U.S. patent application number 17/473846 was filed with the patent office on 2021-12-30 for brake control.
The applicant listed for this patent is Airbus Operations Limited, Airbus Operations (S.A.S.), Airbus (S.A.S.). Invention is credited to Andrew BILL, Utsav OZA.
Application Number | 20210402973 17/473846 |
Document ID | / |
Family ID | 1000005836397 |
Filed Date | 2021-12-30 |
United States Patent
Application |
20210402973 |
Kind Code |
A1 |
BILL; Andrew ; et
al. |
December 30, 2021 |
BRAKE CONTROL
Abstract
An apparatus including a controller configured to generate a
first indication for a vehicle braking system depending upon an
oxidation state of a wheel brake of the vehicle is disclosed. Also
disclosed is a braking system including a controller configured to
receive a first indication, the first indication having been
generated depending upon an oxidation state of a wheel brake of a
vehicle and control the operation of the brake based on the first
indication. Also disclosed is a method of controlling at least one
brake of an aircraft, and an aircraft including the apparatus, the
braking system and a temperature sensor configured to measure a
temperature of a wheel brake of the aircraft and to transmit the
temperature measurement to the apparatus.
Inventors: |
BILL; Andrew; (Bristol,
GB) ; OZA; Utsav; (Bristol, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Airbus Operations Limited
Airbus Operations (S.A.S.)
Airbus (S.A.S.) |
Bristol
Toulouse
Blagnac |
|
GB
FR
FR |
|
|
Family ID: |
1000005836397 |
Appl. No.: |
17/473846 |
Filed: |
September 13, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
16286028 |
Feb 26, 2019 |
|
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17473846 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B60T 8/171 20130101;
B60T 17/221 20130101; B60T 8/58 20130101; F16D 66/021 20130101;
B60T 8/1703 20130101; B64F 5/60 20170101; B60T 2270/406 20130101;
B60T 8/32 20130101; B64C 25/42 20130101; F16D 66/00 20130101; F16D
2066/006 20130101; B64C 25/426 20130101; F16D 2066/001
20130101 |
International
Class: |
B60T 17/22 20060101
B60T017/22; B64F 5/60 20060101 B64F005/60; F16D 66/00 20060101
F16D066/00; F16D 66/02 20060101 F16D066/02; B60T 8/17 20060101
B60T008/17; B60T 8/58 20060101 B60T008/58; B64C 25/42 20060101
B64C025/42; B60T 8/171 20060101 B60T008/171; B60T 8/32 20060101
B60T008/32 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 27, 2018 |
GB |
1803203.7 |
Jul 6, 2018 |
GB |
1811178.1 |
Claims
1. An apparatus, comprising: a controller configured to: determine
a brake temperature threshold for a brake from a plurality of
brakes of a vehicle according to a thermal oxidation state of said
brake, including by determining a lower brake temperature threshold
given a higher level of thermal oxidation of said brake; determine
whether a temperature of said brake exceeds the brake temperature
threshold; and generate a first indication for a braking system to
disable said brake of the plurality of brakes if the temperature of
said brake exceeds the brake temperature threshold for said
brake.
2. The apparatus according to claim 1, wherein: the controller
receives an indication of the temperature of said brake from a
temperature sensor associated with said brake.
3. The apparatus according to claim 1, wherein: the controller
receives a predicted temperature of said brake from a brake
temperature prediction function as the temperature of said
brake.
4. The apparatus according to claim 1, wherein the controller is
configured to: monitor the temperature of said brake; and if the
temperature of said brake no longer exceeds the brake temperature
threshold for said brake, generate a second indication for the
braking system to enable said brake.
5. The apparatus according to claim 1, wherein: if the thermal
oxidation state of said brake is below a predetermined thermal
oxidation level, a first temperature threshold is selected as the
brake temperature threshold of said brake.
6. The apparatus according to claim 5, wherein: if the thermal
oxidation state of said brake is above the predetermined thermal
oxidation level, a second brake temperature threshold lower than
the first temperature threshold is selected as the brake
temperature threshold of said brake.
7. The apparatus according to claim 6, wherein: the second brake
temperature threshold is selected based on the difference between
the thermal oxidation state of said brake and the predetermined
thermal oxidation level.
8. A vehicle comprising the apparatus according to claim 1 and a
braking system, the braking system comprising: a second controller
configured to: receive the first indication; and control said brake
of the plurality of brakes to be disabled if the second controller
receives the first indication.
9. The vehicle according to claim 8, wherein: the second controller
is configured to: receive a second indication that the temperature
of said brake no longer exceeds the brake temperature threshold for
said brake; and control said brake to be enabled if the second
controller receives the second indication.
10. The vehicle according to claim 8, wherein: the vehicle is an
aircraft and the second controller is configured to disable a brake
from the plurality of brakes if a predefined taxiing criterion is
met, wherein the predefined taxiing criterion comprises one or more
of: an aircraft speed threshold defined such that an aircraft speed
less than or equal to the aircraft speed threshold satisfies the
predefined taxiing criterion; and a particular flight phase
indicated by a flight phase indication system of the aircraft.
11. The vehicle according to claim 8, wherein the second controller
is configured to: receive a braking request, the braking request
comprising information relating to a requested braking intensity;
determine, based on the information related to the requested
braking intensity, whether the requested braking intensity exceeds
a braking intensity threshold; and if the requested braking
intensity exceeds the braking intensity threshold, enable at least
one disabled brake from the plurality of brakes.
12. The vehicle according to claim 8, wherein the vehicle is an
aircraft comprising a temperature sensor configured to measure a
temperature of a wheel brake of the aircraft and to transmit the
temperature measurement to the apparatus.
13. A method for controlling at least one wheel brake from a
plurality of wheel brakes of an aircraft, the method comprising:
determining a brake temperature threshold for a wheel brake from
the plurality of brakes according to a thermal oxidation state of
said wheel brake, including by determining a lower brake
temperature threshold given a higher level of thermal oxidation of
said wheel brake; determining whether a temperature of said wheel
brake exceeds the brake temperature threshold; generating a first
indication if the temperature of said wheel brake exceeds the brake
temperature threshold for said wheel brake; and controlling said
wheel brake to be disabled based on the first indication.
14. The method according to claim 13, comprising: (i) monitoring
the temperature of said wheel brake; (ii) determining whether the
temperature of said wheel brake still exceeds the brake temperature
threshold; if the temperature of said wheel brake no longer exceeds
the brake temperature threshold: generating a second indication
that the temperature of said wheel brake no longer exceeds the
brake temperature threshold; and controlling said wheel brake to be
enabled based on the second indication; and if the temperature of
said wheel brake still exceeds the brake temperature threshold,
repeating (i) and (ii).
15. The method according to claim 13, comprising: receiving an
indication of the temperature of said wheel brake from a
temperature sensor associated with said wheel brake.
16. The method according to claim 13, comprising: receiving a
predicted temperature from a brake temperature prediction function
as the temperature of said wheel brake.
17. The method according to claim 13, wherein: if the thermal
oxidation state of said wheel brake is below a predetermined
thermal oxidation level, a first temperature threshold is selected
as the brake temperature threshold of said wheel brake.
18. The method according to claim 17, wherein: if the thermal
oxidation state of said wheel brake is above the predetermined
thermal oxidation level, a second brake temperature threshold lower
than the first temperature threshold is selected as the brake
temperature threshold of said wheel brake.
19. The method according to claim 18, wherein: the second brake
temperature threshold is selected based on the difference between
the thermal oxidation state of said wheel brake and the
predetermined thermal oxidation level.
20. The method according to claim 13, wherein said wheel brake is
disabled if a predefined taxiing criterion is met, wherein the
predefined taxiing criterion comprises one or more of: an aircraft
speed threshold defined such that an aircraft speed less than or
equal to the aircraft speed threshold satisfies the predefined
taxiing criterion; and a particular flight phase indicated by a
flight phase indication system of the aircraft.
21. The method according to claim 13, wherein the method comprises:
receiving a braking request, the braking request comprising
information relating to a requested braking intensity; determining,
based on the information related to the requested braking
intensity, whether the requested braking intensity exceeds a
braking intensity threshold; and if the requested braking intensity
exceeds the braking intensity threshold, enabling at least one
disabled wheel brake from the plurality of wheel brakes.
22. The method according to claim 13, wherein the method is
performed in real-time during a use cycle of the aircraft.
23. The method according to claim 15, wherein the method is
performed repeatedly at a fast rate, with the temperature of said
wheel brake being sampled multiple times per second, up to the
sampling rate of the temperature sensor.
Description
CROSS RELATED APPLICATIONS
[0001] This application is a Continuation of U.S. patent
application Ser. No. 16/286,028, filed Feb. 26, 2019, now pending,
which claims priority to United Kingdom (GB) Patent Application
1803203.7, filed Feb. 27, 2018, and United Kingdom (GB) Patent
Application 1811178.1, filed Jul. 6, 2018, the entire contents of
each of which are hereby incorporated by reference.
TECHNICAL FIELD
[0002] The present invention relates to brake control and
particularly, although not exclusively, to brake control taking
account of a state, such as an oxidation state, of the brake.
BACKGROUND
[0003] Vehicle brakes may include components such as brake discs
composed of Carbon-Carbon composites. The brakes may undergo
thermal oxidation at high temperatures as carbon atoms in the brake
discs react with oxygen. The brakes may need to be serviced or
replaced once a certain amount of thermal oxidation has taken place
for safe functioning of the vehicle
SUMMARY
[0004] A first aspect of the present invention provides an
apparatus comprising: a controller configured to: generate a first
indication for a vehicle braking system depending upon an oxidation
state of a wheel brake of the vehicle.
[0005] Optionally, the controller is configured to determine a
brake temperature characteristic criterion of the brake according
to the oxidation state of the brake; determine whether a
temperature characteristic of the brake satisfies the brake
temperature characteristic criterion; and generate the first
indication for the braking system depending upon whether the brake
temperature characteristic satisfies the brake temperature
characteristic criterion.
[0006] Optionally, the controller receives an indication of the
temperature characteristic of the brake from a temperature sensor
associated with the brake.
[0007] Optionally, the controller receives a predicted temperature
characteristic from a brake temperature prediction function as the
temperature characteristic of the brake.
[0008] Optionally, the controller is configured to: monitor the
temperature characteristic of the brake; and if the temperature
characteristic of the brake no longer satisfies the brake
temperature characteristic criterion, generate a second indication
for the braking system that the temperature characteristic of the
brake no longer satisfies the brake temperature characteristic
criterion.
[0009] Optionally, the temperature characteristic of the brake
comprises a temperature of the brake; and the brake temperature
characteristic criterion is satisfied if the temperature of the
brake exceeds a brake temperature threshold.
[0010] Optionally, the controller is configured such that the
higher the level of thermal oxidation of the brake, the lower the
brake temperature threshold of the determined brake temperature
characteristic criterion is.
[0011] Optionally, if the thermal oxidation state of the brake is
below a predetermined thermal oxidation level, a first brake
temperature characteristic criterion is selected which comprises a
first temperature threshold.
