GB2558770A

GB2558770A - Controller for a braking system of a vehicle

Info

Publication number: GB2558770A
Application number: GB1719657.7A
Authority: GB
Inventors: Enness Michael; Clegg David; Hampson Ric
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2016-11-30
Filing date: 2017-11-27
Publication date: 2018-07-18
Also published as: GB2558769A; GB201719657D0; GB201719656D0; WO2018099864A1; GB201620252D0; GB2558769B; GB2557195A

Abstract

Disclosed is a temperature sensor 60 that includes a thermocouple 66 arranged to measure a temperature of a back plate 56 of a brake pad 54, in-use, and a resilient clip. The resilient clip is for removeably and replaceably mounting the thermocouple to the back plate such that the thermocouple is in contact therewith. The temperature sensor may be biased into contact with the back plate, for instance by spring loading means. The temperature sensor may further comprise a brake pad wear sensor for sensing wear below a threshold thickness of a friction lining. This may take the form of a wire 68 of the thermocouple being supported within an abradable mounting 67, the mounting arranged to position the wire within the friction lining 58. When the friction lining wears below the threshold thickness, the mounting and the wire are worn by a brake disc to provide an open circuit of the thermocouple.

Description

(71) Applicant(s):

Jaguar Land Rover Limited

Abbey Road, Whitley, Coventry, Warwickshire,

CV3 4LF, United Kingdom (72) Inventor(s):

Michael Enness David Clegg Ric Hampson (74) Agent and/or Address for Service:

JAGUAR LAND ROVER

Patents Department W/1/073, Abbey Road, Whitley, Coventry, Warwickshire, CV3 4LF, United Kingdom (51) INT CL:

F16D 66/00 (2006.01) F16D 66/02 (2006.01) (56) Documents Cited:

EP 1997758 A2 EP 1740846 A1

EP 1174636 A2 EP 0999377 A2

EP 0634586 A1 US 5839545 A

US 5668529 A US 4484280 A

US 20150369318 A1

JPH06185555 JP H09144787 JP H1047397 (58) Field of Search:

INT CL F16D Other: WPI, EPODOC (54) Title of the Invention: Controller for a braking system of a vehicle

Abstract Title: Brake pad temperature sensor mounted to a back plate via a resilient clip (57) Disclosed is a temperature sensor 60 that includes a thermocouple 66 arranged to measure a temperature of a back plate 56 of a brake pad 54, in-use, and a resilient clip. The resilient clip is for removeably and replaceably mounting the thermocouple to the back plate such that the thermocouple is in contact therewith. The temperature sensor may be biased into contact with the back plate, for instance by spring loading means. The temperature sensor may further comprise a brake pad wear sensor for sensing wear below a threshold thickness of a friction lining. This may take the form of a wire 68 of the thermocouple being supported within an abradable mounting 67, the mounting arranged to position the wire within the friction lining 58. When the friction lining wears below the threshold thickness, the mounting and the wire are worn by a brake disc to provide an open circuit of the thermocouple.

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CONTROLLER FOR A BRAKING SYSTEM OF A VEHICLE

TECHNICAL FIELD

The invention relates to a vehicle braking system, more particularly, but not exclusively, to a disc brake system. Aspects of the invention are directed to a controller for a braking system, a braking system, a vehicle, and a method of configuring a vehicle for operation based on a health state of a braking system.

BACKGROUND

Vehicles, such as cars or the like, include a braking system for deceleration purposes. Two types of braking systems in existence are categorised as drum brake systems and disc brake systems. In the context of disc brake systems, the braking system includes a disc, or rotor fixed to a side shaft of an axle, and opposing brakes supported either side of the disc in a caliper and arranged to be actuated by hydraulically driven pistons, again supported by the caliper.

Health of the braking system is important since various factors can lead to ineffective braking performance. For instance, the brake disc temperature is important since a high brake disc temperature is associated with a reduced friction coefficient relative to the brake pad. Accordingly, known braking systems include provisions for estimating the brake disc temperature during a braking event. Such provisions include computational models based on vehicle parameters measured elsewhere on the vehicle, such as vehicle speed, vehicle deceleration, and mass of the vehicle. In the event of excessive temperature estimation, measures can be taken to reconfigure the vehicle to accommodate for a potentially ineffective braking system, for instance by warning a driver not to accelerate aggressively.

