Friction gear transmission systems or components – Friction gear includes idler engaging facing concave surfaces – Toroidal
Reexamination Certificate
2001-05-24
2002-09-17
Herrmann, Allan D. (Department: 3682)
Friction gear transmission systems or components
Friction gear includes idler engaging facing concave surfaces
Toroidal
C029S558000, C451S062000, C476S040000
Reexamination Certificate
active
06450916
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-154888, filed May 25, 2000, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a toroidal type continuously variable transmission used as an automotive transmission, for example, and more specifically, to a cam disc of a loading cam mechanism therein.
Investigation is being made into the use of a half-toroidal type continuously variable transmission, such as the one described in Jpn. UM Appln. KOKAI Publication No. 62-71465, for a variator of an automotive transmission. As shown in
FIG. 4
, the continuously variable transmission of this type includes an input shaft
101
, an input disc
102
, an output shaft
103
, an output disc
104
, an adjustable-tilt displacement shaft
105
, power rollers
106
rotatably supported on the displacement shaft
105
, and the like. The rollers
106
are sandwiched between the input and output discs
102
and
104
.
The respective opposite surfaces of the input and output discs
102
and
104
form concave surfaces or traction surfaces
102
a
and
104
a
with an arcuate profile. An outer peripheral surface
106
a
or spherical convex surface of each power roller
106
is in contact with the traction surfaces
102
a
and
104
a
. A loading cam mechanism
107
is located behind the input disc
102
. The mechanism
107
includes a cam disc
108
having a first cam surface
109
, a second cam surface
110
formed on the back of the input disc
102
, and rollers
112
. The rollers
112
are held in given positions between the cam surfaces
109
and
110
by means of a retainer
111
. The cam surfaces
109
and
110
have their respective recesses P
1
and projections P
2
that are alternately arranged in the circumferential direction of the discs
108
and
102
.
If the cam disc
108
rotates as the input shaft
101
is rotated by means of an engine (not shown), the relative positions of the cam surfaces
109
and
110
shift in the circumferential direction of the cam disc
108
. As this is done, the discs
102
and
108
bind each other through the medium of the rollers
112
between the cam surfaces
109
and
110
, whereupon torque is transmitted from the cam disc
108
to the input disc
102
. When the input disc
102
rotates, its rotation is transmitted to the output disc
104
by means of the power rollers
106
.
The transmission gear ratio of the output disc
104
to the input disc
102
can be changed by varying the tilt angles of the power rollers
106
. Thus, a desired transmission gear ratio can be obtained by changing the ratio between the turning radius at the point of contact between each power roller
106
and the input disc
102
and the turning radius at the point of contact between each power roller
106
and the output disc
104
, depending on the tilt angles of the power rollers
106
.
As shown in
FIG. 5
, the cam disc
108
includes the cam surface
109
and a cylindrical portion
108
a
formed on the central portion of the disc
108
. The cylindrical portion
108
a
projects toward the input disc
102
. A clearance groove
108
c
for grinding is formed in a corner portion between the cam surface
109
and the cylindrical portion
108
a
. The groove
108
c
and the cam surface
109
are worked by cam lathe turning that is described in Jpn. Pat. Appln. KOKAI Publication No. 8-61452, for example. After the clearance groove
108
c
is formed, the cam surface
109
is milled with given accuracy by means of a milling machine.
If a bending load acts on the cam surface
109
, however, stress concentrates on a region near the clearance groove
108
c
of the cam disc
108
. This concentration of stress causes the strength of the cam disc
108
to lower. Further, the aforesaid lathe turning for the formation of the clearance groove
108
c
is required besides the milling work for finishing the cam surface
109
with high accuracy. Thus, the manufacture requires a lot of processes and entails high cost.
If the clearance groove
108
c
is formed in the cam disc
108
, moreover, the retainer
111
for holding the rollers
112
may possibly be caught in the clearance groove
108
c
. If the retainer
111
is caught in the groove
108
c
, the rollers
112
are prevented from behaving normally. Accordingly, the loading cam mechanism
107
ceases to be able to generate a predetermined thrust, so that a gross slip or some other trouble may occur in some cases. If the input torque changes suddenly, in particular, the rollers
112
move on the cam surface
109
in a short time, so that the retainer
111
is easily caught in the clearance groove
108
c.
BRIEF SUMMARY OF THE INVENTION
Accordingly, the object of the present invention is to provide a cam disc of a toroidal type continuously variable transmission designed so that concentration of stress on a corner portion between a disc portion and a cylindrical portion can be eased and that the number of working processes can be reduced.
A cam disc according to the invention comprises a disc portion having a cam surface formed thereon and a cylindrical portion protruding from the cam surface in the central portion of the disc portion, and further comprises a lathe-turned portion formed on a part of the cylindrical portion by lathe turning, a milled surface formed on a side face of the cylindrical portion by milling, and a ground surface including the cam surface and a corner curved surface with an arcuate profile formed on a corner portion between the cylindrical portion and the disc portion by grinding.
According to this invention, no clearance groove, such as the one used in a conventional cam disc, is formed in the corner portion between the disc portion and the cylindrical portion, concentration of stress on the corner portion can be eased, so that the strength of the cam disc can be enhanced. Since the corner portion is worked integrally with the side face of the cylindrical portion and the disc portion during the milling work, working processes can be made fewer than in the case of the conventional cam disc with a clearance groove. Since no clearance groove is formed in the corner portion, moreover, there is no possibility of a retainer being caught in a clearance groove.
The cam disc of this invention may comprise a first corner curved surface with an arcuate profile constituting a part of the milled surface and a second corner curved surface with an arcuate profile constituting a part of the ground surface, formed between the first corner curved surface and the cam surface, and having a radius of curvature not smaller than a given value.
A manufacturing method for a cam disc according to the present invention comprises a lathe turning process for lathe-turning at least an end portion of the cylindrical portion, a milling process for working a side face of the cylindrical portion and pre-finishing the cam surface by means of a milling tool, and further forming a first corner curved surface on a corner portion between the cylindrical portion and the disc portion by means of the milling tool, the milling process directly following the lathe turning process, and a grinding process for grinding the cam surface of the disc portion by means of a grindstone so that the first corner curved surface remains and forming a second corner curved surface between the first corner curved surface and the cam surface by means of the grindstone, the grinding process directly following the milling process.
The milling process is carried out by means of, for example, an end mill having an arcuate portion on the distal end portion thereof for working the first corner curved surface. Further, the grinding process is carried out by means of a grindstone having a straight portion for grinding the cam surface and an arcuate portion for grinding the second corner curved surface.
Additional objects and advantages of the invention will be set forth in the description which follows, and
Herrmann Allan D.
NSK Ltd.
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