Headlamp Bulb: Description and Operation
GDL Bulbs
System overview
Bi-Xenon Headlight System:
Bi-Xenon headlight system
Bi-Xenon, a headlight system with projector module, is based on gas discharge technology. The system combines high and low beam into the same lamp.
Due to legal requirements (regarding low beam) for this type of lamp, the vehicle must be equipped with automatic headlight levelling.
There are two gas discharge lamp modules (GDL) - one for each headlight. The one located on the driver's side of the vehicle serves as "master" and communicates with the central electronic module (CEM) via LIN communication.
The other gas discharge lamp module (GDL) serves as "slave" and communicates with the "master" control module via LIN communication.
The gas discharge lamp module (GDL) and ballast are integrated into a single unit and are mounted behind the headlight in the wheel arch liner.
Ballast
WARNING: The ballast, which is located in the wheel arch liner, and the wiring for the Bi-Xenon lamps are high voltage.
An electronic ballast is connected to each headlight. The ballast serves as a voltage regulator and generates alternating current (AC). The ballast and gas discharge lamp (GDL) module are integrated into a single unit.
The main tasks of the ballast are:
1. Light the bulb.
2. Regulate light during operation.
A initial voltage of about 24,000 V for a very brief period (less than 1 ms) is required to light the bulb.
The ballast transforms the vehicle's 12 V (DC) to 1000 V (AC).
The high voltage contact amplifies the voltage an addition 25 times. Once the bulb has been lit, voltage is regulated down to about 100 V, which is required to keep the bulb lit.
Power consumption: 10 W.
Bi-Xenon lamp
The light source consists of a discharge tube surrounded by a glass that filters out harmful UV radiation.
- The discharge tube is filled with a blend of chemical compounds, including the inert gas Xenon.
- An electric arch is created through an electrical discharge between two tungsten electrodes.
- Because the lamp does not have a filament, it is less sensitive to bumps and vibrations.
- Bulb designation: D2S (special for projector modules).
- Power consumption: 35 W.
CAUTION: The bulb contains mercury (less than 0.5 mg), thus classifying it as hazardous waste. Hazardous waste must be handled in accordance with national legislation.
Xenon vs. Halogen.
Xenon:
- higher color temperature, which produces a whiter light
- better reflection of road signs and road markings
- has lower power consumption (about 2/3).
Good to know:
- Daylight has a color temperature of about 5000 degree K. The closer to natural light, the more restful the light is to the eyes. A standard H4 bulb has a color temperature of about 3200 degree K. The Volvo gas discharge bulb has a color temperature of about 4200 degree K.
- With the Bi-Xenon system, high and low beam generates the same light color. The human eye thus has an easier time adjusting to switches between high and low beam.
Design
Headlights
WARNING: The ballast, which is located in the wheel arch liner, and the wiring for the Bi-Xenon lamps are high voltage.
The headlights are operated via the light switch module (LSM). This is on the dashboard at the side of the steering wheel. The light switch module (LSM) is directly connected to the central electronic module (CEM). Low and high beam are operated by moving the left control stalk toward the steering wheel. In the Bi-Xenon lamps, an actuator motor (solenoid) is used to move a cover in front of the lamp in the lamp housing in order to switch between high and low beam.
In cars with Bi-Xenon lamps, the lamps are powered directly via the central electronic module (CEM) without pulse width modulation.
To detect problems with the low beam, the central electronic module (CEM) reads the power consumption of the circuit. If this falls below a certain threshold value a fault will be indicated. The general warning lamp lights in the driver information module (DIM) and a text message is displayed.
Lighting the headlight
It normally takes 3 seconds from activation at the light switch with the ignition on to the lamp lighting.
- As with normal headlights, the lamps remain off while the starter motor is cranking and come on once the engine is running.
- On each occasion that voltage is supplied to the ballast 3 attempts, within 1 second, are made to light the lamp.
Right and left-hand asymmetric lamps
The right and left-hand asymmetric lamps are adjusted mechanically using a simple operation. A lever is accessible when the rear cover on the headlight housing is opened.
A = left-hand asymmetric lamp
B = right-hand asymmetric lamp
Automatic headlight levelling
Motors integrated in the headlights regulate the beam range of the headlights. The motors adjust the headlights vertically depending on load and road conditions to reduce the risk of dazzle.
The motors are regulated via signals from one position sensor at the rear axle and one at the front axle.
and one at the front axle. The position sensor are directly connected to the "master" gas discharge lamp module (GDL). The sensors detect vehicle angle in different load conditions and transmit information to the "master" gas discharge lamp module (GDL), which then sends control signals to the motors regulating beam range.
If there is a fault in the automatic headlight levelling for the Bi-Xenon lamps, the actuator motors will automatically set the beam range to the shortest level.
There are diagnostics for the headlight levelling.
Headlight levelling position sensors (Bi-Xenon)
Cars with Bi-Xenon lamps have two position sensors so that the headlights can be adjusted automatically. Vertical adjustment accounts for load and road conditions to reduce the risk of dazzle.
