METHOD FOR DETECTING A DEFECT IN AN ACCELERATION SENSOR, AND MEASURING SYSTEM

Abstract

A method detects a defect in an acceleration sensor. In order to be able to reliably detect a defect in an acceleration sensor, the acceleration sensor generates a signal which is checked during a test as to whether a variable dependent on the signal fulfills a predefined condition with respect to a reference value and, on the basis of the test, it is determined whether the acceleration sensor is defective.

Claims

1-15. (canceled)

16. A method for detecting a defect in an acceleration sensor, which comprises the steps of: generating, via the acceleration sensor, a signal; carrying out a test to check whether a variable dependent on the signal fulfills a predefined condition in respect of a reference value; and determining on a basis of the test whether the acceleration sensor is defective.

17. The method according to claim 16, wherein the variable is an acceleration determined on a basis of the signal.

18. The method according to claim 16, wherein the variable is a variable calculated by averaging a plurality of consecutive signal values.

19. The method according to claim 16, which further comprises filtering the signal of the acceleration sensor using a filter and the test is carried out for a filtered signal.

20. The method according to claim 16, wherein the reference value is a maximum value of a measurement range of the acceleration sensor and the test checks whether the variable exceeds a predefined multiple of the reference value.

21. The method according to claim 16, which further comprises disposing the acceleration sensor in a movable object and the reference value is dependent on a speed of the movable object, wherein the speed of the movable object is measured by means of a speedometer.

22. The method according to claim 21, which further comprises counting time via a time counter and, if the speed of the movable object is below a predefined lower speed limit, the test checks whether the variable exceeds the reference value by the time a predefined time value is reached.

23. The method according to claim 21, which further comprises counting time via a time counter and, if the speed of the movable object is below a predefined lower speed limit, the test determines how often the variable exceeds the reference value by the time a predefined time value is reached and whether a number of exceedances exceeds a predefined maximum number, wherein the number of exceedances is determined by an exceedance counter and the exceedance counter is reset if the number of exceedances is less than the predefined maximum number and the time reaches the predefined time value.

24. The method according to claim 21, which further comprises counting time via a time counter and, if the speed of the movable object exceeds a predefined upper speed limit, the test checks whether the variable ever exceeds the predefined reference value by the time a predefined time value is reached.

25. The method according to claim 24, which further comprises resetting the time counter each time the reference value is exceeded and the time only continues to be counted by the time counter if the speed of the movable object exceeds the predefined upper speed limit.

26. The method according to claim 21, wherein the acceleration sensor is a sensor for measuring an acceleration at right angles to a direction of travel of the movable object.

27. The method according to claim 16, which further comprises issuing a warning if the acceleration sensor defect is detected.

28. The method according to claim 16, which further comprises disposing the acceleration sensor in a rail vehicle and the acceleration sensor is used for monitoring running stability.

29. The method according to claim 19, which further comprises selecting the filter from the group consisting of a bandpass filter and a high-pass filter.

30. The method according to claim 21, wherein the movable object is a vehicle.

31. A measuring system, comprising: an acceleration sensor; and a monitoring unit configured to detect a defect in said acceleration sensor, said monitoring unit programmed to: receive, via said acceleration sensor, an acceleration signal; carry out a test to check whether a variable dependent on the acceleration signal fulfills a predefined condition in respect of a reference value; and determine on a basis of the test whether said acceleration sensor is defective.

32. A rail vehicle, comprising: a measuring system having an acceleration sensor and a monitoring unit configured to detect a defect in said acceleration sensor, said monitoring unit programmed to: receive, via said acceleration sensor, an acceleration signal; carry out a test to check whether a variable dependent on the acceleration signal fulfills a predefined condition in respect of a reference value; and determine on a basis of the test whether said acceleration sensor is defective.

Description

[0054] The above described characteristics, features and advantages of the invention and the way in which they are achieved will become clearer and more readily comprehensible in conjunction with the following description of the exemplary embodiments which will be explained in greater detail with reference to the accompanying drawings. The exemplary embodiments serve to explain the invention and do not limit the invention to the combinations of features specified therein, nor in relation to the functional features. In addition, suitable features of each exemplary embodiment can also be explicitly considered in isolation, removed from the exemplary embodiment, incorporated in another exemplary embodiment for the supplementation thereof and combined with any of the claims.

[0055] FIG. 1 shows a rail vehicle having a measuring system comprising an acceleration sensor and a monitoring unit;

[0056] FIG. 2 shows a first graph in which an acceleration of the rail vehicle is plotted as a function of time;

[0057] FIG. 3 shows a second graph in which an acceleration of the rail vehicle is plotted as a function of time; and

[0058] FIG. 4 shows a third graph in which an acceleration and a speed of the rail vehicle are plotted as a function of time.

