GB2025101A - Detection of failure of consumers of electrical current - Google Patents

Abstract

To detect the failure of e.g. a lamp (2) supplied from a D.C. source (4) through a switch (3) controlled by a manually-operated member (5), a resistance (1) of much greater value than that of the lamp (2) is connected across the switch (3), and the voltage V1 across the resistance (1) is used for the required detection. If the lamp (2) goes open circuit, then when the switch (3) is non-conductive the voltage V1 is low instead of high, while if the lamp (2) is short circuited then when the switch (3) is conductive, due to the finite resistance of the switch (3), the voltage V1 is high instead of low. To ensure failure detection regardless of the condition of the control member (5), the switch (3) is caused cyclically to incurse momentarily into the opposite state from that dictated by the control member, so that either type of failure can always be detected; appropriate clock pulses are supplied from a generator (6). The equipment is particularly suited to detecting the failure of lights on a motor vehicle. <IMAGE>

Description

SPECIFICATION Detection of failure of consumers of electrical current The invention relates to the detection of certain failures of electrical "consumers", that is to say, of devices or equipment which consumes electric current. These failures may comprise the breaking of the electrical circuits of the consumers, and possibly in addition the short-circuiting of these circuits.

One of the preferred applications of the invention is in the detection of failures of certain electrical accessories mounted on vehicles, e.g. windscreen-wiper motors, and in particular in the detection of the breaking of the filaments of headlights and parking lights (sidelights) on motor vehicles, even during periods when these accessories are not being used.

At present, to give an example, illumination of a vehicle's lights can be indicated to the driver of the vehicle by illumination at the dashboard, but no information is given to the driver on the actual state of the illumination of all the lights, which generally comprise two white or yellow lights at the front of the vehicle and two red lights at the rear. The driver consequently remains ignorant of the possible breaking of the filament of one of the four corresponding bulbs and is thus caused to drive in all good faith with his vehicle in a dangerous state. This observation is equally applicable to braking lights, headlights, etc.

In addition, even if these various current consuming accessories are provided with indicators displaying their working state only during their periods of operation, the advantage of such a display is often reduced because of their delayed nature: in fact, not uncommonly, at the very moment when the operation of a failed consumer is triggered, the driver has insufficient time at his disposal to proceed with the necessary repair, whereas it would have been convenient for him to do it earlier, for example just after the onset of failure, if he could have been informed of it as a matter of routine outside the periods of use of the consumer.

In addition to breakage of filaments or other electrical circuits, causes of failure of the consumers of the type in question also indicated are unintentional short-circuiting of these consumers, for example as a result of water splashing up, a local deformation of sheet metal, or for any other reason.

The present invention is defined in the appended claims, to which reference should now be made.

In the following several preferred embodiments of the invention will be described in a non-limiting way, and with reference to the drawings, in which: Figure 1 is an electrical circuit diagram of a simplified version of a failure detector embodying the invention.

Figure 2 is the electrical diagram of an improved version of such a detector.

Figure 3 is a diagram showing the form of voltages taken off at various points of the detector represented diagrammatically in Fig.

2 according to different operational assumptions.

Figure 4 is the diagram of another version of the detector still further improved from the preceding one.

Figure 5 is a diagram of the same type as that in Fig. 3 corresponding to the version in Fig. 4.

In each case, the electrical receptor or load-for example, a vehicle-lighting bulbfilament-is designated by the reference 2, the electrical direct-current supply source for this receptor, by the reference 4, and its control switch by the reference 3.

The resistance R, of the voltmeter 1 is considerably larger than that, R2, of the receptor: more precisely, the first is generally greater than 100,000 ohms and can reach or even exceed 1 megohm, while the second is of the order of a few ohms or of only a few tens of ohms.

