Method and system for monitoring a track portion

Abstract

The invention relates to a method for monitoring a track portion (2) for the presence or absence of at least part of a rail vehicle (4) moving on the rail (3a, 3b), wherein the method comprises: obtaining first measurement signals (6a) from a first sensor (8a) which is located at the start (7) of the track portion (2); obtaining second measurement signals (6b) from a second sensor (8b) which is located at the end (9) of the track portion (2); evaluating the first measurement signals (6a) and the second measurement signals (6b) to register or count incoming metal bodies and to register or count outgoing metal bodies, wherein both axles or wheels (10a, 10b, 10c, 10d) and any brakes (11a, 11b) present are detected as metal bodies; and inferring the presence or absence of the part of the rail vehicle (4) on the track portion (2) on the basis of the registering or counting.

Description

Method and system for monitoring a track portion FIELD OF THE INVENTION The present invention relates to a method and a system for monitoring a section of track for the presence or absence of at least a part of a rail vehicle moving along the track. PRIOR ART Sections of track are conventionally monitored using components known as axle counters by means of detection of the vehicle wheels by count points (sensors). However, it has been observed that conventional methods and systems for monitoring sections of track do not deliver reliable results in all situations and for all configurations of the rail vehicles. This leads to miscounts, which results in a reduction in the availability of the track clear message. It is therefore an object of the present invention to provide a method or, as the case may be, a system for monitoring a section of track, wherein the reliability of the method is increased and inconvenient or persistent occupancies of the sections of track can be avoided. In particular it is an object of the present invention to propose a method or a system for monitoring a section of track which also delivers reliable results for rail vehicles which in particular also have magnetic rail brakes between the wheels. The object is achieved by means of the subject matters of the independent claims. Advantageous embodiments are specified in the dependent claims. SUMMARY OF THE INVENTION According to an embodiment of the present invention, a method for monitoring a section of track for the presence or absence of at least a part of a rail vehicle moving on the track is provided, wherein the method comprises: obtaining first measurement signals from a first sensor which is located at the start of the track section; obtaining second measurement signals from a second sensor which is located at the end of the track section (at switch or crossing sections, if necessary also further sensors which delimit the track section); evaluating the first measurement signals and the second measurement signals in order to register or count incoming metal bodies and in order to register or count outgoing metal bodies, wherein both axles or wheels and any brakes present are detected as metal bodies; and inferring the presence or absence of the part of the rail vehicle on the track section on the basis of the registering or counting. The method can be implemented in software and hardware. The method can for example be performed or controlled by a system for monitoring a section of track according to an embodiment of the present invention. The monitored track section can for example typically have a length of between 30 m (possibly also shorter, though the length of the track section should always be greater than the maximum axle spacing of a vehicle so that a vehicle cannot project beyond the section) and virtually unlimited. The rail vehicle can be used for example for conveying passengers and / or for transporting goods. Both the first sensor (sensor counting metal bodies entering the track section) and the second sensor (sensor counting metal bodies exiting the track section) can be embodied to detect metal masses or metal bodies which are located above or below the top of the rail or within the detection range of the sensor. The sensors may comprise conventional sensors, in particular axle counting sensors. The sensors must also be capable of detecting the direction of travel. A single sensor may suffice for monitoring stabling sidings in order to detect both incoming and outgoing vehicles. In this case the first sensor is identical with the second sensor. In other embodiments, more than two sensors may be present at various points on the track section, enabling their measurements to be consulted. The rail vehicle can move in the direction extending from the start of the track section to the end of the track section. The rail vehicle does not necessarily have to pass through the entire section of track, but for example can come to a halt before the track section has been completely traveled through or if necessary the direction of travel changes within the track section. According to other embodiments of the present invention, the rail vehicle can travel through the track section completely such that both the first sensor and a second sensor (and / or further sensors, e.g. at a railway switch or crossing point) are passed at the same time by the rail vehicle or a part of the rail vehicle. The rail vehicle can have a