AU2023201226A1

AU2023201226A1 - Wear monitoring system for lubricant-immersed disc brakes

Info

Publication number: AU2023201226A1
Application number: AU2023201226A
Authority: AU
Inventors: Rodney Tink
Original assignee: TINK RODNEY PETER
Current assignee: Tink Rodney Peter
Priority date: 2022-03-07
Filing date: 2023-02-28
Publication date: 2023-09-21

Abstract

A wear monitoring system for a lubricant-immersed disc brake comprises a measuring member, wherein the measuring member is configured to engage with an actuating member of the disc brake to move with the actuating member in use. A displacement sensor measures movement of the measuring member. A system controller is connected to the displacement sensor to determine a wear condition of the disc brake based on information received from the displacement sensor. A sensor housing comprises a fluid-tight cavity that contains the displacement sensor and at least part of the measuring member. The measuring member extends through an opening in a side of the sensor housing to engage with the actuating member. A seal arrangement is provided relative to the opening for preventing ingress of lubricant from the lubricant-immersed disc brake into the fluid-tight cavity through the opening. 1/16 0 C)N N C%4 0 N C~j N~r

Description

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WEAR MONITORING SYSTEM FOR LUBRICANT-IMMERSED DISC BRAKES

Field

[0001] The present invention relates to brake wear monitoring systems and, more particularly, to a system for monitoring the wear condition of lubricant-immersed disc brakes.

Background

[0002] Vehicle brakes often include a means for measuring the current extent of wear on the brakes. For example, lubricant-immersed disc brakes, as commonly used on mining, construction and forestry vehicles, may be provided with wear pin indicators for measuring the thickness of the discs in the brake disc stack. Wear is manually measured by immobilising the vehicle, draining the brake's lubricant and then inserting the pin into the disc stack via an inspection or drainage port so that the pin makes contact with an actuating member of the stack. For example, an innermost end of the pin may be inserted to make contact with the brake piston or with a moveable brake disc in the stack. The position of the opposite end of the pin that protrudes from the port may then be visually compared to a reference point. The distance between the pin end and the reference point provides an indicative measurement of the thickness of each brake disc. Some disc brakes allow for other types of inspection devices, such as thickness gauges, to be inserted directly into an inspection port to determine brake wear. The foregoing methods can be difficult and time consuming to perform, particularly in heavy-duty vehicles where the inspection port is often in a hard-to-reach location. Draining the brake's lubricant before taking each measurement, and subsequently replenishing the lubricant, is also a time consuming and skilled task.

[0003] Thermal expansion of brake components also substantially affects the accuracy of wear measurements. The disc stack and axle housing of a brake can expand and contract significantly with fluctuating temperature conditions. Lubricant-immersed multi-disc brakes are particularly sensitive to temperature changes because the lining discs that hold the layers of lubricant between the discs in the stack are thin and have a low tolerance for wear. Even small fluctuations in operating temperatures can substantially affect the thicknesses and positions of the brake discs relative to the lining discs. The wear condition of the lining discs can only, therefore, be accurately measured when the brake has completely cooled down and is at ambient temperature.

[0004] Brake wear predictions can be calculated by taking wear measurements at regular intervals, plotting the results and then trending the data to predict when the brake discs will reach their minimum thickness. This is an involved and time consuming task to perform.

[0005] The preceding discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.

Summary

[0006] According to the present invention, there is provided a wear monitoring system for a lubricant-immersed disc brake, wherein the wear monitoring system comprises: a measuring member configured to engage with an actuating member of the disc brake to move with the actuating member in use; a displacement sensor for measuring movement of the measuring member; a system controller connected to the displacement sensor, wherein the system controller is operatively configured to determine a wear condition of the disc brake based on information received from the displacement sensor; and a sensor housing comprising a fluid-tight cavity that contains the displacement sensor and at least part of the measuring member, wherein the measuring member extends through an opening in a side of the sensor housing to engage with the actuating member, and wherein a seal arrangement is provided relative to the opening for preventing ingress of lubricant from the disc brake into the fluid-tight cavity through the opening.

[0007] The seal arrangement may comprise one or more annular seal members disposed around the measuring member.

[0008] The one or more annular seal members may comprise rubber gaskets.

[0009] The measuring member may comprise a pin configured for linear translational movement, and the displacement sensor may comprise a linear displacement sensor.

