CA2216494A1 - Vehicle safety monitoring system - Google Patents

Abstract

A wheel and brake monitoring system for a truck. The system is capable of detecting looseness of any wheel assembly or excessive brake travel. Looseness of a wheel assembly is detected by sensing lateral movement of the assembly or rotational movement between two wheels of that assembly. Looseness of a wheel assembly can alternatively be detected by sensing the change in position of the edge of a wheel rim, in relation to a fixed point on the supporting axle assembly. Brake travel is monitored by sensing excessive rotational travel of the slack adjuster associated with each axle. Excessive brake wear for an automobile can also be detected through the use of an embedded sensor wire within the brake pads or shoes.

Description

Title: VEHICLE SAFETY MONITORING SYSTEM

FIELD OF THE INVENTION
This invention relates to a safety monitoring system for vehicles such as transport trucks and trailers.

Recently, considerable media attention has been given to traffic accidents caused by a wheel or wheel assembly becoming detached from a transport truck while the truck is in motion. Once separated from the truck, a detached wheel or wheel assembly becomes an uncontrolled 10 projectile that has considerable weight and momentum. A number of serious injuries and deaths have resulted from such incidents.
While there are requirements for periodic mechanical inspections of transport trucks, generally, monitoring of the mechanical condition and general roadworthiness of such vehicles relies on the 15 diligence and thoroughness of the truck operator and/or driver. Given economic pressures to keep such vehicles in productive use, maintenance and repairs are sometimes neglected. Random unpredictable component failures can of course also be the cause of accidents.
An object of the present invention is to provide a safety 20 monitoring system for vehicles such as transport trucks and trailers.

SUMMARY OF THE INVENTION
In one aspect, the invention provides a safety monitoring ~yslem for the wheels of a vehicle in which each wheel rotates on a carrier that is rotationally supported on the vehicle itself. The ~ysle~l~ includes 25 sensing means adapted to detect excessive axial movement of a wheel outwardly of the vehicle, and rotational movement of a wheel with respect to the associated wheel carrier, together with alarm means adapted to provide a warning in the event of either excessive axial movement of a wheel or rotation movement with respect to the associated wheel carrier.

This aspect of the invention is based on the recognition that it is possible to detect defects that could result in a wheel or wheel assembly becoming detached from the vehicle by monitoring either of these two eventualities. Excessive axial movement of a wheel can occur, for 5 example, in the event of catastrophic failure of a wheel bearing -- allowing the entire wheel assembly to come off the axle. Rotational movement of a wheel with respect to the associated wheel carrier will occur if the wheeI
studs that hold the wheel to the carrier shear.
In principle, the monitoring ~y~lelll of the invention can be 10 applied to a single wheel c~rrie-l by a hub, in which case the system detectsrotational movement of the wheel with respect to the hub. In the case of a dual wheel vehicle having a pair of wheels mounted side-by-side coaxially on the same hub, detection can be effected by sensing relative rotational movement between the two wheels or between one wheel and the hub.
Preferably, of course, sensing means is provided on each wheel of the vehicle, although sensing means could be used on only some wheels of the vehicle, for example, only on the dual wheels where the vehicle has both dual wheels and single wheels.
The alarm means may comprise a visual display panel to 20 alert the driver to a possible malfunction. The display panel can be designed to identify which particular wheel A~s~mhly is defective.
In another aspect of the invention, the monitoring ~ysleln may be applied to the brakes of the vehicle. This aspect of the invention may be used in combination with the wheel monitoring ~yslell, discussed 25 previously, or separately. In this aspect of the invenlion, the monitoring :iy:,le~l is applied to a vehicle having at each wheel a brake actuator including an actuator element that is movable generally longitudinally at each actuation of the vehicles brakes. The ~ystell~ includes means associated with the actuator element of each brake actuator and responsive 30 to said generally longitudinal movement of the element beyond a predetermined limit, together with alarm means adapted to provide a warning if movement beyond the limit occurs at any of the actuators.

In Ontario, the brakes of a transport truck are required to be set so that the actuator element at each wheel has a maximum travel of two inches. If travel beyond that amount is discovered during an inspection of the vehicle, heavy fines are levied. In a vehicle equipped 5 with a monitoring system according to the invention, the ~yslelll may be adjusted to respond and provide a warning if the travel of the actuator element of any one wheel approaches that maximum. This will give the opportunity to adjust the brakes to avoid contravention of applicable regulations.
Different travel limits no doubt will apply in different jurisdictions and the system preferably is adjustable so that the driver or operator can maintain the brakes within whatever regulations apply or within safety limits determined by the individual driver or operator.
In another aspect, the invention provides a safety monitoring 1~ ~ysle,n for the wheels of a vehicle in which each wheel is rotationally supported on a chassis. The ~y~telll includes, in association with at least one of the wheels, a sensor responsive to the presence of the wheel in a defined operational position in relation to the chassis. The sensor is also adapted to detect movement of the wheel beyond a pre-determined 20 amount from the defined position, such movement indicating a potential wheel failure. The ~y~lem also includes an alarm means operationally coupled to said sensor and adapted to provide a warning in the event that movement beyond a predetermined amount is detected.
In this context, the word "chassis" is not be to i"t~l~reled as 25 rerelli.,g only to the frame of the vehicle, but as including any part of the vehicle between the frame and the wheels, e.g. axles and steering components.
This aspect of the invention is based on the recognition that it is possible to detect and anticipate the failure of wheels, bearings andlor 30 axles by monitoring any change in relative position of wheel with respect to its normal operational position. It has been determined that even slight changes in the position of the wheel can give an early warning of faults.

