METHOD FOR DETECTING A RAIL VEHICLE

Description

[0001] The invention relates, as described in independent claim 1, to a method for detecting a rail vehicle in a track section configured as an electrical resonant circuit, wherein the presence of a vehicle in the track section is detected by electronic evaluation of changes in the resonant frequency and damping of the resonant circuit by performing the following steps: Excitation of the resonant circuit with a transmit signal in the form of a current signal having an adjustable transmit frequency f_s, reception of a receive signal in the form of a voltage signal representative of an oscillation of the resonant circuit, regulation of the transmit frequency f_s to the resonant frequency of the resonant circuit, and decision as to whether a vehicle is in the track section, based on a criterion that includes an evaluation of the transmit signal and the receive signal while continuously regulating the transmit frequency.

[0002] The invention relates in particular to a method for detecting tram cars in a track section of relatively short length, especially a length shorter than the length of the tram car. For example, the track section could be a switch. The detection method could then, for example, serve to implement a switch-over protection mechanism that prevents the switch from being changed while a rail vehicle is passing over it.

[0003] A method of this type is known, for example, from DE 103 20 680 A1. Similar methods are described in DE 10 2006 017 220 A1 and DE 10 2017 221 777 A1.

[0004] The track section to be secured is defined by electrically short-circuiting the two rails at each end of this section using a short-circuiting connector. The two short-circuiting connectors and the intervening rail sections then form an electrical circuit that exhibits a certain ohmic resistance as well as a certain capacitance and inductance, and therefore behaves like an electrical (parallel) resonant circuit. Often, the two rail sections are additionally connected via a capacitor, allowing the capacitance of the resonant circuit to be specifically controlled and thus the resonant frequency of the circuit to be adjusted so that the resonance lies at a frequency favorable for measurement purposes and with as little noise as possible from interference signals, for example, at a frequency of 20 to 30 kHz.

[0005] In known methods of this type, a transmission signal with a transmission frequency that ideally matches the resonant frequency of the resonant circuit is fed into the resonant circuit formed by the track section. An electrical quantity (current or voltage) is then tapped at another point in the resonant circuit, which oscillates due to the excitation of the resonant circuit.

[0006] When a rail vehicle enters the track section, at least one axle of the vehicle is temporarily located within the track section, so that the two rail sections are electrically short-circuited by this axle and its associated wheels. This results in a significant change in the resonant frequency and damping.

[0007] If the vehicle's wheelbase is greater than the length of the track section, it is possible for the vehicle to be positioned above the track section, but without an axle within that section that would short-circuit the rails. However, due to the electrical conductivity of the lower surface of the car body, which is located close to the rails, slight changes in inductance and capacitance occur, thus affecting the resonant frequency and damping. Therefore, with sufficient measurement accuracy, the presence of the vehicle can still be detected in this situation.

[0008] A particular feature of trams is that the track section can sometimes also be crossed by road vehicles, which can then simulate the presence of a rail vehicle.

[0009] The object of the invention is to improve the accuracy and reliability of the detection method.

[0010] This problem is solved according to the invention, as defined in independent claim 1, by the fact that A complex transfer function is calculated and further evaluated by dividing the complex amplitude of the received signal by the complex amplitude of the transmitted signal; the decision as to whether a vehicle is in the track section is made by at least one digital measuring unit that operates independently of the oscillator and frequency control unit; the transmitted and received signals are digitized and each converted into a spectrum by a digital Fourier transform; the transimpedance is calculated from the spectra as a function of time; a frequency value is sought at which the magnitude of the transimpedance is at its maximum; and to decide whether a vehicle is in the track section, it is checked whether the maximum magnitude of the transimpedance lies within a predefined frequency and amplitude window.

[0011] In this method, the transmission frequency is not only used to tune the transmitter to the resonant frequency of the oscillator circuit before the actual measurement begins, but the regulation continues throughout the measurement. This has the advantage that the oscillator circuit remains in resonance for the entire measurement period, especially if the circuit is detuned by a vehicle being detected. Thus, due to the resonance, a high-amplitude received signal is obtained throughout the entire measurement period, significantly above the noise level and easily analyzable. A further advantage is that the transmission frequency f_s, which varies to the resonant frequency during the regulation process, can be directly used for analysis, making it easier to detect frequency shifts.

[0012] The transmitted signal is a current signal, and the received signal is a voltage signal tapped between two points of the resonant circuit. Dividing the complex amplitude of the received voltage signal by the complex amplitude of the current signal yields a transfer function, a complex quantity with the dimension of an impedance, which will be called the "transimpedance" and which is well-suited for electronic evaluation of the transmitted and received signals with regard to changes in the resonant frequency and / or the damping of the resonant circuit.

