400 Commonwealth Drive, Warrendale, PA 15096-0001 U.S.A. Tel: (724) 776-4841 Fax: (724) 776-0790 Web: www.sae.org SAE TECHNICAL PAPER SERIES 2007-01-4151 Simulation Study of a Series Hydraulic Hybrid Propulsion System for a Light Truck Young Jae Kim and Zoran Filipi University of Michigan Commercial Vehicle Engineering Congress and Exhibition Rosemont, Illinois October 30-November 1, 2007 Downloaded from SAE International by Birmingham City Univ, Sunday, August 19, 2018The Engineering Meetings Board has approved this paper for publication. It has successfully completed SAE's peer review process under th e supervision of the session organi zer. This process requires a minimum of three (3) reviews by industry experts. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE. For permission and licensing requests contact: SAE Permissions 400 Commonwealth DriveWarrendale, PA 15096-0001-USAEmail: [email protected]: 724-772-4028 Fax: 724-776-3036 For multiple print copies contact: SAE Customer Service Tel: 877-606-7323 (inside USA and Canada)Tel: 724-776-4970 (outside USA)Fax: 724-776-0790Email: [email protected] ISSN 0148-7191 Copyright © 2007 SAE International Positions and opinions advanced in this paper are those of the author(s ) and not necessarily those of SAE. The author is solely responsible for the content of th e paper. A process is available by which discussions will be printed with the pap er if it is publishe d in SAE Transactions. Persons wishing to submit papers to be considered for presentation or publicat ion by SAE should send the manuscript or a 300 word abstract to Secretary, Engineering Meetings Board, SAE. Printed in USADownloaded from SAE International by Birmingham City Univ, Sunday, August 19, 2018Copyright © 2007 SAE International ABSTRACT The global energy situation, the dependence of the transportation sector on fossil fuels, and a need for rapid response to the global warming challenge, provide a strong impetus for development of fuel efficient vehicle propulsion. The task is particularly challenging in the case of trucks due to severe weight/size constraints. Hybridization is the only approach offering significant breakthroughs in near and mid-term. In particular, the series configuration decouples the engine from the wheels and allows full flexibility in controlling the engine operation, while the hydraulic energy conversion and storage provides exceptional power density and efficiency. The challenge stems from a relatively low energy density of the hydraulic accumulator, and this provides part of the motivation for a simulation-based approach to development of the system power management. The vehicle is based on the HMMWV platform, a 4x4 off-road truck weighing 5112 kg. The development of the component models and system integration in SUMULINK are discussed before addressing the configuration (single propulsion motor or two) and component sizing. The power management is based on a thermostatic state-of-charge (SOC) approach, but the optimum threshold power and SOC for accumulator charging are determined based on detailed system analysis, rather than the conventional wisdom of operating the engine at the “sweet spot”. The results indicate significant advantages of reduced threshold power. Relatively low target SOC led to improved ability to capture the braking energy. Engine shut-downs are considered too. The fuel economy predictions for the optimized hybrid system indicate improvements of 68% (with engine shut-downs) under urban driving conditions, and tangible benefits in highway driving. INTRODUCTION Concerns about global crude oil supplies and growing environmental concerns provide a strong impetus for developing fuel-efficient vehicle technologies. The bulk of the fo