The safety monitoring ~yslelll for the wheels of a vehicle preferably includes a sensor mounting bracket which is mounted on the chassis and designed to position the sensor such that it is adjacent to an edge of a rim of the wheel. Further, the sensor is preferably an inductive 5 proximity sensor.
In one embodiment, the sensor is mounted on a drive axle.
In another embodiment, the wheel fault sensor is mounted on a trailer axle.
In a further embodiment, the wheel fault sensor is mounted 10 on a kingpin cap.
In a still further embodiment, the wheel fault sensor is mounted on a brake cam tube.
In another embodiment, the alarm means includes a display panel adapted to provide audible and visual warnings to a driver of the 15 vehicle that the safety monitoring system has detected a wheel fault.
In another aspect of the invention, as applied to the brakes of the vehicle described above, the vehicle brakes include, at each wheel, a cam rod which is turnable about a longitudinal axis to operate a brake at that wheel, and a slack adjuster mounted on the cam rod and having an 20 outer end coupled to the actuator element. The adjuster is adjustable angularly with respect to the rod to compensate for travel of the actuator element beyond a pre-determined limit as a result of brake wear. The monitoring ~ysLem also includes means responsive to movement of the actuator element beyond a pre-determined limit which comprises a sensor 25 responsive to the presence of the slack adjuster and adapted to detect excessive travel of the slack adjuster as indicating excessive brake wear.
Preferably, the brake monitoring system has a sensor-supporting bracket mounted on the ~h~si.s and designed to position said sensor so that the slack adjustor will enter the sensing range of the sensor 30 once excess travel representing excessive brake wear has occurred. Further, the sensor is preferably an inductive proximity sensor.
In one embodiment, the brake monitoring sensor is mounted on a cam tube.
In another embodiment, the brake monitoring sensor is mounted on a kingpin cap.
In another embodiment, the brake monitoring system includes an alarm means which comprises a display panel adapted to provide audible and visual warning to a driver of the wheeled vehicle that the sensing system has detected a brake actuator fault.
In a specific embodiment, the safety monitoring ~yst~
described immediately above, is provided to a transport vehicle 10 comprising a tractor unit and a trailer unit, each having a plurality of wheels carried by at least two axles, wherein each wheel is associated with a sensor responsive to the presence of said wheel and a means associated with the actuator element of an associated brake actuator, and where an alarm means is responsive to detection of a potential failure of any wheel 15 or excessive brake travel at any wheel.
In one embodiment, the brake monitoring aspect of the invention may be applied to a vehicle such as an automobile having drum or disc brakes. In this embodiment, a sensor wire is embedded within a body of friction engendering material such as a brake lining or pad that is 20 applied against a rotating metal element such as a drum or disc when the brakes are operated. When a predetermined amount of brake pad or lining wear has occurred, the sensor wire contacts and forms an electrical connection with the brake disc or drum and shorts to ground, providing a warning signal.

In order that the invention may be more clearly understood, reference will now be made to the accompanying drawings which illustrate a number of preferred embodiments of the invention by way of example, and in which:
Pig. 1 is a partial perspective view of a transport tractor unit, partly broken away to show a hub assembly of one wheel;

Fig. 2 is an exploded perspective view of a typical such assembly;
Fig. 3 is an elevational view of a sensor ring that may be used in the assembly of Fig. 2;
5Fig. 4 is a simplified exploded view showing the sen~ing means of the invention in association with the sensor ring of Fig. 3;
Fig. 5 is a diagrammatic elevational view corresponding to Fig. 4, showing the two wheels assembled with the sensor ring and sensor;
Fig. 6 is an exploded perspective view showing an alternative 10wheel rim configuration;
Fig. 7 is a schematic illustration of a brake monitoring ~y~Le~
in accordance with the invention;
Fig. 8 is a block diagram illustrating the overall monitoring ~y~lem;
15Fig. 9 is a simplified illustration of a driver display panel that may be used as part of the system showed in Fig. 8;
Fig. 10a is a cross-sectional view showing an alternative wheel fault sensing means of the invention;
Fig. 10b is a perspective view showing how a sensor is 20mounted into a bracket using two sensor mounting rings;
Fig. 10c is a perspective view showing an alternative brake fault sensing means of the invention;
Fig. 11a is a perspective view of an embodiment of the alternative wheel and brake fault sensing means as adapted to a trailer 25axle;
Fig. 11b is a side view of the alternative wheel sensing means as adapted to a trailer axle showing how rotatable bracket can variably position sensor along the rim edge of a wheel;
Fig. 11c is a more detailed perspective view of the alternative 30brake fault sensing means as adapted to a cam tube;
Fig. 12 is a perspective view of an alternative embodint~nt of the wheel fault sensing means as adapted to a drive axle;

Fig. 13a is a perspective view of a dual purpose wheel and brake sensing means as adapted to a steering axle kingpin cap;
Fig. 13b is a exploded view of a dual purpose wheel and brake sensor bracket;
Fig. 13c is a cross-sectional view of a dual purpose wheel and brake sensing means as adapted to a steering axle kingpin cap;
Fig. 13d is a cross-sectional view of a dual purpose wheel and brake sensing means as adapted to a steering axle kingpin cap and showing how brake actuator rod travel affects the relative position of the slack 10 adjustor;
Fig. 14 is a block diagram illustrating an alternative embodiment of the overall monitoring ~y~lem of the present invention;
Fig. 15 is an alternative driver display panel that may be used as part of the ~ysLelll shown in Fig. 14;
Fig. 16 is an another alternative driver display panel that may be used as part of the system shown in Fig. 14;
Fig. 17 is an exploded view showing a brake shoe wear monitoring system for use within automobile drum brake assembly in accordance with the invention.

