Cam disk for toroidal type continuously variable transmission

Details Cam disk for toroidal type continuously variable transmission Cam disk for toroidal type continuously variable transmission

1999-07-07

2001-01-23

Wright, Dirk (Department: 3681)

Friction gear transmission systems or components

Friction transmission or element

Particular friction surface

C476S042000

Reexamination Certificate

active

06176806

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a cam disk for a toroidal type continuously variable transmission used as a transmission of a vehicle such as an automobile.
Conventionally, a stage transmission which comprises speed change gears is used as a transmission of an automobile. This type of transmission has a plurality of gears. The combination of gears is changed to transmit torque from an input shaft to an output shaft at a desired transmission ratio. In the conventional transmission, torque is changed stage by stage, when the speed is changed. Thus, the conventional transmission is disadvantageous in that the power transmission efficiency is low and that vibration occurs when the speed is changed. To overcome these disadvantages, in recent years, a continuously variable transmission is put to practical use. With the continuously variable transmission, no vibration occurs when the speed is changed. In addition, since the power transmission efficiency is higher than that of the aforementioned conventional transmission, the fuel efficiency of the engine is improved.
As an example of the continuously variable transmissions, conventionally, a toroidal type continuously variable transmission
120
as shown in
FIG. 14
has been proposed. This type of transmission comprises an input disk
102
, an output disk
103
a
, power rollers
103
b
rotationally in contact with the disks
102
and
103
a
, a loading cam mechanism
106
, etc. The input disk
102
is rotated in association with the input shaft
101
. The input shaft
101
is connected to a drive shaft
122
rotated by an engine serving as a power source. The output disk
103
a
is rotated in association with an output shaft (not shown). The loading cam mechanism
106
presses the input disk
102
and the output disk
103
a
in such directions that the disks get closer to each other.
A toroidal type continuously variable transmission with a single cavity comprises a pair of an input disk
102
and an output disk
103
a
. A toroidal type continuously variable transmission with double cavities comprises two pairs of input disks
102
and output disks
103
a
.
FIG. 14
shows a part of a double-cavity toroidal type continuously variable transmission
120
. The transmission
120
has a first cavity
108
including first input and output disks
102
and
103
a
and power rollers
103
b
, and a second cavity including second input and output disks and power rollers (not shown). The loading cam mechanism
106
is provided, for example, on the side of a power source for driving the input disk
102
of the first cavity
108
. The loading cam mechanism
106
has a cam disk
104
and a roller
105
serving as pressing means. The cam disk
104
is rotatably supported by an input shaft
101
via a ball
125
. The roller
105
is rotatable between the cam disk
104
and the input disk
102
about an axis M
1
crossing an axis P
1
of the input shaft
101
. The input disk
102
is pressed against the output disk
103
a
via the roller
105
.
The cam disk
104
shown in
FIG. 14
integrally comprises a first projecting portion
112
, a second projecting portion
113
, a flange portion
114
and a cam surface
115
. The first and second projecting portions
112
and
113
are projected from a central portion of the disk
104
in both axial directions of the disk
104
. The thickness of the flange portion
114
is gradually reduced from the first projecting portion
112
toward the peripheral portion. The roller
105
is brought into contact with the cam surface
115
. In the central portion of the cam disk
104
, a fitting hole
116
is formed, through which the input shaft
101
is inserted. A continuous raceway
117
is formed in the overall inner circumference of the fitting hole
116
. A continuous raceway
118
is formed in the overall outer circumference of the input shaft
101
. The raceways
117
and
118
have arc-shaped cross sections corresponding to the outer diameter of the ball
125
.
A line segment N
1
connecting bottoms
117
a
and
118
b
of the raceways
117
and
118
is inclined with respect to the axis P
1
of the input shaft
101
. When the first input disk
102
is pressed by the roller
105
in the direction toward the first output disk
103
a
, the counterforce is applied to the input shaft
101
via the ball
125
, thereby pressing the input shaft
101
toward the power source. As a result, the second input disk (not shown) is pressed toward the second output disk. The input shaft
101
and the cam disk
104
are rotatable with respect to each other via the ball
125
rotatably held between the raceways
117
and
118
.
The cam disk
104
comprises teeth
112
a
formed integral with an end portion of the first projecting portion
112
. The teeth
112
a
mesh with teeth
122
a
formed in the drive shaft
122
, so that the cam disk
104
is rotated together with the drive shaft
122
. In other words, the rotation of the drive shaft
122
is transmitted to the cam disk
104
via the teeth
112
a
and
122
a
. As a result, the first input disk
102
and the second input disk are rotated. The rotation of the first input disk
102
is transmitted to the first output disk
103
a
via the first power roller
103
b
. The rotation of the second input disk is transmitted to the second output disk via the second power roller. As a result, the output axis is rotated.
The toroidal type continuously variable transmission
120
can transmit higher torque than the conventional belt type continuously variable transmission described above. However, considerable compressive stress and tensile stress act on the cam disk
104
. More specifically, when the input disk
102
is pressed toward the output disk
103
a
by the roller
105
, much greater compressive stress and tensile stress act on the cam disk
104
as compared to the case of a general mechanical member on which stress is exerted repeatedly, such as, a gear or a bearing.
Particularly in regions enclosed by the dot-chain lines H
1
in
FIG. 14
, considerable compressive stress acts on the cam surface
115
and the raceway
117
. Further, the outer circumference of the flange portion
114
of the cam disk
104
is warped away from the input disk
102
by the counterforce applied to the cam disk
104
when the roller
105
press the input disk
105
toward the output disk
103
a
. For this reason, great tensile stress acts on a region enclosed by the dot-chain line H
2
in
FIG. 14
, i.e., a corner section
119
where the second projecting portion
113
intersects the cam surface
115
. In the teeth
112
a
which mesh with the teeth
122
a
of the drive shaft
122
, great compressive stress acts on a top end portion of the teeth
112
a
enclosed by the dot-chain line H
3
in FIG.
14
. Great tensile stress also acts on a root portion of the teeth
112
a
enclosed by the dot-chain line H
4
.
Conventionally, in one method for producing the cam disk
104
described above, a solid material
126
as shown in
FIG. 15
or a hollow material is cut-worked. The material
126
is shaped into a column by, for example, rolling. In another method, the material is shaped into a form approximate to the cam disk
104
by forging, and subjected to the finishing process, such as grinding. In the method of producing the cam disk
104
by a cutting process from the material, the production yield is very low and a considerable period of time is required for the process. As a result, the production cost is increased.
The material
126
, shaped through the steps of melting, casting and rolling, may contain a relatively much impurities in a portion
126
a
, 30% or less of the diameter of the material from the center. Further, the material
126
, which has been subjected to plastic working such as rolling, has metal flows G formed along the axis I of the material
126
. A metal flow means a line of texture formed in the metal when crystal grains are aligned in a direction during the process of plastically working the metal texture. The metal flow is also called a flow line. The text

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