Method for estimating the speed of a rail vehicle and associated inertial measurement unit - Patents.com

Abstract

The invention relates to a method for estimating the speed of a rail vehicle (100), the rail vehicle (100) being equipped with an inertial measurement unit (1) configured to receive GNSS signals related to a satellite navigation system, the method comprising: analyzing (1031) the received GNSS signals in order to determine a reliability of these GNSS signals; defining a measurement vector comprising measurements obtained by the inertial measurement unit; defining a state vector comprising a component related to the speed of the vehicle, a component related to the attitude of the vehicle and a component related to bias errors in the angular velocity measurements and bias errors in the acceleration measurements; applying (1035) a state estimator to estimate a state vector using the measurement vector; correcting an estimate of the state vector based on the GNSS signals and depending on the determined reliability of these GNSS signals; and extracting from the corrected state vector the speed of the rail vehicle and an error related to the speed of the rail vehicle (100).

Description

[Technical field]

[0001] The present invention relates to an inertial measurement unit and a method for estimating the speed of a rail vehicle by combining inertial measurements with signals from a satellite navigation system.

[0002] It is important for rail fleet management companies to know the position and speed of their trains as accurately and reliably as possible, since knowing the exact position and speed of trains allows them to better organize their operations and thus improve the management of the rail track.

[0003] Various techniques are used in the prior art to determine the speed of rail vehicles, for example tachometers, Doppler radar, accelerometers, GNSS measuring instruments (particularly GPS signals) or beacons regularly placed on the railway track. GNSS is the acronym for Global Navigation Satellite System and GPS for Global Positioning System. However, all these various solutions have drawbacks that limit the reliability of the measurements (slip of the wheels on the rail in the case of tachometers, low reliability in the presence of fog in the case of Doppler radar, drift over time in the case of accelerometers, lack of GNSS reception in tunnels and areas surrounded by steep slopes in the case of GNSS devices, difficult installation and possible deterioration in the case of beacons). However, the safety of train passengers depends on this speed determination, so the reliability of the measurements is a decisive factor.

[0004] There is therefore a need to provide a solution that makes it possible to obtain a reliable estimate of the speed of a rail vehicle, independent of weather conditions and the topology of the rail track.

[0005] To this end, the invention relates to a method for estimating the speed of a railway vehicle during its movement along a railway track, said railway vehicle being equipped with an inertial measurement unit, said inertial measurement unit comprising: Acceleration measurements along three orthogonal axes, Angular velocity measurements about three orthogonal axes, Provide The method is configured to receive GNSS signals associated with a satellite navigation system, the method comprising: - analyzing the received GNSS signals to determine the reliability of said GNSS signals; - defining a measurement vector comprising measurements provided by an inertial measurement unit; defining a state vector including a component related to the speed of the vehicle, a component related to the attitude and orientation of the vehicle (roll, pitch and yaw) and a component related to bias errors in the measurements of acceleration and bias errors in the measurements of angular velocity, applying a state estimator to estimate a state vector using the measurement vector; - correcting the estimate of the state vector based on the GNSS signal and depending on the determined reliability of said GNSS signal, Extracting from the corrected state vector the speed of the rail vehicle and an error related to said speed of the rail vehicle. The present invention relates to a method comprising the steps of:

[0006] If the GNSS signals are deemed reliable, then fusion of the inertial and GNSS signals can be used to determine the vehicle's speed and the error associated with this speed.

[0007] According to another aspect of the invention, determining the reliability of the GNSS signal includes considering the number of satellites providing the signal and the positions of said satellites.

[0008] According to another aspect of the invention, the method includes correcting the alignment between a reference frame associated with the inertial measurement unit and a reference frame associated with the rail vehicle.

[0009] According to another aspect of the invention, the state vector also includes a component related to a misalignment between a reference frame associated with the inertial measurement unit and a reference frame associated with the rail vehicle, whereby the misalignment is recursively estimated by the state estimator.