[0012] Optionally, if the thermal oxidation state of the brake is
above the predetermined thermal oxidation level, a second brake
temperature characteristic criterion is selected which comprises a
second temperature threshold lower than the first temperature
threshold
[0013] Optionally, the second brake temperature characteristic
criterion is selected based on the difference between the thermal
oxidation state of the brake and the predetermined thermal
oxidation level.
[0014] Optionally, the first temperature threshold is above
400.degree. C.
[0015] A second aspect of the present invention provides a braking
system of a vehicle, the braking system comprising a controller
configured to: receive a first indication, the first indication
having been generated depending upon an oxidation state of a wheel
brake of a vehicle; and control the operation of the brake based on
the first indication.
[0016] Optionally, in the braking system according to the second
aspect, the first indication received by the controller is
generated depending upon whether a brake temperature characteristic
satisfies a brake temperature characteristic criterion; and the
controller is configured to: receive a second indication that the
temperature characteristic of the brake no longer satisfies the
brake temperature characteristic criterion; and control the brake
selectively to be enabled or disabled based on the received
indication.
[0017] Optionally, in the braking system according to the second
aspect, the controller is configured to control the brake to be
disabled if it receives the first indication.
[0018] Optionally, in the braking system according to the second
aspect, the controller is configured to control the brake to be
enabled if it receives the second indication.
[0019] Optionally, in the braking system according to the second
aspect, the vehicle is an aircraft and the controller is configured
to disable a brake if a taxiing criterion is met, wherein the
taxiing criterion comprises one or more of: an aircraft speed
threshold defined such that an aircraft speed less than or equal to
the aircraft speed threshold satisfies the predefined taxiing
criterion; and a particular flight phase indicated by a flight
phase indication system of the aircraft.
[0020] Optionally, in the braking system according to the second
aspect, the controller is configured to: receive a braking request,
the braking request comprising information relating to a requested
braking intensity; determine, based on the information related to
the requested braking intensity, whether the requested braking
intensity exceeds a braking intensity threshold; and if the
requested braking intensity exceeds the braking intensity
threshold, enable at least one disabled brake.
[0021] A third aspect of the present invention provides a method
for controlling at least one brake of an aircraft, the method
comprising: generating a first indication depending upon an
oxidation state of a wheel brake of an aircraft; and controlling
the brake to be disabled based on the first indication.
[0022] Optionally, the method according to the third aspect
comprises: determining a brake temperature characteristic criterion
of the brake according to the thermal oxidation state of the brake;
determining whether a temperature characteristic of the brake
satisfies the brake temperature characteristic criterion; and
generating the first indication depending upon whether the brake
temperature characteristic satisfies the brake temperature
characteristic criterion.
[0023] Optionally, the method according to the third aspect
comprises: (i) monitoring the temperature characteristic of the
brake; (ii) determining whether the temperature characteristic of
the brake still satisfies the brake temperature characteristic
criterion; if the temperature characteristic of the brake no longer
satisfies the brake temperature characteristic criterion:
generating a second indication that the temperature characteristic
of the brake no longer satisfies the brake temperature
characteristic criterion; and controlling the brake to be enabled
based on the second indication; and if the temperature
characteristic of the brake still satisfies the brake temperature
characteristic criterion, repeating (i) and (ii).
[0024] Optionally, the method according to the third aspect
comprises receiving an indication of the temperature characteristic
of the brake from a temperature sensor associated with the
brake.
[0025] Optionally, the method according to the third aspect
comprises receiving a predicted temperature characteristic from a
brake temperature prediction function as the temperature
characteristic of the brake.
[0026] Optionally, in the method according to the third aspect, the
temperature characteristic of the brake comprises a temperature of
the brake; and the brake temperature characteristic criterion is
satisfied if the temperature of the brake exceeds a brake
temperature threshold.
[0027] Optionally, in the method according to the third aspect, the
higher the level of thermal oxidation of the brake, the lower the
brake temperature threshold of the determined brake temperature
characteristic criterion is.
[0028] Optionally, in the method according to the third aspect, if
the thermal oxidation state of the brake is below a predetermined
thermal oxidation level, a first brake temperature characteristic
criterion is selected which comprises a first temperature
threshold.
[0029] Optionally, in the method according to the third aspect, if
the thermal oxidation state of the brake is above the predetermined
thermal oxidation level, a second brake temperature characteristic
criterion is selected which comprises a second temperature
threshold lower than the first temperature threshold.
[0030] Optionally, in the method according to the third aspect, the
second brake temperature characteristic criterion is selected based
on the difference between the thermal oxidation state of the brake
and the predetermined thermal oxidation level.
[0031] Optionally, in the method according to the third aspect, the
first temperature threshold is above 400.degree. C.
[0032] Optionally, in the method according to the third aspect, the
brake is disabled if a predefined taxiing criterion is met, wherein
the predefined taxiing criterion comprises one or more of: an
aircraft speed threshold defined such that an aircraft speed less
than or equal to the aircraft speed threshold satisfies the
predefined taxiing criterion; and a particular flight phase
indicated by a flight phase indication system of the aircraft.
[0033] Optionally, the method according to the third aspect
comprises: receiving a braking request, the braking request
comprising information relating to a requested braking intensity;
determining, based on the information related to the requested
braking intensity, whether the requested braking intensity exceeds
a braking intensity threshold; and if the requested braking
intensity exceeds the braking intensity threshold, enabling at
least one disabled brake.
[0034] A fourth aspect of the present invention provides an
aircraft comprising: an apparatus according to the first aspect; a
braking system according to the second aspect; and a temperature
sensor configured to measure a temperature of a wheel brake of the
aircraft and to transmit the temperature measurement to the
apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] Embodiments of the invention will now be described, by way
of example only, with reference to the accompanying drawings, in
which:
[0036] FIG. 1 is a schematic view of an aircraft on which examples
may be deployed;
[0037] FIG. 2 is a schematic view of a brake and a wheel of an
aircraft landing gear according to an example;
[0038] FIG. 3 is a schematic view of an apparatus and a braking
system of a vehicle according to an example;
[0039] FIG. 4a is a first flow diagram of a method of controlling
at least one brake of an aircraft according to an example;
[0040] FIG. 4b is a second flow diagram of a method of controlling
at least one brake of an aircraft according to an example;
[0041] FIG. 4c is a third flow diagram of a method of controlling
at least one brake of an aircraft according to an example;
[0042] FIG. 5 is a fourth flow diagram of a method of controlling
at least one brake of an aircraft according to an example;
[0043] FIG. 6 is a flow diagram of an exemplary method of
determining the thermal oxidation state of a brake of an aircraft
landing gear;
[0044] FIG. 7 is a flow diagram of an exemplary method of
determining the thermal oxidation state of a brake of an aircraft
landing gear;
[0045] FIG. 8 is an exemplary graph illustrating the temperature of
a brake with respect to time;
[0046] FIG. 9 is an exemplary graph illustrating the thermal
oxidation state of a brake with respect to time for a specific
temperature;
[0047] FIG. 10 is an exemplary flow diagram of a method of
determining an amount of brake wear according to an example;
and
[0048] FIG. 11 is an exemplary flow diagram of a method of
predicting a number of good future use cycles with respect to an
aircraft brake according to an example.
DETAILED DESCRIPTION
[0049] The following disclosure relates to systems and processes
for limiting use of a brake of a vehicle, e.g. aircraft brakes,
when the brake reaches certain high temperatures, for the purposes
of reducing the amount of thermal oxidation of the brake during
use.
[0050] FIG. 1 is a simplified schematic view of an aircraft 100.
The aircraft 100 comprises a plurality of landing gear assemblies
102. The landing gear assemblies may include main and nose landing
gears that may be extended during take-off and landing. Each
landing gear assembly 102 includes wheels such as wheel 104. The
aircraft 100 comprises a computing system 106, which may, for
example, comprise one or more processors and one or more computer
readable storage media. The aircraft 100 may also comprise
instruments 108, such as instruments or sensors for measuring
characteristics or parameters related to the aircraft, and
instruments or sensors for measuring environmental characteristics.
It should be appreciated that, in some examples, the instruments
108 may be distributed at various different locations of the
aircraft 100.
[0051] FIG. 2 is a simplified schematic view of a brake 200
associated with the wheel 104 of the aircraft 100. Each of the
wheels of the aircraft 100 may have associated with it a brake such
as brake 200. The brake 200 applies a braking force to inhibit the
rotation of the wheel 104. In this example, the brake 200 comprises
a plurality of brake discs 202 including a pressure plate 204, a
reaction plate 206, and a number of rotors and stators such as the
rotor 208 and the stator 210. In this example, the brake discs 202
include a plurality of rotors and stators, and the brake assembly
200 is therefore a multiple disc brake. In other examples, the
brake assembly 200 may not be a multiple-disc brake. It will be
understood that the type of brake used in an aircraft landing gear
depends on the characteristics of the aircraft in question, such as
size, carrying capacity and the like.
[0052] When the aircraft 100 travels along the ground supported by
the landing gear 102, the rotors rotate with the wheel 104, whereas
the stators, the pressure plate 204 and the reaction plate 206 do
not rotate with the wheel 104. When braking is applied, the
pressure plate 204 is urged towards the reaction plate 206 so that
the brake discs 202 come into contact with one another (as shown in
box 212 of FIG. 2) and friction acts to inhibit the rotational
motion of the rotors, thus generating a braking force.
[0053] Any one or more of the rotors, stators, pressure plate 204
and the reaction plate 206 may be composed of Carbon-Carbon (CC)
composites. A brake including brake discs composed of CC composites
may be referred to as a carbon brake. For example, the brake discs
202 may be composed of a graphite matrix reinforced by carbon
fibers. During use, the brake discs 202 may undergo oxidation.
During an oxidation reaction, oxygen reacts with the carbon of the
brake discs 202 causing carbon atoms to be removed from the brake
discs 202 as carbon dioxide and/or carbon monoxide is produced
leading to a loss of mass. The oxidation state/level of the brake
200 may be expressed as an amount of mass lost due to
oxidation.
[0054] The brake discs 202 may oxidise via catalytic oxidation or
thermal oxidation. Catalytic oxidation may occur when the oxidation
reaction is aided by the action of a catalyst. For example, alkali
metals are known catalysts for oxidation of CC composites.
Catalytic oxidation may be relevant in areas where the air has
relatively high salinity. Catalytic oxidation may also be relevant
at airports that use runway deicers comprising alkali salts.
Thermal oxidation of the brake discs 202 may occur if the brake
discs 202 reach high temperatures. During use, the brake 200,
specifically the brake discs 202, may reach high temperatures. This
is because when the brake 200 is applied to reduce the speed of the
aircraft 100, some of the kinetic energy of the aircraft 100 is
absorbed into the brake assembly 200 as heat causing its
temperature to rise. In the present examples, the components of the
brake 200 composed of CC composites (i.e. the brake discs 202)
undergo oxidation. However, the present disclosure hereafter refers
to the oxidation state of the brake 200.
