Input Coupled and Output Coupled Power Split Transmission Performance Under Comprehensive Working Conditions

Power Split Continuously Variable Transmissions are becoming a prominent topic, made recently popular for the extensive use of this architecture in hybrid passenger cars, even though one of the most important and well-established applications is those of agricultural tractors. The paper will present the comparison between a current production tractor Power Split Input Coupled (IC) architecture and an Output Coupled (OC) designed and set up by the authors, both of which feature hydrostatic transmission as the variable unit. Both the IC and OC architectures will be modelled with a lumped parameter approach, representing the full vehicle and taking into account all the elements from the engine, to hydraulics, to mechanical transmission, until the wheel, including a proper electronic logic control. The models will be used to calculate and compare the power flows through the different paths of the Power Split architecture in different types of cycle. The first class of cycles is an ideal reference condition, which imposes a constant load power, varying the output speed, and can be useful to understand the operating limits and performance of the hydraulic units and to assess the overall efficiency in a comprehensive range of operating conditions. The second class of cycles are taken from DLG-Powermix, which represent some of the most common field and on road working cycles (transport, plough, cultivator etc.). This part will be able to evaluate the energy performance and to determine the impact of hydraulic losses on overall consumption in significant working conditions, thus highlighting the higher efficiency, up to 12% better, which is obtained through the implementation of the alternative output coupled architecture.