LIN bus-based automotive HID headlamps automatically dimming system
HID is a high-pressure gas discharge lamp (High Intensity Discharge) acronym, heavy metals can also be referred to as xenon lamps or headlamps. Compared with the traditional halogen lamp, HID has high brightness, long life, energy saving advantages.
HID is due to the characteristics of high brightness, if exposure to a high degree of regulation when used properly, will be at the bus drivers head to the eye caused by strong, resulting in potential safety problems. HID headlamps in order to regulate the market, the United Nations Economic Commission for Europe (United Nations Economic Commission for Europe) in the ECE-R48 Terms and Conditions: HID headlamps of vehicles and equipment must be equipped with automatic regulation of its exposure to a high degree of systems can be called the level of automatic headlight dimming system. The system will, in accordance with changes in vehicle load HID headlights automatically adjust the pitch of the projection point of view, to ensure that its projected altitude of the scope of the right not only to achieve good lighting effects, not on the face of dazzling drivers of vehicles.
As shown in Figure 1, the system can be divided into three parts, namely a high degree of sensor body, the central control unit and drive the implementation of modules. System works as follows: The system is the main mcu (MC68HC908GZ60) collected before and after body-axis height of the sensor signal, issued by the operator control signal, respectively, to about the level of dimming headlamp stepper motor, rotating motor instructions to the designated location, complete the automatic dimming.
Figure 1 Automatic headlamp dimming system design
System hardware design
Body height sensor
The main principle of the system is to use two reference points for determination of the car (about before the rear axle location) to arrive at the ground from the bad angle of the vehicle signal, thus to the level of regulation. Optical encoder may choose to car-like high-sensors, the changes in body height (suspension deformation changes) converted into the rotation axis sensor to detect the rotation angle of the signal into a voltage signal input MCU. Experiment, the body height of the sensor in the vehicle left front wheel and left rear of the equipment inside a.
Central Control Unit
System used a central control unit Freescale (Freescale) produced mainly MC68HC908GZ60 chip MCU, along with other necessary circuit components control unit. The main characteristics of the chip are as follows: 8-bit HC08-type CPU, the development of resource-rich, good compatibility; chip 60KB flash EEPROM, 2KB RAM; 24-channel A / D converter module, 10-bit precision.
In addition, the choice of Freescale MC33399 chip with the MCU core linked through SCI population, as a LIN bus transceiver. The chip can drive up to 16 nodes.
LIN bus was chosen because it is the motor bus in a more popular, had the advantage of low chip prices, cost-effective. LIN bus signal transmission rate of 19.2kbps, which tends to be used in less demanding on the vehicle security control of occasions, such as electronically controlled doors and windows, the lights switch control.
LIN bus master node circuit schematic diagram shown in Figure 2.
Figure 2 LIN bus master node circuit schematic
Drive the implementation of unit
Drive the implementation of modules, mainly through the acquisition of the LIN bus signal, to control the stepper motor rotation, which led headlamp reflector plate rotation along the vertical direction, the completion of the level of dimming.
The United States here to select AMI Semiconductor's AMIS-30623 stepper motor control chip. The chip is a highly integrated chip, built-in power module, controller, LIN bus transceiver and stepper motor driver. Its main features are: the peak value of current output up to 800mA; to provide a breakdown of up to 16 the number of stepper motor driver; built deceleration algorithm; LIN1.3 specification is fully compatible.
AMIS-30623 as a result of the chip itself can not be re-programmed, and all operations are called through the LIN bus to the completion of its internal function, it is very easy to use. Built-in speed control algorithm for variable-speed stepper motor sport very effective.
LIN bus slave nodes schematic circuit shown in figure 3.
Figure 3 LIN bus slave nodes schematic circuit
System software design
Software, the use of 1ms interrupt regular collection, the arrival of each disruption to take a group of sensor output voltage value. After pre-judgment, a reservation will be valid data, into the formula, drawn to the need for rotation of stepper motor target locations. Through the LIN bus to the AMIS-30623 chips send signals to control the stepper motor according to speed up - speed - speed way of a smooth movement to the appropriate location. The program in the Freescale CodeWarrior 5.7.0 compiled through the environment. The main program flow shown in Figure 4.
System, the main program flow chart of Figure 4
The experimental results
In order to verify the system's dynamic dimming performance, in the laboratory environment to build up a body to simulate the experimental platform pitch movement. Experimental process, the control platform itself for a certain range of pitch movement, measured dimming system step response time of about 420ms, the adjustment time of less than 1s, steady-state error of about 0.035 °, to meet the dynamic auto-dimming of the basic requirements.
The system of vehicle automatic headlamp dimming the basic functions, to further the development of more complex adaptive headlamp system (Adaptive Frontlighting System) laid the foundation.
In addition, the system is based on the LIN bus and a low-power single-chip stepper motor control system. LIN bus as a low-cost fault-tolerant of strong local bus, in the automotive and industrial control environment, such as Chiang Kai-shek to be applied more widely. The system is easy to develop, easy maintenance, low-cost, add up to 16 sub-node, the node before and after the change is fully compatible with the software without re-programming. Therefore, the low-power design in the field of stepper motor control of the promotion of a certain value.
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