WO2024092308A1

WO2024092308A1 - Brake system with sensor

Info

Publication number: WO2024092308A1
Application number: PCT/AU2023/051097
Authority: WO
Inventors: Robert Darby; Andrew French; Gayan Kahandawa; Amal Jayawardena; Linh Nguyen
Original assignee: Fmp Group (Australia) Pty Limited
Priority date: 2022-10-31
Filing date: 2023-10-31
Publication date: 2024-05-10

Abstract

A brake monitoring system (1) comprising: a friction body (5); a sensor component (7); a light source (11); and a light sensor system (17). The sensor component (7) includes a fiber bragg grating (FBG) (9), wherein the friction body (5) is coupled with the sensor component (7) to enable the friction body (5) and sensor component (7) to wear together. The light source (11) transmits (110) a light signal (13) to the fiber bragg grating (9), wherein the fiber bragg grating (9) is configured to receive the light signal (13) and produce a reflected light signal (15), wherein an intensity (19) of the reflected light signal (15) is indicative of a state of wear (21) of the friction body (5). The light sensor system (17) senses (120) the reflected light signal (15), wherein the one or more light sensor systems (17) generates an output (16) indicative of the intensity (19) of the reflected light signal (15) to indicate the state of wear (21).

Description

"Brake system with sensor"

Technical Field

[0001] The present disclosure relates to monitoring of a brake system. This includes monitoring the state of components of a brake system including a state of wear and/or temperature. In some examples, this includes monitoring components including the friction body.

Background

[0002] Brake systems, such as a friction brake, may include one movable surface, such as a rotating disc or drum, and a brake lining (of a friction material or friction body) that is movable to contact the rotating disc or drum. The contact between the movable surface and the brake lining results in friction force between the two surfaces which slows rotation of the movable surface.

[0003] In one application, the brake system is incorporated in a motor vehicle. The brake system is an important part of controlling the motor vehicle by selectively causing the vehicle to slow down as well as maintaining a stationary position when at a stop. When activated, the brake system may convert a substantial portion of the kinetic energy of the vehicle to thermal energy.

[0004] The friction between the brake lining and movable surface also results in wearing of one or both surfaces. Typically the brake lining is the consumable component that has the most wear. In a disc brake system, the consumable brake lining is part of a brake pad. In a drum brake system, the consumable brake lining is part of, or on, the brake shoe. Over time, wearing of these components can diminish the performance of the brake system and therefore these components may need to be serviced and replaced periodically. Known techniques include manual inspection using micrometres to check the thickness of the brake lining (or overall thickness of the brake pad or shoe). However manual inspection of these components by a user or mechanic requires labour, be inconvenient, and periodic servicing may be insufficient if the vehicle is used intensively between inspection intervals. [0005] An existing solution to notify a driver of excessively worn brake components includes using metal squealer tabs on brake pads that rub on brake rotors to provide audible feedback to the driver when the brake pads have worn to the end of the service life.

[0006] Furthermore, components of brake system build up heat with sustained use which can lead to brake fade where braking performance is diminished. Therefore managing the temperature of brake components can be increase brake performance.

[0007] Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

[0008] Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each claim of this application.

Summary

[0009] There is disclosed a brake monitoring system comprising: a friction body; a sensor component comprising a fiber bragg grating (FBG), wherein the friction body is coupled with the sensor component to enable the friction body and sensor component to wear together; a light source to transmit a light signal to the fiber bragg grating, wherein the fiber bragg grating is configured to receive the light signal and produce a reflected light signal, wherein an intensity of the reflected light signal is indicative of a state of wear of the friction body; and one or more light sensor systems to sense the reflected light signal, and wherein the one or more light sensor systems generates an output indicative of the intensity of the reflected light signal to indicate the state of wear.

[0010] The friction body and sensor component wear together such that the fibre bragg grating of the sensor component is, at least in part, a sacrificial component that (along with other parts of the friction body, such as a brake pad) wears away with use. [0011] In some examples of the brake monitoring system, the friction body is coupled with the sensor component to enable thermal expansion or contraction of the friction body to change forces applied to the sensor component, and wherein wavelength characteristics of the reflected light signal is indicative of the forces applied to the sensor component, and wherein the output is further indicative of wavelength characteristics of the reflected light signal to indicate a temperature of the friction body.

[0012] There is disclosed a brake monitoring system comprising: a friction body; a sensor component comprising a fiber bragg grating (FBG), wherein the friction body is coupled with the sensor component to enable thermal expansion or contraction of the friction body to change forces applied to the sensor component; and a light source to transmit a light signal to the fiber bragg grating, wherein the fiber bragg grating is configured to receive the light signal and produce a reflected light signal, wherein wavelength characteristics of the reflected light signal is indicative of the forces applied to the sensor component; and one or more light sensor systems to sense the reflected light signal, wherein the one or more light sensor systems generates an output indicative of wavelength characteristics of the reflected light signal to indicate a temperature of the friction body.

[0013] There is disclosed a brake monitoring system comprising: a friction body; a sensor component comprising a fiber bragg grating (FBG), wherein the friction body is coupled with the sensor component to enable thermal conduction between the friction body to the sensor component; a light source to transmit a light signal to the fiber bragg grating, wherein the fiber bragg grating is configured to receive the light signal and produce a reflected light signal, wherein wavelength characteristics of the reflected light signal is indicative of the forces applied at the sensor component due to thermal expansion and contraction; and one or more light sensor systems to sense the reflected light signal, wherein the one or more light sensor systems generates an output indicative of wavelength characteristics of the reflected light signal to indicate a temperature of the friction body.

[0014] In some examples of the brake monitoring system, the wavelength characteristics of the reflected light signal includes a peak wavelength of the reflected light signal, wherein changes to the peak wavelength of the reflected light signal correspond to distortions of the fiber bragg grating due to the forces applied to the sensor component from thermal expansion or contraction of the friction body. [0015] In some examples the brake monitoring system (1) further comprises: a brake pad comprising the friction body embedded, at least in part, with the sensor component; or a brake shoe with the friction body, wherein the sensor component is embedded, at least in part, in the friction body.

[0016] In some examples of the brake monitoring system, the friction body comprises a friction surface and an axis of the fiber bragg grating is perpendicular to the friction surface.

[0017] In some examples of the brake monitoring system, the one or more light sensor systems comprises at least one photodiode configured to generate a voltage signal from the reflected light signal.

[0018] In some examples of the brake monitoring system, the light sensor system comprises a plurality of photodiodes, wherein the photodiodes are configured to sense the intensity of light at respective specified wavelength(s), or specified wavelength ranges.

[0019] In some examples of the brake monitoring system, the one or more light sensor systems comprises: at least one filter configured to filter the reflected light signal at specified wavelength(s), or specified wavelength ranges, to enable at least one of the photodiodes to generate the voltage signal based on the filtered reflected light signal.

[0020] In some examples of the brake monitoring system, the one or more light sensor systems includes a spectrometer.

[0021] In some examples of the brake monitoring system, the light source is configured to transmit the light signal at a specified frequency or wavelength.

[0022] In some examples of the brake monitoring system, the light source is a laser light source configured to transmit a coherent light signal.

