FR2714613A1 - Automatic fire detection and extinction system for automobiles - Google Patents

Abstract

Each of e.g. 3 flame detectors (22) has an infra-red sensor in a heat-resistant case, mounted near an infra-red monitoring source, e.g. on the bulkhead, directed at fuel-related components. Thermal sensors (e.g. 3) (24) are mounted above the engine. Two extinguishers with pyrotechnic releases and pressure-type monitoring (28) are operated (30) from the controller (18). 5 discrete flashes, identified within 2.5 sec set up a "pre-alarm" state. A 3 sec verification stage follows. If the flash-rate persists during this period, and at least two detectors respond, one extinguisher is activated. Detection is then suspended for 8 sec, then resumed, ab initio. The second extinguisher deals with any subsequent fire. System conditions and alarms are displayed, with a manual override, at a driver's control panel (20).

Description

 The present invention relates to a fire detection and extinguishing device for land vehicles, making it possible in particular to intervene in the engine compartments of automobiles.

There are numerous examples of fire detection systems for motor vehicles in the prior art. When a fire is detected, these systems act either simply by emitting an alarm signal, or by automatically triggering fire extinguishers.
t> for fire detection, sensors are generally used which respond to the heat given off by combustion in the monitored area.

 For example, patent application FR-A-2 654 941 describes a fire detector for vehicles comprising fusible fiber optic loops passing through the areas to be monitored. The ends of each loop are respectively connected to a light source and to an optical sensor which receives the signal from the source in normal state. When the heat of a fire melts any part of the loop, the light signal received by the sensor is modified or interrupted, thus signaling the detection of a fire.

 This type of detector, based on the degradation of a link between a transmitter and a sensor by the heat of a fire, also exists in analogous form with transmission of the signal on the loop by electric wires.

In this case, a coaxial cable supplied with voltage between the core and a metal sheath is generally used, and the appearance of a short circuit is detected due to the melting of the insulator separating the latter.

 These detectors have the disadvantage of having a relatively long response time, since they only act after the heat of the fire has caused sufficient damage to degrade the connection. This response time is all the longer when the loop is far from the start of the focus. Furthermore, such detectors do not make it possible to discern whether the degradation of the connection is actually due to heat or simply to a rupture or other mechanical cause.

 With regard to extinguishing a fire in a vehicle, various means are known.

 For example, there are spreading systems using a set of nozzles distributed on ramps under the vehicle and connected to a central tank, as described in patent applications FR-A-2,536,712 and FR-Ai 583,829. A disadvantage of such a system is that the extinguishing liquid is spread simultaneously in all the places served by the distribution, which does not make it possible to attack the fire in a targeted manner. Furthermore, the ramps must, for practical reasons, be supplied with low pressure, which limits the efficiency, and in particular the speed of the intervention.

 Other extinguishing systems overcome these drawbacks by using autonomous extinguishers filled with gas or liquid under high pressure, as described in patent application FR-A-2 071 033. These extinguishers can be placed anywhere of the vehicle, and are controlled either manually or automatically in the event of an impact or in response to a thermal sensor.

 However, there is still a need for a fire extinguisher system capable of operating in the engine compartment of a motor vehicle, and provided with effective management ensuring that the actuation of the extinguishers takes place as soon as possible. first manifestations of a fire, without however causing the risk of inadvertent ignition.

 Thus, a first object of the present invention is to respond to such a need by means of a detection and extinguishing device making it possible to extinguish a fire automatically even before its heat can damage the engine compartment.

 Another object of the present invention is to allow permanent monitoring of the proper functioning of the entire detection and extinguishing device, and possibly to be able to identify damage both at the detection means and at the extinguishing means.

 These objects are achieved according to the invention thanks to a fire detection and extinguishing device for land vehicles, comprising fire detection and extinguishing means housed in the engine compartment, characterized in that said means of fire detection comprise at least one flame detector sensitive to radiation emitted by a fire, and in that it further comprises control means for activating said extinguishing means in response to predetermined characteristics of the radiation analyzed by means of the flame detector (s).