[0010] The linear displacement sensor may comprise a potentiometer.

[0011] The pin may be biased against the actuating member.

[0012] The pin may be biased against the actuating member by a spring disposed in the fluid-tight cavity.

[0013] The wear monitoring system may comprise at least one temperature sensor for measuring a temperature of the disc brake and/or one or more parts of the wear monitoring system. In such examples, the system controller executes an algorithm that compensates for thermal expansion of the disc brake and/or parts when determining the wear condition using information received from the temperature sensor.

[0014] The wear monitoring system may further comprise sensors for determining when the disc brake is fully applied and in a non-dynamic condition. In such examples, the system controller is configured to determine the wear condition only when information received by the system controller from the sensors indicates that the disc brake is fully applied and in the non-dynamic condition.

[0015] The sensors may comprise: a brake application sensor for determining if a brake piston of the disc brake is fully applied; and a motion sensor for determining if rotatable brake discs of the disc brake are rotating or stationary.

[0016] The brake application sensor may comprise a force sensor for measuring a braking force exerted by the brake piston on the disc brake.

[0017] The disc brake may be a spring applied hydraulically released brake that is operatively held open by hydraulic fluid in use. In such examples, the brake application sensor may comprise a pressure sensor for measuring the pressure of the hydraulic fluid.

[0018] The wear monitoring system may comprise a storage device and the system controller may periodically store wear measurements corresponding to the wear condition on the storage device.

[0019] The system controller may be configured to determine a predicted future wear condition of the disc brake based on the wear measurements stored on the storage device.

[0020] In a first operating mode, the system controller may determine that the wear condition has increased when the information received from the displacement sensor indicates that the actuating member has moved away from the sensor housing.

[0021] In a second operating mode, the system controller may determine that the wear condition has increased when the information received from the displacement sensor indicates that the actuating member has moved toward the sensor housing.

[0022] The system controller may be switchable between the first and second operating modes selectively by a user.

[0023] The actuating member may comprise a brake piston of the disc brake. In another example, the actuating member may comprise a non-rotatable disc of the disc brake that moves translationally to engage with a rotatable disc of the disc brake.

[0024] The present invention also provides a lubricant-immersed disc brake that comprises the wear monitoring system described above.

[0025] The lubricant-immersed disc brake may be a multi-disc brake.

[0026] A wear monitoring system for a lubricant-immersed disc brake is also disclosed, wherein the wear monitoring system comprises: a measuring member configured to engage with an actuating member of the disc brake to move with the actuating member in use; a displacement sensor for measuring movement of the measuring member; a system controller connected to the displacement sensor, wherein the system controller is operatively configured to determine a wear condition of the disc brake based on information received from the displacement sensor; and one or more sensors for determining when the disc brake is fully applied and in a non-dynamic condition, wherein the system controller is configured to determine the wear condition only when information received by the system controller from the one or more sensors indicates that the disc brake is fully applied and in the non-dynamic condition.

Brief Description of Drawings

[0027] Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 is a cross sectional side elevation view of a wear monitoring system for a fluid-immersed disc brake according to an example embodiment of the invention; Figure 2 is a cross sectional side elevation view of a sensor assembly of the wear monitoring system; Figure 3 is an enlarged cross sectional side elevation view of the sensor assembly; Figure 4 is an enlarged cross sectional side elevation view of a front portion of the sensor assembly; Figure 5 is an isometric view of the sensor assembly; Figure 6 is a side elevation view of the sensor assembly installed in a fluid-immersed multi-disc brake;

Figure 7 is a further side elevation view of the sensor assembly and multi-disc brake of Figure 6; Figure 8 is side elevation view of a vehicle wheel axle arrangement that comprises a pair of the sensor assemblies installed in a pair of fluid-immersed disc brakes of the wheel axle arrangement; Figure 9 is a cross sectional side elevation view of a wear monitoring system for a fluid-immersed disc brake according to a further example embodiment of the invention; Figure 10 is a side elevation view of a sensor assembly of the wear monitoring system of Figure 9; Figure 11 is side elevation view of a vehicle wheel axle arrangement that comprises a pair of the sensor assemblies of Figure 10 installed in a pair of fluid-immersed disc brakes of the wheel axle arrangement; Figure 12 is an isometric view of the sensor assembly of Figure 10 shown installed in a disc brake of the wheel axle arrangement of Figure 11; Figure 13 is a plan view of the wheel axle arrangement of Figure 11; Figure 14 is a circuit diagram of a wear monitoring system for a fluid-immersed disc brake according to an example embodiment of the invention; Figure 15 shows a visual display of a human machine interface included in a wear monitoring system for a fluid-immersed disc brake according to an example embodiment of the invention; and Figure 16 is a cross sectional view of a vehicle brake comprising a wear monitoring system for a fluid-immersed disc brake according to a further example embodiment of the invention.

