Friction gear transmission systems or components – Friction gear includes idler engaging facing concave surfaces – Toroidal
Reexamination Certificate
2000-04-10
2002-04-09
Bonck, Rodney H (Department: 3681)
Friction gear transmission systems or components
Friction gear includes idler engaging facing concave surfaces
Toroidal
C384S606000, C384S614000, C476S008000
Reexamination Certificate
active
06368245
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a toroidal-type continuously variable transmission which is improved in a retainer for rollably holding a plurality of rolling elements.
2. Description of the Related Art
In recent years, as a transmission for a car, or as a transmission for various industrial machines, there has been used a toroidal-type continuously variable transmission. And, as the toroidal-type continuously variable transmission, for example, there are known a transmission disclosed in Japanese Utility Model Unexamined Publication No. 6-16753 of Heisei in which a retainer of a power roller bearing is integrally formed of synthetic resin, a transmission disclosed in Japanese Utility Model Unexamined Publication No. 7-35847 of Heisei in which there is formed an oil groove in a retainer to thereby enhance the lubrication efficiency thereof, and a transmission disclosed in Japanese Patent Unexamined Publication No. 7-174146 in which there is formed an oil hole in a retainer to thereby enhance the lubrication efficiency thereof.
The retainer of the above-mentioned power roller bearing is generally structured in such a manner as shown in FIG.
8
.
That is, on the periphery of a rotary shaft
1
, there are rotatably supported an input disk
2
and an output disk
3
having their respective inner peripheral surfaces opposed to each other. Between the input and output disks
2
and
3
, there is interposed a trunnion
4
which is capable of swinging about its pivot shaft (not shown) situated at a torsional position with respect to the center axes of the input and output disks
2
and
3
(Here, “torsional position” means a physical relation which lies in a direction at right angles to the direction of the rotary shaft
1
but does not intersect the rotary shaft
1
). The trunnion
4
includes a displacement shaft
5
and, on the periphery of the displacement shaft
5
, there is disposed a power roller
6
which is rotatably supported in such a manner that it is held between the input and output disks
2
and
3
. Further, between the power roller
6
and trunnion
4
, there is interposed a thrust rolling bearing
7
which is used to receive a thrust-direction load applied to the power roller
6
.
The respective inner peripheral surfaces
2
a
and
3
a
of the input and output disks
2
and
3
are formed as concave surfaces each having an arc-shaped section, while the peripheral surface
6
a
of the power roller
6
is formed as a spherically convex surface; and, the peripheral surface
6
a
is in contact with the inner peripheral surfaces
2
a
and
3
a
. The thrust rolling bearing
7
comprises a plurality of rolling elements
8
and a retainer
9
for rollably holding the plurality of rolling elements
8
.
The retainer
9
is composed of a circular-ring-shaped main body
10
and a plurality of pockets
11
which are respectively disposed in the intermediate portions of the main body
10
in the diameter direction thereof to rollably hold the rolling elements
8
. Further, the retainer
9
includes a plurality of lubricating oil passages
12
respectively formed as recessed grooves which are interposed between the inner and outer peripheries of the main body
10
in such a manner that they cross the pockets
11
.
Therefore, according to the above-structured toroidal-type continuously variable transmission, even when the retainer
9
forming the thrust rolling bearing
7
shifts in the axial direction to thereby cause one surface of the retainer
9
to come into close contact with a surface opposed to the present surface of the retainer
9
, a sufficient amount of lubricating oil is allowed to flow through the lubricating oil passage
12
into the pockets
11
holding the rolling elements
8
. As a result of this, there is eliminated a fear that a part of the thrust rolling bearing
7
can wear excessively or can be seized to its adjoining member.
However, in the thrust rolling bearing
7
used as the power roller bearing of the toroidal-type continuously variable transmission, due to its structure designed for traction contact, as shown in
FIG. 8
, between the thrust rolling bearing
7
and input and output disks
2
and
3
, there can be obtained only two contact points (loading points) respectively shown by arrow marks in
FIG. 9
, while the two contact points have a contact angle of &agr; between them. Therefore, the inner race
7
a
of the thrust rolling bearing
7
not only receives a force in the thrust direction but also generates a component of force in the radial direction at the 180° opposite portion on the circumference thereof, so that the circular-ring-shaped thrust rolling bearing
7
is compressed in the radial direction.
Due to this compression, the inner race
7
a
is deformed into such an elliptical shape as shown in FIG.
9
. Also, due to power transmission, in the traction contact portion, there is produced such a force
2
Ft in the tangential direction as shown in FIG.
10
A. This force turns into a force P which tends to fall down the thrust rolling bearing
7
, as shown in
FIG. 11B
, thereby causing an imbalance in force.
In case where the thrust rolling bearing
7
is used in this condition, the rotational speeds of the rolling elements
8
around the retainer
9
show such distributions as shown in FIG.
11
. That is, the rotational speeds of the rolling elements
8
(the lengths of arrow marks show the rotational speeds of the rolling element
8
around the retainer
9
) in the
2
Ft direction are lower than the rotational speeds of the rolling elements
8
in the anti-
2
Ft direction. Therefore, as shown in
FIG. 12
, the contact loads between the rolling elements
8
and retainer
9
, in the anti-
2
FT direction, as shown by arrow marks (the lengths of the arrow marks represent the intensities of the contact loads), act so as to push the retainer
9
in its rotating direction but, in the
2
Ft direction, acts so as to push the retainer
9
in the opposite direction to the rotating direction thereof. Accordingly, a compressive stress is applied to a pocket
11
a
, whereas a tensile stress is applied to a pocket
11
b
; and thus, during one rotation of the retainer
9
, one pocket
11
receives one cycle of two-way stress loads ranging from the compressive stress to the tensile stress.
Also, conventionally, the lubricating oil passage
12
of the retainer
9
which is used under these conditions, as shown in
FIGS. 13A and 13B
, is formed of a recessed groove (a substantially U-shaped groove which includes two corner portions each formed as an arc R). Therefore, in case where a tensile stress is applied to the pocket
1
, around the recessed groove, there is obtained such stress distribution as shown in
FIG. 14
; that is, there is a fear that the maximum stress X can be applied to the vicinity of the connecting portions between the two corner portions R and the bottom of the groove, thereby causing the retainer
9
to break around and from such connecting portions.
Also, the thrust rolling bearing
7
used as a power roller bearing in a toroidal-type continuously variable transmission handles the rolling elements
8
and retainer
8
as sub-assembling members in an intermediate step, in order to facilitate check and delivery to thereby reduce the manufacturing cost of the bearing in its assembling step. For this purpose, there is employed a so called “ball guide system” in which the retainer
9
is positioned by the rolling elements
8
. In this system, no slide guide surface is provided for the inner and outer races to thereby be able to lower the dynamic torque loss of the bearing. This is especially important in the toroidal-type continuously variable transmission which is required to provide a high power transmission efficiency. In the ball guide system, a pocket clearance is important. In an ordinary bearing as well, the pocket clearance must be set not too large nor too small. Especially, in a power roller bearing for use in a toroidal-type continuously variable transmission, to the pockets
Aramaki Hirotoshi
Goto Nobuo
Imanishi Takashi
Kato Hiroshi
Machida Hisashi
Bonck Rodney H
NSK Ltd.
Sughrue & Mion, PLLC
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