WO2018051124A2

WO2018051124A2 - Removal of glaze from vehicle brakes

Info

Publication number: WO2018051124A2
Application number: PCT/GB2017/052750
Authority: WO
Inventors: Kenneth Edwards
Original assignee: Kenneth Edwards
Priority date: 2016-09-16
Filing date: 2017-09-15
Publication date: 2018-03-22
Also published as: WO2018051124A3; CN111094784B; CN111094784A

Abstract

The performance of a brake within a vehicle's braking system is maintained within a safe operating range by a glaze removal procedure which uses abrasion to convert glaze into particulates which can be removed from the working surfaces of said brake by gravity or by airflow. The abrasion is generated by the instantaneous application of high brake-line pressure when the wheel containing said brake is mounted on a roller brake tester and the glaze is at a temperature below its softening point. A controller may be used to output instructions for the glaze removal process, to monitor the process and to log brake performance.

Description

Title

Removal of Glaze from Vehicle Brakes Background of the Invention

This invention concerns apparatus and methods for monitoring, testing and/or maintaining vehicle brakes, e.g. for the purpose of maintaining the performance of a vehicle's brakes at a level at which they can, over the full wear life of the friction materials on the working surfaces of its brakes, generate the retarding force necessary to meet the statutory requirement for vehicle deceleration.

Much good work has been done to improve the performance of brakes with the result that the only major brake-related problem which vehicle operators currently have to contend with is the build-up of low friction films on the working surfaces of the brakes. These films, known in the industry as "glaze", are formed by environmental pollutants combining with thermoplastic elements which have migrated from within the friction materials. They present a problem because they can seriously reduce the retarding force which a vehicle's brakes can generate.

The statutory annual roadworthiness test for a vehicle includes a brake performance test but, because there can be serious deterioration in the performance of a vehicle's brakes in the period between annual tests, vehicle operators are required to carry out further periodic tests. Current regulations require brake performance to be measured by a procedure by which brake line pressure is applied slowly at a rate of 1 bar per second or less. The procedure does not provide a measure of the retarding force which can be instantaneously available in an emergency.

The two types of braking systems in current use on road vehicles are disc brakes and drum brakes. Disc brakes have fixed friction pads and rotating metal discs, and drum brakes have fixed friction linings and rotating metal drums. Each type of brake operates by generating frictional grip between the working surfaces of the fixed and the rotating members thereby allowing the fixed members to apply a retarding torque to the rotating members. This retarding torque is transmitted to the tyres to generate a vehicle retarding force at the interface between the tyres and the road surface.

Vehicle braking systems are normally designed to provide retarding forces which can decelerate a vehicle, at any load, by about 6 metres per second per second (6m/sec²) when the working surfaces of the brakes are in prime condition. When a vehicle is in service the build-up of glaze on the working surfaces of its brakes gradually reduces the retarding forces which the braking system can generate. The statutory requirement is that the braking system must be capable of decelerating the vehicle by a minimum of 5 metres per second per second (5m/sec²). Hence there is normally a safe operating range of brake system performance within which it can decelerate a vehicle by a rate between 6m/sec² and 5m/sec².

Currently the only way brake performance can be maintained at or above this minimum level is by replacing the friction materials on the working surfaces of the brakes when glaze has reduced the brake system's deceleration capability to 5m/sec² although at that stage they may they have utilised less than half their full wear life. From a commercial standpoint, it is noted that replacement of friction materials before the end of their maximum possible working life results in increased sales of those materials. Thus there has been little commercial motivation to-date to resolve problems associated with the build-up of glaze.

It is an aim of the invention to provide a system for mitigating one or more of the above- identified problems. It may be considered an additional or alternative aim to extend the working life of friction material in vehicle brake systems by removal of glaze in a controlled and practical manner.

Brief Summary of the Invention

We have discovered a novel glaze removal procedure which can be applied by a computer controlled roller brake tester to remove glaze from the working surfaces of automotive brakes and we have developed a novel glaze removal software program and a novel remotely controlled force applicator to enable roller brake testers to apply our novel procedure.

The novel procedure for removing glaze from the working surfaces of automotive brakes is the application of instantaneous shear force generated by an instantaneous application of brake-line pressure when the wheel in which a brake is mounted is being rotated by the drive rolls of a computer controlled roller brake tester.

