Merging Energies

I've been thinking a lot lately about hybridding. A hybrid, in the modem context, is something that will combine multiple energy sources to perform a single function. Two things about this are difficult. First, the device must be fairly intelligent to manage the 2 sources. Simply, plug it in and close the switch will no longer suffice. To totally geek-out, this requires MI MO (multiple input, multiple output) nonlinear controls. But on a more practical level it requires things (components) that can actually merge energy. Is that hard? For hydraulics, pneumatics, and electricity it's a mere T-junction, but how to do it more mechanically? Well, turns out the answer is in the blog title. That clever planetary gear train, or the epicyclic gear train is the best way to do this. I'm wondering how many patents Toyota and others have filed on appropriating this old (albeit wonderful) technology.