GB2130374A - Process and device for locating and monitoring the position of transport vehicles - Google Patents

Abstract

This process permits a vehicle to locate its position on a given route and to identify service stops on a municipal transport system, i.e. underground train, omnibus train, tramway, etc for the purposes of an automatic announcement of stations to travellers. The distance covered by a vehicle between two consecutive stops is measured, and measurements thus made are analysed automatically by comparing them with known distances between consecutive stations on a route which are stored in the form of a table. The comparison permits the station at which a vehicle is located to be calculated. At the beginning of a route (or if the position is "lost") the measurement and comparison is repeated until the position is located. The process may be complemented by detecting other identifiable features of the route which occur between stops such as changes in direction. <IMAGE>

Description

SPECIFICATION Process and device for locating and monitoring the position of transport vehicles This invention covers a process and device for locating and monitoring the position of transport vehicles operating on their own system or otherwise, and which in any case have to follow a route established in advance which has particular features such as bends, changes of direction, changes in slope, etc., and which stop at specific points. The process and device permit a vehicle to locate its position on a given route and to identify service stops on a municipal transport system (the stops being called "station" or "bus stop", depending on whether an underground railway, tramway or bus/trolley bus route is involved) so that an automoatic audible announcement of stops can be provided for travellers.

In the process covered by the invention, the distance covered by the vehicle between two consecutive stops is measured and an automatic analysis is carried out by comparing the measurements with theoretical distances between consecutive stations on the line covered by the vehicle which are stored in the memory.

Since this type of process does not require a fixed infrastructure, it is based fundamentally on the fact that distances between consecutive stations (or inter-station distances) are generally of unequal length on a municipal transport system and that an entire journey (with stops) made by a municipal transport vehicle is fully defined by a unique and distinctive series of distances which may be stored in the form of a table. Thus, when distances measured between two consecutive stops are compared with values in the table, the system establishes agreement between the distance covered between two stops and a given inter-station distance, and calculates the station at which the vehicle is located.

One problem encountered when applying this type of process is the fact that at the beginning of a given route, the driver or other official must carry out a manual initialization operation to ensure that stations are correctly announced, i.e. by pressing a special push-button. If this operation is not carried out in time, or is omitted, the automatic vehicle location process cannot be initiated at the beginning of the line. A similar problem occurs if the vehicle position is accidentally "lost" on the journey, for example, as a result of a detour from the normal route, or as a result of a fault such as an interruption in the system electrical supply.

Again, in this case the vehicle position must be re-established when the vehicle resumes its normal route, or when the fault condition is cleared. Existing systems include no facility for automatically relocating a "lost" position during a journey. At the best, certain systems propose a facility for the driver to operate a special manual control at particular points on a route in order to "reset" the system to a particular station when the vehicle resumes its normal itinerary after a diversion.

This invention resolves such problems by providing an improved process. It permits automatic position finding at the beginning of a route and quick re-establishment of the position when it is "lost". No human intervention is required and there is therefore no risk of error or omission.

Thus, the invention states that when there is a discrepancy between inter-stop distances and stored values, or when a position cannot be determined, further distance measurements and further comparisons will be made repeatedly until the position of the vehicle is ascertained. The position is thus located automatically at the beginning of a route, between the initial stops, or when a "lost" position is re-established.

In order to locate its position in the first instance, a vehicle must travel at least one inter-station distance. If necessary, it will travel two or three inter-station distances on lines where inter-station distances are identical, where there are repetitions in the set of distances in the memory, or where a single measurement provides an indefinite result. Due to the repetitive operation, if a position previously established is "lost" for any reason, the analysis is repeated until the vehicle relocates its position. Thus, the system also permits continuous monitoring of the vehicle position and operation.

By combining the location of stations (or other stops) and measuring the distance covered after a stop has been located, the system covered by the invention also permits the exact position of the vehicle on a route to be accurately established at any time.

By taking advantage of this feature, the system can be used on an underground network: - for providing an automatic announcement to travellers at stations, in particular an advance announce ment (i.e. 60m before arriving at a station). This can easily be achieved, since the location of any station permits the following station to be located using the information stored in the memory.

- for providing a continuous speed check, and imposing maximum speeds on various line sections.

