Determining the wear of a contact strip

Abstract

The invention relates to an assembly and to a method for determining the wear of a used contact strip of a rail-vehicle current collector. Three regions (MB, TB1, TB2) of a contact strip (SL) are monitored by means of magnetic-field sensors (SEN, SEN1, SEN2). A contact wire (FD) contacts the contact strip (SL) in order to feed in a contact-wire current (I). The contact-wire current (I) is subdivided into two partial currents (I1, I2) which flow in associated portions (TB1, TB2) of the contact strip (SL). A central magnetic-field sensor (SEN) is provided for monitoring a central region (MB) of the contact strip (SL) so that a central magnetic field (B) caused by the contact-wire current (I) is measured at a distance encompassing a thickness of the contact strip (SL) in the central region (MB). Two further magnetic-field sensors (SEN1) are provided for monitoring the two portions (TB1, TB2). During a calibration process, the magnetic-field sensors (SEN, SEN1, SEN2) are arranged on an unused contact strip (SL) in such a way that electrical signals (S, S1, S2) from the magnetic fields (B, B1, B2), when added up, yield a cumulative signal value of zero. In a used contact strip, the electrical signals (S, S1, S2), when added up, yield a cumulative signal value that is not equal to zero. This value is used to determine a current thickness of the used contact strip (SL) in the central region (MB).

