JP2012197858A - Fluid dynamic pressure bearing device and axial fan motor provided with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent, in a fluid dnamic pressure bearing device in which axial thrust is applied to a shaft member during rotation of the shaft member, the contact of a flange of the shaft member with a member facing it even in high-speed rotation.SOLUTION: When a downward thrust F is applied to the shaft member 2 during rotation of the shaft member 2, support force F2 of a second thrust bearing portion T2 which supports the flange 2b of the shaft member 2 downward is set smaller than the support force F1 of a first thrust bearing portion T1 which supports the flange 2b of the shaft member 2 upward.

Description

  The present invention relates to a fluid dynamic bearing device that supports a shaft member so as to be relatively rotatable by the pressure of a lubricating fluid generated in a radial bearing gap and a thrust bearing gap, and an axial fan motor including the fluid dynamic bearing device.

  The fluid dynamic pressure bearing device is suitably used, for example, for HDD spindle motors and various fan motors. For example, as shown in FIG. 8, a fluid dynamic bearing device 100 disclosed in Patent Document 1 includes a shaft member 102 having a shaft portion 102a and a flange portion 102b, and a bearing sleeve in which the shaft portion 102a is inserted on the inner periphery. 108, a cylindrical housing 107 having a bearing sleeve 108 fixed to the inner periphery, and a thrust bush 110 that closes one end opening of the housing 107. When the shaft member 102 rotates, a radial bearing gap is formed between the outer peripheral surface 102a1 of the shaft portion 102a and the inner peripheral surface 108a of the bearing sleeve 108, and the shaft member 102 is moved in the radial direction by the oil film pressure generated in the radial bearing gap. The radial bearing portions R1 ′ and R2 ′ supported by At the same time, thrust bearing gaps are formed between one end surface 108c of the bearing sleeve 108 and one end surface 102b1 of the flange portion 102b, and between the end surface 110a of the thrust bush 110 and the other end surface 102b2 of the flange portion 102b. The thrust bearing portions T1 ′ and T2 ′ that support the shaft member 102 in the thrust direction are configured by the pressure of the oil film generated in the thrust bearing gaps.

JP 2003-83323 A

  For example, when the fluid dynamic pressure bearing device 100 described above is incorporated in a spindle motor of an HDD, the weight of the disc mounted on the shaft member 102 is added to the shaft member 102, and the shaft member 102 is pressed downward. When the shaft member 102 rotates, the shaft member 102 is supported upward by the supporting force F2 'of the lower thrust bearing portion T2. At this time, the force pressing the shaft member 102 downward due to the weight of the disk does not change even if the rotation speed of the shaft member 102 increases, so that once the shaft member 102 is supported by levitation, the rotation stops or the external force Unless it is added, it continues to be supported.

  On the other hand, when the fluid dynamic bearing device 100 is incorporated in an axial fan motor, axial thrust is applied to the shaft member 102 as the shaft member 102 rotates. FIG. 8 shows a case where, for example, a downward thrust F ′ is applied to the shaft member 102. At this time, the axial thrust F ′ applied to the shaft member 102 increases as the rotational speed of the shaft member 102 increases, and the shaft member 102 is pushed downward. With respect to this thrust F ′, the shaft member 102 is supported upward by the support force F2 ′ of the lower thrust bearing portion T2 ′. When the shaft member 102 rotates at a high speed of 10,000 r / min or more, the axial thrust F Since 'becomes very large, there is a possibility that it cannot be supported by the supporting force F2' of the thrust bearing portion T2 '.

  Further, the shaft member 102 is pushed further downward not only by the thrust F ′ but also by the support force F1 ′ of the upper thrust bearing portion T1 ′. In particular, at a high speed rotation of 10,000 r / min or more, the supporting force F1 'of the upper thrust bearing portion T1' increases, and the force pressing the shaft member 102 downward cannot be ignored. When the total amount of the support force F1 ′ and the thrust force F ′ for pressing the shaft member 102 downward is larger than the support force F2 ′ of the lower thrust bearing portion T2 ′, the shaft member 102 and the thrust bush 110 are There is a risk of contact.

