Improved Loss Modeling of Hydrostatic Units: Requirement for Precise Simulation of Mobile Working Machine Drivelines

The aim of this paper is to analyze different loss modeling methods for hydrostatic pumps and motors as an input for dynamic system simulation. Using dynamic simulation in an early design phase allows for optimization of driveline, driveline control and working hydraulic within several operating conditions. Using precise loss modeling methods enables prediction of energy consumption and energy losses over various duty cycles. Rising energy costs, enhanced government guidelines and increased environmental awareness require more efficient drive concepts especially in mobile working machines. Because of the complex machine structure with numerous hydraulic power consumers, like driveline, working, steering and braking hydraulic, dynamic system simulation is a need in the early design phase. This paper focuses on partial and full hydrostatic drivelines of mobile working machines which operate mostly on basis of a closed circuit hydrostatic transmission. Hydrostatic power lines connect pump and motor directly without additional losses because of valves or system characteristics. Therefore losses in the hydrostatic units have major relevance for the loss behavior of the hydrostatic transmission. The use of precise loss models is essential for analyzing hydrostatic transmission by means of dynamic system simulation. In the scope of this paper, one physical-empiric and four mathematical loss modeling methods are introduced, investigated and compared. Finally, the most promising modeling method is used for the simulation of a state of the art hydrostatic transmission.