DESCRII~ION OF PREFERRED EMBODIMENTS
Referring first to Fig. 1, a tractor unit is generally indicated at 20 and is shown without ancillary components such, for example, as a fifth wheel a~semhly. The cab is indicated at 22 and the chassis of the vehicIe at 24. Four rear wheel assemblies of the tractor unit are shown and are individually denoted 26.
The frontmost wheel assembly at the left-hand side of the tractor unit in Fig. 1 is shown broken away at 28 to reveal the brake and hub assembly, generally denoted 30, on an axle 32 of the unit. A drum brake assembly is shown at 34 and an actuator for the brake at 36.
Typically, the brakes are air-operated.
A typical truck wheel comprises a hub, a rim and a tire and tube assembly. A rim is attached to the hub and retained at the hub by either single or dual nuts. The tire and tube assembly is then mounted on the rim and inflated. It will be seen that each of wheel assemblies 26 is a dual wheel assembly comprising two wheels disposed coaxially side-by-5 side and carried by the same hub assembly. Fig. 2 shows a typical suchwheel and hub assembly in exploded form and without the tires. The rims of the two wheels are indicated at 38 and 40 and are disposed outwardly of the hub assembly 30.
Hub assembly 30 includes a brake drum 42 and a wheel carrier 10 in the form of a hub 44, which is rotationally supported on the axle 32 of the vehicle by a wheel bearing (not shown). A series of studs 46 extend through aligned holes in the hub 44, brake drum 42 and wheel rims 38 and 40 to clamp the whole assembly to the axle. Nuts for the studs are shown at 48, outwardly of wheel rim 38.
Typically, each of the wheel rims 38 and 40 includes openings such as those shown at 50. When the two wheel rims are clamped together by the studs 46 and nuts 48, the openings in the respective rims are aligned with one another.
The housing of axle 32 (Pig. 1) is diagrammatically indicated in Fig. 2 at 52 and is fitted with a sensor 54 positioned to direct a sensing beam 56 through the aligned openings 50 in the wheel rims 38 and 40. As the wheel assembly rotates, beam 56 will be repeatedly interrupted by the solid portions of the two wheel rims between the openings 50, providing a pulsed signal. In the event that excessive relative rotation takes place between the two wheel rims 38 and 40, the signal from sensor 54 will change, or possibly be cut off if the two wheels turn with respect to one another to an extent sufficient that the openings 50 are no longer aligned.
The sy~Lem will then provide an alarm to the effect that the wheel assembly in question has developed a defect.
Sensor 54 is also sensitive to the distance of the inner wheel rim 40 from the switch. For example, the sensor may be designed to in effect "measure" that distance during the time when beam 56 is interrupted by the solid portions of the rim between the openings 50. The sensor can then respond and give an alarm signal in the event that distance exceeds a defined maximum value, indicating excessive axial outward movement of the wheel assembly.
With certain types of wheel rims, it is conventional to provide an annular ring between the two rims, primarily to protect the rims against mechanical damage due to vibration and slight relative movement when the vehicle is in motion. A typical such ring is indicated at 58 in Fig. 2 and is shown in elevation in Fig. 3. The ring has openings 60 10 to receive the wheel studs 46. According to another aspect of the invention, the ring 58 may be used as a re~er~l~ce that is sensed by sensors of the monitoring ~y~lelll to detect abnormalities. It may be necessary to radially enlarge the ring as compared with conventional protective rings.
Fig. 4 shows such an arrangement, in simplified exploded 15 form. Two wheels of a typical wheel assembly 26 are shown (with tires) in exploded positions at 62 and 64 with a sensor ring 58 in between. A sensor such as a proximity switch assembly 66 is carried at the distal end of an arm 68, the opposite end of which is secured to the axle housing 52 of the vehicle. Arm 68 should be relatively rigid but may be adjustable or capable 20 of being bent so that its shape can be changed to fit different vehicles and bring the proximity switch assembly 66 into appropriate relationship with ring 58.
Fig. 5 is a diagrammatic illustration showing the two wheel rims 38 and 40 (of the wheels 62 and 64) in their assembled condition, with 25 the sensor ring 58 between the two rims. The proximity switch assembly 66 is positioned adjacent the outer edge face of ring 58 as it rotates.
Assembly 66 is designed to be responsive to the axial position of ring 58 with respect to the longitudinal axis A-A of the wheel assembly, and to the relative rotational positions of the two rims 38 and 40. For example, the 30 assembly may include a proximity switch, a signal from which is represented by the arrow denoted 70 in Fig. 5, and which will respond to any axial movement of ring 58 beyond a prescribed limit. A response to -such movement beyond the limit will of course indicate excessive axial movement of the wheel assembly and provide an alarm signal, indicating possible hub bearing failure.
Assembly 66 will also include sensors that are responsive to 5 the relative rotational positions of the two rims 38 and 40, as indicated by the arrows denoted 72 and 74. For example, these sensors may also be proximity switches that respond to the presence or the absence of the openings 50 in the wheel rims (see Fig. 2). These sensors will accordingly provide timed pulses that will coincide as long as there is no relative 10 rotational movement between the two rims. When the sy~telll detects that the pulses represented by the arrows 72 and 74 are out of phase, the ~y~lem will recognize that excessive rotational movement has taken place between the two rims, for example indicating that the wheel studs have sheared, and provide an alarm signal.
Fig. 6 shows an alternative style of wheel rim, the two rims corresponding to the rims 38 and 40 of the previous views being denoted 38' and 40'. This style of wheel rim is designed so that each rim has marginal flanges at each side, as indicated at F. When assembled together, the marginal flange F at the outer side of the rim of the inner wheel (rim 40') confronts the corresponding flange at the inner side of the rim of the outer wheel (rim 38'). A spacer 76 of short cylindrical form is fitted between the two rims and is in effect clamped by the wheel studs and nuts.
Where this style of wheel rim is used, the spacer 76 can be used to provide the ~eferellce for the sensor assembly such as assembly 66 in Figs. 4 and 5.
The proximity switch represented by the arrow 70 in Fig. 5 can be used to "read" the spacer and respond to any deviation from its "datumn axial location when the wheel assembly is fully tightened onto the hub (44 --Fig. 2). If necessAry, openings or markings can be provided on the spacer to be "read" by the sensor.
The previous description of course relates to aspects of the monitoring system of the invention that are designed to detect and respond to defects in a wheel assembly. Fig. 7 illustrates another aspect of the invention that relates to monitoring brake actuator travel. A typical brake actuator is illustrated in simplified form and denoted as 78. As mentioned previously, each wheel of the vehicle will be provided with one of these actuators. The actuators are air-operated and are essentially conventional. Reference numeral 80 denotes a housing for an air-responsive piston of the actuator. A brake actuator rod 82 projects from one end of the housing and has a clevis 84 at its distal end by which the actuator is coupled to the actual brake mechanism (not shown). When the driver applies the brakes, air is supplied to housing 80 to move rod 10 82 longitudinally with respect to housing 80 and apply the brakes.
According to this aspect of the invention, a sensor is associated with the actuator rod 82 and is arranged to be responsive to longitudinal movement of rod 82 at a predetermined threshold limit (e.g.
two inches). Fig. 7 shows two alternative arrangements. In one 15 arrangement, the housing 80 is provided with an opening 86 (not present in a conventional brake actuator) and a sensor ~88 is fitted into the housing so as to monitor longitudinal movement of rod 82 within the housing 80.
In an alternative arrangement, a sensor denoted 90 may be mounted on a supporting bracket 92 so as to monitor movement of the rod externally of 20 housing 80.
For example, the sensors may be proximity switches or other sensors responsive to longitudinal displacement of a rod. Sensors that respond to markings or fittings on the rod (not shown) can be used.
Preferably, provision is made for adjustments so that the sensor can 25 respond to different extents of actuator rod travel, as determined by applicable regulations or other safety criteria. If adjustability is required, it may be desirable to use an external sensor such as sensor 90. Adjustability may be provided by allowing for adjustment of the sensor position or adjustment of fittings on the actuator rod.
In a simple alternative example, one or more limit switches may be used, for example, a stationary limit switch co-operating with adjustable stops on rod 82.

As mentioned previously, the brake monitoring aspect of the invention described previously may be used in combination with or separately from the wheel monitoring aspects described previously.
Conversely, the wheel monitoring aspect may be used without monitoring 5 the brakes.
Prererably, however, the system integrates both functions. Fig.
8 is a diagrammatic illustration of such an integrated ~yslem while Fig. 9 shows a corresponding display that may be provided within the driver's cab of the vehicle.
The box indicated at 94 in Fig. 8 represents a plan view of the tractor unit 20 of Fig. 1. The front wheel ~semblies 26 are shown as are two rear wheel assemblies 96 (which may be single wheels). The display panel shown in Fig. 9 is represented at 98 and an electronic signal processor at 100. The various lines denoted 102 represent signals that are 15 fed to the processor from the wheel assembly sensors and from the brake actuators described previously. Processor 100 may also receive signals representing vehicle speed if n~c~s~ry. An output signal path to panel 98 is indicated at 104. The display panel shown in Fig. 9 includes appropriately designated indicator lights for each wheel and for each of the 20 brakes of the tractor (in the upper portion of the panel denoted 98a). The lower portion 98b of the panel includes corresponding indicator lights for a three axle trailer (not shown).
In a further aspect of the present invention, wheel faults and/or excessive brake actuator rod travel can be detected through the use 25 of specially mounted proximity sensors. Wheel faults can be detected by using a proximity sensor to monitor the change in relative position of an edge of a wheel (e.g. an inner wheel rim) with respect to its normal operational position. Excessive brake actuator rod travel can be detected using a specially mounted proximity sensor which determines when a 30 slack adjuster has experienced excessive rotation, as a result of excessive brake rod travel, by monitoring whether an edge of the slack adjustor has entered into its sensing distance.

