WO2007122546A2

WO2007122546A2 - Method and device for monitoring the condition of halogen bulbs in vehicle headlights

Info

Publication number: WO2007122546A2
Application number: PCT/IB2007/051359
Authority: WO
Inventors: Mathieu H. J. Van Rijswick; Ton R. Mulderij; Jos Van Meurs
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2006-04-21
Filing date: 2007-04-17
Publication date: 2007-11-01
Also published as: WO2007122546A3

Abstract

A method and device for monitoring the condition of halogen bulbs in vehicle headlights and signaling the approaching end of life of the bulb are described. The method comprises the step of detecting a short-circuiting event of a turn in the lamp filament, or the step of detecting a short-circuited turn in the lamp filament. A short-circuiting event is detected by detecting a stepwise increase in lamp current of the order of more than 3%, preferably more than 5%. A short-circuited turn in the lamp filament is detected by providing an image of the glowing filament and visually inspecting the image for dark spots.

Description

Method and device for monitoring the condition of halogen bulbs in vehicle headlights

FIELD OF THE INVENTION

The present invention relates in general to the inspection of vehicle headlights, particularly the light bulbs in vehicle headlights, more particularly halogen light bulbs.

BACKGROUND OF THE INVENTION

A general problem with light bulbs is that their operational life is limited. Although the operational life is long, typically of the order of several hundreds of hours, the end of life of a light bulb occurs suddenly and unexpectedly. This leads to a potentially dangerous situation in the case of a light bulb in a vehicle headlight. An additional problem is that exchanging light bulbs in a motor vehicle is sometimes difficult, especially in dark situations such as during the evening or night. To prevent these difficulties and dangers, there is a general desire to be able to predict the approaching end of life of a light bulb.

In general, depending on the type of lamp, the life of a light bulb may be in the range of 500 hours, but the actual operational life of a light bulb depends on circumstances such as, for example, lamp voltage, the number of times the lamp is switched on and off, etc. Thus it is not very well possible to predict the approaching end of life on the basis of the amount of time the lamp has been operating, or on the basis of the amount of kilometers the vehicle has traveled, etc. This means that in practice a light bulb is exchanged only when the driver finds that the lamp has failed, or, in order to prevent failure of a lamp, when the vehicle is serviced in a workshop. For instance, workshops may use a rule that lamps are exchanged every 25 000 kilometers. However, the owner of the car may feel that the lamps have been exchanged without reason.

It is possible in principle to examine a light bulb by taking the light bulb from the vehicle and inspect it visually through a magnifier, but this involves the steps of removing the lamp and inserting it again into the vehicle, so this kind of inspection is relatively expensive and it is more economical to exchange the lamp anyway.

In view of the above problems, the present invention aims to provide means for inspecting vehicle light bulbs in situ. More particularly, the present invention aims to provide a lamp-monitoring circuit capable of issuing a warning signal to the driver of a vehicle indicating that one or more of the headlight lamps should be replaced. Also, the present invention aims to provide a method and device enabling a service mechanic to inspect the condition of a light bulb in a headlight relatively quickly and simply, without incurring high costs.

The present invention is based on an improved insight into and understanding of the phenomena that play a role at the end of life of a light bulb. The inventors have found that short-circuiting of adjacent turns occurs in the lamp filament. Such short-circuiting can be seen as an indication of the approaching end of life of the filament. The present invention thus aims to provide means for detecting the occurrence or existence of such short-circuiting. When such short-circuiting occurs, the electrical characteristics of the filament change, and the current consumption of the filament changes accordingly. Furthermore, a short-circuited filament turn is without current, so it is only heated through thermal conduction from the neighboring turns. Its temperature will be much lower than the temperature of the neighboring turns, so it generates significantly less light, and therefore it can be seen as a dark turn in an otherwise bright filament.

Systems for inspecting light bulbs and predicting the approaching failure of a lamp are known in the art. US patent 6,784,667 describes several examples as prior art, and the document itself discloses a method based on measuring the resistance of the cold filament. The measured value is compared with a reference value provided by the manufacturer of the light bulb. A problem of this prior art device is that it can only be used when the headlights are off. The user must then specifically actuate the device to perform a measurement. The device is thus not suitable for continuously monitoring the headlights during use. A further problem is that the reference value depends on lamp type and manufacturer, so the reference value stored in the device's memory may be incorrect after an exchange of the light bulb. Furthermore, this device is based on the gradual "boiling away" of the filament, but it does not take into account the short-circuiting of filament turns.

