Note: Descriptions are shown in the official language in which they were submitted.
213632~
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Epicyclic qear with two driven shafts
Description
The invention relates to an epicyclic gear in
accordance with the precharacterizing clause of Patent
Claim 1.
There are many machines in which it is necessary
to drive two shafts with a variable speed difference. In
mixers, for example, it may be necessary to vary the
speed difference between two stirring tools in order to
adapt it to the viscosity of the material to be pro-
cessed.
German Offenlequngsschrift 2,811,887 has dis-
closed a gear of the generic type, in this case for the
purpose of driving a helical conveyor centrifuge. A
helical conveyor centrifuge has a driveable drum and a
conveyor screw rotating in the latter. To process dif-
ferent materials, it is not only necessary for the speed
of the drum to be variable but also the speed of the
screw or the speed difference between the drum and the
screw.
In order to allow infinitely variable control of
the speed difference with just one driving motor, the
drive disclosed in German Offenlegungsschrift 2,811,887
for this helical conveyor centrifuge has a driving motor
which drives the peripheral wheels of two epicyclic gears
via the gear casing, the said gears being coupled to the
drum 80 that the drum rotates at a speed proportional to
the speed of the driving motor. The output shaft of the
first epicyclic gear iQ coupled to the screw and is
driven by the driven shaft of the second epicyclic gear.
If the driving shaft of the ~econd epicyclic gear is held
fast, the driven shaft of the second epicyclic gear,
driven by way of the peripheral wheel of the gear,
rotates in accordance with the transmission ratio between
the peripheral wheel and the driven shaft of the second
epicyclic gear. If, however, the input ~haft of the
second epicyclic gear i8 driven by a variable-speed
motor, the speed of the driven shaft of the second
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epicyclic gear decreases or increa~e~ independently of
the speed of the drum, dep~n~;ng on the direction of
rotation of the input shaft.
If the speed of the drum i8 changed by means of
a change in the speed of the driving motor, the speed
difference between the drum and the screw also changes.
Thus if the drum is to be driven at a constant speed
difference with respect to the screw, the speed dif-
ference must be correspo~;ngly readjusted by means of
the variable-speed motor when there is a change in the
speed of the drum.
The object of the invention is to provide a gear
in which the adjustable speed difference between two
driven shafts can be maintained irrespective of the speed
of the drive.
This object is achieved, according to the inven-
tion, by means of the features of Patent Claim 1.
The gear in accordance with this patent claim
follows the fundamental principle of the solution, namely
that of reducing or increasing the speed of that driven
shaft of the first gear stage which, in a helical con-
veyor centrifuge for example, drives the screw, by means
of the second gear stage, one input shaft of which is
variable in its speed, acting as a control shaft, the
magnitude of the change in speed being dependent solely
on the speed of this control shaft.
In a gear constructed in accordance with this
principle, the speed difference between the driven shafts
of the first stage is thus now dependent only on the
speed of the control shaft of the second stage. A change
in the speed of the driving means, for example of a
driving motor, no longer affects the speed difference.
According to Patent Claim 1, one driven shaft of
the first gear stage, which, according to Claim 14, is
designed as a gear casing with a peripheral wheel, is
driveable by a driving means, the input shaft of this
first gear stage being driven by an output shaft of the
second gear stage, which is arranged on its input side.
This one driven shaft of the first gear stage is
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accordingly coupled directly to the driving means, for
example a driving motor, and is thus driven without any
further speed transformation at the speed of the driving
motor. The other driven shaft of the first stage is
driven via the casing and the planetary gear of the first
stage is driven by the driving means, their speed in turn
being dependent on the speed of the input shaft and of
the driven casing and peripheral wheel of the first
stage. As already mentioned, this input shaft is driven
by one of the two output shafts of the second gear stage.
This output shaft referred to is driveable by a driven
element of the second gear stage, this driven element
interacting via first planet wheels with a sun wheel of
the control shaft.
With this arrangement alone, it would already be
possible to vary the speed difference between the first
and the second driven shaft of the first stage by way of
the control shaft of the second stage. However, the speed
difference would not be dependent solely on the speed of
the control shaft since if the speed of the control shaft
or the input shaft of the first gear stage remains con-
stant but the speed of the driving means and hence of the
peripheral wheel of the first gear stage decreases, the
speed difference between the driven shafts obviously
changes.
