The condition of a pneumatic rubber tyre has been observed during driving, among other things, regarding the air pressure in the tyre, whereby an arrangement is known, where the pneumatic tyre is in contact to the air source so that the tyre can leak even considerably and yet sufficient air pressure remains in it. Also known is observing with a detector the flattening of a tyre due to in-sufficient air pressure either by means of decreasing ground clearance or detecting the increase of the tyre side-protrusion A lot of retread tyres are used in heavy traffic, that is why it has become a great problem that retreadings get loose from tyre on the road most often at full speed, whereat the retreading flies as such or ragged onto the road unfortunately causing sometimes a risk of accident to on-coming cars and those behind, and in worst case driving off the road. For pedestrians and cyclists such loose retreadings can be perilous.

The problem is that no warning system, which would indicate that the retreading is getting loose, is known. Furthermore, it is a disadvantage that the driver does not even notice that retreading has got loose from some of the wheels in the vehicle. This results unavoidably in that soon such a wheel without retreading forms a new rag that gets loose and similar situations will be repeated as presented above.

By means of an arrangement as per the invention the above presented problems are solved and the aim of the invention is to produce a warning system, by means of which the driver can be informed of the wheel condition and of a situation, where retreading or the whole wheel is getting loose, and possibly already in good time before the retreading or the whole wheel actually gets loose.

The arrangement according to the invention is characterized in that close to the wheel an acoustic detector is placed and fitted to receive a sound spectrum sent by the rubber tyre and the corresponding wheel construction or caused by them in the direction of the surroundings or the vehicle constructions, and that the vehicle includes means to handle the said sound spectrum, means to compare sound spectrums, a function to store sound spectrums, programs and apparatus for control of received adaptable sound spectrum, and a function to indicate damage of tyre or other wheel damage by means of comparative sound spectrum control.

The advantage of an arrangement as per the invention is that with quite a small-sized and light apparatus the vehicle wheels can be brought into the circle of detection. Even cordless data transmission is easily accomplished especially in vehicles with trailer and by quite simple techniques it is possible to arrange for the driver a follow-up even separately of each wheel. The sound spectrum sent by the acoustic detector can in digital form be handled and analysed so that the most important types of damage can be discovered merely from the sound spectrum. For instance, already the begin of a retreading or a wheel to get loose can be observed, which is important, so that there is time enough even to make the vehicle stop, while retreading or wheel is still stuck somehow.

Adaptability can be combined with the apparatus, so that gradual changes can be observed and possibly even anticipated and estimated either as not dangerous or dangerous. Also quick changes, for instance due to sudden changes. of the quality of the road surface, are easily"learned"by the apparatus.

In the following the invention is disclosed with reference to the enclosed drawing, where figure 1 shows a vehicle with trailer from the side, figure 2 shows a vehicle bogie with detector, figure 3 shows a recapped tyre of a vehicle. figure 4 shows a display monitor.

It is quite usual that the tread of retreaded tyres gets loose by vehicles with a trailer. It is very difficult for the driver of such vehicles to notice that the rear tyres are loosing their retreading and not in the least that the retreading of a tyre in the trailer is getting loose.

Figure 2 shows the bogie from the side, where wheels 3 have rubber tyres 3 and as protection of wheels there is a fender 8. Detector 1 sensing the condition of tyres 3 is arranged in a place protected by fender 8 and the detector is, for instance, an acoustic microphone receiving sound from tyres especially the ones close to it. If sound from tyres, with other words the whole sound spectrum, is conducted from detector 1, i. e. the microphone, to a device handling the acoustic signal and placed in the drivers'cabin, for instance, the said device is fitted to separate random sounds, for instance from a certain cyclic sound, the frequency of which is of the range of the rotational frequency. In the arrangement as per the invention the sound spectrum is converted into digital form, whereby the handling turns into digital and the result can be analysed. The sound signal appearing at the rotational frequency of the tyre surely tells that retreading that is getting loose, is already loosened from some spot and thus hammering the road. The device can also have a detector measuring the speed of rotation, for instance of some wheel, or data taken from the speed indicator of the vehicle, so that the device could clarify what frequency, whenever, the rotational frequency of the wheel is. If the cycle of disturbance appears at rotational frequency, there must in the tyre surface be an originator to such a disturbance. Even a wheel getting loose gives quite a different sound or vibration compared to other wheels of good condition, and before getting loose it flutters more or less and the exception of its sound in regard to signals coming from the detectors of other wheels is different and clearly separable as a faulty function.

