Patent Publication Number: US-2020290658-A1

Title: Monitoring an Axle of a Railway Vehicle

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a US 371 application from PCT/EP2018/079511 entitled “Monitoring an Axle of a Railway Vehicle” filed on Oct. 26, 2018 and published as WO 2019/081770 A1 on May 2, 2019, which claims priority to GB Application 1717699.1 filed on Oct. 27, 2017. The technical disclosures of every application and publication listed in this paragraph are hereby incorporated herein by reference. 
     The present invention provides an apparatus for monitoring an axle of a wheelset assembly of a railway vehicle. The present invention further provides a method for monitoring an axle of a wheelset assembly of a railway vehicle. 
     Rail axle fractures are one of the causes of major rail accidents throughout the history of rail, and started the study of metal fatigue. Preventing rail axle fractures in service causes significant additional maintenance work—both to carry out axle inspections and to repair damage after incorrect re-assembly of axle end apparatus after axle crack inspections. 
     There has been significant work to study the formation of axle cracks, in-service or with minimum intervention during maintenance, but there have been no successful trials of large deployment of axle crack monitoring equipment (in-service). This is partly due to the target crack-dependent measurands being intrinsically difficult to carry out in the context of all the other noise present in in-service trains, and also to the difficulty of monitoring rail axle end vibration and noise due to poor accessibility for energy and communication. 
     Recent development of vibration energy harvester powered wireless sensor nodes that are mounted on the axle end has solved part of this problem, but there is still the difficulty of differentiating additional vibration due to a fracture in the axle, from noise produced by the interaction of the wheel on the track, both of which have the same fundamental frequency driven from the rotation of the wheels at a given speed. 
     In the prior art, previous efforts to measure rail axle cracking have looked at either acoustic emissions from the fracture as the axle flexes, or the vibration caused by the axle flexing, and the change on the vibration as the crack extends. These tests have been on test rigs, not in an in-service test. 
     Vibration powered wireless sensor nodes (WSNs) have been used to detect bearing, track and wheel health on rail vehicles. The sensors monitor vibration, as discussed above, but the monitoring frequency is limited to 500 Hz. 
     There is therefore a need in the art for an apparatus for, and a method of, monitoring an axle of a wheelset assembly of a railway vehicle, which can provide an improved measurement as compared to known apparatus and methods. 
     There is also a need in the art for an apparatus for, and a method of, monitoring an axle of a wheelset assembly of a railway vehicle which can monitor an axle condition in-service, preferably in real-time. 
     There is a further need in the art for an apparatus for, and a method of, monitoring an axle of a wheelset assembly of a railway vehicle which can monitor an axle condition in-service, and can also provide at least one additional operating or performance parameter of the axle, again in-service, preferably in real-time. 
     The present invention at least partially aims to meet one or more of these needs. 
     Accordingly, the present invention provides an apparatus for monitoring an axle of a wheelset assembly of a railway vehicle, the apparatus comprising a wireless sensor node fitted to a wheelset assembly, the wheelset assembly comprising an axle mounted between opposed wheels, each wheel being fitted to a respective opposite end of the axle, the wireless sensor node comprising a vibration energy harvester for converting mechanical energy from vibration in the wheelset assembly into electrical energy, a sensor for measuring a parameter, and a wireless transmitter for wirelessly transmitting the measured parameter or data associated therewith, and the apparatus further comprising a processor for processing the measured parameter to produce processed data, wherein the sensor is an accelerometer mounted to an end of the axle and the sensor and processor are arranged respectively to measure and process an axle percussion vibration frequency in the form of resonant vibration along the axley. 
     The present invention further provides a method of monitoring an axle of a wheelset assembly of a railway vehicle, the wheelset assembly comprising an axle mounted between opposed wheels, each wheel being fitted to a respective opposite end of the axle, the method comprising the steps of:
         a. providing a wireless sensor node fitted to the wheelset assembly, the wireless sensor node comprising a vibration energy harvester for converting mechanical energy from vibration in the wheelset assembly into electrical energy, a sensor for measuring a parameter, wherein the sensor is an accelerometer mounted to an end of the axle, and a wireless transmitter for wirelessly transmitting the measured parameter or data associated therewith;   b. while the railway vehicle is in motion, the vibration energy harvester receiving input vibration energy which is converted into electrical energy to power the wireless transmitter;   c. while the railway vehicle is in motion, measuring an axle percussion resonant vibration frequency using the sensor, wherein the sensor measures resonant vibration along the axle;   d. while the railway vehicle is in motion, wirelessly transmitting the measured axle percussion resonant vibration frequency or data associated therewith using the wireless transmitter; and   e. processing the measured axle percussion vibration frequency of the resonant vibration along the axle to produce processed data.       

