Sintered bearings

Abstract

To provide a sintered bearing and a bearing device having excellent lubrication performance (sliding characteristics) without requiring peening, rolling and plastic working such as coining, etc.SOLUTION: A sintered bearing is configured by including lubrication oil in a cylindrical sintered body obtained through sinter of material powder mainly composed of a metallic material. Axial one end part serves as a first bearing part and axial the other end part serves as a second bearing part. A sliding surface is constituted by an inner diameter surface of the first bearing and an inner diameter surface of the second bearing. An intermediate portion including a relief part having a diameter larger than those of the inner diameter surface of the first bearing part and the inner diameter surface of the second bearing part is formed in a bearing inner diameter central part. A density difference is provided between the first bearing part and the second bearing part.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a sintered bearing. [Background technology]

[0002] Sintered bearings can be used, for example, as sintered oil-impregnated bearing components for small motors. Sintered bearings can achieve stable rotation speeds and keep current low even under conditions where the supply of lubricating oil is not smooth, such as in motor bearings used at low temperatures and high speeds. Sintered bearings are particularly well-suited for bearings such as automotive cooling fan motors, which are used in a wide range of temperatures, from low to high.

[0003] Conventionally, there is a type in which bearing portions are formed at both axial ends, and an intermediate portion (relief portion) whose inner diameter is larger than the inner diameter of each bearing portion is provided between the bearing portions (Patent Document 1).

[0004] By configuring as described in Patent Document 1, the inner circumferential surface of the intermediate portion does not come into contact with the rotating shaft, and the sliding area on the inner circumferential surface of the bearing hole is reduced. Therefore, compared to sintered bearings in which the inner diameter of the bearing hole is constant over the entire axial length (hereinafter referred to as "straight bearings"), contact between the inner circumferential surface of the bearing hole and the rotating shaft is suppressed, and at the same time, fluid resistance of the lubricant during shaft rotation is reduced, making it possible to reduce frictional resistance generated between the bearing and the rotating shaft. In other words, the sintered bearing of Patent Document 1 makes it possible to reduce frictional resistance with the rotating shaft and reduce noise.

[0005] In particular, a plurality of dimples are provided on the bearing surface of at least one of a pair of bearing parts that rotatably support a rotating shaft. As a result, the portion (range) of the bearing surface where each dimple is provided does not come into contact with the rotating shaft, thereby reducing the sliding area of ​​the bearing surface. This suppresses contact between the bearing surface and the rotating shaft, and at the same time reduces the fluid resistance of the lubricant when the shaft rotates, making it possible to reduce the frictional resistance generated between the bearing surface and the rotating shaft. Therefore, the sliding area on the inner surface of the bearing hole can be reduced without reducing the axial dimension of the bearing surface, making it possible to reduce the frictional resistance generated between the bearing surface and the rotating shaft while suppressing a decrease in oil film strength.

[0006] Furthermore, it has been shown that the impregnated lubricant is stored within each dimple, and when the rotating shaft rotates, the stored lubricant is drawn between the bearing surface and the rotating shaft, thereby reducing the friction coefficient of the bearing surface. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 6253134 Summary of the Invention [Problem to be solved by the invention]

[0008] However, forming dimples on a bearing surface requires plastic processing such as peening, rolling, and coining, which requires additional processing equipment and man-hours, as well as the production of tools for plastic processing that have protrusions, which creates problems in terms of productivity and cost.

[0009] In view of the above, the present invention provides a sintered bearing and a bearing device that have excellent lubrication performance (sliding characteristics) without requiring plastic processing such as peening, rolling, or coining. [Means for solving the problem]

[0010] The sintered bearing of the present invention is a sintered bearing having a sliding surface that slides against a mating shaft member, and is constructed by containing lubricating oil in a cylindrical sintered body obtained by sintering raw material powder whose main component is a metal material, and one axial end is a first bearing portion and the other axial end is a second bearing portion, with the sliding surface being formed by the inner diameter surfaces of the first bearing portion and the second bearing portion, and an intermediate portion is formed in the center of the inner diameter of the bearing having a relief portion with a larger diameter than the inner diameter surfaces of the first bearing portion and the second bearing portion, and a density difference is provided between the first bearing portion, the second bearing portion and the intermediate portion.

