JSAE 20159064 SAE 2015-01-2037 Lubricants )ormulation 7echnology for )uel 6aving3erformance in Automatic Transmissions Masato Yokomizo, Toshiaki Iwai, Keiichi Narita and Mitsugu Kudo Idemitsu Kosan Co., Ltd. Copyright © 2015 SAE Japan and Copyright © 2015 SAE International ABSTRACT The use of Automatic Transmission Fluids (ATFs) with lower viscosity and excellent anti-shudder durability for wet clutch system will be effective for improving fuel saving performance in automatic transmissions. In this study, two ATF formulation techniques were examined. The first trial formulation is to improve fatigue life in gear components even if a lower viscosity ATF is used. The second one is to improve anti-shudder durability for wet lock-up clutch system in AT units. As to fatigue life performance, the relation between molecular weight of Viscosity Index Improver (VII) and film formation property in EHL contact regions were experimentally investigated. ATFs containing VIIs with lower molecular weight tend to increasing EHL film thickness, resulting in a longer gear pitting fatigue life. Calcium detergents and ashless friction modifiers in ATFs were found to give a great impact on the anti-shudder performance. The trial ATF containing these additives demonstrated 1.5 times longer anti-shudder durability compared with a commercial ATF. INTRODUCTION Improving fuel efficiency in passenger vehicles is effective for reducing CO 2 emission gas. Fuel economy regulations will be stricter in worldwide. Therefore, transmission fluids demonstrating a better fuel saving performance are strongly required. Recently, transmission fluids have been specialized for each type of transmission units. For example, Automatic Transmission Flui ds (ATFs) are used in step-type ATs, Continuously Variable Transmission Fluids (CVTFs) are employed in CVTs. Lower viscosity ATFs is attributab le to reducing stirring resistance and dragging resistance between the multiple-disc-clutches. On the other hand, this oil formulation would cause oil leaking from hydraulic system at higher temperature and shortens fatigue life in gear and bearing system. Therefore, it is needed to take these issues to consideration for developing lower viscosity ATFs. Torque converter in AT and CVT units, which is a hydraulic device, used to transfer rotating power from an engine to a transmission and is multiply torque when there is a substantial difference between input and output rotational speed. In a torque converter, lock-up clutch composed of the frictional plate and the steel plate is installed. This frictional pair is directly engaged to transmit the power from the engine to transmission. Since 1990s, electric control and slip controlled lock-up clutch system has been introduced to improve shifting performance and further fuel efficiency. If friction property between the friction plate and the steel plate is not suitable, an uncomfortable vibration, which is called shudder phenomena will occur. Recent years, there is a tendency to direct connecting at lower vehicle speeds frequent using slip control to reduce power loss. Therefore, improving anti-shudder durability of transmission fluid would an effective measure to fuel saving. In ATFs, various kinds of additives are blended in base stocks to meet required performances. For reducing viscosity of fluid, the selection of base stock and viscosity index improver (VII) is important. To extend anti-shudder durability, detergent, dispersant, extreme pressure agent and friction modifier will be contributable. In this study, two formulation techniques were examined. The first one is to improve fatigue life in gear components even if lower viscosity ATFs are used. The second one is to improve anti-shudder durability for wet lock-up clutch system in AT units. STUDY OF IMPROVEMENT OF FATIGUE LIFE IN GEAR COMPONENTS VISCOSITY PROPERTY OF COMMERCIAL FLUIDS Fig.1 shows viscosity