U.S. patent application number 16/285815 was filed with the patent office on 2019-08-29 for brake monitoring.
The applicant listed for this patent is Airbus Operations Limited, Airbus Operations (S.A.S.), Airbus (S.A.S.). Invention is credited to Brice CHERAY, Maud CONSOLA, Rodrigo JIMENEZ.
Application Number | 20190263373 16/285815 |
Document ID | / |
Family ID | 61903195 |
Filed Date | 2019-08-29 |
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United States Patent
Application |
20190263373 |
Kind Code |
A1 |
JIMENEZ; Rodrigo ; et
al. |
August 29, 2019 |
BRAKE MONITORING
Abstract
An apparatus and a method for determining a thermal oxidation
state of a brake of an aircraft landing gear is disclosed.
Determination of the thermal oxidation state of the brake involves
determining a thermal oxidation state of the brake after a braking
event, using a thermal oxidation model based on an initial thermal
oxidation state before the braking event and a temperature profile
of the brake with respect to time.
Inventors: |
JIMENEZ; Rodrigo; (Bristol,
GB) ; CHERAY; Brice; (Blagnac, FR) ; CONSOLA;
Maud; (Toulouse, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Airbus Operations Limited
Airbus Operations (S.A.S.)
Airbus (S.A.S.) |
Bristol
Toulouse
Blagnac Cedex |
|
GB
FR
FR |
|
|
Family ID: |
61903195 |
Appl. No.: |
16/285815 |
Filed: |
February 26, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B60T 8/171 20130101;
F16D 2066/006 20130101; B64C 25/42 20130101; B60T 8/58 20130101;
B64F 5/60 20170101; F16D 66/00 20130101; B60T 2270/406 20130101;
B60T 17/221 20130101; F16D 66/021 20130101; F16D 2066/001 20130101;
B64C 25/426 20130101; B60T 8/32 20130101; B60T 8/1703 20130101 |
International
Class: |
B60T 17/22 20060101
B60T017/22; F16D 66/00 20060101 F16D066/00; F16D 66/02 20060101
F16D066/02; B64F 5/60 20060101 B64F005/60 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 27, 2018 |
GB |
1803203.7 |
Claims
1. An apparatus for determining a thermal oxidation state of a
brake of an aircraft landing gear, the apparatus comprising: a
processor configured to determine a thermal oxidation state of a
brake after a predicted future braking event, using a thermal
oxidation model based on an initial thermal oxidation state before
the predicted future braking event and a predicted temperature
profile of the brake with respect to time.
2. The apparatus according to claim 1, wherein: the initial thermal
oxidation state is updated using the determined thermal oxidation
state after the predicted future braking event; and the processor
is configured to determine the thermal oxidation state after a
subsequent predicted future braking event based on the updated
initial thermal oxidation state.
3. The apparatus according to claim 2, wherein the predicted
temperature profile of the brake is for a predicted future use
cycle of the aircraft, and the processor is configured to determine
respective updated thermal oxidation states after each predicted
future braking event within the predicted future use cycle of the
aircraft.
4. The apparatus according to claim 1, wherein the processor is
configured to determine an amount of brake wear caused by the
predicted future braking event, using a brake wear model based on
an amount of energy absorbed by the brake due to the predicted
future braking event and a density parameter of the brake.
5. The apparatus according to claim 4, wherein the processor is
configured to determine the density parameter of the brake based on
the initial thermal oxidation state before the predicted future
braking event.
6. The apparatus according to claim 4, wherein the processor is
configured to: (i) predict a future thermal oxidation state and a
future brake wear amount after a predicted future use cycle; and
(ii) if one of a thermal oxidation threshold and a brake wear
threshold is reached, determine a number of good future use cycles,
otherwise repeat (i) and (ii) for the next predicted future use
cycle, wherein: each predicted future use cycle comprises a
plurality of predicted future braking events; and 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 predicted future braking events, and
respective predicted density parameters of the brake for respective
predicted future braking events.
7. The apparatus according to claim 4, wherein the processor is
configured to predict a future brake wear amount after a second
plurality of predicted future use cycles, wherein the second
plurality of future use cycles is a number of cycles after which a
brake wear threshold is reached; each predicted future use cycle
comprises a plurality of predicted future braking events; and for
each predicted future use cycle, the predictions are based on
predicted amounts of energy absorbed by the brake during respective
predicted future braking events, and respective predicted density
parameters of the brake for respective predicted future braking
events.
