Train stop

The mechanical shift lock is a system of point-like train control. This ATP system was developed in the early years of the U- and S -Bahn service. In contrast to long-distance trains these transport systems were designed from the outset for dense sequence of moves, many branches, narrow arches and short station distances. In order to avoid collisions and rear-end collisions, a system had to be created which prevents over- driving a to "stop " standing signal.

Basically, there are mechanical and electromagnetic systems, where the mechanical systems have been developed in late 19th century, while electromagnetic systems arose later and the problems of mechanical systems partially eliminated. Nevertheless, mechanical travel locks are still used today, such as at the Berlin S -Bahn or the New York subway. Advantage is the very simple, yet safe and in case of failure easy to overcome execution.

Mechanical traction lock

Basically, mechanical traction lock can only trigger the emergency brakes, but have no way to monitor the vehicle speed.

The function of a mechanical shift lock is always the same regardless of the type. Depending on the signal aspect (" stop" or " travel") is one attached to the track movable mechanical element ( the line stop ) so found that when haltzeigendem signal one attached to the train counterpart is touched, what emergency brake is triggered. If the signal is stationary, the movable element of the route stop is found that the counterpart will not affect the train.

Track-side Assembly

• S -Bahn Berlin (called the so-called route stop, also Bernauer Drive Lock ) A mounted alongside the track in bogie height metal bar touches the trigger on the leading bogie. The route stop works for fahrtzeigendem signal to the side into the free position (see illustration above).
• U -Bahn Berlin, Small Profile: At the signal, there is a metal rod similar to a signal arms at the height of the car roof, this is at haltzeigendem signal in a horizontal position. She lays around on the roofs of the railcar on the cabs fixed ( equal to the first door ) release lever. Often these levers of ignorant was interpreted as a lightning rod. The provision after triggering was done mechanically with a triangular wrench by the driver.
• U -Bahn Berlin, United Profile: A mushroom-shaped lever folds next to the track at the gauge and press the release lever on the leading bogie when the signal " stop" shows.
• Metro New York: A label on the threshold to the right of the right rail T-shaped piece of metal (referred to there as Tripcock ( trigger ) ) works in stop position upward, and operated a motor mounted on the bogie downwardly release lever. In drive position, the T-shaped is folded down.
• London Underground: Similar to New York, a mounted right next to the right rail square element, which is folded into maintenance position upward, and a release lever actuated on the bogie.

In all systems, only the triggering device of the current at the head of the train vehicle is effective. In order for the other trigger each turn not beat with possibly high speed against each route stop, which would lead to high wear, the route stops usually run with a time delay after the stop event of the signal into the barrier layer. For the same reason, the track stops the opposite direction may be brought into the free position. Because that does not in any case depends on the interlocking design possible, the release lever are apportionable in the opposite direction and without consequences.

In mechanically detected signals form the route stop is mechanically coupled to the signal. Route stops at light signals or electrical signals provided form given their own electric traction drive lock. Marshalling and shunting signals are also equipped with range attacks. Where trains have forcibly stopped, for example, before the track or statements from the entrance to car yards, set in the locked position route stops are installed without drive.

On-board equipment

Each vehicle with a driver's cab is equipped with a protruding from the Fahrzeugumgrenzungslinie trigger that corresponds to the track facility. If it is pushed, releases the emergency brake. Usually a special valve in the main air line is opened to the same time, the tensile force is switched off. In order to pass in the event of a fault to a halt pointing signal, can the in-vehicle equipment to the meter valve make temporarily inoperative. With the associated counter you can find evidence that use.

Operational problems

Since the inertia forces increase with the square of the speed, the mechanical shift lock on tracks with low speeds is limited. Doing so may cause damage to the transmission facilities.

Another problem is that the mechanical shift lock no speed monitoring and no Vorsignalbeeinflussung allowed, so the Durchrutschweg or Protection section between the signal and the point must always be of such a size that even a traveling at high speed train to the point of operation can be stopped safely. This leads to relatively long protection sections, and thus longer headways. However, this can be mitigated by overlapping the block portions in which the signal distance is shorter than the protective portion. Several block sections while they must remain free between two trains, however, a block signal is represented by the shorter block sections more quickly and permits the subsequent moving up the train.

Another possibility, which is practiced in the metro New York, is the use of time-dependent ignition interlocks for speed monitoring. Here, the train travels over a trip contact, creating a time measurement is started. The following at a distance of traction lock is placed only after the time in the fuzzy position that requires the train at the applicable speed limit at least between trip contact and traction lock, allowing you to fast-moving train is stopped on the travel ban still in firing position.

By using these options in 1936 headways could be operated safely in 90 seconds, for example, at the Berlin S -Bahn during the Olympic Summer Games.

Despite all these possibilities, the mechanical shift lock has serious shortcomings, which led to the subsequent development of the electromagnetic driving locks.

In the S -Bahn Berlin came in March 2008 to a near-collision in Berlin- Lichtenrade S-Bahn station, as a train a " stop" signal at danger ran over without being stopped. The top speed of all S -Bahn trains was reduced by the Federal Railway Office of 100 km / h to further notice to 80 km / hr. A contract to equip the trains with a radio-based train control system was awarded in 2007.

Electromagnetic Drive Lock

In the electromagnetic driving the lock information is transmitted on magnetic way. In a usually mounted between the two rails box is a permanent magnet whose magnetic field is detected by a receiver located in the vehicle. In addition to the permanent magnet a coil is arranged, which is signal showing current flows through when moving the permanent magnet and a reverse magnetic field is built. Due to the superposition of the two magnetic fields, the effect is almost canceled and the train can pass the driving lock unhindered.