Hybrid vehicles appear to be all the rage these days. Advertisements boast of impressive gains in fuel economy, and newer technologies reduce any lags in performance when compared to traditional gasoline-powered vehicles. But how exactly do hybrid vehicles work to bring about such changes? Today's hybrid cars use a combination of several features.
As you recall from physics classes, a moving car possesses kinetic energy. The faster the car moves, the more the kinetic energy. Applying the brakes uses friction to slow down the wheels. During this process, the kinetic energy gets burned off as heat. In regenerative braking, the electric motor assists in stopping the car. The motor behaves like a generator by capturing some of the kinetic energy before it's lost. This energy is converted into electricity and stored in the rechargeable battery for later use.
Electric Motor Drive/Assist
At the very least, a hybrid vehicle uses two different methods to provide power to the wheels. The current hybrids on the market combine a gasoline engine with one or more electric motors. In order to truly qualify as a hybrid vehicle, though, the motor and battery pack must be large enough to supplement the engine during acceleration. This permits the use of a smaller and more fuel-efficient gasoline engine without sacrificing performance.
Automatic Start and Shutoff
Some conventional vehicles even have the capability to turn off the gasoline engine when idling. When the accelerator is pressed, the engine turns on again instantly. This design saves fuel significantly. Hybrid vehicles accomplish this feat with an electric motor; traditional vehicles use an integrated starter-generator, which usually consists of a beefed up starter motor.
Some automakers incorporate this feature into vehicle design and claim the vehicles as hybrids, but this misnomer is misleading at best. A true hybrid also uses regenerative braking and electric motor drive as described earlier.
Hybrid vehicles that include the above three features are called "mild hybrids." In contrast, "full hybrids" such as the Ford Escape Hybrid SUV and Toyota Prius also offer electric-only drive. This technology powers the vehicle using the electric motor and battery pack; the gasoline engine contributes nothing at this stage. That's why drivers may not realize the car is already turned on – the silent battery system is powering the car rather than the relatively noisy combustion engine. This setup prevents burning gasoline unless the vehicle is operating at its most fuel-efficient capacity. As a result, the gasoline engine doesn't kick in until the car reaches high speeds.
Extended Battery-Electric Range
Today's most advanced hybrid feature is the ability to "plug in" the car to a clean energy grid in order to recharge the battery pack. This imparts the ability to travel up to 60 miles on electric power alone. If the vehicle is not recharged adequately, it can still operate as a full hybrid using the remaining systems outlined above. This feature has yet to gain popularity due to higher up-front costs and to lack of infrastructure to support plugging in vehicles for recharge.
To summarize, these five features largely define today's hybrid vehicles. For a given vehicle, the hybrid type is determined by which features the vehicle offers. When shopping for a hybrid vehicle, understanding the technologies will help you read between the lines to find the best fit for your priorities and lifestyle.
Additional Reading and Resources
Hybrids Under the Hood
How Hybrids Work