Power transmission device

A light, miniaturized power transmission device of the type wherein the power from a drive shaft is transmitted to a driven shaft via a planetary gear mechanism. The planetary gear mechanism has a ring gear, a sun gear disposed concentrically on the radially inner side of the ring gear, and planetary gears disposed between and engaged with the sun gear and the ring gear. At least the meshing portions of the planetary gears, ring gear and sun gear are resiliently held from opposite side surfaces thereof by a pair of side plates attached to said planetary gear mechanism. The side plates permit free orbital movements of the planetary gears and suppresses the relative axial movements of the ring gear, planetary gears and sun gear. A centrifugally operated friction clutch is disposed between the drive shaft and the planetary gear mechanism so as to control the transmission of power from the drive shaft to the planetary gear mechanism. The clutch comprises an annular outer contactor integrally formed with the ring gear, and inner contactors which are connected to the drive shaft for rotation therewith and adapted to be placed under a centrifugal force into frictional contact with the annular outer contactor to thereby transmit the rotation of the drive shaft to the ring gear when the number of revolutions of the drive shaft exceeds a predetermined level.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a power transmission device of the type 
wherein the power from a drive shaft is transmitted to a driven shaft via 
a planetary gear mechanism. 
2. Description of the Prior Art 
A planetary gear mechanism is generally provided with a ring gear, 
planetary gears and a sun gear. In order to allow the planetary gears to 
make a smooth orbital movement, it is necessary that the relative axial 
movement thereof between the ring gear and sun gear be suppressed to a 
suitable extent and that the orbit of the planetary gears be kept 
accurately concentrical with the pitch circles of the ring gear and sun 
gear. In a conventional planetary gear mechanism, the ring gear, planetary 
gears and sun gear have the respective gear supporting mechanisms. This 
causes the structure of the planetary gear mechanism to be complicated. 
Moreover, the space occupied by the gear supporting mechanisms is 
increased. Accordingly, the miniaturization and reduction of weight of the 
planetary gears are restricted to a great extent. In addition, the 
centering of the gears requires a high-precision processing technique. 
When the gears make even a slight eccentric rotation, they are not engaged 
with each other accurately. As a result, noises increase and the gears are 
worn early. 
In order to transmit power from the drive shaft to the planetary gears and 
interrupt such transmission of power, by a centrifugally operated friction 
clutch, an inner contactor of the centrifugally operated friction clutch 
is rotated first by the drive shaft. 
The inner contactor generally has on its outer circumferential surface a 
lining to increase the frictional force between the contact surfaces of 
the inner contactor and an outer contactor. When the number of revolutions 
of the drive shaft exceeds a predetermined level, the inner contactor is 
radially outwardly moved by a centrifugal force to come into frictional 
contact with the outer contactor and thereby transmit the rotation of the 
drive shaft to the outer contactor. 
The rotation of the outer contactor of the centrifugally operated friction 
clutch is immediately transmitted to the ring gear in the planetary gear 
mechanism. When the ring gear is rotated, the planetary gears engaged 
therewith are orbited around the sun gear as the planetary gears revolve 
around their own axes. During such a movement of the planetary gears, they 
transmit only their orbital movements to a driven shaft. 
Since the outer contactor of the centrifugally operated friction clutch in 
a conventional power transmission device and the ring gear in the 
planetary gear mechanism in the same device are separately constructed, it 
is necessary that the power transmission device be provided with not only 
a torque transmission means between the outer contactor and the ring gear 
but also a support means for separately supporting the outer contactor and 
ring gear. 
The centering of the outer contactor and ring gear requires a 
high-precision processing technique. When the ring gear in particular is 
even slightly eccentric, the gears are not engaged with each other 
accurately. This causes an increase in noises and an early wear on the 
gears. 
Since the outer contactor and ring gear are rotated with the respective 
bearing portions, an increased inertia force is generated and a great 
shock occurs due to a sudden operation of the clutch. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a power transmission 
device of a simple structure and a small bulk comprising a light, 
miniaturized planetary gear mechanism which can be operated as it is 
subjected to an automatic centering without using any specially high 
precision processing technique. 
