Procedure for determining a defective brake

Abstract

The invention relates to a method for detecting a defective brake (Bi) on a wheel (2.i) of a vehicle (1), wherein a tire sensor module (3.k) is arranged on at least two wheels (2.i) of the vehicle (1), comprising at least the following steps: - Specifying a first and a second selected tire sensor module from the existing tire sensor modules (3.k); - Determining a first movement behavior of the first selected tire sensor module and a second movement behavior of the second selected tire sensor module, wherein the respective movement behavior is determined as a function of the acceleration values generated and output by the sensor unit of the respective selected tire sensor module; - Comparing the two determined movement behaviors with each other; - Outputting an error signal if the two determined movement behaviors differ from one another and / or if one of the two determined movement behaviors indicates that the wheel (2.i) is braked with the respective selected tire sensor module without the presence of a braking request, wherein the error signal includes that one of the brakes is defective.

Description

The invention relates to a method for determining a defective brake on a wheel of a vehicle, in particular a trailer.In vehicle combinations comprising a motor vehicle and a trailer, in some types no information regarding the state of the brakes is available, because, for example, no electronic brake system is present in the trailer. Thus, brakes of trailers may be locked or locked after a long service life, for example, which leads to excessive wear and / or to an unnecessarily high drive power to be applied if such a locked brake is nevertheless used to drive. However, even in the case of motor vehicles and trailers with a defective electronic part of the brake system, a reliable statement about the state of the individual brakes is not necessarily available. Therefore, in such vehicles, a defect can only be detected late or not and can also not be appropriately taken, from which critical driving situations or unnecessary power losses can arise.The object of the present invention is therefore to specify a method for detecting a defective brake, with which method the disadvantages of the prior art are avoided.This object is achieved by a method according to independent claim 1. The dependent claims indicate preferred refinements.According to the invention, a method for determining a defective brake on a wheel of a vehicle, in particular a trailer or an engine truck, having a plurality of wheels is accordingly provided, wherein a tire sensor module is respectively arranged or fastened on at least two of the wheels, wherein the respective tire sensor module comprises a sensor unit having at least one acceleration sensor for generating and outputting acceleration values, in particular radial acceleration values, and an evaluation unit for processing the acceleration values or radial acceleration values and for generating a data telegram having different data, in particular the acceleration values or information dependent thereon, wherein the data telegram of the respective tire sensor module is wirelessly transmitted to a control device, wherein the method comprises at least the following steps:defining a first selected tire sensor module and a second selected tire sensor module different therefrom from the tire sensor modules present in the vehicle;determining a first movement behavior of the first selected tire sensor module and a second movement behavior of the second selected tire sensor module, wherein the respective movement behavior is determined as a function of the acceleration values, in particular the radial acceleration value, which is generated and output by the sensor unit of the respective selected tire sensor module, wherein the movement behavior characterizes the current or temporal movement of the respective tire sensor module and thus also of the associated wheel;comparing the two determined movement behaviors with one another, in particular for determining a deviation between the two movement behaviors; andoutputting a fault signal if the two determined movement behaviors differ from one another and / or if one of the two determined movement behaviors indicates that the wheel is braked with the respective selected tire sensor module without the presence of a braking request via the respective brake, wherein the fault signal then includes that one of the brakes is defective. The error signal can then be treated accordingly.According to the invention, it is thus advantageously recognized that the information about a braking of a wheel of the respective vehicle can be effected via the individual tire sensor modules. With the aid of the tire sensor modules, braking maneuvers can therefore be detected on all or else on individual wheels in order to monitor the state of the brakes, in particular if this information is not otherwise available. For example, a brake that is locked or locked can also be detected on a trailer, for example after a long service life, the design of which does not allow electronic monitoring of the brakes or the electronic part of the brake system of which has a defect. In this way, the function of the brakes can also be monitored in the motor vehicle in the event of a failure of the electrical part of the (electrohydraulic / electropneumatic) brake system.The monitoring according to the invention can take place on a control device in the vehicle, for example as a component of a telemetry system, or else of a yard controller or a fleet management system. In this way, components installed in any case on the vehicle can be used for such monitoring, wherein the monitoring can also take place redundantly with respect to other monitorings in the vehicle.Preferably, it is further provided that the first selected tire sensor module and the second selected tire sensor module are fixed in such a way thatboth selected tire sensor modules are located on the same vehicle axle of the vehicle, orboth selected tire sensor modules are located on the same side of a longitudinal central axis of the vehicle or on the same vehicle side.This ensures that tire sensor modules are compared with one another, which should exhibit a very similar movement behavior. Thus, the wheels should rotate approximately the same speed on the same axle; a deviation here indicates a possible problem. Likewise, the wheels on the same side