8. The apparatus according to claim 1, wherein: the processor is
configured to predict a future thermal oxidation state after a
first plurality of predicted future use cycles, wherein the first
plurality of future use cycles is a number of cycles after which a
thermal oxidation threshold is reached; each predicted future use
cycle comprises a plurality of predicted future braking events; and
for each predicted future use cycle, the predictions are based on a
respective predicted temperature profile of the brake and a current
thermal oxidation state.
9. The apparatus according to claim 1, wherein the processor is
configured to determine the thermal oxidation state after the
predicted future braking event, using the thermal oxidation model
based on a high temperature interval, the initial thermal oxidation
state and a thermal oxidation rate parameter.
10. The apparatus according to claim 9, wherein the processor is
configured to: compare the predicted temperature profile to a set
of temperature criteria; and if one or more criteria from the set
of temperature criteria are met: identify a high temperature event
corresponding to the predicted future braking event based on the
comparison; and determine the interval of time taken by the high
temperature event as the high temperature interval.
11. The apparatus according to claim 10, wherein the processor is
configured to determine a high temperature event value for the high
temperature interval; and determine an oxidation rate parameter
based on the determined temperature value and physical
characteristic information of the brake.
12. The apparatus according to claim 1, wherein the processor is
configured to select the thermal oxidation model based on the
initial thermal oxidation state.
13. A method for determining a thermal oxidation state of a brake
of an aircraft landing gear, the method comprising: inputting a
predicted temperature profile of a brake with respect to time and
an initial thermal oxidation state of the brake before a predicted
future braking event; and determining a thermal oxidation state of
the brake after the predicted future braking event, using a thermal
oxidation model based on the initial thermal oxidation state and
the predicted temperature profile.
14. The method according to claim 13 comprising: updating the
initial thermal oxidation state using the determined thermal
oxidation state after the predicted future braking event; and
determining the thermal oxidation state after a subsequent
predicted future braking event based on the updated initial thermal
oxidation state.
15. The method according to claim 13 comprising determining an
amount of brake wear caused by the predicted future braking event,
using a brake wear model based on an amount of energy absorbed by
the brake due to the predicted future braking event and a density
parameter of the brake.
16. The method according to claim 15 comprising: (i) predicting a
future thermal oxidation state and a future brake wear amount after
a predicted future use cycle; (ii) if one of a thermal oxidation
threshold and a brake wear threshold is substantially reached,
determining a number of good future use cycles, otherwise repeating
(i) and (ii) for the next predicted future use cycle, wherein: each
predicted future use cycle comprises a plurality of predicted
future braking events; and 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 predicted future
braking events, and respective predicted density parameters of the
brake for respective predicted future braking events.
17. An apparatus for determining a thermal oxidation level of a
brake of an aircraft landing gear, the apparatus comprising: a
processor configured to determine an updated thermal oxidation
level of a brake after a braking event, based on an initial thermal
oxidation level before the braking event and temperature data as a
function of time of the brake, using a model of the evolution of
the thermal oxidation of the brake.
Description
TECHNICAL FIELD
[0001] The present invention relates to determining thermal
oxidation of a brake of an aircraft landing gear.
BACKGROUND
[0002] Aircraft landing gear brakes are normally inspected when the
aircraft is stationary on the ground between flights. Specifically,
an amount of brake wear and thermal oxidation of the brakes may be
checked and a service thereon or replacement thereof may be
performed or scheduled based on the checks.
SUMMARY
[0003] A first aspect of the present invention provides an
apparatus for determining a thermal oxidation state of a brake of
an aircraft landing gear, the apparatus comprising: a processor
configured to determine a thermal oxidation state of a brake after
a braking event, using a thermal oxidation model based on an
initial thermal oxidation state before the braking event and a
temperature profile of the brake with respect to time.
[0004] Optionally, the initial thermal oxidation state is updated
using the determined thermal oxidation state after the braking
event; and the processor is configured to determine the thermal
oxidation state after a subsequent braking event based on the
updated initial thermal oxidation state. In examples, using the
determined thermal oxidation state after the braking event may mean
updating the initial thermal oxidation state to be equal to or
substantially equal to the determined thermal oxidation state after
the braking event. In other examples, the initial thermal oxidation
state may be made equal to a function of the determined thermal
oxidation state after the braking event (for instance, by
multiplying the determined thermal oxidation state by a factor of
1.05, in order to include a 5% margin--other factors and margins
may be employed instead).
