System and method for measuring wheel-rail contact forces and the wheel-rail contact position

Abstract

System and method for measuring wheel-rail contact forces and the wheel-rail contact position, the system comprising a data acquisition device having at least one strain sensor attached to a railway wheel (1), the strain sensor measuring strain measurements of the wheel (1) in a plurality of instants of time while the wheel (1) moves on the rail (2), a memory for storing the strain measurements obtained by the strain sensor during the plurality of instants of times, and a processor that executes a process comprising the steps of reading the strain measurements stored in the memory, and calculating the wheel-rail contact forces (Y, T, Q) and the wheel-rail contact position (p) based on the strain measurements stored in the memory, thus the contact forces and contact position may be estimated using a reduced number of strain sensors that obtains several strain measurements in a plurality of instants of time.

Description

[0001] DESCRIPTION

[0002] System and method for measuring wheel-rail contact forces and the wheel-rail contact position

[0003] TECHNICAL FIELD

[0004] The present invention relates to a system and a method for measuring wheel-rail contact forces and the wheel-rail contact position of a railway vehicle while the wheel moves on the rail.

[0005] PRIOR ART

[0006] The wheel-rail contact forces are a key parameter that determines the dynamic behaviour of a railway vehicle and the interaction between the vehicle and the track. These values are key to understand and improve the operation of the vehicle, improve maintenance operations, among others.

[0007] Known solutions to measure these parameters are based on combining, in real time, several strain signals obtained from a large number of strain sensors in order to obtain an estimation of the wheel-rail contact forces. Most of the previous solutions are instrumented wheelset systems using at least 24 strain sensors, arranged in at least six full bridges, that must be located very accurately in the wheel web. An example of said systems can be shown in US5492002A or ES2334529B2 of the same applicant as the present invention.

[0008] DISCLOSURE OF THE INVENTION

[0009] The object of the invention is to provide a system and a method for measuring wheel-rail contact forces and the wheel-rail contact position, as defined in the claims.

[0010] One aspect of the invention refers to a system for measuring wheel-rail contact forces and the wheel-rail contact position, the system comprising: • a data acquisition device comprising at least one strain sensor attached to a railway wheel, the strain sensor measuring strain measurements of the wheel while the wheel moves on the rail, each strain measurement is dependent on the wheel-rail contact forces and the point where these forces are applied,

[0011] • a memory for storing the strain measurements obtained by the strain sensor, and

[0012] • a processor that executes a process comprising the following steps: o reading the strain measurements stored in the memory, and o calculating the wheel-rail contact forces and the wheel-rail contact position based on the strain measurements stored in the memory.

[0013] Another aspect of the invention refers to a method for measuring wheel-rail contact forces and the wheel-rail contact position, the method comprising:

[0014] • using a data acquisition device comprising at least one strain sensor attached to a railway wheel, the strain sensor measuring strain measurements of the wheel while the wheel moves on the rail, each strain measurement is dependent on the wheel-rail contact forces and the point where these forces are applied

[0015] • storing in a memory the strain measurements obtained by the strain sensor, and

[0016] • executing a process comprising the following steps: o reading the strain measurements stored in the memory, and o calculating the wheel-rail contact forces and the wheel-rail contact position based on the strain measurements stored in the memory,

[0017] According to the invention, the strain sensor obtains several strain measurements of the wheel in a plurality of instants of time, and the wheel rail contact forces and the lateral position of the contact position between the wheel and the rail are calculated based on the strain measurements obtained by the strain sensor during the plurality of instants of time, such that the strain sensor obtains several strain measurements in a plurality of instants of time instead of using several strain sensors that obtain several strain measurements in a single instant of time.

[0018] The proposed invention is based on a reduced number of strain sensors compared prior art solutions. In the simplest case, wheel-rail contact forces and the wheel-rail contact position may be estimated using a single strain sensor that obtains several strain measurements in a plurality of instants of time instead of using several strain sensors that obtain several strain measurements in a single instant of time. This results in a cost-effective system with lower energy consumption and higher reliability due to reduced number of components.

