Patent Publication Number: US-2012029740-A1

Title: Method and device for monitoring speed

Description:
The invention relates to a method for monitoring the speed of rail vehicles and to a device relating thereto. 
     Speed monitoring devices serve usually to regulate the speed of the rail vehicle to a setpoint value and/or to trigger forced braking when a maximum permissible speed is exceeded. The maximum permissible speeds are frequently track-specific maximum speeds, for example on sections of track with a negative gradient, bends in the track with small radii, dead-end tracks or train reversing installations as well as tracks with shortened overlaps. For this purpose, two partial functions are to be implemented, specifically measurement and evaluation of the approach speed of the rail vehicle to a track-side device, and transmission of a braking instruction to the rail vehicle when the speed is over excessive. 
       FIG. 1  illustrates a typical configuration of a known design for solving this problem. The track-side device is composed here of a train stop  1 , for example on the basis of inductively acting coupling coils or magnetically, electro-mechanically or mechanically acting contacts, and a preceding measurement track  2  with two measurement points  3  and  4 , for example on the basis of inductively acting wheel sensors. The rail vehicle  5  is equipped with a device  6  which detects the activation state or deactivation state of the track-side train stop  1  when it travels over it. In the basic position, the train stop  1  is always activated and therefore brings about forced braking of the rail vehicle travelling over it. The measurement and evaluation of the speed is based on the defined distance between the two measurement points  3  and  4  and the determined time interval between the pulses which are recorded by the measurement points  3  and  4 . The speed which is determined is compared with the maximum permissible track speed, wherein the train stop  1  is deactivated only if the speed which is determined is less than or equal to the maximum speed. When the maximum speed is exceeded, the train stop  1  remains active and therefore brings about forced braking by interacting with the rail-vehicle-side device  6 . A disadvantage with this known speed measuring device, in addition to the considerable expenditure on the sensor system, is in particular the principle of measuring at specific times. 
     The invention is based on the object of disclosing a method and a device which permits simpler and at the same time more continuous measurement of speed. 
     According to the method, the object is achieved in that the rail vehicle emits a signal whose propagation time is evaluated on the track side with respect to the speed, and in that the evaluated signal is transmitted back to the rail vehicle. 
     A device according to claim  4  for carrying out the method has for this purpose a vehicle device with a transmitter/receiver module and a track-side device with a receiver/transmitter module, wherein the track-side device has an evaluation unit for evaluating the speed of a signal which is received by the transmitter/receiver module of the vehicle device. 
     In this way, it is possible to monitor speed even without using the conventional, cost-intensive track-side sensor system. Positionally fixed measuring points and the associated cabling are dispensed with. A train stop with the associated cabling is also dispensed with by virtue of the possibility of bidirectional signal transmission. Significantly fewer track-side components are required, said components being particularly susceptible to wear owing to mechanical, climatic and biological/chemical environmental conditions. 
     According to claim  2 , an RFID—radio frequency identification—signal is emitted, evaluated and transmitted back. The propagation time of the RFID signal, which constitutes a measure of the distance and therefore a measure of the speed in its variation over time, can be conveniently determined with extremely high accuracy. As a result, continuous measurement of speed and continuous transmission of a response signal back to the rail vehicle to be monitored are possible. Furthermore, it is advantageous that an RFID vehicle device can be used both for scheduled train operations and for special journeys, for example construction vehicles which do not usually travel on the tracks. A portable design of the vehicle device also allows it to be carried by small units. By virtue of the portability of the vehicle device, there is also the possibility of issuing it before the train travels into the track section which is to be monitored for excess speed and of taking it back or deactivating it at the end of this track section. Furthermore, it is also conceivable to use the device as a fall back level, for main lines or else for temporary track closures, making travel on only one track possible, due, for example, to engineering work. It is also advantageous here that the track-side device can also be embodied in a positionally variable fashion. The positioning of the vehicle-side and track-side RFID components does not require precise orientation between an RFID transmitter/receiver module on the rail vehicle and an RFID receiver/transmitter module on the track. Moreover, the robustness and small size of RFID components are also advantageous when carrying out speed measurements using said components, significantly facilitating temporary use according to the requirements. 
     According to claim  3 , when a maximum permissible speed is exceeded, a signal which triggers forced braking is preferably transmitted back to the rail vehicle. For safety reasons, forced braking is necessary only at an excessive speed, with the result that it is possible to dispense with the transmission back of signal when the speed is adapted. 
    
    
     
       The invention will be explained in more detail below with reference to figurative illustrations, in which: 
         FIG. 1  shows a device for monitoring speed of a known design, and 
         FIG. 2  shows a device for monitoring speed according to the invention. 
     
    
    
     In  FIG. 2 , the assemblies, which are identical for the known device for monitoring speed which is illustrated in  FIG. 1  and explained above, are characterized by the same reference symbols. It is apparent that a measurement track  2  ( FIG. 1 ) which is installed on the track side by means of fixed measuring points  3  and  4  ( FIG. 1 ) and is connected by cable to a train stop  1  is absent. Instead, a vehicle device  7  is provided with a transmitter/receiver module using transponder/reader technology which emits RFID signals  8 , which are received by a track-side device  9  with a receiver/transmitter module using transponder/reader technology, and are evaluated with respect to the vehicle speed. The evaluation is carried out in such a way that a speed which is derived from the propagation time of the signals  8  is compared with a maximum permissible speed. An evaluation unit  10  of the track-side device  9  is used for this. If the maximum permissible speed is exceeded, an RFID response signal  11  is generated, which contains a command to trigger forced braking and is transmitted to the vehicle device  7 . 
     In this way, the current speed is not only measured at a specific point—as in the case of the device for monitoring speed according to FIG.  1 —but rather continuously. The transmission of a command for forced braking to the rail vehicle  5  also takes place continuously and not only when the vehicle travels over a train stop  1  ( FIG. 1 ). This not only simplifies the system components and reduces their number but also increases the reliability to the overall system for monitoring speed.