Aircraft brake control system, aircraft landing gear, aircraft and aircraft braking method

Abstract

The invention relates to an aircraft brake control system, an aircraft landing gear, an aircraft and an aircraft braking method. In one aspect, an aircraft brake control system for controlling anti-skid braking of a wheel of an aircraft is described, comprising a control assembly having: i) an input indicative of an aircraft speed, ii) an input indicative of a wheel speed of the wheel, iii) an input indicative of a braking level, iv) an input indicative of a braking energy supply configuration, v) an optimal slip ratio calculator for calculating an optimal slip ratio of the wheel based at least partly on the indication of the wheel speed and the aircraft speed, vi) a state determiner for determining a state of the wheel, vii) an anti-skid braking calculator for calculating an anti-skid braking command based on the wheel speed, the braking level and the determined state, viii) a state mode controller setting a mode of operation of the state determiner, and iv) an output for indicating the anti-skid braking command to be sent to a brake valve.

Description

[0001] This application is a divisional application of the application filed on March 8, 2022, with application number 202210228297.1 and entitled "Aircraft Braking Control System, Landing Gear, Aircraft and Aircraft Braking Method". Technical Field

[0002] This disclosure relates to aircraft braking control systems.

[0003] This invention relates to an aircraft braking control system. More specifically, but not exclusively, this invention relates to an aircraft braking control system for controlling anti-skid braking of aircraft wheels, the system comprising a control component having an input indicating wheel speed, an input indicating braking level (desired / commanded braking level or actual braking level), an anti-skid braking calculator for calculating an anti-skid braking command based on wheel speed and braking level, and an output indicating the anti-skid braking command to be sent to the braking valve.

[0004] The present invention also relates to other aircraft braking control systems, aircraft landing gear, aircraft, and aircraft braking methods. Background Technology

[0005] Conventional anti-skid systems reduce the braking command level to unlock slipping wheels by decreasing the braking force / torque they experience. Therefore, braking performance is temporarily reduced to unlock the slipping wheel, thereby improving overall braking performance. This also prevents slipping wheels from bursting due to prolonged slippage.

[0006] US 2020 / 0407049 describes an anti-slip braking system that can be employed in standby mode, i.e., when the hydraulic braking fluid available for braking is limited. Here, the reduction in braking command due to anti-slip exceeds the reduction under normal conditions. In the described braking system, the reduction in command is based on a slip error factor (obtained by comparing the dynamic slip of multiple wheels with a target slip value).

[0007] However, the system does not take into account what the wheels might actually be doing (e.g., slipping, skidding, or other actions). The system also does not consider that a fixed target slip value may not be appropriate under current conditions (e.g., the target slip value may be determined for a dry runway and / or cool weather, but a wet runway or hotter weather will affect the level at which the target slip value (when the coefficient of friction is at its maximum) should be).

[0008] Therefore, this may result in applying more or fewer anti-skid braking commands than ideally.

[0009] Furthermore, the anti-slip system does not consider how to prevent slippage in the first place (unlocking the slippage only when slippage occurs), nor does it consider how to further prevent the loss of hydraulic fluid from the system.

[0010] Figure 1 This is a schematic diagram of different anti-skid braking control systems. Here, the anti-skid braking current is calculated using wheel speed and other factors considered by the optimized controller. This anti-skid braking current is subtracted from the command current to provide the brake servo valve current. This servo valve current is used to control the hydraulic braking pressure applied to the wheels.

[0011] The present invention seeks to mitigate the aforementioned problems. Alternatively or additionally, the present invention seeks to provide an improved aircraft braking control system. Summary of the Invention

[0012] According to a first aspect, the present invention provides an aircraft braking control system for controlling anti-skid braking of the wheels of an aircraft. The system includes a control component having: an input indicating wheel speed; an input indicating braking level; an input indicating braking energy supply configuration; an anti-skid braking calculator for calculating an anti-skid braking (current) command based on the wheel speed and braking level; a mode controller for setting an operating mode of the anti-skid braking calculator; and an output indicating an anti-skid braking (current) command to be sent to a braking valve. The mode controller is configured to: set a first mode when the input indicating braking energy supply configuration indicates that a first braking energy supply is being used, in which the anti-skid braking calculator applies a first limit level to the rate of increase of the anti-skid braking (current) command; and set a second mode when the input indicating braking energy supply configuration indicates that a second braking energy supply is being used, in which the anti-skid braking calculator applies a second limit level to the rate of increase of the anti-skid braking (current) command, the second limit level being lower than the first limit level.

[0013] Such a system allows for greater limitation on the rate of increase of the braking command (current) when in a second, such as emergency or auxiliary energy supply configuration. This reduces braking efficiency (because it takes longer to increase braking torque) but is more likely to prevent slippage (which could otherwise occur due to overly aggressive re-braking after slippage has been released). Therefore, such a system reduces the need to release the brake to release slippage and then reapply the brake. Consequently, the total energy required by the braking system is reduced. This can be important when operating the brakes using an emergency or auxiliary supply. The brake valve is configured with one or more energy supplies and uses one or more energy supplies to operate the brakes.

[0014] The braking level indication can be, for example, the desired braking level, a command (current) from the brake pedal in the cockpit, or an automatically calculated braking demand from the automatic braking function, or it can be the actual braking level of the wheels.

[0015] The brake energy supply configuration indication indicates which energy supply is being used for braking. In other words, the brake energy supply configuration indication indicates which energy supply is being provided to the brake valves to provide braking torque to the wheel brakes.

[0016] The first braking energy supply can be a primary or "green" supply. The second braking energy supply can be an auxiliary, backup, or "yellow" supply configured to connect to the brake valve when the primary supply is unavailable.

