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2 Publisher: LuK GmbH & Co. Industriestrasse 3 D Bühl/Baden Telephon +49 (0) 7223 / Fax +49 (0) 7223 / Internet: Editorial: Ralf Stopp, Christa Siefert Layout: Vera Westermann Layout support: Heike Pinther Print: Konkordia GmbH, Bühl Das Medienunternehmen Printed in Germany Reprint, also in extracts, without authorisation of the publisher forbidden.

3 Foreword Innovations are shaping our future. Experts predict that there will be more changes in the fields of transmission, electronics and safety of vehicles over the next 15 years than there have been throughout the past 50 years. This drive for innovation is continually providing manufacturers and suppliers with new challenges and is set to significantly alter our world of mobility. LuK is embracing these challenges. With a wealth of vision and engineering performance, our engineers are once again proving their innovative power. This volume comprises papers from the 7 th LuK Symposium and illustrates our view of technical developments. We look forward to some interesting discussions with you. Bühl, in April 2002 Helmut Beier President of the LuK Group

4 Content 1 DMFW Nothing New? Torque Converter Evolution at LuK Clutch Release Systems Internal Crankshaft Damper (ICD) Latest Results in the CVT Development Efficiency-Optimised CVT Clamping System Nm CVT The Crank-CVT Demand Based Controllable Pumps Temperature-controlled Lubricating Oil Pumps Save Fuel CO2 Compressors Components and Assemblies for Transmission Shift Systems The XSG Family New Opportunities for the Clutch? Electro-Mechanical Actuators Think Systems - Software by LuK The Parallel Shift Gearbox PSG Small Starter Generator Big Impact Code Generation for Manufacturing LuK SYMPOSIUM 2002

5 Torque Converter Evolution at LuK Marc McGrath Bruno Müller Edmund Maucher Bhaskar Marathe George Bailey 2 LuK SYMPOSIUM

6 Introduction For many years, LuK has been recognised as a powertrain specialist with state-of-the-art torsional vibration isolation technology. This expertise lead LuK into the Toque Converter Clutch and Damper powertrain arena. Following the successful completion of the first Torque Converter Clutch projects, LuK focused energy on the entire Torque Converter system. LuK has evolved into a premier Torque Converter (TC) and Torque Converter Clutch (TCC) supplier (figure 1). Today, LuK produces 2.5 Million TCCs and 350 Thousand TCs, and as early as 2005 LuK will produce over 1.5 Million TCs per year LuK produces the first automatic transmission damper (customer: Ford) 1990 LuK starts developing torque converters 1997 LuK begins WT torque converter series production (customer: Allison Transmission) To efficiently develop torque converters, LuK realised a tool was required to link one-dimensional fluid flow, one-dimensional design, twodimensional torus generation, and three-dimensional blade architecture. This realisation lead to the birth of LuK s proprietary. TC Design program. TC Design is capable of collectively calculating torque converter performance, torus geometry, blade angles and configuration. As with most LuK tools, TC Design features a parametric variation feature enabling rapid TC analysis. To complete the development process, TC Design interfaces directly with LuK's commercial 3-D CAD and analysis software. For example, the exported torus shape is imported into blade design software, then the 3-D blade surface is meshed to accommodate Computational Fluid Dynamic (CFD) analysis (figure 2). To further analyse the TC performance, CFD is used to simulate the flows inside the torque converter, providing insight into the physics of the fluid dynamic phenomena. This insight helps to identify TC optimisation opportunities First LuK torque converter business awarded (customer: GM) 2002 LuK will produce 350 Thousand TCs and 2.5 Million TCCs 2006 LuK will produce 1.5 Million TCs Fig. 1: LuK Torque Converter Growth Know How LuK torque converter development is accomplished through an integrated design approach, incorporating analytical simulation, testing, and optimisation. The TC approach reflects LuK's traditional holistic design and development technique, enabling problem identification, creativity and design optimisation before prototypes are built. Commercial tools are not always available to properly perform the necessary development tasks; in such cases, LuK develops proprietary tools. Fig. 2: TC CFD Analysis 16 LuK SYMPOSIUM 2002

