Is it two drive trains? I thought ideally PHEV would be like diesel-electric with electric motors supplying traction and a gas power plant supplying power.
Gears are more efficient (assuming you are not stupid in design) than an electric generator and motor. We cannot make gears that will do the job for a train - they wouldn't fit between the wheels while also doing the needed 90 degree turn to the engine. Once in a while someone makes such a car, but it is generally better to use a transmission.
