This document discusses hybrid electric vehicles (HEVs). It begins by defining an HEV as a vehicle with two or more energy conversion technologies and energy storage units. The document then lists the objectives of HEVs as maximizing fuel economy, minimizing emissions and costs, and maintaining performance. It also outlines some advantages of HEVs over conventional engines like increased fuel efficiency and reduced emissions. The document provides details on the motor components, vehicle propulsion systems, examples of HEV models, and challenges in the development of HEVs.