GB2225887A - Railway monitoring system - Google Patents

Abstract

A system for monitoring the passage of trains on a rail track by measuring train length, employs track circuits which detect the presence of any part (wheel axle) of a train in any part of the track-circuit. A distance indication of the overlap of train and track-circuit is provided by an axle-driven pulse counter on the locomotive AND-ed (23) with the track-circuit 'presence' output, which is transmitted (15-19) from the trackside. Knowledge of the track-circuit length L1, either stored on the locomotive or in a central control station (31), or supplied at the time by the radio link from the trackside, enables the train length L0 alone to be deduced. This train length count is then compared at successive track circuits terminating block sections to give an indication of any discrepancy and the possibility of a carriage having been left in the section. <IMAGE>

Description

Railway Monitoring System This invention relates to a railway monitoring system and particularly to such a system for monitoring the passage of a railway vehicle. By *railway vehicle" Is meant a rail guided vehicle including a railway train or locomotive, a tram, or other single or multiple carriage vehicle.

Railway tracks are commonly divided into block sections of convenient length, eg several thousand metres, within which it is necessary to know of the presence of a train. It is not, however, sufficient to know that some part of a train is clear of a block section, and for this reason the known track circuit is inadequate as a block section monitor. A track circuit comprises a relay connected across the rails at one end of a track section, and a power supply connected across the rails at the other end. The relay is thus de-energised when a train wheel axle shunts the supply at any point within the track section which is defined by insulating joints in the rails. The length of the track section is, however, limited by the increasing resistance of the track and the series resistance provided to limit the current when the train axle is adjacent the power supply.

Insufficient current can be supplied to hold in the relay at significant train distances. Thus a typical track circuit falls far short of the commonly required block section length.

An alternative method of monitoring the passage of a train Is to employ axle counters mounted at the trackside. The number of axles entering and leaving a block section can thus be counted to confirm the passage of the complete train through the section. Axle counters tend, however, to be complex pieces of equipment.

Again, signalling systems, particularly those for lightly-used lines, now use radio data transmission between central computers and computers on-board locomotives, as a means of achieving the safety signalling function.

Such systems may use track-mounted transponders and trainborne interrogators as a means of proving that a train is at a particular location on the railway, but such systems have two significant weaknesses to the railway operator: (1) They do not prove that a train has arrived complete after a journey (i.e. it may have left some vehicles behind it in the block section).

(2) In the case of determining the location of a train as being within a passing loop, clear of the main line, in order to permit movement of another train past the first train, they do not prove that the train is completely contained within the passing loop.

An object of the invention is therefore to provide a railway monitoring system which is both cheap and of course fail-safe, and which overcomes the above difficulties.

According to the present invention, a railway monitoring system for monitoring the passage of a railway vehicle comprises a plurality of track sections each having presence means responsive to the presence of any part of the vehicle within the section to provide a section occupancy signal, and means responsive to the distance moved by the vehicle during the presence of the section occupancy signal to provide an indication of the sum of the lengths of the the vehicle and the section, for making a comparison at a subsequent track section.

The presence means may be located adjacent the track and means provided for communicating the section occupancy signal to the vehicle, the vehicle having radio means for communicating the indication of the sum of the vehicle and section lengths to a control station.

The presence means preferably has trackside radio means for communicating the section occupancy signal to the vehicle.

The control station preferably comprises means for determining any discrepancy in the vehicle length between successive track sections.

The control station may contain information as to the length of each track section and have means for subtracting the individual track section length from the sum of the vehicle and section lengths.

The trackside radio means may be adapted to transmit to the vehicle an identity signal identifying the location of the presence means and may also be adapted to transmit to the vehicle a section length signal indicative of the length of the associated track section.

A railway monitoring system will now be described, by way of example, with reference to the accompanying drawing, of which: Figure 1 is a diagram of a railway locomotive and carriage on a track, including block diagram signalling circuitry; and Figure 2 is a diagram of a block section of track between stations.

A train 1, shown as a locomotive 3 and wagon 5, Is shown on rails 7, the train approaching a section of track known as a track circuit TC which comprises a power source 9 and ballast resistor 11 connected across the rails and a relay 13 also connected across the rails but at a distance L1 from the power source. The relay 13 is thus normally energised, through the rails, and this condition is used to indicate that the track circuit section is free of any train or locomotive. A wheel axle between the power source connection and the relay connection shorts out the power source and the relay drops out to indicate the presence of a rail vehicle within the track circuit.

This effect is restricted to the section between the power and relay connections by the above mentioned insulated joints in the rails.

If, of course, a train (or locomotive) is partly within and partly without the track circuit there will still be an 'occupied' indication so it will not be clear whether the adjacent track is entirely free or not.

In this embodiment of the invention the relay 13 is mounted in a trackside housing toether with a radio transmitter 15 and code message generator 17. The transmitter 15, energised by way of the relay contacts 13A in the drop-out relay condition, transmits a signal modulated by a code indicating 'track circuit occupied'. With the locomotive or carriages within the track circuit a receiver 19 on the locomotive receives the signal which is decoded by a code circuit 21.

