The problem of automobile air conditioning

1. Working principle of automobile air conditioner

In fact, the refrigeration principle of automobile air conditioner is the same as that of our familiar household air conditioner. They all use the principle that when R 12 or R 134a is released by compression, the rapid expansion of the volume will absorb a lot of heat energy for refrigeration. Due to the destruction of ozone layer by R 12, developed countries began to use R 1996 as refrigerant for environmental protection. The structure of automobile air conditioner is similar to that of household split air conditioner. Its compressor is often installed on the engine and driven by belt (or directly). The condenser is installed in front of the radiator of the car, while the evaporator is in the car. When working, the low-pressure gaseous refrigerant coming out of the evaporator flows through the compressor to become high-pressure and high-temperature gas, which is cooled by the condenser radiator pipe and becomes high-pressure and low-temperature liquid. After being dehumidified and buffered by the liquid storage dryer, it flows to the expansion valve at a relatively stable pressure and flow rate, and finally flows to the evaporator after throttling and depressurization. Refrigerant will evaporate in low pressure environment and absorb a lot of heat energy. The air in the carriage continuously flows through the evaporator, so the temperature in the carriage decreases. After the liquid refrigerant flows through the evaporator, it becomes low-pressure gas again and is sucked into the compressor again for the next cycle. In the whole system, the expansion valve is the mechanism to control the refrigerant to enter the evaporator. If too much refrigerant enters the evaporator, it will not evaporate easily, and too little cold air will not be enough. Therefore, the expansion valve is the adjustment center. The compressor is the heart of the system and the power source of system circulation.

Although the principle of automobile air conditioning system is the same as other air conditioning systems, automobile air conditioning is a mobile vehicle air conditioning. Compared with the fixed air conditioning system, its dynamic and rotating conditions are worse. With the chattering of the car, the refrigerant in the air-conditioning system leaks more easily than that in the fixed one, and the air-conditioning system is maintained more frequently than that in the fixed one. The air duct system of air conditioner often sucks dust when inhaling fresh air, blocking the filter screen and evaporator, and often releases refrigerant into the atmosphere when cleaning. Leading to ozone depletion and damaging the environment.

2. Composition of automobile air conditioner

Generally, automobile air conditioner is mainly composed of compressor, electric control clutch, condenser, evaporator, expansion valve, liquid storage dryer, hose, condensing fan, vacuum solenoid valve, idle machine and control system. Automobile air conditioners are divided into high-pressure pipelines and low-pressure pipelines. The high-pressure side comprises a compressor output side, a high-pressure pipeline, a condenser, a liquid storage dryer and a liquid pipeline; The low-pressure side includes evaporator, accumulator, air return pipe, compressor input side and compressor oil pool.

Liquid storage dryer is actually a device for storing refrigerant and absorbing moisture and impurities in refrigerant. On the one hand, it is equivalent to the fuel tank of a car, which supplements the extra space for the leaked refrigerant. On the other hand, like an air cleaner, it filters out impurities doped in refrigerant. The liquid storage dryer is also equipped with a certain silica gel substance to absorb water.

Condenser and evaporator-although they have different names, they are similar in structure. They are all devices that cover a row of winding pipes with metal sheets to dissipate heat, so as to realize the heat exchange between the outside air and the substances in the pipes. Condensation of condenser refers to the condensation of refrigerant from gas to liquid in its pipeline. Its principle is similar to the engine radiator water tank (the only difference is that the water in the water tank is always liquid), so it is often installed in the front of the car to enjoy the cool wind from the front with the water tank. In short, it is the place where the condenser is cold, so that it can radiate heat and condense. Evaporator and condenser are just the opposite, and condenser is the place where refrigerant changes from liquid to gas (that is, evaporates) to absorb heat.

Compressor is the heart of air conditioning refrigeration system and the power source of circulating refrigerant in the system.

Pipes-Metal pipes must be used, because a certain pressure of refrigerant is injected. Especially from the compressor to the condenser to the refrigerant bottle and then to the expansion valve, because it belongs to the high pressure section of the system, the requirements for high pressure resistance are higher than other pipelines.

Compressor-As the name implies, the compressor plays the role of compression, and its function is to make the refrigerant complete the transformation process from gas to liquid, so as to achieve the purpose of cooling and condensing the refrigerant. At the same time, in the whole air conditioning system, the compressor is also the pressure source of the running medium in the pipeline. Without it, the system will not only not cool down, but also lose the power to run.

Classification of compressors:

Piston: The structure of piston compressor is similar to that of engine, including crankshaft, connecting rod, piston and cylinder. However, because it does not generate energy, there are no fuel nozzles and spark plugs. Because of the large space of long-distance trucks or buses, piston compressors with large volume and small loss are often used.