This is made clearer below in the description of
the figures by means of a numerical example.
This unwanted change in the speed difference is
eliminated by means of a gear arrangement in the form of
a further engagement means in one output shaft of the
second gear stage. The aim of this arrangement is to
change the speed of the input shaft of the first stage in
such a way, the speed of the control shaft remaining
constant, that the influence of the change in the speed
of the driving means is compensated.
In the gear in accordance with Patent Claim 1,
this is accomplished by virtue of the fact that one
output shaft, which, according to Claim 2 or 4, is
designed as the gear casing of the second stage and is
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rigidly connected to the driven shaft designed as the
- gear casing of the first stage, has an engagement means
which acts on the driven element of the second stage via
second planet wheels operatively connected to the first
planet wheels, the second planet wheels being operatively
connected to a further input shaft of the second stage by
way of a second sun wheel.
According to Claim 2, this solution is implemen-
ted in terms of construction by designing the driven
element as a first peripheral wheel which is connected
for rotation in common to the output shaft of the second
stage and the engagement means is in the form of a second
peripheral wheel in the casing of the second gear stage,
which, like the casing or peripheral wheel of the first
gear stage, is driven by the driving means. This inter-
acts by way of the second planet wheels with the second
sun wheel, the second planet wheels having the same web
carrier as the first planet wheels of the second gear
stage. If the second sun wheel is now held fast, the
rotation of the second peripheral wheel brings about a
rotation of the web carrier, which also carries the first
planet wheels, which interact with the first peripheral
wheel, which is in turn connected to the output shaft of
the second gear stage and hence to the input shaft of the
first gear stage. A change in the input speed at a
constant speed of the control shaft thus leads to a
change in the speed of the input shaft of the first gear
stage which precisely compensates the unwanted change in
the speed difference which would otherwise occur.
In the gear in accordance with Patent Claim 4, a
similar approach is adopted but in this the output shaft
of the second gear stage is connected for rotation in
common to a first web carrier of the first gear stage,
this web carrier forming the driven element of this stage
and carrying the first planet wheels, which interact with
a freely rotating peripheral wheel and the sun wheel of
the control shaft, a second web carrier connected for
rotation in common to the driven gear casing acting as
the engagement means and carrying the second planet
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wheels, which intera-ct with the peripheral wheel and the
second sun wheel. The second web carrier is here driven
by the driving means via the casing of the second stage.
If the second sun wheel iB fixed, the peripheral wheel is
rotated and an influence i~ therefore exerted on the
speed of the first web carrier, which is connected to the
input shaft of the first gear stage.
The invention furthermore has, especially when
used on helical cG-,veyor centrifuges, a number of advan-
tages over the prior art with respect to the necessarydrives for the machine.
When starting up the helical conveyor centrifuge,
the main drive of the ~-ch;ne~ an electric motor for
example, has to provide considerable acceleration forces,
resulting from the mass moment of inertia of the drum,
the conveyor screw and the charge in the drum to be
overcome. In addition, shearing forces can arise within
the charge where the drum and the screw rotate at
different speeds. This means that in the start-up phase
of the machine, a zero speed difference is desirable in
order to minimize the driving force, the speed difference
in normal operation being set by means of the control
shaft only when the desired speed of, for example, the
drum is reached. In the epicyclic gear according to the
invention, all that is required to achieve a zero speed
difference in the start-up phase is for the control shaft
to be held fast. Accordingly, the variable-speed motor
for driving the control shaft is stationary in this phase
and it is only to set the desired speed difference that
it is simply accelerated from stationary to a relatively
low speed of revolution in a predetermined direction of
rotation. The variable-speed motor can thus be of rela-
tively low-power design and, in addition, the individual
bearings of the control shaft and of the adjoining
epicyclic gear are subjected to only low speeds of
revolution.
According to Patent Claim 3, the input shaft of
the second ~tage is rigidly connected to a third peri-
pheral wheel, which acts via third planet wheels mounted
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on the web carrier on the second, in this case freely
rotating, sun wheel. This special design offer~ addi-
tional advantages over the embodiment in which a rigid
connection is provided between the input shaft and the
second sun wheel of the second stage.