[0017] The primary braking energy supply can be an auxiliary, backup, or "yellow" supply. The secondary braking energy supply can be an emergency supply configured to connect to the brake valve when the auxiliary supply is unavailable.

[0018] Backup energy / fluid supply may include energy accumulators / hydraulic / pneumatic accumulators / batteries with a limited available supply. Accumulators may be located on the yellow energy supply / hydraulic fluid line.

[0019] Primary, auxiliary, and / or emergency supplies can be hydraulic fluid supplies. For example, an emergency supply may include a hydraulic reservoir with only a limited amount of available hydraulic fluid.

[0020] Control components can reside in a single control unit or be distributed among different control units. For example, an anti-skid brake calculator can be in a separate (but connected) unit connected to the output.

[0021] Other components of the anti-skid brake calculator or control assembly may exist in a single control unit or may be distributed among different control units.

[0022] The rise rate is the rise rate of the (current) command.

[0023] The first limit level can be so high that there is practically no limit applied to the current / command. For example, the first limit level could be the system limit. In other words, it could be the current / command scalation rate at which the aircraft system cannot provide a current / command scalation rate higher than that rate.

[0024] The second limit is a lower level, which keeps the rate of increase generally low when using a second energy braking supply. Importantly, the lower rate limit is applied only during the current / command rise, not during the fall, so as not to interfere with the anti-slip function (which reduces braking torque when slippage is detected).

[0025] This invention can be applied to any number of wheels and / or braking systems of an aircraft.

[0026] Preferably, the second restriction level can be between 30% and 90% of the first restriction level, more preferably between 50% and 80% of the first restriction level, and even more preferably between 70% and 75% of the first restriction level.

[0027] These ratios allow for a significant reduction in the current / command rise rate, thereby preventing further slippage.

[0028] Preferably, the mode controller is further configured to: set a third mode when an input indicating the braking energy supply configuration indicates that a third braking energy supply, such as an emergency supply, is being used, in which the anti-slip brake calculator applies a third limit level to the rate of increase of the anti-slip brake (current) command, the third limit level being lower than the second limit level.

[0029] Preferably, the restriction level is variable.

[0030] The second or third limit level (or both) can be variable. This allows the rate of limit increase to be adjusted based on other factors, thereby achieving a suitable balance between braking efficiency and other factors.

[0031] More preferably, the control component includes an input indicating the level of remaining energy in the braking energy supply, and wherein the limit level is adjusted according to the level of remaining energy.

[0032] For example, if a hydraulic fluid accumulator is used as a braking energy supply, such as a third braking energy supply, the rate of ascent will be further limited as the hydraulic fluid is depleted. This strikes a proper balance between braking efficiency and ensuring that the hydraulic fluid does not run out over time.

[0033] This could be a continuous indication of the remaining energy level. Alternatively or additionally, it could be an indication of the remaining energy level within a specific range. Alternatively or additionally, it could be an indication of when the remaining energy level has decreased to a certain range.

[0034] Preferably, the anti-slip calculator includes an anti-slip computer and a limiter device, wherein the anti-slip computer is used to calculate an initial anti-slip (current) command, and the limiter device is used to receive the initial anti-slip (current) command and then apply a rate-of-rise limit.

[0035] In other words, restrictions are applied after the initial anti-slip calculations.

[0036] Alternatively or additionally, limitations can be applied by adjusting the inputs to the initial anti-slip calculation. For example, one or more of the following inputs can be adjusted: changes in compliance calculations, factors / adjustments applied to control speed, or factors / adjustments applied to speed errors.

[0037] Preferably, the anti-skid brake calculator is configured to apply a specified minimum (current) command level to the anti-skid brake (current) command.

[0038] This advantageous feature of the sixth aspect of the invention can be used in conjunction with the first aspect. This feature can also be used in conjunction with the eleventh aspect of the invention.

[0039] According to a second aspect of the invention, an aircraft landing gear is also provided, the aircraft landing gear including the aircraft braking control system as described above and wheels configured to be controlled by the aircraft braking control system in anti-skid braking.

[0040] According to a third aspect of the invention, an aircraft is also provided, which includes the aircraft braking control system as described above or the aircraft landing gear as described above.

[0041] According to a fourth aspect of the invention, an aircraft braking method is also provided, the method comprising the steps of providing an aircraft braking control system as described above, an aircraft landing gear as described above, or an aircraft as described above.

[0042] According to a fifth aspect of the invention, an aircraft braking method is also provided, the method comprising the steps of: noting that a second braking energy supply is being used; calculating an anti-skid braking (current) command; and applying a rate-of- ascent limit to the anti-skid braking (current) command, the limit level being lower than that in the case where a first braking energy supply is being used.

[0043] Preferably, the method further includes the following steps: operating in a first mode, in which a first braking energy supply is used, and in which the anti-slip braking (current) command has an increase rate limited by a first limit level; and switching to a second mode, in which a second braking energy supply is used, and in which the anti-slip braking (current) command has an increase rate limited by a second limit level lower than the first limit level.

[0044] According to a sixth aspect of the invention, an aircraft braking control system for controlling anti-skid braking of the wheels of an aircraft is also provided. The system includes a control component having: an input indicating the wheel speed; an input indicating the braking level; an anti-skid braking calculator for calculating an anti-skid braking (current) command based on the wheel speed and the braking level, wherein the anti-skid braking calculator is configured to apply a specified minimum current / command level to the anti-skid braking (current) command; and an output indicating an anti-skid braking (current) command to be sent to a braking valve.

[0045] For example, such a system allows for the maintenance of minimum braking torque and thus prevents the discharge of the hydraulic brake piston. This prevents energy loss in the braking system (e.g., loss of hydraulic fluid). This can be important when operating the brakes using emergency or auxiliary power supplies. The brake valve is equipped with one or more power supplies and uses one or more power supplies to operate the brakes.