Such models are effective for relatively new braking systems. However, in-use, the braking system components will not behave like new components, due to other factors, such as wear. Accordingly, such models are not necessarily accurate at predicting the health state of the braking system.

It is an object of the present invention to address disadvantages associated with the prior art.

SUMMARY OF THE INVENTION

Aspects and embodiments of the invention provide a controller for a braking system of a vehicle, a braking system, a vehicle, and a method of configuring a vehicle for operation based on a health state of a braking system as claimed in the appended claims.

According to an aspect of the present invention there is provided a controller for a braking system of a vehicle, the controller being arranged to receive information relating to a braking event of the vehicle, and to receive a temperature associated with a brake pad of the braking system, the controller comprising a processor arranged to determine a health state of the braking system based on the information relating to the braking event and the temperature associated with the brake pad, wherein the health state of the braking system includes a brake fluid health state.

By ‘health state’ we mean a state of the braking system which may have an impact on its performance in decelerating the vehicle. Determining the health state based on both the information relating to the braking event and the temperature associated with the brake pad is more accurate since the brake pad temperature can be used to determine real time effects of the braking system, such as wear of the various brake system components, where such effects may not be detectable using the information relating to the braking event alone. In this way, the vehicle can be configured, or driven, in a way to accommodate a braking system health state more accurately.

In an example, the processor is configured to determine the brake fluid health state in dependence on one or more estimates of brake fluid temperature. In this event, the processor may be configured to determine the one or more estimates of brake fluid temperature in dependence on the temperature associated with the brake pad.

Advantageously, the processor may be configured to compare each of the one or more estimates of brake fluid temperature to a temperature limit and to output a warning message to a driver in the event that the estimate of brake fluid temperature exceeds the temperature limit. Optionally, said temperature limit is determined in dependence on the brake fluid health state.

The brake fluid health state may be determined in dependence on a plurality of estimates of brake fluid temperature recorded over time.

Advantageously, the processor may be configured to determine a service life of brake fluid of the vehicle in dependence on the brake fluid health state. The service life may be a remaining time for which the brake fluid can be used prior to replacement of the brake fluid.

The temperature associated with the brake pad of the braking system may be sensed directly from the brake pad.

In an embodiment, the information relating to the braking event is an input received from an energy model associated with the braking event of the vehicle. Alternatively, or additionally, the information relating to the braking event may be information relating to a change in speed of the vehicle over time.

In an embodiment, the processor is configured to determine a health state including a brake pad wear state. Understanding the pad wear is important since worn pads require replacement and may also be associated with compromised frictional interface with a brake disc leading to reduced deceleration of the vehicle.

In an example, the processor is configured to determine a health state including an estimate of brake disc temperature. In this case, the processor may be configured to estimate the brake disc temperature in dependence on the information relating to the braking event.

The processor may be configured to adjust the estimate of brake disc temperature to account for brake pad wear. In this event, the processor may be configured to adjust the estimate of brake disc temperature using the temperature associated with the brake pad.

In an embodiment, the processor is configured to determine a health state including an estimate of brake fluid temperature. Brake fluid temperature may increase by conduction through brake pistons contacting hot brake pads. It is important to understand the brake fluid temperature since excessive temperature may be associated with compromised brake pad actuation or degradation of the fluid.

Advantageously, the processor may be configured to determine a health state including a brake caliper state. In this case, the processor may additionally be configured to determine that a temperature of a brake caliper of the vehicle has exceeded a predetermined threshold temperature for longer than a predetermined length of time.

In an example, the controller is arranged to output an output signal for use in configuring the vehicle based on the heath state of the braking system.

In an embodiment, the controller is arranged to output the output signal in response to either the information relating to the braking event or the temperature associated with the brake pad indicating an unacceptable state. The information or the sensor for sensing the temperature of the brake pad may be erroneous. Using this ‘either/or’ approach thus provides a degree of redundancy leading to more robust health state detection.

In an embodiment, the controller is configured to send the output signal to a health monitoring system for producing a health report detailing the health state of the braking system. The health monitoring report can be used off line for diagnosing faults or merely for routine maintenance, such as brake pad replacement during an annual vehicle inspection, thus making the inspection and other diagnostic tasks easier.

In an embodiment, the controller may be configured to send the output signal to a drive train component to effect a power reduction of the vehicle. In this way, the power used to drive the vehicle will be reduced to prevent excessive acceleration and speeds, which would ordinarily require a high performing braking system. The power reduction can be achieved in several ways including, though not limited to, a force down shift in gear selection or de-rating the vehicle to limit the maximum available acceleration.