Wheel faults can be detected through the use of mounted sensors which detect changes in the position of the wheel from a safe operational position. The inventor has determined that even slight changes in the position of the edge of a wheel with respect to the chassis 5 can provide an early warning of wheel bearing and/or axle faults. The inventor has observed that if a wheel bearing is about to fail (e.g. due to insufficient lubricant), the associated wheel assembly will begin to "play"
or move from its regular position prior to actual failure, for example, over a period of roughly 15 minutes to an hour. The inventor has also observed 10 that if one or more of the wheel studs shear, the remaining studs will start to agitate as a result of the centrifugal force on the unbalanced wheel. This will cause the bearings to vibrate loose until the wheel breaks free from the wheel assembly. Again, this phenomena will occur for period of, for example, 15 minutes to an hour before a full catastrophic failure results.
By monitoring the axial movement of the wheel rim edge beyond a predetermined amount from its normal operational position, the present monitoring system can provide timely wheel fault detection to assist in the pr~venLion of catastrophic wheel failure.
Figs. lOa to 16 illustrate a wheel and brake monitoring ~ysle 20 that can be used to monitor each wheel and associated brake assembly of a transport truck comprising a tractor unit such as the unit 20 shown in Fig.
1, and an associated trailer (not shown).
Fig. lOa shows a wheel monitoring sensor and associated mounting bracket in schematic form. The bracket (only a portion of it is 25 shown) is designated 150 and supports and locates a sensor 152 adjacent to a wheel rim edge 154. Wheel rim are conventionally made out of either steel or aluminum and reference will be made to both types of rims.
Bracket 150 is preLelably made from an aluminum and steel alloy and is designed such that one end of bracket 150 can be secured to truck chassis 24 30 while the other end of bracket 150 positions sensor 152 adjacent to wheel rim edge 154 within the sensing distance of sensor 152.
Sensor 152 is preferably an inductive proximity sensor for detecting the presence or absence of a conductive metal target within a predetermined sensing range such that the movement of a wheel beyond a pre-determined amount away from a defined operational position can be detected. An inductive proximity sensor comprises a LC oscillating circuit, 5 a signal evaluator and a switching amplifier. The circuit's coil generates a high frequency electromagnetic alternating field that is emitted at the sensing face of the sensor. When a conductive metal target enters the field, eddy currents are created within the sensor and a switching signal is produced.
Sensor 152 is preferably a Honeywell SDS 30 millimetre Cylindrical Proximity Sensor (Part No. SDS-C1-B4HM-A8N normally open) with a maximum sensing distance of 16 millimetres and a weather sealed and corrosion-proof jacket for heavy industrial application. It has been determined that the detection distance for sensor 152 varies with the 15 type and thickness of the wheel rim being monitored. It has further been determined that sensor 152 detects the presence of a typical aluminum wheel rim within a sensing distance of 5 millimetres and detects the presence of a steel wheel rim within a sensing distance of 9.5 millim.otres.
Alternatively, sensor 152 can be any suitable non-contact 20 sensing device which can detect the presence or absence of metallic or rubber targets which would conventionally be present on a wheel within a fixed range such that the movement of a wheel beyond a pre-determined amount away from a defined operational position would be detected. For example, the sensor could be selected to respond to the tyre rather than the 25 wheel rim.
As shown in Fig. 10b, sensor 152 is secured into bracket 150 (only a portion of it is shown) using sensor mounting rings 153 and 153', which are moulded out of a material such as nylon. Sensor 152 has a resilient plastic and metal housing with an outer metal threaded surface 30 which can engage with the inner threaded surfaces of mounting rings 153 and 153'. Sensor 152 is inserted into a hole in bracket 150 such that the inner threads of ring 153 engage the outer threads of sensor 152 on one side of bracket 150 and the inner threads surface of ring 153' engage the outer threads of sensor 152 on the other side of bracket 150. When the threaded surfaces of rings 153 and 153' are completely engaged with the threaded surface of sensor 152, sensor 152 is securely mounted within bracket 150. This arrangement permits longitudinal adjustment of the sensor for precise setting of sensing distance.
As described before, sensor 152 is positioned such that rim edge 154 will be within the appropriate sensing distance while it is in its normal operational position. As discussed earlier, the sensing distance is 5 10 millimetres for an aluminum rim and 9.5 millimetres for a steel rim.
Referring back to Fig. 10a, while the wheel is within a defined tolerance from its normal operational position, rim edge 154 will be present within the sensing distance of sensor 152. Once the wheel rim edge 154 moves beyond a pre-determined amount away from its normal operational 15 position, rim edge 154 will no longer be within sensing distance of sensor 152. When this occurs, sensor 152 will output a switching signal indicating that a potential wheel failure has occurred.
While the appropriate tolerance may vary, it has been determined that a deviation of as little as .25 millimetres (or 10 thousands 20 of an inch) at the rim can be an indication of a potential wheel bearing or stud failure in the case of transport truck wheel. Accordingly, for an aluminum wheel rim, sensor 152 is positioned 4.75 millimetres from rim edge 154 so that wheel rim edge 154 will pass out of monitoring range of sensor 152 when it moves .25 millimetres or more away from its normal 25 operational position away from sensor 152. Similarly, for a steel wheel rim, sensor 152 is positioned 9.25 millimetres from rim edge 154 so that wheel rim edge 154 will pass out of monilo~ g range of sensor 152 when it moves .25 millimetres or more away from its normal operational position away from sensor 152.
Correct positioning is achieved using an appropriately dimensioned metal spacer 151 which can have a thickness of either 4.75 millimetres or 9.25 millimetres depending on whether aluminum or steel wheel rims, respectively, are being used. When sensor 152 is so positioned, movement of wheel rim edge 154 of .25 millimetres or more further away from sensor 152 will cause sensor 152 to detect movement of wheel riIn edge 154 out of its sensing distance indicating that a wheel fault has 5 occurred.
As the wheel assembly rotates, sensor 152 will detect the presence of inner wheel rim edge 154 as long as the wheel remains properly aligned with respect to its carrier means and consequently, as long as no wheel faults are present. However, in the event that some form of 10 wheel fault occurs, movement of wheel rim edge 154, beyond the pr~
determined amount of .25 millimetres beyond its normal operating position away from sensor 152, will be detected by sensor 152.
Since bearing or stud faults will cause both wheels of a dual wheel assembly to "play", it is possible to monitor a dual wheel assembly 15 by monitoring the inner wheel alone.
Excessive brake rod travel can be detected using a specially mounted proximity sensor to determine when a slack adjuster has experienced excessive rotation due to excessive brake rod travel. The inventor has observed that as the brake linings and brake drum are worn 20 down by frictional abrasion during repeated application of the brakes, the slack adjuster will rotate further and further as the brakes are applied and that a proximity sensor can be positioned to detect when the slack adjustor rotates to a certain position signifying excessive brake rod travel.
Fig. lOc illustrates an embodiment of such a brake rod travel 25 monitoring ~yS~e~m. Truck brakes are applied by introducing pressurized air through a tube into the brake chamber assembly 155 which in turn extends a brake actuator rod 82. Brake actuator rod 82 acts on the end of a slack adjuster 156 to turn a cam rod 158 which is housed within cam tube 160. Turning of cam rod 158 about its longitudinal axis causes the brake 30 linings to fictionally engage the inside surface of a brake drum (not shown). Air brakes can fail if the brake linings or drum become excessively worn, or if the brakes are not properly adjusted.

