GB2588372A

GB2588372A - An aircraft braking control unit

Info

Publication number: GB2588372A
Application number: GB1914138.1A
Authority: GB
Inventors: Bidmead Ashley
Original assignee: Airbus Operations Ltd
Current assignee: Airbus Operations Ltd
Priority date: 2019-10-01
Filing date: 2019-10-01
Publication date: 2021-04-28
Also published as: GB201914138D0

Abstract

An aircraft braking control unit 1460 and method of operating an aircraft. The control unit includes a cockpit braking input line 1414, another cockpit input line 1412, a measurement input line 1421 (e.g. to input wheel speed or aircraft speed), a braking output line 1464, a brake mode selector 1461, and a brake calculator 1462 for calculating a braking command according to a selected brake mode. The braking mode is selected from multiple brake modes, including a landing gear drive system pushback brake mode, in which a landing gear drive system 1430 drives backwards movement of the aircraft over a ground surface (e.g. during reverse taxiing) and the braking command acts to retard the backwards movement of the aircraft such that a braking torque limit is not exceeded. Selection is made based on the measured variable or a cockpit input. The method includes initiating a landing gear drive system activation control; measuring at least one variable; selecting the landing gear drive system pushback mode based on the cockpit input, the measurement or the activation signal; and driving pushback of the aircraft using the drive system at the same time as commanding braking up to a brake torque limit.

Description

AN AIRCRAFT BRAKING CONTROL UNIT

BACKGROUND OF THE INVENTION

[0001] The present disclosure relates to braking control for and of aircraft.

100021 The present invention concerns an aircraft braking control unit. More particularly, but not exclusively, this invention concerns an aircraft braking control unit, having a cockpit braking input line, for receiving an input of a desired braking level from a cockpit of the aircraft, at least one cockpit input line, for receiving a further input from the cockpit of the aircraft, at least one measured input line, for receiving an input of at least one measured variable of the aircraft, at least one braking output line, for sending a braking command for one or more wheels of the aircraft, a brake mode selector, for selecting a brake mode based on data from the cockpit input line or measured input line, and a brake calculator, for calculating the braking command, according to the selected brake mode.

[0003] The invention also concerns an aircraft control system, an aircraft and a method of operating an aircraft.

[0004] There have been proposals, for example as described in W02015/025131, for providing an aircraft with a landing gear drive system and using that drive system to pushback the aircraft without the use of a pushback tractor, or similar. In WO 2015/025131, it is described how it is important to ensure the longitudinal stability of the aircraft during braking when performing pushback. For example, if the aircraft brakes were applied at a too high torque level, this may cause the load on the nose landing gear steering centring cam to reduce below a predetermined level, the nose wheel to lose contact with the ground or even for the tail to tip back and strike the ground. WO 2015/025131 describes how one method of ensuring longitudinal stability is to ensure the braking pressure is not too high during pushback.

100051 However, WO 2015/025131 does not disclose how to apply such a proposed limitation. For example, there is no disclosure of how the aircraft is to know that such a proposed braking limitation should be applied.

[0006] The present invention seeks to mitigate the above-mentioned problems.

Alternatively or additionally, the present invention seeks to provide an improved aircraft braking control unit.

SUMMARY OF THE INVENTION

[0007] The present invention provides, according to a first aspect, an aircraft braking control unit, having a cockpit braking input line, for receiving an input of a desired braking level from a cockpit of the aircraft, at least one cockpit input line, for receiving a further input from the cockpit of the aircraft, at least one measured input line, for receiving an input of at least one measured variable of the aircraft, at least one braking output line, for sending a braking command for one or more wheels of the aircraft, a brake mode selector, for selecting a brake mode based on data from the cockpit input line or measured input line, and a brake calculator, for calculating the braking command, according to the selected brake mode, wherein the brake mode is selected from a number of possible brake modes, the possible modes including a landing gear drive system pushback brake mode, in which a landing gear drive system drives backwards movement of the aircraft over a ground surface and the braking command acts to retard the backwards movement of the aircraft, wherein, in the landing gear drive system pushback brake mode, the brake calculator calculates the braking command by firstly calculating an equivalent braking command to the desired braking level received from the cockpit and then limiting that equivalent braking command such that a braking torque limit is not exceeded.

[0008] Having a possible brake mode of a landing gear drive system pushback brake mode, enables such a mode to be selected and applied and the required braking limitation to be used, when appropriate.

100091 In addition, the brake mode can be selected based on data from the cockpit input line or measured input line. Hence, the brake mode can be selected using existing inputs to a braking control unit. No additional cockpit control or control line to the braking control unit are required. This means that no further electronic circuits are required and no further controls are required in the cockpit (where space may be limited).

[0010] Such a braking control unit is able to provide for a braking mode suitable for use during pushback of an aircraft using a landing gear drive system, as opposed to an external tug, for example. Hence, suitable braking laws can be applied during pushback.

