Planetary gear reduction system

A planetary gear reduction system, compact in size, high in the ratio of speed reduction and improved in durability as well as easiness for assemblage and adjustment, which essentially comprises planet gear mechanisms disposed in multiple stages and in series within a casing, in which the planet gears individually include a built-in floating intermediate ring member which distributes the load imposed uniformly among the planet gears.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
The present invention relates to a speed reduction system having a high 
reduction ratio. More particularly, the invention concerns a speed 
reduction system which utilizes a planet gear mechanism and can attain the 
speed reduction at a higher ratio for its size which is relatively small, 
and which has a high durability. 
(2) Brief Description of the Prior Art 
Planet gear mechanism are generally characterized in that they can be 
relatively small in size and yet can provide a speed reduction at 
relatively high ratios. However, with such mechanisms, errors in 
processing, if any, would become synergistically manifested during the 
operation, so that an extremely high precision is required to answer in 
the production or assembling of the mechanism: If there are errors with 
respect to gears or in the indexing of planet shafts, the load imposed 
cannot be uniformly distributed on respective planet gears and it often 
happens that the inter-gear meshing or engagement is excessively strong 
with some gears and very weak with the other, permitting to readily occur 
abnormal vibration, abrasion and wearing, and also a great power loss. 
Similarly, with the conventional speed reduction systems it has been 
highly likely that gears or shafts undergo irregular rotation, if 
slightly, whereby the durability of the system is drastically lowered. 
In addition to the foregoing difficulties, conventional speed reduction 
systems present another problem such that since processing should be 
performed at a high precision in order to prevent the above-mentioned 
irregular engagement among the members of planet gear mechanisms, the 
manufacturing cost is inevitably increased. Further, the life of such 
conventional system is extremely short, and various difficulties are 
encountered when it is used under a high load condition. 
A system in which a plurality of planet gear mechanisms are arranged in 
series so as to obtain a high reduction ratio has already been proposed. 
However, the structure of such conventional system is complicated and it 
is very difficult to assemble or disassemble this conventional system. 
Moreover, the system cannot be manufactured at a relatively low cost. (3) 
Objects of the Invention: 
The present invention has been made as a result of investigations made with 
a view to developing a speed reduction system in which the foregoing 
defects involved in the conventional techniques can be eliminated. 
It is therefore a primary object of the present invention to provide a 
speed reduction system in which the engagement between a sun gear and a 
planet gear is very smooth and occurrence of irregular engagements can be 
completely prevented, and which has a high durability and can attain a 
very high reduction ratio at a high transmission efficiency. 
Another object of the present invention is to provide a speed reduction 
system which as a simple structure with a high durability and yet can be 
manufactured at a low cost. 
Still another object of the present invention is to provide a multi-stage 
planetary gear speed reduction system which can be assembled or 
disassembled very easily and simply. 
BRIEF SUMMARY OF THE INVENTION 
In the present invention, it is proposed to have the spring action of an 
oil film enhanced in order to eliminate non-uniform distribution of the 
load on planet gears owing to processing errors, and a first 
characteristic feature of the present invention resides in that as means 
for enhancing the spring action of oil film, a structure herein named 
"floating intermediate ring" is installed in each planet gear. 
More specifically, a floating intermediate ring is fitted to a planet shaft 
through a roller bearing, and planet gears are held in a spaced 
arrangement about the outer periphery of this floating ring member. 
A second characteristic feature of the present invention consists in that a 
carrier holding the planet gear is not supported by a bearing but is 
completely floated and that the sun gear fixed to the carrier is formed in 
a hollow structure to thereby reduce the weight thereof and facilitate the 
displacement required for coping with an error in the processing. 
A third characteristic feature of the present invention comprises that in 
order to facilitate manufacture and assemblage of respective members, the 
sun gear is connected to the carrier for driving the former through spline 
fitting and rotation of internal spur gears is inhibited by one key; in 
addition, the internal spur gears are supported by a very simple structure 
.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The planetary gear reduction system of the present invention has a 
multi-stage structure as shown in FIG. 1, in which a first cover 2 is 
fixed to a casing 1 by a bolt 3, and a second cover 4 is fixed to the 
first cover 2 through a bolt 5. 
