SYNTHESIS OF AN EIGHT-SPEED AUTOMATIC TRANSMISSION FOR HYBRID DRIVES IAV develops future transmission generations by using computer-aided synthesis programs. The new eight- speed planetary automatic transmission for transverse applications results from a total solution amount of 1.6 billion transmission variants. The derivable modular transmission system comprises a conventional trans-mission as well as a mild and a full hybrid version. It offers numerous advantages in comparison with current systems regarding speed number, hybrid functions, efficiency, size and costs. 26INDUSTRY TRANSMISSIONSMORE RATIO RANGE The vehicle transmission harbors major potential for meeting the challenges exhaust gas and fuel consumption. Wide ratio ranges with a high number of well-stepped speeds ensure efficient coverage of the combustion-engine map and deliver plenty of traction. Manual transmissions currently providing a maximum of six speeds and ratio ranges up to Mtotal ≈ 6 will in future hardly be in a position to satisfy these goals. Further ratio steps reduce the driving comfort as a result of the greater amount of gear-shifting effort they involve and the risk of overburdening the driver becomes greater which is why theoretical fuel savings are not necessarily achieved in real operation. Fully automatic transmissions are better suited to providing driving comfort from a large number of ratio steps. Present-day dual-clutch transmissions offer as many as seven speeds and ratio ranges of Mtotal ≈ 6.5. Even higher numbers of Mtotal ≈ 7 are possi- ble with planetary automatic transmissions with up to eight ratios. As a result of the more exacting design-space restrictions in vehicles with front-transverse engines, map converters of this type are only mass-pro-duced with a maximum of six speeds and a ratio range of up to Mtotal ≈ 6. At present, round 80 % of all passenger cars worldwide are powered by front, trans-versally installed combustion engines. It is expected that with production figures rising, this percentage will increase over the next few years. This means that from the aspect of reducing fleet consumption, the signifi-cance of fully automatic, front-transverse transmissions with a greater number of speeds is set to grow. Dual-clutch transmis-sions, particularly those operated electrome-chanically, permit marginally better con-sumption over planetary automatic trans-missions which, in turn, are more compact in design, more cost-effective to make and also provide better driveaway dynamics and shift strategies with greater flexibility [1]. It is for this reason that the following analyses focus on planetary automatic transmissions for front-transverse applications. With planetary automatic transmissions, the traditional approach to providing addi-tionally required ratio steps is to use fur-ther mechanical transmission components, such as gear sets or shift elements. Although this has an adverse effect on costs, weight and size, the trade-off can be resolved by means of innovative gear structures that employ the limited number of transmission components for more speeds. ➊ shows the key aspects develop- ers are aiming to optimize, such as achiev-ing high levels of efficiency, low drag losses and less loads on mechanical com-ponents. Hybridizing the conventional powertrain produces the means for realiz-ing many demands as a result of the addi-tional degree of freedom it offers on the energy-management side. Intelligent mod-ular systems made up of conventional and hybrid transmission variants reduce devel-opment and production costs. The conventional and predominantly intuitive search for new gear structures is less suitable for taking account of these complex challenges. The abundance of DIPL.-ING. ERIK SCHNEIDER is Head of Hardware Development for Transmission and Hybrid Systems at IAV GmbH in Chemnitz (Germany). DIPL.-ING. JÖRG MÜLLER is Manager of the Transmission and Hybrid System Concepts and Synthesis Team at