[0011] According to the sintered bearing of the present invention, by providing a relief portion, the sliding area of ​​the shaft member relative to the sintered bearing can be reduced, thereby reducing sliding resistance. By providing a density difference, oil is actively supplied in the direction of higher density, finer pores due to capillary action. Therefore, in the sintered bearing of the present invention, a circulation path can be formed so that lubricating oil circulates from the intermediate portion to the first bearing portion, and lubricating oil circulates from the intermediate portion to the second bearing portion.

[0012] It is preferable that the first bearing portion is a high-density region and the second bearing portion is a low-density region having a density lower than that of the high-density region, and that between the high-density region and the low-density region there is a lowest-density portion near the low-density region where the density is lower than that of the low-density region, and a density gradient portion where the density increases from this lowest-density portion to the high-density region.

[0013] By providing a density difference in this way, the lubricating oil is stably circulated from the relief portion side to the first bearing portion, and the lubricating oil is stably circulated from the relief portion side to the second bearing portion.

[0014] The density of the first bearing part is 0.08 (g / cm) lower than that of the second bearing part. 3 )~0.56(g / cm 3 ) is high, and the oil content of the first bearing part is set to be 1% to 7% lower than that of the second bearing part, and the density difference between the first bearing part and the second bearing part is set to 0.08 (g / cm 3 )~0.48(g / cm 3) and the difference in oil content can be set to 1% to 6%, and the difference in surface opening rate between the inner diameter surface of the first bearing portion and the inner diameter surface of the second bearing portion can be set to 5 to 45%. By setting them in this way, stable oil circulation can be achieved.

[0015] The bearing device according to the present invention is a bearing device using the sintered bearing, in which the first bearing portion is on the output side of the motor and the second bearing portion is on the opposite side of the motor's output side.

[0016] By placing a high-density region on the output side of the motor where sliding resistance is high, a large amount of lubricating oil is supplied to the output side, reducing the friction coefficient of the bearing surface. As a result, even when used over a wide temperature range, oil circulation and supply work smoothly, improving oil cut-off and ensuring good sliding. In particular, even at low temperatures where oil viscosity increases and smooth oil circulation and supply becomes difficult, oil circulation and supply work smoothly, improving oil cut-off and ensuring good sliding.

[0017] The density of the first bearing portion is set to be 0.08 (g / cm 3 ) higher than the density of the second bearing portion. 3 )~0.48(g / cm 3 ) higher than the density of the second bearing portion, and the oil content of the first bearing portion is 1% to 6% lower than the oil content of the second bearing portion, or the density of the first bearing portion is 0.16 (g / cm 3 )~0.40(g / cm 3 ) can be high, the oil content of the first bearing portion can be 2% to 5% lower than the oil content of the second bearing portion, and the surface opening rate of the inner diameter surface of the first bearing portion can be 5 to 45% lower than the surface opening rate of the inner diameter surface of the second bearing portion. [Effects of the Invention]

[0018] In the present invention, by imparting a density gradient function to a sintered bearing, a lubricating oil circulation path is formed, and a sliding member having excellent lubrication performance / sliding characteristics can be provided, without requiring special processing equipment, processing facilities, or special plastic processing tools.

[0019] In particular, by using the sintered bearing according to the present invention in a bearing device in which the first bearing portion is on the output side of the motor and the second bearing portion is on the opposite side of the motor's output side, oil circulation and supply work smoothly, oil shortage is improved, and good sliding is achieved, even when used over a wide temperature range. As a result, it is possible to improve the reduction and instability of the motor's rotation speed. It is also possible to achieve a reduction in power consumption. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a cross-sectional view of a sintered bearing according to the present invention. [Figure 2] FIG. 2 is an explanatory diagram showing the density distribution of a sintered bearing according to the present invention. [Figure 3] FIG. 2 is an explanatory diagram of oil circulation in a sintered bearing according to the present invention. [Figure 4] 1 is a manufacturing process diagram of a sintered bearing according to the present invention. [Figure 5] FIG. 1 is a simplified diagram of a core pin used in a compression molding process. [Figure 6] FIG. 1 is a plan view of a motor using a bearing device having a sintered bearing according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, an embodiment of the present invention will be described with reference to Figs. 1 to 6. Fig. 6 shows a motor (fan motor) using a bearing device according to the present invention. The bearing device 1 comprises a sintered bearing 2 according to the present invention, a housing 3 having a cylindrical portion 3a that holds the sintered bearing 2 on its inner periphery, and a shaft member 4 that is rotatably supported by the sintered bearing 2. The shaft member 4 is supported by a thrust receiver 5 that is provided at the bottom of the housing 3.

