Clutch drum for automatic automotive transmission

A clutch drum for an automatic transmission features a large diameter portion in which a plurality of first slots define castle-like projections about one end thereon and a second set of slots which originate in the projections near the tops thereof and which extend to and terminate in an essentially frusto-conical portion which interconnects the large diameter portion and a small diameter portion containing a piston therein. The first slots serve to mount clutch discs within the drum while the second slots mount discs about the drum. The relatively wide castle-like projections allow the production of the drum from relatively light gauge sheet metal, which has adequate structural rigidity and a reduced maximum diameter.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to an automatic automotive 
transmission and more specifically to a clutch drum for a planetary gear 
unit of such a transmission. 
2. Description of the Prior Art 
In a previously proposed arrangement, such as shown in FIG. 1 of the 
drawings, a clutch drum 100 has been manufactured via press forming. In 
this arrangement, the plurality of corrugations 101 define both internal 
and external spline teeth which mount a plurality of clutch discs 102,103 
on the exterior and in the interior thereof. This arrangement while being 
light in weight has suffered from the drawback of requiring a degree of 
precision during manufacture which renders mass production thereof 
excessively expensive. 
As a solution to this it has been proposed to press form an arrangement 
such as shown in FIG. 2 of the drawings. In this arrangement a plurality 
of slots 104 define elongate castle-like fingers 105 about the end of the 
drum 106 which serve as spline teeth for mounting clutch discs on the 
exterior and within the interior of the drum. However, this arrangement 
has suffered from the drawback that the sheet from which the drum is 
pressed must be adequately thick so as to endow on the elongate fingers 
105 the required structural strength to withstand the inevitable torque 
variations. This of course increases the weight of the drum and further 
requires more power when pressing due to the gauge or thickness of the 
sheet metal. 
SUMMARY OF THE INVENTION 
The present invention features a clutch drum which is press formed so as to 
have a large diameter portion, a small diameter portion, a frusto-conical 
section interconnecting the large and small diameter portions, a plurality 
of first slots formed in the large diameter portion which slots extend 
from one end thereof toward the small diameter portion and which terminate 
short of the frusto-conical section, the first slots defining at one end 
of the drum a plurality of equidistantly spaced castle-like projections, 
and a plurality of second slots formed in the drum which slots are each 
formed in a projection and which each lead from inboard or the end of a 
projection and terminate in the frusto-conical section. 
With this arrangement, due to the width of the castle-like projections (or 
castles), the thickness of the sheet from which the drum is formed may be 
reduced as compared with the arrangement shown in FIG. 2. With this 
arrangement it will be appreciated that by extending the "second" set of 
slots, so as to terminate in the frusto-conical portion, the clutch discs 
mounted on the exterior of the drum may be slipped into place over the 
small diameter portion while the discs disposed within the large diameter 
portion may be inserted into place through the mouth of the large diameter 
portion. 
Further, by angling the minor edges of the slots which terminate in the 
frusto-conical portion (as shown in FIGS. 5 and 6 of the drawings), it is 
possible to avoid any damage to the seals disposed about a piston which is 
reciprocally received in the small diameter portion of the drum.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Turning firstly to FIGS. 4 and 5, a first embodiment of the present 
invention is shown. In these figures, the numeral 3 denotes a clutch drum 
formed by press working. As shown this drum is formed so as to have a 
large diameter section or portion 3a having an outer diameter RO and an 
inner diameter RI. The drum is also formed to have a small diameter 
portion 3b having an outer diameter ro and an inner diameter ri. An 
integral and essentially frusto-conical or boundary portion 9 
interconnects the large and small diameter portions. A plurality of 
"first" slots 7 are formed in the large diameter portion 3a and are 
arranged to extend parallel to the axis of rotation of the drum 3. These 
slots, as shown, extend from the end of the large diameter portion 3a 
toward the small diameter portion 3b and terminate short of the 
frusto-conical portion 9 (which alternatively may be a frusto hyperboloid 
section or the like) to form a plurality of castle-like projections or 
castles C about the end of the large diameter portion 3a. A second set of 
slots 6 are formed in the large diameter portion 3a and are arranged to 
extend from a level inboard of the ends of the castles and terminate in 
the frusto-conical section 9. This arrangement thus defines a plurality of 
bridge-like portions 3d which close off the slots 6 and interconnect pairs 
of fingers which extend along either side of a castle. 
As best seen in FIG. 5, a plurality of "drive" clutch plates or first discs 
4a having radially inwardly projecting teeth 40 are disposed about the 
large diameter portion 3a with the teeth 40 engaged in the slots 6. These 
discs have a minimum inner diameter which is slightly greater than the 
maximum outer diameter of the minor edges 6a defined in the frusto-conical 
section by the slots 6, so as to allow the ready installation of the discs 
via passing same over the small diameter portion 3b of the drum and 
subsequent insertion of the teeth in the slots 6. A plurality of "driven" 
second clutch discs 5b having radially outwardly extending teeth 50 are 
disposed within the large diameter portion 3a with the teeth engaging in 
the slots 7. 