[0019] For example, in US5492002A a desired accuracy is achieved using several strain sensors comprising four vertical sensors, two lateral sensors and four position sensors. In the equations included on said document, the strain signals are expressed as a sum of different harmonic terms and is necessary to determine where to locate (angular position) the strain sensors and how to combine the signals in order to eliminate undesired harmonics. These calculations are done in order to design the wheel measurement wheelset. During the use of the method, the signals obtained at a certain instant of time are combined (summing or substracting them). Therefore, the proposed invention is based on the variations of the strain signal along the time to infer the values of the forces and the wheel rail contact position, while in said document the instantaneous measurements obtained by the several strain sensors are used to infer the values of the forces and the wheel rail contact position.

[0020] DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 shows the contact forces appearing at the contact position between the wheel 1 and the rail 2.

[0022] Figure 2a shows a system for measuring the wheel-rail contact forces and the wheel-rail contact position according to a first example of the invention.

[0023] Figure 2b shows a system for measuring the wheel-rail contact forces and the wheel-rail contact position according to a second example of the invention.

[0024] Figure 3 is a flow diagram example of the steps perform by the system to calculate the wheelrail contact forces and the wheel-rail contact position.

[0025] DETAILED DISCLOSURE OF THE INVENTION

[0026] Figure 1 schematically shows a wheel 1 of a rail vehicle in position of use on a rail 2.

[0027] Three types of contact forces appear at the contact position p between the wheel 1 and the rail 2. As discloses in Figure 1 , said forces are longitudinal wheel-rail contact force T, lateral wheel-rail contact force Y, and vertical wheel-rail contact force Q.

[0028] The rail 2 extends in a longitudinal direction x and the wheel 1 rests vertically on the rail 2 in a vertical direction z. Longitudinal wheel-rail contact force T, lateral wheel-rail contact force Y, and vertical wheel-rail contact force Q are referenced in the orthogonal reference frame (x, y, z) of Figure 1 .

[0029] The invention proposes a system for measuring wheel-rail contact forces and the wheel-rail contact position. The system comprises:

[0030] • a data acquisition device 3 comprising at least one strain sensor attached to a railway wheel 1 , the strain sensor measuring strain measurements of the wheel 1 in a plurality of instants of time while the wheel 1 moves on the rail 2,

[0031] • a memory 4 for storing the strain measurements obtained by the strain sensor during the plurality of instants of times, and

[0032] • a processor 5.

[0033] The processor 5 executes a process comprising the following steps: o reading the strain measurements stored in the memory 4, and o calculating the wheel-rail contact forces Y, T, and Q and the wheel-rail contact position p based on the strain measurements stored in the memory 4.

[0034] Preferably, as depicted in the flow diagram of Figure 3, the processor 5 may calculate a set of key features from the strain measurements retrieved from the memory 4, and calculate the wheel-rail contact forces Y, T, and Q and the wheel-rail contact position p based on said key features.

[0035] The processor 5 may be a controller, microcontroller, FPGA or any other computationally capable device.

[0036] The processor 5 is operable with the data acquisition device 3 and the processor 5 may comprises one or more processors and a memory for storing instructions that, when executed by the one or more processors, cause the controller to perform the aforementioned steps. In an example, the key features may be coefficients of orthogonal functions obtained along the rotation of the wheel 1 on the rail 2. For example, the orthogonal functions can be selected from Fourier series, harmonic functions, or Chebyshev polynomials. These examples are provided by way of illustration, and they are not intended to be limiting of the present invention.

[0037] Said key features may be the coefficients of the harmonics of Fourier Series along the rotation of the wheel 1 on the rail 2. For example, the key features may be the first, second and third harmonic. The number of harmonics obtained depends on the weight of the harmonics and the accuracy required by the system which depends on the wheel and measuring point where the strain sensor is arranged.

[0038] Said key features are used to obtain a system of equations depending on the wheel-rail contact forces Y, T, and Q and the wheel-rail contact position p, and by solving said system of equations the wheel-rail contact forces and the wheel-rail contact position are obtained.

