Patent Description:
When operating a rail vehicle, it is important to have accurate knowledge about the current adhesion conditions at the wheel-rail interface, i.e. the applicable kinetic friction coefficient. Namely, this is key for speed control in terms of retardation as well as acceleration. To improve the overall throughput and enhance the flexibility of railway traffic, it is envisaged that control systems will be implemented that employ so-called dynamic moving blocks to operate the rail vehicles in a railway network. In simplified terms, this means that the free distances between different rail vehicles are reduced substantially and will be set dynamically depending various parameters, such as the speeds and overall weights of the respective rail vehicles. Of course, the kinetic friction coefficient on each rail segment is also an important parameter in this context. Provided that one has access to reliable values of the kinetic friction coefficient, the rail vehicles may be controlled to accelerate and decelerate in a highly efficient manner.

Today, systems exist for informing rail vehicles about various characteristics of different track segments in a railway network, such that the rail vehicles may adapt their driving behavior accordingly.

For example, <CIT> shows a system for providing at least one of train information and track characterization information for use in train performance, including a first element to determine a location of a train on a track segment and/or a time from a beginning of the trip. A track characterization element to provide track segment information, and a sensor for measuring an operating condition of at least one of the locomotives in the train are also included. A database is provided for storing track segment information and/or the operating condition of at least one of the locomotives. A processor is also included to correlate information from the first element, the track characterization element, the sensor, and/or the database, so that the database may be used for creating a trip plan that optimizes train performance in accordance with one or more operational criteria for the train.

<CIT> describes a method for improving braking performance of a rail vehicle, the method comprising the steps of: a) Associating one or more sensors with one or more components of the rail vehicle, at least one of the one or more sensors comprising an acoustic sensor configured to detect acoustic signals emitted from a wheel-rail interface; b) Acquiring measurements of one or more operating parameters of the rail vehicle using the one or more sensors; c) Transmitting the measurements of the one or more operating parameters to an operating parameter monitoring device; d) Converting, using a computing circuit of the operating parameter monitoring device, the measurements into an output signal message including information relating to the one or more components of the rail vehicle and/or to adhesion conditions at the wheel-rail interface; and e) Transmitting the output signal message electronically to one or more recipients.

<CIT> discloses a system for controlling a railroad train over a segment of track. The system comprises a first element for determining a location of the train on the segment of track; a second element for providing track characterization information for the segment of track; the track characterization information related to physical conditions of the segment of track; and a processor for controlling applied tractive forces and braking forces of the train responsive to the location of the train and the track characterization information to reduce at least one of wheel wear and/or track wear during operation of the train over the segment of track.

<CIT> defines a system and method to determine the friction coefficient by taking into account the speed difference between a target wheelset and another wheelset.

Although the above systems may offer dissemination of information with potential relevance for determining expected traction/ braking conditions, these system generally provide data of unsatisfactory quality. It is therefore not possible to keep the safety margins between the rail vehicles sufficiently short to obtain an optimal throughput of the railroad network.

The object of the present invention is to mitigate the above problems and offer a solution that enables rail vehicles to obtain up-to-date high-quality information about applicable adhesion conditions at the wheel-rail interface in various parts of a railway network.

According to one aspect of the invention, the object is achieved by a data communication system for a railway network, which system contains at least one measurement controller, at least one transmitter apparatus and a set of receiver apparatuses. The at least one measurement controller is configured to be comprised in a respective one of at least one rail vehicle of a data-supplier type. The at least one measurement controller is configured to obtain a basic parameter reflecting an initial value of a friction coefficient relating to a rail segment, e.g. via an incoming message or as a default value. The at least one measurement controller is further configured to produce a validated value of the basic parameter, which validated value reflects an updated friction coefficient between the rail of the rail segment and the wheels of the respective one of the at least one rail vehicle of the data-supplier type. The validated value, in turn is produced through a procedure involving: measuring individual rotational speeds of the axels to which the wheels of the at least one first rail vehicle are connected while applying a gradually increasing traction force to a specific one of said axles; determining, while applying the gradually increasing traction force, an absolute difference between the rotational speed of the specific one of said axles and an average rotational speed of said axles except the specific one of said axles, and in response to the absolute difference exceeding a threshold value deriving a parameter reflecting measured value of the friction coefficient, checking whether the measured value of the friction coefficient lies within an acceptance interval from the basic parameter, and if so assigning the validated value equal to the measured value of the friction coefficient. The at least one transmitter apparatus is configured to be comprised in a respective one of at least one rail vehicle of the data-supplier type and emit a friction data message containing the validated value of the friction coefficient. Each receiver apparatus in the set of receiver apparatuses is configured to be comprised in a respective one of at least one rail vehicle in the railway network and receive the friction data message.

