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Hybrid powertrains derive fuel consumption benefits from using an electric motor. These benefits are more significant in city traffic than on the highway and depend on the vehicle and the driving style. Further detailed research on the fuel consumption of hybrid powertrains during drive-off procedures is rarely found in the literature. Therefore, this study focuses on analyzing the potential of a mild-hybrid powertrain, in which the electric motor is integrated with the transmission (P2.5 concept). The fuel consumption and thermal load in the drive-off element, a wet frictional clutch, are analyzed for a city cycle with a focus on the first drive-off procedure for different driving styles. Particular attention is paid to the influence of different driving styles on the torque demands of the electric motor. These simulations are realized with a so-called backward-forward model. The backward-facing part enables following a given driving cycle without considering a driver model.

The underlying basic model represents a powertrain with automatic transmission including a torque converter. It is based on a greybox-modeling approach, which refers to ordinary differential equations with identified parameters and characteristic curves. The validated basic model is extended in order to reproduce the system behavior and especially the side shaft torque during a gear shift process. Therefore the model is extended by a transmission model with clutches for gear shifting in order to simulate specific powertrain dynamics additionally. The parameters have already been determined for the basic model using a method for isolated and structured parameter identification based on measurement data of an automotive powertrain test bench. A comparable structured parameter identification method is applied to obtain the parameters of the extended model.

Besides optimal engine systems, high-efficiency vehicle transmissions are generally also required to improve fuel economy in automotive applications. For the energy loss analysis in transmissions, most research focused on the major mechanical components, such as gears, bearings and seals, while the other mechanical losses, like synchronizer losses, were usually not considered. With increasing number of synchronizers in modern transmissions, a recent study indicates that the power loss analysis of synchronizers should also be developed and appended for a more accurate investigation on overall power losses in transmissions. The function of synchronizer is to equalize the different rotational speeds of shafts and gear wheels by frictional torques, for which the synchronizer must be cooled and lubricated in order to enhance the service life. With the supplement of lubricants, fluid friction is generated due to the differential speed, when the synchronizer is in neutral position.