This situation will persist while any axle of the train is within the track circuit and thus for a distance equal to the length LO of the train (or rather, of its wheelbase) plus the length L1 of the track circuit: The 'track-circuit-occupied' signal is passed to an AND-gate 23 together with a pulse signal from a pulse tachometer fitted to an axle of the locomotive. The AND-gate output Is applied to a counter 25 which thus accumulates a count corresponding to the sum of the lengths of the train and the track circuit. The counter 23 is part of a computer 27 which controls a radio transmitter 29 to transmit the count back to a control station 31 having a receiver 33 and 'safe' computer 35. A 'safe' computer is one which is designed not to issue incorrect commands even in fault conditions.Stored in the control station is a list of track circuit lengths, the particular track circuit being identified by an address code transmitted to the locomotive by the trackside equipment as part of, or a preliminary to, the 'track occupied' signal, and transmitted to the control station by the locomotive equipment. If, of course, all track circuits are of the same length this identification would not be necessary.

With a knowledge of the track circuit length a subtraction by the computer 35 will produce the train length. As an alternative to subtraction by the control station computer 35, the locomotive computer 27 may perform the subtraction, if the track circuit length is supplied to it as part of the code transmitted from the trackside equipment. The locomotive transmitter then merely sends the calculated train length to the control station. In addition to the track circuit length, the trackside transmitter may transmit the location of the particular track circuit for the locomotive to relay to the control station.

By the above means the control station thus acquires a record of the length of the train passing the particular track circuit.

Such a track circuit would commonly form the entry to a block section BS, as shown in Figure 2, and similarly define the exit from the block section. These track circuits are referenced TC2 and TC3.

Figure 2 illustrates a single track railway with a station A and passing section having entry and exit track circuits TC1 and TC2, a block section BS of some considerable length with entry and exit track circuits TC2 and TC3, and a further station B with its passing section with entry and exit track circuits TC3 and TC4. The lengths of the various track circuits are different in this embodiment, being L1, L2, L3 and L4. The control station 31 is not shown in Figure 2 but has stored data corresponding to the respective track circuIts.

As the train passes from station A to the block section BS through track circuit TC2 a train length count will be determined. On leaving the block section a further train length count is determined, again allowing for the particular track circuit length TC3. If the two values agree to an acceptable tolerance (e.g. to within less than the length of the shortest vehicle in the train), the central safe computer 35 at the control station may deduce that the section of track, ie the block section BS, is unoccupied.

The above system for monitoring the passage of a train or other rail vehicle has a number of advantages. In the above mentioned case where the code transmitted from the trackside to the locomotive is chosen to identify to the signalling system the location on the railway of the measuring track circuit, the need for any separate system of transponders is obviated.

Again, radio-based signalling systems not requiring a safe computer on-board each locomotive may be preferred on the grounds of reduced cost and complexity. The solution proposed can be shown to be safe, even when the locomotive computer is not 'safely' implemented, for the following reasons: If the successive measuring track circuits TC1, TC2 etc. are chosen to be of different lengths, the numbers generated on-board the locomotive at the beginning and end of a block section will be different, and neither malicious action by staff nor equipment failure on-board the locomotive would be likely to result in a block section being falsely shown to be clear.

Effects such as wheel slip and slide, as the locomotive passes over the measuring track circuit section will alter the count, but such alteration will normally result in the block section not being cleared by the central safe computer after the passage of the train. This may represent a loss of reliability of the signalling system, but not a safety problem.

Failure of a measuring track circuit will likewise lead to the block section not being cleared after the passage of a train. Therefore, the track circuit need not be implemented with fail-safe equipment, and could, for example, take the form of a series rail circuit, in which the axles of the train complete a circuit to energise a relay. Such rail circuits are often more economical of power than conventional track circuits, and this may be an important advantage when battery or solar power must be used in remote areas.

Thus it is clear that the safety of operation of this track occupancy monitoring system relies on the minimum of fail-safe equipment, and is therefore relatively inexpensive to implement.

Claims (9)

1. A railway monitoring system for monitoring the passage of a railway vehicle and comprising a plurality of track sections each having presence means responsive to the presence of any part of said vehicle within said section to provide a section occupancy signal, and means responsive to the distance moved by said vehicle during the presence of said section occupancy signal to provide an indication of the sum of the lengths of the said vehicle and said section, for making a comparison at a subsequent said track section.

2. A monitoring system according to Claim 1, wherein said presence means is located adjacent the track and means are provided for communicating said section occupancy signal to said vehicle, said vehicle having radio means for communicating said indication of the sum of the vehicle and section lengths to a control station.

3. A monitoring system according to Claim 2, wherein said presence means has trackside radio means for communicating said section occupancy signal to said vehicle.

4. A monitoring system according to Claim 2, wherein said presence means has inductive loop means for communicating said section occupancy signal to said vehicle.

5. A monitoring system according to any of Claims 2, 3 and 4.

wherein said control station comprises means for determining any discrepancy in said vehicle length between successive said track sections.

6. A monitoring system according to any of Claims 2 to 5, wherein said control station contains information as to the length of each track section and has means for subtracting the individual track section length from said sum of the vehicle and section lengths.

7. A monitoring system according to Claim 3, wherein said trackside radio means is adapted to transmit to said vehicle an identity signal identifying the location of said presence means.

8. A monitoring system according to Claim 7, wherein said trackside radio means is adapted to transmit to said vehicle a section length signal indicative of the length of the associated track section.

9. A railway monitoring system substantially as hereinbefore described with reference to the accompanying drawings.