FR2793056A1 - METHOD AND DEVICE FOR COMMUNICATING ALARM INFORMATION BETWEEN VEHICLES - Google Patents

Abstract

The method device for communicating alarm messages between vehicles makes it possible to transmit an alarm message from transmission means (5) of a transmitting vehicle (10A) to at least one receiving vehicle by a microwave link under the control a management unit (64). According to the invention, the radio link is produced by transmission means (80, 82) allowing an optimized transmission range towards the rear, relative to the normal direction of movement of the transmitting vehicle. According to another aspect of the invention, the transmission means (5) transmit the alarm message in a form capable of being received, at the level of a receiving vehicle, by a reception means not specifically designed to receive this alarm message, for example a card electronic toll payment.

Description

Method and device for communicating alarm information between

  The present invention relates to a method and a device for transmitting alarm information between road vehicles, allowing for example a vehicle to signal a state of its operation or a traffic condition detected towards one or more

  several vehicles in the vicinity.

  Road safety is largely based on the possibility given to drivers of being alerted as soon as possible of a situation which requires rapid intervention, for example emergency braking, avoidance, or the retransmission of information. In application of this principle, several study projects have been carried out to establish an efficient system for transmitting alarm information between vehicles. For example, the European research program Prometheus (CED4 and CED5) is considering ways of transmitting emergency alarms between

  vehicles automatically upon detection of an incident.

  In order to minimize the time taken to transmit the alarm, it is envisaged that the

  communication between vehicles is direct,

  ie without passing through fixed relays.

  For example, patent document ZA-A-9 505 263 published in May 1996 describes a system based on a transmitter / receiver placed on each vehicle

  specifically for vehicle-to-communication

  vehicle. Alarm information is transmitted automatically as soon as a deceleration beyond a certain threshold is detected by an accelerometer provided for this purpose. In addition to the transmission of alarm information, this system enables the hazard warning lights of the receiving vehicle to be switched on automatically.

the alert signal.

  It is understood that, whatever the embodiment envisaged, vehicle-to-vehicle communication in the prior art involves: - at the level of the transmitting vehicle: at least one alarm condition detector (accelerometer, detector of the ABS system during braking, activation of the airbag, impact, the fuel system cut-off system in the event of an impact, etc.) and activated alarm information transmission means in response to this (these) detector (s), and - at the level of the receiving vehicle: a receiver dedicated specifically to listening to an alarm signal transmission from a transmitting vehicle, and a man-machine interface connected functionally

  to the receiver to alert the driver of the vehicle.

  A vehicle can be fitted either only as a receiving vehicle or as both a receiving and a transmitting vehicle. In the first case, the driver of the receiving vehicle can only react to alarm information from a transmitting vehicle. It intervenes usefully at its level in the security system and contributes to its overall efficiency. But the fact remains that an alarm transmission system between vehicles can only function satisfactorily with - a

  minimum proportion of transmitting vehicles.

  However, it turns out that the costs to equip a transmitting vehicle is significantly higher than to equip a receiving vehicle only. Indeed, it is understandable that an owner who plans to participate in the alarm transmission system as a transmitter will want his vehicle to be first equipped as a receiver. It appears that apart from legislation governing its general installation, such a system for transmitting alarms between vehicles requires a simplification of the means of implementation in order to see the light of day. In fact, potential users who would consider equipping themselves as a transmitting vehicle will first want there to be a sufficiently high proportion of receiving vehicles able to benefit from the service they provide. Likewise, potential users who would first consider only equipping themselves as a receiving vehicle will first want there to be a sufficient number of

  transmitting vehicles to justify their investment.

  Thus, there is a market initiation problem linked to the specificity of the equipment used in a conventional system for transmitting alarms between vehicles, in particular for equipping a vehicle.

receiver.

  In view of this problem, the present invention provides a device and a method for communicating alarm messages between vehicles making it possible to transmit an alarm message from transmission means from a transmitting vehicle to at least one receiving vehicle by a radio link under the control of a management unit, characterized in that the radio link is produced by transmission means allowing an optimized transmission range towards the rear, relatively to the normal direction

  movement of the transmitting vehicle.

  What is more, the directivity of the transmission makes it possible to target the transmission to the vehicles which follow the vehicle initiating the alarm message, which are the most concerned. Vehicles located forward, which are not normally affected by the

  alarm messages, will therefore not be disturbed.

  It is possible to optimize the radio transmission towards the rear by using for example at least one or more of the following means: - a directional transmitting antenna, and - a positioning of the transmitting antenna towards the rear of the vehicle, for example on the windshield

rear, on the tailgate, the trunk.

  Advantageously, the alarm message is transmitted so as to be able to be received, at the level of a receiving vehicle, by means of reception not specifically

  intended to receive said alarm message.

  Thus, it becomes possible, thanks to the invention,

  to immediately have a number of pre-

  equipped as receiving vehicles capable of

  benefit from the alarm system between vehicles.

  In this way, the initial conditions for implementing the system will be even more attractive for potential users who plan to equip themselves.

as a transmitting vehicle.

  Preferably, the reception means not specifically provided for receiving the alarm message is an electronic toll card. These cards, known in themselves, allow motorists to pay motorway tolls without having to stop their

  vehicle to perform a manual transaction.

  Typically, the card includes a transponder allowing dialogue by radio wave with a computerized terminal at the entrance to the toll. Thanks to an exchange of data according to a pre-established protocol, the terminal enters an individual identification code of the card, possibly with information concerning the journey, then debits an account associated with the card and validates the passage authorization, for example by controlling the lifting of a barrier. Typically, an electronic toll card also includes signaling means associated with the transponder to indicate to the driver that the passage is validated or, on the contrary, that the passage is not authorized. These signaling means generally take the form of an indicator light and / or of a sound transmitter integrated into the card. They can thus advantageously serve as a man-machine interface for communicating the alarm signals to the driver of the

receiving vehicle.

  This new use of an electronic toll card is all the more suitable since the communication standards employed by them generally employ transmission frequencies in the microwave range, which make it possible to obtain very good directivity. For example, according to ISO 14906 established by the European Committee for Standardization in electronic collection of

  tolls (CEP), the frequency used is 5.8 GHz.

