GB2531746A

GB2531746A - Tyre tread monitoring

Info

Publication number: GB2531746A
Application number: GB1419180.3A
Authority: GB
Inventors: Mcneight David
Original assignee: Pre-Chasm Res Ltd
Current assignee: Pre-Chasm Res Ltd
Priority date: 2014-10-28
Filing date: 2014-10-28
Publication date: 2016-05-04
Also published as: GB201419180D0

Abstract

A system for monitoring vehicle tyre 11 tread depth comprises wheel rotation counting means, distance travelled measuring means and computing means for calculating the tyre circumference from the obtained data and the tread depth from the calculated tyre circumference and the initial new tyre circumference. The distance travelled measuring means preferably comprises GPS 39. The wheel rotation counting means may comprise a transducer 36, 38 of an anti-lock braking system or a traction control system. The system may be integrated with an indirect tyre pressure monitoring system based on tyre diameter. The system may provide a dashboard indication of tread depth and a remote indication to a management facility. Also disclosed is method of calculating vehicle tyre tread depth using said system.

Description

Tyre Tread Monitoring This invention relates to vehicle tyre tread monitoring.

Vehicle tyres are subject to wear and damage. Worn or damaged tyres can be dangerous on road vehicles, and tyres are checked in routine inspection such as the British Government's Ministry of Transport (MOT) annual test. Tyres that do not have a prescribed minimum tread depth will not pass the test. The annual check, however, means that the tyre could have been worn, and dangerous, for some months before.

It is, of course, the responsibility of the vehicle owner to maintain it, and particularly its tyres, in safe and roadworthy condition. Tyre condition, and even tyre inflation, are often overlooked, or not checked regularly enough. Worn or damaged tyres are implicated in around 50% of serious or fatal road injuries.

Tread depth gauges are readily available. They comprise a probe sliding in a cylinder. The probe is inserted into a tyre groove and the cylinder advanced till its end is in contact with the tread. The tread depth is read off a scale, which in some instances is on the other end of the probe projecting from the other end of the cylinder. Such a gauge is best used when the vehicle is on a ramp or when the wheel is off the vehicle, so that the entire width and circumference can be inspected -tyres are often subject to uneven wear through faulty tracking or wheel alignment. Using such gauges when the vehicle is on the road most often means kneeling, squatting or even lying on the ground, and even so only a small part of most tyres will be available for inspection.

Other proposals have been made for tyre tread depth measurement, some involving making an image from structured light illumination that can be analysed to give tyre surface contour information from which tread depth can be calculated. The image can be taken across the width of the tyre to detect uneven wear. One such proposal has the imaging arrangement let into a road surface.

There is no available provision, however, whereby tyre tread depth monitoring can be carried out easily and objectively.

The present invention provides such a tyre tread monitoring function The invention comprises a method of calculating vehicle tyre tread depth comprising measuring the number of rotations of a vehicle wheel per unit distance travelled, calculating from that measurement the circumference of the tyre and calculating the tread depth as a function of the calculated circumference, and a system for monitoring tyre tread depth based on such a method.

Conventional on-board vehicle instrumentation comprises a speedometer and odometer from which speed and distance travelled are derived from rotations of the gearbox output shaft. Speed is inferred from a notional tyre diameter. As tread wears down, the tyre diameter reduces, and the wheels need to rotate more often to cover a given distance. So, as tread wears down, the speedometer and odometer become inaccurate, giving an over reading of both speed and distance travelled. With a true reading of distance travelled, however, the number of rotations of the wheel required to cover that distance gives a measure of tyre circumference, which needs only to be divided by 27r to give tyre radius. Subtracting the measured radius from the initial, new tyre, radius, gives a measure of the amount of tread wear, and subtracting that from initial tread depth gives tread depth remaining.

A true measure of distance can be had from Global Positioning System (GPS) measurements. Many vehicles nowadays are fitted with GPS systems, and these can be integrated with a vehicle management system for the purpose, for example, of advising when an oil service is due.

Vehicles, of course, have more than one tyre, and not all tyres necessarily wear at the same rate. It is desirable to have independent measurements of the rotation of each wheel.

The wheel revolutions counters may comprise magnetic or optical sensors.

The diameter of a tyre is dependent on tyre pressure, and one method for monitoring tyre pressure involves measurement of wheel rotational speeds. An underinflated tyre has a smaller radius, and hence circumference, than a properly inflated tyre. The effect of under-inflation is commensurate with the effect of tread wear over the life of the tyre, but both under-inflation, which is dangerous, and undue tread wear, which is dangerous, act in the same sense, namely to reduce the tyre diameter.

Indirect methods for tyre inflation monitoring involve measurement of tyre diameter through measuring wheel rotational speed. Tyre pressure, of course, depends on temperature, and tyres are warmer when running than when stationary. Tyre pressure increases by about 2kiloPascals per degree Celsius. This and other factors make assessment of running tyre pressure somewhat complex, and, as this is not a direct measurement of pressure, it gives tyre pressure only in relation to a wheel speed measured at proper static inflation pressure. It is used, however, to give a warning of under-inflation, particularly on run-flat tyres, where under-inflation may not be immediately noticed. The system needs recalibrating each time tyre pressure is topped up, which compensates for tread wear since the previous top-up.

Here, however, an opportunity to monitor tread wear is wasted. According to the present invention, this existing tyre pressure monitoring system can be modified to measure tread wear by measuring tyre diameter as a function of wheel revolutions per unit distance travelled over a running period after each inflation to correct pressure, and comparing that with the like figure for the initial running period for the tyre when new.

