Aircraft braking control system

Abstract

An aircraft braking control system for controlling a plurality of brakeable wheels of a landing gear is disclosed. Each brakeable wheel includes a brake actuator and a wheel speed sensor. The system includes a controller configured to receive aircraft control parameters and provide a braking command to the brake actuator of each wheel. The controller is configured to activate a pre-retraction brake in response to an aircraft control parameter indicating a need for landing gear retraction and perform a functional brake test during the pre-retraction brake. A method of operating an aircraft braking system is also disclosed.

Description

Technical Field

[0001] The present invention relates to an aircraft braking control system and a method of operating an aircraft braking system. Background Art

[0002] An aircraft landing gear includes a plurality of wheels, at least some of which are brakeable (which can be understood in this context to mean wheels having associated brakes). In civil aircraft, typically the wheels of the main landing gear are brakeable, where the configuration of the wheels depends on the size and type of the aircraft. For example, a single-aisle civil aircraft (such as the applicant's A320 series) typically may have a pair of main landing gears, each main landing gear having a pair of wheels arranged in pairs on a common axis. A wide-body aircraft (such as the applicant's A350 series) may have a pair of main landing gears, each main landing gear having a double axis with a pair of wheels on each axis.

[0003] A braking system associated with the landing gear typically includes a brake actuator for each brake (which may be multiple actuators for redundancy) and a wheel speed sensor that can be used to provide feedback and can be used, for example, in an anti-skid system. For safety and / or reliability purposes, the braking system may utilize one or more test procedures. For example, the braking system may include a pressure transducer that enables monitoring of the actuators in the braking system in a closed-loop manner. Thus, for example, a pre-landing brake test can be performed during the landing approach, where the brakes are applied together with the pressure transducer for monitoring the resulting output from the brake actuators.

[0004] However, it should be understood that there is a desire to provide additional or improved methods of testing a braking system. For example, a brake test using a brake transducer may only provide a yes / no response test and may not be able to distinguish between the braking responses of individual wheels, for example. For example, an aircraft braking system may apply the same response to each wheel during normal operation and may only apply differential wheel braking as part of an anti-skid system (if a skid condition is detected, it can be understood that this will reduce the braking on individual wheels).

[0005] Accordingly, at least some embodiments of the present invention seek to provide a braking system that can address or reduce at least some of the disadvantages of existing devices. Summary of the Invention

[0006] A first aspect of the present invention provides an aircraft braking control system for controlling a plurality of brakeable wheels of a landing gear, each brakeable wheel including a brake actuator and a wheel speed sensor, wherein the system includes a controller configured to receive aircraft control parameters and provide brake commands to the brake actuators of each wheel, the controller being configured to: receive aircraft control parameters and provide brake commands to the brake actuators of each wheel, the controller being configured to: activate a pre-retraction brake in response to an aircraft control parameter indicating a need to retract the landing gear; and perform a functional brake test during the pre-retraction brake.

[0007] It will be appreciated that on most commercial aircraft, the plurality of brakeable wheels are main landing gear wheels.

[0008] The pre-retraction brake is a brake applied to the wheels of the aircraft after takeoff and before the landing gear is retracted, and can typically be performed automatically during the sequential retraction of the landing gear of the aircraft. For safety reasons, it is not advisable to retract the landing gear while the wheels are rotating. Therefore, when the landing gear is commanded to retract (after takeoff), the brakes are typically activated within a few seconds to stop the wheel rotation. At the end of the pre-retraction brake window, the wheels are typically completely stopped, and the landing gear retraction continues. The inventors have now recognized that the pre-retraction brake provides a useful window during which the braking system according to embodiments of the present invention can perform a functional brake test.

[0009] Advantageously, performing a brake test during the pre-retraction brake can be performed without imposing a significant additional burden on the braking system (such that, for example, additional unnecessary brake wear can be avoided). In addition, the inventors have recognized that by performing a brake test during the pre-retraction brake, wheel speed data can be easily obtained. For example, many aircraft use a simple generator tachometer as a speed sensor. Such sensors are robust and reliable, but are passive sensors that do not provide any feedback when the wheel is stationary. After takeoff, the wheels of the aircraft immediately rotate freely at a relatively high speed. Therefore, the inventors have recognized that a brake test at this time may be beneficial.

