System and method for monitoring the state of a wheel of a rail vehicle

Abstract

The invention relates to a system for monitoring the state of a wheel (210, 420) of a rail vehicle (10), comprising an acquisition unit (20) that is designed, upon a braking event, to acquire at least one operating parameter for the wheel (210, 420), an evaluation unit (40) that is designed to determine a temperature value for the wheel (210, 420) based on the acquired operating parameter; and a control unit (50) that is designed to generate and to output an output on the basis of the determined temperature value. It furthermore relates to a method for monitoring the state of a wheel (210, 420) of a rail vehicle (10), in which, upon a braking event, at least one operating parameter for the wheel (210, 420) is acquired, a temperature value for the wheel (210, 420) is determined based on the acquired operating parameter and an output is generated and output on the basis of the determined temperature value.

Description

The invention relates to a system and a method for monitoring the state of a wheel ofa rail vehicle, in particular during the operation of the rail vehicle.The wheels of a rail vehicle are subjected to heavy loads during braking procedures.Damage to the wheels, for instance due to strong friction or sudden and massiveheating of the material, should be avoided in the process. This is difficult, inparticular, if the brakes are applied very hard in the case of unfavorable adhesionproperties of the underlying surface. For example, this may occur more frequently inregions that are exposed to a maritime climate, especially when there is highhumidity and, accompanying this, poor adhesion between wheel and rail.Systems which prevent a wheel from locking or slipping during the braking processare known. For example, this avoids the formation of flat spots in the otherwisecircular circumference of the wheel. However, under adverse conditions, cases mayoccur in which there is damage to the wheel or there are disadvantageous changesin the material, for example connected with the formation of martensite in the materialof the wheel. Regions of a metal wheel, especially in the region of the wheel tread,where the structure of the material has changed to martensite, are harder and morebrittle than the surrounding material and are therefore often the starting point for theformation of surface cracks and material loss.The practice of examining unpowered wheels at specific intervals using a nondestructive test and, if necessary, removing damaged material, for instance using alathe, is known.For example, a method for detecting a crack in a wheelset of a rail vehicle is knownfrom EP 3 517 927 A1.Further, DE 198 33 027 C1 describes a method for testing a railway wheel.Further, an apparatus for electromagnetic and ultrasonic wheel diagnostics is knownfrom EP 1 485 704 A1.Moreover, EP 3 206 933 A1 describes a method for diagnosing the state of wheels ofa rail vehicle.It is the object of the present invention to advantageously develop a system and amethod of the type set forth at the outset, in particular to the effect of being able torecognize the formation of critical structures in the material of a wheel and / or aninitiation of cracks.According to the invention, this object is achieved by a system for monitoring thestate of a wheel of a rail vehicle.Accordingly, provision is made for a system for monitoring the state of a wheel of arail vehicle to comprise a recording unit configured to record at least one operatingparameter for the wheel in the event of a braking event; an evaluation unit configuredto determine a temperature value for the wheel on the basis of the recordedoperating parameter; and a control unit which is configured to generate and output anoutput on the basis of the determined temperature value.The invention is based on the basic concept of being able to recognize amicrostructural change in the wheel, still during ongoing operation, by means oftemperature monitoring or thermal monitoring. In principle, the microstructurediagrams are known and can be stored in the system. If the thermal monitoring,optionally also the temperature profile over time (i.e., monitoring of the temperaturecurve), and the corresponding comparison or if monitoring the temperature curvealone without comparison indicates that a problematic microstructural transformationis taking place or may take place, or if there is a risk of this happening, then acorresponding warning message is output.This advantageously provides relevant parameters for the state and the safety of awheel and for its maintenance. Furthermore, maintenance costs can be optimized byusing particularly complex methods in a particularly targeted manner. Furthermore,maintenance work can advantageously be planned and carried out according tonecessity rather than fixed time intervals; this avoids unnecessary maintenance work.Further, the wheel can be treated on the lathe even before cracks can form andspread in the material.The state of the wheel can be monitored during the ongoing operation of the railvehicle in particular. This is an important difference from known methods, in whichthe monitoring takes place at predetermined time intervals, for example, and the railvehicle has to be taken to a workshop, for example. In the invention, the datarecorded during the braking event are evaluated directly and conclusions about thestate of the wheel can be output directly.Thus, in the invention, monitoring or diagnostics can be performed in order torecognize the formation of martensite and / or other indications of crack or fractureformation. Further, a risk of weakening of the material can be recognized. Moreover,the diagnosis can be used to detect the occurrence of hazards after braking in thecase of a disadvantageous adhesion profile.A basic