Dynamic Headlight Beam Control

Headlamp levelling control

The 1948 Citroen 2CV was launched in France with a manual headlamp levelling system, controlled by the driver with knob through a mechanical rod linkage. In 1954, Cibié introduced an automatic headlamp levelling system linked to the vehicle’s suspension system to keep the headlamps correctly aimed regardless of vehicle load. The first vehicle to be so equipped was the Panhard Dyna Z. Beginning in the 1970s, Germany and some other European countries began requiring remote-control headlamp levelling systems that permit the driver to lower the lamps’ aim by means of a dashboard control lever or knob if the rear of the vehicle is weighted down with passengers or cargo, which would tend to raise the lamps’ aim angle and create glare. Such systems typically use stepper motors at the headlamp and a rotary switch on the dash marked “0″, “1″, “2″, “3″ for different beam heights, “0″ being the “normal” (and highest) position for when the car is lightly loaded. Internationalised ECE Regulation 48, in force in most of the world outside North America, currently requires such systems on all vehicles. The regulation stipulates a more stringent version of this antiglare measure for vehicles equipped with headlamp bulbs producing more than 2,000 lumens, such as xenon headlamps; such vehicles must be equipped with headlamp self-levelling systems that sense the vehicle’s degree of squat due to cargo load and road inclination, and automatically adjust the headlamps’ vertical aim to keep the beam correctly oriented without any action required by the driver.

Directional headlamps

1928 Willys-Knight 70A Touring. Notice the directional headlight in the middle.

Directional (steering) headlamps on a Citroën DS—the driver can see his way through curves.

These provide improved lighting for cornering. Some automobiles have their headlamps connected to the steering mechanism so the lights will follow the movement of the front wheels. Czech Tatra and 1920s Cadillacs were early implementer of such a technique, producing in the 1930s a vehicle with a central directional headlamp. The American 1948 Tucker Sedan was likewise equipped with a third central headlamp connected mechanically to the steering system. The 1967 French Citroën DS and 1970 Citroën SM were equipped[44] with an elaborate dynamic headlamp positioning system that adjusted the headlamps’ horizontal and vertical positioning in response to inputs from the vehicle’s steering and suspension systems, though US regulations required this system to be removed from those models when sold in the USA.

Advanced front-lighting system (AFS)

There has been a recent resurgence in interest in the idea of moving or optimizing the headlight beam in response not only to vehicular steering and suspension dynamics, but also to ambient weather and visibility conditions, vehicle speed, and road curvature and contour. A task force under the EUREKA organisation, composed primarily of European automakers, lighting companies and regulators began working to develop design and performance specifications for what is known as advanced front-lighting systems, commonly AFS.[45] Manufacturers such as Toyota,[46] Škoda[47] and Vauxhall/Opel[48] have released vehicles equipped with AFS since 2003.

Rather than the mechanical linkages employed in earlier directional-headlamp systems, AFS relies on electronic sensors, transducers and actuators. Other AFS techniques include special auxiliary optical systems within a vehicle’s headlamp housings. These auxiliary systems may be switched on and off as the vehicle and operating conditions call for light or darkness at the angles covered by the beam the auxiliary optics produce. A typical system measures steering angle and vehicle speed to swivel the headlamps.[49] The most advanced AFS systems use GPS signals to anticipate changes in road curvature, rather than simply reacting to them.[50]

Automatic beam switching

Main article: Automatic headlight dimmer

Even when the high beam is warranted by prevailing conditions, drivers generally do not use them.[51] There have long been efforts, particularly in America, to devise an effective automatic beam selection system to relieve the driver of the need to select and activate the correct beam as traffic, weather, and road conditions change. Early systems like Cadillac’s Autronic Eye appeared in 1952 with an electric eye atop the dashboard (later behind the radiator grill) which was supposed to switch between low and high beam in response to oncoming traffic. These systems could not accurately discern headlamps from non-vehicular light sources such as streetlights, they did not switch to low beam when the driver approached a vehicle from behind, and they spuriously switched to low beam in response to road sign reflections of the vehicle’s own headlamps. Present systems based on imaging CMOS cameras can detect and respond appropriately to leading and oncoming vehicles while disregarding streetlights, road signs, and other spurious signals. Camera-based beam selection was first released in 2005 on the Jeep Grand Cherokee, and has since then been incorporated into comprehensive driver assistance systems by automakers worldwide.

Intelligent Light System

Intelligent Light System is a headlamp beam control system introduced in 2006 which offers five different bi-xenon light functions,[52] each of which is suited to typical driving or weather conditions:

  • Country mode
  • Motorway mode
  • Enhanced fog lamps
  • Active light function
  • Cornering light function

Adaptive Highbeam

Main article: Adaptive Highbeam Assist

Adaptive Highbeam Assist is the newest headlamp technology, introduced in spring 2009 in the new generation Mercedes-Benz E-Class. It is based on camera mounted behind the windshield and automatically and continuously adapts the headlamp range to the distance of vehicles ahead or which are oncoming.

The same technology is also present in the BMW 7 series. BMW’s version of this technology, developed in cooperation with Mobileye, uses swiveling headlights that always point in the direction the vehicle is steering so therefore the road ahead is better illuminated and obstacles become visible sooner

Headlamp. (2010, January 9). In Wikipedia, The Free Encyclopedia. Retrieved 19:23, January 9, 2010, from http://en.wikipedia.org/w/index.php?title=Headlamp&oldid=336759396

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