Abrading – Abrading process – Gear or worm abrading
Reexamination Certificate
1999-11-22
2002-02-19
Banks, Derris H. (Department: 3723)
Abrading
Abrading process
Gear or worm abrading
C451S161000
Reexamination Certificate
active
06347980
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for grinding the traction surface of a continuously variable transmission (CVT) disk of a half-toroidal type.
2. Description of the Related Art
Recently, the traction surface of a half-toroidal CVT disk used as a continuously variable transmission of a car has been worked or ground by a grinding machine.
The grinding machine used for such grinding operation includes a cylindrical grinding disk of a plane type and a grinding machine of an angular type. In the plane type grinding machine, a swing angle &thgr;
1
is set at 90° and, in the angular type grinding machine, a swing angle &thgr;
1
is set at 60°; and, a grindstone, which is mounted on the rotary shaft of the grinding machine, is slidably disposed in such a manner that it can cut in a direction perpendicular to the rotary shaft of the grindstone (&thgr;
1
=90°) or at an angle (&thgr;
1
=60°).
In the grinding machine, a work to be ground is held on an XY table. The XY table has not only the function of an X table to slide the work in an X direction but also the function of a Y table to slide the work in a Y direction. The X direction is the sliding direction of the work in the diameter direction thereof, whereas the Y direction is the sliding direction of the work in the rotation axis direction thereof.
In order to be able to carry out both of the X-table and Y-table functions with respect to the upper surface of the XY table, two structural elements required to fulfill their respective functions are piled up in two layers, and they are respectively superimposed on a spindle on the XY table side.
Also, referring further to a table for holding a work as other structural element than the XY table, there has been applied by the present applicants, a grinding machine comprising a swing table which can be slided in a direction perpendicular to the cutting direction of a grindstone (Japanese Patent Unexamined Publication No. 11-226870 of Heisei).
By the way, in the above-mentioned conventional grinding machines, there is found a problem that an actual machining allowance and an apparent machining allowance are different from each other. Also, there is raised another problem as to a grindstone interference diameter. That is, as shown in
FIGS. 2A and 2B
, when a grindstone
26
is outside butted against the grinding surface (that is, the surface to be ground) of a work
28
, if the actual machining allowance is expressed by t, then the following relationships hold between the actual machining allowance t and apparent machining allowance t′ (that is, a dimension over which the grindstone
26
advances from the outside of the machining allowance to a traction surface when it is completed):
t=t
′×cos(&thgr;
1
+&ohgr;
1
) Expression 1
where, &thgr;
1
: spindle swing angle (an angle formed between a direction extending along the cutting direction of the grindstone
26
and a direction extending in parallel to the mounting surface of the work
28
), and
&ohgr;
1
: Arc sin((&phgr;−
pcd
)/(
r−t
)) Expression 2.
Here, pcd expresses a radius which extends from the center of a curved surface of the traction surface of the CVT disk when it is completed to the center of the work
28
(PCD expresses the diameter of pcd), &phgr; expresses the outer peripheral radius of the work
28
, and r expresses the radius of the curved surface of the traction surface of the CVT disk when it is completed.
Also, as shown in
FIGS. 3A and 3B
, when the grindstone
26
is inside butted against the grinding surface of the work, the following relationships hold between the actual machining allowance t and apparent machining allowance t′:
t=t
′×cos(&pgr;2−&thgr;
1
−&ohgr;2) Expression 3,
&ohgr;
2
: Arc sin((
h
1
−h
2
)/(
r−t
)) Expression 4.
Here, h
1
expresses a height which extends from the bottom surface of the work
28
to the center of the curved surface of the traction surface of the CVT disk when it is completed, and h
2
expresses the dimension of the height of the work
28
.
As can be seen from the above-mentioned expressions, in both cases in which the grindstone
26
is outside and inside butted against the grinding surface of the work
28
, a cutting magnification t′/t provides a value larger than 1, which means that the apparent machining allowance is larger than the actual machining allowance and, therefore, there is raised a problem that the cutting time of the grindstone
26
is made long.
Also, as the swing angle is made larger, the grindstone interference diameter must be reduced accordingly. Otherwise, there is caused interference in the outer peripheral portion of the disk with respect to the grindstone and, therefore, the outer peripheral portion of the disk is ground not in a linear contact manner but the work
28
is ground in a surface butting manner, which results in the dull ground shape.
Accordingly, if the grinding operation of the work
28
is executed by the grindstone
26
, then the outside dimension of the grindstone
26
becomes small with the grinding of the work
28
. Thus, if the grindstone diameter that can be used is small, then a spindle, on which the grindstone
26
is mounted, must be rotated at a high speed in order to gain the grindstone peripheral speed. In this case, the diameter of the shaft of the spindle becomes finer or smaller according to the dimension of the small grindstone diameter, thereby causing the rigidity of the spindle shaft to lower. Therefore, if the grindstone
26
is rotated at a high speed in order to enhance the grinding or working efficiency, then there is raised a fear that the rigidity of the spindle shaft can be made insecure. This problem will a rise not only in a case in which the grindstone diameter is reduced as it is used but also in a case in which the diameter of the grindstone
26
is previously set small.
Also, in a case in which the diameter of the grindstone
26
is previously set small, the usable range of the grindstone
26
is small and, therefore, the frequency of replacement of the grindstone
26
increases. This requires more time for replacement of the grindstone
26
, which reduces the operating time of the grinding machine. Thus, the productivity of the work
28
cannot be enhanced, which is a disadvantage in the working or grinding cycle.
Further, if the grindstone diameter used is small, the number of abrasive grains of the grindstone surface actually used in the working or grinding operation is small. This reduces an interval in which the clogged grindstone is dressed, which also provides a disadvantage in the working or grinding cycle.
In addition, in a case in which a grindstone diameter used is equal to or less than a given value, it is difficult to structure a grinding machine. That is, a bracket for embracing the spindle and a grindstone base for carrying the bracket thereon must have mass and size equal to and larger than a given value regardless of the grindstone diameter and, therefore, it is difficult to structure a grinding machine in which only the grindstone diameter is small.
SUMMARY OF THE INVENTION
The present invention aims at eliminating the drawbacks found in the above-mentioned conventional method for grinding the traction surface of a half-toroidal CVT disk. Accordingly, it is an object of the invention to provide a method for grinding the traction surface of a half-toroidal-type CVT disk in which the disk can be ground or worked within the proper range of spindle swing angles and the diameter of a grindstone is set equal to or larger than a given value.
In attaining the above object, according to the first aspect of the invention, there is provided a method for grinding a traction surface of a half-toroidal CVT disk, including the steps of:
preparing a grinding machine including a hold mechanism holding the half-toroidal CVT disk having a given machining allowance; and a machining mechanism including
Ikeda Hiroyuki
Kamamura Yuukou
Tanaka Masami
Banks Derris H.
NSK Ltd.
Sughrue & Mion, PLLC
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