  What is more, the structure of the messages exchanged in a CEP protocol such as that of the ISO 14906 standard can be easily adapted to convey

  information related to alarm messages.

  It is also possible to envisage using as a means of reception not specifically provided for receiving the alarm message a car radio of the receiving vehicle, with the possible addition of a simple input circuit. The invention thus contributes to achieving the virtuous circle which means that the more vehicles involved in the alarm transmission system, the more successful it will be and the more it will attract

other potential users.

  Preferably, the management unit organizes the structure of the alarm message transmitted according to a communication protocol based on an established protocol.

  for electronic toll message communication.

  The frequency of transmission of messages over the air can lie in the microwave range. The invention also provides for the possibility of relaying an alarm message by means of l0 retransmission associated with a receiving vehicle, conferring on the latter the role of retransmitting vehicle. The frequency and the protocol used for the retransmission are preferably the same as for the initial transmission, so that a receiving means can use indifferently an alarm message coming directly from a first

  transmission or retransmission.

  This retransmission allows an alarm message to reach vehicles out of direct reach by radio transmission of the vehicle initiating the message, but which are nevertheless close enough to be affected by

  the event that caused the alarm.

  It therefore allows the use of economical transmitter and retransmitter means, of modest power, while making it possible to obtain an adequate range for

the alarm message.

  According to one embodiment, retransmission means are provided for this purpose, associated with a retransmitting vehicle, for retransmitting a received message over the air, with an optimized transmission range towards the rear relative to the normal direction of movement of the retransmitting vehicle. ,

  to increase the scope of the alarm message.

  Preferably, the number n of retransmissions of the alarm message is limited as a function of the range that we decide to grant to the message: the greater this range granted, the greater the limit number N of retransmissions. Advantageously, the retransmission means comprise means for accounting for retransmissions of alarm messages and for limiting these retransmissions to the limit number N determined according to

  the scope to be given to the alarm message received.

  The limit number N can be determined by the retransmission means dynamically by

  depending on traffic conditions.

  According to a preferred embodiment of the invention, the accounting means comprise: means for reading and writing a variable n in the retransmitted message and means for incrementing this variable during a retransmission, this corresponds to number of

retransmissions of the message.

  For example, the retransmission means can retransmit an alarm message under the condition that the aforementioned variable n indicates that the number of retransmissions of this message already carried out is less than the limit number N of retransmissions

  determined by these retransmission means.

  According to a preferred embodiment, the transmission means and / or the retransmission means cooperate with a navigation system, such as a satellite navigation system, so as to be able to identify the nature of the lane used by the vehicle to which these means are combined. This information makes it possible to establish advantageous criteria both for establishing a condition for the initial transmission of an alarm message and for determining a condition for retransmission of a received message in order to

to increase the scope of it.

  Thus, it can be envisaged, at the level of the transmission means, that these transmit an alarm message when they determine that the speed of the vehicle with which these means are associated is less than a threshold speed established as a function of the nature of the route taken, determined from the navigation system. A speed below this threshold can o10 be considered by the transmission means as a sign of an abnormally slow circulation of the vehicle for the type of lane (for example a motorway), and that it is necessary to communicate a alarm message to reduce the risk of collision by

behind.

  The limit number N of retransmissions can be determined from at least one of the following parameters: - the content of the message transmitted, - the speed of traffic, - the nature of the route taken (determined by the navigation system ), and - traffic conditions (day / night,

bad weather, etc.).

  The invention also relates to the use of an electronic toll card as a receiving means

  in a communication device between vehicles.

  It also relates to the use, in a communication device between vehicles, of alarm messages structured according to a protocol based on a protocol intended for the electronic collection of tolls. Other advantages and characteristics of the invention will appear more clearly on reading

  of the following description of embodiments

  preferred, given purely by way of example

  limiting, with reference to the drawings which appear in appendix, in which: - Figure 1 is a diagram illustrating a communication between a transmitting and receiving vehicle; - Figure 2 is a block diagram of equipment transmitting alarm messages according to the present invention; - Figure 3 is a simplified front view o10 of an electronic toll card; - Figure 4 is a simplified block diagram of the internal architecture of the electronic toll card shown in Figure 3; - Figure 5 is a diagram showing the messages transmitted during an alarm message transmission in accordance with the present invention; - Figure 6 is a simplified block diagram of a receiver-retransmitter equipment according to a second embodiment of the invention; - Figure 7 is a diagram showing an example of selective retransmission of alarm messages according to one aspect of the invention; and - Figure 8 is a flow diagram of a procedure

  selective retransmission of alarm messages.

  The notion of vehicle-to-vehicle transmission of alarm signals in the context of the present invention

  will be briefly explained with reference to Figure 1.

  This figure represents the very simple example of road vehicles 10A, lOB which follow one another at a reasonable distance, for example between 25 and 50 meters. The vehicle at the head 10A has the role of transmitting vehicle while the vehicle which follows the OB has the role

of receiving vehicle.

  As a transmitting vehicle, the vehicle 10A is equipped with one or more on-board sensors, operatively connected to a transmitter located at the rear. Among the different types of possible on-board sensors, one or more can be cited, for example the sensors: for detecting the operation of the ABS braking system, for speed, for activating (manual) the hazard warning lights, for decelerating detection beyond a rate

  predetermined (accelerometer), passage of wipers

  windows in fast speed, detection of low o10 speed while the vehicle is on a fast lane, etc. This latter condition can be detected automatically when the transmitting vehicle is equipped with a road navigation system which makes it possible to

  recognize the type of route taken.

  As will be explained below in more detail, the activation of a sensor takes place automatically and causes instant transmission, by the associated transmitter, of data relating to the triggering parameter linked to this sensor. This data is received and analyzed by a receiving device of the receiving vehicle lOB to appropriately activate a means of alarming the driver of this vehicle (for example a telltale

or an audible warning).

