Detecting train wheel defects with instantaneous angular speed signal

Abstract

A method for detecting defects of a wheel (20) of a railroad vehicle comprises: determining an instantaneous angular speed signal (30) of a shaft (14) connected to the wheel (20), wherein the instantaneous angular speed signal (30) is determined from measurements of a speed encoder (22) connected to the shaft (14) and wherein the instantaneous angular speed signal is indicative of a speed of the shaft (14) at a rotation angle of the shaft (14); determining at least one amplitude (32) of a frequency component (34) of the instantaneous angular speed signal (30) seen as a function of the rotation angle; and detecting a defect based on a magnitude of the at least one amplitude (32).

Description

FIELD OF THE INVENTION

[0001] The invention relates to a method, a controller, a computer program and a computer-readable medium for detecting defects of a wheel of a railroad vehicle. The invention also relates to a train system.BACKGROUND OF THE INVENTION

[0002] Train wheels are subject to degradation, either in the form of flat spots or a "polygonization" of them. Flat spots can occur in case of faulty brakes which block the wheel, leading to larger removal of metallic material. Slippery rails, for example due to leaves, can lead to an abnormal stick-slip of the wheel, which also can cause flat spots. Polygonization of the wheel occurs under normal operation, wherein the wheel slowly changes from a circle to a polygon. Dedicated and expensive measurement equipment, such as a laser scanning device, is needed in order to detect these defects.DESCRIPTION OF THE INVENTION

[0003] It is an objective of the present invention to monitor train wheel degradations, in particular in a continuous way and in particular using available sensors. Further objectives are to reduce maintenance cost and to increase the lifetime of train wheels.

[0004] These objectives are achieved by the subject-matter of the independent claims. Further exemplary embodiments are evident from the dependent claims and the following description.

[0005] A first aspect of the invention relates to a method for detecting defects of a wheel of a railroad vehicle. The railroad vehicle may be part of a train. The wheel may be adapted for rolling on a railway. The defects may relate to deviations of the wheel and in particular its running surface from a circle. Such defects may be flat spots and polygonization.

[0006] The method may be performed automatically by a controller of the railroad vehicle, such as a traction control system.

[0007] According to an embodiment, the method comprises: determining an instantaneous angular speed signal of a shaft connected to the wheel, wherein the instantaneous angular speed signal is determined from measurements of a speed encoder connected to the shaft and wherein the instantaneous angular speed signal is indicative of a speed of the shaft at a rotation angle of the shaft.

[0008] The shaft may be a part of the drive system of the train. The train engine may drive the shaft, which drives the wheel. There may be a gear or transmission between the train engine and the shaft and / or between the shaft and the wheel. The shaft also may be directly connected to the wheel.

[0009] The instantaneous angular speed signal is determined from measurements of a speed encoder connected to the shaft. Such a speed encoder may provide a pulse, whenever the shaft turns by a specific angle, in general substantially smaller than 360° and / or a fraction of 360°. By knowing the number of pulses per complete revolution of the shaft and the time interval between two pulses, the angular speed as a function of the angle of the shaft , i.e., the instantaneous angular speed signal, may be calculated.

[0010] The instantaneous angular speed signal is indicative of a speed of the shaft at a rotation angle of the shaft. The rotation angle may be a value constantly increasing with every revolution of the shaft. The rotation angle need not be provided modulo 360°. It has to be noted that the rotation angle is in general not linear related to time, since the shaft may turn slower and faster depending on the speed of the railway vehicle.

[0011] The instantaneous angular speed signal may be seen as a function of the rotation angle of the shaft and in particular can be calculated directly from the measurements of the speed encoder. It is not necessary to calculate a time dependent angular speed signal and to transform it into a rotation angle dependent angular speed signal.

[0012] The transmission ratio between the shaft and the wheel may be 1, when the wheel is directly connected to the shaft, or may be different from 1, for example, when a transmission is arranged between the shaft and the wheel. However, the transmission ratio may be known. Therefore, the instantaneous angular speed signal also may be seen as a function of the rotation angle of the wheel.

[0013] According to an embodiment, the method further comprises: determining at least one amplitude of a frequency component of the instantaneous angular speed signal seen as a function of the rotation angle. As every function depending on a continuous parameter, the instantaneous angular speed signal can be Fourier transformed, in this case not with respect to time but with respect to the rotation angle. As the pulses are distributed uniformly, that is in equidistant angles, around the rotation axis, the angular speed as a function of angle may also be a uniformly sampled signal. This may be of an advantage, when doing a Fourier transform (or any other operation) on it. However, the frequency component need not be determined by Fourier transformation, but for example also may be determined by applying a filter. The frequency component (which also may be called frequency content) may comprise one or more or a band of frequencies of sinusoidal components of the frequency spectrum of the instantaneous angular speed signal. The amplitude of the frequency component may be the amplitude, the sum, the root-mean-square and / or an average of the amplitudes of these sinusoidal components.

[0014] The frequency component may be chosen, such that a wheel defect can be detected. For example, a frequency of the frequency component (such as an average frequency, a peak frequency, a median frequency, a middle frequency, etc.) may be chosen to be the base rotation frequency of the wheel. The base rotation frequency of the wheel may be one, when there is no transmission between the speed encoder and the wheel, or may be the transmission ratio.

[0015] According to an embodiment, the method further comprises: detecting a defect based on a magnitude of the at least one amplitude. A perfect circular wheel would result in an instantaneous angular speed signal, having zero amplitude for all frequency components different from zero. When there is an amplitude different from zero, which can be discriminated from noise for example by a threshold, there is a problem, which accelerates and decelerates the shaft periodically in linear dependence of the rotation angle of the shaft and therefore indirectly of the wheel. From this, it may be deduced that there is a defect in the mechanical system comprising the wheel, which is mainly the wheel. However, also defects of a transmission or gears may be detected in this way.

[0016] It may be that the defect is detected by comparing the at least one amplitude with one or more thresholds. When one or more of the amplitudes are higher than one threshold or an individual threshold for each frequency component associated with the amplitude, a defect may be detected.

