How It Works Hybrids are the product of years of research, advancements, and growing levels of sophistication. Powered by lithium-ion energy cells, electric engines work in addition to or alone in hybrid vehicles. However, electric motors are not the only additions to the mix. Many hybrids utilize regenerative breaking, automatic engine shut-offs, and electric motor assist. How do these help? Let me explain. Regenerative breaking is a function that significantly increases the practicality of an electric powertrain. When an electric motor runs, electricity is taken from the batteries to power the vehicle. Regenerative breaking simply recharges the battery on-the-go. When a car slows down using the brakes, heat energy is created by the contact of the brake discs and the pads, so engineers developed a technology that will harness this energy so that it can be reused for more electric power. Automatic engine shut-off is a technology being utilized all over the industry including a handful of hybrid offerings from GM, Ford, Honda, and Toyota. When a car is idle, theoretically you are getting 0.0mpg and in stop and go traffic, idling can use quite a bit of gas. The goal of shutting off the gas engine is simply that you can wait on traffic and not have to waste gas at the same time. On a variety of hybrids, the gas engine can even shut-off when the car is at cruising speeds so that the energy efficient electric engine can take over. Another variation of this is used on conventional combustion engines as well and it is known as vehicle cylinder deactivation. Commonly this allows the car to shut-off half the maximum amount of cylinders when the added power is not necessary. An example of this is found in the 2008 Honda Accord V-6. The 6 cylinder engine can deactivate 2 or 3 cylinders accoring to the situation meaning that the car can run at certain speeds as a 4cyl, or 3cyl car. Fuel ecomony strongly benefits from this technology. Finally, another key technology is electric motor assist.It is common (but not in all cases) that hybrid models/variants lack the stronger gas engine performance of non-hybrid siblings or competitors therefore any added force counts. Electric motor assist allows both the gas and electric engines to co-operate so that there is a greater net force pulling the car. Strong cases of this are found in the Lexus GS-450h and in the discontinued Honda Accord hybrid. Both these cars have strong combustion engines and the electric motors are added not only to increase efficiency but performance as well. By adding the electric motor horse power is added and in many cases the addition is greater than 15hp. This can give a hybrid an extra push when passing or traveling uphills that allows them to stand up to peoples performance needs. |  Lexus GS450h Cutaway (for visual purposes) 
See through view of Prius electric motor  Active energy flow diagram found in Toyota Prius |