In an embodiment, the controller may be configured to send the output signal to a human interface for providing a warning message to a driver of the vehicle to indicate the state of the braking system. In this way, the driver will be able to effect changes manually to accommodate any degraded health state of the vehicle.

In an embodiment, the controller is configured to receive a brake pad wear estimate from a brake pad wear sensor. The processor may be arranged to determine the health state of the braking system based on the brake pad wear estimate. Measuring the brake pad wear directly provides further redundancy over and above using the information relating to the braking event and brake pad temperature for determining the health state of the vehicle.

The processor may be configured to calculate an estimate of brake pad wear in dependence on a rate of change of brake pad temperature over time. In an embodiment, the controller is configured to estimate brake pad wear in dependence on a comparison between a rate of change of the temperature associated with the brake pad over time and a baseline, or expected, rate of change of brake pad temperature over time.

In an embodiment, the energy model may be based on one or more inputs, said inputs selected from a list including vehicle deceleration, vehicle speed, vehicle mass, and ambient temperature.

According to a further aspect of the present invention, there is provided a braking system comprising a brake pad temperature sensor and one or more other sensors for producing information relating to a braking event, a brake pad arranged to engage a brake disc to decelerate the vehicle, in-use, and the aforementioned controller. In this case, producing information relating to the braking event may comprise producing an energy model associated with the braking event.

According to a further aspect of the present invention, there is provided a vehicle comprising the aforementioned braking system.

According to a further aspect of the present invention, there is provided a method of configuring a vehicle for operation based on a health state of a braking system of the vehicle, the method comprising;

receiving a temperature associated with a brake pad of the braking system;

determining information relating to a braking event; and determining a health state of the braking system based on the temperature associated with the brake pad and the information relating to the braking event, wherein the health state of the braking system includes a brake fluid health state.

The method may comprise determining the brake fluid health state in dependence on one or more estimates of brake fluid temperature. In this event, the method may comprise determining the one or more estimates of brake fluid temperature in dependence on the temperature associated with the brake pad.

Optionally, the method further comprises comparing each of the one or more estimates of brake fluid temperature to a temperature limit and outputting a warning message to a driver in the event that the estimate of brake fluid temperature exceeds the temperature limit. The method may further comprise determining said temperature limit in dependence on the brake fluid health state.

The method may further comprise determining the brake fluid health state in dependence on a plurality of estimates of brake fluid temperature recorded over time.

Advantageously, the method may further comprise determining a service life of brake fluid of the vehicle in dependence on the brake fluid health state.

In an example, receiving the temperature associated with the brake pad comprises sensing directly the temperature of the brake pad.

In an embodiment, determining information relating to the braking event comprises determining an energy model associated with the braking event.

Advantageously, the method may further comprise outputting a signal for use in configuring the vehicle based on the health state of the braking system.

According to a further aspect of the present invention, there is provided a computer storage medium comprising computer-readable instructions for a computer to carry out the aforementioned method.

According to a further aspect of the present invention, there is provided a nontransitory computer-readable storage medium storing executable computer program instructions to implement the aforementioned method.

According to a further aspect of the present invention, there is provided a temperature sensor, the temperature sensor including a thermocouple arranged to measure a temperature of a back plate of the brake pad, in-use, and a resilient clip for removeably and replaceably mounting the thermocouple to a back plate of the brake pad such that the thermocouple is in contact therewith. Directly measuring the temperature of the brake pad back plate allows for accurate temperature estimations of other brake parameters, such as brake fluid temperature and rotor temperature. The temperature sensor being removeably and replaceably mounted within the back plate allows for the temperature sensor to be changed in the event of a fault without having to replace the entire brake pad, as would be the case where the temperature sensor is permanently connected to the brake pad.

The temperature sensor may be biased into contact with the back plate of the brake pad, in use. For example, the temperature sensor may comprise a means for biasing the sensor into contact with the back plate of the brake pad. The temperature sensor may be spring-loaded, for example, to bias the temperature sensor into contact with the back plate of the brake pad. Optionally, the temperature sensor comprises means for spring-loading the temperature sensor, such that the temperature sensor is biased into contact with the back plate of the brake pad, in use.

