Chain drive for a bicycle

A chain drive for use on a bicycle having a conventional frame and wheels. The chain drive comprises a wheel hub mounted for rotation on the frame. The opposite end portions of the hub are disposed on opposite sides of the frame, respectively. Two sprocket devices are mounted on the opposite end portions, respectively, of the hub for imparting rotation thereto. A pedal operated crank is also mounted for rotation on the frame, and includes two coaxial sprockets secured to the opposite ends of the crankshaft. The crank sprockets are axially spaced, parallel and disposed on the opposite sides, respectively, of the frame. The two sprocket devices and the two crank sprockets are radially aligned, respectively, one sprocket device being associated with one crank sprocket. Two chains are mounted on the aligned sprocket devices and crank sprockets, respectively, for driving the wheel hub by means of the crank.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to bicycles, and more particularly to chain 
drives therefor. 2. Description of the Prior Art 
Conventional chain drives for bicycles normally employ a single pedal 
operated sprocket in combination with a single driving sprocket mounted on 
the hub of the rear wheel. On tandem bicycles, it is conventional to 
employ two pedal operated cranks having interconnecting chain drives as 
well as an additional drive on one side of the bicycle to the rear wheel. 
Racing bicycles commonly employ a single chain drive on one side of the 
bicycle. 
It has been found that the single chain drive arrangements in racing 
bicycles suffer from a loss of conversion efficiency between the torque 
applied to the pedals and the power actually applied to rotate the wheel. 
This is thought to be due to the pedal operated crank flexing some under 
operation stress. It has been discovered that stiffening the crank 
assembly through the use of a symmetrically arranged, double crank system 
provides for an improvement in this conversion efficiency. 
SUMMARY OF THE INVENTION 
In this invention, a pedal operated chain drive includes a wheel hub which 
is mounted for rotation on the bicycle frame. The hub is provided with 
opposite end portions disposed in alignment with the opposite sides, 
respectively, of the bicycle frame. Two sprocket devices are mounted on 
the opposite end portions, respectively, of the wheel hub for imparting 
rotation thereto. A pedal operated crank is also mounted for rotation on 
the frame and has two coaxial sprockets secured thereto for rotation 
therewith. The crank sprockets are axially spaced, parallel and disposed 
on opposite sides, respectively, of the frame. The two sprocket devices 
and the two crank sprockets are radially aligned, respectively, one 
sprocket device with one crank sprocket. Two chains are mounted on the 
aligned sprocket devices and crank sprockets, respectively, for imparting 
rotational drive from the crank to the wheel hub. 
The sprocket devices are free-wheeling relative to the wheel hub when the 
bicycle is coasting forwardly but are drivingly engageable therewith when 
rotated in the forward direction at a rate faster than the wheel hub. In 
one working embodiment, the two sprocket devices are alike, the two crank 
sprockets are alike, and the two chains are alike, the sprocket devices, 
the crank sprockets and the two chains being symmetrically arranged on 
opposite sides of the frame and with respect to the wheel hub and crank. 
Comprehended within the foregoing, the two sprocket devices are oppositely 
threadedly coaxially secured to the wheel hub end portions, respectively, 
the threading being in a tightening direction when forward driving force 
is imparted to the wheel hub. 
It is an object of this invention to provide an improved chain drive for a 
bicycle. 
The above-mentioned and other features and objects of this invention and 
the manner of attaining them will become more apparent and the invention 
itself will be best understood by reference to the following description 
of an embodiment of the invention taken in conjunction with the 
accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawings, the bicycle of FIGS. 1 and 2 is conventional 
insofar as the frame 10 and wheels 12 and 14 are concerned. Mounted on the 
frame is a pedal operated crank assembly which includes two crank arms 16 
and 18, two pedals 20 and 22, and a single shaft 24 secured at its 
opposite ends to the two cranks 16 and 18, which is mounted for rotation 
within the frame 10 by means of the customary bearings and threaded 
retainers (not shown). Rigidly secured to the opposite ends of the shaft 
24 in coaxial alignment are two drive sprockets 26 and 28, respectively, 
these sprockets being identical and disposed in parallelism on the 
opposite sides of the bicycle frame 10. 
The rear wheel 14 includes a hub 28 and the usual spokes 30. The opposite 
end portions 32 and 34 of the hub 28 are oppositely externally threaded as 
shown, for having secured thereto two sprocket devices 36 and 38 by means 
of matching internal threads 40 and 42. A conventional axle or spindle 44 
is coaxially received by the hub 28 and is therein supported by means of 
conventional bearings, cones and threaded retainers. The outer end 
portions of the spindle 44 are received through openings 46 in the frame 
10 and are secured thereto by means of the usual washers and nuts 48 and 
50. 