[0010] According to another aspect of the invention, the method also includes storing errors associated with misalignment between a reference frame associated with the inertial measurement unit and a reference frame associated with the railway vehicle in a memory of the inertial measurement unit for use during a reset of the estimator, particularly when the inertial measurement unit is turned on after being turned off.

[0011] According to another aspect of the invention, the state vector includes 15 components, namely, three components related to the speed of the rail vehicle, three components related to the attitude of the rail vehicle, three components related to bias errors in the angle measurements, three components related to bias errors in the acceleration measurements, and three components related to misalignment between the reference frame associated with the inertial measurement unit and the reference frame associated with the rail vehicle.

[0012] According to another aspect of the invention, the state estimator is a Kalman filter.

[0013] According to another aspect of the invention, the Kalman filter is an extended Kalman filter.

[0014] According to another aspect of the invention, an error related to the speed of the rail vehicle is determined based on a covariance of the state errors provided by a Kalman filter.

[0015] According to another aspect of the invention, the method includes a static initialization step during start-up of the rail vehicle that allows initialization of a mechanism that determines the direction of travel of the rail vehicle while the rail vehicle transitions from a static position to a travel position.

[0016] According to another aspect of the invention, the step of applying the state estimator includes applying a constraint at the center of rotation of the rail vehicle related to zero speed along the transverse axis.

[0017] According to another aspect of the invention, the method includes a validation step making it possible to exclude anomalous or incompatible estimated speeds.

[0018] According to another aspect of the invention, if the GNSS signals are detected to be unreliable, the length of time that the GNSS signals are considered to be unreliable is measured and stored in memory for a predetermined time, and this length of time is used to determine the error associated with measuring the speed of the railway vehicle.

[0019] According to another aspect of the invention, the estimation is performed more frequently than the reception of the GNSS signals.

[0020] The present invention also provides an inertial measurement unit for a railway vehicle, the inertial measurement unit comprising: an accelerometer configured to provide measurements of acceleration along three orthogonal axes; a gyrometer configured to provide angular measurements about three orthogonal axes; A module for receiving GNSS signals related to a satellite navigation system; A processing unit, the processing unit comprising: Analysing the received GNSS signals and determining the reliability of said GNSS signals; Take measurements provided by the accelerometer and gyrometer; applying a state estimator to estimate a state vector based on the obtained measurements, the state vector comprising a component related to the speed of the rail vehicle, a component related to the attitude of the rail vehicle and a component related to a bias error in the angle measurements and a bias error in the acceleration measurements; - correcting the estimate of the state vector based on the GNSS signal and in response to the determined reliability of said GNSS signal; Extracting from the corrected state vector the speed of the rail vehicle and the error associated with said speed of the rail vehicle. The present invention relates to an inertial measurement unit configured to:

[0021] According to another aspect of the invention, the inertial measurement unit also includes, after the step of correcting the estimate of the state vector, determining a velocity error based on a covariance of the error in the state of the state estimator and a value of the reliability of the GNSS signal over a predetermined period of time prior to the determining step.

[0022] Other characteristics and advantages of the invention will become more apparent on reading the following description, given by way of illustrative and non-limiting example, and from the accompanying drawings, in which: [Brief description of the drawings]

[0023] [Figure 1] FIG. 1 is a top view of a rail vehicle equipped with an inertial measurement unit. [Diagram 2] 1 is a schematic diagram of an inertial measurement unit according to the present invention; [Figure 3a] FIG. 1 is a side view of a rail vehicle equipped with an inertial measurement unit and a GNSS antenna. [Figure 3b] FIG. 1 is a front view of a rail vehicle equipped with an inertial measurement unit and a GNSS antenna. [Figure 4] FIG. 1 is a schematic perspective view of a rail vehicle and the various reference frames used; [Diagram 5] 3 is a flow chart of method steps for estimating the speed of a rail vehicle. [Figure 6] 6 is a flow chart of the various sub-steps of application of the state estimator of the method of FIG. 5 .