Slack adjustor 156 is connected to a brake actuator rod 82 by a clevis 84. When the brake actuator rod 82 moves longitudinally at each actuation of the brake, slack adjustor 156 will rotate the cam rod 158, which in turn urges the brake linings into engagement with the brake drum to 5 apply the brakes. In this way, the degree of rotation of slack adjustor 156 will vary in accordance with the distance that brake actuator rod 82 travels.
The brake rod travel monitoring system comprises bracket 150' (only a portion of it is shown) which mounts and locates sensor 152' within the rotational path of slack adjustor 156. Bracket 150' is preferably 10 constructed from an aluminum and steel alloy and formed such that one end of bracket 150' is adapted to be secured to truck chassis 24. The other end of bracket 150' is used to position sensor 152' such that slack adjustor 156 of the brake mechanism will rotate into the sensing distance of sensor 152' when the associated brake actuator rod 82 has travelled beyond a pre-15 deter~nined limit as a result of brake wear.
Sensor 152' is preferably secured into bracket 150' in the samefashion as described in respect of the wheel fault sensing ~ybtelll, using sensor mounting rings 153 and 153'. Sensor 152' is preferably a Honeywell Cylindrical Proximity Sensor (Part No. SDS-C1-B4HM-A8N normally 20 closed) with a max~mum sensing distance of 16 millimetres and a weather sealed and corrosion-proof jacket for heavy industrial application. It has been determined that sensor 152 detects the presence of the body of a typical steel slack adjuster within a sensing distance of 11.1 millimetres.
Sensor 152' is positioned such that slack adjustor 156 comes 25 within 11.1 millimetres, or the sensing distance, of sensor 152' when slack adjustor 156 has rotated through a distance corresponding to excessive travel of brake actuator rod 82. It is generally desired to provide the driver with advance waming that brake actuator rod 82 travel has exceeded 50.8 millimetres (or 2 inches). Accordingly, sensor 152' is positioned such that 30 slack adjustor 156 rotates into sensing distance of sensor 152' when the brake adjustor rod 82 has travelled 44.45 millimetres (or 1.75 inches).
The wheel fault and brake travel monitoring ~ysLe~ is now described with respect to a left trailer wheel. Fig. 11a shows the design and orientation of bracket 150 and sensor 152 assembly used to monitor a wheel 40 attached to trailer axle 162 and bracket 150' and sensor 152' assembly used to monitor excessive travel of brake actuator rod 82.
Bracket 150 of the wheel fault monitoring ~y~lem is mounted on axle housing 52 of trailer axle 162 using a clamp 164. Clamp 164 may either be square or round to accommodate a square or round trailer axle 162. Sensor 152 is shown secured into bracket 150 using sensor mounting rings 153 and 153'. Bracket 150 is adjustable within clamp 164 about a pivot 10 point 166 (see Fig. 11b) so that bracket 150 can accommodate different rim sizes. By suitably rotating bracket 150 about pivot point 166, alternatively positioned sensor 152" can be placed adjacent to rim edge 154" of a smaller wheel rim. It is also apparent that in this way, it is possible to mount bracket 150 and clamp 164 such that sensor 152 is positioned at any angular 15 position about the centre of rotation of the wheel, although it is ~refe~ableto locate sensor 152 at a position on the left wheel conventionally known as "3 o'clock on the wheel", or 90 degrees clockwise around the axle from the top of the wheel when looking down the axle to the wheel.
As previously described, sensor 152 should be placed 4.75 20 millimetres from an aluminum rim edge 154 and 9.25 millimetres from a steel rim edge 154 so that wheel rim edge 154 will pass out of monitoring range of sensor 152 when it moves .25 millimetres or more away from its normal operational position and sensor 152.
Now r.2f~ g to Figs. 11a and 11c, the brake rod travel sensor 25 bracket 150' is described. When the brakes are applied, brake chamber ~s~mhly 155 causes brake actuator rod 82 to travel longitudinally and slack adjuster 156 to rotate as discussed above. Bracket 150' comprises a U-shaped strap 168 and a sensor arm 170. Sensor arm 170 has at one end a mounting flange 171. An elongate opening 173 extends longitudinally of 30 the arm. Strap 168 embraces a cam tube 160 which houses the brake cam rod 158 (Fig. 10c). Strap 168 is placed around cam tube 160 and removably secures sensor arm 170 onto cam tube 160 using nuts 169 that bear against flange 171 of sensor arm 170. Sensor 152' may be variably positioned within opening 173 using sensor mounting rings 153 and 153'.
As discussed above, sensor 152' is positioned such that slack adjustor 156 of the brake mechanism enters the sensing distance of sensor 5 152', when brake actuator rod 82 has travelled beyond a pre-determined limit as a result of brake wear. Specifically, sensor 152' is positioned such that slack adjustor 156 comes within 11.1 millimetres, or the sensing distance, of sensor 152' when slack adjustor 156 has rotated through a distance corresponding to excessive travel of brake actuator rod 82. Sensor 10 152' is positioned such that slack adjustor 156 rotates into sensing distance of sensor 152' when the brake adjustor rod 82 has travelled 44.45 millimetres (or 1.75 inches). Correct positioning can be achieved using an appropriately dimensioned metal spacer 151 with length 11.1 millimetres as previously described.
The wheel fault monitoring ~y~em is now described with respect to a left drive wheel. Fig. 12 shows a side plate bracket 150" and sensor 152 assembly used for monitoring wheels attached to a square drive axle 174. Sensor 152 is shown located at 3 o'clock on the left drive wheel.
Bracket 150" fits closely to the drive wheel assembly and as a result does 20 not monitor axle faults to the degree that bracket 150' can on the trailer axle as bracket 150' is mounted further along the body of the axle. It should be noted that the bracket 150 and sensor 152 assembly for monitoring wheels on the trailer axle can be also used on a drive axle just as side plate bracket 150" can be used on a trailer axle. However, it is preferable to use 25 the rod shaped bracket 150 on a trailer axle where axle faults are more common.
Bracket 150", comprises a U-shaped strap 168' and a sensor arm 170'. Sensor arm 170' has a mounting flange 171' at one end and an opening 176 at the other. Strap 168' is placed around drive axle 174 and is 30 used to removably secure sensor support arm 170' onto drive axle 174 using nuts 169' to engage the mounting flange 171 of sensor arm 170'.
Finally, sensor 152 is securely positioned within opening 176 using sensor mounting rings 153 and 153'. Sensor 152 is positioned adjacent and within sensing distance from the drive axle 174 wheel rim edge 154 (not shown). In the event of a wheel fault, wheel rim 40 will be caused to move beyond a pre-determined amount from its normal 5 operational position, which will in turn, cause sensor 152 to indicate a change in the proximity of rim edge 154. As previously described, sensor 152 is positioned to detect the movement of rim edge 154 of .25 millimetres or more away from its normal operational position and sensor 152. Correct positioning is achieved using an appropriately 10 dimensioned metal spacer 151 which can have a length of either 4.75 millimetres or 9.25 millimetres depending on whether aluminum or steel wheel rims, respectively, are being used.
The brake rod travel monitoring system described in Pigs. 11a and 11c can be installed on drive axle 174 in the manner described with 15 referellce to those figures, but using a U-shaped strap in place in place of the curved strap 168 shown.
Figs. 13a, 13b, 13c and 13d show a dual purpose bracket 178 which is used to mount sensors 152 and 152' for monitoring wheel faults and excessive brake actuator rod travel at a front steering wheel of a 20 vehicle. Since steering wheel rims turn with respect to their supporting axle 32, it is not possible to use brackets of the form described previously.
Figs. 13a, 13b, 13c and 13d show the wheel fault and brake actuator rod travel monitoring apparatus as applied to a right front steering wheel. It should be noted that the wheel fault sensor 152 is positioned at 9 o'clock 25 on the right wheel, whereas it would be positioned at 3 o'clock on the left wheel.
Bracket 178 is mounted on a kingpin cap 180 of a steerin~ axle 182. The wheel turns on a kingpin (not shown) below cap 180.
Bracket 178 is comprises a base 184 at one end of a first arm 30 186 (see Fig. 13b) and a separate second arm 187 and is preferably made from an aluminum and steel alloy. Base 184 is attached to a kingpin cap 180 using metal screws inserted through screw holes 188. Alternatively, base 184 may be welded onto kingpin cap 180 or can be designed to replace kingpin cap 180 entirely. At its end opposite base 184, arm 186 has an opening 190 through which sensor 152 can be mounted using sensor mounting rings 153 and 153'. The second arm 187 is attached to arm 186 5 using a spacer bolt 191 and nuts 192. Sensor 152' is then mounted in an opening 194 in arm 187 using sensor mounting rings 153 and 153'.
Referring now to Fig. 13d, it will be seen that bracket 178 is designed so that the sensors 152 and 152' are positioned adjacent to the wheel rim edge 154 and in the travel path of slack adjuster 156, 10 respectively.
As previously described, sensor 152 is positioned to detect the movement of rim edge 154 of .25 millimetres or more away from its normal operational position and sensor 152. Correct positioning is achieved using an appropriately dimensioned metal spacer 151 which can 15 have a length of either 4.75 millimetres or 9.25 millimetres depending on whether aluminum or steel wheel rims, respectively, are being used.
Further, sensor 152' is positioned such that slack adjustor 156 rotates into sensing distance of sensor 152' when the brake adjustor rod 82 has travelled 44.45 millinletres (or 1.75 inches). Correct positioning can be 20 achieved using an appropriately dimensioned metal spacer with a thickness of 11.1 millimetres, similar to spacer 151 of Fig. lOa.
As previously described, when the brakes are applied, brake chamber assembly 155 causes brake actuator rod 82 to travel longitudinally and slack adjuster 156 to rotate from the positions shown in ghost outline 25 to the positions shown in full outline. Thus, when the brake actuator rod 82 moves longitudinally at each actuation of the brake, slack adjustor 156 will rotate the cam rod 158 and the amount of rotation will vary in accordance with the distance that brake actuator rod 82 travels. Sensor 152' is positioned such that when slack adjustor 156 rotates to compensate for 30 brake actuator rod 82 which has excessive travel, slack adjuster 156 will come within the sensing range of sensor 152'.
While the above embodiments have been described with respect to a conventional tractor-trailer, it should be understood that the wheel fault and brake actuator rod travel monitoring ~y~lems can be adapted to monitor wheel faults for any wheeled vehicle, including trucks, trailers, cube vans and recreational vehicles. Further, bracket 150 may be 5 made of other metals or metal alloys such as iron or from other materials such as kevlar, nylon or rigid petroleum products. Bracket 150 may be constructed in a variety of shapes to negotiate around obstacles on truck chassis 24. Sensor locations, sensing distances and the amount of movement to which the sensor responds will of course vary according to 10 the type of sensor used and the particular vehicle to which the sy~Lelll of the invention is applied.
Fig. 14 is a schematic plan view of a tractor unit 20 of the type shown in Fig. 1 together with a typical trailer. Tractor wheel assemblies 26 are shown as are two trailer wheel assemblies 200 (which may be single 15 wheels). Further, a display unit is shown at 202, a tractor sensor unit is shown at 204 and a trailer sensor unit is shown at 206. Display unit 202 consists of a display 208 and a microcontroller 210. Display 208 is mounted within the cab. Microcontroller 210 receives and transmits data to and from tractor sensor unit 204 and trailer sensor unit 206 and display 208 via 20 cables 212.
Cables 212 also run from monitoring sensors to their appropriate sensor units. The portion of cables 212 running between the trailer and the tractor is flexible and cables 212 are long enough to span the distance between the tractor unit and the trailer unit no matter what 25 positions they assume relative to each other.
Microcontroller 210 includes a microprocessor 214 which contains a read only memory (ROM) 216 to store instruction sets and a random access memory (RAM) 218 to store dynamic data. Both memory units 216 and 218 are controlled and accessed by microcontroller 210 in a 30 conventional manner. Microcontroller 210 continuously monitors the ~y~lem sensors using a well-known RS-485 network and controls LED
arrays, an audible alarm, and the push button inputs of display 208.