[0046] The indication of braking level can be, for example, the desired braking level, a command (current) from the brake pedal in the cockpit, or an automatically calculated braking demand from the automatic braking function, or it can be the actual braking level of the wheels.

[0047] The specified minimum current / command level can be fixed. For example, the minimum current can be approximately 8 mA.

[0048] The anti-slip braking current command may vary between 0 mA and 40 mA under other conditions (without a minimum level).

[0049] Specific minimum command levels can be between 10% and 30% of the maximum available anti-slip braking (current) command. Specific minimum command levels can be between 15% and 20%.

[0050] Control components can reside in a single control unit or be distributed among different control units. For example, an anti-skid brake calculator can be in a separate (but connected) unit connected to the output.

[0051] Other components of the anti-skid brake calculator or control assembly may exist in a single control unit or may be distributed among different control units.

[0052] This invention can be applied to any number of wheels and / or braking systems of an aircraft.

[0053] Preferably, the specified minimum (current) command level is greater than zero.

[0054] Therefore, a set amount of hydraulic fluid can be maintained in the brake.

[0055] This can cause the brake piston to move between 10% and 30% of its maximum stroke length, for example, only about 20% of its maximum stroke length. For example, the maximum stroke length might be 10 cm. When a specified minimum (current) command level is applied, this could result in the brake piston position being 80% of its maximum value. In other words, the brake piston only moves backward 20% of its stroke length.

[0056] More preferably, the specified minimum (current) command level corresponds to the braking pressure that does not produce braking torque.

[0057] The specified minimum (current) command level can be below "Zero Torque Pressure" (ZTP).

[0058] The specified minimum (current) command level can be within 5% of the "Zero Torque Pressure" (ZTP).

[0059] More preferably, the specified minimum (current) command level corresponds to the maximum braking pressure that does not produce braking torque.

[0060] This is known as the "zero torque pressure" (ZTP) level. In other words, the maximum amount of brake hydraulic fluid can be retained in the brake piston when it is not producing braking force. For example, the brake piston may only be in contact with the brake.

[0061] Alternatively, the specified minimum (current) command level corresponds to a braking pressure that produces less than 5% of the maximum braking torque.

[0062] In other words, the (current) command is only slightly higher than ZTP.

[0063] The (current) command level corresponding to ZTP can be 5% to 40% of the maximum available command (current), preferably 10% to 30%, and more preferably about 20%. For example, the ZTP current can be 8 mA, and the maximum available current can be 40 mA.

[0064] Preferably, the aircraft braking control system further includes an input indicating the braking energy supply configuration and a mode controller for setting the operating mode of the anti-skid brake calculator. The mode controller sets a first mode when the input indicating the braking energy supply configuration indicates that a first braking energy supply is being used, in which the anti-skid brake calculator does not apply a specified minimum (current) command level, and sets a second mode when the input indicating the braking energy supply configuration indicates that a second braking energy supply is being used, in which the anti-skid brake calculator applies a specified minimum (current) command level.

[0065] Therefore, when in auxiliary or emergency mode where energy supply may be limited, the system can control the fluid to remain (only) in the brake piston.

[0066] The brake energy supply configuration indication indicates which energy supply the brake is using. In other words, the brake energy supply configuration indication indicates which energy supply the brake valve is set to provide braking torque to the wheel brakes.

[0067] The first braking energy supply can be a primary or "green" supply. The second braking energy supply can be an auxiliary, backup, or "yellow" supply configured to connect to the brake valve when the primary supply is unavailable.

[0068] The primary braking energy supply can be an auxiliary, backup, or "yellow" supply. The secondary braking energy supply can be an emergency supply configured to connect to the brake valve when the auxiliary supply is unavailable.

[0069] Backup energy / fluid supply may include a limited-supply energy accumulator / hydraulic / pneumatic accumulator / battery. The accumulator may be located on the yellow energy supply / hydraulic fluid line.

[0070] Primary, auxiliary, and / or emergency supplies can be hydraulic fluid supplies. For example, an emergency supply may include a hydraulic reservoir with only a limited amount of available hydraulic fluid.

[0071] Preferably, the anti-slip calculator includes an anti-slip computer and an amplification device, the anti-slip computer being used to calculate an initial anti-slip (current) command, and the amplification device being used to receive the initial anti-slip (current) command and then apply a specified minimum (current) command level.

[0072] According to a seventh aspect of the invention, an aircraft landing gear is also provided, the aircraft landing gear including the aircraft braking control system as described above and wheels configured to be controlled by the aircraft braking control system in anti-skid braking.

[0073] According to an eighth aspect of the invention, an aircraft is also provided, the aircraft including the aircraft braking control system as described above or the aircraft landing gear as described above.

[0074] According to a ninth aspect of the present invention, an aircraft braking method is also provided, the method comprising the steps of providing an aircraft braking control system as described above, an aircraft landing gear as described above, or an aircraft as described above.

[0075] According to a tenth aspect of the present invention, an aircraft braking method is also provided, the method comprising the steps of: calculating an anti-skid braking (current) command; and applying a specified minimum (current) command level to the anti-skid braking (current) command.

[0076] Preferably, the method further includes the following steps: operating in a first mode using a first braking energy supply; and switching to a second mode, in which a second braking energy supply is used, and in which the anti-slip brake (current) command applies a specified minimum (current) command level.