The above data communication system is advantageous because it allows sharing of verified friction measures, i.e. information based upon which a rail vehicle carrying the receiver apparatus can rely when for example determining an appropriate distance to a rail vehicle in front. This, in turn, enables an improved overall throughput in the railway network.

According to one embodiment of this aspect of the invention, each receiver apparatus in the set of receiver apparatuses is configured to receive the friction data message over a wireless interface, and each of the at least one transmitter apparatus is configured to emit the friction data message over the wireless interface. Thus, friction data may be exchanged efficiently between rail vehicles, for example during travel in the railway network.

According to another embodiment of this aspect of the invention, each of the at least one measurement controller is configured to produce a friction data message containing: the validated value of the friction coefficient, an identification of the rail segment to which the validated value of the friction coefficient relates, and a point in time when the validated value of the friction coefficient was derived. Thereby, any rail vehicle carrying the receiver apparatus may conveniently determine the relevant rail segment to which the friction coefficient relates as well as a reliability of the received information.

According to yet another embodiment of this aspect of the invention, each receiver apparatus in the set of receiver apparatuses is configured to receive at least two friction data messages relating to the rail segment, and derive an updated value of the friction coefficient for the rail segment based on the at least two received friction data messages. Here, the updated value of the friction coefficient is based on a balancing of the validated values of the friction coefficient included in the at least two friction data messages.

For example, the balancing of the validated values of the friction coefficient may involve comparing the validated value of the friction coefficient of each of the at least two received friction data messages to a threshold level for the friction coefficient, and assigning the updated value of the friction coefficient equal to the validated value of the friction coefficient of a latest received message of the at least two received friction data messages, if the validated value of the friction coefficient of the latest received message is lower than or equal to the threshold level. If, however, the latest received message indicates a friction coefficient above the threshold level, the updated value of the friction coefficient is assigned a friction coefficient equal to the threshold level. As a result, it can be guaranteed that the friction coefficient is not assigned an excessively high value.

Alternatively, the balancing of the validated values of the friction coefficient may involve assigning the updated value of the friction coefficient equal to the validated value of the friction coefficient of a latest received message of the at least two received friction data messages without considering any threshold level. Thus, maximum advantage can be taken of the validated value of the friction coefficient.

According to still another embodiment of this aspect of the invention, the system further contains at least one dispatchment node configured to receive the friction data message from one of the at least one transmitter apparatus via the wireless interface and relay the received friction data message to at least one of the receiver apparatuses in the set of receiver apparatuses via the wireless interface. A communication infrastructure in the form of such dispatchment nodes is beneficial because it bridges distance gaps between different rail vehicles and thus ensures that the friction data message are distributed properly to the intended receiver apparatuses.

Preferably, the at least one dispatchment node is configured to receive at least two friction data messages relating to the particular rail segment, derive an updated value of the friction coefficient for the rail segment based on the at least two received friction data messages, and relay the updated value of the friction coefficient for the rail segment to at least one of the receiver apparatuses. Analogous to the above, the updated value of the friction coefficient is based on a balancing of the validated values of the friction coefficient contained in the at least two friction data messages. Hence, friction data may be aggregated and enhanced in the at least one dispatchment node before being distributed to the rail vehicles in the railway network.

In further analogy to the above, the balancing of the validated values of the friction coefficient may involve assigning the updated value of the friction coefficient equal to the validated value of the friction coefficient of a latest received message of the at least two received friction data messages. Alternatively, the validated value of the friction coefficient of each of the at least two received friction data messages may be compared to a threshold level for the friction coefficient, and only if the latest received message contains a validated value of the friction coefficient lower than or equal to the threshold level, the updated value of the friction coefficient is assigned equal to the validated value of the friction coefficient of the latest received message. Otherwise, the updated value of the friction coefficient is assigned a friction coefficient equal to the threshold level. This advantageous for the same reasons as stated above.

