Accessory Electrification in Class 8 Tractors 2006-01-0215

Fuel costs to operate large trucks have risen substantially in the last few years and, based on petroleum supply/demand curves, that trend is expected to continue for the foreseeable future. Non-propulsion or parasitic loads in a large truck account for a significant percentage of overall engine load, leading to reductions in overall vehicle fuel economy. Electrification of parasitic loads offers a way of minimizing non-propulsion engine loads, using the full motive force of the engine for propulsion and maximizing vehicle fuel economy.

This paper covers the integration and testing of electrified accessories, powered by a fuel cell auxiliary power unit (APU) in a Class 8 tractor. It is a continuation of the efforts initially published in SAE paper 2005-01-0016. Electrified accessories include the engine cooling system, complete with electric water pump and radiator fans; the cabin air conditioning system, including compressor, remote condenser, and fan; and the vehicle compressed air supply system. A 20 kW fuel cell APU supplies 42 VDC power for all electrified accessories. A 34.5 MPa compressed hydrogen storage and supply system, with a capacity of five kg of hydrogen, supplies the APU. Product water from the fuel cell is collected and used as an evaporative-cooling assist for the engine charge air cooler and radiator, thereby minimizing cooling fan-on time. A 42/14 dual-voltage high-efficiency alternator is used to replace the OEM alternator, to provide an alternate source of 42 VDC in the event that the fuel cell is inoperative.

For each electrified accessory, a system description is provided detailing the physical configuration, subsystem design, control strategies, and a summary of energy savings. An overall summary of energy savings during an unloaded (bobtail) cross-country trip is provided.

This work was been performed at Southwest Research Institute and SunLine Transit Agency and is funded by the US Army National Automotive Center. The Class 8 tractor has been tested in service in the desert of southern California, where SunLine Transit Agency is located.