It is further noted that German "Offenlegungsschrift" (document laid open to public inspection) DE- 102.56894 discloses a diagnostic device for inspecting the condition of a light bulb, wherein the power consumption of the lamp is determined and compared with a reference value, and wherein an increased power consumption is taken as an indication of the approaching failure of the light bulb. A problem with a device as proposed by this document is that it is based on the calculated power consumption. During operation in a motor vehicle, however, the lamp voltage is not constant and may typically vary with temperature, battery condition, and the question of whether other power consumers are switched on or off, e.g. heating, airco, brake assistance, etc. Thus power consumption is not a reliable parameter. The document further describes that the power consumption gradually increases from a certain time twi until a certain time t^₂- Consequently, the increase between successive measurements will be relatively small. The document does not mention any minimum value for the increase; therefore the document suggests that any small increase in power consumption should be taken as an indication of approaching failure. However, especially in view of the dependency on lamp voltage, the proposed device may give a warning on the basis of a temporary and harmless increase in power consumption which has no relationship to an approaching failure and which therefore is premature, leading to an unnecessary replacement of light bulbs. This proposed device is accordingly not reliable.

SUMMARY OF THE INVENTION

Based on the above-explained insight and understanding, the present invention provides a method and apparatus as specified in the claims for detecting the occurrence of a short-circuiting of a filament turn, or for detecting the existence of the condition of a short- circuiting of a filament turn. The fact that a short-circuiting of a filament turn takes place is accompanied by a sharp increase in lamp current, i.e. an increase of the order of about 5% within a very short time, of the order of a few seconds or even less, and such an increase can be readily detected. After the moment when the short-circuiting of a filament turn takes place, the lamp remains in a condition of having a short-circuited filament turn, which manifests itself as a dark turn in a bright filament, and such a situation can be detected by projecting an image of the filament and visually inspecting this image.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects, features, and advantages of the present invention will be further explained in the following description with reference to the drawings, in which same reference numerals indicate same or similar parts, and in which:

Fig. IA is a graph showing a characteristic lamp current consumption as a function of time;

Fig. IB is a graph showing a portion of the graph of Fig. IA in some more detail;

Fig. 2 is an image of a glowing lamp filament; Fig. 3 is a block diagram schematically illustrating a monitoring circuit according to the present invention for monitoring the condition of a lamp;

Fig. 4 is a schematic view illustrating an apparatus for visually inspecting the condition of a lamp; Figs. 5A and 5B schematically illustrate a lamp provided with a monitoring circuit according to the present invention for monitoring the condition of the lamp.

DETAILED DESCRIPTION OF THE INVENTION

Fig. IA is a graph showing the current consumption of a specific car lamp of the well-known type H7 as a function of time. Fig. IB is a graph showing the right-hand portion of the curve of Fig. IA on an enlarged scale. In the experiment of Fig. IA, the light bulb was continuously operated at a constant voltage of 13.2 V. A portion 1 of the curve shows that the current gradually decreases from approximately 4.2 A to approximately 4.0 A over a period of more than 400 hours. A second portion 2 of the curve shows that, at a specific moment tl, in this case approximately 480 hours after the start of the experiment, the current increases suddenly to approximately 4.3 A, after which the current again gradually decreases over 120 hours to reach approximately 4.1 A at 610 hours (curve 3). The curve shows further current steps at about 600 hours, 650 hours, 680 hours, 690 hours, and the curve shows that the lamp finally fails at about 700 hours. It is noted that the step at 680 hours actually consists of a combination of two steps occurring shortly after each other.

It is noted that the general shape of Fig. IA is characteristic of all types of vehicle light bulbs, particularly halogen light bulbs used in headlights, although the exact timing of the current steps and the number of current steps before failure may vary from lamp type to lamp type and even from lamp to lamp within the same type. Furthermore, the initial current consumption may differ from lamp to lamp.

