Chain for a bicycle

A right outer link plate of a bicycle chain, when viewed from the rear and top, has a projection swelling outwardly on a center edge thereof to lead a tooth of a sprocket into an outwardly spread recess formed by the projection. A left outer link plate of the bicycle chain, when viewed from the rear end top, has a flat face outside and an outwardly tapered face along a central inside portion to lead a tooth of the sprocket into a recess formed by the tapered face. In a front multi - stage sprocket, unit the projection of the right outer plate catches onto a tooth of the large sprocket and the tooth slips into the outwardly spread recess formed by the projection, assuring that the chain shifts from the small sprocket to the large sprocket easily. Although the center edge on the right outer link plate swells outwardly, the front multi - stage sprocket unit has a comparatively wide space between sprockets, and the projection does not interfere with the large sprocket and disturb speed changes. On the other hand, in the rear multi - stage sprocket unit, the tapered face catches onto the tooth of the large sprocket and the tooth slips into the recess formed by the tapered face, which enables the chain to shift from the small sprocket to the large sprocket. Despite that the rear multi - stage sprocket unit has a comparatively narrow space between sprockets, the left outer link plate is flat outside, and the outer link plate does not interfere with the large sprocket.

BACKGROUND OF THE INVENTION 
1. FIELD OF THE INVENTION 
This invention relates to a chain for a bicycle, and more particularly, to 
a chain for a bicycle having an exterior gear shifting assembly provided 
with a front multi - stage sprocket unit to be shifted by a front 
derailleur, and a rear multi - stage sprocket unit to be shifted by a rear 
derailleur. 
2. DESCRIPTION OF THE INVENTION 
In a conventional exterior gear shifting assembly, a chain set around a 
sprocket of a multi - stage sprocket unit is pushed laterally and 
displaced by a derailleur fitted immediately before the sprocket. The 
chain catches onto the next sprocket at the displaced portion, changing 
the speed. In order for the chain to shift from a large sprocket to a 
small one, it slips down of itself and fits into the small sprocket due to 
tension produced by a rear derailleur, providing that it is pushed toward 
the small sprocket upstream in the large sprocket running direction, and 
is disengaged with the larger sprocket. 
It is difficult, on the contrary, for the chain to shift from the small 
sprocket to the large one. If the chain is pushed toward the large 
sprocket upstream is the small sprocket running direction, it will be 
merely released from the small sprocket but hardly shift to the large one. 
It is necessary to push the chain further toward the large sprocket until 
link plate edges of the chain catch onto teeth of the large sprocket. For 
example, Japanese Utility Model laid open to public inspection, No. 
JIKKOUSHO 62 - 29712, discloses the art of modifying the form of a chain 
to avoid the problem noted above. The disclosed chain has a projection 
that swells outwardly on the edge of each central portion of the right and 
left outer link plates, and an outwardly spread recess to lead a tooth of 
a sprocket. For shifting, the projection catches onto the tooth of the 
sprocket and then the tooth slips into the outwardly spread recess. 
Generally, in an exterior gear shifting assembly, a front multi - stage, 
sprocket unit has a small number of stages such as two or three stages, 
while a rear multi - stage sprocket unit had a large number of stages, 
five or more, for example. And, there is produced a smaller space between 
the small and large sprockets in the rear multi - stage sprocket unit than 
in the front multi - stage sprocket unit. This suggests, therefore, that 
it is preferable for the chain to work on the front - multi sprocket 
differently than on the rear multi - sprocket unit. 
As mentioned above, each edge of the right and left outer link plates of 
the chain swells outwardly. The projection catches on a tooth of a 
sprocket to change the speed, and the chain readily shifts from the small 
sprocket to the large one in the front multi - stage sprocket unit. When 
it shifts from the small sprocket to the large one in the rear multi - 
stage sprocket unit, however, the projection of the outer link plate of 
the chain comes in contact with the large sprocket on the side because the 
space between the small and large sprockets is narrow. Although the chain 
is pushed laterally and displaced toward the large sprocket by the 
derailleur each edge of the projections can not catch onto a tooth of the 
large sprocket because the sprocket contacts with the projection on the 
side. Thus, this arrangement is not free from trouble; it fails to shift 
up the chain. 
