BAS Hybrid

BAS is an acronym for belted alternator starter. It is a category of automotive parallel hybrid technology that uses an electric motor to contribute power to the internal combustion engine's crankshaft via a serpentine belt. By mounting this motor generator unit in the conventional location traditionally used for the standard automotive alternator, it permits a low-cost method of adding mild hybrid capabilities such as start-stop, power assist, and mild levels of regenerative braking. BAS differ from other mild hybrid systems as they are not run off the vehicle's crankshaft.

General Motors introduced a mild hybrid system called belt alternator starter (or BAS) in the 2007 Saturn Vue Green Line. The BAS system is also used in the Chevrolet Malibu Hybrid. It operates similarly to other mild hybrids with a start-stop system, in that it shuts down the engine as the vehicle comes to a stop and instantly restarts it when the brake pedal is released.

The BAS system is capable of providing modest levels of power assist during launch/acceleration and similarly modest levels of "blended" regenerative braking during deceleration. Although unable to operate in pure all-electric EV mode, the BAS system provides improvements to both city and highway fuel efficiency over similar non-hybrid versions. In more powerful eAssist versions, a BAS system can add power to prevent excessive gear changes under variable load. According to the EPA the 2009 Saturn Vue BAS hybrid garners an improvement of 32% city (19>25mpg) and 24% highway (26>32mpg) making the combined economy improvement 27% (22>28mpg) over the base 4cyl FWD version. The system is reasonably simple and inexpensive, making BAS equipped vehicles some of the least expensive hybrids available.

A 36 volt electrical system (operating at 42-45 Volts) is used to operate a permanent magnet motor/generator unit mounted to the engine in a similar fashion to a conventional alternator. Then through a high-tension drive belt, the BAS system is capable of starting or assisting the 2.4L Ecotec engine. A conventional 12V starter motor is retained and used whenever the engine is cold as during initial start-up. The air conditioning compressor continues to be operated through a belt-driven pulley, but for fuel economy improvement it can be disabled in auto-stop mode if the "ECO" A/C mode has been selected by the operator.

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