EPICYCLIC UNIT OF A PLANET GEAR

ELEMENT EPICYCLOIDAL DE TRAIN PLANETAIRE

English Abstract

An epicyclic unit of a planet gear consists of a carrier which
is provided with a journal for initiating the torque and a
flange (1) arranged coaxially to the carrier, said flange
having a spline toothing on its outer casing surface (2) to
support a lamina (4) of a coupling adapted thereto to divert
the torque. The carrier and the flange (1) are coupled to one
another so as to be torsionally fixed and each receive a
bearing pin of planet wheels arranged axially parallel between
the carrier and the flange (1). In order to be able to
manufacture such an epicyclic unit in an inexpensive manner,
it is proposed that the carrier and the flange (1) be made of
cast aluminum and that the spline toothing of the flange (1)
be completely unfinished.

French Abstract

Cette invention concerne un élément épicycloïdal de train planétaire qui se compose d'un porte-satellites mis en rotation par un arbre et d'une couronne (1) ayant le même centre de rotation que le porte-satellites, ladite couronne présentant une denture extérieure cannelée (2) en prise avec la denture intérieure (4) d'un accouplement servant à dévier le couple. Le porte-satellites et la couronne (1) sont solidaires l'un de l'autre et portent chacun l'axe de planétaires à axes parallèles disposés entre le porte-satellites et la couronne (1). Afin de permettre la fabrication d'un tel élément épicycloïdal à coût réduit, il est proposé de réaliser le porte-satellites et la couronne en aluminium moulé et de laisser la denture extérieure cannelée de la couronne (1) à l'état brut.

Claims

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Patent Claims:
1. An epicyclic unit of a planet gear having a carrier which
is provided with a journal to initiate the torque and a
flange which is arranged coaxially to the carrier, said
flange having, on its outer casing surface, a spline
toothing for supporting a lamina of a coupling adapted
thereto to divert the torque, whereby the carrier and the
flange are coupled so as to be torsionally fixed and each
receive a bearing pin of planet wheels which are arranged
axially parallel between the carrier and the flange,
characterized therein that the carrier and the flange (1)
are made of cast aluminum and that the spline toothing of
the flange (1) is completely unfinished.
2. An epicyclic unit according to claim 1, characterized
therein that the opposite flanks (7) of each tooth (3) of
the spline toothing comprise an angle .alpha. of 2° to 4° vis-à-
vis one another and that the bisector of the angle
between the flanks (7) of each tooth (3) extends parallel
to the longitudinal axis (9) of the flange (1) and of the
carrier.
3. An epicyclic unit according to claim 1 or 2,
characterized therein that the lamina (4) can be moved
axially to open the coupling in the direction in which
the teeth (3) of the spline toothing taper.

Description

CA 02221~97 1997-11-20
"Epicyclic Unit of a Planet Gear"
The invention concerns an epicyclic unit of a planet gear
having a carrier which is provided with a journal for
initiating the torque and a flange which is arranged coaxially
to the carrier, said flange having a spline toothing on its
outer casing surface for supporting a lamina of a coupling
adapted thereto to divert the torque, whereby the carrier and
the flange are coupled with one another so as to be
torsionally fixed and each receive a bearing pin of planet
wheels which are arranged axially parallel between the carrier
and the flange.
Epicyclic units of this type are generally known and are
usually made as castings from steel. Since these epicyclic
units cannot be produced with sufficient dimensional accuracy
by casting and, moreover, the surface quality does not meet
the required demands, the epicyclic units according to the
prior art must be machined after the casting process. In
particular, the flanks of the teeth of the spline toothing
used as contact surfaces for the coupling laminae on the outer
casing surface of the flange must be finished to size by
broaching. This comparatively complex and time-consuming
finishing process of the flange and carrier of known epicyclic
units represents a considerable component of the overall
costs.
It is the object of the invention to propose an epicyclic unit
which can be manufactured in a clearly less expensive manner
and yet meets all requirements with respect to stability and
durability.

CA 02221~97 1997-11-20
-- 2
Proceeding from an epicyclic unit of the aforementioned type,
this object is solved according to the invention thereby that
the carrier and the flange are manufactured from die-cast
aluminum and that the spline toothing of the flange is
completely unfinished.
As a result of manufacturing the epicyclic unit of the
invention from die-cast aluminum, the manufacturing costs can
be substantially reduced which, in particular, is also a
result of the fact that no subsequent machining of the carrier
or flange is required since the aforementioned components can
be made by die-casting with a very great dimensional accuracy.
Even the spline toothing of the flange can remain entirely
unfinished which is why the considerable costs for the
broaching required in steel flanges according to the prior art
are now omitted. The machining of the spline toothing which
is no longer required has the further decisive advantage that
the skin of the casting produced by the casting method remains
intact on the surface of the flange and thus offers the
stability required to support the discs. By means of
durability tests with the epicyclic unit of the invention, it
could be shown that the unfinished tooth flanks of the spline
toothing withstand the required number of load alternations
without damage.
Due to the die-casting production by means of permanent molds,
it is necessary that, among other things, the teeth of the
spline toothing be provided with mold release bevels in order
to even be able to remove the finished cast part from the die-
casting mold. These mold release bevels on the teeth, which
are shown in the form of an inclination of the teeth flanks
relative to the longitudinal axis of the flange or the
carrier, facilitates the release of the laminae of the