- for monitoring the fully automatic driving system of a vehicle.

The storge of inter-station distances and the analysis of measurements is effected not only in absolute values but also in relative values, in other words by determining the ratio of consecutive inter-station distances measured and comparing this ratio with the various ratios of consecutive inter-station distances in the memory. By applying the invention process, it is possible to establish a correction factor for wear on vehicle wheels or an error correction factor due to the distance measuring sequence, and it is also very easy to make comparisons by accepting a tolerance of 1% (for example) between the distances measured and the theoretical values stored in the memory.

This process thus ensures the location of a vehicle's position on a route, regardless of the circumstances, and ensures that travellers are correctly notified of stops. Announcements are cancelled when the vehicle repetitive location process is operative and the vehicle position has not been established. Naturally, it is desirable that a vehicle position be ascertained as soon as possible in order to announce stops either at the beginning of a route, when normal line operation is resumed after a breakdown, or when certain indefinite conditions arise, for example, after a line fork.The basic process defined above only uses service stops as distinctive points permitting a vehicle to be located, but one can easily conceive that by multiplying these distinctive points, thus reducing the average distance between them along the route, the vehicle location process will generally be quicker.

Thus, the invention also covers the detection of tangible changes in the direction of the vehicle, and the measurement of distances between changes in direction and vehicle stops adjacent to these points and/or distances between consecutive changes in direction. This detection and measurement is carried out automatically by comparing with information in the memory relating to distinctive points on the line, including service stops and tangible changes in direction.

The detection of tangible changes in direction is achieved by detecting the orientation of certain wheels of the vehicle with respect to the vehicle longitudinal axis. For example, in the case of a vehicle on rails, the measurement of bogie orientation with respect to the body permits detection of the vehicle movement on a typical small-radius curve.

In the case of routes with a relatively broken longitudinal profile, changes in slope may be detected and used as additional distinctive points on condition that they are also stored in the memory.

On a simple route, the process permits the initial position to be established quicker (or a "lost" position to be re-established quicker) due to distinctive changes in direction between two stops. Consequently, stops can be announced which otherwise would not be.

In the case of a forked line, where a transfer to one of the branches of the fork corresponds to a distinctive change in direction, the first vehicle stoppage on either of the two branches may be located and announced directly without error.

Special terminal manoeuvres, i.e. a transfer to a pre-station branch which represents a tangible change in direction with respect to a normal route with post-station manoeuvre, may also be detected and used to obtain an appropriate terminal announcement in all cases, and the correct announcement of initial stops when the vehicle moves in the reverse direction.

When a route is partially served, a change in direction will be detected when a vehicle passes over a feeder which represents a tangible change in direction. Thus, stops may also be announced correctly when the vehicle moves in the opposite direction.

This invention also covers a device for locating and monitoring the position of transport vehicles and which is designed to apply the abovementioned process. This device comprises equipment for measuring the distance covered by the vehicle. The equipment is linked to an electronic unit which includes facilities for storing at least two distances measured between consecutive vehicle stops, one memory in which distances between consecutive stations on the route covered by the vehicle are stored, and a calculation and decision making unit linked to a user system.

The distance measuring equipment comprises for example a strobe wheel mounted on one of the vehicle axles which provide pulses whose intervals correspond to a given basic distance. These pulses can be counted and the first two interstation distances measured are thus determined and stored. The calculation and decision making unit establishes the ratio of these distances and compares it with the various ratios in the memory, in order to establish the station at which the vehicle is located. The user system is obviously a function of the application envisaged, i.e. station automatic announcing system, continuous speed control system or automatic driving system.

Where changes in the vehicle direction are also taken into consideration as specified above, the device also includes angle measuring equipment suitable for detecting changes in the direction of the vehicle. This equipment is linked to the calculation and decision making unit, while the memory holds data relating to changes of direction on the route.

In any case, the invention will be better explained by means of the following description which refers to the attached schematic diagram and which shows (in the form of a few typical examples) the application of this process for locating and monitoring the position of a vehicle, and which provides for the automatic announcement of stations on vehicles operating on their own system.

Figure lisa block diagram of a device for locating and monitoring the position and which applies this process.

Figure 2 is a simplified operational flow diagram for the device and its station announcing function.