To achieve the above object, according to the invention, there is provided 
an improved power transmission device for transmitting power from a drive 
shaft to a driven shaft by way of a planetary gear mechanism which 
includes a ring gear, a sun gear disposed concentrically on the radially 
inner side of the ring gear, and planetary gears disposed between and 
engaged with the sun gear and the ring gear. A pair of side plates are 
attached to the planetary gear mechanism for holding the meshing portions 
of the planetary gears, the ring gear and the sun gear from the opposite 
sides of these gears for free sliding movement relative thereto, the side 
plates acting to suppress relative axial movements of the ring gear, the 
planetary gears and the sun gear while permitting free orbital movements 
of the planetary gears. 
Another object of the present invention is to provide a light, 
miniaturized, simply constructed power transmission device having a 
planetary gear mechanism and a centrifugally operated friction clutch in 
which an outer contactor in the clutch, and a ring gear in the planetary 
gear mechanism are integrally formed to omit bearings therefor so that the 
outer contactor and the ring gear can be automatically centered to thereby 
minimize gear noises, improve durability of the gears, minimize shocks due 
to a sudden operation of the clutch, and increase the underdamping effect. 
The above and other objects as well as advantageous features of the 
invention will become apparent from the following description of the 
preferred embodiments when taken in conjunction with the accompanying 
drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An embodiment of the present invention applied to a drive means in a small 
motorcycle will be described with reference to the accompanying drawings. 
Referring to FIG. 1, a drive shaft 3 is provided via bearings 2 and a seal 
member 2' in a casing 1 which contains a lubricating oil sealed therein. 
A crank arm 5 having a crank pin supporting bore 4, and a counter weight 6 
are provided at the inner end portion of the drive shaft 3, i.e. at that 
end portion of the drive shaft 3 which is on the side of an engine room. 
The drive shaft 3 has a male screw 7 formed on the outer end portion 
thereof and a tapered surface 8 adjacent to the male screw 7. 
A boss member 10 formed integrally with the central portion of a drive 
power transmission plate 9 is fitted around the tapered surface 8 and 
tightly secured thereto with a nut 11 engaged with the male screw 7. 
A ratchet pawl 16 is pivotally supported on a pin 17 on the outer side of 
the drive power transmission plate 9, i.e. on the side opposite to the 
engine room. This ratchet pawl 16 is engageable with ratchet teeth 15 when 
the engine is started, the ratchet teeth 15 being provided on the outer 
circumferential surface of a flange 14 formed at one end portion of a 
hollow engine starting shaft 13 which is rotatably fitted at the other end 
portion thereof around a support shaft 12 projected from the inner surface 
of the casing 1 toward the drive shaft 3. 
Referring to FIGS. 1 and 2, an outer annular contactor 18 supported on 
another member, and a pair of inner arcuate contactors 19, 20 which 
constitute a centrifugally operated friction clutch A according to the 
present invention and which are pivotally supported on pins 21, 22 at the 
respective base end portions which are in opposite positions with respect 
to the diameter of the outer annular contactor 18. Each of the inner 
arcuate contactors 19, 20 is provided with a lining on the outer 
circumferential surface thereof for increasing the frictional force 
between the outer circumferential surface of the inner arcuate contactors 
19, 20 and the inner circumferential surface of the outer annular 
contactor 18. Tension coil springs 23, 24 are provided between the front 
end portion of the inner arcuate contactor 19 and the base end portion of 
the inner arcuate contactor 20, and between the front end portion of the 
inner arcuate contactor 20 and the base end portion of the inner arcuate 
contactor 19. Owing to these tension coil springs 23, 24, the inner 
arcuate contactors 19, 20, which are normally not pressed against the 
outer annular contactor 18, come into frictional contact with the outer 
annular contactor 18 due to a centrifugal force when the number of 
revolutions of the drive shaft 3 exceeds a predetermined level. Thus, the 
rotational movement of the drive shaft 3 is transmitted to the outer 
annular contactor 18. 
At least a part of the outer annular contactor 18 and inner arcuate 
contactors 19, 20, which constitute the centrifugally operated friction 
clutch A is immersed in the lubricating oil in the casing 1. 