[0005] Optionally, the temperature profile of the brake is for a
use cycle of the aircraft, and the processor is configured to
determine respective updated thermal oxidation states after each
braking event within the use cycle of the aircraft.
[0006] Optionally, the processor is configured to determine an
amount of brake wear caused by the braking event, using a brake
wear model based on an amount of energy absorbed by the brake due
to the braking event and a density parameter of the brake.
[0007] Optionally, the processor is configured to determine the
density parameter of the brake based on the initial thermal
oxidation state before the braking event.
[0008] Optionally, the processor is configured to: (i) predict a
future thermal oxidation state and a future brake wear amount after
a predicted future use cycle; and (ii) if one of a thermal
oxidation threshold and a brake wear threshold is reached,
determine a number of good future use cycles, otherwise repeat (i)
and (ii) for the next predicted future use cycle, wherein: each
predicted future use cycle comprises a plurality of braking events;
and 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.
[0009] Optionally, the processor is configured to predict a future
brake wear amount after a second plurality of predicted future use
cycles, wherein the second plurality of future use cycles is a
number of cycles after which a brake wear threshold is substantial
reached; each predicted future use cycle comprises a plurality of
braking events; and for each predicted future use cycle, the
predictions are 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.
[0010] Optionally, the processor is configured to predict a future
thermal oxidation state after a first plurality of predicted future
use cycles, wherein the first plurality of future use cycles is a
number of cycles after which a thermal oxidation threshold is
reached; each predicted future use cycle comprises a plurality of
braking events; and for each predicted future use cycle, the
predictions are based on a respective predicted temperature profile
of the brake and a current thermal oxidation state.
[0011] Optionally, the processor is configured to determine the
thermal oxidation state after the braking event, using the thermal
oxidation model based on a high temperature interval, the initial
thermal oxidation state and a thermal oxidation rate parameter.
[0012] Optionally, the processor is configured to: compare the
temperature profile to a set of temperature criteria; and if one or
more criteria from the set of temperature criteria are met:
identify a high temperature event corresponding to the braking
event based on the comparison; and determine the interval of time
taken by the high temperature event as the high temperature
interval.
[0013] Optionally, the processor is configured to determine a high
temperature event value for the high temperature interval; and
determine an oxidation rate parameter based on the determined
temperature value and physical characteristic information of the
brake.
[0014] Optionally, the processor is configured to select the
thermal oxidation model based on the initial thermal oxidation
state.
[0015] A second aspect of the present invention provides a method
for determining a thermal oxidation state of a brake of an aircraft
landing gear, the method comprising: inputting a temperature
profile of a brake with respect to time and an initial thermal
oxidation state of the brake before a braking event; and
determining a thermal oxidation state of the brake after the
braking event, using a thermal oxidation model based on the initial
thermal oxidation state and the temperature profile.
[0016] Optionally, the method according to the second aspect
comprises: updating the initial thermal oxidation state using the
determined thermal oxidation state after the braking event; and
determining the thermal oxidation state after a subsequent braking
event based on the updated initial thermal oxidation state. In
examples, using the determined thermal oxidation state after the
braking event may mean updating the initial thermal oxidation state
to be equal to or substantially equal to the determined thermal
oxidation state after the braking event. In other examples, the
initial thermal oxidation state may be made equal to a function of
the determined thermal oxidation state after the braking event (for
instance, by multiplying the determined thermal oxidation state by
a factor of 1.05, in order to include a 5% margin in the
calculation--other factors and margins may be employed
instead).
[0017] Optionally, the method according to the second aspect
comprises determining an amount of brake wear caused by the braking
event, using a brake wear model based on an amount of energy
absorbed by the brake due to the braking event and a density
parameter of the brake.
[0018] Optionally, the method according to the second aspect
comprises: (i) predicting a future thermal oxidation state and a
future brake wear amount after a predicted future use cycle; (ii)
if one of a thermal oxidation threshold and a brake wear threshold
is reached, determining a number of good future use cycles,
otherwise repeating (i) and (ii) for the next predicted future use
cycle, wherein: each predicted future use cycle comprises a
plurality of braking events; and 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.
