Toroidal type continuously variable transmission and method...

Details Toroidal type continuously variable transmission and method... Toroidal type continuously variable transmission and method...

1999-01-11

2002-10-22

Joyce, William C (Department: 3682)

Friction gear transmission systems or components

Friction gear includes idler engaging facing concave surfaces

Toroidal

C476S073000

Reexamination Certificate

active

06468180

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a toroidal type continuously variable transmission used as a transmission for vehicles such as automobiles and particularly, to a method of manufacturing a disk for a toroidal type continuously variable transmission.
Heretofore, speed change gears have mainly been used as transmissions for vehicles such as automobiles. The speed change gears comprises a plurality of gears, and the engagement mode of the gears is varied to transmit torque from an input shaft to an output shaft. However, in the conventional speed change gears, torque is varied stepwise and discontinuously at the time of changing the speed. Thus, the speed change gears have drawbacks such as a loss in power transmission and vibration at the time of changing the speed.
Under the circumstances, a continuously variable transmission, in which torque is not varied stepwise or discontinuously at the time of changing the speed, has recently been put to practical use. In the continuously variable transmission, no vibration occurs at the time of changing the speed, and the loss in power transmission is less than that in the speed change gears. In addition, the continuously variable transmission is fuel-efficient when it is mounted in the vehicle. As an example of the continuously variable transmission, a belt type continuously variable transmission is mounted in some type of passenger cars.
On the other hand, as an another example of the continuously variable transmission, a toroidal type continuously variable transmission has been proposed. The toroidal type continuously variable transmission comprises an input shaft rotated by a drive source such as an engine, an input disk, an output disk and power rollers. The input disk is supported on the input shaft and rotated in interlock with the input shaft. The output disk is supported on the input shaft so as to be opposed to the input disk and rotated in interlock with the output shaft. The power roller is provided swingably between the input disk and the output disk and rotatably put into contact with both disks.
The input disk and the output disk have essentially equivalent shapes to each other. One disk
80
of the input disk and the output disk will below be described in reference to FIG.
17
.
The disk
80
has the shape of a disk symmetrical with respect to an axis P
1
. The disk
80
comprises a protrusion
81
, a skirt portion
82
and a mounting hole
83
in one body. The protrusion
81
is projected in the central portion of the disk
80
along the axis P
1
as viewed from the side. The skirt portion
82
is provided outside an outer periphery of the protrusion
81
and a thickness of the disk is gradually thinner along a direction from the protrusion
81
toward its outer edge. The mounting hole
83
penetrates through the protrusion
81
along the axis Pl. The mounting hole
83
accommodates the input shaft inside the hole when the disk
80
is mounted on the input shaft.
The disk
80
is provided with a traction surface
85
over the protrusion
81
and the skirt portion
82
. The traction surface
85
is formed in the sectional shape of an arc whose center coincides with the axis P
1
of a shaft which supports the power roller in a freely swingable manner. The traction surface
85
is formed along all the periphery of the disk
80
.
The toroidal type continuously variable transmission can transmit higher torque as compared with the belt type continuously variable transmission. For this reason, it is considered that the toroidal type continuously variable transmission is effective for continuously variable transmissions for middle and large sized vehicles.
However, the toroidal type continuously variable transmission requires transmission of larger torque. For this reason, the disk
80
and the power roller receive a very large repeated bending stress and a very large repeated shearing stress as compared with general mechanical parts on which a repeated stress acts such as a gear and a bearing. Especially, the disk
80
receives a large stress on an end surface
81
a
of the protrusion
81
.
As a method of manufacturing a disk
80
for the toroidal type continuously variable transmission, for example, a method in which a work formed in a rod shape by a rolling process is subjected to machining or a method which has been disclosed in Jpn. Pat. Appln. Publication No. 9-126289 has been employed. The method shown in Jpn. Pat. Appln. Publication No. 9-126289 is that a work as an to-be-molded object is subjected to forging so to be fashioned into a near final shape and thereafter grinding is performed on the work as a finishing process.
When the above described disk is manufactured by machining a rod-like metal base material mass, a yield is low due to machining loss and a required time for the process is long. Hence, a problem arises that a production cost is increased.
Furthermore, a base material mass used for a disk that has been formed into a rod-like shape through processes such as melting, casting, and rolling, includes most of the disk's impurities in an area defined by a diameter that is 30% or less of the outer diameter of the base material. The increased concentration of impurities in the center of the disk is due to the central portion of the disk cooling at a slower rate than the outer portion of the disk. Moreover, a metal flow, which is a flow of metal structure formed in the process of rolling or the like, is formed along the axis of the base material mass.
When the mass, which contains much of impurities around the central portion, is subjected to machining to manufacture the disk
80
, much of impurities are present in a densely hatched portion X
1
of
FIG. 17
in the vicinity of the inner surface
83
a
of the mounting hole
83
from the bottom surface
84
to the end surface
81
a
of the protrusion
81
. Besides, metal flows J are formed along the axis P
1
of the disk
80
.
For this reason, the disk
80
manufactured by machining is apt to fracture in the portion X
1
which includes a lot of impurities along the metal flow lines J since a great stress acts especially on the end surface
81
a
of the protrusion
81
as compared with general mechanical parts. Accordingly, a disk
80
manufactured by machining has had a tendency to have a relatively shorter life span because of higher stresses applied to the end face, which in turn results in a shorter life span of a toroidal type continuously variable transmission.
In the manufacturing method described in the Jpn. Pat. Appln. Publication No. 9-126289, one kind of a die set is used for forging of a work for a disk till an almost final shape is conferred to the work and thereafter, grinding is applied to attain the disk
80
. In the manufacturing method, therefore, a time length during which the work is in contact with the die set is long. Hence, the die set is apt to shorten its lifetime because of reduction in a surface hardness under influence of heat in forging.
In addition, since a structure of the die set is not one to support a work in the course of forging, the work is subject to deviate from the center of the die set to have an eccentricity, which causes dimensional precision to be deteriorated. Furthermore, since in the final stage of forging, the work occupies a full space of the die set, a part of the work corresponding to a corner of the die set is subject to underfill or burr, which have again caused shaping of the work into desired dimensions to be difficult.
What's worse, since only one kind of die set is used, a need has arisen that an excessive load is imposed for forging a work in the process in order to mold the work into a desired shape. Hence, there has been a risk that a die set is fractured. In order to suppress a required time length for grinding which is performed after the forging, it is a necessity to decrease a grinding removal. In order to decrease the grinding removal, there is a further necessity to suppress a wear of the die set or the like. For this purpose, in the manufacturing method described

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