According to different aspects of the invention, there is provided: a method of removing glaze; a method of monitoring/managing vehicle brake performance; a roller brake tester; a new use of a roller brake tester; a controller for a roller brake tester; and, a data carrier comprising machine readable instructions for operation of the roller brake tester, as defined in the accompanying claims. The invention may comprise causing the engagement of friction material of vehicle brakes, for example by increasing the braking force applied by the friction material in a shear direction with respect to a surface of the friction material

The roller tester, or its controller, may perform any, any combination or all of the following: · instruct the operator applying the glaze removal procedure to bring the maximum pressure of the fluid in the vehicle's braking system to a level which has been predetermined to be the maximum pressure which can safely be instantaneously applied to the brake mechanism.

• pre-set the speed of rotation of the drive rolls. make it possible for an operator, sited remotely from the roller brake tester, to guide the force applicator into safe engagement with pull-down fixtures connected to the axle or chassis of a vehicle. instruct the operator to instantaneously apply the predetermined brake-line pressure. monitor load measuring device(s) to detect any movement of wheels out of safe engagement with the drive rolls.

The method may be performed when the glaze on the vehicle brakes is at a temperature below its softening point, e.g. when the friction material is cool or at ambient temperature.

The method, roller brake tester and/or its controller may record any, any combination, or all of:

(a) the peak brake performance before the application of instantaneous shear force which it has calculated by extrapolation from brake performance at low brake pressures.

(b) the peak brake performance after the application of instantaneous shear force.

(c) the predicted rate of decline of brake performance after each application.

(d) the rate of build-up of retarding force when instantaneous brake-line pressure is applied.

(e) the performance of each brake on the vehicle over the whole working life of the vehicle. The features of the force applicator may comprise;

• its movements may be remotely controlled by the vehicle operator operating interactively with the novel software program.

• it may be fitted with a camera and light source to provide the visibility necessary for the operator to bring it into safe engagement with a pull-down fixture.

• it may lock the wheel under test into safe contact with the drive rolls.

The invention may provide means of ensuring that shear force can safely be applied instantaneously. This may be achieved by any, any combination, or all, of:

• the fitting of a force applicator.

· the glaze removal program or controller instructing the operator to pre-set the maximum safe brake-line pressure and/or speed of rotation of the drive roller(s).

• the glaze removal program or controller monitoring the outputs of the front and rear load measuring devices, so that it can instantaneously reduce power to the drive rolls if the wheel under test is being lifted out of safe contact with the drive rolls. In certain examples (e.g. by fitting to the roller brake tester a remotely controlled force applicator which can engage pull-down fixtures connected to the vehicle's chassis or axles to apply sufficient simulated load to bring the total load on the wheel which houses a brake being tested up to the maximum for which it is designed), the invention may provide means by which the amount of glaze removed from the working surfaces of the brakes of vehicles by each application of instantaneous shear force can be increased, e.g. being optimised or maximised.

The pull-down fixtures connected to a vehicle may be simple mouldings or metal pressings, to protect the axle and any wiring or pipework running along it from damage, or may be structures connected to the axle or chassis which allow engagement by the pull- down device at positions which are remote from the axles or chassis.

An operator, sited remotely from the roller brake tester may, by operating interactively with the glaze removal program, use camera vision to bring the force applicator safely into engagement with a pull-down fixture although the position of the fixture relative to the roller-brake tester may vary due to variations in vehicle load and variations in the positioning of the vehicle on the roller road tester.

This invention may not require any changes to the brake performance test performed by a vehicle operator as part of its the annual test, the purpose of which is simply to measure brake performance. Further, interim tests, if carried out in accordance with the invention, may restore brake performance by removing at least a portion of glaze which caused the deterioration in performance.

Brief description of the Drawings

Certain embodiments of the invention will now be described with reference to the accompanying drawings, in which:

Figurel shows by Line 1 a typical pattern of glaze build-up when a vehicle is in service.

Figure2 shows by Line 3 a typical pattern of decline in brake performance when a vehicle is in service and by Lines 5 and 6 the safe operating range of brake performance 4.

Figure 3 shows by Lines 7 and 8 the rates at which a brake can build up retarding force and by Lines 10 and 1 1 the time taken to build up retarding force from a trigger level 9 to a peak level.

Figure 4 shows by Line 12 brake performance being maintained within an upper sector 13 of the safe operating region 4.

Figure 5 shows by Line 14 brake performance being raised by applications of a glaze removal procedure which only partially removes the glaze which accumulates in the time between applications.

Figure 6 shows by Line 17 the predicted rate of decline of brake performance after an application of a glaze removal procedure. It also shows the vehicle travel 18 at which a further application would be required to keep brake performance within upper sector 13 and the vehicle travel 19 at which a further application would be required to keep brake performance within the safe operating range.