[0077] According to an eleventh aspect of the present invention, an aircraft braking control system for controlling anti-skid braking of the wheels of an aircraft is also provided. The system includes a control component having: an input indicating aircraft speed; an input indicating wheel speed; an input indicating braking level; an input indicating braking energy supply configuration; an optimal slip ratio calculator for calculating the optimal slip ratio of the wheels based at least in part on the wheel speed and the aircraft speed; a state determiner for determining the state of the wheels, including a "small slip" state, in which the determined slip ratio of the wheels is lower than a slip limit higher than the optimal slip ratio; and an anti-skid braking calculator for... The system calculates the anti-slip braking (current) command based on wheel speed, braking level, and a defined state; a state mode controller sets the operating mode of the state determiner, configured to: set a first state determiner mode when an input indicating braking energy supply configuration indicates that a first braking energy supply is being used, and in this first state determiner mode, use a first slip limit value as the slip limit; and set a second state determiner mode when an input indicating braking energy supply configuration indicates that a second braking energy supply is being used, and in this second state determiner mode, use a second slip limit value as the slip limit, the second slip limit value being lower than the first slip limit value; and an output indicating the anti-slip braking (current) command to be sent to the brake valve.

[0078] If the wheel slip (relative to the optimal slip ratio) exceeds a certain limit, such a system allows for the determination of "minor slip". However, in particular, the system can apply different (lower) limits when operating in a second configuration, such as emergency or auxiliary energy supply.

[0079] This reduces braking efficiency (because the braking torque is released at a lower slip ratio), but is more likely to prevent more severe or "deep slippage." Therefore, it reduces the need for a more complete release of the brakes to unlock "deep slippage" and then reapplying the brakes. Consequently, it reduces the total energy required by the braking system. This can be important when operating the brakes using emergency or auxiliary power supplies. Brake valves are configured with one or more energy supplies, and one or more energy supplies are used to operate the brakes.

[0080] The indication of braking level can be, for example, the desired braking level, a command / current from the brake pedal in the cockpit, or an automatically calculated braking demand from the automatic braking function, or it can be the actual braking level of the wheels.

[0081] The brake energy supply configuration indication indicates which energy supply the brake is using. In other words, the brake energy supply configuration indication indicates which energy supply the brake valve is set to provide braking torque to the wheel brakes.

[0082] The first braking energy supply can be a primary or "green" supply. The second braking energy supply can be an auxiliary, backup, or "yellow" supply configured to connect to the brake valve when the primary supply is unavailable.

[0083] The primary braking energy supply can be an auxiliary, backup, or "yellow" supply. The secondary braking energy supply can be an emergency supply configured to connect to the brake valve when the auxiliary supply is unavailable.

[0084] Backup energy / fluid supply may include energy accumulators / hydraulic / pneumatic accumulators / batteries with a limited available supply. Accumulators may be located on the yellow energy supply / hydraulic fluid line.

[0085] Primary, auxiliary, and / or emergency supplies can be hydraulic fluid supplies. For example, an emergency supply may include a hydraulic reservoir with only a limited amount of available hydraulic fluid.

[0086] Control components can reside in a single control unit or be distributed among different control units. For example, an anti-skid brake calculator can be in a separate (but connected) unit connected to the output.

[0087] Other components of the anti-skid brake calculator or control assembly may exist in a single control unit or may be distributed among different control units.

[0088] The optimal slip ratio is the ratio determined as the best possible ratio of wheel speed to expected wheel speed (e.g., based on aircraft speed). At this optimal slip ratio, the value of mu (μ) – the coefficient of friction – is highest. This depends not only on wheel and tire conditions but also on runway conditions (e.g., wet, dry, surface) and other factors. Aircraft braking control systems cannot achieve a set / assumed optimal slip ratio. Instead, they can determine the optimal slip ratio based on various inputs, including wheel speed and aircraft speed varying over time. For example, these inputs could include a reference speed.

[0089] At the optimal slip ratio, the brakes perform well and the wheels do not slip. As the slip ratio increases, the chance of slippage also increases. Therefore, braking systems are typically designed to operate within 10% of the optimal slip ratio. In other words, if the slip ratio is greater than 10% of the optimal slip ratio, braking commands sent to one or more wheels will be reduced (in order to unlock wheels that are slipping or about to slip). Thus, as an example, the first slip limit can be 10% higher than the optimal slip ratio.

[0090] However, when using emergency braking energy supply, the braking system can be designed to operate within, for example, 5% of the optimal slip ratio. In other words, if the slip ratio exceeds 5% of the optimal slip ratio, the braking commands sent to one or more wheels will be reduced. Therefore, as an example, the second slip limit can be 5% higher than the optimal slip ratio.

[0091] Braking commands sent to one or more wheels can (in a "small slip" state) reduce the maximum braking command by 10% to 35%. For example, the maximum braking command might correspond to a braking pressure of 175 bar. A "small slip" state could involve a reduction in braking pressure of 20 to 60 bar (i.e., a reduction to 115 to 155 bar). This reduction in braking pressure will result in a small decrease in braking pressure, but the amount of brake hydraulic fluid loss is negligible (due to the relatively stiff brake piston, and therefore small volume changes causing large pressure changes).

[0092] Anti-slip brake calculators can calculate anti-slip brake (current) commands to reduce the slip ratio below the slip limit. In other words, anti-slip brakes are designed to keep the slip ratio within a set amount (set limit) of the optimal slip ratio.

[0093] This invention can be applied to any number of wheels and / or braking systems of an aircraft.

[0094] Preferably, the first slip limit is 5% to 15% higher than the optimal slip ratio.

[0095] The first slip limit can be 8% to 12% higher than the optimal slip ratio. The first slip limit can be approximately 10% higher than the optimal slip ratio.

[0096] Preferably, the second slip limit is 1% to 7% higher than the optimal slip ratio.

[0097] The second slip limit can be 4% to 6% higher than the optimal slip ratio. The second slip limit can be approximately 5% higher than the optimal slip ratio.

[0098] Preferably, the first slip limit is 1% to 15% higher than the second slip limit.