of the vehicle should rotate approximately the same speed, in particular during cornering; a deviation here likewise indicates a possible problem.Preferably, it is also provided that the defining of the two selected tire sensor modules and the determination of the respectively assigned movement behaviors and the subsequent comparison of the two determined movement behaviors with one another are carried out multiple times, wherein for this purpose a reference module is defined from the existing tire sensor modules, wherein the defined reference module is the first selected tire sensor module at each performance and a different one of the existing tire sensor modules is selected as the second selected tire sensor module at each performance, wherein the second selected tire sensor module is different from the first selected tire sensor module. Thus, starting from the same reference module, a comparison with different other tire sensor modules is always carried out in order to obtain a reliable and possibly plausibility checked result.Preferably, it is then further provided that the defined reference module is that of,which is located on the fastest rotating wheel, orwhich is located on the wheel which rotates at a wheel speed which is closest to a wheel speed median. As a result, it is possible to clearly determine in each case which of the tire sensor modules is the reference module in two different ways. Since problems with the brakes are to be investigated, the greatest difference can be detected starting from the fastest rotating wheel during braking. The use of the wheel speed median is particularly advantageous since a tire which rotates particularly rapidly due to high slip is not considered here as a reference module.Preferably, it is further provided that the determination of the first movement behavior of the first selected tire sensor module and the second movement behavior of the second selected tire sensor module includesa movement state of the respectively selected tire sensor module and / ora running performance of the respectively selected tire sensor module and / orthe radial acceleration value of the tire sensor module selected in each case can be determined. These variables each indicate in what way the respective tire sensor module and thus also the respectively assigned wheel have currently moved or moved over a specific period of time. From this, it can then be deduced from the comparison whether and at which wheels a braking maneuver takes place or has taken place.It is preferably further provided that the movement state of the respectively selected tire sensor module indicates whether or not the respectively selected tire sensor module is braked, wherein it is determined for determining the movement state whether or not two radial acceleration storage values stored offset from one another at a temporal storage distance of, for example, between 4 s and 16 s, which indicate the measured radial acceleration value at the respectively stored point in time, deviate from one another by more than a first threshold value, wherein a movement state "braking" is determined for the respectively selected tire sensor module if the two radial acceleration storage values deviate from one another by more than the first threshold value and otherwise, for example, a movement state "no braking" is determined. From a comparison of the radial acceleration values at different times, it is thus possible to infer the beginning of a braking maneuver at the respective wheel starting from a specific deviation and to output this via a corresponding determination of the "value" for the movement state.Preferably, it is further provided that at least three radial acceleration storage values offset from one another in the temporal storage distance are stored and it is determined in at least two comparison processes whether or not two different ones of the at least three stored radial acceleration storage values deviate from one another by more than the first threshold value. The comparison is therefore not only based on two values, but at least two comparisons are carried out in which at least one of the radial acceleration storage values differs. For example, the most up-to-date radial acceleration storage values may each be compared to the "oldest" radial acceleration storage value to identify one-time outliers (measurement in the ground contact surface) and to avoid erroneous detections for the motion state "braking".Preferably, it is also provided that at least three radial acceleration values are recorded for a time within a sampling rate of, for example, 50 ms for storing the radial acceleration storage values and the recorded radial acceleration value, average in magnitude, is stored as a radial acceleration storage value for the respective time. In this way, one-time outliers (measurement in the ground contact surface) can also be identified or they fall out when selecting the radial acceleration storage value on the basis of the selection of the mean acquired radial acceleration value. This also makes it possible to avoid erroneous detections for the motion state "braking".It is preferably also provided that the movement state of the respectively selected tire sensor module is determined in an evaluation unit on the respectively selected tire sensor module and / or on a control device which is located away from the respectively selected tire sensor module. In this way, the evaluation can be flexibly adapted to the respective conditions and applications and the energy and transmission effort can be kept within the scope according to the conditions and the application.It is preferably further provided that the running performance of the respectively selected tire sensor module specifies which distance the respectively selected tire sensor module and thus also the respectively associated wheel has covered within a defined time period, wherein for determining the running performance the acceleration values detected over the defined time period, in particular the radial acceleration values, are integrated twice in time. From the information about the running performance, a statement can likewise be made by the following comparison as to whether a wheel is braked unintentionally and unnoticed.It is therefore preferably provided that testing is carried out for outputting the error signal,whether the movement states of the two selected tire sensor modules differ from one another, and / orwhether the