concept of the invention consists of a probability of the formation ofmartensite in the wheel of the rail vehicle being determined. This information is thenused to identify whether the wheel needs to be checked, for instance using a nondestructive testing method, and / or whether the wheel needs to be treated, forexample using a lathe.This exploits the fact that modern rail vehicles often record a multiplicity ofparameters that can be used to determine the energies occurring at the contactbetween wheel and rail. In particular, the system makes use of the fact that thespeeds of the wheels and the speed of the rail vehicle, that is to say a referencespeed, can be recorded. These values are already used, for instance to recognize orprevent wheel slippage. By way of example, a "wheel slide protection" (WSP) systemor a similar system is used. Moreover, values recorded by a brake control unit (BCU)can be used, which values record the brake pressures applied by the brake cylinders,for example.The speeds of the wheels and of the vehicle and the cylinder pressures of thebraking system can be used in a simplified thermal model of the material of the treadof a wheel, in particular in order to determine a temperature distribution in thematerial. Such a model can be implemented by the evaluation unit.In order to simulate the rise and / or fall of the temperature in the material asrealistically as possible, for example in order to calculate the temperature peaks at aposition of the wheel per revolution of the wheel, a more detailed thermal model ofthe material of the tread of a wheel, in particular, is necessary, for example forcarrying out a simulation using a finite element method. Calculations based on sucha model may require significant computing power and the calculations may take along time. This usually precludes the use of such a detailed model in an evaluationunit provided directly in the vehicle. Instead, provision can be made for a table whichcontains temperature values and / or a characteristic curve and which the system thenaccesses to be determined away from the rail vehicle on the basis of the moredetailed thermal model; for example, a table and / or a characteristic curve can bestored in a memory unit of the system.In the system, an average temperature of the wheel therefore can be calculatedusing the simplified thermal model and the locally occurring peak values can bedetermined by lookup in a table, with the values stored in the table having beendetermined with greater computational effort and using more complex models. Inparticular, the peak values determined on the basis of the table are added to theaverage temperature. The time-temperature curves obtained in this way can becompared with material-specific curves that describe the conditions for certainchanges in the metal microstructure.A plurality of conditions relating to the formation of certain critical points or materialchanges can be checked, in particular conditions that incrementally build on oneanother.By way of example, it is possible to initially determine whether the conditions aresufficient for the formation of austenite, for instance a specific temperature increasefor a specific time. Further, it is possible to determine whether cooling hassubsequently taken place sufficiently quickly for the formation of martensite.In particular, a probability of martensite having formed is determined. In particular,the probability can be determined for a specific wheel, a pair of wheels or a differentlydefined wheelset.By way of example, an error code that comprises a particular probability ofmartensite formation in a wheel may be generated, output, and / or stored.In one embodiment of the system, the recording unit is also configured to record abraking parameter, in particular a brake pressure of a brake cylinder and / or a brakingforce.As a result, the energy that has to be dissipated during braking via the contactbetween the wheel and the rail can advantageously be determined in a particularlysimple and direct manner. Further, this operating parameter is usually particularlyeasily accessible via a brake control unit of the rail vehicle.In a further embodiment, the operating parameter recorded for the wheel comprises awheel speed, in particular a rotational speed of the wheel, and / or a speed of the railvehicle.As a result, the kinetic energy to be absorbed during braking can advantageously bedetermined easily using basic parameters of the operation of the rail vehicle. It is alsopossible to check whether the wheel locks when braking or continues to turn. Inparticular, the aforementioned values are easily recordable by means of a controldevice which is usually already present and by means of which, for example, thewheel is prevented from slipping during braking.In a development, the operating parameter recorded for the wheel comprises a timederivative of the wheel speed, in particular of the rotational speed of the wheel,and / or of the speed of the rail vehicle. In particular, a first-order and / or higher-ordertime derivative of the wheel speed, in particular of the rotational speed of the wheel,and / or of the speed of the rail vehicle can be recorded.As a result, the dynamics of the braking event are advantageously recordedparticularly easily, and the arising energies can be easily determined.In an embodiment, the at least one operating parameter for the wheel is able to berecorded by means of an anti-slip system. By way of example, the recording unit iscomprised by the anti-slip system, or the anti-slip system can be used as a recordingunit.As a result, the possibilities of an anti-slip system, which is known per se, is possiblyalready present, and can be integrated for instance into a brake control unit of the railvehicle, are advantageously used for recording the operating parameter. The