Volt has two of practically everything: Two forms of portable energy (gasoline and electricity). Two electric motor-generator machines. Two primary modes of operation-using electricity stored in the lithium-ion battery pack or the energy available from 9.3-gallons of premium gasoline carried in a sealed tank. And two distinct transmission ranges. That yields a Rubik's cube of driving possibilities. To provide 40 or so miles of pure-electric operation and 300 or so miles of 'extended' range with the gasoline engine running, the Volt has five distinct operating routines.
1. Leaving home with a fully charged battery pack provides 40 or so miles of driving range with the engine and generator inoperative. The 149-hp permanent-magnet AC motor draws electricity from the 16kWh battery pack to drive the front wheels through a 7.0:1 speed reducer/torque multiplier.
2. Like any energy-conversion device, electric motors are more efficient at certain operating speeds. When the Volt exceeds fifty mph, a clutch holding the planetary gear set's ring gear is released. A second clutch engages to connect that ring gear to the smaller of the two electric motors. Now both electric motors draw electricity from the battery pack and the effective drive ratio shifts to 2.16:1. Top speed is governed at 100mph.
Hybrid Gasoline and Electric Propulsion
3. When the Volt's battery is depleted to a 30-percent or so state of charge, the gasoline engine is automatically started to give the battery a rest. The clutch connecting the gasoline engine to the smaller electric machine closes so that this device, now acting as a generator, can provide electricity to the main electric-drive motor. Another clutch holds the ring gear fixed, yielding a 7.0:1 overall drive ratio between the motor and the half shafts powering the Volt's front wheels. This regime is used for speeds below 30 mph.
4. At higher cruising speeds, the planetary ring gear is again released, shifting the AC motor drive ratio to 2.16:1. The engine continues providing the power to spin the generator which in turn supplies the drive motor with electric current. In addition, the engine supplies torque to the planetary ring gear through the smaller electric machine. (This is the engine driving-the-wheels scenario heretofore denied by GM.) Operating in this regime, the Volt is both a series hybrid and a parallel hybrid.