Patent ID: 12214867

DETAILED DESCRIPTION

FIG.1shows a schematic view of right10and left20main aircraft landing gears and associated brake control, for use with embodiments of the invention.

The right main landing gear10comprises a right landing gear leg and first11and second12wheels. The left main landing gear20comprises a left landing gear leg and first21and second22wheels.

There is a hydraulic fluid system40comprising a normal/“green” supply line41, connected to a “green” hydraulic fluid supply (not shown), and a normal/“green” return line42. These “green” lines41,42are used in normal operation when the “green” hydraulic fluid supply is available.

The hydraulic fluid system40also comprises an alternate/“yellow” supply line44, connected to a “yellow” hydraulic fluid supply (not shown), and an alternate/“yellow” return line45. These “yellow” lines44,45are used when the “green” hydraulic supply is not available.

The hydraulic fluid system40also comprises an accumulator47located on the “yellow” supply line44. This supplies a finite amount of hydraulic fluid through the “yellow” supply line44when the “green” and “yellow” supplies are not available.

A BSCU (Braking and Steering Control Unit) chooses and commands the braking mode. When in normal braking (i.e. when using the “green” supply) the braking is controlled by a normal brake selector valve50and four normal servo valves51a, b, c, dthat provide an individual braking command (of hydraulic fluid) to each of the four wheels21,22,11,12respectively. The normal brake selector valve50is there to prevent uncommanded braking in the case of a servo valve failing open. There are also four fuses52a, b, c, don the hydraulic line between the valves51a, b, c, dand the wheels21,22,11,12. The fuses prevent fluid loss if the hydraulic lines are severed in a failure.

In the normal mode, i.e. using the “green” supply, the braking command to each of the four wheels21,22,11,12is individually controlled. Hence, each individual valve51a, b, c, dcan be provided with a different control current from an antiskid brake control system such that antiskid braking is separately controlled for each wheel.

When the “green” supply is not available, an alternate brake mode is selected by the BSCU. When in alternate braking, the braking is controlled by an alternate brake selector valve54and two direct drive valves55,56that provide a paired braking command (of hydraulic fluid) to the two sets of wheels21and22, and11and12respectively. In other words, valve55controls the braking command to wheels21and22and valve56controls the braking command to wheels11and12. Wheels21and22(in one wheel set) are provided with the same braking command as each other (from valve55). Wheels11and12(in another wheel set) are provided with the same braking command as each other (from valve56). The alternate brake selector valve54is there to prevent uncommanded braking in the case of a servo valve failing open. There are also two fuses57a, bon the hydraulic line between the valves55,56and the wheels pairs21,22,11,12. The fuses prevent fluid loss if the hydraulic lines are severed in a failure.

In the alternate mode, i.e. using the “yellow” supply, the braking command to wheels21,22,11,12is controlled in pairs (wheel sets). Hence, antiskid braking is controlled separately for each wheel pair, not each wheel individually.

The emergency mode (where the “yellow” supply is not available) using the accumulator47is also controlled through valve54and so in the emergency mode the antiskid braking is similarly controlled separately for each wheel pair, not each wheel individually.

There is also a park brake selector valve53able to provide “yellow” hydraulic fluid to the valves55,56. This valve53may be used in combination with the normal brake selector valve50to provide a dual braking command (through both “green” and “yellow” supplies) to the wheels when the aircraft is parked.

FIG.2shows a schematic view of a brake control unit60′ according to a first embodiment of the invention.

The control unit60′ is for controlling the antiskid braking of the right pair of wheels11,12(wheel set) when in alternative or emergency braking mode, but it could equally be applied to the left wheels21,22.

The unit60′ has an input of the wheel speed of the first wheel11(labelled as13) and the wheel speed of the second wheel12(labelled as14). The control unit also has a wheel speed comparator62for determining which are the minimum and maximum wheel speeds from wheel speeds13and14. These are output from the comparator62as minimum wheel speed63and maximum wheel speed64. The unit60′ then outputs (as output66′) the maximum wheel speed64.

