GB1595311A

GB1595311A - Railway signalling apparatus

Info

Publication number: GB1595311A
Application number: GB1768/77A
Authority: GB
Original assignee: GEC General Signal Ltd
Current assignee: GEC General Signal Ltd
Priority date: 1977-01-17
Filing date: 1977-01-17
Publication date: 1981-08-12
Also published as: AU517935B2; AU3228878A; ZA7834B

Description

(54) IMPROVEMENTS IN OR RELATING TO RAILWAY SIGNALLING APPARATUS (71) We, GEC-GENERAL SIGNAL LIMITED, of Elstree Way, Borehamwood, Hertfordshire WD6 lRX, a British Com- pany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to railway signalling apparatus such as can be used to provide automatic train control or to pass control information to a driver of a train.

According to the present invention a railway signalling apparatus comprises two spaced magnetic poles of opposite polarity adapted for location on a railway track, and two magnetic field detectors adapted for mounting on a railway vehicle, each detector being associated with one of the magnetic poles and being arranged to initiate an alternating current signal except when influenced by the magnetic field produced by its associated magnetic pole.

The two spaced magnetic poles may be appropriate magnetic poles of two separate permanent magnets, or may be the opposite poles of a single permanent magnet.

Each detector may comprise a saturable magnetic device having a first winding energised from a source of alternating current so as to drive the device into saturation during each half cycle, and magnetic bias means arranged so that a second winding has an alternating current signal induced therein until the magnetic bias is substantially cancelled by the magnetic field from the magnetic pole.

Preferably the second winding comprises two parts wound in antiphase and arranged to provide an alternating current signal which is twice the frequency of the alternating current source.

The magnetic bias means may be provided by a permanent magnet or by a further winding fed from a direct current source.

The alternating current signals initiated by the or each detector may be arranged to energise an electromagnetic relay or other electrically responsive apparatus.

The invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a schematic representation of railway signalling apparatus embodying the invention; Figure 2 is a plan view of a permanent magnet and a portion of track shown in Figure 1; Figure 3 is a graph illustrating the magnetic fields produced by the permanent magnet shown in Figure 2; Figure 4 is a schematic representation of a modified form of the apparatus shown in Figure 1; Figure 5 is a block schematic circuit diagram of one of the detectors shown in Figures 1 and 4; Figure 6 shows various waveforms which will be used to explain the operation of the circuit of Figure 5; and Figure 7 is a schematic representation of another railway signalling apparatus embodying the invention.

Referring in the first instance to Figures 1 to 3, the railway signalling apparatus comprises a track 1 along which a vehicle 2 is arranged to travel from right to left of the drawing as indicated by the arrow 3. A permanent magnet 4, having a north pole 5 spaced from a south pole 6, is disposed along the track 1 so that the vehicle 2 travelling along the track 1 in the direction of the arrow 3 passes the south pole 6 before the north pole 5. Typically, as indicated in Figure 3, the poles 5 and 6 would be spaced 500 mm apart and each pole would have an effective length of 300 mm, giving a passing time of 16 milliseconds when the vehicle 2 is travelling at 20 metres/second.

The permanent magnet 4 is arranged to co-operate with two biased magnetic field detectors 7 and 8 mounted under the vehicle 2, on the body or on the bogies, and spaced apart in the direction of travel of the vehicle 2, typically 500 mm apart.

The detectors 7 and 8 are connected in a circuit arrangement which includes an oscillator 9 and respective electronic circuits 10 and 11 arranged to supply alternating current pulses to respective safety relays 12 and 13. The detector 7 is magnetically biased so that it responds only to the magnetic field from the north pole 5, while the detector 8 is magnetically biased so that it responds only to the magnetic field from the south pole 6.

The signalling apparatus so far described operates in the following manner. When the detectors 7 and 8 are not in the vicinity of the permanent magnet 1 the electronic circuits 10 and 11 produce continuous trains of pulses which energise the respective relays 12 and 13. As the vehicle 2 approaches the permanent magnet 1 the detector 7 is initially reverse biased by the south pole 6 but the train of pulses produced by the electronic circuit is not affected and the relay 12 remains energised.