running powers of the two selected tire sensor modules deviate from one another by more than a second threshold value, and / orwhether the radial acceleration values of the two selected tire sensor modules deviate from one another by more than a third threshold value, wherein the error signal contains that one of the brakes is defective if the movement states differ from one another without the presence of a braking request and / or the running powers deviate from one another by more than the second threshold value, and / or the radial acceleration values deviate from one another by more than a third threshold value without the presence of a braking request. Thus, a statement about unintentional braking can be determined from a simple comparison via the respective movement behavior, which then correspondingly leads to the output of an error signal for further processing.Preferably, it is also provided that, for the purpose of outputting the fault signal and / or for the purpose of ascertaining whether a braking request is present, a supplementary check is made as to whether a current through a brake light of the vehicle is flowing. In this way, the fault signal can thus be checked for plausibility. Furthermore, the function of the brake light can also be checked if, for example, the individual movement behaviors indicate (intentional) braking of the vehicle, but the brake light is not supplied with current.In the drawings, there are shown: FIG. 1 is a schematic view of a vehicle with tire sensor modules on the wheels; FIG. 2 shows a schematic detailed view of a tire sensor module; FIG. 3 shows a time profile of radial acceleration values; and FIG. 4 shows a flow chart of the method according to the invention.FIG. 1 schematically shows a vehicle 1, for example a motor vehicle or a trailer, having a number N of wheels 2.i (i=1, 2,..., N), wherein a vehicle 1 having N=4 wheels 2.i is shown by way of example. At least two wheels 2.i, preferably each wheel 2.i (N=4), are assigned a tire sensor module 3.k (k=1, 2... ≤N). As shown in FIG. 2, each tire sensor module 3.khas at least one sensor unit 4 which is designed to measure an acceleration a and to output corresponding acceleration values aW via sensor signals S 4. Each wheel 2.i is also assigned a brake B.i.The sensor unit 4 of the respective tire sensor module 3.kthus has at least one acceleration sensor 4 a, wherein the latter is designed to output in particular radial acceleration values arWvia the sensor signal S 4, which characterize a radial acceleration ar of the respective wheel 2.ior of the tire sensor module 3.k. In addition to the acceleration values aW, measured values MW can also be output by the sensor unit 4 via the sensor signal S 4, which characterize further tire states, for example temperature values TW of a temperature sensor 4 band / or pressure values pW of a pressure sensor 4 c.Each of the tire sensor modules 3.kfurther includes an evaluation unit 5, which is designed to process or preprocess the measured values MW; aW, arW, TW, pW or sensor signals S 4 output by the sensor unit 4 and to generate a data telegram DT.kbased thereon. Furthermore, a communication unit 6 is contained in each tire sensor module 3.k, which is designed to transmit the generated data telegram DT.k wirelessly, for example via a high-frequency radio signal, to a control device 7 in the vehicle 1 or outside the vehicle 1. Normally, such a transmission of the data telegram DT.k does not take place continuously, but at relatively long time intervals in order to save energy, for example every 128 s or every 512 s.The respective data telegram DT.k has a certain defined length and a certain defined structure, i.e. the information encoded in the respective data telegram DT.k is always contained in the same section. Thus, for example, the individual measured values MW; aW, arW, TW, pW can be transmitted via the data telegram DT.k in the sections provided in each case and, in addition, in a further section of the data telegram DT.k, for example, a sensor identification ID.k or a unique sensor identifier, on the basis of which the respective tire sensor module 3.k can be uniquely identified. In this way, the control device 7 can decode the information transmitted via the data telegram DT.k and also unambiguously assign it to a specific tire sensor module 3.k and thus also to a specific wheel 2.i on which it is arranged.The data telegram DT.k may also contain a motion state Z.k of the respectively assigned tire sensor module 3.k and / or a running performance L.k of the respectively assigned tire sensor module 3.k, so that the control device 7 may also access this information and unambiguously assign it to the respective wheel 2.i. A corresponding evaluation algorithm A is implemented on the evaluation unit 5 for determining the motion state Z.k and / or the running power L.k. The evaluation algorithm A has in particular access to the measured acceleration values aW, in particular the radial acceleration values arW.The evaluation algorithm A regularly stores the measured radial acceleration value arW as a radial acceleration storage value arSW.m (m=1,...M) after a defined temporal storage distance dtS has elapsed, so that the evaluation algorithm A can resort to it at a later point in time. The storage time interval dtS can be set to a value of between 4 s and 16 s, for example. The number M of different radial acceleration storage values arSW.m can vary depending on the application, wherein at least two (M=2) radial acceleration storage values arSW.1, arSW.2 are stored with the defined temporal storage distances dtS.For the determination of the motion state Z.k, a first comparison value V1 and a second comparison value V2 are read in by the evaluation algorithm A from the at least two stored radial acceleration storage values arSW.m. The first comparison value V 1 is assigned to a first time t 1 and the second comparison value V 2 is assigned to a second time t 2, wherein the first time t 1 is at least the defined temporal storage distance dtSafter the second time t 2. If more than two (M=2) radial acceleration storage values arSW.m are stored, a multiple of the defined temporal storage distance dtS can also lie between the two points in time t 1, t 2.In a first embodiment, the first comparison value V 1 corresponds to the radial acceleration value arW, which was last measured and stored, i.e. the first radial acceleration storage value arSW.1. The second