GB2356277A

GB2356277A - Train protection

Info

Publication number: GB2356277A
Application number: GB9926853A
Authority: GB
Inventors: David Michael Dore; Peter Robert Frost
Original assignee: INTELLIGENT CAB SYSTEMS Ltd
Current assignee: INTELLIGENT CAB SYSTEMS Ltd
Priority date: 1999-11-13
Filing date: 1999-11-13
Publication date: 2001-05-16
Also published as: GB9926853D0

Abstract

A train protection system is disclosed which comprises a box to be mounted adjacent a railway track and containing an electromagnet 12b for generating a magnetic field to be sensed by a passing train. The current supplied to energise the electromagnet 12b is modulated in accordance with a data signal indicative of a maximum safe speed to generate a varying magnetic field to be sensed by a passing train. A receiver 16 on board the train senses the varying magnetic field generated by the trackside electromagnet 12b and reproduces the data signal. A control box on board the train acts to reduce the speed of the train when it exceeds the suggested maximum safe speed indicated by the data signal.

Description

2356277 Train Protection

Field of the Invention

The present invention relates to the safety of railway systems.

Background of the Invention

Currently, most trains are controlled by drivers who are required to react appropriately to trackside signals. These may take the form of traffic-light like devices and speed restrictions. Because of total reliance on the human element, accidents have occurred and are inevitable.

Fully automated trains are in use on isolated lines where there are few variables such as junctions and different trains which travel at vastly different speeds. Such systems are expensive and impractical for use on a large scale. There is therefore a requirement for a system which allows human control of a train but can recognise when a problem exists and hence affect the motion of a train in order to prevent a potentially hazardous incident.

A system that has been in use for many years, known as AWS or automatic warning system, comprises boxes placed between the rails of the track approximately two hundred metres in the rear of a signal, i.e. two hundred metres before the train reaches a signal. Within each box there are located, a permanent south pole magnet and a switchable north pole electromagnet. As a train travels over the box, the south pole permanent magnet acts first to pull towards it a north pole magnet on board the train. This trips a switch on the train. If the signal two hundred metres after the box shows a green light, also called a clear aspect (G), the north pole electromagnet is activated, repelling the trains north pole magnet and re-tripping the switch.

If on the other hand the signal should display a nonclear aspect, the north pole electromagnet is not activated and the train's north pole remains down. This causes an alarm to sound within the cab, alerting the driver that caution is advised. The AWS then allows the driver to show that he has acknowledged the warning by switching off the warning sound.

If the driver fails to acknowledge the warning, the system applies the brakes.

The differing types of non-clear aspect include:, Single Red light (R). This is an instruction to the driver to stop the train and not to proceed on to the next section of line; Single yellow light (Y). This is a warning that the following signal on the line is currently displaying a red light; and Two yellow lights (YY). This is an advance warning indicating that the following signal along the line is currently displaying a single yellow light.

The problem with AWS is that it is a regular occurrence to pass a double yellow signal in the knowledge that by the time the train reaches the next signal, it will show a clear aspect due to the fact that the following section of track is now clear. Because such advance warnings occur so frequently, drivers have been known to cancel the warning sound almost as an automatic reflex action, even if through fatigue the driver has not noticed a signal and taken the appropriate action. In this situation, should the driver cancel three consecutive warnings without thought, the train could travel at high velocity through a red light, which may prove fatal.

- 3 Object of the Invention It is an object of the invention to mitigate this problem by making the system failsafe, thereby removing the 5 driver as the limiting factor in the safety of the train.

Summary of the Invention

According to one aspect of the present invention there is provided a train communicating system transmitter for use in a railway system comprising a box to be mounted adjacent a railway track and containing a permanent magnet and an electromagnet positioned at a distance after the permanent magnet in the direction of travel of a train for generating a magnetic field to be sensed by a passing train, characterised by means for superimposing a data signal on the current supplied to energise the electromagnet to generate an additional varying magnetic field to be sensed by a passing train.

According to a second aspect of the present invention there is provided a train protection system for use in a railway system comprising a box to be mounted adjacent a railway track and containing an electromagnet for generating a magnetic field to be sensed by a passing train, characterised by means for modulating the current supplied to energise the electromagnet in accordance with a data signal indicative of a maximum safe speed to generate a varying magnetic field to be sensed by a passing train, receiving means to be mounted on board a train for sensing the varying magnetic field generated by the trackside electromagnet to reproduce the data signal, and means for reducing the speed of the train when the train speed exceeds the suggested maximum safe speed indicated by the data signal.

The preferred embodiment of the invention improves upon existing technology by transmitting to the train data indicative of the maximum safe speed at which the train should be travelling. Such data may simply indicate the aspect of the following signal or, in other circumstances, the speed limit on the following section of track. This is done by superimposing a data signal onto the direct current used to activate the electromagnet in the AWS trackside box. By further modifying the receiver fixed to the train, the superimposed data signal is communicated magnetically to the train.

