JP3463026B2 - Dynamic pressure type air bearing - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dynamic pressure type air bearing for holding a rotating shaft by means of an air film, and more particularly, a foil provided with a corrugated bump foil and a top foil for supporting the rotating shaft via the air film. Type dynamic pressure type air bearing.

[0002]

2. Description of the Related Art Air bearings are classified into static pressure type and dynamic pressure type, as is well known. Compared with static pressure type which uses external pressure such as a compressor, ambient air is freely used and pressure is generated by rotating the shaft. The dynamic pressure type that causes the occurrence is advantageous in terms of cost, weight reduction and maintenance. In particular, the foil type dynamic pressure type air bearing is a machine used at high speed rotation such as an air cycle machine for an aircraft or a gas turbine engine. It has been widely used for such purposes.

13 and 14 show a conventional foil type dynamic pressure type air bearing, in which a corrugated bump foil 102 is arranged along an inner cylindrical surface 110 of a cylindrical housing 101, and the inner circumference of the bump foil 102 is shown. The top foil 103 is arranged along the surface, and the rotary shaft 105 is rotatably held on the inner peripheral surface of the top foil 103 via an air film 119. Note that FIG. 13 is a diagram for explaining the operation, in which the rotary shaft 105 is expressed to be extremely smaller than the inner diameter of the top foil 103, and the rotary shaft 105 is shown in a largely eccentric position. The inner diameter of the top foil 103 is set to be slightly smaller than the diameter of the shaft 105, and in the stopped state, substantially the entire circumference of the rotating shaft 105 is in contact with the inner peripheral surface of the top foil 103. There is.

In FIG. 14, which is an enlarged partial view of FIG. 13, respective one ends 103a, 102a of the top foil 103 and the bump foil 102 in the circumferential direction are fixed members 120.
And the inner surface 11 of the housing using spot welding or the like.
It is fixed to 0, and only the other ends 103b and 102b are free ends that are movable in the circumferential direction.

The rotating shaft 105 contacts the inner peripheral surface of the top foil 103 to rotate when the rotating speed is low, and when the rotating speed exceeds a predetermined rotating speed (eg, 4000 rpm), it is between the top foil 103 and the outer peripheral surface of the rotating shaft 105. An air film 119 starts to be formed on the top foil 103, and the pressure of the air film 119 pressurizes the top foil 103 outwardly and compresses the bump foil 102 outwardly, whereby the space between the top foil 103 and the rotating shaft 105 is increased. An annular gap, for example, a gap of about 5 μ (air film 119) is secured in the space, and the air shaft 119 is held by the air film 119.

The spring constant of the bump foil 102 in the radial direction is set lower than the spring constant of the air film 119, and when the rotary shaft 105 is displaced in the radial direction, the air film 1
The bump foil 102 is designed to be compressed earlier than 19. Due to such a spring function of the bump foil 102, even when the rotary shaft 105 is displaced in the radial direction as described above, the rotary shaft 105 does not move to the top foil 103.
To prevent direct contact with.

When the bump foil 102 is compressed and deformed as described above, the bump foil 102 extends in the circumferential direction, so that the contact surface Q1 with the top foil 103 and the contact surface Q2 with the inner cylindrical surface 110 of the housing respectively have a friction resistance. And also has the function of damping the vibration due to rotation by the frictional resistance and the damping effect of the air film itself.
As a prior art document, Japanese Patent Laid-Open No. 10-33184
There is No. 6 publication.

[0008]

The dynamic pressure type air bearing having the structure as shown in FIGS. 13 and 14 has the following problems. (1) Deformation when fixing each foil to the housing. As shown in FIG. 14, when the ends 102a and 103a of the bump foil 102 and the top foil 103 are fixed to each other by welding or press fitting into a groove formed on the inner peripheral surface of the housing, a fixing portion is formed in a fixing process such as welding. Distortion may occur in the vicinity, and the cylindricity of the inner surface of the top foil may be impaired. When the cylindricity decreases, the rotating shaft 105
The thickness of the air film 119 between the outer peripheral surface of the film and the top foil 103 is not uniform, and irregularities are formed, and the air film 11 is locally formed.
A thin portion occurs at 9. Then, even if a slight shaft vibration occurs, the film may be broken, the rotating shaft 105 and the top foil 103 are locally brought into direct contact with each other, and frictional resistance is generated, which accelerates wear of the top foil 103.

