Engine idea: steady speed P&G with flywheel/capacitor storage
 

I'm sure anyone who has used pulse and glide much can agree that the speed fluctuations aren't exactly traffic friendly (I.E. other drivers can get confused and/or irritated by it,) but it can really make a significant difference to fuel economy. Unfortunately when using a hybrid and doing pulse and glide it's a bit tricky because the battery storage can discharge much faster than it charges, thus if you were to P&G like a regular vehicle ("rapid" acceleration in the pulse) you'd quickly deplete the batteries.

Flywheels and capacitors on the other hand can absorb energy as fast as the motor/generator that runs it can handle, much faster than batteries. However, the many issues involved in making one that can store as much energy as a conventional battery pack has made them just a theoretical energy store for hybrids.

My idea is this: instead of using the flywheel/capacitor to store ALL the electrical energy, use a much smaller one that would allow the engine to "pulse and glide" on and off at highway speeds while maintaining a constant vehicle speed and not draining the battery pack. During the "pulse" segment the engine would generate enough power to energize the flywheel/cap and keep the vehicle speed steady. Then, during the "glide" segment, the engine would cut off and the flywheel/cap would supply the energy to maintain velocity (and restart the engine.)

Rotareneg -

What I like about this is that it takes advantage of the engine running closer to it's optimum efficiency/RPM for the duration of the pulse.

I don't think it would even need to keep the P&G rock steady to be a success. All it would need to do is dampen the high/low MPH swings.

How would you envision the drive-train layout?

CarloSW2

A capacitor would also accept power faster when braking...

Careful, this isn't exactly true. Putting heavy cyclic loads on a mechanical flywheel can be very dangerous - especially as it ages. This is why, for the most part, there's not too much in the way for gross energy storage in flywheels (stronger/more versatile materials are needed).

Caps are probably a better solution - and don't come with that pesky angular momentum issue :p

I like the idea - I'm fairly certain what you've described is a parallel hybrid with a series mode...