Description of Embodiments

[0028] Referring to Figure 1, an example embodiment of the present invention provides a wear monitoring system 10 for a lubricant-immersed disc brake 12. The wear monitoring system 10 comprises a measuring member 20, wherein the measuring member 20 is configured to engage with an actuating member 16 of the disc brake 12 to move with the actuating member 16 in use, and a displacement sensor 24 for measuring movement of the measuring member 20. A system controller 30 is connected to the displacement sensor 24 that is operatively configured to determine a wear condition of the disc brake 12 based on information received from the displacement sensor 24. The wear monitoring system 10 also comprises a sensor housing 18 that comprises a fluid-tight cavity 32 that contains the displacement sensor 24 and at least part of the measuring member 20. The measuring member 20 extends through an opening 36 in a side of the sensor housing 18 to engage with the actuating member 16. A seal arrangement 40 is provided relative to the opening 36 and the measuring member 20 for preventing ingress of lubricant from the disc brake 12 into the fluid-tight cavity 32 through the opening 36.

[0029] More particularly, in the example depicted the brake 12 is a lubricant-immersed multi-disc brake of the type that is commonly used in heavy-duty mining, construction and forestry vehicles. The sensor housing 18, measuring member 20 and displacement sensor 24, together, form a sensor assembly 14 of the wear monitoring system 10. The particular actuating member 16 of the disc brake 12 that the measuring member 20 engages with is the brake piston of the brake 12. The brake 12 includes a brake stack that comprises a plurality of rotatable brake discs and a plurality of non-rotatable brake discs. The non-rotatable brake discs are arranged in an interleaved, and axially aligned, configuration with the rotatable brake discs. Thin layers of lubricant, typically oil, are held between the non-rotatable and rotatable brake discs by a set of lining discs. The brake piston 16 is connected to the set of non-rotatable brake discs and is configured to actuate the non-rotatable brake discs such that they move linearly toward, to interact with, the rotatable brake discs. When the brake 12 is applied by a driver of the vehicle, the interaction between the two sets of discs puts the thin layer of lubricant between each pair of discs into a shear condition.

The resultant friction that is caused by the fluid shearing inhibits rotation of the rotatable brake discs.

[0030]The wear monitoring system 10 is advantageously configured for lubricant-immersed multi-disc brakes. In this regard, referring to Figures 2-4, the fluid-tight internal cavity 32 of the sensor housing 18 contains the operative electromechanical components of the sensor assembly 14. The housing 18 may be made of a strong, impervious material such as aircraft grade aluminium having an ingress protection (IP) rating of at least IP 67. The measuring member may comprise an elongate measuring pin that is disposed partially inside of the cavity 32. The pin 20 is slidably supported by the housing 18 for linear translational movement relative to the housing 18.

[0031] In the example depicted, the opening 36 comprises an elongate channel 36 that extends through a side wall of the sensor housing 18. The channel 36 provides an entryway into the cavity 32 from the outside of the sensor housing 18. The pin 20 may comprise an elongate end portion 34 that extends through the channel 36 to exit the sensor housing 18. In this configuration, the end portion 34 comes into contact with the brake piston 16 when the pin 20 is moved linearly away from the cavity 32 through the channel 36.

[0032] The system 10 may comprise a biaser 22 which engages the pin 20 and causes the end portion 34 to be biased against the brake piston 16. In the example depicted, the biaser 22 comprises a coil spring disposed in the fluid-tight cavity 32. The coil spring 22 comprises sufficient stored energy such that the end portion 34 applies a gentle and consistent bearing force against a surface or contact portion of the brake piston 16. In other examples, in lieu of a biaser 22, a peripheral tip of the pin 20 may be connected to the brake piston 16 - e.g., by a pivot joint connection - to cause the pin 20 to move with the brake piston 16 in use. In other examples, the pin 20 may engage with one or more actuating members 16 of the disc brake 12 other than the brake piston 16. In one embodiment, the pin 20 may engage with one of the non-rotatable (linearly moveable) discs in the brake stack.

