Key dependency

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The principle of key dependency is a simple method of securing train journeys . It is based on the fact that different types of keys are only available once per operating point . As a result, each key stands for an individual secured position of track elements, for example for the position of a switch .

functionality

On the principle of key dependency, dependencies between the outdoor system and interlockings , dependencies within the interlockings or even entire security systems can be built up. Due to the simple and relatively robust technology, there are many possible uses; in some cases, new key dependencies are also built into modern interlockings.

Basically there are two or more possible positions for each key, it is either locked in one or the other position or is just on the way from one position to the other.

The simplest example is a key-dependent turnout: A key can be released in the interlocking, and this key is then used to unlock the lock on the turnout so that it can be changed. As long as the key is not locked again, train journeys over this switch in its starting position are excluded, since the missing key indicates that the switch is not secured in the required position and could therefore have an incorrect one.

If the turnout can be used by trains in both positions or if there are consequential dependencies, there is another lock for the other end position of the turnout, the key of which can then be removed after the turnout has been changed.

Signal box

As diverse as the application possibilities are, there are so many possibilities for integrating a key dependency into the interlocking logic. Locks for key dependencies can actually be attached to any interlocking design.

Key rack

Main article: Key rack # railroad

Key boards represent the simplest form of integrating key dependencies in interlockings. The dispatcher checks whether all the keys required for the route are on the key board before he releases the train journey. There is therefore no technical signal dependency.

Keyboards are also used in other interlocking designs if points are manually secured with a switch lock in the event of a construction site or a point fault.

Key work

With the key works, almost the entire interlocking consists of key dependencies, a key for a route can only be excluded if the correct switch keys are included. If the route key is excluded, you can set the signal with it (directly or indirectly). At the same time, however, the switch keys for the respective route are locked. Since the keys for the switches can no longer be removed, they can no longer be changed, so the route is secured.

Mechanical signal boxes

In mechanical interlockings, keys can be integrated directly into the signal dependency by means of a lever bank lock, which is placed on a free lever position and moves a locking bar like a lever. Lever bank locks are available with one or two factory locks. The former are used to make system parts with only one position to be secured, such as crossing safety systems, signal-dependent. In the case of lever bank locks with two locks, the transmission angle to the locking bar is extended to the front and ends in a handle, as it is not possible to attach it to the locking bolts of both work locks. With such a bank lock, system parts such as switches can be made signal-dependent in two positions. This possibility is also used to integrate electrically remote-controlled turnouts into mechanical interlocking systems. The counterpart of the work locks of the lever bank lock are then electrical key locks. The associated switch can only be changed if both keys are in these key locks. The presence of the correct key is then checked for each route setting in a similar way to the position of the switches, for example. Integration into the electrical part of the interlocking via a key lock (block circuit) is also conceivable.

Electromechanical signal boxes

In electromechanical interlockings, points can be made key-dependent using special lever bank locks (called “Steigerschloss” after their inventor). The climbing lock is placed on the front edge of the mechanical locking register. It contains two factory locks, both of which can only be removed when the switch lever is in the 45 ° position. Older systems often had a permanently installed riser lock on an unused reserve switch lever. For the integration of a temporarily electrically non-adjustable switch, this only had to be equipped with the relevant locking pieces on the route slider. The Steigerschloss is primarily intended for manually operated turnouts, the turnout lever can only be brought into the respective position if the associated key is locked.

An integration of a key lock in the circuit is also conceivable.

Track diagram interlockings and electronic interlockings

In the case of track diagram interlockings and electronic interlockings , turnouts that are rarely used are usually key-dependent, and most of them are electrically controlled. The turnout key is kept in a key lock in the basic position of the turnout . Often this key lock is not in the signal box, but near the turnout. The dispatcher can release the key lock, the switch operator can lock the key and thus change the switch. However, this means that all routes over this switch are excluded. Allowing a train ride using the main signal travel position via this switch is only possible again when it is locked and the key is locked in the key lock.