[0022] The fan motor includes a bearing device 1, a rotor 10 attached to one end (output side) of a shaft member 4 of the bearing device 1, and a stator 11 provided in a housing 3. The rotor 10 includes a rotor yoke 12 fixed to the shaft member, and a rotor magnet 13 fixed to the inner surface of a peripheral wall 12a of the rotor yoke 12. The stator 11 also includes a laminated core 15 fitted and fixed to the outside of the cylindrical portion 3a of the housing 3, and a coil 16 wound around the laminated core 15.

[0023] 1 and 3, one axial end portion is a first bearing portion 21, and the other axial end portion is a second bearing portion 22, with the inner diameter surface 21a of the first bearing portion 21 and the inner diameter surface 22a of the second bearing portion 22 forming a sliding surface 23 that slides against the mating shaft member 4. In addition, the sintered bearing 2 is formed with an intermediate portion 24 having a relief portion 24a in the center of the inner diameter of the bearing between the first bearing portion 21 and the second bearing portion 22, the relief portion 24a having a larger diameter than the inner diameter surfaces of the first bearing portion 21 and the second bearing portion 22.

[0024] Furthermore, a tapered portion 25 is formed on the outer diameter surface of the sintered bearing 2 on the second bearing portion 22 side. The tapered portion 25 is composed of a cylindrical surface portion 25a on the axially outer side of the second bearing portion 22 and a tapered surface portion 25b that expands in diameter from the cylindrical surface portion 25a toward the axially inner side. Therefore, the second bearing portion 22 includes the cylindrical surface portion 25a and a part of the tapered surface portion 25b. In this case, the outer diameter dimension of the second bearing portion 22 is smaller than the outer diameter dimension of the first bearing portion 21.

[0025] The inner diameters of the first bearing portion 21 and the second bearing portion 22 are set to be the same, and are set to be slightly larger than the outer diameter of the shaft member 4. That is, when the inner diameter of the first bearing portion 21 is D1, the inner diameter of the second bearing portion 22 is D2, and the outer diameter of the shaft member 4 is D (see FIG. 6), D1 = D2 > D. In this case, because a throttle portion 25 is formed on the outer diameter surface on the second bearing portion 22 side, the thickness of the second bearing portion 22 is smaller than the thickness of the first bearing portion 21. Furthermore, the clearance C between the outer diameter surface of the shaft member 4 and the inner diameter surfaces of the first bearing portion 21 and the second bearing portion 22 is, for example, approximately 2 μm to 8 μm. Furthermore, the term "same dimensions" includes a range within the dimensional tolerance.

[0026] 2, in this case, the density of the first bearing portion 21 is set higher than the density of the second bearing portion 22. The first bearing portion 21 and the first-bearing-adjacent portion 26 of the intermediate portion 24 form a high-density region H1, and the second bearing portion 22 and the second-bearing-adjacent portion 27 of the intermediate portion 24 form a low-density region H2. A density fluctuation region H3 is formed between the high-density region H1 and the low-density region H2, and the density of the high-density region H1 is higher than the density of the density fluctuation region H3. The density fluctuation region H3 has a minimum density portion 28 (a portion set to a density lower than that of the low-density region H2) near the low-density region H2, and a density gradient portion 29 where the density increases from the minimum density portion 28 toward the high-density region H1.

[0027] The density of the first bearing portion 21 is 0.08 (g / cm 3 )~0.56(g / cm 3 ), and the oil content of the first bearing portion 21 is set to be 1% to 7% lower than the oil content of the second bearing portion 22. The density difference between the first bearing portion 21 and the second bearing portion 22 is 0.08 (g / cm 3 )~0.48(g / cm 3), and the difference in oil content is set to be 1% to 6%. The difference in surface opening rate between the inner diameter surface of the first bearing part and the inner diameter surface of the second bearing part is set to be 5 to 45%. The surface opening rate refers to the ratio of the sum of the areas of all the openings (total area) per unit area.

[0028] By controlling the pressure balance during molding and by designing the mold, it is possible to set the density after sintering and sizing so that it has a density distribution like that shown in Figure 2. Furthermore, for example, by creating a difference in the inner diameter dimensions of the output side and the opposite side after in-mold sizing, and increasing the finishing allowance during spin finishing on the output side, it is possible to reduce the surface open area ratio. Therefore, by varying the finishing allowance during spin finishing at each location, it is possible to create a difference in the surface open area ratio at each location.

