The Volt Gen 1 used the engine primarily to run the generator, although the mechanical coupling ability existed in Gen 1 as well. Gen 2 optimized the system to couple the engine to the wheels whenever it is efficient to do so, when an engine mode is selected or the battery is run out.
However, besides from the formal classification debates, I submit that the Volt meets the primary customer visible "EREV" behaviour: it drives like an electric car with the full available power (the engine never comes on) until the battery is depleted or a different drive mode is explicitly selected. All other PHEVs use the gas engine to assist when full power is called for by default, unless the "EV" mode is explicitly selected. The Volt, as far as I know, is the only EREV/PHEV that had that behaviour.
The only other example of a series EREV I know of where the engine is small and fully decoupled from the mechanical drive train is the Mazda MX-30R, which never made it to the US and was discontinued in EU and Japan after a short two year lifespan.
However, besides from the formal classification debates, I submit that the Volt meets the primary customer visible "EREV" behaviour: it drives like an electric car with the full available power (the engine never comes on) until the battery is depleted or a different drive mode is explicitly selected. All other PHEVs use the gas engine to assist when full power is called for by default, unless the "EV" mode is explicitly selected. The Volt, as far as I know, is the only EREV/PHEV that had that behaviour.
The only other example of a series EREV I know of where the engine is small and fully decoupled from the mechanical drive train is the Mazda MX-30R, which never made it to the US and was discontinued in EU and Japan after a short two year lifespan.