An explanation of the current characteristic illustrated in Figs. IA and IB is found in the short-circuiting of filament turns. Fig. 2 is an image of the burning filament of a lamp of type H7, clearly showing (at 21 and 22) that two turns are darker than the surrounding turns, indicating that the turns are short-circuited and do not carry current. The short-circuiting occurs within a fraction of a second, causing an immediate decrease in the filament resistance, which explains the stepwise increase in current consumption.

It can further be seen in Fig. IA, and especially in Fig. IB, that the current consumption shows some small fluctuations even at a constant voltage, but the stepwise current increase associated with a short-circuiting of a turn has a specific step size of the order of about 0.2 to 0.3 A, or of the order of about 5% of the lamp current.

The present invention proposes a method and device for inspecting the condition of a light bulb based on the above phenomena. In a first aspect, the present invention proposes a diagnostic monitoring circuit that can be used in a motor vehicle for monitoring a light bulb and issuing a warning signal if this light bulb approaches the end of its operational life. Fig. 3 is a block diagram of an exemplary embodiment of such a monitoring circuit 30. The Figure schematically shows a lamp fitting 31 for a lamp L, which fitting 31 is connected to battery B via mass terminal M and a power line P, with a lamp switch S connected in series with lamp fitting 31. The circuit 30 comprises a processor 36 having a first input 36a coupled to the lamp fitting 31 for receiving the lamp voltage, and having a second input 36b coupled to a current sensor 32 which measures the current through the lamp fitting 31 and hence through the lamp L. A separate voltage sensor may be used for measuring the lamp voltage, or the processor 31 may itself include a voltage sensor.

Supply lines 37 and 38 connect supply inputs of the processor 36 to power line P and mass M. The supply line 38 thus also provides a reference level for the voltage measurements.

The processor 36 has an output 36c coupled to a signaling device 33. The signaling device 33 may be an acoustic signaling device or a visual signaling device, or both. In a preferred embodiment, the signaling device comprises a warning lamp or LED in the car's dashboard.

The circuit 30 further comprises a memory 34, which is shown as being separate from the processor 36 but which may be part of the processor 36 itself. According to a first aspect of the present invention, the processor 36 is designed to make decisions on the basis of lamp current, compensating for voltage fluctuations. In one example, assuming that the current is directly proportional to the voltage, the current as measured may be scaled to a current which would have occurred at a fixed voltage of, for instance, 13.2 V. This can be achieved by dividing the "current as measured" by the "voltage as measured" and by multiplying the result by 13.2 V. In an alternative example, it is possible to simply divide the current as measured by the voltage as measured in order to actually measure the conductivity of the filament, or it is possible to take the inverted conductivity, i.e. the resistance of the filament. In practice, the voltage across the lamp is not directly proportional to the current. A more accurate description of the relationship between current and voltage at a certain time t is given in the following formula:

wherein Io is the current occurring at a certain nominal voltage Vo. Suitably,

Vo may be taken to be equal to 13.2 V. a is a constant exponent in the range of 0.5 to 0.6, typically approximately equal to 0.55.

Thus, for a more accurate compensation, in the case of a lamp current I(t) measured at a lamp voltage V(t), a compensated current Io may be calculated according to the following formula:

Since the device 30 is based on finding stepwise current increases instead of gradual increases, the processor 36 is designed to measure the lamp current at relatively short time intervals, preferably once per minute or less. Furthermore, the processor 36 is programmed to compare the measured current with a reference value. If an increase is detected, and the increase is above a predetermined threshold, then the processor 36 decides that it has found a short-circuiting event. Said threshold preferably corresponds to 3% of the current, more preferably 5% of the current. In a particular embodiment, the reference value is the previous measurement result. In another particular example, the reference value is an average of a predetermined number of previous measurement results, for example 10 measurement results.

In order to increase the reliability further, the processor 36 may be designed to check whether the lamp current stays at the increased level, so that temporary current peaks are ignored.