Figure 7 shows an example of a vehicle's brake performance record.

Figure 8 shows schematically an end view of a force applicator 33 in engagement with a pull-down fixture 31 fitted to axle 32. Figure 9 shows a side view of force applicators 33 mounted on shaft 24 and engaging axle 32.

Figure 10 shows, within the enlarged section of the safe operating range of the brake 4, the increasing rate of build-up of retarding force achieved by glaze removal as the brake- line pressure approaches 6.5 bar. Figure 1 1 shows a force applicator mounted at Angle 39 to the vertical. Detailed Description of the Invention

Our research has found:

• that glaze build-up on the working surfaces of a brake when the vehicle is in service is in the form of an S-curve, as shown in Figure 1 . The precise form of the S- curve for a vehicle depends upon a number of factors, the main ones being the pattern of braking and the glaze resistance of the friction material.

• that the decline in brake performance, as shown in Figure 2, is in the form of an S- curve which is a near mirror image of the S-curve describing glaze build-up. The rate of decline, per kilometre of vehicle travel, is initially low but increases by a factor of 3 or more as the glaze builds up to the level at which brake performance drops out of the safe operating region. Once the S-curve for a particular vehicle is known the future path of decline in brake performance can be predicted. · that glaze on the working surfaces of a brake can, by the application of instantaneous shear force - as distinct from the slow application of shear force currently specified for statutory brake tests - be abraded into particulates which can be removed by gravity or airflow whilst the brake is in situ on a vehicle. In contrast, the slow application of braking force used when performing conventional statutory brake tests serves to warm the friction material and reduce the susceptibility of the glaze to abrasion.

• that the required instantaneous shear force can be generated by frictional grip between the wheel housing the brake and the drive rolls of a roller brake tester when the wheel is mounted on the drive rolls and the brake-line pressure is increased as quickly as it would be in an emergency stop, which for safe operation of a vehicle may be at least 4 bar per second.

• that instantaneous shear force can safely be applied by a roller brake tester: (a) by the fitting of a force applicator which can resist any movement of the wheels out of engagement with the drive rolls by applying a pull-down force which can lock the wheels into safe engagement with the drive rolls.

(b) by pre-setting the brake-line pressure, the speed of rotation of the drive rolls and the power supplied to the drive rolls to pre-determined safe levels. (c) by reactively altering or aborting the procedure (e.g. instantaneously) if the wheels begin to move out of safe contact with the drive rolls. Roller brake testers are fitted with rear-mounted and front-mounted load measuring devices and any tendency for the wheel to move out of safe engagement will increase the load carried by the rear- mounted devices relative to the load carried by the front-mounted devices. By monitoring the load measuring devices any tendency for the wheel to move out of safe engagement when instantaneous shear force is applied can be countered by instantaneously reducing either the speed of the drive rolls or the power input to the drive rolls.

• that the amount of glaze which can be removed by each application of shear force is dependent upon a number of factors, the main ones being the magnitude of the shear force, its rate of build-up when applied, the temperature at which it is applied, the thickness of the glaze at the time it is applied, and the speed of rotation of the drive rolls. The amount will increase with increases in the magnitude of the shear force, the rate of build-up of shear force and the speed of rotation of the drive rolls, and will decrease with increases in temperature and glaze thickness. · that, with currently available friction materials, the amount of glaze which can be removed from the working surfaces of brakes in a single application of shear force will have little beneficial effect on the performance of the brakes if applied when their working surfaces are heavily glazed, but that the removal of even small amounts of glaze from their working surfaces can significantly improve brake performance if applied when they are only lightly glazed.

• that a further potential benefit of applying shear force instantaneously is, as shown in Figure 3, that it can provide a means of measuring the speed at which a brake can generate retarding force. This may be achieved by measuring the time required for the retarding force to rise from a trigger level to a higher level such as the level at which it peaks. The speed at which a brake can generate retarding force is so important that it should be an integral part of all brake tests because:

(a) the only retarding force of any value in an emergency is that which is

immediately available;

(b) balanced braking requires all brakes to act together simultaneously and this is possible only if they can generate retarding force at similar rates;

(c) it provides an early warning of the need to check for problems such as flow

restrictions in pressure pipe lines, the malfunctioning of valves and the incorrect adjustment of slack adjusters.

• that a glaze removal program can, as shown in Figure 6, contain software which at each application predicts the vehicle travel at which the next application of the procedure will be required to maintain brake performance.