     Preferred features of the apparatus and method of the present invention are defined in the respective dependent claims. 
     The apparatus and method of the preferred embodiments of the present invention solve the problem of providing an in-service rail axle measurement, optionally in real-time, which can be utilized in a protocol for crack detection, and optionally also for axle load measurement. As the railway vehicle travels along the track, there are multiple impacts from wheel-rail interaction. The axle assembly vibrates in response to the impacts. The vibration-energy powered wireless sensor detects ringing of the wheelset stimulated by the wheel-rail interaction, analyses the vibration, and then transmits key parameters for further analysis. 
     The apparatus and method of the preferred embodiments of the present invention are predicated on the finding by the present inventors that a percussion vibration can be used to test the axle in-service, and that real-time measurement and analysis can be used to monitor axle condition and can also be used to measure axle loads. 
     The percussion vibration is caused by impacts on the wheelset assembly from the wheel/track interface. Therefore, the preferred embodiments utilise the effect of the “ringing” of the axle excited by wheel-rail impact to detect changes in axle health and load. The percussion vibration measurements are taken using axle end mounted accelerometers, powered by vibration energy harvesters. 
     The invention is based on the finding by the present inventors that wheel-rail impact, during an in-service period of the wheelset and measured in real-time, can be used to excite vibration of the wheelset, and in turn that vibration can be used to detect the state or condition of the axle, in particular the presence/absence of cracks in the axle and/or the axle loading. 
     In contrast, known axle testing methods have not used percussive vibration, in particular during an in-service period of the wheelset and measured in real-time, to diagnose axle condition and/or working/performance conditions such as axle load. 
     As discussed above, in the prior art, vibration powered wireless sensor nodes (WSNs) have been used to detect bearing, track and wheel health on rail vehicles, and the sensors monitor vibration, but the monitoring frequency is limited to 500 Hz, which is too low to detect axle percussive vibrations. When axle testing has previously been carried out on a test rig, there were no impacts to excite other modes of vibration, in particular a percussive mode of vibration. 
     In the preferred embodiments of the present invention, the percussive mode of vibration is typically within a frequency range of from 1000 to 2000 Hz, more typically from 1250 to 1750 Hz, for example about 1500 Hz. These frequencies are higher than the frequencies of up to 500 Hz used in known vibration powered wireless sensor nodes (WSNs) used to detect bearing, track and wheel health on rail vehicles. 
    
    
     
       Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic end view of an apparatus for monitoring a component of a wheelset assembly of a railway vehicle according to an embodiment of the present invention; 
         FIG. 2  is a schematic view of the processing system in the apparatus of  FIG. 1 ; and 
         FIG. 3  is a schematic graph representing the output of the sensor in the apparatus of  FIG. 1  when used for high bandwidth vibration measurements from an in-service passenger train. 
     
    
    