A second outer annular contactor 25, which constitutes a second 
centrifugally operated friction clutch, is secured to that portion of the 
inner surface of the drive power transmission plate 9 which is radially on 
the inner side than the inner arcuate contactors 19, 20. This second 
centrifugally operated friction clutch will be described later. 
Referring to FIGS. 1, 3 and 4, a ring gear 26, which constitutes a part of 
a planetary gear mechanism B in the present invention, is formed 
integrally with that end portion of the outer annular contactor 18 which 
is on the side of the engine room. This ring gear 26 integrally formed 
with the outer annular contactor 18 is engaged with three planetary gears 
27, which are engaged with a sun gear 28. 
Each of the planetary gears 27 carries a pair of side plates 30, 31 on both 
side surfaces thereof. 
A planetary gear supporting pin 29, whereby each of the planetary gears 27 
is supported rotatably and in a spaced relationship on a planetary gear 
supporting plate 32, also supports the side plate 30 such that the side 
plate 30 can be rotated relative to the pin 29. 
The side plates 30, 31 are extended beyond the outer periphery of the 
planetary gear 27 and up to both side surfaces of the ring gear 26 and sun 
gear 28, and relatively slidably hold the ring gear 26 and sun gear 28 
from both side surfaces thereof such that the side plates 30, 31 cooperate 
with each other so as to suppress the relative axial movements of the ring 
gear 26 and sun gear 28 with respect to the planetary gear 27. Each of the 
side plates 30 is formed circularly and provided concentrically with the 
planetary gear 27. The peripheral portion of the side plate 30 is bent 
away from the side surface of the gear 27 so that the peripheral portion 
of the side plate 30 has a smooth cross-sectional shape. Thus, a smooth 
relative sliding contact between the peripheral portion of the side plate 
30 and the gear 26 is promoted. 
On the other hand, the side plate 31 consists of a one-piece plate extended 
over the three planetary gears 27. The ring gear 26 has an axial width 
smaller than that of the planetary gears 27. The peripheral portion of the 
side plate 31 is bent so as to resiliently contact the side surface of the 
ring gear 26. As a result, the ring gear 26 is held by the side plates 30, 
31 at an increased resiliency. 
A planetary gear supporting plate 32 is fixedly mounted on the outer 
circumferential surface of one end portion of a hollow driven shaft 33 
fitted around the drive shaft 3 via a bearing 34, and a sprocket 43 is 
mounted on the circumferential surface of the other end portion of the 
driven shaft 33 via a spline 42. The sprocket 43 is operatively connected 
in the casing 1 to a sprocket on the side of a drive wheel via a drive 
chain 44. In this case, at least a part of the drive chain 44 may be 
immersed in the lubricating oil in the casing 1 with or without immersing 
a part of the centrifugally operated friction clutch A in the same 
lubricating oil as mentioned above. 
Referring to FIGS. 1 and 2, three inner arcuate contactors 35, 36, 37 are 
pivotally supported by pins 38, 39, 40 on that side surface of the 
planetary gear supporting plate 32 which is not opposed to the engine 
room. Linings are provided on the outer circumferential surfaces of the 
inner arcuate contactors 35, 36, 37 for the purpose of increasing a 
frictional force generated between the outer circumferential surfaces of 
the inner arcuate contactors 35, 36, 37 and the inner circumferential 
surface of the outer annular contactor 25. Each of these inner arcuate 
contactors 35, 36, 37 has a circumferentially extended groove, in which a 
coil spring 41 common to the contactors 35, 36, 37 is provided. Owing to 
the coil spring 41, the inner arcuate contactors 35, 36, 37, which are 
normally not pressed against the outer annular contactor 25, come into 
frictional contact therewith by a centrifugal force when the number of 
orbital motion of the planetary gear 27 exceeds a predertermined level, to 
thereby stop the relative rotations of the planetary gear 27 and drive 
shaft 3. At this time, the planetary gear 27 is not rotated around its own 
axis; the planetary gear 27 as well as drive shaft 3, inner arcuate 
contactor 19, outer annular contactor 18, ring gear 26, planetary gear 
supporting plate 32 and driven shaft 33 are rotated together with the sun 
gear 28. 