• that glaze removal by applying shear force instantaneously can provide a measure of brake performance both before and after glaze removal, and hence can, as shown in Figure 10, provide a measure of the increase in brake performance generated by glaze removal. The glaze removal can usefully be seen as a 2 stage process with a first stage wherein the shear force is relatively low and consequently there is little or no glaze removal and a second stage wherein the shear force is relatively high and there is significant glaze removal. The glaze removal software may provide a measure of the increase in retarding force generated by glaze removal by predicting by extrapolation at the end of stage 1 , e.g. as permitted by ISO 21069, the peak retarding force which the brake would have generated if tested prior to the application of the deglazing procedure. This prediction may be compared with the actual peak retarding force achieved at the end of stage 2.

• that software can be used to measure brake performance before and after each application of instantaneous shear force. Said software may be used to predict the path of decline in brake performance after a glaze removal application. This can provide a means of monitoring brake performance over the whole life of a vehicle, as shown in Figure 7. The decline of brake performance may be predicted using a mathematical algorithm or model, e.g. by fitting the decline to a predetermined plot or mathematical expression of the type shown in Figure 2. The current/measured brake performance may be an input into the model. A polynomial expression could for example be used to define the brake performance decline.

• that to prevent a glaze removal procedure being seen by vehicle operators as an added burden it can advantageously be carried out as part of a routine brake test. Ideally it will, at the frequency and vehicle load specified for a brake test be able, to remove all the glaze which has accumulated in the time between tests. Figure 4 shows brake performance being maintained within a narrow range over the full working life of the friction materials by a glaze removal procedure which, when applied, can remove all the glaze which has accumulated since a previous

application. If, when applied at the frequency and load specified for a brake test, a glaze removal procedure can remove only a part of the glaze which has accumulated since a previous application it can still provide a valuable service by extending the safe working life of the friction materials, as shown in Figure 5.

• that high shear forces can be applied by a roller-brake tester if it is fitted with a remotely controlled force applicator, as shown by figures 8 and 9, which can increase drive-roll/tyre grip by engaging pull down fixtures attached to the axle or chassis of a vehicle and, having engaged them, can apply a pull-down force thereto.

• that a force applicator 33, shown mounted vertically below axle 32 in Figure 8, can, as shown in Figure 1 1 , be mounted in a position on the frame of the roller brake tester where the pull-down force it applies to the axle or chassis has a horizontal component opposing the horizontal force generated by drive roll-tyre grip when instantaneous brake-line pressure is applied.

• that although the position of the pull-down fixtures may vary relative to the roller brake tester, due to variations in vehicle load and variations in the positioning of the vehicle on the roller brake tester, engagement of the force applicator with pull-down fixtures can be carried out by remote control. It can be achieved quickly and safely by the fitting of a camera and light source to the pull-down fixture and the provision of application software which permits an operator, to control the movement of the pull-down fixture. By the use of these facilities an operator, sited remotely from the roller brake tester, can guide the force applicator into safe engagement with pulldown fixtures.

• that, if the simulated load is applied to the axle of a vehicle, and consequently does not pass through any load sensing device fitted to the vehicle, full-brake-line pressure can be made available by by-passing the load sensing device.

Implementation of the Research Findings

Figure 1 shows by Line 1 the build-up of glaze per kilometre of vehicle travel. It is in the form of an S-curve in which the rate of build-up is initially low and then increases rapidly as the curve passes through its point of inflexion 2. The build-up beyond point 2 is shown dotted because of the lack of sufficient data to define it with the same certainty as prior to the inflection.

Figure 2 shows by Line 3 a typical pattern of decline in brake performance when a vehicle is in service. It is in the form of an S-curve which is a near mirror image of the S-curve describing glaze build-up. It will be appreciated that a mathematical expression may be fitted to the precise shape of the curve. A family of curves could be accommodated by altering one or more variable in the mathematical expression, e.g. to accommodate some variation in brake performance decline according to know or predictable operation parameters for the brake system.