systemcan be operated particularly efficiently in this way. Further, it can be integratedparticularly easily into existing rail vehicles, since at best no new sensor devicesneed to be provided.That is to say, the rail vehicle has an anti-slip system ("wheel slide protectionsystem", WSP), by means of which the operating parameter for the wheel isrecorded. Furthermore, provision can be made for at least one of the plurality ofoperating parameters recorded for the wheel to be recorded by the anti-slip system.WSP systems are usually already designed in such a way that a wheel speed, avehicle speed, and / or a brake pressure are recorded. It is therefore particularly easyto access these already existing data.In a further embodiment, the temperature value determined for the wheel comprisesan average temperature of a tread of the wheel and / or a temperature distributionalong the tread of the wheel and / or a temperature on a contact surface of the wheel.In particular, whether the wheel continues to turn when braking or whether it locksand slides on the rail is determined in the process.As a result, it is advantageously possible to determine directly whether specifictemperature-related damage to the wheel should be assumed. In particular, phasetransitions or microstructural changes which, for example, promote the developmentof expanding damage regions, such as cracks, may occur when the material isheated and / or cooled.In a development, when determining the temperature value for the wheel, theevaluation unit is configured to determine the average temperature of the tread of thewheel using a simplified thermal model and to determine peak temperatures using alookup table.In this way, an analysis method that is able to be carried out with a manageableamount of computing effort is advantageously combined with more complexsimulation methods.The simplified thermal model makes it possible to determine the averagetemperature of the tread with sufficient accuracy practically in real time on the basisof the recorded operating parameter. The analysis can be carried out, for example,by a computing unit in the rail vehicle itself.The determination of the temperature peaks which may occur during a brakingprocess is usually carried out using very computationally intensive methods andtherefore typically cannot be carried out in real time, at least not with the usual onboard resources of a rail vehicle. Therefore, simulations can be used to determinevalues under different conditions and these values can be stored in a lookup table.The evaluation unit is then configured to determine and apply the value or valuesfrom the lookup table that match the currently recorded operating parameters. In thiscase, the lookup replaces the completely new calculation and allows the results to besufficiently accurate.In particular, the temperature on a contact surface of the wheel with the rail can alsobe determined using the simplified thermal model.In an embodiment, the control unit is configured to generate the output depending onat least one temperature threshold value being reached. The output can also begenerated on the basis of a change in the recorded operating parameter over time.Optionally, the control unit is also configured to determine a probability of occurrenceof a damaged region, in particular a probability of martensite formation, and togenerate the output on the basis of at least one probability threshold value.This advantageously indicates possible problems with the wheel.For example, the probability with which specific conditions, which are defined on thebasis of the recorded operating parameter, can lead to specific damage can beanalyzed. The output can then comprise information regarding the expectedprobabilities of different problems, and countermeasures can be taken in a targetedmanner, for example specific maintenance measures.In a further embodiment, the output comprises a warning message and / or adiagnostic message and / or an error code. In this case, the control unit is optionallyconfigured to store the output in a diagnostic memory.As a result, the output can advantageously be read out at a later stage, for exampleby an authorized user.The output is also able to be output directly. By way of example, an optically oracoustically perceptible signal can be generated depending on the output. By way ofexample, a first signal may be output if the output comprises a specific error codeand a second signal may be output if the output comprises a further error code.The signal can be used, for example, to output a request to carry out a specificmaintenance measure.At least one operating parameter for the wheel is recorded during a braking event inthe method for monitoring the state of a wheel of a rail vehicle. A temperature valuefor the wheel is determined on the basis of the recorded operating parameter, and anoutput is generated and output on the basis of the determined temperature value.The method is designed in particular to operate the system. It therefore has the sameadvantages as the system.Fig. 1A shows an exemplary embodiment of the system.Fig. 1B shows an exemplary embodiment of the method.Figs. 2A and 2B show schematic illustrations of a wheel under different brakingconditions.Fig. 3 shows a time-temperature diagram.Fig. 4 shows a cross-sectional illustration of a wheel and rail.Fig. 5 shows characteristics relating to the formation of austenite.Fig. 6 shows characteristics relating to the formation of martensite.Figure 1A shows an exemplary embodiment of a system 100 according to theinvention.In the exemplary embodiment shown, the system 100 is integrated into a rail vehicleor is a subsystem of a rail vehicle 10.The rail vehicle 10 thus comprises the system 100.The system comprises a recording unit 20.The recording unit 20 is a constituent part of an anti-slip apparatus 