[0024] In these figures, identical elements are given the same reference numbers.

[0025] The following embodiments are examples. Although the description refers to one or more embodiments, this does not necessarily mean that each reference relates to the same embodiment or that these features apply to one embodiment. Individual features of various embodiments may be combined or exchanged to provide other embodiments.

[0026] In this specification, certain elements or parameters may be subscripted, e.g., as a first element or a second element, or a first parameter and a second parameter, or a first criterion and a second criterion, etc. In this case, the subscript may be used to distinguish and indicate similar but non-identical elements or parameters or criteria. This subscripting does not imply a priority of one element, parameter or criterion over other elements, parameters or criteria, and such designations may be readily interchanged without departing from the scope of this specification. Nor does this subscripting imply, for example, a chronological order for evaluating such criteria or such criteria.

[0027] The invention relates to an inertial measurement unit for a rail vehicle. By rail vehicle is meant here any vehicle moving on one or more guide rails. Figure 1 shows an example of a rail vehicle 100, for example a train comprising a locomotive and several cars (two cars in the example of figure 1), moving on rails and equipped with an inertial measurement unit 1 according to the invention. The invention is however not limited to this configuration of the rail vehicle 100, in particular a different number of cars may be used. However, in the context of the invention, the rail vehicle 100 relates to a locomotive equipped with an inertial measurement unit 1, since the position of these cars depends directly on the position of the locomotive. A system of axes X, Y, Z associated with the rail vehicle 100 is also shown in figure 1. The X axis corresponds to the axis of advance of the rail vehicle 100, the Z axis corresponds to the vertical direction when the rail vehicle 100 is on a horizontal rail, and the Y axis completes the system of axes and may be related to the roll, yaw and pitch axes of the rail vehicle 100.

[0028] 2 shows a schematic diagram of an inertial measurement unit 1 according to an example embodiment of the invention. A system of axes X', Y', Z' associated with the inertial measurement unit 1 is shown in FIG.

[0029] The inertial measurement unit 1 comprises an accelerometer 3 arranged to provide measurements of acceleration along three orthogonal axes corresponding to the three axes X', Y' and Z' of a system of axes associated with the inertial measurement unit 1. The measurements are provided by three accelerometers, for example designated 3x, 3y and 3z, which are oriented along the three axes X', Y' and Z' respectively.

[0030] The inertial measurement unit 1 comprises a gyrometer 5 arranged to provide measurements of angular velocity about three orthogonal axes corresponding to the three axes X', Y' and Z' of a system of axes associated with the inertial measurement unit. These measurements are provided, for example, by three gyrometers designated 5x, 5y and 5z, which are oriented along the three axes X', Y' and Z', respectively.

[0031] The inertial measurement unit 1 also comprises a GNSS module 7 for receiving geolocation and navigation signals from a satellite system associated with the satellite navigation system. In practice, the GNSS module 7 may be arranged at least partially outside the inertial measurement unit 1, in particular the GNSS antenna 70 may be arranged on top of the rail vehicle 100 to facilitate good reception of GNSS signals, as shown in Figures 3a and 3b. In this case, the GNSS antenna 70 is connected to the GNSS module of the inertial measurement unit 1 via a wired or wireless connection.

[0032] The GNSS module 7 is thus configured to receive signals from the satellites, making it possible to determine the position and the movement speed of the GNSS antenna 70. The GNSS antenna 70 is configured, for example, to send and receive electromagnetic waves in a predetermined frequency range. The position and speed information is obtained, for example, by triangulation based on the signals exchanged by the four satellites. The GNSS signals from the satellites are received at a first predetermined frequency, for example 5 Hz.

[0033] The inertial measurement unit 1 also comprises a processing unit 9. The processing unit 9 comprises, for example, a microcontroller or microprocessor with ROM or RAM.