[0010] In some embodiments, the functional brake test may include issuing sequential brake commands to the brake actuators of at least a first brakeable wheel and a second brakeable wheel. This can cause at least two brakeable wheels to be braked sequentially. The braking system can independently monitor the wheel speed sensors of each wheel. Advantageously, using sequential braking during the brake test can help distinguish the brake commands and responses for each wheel. For example, if the connectors within the braking system are incorrectly connected, it will be possible to detect that an incorrect wheel is being braked compared to the commanded brake command.

[0011] Issuing sequential braking commands can include issuing a first braking command to at least a first brakeable wheel among the brakeable wheels and issuing a second braking command to at least a second brakeable wheel among the brakeable wheels at a predetermined time after the first braking command. The delay between the first braking command and the second braking command can be selected to be sufficient to enable clear monitoring of the response of the wheel being braked (but can also be selected to be a small enough delay so as not to overly affect the overall pre-retraction braking time).

[0012] At least the first brakeable wheel among the brakeable wheels and at least the second brakeable wheel among the brakeable wheels can each include a plurality of brakeable wheels. Thus, in some embodiments, a first braking command is issued to a first set of brakeable wheels, and a second braking command is issued to a second set of brakeable wheels.

[0013] It can be understood that the wheels on an aircraft are typically configured in multiple sets. For example, the wheels can be arranged as pairs of wheels, and these pairs of wheels can be arranged in sequence on multiple landing gear assemblies. It may be particularly beneficial to provide a braking system that can perform a functional braking test that can distinguish the brakes within a set of wheels (e.g., two wheels in a pair). For example, if there is a configuration error in the braking system, it is most likely to occur between the wheels within a set. Thus, in some embodiments, the wheels within the first set of brakeable wheels and the second set of brakeable wheels are selected such that the wheels in a set of wheels on the aircraft (e.g., pairs of wheels on the aircraft) are in separate sets. In this way, it may be possible to avoid the need to divide the wheels into more than two sets, but for the functional braking test, it is still possible to ensure that the response of the wheels can be easily identified.

[0014] The inventors have recognized that, in order to ensure that a meaningful or reliable braking test can be performed, while also ensuring that the pre-retraction braking is performed without unnecessary additional strain or wear on the brakes, it may be desirable for the controller to ensure that the conditions meet preset requirements before performing the braking test. If the requirements are not met, the controller can simply perform the pre-retraction braking in a conventional manner without performing the braking test. Thus, in some embodiments, the controller can be configured to confirm that the wheel speed indicated by at least one of the wheel speed sensors is higher than a predetermined threshold before performing the functional braking test. Depending on the embodiment, if any wheel is not higher than the predetermined threshold, the controller can cancel the braking test entirely, or can exclude a particular one or more wheels from the test.

[0015] The controller can compare the detected speeds indicated by the respective speed sensors in the speed sensors. For example, this may help identify wheels that are not performing as expected. For example, if a wheel is rotating at a lower speed than another wheel before pre-retraction braking, this may indicate a faulty or damaged bearing of that wheel. Similarly, if a wheel is found to brake more slowly than other wheels under the same braking command, this may indicate a problem with the brake on that wheel. The controller can also be configured to issue a notification when the wheel speed detected by one of the wheel speed sensors does not conform to the expected response speed when a brake actuation command is issued during a functional brake test. The controller can flag or notify the operator of any such problems for further investigation. The notification can be, for example, a local (provided on the aircraft) notification, or can be provided via a networked health monitoring system that communicates with the brake control system.

[0016] In some embodiments, the controller can be configured to adapt at least one control parameter in response to a functional brake test. For example, in some brake systems, if a brake is identified as performing at below normal parameters, it may be possible to adjust the brake actuator response. In some systems, the brake system can include a reconfigurable manifold, for example, the control connections may be able to switch the hydraulic controls or actuators with which they communicate. In such a system, if the connections are found to be incorrectly configured, the controller can remap the connections in response to a functional brake test.

[0017] According to another aspect of the present invention, there is provided an aircraft landing gear system, the aircraft landing gear system comprising: a plurality of wheels, each wheel having: a brake including a brake actuator, and a wheel speed sensor; a landing gear retraction mechanism; and an aircraft brake control system according to an embodiment.