length between 10 m and 500 m, for example. Embodiments of the present invention can also enable the presence of a complete rail vehicle on the track section or its absence to be detected. The measurement signals can be obtained by way of cable connections, optical links or wirelessly by the first sensor or the second sensor. The measurement signals can comprise analog measurement signals, for example values of induced voltages which are generated in the sensors due to passing metal bodies. The evaluation of the first measurement signals and the second measurement signals may for example comprise a comparison with one or more threshold values. As incoming metal bodies may be understood metallic, in particular ferromagnetic, masses or bodies which are parts of the rail vehicle and which move beyond the first sensor into the track section. As outgoing metal bodies may be understood all metallic, in particular ferromagnetic, parts of the rail vehicle which move beyond the second sensor and consequently move outside of the track section. Conventionally, only wheels of rail vehicles were registered. According to the present embodiment of the invention, however, any brakes present, which can be provided in particular between two wheels or between two axles of the rail vehicle, are also detected. The brakes can be used for braking in certain driving situations or under certain external environmental conditions. Embodiments of the present invention do not necessarily require knowledge of the presence of such brakes of the rail vehicle. However, the evaluation can be conducted in such a way that these possibly present brakes can also be detected without presupposing knowledge of their presence. According to an embodiment of the present invention, at least one counter (or register or storage location) can be provided which for example increments the incoming metal body and decrements the outgoing metal body. Consequently, neither the number of incoming metal bodies nor the number of outgoing metal bodies must necessarily be counted. At the end of an evaluation or measurement time, only the reading of the at least one counter can be read out in order to determine whether the part of the rail vehicle is present in or absent from the track section. According to another embodiment, both the number of exits of the metal body and the number of entries of the metal body can actually be counted, in particular in two different counters (or registers or storage locations). The evaluation (generation of a track vacancy notification) is performed following comparison of the counter readings of the countingin and counting-out sensor. If the result of the comparison reveals that exactly the same number of metal bodies have been counted in as have been counted out, then the rail vehicle has exited the track section. In the case of active magnetic rail brakes, the saturation of the rail is detected instead of the metal body. Embodiments of the present invention do not require knowledge of the number of axles or wheels and / or the number of any brakes present on the rail vehicle. Accordingly, differently configured rail vehicles can be supported by embodiments of the present invention since the absence or presence of said vehicles can be reliably determined. According to an embodiment of the present invention, the method is embodied in such a way that the metal bodies comprise elements of the rail vehicle which are arranged vertically close to the rail, in particular wheels and / or wheel axles and / or brakes of the rail vehicle. This enables the method to register not only wheels or wheel axles but also brakes of the rail vehicle, both when the latter enters and when it exits the monitored track section. Thus, the method can be applied to different types of rail vehicles . According to an embodiment of the present invention, the method is embodied in such a way that evaluating the first measurement signals and the second measurement signals comprises: determining a first number of first measurement signals that lie above an upper threshold or that lie below a lower threshold; determining a second number of second measurement signals that lie above the upper threshold or that lie below the lower threshold, where the upper threshold is greater than the lower threshold. As measurement signal level, in particular relative voltage (for example based on a measurement value in the absence of a metal body or rail vehicle), the measurement signals may for example be given as a function of time. The upper threshold and / or the lower threshold may have been ascertained by determining measurement values of known metal bodies or measurement values of vehicles having a known configuration) or training data, wherein for example test measurements can be conducted, wherein different rail vehicles pass the sensors. The configuration of the rail vehicles with regard to the number of wheels and / or to any brakes present may be known for the test measurements. The method can therefore be performed simply by definition of an upper threshold and a lower threshold and by determining whether the respective measurement signals lie above or below the respective threshold. A very simple method is therefore provided for a reliable monitoring of the track section. According to an embodiment of the present invention, a conventionally provided delay of the measurement signals below the lower