[0034] The processing unit 9 is configured to analyze the GNSS signals received by the GNSS module 7 and to determine the reliability of the aforementioned GNSS signals. The GNSS signals, which include for example the number of satellites from which the signals originate, the positions of these satellites (used to determine the accuracy or DOP reduction) and whether multipath signals are present, are analyzed by the processing unit 9. Depending on the result of this analysis and the estimated reliability of the received GNSS signals, the GNSS signals are taken into account or not in the speed estimation performed by the inertial measurement unit 1. Furthermore, if after the analysis of the received GNSS signals the GNSS signals are deemed unreliable, a timer is triggered to measure the length of time during which the GNSS signals are deemed unreliable. This length of time is stored in memory for a predetermined time. The time during which the GNSS signals are deemed unreliable for a predetermined time before the estimation is then taken into account in the estimation of the error associated with the measurement of the speed of the rail vehicle, which will be better explained in the remaining description.

[0035] The processing unit 9 is also configured to obtain the acceleration measurements and angular velocity measurements provided by the accelerometer 3 and the gyrometer 5 .

[0036] Based on the measurements provided by the accelerometer 3 and the measurements provided by the gyrometer 5, the processing unit 9 is configured to apply a state estimator to estimate, based on the measurements obtained, a state vector that includes a component related to the speed of the railcar 100, a component related to the attitude of the railcar 100 (i.e. the orientation of the railcar given by the roll, pitch and yaw angles) as well as a component related to bias errors in the measurements of angles and bias errors in the measurements of acceleration. The processing unit 9 is also configured to correct, based on the GNSS signals provided, if the GNSS signals are considered sufficiently reliable, the estimation of the state vector, so that the speed of the railcar 100 and the errors related to said speed of the railcar 100 can be extracted from the corrected state vector. The state vector is estimated, for example, using a Kalman filter, in particular an extended Kalman filter. This filtering makes it possible to fuse the measurements output by the accelerometer 3, the measurements output by the gyrometer 5 and, possibly, if their reliability is sufficient, the measurements output by the GNSS module 7. This filtering also allows the error associated with the estimated speed of the rail vehicle 100 to be determined from the covariance of the error in the states provided by the Kalman filter.

[0037] The state estimator is applied recursively at a second predetermined frequency which may be greater than the first predetermined frequency, for example greater than twice the first predetermined frequency, for example 50 Hz (i.e. 10 times the first predetermined frequency).

[0038] The processing unit 9 is also configured to take into account constraints related to the movement of the rail vehicle 100 in the state estimator, for example constraints related to zero speed in the transverse axis of the rail vehicle 100 at the centre of rotation (denoted CR in Figures 3a and 3b showing the side and front views of the rail vehicle 100 with the inertial measurement unit 1 and the remote GNSS module 7) of the rail vehicle 100. Thus, by taking into account these constraints, the observability of the system can be improved by increasing the number of measurements without increasing the number of sensors, in other words without increasing the cost of the device.

[0039] The processing unit 9 also has a self-diagnosis function that rejects abnormal values ​​obtained by the state estimator, for example a speed higher than the maximum speed of the railway vehicle 100, or an excessive speed difference between two successive estimated values ​​(the maximum difference may be asymmetric depending on the maximum acceleration and braking forces), or excessive roll or pitch that is not consistent with commonly encountered track topologies.

[0040] The processing unit 9 is also configured to detect and correct misalignments between the reference frame X'Y'Z' associated with the inertial measurement unit 1 and the reference frame XYZ associated with the rail vehicle 100, thereby ensuring a certain self-alignment by estimating recursively over time by a state estimator the misalignment between the reference frame X'Y'Z' associated with the inertial measurement unit 1 and the reference frame XYZ associated with the rail vehicle 100. This self-alignment allows the inertial measurement unit 1 to be placed anywhere on the rail vehicle 100, not necessarily at the center of rotation CR of the rail vehicle 100.