[0055] The aircraft 100 may comprise a braking system 214, which
controls the operation of the brake 200. The braking system 214
causes the brake 200 to be applied in response to a braking request
(e.g. when a pilot of the aircraft 100 presses a brake pedal). For
example, the brake 200 may be hydraulically actuated or
electrically actuated, and the braking system 214 may control the
brake actuation system (not shown) to apply the brake 200. The
braking system 214 may communicate with the brake actuation system
via a wireless or wired communication link.
[0056] FIG. 3 is a simplified schematic view of an apparatus 300
and the braking system 214. The apparatus 300 comprises a
controller 302. The controller 302 is configured to generate a
first indication for the braking system 214 depending upon an
oxidation state of the brake 200. For example, the apparatus 300
may be installed on a vehicle such as the aircraft 100 to generate
the first indication in relation to the brake 200. The apparatus
300 may be installed on any kind of vehicle which comprises one or
more braked wheels. Nevertheless, for convenience, the following
description will be in the context of the aircraft 100.
[0057] In the example of FIG. 3, the braking system 214 comprises a
controller 304. Hereafter, the controller 302 of the apparatus 300
is referred to as the first controller 302 and the controller 304
of the braking system 214 is referred to as the second controller
304, for clarity. The second controller 304 is configured to
receive the first indication, the first indication having been
generated depending upon the oxidation state of the brake 200 (as
described), and control the operation of the brake 200 based on the
first indication. The second controller 304 may receive an
indication from the first controller 302 via a wired or wireless
communication link. Alternatively, the first controller 302 may
write information relating to the indication to a computer readable
storage medium (not shown) and the second controller 304 may read
the information relating to the indication from said computer
readable storage medium.
[0058] The second controller 304 may be configured to control the
brake 200 to be disabled if it receives the first indication. For
example, if the brake 200 is disabled, the second controller 304
may assign a "disabled" status to it. That the brake 200 is
disabled means that when the braking system 214 receives a braking
request, the braking system 214 does not cause the brake 200 to be
applied. The required braking may instead be provided by other
brakes associated with the other wheels of the landing gear
102.
[0059] The operation of the first controller 302 and the second
controller 304 is illustrated by the flow diagram of FIG. 4a, which
represents an example method 400 for controlling at least one brake
of the aircraft 100. The method 400 may be implemented by the first
and second controllers 302, 304. In some examples, the process
blocks of the method 400 may be provided as processor-executable
instructions (e.g. executable by respective processors of the first
and second controllers 302, 304).
[0060] At block 402, the first indication is generated depending
upon the oxidation state of the brake 200. The first controller 302
of the apparatus 300 performs block 402. At block 402, the first
controller 302 receives information regarding the oxidation state
of the brake 200 (the source of the information is described in
further detail hereafter), for example. The first controller 302
may compare the oxidation state to a particular threshold or may
determine a criterion based on the oxidation state and compare
certain characteristics of the brake 200 to that criterion. Such
comparisons are described in further detail hereafter. The first
controller 302 may generate the first indication based on such a
comparison. If the first indication is generated, the method 400
proceeds to block 404
[0061] At block 404, the brake 200 is controlled to be disabled
based on the first indication.
[0062] In some examples, the oxidation state of the brake 200 may
take into account thermal oxidation (i.e. the oxidation state may
be the thermal oxidation state) or catalytic oxidation (i.e. the
oxidation state may be the catalytic oxidation state). In some
examples, the oxidation state may take into account both thermal
oxidation and catalytic oxidation. In the following examples, the
oxidation state of the brake 200 takes account of thermal oxidation
only.
[0063] In some examples, the thermal oxidation state of the brake
200 may be determined using the methods and systems described in an
earlier unpublished application, namely GB patent application
number 1803203.7, attached hereto as an Annex. For example, the
thermal oxidation state of the brake 200 after a braking
event/braking operation may be determined using a thermal oxidation
model based on an initial thermal oxidation state of the brake 200
before the braking event and a temperature profile of the brake 200
with respect to time. The first controller 302 may receive the
thermal oxidation state of the brake 200 from the apparatus which
determines the thermal oxidation state of the brake 200.
Alternatively, the up-to-date thermal oxidation state of the brake
200 may be stored in a computer readable storage medium (e.g. a
computer readable storage medium which is part of the computing
system 106), and the first controller 302 may retrieve the thermal
oxidation state of the brake 200 from said computer readable
storage medium. The first controller 302 may retrieve the thermal
oxidation state of the brake 200 each time the thermal oxidation
state is updated. In some examples, the first controller 302 may
determine the thermal oxidation state of the brake 200 as described
in the earlier unpublished application.
[0064] As described, the oxidation state may be expressed as an
amount of mass lost due to oxidation. In some examples, the first
controller 302 may compare the oxidation state of the brake 200 to
an oxidation threshold and may generate the first indication if the
oxidation threshold is reached. For example, the oxidation
threshold may be between 4% and 6.5%, for instance 5.7%, of the
original mass of the brake 200 lost due to oxidation. In the
example where the oxidation threshold is 5.7%, the oxidation
criterion may be satisfied if the thermal oxidation state reaches
(i.e. is equal to or above) 5.7% of the original mass of the brake
200 lost. In such examples, the brake 200 may be disabled if it is
oxidised beyond a certain level. The oxidation threshold may be set
at a level at which service or replacement of the whole or part of
the brake 200 is deemed necessary for safe functioning.
[0065] Alternatively, or in addition, the first controller 302 may
determine a brake temperature characteristic criterion of the brake
200 according to the oxidation state of the brake 200. The first
controller 302 may determine whether a temperature characteristic
of the brake 200 satisfies the brake temperature characteristic
criterion and generate the first indication for the braking system
214 depending upon whether the brake temperature characteristic
satisfies the brake temperature characteristic criterion. In the
examples where the oxidation threshold is also used and reached by
the oxidation state of the brake 200, the first controller 302 may
not compare the temperature characteristic to the temperature
characteristic criterion. This is because, in such examples, the
brake 200 may simply be disabled because it is too oxidised
irrespective of the temperature characteristic of the brake 200.
The examples described hereafter are in the context of the first
controller 302 comparing the temperature characteristic to the
temperature characteristic criterion.
[0066] FIG. 4b illustrates a particular example of the method 400
in which the brake temperature characteristic criterion is
determined and used in order to generate the first indication.
Blocks 402a to 402c shown in FIG. 4b may be performed as part of
block 402 of FIG. 4a, e.g. by the first controller 302. At block
402a, the brake temperature characteristic criterion is determined
according to the oxidation state of the brake 200. At block 402b,
it is determined whether the temperature characteristic of the
brake 200 satisfies the brake temperature characteristic criterion.
At block 402b, the first controller 302 receives the temperature
characteristic of the brake 200 (the source of brake temperature is
described in further detail hereafter), for example. The first
controller 302 compares the temperature characteristic of the brake
received by the first controller 302 to the brake temperature
characteristic criterion determined at block 402a to determine
whether or not the brake temperature characteristic criterion is
satisfied, for example. If the brake temperature characteristic
criterion is satisfied, the process proceeds to block 402c.
[0067] At block 402c, the first indication is generated depending
upon whether the brake temperature characteristic criterion is
satisfied. The first indication is generated if the brake
temperature characteristic satisfies the brake temperature
characteristic criterion. On the other hand, if the brake
temperature characteristic criterion is not satisfied at block
402b, the method ends and no indication is generated. However, the
block 402b may be performed again when an updated temperature
characteristic of the brake is available. If there is a change in
the thermal oxidation state of the brake 200, the method according
to any of the described examples may be repeated.
[0068] At block 404, The brake 200 is controlled to be disabled
based on the first indication generated at block 402c. For example,
the second controller 304 may be configured to receive the first
indication generated depending upon whether a brake temperature
characteristic satisfies a brake temperature characteristic
criterion. For example, as described, if the first indication is
generated, the second controller 304 may receive the first
indication and may disable the brake 200.
[0069] The first controller 302 may be configured to monitor the
temperature characteristic of the brake 200, and, if the
temperature characteristic of the brake 200 no longer satisfies the
brake temperature characteristic criterion, generate a second
indication for the braking system 214 that the temperature
characteristic of the brake 200 no longer satisfies the brake
temperature characteristic criterion. FIG. 4c is a flow diagram
illustrating additional process blocks which may form part of the
method 400. For example, the method 400 may proceed from block 404
to block 406. At block 406 the temperature characteristic of the
brake is monitored. For example, measurements of the temperature
characteristic as a function of time may be received by the first
controller 302. At block 408, it is determined whether or not the
temperature characteristic of the brake 200 still satisfies the
brake temperature characteristic criterion. For example, the first
controller 302 compares an up to date value of the brake
temperature characteristic to the brake temperature characteristic
criterion. If the temperature characteristic of the brake no longer
satisfies the brake temperature characteristic criterion, at block
410 the second indication that the temperature characteristic of
the brake no longer satisfies the brake temperature characteristic
criterion is generated by the first controller 302.
[0070] The second controller 304 may be configured to receive the
second indication that the temperature characteristic of the brake
no longer satisfies the brake temperature characteristic criterion,
and control the brake selectively to be enabled or disabled based
on the received indication. As described previously, the second
controller 304 may disable the brake 200 if it receives the first
indication. The second controller 304 may control the brake 200 to
be enabled if it receives the second indication. At block 412, the
brake 200 is controlled to be enabled based on the second
indication. For examples, if the brake 200 has been disabled and
the temperature characteristic of the brake 200 no longer satisfies
the brake temperature characteristic criterion, the second
controller 304 may change the status of the brake 200 from
"disabled" to "enabled". The brake 200 when enabled may once again
be controlled by the braking system 214 to provide braking
responsive to a braking request.
[0071] On the other hand, if the brake temperature characteristic
criterion is still satisfied, as determined at block 408, the
process returns to block 406 in order to continue monitoring the
temperature characteristic of the brake 200, and blocks 406 and 408
are repeated.
[0072] The brake temperature characteristic criterion depends on
the oxidation state of the brake. In the examples described
hereafter, the brake temperature characteristic criterion depends
on the thermal oxidation state of the brake 200. Therefore, the
brake 200 may be disabled sooner or later (as its temperature
increases due to braking) depending on its thermal oxidation state,
as explained in further detail hereafter. Managing braking in this
manner, to inhibit thermal oxidation of the brake 200, may prolong
the life of the brake 200.
[0073] The temperature characteristic of the brake may include a
temperature of the brake 200 (i.e. a current temperature). The
temperature of the brake 200 may specifically be the temperature of
the brake discs 202 which may be composed of CC composites as
described. It will be appreciated that the temperature of the
components composed of CC composites is relevant when controlling
the brake 200 to inhibit thermal oxidation because the components
composed of CC composites undergo thermal oxidation. In some
examples, the temperature characteristic may also include a rate of
increase of temperature of the brake 200.
[0074] The brake temperature characteristic criterion may be
satisfied if the temperature of the brake 200 exceeds a brake
temperature threshold. The first controller 302 may be configured
such that the higher the level of thermal oxidation of the brake
200, the lower the brake temperature threshold of the determined
brake temperature characteristic criterion is. In such examples, if
the brake 200 has undergone a large amount of thermal oxidation,
the braking system 214 may disable the brake 200 when it reaches a
lower temperature as compared to a brake with less thermal
oxidation.