  In general, one can consider as an on-board sensor any type of sensor suitable for detecting either an unforeseen change in traffic conditions: bad weather, change in traffic speed, changes in heading, etc., or a vehicle operating anomaly. : impact, airbag activation, overheating, faulty braking, etc. This information is significant for drivers of vehicles in the immediate environment, because it implies the need to adapt urgently to a potential danger, either by braking immediately, or by changing course, or by activating devices. such as a light signaling element, windscreen wipers, etc. Table 1 below summarizes some examples of criteria for triggering an alarm transmission and the situation associated with this transmission as can be deduced by the vehicle.

lOB receiver.

  Table i: criteria for detecting emergency situations Trigger criteria Associated situation Hazard warning lights and speed Vehicle stopped zero Hazard warning lights engaged Slowing down, traffic jam with slowing down Triggering of crash accident sensors (associated with airbags or fuel system) Activation of windshield wipers Heavy rain or sudden disturbance at high speed (visibility transition phase only) Vehicle moving Vehicle slow slowly on fast track Warning signals can also come from a fixed base rather than from a vehicle 10A transmitter when, for example, it is a question of reporting parameters relating to ground conditions: works, 0lo road conditions, traffic jams signaled, dangerous turn, place of compulsory or advised deceleration, etc. In this case, the transmitting means and its associated antenna can be installed on

  signs o when approaching a toll gate.

  The equipment for transmitting and receiving alarm information from 1OA and lOB vehicles will be

  now described with reference to Figures 2, 3 and 4.

  FIG. 2 schematically represents an equipment 5 for transmitting alarm messages from the transmitting vehicle 10A. This equipment includes a set of sensors and detectors 2a-2e functionally connected to a communication module 4 under the control of a central unit 6. In the example, the sensors used are: - a sensor 2a for activating the system ABS when the vehicle is braking 10A, - a tachometric sensor 2b for crossing the engine speed or vehicle speed threshold, making it possible in particular to detect an abnormally low speed for the road used, - a vehicle impact sensor 2c, capable of be an airbag activation detector or impact detectors located for example at the bumpers,

  - a 2d detector of the use of wipers

  windows, sensitive either to their switching on or to their passage at a high speed, and - a detector of the activation of the

distress 2nd.

  The central unit 6 is based on a microprocessor 8 associated with a memory 12. The microprocessor 8 is programmed so as to permanently and real time control the state of the detectors and sensors 2a-2e and to control the transmissions accordingly. alarm messages to the module

communication 4.

  In the example, the central unit 6 is supplied with energy on the one hand by means of a connection 14 to the vehicle supply system, coupled to the battery thereof, and on the other hand by means of '' an emergency power supply 16 equipped with an independent battery. This constitutes a redundant power supply capable of taking over in the event of

  malfunction of the power supply 14 of the vehicle.

  All of these sensors and detectors 2a-2e are connected to the central unit 6 by a Bcom communication bus. The Bcom bus can be bidirectional to allow the unit to transmit an acknowledgment, configuration or reset signal to the sensors and detectors 2a-2e. The data transmission protocol on the Bcom bus allows the central unit 6 to identify the sensor or detector 2a-2 which transmits the data and to decode this data,

according to a classic technique.

  When the central unit 6 determines that data received from one or more of the sensors and detectors 2a-2e reflect a condition which requires the transmission of an alarm message, it commands the activation of the transmission module 4 so that this message can be sent directly to surrounding vehicles. To this end, the communication module 4 comprises a microwave transmitter having a signal input 18 connected to the central unit 6, and an output

  transmitting antenna connected to a transmitting antenna 22.

  The radio transmission carried out from the antenna 22 is optimized in transmission range in the general direction towards the rear. In the example, this preferential transmission is obtained on the one hand by placing the antenna 22 at a location towards the rear of the vehicle, for example on or at

  proximity to rear windshield, tailgate or windshield

  rear impact. In addition, the configuration of the transmit antenna 22 is adapted, according to techniques which are themselves well known, in order to promote a

backward emission.

  The signal transmission range of the antenna 22 is relatively small: less than a kilometer, and

  typically of the order of a hundred meters.

  In the example, the signal is transmitted in frequency modulation on a 5.8 GHz carrier. As will be explained in more detail below, the protocol governing the structure and transmission of alarm messages is based on the European standard ISO 14906 established for electronic data collection systems.

tolls (CEP).

  s The signal supplied to the communication module 4 to be transmitted is therefore structured so that it can be detected and interpreted by an electronic toll card in one or more lOB receiving vehicles

located in the range area.

  The central unit 6 is also connected to an on-board satellite navigation system 24. This system, known in itself, makes it possible to locate the transmitting vehicle 0lA at any time by means of an antenna 26 for receiving location signals from '' a network of geostationary satellites. The satellite navigation system 24 establishes, on the basis of the terrestrial coordinates of the vehicle thus located, the position of the latter relative to a map of the road network contained in memory. In particular, it determines whether the transmitting vehicle is on a fast lane, for example a motorway or a two-lane road. This information is supplied to the central unit 6 in order to allow the latter to determine, by means of the tachometric detector 2b, whether the speed of the transmitting vehicle 10A indeed corresponds to a range of speeds adapted to the path taken. This arrangement makes it possible to control the automatic transmission of an alarm signal if the vehicle is running at

  an abnormally slow speed for the track.

  An electronic toll card, which here constitutes the basic reception equipment of the receiving vehicle

  OB, is shown in Figure 3.

  The electronic toll card 30 is in the form of a box of a format comparable to that of a

  bank card and a few millimeters thick.

  It comprises a transponder (ie a transceiver tuned to a given radio frequency) coupled to a transponder antenna 32, and light and sound indicators, respectively 34 and 36. These indicators 34 and 36 are activated selectively as a function of signals exchanged with an emission source, the latter being an electronic toll terminal in conventional use. In the example, the card 30 is made o10 in accordance with the CEN standard TC278. This type of electronic toll card is widely used and its operation is well known to those skilled in the art. Also, its general architecture, shown in Figure 4, does not

will only be briefly described.

