Bicycle construction

A bicycle construction for tandem operation includes an auxiliary drive means which may be attached to a conventional single operator bicycle between the main drive means and the rear wheel to permit operation by two occupants. The auxiliary drive means comprises a pair of first auxiliary sprockets each connected to an associated one of a pair of independently supported rotary pedals each of which is coupled to an associated fork of a forked rear wheel support. A pair of second auxiliary sprockets is mounted on the main drive means, each of the second auxiliary sprockets being coupled to a respective one of the main rotary pedals. A pair of support columns coupled to the bicycle frame may be provided to serve as an auxiliary seat support, at one end, and as an auxiliary rotary pedal support at its other end. The auxiliary crank arms associated with the auxiliary rotary pedals may be coupled to eccentrically mounted bearing for adjusting the spacing between the auxiliary drive means and the main drive means.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention is directed to the field of vehicles and principally to a 
tandem bicycle construction. 
2. Description of the Prior Art 
Various prior art devices for converting a conventional single passenger 
bicycle to tandem pedalling operation are exemplified in U.S. Pat. No. 
2,277,727 issued to D. A. Swanson on Mar. 31, 1942; U.S. Pat. No. 
2,385,892 issued to D. A. Swanson on Oct. 2, 1945; U.S. Pat. No. 2,723,132 
issued to A. R. Oberwegner on Nov. 8, 1955; and U.S. Pat. No. 3,913,944 
issued to James H. Blow, Jr., applicant herein, on Oct. 21, 1975. The two 
Swanson patents disclose arrangements which require extensive 
modifications of the rear wheel hub portion of the bicycle which would 
preclude its use as a simple attachment to a conventional bicycle. The 
Oberwegner patent discloses a relatively complex mechanism in which the 
auxiliary operation describes a generally elliptical path of movement 
which may be found to be both awkward and uncomfortable for an operator 
unfamiliar with such motion. The Blow patent, although disclosing a 
simpler and more convenient assembly, still requires a careful adjustment 
and alignment of components to insure that the main and auxiliary drive 
mechanisms rotate in correspondence with one another during operation. 
SUMMARY OF THE INVENTION 
The present invention overcomes the limitations and difficulties noted 
above with respect to prior art devices by providing an auxiliary drive 
means which may be readily and conveniently attached to a conventional 
single passenger bicycle to provide a simple and inexpensive tandem 
pedalling arrangement. The auxiliary drive means comprises a pair of 
independently supported auxiliary rotary pedals each of which is coupled 
to a respective fork of the forked rear wheel support intermediate the 
main drive means and the rear wheel on the bicycle frame and drives an 
associated first auxiliary sprocket which is coupled via a chain drive to 
a second auxiliary sprocket located on a respective main rotary pedal. 
Means may be provided to disengage the auxiliary rotary pedals from their 
respective auxiliary sprockets to reduce the torque exerted on the main 
rotary pedals when the bicycle is powered by only one occupant operating 
the main drive means. A pair of auxiliary support columns which are 
readily attachable to the bicycle frame may be provided to serve as an 
auxiliary seat support at their upper ends and as a bearing support for 
the auxiliary rotary pedals at their lower ends. The auxiliary rotary 
pedals are mounted on respective crank arms which may be journalled on 
eccentrically mounted bearings to permit a rapid and simple tension 
adjustment of the chain drive coupling the main and auxiliary drive means. 
The upper ends of the auxiliary support columns may be further coupled to 
one end of a preferably adjustable strut the other end of which is rigidly 
coupled to the bicycle frame to maintain the support columns in a 
predetermined position relative to the bicycle frame. It is, therefore, an 
object of this invention to provide auxiliary drive means for a 
conventional single occupant bicycle construction. 
It is another object of this invention to provide a rapid, simple, and 
inexpensive means for converting a single occupant bicycle construction to 
tandem operation. 
It is a further object of this invention to provide an auxiliary drive 
means which may be readily attached to a conventional single occupant 
bicycle construction. 
It is yet another object of this invention to provide an auxiliary drive 
means for a conventional single occupant bicycle construction wherein the 
auxiliary drive means may be readily attached to and detached from the 
bicycle frame. 
