400 Commonwealth Drive, Warrendale, PA 15096-0001 U.S.A. Tel: (724) 776-4841 Fax: (724) 776-5760 Web: www.sae.org SAE TECHNICAL PAPER SERIES 2003-01-3256 Study of Viscosity Index Improver for Fuel Economy ATF Nobuharu Umamori and Takanori Kugimiya TonenGeneral Sekiyu K.K. Reprinted From: Lubri cants, Rheology and Tribolog y, and Driveline Fluids (SP–1810) Powertrain & Fluid Systems Conference & Exhibition Pittsburgh, Pennsylvania USA October 27-30, 2003Downloaded from SAE International by Brought to you by the University of Texas Libraries, Monday, August 06, 2018All 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]: 724-772-4891Tel: 724-772-4028 For multiple print copies contact: SAE Customer ServiceTel: 877-606-7323 (inside USA and Canada)Tel: 724-776-4970 (outside USA)Fax: 724-776-1615Email: Customer [email protected] ISSN 0148-7191Copyright © 2003 SAE InternationalPositions 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. 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 publication by SAE should send themanuscript or a 300 word abstract of a proposed manuscript to: Secretary, Engineering Meetings Board, SAE. Printed in USADownloaded from SAE International by Brought to you by the University of Texas Libraries, Monday, August 06, 20182003-01-3256 Study of Viscosity Index Improver for Fuel Economy ATF Nobuharu Umamori and Takanori Kugimiya TonenGeneral Sekiyu K.K. Copyright © 2003 SAE International ABSTRACT One very effective way to improve fuel economy of motor vehicles is to reduce the viscosity of the automatic transmission fluid (ATF). However, viscometric constraints often exist for a particular ATF application. The proper choice of viscosity index (VI) improver allows viscosity reduction at lower temperatures, while maintaining viscosity at higher temperatures. This study shows that molecular weight of a VI improver is a key factor to achieve high thic kening efficiency, improved shear stability and limited metal fatigue failure simultaneously. Based on this study, an optimum VI improver has been found and a new fuel economy ATF was developed. INTRODUCTION It is of global interest to improve fuel economy of motor vehicles. This can be accomplished through various modifications ranging from aerodynamics and heat management to improved lubrication of mechanical elements. The automatic tr ansmission (AT) comprises one of the key mechanical elements. Two effective ways to improve AT fuel economy include increase of torque converter efficiency and reduction of ATF viscosity. The former has already been examined during development of a commercial ATF, designed for a slip-controlled lock-up clutch system [1]. In this paper, the latter approach is considered. Reduction of ATF viscosity is not easily achieved without sacrificing reliability. Idea lly, the viscosity at low to moderate operating temperature should be reduced as low as possible for fuel consumption savings. This is because fluid friction losses are particularly large at start-up. It is therefore ve ry important to reduce the effective viscosity at that time. However, the viscosity at higher temperatures should not be reduced much below current levels. If it becomes too low, oil leakage from the AT, especially the hydraulic line, can occur. In addition, the viscosity at higher te mperatures ought to be considered during long-term