[0029] As shown in FIG. 4, the sintered bearing 2 is formed by carrying out a powder mixing step S1, a compression molding step S2, a sintering step S3, a sizing and rotating finishing step S4, and a cleaning and oil impregnation step S5.

[0030] As shown in Fig. 4, the raw material powders used in the powder mixing step S1 are, for example, copper powder, tin powder, iron powder, etc., mixed together and molded into a mixed powder. In this case, various molding aids, such as a lubricant (e.g., metal soap) for improving mold releasability, are added to the mixed powder as needed. However, the raw material powders used are not limited to these, and any powders commonly used for cylindrical sintered bearings can be used.

[0031] In the compression molding step S2, a green compact is formed by press molding using a mold device. This mold device includes cylindrical upper and lower punches, a core pin 30 (see FIG. 5) that forms the inner shape of the green compact, and a die that forms the outer shape of the green compact. In this case, in the compression molding step, an inner diameter step (relief portion 24a) is formed between only one side (the inner diameter surface 21a side of the first bearing portion 21) and the core pin main body 30c. In the sizing step described below, the other side (the inner diameter surface 22a side of the second bearing portion 22) is deformed from the outer diameter direction to reduce its diameter, forming a relief portion 24b in the inner diameter. In other words, the core pin 30 has a first molding portion 30a for molding one bearing surface (the inner diameter surface 21a of the first bearing portion 21), and the outer diameter of this molding portion 30a is smaller than the outer diameter of the core pin main body 30c. This differs from the forced removal method of the undercut portion that utilizes spring back when the mold is released during the compression molding process.

[0032] In the sintering step S3, the green compact obtained in the powder compacting step (compression molding step) is heated to the sintering temperature of the metal powder used to obtain a sintered body. That is, sintering is performed in a predetermined atmosphere and at a predetermined temperature. The predetermined atmosphere can be a vacuum, a reducing gas, an inert gas, or the like, and can be selected depending on the metal powder used.

[0033] In the sizing process S4, the sintered compact, which has undergone sintering deformation, is compressed to a uniform size. The dimensional changes (expansion and contraction) during sintering vary depending on the material composition, sintering temperature, and sintering atmosphere. Specifically, a core pin is inserted into the inner periphery of the sintered compact, and the axial width of the sintered compact is determined by upper and lower punches. The sintered compact is then pressed into the inner periphery of a die. The outer periphery of the sintered compact is compressed and molded by the die, and the inner periphery of the sintered compact is pressed against the outer periphery of a core rod (in-mold sizing). Specifically, in this sizing process, a core pin (not shown) with a plastic deformation margin on its other side (the inner diameter surface 22a side of the second bearing portion 22) is used to draw and deform the sintered compact from the outer diameter direction, thereby reducing its inner diameter and forming a recess 24b in the inner diameter. The core pin used in the sizing process is an inverted version of the core pin 30 used in the compression molding process. The sizing process forms the recess 24b in the inner diameter and improves dimensional accuracy. After the sizing step, the pores open to the inner peripheral surface may be further reduced in size by further performing rotational sizing on the inner peripheral surface of the sintered body. The sizing step includes a first sizing step (in-mold sizing step) and a second sizing step, and the second sizing step includes a rotational sizing step or an in-mold sizing step.

[0034] In the sintered bearing of the embodiment, a constricted portion 25 is formed on the outer diameter surface of the second bearing portion 22. For this reason, a die having an inner diameter bulge for forming the constricted portion 25 is used for sizing on the inner diameter surface.

[0035] The density of the second bearing portion 22 side is likely to be high because it is deformed by pressure during in-mold sizing. For this reason, the pressure balance during molding and mold design are set in advance so that the final density after sintering and sizing is lower than that of the output side.

[0036] After the sizing and rotating finishing process S4, the cleaning and oiling process S5 is carried out. That is, after cleaning and other processes, the material is impregnated with lubricating oil.

[0037] In the impregnation step S5, the sintered bearing 2 that has been formed into a predetermined shape through the sizing step is impregnated with lubricating oil, thereby completing the sintered bearing 2 with its internal pores impregnated with lubricating oil. The impregnation of the internal pores of the sintered bearing 2 with lubricating oil is carried out, for example, by immersing the sintered bearing 2 in a lubricating oil bath filled with lubricating oil for a certain period of time under a predetermined reduced pressure environment. At this time, the impregnation process may be carried out with the lubricating oil heated, in order to ensure that the lubricating oil is impregnated reliably and in a short period of time.