  Further, a dynamic pressure groove having an axially asymmetric shape is formed on the inner peripheral surface 108a of the bearing sleeve 108 in FIG. 8, and the lubricating oil in the radial bearing gap is pushed downward by the dynamic pressure groove. Due to the downward pushing force F3 'of the lubricating oil by the dynamic pressure groove, the shaft member 102 is pushed further downward, and there is a high possibility that the shaft member 102 and the thrust bush 110 come into contact with each other.

  The above problems occur not only when a downward thrust F ′ is applied to the shaft member 102 as shown in FIG. 8 but also when an upward thrust is applied to the shaft member 102. The same problem occurs not only when the shaft member 102 rotates but also when the shaft member 102 is fixed and the bearing sleeve 108 side is rotated.

  The problem to be solved by the present invention is that, in a fluid dynamic pressure bearing device in which a relative thrust in the axial direction is applied to the shaft member with relative rotation of the shaft member, the flange portion of the shaft member and the thrust member are added to the thrust member even at high speed It is to prevent contact with a member facing in a direction.

  The present invention made in order to solve the above-mentioned problems has a shaft member having a shaft portion and a flange portion, a sleeve portion in which the shaft portion is inserted on the inner periphery, and a bottom portion that closes one end opening of the sleeve portion. A bearing member, a radial bearing portion that relatively supports the shaft member in the radial direction by the dynamic pressure action of the lubricating fluid generated in the radial bearing gap between the outer peripheral surface of the shaft portion and the inner peripheral surface of the sleeve portion, and a sleeve portion The shaft member is relatively supported in the thrust direction by the dynamic pressure action of the lubricating fluid generated in the thrust bearing gap between the end face and one end face of the flange part and in the thrust bearing gap between the end face of the bottom part and the other end face of the flange part. In the fluid dynamic pressure bearing device in which the shaft member and the bearing member rotate relative to each other at 10,000 r / min or more, the shaft member moves relative to one side in the axial direction along with the relative rotation. Thrust Of the two thrust bearing parts, the thrust force of one thrust bearing part that pushes the shaft member relatively toward one side in the axial direction is pushed relatively toward the other axial direction. It is characterized by being smaller than the supporting force of the other thrust bearing portion.

  Thus, in the fluid dynamic pressure bearing device according to the present invention, the supporting force of one thrust bearing portion that pushes the shaft member in one direction in the axial direction, that is, in the same direction as the thrust applied with the relative rotation, is deliberately set low. To do. As a result, the force in the direction of pressing the flange portion of the shaft member against the member (bottom portion or sleeve portion) facing in the thrust direction is reduced, so that even when the shaft member is relatively rotated at a high speed of 10000 r / min or more Contact between the flange portion of the member and the member facing the flange portion can be prevented.

  In the above fluid dynamic pressure bearing device, for example, two thrust bearing portions are provided with a thrust dynamic pressure generating portion that generates a dynamic pressure action on the lubricating fluid filled in the thrust bearing gap, and the thrust motion of one thrust bearing portion is provided. The area of the pressure generating part can be made smaller than the area of the thrust dynamic pressure generating part of the other thrust bearing part.

  For example, when the thrust is generated in a direction in which one end surface of the sleeve portion and one end surface of the flange portion are brought closer, the thrust bearing gap of one thrust bearing portion that pushes the shaft member in the same direction as the thrust is It is formed between the end face of the bottom part and the other end face of the flange part.

  The radial bearing is provided with a radial dynamic pressure generating section that generates a dynamic pressure action on the lubricating fluid filled in the radial bearing gap, and this radial dynamic pressure generating section is connected to the other of the lubricating fluid in the axial direction, that is, opposite to the above thrust. If it pushes in toward the side, the situation where the flange part of a shaft member contacts the member which opposes can be prevented more reliably.

  If the other thrust bearing gap is set to 0 when the shaft member is stopped, the other thrust member having a relatively large supporting force can be obtained when the shaft member rotates at a low speed (for example, immediately after starting or immediately before stopping the motor). Since the shaft member can be supported by the bearing portion, the flange portion of the shaft member can be levitated at an early stage relative to the member facing the shaft member.

