Efficiency Increase of a Conventional ICE Powertrain with CVT by 48V-Hybridization with Focus on L-Category Powersport Applications 2022-32-0018

In recent years, E-mobility relevance has increased in the automotive sector, yet pure electric vehicles struggle to establish themselves in the still internal combustion engine (ICE) dominated sector of L-category and powersport applications. Battery electric hybrid L-category vehicles, as considered in this paper, combine both ICE and electric powertrains. Nowadays, numerous ICE L-category vehicles use rubber V-belt continuous variable transmissions (CVT) due to their reliability and user-friendliness, which often outweighs the drawback of relatively low efficiency. This paper not only aims to show, with the help of longitudinal dynamic simulation (LDS), how a state-of-the-art L-category ICE powertrain with special focus on the CVT can benefit from hybridization in terms of overall efficiency, but furthermore points out where the efficiency increase actually comes from and how this new knowledge can be implemented intelligently into a hybrid strategy. For this purpose, a Matlab/Simulink forward LDS model of the vehicle including all its powertrain components is built up. The research vehicle uses an uncontrolled centrifugal clutch (CC) located on the input shaft of the CVT. The hybrid module, consisting of a 48V E-motor, inverter and a battery, is added in parallel hybrid architecture (P3 configuration) between the CVT output and the driven wheel. In this study, load on the CVT is increased during ICE driving by using the E-motor as a generator, while charging the battery at the same time and using this energy for pure electric driving afterwards. This load point shifting strategy (LPS) proves to be especially beneficial during low vehicle speed driving, when both the ICE as well as the CVT load and thus their efficiency is low. The study shows fuel consumption benefits of 43% in the WMTC for the considered vehicle, calculated according to the legislative requirements. Furthermore, the final LPS hybrid strategy is also tested in other, real-world driving scenarios to prove its real-world applicability.