WO2008059421A2

WO2008059421A2 - Halogen lamp for bend-lighting or cornering light

Info

Publication number: WO2008059421A2
Application number: PCT/IB2007/054566
Authority: WO
Inventors: Dieter Wilhelm
Original assignee: Philips Intellectual Property & Standards Gmbh; Koninklijke Philips Electronics N. V.
Priority date: 2006-11-13
Filing date: 2007-11-09
Publication date: 2008-05-22
Also published as: WO2008059421A3

Abstract

The invention relates to a halogen lamp, for bend-lighting or cornering light, of a motor vehicle main headlamp System. The maximum coil temperature is above 3000°C and the switching-off of the lamp at a coil temperature of approx. 3000°C to 3080°C can be performed at a dimming rate of from 7 mV / ms to 17 mV / ms.

Description

HALOGEN LAMP FOR BEND-LIGHTING OR CORNERING LIGHT

The invention relates to a halogen lamp, for bend- lighting or cornering light, of a motor vehicle main headlamp system.

Lamps of this kind are used in, for example, motor vehicle main headlamp systems. The headlamp systems include in particular the main headlamp comprising a high- beam unit and/or a low-beam unit, and a unit for bend- lighting and/or a unit for cornering light. The light source used for the unit for bend-lighting and/or for the unit for cornering light is at least one halogen lamp that is combined with a reflector of the usual kind.

The switching on and off of the unit for bend- lighting and/or the unit for cornering light takes place as a function of, in particular, the light conditions at the time in the surroundings of the main headlamp fitted to a motor vehicle, the motor vehicle main headlamp system having at least one main headlamp forming part thereof. Such light conditions are principally typified by dark surroundings, caused for example by rain or fog, by darkness due to the time of day, or by driving through a tunnel.

Use is made of the unit for bend- lighting, particularly in the medium and high speed ranges (above about 50 km/h), when, at the same time, a relatively small change occurs in the direction of travel, such as happens for example when changing lane or when driving round a curve or bend of relatively large radius.

The unit for cornering light is made use of particularly in the low-speed range (below about 50 km/h) when, at the same time, a relatively large change occurs in the direction of travel, such as happens for example when turning off a road into the entrance to the land surrounding a house or other building or when driving round a curve or bend of relatively small radius.

The switching on or off of the unit for bend- lighting and/or unit for cornering light is performed by an appropriate control unit that is known per se. The unit for bend- lighting is switched on and off automatically on detection of the particular angle to which the steering wheel has been turned at the time. At the time of the switch-off phase, the unit for bend- lighting is turned off by dimming in such a way that the brightness of the light decreases gradually. The unit for cornering light is switched on and off automatically particularly on a direction indicator being operated or on detection of the steering wheel being turned to an appropriate angle. At the time of the switch-off phase, the unit for cornering light is turned off by dimming in such a way that the brightness of the light decreases gradually. The gradual decrease in the brightness of the light is necessary to prevent a sense of uncertainty from being created either in the driver of the vehicle or in other road users such as the occupants of oncoming vehicles or of passing vehicles close to the vehicle presently concerned. An undesirable sense of this kind is created in the event of the unit for bend- lighting and/or the unit for cornering light being switched off abruptly. It has been found that the situation-related switching on or off of the unit for bend- lighting and/or the unit for cornering light results in an undesirable shortening of the life of the halogen lamp used in comparison with the life of a lamp of this kind in normal continuous or driving operation.

Investigations have shown that this shortened life is caused by, in particular, deformation of the geometry of the coil. Such deformation, or what is referred to as distortion, of the incandescent coils of halogen lamps makes it possible for short circuits to occur and these have an adverse effect on the life of the lamp.

It has on the other hand been established that the severity of the deformation is affected by different parameters of the lamp or of its operation. DE 10 2004 012 557 Al for example specifies a solution for a halogen lamp, and particularly for an H8 lamp (having a rated voltage of 12 volts), which is used as a direction indicator light. This solution teaches that, when the lamp is being switched off from an effective value (of approx. 13.0 V) with a gradual decrease in the brightness of the light from it, the voltage is to be set abruptly to 0 V when a threshold value specific to the lamp (of approx. 7 - 9 volts) is reached, to prevent the coil from deforming and hence an undesirable shortening of the life of the lamp from occurring.

This solution was arrived at on the basis of findings derived from tests on the above-mentioned H8 lamp, which in operation operates at a maximum coil temperature of 3000⁰C. However, in halogen lamps of higher output ratings, such as H7 lamps for example, which regularly have a maximum coil temperature of more than 3000⁰C, this solution has not resulted in the undesirable shortening of life being prevented.

However, for certain applications it is necessary even for halogen lamps to be used at a coil temperature higher than the limiting value of 3000⁰C. Because it is possible in principle for the lamp for bend-lighting to be used on the one hand as an extra headlamp and on the other hand as an additional lamp incorporated in the forward headlamp of a motor vehicle main headlamp system, an important consideration in each of these cases, both from the point of view of design and from the technical point of view, is to have a forward headlamp of the smallest possible dimensions.