[0019] A third aspect of the present invention provides an
apparatus for determining a thermal oxidation level of a brake of
an aircraft landing gear, the apparatus comprising: a processor
configured to determine an updated thermal oxidation level of a
brake after a braking event, based on an initial thermal oxidation
level before the braking event and temperature data as a function
of time of the brake, using a model of the evolution of the thermal
oxidation of the brake.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Embodiments of the invention will now be described, by way
of example only, with reference to the accompanying drawings, in
which:
[0021] FIG. 1 is a schematic view of an aircraft on which examples
may be deployed;
[0022] FIG. 2 is a schematic view of a brake and a wheel of an
aircraft landing gear according to an example;
[0023] FIG. 3 is a flow diagram of a first exemplary method of
determining the thermal oxidation state of a brake of an aircraft
landing gear;
[0024] FIG. 4 is a flow diagram of a second exemplary method of
determining the thermal oxidation state of a brake of an aircraft
landing gear;
[0025] FIG. 5 is a graph illustrating the temperature of a brake
with respect to time;
[0026] FIG. 6 is a graph illustrating the thermal oxidation state
of a brake with respect to time for a specific temperature;
[0027] FIG. 7 is a flow diagram of a method of determining an
amount of brake wear according to an example;
[0028] FIG. 8 is a flow diagram of a method of predicting a number
of good future use cycles with respect to an aircraft brake
according to an example; and
[0029] FIG. 9 is a schematic diagram of a computing apparatus.
DETAILED DESCRIPTION
[0030] FIG. 1 is a simplified schematic view of an aircraft 100.
The aircraft 100 comprises a plurality of landing gear assemblies
102. Each landing gear assembly 102 comprises brake assemblies for
providing braking when the aircraft 100 is on the ground. The
aircraft 100 comprises a computing system 104 which may, for
example, comprise one or more processors and one or more computer
readable storage media. The aircraft 100 may also comprise
instruments 106, such as measuring instruments for measuring
characteristics or parameters related to the aircraft, and
instruments for measuring environmental characteristics. The
aircraft 100 may also comprise indicating devices 108 for providing
various indications relating to the aircraft, examples of which
indications will be described herein. The indicating devices may
include screens which display text and/or graphics, dials, light
indicators, sound indicators which emit sound to provide an
indications, and the like.
[0031] FIG. 2 is a simplified schematic view of an aircraft brake
assembly 200 of a landing gear assembly 102. In this example, the
brake assembly 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. In FIG. 2, the brake assembly 200 is shown
associated with a wheel 214 of the landing gear assembly 102. 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, and there
may be more than one wheel associated with any one landing gear
assembly.
[0032] When the aircraft 100 travels along the ground supported by
the landing gear assembly 102, the rotors rotate with the wheel
214, whereas the stators, the pressure plate 202 and the reaction
plate 204 do not rotate with the wheel 214. 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 216 of FIG. 2) and friction acts to inhibit the
rotational motion of the rotors, thus generating a braking
force.
[0033] 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. The methods disclosed herein may be applied to any type of
brake that uses CC composites or carbon ceramics as a friction
material to brake. Examples include race car brakes (e.g. Formula 1
car brakes), other high performance car brakes. The methods
disclosed herein may also be applied to other industrial
applications using CC composites or carbon ceramics, for example,
applications where lubrication of components is more relevant than
friction.
[0034] In order to monitor the temperature of the brake discs 202,
a temperature sensor 212 may be provided. For example, the
temperature sensor 212 may be provided to be in thermal contact
with the brake disc that is likely to, or is known to, reach the
highest temperatures during braking. In the example of FIG. 2, the
temperature sensor 212 is provided on the stator 210. The
temperature sensor 212 may be any type of temperature sensor
suitable for use in an aircraft brake assembly. For example, the
temperature sensor 212 is able to function properly at the
temperature ranges likely to be reached by the brake discs 202. For
example, the temperature sensor 212 may be a thermocouple, a
surface acoustic wave (SAW) sensor, an eddy current sensor, a
resistance thermal sensor, a strain gauge, or the like.
[0035] The temperature sensor 212 may measure the temperature of
the stator 210 at given measurement intervals during a period of
time when use of the brake assembly 200 is expected, for example.