The switch 3 is here directly connected to a manual control member 5 for the operation of the consumer 2. When the switch 3 is open, that is to say, the consumer 2 is not supplied with electric current, the voltage V, displayed on the voltmeter 1 is substantially equal to the voltage V of the source 4 so long as the electrical circuit of the consumer 2 is complete. But when the latter is broken, the said voltage V, is reduced to zero.

One thus has at one's disposal a particularly simple means for detecting the failure of the consumer 2 in the absence of the operation of the latter.

The fall in voltage observed on the voltmeter 1 on cutting out of the consumer 2 can be used in any way desired to cause an alarm and in particular to light up a visual indicator mounted on the dashboard of the vehicle.

If the switch 3 is closed, that is to say, if the consumer has been switched on, determining the actual state of the operation of the latter is less simple, but short incursions into the open-circuit state of the switch 3 allow the same information as before to be obtained, depending on whether the consumer is in the cut-out state or not.

Hereinafter will be described, with reference to Figs. 2 and 3, an advantageous but nonlimiting embodiment of such a detection system with incursions into the open state of the switch when the latter is closed, before we return to the possibilities of use of the simplified circuit in Fig. 1 with regard to the detection of short-circuiting of the consumer 2.

In this embodiment in Figs. 2 and 3, the elements 1 to 4 mentioned above are again found, but a switch 3, such as a transistor, has been chosen, which has a sufficiently rapid response to allow short incursions into the state (open or closed) of this switch op posed to its controlled state without disturbing the operation (supply or absence of supply to the consumer) corresponding to this controlled state.

More precisely, when the switch 3 is closed, the incursions into its open state are effected for very short durations , namely of the order of only a few milliseconds, the interval T between two successive incursions being relatively long, namely of the order of several seconds.

The rectangle 6 in Fig. 2 symbolizes a clock connected to a counter with decoding circuitry which develops at point A the train of pulses represented at the line A in Fig. 3; there being pulses of duration 7 corresponding to the logic state 0 separated by intervals T corresponding to the logic state 1.

The manual control member 5, which here is a switch also supplied by the source 4, produces at a point B, depending on whether its state is open (absence of control) or closed (presence of control), a voltage corresponding respectively to the logic signal 0 or to the logic signal 1.

This voltage is transmitted from the switch 5 to the point B under the control of a blocking bistable 21 which is itself connected to the clock unit 6 and arranged so as to prevent the said transmission for a duration greater than x, for example equal to 2T, when the said switch 5 is operated exactly during the emission of one of the above-mentioned pulses: this arrangement avoids such an opertion, which is very rare since the chances of its occurring are in practice less than 1 per 1000, being transmitted to cause erroneous operation of the detector.

Points A and B are connected to the two inputs of an AND gate 22.

The output C of this gate 22 is applied, through a resistance 7, to the base of the transistor 3, here of the n-p-n- type, the collector and emitter of which are connected to the terminals of a resistance 1 of relatively high value replacing the voltmeter in Fig. 1.

This resistance 1 could possibly be omitted since the grid-leak resistance of the transistor 3 can itself fill the role of the said resistance 1 in certain instances.

The junction D between the resistance 1 and the consumer 2, to which is connected the collector of the transistor 3, is itself connected via an inverter 8 to one of the inputs E of an exclusive-OR gate 9 the other input of wich is connected to point C. A D-type bistable 10 receives respectively at its two inputs the output F of the gate 9 and the clock signal A. It is the output Q of this bistable 10 which supplies an alarm circuit 11, this circuit notably including a visual indicator 1 2.

The operation of this apparatus is as follows.

At the output C of the gate 22 there is a signal which is zero in the absence of control and is identical to signal A in the- presence of control (see Fig. 3). The signal at point D, which corresponds in practice to the voltage V1 mentioned in connection with Fig. 1, takes into account not only this absence or presence of control, but also the intact or open-circuit state of the consumer 2.