The output66′ is what is sent to determine the antiskid braking command that is sent to the direct drive valve56. In other words, the antiskid braking command is calculated based on the output66′ and therefore based on the maximum wheel speed64.

This output66′ of the maximum wheel speed64is done irrespective of other factors. In other words, the control system assumes that the slower wheel is not skidding substantially more than the faster wheel and so it is appropriate to base the antiskid calculation on the higher speed wheel.

The control unit60′ may comprise a number of other inputs that indicate that the alternate/emergency braking mode is in use, similar to inputs43,46as described in relation toFIG.3below.

FIG.3shows a schematic view of a brake control unit60according to a second embodiment of the invention. This unit60is similar to the control unit60′ ofFIG.2but has additional complexity and logic considerations, as will be explained. Where identical elements are referred to, the reference numerals (inFIGS.2and3) do not have a ′. The ′ indicates elements ofFIG.2that are similar, but not the same, to those ofFIG.3.

As before, the control unit60is for controlling the antiskid braking of the right pair of wheels11,12(wheel set) when in alternative or emergency braking mode, but it could equally be applied to the left wheels21,22.

The unit60has an input of the wheel speed of the first wheel11(labelled as13) and the wheel speed of the second wheel12(labelled as14). The control unit also has a wheel speed comparator62for determining which are the minimum and maximum wheel speeds from wheel speeds13and14. These are output from the comparator62as minimum wheel speed63and maximum wheel speed64.

There is also a plurality of inputs, labelled as61. These inputs61comprise the following inputs:a. a “weight on wheel” detection signal from a first sensor in the right landing gear10leg (shock strut). This is labelled as15inFIG.4.b. a “weight on wheel” detection signal from a second sensor in the right landing gear10leg (shock strut). This is labelled as16inFIG.4.c. a “weight on wheel” detection signal from a sensor in the nose landing gear30leg (shock strut). This is labelled as35inFIG.4.d. a signal indicating if the “green” hydraulic supply is available. This is labelled as43inFIG.4.e. a signal indicating if the “yellow” hydraulic supply is available. This is labelled as46inFIG.4. andf. a signal from the Inertial Reference System of the ground speed of the aircraft. This is labelled as75inFIG.4.

The inputs61and the minimum wheel speed63and maximum wheel speed64are input into a logic unit65of the control unit60. The logic unit65, with the various inputs, is shown in the more detailed control unit60view inFIG.4(see below).

The control unit60then outputs (as output66) either the minimum wheel speed63or the maximum wheel speed64. The output66is what is sent to determine the antiskid braking command that is sent to the direct drive valve56. In other words, the antiskid braking command is calculated based on the output66and therefore may be based on the minimum wheel speed63or the maximum wheel speed64.

FIG.4shows a more detailed schematic view of the brake control unit60ofFIG.3.

As already described, the unit60has the various inputs, shown on the left hand side ofFIG.4(from left to right and top to bottom):a. wheel speed13of wheel11.b. wheel speed14of wheel12.c. a “weight on wheel” detection signal from a first sensor in the right landing gear10leg (shock strut). This is labelled as15inFIG.4.d. a “weight on wheel” detection signal from a second sensor in the right landing gear10leg (shock strut). This is labelled as16inFIG.4.e. a “weight on wheel” detection signal from a sensor in the nose landing gear30leg (shock strut). This is labelled as35inFIG.4.f. a signal indicating if the “green” hydraulic supply is available. This is labelled as43inFIG.4.g. a signal indicating if the “yellow” hydraulic supply is available. This is labelled as46inFIG.4. andh. a signal from the Inertial Reference System of the ground speed of the aircraft. This is labelled as75inFIG.4.

The wheel speed comparator62is effectively shown in two parts. A first part, at the top ofFIG.4, labelled as63takes the minimum wheel speed63of the two input speeds13,14. A second part, at the bottom ofFIG.4, labelled as64takes the maximum wheel speed64of the two input speeds13,14.

The “weight on wheel” signals (from the right landing gear10) labelled as15and16are input into an OR box71, which outputs to an AND box77. Hence, if either of the sensors detect that there is weight on the wheels of the right landing gear10, then the AND box77receives a positive signal here.

