Scaled Hardware in the Loop Simulation of the Electric Motors of a CVT for Agricultural Tractors

Electrification is a very current topic for all the mobile machinery whose primary source of power is an internal combustion engine; among those the light weight passenger vehicles represent the first field of application of this trend and also the state of the art of the technology. Agriculture is a huge fuel consumer sector and for this reason the tractor industry is now working on electrification, proposing different approaches for different power sizes: the "Battery Electric Vehicle" topology is proposed for small and mid-power size tractors, while for the big ones various hybrid architectures couple the internal combustion engine to electric units. In this paper a reference tractor is considered, endowed with an input coupled hydro-mechanical Continuously Variable Transmission and an alternative compound architecture is proposed, which provides the same performances and it is more suitable for electrification. The latter is modelled in Simcenter Amesim through a lumped parameter approach, focusing on the transmission and its control. The electric motors efficiency is modelled using the maps provided by the manufacturer. The main focus of this work is the construction of an experimental setup consisting of two electric motors test benches that allows to perform scaled tests reproducing the operation of the motors inside the transmission. The experiments' target is to measure the efficiency of the electric motors and the power electronics in real conditions. A comparison between the experimental and simulated data is performed. Additionally, a methodology is investigated to perform hardware in the loop simulations of the electric subsystem of a hybrid transmission. This methodology allows for the evaluation of control strategies related to the power balance of electric motor-generators and their effect on the recoverable energy.