[0099] The first slip limit can be 3% to 6% higher than the second slip limit.

[0100] Preferably, the state determiner for determining the wheel state includes a "deep slip" state, in which the wheel speed is determined to be lower than a first speed limit below the expected wheel speed.

[0101] For example, the expected speed limit could be 50% of the expected wheel speed. If the wheel speed is below this value—for example, close to zero—then the wheel is considered to be in a state of "deep slippage".

[0102] Braking commands sent to one or more wheels can (in a “deep slip” state) reduce the maximum braking command by 90% to 100%. For example, the maximum braking command may correspond to a braking pressure of 175 bar. The “deep slip” state may involve a reduction in braking pressure from 158 bar to the full 175 bar (i.e., between 0 bar and 17 bar).

[0103] This could involve the near-complete discharge of the brake piston.

[0104] Alternatively, in conjunction with the sixth aspect, the anti-skid brake calculator can be configured to apply a specified minimum (current) command level to the anti-skid brake (current) command.

[0105] Preferably, the control component includes a mode controller that sets the operating mode of the anti-slip brake calculator. The mode controller is configured to: set a first mode when an input indicating the braking energy supply configuration indicates that a first brake is being used, in which the anti-slip brake calculator applies a first limit level to the rate of increase of the anti-slip brake (current) command; and set a second mode when an input indicating the braking energy supply configuration indicates that a second brake is being used, in which the anti-slip brake calculator applies a second limit level to the rate of increase of the anti-slip brake (current) command, the second limit level being lower than the first limit level.

[0106] This advantageous feature of the first aspect of the invention can be used in conjunction with the sixth aspect. This feature can also be used in conjunction with the eleventh aspect of the invention.

[0107] The mode controller and the state mode controller can be the same device.

[0108] According to a twelfth aspect of the invention, an aircraft landing gear is also provided, the aircraft landing gear including the aircraft braking control system as described above and wheels configured to be controlled by the aircraft braking control system in anti-skid braking.

[0109] According to a thirteenth aspect of the invention, an aircraft is also provided, which includes the aircraft braking control system as described above or the aircraft landing gear as described above.

[0110] According to a fourteenth aspect of the invention, an aircraft braking method is also provided, the method comprising the steps of providing an aircraft braking control system as described above, an aircraft landing gear as described above, or an aircraft as described above.

[0111] According to a fifteenth aspect of the invention, an aircraft braking method is also provided, the method comprising the steps of: first, noting that a first braking energy supply is being used, and assessing whether the aircraft wheel is in a "small slip" state by applying a first slip limit to the aircraft wheel; and second, noting that a second braking energy supply is being used, and assessing whether the aircraft wheel is in a "small slip" state by applying a second slip limit to the aircraft wheel, the second slip limit being lower than the first slip limit.

[0112] Of course, it will be understood that features described with respect to one aspect of the invention may be incorporated into other aspects of the invention. For example, the method of the invention may be combined with any features described with reference to the device of the invention, and the device of the invention may be combined with any features described with reference to the method of the invention. Attached Figure Description

[0113] Embodiments of the invention will now be described by way of example only with reference to the accompanying schematic diagrams, in which:

[0114] Figure 1 A schematic diagram of an aircraft braking control system according to the prior art is shown;

[0115] Figure 2 An equivalent schematic diagram of an aircraft braking control system according to a first embodiment of the present invention is shown;

[0116] Figure 3 A simplified schematic diagram of an aircraft braking control system according to a second embodiment of the present invention is shown;

[0117] Figure 4 A simplified schematic diagram of an aircraft braking control system according to a third embodiment of the present invention is shown;

[0118] Figure 5 A simplified schematic diagram of an aircraft braking control system according to a fourth embodiment of the present invention is shown;

[0119] Figure 6 The illustration shows Figure 5 A graph of the "ZTP" value used in the implementation method;

[0120] Figure 7 A simplified schematic diagram of an aircraft braking control system according to a fifth embodiment of the present invention is shown;

[0121] Figure 8 A simplified schematic diagram of an aircraft braking control system according to a sixth embodiment of the present invention is shown; and

[0122] Figure 9 A front view of an aircraft applicable to an aircraft braking control system including any of the embodiments described above is shown. Detailed Implementation

[0123] Figure 1 A schematic diagram of an aircraft braking control system according to the prior art is shown.

[0124] The control system includes a control component 100. Component 100 includes various elements, all of which are represented as parts of the anti-slip calculator 120.

[0125] The anti-slip calculator 120 has a component from the wheel 101 (e.g., Figure 9 The wheel speed input 102 is for wheel 11a). The anti-slip calculator 120 has a brake servo valve command current output 130, which is fed to the brake servo valve 131. The valve 131 uses the current sent to the valve 131 to apply a corresponding amount of braking pressure 132 to wheel 101. The braking pressure 132 is supplied by a braking energy supply (not shown), which is a hydraulic supply, which comes from a normal "green" supply, or from a backup "yellow" supply if the normal "green" supply is unavailable, or from an emergency "reservoir" supply if the backup "yellow" supply is unavailable.

[0126] Now, take a closer look at the anti-slip calculator 120.

[0127] The wheel speed input 102 is branched into two branches. The first branch includes a wheel speed low-pass filter 103, which provides a filtered wheel speed output 104 (where noise is removed from the wheel speed signal 102). The second branch is sent to an optimal controller 110, which uses the wheel speed 102 (plus other factors, such as possible wheel tachometer malfunctions and aircraft speed, not shown) to output an adherence value 111 and a reference speed 112. The adherence value 111 is adjusted by the optimal controller 110 to achieve optimal slip variation based on various factors such as runway surface conditions, braking gain, etc. Optimal slip represents the level of allowable slip. The reference speed 112 is a function of the speeds of all aircraft wheels and represents the overall aircraft speed. The adherence value 111 is subtracted from the reference speed at a summation point 113, and the desired control speed 114 is output.