 Preferably, the detection means comprise at least three flame detectors, and the control means activate said extinguishing means when the predetermined characteristics of the fire radiation are detected by at least two of the flame detectors.

 The predetermined characteristics are advantageously the number n of flickers detected, the maximum interval tl between two successive flickers and, optionally, a minimum duration of appearance of the flickers.

 According to a preferred embodiment of the invention, the control means establish a pre-alarm state of a flame detector as a function of the predetermined number n of flickers succeeding each other within the limit of the maximum interval tl, and a alarm state of this detector when the flickers persist and follow one another, always within the limit of the maximum interval tl, for a predetermined duration t2 after the establishment of the pre-alarm state.

 For example, the number n of flickers is between 3 and 8, preferably 5, the maximum interval tl is from 1 to 5 seconds, preferably 2.5 seconds, and the minimum duration t2 is from 2 to 5 seconds, preferably 3 seconds.

 The flame detectors can be supplemented by one or more thermal detectors housed in the engine compartment and connected to the control means, the latter controlling the switching on of the extinguishers in response to an alarm state of at least one between them.

 According to a particularly advantageous aspect of the invention, means are provided for verifying the proper functioning of the fire detection circuits from the flame detector (s). They include means for emitting light near the flame detector (s) which are electrically controlled so as to simulate a fire by producing radiation having the characteristics of a fire.

 The verification means can also be supplemented by devices for verifying the proper functioning of the or each thermal detector and of the fire extinguishers.

Other characteristics and advantages of the invention will emerge from the description which follows, given by way of example, with reference to the appended drawings in which:
- Figure 1 is a block view of the entire fire protection device according to the invention;
- Figure 2 illustrates the mounting of a flame detector of the device of Figure 1 in the engine compartment of a vehicle; and
- Figures 3a and 3b are flowcharts representing the main steps in the operation of the device of Figure 1.

 The fire detection and extinguishing device shown diagrammatically in FIG. 1 comprises a set of fire detectors 12, a set of fire extinguishers 14, both housed in the engine compartment of a vehicle, and electronic control devices. management 16 housed in the passenger compartment.

The management electronics 16 are broken down into a control unit 18 which
manages fire detectors 12 and fire extinguishers 14, and a
control and display 20 within reach of the driver or a
passenger.

The control and display unit 20, connected to the control unit 18
by a first data link 32, includes the interface elements with
the driver or his passenger, and in particular warning lights and
control 20a as well as the various commands 20b of the operation of the
device.

In the example, the set of detectors comprises three detectors of
flame 22a-22c and three thermal detectors 24a-24c, all connected to the
control 18 by a second data link 26.

Advantageously, the flame detectors 22a-22c are of the type described
in American patent US-A-4 988884 in the name of the applicant.

Figure 2 shows such a detector mounted on its housing. It consists of a housing 50 designed to resist high temperatures and equipped with an optical window 52 behind which is housed an infrared detector sensitive to radiation with a wavelength of 4 to 5 microns, typically radiated by a fire. Each detector is mounted on supports 54 fixed to an element 56 of the engine compartment, for example a
part depending on the partition with the passenger compartment and its window is
oriented towards the most sensitive elements, such as the carburetor or
fuel lines.

The cleanliness of the window 52 is ensured by a nozzle 58 which sends to
this a jet of air from a source of compressed air, for example a
pump provided specifically for this purpose, or bypass from a circuit
engine air.

In the detection field of the detector 22 is mounted a source
light emitting diode 60 emitting in a spectral range
to which the detector is sensitive. This diode is connected to the control unit 18 and makes it possible to verify the correct functioning of the detector, as will be explained below.

 The detector described in the aforementioned patent also contains circuits for analyzing the flickers in the received radiation, making it possible in particular to identify a predetermined number of flickers following one another at a minimum interval. However, the analysis of the detection signals can also be carried out at the level of the control unit 18, in which case any other sensor sensitive to infrared radiation can be envisaged.

