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BMW's ideas tackle IC engine inefficiencies

Acknowledging the inherent inefficiency of the IC engine, BMW has developed methods to improve the energy balance within the vehicle by focusing on two issues: unnecessary consumption of electrical energy and more efficient conversion of energy into electrical power

Intelligent alternator control (IAC) and a regenerative brake system are the technologies to be used for this purpose. De-coupling ancillary drives from the engine began in 2004 with the introduction of electric coolant pumps on straight six engines.

The battery does not require an uninterrupted supply of electrical charge from the alternator; a belt drive from the crankshaft pulley needlessly consumes engine power some of the time.

BMW plans to drive the alternator primarily when the vehicle does a lesser requirement for power from the engine: on the overrun and during braking. When the vehicle is under power, the alternator need not always be operating and so can remain “passive.”

In such operations, for example when accelerating for example, system requirements for electrical power will be met by the battery. The alternator will operate again when battery charge is insufficient or when the next the car brakes or overruns.

This will enable more efficient use of the chemical energy in the fuel, because more of the power developed by the engine will be used to propel the car instead of needlessly driving an electrical consumer. This enables stringer acceleration and can be considered a “passive” form of boosting engine output.

Regeneration of energy is achieved on overrun via the alternator and from the braking system immediately the brakes are applied. A power converter is fitted directly within the system and converts into electricity energy otherwise wasted on the brake discs.

Further efficiency improvements are made through carefully matching the state of charge of the battery to driving conditions and demand placed on the electrical system. Typically, the battery will only be charged to 80 per cent capacity under normal driving, but ensuring the correct reserve of electrical energy requirements when the vehicle is stationary and for starting.

Higher charge levels are only effected during regeneration phases.

Not all lead/acid batteries are suitable for this regime of frequent charging and discharging so in combination with IAC, BMW specifies absorbent glass mat (AGM) types. These use microglass mats between the lead plates, and aid energy storage over long periods. They are far more costly but the higher cycle strength and longer life make then more suitable for applications such as these.

BMW claims that combining these technologies to offer on-demand generation of electrical energy can help to reduce fuel consumption by 4 per cent.