US3921127A

US3921127A - Vehicle danger indicating system

Info

Publication number: US3921127A
Application number: US529942A
Authority: US
Inventors: Jean-Raymond Narbaits-Jaureguy; Henri Billottet
Original assignee: Thomson CSF SA
Current assignee: Thales SA
Priority date: 1973-12-07
Filing date: 1974-12-05
Publication date: 1975-11-18
Anticipated expiration: 1992-11-18
Also published as: ES432658A1; NO744423L; DE2457879A1; NO137977B; SE400399B; FR2279178A1; IT1024351B; NO137977C; DE2457879C3; SE7415330L; DE2457879B2; GB1485779A; CA1028409A; CH601876A5; NL7415922A; JPS5089785A; FR2279178B1; BE822922A

Abstract

A system for indicating danger to a vehicle comprises a fixed part on the ground in the form of sensors which are arranged along a traffic lane and which are capable of detecting a vehicle situated in their zones of sensitivity. Such a signal, termed a presence signal, is transmitted to a centralised master control circuit via all the preceding sensors and in each sensor through which it passes it triggers a signal which gives the distance between the vehicule and the sensor. This signal is received by another vehicle situated in the zone of sensitivity of the transmitting sensor. When compared with a signal which indicates a socalled safe distance, the first signal triggers a danger indicator when this is necessary.

Description

Narloaits-Jaureguy et al.

[11] 3,921,127 r [.451 Nov. 18, 1975 VEHlCLE DANGER INDICATING SYSTEM [75] Inventors: Jean-Raymond Narbaits-Jaureguy;

Henri Billottet, both of Paris, France [73] Assignee: Thomson-CSF, Paris, France [22] Filed: Dec. 5, 1974 [21] App]. N0.: 529,942

[30] Foreign Application Priority Data Primary ExarrtinerThomas B. Habecker Attorney, Agent, or Firml(arl F. Ross; Herbert Dubno [57] ABSTRACT A system for indicating danger to a vehicle comprises a fixed part on the ground in the form of sensors which are arranged along a traffic lane and which are capable of detecting a vehicle situated in their zones of sensitivity. Such a signal, termed a presence signal, is transmitted to a centralised master control circuit Dec. 7, 1973 France 73.43762 via all the preceding sensors and in each sensor [52 US. Cl 340/32; 340/62 through which it passes it triggers a signal which gives [51] Int. cl. GOSG 1/00 the distance between the vehicule and the semen This [58] Field of Search 340/32 signal is received y n h r v l i u d n h zone of sensitivity of the transmitting sensor. When [56] References Cited compared with a signal which indicates a so called safe UNITED STATES PATENTS distance, the first signal triggers a danger indicator when this is necessary. 3,787,679 1/1974 Birkm 340/32 16 Claims, 10 Drawing Figures I l 127 p TRfiNSMlSSION 125 I a ANTENNA V, g I I 9/ 24, m2 I MONOSTABLE MONOHABLE i e i E/ a I I RELEPTION WM T RELEWER 6 k l l 2 125 4 i no [2 I 129 T i +4-4- MONOSTABLE l I U l J US. Patent Nov. 18,1975 SheetlofS 3,921,127

I 132 3 mouosmms MONOSTABLE Q I 222% i VER I 125 E- 130 1550 '13;

WW0 292 w 293 US. Patent Ndv. 18, 1975 Sheet 5 of5 3,921,127

90*? 313 monomm 92 93 SPEED M 910 k 92 523 311 INTERSELT. N030 monosmsua MONOSTABLE (mm QMONOSTABLE YjQY fi 381 MONOSTABLE 0 8 3a Puor LIGHT v VEHICLE DANGEE' INDICATING SYSTEM The present invention relates to a system for indicating dangerito vehicles, the danger under consideration being in particular that of collision with a vehicle in front, i.e. one which is moving along the same traffic lane as the vehicle concerned or is stopped on it.

This being so, the system according to the invention comprises, in combination, means arranged on or near a traffic route which detect the presence and position of vehicles travelling along the route in the same direction, without ignoring any vehicles which may be stopped on it, and means on board the vehicles which, on the basis of the data supplied by the first means, give the distances by which the vehicles are separated from one another and evaluate the least distance which can be permitted between two vehicles following one another before there is a danger of their colliding.