threshold is suppressed. Conventionally, a lower threshold may have been used to detect a problem during the installation of the respective sensor, in particular to detect whether fixing bolts or screws have become loose such that the position of the sensor relative to the rail has disadvantageously changed, e.g. the sensor has dropped from the rail. Conventionally, a measurement signal below the lower threshold was suppressed or delayed in that event. According to embodiments of the present invention, this conventionally provided delay is suppressed since the event whereby a measurement signal lies below the lower threshold is also used to detect metal bodies, in particular to detect a magnetic rail brake, and moreover in a reliable manner. According to an embodiment of the present invention, the method is implemented in such a way that inferring the presence or absence of the rail vehicle comprises: comparing the first number with the second number; inferring the presence or absence of the part of the rail vehicle on the track section from the result of the comparison. If the first number is compared with the second number, it can be determined for example whether the number of incoming metal bodies entering the track section is equal to or different from the number of outgoing metal bodies exiting the track section. A reliable monitoring can be conducted as a result. According to an embodiment of the present invention, the method further comprises: inferring that the track section is clear of the part of the rail vehicle if the first number is equal to the second number; and / or inferring that the track section is not clear of the part of the rail vehicle if the first number is greater than the second number; and / or inferring the presence of a fault if the first number is less than the second number. As a result, simple logical queries are sufficient to reach a reliable diagnosis about the occupancy state of the track section . According to an embodiment of the present invention, the method is embodied in such a way that the upper threshold is chosen such that a measurement signal generated by a deactivated brake, in particular a magnetic rail brake, of the rail vehicle or by a wheel axle or wheel exceeds the upper threshold. Therefore, as a result of establishing that a measurement signal lies above the upper threshold, both a wheel or a wheel axle and a deactivated brake can be reliably detected. According to an embodiment of the present invention, the method is embodied in such a way that the lower threshold is chosen such that a measurement signal generated by an activated brake, in particular a magnetic rail brake, of the rail vehicle lies below and a measurement signal generated by a wheel or a wheel axle lies above the lower threshold. As a result, by determining whether a measurement signal lies below the lower threshold, an activated brake can also be detected. It is thus made possible, by evaluating the respective measurement signals, to reliably detect or register both an activated brake and a non-activated brake. The reliability of the method can be improved as a result. According to an embodiment of the present invention, the method is implemented in such a way that the upper threshold and / or the lower threshold are / is set such that both wheel axles and / or wheels and any magnetic rail brakes present are counted or registered both in the activated and in the deactivated state, wherein a rail friction contact surface of the magnetic rail brake (in the deactivated state) is in particular at a distance of 4 mm to 9 mm from the rail. A magnetic rail brake can be provided for example between two wheel axles or wheels of the rail vehicle, for example in a multiple unit. In order to brake, the magnetic rail brake can be brought into contact with the surface of the rail by way of a rail friction contact surface in order to achieve a braking effect due to a frictional resistance. Embodiments of the present invention can support magnetic rail brakes which are at a relatively small distance from the rail. This can be the case in particular with commuter rail vehicles, such as, say, the subway, urban / suburban mass rapid transit system or tramway. According to an embodiment of the present invention, the part of the rail vehicle has at least one magnetic rail brake which in particular is sometimes activated or is sometimes deactivated (while the measurement signals are being recorded, for example). Conventionally, the presence of magnetic rail brakes can lead to miscounts and consequently to misdiagnoses of the occupancy of a track section. Since, however, magnetic rail brakes can be reliably registered or counted, rail vehicles having at least one magnetic rail brake are also supported. According to an embodiment of the present invention, the method is implemented in such a way that the first measurement signals were recorded continuously while the part of the rail vehicle passes / moves over the first sensor; wherein the second measurement signals were likewise recorded continuously while the part of the rail vehicle passes / moves over the first sensor . The monitoring of the measurement signals can be carried out continuously, but can also be performed on an event-driven basis. An evaluation is performed continuously or when there is no change in the measurement values recorded by the sensors in a specific time period. The