[0023] In some examples, the brake monitoring system further comprises: a processor configured to: receive the output from the one or more light sensor systems; and determine the state of wear based on: (i) the intensity of the reflected light signal from the output; and (ii) one or more reference values corresponding to the intensity of reflected light signal for respective reference state(s) of wear. [0024] In some examples the brake monitoring system further comprises: a processor configured to: receive the output from the one or more light sensor systems; and determine the temperature of the friction body based on: (i) the wavelength characteristics of the reflected light signal from the output; and (ii) one or more wavelength reference values corresponding to the wavelength characteristics of reflected light signal for respective temperature (s) of the friction body.

[0025] In some examples, the brake monitoring system further comprises an optical circulator, or beam splitter, optically connected to the light source, the sensor component, and the light sensor systems, wherein the optical circulator, or beam splitter, is configured to: (i) receive the light signal from the light source and pass the light signal to the fiber bragg grating; and (ii) receive the reflected light signal from the fiber bragg grating and pass the reflected light signal to the light sensor systems.

[0026] There is disclosed a brake system comprising: a brake monitoring system described above; a disc connected to a hub; and a caliper having at least one brake pad, wherein the at least one brake pad includes the friction body, and wherein the caliper is selectively operable to enable the friction body to be in contact with the disc.

[0027] There is disclosed a brake system comprising: a brake monitoring system described above; a drum connected to a hub; at least one brake shoe with the friction body; and a wheel cylinder to actuate the at least one brake shoe, wherein the wheel cylinder is selectively operable to enable the friction body to be in contact with the drum.

[0028] There is disclosed a brake pad comprising: a friction body; a sensor component comprising a fiber bragg grating (FBG), wherein the friction body is coupled with the sensor component to : enable the friction body and sensor component to wear together, wherein wear of the sensor component reduces intensity of light reflected by the fiber bragg grating; and/or enable thermal expansion or contraction of the friction body to change forces applied to the sensor component, wherein forces applied to the sensor component varies the wavelength characteristics of light reflected by the fiber bragg grating; and/or enable thermal conduction between the friction body and the sensor component and thermal expansion or contraction changes forces applied to the sensor component, wherein forces applied to the sensor component varies the wavelength characteristics of light reflected by the fiber bragg grating. [0029] There is disclosed a method of determining a state of wear of a friction body, the method comprising: transmitting a light signal to a fiber bragg grating coupled to the friction body; sensing a reflected light signal from the fiber bragg grating; and determining a state of wear of the friction body based on an intensity of the reflected light signal and one or more reference values corresponding to the intensity of the reflected light signal for respective reference state(s) of wear.

[0030] In a further example, the method further comprises a method of state of wear calibration after installation of an unworn friction body to a brake monitoring system. The method of state of wear calibration comprises: transmitting the light signal to the fiber bragg grating coupled to the unworn friction body; sensing the reflected light signal from the fiber bragg grating; determining an intensity of the reflected light signal to provide at least one calibration value for the unworn friction body, and wherein the one or more reference values includes the at least one calibration value.

[0031] There is disclosed a method of determining temperature of a friction body, the method comprising: transmitting a light signal to a fiber bragg grating coupled to the friction body; sensing a reflected light signal from the fiber bragg grating; determining a temperature of the friction body based on wavelength characteristics of the reflected light signal and one or more wavelength reference value(s) corresponding to wavelength characteristics of reflected light signal for respective reference temperatures(s) of the friction body.

[0032] In a further example, the method of determining temperature of a friction body further comprises a method of temperature calibration. The method of temperature calibration comprising: measuring with a temperature sensor, a temperature of the friction body; transmitting the light signal to the fiber bragg grating coupled to the friction body; sensing the reflected light signal from the fiber bragg grating; and determining wavelength characteristics of the reflected light signal while the friction body is at the temperature, wherein the determined wavelength characteristics provide at least one temperature calibration value, and wherein the one or more wavelength reference value(s) and respective reference temperature(s) includes, or is based on, the at least one temperature calibration value and the measured temperature. [0033] In this specification, reference has been made to wavelength characteristics. The person skilled in the art would appreciate the inversely proportional relationship between wavelength characteristics and frequency characteristics. Therefore reference to wavelength characteristics will include reference to the equivalent, and corresponding, frequency characteristics.

Brief Description of Drawings

[0034] Examples of the present disclosure will be described with reference to:

[0035] Fig. 1 is a schematic cross-section of a brake pad with a sensor component;

[0036] Fig. 2 is a schematic of a brake monitoring system in accordance with a first example;

[0037] Fig. 3 is a schematic of another brake monitoring system where the light sensor system includes a photodiode;

[0038] Fig. 4 is a schematic of another brake monitoring system where the light sensor system further includes a filter and two photodiodes;

[0039] Fig. 5 is a schematic of a further brake monitoring system where the light sensor system includes multiple filters and photodiodes to detect reflect light signals in different respective wavelengths;

[0040] Fig. 6 is a flow diagram of a method of determining a state of wear of a friction body and a method of calibration;

[0041] Fig. 7 is a flow diagram of a method of determining a temperature of a friction body and a method of calibration;

[0042] Fig. 8 is a schematic of another brake monitoring system where the light sensor system includes a spectrometer; [0043] Fig. 9 is a graphical representation of measured peak intensity of the reflected light signal in accordance with one experiment;

[0044] Fig. 10 is a continuation of the graphical representation in Fig. 9;

[0045] Fig. 11 is a graphical representation of the state of wear compared to measured voltage in accordance with a second example experiment;

[0046] Figs. 12a and 12b illustrate graphical representations from results of a third example experiment. Fig. 12a includes a table on the state of wear with actual measurements. Fig. 12b is a graph showing the state of wear compared to measured voltage;

[0047] Fig. 13 illustrates a graphical representation of the state of wear compared to voltage in accordance with a fourth example experiment;

[0048] Figs. 14a and 14b illustrate graphical representations from results of a further example experiment to determine temperature. Fig. 14a is a table showing measured temperature compared to sensed wavelengths of reflected light. Fig. 14b illustrates a graph plotting the relationship between temperature and wavelength of reflected light;

[0049] Fig. 15 is a schematic of a disc brake system having a brake monitoring system;

[0050] Fig. 16 is a schematic of a drum brake system having a brake monitoring system;

[0051] Fig. 17 is a graph showing peak intensity from a broadband light source; and

[0052] Fig. 18 is a schematic of another brake monitoring system including a fdter to remove noise from the reflected light signal.

Description of Embodiments

[0053] Overview of a friction body with a sensor

[0054] Fig. 1 illustrates a brake component, in the form of a brake pad 3, having a friction body 5 and a backing plate 12 supporting the friction body 5. A sensor component 7, comprising a fiber bragg grating (FBG) 9, is coupled with the friction body. In this example, the frication body 5 and sensor component 7 are coupled to enable, at least in part, the friction body 5 and the sensor component 7 to wear together during use. That is, at least part of the FBG 9 and the friction body 5 are sacrificial components during use. As the brake pad 3 is used against a disc rotor, and a friction surface 31 of the friction body 5 is worn progressively towards the backing plate 12, the fiber bragg grating 9 is also worn (such as in direction 24 along axis 33). As will be discussed in detail below, as the fiber bragg grating 9 is worn to a smaller size, the ability of the fiber bragg grating to reflect light is reduced. Thus the intensity of reflected light 15 that is reflected by the fiber bragg grating 9 is indicative of wear of the sensor component 7. In turn, this can be used to determine a state of wear 21 of the coupled friction body 9.

