Brake Energy Regeneration: an energy-saving innovation.

The new BMW 5-Series sedan continues the roll-out of BMW's Brake Energy Regeneration system on US models. To save energy and reduce the vehicle's fuel consumption over time, this system manages the times at which the alternator charges the battery.

Conventionally, a car's alternator runs continuously and thus is always charging the vehicle's battery. In the new BMW 5-Series, it charges only when the vehicle is decelerating or braking; otherwise, it freewheels and draws virtually no power from the engine. An electronically controlled clutch, similar to that used with the air-conditioning compressor, is used to engage and disengage the alternator.

Accommodating the less-frequent charging is a special, more powerful vehicle battery that can satisfy the vehicle's high electrical demands without access to continuous charging. The battery uses a technology called "glass mat," in which its internal plates are separated with saturated absorbent glass-boron silicate rather than the usual liquid electrolyte. This construction sharply reduces the battery's conversion of charging energy to heat, and can provide the necessary electrical power for longer periods between charges.

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