Method, control device and system for determining a tread depth of a tread of a tire

A method for determining a tire tread depth during operation of a vehicle includes determining an instantaneous rotational speed of a vehicle wheel having the tire based on data determined by at least one first sensor, then determining a vehicle speed based on data determined by at least one different second sensor, then determining an instantaneous dynamic wheel radius based on the determined instantaneous rotational speed and the determined instantaneous speed. At least one first tire parameter selected from an instantaneous tire temperature, tire pressure and tire load is determined. An instantaneous dynamic inner wheel radius is determined based on the at least one determined first parameter, wherein the inner wheel radius is the distance between the center of the wheel and the tire-side start or seam of the tread. A tire tread depth is determined based on the determined instantaneous dynamic radius and the determined instantaneous dynamic inner radius.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to a method for determining a tread depth of a tread of a tire during operation of a vehicle having the tire, and to a control device and a system for a vehicle for determining a tread depth of a tread of a tire of the vehicle.

WO 02/12003 A2 discloses a device for monitoring the state of each of a plurality of wheels of a vehicle. The device has a computer, a wheel rotational speed-determining system which generates wheel rotational speeds with respect to each wheel and is coupled to the computer in order to transmit rotational speed signals for each wheel to the computer, and a vehicle speed signal generator. In addition, the device has a computer memory in which data is stored which relates to tire wear rates for tires mounted on each of the wheels, the distance traveled by the tire since installation, distance traveled during the instantaneous journey, average wheel rotational speeds and a scaling factor for estimating the wheel speed on the basis of the vehicle speed signal. In addition, the device has a stored program to be run on the computer for referencing the stored data when wheel speeds outside a tolerance limit which characterize compressed operating conditions are determined.

BRIEF SUMMARY OF THE INVENTION

The object of the invention is to specify a method, a control device and a system for determining a tread depth of a tread of a tire which permit improved determination of the tread depth during operation of a vehicle having the tire.

This object is achieved with the subject matters of the independent claims. Advantageous developments can be found in the dependent claims.

A method for determining a tread depth of a tread of a tire during operation of a vehicle having the tire has, according to one aspect of the invention, the following steps. An instantaneous rotational speed of a wheel of the vehicle having the tire is determined on the basis of data determined by at least one first sensor. In addition, an instantaneous speed of the vehicle is determined on the basis of data determined by at least one second sensor which is different from the at least one first sensor. Furthermore, an instantaneous dynamic radius of the wheel having the tire is determined on the basis of the determined instantaneous rotational speed and the determined instantaneous speed. In addition, at least one first parameter of the tire, selected from the group composed of an instantaneous tire temperature, an instantaneous tire pressure and an instantaneous tire load, is determined. Furthermore, an instantaneous dynamic internal radius of the wheel is determined on the basis of the at least one determined first parameter. The internal radius of the wheel is here the distance between the wheel center and the tire-side start of the tread. In addition, a tread depth of the tread of the tire is determined on the basis of the determined instantaneous dynamic radius and the determined instantaneous dynamic internal radius.

In this context, and in the text which follows, the instantaneous dynamic radius is understood to be that radius which a rigid wheel has in order to have, at a specific speed, the same rolling circumference which the wheel having the tire has at this speed. The rolling circumference is here the distance which a wheel travels without slip during one rotation. The dynamic radius is also referred to as the dynamic wheel radius or dynamic rolling radius. The instantaneous dynamic internal radius is the distance between the wheel center and the tire-side start of the tread of the specified rigid wheel, that is to say of a wheel which, at a specific speed, has the same rolling circumference which the wheel having the tire has at this speed.

The method according to the specified embodiment permits improved determination of the tread depth of the tire during operation of the vehicle. This is done, in particular, by determining the instantaneous dynamic radius, determining the instantaneous dynamic internal radius of the wheel on the basis of the at least one determined first parameter, and determining the tread depth on the basis of the specified variable. In this context, as is explained in more detail below, the basis is the consideration that the dynamic radius of the wheel is composed of the instantaneous dynamic internal radius of the wheel and the tread depth of the tread of the tire, and the instantaneous dynamic internal radius of the wheel depends on the at least one first parameter. By determining the at least one first parameter it is therefore possible to determine the respective instantaneous dynamic internal radius of the wheel and therefore the tread depth can be determined as precisely as possible.

