1. INTRODUCTION For many years, the dominating automatic transmissions were torque converter / planetary gearset automatic transmissions (AT). More recently however, CVT technology and dual-clutch transmissions have created market competition for traditional AT. As a result of the competition from CVT [ 1], [2], [3] and DCT technologies [ 4], [5] with regard to fuel efficiency, CO2 emissions and shifting dynamics, ATs have undergone additional evolutionarystages to ensure their continued relevance and competitiveness [ 6], [ 7], [ 8], [ 9], [ 10] and [ 11]. The fuel efficiency improvement of automatic transmission over time can be shown - simplified with respect to the number of gears - for the different generations over time for the European Drive Cycle NEDC, s. Figure 1. This fuel efficiency improvements are not only achieved due to more gear ratios and increase ratio coverage. The improvements also include innovative developments in basic transmission components, e.g. pumps and clutches. 2013-01-1272 Published 04/08/2013 Copyright © 2013 SAE International doi:10.4271/2013-01-1272 saepcmech.saejournals.org Optimization Potential for a State of the Art 8-Speed AT Albert Dick ZF Friedrichshafen AG Juergen Greiner ZF Getriebe GmbH Anton Locher and Friedemann Jauch ZF Friedrichshafen AG ABSTRACT The legislative and market pressure for CO2 reduction and fuel efficient powertrains lead to a variety of automatic transmission concepts in recent years. The CVT technology, the dual clutch technology (DCT) and optimized architectures of torque converter / planetary gear based automatic transmissions (AT), such as 6, 7, and 8 speed ATs entered the market in the last decade. Also different hybrid technologies have entered the market offering further improvement for fuel consumption especially in city driving. Helpful for OEMs and suppliers to flexibly meet market demands proofed the use of modular hybrid solutions. Clear demand to meet were packages of existing vehicles and powertrains with AT and hybrid transmission (HT), e.g. the modular transmission kit based on the ZF 8 speed AT. Hybrid technology is offering fuel efficiency benefits, but there are also reasons for a slow market penetration. Major obstacles are weight, battery performance, cost, complexity and low benefits for driving conditions outside of urban rush hour traffic, when missing frequent accelerations and slowing down situations for recuperation. Current market expectations foster the necessity, to further develop and optimize the major portion of the market penetration, the conventional powertrain technology. A focused investigation is done for the automatic transmission technology, based on ZF 8-speed family 8HP first generation. To understand the future potentials for a second generation of 8-speed transmissions, a detailed analysis of remaining losses of the current technology for different fuel cycles is provided. Although the results underline the challenge for further improvements on transmission side, a solid engineering base is given to generate and develop innovative ideas for affordable CO2 reductions of a 2nd generation of ZF's 8-speed automatic transmission. Different optimization approaches were investigated in detail and are compared. Furthermore the scope of the 2nd generation 8-speed AT, currently under development and planned for market introduction in the near future, was identified. CITATION: Dick, A., Greiner, J., Locher, A. and Jauch, F., "Optimization Potential for a State of the Art 8-Speed AT," SAE Int. J. Passeng. Cars - Mech. Syst. 6(2):2013, doi:10.4271/2013-01-1272. ____________________________________ 899Downloaded from SAE International by Tsinghua University, Friday, June 08, 2018Figure 1. Fuel Efficiency Improvement by ZF Transmission Technology,, sedan, 2.5L V6, NEDC The ongoing legislative pressure on fuel efficiency and CO2 reductions also drove development of hybrid powertrains. Hybrid technology can offer clear fuel efficienc