Clutch drum, method of manufacturing clutch drum and apparatus for forming tooth profile

At a time of manufacturing a clutch drum formed in a cup shape, having a peripheral wall formed in a tooth profile, and having a circumferential groove for mounting a snap ring in a portion close to an open end of an inside projecting portion, in a stage of forming a peripheral wall of a base material formed in a cup shape into a predetermined tooth profile, after forming in such a manner that a minimum outer diameter of the open end portion of the inside projecting portion is larger than a maximum diameter of the circumferential groove for the snap ring, a cutting process is given to the open end portion of the inside projecting portion 3, so that the circumferential groove is formed. Accordingly, a tooth profile having an uneven amount necessary for transmitting a rotation is secured and no extending portion is produced in the open end portion of the inside projecting portion.

The content of Application No. TOKUGANHEI 9-72050, filed Mar. 25, 1997 in 
Japan, is hereby incorporated by reference. 
BACKGROUND OF THE INVENTION 
The present invention relates to a clutch drum, a method of manufacturing a 
clutch drum and an apparatus for forming a tooth profile which are used 
for manufacturing a clutch drum of an automatic transmission. 
A clutch drum of an automatic transmission in accordance with a related art 
is formed in a cup shape and has a peripheral wall having a tooth profile. 
The clutch drum has a circumferential groove for mounting a snap ring in a 
portion close to an opening end of an inside (or inwardly) projecting 
portion on the peripheral wall. In order to manufacture the clutch drum, a 
tooth profile forming apparatus provided with a punch having an outer 
peripheral surface formed in a tooth profile and a die having an inner 
peripheral surface formed in a tooth profile is used. When the punch to 
which a base material having a cup shape is fitted is combined with the 
die, a peripheral wall of the base material is molded to a predetermined 
tooth profile between the outer peripheral surface of the punch and the 
inner peripheral surface of the die. 
As shown in FIG. 1A, the peripheral wall Cw of the base material Cp has a 
tooth profile portion. A cross sectional shape of the tooth profile 
portion is not changed from an opening end thereof to a closed side 
thereof. 
In the tooth profile portion of the peripheral wall Cw, a circumferential 
groove Cd for mounting a snap ring is formed. The circumferential groove 
Cd is formed by a cutting process. The circumferential groove Cd is formed 
at a portion close to the open end of the inside projecting portion Cm. 
SUMMARY OF THE INVENTION 
It is necessary for the clutch drum to sufficiently secure an uneven amount 
of the tooth profile portion of the peripheral wall Cw so as to transmit a 
rotation inside and outside the tooth profile portion. Accordingly, in 
order to make a formability of the peripheral wall Cw, it is desired to 
make a thickness of the peripheral wall Cw thin. Further, as shown in FIG. 
1B, both end portions 101 in a peripheral direction among the inside 
projecting portion Cm of the peripheral wall Cw is extended in such a 
manner as to be thinner than a central portion 102 by a press molding. 
However, in the tooth profile portion of the peripheral wall Cw, a cross 
sectional shape thereof is not changed from the open end thereof to the 
closed side, and an outer diameter .phi.r1 of the both end portions 101 in 
the inside projecting portion Cm is smaller than an outer diameter of the 
center portion 102. Accordingly, when the portion close to the open end of 
the inside projecting portion Cm is cut so as to form a circumferential 
groove Cd for mounting a snap ring, a groove diameter .phi.d1 of the 
groove Cd is over the outer diameter .phi.r1 of the both end portions 101 
in the inside projecting portion Cm, so that there has been a possibility 
that an extending portion is partially produced at a bottom of the groove 
Cd. When the extending portion is produced in the groove Cd, a strength of 
the clutch drum is deteriorated. Further, it is necessary to remove a burr 
produced in the extending portion. 
In order to correspond to this, when a total thickness of the clutch drum 
is made thick, a weight thereof is largely increased. Further, it is 
necessary to change a shape of a corresponding part with which the crutch 
is engaged to transmit a rotation. Accordingly, a cost thereof is 
increased. Still further, when the material of the clutch drum is changed 
to a material having a high strength, a cost is increased at that degree. 
It is an object of the present invention to provide a clutch drum, a method 
of manufacturing a clutch drum and an apparatus for forming a tooth 
profile which forms a groove for mounting a snap ring together with 
securing a tooth profile necessary for transmitting a rotation and without 
producing an extending portion at a portion close to an open end of an 
inside projecting portion. 
In order to achieve the object mentioned above, in accordance with a first 
aspect of the present invention, there is provided a method of 
manufacturing a clutch drum comprising; 
a first step of forming a peripheral wall of a base material for a clutch 
drum formed in a cup shape into a tooth profile having an inside 
projecting portion and an outside projecting portion, and 
a second step of forming a circumferential groove for mounting a snap ring 
on a portion close to an open end of the inside projecting portion by 
cutting, wherein 
in the first step, a minimum outer diameter of the portion close to the 
open end of the inside projecting portion is made larger than a maximum 
diameter of the circumferential groove. 