30, which isformed in the manner of a WSP (wheel slide protection) system in a manner knownper se.The system 100 further comprises an evaluation unit 40.The system 100 further comprises a control unit 50.The recording unit 20 is configured to record at least one operating parameter for thewheel during a braking event.The recording unit 20 can further be configured to record the presence of the brakingevent itself, for instance by virtue of recording an activity of a brake cylinder.The evaluation unit 40 is configured to determine a temperature value for a wheel ofthe rail vehicle 10 on the basis of the recorded operating parameter.The control unit 50 is configured to generate and output an output on the basis of thedetermined temperature value.In principle, the function of the system 100 can be described as follows:Data used by the evaluation unit 40 to monitor the temperature are recorded bymeans of the recording unit 20. In particular, a temperature or a development of thetemperature over time, which occurs at a wheel during a braking event, isdetermined. This thermal monitoring is used to recognize during ongoing operation ofthe rail vehicle 10 whether the conditions for a specific microstructural change in thewheel are present. In particular, microstructure diagrams known per se are used tothis end.Should it be determined that the conditions for a problematic microstructuraltransformation are present, then an appropriate output can be generated.The system 100 enables the following advantages:Critical states of the wheel can be recognized during the ongoing operation of the railvehicle 10, and operational safety can be improved.Such critical states can be indicated, in particular in direct temporal connection withtheir occurrence and / or at a later point in time.Furthermore, maintenance or repair measures can be initiated, for instance toremedy damage to the wheel which has occurred, or which is at risk of occurring,during the braking event.In addition, maintenance or preventative measures can be initiated in order toprevent damage before it occurs.Furthermore, maintenance work can be carried out as required in order to avoidunnecessary measures.Figure 1B shows an exemplary embodiment of the method which is explained below.The starting point here is, in particular, the exemplary embodiment of the systemexplained above with reference to figure 1A, which is specified in more detail by thefollowing explanations.In particular, a diagnostic method that is able to be executed on a computer device isshown here.In a step S10, at least one operating parameter for the wheel is recorded during abraking event.In the process, a force is determined at a contact surface between the wheel and therail.Data about the speed of the wheel is recorded.Furthermore, a braking force of braking equipment of the rail vehicle is recorded.In particular, the exemplary embodiment provides for a control unit of an anti-slipapparatus (WSP) to process the recorded operating parameters and data.An energy absorbed by the wheel via the contact surface is determined.The variables that occur in this context may include, for instance, a braking force P(t)and a wheel speed Vwheel(t), which each depend on the time t and in particular arerecorded as a function of the time t.A simplified thermal model of the wheel is used in a step S20. A check is carried outas to whether the wheel rotates during braking or whether it locks and slides over therail (wheel lock up). In particular, the values recorded or determined in step S10 areused in the model.An average temperature Tmodel(t) of the wheel tread is determined as a function oftime t using the simplified mode if the wheel turns during braking.The temperature Tmodel(t) for the contact region between the wheel tread and the railis determined as a function of time t using the simplified model if the wheel is lockedduring braking.The temperature Tmodel(t) determined using the simplified model is modified in a stepS30.In the process, use is made of parameters determined in advance by simulationusing an FEM method. For instance, these parameters are provided by a storageunit.In the process, a modified Tmodified(t) is determined as a function of time t.In a step S40, the temperature Tmodified(t) determined thus is compared with apredetermined diagram which comprises a characteristic curve which characterizesthe prerequisites for austenitization of the material of the wheel or its tread.An exemplary diagram 500 which can be used in step S40 is shown in figure 5.In particular, a check as to whether austenitization has taken place is carried out inthe process. Should this not be the case, then it is determined in a step S70 thatthere is no risk of martensite formation.However, should the prerequisites for austenitization be determined as being presentin step S40, then the determined temperature Tmodified(t) is compared with apredetermined further diagram in a step S50, the said further diagram comprising acharacteristic curve which characterizes the prerequisites for the formation ofmartensite for the material of the wheel or its tread.An exemplary diagram 600 which can be used in step S50 is shown in figure 6.In particular, a check is carried out here as to whether the prerequisites for theformation of martensite are present, especially in the case of a sufficiently quickcooling of the material. Should this not be the case, then it is in turn determined instep S70 that there is no risk of martensite formation.However, should the prerequisites for the formation of martensite, for instancesufficiently rapid cooling, be determined as being present in step S50, then a risk ofmartensite formation is determined in a step S60.In the method, an output is subsequently generated and output. By way of example,the latter comprises an error code which indicates whether or