In addition, such a braking control unit is able to select this mode, without an additional input control in the cockpit being required. This enables a landing gear drive system to be fitted to an aircraft and for effective and safe pushback to occur using it, even if there is little or no space in the cockpit for another control. It also minimises the electrical connections needed, which reduces weight, complexity, cost and maintenance requirements.

100111 The braking control unit may also control the steering of the aircraft. For example, it may control the nose landing gear steering angle of the aircraft. It may further have a steering input line for receiving a steering control input from the cockpit. It may further have a steering control output line for sending a steering command to a steering mechanism of the aircraft, for example in the nose landing gear.

[0012] The braking torque limit may be determined in order to ensure longitudinal stability. For example, it may be determined to prevent the aircraft tipping backwards (towards its tail), and/or by ensuring the nose wheel does not part contact with the ground.

[0013] The braking torque limit may be determined based on one or more of the following parameters: ground slope angle, aircraft centre of gravity position, aircraft inertial moment around the aircraft lateral (y) axis, and backwards speed of the aircraft.

[0014] The cockpit input line may be connected to (or be suitable to be connected to) any cockpit control. Advantageously, the cockpit control is one that, in any case (i.e. even if there is no landing gear drive system) required as an input to the braking control unit.

For example, it may be connected to an existing cockpit control that is input to the braking control unit, such as a rudder pedal, a steering device or an autobrake control.

[0015] In the above and the following, the terms "backwards" and "forwards" are used in relation to a conventional aircraft, with the normal flight direction of the aircraft being forwards.

[0016] The braking command may relate to brake pressure applied to the one or more wheels of the aircraft. Alternatively, it may relate to the landing gear drive system motors being used as generators to provide braking torque (i.e. acting in the forwards direction against the backwards movement of the aircraft).

[0017] Preferably, the brake mode selector is configured to select the brake mode based on data from the cockpit input line and also from the measured input line.

[0018] This enables the brake mode to be selected in relation to an input from the cockpit, or elsewhere, received by the cockpit input line, and also from one or more measured inputs. This ensures that the brake mode selected is suitable. For example, the landing gear drive system pushback mode may be selected based on an input received by the cockpit input line (e.g. an indication, for example from the pilot, that the landing gear drive system has been activated) and also a backwards (or zero) aircraft and/or wheel speed. Such an aircraft or wheel speed further indicates that the landing gear drive system is driving backwards movement of the aircraft and so that the selection of the landing gear drive system pushback braking mode is appropriate.

[0019] Preferably, the cockpit input line is connected to a discrete selector control in the cockpit, such that a discrete selection input can be received by the braking control unit.

[0020] For example, the selector control may be activated to choose on/off selections, or to send an activation signal This is different to a continuous desired braking level, for example, where the pilot is able to indicate a continuous range of desired braking level based on a continuous variable pressure applied to rudder pedals in the cockpit, for example.

100211 More preferably, the cockpit input line is connected to an autobrake control in the cockpit, such that an autobrake signal can be received by the braking control unit, through the cockpit input line.

[0022] For example, the autobrake signal may indicate that autobrake is to be turned on, or that a certain mode of the autobrake function is to be selected. Autobrake is the function that enables the aircraft wheel brakes to be automatically actuated, under certain prescribed circumstances, following a particular braking law. This is different from normal braking, in which a pilot is able to actively vary a desired braking level.

[0023] The autobrake control may be a button or a switch, with a set number of discrete positions.

[0024] Preferably, the at least one measured input line provides a measurement of one or more of aircraft speed, wheel speed and engine pressure.

[0025] For example, a measurement of a backwards (or zero) aircraft or wheel speed indicates that the landing gear drive system is driving backwards movement of the aircraft and so that the selection of the landing gear drive system pushback braking mode is appropriate.

[0026] Preferably, the number of possible braking modes further includes an autobrake mode, in which the aircraft is moving forwards over a ground surface and the braking command acts to retard the forwards movement of the aircraft, wherein, in the autobrake mode, the brake calculator calculates the braking command to provide a retardation rate of the aircraft over the ground.

[0027] The braking control unit may also be arranged to receive one or more indications that hydraulic brake pressure is available, an anti-skid system is electrically powered and/or there are no detected failures in the brake system. These indications provide arming criteria that it is safe to arm an autobrake mode.

[0028] This retardation rate may be substantially uniform and may be a low, medium or high rate, depending on the further input received, for example from an autobrake control, from the cockpit of the aircraft. The retardation rate may be chosen to be a set level, for example 3m/s2.

100291 Alternatively, the retardation rate may be based on the location of the aircraft along a runway.

[0030] The autobrake mode may be a landing autobrake mode. The landing autobrake mode may be selected based on an input received by the cockpit input line (e.g. an indication, for example from the pilot, that the aircraft is about to land). The landing autobrake mode may also be selected based on a wheel speed. Such a wheel speed additionally indicates that the aircraft has landed and so that the selection of the landing autobrake mode is appropriate.