Figure 2 also shows hatched area 4 the safe operating range between Line 5, the brake performance required to decelerate a vehicle by 6m/sec², and Line 6, the brake performance required to decelerate the vehicle by 5m/sec². Thus it is possible to determine a point at which brake performance will deteriorate to an unacceptable level, e.g. where the line 3 crosses the lower threshold of the hatched area 4. Whilst the vehicle distance travelled is used as a measure of brake use in this example, it will be appreciated that other measures, e.g. vehicle travel time and/or brake usage/contact time, could alternatively be used if desired. Figure 3 shows by Line 7 the rate at which a brake which is in good working order can build-up retarding force when instantaneous brake-line pressure is applied, and by Line 8 the slower rate when the build-up is restricted by problems such as slowly reacting valves or damage to pressure pipelines. It also shows by Line 10 the time taken by a brake in good working order to build-up retarding force from trigger level 9 to peak level, and by line 1 1 the increased time required when the rate of build-up to the same peak force is restricted. Applying shear force simultaneously allows the maximum rate of build-up to be measured so that any necessary controls can be put in place.

Figures 4 and 5 shows the safe working life of the friction materials on the working surfaces of brakes being extended by use of the invention.

Figure 4 shows by Line 12 brake performance of lightly glazed friction materials being maintained within an upper sector 13 of the safe operating region 4 by applying a glaze removal procedure when the amount of glaze which has accumulated can be removed in a single application of a glaze removal procedure. Removing glaze early in its formation, when brake performance is at a high level, is effective in that it removes it when it is building up slowly and consequently when each unit quantity of glaze removed provides the maximum distance of safe travel for the vehicle.

Figure 5 shows by Line 14 brake performance being raised at each brake test by a glaze removal procedure which only partially removes the glaze which has accumulated since a previous glaze removal procedure, e.g. between tests. Although partial removal does not prevent a decline in brake performance it can significantly reduce vehicle operating costs by extending the safe working life of the friction materials from point 15 to point 16.

Figure 6 shows by line 17 the predicted rate of decline of brake performance after an application of a glaze removal procedure. It provides vehicle operators with a guide as to the vehicle travel 18 at which the next application will be required to keep performance within the upper sector 13 and the vehicle travel 19 at which the next application will be required to keep brake performance in the safe operating region 4. Using this approach, a next glaze removal procedure and/or test can be scheduled for the vehicle, whereby point 18 represents an optimal point of glaze removal and point 19 represents a hard deadline for ensuring vehicle safety. By keeping a log of such data for a vehicle, the historic behaviour of the vehicle operator and the brake performance history can be retrieved at a later date. Such records may provide for improved brake safety monitoring.

Figure 7 shows a typical example of a vehicle brake performance record made possible by applying shear force instantaneously. By Lines 20 it records, for each of the six brakes of a three-axle vehicle, the brake performance before and after each brake test, and by Lines 21 the predicted decline in brake performance in the time between each of the tests. Forty entries of three-monthly test data will provide a record of brake performance over a vehicle operating life of 10 years.

Figure 8 shows an end view of a force applicator 33 in engagement with pull-down fixture 31 fitted to axle 32. Force applicator 33 consists of an outer member 28, an inner member 27 and a pull-down device 30. Axle 32 carries a brake mechanism 38 (shown dotted in Figure 9) which is to be subjected to a glaze removal procedure to remove glaze from the working surfaces of the brake. Tyre 34 of wheel 22 is shown in position on drive rolls 23 of a roller brake tester (not shown) which is to apply the shear forces required for the glaze removal procedure. Force applicator 33 is fixed to shaft 24 and is free to move in 3 axes to allow it, by the application of well-known computer controlled electric, hydraulic or pneumatic means, to be moved along the shaft; to be rotated around the shaft; and to have its length adjusted by the axial movement of its inner member 27 relative to its outer member 28. It can thereby move from its retracted position 29 (shown by dotted lines) to a position where engagement device 30 is safely in engagement with a pull-down fixture 31 .

The vehicle operator is provided with a device having application software which permits remote control of the movement of pull-down device 30 to bring it from its retracted position into engagement with pull-down fixture 31 . It carries a camera and light source 26 to provide the operator with full visibility as pull-down device 30 approaches pull-down fixture 31 .

When safe engagement has been achieved inner member 27 is retracted into outer member 28 thereby applying pull-down force to pull-down device 30 to bring the load on wheel 22 and hence the grip between drive rolls 23 and tyre 34 to the level required for applying the desired level of shear force to the working surfaces of the brake mechanism. The force applicator 33 is shown mounted vertically below axle 32. In some applications it may be preferable to mount it at an angle to the vertical in a position in which the pulldown force has a horizontal component opposing the horizontal force generated by the drive rolls when braking force is applied.

Figure 9 shows a side view of two force applicators 33 mounted on shaft 24 and engaging axle 32. There will be one or more pull-down fixtures 31 fitted onto, or near to, each axle of the vehicle.

