Auto Adaptive Headlamp Technology Discussion

As the fourth generation of automotive light sources, LEDs have many advantages over other traditional light sources. This paper analyzes the feasibility and advancement of automotive LED lighting, introduces its typical driving circuit, and focuses on the application of LED and AFS in automotive headlamps. The problems and countermeasures of LED lighting for car are introduced, and the future development of the car LED is prospected.
1 automotive LED lighting feasibility and advanced
The use of light sources in cars started around the turn of the 20th century. The first to use kerosene lamps and acetylene lamps. Since 1910, they began to use electric light sources and experienced incandescent lamps, halogen lamps and Intensity Discharge Lamps (HIDs). Since 1985, they have entered the LED vehicle Light era. At the same time, the application of LED lights to the Adaptive Front Lighting System (AFS) has emerged.
At present, LED has been used by many car manufacturers to create a variety of lamp styles. Famous brands such as BMW, Ford, Honda, Toyota, Mercedes-Benz, Audi and others have introduced new sedans equipped with a variety of LED lights to attract customers in order to enhance their overall competitiveness. LED has many other advantages do not have the light source: (1) long life, good shock resistance. LED life expectancy theoretically up to 50,000 hours, the actual life expectancy up to 20,000 hours (ordinary halogen bulbs only 150 to 500 hours or so), generally have to exceed the life of the car itself. In addition, the basic structure of the LED is not vulnerable moving parts, so the seismic performance is very good. (2) Energy saving and environmental protection. LED in the low voltage and low current conditions can get enough brightness, the power consumption is only 10% ~ 20% of the same brightness incandescent lamp; LED light source does not contain mercury that endanger human health, the production process and waste will not Cause environmental pollution. (3) fast response. Compared with incandescent lamps, LED lamp response time has reached tens of nanoseconds, so that when the LED as a taillight, you can make the follow-up car drivers an earlier response to reduce traffic accidents. (4) small size. Small LEDs give the car more freedom and versatility to make the car more stylish; the LED light system can be installed at a depth of 80 mm less than traditional light sources, which is important for car styling and internal part placement .
At present, the automobile industry is still a pillar industry in the global economy and is in a critical period of rapid development. It will definitely promote the development of automotive lamps and provide a broad market space for the application of LED in automobiles.
2 car LED lighting drive circuit
LED is a current-controlled semiconductor device, Figure 1 is the LED's volt-ampere characteristic curve. As can be seen from FIG. 1, the curve is relatively steep, and almost no current flows through the LED before the forward voltage is turned on. When the forward voltage exceeds the turn-on voltage, the current rapidly rises, and the luminous brightness L is approximately proportional to the forward current IF: L = KIF, where K is a proportional coefficient, so you can control the LED brightness by controlling the IF. Therefore, in order to ensure the consistency of its brightness, usually using a constant current source driver circuit.
Automotive battery operating voltage range of 9 V ~ 16 V, usually 12 V, but when the car cold start the battery voltage can drop to 4 V, and when the battery defect by the generator directly when the voltage can reach 36 V high pressure. Therefore, for automotive LED lamps, to reliably drive constant current LED string, the drive controller must have accurate voltage and current regulation, protection circuit and dimming function. Therefore, it is necessary to design a driving circuit with good voltage regulation and constant current output.
The current automotive LED driver generally uses two methods to control the forward current. (1) The LED's V-I curve is used to determine the voltage required to apply the LED to produce the expected forward current. The disadvantage is that any change in the forward voltage of the LED can result in a change in the LED current, of which the voltage drop and power dissipation of the ballast resistor waste power and reduce battery life. (2) The use of constant current source to drive the LED. Because this method requires that the LEDs be connected in parallel in the circuit, driving the parallel LEDs requires placing a ballast resistor in each LED string, which leads to reduced efficiency and current mismatch. Therefore, these two methods can not fully reflect the LED should have the superiority. In order to overcome the shortcomings of the existing automotive LED driver, an intelligent and efficient driving method for the automotive LED array has emerged. The method uses the half-bridge DC-DC conversion technology, full-wave rectification technology, opto-electronic coupling technology, to ensure the efficiency of the entire drive circuit; proposed based on embedded system intelligent control scheme, this program uses intelligent PWM steady flow Control and dimming control, with load open / short circuit protection and over-current and over-voltage protection. Figure 2 for the LED array intelligent drive experimental circuit.
As shown in Figure 2, the CPU outputs two fully inverted symmetrical PWM signals A and B, acting respectively on the switching devices so that they turn on in turn. The high-frequency transformer T couples the energy to the secondary and then quickly resumes Diodes D1, D2 full-wave rectification, in order to achieve the LED array drive. LED array drive circuit optocouplers, LED array to complete the drive current monitoring and feedback to the CPU, the formation of a negative feedback current loop intelligent control system to ensure the stability of the drive current reliability.
The company is located in:
For Hyundai headlights configured, only enough brightness is not the only measure of their strengths and weaknesses of the only standard, not smart enough to reflect the technical standards of the level of headlights. Here's "smart" is the headlight in different weather and road conditions have different performance.