The system according to the invention also makes use of equipment which is set up along certain routes to monitor traffic on them. Such equipment consists of sensors which are distributed along the route under surveillance and which are activated one after another by a master control pulse which is emitted by a master control device. The sensors are then able to respond to the passage of a vehicle through a limited zone of socalled sensitivity surrounding them. The signal which is emitted by that sensor which has detected the presence of a vehicle in its zone of sensitivity is transmitted to the centralised master control device via all the previous sensors, which regenerate the signal as it passes through. The time taken by this signal to arrive at the central station from the time after emission of the master synchronising pulse which successively triggers the sensors, gives an indication of the distance between the vehicule detected and the central station. However, within the context of the present invention, it is not enough to know how far away the detected vehicle is, since in the present instance it is necessary to be able to inform all the vehicles of the position of the vehicle in front of them, and thus of the distance separating them, as well as of any alterations in this distance, bearing in mind the reciprocal speeds of the vehicles in question.

In accordance with the invention, there is provided a system for indicating danger to a vehicle, travelling along a traffic lane, particulary when the distance between said concerned vehicle and another in front thereof is substantially lessening, comprising fixed means associated with said traffic lane for detecting the presence of vehicles on said lane, said fixed means having means for transmitting said presence information, means aboard vehicles for receiving said presence information from a vehicle in front of said concerned vehicle and means for generating a safety signal when said presence information as a pulse is within a signal of predetermined length corresponding to a predetermined safety distance from concerned said vehicle.

Other advantages and features of the invention will become apparent in the course of the following description of an embodiment which is illustrated in the figures, which show:

FIG. 1 a modified sensor according to the invention;

FIG. 2 a time diagram indicating the positions of the signals emitted by the sensors;

FIG. 3 a schematic diagram ofa vehicle on-board receiver within the context of the invention;

FIG. 4 a schematic diagram of a circuit for discriminating between the synchronising pulses and the presence pulses;

FIG 5 a diagram of signals as a function of time which relates to the circuit of FIG. 4;

FIG. 6 a graph indicating the safe distance between two vehicles;

FIG. 7 a diagram of a generator for generating a rectangular safety signal;

FIG. 8 a diagram of signals as a function of time to assist in understanding the way in which the generator of FIG. 7 operates;

FIG. 9 a schematic diagram of a warning indicator in the vehicle on-board receiver, and

FIG. 10 a diagram of signals as a function of time which relates to the indicator of FIG. 9.

In the introduction it was seen that the system according to the invention comprises a part which may form the infrastructure of a device for minitoring traffic routes, and a part on board vehicles using the system which, from information emitted by the sensors, will produce a safety signal which indicates whether or not the carrier is in danger of colliding with a vehicle in 'front of it.

FIG. 1 shows an example of a sensor which is set up on or along a traffic route being monitored and which is employed in accordance with the invention.

Such a sensor takes the form of a module containing a miniaturised transmitter and a miniaturised receiver. The miniaturised transmitter is connected to a transmission antenna 125. The miniaturised receiver 121 is connected to a reception antenna 126. The miniaturised transmitter and receiver are connected, via

diodes

127 and 128 respectively, to two

monostable circuits

122 and 124 which are in series. The assembly of all these members is connected to sensors located both upstream and downstream, or to a centre master control device if the sensor concerned is the first one. Such an arrangement implies that, in the context of a surveillance system, transmitter 120 and receiver 121 are triggered simultaneously. The receiver 121 of the sensor is also connected via a diode 129 to a third monostable circuit 123 which is responsible for transmitting a signal indicating the presence of a vehicle in the zone of sensitivity of the sensor, this zone being defined by the radiation from the transmission antenna in the u stream direction, i.e. to a preceding sensor or to the master control device. A conductor 133 which is connected to monostable circuit 123 allows via a diode 130 the transfer of presence information originating from a sensor downstream of that considered. Conductor 133 is also connected to a conductor 1330 which connects it directly to transmitter 120 via diode 1331.

