DE20216290U1 - Pneumatic tire for vehicles, has electrical or electronic sensor in tread to indicate tread height and give warning of unacceptable wear - Google Patents

Abstract

Tire tread incorporates an inductive component (1) in a resonant circuit with a condenser (4). The condenser plates are at right angles to the surface of the tread (3) and have wear properties similar to the tread rubber. As the tread wears, the capacitance value reduces while the remainder of the circuit is unaffected so that the resonant frequency decreases and provides a measure of wear. An independent claim is also included for three alternative methods of monitoring the tread height by using a stationary sender to excite the resonant circuit in the tread at a frequency near the resonant frequency. A stationary receiver, preferably in the same housing, can then measure (a) the damping in the resonant circuit, or (b) the current amplitude in the circuit, or (c) the natural frequency of the circuit. Alternative (c) uses a calibration curve in the computation, using several excitation frequencies. Alternative (b) is simpler but requires accurate calibration. Alternative (a) requires a close proximity between transmitter and sensor for sufficient accuracy. Methods are provided to eliminate errors due to wet road surfaces.

Description

Continental AG 1 202-003-GDE.1 / Wi

30.09.2002 Wi/pk

Description

Vehicle tires

The invention relates to a vehicle tire according to the preamble of patent claim 1. Accordingly, it has a tread with negatives of a depth and positives of a height.

If the tread depth is too low, the water absorption capacity and water drainage speed of the negatives are too low even at low driving speeds to prevent the tread from floating - which would result in almost complete loss of friction. This is why the legal systems for public road traffic require a minimum tread depth, in Germany for example 1.6 mm.

Unfortunately, some drivers do not pay enough attention to these requirements and thereby endanger themselves and others. For this reason, various measures have already been proposed to make it easier for drivers to check the tread depth; a particularly common suggestion is to place at least one coloured stripe in the area of the minimum tread depth, which, in contrast to the otherwise black colour, causes a characteristic colour change in the appearance of the tread when the minimum tread depth is reached *

However, such tires never caught on. The desired color change leads to a significant increase in the cost of the tire because an additional strip has to be mixed, extruded, cut to length and applied during the construction of the blank and because the migration of discoloring components from the surrounding components into the colored strip has to be at least slowed down or buffered for a sufficient time.

These problems do not only occur on the side facing the carcass - as with the white stripes on whitewall tires - but also on the opposite side, where the remaining black tread has to be made to adhere. Moreover, in the case of a colored stripe that is initially hidden, these difficult joining zones are located in a zone that is further away from the cooling surface and is therefore hotter.

And hardly any tire buyer wants to pay a significant additional amount because they are more likely to be penalized if the tread depth falls below the minimum.

The inventors are striving for a "loyal" warning system, i.e. one that at least first - and possibly only - informs the driver. The warning should be visible inside the vehicle, for example through a visual signal on the dashboard, but not on the outside. Preferably, the shortage should not be indicated abruptly, but rather gradually, analogous to the transition that took place mainly in the 1960s from abruptly indicating fuel shortage warnings (for example by switching on a reserve tank) to analogue fuel gauges, since which hardly any vehicle breaks down due to fuel shortages.

The system according to DE-OS 197 16 586 also serves this purpose, taking advantage of the fact that the frequency of torsional natural vibrations is set according to the square root of torsional stiffness and mass moment of inertia. While torsional stiffness is almost independent of the remaining tread depth, the mass of the tread gradually decreases as a result of abrasion and with it the mass moment of inertia, so the natural frequency increases. This change in natural frequency should be used as a correlative to the residual positive height and thus to the remaining tread depth.

Despite its basic functionality, this system suffers from the fact that a large part of the rotational inertia of a tire is invariable, in particular the contribution of the base, the belt layers and the inner liner. As a result, the calibration curve is quite flat, and the measurement accuracy is therefore limited. Furthermore, the torsional stiffness of a pneumatic tire changes significantly with a change in tire pressure; for example, if the driver drives from Munich, which is already warm in spring, to a winter sports resort that is 20°C cooler, the air pressure and thus the torsional natural frequency will drop significantly if the air volume is not adjusted. A tire that is indicated as questionable in Munich then appears to be OK again in the high mountains. This could lead to incorrect judgments and undermine the credibility of such warnings.