Other objects and features of the invention will be pointed out in the 
following description and claims and illustrated in the accompanying 
drawings which disclose, by way of example, the principles of the 
invention and the best modes contemplated for carrying it out.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIGS. 1, 2, 3, and 4 there is shown a bicycle 20 to which 
is attached an auxiliary drive means 22 constructed in accordance with the 
concepts of the invention. The bicycle 20 is of generally conventional 
construction and comprises a tubular frame 24 having at its forward end a 
pair of handlebars 26 coupled to a front wheel 28 rotatable about a shaft 
30. The central portion of the frame includes a main seat 32 at the upper 
end of the frame 24, and a main drive means 34 at the lower end of the 
frame 24. The main drive means 24 includes a main sprocket 36 connected by 
way of a main chain drive 38 to a rear wheel sprocket 40 coupled to a rear 
wheel 42. The rear wheel 42 is attached to the frame 24 by way of an upper 
forked rear wheel support 44 and a lower forked rear wheel support 46. The 
main sprocket 36 is attached to a shaft 48 (FIG. 2) mounted in a bearing 
50 coupled to the frame 24. The shaft 48 extends beyond the bearing 50 at 
both its ends 52 and 54 (FIG. 2), which ends 52 and 54 are each fixedly 
coupled to one end of a respective main crank arm 56, 58, the other end of 
which is coupled to a respective main rotary pedal 60, 62. The main drive 
means 34 is thus operatively employed in a conventional manner to power 
the bicycle 20 for movement along a roadway through the torque exerted by 
a single rider. The auxiliary drive means 22 is readily attached to the 
bicycle frame 24 and may be conveniently employed to utilize the effort of 
a second rider to assist the first rider in propelling the bicycle 20. The 
auxiliary drive means 22 comprises a pair of first auxiliary sprockets 64, 
66, each independently coupled to a respective one of the forks of the 
lower forked rear wheel support 46, a pair of second auxiliary sprockets 
68, 70, sprocket 68 being coupled to the main sprocket 36 and sprocket 70 
being coupled to the main crank arm 58, a first auxiliary chain drive 72 
connecting auxiliary sprocket 64 to auxiliary sprocket 68, a second 
auxiliary chain drive 74 connecting auxiliary sprocket 66 to auxiliary 
sprocket 70, a first auxiliary crank arm 76 for driving auxiliary sprocket 
64, a second auxiliary crank arm 78 for driving auxiliary sprocket 66, a 
first auxiliary rotary pedal 80 rotatably mounted on auxiliary crank arm 
76, and a second auxiliary rotary pedal 82 rotatably mounted on auxiliary 
crank arm 78. The auxiliary crank arms 76 and 78 are each independently 
rotatably coupled to a respective shaft portion 84 extending outwardly 
from a support member 86 attached to a respective fork 87, 87.sup.1 of the 
lower rear wheel support 46 by way of a pair of U-shaped brackets 88 each 
having threaded ends 90 (FIG. 3) inserted through the respective apertures 
92 in an associated bracket 94 and engaged by washers 96 and threaded nuts 
98 for coupling each of the support members 86 to a respective fork 87, 
87.sup.1 of the forked rear wheel support 46. For the sake of explanation, 
there is shown in FIG. 4 an exploded view of the details of the assembly 
of one of the auxiliary crank arms 76 and 78 to a respective support 
member 86, including the first respective auxiliary sprocket 64, although 
it should be understood that both auxiliary crank arm and first auxiliary 
sprocket assemblies are constructed in the same manner. As illustrated in 
FIG. 4, the first auxiliary sprocket 64 comprises a central transverse 
aperture 100 dimensioned to provide a rotating fit over the shaft portion 
84 of the support member 86, and a lock pin receiving hole 102 spaced from 
the aperture 100 and located preferably close to the outer perimeter of 
the sprocket 64. A spacing washer 104 is interposed between the crank arm 
76 and the sprocket 64 to provide clearance for the first auxiliary chain 
drive 72 as it engages the sprocket 64. The auxiliary crank arm 76 is 
provided with a shaft receiving bore 106 having a recessed or undercut 
portion 108 for receiving the enlarged head portion 110 of a mounting bolt 
112 having a threaded shank portion 114 adapted to extend through the 
crank arm bore 106, the washer 104, the sprocket 64, and into threaded 
engagement with an internally threaded aperture 116 located axially within 
the shaft portion 84 of the support member 86. To releasably couple the 
crank arm 76 to the sprocket 64, the crank arm 76 is provided with a 
threaded transverse aperture 118 spaced from the bore 106 and adapted to 
receive the threaded portion 120 of the shank 122 of a lock pin 124. The 
terminating end of the lock pin 124 comprises an unthreaded portion 126 of 
reduced diameter arranged to fit snugly within the hole 102 in the 
sprocket 64. The lock pin 124 is normally threadably engaged within the 
aperture 118 in the crank arm 76 sufficiently to cause the unthreaded 
portion 126 to extend through the aperture 118 and into engagement with 
the sprocket hole 102. In this manner the sprocket 64 is operatively 
coupled to the crank arm 76. Thus, movement of either the sprocket 64 or 
the crank arm 76 will cause a corresponding movement of the other member. 