(2) Increase in sliding resistance when the bump foil is compressed and deformed. When the rotating shaft 105 causes shaft vibration and other causes, for example, FIG.
If the radial load K presses the top foil side in the vicinity of the point P1, the bump foil 102 is compressed as described above and tends to extend in the circumferential direction.

At this time, the area G1 on the free end 102b side of the pressing point P1 can easily extend, but the pressing point P1
In the region G2 closer to the fixed end 102a than 1, the bump foil 102 cannot extend in the circumferential direction, so that the bump foil 102 swells inward in the radial direction and the top foil 103 protrudes inward to excessively contact the rotating shaft 105. I will end up. As a result, the sliding resistance increases and the bearing function deteriorates.

(3) Parts cannot be reused. In the structure in which both foils 102 and 103 are fixed to the housing 101 by welding as shown in FIG. 13, once assembled, the value due to deformation or accumulated tolerance of the fixing portion exceeded the reference value and was rejected during shipping inspection. At times, all parts are not reusable, leaving a problem in terms of parts cost.

(4) Low yield. As described in the above problem (3), in the conventional foil fixing type, all components cannot be reused after assembly, so that strict dimensional accuracy is required for each component in order to manage the bearing clearance. Moreover, even if each component is a dimensional acceptable product, the bearing itself may be rejected due to a cumulative dimensional error during assembly, and the product yield is not good.

(5) Complexity of the shaft assembly work. As shown in FIG. 13, one top foil 103 is used for the rotary shaft 1
In the structure that wraps 05, the air film 119 is interrupted around the rotating shaft 105 at only one position in the vicinity of the fixed portion 120, and the bearing characteristics are stable against a radial load. However, in this structure, in the assembly work of inserting the rotary shaft 105 into the top foil, the free end 103b portion of the top foil 103 moves axially together with the rotary shaft 105, and the top foil 103 is twisted to the rotary shaft 105. Because it wraps around, insertion work becomes very difficult. In order to eliminate such a winding phenomenon of the top foil 103, the rotary shaft 105 is attached to the top foil 103.
Must be inserted while rotating in the direction in which the swells (the direction opposite to the F direction), which requires a special assembling device and complicated assembling work.

[0014]

In order to solve the above-mentioned problems, the invention according to claim 1 of the present application is a corrugated plate-like bump foil which is inserted into the inner cylindrical surface of a cylindrical housing in an adjacent state.
In a dynamic pressure type air bearing having a top foil which is arranged adjacent to the inner peripheral surface of the bump foil and holds a rotating shaft via an air film, outward protrusions are formed at both circumferential end portions of the bump foil. The both projections are engaged with a recess formed in the inner cylindrical surface of the housing with a circumferential play. As a result, the workability of assembling the bump foil is improved, and the parts such as the bump foil can be reused by disassembling them even after the assembly, so that the parts cost can be saved and the yield can be improved. Further, when the bump foil is compressed and deformed, both ends in the circumferential direction can be moved in the circumferential direction in the recess as free ends, so that the bump foil can be prevented from bulging radially inward when the shaft vibrates. The characteristics of can be maintained.

According to a second aspect of the present invention, in the dynamic pressure type air bearing according to the first aspect, protrusions are formed at both axial ends of the top foil, and the protrusions are engaged with engagement grooves formed in the housing. Thus, the top foil is locked in the circumferential direction and the axial direction. As a result, the workability of assembling is improved, and the parts such as the top foil can be reused by disassembling them even after the assembling, so that the parts cost can be saved and the yield can be improved. Moreover, when the shaft is assembled, the top foil will not be twisted and wrapped around the rotary shaft without rotating and inserting the rotary shaft, and the workability of assembling the shaft will be improved.

According to a third aspect of the present invention, in the dynamic pressure type air bearing according to the second aspect, the projections for positioning the top foil have the tip end portions of the overhanging portions formed in the L-shape at both axial ends. It is formed by bending along a folding curve parallel to the axis. By forming the protrusions in this way,
When the top foil is bent and formed into a cylindrical shape, the cylindricity does not change, and the top foil itself is not deformed at the time of forming the protrusion, or the rigidity of only the protrusion forming portion is not increased.

