Abstract
This work investigates the fuel energy and emission reductions possible with the hybridization of a Class 8 tractor-trailer. The truck tractor has two drive axles: one powered by an internal-combustion-engine-based powertrain (CP) and the other powered by an electric powertrain (EP) consisting of an electric drive system supplied by a battery pack, resulting in a through-the-road hybrid. The EP has two modes of operation depending on the direction of power flow: motoring/battery discharging and generating/battery recharging. Switched optimal control is used to select between the two modes of EP operation, and a recently developed distributed switched optimal control is applied. The control is distributed between the CP, the EP, and the vehicle motion operation components. Control-oriented, component-specific power flow models are set forth to describe the dynamics and algebraic relationships. Four different tractor-trailers are simulated: the original CP and three hybrids with engine sizes of 15 L, 11 L, and 7 L. Simulations are performed over a short test cycle and two regulatory driving cycles to compare the fuel use, total energy, and emissions. Results show that the hybrids have reduced fuel use, total energy, and emissions compared to the original CP; the reductions and reference velocity tracking error increases as the engine size is decreased. Particularly, fuel use is reduced by at least 4.1% under a charge sustaining operation and by 9.8% when the battery energy can be restored with an off-board charger at the end of the cycle.
Highlights
The application of hybrid power to a Class 8 6x4 truck tractor with a high roof sleeper cab and a long dry van trailer was investigated under distributed switched optimal control and different engine sizings
The heavy-duty hybrid truck is a through-the-road hybrid with one axle driven by a combustion powertrain and the other axle driven by an electrical powertrain composed of an electric drive system and a battery with two modes of operation: motoring/battery discharging and generating/battery charging
Control-oriented power flow models were created for the combustion powertrain and given for the electrical powertrain
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The novelty and contributions of this work are (1) the development of new, controloriented, operating-mode-specific power flow models for a heavy-duty hybrid vehicle powertrain, (2) the definition of a complete set of Class 8 heavy-duty hybrid truck tractor parameters compatible with the power flow models, (3) the application of a recently developed distributed switched optimal control solution method to the power management of both a conventional and a hybrid truck tractor, and (4) the comparison of a conventional internal combustion engine (ICE) truck tractor and three different heavy-duty truck tractor configurations, delineated by their ICE engine displacements, with respect to fuel, total energy, and CO2 emissions over government regulatory driving cycles while moving a fully loaded trailer These actions support the testing of the hypothesis that a through-the-road hybrid with a reduced engine displacement will result in reduced fuel use, total energy, and CO2 emissions compared to the original vehicle.
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