Burnt oil-impregnated shaft

Abstract

The present invention provides a sintered oil-impregnated bearing in which a stepped surface having axial grooves with a rectangular cross-section arranged at a predetermined pitch along the circumferential direction is formed on the inner diameter surface of the bearing bore, and is capable of effectively exhibiting the dynamic pressure effect. [Solution] The bearing hole is equipped with a radial dynamic pressure generating section having a step surface formed on its inner diameter surface, which has axial grooves with a rectangular cross-section arranged at a predetermined pitch along the circumferential direction. The rectangularity of the axial grooves, calculated from the shape obtained by linearly unfolding the roundness shape of the step surface measured by the least squares center method, is 0.025 or less, and the flatness of the ridges between adjacent axial grooves in the circumferential direction is 0.80 or more. Rectangularity is an index in which the closer the value is to 0, the closer it is to a rectangle, and flatness is an index in which the closer the value is to 1, the more flat the area.

Description

Technical Field

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[0001] The present invention relates to a sintered oil-impregnated bearing.

Background Art

[0002] Sintered oil-impregnated bearings are generally used for bearings that rotationally support small motors such as spindle motors for magnetic disk drives (HDDs), polygon mirrors for laser beam printers (LBPs), and fan motors.

[0003] This type of sintered oil-impregnated bearing can be used, for example, in a hydrodynamic bearing device that provides a hydrodynamic oil film in the bearing clearance by providing hydrodynamic grooves such as herringbone or spiral shapes on the bearing surface and causing the shaft to float and be supported by the action of the hydrodynamic grooves as the shaft rotates.

[0004] By the way, conventionally, there has been a sintered oil-impregnated bearing in which a substantially rectangular stepped portion having a sliding surface concentric with the rotating shaft is provided on the inner diameter surface of the bearing hole in the circumferential direction, and the gap surrounded by adjacent stepped portions, the inner diameter surface of the bearing hole therebetween, and the rotating shaft is substantially rectangular (Patent Document 1). That is, in the sintered oil-impregnated bearing described in Patent Document 1, a step surface having axial grooves with a rectangular cross-section arranged at a predetermined pitch along the circumferential direction is formed on the inner diameter surface of the bearing hole.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] As described in Patent Document 1, in a step surface having axial grooves with a rectangular cross-section arranged at a predetermined pitch along the circumferential direction, if the axial grooves have a perfectly rectangular cross-sectional shape, the oil film pressure will be high, but if they are not perfectly rectangular, the oil film pressure will be high or unstable. Furthermore, the greater the flatness of the ridges between the axial grooves, the larger the contact area can be made, and the lower the contact surface pressure can be made.

[0007] However, the bearing described in Patent Document 1 does not disclose any specification regarding the degree of rectangularity of the cross-sectional shape of the axial groove. Furthermore, regarding the ridges between the axial grooves, it is only stated that they are concentric with the axis of rotation, and there is no disclosure regarding the degree of flatness of these ridges. As a result, the bearing described in Patent Document 1 may not be perfectly rectangular, and in such cases, the oil film pressure may increase or become unstable. Also, if the flatness of the ridges is small, the contact area cannot be increased, and there is a risk that the contact pressure cannot be reduced. For this reason, it was unclear whether the dynamic pressure effect could be effectively utilized with the bearing described in Patent Document 1.

[0008] Therefore, in view of these circumstances, the present invention aims to provide a bearing that can effectively exert a dynamic pressure effect in a sintered oil-impregnated bearing in which a stepped surface having axial grooves with a rectangular cross-section arranged at a predetermined pitch along the circumferential direction is formed on the inner diameter surface of the bearing hole. [Means for solving the problem]