  The fluid dynamic bearing device described above can be incorporated into, for example, an axial fan motor that generates an airflow in the axial direction.

  As described above, according to the present invention, in a fluid dynamic pressure bearing device in which a relative thrust in the axial direction is applied to the shaft member in accordance with the relative rotation of the shaft member, the shaft member even at high speed rotation of 10000 r / min or more. It is possible to prevent contact between the flange portion and the member facing the flange portion.

1 is a cross-sectional view of an axial fan motor incorporating a fluid dynamic bearing device according to an embodiment of the present invention. It is sectional drawing of the said fluid dynamic pressure bearing apparatus. It is sectional drawing of the bearing sleeve of the said fluid dynamic pressure bearing apparatus. It is a top view of the said bearing sleeve. It is a bottom view of the thrust bush of the fluid dynamic pressure bearing device. It is sectional drawing of the fluid dynamic pressure bearing apparatus which concerns on other embodiment. It is sectional drawing of the fluid dynamic pressure bearing apparatus which concerns on other embodiment. It is sectional drawing of the conventional fluid dynamic pressure bearing apparatus.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows an axial fan motor incorporating a fluid dynamic bearing device 1 according to an embodiment of the present invention. The fan motor includes a fluid dynamic bearing device 1 that rotatably supports a shaft member 2, a casing 6 that is attached to the stationary side (bearing member 11) of the fluid dynamic bearing device 1, and the fluid dynamic bearing device 1. And a stator coil 4 and a magnet 5 that are opposed to each other with a gap in the radial direction. The stator coil 4 is attached to the casing 6, and the magnet 5 is attached to the rotor 3. The rotor 3 is integrally provided with a plurality of fans 3a. When the stator coil 4 is energized, the magnet 5 and the rotor 3 are rotated by electromagnetic force between the stator coil 4 and the magnet 5, and an axial airflow is generated by the fan 3a. In this embodiment, the case where an airflow is generated on the upper side in the figure is shown (see arrows). This fan motor has a rotor 3 that rotates at a high speed of 10,000 r / min or more, and is used as a turbo fan incorporated in a medical device, for example. In this embodiment, the fan motor is used in the state shown in FIG. 1, that is, in a state where the direction in which the shaft member 2 protrudes from the bearing member 11 is downward.

  As shown in FIG. 2, the fluid dynamic bearing device 1 includes a shaft member 2 and a bearing member 11. The bearing member 11 includes a sleeve portion 11a in which the shaft member 2 is inserted on the inner periphery, and a bottom portion 11b that closes the upper end opening of the sleeve portion 11a. In the present embodiment, a sleeve portion 11a is constituted by a bearing sleeve 8 made of sintered metal and a cylindrical housing 7 having the bearing sleeve 8 fixed to the inner peripheral surface, and a thrust that closes the upper end opening of the housing 7 is formed. The bush 10 forms a bottom 11b. In the present embodiment, the lower end opening of the bearing member 11 is provided with a seal portion 9 that prevents leakage of lubricating fluid (lubricating oil in the present embodiment) to the outside. In the illustrated example, the seal portion 9 and the housing are provided. 7 is integrally formed.

  The shaft member 2 includes a shaft portion 2a and a flange portion 2b provided at the upper end of the shaft portion 2a, and is integrally formed by cutting a molten material such as stainless steel. The shaft portion 2a has a cylindrical surface-shaped radial bearing surface 2a1 and a tapered surface 2a2 that is gradually reduced in diameter downward. In the illustrated example, the radial bearing surface 2a1 is provided at two locations spaced apart in the axial direction, and a clearance portion 2a3 having a smaller diameter than the radial bearing surface 2a1 is provided between these axial directions. The radial bearing surface 2a1 and the relief portion 2a3 of the shaft portion 2a are opposed to the inner peripheral surface 8a of the bearing sleeve 8 in the radial direction, and the tapered surface 2a2 is opposed to the inner peripheral surface 9a of the seal portion 9 in the radial direction.

