The Engineering Meetings Board has approved this paper for publication. It has successfully completed SAE’s peer review process under the supervision of the session organizer. 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 o r by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE. ISSN 0148-7191 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 the paper. SAE Customer Service: Tel: 877-606-7323 (inside USA and Canada) Tel: 724-776-4970 (outside USA) Fax: 724-776-0790 Email: [email protected] SAE Web Address: http://www.sae.org Printed in USA Copyright © 2009 SAE International ABSTRACT The superior mobility of a military vehicle provides the combat crew with a tactical advantage through increased cross country speed. The suspension system plays a fundamental role in evaluating a vehicle mobility. A mathematical model that allows realistic simulations of vehicles operating in a wide spectrum of environmental conditions may help to lower costs and time required during their development. The paper concerns with vehicle-terrain interaction modeling, for a military tracked tank, through multi-body and block-oriented approaches. It is focused on the consequences that the suspension system has got on the comfort and on the performance. Thus through a multi-body software a realistic three dimensional model of a tracked fighting vehicle is developed. This virtual model confirms some experimental data available on its longitudinal dynamics. In order to simplify the multi-body simulations, a block-oriented approach is adopted to develop a model of the same vehicle. Some dynamic simulations are discussed in order to validate the proposed models and to compare the two different approaches. INTRODUCTION As all vehicles a tank is a mechanical system which receives various actions from the environment during mobility. These actions include forces exchanged with the terrain which reach the driver and the passengers through the suspension system. The longitudinal dynamics of a tracked military vehicle, namely an M113 that is in use with the U.S. military and many other nations involved in NATO, is analyzed by means of three-dimensional multi-body or simplified block-oriented models. The paper deals with the consequences that the suspension system has got on the comfort and on the performance. Increasing dynamic modeling and suspension design of tracked military vehicles means to be able to provide Armed Forces with the equipment they need in order to perform worldwide missions quickly and at low cost [1]. Military vehicle designers must provide the capability for high speed off-road travel under adverse conditions and often in unfamiliar territory. These requirements present a continually increasing challenge to the suspension and traction system engineers, since each new vehicle created for a military application must be more mobile and operate at higher cross country speeds than the vehicle already developed in the military system. These requirements have brought about evolutionary changes in military vehicle suspension design and have forced designers to look for new and better ways to advance the state of the art. For the majority of military applications, the choice of tractive elements is limited to tracks and wheels; hence, the choice of suspension designs is similarly restr ictive. Test experience and actual use have shown most tracked vehicles to be more mobile than wheeled vehicles on unprepared surfac