TECHNICAL FIELD

The present invention relates to a method and a device for automatic traffic control in connection ith-trackbound communication. In particular, the method and the device comprise means for detection of rail-mounted vehicles on a track circuit and identification of the track circuit in order to supervise the movement of the rail-mounted vehicle on the circuit in question. Further, the method and the device make possible the transmission of selective information to the supervision units of adjacent track circuits for control of the movement pattern of a leading or trailing rail-mounted vehicle. The device is based on the utilization of digital information transmission between the units included.

BACKGROUND ART

To obtain different forms of automatic traffic control of rail-mounted vehicles, a number of different methods exist at present. Common for all types of control systems is the need for information to the system and for conveyance of the inf rmation to the supervised vehicle units. This is solved in a number of different ways. For transmission of traffic information to the vehicles, transmitters, inter alia, are located at certain intervals along the track. See, for example, patent DE 229878. A considerable disadvantage of similar methods is that the vehicles out on the track cannot be continuously provided with up-to-date or changed information.

A solution to the problems which arise when utilizing transmitters and receivers placed along the track for information supervision is to use the track itself as signalling circuit. A switch to a so-called track circuit system has then been made. Track sections are arranged, in

which each track section is electrically insulated from the other sections. Such a track section is called a track circuit. This is known technique. Various train block systems are available on the market, in which, inter alia, the tracks are utilized as signalling circuit. Using, for example, rails as conductor of course involves limitations.

For example, it has been very difficult to transmit a sufficient amount of information in the systems that have used the rails as transmitting agent for data messages sent via the rails. In addition, the rails are subjected to disturbances of various kinds and the difficulties in creating a fail-safe information transmission are consequently considerable. It is known to use messages in digital form modulated as tone frequency signals, thus reducing the influence of such disturbances, as is described in, for example, "Die neue Gleisfreimeldung FTG 5917", Josef

Czehowsky, Signal und Draht 74 (1982) . The present invention proposes a different modulating method and a method of increasing the fail-safety in the transmission of messages.

SUMMARY OF THE INVENTION

The following describes a system of functions which are applicable to a system concept which includes a track circuit system combined with an automatic train control system for rail-mounted vehicles. Parts of the invention belong to the state of the art but are applied in a new and special way.

First of all, standard baseband modulation technique for telecommunication systems is chosen to modulate a signal for a track circuit in order to achieve feeding of serial data by way of the rails. At the same time, the level of the baseband signal is used to indicate the presence of shunting vehicle axles on the track circuit. The baseband modulation that is chosen could be, for example, differential phase modulation (DPSK = differential phase shift keying) .

Baseband modulation provides a possibility of synchronous serial data transmission. The data to be transmitted are collected in information messages in so-called telegrams. These telegrams are divided into blocks or frames in accordance with the high-level data link control (HDLC) technique, according to the standard worked out by CCITT. Thus, a bitoriented protocol is used for the information transmission. It is, of course, also possible to use other synchronous protocols, or even asynchronous transmission and asynchronous protocols. The latter protocols are, however, less biteffective than bitoriented protocols, such as, for example, HDLC.

Excellent results have been attained in railways for direct current operation -when utilizing the above-mentioned technique in the frequency range of up to 2000 Hz, and this despite the relatively great spectral bandwidth required for this kind of transmission.

Transmitting serial data and indicating the presence of vehicle axles within a track circuit by means of the carrier of the signal are known, as previously mentioned, and utilized in other control systems. A novelty in the present supervision or control system is the use of standard transmission technique for, for example, telephony and the like in this application.

The address contents of the HDLC telegrams are the basis for track circuit identification, which is of value for separating disturbance signals from the environment or from the influence of other track circuits. Identification by using serial data may also have been performed by others in the past .

The telegrams may contain safety information which is picked up by antennas on the rail-mounted vehicles, located, for example, in front of the first axle. These telegrams are

evaluated in train-borne equipment for speed supervision. The telegrams for the rail-mounted vehicle may also contain other information of non-safety character. Information may also be conveyed from one track circuit to the next in order to provide a railway line with a block system. This also belongs to the state of the art described, for example, in "Vergleich der Systemmerkmale verschiedener Zugbeein- flussungseinrichtungen", Kδth, Eisenbahn Technische Rundschau 20 (1971) .

The novel feature is that all the above-mentioned characteristics are combined and applied to one and the same technical system. The HDLC telegrams provide freedom to place information in one or a number of the frames which build up the telegram, which gives great flexibility when modelling a system for information transmission. Information to the system may be mixed in or between the frames in different ways. Unspecified information may be put in one of the frames in a data telegram or be mixed with safety information in several different frames . In the latter case, the unspecified information may be multiplexed in several frames and time-shared with the safety information which is transmitted in repeated frames. This is a process which is also not used elsewhere.

The track circuit system needs a fail-safe level detector, a function which has been mentioned above. This unit will not be further discussed in this description.

Another novelty is the principle of safe detection of data in the track circuit. The generation of the ^' information and the associated and necessary redundancy are achieved in two separate channels, of which one feeds the track circuit with a signal at one end of the track circuit. The signal received at the other end of the track circuit is compared in a fail-safe way with the output signal in a first comparator. The output signal from the first comparator is forwarded, for example to a track relay or some other safety

unit as, for example, a computerized interlocking system. In this way, any influence of disturbance in the track as well as failures in the transmitter units connected to the track are discovered.