The processor 36 may actuate the signaling device 33 when detecting the first short-circuiting event, corresponding to section 2 of the curve of Figs. IA and IB. It can be seen in the example of Figs. IA and IB, however, that the first short-circuiting event occurs at about two-thirds of the operational life of the lamp, and that the lamp still has about 220 hours of operational life before it will fail. Furthermore, it can be seen that the next short- circuiting event occurs after more than 120 hours, and that this lamp survives more than four short-circuiting events. Of course, there is no guarantee that each and every lamp will survive the second short-circuiting event, but experiments have shown that many lamps do. Therefore, in a possible embodiment, the processor 36 is designed to issue a warning signal only upon the occurrence of the second event. It is also possible that the processor 36 issues a first type of warning signal upon the occurrence of a certain event, for instance the first event, and issues a warning of a second type upon the occurrence of the next event, for instance the second event. For example, the signaling device 33 may comprise two LEDs of different color, for example yellow and red, and the processor 36 may actuate the yellow LED when detecting the first event and the red LED when detecting the second event. To this end, the memory 34 may comprise a counter, and the processor 36 may increase the counter value each time a short-circuiting event is detected.

It is noted that the circuit 30 can be easily adapted for performing a failure detection of the lamp as well. If the processor 36 detects a lamp voltage while detecting that the lamp current is zero, the processor 36 may find that the lamp L has failed and may actuate the signaling device 33.

It is preferred that the processor 36 actuates the signaling device 33 as long as the lamp has not been replaced. This also applies if the user switches the lights off and later switches the lights on again: in that case, the processor 36 should read the status of the lamp L from the memory 34 and should actuate the signaling device 33 accordingly. However, the processor 36 should also be informed if the lamp L has been replaced, because then the memory 34 should be reset. There are several possibilities for achieving this, as will be clear to those skilled in the art. For example, it is possible that a switch detects the removal and replacement of a lamp. It is also possible that the circuit 30 is provided with a separate reset switch to be operated by the user. These possibilities are not illustrated here. The circuit 30 of Fig. 3 may be a dedicated circuit for one lamp L, in which case a car will comprise multiple circuits 30, each corresponding to one specific vehicle lamp. In a particular embodiment, however, the circuit 30 comprises one processor 36 with multiple inputs a, b for monitoring the voltage and current of multiple lamps. The circuit may give a general warning if a short-circuiting event is detected for one lamp, indicating that all lamps should be replaced, but the circuit may alternatively be adapted to indicate which lamp is approaching the end of its life, as will be clear to those skilled in the art.

The above embodiment relates to a warning system incorporated in a vehicle. However, even owners of a vehicle without such a warning system need to be warned of the approaching failure of a lamp. Thus, when a car is being serviced, or simply upon a request from the owner, it is desirable for a service mechanic to be able to inspect a light bulb and predict the expected remainder of its life quickly and inexpensively. Such an inspection should be performed while the lamp is still mounted in the vehicle, because if the mechanic has to remove the lamp for inspection, it will be more cost-effective simply to exchange the lamp anyway. The inspection method for the mechanic should be reliable in the sense that an old lamp approaching the end of its life is spotted with certainty. On the other hand, the method should be reliable in the sense that the owner can check the mechanic.

Fig. 4 schematically illustrates an apparatus 50 that can be used for visually inspecting the filament of a light bulb L mounted in a vehicle V. The apparatus 50 comprises a diaphragm 51 with a small hole 52 and a projection screen 53 opposite the diaphragm 51. The apparatus 50 further comprises a sleeve 54 attached to the diaphragm 51. The sleeve 54 is adapted to the shape of the glass G of a headlight unit such that the sleeve 54 fits the glass G in only one way. The position of the hole 52 relative to the sleeve 54 is such that, when the sleeve 54 is mounted to the glass G, an image of the filament of the lamp L is projected on the projection screen 53. It is noted in this connection that the reflector of a headlight of a modern car has multiple segments and that not all segments are capable of projecting a suitable image, so the relative positioning of the hole 52 with respect to the reflector is important since this determines which beam segment is used for imaging. Since the sleeve 54 fits the glass in only one way, a service mechanic does not have to make adjustments but simply has to place the sleeve 54 in position. A quick inspection of the image on the projection screen 53 will show dark turns or not. If the mechanic finds such dark turns, he determines that the lamp is approaching the end of its life and suggests that the lamp be replaced. He may take a photograph of the image in order to prove this.