The inventors have set themselves the task of specifying the remaining tread depth and/or remaining tread height loyally and unaffected by the prevailing tire pressure with a particularly high accuracy in the range between 4 and 1 mm.

This object is achieved according to the invention by tires according to claim 1. Based on the generic features, these are characterized in that at least one of the positives (4) contains electrical and/or electronic means (10, 11, 12) which provide information about the current height (H) of the positive in question. These should then activate a warning device (W), preferably a warning light in the dashboard of the vehicle in question. An acoustic warning device is also possible; the latter is particularly useful if the defect has already become serious. For example, up to a remaining tread depth of 2.5 mm, a visual warning could be given and from then on an acoustic warning could also be given each time the vehicle is started. As the tread depth continues to decrease, the penetrance of the warning sound could be increased, for example initially only a tone every few minutes, then every minute and from a tread depth of around 1.6 mm, a continuous beep.

When selecting the type of warning (visual or acoustic) and severity, it is advisable to take other parameters into account, especially those relating to rain and driving speed, and possibly also outside temperature; after all, 1.8 mm tread depth in the rain and at 120 km/h is far more dangerous than 1.6 mm tread depth at 180 km/h and completely dry. A rain sensor could provide information about rain, as has already been suggested for controlling windscreen wipers. However, where such a sensor is not available, the switch position of the windscreen wiper could also be used.

In this application, "electrical means" are means that allow the flow of electrical current, such as conductors, resistors, capacitors and coils. Magnetic marks, which are known from DE-OS 196 46 251, for example, are not included because they do not allow the flow of current. According to claim 7 , this preferably does not include a battery or accumulator, but rather a voltage is tapped from a coil, which is generated there by means of induction.

"Electronic means" here means those electrical means which influence the current intensity and/or the voltage and/or the phase position between the two by means other than inductances, capacitances and ohmic resistances, e.g. with optical or mechanical, in particular acoustic effects, as well as switches, transistors, diodes, interconnections thereof such as chips, data storage devices and processors, etc.

The electrical and/or electronic means in said tire positive are to be designed in such a way that some property of at least one of these means changes in clear correlation to the current positive height.

Claim 2 contains the teaching that a capacitor (10) is particularly suitable as such an element, the plates (10a, 10z) of which are arranged approximately perpendicular to the tread periphery and extend radially outwards into the periphery. Then each of the capacitor plates (10a, 10z) is rubbed on its front side in a similar way to the surrounding rubber. The abrasion of the capacitor plates leads to a shortening of their radial extension. Since all other dimensions of the capacitor plates remain unchanged, their capacity is reduced. The loss of capacitor capacity therefore correlates with the loss of tread rubber.

Apart from the capacitor, the other electrical and/or electronic components should of course not be exposed to abrasion.

The capacitor capacitance can be measured in various ways. According to current knowledge, it is best to install such a capacitor in a tire as claimed in claim 2 as part of an oscillating circuit. Its oscillation frequency provides a signal that correlates particularly precisely and reliably with the remaining tread depth: the frequency increases as the capacitance decreases, i.e. as the tread depth decreases.

It is expedient for the radially inner end of the capacitor plates to be arranged only a short distance radially inward from the surface corresponding to the minimum profile depth. In this way, a particularly steep calibration curve is achieved in the area of the minimum profile depth, i.e. the highest accuracy in the most interesting area. Claim 13 contains suitable dimensions for this.

In the undamped case, the natural frequency f of an electrical oscillating circuit is known to be:

-i -I

f = (2pi) (LC) 2

A small amount of damping is caused by the small ohmic resistance in the lines, especially in the conductor windings of the coil. This damping essentially leads to an exponential decrease in amplitude over time after a vibration excitation (whether by a vibration, a pulse or mixed forms or the like), but leaves the natural frequency essentially unchanged.

