Note: Descriptions are shown in the official language in which they were submitted.
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1 BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a planetary
speed changing device in which causes of oscillation of
input shaft are removed to eliminate any abnormal wear
of parts, while suppressing noise and vibration.
Description of the Related Art
Hitherto, various speed changing devices
incorporating internal-meshing type planetary gear
mechanism have been proposed. Among these proposed speed
changing devices, a device called "cyclo speed reducer"
(registered trademark) is well known. This type of
speed changing device has an internally toothed gear
with teeth formed by pins or combinations of pin and
roller, and an externally toothed gear having trochoidal
teeth formed by epitrochoidal parallel curves. The
externally toothed gear has inner pins or inner rollers
which are loosely fitted therein. The externally toothed
gear is rotated by a rotation of an eccentric member
fitted in the externally toothed gear so as to revolve
along the inner periphery of the internally toothed
gear, thereby outputting a torque at a speed which is
reduced from the input rotation speed. This type of
speed changing device is widely used in various fields,
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1 because it can transmit a large torque and because it
provides a large speed reducing ratio.
An example of such cyclo speed reducer will be
explained with reference to Fig. 3. The illustrated
speed changing device is arranged such that a reduced
rotation speed is obtained at an output shaft 2 when a
torque is input through an input shaft 1. This device,
however, can be used such that the output shaft 2 is
fixed so that a rotation output of a reduced speed is
obtained through an internally toothed gear.
A hollow eccentric shaft 3 is fixed to the
input shaft 1 by means of a key (not shown) and a key
groove 4. The eccentric shaft 3 carries two eccentric
members 31 and 32. Externally toothed gears 51 and 52
are fitted on the eccentric members 31 and 32 through
rollers 6. Each o.f the externally toothed gears 51
and 52 has teeth 7 having trochoidal shape and formed
on the outer periphery thereof. An internally toothed
gear 8, which serves also as an output casing, is fixed
in this case. The internally toothed gear 8 has
arcuate teeth provided by outer pins 9 and meshing with
the teeth of the externally toothed gears 51, 52. Each
outer pin 9 may carry an outer roller. The externally
toothed gears have inner pin-receiving bores 10 which
loosely receive inner pins 11 on which are loosely
fitted inner rollers. Each of the inner pins is closely
fitted in a hole formed in an inner pin holding flange 13.
The inner roller 12, however, is not essential and may
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1 be omitted. In the illustrated device, the inner pin
holding flange 13 is formed integrally with the output
shaft 2.
Casings 141 and 142 are united together with
the internally toothed gear 8 clamped therebetween. A
pair of input shaft bearings 151 and 152, which are for
supporting the input shaft 1, are provided on both sides
of the combination of the externally toothed gears 51
and 52. The input shaft bearing 151 is disposed between
the outer periphery of the input shaft 1 and the casing
141, while the input shaft bearing 152 is provided
between the outer peripheral surface of the input shaft
1 and the surface of a recess 131 formed in the inner pin
holding flange 13. A pair of output bearings 161, 162
are disposed between the outer peripheral surface of the
output shaft 2 and the casing 142.
In operation, rotation of the input shaft 1
causes the eccentric members 31 and 32 to rotate. Since
the externally toothed gears 51 a.nd 52 are prevented
from rotating about their own axes due to the presence
of inner pins 11 received in the holes 10, these externally
toothed gears 51 and 52 are caused to orbit at a radius
e. If the difference between the number of the teeth
on each externally toothed gear 51, 52 and the number
of outer pins 9, i.e., the number of teeth on the
internally toothed gear 8 is one, the mesh between the
outer teeth 7 on the externally toothed gears 51, 52 and
the outer pins 9 as the teeth of the internally toothed
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1 gear 8 is offset by one pitch of the teeth. Consequently,
the rotation of the input shaft 1 is transmitted to the
output shaft through the inner pins 11, with the rotation
speed reduced to 1/n (n being the number of teeth of
each externally toothed gear 51, 52) due to the meshing
between the externally toothed gears 51, 52 and the
internally toothed gear 8.
This known planetary speed reducing device
suffers from the following problems.