The at least one first sensor is typically embodied as a rotational speed sensor, that is to say the instantaneous rotational speed of the wheel is determined in this embodiment on the basis of data determined by at least one rotational speed sensor. As a result, the rotational speed of the wheel can be determined in an easy and reliable way.

The determination of the instantaneous rotational speed of the wheel typically includes here determining an instantaneous angular speed of the wheel.

The at least one second sensor is preferably selected from the group composed of a satellite-assisted position-determining sensor, a radar sensor, a lidar sensor, an ultrasonic sensor and an optical camera. By means of the specified sensors, the instantaneous speed of the vehicle can be determined independently of a rotational-speed-based speed determination, and therefore an independent vehicle reference speed can be made available for the determination of the instantaneous dynamic radius and therefore the determination of the tread depth.

In a further embodiment of the method, the instantaneous dynamic internal radius of the wheel is additionally determined on the basis of the determined instantaneous speed of the vehicle. In this context, the basis is the consideration that the instantaneous dynamic internal radius of the wheel additionally depends on the instantaneous speed as well as the already specified variables. The respective instantaneous dynamic internal radius of the wheel can therefore be determined to a further improved degree by means of the specified embodiment.

In addition, the instantaneous dynamic internal radius of the wheel can be determined on the basis of a type of tire and/or the age of the tire. The specified parameters can also influence the internal radius of the wheel and are therefore preferably likewise taken into account during the determination of the internal radius.

The instantaneous dynamic internal radius of the wheel is determined, for example, by means of at least one characteristic curve which is stored in a memory device. The at least one characteristic curve gives here the relationship between the at least one first parameter of the tire and the internal radius of the wheel, the speed of the vehicle and the internal radius of the wheel, the type of tire and the internal radius of the wheel and/or the age of the tire and the internal radius of the wheel.

The at least one characteristic curve can be based on a model of the wheel, that is to say the relationship between the specified variables and the internal radius of the wheel is already stored in advance in the memory device in this embodiment. Furthermore, the at least one characteristic curve can be determined during a driving operation of the vehicle. In the last-mentioned embodiment, the respective characteristic curve is therefore firstly determined in a learning phase, typically after a new wheel has been mounted on the vehicle, and is then used for determining the instantaneous dynamic internal radius.

In a further embodiment of the method, at least one second parameter, selected from the group composed of an instantaneous acceleration of the vehicle, an instantaneous yaw rate of the vehicle, an instantaneous steering angle, an instantaneous torque of a drive engine of the vehicle and an operating state of a brake device of the vehicle, is additionally determined. In this embodiment, the tread depth of the tread of the tire is additionally determined as a function of the at least one determined second parameter. In this context, the basis is the consideration that the tread depth can be determined as precisely as possible during driving situations in which the influence of drive slip or brake slip is low and the vehicle is moved in a straight line. By means of the specified parameters it is easily possible to identify such driving situations and at the same time the influence of drive slip or brake slip and curvature of the roadway can be additionally compensated.

In addition, a warning message can be issued if the determined tread depth of the tread of the tire undershoots a first predetermined threshold value. The warning message can be issued inside the vehicle here. As a result, the occupants of the vehicle, in particular the driver of the vehicle, can be informed of a low tread depth. In addition, the warning message can be transmitted to further vehicles by means of a vehicle-to-vehicle communication device.

In one embodiment of the method, a service device is additionally automatically informed if the determined tread depth of the tread of the tire undershoots a second predetermined threshold value. The second predetermined threshold value can correspond here to the first predetermined threshold value or may be different therefrom. As a result, for example the arrangement of an appointment for the tire to be replaced can be automatically initiated.

In a further embodiment of the method, the determined tread depth of the tread of the tire is transmitted to at least one driver assistance system of the vehicle. The determined tread depth is therefore made available to at least one driver assistance system in the specified embodiment. As a result, the operation of the driver assistance system can be adapted to the respective determined tread depth. The at least one driver assistance system is selected here, for example, from the group composed of an anti-lock brake system, a vehicle movement dynamics control system, in particular an electronic stability program, and an emergency brake system.