[0017] In general, a defect, may be detected by inputting the at least one amplitude into a target function, which outputs one or more statistical values from which it can be determined, whether there is a defect or not. For example, an output of the function may be compared with a threshold to determine, whether there is a defect or not. In one case, a defect is detected, when the at least one amplitude is higher than a threshold. The threshold may be constant, it may be adapted based on a measured noise background, and / or it may be adapted to an average angular speed of the system.With the method, wheel imperfections may be detected using only available sensors in the railroad vehicle. Such a sensor is the speed encoder, which may be mounted on a shaft driven by the engine of the railroad vehicle. The geometric deformation of the wheel leads to a modulation of the instantaneous angular speed signal, which, when analysed in the correct domain, here the angular domain, leads to typical peaks in the angular spectrum, allowing for a continuous monitoring.

[0018] Analysing the instantaneous angular speed as a function of the rotation angle instead of the time is a very sensitive way to detect issues on the wheel. A speed encoder is able to measure the instantaneous angular speed with high precision and is therefore an adequate sensing system for this effect. For example, using the pulses produced by a cogwheel together with the time interval between the passing of two pulses gives both the angle and the speed from pulse to pulse, which is a good basis for the analysis.

[0019] The imperfection of the wheel leads to a modulation of the instantaneous angular speed, where the modulation is given by the geometry, as it has to repeat after each rotation. This leads to extremely narrow and therefore sensitive peaks in the spectrum of the instantaneous angular speed when analysed not in time domain but in angular domain. This allows for an analysis in the setting of a railway vehicle, where speed is in general not expected to be constant even for a rather short time.

[0020] According to an embodiment, a plurality of amplitudes of frequency components of the instantaneous angular speed signal seen as a function of the rotation angle are determined. The frequency components may be different bands of the frequency spectrum.

[0021] According to an embodiment, each of the frequency components corresponds to a multiple of a predefined base frequency. The predefined base frequency may be chosen, to be at a position, where wheel defects can be detected, for example may be a base rotation frequency of the wheel. For example, when a transmission is present between the shaft and the wheel, the base frequency may correspond to the angular speed 1 times the transmission ratio. A defect on the wheel usually will generate a frequency component at the base frequency and multiples thereof.

[0022] According to an embodiment, a defect of the wheel is detected, when a function of the amplitudes, which are determined, is higher than a threshold. The function may be a sum, an average, a root-mean square, etc. The function also may be a classifier, which outputs a statistical value about a probability of a defect. The function may depend in addition to the amplitudes on other properties, like the background noise, the speed etc. In particular, when their frequencies have been chosen to the same type of defect, this may enhance detection quality.

[0023] According to an embodiment, the predefined base frequency is related to a transmission ratio of a transmission between the shaft and the wheel. In general, the speed encoder may be mounted on a wheel shaft, on an intermediate shaft or on a motor shaft. When a transmission is present between the shaft of the speed encoder and the wheel, the transmission ratio of the transmission shifts the specific frequencies of a wheel defect, which may be integer multiples of a base rotation frequency to a non-integer base. A transmission ratio different from 1 may additionally help to distinguish defect signals from speed encoder imperfections.

[0024] According to an embodiment, the function of the amplitude additionally depends on a background noise level and / or a speed of the railroad vehicle. The background noise level may be determined with a microphone positioned in the railroad vehicle. The speed of the railroad vehicle may be provided by a superordinated controller.

[0025] According to an embodiment, the at least one amplitude of the frequency component is determined with a band-pass filter applied to the instantaneous angular speed signal. The frequency component may be a frequency band, which is filtered out.

[0026] According to an embodiment, a plurality of amplitudes of frequency components is determined with a comb filter applied to the instantaneous angular speed signal. The comb filter may be composed of a plurality of band-pass filters.

[0027] According to an embodiment, the method further comprises: determining a frequency spectrum of the instantaneous angular speed signal seen as a function of the rotation angle. The frequency spectrum may be a function with amplitudes of frequencies of the instantaneous angular speed signal. For example, the frequency spectrum may be determined by Fourier transforming the instantaneous angular speed signal seen as a function of the rotation angle. The at least one amplitude of a frequency component may be determined from the frequency spectrum.

[0028] According to an embodiment, the method further comprises: identifying peaks in the frequency spectrum. It is further possible that frequencies or frequency components are determined, where the amplitude and / or peaks are higher than a threshold.

[0029] According to an embodiment, the method further comprises: detecting a defect of the wheel, when peaks related to an angular speed of the wheel are present. When a peak is detected, which is at a frequency, which according to a transmission ratio is the base angular speed of the wheel, this indicates a wheel defect. As further example, when the peaks have a specific pattern, such as higher harmonics of the base frequency, these peaks may be related to the base frequency and to a wheel defect.

[0030] A peak may be seen as frequency component. It is possible that the one or more frequency components, which are used for determining the amplitudes for defect detection, are determined from the instantaneous angular speed signal. As described above, however, the frequency component may be preset and may be filtered out from the instantaneous angular speed signal with a preset filter.

[0031] According to an embodiment, a defect is detected, when a plurality of peaks with frequencies, which are a multiple of a base frequency, i.e., a fundamental frequency and higher order harmonics, is identified. A specific pattern are peaks with frequencies that are a multiple of a base frequency or fundamental frequency. These peaks indicate a defect related to a mechanical component of the drive system, rotating with an angular speed of the fundamental frequency possibly multiplied with a transmission ratio of a transmission between the speed encoder and the mechanical component.

[0032] According to an embodiment, the method further comprises: determining the instantaneous angular speed signal from a pulse signal provided by the speed encoder. The speed encoder may comprise an encoder wheel with a plurality of periodic elements generating the pulses. The elements may be teeth or windows, which may be detected by occluding light or changing a magnetic field. The number of elements around the encoder wheel and / or the number of pulses per complete revolution of the encoder wheel are known. The speed encoder may provide both the angle information as pulses of the encoder wheel and the speed through the time between pulses. These data may be used to calculate the speed as a function of the rotation angle (and not of time).

[0033] A further aspect of the invention relates to a controller for carrying out the method such as described herein. For example, the controller may be or may be part of a traction control system of the railroad vehicle.