[0075] In some examples, the brake temperature characteristic
criterion may alternatively or in addition include a temperature
increase rate threshold. In such examples, where the temperature
characteristic includes a rate of increase of temperature of the
brake 200, the brake temperature characteristic criterion may be
satisfied if the rate of increase of temperature of the brake 200
exceeds the temperature increase rate threshold. The following
examples are described in the context of the temperature
characteristic comprising a temperature of the brake 200 and the
brake temperature characteristic criterion being satisfied if the
temperature of the brake 200 exceeds the brake temperature
threshold.
[0076] In some examples, the thermal oxidation state of the brake
200 may be compared to a predetermined thermal oxidation level. In
such examples, if the thermal oxidation state of the brake 200 is
below the predetermined thermal oxidation level, the first
controller 302 selects a first brake temperature characteristic
criterion which comprises a first temperature threshold. The first
temperature threshold may be relatively high so that the brake 200
can get relatively hot before being disabled by the braking system
214, but not so hot that there is significant thermal oxidation for
a significant period of time.
[0077] For some brakes, it may be expected that thermal oxidation
may occur at a relatively low rate at temperatures over 400.degree.
C. and at a relatively higher rate at temperatures over 750.degree.
C. There may not be significant thermal oxidation below 400.degree.
C. The first temperature threshold may therefore be above
400.degree. C. For such brakes, the first temperature threshold set
at, for example, 600.degree. C. would allow use of the brakes up to
a relatively high temperature without the risk of the temperature
reaching a level where there is a relatively high rate of thermal
oxidation.
[0078] If the thermal oxidation state of the brake 200 is above the
predetermined thermal oxidation level, the first controller 302 may
select a second brake temperature characteristic criterion which
comprises a second temperature threshold lower than the first
temperature threshold. Therefore, when the thermal oxidation state
of the brake 200 exceeds the predetermined thermal oxidation level,
the brake 200 is disabled at a lower temperature. This is so that
when the thermal oxidation state of the brake 200 becomes advanced,
it is prevented from being exposed to as high temperatures in order
to further inhibit thermal oxidation and prolong the life of the
brake 200.
[0079] In some examples, the second temperature threshold may be
400.degree. C. In some examples, the second brake temperature
characteristic criterion may be selected based on the difference
between the thermal oxidation state of the brake 200 and the
predetermined thermal oxidation level. For example, above the
predetermined thermal oxidation level, the greater the level of
thermal oxidation of the brake 200, the lower the second
temperature threshold may be. For example, the second temperature
threshold may be a value under 600.degree. C. and may decrease as
the thermal oxidation state of the brake 200 continues to increase
above the predetermined thermal oxidation level.
[0080] The first controller 302 may determine the brake temperature
characteristic criterion by using the thermal oxidation state of
the brake 200 as an input into an algorithm for determining the
brake temperature characteristic criterion. The algorithm may take
account of the physical properties of the brake 200. For example,
it may be the case that the brake 200 undergoes thermal oxidation
at a high rate below a temperature of 750.degree. C. In such an
example, the first temperature threshold may be set lower than
600.degree. C. The first controller 302 may implement instructions
stored on a computer readable storage medium (e.g. one included in
the computing system 106) to perform the algorithm. In some
examples, the first controller 302 may access (from a computer
readable storage medium to which it has access) a look-up table,
which stores thermal oxidation states of the brake 200 and
corresponding predetermined brake temperature characteristic
criteria. The first controller 302 may determine the brake
temperature characteristic criterion using the look-up table. In
some examples, the first controller 302 may be configured to
generate such a look-up table using an algorithm of the
aforementioned kind.
[0081] As described, thermal oxidation of the brake discs 202 may
occur at high temperatures. The brake 200 of the aircraft 100 may
need to be serviced or replaced once the oxidation state of the
brake 200 reaches a certain level to ensure safe functioning. As
described, the brake 200 of the aircraft 100 may need to be
serviced or replaced if the oxidation threshold is reached. The
predetermined thermal oxidation level may be set at a value below
the oxidation threshold to inhibit thermal oxidation as the thermal
oxidation state of the brake 200 approaches the oxidation threshold
(e.g. 4% to 6.5% of the original mass of the brake 200 lost).
[0082] In order to compare the temperature characteristic of the
brake 200 to the determined brake temperature characteristic
criterion and to monitor the temperature characteristic of the
brake 200, the first controller 302 may receive information
regarding the temperature characteristic of the brake 200 from a
temperature sensor 216 associated with the brake 200 (see FIG. 2).
The temperature sensor 216 may be provided in thermal contact with
one of the brake discs. In the example of FIG. 2, the temperature
sensor 216 is provided on the stator 210. In this example, the
stator 210 is the brake disc likely to reach the highest
temperatures. The temperature sensor 216 may be any type of
temperature sensor suitable for use in an aircraft brake assembly.
For example, the temperature sensor 216 is able to function
properly at the temperature ranges likely to be reached by the
brake discs 202. For example, the temperature sensor 216 may be a
thermocouple, a surface acoustic wave (SAW) sensor, an eddy current
sensor, a resistance thermal sensor, a strain gauge, or the like.
The first controller 302 may receive brake temperature measurements
from the temperature sensor 216 via a wired or wireless
communication link. If a temperature sensor is provided on a part
of the brake 200 other than on one of the brake discs 202, the
temperature of the brake discs 202 may be determined using an
indication of the relationship between a temperature measured by
said temperature sensor and the temperature of the brake discs 202.
In some examples, the indication of the relationship may be
determined by experiment. In some examples, the indication of the
relationship may be determined using a brake thermal model.
[0083] The first controller 302 may receive brake temperature
measurements from the temperature sensor 216 in real-time. The
first controller 302 may continuously receive brake temperature
measurements, or alternatively may periodically receive discrete
items of brake temperature information. In some examples, the
controller 302 may request brake temperature measurements from the
temperature sensor 216 and receive brake temperature measurements
in response. A rate of increase of temperature of the brake 200 may
be determined based on at least two measurements of the temperature
at different times.
[0084] The first controller 302 may receive a predicted temperature
characteristic from a brake temperature prediction function as the
temperature characteristic of the brake 200. The brake temperature
prediction function may predict the temperature of the brake 200
based on the energy input into the brake 200 during a braking
event. A braking event is, for example, an event comprising one or
more applications of the brake 200. Using the energy input into the
brake 200, the mass of the brake 200 and the specific heat capacity
of the brake 200, a change in temperature of the brake 200 caused
by the input energy can be determined. The temperature of the brake
200 may then be determined using the temperature change, i.e. by
adding it to an initial temperature of the brake 200. The initial
temperature before the braking event may be known from previous
iterations of such a calculation. On the other hand, if the energy
input is due the first brake application of the day (i.e. the brake
200 has not been applied for a significant amount of time), the
initial temperature may be taken to be the environmental
temperature.
[0085] In some examples, the brake thermal model (e.g. a
computational fluid dynamics model) may be used to predict a
temperature of the brake 200 given an amount of energy input into
the brake 200. For example, the physical properties of the brake
200 (e.g. mass, heat capacity, etc.), environmental characteristics
and the energy input into the brake 200 may be input into the brake
thermal model, and the brake thermal model may output a predicted
temperature of the brake 200. The environmental characteristics may
include ambient temperature (e.g. in the vicinity of the brake
200), wind conditions, or other characteristics which may affect
the temperature of the brake 200. The environmental characteristics
may be measured by instruments included in instruments 108, for
example.
[0086] In some examples, the rate of increase of temperature of the
brake 200 may be predicted based on the energy input into the brake
200 by the brake temperature prediction function. For example, the
rate of increase may be predicted based on the energy input into
the brake and the physical properties of the brake 200 using the
brake thermal model.
[0087] As described, the thermal oxidation state of the brake 200
is related to the amount of mass of the brake 200 lost due to
thermal oxidation which may be taken into account when determining
the mass of the brake 200. The mass lost due to wear of the brake
discs 202 may also be taken into account. For example, the
instruments 108 may comprise a brake wear sensor associated with
the brake 200. The brake wear sensor may provide an indication of a
reduction in length L of the brake discs 202. Using the reduction
in length L due to wear, a reduction in the mass of the brake 200
due to wear may be determined. In some examples, the mass of the
brake 200 may be determined by subtracting the amount of mass lost
due to thermal oxidation and the amount of mass lost due to brake
wear from the initial mass of the brake 200 (e.g. as specified by
the brake manufacturer or measured at installation of the brake 200
into aircraft 100).
[0088] The energy input into the brake 200 may be determined using
measurements from instruments included in instruments 108. The
instruments 108 may include a torque sensor for measuring the
torque reacted by the brake 200 and a tachometer for measuring the
rotational speed of the wheel 104. In such examples, the energy
input into the brake 200 is calculated by integrating the product
of the wheel speed and torque over time.
[0089] The first controller 302 may receive a predicted temperature
if, for example, the temperature sensor 216 malfunctions or the
first controller 302 is not able to receive brake temperature
measurements from the temperature sensor 216. In some examples, a
processor (e.g. a processor of the computing system 106) may
determine whether to provide the first controller 302 with a brake
temperature measurement from the temperature sensor 216 or a
predicted temperature from the brake temperature prediction
function. In some examples, the first controller 32 may receive a
brake temperature measurement from the temperature sensor 216 and a
predicted temperature from the brake temperature prediction
function, and determine which temperature value to use. For
example, if there is a large discrepancy in the two values, the
temperature value closest to what might be expected given the mass,
speed, etc. of the aircraft 100 may be used.
[0090] During use of the aircraft 100, there may be instances where
it is not desirable to have one or more of the brakes of the
aircraft 100 disabled. For example, it may be desired that all the
brakes are used during landing to reduce the speed of the aircraft
100. The second controller 304 may be configured to disable a brake
if a taxiing criterion is met. In such examples, brake 200 may only
be disabled responsive to the second controller 304 receiving the
first indication during a taxiing phase as defined by the taxiing
criterion.
[0091] The taxiing criterion may comprise one or more of an
aircraft speed threshold and a particular flight phase of the
aircraft 100. The aircraft speed threshold may be defined such that
an aircraft speed less than or equal to the aircraft speed
threshold satisfies the taxiing criterion. For example, the
aircraft speed threshold may be 30 knots. In such examples, the
second controller 304 does not disable the brake 200 upon receiving
the first indication if the speed of the aircraft is above 30
knots. This is because, at higher speeds a greater braking force
may be required to reduce the speed of the aircraft 100 within a
certain time or distance. The second controller may receive
information relating to the aircraft speed from an on-board
instrument (i.e. an instrument included in instruments 108), or a
processor of the computing system 106.