Recent exterior shifting assemblies for bicycles tend to have a larger 
number of stages and an increased ratio of speed changes, so the number of 
stages in the rear multi - stage sprocket unit inevitably increases. 
Therefore, the space between sprockets will be narrower, and then it may 
become more difficult for the chain as described earlier to shift, because 
it has projections on the right and left outer link plates. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a chain for a 
bicycle which can shift smoothly and firmly not only in a front multi - 
stage sprocket unit, but also in a rear multi - stage sprocket unit. 
It is another, more particular object of the present invention to provide a 
chain for a bicycle which can readily shift without fail for use with a 
rear multi - stage sprocket unit having a large number of stages and a 
narrow space between sprockets. 
It is furthermore another object of the present invention to provide a 
chain for a bicycle well improved to enable an outer plate of the chain to 
catch onto a tooth of a large sprocket gently, causing the chain to shift 
to the large sprocket from a small one in the rear multi - stage sprocket 
unit. 
In the present invention, one of a pair of outer link plates, which is 
situated on the large sprocket side of a front multi - stage sprocket unit 
and which corresponds to a right link plate of a bicycle when viewed from 
rear and top, swells outwardly along its center edge, forming a recess to 
lead a tooth of a sprocket. The other outer link plate, which is situated 
on the large sprocket side in the rear multi - stage sprocket unit, and 
which corresponds to a left outer link plate of the bicycle when viewed 
from the rear and top, is formed planar outside and is tapered outwardly 
from its center edge, producing a recess to lead a tooth of a sprocket. 
In such a front multi - stage sprocket unit as composed according to the 
present invention, the chain is biased toward the large sprocket by the 
front derailleur to have the projection of the right outer plate catch 
onto a tooth of a sprocket, and the tooth may slip into the outwardly 
spread recess formed by the projection, getting the chain to shift from 
the small sprocket to the large one with ease. Since the right outer link 
plate projects outwardly on the center edge, but the front multi - stage 
sprocket unit has a small number of stages and a comparatively wide space 
between sprockets, it does not happen that the projection interferes with 
the large sprocket on the side and disturbs speed changes. 
On the other hand, the chain in the rear multi - stage sprocket unit is 
biased toward the large sprocket by the rear derailleur, thereby the 
tapered face of the edge of the left outer link plate catches onto a tooth 
of a large sprocket, which can slip into the recess formed by the tapered 
face. This assures that the chain shifts from the small sprocket to the 
large one without any difficulty. As mentioned earlier, the rear multi - 
stage sprocket unit has a large number of stages and a comparatively 
narrow space between sprockets, but the left outer link plate is formed 
flat outside, so the plate does not interfere with the large sprocket, and 
the chain is shifted with ease.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 through FIG. 3 show an embodiment of the present invention. A chain 
1 for a bicycle comprises a roller chain and is basically composed of left 
and right outer link plates 2 and 3, right and left inner link plates 5, a 
roller 6, a bush (not shown), and a pin 7. The chain 1 for a bicycle has 
an inner link 9 wherein the right and left inner link plates 5, are 
coupled by means of bushes with each other at their front and rear ends, 
and wherein the roller 6 is fitted rotatably onto the bush. The chain 1 
has an outer link 10 wherein the right and left outer link plates 2 and 3 
are coupled with each other at their front and rear ends by means of the 
pin 7 fitted into the bush to form an endless chain. The inner link 9 has 
a conventional form, however, and the outer link 10 and the outer link 
plates 2 and 3, in particular, have the forms showing a feature of the 
present invention. 
An exterior gear shifting assembly 11, as shown in FIG. 10, is comprised of 
a front multi - stage sprocket unit 13 provided with, for example, two 
stages, a rear multi - stage sprocket unit 15 provided with, for example, 
four stages, the chain 1, a front derailleur 16 and a rear derailleur 17. 