Swashplate: Swashplate compressor is used for ordinary cars and small commercial vehicles. It is widely used because of its small size, light weight and easy installation and layout in a narrow engine room.

Although there are great differences in structure, in fact, these two kinds of compressors convert the kinetic energy of engine rotation into the reciprocating motion of the piston in the compressor, which forms pressure on the pipeline of air conditioning system and achieves the purpose of compressing refrigerant.

Car air conditioners don't need to stop for three minutes after each shutdown, like home air conditioners. In fact, the car air conditioner should be turned on once a week even in winter, so that all parts are lubricated. In addition, check the dust screen. If there is too much dust attached, it should be replaced in time. It is best to wash the condenser of the front of the car with a high-pressure water gun every time you wash the car, so as to avoid the cooling blades from being blocked by sundries (insects, leaves, etc.). ) and affect the cooling effect.

It is worth mentioning that the rotating shaft of the compressor is connected with the crankshaft of the engine through a magnetic clutch and a belt to obtain power. Why is there a magnetic clutch? Because when the sensor installed at the outlet of the evaporator senses that the temperature of the wind is not low enough, it will close the electromagnetic clutch of the compressor through the circuit, so that the compressor can run with the engine to realize refrigeration. When the air outlet temperature is lower than the set temperature, the electromagnetic clutch is controlled to cut off, so that the compressor does not work. If this control fails, the compressor will continue to work, causing the evaporator to freeze and the pipeline pressure to exceed the standard, which will eventually destroy the system and even cause damage.

At present, most automobiles (mainly civil automobiles) use two kinds of refrigerants: R- 12 refrigerant and R- 134a refrigerant. R- 12 refrigerant is a common refrigerant, which contains substances that will destroy the ozone layer-Freon, which will produce substances harmful to human body when exposed to open fire; R- 134a is a new type of environment-friendly refrigerant, which is non-toxic, colorless, non-flammable and non-explosive, and has good thermal stability. More importantly, R- 134a refrigerant will not destroy the ozone layer.

The chemical structures of these two refrigerants are different from each other, so they are not common in automobiles. Moreover, the refrigeration oil they use together is also immiscible. If the refrigerant is added improperly, it will damage the system, such as the corrosion of rubber hose. The reason why R 134a is used instead of R 12 is that its thermal properties are similar to R 12, and it is a chlorine-free freon with zero ozone destruction system. Therefore, R 134a, which is often referred to as environmental protection refrigerant, has basically been used in new cars.

3. Classification of automobile air conditioning system (by power supply)

1. Independent air conditioning: There are special power sources (such as two internal combustion engines) to drive the whole air conditioning system. Generally used for long-distance freight, high-floor buses and other vehicles. Independent air conditioning needs two engines, which leads to high fuel consumption, high cost and great difficulty in maintenance. It requires very skilled engine maintenance personnel, and engine accessories are not easy to obtain, especially imported engines. In addition, design and installation are more likely to lead to system quality problems, and additional driving engines increase the probability of failure.

2. Non-independent air conditioning: an air conditioning system that directly uses the driving force (engine) of the car. The dependent air conditioner is driven by the main engine and controlled by the electromagnetic clutch. When the power supply is turned on, the clutch is disconnected and the compressor stops, so as to adjust the supply of cold air and achieve the purpose of controlling the temperature in the compartment. Its advantages are simple structure, convenient installation and arrangement and low noise. Because it needs to consume the power of the main engine 10%- 15%, it directly affects the acceleration performance and climbing ability of the car. At the same time, its refrigeration capacity is affected by the vehicle speed. If the car stops running, its air conditioning system will also stop running. Nevertheless, dependent air conditioners have gradually become the leading products in the market because of their low cost (relatively independent air conditioners) and excellent quality. At present, most cars, vans and minibuses use this kind of air conditioner. Non-independent air conditioning at present.

Four. Characteristics of automobile air conditioning system

(1) The air conditioner vibrates greatly during operation.

As mentioned earlier, the automobile air conditioner is a mobile vehicle air conditioner. Because the road is uneven, the car bumps and vibrates greatly during driving, so the connecting pipeline in the device should adopt flexible refrigerant pipeline.

(2) The condenser is close to the radiator of the engine, so its condensation temperature is often low and high, so its working conditions are worse than other air conditioning devices.

(3) The compressor of the automobile air conditioning system is directly driven by the engine and realized by the belt transmission mechanism. When the compressor is not working, it can be disconnected from the engine, which is realized by electronic clutch. When the air conditioning system stops working, the tightness of the belt should be checked frequently to determine whether the clutch operates correctly. Sometimes the clutch affects the compressor shaft seal due to bearing damage, resulting in refrigerant leakage at the compressor shaft seal. Therefore, check the early signs of clutch bearing damage.