The “weight on wheel” signal (from the nose landing gear30) labelled as35is input to the AND box77. Hence, if the sensor detects that there is weight on the wheels of the nose landing gear10, then the AND box77receives a positive signal here.

The two wheel speeds13,14are also input into logic boxes72,73to determine if they are under 20 knots, respectively. These signals are provided to an OR box74, which outputs to an AND box77. Hence, if either of the wheel speeds13,14are under 20 knots, the AND box77receives a positive signal here.

The signal43indicating if the “green” hydraulic supply is available is input to AND box77. The AND box77receives a positive signal if the “green” supply is not available.

The signal46indicating if the “yellow” hydraulic supply is available is input to AND box77. The AND box77receives a positive signal if the “yellow” supply is not available.

The Inertial Reference System signal75of the ground speed of the aircraft is inputted to a logic box76that outputs a positive signal to the AND box77as long as the aircraft ground speed is over 15 m/s.

Hence, the AND box77receives all positive signals if:a. the aircraft has landed on the main gear and then has rotated onto its nose gearb. any of the wheels have not reached a speed of 20 knotsc. the “green” and “yellow” hydraulic supplies are not available, andd. the aircraft speed is over 15 m/s.

These first two of these (a and b) indicate that a wheel or a wheel speed monitor may have failed. This is because an aircraft that has landed on its main wheels and then rotated onto its nose wheel(s) would be expected to have main landing gear wheels that have spun up to above 20 knots. This is because the main wheels would have had a chance to do that prior to the nose wheels rotating to the ground. Also, no brakes would yet be applied to the wheels and so the wheels should not be skidded.

The third of these (c) is to ensure that the antiskid brake command is only calculated in the way to be described when both the yellow and green supplies are not available. i.e. that that hydraulic power is coming from the accumulator47and the emergency braking mode is being used.

The last of these (d) is to ensure that the aircraft is at a speed where skidding is possible. In other words, the antiskid brake command is not to be calculated as described when the aircraft is under 15 m/s as then no skidding would be expected.

If the AND box77receives all positive signals, it outputs a positive signal to logic box78. Logic box78comprises a timer of 5 seconds and outputs a positive signal if it has received a positive signal from the AND box77for the last 5 seconds.

The positive signal from box78is sent to a switch79. The switch79also receives the minimum wheel speed63and the maximum wheel speed64. The switch79starts (as a default) by linking its output to the minimum wheel speed63. However, whenever it receives a positive signal from the logic box78it switches its output to be the maximum wheel speed64.

Hence, the switch79outputs the maximum wheel speed64if all of the inputs into the AND box77are positive for the last 5 seconds. Otherwise, it outputs the minimum wheel speed63. The switch79outputs to an antiskid brake calculator80that calculates the required antiskid brake command based on the wheel speed (either maximum64or minimum63) input into it. It then outputs this antiskid brake command current81. This command current81is what is sent to the direct drive valve56to control the brake command to the right wheels11,12.

The way the control system60(and a similar control system for the left landing gear wheels) works, in use, when in emergency mode, will now be described in relation to four scenarios:

FIG.5ashows a first wheel scenario that may occur in the aircraft landing gear ofFIG.1.

Here, all four wheels11,12,21,22are intact and the wheel tachometers functioning correctly. Here, when the aircraft has landed on the main gear and then has rotated onto its nose landing gear all of the four wheels would have reached speeds of over 20 knots and the aircraft ground speed would be over 15 m/s.

Hence, as all wheels11,12,21,22are over 20 knots, the output from logic box74(in both the right and left landing gear control units60) would be negative and so this would not “trigger” the AND box77and so the switches79of the two control units60would continue to output the minimum wheels speeds63to the antiskid brake calculators80.

Hence, when one of the wheels out of11or12skidded, the antiskid brake command sent to those two wheels11,12(from valve55) would be calculated based on the minimum wheel speed63in order to release the skidded (lowest speed) wheel. Similarly, when one of the wheels out of21or22skidded, the antiskid brake command sent to those two wheels21,22(from valve56) would be calculated based on the minimum wheel speed63in order to release the skidded (lowest speed) wheel.