In an embodiment, the temperature sensor may comprise a brake pad wear sensor for sensing brake pad wear below a predetermined thickness of a friction lining of the brake pad.

In an embodiment, the brake pad wear sensor may comprise a wire of the thermocouple supported within an abradable mounting, the mounting arranged to position the wire within the friction lining at a position associated with the predetermined thickness of the friction lining, wherein the mounting and wire may be arranged to wear in response to contact with a brake disc at the predetermined friction lining thickness to provide an open circuit of the thermocouple. Utilising a wire of the thermocouple for the pad wear detector is simple and requires no additional components as would be the case where the wear sensor is provided as a separate part.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a schematic view of a vehicle incorporating a braking system in accordance with an embodiment of the present invention;

Figure 2 shows a block diagram of a controller from the braking system of Figure 1; Figure 3 shows a side section view of part of a disc brake of the braking system from Figure 1;

Figure 4 shows a front section view of a brake pad from the disc brake from Figure 3; Figure 5 shows a top section view of the brake pad from Figure 4;

Figure 6 shows a flow chart of a method of configuring a vehicle in response to a health state of the braking system from Figure 1;

Figure 7 shows a graph associated with determining a wear state of the brake pad from Figure 4; and

Figure 8 shows a flow chart of a method of determining a brake disc temperature.

DETAILED DESCRIPTION

With reference to Figure 1, a vehicle 10 includes a body 12 driven by a set of wheels

14. The body 12 supports a drive train for supplying power to front and rear axles 16, 18 for powering the wheels 14.

The drive train includes an engine 20, a gear box 22, a central drive unit 24 for transferring power to the front and rear axles 16, 18, and final drive unit 26 on each axle for accommodating differences in speeds of respective near and off-side wheels 14 during a turn.

The vehicle 10 also includes a braking system including a disc brake 28 on each side shaft of the front and rear axles 16, 18. The disc brakes 28 of the braking system are described in further detail below.

The braking system also includes a controller 30 receiving inputs from various sources and outputting signals to other systems of the vehicle 10. The operation of the controller 30 is best understood with reference to the methods described below, however in summary, the controller 30 receives inputs from a temperature sensor and a pad wear sensor of each brake pad of the disc brakes 28, and from an energy model 32. Measurements from a vehicle speed sensor 34, a vehicle mass sensor 36, and an ambient temperature sensor 38 are used as inputs to the energy model 32.

The controller 30 is shown in more detail in Figure 2, and comprises an input 40 for receiving inputs from the aforementioned sources, a processor 42 for processing electronic control data stored in a data store 44, an output 46 for outputting signals to the other systems of the vehicle 10. The controller 30 and the energy model 32 are provided as electronic data in a non-volatile memory component of an on board computer of the vehicle 10.

With further reference to Figure 1, the controller 30 is arranged to output the signals to the gear box 22, a human machine interface 48, and a maintenance control centre 50.

The human machine interface 48 is a dashboard mounted display in the form of a touchscreen. The display can display images and warnings to a driver of the vehicle 10. In addition, the interface 48 can provide sound bites for audible warnings to the driver.

The maintenance control centre 50 includes a memory function for storing messages generated by various systems during operation of the vehicle 10. In this embodiment, the centre 50 stores the signals generated by the controller 30 for use in off-line diagnostics during maintenance of the vehicle 10 or for health monitoring purposes during periodic vehicle inspections.

With reference to Figure 3, the each disc brake 28 includes a brake disc 52 mounted to a respective side shaft (not shown). In addition, the disc brake 28 includes a brake caliper (not shown) to position opposing brake pads 54 either side of the brake disc

52. Opposing pistons (again not shown) are used to actuate the brake pads 54 for applying pressure to opposing faces of the brake disc 52.

The brake pad 54 includes a back plate 56 and a friction lining 58. The back plate 56 is in contact with the piston and the friction lining 58 is arranged to contact a brake disc face. The friction lining 58 has a thickness, which thickness reduces in use due to wear as a result of contact with the brake disc face.

The brake pad 54 also includes a sensor 60 and a cable 62 connecting the sensor 60 to the input of the controller 30 (shown in Figure 2). In addition, the sensor 60 includes a resilient clip 64 for removeably and replaceably installing the sensor 60 to the back plate 56.