[0038] By providing a density difference, capillary action actively supplies oil in the direction of higher density, finer pores. As a result, in the sintered bearing of the present invention, a circulation path can be formed so that lubricating oil circulates from the intermediate region 24 side to the first bearing portion 21, and lubricating oil circulates from the intermediate region 24 side to the second bearing portion 22, as shown by the arrows in Figure 3.

[0039] According to the sintered bearing of the present invention, by providing the recess 24a, the sliding area of ​​the shaft member against this sintered bearing can be reduced, thereby reducing sliding resistance, and further, by forming an oil circulation path, the supply of lubricating oil in the sliding part is stabilized.

[0040] For this reason, the sintered bearing of the present invention does not require special processing equipment, processing facilities, or special plastic processing tools, and by providing the sintered bearing with a density gradient function, it is possible to form a circulation path for lubricating oil and provide a sliding member with excellent lubrication performance / sliding characteristics.

[0041] It is preferable that the first bearing portion 21 is a high-density region H1, the second bearing portion 22 is a low-density region H2 having a density lower than that of the high-density region H1, and that between the high-density region H1 and the low-density region H2 there is a lowest-density portion 28 near the low-density region H2 having a density lower than that of the low-density region H2, and a density gradient portion 29 in which the density increases from this lowest-density portion 28 to the high-density region H1.

[0042] By providing such a density difference, the circulation of the lubricating oil from the relief portion side to the first bearing portion 21 and the circulation of the lubricating oil from the relief portion side to the second bearing portion 22 are stably carried out.

[0043] In particular, it is preferable to provide a density gradient section 29 in which the density increases from the lowest density section 28 toward the high density region H1. By providing a density gradient in this way, the lubricating oil is supplied sequentially from the lowest density section 28 toward the high density region H1, stabilizing oil circulation.

[0044] The density of the first bearing portion 21 and the second bearing portion 22 is 0.08 (g / cm 3 ) lower than the density of the lowest density portion. 3 )~0.56(g / cm 3 ) is high, and the oil content of the first bearing part and the second bearing part is set to be 1% to 7% lower than the oil content of the lowest density part, and the first bearing part and the second bearing part have a density difference of 0.08 (g / cm 3 )~0.48(g / cm 3 ) and the difference in oil content can be set to 1% to 6%, and the difference in surface opening rate between the inner diameter surface of the first bearing portion and the inner diameter surface of the second bearing portion can be set to 5 to 45%, and by setting them in this way, stable oil circulation can be obtained.

[0045] The bearing device according to the present invention is a bearing device using a sintered bearing 2, with the first bearing portion 21 on the output side of the motor and the second bearing portion 22 on the opposite side of the motor's output. Therefore, by arranging the high-density region H on the output side of the motor, where sliding resistance is high, a large amount of lubricating oil is supplied to the output side, reducing the friction coefficient of the bearing surface. This allows smooth oil circulation and supply, improved oil cutoff, and good sliding, even when used over a wide temperature range. In particular, even at low temperatures, where oil viscosity increases and smooth oil circulation and supply become difficult, smooth oil circulation and supply are achieved, improved oil cutoff, and good sliding.

[0046] In such a bearing device, the density of the first bearing portion 21 is set to be 0.08 (g / cm 3 ) lower than the density of the second bearing portion 22.3 )~0.48(g / cm 3 ) higher than the density of the second bearing portion 22, and the oil content of the first bearing portion 21 is 1% to 6% lower than the oil content of the second bearing portion 22. 3 )~0.40(g / cm 3 ) can be high, the oil content of the first bearing portion can be 2% to 5% lower than the oil content of the second bearing portion, and the surface opening rate of the inner diameter surface of the first bearing portion can be 5 to 45% lower than the surface opening rate of the inner diameter surface of the second bearing portion.

[0047] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and various modifications are possible, and the present invention may not have the constricted portion 25. Furthermore, in the embodiment, a gradient of increasing density is provided, in which the density of the density fluctuation region H3 increases from the lowest density portion 28 toward the high density region H1, but such a gradient may not be provided.

