[user removed]

If you can get the overall powertrain efficiency high enough, then you can use P&G techniques while maintaining a constant speed, even at freeway speeds. This is the crucial factor which can not be done electrically.

If this level of efficiency is achieved, then you can design the engine to only operate at it's best BSFC and you now have a vehicle that is capable of significantly greater efficiency under all but the most severe scenarios, like climbing Pikes Peak.

The energy density of a hydraulic accumulator is a function of it's working pressure. In the Bosch-Peugeot design it's around 4300 PSI. Americas cup racers are 12,000 PSI, almost 3 times the energy density.

That's not a future prediction or a theoretical possibility, it's being done right now. Basically the energy density means the amount of horsepower-seconds of energy you have that can be released in seconds. This provides and energy recovery-application storage capacity that has a lefespan measured in hundreds of thousands of miles.

Increasing the aero efficiency of any car means the engine efficiency is reduced as you make the engine produce less power for a constant speed. if the HH vehicle can be built then increasing the aero efficiency means the system requires less average power delivery so the engine simply runs for less time, while maintaining peak efficiency, and the mileage improves in direct proportion to the reduced average loads.

The arguments about total storage capacity and comparisons to battery packs miss the point. With energy storage efficiencies of above 80% and infinite ratios for constant power application regardless of storage. A battery is like a fuel tank. A powertrain with capacitive regenerative storage and the capability of matching engine BSFC to the precise amount of power to the wheels to maintain velocity is a completely different animal.

If you choose to not believe that then consider using a battery as the energy storage unit but use the HH powertrain to provide regeneration and allow peak BSFC of the battery and motor regardless of the vehicles speed or load.

I was looking at the newest Brammo Enertia motorcycle, would love to have one. It has a liquid cooled electric motor and a 6 speed transmission. Why would they have either component if it was not necessary and or more efficient. The answer is they have those components becasue they are both necessary and more efficient, when you consider all of the potential operational parameters. I just can't see 16 grand for a bike, when I can ride my TU250 for $2300 and 85 MPG.

regards
Mech