[0055] In this example, the sensor component 7 is coupled to the friction body 5 so that thermal expansion 8 or contraction of the friction body 5 change forces applied by the friction body 5 to the sensor component 7. In some specific examples, the fiber bragg grating 9 is embedded in the friction body 5.

[0056] Taking into account the respective coefficients of thermal expansion of the friction body 5 and fiber bragg grating 9, as the temperature of the brake pad 3 changes this alters forces 10 of the friction body 5 against the fiber bragg grating 9. These different forces 10 change the reflection characteristics of the fiber bragg grating 9, including varying the wavelength characteristics 23 of light reflected by the fiber bragg grating 9. In some examples, this can include a general shift in wavelength (or general shift in peak wavelength, or centre wavelength) of the reflected light. Thus determining the reflected wavelength characteristics 23 can be used to determine a temperature 25 (including approximate temperature or temperature range) of the brake pad 3 and friction body 3.

[0057] Although the above example of the brake component is a brake pad 3, it is to be appreciated that the brake component having the friction body can be in other forms, such as a brake shoe. [0058] Overview of a brake monitoring system

[0059] Fig. 2 illustrates an example of a brake monitoring system 1 to monitor a state of wear 21 of the friction body 5 having the sensor component 7 and fiber bragg grating 9. A light source 11 is configured to transmit 110 a light signal 13 to the fiber bragg grating. This can be transmitted via an optical fiber cable 18, or light pipe, that optically connects the light source 11 to the sensor component 7. In this example, a three port optical circulator 20 is configured in the optical path to enable the light signal 13 to be transmitted through to the sensor component 7. The light signal 13 is reflected in the fiber bragg grating 9 to produce a reflected light signal 15 back towards the optical circulator 20. The characteristics of the reflected light signal 15 from the fiber bragg grating 9 can be used to determine a state of wear and/or temperature. The optical circulator 20 is configured to receive the reflected light signal 15 and pass the reflected light signal 15 towards a light sensor system 17.

[0060] The light sensor system 17 is configured to sense 120 reflected light signal 15 to determine characteristics of that reflected light signal 15. In one example, the light sensor signal system 17 is configured to generate an output 16 that is indicative of the intensity 19 of the reflected light signal 15 to indicate a state of wear 21.

[0061] In further examples the light sensor system 17 is configured to generate an output 16 that is indicative of wavelength characteristics 23 (that can include frequency/wavelength) of the reflected light signal 15 and used to indicate a temperature of the friction body (5).

[0062] The light sensor system 17 (that can include multiple light sensor systems 17) can utilise a variety of types of sensors. In some examples, this can include a spectrometer 28 to measure intensity as well as frequency characteristics (as illustrated in Fig. 8).

[0063] In other examples, the light sensor system 17 may include one or more photodiodes 35, 36 to measure intensity of the reflected light 15. In further examples, the light sensor system 17 includes one or more filters to assist in sensing of wavelength characteristics 23 (as illustrated in the examples shown in Figs. 4, 5, and 18). Systems using photodiodes 35, 36 may involve lower cost components compared to high end data acquisition devices such as spectrometers. [0064] Example of a brake monitoring system for determining a state of wear

[0065] Fig. 3 illustrates an example of a brake monitoring system configured to determine the state of wear. This example shares similar features to the overview example of Fig. 2 but with additional details of the components including the light sensor system 17.

[0066] Light source 11

[0067] The light source 11, in this example, a light source configured to transmit the light signal 13 at a specified frequency/wavelength. Specifically, this can include a laser light source configured to transmit a coherent light signal. In this example, the laser light sources emits light with a wavelength of around 1550nm. An advantage of a laser light source is to provide a consistent light signal 13 that can increase accuracy of the monitoring system. The coherent light signal from the laser light source may also assist improved signal transmission and separation at the fiber circulator 20 (or beam splitter).

[0068] An example of a laser light source is a LPS 1550 pigtailed laser diode offered by Thorlabs, Inc, that outputs laser light at a nominal wavelength of 1550nm.

[0069] It is to be appreciated that in alternative examples, the light source 11 may transmit a broad range of frequency/wavelengths.

[0070] Optical fiber cable 18 or light pipe

[0071] One or more optical fiber cable 18 enables transmission of the light signal 13 and/or reflected light signal 15. These are configured to carry light signals with minimal loss. In this example, there are three optical fiber cables 18, a first connecting the light source 11 to the fiber circulator 20 where the first optical fiber cable in this configuration carries the light signal 13. The second optical fiber cable 18” connecting the fiber circulator 20 to the sensor component 7 and fiber bragg grating 9, where the second optical fiber cable 18’ carries both: (i) the light signal 13 in the direction towards the fiber bragg grating 9; and (ii) the reflected light signal 15 in the direction away from the fiber bragg grating 9. The third optical fiber cable 18’” connect the fiber circulator 20 to the light sensor system 17, such as the photodiode 35. [0072] 3 Port Fiber circulator

[0073] An optical circulator 20 optically connected (via optical fiber cable 18) to the light source 11, the sensor component 7, and the light sensor systems 17. The optical circulator 20 is configured to: (i) receive the light signal 13 from the light source 11 and pass the light signal 13 to the fiber bragg grating 9; and (ii) receive the reflected light signal 15 from the fiber bragg grating 9 and pass the reflected light signal 15 to the light sensor systems 17. In some examples, an equivalent function of the optical circulator 20 is achieved with a beam splitter.

[0074] An example of a 3 port fiber circulator includes is 6015-3-APC offered by Thorlabs, Inc.

[0075] Brake pad 3 or brake shoe

[0076] The friction body 5 may be part of a brake pad 3 (for use in disc brakes) or a brake shoe for use in drum brakes. Fig. 1 illustrates a brake pad 3 having a friction body 5 embedded, at least in part, with the sensor component 7. Thus as the friction body 5 is worn (in direction 24 along axis 33) by a rotor, the sensor component 7 is also worn.

[0077] It is to be appreciated that for a brake shoe, the friction body 5 of the brake shoe similarly has a sensor component that is embedded, at least in part, in the friction body. Similarly, the sensor component wears with the friction body as the brake shoe is worn against the drum of a drum brake system (which will be described separately below).

[0078] Sensor component 7 and Fiber Bragg Grating 9

[0079] The sensor component 7 includes a fiber bragg grating 9. Fiber bragg gratings reflect light rays of particular wavelengths and transmits others. In this example, the fiber bragg grating is selected to reflect the light signal 13 from the light source 11. Thus for a system where the nominal wavelength from the light source 11 is around 1550nm, the fiber bragg grating should be selected to reflect light at, or around, 1550nm. [0080] The fiber bragg grating may be embedded into an aperture 14 at the friction body 5 and set into that position by resin. Thus as the brake component wears, this wears the friction body, resin, and fiber bragg grating 9.

[0081] Referring to Fig. 1, the friction body 5 includes a friction surface 31 and an axis of the fiber bragg grating 9 is perpendicular to the friction surface 31. This aids in consistent wear of the fiber bragg grating that is proportional the state of wear of the friction body 5. The result is more accurate determination of the state of wear by the brake monitoring system 1.