[0034] A further aspect of the invention relates to a computer program for detecting defects of a wheel of a railroad vehicle, the computer program comprising instructions which, when being executed by a processor, carry out the method such as described herein. A further aspect of the invention relates to a computer-readable medium, in which such a computer program is stored. The controller may comprise a processor and a memory, in which the computer program is stored.

[0035] In general, a computer-readable medium may be a hard disk, an USB (Universal Serial Bus) storage device, a RAM (Random Access Memory), a ROM (Read Only Memory), an EPROM (Erasable Programmable Read Only Memory) or a FLASH memory. A computer-readable medium may also be a data communication network, e.g., the Internet, which allows downloading a program code. In general, the computer-readable medium may be a non-transitory or transitory medium.

[0036] A further aspect of the invention relates to a train system. The train system comprises a shaft connected to a wheel of the railroad vehicle, a speed encoder connected to the shaft, and a controller for detecting defects of the wheel.

[0037] It has to be understood that some features of the present invention are described with respect to one of the aspects only for conciseness reasons and to avoid unnecessary repetitions, but that these features may be easily transferred to one or more of the other aspects by the person skilled in the art.

[0038] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The subject-matter of the invention will be explained in more detail in the following text with reference to exemplary embodiments which are illustrated in the attached drawings. Fig. 1 shows a train system according to an embodiment of the invention. Fig. 2 shows diagrams with spectra of angular speed. Fig. 3 shows a flow diagram for a method for detecting wheel defects according to an embodiment of the invention.

[0040] The reference symbols used in the drawings, and their meanings, are listed in summary form in the list of reference symbols. In principle, identical parts are provided with the same reference symbols in the figures.DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0041] Fig. 1 shows a train system 10, which may be part of a railway vehicle. The train system 10 comprises an engine or drive 12, a shaft 14, which interconnects the engine 12 with a transmission 16. The transmission 16 is connected via a further shaft 18 with one or more wheels 20 of the railway vehicle.

[0042] A speed encoder 22 is attached to the shaft 14, which comprises an encoder wheel 24 and a sensor 26, which for example may generate a signal with a pulse, whenever an element of the encoder wheel 24 of speed encoder 22 passes a detector, such as a light sensor, which senses light from a light source occluded by the element, or a magnetic or eddy-current sensor, which senses the presence or absence of a teeth. The measurement signal of the speed encoder 22 produced by the sensor 26 is transmitted to a controller 28, which may be a part of a traction control system for the train system 10. In general, the speed encoder 22 also may be attached to the shaft 18.

[0043] The speed encoder 22 provides the instantaneous angular speed of the shaft 14 with high angular resolution and time accuracy, both as a function of the rotation angle and as a function of time. The instantaneous rotation angle θ of the shaft 14 may be determined from the encoder position count of the speed encoder 22, for example by multiplying with a known angle between two consecutive elements in the encoder wheel. The instantaneous angular speed is dθ / dt.

[0044] Knowing the instantaneous angular speed dθ / dt as a function of the rotation angle allows to analyse the power spectra in the angular frame and to accurately identify angular speed fluctuations. These angular speed fluctuations may be of geometric origin, for example of changes in shape of the wheel 20. If one disregards the slip between the wheel 20 and the rails, translation speed v(t), and instantaneous angular speed of the wheel, dθ / dt with respect to time, are related by the constraint dθ / dt = v(t) / R (θ(t)), where R(θ(t)) is the radius of the wheel 20 measured from its rotation centre to the instantaneous contact point with the rail. A perfect wheel 20 (without any deformation) has a constant radius, R. Variations in dθ / dt can be due to the variable translational speed v(t), and can also originate from imperfections of the train wheel, with R(θ(t)) being a function of the rotation angle. Imperfections of the encoder wheel 24 (such as off-centring, or different teeth shapes) may also add geometric modulations to the estimated instantaneous angular speed, because one derives the rotation of the shaft 14 from the measurement of the encoder wheel 24 attached to it.

[0045] Instantaneous angular speed fluctuations due to geometric distortions are periodic as a function of the rotation angle, but are not perfectly periodic in time, because the instantaneous angular speed with respect to time is never truly constant. If the translation speed of the railway vehicle changes, the periodicity of the geometric features is lost with respect to time, and their contribution may be misinterpreted as noise in a standard time-series analysis. Thus, in order to make efficient use of the information regarding geometric distortions, it is beneficial to work in the rotation frame, processing the instantaneous angular speed dθ / dt as a function of the rotation angle.

[0046] The speed encoder 22 provides the position count x i at time point t i . The instantaneous angular speed dθ / dt at time point t i is v i =1 / ( α (t i+1 -t i ) ), wherein α is the angular resolution of the speed encoder 22, for example the angular distance between two elements of the encoder wheel 24. This implies that velocity changes are only registered every time the position count changes. For this reason, the speed encoder 22 provides a one-to-one relationship between instantaneous angular speed v; and position count x i .

[0047] Fig. 2 shows spectra of an instantaneous angular speed in the time domain, where frequencies are in events per second [Hz] (upper diagram), and in the rotation count frame, where frequencies k are in events per revolution (lower diagram). The instantaneous angular speed was determined from measurements of a speed encoder 22, such as shown in Fig. 1. As can be seen in Fig. 2, geometrical features appear smeared out in the time frame spectrum.

[0048] The lower diagram shows that deformations in the wheels 20 cause perfectly periodic modulations of the instantaneous angular speed in the rotation frame. The modulations appear at k-values that are multiples of a transmission ratio of the transmission 16. In the example shown in Fig.2, the transmission ratio is g = 0.221 and the corresponding sharp lines / narrow peaks are clearly visible at k = 0.221, 0.442, 0.663, 0.884, .... Since the transmission ratio is generally non-integer, components from wheel deformation do not overlap with the components from the imperfections of the encoder wheel (which are also geometric and appear at integer repetency values, here at k =1). If the speed encoder 22 is on the wheel shaft 18, wheel deformations and encoder imperfections will both appear at integer k-values.

[0049] Fig. 3 shows a flow diagram illustrating a method for detecting defects of the wheel 20, which may be performed automatically by the controller 28. In particular, a computer program may run in the controller 28 performing the method.