A discussion will be made as to the manner in
which the input shaft 1 and the output shaft 2 are
loaded, with specific reference to Fig. 4. As shown in
this Figure, the rotational load W1 applied by the input
shaft 1 to the output shaft 2 acts at the end of the
input shaft bearing 152. On the other hand, the load
W2 applied by the externally toothed gears (omitted
from Fig. 4) to the output shaft 2 acts on the inner
pin 11. At the same time, the load W3 applied by the
externally toothed gears to the input shaft 1 acts on
the input shaft 1 as illustrated. Thus, the loads W1
and W2 applied to the output shaft 2 act on points which
are on the same side of the output shaft bearings 161,
162 as the input shaft 1, so that the output shaft 2
receive these loads in a cantilevered manner. Consequ-
ently, a moment is produced to cause the axis of the
output shaft 2 to be inclined at an angle a to the axis
O1 of the shaft under no load.
On the other hand, the load W3 applied to the
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1 input shaft 1 acts to produce a moment which, in combina-
tion with the inclination of the output shaft 2, causes
the input shaft 1 to be inclined at an angle B to the
axis Ol.
Consequently, both the input and output shafts
rotate with their axes deviated from the axis of rotation,
resulting in problems such as extraordinary wear of parts
and generation of noise and vibration.
Referring now to Fig. 5, when a radial load F
is applied from the exterior to the input shaft 1,
the input shaft 1 is inclined at an angle B' with respect
to the original axis Ol, while the output shaft 2 also
is inclined at an angle a' with respect to the original
axis Ol, thus causing abnormal wear and generation of
vibration and noise.
The inclinations of the output shaft 2 and the
input shaft 1 are attributable to the fact that the
input shaft 1 receives the load W3 from the externally
toothed gears 51, 52 and that the load W3 is supported by
the input bearings 151 and 152.
In the known planetary speed changing device
described above, the balance of load is attained when
torque is equally distributed to both externally toothed
gears 51 and 52. However, since these two externally
toothed gears are not disposed on the same plane, a
moment is produced to act on the eccentric members 3 or
the input shaft 1 by the loads acting on the externally
toothed gears 51, 52. It has therefore been necessary
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1 to provide input shaft bearings 151, 152 for supporting the
input shaft 1. The moment acting on the input shaft 1 is the
product of the force acting on the externally toothed gears
51, 52 and the distance between the externally toothed gears
51 and 52. The externally toothed gears 51 and 52 are
supported by the eccentric member 3 and the rollers 6. These
eccentric members 3 and the rollers 6 are required to have
certain minimum lengths from the viewpoint of load capacity.
Thus, there is a practical limit in the reduction of the space
between two externally toothed gears 51 and 52.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is
to provide a planetary speed changing device in which the
causes of inclination of the input shaft are eliminated to
avoid problems such as abnormal wear of parts and generation
of vibration and noise.
To this end, the present invention provides a
planetary speed changing device comprising: an input shaft;
eccentric members provided on said input shaft; two externally
toothed gears fitted on said eccentric members; an internally
toothed gear having internal teeth formed by outer pins and
meshing with the teeth of said externally toothed gears; inner
pin receiving holes formed in said externally toothed gears;
inner pins loosely received in said inner pin receiving holes;
inner pin holder rings in which said inner pins are closely
fitted; coupling means for coupling said inner pin holder
rings to an output shaft, wherein: said inner pin holding
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1 rings are provided on both sides putting said two externally
toothed gears therebetweeen; and thrust bearings are provided
between each said inner pin holder ring and said eccentric
members.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a sectional view of an embodiment of the
present invention;
Fig. 2 is a sectional view taken along the line
II-II of Fig. l;
Fig. 3 is a sectional view of a known planetary
speed reducing device;
Fig. 4 is a schematic illustration showing points
of action of the torque load and consequent inclinations of
the input shaft and the output shaft in the known planetary
speed reducing device; and
Fig. 5 is a schematic illustration of inclinations
of output and input shafts caused by application of external
force.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to Figs. 1 and 2, there is shown a
planetary speed changing device embodying the present
invention in which rotation of an input shaft 21 is output
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1 as a rotation of a reduced speed from an output shaft
22. This, however, is not exclusive and the embodiment
may be used such that the rotation of a given speed
is input to the output shaft 22 and a rotation of an
increased speed is taken out from the input shaft 21.
A hollow eccentric shaft 23 is mounted on the
input shaft 21 and is coupled to the input shaft 21
through a flexible coupling means 24 capable of absorbing
any radial displacement such as a spline coupler or an
Oldham's mechanism. A pair of eccentric members 231,
232 are formed on the eccentric shaft 23. Externally
toothed gears 251, 252 are mounted on the eccentric members
231, 232 through angular bearings 261, 262. The angular
bearings 261, 262 are composed of ball bearings or roller
bearings and have functions to bear both axial and
radial loads. These angular bearings 261, 262 are arranged
such that they bear forces Fl, F2 of opposite directions.