One position sensor is located next to the rear axle and is connected to the left rear control arm via a link system. The other position sensor is located next to the right front axle and is connected to the right front control arm via a link system.
Vehicle angle is measured by the sensors being actuated via the respective link system.
The position sensors are directly connected to the "master" gas discharge lamp module. The signals are received by the "master" control module. If speed is above 5 km/h (3 mph), an average value is calculated. The processed information is sent to the "slave" gas discharge lamp module (GDL) via LIN communication.
The position sensors are calibrated using VIDA. The calibration is saved in the "master" control module. The calibration needs to be repeated if the control module or a position sensor has been replaced.
Calibration
CAUTION: Position sensor calibration is required after work such as sensor removal/installation, or replacement of a sensor, the control module, rear axle, front axle, bushings, shock absorber or springs.
Calibrate as per the tab DIAGNOSTICS/VEHICLE COMMUNICATION/Central electronic module (CEM).
Calibration must always be performed with the vehicle unlocked and stationary on a level surface.
There are diagnostics for the position sensors.
Beam adjustment is carried out conventionally (via adjustment screws by the headlight).
Safety
- In the event of a short-circuit on the high tension side the power supply cuts in less than 10 ms
- If the high voltage circuit is broken (such as due to an open circuit, defective bulb or no bulb in the lamp socket), during each activation the system attempts to light the lamp for a period of 700 ms. During the period, there is high voltage across the ballast.
- Approximate temperatures of components during operation: Ballast = 130 degrees C (265 degrees F), Bulb holder = 170 degrees C (340 degrees F), Bulb = 400 degrees C (750 degrees F).
- The glass body of the Bi-Xenon-lamp is filled with different gases and metal vapors which are under pressure. The lamp can explode as it is under gas pressure.
WARNING: Follow the safety instructions and recommendations in VIDA carefully when working with high voltage. Use safety goggles when handling the bulb. Risk of explosion. The electrical system must be switched off before starting work. Risk of burn injury. The components operate at very high temperatures.
High voltage unit
- High voltage is required to light the Bi-Xenon lamp.
- A high voltage unit is connected to each Bi-Xenon lamp. This transforms 12-V voltage to the approximately 24,000 V required to light the lamp. Once the lamp is on, voltage is lowered to the approximately 100 V required to keep the lamp lit.
- Each time voltage is supplied to the high voltage unit, an attempt is made to light the Bi-Xenon lamp. If this voltage does not exceed 9.5 V during a time period of 200 ms, the lamp does not light. If voltage is too low, such as after a voltage-consuming cold start, the lamp does not light just because the engine is running and the alternator begins charging. A new attempt must be made to start the lamp by turning the light switch to the "0" or parking light position and then back to the low beam position.
WARNING: Because of the high voltage it is important to follow the instructions for working with Bi- Xenon lamps and the high voltage unit!
Function
Headlights
If the knob is in the correct position in the light switch module (LSM) (3/111), the central electronic module (CEM) is instructed to light low beam.
The central electronic module (CEM) (4/56) powers the Bi-Xenon lamps directly via an output.
To switch to high beam, the left control stalk is pulled toward the steering wheel. A directly connected signal is sent from the steering wheel module (SWM) (3/254) to the central electronic module (CEM), which passes on the request to the "master" gas discharge lamp module (GDL) via LIN communication.
The "master" module passes on the request to the "slave" module via LIN communication. Both LIN control module regulate the actuator motor solenoid), which controls the position of the cover so that high beam is obtained for the Bi-Xenon light.
The central electronic module (CEM) also transmits a CAN signal to the driver information module (DIM) (5/1) to light the indicator lamp for high beam.
There is a Limp Home function which ensures that low beam still works if there is a fault in the control area network (CAN). For Bi-Xenon lamps the beam is then set to the shortest range.
Automatic headlight levelling
Automatic headlight levelling is controlled by the "master" gas discharge lamp module (GDL). The position sensors (7/120-121) on the front and rear suspensions transmit signals to the "master" control module (4/112) about the angle of the car in terms of the load conditions.
The "master" control module calculates the relevant angle for the headlights and sends the information to the "slave" gas discharge lamp module (GDL) (4/113) via LIN communication.
The central electronic module (CEM) (4/56) receives a speed signal from the brake control module (BCM) (4/16) via CAN communication. It then sends this signal on to the "master" control module via LIN communication. Once the position sensors have transmitted information on a change in vehicle angle, it takes about 9 seconds until the beam range has been adjusted. If speed is above 5 km/h (3 mph), an average value is calculated. The processed information is sent to the "slave" gas discharge lamp module (GDL) via LIN communication.
Regulation when the vehicle is stationary
When the ignition is switched on, the position sensors are read and the headlight levelling motors adjust the headlights.
Regulation when the vehicle is in motion
In the event of large angle changes while driving, the headlights are regulated. There is a built-in delay in the system so that it does not react to momentary changes, such as unevenness in the road surface.
The actuator motors are then operated from the relevant gas discharge lamp module (GDL) via an analog signal, where the signal level is set to the angle the lamps need to be set to.