[0017]

[0018]

1 is an exploded perspective view of a foil type dynamic pressure type air bearing to which the present invention is applied. The air bearing is fitted into a cylindrical housing 1 and an inner cylindrical surface 10 of the housing 1. The bump foil 2 has a corrugated shape, and the top foil 3 is fitted into the inner peripheral surface of the bump foil 2 and holds the rotating shaft 5 through an air film.

The inner cylindrical surface 10 of the cylindrical housing 1 is formed with key groove-shaped recesses 11 extending over the entire length in the axial direction, and a plurality of engagement grooves 1 extending radially are formed on both end surfaces in the axial direction.
2 is formed. Both foils 2 and 3 are formed by processing a single sheet into a cylindrical shape, and have openings (gaps) W1 and W5 at one location in the circumferential direction. At both ends of the bump foil 2 in the circumferential direction sandwiching the opening W1, the outward projections 2a engageable with the recesses 11 of the housing 1,
2b is formed by bending, and a plurality of projections 15 that can be engaged with the engaging grooves 12 of the housing 1 are formed by bending on both axial edges of the top foil 3.

FIG. 3 is a front view of the housing 1. For example, five radial engaging grooves 12 formed on both end surfaces in the axial direction are formed, and together with the one concave portion 11, six grooves are formed in the circumferential direction. They are placed on equal points.

FIG. 4 is a sectional view taken along the line IV-IV in FIG. 3, in which the annular step surfaces 18 for preventing the bump foils from protruding radially inward are formed at both axial ends of the inner cylindrical surface 10. Has been done. FIG. 6 is an enlarged view of the step surface 18 portion of FIG.
FIG. 6 is an enlarged view of a VI-VI cross section, showing a radial height H1 of the step surface 18.
Is set to be smaller than the wave height H2 of the bump foil 2, so that even if the rotary shaft 5 is displaced in the radial direction, within the certain range (H2-H1), the radial inner end 18a of the step surface 18 is increased. The rotary shaft 5 does not come into contact with the. For example, the height H1 of the step surface 18 is set to 0.3 mm with respect to the wave height H2 of the bump foil 2 = 0.5 mm, and the rotary shaft 5 can be displaced in the radial direction within a range of less than 0.2 mm. Has become.

FIG. 7 is a front view of the bump foil 2.
It is made of a thin-film metal having a thickness of about 50 μm to 100 μm, and is formed in a corrugated shape over substantially the entire surface except for a certain section from one protrusion 2b. As the material of the bump foil 2, a high-grade spring material obtained by subjecting a nickel alloy (for example, 75% nickel) to age hardening is used, and has a hardness of HRC.
It is about 35 to 40, and is intended to prevent fatigue under high temperature and high load.

The outer diameter D2 of the bump foil 2 in an unassembled state (free state) is set to, for example, about 50 to 60 mm, and the inner diameter D1 (= of the inner cylindrical surface 10 of the housing shown in FIG. 4).
It is set larger than 40 mm).

FIG. 2 is a partial front view of the bearing assembly completed state. The radial spring constant of the bump foil 2 is determined by the thickness of the bump foil 2 and the pitch between the waves.
It is set to be lower than the spring constant of an air film (air spring) 19 formed between the top foil 3 and the outer peripheral surface of the rotary shaft 5, so that the air film 19 can be set against the radial load of the rotary shaft 5. Bump foil 2 while maintaining the thickness of
Is designed to be compressed in the radial direction.

The interval W1 between the projections 2a and 2b on both ends of the bump foil 2 which engages with the recess 11 of the housing 1 is smaller than the width W2 of the recess 11 in the circumferential direction at the time of mounting, and is a predetermined value in the circumferential direction. They are engaged with each other with a clearance (play) d1 + d2.

FIG. 8 is a front view of the top foil 3,
The protrusions 15 formed at both ends in the axial direction are arranged at each point divided into six equal parts in the circumferential direction together with the opening W5. Although a nickel alloy (for example, 75% nickel) is used as the material of the top foil 3, the hardness is set to about HRC10 to 20 by performing annealing to improve the adhesion and contact with the rotating shaft 5. There is. On the other hand, the thickness of the top foil 3 is thicker than that of the bump foil 2, for example, 10
It is set to about 0 to 200 μmm, which prevents deformation in the radial direction and maintains cylindricity. The inner peripheral surface of the top foil 3 is coated with a low-friction material such as fluorine or molybdenum disulfide, which reduces frictional resistance and wear when it comes into direct contact with the rotating shaft 5 at low speed rotation. I am trying to On the other hand, the outer peripheral surface of the top foil 3 is plated with silver or copper,
As a result, a smooth damping effect can be obtained at the contact surfaces Q1 of both foils 2 and 3 in FIG.

