Design and Proof Testing of a Composite Containment System for Mobile Applications

As the need for energy storage increases on future hybrid electric vehicles, the desire for increased performance, energy/power densities, and component life increases proportionally. Flywheel batteries have demonstrated power density and life superiority over conventional chemical batteries; however, fears of unexpected and uncontained failures may prevent their widespread acceptance in the United States marketplace. The University of Texas at Austin Center for Electromechanics (UT-CEM) has designed, built, and tested a full-scale composite flywheel containment system for use in mobile applications. The flywheel containment system that will be described stems from an in-depth investigation into the type of faults that are most likely to occur in mobile applications. In all cases, the worst-case scenario results in a challenge to flywheel integrity; therefore, a comprehensive flywheel containment system is considered the “last line of defense” in protecting personnel and equipment. The containment system described is an energy absorption device used in parallel with a UT-CEM flywheel on the hybrid electric Advanced Technology Transit Bus (ATTB). The most important aspect of the containment device is the free-rotating composite liner intended to absorb the energy of a flywheel failure. The current containment design has been developed over a six-year period during the participation of UT-CEM in the DARPA/DOT Flywheel Containment Program. A comparison between a previous full scale containment test (November 1999) and the current configuration is made, illustrating how “lessons learned” from the previous test are integrated into the latest design. The test was conducted in August 2002 and a detailed description of the mounting configuration, test setup, and data acquisition is presented along with results. Of particular interest to the design team was torque on the aluminum containment housing, axial and hoop stresses in the housing, and acceleration. The test was successful in that the composite debris was contained and all metallic structures remained fully intact. INTRODUCTION In May 1996, Argonne National Laboratory (ANL) was contracted to perform a flywheel battery (FWB) safety assessment for a transit bus [1]. All of the key components of the UT-CEM flywheel battery (energy stored, composite flywheel, speed, magnetic bearings, etc.) had been determined and were used as input into the safety assessment model. ANL recommended a “defense in depth” approach to flywheel safety that included: • engineering to avoid accidental initiation of events • incorporating a safety system for the detection of problems • instituting a mitigation system to minimize the risk of low probability events that could result in a significant energy release In their study, ANL engineers identified the five most likely modes of failure: slow loss of vacuum (a leak), rapid loss of vacuum (a failed hose or pump), failure of magnetic bearings, inadvertent flywheel over speed, and startup without vacuum. In all five of the failure modes described above, the worst-case scenario would result in a challenge to the containment system. After a careful review of the report, UT-CEM made the decision to implement the threephase “defense in depth” approach to prevent the onset of flywheel failure initiators. The first step was to apply good engineering principles in the design phase of the project. Secondly, adequate instrumentation (vacuum, magnetic bearing displacement, and speed sensors) combined with a friendly user interface was designed so that a fault in the system would be indicated and easily recognized. As a third line of defense, a lightweight, rotatable composite liner was designed, tested, and built in the unlikely event of a flywheel burst. J.J. Zierer, J.H. Beno, R.J. Hayes, J.L. Strubhar, R.C. Thompson and T. Pak 2004-01-0005 THIS DOCUMENT IS PROTECTED BY U.S. AND INTERNATIONAL COPYRIGHT It may not be reproduced, stored in a retrieval system, distributed or transmitted, in whole or in part, in any form or by any means. Downloaded from SAE International by Brought to you by the University of Texas Libraries, Wednesday, October 02, 2013 11:06:59 AM