Figure 10 shows, within the enlarged section of the safe operating range 4, the increasing rate of build-up of retarding force achieved by glaze removal as the brake-line pressure approaches 6.5 bar, the maximum pressure normally available on vehicles. It shows the retarding force rising to point 35 and it also shows the lower retarding force 36 which would have been available if glaze removal had not been applied. The increase 37 in retarding force from 36 to 35 provides a measure of the improvement in brake

performance obtained by deglazing. In different vehicle examples, the full 6.5 bar brake line pressure may not be available. Accordingly the process for deglazing may apply pressure up to the maximum available safe brake line pressure for the vehicle, which will typically be greater than 2 bar, 3 bar or 4 bar. Figure 1 1 shows the force applicator 33 mounted at an angle 39.

Working embodiments and the method of operation are described in further detail below. The vehicle carrying the brakes to be deglazed may optionally have two pull-down engagement fixtures per axle.

The deglazing process will be carried out on a mobile or fixed roller brake tester which has a computer/controller running a plurality of modules of machine readable code, e.g. in the form of one or more software application or program. The controller can optionally run either of: a standard brake test program, and a combined deglazing and test program. The combined program will output instructions to the operator to apply brake-line pressure in a manner in accordance with the invention to perform deglazing. The controller may monitor and record this process as described in further detail below. In some other examples, the controller may control one or more operational variable of the process. It is envisaged that adoption of the invention may require implementation on existing roller brake testing hardware, e.g. such that the controller outputs instructions for manual operator implementation. However it is proposed that further embodiments will allow automated control of any, any combination , or all such operational parameters such that the test and/or deglazing process can be automated or semi-automated. The roller brake tester will have access (either within the tester memory, or connected thereto over a local or wide area network) a data store comprising all relevant details of the vehicle carrying the brakes to be deglazed so that the tester can identify the vehicle and perform read/write operations to the records for the vehicle. Where a pull-down device is provided, the controller can move the pull-down device into a position immediately adjacent to the pull-down fixture it is to engage based on vehicle

identification. In such an arrangement the pull-down mechanism could

automatically/remotely engage pull-down fixtures connected to the axle or chassis of the vehicle. The sequence of operations to achieve removal of glazed material will be as follows: (a) the wheels carrying the brakes to be tested will be brought into position on the drive rolls of a roller-brake tester;

(b) the deglazing program of the controller will operate interactively with the vehicle operator to allow the operator to remotely control the movement of the pull-down device into engagement with a pull-down fixture.

(c) the deglazing program will prompt the operator: (1 ) to apply any necessary simulated load to bring the load on the wheel carrying each brake in turn up to the maximum it is designed to carry;

(2) to operate the procedure for by-passing any load-sensing device fitted to the vehicle to ensure that full brake-line pressure is available;

(3) to start the drive-rolls;

(4) to apply full brake-line pressure as quickly as is safely possible.

(d) the deglazing program will record and/or provide a display/print-out showing any, any combination, or all of:

the actual retarding force achieved;

an estimate of the retarding force which would have been achieved if glaze had not been removed during the process;

an estimate of the distance of travel (or other measure of use/time) at which a further application of glaze removal will be needed; and/or

a record of the performance of the vehicle's brakes at every previous brake test.

In order to apply the required instantaneous shear force on the friction material of the brakes an 'instantaneous' brake line pressure is used. In practical terms the rate at which the brake system needs to be applied can be used to define a suitable minimum threshold for deglazing of at least 3 bar/s, 4 bar/s or 5 bar/s.

A determination of safe operating parameters may be made by the controller prior to outputting instructions to the operator. It will be appreciated that the deglazing operation requires typically faster rotation of the drive rollers and more aggressive operation of the vehicle brakes. The controller may control the drive rollers in a first speed range for a routine brake test and a further (i.e. higher) speed range for a deglazing operation.

The controller may monitor rotation speed and the load applied to each load sensor by the vehicle during the procedure. In the event that the load reduces at a rate or to a threshold value indicative of the vehicle lifting off a roller, the controller may take action to reduce rotation speed or braking force. In further examples, the controller may be in communication with the on-board controller of a vehicle and may access sensor data and/or records of the vehicle control system. Thus, rather than relying on historic or manually entered data the controller can obtain the data required to determine safety parameters and/or de-glazing operation settings.

The controller can monitor the retarding force applied by the braking system when in place on the roller tester. Thus the controller can determine whether the rate of increase in braking force and/or maximum/peak force achieved is sufficient to create the shear force required for deglazing. The controller may monitor either or both such parameters to be able to output an indication of successful deglazing.