Description

Determining the wear of a contact strip The invention relates to an arrangement and a method for ascertaining the wear of a worn contact strip of a rail vehicle current collector. A current collector of a rail vehicle is equipped with one or two pairs of contact strips. The contact strips are subject to wear while the rail vehicle is traveling in contact with an electrical overhead line that is provided therefor. It becomes necessary to exchange the contact strips as soon as at least one of the contact strips, which are present in pairs, reaches a predetermined limit value, for example a minimum thickness of the contact strip. If the minimum thickness, as required limit value, is fallen below significantly, the risk arises of energy transmission via the contact strip failing, and thus of the rail vehicle failing. Current collectors are commonly equipped with what is known as an automatic drop-down system that automatically lowers the pairs of contact strips when the minimum thickness is reached or fallen below. A worn contact strip is particularly critical in the case of what are known as multisystem vehicles, which use different energy provision systems (AC overhead line, DC overhead line, etc.) to drive the rail vehicle alternately. On account of the limited installation space in these rail vehicles, only one current collector is often provided on board the rail vehicle for an energy provision system, there being no further current collectors for any conceivable redundancy for said current collector. When maintenance is performed periodically on the current collector or on its contact strips, the current state or the current thickness of the contact strips is determined through measurements (using for example caliper gauges, measuring templates or the like). The current state of the contact strips is caused by: - the distance traveled, - the average speed of the rail vehicle, - the friction between the overhead line and the contact strip, - the thermal loading on the contact strip during current transmission, - the contact situation between the contact strip and the overhead line, this being caused and influenced by icing, wear state, surface structure, sparking, etc., - etc. Once measurement is complete, empirical values are taken as a basis by maintenance specialists to determine, in a relatively rough estimate, whether the contact strip in question is able to carry on being operated for a provisional future range or whether it needs to be replaced. If, in the rail vehicle subject to maintenance, subsequent usage conditions create more loading than expected, the estimated range does not correspond to reality, and therefore the likelihood of failure of the rail vehicle subject to maintenance increases. To counter this problem, maintenance specialists estimate the future range on a somewhat conservative basis, which leads to the contact strips being dispensed with as a precautionary measure, even though they would still be able to remain in service for longer. Aside from maintenance, it is at present not possible to ascertain or estimate a remaining thickness of a worn contact strip and an associated remaining range of the rail vehicle at a desired time. The object of the present invention is therefore to specify an improved method and a suitable arrangement for ascertaining the wear of contact strips in the case of a rail vehicle current collector in order to determine a remaining thickness of the worn contact strips at any time. This object is achieved by the features of patent claim 1. Advantageous developments are specified in the dependent patent claims. The invention relates to an arrangement and a method for ascertaining the wear of a contact strip of a rail vehicle current collector. A contact strip has, along its length, a central region, a first subregion and a second subregion. The central region is arranged (preferably centrally) between the two subregions. A contact wire makes contact with the contact strip in order to feed a contact wire current into the contact strip. The contact wire current splits there into a first partial current that flows in the first subregion and into a second partial current that flows in the second subregion. The two partial currents are of substantially the same magnitude. A central magnetic field sensor is provided for the purpose of monitoring the central region, such that the central magnetic field sensor measures a central magnetic field, caused by the contact wire current, at a distance that includes a thickness of the contact strip in the central region. A first magnetic field sensor is provided for the purpose of monitoring the first subregion, such that the first magnetic field sensor measures a first magnetic field, caused by the first partial current, at a distance that includes a thickness of the contact strip in the first subregion. A second magnetic field sensor is provided for the purpose of monitoring the second subregion, such that the second magnetic field sensor measures a second magnetic field, caused by the second partial current, at a distance that includes a thickness of the contact strip in the second subregion. In a calibration, the magnetic field sensors are arranged on a non-worn contact strip for region-monitoring purposes such that electrical signals formed from the measured magnetic fields, when summed, have a sum signal value of zero. In the case of a subsequently worn contact strip, the electrical signals formed from the measured magnetic fields, when summed, have a sum signal value other than zero. The sum signal value of the worn contact strip is supplied to a vehicle diagnostic device, which, based thereon and in comparison to the calibration, determines a current thickness of the worn contact strip in the central region. In one advantageous development, the contact wire makes contact with the contact strip on a first side of the contact strip by way of a back and forth motion. In one advantageous development, the central magnetic field sensor is arranged on a second side, opposite the first side, of the contact strip. In one advantageous development, the first magnetic field sensor is arranged on a second side, opposite the first side, of the contact strip. In one advantageous development, the second magnetic field sensor is arranged on a second side, opposite the first side, of the contact strip. In one advantageous development, the contact strip is connected to a contact strip holder. At least one of the magnetic field sensors is preferably fastened to the contact strip holder. In one advantageous development, the contact wire and the contact strip are preferably oriented substantially perpendicular to one another in the contact region so as to form a system geometry. In one advantageous development, the system geometry means that the first and second magnetic field are arranged in respective parallel planes that are orthogonal to the plane of the central magnetic field, such that the magnetic fields are decoupled from one another for the magnetic field measurement by virtue of the distance between them and orthogonality. In one advantageous development, the sums of the signals of the magnetic field sensors are processed based on their averages, preferably in predefined time