Abstract
The operating field of hydrostatic drive system is presented. Subdivision of the hydraulic motor and pump work parameters into parameters independent of and dependent on the operation of displacement machines and the system is justified. A research project is proposed aimed at development of methods determining the energy characteristics of pumps and rotational hydraulic motors as well as modified methods of determining the energy characteristics of hydrostatic drive systems with selected structures of hydraulic motor speed control. The paper is an extended version of reference [11].