It will be seen that a sensor such as that described above can operate in two ways, depending on whether it is simply indicating the presence of a vehicle within its 'zone of sensitivity or whether it is serving as a transmission relay for a presence signal supplied by a following sensor. It is not necessary to dwell on explaining the way in which the sensor operates in the first case envisaged. In the second case it will be realised that a signal which indicates that a vehicle is present in the active zone of a sensor which is located further away from the master control device than the one being considered will appear on conductor 133. This signal travels on the one hand through diode 130 to monostable circuit 123, which it triggers and which transmits a regenerated pulse to the preceding sensor or to the master control device, and on the other hand via diode 1331 to transmitter 120, which it triggers and which transmits a signal from its antenna 125, which signal may be received by a vehicle situated in the sensitivity zone of the said sensor. It is as well to point out that the transmissions which are due on the one hand of the periodic interrogation of the sensor by the master control device or the preceding sensor and on the other of that caused by an indication of presence originating from another sensor, are distinguished from one another to avoid any possibility of error. To do this, it is possible, as an example, to give the two

monostable circuits

123 and 124 different operating times. As an example the duration of the response of circuit 123 may be three times shorter than that of circuit 124 which, as has been seen, transmits to a succeeding sensor the triggering pulse which it has itself received.

FIG. 2 is a time-function diagram summarising the way in which a sensor which is part of the system according to the invention operates. On line appears a pulse 200 which is the pulse for triggering the first sensor and which originates from the master control device (not shown). On line 21 appears a pulse 210 which is to trigger the second sensor.

On line 22 appears a pulse 220 which is emitted by the antenna 125 of the transmitter of the first sensor.

On line 23 appears a pulse 230 transmitted by receiver 121 which relates to a vehicle situated in the sensitivity zone of the sensor.

Line 24 indicates that there is no vehicle in this zone.

On line 25 appears a pulse 250 which is the pulse emited by the transmitter of the second sensor in response to the triggering pulse 210 which is transmitted by the first sensor (line 21).

On line 26 appears a pulse 260 which is received by the receiver of the second sensor in the event of there being a vehicle in its sensitivity zone. If there is no vehicle, there is no pulse (line 27).

On line 28 appears a pulse 280 which is produced after a period dt (symbolised' by pulse 281) measured from the pulse 210 for triggering the second sensor. This pulse 280 will go on to trigger the third sensor.

On line 29 appears a pulse 290 which is emitted by the transmitter of the third sensor when triggered by pulse 280.

No mulse appears on line 290, which shows that there is no vehicle in the sensitivity zone involved.

On line 291 appears a pulse 2920 which is formed after a delay dt (symbolised by pulse 2921) and which will go on to trigger the fourth sensor.

On line 292 appears a pulse 2930 which is emitted by the transmission antenna of the fourth sensor and on line 293 appears a pulse 2940 which indicates that there is a vehicle present in the sensitivity zone involved.

Such a diagram may be continued to cover all the successive sensors in the system.

The pulse 2940 which indicates that there is a vehicle present in the sensitivity zone of the fourth sensor is transmitted to the master control device via the preceding sensors in which, in accordance with the invention it triggers the appropriate transmitter in each instance. Thus, pulse 2941 on line 29 indicates that the transmitter of the third sensor has emitted a signal at the moment when pulse 2940 passes through. Similarly, passage of this pulse through the second sensor triggers the transmitter of this sensor, and the transmitter transmits the signal represented by pulse 2942 on line 25. Under the same conditions, the first sensor transmits a pulse 2943. In view of the speed at which the pulses are transmitted from one sensor to another, it may be assumed that the various transmitters are triggered simulta neously, hence the position of pulses 2940 to 2943 on the same vertical line in the diagram in FIG. 2.

If it is assumed that a vehicle is situated in the sensitivity zone of the first sensor for example, the difference in time between the pulse 220 which causes its transmitter to operate and the pulse 2943 which is emitted by the said transmitter in response to the arrival at the said sensor of information that a vehicle is present in the sensitivity zone of another sensor, allows the distance separating the two vehicles involved to be established, bearing in mind that the sensors are usually all spaced the same distance apart.

Thus, when the vehicle concerned receives the signal represented by pulse 2943, this gives an indication of the distance between the two vehicles.

FIG. 3 is a schematic diagram of the receiver onboard a vehicle which operates in the context of the system according to the invention.

This receiver installation on-board a vehicle includes an antenna 30 which is capable of picking up transmissions from transmitters similar to of sensors associated with the system. This antenna may be of the frame type, e.g. the whip type. It feeds a receiver proper 31 which is tuned to the same frequency band as the transmitters 120 and which will not be described individually in detail. At 310 this receiver supplies a video frequency signal which travels along an operating chain.

