ADVANCED FRONT LIGHTING SYSTEMS
June 16, 2003 -The introduction of high-intensity discharge (HID) headlamps in 1993 on the BMW 750iL was just the beginning of a revolution of change in front lighting systems on vehicles. HID headlamps use xenon gas-filled bulbs to produce light that is two-to-three times brighter, while consuming less electrical power, than standard halogen bulbs. Early versions only used the xenon bulbs for low beam headlamps and had standard halogen bulbs for high beam applications. Many applications today use bi-xenon projector headlamps that produce both the low and high beam lights from the same bulb. Legislation in Europe requires these extra-bright headlamps to have an automatic leveling feature to minimize headlamp glare from oncoming vehicles. These automatic leveling headlamps have also found their way onto luxury vehicles, equipped with bi-xenon headlamps, in the North American market.
Automatic leveling headlamp systems use a control module and various sensors for vehicle height, pitch and yaw rates to automatically adjust the angle of the headlamps in response to changes in the road surface. The headlamp projector unit is swiveled up or down in the lens or body of the headlamp by an electric motor (see Figure 1). This keeps the light beam at the same angle to the road surface during acceleration, braking, and body pitch and roll due to changing road surfaces.
One system works by lowering the headlamps to a home position when the headlamps are turned ON. The headlamps then raise to the proper level based on commands from the control module. See the video for an example of this start-up operation.
These recent advances in front lighting technology have revived and improved on an old idea that had all but disappeared. In 1948, the Tucker Corporation produced 51 vehicles that, among other innovative ideas, had a center headlamp that swiveled with the turning of the steering wheel to light a curve before the vehicle entered it. Then in the early 1970s, Citroen had headlamps that turned in sync with the steering wheel on its short-lived SM model. Now vehicle makers have revived the idea of headlamps that shine around corners, and through the use of electronics and computer controls, are working to perfect its operation.
Different versions of active front lighting systems are currently available from three European vehicle makers: Audi, BMW and Mercedes-Benz. Lexus is also offering a turning headlamp system as an option on the 2004 RX 330. The Audi system is only available in Europe so far, on the 2004 A8. BMW and Mercedes-Benz are offering the systems on North American vehicles. The BMW system is available as an option on the 3-series coupe and convertible. The Mercedes-Benz system is being offered on the E-class sedan.
Audi Adaptive Light
Audi and Hella Corporation developed "adaptive light" cornering headlamps for use on the new A8. This system has an additional static non-movable lamp located between the low and high beam headlamps in the HID xenon headlamp assembly (see Figure 2). The additional lamp uses a free-form reflector and halogen bulb positioned at about a 15° angle to the side relative to the other headlamps. This lights the area directly adjacent to the low beam lamps at 90° in relation to the centerline of the vehicle. The system control module uses inputs from vehicle speed, steering angle, and turn-signal operation to determine whether or not to activate the cornering lamp. The cornering lamp will only function at speeds of 70 km/h (43 mph) or less with the headlamps on low beam. When the vehicle is shifted in reverse, both front cornering lamps are illuminated to increase the peripheral vision around the front end of the vehicle.
Mercedes-Benz Active System
Mercedes-Benz uses a different approach, a totally active system, called "Active Cornering Headlamp System." With this system, the headlamps swivel in the direction of the curve or corner (see Figure 3). The system uses bi-xenon projector headlamps that have an electronics unit and electric motor to swivel the projector unit inside the assembly. The bi-xenon headlamps produce both the low and high beams from a single xenon lamp. The headlamps are controlled by a control module that receives inputs on vehicle speed and steering angle to determine how fast and how far to swivel the lamps. This system works at all speeds, and with the headlamps in both low and high beam. The system matches the speed of the vehicle, the swiveling mechanism reacting almost instantly at high speeds and progressively slower as vehicle speed decreases.
BMW Adaptive Light Control
BMW uses a system called "Adaptive Light Control" that also has swiveling bi-xenon projector headlamps (see Figure 4). The projector swivels in a range from 15° outward to 8° inward. This system takes the approach one step further; the control module receives input on vehicle speed, steering angle and lateral acceleration, as well as using data from the BMW navigation system. By using data from the Global Positioning Satellite (GPS) navigation and electronic road map features in the navigation system, the system can adjust the headlamps for optimal lighting of the road ahead.
Halogen Applications To Come
While current advanced lighting systems are all built around HID xenon lights and are found in luxury models, lighting suppliers and vehicle makers are working on systems that use standard halogen headlamps. Just as other innovative safety systems such as airbags and anti-lock brake systems did in the past, some form of these systems could find their way into small and mid-sized vehicles in the future.