[hx87]

GM initially promised that the first generation Volt would be fully series-hybrid--the engine would drive the electrical generator and have no mechanical connection to the rest of the powertrain. This means that the engine can spin at its most efficient RPM (most of the time, peak torque RPM) regardless of how fast the car is going and thus everything on this engine could be optimized to run at that speed, which reduces wear and maintenance requirements. However at the last moment GM revealed that at certain times the engine would drive the wheels directly, probably to prevent some idiots from driving at maximum power and depleting the battery.

[projektfu]

The Volt has a planetary gear system that is engaged at highway speeds when the gas engine is being used anyway. At certain speeds, it uses less gas to maintain speed that way instead of generating electricity and using it. When it is more efficient for the engine to supply electricity only, that is how it is done. I don't view this as a compromise at all. It wouldn't make sense to chose a less efficient path just to maintain some sort of purity.