Friction gear transmission systems or components – Friction transmission or element – Particular friction surface
Reexamination Certificate
2002-08-16
2003-12-23
Joyce, William C (Department: 3682)
Friction gear transmission systems or components
Friction transmission or element
Particular friction surface
C476S040000, C148S319000
Reexamination Certificate
active
06666792
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a toroidal continuously variable transmission, and more specifically, to a toroidal continuously variable transmission designed for use in vehicles such as automobiles.
2. Description of the Related Art
As a toroidal continuously variable transmission
20
, the one shown in
FIG. 1
has been known.
Inside a housing (not shown), an input disk
1
and an output disk
2
are coaxially arranged so as to 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
have a substantially similar shape and are arranged symmetric. The surfaces of these disks facing each other are toroidal surfaces jointly forming a substantial semicircle sectional view taken axially. A pair of power roller bearings
6
and
7
for transmitting power are arranged in toroidal cavities defined by the toroidal surfaces of the input and output disks
1
and
2
, in such a way that the bearings
6
and
7
be in contact with the input and output disks
1
and
2
.
The 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
7
is composed of 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.
In other words, the power roller
6
a
also functions as the inner ring, which is a structural component of the power roller bearing
6
, and the power roller
7
a
also functions as the inner ring, which is a structural component of the power roller bearing
7
. In this structure, 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 obliquely supported around a pivot axis O, which is the center of the toroidal surfaces of the input and output disks
1
and
2
.
Likewise, the power roller
7
a
is rotatably coupled to a trunnion
11
by means of a pivot
9
, the outer ring
7
b
and rolling members (steel balls)
7
c
, and at the same time obliquely supported by a pivot axis O, which is the center of the toroidal surfaces of the input and output disks
1
and
2
. A lubricant having a large viscosity or friction resistance is supplied onto the contact surfaces of the input disk, output disk
1
,
2
and the power rollers
6
a
,
7
a.
A driving force is exerted on the input disk
1
and 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
with a needle
12
interposed between them (that is, the input disk
1
and output disk
2
are not directly affected by the movement of the rotating shaft
3
). The output shaft
14
, which is arranged in parallel to the input shaft
3
and rotatably supported by a housing (not shown) via angular members
13
, is connected to the output disk
2
.
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 is transmitted and rotates the loading cam
4
, the rotation force is transmitted to the input disk
1
through the cam roller
5
, thereby rotating the input disk
1
. The power generated by 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. When the trunnions
10
and
11
are moved 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 each of the power rollers
6
a
and
7
a
and that of the rotation of the input disk
1
become off balance, and the component force of the torque of the input disk
1
makes the power rollers
6
a
and
7
a
to rotate obliquely around the pivot axes O. As a result, the power rollers
6
a
and
7
a
obliquely moves on the curved surfaces of the input and output disks
1
and
2
.
Since the power rollers
6
a
and
7
a
are obliquely rotated on the curved surfaces of the input and output disks
1
and
2
, a velocity ratio changes, with the result that deceleration and acceleration are performed. An example of a conventional toroidal continuously variable transmission having such a structure is shown in Jpn. UM. Appln. Publication No. 2-49411.
As the input disk, output disk and power roller bearing, those formed of AISI52100 (JIS SUJ2 corresponding to high carbon chromium steel) are conventionally known as described in “NASA Technical note NASA ATN D-8362”.
The present inventors have filed an invention (Jpn. Pat. Appln. KOKAI Publication No. 7-71555) in which the input disk, output disk and the power roller bearing are subjected to surface treatment such as carburization or carbonitriding processing to improve a resistant life. Alternatively, the surface treatment is limited to carbonitriding in Jpn. Pat. Appln. KOKAI Publication No. 9-79336, in which the nitrization amount and residual austenite are defined.
In the toroidal continuously variable transmission, the input disk, output disk, power roller, and loading cam repeatedly receive an extremely large bending stress and shearing stress as compared to machine parts such as a gear, which generally receives stress repeatedly. For this reason, it has been proposed that these disks, power roller, and cam disk should be formed of a material having a high fatigue strength and treated with heat to improve the fatigue strength.
For example, in Jpn. Pat. Appln. KOKAI Publication No. 7-71555, the input disk, output disk, power roller and power roller are formed so as to have a hardened layer whose effective depth is 2.0 mm or more and 4.0 mm or less. In Jpn. Pat. Appln. KOKAI Publication No. 7-286649, shot peening is performed after the heat treatment. In Jpn. Pat. Appln. KOKAI Publication No. 11-141638, assuming that dynamic maximum shearing stress is generated at a position Z
0
, the hardness of the hardened layer at a position satisfying 3.0 Z
0
to 5.0Z
0
is set at 650 or more.
However, recently, it has been demanded that the toroidal continuously variable transmission should be further miniaturized and the output of transmission torque be further increased. Therefore, mechanical parts are required to have higher fatigue strength than conventional ones.
BRIEF SUMMARY OF THE INVENTION
The present invention has been attained to overcome the aforementioned problems. The present invention is to provide a toroidal continuously variable transmission having a long life and capable of suppressing the peeling-off of the traction surface of the toroidal surface formed of an input disk and an output disk and of the traction surface of a power roller and simultaneously improving the lives against fatigue cracking of the input disk, output disk, and power roller by constructing the toroidal continuously variable transmission such that at least one of the input disk, output disk, and the inner ring of the power roller bearing is formed of an alloy steel and subjected to either carburizing polishing and polishing or carbonitriding processing and polishing, and at least one of
Christensen O'Connor Johnson & Kindness PLLC
Joyce William C
NSK Ltd.
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