BMW announced: Intelligent Alternator Control and Regeneration of Brake Energy


Efficient Use of Energy for Enhanced Driving Dynamics: Intelligent Alternator Control and Regeneration of Brake Energy

The objective pursued by BMW's engine development specialists is to maximise the standard of driving dynamics developed from every litre or gallon of fuel. And indeed – the combustion engines featured in BMW's latest models offer a significantly higher level of efficiency than the power units in former model generations, consuming less fuel but providing more power and performance.

The fact nevertheless remains that even today only about 25–30 per cent of the energy contained in fuel is actually used for driving the vehicle. Most of the energy consumed is still converted into heat, although the fuel burnt also serves to generate electrical energy for the on-board network. To make the development of electrical energy in the vehicle more efficient,
BMW has developed Intelligent Alternator Control (IAC) serving to generate electric power exclusively in overrun and when the driver is applying the brakes. On the road, this means more energy for enhanced driving dynamics when driving under power with the engine “pulling” the car, for example when accelerating. And to enhance driving efficiency to an even higher level, IAC also incorporates a system for regenerating brake energy. The demand for electrical energy is consistently increasing in the modern automobile. Air conditioning, telecommunications, entertainment, as well as new components for enhanced safety and driving dynamics such as suspension management, Active Steering, engine management, and ABS all require electric power. Hence, the generation of electricity for the car’s on-board network consumes an increasing share of the power generated by the engine. Precisely for this reason BMW has developed IAC in order to generate electrical energy in the car even more efficiently and use that energy for a wider range of purposes and functions.

Already reality today: intelligent management of the flow of energy.

BMW is pursuing two objectives in this process: First, to limit the overall consumption of energy without any loss of function. Second, to control the conversion of energy from fuel into electric power with enhanced efficiency, minimising losses in the overall energy balance. BMW’s current models already incorporate important features and technologies to reach both of these objectives, intelligent management of the flow of energy already being ensured in series production. One example is the new electrical coolant pumps in BMW's straight-six power units already operating exactly – and only – when required, meaning that they develop
their maximum output and performance only at high and very high speeds, while remaining passive immediately after the engine has been started, ensuring in this way that the engine is warmed up more quickly. This alone helps to reduce fuel consumption in the EU homologation test by approximately 2 per cent. BMW has also developed a further energy management system now monitoring the status of the battery in an increasing number of model series: The Intelligent Battery Sensor (IBS) ensures a sufficient level of electrical energy at all times for starting and re-starting the car, preventing any overload in the supply of energy and the risk of discharging the battery as a result. Following clearly defined priorities, the flow of energy to functions serving exclusively to enhance motoring comfort (such as the seat heating or air conditioning) may therefore be reduced, providing sufficient energy at all times for safety-relevant functions and maintaining an adequate reserve for starting
the engine.

Controlled generation of electric power preventing the loss of energy.

Apart from fuel consumption, Intelligent Alternator Control is also able to enhance the time of energy conversion in the interest of maximum efficiency. So far, electrical energy has been generated consistently under all driving conditions and in all phases of motoring, the alternator is driven permanently by a belt running on the crankshaft. In future the alternator is to be driven primarily when the car itself has no need for engine power, that is in overrun or when applying the brakes, while remaining “passive” when the car is under power, with the engine “pulling” the vehicle. This will provide a greater share of the energy contained in the fuel for actually propelling the vehicle, for example when accelerating, with the onboard network being supplied with power exclusively by the battery under such conditions. The alternator, in turn, only becomes active again when the engine switches to overrun or if the battery charge is insufficient.

Brake Energy Regeneration: Turning the brakes into a source of energy.

The objective of this development is to generate electrical energy without using engine power and, accordingly, any of the energy contained in the fuel. Such “inexpensive” electrical energy is generated not only during overrun via the alternator, but also when applying the brakes through recuperation of energy released in the process, a power converter fitted directly within the brake system converting the energy generated upon application of the brakes into electric power and thus feeding energy previously wasted on the brake discs into the car’s on-board network. Direct conversion of fuel into electrical energy is restricted to just a few exceptional cases. An important prerequisite for energy management geared to current driving conditions is to control the battery charge specifically as required. Depending on ambient conditions, therefore, the battery is charged to only about 80 per cent of its capacity whenever the engine is pulling the vehicle, always maintaining an adequate reserve for the consumption of energy at a standstill and for starting the vehicle. A higher charge level is generated only when the vehicle is in overrun or upon application of the brakes, that is in phases with a better energy balance. With the number of charge cycles increasing thanks to these specific control functions, BMW combines Intelligent Alternator Control with modern AGM (absorbant glass mat) batteries able to handle a far higher load than conventional lead/acid batteries by embedding acid in microglass fibre mats between the layers of lead. Such batteries are able to store energy for a long time even when charged and discharged frequently.

Applying the brakes generates electric power, pressing down the gas pedal develops dynamic performance.

Intelligent Alternator Control combined with Brake Energy Regeneration offers two important benefits in practice. First, on-demand generation of electrical energy helps to reduce fuel consumption in the EU homologation test by approximately 4 per cent. Second, the driver benefits directly from the alternator being disconnected when the engine is running under power, enjoying more power for acceleration and dynamic motoring. As a result, Efficient Dynamics means not just enhanced economy, but also greater driving pleasure. Intelligent management of electrical energy offers a significant potential for enhancing the all-round economy of the modern automobile. The strategy is to minimise any loss of energy, increase the regeneration of energy, and streamline the process of mechanical conversion, providing the highest possible share of energy conversion into dynamic, sporting performance.

Every step taken for this purpose is able to significantly reduce fuel consumption, an appropriate combination of the various strategies also helping to enhance driving pleasure. And a further point is that Intelligent Alternator Control combined with Brake Energy Regeneration can be used throughout BMW's entire range of models, offering advantages in terms of Efficient Dynamics to a large number of customers even today.

Source: BMW Press

Btw. Prof. Goeschel said today the system would be available in some BMW vehicles already next year.