[0128] The filtered wheel speed 104 is subtracted from the control speed 114 at the summation point 115, and a speed error 116 is output. This speed error 116 is provided to the anti-slip filter 121, which calculates how much pressure (and therefore how much current) needs to be removed from the brake based on the speed error 116. The anti-slip filter 121 then outputs an anti-slip current 122 (the current to be removed from the command current).

[0129] Therefore, the anti-slip current 122 is subtracted from the commanded braking current 123 (e.g., from the brake pedal in the cockpit) at the summation point 124 and output as the brake servo valve command current 130.

[0130] Therefore, when there is a significant difference between the wheel speed (which is filtered to remove false readings, noise, etc.) and the control speed (related to the aircraft speed), the anti-slip filter ensures that the current command 130 sent to the brake servo valve 131 is reduced. Thus, when the wheel speed is low and it appears that slippage is occurring or may be imminent, the brake pressure is released to release the slipping wheel.

[0131] Importantly, the Optimal Calculator 110's calculations take into account various conditions (e.g., runway conditions) and are able to assess the condition of the wheels.

[0132] Figure 2 An equivalent schematic diagram of an aircraft braking control system according to a first embodiment of the present invention is shown.

[0133] In the following description, where similar elements have been described before, the same reference numerals will be used. New or significantly modified elements will be indicated by reference numerals beginning with "2".

[0134] The control system includes a control component 200. Component 200 includes various elements, all of which are represented as parts of the anti-slip calculator 220. These elements are the same as those in the anti-slip calculator 120, but with additional components.

[0135] This additional component is a current rise rate limiter 235. The current rise rate limiter 235 receives an output 234 from the summing point 124. This output 234 is the same as the current 130 that has been sent to the brake servo valve 131 in the first embodiment. However, here (through the rise rate limiter 235) a rise rate limit is applied to the current 130 / 234, and the "rise rate limited" current 230 is instead the current supplied to the brake servo valve 131.

[0136] The current rise rate limiter 235 limits the current rise to more than 70% of the system's maximum current rise rate.

[0137] Therefore, this prevents excessively aggressive reapplication of braking pressure after a skidding event. This reduces the likelihood of triggering another skid. Consequently, the braking energy supply (hydraulic fluid) is conserved.

[0138] Figure 3 A simplified schematic diagram of an aircraft braking control system according to a second embodiment of the present invention is shown.

[0139] In the following description, where similar elements have been described before, the same reference numerals will be used. New or significantly modified elements will be indicated by reference numerals beginning with "3".

[0140] The control system includes a control component 300. Component 300 includes various elements, all of which are represented as part of the anti-slip calculator 320.

[0141] The component has an input 305 that indicates the hydraulic supply being used. This will indicate whether an emergency hydraulic supply is being used.

[0142] The components of the anti-slip calculator 320 are similar to those of the anti-slip calculator 220. Component 325 represents the initial anti-slip calculator, equivalent to the anti-slip calculator 120 in the prior art. Component 325 outputs the initial anti-slip current 326. The current rise rate limiter 235 of the first embodiment is effectively replaced by the mode controller 327. The mode controller 327 applies the same current rise rate limit as 235, such that the brake servo valve command current 330 is limited to the rate at which the brake servo valve command current 330 can rise. However, the mode controller 327 applies this rate limit only when the input 305 indicates that the emergency braking power supply is being used. Otherwise, the rate limit is not applied.

[0143] Figure 4 A simplified schematic diagram of an aircraft braking control system according to a third embodiment of the present invention is shown.

[0144] In the following description, where similar elements have been described before, the same reference numerals will be used. New or significantly modified elements will be indicated by reference numerals beginning with "4".

[0145] The control system includes a control component 400. Component 400 includes various elements, all of which are represented as part of the anti-slip calculator 420.

[0146] Component 425 represents the initial anti-slip calculator, equivalent to the anti-slip calculator 120 in the prior art. Component 425 outputs an initial anti-slip current 426. Then, the current increasing device 419 applies a minimum current (a minimum current of 8 mA, 20% of the maximum available current of 40 mA) to the output 426, so that the output of the brake servo valve command current 430 has a minimum value.

[0147] At the minimum current of 8 mA, the brake piston moved approximately 20% of its maximum stroke length. Here, the brake piston moved 2 cm backward from its maximum stroke length of 10 cm to a length of 8 cm.

[0148] This current value and piston movement correspond to the braking pressure of "zero torque pressure" ("ZTP"). In other words, the brake piston is in contact with the brake and applies zero torque to the brake.

[0149] This is due to Figure 6 The curve graph 600 is shown in the figure.

[0150] Graph 600 shows how the fluid volume (y-axis) 602 in the brake piston changes with the pressure (x-axis) 601 in the brake piston. It can be observed that at low brake piston pressures, the volume in the piston remains low (region 603), but then rises smoothly (region 604). The volume in the piston then remains stable (region 605) because the increased brake piston pressure results in minimal volume change. Cross 606 indicates the "ZTP" pressure value. Here, the piston is not applying actual pressure to the brake because the piston has moved away from the wheel. However, the piston moves away only very slightly, and therefore the volume reduction (starting from region 605) is negligible. This minimizes the brake fluid loss in the system.

[0151] Figure 5 A simplified schematic diagram of an aircraft braking control system according to a fourth embodiment of the present invention is shown.

[0152] In the following description, where similar elements have been described before, the same reference numerals will be used. New or significantly modified elements will be indicated by reference numerals beginning with "5".

[0153] The control system includes a control component 500. Component 500 includes various elements, all of which are represented as parts of the anti-slip calculator 520.

