts 8 and 8 in reverse directions and each of the screw shafts 
7 axially moves back and forth and accordingly, the left and right 
trunnions 4 and 4 move in opposite directions along the pivot axis Z--Z. 
Thus, each of the traction rollers 3 is displaced in the direction of the 
pivot axis Z--Z and thereofore, the automatic transmission action in a 
well-known infinitely variable transmission occurs and the traction 
rollers 3 and accordingly, the trunnions 4 pivotally move about the pivot 
axis Z--Z, and the direction of the pivotal movement is such that it 
follows the rotation of the ball nuts 8 and therefore, as the screw shafts 
7 lead, the trunnions 4 (the traction rollers 3) return to their original 
position and when they have returned to their neutral position, that is, 
when a condition in which the axis of rotation of the traction rollers 3 
intersects the axis of the input and output shafts has been restored, the 
rotation of the traction rollers 3 is stopped. That is, the aforementioned 
automatic transmission action comes to an end and the speed can be changed 
to a desired transmission ratio corresponding to the amount of movement of 
the transmission rod 14. 
The amount of displacement of the trunnions in the direction of the pivot 
axis Z--Z during speed change is very small and this displacement is 
remarkably enlarged at the ends of the speed change levers 11 through a 
screw device and therefore, the aforementioned traction force Ft is 
remarkably reduced at these end portions and accordingly, the operating 
force required to move the speed change rod 14 for speed change may be of 
a much smaller value as compared with a case where the shaft ends of the 
trunnions are directly pushed in the direction of the axis Z--Z to effect 
speed change. 
Also, the pivotal movement of the trunnions 4 has a resistance caused by 
the urging force of the screws created by the traction force Ft being 
applied in the direction of the axis Z--Z, and the component of the 
traction force in the direction of speed change perpendicular to the 
traction force Ft created by the displacement of the trunnions 4 in the 
direction of the axis Z--Z overcomes the above-mentioned resistance to 
pivotally move the trunnions and thereby effect speed change and 
therefore, if the friction force of the screw device is great, smooth 
speed change cannot be expected in some cases, but if a ball screw 
structure is adopted as in the above-described embodiment, the low 
friction property thereof will succeed in reducing the pivotal movement 
resistance of the trunnion device and only the axial load (the traction 
force Ft) acts on the ball screws and any radial load which is harmful to 
the friction of the ball screws is not exerted on the ball screws and 
therefore, very smooth transmission action and durability can be expected. 
However, the present invention is not restricted to the ball screw device, 
but may also be a sliding screw device. 
In contrast with the above-described embodiment, an embodiment in which a 
ball nut which is a female screw is formed at 81 on a shaft end of each 
trunnion as shown in FIG. 3 and a threaded shaft 71 which is a male screw 
is rotatably and axially stationarily supported on the housing 15 through 
a bearing 9 and the speed change lever 11 is mounted on the threaded shaft 
7 may result in a similar operation and effect. 
The structure of the supporting device for mounting the trunnion devices on 
the housing for slight movement in the direction of the pivot axis Z--Z is 
neither restricted to the present embodiment, but may also be suspended, 
for example, by a spring device. 
As described above, the transmission of the present invention does not 
employ a complex hydraulic servo mechanism and a hydraulic source or 
gears, but is of a simple structure simply using a screw device as a speed 
change link mechanism and therefore can be made compact and light in 
weight and thus provides a long-lived and inexpensive infinitely variable 
traction roller transmission. Particularly, it skillfully utilizes the 
automatic transmission action and can accurately and reliably obtain a 
desired transmission ratio by a small operating force and therefore 
greatly contributes to putting into practical use the infinitely variable 
traction roller transmission which has recently been attracting attention 
as a part of the remedy of fuel consumption of vehicles.