FOREIGN PRIORITY

This application claims priority to European Patent Application No. 18166073.9 filed Apr. 6, 2018, the entire contents of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a hydraulic power drive unit (PDU) configured for relieving torque locked into a transmission system, for example in the event of a transmission system jam. In particular, the present invention relates to a PDU that enables torque locked into transmission systems of aircraft high-lift systems to be relieved. The PDU may be used, for example, to operate the flaps and slats on an aircraft's wing.

BACKGROUND OF THE DISCLOSURE

The wings of fixed wing aircraft are optimised for speed and efficiency during the cruise period of a flight, since this is normally the longest portion of the flight. Such optimisation reduces the amount of drag caused by the wings, but also reduces the amount of lift that can be generated by the wings. Aircraft of this type utilise high-lift devices, such as flaps and slats provided on the aircraft's wings, so that the amount of lift generated by the wings can be altered as required during different periods of the flight. For instance, the high-lift devices can be operated during take-off and landing in order to increase the amount of lift generated by the wings so as to reduce the distances and speeds required for take-off and landing.

High-lift devices are typically arranged along the length of both wings, and are operated by high-lift transmission systems connected to a hydraulic PDU. A conventional high-lift transmission system comprises two transmission shafts extending along respective wings of the aircraft the two transmission shafts being coupled to actuators associated with the high-lift devices. These transmission shafts are also connected to a hydraulic PDU generally situated centrally in the fuselage of the aircraft to provide rotation and torque to the transmission system and to enable movement of the high-lift devices. The transmission system transmits rotation and torque generated by the PDU to the high-lift devices, and causes movement of the high-lift devices so as to increase or reduce the amount of lift generated by the wing.

Hydraulic PDUs utilise pressurised hydraulic fluid to provide power to machinery. A typical PDU used for the operation of high-lift transmission systems comprises a hydraulic motor and a brake system. When hydraulic fluid is supplied to the hydraulic motor, the motor provides rotation and torque to the transmission shafts of the transmission system. The brake system is biased by a brake biasing force to prevent rotation of the motor and thereby the transmission shafts until hydraulic fluid is provided to the brake system. In this way, any undue movement of the high-lift devices, for example caused by the effect of airloads applied to the wings, can be prevented.

When movement of the high-lift devices is required, pressurised hydraulic fluid is provided to both the hydraulic motor and the brake system. This releases the brake, allowing for rotation of the hydraulic motor, and drives the hydraulic motor which provides torque to the transmission shafts and results in displacement of the high-lift devices.

High-lift transmission systems can sometimes become jammed in such a way that one or both of the transmission shafts are prevented from rotating. For example, jamming may occur if foreign objects or contaminants enter the system, perhaps as a result of maintenance error. Alternatively, increased loads on high-lift transmission systems caused by, for example, ice formation can result in the activation of protective torque limiters, effectively causing a jam in the system. In conventional systems, the PDU continues to provide torque to the transmission shaft until the PDU drives up to its full stall torque and a stall is detected (because when a jam occurs and the speed is zero, the PDU produces maximum torque, stall torque, in order to try to accelerate the system up to the required speed). Thus, torque continues to be applied to the jammed transmission shaft and the transmission shaft becomes twisted and loaded in torsion.

Typically, once a jam in the transmission system is detected, the PDU is disconnected from the supply of hydraulic fluid and the PDU is depressurised. Depressurisation of the PDU stops the hydraulic motor from rotating and simultaneously applies the brake. By applying the brake, the motor and the transmission shafts are prevented from rotating. Thus, the transmission shaft remains loaded in torsion and the torque applied by the PDU becomes locked into the transmission shaft. In order to withstand these forces without deformation, transmission shafts may be made to have a sufficiently large diameter to prevent failure. It will be appreciated that an increase in the diameter of the transmission shafts leads to increased weight.

The loads applied to the transmission shafts may also be applied to the actuators and joints in the transmission system through their connections with the transmission shafts. For example, the transmission system may incorporate transmission joints, such as universal joints, to connect several transmission shafts. In order to withstand these loads, these components are often oversized to increase their strength. Again, this adds weight to the transmission system.

Further, in the context of a high-lift transmission system of a fixed wing aircraft, the transmission shafts that transmit torque from the PDU to the high-lift devices are typically not positioned on the neutral axis of the wing. Therefore, as a wing bends during flight the length of the transmission shaft has to change in order to maintain a connection with the PDU and the other components arranged along the wing (e.g. actuators, gearboxes, steady bearings, universal joints). This length adjustment is generally enabled by sliding spline joints positioned at interfaces between the transmission shaft and other fixed components of the high-lift transmission system.