This chain includes a circuit 32 which determines whether the signal received at 310 comes from a transmitter which has been triggered by a synchronising signal. Circuit 32 which can be called synchro separator is connected to a circuit 34 which generates a so-called safety rectangular wave pulse and the output of which is connected to the input of an AND circuit 36 the second input of which is connected directly to a circuit 33 and whose output feeds a danger indicating device 39. Circuit 33 is connected to circuit 32. The purpose of circuit 33 is then to determine whether the signal received at 310 is a presence signal which has triggered the transmitter of the sensor on its way through. This circuit 33 is called presence signal separator.

The output of circuit 32 is also connected, on the one hand directly and on the other via an AND circuit 35, to a so-called watch device 38. The second input of AND circuit 35 is connected to a circuit 37 which gives an indication of the speed of the vehicle in which the receiver is installed. This speed sensor, which may for example be a phonic wheel, a tachometric alternator, etc. is connected to circuit 34 which is the generator for the rectangular wave safety pulse. This circuit 34 is also connected to a circuit 390 which provides information on external conditions, such as the coefficient of friction of the road surface according to whether it is dry, wet, icy, etc, this being termed grip. The output of the generator for generating the rectangular wave safety pulse is connected to a second input of AND circuit 36, the output of which feeds a danger indicating device 39, as already mentioned.

It will be apparent that the functions performed by

circuits

32 and 33 in the receiver are of some importance since it is they who allow the responses from the transmitter 120 of a sensor which are given, as a result of the presence ofa vehicle in the zone of sensitivity involved, in response to an interrogation triggered by a synchronising pulse which has either come directly from a master control device or is delayed relative to the direct pulse to be separated from responses given as a result of relayed information originating from sensors situated backwards from the one concerned.

It has been seen that the times for which

monostable circuits

124 and 123 operate differ according to whether the sensor concerned is triggered by the preceding sensor (circuit 124) or the succeeding sensor (circuit 123). From the length of the signal delivered at 310 by the receiver proper 31, either circuit 32 determines that the vehicle receiving the signal is in the zone of sensitivity of the sensor concerned, or circuit 33 supplies information that a vehicle is present in the Zone of sensitivity of a succeeding sensor.

The object of generator 34, which produces a rectangular wave pulse termed the safety pulse which will be described later, is to produce a rectangular-wave pulse the duration of which is proportional to the so-called safe distance which the vehicle needs to maintain between it and the vehicle in front of it on the same traffic lane. The length of this signal or rectangular-wave is a function of the speed of the vehicle in question and of traffic conditions and relates to, inter alia, the grip of the vehicle on the road surface as determined by the nature of the surface and the state of it at the time. AND circuit 36, which is connected both to generator 34 and to circuit 33, emits a pulse along a conductor 315 which links it to a display-equipped danger indicating device 39 when the information that a vehicle is present is simultaneous with that for the safe distance. When no information that a vehicle is present is supplied, the driver of the vehicle concerned receives a socalled pilot indication from a device 38, which indicates that the equipment is working. This device consists of a so-called pilot-light window 380 which indicates that the surveillance system which incorporates the sensors is working, and of a second lighted window 381, which may be of a different shape to the previous one, which only operates for a brief moment and indicates to the driver that he is travelling at a speed which is considered too slow, or even at no speed at all, and that he may be a source of danger.

FIG. 4 shows an embodiment of

circuit

32 and 33 and FIG. 5 shows the waveforms at various points in these circuits.

These circuits consist in essence of a circuit 40 which performs a double differentiation and two

diodes

41 and 42 of different polarities, one of which 41 is connected to a monostable circuit 43 the output of which feeds on the one hand an AND circuit 44 and on the other hand a second monostable circuit 45 similar to the first, via a circuit 46 which performs a double differentiation and a diode 47. An AND circuit 48 is connected to the output of monostable circuit 45. The other input of AND circuit 48, which is commoned to AND circuit 44, is connected to diode 42.

The way in which such a circuit operates will be explained with the help of the waveforms in FIG. 5.