[0154] Component 425 represents the initial anti-slip calculator, equivalent to the anti-slip calculator 120 in the prior art. Component 425 outputs an initial anti-slip current 426. Then, the current increasing device 419 applies a minimum current to the output 426, so that the output of the brake servo valve command current 530 has a minimum value. This is consistent with... Figure 4 The situation is similar.

[0155] However, the current booster 419 applies the minimum current value only when the input 305 indicates to the mode controller 527 that the emergency braking power is being used. The mode controller 527 sends a signal 528 to the current booster 419 so that the current booster 419 knows whether to apply the minimum current level.

[0156] Figure 7 A simplified schematic diagram of an aircraft braking control system according to a fifth embodiment of the present invention is shown.

[0157] In the following description, where similar elements have been described before, the same reference numerals will be used. New or significantly modified elements will be indicated by reference numerals beginning with "7".

[0158] The control system includes a control component 700. Component 700 includes various elements, all of which are represented as part of the anti-slip calculator 720.

[0159] Component 725 represents the main anti-slip calculator, which is equivalent to / similar to the anti-slip filter 121 in the prior art.

[0160] Input 705 to component 700 indicates the aircraft speed. Then, the optimal slip ratio calculator 706 uses the aircraft speed 705, the wheel speed 102, and other factors to calculate the optimal slip ratio, outputting 707. This optimal slip ratio is output to the state determiner 717.

[0161] The state determiner also receives a state mode 709 from the state mode determiner 708. The state mode determiner 708 determines the mode in which the state determiner 717 should operate, and this determination is based on the input 305 of the brake supply being used. Therefore, if input 305 indicates that an emergency brake supply is being used, the state mode determiner (via output 709) specifies that the state determiner 717 applies a certain determination procedure. In this case, the state mode determiner specifies that for the "small slip" to be determined, the wheel speed must be within 5% of the optimal slip ratio speed. Otherwise, the state determiner will determine "small slip" when the wheel speed is within 10% of the optimal slip ratio speed.

[0162] The state determiner 717 also determines other wheel states, such as "deep slippage," which is determined if the wheel speed 102 is less than 50% of the expected wheel speed (based on aircraft speed and other factors). There are seven other states, which will not be described here.

[0163] The state determiner 717 outputs 718 the determined state of the wheel 101, and the anti-slip calculator 425 can calculate the appropriate anti-slip current (or brake servo valve command current 730) based on this determination (and wheel speed 102, etc.).

[0164] For example, when a "small slip" is determined, the anti-slip calculator 725 calculates the current 730 to slightly reduce the braking pressure in order to release the slip. Here, the braking pressure can be released from 20 bar to 60 bar (from the maximum braking pressure of 175 bar).

[0165] When “deep slip” is determined, the anti-slip calculator 725 calculates a current 730 to completely reduce the braking pressure (or reduce the braking pressure to the ZTP level). Here, the current 730 causes the brake piston to move 5 cm (half of the piston’s maximum stroke length).

[0166] Figure 8 A simplified schematic diagram of an aircraft braking control system according to a sixth embodiment of the present invention is shown.

[0167] In the following description, where similar elements have been described before, the same reference numerals will be used. New or significantly modified elements will be indicated by reference numerals beginning with "8".

[0168] The control system includes a control component 800. Component 800 includes various elements, all of which are represented as parts of the anti-slip calculator 820.

[0169] Anti-slip calculator 820 and Figure 7 The anti-slip calculator 720 is very similar. However, the anti-slip calculator 820 also includes... Figure 5 The mode controller is similar to mode controller 527. Mode controller 527 includes output 528, which indicates to main anti-slip calculator 725 whether emergency braking supply is being used. Therefore, if emergency braking is being used, main anti-slip calculator 725 applies current rise rate limiting.

[0170] Figure 9 A front view of an aircraft 10 is shown, which is applicable to an aircraft braking control system including any of the embodiments described above.

[0171] The aircraft 10 has: a nose landing gear 13 having wheels 13a and 13b; a left main landing gear 11 having wheels 11a and 11b; and a right main landing gear having wheels 12a and 12b. The described control system and components can be applied to any wheel or wheel assembly on the aircraft 10.

[0172] Although the invention has been described and illustrated with reference to specific embodiments, it will be understood by those skilled in the art that the invention leads itself to many different variations not specifically described herein. Some possible variations will now be described by way of example only.

[0173] In the example above, the brake servo valve is controlled by a current command. However, any suitable brake servo valve and any suitable control method / command can be used.

[0174] For example, the valve can be mechanically controlled. For instance, one or more hydraulic components, such as a hydraulic flow limiter, can be used to control the rate of pressure rise.

[0175] As another example, an electric motor can be used as an actuator, and the position of the actuator can be commanded using current, which will pass through a Wheatstone bridge to operate the motor.

[0176] Any suitable rate of ascent limit value can be used.

[0177] Supply input 305 can indicate when the backup supply is used. When the backup supply is being used, a current rise rate limit can be applied.

[0178] When supply input 305 indicates that the brake supply is not an emergency (or backup) supply (e.g., a normal supply), a different (higher) current rise rate limit can be applied. For example, this might be solely to reduce oscillations in the system and minimize tire damage.

[0179] When power input 305 indicates that the braking supply is an emergency supply, different (lower) current rise rate limits can be applied.

[0180] A rise rate limit 235 can be applied at any suitable part / step of the control assembly. For example, the rise rate of the compliance value 111 can be limited by the optimal controller 110, which in turn limits the rise rate of the speed error 116 and the control speed 114. The rise rate limit 235 can be applied as a limit on the rise rate of the speed error 116 or the control speed 114. The rise rate limit 235 can also be applied as a limit on the rise rate of the anti-slip filter 121 and / or the anti-slip current 122.