  The card 30 includes a microprocessor 38 programmed to execute a management program in association with a memory 40. The microprocessor 38 communicates with the outside by means of a transponder 42 connected to the above-mentioned antenna 32. The indicators 34 and 36 are controlled by a driving circuit 44 connected to

an output of the microprocessor 38.

  The light indicator 34 comprises for example one or more light-emitting diodes (LEDs). It can be controlled to emit different information, each identifiable by the driver either by a flashing rhythm or a sequence of flashes, or by a static or dynamic light configuration in the case

  using several light sources. -

  The sound indicator 36 consists of a buzzer integrated into the card 30. It can be controlled to emit the same information as the light indicator 34, in which case it serves to reinforce the communication of information . It can also be ordered to provide information different from that carried by the light indicator 34, in order to allow the number of possible information items that can be transmitted to the driver to be enlarged. All of the elements of the card 30 are powered by an internal battery 46. The transponder antenna 32 can be incorporated within the card as shown in FIG. 4, or it can be a

external element.

  To avoid manipulation when approaching each toll, which would be detrimental to security and contrary to the aim of simplifying the crossing of tolls, the electronic toll card 30 is normally designed to remain on standby while the vehicle is in use.

vehicle during a trip.

  In normal use, the card 30 is placed in a location close to the driver so that the signals from the indicators 34 and 36 can be easily perceived, for example in a box on the dashboard on the edge of the windshield. This latter position is particularly recommended for cards which use a built-in transponder antenna 32 in order to allow good exchange of microwave signals.

with the outside.

  Thus, it appears that the indicators 34 and 36 of the electronic toll card 30 constitute an effective human-machine interface for signaling information received by the transponder 42 when the latter

  operates in alarm message reception mode.

  In a simple embodiment of an alarm transmission system, the invention exploits the fact that outside a toll zone, any message sent by the electronic toll card by means of the indicators 34 and 36 The aforementioned will be perceived by the driver as being necessarily alarm information coming from a 0lA transmitting vehicle (or retransmitter, as will be seen later). Indeed, outside the toll zones, the electronic toll card always remains in the standby state but normally does not receive any signal at its listening frequency. In this way, there is no disadvantage in using the same messages at the level of the indicators 34 and 36 both to inform the conditions of use of the electronic toll collection and to alert the driver, these messages being distinguished

  1o naturally according to the context of their appearance.

  It then becomes possible to use the same signal and data structures as used by an electronic toll terminal for sending alarm messages. There will now be described briefly with reference to FIG. 5 an example of a protocol for exchanging signals between a transmitting vehicle 10A and a receiving vehicle 0lB, adapted from the standard based on the DSRC standard for the communication of electronic toll messages. The adaptation essentially consists in assimilating the transmitting equipment described with reference to 'Figure 2 to the means of

  transmission of the fixed electronic toll terminal.

  When the IOA transmitting vehicle detects a condition which requires the transmission of an alarm message, the transmitting equipment 5 first transmits by its transmitting antenna 22 an initialization message (FIG. 5) to the receiving vehicles 0lB in back. This message 50 is formatted as the message designated "BST" in the DSRC standard. It switches the electronic toll card 30 which receives it from standby mode to active mode. In this active mode, the card 30 is ready to execute an action command. Then, the transmitting equipment transmits a command message 52 for the activation of at least one of the indicators 34, 36 of the electronic toll card 30. This message 52 is formatted as the message "SET-MMI" of the ISO0 14906 standard. On execution of this command, the card activates the indicator (s) concerned 34, 36 for a predetermined period, thus alerting the driver of the receiving vehicle lOB of a situation.

unexpected road trip.

  The specifics of the ISO 14906 transmission standard are given in the document bearing the reference "prENV ISO 14906; 1998E" of the European Committee for Standardization. Its content is incorporated here by reference. A second embodiment of the equipment for the receiving vehicle will now be described with reference to the block diagram of FIG. 6, also making it possible to retransmit the alarm information to other vehicles at the rear. In this

  description, the elements having a function analogous to

  those already described have the same references.

  This equipment can be used in place of or in addition to the electronic toll card 30 which constitutes the receiving equipment according to the first embodiment. It can also be functionally integrated with alarm detection and transmission equipment, for example as described with reference to FIG. 2. In this case, the combined equipment will be able to both detect and analyze alarm conditions , transmit alarm messages initiated from his vehicle, receive alarm messages from other vehicles and retransmit these messages, possibly after having estimated the need for retransmission. As shown in FIG. 6, the equipment for reception and retransmission of alarm messages 65 comprises reception means comprising a reception antenna 60 linked to a microwave receiver 62 which relays the information received to a management unit 64 The management unit 64 comprises a microprocessor 66 and a memory 68 according to a conventional architecture, making it possible to execute a management program and to control the various organs of the equipment, as will be explained below. The management unit 64 is supplied with the main electrical supply of the vehicle (wiring 14) and can optionally be connected to a backup supply (not shown) as for the

10A transmitter vehicle.

  A multifunction indicator 70, constituting a man-machine interface of the equipment, is functionally connected to the management unit 64 by a dedicated bus 72. In the example, the indicator 70 comprises a data display device 74 comprising indicator lights and an alphanumeric and / or graphical screen of the electroluminescent or liquid crystal type, as well as a speech synthesis device 76. The multifunction indicator 70 can be integrated into the dashboard or constitute a dressed sub-assembly capable of be located near the driver, for example at the center console of vehicle B. The above-mentioned human-machine interface is supplemented by an audible indication device 78, such as a small speaker or a buzzer, which can be either housed separately or physically integrated into

the multifunction indicator 70.

  The microwave retransmission means comprise a transmitting antenna 80 connected to a microwave transmitter 82 which receives the data transmitted by the management unit 64. In the example, the data exchanged between the management unit 64 on the one hand and the receiver 62 and the transmitter 82 on the other hand are relayed by a common bidirectional link 84. The same frequency is used both for transmitting data from a transmitting vehicle 10A and for

  retransmit data on the transmitting antenna 80.