[0009] The sintered oil-impregnated bearing of the present invention is a sintered oil-impregnated bearing in which a shaft member is inserted into a bearing hole, and comprises a radial dynamic pressure generating section formed on the inner diameter surface of the bearing hole, having a step surface with axial grooves having a rectangular cross-section arranged at a predetermined pitch along the circumferential direction, wherein the rectangularity of the axial grooves calculated from the shape obtained by linearly unfolding the roundness shape of the step surface measured by the least squares center method is 0.025 or less, and the flatness of the hills between adjacent axial grooves in the circumferential direction is 0.80 or more, wherein the rectangularity is calculated based on the inclination of the groove side surface between a first part at 20% of the groove depth from the circumscribed circle and a second part at 20% of the groove depth from the inscribed circle, and the rectangularity is an index in which the value approaches 0 as it approaches rectangular, and the flatness is calculated based on the ratio of the total width dimension of the hill at the second part to the total length of the shape obtained by linearly unfolding, and the flatness is an index in which the value approaches 1 as it approaches flat. In other words, flatness is an indicator where 1 is the maximum, and as it approaches 1, the contact area increases, reducing the contact area and allowing the dynamic pressure effect to be fully realized. Here, the least squares center method finds the reference circle at which the square of the error is smallest, and then finds the radii of the circumscribed and inscribed circles concentric with this reference circle. In this case, the roundness is (radius of the circumscribed circle) - (radius of the inscribed circle). Here, the circumscribed circle is the maximum groove depth (maximum diameter), and the inscribed circle is the minimum groove depth (minimum diameter). Linear expansion is the process of expanding the polar coordinates obtained from the roundness data into Cartesian coordinates, and Cartesian coordinates are obtained by analyzing the roundness data using flatness.

[0010] In the sintered oil-impregnated bearing of the present invention, the cross-sectional shape of the axial groove is close to rectangular, resulting in increased oil film pressure. Furthermore, the flatness of the ridges is increased, and the flat areas of the ridges are widened, resulting in a larger contact area and reduced contact pressure. Therefore, the dynamic pressure effect can be effectively utilized.

[0011] Since the rectangularity is calculated based on the slope of the groove side surface between the first section at 20% of the groove depth (from the maximum groove depth) and the second section at 20% of the groove depth (from the minimum groove depth), the rectangularity can be calculated stably.

[0012] In particular, when the total length of the shape obtained by linearly unfolding the roundness shape of the step surface measured by the least-squares center method is defined as W1, the total groove width at the first part of all grooves is defined as W2, and the total width of all raised parts at the second part is defined as W3, W1-(W2+W3) is defined as the inclined portion data, the ratio of the inclined portion data to the total length is calculated, and the value obtained by dividing this calculated value by the number of grooves is set to be the rectangularity. By setting it in this way, the reliability of the calculated rectangularity is improved.

[0013] The total width of all the hills in the second section can be defined as W3, and the ratio of W3 to the total length W1 (W1 / W3) can be calculated. This calculated value can then be divided by the value obtained by hill-to-groove ratio / (hill-to-groove ratio+1) to obtain the flatness. By setting it in this way, the reliability of the calculated flatness is improved.

[0014] It is preferable that the groove depth of the axial groove is 2 μm or more. In this case, the groove depth is at the axial midpoint of the axial groove. By setting it in this way, dynamic pressure can be generated stably.

[0015] The aforementioned groove-to-hill ratio is the groove-to-hill ratio on the squared centerline (mean square height) in the axial groove, and it is preferable that this groove-to-hill ratio is between 0.1 and 1.0. In this case, when the width dimension of the hill is W10 and the width dimension of the groove is W11, the groove-to-hill ratio becomes W10 / W11. By setting it in this way, it is possible to generate dynamic pressure and secure a sliding surface area, thereby obtaining stable rotational motion. Here, the squared centerline in the axial groove refers to the mean square height in the axial groove. [Effects of the Invention]

[0016] This makes it possible to numerically determine the shape of the raised portion of bearings (sintered oil-impregnated bearings) that excel in oil film formation. As a result, it is possible to provide sintered oil-impregnated bearings that can effectively exert the dynamic pressure effect as a product. [Brief explanation of the drawing]

[0017] [Figure 1]This is a diagram of the shape obtained by linearly developing the roundness shape of the stepped surface measured by the least squares center method on the inner diameter surface of the bearing hole of the present invention. [Figure 2] This is a cross-sectional view of a spindle motor using a sintered oil-impregnated bearing. [Figure 3] This is a cross-sectional view of a sintered oil-impregnated bearing. [Figure 4] This is a longitudinal sectional view of a sintered oil-impregnated bearing [Figure 5] This is a block diagram showing the steps of a method for manufacturing a sintered oil-impregnated bearing. [Figure 6] This is an enlarged view of the main part of FIG. 1. [Figure 7] Axial grooves are shown, where (a) is a simplified cross-sectional view of a non-defective product and (b) is a simplified cross-sectional view of a defective product. [Figure 8] This is a simplified diagram showing the roundness shape measured by the least squares center method.