The bearing sleeve 8 is formed in a substantially cylindrical shape with a sintered metal mainly composed of copper, iron, or both. A radial bearing surface facing the radial bearing gap is provided on the inner peripheral surface 8a of the bearing sleeve 8, and in this embodiment, as shown in FIG. 3, the radial bearing is provided at two locations separated in the axial direction of the inner peripheral surface 8a. Surfaces A1 and A2 are provided. On the radial bearing surfaces A1 and A2, radial dynamic pressure generating portions for generating a dynamic pressure action on the lubricating oil in the radial bearing gap are formed. In the illustrated example, a plurality of herringbone-shaped dynamic pressure grooves 8a1, a hill portion 8a2 provided between the circumferential directions of the dynamic pressure grooves 8a1, and a substantially axial center portion of the radial bearing surfaces A1 and A2 are provided. A radial dynamic pressure generating portion is constituted by the cylindrical portion 8a3. The hill portion 8a2 and the cylindrical portion 8a3 are continuously provided on the same cylindrical surface (indicated by cross hatching in FIG. 3). In the illustrated example, the dynamic pressure grooves 8a1 and lands 8a2 of the lower radial bearing surface A1 is formed asymmetrically in the axial direction, specifically, the axial dimension X ₁ of the region below the cylindrical portion 8a3, It is larger than the axial dimension X ₂ of the upper region from the cylindrical portion _{8a3 (X 1> X 2)} . The dynamic pressure groove 8a1 and the hill portion 8a2 of the upper radial bearing surface A2 are formed symmetrically in the axial direction.

  A thrust bearing surface facing the thrust bearing gap is formed on the upper end surface 8 c of the bearing sleeve 8. A thrust dynamic pressure generating portion for generating a dynamic pressure action on the lubricating oil filled in the thrust bearing gap is formed on the thrust bearing surface. In this embodiment, as shown in FIG. 4, the pump-in type spiral-shaped dynamic pressure groove 8c1, the hill part 8c2 provided between the circumferential directions of the dynamic pressure groove 8c1, and the inner diameter end of the hill part 8c2 A thrust dynamic pressure generating portion is configured by the flat annular portion 8c3 connected in an annular shape. The hill portion 8c2 and the annular portion 8c3 are continuously provided on the same plane (shown by cross-hatching in FIG. 4). In the illustrated example, the thrust dynamic pressure generating portion is formed on the entire upper end surface 8c of the bearing sleeve 8, that is, the entire region between the inner peripheral chamfer and the outer peripheral chamfer.

  An axial groove 8d1 is formed on the outer peripheral surface 8d of the bearing sleeve 8 over the entire axial length (see FIG. 3). The number of the axial grooves 8d1 is arbitrary. In the present embodiment, for example, three axial grooves 8d1 are arranged at equal intervals in the circumferential direction (see FIG. 4).

  As shown in FIG. 2, the housing 7 is formed in a substantially cylindrical shape by metal machining or resin injection molding. The outer peripheral surface 8d of the bearing sleeve 8 is fixed to the inner peripheral surface 7a of the housing 7 by means such as gap adhesion, press-fitting, and press-fitting adhesion (press-fitting with an adhesive interposed).

  A seal portion 9 is integrally provided at the lower end portion of the housing 7. The inner peripheral surface 9a of the seal portion 9 is formed in a cylindrical surface shape, and is opposed to the tapered surface 2a2 provided on the outer peripheral surface of the shaft portion 2a in the radial direction, and the radial dimension is gradually reduced upwardly between them. A wedge-shaped seal space S is formed. Due to the capillary force of the seal space S, the lubricating oil is drawn to the closed side (upper side in the figure) of the bearing member 11, thereby preventing oil leakage. In this embodiment, since the taper surface 2a2 is formed on the shaft portion 2a side, the seal space S also functions as a centrifugal force seal. The oil level of the lubricating oil filled in the internal space of the bearing member 11 sealed by the seal portion 9 is always maintained within the range of the seal space S. That is, the seal space S has a volume that can absorb the volume change of the lubricating oil.