Figure 3 is a diagram representing a single section of a municipal transport route and constitutes a numerical example illustrating in a more concrete form the facilities of the location device covered by the invention.

Figures 4, 5, 6 and 7 are diagrams representing various special route configurations and illustrating the application of the process covered by the invention (with detection of changes in direction).

The device for locating and controlling the position covered by the invention must include (as shown in diagrammatic form at the bottom of Figure 1) equipment (2) for measuring the distance covered by the vehicle, or a series of vehicles coupled together, such as an underground train. This equipment may comprise a strobe wheel mounted on one of the axles of the vehicle or series of vehicles which transmits pulses, each of which corresponds (for example) to a basic distance covered of 0.05m. The measuring equipment (2) is linked to a unit for calculation and decision making (3) which belongs to an electronic unit (4). The latter includes a memory (5) which is linked to the calculation and decision making unit (3). The memory (5) is used for storing typical data for the route covered by the vehicle concerned.Thus, the memory (5) contains at least the successive distances between stations on the route covered by the vehicle concerned. These are recorded in the form of a table.

As an option, the electronic unit (4) may receive the following, as shown in (6) (7) and (8): - data from fixed equipment such as a ground loop or marker - data from the vehicle internal automatic system - data from the vehicle driving cab (provided by the driver using a key or a push-button).

These optional facilities permit the system to be initialised orto be provided with additional information such as the direction of motion of the vehicle or its starting point. This data may facilitate or accelerate the position locating process described below with reference to the organisation chart of Figure 2.

Finally, the calculation and decision making unit (3) is linked to a user system (9) such as an automatic station announcing system.

When the system is initialised, the first inter-station distances are measured using the equipment described above. At least the first two inter-station distances are established and stored, and their ratio is compared with the various ratios in the memory in the form of a table. if the ratio of the distance measured corresponds to a typical ratio in the memory (within a tolerance of 1%, for example) the inter-station distances already covered, and the stations at which the vehicle arrives, are located. The correction factor for wear on the vehicle wheels (corresponding to a reduction in their diameter) is also established and stored at this time.

If there is no agreement between the ratio relating to the first distance measurements and one of the ratios in the memory, or if an indeterminate condition obtains, a further distance measurement and a further comparison will be made until the position of the vehicle on the route is positively identified.

When a vehicle stops at a station and it is located, the equipment measuring the distance covered is reset to zero and the distance covered is therefore measured and acquired starting from the station concerned.

This distance covered is compared with a value equal to X-60, a formula in which X represents the length in metres of the inter-station distance which is being covered. When the two compared values are equal (i.e.

when the vehicle is located 60m from the next station) the automatic announcing system notifies the travellers of the station using an audible announcement (recorded or reconstituted voice) and/or visual indication.

Acquisition of the distance covered continues after the announcement of the next station, until the vehicle stops. It must be noted that the equipment for measuring the distance (2) constitutes a stoppage detector because of the pulse operation (see above). An absence of pulses must correspond to a vehicle stoppage.

At each stop, the system checks whether the vehicle is at a station (using an accepted tolerance of 1% for example, on the distance). If this check shows agreement between the distances, the distance measurement is simply reset to zero. The system continues to operate as described above, and automatically announces the following station 60m before arriving at that point. If there is no agreement (i.e. in the case of a stoppage between two stations, or when a station is "jumped"), the entire location programme is reset to the beginning.

The system not only locates the position of a vehicle, but continuously monitors this position and re-establishes it if it is "lost". Disturbance to user systems, such as the station automatic announcer are thus kept to a minimum.

Figure 3 partially represents an underground line where the stations (identified by the letters A, B, C, etc) are separated by distances shown by way of example and expressed in metres. Thus, the following table of distances is stored in the memory: 600 AB 420 BC 510 CD 420 DE 640 EF It is initially assumed that a train circulating on the line in the direction of the arrow, has stopped at station (B), and that the system has not yet located the position of the train.

The first distance measured between stations (B) and (C) shows a result of 423m which comes within the tolerance range of 420m + 1%. However, notwithstanding any agreement which may then be found, the position of the train remains indefinite, since the inter-station distance (DE) is also equal to 420m.

