April 6, 2005
by Jim Kerr
2005 Cadillac STS. Click image to enlarge
Cadillac has led other car makes with many innovations over the years. From being the first manufacturer to install electric engine starters way back in 1912, to synchro-mesh manual transmissions in its 1929 models and infrared night vision in 2000, technology limits have been pushed further forward. Now, Cadillac has introduced another first: Intellibeam.
Intellibeam, an option on the 2005 Cadillac STS, is a new way of controlling high-beam headlamps. The concept is not new. In 1952, Cadillac introduced the Autronic Eye system, which used a dash-mounted sensor to automatically dim the high beam headlamps for oncoming traffic. Intellibeam does this too, but in a much more sophisticated way.
Using a small light-sensing chip that is able to detect light similar to the way the human eye does, Intellibeam will turn off the high beam headlamps as oncoming traffic approaches. Rather than switching directly from high-beam to low-beam operation, the Intellibeam system gradually dims the high beams as approaching vehicles get closer. The high beam indicator on the dash shows they are either on or off, but the actual operation of the high beams provides gradual dimming or increases in illumination.
This is a great safety feature. Normally, when headlamps are dimmed from high beam to low beam, there is a period of time when the space between the two vehicles is dark and hard to see. Intellibeam provides maximum illumination all the time, eliminating these difficult areas.
The Intellibeam’s digital light sensor and electronics are located in a module mounted on the back side of the interior rear view mirror. The light sensor analyzes the light colour, intensity and movement to distinguish between vehicle lights and other light sources along the roadside. This was a problem with earlier automatic dimming systems, which could be triggered by street or yard lights, or illuminated signs, causing the high beams to flash off and on. Intellibeam is designed to ignore non-vehicular light sources.
The Intellibeam module controls a high-beam headlamp driver module. This module looks just like a relay, but is a solid-state device that uses pulse width modulation – a rapid on/off switching of the voltage on a circuit — to control the output to the headlamp filament. Typically, the voltage is switched from battery voltage or charging system voltage to zero volts several times a second. Some headlamp modules I have tested will do this at 128 cycles per second! By controlling the on time in relationship to the off time, the average voltage of circuit is regulated. For example, if the high voltage is 12 volts and the low is zero, and the on time is equal for both, the average voltage would be six volts. If the high voltage time was longer than the zero voltage time, then the average would be higher.
Many automotive systems, such as EGR, canister purge and interior lamp dimming, use pulse width modulation to control their operation.