With reference to Figure 4, the sensor 60 includes a thermocouple 66 such that the sensor 60 acts as a temperature sensor. The thermocouple 66 includes a mounting 67 supporting a first wire 68 and a second wire 70, which wires 68, 70 are made from dissimilar metallic materials. The first wire 68 in this embodiment is made from Nickel (Ni) and the second wire 70 is made from Nickel Chromium (NiCr). An interface point 72 is provided between the wires 68, 70 and situated in direct contact with the back plate 56. The interface point 72 is a welding spot for joining the dissimilar metallic materials of the respective wires 68, 70. In response to a temperature change at the interface point 72, the resistance between the wires 68, 70 changes such that the temperature can be determined using a set of associated voltages. The sensor 60 is spring-loaded, such that the sensor 60 is biased into contact with the back plate 56.

With reference to Figure 5, the sensor 60 also acts as a brake pad wear sensor to determine any excessive pad wear. The pad wear sensor employs one of the thermocouple wires, in this embodiment the first wire 68. The first wire 68 is positioned within the mounting 67 so as to protrude away from the back plate 56 and into the friction lining 58. In fact, an outermost position of the first wire 68 is positioned at a predetermined thickness (t) of the friction lining 58. This predetermined thickness (t) signifies a minimum thickness below which the brake pad 54 requires replacement. An abradable material is used for the mounting 67 such that when the mounting 67 is exposed to the brake disc 52 (shown in Figure 3), after the outer lining 58 has worn away, the mounting 67 and the first wire 68 wear by abrasion against the disc 52. In this way, an open circuit is caused which indicates that the the lining 58 has worn below the predetermined thickness (t).

In this way, the sensor 60 acts as a temperature sensor, using the thermocouple 66 to measure the temperature of the back plate 56, and as a pad wear sensor to determine when the friction lining 58 has worn below an acceptable thickness.

Returning to Figure 1, the vehicle speed sensor 34 can take various forms. In one embodiment, the vehicle speed sensor 34 is an inductive type wheel speed sensor as is commonly known in the art. Such a sensor determines vehicle speed by monitoring rotary speed of the wheel. Vehicle speed and also acceleration and deceleration can be measured in this way. Alternatively, a global positioning system (GPS) can be used.

The vehicle mass sensor 36 comprises a tyre pressure sensor arranged to monitor pressure of each tyre and deduce the weight of the vehicle 10 accordingly. Other sensor types could also be used, for instance a strain gauge type sensor or quartz type sensor mounted to each axle 16, 18. Alternatively, the mass may be estimated by comparing the behaviour of the vehicle 10 in various manoeuvres to expected profiles. For instance, vehicle acceleration will be impacted by the pay load and also braking distance. In addition, the distribution of weight can be determined by monitoring brake pad temperature on the front axle 16 versus those on the rear axle 18, since a higher load will be experienced by the front axle during a high front loaded vehicle 10, for instance.

The ambient temperature sensor 38 comprises a thermistor in fluid communication with an exterior environment of the vehicle 10. The thermistor includes a temperature sensitive resistor so as to determine the ambient temperature in contact with the resistor by changes in voltage during operation.

Operation of the controller 30 (shown in Figure 1) is best described with reference to the flow chart shown in Figure 6.

As mentioned previously, a number of vehicle parameters are continuously monitored at steps 100 - 106. In particular, at step 100, vehicle deceleration is monitored using the speed sensor 34. At step 102, vehicle speed is also monitored using the same speed sensor 34. The vehicle mass is monitored using the mass sensor 36, at step 104. Similarly, the ambient temperature is monitored using the temperature sensor 38, at step 106.

The energy model 32 takes the form of an algorithm, and uses the monitored vehicle deceleration, vehicle speed, vehicle mass and ambient temperature from steps 100106 to determine a plurality of energy levels associated with the vehicle 10. In particular, the plurality of energy levels includes a kinetic energy of the vehicle 10, and an energy that has been transferred to each of the disc brakes 28 during a braking event. Based on the determination of the energy that has been transferred to each of the disc brakes 28, the energy model 32 is able to determine a one dimensional temperature value for each brake disc 52 (shown in Figure 3) at step 108, and estimates how the one dimensional disc brake temperature will change, or decay, over time following the braking event.

At step 110, the brake pad back plate temperature is continuously monitored using sensor 60. In addition, at step 112, the controller 30 monitors for the presence of an open circuit caused by wear of the mounting 67 and of the first wire 68 in any of the sensors 60. If any open circuits are detected, the controller 30 emits a warning at step 114 to the human machine interface 48 to display and/or audibly warn a driver that a brake pad 54 needs replacing.