  The thrust bush 10 is formed in a substantially disk shape by metal pressing or resin injection molding, and is fixed to the upper end portion of the inner peripheral surface 7a of the housing 7 by means such as gap bonding, press-fitting, and press-fitting adhesion. A thrust bearing surface that faces the thrust bearing gap is formed on the lower end surface 10 a of the thrust bush 10. A thrust dynamic pressure generating portion for generating a dynamic pressure action on the lubricating oil filled in the thrust bearing gap is formed on the thrust bearing surface. In the present embodiment, as shown in FIG. 5, the pump-in type spiral-shaped dynamic pressure groove 10a1, the hill portion 10a2 provided between the circumferential directions of the dynamic pressure groove 10a1, and the inner diameter end of the hill portion 10a2 A thrust dynamic pressure generating portion is configured by the flat annular portion 10a3 connected in an annular shape. The hill portion 10a2 and the annular portion 10a3 are continuously provided on the same plane (shown by cross-hatching in FIG. 5). On the inner diameter side of the annular portion 10a3, a relief portion 10a4 lowered by one step is provided.

  The area of the thrust dynamic pressure generating portion provided on the lower end surface 10a of the thrust bush 10 (in the example shown in FIG. 5, the area of the annular region between the outer diameter end of the hill portion 10a2 and the inner diameter end of the annular portion 10a3) Is the area of the thrust dynamic pressure generating portion provided on the upper end surface 8c of the bearing sleeve 8 shown in FIG. 4 (in the example shown in FIG. 4, between the outer diameter end of the hill portion 8a2 and the inner diameter end of the annular portion 8a3). The area of the annular region). In the illustrated example, the outer diameter r21 and the inner diameter r22 (see FIG. 5) of the thrust dynamic pressure generating portion of the thrust bush 10 are respectively the outer diameter r11 and the inner diameter r12 (see FIG. 5) of the thrust dynamic pressure generating portion of the bearing sleeve 8. (Refer to FIG. 4) (r21 <r11, r22 <r12).

  After assembling the above members, the fluid inside the housing 7 including the internal pores of the bearing sleeve 8 is filled with lubricating oil, whereby the fluid dynamic bearing device 1 shown in FIG. 2 is completed. At this time, the oil level is held inside the seal space S.

  When the shaft member 2 rotates, a radial bearing gap is formed between the radial bearing surfaces A1 and A2 of the inner peripheral surface 8a of the bearing sleeve 8 and the radial bearing surface 2a1 of the shaft portion 2a. The pressure of the oil film formed in the radial bearing gap is increased by the radial dynamic pressure generating portion (dynamic pressure groove 8a1) formed on the radial bearing surfaces A1 and A2, and the shaft member 2 is increased by this pressure (dynamic pressure action). The radial bearing portions R1 and R2 are configured to support non-contacting in a radial direction.

  At the same time, a thrust bearing gap is formed between the lower end face 2b1 of the flange portion 2b and the upper end face 8c of the bearing sleeve 8, and the pressure of the oil film in the thrust bearing gap causes the thrust movement of the upper end face 8c of the bearing sleeve 8. A first thrust bearing portion T1 that is raised by the pressure generating portion and levitates and supports the shaft member 2 is configured by this pressure (dynamic pressure action). Further, a thrust bearing gap is formed between the upper end face 2b2 of the flange portion 2b and the lower end face 10a of the thrust bush 10, and the pressure of the oil film in this thrust bearing gap is the thrust dynamic pressure of the lower end face 10a of the thrust bush 10. A second thrust bearing portion T2 that is raised by the generating portion and supports the shaft member 2 downward is formed by this pressure (dynamic pressure action).

  When the shaft member 2 rotates, the fan 3a rotates to generate an upward airflow (see FIG. 1), and the rotor 3 and the shaft member 2 receive a downward thrust F in the axial direction by this reaction (see FIG. 2). . Since the shaft member 2 rotates at a high speed of 10,000 r / min or more, and at a high speed of 30000 r / min or more (maximum 40000 r / min) when the speed is high, the air volume by the fan 3a is increased, and thus the downward thrust F is also increased. Therefore, the force that pushes the shaft member 2 downward (the thrust F and the support force F2 of the second thrust bearing portion T2) is larger than the force that pushes the shaft member 2 upward (the support force F1 of the first thrust bearing portion T2). Then, the lower end surface 2b1 of the flange portion 2b may come into contact with the upper end surface 8c of the bearing sleeve 8 while rotating at high speed.