According to another aspect of the invention, the object is achieved by a computer-implemented method for data communication in a railway network, which method is implemented in at least one processing circuitry and involves: obtaining, in a measurement controller comprised in a rail vehicle of a data-supplier type, a basic parameter reflecting an initial value of a friction coefficient relating to a rail segment in the railway network, and producing, in the measurement controller, a validated value of the basic parameter. The validated value reflects an updated friction coefficient between the rail of the rail segment and the wheels of the respective one of the at least one rail vehicle of the data-supplier type. The validated value is produced through a procedure involving: receiving data representing measurements of individual rotational speeds of the axels to which the wheels of the at least one first rail vehicle are connected while applying a gradually increasing traction force to a specific one of said axles, determining, while applying the gradually increasing traction force, an absolute difference between the rotational speed of the specific one of said axles and an average rotational speed of said axles except the specific one of said axles, and in response to the absolute difference exceeding a threshold value deriving a parameter reflecting a measured value of the friction coefficient, checking whether the measured value of the friction coefficient lies within an acceptance interval from the basic parameter, and if so, assigning the validated value equal to the measured value of the friction coefficient. Moreover, a friction data message is emitted from a transmitter apparatus comprised in the rail vehicle of the data-supplier type, which friction data message contains the validated value of the friction coefficient. Further, the method involves receiving the friction data message in a receiver apparatus comprised in a rail vehicle in the railway network. The advantages of this method, as well as the preferred embodiments thereof are apparent from the discussion above with reference to the proposed friction testing system.

According to a further aspect of the invention, the object is achieved by a computer program loadable into a non-volatile data carrier communicatively connected to a processing unit. The computer program includes software for executing the above method when the program is run on the processing unit.

According to another aspect of the invention, the object is achieved by a non-volatile data carrier containing the above computer program.

In <FIG>, we see a schematic illustration of a rail vehicle <NUM> containing equipment that form part of a data communication system according to one embodiment of the invention. <FIG> shows a schematic railway network <NUM> in which the proposed data communication system may be implemented.

The data communication system includes a set of receiver apparatuses. <FIG> shows an example of such a receiver apparatus <NUM> that is comprised in the rail vehicle <NUM> and which receiver apparatus <NUM> is configured to receive a friction data message M(µ) from at least one other rail vehicle in the railway network <NUM>. The friction data message M(µ) relates to a particular rail segment of the railway network <NUM>, for example as illustrated by <NUM> in <FIG>.

The data communication system also includes at least one measurement controller. <FIG> shows an example of such a measurement controller <NUM> that is comprised in the rail vehicle <NUM>. By definition thereby, the rail vehicle <NUM> is a rail vehicle of a data-supplier type, i.e. a source for producing validated friction information as will be described below.

The measurement controller <NUM> is configured to obtain a basic parameter µ reflecting an initial value of a friction coefficient µe relating to the rail segment <NUM>. For example, the basic parameter µ may be received in the receiver apparatus <NUM> via a friction data message M(µ) from another rail vehicle in the railway network <NUM>. Then, the receiver apparatus <NUM> may forward the basic parameter µ to the measurement controller <NUM>. Alternatively, or in addition, the measurement controller <NUM> may produce the basic parameter µ, for instance based on a default assumption, or an historic entry stored in the rail vehicle <NUM>. Consequently, the basic parameter µ may originate from another rail vehicle in the railway network <NUM>, dedicated friction test equipment performing measurements on the rail segment <NUM>, or the rail vehicle <NUM> itself, for example through deduction based on neighboring measuring points.

Nevertheless, the measurement controller <NUM> is configured to produce a validated value of the basic parameter µ. The validated value reflects an updated friction coefficient µe between the rail <NUM> of the rail segment <NUM> and the wheels <NUM>, <NUM>, <NUM> and <NUM> of the rail vehicle <NUM> of the data-supplier type. The validated value is produced through a procedure involving the following steps.

