The US Department of Energy has provided funding to Caterpillar to investigate the benefits of increased electrical auxiliaries for highway trucks.  Electrical auxiliaries include the oil pump, the water pump, the air compressor for the vehicle brake system and an electric HVAC (Heating Ventilation & Air Conditioning) system. 

The heart of the system is the SR Drive^® starter/generator unit which is mounted between the engine and gearbox inside a modified flywheel housing.  The intention of the starter/generator is both to provide a direct-drive capacity to start the engine and also to generate the required electrical power for the various auxiliaries.

Switched Reluctance Drives Ltd supplied a 340V, 1200Nm, 30kW crankshaft mounted SR Drive^® starter-generator designed specifically to fit within the challenging space envelope occupied by the conventional flywheel and clutch. 
The system uses position sensorless control to provide rapid engine starting and to maximise system reliability in the extreme environment in which it is located.

Extensive on-highway trials have shown the system to be robust, requiring no maintenance intervention since the truck was commissioned in 2003. The same trials have confirmed a significant fuel economy benefit and work is underway to make further improvements by increasing the functionality of the ISG to provide engine assist during pull away.

Developed as part of the US DoE programme reference DE-FC04-2000AL67017.