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A NOVEL NEW BICYCLE DRIVE
A new bicycle drive is presented with significant advantages over conventional chain drives. The drive is
described in the attached Australian Provisional Patent specification titled “Chainless Bicycle Drive”.
The primary advantage of this new drive is that all lubricated drive components are fully enclosed and
thus don’t have the potential of staining and jamming cloths as it is the case with conventional, exposed,
grease lubricated chain drives.
Added advantages are, a considerably improved driving efficiency, simplified drive wheel change out, a
simpler frame design and zero maintenance on any drive component.
The improved driving efficiency is mainly due to the replacement of the drive chain, with a planetary gear.
All pivots use rolling element bearings with low friction seals.
In addition to the efficiency gain in the mechanical drive components, the efficiency of the human leg
joints is also improved, due to the fact that the arc motion of the leg joints requires only one quarter of the
horizontal movement for a given vertical power stroke, as compared to the circular motion of a
conventional bicycle crank.
There is no weight penalty when compared to a conventional chain driven bicycles.
Figure 1 shows the complete bicycle, which can be readily disassembled into the front wheel / frame
assembly, shown in Figure 2 and the drive wheel shown in Figure 3. Figure 4 shows the drive mechanism.
Figure 5 shows an example of a basic frame design. The frame does not require a crank support between
the wheels and thus is simpler in design and offers more scope for design styles to suit a specific market.
Figure 6 shows a cross-section through a fixed gear train with the ratio of 2.8:1 and Figure 7 shows the
same gear train in an exploded view.
Figure 8 shows a five speed, compound planetary gear assembly with a surprisingly simple gear shift
mechanism.
The gear ratios are: 1.0:1, 1.3:1, 1.8:1, 2.5:1, 3.5:1
It has nearly perfect geometric gear spacing, and the same gear span as a typical, conventional 18 gear
chain drive. The ring gear has an outside diameter of 82 mm and does readily fit between the hub and the
crank, similar to the fixed gear train shown in Figures 5 and 6.
Rolling element bearings on the planet gears and on the inner sun gear, with a free floating planet cage,
ring gear and outer sun gear ensure the highest possible gear efficiency.
There is plenty of scope for a finer gear spacing and larger gear span similar to well established gear hub
designs. The big advantage of this new drive, however, is that the efficiency is not impeded by the
relatively low efficient chain drive.
Figure 9 shows a stress analysis of a typical, forged, low cost pedal arm (the heaviest single item in the
drive train). A more sophisticated, hollow design would be applicable for a better strength to weight ratio
required on sports bicycles.
Extensive prototype testing confirmed that the drive ergonomics of this new drive are equal or better than
a conventional bicycle crank drive.