A second measurement must therefore be made between stations (C) and (D). This measurement provides a result of 514m which comes within the tolerance range of 514m + 1%. The sequence of measured values is thus indicative of the position of the train on the line. When station (D) is reached, the system locates this station.

The system then determines the wear correction factor for the wheels using ratios roughly equal to 423/420 or 514/510.

Known that the next station (E) is 420m away from station (D), the system then measures the distance covered after leaving station (D) and compares this distance with the value 420 - 60 = 360m in order to detect the time the train is located 60m from station (E). The name of station (E) (corresponding to the next stop) is then announced in the travellers' compartments. When station (E) is reached, the count is reset to zero. Since the following inter-station distance (EF) represents a route of 640m, station (F) will be announced when the train leaving station (E) has covered 640 - 60 = 580m, and so on.

After covering the first inter-station distance, if the train stops 220m from station (B), i.e. between stations (B) and (C), the first two distances measured will be 220m and 200m. This does not correspond with distances in the memory, or to ratios between these distances. The position will be located in this case using the following inter-station distances (CD) and (DE). When station (E) is reached, the train will locate its position and station (F) will be announced 60m in advance.

For simplicity of explanation, we have until now considered a vehicle covering a route in a given direction.

In the normal case of a municipal transport vehicle making forward and reverse journeys on a given route, the system may well operate in a cyclic manner, and it is therefore not necessary in this case to restart the entire location process after each departure from a line terminal.

As shown in the lower part of Figure 1, the device covered by the invention also includes angle measuring equipment (10) which is linked to a calculation and decision making unit (3). This equipment comprises a sensor which detects the orientation of the vehicle wheels with respect to its longitudinal axis, thus permitting changes in the direction of the vehicle to be detected. One can envisage either an angular sensor measuring and transmitting all angular values, or a microswitch operated by a cam in such a way that angles in excess of a certain minimum value (corresponding to tangible changes in direction or likely to identify particular or individual points on the route) are not taken into consideration.

The memory (5) includes not only successive distances between stations on a route, as specified above, but also line features invoking these individual points, i.e. distances between changes in direction and stations adjacent to these points, distances between changes in direction which occur between two consecutive stations, the actual changes in direction at these points (i.e. to the right or left) and if necessary, distinctive angular values at these points, etc.

Thus a vehicle is located by taking into consideration movements at all conspicuous points on a route, i.e.

station stops or changes in direction, and by measuring the distance between the successive points. It must be noted that the distance measuring equipment (2) constitutes a stop detector because of its pulse operation (see above). The absence of pulses must correspond to a vehicle stoppage.

Figure 4 illustrates the facilities this device provides in the case of a single route (L) (i.e. an underground railway) with a series of stations (S1, S2, etc.) and two distinctive curves (C1 and C2) located between two stations (S2 and S3). The first curve (C1) is located at a distance dl from station (S2), and the second curve (C2) is located at a distance d2 from the first. A vehicle travelling on route (L) in the direction known by the arrows will therefore locate and detect the conspicuous points (P1, P2, etc.) constituted by stations (S1, S2, etc.) and curves (C1 and C2) in sequence.

Consequently, if the vehicle position is not yet shown, or is "lost" when travelling to station (S2), the detection of movement at points (P3) and (P4) and the measurement of the corresponding distances dl and d2 will permit the vehicle to locate itself between stations (S2) and (53) and to make a correct announcement at station (S3).

Figure 5 shows the arrangement of a forked line with a fork (BIF) between stations (S3) and (S4). This constitutes the start of a branch (L') from the main line (L). The location of the branch (BIF) where the branch (L') is identified by the angle constitutes an additional conspicuous point (P4) which is located at a distance d from station (S3).

Thus, when a vehicle moving in the direction of the arrows leaves station (53), the detection of a change in direction after the vehicle has covered the distance d permits the vehicle to establish that it is travelling on the branch (L'). The first station (S4') on branch (L') will therefore be located and may be announced. On the other hand, if the vehicle remains on the main line (L), no change of direction will be detected, and the measurement of the distinctive distance between stations (53) and (54) will permit station (S4) to be located and announced. The automatic station announcing system therefore operates correctly in all cases, with no omission of stations which are not located and without the need for prior manual switching in accordance with the vehicle destination.