[0041] Furthermore, the processing unit 9 may be configured to store in an internal memory or in a memory of the inertial measurement unit 1 an estimate of the misalignment between the reference frame X'Y'Z' associated with the inertial measurement unit 1 and the reference frame XYZ associated with the rail vehicle 100. This stored estimate may be used as an initial value when the state estimator is reset, in particular when the inertial measurement unit 1 is turned on after having been turned off.

[0042] Thus, by using an inertial measurement unit 1 configured to fuse the three-axis acceleration measurements provided by the accelerometer 3, the three-axis angular velocity measurements provided by the gyrometer 5 and the GNSS data provided by the GNSS module 7 to estimate the reliability of the GNSS data and the misalignment between the orientation of the sensor and the orientation of the railway vehicle 100, it is possible to provide a reliable estimate of the speed of the railway vehicle 100 and an estimate of the error associated with this speed.

[0043] The invention also relates to a method for estimating the speed of a rail vehicle 100 during its movement along a rail track. The rail vehicle 100 is notably equipped with an inertial measurement unit 1 as described above.

[0044] The various steps of the method are described with reference to the steps of the flowchart in Figure 5. Some of the steps presented may be optional and the order of the steps may differ from that presented.

[0045] The first step 101 is a pre-initialization step carried out in a stationary state at the start of the rail vehicle 100. This step 101 has a limited duration, for example 15 seconds, and makes it possible in particular to initialize the sensors in order to be able to subsequently determine the direction of movement (forward or reverse) of the rail vehicle 100.

[0046] The second step 102 is a second preliminary step of updating various timers that allow monitoring the passage of time.

[0047] The third step 103 concerns the application of a state estimator that allows the determination of the speed of the rail vehicle 100 and the uncertainty or error associated with this speed. This third step 103 includes a number of sub-steps that are described in detail in the remainder of this specification.

[0048] A fourth step 104 concerns obtaining the value of the misalignment between the reference frame associated with the inertial measurement unit 1 and the reference frame associated with the rail vehicle 100, estimated in step 103, and storing this value in a memory, for example a flash memory. This stored value is read out when the inertial measurement unit 1 is switched on, so that it is possible to resume from the last estimation made before the inertial measurement unit 1 was switched off. Such storage provides a fast convergence of the misalignment value, which may take several hours to converge if there is no initial value, and ensures that an accurate speed estimation is obtained as soon as the inertial measurement unit 1 is switched on.

[0049] A fifth step 105 concerns the provision of output data, in particular the speed of the rail vehicle 100 and the associated uncertainty estimated in step 103. Depending on the customer's needs, other data estimated in step 103 can also be extracted and provided. The provision corresponds for example to the transmission of a data signal to the cockpit of the rail vehicle 100.

[0050] Next, step 103 will be described in detail with reference to the flowchart of FIG.

[0051] A first sub-step 1031 concerns the analysis of the GNSS signals received by the GNSS module 7, whereby it is determined whether the reliability of the GNSS signals is sufficient to be taken into account in the determination of the speed of the rail vehicle 100. This analysis takes into account the number of satellites from which the signals originate, the position of the satellites from which the signals originate (used to determine the accuracy or DOP reduction) or the fact that the received signals are in particular reflected from the terrain around the rail vehicle 100 (multipath). All these parameters are taken into account to determine the reliability of the supplied GNSS signals. This determined reliability may be compared with a predefined threshold. If the determined reliability is lower than the predefined threshold, the GNSS signals are not taken into account in the estimation of the speed of the rail vehicle 100, in which case only the accelerometer measurements and the gyrometer measurements are used. If the determined reliability is higher than the predefined threshold, the GNSS signals are taken into account, i.e. they are fused with the accelerometer 3 measurements and the gyrometer 5 measurements in the estimation of the speed of the rail vehicle 100. The GNSS signals make it possible to estimate the speed of the rail vehicle 100 and the error in this speed.