In accordance with the method mentioned above, as the peripheral wall of 
the base material is formed in a predetermined tooth profile, an uneven 
amount of the tooth profile necessary for transmitting a rotation is 
secured easily. Further, since the minimum outer diameter of the portion 
close to the open end of the inside projecting portion is made larger than 
the maximum diameter of the circumferential groove for the snap ring, a 
generation of an extending portion is avoided when the portion close to 
the open end of the inside projecting portion is cut to form the 
circumferential groove for the snap ring. 
Accordingly, a strength is prevented from being deteriorated, and a 
removing operation of a burr is not necessary. As a result, it is realized 
that the clutch drum is made light and a cost thereof is reduced. 
In accordance with a second aspect of the present invention, there is 
provided a method of manufacturing a clutch drum comprising; 
a first step of forming a peripheral wall of a base material for a clutch 
drum formed in a cup shape into a tooth profile having an inside 
projecting portion and an outside projecting portion, and 
a second step of forming a circumerential groove for mounting a snap ring 
on a portion close to an open end of the inside projecting portion by 
cutting, wherein 
in the first step, the portion close to the open end of the peripheral wall 
is formed to be thicker than a closed side thereof, and 
in the second step, a maximum diameter of the circumferential groove is 
formed in such a manner as to be smaller than a minimum outer diameter of 
the portion close to the opening end of the inside projecting portion. 
In accordance with the method mentioned above, as the peripheral wall of 
the base material is formed in a predetermined tooth profile, the minimum 
outer diameter of the portion close to the open end of the inside 
projecting portion made thicker than the other portions is larger than the 
maximum diameter of the circumferential groove for the snap ring. 
Accordingly, an uneven amount of the tooth profile necessary for 
transmitting a rotation is secured easily when the portion close to the 
open end of the inside projecting portion is cut to form the 
circumferential groove for the snap ring. 
Accordingly, a weight of the clutch drum is slightly increased, however, a 
clutch drum having a higher strength at a degree of making the thickness 
of the portion close to the open end of the inside projecting portion 
having the circumferential groove for the snap ring formed thicker than 
the thickness of the other portion is manufactured. 
In accordance with a third aspect of the present invention, there is 
provided a clutch drum of cup shape having a peripheral wall, comprising: 
a tooth profile portion formed in the peripheral wall and having an inside 
projecting portion and an outside projecting portion; and 
a circumferential groove for mounting a snap ring on a portion close to an 
open end of the inside projecting portion by cutting; wherein 
a minimum outer diameter of the portion close to the open end of the inside 
projecting portion is larger than a maximum diameter of the 
circumferential groove.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An embodiment in accordance with the present invention will be described 
below with reference to the attached drawings. 
FIGS. 2A, 2B and 2C show a clutch drum manufactured by a method of 
manufacturing a clutch drum in accordance with a first embodiment of the 
present invention and FIGS. 3A and 3B show an apparatus for forming a 
tooth profile in accordance with a first embodiment. 
As shown in FIGS. 2A and 5, the clutch drum 1 is formed in a cup shape 
having a peripheral wall 2. A tooth profile portion 5 is formed in the 
peripheral wall 2. The tooth profile portion 5 of the peripheral wall 2 
has an inside (inwardly) projecting portion 3 and an outside (or 
outwardly) projecting portion 6 which are alternately and continuously 
provided, and in the portion close to the open end of the inside 
projecting portion 3, a circumferential groove 4 for mounting a snap ring 
is formed. 
As shown in FIG. 2B, in the clutch drum 1, a closed end section S, a center 
section T and an open end section U among the tooth profile portion 5 of 
the peripheral wall 2 respectively have a different sectional shape from 
each other. In the closed end section S and the center section T, a 
rotation is transmitted inside and outside thereof. On the contrary, in 
the open end section U, as shown in FIG. 2C, a minimum outer diameter 
.phi.R of the inside projecting portion 3 is formed in such a manner as to 
be greater than a predetermined groove diameter (a maximum diameter) 
.phi.D of the circumferential groove 4. 
As shown in FIG. 3A, an apparatus for forming a tooth profile used at a 
time of manufacturing the clutch drum 1 is provided with a female die 11, 
a punch 12, a male die 13, a step forming die 16, a tooth profile forming 
die 20 and a pad 17. The punch 12 is fixed to the female die 11 and has an 
outer peripheral surface formed in an outer tooth profile. The male die 13 
moves close to and apart from the female die 11. The step forming die 16 
and the tooth profile forming die 20 are fixed to the male die 13 through 
a retainer 14 and a ring plate 15. The peripheral wall CW of the base 
material CP is press molded into a predetermined shape between the dies 
16,20 and the punch 12. The tooth profile forming die 20 has an inner 
peripheral surface formed in an inner tooth profile. The pad 17 presses 
the base material CP fitted to the punch 12 at a time of forming on the 
punch 12. In this case, reference symbol CW is attached to the peripheral 
wall of the base material CP before deformation, and reference numeral Z 
is attached to the peripheral wall of the base material CP (the clutch 
drum 1) after deformation, thereby differentiating the both of them. 