[0050] In step S10, the controller 28 determines an instantaneous angular speed signal 30 of the shaft 14 as a function of the rotation angle. The instantaneous angular speed signal 30 is indicative of a speed of the shaft 14 at a rotation angle of the shaft 14. The instantaneous angular speed signal 30 as a function of the rotation angle is determined from measurements of the speed encoder 22. This may be done like described above.

[0051] In step S12, one or more amplitudes 32 of one or more frequency components 34 of the instantaneous angular speed signal 30 as a function of the rotation angle are determined. Fig. 2 shows such amplitudes 32 and frequency components 34. The frequency components 34 may be small bands around predefined frequencies, which relate to geometric features of the wheel 20.

[0052] For example, each of the frequency components 34 corresponds to a multiple of a predefined base frequency k. The predefined base frequency k may be chosen, to be at a position, where wheel defects can be detected, for example may be a base rotation frequency of the wheel 20.

[0053] The predefined base frequency k may be related to a transmission ratio g of a transmission 16 between the shaft and the wheel. In the case as discussed with respect to Fig. 2, where a transmission 16 is present between the shaft 14 and the wheel 20, the base frequency k corresponds to the angular speed 1 times the transmission ratio. In the example of Fig. 2, the transmission ratio is g = 0.221 and the base frequency is k = 0.221.

[0054] The at least one amplitude 32 of the frequency component 34 may be determined with a band-pass filter applied to the instantaneous angular speed signal 30. For example, the frequency component may be a frequency band, which is filtered out.

[0055] A plurality of amplitudes 32 of frequency components 34 may be determined with a comb filter applied to the instantaneous angular speed signal 30. The comb filter may be composed of a plurality of band-pass filters.

[0056] In step S14, a defect is detected, by inputting the plurality of amplitudes 32 into a function and / or classifier. The output of the function and / or classifier may be indicative of the presence of a defect. The output may be two different values for the presence of a defect or not. The output may be a statistical value, which may be compared to a threshold for determining whether there is a defect or not. For example, when the at least one amplitude 32 is higher than a threshold, a defect may be detected . A perfect circular wheel would result in an instantaneous angular speed signal 30, having zero amplitude for all frequency components 34 different from zero. The threshold may be chosen to discriminate an amplitude different from zero from noise.

[0057] When more than one amplitude 32 has been determined, a defect may be detected, when the sum of the amplitudes 32 is higher than the threshold. When the amplitudes 32 are summed up, in particular, when their frequencies have been chosen to the same type of defect, this may enhance detection quality.

[0058] The frequency components 34 may be preset frequencies and / or frequencies bands, which have been selected, for example based on the known transmission ratio of the transmission 16.

[0059] However, optionally, it is also possible that the frequency components 34 are determined from the instantaneous angular speed signal 30.

[0060] Optionally, in step S12, a frequency spectrum 36 of the instantaneous angular speed signal 30 seen as a function of the rotation angle is determined. For example, the frequency spectrum may be determined by Fourier transforming the instantaneous angular speed signal 30.

[0061] In general, the one or more amplitudes 32 of one or more frequency components 34 may be determined from the frequency spectrum 36. In this case, no filters are necessary.

[0062] However, it is also possible that the interesting frequency components and / or peaks 34 may be identified in the frequency spectrum 36. It is further possible that frequencies or frequency components are determined, where the amplitude 32 and / or peaks 34 is higher than a threshold.

[0063] A defect of the wheel 20 then may be detected, when peaks 34 related to an angular speed of the wheel 20 are present. When a peak 34 is detected, which is at a frequency, which according to the transmission ratio g is related to the base angular speed of the wheel 20, this indicates a wheel defect. When the peaks 34 have a specific pattern, such as higher harmonics of the base frequency, these peaks 34 may be related to the base frequency and to a wheel defect. Thus, a defect may be detected, when a plurality of peaks 34 with frequencies, which are a multiple of a base frequency, is identified.

[0064] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art and practising the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or controller or other unit may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.LIST OF REFERENCE SYMBOLS

[0065] 10train system 12engine 14engine shaft 16transmission 18wheel shaft 20wheel 22speed encoder 24encoder wheel 26sensor 28controller 30instantaneous angular speed signal 32amplitude 34frequency component 36frequency spectrum

Examples

Embodiment Construction

[0041]Fig. 1 shows a train system 10, which may be part of a railway vehicle. The train system 10 comprises an engine or drive 12, a shaft 14, which interconnects the engine 12 with a transmission 16. The transmission 16 is connected via a further shaft 18 with one or more wheels 20 of the railway vehicle.

[0042]A speed encoder 22 is attached to the shaft 14, which comprises an encoder wheel 24 and a sensor 26, which for example may generate a signal with a pulse, whenever an element of the encoder wheel 24 of speed encoder 22 passes a detector, such as a light sensor, which senses light from a light source occluded by the element, or a magnetic or eddy-current sensor, which senses the presence or absence of a teeth. The measurement signal of the speed encoder 22 produced by the sensor 26 is transmitted to a controller 28, which may be a part of a traction control system for the train system 10. In general, the speed encoder 22 also may be attached to the shaft 18.

[0043]The speed enc...

FIELD OF THE INVENTION

[0001] The invention relates to a method, a controller, a computer program and a computer-readable medium for detecting defects of a wheel of a railroad vehicle. The invention also relates to a train system.BACKGROUND OF THE INVENTION

[0002] Train wheels are subject to degradation, either in the form of flat spots or a "polygonization" of them. Flat spots can occur in case of faulty brakes which block the wheel, leading to larger removal of metallic material. Slippery rails, for example due to leaves, can lead to an abnormal stick-slip of the wheel, which also can cause flat spots. Polygonization of the wheel occurs under normal operation, wherein the wheel slowly changes from a circle to a polygon. Dedicated and expensive measurement equipment, such as a laser scanning device, is needed in order to detect these defects.DESCRIPTION OF THE INVENTION

[0003] It is an objective of the present invention to monitor train wheel degradations, in particular in a continuous way and in particular using available sensors. Further objectives are to reduce maintenance cost and to increase the lifetime of train wheels.

[0004] These objectives are achieved by the subject-matter of the independent claims. Further exemplary embodiments are evident from the dependent claims and the following description.