[0048] Furthermore, the sintered bearing according to the present invention can be incorporated into and used not only in spindle motors for disk drive devices such as HDDs, but also in fan motors for cooling fans, polygon scanner motors for laser beam printers, etc. Furthermore, it is particularly suitable for bearings for automotive cooling fan motors, which are used over a wide temperature range from low to high temperatures. [Example]

[0049] The motor characteristics were investigated when a sintered bearing according to the present invention was used in a fan motor. The results are shown in Table 1. In this case, sintered bearings of Examples 1 to 5 and Comparative Examples 1 to 3 were produced. The sintered bearings of Examples 1 to 5 and Comparative Examples 1 to 3 had the shape shown in FIG. 1, with the first bearing portion 21 on the output side and the second bearing portion 22 on the non-output side. The inner diameters of the first bearing portion 21 and the second bearing portion 22 were φ3 mm, the outer diameters of the bearings were φ8 mm, and the widths (axial lengths) were 10 mm. The clearance between the bearing surface 23 (the inner diameter surface of the first bearing portion 21 and the inner diameter surface 22a of the second bearing portion 22) and the shaft member 4 was 4 μm, and the clearance between the recess 24a and the shaft member 4 was approximately 100 μm. [Table 1]

[0050] In Example 1, the density of the output side of A was set to 6.59 (g / cm 3 ), and the density of the opposite output side of B is 6.11 (g / cm 3 ), and the density of the lowest density part of C is 6.03 (g / cm 3 ), and in Example 2, the density of the output side of A is 6.51 (g / cm 3 ), and the density of the opposite output side of B is 6.11 (g / cm 3 ), and the density of the lowest density part of C is 6.03 (g / cm 3 ), and in Example 3, the density of the output side of A is 6.43 (g / cm 3 ) and the density of the opposite output side of B is 6.19 (g / cm 3 ) and the density of the lowest density part of C is 6.11 (g / cm 3 ), and in Example 4, the density of the output side of A is 6.35 (g / cm 3 ) and the density of the opposite output side of B is 6.19 (g / cm 3 ) and the density of the lowest density part of C is 6.11 (g / cm 3 ), and in Example 5, the density of the output side of A is 6.35 (g / cm 3 ), and the density of the opposite output side of B is 6.27 (g / cm 3 ) and the density of the lowest density part of C is 6.19 (g / cm 3 ) was decided.

[0051] Regarding the bearing density, in Comparative Example 1, the density of the output side of A was set to 6.27 (g / cm 3 ), and the density of the opposite output side of B is 6.35 (g / cm 3 ) and the density of the lowest density part of C is 6.19 (g / cm 3 ), and in Comparative Example 2, the density of the output side of A was 6.19 (g / cm 3 ), and the density of the opposite output side of B is 6.43 (g / cm 3 ) and the density of the lowest density part of C is 6.11 (g / cm 3 ), and in Comparative Example 3, the density of the output side of A was 6.11 (g / cm 3 ), and the density of the opposite output side of B is 6.51 (g / cm 3 ), and the density of the lowest density part of C is 6.03 (g / cm 3 ) was decided.

[0052] In sintered bearings with shapes such as those shown in Figure 1, the density of the non-output side is usually high because it is narrowed by in-mold sizing. For this reason, in each example and comparative example 1, the density of the non-output side was initially reduced by adjusting the pressure balance during molding and mold design so that the final density after sizing would be lower than that of the output side. In comparative example 2, the density of the compact was adjusted so that the output side was nearly equal to the non-output side, and in comparative example 3, the density of the compact was adjusted so that the output side was less than the non-output side.

[0053] The oil content in Example 1 was 19% on the output side of A, 25% on the opposite side of B, and 26% in the lowest density part of C; in Example 2, it was 20% on the output side of A, 25% on the opposite side of B, and 26% in the lowest density part of C; in Example 3, it was 21% on the output side of A, 24% on the opposite side of B, and 25% in the lowest density part of C; in Example 4, it was 22% on the output side of A, 24% on the opposite side of B, and 25% in the lowest density part of C; and in Example 5, it was 22% on the output side of A, 23% on the opposite side of B, and 24% in the lowest density part of C.

[0054] The oil content was 23% on the output side of A, 22% on the anti-output side of B, and 24% in the lowest density part of C in Comparative Example 1; 24% on the output side of A, 21% on the anti-output side of B, and 25% in the lowest density part of C in Comparative Example 2; and 25% on the output side of A, 20% on the anti-output side of B, and 26% in the lowest density part of C in Comparative Example 3.