In the event that the braking force threshold for deglazing is not met, the operator may be instructed to repeat a de-glazing operation. However any repeat operation will typically be after a time delay sufficient to allow cooling of the friction material of the brakes to a suitably low level that any glaze is in a state that it is susceptible to deglazing. Additionally or alternatively, a failed deglazing attempt may be recorded such that the predicted decline in brake performance is used to schedule a further deglazing operation earlier than would have been required if deglazing had been successful. In other examples, in addition to controlling the roller brake tester, the controller may have access to vehicle controls and may output control instructions to the vehicle brake system or any other systems that may be advantageous to control automatically, rather than manually. Advantages of the Invention

The invention may quickly provide significant benefits in terms of both safety and cost reduction because it can be implemented without any change to vehicle brake

mechanisms and without any changes to current legislation.

By maintaining vehicle brake performance within a safe operating range at all times, the invention has the potential to reduce the number of accidents on European roads and thereby save hundreds of lives and thousands of serious injuries each year. The invention may significantly reduce vehicle operating costs by enabling vehicle operators to utilise the full wear life of friction materials.

The invention may provide a means of measuring brake performance at all loads up to full-load without the need for the vehicle to be pre-loaded to any specified level.

Claims

Claims:

1 . A method of removing glaze from friction material of a vehicle braking system, the method comprising:

mounting the vehicle on a support structure;

rotating a driven axle of the vehicle so as to cause relative rotation between the driven axle and the support structure;

causing engagement of the friction material of the vehicle braking system to resist rotation of the driven axle at a rate sufficient to abrade glaze from the friction material.

2. A method according to claim 1 , wherein the support structure is a static support structure comprising one or more roller against which a wheel of the vehicle is positioned during rotation of the driven axle, the method comprising rotating the wheel on the roller.

3. A method according to claim 1 or 2, wherein the support structure comprises a roller break tester

4. A method according to any preceding claim, wherein causing the engagement of friction material comprises applying an instantaneous brake line pressure in the vehicle braking system.

5. A method according to any preceding claim, wherein causing the engagement of the friction material comprises applying a brake line pressure in the vehicle braking system within a time period of less than 5s, 4s, 3s, 2s or 1 s.

6. A method according to any preceding claim, wherein causing the engagement of the friction material comprises applying a brake line pressure in the vehicle braking system at a rate of 4 bar per second or more.

7. A method according to claim 4, 5 or 6, wherein applying a brake line pressure comprises applying a maximum possible brake line pressure.

8. A method according to claim 7, wherein the maximum possible brake line pressure is determined at least in part based on the load applied to the support structure by the vehicle.

9. A method according to any preceding claim comprising increasing the frictional engagement of the frictional material against an opposing working surface of the vehicle braking system at a rate greater than a predetermined minimum de-glazing rate.

10. A method according to claim 9, wherein the rate is greater than 1 ,500 Ib/s, 2000 Ib/s, 2500 Ib/s, 3000 Ib/s or 3500 Ib/s.

1 1 . A method according to any preceding claim comprising monitoring the brake line pressure and/or a retarding force applied by engagement of the friction material.

12. A method according to claim 1 1 comprising:

monitoring the rate of increase of the brake line pressure and/or the retarding force; and optionally

outputting an indication of successful glaze removal and/or disengaging the friction material if said rate of increase is greater than a predetermined threshold rate.

13. A method according to claim 1 1 or 12 comprising :

monitoring a maximum value of brake line pressure and/or retarding force achieved during engagement of the friction material; and optionally

outputting an indication of successful glaze removal and/or disengaging the friction material if said maximum value is greater than a predetermined threshold value.

14. A method according to any one of claims 1 1 -13, comprising monitoring the rate of increase of retarding/shear force during engagement of the friction material and identifying a change in said rate attributed to removal of glaze from the friction material.

15. A method according to claim 14, comprising disengaging the friction material and/or outputting an indication of successful glaze removal upon identifying said change.

16. A method according to any one of claims 1 1 -15, comprising determining a predicted retarding force achieved by the vehicle braking system in the absence of glaze removal and logging it with a record of the retarding force recorded during and/or after glaze removal.

17. A method according to any preceding claim further comprising testing the vehicle braking system during engagement of the friction material.

18. A method according to any preceding claim, comprising logging brake

performance of the vehicle braking system prior to glaze removal from the friction material and/or after glaze removal from the friction material.

19. A method according to any one of claims 1 1 -18 comprising reading from and/or writing to a log of historical vehicle brake performance data so as to maintain a retrievable record for said vehicle.