It is noted that the image of the filament on the projection screen 53 does not have to be an exact, sharp image: a dark turn can be visually detected even in a vague image. The sleeve 54 and diaphragm 51 may be fixedly attached to each other, so that the apparatus 50 is adapted for use with one specific type of car only. Other types of cars having the same headlight unit can be inspected using the same device 50. For inspecting different types of cars, having different types of headlight units, the device 50 preferably comprises a plurality of different sleeves capable of being attached to and detached from the combination of diaphragm 51 and projection screen 53. In that case, a service mechanic will adapt the apparatus 50 to a specific car being serviced by choosing the correct sleeve. However, in view of the simplicity of the device, it is preferred that the sleeve is fixedly attached and that, for servicing different types of cars, different devices 50 with suitable sleeves 54 are provided, because in such a case a service mechanic does not have to spend time in selecting and fixing a sleeve to the diaphragm 51.

The present invention thus succeeds in providing a method and device for monitoring the condition of halogen bulbs in vehicle headlights and signaling the approaching end of life of the bulbs. The method comprises the step of detecting a short- circuiting event of a turn in the lamp filament, or the step of detecting a short-circuited turn in the lamp filament. A short-circuiting event is detected by detecting a stepwise increase in lamp current of the order of more than 3%, preferably more than 5%. A short-circuited turn in the lamp filament is detected by providing an image of the glowing filament and visually inspecting the image for dark spots.

It should be clear to those skilled in the art that the present invention is not limited to the exemplary embodiments discussed above, but that several variations and modifications are possible within the protective scope of the invention as defined in the appended claims. For example, instead of a circuit that is part of the vehicle, it is also possible that the monitoring circuit is part of the exchangeable lamp itself. This offers the advantage that the behavior of the monitoring circuit can be accurately adapted to the specific characteristics of the lamp. Fig. 5 A schematically illustrates a lamp 60 comprising a lamp filament 62, a glass bulb 61 encompassing the filament, and a lamp cap 63 providing the mechanical and electrical connection to the lamp fitting 31. The lamp cap 63 has contacts 64, 65, which connect to support wires 74, 75 extending through the cap 63 and carrying and supplying the filament 62. A monitoring circuit 70 is located in the lamp cap 63 and receives power via the support wires 74, 75. The monitoring circuit 70 comprises a current sensor 67 and a voltage sensor 66 whose inputs are connected to the support wires 74, 75. The monitoring circuit 70 further comprises a processor 68 that receives the voltage measurement signal and the current measurement signal. The processor 68 provides an output signal for use by signaling means on board the vehicle. The output signal from the processor 68 may be transferred to said signaling means via a wireless signal path or via one of the contacts 64, 65. The processor 68 operates like the processor 36 described above; the memory associated with the processor is not shown in Fig. 5A for simplicity's sake.

Fig. 5B illustrates an alternative embodiment, wherein the lamp 60 also comprises signaling means 69, so that any signaling is performed by the lamp itself. This has the advantage that the signaling does not depend on circuitry on board the vehicle: it will still be possible for car drivers whose cars are not prepared for cooperation with lamps with built- in monitoring circuitry to obtain the facility of signaling the approaching end of life simply by buying lamps with built-in monitoring circuitry and built-in signaling means.

In the above, the present invention has been explained with reference to block diagrams which illustrate functional blocks of the device according to the present invention. It is to be understood that one or more of these functional blocks may be implemented in hardware, where the function of such a functional block is performed by individual hardware components, but it is also possible that one or more of these functional blocks are implemented in software, so that the function of such a functional block is performed by one or more program lines of a computer program or a programmable device such as a microprocessor, micro controller, digital signal processor, etc.

Claims

CLAIMS:

1. Monitoring circuit (30) for monitoring the condition of a bulb (L) and generating a signal when the bulb is approaching the end of its life, the circuit comprising: a voltage sensor for measuring lamp voltage; a current sensor (32) for measuring lamp current; - a processor (36) for receiving measured lamp voltage and measured lamp current signals; at least one memory (34) associated with the processor (36); at least one controllable signaling means (33) controlled by the processor (36); wherein the processor is designed to compensate the lamp current for lamp voltage variations, to monitor the compensated lamp current, to compare the instantaneous compensated lamp current with a reference value stored in the memory (34), to detect that a short-circuiting event has occurred if the comparison results indicate a substantial stepwise increase in the lamp current, and to actuate the signaling means (33) upon detection of a short-circuiting event; and - wherein the reference value stored in the memory (34) is based on at least one recent current measurement.