The sprocket devices 36 and 38 are conventional in the respect that they 
are of a free-wheeling design, including a one way clutch or ratchet. 
Suitable such devices are sold under the trademark SUN TOUR and are 
manufactured and sold by Maeda Industries, Ltd. of Japan. In particular, 
these sprocket devices 36 and 38 are so arranged that when they are 
rotated forwardly at a rate faster than the rotation of the wheel hub 28, 
lock-up occurs and a driving force is imparted to the wheel hub by means 
of the sprocket device 36, 38. On the other hand, when the bicycle is 
coasting, and no rotational drive is imparted to the sprocket devices 36, 
38, the wheel hub 28 rotates freely relative to the sprocket portions of 
the devices 36, 38. 
In a working embodiment of this invention, the threads 32 are righthand and 
the threads 34 are lefthand. The reason for this is that applied forward 
torque to both of the sprocket devices 36 and 38 will be in a tightening 
direction thereby assuring that the rotational force applied to the hub 28 
will not loosen the sprocket devices. 
The sprockets 26 and 28 and the sprocket devices 36 and 38 on opposite 
sides of the frame 10 are in radial alignment. Around these aligned sets 
are trained two like drive chains 52 and 54. 
In operation, the bicycle is manipulated in a conventional manner, the 
pedals 20 and 22 being operated by the feet to cause rotation of the 
sprockets 26 and 28 and the sprocket devices 36 and 38. When pedaling in a 
foward direction, the one way clutch or ratchet devices within the 
sprocket devices 36 and 38 engage thereby interlocking the sprockets and 
chains with the wheel hub 28. The wheel hub 28 is driven in a forward 
direction. If it is desired to coast, the rider stops pedaling whereupon 
the sprocket devices 36 and 38 stop rotating. The wheel hub 28 continues 
to rotate by reason of the one way clutch or ratchet. 
By reason of the sprockets 26 and 28 being mounted on opposite ends of the 
crank shaft 24 and immediately adjacent to the respective crank arms 16 
and 18, the crank assembly is rendered more rigid during operation. 
Because of this greater rigidity and consequent stiffness, more useful 
power can be transmitted from the sprockets 26 and 28 to the companion 
wheel sprocket devices 36 and 38, respectively. Even transmission of 
torque to the rear wheel is assured by reason of the fact that the 
portions of the chain drive on opposite sides of the bicycle frame are 
congruent and symmetrically arranged. Therefore, as the crank arms 16 and 
18 are rotated, an even balance of torque is applied to the rear wheel. 
The sprockets 26 and 28 may be in the form of a Sugino chain-ring as 
manufactured by Sugino of Japan or a Sun Tour as manufactured by Maeda 
Industries, Ltd. of Japan. The crank arms 16 and 18 are preferably 
fabricated of a lightweight but strong alloy. 
FIG. 5 illustrates a preferred form of the rear hub assembly, like numerals 
indicating like parts. The lefthand end of the hub 28 is formed with two, 
stepped diameter threaded end portions 34a and 56, portion 34a having a 
righthand thread and portion 56 a lefthand thread. The sprocket device 38a 
has an internal righthand thread 42a which matches righthand thread 34a. 
When sprocket device 38a is fully threaded onto the thread 34a, the end 
portion 56 protrudes therebeyond to receive a lock ring 48 having lefthand 
female threads which match the threads on portion 56. Lock ring 58 is 
tightened against the radial shoulder 60, and clearance is provided 
between lock ring 58 and sprocket device 38a to permit relative rotation 
therebetween. This clearance corresponds to that provided when lefthand 
frame member 10 (FIG. 3) is engaged with the outer end of end portion 34. 
Finally (FIG. 5) lefthand frame element 10 is abutted against the outer end 
of end portion 56 and/or lock ring 58 by tightening lefthand nut 50 onto 
the spindle 44. 
The FIG. 5 design is preferred for the reason that the sprocket device 38a 
does not have to be provided with lefthand threads, the more common 
righthand threads being more available and therefore more economical. Only 
the end portion 56 and lock ring 58 need to have lefthand threads. By 
reason of the lefthand threads on the reduced diameter end portion 56, any 
frictional rubbing of the sprocket device 38a with the lock ring 58 will 
serve to maintain the latter tightened. The diameter of the end portions 
32, 34 and 34a is preferably the same. 
While there have been described above the principles of this invention in 
connection with specific apparatus, it is to be clearly understood that 
this description is made only by way of example and not as a limitation to 
the scope of the invention.