 The three thermal detectors 24a-24c are preferably mounted at the top of the engine block so as to be exposed to heat as much as possible. Such detectors are well known in the art, and include for example an element with a high coefficient of thermal expansion mounted in a switch. The switch is designed to close an electrical circuit and thus signal an alarm when the element is subjected to a temperature exceeding a determined threshold. In the example, the three detectors 24a-24c are connected in parallel in the circuit, so that an alarm is signaled if only one of them is activated.

 It will be noted that the thermal detectors 24a-24c constitute a redundancy with respect to the flame detectors 22a-22c and can optionally be eliminated while remaining within the scope of the invention.

 The set of extinguishers 14 comprises two extinguishers 28a, 28b, each forming an extinguishing group controlled independently from the control unit by a third data link 30.

 Each fire extinguisher 28a, 28b is in the form of a cylinder containing an extinguishing agent, such as halon, under high pressure.

The extinguisher is activated by perforating a seal at the outlet, thanks to a pyrothechnic charge controlled by the management unit 26. The gas is evacuated and distributed throughout the volume of the engine compartment in a few milliseconds after the perforation of the seal.

 A pressure switch integrated into the extinguisher and connected to the management unit 26 makes it possible to control the charge of the extinguishing agent at any time.

 The control of the extinguishers 28a, 28b as a function of the signals collected by the set of flame detectors 22a-22c will now be explained with the aid of the flow diagram of FIGS. 3a and 3b.

 In this example, the steps shown there enable the alarm output of a flame detector to be activated in two successive steps. The first step consists in establishing a pre-alarm state when the detector identifies a number n of flickers equal to 5, succeeding each other at an interval tl not exceeding 2.5 seconds. The second step then intervenes to check whether the pre-alarm condition persists during a period t2 of at least 3 seconds, during which the flickering must also follow one another at the abovementioned interval t1.

 Firstly, the system is activated (50) from one of the switches 20a of the control unit 20. The next step (52) consists in designating by default the extinction group m to be activated in the event of detection of fire conditions. In the example, the group initially designated (m = 1) simply corresponds to the extinguisher 28a, the other extinguisher 28b forming the second group (m = 2).

 The following steps in FIG. 2a relate to the management of only one of the flame detectors (for example 22a), these steps being identical and followed independently for each of the three detectors.

 Thus, for the detector 22a, a step (54) is carried out for initializing a register which accounts for the number n of scintillations detected and for the respective time bases for the periods tl and t2.

 Then, the detector is put on permanent standby to detect a flicker in its sensitivity field. A flicker can be identified, for example, by exceeding the intensity of the radiation beyond a threshold level followed by a return below the threshold within a predetermined period. The parameters can be set empirically.

However, one can get rid of such a setting by using the flame detector described in document US-A-4,988,884, which integrates a flicker detection function in its analysis circuit.

 As soon as a flicker is detected (56), the flicker counter is incremented by one (58). In the case of a first flicker (n = l) a switch (60) makes it possible to proceed directly to the start of the time base tl (62), fixing the beginning of the interval of 2.5 seconds during which must appear a successive flicker. Thus, a loopback (64) is carried out towards the flicker detection step (56).

 Upon detection of a second flicker, it is determined whether it occurs within the 2.5 second interval (66) started by the previous flicker. If this is not the case, a loopback (68) is carried out towards the initialization step (54) to ignore the previous detections and restart the process from the beginning.

 If, on the other hand, the second flickering does occur in the interval of 2.5 seconds, the time base tl (70) is reset to zero and it is started again (62) to establish a new interval before looping back ( 64) to a new flicker detection step (56).

 These steps (56-64) are repeated systematically for the following flickers. When five flickers have been detected in this way, the first pre-alarm stage is established. Then, a switching step (72) takes place before the time base tl is reset to zero to start the second step aimed at verifying that the fire detection conditions thus determined persist during the period t2 of at least three seconds .

