Belt alternator starter

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General Motors introduced a mild hybrid system called belt alternator starter (or BAS) in the 2007 Saturn Vue Green Line. It operates similar to the "start-stop" system used in the Chevrolet Silverado Hybrid in that it shuts down the engine when the vehicle comes to a stop and instantly restarts it when the brake pedal is released. A 36 volt electrical system is used to operate all accessory equipment, making the system essentially invisible to the driver. The air conditioning continues to be operated through the crankshaft pulley, but is disabled in auto-stop mode when the "eco" mode is selected.

The BAS system goes slightly further than the Silverado, however, in providing modest power assist for "acceleration feel", according to GM. Although not as effective as other systems, the BAS system is expected to provide about 20% fuel efficiency gain for the compact Vue. The system is reasonably simple and inexpensive, making the Vue Green Line the least expensive hybrid SUV available while also having the highest fuel economy.

One major benefit of the BAS technology is that it fits in the same space as a conventional engine. No modifications were required to the Vue's chassis to accommodate the BAS system, with the battery pack housed in the spare tire well. This allows the Vue Green Line to be produced on the same assembly line as the normal Vue, producing substantial cost savings and allowing the company to adjust production more easily.

The BAS system uses a conventional 4T45-E automatic transmission, although it has been modified to include a more efficient final-drive ratio and includes an electrically-driven pump to provide pressure in auto-stop mode.

This system has already found its way to two other GM models, the Saturn Aura and the 2008 Chevrolet Malibu.