[0005] A first aspect of the invention relates to a method for detecting defects of a wheel of a railroad vehicle. The railroad vehicle may be part of a train. The wheel may be adapted for rolling on a railway. The defects may relate to deviations of the wheel and in particular its running surface from a circle. Such defects may be flat spots and polygonization.

[0006] The method may be performed automatically by a controller of the railroad vehicle, such as a traction control system.

[0007] According to an embodiment, the method comprises: determining an instantaneous angular speed signal of a shaft connected to the wheel, wherein the instantaneous angular speed signal is determined from measurements of a speed encoder connected to the shaft and wherein the instantaneous angular speed signal is indicative of a speed of the shaft at a rotation angle of the shaft.

[0008] The shaft may be a part of the drive system of the train. The train engine may drive the shaft, which drives the wheel. There may be a gear or transmission between the train engine and the shaft and / or between the shaft and the wheel. The shaft also may be directly connected to the wheel.

[0009] The instantaneous angular speed signal is determined from measurements of a speed encoder connected to the shaft. Such a speed encoder may provide a pulse, whenever the shaft turns by a specific angle, in general substantially smaller than 360° and / or a fraction of 360°. By knowing the number of pulses per complete revolution of the shaft and the time interval between two pulses, the angular speed as a function of the angle of the shaft , i.e., the instantaneous angular speed signal, may be calculated.

[0010] The instantaneous angular speed signal is indicative of a speed of the shaft at a rotation angle of the shaft. The rotation angle may be a value constantly increasing with every revolution of the shaft. The rotation angle need not be provided modulo 360°. It has to be noted that the rotation angle is in general not linear related to time, since the shaft may turn slower and faster depending on the speed of the railway vehicle.

[0011] The instantaneous angular speed signal may be seen as a function of the rotation angle of the shaft and in particular can be calculated directly from the measurements of the speed encoder. It is not necessary to calculate a time dependent angular speed signal and to transform it into a rotation angle dependent angular speed signal.

[0012] The transmission ratio between the shaft and the wheel may be 1, when the wheel is directly connected to the shaft, or may be different from 1, for example, when a transmission is arranged between the shaft and the wheel. However, the transmission ratio may be known. Therefore, the instantaneous angular speed signal also may be seen as a function of the rotation angle of the wheel.

[0013] According to an embodiment, the method further comprises: determining at least one amplitude of a frequency component of the instantaneous angular speed signal seen as a function of the rotation angle. As every function depending on a continuous parameter, the instantaneous angular speed signal can be Fourier transformed, in this case not with respect to time but with respect to the rotation angle. As the pulses are distributed uniformly, that is in equidistant angles, around the rotation axis, the angular speed as a function of angle may also be a uniformly sampled signal. This may be of an advantage, when doing a Fourier transform (or any other operation) on it. However, the frequency component need not be determined by Fourier transformation, but for example also may be determined by applying a filter. The frequency component (which also may be called frequency content) may comprise one or more or a band of frequencies of sinusoidal components of the frequency spectrum of the instantaneous angular speed signal. The amplitude of the frequency component may be the amplitude, the sum, the root-mean-square and / or an average of the amplitudes of these sinusoidal components.

[0014] The frequency component may be chosen, such that a wheel defect can be detected. For example, a frequency of the frequency component (such as an average frequency, a peak frequency, a median frequency, a middle frequency, etc.) may be chosen to be the base rotation frequency of the wheel. The base rotation frequency of the wheel may be one, when there is no transmission between the speed encoder and the wheel, or may be the transmission ratio.

[0015] According to an embodiment, the method further comprises: detecting a defect based on a magnitude of the at least one amplitude. A perfect circular wheel would result in an instantaneous angular speed signal, having zero amplitude for all frequency components different from zero. When there is an amplitude different from zero, which can be discriminated from noise for example by a threshold, there is a problem, which accelerates and decelerates the shaft periodically in linear dependence of the rotation angle of the shaft and therefore indirectly of the wheel. From this, it may be deduced that there is a defect in the mechanical system comprising the wheel, which is mainly the wheel. However, also defects of a transmission or gears may be detected in this way.

[0016] It may be that the defect is detected by comparing the at least one amplitude with one or more thresholds. When one or more of the amplitudes are higher than one threshold or an individual threshold for each frequency component associated with the amplitude, a defect may be detected.

[0017] In general, a defect, may be detected by inputting the at least one amplitude into a target function, which outputs one or more statistical values from which it can be determined, whether there is a defect or not. For example, an output of the function may be compared with a threshold to determine, whether there is a defect or not. In one case, a defect is detected, when the at least one amplitude is higher than a threshold. The threshold may be constant, it may be adapted based on a measured noise background, and / or it may be adapted to an average angular speed of the system.With the method, wheel imperfections may be detected using only available sensors in the railroad vehicle. Such a sensor is the speed encoder, which may be mounted on a shaft driven by the engine of the railroad vehicle. The geometric deformation of the wheel leads to a modulation of the instantaneous angular speed signal, which, when analysed in the correct domain, here the angular domain, leads to typical peaks in the angular spectrum, allowing for a continuous monitoring.

[0018] Analysing the instantaneous angular speed as a function of the rotation angle instead of the time is a very sensitive way to detect issues on the wheel. A speed encoder is able to measure the instantaneous angular speed with high precision and is therefore an adequate sensing system for this effect. For example, using the pulses produced by a cogwheel together with the time interval between the passing of two pulses gives both the angle and the speed from pulse to pulse, which is a good basis for the analysis.

[0019] The imperfection of the wheel leads to a modulation of the instantaneous angular speed, where the modulation is given by the geometry, as it has to repeat after each rotation. This leads to extremely narrow and therefore sensitive peaks in the spectrum of the instantaneous angular speed when analysed not in time domain but in angular domain. This allows for an analysis in the setting of a railway vehicle, where speed is in general not expected to be constant even for a rather short time.

[0020] According to an embodiment, a plurality of amplitudes of frequency components of the instantaneous angular speed signal seen as a function of the rotation angle are determined. The frequency components may be different bands of the frequency spectrum.