 Thus, as soon as the fifth flicker is detected, one proceeds, by a switch (74) to the start of the time base t2 fixing the delay of three seconds before the output of the alarm signal. Note that during this three-second period, flickering should continue to be detected under the same conditions as for the first five. Thus, the process of detecting new flickers is continued from the resetting of the counter tl (62) and passing through the step (66) of verification of non-exceeding of the interval 2.5 seconds.

 For all the other flickers occurring beyond the fifth, it is checked (78) if the three seconds have elapsed (although this may not be possible with the sixth flicker). If this is not the case, the process continues from resetting the counter tl (62) to zero.

 If the three seconds have passed, the fire detection conditions will have been checked by the flame detector 22a. In this case, the detector (80) is put into an alarm state.

 It will be noted in the foregoing that the delay of three seconds after the detection of the fifth flicker requires in total the detection of seven or more flickers for the setting in alarm state. As a variant, it is possible to start the time delay t2 of three seconds as soon as the first flicker is detected, that is to say by transposing the step 76 at the start of t2 just after the positive verification of n = 1 to l step 60. In this case, the first and second steps are concomitant, so that the alarm condition of the detector is established if five or more flickers occur in succession at an interval not exceeding 2.5 seconds and this for three seconds.

 Reference will now be made to the flow diagram of FIG. 2b, which shows diagrammatically the steps for activating the extinguishers from the alarm states of each of the three flame detectors 22a-22c. These states are constantly monitored (82) to detect if at least two of the three flame detectors 22a-c signal an alarm state (84). If this is the case, the extinguisher corresponding to the previously defined group (86) is activated.

 Once the fire extinguisher is activated, there is an eight-second pause during which any new flicker is ignored. This pause allows the extinguisher time to act on the fire before taking any other decision on the actions to follow.

 After the pause, the next group's extinguisher is designated and the detection process is resumed from the initialization step (54).

 It will be noted that the active group extinguisher can also be activated on direct command by any of the thermal detectors 24a-c.

 Furthermore, the display and control unit 20 is equipped with a switch making it possible to manually activate either the extinguisher of the active group, or all the extinguishers simultaneously.

 The detection and extinguishing device also includes, as a set of verification of the correct functioning of the detectors 12, of the fire extinguishers 14 and of the management unit 16. These verifications are triggered automatically at regular intervals, for example every 5 to 10 seconds, as well as on request from the display and control unit 20a.

The operating state of each flame detector 22a-22c is checked by means of the corresponding light-emitting diode 60. By activating the diode so as to simulate a flicker, one checks not only the response of the corresponding detector, but also the connection with the management unit 16. The test can comprise either a single cycle of stop operation of the diode, or repeated cycles to simulate a sequence leading to an alarm signal, which also makes it possible to verify the operation of signal management at the level of the control unit
18.

 With regard to the thermal detectors 4a-24c, one can be satisfied with checking the electrical continuity of the loop on which they are mounted in parallel. To do this, the circuit includes a relay controlled by the management unit 26 allowing the shuntagc of the detector terminals at the end of the loop.

 The state of each extinguisher 28a, 28b is checked, on the one hand from the signal collected from the pressure switch, which makes it possible to control the filling state of the extinguisher and, on the other hand by testing the continuity of the circuit. initiating the pyrotechnic charge allowing rupture of the cover.

 Any damage detected by the tests is indicated on the display 20a of the housing 20 by indicator lights, making it possible to identify the element or elements in question.

 If it is found that one of the extinguishers 28a, 28b has failed, it is automatically assigned to the last group to be used. In the example limited to two extinguishers, the extinguishers are simply inverted if that of the group m = 1 (cf. FIG. 2a, step 52) is defective.