With regard to motor vehicle lighting, and thus with regard to motor vehicle main headlamp systems too, the current focus of development is to enable lighting units to be used that are of the smallest possible volume when installed, because a particular feature of units of this kind is that they give designers fresh opportunities in the area of motor vehicle design and styling.

What this often also results in is smaller light-emitting areas, which then require in particular a higher light yield to enable lighting of adequate strength to be obtained for driving purposes.

Also, halogen lamps of this kind, such for example as H7, H8 and H9 lamps, have to conform to current standards (IEC 60809 and ECE 37) with regard to light, power and geometry. These lamps are used in vast numbers and when operating at 13.2 V their coil temperature is usually more than 3000⁰C and would thus, as described, result in the coils deforming, with the ensuing consequence of a shortened life.

It is an object of the invention to specify a halogen lamp that is able to be operated at a higher output, in which case the maximum coil temperature is at least above 3000⁰C, and a method of operating a lamp of this kind. The life of this halogen lamp, which has to be capable of being used as a light source for bend- lighting or cornering light, is to be higher than the life that has, to date, existed in such applications.

This object is achieved by a halogen lamp having the features given in claim 1. It is important to the invention in this case for the switching-off of the lamp to be able to be performed, at a coil temperature from approx. 3000⁰C to 3080⁰C, at a dimming rate of from 7 mV / ms to 17 mV / ms.

Improved life is thus ensured for all types of lamp that comply with standards IEC 60809 and ECE 37 for vehicle lighting and that are used for bend-lighting or cornering light in a motor- vehicle main headlamp system, where the maximum coil temperature of the said types of lamp is above 3000⁰C.

Investigations carried out by the applicant have produced the following findings: The shortening of life for the above-mentioned applications, particularly in the case of halogen lamps subject to high loads, is due to the distortion of coil geometry that occurs, as a consequence of which there are short-circuits between the turns of the coil and, because of the lower resistance, an increased flow of current through the coil. The coil temperature thus rises and so too does the risk of vaporization of tungsten that, on the melting point of tungsten being reached, regularly results in the coil, or certain coils, burning out.

This distortion is caused by the interaction of the high coil temperatures, i.e. coil temperatures of more than 3000⁰C combined with slow switch-off of the lamp, using for example what are referred to as switch-off ramps that are known from the prior art. This undesirable effect occurs both in what is referred to as DC operation employing ramp control and also in what is referred to as PWM (pulse width modulation) operation.

In PWM operation, the reduction in the lamp voltage is achieved by means of, for example, a square-wave pulsed voltage of a frequency of between 100 and 1000 Hz by controlling what is called the duty cycle. The square-wave voltage is generally of values of between 13 and 16 V in this case. A 100% duty cycle would thus correspond approximately to an ordinary DC voltage.

Surprisingly, it has been found that there is a maximum coil temperature, measured over at least 3 full turns of the coil, below which distortion of the coil geometry does not occur. This value of maximum coil temperature is approx. 3000⁰C regardless of the type of halogen lamp.

It is also apparent that distortion of the coil geometry occurs all the faster at coil temperatures above 3000⁰C, and hence that the shortening of life in comparison with standard DC operation occurs all the faster the higher is the coil temperature and the longer is the time covered by the switch-off ramp. An improvement in the situation with regard to the life of halogen lamps can therefore be achieved by selecting, as lamps for applications that, due to the function performed, call for frequent switching on and off, such for example as lamps for a unit for bend- lighting or cornering light, lamps that have a maximum coil temperature of less than 3000⁰C or rather ones that operate at such a temperature while complying with the relevant standards, such for example as standards IEC 60809 and ECE 37 for motor vehicle lighting.

In operation appropriate to the given application, i.e. in particular as a bend- lighting lamp, a coil temperature below the limiting value of 3000⁰C thus has to be maintained. This can be achieved by reducing the operating voltage to, depending on the type of lamp, approx. 12.9 to 12.4 V. Under these conditions, i.e. below the limiting value of 3000⁰C, the time covered by the switch-off ramp is totally non-critical and the lamp achieves a life comparable to that achievable in DC operation, as a headlamp lamp, which operation is otherwise similar to the given application. The time covered by the switch-off ramp and its other parameters can thus be freely selected, thus enabling the switch-off ramp to be adjusted in particular to suit the given purpose.

If an adequate area of reflective surface is available in the headlamp then, to prevent the adverse effects described from affecting the life of the lamp, the said surface should be so designed that a temperature for the light-emitting body (coil) required of less than 3000⁰C is all that is required.

This may for example be achieved by, in lamps having a higher coil temperature, reducing the operating voltage by means of pulse width modulation.

However, for certain applications it is also necessary for halogen lamps that have a coil temperature above the limiting value of 3000⁰C to be used, in which case the above-mentioned solutions are not good enough as far as the life being aimed for is concerned.