Embodiments for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present invention will be described based on FIGS. 1 to 8. FIG. 2 shows a spindle motor used in a disk drive device of an HDD. This spindle motor includes a hydrodynamic bearing device 1, a disk hub 3 fixed to a shaft member 2 of the hydrodynamic bearing device 1, a stator coil 4 and a rotor magnet 5 opposed through a radial gap, and a bracket 6. The stator coil 4 is fixed to the bracket 6, and the rotor magnet 5 is fixed to the disk hub 3. The housing 7 of the hydrodynamic bearing device 1 is fixed to the inner diameter surface of the bracket 6. A predetermined number (two in the illustrated example) of disks 10 are held on the disk hub 3. When the stator coil 4 is energized, the rotor magnet 5 rotates, and accordingly, the disk 10 held on the disk hub 3 rotates integrally with the shaft member 2

[0019] The hydrodynamic bearing device 1 includes a sintered oil-impregnated bearing 8 according to an embodiment of the present invention, a shaft member 2 inserted into the inner circumference of the sintered oil-impregnated bearing 8, a bottomed cylindrical housing 7 with the sintered oil-impregnated bearing 8 fixed to its inner diameter surface, and a seal member 9 disposed at the opening of the housing 7. In the following description of the hydrodynamic bearing device 1, for convenience, the opening side of the housing 7 in the axial direction is referred to as the upper side, and the opposite side is referred to as the lower side.

[0020] Between the lower end surface 8e of the sintered oil-impregnated bearing 8 and the upper end surface 7b1 of the bottom 7b of the opposing housing 7, a flange portion 2b provided at the lower end of the shaft member 2 is accommodated.

[0021] The sintered oil-impregnated bearing 8 has a bearing hole 8A into which the shaft member is inserted. On the inner diameter surface 8A1 of the bearing hole 8A, a first radial dynamic pressure generating portion 8a and a second radial dynamic pressure generating portion 8b are formed at two locations spaced apart in the axial direction. As shown in FIG. 3, the first radial dynamic pressure generating portion 8a is constituted by a stepped surface having a plurality of (in the illustrated example, 4) axially grooved G (G1) having a rectangular cross-section at a predetermined pitch (in the illustrated example, a 90-degree pitch) along the circumferential direction. Also, a mound portion H (H1) is provided between the axially grooved G1, G1 adjacent to each other in the circumferential direction. The second radial dynamic pressure generating portion 8b is also constituted by a stepped surface having a plurality of (in the illustrated example, 4) axially grooved G (G2) having a rectangular cross-section at a predetermined pitch (in the illustrated example, a 90-degree pitch) along the circumferential direction. Also, a mound portion H (H2) is provided between the axially grooved G2, G2 adjacent to each other in the circumferential direction.

[0022] In the fluid bearing device configured as described above, when the shaft member 2 rotates, the formation region of the axially grooved G formed on the inner diameter surface of the sintered oil-impregnated bearing 8 forms a radial bearing clearance with the outer peripheral surface 2a of the opposing shaft member 2. Therefore, due to the dynamic pressure action of the lubricating oil generated by the axially grooved G, as shown in FIG. 2, a first radial bearing portion R1 and a second radial bearing portion R2 that non-contact support the shaft member 2 in the radial direction are respectively constituted.