A more complicated loss of vibrational energy over time occurs on wet roads, especially when the water there is highly saline, which increases the water's inherent conductivity:

This leads to a partial plate short circuit of the capacitor, namely on the radially outer face, which is always exposed from abrasion. The charge transfer there between the two capacitor plates affects the electrical vibration behavior in the same way as a resistor connected in parallel to the capacitor, which slightly increases the natural frequency - because the charge stored in the capacitor drops slightly - and significantly increases the damping. The former makes the tire appear slightly more critical on wet roads than on dry ones, which is tolerable.

Of the three variants mentioned in claim 14, c) is the best (but also the most complex) because it takes advantage of the favorable insensitivity of the natural frequency to a change in the electrical road resistance and also the safety-enhancing orientation of the minor measurement error.

Variants a) and b), on the other hand, show larger measurement errors over a variance in the electrical road resistance. It may therefore be advisable that, in accordance with claim 19, the display device on the dashboard only ever shows the last minimum tread depth recorded, thus ignoring the larger values generated on wet roads. Accordingly, an acoustic warning device should of course also refer to the minimum. As long as the tire is operated in a climate in which one dry kilometer occurs every 2,000 km, the measurement accuracy achieved is sufficiently high. Further explanations and preferred designs follow later (from page 12, bottom paragraph).

Back to variant c) according to claim 14, according to which an oscillation frequency is to be determined, which is done by a time span measurement.

In order to achieve high measurement accuracy, a time span measurement should not start immediately with the first zero crossing of the oscillating current, but rather with the second zero crossing after excitation, for example, and it should stop with the sixth zero crossing, for example. This gives a signal for 2T with good reproducibility. The reciprocal of this times 2 provides the natural frequency f; this times 2pi provides the circular natural frequency "small Omega".

In this preferred example, even with additional damping due to partial plate short-circuiting caused by moisture, at least the third period after excitation must have such a large amplitude that the zero crossing at the end of it is steep enough to determine the point in time marked by it with sufficient precision. It has been found that this is easily achieved with a sufficiently high oscillation frequency so that T is sufficiently small.

Since the amount of charge and thus vibration energy lost due to partial plate short-circuiting at the end faces depends on the amount of charge available and the time of oscillation, the drop in amplitude over the number of periods can be kept sufficiently small by selecting a sufficiently high frequency. Because of the double influence of the charge available, the initial capacitance of the capacitor should be as large as possible; so that the natural frequency of oscillation is nevertheless sufficiently high, the inductance should be small. According to claim 8, the initial capacitance of the capacitor to be abraded and built into the oscillating circuit should be at least 100 nF (nanoFarads) and the inductance built into the oscillating circuit should be at most 20 μΩ (microHenry). More preferably, according to claim 9, the initial capacitance of the capacitor to be abraded and built into the oscillating circuit should be about 1000 nF (nanoFarads) and the inductance built into the oscillating circuit should be about 10 μΩ (microHenry). (MicroHenry).

If even better materials and/or manufacturing processes for capacitor production become available in the future, allowing an even higher charge density, then it would be even better if the capacitance were even higher and the inductance even lower, particularly preferably the initial capacitance 10,000 nF = 10 pF and the inductance 1 μ�EEgr;.

In each of the aforementioned cases, the initial capacitance of the capacitor to be abraded and built into the resonant circuit and the inductance built into the resonant circuit should be coordinated with one another in such a way that the resonant circuit in its new state has a natural frequency between 10 and 1,500 kHz, particularly preferably according to claim 12 between 40 and 120 kHz.

This ensures the use of commercially available timing elements and antennas. According to claim 13, the capacitor built into the oscillating circuit and to be rubbed off should be positioned in the tire in such a way that it still has at least 10%, preferably 15 to 20%, of its initial capacity when the permissible remaining tread depth is reached. This ensures that vibration energy introduced by the non-rotating transmitter does not decay too quickly.