Figure 6 shows the terminal station (T) and the first normal station (S) on a line where the two tracks (V1) and (V2) are shown separately. These two tracks are linked by an initial feeder (R1) located after the station which is normally used for a change of direction after a vehicle stops in front of a platform (tm). Another feeder (R2) located before the station permits a transfer from track (Vl)to track (V2) without the vehicle reaching platform (tm). In this case, the vehicle restarts directly from the platform of terminal (T) at which it arrives.

When a vehicle leaves station (S) and moves towards station (T) (and assuming that the vehicle has to carry out a pre-station manoeuvre), a change of direction will be detected at point (P) where the points constituting the start of feeder (R2) are located. Point (P) is located on track (V1) at a specific distance from station (S). Thus, the pre-station manoeuvre is detected and the station automatic announcing system may thus announce the terminal station (T) drawing the attention of travellers to the non-exit side and (when the vehicle leaves in the reverse direction on track V2), correctly announce the first station reached (S) without the need for system manual reinitialization.

Finally, Figure 7 shows the case of a vehicle operating a partial service. This vehicle leaves station (S3) for station (S4) and changes direction between stations (S2) and (S3). The vehicle stops on track (V1) in front of platform (tm) and leaves in the reverse direction on feeder (R) which terminates on track (V2). In this case, the stoppage at platform (tm) and the change in direction detected when the vehicle travels on feeder (R) are indicative of the fact that the vehicle is not operating on its normal route in the direction of stations (S1) and (S2), but is returning to station (S3) in order to continue to station (S4).The vehicle position will thus be located when it restarts on track (V2), and station (S4) and subsequent stations will consequently be announced correctly even though the vehicle provides a partial service and does not start at the beginning of the line.

The process covered by this invention is more particularly applicable (although not exclusively) to municipal transport vehicles operating on their own system with frequent stops, i.e. underground railways, tramways and omnibus trains which operate on rails where distinctive points such as small-radius curves and points are well defined and where movements at these points can easily be detected, i.e. using a sensor which measures the angle between a bogie and the body of the vehicle. Additional individual points, such as adequately pronounced changes in slope may also be detected (and used) by means of suitable sensors.

As a result of the above, it goes without saying that this invention is not limited to the applicational examples shown above for the position location and monitoring process. On the contrary, it embraces all variations based on the same principle. The invention is applicable in particular to all vehicles (including buses and trolley-buses), regardless of the user system. All uses are possible, whether individual or combined (i.e. simultaneous use for announcing stations and monitoring speed).

Claims (20)

1. Process for locating and monitoring the position of transport vehicles, which permits a vehicle to locate its position on a given route and to identify the service stops on a municipal transport system, (thus providing automatic announcement to travellers of stops or stations), by measuring the distance covered by the vehicle between two consecutive stops and automatically analysing distance measurements by comparing them with stored values of theoretical distances between consecutive stations on the route covered by the vehicle.It is identified by the fact that when there are discrepancies between measured distances between vehicle stops and the values in the memory, or when a distance cannot be determined, further distance measurements and comparisons will be made in a repetitive manner until the position of the vehicle is located, thus permitting automatic location of position at the beginning of a route and between initial stops, or relocation of a "lost" position.

2. Process for locating and monitoring position in accordance with claim 1, and identified by the fact that the storage of distances between stations and the analysis of distances measured is effected not only in absolute values but also in relative values, i.e. by determining the ratio of the consecutive inter-station distances measured, and by comparing this ratio with the various consecutive inter-station distance ratios in the memory.

3. Process for locating and monitoring position in accordance with claims 1 and 2, and identified by the fact that comparisons between distance measurements and values in the memory are effected using a tolerance of 1%, for example.

4. Process for locating and monitoring position in accordance with any of claims 1 to 3, and identified by the fact that at the time a vehicle position is located, the wear correction factor for the vehicle wheels and the error factor due to the distance measuring sequence are established and stored.

5. Process for locating and monitoring position in accordance with any of claims 1 to 4, and identified by the fact that when the vehicle position is located, the distance covered by the vehicle continues to be measured with zero resetting after each stop, and a check is made at each stop to ensure that the measured distance agrees with the stored value. If there is no agreement, the entire location programme is restarted.