One embodiment of a tyre tread depth monitoring system according to the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a side view of a tyre Figure 2 is a diagrammatic section through a tyre showing tread depth; Figure 3 is a diagrammatic view of an automobile showing system components; Figure 4 is a diagrammatic view of the system.

The drawings illustrate a method of monitoring vehicle tyre 11 tread depth d comprising measuring the number of rotations of a vehicle wheel per unit distance travelled, calculating from that measurement the circumference of the tyre I I and calculating the tread depth d as a function of the calculated circumference.

Figure 1 shows a tyre I I having a circumference itD I, where Dl is the tyre diameter. D2 is the diameter of the bottom of the tread. Tread depth d is equal to D1 -D2. Figure 2 shows a small region of the tyre 11 in cross section, showing thread depth d between the tyre surface S and the base B of the tread. A minimum safe tread depth is indicated by dashed line M. This might be a legal minimum, e.g. 1.6 mm in the United Kingdom, or a larger amount, say 3 mm, that might be regarded as a more desirable depth at which tyres should be changed.

Figure 3 illustrates an automobile having a chassis 31, four wheels on axles 37, an engine 32, gearbox 33 and gearbox output, or transmission shaft 34 driving the rear wheels through a differential gear 35.

Transducers 36 on transmission shaft 34 and 38 on each wheel axle 37 measure the rotation rate of the shaft 34 and each wheel severally. The wheel transducers 38 can be the transducers used in antilock braking/traction control systems (ABS/TCS). A GPS system 39 measures vehicle speed and distance travelled.

Figure 4 is a block diagram of the system. GPS system 39 and transducers 36, 38 input vehicle speed/distance travelled, transmission shaft 34 rotation and wheel rotation to a processor 41.

Tyre circumference, for each tyre 11, is computed as SiN, where S is a given distance, say lkm, and N is the number of wheel rotations during that distance. Tyre diameter DI is then S/Nit. Tread wear since new is (D1(,,e0 -D1)/2 and tread depth remaining is T - ",) -D I)/2 where T is tread depth when new, which is, of course (D1(,,,,,, -D2)2.

GPS distance, or some other transmission shaft-independent distance measure is used, not the vehicle's odometer, which conventionally takes its input from the transmission shaft revolutions, assuming the tyres are new on the driven wheels, and this would not reveal any tyre wear. As tyres wear, or if they are run under inflated, the odometer registers increasingly inaccurate distance. An accelerometer or ring laser gyroscope could be used instead of GPS.

Indirect tyre pressure monitoring systems based on wheel revolution rate involve differences in tyre diameter due to over or under inflation. The systems need calibrating each time the tyres are inflated. It is important, of course, for monitoring tread depth that tyres are correctly inflated, and the measurement is best made, therefore, immediately after tyres have been inflated, and the measurement can be triggered by the signal to recalibrate the pressure monitoring system.

A correctly inflated tyre, when new, may have a circumference of, say, 2500mm. If the measurement is made over the first kilometre, the wheel will rotate 1000/2,5 or 400 times. If the circumference is, through tread wear, reduced to 2470mm, corresponding to a reduction in tread depth of about 5mm, the number of revolutions will be about 405.

For greater accuracy, measurement may be taken over two or five kilometres, during which it may be assumed that the tyre remains correctly inflated. Thereafter, continued monitoring will indicate reduction in tyre diameter due to a combination of tread wear and pressure loss, until the next tyre inflation and recalibration.

The system can display a tread measurement result as part of a dashboard display, displaying either tread depth or a pass-fail indication. However, the processor 41 may communicate with a management facility such as a garage, a tyre service, a fleet management operation, or an insurance company, or a regulatory authority. This may be done directly, through a vehicular aerial 44, Figure 4, or through a smartphone 45 loaded with software. Wear measurements can be used to predict the need for replacement tyres, and even to search for replacement bargains or to make a replacement appointment, and to make sure that a replacement service has tyre in stock when called for.

Claims

Claims: 1 A method of calculating vehicle tyre tread depth comprising measuring the number of rotations of a vehicle wheel per unit distance travelled, calculating from that measurement the circumference of the tyre and calculating the tread depth as a function of the calculated circumference.
2 A method according to claim I, in which distance travelled is measured by a gearbox output shaft independent method.
3 A method according to claim 2, in which distance travelled is measured by GPS.
4 A method according to any one of claims 1 to 3, in which wheel rotation is measured independently for each wheel of the vehicle.
A method according to claim 5, in which wheel rotation is measured by a transducer of an antilock braking system and/or traction control system on a vehicle so equipped.
6 A system for monitoring vehicle tyre tread depth comprising wheel rotation counting means and distance travelled measuring means, and computing means calculating wheel circumference from wheel rotations and distance travelled and calculating tread depth from computed wheel circumference and initial, new tyre circumference.
7 A system according to claim 7, integrated with an indirect tyre pressure monitoring system based on tyre diameter.
8 A system according to claim 6 or claim 7, in which tyre diameter is measured during an initial period after tyre inflation during which circumference is assumed unchanged through pressure loss 9 A system according to claim 8, in which circumference is thereafter monitored continuously as an indication of combined tread wear and tyre pressure loss.A system according to any one of claims 6 to 9, giving a dashboard indication of tread depth.11 A system according to any one of claims 6 to 10, giving a remote indication of tread depth to a management facility.12 A system according to claim 11, including smartphone software mediated reporting.