First, individual rotational speeds ω<NUM>, ω<NUM>, ω<NUM> and ω<NUM> are measured of the respective axels to which the wheels <NUM>, <NUM>, <NUM> and <NUM> respectively of the rail vehicle <NUM> are connected while applying a gradually increasing traction force AF to a specific one of the axles, say <NUM>.

Then, while applying the gradually increasing traction force AF to the specific one of the axles, an absolute difference is determined between the rotational speed ω<NUM> of the specific one of the axles and an average rotational speed of the other axles, i.e. all the axles except the specific one of the axles. In response to the absolute difference exceeding a threshold value, a parameter µm is derived that reflects a measured value of the friction coefficient µe.

The measurement controller <NUM> is further configured to check whether the measured value of the friction coefficient µe lies within an acceptance interval from the basic parameter µ, say ± <NUM> %, from the initial value of the friction coefficient µe. If the measured value of the friction coefficient µe lies within the acceptance interval, the measurement controller <NUM> is configured to assign the validated value equal to the measured value of the friction coefficient µe. Of course, the acceptance interval need not be ± <NUM> %. On the contrary, any wider or narrower extension of this interval is likewise conceivable.

If, however, the measured value of the friction coefficient µe does not lie within the acceptance interval, the measurement controller <NUM> is preferably configured to repeat the above steps to derive a new measured value of the friction coefficient µe.

Referring now to <FIG>, we will explain how the validated value of the friction coefficient µe may be derived by studying the absolute difference between the rotational speed ω<NUM> of the specific one of the axles and the average rotational speed of the other axles ω<NUM>, ω<NUM> and ω<NUM> while applying the gradually increased traction force to the specific one of the axles. <FIG> shows a graph illustrating an example of how the kinetic friction coefficient µk is expressed as a function of the wheel slippage s, which here is understood to designate a common term for a spinning or sliding motion of the wheel relative to the rail resulting from an applied traction or braking force respectively. In other words, the wheel slippage s is applicable to retardation as well as acceleration.

Characteristically, the kinetic friction coefficient µk increases relatively proportionally with increasing wheel slippage s. When approaching a peak value µe, however, the kinetic friction coefficient µk levels out somewhat. The friction coefficient peak value µe is associated with an optimal wheel slippage se after which a further increase of wheel slippage s results in a gradually reduced kinetic friction coefficient µk.

According to the invention, a parameter µm is determined that reflects the friction coefficient between the rail vehicle's <NUM> wheels and the rails upon which the rail vehicle <NUM> travels. Ideally, the peak value µe should be derived. For example, the peak value µe may be derived as follows. When the absolute difference | ω<NUM> - ωa | between the first and second wheel speed signals ω<NUM> and ωa exceeds the threshold value, this corresponds to a situation where the at least one wheel <NUM> on the specific one of the wheel axles experiences a wheel slippage sm near the optimal wheel slippage se. The kinetic friction coefficient µk is given by the expression: <MAT> where.

Under the assumption that the wheel slippage sm is near the optimal wheel slippage se, the peak value µe of the kinetic friction coefficient µk may be estimated relatively accurately.

In addition to the above, the data communication system according to the invention includes at least one transmitter apparatus, which in <FIG> is exemplified by the unit <NUM> comprised in the rail vehicle <NUM> of the data-supplier type. The transmitter apparatus is configured to emit the friction data message M(µe) containing the validated value of the friction coefficient µe, such that at least one other rail vehicle in the railway network <NUM> may obtain information about said validated value by receiving the friction data message M(µe).

Consequently, each of the at least one rail vehicle <NUM>, <NUM>, <NUM> and <NUM> in the railway network <NUM> that is equipped with a receiver apparatuses <NUM> can make use of the validated value of the friction coefficient µe, for example when keeping a particular distance to a rail vehicle in front, accelerating and/or when braking.

