Well, we need hybrid automotive systems which only have the purpose of maki ng a lightweight four-wheel-drive.
The four-wheel-drive would operate when accelerating, when at high RPM, and when pulling away from a stop. And this assistance that it provides for pu lling away from a stop is where it adds efficiency to the car.
See, this hybrid car doesn't have an all-electric mode. It has small batter ies, small motors, and small generators such that it is only designed and i ntended to assist the internal combustion engine.
Well, I'll call it a Hi Bird system. Now since the system adds efficiency w hen pulling from a stop and since it adds four-wheel-drive in other situati ons then the internal combustion engine should actually be used to keep the batteries charged. Also, the system is small to be lightweight and needs c harging. So should the Hi Bird system have regenerative braking ? I don't k now but I'm tempted to say no so that the car has normal braking action and to reduce complexity and expense.
Should the Hi Bird system have overnight charging ? I'm tempted to say yes but since so many people live in apartments and condos then why bother ?
Now how does the internal combustion engine keep the small batteries charge d ? Well, the engine charges the batteries at highway speed and gives up ab out 1 MPG in highway driving to gain about 2 MPG in city driving but also t o gain that four-wheel-drive.
The BMW i8 ? No, the i8 has an all-electric mode and thus has very large an d expensive batteries. But the I8 does have layout such that the internal c ombustion engine is in the rear and drives the rear wheels while the electr ic motor is in the front and drives the front wheels. Then the batteries ar e front-mid-ship so that the car itself doesn't have a flywheel tendency wh en turning. In other words it is best to keep the mass of the car between t he front and rear axle lines .