“Voltec” is the brand name for GM’s revolutionary extended-range electric vehicle (E-REV) technology that uses electricity as its primary power source and gasoline as its secondary power source to generate electricity. The main components of the Voltec electric propulsion system include a T-shaped battery pack, an 111 kW electric drive unit, and an engine generator of electricity.

An E-REV like the Chevrolet Volt represents a significant departure from conventional hybrids. In a E-REV, the wheels are turned by an electric drive unit, whereas in conventional hybrids the wheels are turned by an electric motor, a gasoline engine, or both. For short trips, E-REVs will run on battery power alone. For longer trips, additional electricity can be supplied by an internal combustion engine or a fuel cell. The battery and propulsion systems are sized so that when sufficient energy is available from the battery, the engine (or fuel cell) is not required for operation. During this electric only phase of driving, the battery, motor, and power electronics are designed to deliver full performance, acceleration, top speed, hill climbing on electric power alone.

How Voltec Works

Energy is stored on board in a 16-kWh, “T”-shaped lithium-ion battery pack. The battery pack powers the electric drive unit, which is capable of meeting full vehicle speed and acceleration performance while driving the car electrically for up to 40 miles (64 km) (based on EPA city cycle) without using a drop of gas. For longer trips, the Volt’s on-board range-extending engine is used to drive an electric generator when the battery’s energy has been depleted. The range extender, which can be powered by gas/E85 Ethanol, is able to generate additional electricity to power the car for hundreds of miles.

A new and distinct propulsion system category that would comprehend E-REVs has been proposed by the California Air Resources Board, which GM expects that the Chevrolet Volt will become the first to qualify. Other government agencies are also considering the unique benefits of E-REVs.

Benefits

There are many benefits of an E-REV like the Chevrolet Volt. The main benefits include energy diversification, reduced oil consumption, and reduced emissions.

According to a Society of Automotive Engineers study published by GM in April 2008, an E-REV will consume, on average, less than half of the gasoline compared to a plug-in hybrid and substantially reduce regulated emissions resulting from initial trip starts. According to a 2003 Omnibus Household survey by the U.S. Department of Transportation, nearly 80 percent (76 percent) of U.S. drivers commute 40 miles or less daily.

GM estimates that the Chevy Volt will save about 500 gallons (1,892 liters) of gasoline based on 40 miles of daily driving and 15,000 miles annually. For drivers that commute 60 miles (96 km) per day or 21,000 miles annually, about 550 gallons (2,081 liters) of gasoline could be saved.

As a baseline comparison, GM estimates that the cost per mile to operate an E-REV like the Chevy Volt is approximately two cents per mile electrically versus 12 cents per mile using gasoline priced at $3.60 per gallon.

Not a “hybrid”

In practice, hybrid vehicles typically require both sources – engine and battery – to provide full vehicle performance capability. In a hybrid vehicle, the combustion engine is typically the larger of the two propulsion sources, and provides most of the power during high power vehicle maneuvers like off-line starts and freeway cruising. A plug-in hybrid operates the same way, but can be recharged by plugging in. Even with useful energy in the battery, the engine will often be operating to achieve vehicle peak loads. An E-REV is unique from a hybrid or plug-in hybrid in that the vehicle’s wheels are always driven electrically by an electric drive unit.