The RS-485 network is a commonly used specialized data interface which allows for the configuration of inexpensive local networks that can support as many as 32 driver/receiver pairs and can operate in the presence of electrically noisy environments.
Tractor sensor unit 204 and trailer sensor unit 206 each contain dip-switches 220 and 222, respectively, which can be set to determine the number of axles to be monitored, preferably between one and five axles for each sensor unit. Each sensor is polled at an interval not greater than lms. If a fault is detected by the appropriate sensor unit, 10 display unit 202 receives and latches a signal representing an alarm for the appropriate axle wheel into RAM 218 of microcontroller 210. Display 208 will then visually and audibly alert the driver as to the relevant detected ~yslem faults.
Fig. 15 shows display 208, tractor sensor unit 204 and trailer 15 sensor unit 206. Display 208 provides visual and auditory warnings to the driver indicating when wheel or brake faults have been detected by sensors 152 and 152', respectively, using a 3 by 8 bi-colour LED array 209 and a built-in speaker (not shown). LED array 209 comprises 24 bi-colour LEDs which indicate sensor status according to their colour. A green LED indicates that 20 no wheel or brake fault has been detected and a red LED indicates that a wheel or brake fault has been detected. Each axle is provided with three indicating LEDs, a left one indicating a left wheel fault, a middle one indicating a brake fault, and a third right hand side one indicating a right wheel fault. Display 208 provides eight indicating LED rows. In the case 25 where a tractor/trailer has more than eight axles, a single row of indicating LEDs can be further configured to indicate the status for two axles.
Display also incorporates three push buttons 211 to allow the driver to interact with the wheel fault and brake travel monitoring ~y~le~
ACK allows the driver to acknowledge alarm conditions, RESET allows 30 the driver to reset the ~y~lem to see if a fault has been cleared and BRIGHT
allows the driver to adjust the brightness levels of the LEDs to adjust for ambient light conditions.