[0031] This retardation rate may be a very high rate, depending on the further input received, for example from an autobrake control, from the cockpit of the aircraft. The brake calculator may calculate the braking command to provide a retardation rate of the aircraft over the ground, limited to prevent wheel tyre burst.

[0032] The autobrake mode may be a rejected take-off (RTO) autobrake mode. The rejected take-off autobrake mode may be selected based on an input received by the cockpit input line (e.g. an indication, for example from the pilot, that the aircraft is about to take off). The rejected take-off autobrake mode may also be selected based on an indication that the take-off is rejected, for example, such as the engine throttle level and deployment of spoilers.

[0033] The autobrake mode may be disarmed (de-selected) by one or more of a received input of desired braking level from a cockpit of the aircraft (e.g, from pressure applied to rudder pedals in the cockpit), retraction of spoilers, aircraft take-off, deactivation of an autobrake control, or the loss of one or more arming criteria.

[0034] Preferably, the brake mode selector is able to cancel selection of the landing gear drive system pushback brake mode based on data from the cockpit input line and/or measured input line.

[0035] More preferably, the brake mode selector is able to cancel selection of the landing gear drive system pushback brake mode based on a measured input of aircraft and/or wheel speed.

[0036] For example, a forward aircraft or wheel speed indicates that the landing gear drive system is no longer driving backwards movement of the aircraft and so that the -7 -selection of the landing gear drive system pushback braking mode is no longer appropriate.

[0037] Preferably, the brake mode selector is able to select a further brake mode based on data from the cockpit input line and/or measured input line.

[0038] For example, a landing autobrake mode may be selected based on an input received by the cockpit input line (e.g. an indication, for example from the pilot, that the aircraft is about to land). A rejected take-off (RTO) autobrake mode may be selected based on an input received by the cockpit input line (e.g. an indication, for example from the pilot, that the aircraft is about to take off) and/or an indication of the engine throttle level (for example, indicating that take-off is imminent.) [0039] According to a second aspect of the invention there is also provided an aircraft control system comprising an aircraft braking control unit as claimed in any preceding claim, and a landing gear drive system control unit.

[0040] Preferably, the landing gear drive system control unit has a cockpit input line for receiving an input from a cockpit of the aircraft.

100411 More preferably, the cockpit input line of the landing gear drive system control unit is connected to a landing gear drive system activation control, in the cockpit, such that a landing gear drive system activation signal can be received by the landing gear drive system, through the cockpit input line.

[0042] When activated, the landing gear drive system is able to drive forwards and/or backwards motion of one of more landing gear wheels of the aircraft.

[0043] Preferably, the landing gear drive system control unit has an output line connected to the cockpit input line of the braking control unit, such that the landing gear drive system control unit can send a landing gear drive system activation signal to the braking control unit, and wherein the brake mode selector is configured to select a brake mode based on the landing gear drive system activation signal or data from the measured input line.

[0044] Hence, there is no need for the pilot to both activate the landing gear drive system and also indicate to the braking control unit that the landing gear drive system pushback brake mode is desired. This is done by just one step.

100451 More preferably, the brake mode selector is configured to select the brake mode based on the landing gear drive system activation signal and also from data from the measured input line [0046] Preferably, the brake mode selector is able to cancel selection of the landing gear drive system pushback brake mode based on data from the cockpit input line, the landing gear drive system activation signal and/or measured input line.

[0047] More preferably, the brake mode selector is able to cancel selection of the landing gear drive system pushback brake mode based on a measured input of aircraft and/or wheel speed.

[0048] For example, a forward aircraft or wheel speed indicates that the landing gear drive system is no longer driving backwards movement of the aircraft and so that the selection of the landing gear drive system pushback braking mode is no longer appropriate.

[0049] Preferably, the brake mode selector is able to select a further brake mode based on data from the cockpit input line, the landing gear drive system activation signal and/or measured input line.

[0050] For example, a landing autobrake mode may be selected based on an input received by the cockpit input line (e.g. an indication, for example from the pilot, that the aircraft is about to land) as well as an indication that the landing gear drive system is deactivated. A rejected take-off (RTO) autobrake mode may be selected based on an input received by the cockpit input line (e.g. an indication, for example from the pilot, that the aircraft is about to take off) and/or an indication of the engine throttle level (for example, indicating that take-off is imminent) and/or an indication that the landing gear drive system is de-activated.

[0051] According to a third aspect of the invention there is also provided an aircraft including at least one landing gear, including one or more wheels able to be driven backwards by a landing gear drive system of the aircraft, wherein the aircraft comprises an aircraft braking control unit or an aircraft control system, as described above.