[0082] As the fiber bragg grating 9 wears in direction 24 along the axis 33, this results in reduced capacity for the fiber bragg grating 9 to reflect the light signal 13. Thus as the friction body 5 and fiber bragg grating 9 is progressively worn the reflected light signal 15 diminishes in intensity (assuming other things being equal, such as constant intensity of the light signal 13).

[0083] The reflective characteristics of the fiber bragg grating 9 can also change with pressure and distortion of the fiber bragg grating 9. For example, as the temperature increases, the sensor component 7 (including the fiber bragg grating 9) can stretch due to strain forces. This can cause the peak reflected wavelength (or spectrum of wavelengths) to change. In other examples, as the friction body 5 increases in temperature, the material of the friction body 5 expands and can apply forces against the fibre bragg grating 9 that can also affect the reflected wavelength(s) of the fibre bragg grating 9. This can include distortion of the fiber bragg grating 9 due to the thermal expansion and contraction of the friction body 5. Thus temperature can affect the wavelength characteristics of the reflected light signal 15, which in turn, can be used to indicate temperature of the friction body 5.

[0084] In some examples, the sensor component 7 is embedded in the friction body 5 such that they are thermally coupled (i.e. thermal conduction between the friction body 5 and sensor component). In turn, thermal expansion or contraction at the sensor component 7 (due at least in part to changes in temperature at the friction body 5) cause changes to wavelength characteristics 23 of the reflected light signal 15. Thus in some examples, the sensor component 7 does not solely rely on the thermal expansion or contraction of the friction body 5 but rather the expansion and contraction of the case/body of the sensor component 7. [0085] In some examples, the sensor component 7 may be thermally coupled to the friction body 5 by another material. In some examples, this other material may be flexible and resilient such that expansion or contraction of the friction body 5 does not impart significant forces directly on the sensor component 7. Instead, a casing of the sensor component 7 that surrounds the fiber bragg grating 9 imparts changes in forces to the fiber bragg grating 9 as the casing expands and contracts.

[0086] In further examples, the friction body 5 and sensor component 7 may, in practice, be considered a single body that expands and contracts together.

[0087] Examples of the fiber bragg grating 9 includes regular sensors (Acrylate coating fiber) and high temperature sensors (e.g. copper coating fiber, or gold coating fiber).

[0088] In some examples, the fiber bragg grating 9 can include a wideband FBG filter that is configured to reflect light from a relatively wide band of frequencies and to maximise reflected light. This can be desirable to provide a sensor component 7 that can operate with a variety of light sources 11 . This can include different light sources 11 that transmit light signals 13 of different respective frequencies, or alternatively a light signal 13 than comprises multiple frequencies (or range of frequencies). In some examples, this may enable an example brake pad 3 to be used with different models and configurations of brake monitoring systems 1 that can be advantageous for supply and other logistics reasons.

[0089] In some examples, the fiber bragg grating 9 is configured to reflect light in the wavelength range of 1200nm to 1700nm. In further examples, the fiber bragg grating 9 is configured to reflect light in the 1500nm to 1600nm range. In particular examples, the fiber bragg grating 9 is configured to reflect light around 1505nm wavelength.

[0090] Operation around the 1550nm wavelength range (and other ranges mentioned above) may be desirable as these wavelengths are used in light sources 11 for telecommunications thus components of such light sources 11 (as well as associate FBG 9, optical fiber cable 18, etc.) may be used or adapted for the system 1. This can include commercial off the shelf components. [0091 ] Light sensor system 17

[0092] The light sensor system 17 is configured to detect an intensity 19 of the reflected light signal 15 and/or wavelength characteristics of the reflected light signal. In some examples, the light sensor system 17 includes a spectrometer 28.

[0093] However, a spectrometer can be prohibitively expensive and complex for this application and alternative sensor systems can be more practical. Furthermore, required accuracy of the state of wear and/or temperature in practical applications may be low and less accurate, but simpler and more cost effective sensors, may be adequate.

[0094] Fig, 3 illustrates a system where the light sensor system 17 includes a photodiode 35 that is configured to receive the reflected light signal 15 and generate a voltage signal 37 (that is linked to the intensity of the reflected light signal). An example of a photodiode includes PDAA50B2 offered by Thorlabs, Inc. A voltage reader 22 reads the voltage signal 37 and generates an output 16 (such as the voltage of the voltage signal 37). This output 16, in this example, is proportional (or can be otherwise mapped to) the intensity of the reflected light signal 15 and, in turn can be used to indicate a state of wear 21. In this example, the output 16 indicative of the voltage is sent for signal processing at a processor 51. The processor 51 may determine the state of wear 21 from the output 16 together with formula(s), lookup table, historical data, libraries, or training data, computer generated models, etc.

[0095] In some examples, the light sensor system includes a plurality of photodiodes 35, 36 as illustrated in the examples in Fig. 4 and Fig. 5. In this system 1, the plurality of photodiodes 35, 36 are configured to sense the intensity of light at respective wavelength(s), or respective wavelength ranges. This can be useful for detecting reflected light signals 15 where the wavelength has shifted due to changes in temperature (or other factors that may shift the reflected light signal such as forces imparted on the fiber bragg grating 9).

[0096] Filters 41

[0097] In some examples, the photodiodes 35, 36 are configured to detect different wavelengths by use of one or more filters 41. [0098] Referring to Fig. 4, the light sensor system 17 further includes an additional 3 port fiber circulator 26 that receives the reflected light signal 15. This additional 3 port fiber circulator 26 in turn passes the reflected light signal 15 to a fiber bragg grating filter 41. The fiber bragg grating filter 41 is configured to: i. Enable some specified wavelengths (or wavelength ranges) to pass through the fiber bragg grating filter 41; and ii. Reflect other specified wavelengths (or wavelength ranges) back to the additional 3 port fiber circulator 26.

[0099] In this example, the other specified wavelengths that pass include a first filtered reflected light signal 43 that is then passed to a light connected first photodiode 35. Thus the first photodiode 35 is configured to sense intensity of light 19 at specified wavelengths (or range of wavelengths) that correspond to wavelengths that are allowed to pass the fiber bragg grating filter 41.

[0100] The reflected specified wavelengths at the fiber bragg grating filter 41 include a second filtered reflected light signal 43 ’ that passes back through the additional 3 port fiber circulator 26 and to a second photodiode 36. Thus the second photodiode 36 is configured to sense intensity of light at specified wavelengths (or range of wavelengths) that correspond to wavelengths that are reflected by the fiber bragg grating filter 41. In some examples, the light reflected by the fiber bragg grating filter is around a specified wavelength and may be considered as a notch filter (to stop light particular wavelengths in the first filtered reflected light signal 43 to be received at the first photodiode 35).

[0101] The respective voltage signals 37, 37’ from the photodiodes 35, 37 are then transmitted to voltage reader 22 so that the intensity of light at the different wavelength components can be determined. In this example, a multichannel voltage reader 22’ is used although it can be appreciated that in alternative configurations each photodiode 35, 36 can have a respective individual voltage reader 22. The output 16 from the voltage reader 22 is then received by a processor 51 for processing. As the intensity of light at different wavelengths (or wavelength ranges) are sensed, the processor 51 can process this data to determine wavelength characteristics 23 of the reflected light signal 15 from the sensor component 7, which can include peak wavelength to aid determination of temperature as discussed in another section below.

