Headlamp Control Module (HCM) [2010-2011]: Function

AUTOMATIC HEADLIGHT LEVELLING 

Courtesy of VOLVO CARS CORPORATION

For vehicles without Four-C (Continuously Controlled Chassis Concept), the position sensors (7/119, 7/121) for rear wheel suspension and front wheel suspension send information to the headlamp control module (HCM) (4/118) on vehicle angle as regards load conditions, acceleration and braking.

For vehicles with Four-C (Continuously Controlled Chassis Concept), the suspension module (SUM) (4/84) sends information to the headlamp control module (HCM) on vehicle angle as regards load conditions, acceleration and braking.

The headlamp control module (HCM) uses the information from the position sensors or suspension module (SUM) to calculate the actual angle for the headlamps.

For vehicles with active headlamps, the headlamp control module (HCM) transmits information on the actual angle to the left headlamp control unit (LHCU) and right headlamp control unit (RHCU) via serial communication. The adjustment motors are then controlled by the left headlamp control unit (LHCU) or right headlamp control unit (RHCU), respectively, via an analog signal.

For vehicles without active headlamps, the headlamp control module (HCM) regulates the relevant adjustment motor via a signal.

ACTIVE HEADLAMPS (VEHICLES WITH ACTIVE HEADLAMPS ONLY) 

Courtesy of VOLVO CARS CORPORATION

Active headlamps are an intelligent headlamps system that optimizes lighting of the road surface at night by expanding the light beam. The motorized headlamps are controlled by the headlamp control module (HCM), which retrieves signals from the CAN network and, in some cases, from directly connected sensors.

For the active headlamp function to be enabled, the headlamp control module (HCM) (4/118) requires information on the following: vehicle speed, current gear, light conditions and steering angle.

The headlight control module (HCM) receives information from the following control modules:

• Brake control module (BCM) (4/16) for information on vehicle speed
• Transmission control module (TCM) (4/28) for information on current gear (automatic transmission)
• Central electronic module (CEM) (4/56) for information from the reversing light switch (3/10) (manual transmission)
• Central electronic module (CEM) (4/56) for information from the twilight sensor (7/12)
• Steering wheel angle sensor (SAS) (3/130) for information on steering angle

The active headlamp function is only enabled if the following conditions are met:

• The vehicle must be in motion, that is to say travelling at a speed greater than 3.6 km/h (2.2 mph).
• Reverse gear must not be engaged.
• No daylight light conditions.

Also, the function active headlamp must be activated. The function active headlamp is deactivated/activated via the menu system in Infotainment control module (ICM) (3/281).

When the function is active, the headlamp control module (HCM) receives continual information on vehicle speed and steering angle. Vehicle speed is obtained from the brake control module (BCM) while steering angle information comes from the steering wheel angle sensor module (SAS) (3/130). This information enables the headlamp control module (HCM) to calculate the current turn-out of the light beam.

LIGHTING BI-XENON LAMPS 

There is normally a 3 second delay between activation with the light switch or ignition on and the Bi-Xenon lamp coming on.

• As with normal headlamps, Bi-Xenon lamps remain off while the engine is cranking and come on once the engine is running.
• Each time voltage is supplied to the ballast (from the central electronic module (CEM)), 3 1-second attempts are made to light the Bi-Xenon lamp.

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 component temperatures during operation: Ballast = 130 °C (266 °F), Lamp holder = 170 °C (338 °F), Bi-Xenon lamp = 400 °C (752 °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.