Is the Chevy Volt a EREV or a PHEV?

Mac versus PC. Console gaming versus Windows gaming. Mayonnaise versus Miracle Whip. Imperial versus Metric. Toilet paper over or under the roll. Squeezing toothpaste from the bottom or middle.

All these things have polarized people, up to and including divorce. The latest debate — at least on the Internet — is whether the Chevy Volt is an extended-range electric vehicle or a plug-in hybrid.

Chevy Volt: EREV or PHEV?

Chevy Volt: EREV or PHEV?

For some background, let’s talk about car types that we aren’t polarized on:

  • Gas powered cars have an engine that runs through a transmission via a clutch to run the wheels. Many EV enthusiasts call gas-powered cars “ICE” (internal combustion engine) vehicles.
  • Purely electric vehicles have a battery and an electric motor that, through a simple reduction gear, runs the wheels.
  • Hybrid vehicles, like the Toyota Prius, have an ICE with a small electric motor on the same drivetrain which goes through a transmission and clutch to drive the wheels. While the ICE can be turned off allowing for low-speed EV driving, that’s not typical of how the Prius works.
  • Plug-in hybrid vehicles are like regular hybrids, but with a larger battery and the ability to charge from an external electrical source. This allows them to drive farther in electric-only mode than their hybrid cousins.

Now, let’s talk about the Chevy Volt. When the vehicle was first introduced, Chevrolet said it would be an extended-range electric vehicle (EREV), where the ICE has no direct connection to the drivetrain. Wonderful! That is the definition of an EREV. This is exactly how the BMW i3 and the Fisker Karma works. Only the electric motor runs the wheels.

However, after doing efficiency testing, Chevrolet found that certain conditions — especially during high-speed driving — that it was more efficient to have the electric motor and the ICE powering the drivetrain. To facilitate this, Chevy designed a clever 3-clutch system.

Illustration of the drive motor, charging motor, and the ICE.

Illustration of the drive motor, charging motor, and the ICE.

The Volt can be powered directly from the drive motor, like an EV, when all the clutches are opened. However, when all the clutches are closed, there is a direct connection between the two motors and the ICE to the drivetrain. This fits the definition of a plug-in hybrid, or a “parallel hybrid” system.

See how the three clutches work:

In conclusion, the Volt is a wonderful vehicle, making electric driving available to the masses. Only a slight technicality makes the Volt a PHEV instead of an EREV.

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