Instead of the acoustic sound detector also a signal from a vibration detector, placed possibly in connection with a wheel, is handled correspondingly, whereby also from that signal it can be observed whether it has a stronger cycle at wheel rotational frequency. The vibration detector is fixed for instance in the wheel axle, since, certainly, vibration is conducted over the suspension also to the chassis. However, thanks to the digital handling of the signal the spectrum received from the acoustic detector is even alone sufficient as information for observing the most important, slowly proceeding damages.

In one embodiment of the invention in the memory of the arrangement sound data regarding an undamaged wheel and different kinds of damaged wheels and bearing damages has been stored, either as laboratory runs or measured on the road. In this way into the apparatus sound samples have been stored, with which sound spectrums measured from the wheel are compared.

There can be other types of detectors, for instance a distance detector, by means of which observations can be made, whether the centrifugal force has loosened the retreading to a greater radius, which tells that loosening has taken place. Furthermore, a radiation-receiving detector can be used, whereby such a detector receives caloric radiation and then the warming-up of tyre can be observed. It is also possible to fit into connection with a wheel a detector receiving also light beams, whereby a part of the retreading that is getting loose begins to rotate with a greater radius, breaks the travel of the light-beam and informs that the retreading has got loose.

Signals from any detector type are handled by means of a device included in the arrangement. The device is fitted, according to the detector type in use, to separate from the signal string only the signal disturbances repeated by each wheel rotation, peak values or other indications from the detector. This kind of repeated signal peaks can be separated immediately after they have got started, since the retreading has got loose.

If in all or in all one side wheels the same disturbance is detected, it does not tell about damages of retreading but possibly of cyclic disturbances of the road, whereby these must be separated out.

Figure 3 shows a retreaded tyre 3, where there is on the outer circle a vulcanized tread 4.

Vulcanized tread 4 has a band furnished with a butt joint 7 around the tyre. Especially from butt joint 7 retreading 4 begins to get loose and the loose end beats at first the road, then the fender and gets quite fast entirely loose from the tyre. The loose end causes immediately, even if loose only from a 5 cm distance, beating of road resulting in strong sound and vibration. Retreading can be off the tyre even from another spot and then also the same phenomena takes place, since the centrifugal force causes in the tyre in that spot a blister or similar swelling outwards.

. With a sound detector it is also possible to notice, when a tyre becomes empty, since a tyre with a too small amount of air pressure gives a louder sound at least to its intensity and even by different frequency compared to other tyres with proper pressure. By means of the device it is possible to separate such a tyre and to give a signal of it.

Figure 4 shows a monitor version, where an individual signal of each tyre coming from wheels sent by said detector and possibly handled is shown at real time. From the signals damage of retreading or whether a wheel is getting loose can be concluded. Naturally, the device includes an alarm limit set on basis of experiments, whereby observation of damage is not dependent of monitor control. The monitor can be even of smaller size displaying the detector signal from a chosen wheel.

For instance, there can be in the cabin only a row of indicator lights with a lamp for each wheel or for the bogie. The device switches on the signal light of the wheel, from which the arriving signal has been observed to meet the criteria of retreading damage or criteria of a wheel getting loose.

The arrangement as per the invention includes a control unit with storing capacity. Thus the apparatus can be programmed and includes adaptability and"learning ability"regarding proceeding of different damages and how they appear in the received sound spectrum. Thus, by means of the apparatus, for instance the wear of tyre can be observed. It has effect by a short time span and changes, however, the spectrum in the long run. The apparatus is programmed to separate sound changes due to wear and the remaining service life of the tyre can even be figured out observing the share of sound spectrum notable from the perspective of wear.

The different sound spectrums of wheels are compared among themselves so that the sound spectrums of each wheel are compared with stored spectrum data. Comparison is most important observation and done momentarily or by long intervals in order to find out slow changes. Spectrum data can be achieved and stored from the sound of an undamaged tyre, fall of tyre pressure, retreading getting loose and bearing faults in addition to wear. Other data achievable from the vehicle is, as occasion demands, joined to the arrangement according to the invention, such as speed, load data, road conditions.

The detectors can be combined detectors measuring one or many of the following measurable variables: sound, vibration, tyre temperature, distance from tyre tread.