[0023] Simultaneously, the pressure of the lubricating oil film formed in the thrust bearing gap between the lower end surface 8e (dynamic groove forming region) of the sintered oil-impregnated bearing 8 and the upper end surface of the flange portion 2b facing it, and in the thrust bearing gap between the upper end surface 7b1 (dynamic groove forming region) of the bottom portion 7b of the housing 7 and the lower end surface of the flange portion 2b facing it, is increased by the dynamic pressure action of the dynamic groove. Then, the pressure of these oil films forms the first thrust bearing portion T1 and the second thrust bearing portion T2, respectively, which provide non-contact support to the flange portion 2b (shaft member 2) in the thrust direction.

[0024] The upper end face 8d of the sintered oil-impregnated bearing 8 has an annular groove (not shown) and a plurality of radial grooves (not shown) provided on the inner diameter side of the annular groove. The outer circumferential surface 8c of the sintered oil-impregnated bearing 8 has a plurality of axial grooves 8c1 provided at equal intervals in the circumferential direction. Through these axial grooves 8c1, annular groove, radial grooves, etc., the space on the outer diameter side of the flange portion 2b of the shaft member 2 communicates with the seal space, thereby preventing the generation of negative pressure in this space.

[0025] Incidentally, the sintered oil-impregnated bearing 8 is manufactured by the process shown in Figure 5. That is, this manufacturing process proceeds in the order of powder compaction process S1, sintering process S2, and dynamic pressure groove formation process S3. The powder compaction process S1 is a process of compressing metal powder such as Cu powder, Cu alloy powder, Fe powder, or Fe powder coated with Cu into a cylindrical shape; the sintering process S2 is a process of sintering the powder compact obtained in the powder compaction process at a predetermined sintering temperature; and the dynamic pressure groove formation process S3 is a process of forming a dynamic pressure groove on the inner diameter surface after sealing treatment.

[0026] Prior to the compaction molding process S1, a raw material powder mixing process is performed. Here, the raw material powder mixing process is a process in which raw material powder for the sintered oil-impregnated bearing 8 is produced by mixing multiple types of powders.

[0027] If the groove formed on the inner diameter surface 8A1 of the bearing hole 8A is not an axial groove but a herringbone-shaped groove, then when the core rod with the mold formed on its outer circumference is pulled out of the hole in the sintered body during the dynamic groove formation process, the hole in the sintered body will be separated from the mold of the core rod, which has been expanded by springback. Therefore, when the core rod is pulled out of the sintered body, some of the ridges between the grooves will be scraped away.

[0028] However, if the sintered body has axial grooves G, the core rod can be pulled out of the sintered body along the axial direction without utilizing springback. Moreover, the risk of the ridges H between the grooves being worn away is reduced.

[0029] If the axial groove G has a perfectly rectangular cross-sectional shape, the oil film pressure will increase. Also, if the ridges H between the axial grooves are large, the contact area can be increased, and the contact pressure can be reduced.

[0030] Therefore, in this bearing, the rectangularity of the axial groove, calculated from the shape obtained by linearly unfolding the roundness shape of the step surface measured by the least squares center method, is 0.025 or less, and the flatness of the ridges between adjacent axial grooves in the circumferential direction is 0.80 or more. Here, the least squares center method involves finding the reference circle at the point where the square of the error is smallest, and then determining the radii of the circumscribed and inscribed circles concentric with this reference circle. In this case, the roundness is (radius of the circumscribed circle) - (radius of the inscribed circle). Figure 8 shows the roundness shape measured by the least squares center method.

[0031] In this case, the rectangularity is calculated based on the inclination of the groove sides Ga and Gb (see Figure 6) between the first section (section D) at 20% of the groove depth (dimension C) from the maximum groove depth (value at section A), and the second section (section E) at 20% of the groove depth (dimension C) from the minimum groove depth (value at section B), as shown in Figure 1. The flatness is calculated based on the width dimension of the hill H at the second section (section E). The maximum groove depth (value at section A) represents the circumscribed circle shown in Figure 8, and the minimum groove depth (value at section B) represents the inscribed circle.

[0032] Specifically, the rectangularity is calculated by taking W1 as the total length of the linearly unfolded shape of the step surface measured using the least squares center method, W2 as the total groove width at the first part (part D) of all grooves, and W3 as the total hill width of all hills at the second part, then taking W1 - (W2 + W3) as the inclined portion data, calculating the ratio of the inclined portion data to the total length, and dividing that calculated value by the number of grooves (four in this embodiment).