[0092] The particular flight phase may be indicated by a flight
phase indication system of the aircraft 100. The particular flight
phase may be the taxiing phase after landing and/or the taxiing
phase before take-off, for example. The flight phase indication
system may be implemented at least in part by the computing system
106 of the aircraft 100. In such examples, the second controller
304 does not disable the brake 200 unless the flight phase is
indicated to be the taxiing phase after landing and/or the taxiing
phase before take-off. By disabling the brake 200 responsive to the
first indication only when the aircraft is in a taxiing phase as
defined by the taxiing criterion, the brake 200 is made available
to provide braking during other phases in which reducing the speed
of the aircraft 100 is a higher priority than protecting the brake
200 against thermal oxidation.
[0093] As described, the braking system 214 causes the brake 200 to
be applied in response to a braking request. The second controller
304 of the braking system 214 may be configured to receive a
braking request when a pilot of the aircraft 100 presses a brake
pedal. The braking request may comprise information relating to a
requested braking intensity. For example, the braking request may
include information about how hard/far the pilot has pressed the
brake pedal.
[0094] In some cases, a significant amount of braking may be
required. For example, the pilot may press the brake pedal hard to
bring the aircraft 100 to an immediate stop or to significantly
reduce the aircraft speed in a short amount of time. In such cases,
it may not be desired to have any of the brakes of the aircraft 100
disabled so that sufficient braking can be provided. The second
controller 304 may determine, based on the information related to
the requested braking intensity, whether the requested braking
intensity exceeds a braking intensity threshold. If the requested
braking intensity exceeds the braking intensity threshold, the
second controller 304 may enable at least one disabled brake. For
example, if the brake 200 has been disabled responsive to the first
indication, the second controller 304 may enable the brake 200 in
response to the requested braking intensity exceeding the brake
intensity threshold.
[0095] FIG. 5 is a flow diagram illustrating a method 500 performed
by the second controller 304 of enabling a disabled brake in
response to a braking request with high braking intensity. At block
502, a braking request comprising information related to the
requested braking intensity is received. For example, as described,
the second controller 304 receives the braking request. At block
504, the second controller 304 determines, based on the information
related to the requested braking intensity, whether the requested
braking intensity exceeds the braking intensity threshold. If the
requested braking intensity exceeds the braking intensity
threshold, the method 500 proceeds to block 506 and at least one
disabled brake is enabled. For example, if the brake 200 has
previously been disabled responsive to the first indication, the
brake 200 may be enabled by the second controller 304 at block 506.
In this manner, depending on the requested braking intensity, the
brake 200 may again be enabled to provide braking if relatively
high braking intensity is required.
[0096] On the other hand, if the requested braking intensity does
not exceed the braking intensity threshold, the method 500 ends.
The method 500 may be repeated each time a braking request is made
so that the requested braking intensity can be provided.
[0097] All or part of the described methods may be performed in
real-time, during aircraft operation. For example, the described
methods may be performed in real-time when the aircraft 100 is in a
taxiing phase and/or when a braking event is occurring. For
example, the temperature characteristic of the brake 200 may be
compared to the brake temperature characteristic criterion
repeatedly. For instance, the first controller 302 may repeatedly
determine whether the temperature characteristic of the brake 200
satisfies the brake temperature characteristic criterion during a
braking event. The second controller 304 may control the brake 200
as described in real-time based on this determination. For example,
the second controller 304 may receive an indication each time the
brake temperature characteristic criterion is determined to be
satisfied or no longer satisfied (i.e. the second control 304 may
receive first and second indications, as appropriate, in real-time)
and control the brake 200 selectively to be enabled or disables
depending on the received indications.
[0098] For example, all or part of the described methods may be
performed repeatedly at a fast rate, with the temperature of the
brake 200 being sampled multiple times per second, up to the
sampling rate of the temperature sensor.
[0099] FIG. 6 summarizes an exemplary method 600 of determining a
thermal oxidation state of a brake, such as the brake assembly 200,
of an aircraft landing gear assembly 102. The method 600 involves
determining a thermal oxidation state of the brake assembly 200
after a braking event, using a thermal oxidation model based on an
initial thermal oxidation state (which may also be referred to as
the initial thermal oxidation level) before the braking event and a
temperature profile of the brake with respect to time. The
determined thermal oxidation state of the brake assembly 200 after
the braking event may be referred to as an updated thermal
oxidation state. This is because the thermal oxidation state of the
brake assembly 200 after the braking event takes account of the
change in the initial thermal oxidation state due to the braking
event.
[0100] The braking event is an event relating to the application of
the brake assembly 200. For example, a braking event may comprise
one or more applications of the brake assembly 200 to slow or stop
the aircraft 100. In some examples, the braking event may be a part
of a time during which the brake assembly 200 is continuously being
applied. Any time the brake assembly 200 is applied, the
temperature of the brake assembly 200 may rise. This is because
when brake assembly 200 is applied to reduce the speed of the
aircraft 100, some of the kinetic energy of the aircraft 100 is
absorbed into the brake assembly 200 as heat causing its
temperature to rise. Therefore, whether or not the brake assembly
200 has been applied can be determined based on temperature
variations of the brake assembly 200.
[0101] At block 602 of the method 600, the temperature profile and
the initial thermal oxidation state of the brake assembly 200 are
input. As explained above, the temperature profile indicates a
variation of temperature with time. The input temperature profile
may, for example, relate to a use cycle of the aircraft 100. For
example, the temperature profile may be for an entire use cycle of
the aircraft 100, e.g. the time from when the aircraft 100 is at a
departure gate before a flight to when the aircraft 100 is at an
arrival gate after a flight. Specifically, the temperature profile
may indicate the variation of temperature over time for all braking
events that take place during a cycle. In other examples, the
temperature profile may not be for an entire use cycle of the
aircraft 100. For example, the temperature profile may be over a
single braking event, or a part of a cycle with many braking
events. In some examples, a number of temperature profiles
belonging to a particular use cycle may be used to determine the
thermal oxidation state of the brake assembly 200 after that use
cycle.
[0102] The temperature profile may, for example, relate to a use
cycle that has occurred. In other words, the temperature profile
may include actual data from the temperature sensor 216 of the
aircraft 100 during a previous use cycle. In such examples, the
temperature profile relates to real data. On the other hand, in
some examples, the temperature profile may be a predicted
temperature profile of a predicted future use cycle of the aircraft
100. In that context, a braking event may be a predicted future
braking event.
[0103] The initial thermal oxidation state of brake assembly 200 is
the thermal oxidation state of the brake assembly 200 before the
braking event for which the updated thermal oxidation state is
being determined. For example, for a new brake assembly 200
installed in aircraft 100, the initial oxidation state may indicate
no oxidation. In some examples, the initial oxidation state for a
newly installed brake assembly 200 may be set at installation by
aircraft maintenance personnel and may either indicate no oxidation
or some oxidation as assessed by the person(s) performing the
installation. In examples where the brake assembly 200 is not new,
the initial oxidation state may be the oxidation state calculated
at a previous instance of method 600 being performed. In some
examples, a brake or a brake component which is not new may be
installed on aircraft 100. If the temperature profile information
for all previous braking events involving that brake or brake
component is available, the thermal oxidation state at installation
may be determined using the available temperature profile
information using method 600, or by other methods disclosed
herein.
[0104] At block 604 of method 600, a thermal oxidation state after
the braking event (updated thermal oxidation state) is determined
using a thermal oxidation model. For example, a thermal oxidation
model is applied based on the input temperature profile and the
initial thermal oxidation state of the brake assembly 200. A
thermal oxidation model, for example, indicates how the thermal
oxidation state is expected to change with time for various
temperatures starting from the initial thermal oxidation state. A
thermal oxidation model is a model of the evolution of the thermal
oxidation of the brake. Which thermal oxidation model is used may
depend, for example, on the initial thermal oxidation state. The
details and selection of appropriate thermal oxidation models is
described further below. In some examples, the method 600 may be
performed live during a use cycle of the aircraft 100. In the case
of the method 600 being performed live (i.e. in real time or near
real time), the temperature profile used may be from the
temperature data acquired thus far by the temperature sensor 216,
for example. At block 604, therefore, it is determined how the
oxidation state, starting from the initial oxidation state, has
changed as a result of the increased temperature associated with
the braking event in question.
[0105] After the updated thermal oxidation state has been
determined, the initial thermal oxidation state may be set to the
updated thermal oxidation state. In this way, the initial thermal
oxidation state is kept up to date with all previous braking
events. In examples where the temperature profile relates to more
than one braking event, the method 600 may be performed again in
order to determine an updated thermal oxidation state after a
subsequent braking event. Updating the initial thermal oxidation
state in this manner may ensure that the initial thermal oxidation
state being used for a subsequent braking event accounts for all
the previous braking events.
[0106] In examples where the temperature profile for an entire use
cycle of the aircraft 100, the method 600 may be performed to
determine respective updated thermal oxidation states after each
braking event within that use cycle. It will be understood that
this process may be carried out sequentially in relation to the
chronology of the braking events. This is so that the determination
of the updated thermal oxidation state for each of the braking
events is done from a starting point (an initial thermal oxidation
state) which takes account of all previous braking events.
[0107] In the method 600, the updated thermal oxidation state after
a braking event may, for example, be determined based on a high
temperature interval, the initial thermal oxidation state and a
thermal oxidation rate parameter, using an appropriate thermal
oxidation model.
[0108] FIG. 7 is a flow diagram of a method 700 showing acts that
may be performed as part of method 600. For example, the method 700
involves more specific examples of the block 604 of the method 600.
Block 702 is identical to block 602 of the method 600, in that a
temperature profile of the brake with respect to time and the
initial thermal oxidation state of the brake assembly 200 are
input. At block 704, the temperature profile is compared to a set
of temperature criteria. The set of temperature criteria may
include a set of temperature thresholds. For example, the set of
temperature criteria may include a first temperature threshold of
400.degree. C. and a second temperature threshold of 750.degree. C.
In other examples, different temperature thresholds may be used
depending on the physical properties of the brake assembly 200. The
comparison of the temperature profile may, for example, take place
sequentially in time order of the temperature data contained in the
temperature profile. For example, a temperature value may be
compared to the set of temperature thresholds, and subsequently,
the next temperature value in time may be compared to the set of
temperature thresholds.
[0109] At block 706, it is determined if one or more of the
temperature criteria are met. If, for example, none of the
temperature thresholds are exceeded, the method 700 ends. It will
be appreciated that thermal oxidation of the CC composite of the
brake discs 202 is a process that is most significant at high
temperatures. A comparison of the temperature profile with the set
of temperature thresholds therefore identifies high temperature
events corresponding to braking events that may result in thermal
oxidation. As mentioned above, a braking event is, for example, an
application of the brake assembly 200. However, a high temperature
event is an event during which the temperature of the brake
assembly exceeds at least one of the temperature thresholds as a
result of a braking event. For example, if during a braking event
(i.e. a braking application) the temperature of the brake assembly
200 remains below all temperature thresholds, then no high
temperature events occurred during that braking event. On the other
hand, if during a braking event the temperature of the brake
assembly exceeds a temperature threshold, the part of the braking
event for which that temperature threshold is exceeded may be
referred to as a high temperature event. If more than one
temperature threshold is exceeded, a high temperature event may be
the part of the braking event for which the highest temperature
threshold is exceeded.
