Automotive Intelligent Lighting System Based On CAN Bus

Since automobile is invented, its safety problem has been widely concerned by people all the time. According to statistics, there are about millions of people dead in traffic accidents every year. With the number of automobiles growing, the technology of automobile safety has got more and more attention. As one of the three major safety units in the automobile, lighting system is the most important part of automotive safety devices, which provide driver a good eye sight in the night.Currently, the automotive lighting system is undergoing a significant change. Not only kinds of light material are used more widely, but also the system is getting increasingly intelligent, which makes automobiles can provide the best lighting according to a variety of complex and difficult situations. So the drivers can concentrate on judging the driving situation correctly with more time and focus, and take proper actions to exclude some existing dangers, and make safety and comfort possible during driving.Automotive intelligent lighting systems can be identified as a device which can change light according to driving environment and weather conditions. It can provide drivers a more clear visibility. After introducing the components of intel- ligent lighting system, combined with the existing technical means and capability, this paper identifies the types of lights and control objectives in this lighting system for intelligent control. The main work covers:Identify the control objective of high beam, dipped headlight as the illumi- nation distance of the moving lights, whose value should be at least greater than the braking distance when the automobile encounters obstacles and emergency. And identify the control objective of rear fog light as compensating the light intensity according to different weather conditions. According to control objectives of high beam, dipped headlight and rear fog lamp, this paper designs and implements the intelligent lighting control system; proposes the measurement and implementation method of speed, humidity, and other parameters; raises the light controlling algorithm and its implementation; establishes the CAN bus networks to transfer the parameters needed by the lighting control nodes. The parameters are acquired from the constructed JETTA CI lighting system. The whole system design includes the following parts:1. Design the intelligent control strategies.After studying on the premise of meeting the national standards of GB4599 -1994, GB4785-1998, GB7258-2004, and GB11554-1998, this paper details the intelligent control strategies of high beam, dipped headlight and rear fog lamp in automobile lighting system, and uses the deduced control strategies to guide the strategies lighting control node to implement intelligent control.2. Design and implement CAN bus communication system.This system uses the CAN bus with high efficiency and reliability to transmit the parameters acquired by collection nodes, and then sends them to lighting control nodes to implement intelligent control. At the same time, this system designs and implements the hardware structure of CAN bus, based on which the software function is designed and the application layer protocols are defined:(1) Specify the allocation scheme of the CAN flags and define the priorities of all frames.(2) Set the bytes limit of transmission data. On the premise of basic functions, the smaller the data length is, the data transmission time is, smaller and more stable.(3) Identify the information element definition, which can make the message user and definer understand the meanings and types of each datagram more easily.3.Design and implement system communication mechanismThe system designs a central control node, which is the heart of the system nodes and controls information transmission on CAN bus. Central control node reads the parameters acquired by collection nodes regularly, saves and updates the collected parameters in buffer. Meanwhile, it scans the light state regularly. If the state is on, based on the type of lights, the necessary environmental parameters are retrieved from the buffer and transferred through CAN bus with the lights order information to the corresponding light control node. If the state is off, the system sends order to close light.4. Design and implement the parameters acquisition nodes in intelligent control(1) Speed Collection NodeThe control of high beam and dipped headlight needs automobile's speed information in intelligent control system. Whereas Jetta uses the pulse method to measure automobile speed, this paper designs the speed collection node based on the pulse method.(2)The Light Intensity Collection NodeIn the intelligent control system, the light intensity information is needed to control the rear fog light. This paper uses a photosensitive resistivity measurement to get the light intensity information and converts the light intensity values to electrical signal, by which the level of the light intensity is assessed.(3) Humidity Collection Node:When fogging, the consistency information is needed to control the dipped headlight and the rear fog light. According to the character of relative humidity in fog weather greater than 90%, this paper uses humidity sensor to measure the relative humidity values which can be converted to electrical signal and used to assess the fog consistency.5. Design and implement the lighting control nodes in intelligent controlBetween high beam and dipped headlight, the control strategy is different, but the hardware structure of the angle controlling circuit is same. In addition, the light intensity controlling circuit of the rear fog light can be accomplished by the controlling circuit of high beam and dipped headlight. Hence, the hardware circuit of the three lighting controlling node is composed of light intensity control and angle control.The light intensity of the lighting control node is accomplished by A/D converter and magnifier. The angle control of the lighting control nodes are accomplished by controlling stepper motor. Due to the restriction of Jetta lighting system, this paper doesn't transform the mechanical structure of lightings. The angle control experi- ment is confirmed by counting the step of stepper motor.Finally, our theory on high beam, dipped headlight and rear fog lamp is validated by automobile bench test. The automobile lamp is changed according the anti- cipated result as the traffic environment is changed.