[0102] Fig. 5 illustrated another example including three photodiodes 35, 36, 38 to enable sensing of light at three respective specified wavelengths, or wavelength ranges. This is similar to the example in Fig. 4, but with a further 3 port fiber circulator 26’ and a further fiber bragg grating filter 41’. The further fiber bragg grating filter 41 ’ is configured to further separate wavelengths from the second filtered reflected light signal 43 ’ received from the first fiber bragg grating filter 41. Thus this configuration can enable the processor to receive data on the intensity of light in three separate wavelengths (or wavelength bands) that can increase accuracy in determination of wavelength characteristics of light reflected from the fiber bragg grating 9 of the sensor component 7.

[0103] It is to be appreciated that in other examples, alternative filter types can be used. These can include one or more combinations of notch filters, band pass filters, band stop filters, etc.

[0104] Processor 51 and reference and signal processing

[0105] The brake monitoring system 1 can also include a processor 51 configured to receive 130 and process the output 16 from the light sensor system 17. The processor 51 is also associated with memory and/or other data storage (not shown) that can include software, configuration and calibration data, reference values, training data, libraries, etc.

[0106] The processor 51 is configured to process the output to determine a state of wear 21 of the friction body 5 and/or a temperature 25 of the friction body 5. In some examples, the processor 51 determines 140 the state of wear 21 based on: the intensity 19 of the reflected light signal 15 from the output 16; and one or more reference values 53 corresponding to the intensity of reflected light signal for a respective reference state of wear 55.

[0107] In some examples, the processor 51 is an ESP32 system on a chip microcontroller to receive and process the signals 37, 37’ and/or output 16.

[0108] The reference values may be derived from testing data by the manufacturer where they have measured actual wear of a reference friction body (such as with a micrometre, physical measurement caliper, etc.) and recorded this with a corresponding intensity of reflected light signal from a sensor component of that reference friction body. In some examples, the measurements of light intensity and/or wavelength characteristics at the manufacturer are made with spectrometers or other high accuracy sensors to increase data quality for the reference values.

[0109] In some examples, these measurements may be provided as reference values in a lookup table. In other examples, these measurements are modelled (such as by linear interpolation, polynomial interpolation, etc.), and reference values are based on these models.

[0110] Similarly, wavelength characteristics of the reflected light with respective reference temperatures or temperature ranges can be measured by the manufacturer (or by a testing facility on behalf of the manufacturer) to obtain reference values for the brake monitoring system 1 to determine temperature of the friction body 5.

[0111] In some examples, additional electrical fdters may be used to filter out electrical noise. This may include providing an electrical filter to exclude (or reduce) noise from the voltage signals 37, 37’ (that are the output from the photodiodes 35). In some examples, the electrical filter may be configured or adapted to pass anticipated electrical signals 37 of the FBG 9, light source 11, and photodiode 35 combination of the system 1. In particular, passing electrical signals 37 that can be utilised for wear and temperature determination and excluding other signals that is likely to be noise. In some examples, such filters are low-pass electrical filters.

[0112] In some alternative examples, electrical filters may be used to filter noise from the output 16 of the voltage readers 22.

[0113] Example method 100 of calibration and determining state of wear

[0114] Fig. 6 illustrates one example method 100 of determining a state of wear.

[0115] The illustrated method may include an initial method of state of wear calibration after installation of an unworn friction body 5 to the brake monitoring system 1 (although this calibration may not be required every time). Calibration may be desirable as the actual friction body 5 in the brake monitoring system 1 may be different to the ideal or reference standard. Thus calibration measurements are recorded of a newly installed friction body 5 with 100% of material, and such calibration measurements are used to offset, or take into account, small variations specific to the brake monitoring system 1 compared to the reference system at the manufacturer.

[0116] The method of state of wear calibration can include transmitting 101 the light signal to the fiber bragg grating 9 coupled to the unworn friction body 5. The reflected light signal 15 from the fiber bragg grating is then sensed 102, such as by the light sensor system 7 or other calibration instrument capable of measuring the reflected light signal 15. Calibration further includes determining 104 an intensity 19 of the reflected light signal 15 to provide at least one calibration value 52 for the unworn friction body 5. One or more reference values 53 includes, or is based on, the at least one calibration value 52.

[0117] After optional calibration, the brake monitoring system 1 can be used to determine wear as illustrated in Fig. 6. The method includes: transmitting 110 a light signal to a fiber bragg grating 9 coupled to the friction body 5; and sensing 120 the reflected light signal 15 from the fiber bragg grating 9 with the light sensor system 17. The processor receives 130 an output from the light sensor system and determines 140 a state of wear 21 of the friction body 5 based on: (i) the intensity 19 of the reflected light signal 15; and (ii) one or more reference values 53 corresponding to the intensity of the reflected light signal for respective reference state(s) of wear 55.

[0118] Example of a brake monitoring system to determine temperature

[0119] It is to be appreciated that the system 1 can be configured to functionally determine both the state of wear and the temperature. Or in some alternative examples, only monitoring temperature. Determination of temperature may be achieved with examples of the system described above where sufficient information regarding wavelength characteristics can be derived or otherwise obtained by the light sensor system. This can include the examples shown in Figs. 4 and 5 that include multiple photodiodes to sense temperature at different respective wavelengths, or other examples that include a spectrometer 28. [0120] Example method 100 of calibration and determining temperature

[0121] Fig. 7 illustrates one example method 100 of determining temperature of the friction body. Some of the steps are similar to, or the same, as the steps in the method of determining the state of wear and are provided with the same reference numerals. It is to be appreciated that the methods may be performed concurrently or in conjunction.

[0122] The illustrated method may include an optional initial method of temperature calibration of the friction body 5. This may be done with the friction body 5 at an ambient temperature, or at a known temperature to obtain consistent, stable, and/or accurate data. Similar to calibration for state of wear, calibration measurements are used to account for differences between a particular friction body and those of a reference system at the manufacturer.

[0123] The method of temperature calibration can include measuring 106, with a temperature sensor 61, a temperature 62 of the friction body 5 (for example, 20 degrees Celsius). In some alternatives, the temperature sensor 61 may indirectly measure the temperature of the friction body 5 by measuring the ambient temperature (with the assumption that the friction body 5 resting in the ambient environment has a similar temperature). The method includes transmitting 107 a light signal to the fiber bragg grating 9 coupled to the friction body 5 and sensing 108 the reflected light signal 15 from the fiber bragg grating. Calibration further includes determining 109 wavelength characteristics 64 of the reflected light signal 15 while the friction body 5 is at the temperature 62 to provide at least one temperature calibration value 65. This can involve determining the peak wavelength, centre wavelength, etc. of the reflected light signal 15. As an example, this may include determining that the peak wavelength is around 1545nm (in contrast to the nominal 1550nm from an example laser light source).

[0124] The temperature calibration value 65 and the measured temperature is used to update, or adjust, one or more wavelength reference value(s) 57 and respective temperatures. For example, say laboratory or manufacturer’s testing measures a peak wavelength around 1540nm for a temperature of 20 degree Celsius. However, during calibration, the measurements are 1545nm for a temperature of 20 degrees Celsius for that particular system. The difference measured during calibration (in this case of 5nm) can then be used to adjust the reference values to provide more accurate real world temperatures readings.