intervals. In one advantageous development, the calibration is carried out whenever a non-worn contact strip is installed on the rail vehicle. In one advantageous development, the calibration is performed at room temperature of the current collector. The present invention makes it possible to determine a remaining actual thickness of the worn contact strip at any time. This enables an improved estimate of the future or remaining range of the rail vehicle using the contact strip in question. The present invention enables improved or extended use of the contact strip based on real wear and free from estimates. The present invention makes it possible to determine the thickness of the worn contact strip with high accuracy and without the need for manual measurements. This saves time, effort and ultimately costs both in terms of maintenance and in terms of contact strip replacement. The invention will be explained in more detail below with the aid of a drawing, in which: FIG 1 shows a view of currents and magnetic fields in the case of a contact strip as a basis for the present invention, FIG 2 shows magnetic field sensors used according to the invention, with reference to FIG 1, FIG 3 shows an overview of the magnetic field sensors, magnetic fields and currents in the case of a non-worn contact strip, with reference to FIG 1 and FIG 2, FIG 4 shows a plan view of the contact strip, with reference to FIG 3, and FIG 5 shows an overview of the magnetic field sensors, magnetic fields and currents in the case of a worn contact strip, with reference to the above figures. FIG 1 shows, as a basis for the present invention, a view of currents I, I1, I2 and magnetic fields B, B1, B2 in the case of a contact strip SL in contact with a contact wire FD. A contact wire current I flows from the contact wire FD into the contact strip SL and branches off there into a first partial current I1 and into a second partial current I2 so as to reach further components inside the rail vehicle via associated stranded wires LI provided at both ends of the contact strip SL. The first partial current I1 flows through a first subregion TB1 of the contact strip SL, whereas the second partial current I2 flows through a second subregion TB2 of the contact strip SL. The two partial currents I1, I2 are approximately the same, but oriented counter to one another. The following applies for their absolute values: I = I1 + I2. The contact wire current I flowing in the contact wire FD generates a magnetic field, referred to as central magnetic field B. Its approximately circular and closed induction lines lie in a plane orthogonal to the longitudinal axis of the contact wire FD. In accordance with the known Biot-Savart law, a magnetic field strength of the central magnetic field B is inversely or indirectly proportional to a considered distance r from the contact wire FD. The following thus applies: B - 1 / r The first partial current I1 generates a first magnetic field B1 the approximately circular and closed induction lines of which lie in a plane orthogonal to the longitudinal axis of the contact strip SL. A magnetic field strength of the first magnetic field B1 is inversely or indirectly proportional to a considered distance from the contact strip SL, such that the following applies: B1 - 1 / distance. The second partial current I2 generates a second magnetic field B2 the approximately circular and closed induction lines of which lie in a plane orthogonal to the longitudinal axis of the contact strip SL. A magnetic field strength of the second magnetic field B2 is inversely or indirectly proportional to a considered distance from the contact strip SL, such that the following applies: B2 - 1 / distance. FIG 2 shows magnetic field sensors SEN, SEN1 and SEN2, used according to the invention, of the contact strip SL and their signals S, S1 and S2, with reference to FIG 1. First of all, the following observation is made for the two contact strips, shown here, of a current collector: - Current collectors are generally equipped with two contact strips. Energy is often supplied from the contact wire of an overhead line via the two contact strips by two substations that are located upstream and downstream of an associated contact point, respectively. - Since the two contact strips are at the same electrical potential, it may be assumed that the current flowing in a wire section between the two contact strips is negligibly small in comparison to the current collected by each of the individual contact strips. - This makes it possible, in the present invention, to analyze just a simplified case in which only one contact strip SL draws the contact wire current I from the contact wire FD. The contact wire FD and the contact strip SL are oriented perpendicular to one another, so as to form a particular system geometry: - the magnetic fields B1 and B2 lie in respective parallel planes, - these planes are each orthogonal to the plane in which the central magnetic field B lies. Magnetic field sensors SEN, SEN1 and SEN2 are installed in the region of the contact strip SL, preferably on an associated contact strip holder, and record the respective magnetic field strength of the magnetic fields B, B1, B2 at the installation points and convert them into respective electrical signals S, S1 and S2. A central magnetic field sensor SEN is arranged below and in a central region MB of the contact strip SL. The central sensor SEN is preferably fastened to a contact strip holder carrying the contact strip SL. The central magnetic field sensor SEN, as a result of its installation situation and the thickness of the contact strip SL, is at a distance from the contact wire FD in the central region MB of the contact strip SL and records the magnetic field strength of the central magnetic field B at this position from said central magnetic field. The central magnetic field sensor SEN converts this magnetic field strength into an electrical (central) signal S of the central sensor SEN. A first magnetic field sensor SEN1 is arranged below and in the first subregion TB1 of the contact strip SL. The first sensor SEN1 is preferably likewise fastened to the contact strip holder. The first magnetic field sensor SEN1 is at a predetermined distance from the central magnetic field sensor SEN. The first magnetic field sensor SEN1, as a result of its installation situation and the thickness of the contact strip SL, is at a distance from the contact strip SL in the first subregion TB1. The first magnetic field sensor SEN1 records the magnetic field strength of the first magnetic field B1 at this position from said first magnetic field and converts this magnetic field strength into an electrical first signal S1 of the first sensor SEN1. A second magnetic field sensor SEN2 is arranged below and in the second subregion TB2 of the contact strip SL. It is preferably likewise fastened to the contact strip holder. The second magnetic field sensor SEN2 is at the same predetermined distance from the central magnetic field sensor SEN as the distance between the first magnetic field sensor SEN1 and the central sensor SEN. The two magnetic field sensors are thus arranged mirror-symmetrically with respect to the central magnetic field sensor SEN. The second magnetic