[0055] The difference in density between part A and part B (AB) was 0.48 (g / cm 3 ), and in Example 2 it was 0.40 (g / cm 3 ) in Example 3, and 0.24 (g / cm 3 ), and in Example 4 it was 0.16 (g / cm 3 ), and in Example 5 it was 0.08 (g / cm 3 The difference in density between the A part and the B part (AB) in Comparative Example 1 was −0.08 (g / cm 3 ) in Comparative Example 2, and -0.24 (g / cm 3 ), and in Comparative Example 3 it was -0.40 (g / cm 3 )

[0056] The difference in oil content between part A and part B (AB) is −6(%) in Example 1, −5(%) in Example 2, −3(%) in Example 3, −2(%) in Example 4, and −1(%) in Example 5. The difference in oil content between part A and part B (AB) is +1(%) in Comparative Example 1, +3(%) in Comparative Example 2, and +5(%) in Comparative Example 3.

[0057] The motor characteristics (-30°C environment) were as follows: in Example 1, the rotation speed was 820 (rpm), the current value was 64 (mA), and the starting voltage was 7.9 (V); in Example 2, the rotation speed was 890 (rpm), the current value was 62 (mA), and the starting voltage was 7.5 (V); in Example 3, the rotation speed was 910 (rpm), the current value was 61 (mA), and the starting voltage was 7.5 (V); in Example 4, the rotation speed was 880 (rpm), the current value was 62 (mA), and the starting voltage was 7.5 (V); and in Example 5, the rotation speed was 830 (rpm), the current value was 65 (mA), and the starting voltage was 7.8 (V).

[0058] The motor characteristics (-30°C environment) were as follows: in Comparative Example 1, the rotation speed was 770 (rpm), the current value was 68 (mA), and the starting voltage was 8.3 (V); in Comparative Example 2, the rotation speed was 720 (rpm), the current value was 70 (mA), and the starting voltage was 8.5 (V); and in Comparative Example 3, the rotation speed was 650 (rpm), the current value was 72 (mA), and the starting voltage was 8.9 (V).

[0059] In Table 1, ◎ (excellent) indicates a rotation speed of 860 rpm or more, a current value of 62 mA or less, and a starting voltage of 7.6 V or less, ○ (good) indicates a rotation speed of 800 rpm or more, a current value of 66 mA or less, and a starting voltage of 8.0 V or less, △ (passable) indicates a rotation speed of 700 rpm or more, a current value of 70 mA or less, and a starting voltage of 8.6 V or less, and × (unacceptable) indicates a rotation speed of less than 700 rpm, a current value of more than 70 mA, and a starting voltage of more than 8.6 V. In other words, ◎, ○, and △ indicate passing products, while × indicates failing.

[0060] In this way, the density difference between the output side and the opposite side is 0.08 to 0.48 (g / cm 3 ), and the difference in oil content between the output side and the opposite side is preferably set to 1 to 6%, and further, the difference in density between the output side and the opposite side is preferably set to 0.16 to 0.40 (g / cm 3 ) and the difference in oil content between the output side and the anti-output side is preferably set to 2 to 5%.

[0061] Next, the relationship between the surface opening ratio of the bearing surface and motor characteristics (in a -30°C environment) was investigated. Examples 6 to 9 and Comparative Examples 4 and 5 were prepared with the same dimensions, shape, and density specifications as the sintered bearing of Example 3, but with different surface opening ratios, and these were investigated. The surface opening ratio of Example 6 was 10% on the output side of A and 55% on the opposite side of B. The surface opening ratio of Example 7 was 25% on the output side of A and 55% on the opposite side of B. The surface opening ratio of Example 8 was 35% on the output side of A and 55% on the opposite side of B. The surface opening ratio of Example 9 was 50% on the output side of A and 55% on the opposite side of B. The surface opening ratio of Comparative Example 4 was 5% on the output side of A and 55% on the opposite side of B. The surface opening ratio of Comparative Example 5 was 55% on the output side of A and 55% on the opposite side of B.