[0033] The displacement sensor 24 may comprise a linear displacement sensor, such as a linear potentiometer, that measures the position of the pin 20 relative to the housing 18 at any point in time. In one example, the potentiometer 24 may have an overall linear travel range of approximately 10 millimeters, an infinite resolution with repeatability precision of 0.01 millimeters, an expected life of x10 / 6 cycles, an overall resistance of 2kD ±20% and an allowed travel velocity of 5 m/s on traction and 1 m/s on extension. The spring-loaded pin 20 is preferably configured such that it remains biased against the brake piston 16 over the full operational range of the piston 16 regardless of the brake's wear condition. For heavy-duty vehicles, the required operational range is typically 3-9 millimeters. The sensor 24 may comprise a transducer that generates a 4-20mA signal corresponding to the measured position.

[0034] The channel 36 that receives the pin 20 comprises a seal arrangement 40 that provides a fluid-tight seal between the pin 20 and channel 36. The seal arrangement 40 may comprise an annular seal member, such as a rubber-based gasket, disposed circumferentially around the pin 20. The gasket 40 is located in an annular compartment formed in an internal cylindrical wall of the channel 36. The annular compartment extends around the longitudinal axis of the channel 36 so that the gasket 40 is held in abuting contact with the pin 20. In examples, the seal arrangement 40 may be made of a synthetic rubber and fluoropolymer elastomer such as FKM, FPM or the commercially-available Viton@ product. Other possible materials for the seal arrangement 40 include nitrile butadiene rubber (NBR) or any other material providing a fluid tight seal that is compatible with the necessary fluid type and temperature requirements.

[0035] The seal arrangement 40 ensures that the internal cavity 32 remains fluid-tight during use and, therefore, shields the electromechanical components housed inside the cavity 32 from the heated oil of the lubricant-immersed multi-disc brake 12.

[0036] The system 10 may also comprise at least one temperature sensor 26 for measuring a temperature of the disc brake 12 and/or wear monitoring system 10 including internal parts thereof, such as the temperature of the sensor assembly's 14 internal componentry. The system controller 30 is connected to the temperature sensor 26 to receive temperature information therefrom. The system controller 30 executes an algorithm that compensates for thermal expansion of the disc brake 12 and/or sensor assembly 14 when determining the wear condition of the disc brake 12 in response to the temperature information. The temperature sensor 26 may be a transducer generating a 4-20mA signal corresponding to the measured temperature. The temperature sensor 26 may comprise a thermocouple, a resistance temperature detector (RTD), a negative temperature coefficient (NTC) thermistor, a semiconductor-based sensor or another suitable temperature monitoring device.

[0037] In other examples, each of the sensors 24, 26 may generate digital signals that encode the relevant measured readings. The digital signals may be transmitted to the system controller 30 via a communications bus. For example, the sensors 24, 26 and the controller 30 may be connected together via an internal packet-switched network implementing an industry standard message-based control protocol such as CANbus or Modbus.

[0038] In the example depicted, the temperature sensor 26 is arranged within the internal cavity 32 of the sensor housing 18 and is, therefore, able to measure the temperature of the pin 20, cavity 32 and/or housing 18 of the sensor assembly 14. The temperature sensor 26 is also advantageously positioned proximal to the mounting point of the sensor assembly 14 on the axle housing of the brake 12. In this position, the temperature sensor 26 may accurately measure the operative components of the disc brake 12, such as the axle housing, brake axle, brake piston 16 and the non-rotatable and rotatable discs of the brake 12. In other examples, the temperature sensor 26 may be attached (or one or more additional temperature sensors may be attached) to the axle housing of the disc brake 12. Preferably, the temperature sensor 26 has an operating temperature range of at least -30 degrees Celsius to 150 degrees Celsius.

[0039] The displacement sensor 24 and temperature sensor(s) 26 may each be connected to the system controller 30 by a wired or wireless communication means. In the example depicted, the two sensors 24, 26 are connected to the controller 30 by a pair of respective cables 42 that carry the 4-2mA sensor output signals. The cables 42 exit the housing 18 via an aperture toward the rear end of the housing 18. Rubber sealing elements may be provided in the aperture to prevent the ingress of solid and liquid contaminants. The system 10 may comprise a set of the sensor assemblies 14 installed in a set of vehicle brakes 12 that are each connected to the controller 30. For example, Figure 14 shows an arrangement of four vehicle brakes 12 having four respective sensor assemblies 14 connected to a single master controller 30. The master controller 30 may form part of a broader vehicle control and telemetry system that receives and processes inputs from a variety of vehicle sensors, such as pressure, temperature, speed, acceleration, fluid level and position sensors.

