3308546 - 5540B headlamps

XENON HEADLAMPS

This type of lighting used for the dipped headlamps involves a bulb containing xenon gas.

These headlamps have the following features:

  • more effective lighting
  • increased range and regulation of the luminous beam
  • lower consumption at operating temperature
  • longer lasting bulb.
Each headlamp is equipped with an electronic control unit for checking the supply voltage.As a result of the extremely intense luminosity, the adoption of xenon headlamps means that a dynamic alignment control system is required.

This system is controlled by its own electronic control unit which operates on two levels:

  • statically, carrying out the realignment according to the vehicle load.
  • dynamically, maintaining the alignment to compensate for vehicle pitching.

Location of components

1, Xenon headlamps 2, Headlamp control unit 3, Stepping motor 4, Headlamp alighment correction control unit 5, Vehicle geometry front sensor 6, Vehicle geometry rear sensor

Light cluster

The light cluster has a power luminous beam at its disposal which, in order to be used to best effect, requires:

  • a reflective surface (1) which collects the luminous beam
  • a screen (2) which determines the shape of the luminous beam
  • a spherical lens (3) which determines the depth of the luminous beam on the road.
The xenon lamp consists of a bulb containing low pressure xenon gas and two electrodes.In order to emit the light an electric arc is needed between the two electrodes and it must be maintained.
Characteristics of xenon bulbs:flow emitted (Lm) 3000efficiency (Lm/W) 85average life (h) 3000supply voltage AC (V) 15000operating voltage AC (V) 80

Each headlamp is equipped with a control unit which has the following functions:

  • checking the value of the operating voltage/current
  • striking the arc at the electrodes and causing the salts to evaporate during ignition.

The operation of the xenon headlamps can be divided into three stages:

  • Ignition, the control unit produces a high voltage (up to 20000V alternating current) capable of producing an arc (electrical discharge) between the bulb electrodes.
  • Maintaining the arc, the control unit supplies the bulb with an excess current for several seconds which causes the rapid evaporation of the metallic halides contained in the bulb.
during this stage and for less than a second, the intensity of the luminous beam is greater than during normal operation.
Operation, the control unit supplies the bulb with a constant voltage of 80V alternating current.
Make sure that the ignition is in the OFF position, then disconnect the negative (-) battery terminal before carrying out any operation on the light clusters.

AUTOMATIC DYNAMIC HEADLAMP ALIGNMENT

As a result of the high light intensity, the adoption of xenon headlamps requires an automatic, dynamic system to check the headlamp alignment.This system is managed by an electronic control unit which operates the stepping actuators fitted on each dipped headlamp. The actuators are operated by processing the signals coming from the two alignment sensors.

The advantages of using an automatic, dynamic headlamp alignment control system are:

  • it avoids glare from oncoming vehicles
  • it stabilizes the area illuminated for improved active safety.

Location of components

1, Xenon headlamps 2, Stepping motor 3, Headlamp alignment correction control unit 4, Vehicle geometry front sensor 5, Vehicle geometry rear sensor

Headlamp alignment correction control unit

This is located under the driver's seat, in a horizontal position and "slide" on the support fixed to the bodyshell.
1, Earth from 2 to 8, Not connected 9, Sensors supply earth 10, Not connected 11, Line K 12, Rear sensor inlet 13, Front sensor inlet 14, Sensor supply positive 15, Instrument panel outlet 16, Side light positive 17, Stepping actuator polarization 18, Impulses for stepping motor actuators

DESCRIPTION

The control unit compares the signals coming from the alignment sensors and calculates the vehicle geometry.A "correction" signal is sent to the stepping motor actuators to adjust the alignment of the luminous beam to the vehicle geometry calculated.

To avoid oscillations of the dipped headlamp beam in the following cases:

  • particular types of roads (cobblestones, unmade, etc.)
  • sharp movements of the vehicle caused by the driver (clutch release, gear change, etc.)
the control unit enters into "noise mode" operation which reduces the number of corrections to be made to the light cluster.The system manages the operation of the system and in the case of a failure with one of the components or a decrease in the supply voltage.- Front sensor defective: the geometry is calculated by replacing the sensor voltage reading with a fixed value memorized.- Rear sensor defective: the system moves to the safety operating mode and keeps the headlamps in a pre-set position known as the "refuge position". This position is the maximum permissible position.- Failed actuator connection: if the acutator operating signal is missing, the actuators assume the "refuge position"- Control unit failure: according to the type of failure, the system can remain in the position at the time of the fault or place itself in the "refuge position".- Voltage decrease: when the voltage goes below 9 Volt, the system remains in the same position as at the time of the fault.

Headlamp alignment sensors

They are the resistive type and one is fitted on the front suspension on the left hand side and the other on the rear suspension on the left hand side.The actuators are supplied by the control unit (5 V) and provide a linear output signal proportional to the position of the suspension.The connection between the sensor rotation axie and the rear suspension is made by means of a "connecting rod - crank" system hinged on a self-lubricating ball joint.The crank (1) is an integral part of the actuator and is fixed to the rotation axis.The connecting rod (2) is fixed to the suspension lower track control arm (3) by a bracket.
The connection between the sensor rotation axis and the front suspension is made by means of "connecting rod - crank" system hinged on a self-lubricating ball joint.The crank (1) is an integral part of the actuator and is fixed on the rotation axis.The connecting rod (2) is fixed on the suspension lower track control arm (3) by a bracket (4).

Stepping actuators

They are fitted directly on the headlamps and consist of:

  • an electric stepping motor
  • a screw-female screw reduction gear which transforms the rotary motion of a hinged push rod into a linear motion by means of a ball joint on the parabola.
An electronic unit operates the coils according to the signals coming from the electronic control unit.