[0110] The temperature thresholds may be set based on temperatures
above which a significant amount of thermal oxidation is expected
to occur. Therefore, the method 700 ends if none of the temperature
thresholds are exceeded. This is because, in this example, no
braking events causing a sufficiently high temperature for thermal
oxidation have occurred. In such examples, the updated thermal
oxidation state after the braking event may simply be set to the
initial thermal oxidation state before the braking event in
question.
[0111] On the other hand, if at least one of the temperature
thresholds is exceeded, at block 708 of the method 700, a high
temperature event corresponding to the braking event in question is
identified. A high temperature event corresponds to the part of the
temperature profile which is above the highest of the exceeded
temperature thresholds. This is because the part of the temperature
profile which is above the highest of the exceeded thresholds
corresponds to the part of the braking event for which the highest
temperature threshold is exceeded. The identification of a high
temperature event is described with reference to FIG. 8. FIG. 8 is
a graph illustrating a part of an example temperature profile. In
the graph of FIG. 8, the vertical axis represents temperature of
the brake assembly 200, and the horizontal axis represents time. In
this example, profile part 802 indicates that the temperature of
the brake assembly 200 exceeds a first temperature threshold 804
and a second temperature threshold 806. In this example, the high
temperature event is identified as the part of the profile 802
above the second temperature threshold 806 as the second
temperature threshold 806 is the highest temperature threshold
which is exceeded.
[0112] The amount of thermal oxidation which occurs above the
second temperature threshold 806 may be significantly greater for a
given interval of time compared to the thermal oxidation above the
first temperature threshold 804 but below the second temperature
threshold 806. Therefore, in this example, the parts of the
temperature profile below the second temperature threshold 806 are
not taken into account. In other examples, for example when the
method 700 is used for live oxidation state monitoring as described
further below, the parts of the temperature profile between the two
temperature thresholds may be taken into account. It should be
appreciated that the graph of FIG. 8 is merely an illustration of
an example for explanatory purposes.
[0113] At block 710, the interval of time taken by the high
temperature event is determined to be the high temperature
interval. As mentioned above, the updated thermal oxidation state
may be determined based on (among other factors) the high
temperature interval. In the example of FIG. 8, the high
temperature interval is determined to be the time interval 808.
[0114] At block 712, a high temperature event value of the brake
assembly 200 is determined for the high temperature interval. The
high temperature event value is a value of temperature ascribed to
the high temperature event. In some examples, the high temperature
event value is the average temperature during the high temperature
interval. Alternatives to the high temperature event value being
the average temperature are described below in the context of live
oxidation monitoring.
[0115] At block 714, an oxidation rate parameter is calculated
based on the high temperature event value and physical
characteristic information of the brake. For example, the oxidation
rate parameter for the thermal oxidation reaction may be determined
based on the Arrhenius equation shown as Equation 1 below:
k .function. ( T ) = A .times. e - E A / R .times. T ( 1 )
##EQU00001##
[0116] In Equation 1, k(T) is the thermal oxidation rate, A is a
pre-exponential constant, E.sub.A is the activation energy of the
carbon atoms of the CC composite components of brake assembly 200,
R is the universal gas constant and T is the temperature. In this
example, for a particular high temperature event, the temperature T
in Equation 1 is set to the high temperature event value for the
purpose of block 714. In this example, the thermal oxidation rate
k(T) is the oxidation parameter determined at block 714. The values
of activation energy E.sub.A, and the pre-exponential constant A
may depend on the physical properties of the CC composite
components of brake assembly 200 (in this example, the brake discs
202). For example, the values of these parameters may depend on the
density, porosity, manufacturing process, contaminants present in
the CC composite structures, the surface finish of the components
and surface coatings of the brake assembly 200. The values of the
activation energy E.sub.A, and the pre-exponential constant A may
also vary depending on the high temperature event value and the
initial thermal oxidation state. Therefore, in order to determine
the oxidation parameter, appropriate values of activation energy
E.sub.A, and the pre-exponential constant A may be selected based
on the physical properties of the brake assembly 200, the high
temperature event value and the initial thermal oxidation state
before the braking event in question.
[0117] For example, the activation energy E.sub.A may be related
inversely to temperature. The activation energy E.sub.A may become
lower at a temperature at which oxygen molecules are able to
penetrate past the surface of the brake discs 202 and oxidation of
carbon deeper in the brake discs 202 can take place. The
appropriate values of activation energy E.sub.A, and the
pre-exponential constant A may, for example, be determined
experimentally for different initial thermal oxidation amounts,
temperatures and physical properties of the brake being considered
before the method 700 is implemented.
[0118] FIG. 9 is a graph of an example of the evolution with time
of thermal oxidation of the brake discs of a brake assembly 200 for
a specific temperature. The vertical axis of the graph in FIG. 9
represents a measure of the thermal oxidation indicated by the
thermal oxidation state Ox. For example, the thermal oxidation
state Ox may be the proportion of mass of the brake assembly 200
lost due to thermal oxidation of the brake discs 202. The evolution
curve 902 shows how the proportion of mass lost due to thermal
oxidation advances with time at the specific temperature. It should
be noted that a different evolution curve would indicate the
variation of the thermal oxidation state Ox over time for a
different temperature value.
[0119] In this example, the thermal oxidation state Ox advances
with time differently below a thermal oxidation state level 904,
than it does above the thermal oxidation state level 904. The
thermal oxidation state Ox (i.e. mass lost due to thermal
oxidation) is shown to increase non-linearly with time below
oxidation state level 904 and substantially linearly with time
above oxidation state level 904, in this example. In this example,
the thermal oxidation state increases at an accelerated rate with
time until thermal oxidation state level 904 is reached. After
thermal oxidation state level 904 is reached, the rate of change of
thermal oxidation state Ox with time remains generally constant.
The part of the graph of FIG. 9 below thermal oxidation state level
904 may be considered as a first thermal oxidation zone, namely
Zone 1, and the part of the graph of FIG. 9 above thermal oxidation
state level 904 may be considered as a second thermal oxidation
zone, namely Zone 2, for example.
[0120] In some examples, different values of the activation energy
E.sub.A, and the pre-exponential constant A may be used depending
on which thermal oxidation zone the brake assembly 200 is in as
indicated by the initial thermal oxidation state.
[0121] At block 716, a thermal oxidation model is selected based on
the initial thermal oxidation state before the braking event. The
thermal oxidation model describes the evolution of the thermal
oxidation state Ox of the brake assembly 200 for different values
of temperature. A thermal oxidation model which describes the
evolution of the thermal oxidation state Ox in Zone 1 may be
selected when the initial thermal oxidation state is in Zone 1. A
thermal oxidation model which describes the evolution of the
thermal oxidation state Ox in Zone 2 may be selected when the
initial thermal oxidation state is in Zone 2. For example, a first
thermal oxidation model, Model 1, may be selected for Zone 1, and a
second thermal oxidation model, Model 2, may be selected for Zone
2. Model 1 for Zone 1, describing the non-linear change of thermal
oxidation state Ox with time, may be represented by Equation 2.
Model 2 for Zone 2, describing the linear change of thermal
oxidation state Ox with time, may be represented by Equation 3
below.
Ox = 1 - [ 1 - { k .function. ( T ) .times. t e .times. q
.function. ( 1 - n ) } 1 / 1 - n ] ( 2 ) Ox = k .function. ( T )
.times. t e .times. q ( 3 ) ##EQU00002##
[0122] In Equation 2 and Equation 3 above, k(T) is the thermal
oxidation rate as defined by Equation 1. The parameter t.sub.eq is
the equivalent time, which is the time it would take, at
temperature T, to reach the thermal oxidation state Ox. The
parameter n is referred to as the equation order and depends on the
properties of the CC composite used in the brake assembly 200. The
parameter n may, for example be experimentally determined for a
brake using a particular CC composite.
[0123] In some examples, different thermal oxidation models to
those described by Equations 2 and 3 may be used. In some examples,
a single thermal oxidation model may be used which describes the
evolution of the thermal oxidation state Ox for all thermal
oxidation states Ox that are relevant to the brake assembly 200. In
some examples, more than two thermal oxidation models may be used
for respective ranges of thermal oxidation states Ox. The method
700 may be modified appropriately in order to use such alternative
thermal oxidation models. For example, a different set of inputs
may be applied to the thermal oxidation model, as appropriate, than
are described in this specific example of the method 700.
[0124] It will be understood that block 716 may be performed at any
stage of the method 700 once block 702 has been performed, because
block 716 requires the initial thermal oxidation state.
[0125] At block 718, the updated thermal oxidation state for the
high temperature event is determined using the selected thermal
oxidation model based on the high temperature interval, the initial
thermal oxidation state and the determined thermal oxidation rate
parameter. For example, the time it would take to reach the initial
thermal oxidation state from zero at the high temperature value is
determined and the high temperature interval is added to this time
in order to determine the value of t.sub.eq to be used in the
selected thermal oxidation model. Inputting the thus determined
value of t.sub.eq, as well as the thermal oxidation parameter into
the equation selected from Equations 2 and 3 above results in, as
an output, the updated thermal oxidation state of the brake
assembly 200 after the high temperature event.
[0126] The updated thermal oxidation state may be set to the new
initial thermal oxidation state for a subsequent use of the method
700 for a subsequent high temperature event in the temperature
profile.
[0127] In some examples, the method 600 and/or 700 may be performed
live during a use cycle when braking events are taking place. In
such examples, part of the method 700, for example, may be modified
to allow live brake oxidation monitoring, and the temperature
profile may correspond to temperature values being measured live.
For example, temperature information which the temperature sensor
216 provides may continuously be compared to the set of temperature
criteria as per block 704 of method 700, and high temperature
events may be identified substantially as they occur. It will be
understood that even though this kind of oxidation state monitoring
is described as live, the extent to which it occurs in real time
will depend on various hardware and software (e.g. processing
speed) limitations. For example, there may be a time delay between
temperature values corresponding to a high temperature event being
measured by the temperature sensor 216, and those values resulting
ultimately in updated thermal oxidation states of the brake
assembly 200.
[0128] For example, high temperature events may be identified as
smaller parts of the temperature profile than in the example
described above. Referring again to FIG. 8, the part of the profile
part 802 occurring within the time interval indicated as 810 may be
taken to be a high temperature event and the interval 810 as its
high temperature interval. In this example, the high temperature
event value may be taken to be the temperature measured at the
beginning or the end of the high temperature interval 810, for
example, or the average of the two temperature values. Unlike the
above example, in the case of live monitoring, parts of the
temperature profile between the first and second temperature
thresholds may be taken into account even when the temperature
exceeds the second temperature threshold 806. In the case of live
monitoring, any part of the temperature profile above at least one
temperature threshold, such as the part identified by interval 810,
may be identified as a high temperature event. It will be
understood that such modifications may allow the thermal oxidation
state of the brake assembly 200 to be updated as high temperature
events corresponding to braking events are taking place. In some
examples, high temperature events may be identified based on the
time between subsequent temperature measurements taken by the
temperature sensor 216. For example, the interval 810 may be the
interval of time between subsequent temperature measurements taken
by the temperature sensor 216.