The assembly 11 is generally situated on the right of a frame 12 of a 
bicycle when viewed from rear and top. The front multi - stage sprocket 
unit 13 contains a large sprocket 19 outside and a small sprocket 20 
inside (toward the frame side), while the rear multi - stage sprocket unit 
15 a large sprocket 21 inside (toward the frame side) and a smaller 
sprocket 22 outside. The front multi - stage sprocket unit 13 has a small 
number of stages, while the rear multi - stage sprocket unit 15 has a 
large number of stages. The units tend recently to have a larger number of 
stages. Therefore, a space A between sprockets in the front multi - stage 
sprocket unit 13 (see FIG. 8) is wider than a space B between sprockets in 
the rear multi - stage sprocket unit 15 (see FIG. 9). 
When the chain 1 is set around the front and rear multi - stage sprocket 
units 13 and 15, the outer link plate 3 (referred to as "right outer link 
plate" hereafter) which is arranged outside the frame 12, has projections 
3a which swell outwardly on the upper and lower edges of a central portion 
of the outer link plate 3, forming recesses C which spread outwardly on 
the outer link 10, as shown in FIG. 1 or FIG. 3. 
The right outer link plate 3 has the projection 3a which catches onto a 
tooth of a sprocket, slidably leading it to the recess C and, enabling the 
chain 1 to shift gently and firmly from the small sprocket 20 to the large 
sprocket 19 in the multi - stage sprocket unit 13. 
When the chain 1 is set around the front and rear multi - stage sprocket 
units 13 and 15, on the other hand, the outer link plate" 2 (referred to 
as "left outer link plate hereafter) arranged inside the frame 12, has an 
outside face 2a which is flat, and outwardly tapered faces 2b in a central 
portion inside the link plate 2. Further, the tapered face 2b of the plate 
2 forms a recess D inside the outer link 10. Since the left outer link 
plate 2 has the tapered face 2b, which catches onto a tooth of a sprocket, 
slidably leading the tooth into the recess D, the chain 1 shifts smoothly 
and firmly from the small sprocket 22 to the large sprocket 21 in the rear 
multi - stage sprocket unit 15. 
FIG. 4 is an elevation of the left outer link plate 2 and the slant - lined 
part shows the tapered face 2b. The outwardly tapered face 2b may be 
different in depth at the front and the rear of the outer link plate 2 as 
shown in FIG. 5. Namely, the tapered face 2b is so formed that it is 
deeper on the downstream of the running direction of the chain and 
shallower on the upstream so it catches on a tooth of the sprocket at the 
deeper part thereof. It is also possible that the tapered face 2b is 
formed only on the side where it catches onto the sprocket, as shown in 
FIG. 6 and FIG. 7. 
The projection 3a of the right outer link plate 3 is produced by pressing 
while the tapered face 2b of left outer link plate 2 is produced by 
chamfering. From a point of gearing function, it is sufficient for the 
right and left outer link plates 2 and 3 to have the tapered face 2b and 
the projection 3a only on the inner circumference (downward) of the 
endless chain 1. However, it is preferable to form the tapered face 2b and 
the projection 3a on the upper and lower sides of the plates 2 and 3 for 
convenience of pressing and assembling. This assures that any biased force 
does not work upon the plate 2 and 3 and that they can be assembled 
regardless of the differences between top and bottom. FIG. 8 shows 
schematically how the chain 1 shifts from the small sprocket 20 to the 
large sprocket 19 in the front multi - stage sprocket unit 15, rotating 
clockwise when viewed from the right. The chain 1 is pushed rightward as 
shown in FIG. 8 and is displaced by the front derailleur 16 on the 
upstream of its running direction, which enables the projection 3a of the 
right outer link plate 3 at the displaced portion to catch onto a tooth 
19a of the large sprocket 19, leading the tooth 19a into the outwardly 
spread recess C. The chain 1 thereby shifts to the large sprocket 19. 