[0013] Since the resonant circuit formed by the track section behaves like a parallel resonant circuit (parallel connection of capacitance and inductance), the magnitude of the transimpedance exhibits a maximum at resonance, and the phase of the transimpedance coincides with the phase of the transmitted signal at resonance. In other words, the resonance state is characterized by the fact that the relative phase of the received signal with respect to the phase of the transmitted signal is 0°. This relative phase is therefore suitable as a feedback signal for controlling the transmission frequency within the framework of the method according to the invention and simultaneously enables sensitive detection of changes in the resonance frequency.

[0014] Advantageous embodiments of the invention are set out in the dependent claims.

[0015] In one embodiment, a digital frequency controller is used to regulate the transmission frequency. For example, the transmit and receive signals can be digitized using analog-to-digital converters, allowing a digital phase detector to determine the phase difference between the two signals. Based on this phase difference, a numerical oscillator is driven, which regulates the frequency of the transmit signal to maintain a phase difference of 0°. The oscillator's digital output signal is then converted into an analog signal and amplified by a digital-to-analog converter to generate the transmit signal.

[0016] For redundancy, the digital evaluation of the transmitted and received signals to determine whether the track section is occupied or clear can be performed using several digital measuring units operating in parallel. High operational reliability is achieved by ensuring that the measuring units operate independently of the digital frequency controller.

[0017] The decision-making body that determines whether a vehicle is on the track section can provide a binary output signal (occupied / free). The transition window from "occupied" to "free" can be smaller than the transition window from "free" to "occupied," resulting in a certain degree of hysteresis in the system.

[0018] The following section explains an exemplary embodiment in more detail with reference to the drawing.

[0019] They show: Fig. 1 a circuit diagram of a track section configured as an electrical resonant circuit, together with a detection device for carrying out the method according to the invention; Fig. 2 a block diagram of a digital oscillator for generating a transmitted signal with a regulated frequency; Fig. 3 graphical representations of the magnitude of a transimpedance of the resonant circuit as a function of frequency, for states with or without a vehicle on the track section; Fig. 4 graphical representations of the phase of the transimpedance as a function of frequency for the same states as in Fig. 3 Fig. 5 is a block diagram of a measuring unit for detecting a vehicle on the track section; Fig. 6 is an example of an impedance / frequency spectrum with tolerance windows for determining the detection result; and Fig. 7 is a more detailed block diagram of the Fig. 1 The detection device shown.

[0020] In Fig. 1A track section 10 is shown, the rails 12 of which, together with two short-circuit connectors 14 that delimit the track section at both ends, form an electrical resonant circuit 16. An electronic detection device 18 is connected to the resonant circuit 16, which injects a transmit signal I_s as a current signal into the two rails 12 at a feed point S and taps a receive signal U_e as a voltage signal from the rails 12 at a receiving point E.

[0021] Parallel to the short-circuit connectors 14, a capacitor C is connected between the two rails 12 of the track section, which allows the natural frequency of the resonant circuit 16 to be adjusted as required. Typically, this natural frequency is in the range of 20 to 30 kHz.

[0022] In Fig. 2An oscillator and frequency control unit 20 is shown, which is part of the detection device 18 and generates the transmit signal I_s that excites the resonant circuit 16 to oscillation. The analog transmit signal I_s, present at the output of an amplifier 22, is tapped and measured internally, and the measured current is fed back to an analog-to-digital converter 24. The voltage tapped at the receiving point of the resonant circuit 16 as the received signal U_e is transmitted to another analog-to-digital converter 26 of the oscillator and frequency control unit. A digital computer 28 has a phase detector 30 as its input stage, which receives the digitized transmit and receive signals from the analog-to-digital converters 24 and 26 and calculates the relative phase φ of the received signal relative to the transmitted signal.A comparator stage 32 compares the relative phase φ with the setpoint 0° and passes the comparison result to a control stage 34 (for example, a PID controller), which generates a setpoint for the transmission frequency f_s based on the comparison result. Using this setpoint, a numerical oscillator 38 generates, for example, a sinusoidal digital transmission signal with the transmission frequency f_s. This signal is converted into an analog signal in a digital-to-analog converter 40, which is then amplified in the amplifier 22 to form the analog transmission signal I_s.