  In the present invention, the support force F2 of the second thrust bearing portion T2 is deliberately reduced to reduce the force pressing the shaft member 2 downward, and the flange portion 2b of the shaft member 2 and the upper end surface 8c of the bearing sleeve 8 To prevent contact. Specifically, the support force F2 (see FIG. 2) of the second thrust bearing portion T2 is set smaller than the support force F1 of the first thrust bearing portion T1 (F1> F2). In this embodiment, the area of the thrust dynamic pressure generating portion (dynamic pressure groove 10a1, hill portion 10a2, and annular portion 10a3, see FIG. 4) formed in the thrust bush 10 is the thrust dynamic pressure formed in the bearing sleeve 8. It is made smaller than the area of the generating part (dynamic pressure groove 8c1, hill part 0c2, and annular part 8c3, see FIG. 5). Furthermore, in this embodiment, the thrust dynamic pressure generating portions formed on the upper end surface 8c of the bearing sleeve 8 and the lower end surface 10a of the thrust bush 10 are both pump-in types, and the annular portion 8c3 is formed at the inner diameter end. Since 10a3 is provided, the pressure of the oil film formed in the thrust bearing gap between the thrust bearing portions T1 and T2 becomes maximum at the annular portions 8c3 and 10a3. Therefore, as shown in the drawing, the diameter of the annular portion 10a3 that maximizes the support force F2 of the second thrust bearing portion T2 is smaller than the diameter of the annular portion 8c3 that maximizes the support force F1 of the first thrust bearing portion T1. By doing so, the supporting force F2 of the second thrust bearing portion T2 becomes smaller than the supporting force F1 of the first thrust bearing portion T1 in combination with the difference in the area of the thrust dynamic pressure generating portion.

  As shown in FIG. 2, since the bearing sleeve 8 has a cylindrical shape having an inner hole, the area of the upper end face 8c of the bearing sleeve 8 is smaller than the area of the lower end face 10a of the thrust bush 10 by the amount of the inner hole. Become. For this reason, when the thrust dynamic pressure generating portion is formed on the entire lower end surface 10a of the thrust bush 10 and the entire upper end surface 8c of the bearing sleeve 8, the former area becomes larger than the latter area. In the present invention, the thrust dynamic pressure generating area formed on the lower end face 10a of the thrust bush 10 is deliberately taken into consideration in consideration of the balance of the thrust support force when the thrust force F is applied when the shaft member 2 rotates at a high speed. The supporting force F2 by the second thrust bearing portion T2 is made smaller than the supporting force F1 of the first thrust bearing portion T1.

  In addition, as described above, when the lubricating oil inside the bearing member 11 is caused to flow by the radial dynamic pressure generating portion and the thrust dynamic pressure generating portion, local negative pressure may be generated inside the bearing member 11. . In the present embodiment, as shown in FIG. 2, by forming an axial groove 8d1 on the outer peripheral surface 8d of the bearing sleeve 8, the space Q1 on the outer diameter side of the flange portion 2b and the seal space S are communicated, This space Q1 is always maintained at atmospheric pressure. Then, the pump-in type dynamic pressure groove 8c1 formed on the upper end face 8c of the bearing sleeve 8 pushes the lubricating oil into the inner diameter side from the space Q1 on the outer diameter side of the flange portion 2b. Negative pressure in the space Q2 facing the inner peripheral chamfer of the end face 8c is prevented. Also, the pump-in type dynamic pressure groove 10a1 formed on the lower end face 10a of the thrust bush 10 pushes the lubricating oil into the inner diameter side from the space Q1 on the outer diameter side of the flange portion 2b. Negative pressure in the space Q3 facing the escape portion 10a4 is prevented. Further, as shown in FIG. 3, the radial dynamic pressure generating portion (dynamic pressure groove 8a1) of the lower radial bearing surface A1 formed on the inner peripheral surface 8a of the bearing sleeve 8 has an axially asymmetric shape. Lubricating oil filled in the radial bearing gap of the first radial bearing portion R1 is pushed upward, and generation of negative pressure in the space Q4 facing the escape portion 2a3 of the shaft portion 2a is prevented.