As shown in FIG. 3B, a projecting portion 21 of the tooth profile forming 
die 20 is constituted by a taper portion (a first portion) 21a close to a 
closed end (an upper portion in the drawing) which inwardly deforms the 
peripheral wall CW of the base material CP of the clutch drum 1 at a 
predetermined amount, a small diameter portion (a second portion) 21b 
continuously provided in the taper portion 21a, and a taper portion (a 
third portion) 21c close to an open end (a lower portion in the drawing) 
which deforms the portion close to the open end of the clutch drum base 
material CP less than a predetermined amount. The recess portion 22 of the 
tooth profile forming die 20 is constituted by a taper portion (a first 
portion) 22a close to the closed end (the upper portion in the drawing) 
and having substantially an equal length M to each other in an axial 
direction, a taper portion (a third portion) 22c close to an open end (the 
lower portion in the drawing), and a small diameter portion (a second 
portion) 22b positioned between the taper portions 22a and 22c. 
The taper portion 21c close to the open end of the projecting portion 21 
has a length N in the axial direction larger than that of the taper 
portion 22c close to the open end of the base material of the recess 
portion 22. The taper portion 21a close to the closed end of the 
projecting portion 21 and the small diameter portion 21b respectively have 
length 0 and P in the axial direction smaller than that of the taper 
portion 22a close to the closed end of the recess portion 22 and the small 
diameter portion 22b. By using the tooth profile forming die 20, the 
peripheral wall Z of the clutch drum base material CP is formed in a tooth 
profile having different cross sectional shapes in the closed end section 
S, the center section T and the open end section U. 
At a time of manufacturing the clutch drum 1 mentioned above, at first, the 
clutch drum base material CP formed in a cup shape is fitted to the punch 
12 of the tooth profile forming apparatus, the clutch drum base material 
CP is pressed by the pad 17, and the dies 16 and 20 are descended together 
with the male die 13. 
In this step, the closed end taper portion 21a and the small diamter 
portion 21b of the projecting portion 21 in the tooth profile forming die 
20 deforms the peripheral wall CW of the base material CP at a 
predetermined amount, so that the closed end section S and the center 
section T are formed. Accordingly, the tooth profile portion 5 having an 
uneven amount necessary for transmitting a rotation is securely and easily 
formed. On the contrary, the open end taper portion 21c of the projecting 
portion 21 in the tooth profile forming die 20 deforms the open end 
portion of the clutch drum base material CP less than the predetermined 
amount, so that the open end section U is formed. 
In all the sections S, T and U, the both end portions 7 in the peripheral 
direction among the inside projection portion 2 of the peripheral wall CW 
are extended thinner than the center portion 8 thereof by press molding. 
In the section U among all the sections S, T and U, a deformation amount 
is smaller than that of the other sections S and T, and both end portions 
7a are thick. In other words, in the section U, a difference of the 
thickness is small between the center portion 8 and the both end portions 
7a (refer to FIG. 2C). Accordingly, in the section U, the inside 
projecting portion 3 having a minimum outer diameter .phi.R is larger than 
a predetermined groove diameter .phi.D of the circumferential groove 4 for 
the snap ring is formed. 
After forming the peripheral wall 2 in a predetermined tooth profile in 
this manner, a cut process is given to the open end portion of the inside 
projecting portion 3 so as to form the circumferential groove 4 for the 
snap ring, so that the clutch drum 1 is obtained. Since the minimum outer 
diameter .phi.R of the open end portion of the inside projecting portion 3 
is larger than the predetermined groove diameter .phi.D of the 
circumferential groove 4 for the snap ring at a time of cutting, the 
bottom portion of the circumferential groove 4 is prevented from being 
produced an extending portion. 
FIG. 3 shows an end surface of a clutch drum manufactured by a method of 
manufacturing a clutch drum in accordance with a second embodiment of the 
present invention. 
In the method of manufacturing the clutch drum in accordance with this 
embodiment, a base material CPa for a clutch drum formed in a cup shape 
and having a peripheral wall CWa including a portion close to an open end 
formed in such a manner as to be thicker than the other portions is used. 
Accordingly, a minimum outer diameter .phi.R of the open end portion in 
the inside projecting portion 33 formed at a stage of forming the 
peripheral wall CWa of the base material CPa in a predetermined tooth 
profile becomes larger than a predetermined groove diamter (a maximum 
diameter) .phi.D of a groove 34 for mounting a snap ring. Therefore, by 
giving a cutting process to the open end portion of the inside projecting 
portion 33 after forming the peripheral wall CWa in a predetermined tooth 
profile, the circumferential groove 34 is formed without producing the 
extending portion. 
At this time, since only the portion in which the circumferential groove 34 
is formed is thick, the tooth profile necessary for transmitting a 
rotation is secured. Further, a weight thereof is slightly increased, 
however, a strength of the clutch drum 31 is increased at a degree that 
the open end portion of the inside projecting portion 33 having the 
circumferential groove 34 formed is made thicker than the other portion. 
In this case, a detailed structure of a method of manufacturing a clutch 
drum and an apparatus for forming a tooth profile in accordance with the 
present invention is not limited to the structure of the embodiments 
mentioned above.