Multi-geared bicycle transmission assembly comprising internal gear sets

A transmission assembly for a bicycle which is able to achieve variations in rotational force and velocity through internal gearing mechanisms which require no variation in sprocket diameter. The transmission assembly includes a front and rear transmission means, and a chain which connects them. Each transmission means includes one or more sprockets and gear sets with which the chain connects. Each gear set then includes a sun gear, a plurality of planetary pinions which rotate and revolve around the sun gear, a ring gear encasing the planetary pinions, and a carrier to which the planetary pinions are attached. This assembly helps prevent the chain from derailling, quickens the shifting process, and simplifies the structure and construction of transmission assemblies for bicycles.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to transmission assemblies for bicycles, and 
especially to multi-geared transmission assemblies which provide 
selectable velocity ratios. 
2. Description of the Related Art 
Bicycles are lightweight, two-wheeled, steerable machines which have been 
used for transportation, racing, and touring throughout the world over the 
past two centuries. 
Bicycles are propelled by a rider who applies a force to the bicycle 
transmission assembly using a crank. The transmission assembly is then 
used to transmit the force to the rear wheel where it is used to drive the 
bicycle. 
Therefore, efficient transmission assemblies which are capable of improving 
the bicycle speed for a given pedalling rate are essential. For this 
reason, two types of transmission assemblies have been developed: the 
epicyclic, which alters the speed of the driver sprocket relative to the 
rim of the wheel, and the derailleur, which requires movement of the chain 
from sprocket to sprocket. 
Epicyclic gears are made in two-, three-, four-, and five-speed models 
incorporated in the rear hub. They are controlled by levers or twist-grip 
mechanisms, utilizing cables mounted on the handlebars or on the frame 
tubes. Two-speed hub gears are most often made in brake-hub form, 
controlled by a rotating sprocket in the reverse direction. 
The conventional derailleur gears consist of a mechanism to move the chain 
from one sprocket wheel to another of different size. By varying the size 
of the driving sprockets, the rear wheel can be made to pass through more 
or fewer revolutions for each turn of the crank. Cyclists can use up to 
six sprocket wheels on the rear freewheel and three on the crank. The 
mechanism is spring loaded to absorb chain slack and is controlled by a 
cable from the frame or handlebars. 
As shown in FIG. 8, the above-described conventional bicycle includes the 
following parts: a transmission assembly, front and rear wheels 86 and 87, 
pedal 72, seat 81, handle 84, and frame 80 which includes rear wheel tip 
74, seat stay 82, seat tube 71, fork 85, fork tip 75, down tube 88, and an 
optional crossbar 83. 
A bicycle transmission assembly which incorporates the derailleur mechanism 
includes front and rear sprocket assemblies 50 and 51 rotatably coupled to 
frame 80 for receiving chain 73. The transmission assembly also includes 
front and rear derailleur assemblies 53 and 54 for enabling chain 73 to be 
shifted from one sprocket to another. Chain 73 is then included in the 
transmission assembly for transferring force from the front sprocket 
assembly 50 to the rear sprocket assembly 51. 
The front sprocket assembly frequently incorporates a two-stage sprocket to 
provide both high gear 60 and low gear 61 as shown in FIG. 6. Assembly 50 
is mounted between the lower portion of seat tube 71 and the base of pedal 
72, being rotated about fixed shaft 56. 
A front derailleur is also provided for shifting between the sprockets. 
Derailleur 53 is connected to seat tube 71 by connecting band 62. It 
includes chain guide 65 which supports chain 73 at the level of the 
highest sprocket 60. Link means is used to pivot derailleur 53 about hinge 
59', thereby moving chain guide 65 laterally over high and low speed 
sprockets 61 and 60. 
When chain guide 65 is shifted, chain 73 is forced toward the adjacent or 
receiving sprocket until a cog of the adjacent sprocket catches it. Chain 
73 is then completely transferred to the receiving sprocket after one full 
rotation at which time the shift is completed. 
The rear transmission means is similar in style to the front transmission 
means described above since both incorporate multi-stage sprocket 
assemblies. However, multi-stage rear sprocket assembly 51 often 
incorporates up to six stages in its multi-stage sprocket as shown in FIG. 
7. 
The rear transmission means includes multi-stage rear sprocket 52 which is 
mounted between hub 55 and rear tip 74, where it rotates about fixed shaft 
56. It also includes rear derailleur assembly 54 which is mounted below 
and outside rear tip 74. Finally, chain 73 connects guide gear 57 to 
multi-stage rear sprocket 52. 
A cable (not shown) is then used to apply or release pressure on rear 
derailleur 54 causing it to pivot around hinge 59 thereby realigning chain 
73 with a different sprocket. Chain 73 is then shifted and transferred to 
the receiving sprocket after one full rotation has been completed. 
