Development Of Automobile Air Conditioner Control System Based On CAN Bus

With the development of domestic automobile industry, automobile manufacturers value the automobile air conditioner highly more and more. It is an important factor to evaluate the performance for automobile. Manual air conditioner control system can not do some automatic control, such as ambient temperature, intensity of sunlight, development of shade, driving speed. The control quality is not so good and it needs driver to operate which will increase driver's workload. As a general technique to increase national competition, the research and development of automatic air conditioner will be the international focus for decades.This paper centers on the scientific and technological project of Changchun city which is named"BCM based on multi-bus connection". By using CAN bus technology, we have realized automobile air conditioner control system which has been connected to a whole network. We have developed the protocol according to SAE J1939. And then we implement the air conditioner automatic control preliminarily by using increment PID control algorithm.The traditional air conditioner control system used the way of direct control and the equipment are independent with each other. They are dependent on steel cable and vacuum valve for control. This way is inefficient and increases the workload of drivers. The networking of automobile air conditioner control system has changed the relationship between the controlled object and the controlled signals. According to the practical require different nodes on the network have different functions: signal collection nodes collect control signals from the network. And control nodes execute kinds of control functions. The nodes connect with each other by bus and share the information through the bus too. The data can transfer reliably according to the protocol. The control signals collection nodes send these signals to bus network. And then the control nodes monitor the bus to receive the relevant data. After that, we realize the control logic and control algorithm by software. At last, we complete the control function by intelligent equipment.The way of transferring information between nodes is described in CAN protocol. The system refers to the SAE J1939 which is widely used in automobile electronics field. Then we work out a protocol for the system. The SAE J1939 protocol is developed by the Truck and Bus Control and Communications Network Subcommittee of the Truck and Bus Electrical and Electronics Committee. Their goal is to build a standard which can connect different in-vehicle electrical systems. The design of the protocol includes Physical Layer, Data Link Layer, Network Layer and Application Layer. The protocol of Application Layer provides the information format, the information direction and information detail. We should consider that the protocol must be integrated, compatible and expansible.There are eight nodes in the system: control node, temperature collection node, display node, air mixture door node, blower node, air intake door node, center air outlet node and defrost/floor node. The temperature collection node collects the internal temperature by temperature sensor and then sends the temperature to the control node. The air mixture door node controls the mixture of cool air and warm air to control the temperature. The blower node controls the speed which intake to the car. The air intake door node is responsible for choosing the way of air intake. The center air outlet node controls the way how the mixture air blow into the car. The defrost/floor node is responsible for choosing the mode of defrost and floor.All the nodes above must send their state information to the control node. According to the information, the control node sends the relevant commands to them. At the same time, the control node sends the information to the display node. After receiving information, the display node displays the information on its liquid crystal display.In this system, we use the following circuit:Control node: CAN controller SJA1000, CAN driver PCA82C250, microcontroller 89S51, keyboard.Temperature collection node: CAN controller SJA1000, CAN driver PCA82C250, microcontroller 89S51, temperature sensor AD590, A/D converter ADC0804, operational amplifier UA741. Display node: CAN controller SJA1000, CAN driver PCA82C250, microcontroller 89S51, liquid crystal display LCD1602.Air mixture door node: CAN controller SJA1000, CAN driver PCA82C250, microcontroller 89S51, stepping motor, driver L298N.Blower node: CAN controller SJA1000, CAN driver PCA82C250, microcontroller 89S51, direct-current motor, driver L298N.Air intake door node: CAN controller SJA1000, CAN driver PCA82C250, microcontroller 89S51, direct-current motor, driver L298N. Center air outlet node: CAN controller SJA1000, CAN driver PCA82C250, microcontroller 89S51, LED.Defrost/floor node: CAN controller SJA1000, CAN driver PCA82C250, microcontroller 89S51, LED.The software programs is consist of node initial program, CAN send/receive program, stepping motor driver, direct-current motor driver, temperature collection program, liquid crystal display program, keyboard interface program and serial port transferring program. Node initial program will lead the node to work. CAN send/receive program will connect all nodes in the system. The stepping motor driver can make the stepping motor rotate at a given strategy. The direct-current motor driver is responsible for driving the direct-current motor. The liquid crystal display program will display the relevant information. The keyboard interface program can ensure that the inputs are correct and stable. Serial port transferring program is used to debug other programs and watch over the speed of them in time.The automobile air conditioner control system is implemented in this paper. By using CAN bus, automobile air conditioner control system will develop to networking and intelligence. The networking model of air conditioner control system is implemented. We have realized the system with eight nodes. We study on automatic control, and this will become a foundation of BCM based on multi-bus connection in theory and practice.