http://www.autobloggreen.com/2007/12...ernment-tests/

 

Sweet. I wonder if SEPTA will buy any.

 

I thought a lot of buses were already using GM's 2-mode hybrid system, so is this superior, and if so, how?

 

I believe up to now the technology has only been available on big buses. Now its going to be available on mini-buses. So I guess now the kids riding the short bus will be greener.

 

Actually, the buses use the Allison (which was owned by GM at the time) 2 mode hybrid system.

But the difference here is that, like the Volt or a diesel/electric locomotive, the bus in this discussion is a series hybrid, not a parallel hybrid (like the current buses, the Prius, etc.). So the engine acts as a generator; it does not directly drive the wheels.

 

The 2 mode hybrid uses both gas and electric to drive the transmission. This one is all electric to drive the transmission. The V8 is only for generating power when the batteries are low, just like the Volt.

 

So do they really need a V8 to drive a generator? Couldn't it be done with a smaller motor or is the size of the generator require a V8 to turn it?

 

Id imange that if they didnt need a V8 they would have went with something smaller.

 

If the batteries are large enough and can accept a very rapid charge rate, then it's possible to use a relatively tiny IC engine. The problem is that the batteries likely aren't large enough, and most lithium chemistries don't like accepting charge at a high rate (A123 makes some claims about their cells that have yet to be validated). Thus, it's necessary to have a relatively large IC engine - such as the ~275HP unit on this bus.

Throw some ultracapacitors in parallel with electrochemical batteries and it's a bit different story.