GB2356707A - Train speed safety system - Google Patents

Description

2356707 TRAIN SAFETY SYSTEM The present invention relates to a method and

apparatus for enhancing the safety of a railbound vehicle in the presence of crosswinds.

When a crosswind of a given speed is present, the maximum safe operating speed of a train is known. At present, weather forecasts are used to predict the maximum likely crosswind and train operating speeds are restricted, if necessary, within a wide safety margin. This means that if forecast winds do not actually blow, train speeds are restricted unnecessarily and revenue is lost. Real time wind speed and direction measurements can be made to supplement the weather forecasts, but since these measurements are made at a fixed point, often very far from the train, they are of limited value.

It is known from Gawthorpe, R.G. "Aerodynamics of trains in the open air", Railway Engineer International, pp 7-12, May/June 1978, how to make an on-board measurement of airflow relative to a train. Additionally, Tran, V.T. in "Crosswind Feedforward Control - A Measure to Improve Vehicle Crosswind Behaviour", Vehicle System Dynamics, pp 165-209, Volume 23 No. 3, April 1994, describes using airflow measurements taken on board a road vehicle to make corrections to the vehicle's active steering system.

Clearly, this latter disclosure is of little help to railbound vehicles.

It is an aim of the invention to make a more accurate estimate of the immediate safe operating speed of a railbound vehicle in the presence of a crosswind and thus to enhance safety at the same time as reducing unnecessary speed restrictions.

Accordingly, the present invention provides a method of enhancing the safety of a railbound vehicle, comprising measuring, on board the vehicle, the airf low relative to the vehicle and predicting, on the basis of the measurement, whether the speed of the vehicle in the immediate future will be safe.

Preferably, both the direction of the airflow, in terms of its angle of attack relative to the vehicle, and the speed of the airflow (obtained by measuring the dynamic pressure) are measured.

In a preferred embodiment of the method, the actual wind velocity, actual train velocity and cant deficiency are compared with a database table or algorithm giving information about permitted operating speeds. The method may also or alternatively comprise taking into account other data such as the position of the vehicle on a known track.

is An embodiment of the method comprises the steps of:

a) at the start of a journey, entering a predicted wind velocity into a control computer; b) calculating an operational envelope, giving maximum speeds during the journey, on the basis of the predicted wind strength; C) during the journey, measuring and recording actual values of wind velocity and fitting said values to a statistical model of typical winds for the journey; and d) updating the operational envelope on the basis of conditions predicted by the statistical model.

The updating of the operational envelope may involve prohibiting the vehicle from operating such that the likely maximum rate of increase in wind load on the vehicle and on any further vehicles coupled thereto, combined with the -maximum increase in load on the vehicle(s) from permitted cant deficiency, is greater than the achievable rate of decrease in other loads contributing to relevant safety - 3 criteria through full emergency braking.

Preferably, data collected by a vehicle is downloaded to a fixed computer database, either in a wireless manner whilst the vehicle is in motion or via a land-link when the 5 vehicle is stationary.

The present invention also provides apparatus for enhancing the safety of a railbound vehicle, comprising onboard means for measuring the airflow relative to the vehicle and means responsive to the measuring means for predicting whether the speed of the vehicle will be safe in the immediate future.

Preferably, the airflow measuring means comprises means for measuring both the direction of the airflow, in terms of its angle of attack relative to the vehicle, and the d ynamic pressure of the airflow, and means for calculating the speed of the airflow from its dynamic pressure. The airflow measuring means may comprise pitot tubes, airstream vanes, static pressure sensors or other means.

In a preferred embodiment, the apparatus comprises means for comparing the actual wind velocity, actual train velocity and cant deficiency with a database table or algorithm giving information about permitted operating speeds. Means for determining the location of the vehicle on a track may comprise a series of transponders fixed relative to the truck, an inertial navigation system or a global positioning system.

The apparatus may comprise a fixed computer database and wireless or wired means for downloading data from the vehicle to the database.

The invention will now be described in more detail by way of example only, with reference to the accompanying 4 drawings, in which:- Figure 1 is a vector diagram showing the airf low incident on a vehicle; Figure 2 is a schematic transverse section showing S vehicle parameters taken into account in embodiments of the invention; and Figure 3 is a map showing airf low vectors calculated in an embodiment of the invention.