The lengths of the given measurement intervals may vary, for
example. The given measurement intervals may be regular, irregular
or regular for one period of time and irregular for another period
of time. For example, the temperature sensor 212 may measure the
temperature such that a profile of the temperature of the stator
210 is captured with respect to time. In other words, the
temperature sensor 212 measures the temperature of the stator 210
at given measurement intervals such that temperature information as
a function of time is captured. For example, a processor of the
computing system 104 may control the operation of the temperature
sensor 212 based on instructions stored in a computer readable
storage medium of the computing system 104. Temperature
measurements captured by the temperature sensor 212 may be stored
in a storage medium of the computing system 104, for example, along
with associated time data.
[0036] During use of the brake assembly 200, oxidation of the CC
composite of the brake discs 202 may occur. More specifically,
thermal oxidation of the brake discs 202 may occur during braking
applications as a result of the brake discs 202 reaching high
temperatures for significant periods of time. A measure of thermal
oxidation may, for example, be the proportion of the brake mass
lost due to thermal oxidation. During a thermal 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. Therefore the thermal oxidation
state of a brake (which may also be referred to as the thermal
oxidation level) can be expressed as an amount of mass lost due to
thermal oxidation. Thermal oxidation of the CC composite of the
brake discs 202 may, for example, take place at temperatures above
400.degree. C. In addition, for example, wear of the brake discs
202 may occur due to friction during braking. After a period of
use, the brake assembly 200 or its components may require servicing
or replacement. Typically, various aspects of aircraft brakes are
inspected by ground crew when an aircraft such as aircraft 100 is
on the ground. The ground crew may from visual inspection alone
determine whether or not the brake assembly 200 is in a condition
suitable for further use or whether a service or replacement is
required. If a determination is made that a service or a
replacement in relation to the brake assembly 200 is required at a
time other than that of a planned service or the like, the aircraft
100 to which the brake assembly 200 belongs may be "grounded" until
a service or replacement is performed. Here, the term "grounded"
means that the aircraft 100 is not permitted to fly, for example,
while carrying passengers. Such inspections by ground crew ensure
safe operation of the aircraft 100.
[0037] FIG. 3 summarizes a method 300, according to an embodiment
of the present invention, of determining a thermal oxidation state
of a brake, such as the brake assembly 200, of an aircraft landing
gear assembly 102. The method 300 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.
[0038] 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.
[0039] At block 302 of the method 300, 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.
[0040] 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 212 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.
[0041] 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 300 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 300, or by other methods disclosed
herein.
[0042] At block 304 of method 300, 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 300 may be
performed live during a use cycle of the aircraft 100. In the case
of the method 300 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 212,
for example. At block 304, 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.
[0043] 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 300 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.
[0044] In examples where the temperature profile for an entire use
cycle of the aircraft 100, the method 300 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.
[0045] In the method 300, 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.
[0046] FIG. 4 is a flow diagram of a method 400 showing acts that
may be performed as part of method 300. For example, the method 400
involves more specific examples of the block 304 of the method 300.
Block 402 is identical to block 302 of the method 300, 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 404, 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.
[0047] At block 406, 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 400 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.
[0048] The temperature thresholds may be set based on temperatures
above which a significant amount of thermal oxidation is expected
to occur. Therefore, the method 400 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.
[0049] On the other hand, if at least one of the temperature
thresholds is exceeded, at block 408 of the method 400, 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. 5. FIG. 5 is
a graph illustrating a part of an example temperature profile. In
the graph of FIG. 5, the vertical axis represents temperature of
the brake assembly 200, and the horizontal axis represents time. In
this example, profile part 502 indicates that the temperature of
the brake assembly 200 exceeds a first temperature threshold 504
and a second temperature threshold 506. In this example, the high
temperature event is identified as the part of the profile 502
above the second temperature threshold 506 as the second
temperature threshold 506 is the highest temperature threshold
which is exceeded.
[0050] The amount of thermal oxidation which occurs above the
second temperature threshold 506 may be significantly greater for a
given interval of time compared to the thermal oxidation above the
first temperature threshold 504 but below the second temperature
threshold 506. Therefore, in this example, the parts of the
temperature profile below the second temperature threshold 506 are
not taken into account. In other examples, for example when the
method 400 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. 5 is merely an illustration of
an example for explanatory purposes.
[0051] At block 410, 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. 5, the high
temperature interval is determined to be the time interval 508.
[0052] At block 412, 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.