[0052] A second substep 1032 concerns the analysis of the movements and vibrations of the rail vehicle 100, using the accelerometers 3 and gyrometers 5, in order to determine whether the rail vehicle 100 is stationary or moving, and further the direction of movement (forward or backward) of the rail vehicle 100. This makes it possible to stop the estimation, in particular when the rail vehicle 100 is stationary and no GNSS signals are received, for example when stopped in an underground station. Stopping the estimation in such cases makes it possible to avoid instabilities of the state estimator, which may give rise to erroneous estimations.

[0053] A third sub-step 1033 concerns the measurement of the length of time during which the GNSS signals are considered unreliable. The length of time during which the GNSS signals are considered unreliable over a predefined time interval is stored in a memory and used to calculate the uncertainty related to the speed of the rail vehicle 100. This predefined time interval corresponds, for example, to several minutes or tens of minutes. In particular, when the GNSS signals are not taken into account, the speed estimation is performed based only on the inertial measurements, i.e. the measurements of the accelerometer 3 and the measurements of the gyrometer 5, so that the uncertainty related to the estimation of the speed of the rail vehicle 100 increases over time until the GNSS signals are again reliable. If the GNSS signals are alternately considered reliable and unreliable, it is necessary to know the history of the reliability of the GNSS signals over the previous moment or even the previous minutes, so that these GNSS signal instabilities can be taken into account in the calculation of the uncertainty in the speed of the rail vehicle 100.

[0054] A fourth sub-step 1034 concerns the detection of an anomaly in the calculation of the state estimator, corresponding for example to a saturation or a malfunction of the processing unit 9. If an anomaly is detected, the estimator is reset the next time it is detected in sub-step 1032 that the rail vehicle 100 has stopped.

[0055] A fifth sub-step 1035 concerns the updating of the state estimator based on the last measurements and possibly the GNSS signal if reliability is sufficient.

[0056] To do this, a state vector E is defined with 15 elements.

[0057]

number

number

number

number

[0058] An observation vector O with five components is also defined.

[0059]

number

number

number

number

number

number

[0060] The prediction at time k+1 is O(k+1)=f(O(k)) is defined by where f is

number

number

number

number

number

number

number

[0061] Next, the relationship

number

number

number

number

[0062] The inertial reference frame XiYiZi corresponds to an absolute reference frame whose origin is the center of the Earth and does not follow the Earth's rotation. Its axes point to stars that are far enough away that they appear fixed relative to the center of the Earth. Axis Xi points to the vernal equinox, axis Zi is parallel to the axis of rotation of the Earth, and axis Yi is orthogonal to Xi and Zi, completing the system of axes XiYiZi. It is necessary to use an inertial reference frame because the rotation of the Earth (relative to the inertial reference frame) is measured by the gyrometer 5 and therefore needs to be taken into account to estimate the speed of the rail vehicle 100.

[0063] The Earth reference frame XtYtZt has its origin at the center of the Earth, with axis Zt parallel to the Earth's axis of rotation, axis Xt pointing to the Greenwich meridian (longitude=0), and axis Yt perpendicular to Xt and Zt, completing the system with axes XtYtZt.

[0064] The measurement value of gyrometer 5 is

number

number

[0065] Next,

number

number

number

number

[0066] Accelerometer 3 measured

number

[0067] In order to establish a relationship between the estimated state parameters, the observation measurements provided by the GNSS module 7 and the speed relative to the center of rotation CR of the railway vehicle 100, a correction model h is defined which is used in the Kalman filter to transform (i.e. change the reference coordinate system) and transpose (i.e. change the origin) the speed estimated by the Kalman filter for a subsequent time period and compare it with the measured speed at this subsequent time period.