The structure of the planetary gear reduction system of the present 
invention will now be described according to the order or sequence of the 
transmission of power. 
An input shaft 6 is rotatably supported in a hole formed in a central 
portion of the second cover 4 by means of bearings 7 and 7', and a sun 
gear 8 is mounted at the top or inward end of the shaft 6. A plurality of 
planet gears 9 are engaged with the periphery of the sun gear 8, and each 
planet gear 9 is supported on a planet shaft 12 through a floating 
intermediate ring 10 and a needle bearing 11. The planet shaft 12 is fixed 
to a carrier 13, and a second sun gear 14 is fixed to the center of the 
carrier 13. An internal spur gear 15 is disposed in the interior of the 
first cover 2, and this gear 15 is engaged with the planet gears 9. 
Engageable with the second sun gear 14 are planet gears 16, which revolve 
within an internal spur gear 17. A floating intermediate ring member 18, a 
needle bearing 19, a planet shaft 20 and a carrier 21 are assembled in the 
same manner as in the above-mentioned planet gear mechanism of the first 
stage. 
A third sun gear 22 is fixed to the central portion of the carrier 21 to 
drive planet gears 24 engageable with an internal spur gear 23. Reference 
numerals 25, 26, 27 and 28 represent a floating ring member, a needle 
bearing, a planet shaft and a carrier, respectively. The carrier 28 is 
fixed to an output shaft 29 through spline 29', and the shaft 29 is 
supported by bearings 30 and 30' fixed to the casing. 
FIG. 2 if a front view illustrating the planet gear mechanism of the second 
stage, and FIG. 3 is a sectional side view showing the gear mechanism of 
FIG. 2 with the internal spur gears removed away. 
The end portion 14a of the second sun gear 14 is stepped, and a spline 21a 
formed on the carrier 21 is press fitted to the stepped end portion 14a of 
the second sun gear 14. If the carrier 21 and the sun gear 14 are formed 
separately and independently from each other as in the present embodiment, 
manufacture of these members can be remarkably facilitated, and when these 
members are integrated with each other by utilizing spline fitting, the 
integration can be complete and shaking which otherwise is likely during 
the operation can be substantially checked. 
Fixation of the planet shaft 20 to the carrier 21 can be accomplished 
according to various methods. For example, an annular groove may be formed 
in the hole of the carrier, and after the planet shaft 20 is inserted into 
this hole, a notch may be formed in the terminal portion of the planet 
shaft 20 by a chisel or the like and such terminal portion of the shaft 
may be bulged in the annular groove to effect fixation. Further, there may 
be adopted a method in which contrary to the above mentioned method an 
annular groove is formed in the circumferential direction of the planet 
shaft and a part of the wall of the hole of the carrier is bulged into the 
annular groove to effect fixation. 
As shown in FIG. 3, there are side plates 31 and 31' formed about the sides 
of the needle bearing 19, floating ring member 18 and planet gear 16, and 
another side planet 32 is disposed on the outside of the side plate 31', 
whereby each of the above-mentioned members are prevented from falling 
down out of the planet shaft 20. In this case, it is preferred that a part 
of the planet shaft 20 be notched to prevent the side plates 31' and 32 
from rolling or rotating. 
Three planet gears 9, 16 and 24 supported on the corresponding shafts 
mounted on the corresponding carriers revolve, in a set, around the sun 
gears 8, 14 and 22 engaged therewith. Each planet gear is floatingly 
supported on the corresponding carrier, and this feature of the structure 
will be described in detail hereinafter. 
As shown in FIG. 1, a cylindrical portion is cut out from the interior of 
the casing 1, and internal spur gears 17 and 23 are fitted in the 
cylindrical hollow portion and fixed to the casing 1 by utilizing one key 
member. As shown in FIG. 2, a key groove 17a is formed on the peripheral 
face of the internal spur gear 17, and a similar groove is also formed in 
the confronting portion of the casing 1 though not specifically 
illustrated in the drawings. The key is applied through those key grooves 
to fix the internal spur gears and prevent them from rotating. 