[0021] According to an embodiment, each of the frequency components corresponds to a multiple of a predefined base frequency. The predefined base frequency may be chosen, to be at a position, where wheel defects can be detected, for example may be a base rotation frequency of the wheel. For example, when a transmission is present between the shaft and the wheel, the base frequency may correspond to the angular speed 1 times the transmission ratio. A defect on the wheel usually will generate a frequency component at the base frequency and multiples thereof.

[0022] According to an embodiment, a defect of the wheel is detected, when a function of the amplitudes, which are determined, is higher than a threshold. The function may be a sum, an average, a root-mean square, etc. The function also may be a classifier, which outputs a statistical value about a probability of a defect. The function may depend in addition to the amplitudes on other properties, like the background noise, the speed etc. In particular, when their frequencies have been chosen to the same type of defect, this may enhance detection quality.

[0023] According to an embodiment, the predefined base frequency is related to a transmission ratio of a transmission between the shaft and the wheel. In general, the speed encoder may be mounted on a wheel shaft, on an intermediate shaft or on a motor shaft. When a transmission is present between the shaft of the speed encoder and the wheel, the transmission ratio of the transmission shifts the specific frequencies of a wheel defect, which may be integer multiples of a base rotation frequency to a non-integer base. A transmission ratio different from 1 may additionally help to distinguish defect signals from speed encoder imperfections.

[0024] According to an embodiment, the function of the amplitude additionally depends on a background noise level and / or a speed of the railroad vehicle. The background noise level may be determined with a microphone positioned in the railroad vehicle. The speed of the railroad vehicle may be provided by a superordinated controller.

[0025] According to an embodiment, the at least one amplitude of the frequency component is determined with a band-pass filter applied to the instantaneous angular speed signal. The frequency component may be a frequency band, which is filtered out.

[0026] According to an embodiment, a plurality of amplitudes of frequency components is determined with a comb filter applied to the instantaneous angular speed signal. The comb filter may be composed of a plurality of band-pass filters.

[0027] According to an embodiment, the method further comprises: determining a frequency spectrum of the instantaneous angular speed signal seen as a function of the rotation angle. The frequency spectrum may be a function with amplitudes of frequencies of the instantaneous angular speed signal. For example, the frequency spectrum may be determined by Fourier transforming the instantaneous angular speed signal seen as a function of the rotation angle. The at least one amplitude of a frequency component may be determined from the frequency spectrum.

[0028] According to an embodiment, the method further comprises: identifying peaks in the frequency spectrum. It is further possible that frequencies or frequency components are determined, where the amplitude and / or peaks are higher than a threshold.

[0029] According to an embodiment, the method further comprises: detecting a defect of the wheel, when peaks related to an angular speed of the wheel are present. When a peak is detected, which is at a frequency, which according to a transmission ratio is the base angular speed of the wheel, this indicates a wheel defect. As further example, when the peaks have a specific pattern, such as higher harmonics of the base frequency, these peaks may be related to the base frequency and to a wheel defect.

[0030] A peak may be seen as frequency component. It is possible that the one or more frequency components, which are used for determining the amplitudes for defect detection, are determined from the instantaneous angular speed signal. As described above, however, the frequency component may be preset and may be filtered out from the instantaneous angular speed signal with a preset filter.

[0031] According to an embodiment, a defect is detected, when a plurality of peaks with frequencies, which are a multiple of a base frequency, i.e., a fundamental frequency and higher order harmonics, is identified. A specific pattern are peaks with frequencies that are a multiple of a base frequency or fundamental frequency. These peaks indicate a defect related to a mechanical component of the drive system, rotating with an angular speed of the fundamental frequency possibly multiplied with a transmission ratio of a transmission between the speed encoder and the mechanical component.

[0032] According to an embodiment, the method further comprises: determining the instantaneous angular speed signal from a pulse signal provided by the speed encoder. The speed encoder may comprise an encoder wheel with a plurality of periodic elements generating the pulses. The elements may be teeth or windows, which may be detected by occluding light or changing a magnetic field. The number of elements around the encoder wheel and / or the number of pulses per complete revolution of the encoder wheel are known. The speed encoder may provide both the angle information as pulses of the encoder wheel and the speed through the time between pulses. These data may be used to calculate the speed as a function of the rotation angle (and not of time).

[0033] A further aspect of the invention relates to a controller for carrying out the method such as described herein. For example, the controller may be or may be part of a traction control system of the railroad vehicle.

[0034] A further aspect of the invention relates to a computer program for detecting defects of a wheel of a railroad vehicle, the computer program comprising instructions which, when being executed by a processor, carry out the method such as described herein. A further aspect of the invention relates to a computer-readable medium, in which such a computer program is stored. The controller may comprise a processor and a memory, in which the computer program is stored.

[0035] In general, a computer-readable medium may be a hard disk, an USB (Universal Serial Bus) storage device, a RAM (Random Access Memory), a ROM (Read Only Memory), an EPROM (Erasable Programmable Read Only Memory) or a FLASH memory. A computer-readable medium may also be a data communication network, e.g., the Internet, which allows downloading a program code. In general, the computer-readable medium may be a non-transitory or transitory medium.

[0036] A further aspect of the invention relates to a train system. The train system comprises a shaft connected to a wheel of the railroad vehicle, a speed encoder connected to the shaft, and a controller for detecting defects of the wheel.

[0037] It has to be understood that some features of the present invention are described with respect to one of the aspects only for conciseness reasons and to avoid unnecessary repetitions, but that these features may be easily transferred to one or more of the other aspects by the person skilled in the art.

[0038] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The subject-matter of the invention will be explained in more detail in the following text with reference to exemplary embodiments which are illustrated in the attached drawings. Fig. 1 shows a train system according to an embodiment of the invention. Fig. 2 shows diagrams with spectra of angular speed. Fig. 3 shows a flow diagram for a method for detecting wheel defects according to an embodiment of the invention.

[0040] The reference symbols used in the drawings, and their meanings, are listed in summary form in the list of reference symbols. In principle, identical parts are provided with the same reference symbols in the figures.DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0041] Fig. 1 shows a train system 10, which may be part of a railway vehicle. The train system 10 comprises an engine or drive 12, a shaft 14, which interconnects the engine 12 with a transmission 16. The transmission 16 is connected via a further shaft 18 with one or more wheels 20 of the railway vehicle.

