Torque Gap Filler: A Possible Solution for Reducing the 'Shift Torque Hole' in AMT Transmission

摘要

Due to the continuously increasing of oil price and the new environmental regulations today, one of the most important incentives for developments in the world vehicle market are fuel consumption and exhaust emissions. At least of equal importance are comfort, safety, and vehicle performance, which are normal expectations of the customer. For these reasons, in recent years the OEMs and the suppliers have increased their focus on power-train systems and in particular on transmission systems, in order to increase both performance and efficiency. Ten years ago a new transmission system was introduced on the market as a new technology positioned between the manual transmission (MT) and the conventional automatic transmission (AT). This system, called automatic manual transmission (AMT), offers the driver the benefit of having an aid in the control of the clutch and the gear box, improving at the same time the driving comfort (especially in congested traffic) and the vehicle performance. In addition, AMT grants an improved efficiency in the torque transmission, in comparison to the conventional automatic transmission, due to an optimized control during the shifting and the launch phase. In this way AMT can be considered a good compromise between comfort on one hand and performances and efficiency on the other hand. Magneti Marelli has developed several applications of AMT in the last ten years, based on several types of vehicle from light duty tracks to sporty vehicles, from segment B to segment E vehicles. In sporty vehicles, the performances of AMT are well accepted by the customers as well the improved efficiency in the light duty tracks, while in vehicles where comfort is the main goal, the typical torque interruption during the gear shift is a weak point, especially compared to the conventional automatic transmission. Still, the AMT system is a very attractive transmission in terms of efficiency and cost-effectiveness especially when compared with other automatics. In order to overcome the torque interruption penalty, a system which assures the torque transmission in every phase of the gear shift has been analyzed. It consists in a further technological development of the AMT system, where a device has been introduced in order to have a short term mechanical link between the engine shaft and the output shaft. The solution, presented in this paper, results from the cooperation between Magneti Marelli and DTI, linking the experience of Magneti Marelli in the transmission control and the knowledge of DTI in the development of such transmission device. A mathematical model has been developed with the cooperation of Politecnico of Turin and the results of the simulations are shown as well as the improvement in the performances in comparison with the current AMT system.