Experimental Investigation of the Drag Losses in the Shifting Elements of Automatic Transmissions

Nowadays market trends in the automotive industry followed by OEMs productions show the increasing spread of industrial, commercial and passenger vehicles equipped with non-manual transmissions. Automatic Transmission (AT) and Dual Clutch Transmission (DCT) gearboxes are characterized by an increased comfort level and a powershift gear change thanks to wet multi-disk clutch-packs. Despite clutch-pack devices bring several advantages in terms of comfort, shifting time, thermal stability and load capacity, they work in a cooling lubricating fluid that, due to oil shear when in disengaged mode and with a relative differential speed between the plates, generates significant power losses and increase vehicle CO2 emissions and fuel consumption. Wet multi-disk clutch-packs are used in a multitude of fields, not exclusively in the automotive one. As mentioned, there are common applications in Passenger Vehicles drivelines (from low-end segments to high-end segments), in Light-Duty and Heavy-Duty Vehicles powertrains, but they are used also in agricultural tractors drivelines, in marine field as in boats and ships drivelines, in industry machinery and in many other fields. As part of a series of research projects, an experimental research on the drag torque test-bench LK-4 at FZG has been conducted with the goal to deeply study the phenomenon of energy loss in and scientifically investigated the various factors that influence the drag torque process for DL disengaged wet multi-disk clutch-packs in real world usage operations. Furthermore, the trends of the characteristic clutch-pack design parameters and the operating parameters inside the transmission have been highlighted through scientifically based model with the final purpose to give some guidelines to future loss-reduced clutch designs.