[0052] According to a fourth aspect of the invention there is also provided a method of operating an aircraft, the method including the following steps i) initiating a landing gear drive system activation control to activate a landing gear drive system of the aircraft, ii) measuring at least one variable, and iii) selecting a landing gear drive system pushback braking mode, based on the measured variable, a cockpit input from a control in the cockpit or a landing gear drive system activation signal from the landing gear drive system, and, at the same time as each other, performing the following two steps iv) using the landing gear drive system to drive pushback of the aircraft over a ground surface, and v) commanding braking of one or more wheels of the aircraft, the braking command acting to retard backwards movement of the aircraft and being calculated to limit the braking command to a braking torque limit.

[0053] The landing gear drive system activation control may be in the cockpit.

[0054] "At the same time as each other", refers to steps iv) and v). In other words, step iv) is performed at the same time as step v). Of course, step iv) or v) may also be performed while the other step (v or iv) is not being performed. It is required that in at least one time period, both step iv) and v) are performed. In other time periods, only one or neither of steps iv) and v) may be performed.

100551 Preferably, the selecting of a landing gear drive system pushback braking mode is performed by the braking control unit of the aircraft.

100561 More preferably, the selecting of the landing gear drive system pushback braking mode is based on the landing gear drive system activation signal and wherein the method comprises the step of the landing gear drive system sending the landing gear drive system activation signal to the braking control unit.

[0057] The selecting of the landing gear drive system pushback braking mode may be based on a combination of the landing gear drive system activation signal and the measured variable.

[0058] Even more preferably, the landing gear drive system sends the landing gear drive system activation signal to the braking control unit via a cockpit input line, for sending the cockpit input to the braking control unit.

[0059] Preferably, the selecting of the landing gear drive system pushback braking mode is based on the cockpit input from a control in the cockpit.

-10 - 100601 The cockpit input line may be connected to any cockpit control.

Advantageously, the cockpit control is one that, in any case (i.e. even if there is no landing gear drive system) required as an input to the braking control unit. For example, it may be connected to a rudder pedal, a steering device or an autobrake control.

[0061] The selecting of the landing gear drive system pushback braking mode may be based on a combination of the cockpit input from a control in the cockpit and the measured variable.

[0062] Preferably, the selecting of the landing gear drive system pushback braking mode is based on the measured variable.

[0063] For example, the landing gear drive system pushback braking mode may be selected based on a backwards (or zero) aircraft and/or wheel speed. Such an aircraft or wheel speed indicates that the landing gear drive system is driving backwards movement of the aircraft and so that the selection of the landing gear drive system pushback braking mode is appropriate.

[0064] Preferably, the method further comprises the step of cancelling selection of the landing gear drive system pushback braking mode based on the measured variable, a cockpit input from a control in the cockpit or a landing gear drive system activation signal from the landing gear drive system.

[0065] For example, a forward aircraft or wheel speed indicates that the landing gear drive system is no longer driving backwards movement of the aircraft and so that the selection of the landing gear drive system pushback braking mode is no longer appropriate.

[0066] More preferably, the method further comprises the step of selecting a further braking mode based on the measured variable, a cockpit input from a control in the cockpit or a landing gear drive system activation signal from the landing gear drive system.

[0067] For example, a landing autobrake mode may be selected based on an input received by the cockpit input line (e.g. an indication, for example from the pilot, that the aircraft is about to land). A rejected take-off (RTO) autobrake mode may be selected based on an input received by the cockpit input line (e.g. an indication, for example from the pilot, that the aircraft is about to take off) and/or an indication of the engine throttle level (for example, indicating that take-off is imminent).

[0068] It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa.

DESCRIPTION OF THE DRAWINGS

[0069] Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which: [0070] Figure I shows a schematic view of part of a control system according to a first embodiment of the invention; [0071] Figure 2 shows a schematic view of the control system of Figure I; [0072] Figure 3 shows a schematic view of part of a control system according to a second embodiment of the invention; 100731 Figure 4 shows a schematic view of the control system of Figure 3; and 100741 Figure 5 shows a front view of an aircraft including the control system of Figures 1 and 2 or that of Figures 3 and 4.

DETAILED DESCRIPTION

100751 Figure 1 shows a schematic view of part of a control system 1400 according to a first embodiment of the invention.

100761 The control system 1400 comprises an autobrake button 1411 that is connected to a braking and steering control unit (BSCU) 1460 through an autobrake command line 1411. The command line 1412 is provided with positive 1412a and negative 1412b lines.

[0077] Figure 2 shows a schematic view of the control system 1400 of Figure 1 [0078] Here, it can be seen that the control system 1400 is made up of various parts: a cockpit control panel 1410, a measurement system 1420, a landing gear drive system -12 -control unit 1430, the BSCU 1460 and various command lines etc. between these different parts (described in more detail below).

[0079] Also shown in Figure 2 are nose landing gear wheels 1440 and main sanding gear wheels 1450, and command lines to those (described in more detail below).