When the detectors 7 and 8 come into alignment with the respective poles 5 and 6, both detectors 7 and 8 are forward biased so that they both respond and cause the electronic circuits 10 and 11 to cease producing pulses. Consequently both of the relays 12 and 13 are de-energised. The two relays 12 and 13 can either be arranged to re-energise after the detectors 7 and 8 pass out of the magnetic fields of their associated magnetic poles 5 and 6, or they can be arranged to "lock out and be reset by suitable circuits.

Preferably the apparatus is arranged to provide the most restrictive command in a train control system, but as shown in Figure 4 it is possible to locate a transmitter 50 and a loop 51 on the track arranged to co-operate with a receiver 52 and a loop 53 carried by the vehicle 2 and thus provide conventional track to vehicle 2 and thus provide conventional track to vehicle communication to change this most restrictive command to a less restrictive command. Moreover, the vehicle may be provided with suitable logic circuits 54 and display apparatus 55 to display the communicated information to a driver of the vehicle 2.

Because the detectors 7 and 8 are arranged to respond to respective magnetic fields produced by spaced north and south poles the apparatus is unlikely to be subject to spurious operation by magnetic fields produced by a.c. or d.c. traction currents.

Moreover, the apparatus is "fail-safe " in that magnetic fields produced by tractor return currents flowing in the track 1 can only result in one or both relays 12 and 13 being de-energised, thus providing the most restrictive command of the control system. Moreover, until and unless the pulses cease and the relays 12 and 13 are de-energised, the presence of the pulses provides a continuous check that the detectors 7 and 8 and the electronic circuits 10 and 11 are functioning.

While the railway signalling apparatus described above incorporates two detectors 7 and 8 arranged to co-operate with respective magnet poles 5 and 6 and having associated electronic circuits 10 and 11 and associated relays 12 and 13, it will be appreciated that railway signalling appatus in accordance with the invention may comprise only a single detector arranged to co-operate with a single magnet pole and having one associated electronic circuit and one relay. Such a railway signalling apparatus can be used to provide a "marker" for non-vital control purposes or to provide a safety marker in systems not subject to high levels of traction currents.

One detector and its associated apparatus will now be described in more detail with reference to Figures 5, in which the detector 8 comprises a ferrite ring core 14 typically 3 mm in diameter and having a primary winding 15 evenly distributed around the core 14 and a secondary winding 16 wound in two parts 17 and 18 at diametrically opposite sides of the core 14. The two parts 17 and 18 of the secondary winding 16 have an equal number of turns and are wound antiphase. A small permanent magnet 19 provides a magnetic bias substantially equal to the minimum field strength of the associated south pole 6 of the permanent magnet 4, although this magnetic bias could equally well be provided by a coil fed from a d.c. source on the vehicle 2.

The electronic circuit 11 into which the output of the secondary winding 16 is fed comprises a preamplifier 20 feeding a threshold and discriminator circuit 21 arranged to produce an output pulse when an input pulse is of a predetermined polarity and has an amplitude above a preset value. The output of the discriminator circuit 21 is passed to a latching circuit 22 by way of a pulse shaping circuit 23. The output of the latching circuit 22 is passed by way of a filter 24 and a relay driving circuit 25 to the associated relay 13. The relay driving circuit 25 is an a.c. safety circuit driving a standard safety signalling relay 13 through capacitors and rectifiers.

When two detectors are used as in Figure 1 the other detector 7 and its associated electronic circuit 10 are of similar construction except that the bias magnet 19 is of opposite polarity.

The detector 8 and associated electronic circuit 11 function in the following manner to provide a pulse train to energise the relay 13. The primary winding 15 is ex cited by an alternating current at a frequency typically of 5 KHz supplied by the oscillator 9, so that the core 14 is driven into saturation each half cycle. The voltage developed across the primary winding 15 is generally sinusoidal as represented by the line 26 in Figure 6 but has spikes 27 induced into it each time the core 14 saturates. When the detector 8 is not adjacent the south pole 6 the magnetic flux produced by the magnet 19 adds to the instantaneous flux produced by the primary winding 15 in one side of the core and opposes the flux produced in the other side of the core 14.The two sides of the core 14 therefore saturate at different times during a cycle of input current from the oscillator 9 so that the output voltage across the secondary winding 16 consists of a succession of sharp unidirectional pulses 28 which are applied to the preamplifier 20.

