Optimization Potential for a State-of-the-Art 8-Speed AT

摘要

The increasing legislative and market pressure for CO_2 reduction and fuel efficient power-trains has lead to a variety of automatic transmission concepts in recent years. CVT technology, dual clutch technology (DCT) and optimized architectures of automatic transmissions (ATs), based on torque converter/planetary gearsets such as 6, 7, and 8 speed ATs entered the market during the last decade. In addition different hybrid technologies have entered the market offering further improvement for fuel consumption especially in dynamic driving. The application of modular hybrid solutions proved to be helpful for OEMs and suppliers to flexibly meet market demands. The installation space of existing vehicle applications demands solutions which can accommodate conventional automatic transmissions and hybrid drives 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 slow market penetration. Major obstacles are weight, battery performance, cost, complexity and low benefits for driving conditions outside of urban rush hour traffic, where there is no frequent acceleration and braking for recuperation. The current market expectations result in the necessity of further developing conventional transmission technologies in order to, on this basis, achieve additional consumption potential thanks to optimization. An investigation focusing on automatic transmission technology is performed based on the first generation of ZF s 8-speed family, the 8HP. To understand the future potential for a 2nd 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 improvement on the transmission side, a solid engineering base is given to generate and develop innovative ideas for affordable CO_2 reductions of a 2nd generation of ZF's 8-speed automatic transmission. Different optimization approaches were investigated in detail and compared. Furthermore we identified the scope of the 2nd generation of the 8-speed AT, which is currently under development and planned for market introduction in the near future.