BMW to Offer Intelligent Alternator Control/Regenerative Braking on Non-Hybrid 5-Series

12 January 2007

BMW will begin offering its Intelligent Alternator Control and Brake Energy Regeneration on select models of the new 2008 5-Series. Announced last year at the Paris Auto Show, the Intelligent Alternator Control (IAC) system generates electric power for a car’s on-board network exclusively in overrun and during braking. (Earlier post.)

On a conventional car, the alternator, which generates electrical power, is permanently driven via a belt from the crankshaft. The BMW system, however, limits the use of the alternator mostly to drive phases in which the engine is not required to deliver drive power—e.g., in overrun and when applying the brakes.

,Accordingly, a greater share of the fuel energy is applied to drive the car. The use of the IAC can reduce fuel consumption by approximately 3%. The supply of power to the on-board network will be provided exclusively by the battery, the alternator only being re-activated when the engine moves into overrun or if battery charge is insufficient.

The battery is charged to only about 80% of its capacity as long as the engine is propelling the car, depending on ambient conditions. A reserve charge adequate for the consumption of power while the car is at a standstill and enabling the driver to start at any time is maintained under all circumstances.

Battery charge exceeding the 80% threshold is generated only in overrun and while the driver is applying the brakes. Since the number of charge cycles increases as a function of such battery management, BMW’s Intelligent Alternator Control uses modern AGM (absorbant glass mat) batteries able to handle greater loads than conventional lead acid batteries. An AGM battery holds the acid content in micro-glass-fibre mats between the individual layers of lead, thus retaining its ability to store energy also when charged and discharged frequently and in many ongoing cycles.

In addition to the reduction in fuel consumption, the driver benefits directly from the alternator being disconnected whenever the engine is propelling the car, since this ensures more power for dynamic acceleration and superior performance—attributes BMW considers its hallmark.

The new 5 Series with the new 6-cylinder engines is also using a new on-demand electrical coolant pump that consumes significantly less power than a conventional pump and helps the engine reach its normal operating temperature earlier.

Operating on-demand, the Varioserv steering assistance pump, varying the curve ring as a function of pressure and volume flow, avoids the usual increase in drive losses as a function of higher engine speeds. And when the driver and passengers do not require the air conditioning, the a/c compressor is disconnected to reduce drag forces to a minimum.

Use of the on-demand pump can reduce fuel consumption by up to 2%.