Hybridization of the diesel engine has been done here and there mostly by Mercedes Benz. Ultimately, adding a hybrid drivetrain to a diesel engine has complications that gasoline-hybrids don’t suffer from, namely cost (diesel engines are already more expensive to make than gasoline engines) and decreasing returns (diesel engines are already efficient, sometimes as efficient as a comparable hybrid system in mixed driving). VW may have a solution to these problems with their EA288 Evo “mild” hybrid.
The “mild” hybrid design solves the first problem as it is much less expensive than a full hybrid drivetrain. A “mild” system does not use an electric motor directly for powering the wheels. Rather, systems like the one in VW’s EA288 Evo use what could be considered a “super” alternator that puts out 48 volts, rather than the traditional 12, that is used to charge a 48-volt battery, in addition to the normal 12-volt automotive battery. The alternator would be able to work as a motor in some situations, such as engine starting.
The 48 volt system would power accessories that would normally be powered by a belt to be powered using electricity instead. However, VW uses the 48 volt system to drive the air conditioning compressor as well. Stop-start engine systems are already used to turn off the engine when stopped at a traffic light, but typically are disabled when the air conditioning is on. With electronic HVAC the systems would remain fully functional even when the engine is off. The engine could even be turned off and disconnected via a one-way clutch when coasting.
The simplicity of this system is the most impressive part. VW claims this system can be installed in all existing platforms that use the EA288 engine family already. Plus, it addresses diesel’s largest weakness – fuel usage and emissions when idling or in stop-and-go traffic. The small fuel savings, meanwhile, push the already efficient TDI line further above most hybrids.