not there was a risk ofmartensite formation.In a further exemplary embodiment of the method, a probability of martensite havingformed is also determined in step S60. The output generated may comprise thisprobability.In a further exemplary embodiment of the method, a probability of martensite havingformed can be alternatively or additionally determined in a manner analogous theretoin step S70. The output generated may comprise this probability.In particular, a threshold value may be specified and the determined value of theprobability of martensite having formed can be compared with the threshold value.The output can then be generated on the basis of this comparison. For example, awarning message can be generated and output if the threshold value has beenexceeded.Integrated sensors, in particular, are provided in the case of an anti-slip apparatus30, by means of which the wheel should be prevented from slipping on the rail.For instance, the recording unit 20 may comprise sensors of the MGS3 type.The values and parameters recorded by the recording unit 20 make it possible todetermine the current heat on the wheel surface in real time or almost in real time.Even with current anti-slip equipment (WSP, "wheel slide protection"), it is not alwayspossible to prevent the wheels from being overloaded, especially due to the input ofenergy or heat during a braking process. However, it is possible to detect that slidingoccurs on the basis of the data recorded by the anti-slip equipment, and / or theduration of a sliding process of a wheel or a wheelset can be determined. A suitablethermal model of the wheel and known material properties of the wheel can be usedto determine whether and how transitions between different material states occur, forinstance between different microstructures or phases of a metal material.Typically, relatively large regions of particularly hardened material are prone tocracks developing there or material flaking off, for example. To prevent this, provisioncan be made for example for a diagnostic memory to be read out at regular intervals,for example monthly or on specific occasions, for instance during regularmaintenance of the wheel or wheelset. The data stored in the diagnostic memory canbe used to determine whether the wheel should be treated using a lathe. Further, onthe basis of the data stored in the diagnostic memory, it is possible to determine thatno treatment using a lathe is required. Further, on the basis of the data stored in thediagnostic memory, it is possible to determine that a non-destructive diagnosis of thewheel or wheelset should be carried out, for instance by means of ultrasound, inorder to detect cracks and / or local changes in the hardness of the material.Figures 2 to 6 show further exemplary details of the system and the method, whichare explained below.A model by means of which the formation of a potentially hardened material texturecan be determined is described below in exemplary fashion. In particular, martensiteformation can be determined and / or a probability of martensite formation havingoccurred during a braking event is determined.The wheel speed, the vehicle speed, and the brake pressure applied by a brakecylinder are recorded by means of the sensors comprised in the recording unit.A simplified thermal model which is provided by means of the evaluation unit, forexample, is accessed.The simplified thermal model can be provided, for instance, on a plug-in card and / ora computing unit of a central control unit.By way of example, the energy absorbed by the wheel is determined first, forinstance according to the following model, which is explained with reference to figure2A and figure 2B, and also figure 4:To calculate the absorbed energy for a wheelset, for example with wheels i = 1, 2, 3,4 in the case of a four-wheel wheelset, the sliding speed is multiplied by the actualbraking force at the contact between the wheel 210, 420 and the rail 440.A contact force is determined on the basis of the pressure of the brake cylinders.Further, the angular acceleration of the wheelset is additionally taken into account,where J denotes a moment of inertia of the wheels:Pi = (vi-vref) . {Fi(Pci)+J.v1 / R2}Here, Fi denotes the braking force acting on an individual wheel 210, 420 at thecontact surface between wheel 210, 420 and rail 440. This is a direct function of theactual brake pressure pc. This function F(pc) can be determined for instance usingthe general calculations of a braking process, for instance as described in UIC 544-1.There are WSP systems that determine this force directly, with the actualacceleration of the wheelset being recorded so that the latter can be used directly.The surface temperature can subsequently be determined, it being possible, inparticular, to take into account that a permanent heat partition of approximately 50%may quickly arise in this case, that is to say approximately 50% of the heat generatedis absorbed by the wheel. This is described, for example, in P.T. Zwierczyk, "Thermalstress analysis of a railway wheel-rail rolling-sliding contact", Budapest 2015. Adifferent partition can be assumed for further models, for instance depending oncertain environmental parameters.A simplified thermal model of the wheel 210, 420 can be determined.Two states, in particular, are distinguished in the simplified thermal model:a) If the wheel 210, 420 is not turning, that is to say if it is locked, then theassumption is made that the energy is absorbed via the contact point orcontact region 230 between the surface of the wheel and the rail. This case isshown in figure 2A in particular.b) If the wheel 210, 420 is turning, then the assumption is made that the energyis absorbed uniformly across the tread 230 of the wheel 210, 420 at thecontact points between the surface of the wheel 210, 420 and the rail 