  In the example, this frequency is that used for the first embodiment, namely a frequency used for the exchange of data with the cards of

  Electronic toll collection, i.e. 5.8 GHz for ISO 14906.

  Also, it is possible to combine the receiving and transmitting antennas, respectively 60 and 80 into a single hardware antenna, as soon as this antenna is able to receive transmissions from a vehicle located at the front and to transmit with a certain directivity towards the rear. However, it may be preferable to envisage for the emission a specific antenna 80 positioned at a location of the vehicle which favors the radio transmission towards the rear, like the transmit antenna 22 described with reference to the Figure 2. Thus, the transmitting antenna 80 will advantageously be at the rear of the vehicle, for example near the rear windshield, or on the tailgate or trunk of the vehicle. This antenna 80 could be a directive antenna in order to confer a better concentration of the energy.

  electromagnetic backwards.

  The receiving antenna 60 can then be positioned to allow good reception of a

  signal from the front, for example on the screen

  breeze or near it.

  Alarm information is also retransmitted in the form of warning lights by activation

  LOB vehicle emergency warning lights 86.

  This function is performed by a specific command

  of the management unit 64 via a wired link 88.

  The management unit 64 is connected by a wire link 90 to a tachometer sensor 92, like the tachometer sensor 2b described with reference to FIG. 2. This sensor 92 can be produced by any known means, being for example coupled at the counter

  gearbox or tachometer and gearbox.

  As will be explained below, the speed data thus obtained make it possible to govern

  specific retransmission conditions.

  When the management unit 64 receives an alarm message, this being able to be emitted by a transmitting vehicle 10A according to the criteria described with reference to FIG. 2, the management unit 64 transmits the alarm to the indicator multifunction 70 and possibly at

the sound indicator 78.

  If the alarm contains a specific message making it possible to specify to the driver of the retransmitting vehicle 10B the nature and the origin of the alarm, this message will be presented by means of the display 74 or of the text-to-speech device 76. The message can indicate in particular if the transmitting vehicle 10A performs emergency braking, if it has received an impact (detected by the shock detector 2c, FIG. 2), or if it has

  detected severe weather (wiper sensor

  2d), etc. After receiving the alarm, the lOB vehicle goes into retransmission mode in order to relay, if necessary, the alarm to the following vehicle (s). This retransmission takes place by the automatic activation of a light signaling and by the retransmission by radio of the message, via

the transmitting antenna 80.

  At the level of retransmission by light signaling, the management unit 64 controls the activation of the hazard lights 86 of the 0lB vehicle. These lights are activated for a period t which depends on the nature of the incident. This time is reset each time a new message is received. By way of example, the transmitting vehicle transmits a number n of alarm messages (which may be identical) succeeding each other at a predetermined interval equal to or less than the abovementioned duration t. Thus, it is possible to provide that as long as the transmitting vehicle 10A transmits its alarm message (s), the retransmitting vehicle 0lB keeps its hazard warning lights on. The number n of alarm messages transmitted can be a function of the severity of the detected situation or the speed of the

10A transmitter vehicle.

  The driver of the retransmitter vehicle 10B has the option of stopping this activation via his button.

  classic hazard warning light control.

  Then, or in parallel, the management unit 64 determines the speed of the retransmitting vehicle using the tachometer sensor 92. This information concerning the speed of the retransmitting vehicle is useful for managing the retransmission of the alarm message. A retransmitting vehicle retransmits an alarm message selectively as a function of the range which it considers necessary to grant to this message from the vehicle at the origin of this message. If the vehicle

  retransmitter considers that this range must be

  beyond the distance separating it from the vehicle originating the message, it retransmits the alarm message so that it can be intercepted by

another vehicle further downstream.

  This principle takes into account, on the one hand, that the range of a radio broadcast (or re-broadcast) from a vehicle may be less than the range that the alarm information should have, and of other than that the radio transmission according to the present invention has a preferential range towards the rear with respect to the direction of

o10 moving the vehicle.

  In order to limit the scope of an alarm message thus relayed to distances for which it remains relevant, an accounting is carried out, managed at the level of the retransmitting vehicle (s), of the number of messages retransmitted. As will be explained in more detail below, this accounting consists in adding to the alarm message a numeric field which indicates the number of times that this message has already been transmitted from the originating vehicle. A retransmitting vehicle receiving the alarm message with this indication will then evaluate, according to different possible criteria, whether or not to retransmit this message to

  again to increase its reach downstream.

  The vehicle alarm message is thus relayed only to the extent that it is deemed necessary to extend its reach to vehicles which may be affected by this message, but which could not have intercepted the radio transmission coming directly from the vehicle to

the origin of the message.

  This notion of selective retransmission of alarm messages will be illustrated by a concrete example,

with reference to Figures 7 and 8.

  FIG. 7 schematically represents a section of road 94 on which runs in the same direction a

  series of vehicles identified by the prefixes Vi to V12.

  For reasons of space, the section 94 is shown on two superposed sections. The development of section 94 from the lead vehicle VTA is from left to right for the upper section and from right to left for the lower section, the two edges

  rights of the sections being supposed to meet.

  In the figure, the numbers 1 to 12 which appear after the letter V in the vehicle identification correspond to the rank of a vehicle by

  compared to the first vehicle (lead vehicle Vi).

  Each vehicle is also identified by a suffix, entered after the aforementioned number, according to the type of equipment available to it for handling alarm messages, as follows: TA: initiator of first alarm message, RT: receiver and selective retransmitter of alarm message and RE: receiver only

alarm message.

  In the example, it is assumed that the lead vehicle ViTA has detected an alarm transmission condition. As explained above, it can be an automatic response to an operating parameter (braking detection with ABS, shock detection, etc.) or a response to a voluntary act on the part of the driver (switching of the wipers). in fast mode, switching on the hazard warning lights, fog lights, etc.). The alarm message can also originate from the reception by the vehicle VlTA of information coming from a fixed station on the road, for example a beacon indicating a

slowdown required.