To disengage the crank arm 76 from the sprocket 64, the lock pin 124 is 
rotated sufficiently in a suitable direction to cause the unthreaded 
portion 126 to be withdrawn from the hole 102. This feature may be found 
to be extremely useful where the main drive means 34 is being employed to 
operate the bicycle 20 and it is desired to remove the load of the 
auxiliary drive means 22 therefrom. With the auxiliary crank arm 76 
disengaged from its associated sprocket 64, the auxiliary sprocket 64 will 
be free to rotate in response to the movement of the auxiliary chain drive 
72 without a corresponding movement of the crank arm 76. Since both 
auxiliary crank arms 76 and 78 may be disengaged in this manner, a 
substantial reduction in the load exerted on the main drive means 34 may 
be accomplished. A similar arrangement may be readily employed in coupling 
the main crank arms 56 and 58 to their respective second auxiliary 
sprockets 68 and 70, when desired, although such construction will require 
a modification of each of the main crank arms 56 and 58 to include an 
aperture similar to 118 for receiving the lock pin 124. Alternatively, the 
second auxiliary sprocket 68 is coupled directly to the main sprocket 68 
so that both move in unison when either is driven. The second auxiliary 
sprocket 70 is constructed preferably in the manner shown in FIG. 12 and 
comprises a bracket means 128 having spaced leg portions 130 and 130.sup.1 
arranged to straddle the main crank arm 58 to provide a coupling 
therebetween as shown in greater detail in FIG. 11. The sprocket 70 is 
further provided with a shaft receiving opening 132 for mounting the 
sprocket 70 on the shaft 48 and is dimensioned to provide a close rotating 
fit therebetween. Each of the remaining auxiliary sprockets 56, 64, and 66 
may be constructed in a similar manner, if necessary or desirable, to 
provide a non-releasable coupling between such sprockets and their 
associated crank arms. As further shown in FIG. 1, there is provided an 
auxiliary seat 134 which may be conveniently attached to a horizontal 
support 136 typically included on a conventional single rider bicycle. The 
auxiliary seat 134 is adapted to carry the second rider who may then 
assist the first rider in powering the bicycle 20. 
FIGS. 5 through 8 illustrate a further embodiment of a support means 138 
for coupling the first auxiliary sprockets 64 and 66 their associated 
auxiliary crank arms 76 and 78, to the bicycle frame 24. The support means 
138 comprises a right and left auxiliary support column 140 and 142 (FIG. 
6) each being essentially a mirror image of the other. Each support column 
140 and 142 further includes a respective backing plate 144, 146 (FIG. 6) 
having a respective first preformed portion 148, 150 located adjacent an 
oppositely formed first preformed portion 152, 154, respectively, on each 
of the support columns 140 and 142, for engaging a respective fork 156, 
156.sup.1 (FIG. 6) of the upper forked rear wheel support 44 therebetween. 
A similar arrangement of second preformed portions is provided at the 
lower end of each of the support columns 140 and 142 and backing plates 
144 and 146 as illustrated with respect to the right support column 140 
and its associated backing plate 144 in FIG. 8 and indicated by the 
numerals 158 and 158.sup.1 therein. The second preformed portions are 
arranged to engage the respective forks 87 and 87.sup.1 of the lower 
forked rear wheel support 46 in the manner shown in FIG. 8 with respect to 
the fork 87. Coupling bolts such as 160 are provided to draw the backing 
plates 144 and 146 and respective support columns 140 and 142 together to 
secure these parts to the bicycle frame in the desired location. As 
further illustrated in FIG. 6, each support column 140, 142 comprises an 
upper end 162, 164, respectively, suitably configured so that, as the 
support columns 140 and 142 are mounted on the bicycle frame 24 in the 
manner shown in FIG. 5, the ends 162 and 164 closely straddle a support 
post 166 extending from an auxiliary seat 168 and are held in engagement 
therewith by means of a coupling bolt 170 (FIG. 6) extending through 
aligned apertures in the post 166 and the ends 162 and 164 of the support 
columns 140 and 142, respectively. Both the post 166 and the ends 162 and 
164 may be provided with a series of spaced apertures such as shown at 172 
in FIG. 5 to permit adjustment of the height of the auxiliary seat 168. 