occupancy status of the track section is then derived therefrom. According to an embodiment of the present invention, the first sensor and / or the second sensor are / is configured as a metal sensor, in particular as a count point of an axle counting system. This means that conventional sensors can be supported, which can facilitate the implementation of the invention. According to an embodiment of the present invention, the first sensor and / or the second sensor comprise / comprises: an electromagnetic generator coil mounted on a side of a rail of the track for the purpose of generating an alternating magnetic field; an electromagnetic detection coil mounted on the other side of the rail of the track for the purpose of detecting an alternating magnetic field by induction of a voltage which in particular represents the measurement signals . The generator coil can for example generate a (higher-frequency) alternating magnetic field at a frequency of several kilohertz (e.g. between 30 kHz and 1000 Hz). The alternating magnetic field generated by the generator coil can also extend into the range of the detection coil. When a metal body, in particular a ferromagnetic metal body (for example a wheel or a magnetic rail brake of a rail vehicle), enters the space between the generator coil and the detection coil, the magnetic field generated by the generator coil may be changed. As a result, the voltage induced in the receiver coil, which is induced in the detection coil due to the changed magnetic field, can be changed with respect to a voltage induced in the absence of the metal body. In this case the measurement signal can represent for example the level of the induced voltage, in particular in relation to an induced voltage (e.g. ratio) in the absence of any metal body between the exciter coil and the detection coil, that is to say in the absence of any metal body moving on the surface of the rail. According to an embodiment of the present invention, the rail vehicle is an intercity rail vehicle or a local commuter rail vehicle, in particular a subway, a tramway or an urban / suburban mass rapid transit system. It should be understood that features which have been explained, provided or applied, individually or in any combination, in connection with a method for monitoring a track section can equally be applied individually or in any combination also to a system for monitoring a track section according to embodiments of the present invention, or vice versa . According to an embodiment of the present invention, a system for monitoring a track section for the presence or absence of at least a part of a rail vehicle moving on the track is provided, wherein the system comprises: an input port which is configured: to obtain first measurement signals from a first sensor located at the start of the track section; to obtain second measurement signals from a second sensor located at the end of the track section; an evaluation block which is configured: to evaluate the first measurement signals and the second measurement signals in order to register or count incoming metal bodies and in order to register or count outgoing metal bodies, wherein both axles or wheels and any brakes present are detected as metal bodies; and to infer the presence or absence of the part of the rail vehicle on the track section based on the registration or count. Embodiments of the present invention will now be explained with reference to the attached drawings. The invention is not limited to the illustrated or described embodiments. BRIEF DESCRIPTION OF THE DRAWINGS Fig . 1 schematically illustrates a system for monitoring a track section according to an embodiment of the present invention, Fig. 2 illustrates in a schematic side view a part of a rail vehicle whose presence on a track section is monitored according to an embodiment of the present invention, Fig. 3 illustrates measurement signals and count pulses according to a conventional method, Fig. 4 illustrates measurement signals and corresponding count pulses which are recorded or evaluated according to embodiments of the present invention, Fig . 5 shows experimental results obtained according to embodiments of the present invention. DETAILED DESCRIPTION OF EMBODIMENTS The system 1 of Fig. 1 for monitoring a track section 2 for the presence or absence of at least a part of a rail vehicle 4 moving on the rails 3a, 3b of the track 40 comprises an input port 5a, 5b in order to obtain first measurement signals 6a from a first sensor 8a located at the start 7 of the track section 2 and in order to obtain second measurement signals 6b from a second sensor 8b located at the end 9 of the track section 2. The system 1 further comprises an evaluation block which is configured to evaluate the first measurement signals 6a and the second measurement signals 6b in order to register or count incoming metal bodies 10a, 10b, 10c, lOd and Ila, 11b of the rail vehicle 4, wherein both axles or wheels 10a, 10b, 10c, lOd and any brakes Ila, 11b present are detected as metal bodies. The evaluation block of the system 1 is further configured to infer the presence or absence of the part of the rail vehicle 4 on the track section 2 based on the registration or count. The system 1 is embodied to perform or control a method for monitoring the track section 2. The rail vehicle 4 moves on the two rails 3a, 3b of a track 40 in the direction