[0033] If we let w2 be the width of one groove G in the first section (section D), then the total groove width W2 is (w2 + w2 + w2 + w2 = 4w2) because there are four grooves G in this case. Also, if we let w3 be the width of one hill H in the second section (section E), then the total hill width W3 is (w3 + w3 + w3 + w3 = 4w3) because there are four hill H in this case.

[0034] Therefore, the data for the inclined section, W1-(W2+W3), becomes W1-(4w2+4w3). Also, if the groove width in the second section (section E) is w4, then the total groove W4 is (w4+w4+w4+w4=4w4) because there are four grooves G in this case. Furthermore, the groove width w4 in the second section (section E) is w5+w2+w6.

[0035] Therefore, w4 - w2 = w5 + w6. Here, w5 is the inclination of one groove side surface Ga of groove G, and w6 is the inclination of the other groove side surface Gb. The inclination of one groove side surface Ga is given by w5 = Ltanα, where α is the inclination angle of this groove side surface Ga (inclination angle with respect to the groove depth direction) and L is the dimension between the first part (part D) and the second part (part E), as shown in Figure 6. The inclination of the other groove side surface Gb is given by w6 = Ltanβ, where β is the inclination angle of this groove side surface Gb (inclination angle with respect to the groove depth direction) and L is the dimension between the first part (part D) and the second part (part E).

[0036] The data for the inclined portion is W1 - (4w2 + 4w3). Therefore, (W1 - (4w2 + 4w3)) / W1 is the degree of rectangularity. In this case, if it is a perfect rectangle, W1 = (4w2 + 4w3), and the degree of rectangularity is 0. In other words, in this invention, the degree of rectangularity is a value (index) that approaches 0 as it approaches a rectangle. Therefore, by setting the degree of rectangularity to 0.025 or less, it is considered to be approaching a perfect rectangle.

[0037] Furthermore, the total length of the shape obtained by linearly unfolding the circularity shape of the step surface measured by the least squares center method is defined as W1, and the total width of all the hills in the second part is defined as W3 (w3 + w3 + w3 + w3). The ratio of W3 to the total length W1 (W1 / W3) is calculated, and the flatness value obtained by dividing this calculated value by a value expressed as hill-groove ratio / (hill-groove ratio + 1) is defined as the flatness. This is because the hill-groove ratio affects this calculated value. Flatness is an index in which the closer the value is to 1, the larger the flat area.

[0038] Here, the hill-to-groove ratio is the ratio of the hill width to the groove width on the squared centerline (mean square height Ra (see Figure 6)). In this case, as shown in Figure 6, when the hill width is W10 and the groove width is W11, the hill-to-groove ratio is W10 / W11.

[0039] For example, if the hill-to-groove ratio is 2, as shown in Table 1 below, with a hill-to-groove ratio of +1, the hill portion ratio becomes 2 (hill-to-groove ratio) and the groove portion ratio becomes 1, so hill-to-groove ratio +1 = 3. Therefore, hill-to-groove ratio / (hill-to-groove ratio +1) becomes 0.67. Also, the calculated value (W1 / W3) calculated from the linearly unfolded coordinate data (value assuming a perfect rectangle: 0.667) is obtained, and the ratio in this case is 1.0, and when it is 1.0, the flat area becomes wider. [Table 1]

[0040] Table 1 shows the cases where the flatness is 1.0 for hill-to-groove ratios other than 2.0, such as 0.2, 0.5, 1.0, and 3.0. When the hill-to-groove ratio is 0.2, the hill-to-groove ratio + 1 becomes 1.2, and the hill-to-groove ratio / (hill-to-groove ratio + 1) becomes 0.17, and the value assuming a perfect rectangle is 0.167, resulting in a flatness of 1.0. When the hill-to-groove ratio is 0.5, the hill-to-groove ratio + 1 becomes 1.5, and the hill-to-groove ratio / (hill-to-groove ratio + 1) becomes 0.33, and the value assuming a perfect rectangle is 0.333, resulting in a flatness of 1.0. When the hill-to-groove ratio is 1.0, the hill-to-groove ratio + 1 becomes 2, and the hill-to-groove ratio / (hill-to-groove ratio + 1) becomes 0.50, and the value assuming a perfect rectangle is 0.500, resulting in a flatness of 1.0. The flatness is 1.0. If the hill-to-groove ratio is 3.0, then the hill-to-groove ratio + 1 becomes 4.0, and the hill-to-groove ratio / (hill-to-groove ratio + 1) becomes 0.75. Assuming a perfect rectangle, the value becomes 0.750, and the flatness is 1.0.

