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Integrated communicating Solid-State Light Engine (ISLE) for use in Automotive Forward Lighting and information exchange between vehicles and infrastructure

Final Report Summary - ISLE (Integrated communicating Solid-State Light Engine (ISLE) for use in Automotive Forward Lighting and information exchange between vehicles and infrastructure)

The ISLE project aimed to develop a new manufacturing technology to produce a new generation of headlamps for vehicles, which could be the base for a future car-to-car or of car-to-infrastructure communication system. For this, new optical concepts for beam forming needed to be developed and had to be approved for production. This included also processing LED chips into a packaging for emitting white light, which again needed to be optimally decoupled into the beam forming elements. In addition, a suitable concept for communication and an appropriate electronic driving circuit was developed. All together was put in an automotive environment.

The original idea aimed at simplifying the production process of headlamps by:
- reducing the number of production steps;
- reducing the components electric bulb, reflector and housing to just one injection moulded component;
- reducing the production time;
- reducing the manufacturing costs.

The major topics for the project covered:
- providing a white LED, which fulfils the requirements in respect of colour, applying optical elements and efficiency;
- development and implementation of an efficient optical concept an ensure the large scale production suitable for automotive application;
- showing, that a communication can be achieved by modulating the light of LEDs in a automotive headlamp;
- to develop an integrated electronic driver circuit with all necessary functionality and implementing the concept into an integrated circuit;
- solving problems such as thermal management, occurring for a complete headlamp system integration, when LEDs are used;
- support all activities to make LED headlamps legal on the road.

One of the key items within this project was the LED emitting white light. This source had to be combined with optical elements for beam forming. But it is essential, that losses in light are minimised. In order to transform the blue light emitted from the chip into white light, a suitable phosphor had to be developed. Beside conversion efficiency special requirements in respect of light colour had to be fulfilled within the necessary range of temperature. Moreover, a suitable way of placing the phosphor powder on top of the sub-mount chip assembly had to be found. A converter foil was the final solution, which also ensured constant colour in all emitting directions.

With the beginning of the project, two different technologies seemed particularly interesting for optics design, as there was:
- tailored beam technology; and
- folded edge ray or (RXI) technology.

The tailored beam concept was worked out up the stage for creating tooling data for both, high (driving) and low (passing) beam. Because the tailored beam concept is more sensitive to the light source characteristics, which was not available for the ISLE- LED on proper time, the concept had to be worked out on the base of a commercially available 5 by 1 OSRAM O-Star LED module. The concept finally used a light pipe in front of the LED-module and a Fresnel-lens for the driving (high) beam. The passing beam contains modules with Fresnel and 3D tailored free form lenses in front of a light pipe.

The concept for communication is based on a frequency shift keying technology (FSK). The concept ensures together with the electronically driving concept no light loss either with or without sending data. The additional advantages are:
- immunity due to amplitude variations of the signal. This is important if car movement and vibrations are considered.
- the effect of the noise is reduced.
- it is insensitive to non-linear amplification both in the emitter and receiver.
- simple integration with the LED driver circuit, based on PWM at (near) zero extra cost.

Beside the sender a receiver was built. Simulated and measured data showed perfect correlation in the laboratory tests of single components. At the end, the communication performance of the system headlamp-receiver was tested. The maximum communication distance of the actual headlamps was found to be 29 m for the passing (low) and 39 m for the driving (high) beam, which is only about the eleventh part of the theoretical predicted communication distance. In this arrangement, it was at least shown, that a communication is possible, but that further improvements on the LED, the optical components and the receiver's sensitivity would be necessary.

Electronic hardware was built up according to the concept for driving the LEDs and fulfilling the requirements according to the communication concept. It provides a constant voltage rail supply and pulse width modulated (PWM) current control and serves for most efficiently supplying the LEDs. Also provision for thermal runaway and LED failure are provided. Within the project driver boards in SMD-technology were built up.

The consortium presented a set of a fully functional headlamp device using LEDs as light source and performing a driving and passing beam. The out coming light can be modulated in order to communicate information to the infrastructure. The device almost provides outline dimensions in accordance with generally available space in today's cars. The system is capable to be mounted on a test rack in front of a vehicle.