It is preferable if the measurement controller <NUM> is configured to produce the friction data message M(µe) such that it contains not only the validated value of the friction coefficient µe, however also an identification of the rail segment to which the validated value of the friction coefficient µe relates and a timestamp designating a point in time when the validated value of the friction coefficient µe was derived. <FIG> exemplifies this by showing a friction data message M(µe, ID<NUM>, t<NUM>) including an identification ID<NUM> of the rail segment <NUM> to which the validated value of the friction coefficient µe relates, and a point in time t<NUM> when the validated value of the friction coefficient µe was derived.

Preferably, each receiver apparatus <NUM> is configured to receive the validated value of the friction coefficient µe over a wireless interface via the friction data messages M(µe), and each transmitter apparatus <NUM> is configured to emit the validated value of the friction coefficient µe over the wireless interface via the friction data messages M(µe). Namely, this allows for convenient sharing of high-quality friction information between the different rail vehicles <NUM>, <NUM>, <NUM> and <NUM> in the railway network <NUM>.

To maintain accurate and updated records about the adhesion conditions at the wheel-rail interface in the railway network <NUM>, according to one embodiment of the invention, each receiver apparatus <NUM> is configured to receive at least two friction data messages M(µe) relating to the same rail segment, say <NUM>, and derive an updated value of the friction coefficient for the rail segment <NUM> based on the at least two received friction data messages M(µe). The updated value of the friction coefficient is based on a balancing of the validated values of the friction coefficient µe included in the at least two friction data messages M(µe). Technically, however, the balancing may involve any kind of weighing together of the validated values of the friction coefficient µe, such as calculating average or median value.

According to one embodiment of the invention, the balancing of the validated values of the friction coefficient µe involves comparing the validated value of the friction coefficient µe of each of the at least two received friction data messages M(µe) to a threshold level for the friction coefficient. If the validated value of the friction coefficient µe of a latest received message is lower than or equal to the threshold level, the updated value of the friction coefficient is assigned equal to the validated value of the friction coefficient µe of the latest received message of the at least two received friction data messages M(µe). Otherwise, the updated value of the friction coefficient is assigned a friction coefficient equal to the threshold level. Thus, the friction coefficient will never be assigned a better/higher value than the threshold level. This facilitates complying with regulatory requirements that may prescribe maximum values for the friction coefficient.

Alternatively, according to another embodiment of the invention, the balancing of the validated values of the friction coefficient µe involves assigning the updated value of the friction coefficient equal to the validated value of the friction coefficient µe of a latest received message of the at least two received friction data messages M(µe), i.e. without considering any maximum value for the friction coefficient.

Referring again to <FIG>, according to one embodiment of the invention, the data communication system contains at least one dispatchment node <NUM>. Each dispatchment node <NUM> is configured to receive the friction data message M(µe, ID<NUM>, t<NUM>) from at least one transmitter apparatus <NUM> via the wireless interface. Here, a rail vehicle <NUM> comprises a transmitter apparatus <NUM> that emits the friction data message M(µe, ID<NUM>, t<NUM>). Moreover, each dispatchment node <NUM> is configured to relay the received friction data message M to at least one of the receiver apparatuses <NUM> in the set of receiver apparatuses via the wireless interface. Here, a respective receiver apparatus in each of the rail vehicles <NUM>, <NUM> and <NUM> respectively receives the friction data message M(µe, ID<NUM>, t<NUM>) from the dispatchment node <NUM>. Consequently, it is sufficient for the rail vehicles <NUM>, <NUM>, <NUM> and <NUM> to be communicatively connected to at least one dispatchment node <NUM> in order to exchange friction information with other rail vehicles in the railroad network <NUM>.

According to one embodiment of the invention, the dispatchment node <NUM> is configured to receive at least two friction data messages M(µe, ID<NUM>, t<NUM>) relating to a particular rail segment, say <NUM>. The dispatchment node <NUM> is further configured to derive an updated value of the friction coefficient for the rail segment <NUM> based on the at least two received friction data messages M(µe, ID<NUM>, t<NUM>). Analogous to the above, the updated value of the friction coefficient is based on a balancing of the validated values of the friction coefficient µe comprised in the at least two friction data messages M(µe, ID<NUM>, t<NUM>). The dispatchment node <NUM> is configured to relay the updated value of the friction coefficient for the rail segment <NUM> to at least one of the receiver apparatuses <NUM> by emitting a friction data message M over the wireless interface.