It is assumed that the consumer is opencircuit during the periods which have been represented diagrammatically by a heavy portion of the line K of the diagram of Fig. 3, that is to say, respectively from the instant t, to the instant t2 and from the instant t4 to the instant tS, and only during these periods. It is also assumed that the instant t3 from which a control intervenes, that is to say, from which the switch is closed, is between the instants t2 and 14.

The signal developed at E, which is the inverse of the signal collected at D, is then: identical to the signal C in the absence of cutting-out of the consumer 2, that is to say, before t1, from t2 to t4 and after t5, -and permanently of logic state 1 during cutting-out, that is to say, during the periods t1 to t2 and 14 to t.

The gate 9 continuously compares the logic states at C and at E and the result of this comparison is taken at the output F of this gate: it can be seen that at F the logic state 0 appears permanently in the absence of cutting-out of the consumer and that the logic state 1 appears there permanently at the time of the first cutting-out, that is to say, from t, to t2 (absence of control) and only during the clock pulses at the time of the second cuttingout, namely from t4 to t5 (presence of control).

Finally the bistable 10 memorizes the result obtained at F in step with a clock so as to display at its output Q the detected fault (cutting-back) while it exists: in the present instance the rising edges defining the end of the clock pulses A trigger or maintain the display in question as long as the signal F presents a logic state 1 and this display is conversely omitted or held non-existant at the instants, corresponding to such rising edges, for which the signal F presents a logic state 0.

It will be noted that the triggering and holding of the display at the end of the clock pulses emitted between the instants t4 and t5 are made possible by the fact that the corresponding pulses taken at the point F have a very slight delay in relation to those from the generator train A.

As a consequence of this, it is noted that in the absence as well as in the presence of a control signal, that is to say, whether the switch 5 is in an open or closed state, cuttingout of the consumer 2 is represented by the lighting up of the indicator 1 2 at the end of a time at the most equal to T + T, a time equal to a few seconds.

Returning now to the circuit diagram in Fig.

1, the possibility of an unintentional shortcircuit of the consumer 2 will now be examined. Such a short-circuit has been represented diagrammatically by the dashed line 13 in this Fig. 1.

The resistance R1 of the voltmeter 1 is always assumed to be greater than the resistance R2 of the consumer and, in addition, this time the said resistance R2 is assumed to be decidely greater than the resistance R3 of the closed switch 3, and the latter resistance R3 decidedly greater than the resistance of the short-circuit 1 3.

If, in these conditions, the closed state of the switch 3, that is to say, the supplyposition for the consumer 2 is considered, it is observed that the voltage V1 displayed on the voltmeter is practically zero when the consumer is intact and conversely practically equal to the voltage of the source 4 when this consumer is short-circuited.

Here again, one can envisage a direct use of this observation for the purposes of detection of the short-circuit concerned when the switch is closed.

But it is particularly advantageous, as in the detection of cutting-out which has been described above with reference to Figs. 2 and 3, to provide means for also ensuring the detection of short-circuits when the switch is open, by proceeding with short incursions into its closed state.

With reference to Figs. 4 and 5, such an embodiment will be described which lends itself both to the detection of cut-outs of the consumer in a similar way to that previously described, and to the detection of short-circuits of the said consumer, whether the control member of the switch is placed in the open or closed state.

In this embodiment the references designating members identical to those previously described have been retained.

In the exceptional case (since the chances of its occurring unexpectedly are generally less than 1 in 1000) of the control exerted on the member 5 occurring exactly during the emission of a clock pulse by the unit 6, there could be a risk of incorrect detection: to avoid such a risk, a blocking bistable 14, itself connected to the said unit 6, is provided, as before, at the input of the apparatus.

The control signal B' developed by the actuation of the member 5 and, if need be, so blocked, is applied to one of the two inputs of an exclusive-OR gate 16, at whose other input is applied a train of pulses A' inverted relative to the train A above (see Fig. 5).

