How to give a Prius four-wheel drive

This cut-away rear axle from a Prius illustrates the approach used to give the car four-wheel drive. Developed by Aisin, it uses a relatively small 5 kW induction motor which primarily just provides a boost when the car needs it. Extra efficiency comes from blended gears and a structure that tends to suppress the resistance arising from oil stirring.
NEXT PAGE: Wham, bam, active air dam