7 Engine and transmission combinations possess a vibration mode where the turbine inertia, transmission inertia and transmission input shaft stiffness resonate at the engine combustion frequency. Certain vehicles exhibit this condition at an engine speed and magnitude which prohibits TCC engagement, due to associated noise issues, thus degrading fuel economy. The turbine damper alters the drive train natural frequencies, eliminating this particular vibration mode and accordingly providing fuel economy and NVH improvements. These improvements have been recognised by the automotive industry and the automotive press (figure 4). torus characteristic baseline LuK weight 15.2 kg 9.7 kg inertia 0.21 kg m² 0.12 kg m² torus oil volume 6010 cm³ 2960 cm³ K-Factor size 305 mm 280 mm Fig. 3: Torque Converter Size Reduction LuK TC development tools yield TCs with characteristics that were previously unthinkable. A recent challenge was to reduce the TC size, weight and inertia, while simultaneously flattening the K-Factor curve, and increasing the engine torque (figure 3). Furthermore, LuK has developed tools to simulate the performance of the entire vehicle, to estimate changes in fuel economy, NVH, and vehicle performance for various TC and TCC designs. Perhaps the most famous damper solution is the Turbine Damper, which was developed utilising LuK s TC and TCC tools. Fig. 4: Turbine Damper on the Road of Success LuK SYMPOSIUM

8 Future The key to LuK s TC growth has been to address today s needs, while focusing on tomorrow s challenges. To continue developing innovative TC and TCC concepts, global powertrain trends must be considered. Future consumers will demand more of the same: fuel economy durability performance comfort cost Powertrain engineers will approach the consumer s desires quite differently this decade. With respect to TC development, multiple new powertrain arrangements and themes need to be considered: CVT 6-speed stepped automatic cylinder shut-off starter alternator systems increased torque/cylinder diesels / direct injection gasoline engines lower TCC lock-up speeds TC idle disconnect Building on these trends, LuK has numerous creative new ideas to address the future challenges. The remainder of this paper will highlight a selection of LuK s advanced concepts. Fig. 5: Slipping TCC Theory and Components 18 LuK SYMPOSIUM 2002

9 Grooved Cover Slipping the TCC is an additional approach to solving NVH issues. Unlike a damper approach, slipping the TCC provides vibration isolation by absorbing or filtering the engine s vibrational energy before it excites the powertrain (figure 5). Although slipping implies efficiency reduction, the slipping TCC efficiency is generally higher than the TC alone. An additional efficiency gain is achieved by operating the engine at a more favourable fuel consumption condition. The undesired energy loss is converted to heat carried away by conduction and transmission oil convection. It is critical to reduce the temperature so the friction material or the transmission fluid does not deteriorate. Deteriorated material and/or oil can lead to detrimental shudder or TCC control conditions. Fig. 6: Grooved Cover Cooling Today, LuK has both development and production experience with two slipping TCC concepts, organic facings with cooling grooves and carbon facings (figure 5). The grooved organic facing offers desired friction characteristics and a possible cost advantage, where as the carbon technology offers improved durability especially for high energy applications. As the current friction materials wear over life, the cooling flow diminishes degrading the cooling performance. LuK is currently developing the Grooved Cover concept. This concept maintains a constant flow over life (figure 6). Since grooves in the cover don t wear, they don t need to be as deep. Therefore, a greater number of grooves can be used improving the friction interface flushing (figure 7). Additionally, the sides of the grooves in the steel add surface area for heat transfer to the oil via convection. The result is better cooling efficiency than a grooved paper TCC with the same flow rate. Fig. 7: Comparison of Cover and Facing Grooves LuK SYMPOSIUM

