GB2027244A - Signalling device for guided vehicles - Google Patents

Abstract

The device includes a permanent magnet (1) above which is placed a frame coil (20) fed with an alternating current between terminals (21 and 22), and transmitting a flux carrying information which is picked up by a receiving frame coil on a vehicle during an enabling rectangular pulse produced by a detecting device which is coupled to the receiving coil and sensible to the flux of the permanent magnet. <IMAGE>

Description

SPECIFICATION Signalling device for guided vehicles The present invention relates to a signalling device for guided vehicles.

Various types of signalling beacons are known in the art, wherein a continuous magnet placed between the rails of a railway track operates a sensor installed in a vehicle moving on said track. Such a device is, for example, described in the French patent No.

1,122,154 to the same assignee.

Such devices proved very satisfactory in practical use but become less useful at a time where automation of railway vehicles tends to increase. In fact, the amount of information that can be transferred to a railway vehicle by such continuous magnet beacons is comparatively limited and can almost uniquely be used to supply warning signals. Nowadays, one wishes to transmit by means of beacons to railway vehicles more numerous signals in order to allow regulating of the railway traffic.

Therefore, a transmission coil unit placed next to the railway track and a corresponding receiving coil unit placed on the vehicle are being considered. Such a device itself proves little satisfactory as numerous stray phenomena surround a railway track, which are mainly due to the influence of traction currents.

Therefore, it has been also suggested to associated continuous or permanent magnet beacons to transmitting coil systems, said beacons providing a "window" during which the receiving coil is enabled in order to receive possible signals from the transmitting coil.

The object of the present invention is to provide a new signalling beacon for railway vehicles which combines a permanent magnet and a frame transmitting low frequency signals, said beacon and its associated receiver being substantially insensible to stray signals and allowing the transmission of signals in a comparatively wide frequency range.

Another object of the invention is to provide a beacon and a detecting device reliable, of a low cost, and which allow transmitting a bigger number of information.

To achieve this object and other objects, the present invention provides a signalling device for railway vehicles comprising a transmitter placed at the level of the track constituted of a magnet to produce a continuous transverse magnetic flux in relation to the direction of the track, and a means producing a variable magnetic flux, and a receiver placed at the level of the railway vehicle fitted with continuous and variable flux receiving means. The means producing a variable magnetic flux is composed of a frame placed in a plane parallel to that of the track and transmitting a magnetic flux orthogonal to the track plane according to a path distinct from that of the continuous magnetic flux. Preferably, the opposed longitudinal ends of the frame are folded downwards.

The invention will now be explained in more details with reference to the accompanying drawings.

Figure 1 is a view of a beacon signalling device transmitting a continuous magnetic flux; Figure 2 shows an example of a circuit for detecting the continuous magnetic flux; Figure 3 shows a combination of a continuous magnetic flux beacon with a variable magnetic flux beacon according to the invention; and, Figure 4 shows characteristics of the field transmitted by a frame according to the invention.

Fig. 1 shows a transmitting beacon 1 which is placed between the rails of a railway track transversally to said track and a receiver 2 which is placed correspondingly under a railway vehicle and which is designed to cooperate with the transmitting beacon 1 when it passes over the latter. The beacon comprises a continuous magnet 3, for example, a permanent magnet or an electro-magnet supplied with DC current, and polar parts 4, 4' facing upwards (towards the receiver).

The receiver includes a magnetic circuit comprised of magnetic parts 5 to 8 as illustrated in the figure, so that the flux of magnet 3 tends to make a closed path between polar parts 4 and 4' through the circuit including 5 to 8 elements when the receiver happens to be above the beacon. Between parts 6 and 7 is placed an element sensible to a magnetic flux, for example, a coil with a saturable core or a Hall effect device. In the latter case, two magnets 10 are provided in order to saturate the saturable core coil 9, when idle. It is only when the receiver overhangs the beacon that the magnetic flux from magnet 3 unsaturates the core of coil 9. As a consequence, the characteristics of said coil are altered.

