The Gen 0 (P110), Gen 1 (P111) and Gen 2 (P210) transaxles operate quite similarly, but with electronics controls which improved dramatically with each successive generation. All of the above have a single ring gear, a single carrier and a single sun gear. The action of this conceptually simple device is to "sum" the widely varying "angular velocities" from the sources: the MG1 into the sun gear, the ICE into the carrier and the MG2 into the ring gear. The Gen 3 transaxles (P410; full-sized Prius, 2010 and later) and (P510; Prius c, all) expand upon the capabilities to include a second ring gear, a second carrier and a second sun gear. The MG2 is connected to the second sun gear, The second carrier is held fixed to the transaxle's case, and the second ring gear is a physical extension of the first ring gear. This second gear set forms the "motor speed reduction" system, which provides for a much smaller MG2, while it is also is much more powerful (a 2.5:1 ratio). Again, these components "sum" the "angular velocities", by employing components which are much better matched to the "mission function", and in a smaller, lighter weight package. The P410 and P510 got rid of the chain. In the P510, the lubricant also provides the transaxle's cooling function.
Try this Guy on You Tube. He is saying the same thing but with an actual Prius gearset as an example.
There are two different ratios employed in the MSRD, one slightly greater than 2.5:1. and one slightly less than 2.5:1. It is not a surprise that, for all intents and purposes, the average of these two, 2.5, is a good enough approximation. Certainly, as to the mechanical components, who was an American TRW scientist and inventor. Also, certainly, as to the electrical components, who were Japanese Toyota scientists and inventors.