[0040] Figure 5 provides a non-sectional view of the sensor assembly 14. The pin outwardly extends from one end of the sensor assembly 14 and the two signal-carrying cables 42 extend from an opposite end. As shown in Figures 6 to 8, in this configuration the sensor assembly 14 is particularly suited for inboard lubricant-immersed disc brakes 12 that are inwardly disposed on a wheel axle assembly 44 relative to the axle's wheel hubs 46. As best shown in Figure 8, in this arrangement each sensor assembly 14 is disposed on the axle 44 housing between a disc brake 12 and wheel hub 46 of the axle 44. The pin 20 of each sensor assembly 14 is arranged so that it contacts the brake piston 16 of a disc brake 12 on the side of the piston 16 that is connected to the brake disc pack. In such examples, the system controller 30 may determine that the wear condition of a disc brake 12 has increased when the information received from the relevant displacement sensor shows that the brake piston 16 of the disc brake 12 has moved toward the relevant sensor assembly 14. The sensor housing 18 is attached to the brake axle housing and concentrically to the pin 20. This arrangement allows the sensor housing 18 to be indexed to keep the sensor assembly 14 free from damage that may occur as a result of debris passing underneath the vehicle during use.

[0041] Figures 9 to 12 show a further example of the sensor assembly 14 that is configured for use with wheel-mounted lubricant-immersed disc brakes 12 that are outwardly disposed on the wheel hubs 46 of a wheel axle assembly 44. As best shown in Figure 11, in this configuration each disc brake 12 is disposed on the axle 44 housing between a sensor assembly 14 and a wheel hub 46 on the axle 44. The pin 20 of each sensor assembly 14 is arranged so that it contacts the brake piston 16 of a disc brake 12 on the side of the piston 16 that comprises the spring of the brake disc pack. In such examples, the system controller 30 may determine that the wear condition of a disc brake 12 has increased when the information received from the relevant displacement sensor shows that the brake piston 16 has moved away from the relevant sensor assembly 14. The sensor assembly 14 in Figures 9 to 12 is operatively equivalent to the example shown in Figures 1-5 but includes some modifications to allow the sensor assembly 14 to be installed in wheel-mounted lubricant-immersed disc brakes 12. For example, the sensor housing 18 is more compact in size and the signal-carrying cables 42 extend upward from an uppermost wall of the sensor housing 18. The sensor assembly 14 also comprises a pair of annular oil sealing members 40 that are arranged around the pin 20 and spaced apart from one another. The system controller 30 may comprise two selectable operating modes that enable an operator to configure the system 10 for use with inboard or wheel-mounted lubricant-immersed disc brakes 12 respectively during installation of the system 10.

[0042]The skilled person will appreciate that wear measurements of optimum accuracy can be taken when the disc brake 12 is fully applied and in a non-dynamic condition. More particularly, optimum wear measurements are taken when the rotatable brake discs of the disc brake 12 are stationary and when the brake piston 16 is applying its maximum braking force. Under these conditions, the thickness of the oil film between each pair of interacting brake discs will have negligible impact on the wear measurements that are taken. This is because when the discs are rotating relative to each other, the lubricant forms thin layers of film hydro-dynamically between pairs of adjacent discs. These layers of film have a measurable thickness. When disc rotation stops, the fluid film is no longer hydrodynamic and the fluid is "squeezed" out such that the discs come together and almost make contact with each other, save for a microscopic layer of residual fluid. The brake stack in motion, therefore, has a larger overall dimension than when it is at a standstill. To compensate for this, the system 10 may, therefore, also comprise (i) a motion sensor (not shown) for determining if the rotatable brake discs of the disc brake 12 are rotating or stationary, and (ii) a brake application sensor (not shown) for determining if and when the brake piston 16 is fully applied onto the brake stack. For the brake application sensor, a force sensor (not shown) may be used for measuring the braking force that is currently being exerted by the brake piston 16 on the stack. The algorithm executed by the system controller 30 may use information received from the motion and force sensors when determining the wear condition of the brake 12. In examples where the system 10 is installed in a vehicle equipped with spring-applied, hydraulically released (SAHR) brakes, a pressure sensor of the SAHR brake may be used for the brake application sensor. The measurements taken by the pressure sensor may be used in lieu of the force sensor measurements as it can be assumed that maximum braking force is applied by the SAHR brake when 0 bars of hydraulic fluid pressure is measured. In other examples, in lieu of the motion sensor that directly monitors the state of the rotatable brake discs, one or more vehicle speed or wheel axle speed sensors may be used to determine, indirectly, if the rotatable brake discs are stationary or not.