[0080] The cockpit control panel 1410 comprises various control devices and displays. Only those relevant to the embodiment will be described, but of course, it is expected that the cockpit control panel with also have further controls and displays, as is conventional.

[0081] As shown in Figure 2, the cockpit control panel 1410 has: - the autobrake button 1411, - rudder pedals 1413, - a steering column 1415, and - a landing gear drive system on/off switch 1417.

[0082] The autobrake button 1411 is conventionally used to prime the BSCU 1460 in order for the BSCU 1460 to apply the most appropriate autobrake mode.

100831 For example, if the autobrake button 1411 is pressed while the aircraft is stationary on a runway, a "rejected take off' (RIO) autobrake mode may be primed. In such a mode, if rejected take-off is detected (for example, by detecting that spoilers have been deployed and/or that the engine is throttled from a high power setting), the BSCU 1460 acts to brake the aircraft (using the brakes on the main landing gear wheels 1450) as hard as possible, whilst ensuring that tyres of the aircraft do not burst.

[0084] As another example, if the autobrake button 1411 is pressed while the aircraft is flying, a "landing" autobrake mode may be primed. In such a mode, if landing is detected (for example by detecting a rolling speed of an aircraft wheel and/or an altitude level and/or pressure detected at the wheels), the BSCU 1460 acts to brake the aircraft (using the brakes on the main landing gear wheels 1450) in a controlled manner to give an effective deceleration at a comfortable and suitable magnitude. This may be based on a set deceleration level (for example, 3m/s2) or it may be based on runway data and aircraft positioning, e.g. along the runway, (if available).

[0085] These autobrake modes are well known to the skilled person.

-13 - 100861 The rudder pedals 1413 are used to control yaw of the aircraft during flight and braking of the left and right main landing gear wheels 1450 whilst on the ground, as is well known to the skilled person.

[0087] The steering column 1415 controls the steering angle of the aircraft arid this is achieved through controlling the angle of the nose landing gear wheels 1440, as is well known to the skilled person.

[0088] The landing gear drive system on/off switch 1417 activates and deactivates a landing gear drive system that is used to drive rotation of one or more wheels of the main landing gear 1450. The wheels 1450 are able to be driven in a backwards direction so that the aircraft can be push-backed from an aircraft terminal, after embarkation, for example.

[0089] A suitable landing gear drive system is described in WO 2014/023941. Here, a motor is connected to a drive pinion. The drive pinion can be selectively meshed with a driven gear that is attached to the aircraft wheel 1450. When the motor is activated and the drive pinion is meshed with the driven gear, the wheel 1450 is caused to rotate.

100901 A measurement system 1420 is provided that may measure various values relevant to operation of the aircraft. In particular, as relevant to the present embodiment, the measurement system measures an aircraft speed, a wheel speed of at least one of the wheels 1440, 1450 of the aircraft and an engine pressure. Any number of other measurements may also be taken, as is conventional.

[0091] A landing gear drive system control unit 1430 is provided to control meshing (and non-meshing) of the drive pinion and driven gear and the activation, power setting and direction of the motor. The landing gear drive system on/off switch is connected to the landing gear drive system control unit 1430 by a landing gear drive system activation line 1418. The landing gear drive system control unit 1430 is connected to the main landing gear wheels 1450 by a landing gear drive system control line 1431. This is how the landing gear drive system control unit 1430 controls the landing gear drive systems on the main landing gear wheels 1450.

[0092] The BSCU 1460 comprises a brake mode selector 1461. This selector is conventionally responsible for choosing the autobrake mode, as described above. In addition, in the present embodiment, the brake mode selector 1461 has a "pushback" -14 -braking mode that can be selected. This mode is selected when the autobrake button 1411 has been pressed and pushback of the aircraft has been detected, as will be described later.

[0093] The brake mode selector 1461 is provided with measurement signals from the measurement system 1420 through a measurement signal line 1421. The brake mode selector 1461 is also provided with an autobrake input signal from the autobrake button 1411 through the autobrake command line 1412.

[0094] The BSCU 1460 also comprises a brake calculator 1463. The brake calculator is provided with the selected brake mode from the brake mode selector 1461 through brake mode selection line 1462. The brake calculator 1463 is also provided with a brake command from the rudder pedals 1413 through a brake command line 1414. The brake calculator 1463 calculates a brake control required (for example, the torque the brakes are to apply) based on the brake mode selected and the brake command, as will be described later. This braking control is provided to the main landing gear wheels 1450 through brake control line 1464.

100951 The BSCU 1460 also comprises a steering calculator 1465. The steering calculator 1465 is provided with a steering command from the steering column 1415 through a steering command line 1416. The steering calculator 1465 calculates a steering control required (for example, the angle of the nose landing gear wheels) based on the steering command. This steering control is provided to the nose landing gear wheels 1440 through steering control line 1466.