     Referring to  FIGS. 1 to 3 , there is shown an apparatus  2  for monitoring a component  4  of a wheelset assembly  6  of a railway vehicle  8 . The railway vehicle  8  may be a locomotive, a passenger carriage or a freight car or truck. The wheelset assembly  6  comprises an axle  4 , which is the component to be monitored, mounted between opposed wheels  10 ,  12 , each wheel  10 ,  12  being fitted to a respective opposite end  14 ,  16  of the axle  4 . In use, the wheels  10 ,  12  run on respective rails  50 ,  52  of a railway track  54 . 
     A wireless sensor node  18  is fitted to the wheelset assembly  6 . In the illustrated embodiment, the wireless sensor node  18  comprises a vibration energy harvester  20  for converting mechanical energy from vibration in the wheelset assembly  6  into electrical energy. A sensor  22  is provided for measuring a parameter, and in particular the sensor  22  is an accelerometer mounted to an end  14 ,  16  of the axle  4 . A wireless transmitter  24  is provided for wirelessly transmitting the measured parameter or data associated therewith to a remote location for further processing and/or analysis; the remote location may be within the railway vehicle  8  which includes the tested wheelset assembly  6 , or within a locomotive or other vehicle of a train which includes the wheelset assembly  6 . Typically, each wheelset assembly  6  within a train is provided with a monitoring apparatus as described herein. 
     Preferably, as illustrated, the apparatus  2  comprises two of the wireless sensor nodes  18 . Each wireless sensor node  18  is fitted to a respective opposite end  14 ,  16  of the axle  4 , and each wireless sensor node  18  comprises a respective sensor  22  which is an accelerometer mounted to a respective end  14 ,  16  of the axle  4 . 
     The apparatus  2  further comprises a processor  26  for processing the measured parameter to produce processed data. In the illustrated embodiment, the processor  26  is integral with the wireless sensor node  18 , and the wireless transmitter  24  is arranged wirelessly to transmit the processed data. However, in alternative embodiments, the processor  26  is remote from the wireless sensor node  18 , and the wireless transmitter  24  is arranged wirelessly to transmit the measured data which is then remotely processed by the processer  26  to produce the processed data. 
     The sensor  22  and processor  26  are arranged respectively to measure and process an axle percussion vibration, in particular the axle percussion vibration in the form of resonant vibration along the axle. The resonant vibration along the axle is typically within a frequency range of from 1000 to 2000 Hz, more typically from 1250 to 1750 Hz, for example about 1500 Hz. 
     The sensor  22  measures the percussion vibration, and from that measurement the frequency of the percussion vibration is determined. The determined frequency is dependent upon the axle condition and the axle load. 
     The processor  26  includes a baseline module  28  which is adapted to predetermine a baseline for the axle percussion vibration, a baseline comparator module  30  to compare a current axle percussion vibration against the predetermined baseline and an analyser module  32  to determine a parameter of the current axle percussion vibration from the comparison. That parameter comprises part of the processed data. Typically, the wireless sensor node  18  is adapted to be operated continuously over a monitoring period thereby continuously to measure the axle percussion vibration and continuously to compare the axle percussion vibration at any given time against a baseline value. 
     These components permit an axle percussion vibration frequency value to be continuously measured and compared against a baseline to eliminate or minimise background noise. The measured frequency value can be employed to provide an indication of axle condition in real-time and during service of the wheelset assembly  6 . 
     In the preferred embodiments, the processor  26  includes a load calculator module  34  which comprises a comparison module  36  to compare a frequency of the axle percussion vibration against a predetermined reference frequency value associated with an axle load and a calculation module  37  to calculate a load on the axle based on the comparison. 
     These components permit an axle percussion vibration frequency value to be continuously measured and compared against a calibrated reference value to provide an indication of axle load in real-time and during service of the wheelset assembly  6 . 
     As described above, preferably, as illustrated, the apparatus  2  comprises two of the wireless sensor nodes  18 . These nodes  18  can be operated independently. The apparatus  2  may further include a measurement comparison module  38  in the processor  26  to compare a first frequency of the axle percussion vibration measured by the sensor  22  of a first wireless sensor node  18  against a second frequency of the axle percussion vibration measured by the sensor  22  of a second wireless sensor node  18 . A comparison output module  40  in the processor  26  is provided to calculate the resonant vibration along the axle  4  based on the comparison. The measurement comparison module  38  is adapted to compare different ratios of one or more harmonic frequencies of the axle percussion vibration measured by the respective sensors  22  of the first and second wireless sensor nodes  18 . 
     The apparatus  2  is used in a method of monitoring a component, in particular the axle  4 , of the wheelset assembly  6 . 
     In the method, a wireless sensor node  18  as described above is fitted to the wheelset assembly  6 , so that the sensor  22 , in particular the accelerometer, is mounted to an end  14 ,  16  of the axle  4 . As described above, in the preferred embodiment there are two wireless sensor nodes  18  each fitted to the wheelset assembly  6 , so that each respective sensor  22  is mounted to a respective end  14 ,  16  of the axle  4 . 
     While the railway vehicle is in motion, the vibration energy harvester  20  receives input vibration energy which is converted into electrical energy to power the wireless transmitter  24 . When the processor  26  is integrated into the wireless sensor node  18  the vibration energy harvester  20  can provide the electrical energy to operate the processor  26 . The vibration energy harvester  20  can provide the electrical energy to operate any other powered components of the wireless sensor node  18 . 
     Also while the railway vehicle is in motion, during an in-service period, the axle percussion vibration is measured using the sensor  22  and the measured axle percussion vibration or data associated therewith is wirelessly transmitted using the wireless transmitter  24 . 
