Influence of a CVT on the fuel consumption of a parallel medium-duty electric hybrid truck

Hybrid electric vehicles are being developed to reduce the pollutant emissions and the fossil-fuel consumption of transportation. Innovative technologies are inserted to improve the performance of hybrid vehicles, including trucks and buses. Thereby, trends towards gear shifting automation motivate the research on replacing a discrete conventional Automated Manual Transmission (AMT) with a Continuously Variable Transmission (CVT). Theoretically, such a transmission enables better operation points of the thermal engine, and therefore a reduction of its fuel consumption and emissions. However, the conventional (hydraulic actuated) CVT efficiency during quasi-stationary operation is typically lower than the efficiency of a classical discrete gearbox, which leads to higher fuel consumption. This paper is focused on the study of the interests of a CVT for a medium-duty Hybrid Electric Truck (HET). The complete model and control of CVT-based and AMT-based HET are described in a unified way using Energetic Macroscopic Representation (EMR). These models are transformed to backward-models to be computed by the Dynamic Programming Method (DPM). Such a method leads to define the (off-line) optimal energy management strategies for a fair comparison of both hybrid trucks. For the studied driving cycle, the hybridization allows a fuel saving of 10% with an AMT and 3% with a CVT. The fuel consumption is higher for the CVT-based HET in comparison with the AMT-based HET due to the lowest efficiency of the CVT (85%) compared to the AMT (around 92%). However, future (on-demand) CVTs with an increased efficiency could be a solution of interest to reduce the fuel consumption of such applications. The developed method can be used to test these new CVTs, other vehicles or other driving cycles. (C) 2018 International Association for Mathematics and Computers in Simulation (IMACS). Published by Elsevier B.V. All rights reserved.