[0018] Another aspect of the present invention can provide an aircraft, the aircraft comprising: a plurality of brakeable wheels, each brakeable wheel including a brake actuator and a wheel speed sensor, and the aircraft including an aircraft brake control system according to an embodiment.

[0019] Another aspect of the present invention provides a method of operating an aircraft brake system, the aircraft brake system including a plurality of brakeable wheels, each wheel including a brake actuator and a wheel speed sensor, the method including performing a functional brake test during pre-retraction braking in response to a landing gear retraction command.

[0020] The functional brake test can include monitoring speed; sequentially activating the brake actuators of the plurality of brakeable wheels; and monitoring the response of the wheel speed of each brakeable wheel to the sequential brake actuations. Monitoring the speed of the brakeable wheels can include, for example, monitoring the wheel speed deceleration curve after takeoff.

[0021] The method may also include checking that the speed of each brakeable wheel is above a threshold before performing a functional brake test.

[0022] The method may include performing functional brake tests on multiple sets of wheels. At least one wheel in each set may be tested non-simultaneously with the other wheels in its wheel set. Testing at least one wheel in a first set of wheels may be performed simultaneously with testing at least one wheel in a second set of wheels.

[0023] Another aspect of the invention includes an aircraft braking system that includes: a plurality of brake actuators, each brake actuator associated with one of a plurality of wheels; a plurality of sensors for measuring the speed of each of the plurality of wheels; and a processor that includes: an input for receiving aircraft system commands, an output for issuing instructions to the plurality of brake actuators, and a machine-readable medium that includes instructions executable by the processor in response to an input indicating landing gear retraction to perform the following operations: activating a first brake actuator of the plurality of brake actuators without activating a second brake actuator of the plurality of brake actuators; and activating the second brake actuator of the plurality of brake actuators after a predetermined time delay following activation of the first brake actuator; and monitoring the speed sensors of each of the plurality of wheels during activation of both the first brake actuator and the second brake actuator of the plurality of brake actuators.

[0024] Another aspect of the invention includes an aircraft that includes an aircraft braking system according to an embodiment.

[0025] Although the invention has been described above, the invention extends to any inventive combination of the features set out above or in the following description or drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0027] Figure 1A and Figure 1B shows a schematic view of a commercial aircraft according to an embodiment;

[0028] Figure 2 shows a schematic representation of an aircraft braking system according to an embodiment;

[0029] Figure 3A and Figure 3B shows a typical physical configuration of an aircraft landing gear with a brake system manifold;

[0030] Figure 4A 、 Figure 4B and Figure 4C graphically represents sequential braking according to an embodiment;

[0031] Figure 5 A flowchart of a method according to an embodiment is shown. Detailed implementation

[0032] Figure 1A and Figure 1B A commercial aircraft 100 is shown in, in this case an example of the applicant's A320 series. The aircraft is provided with a front landing gear 110 carrying a pair of twin wheels and a pair of main landing gears 120 each having an additional pair of twin wheels. Generally, in most commercial aircraft, the front landing gear 110 is not provided with brakes because the front landing gear 110 only supports a relatively low proportion of the aircraft weight. The main landing gear wheels are typically provided with brakes (which will generally include hydraulically actuated brakes having a stack of rotor and stator discs located within the wheel hub). In the present application, a wheel having an associated brake is referred to as a brakeable wheel. It will be understood that the specific configuration of the wheels and landing gears will depend on the aircraft configuration and does not limit the present invention. For example, the main landing gear may also include multiple sets of twin wheels and such an arrangement is common on larger aircraft. The main landing gear wheels and associated braking systems are typically identified by numbering. Thus, as Figure 1B shown, when the aircraft is viewed from the front, the wheels on the main landing gear are numbered from left to right as wheels 1 to 4 in sequence, and this numbering will be used in the following description.

[0033] Brakes are both safety-critical systems and "rotatable" components (i.e., components that must be replaced or "rotated" at frequent intervals) because brakes wear during use. Therefore, it is important to be able to monitor or test brake performance without subjecting the brakes to additional unnecessary wear.