[0059] FIG. 1 schematically illustrates a rail vehicle 2 having a measuring system 4. The measuring system 4 comprises an acceleration sensor 6 and a monitoring unit 8. The rail vehicle 2 also has a speedometer 10 for determining a speed of the rail vehicle 2. The speedometer 10 comprises a rotational speed sensor and determines the speed of the rail vehicle 2 on the basis of a rotational speed. The acceleration sensor 6 and the speedometer 10 of the rail vehicle 2 are disposed on a wheelset axle 12 of the rail vehicle 2.

[0060] The monitoring unit 8 comprises a high-pass filter 14, a bandpass filter 16, a monitoring counter 18, a first time counter 20, and a second time counter 22. The first time counter 20 counts a first time and the second time counter 22 counts a second time. The monitoring counter 18 and the time counter 20, 22 can be a separate device in each case or be implemented as a software function in the monitoring unit 8.

[0061] The acceleration sensor 6 is a sensor for measuring a lateral acceleration of the rail vehicle 2. When the acceleration sensor 6 is working properly, the acceleration sensor 6 therefore measures the lateral acceleration of the rail vehicle 2. That is to say, the acceleration sensor 6 produces a signal in the form of a voltage which is dependent on the lateral acceleration of the rail vehicle 2. A lateral acceleration calculated from the signal consequently corresponds to the true lateral acceleration if the acceleration sensor is defect-free, i.e. working properly. On the other hand, if the acceleration sensor 6 is defective, the lateral acceleration calculated from the signal is not necessarily the true lateral acceleration of the rail vehicle 2.

[0062] The measurement of the lateral acceleration of the rail vehicle 2 is used to monitor the running stability of the rail vehicle 2.

[0063] In addition, the monitoring unit 8 is used to detect a defect in the acceleration sensor 6. The monitoring unit 8 checks whether a variable dependent on the signal of the acceleration sensor 6 fulfills a predefined condition in respect of a reference value, and determines on the basis of the test whether the acceleration sensor 6 is defective. The signal-dependent variable is the lateral acceleration that is determined from the signal. In particular, the test checks whether lateral acceleration values fulfill a predefined condition in respect of a reference value.

[0064] In this exemplary embodiment, the bandpass filter 16 is a filter for the frequency range 3 to 9 Hz. In the frequency range 3 to 9 Hz, mechanical vibrations typically occur because of the lateral accelerations of the rail vehicle 2. Consequently, the bandpass filter 16 allows through the frequency range 3 to 9 Hz.

[0065] The signal produced by the acceleration sensor 6 is filtered and averaged and the individual signal values are converted into an acceleration value in each case by a unique conversion rule.

[0066] Three tests are then carried out in which it is checked in each case whether the lateral acceleration fulfills a predefined condition in respect of a reference value. In the three tests, three different conditions are checked in respect of three different predefined reference values. Two of the conditions are dependent on the speed of the rail vehicle 2. For these two conditions it is assumed that particular lateral accelerations are likely at particular speeds of the rail vehicle 2. If such lateral accelerations are not achieved, an acceleration sensor defect 6 is assumed, i.e. detected. The three tests will now be discussed with reference to FIGS. 2 to 4.

[0067] FIG. 2 shows a first graph in which the lateral acceleration a of the rail vehicle 2 determined using the acceleration sensor 6 is plotted as a function of time t. This graph serves to illustrate the first test.

[0068] The first test is carried out independently of the speed of the rail vehicle 2. In the first test it is checked whether the lateral acceleration a is greater than a first reference value r.sub.1. The first reference value r.sub.1 is a maximum value of the measurement range of the acceleration sensor 6.

[0069] To calculate the lateral acceleration a, the signal of the acceleration sensor 6 is fed to the monitoring unit 8. In the monitoring unit 8 the signal is filtered by means of a bandpass filter 16. The filtered signal is then averaged by the monitoring unit 8 by means of moving averaging of absolute values over a predefined time period. Absolute value averaging means that the absolute value is first formed from each signal value and then arithmetic averaging is performed over a plurality of signal values, all lying within the predefined time period. The predefined time period is e.g. 0.5 s.

[0070] The signal values of the filtered, averaged signal are converted into acceleration values by means of a conversion rule.

[0071] The first reference value r.sub.1 can be e.g. 10 m/s.sup.2. In the first test it is checked whether the acceleration values exceed a predefined multiple a.sub.1 of the first reference value r.sub.1. The multiple a.sub.1 of the first reference value r.sub.1 can be e.g. 1.5 times the first reference value r.sub.1. This means that the lateral acceleration a (or rather each acceleration value determined) is compared with the multiple a.sub.1 of the first reference value r.sub.1, e.g. 1.5 times the first reference value r.sub.1.