The invention also relates to a control device for a vehicle for determining a tread depth of a tread of a tire of the vehicle. The control device has at least one receiver device which is designed to receive an instantaneous rotational speed of a wheel of the vehicle having the tire, an instantaneous speed of the vehicle and at least one first parameter of the tire selected from the group composed of an instantaneous tire temperature, an instantaneous tire pressure and an instantaneous tire load. In addition, the control device has a first determining device which is designed to determine an instantaneous dynamic radius of the wheel having the tire on the basis of the received instantaneous rotational speed and the received instantaneous speed. In addition, the control device has a second determining device which is designed to determine an instantaneous dynamic internal radius of the wheel on the basis of the at least one received first parameter. The internal radius of the wheel is here the distance between the wheel center and the tire-side start of the tread.

Furthermore, the control device has a third determining device which is designed to determine a tread depth of the tread of the tire on the basis of the determined instantaneous dynamic radius and the determined instantaneous dynamic internal radius.

The control device can be embodied as a stand-alone control device for the vehicle or can be a component of a further control device, for example of a control device of an anti-lock brake system or of a vehicle movement dynamics control system.

Furthermore, the invention relates to a system for a vehicle for determining a tread depth of a tread of a tire of the vehicle. The system has a control device according to the specified embodiment, and at least one wheel unit. The at least one wheel unit can be arranged here in the tire and has at least one sensor selected from the group composed of a temperature sensor, a pressure sensor and a tire load sensor.

The control device and the system for determining the tread depth have the advantages already specified in relation to the corresponding methods, which advantages will not be presented once more at this point in order to avoid repetitions, and are suitable, in particular, for carrying out the method according to the invention, wherein this can also relate to the embodiments and developments. For this purpose, the control device and the system can have further suitable devices and components.

DESCRIPTION OF THE INVENTION

FIG. 1shows a flowchart of a method for determining a tread depth of a tread of a tire during operation of a vehicle having the tire, according to a first embodiment. The vehicle is typically a motor vehicle, for example a passenger car or a truck.

In a step50, an instantaneous rotational speed of a wheel of the vehicle having the tire is determined on the basis of data determined by at least one first sensor. For example, an instantaneous angular speed co of the wheel is determined. The at least one first sensor is preferably embodied as a rotational speed sensor for this purpose.

In a step60, an instantaneous speed vrefof the vehicle, that is to say the longitudinal speed of the vehicle, is determined on the basis of data determined by at least one second sensor which is different from the at least one first sensor. The determination of the instantaneous speed vreftypically includes determining a value of a distance traveled by the vehicle in a specific time interval, on the basis of data determined by the at least one second sensor. The at least one second sensor is embodied, for example, as a satellite-assisted position-determining sensor for this purpose. Furthermore, the at least one second sensor can be embodied as a radar sensor, lidar sensor, ultrasonic sensor or optical camera, and therefore a distance of the vehicle from objects which are detected as positionally fixed can be determined at various times, and the distance traveled by the vehicle can be determined therefrom.

Furthermore, in a step90, an instantaneous dynamic radius R of the wheel having the tire is determined on the basis of the determined instantaneous rotational speed and the determined instantaneous speed. This is done in the embodiment shown by means of the relationship vref=R·ω, where vrefis, as already explained, the instantaneous speed of the vehicle, R is the instantaneous dynamic radius of the wheel and ω is the instantaneous rotational speed of the wheel.

In a step100, at least one first parameter of the tire is determined, wherein the at least one first parameter is selected from the group composed of an instantaneous tire temperature T, an instantaneous tire pressure P and an instantaneous tire load. Preferably all of the specified parameters are determined here. The specified parameters are typically determined by means of a wheel unit which is arranged in the tire, as is explained in more detail in relation to the further figures.

Furthermore, in a step110, an instantaneous dynamic internal radius r0of the wheel is determined on the basis of the at least one determined first parameter and the determined instantaneous speed vrefand the type of the tire, wherein the type of the tire is stored, for example, in a memory device of the wheel unit. The internal radius r0of the wheel is here the distance between the wheel center and the tire-side start of the tread. The instantaneous dynamic internal radius r0of the wheel is preferably determined by means of at least one characteristic curve which is stored in a memory device.