Since the space A between the small sprocket 20 and the large sprocket 19 
is comparatively wide, it does not happen then that the projection 3 a, 
comes in contact with the large sprocket 19 on the side thereof, although 
the projection 3a swells outwardly on the right link plate 3. 
FIG. 9 shows schematically how the chain 1 shifts from the small sprocket 
22 to the large sprocket 21 in the rear multi - stage sprocket unit 15. 
There is some difference in the arrangement of the small and large 
sprockets between the rear multi - stage sprocket unit 15 and the front 
multi - stage sprocket unit 13. The chain 1 is displaced and biased 
leftward as shown in FIG. 9 by the rear derailleur 17 beneath the sprocket 
unit 15 and moves onto the large sprocket 21 from the small sprocket 22. 
The space B between the small sprocket 22 and the large sprocket 21 is 
narrower than the space A between the sprockets in the front multi - stage 
sprocket unit 13. The left outer link plate 2 of the chain 1 does not 
swell outwardly, but is flat at 2a. In addition, the plate 2 is tapered at 
the enter bottom and its periphery 2b to help the chain change in 
operating position. 
The rear multi - stage sprocket unit 15 rotates clockwise when viewed from 
the right. The tapered face 2b in the center of the left outer link plate 
2 catches onto a tooth 21a of the large sprocket 21 to slidably lead the 
tooth into the space D, thereby making the chain 1 shift. If a 
conventional chain, having the right and left outer link plates swelling 
outwardly, is used for a bicycle, it is biased leftward by the rear 
derailleur 17, getting the left outer link plate in contact with the large 
sprocket 21 on the side thereof. If this is the case, it may happen that 
the chain falls down from the large sprocket over and over trying to catch 
onto it, which makes a jingling noise. The chain eventually does not shift 
to the large sprocket. If the chain 1 according the present invention is 
used, however, for the bicycle, it can surely shift to the large side 
sprocket 21 almost the same way in operation of the derailleur 17 as in 
the conventional chain used as noted above. This occurs even if the 
derailleur 17 is not operated enough. 
THE TECHNICAL ADVANTAGES OF THE INVENTION 
The chain 1 according to the present invention has the left and right outer 
link plates 3 and 2 formed to be suitable for the front and rear multi - 
stage sprocket units 13 and 15. 
For the front multi - stage sprocket unit 13 having the comparatively wide 
space A between the sprockets, the projection 3a of the right outer link 
plate 3 and the outwardly spread recess C function efficiently. For the 
rear multi - stage sprocket unit 1 having the narrower space B between the 
sprockets, the flat face 2a outside the outer link plate 2 works to 
prevent any sprocket from interfering with a projection on the left outer 
link plate. Furthermore, the chain 1 according to the present invention 
has the tapered face 2b and the space D formed inside the left outer link 
plate 2, so that it can shift from the small sprocket 22 to the large 
sprocket 21 without any noise and unpleasant vibration. Consequently, it 
is not observed that the left outer link plate is pushed against the large 
sprocket 21 to the extent that the chain is not ready until it catches 
onto the tooth 21a, unlike any conventional chain. And the tapered face 2b 
and space D formed on the center edge of the left outer link plate 2 
enable the chain 1 to shift from sprocket to sprocket smoothly and firmly. 
The left outer link plate 2 does not have any projection swelling outwardly 
and make the chain shift easily. As a result, the space B between the 
sprockets can be narrower. This makes it possible to increase the number 
of stages of the rear multi - stage sprocket unit 15, and the gear change 
stages and gear ratios of the exterior gear shifting assembly for the 
bicycle. 
Since the right outer link plate 3 in the front multi - stage sprocket 13 
is provided with the projection 3a and the outward spread recess C, this 
can be very effective in shifting the chain from the small sprocket 20 to 
the large sprocket 19, even when a heavier tension is put on the chain to 
go up a slope.