In the case where the magnetic field sensible element 9 is composed of a saturable core coil, said coil can be included in the circuit of an oscillator 11, coupled to a detecting circuit 1 2 as shown in Fig. 2. Oscillator 11 includes various elements as shown in Fig. 2 which are well known in the art. When coil 9 is saturated, it shows a very low inductance and does not intefere with the operation of the oscillator. On the contrary, as soon as coil 9 is unsaturated, oscillator 1 stops oscillating. The oscilation or no-oscillation of oscillator 11 is detected by a detecting circuit 1 2 as shown in Fig. 2 which will not be described any further as it is well known in the art.Said circuit 1 2 provides at its output 1 3 either a high or a low level signal depending on the fact that oscillator 11 is oscillating or not. It will be appreciated that the assembly shown in Fig. 2 constitutes a safety circuit. In fact, the oscillator normally oscillates permanently except when passing above a beacon. If the circuit of the oscillator fails, for example, as a result of the breaking of a connection, the oscillator will cease oscillating and a warning signal will be issued in the same way as during a passage above a beacon.

Fig. 3A is a schematic top view showing an example of a beacon according to the present invention. Said beacon includes, on one hand, a continuous magnet beacon 1, as shown in Fig. 1, and a frame 20, for example with a rectangular shape, which is placed above the magnet, said magnet extending substantially along the mid-line of the frame. Said frame 20 includes two input terminals 21 and 22. It also generally includes several coils (e.g. 10).

The receiver includes one one hand a continuous field receiving element as shown in Fig. 1 and a frame placed arranged to face frame 20 when the detecting circuit 1 2 is brought above the continuous magnet coil 1. So, when the receiver is above the beacon, information signals can be transmitted from the transmitting frame to the receiving frame.

It will be appreciated that, while the continuous magnetic field follows a path from polar part 4 to polar part 5 through a gap, and then from polar part 8 to polar part 4' through gaps (see Fig. 1), the path of magnetic flux between both frames is different and orthogonal to the track. This allows to limit the side dispersion of the magnetic field supplied by the frame, and to limit the possible interferences and cross-talks between adjacent beacons and corresponding receivers. On the other hand, where magnet 3 is an electro-magnet including, as known in the art, cooling fins and metallic winding cooled by natural convexion, losses are reduced as compared to the case where a transmitting coil is concentric to magnet 3 and a receiving coil to either part 6 or 7 of the receiver. The action of stray phenomena is also low in the vertical direction relative to the transversal direction.

The transmitting-receiving device according to the present invention will be used in order that the signal supplied by the continuous field, for example, the rectangular pulse available at the output 1 3 shown in Fig. 2, will be used to supply an enable window inside which only the signals coming from the transmitting frame received by the receiving frame will be taken into account.

Fig. 4 shows the mean magnitude received at the level of the receiving frame when the transmitting frame is fed with an alternating field with a constant magnitude, versus the relative position of both frames. (Displacement as ordinate) As an example, in Fig. 4, the rectangular pulse A, obtained from the permanent magnet beacon shows the range within which the receiving frame is subject to be enabled owing to the action of the continuous magnet. Curve B shows the magnitude of received signals for a transmission with a constant magnitude in the case where the frame is flat. It will be appreciated that curve B includes a comparative wide central peak and side lobes of a non negligible magnitude.

So, if the detection threshold is fixed at a comparative low value, as shown, for example, by the dashed line Vs (threshold voltage), in order to widen the receiving range, signals can be captured at the level of the left-side lobe, then no signal is captured, then a comparative long range of signal is captured at the level of the central peak, and finally a short range of signals is captured at the level of the second side-lobe. This phenomenon constitutes an important drawback owing to the fact that the presence of signals in the side-lobe followed by the absence of signals can be interpreted in an erroneous manner by the detecting device. This is particularly embarrasing in the case of devices operating in a safety manner where the absence of signals corresponds to a warning condition.

In order to overcome said drawback, according to one embodiment of the present invention, one provides, as shown in the schematic side view of Fig. 3B, to fold downwards the end portions 23 of the edges of frame 20. This allows to obtain a response curve as shown by the curve in dashes C in Fig. 4 where the central peak is slightly and favourably widened and where the side-lobes are suppressed. This allows, on the one hand, to avoid the various drawbacks previously indicated which concern the side-lobes, on the other hand, to place successively and adjacently various beacons in the direction of displacement of the railway vehicle.It is necessary to insist on the harmful influence of the side-lobes, pointing out in particular that curve B of Fig. 4 has been drawn for a sensor and a transmitter in relative translation movement with constant spacing; but, when a train is passing, owing to the movement of the suspension, it may happen than the sensor is placed nearer the transmitter when passing above a side-lobe than when passing above the central peak. The effect of the side-lobe is then considerably amplified.