The output C' of this gate 1 6 is applied, as the signal C was before, but here via two inverters 1 5 and 1 8 connected in series, to the resistance 7 and to one input of the exclusive-OR gate 9. This output C' is also applied here to the second input of the D-type bistable 1 0 which, as before, receives at its other input the output F' of the gate 9 and is affected at the detection of cut-outs, the output Q' of this bistable supplying the alarm system 11.

A second D-type bistable 1 7 is also provided here, effective for the detection of shortcircuits and receiving respectively at its two inputs on the one hand the output F' of the gate 9 and on the other hand the inverse of the output C', taken from between the inverters 15 and 18.

The output Q" of this second bistable 1 7 itself supplies an alarm system 1 9 including a visual indicator 20.

The operation of the improved apparatus thus described is similar to that of the simpler apparatus represented diagrammatically in Fig. 2.

Shown again on the line K of Fig. 5 are the periods which correspond to the faults to be detected, these periods being also defined by the instants t, and t2 on the one hand and t4 and t5 on the other hand, the instant t3 corresponding to the onset of an operational control of the consumer 2 being situated as before between the instants t2 and 14.

The four lines of the diagram in Fig. 5 designated by the bracket I relate to the detection of a cut-out or open circuit condition and the four lines of the said diagram designated by the bracket II correspond to the detection of a short-circuit, the periods in which these faults appear being the same in both cases, namely those defined above.

The principal difference between assumption I and the situation analysed in connected with Figs. 2 and 3 resides in the fact that, at the output F' of the gate 9, in the absence of control and in the presence of a cut-out, the logic state 1 gives way to the logic state 0 during the clock pulses instead of being permanently maintained.

In assumption II, practically opposite results from those observed in connection with assumption I are observed, in the sense that at the output F' of the gate 9, in the presence of a short-circuit, the logic state 1 only appears during clock pulses in the absence of control, and conversely appears permanently, except at the time of the said pulses, in the presence of a control.

Thanks to the inversion which has been provided between the two series of clock pulses applied respectively at the two second inputs of the two bistables 10 and 17, only the output 0' of the first bistable 10 is affected by the cut-outs of the consumer 2 and leads to lighting up of the corresponding indicator 1 2 while only the output 0" of the second bistable 1 7 is affected by short-circuits of the said consumer, which are represented by the lighting up only of the indicator 20.

As many visual indicators 1 2 and 20 (or equivalent alarm systems) can be provided as there are consumers 2 to be monitored.

For simplicity, there will generally be a preference for grouping together all fault detections of one and the same type by allocating one single common indicator or system for these detections: thus, all the outputs Q' of the bistables 10 (Fig. 4) connected to various consumers 2 can be connected together so as to supply one single common indicator 12, while all the ouputs Q" of the bistables 1 7 are similarly connected so as to turn on one single common indicator 20.

In this case, lighting up of the indicator 1 2 indicates to the driver the open-circuiting of one of the consumers being monitored and this information is quite sufficient in most cases since it is then very easy to establish the identity of the failed consumer; the same is true for lighting up of the indicator 20.

To simplify the apparatus further, one single common alarm system can be supplied by and for all the various outputs Q' and Q" of various bistables, which, in the embodiments mentioned above, will cause the indicators 1 2 and 20 to be replaced by one single indicator: here again, the main point of the task of the apparatus will be achieved when the driver is alerted to the existence of a failure, identification of the damaged consumer and that of the failure affecting this consumer then posing no particular problems.

Consequently, no matter which embodiment is adopted, an apparatus is finally obtained whose form, operation and advantages (particularly the possibility of alerting the user of the vehicle to the existence of a failure affecting at least one of the electrical members of this vehicle, even outside the periods of operation of these members) follow sufficiently from the above.

As is evident and as already results, moreover from the above, the invention is not at all limited to those of its modes of application and embodiment which have been more especially envisaged; it embraces, on the contrary, all the variants thereof.