Furthermore, tuning to a high frequency band leads to an advantageous miniaturization of the electrical elements capacitor and/or in particular the coil; it is even possible to lead only one conductor from one capacitor plate to the other without forming a separate "coil" element, with this conductor acting as the only turn of a coil or even - in the case of a direct connection - only due to its - even lower - self-inductance. The preferred frequencies for such an oscillating circuit are between 10 kHz and 1,500 kHz, the most preferred between 40 and 120 kHz.

It is advisable to place the exciter of the oscillating circuit housed in the rotating tire in the non-rotating environment of this wheel. In radio engineering terms, this exciter could also be called a "transmitter". In the same language, the oscillating circuit could be called a frequency-selective reverberation generator. The reverberation it emits is received in a "receiver" which is in turn conveniently placed in the non-rotating environment of the wheel to be monitored, in simple designs in the same housing as the transmitter.

t *

If working in the low frequency range, for example at 15 kHz, a particularly high signal yield would be achieved if the receiver was positioned behind the transmitter in the direction of rotation; for a driving speed of, for example, 20 m/s (= 72 km/h), a tire rolling circumference of 2 m and a measurement interval end of 3T, this optimal phase shift would be 0.72°. For the range of actually preferred frequencies, for example 50 kHz, this value would therefore be 0.216°.

If the latter further development is dispensed with, it is possible to use the transmitter itself as a receiver, especially at even higher frequencies.

After this detailed description of how the capacitor is to be integrated into an electrical circuit, now back to the capacitor itself:

According to claim 3, the capacitor plates (10a, 10z) should be made of such a material that their front abrasion speed approximately matches the abrasion speed of the surrounding rubber. This can be achieved by loosely sintering them from metal or by manufacturing them from graphite instead of metal. It is particularly advantageous to arrange two thin plates made from a soot-filled rubber mixture in a block made from a silica-filled rubber mixture; then the differences in abrasion and rigidity between the sensor (which could also be called a transponder) and the surrounding rubber can be kept particularly small.

The capacitor plates can tolerate a higher abrasion rate than the surrounding rubber to a greater extent than the reverse, an increased abrasion resistance. In the latter case, the capacitor would gradually protrude, produce unpleasant noises, indicate too great a tread depth and threaten to break if it protrudes too far.

According to claim 4, at least one - possibly the outer one (10a) of the capacitor plates is tubular. The required second plate (10z) and possibly further plates is or are arranged concentrically within it. This concentric structure makes the transponder sensor particularly compact and also has the advantage that its bending - suffered during the transmission of any tangential forces - does not lead to edge loads and local stress peaks due to the lack of edges. The radially innermost plate (10z) can also be solid - i.e. not tubular - preferably as a wire or wire rope.

Accepting a lower capacity per installation space but better mechanical material compatibility, it is also possible to manufacture all or some of the layers of a capacitor, which are usually made of metal, from a rubber mixture containing soot or an intrinsically conductive polymer or a mixture of these, and to manufacture the insulating layers from a rubber mixture that is free of soot and is preferably reinforced with silica. A capacitor constructed in this way promises to be able to absorb considerable deformations without damage.

When using rigid capacitors, it is recommended to embed them in a rubber compound that is softer than the surrounding tread rubber to protect them from mechanical overload.

·

In order to be able to manage with a particularly low inductance, it is recommended to generate a relatively large capacitance. For this purpose, wound capacitors are preferably used according to claim 5. In "wound capacitors" an insulating film serving as a dielectric is wound onto a first metal layer, then a second metal layer and finally a second insulating film. In the top view, such a capacitor shows an image of four spirals wound into one another, namely two metal foils and two dielectric layers between two metal layers each.

