This is a control system patent. Toyota is building on prior art, in this case the TRW patent and its successors.
A controls patent is a natural and necessary result of the situation in 1973. From the article you linked:
"... the modern hybrid era had its stirrings in the late 1960s at an aerospace, credit reporting, and automotive parts conglomerate named TRW. Researchers there invented the modern idea of a power-split hybrid using a planetary gear set, a gasoline engine, and two electric motors. ...in order to be efficient and useful such a transmission needs to be carefully controlled. A hybrid transmission control computer was not a realistic possibility at that time so its design was not really practical for use in an ordinary consumer vehicle." (emphasis added)
Edited by fbov, 01 March 2018 - 12:21 PM.