laser light in the bmw i8 design, system integration and test

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AUTHORS DIPL.-ING. STEFAN WEBER is Project Leader for Laser Light at BMW AG in Munich (Germany). DR. ALEXANDER BUCK is Test Specialist for Lighting Systems at BMW AG in Munich (Germany). DIPL.-ING. CHRISTIAN AMANN is Leader of the Department Light and Sight at BMW AG in Munich (Germany). MILESTONES Vehicle lighting systems are developing constantly and rapidly. In addition to new supplementary functions, which are mostly based on cameras and sensors, the enhancement and new development of light sources enables both increased safety levels and new design options. Following on from the emergence of xenon lamps in the 1990s, light-emitting diodes based on semiconductors are cur- rently being deployed in vehicle lights to an increasing extent [1]. With the development of a new, laser- based light source with significantly enhanced luminance, it is possible to set up efficient headlights with high lighting intensity in the smallest installation space. The first series production launch for a headlight with laser technology will be in the BMW i8. In addition to the con- ception of the optical system, the main tasks in the development of the first laser headlight involved the integration of the new light source into the vehicle envi- ronment. This includes the validation of the individual components and of the complete system parallel to development, taking account of the special require- ments for use in an automobile. This article from BMW describes the design, the package optimised vehicle integration and test of the light system in addition to an publication in ATZelektronik in August 2014, which focusses controlling of the laser and E/E integration [2]. DOUBLING THE RANGE OF LIGHT Two technical variables with regard to light are decisive for the so-called light performance “on the road”, that means for the quality of the illumination of a head- light is important: : the light intensity in selected measur- ing points and angular ranges : the luminous flux in the relevant measurement grid, that means the actual light volume in front of the vehicle. DEVELOPMENT LIGHTING TECHNIQUES 44

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Page 1: Laser Light in the BMW i8 Design, System Integration and Test

AUTHORS

DIPL.-ING. STEFAN WEBERis Project Leader for Laser Light at

BMW AG in Munich (Germany).

DR. ALEXANDER BUCKis Test Specialist for Lighting Systems

at BMW AG in Munich (Germany).

DIPL.-ING. CHRISTIAN AMANNis Leader of the Department Light and

Sight at BMW AG in Munich (Germany).

MILESTONES

Vehicle lighting systems are developing constantly and rapidly. In addition to new supplementary functions, which are mostly based on cameras and sensors, the enhancement and new development of light sources enables both increased safety levels and new design options. Following on from the emergence of xenon lamps in the 1990s, light-emitting diodes based on semiconductors are cur-rently being deployed in vehicle lights to an increasing extent [1].

With the development of a new, laser-based light source with significantly enhanced luminance, it is possible to set up efficient headlights with high lighting intensity in the smallest installation space.

The first series production launch for a headlight with laser technology will be in the BMW i8. In addition to the con-ception of the optical system, the main tasks in the development of the first laser headlight involved the integration of the new light source into the vehicle envi-

ronment. This includes the validation of the individual components and of the complete system parallel to development, taking account of the special require-ments for use in an automobile.

This article from BMW describes the design, the package optimised vehicle integration and test of the light system in addition to an publication in ATZelektronik in August 2014, which focusses controlling of the laser and E/E integration [2].

DOUBLING THE RANGE OF LIGHT

Two technical variables with regard to light are decisive for the so-called light performance “on the road”, that means for the quality of the illumination of a head-light is important: : the light intensity in selected measur-

ing points and angular ranges : the luminous flux in the relevant

measurement grid, that means the actual light volume in front of the vehicle.

DEVELOPMENT LIGHTING TECHNIQUES

44

Lighting Techniques

Page 2: Laser Light in the BMW i8 Design, System Integration and Test

The main lighting functions of the head-light, low-beam headlights and high-beam headlights, make the toughest demands with regard to the technical lighting variables. This is why it is nec-

essary for the development of a new high-luminance light source to focus on one of the two main lighting functions, the high-beam headlights. With the high-beam function, the illumination

range, which is relevant to safety, the so-called 1-lx range can be equated to the root of the light intensity of both head-lights, ➊. The light intensity I is ideal-ised proportional to the aperture A of the

➊ Bird’s-eye view of the light distribution; the outermost contour corresponds to the 1-lx line

LASER LIGHT IN THE BMW I8 DESIGN, SYSTEM INTEGRATION AND TESTA light source based on laser diodes will be used for the first time in a series vehicle in the BMW i8.

The significantly increased luminance enables double the range of the high beam headlight while simultaneously

reducing the installation space required. This article from BMW describes the package optimised design, the

system integration and test of the light system in addition to an publication in ATZelektronik wordwide in August

2014, which focusses on controlling of the laser for series production and the E/E integration.