The signal to be processed appears at input 310 and it may consist of a synchronising pulse 500 and a presence pulse 501 of greater length (waveform 50). Differentiation circuit 40, which consists of resistors 400, 401, and 402 and capacitors 403 and 404, differentiates

pulses

500 and 501 and produces from them pulses 510-511 and 512-513 respectively (waveform 51). Diode 41 allows positive-going pulse 510 to pass and this triggers monostable circuit 43. The latter produces a pulse the length of which is substantially twice that of the synchronising pulse. Conversely, diode42 is so connected as to separate out the negative-going pulse 511, which is applied to AND

circuits

44 and 48. From

waveforms

52 and 53 together, it is clear that the pulse 511 which is present in the pulse produced by the monostable circuit 43, which latter pulse is applied to AND gate 44 passes through. The synchronising pulse which is present in the signal applied to input 310 has thus been correctly separated out. It is also apparent from a study of

waveforms

52 and 53 that the pulse 513 which is produced from the presence pulse 501 is not separated out.

The output of monostable circuit 43 is also connected to a circuit 46, which consists of three

resistors

460, 461 and 462 and two capacitors 463 and 464. Because of this,

pulses

520 and 521

produce pulses

540, 541, 542 and 543. Diode 47 is connected to the input of monostable circuit 45 in a direction such that it is triggered by a negative-going

pulse

541 or 543. The time for which this circuit operates is equivalent to approximately twice the length of the synchronising pulse. The monostable circuit supplies pulses such as 550, 551 which can be seen in waveform 55. Study of

waveforms

51, 52 and 55 will show that only the negative-going pulse 513 which is formed from the presence pulse 501 is separated out and this appears at the output of AND circuit 48 to which is applied the pulse from monostable circuit 45.

Outputs

311 and 36 of AND

circuits

44 and 48 are connected to the circuit 34 for generating the rectangular wave safety pulse (input 311) and to AND circuit 36 respectively both of which are shown in FIG. 3. At these outputs may be provided two monostable circuits (not shown) which are triggered by the negative-going pulses which appear at them, so that

circuits

34 and 36 will have positive-going pulses applied to them.

FIG. 7 is a schematic diagram of the generator for generating the rectangular-wave safety pulse. The length of the rectangular pulse is, as has been stated, proportional to the so-called safe distance for the vehicle, this safe distance depending on the speed of the vehicle and on the running conditions and state of grip on the highway (

circuits

37 and 390 in FIG. 3).

If this data is plotted on a graph, FIG. 6 is obtained. This shows the safe distance 0A which is struck on the x axis from a point 62 which represents the intersection between a straight line 60 struck from the y axis at B, with OB representing a voltage proportional to the speed of the vehicle, and a sawtooth voltage of which the slope a is proportional to the grip offered by the ground. The origin 0 of the coordinate axes represents the moment at which is emitted the synchronising pulse which is given either by the master control device belonging to the surveillance system or by the preceding sensor.

The embodiment of rectangular-wave safety pulse generator shown in FIG. 7, is associated with explanatory waveforms of FIG. 8.

The generator consists essentially of a first monostable circuit connected to its input 311, of which the output is connected to a circuit 3900 of the contactswitch type which indicates external conditions and to a device 700 for resetting to zero, and of a second monostable circuit 74 which is connected to the circuit described above and supplies the said rectangular-wave safety pulse.

The way in which this circuit operates is as follows:

Input 311 to the generator, which forms the output of circuit 32 and at which the synchronising pulses from the sensors appear, applies these pulses to monostable circuit 70. The latter is triggered and operates for a length of time T which is shorter than that t between two successive synchronising pulses. These pulses are shown in line 81 in FIG. 8. Monostable circuit 70 thus supplies a rectangular-wave pulse 709 which can be seen in line 82 in FIG. 8. This signal 709 passes through an integrator device 3900 of variable time-constant which, via a switch 705 which moves selectively to one of the three

capacitors

702, 703, 704 feeds in the socalled external conditions which are present in and displayed by circuit 390 (FIG. 3). At output 706 of this circuit is obtained a sawtooth signal which is shown in line 83 FIG. 8 and the gradient a of which is proportional to what has been termed the grip of the carriageway. At the end of each cycle this sawtooth signal is reset to zero by the leading edge of the next synchronising pulse, which acts through resetting circuit 700. This latter consists of a double differentiating circuit (capacitor 710, resistor 711 and capacitor 712 and resistor 713) at the output 714 of which is obtained a short pulse which is shown in line 84 in FIG. 8. This pulse is applied to the base electrode of a semiconductor component, namely a transistor 71, and makes it conductive, thus causing the discharge of one of the capacitors 702 to 704, which had been charged in accordance with external conditions. The sawtooth generator is once again capable of operation for a fresh synchronising pulse. The pulses proportional to the speed of the vehicle which are produced in circuit 37 in FIG. 3 are applied to input 313 of the safety square-wave generator. At this input diode 720 supplies the positive pulses shown in line 85 in FIG. 8, t1: ese being integrated by capacitor 721 which is in turn discharged by resistor 722.