[0039] In any case, other methods can be used for obtaining the system of equations, as for example Lebesgue coefficients or Artificial Neural Networks or other type of equation obtain from the stain measurements.

[0040] Preferably, the strain sensor measures the strain measurements during a whole round of the wheel 1 on the rail 2 assuring a low energy consumption system. In other examples, the system may be active during a different number of wheel turns.

[0041] The invention further proposes a method for measuring wheel-rail contact forces and the wheel-rail contact position, the method comprising:

[0042] • using a data acquisition device 3 comprising at least one strain sensor attached to a railway wheel 1 , the strain sensor measuring strain measurements of the wheel 1 in a plurality of instants of time while the wheel 1 moves on the rail 2,

[0043] • storing in a memory 4 the strain measurements obtained by the strain sensor during the plurality of instants of times, and

[0044] • executing a process comprising the following steps: o reading the strain measurements stored in the memory 4, and o calculating the wheel-rail contact forces Y, T, and Q and the wheel-rail contact position p based on the strain measurements stored in the memory. Preferably, the process comprises calculating a set of key features from the strain measurements retrieved from the memory 4, and calculating the wheel-rail contact forces Y, T, and Q and the wheel-rail contact position p based on said key features calculated in the previous step.

[0045] The data acquisition device 3 may comprise one strain sensor or two strain sensors attached to the railway wheel 1 , the one strain sensor or the two strain sensors measuring strain measurements of the wheel 1 in a plurality of instants of time while the wheel 1 moves on the rail 2.

[0046] According to a first example of the invention, shown in Figure 2a, the data acquisition device 3 consists of a single strain sensor connected in a quarter bridge circuit configuration.

[0047] According to said first example, the strain sensor measures at least 16 strain measurements during a whole round of the wheel 1 on the rail 2.

[0048] According to a second example of the invention, shown in Figure 2b, the data acquisition device 3 consists of two strain sensors. Each strain sensor may be connected in a respective independent quarter bridge configuration, like the first example, or the two strain sensors may be connected in a half bridge configuration.

[0049] According to said second example, the two strain sensors measures at least 16 strain measurements during a half round of the wheel 1 on the rail 2.

[0050] Preferably, the strain sensor is a strain gauge.

[0051] According to all of this, a strain sensor obtains several strain measurements of the wheel 1 in a plurality of instants of time tk, tk+1, tk+2, ... tk+N, wherein each strain measurement is dependent on the wheel-rail contact forces Y, T, and Q and the point p where these forces are applied, so each strain measurement is obtained in a different instant of time.

[0052] For example, the forces may be expressed according to the following expression: Preferably, the strain measurements are obtained during a whole round of the wheel 1 on the rail 2 or less. The strain measurements can be obtained during more than one wheel revolution, but periodicity may be lost and the forces may be calculated less accurately.

[0053] A set of key features is obtained for each strain measurement, and a system of equations is obtained with said key features, wherein each equation correspond to a key feature and is dependent on the wheel-rail contact forces Y, T, and Q and the point p where these forces are applied, thus, by solving said system of equations the wheel-rail contact forces, and the wheelrail contact position may be estimated.

[0054] Said key features are coefficients of orthogonal functions. Preferably, said key features are coefficients of the harmonics of Fourier Series, however, this is not limitative and other coefficients of orthogonal functions may be used to obtain a system with enough equations to estimate the forces, and the wheel-rail contact position.

[0055] Two non-limiting examples for calculating forces using Fourier’s series are shown below.

[0056] Example 1 :

[0057] The following is a non-limitative example of a system, according to Figure 2a, comprising a data acquisition device 3 with a single strain sensor attached to the wheel 1 for calculating the wheel-rail contact forces Y, T, Q and the wheel-rail contact position p based on the stain measurements obtained by said single strain sensor.