[0043] The system 10 may also comprise a storage device and the system controller 30 may be configured to calculate wear measurements corresponding to the wear condition of the disc brake 12 and to store these measurements on the storage device periodically. The system controller 30 may also be configured to trend the stored wear measurements to determine a predicted future wear condition of the disc brake 12. In further examples, the storage device may also be used by a collision avoidance system (CAS) installed in the vehicle. When the CAS initiates an automatic brake application to avoid a collision between the vehicle and another vehicle or person, the position of each brake piston may be measured and stored in real time. The stored piston positions may subsequently be used offline to analyse and verify the performance of the brakes during collision avoidance events and to determine if vehicle acceleration during such events is within an acceptable range.

[0044] The controller 30 may comprise a processor, a programmable logic controller (PLC), a programmable logic array (PLA) or similar electronic controller device. The controller 30 may comprise a single integrated electronic controller device or multiple controller devices (including multiple processors or PLAs) connected together via a bus, network or similar communications system. In examples where the controller 30 comprises a processor, the processor may be implemented as a single integrated circuit, two or more integrated circuits, or may be a component of a multi-chip module. The storage device may comprise a volatile or non-volatile memory device, such as RAM, ROM, EEPROM or flash memory or any other device capable of storing data. The storage device may be integral with the controller 30 or it may be an external storage device in communication with the controller 30 via a communication means.

[0045] Referring to Figure 15, the system 10 may also comprise a human machine interface (HMI) 50 that is used to display current and predicted wear measurements calculated by the system controller 30. In the example screen that is depicted, the HMI 50 displays a current brake disc thickness 52, in millimeters, for each of four brakes of a vehicle. The HMI 50 also displays a current brake temperature 54, in degrees Celsius, for each brake. An icon is arranged above each displayed value that turns red if the relevant value is outside a safe operational range or minimum value and turns green if the measurement is within the safe operational range or minimum value. In other examples, the system controller 30 may display a date, or a duration of time, for each brake that corresponds to the point in time at which the relevant brake thickness will fall below a safe operational minimum based on a predicted future wear condition calculated by the system controller 30. The system controller 30 may also compare the brake thickness and temperature measurements received from each brake 12. Based on these comparisons, and trended future brake conditions, the system controller 30 may detect brake anomalies prior to brake failure and report such anomalies via the HMI 50.

[0046] In use, when the monitoring system 10 is first installed into a brake 12, the dimensions of the piston 14 and/or discs of the brake 12 will be manually measured and the system 10 will be calibrated accordingly. For a new brake pack that has not undergone any wear, the monitoring system 10 will be calibrated such that it recognises that the pack has 100% of its useful life remaining. Based on data provided by the manufacturer of the vehicle's axle 44, an end-of-life limit will be set and displayed on the HMI 50 when the minimum disc thickness has been reached. This may be displayed as 0% of useful life remaining on the HMI 50. The monitoring system 10 may advantageously be installed and operated in a manner that does not interfere with the original equipment manufacturer's (OEM) standard method for taking manual wear measurements for the relevant vehicle brake pack.

[0047] Referring to Figure 16, there is shown a vehicle brake assembly 58 comprising a wear monitoring system according to a further example embodiment of the invention. The wear monitoring system comprises a sensor assembly 14 comprising a housing 18 that contains a slidable measuring pin 20 that bears against the brake piston 66 of the brake assembly 58. The brake assembly 58 also comprises a brake carrier 60, brake housing 62, intermediate piece 64, piston 66, inner disc 68, outer disc 70, a first O-ring 72, a second O-ring 74, a screw 76, screw plug 78, seal ring 80, a third O-ring 82, spring set 84, connection piece 86, seal ring 88, bleeder valve 90, a first sealing set 92, a second sealing set 94, guide ring 96, screw plug 98, seal ring 100, face seal 102 and a warning label 104.