2. Monitoring circuit according to claim 1, wherein the reference value stored in the memory (34) is equal to the compensated lamp current of the previous measurement.

3. Monitoring circuit according to claim 1, wherein the reference value stored in the memory (34) is equal to an average of the compensated lamp currents of the last N previous measurements, N being an integer, preferably of the order of 10.

4. Monitoring circuit according to claim 1, wherein the lamp voltage and lamp current are monitored with a measuring frequency of at least six times per hour, preferably at least once per minute.

5. Monitoring circuit according to claim 1, wherein the processor (36) is designed to actuate the signaling means (33) if the comparison shows that the instantaneous compensated lamp current is more than 3% higher than the reference value, preferably more than 5% higher than the reference value.

6. Monitoring circuit according to claim 1, wherein the processor (36) is designed to skip n short-circuiting events and to actuate the signaling means (33) upon detection of the (n+l)^th short-circuiting event, n being an integer preferably equal to 1 or 2.

7. Monitoring circuit according to claim 1, wherein the processor (36) is designed to actuate a first signaling means upon detection of an n^th short-circuiting event and to actuate a second signaling means upon detection of the (n+l)^th short-circuiting event, n being an integer preferably equal to 1 or 2.

8. Method of monitoring the condition of a bulb (L) and signaling the approaching end of life of the bulb, said bulb having a lamp filament, the method comprising the step of detecting a short-circuiting event of a turn in the lamp filament.

9. Method according to claim 8, the method comprising the step of detecting a stepwise increase in the lamp current of the order of more than 3%, preferably more than 5%.

10. Method of inspecting the condition of a bulb (L) and signaling the approaching end of life of the bulb, said bulb having a lamp filament, the method comprising the step of detecting a short-circuited turn in the lamp filament.

11. Method according to claim 10, the method comprising the steps of turning the bulb ON, providing an image of the glowing filament, and visually inspecting the image for dark spots.

12. Apparatus (50) for use in the method of claim 10, the apparatus comprising: a diaphragm (51) with a small hole (52); a projection screen (53) attached to the diaphragm (51) and aligned with the hole (52); a positioning sleeve (54) attached to the diaphragm (51); wherein the positioning sleeve has a shape adapted to the shape of a headlight unit (G) such that the positioning sleeve fits the headlight unit in only one way, and such that, when the positioning sleeve is fitted to the headlight unit, an image of the filament is projected onto the projection screen (53).

13. Apparatus according to claim 12, comprising a set of multiple exchangeable positioning sleeves (54), each adapted to a specific type of headlight unit.

14. Apparatus according to claim 12, further comprising a photo camera for documenting the filament image.

15. Lamp (60), comprising a lamp cap (63), a filament (62), contacts (64, 65), and supply lines (74, 75) extending through the lamp cap (63) and connecting the filament (62) to the contacts (64, 65); - the lamp further comprising: a monitoring circuit (70) for monitoring the condition of the filament (62) and generating a signal when the filament approaches the end of its life, the circuit comprising: a voltage sensor (66) having inputs connected to the supply lines (74, 75) for measuring the lamp voltage; - a current sensor (67) for measuring the lamp current; a processor (68) receiving measured lamp voltage and measured lamp current signals; at least one memory associated with the processor (68) for storing reference values; - wherein the processor is designed to compensate the lamp current for lamp voltage variations, to monitor the compensated lamp current, to compare the instantaneous compensated lamp current with a reference value stored in the memory, to detect that a short- circuiting event has occurred if the comparison results indicate a substantial stepwise increase in lamp current, and to provide an output signal for a signaling means upon detection of a short-circuiting event; and wherein the reference value stored in the memory is based on at least one recent current measurement.

16. Lamp according to claim 15, further comprising a signaling means (69) arranged in the lamp cap (63), said means receiving the output signal from the processor (68).