Little did James Atkinson know that when his gasoline engine was patented on August 2, 1887, that it paved the way for the myriad of hybrid cars on the road today. Using a longer intake cycle than the standard four-stroke engine, the Atkinson cycle engine ensures a more efficient conversion of heat to mechanical energy. That comes with disadvantages inherent to its design, however. With a smaller window devoted to compressing the intake air (and the intake valve being open longer), the engine has less power density than a standard Otto cycle engine with a similar displacement, and makes less torque at low rpm.
On hybrids, this downside is mitigated with an electric motor, which makes the most torque at a low rpm. It's technology used not only in cars like the Toyota Prius, but also in the Mercedes-Benz S400 Hybrid, Hyundai Sonata Hybrid and Ford Fusion Hybrid.