Hydraulic power drive unit

An aircraft comprising:

• a fuselage;
• a wing extending from the fuselage;
• one or more high-lift devices arranged on the wing for altering the amount of lift generated by the wing;
• and
• a high-lift actuation system comprising:
• one or more actuators;
• a transmission shaft, wherein the transmission shaft is coupled to the one or more actuators to supply torque and rotation to the one or more actuators;
• and
• a hydraulic power drive unit (PDU) coupled to the transmission shaft to supply torque and rotation to the transmission shaft, wherein the transmission shaft extends at least partly along the wing and wherein each of the one or more high lift devices is coupled to at least one of the one or more actuators for actuation of the one or more high lift devices, and the hydraulic PDU is arranged in the fuselage;
• and
• wherein the hydraulic PDU comprises:
• a hydraulic motor for converting hydraulic pressure into torque and rotation;
• a hydraulic brake system for applying a braking force to the hydraulic motor to prevent rotation of the hydraulic motor, wherein the hydraulic brake system is biased to apply the braking force to the hydraulic motor to prevent rotation of the hydraulic motor, and configured to remove the braking force in response to a supply of hydraulic pressure;
• and
• a hydraulic circuit for supplying a flow of hydraulic fluid to the hydraulic motor to pressurise and thereby operate the hydraulic motor and for supplying hydraulic fluid to the hydraulic brake system to pressurise the hydraulic brake system and thereby remove the braking force;
• wherein the hydraulic circuit comprises a brake supply line for supplying the hydraulic fluid to the hydraulic brake system;
• wherein the brake supply line comprises a flow restricting device to restrict backflow of the hydraulic fluid in the brake supply line away from the hydraulic brake system;
• and
• wherein the hydraulic circuit is configured to enable depressurisation of the hydraulic motor while simultaneously preventing depressurisation of the hydraulic brake system to prevent application of the braking force.

A method for operating a power drive unit (PDU) comprising:

• supplying hydraulic fluid to a hydraulic motor via a hydraulic circuit to pressurise the hydraulic motor which converts hydraulic pressure into torque and rotation;
• and
• supplying hydraulic fluid to a hydraulic brake system via a brake supply line of the hydraulic circuit to pressurise the hydraulic brake system and thereby remove a braking force applied to the hydraulic motor so as to allow for rotation of the hydraulic motor;
• followed by
• depressurising the hydraulic motor whilst restricting backflow of hydraulic fluid in the brake supply line away from the hydraulic brake system such that the hydraulic motor is depressurised whilst depressurisation of the hydraulic brake system is simultaneously prevented thereby preventing application of the braking force;
• wherein the step of depressurising the hydraulic motor whilst restricting backflow of hydraulic fluid in the brake supply line is carried out following the detection of an event suggestive of a stall event of the motor.