The sharp pulses 28 are passed to the threshold and discriminator circuit 21 and then to the pulse shaping circuit 23 which produces a square wave at the same frequency as the sharp pulses, i.e. 10 KHz.

The square wave output from the pulse shaping circuit 23 is passed to the solid state latching logic circuit 22 which produces a 10 KHz square wave continuously until and unless its input is interrupted.

The square wave output then ceases and can only be reinstated by energising a reset input 29. The output from the latching circuit is passed through the 10 KHz bandpass filter 24 to exclude spurious signals and is applied to the driving circuit 25 to energise the relay 13.

When the detector 8 is aligned with the south pole 6, the magnetic flux produced by the south pole 6 cancels the magnetic flux produced by the magnet 19 and the two sides of the core 14 saturate at substantially the same time. Since the two parts 17 and 18 of the secondary winding 16 have the same number of turns and are wound in antiphase, the voltages induced in the two parts 17 and 18 are equal and opposite and the sharp pulses 28 cease. Because the sharp pulses 28 from the detector 8 produce the 10 KHz square wave output at the latching circuit 22 which holds the relay 13 energised whenever the detector 8 is not adjacent the south pole 6, the detector 8 is self-proving.The other detector 7 and its associated electronic circuit 10 operate in a similar manner except that the voltage across the output winding in the absence of a north pole results in sharp pulses 30 of opposite polarity.

Turning now to Figure 7, the railway signalling apparatus comprises a track 31 along which a vehicle 32 is arranged to travel from right to left of the drawing as indicated by the arrow 33. A permanent magnet 34 presenting a south pole is disposed along the track 31 and spaced from an electromagnet 35 which can be energised to present a north pole, so that the vehicle 32 travelling along the track 31 first passes the permanent magnet 34 and then passes the electromagnet 35. The permanent magnet 34 constitutes a fail-safe marker and the electromagnet 35 which is spaced 760 mm in advance is provided to reset the equipment on the vehicle 32 at clear signals. This arrangement of track equipment is the same as that employed in the British Railways Automatic Warning System.

The permanent magnet 34 is arranged to co-operate with a biased magnetic field detector 38 carried by the vehicle 32, while the electromagnet 35 is arranged to cooperate with a magnetic field detector 37 also carried by the vehicle 32. The detectors 37 and 38 are spaced apart in the direction of travel of the vehicle 32. The detectors 37 and 38 are connected in a circuit arrangement which includes an oscillator 39 arranged to provide a sinusoidal output at a frequency of 5 KHz, and respective electronic circuits 40 and 41. The output signals from the electronic circuit 40 are applied to a safety OR gate 42 while the output signals from the electronic circuit 41 are applied to a safety AND gate 43 to which is also applied the output signals from the OR gate 42. The output signals from the AND gate are passed to a safety relay 44 by way of a filter and relay driving circuit 45.

The signalling apparatus shown in Figure 7 operates in the following manner. The biased detector 38 and electronic circuit 41 are similar to those illustrated in Figure 5 and produce a continuous square wave output at a frequency of 10 KHz which is applied by way of the AND gate 43 and the filter and driving circuit 45 to energise the relay 44. When the detector 38 is brought into proximity with the south pole of the permanent magnet 34 the magnetic bias of the detector 38 is cancelled so that the square wave output of the electronic circuit 41 is interrupted and the relay deenergised.

