Bicycle with derailleur arrangement

A bicycle having a rear derailleur arrangement for its drive chain which includes a four-bar linkage consisting of a support, two links, and a coupler, first and second pivots securing the support to the links, and third and fourth pivots securing the coupler to respective links. The support is fixedly fastened to the rear wheel shaft whose axis is parallel to a plane which is perpendicular to the parallel axes of the pivots and defines an angle of 15.degree.-45.degree. with the vertical in the normal operating position of the bicycle. A guide sprocket for the chain is secured to the coupler for rotation in a plane perpendicular to the shaft axis. All four pivots are offset from the shaft in a downward direction, and the first and second pivots are farther from the shaft than the third and fourth pivots.

This invention relates to bicycles equipped with devices for varying the 
transmission ratio between the pedals and the chain-driven rear wheel of a 
bicycle, and particularly to improvements in a derailleur arrangement in 
which the drive chain may alternatively be trained over sprockets of 
different diameters on the rear wheel hub. 
More specifically, the invention is concerned with improvements in known 
derailleur arrangements exemplified in U.S. Pat. No. 3,364,762 in which a 
guide sprocket may be moved by a parallelogram linkage along a plurality 
of sprockets on the rear wheel shaft of the bicycle for shifting the drive 
chain between the several sprockets. 
It is the primary object of this invention to provide a bicycle with a 
derailleur arrangement of the basically known type which permits smooth 
shifting of the chain between the several driven sprockets, is capable of 
easily performed routine adjustments, and is simple in its construction. 
With these and other objects in view, as will hereinafter become apparent, 
the bicycle of the invention is equipped with a derailleur arrangement 
including a four-bar linkage, that is, a support member, two link members, 
a coupler, and four pivots having parallel axes. The first and second 
pivots secure the support member to the link members respectively, and the 
third and fourth pivots respectively secure the coupler member to the link 
members. The support member is fixedly fastened to the frame of the 
bicycle, preferably to the shaft of the rear wheel, in a position in which 
a plane perpendicular to the axes of the pivots is parallel to the rear 
wheel shaft and inclined relative to the vertical at an angle of 
15.degree. to 45.degree. when the bicycle stands on a horizontal surface 
and its wheel axes are parallel. The guide sprocket which shifts the drive 
chain between several coaxial sprocket wheels on the rear wheel is secured 
to the coupler member for rotation in a plane perpendicular to the rear 
wheel axis. The several pivots are offset from the rear wheel shaft in a 
downward direction, the first and second pivots being lower than the third 
and fourth pivots.

Referring initially to FIG. 9, there is shown as much of an otherwise 
conventional, ten-speed bicycle equipped with a derailleur arrangement 
according to this invention as is needed for an understanding of the same. 
The bicycle frame 50 carries two wheels 51, 52 of equal diameter which 
rotate in the plane of the frame when their axes are parallel as is shown 
in FIG. 9. The rear wheel 52 may be driven by rotating an assembly 53 of 
pedals and two chain wheels, the associated chain 59 being shifted in a 
conventional manner between the two chain wheels by means of a front 
derailleur 54. A rear derailleur arrangement 55 with the improvement of 
which this invention is more specifically concerned permits the drive 
chain 59 to be shifted by a guide sprocket 21 among five coaxial gear 
wheels 56. The two derailleurs 54, 55 are operated by means of a set of 
shifters 57 mounted on the frame 50. The wheels 51, 52 define a common 
tangential plane 58 below the frame 50 and a family of lines 8 
perpendicular to the plane 58. When the bicycle travels over flat ground, 
the plane 58 is horizontal, and the lines 8 are vertical. They will be 
referred to hereinafter as being horizontal and vertical, regardless of 
their actual angular relationship to the field of terrestrial gravity. 
FIGS. 1-3 illustrate the rear derailleur arrangement and as much of other, 
conventional elements of the bicycle of FIG. 9 as is needed for an 
understanding of the invention. The derailleur arrangement includes a 
two-part bracket 46 whose parts are adjustably connected by a bolt 46a. 
