KR20070102809A - High precision radial foil bearing - Google Patents

Abstract

A high precision radial foil bearing is provided to maintain the original shape even when an initial assembling pre-load is applied to the radial foil bearing, thereby reducing driving torque. A high precision radial foil bearing includes a bearing housing(1), a bump(2), a top foil(3), and a key(4). If a pre-load is applied to the top foil, the top foil is pressed inward to make friction with a shaft(6). By making the thickness of the top foil large sufficiently, the top foil maintains the original shape. A gap between a shaft and the top foil can be always maintained at the minimum so that the friction can be minimized even in a stop state. The top foil can maintain the original shape by interposing a spacer between the key and a cut surface(5).

Description

High Precision Radial Foil Bearings

Fig. 1: Conventional form of radial foil bearing

Fig. 2: Foil bearing with high preload

Fig. 3: Foil bearing with more precision by installing spacer

Bearings are largely divided into rolling bearings (with balls or rollers), oil-free bearings (friction with active materials), sliding bearings (with oil), gas bearings, magnetic bearings (contactless operation with magnetic force) Lose. Sliding bearings are divided into dynamic and static pressures, and dynamic sliding bearings support the shaft by the oil generated by the relative sliding movement, and the static sliding bearing supports the shaft by supplying high pressure oil from the outside of the bearing. Gas bearings operate on the same principle as sliding bearings, except that gas is used instead of oil. If pressurized gas is put from outside, it is a constant pressure gas bearing. If pressure is generated by relative sliding, it is a dynamic pressure gas bearing.

Dynamic pressure bearings are widely used in high-speed rotating applications due to their low friction loss and the need for liquid lubricating oils. Especially, dynamic pressure bearings are mainly used in high-speed applications that are difficult to support with rolling bearings and where it is difficult to use liquid lubricants. Dynamic gas bearings are divided into grooved bearings, tilting pad bearings, and foil bearings. Bearings with grooves generate pressure by installing grooves, and spiral grooved bearings are typical examples. Hydrodynamic fluid-film tilt pad bearings have a disadvantage in that the risk of breakage increases if the conditions of use are very limited. For example, these bearings are very susceptible to shock, shaft misalignment and thermal deformation because their stiffness drops sharply above or below design conditions. In comparison, foil bearings, called compliant hydrodynamic fluid-film bearings, offer significantly higher performance than fixed tilt pad bearings, and have made significant progress in recent 20 years. Sufficient durability and stability have been confirmed, and it is used in high-speed rotary machines such as ultra-high speed cryogenic turbocompressors in excess of 100,000 RPM. The bearings can be used even in the presence of some liquids, and offer the advantage of flexibility and low cost. Foil bearings in aviation have been used since 1970, mainly in the air cooling machine (ACM), a key component that controls the pressure and temperature in the cabin in the environmental control system (ECS). In this application, the foil bearing does not have an oil system, so it does not contaminate the inside of the cabin and allows stable operation for a sufficiently long time compared to the ball bearing without a fixed maintenance schedule. And in case of bearing failure, it provides the advantage of almost no damage of turbo components, and the foil bearing used in Boeing 747 operates over 100,000 hours without repair.

Foil bearings are largely divided into two types. As shown in FIG. 1, a leaf type that partially overlaps each wing-shaped foil in a rotational direction and supports the shaft, and supports the foil in various forms on the outside of the foil as one foil as shown in FIG. It is divided into the bump type which arranges the spring. The leaf type is applicable to the case where the supporting load is small and the external impact is small, and the starting torque has a big disadvantage. On the other hand, the bump type is known to have a small starting load, excellent durability and rigidity, but it is difficult to design and produce, and it is difficult to secure stability. It's bad. A bump foil, which acts as a spring in the bearing housing, is welded to the bearing housing, and a top foil in contact with the shaft and the journal is in contact with the bearing housing. It is welded to the housing. As the shaft rotates to draw air, the top foil and bumps deform and create a space for forming a load-bearing fluid film. The geometry for generating the fluid film in the foil bearing is provided by the elastic deformation of the top foil. As the number of turns increases, the top foil and bumps are pushed outwards, and when the shaft is out of the center, the space of the converging wedge is formed. In this case, the foil bearing has a characteristic that the top foil is deformed, so that the design can be performed well so that an optimum shape can be obtained in which proper dynamic pressure is generated without complicated machining by the deformation of the fine top foil. In addition, since there is a margin in the radial direction, an advantage of being able to cope with an increase in the shaft diameter due to the high speed rotation can be obtained. What determines these properties is the thickness of the top foil and the shape of the bumps supporting the top foil. In particular, the design of the bump determines the stiffness and damping required by the shaft system, so the shape, thickness, height, pitch, and number of bumps are the most important factors that determine the bearing performance. .

