What Is a Hybrid Electric Vehicle?

A hybrid electric vehicle (HEV) combines two or more sources of power, such as an internal combustion engine (ICE) and a battery, or a fuel cell and a battery with an electric drive motor. FutureTruck teams have focused on developing HEVs with

A spark-ignited ICE and battery,
A compression-ignition (diesel) ICE and battery, or
A fuel cell and battery.

In each case, the engine or fuel cell is the primary power source for the vehicle.

To conserve fuel, the engines have been downsized to meet the average power (as opposed to peak power) requirement of the vehicle. During high load conditions, such as for passing and steep inclines, the energy stored in the battery is used to operate an electric motor, providing additional power. Some HEVs also recapture energy normally lost during braking (a process called regenerative braking) to help recharge the battery.

These types of HEVs generally don't ever need to be plugged in and charged — they recharge themselves during operation. One exception to the "plug-less" HEV concept is the FutureTruck vehicle designed by the team from the University of California, Davis, which developed a plug-in HEV to reduce vehicle tailpipe emissions and maximize vehicle energy efficiency. This design philosophy permits a more powerful battery and electric-drive system, which increases the "electric only" driving distance of the vehicle and means some of the energy the vehicle uses is "off board" energy (electricity) that can come from renewable sources. The fact that the vehicle can be driven a longer distance in electric only (50 miles or so) means that it is more attractive in high pollution areas.

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