The values of the resistor and the capacitor are selected so as to make the maximum repetition frequency of the speed pulses fall within the 6113 gradient of the resistance capacitance combination. If this condition is met a voltage is obtained at the terminals of the circuit which is proportional to speed. This voltage is applied to the base of semiconductor component, namely a transistor 72, which is mounted as an emitter follower, with the result that its emitter gives a voltage which is a replica of the first but is capable of feeding the emitter of transistor 73 without any appreciable change in its value. It will be realised that this voltage is equivalent to reference 60 in FIG. 6.

Thus, transistor 73 receives at its emitter a voltage which is shown in line 86 in FIG. 8 and at its base the sawtooth voltage, the generation of which has been described. When these two signals reach the same potential, transistor 73 conducts, its collector potential drops, and a negative-going pulse, such as is shown in line 87 in FIG. 8, is obtained which is applied to monostable circuit 74 at 741. Input 742 of the monostable circuit receives the synchronising pulses which appear at 311. It can thus be seen that the signal applied at 741 will cause a reset to zero.

When monostable circuit 74, the operating time of which is shorter than the interval between two synchronising pulses, is triggered by a synchronising pulse, it delivers at 317 at signal'such as is shown in line 88 in FIG. 8. In the diagram, the maximum length of such a signal is shown in broken lines but the negative-going pulse in line 87 which is applied to input 741 of the monostable circuit generally resets it to zero before this length is reached. At output 317 of the monostable circuit 74 is generally obtained a rectangular wave pulse the length of which represents the safe stopping distance for the vehicle when allowance is made for its speed and the other external conditions already defined.

In combination with the diagram in FIG. 10, FIG. 9 shows an example of the way in which the so-called danger device 39, which forms part of the reception equipment fitted on board vehicles, may be triggered. This device operates if there is coincidence between the rectangular wave safety pulse discussed above and the signal indicating the presence of another vehicle which has been detected by another sensor.

The speed pulses which appear at 313 (line 101 in FIG. 10) are applied to a monostable circuit 90, the operating time of which is T1 and which supplies pulses which can be seen in line 102 in FIG. 1.0. These pulses are applied to a gate 91, which they open, so as to z. through the synchronising pulses whi h 313i; input 311 (line in FIG. 10). The puisi which are supplied by gate 91, which can be seen in line 103 in FIG. 8, are applied to another monostable circuit 92, the operating time of which is T2 and which supplies the pulses which can be seen in line 104 in FIG. 10. A combination formed by a capacitor 921 and a resistor 922 at the output of circuit 92 differentiates the signals which appear at output 920, converting them into a sawtooth signal which appears at 923 and which can be seen in line 105 in FIG. 10. A so-called intersection circuit 93, such as that formed by transistor 73 and capacitor 732 in FIG. 7, which has a threshold 930 which can be adjusted by a potentiometer, enables a train of negative-going pulses to be produced (line 106 in FIG. 10) when the value of the sawtooth drops below this threshold, which train triggers a third monostable circuit 94 which supplies pulses such as those shown in line 107 in FIG. 10 and feeds indicator 381. Since this monostable circuit is capable of being active for periods which may be as long as several seconds, the light signal for danger is very obvious to the user. When mounted on the vehicles rear-view mirror for example it will be capable of inducing the driver to look about him.

It will be realised that if the vehicle is moving at high speed it will nevertheless pick up a sufficient number of synchronising pulses to allow the sawtooth to be quickly regenerated and its voltage level to be prevented from dropping below that of the threshold 930 set by potentiometer 932. At 380 is shown the so-called pilot indicator window which is marked 380 in FIG. 3 or pilot light. When lit this window indicates to the driver that he is on a traffic route where the surveillance system is working. To do this the synchronising pulses which appear at input 311 are applied to a monostable circuit 95 the pulses from which act on the window directly.