indicated by the arrow 12. In the illustrated embodiment of Fig. 1, the rail vehicle 4 comprises at least one multiple unit which has two wheel axle pairs 10a, 10b, 10c, lOd, wherein a magnetic rail brake Ila, 11b is mounted in each case between each two wheel axles 10a, 10b or 10c, lOd. The two rails 3a, 3b form the track 40 together with thresholds (not shown) and track ballast or nonballasted track. The sensors 8a, 8b each comprise, by way of example, a generator coil 13 which is mounted on a side of a rail 3b of the track and is embodied to generate an alternating magnetic field. The sensors 8a, 8b further comprise an electromagnetic detection coil 14 which is embodied for detecting an alternating magnetic field by induction of a voltage. In this case the measurement signals 6a, 6b can represent in particular a relative (or absolute) induced voltage, which is given as a fraction of an induced voltage which is generated if no metal body passes the respective sensor 8a, 8b. The sensors 8a, 8b are therefore configured as metal sensors, which conventionally can also be referred to as count points. The system 1 can further comprise the first sensor 8a and the second sensor 8b. In Fig. 1, the rail vehicle 4 is illustrated at a point in time after the wheel axles 10c, lOd and the magnetic rail brake 11b have already passed the first sensor 8a. Thereafter, the rail vehicle 4 passes or the wheels or wheel axles 10a, 10b and the magnetic rail brake Ila also pass the first sensor 8a. During a later second time period, the rail vehicle 4 and in particular also the respective wheel axles and the magnetic rail brakes pass the second sensor 8b. Fig. 2 illustrates in a schematic side view a part of the rail vehicle 4 which moves on the rail 3a, 3b. In this case the rail vehicle 4 comprises a wheel 10a having a wheel axle, a wheel 10b and a magnetic rail brake Ila, which is arranged between the wheels or wheel axles 10a and 10b. The wheels 10a, 10b are mounted together with the magnetic rail brake Ila on a bogie truck 12a. The distance d of a rail friction contact surface 41 of the magnetic rail brake Ila from the surface of the rail 3b, which is designated by d, can amount for example to 4 to 9 mm. Fig. 3 illustrates in two coordinate systems having a respective abscissa 15, which indicates time, and in a respective ordinate 16, which indicates the relative induced voltage in the detection coil 14 which represents the measurement signal of a sensor, or indicates the digitized wheel pulse on an ordinate 17, which analog measurement signals 18, 19 which were recorded in a conventional method and which have in each case been converted into pulses or pulse profiles 20, 21. In this case it was merely established whether the respective measurement signal 18, 19 exceeds a conventional upper switching threshold 22 or not. If the measurement signal 18, 19 exceeds the conventional upper switching threshold, which lies e.g. at 1.58, then the signal is rated as a count pulse 20, 21 and consequently is counted as a wheel or as a wheel axle of the rail vehicle. A lower conventional switching threshold 22a (e.g. at 0.85) serves for detecting a drop. Wheels or wheel axles of the rail vehicle are actually present in the sections 23, 24, 25, 26. In sections 27, 28, however, brakes are present, but no wheels or wheel axles. A relatively small signal in the region of the brake 27 is not classified as a wheel pulse in the measurement section 18 since the measurement signal of the relatively small brake (meaning the relative increase in the voltage induced in the detector coil 14 resulting from the metal mass of the brakes) in section 27 lies below the conventional upper threshold 22. However, a relatively large brake in section 28 generates a measurement signal 19 which lies above the conventional upper threshold 22 and consequently leads to its evaluation as a count pulse. In this conventional case, a relatively large brake is therefore wrongly evaluated as the presence of a wheel, as indicated by a flash of lightning. Embodiments of the present invention can avoid such miscounts by means of brakes which cause an increase in the induced voltage in the region of the threshold 22 . According to an embodiment of the present invention, examples of measurement signals and derived pulse counts or count pulses are illustrated in Fig. 4. The abscissae 15 indicate time, the ordinate 16 indicates the relative induction voltage and the ordinate 17 indicates a count pulse. An upper threshold 30 and a lower threshold 31 are defined. The measurement signals 32 were recorded by a rail vehicle which has at least two wheel axles 10a, 10b as well as a magnetic rail brake Ila. The magnetic rail brake was deactivated, i.e. passive, when the measurement signals 32 were recorded. The measurement signals 32 generated due to the presence of the wheels or wheel axles 10a, 10b as well as due to the presence of the magnetic rail all exceed the upper threshold 30 and are therefore rated as pulses in the count pulse profile 33. The measurement signal curve 34 in Fig. 4 illustrates the measurement signals of the same section of the rail vehicle when the magnetic rail brake 10a is activated, i.e. active. In this case the measurement signals 34 generated due to the presence of the wheel axles or wheels 10a, 10b again exceed the upper threshold 30. Unlike in the measurement signals 32, however, the