An advantage of the frame system according to the present invention rests in the fact that a comparatively important pass-band can be used owing to the low number of useful coils (in a practical application about 40 coils for the receiving frame for an interval of about 8 cm between the transmitter and the receiver). The pass-band is then very wide up to 1 MHZ, and a transmitting power of about 4-5 watts is sufficient to supply received signals of about a few hundreds mV. So the beacon can be used according to the present invention to transmit a plurality of frequency modulation signals or under digital form, so allowing, in addition to detecting the absence of rectangular pulse as obtained from the permanent magnet, the transmission, for ex ample by means of various carriers, of at least two additional indicating signals relating, for example, to the traffic conditions.

In a practical embodiment of the invention, the frame and magnet assembly of the transmitting beacon in the configuration shown in Figs. 3A, 3B, is encapsulated in a synthetic resin. However it is also possible to place in different relative positions the permanent magnet beacon and the transmitting frame 20, for example by setting them off longitudinally or laterally. In such a case, in order to match the registering of transmitting and receiving frames on one hand, and of the magnet beacon and the relating detecting device on the other hand, in order that, when the vehicle is moving, the magnet beacon-detecting device pair supply an A enable rectangular pulse substantially at the center of the transtting curve B of the emitting-receiving frames, the receiving device and the receiving frame will be offset accordingly on the vehicle.

Whereas the present invention has been described with respect to a specific embodiment thereof, it will be understood that various changes and modifications will be suggested to one skilled in the art, and it is intended to encompass such searches and modifications as are within the scope of the appended claims. In particular, the relative position of the transmitter and of the receiver can be reversed, i.e. the transmitter can be placed on the moving vehicle and the receiver on the ground.

On the other hand, as far as the present description is concerned, it will be appreciated that the term "railway vehicle" should be interpreted very widely and is not limited to a vehicle guided by one or several rails but concerns any vehicle moving on a track, or passing through fixed points. The device according to the present invention can also be placed in order to maintain a non-guided vehicle on a given path.

Claims (11)

1. A signalling device for a guided vehicle comprising a transmitter placed at the level of the track including a magnet to produce a transverse continuous magnetic flux in relation to the direction of the track and a means for producing a variable magnetic flux, and a receiver placed at the level of the railway vehicle, fitted with a means for receiving the continuous flux and a means for receiving the variable flux; wherein said means for producing the variable magnetic flux is a frame placed in a plane parallel to the track and transmitting a magnetic flux which is orthogonal to the track plane according to a path distinct from that of the continuous magnetic flux.

2. A device as claimed in claim 1 wherein said means for receiving the variable flux includes a receiving frame, said magnet, said transmitting frame, as well as said means for receiving the continuous flux and said receiving frame being arranged in order that, for a given position of the vehicle, said magnet and said receiving means on one hand and said transmitting and receiving frames on the other hand mutually face.

3. A device as claimed in 1 or 2, wherein said transmitting frame has opposed longitudinal ends which are folded downwards.

4. A device as claimed in 1 to 3, wherein said transmitting frame is place above said a magnet.

5. A device as claimed in 1 to 4, wherein said magnet is a permanent magnet.

6. A device as claimed in 1 to 4, wherein said magnetic is an electro-magnet.

7. A device as claimed in 1 to 6, wherein said means for receiving variable flux includes a frame similar to said transmitting frame.

8. A device as claimed in 1 to 7, wherein said means for receiving the continuous magnetic flux includes a means responsive to a magnetic field such as a saturable coil or a Hall effect device.

9. A device as claimed in 1 to 8, wherein detecting the variable magnetic flux is only allowed while detecting the continuous magnetic flux.

10. A device as claimed in 1 to 3 wherein the signals transmitted by said transmitting frame are digital signals.

11. A device as claimed in 1 to 3 wherein the signals transmitted by said transmitting frame are frequence modulated signals.

1 2. A signalling device for a guided vehicle substantially as hereinbefore described with reference to the accompanying drawings.