PUB - Investigating the Condition Monitoring Potential of Oil Conductivity for Wear Identification in Electro Hydrostatic Actuators

More electric aircrafts are the future of modern personnel and cargo transportation. To achieve this goal, the conventional centralized hydraulic flight control system, which is responsible for the operation of the aircraft, needs to be replaced by decentralized electro-hydraulic actuators (EHA). The conventional hydraulic system consists of a large pump within the airplanes fuselage. To meet safety requirements, the entire system needs to be redundant resulting in additional heavy components. To further reduce fire risk, expensive and hazardous oils are used. To overcome the drawbacks of present systems individual small piston pumps powered by high dynamic electric motors are installed. Two actuators can be installed in close proximity to achieve redundancy and the limited oil volume in each EHA decreases the fire risk and making the need for large volumes of hazardous oil obsolete. Therefore, compared to the conventional system, the complexity can be reduced and safety can be increased at the same time.

Content

Authors, Duensing, Yannick; Richert, Oliver; Schmitz, Katharina

To meet future goals of more electric airplanes conventional hydraulic airplane control systems, consisting of redundant centralized pumps within the airplane’s fuselage, need to be substituted for compact electro-hydraulic actuators (EHA). The capsulated architecture of EHAs results in higher safety due to separate hydraulic circuits, simple practicability of redundancy, decreased maintenance because of simplified error location detection as well as an overall reduction in weight and complexity of the airplane control system. Currently, EHAs are only used as backup devices as the reliability does not achieve normative requirements for a frontline application. Thus, recent studies aim to increase the reliability. The axial piston pump of current EHA is the source of most failures. High dynamic requirements and challenging operation points and environments result in wear of contact pairs such as swash plate/piston shoes, pistons/cylinder block and cylinder block/valve plate. In the scope of the project MODULAR at ifas one goal is to increase the robustness of the contact surfaces. A second goal addresses the topic of developing a condition monitoring approach to constantly track the pumps’ health status. Next to signals such as pressures and temperatures, acceleration and oil status signals describing the actual particle contamination are needed. In this contribution different methods of oil status detection are explained and the method of electric conductivity analysis for condition monitoring is further investigated. Filtered HLP46 is used and impurities in form of metallic powders are added. Furthermore, degraded oil of a disc-on-disc Tribometer test bench is measured and compared.