Multi-stage sprockets of varying diameters provide a means of improving the 
bicycle speed for a given pedalling rate. However, using them requires the 
chain to be a distance from the hub greater than the largest sprocket 
perimeter. Consequently, there is a large distance between the chain and 
the smaller sprockets. This results in decreased control and frequent 
chain derailling. 
Multi-stage sprockets of varying diameters are also deficient in terms of 
manufacturing due to their complexity. 
SUMMARY OF THE INVENTION 
The purpose of the present invention is to simplify the structure of the 
conventional multi-sprocket bicycle transmission while increasing control 
during each shift. 
By providing a multi-geared bicycle transmission assembly comprising 
internal gear sets, sprockets of varying diameter are not necessary to 
achieve varying gear ratios. Because the sprockets in this transmission 
assembly may be of equal diameter, the chain is positioned closer to all 
sprockets thereby increasing transmission control. Manufacturing is also 
simplified when using sprockets of equal diameter causing production costs 
to decrease. 
A bicycle transmission assembly in accordance with the present invention 
includes a front transmission means, a rear transmission means and a 
chain. 
The front transmission means within the assembly includes one or more 
planetary gear sets, a sprocket positioned aside the planetary gear sets, 
a front sprocket selector positioned above both the planetary gear sets 
and the sprocket, and a flange formed at a side of the seat tube. 
Each planetary gear set within the front transmission means includes a 
sprocket, a plurality of planetary pinions, a carrier, a sun gear, and a 
ring gear. They provide a means of decreasing the driving force, thereby 
increasing the rotational velocity of the sprocket attached to them. 
Therefore, it is not necessary to change the sprocket size to change the 
number of revolutions made by the rear wheel for each turn of the crank.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
A preferred embodiment of a bicycle transmission assembly in accordance 
with the present invention is described referring to FIGS. 1, 2, 3, 4, and 
5. 
FIG. 5 shows a schematic view of the bicycle transmission assembly which 
includes front transmission means 4, rear transmission means 6, and chain 
73 linking the two transmission means, chain 73 being entrained around a 
sprocket from each of them. 
Front transmission means 4 is rotatably coupled to seat tube 71, with both 
crank shaft 70 and pedal 72 attached to it. Similarly, rear transmission 
means 6 is rotatably coupled to fixed shaft 56 at hub 5 of rear tip 74. 
Internal gear sets 2 and 9 may be incorporated into the front and rear part 
of the transmission assembly, respectively. Each gear set is provided as a 
means for modification of both the rotational force and the rotational 
velocity within its assembly. Therefore, the sprockets of internal gear 
sets 2 and 9 are able to rotate faster or slower than the hub about which 
they are centered. 
FIG. 1 shows an enlarged view of front transmission means 4 which includes 
flange 10 mounted on the base of seat tube 71, and first sprocket 1 
mounted on crank shaft 70, being insertable into seat tube 71. Further 
included are front sprocket selector 53 mounted on the neck of seat tube 
71, and pedal 72 mounted on the end of crank shaft 70. Front transmission 
means 4 also includes front planetary gear set 2 mounted on crank shaft 
70, between flange 10 and first sprocket 1. 
FIG. 3 shows an exploded view of said front planetary gear set 2. It 
includes first sun gear 11 fixed on flange 10. Front planetary gear set 2 
also includes first planetary pinions 12 arranged on the perimeter of sun 
gear 11. These first planetary pinions are adjacent to front carrier 14 
and encased by first ring gear 13. A second sprocket 3 is then formed on 
the perimeter of first ring gear 14. 
First sprocket 1 of the front transmission means is constructed with teeth 
along the perimeter of a solid wheel. Any rotational force applied to 
crank shaft 70 will therefore be maintained as it is transmitted to the 
perimeter of the sprocket for driving chain 73. 
Although second sprocket 3 may be similar in diameter to first sprocket 1, 
the driving force applied to it from crank shaft 70 is effectively 
decreased by the revolution and rotation of first planetary pinions 12. 
This results in an increases in rotational velocity for both first ring 
gear 13 and second sprocket 3. Therefore, second sprocket 3 rotates faster 
than the crank shaft driving it. 
Because second sprocket 3 modifies both rotational velocity and force, and 
first sprocket 1 transmits rotational velocity and force applied to it 
without modification, the rotational force and rotational velocity vary 
between first and second sprockets 7 and 8. 
First sprocket 1 and front carrier 14 are further comprised of ratchet 
means 16 and 15 located on their inner boundary. Projection means 15' and 
16' are then coupled to crank shaft 70 where first sprocket 1 and front 
carrier 14 mount. 