[0125] Such wavelength reference value(s) 57, and associated respective temperature(s), are used during normal operation to determine the temperature of the friction body 5 as illustrated in Fig. 7. Similar to the above described method of wear measurement, this includes: transmitting 110 a light signal to a fiber bragg grating 9 coupled to the friction body 5; sensing 120 the reflected light signal 15 from the fiber bragg grating 9 with the light sensor system 17, and receiving 130 the output from the light sensor system 17. The difference with the earlier example is that the processor determines 150 a temperature of the friction body based on the sensed wavelength characteristics of the reflected light signal 15 that is compared with the one or more wavelength reference values 57 (which is based on, or includes wavelength characteristics that are linked to respective reference temperatures).

[0126] Examples results from experiments

[0127] Examples of experimental results and modelling of the state of wear and temperature of the brake monitoring system 1 are described below.

[0128] First example of intensity of reflected light signal

[0129] Figs. 9 and 10 show a graphical representation of the measured peak intensity 19 of the reflected light signal 15 in one experiment. This is based on a system 1 similar to the one shown in Fig. 8 where a spectrometer 28 is use to obtain data on reflected light signal 15. In particular, this shows a series of graphs 200 with results from a spectrometer with peak 201 intensity (amplitude) of the reflected light signal 15 on a vertical axis 203 and the corresponding wavelength on the horizontal axis 205.

[0130] The series of graphs 200 progressively show a decline in peak intensity of the reflected light signal as a prototype brake pad is worn. To the left of each graph is a corresponding numerical representation 207 of the maximum peak in dBm (decibel- milliwatts) that declines through the series. [0131] This experimental data illustrates the concept that as the sensor 7 (including fiber bragg grating 9) wears off, the peak reflected spectrum decreases. In addition, the area 211 under the curve 209 also decreases that, in turn, will give a lower detected voltage level.

[0132] In some examples, it may be desirable to look at wavelengths around a specified range 213 of wavelengths (in particular those around the wavelength of light from a laser light source 11). This can be important to exclude light from other sources (such as visible sunlight, thermal radiation, etc.). Therefore a range gate may be used to isolate measurements of light from a wavelength/frequency range. In systems using a spectrometer 28, this may be achieved digitally be excluding data from wavelengths outside that range. In other examples, one or more filters may be used to exclude wavelengths outside the desired frequency range. This may include using a band pass filter, or combinations of other filter types to enable the light sensor system 17 to detect the reflected light in the desired spectrum.

[0133] Second example of intensity of reflected light signal

[0134] Fig. 11 shows a graphical representation 220 of measurements from a second example experiment. This graph illustrates a state of wear of the sensor 7 on the horizontal axis 221 unworn at the left hand side and with progressive wear towards the right hand side. The vertical axis 223 represents measured voltage from the light sensor system 17 that is indicative of intensity of the reflected light 15.

[0135] The curve 225 show the voltage drop as the sensor 7 is progressively worn, which indicates intensity is decreasing. In the results of this particular prototype example, the curve 225 is not linear. This may be attributable to manufacturing issues. For example, there may be unevenness in the gratings such that there is different reflective capacity at different parts of the sensor.

[0136] It is to be appreciated that even though this curve is not linear, if such a curve 225 is consistent in manufactured brake systems 1, this data can be still be modelled or used in reference values to provide accurate determination of states of wear. [0137] Third example of intensity of reflected light signal

[0138] Figs. 12a and 12b illustrate graphical representations of results from a third example experiment. Fig. 12a includes a table 230 of recorded measurements of the thickness of the friction body 5 in the right hand column 231. The left hand column 233 include wear values where “0” corresponds to an unworn friction body 5 with a thickness of 3.84mm. Wear value “10” corresponds to a worn friction body 5 where the thickness has been worn down to 1.019mm.

[0139] Fig. 12b illustrates a graph 235 that plots the measured voltage 236 (on the vertical axis) against the various states of wear 233 (on the horizontal axis). This graph 235 includes the actual results plotted on a curve 237. This graph 235 also includes a line 238 fitted to the results. This line 238 may be fitted to the results in a number of ways. This can include simple linear regression, orthogonal regression, etc.

[0140] The line 238 can be used as, or to generate, reference values for determinations of the state of wear. It is to be appreciated in other examples, a curve may be fitted to the actual data and may use polynomial regression (or other techniques) to model the curve. It is to be appreciated that modelling reference values may also include interpolating additional data points.

[0141] Fourth example of intensity of reflected light signal

[0142] Fig. 13 illustrates a graphical representation of results from a fourth example. This includes the state of wear 233 on the vertical axis. The horizontal axis indicates voltages measured at the light sensor system that represents the intensity of reflected light. In this example the results are fitted to a line 241.

[0143] Fifth example showing change in wavelength with temperature

[0144] Figs. 14a and 14b illustrates the results from a further experiment that shows changes in peak wavelength caused by changes in temperature. The table 250 in Fig. 14a shows values of measured temperature (made by a separate sensor such as an infrared thermometer, thermographic camera, etc.) of the friction body 5. These plurality of temperature measurements are paired with respective detected peak wavelengths 253 (which is indicated in nanometres) at the light sensor system 7. As shown in the right hand column of the table 250, the detected peak wavelengths 253 increase in length as the temperatures increases. At the initial ambient temperature, the detected wavelength is at 1554.15nm which is close to the nominal peak wavelength of 1550nm from the example light source 11. As the temperature increases, such as to 250 degrees Celsius, the detected wavelength increases to 1559.006nm.

[0145] The data from this experiment is provided in the graph 260 shown in Fig. 14b. The horizontal axis 261 represents the temperature in Celsius and the vertical axis 263 represents the wavelength in nanometres. The data plotted on curve 265 shows a roughly linear relationship between temperature and change in peak wavelength. A fitted line 267 may be modelled to provide wavelength reference values 57 (corresponding to values of the vertical wavelength axis 263) and respective reference temperatures 59 (corresponding to values on the horizontal temperature axis).

[0146] Advantages

[0147] Advantage of examples of the described brake monitoring system 1 include the ability to continuously measure brake pad wear in real-time (or near real time). This can include the degree to which the friction body 5 is worn as opposed to known systems that may provide binary information on whether the brake is serviceable or not serviceable (such as with metal squealer tabs). This is also in contrast to traditional systems where manual inspection of the friction body 5 requires cooling down of the brakes and removal of wheels to allow manual inspection. In some examples, this system may also allow fleet monitoring of brake systems in vehicles remotely from an operations centre.

[0148] Another advantage of examples of the brake monitoring system is measurement of wear with a granularity of sub millimetre accuracy. In some examples, this can even be to micrometre levels of accuracy.

[0149] Advantages of further examples of the brake monitoring system 1 include accurate measurement of temperature of the friction body 5 which has been traditionally hard to accurately measure whilst in use. The measurements, due to shift in wavelength, may provide more accurate data on the temperature at the disc and brake pad interface. [0150] Variation

[0151] Application to brake systems

[0152] Fig. 15 illustrates a disc brake system 2 comprising a brake monitoring system 1 that monitors at least one brake pad 3 having the friction body 5. The brake system 2 also includes a disc 75 (also known as a rotor) connected to a hub 76. A caliper 77 with at least one brake pad 3 is selectively operable to enable the friction body to be in contact with the disc 75 for braking.

[0153] The brake monitoring system 1 can provide state of wear data of the friction body 5 and/or the temperature.