 However, an attempt is nevertheless made to activate a fire extinguisher deemed defective, either if this is the case for all, or when all the others are already discharged and a new fire is detected. In the first case, the distribution of groups can follow a hierarchy by giving priority first to an extinguisher having a low pressure noted by the pressure switch, and then to an extinguisher having a failure in the pyrotechnic charge.

 Indeed, it has been noted that a fire extinguisher with a weakened pressure can nevertheless prove to be effective, while a defective fire extinguisher at the level of the pyrotechnic circuit has only a small chance of functioning.

Claims (16)

Claims  1. Fire detection and extinguishing device for land vehicles, comprising fire detection and extinguishing means (13, 14) housed in the engine compartment,  characterized in that said fire detection means comprise at least one flame detector (22a-22c) sensitive to radiation emitted by a fire,  and in that it further comprises control means (18) for activating said extinguishing means in response to predetermined characteristics of the radiation analyzed by means of the flame detector (s).  2. Device according to claim 1, characterized in that said detection means comprise at least three flame detectors, and in that said control means (18) activate said extinguishing means (14) when said predetermined characteristics of the radiation are detected by at least two of the flame detectors (22a-22c).  3. Device according to claim 1 or 2, characterized in that said predetermined characteristics include the number of flickers detected and the maximum interval (ti) between two successive flickers.  4. Device according to claim 3, characterized in that said predetermined characteristics further comprise a minimum duration of appearance of flickers.  5. Device according to claim 4, characterized in that the control means (18) comprise means for establishing a pre-alarm state of a flame detector (22a-22c) as a function of a number (n) predetermined flickering in succession within the limit of said maximum interval (tl), and an alarm state of this detector when said flickering persist and succeed, always within the limit of said maximum interval (tl), for a minimum duration (t2) after establishing the pre-alarm state.  6. Device according to claim 5, characterized in that said number of flickers is between 3 and 8, said maximum interval (tl) is from 1 to 5 seconds, and said minimum duration (t2) is from 2 to 5 seconds.  7. Device according to claim 6, characterized in that said number of flickers is equal to 5, said maximum interval (tl) is 2.5 seconds, and said minimum duration (t2) is 3 seconds.  8. Device according to any one of claims 1 to 7, characterized in that said detection means (12) further comprise at least one thermal detector (24a-24c) housed in the engine compartment and connected to said control means ( 18), the latter controlling the switching on of the extinguishing means in response (14) to an alarm state of at least one thermal detector.  9 Device according to any one of claims 1 to 7, characterized in that said control means (18) further comprises means for verifying the proper functioning of the fire detection circuits from the detector (s) flame (22a-22c), said verification means comprising light emitting means (60) near the flame detector (s) and electrically controlled so as to simulate a fire by producing a radiation having the characteristics of a fire.  10. Device according to claim 9, characterized in that said control means further comprise:  means for verifying the proper functioning of said thermal detector (24a-24c), comprising means for controlling the electrical continuity of the circuit connecting the latter to the control means, and  means of verifying the extinguishing means, comprising sensors sensitive to the degree of filling of the latter.  11. Device according to claim 9 or 10, characterized in that said verification means can be activated either automatically at predetermined intervals, or under manual control and produce an alert signal in the event of a fault.  12. Device according to any one of claims 1 to 11, characterized in that said extinguishing means (14) can be activated by manual control.  13. Device according to any one of claims 1 to 12, characterized in that said extinguishing means (14) are divided into several independent groups (28a, 28b) comprising at least one extinguisher, which groups are activated one by one. times according to a determined sequence each time a fire is detected.  14. Device according to claim 13, characterized in that said control means (18) comprise a timing circuit started after each activation of a group (28a, 28b) to inhibit activation of the next group in the sequence for a predetermined period.  15. Device according to claim 13 or 14, characterized in that any group (28a, 28b) determined by the test means as not being in good working order is placed last in the sequence.  16. Device according to any one of claims 1 to 15, characterized in that it further comprises means (58) for cleaning the optical window (52) of the flame detector (s) (22a-22c ) operating by applying an air jet against it.