[0023] In an advantageous embodiment, the phase detector 30 is a frequency-selective phase detector that evaluates the received signal only within a narrow frequency band around the transmit frequency. This allows interference signals that could otherwise disrupt the phase detector to be suppressed. This can be achieved, for example, with a bandpass filter upstream of the actual phase detector or by phase measurement using a discrete Fourier transform. In this case, the input data for the phase detector includes, in addition to the transmitter current and the receiver voltage, the current transmit frequency.

[0024] The transimpedance Z of the resonant circuit 16 is defined as the quotient of the complex amplitude of the received signal U_e and the complex amplitude of the transmitted signal I_s. Electrically, the resonant circuit 16 behaves like a parallel resonant circuit in which the capacitance and inductance are connected in parallel. In the case of resonance, i.e., when the transmitted frequency f_s matches the resonant frequency of the circuit, the magnitude of the transimpedance Z reaches a maximum, and the phase of the complex transimpedance (which is equal to the phase difference φ between the received and transmitted signals) assumes the value 0°.

[0025] In Fig. 3The magnitude of the transimpedance |Z| as a function of the transmission frequency f_s is given by a curve F, represented by a solid line, for the case where the track section is clear, i.e., no vehicle is on this track section, and the natural frequency of the resonant circuit 16 is set to 20 kHz. The curve F therefore has a distinct maximum at 20 kHz.

[0026] Accordingly, in Fig. 4 The curve F', shown as a solid line, represents the magnitude of the transimpedance as a function of the transmission frequency for the case where the track section is clear. It can be seen that this curve intersects the 0° line at 20 kHz.

[0027] Under these conditions, the oscillator and frequency control unit 20 regulates the transmission frequency f_s to the resonance value of 20 kHz.

[0028] If, on the other hand, a vehicle enters or leaves track section 10, such that at least one axle of the vehicle is on the track section and short-circuits the rails 12, this leads to a significant decrease in the transimpedance and a shift in the resonant frequency. This case is described in Figures 3 and 4 The curves E and E' are represented by dotted lines. Dashed lines illustrate the case where track section 10 is occupied, i.e., a vehicle is on the track section, but no axle of the vehicle lies within the track section, so that the rails 12 are not short-circuited. In this case, there is only a slight shift in the resonant frequency and a slight decrease in the maximum transimpedance due to the metal surface of the vehicle body.

[0029] If track section 10 is a section of tram track and is, for example, being crossed by a car, the deviation of the transimpedance curves from curves F and F' may be smaller or larger than that of curves B and B'. However, this difference alone is generally insufficient to reliably determine whether a rail vehicle is actually on the track section and therefore the switch must not be thrown, or whether the track section is merely being crossed by a car.

[0030] In Fig. 5A block diagram shows a measuring unit 42, which serves to determine, based on the transmitted and received signals U_s, whether the track section is clear or occupied by a rail vehicle. The transmitted and received signals are each digitized by means of an analog-to-digital converter 44 and 46, respectively. The digitized signals are each subjected to a fast Fourier transform (FFT) in a processor unit 48, so that the spectra of the complex amplitudes of the transmitted and received signals are obtained. A division element 50 calculates the equally complex transimpedance Z as a function of frequency from these complex amplitudes. The amplitudes of the transmitted signal, the received signal, and the transimpedance, each as a function of frequency f, are passed to a selection element 52, which searches for a frequency f_pk at which the magnitude of the transimpedance is at its maximum.This frequency f_pk, as well as the transimpedance Z and the transmit signal I_s at this frequency, are passed to a decision module 54, which uses these quantities to determine the state of track section 10.

[0031] For the sake of simplicity, it is assumed that the decision module 54 only delivers a binary signal as a result, which can either have the value "free" or the value "occupied".

[0032] An example of a possible decision algorithm will be given using the following: Fig. 6The diagram illustrates a simplified spectrum (function of frequency f) of the magnitude |Z| of the transimpedance. For simplicity, only two peaks, P1 and P2, are shown, differing in their frequency and amplitude. Peak P1 represents the case where the track section is clear, while peak P2 represents the case where the track section is occupied by a train. Peak P1 lies within two nested windows of different sizes, W1 and W2, each with a certain extent in both the dimension f (frequency) and the dimension |Z| (amplitude). Strictly speaking, these windows are three-dimensional and also have a certain extent in the dimension of the transimpedance's phase, but this is not apparent in the two-dimensional diagram. Fig. 6cannot be represented. In the phase dimension, the windows are centered on the phase difference of 0° and have only a small extent, so that it is ensured that a detected peak is only evaluated when the phase is almost 0° and the resonant circuit is therefore in resonance.

