Single-chip ICs optimize adaptive front lighting system design

High intensity discharge (HID) vehicle headlights are increasingly becoming the technology of choice for vehicle manufacturers across the globe. In order to make maximum use of the excellent illumination HID provides, and at the same time reduce the risk of glare caused by poorly directed HID beams, adaptive front lighting systems (AFS) are gaining increased importance.

These systems compensate for changes in a vehicle's inclination relative to the road surface by making slight vertical adjustments to the headlamp's light beam. They also cause the headlamps to swivel in response to a change in the vehicle's turning direction. The result is a light beam that dramatically improves the driver's cornering visibility by providing the optimum and safest illumination of the road ahead.

Automatic leveling—reduced glare
Automatic headlamp leveling systems work to keep light parallel to the road surface regardless of the vehicle's tilt (see below). A vehicle may tilt as a result of a standstill event, such as boarding passengers, loading the trunk, or even filling the fuel tank. Also while driving, the vehicle tilt changes during braking or acceleration. In both cases, the headlamps must be maintained level with the roadway. Automatic headlamp leveling systems correlate their adjustment angles based on a variety of sensor data—in particular suspension compression data from the front and rear axles.

Swiveling to improve safety
A vehicle's data network contains real-time sensor data on steering angle and wheel speed. Based on this information, AFS equipped headlamps can tailor the light distribution with the vehicle's turning angle, so that upcoming curves and turn-offs receive maximum illumination, especially at the driver's gaze point (see below). Such a significant increase in light helps reduce driver stress and fatigue and improves the ability to see obstacles that fixed-beam headlamps might not illuminate. Various studies on swivel-beam headlamps have shown up to a 300% increase in the illumination of the driver's gaze point as the vehicle turns into a corner.

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Stepper motor control
The movement of each vehicle headlamp is achieved using stepper motors—one for vertical movements and one for horizontal (see figure below). The motors are fed with, and react to, data from numerous sensors around the vehicle. Communication is carried out via the vehicle's data network system. The LIN bus is a practical choice for headlamp control, while the CAN bus collects and distributes the sensor data throughout the vehicle. Stepper motors are ideal for headlamp adjustment applications because the motors are low cost, very rugged, and provide a high torque in relation to their size.

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