[0068] Y(k)=h(X(k)) The modified model h is

number

number

number

[0069] The update of the state estimator therefore includes a prediction phase in which the state of the system (in particular the speed of the railway vehicle 100) and the associated uncertainties are predicted based on the inertial measurements, i.e. the accelerometer 3 measurements and the gyrometer 5 measurements, and then a correction phase in which the estimate of the state of the system is corrected using a correction model, based on equations relevant to the railway application and on the data supplied by the GNSS module 7.

[0070] A sixth sub-step 1036 concerns the evaluation of the confidence interval of the speed estimate performed in sub-step 1035 .

[0071] The objective of this evaluation is to ensure that the estimated speed associated with the confidence interval meets the performance and safety criteria set by the railway standard, e.g., that the error between the actual speed and the estimated speed falls within the confidence interval 99.99% of the time, or that the confidence interval is narrower than the value set by the railway standard 99.9% of the time.

[0072] The confidence interval may be defined based on the uncertainty estimated by the Kalman filter. Alternatively, the confidence interval may be empirically determined based on a large number of measurements provided in various configurations. A curve, for example a polynomial, may be obtained by polynomial regression applied to all measurements. Furthermore, in both cases, a weighting factor may be applied depending on certain criteria, for example depending on whether or not convergence of the mismatch was obtained during the estimation.

[0073] According to a particular embodiment, the determination method uses a value estimated by a Kalman filter under certain conditions, for example when the signal provided by the GNSS module 7 is reliable, and an empirically obtained value when the signal provided by the GNSS module 7 is unreliable. In this embodiment, weighting factors may be applied.

[0074] The seventh sub-step 1037 concerns the validation of the estimates (states (including speed), uncertainties, confidence intervals of the speed). For this purpose, various tests are performed. The estimated dynamics are compared, for example, with the theoretical dynamics of the rail vehicle 100. Estimations of the errors of the sensors (accelerometer 3 and gyrometer 5) may be compared with the known sensor uncertainties.

[0075] The eighth sub-step 1038 concerns updating the estimated misalignment between the reference frame X'Y'Z' associated with the inertial measurement unit 1 and the reference frame XYZ associated with the rail vehicle 100 and calculating its uncertainty.

[0076] Thus, by using an inertial measurement unit 1 supplying three-dimensional measurements of acceleration and angular velocity coupled to a GNSS module, and by using an estimator that allows the measurements supplied by the inertial sensors and the measurements supplied by the GNSS module 7 to be fused if the GNSS signals are sufficiently reliable, an estimate of the speed of the rail vehicle 100 and an estimate of the error associated with this estimated speed can be obtained. Furthermore, by determining a confidence interval associated with the speed estimate, it is ensured that the measurements performed meet railroad standards. Finally, by determining the misalignment between the reference frame coupled to the inertial measurement unit 1 and the reference frame coupled to the rail vehicle 100, it is possible to place the inertial measurement unit 1 at any position on the rail vehicle 100.

Claims

1. 1. A method for estimating the speed of a rail vehicle (100) during movement of the rail vehicle (100) along a rail track, comprising: The railway vehicle (100) is equipped with an inertial measurement unit (1), and the inertial measurement unit (1) Acceleration measurements along three orthogonal axes; - Angular velocity measurements about three orthogonal axes; and and configured to receive GNSS signals associated with a satellite navigation system, the method comprising: - analyzing the received GNSS signals to determine the reliability of the GNSS signals (1031); - defining a measurement vector comprising the measurements provided by the inertial measurement unit; - defining a state vector including a component related to the velocity of the vehicle, a component related to the attitude of the vehicle and components related to bias errors in the acceleration measurements and bias errors in the angular velocity measurements; applying a state estimator to estimate the state vector using the measurement vector (1035); - modifying the estimate of the state vector based on the GNSS signals and in response to the determined reliability of the GNSS signals; extracting from the corrected state vector the speed of the rail vehicle and an error associated with the speed of the rail vehicle; The method includes:

2. The method of claim 1 , wherein determining the reliability of the GNSS signal includes considering the number of satellites providing the signal and the locations of the satellites.