[0181] Supply input 305 may include an indication of the actual amount of remaining energy (hydraulic fluid) in the accumulator / emergency supply. The rate of increase limit may vary depending on the remaining amount, decreasing as the supply is depleted.

[0182] Minimum current / command 419 can be applied at any suitable part / step of the control assembly. For example, minimum current / command 419 can be made as a part of anti-slip filter 121 and / or anti-slip current 122.

[0183] Variations in the permissible slip level can be applied at any suitable part / step of the control component. For example, this variation can be made to a portion calculated based on the value 111.

[0184] You can use any suitable percentage relative to the optimal slip ratio.

[0185] In addition to "small slip" and / or "deep slip", the state determiner can have other states.

[0186] Any component can be combined with other components. For example, the current / command increase device 419 can be included. Figure 7 or Figure 8 In the control components. For example, the current / command increase device 419 is effectively applied between the main anti-slip calculator 725 and the outputs 730 / 830.

[0187] The actual braking level of the wheel can be used instead of the indication of the desired braking level (i.e., command pressure / command torque / command force).

[0188] The described control system and components can be applied to any wheel or wheel assembly on any aircraft.

[0189] Braking energy can be supplied by electricity or pneumatics.

[0190] Various limitations / limits may be applied to any suitable choice of available braking configuration (the braking supply being used). For example, some or all of the limitations described may be applied only when in emergency braking mode, emergency mode and standby mode, or all three modes.

[0191] Where references have been made to elements or components having known, obvious, or foreseeable equivalents in the foregoing description, such equivalents are incorporated herein as if separately stated. The true scope of the invention should be determined with reference to the claims, and should be interpreted as including any of these equivalents. The reader will also understand that elements or features of the invention described as preferred, advantageous, convenient, etc., are optional and do not limit the scope of the independent claims. Furthermore, it should be understood that in some embodiments of the invention, such optional elements or features, while potentially beneficial, may not be desirable and therefore may not be present in other embodiments.

[0192] It should be noted that throughout this specification, "or" should be interpreted as "and / or".

[0193] Although the invention has been described above primarily in the context of applications in fixed-wing aircraft, it can also be advantageously applied to a variety of other applications, including but not limited to applications in vehicles such as helicopters, drones, trains, automobiles, and spacecraft.

Claims

1. An aircraft braking control system, the aircraft braking control system being used to control the anti-skid braking of the aircraft's wheels, the system comprising a control component, the control component having: i) Input indicating the aircraft's speed, ii) An input indicating the wheel speed of the wheel, iii) Input indicating braking level, iv) Input indicating the braking energy supply configuration, v) Optimal slip ratio calculator, said optimal slip ratio calculator being used to calculate the optimal slip ratio of the wheels based at least in part on indications of the wheel speed and the aircraft speed. vi) A state determiner, the state determiner being used to determine the state of the wheel, the state determiner comprising: - In the "slight slippage" state, the slip ratio of the wheel is defined as being lower than the slip limit above the optimal slip ratio. vii) Anti-skid braking calculator, which calculates anti-skid braking commands based on the wheel speed, the braking level, and the determined state. viii) A state mode controller, which sets the operating mode of the state determiner, and is configured to: - When the input indicating the braking energy supply configuration is using a first braking energy supply, a first state determiner mode is set, and in the first state determiner mode, a first slip limit value is used as the slip limit, and - When the input indicating the braking energy supply configuration is using a second braking energy supply, a second state determiner mode is set, and in the second state determiner mode, a second slip limit value is used as the slip limit, the second slip limit value being lower than the first slip limit value, and iv) Output, which indicates the anti-slip braking command to be sent to the brake valve.

2. The aircraft braking control system according to claim 1, wherein, The first slip limit is 5% to 15% higher than the optimal slip ratio.

3. The aircraft braking control system according to claim 1 or claim 2, wherein, The second slip limit is 1% to 7% higher than the optimal slip ratio.

4. The aircraft braking control system according to any one of claims 1 to 3, wherein, The first slip limit is 1% to 15% higher than the second slip limit.

5. The aircraft braking control system according to any one of claims 1 to 4, wherein: The state determiner for determining the state of the wheel includes: - "Deep slippage" state, in which the wheel speed is determined to be lower than a first speed limit higher than the expected wheel speed.

6. The aircraft braking control system according to any one of claims 1 to 5, wherein, The control component includes a mode controller, which sets the operating mode of the anti-skid brake calculator, and the mode controller is configured to: - When the input indicating the braking energy supply configuration is using a first braking energy supply, a first mode is set. In this first mode, the anti-skid brake calculator applies a first limit level to the rate of increase of the anti-skid brake command. - When the input indicating the braking energy supply configuration is using a second braking energy supply, a second mode is set, in which the anti-skid brake calculator applies a second limit level to the rate of increase of the anti-skid brake command, the second limit level being lower than the first limit level.

7. An aircraft landing gear comprising an aircraft braking control system according to any one of claims 1 to 6 and wheels configured to be controlled by the aircraft braking control system in anti-skid braking.

8. An aircraft comprising an aircraft braking control system according to any one of claims 1 to 6 or an aircraft landing gear according to claim 7.

9. A method for braking an aircraft, comprising the following steps: Provide an aircraft braking control system according to any one of claims 1 to 6, an aircraft landing gear according to claim 7, or an aircraft according to claim 8.

10. A method for braking an aircraft, comprising the following steps: first: - Note that the first braking energy supply is being used, and - The presence of a "small slip" condition in the wheel is assessed by applying a first slip limit to the wheel. And secondly: - Note that a second braking energy supply is being used, and - The wheel is assessed for being in a "slight slip" state by applying a second slip limit to the wheel, the second slip limit being lower than the first slip limit.

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