Travel lock
The mechanical travel lock is a system of punctual train control . It was developed in the early years of the underground and S-Bahn traffic. In contrast to long-distance railways, these transport systems were designed from the outset for dense train sequences, many junctions, tight curves and short distances between stations. In order to avoid collisions and rear-end collisions, a system had to be created that prevents signals indicating stopping points from being run over.
history
Basically, there are mechanical and electromagnetic systems, with the mechanical systems already being developed at the end of the 19th century, while electromagnetic systems emerged later and partially eliminated the problems of the mechanical. Nevertheless, mechanical travel locks are still used today, for example on the Berlin S-Bahn or the New York subway . The advantage is the very simple, yet safe design that can be easily overcome in the event of a fault.
The driving locks on the Berlin S-Bahn are also called Bernau driving locks or Bernau type driving locks because they were first tested and introduced at the end of the 1920s on the already electrified line to Bernau. The prototype was presented to the public in Blankenburg station in 1926. It will then be installed on the Szczecin Railway between Bernau and Nordbahnhof - the latter was called Szczecin Railway Station until 1950 and was the terminus of the line until 1936 (the lines were then extended into the new north-south tunnel ). The other installations follow the "electrification" of the S-Bahn - the first series of electric multiple units was also called the Bernau type , corresponding to its first use .
Mechanical travel lock
In principle, mechanical travel locks can only trigger emergency braking, but do not offer the option of transmitting pre-signaling information.
The function of a mechanical travel lock is always the same regardless of the type. Depending on the signal aspect (“stop” or “run”), a movable mechanical element attached to the track (the track stop) is set so that when the signal indicates a stop, a counterpart attached to the train (the release lever) is touched, which triggers an emergency brake. If the signal reaches a travel concept, the movable element of the route stop is set so that the release lever is not touched.
Trackside equipment
A metal rail attached next to the track at bogie height - the so-called track stop - touches the release lever on the leading bogie. The section stop, which is vertical in the blocked position, folds back about 45 ° into the open position when the signal is pointing to the traffic (see figure above). At the end of 2019, 169 km were still equipped with the driving lock.
- U-Bahn Berlin , small profile : At the signal there was a metal rod similar to a signal wing at the height of the car roof, this was in a horizontal position when the signal was to stop. She threw the release lever attached to the roofs of the railcars above the driver's cabs - at the level of the first door. Often this lever was interpreted as a lightning rod by the inexperienced. The driver reset it mechanically using a triangular key.
- U-Bahn Berlin, large profile : A mushroom-shaped lever folded into the clearance profile next to the left rail and actuated the release lever on the leading bogie when the "Stop" signal showed.
- New York subway : A T-shaped piece of metal attached to the threshold to the right of the rail - referred to there as a tripcock (release lever) - folds up into the stop position and actuates a release lever that protrudes downward on the bogie. In the driving position, the metal piece is folded down.
- London Underground : Similar to New York, a square element attached to the right of the rail, which is folded up in the stop position, and actuates a release lever on the bogie.
In all systems, only the release mechanism of the vehicle at the head of the train is effective. So that the other release levers of each train do not hit each line stop at high speed, which would lead to high wear, the line stops usually only run with a time delay after the signal has stopped in the blocked position. For the same reason, the route stops in the opposite direction are also brought into the open. Because this is not always possible, depending on the type of interlocking, the release levers can be moved freely in the opposite direction without any consequences.
In the case of mechanically generated shape signals , the linear stop is mechanically coupled to the signal. Route stops on light signals or electrically generated shape signals receive their own electric travel lock drive . Shunting and track blocking signals are also equipped with route stops. Where the trains are forced to stop, for example in front of the end of the track or in front of the entrance to the car halls, fixed route stops without a drive are installed in the blocked position.
On-board equipment
Every vehicle with a driver's cab is equipped with a release lever that protrudes from the vehicle boundary and corresponds to the track equipment. If it is operated, an emergency brake is triggered . As a rule, a special valve in the main air line is opened for this purpose and the pulling force is switched off at the same time. In order to be able to drive past a signal indicating a stop in the event of a fault, the vehicle equipment can be temporarily deactivated with the counter valve . Use can be verified with the associated counter.
Operational problems
Since the inertia forces increase with the square of the speed, the mechanical travel lock is limited to railways with low speeds. Otherwise the transmission equipment can be damaged.
Another problem is that the mechanical travel lock does not allow speed monitoring and no pre-signal influencing, which is why the slip path or protective section between the signal and the danger point must always be large enough that a train traveling at top speed can be safely stopped as far as the danger point. This leads to relatively long protective sections and thus longer headway times . However, this can be mitigated by overlapping block sections where the signal spacing is shorter than the guard section. Although several block sections must remain free between two trains, the shorter block sections enable a block signal to be released more quickly and enable the following train to move up.
Another option that is practiced on the New York Subway is the use of time-dependent travel locks for speed monitoring. The train runs over a release contact, which starts a time measurement. The section stop following at a defined distance is only brought into the open position after a delay time that the train needs at least between the trigger contact and the section stop at the applicable maximum speed, so that a train moving too fast is stopped by the section stop that is still in the blocked position.
By using these possibilities z. B. on the Berlin S-Bahn during the 1936 Summer Olympics, train sequences of 90 seconds can be safely driven.
Despite all these possibilities, the mechanical travel lock has serious shortcomings, which led to the subsequent development of the electromagnetic travel locks.
At the Berlin S-Bahn there was a near-accident in the Berlin-Lichtenrade S-Bahn station in March 2008 when a train ran over a stop signal without being forced to brake. The top speed of all S-Bahn trains has been approved by the Federal Railway Authority of 100 km / h until further to 80 km / h reduced. An order to equip the trains with a radio-based train control system (ZBS) was awarded in 2007. The Federal Railway Authority approves the use of the mechanical travel lock in the Berlin S-Bahn network until the end of 2025. From 2024, all routes must be converted to ZBS.
Electromagnetic travel lock
With the electromagnetic travel lock, information is transmitted on a magnetic path. A permanent magnet, whose magnetic field is detected by a receiver located on the vehicle, is located in a box that is usually attached between the two rails. In addition to the permanent magnet, a coil is arranged through which current flows when the signal is pointing to the road and builds up a magnetic field opposite to the permanent magnet. The superposition of the two magnetic fields almost neutralizes the effect, and the train can pass the traffic lock unhindered.
literature
- Hans-Jürgen Arnold among others: Railway safety technology. 4th edited edition. VEB Verlag for Transport, Berlin 1987, ISBN 3-344-00152-3 .
Web links
Individual evidence
- ↑ If there is construction on the Ostring… . Item 3 - Issue 14 - Building - Page 12 July 3, 2011.
- ↑ http://www.stadtschnellbahn-berlin.de/technik/zbs/index.php
- ↑ Infrastructure status and development report 2019. (PDF) Performance and financing agreement II. In: eba.bund.de. Deutsche Bahn, April 2020, p. 124 , accessed on May 17, 2020 .
- ↑ New safety technology for the S-Bahn . Electronics are to replace mechanical emergency brakes on trains by 2017. In: The world . April 7, 2008 ( online [accessed February 14, 2013]).
- ↑ News in brief - S-Bahn . In: Berliner Verkehrsblätter . No. 1 , 2016, p. 12 .