[0058] The strain measurement s obtained with the strain sensor is dependent on the wheel-rail contact forces and the point where these forces are applied, according to the following expression: where: s is the strain in the measured point of the wheel 1 , f is the longitudinal wheel-rail contact force T, f2is the lateral wheel-rail contact force Y, f3is the vertical wheel-rail contact force Q, y is the lateral position of the contact position p between the wheel 1 and the rail 2, and <p is the angle rotated by the wheel 1 which is the angle between a first segment defined between the centre c of the wheel 1 and contact position p and a second segment defined between the wheel 1 and the strain sensor 3. (See Figure 2)

[0059] The strain measurements are measured in a plurality of instants of time, being the different strain measurements obtained at said plurality of instants of time stored in the memory 4.

[0060] The influence of the contact position p between the wheel 1 and the rail 2 can be transformed into an equivalent torque f4due the Saint-Venant Principle obtaining the following expression:

[0061] S = S( 2, / 3 <P) where4is the torque that includes the effect of the contact position p change.

[0062] The wheel behaves as an elastic material so the strain measurements may be represented according to the following equation (1): where are the elastic influence coefficients EIC, which are periodic functions of the wheel rotation angle p and j is an index related to the wheel-rail contact forces (j)1...3) and torque (j=4).

[0063] The elastic influence coefficients EIC are known coefficients previously calculated. Said coefficients depend on the wheelset and for example may be obtained by finite elements, or experimentally on a calibration bench.

[0064] Consequently, the elastic influence coefficients aj may be written through Fourier Series FS according to the following equation (2): where <p e [0,2TT] is the angle rotated by the wheel. h is an index related to the harmonic index of the Fourier Series and H is the maximum number of harmonics considered in the Fourier Series. For example, the maximum number H is limited by the number of measurements taken by the strain sensor in a whole rotation of the wheel. For example, if 16 strain measurements are taken H maximum is 4.

[0065] For s(t) and / (t) a Fourier series FS along one-wheel rotation is obtained according to the following equations

[0066] Combining equations (2) to (4) into equation (1), the following equation 5 is obtained: where m and and n are summation indices ranging from 1 to the maximum number of harmonics considered H. By expanding the equation (5), the following equation (6) is obtained:

[0067] Multiplying equation (1) by cos kep and integrating between a whole wheel rotation 0 and 2n (and doing the same, but multiplying by sin kep), the following equations (8) are obtained: where k are Fourier coefficients between 0 and 8 (K=1 , K=2, K=3 y K=4, K=5,... y K=8) and where Lkmn, Mkmn, Nkmnand Pkmnare values that may be calculated for the different values of k,m,n according to the following equations (9) to (12):

[0068] Therefore, the following equations (13) and (14) allow to calculate the wheel-rail contact forces and the wheel-rail contact position:

[0069] In the simplified case where the wheel-rail contact forces are assumed to be constant during one revolution, the following equations are obtained:

[0070] Sfc

[0071] Sfc

[0072] Expanding the above equations, the following key features are obtained, where N is the number of harmonics taken into account.

[0073] Said key features allows to obtain a system of equations which are formed based on the previously calculated influence coefficients akjand the unknown / i, / 2, / 3, and / 4which are the wheel-rail contact forces and the wheel-rail contact position to be estimated.

[0074] Said key features are coefficients of the harmonics of Fourier Series skand skwhich are obtained from the strain measurements in the time domain performing a DFT (Discrete Fourier Transform). As indicated before, the coefficients djkand ajkare independent of the applied forces (due to the linear behavior of the material of the wheel and rail) and can be precalculated (via finite element method FEM or by experimental fitting).

[0075] In order to obtain the wheel-rail contact forces and the wheel-rail contact position fjQit is necessary to take into account a sufficient number of harmonics to obtain a resoluble system equation. Obviously, the number of harmonics can be bigger obtaining an overdetermined system of equations. These systems can be solved by standard mathematical methods like for example the Penrose pseudoinverse matrix.

[0076] Example 2

[0077] The following is another non-limitative example of a system, according to figure 2b, comprising a data acquisition device 3 with two strain sensors attached to the wheel 1 for calculating the wheel-rail contact forces Y, T, Q and the wheel-rail contact position p based on the strain measurements obtained by said two strain sensors.