However, a high capacitance can also be achieved in a space-saving and particularly low-resistance manner by the capacitor (10) being constructed from a straight plurality of plates (10a, 10b, 10c, 10z) greater than 2, which are alternately connected to one and the other coil side. This principle of alternating nesting can be implemented not only with a flat design of the capacitor plates, but also together with the previously mentioned concentricity of the plates. For example, the plate-tube sequence from outside to inside could be: AaBbCc. A, B and C form one pole and a, b and c the other.

According to claim 14, a tire according to the invention as described up to this point is necessary for setting up a device according to the invention for monitoring the positive height of a vehicle tire, but is not yet sufficient; one also needs an energy supply to the sensor in the tire and some type of data transmission from the sensor ultimately to the warning light and/or warning loudspeaker or the like, the decisive hurdle for the data transmission being the transition from a rotating body (tire) to a non-rotating body (body or wheel suspension parts thereof); the data transmission by cable within the body does not require any further description, since it is sufficiently known to the average person skilled in the art.

... &ggr; ₃

In order to be able to manage with a particularly low inductance, it is recommended to generate a relatively large capacitance. For this purpose, wound capacitors are preferably used according to claim 5. In "wound capacitors" an insulating film serving as a dielectric is wound onto a first metal layer, then a second metal layer and finally a second insulating film. In the top view, such a capacitor shows an image of four spirals wound into one another, namely two metal foils and two dielectric layers between two metal layers each.

However, a high capacitance can also be achieved in a space-saving and particularly low-resistance manner by the capacitor (10) being constructed from a straight plurality of plates (10a, 10b, 10c, 10z) greater than 2, which are alternately connected to one and the other coil side. This principle of alternating nesting can be implemented not only with a flat design of the capacitor plates, but also together with the previously mentioned concentricity of the plates. For example, the plate-tube sequence from outside to inside could be: AaBbCc. A, B and C form one pole and a, b and c the other.

According to claim 14, a tire according to the invention as described up to this point is necessary for setting up a device according to the invention for monitoring the positive height of a vehicle tire, but is not yet sufficient; one also needs an energy supply to the sensor in the tire and some type of data transmission from the sensor ultimately to the warning light and/or warning loudspeaker or the like, the decisive hurdle for the data transmission being the transition from a rotating body (tire) to a non-rotating body (body or wheel suspension parts thereof); the data transmission by cable within the body does not require any further description, since it is sufficiently known to the average person skilled in the art.

tfft ··· · - t

According to claim 14 , the energy is fed in as electromagnetic vibration excitation, with the electromagnetic vibration exciter being arranged non-rotating as close as possible to the wheel to be supplied in the body, preferably on a wheel suspension part, e.g. a trailing arm. The vibration exciter, which could also be referred to as a transmitter in the case of such a remote effect, must cause a resonance in the sensor oscillating circuit; to do this, it must have an excitation frequency close to the natural frequency of the electrical oscillating circuit in the tire (1). The vague words "close" mean such a good match between the two frequencies that a sufficient signal yield is achieved; this is usually the case with a frequency deviation of less than 2%.

According to claim 14, the data transmission to the non-rotating body takes place in that the resonance signal of the sensor in the tire reaches a sensor in the non-rotating body, which could also be referred to as a receiver. This receiver can be designed in such a way that it

a) the damping of the excitation vibration by the oscillating circuit (10, 11, 12) placed in the tyre or

b) the oscillation amplitude of the oscillating circuit (10, 11, 12) placed in the tyre or

c) the natural frequency of the oscillating circuit (10, 11, 12) placed in the tyre is recorded.

The variant according to c) is expediently carried out according to claim 15, for which the vibration exciter or transmitter must contain such a self-regulating device that it adjusts the excitation frequency to match the resonance frequency of the oscillating circuit (10, 11, 12) arranged in the tire. This can be done, for example, by starting from such an excitation frequency f^, which approximately matches the tread depth of a new tire, the excitation frequency is initially reduced by 3% to an excitation frequency f^ and the strength of the sensor resonance signal is recorded as SRSi.

