TorqueLINE Cone Clutch: Thermo-Mechanical Stability of Cone Clutches for ATs

摘要

Though hybridization and electrification have both gained an important position in the development of modern drivetrains, traditional drivetrain concepts will still dominate the market in the short-to-medium term. The need for a further reduction of local CO_2 emissions of passenger vehicles is however impellent. Traditional automatic transmissions with torque converter own a consolidated share of the overall transmission market, especially in northern America and Europe within the premium segment. The key for their success is to be found in their high power density and the capability of performing powershifts while still guaranteeing excellent shifting comfort. A considerable effort has been put over the last years in developing ATs with a steadily growing number of gear ratios and total spread, in order to optimize the ICE operation regions. Nonetheless, an important source of losses in ATs is still determined by drag torque of disengaged wet multiple disc clutches. To reduce said losses, the latter can be substituted in some cases by dog clutches, causing however a perceptible reduction in shifting comfort. To unite the advantages of a multiple disc friction clutch in terms of shifting comfort with the low drag losses and high transmittable torques via form-fit of a dog clutch, a new shifting element - TorqueLINE Cone Clutch - has been developed in a joint project between HOERBIGER and FZG, Technical University of Munich. A cone clutch instead of a multiple disc clutch has been chosen to generate the synchronizing friction torque, reducing the friction surface and thus the drag losses. The advantages of this choice and its potentials have been experimentally proved at HOERBIGER and FZG and can be found in [8]. However, as the friction surface of a clutch reduces, remaining the load equal, specific friction loss - i.e. the energy loss per unit area - increases accordingly. Hence, as considerably higher temperatures arise during the synchronizing phase, a thermal stability analysis is indispensable for determining the load limits of the new clutch. For this purpose, a coupled thermo-mechanical finite element analysis was developed and will be described at the paper. To prove the model's validity, temperature measurements on the prototypes have been performed during test-rig runs under varying load conditions. These are compared to the simulative results delivered by the thermo-mechanical FE model that was set up.