[0078] The strain measurements are measured in a plurality of instants of time, being the different strain measurements obtained at said plurality of instants of time stored in the memory 4. In this example, the strain measurements of the two strain sensors are also stored in the memory 4.

[0079] Same method as example 1 is applied to calculate the wheel-rail contact forces and the wheelrail contact position, but in this case, the equations show the super index term r, where r = 1 denotes the strain measurement obtain with the first strain sensor and r = 2 denotes the strain measurement obtained with the second strain sensor.

[0080] Following the example 1 of a single strain sensor, the wheel behaves as an elastic material so the strain measurements obtained by said two strain sensors may be represented according to the following equation (17):

[0081] N sr( = ^ fj aj (<p) ; j = 1 ...4; r = 1,2 (17) j

[0082] In this second example, the elastic influence coefficient aj(<p) are different for ; r = 1 and r = 2 as long as the radial positioning of the strain sensor on the wheel 1 are different. The elastic influence coefficients aj are periodic functions of the rotation angle <p and may be written through Fourier Series FS according to the following equation (18): 1,2. (18)

[0083] For s(t) and )(t) a Fourier Series FS along one-wheel rotation is adopted, according to the following equations (19) and (20):

[0084] Following the same mathematical treatment as explained for example 1 , the following equations (21) and (22) are obtained In the case where that only the mean values of the forces during one whole rotation is seek the following equations (23) and (24) are obtained: 1,2

[0085] (23) 1,2 (24) Expanding the above equations, the following key features are obtained, where N is the number of harmonics taken into account.

[0086] As it can be observed, for the same number of harmonics taken into account (N), the number of equations is doubled with respect to example 1 , thus the system is more accurate but another strain sensor is required to be employed. It can be seen that the equations corresponding to the first strain sensor are the same equations obtained in the example 1 for the single strain sensor.

[0087] The system of equations may be solved in the same way that in example 1 , for example using the Penrose pseudoinverse matrix.

[0088] As indicated above, instead of the Fourier series FS used in the previous examples 1 or 2, other orthogonal functions may be applied for calculating the wheel-rail contact forces Y, T, and Q and the wheel-rail contact position p, as explained below.

[0089] The strain measurement srobtained with a strain sensor r during a wheel rotation p e [0,27r],of the wheel 1 , which is dependent on the wheel-rail contact forces f2, and the wheel-rail contact position fa where these forces are applied, may be expressed according the following equation (25):

[0090] Where p is the angle rotated by the wheel 1, fj are the wheel-rail contact forces Y, T, and Q and the wheel-rail contact position p, aj(<p) are the elastic influence coefficients EIC, f>cis the angular position of the strain sensor r, measured with respect to the radius for which p is 0, and rcis its radial position.

[0091] In order to estimate the forces at the wheel-rail contact throughout a wheel rotation p e [0,2TT] , a set of orthogonal functions bjn(<p) may be adopted. Through these functions, the forces at the contact may be estimated according to the following equation (26): where qjnare the key features that allow to obtain a system of equations for calculating the wheel-rail contact forces Y, T, Q and the wheel-rail contact position p. Said key features are the coefficients of the orthogonal functions.

[0092] Therefore, based on this approach, the coefficients are calculated in a way that minimizes the difference between the strain measurement srand the estimated one from according to the following equation (27).

[0093] Examples of orthogonal functions are Fourier series, harmonic functions, Chebyshev polynomials, among others.