measurement signal 34 in the region of the active magnetic rail brake does not exceed the upper threshold 30, but lies below a lower threshold 31. The upper threshold 30 can lie for example in a range of 1.2 to 1.35 of a relative induction voltage (or relative wheel elevation). The lower threshold 31 can lie for example in a range of 0.8 to 0.9 of a relative induction voltage (or relative wheel elevation). For the case of the active brake also, therefore, the evaluation leads to a count pulse profile 35 which counts both the wheels or wheel axles 10a, 10b and the active brake Ila as count pulses . Conventionally observed miscounts in axle counting methods due to any magnetic rail brakes present (activated or deactivated) can therefore be reduced or even prevented altogether. Magnetic rail brakes exist in a variety of forms and, depending on their design, some of them lead to exerting a strong impact on the wheel sensor. Conventionally, when in addition the affected vehicles also have small wheels, a reliable operation with axle counters is often no longer assured. Conventionally caused track clear notification faults reduce the availability and ultimately also the acceptance of these systems. Conventionally, attempts are made to set the sensitivity of the count points such that wheels of a rail vehicle are reliably detected at all times and the magnetic rail brakes located between the wheels of a chassis are never detected. However, this conventional method works only when the amplitudes of the wheel signals generated in the count point are significantly different from the amplitudes of the brake signals. When amplitudes of wheels and brakes are similarly large, setting the count point with the cited requirements is not always possible. In this case the use of axle counters with count points can lead to problems in terms of availability. Embodiments of the present invention may include the following details, but do not form essential features of the present invention . Conventionally occurring problems can be resolved or reduced in a first step if all of the brakes are reliably counted. However, the simple registration and counting of the brakes is only possible if these are disposed in the passive state. In this state, the brakes are not supplied with power and move several millimeters above top of rail. Due to the large metal mass, the brakes affect the count points to a greater or lesser extent, depending on the design of the brake and its distance from the sensor. By lowering the (upper) switching threshold (compared with a conventional design), all the brakes are reliably included in the count. Thus, the upper threshold 30 defined according to an embodiment of the present invention can be less than a conventionally used upper switching threshold. If a vehicle with activated brakes passes a count point, there is a critical change in the signaling behavior and the conventional processing of the signals fails at this point. Due to high magnetic fields under the active brake, there is a change in the magnetic properties of the rail (saturation effects). The receive signal of the count point is reduced as a result and a detection as in the case of the wheels is not possible, at least not in the conventional way. To remedy this, an embodiment of the present invention advantageously proposes to use the lower switching threshold of the count points also. Conventionally, the lower switching threshold of the count points serves to detect a dropping of the sensor. If, for example, the fastening bolts on the wheel sensor have worked loose and the sensor moves away from the rail, this must be disclosed for safety reasons (drop detection). Conventionally, undershooting the lower threshold is delayed in time in the count point and is not relayed immediately. According to an embodiment of the present invention, however, the conventionally applied delay is switched off. Consequently, when undershooting the lower threshold, activated brakes generate the same signals as passive brakes when the upper threshold is exceeded. According to embodiments of the invention, a method is proposed by means of which both passive (deactivated) and active (activated) brakes, in particular magnetic rail brakes, are reliably detected and how wheels can be counted. Fig. 5 shows in coordinate systems with abscissae 15, which indicate time, and with ordinates 16, which indicate the absolute induction voltage or an ordinate 17, which indicates the count pulse, measurement signals 36 of a rail vehicle which has eight axles or wheels and, therebetween or between pairs of wheels, in each case magnetic rail brakes, which are activated in the first half of Fig. 5 and deactivated (passive) in the second half of Fig. 5. The upper threshold 30 and the lower threshold 31 are also shown. The upper threshold 30 lies at 1.28 and the lower threshold lies at 0.85, though these values can be set according to use case or on a situation-specific basis. The count pulse profile 37 illustrates that both the wheels or wheel axles and the magnetic rail brakes can be reliably detected in the activated and in the deactivated state. The rail vehicle comprises two cars, each having two trucks, wherein the magnetic rail brakes are active in the first car and passive in the second car. With the aid of the proposed method or system, monitoring of a track section can be accomplished in a reliable manner.