The transmission is also continuously checked by a second comparator which compares the information contents in two telegrams generated in two separate units before the information of the transmitting channel is transmitted to the track. This is necessary because when there is a rail- mounted vehicle on the track circuit, no signals reach the receiving unit on the track, which makes the output signal of the first comparator of no interest.

Different temporary disturbances and influences may be filtered out by imparting significance only to repetitive telegrams, where the demand is placed such that at least m out of n telegrams must be unmistakably given the same information content. As a consequence of this, the proposed method may provide the advantage that a smaller amount of redundant information need be fed to the track, since the information of the output signal has been verified by the above-described signal generation and the ensuing comparison. For that reason the telegrams can also be accepted by rail-mounted vehicles which utilize the same filtering technique and which with certainly sense the information as safe. Thus, more information can be transmitted per unit of time. However, the safety information must be made relevant of m out of n telegrams, which, of course, reduces the information flow in the channel. The bit error rate in the digital signals must therefore be fairly low to provide an acceptable system. However, this requirement does not affect the safety.

In the above-mentioned systems, it is required that the transmitter feeds signals towards the rail-mounted vehicle. When changing the direction of traffic, the transmitter/ receiver must change places .

BRIEF DESCRIPTION OF THE DRAWING

The accompanying figure shows a schematic view of a proposed linking of units which gives the system the functions aimed at in the description.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A proposed embodiment of the present invention with a method and a device for carrying out the method will be described with reference to the accompanying figure.

A first encoder El produces telegrams to be sent to a track circuit. Each such telegram contains, in the general case, three different parts comprising a to c, in which

a) is safety information for the receiver of the track circuit, i.e. information which is unique for each track circuit,

b) is fail-safe safety information for the rail-mounted vehicle with contents such as, for example, allowed speed over the track circuit,

c) is safety information to the rail-mounted vehicle, for example an indication as to the destination, stopping points for the vehicle, order for freewheeling, or some information for the operator.

The a-part of a telegram is always the same in a track circuit, whereas the b- and c-parts may be changed from time to time depending on the traffic situation and the like. ■

In a second encoder E2, the same data messages as in the first encoder El are produced but not necessarily in the same format .

The telegrams which are built up in the two encoders El and E2 are controlled by external control signals, which carry the information which is to be conveyed via the track circuit system. These control signals are symbolized in the figure by the arrows at 1.

The signal with messages in the form of telegrams from the first encoder El is forwarded to a combined code generator- transmitter G as well as to a second comparator C2. The combined code generator-transmitter G is connected to an amplifier A and transmits to this the telegrams which have been produced by the first encoder El for the track circuit.

A track circuit is a section of a railway line, in which such a section is electrically delimited from adjacent sections by, for example, an electrical insulation 3 between the track circuits.

The amplifier A converts the signal voltage from the code generator-transmitter G to a level and shape adapted for transmission to the track circuit. This amplifier A is provided with an adjustment device which makes possible adaptation of the voltage level to the length of the track circuit connected. The signals from the amplifier A are fed to the track circuit with one pole to each rail 2 and are preferably connected at the end point of the track circuit.

The signal voltage which is fed via the track is picked up at the other end point of the track circuit by a receiver B with an interf ce for reception from the track circuit . The receiver B comprises screening circuits which filter out the desired signal from electrical interference, if any, in the track.

The received signal is forwarded to a fail-safe level or threshold detector TD, which in a reliable manner measures the amplitude of the signal voltage in the track to determine whether the signal voltage level lies above or

below a certain value, which indicates a free track circuit or a track circuit occupied by a vehicle.

From the level detector TD the signal is forwarded in the reception channel to a decoder D, where the code message is again quantified.

As mentioned above, both encoders El, E2 produce data codes with the same telegram contents. The signals from the two encoders El, E2 are brought to the second comparator C2 where the code messages are compared in a fail-safe manner. If there is no correspondence between the two separate signals, the transmission from the code generator G is cut.

Also the signal received from the track circuit is compared with the transmitted signal in a fail-safe manner, among other things to avoid that a signal from adjacent track circuits can be received in case of a fault in insulating joints 3. Such a comparison is made at least of the a-part in the telegram and is carried out in a first comparator Cl, where the signal transmitted to the track circuit is fetched from the data encoder E2 and the signal received from the track circuit is fetched from the decoder D. If the contents of the two channels in the a-part of the telegram are equivalent, a fail-safe output signal 4 is generated from the first comparator Cl. This output signal 4 indicates a track circuit free from vehicles. This output signal 4 from the track circuit system is utilized for controlling different devices in the signal system of which the track circuit forms a part.

A rail-mounted vehicle adapted to the track circuit system has a receiver with an antenna near the rail in front of the first axle in the direction of travel. Since the signals in the track have different polarities in the two rails, the vehicle may suitably be equipped with two antennas, which pick up the same signal but with opposite polarity. When these signals are added, a more powerful input signal is

received by the receiver while at the same time disturbing signals from the two antennas cancel each other.

The rail-mounted vehicle according to the above is provided, in principle, with the same type of data communication receiver as the track circuit system and thereby senses telegrams received from the track circuit as failsafe; thus, the rail-mounted vehicle can be supervised by the system.