In further analogy to the above, according to one embodiment of the invention, the balancing of the validated values of the friction coefficient µe involves comparing the validated value of the friction coefficient µe of each of the at least two received friction data messages M(µe, ID<NUM>, t<NUM>) to a threshold level for the friction coefficient, assigning the updated value of the friction coefficient equal to the validated value of the friction coefficient µe of a latest received message of the at least two received friction data messages M(µe, ID<NUM>, t<NUM>), if the validated value of the friction coefficient µe of the latest received message is lower than or equal to the threshold level. Otherwise, the dispatchment node <NUM> is configured to assign the updated value of the friction coefficient to a friction coefficient equal to the threshold level.

Alternatively, according to one embodiment of the invention, the balancing of the validated values of the friction coefficient µe effected by the dispatchment node <NUM> simply involves assigning the updated value of the friction coefficient equal to the validated value of the friction coefficient µe of the latest received message of the at least two received friction data messages M(µe, ID<NUM>, t<NUM>).

<FIG> shows a block diagram of the measurement controller <NUM> according to one embodiment of the invention. The measurement controller <NUM> is configured to receive the wheel speed signals ω<NUM>, ω<NUM>, ω<NUM> and ω<NUM>, and ωa and output a signal defining the traction force AF to be applied as well as a value of the updated friction coefficient µe. The measurement controller <NUM> includes processing circuitry in the form of at least one processor <NUM> and a memory unit <NUM>, i.e. non-volatile data carrier, storing a computer program <NUM>, which, in turn, contains software for making the at least one processor <NUM> execute the actions mentioned in this disclosure when the computer program <NUM> is run on the at least one processor <NUM>.

In order to sum up, and with reference to the flow diagram in Figure <NUM>, we will now describe the computer-implemented method for data communication in a railway network <NUM> that is carried out by the measurement controller <NUM> according to a preferred embodiment of the invention.

In a first step <NUM>, it is checked whether a basic parameter µ has been obtained, which basic parameter µ reflects an initial value of a friction coefficient µe relating to a particular rail segment <NUM> in the railway network <NUM>. If the basic parameter µ has been obtained, for example via a received friction data message M(µ), steps <NUM> and <NUM> follow; and otherwise, the procedure loops back and stays in step <NUM>.

A validated value of the basic parameter µ is produced by executing steps <NUM> to <NUM>. The validated value reflects an updated friction coefficient µe between the rail <NUM> of the rail segment <NUM> and the wheels the rail vehicle <NUM> of the data-supplier type, i.e. in which the procedure is executed.

In step <NUM>, a rotational speed of a specific one of the wheel axles of the rail vehicle <NUM> of the data-supplier type is obtained, and in step <NUM>, preferably parallel to step <NUM>, an average rotational speed of the axles except the specific one of the axles is obtained.

In a step <NUM> following step <NUM>, a traction force AF is applied to the specific one of the axles, and in a step <NUM> subsequent to steps <NUM> and <NUM>, it is checked if an absolute difference between the rotational speed of the specific one of the axles and the average rotational speed of the axles except the specific one of the axles exceeds a threshold value. If so, a step <NUM> follows; and otherwise, the procedure loops back to steps <NUM> and <NUM>. Next time, when reaching step <NUM>, the traction force AF is applied at a somewhat larger magnitude than last time, such that for each run through the loop the traction force AF is gradually increased.

In step <NUM>, a parameter µm is derived, which reflects a measured value of the friction coefficient µe. The measured value of the friction coefficient µe is derived as described above referring to <FIG>.

Thereafter, a step <NUM> checks if the measured value of the friction coefficient µe lies within an acceptance interval from the friction coefficient µe reflected by the basic parameter µ obtained in step <NUM>. If the measured value of the friction coefficient µe is found to lie within the acceptance interval, the validated value of the basic parameter µ is assigned equal to the measured value of the friction coefficient µe, and a step <NUM> follows. Otherwise, the procedure loops back to steps <NUM> and <NUM> for deriving a new measured value of the friction coefficient µe.

