Time：2020.01.02 Source：Roller Bearings Suppliers
To reduce exhaust pollution, the environmental protection departments of various countries have increasingly increased the requirements for automobile exhaust emission standards and increased the tax rate of large-displacement vehicles. Therefore, on the one hand, the majority of automobile companies are reducing the emissions of automobiles, and on the other hand, they are reducing the emissions of exhaust pollutants. The turbocharger uses the exhaust gas of the engine to drive the turbine to rotate, which in turn drives the compressor that is coaxial with the turbocharger to increase the pressure in the combustion chamber of the engine and increase its oxygen content. The turbocharger achieves a win-win situation of power and fuel efficiency without consuming the useful power of the engine. Therefore, the role of superchargers in automobiles is even more critical.
What is turbo bearings？
With the popularization and application of turbochargers, the requirements for automotive turbochargers are increasing day by day, and they are required to have high efficiency and long enough life under severe conditions of high temperature and high speed. As a critical moving part of a turbocharger, its structure is related to the reliability and durability of the turbine.
Types and comparison of turbocharged bearings
Turbocharger bearings are mainly divided into two categories, one is floating bearings, and the other is rolling bearings.
At present, turbocharger bearings mostly adopt floating bearings, that is, dynamic pressure sliding bearings. The floating bearings is a ring on the shaft. There is a gap between the ring and the shaft and between the ring and the bearings seat, forming a double-layered oil film. The ring floats between the shaft and the bearings housing. Generally, the inner layer gap is about 0.05mm, and the outer layer gap is about 0.1mm. The wall thickness of the bearings is about 3.0-4.5mm, and it is made of tin-lead bronze alloy. The surface of the bearings is plated with a layer of lead-tin alloy or metal indium with a thickness of about 0.005-0.008mm. When the supercharger works, the bearings rotates between the shaft and the bearings housing. The floating bearings has a compact structure, low price, high reliability, and low radial space requirements, which is conducive to the lightweight design of the turbocharger. The oil film forms well during operation, effectively separating the rotating parts from the non-rotating parts, so it has a long life. Therefore, the current turbocharger bearings mostly adopt floating bearings. However, floating bearings also have their shortcomings, such as ample radial clearance, low accuracy of rotor dynamic control, high pressure and quality requirements for lubricants, and high-speed operation, massive frictional torque, an eddy of the oil film may cause noise and vibration.
Rolling bearings can be seen more on performance models. As the name suggests, rolling bearings are the installation of balls on the turbine shaft to replace the position of the oil in the floating bearings. The advantage of rolling bearings is precisely the opposite of floating bearings: smaller friction, lower turbine hysteresis effect, and more favorable for the power limit; it can effectively control the dynamics of the turbine shaft; the oil pressure and quality can be slightly reduced, Which indirectly increases the life of the turbine. The disadvantages are also apparent, that is, life is not as good as that of floating bearings. Generally, the life limit is reached from 70,000 to 80,000 kilometers, and the maintenance cost is expensive and difficult to maintain. However, because ball bearings are extremely attractive in terms of power improvement, rolling bearings are still the mainstream equipment on performance models. Compared with this, rolling bearings have significant advantages: small friction torque during rotation, which can effectively reduce the turbine response time, and at the same time have higher mechanical efficiency, which can effectively reduce engine fuel consumption; rolling bearings can achieve reasonable clearance through pre-tensioning control, thereby improving the rotation accuracy of the rotor system, and enabling precise control of the turbine shaft dynamics. The disadvantages are that life is not as long as the floating ring bearings, and the later maintenance is difficult, and the cost is high. However, it has the advantages of high accuracy, high-temperature resistance, and small vibration. It has high reliability, low noise, and high axial load carrying capacity in high-speed, high-temperature, harsh working conditions. Therefore, the rolling bearings will become a better choice for turbocharger bearings, with high application value and good development prospects.