To this pilot indicator is generally coupled a so-called warning indicator window 381 which shows the driver that he is travelling at too slow a speed and is a potential danger to those following. It may also indicate that the vehicle is no longer on a monitored route or that the surveillance system is out of action and that the driver can no longer rely on it.

It will be seen that the operating times of the various monostable circuits and the level of voltage 930 are selected as a function of the repetition frequency of the fixed s ystem, of the frequency speed ratio of the speed sensor 37 (FIG;'3), and "of" the operating conditions which are assumed "to be best by the builder of the systern. i

There has thusbeen described a danger indicating system for a vehicle which gives awarning when a vehicle approaches dangerously close to a vehicle in front.

Of course, the invention isnot limited to the'embodiment described and shown which was given solely by way of example.

What is claimed is:

l. A system for indicating danger to a vehicle, travelling along a traffic lane, particulary when the distance between said concerned vehicle and another in front thereof is substantially lessening, comprising fixed means associated with said traffic lane for detecting the presence of vehicles on said lane, said fixed means having means for transmitting said presence information,

means aboard vehicles for receiving said presence in-.

formation and deriving therefrom whether said presence information comes from a vehicle in front of said concerned vehicle and means for generating a safety signal when said presence information as a pulse is within a signal of predetermined length corresponding to a predetermined safety distance from said concerned vehicle.

2. A system as claimed in claim 1 comprising fixed means having a plurality of sensors associated with said traffic lane, said sensors being distributed along said lane, a master control device emitting synchronising pulses for triggering said sensors sequentially and said triggering resulting in a sensitivity zone around said sensors in which a vehicle can be detected, transmitting means in said sensors for transmitting a presence signal relating to a vehicle in such sensitivity zone to the said master control device via all the preceding sensors in turn, and said presence signal triggering said sensors as it passes therethrough, receiving means aboard vehicles adapted to receive said signals transmitted by said sensors, said means comprising means for discriminiating between said received signals derived from said synchronising pulses and said received signals derived from said presence signals, a safety pulse generator means for generating said danger signal when said presence signal from a vehicle in front of that concerned is within a predetermined distance from said concerned vehicle and means for displaying said danger signal.

3. A system as claimed in claim 2, wherein said receiving means aboard said vehicle comprises means for sensing the speed of said vehicle, means for sensing external conditions relating to said lane, both said means feeding to said safety pulse generator delivering said danger signal as a function of the speed of said vehicle and said external conditions.

4. A system as claimed in claim 1 wherein said receiving means aboard said vehicle includes a watch device having an indicator which is fed directly by said synchronising pulses. I

5. A system as claimed in claim 4 wherein said watch device includes further a warning indicator which is fed via a complemented AND circuit by said synchronising pulses and by pulses proportional to the speed of said vvehicle which are supplied by said speed sensing means, said warning indicator indicating that said vehicle is travelling at a speed considered to be too low,

being possibly zero.

6. A system as claimed in claim 1 wherein said receiving means comprises at least one circuit for discriminating between said synchronising pulses and said presence pulses on the basis of one of their differing characteristics, length and frequency as the case may be.

7. A system as claimed in claim 2 comprising a plurality of sensors, said saisors having each a transmitter, a

receiver, and atransit channel for transmitting said presence signal from another sensor situated behind and regenerating it as it passes therethrough, sais signal triggering said transmitter of said sensor and means for determining the delay between said signal and the synchronising pulse applied to the said sensor for deriving the distance separating said vehicle from said sensor.

8. A system as claimed in claim 5 wherein a vehicle situated in the zone of sensitivity of a sensor receives the signals indicating the presence of another vehicle which has been detected by another sensor and transmits and re-emits them.

9. A system as claimed in claim 2 wherein said discriminating means comprises a circuit for separating said synchronising pulses and a circuit connected to said latter for separating said presence signals said circuits including a double differentiation circuit receiving a signal from a sensor, a first monostable which is triggered by the positive-going peaks delivered by said double differentiation circuit, a first input of a AND circuit connected to say first monostable, a second input of said AND circuit receiving the negative-going peaks from said double differentiation circuit, a second double differentiation circuit which is connected to the output of said first monostable circuit, a diode and a second monostable so connected that said second monostable circuit is triggered by the negative-going peaks from said second double differentiation circuit and second AND circuit which is connected to the output of the said second monostable circuit and receives at its other input said negative-going peaks from said first double differentiating circuit said first AND circuit supplying a pulse corresponding to a synchronising pulse and said second AND circuit supplying a pulse corresponding to a presence pulse.