  Furthermore, the transmission or retransmission of the alarm message comprises on the one hand the activation of the hazard lights, which constitutes an optical transmission, and on the other hand the transmission over the air of the message. In what follows, we will only consider the aspect of radio transmission, it being established that all vehicles which transmit or retransmit the alarm message also activate their hazard lights The alarm message is transmitted by the transmitting antenna 18 of the initiating vehicle VlTA so that its range is accentuated towards the rear, as explained above, that is to say towards the vehicles

V2-V12 which follow.

  The frequency and the transmission protocol are here selected to correspond to the standards for the exchange of electronic toll messages, for example in accordance with the ISO 14906 standard already described with reference to FIG. 5. In this way, the alarm message can be intercepted by any vehicle with an electronic toll card in accordance with the first embodiment

(Figures 3 and 4).

  In the example, the alarm messages are structured in accordance with the protocol shown in FIG. 5 (components 50 and 52). Depending on the degree of development of the system, the message may also include a component 53 (represented by dotted lines) containing information such as the type of incident. This component 53 can be structured in the same way as the message "set.req." of the aforementioned standard IS04096. Component 53 also includes a space for a numeric field in which is entered a variable number n which corresponds to the number of retransmissions whose alarm message has

is about.

  For reasons of simplification, the range of radio transmission, whether it is the first transmission or a retransmission, is considered to be always the same, from the transmission or retransmission antenna. This range is represented in FIG. 7 by the length of an arrow P, the base of which establishes the starting point of the transmission or retransmission and the point marks the limit of its coverage. The number following the "P" designates the vehicle identification number

  transmitter of the signal having the considered range.

  The chain of transmission and retransmission of

  the example of figure 7 is analyzed as follows.

  The chain begins when the vehicle IVTA emits an alarm message at a point 0 of the section 94, which will serve as a reference point. The range P1 of this radio transmission, limited to the distance dl from the reference point O, means that the message is received by the two vehicles V2RT and V3RE which follow

  immediately behind, and by these vehicles only.

  Among these two vehicles V2RT and V3RE, only the first (V2RT) is equipped to carry out a selective retransmission. The other V3RE vehicle can simply be equipped with an electronic toll card,

  allowing only to receive the alarm message.

  In the example, when it is a first message transmission (here by the vehicle VlTA), the digital field of number n of transmissions or retransmissions is left absent. This absence is justified because on the one hand the digital field is not strictly necessary for an initial transmission and on the other hand the transmission of such a field will tend to lengthen the total time of its development, its transmission and his analysis. However, the vehicles most immediately affected by the alarm message are those which are in the range area Pi, for which it is particularly important to limit this total time as much as possible. By receiving the alarm message, the central unit 64 of the vehicle V2RT will determine whether or not to retransmit it to vehicles further downstream. To this end, the unit 64 executes a routine which will be

  described with reference to the flowchart in Figure 8.

  At the start 100 of this routine, the central unit 64 is in the waiting phase for an alarm message received on o10 the antenna 60 of the microwave receiver 62 (step 102). Upon receipt of an alarm message, the central unit will first control the operation of the alarm means for the driver of the vehicle, for example by means of the multifunction display 70 (step 104). If the message includes a component 53 (figure) allowing the identification of the type of alarm message (emergency braking, slowing down to be expected, sudden change in climatic conditions, etc.), the information linked to this type of message will be also supplied to the driver by means of display 74 and / or

speech synthesizer 76.

  Then, the central unit 64 loads data which will enable it to assess the need for

  retransmit the alarm message just received.

  In general, these data are such as to make it possible to estimate the total distance that the alarm message must travel from its starting point 0. In the example, this distance is evaluated on the basis of the speed of the traffic and eventually

the type of route taken.

  Traffic speed is considered to be

  being equal to that of the vehicle having received the message.

  It is therefore obtained directly by reading the data

  of the tachometer sensor 92 of this vehicle (step 106).

  The nature of the route taken is determined by means of the satellite navigation system 24. As explained above, the latter detects the instantaneous position of the vehicle and reports this information on a road map contained in memory. The map contains, for each road, or for each section of road, an identification of its nature: national or departmental road, road in urban areas, expressway, motorway, hilly area, etc. o10 This identification is read by the central unit 64

(step 108).

  From the information read in steps 106 and 108, the central unit 64 will establish its own estimate of the number of times N that it is necessary to retransmit the message from its origin (step). This number N is related to the range P of each retransmission by radio. The greater the distance it will be deemed necessary to convey the message from the initiating vehicle VlTA, the greater the number of retransmissions N deemed necessary

will be high.

  Several criteria can be used for this distance evaluation. In the example, the central unit 64 is designed to estimate a number of necessary retransmissions N which: - increases with the speed of the traffic, - is automatically made higher if the component of the message 53 (possibly present) indicates an accident or emergency braking, and - increases all the more as the speed of circulation is low compared to the speeds normally practiced on the section, as determined from the navigation means by

satellite 24.

  Once this value N has been evaluated, the central unit 64 begins a procedure aimed at determining whether the alarm message just received has already been retransmitted.

at least N times.

  It will be noted that this number N of retransmissions required can be determined only when an alarm message is received, or periodically at any time. In the latter case, each new value of N is updated and kept in memory. Such an arrangement can be advantageous in terms of saving computing time during the critical retransmission phase. To this end, the central unit 64 first searches for the presence in the alarm message of a digital field indicating the number of retransmissions of which

  this has already been the subject (step 112).

  In the case of the V2RT vehicle in Figure 7, this

  field is empty, being a first transmission.

  The central unit 64 then establishes that the number n of retransmissions already carried out is equal to 0 (step 114). Then, the central unit 64 determines whether this number n is less than the number N of retransmissions required (step 116). We will assume that this is the case. Indeed, with regard to the vehicle which immediately follows the initiating vehicle VlTA, the number N will only be 0 in special situations (for example in slow traffic on a small lane

in an urban environment).

  The central unit 64 then proceeds to account for this retransmission, which in this case consists of

  change the value of n from 0 to 1 (step 118).

