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.