One of the two parts is hooked over the shaft 4 of the rear wheel 52 and 
secured thereon by nonillustrated nuts, the other part being fixedly 
fastened to an approximately channel-shaped support 15 for the operating 
elements of the derailleur arrangement. The shaft 4 carries a cluster 4a 
of five sprockets 56 of which four are indicated in phantom view only in 
FIG. 2. The sprockets increase in diameter from the bracket 46 toward the 
hub of the driven rear wheel 52. The sprockets and other conventional 
elements of the bicycle have been omitted from most Figures of the drawing 
to avoid crowding. 
The support 15 is one of the elements of a four-bar linkage whose other 
elements are protected against accidental damage by the web 19 of the 
support 15 which projects beyond other parts of the derailleur mechanism 
away from the rear wheel 52, as is evident from FIG. 2. The other elements 
of the linkage, best seen in FIG. 3, are two sheet metal links 10, 11 
secured to the support 15 by respective pivots 3, 3' remote from the shaft 
4, and a coupler 1 attached to the links 10, 11 by respective pivots 6, 6' 
nearer the shaft. The parallel axes of the four pivots 3, 3', 6, 6' define 
a parallelogram in a plane 5, perpendicular to the pivot axes and parallel 
to the axis of the shaft 4, and inclined at an angle .alpha. of about 
15.degree. to 45.degree. relative to the vertical 8. 
The link 10 is a two-armed lever whose longer arm connects the pivots 3, 6, 
and whose shorter, L-shaped arm 12 extends beyond the associated pivot 3 
and is engaged by one end of a spiral spring 42 coiled about the pivot 3. 
The other end of the spring 42 engages the support 15 and thereby biases 
the linkage toward the position shown in FIG. 3. The linkage may be moved 
away from the illustrated position in the plane 5 by a Bowden cable 
leading to one of the manually operable shifters 57. The sheath 13 of the 
cable abuts against the support 15. The tension wire 14 has a free end 17 
attached to the arm 12 and guided in an arc of about 90.degree. over a cam 
18 on the arm whose engagement face spirals about the axis of the pivot 3 
in such a manner that the radial distance of the pivot axis from the point 
of first engagement between the wire 14 and the cam 18 decreases when the 
cam is moved counterclockwise by the wire 14 from the position seen in 
FIG. 3. The angle .gamma. between the longitudinal axis of the link 10 
through the pivots 3, 6 and a plane 9 perpendicular to the shaft 4, 
represented in FIG. 3 by a chain-dotted line, should not exceed 
15.degree., and may be zero in the illustrated, terminal position of the 
four-bar linkage. 
The link 11 is a flat plate having a narrow end near the pivot 3' and a 
wider end near the pivot 6'. Upturned lugs on the wider end hold two 
abutment screws 44 which are readily adjusted for limiting the range of 
movement of the linkage. The axes of the screws 44 are inclined relative 
to the shaft 4 at an angle .delta. of 30.degree. to 50.degree.. In 
respective terminal positions of the linkage, the screws 44 abut against a 
projection on the coupler 1, best seen in FIG. 2, and against the support 
15. 
The chain guiding and tensioning mechanism 2 is mounted on an integral lug 
20 of the coupler 1. A long bolt 26 parallel to the shaft 4 passes through 
an opening in the lug 20. A bearing bushing 27 is axially secured between 
the head of the bolt 26 and the lug 20. The bushing rotatably supports two 
chain guides 23, 24 of flat sheet metal and a guide sprocket 21 between 
the guides 23, 24. A tensioning sprocket 22 is mounted between the guides 
23, 24 on a bolt 22a and bushing 22b for rotation in a common plane with 
the sprocket 21 which, in the illustrated position, is aligned with the 
smallest chain sprocket 56 on the shaft 4. The portion of the bolt 26 
between the lug 20 and a nut 26a on the end of the bolt carries an 
otherwise cylindrical sleeve 30 whose polygonal ends 32 are conformingly 
received in recesses of the lug 20 and of a washer 31 backed by the nut 
26a. Respective ends of a yieldably resilient helical torsion spring 25 
coiled about the sleeve 30 are secured to the washer 31 and to the chain 
guide 24 so as to bias the mechanism 2 clockwise, as viewed in FIG. 1, 
thereby to tension the chain normally trained over the sprocket 22, but 
omitted from FIGS. 1 to 8. The tension of the spring 25 is readily 
adjusted after loosening of the nut 26a. 
