198001492 - 5540 XENON HEADLAMPS (Xenon Gas headlamps)
GAS DISCHARGE - XENON HEADLAMPS
Front light cluster (xenon gas discharge version)
The need to improve the performance of current systems based on halogen bulbs in terms of the light energy emitted and the spectral distibution and life of the bulb has led to the development of gas discharge headlamps technology and the devices that allows its operation on the vehicle.There are basically three types of advantage from the development of this technology:- the increased light efficiency allows a reduction in the absorption of electrical energy;- the high light flow emission makes it possible to reduce the dimensions of the light cluster (in particular the height) with greater freedom in the design of the front section;- the bulb lasts, on average, twice as long as a halogen bulb.Gas discharge headlamps are therefore a system:- providing a WHITE light and light FLOW that is brighter than halogen- that regulates the beam AUTOMATICALLY in order not to create glare and to have the light always positioned correctly in relation to the roadTraditional lamp light beam (isolux curve).Discharge lamp light beam (isolux curve).Every light cluster includes the components necessary for the operation of the discharge bulb (bulb, control unit, control motor): the traditional components are also present (side lights, direction indicators, main beam).The unit consists of:Bulbs present- xenon D1S bulb for "Bi-Litronic" dipped/main beam headlamps function- H1 halogen bulb for main beam headlights spot (flasher) function 12V-55W.- All glass W5W bulb for side lights function -12V-5W- All glass PY21W bulb for direction indicators function - 12V-21WBi-Litronic function:The switching between the dipped and main beam functions for xenon bulbs takes place by means of a suitably shaped metal screen that is lowered for dipped operation and raised for main beam operation.The movement of the screen is produced by a coil which, when activated, moves a pin which pushes on the screen and lowers it.When the coil is no longer activated, a spring returns the screen to its original position.a) screen lowered: main beam headlightb) screen in rest position: dipped headlightXenon bulb
Xenon bulbs consist of a bulb containing two electrodes spaced a few millimetres apart and filled with low pressure xenon gas.The emission of light is produced by an arc between the two electrodes which is maintained during the operation of the bulb; this process is similar to what takes place in neon lights.Unlike the latter however, in automotive applications, it is unthinkable to have to wait for a few minutes before the process stabilizes, therefore the light cluster has an electronic control device (control unit) that allows operation, as far as the warming up times are concerned, comparable to traditional headlamps.A high voltage (18-23KV) is needed for the activation of the bulb and then a medium voltage for operation (80-120 V): this is achieved courtesy of an ignitor built into the actual bulb and a ballast located in the control unit.1 - Lamp2 - Ignitor3 - Ceramic insulation4 - ConnectorOperation: the operation of a xenon bulb is divided into four stages:- Ignition: During this stage the ballast produces a voltage capable of causing the engagement of a suitable device located in the igniter. A step-up transformer circuit transfers the suitably amplified excess voltage to the bulb thereby causing a discharge between the electrodes.- Take-over (arc maintenance) during this stage (lasting several seconds) the bulb receives the excess power supply necessary for producing the rapid evaporation of the metallic halides contained in the bulb in order to guarantee that the operating brightness is reached quickly. In these conditions the bulb produces a light flash that is twice the intensity of normal for a period of about 100 microseconds.- Warm up for a period of about two minutes, the ballast regulates the light intensity determining the physical state of the bulb from its impedance properties (closed loop control).- Steady state: the light beam is controlled continuously in closed loop in the steady state.The igniter is located in the base of the actual bulb, whilst the ballast is located in the control unit.Electronic control unit
The electronic control unit co-ordinates the operation of the entire system:- it receives the power supply, dipped and main beam headlamp control- it receives the signals from the position sensors- it receives the speed signal- it controls the bulb- it controls the angle adjustment motor- it is equipped with a diagnostic functionIt is located in the lower part of both headlampsOne of the two control units carries out the MASTER function (left headlamp): the sensors, that detect the vehicle geometry are connected to it whilst the other (right) lamp has a SLAVE function and is connected to the MASTER lamp by a special serial line:Wiring diagram and connector
(14-way) connector for lamp power supplyPIN OUT:1- Dipped headlamps control2 - Direction indicators control3 - Bulb earth4 - Side lights control5 - Speedometer signal (only on MASTER)6 - Ignition-operated control power supply7 - Signal from sensor on front suspension (only on MASTER)8 - Power supply for sensors (only on MASTER)9 - Serial line between the two control units10 - Signal from sensor on rear suspension (only on MASTER)11 - Diagnostic K line12 - Earth signal for sensors (only on MASTER)13 - Main beam headlamps control14 - Control unit earthAutomatic headlamp alignment correcter
As a result of the brightness of the bulb light beam, the vehicle must be equipped with an automatic headlamp alignment correcter to prevent the drivers of oncoming vehicles being dazzled. The device intervenes in certain conditions:- static type, due to the distribution of the load;- dynamic type, due to acceleration and deceleration.The automatic correcter also guarantees improved driving comfort because the area lit is kept stable and your eyes do not have to constantly adapt to the variations in the lighting.The device consists of:- a stepping actuator for each headlamp.- two load sensors, connected to the front and rear suspension.Correction
This is carried out through the load sensor signal which, connected to the suspension, provide a reading on the vehicle load status.The control unit is activated at every Key on and resets the headlamps to the exact distance (calculated depending on the vehicle load) which consists of completely lowering and then positioning the reflector.The load sensor signals are periodically acquired and a suitable average taken in order to readjust the position of the headlamp if necessary (e.g. fuel consumption whilst driving). This adjustment is not immediate, but is filtered over time to avoid undesired corrections (e.g. if there are potholes, uneven road surface, etc.).This correction is also made with the lights off, so that the moment the beam is switched on it is already correctly positioned.Load sensors
The sensors are fastened to the vehicle bodyshell, whilst a suitable shaped lever follows the movement of the suspension.The sensor receives a power supply from the headlamp control unit and provides a linear output signal proportional to the position of the suspension in relation to the bodyshell.A - Part fastened to the bodyshellB - Part fastened to the suspension linkagea - Lever angleV - Sensor output signal voltageAdjustment actuator
A stepping actuator inside the light cluster carries out this adjustment. It consists of an electric stepping motor and a worm screw reduction unit which transforms the rotary motion of a hinged push rod into linear motion by means of a ball joint on the reflective surface.Self-diagnosis
The electronics that manage the system have an autodiagnostic function that continuously checks operation.The control unit carries out continuous self-diagnosis of system operation. In particular it detects and stores any faults.The faults memorized in the control unit can be analyzed using the Examiner or other diagnostic equipment.Recovery
The autodiagnostic management logic also has a recovery function: if errors are detected, the system no longer works properly and therefore the incorrect adjustment of the light beam could be dangerous and dazzle other vehicles.The light beam is therefore positioned downwards in order not to dazzle anyone, but allows sufficient light to drive safely to a service centre.Resetting
If the master control unit (in the left headlamp) is replaced, a self-learning procedure must be carried out, connecting to the diagnostic equipment, which makes it possible to automatically reset the system which should recognize the the position of the headlamp correctly aligned in position 0 from where the various adjustments can be set.