In the case of WSSB signal boxes, the possibility of temporarily making turnouts that cannot be remotely operated electrically is key-dependent and provided from the outset and, as a rule, also prepared in terms of switching. For this purpose, there are one, in larger train stations there are also several cabinets with electric key locks. Depending on the interlocking design, they are connected via a connector in place of the turnout switch (GS I), the operating mode connector (GS II DR) or a special program plug location on the turnout group (all track plan designs) without additional switching work.

Construction stages

If the route is being built, turnouts or points whose normal drive can no longer be used are often made key-dependent. Since the points are set on site, additional monitoring by the interlocking technology is no longer necessary, only a key lock or a simple lock has to be integrated into the interlocking. This means that not much needs to be changed in the signal box itself. Individual track blocks or construction points are also turned into remote-controlled points depending on the key. In the hand lock attached to the switch, a bolt must be pressed against the remote switch tongue so that the key of the switch or track lock can be locked out. As long as the key is locked in the switch, it can be placed anywhere from the signal box, the locked track barrier or construction switch offers flank protection. If a vehicle is to enter the construction track, the turnout is set accordingly and the construction track lock can be stored using the key dependency.

Outdoor facilities

Most key dependencies secure switches, crossings with movable double frogs and track barriers. But it is also possible to secure other obstacles, such as moving bridges.

Each of these objects is equipped with a lock, the hand lock, if necessary with a lock for each position.

Switches

There are several variants of switch hand locks. All designs are based on the same basic principle: Either you have excluded the key (and locked it in the switchboard for it) and cannot set the turnout, or if you have locked the key, you can set the turnout, but trips over the original position of the turnout are through excluded the key missing in the interlocking.

Turnouts can either have only one lock for only one position, or two locks, each for one position:

  • Switches that are only used in one position by train routes are usually only secured in this position. As long as the key is locked in the signal box, it is known how the points are, and trains can travel over this point. If the key is excluded, train journeys are excluded and the points can be set. Shunting runs on the main track and into the siding are allowed.
  • If the turnout is used by trains in both positions, both positions are secured with locks. To change the turnout, both keys must be enclosed in the turnout; only the key that corresponds to the position of the turnout can be excluded. If this key is locked in the signal box, trains can travel over the respective position of the switch.

Dead bolt hand lock

Simple bolt hand lock that locks the two bolt bars

Bolt hand locks are firmly attached to the turnouts and are used for the scheduled locking of turnouts. The switch tongues are connected to locking bars (also called locking bars), which are held in place by the lock. If the turnout is only to be locked in one position, a simple bolt hand lock is used. The points can be locked in both positions with the help of a double hand lock. The double bolt hand lock consists of two simple bolt hand locks, both of which act on the bolt bars. Often the bolt hand lock sits on the switch lever.

Switch lock

Switch lock: The lock with sliding bolt prevents the switch from being
repositioned .

Switch locks are used to temporarily lock a switch. If the tongue is on the side of the lock, a sliding bolt can be pushed against it and locked with the lock. The remote switch tongue and the adjacent switch via the switch lock are blocked and the switch can no longer be set. If you unlock the lock, the points can be adjusted again. The locking bolt is moved and the key can no longer be removed from the lock. The switch lock is attached to the rail with two screws. The holes required for this must be provided in the stock rail.

Since the adjacent switch tongue is only secured indirectly, switch locks can only be used if the point lock is intact.

Tongue lock

Tongue lock without permanently attached lock

Tongue locks are used to temporarily close adjacent or remote switch blades. Similar to a screw clamp , an adjacent switch tongue can be clamped to the stock rail or a remote switch tongue can be kept at a distance. The threaded spindle of the tongue lock is blocked via the handwheel using a locking slide, which is locked by a lock.

Since the tongue lock has to be removed to switch the switch, it cannot be guaranteed that the switch tongue is locked in the correct position. Tongue locks cannot therefore be used for signal dependencies.

Hand lock 73

The hand lock 73 (Hv 73) is similar to a tongue lock. This is also attached to the rail foot of a stock rail with two clamping pieces and a threaded spindle. With the help of a locking block, either the adjacent switch tongue is clamped to the stock rail or the remote switch tongue is kept at a distance. The locking block is fixed using the threaded slide bolt and the handwheel and secured with a safety bolt. In addition, a lock can be attached, through which a key dependency can be guaranteed.