Referring now to Pigs. 14 and 15, when the monitoring ~yslem is powered-up or when the driver presses the RESET button, display unit 202 performs a self-test of LED array 209 and the audible alarm.
Display unit 202 then begins polling tractor sensor unit 204 and trailer 5 sensor unit 206 using basic ASCII commands to determine the status of sensors 152 and 152'. While sensors 152 and 152' do not detect wheel faults or excessive brake travel, all LEDs relating to monitored axles will be green and those LEDs not used will be off. When a fault occurs, the corresponding LED will change from green to a blinking red and an 10 audible alarm will sound and continue until the driver presses the ACK
button. Once the ACK button is depressed, the audible alarm will stop and the corresponding LED will cease blinking. The RESET button can be used to reset the system or to check to determine whether a fault has been cleared.
Specifically, upon initiation microcontroller 210 will send an ASCII character "R" to tractor sensor unit 204 and trailer sensor unit 206.
Upon receipt of the character "R", tractor sensor unit 204 and trailer sensor unit 206 initiate a read of their corresponding dip switches 220 and 222, respectively to determine the number of axles which are required to be 20 monitored and commence monitoring procedure.
Microcontroller 210 then sends an ASCII character "A" to retrieve status of the axles being monitored within tractor sensor unit 204 and then an ASCII character "B" to retrieve status of axles from the trailer sensor unit 206. At this point, tractor sensor unit 204 and trailer sensor 25 unit 206 respond with a five digit code, with each digit representing the particular status of an axle. The following table lists the codes and their respective meanings.

DIGlT CONDITION
8 Axle not monitored 7 Axle not monitored, no-fault 6 Right Wheel fault 5 Brake fault 4 Brake fault and Right wheel fault 3 Left Wheel fault 2 Left Wheel fault and Right Wheel fault Brake fault and Left Wheel fault 0 Brake fault and Right Wheel fault and Left Wheel fault Upon receiving the two five digit strings, microconllolIer 210 then determines the appropriate display for display 208. As an example, when the five digit string 77588 is received from tractor sensor unit 204, 5 microcontroller 210 will determine that axle 1 and 2 are fault-free and that axle 3 has a brake fault. Display 208 will then be provided with the a~ro~iate data signals which will cause the middle LED in row 3 to turn from green to a flashing red and the audible alarm to be sounded. In such a fashion, the driver will be alerted to axle three's brake fault.
Microprocessor 210 also provides display unit 208 with a signal which causes a separate visual warning when the trailer connection has been disconnected. When a disconnection occurs, the LED array 209 will flash a distinct "X" pattern across LED array 209. This ensures that the driver will be notified if the system is not in full operation.
Fig. 16 shows an alternative display 208 comprising a digital display 224 and push buttons 226, display 208 being connected to the monitoring ~y~teln using cables 212. Digital display 224 is a conventional LCD display which allows display 208 to have a reduced width, height, and thickness since the circuitry required to drive the LCD display is less buLky than that required to drive the LED display panel described above.
Accordingly, the use of digital display 224 minimizes the space required to mount display 208 within a truck cab. Digital display 224 provides driver with a description as to whether a fault has been detected and if so, what kind of fault has occurred and on which axle.
It should be noted that while this safety monitoring ~y~lelll is intended to be used to detect wheel faults and excessive brake travel, it is also possible to use the system as a driving training ~yS~ by alerting a trainee when they have made an inappropriate turn. When an inappropriate turn is made which may lead to the jackknifing of the 5 tractor-trailer rig, it has been determined that the vehicle's trailer wheels will turn so violently that the wheel rim edge 154 of each wheel will leave the sensing range of wheel sensor 152 which will cause a wheel fault indication to be given to the driver. The occurrence of such an in-lic~tion will inform the driver that a dangerously narrow turn has been made.
Fig. 17 shows an exploded view of a brake monitoring ~y~lel~
for use in an automobile or other vehicle that uses a conventional drum brake assembly. A sensor wire 228 is embedded into brake linings 229 on shoes 230 and extends through backing plate 232 to a brake sensor unit (not shown) which may be essentially of the form described previously in the 15 context of a truck brake monitoring system. Sensor wire 228 is positioned a distance from the surface of brake linings 229 equivalent to the pre-determined amount of brake lining wear desired to be detected.
When the brake linings 229 wear down by the pre-determined amount, sensor wire 228 will be exposed along the surface of 20 brake linings 229 and will short to ground through the brake drum (not shown). Even in the case of uneven brake pad wear, sensor wire 228 will be exposed over certain areas of the approximately cylindrical surface of brake linings 229. When sensor wire 228 makes electrical contact with the brake drum, the brake sensor of the monitoring system will respond and 25 warn the driver that the brake linings should be replaced.
This technique can also be used in association with a disc brake assembly. Por such an application, a sensor wire simil~r to 228 will be embedded within at least one of the brake pads. When the pad wear down to a pre-determined extent, the sensor wire will be exposed and will 30 make electrical contact with the brake disc causing the sensor wire to short. The brake sensor will then warn the driver to replace the pads.
It should of course be appreciated that the preceding description relates to particular preferred embodiments of the invention only and that many modifications are possible within the broad scope of the invention. While examples of sensor configurations and types have been given, it should be noted in particular that applicant does not intend 5 to be limited to any particular one of these examples and that different types of sensors and configurations may be used within the broad scope of the invention. It may even be possible to provide sensor means in the wheel rim itself, for example, in the form of a computer chip.