[0072] The graph in FIG. 2 is subdivided into two time intervals A, B, the first time interval A preceding the second time interval B. In the first time interval A, the acceleration values are below the multiple a.sub.1 of the first reference value r.sub.1. The acceleration sensor 6 is deemed operational in the first time interval A according to this first test. After the time interval A, the lateral acceleration a increases significantly, e.g. because of a wiring fault in the acceleration sensor 6 or because a spurious signal is injected. In the second time interval B, the acceleration values exceed the multiple a.sub.1 of the first reference value r.sub.1, so that an acceleration sensor defect 6 is detected and a warning is issued.

[0073] In addition, the bandpass filter 16 is checked for operability by means of the first test. For example, there may be a defect in the bandpass filter 16 if the variable exceeds the predefined multiple a.sub.1 of the first reference value r.sub.1.

[0074] Due the warning issued, the bandpass filter 16 and the acceleration sensor 6 can be checked, and repair or replacement of the defective element carried out if necessary.

[0075] FIG. 3 shows a second graph in which the lateral acceleration a of the rail vehicle 2 determined using the acceleration sensor 6 is plotted as a function of time t. This graph serves to illustrate the second test.

[0076] The second test is carried out if the speed of the rail vehicle 2 falls below the predefined lower speed limit, e.g. 0.5 km/h. The second test is also carried out in respect of a second reference values r.sub.2.

[0077] It is assumed that, in the case of a speed of the rail vehicle 2 below the lower speed limit, only acceleration values below the second reference value r.sub.2 are likely. The reason is that normally only small lateral accelerations a act on the rail vehicle 2 when the vehicle is traveling very slowly or is at a standstill. On the other hand, if acceleration values above the second reference value r.sub.2 are measured, an acceleration sensor defect 6 is assumed, i.e. detected.

[0078] To calculate the lateral acceleration a, the signal of the acceleration sensor 6 is passed to the monitoring unit 8. In the monitoring unit 8 the signal of the acceleration sensor 6 is filtered by means of the high-pass filter 14 so that an offset voltage is attenuated in the signal or rather filtered out of the signal. The high pass filtered signal is then averaged by means of moving quadratic averaging over a time period of e.g. 0.5 s.

[0079] The signal values of the filtered, averaged signal are then converted into acceleration values by a conversion rule.

[0080] In this second test it is checked whether the acceleration value exceeds the second reference value r.sub.2 by the time the first time counted by the first time counter 20 reaches a predefined first time value. The second reference value r.sub.2 can be e.g. 3.0 m/s.sup.2.

[0081] The graph in FIG. 3 is subdivided into three time intervals C, D, E, the first time interval C preceding the second time interval D. The second time interval D in turn precedes the third time interval E.

[0082] In the first time interval C, the lateral acceleration a is significantly below the second reference value r.sub.2. The acceleration sensor 6 is deemed operational according to this test in time interval C. After the first time interval C, the lateral acceleration a increases markedly, e.g. because of an electronic fault in or at the acceleration sensor 6, and lies close to the second reference value r.sub.2 in the subsequent time intervals D and E. The lateral acceleration a exceeds the second reference value r.sub.2 in the time intervals D and E at the points indicated by arrows.

[0083] The second test is also used to determine how often the lateral acceleration a exceeds the second reference value r.sub.2 by the first time the predefined first time value is reached. The test also checks whether the number of exceedances exceeds the predefined maximum number, e.g. nine. The number of exceedances is counted by the above mentioned exceedance counter 18.

[0084] Testing to ascertain whether the number of exceedances exceeds a predefined maximum number is carried out in order to exclude the possibility that a one-off event, such as e.g. a passing train or a one-off mechanical impact on a wheel truck of the rail vehicle 2, causes a warning to be issued on account of a presumed defect in the acceleration sensor 6.

[0085] Ifunlike in the case describedthe number is less than the predefined maximum number and the first time reaches the predefined first time value, the exceedance counter 18 is reset to zero.

[0086] In the third time interval E, the number of exceedances has exceeded the predefined maximum number and the first time has reached or exceeded the predefined first time value. In order words, in the case of a predefined maximum number of e.g. nine, the exceedance counter 18 has counted e.g. ten (or more) exceedances before the first time reaches the predefined first time value. An acceleration sensor defect 6 is consequently identified. A warning is issued and the signal of the acceleration sensor 6 is no longer involved in assessing the running stability of the rail vehicle 2.

[0087] The first time is decremented by the first time counter 20 from an initial value (e.g. 30 min), said first time counter 20 being reset to the initial value when the first time reaches the predefined first time value of zero. The first time counter 20 is stopped if the speed of the rail vehicle 2 is equal to or above the predefined lower speed limit. If the speed of the rail vehicle 2 falls below the predefined lower speed limit again, the time counter 20 resumes counting.