  At this time, the lubricating oil in the radial bearing gap is pushed upward by the radial dynamic pressure generating portion of the lower radial bearing surface A1, whereby the shaft member 2 receives the upward support force F3 (see FIG. 2). When the shaft member 2 rotates at a high speed, the upward support force F3 increases to counter the downward thrust F, and the lower end surface 2b1 of the flange portion 2b of the shaft member 2 contacts the upper end surface 8c of the bearing sleeve 8. Can be prevented more reliably.

  Further, when the shaft member 2 is stopped, the lower end surface 2b1 of the flange portion 2b and the upper end surface 8c of the bearing sleeve 8 come into contact with each other, and the thrust bearing gap of the first thrust bearing portion T1 becomes zero. When the motor is started from this state and the shaft member 2 is rotated, the shaft member 2 is levitated by the supporting force F1 of the first thrust bearing portion T1. At this time, the shaft member 2 is levitated at an early stage by the first thrust bearing portion T1 having a relatively large supporting force, so that the shaft member 2 is levitated at an early stage to contact the flange portion 2b and the bearing sleeve 8. Sliding can be prevented as much as possible.

  The present invention is not limited to the above embodiment. Hereinafter, although other embodiment of this invention is described, the same code | symbol is attached | subjected to the location which has the function similar to the said embodiment, and duplication description is abbreviate | omitted.

  In the above embodiment, the axial flow fan motor shown in FIG. 1 is used with the opening side of the bearing member 11 as the lower side and the closing side as the upper side. However, the present invention is not limited to this. You may use it upside down. In this case, due to the gravity of the rotor 3, a downward force is applied to the shaft member 2, that is, a force opposite to the upward thrust F applied to the shaft member 2 as it rotates, so that the flange portion 2 b is pressed against the bearing sleeve 8. The direction force is reduced.

  In the above embodiment, the housing 7 and the seal portion 9 are integrally formed. However, the present invention is not limited to this. For example, as shown in FIG. 6, the housing 7 and the seal portion 9 may be formed separately. Good. In the above embodiment, the housing 7 and the thrust bush 10 are formed separately. However, the present invention is not limited to this. For example, as shown in FIG. 6, the housing 7 and the thrust bush 10 may be integrally formed. .

  Moreover, in said embodiment, although the wedge-shaped seal space S is formed between the taper surface 2a2 of the outer peripheral surface of the axial part 2a, and the cylindrical inner peripheral surface 9a of the seal part 9, it is not restricted to this. For example, as shown in FIG. 7, the inner peripheral surface 9a of the seal portion 9 is a tapered surface that gradually increases in diameter downward, and the outer peripheral surface of the shaft portion 2a facing this is a cylindrical surface. A seal space S having a wedge-shaped cross section may be formed therebetween.

  Further, in the above embodiment, the herringbone-shaped dynamic pressure groove 8a1 is shown as the radial dynamic pressure generating portion formed on the radial bearing surface 2a1 of the shaft portion 2a. The radial dynamic pressure generating portion may be constituted by a groove, an axial groove, or a multi-arc surface. Further, in the above-described embodiment, the case where the radial dynamic pressure generating portions are formed at two locations separated in the axial direction of the inner peripheral surface 8a of the bearing sleeve 8 is shown, but not limited thereto, the radial dynamic pressure generating portions are It may be formed only at one place, or two radial dynamic pressure generating portions may be continued in the axial direction. In the above embodiment, the radial dynamic pressure generating portion of the upper radial bearing surface A1 has an asymmetric shape in the axial direction, and the lubricating oil in the radial bearing gap is pushed upward. If pushing is not necessary, the radial dynamic pressure generating portion of the upper radial bearing surface A1 may have a shape that is symmetrical in the axial direction.