Ys

»· • t

t t»·»

A short time later, for example 3 seconds later, an excitation frequency f2 is set which is only 1.5% below £3 and the strength of the sensor resonance signal is recorded as SRS2. Similarly, a further short period of time later, an excitation frequency fq. is set which is 1.5% above f^ and the strength of the sensor resonance signal thus excited is recorded as SRS4. Then a further short period of time later, an excitation frequency f5 is set which is 3% above fß and the strength of the sensor resonance signal thus provoked is stored as SRS5.

Using the five measurement points thus obtained in a diagram of the sensor resonance signal strength over the excitation frequency, a polynomial train of lower degree than the number of measurement points, preferably of third degree, is then conveniently placed in the logic part of the receiver according to the error-square method in order to eliminate any random measurement errors, i.e. according to the formula:

SRS(f) = a + bf + cf ² + df ³

The maximum is then determined from this function. If the frequency f _max of this maximum is in the interval between ±2 and f4, it is recognized as the resonance frequency of the sensor. If, however, this frequency is outside this interval, i.e. it represents an edge maximum, the series of measurements is repeated with a new average frequency f^; in the case where f _max is greater than or equal to f$ , the new frequency f3 is chosen to be greater than the old one, preferably 1% greater, and the four other frequencies in the vicinity are also selected accordingly; in the opposite case, where f _max is less than or equal to f2, the new frequency f3 is chosen to be smaller than the old one, preferably 1% smaller, and the four other frequencies in the vicinity are also selected accordingly. If necessary, the series of measurements are repeated until the frequency of the resonance maximum is greater than f2 and less than fq .

• · ϕ

·

·

• *

With the selected query steps in 1.5% increments, the iteration is sufficiently fast and sufficiently accurate; the resonance frequency is determined to an accuracy of about 0.8 percent. Of course, it is also possible to increase the accuracy by selecting an even closer increment, for example in 0.5% increments, and/or to increase the number of measurement points considered within each iteration step, for example from 5 to 7, so that the average frequency is then not fß but f$ and then to tighten the tolerance condition, for example to require f _max greater than f3 and less than f$' _f, but this then requires a larger number of iteration steps.

To ease the conflict between the desire for even greater accuracy on the one hand and the desire for only a small number of iteration steps on the other, it is also possible to iterate in coarser steps first and then in finer ones at the end.

The excitation frequency, however determined in detail, which receives the maximum resonance signal from the sensor as a response, is used as a correlative to the positive height (H) according to claim 16 at the latest after completion of the iteration using a calibration curve or a calculation program. The latter could first form the reciprocal of the excitation frequency, then the square root of this and multiply this by a calibrated proportionality factor.

The method variant b) of claim 14 is included as a single step in the method according to c). The restriction to a single amplitude measurement naturally leads to the lowest possible expenditure. However, in order to achieve sufficient accuracy, increased expenditure is required for calibration; calibration of each individual transmitter-sensor-receiver pairing may even be necessary.

·

In contrast to frequency, amplitude is very sensitive to changes in attenuation.

In general, the resonance amplitude changes over frequency more strongly and thus improves measurement accuracy the lower the damping and thus the logarithmic decrement. The excitation frequency should be close to, but not exactly at, the resonance frequency. The best way to choose the excitation frequency is to select it so that it matches the sensor resonance frequency at a tread depth of 1.0 mm. Then you always stay on one side - in this case the left - of the amplitude response, so that the calibration curve is strictly monotonic. This avoids the problem that at the resonance maximum even the curve of the amplitude response over frequency has a slope of zero, meaning there is no measurement accuracy. With this simple variant, measurement accuracy is low at large tread depths, but sufficiently high near the critical tread depth, and the latter is what matters for consumer vehicles.

The method variant a) according to claim 14 requires a very small distance between transmitter and sensor and between sensor and receiver in order to ensure that the transmitter attenuation by the sensor becomes significant compared to other attenuation influences.

Based on variant c) of claim 14 and the self-regulating device according to claim 15 , claim 17 teaches that the device - if necessary after achieving a rough match - determines the control deviation, i.e. the difference between the natural frequency of the oscillating circuit placed in the tire and the excitation frequency of the exciter, by means of a comparison between the two reverberations by means of another method variant, such as b) (amplitude comparison) of claim 14 or a completely different method.