FIG. 9 is a development view of the top foil 3 before the projection 15 is formed by bending, and L-shaped projecting pieces 21 for forming projections are in the same plane as the top foil 3 on both end edges in the axial direction. Each of the L-shaped overhanging pieces 21 is formed in such a manner that the tip end portion 15a thereof projects in the axial rotation direction F side, and the tip end portion 15a of the overhanging piece 21 is folded in parallel with the shaft core. By bending the curve B outward in the radial direction, the projection 15 is formed in a posture substantially perpendicular to the circumferential surface as shown in FIG. As described above, the protrusion 15 engages with the radial engagement groove 12 of the housing 1, and serves to prevent the top foil 3 from being pulled out in the axial direction and to regulate the rotation in the circumferential direction. Further, due to the rotation of the rotary shaft 5, the projection 15 is in contact with the end face 12a of the radial engagement groove 12 on the rotational direction F side,
As the top foil 3 expands and contracts in the radial direction, the end surface 1
By rubbing in the radial direction with respect to 2a, a friction damping function is also exerted.

[0028]

[Assembly Method] In FIG. 1, the bump foil 2 is reduced in diameter, and the projections 2a and 2b are inserted into the housing 1 in a state of being aligned with the recess 11 of the housing 1. After the insertion, it opens outward in the radial direction due to the restoring force, and comes into contact with the inner cylindrical surface 10 of the housing at a constant pressure. The top foil 3 is also inserted into the bump foil 2 in a reduced diameter state. After the insertion, the restoring force opens outward in the radial direction and contacts the inner peripheral surface of the bump foil with a constant pressure.
Engage with.

After assembling both foils 2 and 3 in the housing 1 as described above, the rotary shaft 5 is inserted. In this rotary shaft insertion work, the inner diameter of the top foil 3 in the mounted state is slightly smaller than the outer diameter of the rotary shaft 5,
The top foil 3 will be inserted with a slight expansion,
The top foil 3 is positioned in the circumferential direction and the axial direction by the engagement between the engaging groove 12 and the protrusion 15, so that the top foil 3 is spirally wound around the rotating shaft 5 or is axially moved in the housing. It does not protrude from 1. That is, it is possible to easily fit the inside of the top foil 3 without rotating the rotary shaft 5.

As described above, since the bearing is assembled without forming a fixed portion such as a welded portion, the cumulative tolerance of the dimensional accuracy of the housing 1 and both foils 2 and 3 becomes large, and the bearing as a whole is rejected at the time of shipping inspection. Even then, it can be easily disassembled, and by replacing only the parts that are not in good condition after disassembly, it is possible to reassemble the product with the accumulated error within the standard.

Further, the protrusions 15 of the top foil 3 have L-shaped projecting pieces 21 at both ends of the top foil 3 as shown in FIG.
And the tip 15a of the curved line B is parallel to the axis.
Since the top foil 3 is bent and formed, the cylindricity does not change when the top foil 3 is bent and formed, and the top foil itself is deformed when forming the protrusion, or only the protrusion forming portion is formed. There is no increase in rigidity. By the way, if the protrusions are directly bent and formed on both ends of the top foil 3, the rigidity of the roots of the protrusions is increased, the cylindricity is affected, and the top foil itself may be deformed during the bending and forming.

[0032]

In FIG. 2, when the shaft is attached, the outer circumference of the rotary shaft 5 is substantially the entire circumference except for the opening W5.
Is in contact with the inner peripheral surface of.

When the rotary shaft 5 starts to rotate in the F direction, the top foil 3 tries to rotate with the rotary shaft 5 in the F direction due to friction, but the projection 15 abuts on the end face 12a of the engaging groove 12, It is locked in the direction of rotation. On the other hand, the bump foil 2 slides in the direction opposite to the rotation direction F due to thermal expansion and friction, for example, by the gap d1, and then the projection 2a comes into contact with the end surface 11a of the recess 11 and the circumferential direction. Locked in.

As shown in FIG. 10, the protrusion 15 of the top foil 3 is formed by bending the tip of the L-shaped overhanging piece 21 in the rotational direction F, so that the end face 12 of the engaging groove 12 on the rotational direction F side 12 is formed.
Even if it is strongly pressed against a, it is pressed toward the protruding piece side, high rigidity can be maintained, and the projection 15 is unlikely to be deformed.

