Critical operation range of electro-hydrostatic actuator pumps based on cylinder block tilting states

The electro-hydrostatic actuator (EHA) pump is required to operate in a wide range of pressures and speeds to meet the variable output power demands. However, the reliable operation range of EHA pumps is restricted, and the cylinder block tilting is considered a serious factor. This paper presents an analytical approach for evaluating the critical operation range of EHA pumps based on a criterion for cylinder tilting states. It explicitly reveals the fundamental principle of the cylinder block tilting limiting the operation range. The criterion is verified with the measured tilting angle and leakage flow. Results show that the calculated critical conditions accurately identify the inflection point of performance changes. Beyond the critical operation range, the severe cylinder block tilting leads to a sharp increase in leakage and may even result in a sudden failure. Furthermore, the impacts of the center spring force, the piston-slipper assembly mass, and the position of the spline reaction on the critical operation range are investigated.