[0129] The methods 600 and 700 may be used in order to determine
the thermal oxidation state of the brake assembly 200 after an
actual use cycle of the aircraft 100 or in a live manner during an
actual use cycle. In such examples, this may be done based on one
or more temperature profiles encompassing braking events within
that use cycle. As mentioned above, in some examples, the thermal
oxidation state of the brake assembly 200 is determined in respect
of a use cycle which has actually occurred using temperature
profile information collected by the temperature sensor 216.
[0130] On the other hand, in some examples, the method 600 or 700
may be used to predict a future thermal oxidation state of the
brake assembly 200 after a first plurality of predicted future use
cycles of the aircraft 100. The first plurality of future use
cycles may be a number of cycles after which a thermal oxidation
threshold is reached. Each predicted future use cycle may include a
respective plurality of braking events. For each predicted future
use cycle, the predictions may be based on a respective predicted
temperature profile of the brake assembly 200 and a current thermal
oxidation state. The current thermal oxidation state is, for
example, the oxidation state taking into account all the previous
braking events experienced by the brake assembly 200.
[0131] For example, the predicted temperature profiles may be input
into the method 600 or 700, for example in time order, to determine
the future thermal oxidation state of brake assembly 200. The
predicted temperature profile of a predicted future use cycle may
be predicted based on previous temperature profiles for previous
actual use cycles of the aircraft 100. For example, using the parts
of previous temperature profiles relating to the landing phase,
landing phase parts of the temperature profile for a future use
cycle may be predicted. For the purpose of predicting a future
thermal oxidation state, high temperature intervals, high
temperature event values, etc. may be stored in a computer readable
storage medium when the method 600 or 700 is being carried out for
actual use cycles of aircraft 100.
[0132] In some examples, data from previous cycles may not be
available, for example, because brake the assembly 200 may be new.
In some examples, enough data may not be available to reliably
predict temperature profiles for predicted future use cycles. In
such examples, predetermined temperature profiles may be used. The
predetermined temperature profiles may be profiles typically
expected for the future use cycle of aircraft 100.
[0133] The predicted temperature profiles may, for example, take
into account the future flight schedule of the aircraft 100. For
example, the aircraft 100 may be expected to land at an airport
with a short runway requiring high energy (i.e. high temperature)
braking upon landing for some of its predicted future use cycles.
For those predicted future use cycles, the predicted temperature
profiles may indicate high energy braking upon landing. It will be
appreciated that various other factors may be taken into account
when predicting temperature profiles such as taxiing time at
various phases of a predicted future use cycle, waiting time
between a taxiing phase and the preceding landing phase, and the
like.
[0134] As mentioned above, the first plurality of predicted future
use cycles may be a number of predicted future cycles after which
the predicted future thermal oxidation state reaches a thermal
oxidation threshold. For example, the prediction of the future
thermal oxidation state may stop after a cycle in which the thermal
oxidation threshold is reached. In some examples, the prediction of
the future thermal oxidation state may stop as soon as the thermal
oxidation threshold is reached. The thermal oxidation threshold may
be an oxidation state at which servicing or replacement of the
brake assembly 200 or a component of the brake assembly 200 is
required. For example, the brake assembly 200 may require a service
if its mass is reduced by between 4% and 6.5%, for instance 5.7%,
where the selected percentage threshold may vary depending, for
instance, on the original, manufactured disc density. In this
example, the first plurality of predicted future use cycles is the
number of cycles it takes for the proportion of mass lost due to
thermal oxidation to reach or exceed, for instance, 5.7% (i.e.
being within the range 4% to 6.5%).
[0135] On the other hand, in some examples, the prediction of the
future thermal oxidation state may stop at the end of a predicted
future use cycle during which the future thermal oxidation state
approaches close to the thermal oxidation threshold such that the
future thermal oxidation state can be expected to reach the thermal
oxidation threshold during the next predicted future use cycle. In
such examples, the thermal oxidation threshold may be considered
reached within the first plurality of predicted future use cycles.
This is because, in reality, an aircraft 100 with a brake assembly
200 expected to reach the thermal oxidation threshold in a strict
sense in the very next cycle would not be permitted to fly and a
service or replacement relating to the brake assembly 200 may take
place at that point.
[0136] Using the first plurality of predicted future use cycles, an
indication may be given as to how many use cycles can take place
before the brake assembly 200 or a component of the brake assembly
200 requires servicing or replacement due to thermal oxidation. In
the examples where the thermal oxidation threshold is strictly
reached or exceeded during the last of the first plurality of
future cycles, the number of cycles before a service or replacement
is required due to thermal oxidation may be predicted as one fewer
than the number of cycles in the first plurality. In examples where
the prediction of the future thermal oxidation state stops when the
thermal oxidation threshold is expected to be reached in the next
cycle after the first plurality, the first plurality is taken as
the number of cycles before a service or replacement due to thermal
oxidation is required.
[0137] FIG. 10 is a flow diagram of a method 1000 of determining an
amount of brake wear caused by a braking event, using a brake wear
model based on an amount of energy absorbed by the brake assembly
200 due to the braking event and a density parameter of the brake
assembly 200. The amount of brake wear may be determined for all
braking events where energy is input into the brake assembly 200 in
a process involving friction that would cause a surface of the
brake discs to wear. For example, wear of the brake discs due to
friction may cause the length of the brake discs 202 (length L as
shown in FIG. 2) to decrease as brake disk material is lost by the
action of friction.
[0138] For example, the amount of brake wear may be determined for
those braking events which do not involve any high temperature
events. For the method 1000, a braking event may, for example, be
identified based on the temperature profile as an event where the
temperature of the brake assembly 200 increases. In some examples,
a braking event may simply be identified based on an indication
that brake assembly 200 has been applied. For example, the
computing system 106 of the aircraft 100 may detect when brake
assembly 200 is applied and released.
[0139] At block 1002 of the method 1000, the energy input into the
brake assembly 200 during the braking event is determined. The
energy input into the brake assembly 200 may, for example, be
determined based on the characteristics of the aircraft 100 during
the braking event, such as a mass of the aircraft 100, the velocity
of the aircraft 100 during the braking event, etc. The energy
absorbed by the brake assembly 200 can be calculated based on such
characteristics of the aircraft 100 by determining the kinetic
energy of the aircraft 100. For example, a given proportion of the
kinetic energy of the aircraft 100 may be absorbed by the brake
assembly 200 to reduce the kinetic energy of the aircraft 100. In
some examples, the energy input into the brake assembly 200 may be
determined based on measurements acquired by the instruments 108 of
the aircraft 100. For example, the instruments 108 may include a
tachometer associated with the wheel 104 to which the brake
assembly 200 is associated. In such examples, the tachometer
measures the rotational speed of the wheel 104, and the energy
absorbed by the brake assembly 200 can be determined using the
change of the rotational speed with respect to time.
[0140] In other examples, if the mass of the brake assembly 200 is
known, the energy absorbed may be determined based on the increase
in temperature of the brake assembly 200 taking into account the
specific heat of the brake assembly 200. In some examples, the mass
of the brake assembly 200 may be determined based on the thermal
oxidation state of the brake assembly 200 determined according to
the above described methods, because, as described above, the
thermal oxidation state may be expressed as an amount of mass lost
from brake assembly 200 due to thermal oxidation.
[0141] At block 1004 of the method 1000, a density parameter of the
brake assembly 200 is determined. The density parameter, for
example, is a parameter indicating the decrease in density of the
brake assembly 200 compared with the original density, taking into
account lost mass. The density of the brake assembly 200 may
decrease, for example, due to thermal oxidation. It will be
understood that thermal oxidation causes a reduction in mass
because carbon atoms react with oxygen to form carbon dioxide or
carbon monoxide and are thus removed from brake discs 202. However,
thermal oxidation may not necessarily change the volume of the
brake discs 202. This is because thermal oxidation may not act
uniformly on a particular surface of a brake disc and may take
place up to a certain depth inside the brake disc.
[0142] The density parameter may be expressed as (1-Ox) where the
thermal oxidation state Ox is expressed as a number between zero
and one. For example, the density of the brake assembly 200 is
reduced by a factor (1-Ox) compared to the initial density before
any thermal oxidation took place (i.e. when the brake assembly 200
was new). Therefore, the density parameter may be determined based
on the initial oxidation state before the braking event.
[0143] In some examples, the reduced density of the brake assembly
200 may be determined based on measurements by instruments included
in the instruments 108. For example, the mass of the brake assembly
200 may be calculated based on an amount of energy absorbed by the
brake assembly 200 (based on measurements from a tachometer, for
example) and the consequent increase in its temperature (based on
measurements from temperature sensor 216, for example). The reduced
density of the brake assembly 200 may be determined based on the
calculated mass of the brake assembly 200. The aircraft 100 may
include a wear pin associated with brake assembly 200. Typically, a
wear pin provides an indication of the reduction in length L of a
brake and therefore an indication of the brake wear. The wear pin
may be checked between cycles by ground crew, for example, and an
updated volume value of the brake assembly 200 acquired. In some
examples, there may be other ways to measure the change in length L
of the brake assembly 200. For example, a length sensor may be
provided for the brake assembly 200, and/or electrically actuated
brakes may be used. An updated volume value may be determined,
based on reduced length L, and used to determine the reduced
density from the mass. During a single cycle, the change in volume
of brake assembly 200 may be insignificant for the purpose of
calculating the density parameter, and an updated volume may be
acquired after a number of cycles. From the reduced density, the
density parameter may be determined.
[0144] At block 1006 of the method 1000, an amount of brake wear
caused by the braking event is determined, using a brake wear model
based on the energy absorbed by the brake assembly 200 and the
density parameter from block 1004. For example, the mass of the
brake assembly 200 lost due to wear during the wear event is
determined using the brake wear model of Equation 4 below.
m w .times. e .times. a .times. r = W + X .times. E brake + Y
.times. E brake 2 + Z .times. E brake 3 ( 1 - Ox ) ( 4 )
##EQU00003##
[0145] In Equation 4 above, m.sub.wear is the mass lost due to wear
during the braking event, E.sub.brake is the energy absorbed by the
brake assembly 200, and W, X, Y and Z are constants. The constants
W, X, Y and Z may, for example, be determined by experiment
beforehand, and may vary depending on the properties of the brake
assembly 200. The brake wear amount for a braking event may be
determined as a reduction in length L of the brake assembly 200
based on the reduction of mass due to brake wear during that
braking event.
[0146] As mentioned above, the initial thermal oxidation rate is
used to determine the density parameter in some examples. In these
examples, when a braking event takes place during which a high
temperature event also occurs, the initial thermal oxidation state
may be used for the determination of block 1006. This is because
brake wear occurs on a much shorter timescale than thermal
oxidation.
[0147] The amount of brake wear determined for a braking event may
be added to the amount of brake wear from all previous braking
events of the brake assembly 200 in order to determine the total
brake wear amount.
[0148] The method 1000 may, for example, be performed live during a
time when braking events are taking place, or for a use cycle which
has already occurred using the relevant data from that use cycle.