Claims

1 A method for monitoring a track section (2) for the presence or absence of at least a part of a rail vehicle (4) moving on the rail (3a, 3b), wherein the method comprises:obtaining first measurement signals (6a) of a first sensor (8a) located at the start (7) of the track section (2);obtaining second measurement signals (6b) of a second sensor (8b) located at the end (9) of the track section (2);evaluating the first measurement signals (6a) and the second measurement signals (6b) in order to register or count incoming metal bodies and in order to register or count outgoing metal bodies, wherein both axles or wheels (10a,10b,10c,lOd) and any brakes (Ila, 11b) present are detected as metal bodies;inferring the presence or absence of the part of the rail vehicle (4) on the track section (2) based on the registration or count.

2. The method as claimed in the preceding claim, wherein the metal bodies comprise elements of the rail vehicle which are arranged vertically close to the rail (3a, 3b), in particular wheels (10a,b,c,d) and / or wheel axles and / or brakes (lla,b) of the rail vehicle.

3. The method as claimed in one of the preceding claims, wherein the evaluation of the first measurement signals (6a) and the second measurement signals (6b) comprises:determining a first number of first measurement signals (6a) lying above an upper threshold (30) or lying below a lower threshold (31);determining a second number of second measurement signals (6b) lying above the upper threshold (30) or lying below the lower threshold (31), wherein the upper threshold is greater than the lower threshold.

4. The method as claimed in the preceding claim, wherein a conventionally provided delaying of the measurement signals below the lower threshold (31) is suppressed.

5. The method as claimed in one of the preceding claims 3 or 4, wherein inferring the presence or absence of the rail vehicle comprises:comparing the first number with the second number; inferring the presence or absence of the part of the rail vehicle (4) on the track section (2) from the result of the comparison .

6. The method as claimed in the preceding claim, further comprising:inferring that the track section (2) is clear of the part of the rail vehicle (4) if the first number is equal to the second number; and / orSI inferring that the track section (2) is not clear of the part of the rail vehicle (4) if the first number is greater than the second number; and / or inferring the presence of a fault if the first number is less than the second number.

7. The method as claimed in one of the preceding claims 3 to 6, wherein the upper threshold (30) is chosen such that a measurement signal generated by a deactivated brake, inparticular a magnetic rail brake (Ila, b), of the rail vehicle or by a wheel axle or wheel exceeds the upper threshold.

8. The method as claimed in one of the preceding claims 3 to 7, wherein the lower threshold (31) is chosen such that a measurement signal generated by an activated brake, in particular a magnetic rail brake (lla,b), of the rail vehicle lies below and a measurement signal generated by a wheel or a wheel axle lies above the lower threshold.

9. The method as claimed in one of the preceding claims 3 to 8, wherein the upper threshold (30) and / or the lower threshold (31) are / is set such that both wheel axles and / or wheels (10a,b,c,d) and any magnetic rail brakes (lla,b) present are counted or registered both in the activated and in the deactivated state, wherein a rail friction contact surface (41) of the magnetic rail brake (in the non-activated state) is in particular at a distance of 4 mm to 9 mm from the rail (3b) .

10. The method as claimed in one of the preceding claims, wherein the part of the rail vehicle (4) has at least one magnetic rail brake (lla,b) which in particular is sometimes activated or sometimes deactivated.

11. The method as claimed in one of the preceding claims, wherein the first measurement signals (6a) were recorded continuously while the part of the rail vehicle passes / moves over the first sensor;wherein the second measurement signals (6b) were recorded continuously while the part of the rail vehicle passes / moves over the first sensor.

12. The method as claimed in one of the preceding claims, wherein the first sensor (8a) and / or the second sensor (8b) are / is configured as a metal sensor, in particular a count point.

13. The method as claimed in one of the preceding claims, wherein the first sensor and / or the second sensor comprise / comprises :an electromagnetic generator coil (13), mounted on a side of a rail of the track, for generating an alternating magnetic field;an electromagnetic detection coil (14), mounted on the other side of the rail of the track, for detecting an alternating magnetic field by induction of a voltage which in particular represents the measurement signals.

14. The method as claimed in one of the preceding claims, wherein the rail vehicle (4) is an intercity rail vehicle or a local commuter rail vehicle, in particular a subway, a tramway or an urban / suburban mass rapid transit system.

15. A system for monitoring a track section (2) for the presence or absence of at least a part of a rail vehicle (4) moving on the track, wherein the system comprises:an input port (5a,5b) which is configured: to obtain first measurement signals (6a) from a first sensor (8a) located at the start (7) of the track section (2);to obtain second measurement signals (6b) from a second sensor (8b) located at the end (9) of the track section (2) ;an evaluation block which is configured to:evaluate the first measurement signals (6a) and the second measurement signals (6b) in order to register or count incoming metal bodies and in order to register or count outgoing metal bodies, wherein both axles or wheels (10a,b,c,d) and any brakes (lla,b) present are detected as metal bodies; andinfer the presence or absence of the part of the rail vehicle (4) on the track section (2) based on the registration orcount.

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