09I2014 Volume 116 45

Lighting Techniques

Page 3: Laser Light in the BMW i8 Design, System Integration and Test

optical system, that means for example the surface area of the deployed reflector, the number of light sources N, the opti-cal system efficiency (output luminous flux on the road in relation to input lu minous flux of the light sources) as well as the luminance of the light source Ls, Eq. 1:

EQ. 1 I A∙N∙ ∙LS

In the history of headlight development, the application of xenon high-pressure gas-discharge bulbs with increased lumi-nance and luminous flux have enabled a significant increase in the range of high-beam headlights compared to halogen systems. High-end LED headlights sur-pass the performance of the xenon system despite the luminance remaining the same.

On account of the compact shape of the LEDs, more light sources can be used and their radiation characteristics enhance the optical system efficiency . Further enhancement to the range of the high beam, however, is subject to strict limits, as the installation space and design mean that the surface area A and the number N of LEDs is limited. As can

be seen in Eq. 1, the use of a light source with higher luminance Ls enables an increase in the light intensity – and thus the range – without having to accept dis-advantages in other places.

HIGH PERFORMANCE THROUGH POINT LIGHT SOURCE

For this reason, since 2009 the BMW Group and their development partners

➋ Concept demonstrator of the BMW laser light source; the beam of three blue laser diodes is deflected via mirrors onto a YAG phosphor where the blue laser light is converted into white light and from there falls onto a secondary optical system

➌ Exploded-view drawing of the BMW i8 laser headlight

① Lens cover② Design cover③ Daytime driving / position light with

integrated turn indicator④ Daytime driving / position light with

integrated design element⑤ Bi-LED unit

⑥ Adjustment mechanism⑦ Control units⑧ Housing⑨ Laser light unit⑩ Laser light engine⑪ Laser light unit reflector⑫ Laser light heat sink

DEVELOPMENT LIGHTING TECHNIQUES

46

Page 4: Laser Light in the BMW i8 Design, System Integration and Test

have been developing a new light source based on laser diodes to meet these requirements and provide cus-tomers with vehicle lighting that is an optimised combination of safety, func-tion, and design without compromises. The first white light sources based on laser diodes with high luminance, for example, were developed for applica-tions in projectors as well as medical technology.

The key to increasing the luminance lies in reducing the size of the illuminat-ing surface area while the luminous flux remains the same. This is made possible by the deployment of high-performance laser diodes where the light can be focused on the light-converting phospho-rous, ➋. The luminance of the laser light source is increased for operating condi-tions typical of vehicles by more than a factor of one compared to current LEDs.

PACKAGE OPTIMISATION

The new laser light source will be used for the first time in the headlight of the BMW i8 electric sports car. Here, it spe-cifically supplements the optical modules of the full LED headlight. The compo-nents of the system is shown in ➌. Each light source is optimised for deployment according to its optical properties for the specific application.

In this way, the LED modules in the headlight of the BMW i8 generate homo-geneous and wide illumination with high efficiency. The laser-based spot module generates a bundled light distri-bution with a very high range [3].

With the combination of LED high-beam headlights (100 lx) and laser booster (240 lx), the legal maximum of 344 lx specified in the ECE area of appli-cability (measured at 25 m, which corre-sponds to 215.000 cd and/or 430.000 cd for the left-hand and right-hand head-lights) can be reached. This corresponds to a 1-lx range of more than 600 m.

The aperture of the reflector of the laser module is under 30 mm. In com-parison, xenon headlights have a lens diameter of approximately 70 mm; halo-gen headlights have a reflector size of approximately 120 mm while achieving a significantly lower light intensity. A unique feature in the automotive envi-ronment is the light intensity of 240 lx with a power input of only approxi-mately 12 W.

INTEGRATION OF THE LASER LIGHT SOURCE IN THE VEHICLE ENVIRONMENT

The high level of luminance enables additional optimisations with regard to installation space and weight of the

headlight. The surface area of the reflec-tor can be reduced in size to up to one tenth of that of LED headlights. The height of the reflector is reduced from the previous approximately 9 to less than 3 cm. This enables a very attractive, flat design of the headlight and of the com-plete vehicle, as well as optimal aerody-namics and compliance with important pedestrian protection parameters. Along with the laser light technology for the high-beam headlight, the headlight of the BMW i8 has also been given a sec-ond, wide-design daytime driving light clasp. A passively illuminated blue band draws attention to the innovative tech-nology of the light unit, ➍.