[0062] The difference in surface opening rate between part A and part B (BA) was 45% in Example 6, 30% in Example 7, 20% in Example 8, 5% in Example 9, 50% in Comparative Example 4, and 0% in Comparative Example 5. In Examples 6, 7, and Comparative Example 4, the surface opening rate can be reduced by providing a difference in the inner diameter dimensions of the output side and the anti-output side after in-mold sizing and increasing the finishing allowance during rotary finishing on the output side. [Table 2]

[0063] In Table 2, "inner diameter NG" indicates a state in which the opening on the output side inner diameter surface has become glazing or burned, indicating that the condition of the inner diameter surface is not good. Also, "unable to produce" indicates that a sample with the target surface opening ratio could not be produced in the final rotating finishing stage. Although the surface opening ratio was changed in the rotating finishing for a sample with the same dimensions, shape, and density specifications as the sintered bearing of Example 3, it was not possible to achieve a surface opening ratio of 55% on side A, even with the finishing allowance minimized.

[0064] The motor characteristics (-30°C environment) were as follows: Example 6 had a rotation speed of 870 rpm, a current of 63 mA, and a starting voltage of 7.6 V; Example 7 had a rotation speed of 920 rpm, a current of 61 mA, and a starting voltage of 7.5 V; Example 8 had a rotation speed of 910 rpm, a current of 61 mA, and a starting voltage of 7.5 V; and Example 9 had a rotation speed of 840 rpm, a current of 64 mA, and a starting voltage of 7.7 V. Comparative Example 4 had problems with the condition of the bearing inner diameter surface on the output side, such as glazing and burning of the openings. Comparative Example 5 was unable to achieve a surface opening ratio of 55% on the A side. The symbols ⊚ and ◯ in Table 2 are the same as those in Table 1.

[0065] The difference in surface opening ratio between the output side and the opposite side is preferably set to 5 to 45%, and more preferably set to 20 to 30%. [Explanation of symbols]

[0066] H1 high density area H2 low density region H3 Density fluctuation area 1 Bearing device 2. Sintered bearings 21 1st bearing part 21a Inner surface 22 2nd bearing part 22a Inner diameter surface 23 Sliding surface 24a Relief 26 Adjacent to bearing 27 Adjacent to bearing 28 Lowest density part

Claims

1. A sintered bearing having a sliding surface that slides against a mating shaft member, a sintered bearing comprising a cylindrical sintered body obtained by sintering raw material powder composed primarily of a metallic material, the sintered body containing lubricating oil, one axial end being a first bearing portion and the other axial end being a second bearing portion, the sliding surfaces being made up of the inner diameter surfaces of the first bearing portion and the second bearing portion, and an intermediate portion having a relief portion in the center of the bearing inner diameter that is larger in diameter than the inner diameter surfaces of the first bearing portion and the second bearing portion, a density difference being provided between the first bearing portion, the second bearing portion and the intermediate portion, the first bearing portion being a high-density region and the second bearing portion being a low-density region having a density lower than that of the high-density region, and a minimum-density region between the high-density region and the low-density region, the minimum-density region being lower in density than the low-density region, and a density gradient region in which the density increases from the minimum-density region to the high-density region.

2. The density of the first bearing portion is 0.08 (g / cm 3 ) ~ 0.56 (g / cm 3 2. The sintered bearing according to claim 1, wherein the oil content of the first bearing portion is 1% to 7% lower than that of the second bearing portion.

3. The density difference between the first bearing portion and the second bearing portion is 0.08 (g / cm 3 ) ~ 0.48 (g / cm 3 2. The sintered bearing according to claim 1, wherein the difference in oil content is 1% to 6%.

4. 2. The sintered bearing according to claim 1, wherein the difference in surface opening ratio between the inner diameter surface of the first bearing portion and the inner diameter surface of the second bearing portion is 5 to 45%.

5. A bearing device using the sintered bearing described in claim 1, characterized in that the first bearing portion is the output side of the motor and the second bearing portion is the anti-output side of the motor.

6. The density of the first bearing portion is set to be 0.08 (g / cm 3 ) higher than the density of the second bearing portion. 3 ) ~ 0.48 (g / cm 3 6. The bearing device according to claim 5, wherein the oil content of the first bearing portion is 1% to 6% lower than the oil content of the second bearing portion.

7. The density of the first bearing portion is set to be 0.16 (g / cm 3 ) higher than the density of the second bearing portion. 3 ) ~ 0.40 (g / cm 3 6. The bearing device according to claim 5, wherein the oil content of the first bearing portion is 2% to 5% lower than the oil content of the second bearing portion.

8. 6. The bearing device according to claim 5, wherein the surface opening ratio of the inner diameter surface of the first bearing portion is 5 to 45% lower than the surface opening ratio of the inner diameter surface of the second bearing portion.

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