[0053] At block 414, 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(T)=Ae-.sup.E.sup.A.sup./RT (1)
[0054] 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 414. In this example, the thermal oxidation rate
k(T) is the oxidation parameter determined at block 414. 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.
[0055] 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 400 is implemented.
[0056] FIG. 6 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. 6
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 602 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.
[0057] In this example, the thermal oxidation state Ox advances
with time differently below a thermal oxidation state level 604,
than it does above the thermal oxidation state level 604. 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 604 and substantially linearly with time
above oxidation state level 604, in this example. In this example,
the thermal oxidation state increases at an accelerated rate with
time until thermal oxidation state level 604 is reached. After
thermal oxidation state level 604 is reached, the rate of change of
thermal oxidation state Ox with time remains generally constant.
The part of the graph of FIG. 6 below thermal oxidation state level
604 may be considered as a first thermal oxidation zone, namely
Zone 1, and the part of the graph of FIG. 6 above thermal oxidation
state level 604 may be considered as a second thermal oxidation
zone, namely Zone 2, for example.
[0058] 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.
[0059] At block 416, 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(T).times.t.sub.eq(1-n)}.sup.1/1-n] (2)
Ox=k(T).times.t.sub.eq (3)
[0060] 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.
[0061] 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
400 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 400.
[0062] It will be understood that block 416 may be performed at any
stage of the method 400 once block 402 has been performed, because
block 416 requires the initial thermal oxidation state.
[0063] At block 418, 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.
[0064] The updated thermal oxidation state may be set to the new
initial thermal oxidation state for a subsequent use of the method
400 for a subsequent high temperature event in the temperature
profile.
[0065] In some examples, the method 300 and/or 400 may be performed
live during a use cycle when braking events are taking place. In
such examples, part of the method 400, 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
212 provides may continuously be compared to the set of temperature
criteria as per block 404 of method 400, 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 212, and those values resulting
ultimately in updated thermal oxidation states of the brake
assembly 200.
[0066] 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. 5, the part of the profile
part 502 occurring within the time interval indicated as 510 may be
taken to be a high temperature event and the interval 510 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 510, 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 506. 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 510,
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 212. For example, the interval 510 may be the
interval of time between subsequent temperature measurements taken
by the temperature sensor 212.
[0067] The methods 300 and 400 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 214.
[0068] On the other hand, in some examples, the method 300 or 400
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.
[0069] For example, the predicted temperature profiles may be input
into the method 300 or 400, 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 300 or 400 is being carried out for
actual use cycles of aircraft 100.
[0070] 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.
[0071] 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.
[0072] 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%).
[0073] 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.
[0074] 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.
[0075] FIG. 7 is a flow diagram of a method 700 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.
[0076] 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 700, 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 104 of the aircraft 100 may detect when brake
assembly 200 is applied and released.
[0077] At block 702 of the method 700, 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 106 of
the aircraft 100. For example, the instruments 106 may include a
tachometer associated with the wheel 214 to which the brake
assembly 200 is associated. In such examples, the tachometer
measures the rotational speed of the wheel 214, and the energy
absorbed by the brake assembly 200 can be determined using the
change of the rotational speed with respect to time.
[0078] 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.
[0079] At block 704 of the method 700, 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.
[0080] 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.
[0081] In some examples, the reduced density of the brake assembly
200 may be determined based on measurements by instruments included
in the instruments 106. 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 212, 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.
[0082] At block 706 of the method 700, 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 704. 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 wear = W + X .times. E brake + Y .times. E brake 2 + Z .times. E
brake 3 ( 1 - 0 x ) ( 4 ) ##EQU00001##
[0083] 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.
[0084] 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 706. This is because
brake wear occurs on a much shorter timescale than thermal
oxidation.
[0085] 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.
[0086] The method 700 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 700 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 700 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.
[0087] For the purpose of predicting the future brake wear amount,
the method 700 may be used in combination with the method 300 or
400. 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.
[0088] 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).
[0089] 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.
[0090] 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.
[0091] FIG. 8 is a flow diagram of a method 800 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 800 may be performed for a number
of predicted future use cycles until the first of the thresholds is
reached. The method 800 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.
[0092] 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.
[0093] At block 802 of the method 800, 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 804 of the method
800, 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 700.
[0094] At block 806 of the method 800, 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 800 proceeds to block 808 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 800 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 800 has been performed thus far.