FIG.5bshows a second wheel scenario that may occur in the aircraft landing gear ofFIG.1.

Here, wheel21has failed e.g. burst (or its tachometer has failed). Here, when the aircraft has landed on the main gear and then has rotated onto its nose landing gear all of wheels11,12,22would have reached speeds of over 20 knots (and would be indicated as such by their respective tachometers) and the aircraft ground speed would be over 15 m/s. However, the tachometer for wheel21would show a zero or low speed.

Hence, as both wheels11,12are over 20 knots, the output from logic box74(in the right landing gear control unit60) would be negative and so this would not “trigger” the AND box77and so the switch79would continue to output the minimum wheel speed63to the antiskid brake calculator80. Hence, when one of the wheels out of11or12skidded, the antiskid brake command sent to those two wheels11,12would be calculated based on the minimum wheel speed63in order to release the skidded (lowest speed) wheel.

However, as wheel21would appear to have a speed less than 20 knots, the output from logic box74(in the left landing gear control unit60) would be positive and so this would “trigger” the AND box77and so the switch79would then output the maximum wheel speed64(i.e. the speed of wheel22) to the antiskid brake calculator80. Hence, when wheel22skidded, the antiskid brake command sent to it (and wheel21) is calculated based on the maximum wheel speed64(which would be that of wheel22) and so this releases the skid of wheel22.

FIG.5cshows a third wheel scenario that may occur in the aircraft landing gear ofFIG.1.

Here, both wheels21and11have failed e.g. burst (or their tachometers have failed). Here, when the aircraft has landed on the main gear and then has rotated onto its nose landing gear, wheels22,12would have reached speeds of over 20 knots (and would be indicated as such by their respective tachometers) and the aircraft ground speed would be over 15 m/s. However, the tachometer for wheels21and11would show a zero or low speed.

Hence, as wheel11would appear to have a speed less than 20 knots, the output from logic box74(in the right landing gear control unit60) would be positive and so this would “trigger” the AND box77and so the switch79would then output the maximum wheel speed64(that of wheel12) to the antiskid brake calculator80. Hence, when wheel12skidded, the antiskid brake command sent to it (and wheel11) is calculated based on the maximum wheel speed64(which would be that of wheel12) and so this releases the skid of wheel12.

Similarly, as wheel21would appear to have a speed less than 20 knots, the output from logic box74(in the left landing gear control unit60) would be positive and so this would “trigger” the AND box77and so the switch79would then output the maximum wheel speed64(that of wheel22) to the antiskid brake calculator80. Hence, when wheel22skidded, the antiskid brake command sent to it (and wheel21) is calculated based on the maximum wheel speed64(which would be that of wheel22) and so this releases the skid of wheel22.

FIG.5dshows a fourth wheel scenario that may occur in the aircraft landing gear ofFIG.1.

Here, wheels21and22have failed e.g. burst (or their tachometers have failed). Here, when the aircraft has landed on the main gear and then has rotated onto its nose landing gear, wheels11,12would have reached speeds of over 20 knots (and would be indicated as such by their respective tachometers) and the aircraft ground speed would be over 15 m/s. However, the tachometer for wheels21and22would show a zero or low speed.

Hence, as both wheels11,12are over 20 knots, the output from logic box74(in the right landing gear control unit60) would be negative and so this would not “trigger” the AND box77and so the switch79would continue to output the minimum wheel speed63to the antiskid brake calculator80. Hence, when one of the wheels out of11or12skidded, the antiskid brake command sent to those two wheels11,12would be calculated in order to release the skidded wheel, i.e. would be based on the minimum wheel speed (the skidded wheel).

However, as wheels21and22would appear to have a speed less than 20 knots, the output from logic box74(in the left landing gear control unit60) would be positive and so this would “trigger” the AND box77and so the switch79would then output the maximum wheel speed64to the antiskid brake calculator80. Hence, say wheel21had failed (tachometer showing zero speed) and wheel22had a faulty tachometer (perhaps showing a lower than actual speed) and had then skidded, the antiskid brake command sent to wheels21,22is calculated based on the maximum wheel speed64(the speed of wheel22) and so this would likely release the skid of wheel22.