In the event that the high-lift transmission system becomes jammed, the torque applied by the PDU becomes locked into the transmission shaft and the sliding spline joints are forced to slide under high levels of torque. Applying torque to a sliding spline joint causes increased friction between the faces of the cooperating splines of the joint, making it more difficult for the splines to slide relative to each other. This friction between the faces of the splines is proportional to the torque applied to the sliding spline joints and the coefficient of friction between the spline faces. This can lead to large push and pull loads and can generate large forces along the longitudinal axis of the spline joints into their mating components. These push and pull loads may be termed plunge loads. In order to withstand these forces, the components of the system are required to be made larger and stronger, leading to increased weight in the system.

In the context of aircraft systems, it is generally advantageous to reduce weight as much as possible to improve efficiency of the aircraft. Hence, there is a need for an improved PDU and transmission system for high-lift systems.

SUMMARY OF THE DISCLOSURE

Viewed from a first aspect, the present disclosure provides a hydraulic power drive unit (PDU) for a transmission system, the hydraulic PDU comprising: 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; and 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; such that the hydraulic circuit is configured to enable depressurisation of the hydraulic motor whilst simultaneously preventing depressurisation of the hydraulic brake system thereby preventing application of the braking force.

It will be appreciated that by supplying a hydraulic fluid to the hydraulic motor the hydraulic fluid flows through the hydraulic motor so that it can operate to generate torque and rotation.

It will also be appreciated that simultaneous depressurisation of the hydraulic motor whilst preventing depressurisation of the hydraulic brake system will prevent application of the braking force and thereby allow free rotation of the hydraulic motor. By allowing free rotation of the hydraulic motor, any torque locked into a transmission shaft driven by the hydraulic PDU can be relaxed (i.e. released).

It will be further appreciated that where the supply of hydraulic fluid is described herein, this should be understood as the supply of hydraulic fluid pressure, i.e. pressurised hydraulic fluid. Equally, where hydraulic pressure is described, this will be understood as hydraulic fluid pressure, i.e. pressurised hydraulic fluid. As is very well understood, in the context of hydraulic systems, hydraulic fluid is supplied under pressure to carry out some operation, e.g. the supply of hydraulic fluid to the hydraulic brake system of the present disclosure pressurises the brake system to remove the braking force.

The flow restricting device may be a non-return valve that prevents backflow of hydraulic fluid in the brake supply line. The non-return valve may also be termed a check valve. The flow restricting device may alternatively be an active flow control valve that may be actively controlled to restrict or prevent flow of hydraulic fluid through the brake supply line.

In addition to one or more of the features described above, or as an alternative, the hydraulic circuit may be configured to enable depressurisation of the hydraulic motor by means of a motor return line. Fluid supplied to the hydraulic motor may flow away from the hydraulic motor via the motor return line to depressurise the motor.

In addition to one or more of the features described above, or as an alternative, the hydraulic circuit may be configured to depressurise the hydraulic motor upon detection of an event suggestive of a stall event.

The hydraulic PDU may comprise one or more sensors for detecting, or providing information from which can be detected, an event suggestive of a stall event of the hydraulic motor. In the event that the hydraulic motor stalls, it will stop rotating. Sensors may be provided to measure the angular speed and/or angular displacement of the output of the hydraulic PDU, e.g. an output shaft of the hydraulic motor. The output of such sensor(s) can be monitored for lack of movement which is indicative of a stall event. For example, the output of the sensors may be compared to what would be expected based on the input provided to the motor. If the output is not what is expected, e.g. the angular speed and/or displacement is less than expected, this may be indicative of a stall event. For example, the sensors may be angular displacement sensors. The measurements obtained by these may be differentiated to find the angular speed. The angular speed may be compared to a value, e.g. an expected value or a predetermined value. If the speed is less than the value, it is detected that an event suggestive of a stall event has occurred.

In addition to one or more of the features described above, or as an alternative, the hydraulic motor may rotate freely when the braking force is not applied by the hydraulic brake system.

In addition to one or more of the features described above, or as an alternative, the brake supply line may comprise a brake solenoid valve to control the flow of fluid to the hydraulic brake system and allow for depressurisation of the hydraulic brake system.