440.This case is shown in figure 2B in particular.In a modification of the case explained under b), the further assumption is made thatthe heat is absorbed at a point on the contact surface between wheel 210, 420 andrail 440 and then released again during further rotation of the wheel 210, 420 until thepoint comes into contact with the rail 440 again.Figure 3 shows an example of a temperature curve determined according to thismodified model: At the peaks in temperature, the observed point on the tread of thewheel 210, 420 touches the rail 440 and absorbs heat, and then contact is brokenand the point cools again. The average temperature of the wheel is shown as adashed line; the temperature with additional peaks is shown as a solid line.In figure 2A, the model is shown for the case where the wheel is turning, while figure2B shows the case where the wheel 210, 420 is locked ("lock up"), with the wheel210, 420 sliding over the rail 440.In a model for the case shown in figure 2A, Tcircle denotes a temperature, in particularan average temperature, of the tread.In this example, the mass of the tread 220 is calculated in advance. In this case, usecan be made of the Kalker method, for example, in which the radius of the wheel 210and the width of the surface 220 are determined specifically for the vehicle. Further,the depth of the tread can be calculated on the basis of simulations.The result is roughly the following representation:Equation :Further, in a model for the case shown in figure 2B, it is possible to determine atemperature Tspot of the contact point 230. By way of example, the region of thecontact point 230 can be assumed to have an area of approximately 1 cm2 and adepth of 2 mm.The area can be calculated specifically for the vehicle. The Kalker method, forexample, can be used in the process. Further, the depth of the tread can becalculated on the basis of simulations.The result is roughly the following representation:Equation :or more simply:Equation :Figure 3 shows an example of how the temperature at a point in the region of thetread of the wheel 210, 420 changes during braking if the wheel 210, 420 turnsduring a braking process. The increase in the average temperature in the region ofthe tread is shown as a dashed line 310. Additionally, the temperature peaks shownas a solid line 320 should be considered, with the peaks in each case occurring asthe point contacts the rail and absorbs energy, and the energy subsequently beingreleased again and the temperature dropping accordingly (source: P.T. Zwierczyk,"Thermal stress analysis of a railway wheel-rail rolling-sliding contact", Budapest2015).The average temperature along the circumference of the tread 230 changes slowly incomparison with the temperature peaks. The average temperature is determinedusing the simplified model explained above with reference to figure 2A. In thisexample, at least one parameter is determined by fitting using a finite elementmethod (FEM), in particular the dashed line 310 in figure 3.Exemplary values for a model used are given in tabular form below. In particular,physical constants, vehicle-specific constants, and values determined by fitting areshown in a validation using an FEM method and a simulation of the temperaturedistribution. In particular, the following are listed: The diameter of the wheel(D_wheel), the diameter of the contact region (d_spot) between the wheel and therail, the thickness of the contact region in the depth of the material of the wheel (h),the area of the contact region (Aspot) or the annular tread (Aring) of the wheel, thevolume of the contact region (Vspot) or annular tread (Vring) of the wheel, the density(ro) of the material, the mass of the contact region (mspot) or annular tread (mring) ofthe wheel, the heat transfer of the material (steel heat transfer, lam), the heat transferof the tread (lambda ring) or the contact region (lambda spot), and the specific heat(c) of the material. Table :The parameters shown are further illustrated in figure 4 in an exemplary cross sectionof a wheel on a rail.A temperature versus time curve can now be used, for instance on the basis of thedata shown in figure 3.In particular, the temperature changes during the braking event, that is to say inparticular temperature rises and temperature drops, are taken into account here.In the process, a check is carried out as to whether, for instance, a certaintemperature value has been reached or exceeded. For example, when a certaintemperature is reached, a pearlite texture of the wheel material may be changed toan austenite structure. Such a point is marked in figure 5 as point "AC3", for example,with the diagram 500 showing characteristic curves of an austenitization of a steelmaterial of the wheel in exemplary fashion.A further check is carried out as to whether, for instance, the temperature drops soquickly after reaching the value sufficient for austenitization that martensite is formed.A corresponding characteristic curve is shown in figure 6, for example. In particular,the graph represents a time-temperature transformation diagram (continuous coolingtransformation, CCT).In the illustrated case, the following material composition is assumed: 0.33% C,1.12% Mn, 0.30% Si, 0.027% S, 0.018% P, 0.24% Ni, 0.11% Cr, 0.04% Mo, 0.19%Cu, 0.010% Al, grain size 8-9, austenitized at 850°C (1562°F) for 1 h.Figure 6 shows a CCT diagram 600 for an exemplary steel as the material of thewheel. This diagram relates to the texture of the material as a function of cooling rate.LIST OF REFERENCE SIGNS10 Rail vehicle20 Recording unit30 Anti-slip apparatus; WP system40 Evaluation unit50 Control unit100 System210 Wheel220 Tread230 Contact region310 Dashed line320 Solid line420 Wheel (cross section)440 Rail (cross section)500 Diagram600 DiagramS10 StepS20 StepS30 StepS40 StepS50 StepS60 StepS70 Step.