comparison value V2 corresponds to a radial acceleration value arW, which was measured and stored previously or earlier in time, for example the second radial acceleration storage value arSW.2, which was stored previously for example a storage distance dtS in time.If the current first comparison value V 1 deviates downward from the older second comparison value V 2 by more than a defined first threshold value S 1, this indicates that the respectively assigned tire sensor module 3.k, and thus also the corresponding wheel 2.i, is currently braked in any braking maneuver. Consequently, for this tire sensor module 3.k, the evaluation algorithm A determines "braking" or a similar designation as the movement state Z.k, which designation is assigned to a braking maneuver of the respective wheel 2.i, and outputs it via the data telegram DT.k. If the deviation is less than the first threshold value S 1, for example, "no braking" or the like can be set and output as the movement state Z.k. Instead of "braking" and "no braking", a number, for example "1" for "braking" and "0" for "no braking", can also be defined for the movement state Z.k.In addition, it can be provided that, in the presence of the motion state Z.k "braking" or the like for the relevant tire sensor module 3.k, an immediate wireless transmission of the data telegram DT.k is enforced, so that the control device 7 can immediately receive and evaluate the data telegram DT.k.The first threshold value S 1 is defined in such a way that the motion state Z.k "braking" or the like is not output, for example, even during normal coasting of the vehicle 1. For this purpose, when reading and storing the radial acceleration values arW or radial acceleration storage values arSW.m with a storage time interval dtS of 4 s, a first threshold value S 1 of, for example, at least 20% of the first comparison value V 1 can be set, and when reading and storing the radial acceleration values arW or radial acceleration storage values arSW.m with a storage time interval dtS of 16 s, a first threshold value S 1 of, for example, at least 50% of the first comparison value V 1 can be set. For different temporal storage distances dtS, the first threshold values S 1 are adjusted accordingly.By way of example, FIG. 3 specifies a temporal profile of the radial acceleration values arW, where the aforementioned equation is shown. This comparison is carried out on the basis of the two comparison values V1 (arSW.1), V2 (arSW.2), wherein two exemplary embodiments are shown at two different times in FIG. 3. These comparison values V 1, V 2 deviate from one another by more than the first threshold value S 1, i.e. a sudden drop results. This sudden drop differs from the slow drop in the radial acceleration values arW at later points in time in the right-hand part of the time profile, which is caused by the vehicle 1 rolling out.In order to increase the accuracy of the evaluation and determination of the movement state Z.k of the respective tire sensor module 3.k and to avoid false detection on the basis of an impaired acceleration measurement, for example an acceleration measurement in the ground contact surface of the wheel 2.i, the respective comparison values V 1, V 2 are selected, for example, as follows according to a further embodiment:First, a number M of at least three radial acceleration storage values arSW.m are stored. The first comparison value V1 used is the radial acceleration value arW which was last measured and stored, i.e. the first radial acceleration storage value arSW.1. A radial acceleration value arW is used as second comparison value V 2, which has been measured and stored the earliest in time of the at least three stored radial acceleration storage values arSW.m, i.e., for example, the third radial acceleration storage value arSW.3, which was stored at a third point in time t 3 (before second point in time t 2 and before first point in time t 1).For these two comparison values V 1, V 2, in a first comparison process C 1, the above-mentioned comparison with a correspondingly defined first threshold value S 1 is carried out. Furthermore, a second comparison process C 2 is carried out, in which the radial acceleration value arW, which has been measured and stored as second time, i.e. the second radial acceleration storage value arSW.2, which has been stored at the second point in time t 2 (before the first point in time t 1), is used as the first comparison value V 1. The third radial acceleration storage value arSW.3, which was measured and stored the earliest time by the three radial acceleration storage values arSW.m, is used again as the second comparison value V 2. This is indicated by way of example in FIG. 3.If it is determined in both comparison processes C 1, C 2 that the more up-to-date first comparison value V 1 (arSW.1 or arSW.2) deviates downward from the older second comparison value V 2 (arSW.3) by more than the defined first threshold value S 1, then "braking" or a similar designation which is associated with a braking maneuver of the respective wheel 2.i is defined for this tire sensor module 3.k as the movement state Z.k by the evaluation algorithm A and is output via the data telegram DT.k. If this is the case for only one or none of the two comparison processes C 1, C 2, "no braking" or the like is output as the movement state Z.k. By this procedure, a one-time short drop of the radial acceleration value arW to zero is not incorrectly recognized as a braking maneuver during an acceleration measurement in the ground contact surface of the wheel 2.i.In further embodiments, according to this system, for a number M>3, further radial acceleration storage values arSW.mthat are measured and stored in a correspondingly offset manner with respect to one another can also be compared with one another in one or more comparison processes in order to determine the movement state Z.kfor the corresponding tire sensor module 3.k.Furthermore, for the described exemplary embodiments, it can be provided in each case that, before the storage of the respective radial acceleration storage value arSW.mfor the respective time tm(m=1,...,M), three radial acceleration values arW, for example, are detected internally in chronological succession at a sampling rate R of, for example, 50 ms. As a radial acceleration storage value arSW.m, for the respective time tm, only the radial acceleration value arW, average in terms of amount, is then permanently stored, i.e. that