[0095] On the other hand, if it is determined that the brake wear
threshold is reached, the method proceeds to block 808 where a
number of good future use cycles is determined, and the method 800
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 800 has been performed thus
far.
[0096] If, for example, both the thresholds are reached, the method
800 proceeds to block 808 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 800
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 800 has been performed thus far.
[0097] If the brake wear threshold is not reached, the method 800
proceeds to block 810 and blocks 802 to 810 are repeated for the
next predicted future use cycle.
[0098] 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 800 may be performed in any suitable order. For example
block 804 may be performed before block 802 and/or block 810 may be
performed before block 806.
[0099] One or more of the above described methods, namely the
methods 300, 400, 700 and 800, 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 104 of the
aircraft 100, for example, based on instructions stored in a
computer readable storage medium of the computing system 104. For
example, monitoring of the thermal oxidation state (subsequent to
use cycles or live) may be performed by a processor of computing
system 104. 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 104. The methods may be
performed, for example, using data from the instruments 106. For
example, temperature data as measured by the temperature sensor 212
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 104. 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 104.
[0100] An indicating device 108 of the aircraft 100 may be used to
provide the pilots and/or ground crew indications relating to the
thermal oxidation state, brake wear amount, a number of cycles
before the thermal oxidation threshold is reached, a number of
cycles before the brake wear threshold is reached and/or a number
of good future use cycles. For example, such indications may allow
the ground crew to assess aspects of the brake assembly 200 more
quickly than visual or other physical inspection alone. Such
indications may also allow appropriate scheduling of services and
replacements in relation to the brake assembly 200. This may
prevent delays due to grounding of the aircraft 100 at a time when
a service or replacement is not scheduled because ground crew
determine an issue with the brake assembly 200 which could not have
been known without predictions relating to thermal oxidation and/or
brake wear.
[0101] Indications regarding thermal oxidation and/or brake wear to
the pilot(s) may assist, for example, in the pilots indicating to
ground crew when a service or replacement in relation to the brake
assembly 200 may be required. Indications of the state of the brake
assembly 200 for a previous cycle may also assist the pilot(s) of
the aircraft 100 in assessing their brake application behaviour.
For example, the indications may show that a particular change in
braking behaviour may lead to less thermal oxidation per cycle and
a greater number of good future use cycles. For example, this may
occur in the case where the thermal oxidation threshold is
predicted to be reached first. When one or more of the above
described methods are being performed live by a processor of
computing system 104, indications in relation to the thermal
oxidation and/or brake wear of the brake assembly 200 may allow the
pilot(s) to adjust brake application behaviour substantially in
real time in order to preserve the brake assembly 200. For example,
the pilot(s) may not start taxiing the aircraft 100 immediately
after a landing with high energy braking, if permitted to do so,
such that the temperature of the brake assembly 200 does not remain
above a temperature threshold relating to thermal oxidation.
[0102] One or more of the above described methods, namely the
methods 300, 400, 700 and 800, 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 computing apparatus such as computing apparatus 900
shown in FIG. 9, for example. The computing apparatus 900 may be
external to the aircraft 100. Computing apparatus 900 may comprise
a processor 902 and a computer readable storage medium 904. The
processor 902 may be configured to execute instructions stored on
the storage medium 904. The storage medium 904 may store
instructions for performing all or part of any of the above
described methods. Data, such as temperature profile information,
may be provided to the computing apparatus 900 for performing the
methods disclosed herein. In the case of live monitoring, data from
the aircraft may be transmitted to the computing apparatus 900. For
example, any of the above methods may be performed by computing
apparatus 900 and the resulting indications reported to personnel
responsible for the care and/or use of the aircraft 100.
[0103] All or part of the instructions for performing the above
described methods may be generated and/or the methods may be
performed using any suitable software or combination of software.
In one example, "MATLAB" may be used to generate all or part of the
instructions for a processor such as processor 902 or a processor
of computing system 104 to carry out any of the above methods. 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.
[0104] It will be appreciated that the methods disclosed herein
allow monitoring (live or subsequent to a use cycle) of the thermal
oxidation state and/or brake wear state. The methods also allow
predictions in relation to future thermal oxidation states and
brake wear states of the brake assembly 200.
[0105] 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 above with reference to
one or more preferred embodiments, 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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