[0096] In use, when a pilot wishes to use the landing gear drive system, they press the landing gear drive system on/off switch 1417. This sends an activation signal (through landing gear drive system activation line 1418) to the landing gear drive system control unit 1430 to activate the landing gear drive systems on the main landing gear wheel 1450. This enables the landing gear drive system control unit 1430 to control the main landing gear wheels 1450 (through landing gear drive system control line 1431) to be rolled backwards for pushback.

[0097] The pilot also presses the autobrake button 1411, and this signal is passed (through the autobrake button command line 1412) to the brake mode selector 1461.

-15 - 100981 The brake mode selector 1461 also receives aircraft speed, wheel speed and engine pressure from the measurement system 1420 (through measurement signal line 1421). It uses these measurements and signals to choose the braking mode [0099] For example, in the scenario above, pushback of the aircraft will have been detected, for example by a backwards (or zero) aircraft speed or a backwards (or zero) rolling speed of one or more wheels. Hence, the brake mode selector 1461 will choose the pushback braking mode and send this information to the brake calculator 1463 (through the brake mode selection line 1462).

1001001 The brake calculator 1463 then uses the brake mode (here, the pushback braking mode) to calculate the brake control required. The brake calculator 1463 is also provided with pilot braking command information (provided through the rudder pedals 1413 and braking command line 1414).

1001011 When in the pushback braking mode, the brake calculator 1463 firstly calculates an equivalent braking command to the desired braking level received from the cockpit (rudder pedals 1413) and then limits that equivalent braking command such that a braking torque limit is not exceeded. That braking torque limit is a fixed torque limit (one at which, the aircraft is assessed to be longitudinally stable).

1001021 Hence, if the braking commanded (at the rudder pedals 1413) is high, the brake calculator 1463 will send a lower command to the main landing gear wheels 1450 (through brake control line 1464).

1001031 In a second scenario, the autobrake button 1411 is pressed while the aircraft is stationary on a runway, and a "rejected take off" (RTO) autobrake mode is primed. In such a mode, if rejected take-off is detected (for example, by detecting that spoilers have been deployed and/or that the engine is throttled from a high power setting), the BSCU 1460 acts to brake the aircraft (using the brakes on the main landing gear wheels 1450) as hard as possible, whilst ensuring that tyres of the aircraft do not burst.

1001041 In a third scenario, the autobrake button 1411 is pressed while the aircraft is flying, and a "landing" autobrake mode is primed. In such a mode, if landing is detected (for example by detecting a rolling speed of an aircraft wheel and/or an altitude level and/or pressure detected at the wheels), the BSCU 1460 acts to brake the aircraft (using -16 -the brakes on the main landing gear wheels 1450) in a controlled manner to give an effective deceleration at a comfortable and suitable magnitude. This is based on a set deceleration level (of 3m/s2).

1001051 Figure 3 shows a schematic view of part of a control system 1400' according to a second embodiment of the invention. The control system 1400' is similar to that described in relation to Figures 1 and 2 and like numerals will be used for like elements. Only differences between the two embodiments will be described.

1001061 As can be seen in Figure 3, the control system 1400' further comprises a landing gear drive system activation signal line 1432. This signal line 1432 is provided with positive 1432a and negative 1432b lines. These lines 1432a, 1432b connect between the landing gear drive system control unit 1430 and the positive and negative lines of the autobrake button command line 1412a, 14 I 2b, respectively.

1001071 Here, and as shown in Figure 4, which is a schematic view of the control system 1400' of Figure 3, the landing gear drive system control unit 1430 can send a signal to the brake mode selector 1461 (via the landing gear drive system activation signal line 1432 and the autobrake button command line 1412) to indicate that the landing gear drive system is activated. In other words, the landing gear drive system control unit 1430 effectively -hijacks" the autobrake button command line 1412 to send a signal to the brake mode selector 1461 that the landing gear drive system is activated.

1001081 In use, the function of the control system 1400' is the same as 1400 for the autobrake modes. However, it functions slightly differently with regard to aircraft pushback.

1001091 When a pilot wishes to use the landing gear drive system with control system 1400', they press the landing gear drive system on/off switch 1417. This sends an activation signal (through landing gear drive system activation line 1418) to the landing gear drive system control unit 1430 to activate the landing gear drive systems on the main landing gear wheel 1450. This enables the landing gear drive system control unit 1430 to control the main landing gear wheels 1450 (through landing gear drive system control line 1431) to be rolled backwards for pushback.

1001101 In addition, the landing gear drive system control unit 1430 sends a signal to the brake mode selector 1461 (via the landing gear drive system activation signal line 1432 and the autobrake button command line 1412) to indicate that the landing gear drive system is activated. Hence, there is no need for the pilot to press the autobrake button 1411 to provide this indication to the brake mode selector 1461.