[0154] Fig. 16 illustrates a drum brake system 4 that includes a brake monitoring system 1 that monitors at least one brake shoe 73 having a friction body 5. A drum 78 is connected to a hub 76 that rotate with each other and are operatively connected to the wheel of a vehicle. A wheel cylinder 79 actuates the at least one brake shoe wherein the wheel cylinder 79 is selectively operable to enable the friction body 5 to be in contact with the drum 78 for braking. For illustrative clarity, the brake shoe 73 connected to the monitoring system 1 at the left hand side is separated from the drum 78 in this figure but it is to be appreciated that the brake shoe 73 will be included inside the drum 78 as shown on the right hand side.

[0155] Retrofit kit

[0156] In some examples, the brake monitoring system 1 is a retrofit kit that can be installed in existing vehicles and/or brake systems. The retrofit kit includes the light source, light sensor system 17 and replacement brake pad 3/brake shoes 73 than include the sensor component 7. The retrofit kit may also include the optical fiber cable 18, optical circulator 20, and processor 51. In some examples, the kit may also include a communication interface to enable wear and temperature data to be transmitted from the brake monitoring system 1 to a mobile communication device such as a smart phone, tablet. In other examples, this data may be communicated to in vehicle electronics via wireless, or wired, or optical means. In further examples, the data can be transmitted to a diagnostic tool for mechanics, or other maintenance operators to monitor. [0157] Machine learning with training data

[0158] In examples where a spectrometer 18 is used, determination of the peak wavelength is made by the instrument itself -but such sensors can be complex and expensive. In the examples illustrated in Figs. 4 and 5, photodiodes 35, 36, 38 (which are relatively inexpensive) are configured to measure intensity of reflected light at different respective wavelengths (or wavelength bands). The various combinations of intensities between the different photodiodes 35, 36, 38 may be used to determine the peak wavelength. However, raw data received from such individual photodiode sensors may not be sufficient in itself to determine the peak wavelength. Thus machine learning algorithms may be applied to train and build mathematical models so that the peak wavelengths can be determined based on sensed combination of intensities from the different photodiodes 35, 36, 38.

[0159] In some examples, this may include supervised learning with training data based on data received from the photodiodes 35, 36, 38 and the desired output of particular peak wavelength based on wavelength measurements by a spectrometer 18. Alternatively, a further model will base the desired output on the actual temperature of the friction body (with temperature measured by a separate thermometer).

[0160] In some examples, training may include training a neural network to generate a model to enable estimation of temperature of the friction body 5 based on received outputs 16. This may be important as various factors can affect the outputs 16. These include:

• Variance in manufacturing of components of the system;

• The amount of wear on the FBG may affect wavelength characteristics 23 of the reflected light signal 15 in a non-linear manner or in a way that can be simply modelled. Thus determination of temperature may include, amongst other things, data on the state of wear and/or the intensity 19 of the reflected light signal.

• Certain patterns can be used to enhance the models. For example, the change of the state of wear is generally gradual consistent and results in permanent changes in intensity of the reflected light (and voltage signal 37). However, changes in temperature can be relatively fast, temporary, and sudden (i.e. in the space of seconds and minutes). Thus using machine learning may be useful in identifying such patterns to enhance accuracy of the models and predicted temperature and state of wear.

[0161] It is to be appreciated that other machine learning approaches can be applied.

[0162] Broadband light source 11

[0163] In some alternative examples, the light source 11 may provide a broadband laser light signal instead of a single peak at a nominated frequency or wavelength. Such alternative examples may have advantageous applications to give a strong light signal 13 (and resultant reflected light signal 15) even if the wavelength shifts to high (or varying) temperatures. This can ensure that the light signals 13 are within the reflector operating frequency/wave length range of the fiber bragg grating 9. Fig. 17 illustrates a graph 81 of peak intensity versus wavelength and where a broadband light source 11 will has a curve 83 that has a wide band of peak intensity.]

[0164] Noise reduction filter

[0165] Fig. 18 illustrates an alternative example brake monitoring system 1 for measuring the state of wear 21. In this system 1, a fiber bragg grating filter 42 is provided to reduce noise in the reflected light signal 15. This may include noise from light that has wavelengths that fall outside the expected wavelengths from the light source 11. Thus the reflected light signal 15 is filtered by the fiber bragg grating filter 42 (which in this configuration reflects wavelengths from a desired wavelength band) to produce a filtered light signal 44 that is then detected by the photodiode 35. This example differs from the example illustrated in Fig. 4 in that light of some wavelengths (such as the equivalent of the first filtered reflected light signal 43 in Fig. 4) will not be detected by the system illustrated in Fig. 18. This alternative system, by design, does not detect such wavelengths as they are considered to be noise. It is to be appreciated that other filters can be used (including filters that “pass” specified wavelengths instead of reflecting as provided in the fiber bragg grating filter 42).

[0166] It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

CLAIMS:

1. A brake monitoring system (1) comprising:

- a friction body (5);

- a sensor component (7) comprising a fiber bragg grating (FBG) (9), wherein the friction body (5) is coupled with the sensor component (7) to enable the friction body (5) and sensor component (7) to wear together;

- a light source (11) to transmit (110) a light signal (13) to the fiber bragg grating (9), wherein the fiber bragg grating (9) is configured to receive the light signal (13) and produce a reflected light signal (15), wherein an intensity (19) of the reflected light signal (15) is indicative of a state of wear (21) of the friction body (5); and

- one or more light sensor systems (17) to sense (120) the reflected light signal (15), and wherein the one or more light sensor systems (17) generates an output (16) indicative of the intensity (19) of the reflected light signal (15) to indicate the state of wear (21).

2. A brake monitoring system (1) according to claim 1, wherein the friction body (5) is coupled with the sensor component (7) to enable thermal expansion (8) or contraction of the friction body (5) to change forces (10) applied to the sensor component (7), and wherein wavelength characteristics (23) of the reflected light signal (15) is indicative of the forces (10) applied to the sensor component (7), and wherein the output (16) is further indicative of wavelength characteristics (23) of the reflected light signal (15) to indicate a temperature (25) of the friction body (5).

3. A brake monitoring system (1) comprising:

- a friction body (5); - a sensor component (7) comprising a fiber bragg grating (FBG) (9), wherein the friction body (5) is coupled with the sensor component (7) to enable thermal expansion (8) or contraction of the friction body (5) to change forces (10) applied to the sensor component (7);

- a light source (11) to transmit (110) a light signal (13) to the fiber bragg grating (9), wherein the fiber bragg grating (9) is configured to receive the light signal (13) and produce a reflected light signal (15), wherein wavelength characteristics (23) of the reflected light signal (15) is indicative of the forces (10) applied to the sensor component (7); and

- one or more light sensor systems (17) to sense (120) the reflected light signal (15), wherein the one or more light sensor systems (17) generates an output (16) indicative of wavelength characteristics (23) of the reflected light signal (15) to indicate a temperature (25) of the friction body (5).