Next, the controller 30 (shown in Figure 1) performs a plausibility check of the energy model 32, at step 115. A proportion of the energy that is transferred to each brake disc 52 during a braking event is subsequently transferred to the corresponding brake pads 54, primarily through conduction. The controller 30 is able to derive an estimated brake pad temperature using the one dimensional brake disc temperature value calculated by the energy model 32 at step 108. The controller 30 subsequently compares the estimated brake pad temperature to the brake pad temperature measured using the respective sensor 60.

It is determined that the energy model 32 is plausible when the estimated and sensed brake pad temperatures are within a predetermined tolerance of one another. However, if a difference between the respective temperatures exceeds a predetermined tolerance threshold then the controller 30 disregards the input from the energy model 32 and ceases to perform the subsequent steps in the flow chart of Figure 6. Each axle 16, 18 is associated with four brake pads 54, each having a respective brake pad temperature sensor 60. Therefore, the plausibility check provides a robust assessment of the energy model 32, since the controller 30 is able to detect an error from any one of the brake pad sensors 60 and to disregard this measurement. The plausibility check is executed continuously, to check that the estimated brake pad temperature remains within a tolerance of the respective sensed brake pad temperature.

As part of the plausibility check or, alternatively, in a separate step, the controller 30 may determine whether the sensed brake pad temperature of one or more of the brake pads 54 is indicative of an obvious error state. An obvious error state may be indicated in the event that the controller 30 determines a sensed brake pad temperature has risen by a large amount in an implausible length of time, for example by around 500^eC in around 0.5 seconds.

At steps 116 to 120 of Figure 6, the controller 30 calculates the health state of various functions of the braking system using respective mathematical functions, or transfer functions.

The energy model 32 does not take brake pad wear rate into consideration, and the estimated brake pad temperature derived from the output of the energy model 32 thus corresponds to temperature behaviour that would be expected of a new, unworn brake pad. As a brake pad 54 becomes progressively more worn, the energy transferred from the brake disc 52 must be absorbed by a brake pad 54 of reduced mass. As such, the remaining mass of a worn brake pad 54 is heated to a greater extent than a corresponding un-worn brake pad 54. To account for this, at step 116, the controller 30 (shown in Figure 1) estimates a state of pad wear using a designated transfer function, as will now be described.

Referring to Figure 7, during a braking event, the temperature of a brake disc (as shown by the solid line) increases roughly linearly to a peak, at the point of removal of brake pad pressure. After the peak, the disc temperature decreases, eventually to a steady state. New brake pads experience a similar temperature curve to that exhibited by the brake disc 52, though at a much lower gradient and to a much lower peak, as shown by the dot-dash line. The temperature gradient of worn brake pads increases during a braking event in a manner as indicated by the dotted line. A phase delay exists between the peak in brake disc temperature and the peak in brake pad temperature, due to the time taken for heat to be transferred from the brake disc 52 to the brake pad 54.

The controller 30 is configured to calculate a rate of change over time, or gradient, of the one dimensional brake disc temperature output from the energy model 32. The controller 30 is also configured to determine a baseline, or expected, rate of change over time of brake pad temperature. To this end, the controller 30 may be provided with data points, or calibration values, corresponding to a rate of change of temperature over time of a known brake pad during a braking event. In this instance, an estimate of brake pad wear can be determined through a comparison of the rate of change of the measured brake pad temperature from the sensors 60, the rate of change of the one dimensional brake disc temperature from the energy model 32 and the calibration values, for a specific time during a braking event.

Alternatively, the controller 30 may make use of a learning algorithm. In this case, the controller 30 is notified upon the installation of a new brake pad 54, and takes initial measurements using the sensor 60 in order to establish an expected pattern of rate of change of brake pad temperature during a braking event. The controller 30 proceeds to continuously monitor the rate of change of measured brake pad temperature over time during subsequent braking events, and compares these rates of change to the gradients of the baseline pattern. Specifically, the controller 30 calculates the rate of change of measured brake pad temperature as a percentage of the corresponding gradient of the baseline pattern. In combination with the calculated rate of change of the one dimensional brake disc temperature from the energy model 32, this percentage can be used by the controller to derive a value for estimated brake pad wear.