» t * C

The reverberation of the excitation signal should therefore be compared with the reverberation of the resonant circuit signal. The reverberation of the excitation signal becomes clear after leaving the excitation zone or after the excitation is switched off.

The two reverberations have frequencies that are close to each other and therefore form a beat. The frequency of this beat is significantly lower than the signals that are indirectly compared. The best way to further adjust the excitation frequency to the resonant circuit frequency is to consider the frequency of the beat: a high beat frequency indicates a greater deviation between the two frequencies than a lower beat frequency. Additionally or alternatively, the beat can also be determined based on its phase position to the resonant circuit reverberation or excitation reverberation and/or its amplitude.

nig

The invention is explained in more detail below using an embodiment with associated figures. It shows:

Fig. 1 shows schematically a pneumatic vehicle tire with a tread and an electrical oscillating circuit arranged in the tread,

Fig. 2 shows a schematic detail of the electrical oscillating circuit,

Fig. 3 Resonance curves of this resonant circuit for different assumed shunt resistances R2, which simulate the fluctuating road conductivity (especially due to fluctuating humidity),

Fig. 4 Resonance curves of the same resonant circuit, but with the capacitance of the capacitor worn down to 50 % of the original value, again over the same, assumed different values of shunt resistors R2,

Fig. 5 Resonance curves of the same resonant circuit, but with the capacitance of the capacitor worn down to 15 % of the original value, again over the same, differently assumed shunt resistors R2 and

Figure 1 shows a schematic drawing of the oscillating element that is inserted in the profile block 3 with an inductance 1, the belt layers 2 and a capacitance 4.

Figure 2 shows a schematic detail of the electrical oscillating circuit. The initial capacitance of the capacitor to be abraded and built into the oscillating circuit is exactly 1000 nF (nanaFarad). This high capacitance is only possible with a design according to claim 6. The inductance built into the oscillating circuit is exactly 10μ�EEgr; (microHenry). The unavoidable line resistances are assumed to be 1 Ohm.

R2 is a variable shunt resistance. If R2 = 0, there would practically be a plate short circuit, if R 2 = Inf, there would be a dry road. In the following, it is assumed that the contact resistance on wet roads is above 10 ohms.

Claims (18)

