Planetary gear set and assembly method

A planet gear set and method of assembling the carrier on the sun and ring gear particularly suited for automation of the carrier assembly operation. The sun gear of the planetary set has a staging annulus formed on one end thereof defined between the addendum and dedendum circles of the sun gear teeth. The sun gear also has a frustoconical concentricity chamfer formed on the same end with one edge contiguous with dedendum circle edge of the staging annulus. The carrier, with the planet gears thereon, is aligned on the axis of rotation of the sun gear and advanced toward the same. If the sun gear is eccentric relative to its axis of rotation, the planet gears engage the concentricity chamfer and cam the sun gear to an aligned position which is achieved when the carrier achieves a staged position relative to the sun gear. In the staged position, the addendum circles of the planet gears are tangent to the dedendum circle edge of the staging annulus. The carrier is then mildly biased toward the sun gear and rotated, whereupon the teeth of the planet gears sequentially achieve meshing engagement with the sun gear teeth.

RELATED APPLICATION 
The subject matter of this application relates to the subject matter of 
copending U.S. patent application Ser. No. 707,391 now U.S. Pat. No. 
4,640,294, filed Mar. 1, 1985 by Richard A. Ordo and assigned to the 
assignee of this invention. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to planetary gear type automotive 
transmissions and, more particularly, to a planetary gear set and method 
of assembling the same in an automated operation. 
2. Description of the Prior Art 
In assembling planetary gear type automotive transmissions, it is common 
practice to mount the transmission case on a fixture which permits 
end-for-end inversion of the case so that internal components can be 
installed from opposite ends of the case. It is also common to install a 
planetary gear set in a sequence which includes installation of the sun 
gear and ring gear of the set on the case before the planet gears and 
planet carrier of the set. As an element of this last mentioned step, the 
planet gears, which are already mounted on the carrier and independently 
rotatable relative to each other, are usually "timed" on either the sun 
gear or the ring gear. Timed, as the term is used herein, means meshing 
engagement of all of the planet gears with one of the sun and ring gear 
(hereinafter the "timing gear") before engagement of any of the planet 
gears with the other of the sun and ring gears. After the planet gears are 
timed on the timing gear, they easily mesh with the other of the sun and 
ring gear because the planet gears then rotate in unison. A robot for 
automatically performing this last step can be programmed to advance the 
carrier along a fixed axis and to rotate it about that axis but may 
require expensive machine vision technology because the necessary precise 
alignment of the planet carrier on the axis of rotation of the timing gear 
may not be easily achieved due to manufacturing tolerances in the 
components of the transmission and the end-for-end inversions of the case. 
Where the ring gear is part of a disc clutch assembly, as is common, the 
assembly procedure is even more difficult because the ring gear may bear a 
markedly eccentric relationship to the sun gear. The planetary gear set 
and assembly method according to this invention enables the planet carrier 
assembly operation to be performed by a robot, without machine vision 
technology, programmed only to advance the carrier along an axis and to 
rotate the carrier about that axis. 
SUMMARY OF THE INVENTION 
This invention is a new and improved planetary gear set and an assembly 
method for assembling the planet carrier with the planet gears thereon 
between the sun gear and the ring gear where the latter two gears are 
installed on a support structure prior to the carrier. The new and 
improved planetary gear set includes locating means on the timing gear 
which positions the planet carrier in a staged position relative to the 
timing gear wherein the axes of rotation of the carrier and the timing 
gear are colinearly aligned with each of the planet gears disposed in a 
plane perpendicular to the axis of rotation of the carrier so that when 
the carrier is rotated and mildly biased toward the timing gear, the 
planet gears quickly and easily achieve meshing engagement with the timing 
gear. The means whereby the planet carrier is staged relative to the 
timing gear includes a staging annulus on an end of the timing gear in a 
plane perpendicular to the axis of rotation of the timing gear and a 
centering shoulder or concentricity chamfer on the timing gear having one 
edge contiguous with the staging annulus, the staging annulus being 
defined by and between the addendum and dedendum circles of the timing 
gear and being interrupted by the tooth spaces between the timing gear 
teeth. In a preferred embodiment of the planetary gear set and assembly 
method according to this invention, the timing gear is the sun gear so 
that during advancement of the carrier the planet gears contact the 
concentricity chamfer and cam the sun gear into alignment on the axis of 
rotation of the planet carrier which alignment is achieved in the staged 
position of the carrier relative to the sun gear, the staged position 
being characterized by engagement of an end of each of the planet gears on 
the sun gear on the staging annulus. Also in the preferred embodiment, a 
disc clutch is disposed between the ring gear and the support structure 
and a frustoconical bevel surface is formed on an end of the ring gear 
overlapping the ends of the ring gear teeth so that after the planet gears 
are timed on the sun gear and further advanced toward the ring gear while 
the carrier rotates, the teeth on the planet gears engage the bevel 
surface and cam the ring gear into alignment on the axis of rotation of 
the carrier and then substantially simultaneously achieve meshing 
engagement with the ring gear teeth.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings, a planetary gear set 10 according to this 
invention is to be assembled onto a supporting structure 12, such as a 
transmission case, which defines a main axis 14 fixed relative to the 
case. The planetary gear set 10 includes a sun gear 16, a ring gear 18, a 
plurality of planet gears 20a-d and a planet carrier 22. The ring gear 18 
is connected to the case 12 through a disc clutch 24. 
