Systems and methods for controlling propeller control unit fluid pressure

A propeller control unit for an aircraft propulsion system including a propeller, the propeller control unit comprising:

• an actuator configured to rotate propeller blades of the propeller to control a pitch of each of the propeller blades;
• a pump configured to direct hydraulic fluid to the actuator;
• a flow regulator in fluid communication with the pump, the flow regulator configured to control a hydraulic fluid pressure of the hydraulic fluid downstream of the pump;
• an auxiliary relief valve and a servo valve, the auxiliary relief valve and the servo valve in fluid communication with the pump;
• a pressure sensor in fluid communication with the pump, the pressure sensor disposed downstream of the pump, the pressure sensor disposed upstream of the actuator and the flow regulator, and the pressure sensor configured to measure the hydraulic fluid pressure and generate a hydraulic fluid pressure signal;
• and
• a controller in signal communication with the pressure sensor, the controller including a processor and a non-transitory memory storing instructions, the processor connected in communication with the non-transitory memory, the instructions when executed by the processor, cause the processor to:
• monitor the hydraulic fluid pressure signal from the pressure sensor;
• identify an over-pressure condition is present or absent based on a pressure range for the hydraulic fluid pressure signal;
• identify an under-pressure condition is present or absent based on the pressure range for the hydraulic fluid pressure signal;
• identify a degraded operational condition of the flow regulator based on identification of the over-pressure condition or the under-pressure condition of the hydraulic fluid pressure signal which occurs for an amount of time exceeding a time threshold;
• and
• open the auxiliary relief valve when the hydraulic fluid pressure signal exceeds a hydraulic fluid pressure threshold;
• wherein each of the servo valve, the pump, the flow regulator, and the auxiliary relief valve bound a main hydraulic fluid flow path of the propeller control unit, the pressure sensor in fluid communication with the main hydraulic fluid flow path, the auxiliary relief valve configured to control the hydraulic fluid pressure in the main hydraulic fluid flow path independent of the flow regulator.