In the low speed rotation range up to about 4000 rpm, the air film 19 is not formed, and the rotating shaft 5 rotates while being in direct contact with the inner peripheral surface of the top foil 3.
That is, the rotary shaft 5 is supported by the inner peripheral surface of the top foil coated with a low-friction material, and is in a bearing state similar to a normal bearing metal or the like.

In the high speed rotation range, air is caught between the top foil 3 and the rotary shaft 5 to start forming an air film 19, and the pressure of the air film 19 pushes the top foil 3 outward in the radial direction. As a result, the bump foil 2 is compressed in the radial direction, a constant gap (for example, a gap of about 5 μm) is generated between the top foil 3 and the rotating shaft 5, and the bump foil 2 rotates in a non-contact state with the top foil 3. That is, the entire circumference of the rotary shaft 5 rotates while being held by the air film 19.

In the dynamic pressure type air bearing, rigid body mode resonance occurs due to entrainment at low speed rotation, bending resonance occurs at high speed rotation, and a large radial load is applied when passing through each resonance point. For example, if a radial load K is applied to the point P1 in FIG. 10, the top foil 3 is pressed in the K direction via the air film 19 at the point P1, and the bump foil 2 is compressed in the K direction. As a result, the air film 19 is prevented from being broken and the rotational vibration or the like due to the resonance action is damped.

The damping action on the rotation shaft vibration will be described in detail. When the bump foil 2 is compressed outward in the radial direction, the bump foil 2 extends to both sides in the circumferential direction from the pressing point P1 as a base point, and the extension in the circumferential direction causes the bump foil 2 and the top foil 3 to be separated from each other. A frictional resistance is generated on each of the contact surface Q1 and the contact surface Q2 between the bump foil 2 and the inner cylindrical surface 10 of the housing.
The vibration of the rotating shaft is damped by the damping action of the air film itself and the frictional resistance caused by the projection 15 of the top foil 3 and the groove 12 being rubbed in the radial direction.

When the bump foil 2 extends in the circumferential direction, no matter which of the two projections 2a, 2b of the bump foil 2 is in contact with the concave end surface 11a or 11b, both projections 2a, 2b. Since a constant gap W1 is secured between the bump foil 2 and the bump point 2 at the pressing point P1.
Can freely extend in both the rotational direction F and the opposite direction, and the fixed side does not swell inwardly as in the conventional example.

[0040]

[Other Embodiments of the Invention] (1) FIG. 11 shows a modified example of the bump foil 2, which is an example in which it is divided into two bump foils 31, 31 in the axial direction. When the parallelism of the rotary shaft with respect to the housing is maintained with high accuracy, the single-piece bump foil 2 as shown in FIG. 1 can be used to save the number of parts and facilitate the assembling. However, if it is expected that the parallelism of the rotary shaft 5 with respect to the housing 1 will be deteriorated as shown in FIG. 12, split bump foils 31, 31 are used, and each bump foil is inclined even when the rotary shaft is tilted. The flexibility of 31, 31 can be maintained. Bump foil 31,
31 is positioned in the axial direction by the outward projection 31.
a, 31b and non-corrugated portions 31c, 31c in the vicinity thereof are brought into contact with each other.

When the rotary shaft 5 is inclined with respect to the housing 1 as shown in FIG. 12, the split type bump foils 31, 3 are provided.
1, the whole spring constant is distributed to each bump foil 31, 31, so that high surface pressure does not act on the rotary shaft 5 at both axial end portions P6, P7 of the top foil 3. The bearing function of the air film 19 can be maintained.

[0042]

INDUSTRIAL APPLICABILITY The present invention has a cylindrical housing 1, a bump foil 2 having a corrugated diameter which is inserted adjacent to an inner cylindrical surface 10 of the cylindrical housing 1, and the bump foil 2.
In the dynamic pressure type air bearing having the top foil 3 which is arranged adjacent to the inner peripheral surface of the above and holds the rotating shaft 5 through the air film 19, the following effects can be obtained.

