Truck Essential Power Systems Efficiency Improvements for Medium-Duty Trucks (2007)

With a variety of hybrid vehicles available in the passenger car market, electric technologies and components of that scale are becoming readily available. Commercial vehicle segments have lagged behind passenger car markets, leaving opportunities for component and system development. Escalating fuel prices impact all markets and provide motivation for OEMs, suppliers, customers, and end-users to seek new techniques and technologies to deliver reduced fuel consumption. The research presented here specifically targets the medium-duty (MD), Class 4-7, truck market with technologies aimed at reducing fuel consumption. These technologies could facilitate not only idle, but also parasitic load reductions. The development efforts here build upon the success of the More Electric Truck (MET) demonstration program at Caterpillar Inc. Employing a variety of electric accessories, the MET demonstrated the improvement seen with such technologies on a Class 8 truck. The Truck Essential Power Systems Efficiency Improvements for Medium-Duty Trucks (TEPS) team scaled the concepts and successes of MET to a MD chassis. The team designed an integrated starter/generator (ISG) package and energy storage system (ESS), explored ways to replace belt and gear-driven accessory systems, and developed supervisory control algorithms to direct the usage of the generated electricity and system behavior on the vehicle. All of these systems needed to fit within the footprint of a MD vehicle and be compatible with the existing conventional systems to the largest extent possible. The overall goal of this effort was to demonstrate a reduction in fuel consumption across the drive cycle, including during idle periods, through truck electrification. Furthermore, the team sought to evaluate the benefits of charging the energy storage system during vehicle braking. The vehicle features an array of electric accessories facilitating on-demand, variable actuation. Removal of these accessories from the belt or geartrain of the engine yields efficiency improvements for the engine while freeing those accessories to perform at their individual peak efficiencies to meet instantaneous demand. The net result is a systems approach to fuel usage optimization. Unique control algorithms were specifically developed to capitalize on the flexibility afforded by the TEPS architecture. Moreover, the TEPS truck technology mixture exhibits a means to supplant current accessory power sources such as on-board or trailer-mounted gasoline-powered generators or air compressors. Such functionality further enhances the value of the electric systems beyond the fuel savings alone. To demonstrate the fuel economy improvement wrought via the TEPS components, vehicle fuel economy testing was performed on the nearly stock (baseline) truck and the TEPS truck. Table 1 illustrates the fuel economy gains produced by the TEPS truck electrification. While the fuel economy results shown in Table 1 do reflect specific test conditions, they show that electrification of accessory hardware can yield significant fuel savings. In this case, the savings equated to a 15 percent reduction in fuel consumption during controlled on-road testing. Truck electrification allows engine shutdown during idle conditions as well as independent on-demand actuation of accessory systems. In some cases, independent actuation may even include lack of operation, a feature not always present in mechanically driven components. This combination of attributes allows significant improvements in system efficiency and the fuel economy improvements demonstrated by the TEPS team.