20. A method according to any preceding claim comprising adapting a load applied to the support structure via the vehicle so as to increase the maximum rate at which the friction material can resist rotation of the driven axle and/or the maximum braking force that can be applied by the friction material.

21 . A method according to claim 17, comprising applying a pull-down load between an axle or chassis of the vehicle and the support structure to increase grip between a vehicle wheel and the support structure or a roller thereof.

22. A method according to any preceding claim comprising configuring the vehicle braking system to apply maximum brake-line pressure including by-passing an automatic load-sensing device fitted to the vehicle.

23. A method according to any preceding claim comprising setting one or more safety threshold for an operational parameter of the glaze removal process and monitoring adherence to said threshold at least during engagement of said friction material.

24. A method according to claim 23, comprising setting a rotation speed for the driven axle or a roller of the support structure and/or setting a fluid pressure for the vehicle braking system.

25. A method according to any preceding claim, wherein causing the engagement of the friction material is performed when the friction material is initially at ambient temperature or a sub-operating temperature.

26. A method of managing vehicle braking system health comprising repeating the method of any one of claims 1 -25 at routine or scheduled intervals during the operational life of the vehicle braking system.

27. A method according to claim 26 comprising using a mathematical model to predict a decay in braking performance of the vehicle braking system through use in the event that the glaze removal method is not used and scheduling use of the method of any one of claims 1 -25 based on said predicted decay.

28. A roller brake tester comprising a controller arranged to output instructions for removal of glaze from a friction material of a vehicle braking system for a vehicle on the roller brake tester.

29. A roller brake tester according to claim 28, wherein the controller comprises machine readable code for outputting instructions for performing the method of any one of claims 1 to 25.

30. A roller brake tester according to claim 28 or 29 comprising one or more sensor for monitoring a retarding/shear force applied by the friction material during engagement of the vehicle brake system during use of the roller brake tester.

31 . A roller brake tester according to any one of claims 28-30 comprising a load applicator applying a tensile load between the vehicle and the roller brake tester.

32. A roller brake tester according to claim 31 wherein the load applicator is mounted on the roller brake tester and arranged to engage with an axle or chassis of the vehicle.

33. A roller brake tester according to claim 31 or 32, wherein the load applicator comprises an engagement mechanism for actuating the load applicator between disengaged and engaged conditions and a remote control for controlling operation of the engagement mechanism.

34. A roller brake tester according to claim 33, wherein the controller and/or remote control comprises an interactive computer program for allowing an operator to guide the load applicator into the engaged condition.

35. A roller brake tester according to any one of claims 31 to 34, wherein the load applicator is pivotably mounted to the roller brake tester.

36. A roller brake tester according to any one of claims 28 to 35, comprising a load sensor and the controller is arranged to determine a maximum value for brake line pressure and/or the retarding force that can be applied via the vehicle braking system during glaze removal.

37. A roller brake tester according to any one of claims 28 to 36 comprising a load sensor and the controller is arranged to monitor the loading of the roller brake tester by the vehicle during glaze removal and to control rotation speed and/or engagement of the friction material in order to prevent said loading falling below a threshold value.

38. A roller brake tester according to any one of claims 28-37, wherein the controller is arranged to log a sensed value of brake performance before and/or after glaze removal.

39. A roller brake tester according to claim 38, wherein the controller is arranged to update a record of vehicle brake system history with said sensed values of brake performance.

40. The use of a vehicle brake roller tester for removing glaze from friction material of a vehicle braking system.

41 . A controller for a roller brake tester arranged to output instructions for removal of glaze from a friction material of a vehicle braking system when using the roller brake tester.

42. A data carrier comprising machine readable instructions for operation of a controller of apparatus for removing glaze from friction material of a vehicle braking system to:

monitor rotation of a driven axle of the vehicle;

output instructions for engagement of the friction material of the vehicle braking system to resist rotation of the driven axle; and

monitor one or more operating parameter of the apparatus to record and/or assess glaze removal.

43. A data carrier comprising machine readable instructions for operation of one or more processor of a vehicle brake management system to:

receive brake performance data for a vehicle braking system both prior to and following a glaze removal method according to any one of claims 1 to 27;

determining predicted future brake performance decay data for said vehicle braking system through use in the absence of further glaze removal;

identifying a period of use of the vehicle after which a further glaze removal operation should be performed according to the predicted brake performance decay data; and

outputting said period of use for scheduling of the further glaze removal operation.