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 2007-01-3977 Enhanced Stability of Transmission Clutch Engagement with Temperature-Dependent ATF Friction T. M. Cameron Kettering University R. Iyer, T. McCombs, H. Maelger, T. Rollin, S. Tersigni and T.-C. Jao Afton Chemical Corporation Powertrain & Fluid Systems Conference & Exhibition Rosemont, Illinois October 29-November 1, 2007Downloaded from SAE International by Imperial College London, Friday, August 10, 2018The 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 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: permissions@sae.orgTel: 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: CustomerService@sae.org 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 the paper. A process is available by which discussions will be printed with the paper if it is published in SAE Transactions. Persons wishing to submit papers to be considered for presentation or publication by SAE should send the manuscript or a 300 word abstract to Secretary, Engineering Meetings Board, SAE. Printed in USADownloaded from SAE International by Imperial College London, Friday, August 10, 2018ABSTRACT Multiple plate disc clutches are used extensively for shifting gears in automatic transmissions. In the active clutches that engage or disengage during a shift the au-tomatic transmission fluid (ATF) and friction material ex-perience large changes in pressure, P, sliding speed, v, and temperature, T. The coefficient of friction, μ, of the ATF and friction material is a function of these variables so μ = μ(P,v,T) also changes during clutch engagement. These changes in friction coefficient can lead to noise or vibration if the ATF properties and clutch friction material are improperly matched. A theoretical understanding of what causes noise, vibra- tion and harshness (NVH) in shifting clutches is valuable for the development of an ATF suitable for a particular friction material. Here we present a theoretical model that identifies the slope, ˜P/˜T, of the coefficient of fric- tion with respect to temperature as a major contributor to the damping in a clutch during engagement. The model predicts that negative ˜P/˜T during clutch engagement increases the damping and reduces the risk of self- excited vibration or other NVH phenomena. Experimen-tal data supporting the model are presented. In the thin film or hydrodynamic regimes of friction, ˜P/˜T is typically negative since fluid viscosity and shear stress generally decrease as the temperature rises. However, the final lockup of an engaging clutch is controlled by boundary friction where ˜P/˜T is normally positive. Con- sequently, in the boundary friction regime the ATF addi- tive chemistry is important for suppressing NVH during clutch engagement by achieving negative ˜P/˜T with a particular friction material. INTRODUCTION A vehicle powertrain experiences a combination of tor- sional and axial vibrations that affect vehicle perform-ance and occupant comfort. These vibrations and their effects are major elements of noise, vibration and harsh-ness (