CA 02221~97 1997-11-20
coupling. As a rule, the coupling is opened by means of
spring tension, for which a cup spring is usually used.
Whereas, when the coupling is closing in the case of a
hydraulically operated clutch, this is accomplished by
applying the appropriate oil pressure, the running up of the
laminae against the mold release bevels on the tooth flanks
does not represent any kind of problem, the running off of the
laminae from the inclined flanks acts in a supporting manner
on the opening process of the coupling produced by spring
tension.
A preferred compromise with respect to the mold releasability
of the flange and the operability of the coupling is shown
when the opposite flanks of each tooth of the spline toothing
comprise an angle of 2~ to 4~ with one another and the angle
bisector between the flanks of each tooth extends parallel to
the longitudinal axis of the flange or carrier.
Finally, the invention proposes that the laminae for opening
the coupling is axially movable in the direction in which the
teeth of the spline toothing taper.
This type of an adjustment of the mold release bevels is
preferred when, as common in hydraulic couplings of infinitely
variable automatic transmissions for passenger cars, the
coupling is opened by spring tension while the coupling is
closed by the action of oil pressure.
The invention shall be described in greater detail in the
following with reference to an embodiment of a flange of the
epicyclic unit which is illustrated in the drawing in the form
of a diagrammatic sketch, showing:

CA 02221~97 1997-11-20
~igure 1 a side view of a flange with a coupling lamina
which is engaged and
~igure 2 a top view onto the outer casing surface of the
flange provided with a spline toothing, with a part
of the lamina shown in section.
Figure 1 shows a representation in principle of a flange 1 of
an epicyclic unit of a planet gear. The flange 1 and a
carrier (not shown in the drawing) of the epicyclic unit are
joined together with aid of screws and each have bearing bores
for the planet wheels (also not shown in the drawing) which
are situated between the flange 1 and the carrier.
The flange 1 is provided with a number of teeth 3 of a spline
toothing on its outer casing surface. The teeth 3 of the
spline toothing exhibit an essentially trapezoidal cross-
section and are spaced equidistantly about the outer casing
surface 2 of the flange 1.
A lamina 4 of a coupling is arranged coaxially with the flange
1, adapted to the spline toothing of the outer casing surface
2 of the flange 1. The inner casing surface of the lamina 4
is provided with a number of teeth 6 which have a slightly
smaller width than the spaces between the teeth 3 on the outer
casing surface 2 of the flange 1. Due to the form-locking
between the lamina 4 and the flange 1 thus present, a torque
can be transmitted between each of the two aforementioned
parts. In this case, a flank 7 of a tooth 3 of the flange 1
is supported on a flank 8 of a tooth 6 of the lamina 4.
Figure 2 shows a top view onto the outer casing surface 2 of
the flange 1 on which the teeth 3 of the spline toothing have

CA 02221597 1997-11-20
been made. The flanks 7 of the teeth 3 do not thereby extend
parallel with a centre of rotation 9 of the flange 1 but are
inclined at an angle of 1.5~ thereto. Opposite flanks 7 of
the same tooth 3 thus comprise an angle ~ of 3~. The
inclination of the flank 7 of the teeth 3 relative to the
centre of rotation 9 of the flange 1 is shown greatly enlarged
in Figure 2 to better illustrate it. In reality, the
incline of the flanks cannot be seen with the naked eye.
On the left side of Figure 2, a section of a tooth 6 of the
lamina 4 is shown which is supported with its flank 8 on the
flank 7 of the left tooth 3. An annular clutch disc 10 and 11
is situated on each of the two sides of the lamina 1, one of
said discs being used to drive forward and the other to drive
backward. To release the clutch disc 10, the set consisting
of the lamina 4 and the clutch discs 10 and 11 is shifted
axially in direction of arrow 12. This movement is produced
by the force of a cup spring (not shown) and promoted by the
running off of the lamina 6 from the inclined flanks 7 of the
teeth 3. The teeth 6 of the lamina 4 consist of steel, while
the flange 1 including the teeth 3 are made of cast aluminum.
However, since the flange 1 remains completely unfinished
after the casting process and the flanks 7 of the teeth 3 are,
as a result, still provided with a hard casting skin, there
are no signs of excessive wear whatsoever in spite of the
torque transmission between the lamina 4 and the teeth 3 of
the spline toothing. The durability of the flange 1 of the
invention made of cast aluminum was shown by menas of various
stress tests.

Representative Drawing