The derailleur arrangement is mounted on the rear wheel shaft 4 by means of 
the bracket 46 in such a manner that the plane 5 of movement of the 
four-bar linkage is within the range of 15.degree. to 45.degree.. When the 
Bowden cable is operated, the guide sprocket 21 travels in a circular arc 
closely parallel to the tapering surface which envelops the rear wheel 
sprockets 56. The free length of the non-illustrated chain between the 
guide sprocket 21 and the selected sprocket 56 remains virtually unchanged 
at the several transmission ratios. 
The links 10, 11 must move through longer arcs when the chain is shifted 
between the largest rear wheel sprockets than during shifting between the 
smaller sprockets 56, and the different movements are achieved by equal 
longitudinal movements of the Bowden wire 14 and corresponding equal 
movements of the associated shifter 57 because of the cam 18 which shifts 
the point of engagement between the wire 14 and the arm 12 nearer toward 
the axis of the pivot 3 as the sprocket 21 moves from the illustrated 
position toward radial alignment with the bigger sprockets 56. The Bowden 
cable runs between the flanges of the support 15 and is thereby protected 
against accidental damage. The wire 14 and the sheath 13 extend from the 
arm 12 in a direction generally toward the shaft 4, and thus toward the 
bicycle frame 50, not itself seen, to which they are fastened by clips in 
the conventional manner. The unsupported length of the cable between the 
derailleur arrangement and the bicycle frame is thus reduced to a minimum. 
The abutment screws 44 are readily accessible for adjustment, yet they do 
not project longitudinally beyond the link 11, and are thus protected by 
the link against accidental damage. Their angular offset of about 
30.degree. to 50.degree. relative to the axis of the shaft 4 makes such an 
arrangement possible. 
In the modified derailleur arrangement shown in FIGS. 4 to 6, the 
individual elements have been provided with the same reference numerals as 
their functional equivalents in FIGS. 1 to 3, significant structural 
differences, if any, being indicated by primed reference numerals. 
The approximately channel-shaped support 15 is adjustably fixed to the 
shaft 4 by a bracket 46. It largely envelops the other elements of a 
four-bar coupling, the two links 10', 11', and the coupler 1', the linkage 
being assembled by means of pivots 3, 3', 6, 6'. The coupler 1' has two 
parallel lugs 33 perpendicular to the axis of the shaft 4. A sleeve 34 is 
rotatably received in openings of the lugs 33 and coaxially receives the 
bolt 26. A chain guiding sprocket 21 is journaled on the portion of the 
bolt 26 between the head of the bolt and one of the lugs 33 on a bushing 
27, the same portion of the bolt also accomodating two flat chain guides 
23, 24. A tensioning sprocket 22 is arranged between the guides 23, 24. 
The coil spring 25 enveloping the sleeve 34 is fastened at one end to the 
flat guide 24 and at the other end to a radially notched adjusting disc 
36. An integral abutment 37 projecting from the adjacent lug 33 into a 
notch of the disc 36 prevents angular displacement of the latter under the 
force of the spring 25 so that the chain guiding and tensioning device 2' 
is biased clockwise, as viewed in FIG. 4 The tension of the spring 25 may 
be varied by shifting the abutment 37 among the notches in the disc 36. 
Washers 35 are axially interposed between the several elements mounted on 
the bolt 26 as needed. 
The two abutment screws 43 which limit relative angular displacement of the 
several members of the four-bar linkage are mounted on the support 15 and 
cooperate with respective abutment portions of the link 10' in the two 
terminal positions of the linkage. They are readily accessible without 
disassembling the derailleur arrangement because their axes enclose an 
angle .delta. of about 30.degree. to 50.degree. with the orthogonal 
projection of the shaft axis in the plane 5 of linkage movement, as is 
shown in FIG. 6. They are protected against accidental damage by the 
support 15, particularly by the web 19. 
The Bowden cable which may be operated to move the linkage members relative 
to each other has not been shown in FIGS. 4 to 6 nor the cam arrangement 
which causes different angular displacement of the linkage members in 
response to equal, sequential, longitudinal movements of the Bowden wire. 
It will be understood that the embodiment of FIGS. 4 to 6 is identical in 
this respect with that of FIGS. 1 to 3. 