The instantaneous dynamic internal radius r0of the wheel typically increases here as the tire temperature rises and the tire pressure rises. In contrast, an increasing tire load typically leads to a reduction in the instantaneous dynamic internal radius r0. As the instantaneous speed of the vehicle rises, the instantaneous dynamic internal radius r0typically increases, wherein the increase in the internal radius r0typically reaches saturation when a specific speed range is reached.

The specified dependencies can be taken into account by determining the at least one first parameter and the instantaneous speed vrefand the type of the tire during the determination of the instantaneous dynamic internal radius r0of the wheel, and can therefore be compensated.

In addition, in a step120, a tread depth tPof the tread of the tire is determined on the basis of the determined instantaneous dynamic radius R and the determined instantaneous dynamic internal radius r0. This is done in the embodiment shown on the basis of the relationships vref=[r0(vref, T, P, tire load, type of tire)+tP]·ω and vref=R·ω. From these, the relationship R=r0(vref, T, P, tire load, type of tire)+tPis obtained, by means of which relationship the tread depth tPcan be determined.

tP is here in the embodiment shown a measure of the dynamic behavior of the tread depth of the tread of the rigid wheel which has already been explained and which has, at a specific speed, the same rolling circumference which the wheel having the tire has at this speed. The determined value therefore characterizes the behavior of the tread depth in the driving operation of the vehicle, wherein during the determination of the value it is assumed that there is a rigid wheel which is equivalent to the wheel of the vehicle.

The steps50to120are typically carried out continuously during operation of the vehicle, that is to say the tread depth is determined continuously during the driving operation. In this context, it is possible to determine both an absolute value of the tread depth and also a relative change in the tread depth with respect to a previously determined value.

The tread depth is preferably determined here for all the tires of the vehicle, that is to say the instantaneous rotational speed, the instantaneous dynamic radius, the at least one first parameter and the instantaneous dynamic internal radius are determined separately for each tire or each wheel. The tread depth is subsequently determined for each tire from these values.

FIG. 2shows a flowchart of a method for determining a tread depth of a tread of a tire during operation of a vehicle having the tire, according to a second embodiment. The vehicle is, for example, again a passenger car or a truck.

In a step50, an instantaneous rotational speed of a wheel of the vehicle having the tire is determined on the basis of data determined by at least one first sensor, corresponding to step50of the first embodiment shown inFIG. 1.

Furthermore, in a step60, an instantaneous speed of the vehicle is determined on the basis of data determined by at least one second sensor which is different from the at least one first sensor, corresponding to the step60of the first embodiment shown inFIG. 1.

In a step70, at least one second parameter is determined selected from the group composed of an instantaneous acceleration of the vehicle, an instantaneous yaw rate of the vehicle, an instantaneous steering angle, an instantaneous torque of a drive engine of the vehicle and an operating state of a brake device of the vehicle.

For this purpose, in a step80, it is determined on the basis of the at least one determined second parameter whether the instantaneous driving situation constitutes a driving situation in which no slip or as little slip as possible occurs and in which the vehicle is traveling essentially in a straight line.

For example it is determined whether the at least one second parameter exceeds a predetermined threshold value or whether the brake device of the vehicle is activated at the time.

If it is determined in step80here that the instantaneous driving situation does not constitute a driving situation in which no slip or as little slip as possible occurs and in which the vehicle is traveling essentially in a straight line, for example if the second parameter exceeds the predetermined threshold value and/or the brake device is activated, the steps50,60,70and80are carried out repeatedly.

On the other hand, if it is determined in step80that the instantaneous driving situation constitutes a driving situation in which no slip or as little slip as possible occurs and in which the vehicle is traveling in an essentially straight line, for example if the second parameter does not exceed the predetermined threshold value and the brake device is not activated, in a step90an instantaneous dynamic radius of the wheel having the tire is determined on the basis of the determined instantaneous rotational speed and the determined instantaneous speed corresponding to step90of the embodiment shown inFIG. 1. A situation in which the influence of drive slip or brake slip is low is present, for example, if a driving situation with very low acceleration is detected, that is to say the longitudinal acceleration and the lateral acceleration are virtually zero, the brake device is not activated, the engine torque is also virtually zero, the change in the determined instantaneous speed of the vehicle over time is virtually zero, and the rotational speeds of all the wheels of the vehicle are approximately the same.