* This new value n = 1 is entered in the number of retransmissions field, which will be added to the alarm message at the level of component 53 (step). The alarm message with the number of retransmissions field is then retransmitted (step 122) and the retransmission procedure ends (step 124). In the example of FIG. 7, the retransmission by the vehicle V2RT extends the range of the alarm message from its origin point 0 to a distance d2 (arrow P2). This allows the message to be received by the V4RT vehicle, which is equipped with means of

  retransmission just like the V2RT vehicle.

  On reception of the message retransmitted by the vehicle V4RT, the central unit 64 of the vehicle V4RT will execute steps 100 to 124 of the routine for evaluating the need to retransmit (FIG. 8). The execution of steps 100 to 112 will then be carried out at the level of the vehicle V4RT as described above. However, the presence this time of the numerical field of the number n of retransmissions already carried out will cause the step 114 of zeroing of this number to be omitted. The number n will therefore remain equal to 1 to

step 116.

  It is assumed that the central unit 64 of the vehicle V4RT estimates that the number N of retransmissions necessary is greater than 1. In this way, the value n is incremented by one unit (putting n equal to 2) (step 118), the numeric field is updated with the new value of n (step 120) and the alarm message

  is retransmitted with the updated field (step 122).

  This second retransmission of the alarm message by the vehicle V4RT thus extends the range of the original message to the distance d4 (arrow P4), allowing the latter to also reach the vehicles V5RT, V6RT

and V7RE.

  These first two vehicles V5RT and V6RT are equipped with means for retransmission of messages identical to those of vehicles V2RT and V4RT. In this case, each of the vehicles V5RT and V6RT retransmits the same message according to steps 100 to 124 of the routine for evaluating the need to retransmit. It is assumed that each of the vehicles V5RT and V6RT considers that it is appropriate to retransmit the message that they have received. The retransmitted messages of the two vehicles V5RT and V6RT then each include the value n = 3 in the

numeric field.

  In this case, it can be seen that the range area P5 of the terrestrial retransmission of the vehicle V5RT, limited to the distance d5, is entirely covered by the retransmissions of the vehicles V4RT and V6RT. However, such redundancy is in no way embarrassing and on the contrary makes it possible to offer security in the chain of retransmissions. The third retransmission of the alarm message

  reaches the limit d6 of the P6 range of the V6RT vehicle.

  It is detected by the three V7RE, V8RE and V9RT vehicles located behind the V6RT vehicle. Note that among these three vehicles, the first two (V7RE and V8RE) are equipped only to receive the retransmitted message, being for example each provided with a

  receiver in the form of an electronic toll card.

  On reception of the third retransmission of the alarm message, the vehicle V9RT, being retransmitted, executes the aforementioned routine for determining the need to retransmit (FIG. 8). It is assumed that the central unit 64 of the vehicle V9RT estimates that the number N of retransmissions required is equal to 4 (step 110). According to steps 118 to 124 (FIG. 8), the vehicle V9RT will therefore retransmit the alarm message. The number n in the

  numeric field will then go from 3 to 4.

  This fourth retransmission, the range P9 of which makes it possible to reach the cumulative distance d9 from the vehicle VlTA initiating the message, is detected by the two vehicles V1ORE and VllRT which follow. Among these, only the V11RT vehicle is equipped to allow a possible retransmission, the vehicle

  V1ORE being only equipped as a receiver.

  On receipt of the fourth retransmission of alarm message, the vehicle VllRT in turn executes the routine for determining the need to retransmit according to FIG. 8. In the example, the central unit 64 of the vehicle VllRT estimates at l step 110 that the number N of retransmissions necessary is also equal to 4. The unit will then establish in step 116, by reading the value n = 4 in the digital field of retransmissions, that the alarm message has already been transmitted four times, and it is therefore no longer necessary to retransmit it. The retransmission procedure will then be interrupted (step 126) following step 116. ' The digital field of retransmissions will not be incremented and the

message will not be forwarded.

  In this way, the V12RE vehicle, judged too far from the VlTA vehicle to be affected by the message

  will not receive this message.

  Thus, the procedure of recorded retransmissions of the alarm messages made it possible, in the example of FIG. 7, to relay the message from the initiating vehicle VlTA well beyond the range P1 of the radio transmission permitted by this vehicle, up to at a distance d9 from the reference point 0. As a result, the alarm message could be communicated not only to the vehicles V2RT and V3RE having received it directly from the initiating vehicle VlTA,

  but also to vehicles V4RT to VllRT.

  However, the limitation of the number of retransmissions means that the alarm message is transmitted up to reasonable range limits and dynamically adapted to the traffic conditions as perceived and evaluated at the level

retransmitting vehicles.

  It will be understood that the different embodiments presented o10 allow many variations while remaining within the scope of the present invention. For example, it is clear that a vehicle could possibly be equipped only as a message initiating vehicle, or only as a

  that retransmitter of alarm messages.

  Furthermore, it is easy to envisage a variant according to which the vehicle initiating the alarm message transmits with its message the digital field of the aforementioned number n (for example by putting n = 0) in order to keep the same message structure both for the transmission only for retransmission of the message. It will be noted that the invention can be implemented with all possible combinations of different numbers of monitored parameters (shock detection, braking with ABS, etc.) to determine the appearance of an alarm condition. It also makes it possible to manage parameters other than those cited in the examples, these being established as a function of security needs, conditions

  system usage and economic factors.

  As regards the evaluation of the number N of retransmissions necessary, it is possible to envisage as a variant that this number is evaluated only once, following for example the procedure of FIG. 8 and on the basis of the same criteria. This single evaluation of the number N may be carried out by the first retransmitting vehicle (V2RT in FIG. 7) or by the vehicle (VlTA) initiating the message. The numeric field can then include both the number N of retransmissions necessary and the number n of retransmissions already carried out. This provision would be conceivable if this resulted in a significant saving in computation time in a chain of

retransmission of messages.

  Finally, the content of the transmitted or retransmitted alarm message can incorporate all kinds of data depending on the established communication protocol. These data can be taken into account selectively by the vehicles that receive them. For example, a vehicle equipped with a reception device which can communicate, as a man-machine interface, only a limited range of messages, such as the case of an electronic toll card, may ignore some of the data which it

will be superfluous.

