# Influence of Drivetrain Hybridization on Transmission Lifetime
## 1 Introduction
[21] use a simulation model to predict the load spectra and damage in the gears of a vehicle transmission. The computational approaches mentioned so far are suitable for evaluating reliability in product development. In addition, experimental methods are used to ensure the reliability of the implemented physical product. For this purpose, load spectra in the form of test cycles are used in running tests. In [22], [PERSON] et al. present a method of carrying out customer-representative gear testing with regard to service life in a time- and cost-optimized manner. Figure 1: Arrangements of the EM (electric machine) in basic parallel hybrid topologies (P0-P4) and exemplary arrangement through combination (P0P2). Transmissions in hybrid drivetrains can be subject to additional loads compared to their use in conventional drivetrains, which must be taken into account in order to dimension the components and ensure reliable operation. In [23], [PERSON] et al. investigate the influence of a parallel and a power split hybrid drivetrain on the transmission input torque and compare the results to a conventional drivetrain. For this purpose, they use a simulation model and evaluate it for a given vehicle with varying drivers and driving routes. In [24], [PERSON] summarizes the influences of hybridization on the component loads in the transmission as a \"hybrid effect.\" To this end, [PERSON] mentions additional torques in drive and coast operation during boosting and regeneration, additional functions such as electric launch, changed vehicle parameters such as weight and changed component properties such as housing geometry. It is pointed out that it is necessary to take coast operation into account in the lifetime calculation, since regeneration can increase the load in negative power flow direction. An application-oriented reduction of the transmission input torque to achieve a target gear lifetime is presented in [25]. In the presented studies, the critical role of gears on transmission lifetime is well established. Like gears, bearings are among the high-risk transmission components [26] and cause 15% of transmission failures, making them the second most frequent cause of transmission failures after gears [8]. A literature search revealed few studies on bearing lifetime in automotive transmissions and especially hybrid applications. The aim of this paper is to investigate the influence of hybridization in terms of regeneration on the lifetime of bearings as highly critical elements in a dual clutch transmission. For this purpose, we use a detailed drivetrain model of a parallel HEV. In the drivetrain topologies P0, P1 and P2, the EM is placed upstream of the transmission and has to transmit additional power in the coast direction to achieve regeneration. The power transfer leads to additional loads acting on the machine elements and to a distinct lifetime behavior. The remaining part of the paper is structured as follows. Section 2 first introduces the use case considered for this study. Afterwards, the underlying method used for calculating the lifetime and the system simulation model are introduced and explained. Section 3 presents the results of the simulation and lifetime calculations for a conventional and a hybrid drivetrain, as well as a sensitivity analysis. Finally, Section 4 gives a brief summary, a conclusion and an outlook regarding necessary and possible future work.