[0042] A speed encoder 22 is attached to the shaft 14, which comprises an encoder wheel 24 and a sensor 26, which for example may generate a signal with a pulse, whenever an element of the encoder wheel 24 of speed encoder 22 passes a detector, such as a light sensor, which senses light from a light source occluded by the element, or a magnetic or eddy-current sensor, which senses the presence or absence of a teeth. The measurement signal of the speed encoder 22 produced by the sensor 26 is transmitted to a controller 28, which may be a part of a traction control system for the train system 10. In general, the speed encoder 22 also may be attached to the shaft 18.

[0043] The speed encoder 22 provides the instantaneous angular speed of the shaft 14 with high angular resolution and time accuracy, both as a function of the rotation angle and as a function of time. The instantaneous rotation angle θ of the shaft 14 may be determined from the encoder position count of the speed encoder 22, for example by multiplying with a known angle between two consecutive elements in the encoder wheel. The instantaneous angular speed is dθ / dt.

[0044] Knowing the instantaneous angular speed dθ / dt as a function of the rotation angle allows to analyse the power spectra in the angular frame and to accurately identify angular speed fluctuations. These angular speed fluctuations may be of geometric origin, for example of changes in shape of the wheel 20. If one disregards the slip between the wheel 20 and the rails, translation speed v(t), and instantaneous angular speed of the wheel, dθ / dt with respect to time, are related by the constraint dθ / dt = v(t) / R (θ(t)), where R(θ(t)) is the radius of the wheel 20 measured from its rotation centre to the instantaneous contact point with the rail. A perfect wheel 20 (without any deformation) has a constant radius, R. Variations in dθ / dt can be due to the variable translational speed v(t), and can also originate from imperfections of the train wheel, with R(θ(t)) being a function of the rotation angle. Imperfections of the encoder wheel 24 (such as off-centring, or different teeth shapes) may also add geometric modulations to the estimated instantaneous angular speed, because one derives the rotation of the shaft 14 from the measurement of the encoder wheel 24 attached to it.

[0045] Instantaneous angular speed fluctuations due to geometric distortions are periodic as a function of the rotation angle, but are not perfectly periodic in time, because the instantaneous angular speed with respect to time is never truly constant. If the translation speed of the railway vehicle changes, the periodicity of the geometric features is lost with respect to time, and their contribution may be misinterpreted as noise in a standard time-series analysis. Thus, in order to make efficient use of the information regarding geometric distortions, it is beneficial to work in the rotation frame, processing the instantaneous angular speed dθ / dt as a function of the rotation angle.

[0046] The speed encoder 22 provides the position count x i at time point t i . The instantaneous angular speed dθ / dt at time point t i is v i =1 / ( α (t i+1 -t i ) ), wherein α is the angular resolution of the speed encoder 22, for example the angular distance between two elements of the encoder wheel 24. This implies that velocity changes are only registered every time the position count changes. For this reason, the speed encoder 22 provides a one-to-one relationship between instantaneous angular speed v; and position count x i .

[0047] Fig. 2 shows spectra of an instantaneous angular speed in the time domain, where frequencies are in events per second [Hz] (upper diagram), and in the rotation count frame, where frequencies k are in events per revolution (lower diagram). The instantaneous angular speed was determined from measurements of a speed encoder 22, such as shown in Fig. 1. As can be seen in Fig. 2, geometrical features appear smeared out in the time frame spectrum.

[0048] The lower diagram shows that deformations in the wheels 20 cause perfectly periodic modulations of the instantaneous angular speed in the rotation frame. The modulations appear at k-values that are multiples of a transmission ratio of the transmission 16. In the example shown in Fig.2, the transmission ratio is g = 0.221 and the corresponding sharp lines / narrow peaks are clearly visible at k = 0.221, 0.442, 0.663, 0.884, .... Since the transmission ratio is generally non-integer, components from wheel deformation do not overlap with the components from the imperfections of the encoder wheel (which are also geometric and appear at integer repetency values, here at k =1). If the speed encoder 22 is on the wheel shaft 18, wheel deformations and encoder imperfections will both appear at integer k-values.

[0049] Fig. 3 shows a flow diagram illustrating a method for detecting defects of the wheel 20, which may be performed automatically by the controller 28. In particular, a computer program may run in the controller 28 performing the method.

[0050] In step S10, the controller 28 determines an instantaneous angular speed signal 30 of the shaft 14 as a function of the rotation angle. The instantaneous angular speed signal 30 is indicative of a speed of the shaft 14 at a rotation angle of the shaft 14. The instantaneous angular speed signal 30 as a function of the rotation angle is determined from measurements of the speed encoder 22. This may be done like described above.

[0051] In step S12, one or more amplitudes 32 of one or more frequency components 34 of the instantaneous angular speed signal 30 as a function of the rotation angle are determined. Fig. 2 shows such amplitudes 32 and frequency components 34. The frequency components 34 may be small bands around predefined frequencies, which relate to geometric features of the wheel 20.

[0052] For example, each of the frequency components 34 corresponds to a multiple of a predefined base frequency k. The predefined base frequency k may be chosen, to be at a position, where wheel defects can be detected, for example may be a base rotation frequency of the wheel 20.

[0053] The predefined base frequency k may be related to a transmission ratio g of a transmission 16 between the shaft and the wheel. In the case as discussed with respect to Fig. 2, where a transmission 16 is present between the shaft 14 and the wheel 20, the base frequency k corresponds to the angular speed 1 times the transmission ratio. In the example of Fig. 2, the transmission ratio is g = 0.221 and the base frequency is k = 0.221.

[0054] The at least one amplitude 32 of the frequency component 34 may be determined with a band-pass filter applied to the instantaneous angular speed signal 30. For example, the frequency component may be a frequency band, which is filtered out.

[0055] A plurality of amplitudes 32 of frequency components 34 may be determined with a comb filter applied to the instantaneous angular speed signal 30. The comb filter may be composed of a plurality of band-pass filters.

[0056] In step S14, a defect is detected, by inputting the plurality of amplitudes 32 into a function and / or classifier. The output of the function and / or classifier may be indicative of the presence of a defect. The output may be two different values for the presence of a defect or not. The output may be a statistical value, which may be compared to a threshold for determining whether there is a defect or not. For example, when the at least one amplitude 32 is higher than a threshold, a defect may be detected . A perfect circular wheel would result in an instantaneous angular speed signal 30, having zero amplitude for all frequency components 34 different from zero. The threshold may be chosen to discriminate an amplitude different from zero from noise.

