Mild hybrids with a small electric motor/generator (as compared to full hybrids) have the ability to crank over the engine, provide an on-demand acceleration power boost, and incorporate regenerative braking. The electric motor/generator is not sized to provide sustained electric-only mode, but by reducing peak demands on the engine it does allow the engine to be downsized (without losing performance). Mild hybrid vehicles also apply automatic start-stop technology.
Belt-Driven Electric Motor/Generator. In a belt-driven electric motor/generator system, the alternator and starter are combined into one unit. Also known as a belt-alternator-starter (BAS) system, the electric motor/generator connects to the engine via a serpentine belt and is mounted like a traditional alternator. GM calls their system eAssist.
Crank-Driven Electric Motor/Generator. In a crank-driven electric motor/generator system, the unit is connected between the engine and transmission. Like the belt-driven system, the crank-driven electric motor/generator works with the engine to supply additional power when needed. Honda Motor Company calls their system Integrated Motor Assist (IMA).