Fluid power supply unit for agricultural tractors: towards energy saving through simulation

The final aim of the research is to test and verify the effectiveness of high efficiency hydraulic architectures in agriculture tractors. In this paper the attention has been focused on the fluid power delivery group of the vehicle in order to generate a model of the fluid power supply unit used to supply the high pressure circuit of an agricultural tractor able to replicate the performances and the dynamic behaviour of the actual system. The group is composed of a variable displacement axial piston pump equipped with pressure and flow compensators. Despite the evident advantages of the use of this system in the hydraulic applications for off-road vehicles, there are still some critical issues mainly due to instability in some operating onditions and to energy dissipation, that is a direct consequence of the use of dissipative elements to maintain control and avoid interference of loads. In this work an axial piston pump is modelled in detail and analysed in terms of dynamic behaviour of the swashplate, in particular two different versions of the displacement actuations are considered, the first realized using a single actuator that works against the pistons momentum and against a spring, the second that uses a bias and a control actuator to manage the displacement variation. A simple duty cycle is used to study the performance of the pressure and flow compensators. The dynamic behaviour of the two pumps isanalysed and compared allowing to evidence the main design parameters that play a relevant role in the pump performances; this is a key step for the future work, which aims at introducing electronic control for the pump displacement.