Variator disc and a method of fabricating the same

Details Variator disc and a method of fabricating the same Variator disc and a method of fabricating the same

2002-02-27

2004-02-03

Joyce, William C. (Department: 3682)

Friction gear transmission systems or components

Friction transmission or element

Particular friction surface

C476S040000, C148S319000, C148S571000, C148S573000

Reexamination Certificate

active

06685596

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a variator disc mounted in a toroidal continuously variable transmission and a method of fabricating the same.
FIG. 6
is a schematic diagram showing a variator for use in a toroidal continuously variable transmission mounted in vehicles and the like. The variator
10
includes an input shaft
13
driven into rotation by a vehicular power source
12
. The input shaft
13
carries an input disc
15
on respective places near opposite ends thereof. These input discs
15
are each formed with a spline hole
15
a
at a center thereof, the spline hole formed with plural lines of spline grooves. The input disc
15
has the spline hole
15
a
meshed with a spline shaft
13
a
of the input shaft
13
so that the input disc is rotated in unison with the input shaft
13
as permitted of a minor movement axially of the input shaft
13
. The input disc
15
is further formed with a concave race
15
b
on one side surface thereof.
An output portion
18
of the variator
10
is relatively rotatably carried on an axially central portion of the input shaft
13
. The output portion
18
includes an output member
19
and a pair of output discs
20
integrally rotatably carried on the output member
19
. The output disc
20
is formed with a concave race
20
b
on one side surface thereof in face-to-face relation with the race
15
b
of the input disc
15
. The output member
19
is formed with a spline shaft
19
c
on each of the outer peripheries of opposite ends thereof. The spline shaft
19
c
is meshed with a spline hole
20
c
formed at the output disc
20
. The output member
19
is further formed with a sprocket gear
19
a
on an outer periphery of its central portion, the sprocket gear meshed with a power transmission chain
23
. Three disc-like rollers
21
are interposed between the race
15
b
of the input disc
15
and the race
20
b
of the output disc
20
in face-to-face relation. The rollers
21
are in rolling contact with the races
15
b,
20
b,
as arranged with equal circumferential spacing. Each of the rollers
21
is rotatably carried by a carriage
22
, and is adapted to be adjusted for its position relative to the races
15
b,
20
b
by means of the carriage
22
.
Thus, the variator
10
is configured as a so-called double cavity type which includes a pair of sets, each of which consists of the input disc
15
, output disc
20
and rollers
21
. The variator is arranged such that the input discs
15
transmit torque to the output discs
20
via the six rollers
21
. The variator is adapted to vary the speed of rotation (transmission gear ratio) of the output discs
20
by adjusting the positions of the six rollers
21
by means of the carriages
22
(see two-dot chain line in FIG.
6
).
The input disc
15
is formed from, for example, a bearing steel. The input disc is generally fabricated by the steps of heat treating a blank for hardening, the blank formed with the spline hole
15
a
and the concave race
15
b
by machining; finishing the spline hole
15
a
by broaching; and then finishing the race
15
b
by machining or grinding using an inside periphery (surface of minimum inside diameter) of the spline hole
15
a
as a working reference.
The variator
10
is required to maintain the individual rollers
21
in contact with the races
15
b,
20
b
of the discs
15
,
20
at high contact pressure in order to ensure the torque transmission between the input discs
15
and the output discs
20
. Hence, it is a general practice to specify Vickers hardness (Hv) of the race surfaces
15
b,
20
b
to be 700 or more thereby ensuring the fatigue strength of the races
15
b,
20
b.
However, the heat treatment of the discs
15
,
20
generally includes the steps of charging the blank in an oven for heating the whole body of the blank in high temperature atmosphere; quenching the blank; and tempering the same. Accordingly, the overall surface of the blank is hardened to the hardness of not less than Hv700 which is required of the races
15
b,
20
b.
In a case where the spline hole
15
a,
20
c
of the disc
15
,
20
is subjected to an excessive load resulting from unbalanced load or the like, the spline hole
15
b,
20
b
may develop cracks at its bottom and the cracks may further develop to cause fracture of the disc
15
,
20
at worst. Furthermore, since the spline holes
15
b,
20
b
are low in machinability, it is difficult to broach the heat treated spline holes
15
b,
20
b.
This results in the increase of the machining cost.
OBJECT OF THE INVENTION
It is an object of the invention to provide a variator disc capable of preventing the occurrence of cracks in its spline hole.
It is another object of the invention to provide a variator disc facilitating the finishing of the heat treated spline hole.
It is still another object of the invention to provide a fabrication method for variator disc which facilitates the fabrication of the inventive disc.
SUMMARY OF THE INVENTION
A variator disc in accordance with the invention is used in a variator of a toroidal continuously variable transmission, the disc including a concave race at least on one side surface thereof for rolling movement of rollers; and a spline hole at its center which is meshed with an input shaft; and having a surface hardness of not less than Hv700 at the race; and a surface hardness of not more than Hv600 at the spline hole; wherein at least a thin portion between the spline hole and an inside circumferential edge of the race is varied in hardness between a hardened layer of a bottom of the spline hole and a hardened layer of the race by an amount of not less than Hv20 per 1-mm depth.
According to the variator disc thus arranged, even if the spline hole is subjected to an excessive load, the occurrence of cracks at the bottom of the hole can be prevented because the spline hole has the surface hardness of not more than Hv600. Furthermore, the spline hole is easy to finish by machining and hence, the machining cost therefor is reduced. In addition, at least the thin portion is varied in hardness between the hardened layer of the bottom of the spline hole and the hardened layer of the race by the amount of not less than Hv20 per 1-mm depth. Because of such a great rate of the hardness variation, the thin portion need not be increased in thickness but the hardened layer of the spline hole can be decreased in hardness while a sufficient hardness of the hardened layer of the race is maintained as it is. Accordingly, the race has a sufficient depth of hardened layer in the thin portion, as well, so that the race can exhibit a favorable durability. If the amount of hardness variation is less than Hv20 per 1-mm depth, the thin portion must be increased in thickness in order to achieve an adequate hardness of the hardened layer of the race. This leads to the need for accordingly increasing the outside diameter of the disc. According to the invention, however, the hardened layer of the spline hole can be decreased in hardness without entailing an unwanted increase of the outside diameter of the disc.
A method of fabricating the variator disc of the invention comprises the steps of: heat treating a blank for the disc for adjusting a surface hardness thereof to not less than Hv700; annealing the spline hole by high frequency heating while cooling the race; and finishing the spline hole and the race.
According to this method, the spline hole of the disc is annealed while cooling the race of the disc. Therefore, the race is prevented from being decreased in hardness by the thermal influence of the annealing of the spline hole. In addition, at least the thin portion can be effectively varied in hardness between the hardened layer of the bottom of the spline hole and the hardened layer of the race. Accordingly, the disc of the invention can be fabricated easily.
According to the method of fabricating the variator disc, it is preferred that a cooling jig is positioned in parallel with the race as defining a minor gap therebetween and that the race is cooled by c

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