10 Speed Dependent Cooling For driving comfort, it is advantageous to engage the TCC at high differential speed and/or torque levels, requiring the TCC to dissipate large power amounts. For this scenario, it is beneficial to increase the cooling flow relative to power. Unfortunately, with today's production concepts, the flow is dependent on the required TCC torque. To fulfil this need, LuK is developing an innovative concept (figure 8). The concept links the cooling flow to the TCC slip speed or relative engine/transmission speed. The increased flow is achieved by transferring oil from the apply pressure side to piston chambers and then to the release pressure side. The cooling flow or oil transfer rate is dependent on the relative speed between the TC cover (engine) and the TCC piston (transmission). Since TCC torque capacity is defined by apply pressure, the amount of oil transferred from one side to the other side is maintained proportional to the torque. Accordingly, the cooling flow varies relative to power levels. Multifunction Torque Converter It is possible to further minimise losses associated within the torque converter. To maximise efficiency the TCC should remain engaged as much as possible, yet, powertrain natural frequencies often limit TCC operation to higher engine speeds. In manual transmission vehicles, this limitation is overcome with a dual mass flywheel designed to lower these natural frequencies, allowing lower operating speeds. When a vehicle is stopped at traffic lights, the torque converter is pumping fluid but no useful work is being done. Some manufacturers shift the transmission into neutral by opening a clutch in the transmission. To move the vehicle, the clutch must be reengaged quickly, which requires the freewheeling transmission components to come to an abrupt stop (figure 9). This must be done carefully or there will be a bump when the clutch engages, similar to what is felt when a transmission is shifted into drive. LuK has devised two- and three-pass Multi- Function Torque Converter (MFTC) concepts to 1. lower powertrain natural frequencies, and Fig. 8: Power Dependent Cooling TCC Concept 2. provide an idle disconnect function. 20 LuK SYMPOSIUM 2002

11 Fig. 9: Benefit of Idle Disconnect in the TC A cross-section of a two-pass concept is shown in figure 10. A second clutch, an impeller clutch, has been introduced between the cover and impeller (or TC pump). The TCC release pressure (channel 2 in figure 10) is fed between the input shaft and stator shaft, and the TCC apply pressure (channel 1 in figure 10) is fed between the pump hub and stator shaft. At stops both pressures are kept high, therefore no torque is transmitted to the impeller and the converter drag is eliminated. When the driver releases the brake, the TCC apply side is open and the release pressure applies the impeller clutch, which is designed for adequate torque capacity while maintaining cooling flow (figure 11). The engagement is invisible to the operator, because only the relatively small impeller inertia is accelerated instead of decelerating the turbine and transmission components. To lock the TCC, apply pressure pushes between the impeller and cover and the impeller slides toward the turbine (figure 12). The torque now flows from the cover, through the damper, through the TCC, and to the input shaft. The cover inertia is fixed to the engine, and the impeller and turbine are fixed to the input shaft, moving the impeller inertia from the engine into the powertrain thereby lowering its natural frequency. Idle resonance and start-up/shut-off noise issues are completely avoided with this concept. LuK SYMPOSIUM

12 Fig. 10: Multi-Function Torque Converter (Idle Disconnect Mode) Fig. 11: Multi-Function Torque Converter (Torque Converter Mode) Fig. 12: Multi-Function Torque Converter (TCC Lock-up Mode) 22 LuK SYMPOSIUM 2002

13 Torque Reverse Converter To provide reverse motion, a continuous variable transmission (CVT) requires a planetary gear set with two clutch packs. Vehicle launch is achieved via a start up element. This can be a fluid coupling or a torque converter. Both the start up element and the reverse gear arrangement are only employed during limited vehicle operations, launch and backing. Unfortunately, a considerable portion of the CVT cost is consumed by the planetary gear set and the start up element. To reduce the cost, LuK s idea is to combine the two auxiliary functions into one structural element. In the forward operation, the TC stator redirects the turbine exiting fluid into the impeller, enabling torque multiplication. The redirection attempts to rotate the stator in the opposing direction as compared to the turbine and impeller. The stator counter rotation is restricted via its connection to the transmission case. Connecting the stator to the transmission input shaft would propel the vehicle backward. To achieve the required reverse torque, torque multiplication can be regained by connecting the turbine to the transmission case. Creative connections within the torque converter interchanging the transmission input shaft and transmission case connections will provide both forward and reverse vehicle operations. A four-element torque converter is utilised to independently control forward and reverse characteristics. Three elements of the torque converter are active in forward mode (figure 13). In the reverse mode, all four elements are active (figure 14). LuK s Torque Reverse Converter (TRC) concept realises the required start-up and reverse function in a single unit. This configuration not only reduces cost, it saves crucial space as well. Fig. 13: Torque Reverse Converter (Forward Operation) Fig. 14: Torque Reverse Converter (Reverse Operation) LuK SYMPOSIUM