[0034] Figure 2 A braking system 200 according to an embodiment is shown in. For clarity, the system is shown on a single landing gear 210, but it should be understood that the wheels of the other landing gear will also be configured in the same manner. Figure 2 The example in shows a landing gear carrying wheels 1 and 2 (which will be denoted by 221 and 222 respectively in this figure). The braking system 200 has a controller 250 which may be a brake and steering control unit and may have various functions such as anti-skid braking, pre-retraction braking and brake testing. The braking system 200 includes brakes 241, 242 associated with each of the wheels 221 and 222 and wheel speed sensors 231 and 232. The wheel speed sensors 231 and 232 communicate with the controller 250. The wheel speed sensors 231 and 232 may be any convenient device in addition to, for example, tachometers of the generator type embedded within the axle of the wheel.

[0035] Brakes 231 and 232 can be connected via hydraulic lines 261 and 262. Typically, a hydraulic manifold 290 is provided, which can act as an interface between the hydraulic lines 261 and 262 and the controller 250. The manifold 290 can include actuators in the form of corresponding hydraulic servo mechanisms 281 and 282 for each of the brakes 241 and 242. Corresponding pressure transducers 271 and 272 can be provided for monitoring the response of the hydraulic system, and the pressure transducers 271 and 272 can provide closed-loop feedback regarding the actuation of the servo mechanisms 281 and 282.

[0036] Figure 3A and Figure 3B shows the physical arrangement of the manifold 290. As Figure 3A can be seen, the manifold can be located in the upper part of the landing gear 210. As Figure 3B can best be seen, the manifold 290 includes connections for the transducers 271 and 272 and the servo mechanisms 281 and 282. A particular error that can occur in use is that the connections to the transducers 271 and 272 or the servo mechanisms 281 and 282 are cross-connected. In such a case, the commands to one servo mechanism associated with the same wheel and the response detected in the other transducer are provided to the controller 250. Similarly, cross-connections can also occur at the tachometers 231 and 232, particularly at the pair of tachometers on the common axis for a corresponding pair of wheels. Typically, such cross-connections will not be a problem because the braking commands for each wheel in a pair of wheels are usually the same. However, this also means that cross-connections may not be detected. Cross-connections may only become apparent (and / or problematic) when the anti-skid system of the braking system is activated. The anti-skid system is activated when the tachometer 231 or 232 detects a mismatch between the wheel speed and the aircraft speed and thus a skid condition occurs. The braking system 200 will then reduce the braking on the skidding wheel until the skid stops. If there is a cross-connection on the servo valve or tachometer, there is a risk that the braking system 200 will reduce the braking on the non-skidding wheel because that wheel has been connected to the servo mechanism for the wheel suffering the skid. Embodiments of the present invention can enable such cross-connections to be simply and easily detected by means of a routine braking test introduced during pre-retraction braking.

[0037] The operation of sequential braking will now be further described with reference to Figures 4A to 4C which shows a graph of wheel speed and braking versus time. The graph shows the period from when a landing gear retraction command is given (at t = 0) until the landing gear has been retracted (when the "not downlock" state of the landing gear is confirmed). According to an embodiment of the present invention, the wheels are braked in separate groups, where Figures 4A to 4C Figure 4A Figure 4AThe illustration shows the application of braking for wheels 2 and 3 (the inner wheels of the two main landing gears) starting at t = 0, as shown by line B(2&3). The braking of the other wheels is delayed and starts at t = t1, as shown by line B(l&4). The resulting wheel speeds under braking are plotted, where Figure 4A shows the boundaries for the wheel speeds, which are defined by the upper line 400 showing the average speed and the line 410 showing the average minus two standard deviations. The initial left-hand portions of lines 400 and 410 represent the average wheel condition with freewheel deceleration. At t = 0, landing gear retraction is triggered, and the braking system initiates pre-retraction braking for wheels 2 and 3 (inner wheels). As shown by lines SAvg(2&3) and SMin(2&3) and SAvg(l&4) and SMin(l&4), it can be expected that the wheels will follow different deceleration curves, as shown by lines 420 and 430 for the average wheel speed and the minimum wheel speed (average less than 2 sigma) in the central region of the figure. At t = t1, it can be expected that the inner wheels have stopped rotating, and braking is applied to the outer wheels (1 and 4). Then, wheels 1 and 4 should decelerate between the average time limited by line 420 and the average minimum defined by line 430.