10. A system as claimed in claim 3 wherein said safety pulse generator comprises, a first monostable circuit which is triggered by said synchronising pulses a first integrator circuit (3900) having means for selecting said external data and supplying a sawtooth signal the slope of which is proportional to said external data, a second integrator circuit fed with said speed pulses (313) and supplying a DC voltage proportional to said speed of said vehicle, an intersection circuit connected to said previous circuits and which supplies short, negative-going pulses, a second monostable circuit which is triggered by said synchronising pulses and is blocked by said negative-going pulses and which delivers at its output rectangular pulse signals the length of which is proportional both to said speed of said vehicle and to said selected external conditions.

11. A system as claimed in claim 10 wherein said first integrator circuit (3900) comprises a plurality of capacitors (702, 703, 704) in parallel, the terminals of which are capable of being selected by a moving contact 705 in accordance with said external conditions which need to be taken into consideration.

12. A system as claimed in claim 10 wherein said safety pulse generator includes further a device for resetting to zero at each synchronising pulse.

13. A system as claimed in claim 4 wherein the time of operation of said monostable circuits is less than the repetition period of said synchronising pulses.

12 negative going pulses a third monostable circuit triggered by said train of negative pulses and having an output feeding a warning indicator.

15. A system as claimed in claim 14 comprising further a fourth monostable circuit which is triggered by said synchronising pulses and supplies a pilot light directly.

16. A danger indicating system for vehicles substantially as described with reference to the appended figures.

Claims

1. A system for indicating danger to a vehicle, travelling along a traffic lane, particulary when the distance between said concerned vehicle and another in front thereof is substantially lessening, comprising fixed means associated with said traffic lane for detecting the presence of vehicles on said lane, said fixed means having means for transmitting said presence information, means aboard vehicles for receiving said presence information and deriving therefrom whether said presence information comes from a vehicle in front of said concerned vehicle and means for generating a safety signal when said presence information as a pulse is within a signal of predetermined length corresponding to a predetermined safety distance from said concerned vehicle.

4. A system as claimed in claim 1 wherein said receiving means aboard said vehicle includes a watch device having an indicator which is fed directly by said synchronising pulses.

5. A system as claimed in claim 4 wherein said watch device includes further a warning indicator which is fed via a complemented AND circuit by said synchronising pulses and by pulses proportional to the speed of said vehicle which are supplied by said speed sensing means, said warning indicator indicating that said vehicle is travelling at a speed considered to be too low, being possibly zero.

7. A system as claimed in claim 2 comprising a plurality of sensors, said saisors having each a transmitter, a receiver, and a transit channel for transmitting said presence signal from another sensor situated behind and regenerating it as it passes therethrough, sais signal triggering said transmitter of said sensor and means for determining the delay between said signal and the synchronising pulse applied to the said sensor for deriving the distance separating said vehicle from said sensor.

10. A system as claimed in claim 3 wherein said safety pulse generator comprises, a first monostable circuit (70) which is triggered by said synchronising pulses a first integrator circuit (3900) having means for selecting said external data and supplying a sawtooth signal the slope of which is proportional to said external data, a second integrator circuit fed with said speed pulses (313) and supplying a DC voltage proportional to said speed of said vehicle, an intersection circuit connected to said previous circuits and which supplies short, negative-going pulses, a second monostable circuit which is triggered by said synchronising pulses and is blocked by said negative-going pulses and which delivers at its output rectangular pulse signals the length of which is proportional both to said speed of said vehicle and to said selected external conditions.

14. A system as claimed in claim 5 wherein said watch device comprises, a first monostable circuit which is triggered by said speed pulses, a gate circuit which is connected to said monostable circuit and which, when open, allows through said synchronising pulses a second monostable circuit (92) which is triggered by said synchronising pulses, an integrator circuit which supplies a sawtooth signal an intersection circuit which has an adjustable threshold to set a minimum speed for said vehicle, the intersection between said threshold and said sawtooth signal producing a train of negative going pulses a third monostable circuit triggered by said train of negative pulses and having an output feeding a warning indicator.