Toroidal continuously variable transmission and...

Details Toroidal continuously variable transmission and... Toroidal continuously variable transmission and...

2002-07-11

2003-12-09

Fenstermacher, David (Department: 3682)

Friction gear transmission systems or components

Friction transmission or element

Particular friction surface

C476S040000

Reexamination Certificate

active

06659909

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a toroidal continuously variable transmission and a method of manufacturing the same. More specifically, the present invention relates to a toroidal continuously variable transmission designed for use in a vehicle, such as an automobile, and a method for manufacturing the same.
2. Description of the Related Art
As a toroidal continuously variable transmission, the one shown in
FIG. 1
has been conventionally known.
Inside a housing (not shown), an input disk
1
and an output disk
2
are coaxially arranged in such a manner that they face each other. An input shaft
3
extends through the axis of the toroidal transmission including the input and output disks
1
and
2
. A loading cam
4
is disposed at one end of the input shaft
3
. The loading cam
4
is configured to transmit the driving force (torque) of the input shaft
3
to the input disk
1
through a cam roller
5
.
The input and output disks
1
and
2
are substantially similar in shape and arranged to be symmetric. The facing surfaces of these disks are toroidal surfaces and jointly form substantial semicircles when viewed in a section taken axially. A pair of power roller bearings
6
and
7
, which are in contact with the input and output disks
1
and
2
, are inserted into toroidal cavities defined by the toroidal surfaces of the input and output disks
1
and
2
.
Power roller bearing
6
includes a power roller
6
a
which rolls on the toroidal surfaces of the input and output disks
1
and
2
(and which corresponds to an inner ring of the power roller bearing
6
), an outer ring
6
b
and a plurality of rolling members (steel balls)
6
c
. The other power roller bearing, i.e., power roller bearing
7
, includes a power roller
7
a
which rolls on the toroidal surfaces of the input and output disks
1
and
2
(and which corresponds to an inner ring of the power roller bearing
7
), an outer ring
7
b
and a plurality of rolling members (steel balls)
7
c.
As can be seen from the above, the power roller
6
a
functions as the inner ring that is a structural element of the power roller bearing
6
, and the power roller
7
a
functions as the inner ring that is a structural element of the power roller bearing
7
. The power roller
6
a
is rotatably coupled to a trunnion
10
by means of a pivot
8
, the outer ring
6
b
and the rolling members
6
c
, and at the same time can be inclined in such a manner that a pivot axis O, which is the center of the toroidal surfaces of the input and output disks
1
and
2
, is the center of the inclining movement.
Likewise, power roller
7
a
is rotatably coupled to a trunnion
11
by means of a pivot
9
, outer ring
7
b
and rolling members (steel balls)
7
c
, and at the same time can be inclined in such a manner that a pivot axis O, which is the center of the toroidal surfaces of the input and output disks
1
and
2
, is the center of the inclining movement. A lubricant having a great viscosity or friction resistance is supplied onto the surfaces of the input and output disks
1
and
2
and those of the power rollers
6
a
and
7
a
. A driving force exerted on the input disk
1
is transmitted to the output disk
2
through a lubricant film and the power rollers
6
a
and
7
a.
The input and output disks
1
and
2
are independent of the input shaft
3
by means of a needle
12
interposed between them (that is, the input and output disks
1
and
2
move without reference to the rotating shaft
3
). The output disk
2
is connected to an output shaft
14
which is parallel to the input shaft
3
and is rotatably supported by a housing (not shown) by means of angular members
13
.
In the toroidal continuously variable transmission
20
, the driving force of the input shaft
3
is transmitted to the loading cam
4
. When the driving force, thus transmitted, rotates the loading cam
4
, the rotation is transmitted to the input disk
1
through the cam roller
5
, thereby rotating the input disk
1
. The driving force based on the rotation of the input disk
1
is transmitted to the output disk
2
by way of the power roller
6
a
and the power roller
7
a
. As a result, the output disk
2
rotates together with the output shaft
14
.
At the time of transmission, the trunnions
10
and
11
are moved a little toward the pivot axes O. By moving the trunnions
10
and
11
toward the axes, the intersection between the axis of rotation of the power rollers
6
a
and
7
a
and the axis of the input and output disks
1
and
2
is shifted slightly from the original position. As a result, the circumferential velocity of the rotation of the power rollers
6
a
and
7
a
and that of the rotation of the input disk
1
become off balance, and part of the torque of the input disk
1
serves to rotate the power rollers
6
a
and
7
a
around the pivot axes O. As a result, the power rollers
6
a
and
7
a
slide and incline on the curved surfaces of the input and output disks
1
and
2
.
When the toroidal continuously variable transmission is driven, high contract pressure tends to act between the input and output disks
1
and
2
on one hand and the power rollers
6
a
and
7
a
on the other hand, and the maximal value of the contact pressure is as high as 4 Gpa or thereabouts. In addition to this problem, the bearing surfaces of the power rollers
6
a
and
7
a
are also exerted with high pressure per unit area, and may peel off in a short time.
Under the circumstances, peeling or damage to the traction portions of the toroidal surfaces of the input and output disks
1
and
2
, those of the power rollers
6
a
and
7
a
, and those of the power rollers
6
a
and
7
a
must be prevented for increasing reliability. In addition, since the input and output disks
1
and
2
and the power rollers
6
a
and
7
a
must repeatedly undergo bending stress, fatigue cracking tend to occur. The input and output disks
1
and
2
and the power rollers
6
a
and
7
a
must be improved so that they hardly suffer fatigue and can withstand long use against a bending stress.
Jpn. Pat. Appln. KOKAT Publication No. 7-71555 is intended to provide a toroidal continuously variable transmission wherein the traction surfaces of input and output disks and those of power rollers have an improved rolling-resistant life, and wherein the input and output disks and the power rollers have an improved anti-fatigue cracking life. To attain this object, the disks and the power rollers are subjected to carbonitriding and grinding. Alternatively, they are subjected to carbonitriding and grinding, and are further processed in such a manner that at least either the disks or the power rollers have a hardened layer whose effective depth is not less than 2.0 mm and not more than 4.0 mm.
According to Jpn. Pat. Appln. KOKAI Publication No. 2001-82566, at least one of an input disk, an output disk and a power roller is formed of medium carbon steel having a carbon content of 0.3% to 0.5%, and is subjected to carburization or carbonitriding processing and further to hardening and annealing so that the hardness of the core portion is not less than HRC35. By this processing, an improved life against fatigue is attained.
However, the disks and power rollers are improved by carburization executed at a temperature in the range of 920 to 960° C. or by carbonitriding processing executed at a temperature in the range of 930 to 950° C., and this process is continued 20 to 30 hours. After the heat treatment, therefore, a large-sized carbide or carbonitride is undesirably formed in the metal structure of the disks and power rollers. Since this carbide or carbonitride degrades the fatigue strength of the disks and power rollers, the formation of such a substance must be prevented. In the case of a traction drive such as a toroidal continuously variable transmission, the traction force exerted on the rolling surfaces gives rise to a tangential force. If a carbide or carbonitride is present in a crystalline grain boundary, a stress tends to concen

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