6. Process for locating and monitoring position in accordance with any of claims 1 to 5, and identified by the fact that an automatic announcement of each station is made in advance of the vehicle arriving at the station by comparing the distance covered (measured after stopping at the preceding station) with the stored value of the inter-station distance being covered, less a given distance.

7. Process for locating and monitoring position in accordance with any of claims 1 to 6, and identified by the fact that tangible changes in the direction of the vehicle are also detected, and by the fact that distances between changes in direction and vehicle stops adjacent to these points and/or distances between consecutive changes in direction are measured. The detection and measurement is automatically used for comparing with stored data relating to distinctive points on the route including service stops and tangible changes in direction.

8. Process for locating and monitoring position in accordance with claim 7, and identified by the fact that tangible changes in direction are detected by measuring the orientation of certain vehicle wheels with respect to the vehicle longitudinal axis.

9. Process for locating and monitoring position in accordance with claims 7 or 8, and identified by the fact that changes in slope are also detected and used as additional distinctive points.

10. Device for locating and monitoring the position of transport vehicles and designed to apply the process covered by any of claims 1 to 9. It is identified by the fact that it includes equipment (2) for measuring the distances covered by the vehicle. This equipment (2) is connected to an electronic unit (4) which includes facilities for storing at least two distances measured between consecutive vehicle stops, a store (5) in which distances between consecutive stations on a route covered by the vehicle are stored, and a calculation and decision making unit (3) linked to a user system (9).

11. Device for locating and monitoring position in accordance with claim 10, and identified by the fact that the equipment (2) for measuring the distance covered comprises a strobe wheel mounted on one of the vehicle axles which transmits pulses whose interval corresponds to a given basic distance.

12. A device for locating and monitoring position in accordance with claims 10 and 11,and identified by the fact that it also includes equipment for measuring angles (10) and thus suitable for detecting changes in the direction of a vehicle. This equipment (10) is connected to a calculation and decision making unit (3), and the memory (5) also stores data relating to changes in direction (Cl, C2, B1 F and P) on a route.

13. Device for locating and monitoring position in accordance with claim 12, and identified by the fact that the angle measuring equipment (10) comprises an angular sensor.

14. Device for locating and monitoring position in accordance with claim 12, and identified by the fact that the angle measuring equipment (10) comprises a microswitch operated by a cam to ensure that angles exceeding a certain minimum value are not taken into account.

15. Device for locating and monitoring the position of transport vehicles operating on their own systems in accordance with claims 12 to 14, and identified by the fact that changes in direction are detected using a sensor which measures the angle between a bogie and the vehicle body.

16. A method of locating and monitoring the location oftransportvehicles on a predetermined route by measuring the distance covered by the vehicle between two consecutive stops and comparing the measured distance with stored theoretical distances in which discrepancies between measured and stored distances or non-measurement of distances causes further distance measurements and comparisons to be made in a repetitive manner until a match is found and the vehicle is located.

17. A device for locating and monitoring the location of transport vehicles, including measuring means for measuring the distance travelled by the vehicle, electronic means connected to said measuring means and including a memory in which predetermined distances between consecutive stations are stored and a calculator and decision making arrangement linked to a user system.

18. A method of locating and monitoring the location of a transport vehicle, substantially as hereinbefore described with reference to the accompanying drawings.

19. A device for locating and monitoring the location of a transport vehicle, substantially as hereinbefore described with reference to the accompanying drawings.

20. Any novel subject matter or combination including novel subject matter herein disclosed, whether or not within the scope of or relating to the same invention as any of the preceding claims.

20. Any novel subject matter or combination including novel subject matter herein disclosed, whether or not within the scope of or relating to the same invention as any of the preceding claims.

New claims filed on January 26 1984 Superseded claims 1 to 20 New or amended claims:

1. A process for locating and monitoring the position of transport vehicles, which permits a vehicle to locates position on a given route and to identify the service stops on a municipal transport system by measuring the distance covered by the vehicle between two consecutive stops and automatically analysing distance measurements by comparing them with stored values of theoretical distances between consecutive stations on the route covered by the vehicle in which when there are discrepancies between measured distances between vehicle stops and the values in the memory, or when a distance cannot be determined, further distance measurements and comparisons will be made in a repetitive manner until the position of the vehicle is located, thus permitting automatic location of position at the beginning of a route and between initial stops, or relocation of a "lost" position.