field sensor SEN2, as a result of its installation situation and the thickness of the contact strip SL, is at a distance from the contact strip SL in the second subregion TB2. The second magnetic field sensor SEN2 records the magnetic field strength of the second magnetic field B2 at this position from said second magnetic field and converts this magnetic field strength into an electrical second signal S2 of the second sensor SEN2. The particular system geometry and the above-described positions of the sensors SEN, SEN1 and SEN2 means that - the central magnetic field sensor SEN, which records the central magnetic field B, is insensitive to the two magnetic fields B1 and B2, - the first magnetic field sensor SEN1, which records the first magnetic field B1, is insensitive to the central magnetic field B, - the second magnetic field sensor SEN2, which records the second magnetic field B2, is insensitive to the central magnetic field B, - due to the spatial distance between the first magnetic field sensor SEN1 and the second magnetic field sensor SEN2, the first magnetic field sensor SEN1 is insensitive to the second magnetic field B2, and - due to the spatial distance between the first magnetic field sensor SEN1 and the second magnetic field sensor SEN2, the second magnetic field sensor SEN2 is insensitive to the first magnetic field B1. FIG 3 shows, in a side view and with reference to FIG 1 and FIG 2, an overview of the magnetic field sensors or sensors SEN, SEN1, SEN2, the magnetic fields B, B1, B2 and the currents I, I1, I2 in the case of a non-worn contact strip SL. The central magnetic field sensor SEN, due to the non-worn contact strip SL, is located relatively far away from the contact wire FD; there is thus typically a distance of ^ 40 mm between the two. The particular system geometry outlined above allows the magnetic field sensors SEN, SEN1 and SEN2 to be calibrated via the respective positioning. The calibration is carried out such that the electrical signals S, S1 and S2 adopt a signal value of “0” in the case of a nonworn contact strip SL when, in the case of the non-worn contact strip SL, a contact point of the contact wire FD with the contact strip SL lies in the middle of the contact strip SL. This leads, with a signal S0 as resulting signal of the sensors SEN, SEN1 and SEN2, to the following equation: S0 = S1 + S2 — S = 0 This configuration corresponds to a state of equilibrium in which the effects of the magnetic fields B, B1 and B2 generated by the currents I, I1 and I2 cancel one another out. During operation of the rail vehicle, the contact wire FD, as is known, is guided actively back and forth over the contact strip SL, wherein this active guidance is realized by virtue of the contact wire FD being suspended along the route traveled by the rail vehicle. Increased material removal thus takes place in the central region MB of the contact strip SL on the surface of the contact strip SL than is the case on the surface of the contact strip (SL) in the two subregions TB1, TB2 of the contact strip SL. As outlined above, the magnetic field sensors SEN1 and SEN2 are positioned to the side in the subregions TB1, TB2 and below the contact strip SL or at corresponding points of the contact strip holder. The central magnetic field sensor SEN is positioned in the central region and below the contact strip SL or at a corresponding point of the contact strip holder. The central magnetic field sensor SEN thus monitors the thickness of the contact strip SL in the central region MB. The sensors SEN1 and SEN2 accordingly monitor the thickness of the contact strip SL in the associated subregions TB1, TB2 of the contact strip SL. FIG 4 shows a plan view of the contact strip SL with reference to FIG 3. FIG 5 shows an overview of the magnetic field sensors SEN, SEN1, SEN2, the magnetic fields B, B1, B2 and the currents I, I1, I2 in the case of a worn contact strip SL, with reference to the preceding figures FIG 1 to FIG 4. In comparison to FIG 3, the central magnetic field sensor SEN, which is arranged in the central region MB of the contact strip SL, is now located closer to the contact wire FD due to the increased material removal there. There is thus typically now a distance of considerably ^ 40 mm between the two, for example 25 mm. The value of 25 mm is often adopted as an operative limit and constitutes a minimum thickness for the contact strip SL. Due to the increased material removal in the central region MB, the associated signal S of the central magnetic field sensor SEN changes in comparison to the calibration described above, while the signals S1 and S2 of the associated two magnetic field sensors SEN1 and SEN2 remain substantially the same. On account of the Biot-Savart law, this is attributed to the fact that the sensors SEN1 and SEN2 maintain their distance from the source of the magnetic fields B1 and B2 with almost no change (because they are installed below subregions of the contact strip that are subject to less loading), whereas the central magnetic field sensor SEN, due to the material removal, sees its distance from the source of the magnetic field B (contact wire FD, current I) continue to reduce. The increased material removal in the central region MB of the contact strip SL leads to a change in the geometry and thus to a change in the equilibrium set at calibration. The following now applies for the worn contact strip SL shown: SO = S1 + S2 — S + 0. The electrical signal S0 is prepared accordingly and transmitted to a reception apparatus of a vehicle diagnostic apparatus. The vehicle diagnostic apparatus is preferably designed as part of the rail vehicle or is part of a remote monitoring system used to monitor the rail vehicle via a fixed control station, referred to as the land side. The vehicle diagnostic apparatus is used to monitor the wear state of the contact strip SL, wherein this monitoring is up-to-date at all times with regard to the wear state, and the monitoring is able to be performed continuously. In spite of the generally high system voltages, the sensors SEN, SEN1 and SEN2 require only little energy to generate signals. This makes it possible to supply energy to the sensors SEN, SEN1, SEN2 using a rechargeable and / or exchangeable battery, with the battery being provided in the sensor. Additional wiring of the magnetic field sensors, with all of the disadvantages this entails, is thus avoided on the rail vehicle. The magnetic field sensors are preferably protected from temperature fluctuations that occur during operation of the rail vehicle. This means that the signal measurements are able to be performed reliably at any temperature. The signals S, S1 and S2 that contribute to the formation of S0 are preferably not processed based on their instantaneous value, but rather based on their average. This reduces the influence of deviations that arise in particular due to temperature fluctuations. The averages are preferably formed in predefined time intervals. The described calibration for specifying or setting S0 = 0 is preferably performed whenever a new, that is to say non-used, contact strip is installed on the rail vehicle. The calibration preferably takes place at room temperature and at rest conditions of the current collector.