For integration of the laser light source into the vehicle in series development, it is important to bear in mind the specific requirements of an automobile headlight. On account of the worldwide deploy-ment, the component is configured to provide its complete functionality under a wide range of marginal conditions. For a headlight, this means, among other things, withstanding an outside temp-erature range of -40 to +120 °C caused by waste heat from the engine com-partment. Over and above this, the con-figuration must meet the high quality requirements for its function over the entire vehicle service life.

In addition to the development of an LED headlight, special attention is paid to laser-specific criteria such as product safety and thermal system design. Both the stability of the light values and the robustness of the system are ensured from the outset parallel to development and validated in a complex and very demanding process [4].

VALIDATION – FROM THE SIMULATION TO THE HARDWARE

For development, the requirements for the headlight are derived all the way down to the individual components within the laser light source. Meeting these requirements is ensured during the conception phase in parallel by means of simulations and hardware tests with prototypes.

For example, depending on the road conditions, vibrations occur while the vehicle is being driven, and these are transferred all the way inside the compo-nents. On each of these levels, various specially designed sequential tests are

➍ The flat version of the BMW i8 laser headlight and with a blue design feature

09I2014 Volume 116 47

Page 5: Laser Light in the BMW i8 Design, System Integration and Test

carried out, for example a combination of a vibration test and frequent tempera-ture changes.

INTEGRAL SAFETY CONCEPT

On account of the deployment of high-performance laser diodes, the develop-ment of a robust product safety concept that reliably excludes possible danger in any situation played an important role. The result is an integral, multi-stage safety system. Its basis is high mechani-cal stability and the use of qualified materials suitable for deployment in automobiles. An aluminum housing pro-vides the protection function for acci-dents at low and medium speeds. Fur-thermore, in the event of accidents at above 40 km/h, the power supply to the light source is automatically interrupted to prevent laser beams from escaping if the unit is damaged.

Internal faults in the light source are detected by an optical sensor system and

lead to a shutdown of the laser diodes within a few milliseconds. Potential daz-zle is reliably excluded by the activation conditions. The laser booster is con-trolled in a situation-adaptive manner and is only activated at speeds above 70 km/h.

THERMAL MANAGEMENT

The electromagnetic radiation from semi conductor light sources deployed for vehicle lighting is located in the visible range that means that it can be used for lighting. Despite the high efficiency of these components, only part of the elec-trical power output is converted into light. The remaining power output heats up the component. In order to ensure a long service life and high efficiency, the temperature of the light source is checked. In practice, this occurs by means of heat output to a heat sink. A cooling circuit of the warm air over the inside of the lens cover of the headlight –

the coldest point on the headlight while the vehicle is being driven – prevents overheating.

In comparison with LEDs, laser diodes have an increased cooling requirement, as they suffer a severe loss of efficiency at high temperatures. The air flow and thermal management are therefore one of the greatest challenges for the configuration of the headlight. As early as the development phase, flow simulations ensure that there is optimal cooling of the laser light source to pro-vide full power output in all driving sit-uations, ➎ (top). For example, the shape of the heat sink and the position of fans is continuously subjected to iterative loops to achieve circulation and thus temperatures at the light source that are as low as possible. The simulations are compared with real measurements on specially prepared prototype headlights in climate test cabinets or in the vehicle, ⑤ (bottom).

CONCLUSION

The total of its properties makes the BMW laser light the ideal light source for the high-beam headlights in the automo-bile. It combines unsurpassed perfor-mance and safety with high efficiency and particularly small dimensions. Its enhanced luminance and therefore very high illumination range enable a further improved visibility and a larger view towards the front when driving in dark-ness. It thus ensures relaxed, more com-fortable driving and more safety in road traffic.

REFERENCES[1] Hanafi, D.; Erdl, H.; Weber, S.: A New Efficient, Compact Vehicular Illumination System Using High-power Semiconductor Laser Diodes. In: Proc. of ISAL (2013), Darmstadt, pp. 168-179[2] Werkstetter, M.; Weber, S.; Hirth, F.; Amann, C.: Laser Lihgt in the BMW i8 – Controlling and E/E Integration. In: ATZelektronik Worldwide 9 (2014), No. 4, pp. 14-18[3] Hying, R.; Nauen, A.: Laser Activated Remote Phosphor – the Way to Ultra-high Luminance in Headlamps. In: Proc. of ISAL (2013), Darmstadt, pp. 121-125[4] UN-ECE Regulation No. 48, Revision 8, 6.22.9.4

➎ Thermal configuration of the headlight: flow simulation (top) and real temperature measurement in the climatic test cabinet with temperature sensors fitted in the headlight (bottom)

DEVELOPMENT LIGHTING TECHNIQUES

48

Page 6: Laser Light in the BMW i8 Design, System Integration and Test

09I2014 Volume 116 49

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