why in Toyota Prius, ICE connected with planet-carrier,sun with generator and Motor with Ring?

If the ICE was on the carrier, it would have a fixed speed for any one speed of the wheels, just as MG2 has now. MG2, like any motor, makes maximum torque at 0 RPMs, so is well suited to driving the car at low RPMs. Engines can't 'run' at 0 RPMs, that is why manuals need a clutch.

 

Toyota's Power Split Device is very simple and reliable solution.
[ame="http://en.wikipedia.org/wiki/Hybrid_Synergy_Drive"]Hybrid Synergy Drive - Wikipedia, the free encyclopedia[/ame]

In contrast, GM's "two-mode hybrid system" is very complex and has a lot of clutches.
[ame="http://en.wikipedia.org/wiki/Global_Hybrid_Cooperation"]Global Hybrid Cooperation - Wikipedia, the free encyclopedia[/ame]

Ken@Japan

 

Hi Ken. Thanks for posting that link to the Synergy Drive article with the cut-away view of the transmission. (I'd seen image in several peoples avatars, but they were too small to see and I didn't know where the original was from).

I was really interested to see what MG1 and MG2 looked like. I wasn't totally sure of what I was looking at, so I labelled some stuff to what I think it is and hope that someone can check over my attached image and see if it's correct.

Please take a look :

 

All your labellings are correct, but Toyota Japan named the MG1 as "Generator" and MG2 as "Motor".

Anyway, following pictures are shown about Gen2 and Gen3 Prius units from Toyota's image library.
Newsroom : Image Library / Toyota

Ken@Japan

 

It is the Power Split Device.
Do you know the ICE (planet-carrier) torque is splitted always 72% to the ring gear and always 28% to sun gear?

Ken@Japan

 

Interesting pics Ken. It looks like they saved some weight in the 2010 model. MG2 in particular looks like it's probably making use of improvements in magnetic materials to save some weight.