[0088] FIG. 4 shows a fourth graph in which the lateral acceleration a and the speed v of the rail vehicle 2 are plotted as a function of time t. The lateral acceleration a has been determined using the acceleration sensor 6. The speed v has also been determined using the speedometer 10. The lateral acceleration a is shown as a continuous line and the y-axis for the lateral acceleration a is on the left-hand side of the drawing. In addition, the speed v is shown as a dashed line and the y-axis for the speed v is on the right-hand side of the drawing. This third graph serves to illustrate the third test.

[0089] The third test is carried out if the speed v of the rail vehicle 2 exceeds a predefined upper speed limit v.sub.o, e.g. 160 km/h. In addition, the third test is carried out in respect of a third reference value r.sub.3.

[0090] For this test it is assumed that, at a speed v of the rail vehicle 2 above the upper speed limit v.sub.o, at least some of the acceleration values are likely to be above the third reference value r.sub.3. The reason is that normally higher lateral accelerations a act on the rail vehicle 2 when the vehicle is traveling at high speed. On the other hand, if the acceleration values never exceed the third reference value r.sub.3, an acceleration sensor defect 6 is assumed, i.e. detected.

[0091] To calculate the lateral acceleration a, the signal of the acceleration sensor 6 is passed to the monitoring unit 8. In the monitoring unit 8 the signal is filtered by means of a high-pass filter 16. The filtered signal is then averaged by the monitoring unit 8 by means of moving quadratic averaging over a time period of e.g. 0.5 s.

[0092] The signal values of the filtered, averaged signal are then converted into acceleration values by a conversion rule.

[0093] In the third test it is checked whether the lateral acceleration a ever exceeds the third reference value r.sub.3 by the time the second time reaches a predefined second time value of e.g. 2 h. The third reference value r.sub.3 can be e.g. 0.3 m/s.sup.2.

[0094] The second time is incremented starting from zero by the second time counter 22.

[0095] The graph in FIG. 4 is subdivided into five time intervals F, G, H, J, K, the first time interval F preceding the second time interval G. The second time interval G in turn precedes the third time interval H which precedes the penultimate time interval J. The penultimate time interval J precedes the last time interval K. In the first time interval F, the acceleration values are continuously above the third reference value r.sub.3, whereas the lateral acceleration a decreases significantly after the time interval F, e.g. because of cable breakage inside the acceleration sensor 6, and the lateral acceleration a is continuously below the third reference value r.sub.3 after the time interval F.

[0096] In the first time interval F, the speed v of the rail vehicle 2 exceeds the predefined upper speed limit v.sub.o. As already mentioned, in this time interval F the lateral acceleration a is constantly above the third reference value r.sub.3. The acceleration sensor 6 is deemed to be fully operational in the time interval F. In this case, the second time counter 22 increments the time starting from zero, but the second time counter 22 is reset to the initial zero value each time the third reference value r.sub.3 is exceeded.

[0097] In the second time interval G, the speed v of the rail vehicle 2 exceeds the predefined upper speed limit v.sub.o, so that the time is counted by means of the second time counter 22. However, the lateral acceleration a after the time interval F is constantly below the third reference value r.sub.3 in this time interval G, with the result that the second time counter 22 is not reset, i.e. the time continues to be counted by the second time counter 22.

[0098] In the third time interval H, the speed v of the rail vehicle 2 is less than or equal to the predefined upper speed limit v.sub.o, with the result that the second time counter 22 is stopped, i.e. the time does not continue to be counted.

[0099] In FIG. 4, the time axis has a break between the third time interval H and the penultimate time interval J, and additional time intervals can follow the third time interval H.

[0100] In the penultimate time interval J, the speed v of the rail vehicle 2 exceeds the predefined upper speed limit v.sub.o, with the result that the time continues to be counted by means of the second time counter 22. The lateral acceleration a after the time interval F is continuously below the third reference value r.sub.3 in this time interval J, which means that the second time counter 22 is not reset. At the end of the time interval J, the second time counter 22 reaches the predefined second time value.

[0101] In the last time interval K, the second time counter 22 has reached or exceeded the second time value. The lateral acceleration a has therefore never exceeded the predefined third reference value r.sub.3 by the time the predefined second time value has been reached. Consequently, an acceleration sensor defect 6 is identified in the last time interval. A warning is issued and the signal of the acceleration sensor 6 is no longer involved in evaluating the running stability of the rail vehicle 2.

[0102] The rail vehicle 2 can in principle have yet more acceleration sensors which can monitor for a defect in a manner similar to that described in the exemplary embodiment.

[0103] Although the invention has been illustrated and described in detail on the basis of the preferred exemplary embodiment, the invention is not limited to the example disclosed and other variations will be apparent to persons skilled in the art without departing from the scope of protection sought for the invention.