123 The Torque Converter as a System Dr.-Ing. Volker Middelmann Dipl.-Ing. Uwe Wagner Introduction Since its introduction in the 1940s, the torque converter has been utilized as a proven coupling element between the engine and automatic transmission. Its advantages result fr om the principle of hydrodynamic power transfer from engine to transmission. The available torque amplification (torque ratio) improves acceleration and performance. The ever-present and, in principle, necessary slip isolates the drivetrain from the engine torsional vibrations, prevents Tip-in reactions and provides comfortable transmission shifts. Lock-up clutches with dampers are used to bypass the torque converter and minimize the losses due to slip in the torque converter. In contrast to automatic transmissions which have had their functionality continuously improved, torque conv erter design and concept have not been changed significantly throughout the preceding decades. Even the introduction of lock-up clutches in the 1970s hardly changed the principles of torque converter concept, layout and design. This is surprising because of the well-known potential provided by the torque converter system. With a well-tuned lock-up control strategy and appropriate hardware components, tremendous improvements in performance and significant fuel savings can be realized. In the last Symposium in 1994, LuK presented an innovative torque converter system called the LuK-TorC on-System. This system still uses the advantages of the torque converter but minimizes the disadvantages by introducing a high-performance lock-up clutch and an aggressive lock-up control strategy. Depending on the application, the LuK-TorCon-System provides significant improvement s in performance and fuel economy. Furthermore, the system enables us to gain the same performance characteristics using a conventional 4-step automatic transmission instead of a more expensive 5-step automatic transmission. However, the demand for further improvements in performance and fuel economy dictates additional optimization steps. In this context, the selection and tuning of the lock-up control strategy is as important as the design and tuning of the three hardware components: hydrody namic circuit, lock-up clutch and 124 damper. In fact, only with this holistic approach is it possible to attain the entire advantages provided by t he torque converter system. In spite of these circumstances, over the last few years, LuK has developed torque converter systems, which prov ide superior characteristics compared to conventional systems. With reduced envelope, lower weight and equal costs, the LuK torque converter systems deliver more functionality, greater flexibility and enables to reduce fuel economy and emissions and increase vehicle performance. LuK has increased the torque converter development capacity and capabilities in Bühl, and in Wooster, USA, where we have established a second Torque Converter Development Center. At LuK, Inc., USA, we started producing both medium and heavy duty torque converters for Allison’s World Transmission Series in 1997. Figure 1 shows the MD Torque Converter, that also utilizes the advantages of a lock-up clutch. /G73 /G74 /G61 /G74 /G6F /G72/G74 /G75 /G72 /G62 /G69 /G6E /G65 /G63 /G6F /G76 /G65 /G72 /G20 /G26 /G20 /G64 /G61 /G6D /G70 /G65 /G72 /G73 /G69 /G7A /G65 /G3A /G20 /G20 /G20 /G20 /G20 /G20 /G20 /G20 /G20 /G20 /G20 /G20 /G20 /G20 /G20 /G4D /G44 /G20 /G3D /G20 /G33 /G36 /G38 /G20 /G6D /G6D /G48 /G44 /G20 /G3D /G20 /G34 /G31 /G39 /G20 /G6D /G6D /G48 /G44 /G20 /G3D /G20 /G37 /G39 /G2E /G38 /G20 /G6B /G67/G77 /G65 /G69 /G67 /G68 /G74 /G3A /G20 /G20 /G20 /G20 /G20 /G20 /G20 /G20 /G20 /G20 /G20 /G4D /G44 /G20 /G3D /G20 /G35 /G32 /G2E /G36 /G20 /G6B /G67/G70 /G75 /G6D /G70 Figure 1: Components of the MD torque converter series 125 History and Global Development of Automatic Transmissions and their Influence on Modern Torque Converter Concepts