radial acceleration value arW which lies between the two other radial acceleration values arW in terms of amount.If the three radial acceleration values arW "0 g", "80 g" and "75 g" are thus measured with the sampling rate R of, for example, 50 ms, the radial acceleration value arW of "75 g" for the respective time tm is stored as the radial acceleration storage value arSW.m. Such a selection and storage takes place at any point in time tm, so that the subsequent comparison of the two comparison values V 1, V 2 can be carried out on the basis of radial acceleration storage values arSW.m stored in this way. This reduces the probability that a radial acceleration value arW measured in the ground contact area is adopted as the radial acceleration storage value arSW.m (see above. Radial acceleration value arW="0 g").For the determination of the running performance L.k, the evaluation algorithm A reads in the acceleration values aW, in particular the radial acceleration values arW, over a defined period dt, which are determined regularly by the respective tire sensor module 3.k, for example with the storage distance dtS. By double integration over time period dt, a distance can then be obtained which has covered the respective tire sensor module 3.kand thus also the respectively assigned wheel 2.i. This corresponds to the running performance L.k of the respective tire sensor module 3.k.With all the information wirelessly transmitted to the control unit 7 via the respective data telegram DT.k, i.e. the motion state Z.k determined via the evaluation algorithm A and / or the running power L.k determined via the evaluation algorithm A as well as the detected measured values MW; aW, arW, TW, pW, it can be determined in the control unit 7 by a function algorithm F, which is implemented, for example, as hardware or as software, as described below with reference to the flow chart of FIG. 4 whether a defect is present at the brakes B.i of the respective wheels 2.i or whether these are still functioning:In an initial step ST0, the above-mentioned steps are first started. This means that information is determined and provided, i.e. the movement states Z.k determined via the evaluation algorithm A and / or the running powers L.k determined via the evaluation algorithm A and the respectively detected measured values MW; aW, arW, TW, pW.In a first step ST 1, a first selected tire sensor module 3 a 1 and a second selected tire sensor module 3 a 2 which is different from the first selected tire sensor module 3 a 1 are defined from the present tire sensor modules 3.k. The selection is made, for example, in such a way that the first selected tire sensor module 3 a 1 and the second selected tire sensor module 3 a 2 are located on the same vehicle axle FA of the vehicle 1, e.g., on a front axle VA or one of the rear axles HA. Alternatively, the selection may be made such that the first selected tire sensor module 3 a 1 and the second selected tire sensor module 3 a 2 are located on the same vehicle side of the vehicle 1. The vehicle side relates to the position relative to a longitudinal central axis LM of the vehicle 1, i.e. to the right or left of the longitudinal central axis LM of the vehicle 1. Thus, the wheels 2.i usually rotate approximately the same speed on the same vehicle axle FA, so that a deviation can indicate a possible problem. Likewise, in particular during cornering, the wheels 2.i on the same vehicle side of the vehicle 1 generally rotate approximately the same speed, so that a deviation can also indicate a possible problem here.In a second step ST 2, a first movement behavior BV 1 of the first selected tire sensor module 3 a 1 and a second movement behavior BV 2 of the second selected tire sensor module 3 a 2 are ascertained. The respective movement behavior BV 1, BV 2 can be specified, for example, by the movement state Z.k and / or the running performance L.k and / or the acceleration value aW, in particular the radial acceleration value arW, which are transmitted via the data telegram DT.k of the respectively selected tire sensor module 3 a 1, 3 a 2.In a third step ST 3, the movement behavior BV 1, BV 2 of the selected tire sensor modules 3 a 1, 3 a 2 is compared with one another, i.e. it is determined to what extent the movement states Z.k and / or the running powers L.k and / or the radial acceleration values arW of the selected tire sensor modules 3 a 1, 3 a 2 deviate from one another.In a fourth step ST4, an error signal SF is then generated as follows:If it is determined by the function algorithm F at a specific evaluation time that the movement states Z.k (movement behavior BV 1, BV 2) of the two selected tire sensor modules 3 a 1, 3 a 2 deviate from one another, e.g. "braking" for the first selected tire sensor module 3 a 1 and "not braking" for the second selected tire sensor module 3 a 2, it can be concluded that a defect is present at the brakes B.i at least on one of the wheels 2.i, insofar as such a braking behavior deviating in a wheel-by-wheel manner is not to be expected.An error signal SF can then be generated and output by the control unit 7 or the error algorithm F. In particular, the fault signal SF can indicate that a defect with the brakes B.i is present on that wheel 2.i at which the respective selected tire sensor module 3 a 1, 3 a 2 with the motion state Z.k "braking" is present or, acting in the same way, no defect is present on the brakes B.i at which the respective selected tire sensor module 3 a 1, 3 a 2 with the motion state Z.k "no braking".The defective brakes B.i at the respective wheel 2.i can be blocked, for example, which cannot be otherwise determined, in particular in the case of a trailer without an electronic brake system or with a defective electronic brake system. However, such a blocked brake B.i can be detected by the function algorithm F as described by way of the movement states Z.k of the respectively selected tire sensor modules 3 a 1, 3 a 2, in particular if it is determined by the function algorithm F that no braking request for the trailer is present or is likely. For this purpose, the function algorithm F can also rely on a plurality of comparisons according to the third step ST 3 with respectively different selected tire sensor modules 3 a 1, 3 a 2 defined in the first step ST 1.The selection of the tire sensor modules 3.kfor these multiple comparisons can be effected in the first step ST 1 according to one embodiment in such a way