In addition to one or more of the features described above, or as an alternative, the hydraulic circuit may comprise a return line connected to the brake solenoid valve through which fluid may flow from the hydraulic brake system and the hydraulic brake system thereby depressurised, according to the control of the brake solenoid valve.

The brake solenoid valve may be a two-position solenoid valve. The brake solenoid valve may enable supply of hydraulic fluid to the hydraulic brake system when the brake solenoid valve is energised. The brake solenoid valve may enable depressurisation of the hydraulic brake system when the brake solenoid valve is de-energised.

In addition to one or more of the features described above, or as an alternative, the hydraulic motor may be a reversible hydraulic motor.

In addition to one or more of the features described above, or as an alternative, the hydraulic circuit may comprise a flow-reversing means for controlling a direction of the supply of hydraulic fluid to the hydraulic motor.

In addition to one or more of the features described above, or as an alternative, the flow-reversing means may comprise an electrohydraulic servo valve (EHSV). The EHSV may have three states; a first state in which hydraulic fluid is prevented from flowing through the EHSV, a second state in which hydraulic fluid may be supplied to an input of the hydraulic motor (e.g. for clockwise rotation), and a third state in which hydraulic fluid may be supplied to an output of the hydraulic motor (e.g. for anticlockwise rotation). The EHSV may be a linear EHSV for enabling linear control of the flow of hydraulic fluid to the hydraulic motor and hence control of speed.

The hydraulic circuit may comprise an enable solenoid valve for controlling the flow of hydraulic fluid into the hydraulic circuit. The enable solenoid valve may be a two-position solenoid valve. Additionally, the hydraulic circuit may comprise an enable spool valve that controls the flow of hydraulic fluid into the hydraulic circuit based on operation of the enable solenoid valve.

Operation of the hydraulic PDU may be controlled by a controller, which may be or comprise a computer. Hence, the present disclosure also provides a system comprising a hydraulic PDU according to any of the above described embodiments and a controller for controlling the operation of the hydraulic PDU. The controller may be configured to supply electrical control signals to the hydraulic PDU to control the supply of hydraulic fluid to the hydraulic motor and/or the hydraulic brake system. The controller may supply electrical control signals to the hydraulic PDU to control depressurisation of the hydraulic motor and/or the hydraulic brake system.

Typically, the hydraulic power drive unit is for a transmission system of an aircraft, in particular a transmission system for the operation of high-lift devices on an aircraft.

Viewed from a second aspect, the present disclosure provides a high-lift actuation system for operation of high-lift devices of an aircraft, the 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 PDU according to any of the above described embodiments coupled to the transmission shaft to supply torque and rotation to the transmission shaft. The high lift actuation system may further comprise a controller configured to control the operation of the hydraulic PDU.

It will be appreciated that the high-lift actuation system may typically comprise more than one transmission shaft, each being coupled to one or more actuators to supply torque and rotation to the one of more actuators. The hydraulic PDU will therefore be coupled to the transmission shafts to supply torque and rotation to the transmission shafts.

The hydraulic PDU makes it possible to enable depressurisation of the hydraulic motor whilst simultaneously preventing depressurisation of the hydraulic brake system. Thus, application of the braking force can be prevented and the hydraulic motor can be allowed to rotate freely. It will be appreciated that by allowing free rotation of the hydraulic motor, any torque that is locked into the transmission shaft can be relaxed.

The high lift actuation system may further comprise one or more sensors for providing information from which a jam can be detected. For example, sensors may be provided for measuring the angular speed and/or displacement of the transmission shaft. Such sensors are typically part of hydraulic actuation systems for positional control, therefore, it will generally not be necessary to add additional sensors in order to detect a jam. The output of such sensor(s) can be monitored for lack of movement which is indicative of a jam in the system. For example, the output of the sensors may be compared to what would be expected based on the input provided to the motor or compared to a pre-determined value. If the output is not what is expected, e.g. the angular speed and/or displacement is less than expected, this may be indicative of a jam. Sensors may also be attached to other components of the high-lift actuation system. Sensors may alternatively or additionally be provided for measuring the output of the hydraulic PDU. For example, sensors may be provided for measuring the angular displacement of the output of the hydraulic PDU (e.g. an output shaft of the hydraulic motor). The angular speed may be determined from the angular displacement, and this compared to an expected value or pre-determined value. If the measured angular speed is less than the expected or pre-determined value, this is indicative of a jam.

The presence of a jam in the system is suggestive of a stall event of the hydraulic motor of the hydraulic PDU. Hence, detecting a jam in the high-lift actuation system infers a stall event of the hydraulic motor.

Viewed from a third aspect, the present disclosure provides 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 according to any of the above described embodiments, wherein the transmission shaft extends at least partially 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.

The high-lift devices may comprise slats arranged along a leading edge of the wing. Alternatively, the high-lift devices may comprise flaps arranged along a trailing edge of the wing.

The aircraft may further comprise sensors for providing information from which a jam can be detected. Such sensors have been discussed above. For example, sensors may be provided for measuring the position of the high-lift devices. The sensors may be positioned along the wing adjacent the one or more high-lift devices. These sensors may also provide information indicative of the motion, or lack thereof, of the high-lift devices. Sensors may be provided for measuring the output of the hydraulic PDU, e.g. the angular displacement, from which angular speed can be determined. It will be appreciated that detection of the presence of a jam in the system is suggestive of a stall event of the hydraulic motor of the hydraulic PDU.

In a further aspect of the present disclosure, there is provided 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.

Restricting backflow of hydraulic fluid in the brake supply line may comprise preventing backflow of hydraulic fluid in the brake supply line. Backflow of hydraulic fluid in the brake supply line may be prevented by means of a non-return valve in the brake supply line.

In addition to one or more of the features described above, or as an alternative, the method may further comprise the subsequent step of depressurising the hydraulic brake system to thereby apply the braking force to the hydraulic motor to prevent rotation of the hydraulic motor. The hydraulic brake system may be depressurised by means of a brake solenoid valve which directs flow of hydraulic fluid away from the hydraulic brake system through a return line separate to the brake supply line. When fluid is directed to flow away from a device, it will be appreciated that this means it is depressurised. It will be well understood in the context of hydraulic systems that if fluid flows away from something, this does not necessarily mean that all fluid flows away. Some fluid may flow away and still cause depressurisation.

In addition to one or more of the features described above, or as an alternative, the step of depressurising the hydraulic motor whilst restricting backflow of hydraulic fluid in the brake supply line may be carried out following the detection of an event suggestive of a stall event of the motor. Therefore the method may further comprise the step of detecting an event suggestive of a stall event of the motor.

The disclosure also provides a method of operating a high-lift actuation system for operating high-lift devices of an aircraft, wherein the high-lift actuation system comprises: 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 of more actuators; and a hydraulic PDU coupled to the transmission shaft; wherein the hydraulic PDU is operated according to any of the embodiments described above to supply torque and rotation to the transmission shaft.

The method may further comprise controlling the operation of the hydraulic PDU with a controller.

The method may further comprise detecting a jam in the high-lift actuation system. This may comprise measuring the position of parts of the high-lift actuation system measured by one or more positional sensors. It may further comprise determining an angular speed from the measured position. If this is less than an expected value, a jam is detected. The expected value may be a value based on the input to the hydraulic motor or an otherwise pre-determined value.

For example, this may comprise monitoring the angular speed and/or displacement of the transmission shaft and, if the angular speed and/or displacement of the transmission shaft is less than expected based on the input to the motor, it is determined that a jam may have occurred. Alternatively or additionally, this may comprise measuring the angular displacement of the output of the hydraulic PDU, e.g. the output shaft of the hydraulic motor, and calculating the angular speed from the angular displacement. If this is less than expected, it is determined that a jam may have occurred.

If it is determined that a jam may have occurred this is suggestive of a stall event. The step of depressurising the hydraulic motor whilst restricting backflow of hydraulic fluid in the brake supply line may only be carried out if it is determined that a jam may have occurred.

In another aspect, the disclosure provides a method of relaxing torque locked into a transmission shaft of an aircraft high-lift actuation system driven by a hydraulic motor of a hydraulic PDU, comprising: determining whether a jam may have occurred in the high-lift actuation system, and if it is determined that a jam may have occurred, then: de-pressurising the hydraulic motor to remove torque from an output shaft of the hydraulic PDU whilst simultaneously restricting backflow of hydraulic fluid in a brake supply line of a hydraulic brake system acting on the hydraulic motor, so as to prevent depressurisation of the brake system and thereby prevent application of a braking force to the hydraulic motor, whereby torque locked-in to the transmission shaft is relaxed; followed by depressurising the hydraulic brake system so as to apply the braking force to the hydraulic motor. Relaxing torque may also be considered as releasing torque.

It will be appreciated that features described in relation to a certain aspect of the disclosure may be equally applicable to other aspects of the disclosure and vice versa.