Claims

1. A system for monitoring the state of a wheel (210, 420) of a rail vehicle (10), comprising a recording unit (20) configured to record at least one operating parameter for the wheel (210, 420) in the event of a braking event; an evaluation unit (40) configured to determine a temperature value for the wheel (210, 420) on the basis of the recorded operating parameter; and a control unit (50) which is configured to generate and output an output on the basis of the determined temperature value.

2. The system as claimed in claim 1, characterized in that the recording unit (20) is also configured to record a braking parameter, in particular a brake pressure of a brake cylinder and / or a braking force.

3. The system as claimed in either of the preceding claims, characterized in that the operating parameter recorded for the wheel (210, 420) comprises a wheel speed, in particular a rotational speed of the wheel (210, 420), and / or a speed of the rail vehicle (10).

4. The system as claimed in any one of the preceding claims, characterized in that the operating parameter recorded for the wheel (210, 420) comprises a time derivative of the wheel speed, in particular of the rotational speed of the wheel (210, 420), and / or of the speed of the rail vehicle (10).

5. The system as claimed in any one of the preceding claims, characterized in that the at least one operating parameter for the wheel (210, 420) is able to be recorded by means of an anti-slip system (30).

6. The system as claimed in any one of the preceding claims, characterized in that the temperature value determined for the wheel (210, 420) comprises an average temperature of a tread of the wheel (210, 420) and / or a temperature distribution along the tread of the wheel (210, 420) and / or a temperature on a contact surface of the wheel (210, 420).

7. The system as claimed in claim 6, characterized in that when determining the temperature value for the wheel (210, 420), the evaluation unit (40) is configured to determine the average temperature of the tread (220) of the wheel (210, 420) using a simplified thermal model and to determine peak temperatures using a lookup table.

8. The system as claimed in any one of the preceding claims, characterized in that the control unit (50) is configured to generate the output depending on at least one temperature threshold value being reached; and the control unit (50) is optionally configured to determine a probability of occurrence of a damaged region, in particular a probability of martensite formation, and to generate the output on the basis of at least one probability threshold value.

9. The system as claimed in any one of the preceding claims, characterized in that the output comprises a warning message and / or a diagnostic message and / or an error code; wherein the control unit (50) is optionally configured to store the output in a diagnostic memory.

10. A method for monitoring the state of a wheel (210, 420) of a rail vehicle (10), wherein at least one operating parameter for the wheel (210, 420) is recorded during a braking event; a temperature value for the wheel (210, 420) is determined on the basis of the recorded operating parameter; and an output is generated and output on the basis of the determined temperature value.