If, namely, in this design in accordance with
Claim 3, the control shaft of the second stage is fixed,
the speed difference between the driven shafts of the
first stage can be set by means of the rotatable further
input shaft of the second stage independently of the main
drive speed and specifically, in this case, with a speed
ratio of 1:1 between the further input shaft and the
output shaft of the second stage. If, on the other hand,
the further input shaft is held fast and, instead, the
control shaft of the second stage is used to set the
speed difference, the same relationships as in the
embodiment according to the invention in accordance with
Claim 2 are once again established.
According to Patent Claim 5, the input shaft of
the second stage is advantageously designed 80 as to be
fixed, thereby reducing the manufacturing outlay for the
gear while nevertheless providing the desired control-
lability. If, on the other hand, the second sun wheel is,
in accordance with Patent Claim 5, designed to be drive-
able via the input shaft, the speed difference can beadditionally varied via this input shaft.
According to Patent Claims 8 and 9, the gear
casing is used to drive the second peripheral wheel or
the second web carrier. This makes the gear simpler in
construction since the gear casing, which is present in
any case, is at the same time used to drive the gear.
However, it is also possible that a stationary gear
casing will be desired, for safety reasons for example,
and in this case the gear elements to be driven can be
driven by way of conventional driving means such as gear
wheels and shafts, c~;n~ or belt drives.
According to Patent Claim 10, the common peri-
pheral wheel provided for the first and second planet
wheels of the second gear stage has separate tracks for
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the planet wheels. This makes it possible to provide the
tracks with different toothing optimally suited to the
respective requirements.
It is, of course, also possible for separate
peripheral wheels to be provided in the second gear stage
and for these to be coupled or at least capable of being
coupled to one another.
It is possible to use both planetary gears and
cycloid gears for the epicyclic gear described. Nor is
there a problem in combining a planetary gear stage with
a cycloid gear stage to obtain an ideal epicyclic gear
dep~n~;ng on requirements as to the transmission ratio,
loadability and r~nning properties.
Further advantageous developments of the inven-
tion form the sub~ect-matter of the rema;n;ng subclaims.
The invention will now be explained in greater
detail with reference to the figures by means of a number
of exemplary embodiments.
Figure 1 shows the entire epicyclic gear in a
first ~hodiment,
Figure 2 shows, in a sketch, the second gear
stage of an epicyclic gear in accordance with Figure 1,
Figure 3 shows, in a sketch, the second gear
stage of an epicyclic gear in accordance with a second
embodiment,
Figure 4 shows, in a sketch, the second gear
stage of an epicyclic gear in accordance with a third
embodiment and
Figure 5 shows, in a sketch, the second gear
stage of an epicyclic gear as a further development of
the gear shown in Figure 2.
The epicyclic gear in accordance with Fig. 1
consists of a first, cycloid gear stage and of a second
planetary gear stage. A gear casing 3 of the first gear
stage has a toothing 2 via which rotation is imparted to
the gear casing 3 by a driving motor (not shown). The
gear casing 3 simultaneou~ly serves as the first driven
shaft of the first gear stage, to which the drum of a
helical conveyor centrifuge can be connected, for
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example. A second driven shaft 4 of the first gear stage
is formed by the output shaft proper of the epicyclic
gear, which is operatively connected via the cycloid gear
to the casing 1 of the first stage.
The second gear stage likewise has a ca~ing 1,
which is rigidly connected to the casing 3 of the first
stage and, together with the latter, forms a common
casing body for the epicyclic gear. A control shaft 5 of
the second stage, which is connected to a variable-speed
motor (not shown), is situated on a side of the common
casing body remote from the second driven shaft 4 of the
first stage. Situated on this side, coaxially with the
control shaft 5, is a further input shaft 6 of the second
stage.
The mode of operation of the epicyclic gear is
explained below by means of the construction of the gear,
starting from the input side.
The gear casing 1, 3 is rotated by means of the
toothing 2. An internal gear ring 7 of the cycloid gear
stage is rigidly connected to the gear casing 1, 3, the
said gear ring rotating with the gear casing 1, 3. The
internal gear ring 7 interacts via two cam discs 8 with
two eccentrics 10 seated on an output shaft 9 of the
second gear stage and serving, in this exemplary embodi-
ment, as the input shaft of the first gear stage. The cam
discs 8 are mounted on pins 11 which, in turn, are con-
nected to the second driven shaft 4 of the first stage.