Traditional headlight lighting level control and direction
Decades ago people had thought of a solution to improve headlamp performance, except when the starting lineup looked primitive. On the Citroen 2CV model introduced in 1948, the driver can adjust the angle of the lighting by a lever connected to the headlight, so that the illumination range of the lamp is not affected when the vehicle load changes. Subsequently, the engineer installed a servo mechanism inside the headlight assembly, which can drive the headlights to change the irradiation angle entirely through the gear set. However, for a long time, this solution is only for adjusting the lighting distance. At present, many models with headlamp height adjustment function can be regarded as a derivative of this technology.
Directly forward headlights illuminate the road just in front, but the road is not always straight, encountered a corner, the direct light of the defects exposed. We can not see the inside of the bend before the vehicle enters the bend, which has the potential to affect the safety of driving. In the thirties of last century when electronic technology was not yet enlightenment, the solution that people came up with was still purely mechanical. Some car companies think of using the third headlamps connected to the steering mechanism to illuminate the road in the curve. According to this program, the third lamp can be turned around with the turning angle of the steering machine, basically meeting the needs of the curve lighting at that time.
These are the means by which engineers improved their headlamps during the Enlightenment. Today, as the road becomes more complicated and faster and faster, the integration of electronic technology into headlamps has become a trend of the times.
AFS headlight system
For the current variety of active headlight systems, the industry has a proper noun --- Advanced front-lighting system. The cut is the AFS Adaptive Headlight that we often see in the new car configuration table. But in fact many headlights used by manufacturers are not adaptive headlamps.
Unlike the previously described mechanistic solutions to the problem of headlamp lighting, today's AFS rely on electronic sensors to work. These sensors detect ambient light and then decide whether to turn on the headlights automatically; they also monitor the speed of the vehicle, body posture, etc. and adjust the headlight's lighting angle in good time. Since 2003, many automobile manufacturers such as BMW of Germany, Toyota of Japan, Czech Kodak and etc. all begin to dispose AFS to its products.
Automatic beam control
Set in the headlights of light near and far two lights, at what time choose to use which set of beams has become a new problem that many drivers stumped. Here Chinese drivers and American drivers in the lighting habits there is a clear distinction. A large part of domestic drivers like to turn on the high-beam lights at night, and the reason given is that they can irradiate the farther the distance and obtain a larger visual range. In the United States where the road lighting conditions are better, Drivers generally do not like to use high beam light. These two driving habits have a negative impact on safe driving, long-term high-light is easy to make the driver of the opposite car can not see the road, the low light at high speed and can not cover far enough distance.
There are two ways to solve this problem. The road laws and regulations are gradually being improved to guide the drivers to use the lights properly. Automobile manufacturers reduce the frequency of distracted drivers' attention while driving by means of technical means. As a result, automatic beam control system came into being. The system consists of a photoresistor and the circuits connected to it. The photosensitive resistor detects the light of the target vehicle during the meeting, and then automatically switches the high beam to low beam. When the opposite vehicle lights disappear, the high beam then automatically turns on. During the driving process, drivers no longer need to manually intervene with vehicle lighting. Automatically switching between near and far lights will not affect the driver's vision of the passing car. Driving on roads is safer than ever before.
However, subject to technical limitations, the ASF can not make an accurate distinction between lights emitted by vehicles or other external light sources at this time, and false positives can occur from time to time. The Jeep Grand Cherokee introduced in 2005 replaced the photoresistor with a digital camera, which has a good ability to distinguish the source of external ambient light. Since then, the camera-based AFS lighting system has become an important part of the vehicle's driving assistance system.
Intelligent lighting system
Intelligent lighting system came out in 2006, is a kind of five different light-emitting mode with bi-xenon bulb lighting system. The system offers five light patterns for city roads and highways, respectively, and incorporates enhanced fog lights, turn-by-turn lighting and active lighting.
Adaptive high beam lighting system
Adaptive highbeam assist is an adaptive high beam lighting system used by Mercedes-Benz in the market that was designed to prevent lights from affecting both the oncoming vehicle and the driver in front of the vehicle. The system was first applied to the 2009 launch of the Mercedes-Benz E-Class. The system can steplessly adjust the range of light irradiation, rather than a simple two-level switching far and near light. Depending on the traffic flow and the road lighting conditions, the high beam can extend from 65 meters up to 300 meters. This system also uses the camera as a light-sensitive element, so that the reliability of the work is greatly improved. Then Mercedes-Benz in the S-class, CLS and C-class models also applied this technology. Other vendors also have similar technology.
  Glare-free high beam and dot matrix headlights
Glare-free high beam and dot-matrix headlights can be seen as the highest level of the current headlight symbol. Glare-free high-beam headlamps are based on an adaptive high-beam lighting system, with the core components still being used for sensitive cameras. Part of its upgrade lies in the left and right two headlights can switch lighting modes independently. In the easy to affect the other side of the driver's headlamps can dynamically switch the lighting range, to ensure that it does not direct other drivers; the other side of the headlight is as far as possible to ensure adequate far lighting range for the driver to provide good Vision. Volkswagen's 2011 Touareg, Phaeton and overseas version of Passat became the first model equipped with this technology.
Dot matrix headlights
Lattice lights in the Mercedes-Benz camp was named the local lighting system. The high beam of a local lighting system consists of 100 LED light-emitting elements that can be individually activated by the system, so that when a car comes on-board, the system will precisely calculate the area in which other road users are located and close the Area-related LED. The system can do this with the help of an infrared camera. In addition, pure electronic modules used in the system respond much faster than the currently used mechanical shutter / roller technology.