Ratchet means 15 and 16 then brace against projection means 15' and 16' 
when the sprockets are rotating in the forward direction, thereby allowing 
for forward driving capability. Alternatively, the ratchet means slide 
freely over the projection means when the sprockets are rotating in the 
reverse direction, thereby maintaining rotational mobility in the reverse 
direction. 
Therefore, the ratchet means are used to maintain the rotational mobility 
in both the forward and reverse direction, while restricting the driving 
capability to the forward direction. 
Second sprocket 3 is indirectly driven by front carrier 14 which uses said 
ratchet means 15 to couple with crank shaft 70. Consequently, second 
sprocket 3 maintains its rotational mobility while being restricted to a 
forward driving capability. 
Another component in front transmission means 4 is front sprocket selector 
53 which is joined to seat tube 71 using link means 63 and coupling band 
62. Sprocket selector 53 includes chain guide 65 which supports chain 73 
at a constant height. Because the sprockets may be of equal diameter, 
chain 73 is able to maintain close proximity with all sprockets. 
Consequently, the chain experiences no vertical movement in the front 
transmission means which results in a faster, more efficient shift as 
follows. 
Chain guide 65 is shifted laterally when sprocket selector 53 is adjusted 
for a new sprocket. Chain 73 is thereby forced laterally toward the 
adjacent or receiving sprocket until a cog of this adjacent sprocket 
catches it. The chain is then completely transferred to the receiving 
sprocket after one full rotation has been completed. 
FIG. 2 is an enlarged view of rear transmission means 6 including hub 
extension 17 of rear hub 5, and third sprocket 7 mounted on the hub 
extension and inside the rear tip 74. Rear planetary gear set 9 is also 
mounted on the hub extension between third sprocket 7 and rear tip 74. 
Rear sprocket selector 54 is then attached to the lower, outside portion 
of rear tip 74 from which it hangs. 
As shown in FIG. 4, rear planetary gear set 9 includes rear carrier 18 
which forms fourth sprocket 8 on its outer perimeter and has second sun 
gear 20 adjacent to it. It also includes second planetary pinions 19 which 
are fixed on the rear carrier, being arranged on the perimeter of the 
second sun gear 20. Second ring gear 21 is then attached to rear tip 74 to 
encase planetary pinions 19. 
Third sprocket 7 is constructed with sprocket teeth mounted on the 
perimeter of a solid wheel similar to the first sprocket. Therefore, any 
rotational force applied to the third sprocket in the forward direction 
will be maintained and transmitted to rear hub extension 17. 
Although fourth sprocket 8 may be similar in diameter to third sprocket 7, 
the driving force transmitted to it is effectively decreased due to its 
internal gearing. This results in proportionate increases in rotational 
velocity for second sun gear 20 which drives hub extension 17. Hub 5 and 
rear wheel (not shown) are thereby driven at a faster rate than the fourth 
sprocket 8 due to their coupling with hub extension 17. 
Because fourth sprocket 8 increases rotational velocity by decreasing 
rotational force, and third sprocket 7 transmits the rotational force and 
velocity applied to it without modification, both rotational force and 
velocity vary between third and fourth sprockets 7 and 8 as was the case 
with the first and second sprockets. 
Therefore, rotational force and velocity variations are achievable in both 
the front and rear transmission means without variations in sprocket 
diameter. 
Third sprocket 7 and second sun gear 20 are further comprised of ratchet 
means 22 and 22' located on their inner boundary. Projection means 23 and 
23' are then coupled to hub extension 17 where third sprocket 7 and second 
sun gear 20 mount. 
In a manner similar to that applied in the front transmission, the ratchet 
means 22 and 22' then brace against projection means 23 and 23' when the 
sprockets are rotating in the forward direction, and slide freely over the 
projection means when the sprockets are rotating in the reverse direction. 
Therefore, the ratchet and projection means of the rear transmission means 
are used to maintain the rotational mobility in both the forward and 
reverse direction, while restricting the driving capability to the forward 
direction. 
Another component in rear transmission means 6 is rear sprocket selector 54 
which is coupled outside rear tips 74. It has guide gear 57 attached to 
its lower inside portion which is used to move chain 73 laterally across 
the rear sprockets. Because the rear sprockets may also be of equal 
diameter, chain 73 is able to maintain close proximity with all sprockets. 
Consequently, the chain experiences no vertical movement in the rear 
transmission means which results in a faster, more efficient shift as 
follows. 
Guide gear 57 is shifted laterally when rear sprocket selector 54 is 
adjusted for a new sprocket. Because chain 73 is connected to and 
positioned by guide gear 57, lateral movements of the guide gear will 
cause lateral movements of the chain across the sprockets. Therefore, 
chain 73 is forced laterally toward the adjacent or receiving sprocket 
until a cog of this sprocket catches it. The chain is then completely 
transferred to the receiving sprocket after one full rotation has been 
completed. 