In the first exemplary embodiment, the input shaft of the
first stage is formed by the eccentrics 10 of the cycloid
gear. However, it is also possible to provide the input
shaft as an external component on which correspo~;ng
eccentrics are arranged in a manner fixed in terms of
rotation and which is coupled to the output shaft 9 of
the second gear stage by means of a suitable shaft
coupling.
If the input shaft of the first gear stage, i.e.
the output shaft 9 of the second gear stage, is held
fast, the driving motor rotates the internal gear ring 7,
whereby the cam discs 8 are rotated in accordance with
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g
the transmission ratio. The rotary motion of the cam
discs 8 is in turn transmitted via the pins 11 to the
second driven shaft 4 of the second stage. If the output
shaft 9 of the second stage is rotated in addition, the
speed of the second driven shaft 4 of the first stage is
reduced or increased, dep~n~;ng on the direction of
rotation of the output shaft 9 of the second stage.
The mode of operation of the second gear stage is
explained by means of its construction, starting from the
control shaft 5.
According to the first exemplary embodiment in
Figs. 1 and 2, the control shaft 5 is connected for
rotation in common to a first sun wheel 12 which drives
first planet wheels 13 mounted on webs 14 of a freely
rotating web carrier 15. The first planet wheels 13
interact with a peripheral wheel 16, which is connected
for rotation in common to the output shaft 9 of the
second gear stage or input shaft of the first gear stage.
The further input shaft 6 of the second stage is
provided with an integral, second sun wheel 17, which
interacts by way of second planet wheels 18 mounted on
the same webs 14 as the first planet wheels 13 with a
second peripheral wheel 19 which is connected for rota-
tion in common to the gear casing 1 of the second stage,
driven by the driving motor.
The construction of the second gear stage is
somewhat clearer from the sketch in accordance with
Figure 2.
In normal operation, the input shaft 6 of the
second stage is fixed and the speed difference between
the two driven shafts 3, 4 of the first stage thus
depends solely on the speed of the control shaft 5.
If the transmission ratio of the internal gear
ring 7 and the driven shaft 4 of the first ~tage i8
56:55, then, with the input shaft of the first stage
fixed, the driven shaft 4 rotates at a speed of
4072.7 rpm when the speed of the internal gear ring 7 is
4000 rpm. If the transmi~sion ratio of the input shaft
and the driven shaft 4 of the first stage is 55:1, then,
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'- - 10 -
with the internal gear ring 7 held fast, the driven shaft
4 rotates at a speed of -29.1 rpm when the speed of the
input shaft of the first stage is 1600 rpm.
If the internal gear ring 7 and the input shaft
of the first stage are rotated at the speeds given in a
direction of rotation in which the speeds are added
together, the resulting speed at the driven shaft 4 is
4044 rpm. The speed difference between the driven shaft
4, as the output shaft proper of the epicyclic gear, and
the casing of the first stage as a second driven shaft 3
of the epicyclic gear, the latter shaft rotating at the
input speed of 4000 rpm, is thus 44 rpm.
If the speed of the internal gear ring 7 now
decreases to 3600 rpm while the speed of the input shaft
of the first stage remains the same, the resulting speed
at the driven shaft 4 is 3636 rpm, the speed difference
thus being 36 rpm.
In order to achieve a constant speed difference,
even when the input speed of the gear casing 1, 3
changes, the speed of the input shaft of the first stage
must be changed as the input speed changes. In the
abovementioned case, the speed of the input shaft of the
first stage must be reduced to 1200 rpm. This change in
speed is performed in the second gear stage. The reduc-
tion in the speed of the second peripheral wheel 19(attached to the gear casing 1) of the second stage due
to the reduced input speed results in a change in the
speed of the web carrier 15 and the speed of the first
peripheral wheel 16 - rigidly connected to the output
shaft 9 of the second stage - and hence of the input
shaft of the first stage is thereby reduced, with the
gear design selected, by 400 rpm, with the result that
the desired speed difference of 44 rpm between the two
driven shafts 3 and 4 of the first stage is maintained
automatically.
Figure 3 shows the second gear stage in accor-
dance with a second embodiment. In this embodiment, the
first gear stage is identical with that in the first
embodiment. The first gear stage is therefore not
.
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11 -
described again.