  In the above embodiment, the spiral dynamic pressure groove is shown as the thrust dynamic pressure generating portion formed in the flange portion 2b. However, the present invention is not limited to this, and for example, a herringbone-shaped dynamic pressure groove may be adopted. Good.

  Further, in the above embodiment, the dynamic pressure generating portion is formed on the inner peripheral surface 8a, the upper end surface 8c, and the lower end surface 10a of the thrust bush 10 of the bearing sleeve 8. A dynamic pressure generating portion may be formed on the outer peripheral surface (radial bearing surface 2a1) of the shaft portion 2a, the lower end surface 2b1 and the upper end surface 2b2 of the flange portion 2b.

  In the above embodiment, the lubricating fluid is a lubricating oil. However, the present invention is not limited to this. For example, a fluid such as a magnetic fluid or air can be used.

  In the above embodiment, the shaft member 2 is rotated. However, the present invention is not limited to this, and the shaft member 2 may be fixed and the bearing member 11 may be rotated. In this case, the rotor 3 (fan 3a) is attached to the bearing member 11.

DESCRIPTION OF SYMBOLS 1 Fluid dynamic pressure bearing apparatus 2 Shaft member 2a Shaft part 2b Flange part 3 Rotor 4 Stator coil 5 Magnet 6 Casing 7 Housing 8 Bearing sleeve 9 Sealing part 10 Thrust bush 11 Bearing member 11a Sleeve part 11b Bottom part A1, A2 Radial bearing surface R1 , R2 Radial bearing portion T1, T2 Thrust bearing portion S Seal space F Thrust F1 Support force F1 by the first thrust bearing portion Support force by the second thrust bearing portion

Claims (6)

A shaft member having a shaft portion and a flange portion; a sleeve portion in which the shaft portion is inserted into an inner periphery; a bearing member having a bottom portion that closes one end opening of the sleeve portion; and an outer peripheral surface of the shaft portion. A radial bearing portion that relatively supports the shaft member in a radial direction by a dynamic pressure action of a lubricating fluid generated in a radial bearing gap between the inner peripheral surface of the sleeve portion, one end surface of the sleeve portion, and one of the flange portions Two thrust bearing gaps are supported relative to each other in the thrust direction by the dynamic pressure action of the lubricating fluid generated in the thrust bearing gap between the end face and the thrust bearing gap between the end face of the bottom part and the other end face of the flange part. A fluid dynamic bearing device comprising a thrust bearing portion, wherein the shaft member and the bearing member relatively rotate at 10,000 r / min or more;
The shaft member receives a relative thrust toward one axial direction with relative rotation, and relatively pushes the shaft member toward one axial direction of the two thrust bearing portions. A fluid dynamic bearing device characterized in that the supporting force of one thrust bearing portion is smaller than the supporting force of the other thrust bearing portion that relatively pushes the shaft member toward the other axial direction.   The two thrust bearing portions are provided with a thrust dynamic pressure generating portion for generating a dynamic pressure action on the lubricating fluid filled in the thrust bearing gap, and the area of the thrust dynamic pressure generating portion of the one thrust bearing portion is The fluid dynamic bearing device according to claim 1, wherein the thrust dynamic pressure bearing device is smaller than an area of the thrust dynamic pressure generating portion of the other thrust bearing portion.   The thrust is generated in a direction in which one end surface of the sleeve portion and one end surface of the flange portion are brought close to each other, and a thrust bearing gap of the one thrust bearing portion is formed between the end surface of the bottom portion and the other end surface of the flange portion. The fluid dynamic bearing device according to claim 1, wherein the fluid dynamic bearing device is formed therebetween.   A radial dynamic pressure generating portion that generates a dynamic pressure action on the lubricating fluid filled in the radial bearing gap is provided in the radial bearing portion, and the radial dynamic pressure generating portion pushes the lubricating fluid toward the other axial direction. The fluid dynamic bearing device according to claim 1.   The fluid dynamic bearing device according to any one of claims 1 to 4, wherein a thrust bearing gap of the other thrust bearing portion becomes 0 when the shaft member is stopped.   An axial fan motor having the fluid dynamic pressure bearing device according to claim 1 and generating an air flow in an axial direction.

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