     The sensor measures resonant vibration along the axle which is typically within a frequency range of from 1000 to 2000 Hz, more typically from 1250 to 1750 Hz, such as about 1500 Hz. The sensor  22  measures the percussion vibration, and from that measurement the frequency of the percussion vibration is determined. The determined frequency is dependent upon the axle condition and the axle load. 
       FIG. 3  is an example of a graph when the apparatus was used for high bandwidth vibration measurements from an in-service passenger train, the graph showing the relationship between sensor output, in dB, and frequency, in Hz. The graph shows the vibration spectrum of the sensor output, for one particular wheelset that was tested in-service using the apparatus of the present invention. In this example, a distinct vibration output peak profile was exhibited at a frequency centred about 1500 Hz. The percussion vibration from axles of train wheelsets typically fall within this range, although the vibration output peak profile may vary between axles and wheelsets. 
     The measured axle percussion vibration, in particular data of the resonant vibration along the axle  4 , is processed by the processor  26 , which is either integral to, or remote from, the wireless sensor node  18 , to produce processed data which may include the frequency of the percussion vibration. 
     When the processed data is processed by the processor  26  which is integral with the wireless sensor node  18 , the processed data is wirelessly transmitted. 
     The processing by the processor  26  is preferably carried out in real-time simultaneously with the measuring and transmitting steps to measure the axle percussion vibration and transmit the axle percussion vibration or data associated therewith. 
     In the preferred embodiment, wherein the processing step includes the sub-steps of (i) comparing a current axle percussion vibration against a predetermined baseline for the axle percussion vibration and (ii) determining a parameter of the current axle percussion vibration from the comparison, the parameter comprising part of the processed data. Preferably, the wireless sensor node is operated continuously over a monitoring period thereby continuously to measure the axle percussion vibration. During the processing, the axle percussion vibration frequency at any given time is continuously compared against a predetermined baseline value. In this way an axle percussion vibration frequency value can be continuously measured and compared against a baseline to eliminate or minimise background noise, and provide an accurate value of the percussion vibration frequency of the axle which can provide a status indication of the axle. This can be used to analyse whether or not cracks or other faults are present in the axle. 
     The method and apparatus can also be used to measure axle load. The processing step (e) preferably includes the sub-steps of (I) comparing a frequency of the axle percussion vibration against a predetermined reference frequency value associated with an axle load, and (II) calculating a load on the axle based on the comparison. This enables the measured percussion vibration frequency of the axle to be calibrated against a predetermined reference frequency value to enable axle load to be calculated. 
     When the apparatus comprises two wireless sensor nodes  18 , each wireless sensor node  18  being fitted to a respective opposite end  14 ,  16  of the axle  4  described above, each wireless sensor node  18  is operated to measure a respective axle percussion vibration frequency value to provide data relating to the measured axle percussion vibration. In the processing step (e), preferably there are sub-steps of (x) comparing a first frequency of the axle percussion vibration measured by the sensor  22  of a first wireless sensor node  18  against a second frequency of the axle percussion vibration measured by the sensor  22  of a second wireless sensor node  18 , and (y) calculating the resonant vibration along the axle based on the comparison. The comparison typically compares different ratios of one or more harmonic frequencies of the axle percussion vibration measured by the respective sensors  22  of the first and second wireless sensor nodes  18 . 
     The preferred embodiments of the present invention provide an apparatus, and an associated method, that exploit the power available from vibration energy harvesters to monitor vibration that has not been studied in the prior art for the purpose of axle crack formation. In particular, percussion vibration on the axle is monitored. The percussion vibration causes the axle to “ring” at a resonant frequency. If the resonant frequency changes, or if the percussion vibration fails to cause the axle to “ring” at the desired resonant frequency, then a potential fault in the axle can be highlighted and investigated further. This monitoring protocol can be conducted in-service and in real-time. 
     The preferred embodiments of the present invention provide that the percussion vibration is excited by wheel-rail impacts, and occurs at the natural vibration, i.e. the resonant frequency, of the wheelset, which comprises the wheels and axle assembly, that is present when the assembly receives impact energy. Using vibration that is excited by wheel-rail impact to monitor the state of the axle is a novel approach to axle health/condition monitoring, which exhibits a number of technical advantages. 
     First, the percussion vibration frequency is axle load dependent, which thereby allows wagon and axle loads to be monitored. 
     Second, small changes in the state of the axle produce a change in the vibration frequency spectra that can be monitored, and so the apparatus and method have high sensitivity. 
     Third, the frequency output of percussion vibration is above other sources of vibration noise in the system, typically being about 1500 Hz, which provides a noiseless or low noise signal to be analysed. 
     Fourth, the percussion vibration frequency is independent of train speed, so can be separated from other noise sources. 
     Fifth, the continuous, or near-continuous, monitoring from a vibration powered wireless sensor node (WSN) permits the establishment of a baseline for the percussion vibration, to enable reliable analysis of the percussion vibration frequency for any given axle. 
     Sixth, correlation of the percussion vibration frequency over time with known loads permits calibration of the load sensing capabilities of the percussion vibration frequency, thereby permitting axle loads to the calculated. 
     Seventh, comparison of measurements made at both ends of the axle (for example of the different ratios of the harmonics) can enhance the sensitivity of the apparatus. 
     Eighth, long term measurements can build-up a consistent trend for variation with time of the percussion vibration frequency, further enhancing the sensitivity of the apparatus and method to achieve reliable axle condition monitoring and axle load measuring. 
     Various modifications to the preferred embodiments of the present invention will be apparent to those skilled in the art.