In step <NUM>, a message M(µe) containing the validated value of the basic parameter µ is emitted, for example over a wireless interface, so that it may be received by other rail vehicles in the railway network <NUM>. After that, the procedure loops back to step <NUM>.

All of the process steps, as well as any sub-sequence of steps, described with reference to <FIG> may be controlled by means of a programmed processor. Moreover, although the embodiments of the invention described above with reference to the drawings comprise processor and processes performed in at least one processor, the invention thus also extends to computer programs, particularly computer programs on or in a carrier, adapted for putting the invention into practice. The program may be in the form of source code, object code, a code intermediate source and object code such as in partially compiled form, or in any other form suitable for use in the implementation of the process according to the invention. The program may either be a part of an operating system, or be a separate application. The carrier may be any entity or device capable of carrying the program. For example, the carrier may comprise a storage medium, such as a Flash memory, a ROM (Read Only Memory), for example a DVD (Digital Video/Versatile Disk), a CD (Compact Disc) or a semiconductor ROM, an EPROM (Erasable Programmable Read-Only Memory), an EEPROM (Electrically Erasable Programmable Read-Only Memory), or a magnetic recording medium, for example a floppy disc or hard disc. Further, the carrier may be a transmissible carrier such as an electrical or optical signal which may be conveyed via electrical or optical cable or by radio or by other means. When the program is embodied in a signal, which may be conveyed, directly by a cable or other device or means, the carrier may be constituted by such cable or device or means. Alternatively, the carrier may be an integrated circuit in which the program is embedded, the integrated circuit being adapted for performing, or for use in the performance of, the relevant processes.

The term "comprises/comprising" when used in this specification is taken to specify the presence of stated features, integers, steps or components. The term does not preclude the presence or addition of one or more additional elements, features, integers, steps or components or groups thereof. The indefinite article "a" or "an" does not exclude a plurality. In the claims, the word "or" is not to be interpreted as an exclusive or (sometimes referred to as "XOR"). On the contrary, expressions such as "A or B" covers all the cases "A and not B", "B and not A" and "A and B", unless otherwise indicated.

It is also to be noted that features from the various embodiments described herein may freely be combined, unless it is explicitly stated that such a combination would be unsuitable.

Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

Claim 1:
A data communication system for a railway network (<NUM>), which system comprises:
at least one measurement controller (<NUM>) configured to:
be comprised in a respective one of at least one rail vehicle (<NUM>) of a data-supplier type,
obtain a basic parameter (µ) reflecting an initial value of a friction coefficient (µe) relating to a rail segment (<NUM>) in the railway network (<NUM>), and
produce a validated value of the basic parameter (µ), which validated value reflects an updated friction coefficient (µe) between the rail (<NUM>) of the rail segment (<NUM>) and the wheels (<NUM>, <NUM>, <NUM>, <NUM>) of the respective one of the at least one rail vehicle (<NUM>) of the data-supplier type, and which validated value is produced through a procedure involving:
measuring individual rotational speeds (ω<NUM>, ω<NUM>, ω<NUM>, ω<NUM>) of the axels to which the wheels (<NUM>, <NUM>, <NUM>, <NUM>) of the at least one first rail vehicle are connected while applying a gradually increasing traction force (AF) to a specific one of said axles,
determining, while applying the gradually increasing traction force (AF), an absolute difference between the rotational speed (ω<NUM>) of the specific one of said axles and an average rotational speed of said axles except the specific one of said axles, and in response to the absolute difference exceeding a threshold value
deriving a parameter (µm) reflecting a measured value of the friction coefficient (µe);
checking whether the measured value of the friction coefficient (µe) lies within an acceptance interval from the basic parameter (µ), and if so
assigning the validated value equal to the measured value of the friction coefficient (µe), and
at least one transmitter apparatus (<NUM>) configured to:
be comprised in a respective one of at least one rail vehicle (<NUM>) of the data supplier type, and
emit a friction data message (M(µe)) containing the validated value of the friction coefficient (µe); and
a set of receiver apparatuses (<NUM>) each of which is configured to:
be comprised in at least one rail vehicle (<NUM>, <NUM>, <NUM>, <NUM>) in the railway network (<NUM>) and
receive the friction data message (M(µe)).