Claims

Patent claims1. An arrangement for ascertaining the wear of a contact strip (SL) of a rail vehicle current collector,- having a contact strip (SL) that has, along its length, a central region (MB), a first subregion (TB1) and a second subregion (TB2), wherein the central region (MB) is arranged between the two subregions (TB1, TB2),- having a contact wire (FD) that makes contact with the contact strip (SL) in order to feed a contact wire current(I) into the contact strip (SL), which contact wire current splits there into a first partial current (I1) that flows in the first subregion (TB1) and into a second partial current (I2) that flows in the second subregion (TB2),- in which a central magnetic field sensor (SEN) is provided for the purpose of monitoring the central region (MB), such that the central magnetic field sensor (SEN) measures a central magnetic field (B), caused by the contact wire current (I), at a distance that includes a thickness of the contact strip (SL) in the central region (MB),- in which a first magnetic field sensor (SEN1) is provided for the purpose of monitoring the first subregion (TB1), such that the first magnetic field sensor (SEN1) measures a first magnetic field (B1), caused by the first partial current (I1), at a distance that includes a thickness of the contact strip (SL) in the first subregion (TB1),- in which a second magnetic field sensor (SEN2) is provided for the purpose of monitoring the second subregion (TB2), such that the second magnetic field sensor (SEN2) measures a second magnetic field (B2), caused by the second partial current (I2), at a distance that includes a thickness of the contact strip (SL) in the second subregion (TB2),- in which, in a calibration, the magnetic field sensors (SEN, SEN1, SEN2) are arranged on a non-worn contact strip (SL) for region-monitoring purposes such that electricalsignals (S,  S1,  S2) formed from the measured magneticfields (B1, B1, B2), when summed, have a sum signal valueof zero,- in which, in the case of a subsequently worn contact strip, electrical signals (S, S1, S2) formed from the measuredmagnetic fields (B, B1, B2), when summed, have a sum signalvalue other than zero, said sum signal value being supplied to a vehicle diagnostic device (FDV) in order, based thereon and in comparison to the calibration, to determine a current thickness of the worn contact strip (SL) in the central region (MB).