By using an alternating frequency as the superimposed data signal the average current and hence average magnetic field transmitted from the track to the train is unchanged. This has the advantage of using most of the technology of the current AWS system but not interfering with its op(ration should a train not fitted with the system use the track after the new system is installed.

On board the train, there is a control box containing a pre-programmed course of action that depends on the data signal received from the track. The control box is connected to the speed sensor, the braking system and to a display system which communicates the meaning of the data signal to the driver. Should the velocity of the train not be consistent with the directions given by the control box, the brakes of the train are applied.

By using this system, the driver of the train has to comply with the rules given by the control box, yet still has limited control of the train. This introduces a failsafe. The driver cannot proceed beyond a single yellow signal without the internal control box knowing and limiting the speed of the train. If the train should then proceed beyond a red signal it is automatically stopped. Since the speed of the train is significantly reduced after the single yellow signal, the train can be easily stopped within the standard two hundred metres that is allowed after a red signal before the potential hazard occurs (e.g. a junction).

Conventional AWS includes an additional failsafe in that the presence of a red signal ahead is indicated by not energising the electromagnet at all. In this way, the train mounted switch is not re-tripped back to its normal position. The same precaution may be used in the present invention in that the total absence of a data signal may also be used to indicate a red light. The lack of a data signal given that the train mounted switch has been tripped by the permanent south pole magnet now indicates a danger to the control box which subsequently brakes the train. It is this feature which further renders the present invention "failsafe". If power is removed from the modified AWS box, the train automatically applies the brakes.

The combination of the rules applied within the train control box and its connection to the braking and speed measuring systems, prevent the modified train, under any circumstance, from traversing a red light at significant speed. This includes the unlikely event of a driver falling asleep, unconscious or even being absent from the cab.

Brief Description of the Drawings

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a schematic representation of a track installation and a train mounted receiver, Figure 2a is a flow chart showing the operation of a conventional AWS system when a clear signal is approached, Figure 2b is a flow chart showing the operation of a conventional AWS system when a caution or danger signal is approached, and Figure 3 is a schematic representation of a railway line indicating the transmission of data to the train as the signals change from clear to danger.

In Figure 1 there is shown schematically the hardware used in a conventional AWS system. Two hundred metres before reaching a signal 10, a train carrying a receiver armature 14 passes over an approach inductor 12 having two magnets 12a and 12b. The magnet 12a is a permanent magnet with an upwardly facing south pole whereas the magnet 12b is an electromagnet with an upwardly facing north pole that is only energised when the signal 10 is displaying a green light (clear aspect).

is The present invention may be implemented by modifying a conventional AWS trackside box to enable an alternating field to be superimposed on the field generated in the e14ctromagnet and by additionally placing a similar modified AWS box or signal inductor 18 at the signal. This superimposed magnetic field is sensed by a coil 16 mounted on board the train, the output signal of the coil being suitably'processed to reproduce the data signal.

The operation of a conventional AWS system, when a clear signal is approached, is represented by the flow chart in of Figure 2a. As indicated in the box 21, as the signal is clear, no action is required by the driver. Because the electromagnet 12b is on, the armature 14 in the train that acts as a means for automatically sensing the status of the signal 10, briefly toggles between states as the train passes in the direction represented by the arrow in Figure 1 over the inductor 12. As described in box 22,,this brief toggling of the armature results in the sounding an "all clear" bell and in the setting of a visual indicator in the cab to all black.

The course of events when the signal 10 displays a red light (danger), a single yellow light (caution) or two yellow lights (preliminary caution) is shown in Figure 2b for a conventional AWS system. 5 In this case, only the south pole permanent magnet in the inductor box 12 generates a magnetic field because the magnet 12b is not energised (block 25). As a result, when the armature 14 passes over the ramp, the train receiver in block 24 transmits the AWS magnet signal to a control unit that immediately sounds a horn and sets a visual indicator. The driver is expected if alert to respond to the horn sound by depressing an AWS reset button mounted in the cab.

If the AWS button is depressed within three seconds of the armature 14 passing over the inductor 12 (block 26), then a warnin g horn ceases and a visual indicator is changed to.black and yellow to act as a reminder (block 28). As the driver is alert, he will adjust the train speed himself as appropriate as indicated in the block 30.

If however, the driver fails to acknowledge the caution and does not press the reset button within three seconds (block 27) then the warning horn will sound continuously and the train brakes will be applied fully. Only after a predetermined period (usually seven seconds) has elapsed or a predetermined drop in speed (usually to below 6kph) has been achieved can the driver regain control of the train by depressing the AWS reset button.

As earlier mentioned, the instinctive depression of the AWS button can result in a warning signal being disregarded by a driver, in that he can acknowledge the horn signal but not act upon it. In other words, it has been assumed that the action in block 30 of Figure 2b is an inevitable consequence of the action taken in block 26 when in practice this is not necessarily the case when the driver acts outs of reflex rather than conscious decision.

