Re: Designing a Planetary Gearbox to increase speed?
 

Here is a link to some BSFC maps:
http://ecomodder.com/wiki/index.php/...on_(BSFC)_Maps
BSFC or Brake Specific fuel consumption shows how much fuel is consumed for each useable work unit produced at a given operating point.
If you look at the:
Mercedes Benz 300SD OM617 5 cylinder turbo diesel map,

You will see behaviour that Don R is talking about. where there is a sweet spot to run the engine from a (fuel in)/(work out). For that engine, the sweet spot is between about 1900 and 2600 rpm and the engine is about 60-90% fully loaded.
For gas and diesel engines, the general rule of thumb for peak efficiency is around 50% max rpm and at and above 50% load. This is a very general statement.

If you had a 1 speed gearbox, you would figure out the most important attribute,a nd size your gearbox to match that (acceleration, top speed, fuel economy). For Supermileage, we had a single speed drivetrain.

If you want it all, then you would go for a CVT or continuously variable transmission that would (in theory), give you the optimal ratio for whatever scenario you are driving. These gearboxes tend to have other issues (efficiency, cost, longevity, weight....).

The Toyota Hybrid system does a really good job of acting like a CVT without some of the draw-backs, and with some other benefits. Its not "perfect", but it is a really good system for a car, and a pretty neat one to figure out.

BTW, you can replace the generator/electric motor with Hydrualic pump/Hydrualic motor and achieve a similar set up... Of pressurized air... Or... Check out this Dana HVT. It is a 3 range IVT (infinitely variable transmission) powersplit...
http://www.youtube.com/watch?v=jsgw7ozlfJ0

Re: Designing a Planetary Gearbox to increase speed?
 

Does anyone know: What's the word on the street about the CVT in Nissan Altima concerning the issues mentioned above?

Re: Designing a Planetary Gearbox to increase speed?
 

Nissan and CVTs have a pretty long history, so a little searching should give you some background. I believe they use a "push style" belt which is pretty neat. Check out "Van Doorne" for some history on the push belt.

Re: Designing a Planetary Gearbox to increase speed?
 

Engine efficiency is not (necessarily/generally) a function of incomplete fuel combustion. Engines do not provide 100% of the energy produced by burning fuel as useful mechanical energy. The balance of the energy is released as heat.

A modern gasoline engine has an efficiency typically in the range of 25-30%.

Engines operate most efficiently within a certain rpm range. This provides the connection between gear ratios and engine efficiency.