In addition, in a step100, at least one first parameter of the tire is determined, selected from the group composed of an instantaneous tire temperature, an instantaneous tire pressure and an instantaneous tire load.

In a step110, an instantaneous dynamic internal radius of the wheel is determined on the basis of the at least one determined parameter, and in a step120a tread depth of the tread of the tire is determined on the basis of the determined instantaneous dynamic radius and the determined instantaneous dynamic internal radius. The steps100,110and120correspond here to the steps100,110and120according to the first embodiment shown inFIG. 1.

In addition, the determined tread depth of the tread of the tire in the embodiment shown is transmitted, in a step130, to at least one driver assistance system of the vehicle, for example to an ABS or ESP system.

In a step140it is determined whether the determined tread depth of the tread of the tire undershoots a predetermined threshold value, for example 2 mm.

If the determined tread depth does not undershoot the predetermined threshold value, the steps50to80and, if appropriate,90to140are carried out repeatedly.

In contrast, if the determined tread depth undershoots the predetermined threshold value, in a step150a warning message is issued by means of an output device of the vehicle. In addition, in this case a warning message can be transmitted automatically to further vehicles and/or a service device can be informed automatically, for example for the arrangement of an appointment.

In particular, by means of the methods according to the invention which are shown inFIGS. 1 and 2it is possible to classify a change in the wheel radius as a change in tire pressure, as a change in load or as a temperature-related change. These effects can therefore be compensated and the remaining change in the wheel radius classified as a change in the tread depth.

As a result, by means of the specified methods an individual tire tread depth can be determined on the basis of a sensor fusion approach. This approach accesses here, for example, signals of a tire unit, of the ABS/ESP system and of the navigation system. In addition, it is possible to access signals of the engine controller, which can increase the accuracy of the determination.

It is also to be noted here that speed differences between wheels on the inside bends and on the outside bends when cornering should typically be negligible. Such influences can either be compensated, for example on the basis of yaw rate information and steering angle information, or driving situations can be identified in which bend effects hardly occur, for example in turn by means of steering wheel angle information and yaw rate information or if the rotational speeds of all the wheels of the vehicle are approximately the same. For this purpose, a filter process is preferably used which permits only the driving situations described above with low slip or low bend effects and averages them over a certain time period.

The specified methods therefore make available a vehicle movement dynamics-based approach in order to estimate and/or determine the tread depth. In this context, it is assumed, for example, that the distance traveled, measured by means of a GPS system, over a predefined time period is related to the number of rotations of a tire which is measured, for example, by an ABS/ESP system. This relationship depends, in particular, on the dynamic wheel radius, which in turn depends on the tread depth.

FIG. 3Ashows a schematic illustration of a vehicle3with a control device11for determining a tread depth of a tread of a tire2of at least one wheel4of the vehicle3.

The vehicle3in the illustration shown is a motor vehicle in the form of a passenger car and it has, in total, four wheels, a front wheel and a rear wheel of which are shown inFIG. 3A. Further details are explained in more detail in relation to the following figures.

In this respect,FIG. 3Bshows a schematic cross section through one of the wheels4of the vehicle shown inFIG. 3A.

As is shown inFIG. 3B, the tire2of the wheel4has a tread1(illustrated schematically by means of an interrupted line) with a tread depth tP. The wheel4has an internal radius r0, wherein the internal radius r0of the wheel4is the distance between a wheel center7and a tire-side start8of the tread1. The internal radius r0of the wheel4therefore indicates the radius of the wheel4without the tread1of the tire2. Furthermore, a rolling direction of the wheel4is illustrated schematically inFIG. 3Bby means of an arrow A.

