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Hybrid Technology Terms

Understanding the Different Classes of Hybrid Vehicles

By

2012 Toyota Prius Plug-in Side View

Toyota recently introduced a plug-in version of its popular hybrid with the launch of the 2012 Prius Plug-in.

Photo: Toyota Motor Corporation

Hybrid technology continues to evolve as consumers demand more from these alternative energy vehicles. But with several variations of hybrid technology being utilized in vehicle manufacture the last several years, it can get confusing to understand how a hybrid works and what defines a hybrid vehicle.

Hybrid vehicles exist to improve fuel efficiency. Like the label suggests, these vehicles have two sources of power lurking under the hood: a conventional gas combustion engine as well as an electric motor. How these two work in unison is core of hybrid vehicle existence.

To Plug or Not to Plug
So-called plug-in hybrid cars are designed to go long distances powered only by the electric motor. These plug-in hybrids still need to be plugged in between drives to keep the batteries charged and the electric motor available, much like a full electric car, if the driver wants to take full advantage of the fuel efficiency these vehicles have to offer. These plug-in hybrids still have a gas combustion engine on board, allowing the driver to continue driving even beyond the limits of its electric motor. An example of a plug-in hybrid is the Chevy Volt.

However, conventional hybrid vehicles do not need to be plugged in. When the on-board batteries of these hybrids fall below a certain level of charge, their gas engines will automatically be engaged, charging the batteries, driving the car and even charging the electric motor if necessary. That's why this kind of hybrid car never needs to be plugged into an electrical outlet overnight. There are many examples of this kind of hybrid, including the Toyota Prius, with many more appearing on the market each year.

Plug-in hybrid cars typically have larger battery packs and are aimed at getting approximately 2x the fuel efficiency of conventional hybrids. Plug-in hybrids operate very much like an electric vehicle, except that they do have a gas combustion engine to take over should the battery become depleted. These plug-in hybrids answer consumer concerns that they could become stranded in an all-electric car.

Electric Motor Versus Gasoline Engine
When driven at slower speeds, such as those found in residential street driving or stop and go traffic, the hybrid vehicle will save fuel use by relying primarily on its electric motor which is powered by rechargeable batteries. When the brake is pressed, the car's wheels engage an electric generator which creates an additional "load" to help slow the car down. Referred to as regenerative braking, the more important piece of this process is that the generator also converts the car's mechanical energy back into electricity. This electricity is used to recharge the car's batteries that power the motor.

But what about when you're cruising down the highway? Your car's internal computer will tell it to switch over to the gas-burning engine as the primary energy source for the car. Hybrid cars generally have a smaller engine designed with variable valve timing intelligence as well as other technological advancements that help the hybrid vehicle burn fuel as efficiently as possible, contributing to better efficiency even while under the power of the gasoline combustion engine.

However, there are also times when both the gas-powered engine and the vehicle's electric motor will work in tandem. For instance, when you merge into traffic or speed up to pass someone, your hybrid will rely on its electric motor to give your car that added burst of power to complete the task as efficiently as possible.

It's easy to see why hybrid vehicles of both types have garnered increased interest as gas prices have continued to climb. When idling, these vehicles can sit quietly and avoid burning fuel whereas conventional cars will be wasting fuel by the minute. Hybrids are primarily targeted to alleviate concerns consumers have had over managing an all-electric vehicle and have therefore grown more steadily in popularity than their all-electric counterparts.

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