The detector 37 and the electronic circuit 40 are arranged to respond only to a north magnetic pole which is produced when the electromagnet 35 is energised. The detector 37 is similar to that illustrated in Figure 5 except that the bias permanent magnet 19 is not fitted. The detector 37 thus produces no output pulses when away from external magnetic fields. The electronic circuit 40 is arranged to respond only to pulses produced whilst the detector 37 is aligned with the energised electromagnet 35. Thus when the vehicle 32 passes a clear signal the relay which has been de-energised by the detector 38 will be almost immediately reset by a 10 KHz square wave output from the electronic circuit 40 which is applied to the AND gate 43 by way of the OR gate 42. A signal clear indication may be obtained from the output of the electronic circuit 40 if required.When the vehicle passes a red signal the north magnetic pole is not presented by the electromagnet 35 and the relay 44 remains de-energised.

The OR gate 42 may also be provided with a reset input 46.

WHAT WE CLAIM IS: - 1. A railway signalling apparatus com- prising two spaced magnetic poles of opposite polarity adapted for location on a railway track, and two magnetic field detectors adapted for mounting on a railway vehicle, each detector being associated with one of the magnetic poles and being arranged to initiate an alternating current signal except when influenced by the magnetic field produced by its associated magnetic pole.

2. A railway signalling apparatus as claimed in Claim 1, wherein the two spaced magnetic poles are appropriate magnetic poles of two separate permanent magnets.

3. A railway signalling apparatus as claimed in Claim 1, wherein the two spaced magnetic poles are the opposite poles of a single permanent magnet.

4. A railway signalling apparatus as claimed in any preceding claims, wherein each magnetic field detector comprises a saturable magnetic device having a first winding energised from a source of alternating current so as to drive the device into saturation during each half cycle, and magnetic bias means arranged so that a second winding has an alternating current signal induced therein until the magnetic bias is substantially cancelled by the magnetic field from the magnetic pole.

5. A railway signalling apparatus as claimed in Claim 4, wherein the second winding comprises two parts wound in antiphase and arranged to provide an alternating current signal which is twice the frequency of the alternating current source.

6. A railway signalling apparatus as claimed in Claim 4 or Claim 5, wherein the magnetic bias means is provided by a permanent magnet.

7. A railway signalling apparatus as claimed in Claim 4 or Claim 5, wherein the magnetic bias means is provided by a further winding fed from a direct current source.

8. A railway signalling apparatus as claimed in any preceding claim including an electrically responsive apparatus arranged to respond to the alternating current signals initiated by each magnetic field detector.

9. A railway signalling apparatus as claimed in any preceding claim including an electromagnetic relay arranged to respond to the alternating current signals initiated by a magnetic field detector.

10. A railway signalling apparatus as claimed in any preceding claims including a transmitter adapted for location on the railway track and arranged to co-operate with a receiver adapted for location on the railway vehicle to provide track to vehicle communication.

11. A railway signalling apparatus as claimed in Claim 10, including display apparatus adapted for location on the railway vehicle to display information communicated by use of the transmitter and receiver.

12. A railway signalling apparatus substantially as hereinbefore described with reference to Figures 1 to 3 of the accompanying drawings.

13. A railway signalling apparatus as claimed in Claim 12, modified substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings.

14. A railway signalling apparatus substantially as hereinbefore described with reference to Figure 7 of the accompanying drawings.

15. A railway signalling apparatus as claimed in any one of Claims 12 to 14, having a magnetic field detector substantially as hereinbefore described with reference to Figures 5 and 6 of the accompanying drawings.

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**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the vehicle 32 passes a clear signal the relay which has been de-energised by the detector 38 will be almost immediately reset by a 10 KHz square wave output from the electronic circuit 40 which is applied to the AND gate 43 by way of the OR gate 42. A signal clear indication may be obtained from the output of the electronic circuit 40 if required. When the vehicle passes a red signal the north magnetic pole is not presented by the electromagnet 35 and the relay 44 remains de-energised. The OR gate 42 may also be provided with a reset input 46. WHAT WE CLAIM IS: -

1. A railway signalling apparatus com- prising two spaced magnetic poles of opposite polarity adapted for location on a railway track, and two magnetic field detectors adapted for mounting on a railway vehicle, each detector being associated with one of the magnetic poles and being arranged to initiate an alternating current signal except when influenced by the magnetic field produced by its associated magnetic pole.

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