In addition, inFIG. 3Ba wheel unit17is shown which is arranged in the tire2. If such a tire unit or wheel unit17is directly in the tire contact area, that is to say in the contact area between the roadway48and the tire2, or on the inside of the tread, said tire unit or wheel unit17can additionally detect the interaction between the roadway48and the tire2directly, for example by means of an acceleration sensor, a shock sensor or a piezo element. In this instance, the individual tire load can be determined by measuring the length of the tire contact area in conjunction with measuring the tire pressure and possible measurement of the tire temperature and speed, that is to say the tire load is a function of the length of the tire contact area, of the tire pressure, of the temperature and of the speed.

As is explained in more detail below, by means of sensors of the wheel unit17which are not illustrated in more detail inFIG. 3Band on the basis of further determined parameters it is possible to determine an instantaneous tread depth of the tread1of the tire2during operation of the vehicle. When the value of the instantaneous tread depth is determined, it is assumed here, as already explained, that there is a rigid wheel which is equivalent to the wheel of the vehicle.

In this respect,FIG. 4shows a system16for determining a tread depth of a tread of a tire of the vehicle which is not illustrated in more detail inFIG. 4. Components with the same functions as inFIGS. 3A and 3Bare characterized with the same reference symbols and not explained again in the text which follows.

The system16has a control device11and a wheel unit17for each wheel or each tire of the vehicle, wherein for reasons of clarity only one such wheel unit17is illustrated inFIG. 4.

The wheel unit17can be arranged in the respective tire, and in the embodiment shown said wheel unit17has in each case a temperature sensor18for determining an instantaneous tire temperature, a pressure sensor19for determining an instantaneous tire pressure and a tire load sensor20for determining an instantaneous tire load. In addition, the wheel unit17has a memory device27, wherein, for example, data relating to a type of the tire and/or the age of the tire can be stored in the memory device27. In particular, characteristic tire properties such as, for example, the type of the tire, age, dimension, DOT number and treadwear rating, can be stored and made available. Furthermore, the wheel unit17has a transmitter device28by means of which the specified data can be transmitted to the control device11.

The control device11has for this purpose a receiver device12which is designed to receive an instantaneous tire temperature value, an instantaneous tire pressure value and an instantaneous tire load value from the transmitter device28.

In addition, the receiver device12is designed to receive an instantaneous rotational speed value of the wheel of the vehicle having the tire. For this purpose, the receiver device12is connected via a signal line47to a control device31which is embodied in the embodiment shown as an ABS or ESP control device. The control device31is also connected via a signal line32to a first sensor5in the form of a rotational angle sensor. In this context, each wheel of the vehicle is assigned a separate first sensor5, wherein for reasons of clarity only one such first sensor5is illustrated inFIG. 4.

In addition, the control device31is connected via a signal line33to an acceleration sensor21which is designed to determine a longitudinal acceleration of the vehicle and a lateral acceleration of the vehicle. Furthermore, the control device31is connected via a signal line34to a yaw rate sensor22, and via a signal line35to a steering angle sensor23. Furthermore, the control device31is connected via a signal line36to a sensor24which is designed to determine an operating state of a brake device (not illustrated in more detail) of the vehicle. For example, the sensor24can transmit a brake light signal of the brake device to the control device31. The data determined by the specified sensors is processed in the control device31, and the values determined therefrom are transmitted to the receiver device12.

The receiver device12is also connected via a signal line37to a navigation system25which has a second sensor6in the form of a position-determining sensor. On the basis of data determined by the second sensor6, an instantaneous speed of the vehicle can be determined by the navigation system25and made available to the control device11by means of the receiver device12.

In addition, the receiver device12is connected via a signal line38to an engine control device26of a drive engine (not illustrated in more detail) of the vehicle. As a result, an instantaneous torque of the drive engine can be transmitted to the control device11.

The control device11also has a first determining device13which is designed to determine an instantaneous dynamic radius of the wheel having the tire, on the basis of the instantaneous rotational speed value received by the receiver device12and the received instantaneous speed value. For this purpose, the first determining device13is connected via a signal line39to the receiver device12.