Basically, the second embodiment depicted differs
from the first embodiment in that the first and second
sets of planet wheels 113, 118, which act on the first
and second sun wheel 112, 117 respectively of the second
stage, have a common freely rotating satellite 120 but in
this case are mounted on separate webs 114, 121. The
first planet wheels 113 are mounted on first webs 114,
which are connected by a first web carrier 115 to the
output shaft 109 of the second stage. Second webs 121 are
connected to the gear casing 101 of the second stage, the
casing being driven by the driving motor. Thus, in con-
trast to the first embodiment, the rotation of the gear
casing 101 does not influence the speed of the web
carrier but the speed of the common freely rotating
satellite 120; influencing the speed of the satellite 120
in turn influences the speed of the first webs 114 and
hence that of the driven shaft 109 of the second stage.
Figure 4 shows the second gear stage of a third
embodiment correspon~;ng in terms of the construction of
the gear to the second embodiment in accordance with Fig.
3. The difference with respect to the second embodiment
is, however, that a cycloid gear is used for the second
gear stage instead of a planetary gear.
The first sun wheel is here replaced by a first
double eccentric 212 and the second sun wheel is replaced
by a second double eccentric 217. The double eccentrics
212, 217 interact with cam discs 213, 218 which replace
the planet wheels. The cam discs 213 interacting with the
first double eccentric 213 are mounted on first pins 214,
which replace the first webs and are again rigidly con-
nected to the driven shaft 209. The second cam discs 218
are mounted on second pins 221 which, like the second
webs of the second embodiment, are rigidly connected to
the gear casing 201, which is driven by the driving
motor. The mode of operation of this gear stage is
accordingly identical with that of the second P~hodiment.
Figure 5 shows another exemplary embodiment of
the second gear stage of the epicyclic gear according to
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- 12 -
the invention.
- According to this exemplary embodiment, the
output shaft 9 of the second stage is formed integrally
with a first peripheral wheel 16, which acts via planet
wheels 13 mounted on freely movable web carriers 14, 15
on a sun wheel 12 which is integrally connected to the
control shaft 5 of the second stage. Second planet wheels
18 are mounted on the web carriers and these planet
wheels make rolling contact with a peripheral wheel 19
attached to the gear casing 1 of the second stage and are
in engagement with a second, freely rotating sun wheel
17. According to Fig. 5, this second sun wheel 17 is
mounted on the control shaft 5 of the second stage and
has another toothed track, in which the teeth of third
planet wheels 20 engage. The third planet wheels are
likewise mounted on the web carriers 14, 15 and have
~;m~n~ions correspo~;ng to those of the first and second
planet wheels.
The third planet wheels 20, for their part, make
rolling contact with a third peripheral wheel 21, which
is rigidly connected to a further input shaft 6 of the
second ~tage and has the same rolling diameter as the
first peripheral wheel 16 of the second stage. As in the
previous exemplary embodiments, the control shaft 5 and
the further input shaft 6 are arranged coaxially, the
input shaft 6 being designed as a hollow shaft in which
the control shaft 5 is mounted so as to be rotatable
relative to the input shaft 6.
If, in this exemplary embodiment, the further
input Yhaft 6 of the second gear stage is fixed as in the
exemplary e_bodiments described above, it is po~sible to
adjust the speed difference between the first and second
driven shafts 3, 4 of the first gear stage exclusively by
means of the speed of the control shaft 5, a change in
the speed of the control shaft resulting in a change in
the speed difference concerned in accordance with the
transmission ratio of the second gear stage.
If, however, the control shaft 5 of the second
stage is now held fast in the exemplary embodiment in
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_ - 13 -
accordance with Fig. 5 and the change in the speed
difference i8 performed by means of the further input
shaft 6, different transmission ratios are obtained
between the input shaft 6 and the output shaft 9 of the
second stage, which latter shaft is rigidly connected to
the input shaft of the first stage. According to Fig. 5,
the third peripheral wheel 21, which i~ connected to the
input shaft 6, is of identical design to the first
peripheral wheel 16, which is connected to the output
shaft 9 of the second gear stage. This means that it is
possible to perform a change in the speed of the output
shaft 9 and hence of the input shaft of the first stage
in a ratio of 1:1 to the change in the speed of the
further input shaft 6 of the second stage m~k; ng it
possible to adjust the speed difference between the two
driven shafts 3, 4 of the first stage in a simple manner
at the variable-speed drive itself.
