United States Department of Transportation
i
Improving the Energy Density of Hydraulic Hybrid Vehicles (HHVS) and Evaluating Plug-In HHVS
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2010-10-01
[PDF-436.55 KB]
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Edition:Final report
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NTL Classification:NTL-ENERGY AND ENVIRONMENT-ENERGY AND ENVIRONMENT;NTL-ENERGY AND ENVIRONMENT-Alternative Fuels;
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Abstract:This report describes analyses performed by researchers at The University of Toledo (UT) in collaboration with researchers at the University of Detroit Mercy (UDM) on the project “Improving the Energy Density of Hydraulic Hybrid Vehicles (HHVs) and Evaluating Plug-In HHVs.” UT researchers proposed a way to increase the energy density of standard hydraulic hybrid vehicles through an air tank/switching design. Basing on a symbolic program developed in MATLAB/Simulink of a Class VI delivery truck powered by a 7.3 liter diesel engine and a hydraulic pump/motor unit, a parallel hybrid simulation model for the new system was developed. The simulation model includes all the system components such as the vehicle, the air tank, the accumulators, the pressure exchangers, the hydraulic pump/motor, the compressor and the internal combustion engine (ICE). The power management system is implemented based on using all the available hydraulic power. The main objective of this model is to evaluate the average fuel economy (FE) for the Hydraulic hybrid vehicle (HHV) with the added compressedair system. This model is tested basing on the federal urban drive schedule (FUDS). The simulation results with various configurations have not shown a significant improvement in the fuel economy. This report provides a detailed analysis about the results from the system structure and the energy losses. In this system, there are two alternating accumulators. Every time the accumulator switches to a reservoir, energy will be lost. When the engine drives the compressor to recharge the air system, a large engine would be needed to power such a compressor. These are the main reasons for the poor fuel economy of the proposed HHV system. The scope of the UDM analysis included two tasks: verification of UT’s results through some relatively simple thermodynamic calculations, and evaluation of the “plug-in” feature of a modified air system. The calculations confirmed UT’s conclusions about the infeasibility of the original design, and a Simulink model developed to evaluate the plug-in feature demonstrated that even with some design improvements, the air system still results in significant energy loss through the venting that must occur as part of the accumulator switching process. Simulations of a truck and two passenger vehicles were performed.
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