that the first selected tire sensor module 3 a 1 as reference module RM is always the one which is located on the fastest rotating wheel 2.i, i.e. has the highest wheel speed v2.i. This can be derived directly from the motion state Z.k and / or the running power L.k and / or the detected acceleration values aW, in particular radial acceleration values arW, of the existing tire sensor modules 3.k. The second selected tire sensor module 3 a 1 is then, for each comparison to be carried out, a different value than the always identical first selected tire sensor module 3 a 1 or the reference module RM.Alternatively, the first selected tire sensor module 3 a 1 as the reference module RM can always be that which is located on that wheel 2.i which rotates at a wheel speed v2.i which is closest to a wheel speed median value vM. The wheel speed v2.ior the wheel speed median value vMcan be established here, for example, on the basis of the recorded acceleration values aW, in particular radial acceleration values arW, of the respective tire sensor modules 3.k. The second selected tire sensor module 3 a 1 is then, for each comparison to be carried out, a different value than the always identical first selected tire sensor module 3 a 1 or the reference module RM.A possible defect of a brake B.i can also be checked for plausibility by further information available to the function algorithm F relating to the brakes B.i of the trailer. Thus, the fault signal SF can be checked for plausibility, for example, by checking whether a current I flows through a brake light 10 of the trailer. If no such current I is detected and if the motion state Z.k "braking" is determined for only one tire sensor module 3.k overall, a blocked brake B.i can be inferred with high probability by the function algorithm F. If, conversely, the motion state Z.k of "braking" has been determined for all tire sensor modules 3.k and no current I flows through the brake light 10, the function algorithm F can infer a defect in the brake light 10 and this can likewise be output via the fault signal SF.The described procedure is not limited only to a defect at the brakes B.i of a trailer. In the same way, a defect can also be detected at the brakes B.i of an engine truck, wherein this information is then available as redundant information, for example in the event of a failure of the electronic part of a brake system, which can then normally no longer detect such a defect.If it is determined by the function algorithm F at a specific evaluation time that the running powers L.k (movement behavior BV 1, BV 2) of the two selected tire sensor modules 3 a 1, 3 a 2 deviate from one another, and optionally also from a running power of the vehicle 1, which is available, for example, via telematics, it can also be concluded that there is a defect at the brakes B.i at least at one of the wheels 2.i. A locked brake B.i leads to a reduced rotational speed for the corresponding wheel 2.i and therefore also to a reduced running power L.k. If the same time periods dt are set in each case for the respective running powers L.k (movement behavior BV 1, BV 2) of the two selected tire sensor modules 3 a 1, 3 a 2, for example a time period dt of one day or one week or an identical other time period dt, these can be directly compared with one another and fault-caused differences can be detected. For such a comparison, however, an average running performance L.k (per defined time period dt) for the two selected tire sensor modules 3 a 1, 3 a 2 can also be determined and compared.If it was recognized by the function algorithm F that the respectively compared running powers L.k of the two selected tire sensor modules 3 a 1, 3 a 2 deviate from one another by more than a second threshold value S 2, a malfunction or a defect of the brake B.i of the respectively assigned wheel 2.i can be deduced and a corresponding fault signal SF can be generated and output. In this case, the additional measured values MW which are transmitted via the respective data telegram DT.k can also be taken into account, for example the temperature values TW and / or the pressure values pW, in order to plausibilize the result.If it is determined by the function algorithm F at a specific evaluation time that the acceleration values aW, in particular radial acceleration values arW (movement behavior BV 1, BV 2), of the two selected tire sensor modules 3 a 1, 3 a 2 deviate from one another, transmitted as measured values MW via the data telegram DT.k, it can also be concluded that a defect is present at the brakes B.i at least at one of the wheels 2.i. For this purpose, the same evaluation algorithm A is integrated in the function algorithm F, for example, which, in the embodiment described above, compares the radial acceleration storage values arSW.mof the same tire sensor module 3.kwith one another for different points in time tmand, on the basis of this comparison, determines the movement state Z.kof the relevant tire sensor module 3.k.In third step ST 3, for this purpose, evaluation algorithm A determines a radial acceleration value arW from data telegram DT.k of first selected tire sensor module 3 a 1 as first comparison value V 1, and a radial acceleration value arW from data telegram DT.k of second selected tire sensor module 3 a 2 as second comparison value V 2, both radial acceleration values arW or comparison values V 1, V 2 having been measured at approximately the same time tm. If it is determined in the fourth step ST 4 that the two comparison values V 1, V 2 deviate from one another by more than a third threshold value S 3, the movement state Z.k "braking" or the like is assigned to that selected tire sensor module 3 a 1, 3 a 2 to which the higher (acceleration value) of the two comparison values V 1, V 2 is assigned, and the movement state Z.k "no braking" is assigned to the respective other selected tire sensor module 3 a 1, 3 a 2. The third threshold value S 3 is defined in such a way that slight wheel-by-wheel deviations in the radial accelerations ar of two wheels 2.i, which could result from known wheel-by-wheel differences, are permitted.In this comparison of the radial accelerations ar, the functional algorithm F can therefore only infer the motion state Z.k "braking" of an individual wheel 2.i when one of the wheels 2.i is ideally un braked or coasts and the respective other wheel 2.i is being braked, for example on account of a blocked brake B.i. If accordingly both comparison