An electric vehicle air conditioning controller based on single chip computer is studied. It has the advantages of low cost, accurate temperature control, simple, convenient, energy-saving and pollution-free, and has good application and development prospects. It is an inevitable trend for the development of automobile industry that new energy vehicles gradually replace traditional petroleum energy vehicles. As a typical representative of them, electric vehicles have made rapid development in recent years. With the improvement of people’s living standard, people’s requirement for comfort of car interior environment is becoming higher and higher.
Among them, automobile air conditioning as one of the important indicators of automobile comfort, has a good research and development prospects. This paper studies an electric vehicle air conditioning controller based on single chip computer. The controller has the advantages of low cost, convenient use and easy mass production.
The structure block diagram of the air conditioning controller described in this paper is shown in Fig. 1. From the diagram, it can be seen that the controller is mainly composed of Freescale MCU, in-car and out-of-car temperature sensor, blow-face and foot temperature sensor, evaporator temperature sensor, function keys, mixed mode internal and external circulating actuator, blower module, compressor module, etc. Composition, controller and compressor, controller and vehicle control unit (VCU) use CAN communication protocol for real-time communication. The air conditioning controller can work in both automatic and manual modes. When the user presses the AUTO button and sets the target temperature by the button, the air conditioner works in the automatic mode. The controller continuously adjusts the speed of compressor and blower according to the data collected by the temperature sensor in the car until the temperature in the car reaches the target temperature set by the user. When the user does not press the AUTO button, the air conditioner works in manual mode by default. The user needs to manually select the speed of the blower and the opening of the mixed door knob to control the air volume of the air outlet and the ratio of hot and cold air. Sensors such as in-car temperature sensor, out-of-car temperature sensor, face-blowing temperature sensor, foot-blowing temperature sensor and evaporator temperature sensor are all resistive temperature sensors. The principle of the temperature measuring circuit of the sensor is that the external resistive sensor is connected in series with the resistance of known size to form a voltage dividing circuit [2]. Feedback voltage value from voltage divider.
MCU collects feedback voltage value through AD port. Through calculation, resistance value of external sensor can be obtained and converted to corresponding temperature. This design needs 12V and 5V power supply. Because the on-board power supply can provide 24V DC power output, thermostatic element it needs to design 24V to 12V and 12V to 5V circuits. The 24V to 12V circuit mainly supplies power to 12V equipments such as blowers. LM2596-12 power supply chip is used. When 24V input is input from one pin of the chip, 5V voltage will be output at two pins.
V power supply mainly supplies power to MCU and valve actuators such as mixing, mode, internal and external circulation. LM78L05 is a voltage conversion chip, which can convert the input 12V voltage to 5V voltage output [4]. Therefore, when the 12V power supply is connected to the chip, 5V output can be obtained. This controller mainly includes AUTO automatic air conditioning keys, temperature adjustment keys, internal and external circulation keys, mode selection keys, temperature selection keys, air volume selection keys and so on. One end of the circuit is grounded, the other end is connected with 5V power supply, and then the two ends of the capacitor are connected with keys in parallel. When the button is not pressed, the 5V power supply charges the capacitor. The MCU collects the high level. When the button is pressed, the MCU collects the low level. Therefore, the MCU can judge whether the button is pressed by collecting the level of the capacitor non-grounding terminal. The system controller adopts Freescale MC9S08LG32 single chip computer and builds the minimum system according to the chip datasheet. The valve actuators, such as mode, mixing, internal and external circulation, are driven by NCV7708 driver chip. NCV7708 contains six half-bridges, which can form three full-bridge control motors. NCV7708 motor driver chip is controlled to control three valve actuators: mode, mixing and internal and external circulation.
The flow chart of the system program is shown in Figure 2. This paper studies an electric vehicle air conditioning controller based on single chip computer. The controller has the advantages of low cost, accurate temperature control, simple, convenient, energy-saving and pollution-free. It can be well applied in electric vehicles, and has a good development and application prospect.