Furthermore, military bearings require higher speeds, harsher environments and shock resistance, and high-speed, high-power, high-efficiency BLDC motors cannot deliver the performance required by conventional oil-lubricated bearings. In addition, it is known to be able to withstand structurally sufficient misalignment, heat and vibration, and it is known that it is advantageous to separate the bumps in the axial direction and the rotation direction in order to obtain the maximum supporting force.

Related patents filed in the United States are as follows. 4,300,806; 5,915,841; 5,988,885; 4,465,384; 5,498,083; 5,584,582; 6,024,491; 6,190,048 B1; 4,624,583; 3,893,733; 3,809,443; 4,178,046; 4,654,939; 4,005,914; 5,911,511; 5,534,723; 5,427,455; 5,866,518

It can be seen that the principle has already been filed and expired in the 1970s, and efforts have been made to improve performance by changing bumps and top foils. In addition, 5,866,518 it can be seen that a lot of efforts to develop a metallic dry lubricant that is applicable to high temperatures and excellent adhesion.

The present invention relates to a bump type foil bearing, which aims to improve bearing capacity and provide precise rotation.

The conventional foil bearings are pre-loaded in order to increase the rotational accuracy, and the shaft 6 and the top foil 3 are tightened to the preload of the bump 2 at the time of stopping, so that the shaft 6 and the top gun are rotated. In order for the work 3 to be spaced apart, the frictional state is maintained up to a considerable number of revolutions. Therefore, there is a problem that the load at start-up increases and wear occurs early. However, if the preload is reduced and the assembly is reduced, the load or wear at the start is reduced, but it is difficult to apply it in the case of requiring high precision rotation due to the increase of the behavior of the shaft during rotation.

Therefore, the present invention is to provide a radial foil bearing which gives a preload to increase the rotational precision while reducing the friction from the standstill.

The present invention consists of a bearing housing 1, a bump 2, a top foil 3, and a key 4 as shown in FIG.

In the case of preload, the top foil 3 is pressed toward the inner diameter to rub against the shaft 6, so that the thickness of the top foil 3 is now known to be conventional (0.1t thin plate for 60 mm diameter bearings). It is thicker than bending or used as it is, so that the circular shape is maintained by itself so that the bump is preloaded, but the gap between the shaft and the top foil is not reduced so that the minimum gap is maintained at all times, so that the friction is minimal even at the standstill. Can be

In this case, it was confirmed that sufficient thickness would satisfy the following relationship through structural stiffness and performance test.

t: thickness [mm]

D: Shaft diameter [mm]

At this time, since the top foil 3 is sufficiently thick, the top foil 3 is processed into a lathe and manufactured by cutting for precise shape. Therefore, when the cutting surface abuts and gives a preload to the bump 2, the inside diameter of the top foil is not an exact circle. do. Therefore, as shown in Figure 2 when the cutting surface abuts to give a preload there is a disadvantage that the bearing capacity is lowered.

In order to solve this problem, if the spacer is placed between the key 4 and the cutting surface 5 as shown in Fig. 3, the top foil 3 can be kept in a circular shape. The space of the cut plane varies depending on the equipment, and a spacer equal to the cutting thickness can be used.

As described above, the circular top is maintained by the rigidity of the thick top foil itself so that the circular shape is maintained even when the initial assembly preload is not applied. Therefore, the starting torque is reduced and the rotational precision is increased by applying the preload.

Claims (2)

For a radial foil bearing comprising a top foil 3 having the following thickness;

t: thickness [mm] D: Shaft diameter [mm] Radial foil bearing, characterized in that the cutting surface of the top foil (3) abuts against each other to apply a preload so that the top foil (3) and the shaft (6) is assembled so that there is no interference Radial foil bearing according to claim 1, characterized in that it comprises a spacer (7) welded to the key (4).

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