Track closures

Key- dependent track locks often have a lock in both positions, as with the turnouts, only the key that corresponds to the position of the track lock can be excluded here. The key for the track lock that has been placed on the system usually comes from the signal box, while the key for the track lock that is placed is used to unlock a sequence-dependent switch.

Consequence dependencies

Example of a follow-up dependency of a turnout in the siding from a track block

Two guideway elements are sequence-dependent if they have to be placed one after the other; the second element can only be placed when the first is in the correct position. Most of the time, a switch is dependent on the sequence of a track block or the associated protection switch / flank protection switch .

Follow-up dependencies can be implemented relatively easily with key dependencies. With the key from the signal box, you can unlock and move the first track element (very often a track lock). In the other position you get another key with which you can unlock and set the second track element (usually the associated switch). If necessary, this can also be locked in the second position.

In this way, two guideway elements can be secured, but in the interlocking both are only integrated as one element. Only the labeling indicates that two elements can be changed with one key: The element that was changed first is shown normally on the labeling of the key, the sequence-dependent element is in brackets below.

Sequence dependency order

The typical example of a consequential dependency is a turnout with a track blocker that provides flank protection. Historically, the track blockade was first put down and then the switch was placed on the siding. The advantage of this is that you cannot accidentally drive upside down on the track barrier, as this will then be damaged and the derailment will go in the wrong direction. The disadvantage is that a shunting run from the siding could accidentally open the wrongly set points.

More recently there has been a move towards building the sequential dependency the other way around in the case of signal boxes that are not locally manned, the points are set first, and the track barrier can be removed with the key of the points in the changed position. The reason is that the points can no longer be opened, but you could drive the wrong way around on the applied track block. An opened switch would have to be checked at great expense, for this reason this was often covered up. A defective track blocker is much more difficult to cover up.

Other key dependencies

Obstacles in the route can be built depending on the key. Objects that temporarily protrude into the light space, such as B. water cranes , get a lock whose key can only be locked if the clear space is free. In the interlocking, journeys can only be released accordingly if the key is locked in the interlocking or a key lock.

Similar methods can be used for lift bridges, gates at factory entrances or the like. The respective key can only be locked if the track is accessible.

Connection points

Because of the cost of building electrical point machines, key-dependent points are still installed today and also when new electronic signal boxes are built in connection points (short for Anst ).

In the case of alternative connection points ( Awanst for short ), the service drive runs as a blocked drive from the station to the Awanst and the key located there in a key lock can be released by the signal box of the exit station. This key can be used to change the connection point, but this is mostly dependent on the consequences of a flank protection point or track block. When the operator drive has entered the connection, the route can be released again using the key.

A trip in the opposite direction, i.e. from the siding to the line, works in principle in the same way.

At normal junctions, it is not possible to lock the track in and then release it again. For this reason, the key can also be kept in the responsible signal box at the station and is taken with every service trip.

literature

  • H.-J. Arnold: Railway safety technology . transpress, Berlin 1987, ISBN 3-344-00152-3 .

Individual evidence

  1. ^ A b c Arnold, Hans-Jürgen: Eisenbahnsicherungstechnik . 4th, arr. Aufl. Transpress, Verl. For Transport, Berlin 1987, ISBN 3-344-00152-3 .
  2. ^ Fenner Wolfgang, Naumann Peter, Trinckauf Jochen: Railway safety technology: controlling, securing and monitoring routes and speeds in rail traffic . 2nd edition Publicis Corporate Publ, Erlangen 2003, ISBN 3-89578-177-0 .
  3. Dirk H. Enders: HV 73 Sp - The creation of a hand lock with a locking device . In: Eisenbahn-Unfallkasse (Ed.): BahnPraxis . No. 6/2009 . Bahn Fachverlag, Mainz 2009, p. 8–11 ( uv-bund-bahn.de [PDF]).