The invention seeks to mitigate this problem by monitoring the speed of the train and assuring that it does not at any time exceed the-speed dictated by the processor in the train.

This is achieved in the preferred embodiment of the invention by associating a code with each frequency transmitted by the alternating field of the modified electromagnet. These codes are as follows and are consistent with those indicated in Figure 3:

1. Signal is clear (G).

2. Signal is at preliminary Caution (YY).

3. Signal is at Caution (Y).

4. Approach to a Danger signal which has now cleared to a proceed aspect.

5. Approach to a Danger signal; train must not exceed e.g. 15mph from this point.

Those skilled in the art will appreciate that further codes may, if desired, be used such as those required at permanent speed restrictions and temporary speed restrictions. Following the direction of the train along the track in Figure 3 and considering each signal in order of travel: 30 Sicjnal Clear At the approach to a clear signal, the driver need take no action. 35 At the approach inductor 12, the permanent magnet sets the brake demand which is then cancelled by the message; F1 signal clear" - code 1. On receipt of this message the train processor illuminates the green signal aspect on the visual indicator in front of the driver in the cab.

On transit of the signal inductor the permanent magnet sets the brake demand which is then cancelled by the 5 message: "signal clear" - code 1.

Signal at Preliminary Caution On transit of the approach inductor 12 the permanent magnet 12a sets the brake demand which is cancelled by the message: "signal off" code 4.

At the approach to the preliminary caution signal (YY) the driver must depress the acknowledge button on the desk.

The button lights and flashes until transit of the signal inductor.18, at which time the permanent magnet provisionally sets the brake demand which is then cancelled by7the message: "signal preliminary caution" - code 2.

On receipt of the message "signal preliminary caution" and provided the signal was pre-acknowledged, the train processor illuminates the "two yellow" signal aspect on the visual indicator and the acknowledge button light goes out.

Signal at Caution On transit of the approach inductor 12 the permanent magnet 12a sets the brake demand which is cancelled by the message: "signal off" - code 4.

At the approach to the caution signal (Y) the driver must depress the acknowledge button on the desk. The button lights and flashes until transit of the signal inductor 18, at which time the permanent magnet provisionally sets the brake demand which is then cancelled by the message; "signal caution" - code 3.

On receipt of the message "signal caution" and provided the signal was pre-acknowledged, the train processor illuminates the yellow signal aspect on the visual indicator and the acknowledge button light goes out. However, if either at or after the point of transit of the signal inductor 18 the train speed exceeds say 50mph, a brake demand is activated by the train processor.

Signal at danger The train speed at the approach inductor 12 for a danger signal is limited to a maximum of say 50 mph by the previously received "signal caution" message. Transit of the approach inductor 12 sets the brake demand, after which..

receipt of the "signal on" message - code 5 causes the red signal aspect on the desk to light. The train processor now limits the speed to say 15mph. If, however, the signal has cleared, the approach inductor 12 transmits the message: "signal off" - code 4.

Since the signal inductor 18 transmits no message for a danger signal, any attempt to pass the danger signal results in immediate brake demand. The acknowledgement button flashes and a warning tone sounds.

Because the approach speed is limited to say 15mph by the approach inductor 12, the signal inductor 18 now acting as a train stop, prevents any significant overrun.

Claims

1. A train communicating system transmitter for use in a railway system comprising a box to be mounted adjacent a railway track and containing: a permanent magnet; and an electromagnet positioned at a distance after the permanent magnet in the direction of travel of a train for generating a magnetic field to be sensed by a passing train; characterised by means for superimposing a data signal on the current supplied to energise said electromagnet to generate an additional varying magnetic field to be sensed by a passing train.

2. A train communicating system comprising a transmitter as',claimed in claim 1 and further comprising receiving means to be mounted on board a train for sensing the varying magnetic field generated by the trackside electromagnet to produce an information signal indicative of track conditions.

3. A train protection system comprising a train communication system as claimed in claim 2, further comprising: means for measuring the speed of the train; and means for reducing the speed of the train when the measured speed exceeds a maximum safe speed indicated 30 by the data signal.

4. A train communicating system as claimed in claim 3, further comprising a switching mechanism to be mounted on board a train, tripped by the detection of the field of said permanent magnet.

5. A train communicating system as claimed in claim 4, further comprising means for stopping the motion of the train when no current is induced from the traversal of the electromagnet by the train after the switching mechanism has been tripped.

6. A train protection system for use in a railway system comprising a box to be mounted adjacent a railway track and containing an electromagnet for generating a magnetic field to be sensed by a passing train, characterised by means for modulating the current supplied to energise the electromagnet in accordance with a data signal indicative of a maximum safe speed to generate a varying magnetic field to be sensed by a passing train,., receiving means to be mounted on board a train for sensing the varying magnetic field generated by the trackside electromagnet to reproduce the data signal, and means for reducing the speed of the train when the train speed exceeds the suggested maximum safe speed indicated by the data signal.

7. A train protection system constructed substantially as herein described with reference to and as illustrated in the accompanying drawings.