LuK, one of the brands of the Schaeffler Group, recently introduced a multi-function torque converter (MFTC) designed to overcome some of the challenges posed by the coupling of a turbodiesel engine with an automatic transmission.
|The LuK Multi-Function Torque Converter.
Diesel engines pose several challenges to the automatic transmission: Firstly, the combustion process is more violent, leading to potential NVH problems. Due to higher idle speeds to reduce particulate emissions, idle losses in the torque converter are also higher. With an idle speed of approximately 800 rpm and a typical torque converter designed for 400 Nm, these losses are about 3 kW, according to LuK—about one third of the average power required to actually drive the city cycle. Finally, the turbo charger is difficult to accelerate with the torque converter holding down engine speeds. This leads to a sluggish launch with an automatic transmission.
The LuK MFTC addresses these through the use of an additional clutch, through which the impeller inertia can be disconnected from the engine.
NVH problems won’t occur as the impeller inertia is connected to the transmission when the converter is locked. This lowers the resonance frequency of the driving mode below idle speed and allows the lock-up clutch to be closed in all driving conditions.
Idle losses are eliminated by disconnecting the impeller when the vehicle comes to a standstill, for example at traffic lights. Finally, the impeller clutch can be modulated during the launch, resulting in a launch to be controlled as in a dual clutch transmission. The engine speed is allowed to quickly rise, which speeds up the turbo and provides maximum torque.
Additionally, the MFTC offers torque multiplication, enabling driving dynamics superior to manual and dual clutch transmissions, according to LuK.
The Multi-Function Torque Converter improves diesel fuel economy by up to 5%; eliminated vibration and boom; and delivers dynamic launch performance with 0-60 mph times reduced by up to 0.8 seconds compared with a conventional torque converter.