[0048] The wear monitoring system includes a system controller that executes an algorithm that compensates for thermal expansion of the vehicle brake 58 and the sensor assembly 14 when determining the wear condition of the vehicle brake 58. An example algorithm will now be described. The end of the measuring pin 20 that is located away from the brake piston 66 outwardly protrudes by a distance that is labelled 'X'shown in the enlargement 14 provided in Figure 16. The skilled person will appreciate that the bottom right corner of the brake 58 always stays in the same position regardless of any temperature changes. By using this corner as a reference point, the amount by which distance 'X' changes in proportion to temperature changes can be calculated using the formule:

X@T = X@20-c - ajLIAT + a 2nL 2AT + a 3mAT + a4L 4AT + a5 L5AT

[0049] In the above formulae, X@' is the value of X at the current temperature when the parking brake is fully applied; 'X@2 0 c' is the value of X at 20°C when the parking brake is fully applied; 'AT is the difference between the current temperature and 20°C; 'a, & Ll' are the coefficient of thermal expansion and length of the brake housing, at 20°C, respectively; 'a 2 & L 2 ' are the coefficient of thermal expansion and width of the inner discs 68, at 20°C, respectively; 'a3 & L3

' are the coefficient of thermal expansion and length of the outer discs 70, at 20°C, respectively; 'a 4 & L 4 ' are the coefficient of thermal expansion and length of the brake piston 66, at 20°C, respectively; 'a5 & L5 ' are the coefficient of thermal expansion and length of the measuring pin 20, at 20°C, respectively; 'n' is the number of inner discs 68 that make up the brake 58; '' is the number of outer discs 70 that make up the brake 58.

[0050] The brake discs 68, 70 are considered fully worn when X@ 2 0 C= 0, as calibrated by the relevant axle manufacturer. The formulae can, therefore, be rearranged to solve for X@ 2 0 -c as follows:

X@20'c = X@T+ aILIAT - a 2nL 2AT- a3 mLAT - a 4L4A T - a5 L5 hT

:*. X@20c = X@T+ (ajL - a 2nL2 - a3 mL 3 - a 4L4 - a5 L)AT

[0051]The above approach enables temperature compensation to be implemented in the brake wear measurements to improve the accuracy of the wear monitoring system. The value of X@Tis measured by the brake wear sensor in real time. Compensating for the current temperature allows X@ 2 0 'C to be determined, and when this equals 0 it can be determined that the brakes are worn.

[0052] Now that example embodiments of the wear monitoring system have been described, it will be apparent that it provides a number of advantages over the prior art, including the following:

(i) The operative electromechanical components of the sensor assembly 14 are contained in a fluid-tight cavity 32 inside a sensor housing 18. The housing

18 prevents these components from coming into contact with the heated and pressurised lubricant of the disc brake 12;

(ii) The measuring pin exits the fluid-tight housing 18 via a channel 36 to engage with an actuating member 16 of the disc brake 12. The channel 36 is fluid tight by virtue of a seal arrangement 40 that prevents ingress of brake lubricant into the housing 18. The particular configuration of the fluid-tight cavity 32 and seal arrangement 40, therefore, allows the wear monitoring system to be used with lubricant-immersed disc brakes;

(iii) In embodiments, the wear monitoring system determines the wear condition of the disc brake 12 only when the brake is fully applied and in a non-dynamic condition. This ensures that the wear measurements are of optimal accuracy for lubricant-immersed disc brakes;

(iv) In embodiments, the wear monitoring system algorithmically compensates for thermal expansion of the disc brake 12 and/or sensor assembly 14 when calculating wear condition measurements.

[0053] Prior art brake wear monitoring systems are not suitable for lubricant-immersed disc brakes of the type that the present invention has been developed for. For example, the following patent publications disclose brake wear sensor systems that are only designed for dry, friction type brake stacks: (i) International (PCT) patent application no. PCT/US2017/044779 published on 8 February 2018 (publication no. WO/2018/026745); (ii) International (PCT) patent application no. PCT/GB2006/000062 published on 13 July 2006 (publication no. WO/2006/072802); (iii) European patent application no. 06120276.8 published on 14 March 2007 (publication no. EP 1 762 746 A2); and (iv) European patent application no. 07118594.6 published on 23 April 2008 (publication no. EP 1 914 135 Al). None of the systems disclosed in the foregoing patent publications are capable of working with oil immersed brakes that operate by fluid shearing.

