Optimization of hydro-mechanical power split transmissions

The increasing attention to comfort, automation and drivability is pushing the driveline technology to ever complex solutions, such as power-shift or continuously variable transmissions. Between these, the hydro-mechanical solution seems promising for heavy duty vehicle, due to the reliability and the capability of transferring high power. However, the double energy conversion occurring in the hydraulic branch of the transmission could lower excessively the total efficiency, highlighting the needs for a careful design of the whole system.In this work, the design of a hydro-mechanical transmission is defined as an optimization problem in which the objective function is the average efficiency of transmission, while the design variables are the displacements of the two hydraulic machines and gear ratios of ordinary and planetary gears. The optimization problem is solved by a “direct search” algorithm based on the swarm method, which showed a good speed convergence and the ability to overcome local minima.The optimization design method will be applied to study the transmission of two vehicles: a 62 kW compact loader and a high power agricultural tractor.

► The design of hydro-mechanical transmissions is treated as an optimization problem.
► A steady simulator and a swarm optimizer are coupled into an optimization procedure.
► The aim of the procedure is the definition of the maximum efficiency configuration.
► The procedure allows the automatic optimum preliminary design.
► Two different test cases are reported to show the capability of the proposed procedure.