[0041] Figure 7 shows the linearly unfolded shape of the roundness of the step surface measured by the least squares center method. In Figure 7(a), the rectangularity is 0.019 and the flatness is 0.805. In Figure 7(b), the rectangularity is 0.041 and the flatness is 0.706. In other words, in Figure 7(a), the rectangularity is less than 0.025 and the flatness is greater than 0.80, while in Figure 7(b), the rectangularity is greater than 0.025 and the flatness is less than 0.80. Therefore, Figure 7(a) is a good product, and Figure 7(b) is a defective product.

[0042] It is preferable to set the hill-to-groove ratio to 0.1 to 1.0. If it is less than 0.1, the hill portion H is too small, making it difficult to obtain a stable rotational force, and conversely, if it exceeds 1.0, the groove G is too small, making it difficult to obtain a stable dynamic pressure. For this reason, in terms of flatness, the closer the flatness value is to 1, the larger the flat portion.

[0043] In the sintered oil-impregnated bearing of the present invention, the cross-sectional shape of the axial groove G is close to rectangular, increasing the oil film pressure, and the flatness of the ridge portion H is large, widening the flat portion of the ridge portion and increasing the contact area, thereby reducing contact. Therefore, the dynamic pressure effect can be effectively utilized. As a result, it is possible to numerically determine the shape of the ridge portion of a bearing (sintered oil-impregnated bearing) that is excellent in oil film formation. Therefore, it is possible to provide a sintered oil-impregnated bearing that can effectively utilize the dynamic pressure effect as a product.

[0044] Since the rectangularity is calculated based on the slope of the groove side surface between the first point at 20% of the groove depth (from the maximum groove depth) and the second point at 20% of the groove depth (from the minimum groove depth), the rectangularity can be calculated stably.

[0045] It is preferable that the groove depth of the axial groove G is 2 μm or more. By setting it in this way, stable dynamic pressure can be generated.

[0046] A groove-to-hill ratio of 0.1 to 1.0 is preferable. By setting it in this way, dynamic pressure can be generated, and a sufficient sliding surface area can be secured, resulting in stable rotational motion.

[0047] In particular, when the total length of the shape obtained by linearly unfolding the roundness shape of the step surface measured by the least-squares center method is defined as W1, the total groove width at the first part of all grooves is defined as W2, and the total width of all raised parts at the second part is defined as W3, W1-(W2+W3) is defined as the inclined portion data, the ratio of the inclined portion data to the total length is calculated, and the value obtained by dividing this calculated value by the number of grooves is set to be the rectangularity. By setting it in this way, the reliability of the calculated rectangularity is improved.

[0048] The total width of the entire mound in the second section is defined as W3, and the ratio of W3 to the total length W1 (W1 / W3) is calculated. The flatness can then be obtained by dividing this calculated value by the following formula. By setting it in this way, the reliability of the calculated flatness is improved. Flatness is an indicator where 1 is the maximum, and as it approaches 1, the contact area increases, reducing the contact area and allowing the dynamic pressure effect to be fully exerted.