[0054] For the purpose of this specification, the word "comprising" means "including but not limited to", and the word "comprises" has a corresponding meaning. It is to be understood that, if any prior art is referred to herein, such reference does not constitute an admission that the prior art forms a part of the common general knowledge in the art, in Australia or any other country.

[0055] The above embodiments have been described by way of example only and modifications are possible within the scope of the claims that follow.

Claims

1. A wear monitoring system for a lubricant-immersed disc brake, comprising: a measuring member configured to engage with an actuating member of the disc brake to move with the actuating member in use; a displacement sensor for measuring movement of the measuring member; a system controller connected to the displacement sensor, wherein the system controller is operatively configured to determine a wear condition of the disc brake based on information received from the displacement sensor; and a sensor housing comprising a fluid-tight cavity that contains the displacement sensor and at least part of the measuring member, wherein the measuring member extends through an opening in a side of the sensor housing to engage with the actuating member, and wherein a seal arrangement is provided relative to the opening for preventing ingress of lubricant from the disc brake into the fluid-tight cavity through the opening.

2. The wear monitoring system according to claim 1, wherein the seal arrangement comprises one or more annular seal members disposed around the measuring member.

3. The system according to claim 2, wherein the one or more annular seal members comprise rubber gaskets.

4. The wear monitoring system according to any one of the preceding claims, wherein the measuring member comprises a pin configured for linear translational movement, and wherein the displacement sensor comprises a linear displacement sensor.

5. The system according to claim 4, wherein the linear displacement sensor comprises a potentiometer.

6. The wear monitoring system according to claim 4 or 5, wherein the pin is biased against the actuating member.

7. The wear monitoring system according to claim 6, wherein the pin is biased against the actuating member by a spring disposed in the fluid-tight cavity.

8. The wear monitoring system according to any one of the preceding claims, wherein: the wear monitoring system comprises at least one temperature sensor for measuring a temperature of the disc brake and/or one or more parts of the wear monitoring system; and wherein the system controller executes an algorithm that compensates for thermal expansion of the disc brake and/or parts when determining the wear condition using information received from the temperature sensor.

9. The wear monitoring system according to any one of the preceding claims, further comprising one or more sensors for determining when the disc brake is fully applied and in a non-dynamic condition, and wherein the system controller is configured to determine the wear condition only when information received by the system controller from the sensors indicates that the disc brake is fully applied and in the non-dynamic condition.

10. The wear monitoring system according to claim 9, wherein the sensors comprise: a brake application sensor for determining if a brake piston of the disc brake is fully applied; and a motion sensor for determining if rotatable brake discs of the disc brake are rotating or stationary.

11. The wear monitoring system according to claim 10, wherein the brake application sensor comprises a force sensor for measuring a braking force exerted by the brake piston on the disc brake.

12. The wear monitoring system according to claim 10, wherein the disc brake is a spring applied hydraulically released brake that is operatively held open by hydraulic fluid in use, and wherein the brake application sensor comprises a pressure sensor for measuring a pressure of the hydraulic fluid.

13. The wear monitoring system according to any one of the preceding claims, comprising a storage device, wherein the system controller periodically stores wear measurements corresponding to the wear condition on the storage device.

14. The wear monitoring system according to claim 13, wherein the system controller is configured to determine a predicted future wear condition of the disc brake based on the wear measurements stored on the storage device.

15. The wear monitoring system according to any one of the preceding claims, wherein in a first operating mode the system controller determines that the wear condition has increased when the information received from the displacement sensor indicates that the actuating member has moved away from the sensor housing.

16. The wear monitoring system according to any one of claims 1 to 14, wherein in a second operating mode the system controller determines that the wear condition has increased when the information received from the displacement sensor indicates that the actuating member has moved toward the sensor housing.

17. The wear monitoring system according to claim 15 and 16, wherein the system controller can be switched between the first and second operating modes selectively by a user.

18. The wear monitoring system according to any one of the preceding claims, wherein the actuating member comprises a brake piston of the disc brake.

19. A lubricant-immersed disc brake, comprising the wear monitoring system according to any one of the preceding claims.

20. The lubricant-immersed disc brake according to claim 19, wherein the lubricant-immersed disc brake is a multi-disc brake.