lol, don't forget the second motor, the electric one. Only the gas one is "disconnected" through the planetary gear transmission. (It's not really disconnected.)

 

Is the electric motor always connected to the wheels? It must turn independently just like the gas engine does. If it didn't it would create drag on the car while going down hill and reduce MPG.

Also, how is the planetary gear transmission different than a regular transmission? I'm not being facetious, I really want to know. It seams that in a regular car the engine is just disconnected through the gears, so does that mean it's not really disconnected either?

 

Check out Wikipedia Epicyclic gearing - Wikipedia, the free encyclopedia
Basically you can have two power sources, and somehow shift the load from one input to the other input with fine granularity. I read it has only seven moving parts in the transmission, unbelievable. The electric motor should pose little load when electrically disconnected (no power, no regenerative braking).

Another cool thing about the Prius is the Kammback shape, check Wikipedia on that one too. (No, I don't have one! Just a rabid internet reader...)

 

Wow, that little flash example of the Prius' system that is linked at the end is really cool. Especially cool is that you can vary the engine speed without effecting the output speed of the driveshaft.

I think the Prius is a little more complex. It has to have some way to separate the generator from the system, and hold that set of gears stationary. Otherwise the ICE would never actually be driving the wheels. My guess is they also have a way to separate the electric motor from the driveshaft.

Yeah the aerodynamic stuff on the Prius is pretty amazing. I would like to see more of those principals applied to non-hybrid vehicles! I've been considering getting vortex generators for my Fit. They are an interesting design that is supposed to create a kind of "virtual Kammback" by creating vortices in the air at the rear of the vehicle. The Mitsubishi EVO uses them, so there is some validity to it at least in performance applications.

 

Coasting with the engine OFF is generally illegal but coasting (with clutch on MT) with the engine ON is not illegal. I think some people have confused the coasting with engine OFF rule with powered coasting (e.g. clutch pushed all the way down), the latter of which is generally okay to do. This of course applies only to manual/standard transmissions; driving an automatic in neutral is illegal in many areas. But taking your foot off the gas in an automatic is roughly the same as coasting anyway. Coasting (using clutch to fully disengage the engine) to a signal light or stop sign or other stop sign where you will change gears should not be a problem - the clutch plate is completely disengaged from the flywheel ("riding the clutch" where the clutch pedal is partially depressed is BAD). Coasting (with clutch down) on long downhills at highway speeds may cause excess clutch wear upon re-engagement if the engine and transmission speeds are not well matched.

(Updated this post to clarify I was referring to coasting with the clutch on standard transmission - not coasting in neutral in an automatic. Drivers with automatic transmissions are out of luck except that they mostly coast if they are not pressing the throttle pedal anyway.)

 

Coasting with gears in neutral is a 3 point violation in VA.