values V 1, V 2 are identical, an assignment of a specific movement state Z.k can initially be omitted within the scope of this method, since no relevant differences are then obtained from which it is possible to infer individual defective brakes B.i.If, however, a deviation of more than the third threshold value S 3 is determined during the comparison of the two comparison values V 1, V 2 by the evaluation algorithm A (compare the movement state Z.k "braking" for only one of the two selected tire sensor modules 3 a 1, 3 a 2), then it can be concluded by the function algorithm F that that brake B.i on that wheel 2 having the selected tire sensor module 3 a 1, 3 a 2 is defective, in particular is blocked, with the comparison value V 1, V 2 that is higher in terms of amount or the radial acceleration value arW that is higher in terms of amount (compare the movement state Z.k "braking").In order to plausibilize this, the comparison in step ST 3 can be carried out with further tire sensor modules 3.kprovided on the vehicle 1, i.e. other comparison values V 1, V 2 from other radial acceleration values arW of data messages DT.kof further tire sensor modules 3 a 1, 3 a 2 selected in the first step ST 1 are determined by the evaluation algorithm A and compared with one another. The respective comparison can also be repeated at other times in order to avoid measurement inaccuracies or unusable measurements in the ground contact area. If a defect of a brake B.i is confirmed, the fault algorithm F can generate a corresponding fault signal SF and output this. This can be checked for plausibility by means of additional information available to the function algorithm F.The evaluation algorithm A, which carries out the above-mentioned comparisons between different radial acceleration values arW in the different embodiments, can in principle be implemented on the respective tire sensor module 3.kand / or on the control device 7, as described in relation to the different embodiments. Therefore, the above-mentioned method can also be used. A plurality of radial acceleration (storage) values ar(S)W of an individual tire sensor module 3.k are also compared on the control unit 7 at different times tm for ascertaining the movement state Z.k, for example via the function algorithm F and / or the evaluation algorithm A. Processing on the tire sensor module 3.k itself can then be omitted or is no longer necessary, it being possible for the respectively relevant measured values MW or information for this to be wirelessly transmitted to the control unit 7 via the individual data messages DT.k. This can be carried out individually on the control device 7 for all tire sensor modules 3.k. These movement states Z.k then determined on the control device 7 can be used as movement behavior BV 1, BV 2 for the method described in the same way as described.The same applies to the determination of the respective running performance L.k, which can likewise be determined on the control unit 7 from the respective data telegrams DT.k with the respective measured values MW, for example via the function algorithm F and / or the evaluation algorithm A. These running performances L.k then determined on the control unit 7 can be used in the same way as described as movement behavior BV 1, BV 2 for the described method.The function check described in steps ST 1 to ST 4 preferably takes place continuously, in particular at the beginning of a trip, wherein smaller measurement intervals can then also be provided, since a blocked brake can occur increasingly, for example, after a long service life.List of reference characters1 Vehicle 2.i i. wheel of the vehicle 1 3.k k. tire sensor module 3 a 1 first selected tire sensor module 3 a 2 second selected tire sensor module 4 sensor unit 4 aacceleration sensor 4 btemperature sensor 4 cpressurizing sensor 5 evaluation unit 6 communication unit 7 control device 10 brake light a acceleration ar radial acceleration arW radial acceleration value arSW.m. radial acceleration storage value aW acceleration value A evaluation algorithm B.i brake of the i. wheel 2.i BV 1 first movement behavior of the first selected tire sensor module 3 a 1 BV 2 second movement behavior of the second selected tire sensor module 3a2 C1 First comparison process C2 Second comparison process dt Time period dtS Storage distance DT.k Data telegram of the k.tire sensor module 3.k F Function algorithm FA Vehicle axle HA Rear axle of the vehicle 1 I Current ID.k Sensor identification of the k.tire sensor module 3.k L.k Running power of the k.tire sensor module 3.k LM Longitudinal central axis of the vehicle 1 M Number of radial acceleration storage values arSW.m MW Measured value N Number of wheels 2.i of the vehicle 1 pW Pressure value R Sampling rate RM Reference module S1 First threshold value S2 Second threshold value S3 Third threshold value Threshold value S4 Sensor signal tm m. time TW Temperature value v2.i Wheel speed of the i Wheel 2.i V1 First comparison value V2 Second comparison value VA Front axle of the vehicle 1 vM Wheel speed median value Z.k Movement state of the k Tire sensor module 3.k i,k,m Index ST1, ST2, ST3, ST4 Steps of the method

Claims

Method for determining a defective brake (B.i) on a wheel (2.i) of a vehicle (1), in particular a trailer, having a plurality of wheels (2.i), wherein a tire sensor module (3.k) is arranged in each case on at least two of the wheels (2.i), wherein the respective tire sensor module (3.k) has a sensor unit (4) for generating and outputting acceleration values (aW), in particular radial acceleration values (arW), and an evaluation unit (5) for processing the acceleration values (aW) and for generating a data telegram (DT.k), wherein the data telegram (DT.k) of the respective tire sensor module (3.k) is transmitted wirelessly to a control unit (7), wherein the method comprises at least the following steps: - defining a first selected tire sensor module (3a1) and a second selected tire sensor module (3a2) from the existing tire sensor modules (3.k) (ST1); determining a first movement behavior (BV1) of the first selected tire sensor module (3a1) and a second movement behavior (BV2) of the second selected tire sensor module (3a2) (ST2), wherein the respective movement behavior (BV1, BV2) is determined as a function of the acceleration values (aW), in particular the radial acceleration values (arW), which are generated and output by the sensor unit (4) of the respective selected