The externally toothed gears 251, 252 have external teeth
27 having a trochoidal teeth shape. An internally toothed
gear 28 is formed as a unit with the casing. The inter-
nally toothed gear 28 has arcuated teeth provided by
outer pins 29 which engage with the teeth of the external-
ly toothed gears 251, 252. An external roller 291 is
loosely mounted on the outer pin 29. The use of outer
pins 291, however, is not essential. The externally
toothed gears 251, 252 are provided with inner pin
receiving bores 30 which loosely receive inner pins 31.
An inner roller 32 loosely fits on each inner pin 31.
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1 The inner pins 31 closely fit in bores formed in inner
pin holder rings 331, 332 so as to be held by these
rings. The use of the inner roller 32, however, is not
essential. The inner pin holder rings 331, 332 are
arranged on both sides of the externally toothed gears
251, 252. Thrust bearings 341, 342 are provided between
the inner pin holder rings 331, 332 and the eccentric
members 231, 232. One 332 of the inner pin holder rings
is connected to the output shaft 22 not directly but
through a flexible coupling mechanism 35 capable of
absorbing offset of axis, e.g., a spline coupler.
In this embodiment, the output shaft of a
driving motor M is used as the input shaft 21. No
bearing is used for supporting the input shaft 21, except
the bearing 36 adjacent the motor M.
The following actions are performed during
the operation of the embodiment having the described
construction.
A moment is produced to act on the eccentric
shaft 23 by the loads exerted by the externally toothed
gears 251, 252. According to the invention, this
moment is borne by the thrust bearings 341, 342 which
are provided on both sides of the eccentric members
231, 232, thus eliminating necessity for radial bearings
which would bear this moment. This arrangement is one
of the remarkable features of the invention. Further-
more, no radial load is transmitted from the eccentric
shaft 23 to the input shaft 21 by virtue of the fact
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1 that the eccentric shaft 23 and the input shaft 21
are coupled by a radially displaceable joint such as a
spline coupler or an Oldham's ring. Consequently, the
input shaft 21 receives only a torsional load produced
by the torque which is being transmitted, and receives
no radial load, with the result that vibration and
noise due to oscilaltion of the input shaft 21 are
eliminated. In addition, bearings for supporting the
input shaft 21 are made smaller or may be omitted.
In addition, since the externally toothed gears
251, 252 are supported by angular bearings 261, 262 which
are arranged in a face-to-face relation, i.e., such
that the lines indicating the forces acting on these
bearings are inclined to oppose each other as indicated
at Fl and F2, the spun between these two externally
toothed gears 251, 252 is substantially shortened to
reduce the moment.
The above-described face-to-face arrangement
of the angular bearings 261, 262 offers also the follow-
ing advantage. When the load acting on one 251 of the
externally toothed gears is increased, the angular
bearing 261 acts to displace the angular bearing 262
outwardly, i.e., toward the output shaft 22, whereby the
load on the externally toothed gear 252 is increased.
Thus, the above-mentioned face-to-face arrangement of
the angular bearings 261, 262 provides an automatic
centering function of the externally toothed gears 251,
252, so as to ensure an equal load distribution to both
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1 externally toothed gears 251, 252, thus eliminating
any abnormal wear, as well as vibration and noise,
attributable to uneven load distribution to these gears.
The embodiment described hereinbefore is only
illustrative and the invention can be applied to
various internal meashing type planetary gear mechanisms,
and all such applications are within the scope of the
present invention.
As will be understood from the foregoing
description, the present invention offers the following
advantages.
The moment acting on the eccentric shaft can be
stably born in lateral directions by the thrust bearings.
Furthermore, partly because the eccentric shaft and
the input shaft are coupled by a radially displaceable
flexible coupling mechanism, and partly because radial
load acting on the input shaft is eliminated, it is
possible to remarkably suppress vibration and noise
attributable to oscillation of the input shaft and to
reduce the size of bearings supporting the input shaft
or to omit these bearings.
In addition, since the externally toothed
gears are supported by angular bearings whcih are arranged
in face-to-face relation, the lines indicating actions
of these bearings are inclined to oppose each other,
so that the spun between the pair of externally toothed
gears is materially shortened to reduce the moment.
This face-to-face arrangement of the angular bearings
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1 serves such when the load on one of the externally
toothed gear increases, the load on the other externally
toothed gear is automatically increased, thus producing
an automatic centering function. Consequently, load is
equally distributed to both externally toothed gears, thus
remarkably suppressing abnormal wear of these gears, as
well as noise and vibration.
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