FIG.6shows an aircraft100comprising the right (not shown inFIG.6) and left20main landing gear ofFIG.1. The aircraft also has nose landing gear30.

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.

In the above examples, the control function takes place in a single unit (60or60′). However, the same inputs, logic, output could be distributed over a control assembly, with different parts of the linked assembly being located in different portions of the aircraft, for example.

In the above examples, there are two wheels (11and12, and21and22) in each of two wheel sets. However, there could be any number of wheel sets on each landing gear and each wheel set could have any number of wheels (above one). What may define a wheel set is that the wheels of the wheel set are commonly brake controlled in a braking mode.

All or only some (but at least two) of the wheels in the wheel set may have their wheel speed indication inputted to the control assembly.

It does not have to be the highest (or maximum) wheel speed in the wheel set that is used for the antiskid brake calculation, even when the switch79has been triggered. It could be a different wheel speed from the wheel set. It may be the highest wheel speed of the wheel set that is still below a certain likely skid threshold value. The likely skid threshold value may represent a speed above which the wheel is unlikely to be skidding. Hence, the braking command may be reduced only for wheels that are actually likely to be skidding. This likely skid threshold value may be between 5 and 50 knots. It may be between 10 and 30 knots. It may be between 15 and 25 knots. It may be approximately 20 knots.

In the above examples, thresholds of 20 knots and 15 m/s are used, but any suitable threshold values may be used.

In the above examples, a timer of 5 seconds is used but any suitable time period may be used.

In the above examples, the antiskid braking is controlled as described in the emergency mode only. However, it could additionally or alternatively be used in the alternate (“yellow” supply) mode. Here, the “yellow” supply not available input46to the control unit60would not be required to trigger the AND box77, or it may be required to be negative (i.e. that the “yellow” supply is available) to trigger the AND box77.

The input(s)61may include one or more inputs from:i) the cockpit (for example from activating a pilot button, that an image from a camera pointing at the wheel/wheel set indicates that a wheel or tyre has failed—e.g. the pilot can see that a tyre has burst),ii) an AI (Artificial Intelligence) computer (that an image from a camera pointing at the wheel/wheel set indicates that a wheel or tyre has failed—e.g. the AI detects that a tyre has burst),iii) a laser monitoring wheel rotation or tyre position (the laser could detect a burst before landing due to the wheel/tyre not rotating as expected),iv) a tyre pressure monitor (able to detect tyre failure),v) a light sensor inside the tyre or wheel (if it is able to detect light, this indicates the tyre has failed),vi) an ultrasound sensor (able to detect tyre failure),vii) a proximity sensor detecting a tyre location (a missing tyre location indicates it has failed), andviii) a torque sensor, load sensor or vibration sensor (indicating an imbalance of the wheel, landing gear or attitude of the axle that could indicates tyre bursts).

The input(s)61may include one or more inputs from:i) an electronic monitor of a wheel tachometer,ii) functional monitoring of the tachometer, andiii) a second or further tachometer.

The tachometer, or second of further tachometers, may comprise hall effect sensors or lasers/LED light tachometers.

The input(s)61may include an indication of a flight phase of the aircraft, which may be obtained from a flight management computer, and/or from an indication of whether or not thrust reversers of the aircraft are active and/or whether or not spoilers of the aircraft are active and/or from an indication from ground proximity sensors of the aircraft.

In the above examples, hydraulic fluid is used as an energy supply, instead electrical energy may be used instead of some or all of the supplies.

In the above examples, the braking command is applied to the main (right and/or left) landing gear wheels. However, it could additionally or alternatively be applied to the nose landing gear wheels.

Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein 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.

It should be noted that throughout this specification, “or” should be interpreted as “and/or”.

Although the invention has been described above mainly in the context of a fixed-wing aircraft application, it may also be advantageously applied to various other applications, including but not limited to applications on vehicles such as helicopters, drones, trains, automobiles and spacecraft.