2. The arrangement as claimed in claim 1,- in which the contact wire (FD) makes contact with the contact strip (SL) on a first side by way of a back and forth motion,- in which the central magnetic field sensor (SEN) is arranged on a second side, opposite the first side, of the contact strip (SL), and / or- in which the first magnetic field sensor (SEN1) is arranged on a second side, opposite the first side, of the contact strip (SL), and / or- in which the second magnetic field sensor (SEN2) is arranged on a second side, opposite the first side, of the contact strip (SL).

3. The arrangement as claimed in either of the preceding claims, in which the contact strip (SL) is connected to a contact strip holder and at least one of the magnetic field sensors (SEN, SEN1, SEN2) is fastened to the contact strip holder.

4. The arrangement as claimed in one of the preceding claims, in which the contact wire (FD) and the contact strip (SL) are oriented substantially perpendicular to one another in the contact region so as to form a system geometry.

5. The arrangement as claimed in claim 4, in which the system geometry means that the first and second magnetic field (B1, B2)are arranged in respective parallel planes that are orthogonal to the plane of the central magnetic field (B), such that themagnetic fields (B0, B1, B2) are decoupled from one another forthe magnetic field measurement by virtue of the distance between them and orthogonality.

6. A method for ascertaining the wear of a contact strip (SL) of a rail vehicle current collector,- in which a contact strip (SL) is divided, along its length, into a central region (MB), into a first subregion (TB1) and into a second subregion (TB2), wherein the central region (MB) is arranged between the two subregions (TB1, TB2),- in which a contact wire (FD) makes contact with the contact strip (SL) in order to feed a contact wire current (I) into the contact strip (SL), which contact wire current splits there into a first partial current (I1) that flows in thefirst subregion (TB1) and into a second partial current (I2) that flows in the second subregion (TB2),- in which a central magnetic field sensor (SEN) is used to monitor the central region (MB) in order to measure a central magnetic field (B), caused by the contact wire current (I), at a distance, wherein the distance includes a thickness of the contact strip (SL) in the central region (MB),- in which a first magnetic field sensor (SEN1) is used to monitor the first subregion (TB1) in order to measure a first magnetic field (B1), caused by the first partial current (I1), at a distance, wherein the distance includes a thickness of the contact strip (SL) in the first subregion (TB1),- in which a second magnetic field sensor (SEN2) is used to monitor the second subregion (TB2) in order to measure a second magnetic field (B2), caused by the second partial current (I2), at a distance, wherein the distance includes a thickness of the contact strip (SL) in the second subregion (TB2),- in which, in a calibration, the magnetic field sensors (SEN, SEN1, SEN2) are arranged on a non-worn contact strip (SL) for region-monitoring purposes such that electrical signals (S,  S1,  S2) formed from the measured magneticfields (B1, B1, B2), when summed, have a sum signal valueof zero,- in which, in the case of a subsequently worn contact strip, electrical signals (S, S1, S2) formed from the measuredmagnetic fields (B, B1, B2), when summed, have a sum signalvalue other than zero, said sum signal value being supplied to a vehicle diagnostic device (FDV) that, based thereon and in comparison to the calibration, determines a current thickness of the worn contact strip (SL) in the central region (MB).

7. The method as claimed in claim 6, in which the contact wire (FD), which is oriented substantially perpendicular to the contact strip (SL) in the contact region with the contact strip (SL), forms a system geometry.

8. The method as claimed in claim 7, in which the system geometry means that the first and second magnetic field (B1, B2), which are arranged in respective parallel planes and which are both orthogonal to the plane of the central magnetic field (B), are decoupled from one another for the magnetic field measurement by virtue of the distance between them and orthogonality.

9. The method as claimed in one of claims 6 to 8, in which the sums of the signals (S, S1, S2) of the magnetic field sensors(SEN, SEN1, SEN2) are processed based on their averages, preferably in predefined time intervals.

10. The method as claimed in one of claims 6 to 9, in which the calibration is carried out whenever a non-worn contact strip is installed on the rail vehicle, and / or in which the calibration is performed at room temperature of the current collector.

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