2. A process for locating and monitoring position in accordance with claim 1, in which the storage of distances between stations and the analysis of distances measured is effected not only in absolute values but also in relative values, i.e. by determining the ratio of the consecutive inter-station distances measured, and by comparing this ratio with the various consecutive interstation distance ratios in the memory.

3. A process for locating and monitoring position in accordance with claims 1 and 2, in which comparisons between distance measurements and values in the memory are effected using a tolerance of 1%, for example.

4. A process for locating and monitoring position in accordance with any of claims 1 to 3, in which at the time a vehicle position is located, the wear correction factor for the vehicle wheels and the error factor due to the distance measuring sequence are established and stored.

5. A process for locating and monitoring position in accordance with any of claims 1 to 4, in which when the vehicle positio is. located, the distance covered by the vehicle continues to be measured with zero resetting after each stop, a check is made at each stop to ensure that the measured distance agrees with the stored value and if there is no agreement, the entire location programme is restarted.

6. A process for locating and monitoring position in accordance with any of claims 1 to 5, in which an automatic announcement of each station is made in advance of the vehicle arriving at the station by comparing the distance covered (measured after stopping at the preceding station) with the stored value of the inter-station distance being covered, less a given distance.

7. A process for locating and monitoring position in accordance with any of claims 1 to 6, in which tangible changes in the direction of the vehicle are also detected, and in which distances between changes in direction and vehicle stops adjacent to these points and/or distances between consecutive changes in direction are measured, the detection and measurement being used automatically for comparing with stored data relating to distinctive points on the route including service stops and tangible changes in direction.

8. A process for locating and monitoring position in accordance with claim 7, in which tangible changes in direction are detected by measuring the orientation of certain vehicle wheels with respect to the vehicle longitudinal axis.

9. A process for locating and monitoring position in accordance with claims 7 or 8, in which changes in slope are also detected and used as additional distinctive points.

10. A device for locating and monitoring the position of transport vehicles and for applying the process claimed in any one of claims 1 to 9, including equipment for measuring the distances covered by the vehicle, said equipment being connected to an electronic unit which includes facilities for storing at least two distances measured between consecutive vehicle stops, a store in which distances between consecutive stations on a route covered by the vehicle are stored, and a calculation and decision making unit linked to a user system.

11. A device for locating and monitoring position in accordance with claim 10, in which the said equipment for measuring the distance covered comprises a strobe wheel mounted on one of the vehicle axles which transmits pulses whose interval corresponds to a given basic distance.

12. A device for locating and monitoring position in accordance with claims 10 and 11, including also equipment for measuring angles and thus suitable for detecting changes in the direction of a vehicle, said angle measuring equipment being connected to a calculation and decision making unit, the said memory also storing data relating to changes in direction on a route.

13. A device for locating and monitoring position in accordance with claim 12, in which the angle measuring equipment comprises an angular sensor.

14. A device for locating and monitoring position in accordance with claim 12, in which the angle measuring equipment comprises a microswitch operated by a cam to ensure that angles exceeding a certain minimum value are not taken into account.

15. A device for locating and monitoring the position in accordance with claims 12 to 14, in which changes in direction are detected using a sensor which measures the angle between a bogie and the vehicle body.

16. A method of locating and monitoring the location of transport vehicles on a predetermined route by measuring the distance covered by the vehicle between two consecutive stops and comparing the measured distance with stored theoretical distances in which discrepancies between measured and stored distances or non-measurement of distances causes further distance measurements and comparisons to be made in a repetitive manner until a match is found and the vehicle is located.

17. A device for locating and monitoring the location of transport vehicles, including measuring means for measuring the distance travelled by the vehicle, electronic means connected to said measuring means and including a memory in which predetermined distances between consecutive stations are stored and a calculator and decision making arrangement linked to a user system.

18. A method of locating and monitoring the location of a transport vehicle, substantially as hereinbefore described with reference to the accompanying drawings.

19. A device for locating and monitoring the location or a ofa transportvehicle, substantially as hereinbefore described with reference to the accompanying drawings.