4. A brake monitoring system (1) comprising:

- a friction body (5);

- a sensor component (7) comprising a fiber bragg grating (FBG) (9), wherein the friction body (5) is coupled with the sensor component (7) to enable thermal conduction between the friction body to the sensor component (7);

- a light source (11) to transmit (110) a light signal (13) to the fiber bragg grating (9), wherein the fiber bragg grating (9) is configured to receive the light signal (13) and produce a reflected light signal (15), wherein wavelength characteristics (23) of the reflected light signal (15) is indicative of the forces (10) applied at the sensor component (7) due to thermal expansion and contraction; and

5. A brake monitoring system (1) according to any one of claims 2 to 4, wherein the wavelength characteristics (23) of the reflected light signal (15) includes a peak wavelength of the reflected light signal (15), wherein changes to the peak wavelength of the reflected light signal (15) correspond to distortions of the fiber bragg grating (9) due to the forces (10) applied to the sensor component (7) from thermal expansion (8) or contraction of the friction body (5).

6. A brake monitoring system (1) according to any one of the preceding claims further comprising:

- a brake pad (3) comprising the friction body (5) embedded, at least in part, with the sensor component (7); or

- a brake shoe (73) with the friction body (5), wherein the sensor component is embedded, at least in part, in the friction body (5).

7. A brake monitoring system (1) wherein the friction body (5) comprises a friction surface (31) and an axis (33) of the fiber bragg grating (9) is perpendicular to the friction surface (31).

8. A brake monitoring system (1) according to any one of the preceding claims wherein the one or more light sensor systems (17) comprises at least one photodiode (35) configured to generate a voltage signal (37) from the reflected light signal (15).

9. A brake monitoring system (1) according to claim 8 wherein the light sensor system (17) comprises a plurality of photodiodes (35, 36), wherein the photodiodes (35, 36) are configured to sense the intensity of light (19) at respective specified wavelength(s) (40), or specified wavelength ranges.

10. A brake monitoring system (1) according to claim 8 or 9 wherein the one or more light sensor systems (17) comprises:

- at least one filter (41) configured to filter the reflected light signal (15) at specified wavelength(s) (40), or specified wavelength ranges, to enable at least one of the photodiodes (35) to generate the voltage signal (37) based on the filtered reflected light signal (43).

11. A brake monitoring system (1) according to any one of claims 1 to 7 wherein the one or more light sensor systems (17) includes a spectrometer.

12. A brake monitoring system (1) according to any one of the preceding claims wherein the light source (11) is configured to transmit the light signal (13) at a specified frequency or wavelength.

13. A brake monitoring system (1) according to claim 12 wherein light source (11) is a laser light source configured to transmit a coherent light signal (13).

14. A brake monitoring system (1) according to any one of the preceding claims, when dependent on claim 1, further comprising:

- a processor (51) configured to:

- receive (130) the output (16) from the one or more light sensor systems (17); and

- determine (140) the state of wear (21) based on:

- the intensity (19) of the reflected light signal (15) from the output (16); and

- one or more reference values (53) corresponding to the intensity of reflected light signal for respective reference state(s) of wear (55).

15. A brake monitoring system (1) according to any one of the preceding claims, when dependent on claims 2 or 3, further comprising:

- a processor (51) configured to:

- determine (150) the temperature (25) of the friction body (5) based on: - the wavelength characteristics (23) of the reflected light signal (15) from the output (16); and

- one or more wavelength reference values (57) corresponding to the wavelength characteristics of reflected light signal for respective temperature(s) (59) of the friction body (5).

16. A brake monitoring system (1) according to any one of the preceding claims further comprising an optical circulator (20), or beam splitter, optically connected to the light source (11), the sensor component (7), and the light sensor systems (17), wherein the optical circulator (20), or beam splitter, is configured to:

- receive the light signal (13) from the light source (11) and pass the light signal (13) to the fiber bragg grating (9); and

- receive the reflected light signal (15) from the fiber bragg grating (9) and pass the reflected light signal (15) to the light sensor systems (17).

17. A brake system (2) comprising: a brake monitoring system (1) according to any one of claims 1 to 16, a disc (75) connected to a hub (76); and a caliper (77) having at least one brake pad (3);

- wherein the at least one brake pad (3) includes the friction body (5), and

- wherein the caliper (77) is selectively operable to enable the friction body (5) to be in contact with the disc (75).

18. A brake system (4) comprising: a brake monitoring system (1) according to any one of claims 1 to 16, a drum (78) connected to a hub (76); at least one brake shoe (73) with the friction body (5), and a wheel cylinder (79) to actuate the at least one brake shoe (73), wherein the wheel cylinder (79) is selectively operable to enable the friction body (5) to be in contact with the drum (78).

19. A brake pad (3) comprising:

- a friction body (5);

- a sensor component (7) comprising a fiber bragg grating (FBG) (9), wherein the friction body (5) is coupled with the sensor component (7) to:

- enable the friction body (5) and sensor component (7) to wear together, wherein wear of the sensor component (7) reduces intensity of light reflected by the fiber bragg grating (9); and/or

- enable thermal expansion (8) or contraction of the friction body (5) to change forces (10) applied to the sensor component (7), wherein forces (10) applied to the sensor component (7) varies the wavelength characteristics (23) of light reflected by the fiber bragg grating (9); and/or

- enable thermal conduction between the friction body (5) and the sensor component (7) and thermal expansion or contraction changes forces applied to the sensor component (7), wherein forces (10) applied to the sensor component (7) varies the wavelength characteristics (23) of light reflected by the fiber bragg grating (9).

20. A method of determining a state of wear (21) of a friction body (5), the method comprising:

- transmitting (110) a light signal to a fiber bragg grating (9) coupled to the friction body (5); - sensing (120) a reflected light signal (15) from the fiber bragg grating (9); and

- determining (140) a state of wear (21) of the friction body (5) based on an intensity (19) of the reflected light signal (15) and one or more reference values (53) corresponding to the intensity of the reflected light signal for respective reference state(s) of wear (55).

21. A method of determining a state of wear (21) of a friction body (5) according to claim 20, further comprising a method of state of wear calibration after installation of an unworn friction body (5) to a brake monitoring system (1), method of state of wear calibration comprising:

- transmitting (101) the light signal to the fiber bragg grating (9) coupled to the unworn friction body (5); sensing (102) the reflected light signal (15) from the fiber bragg grating (9);

- determining (104) an intensity (19) of the reflected light signal (15) to provide at least one calibration value (52) for the unworn friction body (5), and

- wherein the one or more reference values (53) includes the at least one calibration value (52).

22. -A method of determining temperature (25) of a friction body (5), the method comprising: transmitting (110) a light signal to a fiber bragg grating (9) coupled to the friction body (5); sensing (120) a reflected light signal (15) from the fiber bragg grating (9); and determining (150) a temperature (25) of the friction body (5) based on wavelength characteristics (23) of the reflected light signal (15) and one or more wavelength reference value(s) (57) corresponding to wavelength characteristics of reflected light signal for respective reference temperatures(s) (59) of the friction body (5).

23. A method of determining temperature (25) of a friction body (5) according to claim

22, further comprising a method of temperature calibration, method of temperature calibration comprising: measuring (106) with a temperature sensor (61), a temperature (62) of the friction body (5)T

- transmitting (107) the light signal to the fiber bragg grating (9) coupled to the friction body (5); sensing (108) the reflected light signal (15) from the fiber bragg grating (9); and

- determining (109) wavelength characteristics (64) of the reflected light signal (15) while the friction body (5) is at the temperature (62),

- wherein the determined wavelength characteristics (64) provide at least one temperature calibration value (65), and wherein the one or more wavelength reference value(s) (57) and respective reference temperature(s) (59) includes, or is based on, the at least one temperature calibration value (65) and the measured temperature (62).