The disc clutch 24 includes a clutch pack 25 consisting of a plurality of 
outer discs 26 and a plurality of inner discs 28 interleaved between the 
outer discs. Each outer disc has a circumferential array of outer spline 
teeth 30 slidably engaged in a corresponding plurality of spline grooves 
32 in the case 12 centered about the axis 14. Each of the inner discs 28 
has an internal circumferential array of spline teeth 34 slidably engaged 
in a corresponding plurality of spline grooves 36 in the ring gear which 
are parallel to the axis 14 when the ring gear is centered about or 
aligned on the axis. Each of the inner discs 28 has a friction lining 38 
on each face of the disc which slidably engages an opposing face on the 
adjacent one of the outer discs 26. 
The clutch pack 25 is stacked against an annular backing plate 40 on the 
case 12 and engaged by an annular piston, not shown, which compresses the 
clutch pack against the backing plate. When the clutch is thus engaged, 
the ring gear 18 is held stationary relative to the case and when the 
clutch is released the ring gear is freely rotatable relative to the case 
as the inner discs 28 rotate relative to the stationary outer discs 26. 
The ring gear and the attached inner discs 28 are free to translate in 
planes perpendicular to the axis 14 by an amount corresponding generally 
to the clearance between the inner diameters of the outer discs 26 and the 
outer diameter of the ring gear which circumscribes the spline grooves 36. 
The planet carrier 22 includes a cylindrical shaft portion 42 having a 
longitudinal axis 43 and an annular cage portion 44 integral with the 
shaft portion. The shaft portion 42 has an internal pilot bore 46 at one 
end thereof in which is supported a pilot bearing 48. The cage portion 44 
defines a plurality of planet axes 50a-d parallel to and disposed in a 
circle about the longitudinal axis 43 of the cylindrical shaft portion 42. 
A plurality of axle pins 52a-d are rigidly supported on the cage portion 
44 and aligned on the corresponding ones of the planet axes 50a-d. Each of 
the planet gears 20a-d is rotatably supported on a corresponding one of 
the axle pins 52a-d for rotation about the corresponding one of the 
planet axes. The planet gears are separated from the cage portion 44 by a 
plurality of annular thrust bearings 54. 
Each of the planet gears has an array of gear teeth 56a-d thereon which 
extend the length of the planet gears parallel to the planet axes 50a-d. 
One end of each of the planet gears is machined in a plane perpendicular 
to the planet axes 50a-d to form an annulus 57a-d extending radially 
inward from the addendum circle 58a-d of the gear to inboard of the 
dedendum circle 59a-d of the gear. The annuli 57a-d are interrupted by the 
tooth space between the planet gear teeth 56a-d. The annuli 57a-d are 
generally coplanar. However, they are not exactly coplanar due to 
manufacturing tolerances in the thrust bearings 54 and in the planet gears 
20a-d. 
The ring gear 18 has an internal circumferential array of gear teeth 60 
thereon adapted for meshing engagement with the gear teeth 56a-d on the 
planet gears. At the end thereof opposite the backing plate 40, the ring 
gear 18 has an internal bevel defining a frustoconical bevel surface 61 
extending radially inward from an annular peak 62 radially outboard of the 
dedendum circle 63 of the ring gear teeth to the addendum circle 64 of the 
ring gear teeth. The bevel surface 61 is interrupted by the tooth spaces 
between the ring gear teeth 60. 
The sun gear 16 is disposed on the end of a transmission shaft 66 mounted 
on the case 12 for rotation about the axis 14. The sun gear has an array 
of gear teeth 67 extending generally the length of the sun gear. The sun 
gear is machined at one end in a plane perpendicular to the longitudinal 
axis of the gear, not specifically illustrated, to define a staging 
annulus 68 bounded at its radially outermost extremity by the addendum 
circle 69 of the sun gear teeth 67 and at its radially innermost extremity 
by the dedendum circle 70 of the sun gear teeth. Each of the gear teeth 67 
terminates in the staging annulus 68 so that the latter is regularly 
interrupted by the tooth spaces between the gear teeth 67. A frustoconical 
guide shoulder or concentricity chamfer 72 on the sun gear has a radially 
outermost edge 74 contiguous with the dedendum circle 70 defining the 
innermost edge of the staging annulus 68 and a radially innermost edge 76. 
In plan view, FIG. 2, the concentricity chamfer projects as an annulus 
having a radial depth d. The sun gear 16 further includes an integral 
cylindrical pilot 78 aligned on the longitudinal axis of the sun gear and 
projecting from an end surface 80 of the sun gear. The pilot 78 engages 
the pilot bearing 48 whereby the distal end of shaft 66 is rotatably 
supported on the carrier 22. 