[0043]

[0044]

[0045]

(1) A recess 1 is formed in the inner cylindrical surface 10 of the housing 1.
1 is formed and outward projections 2a and 2b are formed on both ends of the bump foil 2 in the circumferential direction, and both projections 2a and 2b are engaged with the recess 11 with a circumferential play. When,
Assembling workability is improved, and parts such as bump foils can be reused by disassembling even after assembling, so that part cost savings and yield improvement can be achieved. Moreover, when the bump foil 2 is compressed and deformed, both ends 2a and 2b in the circumferential direction are formed.
Can move circumferentially in the recess 11 as a free end, so that the bulging of the bump foil 2 inward in the radial direction can be prevented and the characteristics of the bearing can be maintained.

(2) The concave portion 1 is formed in the inner cylindrical surface 10 of the housing 1.
1 is formed and outward projections 2a and 2b are formed on both ends of the bump foil 2 in the circumferential direction, and both projections 2a and 2b are engaged with the recess 11 with a circumferential play. When,
Even when the rotary shaft 5 is displaced in the radial direction due to axial vibration or other causes and the bump foil 2 is compressed at one pressing point P1, it can freely extend on both sides in the circumferential direction with the pressing point P1 as a boundary. The shaft vibration can be efficiently damped.

(3) According to the second aspect of the invention, the projections 15 are formed on both axial ends of the top foil 3, and the projections 15 are engaged with the engaging grooves 12 formed in the housing 1. When the top foil 3 is locked in the circumferential direction and the axial direction, it is not necessary to fix the axial position by welding or the like as compared with the foil fixing type as shown in FIGS. 13 and 14, and the rotary shaft assembly is used. At the time of attachment, it is not necessary to insert the rotary shaft while rotating it by using a special insertion tool, and the assembling workability is improved.

(4) As in the invention described in claim 3, the tip end portions of the overhanging pieces (overhanging portions) 21 formed by overhanging the top foil 3 in the axial direction in the L-shape are folded in parallel with the axis. Curve B
When the projections 15 for positioning are formed by bending by means of, the cylindricity does not change when the top foil 3 is bent and formed into a cylindrical shape, and the top foil itself is not deformed during projection formation. It does not occur or the rigidity of only the projection forming portion is not increased.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of a foil type dynamic pressure type air bearing to which the present invention is applied.

FIG. 2 is a partial front view of the foil dynamic pressure type air bearing of FIG.

FIG. 3 is a front view of a cylindrical housing.

4 is a cross-sectional view taken along the line IV-IV of FIG.

5 is a partial view as seen from an arrow V in FIG.

FIG. 6 is a partial view taken along line VI-VI of FIG.

FIG. 7 is a front view of a bump foil.

FIG. 8 is a front view of the top foil.

FIG. 9 is a development view of the top foil before bending.

10 is an enlarged view of a portion indicated by an arrow X in FIG.

FIG. 11 is a perspective view showing a modified example of the bump foil.

FIG. 12 is a schematic cross-sectional view for explaining the action of the split type bump foil of FIG.

FIG. 13 is a sectional view of a conventional example.

FIG. 14 is a partially enlarged view of FIG.

[Explanation of symbols]

1 Cylindrical housing 2 bump foil 2a, 2b Bump foil outward projection 3 top foil 5 rotation axes 10 Inner cylinder surface 11 recess 12 radial engagement groove 15 Top foil protrusion 18 steps

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) F16C 27/02

Claims (3)

(57) [Claims] 1. A corrugated plate-shaped bump foil inserted into an inner cylindrical surface of a cylindrical housing in an adjacent state, and a rotary shaft held by an air film disposed adjacent to an inner peripheral surface of the bump foil. In a dynamic pressure type air bearing having a top foil, a bump outwardly protruding in the radial direction is formed at both ends in the circumferential direction of the bump foil, and the both protrusions are formed in a recess formed in the inner cylindrical surface of the housing.
A dynamic pressure type air bearing characterized in that it is engaged with a play in the circumferential direction. 2. The dynamic pressure type air bearing according to claim 1 , wherein projections are formed at both axial ends of the top foil, and the projections are engaged with engagement grooves formed in the housing, whereby the top foil is circular. A dynamic pressure type air bearing characterized by being locked in the circumferential direction and the axial direction. 3. The dynamic pressure type air bearing according to claim 2, wherein the projections for positioning the top foil are bent in parallel with the shaft core at the tips of the overhanging parts formed in the L shape at both axial ends. A dynamic pressure type air bearing characterized by being bent and formed by a curved line.