Date of Award

5-2010

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Mechanical Engineering

Advisor

Ayalew, Beshah

Committee Member

Vahidi , Ardalan

Committee Member

Law , Harry

Abstract

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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