The sun gear 28 is mounted via a spline 46 on the outer circumferential 
surface of one end portion of a sleeve 45 which is mounted on the driven 
shaft 33 such that the sleeve 45 can be rotated relative to the driven 
shaft 33, and a ratchet pawl supporting plate 47 is fixedly mounted on the 
outer circumferential surface of the other end portion of the sleeve 45. 
Referring to FIGS. 1 and 5, the ratchet pawl supporting plate 47 is 
provided with a pair of ratchet pawls 51 which are pivotally supported 
thereon by pins 52. The ratchet pawls 51 is adapted to be engaged with 
ratchet teeth 50' formed on the inner circumferential portion of an 
annular ratchet teeth supporting member 50 which is attached with bolts 49 
to a bracket 48 projected from the inner surface of the casing 1. The 
ratchet pawls 51 is constantly biased so as to be engaged with the ratchet 
teeth 50' by a spring 54 supported on a shaft 53 of the ratchet pawl 
supporting plate 47. 
When the ratchet pawls 51 receive a rotational force exceeding a 
predetermined level in the same direction in which the drive shaft 3 is 
rotated, the ratchet pawls 51 are disengaged from the ratchet teeth 50' so 
as to be swung by a centrifugal force to positions illustrated by chain 
lines in FIG. 5, where the ratchet pawls 51 are not in contact with the 
ratchet teeth 50'. In other words, when the inner arcuate contactors 35, 
36, 37 come into frictional contact with the outer annular contactor 25 to 
allow the ring gear 26, planetary gear 27, sun gear 28 and driven shaft 33 
to be rotated together with the drive shaft 3, the ratchet pawls 51 are 
swung away from the ratchet teeth 50' to positions where the ratchet pawls 
51 are not in contact with the ratchet teeth 50'. This allows the ratchet 
pawls and teeth 51, 50' to generate no meshing sounds therebetween when 
the drive shaft 3 is rotated at a high speed without reducing the speed. 
Even when the sun gear 28 comes near being rotated in a direction opposite 
to the direction in which the drive shaft 3 is rotated, the ratchet pawls 
51 safely come into engagement with the ratchet teeth 50' so that the 
rotation in the aforesaid direction of the sun gear 28 can be prevented. 
Referring to FIG. 1, an energy storing coiled spring 55 is fastened at its 
one end to the outer circumferential surface of the outer end portion of 
the hollow, engine starting shaft 13, and at the other end thereof to the 
inner surface of the casing 1. An energy storing transmission chain 57 is 
provided between a sprocket 56, which is integrally formed on the outer 
circumferential surface of the hollow, engine starting shaft 13, and a 
sprocket (not shown) cooperating with an engine starting pedal (not 
shown). The hollow, engine starting shaft 13 is supported reinforcingly in 
a pressed manner by a reinforcing presser member 58. 
In the above-described construction, the engine starting pedal is stepped 
to rotate the hollow, engine starting shaft 13 via the energy transmission 
chain 57 so that energy is stored in the energy storing coiled spring 55. 
When the energy stored in the spring 55 is released at a time, a 
rotational force is thereby generated, which is transmitted to the engine 
via the hollow, engine starting shaft 13, ratchet pawl 16, drive power 
transmission plate 9 and drive shaft 3, to start the engine. 
When the engine is started, the rotational force generated thereby is 
transmitted to the drive shaft 3 and the drive power transmission plate 9 
so that the ratchet pawl 16 is disengaged from the ratchet teeth 15 by a 
centrifugal force. When the number of revolutions of the engine exceeds a 
predetermined level, the inner arcuate contactors 19, 20 come into 
frictional contact with the outer annular contactor 18. As a result, the 
rotation of the drive shaft 3 is transmitted to the drive wheel via the 
outer annular contactor 18, ring gear 26, planetary gear 27, planetary 
gear supporting plate 32, driven shaft 33, sprocket 43 and drive chain 44. 
While the rotation of the drive shaft 3 is thus transmitted to the drive 
wheel, the ratchet pawls 51 are engaged with the ratchet teeth 50' so that 
the sun gear 28 is not rotated. 
