Abstract
In the course of public discussions on fuel consumption and CO2 emissions, the efficiency of the drivetrain components, including thermal dependence, has become more and more important. Automatically shifting transmissions have a key position in this regard: the shift strategy determines the operating point of the engine and therefore the overall efficiency of the drivetrain on the one hand. As converters in the drivetrain, they also cause power loss on the other, which has to be minimised.
A tool for the calculation and minimisation of power loss for manual and dual-clutch transmission was therefore developed at the Institute of Automotive Engineering and verified through measurements. The overall efficiency of the transmission can be calculated with the model as well as the loss of the individual transmission components depending on transmission input speed and torque, engaged gear and transmission oil temperature. The power loss caused by bearings, gearing, seals, synchronization devices, clutches and hydraulic loss of the gearing, independent of load, is described. Moreover a simplified thermal model of the engine- transmission-block including the fluid circles is presented.
In this paper, the results in terms of increasing the efficiency of dual-clutch transmissions through optimisation of hardware components, e.g. use of energy-efficient bearings or optimisation of gearing surfaces, will be presented. Furthermore, the effects of temperature distribution in the transmission as well as the potential of minimising loss at low temperatures through thermal management will be illustrated.
These considerations take the environmental temperature of different cycles, including representative customer use into account, based on experience with the so-called 3D method (e.g. [1], [2]).
Keywords: Dual Clutch Transmissions, Efficiency, 3-D Method, Thermal Management, Customer Use