Figures 1 and 2 show parameters which are either measured or calculated in embodiments of the invention. In a simple embodiment the following four parameters are measured using sensors mounted on the end vehicles of a train (which will normally be those most exposed to crosswinds):

is sp train speed c.d. train cant deficiency (c.d. = 2b sin a where a is the angle between a line normal to the track and P., the resultant of gravitational and inertial forces) angle of attack of the resulting airflow q dynamic pressure of the resulting airflow.

0 and q are measured in real time and for every instant of time using relatively inexpensive sensors such as pilot tubes, airstream vanes or static pressure sensors on the surface of the vehicle. If necessary, a gyroscope is used to measure the cant angle or superelevation SE, which is 2b sin T, where T is the angle by which a line normal to track deviates from vertical. The cant deficiency is measured using an accelerometer, since it is proportional to the lateral aLxlebox acceleration.

The train speed sp is normally known. To obtain the train's global velocity V it is necessary to know the geometry of the railway track and the train's exact position at each instant of time. This is achieved by keeping a record of the track number tk (including any scheduled or unscheduled changes of track) and the direction of travel and by integrating the train speed to calculate the distance travelled. The train's exact location is updated using line-side or in-track transponders, called balises or waypoints, sufficiently often to ensure adequate accuracy. Alternatively, an inertial navigation system or a global positioning system can be used.

The measured variables sp, and q are used to calculate the dependent variables u, the total airflow velocity relative to the train, and w, the wind velocity relative to the train-fixed coordinate system. Both the measured and derived variables are subjected to suitable filtering and other beneficial signal processing before being used by a control computer.

The control computer stores algorithms and functions that define safe operations. The computer uses the proces sed signals described above and is pre-programmed with data relating to the mass, stiffness and damping properties of the train as well at the aerodynamic properties of the 2S train and the surrounding terrain. The computer checks whether the combination of conditions is safe, both at the time of detection and also within a period of the next one to two minutes to predict whether operation will be safe in that period. If unsafe operation is predicted, the train is commanded to slow down. The size of the preview window required to ensure safe operation is a function of the train's speed and its braking performance at that speed.

This statistical preview can take many forms, depending on what is known and what is to be predicted, the duration of the preview window, the size of the safety margin required and the complexity of the system. In its simplest form, the system must allow for a train travelling at a known speed to enter a curve without prior knowledge and transit it at maximum permitted cant deficiency depending on the ambient and immediately predicted wind conditions. This can be accomplished using the following routine:

a) At the start of a journey the operating authority obtains a predicted wind strength using information obtained from other trains operating at the time, selected line-side measurements or weather forecasts. The train driver enters the predicted wind strength into a control computer and the information is read back to the operating authority as a check.

b) An operational envelope is initially based on the predicted wind strength entered into the control computer.

C) Once the train is under way, and at the same time as monitoring the train safety dependent on the permitted operational envelope, the control computer starts measuring and recording the magnitude of w, the strength of the wind at each instant in time. The instantaneous value of w is obtained from the instantaneous values of sp, 9 and q measured aboard the train. A statistical model of typical winds for the relevant track route is then fitted to the measured and recorded w-data. As enough data are collected to make the fitted model significantly representative of actual conditions, the permitted operational envelope is updated successively, to reflect conditions predicted by the model with increasing confidence. Two models are in existence for each 35- railway route, one for each direction. The complexity of any model matches the complexity of the control algorithms of functions selected for the particular operator's crosswind safety monitoring system.

d) In the simplest system, the algorithms or functions stored in the control computer ensure 5 that no operations will be permitted where it is possible for the train to transgress from a safe set of operational conditions to an unsafe set, given the wind conditions. More specifically, given a fitted wind model with its current predicted maximum wind strength and current maximum likely time-dependent rate of increase in wind strength, the train may not be operated in such a fashion that the likely maximum rate of increase in wind load on the train (dependent on wind strength, train speed and relative wind direction), combined with the maximum increase in load on the train from permitted cant deficiency, is greater than the achievable rate of decrease in other loads contributing to any relevant safety criteria through full emergency braking.

Full emergency braking will reduce the cant deficiency at curves, c.d., and the dynamic pressure on the train, q.

Note that the angle of attack of the airf low, 0, may increase during braking, but, even so, the train will still be moving to a safer operating regime since q is decreasing.