14 Starter Alternator Torque Converter LuK has been involved with the development of starter alternator systems since the early 1980s. The advantages of starter alternator Systems are increased electrical power and reduced fuel consumption, providing both comfort and economy. Combining a starter alternator with a TC equipped drive train places new demands on the torque converter design, and offers the ability to disconnect the engine from the TC and starter alternator while maintaining continuous transmission pump operation. These demands are required to foster inertia starts and brake regeneration. LuK is focusing on TC solutions that meet the previously mentioned demands. LuK is developing several torque converter starter alternator arrangements in conjunction with various starter alternator suppliers (figure 15). LuK s future advanced development efforts are concentrating on possible configurations with the multifunction-torque-converter where the demands can be fulfilled without requiring extra parts (figure 16). Fig. 15: Starter Alternator Solutions Fig. 16: MFTC Starter Alternator Concept 24 LuK SYMPOSIUM 2002

15 Summary At LuK, the design and development of torque converters is achieved through an integrated design approach, incorporating analytical simulation, testing, and optimisation. This approach is a systematic design and development process that uses several analytical tools. Where commercial software was not available to perform the necessary tasks, programs were developed internally. This process was intended to optimise and improve designs, but it also allows for identification of problem areas before prototypes are built. This results in high-efficiency optimum torque converter designs. The torque converter clutch (TCC) and damper are integral parts of the torque converter, and LuK has similar analytical tools to design these components and predict their performance. LuK s 20 years of experience results in a perfect marriage between the TCC and torque converter performance. Tools have been developed to predict powertrain torsional vibrations, so that damper characteristics can be optimised. TCC thermal models are built so that cooling concepts can be designed which allow continuous slipping of the clutch to isolate vibrations. In addition, LuK has developed inhouse software to simulate the performance of the entire vehicle. Changes in fuel economy and vehicle performance for various torque converter designs can be predicted before a prototype vehicle is even made. Another benefit of this integrated design and development approach is that innovative solutions that may otherwise be overlooked, such as improved TCC cooling for slipping applications, unique TCC damper configurations, and TC systems such as the multifunction, reverse gear, and starter-alternator torque converters, become apparent. LuK is presently working on the following innovative torque converter concepts: TCCs with grooved covers instead of grooved facings to increase interface cooling in slipping systems Slip dependent cooling to increase the volume of cooling flow as the power generated by the slipping TCC increases Multi-Function Torque Converter as a combination of a dual-mass flywheel and a torque converter Torque converter incorporating reverse gear Torque converters for starter alternator systems References [1] Middlemann, V.; Wagner, U: The Torque Converter as a System, 6 th LuK Symposium [2] Jürgens, G.: Transmission Systems: A Comparitive View, 5 th LuK Symposium [3] Middlemann, V.; Gundlapalli, R.; Halene, C.; Marathe, B.: Development of Axially-Squashed Torque Converters for Newer Automatic Transmissions, 2000 ASME International Fluids Engineering Division Annual Summer Meeting, June 11-15, 2000, Boston, MA, FEDSM [4] Kozarekar, S.; Maucher, E.; Marathe, B.: Analysis of 3-Element Torque Converter as Reverse Gear, 2000 ASME International Fluids Engineering Division Annual Summer Meeting, June 11-15, 2000, Boston, MA, FEDSM LuK SYMPOSIUM