Each support column 140, 142 and its associated backing plate 144, 146 is 
provided at its lower end with a transverse bore or opening as shown in 
FIG. 9 for receiving the mounting post 174 of a support member 176. The 
mounting post 174 is provided with a threaded end portion 178 for 
receiving a nut 180 to lock the post 174 to the respective lower ends of 
the support columns 140 and 142, and the respective backing plates 144 and 
146. An enlarged portion 182 is located at the base of the mounting post 
174 to limit the extent of insertion of the post 174 into the respective 
apertures in the support columns and backing plates. Extending outwardly 
from the enlarged portion 182 of the support member 176 in a direction 
opposite to the mounting post 174 is a bearing portion 184 for receiving 
an associated auxiliary sprocket 64, 66, and auxiliary crank arm 76, 78, 
as shown in the exploded view in FIG. 8 which illustrates a portion of the 
right side assembly of the auxiliary drive means although it should be 
understood that both sides are similarly constructed. The bearing portion 
184 is provided with a threaded aperture 186 similar to aperture 116 for 
receiving the mounting bolt 110. The bearing portion 184 may be oriented 
either in axial alignment with the post 174, or may be eccentrically 
located, as shown in FIG. 9, to provide a convenient means for taking up 
the slack in the auxiliary drive chain, 72, 74 after assembly. As shown in 
FIG. 10, rotation of the support member in the direction indicated by the 
arrow 188 will cause the eccentrically mounted bearing portion 184 to 
shift its position from a central axis rearwardly to increase the distance 
between the front main or auxiliary sprockets 36 and 70, respectively, and 
the associated rear or first auxiliary sprockets 64 and 66. Thus, each 
auxiliary chain drive 72 and 74 may be independently tightened or loosened 
for purposes of assembly or disassembly. The initial adjustment of the 
auxiliary chain drives 72 and 74 is accomplished by properly positioning 
the auxiliary support columns on the bicycle frame 24 prior to tightening 
the bolts 160 so that the chain drives 72 and 74 may be slipped over the 
respective sprockets on each side of the bicycle. The slack in the chain 
drives 72 and 74 may then be at least partially taken up by urging the 
lower ends of the auxiliary support columns 140 and 142 and their 
respective backing plates 144 and 146 rearwardly and then tightening the 
bolts 160. The final adjustment may then be made by rotating the support 
member 176 in a suitable direction to cause the first auxiliary sprockets 
64 and 66, and their associated auxiliary crank arms 76 and 78 to be 
repositioned in the manner described heretofore. As further illustrated in 
FIGS. 5 and 7, a strut means 190 may be connected between the upper ends 
162 and 164 of the support columns 140 and 142, respectively, and a 
forward portion 192 of the bicycle frame 24. The strut means 190 comprises 
a forked rearward end 194 arranged to straddle the respective upper ends 
162 and 164 of the support columns 140 and 142. The other end of the strut 
means 190 is provided with a slotted opening 196 oriented at a suitable 
oblique angle to longitudinal axis of the strut means 190 to receive the 
portion 192 of the frame 24. Transverse openings such as 198 and 200 are 
provided at each end of the strut means 190 to receive mounting bolts or 
the like for clamping the strut means 190 to the respective adjacent 
parts. The strut means may comprise either a single element, or may be 
divided transversely into two sections coupled together with an adjusting 
sleeve 202 which may comprise a threaded interior (not shown) adapted to 
engage the adjacent ends of the two sections which may then be suitably 
externally threaded (not shown) so that rotation of the adjusting sleeve 
202 in a suitable direction will cause the strut means 190 to elongate or 
contract in length in response thereto. The strut means 190 may then be 
employed to provide additional stiffening of support columns 140 and 142, 
and a further means for adjusting the position of the support members 176 
relative to the main drive means 34. 
It should be understood that, in assembling the auxiliary drive means 22 to 
the bicycle frame 24, the auxiliary crank arms 76 and 78 should be 
positioned in opposite directions to one another along parallel axes for 
convenience in operation, and should coincide with the main crank arms 56 
and 58 for symmetry of movement, although this latter arrangement is not 
necessary for proper functioning of the device.