'In effect, this will limit train speed and cant deficiency so that the likely maximum wind loads on the train, combined with other loads on the train, are unlikely to put the train beyond accepted safety criteria. These other loads arise from cant deficiency and track irregularities, i.e. track-vehicle dynamics, and other sources.

The crosswind safety monitoring system described so far (sensors, concept of check algorithms, functions defining operational envelopes, and a control computer) is easily developed into a more sophisticated system with tighter but safe performance closer to that theoretically possible. The inclusion of this potential for development is deliberate as it enables the system to be tailored to the needs of individual operators, safety cultures, and different national (and international) safety authorities.

The system described so far works with the magnitude of the prevailing wind and the train speed, both of which lack information on direction (i.e. they are scalar, not vector quantities).

Examples of extensions to the function of the system through inclusion of directional information, are given below:

A limited extension to the system described above is achieved by introducing three new measured variables: tk, the identification of the track number the train is using, dt, the direction of travel along the track (up or down, or whatever local nomenclature is used to indicate running direction along the route), and s, the position of the train on any track or the distance along any track from any known balise or waypoint. (See Figure 3). These data may also be provided or updated by sufficiently accurate global positioning systems.

Each track route has a table defining the global alignment of the direction tangent of each track, tk, as a function of train location or distance, s, and for each direction of travel, dt. For example, double track with bi directional running will need four tables, one for each of two directions for each of two tracks, for complete definition. If the tracks at high-speed locations are -always parallel, then redundancy of information will result in these areas, and significant simplifications can be made for multi-track routes. Simplifications can almost certainly be made for low speed locations, even if they are quite complex areas such as stations, due to the larger safety margins of trains travelling at slow speed and reduced cant deficiency.

on-line measurements of sp, 0, q, and s, together with knowledge of tk and dt, can now be used to derive W, the global wind speed and direction for each moment in time at the train's instantaneous locations, s. Creating a global wind velocity model from the W-data collected by the train, and optionally using data from trackside stationary wind measuring apparatus then enables the control computer to work out a track-specific operational envelope for the journey concerned. This would use knowledge of the likely global direction and maximum strength of W, together with the range of track orientation and curve data along the track route to be travelled on, to define a journey-specific operational envelope. Limitations on maximum train speed, sp, and maximum cant deficiency, c.d., (the latter regulated by dictating a maximum speed in each curve) would, therefore, be derived from the operational envelope.

Any limitations derived in this manner are likely to be less restrictive than the limitations imposed by considering train speed, cant deficiency and wind magnitude (scalars without directional information) alone.

A yet more enhanced and sophisticated crosswind safety monitoring function involves the same fitting of a global wind velocity model to the W-data collected by the train as prescribed above, but subsequently followed by more detailed and specific use of the data obtained, including use of the predicted global velocity of the train, V, stored in the computer as a journey-profile, and the actual global veloci ty of the train V achieved in traffic.

Each fitted global wind model in this enhanced function enables the control computer to predict the likely combination of W (global wind velocity), V (global train velocity) and c. d. (cant def iciency) at each coming location, s, along the entire length of the proposed track, tk, and direction of travel, dt. Any potential conflict with the operational envelope, defining permitted combinations of these variables, can be checked for, and predicted conflicts resolved in advance by the control computer imposing suitable speed restrictions to be obeyed by the train as these conflict locations are passed.

Clearly, the track data of the track to be used (including data on the superelevation and radius of every curve) and the expected global train velocity profile for each journey must be known to the control computer in advance of the start of each journey.

Safety monitoring separate from the statistical wind model is always conducted by the control computer in order to command emergency braking if a dangerous situation is detected or predicted in the immediate future (i.e. if the boundaries of the operational envelope are exceeded, or predicted to be about to be exceeded). This prediction method is separate from, and different to, the ones defined above. it involves the use of the near instantaneous rates of change of all the variables involved in safety monitoring to predict closeness to safety criteria limits in the immediate to near future.

It is possible to include a cut-out function dependent on train speeds, locations, or other circumstances where it is known in advance that no safety risk is posed to the train from crosswinds irrespective of likely or forecast terrestrial wind strengths.

An example of railways that might benefit from such a function include one well known area in the U.S.A. comprising the Subterranean Penn Station in New York with its connecting Hudson River and East River tunnels. Much of the high speed Shinkansen track routes in Japan are in tunnels, and the Eurotunnel shuttle service through the channel tunnel between France and the UK is only exposed to the elements in each terminal area. The many long Alpine tunnels provide another example of automatic protection from terrestrial winds.