Since a lubricating oil is sealed in the casing 1 such that at least a part 
of the centrifugally operated friction clutch A is immersed therein in a 
normal condition, the lubricating oil is scooped up by the clutch A as it 
is rotated, so as to be supplied to the planetary gear mechanism B 
disposed adjacent to the clutch A. Since no partition wall is provided 
between the clutch A and planetary gear mechanism B, nothing obstructs the 
flow of the lubricating oil. Namely, the lubricating oil scooped up by the 
clutch A can be effectively supplied to the planetary gear mechanism B. 
When at least a part of the drive chain 44 is immersed in the lubricating 
oil in the casing 1 with or without immersing the centrifugally operated 
friction clutch A in the same lubricating oil, the oil can be scooped up 
by the chain 44 in accordance with the rotation of the drive chain 44 so 
as to be supplied to the planetary gear mechanism B disposed adjacent to 
the drive chain 44. Since the drive chain 44 is disposed on the opposite 
side of the centrifugally operated friction clutch A with respect to the 
planetary gear mechanism B, and since the ratchet pawl supporting plate 47 
fixed to the sun gear is not rotated, nothing obstructs the lubricating 
effect of the drive chain 44 on the planetary gear mechanism. Namely, the 
planetary gear mechanism can be smoothly lubricated. 
When the number of revolutions of the drive shaft 3 is further increased to 
reach a high speed region, the inner arcuate contactors 35, 36, 37 come 
into frictional contact with the outer annular contactor 25 so that the 
ring gear 26, planetary gear 27 and sun gear 28 are rotated with the drive 
shaft 3 in the same direction. As a result, the ratchet pawls 51 are 
disengaged from the ratchet teeth 50'. Consequently, the driven shaft 33 
and sprocket 43 are rotated at the same speed as the drive shaft 3, and 
the rotational force is transmitted to the drive wheel via the drive chain 
44. 
At this time, the ring gear 26, planetary gear 27 and sun gear 28 are 
rotated together so that the planetary gear mechanism B requires no 
lubricating oil in particular. 
FIGS. 6 and 7 illustrate another example of planetary gear mechanism B. 
In this planetary gear mechanism, a ring gear 26' integrally formed with an 
outer annular contactor which constitutes a centrifugally operated 
friction clutch in the present invention has an annular bent portion. A 
pair of side plates 30', 31' supported on planetary gears 27' pivotally 
connected by pins 29' to a planetary gear supporting plate 32' which is 
mounted on a driven shaft 33' are circularly formed and extended up to the 
bent portion of the ring gear 26' and the side surface of the sun gear 28' 
spline-connected to a sleeve 45'. The circular side plates 30', 31' can be 
simply formed. The ring gear 26' having an annular bent portion is held by 
a pair of side plates 30', 31'. Therefore, the resilient holding 
capability of the side plates 30', 31' can be effectively utilized. 
As described in the foregoing, in accordance with the present invention, a 
pair of side plates attached to the planetary gear mechanism act to 
clampingly hold at least the intermeshing portions of the ring gear, the 
planetary gears and the sun gear from the opposite sides of these gears 
for free sliding movement relative thereto, suppressing relative axial 
movements of the ring gear, the planetary gears and the sun gear while 
permitting free orbital movements of the planetary gears. This arrangement 
not only contributes much to the simplification of construction, reduction 
in installation space, miniaturization in size and weight of the planetary 
gear mechanism but also enables the automatic centering of the respective 
gears. As a result, there is no need for any special precision processing 
with high tolerances and smooth meshing engagements between various gears 
are ensured to reduce generation of noises, excessive wear and damages due 
to improper gear engagements for improved durability. 
Further, the outer contactor of the centrifugally operated friction clutch 
is formed integrally with the ring gear of the planetary gear mechanism, 
which adds to the further simplification of construction, processing and 
assembling operations and also to the reduction in the overall weight of 
the outer contactor and the ring gear as compared with the conventional 
separate formation of these components to thereby minimize damages and 
shocks due to sudden operation of the centrifugally operated friction 
clutch. 
Without further analysis, the foregoing will so fully reveal the gist of 
the present invention that others can, by applying current knowledge, 
readily adapt it for various applications without omitting features that, 
from the standpoint of the prior art, fairly constitute essential 
characteristics of the generic or specific aspects of this invention, and 
therefore, such adaptations should and are intended to be comprehended 
within the meaning and range of equivalents of the following claims.