In particular, with reference to Figs. 2 and 4, two embodiments have been described above, allowing: -on the one hand, the timed control of the conduction and blocking of the transistor 3, -and also the use of the voltage V, developed at point D, as the voltage which repre- sents the fault to be detected.

But, without going beyond the scope of the invention, one could adopt means other than those described to ensure this persisting control and this use, such means involving wired or programmed logic in particular.

It should also be noted that the invention lends itself especially well to the simultaneous monitoring of a great number of consumers 2 using multiplexing techniques: in particular, if a vehicle is already equipped with such a system, it is particularly simple and convenient to adapt the improvements according to the invention to suit it, this adaptation being simply achieved by the local addition of a few particularly reliable electronic circuits which are compact and able to be mass produced.

Claims (11)

1. Apparatus for detecting certain failures of a consumer of electrical current when the consumer is being connected in series with a direct-current supply source and with a switch connected to a (preferably manual) control member, the apparatus comprising a resistance of value R1 far greater than the resistance R2 of the consumer and connected in parallel across the switch, and means for utilizing for the purposes of the required detection the voltage V, across this resistance R1.

2. Detection apparatus according to claim 1, including means for causing an alarm signal for the open state of the switch in response to the absence of the voltage V1, this absence indicating the breaking of the electrical circuit of the consumer.

3. Detection apparatus according to claim 2, including means for ensuring, for the closed position of the switch control member, momentary incursions, preferably repeated cyclically, into the open state of the switch, and means for causing an alarm signal if the absence of the voltage V, is observed during the said incursions.

4. Detection apparatus according to any preceding claim, in which the switch is chosen so that its internal resistance R3 is relatively high while being distinctly less than the resistance R2 of the consumer, and including means for causing an alarm signal for the closed state of this switch in response to the changing of the voltage V, from a practically zero value to a value substantially equal to that of the source, this change indicating the short-circuiting of the consumer.

5. Detection apparatus according to claim 4, including means for ensuring, for the open position of the switch control member, momentary incursions, preferably repeated cyclically, into the closed state of the switch, and means for causing an alarm signal if a substantial increase in the voltage V, is observed during the said incursions.

6. Detection apparatus according to either of claims 3 and 5, in which the switch is of an electronic type and is connected to a clock emitting a train of pulses, especially with a duration of a few milliseconds spaced in relation to one another by intervals of a few seconds, in such a way that it normally occupies its position (open or closed) corresponding to that required by the control member except during the said pulses.

7. Detection apparatus according to claim 6, including means for causing an alarm signal, preferably for lighting up a visual indicator, as a function of the value of the voltage V1, these means comprising a first gate whose two inputs are respectively supplied with the above-mentioned pulse train and with a signal produced by the control member and whose output is applied to a transistor constituting 'the electronic switch, and in addition an ex olusive-OR gate receiving respectively at its two inputs the inverse of the voltage V, and the output of the first gate, and furthermore a bistable respectively receiving at two of its inputs the output of this exclusive-OR gate and either the output of the first gate in the case of the detection of a cut-out, or the inverse of the latter output in the case of the detection of a short-circuit, the alarm signal being produced at an output of the said bistable.

8. Detection apparatus according to any preceding claim, in which a single common alarm system (preferably a visual indicator) is allocated to the detection of each type of fault produced in the group of consumers to be monitored.

9. Detection apparatus according to any of claims 1 to 7, in which a single common alarm system (preferably a visual indicator) is used for the detection of all the faults detectable in the various consumers to be monitored.

10. Detection apparatus according to any preceding claim, in which the consumer is a bulb filament for a headlight, parking light or braking light of a motor vehicle, the detection of a failure of this consumer preferably result ing in the lighting up of a visual indicator on the dashboard of this vehicle.

11. Apparatus for detecting failures of a consumer of electrical current, substantially as herein described with reference to the drawings.

1 2. A motor vehicle provided with detection apparatus in accordance with any preceding claim.