In a typical transmission assembly scenario, the transmission case 12 is 
inverted end for end several times as components are installed from 
opposite ends in a sequence most convenient for the particular 
transmission. For example, it may be convenient to assemble the clutch 
pack 25 and the ring gear 18 onto the case with the spline grooves 32 
facing up, as depicted in FIG. 1, followed by an inversion of the case and 
installation of the shaft 66 with the sun gear 16 thereon from the 
opposite end of the case followed by yet another inversion of the case and 
final assembly of the planet carrier 22. At the occurrence of each 
inversion, the already assembled components usually migrate to one extreme 
position in their tolerance range under the influence of gravity as the 
case pivots. Accordingly, in the step of assembling the carrier 22 with 
the planet gears 20a-d thereon between the sun gear and the ring gear, a 
situation is encountered wherein the longitudinal axis of the sun gear 
will typically not coincide with the longitudinal axis 14 of the 
transmission case and the ring gear 18 will typically exhibit a marked 
eccentricity relative to the sun gear. 
With the ring gear and sun gear not aligned on the axis 14, simple robotic 
performance of the carrier assembly step proceeds as follows. The assembly 
robot, programmed for gripping the carrier 22 with the longitudinal axis 
43 of the shaft portion 42 held in colinear alignment with the 
longitudinal axis 14 of the transmission case and for selectively 
advancing the carrier along the axis and rotating the same about the axis, 
grips the carrier and transports the same to a position aligned on the 
axis 14 above the sun gear and the ring gear. The carrier 22 is then 
advanced along the axis 14 toward the sun gear until one or more of planet 
gears 20a-d, at the addendum circles 58a-d thereof, engages the sun gear 
on the concentricity chamfer 72. The particular one or more of the planet 
gears which first engage the sun gear depends upon the random eccentricity 
of the sun gear relative to the axis 14. The planar projection d of the 
concentricity chamfer is correlated with the maximum amount of 
eccentricity which the sun gear may exhibit so that the planet gears, at 
the addendum circles thereof, will always first engage the sun gear on the 
concentricity chamfer. 
Continued advancement of the planet carrier 22 toward the sun gear after 
initial engagement on the concentricity chamfer 72 results in development 
of a camming force between the planet gears and the sun gear whereby the 
latter is forced in a direction perpendicular to the axis 14. The carrier 
22 is advanced under a longitudinally applied force sufficient to affect 
camming until it achieves a staged position relative to the sun gear 16 
wherein the annuli 57a-d on the planet gears overlap and abut the staging 
annulus 68 on the sun gear. In the staged position of the carrier, each of 
the addendum circles 58a-d of the planet gears is generally tangent to the 
outer edge 74 of the concentricity chamfer so that the sun gear 16 is 
substantially precisely aligned on the axis 14. 
In the staged position of the carrier relative to the sun gear 16, the 
planet axes 50a-d are parallel to the main axis 14 of the transmission 
case. The ends of one or more of the planet gear teeth 56a-d, however, 
rest on the ends of the sun gear teeth 67 in the staging annulus 68 so 
that continued advancement of the planet carrier is blocked. With a 
relatively mild bias of the carrier 22 toward the sun gear, the carrier is 
rotated about the axis 14 so that the edges of planet gear teeth 56a-d 
sweep across the staging annulus 68. Because of the slight bias toward the 
sun gear and because of the aforementioned lack of precise coplanar 
alignment of each of the annuli 57a-d on the planet gears, sequential 
meshing engagement of the planet gear teeth 56a-d is quickly achieved as 
the planet gear teeth sweep across the staging annulus and encounter the 
tooth spaces between the sun gear teeth 67. 
With the planet gears 20a-d thus timed on the sun gear and rotating in 
unison as the carrier rotates, the carrier 22 is further advanced along 
the axis 14. The planet gear teeth 56a-d progressively further 
longitudinally overlap the sun gear teeth 67 as one or more of the planet 
gears, at the addendum circles 58a-d thereof, engage the eccentrically 
located ring gear 18 on the frustoconical bevel surface 61. The location 
of the engagement between the planet gears and the frustoconical bevel 
surface is randomly determined by the particular eccentricity of the ring 
gear. If initial engagement of the planet gears on the frustoconical bevel 
surface 61 is radially outboard of the dedendum circle 63 of the ring gear 
teeth 60, a camming force is developed by the planet gears on the ring 
gear 18 whereby the latter is translated perpendicular to the axis 14. 
When the addendum circles 58a-d of the planet gears are tangent to the 
dedendum circle 63 of the ring gear teeth, the planet gear teeth 56a-d 
simultaneously mesh with the ring gear teeth because of the timed rotation 
of the planet gears relative to the ring gear. The carrier 22 is then 
advanced to the fully assembled position with the planet gears disposed 
squarely between the ring gear 18 and the sun gear 16.