It should be appreciated that an estimate of brake pad wear may alternatively be determined using only the rate of change of brake pad temperature measured by the sensors 60 along with the expected rate of change of brake pad temperature, from either the calibration values or the learning algorithm.

Referring again to Figure 6, the brake pad wear estimation is documented in a brake system health report at step 134. In the event that the estimated brake pad wear is found to exceed a predetermined threshold level, a brake warning indicator may be switched on in the vehicle, in order to indicate a need to replace the brake pad 54 to a driver of the vehicle 10 or to maintenance personnel. The controller 30 may be notified at the time at which one or more new brake pads have been installed in the vehicle 10 and, in this case, the rate of change of the estimated brake pad wear can also be used to detect when these new brake pads are inappropriate, or of an unacceptable quality.

In this way, the driver and/or maintenance personnel are forewarned of problems associated with brake pad wear, and can replace the brake pad 54 prior to any damage to the sensor 60. Therefore, the sensor 60 can be re-used, rather than replaced.

At step 118, the controller 30 (shown in Figure 1) uses the estimated one dimensional brake disc temperature from the energy model 32 and the measured brake pad temperature from the respective sensor 60 as inputs to a designated transfer function, in order to calculate an improved estimate for the brake disc temperature. In particular, with reference to Figure 8, the sensed brake pad temperature from the sensor 60 is used at step 121 to determine if a correction of the estimated one dimensional brake disc temperature is required in order to account for brake pad wear.

This determination is made at step 121 by comparing the rate of change of sensed brake pad temperature to a corresponding expected rate of change of brake pad temperature, as has been described previously. When an adjustment for worn pads is required, the brake disc estimated temperature is adjusted accordingly to provide an improved brake disc temperature estimate. This is shown schematically at step 122.

In the event that the rate of change of sensed brake pad temperature matches the expected rate of change of brake pad temperature, no adjustment is required, and the brake disc temperature estimated by the energy model 32 continues to be used as the estimated brake disc temperature. In this way, the accuracy of the brake disc temperature estimate from the energy model 32 is improved, by accounting for the real-time measurement and interpretation of brake pad temperatures from the sensors 60.

With further reference to Figure 6, at step 120 the brake disc temperature estimate, adjusted as necessary to account for brake pad wear, is input into a further transfer function in order to estimate a value for brake fluid temperature. The calculations executed by the transfer function are based on the known relationship between brake pad temperature and brake fluid temperature; namely, the fact that brake fluid temperature increases during a braking event due to an increased piston temperature resulting from thermal conduction from the brake pad 54. In addition, the transfer function accounts for increases in brake fluid temperature that occur as a result of thermal inertia after a braking event has ended. For example, in the event that the brake pad 54 and/or brake pistons are at a higher temperature than the brake fluid after a braking event, the brake pad 54 and brake pistons will continue to cause a temperature increase in the brake fluid, until equilibrium is reached. The executed calculations advantageously account for such situations.

Estimated values for the brake fluid temperature are continuously recorded, such that the controller 30 is able to create a log of brake fluid temperatures over time. The recorded values can subsequently be used to estimate the extent to which the brake fluid has been degraded by historical temperature increases and fluctuations, and therefore to determine a current health state of the brake fluid. The brake fluid health state can, in turn, be used to predict a remaining service life of the brake fluid, which is continuously updated to account for new values for brake fluid temperature. In an example, a warning is output to the driver in the event that the remaining service life of the brake fluid falls below a predetermined value, to encourage the driver to arrange maintenance of the vehicle 10.

In an alternative embodiment, the transfer function for estimating a value for brake fluid temperature receives separate inputs corresponding to the output from the energy model 32 and the sensed brake pad temperature. This allows for the transfer function to compute two values independently of one another; one using the output from the energy model 32, and one using the sensed brake pad temperature. In this way, when either result is deemed to be unacceptable, a corresponding output for configuring the vehicle 10 (as described below) can be made. In this case, the controller 30 is more conservative and is less robust to errors in either the algorithm of the energy model 32 or the sensed brake pad temperature.

At step 132, the most recently-estimated brake fluid temperature is compared to a temperature limit. When the brake fluid temperature exceeds the temperature limit, a warning is output to the driver at step 114. The temperature limit is a dynamic value, accounting for the fact that a suitable operating temperature of the brake fluid is altered as the health state of the brake fluid changes. To this end, the determined health state of the brake fluid is used as an input to step 132, and the temperature limit adjusted in response. For example, in the event that the brake fluid is determined to have been degraded to a certain extent as a result of one or more temperature increases, the temperature limit is reduced by a corresponding amount, such that a lower brake fluid temperature is required to trigger the warning 114 to the driver.

