Patent Description:
Aircraft use actuation systems in a wide range of applications. In particular, actuators may be used to operate movable surfaces of the aircraft, for example wing flaps and wing slats, for example in high lift systems.

Typically, a plurality of movable surfaces are provided on each wing of the aircraft, each surface being moved by one or more actuators, for example rotary actuators or ballscrews.

The actuators are driven by a common power drive unit, for example an electric motor which produces a rotary output. That output is transmitted to the actuators via a power transmission line which typically comprises a plurality of coupled drive shafts and which links the actuators together so as to ensure synchronous operation of the actuators and movement of the movable surfaces.

A problem that may arise in such systems is that a part of the actuation system may jam in use. For example, one of the movable surfaces or actuators may jam. When that occurs, the entire torque of the system may feed into the jammed component leading to excessive loads in the system. This means that in the absence of some mitigation, the relevant structure would have to be sized to resist such loading. This will result in weight penalties on the aircraft, which is undesirable.

<CIT> describes a control system may be used to control actuators that actuate movement of flight control surfaces of an aircraft. Each actuator is couplable to a flight control surface and includes a motion control assembly having a hydraulic motor and a drive path from the hydraulic motor to the flight control surface.

<CIT> describes an aircraft flap drive apparatus includes first and second centralized drive units that respectively rotationally drive first and second drive lines in both wings.

According to an aspect, there is provided an actuation system as recited in claim <NUM>. In accordance with various embodiments, the disclosure provides the actuation system as recited in each of claims <NUM> and <NUM>.

In accordance with the disclosure, therefore, a clutch disengages the power drive unit from the actuators upon sensing of an abnormal load condition. This provides a rapid decoupling of the drive, preventing damage to the system. The system is further protected by the brake which brakes the actuators and thereby prevents uncontrolled movement of the actuators.

The abnormal load condition may, for example, be a jam condition in the actuation system.

The at least one sensor for sensing an abnormal load condition may be configured to sense one or more of: a system load. a system torque, a system speed and a system position.

At least one sensor may be associated with each actuator.

The at least one sensor for sensing an abnormal load condition may be configured to sense at least one of an actuator load, actuator torque, actuator speed or actuator position.

In various embodiments, the clutch control may further be configured to actuate the brake upon the at least one sensor sensing the abnormal load condition.

The disclosure also provides an aircraft actuation system comprising an actuation system in accordance with the disclosure and a plurality of movable surfaces, the movable surfaces being moved by the plurality of actuators.

Respective movable surfaces may be arranged on respective wings of the aircraft with respective sections of the transmission line connected between the power drive unit and the actuators in each wing. A brake may be provided on each section of the transmission line.

A wing tip brake may be also operable in response to detection by asymmetry detectors on each transmission line section of asymmetrical deployment of the movable surfaces.

The disclosure also provides a method of preventing excessive loads in an actuation system as recited in claim <NUM>.

The method may comprise sensing a parameter indicative of system load, for example a system load, a system torque, a system speed or a system position and determining whether the sensed parameter indicates an abnormal load.

Some embodiments of the disclosure will now be described by way of example only with reference to the accompanying drawings in which:.

<FIG> illustrates an aircraft comprising a plurality of leading edge slats <NUM> on each wing <NUM> of the aircraft <NUM>. The slats <NUM> are selectively deployed and retracted by an actuation system <NUM>. The actuation system <NUM> comprises rotary actuators <NUM>, for example ballscrew actuators <NUM>. Each actuator <NUM> is powered by a rotary drive from a common power drive unit <NUM> such as an electric motor. Drive is transmitted from the power drive unit <NUM> via a transmission line <NUM>, which comprises series of power transmission shafts <NUM>, which connect the actuators <NUM> in series. The transmission shafts <NUM> may be joined by suitable couplings, not shown. The transmission line <NUM> is split into two sections 14A, 14B, extending along a respective wing <NUM>. A gearbox <NUM> may be provided to split the transmission line <NUM> into the two sections 14A, 14B.

A brake <NUM> is provided in each transmission line section 14A, 14B. This brake is typically towards the end of the transmission line section 14A, 14B, normally in the transmission line between the second from last and last actuator <NUM> on each wing <NUM> and is known as a wing tip brake. An asymmetry sensor <NUM>, which detects differences in position between the transmission line sections 14A, <NUM> B, is also provided on each transmission line section 14A, 14B. Asymmetrical operation of the slats <NUM> on the wings <NUM> is undesirable as it will create an asymmetrical aerodynamic effect, which is highly undesirable. Upon a difference being detected, the asymmetry sensor <NUM> will operate to cut or reduce power to the drive unit <NUM> and trigger the wing tip brake <NUM> so as to brake the transmission line and prevent further operation of the actuators <NUM>.

As discussed above, the actuators <NUM> deploy and retract the slats <NUM>. Should one of the actuators <NUM> or slats <NUM> jam, then potentially the entire output of the power drive unit <NUM> may be input into that actuator <NUM> or slat <NUM> leading to very high loads. The actuator <NUM> or slat <NUM> and the surrounding aircraft structure would then have to be sized to react those loads, which may result in additional weight, which is undesirable. Some systems incorporate mechanical torque limiters with each of the actuators <NUM> which will limit the torque transmitted into the actuator <NUM> when a jam occurs. While effective, these torque limiters introduce low temperature drag into the system and may therefore need extra power from the drive unit <NUM> to operate the system. Mechanical torque limiters may also have limited accuracy and may therefore be set to operate at high torques resulting in increased aircraft system and structural weight.

<FIG> illustrates an actuation system <NUM> in accordance with the disclosure which mitigates the effects of system overloading in a different manner.

The actuation system <NUM> of <FIG> comprises a plurality of actuators <NUM>, a common power drive unit <NUM> for driving the actuators <NUM> and a transmission line <NUM> transmitting drive from the common power drive unit <NUM> to the plurality of actuators <NUM>, as described above. The system also includes a wing tip brake <NUM> and asymmetry detector <NUM> on each transmission line section 14A, 14B as described above.

In the system according to the disclosure, however, a clutch <NUM> is arranged in the transmission line <NUM> between the power drive unit <NUM> and the plurality of actuators <NUM> for selectively disconnecting the power drive unit <NUM> from the plurality of actuators <NUM>, as will be described further below. The clutch <NUM> is arranged in the transmission line <NUM> at a point upstream of the splitting of the transmission line <NUM> into its two sections 14A, 14B such that on operation of the clutch <NUM> the power is disconnected to all the actuators <NUM>.

In normal operation, the clutch <NUM> will transmit power into the transmission line <NUM> and thus into the actuators <NUM>. However, in the event of an abnormal load condition in the system, for example a jam occurring in an actuator <NUM> or slat <NUM>, the clutch <NUM> will be disengaged from the power drive unit <NUM> so as to disconnect the power drive unit from the actuators, as will be described below.

To effect this disconnection, a plurality of sensors <NUM> is provided. At least one sensor <NUM> may be associated with each actuator <NUM>. The sensor may be arranged on the input or the output of the actuator. It may however be advantageous to place the sensor on the output, as this is closer to the surface being controlled.

Sensors <NUM> may also be positioned at different locations in the transmission line <NUM>. For example, sensors <NUM> may be positioned on the transmission line sections 14A, 14B. The sensors <NUM> sense a parameter that is indicative of an abnormal load condition occurring at an actuator <NUM> as may occur when an actuator <NUM> or the slat <NUM>, which it moves, jams. In those circumstances, the load applied to the actuator <NUM> will rise abnormally, this being sensed by the sensor <NUM>.

The sensor <NUM> may sense any parameter which is indicative of the abnormal load. Thus for example the sensor <NUM> may sense a system load, a system torque, a system speed and a system position. For example, the sensor <NUM> may sense an input torque or output torque in the actuator <NUM>, a load in the actuator <NUM>, a speed of the actuator <NUM>, or an input or output position of the actuator <NUM>. Measurement of a load, torque or speed may be particularly advantageous as providing a rapid indication of an abnormal condition.

The sensors <NUM> are connected to an electronic clutch control unit <NUM> that processes the sensor <NUM> signals and determine whether they are indicative of an abnormal load condition. If the clutch control unit <NUM> determines that an abnormal load condition exists, then it will operate to disengage the clutch <NUM> so as disconnect the power to the actuators <NUM>, to prevent further load being applied to the system. The clutch control unit may, for example send a disconnect command <NUM> to the clutch <NUM>, for example to a solenoid of the clutch <NUM>.

While the drive to the actuators <NUM> may be disconnected by disengagement of the clutch <NUM>, loads will still be present in the actuation system, for example due to aerodynamic loading of the slats <NUM> and inertia in the transmission line <NUM>. To mitigate the effects of these loads, the actuation system <NUM> further comprises a brake that brakes the transmission line <NUM> and thus the actuators upon operation of the clutch <NUM>.

In one embodiment, a dedicated brake may be provided, for example on each transmission line section 14A, 14B. In one embodiment, however, the clutch disconnection command <NUM> signal could also be used to initiate operation of the wing tip brakes <NUM> already present in the system and normally operable in response to the asymmetry detectors <NUM> detecting an asymmetrical operation of the slats <NUM>. This avoids the need for additional brakes in the system, thereby avoiding a weight penalty associated with such.

Normally, and as known in the art, in such circumstances, in addition to operating the wing tip brakes <NUM>, a signal <NUM> is sent to a power drive control unit <NUM> to stop or at least reduce the speed of the power drive unit <NUM>. Operation of the wing tip brakes <NUM>, or any other transmission line brake in a system of the disclosure, may also be used to control the power drive unit <NUM>.

The embodiment described above is advantageous in that it provides for rapid disconnection of power to the actuators <NUM> and therefore limitation of abnormal loads in the actuators without the need for mechanical torque limiters. It also provides for rapid braking of the transmission line either by brakes <NUM> already present in the system, or by a dedicated brake.

The clutch <NUM> can be of any suitable construction and is provided in the transmission line <NUM>. For example, it could be incorporated in an output of the power drive unit <NUM> or in an input to a gearbox <NUM> that splits the transmission line <NUM> into two sections 14A, 14B, or as a stand-alone unit mounted in the transmission line <NUM>. It may comprise a solenoid or hydraulics for actuation for example.

<FIG> illustrates a clutch <NUM> that may be used in a system of the disclosure. The clutch <NUM> comprises a clutch housing <NUM>, an input shaft <NUM> and an output shaft <NUM>. Friction plates <NUM>, <NUM> are coupled to the input shaft <NUM> and output shaft <NUM> respectively. The friction plates <NUM>, <NUM> are biased into contact by a coil spring <NUM> received within a spring housing <NUM>. The clutch further comprises a solenoid <NUM> which can be activated to disengage the clutch <NUM> by pulling the friction plate <NUM> coupled to the output shaft <NUM> away from the friction plate <NUM> coupled to the input shaft <NUM>, in a conventional manner. The solenoid <NUM> could be replaced by a hydraulic system in other embodiments.

However, the clutch <NUM> further comprises a static friction plate or ring <NUM> with which the friction plate <NUM> coupled to the output shaft <NUM> will engage when the clutch <NUM> is disengaged. This will act to brake the transmission line <NUM> to which the output shaft <NUM> is coupled. Such a clutch may be advantageous as providing a compact braking arrangement.

As discussed above, an abnormal loading condition can be detected by the sensors <NUM>. Various techniques may be employed, for example using a threshold exceedance method or by comparison with a system model predicting the behaviour of a healthy system.

An example of the first of these techniques is illustrated in <FIG>. In this embodiment, signals <NUM> from the sensors <NUM> in either wing <NUM> are compared against a predetermined threshold value in a step <NUM>, and if a signal exceeds the threshold, a clutch disengagement signal <NUM> is produced. As illustrated, the system may comprise a confirmation count step <NUM> to confirm that the signal is a true signal, i.e. it persists for longer than a predetermined time period or counts, before the signal is passed to the clutch control <NUM> to disengage the clutch <NUM>. This avoids the actuation system <NUM> from being shut down by brief spurious event.

An example of the second of these techniques is illustrated in <FIG>. In this embodiment, a command signal <NUM> is processed by a mathematical model <NUM> to predict a predicted sensor signal <NUM> that is then compared with the actual sensor signal <NUM> and if the difference <NUM> between the actual sensor measurement <NUM> and the predicted sensor measurement exceeds a predetermined threshold <NUM>, a clutch disengagement signal <NUM> is produced.

Of course, these are merely examples of abnormal condition detection techniques and the skilled person will easily be able to implement other suitable techniques.

From the above it will be understood that the disclosure provides an electronic system for disengaging a power drive unit from a plurality of actuators to protect the actuation system from abnormal operating conditions, particularly jams. This obviates the need for mechanical torque limitation devices. It allows for rapid and simple disengagement of the power drive unit and further brakes the system so as to prevent further movement of the actuators.

While the disclosure has been described in the context of an aircraft slat system, it may equally be applied to other actuation systems both on aircraft and elsewhere (for example an aircraft flap).

Also, while the illustrated embodiment comprises a common power drive unit <NUM> for driving the actuators <NUM> on both wings <NUM> of the aircraft, in other embodiments a respective power drive unit could be used to drive the actuators <NUM> of each wing <NUM> independently. In that event, a respective clutch <NUM> may be provided in each transmission line 14A, 14B. Sensing of an abnormal load condition in one of the actuators <NUM> could be operative to disconnect the clutch in the transmission line for just the affected transmission line 14A, 14B or in both transmission lines 14A, 14B.

Claim 1:
An actuation system (<NUM>) comprising:
a plurality of actuators (<NUM>);
a common power drive unit (<NUM>) for driving the actuators (<NUM>);
a transmission line (<NUM>) transmitting drive from the common drive unit (<NUM>) to the plurality of actuators (<NUM>);
a clutch (<NUM>) arranged in the transmission line (<NUM>) between the power drive unit (<NUM>) and the plurality of actuators (<NUM>) for selectively disconnecting the power drive unit (<NUM>) from the plurality of actuators (<NUM>);
at least one sensor (<NUM>) for sensing an abnormal load condition in the actuation system (<NUM>);
a clutch control (<NUM>), the at least one sensor (<NUM>) being operatively coupled to the clutch control (<NUM>), the clutch control (<NUM>) being configured such that when the at least one sensor (<NUM>) senses an abnormal load condition, the clutch control (<NUM>) is operative to disengage the clutch (<NUM>) so as to disconnect the power drive unit (<NUM>) from the plurality of actuators (<NUM>); and
a brake (<NUM>) operative to brake the actuators (<NUM>) upon disengagement of the clutch (<NUM>); and
characterised in that the clutch (<NUM>) comprises the brake (<NUM>) integrated into the clutch (<NUM>), thereby automatically operating the integrated brake (<NUM>) upon disengagement of the clutch (<NUM>).