It becomes possible for the halogen lamp according to the invention to be used for bend-lighting, on the one hand as an extra headlamp and on the other hand as an additional lamp incorporated in the forward headlamp. In both cases, the lamp according to the invention may be considered as a headlamp of the smallest possible dimensions both from the point of view of design and styling and from the technical point of view.

It becomes possible for the lamp according to the invention to be used in lighting units of the smallest possible volume when installed, and in this way new opportunities are opened up for designers in respect of motor vehicle design and styling. The halogen lamp according to the invention, such for example as an H7, H8 or H9 lamp of this kind, also complies with current standards (IEC 60809 and ECE 37). In cases according to the invention where the lower light yield that goes hand in hand with the reduction in the coil temperature is unacceptable, an improvement in the situation can be achieved by a targeted change in the ramp time. What is suitable and sensible as a metric for this purpose is the rate of dimming, i.e. the change in voltage per unit of time along the ramp. What may be considered critical are values of less than 7 mV / ms in the temperature range above 3080⁰C because, compared with DC operation, these reduce life to approx. 20%. In accordance with the invention, the switching-off of the lamp at a coil temperature from approx. 3000° to 3080⁰C can be performed at a dimming rate of from 7 mV / ms to 17 mV / ms.

Dependent claims 2 to 5 specify advantageous embodiments of the lamp according to the invention, though without constituting an exhaustive list thereof.

It is preferable for the dimming rate to be of a value of from 10 mV / ms to 17 mV / ms, which is suitable for the given application, particularly from the point of view of time.

It is, furthermore, preferable for the halogen lamp to be an H7 or H8 lamp that complies with German regulation R37.

It is also preferable for the switching-off according to the invention to be performed by PWM operation.

The object of the invention is also achieved by a method of operating a halogen lamp that has the features given in claim 6. The object of the invention is also achieved by a circuit for operating a halogen lamp for bend-lighting or cornering light in a motor vehicle main headlamp system whose maximum coil temperature is above 3000⁰C, the circuit making provision for the switching-off of the lamp to be performed, at a coil temperature from approx. 3000⁰C to 3080⁰C, at a dimming rate of from 7 mV / ms to 17 mV / ms. These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.

In the drawings: Fig. 1 is a graph of measurements made for halogen lamps according to the invention that illustrate life as a function of coil temperature and dimming rate.

Compared with the existing prior art, and in particular with the teaching of DE 10 2004 012 557 Al, life is not affected by whether, in the temperature range above 3000⁰C, switch-offtakes place abruptly at a given threshold value that is classed as critical.

In the tests described in DE 10 2004 012 557 Al, a dimming rate was employed that was approx. 6 mV / ms and that is plotted in the graph.

The effect of the method of operating, in a motor vehicle main headlamp system, a halogen lamp for bend-lighting or cornering light whose maximum coil temperature is above 3000⁰C, in which method the switching-off at a coil temperature from approx. 3000⁰C to 3080⁰C takes place at a dimming rate of from 7 mV / ms to 17 mV / ms can thus be seen from Fig. 1.

Something else that is apparent is, in particular, how, in the temperature range above 3000⁰C, and in particular between 3000° and 3080⁰C, the switch-off rate of the ramp correlates with the coil temperature.

Above a critical temperature of 3080⁰C there is a considerable shortening of life that can be acted on to only a slight extent by means of the dimming rate.

Claims

1. A halogen lamp, for bend- lighting or cornering light, of a motor vehicle main headlamp system, wherein the maximum coil temperature of the halogen lamp is above 3000⁰C and the switching-off of the lamp at a coil temperature of approx. 3000° to 3080⁰C can be performed at a dimming rate of from 7 mV / ms to 17 mV / ms.

2. A lamp as claimed in claim 1, characterized in that the value of the dimming rate is from 10 mV / ms to 17 mV / ms.

3. A lamp as claimed in claim 1, characterized in that the maximum coil temperature is above 3020⁰C.

4. A lamp as claimed in claim 1, characterized in that the halogen lamp is an H7 or H8 lamp that complies with German regulation R37.

5. A lamp as claimed in claim 1, characterized in that the switching-off is performed by means of PWM operation.

6. A method of operating a halogen lamp for bend- lighting or cornering light whose maximum coil temperature is above 3000⁰C in a motor vehicle main headlamp system, wherein the switching-off of the lamp at a coil temperature of approx. 3000° to 3080⁰C can be performed at a dimming rate of from 7 mV / ms to 17 mV / ms.

7. A circuit for operating a halogen lamp for bend- lighting or cornering light whose maximum coil temperature is above 3000⁰C in a motor vehicle main headlamp system, wherein the circuit makes provision for the switching-off of the lamp at a coil temperature of approx. 3000⁰C to 3080⁰C to be performed at a dimming rate of from 7 mV / ms to 17 mV / ms.