1. Vehicle tyre with a tread having negatives of a depth and positives of a height, characterized in that at least one of the positives contains electrical or electronic means which provide information about the current height of the positive in question. 2. Vehicle tyre according to claim 1, characterized in - that at least one of the positives contains as electrical or electronic means a capacitor, a coil and lines therebetween, - which are connected to form an electrically oscillating circuit, - the plates of the capacitor extend substantially radially and reach to the periphery of the positive, - so that their front sides participate in the abrasive road contact and the capacitance of the capacitor decreases with decreasing positive height, - the other electrical or electronic components are arranged radially inwards so that they are not exposed to abrasive contact with the road surface when the minimum tread depth is reached, - so that the natural frequency of the resonant circuit increases as the positive height decreases. 3. Vehicle tire ( 1 ) according to claim 2, characterized in that the capacitor plates ( 10a , 10z ) consist of such a material that their front abrasion speed approximately corresponds to the abrasion speed of the surrounding rubber. 4. Vehicle tire ( 1 ) according to claim 2 or 3, characterized in that the capacitor ( 10 ) has a tubular plate ( 10a ) and a second plate ( 10z ) or a wire arranged concentrically therein. 5. Vehicle tire ( 1 ) according to claim 2 or 3, characterized in that the capacitor ( 10 ) is produced in a manner known per se by winding. 6. Vehicle tire ( 1 ) according to at least one of claims 2 to 5, characterized in that the capacitor ( 10 ) is constructed from a straight plurality of greater than 2 plates ( 10a , 10b , 10c , 10z ) which are alternately connected to one and the other coil side. 7. Vehicle tire ( 1 ) according to at least one of the preceding claims, characterized in that it is free of any battery. 8. Vehicle tire ( 1 ) according to at least one of the preceding claims, characterized in that the initial capacitance of the capacitor to be abraded and built into the resonant circuit is at least 100 nF (nanoFarad) and the inductance built into the resonant circuit is at most 20 µH (microHenry). 9. Vehicle tire ( 1 ) according to claim 8, characterized in that the initial capacitance of the capacitor to be abraded and built into the resonant circuit is approximately 1000 nF (nanoFarad) and the inductance built into the resonant circuit is approximately 10 µH (microHenry). 10. Vehicle tire ( 1 ) according to claim 8, characterized in that the initial capacitance of the capacitor to be abraded and built into the oscillating circuit is approximately 10,000 nF (nanoFarad) and the inductance built into the oscillating circuit is approximately 1 µH (microHenry). 11. Vehicle tire ( 1 ) according to at least one of the preceding claims, characterized in that the initial capacitance of the capacitor to be abraded and built into the oscillating circuit and the inductance built into the oscillating circuit are coordinated such that the oscillating circuit in the new state has a natural frequency between 10 and 1,500 kHz. 12. Vehicle tire ( 1 ) according to claim 8 and claim 11, characterized in that the initial capacitance of the capacitor to be abraded and built into the oscillating circuit and the inductance built into the oscillating circuit are adjusted so that the oscillating circuit in the new state has a natural frequency between 40 and 120 kHz. 13. Vehicle tire ( 1 ) according to claim 2, characterized in that the capacitor built into the oscillating circuit and to be abraded is positioned in the tire in such a way that it still has at least 10%, preferably 15 to 20%, of its initial capacity when the permissible remaining tread depth is reached. 14. Device ( 20 ) for monitoring the positive height (H) of a vehicle tire ( 1 ), characterized in that - that it contains a vehicle tire ( 1 ) according to one of claims 1 to 13 - and at least one non-rotating electrical vibration exciter (E) having an excitation frequency close to the natural frequency of the electrical oscillating circuit in the tire ( 1 ) - and a sensor (S) which a) the damping of the excitation vibration by the oscillating circuit ( 10 , 11 , 12 ) placed in the tyre or b) the oscillation amplitude of the oscillating circuit ( 10 , 11 , 12 ) placed in the tyre or c) the natural frequency of the oscillating circuit ( 10 , 11 , 12 ) placed in the tire is recorded. 15. Device according to claim 14, variant c), characterized in that the vibration exciter contains a self-regulating device such that it adjusts the excitation frequency to match the resonance frequency of the oscillating circuit ( 10 , 11 , 12 ) arranged in the tire ( 1 ), the excitation frequency thus set being used as a correlative to the positive height (H). 16. Device according to claim 15, characterized in that it contains a calibration curve stored in order to establish a correlation between the tracked excitation frequency and the remaining positive height (H) or a calculation program which essentially first forms the reciprocal of the tracked excitation frequency and then takes the square root from this and multiplies this square root by a proportionality factor - preferably determined by calibration. 17. Device according to claim 15 or 16, characterized in that - if necessary after achieving a rough agreement using another method, such as amplitude comparison - it determines the control deviation, i.e. the difference between the natural frequency of the oscillating circuit ( 10 , 11 , 12 ) placed in the tire and the excitation frequency of the exciter (S) using the frequency and/or phase position and/or amplitude of the beat between the reverberation of the excitation signal and the reverberation of the oscillating circuit signal from the tire ( 1 ) after leaving the excitation zone or switching off the excitation. 18. Device according to one of claims 14 to 17, characterized in that at least one of the oscillating circuits ( 10 , 11 , 12 ) arranged in the tire ( 1 ) simultaneously serves as a marker for other time-period measuring monitoring devices, in particular for detecting the wheel speed and/or wheel longitudinal and/or wheel lateral force for controlling the braking or drive or lateral slip.