[0033] The dimensions of window W1 in terms of frequency and amplitude are chosen such that a peak lies within this window only if the track section is truly clear, i.e., no vehicle axle is located in the track section (curves E and E' in Figures 3 and 4 ) and there is also no car body of a rail vehicle above the track section (curves B and B' in Figures 3 and 4If the peak lies within window W1, the decision result is therefore "free". If a car now drives over the track section, this leads to a shift of the peak, but this shift is so small that the peak still remains within the larger window W2. The decision module 54 then remains in the "free" state. However, if a rail vehicle enters the track section, at least one axle causes a short circuit, and the peak shifts to a point outside window W2 (peak P2). The decision module 54 then switches to the "occupied" state. If the axle of the rail vehicle then leaves the track section again, but the car body is still above the track section, the peak moves back into window W2, but remains outside window W1. Under these circumstances, the decision module remains in the "occupied" state.Only when the peak moves back into window W1 does the state change back to "free".

[0034] In Fig. 7 A more detailed block diagram of the complete detection device 18 is shown. In this example, the detection device comprises the oscillator and frequency control unit 20 and two independently operating measuring units 42, both of which measure the in Fig. 5The setup shown is as follows. A separation stage 56 is designed to split the transmit signal I_s generated by the oscillator and frequency control unit 20 into a signal that is fed into the resonant circuit 16 and signals that are applied to the transmit signal inputs of the two measuring units 42. A further separation stage 58 is designed to split the received signal U_e received by the resonant circuit into a signal that is fed back to the oscillator and frequency control unit 20 and signals that are applied to the receive signal inputs of the two measuring units 42. Overall, the detection device 18 thus forms a redundant measuring system in which the two measuring units 42 operate independently of each other and also independently of the oscillator and frequency control unit 20, so that susceptibility to interference is reduced to a minimum.

Claims

1. A method for detecting a rail vehicle in a track section (10) that is configured as an electric resonant circuit (16), wherein the presence of a vehicle in the track section is detected by electronic evaluation of changes in the resonant frequency and damping of the resonant circuit (16) by performing the following steps: - exciting the resonant circuit (16) with a transmission signal (I_s) in the form of a current signal which has an adjustable transmission frequency f_s, - receiving a receiving signal (U_e), in the form of a voltage signal representative of an oscillation of the oscillating circuit (16), - adjusting the transmission frequency f_s to the resonant frequency of the resonant circuit (16), and - deciding whether a vehicle is in the track section on the basis of a criterion that includes an evaluation of the transmission signal (I_s) and the receiving signal (U_e) with continuous control of the transmitting frequency, characterized in that: - a complex transmission function is calculated and further evaluated by dividing the complex amplitude of the receiving signal by the complex amplitude of the transmitting signal, - the decision whether a vehicle is in the track section is made by at least one digital measurement unit (42) operating independently of the oscillator and frequency controll unit (20), and - the transmission signal (I_s) and the receiving signal (U_e) are digitized and converted into a spectrum by a digital Fourier transform, the transimpedance (Z) is calculated from the spectra as a function of time, a frequency value is sought at which the amount of the transimpedance is maximum, and for deciding whether a vehicle is in the track section, it is checked whether the maximum of the transimpedance amount is within a given frequency and amplitude window (W1, W2).

2. The method of claim 1 wherein a digital frequency controller is used f_s to control the transmission frequency.

3. The method of claim 2, wherein the digital frequency controller is part of an oscillator and frequency controller unit (20) in which a setpoint value for the transmitting frequency f_s is formed by comparing the phase difference (φ) between the transmission signal and the receiving signal, an oscillating digital signal with a frequency corresponding to the setpoint is formed with a numerical oscillator (38), from which the transmitting signal (I_s) is then derived by digital / analogue conversion.

4. The method of claim 3, wherein the digital frequency controller comprises a frequency-selective phase detector.

5. The method according to any of the preceding claims, wherein a decision module (54) which decides whether a vehicle is in the track section changes from an "occupied" state to a "free" state when the maximum is in a first window (W1) and returns from the "free" state to the "occupied" state only when the maximum is outside a larger second window (W2).

6. A device for detecting a rail vehicle in a section of track (10), charactrized by an electronic detection device (18) configured to execute the method according to any one of claims 1 to 5.

7. A software product comprising program code which, when loaded into an electronic detection device (18) according to claim 6, causes the detection device to execute the method according to any one of claims 1 to 5.