The method 1000 may also be used in order to predict a future brake
wear amount for the brake assembly 200 after a second plurality of
predicted future use cycles of the aircraft 100. The second
plurality of predicted future use cycles may be a number of cycles
after which a brake wear threshold is reached. Each predicted
future use cycle may include a respective plurality of braking
events. For example, the method 1000 may be performed for each
braking event in the second plurality of predicted future use
cycles. The wear amount from each of those braking events may be
added up to predict the future brake wear amount for the second
plurality of predicted future use cycles. For each predicted future
use cycle, the predictions may be based on predicted amounts of
energy absorbed by the brake during respective braking events, and
respective predicted density parameters of the brake for respective
braking events. For example, braking events may be identified and
energy absorbed by brake assembly 200 for those braking events
determined based on the predicted temperature profiles. In other
examples, predicted amounts of absorbed energy may be based on data
from previous cycles. If the brake assembly 200 is new, or enough
previous data is not available, the predicted amounts of energy may
be predetermined.
[0149] For the purpose of predicting the future brake wear amount,
the method 1000 may be used in combination with the method 600 or
700. In these examples, the up to date initial thermal oxidation
state just before each predicted braking event (e.g. a predicted
future braking event) is known. In this way, the mass of the brake
assembly 200, and therefore the density parameter, may be
determined using the initial thermal oxidation before the future
braking event in question.
[0150] As mentioned above, the second plurality of predicted future
use cycles may be a number of predicted future cycles after which
the predicted future brake wear amount reaches a brake wear
threshold. For example, the prediction of the future brake wear
amount may stop after a cycle in which the brake wear threshold is
reached. In some examples, the prediction of the future brake wear
amount may stop as soon as the total brake wear amount reaches the
brake wear threshold. The brake wear threshold may be a total
amount of brake wear at which servicing or replacement of the brake
assembly 200 or a component of the brake assembly 200 is required.
For example, a brake assembly such as the brake assembly 200 of
FIG. 2 may require a service if its length L has been reduced by,
say, 22% to 24%, depending, for example, on the kind of discs and
original, manufactured density thereof. For an exemplary disk
having an original length L of around 221 mm, a reduction in length
of around 50 mm may trigger servicing or replacement. In this
example, the second plurality of predicted future use cycles is the
number of cycles it takes for the total brake wear amount to reach
or exceed, for instance 50 mm (again, for an original disc having a
length L of around 221 mm).
[0151] On the other hand, in some examples, the prediction of the
future brake wear amount may stop at the end of a predicted future
use cycle during which the total brake wear amount approaches close
to the brake wear threshold such that the total brake wear amount
can be expected to reach the brake wear threshold during the next
predicted future use cycle. In such examples, the brake wear
threshold may be considered reached within the second plurality of
predicted future use cycles. This is because, in reality, an
aircraft 100 with the brake assembly 200 expected to reach the
brake wear threshold in a strict sense in the very next cycle would
not be permitted to fly and a service or replacement relating to
the brake assembly 200 may take place at that point.
[0152] Using the second plurality of predicted future use cycles,
an indication may be given as to how many use cycles can take place
before the brake assembly 200 or a component of the brake assembly
200 requires servicing or replacement due to brake wear. In the
examples where the brake wear threshold is strictly reached or
exceeded during the last of the second plurality of future cycles,
the number of cycles before a service or replacement is required
due to brake wear may be predicted as one less than the number of
cycles in the second plurality. In examples where the prediction of
the future brake wear amount stops when the brake wear threshold is
expected to be reached in the next cycle after the second
plurality, the second plurality is taken as the number of cycles
before a service or replacement due to brake wear is required.
[0153] FIG. 11 is a flow diagram of a method 1100 for determining a
number of good future use cycles until one of the thermal oxidation
threshold and the brake wear threshold is reached. The number of
good future use cycles is the remaining number of future use cycles
before one of the thermal oxidation threshold or the brake wear
threshold is reached. The method 1100 may be performed for a number
of predicted future use cycles until the first of the thresholds is
reached. The method 1100 involves predicting a future thermal
oxidation state and a future brake wear amount after a predicted
future use cycle and, if one of the thermal oxidation threshold and
the brake wear threshold is reached, determining a number of good
future use cycles before either of the thresholds is reached. If
one of the thresholds is not reached, the predictions are performed
for the next predicted future use cycle. As in the above examples,
each predicted future use cycle includes a plurality of braking
event. For each predicted future use cycle the predictions are
based on a respective predicted temperature profile of the brake, a
current thermal oxidation state, predicted amounts of energy
absorbed by the brake during respective braking events, and
respective predicted density parameters of the brake for respective
braking events.
[0154] The number of good future use cycles is a number of cycles
after which servicing or replacement of the brake assembly 200 or a
component of the brake assembly 200 is required. It will be
appreciated that service or replacement in relation to the brake
assembly 200 may be carried out when one of the thermal oxidation
threshold or the brake wear threshold is first reached. Which
threshold is reached first may, for example, depend on the way the
aircraft 100 is handled during use and its flight schedule. For
example, if the aircraft 100's schedule involves flying to mostly
airports with long runways, short taxiing routes, etc., the brake
wear threshold may be reached first. This is because, in such
examples, the temperature of the brake assembly 200 may not often
exceed any of the temperature thresholds relating to thermal
oxidation. On the other hand, the aircraft 100 may often experience
high energy braking (e.g. due to short runways) causing
temperatures above the thresholds related to thermal oxidation. In
such examples the thermal oxidation threshold may be reached
first.
[0155] At block 1102 of the method 1100, a future thermal oxidation
state after a predicted future use cycle is predicted. The
prediction of the future thermal oxidation state is performed as
described above, for example, using an appropriate thermal
oxidation model based on a predicted temperature profile of the
predicted future use cycle in question. At block 1104 of the method
1100, a future brake wear amount after the same predicted future
use cycle is predicted. The prediction is performed as described
above in the context of method 1000.
[0156] At block 1106 of the method 1100, it is determined whether
the thermal oxidation threshold and/or the brake wear threshold is
reached. For example, if the thermal oxidation threshold is
reached, the method 1100 proceeds to block 1108 at which a number
of good future use cycles, before either of the thermal oxidation
threshold or the brake wear threshold is reached, is determined,
and the method 1100 ends. For example, if the thermal oxidation
threshold is strictly reached or exceeded after a given number of
predicted future use cycles, the number of good future use cycles
is one less than that given number. For example, if the thermal
oxidation threshold is expected to be reached in the very next
predicted future use cycle, the number of good future use cycles is
determined as the number of predicted future use cycles for which
the method 1100 has been performed thus far.
[0157] On the other hand, if it is determined that the brake wear
threshold is reached, the method proceeds to block 1108 where a
number of good future use cycles is determined, and the method 1100
ends. For example, if the brake wear threshold is strictly reached
or exceeded after a given number of predicted future use cycles,
the number of good future use cycles is one less than that given
number. For example, if the brake wear threshold is expected to be
reached in the very next predicted future use cycle, the number of
good future use cycles is determined as the number of predicted
future use cycles for which method 1100 has been performed thus
far.
[0158] If, for example, both the thresholds are reached, the method
1100 proceeds to block 1108 where a number of remaining good future
use cycles, before either the thermal oxidation threshold or the
brake wear threshold is reached, is determined and the method 1100
ends. In this example, if at least one of the thresholds is
strictly reached or exceeded after a given number of predicted
future use cycles, the number of good future use cycles is one less
than that given number. Otherwise, the number of good future use
cycles is determined as the number of predicted future use cycles
for which the method 1100 has been performed thus far.
[0159] If the brake wear threshold is not reached, the method 1100
proceeds to block 1110 and blocks 1102 to 1110 are repeated for the
next predicted future use cycle.
[0160] In this way, a number of good future use cycles may be
predicted based on which of the thermal oxidation threshold and the
brake wear threshold is reached first. This is because, the brake
assembly 200 may require a service or replacement, or a component
of the brake assembly 200 may require a service or replacement once
the first of these thresholds is reached. It will be appreciated,
for example, that brake assembly 200 will not continue to be used
if the thermal oxidation threshold is reached but the brake wear
threshold is not. It should also be appreciated that blocks of the
method 1100 may be performed in any suitable order. For example
block 1104 may be performed before block 1102 and/or block 1110 may
be performed before block 1106.
[0161] One or more of the above described methods, namely the
methods 600, 700, 1000 and 1100, or any of their variations (e.g.
live determination of oxidation or brake wear, or prediction of
future thermal oxidation state or future brake wear, etc.) may be
performed by a processor of the computing system 106 of the
aircraft 100, for example, based on instructions stored in a
computer readable storage medium of the computing system 106. For
example, monitoring of the thermal oxidation state (subsequent to
use cycles or live) may be performed by a processor of computing
system 106. Alternatively, or in addition, monitoring of the brake
wear (subsequent to use cycles or live) may be performed by a
processor of the computing system. Alternatively, or in addition to
any of these examples, predictions relating to the future thermal
oxidation state and/or the future brake wear state may be performed
by a processor of the computing system 106. The methods may be
performed, for example, using data from the instruments 108. For
example, temperature data as measured by the temperature sensor 216
may be used. In the case of prediction, the future temperature
profiles and/or other predicted data may be predicted by a
processor of the computing system 106. Alternatively, the data for
prediction may be determined on a computing system not on board the
aircraft 100, and may be stored in a computer readable storage
medium of the computing system 106.
[0162] In the foregoing examples, the apparatus 300 is described as
being installed on a vehicle such as the aircraft 100. The
apparatus 300 may be comprised in the computing system 106 of the
aircraft 100. For example, the first controller 302 may be
implemented by a processor of the computing system 106. Said
processor may implement instruction stored on a computer readable
storage medium of the computing system 106 to implement the
functions of the first controller 302. The braking system 214 may
be implemented by the computing system 106 in a similar manner.
Alternatively, the apparatus 300 and/or the braking system 214 may
be implemented by items of apparatus separate to the computing
system 106. For example, there may be dedicated processors to
implement the functions of the first controller 302 and/or the
second controller 304 provided on the aircraft 100. In some
examples, the foregoing described functions and processes of the
apparatus 300 may be performed by the braking system 214. In some
examples, the first controller 302 and the second controller 304
may be implemented by the same processor or the same group of
processors. In some examples, the first controller 302 and the
second controller 304 may be implemented by different processors or
different groups of processors.
[0163] All or part of the instructions for performing the
aforementioned processes may be generated and/or the processes may
be performed using any suitable software or combination of
software. In one example, "MATLAB" and/or "SCADE" may be used to
generate all or part of the instructions for respective processors
to carry out any of the aforementioned processes. In other
examples, other software packages may be used. For example, any
suitable programming language, development environment, software
package, or the like may be used. Other examples of programming
languages include PYTHON, C++, C, JAVASCRIPT, FORTRAN etc.
[0164] It is to noted that the term "or" as used herein is to be
interpreted to mean "and/or", unless expressly stated otherwise.
Although the invention has been described herein with reference to
one or more preferred examples, it will be appreciated that various
changes or modifications may be made without departing from the
scope of the invention as defined in the appended claims.
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