This is an attempt at a high eff powered bicycle design. Electric bikes can now exceed 40 & 50 mph using off the shelf parts. Some are even trying to use a pedal generator to help, but we know an electric generator won't be much better than 50% eff. The most eff are R/C motors, which offer inrunner (conv) & outrunner (stationary shaft/axle) i.e. the rotor/stator switch functions. Wasn't aware of the concept until looking n2 electric bikes.
So when researching hydraulic motors, there were no outrunner designs to be easily found. An outrunner would replace the hub assy of the wheel, using one side of the axle for input pressure and output through the other side. This is why I am reaching out to this forum, any good leads to start from on a design The closest I have come to finding a potential solution is based on this:
[nomedia="http://www.youtube.com/watch?v=WFsVAXYeHm8&feature=related"]YouTube - EABS Insight of an air car engine[/nomedia]
Though axial piston pumps are used in hydrostatic transmission now, and show more potential IMO. [nomedia="http://www.youtube.com/watch?v=D6FHU54qyRE&feature=related"]YouTube - Axial Piston Pump Animation[/nomedia]
Optimal use would control the swash plate w/ the brake rotor, creating a pump (adv of high pressure w/ axial) for regenerative braking. Here is where the energy saving would be greatest.
Pedals would power a variable output vane pump. High eff electric motor would power a pump (gear, vane, or axial). Frame would transfer fluid and serve as a pressure accumulator. Main drawback being 90deg turns in plumbing.
Battery tech has improved to where a 5# LiFePo can hold the energy comparable to a 60# SLA (sealed lead acid). Some claim this has only been reached in the last 2yr.
Here is a unique reciprocating ICE I ran across in my research, applications?
[nomedia="http://www.youtube.com/watch?v=pjH2I076agQ&feature=feedlik"]YouTube - Revetec Technology Presentation - Part 2[/nomedia]
You may want to investigate the Ohlins/Yamaha hydraulic motorcycle 2-wheel drive.