Valrico, FL--Bicycle designers continue to search for their Holy Grail: smooth, infinitely variable speed-shifting. The latest challenge to the common derailleur offers this and more; the possibility of front- or dual-wheel drive, hydraulic braking with ABS, and solar-charged power assist.
Two parts, a pedal engine and wheel motor, make up the drive system. Both rely on a patented, positive-displacement fluid pump. One pump converts rotary pedal motion to piston motion. The other, which drives the wheel, changes reciprocating action back to a rotary output.
Pump operation is simplicity itself. Components include a crankshaft, twin- piston assembly, a pair of crankpin drivers, and two cylinders. Solid arcuate surfaces, built into the piston assembly, interface with the crankpin drivers to eliminate connecting rods and wrist pins.
The rigid shuttle-frame design, says inventor Doug Brackett, permits a lightweight unit small enough to fit any bike frame. The drive system's pedal engine replaces the normal sprocket assembly, while the wheel motor mounts at the hub.
As illustrated, the wheel motor has cam-activated valves and a set piston-stroke length. The pedal engine has pressure-activated valves and a variable piston-stroke length. Shifting varies the pedal engine's piston-stroke length to deliver a variable volume of fluid to the wheel motor. Result: smooth, infinitely variable speed control.
"By sizing wheel motor displacement four times smaller than the pedal engine," Brackett claims, "a 1:4 high-to-low operating range results. Within the ratio, any gear can be shifted to or from at full pedal power with instantaneous smoothness. In other words, the bicycle can be shifted from highest to lowest gear, or any speed in between, in one step under full power."
A shifter, located on the handlebar, changes gears.
Additional details...Dan Stoddard, Power Bike Co., 482 Congress St., Portland, ME 04101, (207) 828-1269, or [email protected]
Internal combustion engines