Claims

CLAIMS1. System for measuring wheel-rail contact forces and the wheel-rail contact position, the system comprising:• a data acquisition device (3) comprising at least one strain sensor attached to a railway wheel (1), the strain sensor measuring strain measurements of the wheel (1) while the wheel (1) moves on the rail (2), each strain measurement is dependent on the wheelrail contact forces and the point where these forces are applied,• a memory (4) for storing the strain measurements obtained by the strain sensor, and• a processor (5) that executes a process comprising the following steps: o reading the strain measurements stored in the memory (4), and o calculating the wheel-rail contact forces (Y, T, Q) and the wheel-rail contact position (p) based on the strain measurements stored in the memory (4), characterized in that the strain sensor obtains several strain measurements (s) of the wheel (1) in a plurality of instants of time, and the wheel rail contact forces (Y,T, Q) and the lateral position of the contact position (p) between the wheel (1) and the rail (2) are calculated based on the strain measurements (s) obtained by the strain sensor during the plurality of instants of time, such that the strain sensor obtains several strain measurements in a plurality of instants of time instead of using several strain sensors that obtain several strain measurements in a single instant of time.

2. System according to claim 1 , wherein the processor (5): o calculates a set of key features from the strain measurements retrieved from the memory (4), and o calculates the wheel-rail contact forces (Y, T, Q) and the lateral position of the contact position (p) between the wheel (1) and the rail (2) based on said key features calculated in the previous step.

3. System according to claim 2, wherein the key features are the coefficients of orthogonal functions obtained along the rotation of the wheel (1) on the rail (2).

4. System according to claim 3, wherein the orthogonal functions can be selected from Fourier series, harmonic functions, or Chebyshev polynomials.

5. System according to claim any of the preceding claims, wherein the strain sensor measures the strain measurements during a whole round of the wheel (1) on the rail (2).

6. System according to claim 5, wherein the data acquisition device (3) consists of a single strain sensor connected in a quarter bridge circuit configuration.

7. System according to claim 6, wherein the strain sensor measures at least 16 strain measurements during a whole round of the wheel (1) on the rail (2).

8. System according to claim 5, wherein the data acquisition device (3) consists of two strain sensors, and wherein each strain sensor is connected in a respective independent quarter bridge configuration, or the two strain sensors are connected in a half bridge configuration.

9. System according to claim 8, wherein the two strain sensors measure at least 16 strain measurements during a half round of the wheel (1) on the rail (2).

10. Method for measuring wheel-rail contact forces and the wheel-rail contact position, the method comprising:• using a data acquisition device (3) comprising at least one strain sensor attached to a railway wheel (1), the strain sensor measuring strain measurements of the wheel (1) while the wheel (1) moves on the rail (2), each strain measurement is dependent on the wheel-rail contact forces and the point where these forces are applied• storing in a memory (4) the strain measurements obtained by the strain sensor, and• executing a process comprising the following steps: o reading the strain measurements stored in the memory (4), and o calculating the wheel-rail contact forces (Y, T, Q) and the wheel-rail contact position (p) based on the strain measurements stored in the memory, characterized in that the strain sensor obtains several strain measurements (s) of the wheel (1) in a plurality of instants of time, and the wheel rail contact forces (Y,T, Q) and the lateral position of the contact position (p) between the wheel (1) and the rail (2) are calculated based on the strain measurements (s) obtained by the strain sensor during the plurality of instants of time, such that the strain sensor obtains several strain measurements in a plurality of instants of time instead of using several strain sensors that obtain several strain measurements in a single instant of time.

11. Method according to claim 10, wherein the process comprises: o calculating a set of key features from the strain measurements retrieved from the memory (4), and o calculating the wheel-rail contact forces (Y, T, Q) and the lateral position of the contact position (p) between the wheel (1) and the rail (2) based on said key features calculated in the previous step.

12. Method according to according to claim 11 , wherein the key features are the coefficients of orthogonal functions obtained along the rotation of the wheel (1) on the rail (2).

13. Method according to any of claims 10 to 12, wherein the strain measurements are measured during a whole round of the wheel (1) on the rail (2).

14. Method according to claim 13, wherein at least 16 strain measurements are obtained during a whole round of the wheel (1) on the rail (2) using a single strain sensor connected in a quarter bridge circuit configuration.

15. Method according to claim 13, wherein at least 16 strain measurements are obtained during a whole round of the wheel (1) on the rail (2) using two strain sensors, and wherein each strain sensor is connected in a respective independent quarter bridge configuration, or the two strain sensors are connected in a half bridge configuration

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