| With the rapid development of the domestic economy and people's living standard, now vehicle automatic air conditioning control system have become essential in the automotive product units. Air conditioning is one of the big assemblies in the vehicle, and also one of the four vehicle environments (which content of audio, lighting, instrumentation meters and air-conditioning).Therefore, air-conditioning is a very important component for vehicle, and also an important quality index of a car.As one of the important technical means in vehicle air conditioning, air conditioning technology is getting more and more attention by the researchers and manufacturers.The product that designed in the paper will be used in the truck, engineering vehicles and special vehicles, etc. Different from the products that used in the cars, the new one will be comfortable, reliable, economical and lower in fuel consumption. Taking into account the complexity of the climatic conditions in China, the air-conditioning system must be adapt to high and low temperature, dry climate, high humidity and other bad climatic conditions.Based on the overall plan and design scheme of the project, design platform was chose. We chose the original manual air-conditioning system as reference platform which help us use the mature parts of original air-conditioning system which can reduce development costs.Refer to the research of similar automotive air conditioning and the original one, we made the technical program, design principles and technical requirements of the project, With the changing work environment and lack in insulation, vehicle air conditioning is nonlinear, multi-interference and delay system. The traditional PID method is difficult to achieve the desired control effect because of the difficult in control models, Based on the research at home and abroad, the paper proposed the fuzzy_PID control strategy with variable parameters to control the in-vehicle temperature based on fuzzy theory and PID control method.Comparing with the characteristics of traditional PID control, fuzzy control and fuzzy PID control method, the traditional PID control is stable, simple, reliable, but it is difficult in process parameters and mathematical model determining. Fuzzy theory has advantages in modeling, but it can't avoid the steady-state error. Fuzzy-PID method can on-line adjust parameters to meet the needs of precise control of temperature. So it was used as a temperature control strategy.In the fuzzy-PID controller design scheme, input variables of the fuzzy controller content of error and rate of change of error, and the output variable is PID control parameters. Fuzzy-PID controller design steps are summarized as follows: parameter calibration→definition of fuzzy sets→determination of the fuzzy control rules for solving fuzzy control table→the amount of system control.Based on the design scheme of the project, mathematical model of heat was established. With the input of temperature outside of the vehicle, light intensity and speed, based on the Fuzzy-PID controller, the air conditioning system control the speed of rotation of fan and air door opening to keep the temperature inside the vehicle and automatically select the appropriate target of the air mode. System simulation under the same conditions using different control strategies were compared between the steady-state analyses of the corresponding method. We compared the different control strategies with the simulation system under the same conditions.The conclusion shows that the traditional fuzzy control system has short respond time, but steady-state error always exists. And the PID control system response is slow. But the fuzzy PID controller we chose in the paper has moderate response rate and has no steady state error. So it can comfort the use of the air-conditioning system.Based on the detailed design in function and real-time information of internal and external environment, we designed the hardware and software of the air-conditioning system which consist of controller, anti-interference, communication protocols, etc.The hardware of controller mainly consists of input module, output module of control signal, CAN communication module and the information display module. Input module gathers the temperature inside the vehicle and temperature and light intensity outside of the vehicle. The data then will be the input of the MCU. The output module is responsible for storage and computation and output of data. Display module will display information through human-machine interface.The software of the controller mainly has the function of signal collecting, key scan, motor driving, implementation and show of control algorithm, transmission of CAN bus data and temperature control. The system software is designed with structured programming methods.Anti-jamming capability of the whole system is an important indicator of system reliability. We designed the hardware and software considering of the anti-jamming capability.Fault diagnosis of air-conditioning system is carried out for the sensors and actuators which can be divided into sensors diagnosis and implementing diagnosis based on content. The system diagnosis can be got through electronic circuit components.System CAN communication protocol is written based on the SAE J1939 criterion. So the communication protocol supports basic physical layer with the use of extended frame mode which has baud rate 250KBPS for J1939.The communication protocol supports data link layer and commands and request or response and multi-packet data transmission for J1939.In the final, we test the air-conditioning control system with the real data. The results show that the steady-state response and transient response of the whole system are in line with the design requirements. The experimental result is close to the simulation results under steady state conditions. The value of the difference between the target temperature and real data is less than 0.5℃.The analysis of the result shows that the whole system can well meet the design objectives.
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