If the several sprockets 56 on the shaft 4 of the rear wheel 52 differ 
greatly in the number of their teeth, it may be advantageous to space the 
axis of rotation of the chain guiding sprocket from the pivot axis of the 
chain guiding and tensioning device. Modifications of the devices of FIGS. 
2 and 5 satisfying this requirement are shown in FIGS. 7 and 8 
respectively only to the extent that they differ from the afore-described 
apparatus. 
The apparatus partly illustrated in FIG. 7 is identical with that described 
above with reference to FIGS. 1 to 3 except as specifically illustrated 
and described. The lug 20 of the coupler 1 is formed with an opening 
through which the threaded end of a bolt 38 passes. An internally threaded 
nipple 39 having a flange 40 is mounted on the bolt 38 in abutting 
engagement of the flange with the lug 20 and provides a bearing for the 
flat chain guide 29 of the guiding and tensioning device 2a. The chain 
guiding sprocket 21 and the chain tensioning sprocket 22 are mounted 
between the chain guide 29 and another flat chain guide 28 on respective 
bolts and sleeves as described above, the axis of rotation of neither 
sprocket coinciding with the pivot axis of the bolt 38. 
A sleeve 30 is mounted on the bolt 38 between the recessed face of the lug 
20 and the recessed face of the washer 31, and its polygonal ends 32 
engage the recesses as described above. The washer 31 is axially secured 
by the head of the bolt 38, and a spring 25 biases the chain guide 29 for 
tensioning engagement of the sprocket 22 with the non-illustrated drive 
chain. 
A modification of the apparatus of FIG. 5 analogous to that described above 
with reference to FIG. 7 is shown in FIG. 8, the device being identical 
with that illustrated in FIGS. 4 to 6 as far as not explicitly stated and 
shown otherwise. 
The threaded end of a bolt 38 is fixedly fastened to a chain guide 29' 
connected to another chain guide 38 by two bolts supporting radially 
aligned sprockets 21, 22 neither of which is coaxial with the bolt 38. A 
sleeve 34 coaxially mounted on the bolt 38 is rotatably received in 
aligned openings of two lugs 33 of a coupler 1' so that the illustrated 
chain guiding and tensioning device 2" may pivot on the coupler 1' and is 
biased by a torsion spring 25 whose one end engages a radial notch in an 
adjusting disc 36 angularly secured on a lug 33 as described above. The 
other end of the spring 25 is fastened to the sleeve 34 and thereby to the 
chain guide 29'. 
The several embodiments of the invention described above are relatively 
simple to build. High precision is needed only in drilling the openings in 
the members of the four-bar linkage which receive the pivot pins. The 
bores are readily located with reference to parallel or perpendicular 
surfaces of the linkage members without requiring complex jigs. 
The preferred angle .beta. of 30.degree. to 50.degree. between the line 7 
connecting the axes of the pivots 3, 3' and the orthogonal projection of 
the axis of the shaft 4 in the plane 5 permits the two terminal positions 
of the four-bar linkage to be approximately equidistant from an 
intermediate position in which flexing of the drive chain is at a minimum. 
When the line connecting the axes of the pivots 3 and 6 encloses a very 
small angle, smaller than 15.degree., in the illustrated limiting position 
of highest speed, the chain may be shifted to larger sprockets on the 
shaft 4 by a greater angular displacement of the links 10, 11 than would 
otherwise be possible, so that the links can be made correspondingly 
shorter, or a greater number of coaxial sprockets can be swept by the 
sprocket 21. 
The embodiments of the invention shown in FIGS. 7 and 8 may be used with 
bicycle frames not capable of being fitted with the derailleur 
arrangements in which the axis of rotation of the chain guiding sprocket 
coincides with the axis of pivoting movement of the chain tensioning 
device. Adaptation to such unusual frames is also facilitated by adjusting 
the two-part bracket 46. 
While the invention has been disclosed with reference to a parallelogram 
linkage in which each pair of pivot axes is spaced the same distance as 
the other pair, many of the advantages of the invention are available with 
linkages having only two members of equal effective length, or even four 
members of different lengths. 
It should be understood, therefore, that the foregoing disclosure relates 
only to preferred embodiments of the invention, and that it is intended to 
cover all changes and modifications of the examples of the invention 
herein chosen for the purpose of the disclosure which do not constitute 
departures from the spirit and scope of the attached claims.