Metal deforming – By use of tool acting during relative rotation between tool... – During rotation of work
Reexamination Certificate
2001-09-20
2004-02-17
Tolan, Ed (Department: 3725)
Metal deforming
By use of tool acting during relative rotation between tool...
During rotation of work
C072S085000
Reexamination Certificate
active
06691542
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention generally relates to a method and an apparatus for manufacturing a cylindrical member by flow forming, and a cylindrical member having inner splines that is manufactured by using the method and the apparatus. More particularly, the invention relates to a method and an apparatus for partially thickening a blank, and a product manufactured by using the method and the apparatus, which are preferably applied to a front cover of a torque converter having inner splines.
2. Description of Related Art
Conventionally, some parts of the automatic transmission have splines formed at radially inward positions. For example, Japanese Laid-Open Publication No. 9-317848 describes a front cover of a torque converter. This front cover has inner splines for engaging the components such as outer friction plates in a lockup clutch composed of a multiple disc clutch. In this front cover, a drum member having the splines formed at its inner peripheral surface are welded within the front cover of sheet metal.
A cylindrical member having such splines, e.g., a front cover, is constructed by integrally welding a main body and another member having the splines. This requires troublesome processes such as welding, and also requires advanced production management such as preventing a residual sputtering material from being left within the product. Moreover, the number of parts is increased, resulting in increased costs.
For example, U.S. Pat. No. 5,718,311 describes a method for integrally forming a front cover portion and spline grooves by flow forming. However, in such a simple flow forming method, the thickness of the splined portion is significantly reduced. In view of the strength, a countermeasure is required such as forming the entire structure from a thick blank. Forming not only the splined portion but also the entire structure with a large thickness causes additional problems like increased weight of the torque converter.
In order to solve the above problems, the applicant proposed a method for manufacturing a cylindrical member having splines in Japanese Laid-Open Publication No. 11-266062. According to this method, as shown in FIG.
12
(
a
), a disk-shaped blank
1
is fixedly held between a tailstock
2
and a mandrel
3
. A multiplicity of tooth spaces
3
a
corresponding to the splines are formed at the outer peripheral surface of the mandrel
3
. These tooth spaces
3
a
may either extend in the central-axis (Z-axis) direction, or may be slightly tilted with respect to the central axis. As shown in FIG.
12
(
b
), a thickening roller
5
having a dish-shaped outer peripheral surface
5
a
is rotated and moved in the direction A, thereby pressing the blank
1
from the outer peripheral end face. As a result, the thickness of the blank
1
is increased (from t
1
to t
2
), and the blank
1
is bent toward the mandrel
3
. As shown in FIG.
12
(
c
), a forming roller
6
is then rotated and moved in the direction B (Z-axis direction). As a result, the portion
1
a
thickened by the thickening roller
5
is spread along the mandrel
3
by plastic deformation, whereby the thickness thereof is reduced (from t
2
to t
3
). The material thus spread is forced into the grooves
3
a
, whereby the splines
1
b
are formed.
According to the flow forming proposed by the applicant, only the portion of the front cover (cylindrical member)
1
corresponding to the splines
1
b
is thickened, and the front cover need not entirely be thickened, enabling reduction in weight of the torque converter. However, the blank to be formed into the cylindrical portion is entirely pressed to form the thick portion (see FIG.
12
(
b
)), causing work hardening. Therefore, the material does not sufficiently flow into the space between the teeth
3
a
of the mandrel
3
in the subsequent step of forming the splines
1
b
with a roller
6
. Accordingly, the accuracy of the splines may possibly be degraded. This problem becomes remarkable in forming the cylindrical member having a longer cylindrical portion. Moreover, the forming roller
6
is moved in the direction B. Therefore, the roller
6
pulls a shoulder portion
1
e
at the boundary between a circular plate portion
1
c
and a cylindrical portion
1
d
. As a result, a sufficient amount of material is less likely to remain in the shoulder portion, although the shoulder portion is subjected to large stresses for the structural reason.
Moreover, this flow forming requires large processing energy in order to thicken the entire columnar portion of the blank
1
. In the case where the blank
1
as punched with a press is directly used, the accuracy of the outer peripheral end face
1
f
is not enough. When pressed against the outer peripheral end face of the blank, the thickening roller
5
is subjected to the large loads, and therefore the outer periphery of the thickening roller
5
is damaged by the rough end face
1
f
of the blank, resulting in relatively short lifetime of the roller. However, finishing the outer peripheral end face of the blank with high accuracy would require additional processes such as cutting process.
The applicant also proposed a driving apparatus for hybrid vehicles in which an electric motor
11
is mounted radially outside the torque converter
10
as shown in
FIG. 13
(e.g., Japanese Patent Application No. 11-84924 and Japanese Patent Application 11-104540, which had not been laid-open upon filing of the present application). As shown in
FIG. 13
, a front cover
12
of a torque converter
10
has a stepped structure having an axially extending flat portion
12
a
in a radially intermediate portion. The front cover
12
also has a vertical portion (bottom)
12
b
located radially inside the flat portion. An enlarged diameter portion
12
c
is formed radially outside the flat portion
13
in order to accommodate a turbine runner
13
. An electric motor
11
composed of a rotor
11
a
and a stator
11
b
is mounted radially outside the flat portion
12
a
with a predetermined space c interposed between the rotor and the flat portion
12
a
. The lockup clutch
15
is mounted radially inside the flat portion
12
a.
The lockup clutch
15
is composed of a multiple disc clutch having a multiplicity of external friction plates (drive plates and backup plates)
16
and inner friction plates (driven plates)
17
. The drum member
19
has its one end welded to the front cover
12
and extends along the flat portion
12
a
. Inner splines
19
a
are formed in the drum member
19
. The outer friction plates
16
are engaged with the inner splines
19
a
. The inner friction plates
17
are engaged with hubs
23
connected to an input shaft
22
of a transmission
21
(automatic transmission (A/T) or continuously variable transmission (CVT)) through a damper spring
20
.
The lockup clutch
15
is connected with a hydraulic pressure of a piston
26
driven with a hydraulic pressure supplied to an oil chamber
25
. The torque capacity of the lockup clutch
15
is determined by the lining area of the friction members
16
,
17
. As described above, however, the outer friction plates
16
are engaged with the splines
19
a
formed in the drum member
19
. Therefore, the friction members are located radially inward as compared to the case where the splines are directly formed in the front cover
12
. Moreover, the length thereof is also reduced. Accordingly, a sufficient lining area of the friction members cannot be ensured, and therefore sufficient torque capacity of the lockup clutch cannot be ensured with respect to the maximum required design hydraulic value.
In this lockup clutch
15
, the outer friction plates
16
are engaged with the drum member
19
that is a member separate from the front cover
12
. As described above, from the manufacturing and functional point of view, it is desirable to eliminate the drum member and form the inner splines
19
a
in the front cover itself. However, in the case where an integral front cover
12
is formed by the aforementioned flow forming (see FIG
Adachi Takehiko
Fukukawa Osamu
Nagai Hideyuki
Nakajima Masaki
Aisin AW Co. Ltd.
Lorusso, Loud & Kelly
Tolan Ed
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