Data collected by each train is downloaded to a central database, either via radio or satellite link or, at the end of each journey, by a land-link. This enables the build-up of sufficient track- route- specific wind data to help the creation of the wind velocity models for each track routes as required by the preview function selected for each system.

Initial commissioning of each operator's system involves a prolonged phase of measurement only, conducted by trains running under existing safety regulations. This enables the build up of sufficient data for creating the initial wind models at the level of complexity and conf idence required.

once the crosswind saf ety monitoring system is, in service, the database can be used, firstly, to update the long-term wind models, and secondly, to pass recent measurements (or latest "fitted" wind models) registered in the database by one train on a particular route, to subsequent trains on the same route. This transfer of "current data" can again be performed via radio or satellite link during running, or via a land-link before each train departure. Thus, rather than each train having to "learn" the ambient wind conditions during the start of its journey, it can be helped to learn faster and more effectively from the central database which is being fed information at regular and frequent intervals by other trains already underway or which have just completed their journeys.

Claims (19)

1 A method of enhancing the safety of a railbound vehicle, comprising measuring, on board the vehicle, the airflow relative to the vehicle and predicting, on the basis of the measurement, whether the speed of the vehicle in the immediate future will be safe.

2. A method according to claim 1, wherein both the direction of the airflow, in terms of its angle of attack relative to the vehicle, and the speed of the airflow are measured.

3. A method according to claim 2, wherein the actual wind velocity, actual train velocity and cant deficiency are compared with a database table or algorithm giving information about permitted operating speeds.

4. A method according to claim 1, 2 or 3, comprising taking into account the position of the vehicle on a known track.

S. A method according to claim 1, 2, 3 or 4, comprising automatically using a vehicle control system to initiate a safety related action if said measurement and said prediction indicate the action to be desirable.

6. A method according to claim 5, wherein the safety related action comprises applying a brake.

7. A method according to any preceding claim, comprising the steps of:

a) at the start of a journey, entering a predicted wind velocity into a control computer; b) calculating an operational envelope, giving maximum speeds during the journey, on the basis 30 of the predicted wind strength; C) during the journey, measuring and recording actual values of wind velocity and fitting said values to a statistical model of typical winds for the journey; and d) updating the operational envelope on the basis of conditions predicted by the statistical model.

8. A method according to claim 7, wherein updating of the operational envelope involves prohibiting the vehicle from operating such that the likely maximum rate of increase in wind load on the vehicle and on any further vehicles coupled thereto, combined with the maximum increase in load on the vehicle(s) from permitted cant deficiency, is greater than the achievable rate of decrease in other loads contributing to relevant safety criteria through full emerge ncy braking.

9. A method according to any preceding claim, wherein data collected by a vehicle is downloaded to a fixed computer database.

10. A method according to any preceding claim, comprising collecting airflow dataL from a plurality of vehicles operating on a track or network and creating a wind flow model for the track or network as a function of time and location.

11. A method according to claim 10, including combining said airflow data with further data from trackside stationary wind measuring apparatus.

12. A method according to claim 10 or 11, comprising using the wind flow model data to create a predictive model that can be transferred to vehicles travelling at different locations.

13. Apparatus for enhancing the safety of a railbound vehicle, comprising on-board means for measuring the airf low - 14 relative to the vehicle and means responsive to the measuring means for predicting whether the speed of the vehicle will be safe in the immediate future.

14. Apparatus according to claim 13, wherein the airflow measuring means comprises means for measuring both the direction of the airflow, in terms of its angle of attack relative to the vehicle, and the dynamic pressure of the airflow, and means for calculating the speed of the airflow from its dynamic pressure.

15. Apparatus according to claim 14, comprising means for comparing the actual wind velocity, actual train velocity and cant deficiency with a database table or algorithm giving information about permitted operating speeds.

is

16. Apparatus according to claim 13, 14 or 15, comprising means for determining the location of the vehicle on a track.

17. Apparatus according to claim 16, wherein the location determining means comprises a series of transponders f ixed relative to the track.

18. Apparatus according to claim 16, wherein the location determining means comprises a global positioning system.

19. Apparatus according to any one of claims 13 to 2S 18, comprising a fixed computer database and means for downloading data from the vehicle to the database.