1001111 Similar to control system 1400, the brake mode selector 1461 of control system 1400' also receives aircraft speed, wheel speed and engine pressure from the measurement system 1420 (through measurement signal line 1421) It uses these measurements and signals to choose the braking mode, as before.

1001121 Figure 5 shows a front view of an aircraft 1000 including the control system 1400 of Figures 1 and 2 or that 1400' of Figures 3 and 4. The aircraft 1000 has a nose landing gear 1100 and two sets of main landing gear 1200, 1300. A wheel of each main landing gear 1200, 1300 is provided with a landing gear drive system, as described above. In addition, the braking of the wheels of the main landing gears 1450 is controlled by the control system 1400, 1400', as described above.

1001131 Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

1001141 The autobrake button 1411 may be a setting switch, rather than a button. For example, it may have a "rejected take-off (RTO) setting, one or more "landing" settings and an "off' setting.

1001151 A different button, control or switch of the cockpit may be used to send a signal to the brake mode selector 1461. Ideally, it is one that is already in existence and already has an input to the brake mode selector 1461 or BSCU 1460, and is required for purposes unrelated to having a landing gear drive system. For example, this control may be one of: steering command control, rudder pedals, braking command control, landing gear retraction/extension button.

1001161 The landing gear drive system on/off switch may instead be a setting switch with more than two settings. For example, it may have a direction and/or speed/torque -18 -setting. These settings may sent to the brake mode selector 1461 via the landing gear drive system activation signal line 1432.

1001171 The braking of the main landing gear wheels 1450 may be achieved using brake pedals that may be separate from the rudder pedals 1413.

1001181 The braking system may brake one or more nose landing gear wheels 1440.

1001191 The steering column 1415 may be in the form of a yoke, joystick, tiller or any other suitable steering control.

1001201 The steering may be done using one or more main landing gear wheels 1450.

1001211 The steering function may be provided by a separate control unit/system.

1001221 The (or another) measurement system 1420 may provide one or more measurements to the cockpit panel 1410 through a cockpit measurement input line.

1001231 The measurement system 1420 may measure additional or alternative measurements.

1001241 The landing gear drive system may drive rotation of one or more nose landing gear wheels 1440.

1001251 There may be further input/command lines from the cockpit control panel 1410 to the BSCU 1460 1001261 The braking torque limit of the pushback braking mode may not be fixed and may, instead, be calculated based on ensuring longitudinal stability using one or more of the following parameters: ground slope angle, aircraft centre of gravity position, aircraft inertial moment around the aircraft lateral (y) axis, and backwards speed of the aircraft. One or more of these variables may be passed to the brake calculator 1463 from the (or another) measurement system (not shown).

1001271 The set deceleration in "landing" autobrake mode may be any suitable value to give effective deceleration at a comfortable and suitable magnitude. Alternatively, it may be based on runway data and aircraft positioning (for example, how far along the runway the aircraft is), if this information is available to the brake calculator 1463 from the (or a) measurement system.

1001281 Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein -19 -incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.