[0038] Several criteria can be identified by plotting the wheel speed variations, and will be further referred to Figure 4B and Figure 4C to illustrate the several criteria. First, as Figure 4B shown, an initial check can be performed to confirm that the initial wheel speed has sufficient inertia for a functional braking test and to identify any initial anomalies. As shown by arrow A, the first criterion can be to confirm that the wheel speed is greater than a threshold minimum, for example 85 kts in the figure. An initial comparison can also be made between the speeds of the wheels in the wheel set. For example, if the difference in speed between the wheels is greater than 20 kts, this can be considered anomalously asymmetric and may require investigation. The thresholds for the minimum speed and speed asymmetry can be selected to exclude only a small percentage (e.g., less than 1%) of irrelevant cases, such that a functional braking test will be performed in most cases.

[0039] As shown by arrow B at t = t1, the system can check that the wheel speeds of the inner wheels (2 and 3) intended to be braked and the outer wheels (1 and 4) that should freewheel are as expected. For example, the freewheel speed can be checked to confirm that the wheel speeds of the non-braked wheels (1 and 4) have not decreased by more than a predetermined amount between t = 0 and t = t1. This confirms that the wheels have not been inadvertently braked (i.e., when commanded for wheels 2 and 3) and that no other anomalies have occurred. At this stage, the controller can also check that the wheel speeds of the wheels that have been braked (2 and 3) are below a maximum value (e.g., 10 kts). It should be understood that these checks will enable the controller, for example, to identify whether a cross-connection has occurred.

[0040] Figure 4C Shows further criteria that the controller may apply at the end of the sequential pre-retraction braking. First, as shown by arrow C, at t = t1, the controller can confirm which wheels have been successfully braked. Then, at the end of the sequential pre-retraction braking, the controller can confirm that all wheels have been successfully braked, as shown by arrow D.

[0041] The method of an embodiment of the present invention may be represented by Figure 5 a flowchart. The method is initiated by issuing a landing gear retraction command in block 510. In block 520, the braking system performs pre-retraction braking in response to the landing gear retraction. According to an embodiment of the present invention, the pre-retraction braking is performed in parallel with the functional braking test. In block 530, the braking control system monitors the rotational speed of the wheels of the landing gear. In block 540, an initial check (as discussed above) is performed to ensure that the wheel speed exceeds a threshold. If the threshold is not exceeded, the control system may determine that the functional braking test will be ineffective or unreliable and may skip the test and continue with normal pre-retraction braking and subsequent landing gear retraction, as represented by arrow 545 and block 546.

[0042] When it is checked in block 540 that the threshold is met, the controller will activate the sequential braking function test in blocks 550 and 560. As discussed above, the sequential braking function test utilizes the wheel speed at takeoff such that in block 570, a tachometer (or other wheel speed sensor) can independently monitor the wheel speed response to the sequential braking. In block 580, the results of the braking function test can be notified. For example, if the results show no anomalies, these results can be recorded or shared with a health monitoring system to assist with predictive maintenance. If the results show anomalies, these results may be flagged to the crew or through a maintenance system such that corrective actions and / or inspections can be performed. In some embodiments, the system may additionally or alternatively implement corrective actions. For example, the system can identify errors or faults that can be accommodated or mediated. For example, the controller can change the braking mode or can internally reassign pairings between cross-connected components, such as the pairing of the tachometer with the servo valve.

[0043] Finally, in block 590, the landing gear is retracted at the end of the window for pre-retraction braking. At this time, all wheels should be properly braked (although it can be recognized that the landing gear retraction will occur automatically). In an embodiment of the present invention, the method will be performed in a time window similar to normal pre-retraction braking to ensure that the landing gear retraction is not unnecessarily delayed. For example, the total pre-retraction braking time window can be about 2 seconds and thus t1 can be about 1 second.

[0044] It should be noted that, unless otherwise explicitly stated, the term "or" as used herein shall be construed to mean "and / or".

[0045] Although the present invention has been described above with reference to preferred embodiments, it should be understood that various changes or modifications can be made without departing from the scope of the present invention as defined by the appended claims.