Turning now to FIG. 3 the above described clutch drum arrangement is shown 
disposed within a planetary gear transmission 10 wherein the numeral 11 
denotes an engine crankshaft which is connected to a torque converter 12 
which receives torque from the engine and transmits same to the planetary 
gear unit through a hollow turbine or input shaft 13. One end of the input 
shaft is splined to a clutch drum unit 14 which has a clutch hub 15 formed 
integrally therewith. The clutch hub 15 has a plurality of "drive" fourth 
discs 5a splined thereon for synchronous rotation therewith. These discs 
as shown in FIG. 5 are interleaved with the discs 5b disposed within the 
large diameter portion 3a of the drum 3. 
A piston 8 is disposed within the small diameter portion 3b of the clutch 
drum 3 so as to define a variable volume fluid chamber 17. This chamber is 
selectively fed pressurized fluid from a control circuit incorporated in 
the lower part of the transmission via a passage 37 including radial bores 
formed in the hollow shaft 16. A coil spring 18 is disposed between the 
piston 8 and a spring retainer 20 which is held in place by snap ring 19 
fixed to the exterior of the hollow shaft 16. This spring biases the 
piston 8 to the right (as seen in the drawings) to minimize the volume of 
the chamber 17. 
A retaining plate 21 is interposed between a snap ring 22 which is secured 
to the inner periphery of the drum 3 and the interleaved clutch discs 5a 
and 5b. This retaining plate serves to retain the discs in the drum and to 
act as a reaction member for the clutch plates when the clutch is engaged. 
The just described clutch drum 3, the clutch discs 5a, 5b, spring 18, 
piston 8 and the spring retainer 20, con a "second" clutch generally 
denoted by the numeral 23. 
A clutch drum 26 is secured to a stationary casing 25 and has a plurality 
of third clutch discs 4b splined to the inner periphery thereof. These 
discs are interleaved with the discs 4a disposed on the outer periphery of 
the drum 3. A retaining plate 27 is secured to the inner periphery of the 
clutch drum 26 by a snap ring 28. This plate both secures the clutch discs 
4b within the drum 26 and also acts as a reaction member when the clutch 
is engaged. A piston 29 is disposed within a cavity formed in the clutch 
drum 26 to define a variable volume chamber 30. This chamber fluidly 
communicates with a passage 31 formed in the casing 25. Lugs 32 and 33 are 
provided on the clutch drum 26 are biased apart by a spring 34 and 
function to bias the discs 4a and 4b apart when the chamber 30 is not 
pressurized. 
The clutch drum 3, the clutch discs 4a, 4b, the spring 34, the piston 29, 
the clutch drum 26, chamber 30, lugs 32, 33 and the retaining plate 27 
define a "first" clutch 24 which has a braking function. viz., functions 
as a brake. 
As the clutch drum 3 is splined to the hollow shaft 16 which in turn 
supports a first sun gear 36 of the planetary gear train 35, and the 
clutch drum 3 is rotatably supported in the casing 25 so that the boss 
portion thereof communicates with the passage 37; when fluid pressure is 
directed through the passage 37 to the chamber 17, the piston 8 presses 
the clutch plates discs 5a and 5b together against the bias of the spring 
18 so that the "second" clutch 23 is engaged and connects the first sun 
gear 36 with the input shaft 13 through the clutch drum 3 and clutch drum 
unit 14. Under these conditions, due to the inherent structural strength 
of the castles C, power is transmitted smoothly and securely. 
When the passage 31 is pressurized, the pressure developed in the chamber 
30 causes the piston 29 to press the clutch discs 4a, 4b together against 
the bias of the spring 34 interposed between the lugs 32, 33 and thus 
engages the "first" clutch. Thus the clutch drum 3 is braked via the 
connection to the stationary casing 25. As before, the inherent strength 
of the clutch drum 3 ensures that power is smoothly and securely 
transmitted. For further details relating to the above disclosed 
transmission reference is made to the technical publication "ATZ" 71 
Jahrgang. Nr. 9 September 1969 Pages 307 to 309. 
FIG. 6 shows a variation of the arrangement described hereinbefore wherein 
the surface area of the piston 8 which engages the first of the clutch 
discs 5b is increased to ensure a positive grip therebetween. 
FIG. 7 shows a second variation wherein the clutch disc 5b' which is 
directly engaged by the piston 8 is thicker than the others so that 
bending or the like due to the movement of the piston and/or friction 
generated heat, is eliminated. 
Thus, in summary, the present invention features a readily produced light 
and sturdy clutch drum which also permits the radial dimension of the drum 
to be minimized as the inner diameter RI of the large diameter portion 3a 
is essentially equal to the outer diameter ro of the small diameter 
portion 3b.