Furthermore, the control device11has a second determining device14which is designed to determine an instantaneous dynamic internal radius of the wheel on the basis of the received instantaneous tire temperature value, the received instantaneous tire pressure value, the received instantaneous tire load value as well as the type of the tire and/or the age of the tire. The age of the tire can be determined for example, on the basis of the date of manufacture stored in the memory device27, as a result of which, in particular, it is possible to detect whether there is a novel tire which the system16is then able to learn about.

The second determining device14is connected here via a signal line40to the receiver device12, and in the embodiment shown said determining device14is designed to determine the instantaneous dynamic internal radius of the wheel by means of a multiplicity of characteristic curves stored in a memory device9. The memory device9is for this purpose connected via a signal line43to the second determining device14.

The control device11also has a third determining device15which is designed to determine a tread depth of the tread of the tire on the basis of the determined instantaneous dynamic radius and the determined instantaneous dynamic internal radius. For this purpose, the third determining device15is connected via a signal line41to the first determining device13and via a signal line42to the second determining device14.

The third determining device15is designed, in the embodiment shown, to determine whether the respective instantaneous driving situation constitutes a driving situation in which no slip or as little slip as possible occurs and in which the vehicle is traveling essentially in a straight line, on the basis of the values of the instantaneous acceleration of the vehicle, of the instantaneous yaw rate of the vehicle, of the instantaneous steering angle, of the instantaneous torque of the drive engine and of the operating state of the brake device which are received by the receiver device12.

If the third determining device15determines here that the instantaneous driving situation does not constitute a driving situation in which no slip or as little slip as possible occurs and in which the vehicle is traveling essentially in a straight line, this information can be transmitted to the first determining device13and/or the second determining device14, and the determination of the instantaneous dynamic radius or of the instantaneous dynamic internal radius can be omitted in these situations. For this purpose, in particular the signal lines41and42are embodied as bidirectional signal lines. In addition, in such situations the values which have already been determined during the determination of the tread depth can be ignored.

In addition, the third determining device15is designed in the embodiment shown to determine whether the determined tread depth of the tread of the tire undershoots a predetermined threshold value. If this is the case, a warning message can be output by means of an output device30of the vehicle and transmitted to further vehicles by means of a transmitter device29. The third determining device15is for this purpose connected to the output device30via a signal line45and to the transmitter device29via a signal line44.

In addition, the determined tread depth of the tread of the tire can be transmitted to a driver assistance system10of the vehicle. For this purpose, the third determining device15is connected via a signal line46to the driver assistance system10, which is embodied, for example, as a brake assistant or emergency brake system.

The tread depth of a tire has here a decisive influence on the behavior of the vehicle. This applies, in particular, in critical driving situations. On the one hand, the maximum frictional engagement between the tire and the roadway, that is to say the grip, is heavily dependent on the respective properties of the roadway, for example the covering of the roadway or the presence of snow or ice on the roadway. On the other hand, the frictional engagement for the respective conditions can be optimized by specific tire properties. These include, in particular, a tire tread which is optimized for the respective weather conditions. The effectiveness of the tire tread is decisively determined here by the tread depth. For example, in the case of aquaplaning the water between the roadway and the tire can no longer be expelled owing to a tread which is no longer sufficient.

As a result, the best possible frictional engagement between the tire and the roadway can be ensured by a sufficient tread depth, in particular in critical driving situations. For this reason there are typically legal requirements for a minimum tread depth which can also vary here according to the season.

The present invention advantageously makes available a method and a control device and a system with which the tread depth can be estimated and/or determined during travel. This information can be made available, in particular, to the driver so that the driver changes tires with an excessively low tread depth in good time. This makes it possible to avoid specific hazardous situations, in particular aquaplaning and a loss of grip on snow-covered roadways, and associated accidents.

Furthermore, the determined tread depth can be made available to other vehicle systems, in particular active safety systems, for example an ABS or ESP. This permits the respective regulation strategies of the reduced grip situation to be adapted and therefore optimized.

Furthermore, the medium-term time tread of the tread depth permits conclusions to be drawn about the change of tires according to the season. As a result it is possible to estimate whether the respective tire still has sufficient tread for the coming season or should be replaced.

LIST OF REFERENCE SYMBOLS

10driver assistance system

20tire load sensor

22yaw rate sensor

26engine control device

A arrow