[0049] Although embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and can be modified in various ways. In the embodiments, the inner diameter surface 8A1 of the bearing hole 8A of the sintered oil-impregnated bearing 8 had two radial dynamic pressure generating sections, a first radial dynamic pressure generating section 8a and a second radial dynamic pressure generating section 8b, spaced apart in the axial direction. However, the sintered oil-impregnated bearing 8 may have only one radial dynamic pressure generating section on its inner diameter surface. That is, in the sintered oil-impregnated bearing 8 shown in Figure 4, the axial groove G1 and axial groove G2 were separated, but as shown by the dashed line in Figure 4, the axial groove G1 and axial groove G2 may be continuous. Also, in the embodiments, the number of axial grooves in one radial dynamic pressure generating section was four, but it is not limited to four, and the number of axial grooves can be increased or decreased as desired. In the above embodiment, the case in which the sintered oil-impregnated bearing 8 is fixed and the shaft member 2 rotates was shown, but the invention is not limited to this, and a configuration in which the shaft member 2 is fixed and the sintered oil-impregnated bearing 8 is rotated, or a configuration in which both the shaft member 2 and the sintered oil-impregnated bearing 8 are rotated can also be adopted.

[0050] Incidentally, the rectangularity and flatness are the average of multiple axial grooves and the average of multiple ridges. Therefore, it is not necessary for all of the multiple grooves to have a rectangularity of 0.025 or less and a flatness of 0.80 or more; even if one or several grooves do not meet these requirements, it is sufficient if the average rectangularity is 0.025 or less and the flatness is 0.80 or more.

[0051] The fluid dynamic bearing device incorporating the sintered oil-impregnated bearing 8 according to the present invention is not limited to spindle motors used in HDD disk drive devices, but can also be widely used in other small motors such as spindle motors incorporated in other information equipment, polygon scanner motors in laser beam printers, color wheels in projectors, or cooling fan motors. [Explanation of Symbols]

[0052] 2 Shaft member 8a Radial dynamic pressure generation unit 8b Radial dynamic pressure generation unit G-axis direction groove H hill Part D, Section 1 Part E, Section 2

Claims

1. A sintered oil-impregnated bearing in which a shaft member is inserted into a bearing hole, The bearing hole is provided with a radial dynamic pressure generating section having a stepped surface on its inner diameter surface, which has axial grooves with a rectangular cross-section arranged at a predetermined pitch along the circumferential direction. The rectangularity of the axial groove, calculated from the shape obtained by linearly unfolding the circularity shape of the step surface measured by the least squares center method, is 0.025 or less, and the flatness of the ridges between adjacent axial grooves in the circumferential direction is 0.80 or more with a maximum of 1. The rectangularity is calculated based on the inclination of the groove side surface between the first part at 20% of the groove depth from the circumscribed circle and the second part at 20% of the groove depth from the inscribed circle, and the closer the value of the rectangularity is to 0, the closer it is to a rectangle. The flatness is calculated based on the ratio of the total width dimension of the ridge at the second part to the total length of the shape obtained by linearly unfolding. The flatness is an index in which the flatter the value approaches 1, and the total length of the shape obtained by linearly unfolding the roundness shape of the step surface measured by the least squares center method is taken as W1, and the total width of all the hills in the second part is taken as W3, and the ratio of W3 to the total length W1 (W3 / W1) is calculated, and the flatness is the value obtained by dividing the calculated value by the hill-groove ratio / (hill-groove ratio + 1), and the hill-groove ratio is the ratio of the hill width to the groove width on the square center line, and when the width dimension of the hill is taken as W10 and the width dimension of the groove is taken as W10 / W11, the sintered oil-impregnated bearing is characterized in that

2. The sintered oil-impregnated bearing according to claim 1, characterized in that when the total length of the shape obtained by linearly unfolding the roundness shape of the step surface measured by the least squares center method is taken as W1, the total groove width at the first portion of the entire groove is taken as W2, and the total width of the entire ridge portion at the second portion is taken as W3, W1 - (W2 + W3) is taken as the inclined portion data, the ratio of the inclined portion data to the total length is calculated, and the value obtained by dividing the calculated value by the number of grooves is the rectangularness.

3. The sintered oil-impregnated bearing according to claim 1, characterized in that the groove depth of the axial groove is 2 μm or more.

4. The sintered oil-impregnated bearing according to claim 1, characterized in that the groove-to-groove ratio is the groove-to-groove ratio on the squared center line in the axial groove, and this groove-to-groove ratio is 0.1 to 1.0.

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