Claims

1. An aircraft braking control system for controlling a plurality of brakeable wheels of a landing gear, each brakeable wheel including a brake actuator and a wheel speed sensor, wherein, The system includes: a controller configured to receive aircraft control parameters and provide braking commands to the braking actuators of each wheel, the controller being configured to: activate pre-retraction braking in response to aircraft control parameters indicating a need for landing gear retraction; and perform a functional braking test during the pre-retraction braking, the functional braking test including: issuing sequential braking commands to a first braking actuator of a first brakeable wheel and a second braking actuator of a second brakeable wheel among the plurality of brakeable wheels to sequentially brake the first brakeable wheel and the second brakeable wheel; and independently monitoring the wheel speed sensors of each wheel, wherein issuing the sequential braking commands includes issuing a first braking command to the first brakeable wheel to activate the first braking actuator, and issuing a second braking command to the second brakeable wheel to activate the second braking actuator at a predetermined time after issuing the first braking command.

2. The aircraft braking control system according to claim 1, wherein, Issuing the first braking command to a first set of brakeable wheels and the second braking command to a second set of brakeable wheels.

3. The aircraft braking control system according to claim 2, wherein, The wheels within the first set of brakeable wheels and the second set of brakeable wheels are selected such that pairs of wheels on the aircraft are in separate groups.

4. The aircraft braking control system according to any one of claims 1-3, wherein, The controller is configured to confirm that the wheel speed indicated by at least one of the wheel speed sensors is higher than a predetermined threshold before performing the functional braking test.

5. The aircraft braking control system according to any one of claims 1-3, wherein, The controller is configured to compare the detected speeds indicated by the respective wheel speed sensors.

6. The aircraft braking control system according to any one of claims 1-3, wherein, The controller is configured to issue a notification when the wheel speed detected by one of the wheel speed sensors does not conform to the expected response speed when a braking actuation command is issued during the functional braking test.

7. The aircraft braking control system according to any one of claims 1-3, wherein, The controller is configured to adapt at least one control parameter in response to the functional braking test.

8. An aircraft landing gear system, comprising: a plurality of wheels, each wheel having: a brake including a braking actuator, and a wheel speed sensor, a landing gear retraction mechanism; and the aircraft braking control system according to any one of the preceding claims.

9. An aircraft, comprising: A plurality of brakeable wheels, each brakeable wheel including a braking actuator and a wheel speed sensor; and the aircraft braking control system according to any one of claims 1 to 7 or the aircraft landing gear system according to claim 8.

10. A method of operating an aircraft braking system, the aircraft braking system including a plurality of brakeable wheels, each wheel including a brake actuator and a wheel speed sensor, the method including performing a functional brake test during a pre-retraction braking in response to a landing gear retraction command, and wherein, The functional braking test includes: monitoring the speed of each brakeable wheel; sequentially activating the braking actuators of the plurality of brakeable wheels by activating a first braking actuator of a first brakeable wheel among the plurality of brakeable wheels without activating a second braking actuator of a second brakeable wheel among the plurality of brakeable wheels, and activating the second braking actuator after a predetermined time delay after activating the first braking actuator; and monitoring the response of the wheel speed of each brakeable wheel to the sequential braking actuation.

11. The method according to claim 10, wherein, The method further includes checking that the speed of each braking wheel is higher than a threshold before performing the functional braking test.

12. The method according to claim 10 or 11, wherein, The method includes performing the functional braking test on multiple groups of wheels, and wherein at least one wheel in each group of wheels is tested non-simultaneously with the other wheels in that group.

13. The method according to claim 12, further comprising testing at least one wheel of the first set of wheels simultaneously with at least one wheel of the second set of wheels.

14. An aircraft braking system, comprising: a plurality of brake actuators, each brake actuator being associated with one of a plurality of wheels; a plurality of sensors for measuring the speed of each of the plurality of wheels; and a processor, comprising: an input for receiving aircraft system commands, an output for issuing instructions to the plurality of brake actuators; and a machine-readable medium comprising instructions executable by the processor in response to an input indicating landing gear retraction to perform the following operations: activating a first brake actuator of the plurality of brake actuators without activating a second brake actuator of the plurality of brake actuators; and activating the second brake actuator of the plurality of brake actuators after a predetermined time delay after activating the first brake actuator; and monitoring the speed sensors of each of the plurality of wheels during activation of both the first brake actuator and the second brake actuator of the plurality of brake actuators.

15. An aircraft comprising the aircraft braking system according to claim 14.

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