tire sensor module (3a1, 3a2); comparing the two determined movement behaviors (BV1, BV2) with one another (ST3); outputting an error signal (SF) if the two determined motion behaviors (BV 1, BV 2) deviate from one another and / or if one of the two determined motion behaviors (BV 1, BV 2) indicates that the wheel (2.i) is braked with the respective selected tire sensor module (3 a 1, 3 a 2) without the presence of a braking request, wherein the error signal (SF) includes that one of the brakes (B.i) is defective.Method according to Claim 1, characterized in that the first selected tyre sensor module (3a1) and the second selected tyre sensor module (3a2) are fixed in such a way that - both selected tyre sensor modules (3a1, 3a2) are located on the same vehicle axis (FA) of the vehicle (1), or - both selected tyre sensor modules (3a1, 3a2) are located on the same side of a longitudinal central axis (LM) of the vehicle (1).Method according to Claim 1 or 2, characterized in that the fixing of the two selected tyre sensor modules (3a1, 3a2) (ST1) and the ascertainment of the respectively assigned movement behaviors (BV1, BV2) (ST2) and the comparison of the two ascertained movement behaviors (BV1, BV2) with one another (ST3) are carried out a plurality of times, a reference module (RM) being specified for this purpose from the present tyre sensor modules (3.k), wherein the defined reference module (RM) is the first selected tire sensor module (3a1) at each performance and a different one of the existing tire sensor modules (3.k) is selected as the second selected tire sensor module (3a2) at each performance, wherein the second selected tire sensor module (3a2) is different from the first selected tire sensor module (3a1).Method according to claim 3, characterized in that said fixed reference modulus (RM) is that - which is located on the fastest rotating wheel (2.i), or - which is located on the wheel (2.i) rotating at a wheel speed (v2.i) closest to a wheel speed median (vM).Method according to one of the preceding claims, characterized in that the determination of the first movement behavior (BV1) of the first selected tyre sensor module (3a1) and of the second movement behavior (BV2) of the second selected tyre sensor module (3a2) comprises the determination of a movement state (Z.k) of the respectively selected tyre sensor module (3a1, 3a2) and / or a running performance (L.k) of the respectively selected tyre sensor module (3a1, 3a2) and / or the radial acceleration value (arW) of the respectively selected tyre sensor module (3a1, 3a2).Method according to Claim 5, characterized in that the state of movement (Z.k) of the respectively selected tyre sensor module (3a1, 3a2) specifies whether or not the respectively selected tyre sensor module (3a1, 3a2) is braked, wherein, in order to ascertain the state of movement (Z.k), it is ascertained whether or not two radial acceleration storage values (arSW.m) which are stored offset with respect to one another at a storage time interval (dtS) and specify the measured radial acceleration value (arW) at the respectively stored time (tm) deviate from one another by more than a first threshold value (S1), wherein a state of movement (Z.k) "braking" is ascertained for the respectively selected tyre sensor module (3a1, 3a2), if the two radial acceleration storage values (arSW.m) deviate from one another by more than the first threshold value (S1).Method according to Claim 6, characterized in that at least three radial acceleration storage values (arSW.m) which are offset with respect to one another in the temporal storage distance (dtS) are stored and it is determined in at least two comparison processes (C1, C2) whether or not two different ones of the at least three stored radial acceleration storage values (arSW.m) deviate from one another by more than the first threshold value (S1).Method according to Claim 6 or 7, characterized in that, in order to store the radial acceleration storage values (arSW.m), at least three radial acceleration values (arW) are recorded for a point in time (tm) within a sampling rate (R) of, for example, 50 ms, and the radial acceleration value (arW) recorded, average in terms of absolute value, is stored as a radial acceleration storage value (arSW.m).Method according to one of Claims 5 to 8, characterized in that the state of movement (Z.k) of the respectively selected tyre sensor module (3a1, 3a2) is determined in an evaluation unit (5) on the respectively selected tyre sensor module (3a1, 3a2) and / or on a control unit (7) which is located away from the respectively selected tyre sensor module (3a1, 3a2).Method according to one of Claims 5 to 9, characterized in that the running performance (L.k) of the respectively selected tyre sensor module (3a1, 3a2) specifies which distance the respectively selected tyre sensor module (3a1, 3a2) has covered within a defined time period (dt), wherein, in order to determine the running performance (L.k), the acceleration values (aW) detected over the defined time period (dt), in particular the radial acceleration values (arW), are integrated twice in time.Method according to one of Claims 5 to 10, characterized in that, in order to output the error signal (SF), it is checked - whether the states of movement (Z.k) of the two selected tyre sensor modules (3a1, 3a2) differ from one another, and / or - whether the running powers (L.k) of the two selected tyre sensor modules (3a1, 3a2) differ from one another by more than a second threshold value (S2), and / or - whether the radial acceleration values (arW) of the two selected tyre sensor modules (3a1, 3a2) differ from one another by more than a third threshold value (S3), wherein the error signal (SF) contains that one of the brakes (B.i) is defective, if the movement states (Z.k) differ from one another without the presence of a braking request and / or the running powers (L.k) differ from one another by more than the second threshold value (S 2), and / or the radial acceleration values (arW) differ from one another by more than a third threshold value (S 3) without the presence of a braking request.Method according to one of the preceding claims, characterized in that, in order to output the fault signal (SF) and / or to determine whether a braking request is present, a supplementary check is made as to whether a current (I) flows through a brake light (10) of the vehicle (1).

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