3. 3. The method of claim 1, further comprising the step of correcting (1038) the alignment between a reference coordinate system (X'Y'Z') associated with the inertial measurement unit (1) and a reference coordinate system (XYZ) associated with the railway vehicle (100).

4. 4. The method of claim 3, wherein the state vector also includes a component related to a misalignment between the reference coordinate system (X'Y'Z') associated with the inertial measurement unit and the reference coordinate system (XYZ) associated with the rail vehicle (100), whereby the misalignment is recursively estimated by the state estimator.

5. 4. The method of claim 3, further comprising the step of: storing in a memory of the inertial measurement unit an error associated with the misalignment between the reference coordinate system (X'Y'Z') associated with the inertial measurement unit (1) and the reference coordinate system (XYZ) associated with the rail vehicle (100) for use during a reset of the estimator.

6. 3. The method of claim 1, wherein the state vector includes 15 components: three components related to the velocity of the rail vehicle, three components related to the attitude of the rail vehicle, three components related to the bias error in the angle measurements, three components related to the bias error in the acceleration measurements, and three components related to a misalignment between a reference frame associated with the inertial measurement unit and a reference frame associated with the rail vehicle.

7. 3. The method of claim 1, wherein the state estimator is a Kalman filter.

8. The method of claim 7 , wherein the Kalman filter is an extended Kalman filter.

9. The method of claim 7, wherein the error related to the velocity of the rail vehicle (100) is determined from a covariance provided by the Kalman filter.

10. 3. The method of claim 1, further comprising a static initialization step (101) during start-up of the railway vehicle (100) that allows initialization of a mechanism that determines the direction of movement of the railway vehicle (100) while the railway vehicle (100) transitions from a static position to a moving position.

11. 3. The method of claim 1, wherein the step of applying the state estimator comprises applying a constraint related to zero velocity along a lateral axis at the center of rotation of the rail vehicle.

12. 3. A method of estimating according to claim 1 or 2, comprising a validation step (1037) making it possible to exclude anomalous or incompatible estimated speeds.

13. 3. The method of claim 1, further comprising the steps of: if the GNSS signal is detected to be unreliable, measuring the length of time during which the GNSS signal is deemed unreliable and storing it in memory for a predetermined time; and using the length of time to determine the error associated with measuring the speed of the railway vehicle.

14. 3. The method of claim 1, wherein the estimation is performed more frequently than the reception of the GNSS signals.

15. An inertial measurement unit (1) for a railway vehicle (100), comprising: The inertial measurement unit an accelerometer (3) configured to provide measurements of acceleration along three orthogonal axes; a gyrometer (5) configured to provide angular measurements about three orthogonal axes; a module (7) for receiving GNSS signals related to a satellite navigation system; - a processing unit (9) comprising: - analyzing the received GNSS signals to determine the reliability of the GNSS signals; - obtaining the measurements provided by the accelerometer (3) and the gyrometer (5); applying a state estimator to estimate a state vector based on the acquired measurements, the state vector including a component related to the speed of the rail vehicle, a component related to the attitude of the rail vehicle, and components related to bias errors in the angle measurements and bias errors in the acceleration measurements; - modifying the estimate of the state vector based on the GNSS signals and in response to the determined reliability of the GNSS signals; Extracting from the corrected state vector the speed of the rail vehicle (100) and an error associated with the speed of the rail vehicle (100). An inertial measurement unit (1) configured as follows.

16. 16. The inertial measurement unit (1) of claim 15, further comprising, after the step of correcting the estimate of the state vector, a step of determining a velocity error based on a covariance of an error in the state of the state estimator and the value of the reliability of the GNSS signals over a predetermined period of time prior to the determining step.

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