The above-mentioned transmission assembly functions to transmit a forward 
rotational force applied to pedal 72 through crank shaft 70, front 
transmission means 4, chain 73, rear transmission means 6, and rear hub 5, 
finally to drive the rear wheel (not shown) in the forward direction. 
The rotational velocity ratio is a measure of the amount of rotational 
velocity output at the rear wheel compared to the amount of rotational 
velocity at the crank shaft. 
By adjusting the sprocket selectors, chain 73 may be connected to sprockets 
of varied internal gearing in both the front and rear transmission means. 
Therefore, the rotational velocity ratio may be modified by simply 
selecting various gear combinations. 
Due to the difference in rotational velocity between the first and second 
sprockets 1 and 3 or between the third and fourth sprockets 7 and 8, the 
chain may derail during the shifting process. Ratchet means 15,16,22,24 on 
the front and rear transmission means serve to prevent this. 
By transmitting the rotational force in only one direction, the ratchet 
means allows slipping of the slower sprocket in the forward direction. 
Therefore, this sprocket is able to achieve the same rotational velocity 
as the faster sprocket during the chain's transition between sprockets. 
Once the chain has completed this transition, the two sprockets are no 
longer connected by it, and they return to their respective rotational 
velocities. 
When chain 73 is used to couple the first and third sprockets 1 and 7, any 
rotational force applied to pedal 72 will be preserved and directly 
transferred to rear hub 5 as previously discussed. Because of this, the 
rear wheel is driven with the same rotational force as applied to pedal 
72. Therefore, coupling first and third sprockets 1 and 7 provides a 
velocity ratio of 1:1 which is well below the lowest available in 
conventional transmissions. 
The first and fourth sprockets 1 and 8 are coupled when chain 73 is shifted 
by rear sprocket selector 54 to the fourth sprocket. Therefore, the 
effective rotational force from pedal 72 to the rear wheel is decreased 
due to rear planetary gear set 9. This results in an increased velocity 
ratio to 1:3.09 as described above. 
The second and third sprockets 3 and 7 are coupled when chain 73 is shifted 
by front sprocket selector 53 to second sprocket 3. Therefore, the 
effective rotational force from pedal 72 to the rear wheel is further 
decreased due to front planetary gear set 2. This results in an increased 
velocity ratio to 1:1.41. 
The second and fourth sprockets 3 and 8 are coupled when chain 73 is 
shifted by both front sprocket selector 53 and rear sprocket selector 54. 
Therefore, the effective rotational force from pedal 72 to the rear wheel 
is decreased due to front planetary gear set 2 and rear planetary gear set 
9. This results in a velocity ratio of 1:4.36 which is well above the 
highest available in conventional transmissions. 
The velocity ratios for the above sprocket combinations are determined by 
applying the formulas (1) and (2) below: 
EQU R1(.omega.+.PHI.)=R2(.psi.-.omega.) 
EQU R3(.alpha.-.omega.)=R2(.psi.-.omega.) 
where .alpha.is the rotational angle of the ring gear, R.sub.1 is the inner 
diameter of the sun gear, .omega. is the displacement angle of the 
planetary pinion center, R.sub.2 is the inner diameter of the planetary 
pinion, .psi. is the rotational angle of the planetary pinion, R.sub.3 is 
the inner diameter of the ring gear, and .PHI. is the rotational angle of 
the sun gear. 
When all sprockets 1,3,7,8 are formed equivalent in diameter size and 
sprocket teeth number, both front planetary gear set 2 and ring gear 21 of 
rear planetary gear set 9 are stationary whereby .PHI. and .alpha. are 
each zero. Consequently, coupling first sprocket 1 with third sprocket 7 
yields a 1:1 velocity ratio, second sprocket 3 with third sprocket 7 a 
1:1.4 velocity ratio, first sprocket 1 with fourth sprocket 8 a 1:3.09 
velocity ratio, and second sprocket 3 with fourth sprocket 8 a 1:4.36 
velocity ratio. 
As described above, according to the present invention, the transmission in 
the bicycle transmission assembly is realized by coupling front 
transmission means 4 with rear transmission means 6. Therefore, when each 
sprocket is of equal diameter, the assembly is simplified in its 
construction as the conventional multi-stage sprocket has been replaced 
with internally geared front and rear gear sets 2 and 9. 
Although the transmission assembly described above contains two gears in 
the front and two in the rear, the assembly above may be used with one or 
more gears in either the front or rear transmission means. Therefore, 
while the preferred embodiments of the present invention have been 
illustrated and described, it is intended that the following appended 
claims be interpreted as including all such alterations and modifications 
as fall within the true scope and spirit of the present invention.