When there are a plurality of internal spur gears disposed, it is preferred 
that a spacer 33 be provided between every two adjacent internal spur 
gears to determine their relative positions with respect to the lateral 
direction. In some cases it may be preferred to have no key groove formed 
on the side of the casing 1, and then the internal spur gears may be fixed 
to the casing by utilizing stop screws or the like. 
In the present invention, it forms an important feature that the carriers 
holding the planet gears thereon are floatingly supported, and in order to 
attain this feature, it is necessary that the weights of the sun gears and 
carriers should be reduced to facilitate the floating movement thereof. 
Therefore, each of the sun gears 14 and 22 is formed in the central 
portion thereof with a hollow hole 34 to reduce the thickness. In addition 
to the effect of reducing the weight, this hollow hole 34 exerts an effect 
of containing the holding therein a lubricating oil. 
In the present invention, the carriers 13 and 21 are rotatable in the state 
not supported by any bearing, and it forms another important feature of 
the present invention that the planet gears are floatingly supported on 
planet shafts fixed to such carriers. 
It also is important with the present invention that the planet gears are 
supported on planet shafts through floating intermediate rings. The 
floating ring member generates spring action of an oil film between itself 
and the planet gear, and makes uniform imposition of load on the plurality 
of planet gears. This floating structure and its function will now be 
described in greater detail. 
Referring to FIGS. 2 and 3, the floating ring 18 is supported on the planet 
shaft 20 through a roller bearing, and outer to the ring member 18 there 
is the planet gear 16 disposed with a suitable clearance C for generating 
an oil film provided between the member 18 and the gear 16. The 
intermediate ring 18 and the gear 16 are so arranged as to turn or rotate 
together. 
FIGS. 4 and 5 are diagrams taken for a theoretical explanation of the 
principle of the above-mentioned spring action and the relation among the 
floating intermediate ring 20', planet gear 16' and sun gear 14'. Herein, 
the theory of the plane bearing of the case where both shaft and bearing 
turn or rotate together will be applied. 
Symbols in FIGS. 4 and 5 have the following meanings: 
Pm: Bearing load per unit area 
Q: Point of minimum thickness of oil film 
Q': Load point 
.phi., .phi.': Eccentric angle 
O: Center of floating intermediate ring 
O': Center of the planet gear 
Supposing that the bearing load Pm increases, then the eccentric angle 
.phi. becomes reduced to .phi.' and Q becomes closer to Q', in accordance 
with the beraring theory. In this case, the center O' shifts from the 
point 0' to the point O" while drawing a locus resembling a semicircle 
having the radius clearance C as the diameter as shown in FIG. 5. Namely, 
as the load increases, the center O' of the planet gear 16' moves toward 
the direction of load by a distance P'P". 
This movement of the planet gear 16' means the spring action, and the 
compliance of this spring action is expressed as follows: 
##EQU1## 
Supposing that the radius of the floating intermediate ring is r, that the 
eccentricity is n and that the viscosity coefficient of the lubricating 
oil is .mu., 
##EQU2## 
Therefore, the compliance is compressed as follows: 
##EQU3## 
wherein f(n) is a function of n. 
Thus, in order to obtain a large spring action, it is necessary to obtain a 
greater value of the compliance , and it is preferred to make that from 
the above formula (3) a larger radius clearance can be obtained within a 
range in which an oil film is generated. Further, as before stated the 
relation between the floating intermediate ring and the planet gear 
corresponds to the plane bearing in the case where both shaft and bearing 
turn or rotate together, therefore the Sommerfeld value is two times of 
the value of an ordinary bearing and is expressed as follows: 
##EQU4## 
(Oscar Pinks & Beno Sternlicht: "Theory of Hydrodynamic Lubrication"; 
McGraw Hill, 1961). 