1001291 It should be noted that throughout this specification, "or-should be interpreted as "and/or".

Claims

-20 -CLAIMSAn aircraft braking control unit, having: - a cockpit braking input line, for receiving an Input of a desired braking level from a cockpit of the aircraft, -at least one cockpit input line, for receiving a further input from the cockpit of the aircraft, - at least one measured input line, for receiving an input of at least one measured variable of the aircraft, - at least one braking output line, for sending a braking command for one or more wheels of the aircraft, - a brake mode selector, for selecting a brake mode based on data from the cockpit input line or measured input line, and -a brake calculator, for calculating the braking command, according to the selected brake mode, wherein the brake mode is selected from a number of possible brake modes, the possible modes including a landing gear drive system pushback brake mode, in which a landing gear drive system drives backwards movement of the aircraft over a ground surface and the braking command acts to retard the backwards movement of the aircraft, wherein, in the landing gear drive system pushback brake mode, the brake calculator calculates the braking command by firstly calculating an equivalent braking command to the desired braking level received from the cockpit and then limiting that equivalent braking command such that a braking torque limit is not exceeded.
-21 - 2. An aircraft braking control unit as claimed in claim 1, wherein the brake mode selector is configured to select the brake mode based on data from the cockpit input line and also from the measured input line.
3. An aircraft braking control unit as claimed in claim 1 or claim 2, wherein the cockpit input line is connected to a discrete selector control in the cockpit, such that a discrete selection input can be received by the braking control unit.
4. An aircraft braking control unit as claimed in claim 3, wherein the cockpit input line is connected to an autobrake control in the cockpit, such that an autobrake signal can be received by the braking control unit through the cockpit input line.
5. An aircraft braking control unit as claimed in any preceding claim, wherein the at least one measured input line provides a measurement of one or more of aircraft speed, wheel speed and engine pressure.
6. An aircraft braking control unit as claimed in any preceding claim, wherein the number of possible braking modes further includes an autobrake mode, in which the aircraft is moving forwards over a ground surface and the braking command acts to retard the forwards movement of the aircraft, wherein, in the autobrake mode, the brake calculator calculates the braking command to provide a retardation rate of the aircraft over the ground.
7. An aircraft braking control unit as claimed in any preceding claim, wherein the brake mode selector is able to cancel selection of the landing gear drive system pushback brake mode based on data from the cockpit input line and/or measured input line.
8. An aircraft braking control unit as claimed in claim 7, wherein the brake mode selector is able to cancel selection of the landing gear drive system pushback brake mode based on a measured input of aircraft and/or wheel speed.
-22 - 9. An aircraft braking control unit as claimed in claim 7 or claim 8, wherein the brake mode selector is able to select a further brake mode based on data from the cockpit input line and/or measured input line.
10. An aircraft control system comprising: -an aircraft braking control unit as claimed in any preceding claim, and -a landing gear drive system control unit.
11. An aircraft control system as claimed in claim 10, wherein the landing gear drive system control unit has a cockpit input line for receiving an input from a cockpit of the aircraft.
12. An aircraft control system as claimed in claim 1!, wherein the cockpit input line of the landing gear drive system control unit is connected to a landing gear drive system activation control in the cockpit, such that a landing gear drive system activation signal can be received by the landing gear drive system through the cockpit input line.
13. An aircraft control system as claimed in claim 10, claim 11 or claim 12, wherein the landing gear drive system control unit has an output line connected to the cockpit input line of the braking control unit, such that the landing gear drive system control unit can send a landing gear drive system activation signal to the braking control unit, and wherein the brake mode selector is configured to select a brake mode based on the landing gear drive system activation signal or data from the measured input line.
14. An aircraft control system as claimed in claim 13, wherein the brake mode selector is configured to select the brake mode based on the landing gear drive system activation signal and also from data from the measured input line.
Ii. An aircraft control system as claimed in any of claims 10 to 14, wherein the brake mode selector is able to cancel selection of the landing gear drive system pushback brake -23 -mode based on data from the cockpit input line, the landing gear drive system activation signal and/or measured input line.
16. An aircraft control system as claimed in claim 15, wherein the brake mode selector is able to cancel selection of the landing gear drive system pushback brake mode based on a measured input of aircraft and/or wheel speed.
17. An aircraft control system as claimed in claim 15 or claim 16, wherein the brake mode selector is able to select a further brake mode based on data from the cockpit input line, the landing gear drive system activation signal and/or measured input line.
18. An aircraft including at least one landing gear, including one or more wheels able to be driven backwards by a landing gear drive system of the aircraft, wherein the aircraft comprises an aircraft braking control unit according to any of claims 1 to 9 or an aircraft control system according to any of claims 10 to 17.
19. A method of operating an aircraft, the method including the following steps: i) initiating a landing gear drive system activation control to activate a landing gear drive system of the aircraft, ii) measuring at least one variable, and iii) selecting a landing gear drive system pushback braking mode, based on the measured variable, a cockpit input from a control in the cockpit or a landing gear drive system activation signal from the landing gear drive system, and, at the same time as each other, performing the following two steps: iv) using the landing gear drive system to drive pushback of the aircraft over a ground surface, and -24 -v) commanding braking of one or more wheels of the aircraft, the braking command acting to retard backwards movement of the aircraft and being calculated to limit the braking command to a braking torque limit.
20. A method of operating an aircraft as claimed in claim 19, wherein the selecting of a landing gear drive system pushback braking mode is performed by the braking control unit of the aircraft.
21. A method of operating an aircraft as claimed in claim 20, wherein the selecting of the landing gear drive system pushback braking mode is based on the landing gear drive system activation signal and wherein the method comprises the step of the landing gear drive system sending the landing gear drive system activation signal to the braking control unit.
22. A method of operating an aircraft as claimed in claim 21, wherein the landing gear drive system sends the landing gear drive system activation signal to the braking control unit via a cockpit input line, for sending the cockpit input to the braking control unit.
23. A method of operating an aircraft as claimed in any of claims 19 to 21, wherein the selecting of the landing gear drive system pushback braking mode is based on the cockpit input from a control in the cockpit.
24. A method of operating an aircraft as claimed in any of claims 19 to 23, wherein the selecting of the landing gear drive system pushback braking mode is based on the measured variable.
25. A method of operating an aircraft as claimed in any of claims 19 to 24, wherein the method further comprises the step of cancelling selection of the landing gear drive system pushback braking mode based on the measured variable, a cockpit input from a control in the cockpit or a landing gear drive system activation signal from the landing gear drive system -25 -
26. A method of operating an aircraft as claimed in claim 25, wherein the method further comprises the step of selecting a further braking mode based on the measured variable, a cockpit input from a control in the cockpit or a landing gear drive system activation signal from the landing gear drive system.