Claims (27)

R E V E N D I C A T IONS   1. Device for communication of alarm messages between vehicles (10A, 0lB) making it possible to transmit an alarm signal (50, 52, 53) from transmission means (5) of a transmitting vehicle (10A) to the at least one receiving vehicle (O10B) by a radio link under the control of a management unit (64), characterized in that the radio link is produced by transmission means (80, 82) allowing an optimized transmission range to rear, relative to the normal direction of travel of the transmitting vehicle (10A).   2. Device according to claim 1, characterized in that the transmission means (5) transmit the alarm message (50, 52, 53) in a form capable of being able to be received, at the level of a receiving vehicle (10OB ), by reception means (30) not specifically designed to receive said alarm message. 3. Device according to claim 2, characterized in that the reception means not specifically provided for receiving the alarm message is a card Electronic toll collection (30).   4. Device according to claim 3, characterized in that the management unit (64) organizes the structure of the transmitted alarm message (50, 52, 53) according to a communication protocol based on an established protocol   for electronic toll message communication.   5. Device according to any one of   claims 1 to 4, characterized in that the   frequency of message transmission over the air is in the microwave range,   this frequency being for example 5.8 GHz.   6. Device according to any one of   Claims 1 to 5, characterized in that it comprises   further retransmission means (65), associated with a retransmitting vehicle (V2RT, V4RT, etc.), for retransmitting a received message (50, 52, 53) over the air with a relatively optimized transmission range towards the rear in the normal direction of movement of the retransmitting vehicle, so   increase the range of the alarm message.   7. Device according to claim 6, characterized in that the retransmission means (65) comprise means (64) for accounting for retransmissions of alarm messages (50, 52, 53) and for limiting these retransmissions to a limit number N determined according to the   scope to be granted to the alarm message received.   8. Device according to claim 7, characterized in that the limit number N is determined by the retransmission means (65) dynamically by   depending on traffic conditions.   9. Device according to claim 7 or 8, characterized in that the accounting means comprise: means (64) for reading and writing a variable n in the retransmitted message (50, 52, 53), we correspond the number of message retransmissions carried out, and means (64) for incrementing this variable during a retransmission. 10. Device according to claim 9, characterized in that the retransmission means (65) retransmit an alarm message under the condition that the variable n indicates that the number of retransmissions of this message already carried out is less than the limit number N of broadcasts   determined by these retransmission means.   11. Device according to any one of   o10 claims 1 to 10, characterized in that the means   transmission (5) and / or the retransmission means (65) cooperate with a navigation system, such as a satellite navigation system (24, 26), so as to be able to identify the nature of the route taken by the vehicle with which these means are associated. 12. Device according to claim 11, characterized in that the transmission means (5) transmit an alarm message when they determine that the speed of the vehicle with which these means are associated is less than a speed-threshold established as a function of the nature of the route taken, determined from navigation system (24, 26).   13. Device according to any one of   claims 7 to 12, characterized in that the number   limit N of retransmissions is determined from at least one of the following parameters: - the content of the message transmitted, - the speed of traffic, - the nature of the route taken, and - traffic conditions (day / night, bad weather, etc.).   14. Device according to claim 13, characterized in that the limit number N of retransmissions is determined from at least the nature of the route taken, this being determined by means of a navigation system (24, 26 ). 15. Use of an electronic toll card (30) as a means for receiving alarm messages in a vehicle-to-vehicle communication device according to one   any of claims 1 to 14.   16. Use, in a communication device between vehicles, of alarm messages structured according to a protocol based on a protocol intended for the electronic toll collection.   17. Method for communicating alarm messages between vehicles (10A, 0lB) making it possible to transmit an alarm signal (50, 52, 53) from transmission means (5) of a transmitting vehicle (10A) to the at least one receiving vehicle (10B) via a radio link under the control of a management unit (64), characterized in that the radio link is produced with an optimized transmission range towards the rear, relatively to the normal direction of   displacement of the transmitting vehicle (1OA).   18. The method of claim 17, characterized in that the alarm message (50, 52, 53) is transmitted in a form capable of being able to be received, at a receiving vehicle (0lB), by a receiving means (30) not specifically designed to receive said alarm message.   19. The method of claim 18, characterized in that the reception means not specifically provided for receiving the alarm message is a card electronic toll collection (30).   20. The method of claim 19, characterized in that the structure of the transmitted alarm message (50, 52, 53) is organized according to a communication protocol based on an established protocol of   communication of electronic toll messages.   21. Method according to any one of the claims   17 to 20, characterized in that it further comprises retransmission by radio means, at the level of a retransmitting vehicle (V2RT, V4RT, etc.), of a message (50, 52, 53) received, with a range of optimized rearward transmission relative to the normal direction of movement of the retransmitter vehicle, so   increase the range of the alarm message.   22. Method according to claim 21, characterized in that the retransmissions of alarm messages (50, 52, 53) are counted and to limit these retransmissions to a limit number N determined according to the   scope to be granted to the alarm message received.   23. Method according to claim 22, characterized in that the limit number N is determined so   dynamic depending on traffic conditions.   24. Method according to any one of the claims   22 or 23, characterized in that the accounting is carried out by means of a variable n in the retransmitted message (50, 52, 53), this variable being   incremented during a retransmission.   25. The method of claim 24, characterized in that an alarm message is retransmitted on the condition that the variable n indicates that the number of retransmissions of this message already carried out is less than the limit number N of retransmissions   26. Method according to any one of claims   16 to 25, characterized in that the nature of the route taken is determined by means of a navigation system, such as a satellite navigation system (24, 26) and in that a alarm message when the circulation speed is lower than a threshold speed established according to   the nature of the route thus determined.   27. Method according to any one of the claims   22 to 26, characterized in that the limit number N of retransmissions is determined on the basis of at least one of the following parameters: - the content of the message transmitted, - the speed of the traffic, - the nature of the route taken , and - traffic conditions (day / night, bad weather, etc.).