More specifically, the Summerfeld value of an ordinary plane bearing void 
of the floating ring member is expressed: 
##EQU5## 
and if the eccentricity is the same, the radius clearance C of the bearing 
including the ring member should be .sqroot.2 times of the radius 
clearance of the ordinary bearing. This means an increase in the 
compliance in the above formula (3). The above is the theoretical reason 
why a larger spring action can be obtained by the oil film when the 
floating ring member is used. 
As shown in FIGS. 2 and 3, the planet gear 16 is supported through the 
floating ring member 18, a radius clearance C is formed between the ring 
18 and the planet gear 16, and an oil film is formed in such clearance. 
Through such arrangement according to the present invention, the spring 
action is given the planet gear 16 while it is indirectly supported on the 
planet gear shaft 20, whereby the load imposed on the respective planet 
gears can be effectively made uniformly or evenly distributed, and this 
means a very important action in the planet gear mechanism. 
Further, as before stated the planet gear is supported on the planet gear 
shaft elastically by the oil film through the floating intermediate ring, 
therefore even if the sun gears except the one of the first stage and 
carriers integrated therewith are floatingly supported, various errors on 
the gears can be compensated for and the engagement of engageable members 
can be maintained very smoothly. 
Furthermore, according to the present invention the planet gear mechanism 
is constructed in principle as shown in FIGS. 2 and 3, and a multiple 
stage planetary gear reduction system can therefore be assembled very 
easily by inserting and fitting a plurality of plane gear mechanisms 
having such structure in succession into the casing. Therefore, the 
manufacturing and assembling operations can be remarkably facilitated, and 
also such as an inspection, repairing and adjustment can be performed very 
easily. 
The functions of the multi-stage planetary gear reduction system shown in 
FIG. 1 will now be described. 
From the input shaft 6, an input of a high rotation number is supplied to 
drive the second sun gear 14 through the first sun gear 8, planet gears 9 
and carriers 13. 
The power to the second sun gear 14 is transmitted to planet gears 16, 
carriers 21 and the third sun gear 22 to drive the output shaft 29 through 
planet gears 24 and carriers 28. As is seen from the foregoing, three 
stages of the planet gear mechanisms are disposed between the input shaft 
6 and the output shaft 29. Accordingly, although the size of the entire 
system is remarkably diminished, a high speed reduction ratio can be 
attained according to the present invention. 
Particularly, according to the present invention, as illustrated in FIGS. 2 
and 3 the planet gear 16 is not directly supported on the shaft 20 but is 
indirectly supported through the bearing 19 and floating intermediate ring 
member 18, and an oil film is formed in the clearance C between the ring 
18 and gear 16. As theoretically analyzed hereinbefore, this oil film 
exerts a large spring action. Accordingly, the planet gear 16 is allowed 
to move independent of the movement of the integrated assembly of the sun 
gear 14, carriers 21 and shafts 20. Therefore, the planet gear 16 can move 
smoothly and lightly while correcting or compensating for an engagement 
error, if any. As a result, the load is imposed in a uniformly distributed 
manner on respective planet gears, and there can be attained various 
advantages. For example, the durability of the reduction system can be 
remarkably improved, the loss of power can be drastically suppressed, and 
the power transmission efficiency can be high. 
Moreover, the sun gear 14, carrier 21 and planet shaft 20 assembled in an 
integrated arrangement are not supported through a bearing, and the sun 
gear is reduced in its weight by forming a hollow portion in the interior 
thereof. Accordingly, the integrated assembly of the above members can 
move very lightly and smoothly, and an irregular engagement among the 
gears can be effectively eliminated. 
The planetary gear reduction system of the present invention can be 
assembled by inserting and fitting unitary assemblies individually 
consisting of a sun gear, carriers, planet gears and an internal spur 
gear, in succession into the casing as shown in FIGS. 2 and 3. Therefore, 
such operations as assembling, disassembling, adjustment of relative 
positions of respective members and replacement of respective members can 
be performed very easily. 
As will be apparent from the foregoing description, the structure of the 
planetary gear reduction system of the present invention is very simple 
although it has an excellent capacity of correcting engagement errors, and 
the present invention can therefore provide a speed reduction system 
reduced in weight.