Система кабинной сигнализации TVM для высокоскоростных железных дорог

Railway cab signaling technology used on high speed rail

Transmission Voie Machine (TVM, English: track to train transmission) is a form of in cab signalling originally deployed in France and is mainly used on high speed railway lines. TVM 300 was the first version, followed by TVM 430. TVM 300 was developed in the 1970s as part of the TGV project. At speeds faster than 220 kilometres per hour, TGV trains only run along dedicated tracks designated as lignes à grande vitesse (LGV). When travelling at high speed, it is not possible for the driver to accurately see colour light railway signals at the side of the track. Signalling information is instead transmitted to the train and displayed on the train driver's dashboard. The driver is shown the safe operating speed, measured in kilometres per hour. The 1980s developed TVM 430 system provides more information than traditional signalling systems would allow, including track gradient profiles and information about the state of signalling blocks further ahead. This high degree of automation does not remove the train from driver control, although there are special safety mechanisms that can safely bring the train to a stop in the event of driver error.

The TVM system was developed by the French group Compagnie de Signaux et d'Entreprises Electriques (CSEE), now part of Hitachi Rail STS. Two versions of TVM signalling, TVM 430 and TVM 300, are in use on the LGV. TVM 430, a newer system, was first installed on the LGV Nord to the Channel Tunnel and Belgium, and supplies trains with more information than TVM 300. Amongst other benefits, TVM 430 allows a train's onboard computer system to generate a continuous speed control curve in the event of an emergency brake activation, effectively forcing the driver to reduce speed safely without releasing the brake. TVM 430 was presented from an intended "modular and flexible" range of signalling system levels from TVM 400 up to TVM 440 (optional automatic train control) and TVM 450 (full driverless control).

The line is divided into signal block sections of about 1,500 metres (~1 mi), the boundaries of which are indicated by blue square signs printed with a yellow on white triangle. A digital display on the train driver's dashboard shows the maximum permitted speed for a train's current block, as well as a target speed based on the status of the line ahead. The maximum permitted speed is based on factors such as the proximity of trains ahead (with steadily decreasing maximum permitted speeds in blocks closer to the rear of the next train), junction placement, speed restrictions, the top speed of the train and distance from the end of LGV route. Trains at high speed take several kilometres to stop. Since trains will require more than one signal block to slow down, drivers are alerted to reduce speed gradually, several blocks before any required stop. The signalling system is permissive; the driver of a train is permitted to proceed into an occupied block section without first obtaining authorisation. Speed in this situation is limited to 30 kilometres per hour (19 mph) and if speed exceeds 35 km/h (22 mph), the emergency brake is applied and the train stops. If the board marking the entrance to the block section is accompanied by a sign marked Nf, the block section is not permissive, and the driver must obtain authorisation from the Signalling and Control Centre (Poste d'Aiguillage et de Régulation) before entering the block. Once a route is set, or the signalling centre has provided authorisation, a white lamp below the marker board is lit to inform the driver. The driver then acknowledges the authorization using a button on the train's control panel. This temporarily overrides the emergency braking system, which would otherwise stop the train when proceeding past the non permissive marker's ground loop. When trains enter or leave the LGV from lignes classiques, they pass over a ground loop which automatically switches the driver's dashboard indicators to the appropriate signalling system. For example, a train leaving the LGV onto a French ligne classique would have its TVM signalling system deactivated and its traditional KVB (Contrôle Vitesse par Balise, English: beacon speed control) system enabled.

It is one of the more advanced railway signalling systems in the world, although the implementation itself is still based on relays rather than solid state electronics. There are two components to the TVM 430 system: one ground based, the other on board the train. Both run using Motorola 68020 class processors, and are programmed in Ada, a computer language often used in safety critical systems. The system makes extensive use of redundancy; the mean time between dangerous failures is estimated to be over 1 million years. The ground based segment of TVM 430 resides in trackside boxes, which control stretches of track about 15 km (9.3 mi) long. Each one is linked to the line's centralized traffic control centre, and directly controls about ten blocks of track, each with its own track circuit. Signaling information is encoded in AC signals which are fed into the rails of each block. There are four different carrier frequencies available in TVM 430 and they are used alternately in pairs on both tracks of the TGV line. On one track, blocks use alternately 1,700 Hz and 2,300 Hz, while on the other track blocks use alternately 2,000 Hz and 2,600 Hz. Upon these carrier frequencies can be modulated 27 separate audio frequencies, any combination of which can be present at one time; the earlier TVM 300 used eighteen separate frequencies, only one of which could be present at any time. Each block has a receiver at the opposite end to the transmitter, and the loss of the track circuit signal (owing to shorting by train wheels or due to a failure) is interpreted as an indication that the block is occupied. Signalling block boundaries are equipped with electrical separation joints that prevent adjacent blocks from interfering with each other, whilst still letting the traction return current (at 50 Hz) pass through. These tracks circuits are referred as a UM71 C track circuit. The signals which are present in the rail are detected by antennas mounted underneath the front airdam of TGV trains, approximately 1 metre (3 ft) forward of the front axle. These antennas work by inductively coupling to the AC signal shunted between the rails by the first axle. There are four redundant antennas per train, two at each end. Only the two at the "front" of the train (in the direction of travel) are used. The signal from the track circuit is filtered, conditioned, and decoded on board the train by two redundant digital signal processors.

A "black box" similar to an aircraft flight data recorder, passively watches over the entire process, monitoring a variety of parameters and recording the events. In TVM 430 equipped trainsets, older paper strip recording equipment has been replaced by the ATESS digital recording system. Every action taken by the driver (throttle, brakes, pantographs) as well as signalling aspects (for TVM 430, KVB, and conventional signals) are recorded on magnetic tape for later analysis using a desktop computer. Another system, known as VACMA, oversees the driver's alertness. It consists of a foot pedal control that the driver needs to hold down for the TGV to move. This pedal must be released then re pressed once every 60 seconds if no other activity takes place. There is one period of time before a buzzer sounds, and another period of time before the automatic emergency brakes come on. The control can be released for a very short period of time before a buzzer sounds, and another very short period of time before the automatic emergency brakes come on.

A small amount of over speed allowance is made before the train's emergency brakes are applied. At speeds below 80 km/h, the allowance is five kilometres per hour. At nominal speeds of 80–160 km/h, the tolerance is ten kilometres per hour and at speeds in excess of 160 km/h, it is fifteen kilometres per hour.