APPLICATION OF HIGHLY TRANSPARENT LIQUID SILICONE RUBBER IN AUTOMOTIVE HEADLAMPS

摘要

Dynamic light distributions, adjusting adaptively and automatically to different driving and lighting conditions, are already state of the art. One way to implement variable light distributions in one system is a projection module with a shaped cylinder. This cylinder, rotating around its longitudinal axis, has different outlines on its lateral surface. The cylinder is located in the pathway of rays between the module's reflector and its lens. Thus, it uses a subtractive way to implement different light distributions. In contrast, future cars will feature adaptive and active light functions realized by activating additional light sources in LED matrix headlamps. To implement variable light functions such as glare-free high beam, marking light or bending light, in LED matrix headlamps the luminous flux emitted is being split up into discrete solid angles. This way, the illumination of the motor vehicle's foreground is not forced into fixed patterns but can be adjusted freely to fit the demands of the particular driving situation. So-called primary optics, directly put onto the LED-chip, are being used to prevent the Lambert characteristic of the light-emitting diodes in a close matrix structure. This paper should prove LED matrix systems do not only enhance the possibilities with regards to light distribution and appearance of headlamps. They also demand the application of "new" materials and concepts. Among those, liquid silicone rubber (LSR) stands out for being resistant against high temperatures, violet and ultraviolet radiation while at the same time providing excellent transmission characteristics. When used as light guidance elements LSRs can directly be exposed to white LEDs. Compared to glass, transparent LSRs offer further technical advantages, especially for industrial mass production. On top of the afore mentioned advantages of LSRs compared to glass and thermoplastic polymers, the flexibility of the elastomer can be used to control optical characteristics of secondary optics in a headlamp mechanically. Light distributions could be controlled by flexible lens systems. The lens in the human eye serves as a natural prototype, changing its focal length by contracting a circular muscle. An actuator system similar to the human eye could therefore contribute to the realization of an accommodating headlamp.