Claims (24)

1. A safety monitoring system for a vehicle having wheels, each of which rotates on a carrier that is rotationally supported on the vehicle, the system comprising:
sensing means adapted to detect excessive axial movement of a wheel outwardly of the vehicle and rotational movement of the wheel with respect to the associated wheel carrier, and alarm means adapted to provide a warning in response to either of excessive axial movement of a wheel or rotational movement of the wheel with respect to the associated wheel carrier.

2. A system as claimed in claim 1, wherein the vehicle includes at least one dual wheel assembly which includes a pair of wheels disposed coaxially side-by-side, and wherein said sensing means is adapted to detect said rotational movement of the wheel with respect to the associated wheel carrier by responding to relative rotational movement between the two wheels.

3. A system as claimed in claim 2, wherein said sensing means is carried by a housing of an axle on which said wheel assembly is rotationally supported, and wherein said sensing means is adapted to project a sensing beam through openings in rims of said dual wheels which are aligned when the wheels are correctly assembled on the vehicle and which is adapted to respond to misalignment of said openings or outward axial movement of the wheel assembly.

4. A system as claimed in claim 2, further comprising a sensor ring mounted between said wheels, and wherein said sensing means comprises a sensor assembly positioned adjacent an outer edge of said ring and adapted to respond to outward axial movement of said ring from a datum location and relative rotational movement between said wheels on opposite sides of said ring.

5. A system as claimed in claim 1, wherein said alarm means comprises a display panel adapted to provide a visual indication to a driver of the vehicle of a defect detected by said sensing means.

6. A system as claimed in claim 1, wherein said vehicle has, at each wheel, a brake actuator including an actuator element that is movable generally longitudinally at each actuation of the vehicles brakes, wherein the system further includes means associated with the actuator element at each said brake actuator and responsive to said generally longitudinal movement of the element beyond a predetermined limit, and wherein said alarm means is adapted to provide a warning if movement beyond said limit occurs at any of said actuators.

7. A safety monitoring system for a vehicle having wheels rotationally supported on a chassis, the system comprising:
in association with at least one of said wheels, a sensor responsive to the presence of said wheel in a defined operational position with respect to said chassis and adapted to detect movement of said wheel beyond a pre-determined amount away from said defined position as indicating a potential failure relating to said wheel; and alarm means operatively coupled to said sensor and adapted to provide a warning in the event that said movement beyond a predetermined amount is detected.

8. A system as claimed in claim 7, wherein said sensor is supported by a bracket mounted on the chassis and designed to position said sensor adjacent to an edge of a rim of said wheel.

9. A system as claimed in claim 8, wherein the bracket is designed for mounting on a trailer axle.

10. A system as claimed in claim 8, wherein the bracket is designed for mounting on a drive axle.

11. A system as claimed in claim 8, wherein the bracket is designed for mounting on a kingpin cap.

12. A system as claimed in claim 8, wherein said sensor is an inductive proximity sensor which detects the movement of said rim edge of said wheel beyond a pre-determined amount away from said defined position.

13. A system as claimed in claim 7, wherein the alarm means comprises a display panel adapted to provide audible and visual warning to a driver of the wheeled vehicle that the sensing system has detected a wheel fault.

14. A safety monitoring system for a vehicle having wheels, a chassis and, at each wheel, a brake actuator including an actuator element that is movable generally longitudinally at each actuation of the vehicles brakes, the system comprising means associated with the actuator element at each said brake actuator and responsive to said generally longitudinal movement of the element beyond a predetermined limit, and alarm means adapted to provide a warning if movement beyond said limit occurs at any of said actuators.

15. A system as claimed in claim 14, wherein the vehicle brakes include, at each wheel, a cam rod which is turnable about a longitudinal axis to operate a brake at that wheel, and a slack adjuster mounted on said cam rod and having an outer end coupled to said actuator element, the adjuster being adjustable angularly with respect to said rod to compensate for travel of said actuator element beyond a pre-determined limit as a result of brake wear, and wherein said means responsive to movement of the actuator element beyond a pre-determined limit comprises a sensor responsive to the presence of said slack adjuster and adapted to detect excessive travel of said slack adjuster as indicating excessive brake wear.

16. A system as claimed in claim 15, wherein said sensor is supported by a bracket mounted on the chassis and designed to position said sensor is positioned so that the slack adjustor will enter the sensing range of the sensor once excess travel representing excessive brake wear has occurred.

17. A system as claimed in claim 16, wherein the supporting bracket is designed for mounting on a cam tube.

18. A system as claimed in claim 16, wherein the supporting bracket is designed for mounting on a kingpin cap.

19. A system as claimed in claim 16, wherein said sensor is a inductive proximity sensor which detects movement of the actuator element beyond a pre-determined limit.

20. A system as claimed in claim 14, wherein the alarm means comprises a display panel adapted to provide audible and visual warning to a driver of the wheeled vehicle that the sensing system has detected a brake actuator fault.

21. A system as claimed in claim 7, wherein said vehicle has, at each wheel, a brake actuator including an actuator element that is movable generally longitudinally at each actuation of the vehicles brakes, wherein the system further includes means associated with the actuator element at each said brake actuator and responsive to said generally longitudinal movement of the element beyond a predetermined limit, and wherein said alarm means is adapted to provide a warning if movement beyond said limit occurs at any of said actuators.

22. A system as claimed in claim 8 or 16, wherein said sensor has a housing which is received in an opening in said bracket, so that portions of the housing extend from opposite sides of said bracket, said portions being externally screw threaded and fitted with correspondingly internal, screw threaded elements for clamping against the bracket.

23. A transport vehicle comprising a tractor unit and a trailer unit, each having a plurality of wheels carried by at least two axles, wherein the vehicle is provided with a safety monitoring system as claimed in claim 21, and wherein each wheel has associated therewith a said sensor responsive to the presence of said wheel, and a said means associated with the actuator element of an associated brake actuator, and wherein said alarm means is responsive to detection of a potential failure of any wheel or excessive brake travel at any wheel.

24. A safety monitoring system for automobile having braking means which includes a body of friction-engendering material that is applied against a rotating metal element when the brakes are operated, wherein said body of friction-engendering material has embedded therein a sensor wire which is arranged to form an electrical connection with said metal element when a pre-determined amount of said body has worn away, and alarm means operatively coupled to said sensor wire and adapted to provide a brake alarm warning.