The Power of Air : The Theory of Air Bearing

We use many different types of rotary engines and motors in our daily lives and one of the most important elements for ensuring these motors run properly is lubrication. There are various types of lubrication methods that can be implemented in a rotary motor. One of the most common motors we use every day is a car engine and motor oil is used to lubricate and seal car engines so that they run smoothly. Even small motors need grease for lubrication. Air conditioners are no different. Air conditioners require oil and grease for lubrication as well.
In products such as refrigerators and air conditioners with compressors, lubrication for the compressors is most important. Large-scale centrifugal chillers used for cooling large buildings use high speed rotary engines to compress refrigerant and lubrication of these engines is also very important. What’s more, since the lubrication must be circulated along with the refrigerant, different types of oil must be used depending on the type of refrigerant in order to maintain viscosity and these oils can be very expensive. A compressor can actually combust if it runs without oil for as little as 5-6 seconds and there are multiple components required for the oil circulation system. Equipment such as oil filters, oil pumps and oil tanks must be maintained and if one of these elements fails, the refrigeration system is prone to serious damage. If the cycle is not managed to match the load of the system, controlling the oil flow becomes difficult and the entire system can fail as well.

Figure 1. Oil components for an air conditioning system

In order to overcome these difficulties in managing an oil system, compressors that do not use oil are being developed. Methods such as magnetic bearings and ceramic bearings are being used to improve the durability of the bearing systems. Magnetic bearings use electromagnetic energy to create a repulsive force between the motor shaft and the bearings themselves.

Figure 2

As shown in figure 2, the core of this technology is the ability to detect the rotor location with sensors and maintain the proper rotor position using electromagnetic force.

Figure 3

Air bearings is another method of used in place of lubrication. Air bearings uses the pressure from the refrigerant in an air conditioner itself to create space between the shaft and the leaf of the rotor. When the motor is stationary, the motor shaft drops down and the leaf does not receive pressure from the system and it makes contact with the shaft. Because of this, the shaft begins to rotate at a low speed and slowly builds up pressure to the leaf which raises the shaft and creates space between the shaft and the leaf. As the rotation speed of the shaft increases, the pressure stabilizes and a controllable space is maintained between the shaft and the leaf to run the air conditioner with oil lubricant. (Figure 3)

Figure 4. Air bearing

The air bearing structure is simple and since there is no contact between any substance and the components, there is no friction in the system and it runs more efficiently. Where trouble can occur is when the motor is stationary and the shaft and leaf make contact. However, LG Electronics has developed a specialized coating technology that prevents damage at this point and has tested the procedure over 10,000 times without any abnormalities.

There are many alternatives to oil lubrication systems including magnetic bearings and ceramic bearings as mentioned above. But a highly efficient alternative that is growing in popularity is the air bearing system, which LG Electronics has improved with its innovation technology. We can expect to see more of these air bearing systems implemented in the future and LG Electronics will continue to develop technology to enhance them.

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