[0057] When more than one amplitude 32 has been determined, a defect may be detected, when the sum of the amplitudes 32 is higher than the threshold. When the amplitudes 32 are summed up, in particular, when their frequencies have been chosen to the same type of defect, this may enhance detection quality.

[0058] The frequency components 34 may be preset frequencies and / or frequencies bands, which have been selected, for example based on the known transmission ratio of the transmission 16.

[0059] However, optionally, it is also possible that the frequency components 34 are determined from the instantaneous angular speed signal 30.

[0060] Optionally, in step S12, a frequency spectrum 36 of the instantaneous angular speed signal 30 seen as a function of the rotation angle is determined. For example, the frequency spectrum may be determined by Fourier transforming the instantaneous angular speed signal 30.

[0061] In general, the one or more amplitudes 32 of one or more frequency components 34 may be determined from the frequency spectrum 36. In this case, no filters are necessary.

[0062] However, it is also possible that the interesting frequency components and / or peaks 34 may be identified in the frequency spectrum 36. It is further possible that frequencies or frequency components are determined, where the amplitude 32 and / or peaks 34 is higher than a threshold.

[0063] A defect of the wheel 20 then may be detected, when peaks 34 related to an angular speed of the wheel 20 are present. When a peak 34 is detected, which is at a frequency, which according to the transmission ratio g is related to the base angular speed of the wheel 20, this indicates a wheel defect. When the peaks 34 have a specific pattern, such as higher harmonics of the base frequency, these peaks 34 may be related to the base frequency and to a wheel defect. Thus, a defect may be detected, when a plurality of peaks 34 with frequencies, which are a multiple of a base frequency, is identified.

[0064] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art and practising the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or controller or other unit may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.LIST OF REFERENCE SYMBOLS

[0065] 10train system 12engine 14engine shaft 16transmission 18wheel shaft 20wheel 22speed encoder 24encoder wheel 26sensor 28controller 30instantaneous angular speed signal 32amplitude 34frequency component 36frequency spectrum

Examples

Embodiment Construction

[0041]Fig. 1 shows a train system 10, which may be part of a railway vehicle. The train system 10 comprises an engine or drive 12, a shaft 14, which interconnects the engine 12 with a transmission 16. The transmission 16 is connected via a further shaft 18 with one or more wheels 20 of the railway vehicle.

[0042]A speed encoder 22 is attached to the shaft 14, which comprises an encoder wheel 24 and a sensor 26, which for example may generate a signal with a pulse, whenever an element of the encoder wheel 24 of speed encoder 22 passes a detector, such as a light sensor, which senses light from a light source occluded by the element, or a magnetic or eddy-current sensor, which senses the presence or absence of a teeth. The measurement signal of the speed encoder 22 produced by the sensor 26 is transmitted to a controller 28, which may be a part of a traction control system for the train system 10. In general, the speed encoder 22 also may be attached to the shaft 18.

[0043]The speed enc...

Claims

1. A method for detecting defects of a wheel (20) of a railroad vehicle, the method comprising: determining an instantaneous angular speed signal (30) of a shaft (14) connected to the wheel (20), wherein the instantaneous angular speed signal (30) is determined from measurements of a speed encoder (22) connected to the shaft (14) and wherein the instantaneous angular speed signal is indicative of a speed of the shaft (14) at a rotation angle of the shaft (14); determining at least one amplitude (32) of a frequency component (34) of the instantaneous angular speed signal (30) seen as a function of the rotation angle; detecting a defect based on a magnitude of the at least one amplitude (32).

2. The method of claim 1, wherein a plurality of amplitudes (32) of frequency components (34) of the instantaneous angular speed signal (30) seen as a function of the rotation angle is determined; wherein each of the frequency components (34) corresponds to a multiple of a predefined base frequency; wherein a defect is detected, when a function of the amplitudes (32) is higher than a threshold.

3. The method of claim 2, wherein the predefined base frequency is related to a transmission ratio of a transmission (16) between the shaft (14) and the wheel (20); and / or wherein the function of the amplitude (32) additionally depends on a background noise level and / or a speed of the railroad vehicle.

4. The method of one of the previous claims, wherein the at least one amplitude of the frequency component (34) is determined with a band-pass filter applied to the instantaneous angular speed signal (30).

5. The method of one of the previous claims, wherein a plurality of amplitudes (32) of frequency components (34) is determined with a comb filter applied to the instantaneous angular speed signal (30).

6. The method of one of the previous claims, further comprising: determining a frequency spectrum (36) of the instantaneous angular speed signal (30) seen as a function of the rotation angle.

7. The method of claim 6, wherein the at least one amplitude (32) of a frequency component (34) is determined from the frequency spectrum (36).

8. The method of claim 6 or 7, wherein the frequency spectrum (36) is determined by Fourier transforming the instantaneous angular speed signal (30) seen as a function of the rotation angle.

9. The method of one of claims 6 to 8, further comprising: identifying peaks (34) in the frequency spectrum (36); detecting a defect, when peaks (34) related to an angular speed of the wheel are present.

10. The method of claim 9, wherein a defect is detected, when a plurality of peaks (34) with frequencies, which are a multiple of a base frequency, is identified.

11. The method of one the previous claims, further comprising: determining the instantaneous angular speed signal (30) from a pulse signal provided by the speed encoder (22), wherein the speed encoder (22) comprises an encoder wheel (24) with a plurality of periodic elements generating the pulses.

12. A controller (28) for carrying out the method of one of the previous claims.

13. A computer program for detecting defects of a wheel (20) of a railroad vehicle, the computer program comprising instructions which, when being executed by a processor, carry out the method of one of claims 1 to 11.

14. A computer-readable medium, in which a computer program according to claim 13 is stored.

15. A train system (10), comprising: a shaft (14) connected to a wheel (20) of the railroad vehicle; a speed encoder (22) connected to the shaft (14); a controller (28) for detecting defects of the wheel (20) according to claim 12.

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