A hydraulic hybrid vehicle draws propulsion power from an internal combustion engine as its prime mover and a gas-charged hydro-pneumatic accumulator as its energy buffer. The accumulator serves the purposes of storing regenerated braking energy and supplementing engine power as determined by an on-board power management strategy. In the configuration known as a series hydraulic hybrid powertrain, the engine is mechanically decoupled from the vehicle's wheels thereby offering excellent opportunities for maximizing energy efficiency and reducing pollutant emissions.;This thesis dealt with the development of a causally interconnected, non-linear, dynamic model of a series hydraulic hybrid powertrain featuring independently controllable wheel-end drives. Using the model so developed, the work investigated the potentials of three proposed power management strategies on the fuel/energy use of a test vehicle. The strategies studied included: a real-time implementable rule-based strategy, an on-line solvable instantaneous consumption minimization strategy, and a non-causal trip/globally optimal power management strategy based on dynamic programming.;The results indicated that, when properly designed, all three power management strategies can help realize the fuel economy benefits of the proposed hydraulic hybrid drive system. Over a standard city drive cycle, the rule-based power management strategy was shown to provide a fuel economy improvement of more than 30% with four-motor drive over the conventional drive system. The trip/globally optimal strategy obtained via dynamic programming gave an average of over 50% higher fuel economy improvement with four-motor drive. The instantaneous consumption minimization strategy, which is adopted to overcome the non-causality of dynamic programming and the lack of rigorous optimality of the rule-based strategy, gave fuel economy improvements that generally fell between the other two strategies. Results are also included from the analysis of the effects of accumulator size and two-motor vs. four motor drive options along with the choice of the power management strategy.
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