Step 134 details the documentation of the pad state of wear, brake disc temperature estimation, and brake fluid temperature estimation in the brake system health report. The health report is stored in the maintenance control centre 50 of the braking system, and is continuously updated with information relating to the estimated pad wear, estimated brake disc temperature and estimated brake fluid temperature and brake fluid service life. The brake system health report can be used subsequently by a maintenance person for performing diagnostic activities or servicing the vehicle 10.

The brake system health report may be used to identify unexpected or undesirable behaviours in the braking system. For example, the brake system health report may indicate that the brake pads 54 have exceeded a predetermined threshold temperature, such that the material composition of the brake pads 54 is likely to have been altered.

The brake system health report may additionally or alternatively be used to indicate a health state of the brake calipers of the vehicle 10. In particular, the brake system health report can be used to determine that a temperature associated with the brake calipers has exceeded a predetermined threshold level for longer than a predetermined length of time, such that the brake calipers are likely to have deformed or caliper seals deteriorated. For example, the processor 42 may be configured to determine that a temperature of one or more of the brake calipers has exceeded 100^eC for a predetermined period of time.

Step 136 shows an active output from the controller 30; specifically, de-rating the vehicle 10 in response to the brake disc temperature estimated at step 118 or in response to the brake fluid temperature estimated at step 120. By way of illustration, the vehicle 10 can be de-rated by configuring the gear box to down shift in gear, particularly when descending a hill, so as to relieve subsequent burden on the braking system. Similarly, the engine may be configured to limit the available acceleration or speed so that excessive braking is not required to decelerate the vehicle 10.

In this way, it can be seen that by virtue of the health report, by actively de-rating the vehicle 10, or merely by warning the driver of the braking system’s health so the driver can taking action to accommodate for the health of the braking system, the vehicle 10 can be configured based on the health state of the braking system so as to relieve any burden during subsequent braking events.

Advantageously, the health report is generated in response to estimates for pad wear, brake disc temperature and brake fluid temperature that account for real-time measurements from the brake pad temperature sensors 60. In this way, the health report provides an accurate indication of the status of the braking system, and allows for the most appropriate course of action to be taken in response.

Reference has been made herein to a measured brake pad temperature, sensed directly from a back plate 56 of a brake pad 54 by way of sensors 60. However, it will be appreciated that the temperature of each brake pad 54 could be obtained in any one of a number of ways. For example, a thermocouple could alternatively be positioned within the friction lining 58 of the brake pad 54, to directly measure a temperature associated with the friction lining 58. Alternatively, or additionally, an infra-red sensor could be mounted in the vehicle 10 at a position remote from the brake pad 54, this sensor being directed towards a surface of the brake pad 54 to detect infrared radiation emitted from the brake pad 54. It is also envisaged that a state-changing gauge could be mounted to the surface of the brake pad 54, for use with a corresponding optical reading device.

Claims

1. A temperature sensor, the temperature sensor including a thermocouple arranged to measure a temperature of a back plate of the brake pad, in-use, and

5 a resilient clip for removeably and replaceably mounting the thermocouple to the bake plate such that the thermocouple is in contact therewith.

2. The temperature sensor of Claim 1, wherein the temperature sensor is biased into contact with the back plate of the brake pad, in use.

3. The temperature sensor of Claim 2, wherein the temperature sensor comprises means for spring-loading the temperature sensor, such that the temperature sensor is biased into contact with the back plate of the brake pad, in use.

15

4. The temperature sensor of any preceding claim comprising a brake pad wear sensor for sensing brake pad wear below a predetermined thickness of a friction lining of the brake pad.

5. The temperature sensor of Claim 4 wherein the brake pad wear sensor

20 comprises a wire of the thermocouple supported within an abradable mounting, the mounting arranged to position the wire within the friction lining at a position associated with the predetermined thickness of the friction lining, wherein the mounting and wire are arranged to wear in response to contact with a brake disc at the predetermined friction lining thickness to provide an open circuit of the

25 thermocouple.

Mr Christian GibsonFaux

2 May 2018

Intellectual

Property

Office

Application No: