Sintered bearing

Abstract

This sintered bearing is constructed by causing a cylindrical sintered body, which is formed by sintering raw material powder containing a metal material as a main component, to contain lubricating oil. One end in the axial direction is defined as a first bearing portion, and the other end in the axial direction is defined as a second bearing portion. A sliding surface is constituted by an inner surface of the first bearing portion and an inner surface of the second bearing portion, and an intermediate portion having a relief portion with a larger diameter than the inner surface of the first bearing portion and the inner surface of the second bearing portion is formed at a bearing inner central portion. A density difference is provided between the first bearing portion, the second bearing portion, and the intermediate portion.

Description

Sintered bearings

[0001] This invention relates to a sintered bearing.

[0002] Sintered bearings can be used, for example, as sintered oil-impregnated bearing components in small motors. Sintered bearings can achieve stable rotational speeds even under conditions where lubricating oil supply is not smooth, such as in motor bearings used at low temperatures and high rotational speeds, and can keep current values ​​low. In particular, sintered bearings are suitable for bearings in automotive cooling fan motors and other applications that are used in a wide temperature range from low to high temperatures.

[0003] Conventionally, there are bearing sections formed at both ends in the axial direction, with an intermediate section (relief section) between the bearing sections whose inner diameter is larger than the inner diameter of each bearing section (Patent Document 1).

[0004] 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 bore is reduced. Therefore, compared to a sintered bearing in which the inner diameter of the bearing bore is formed to be the same along the entire length in the axial direction (hereinafter referred to as a "straight bearing"), contact between the inner circumferential surface of the bearing bore and the rotating shaft is suppressed, and at the same time the fluid resistance of the lubricant during shaft rotation is reduced, making it possible to reduce the 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 to reduce noise.

[0005] In particular, multiple dimples are provided on at least one bearing surface of a pair of bearing sections that rotatably support the 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, thus reducing the sliding surface area of ​​the bearing surface. Therefore, contact between the bearing surface and the rotating shaft is suppressed, and at the same time, the fluid resistance of the lubricant during shaft rotation is reduced, making it possible to reduce the frictional resistance between the bearing surface and the rotating shaft. Consequently, the sliding surface area on the inner circumferential surface of the bearing bore can be reduced without reducing the axial dimension of the bearing surface, and frictional resistance between the bearing surface and the rotating shaft can be reduced 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 out between the bearing surface and the rotating shaft, thereby reducing the coefficient of friction of the bearing surface.

[0007] Patent No. 6253134

[0008] However, forming dimples on bearing surfaces requires plastic deformation processes such as peening, rolling, and stamping, which presents problems in terms of productivity and cost due to the additional processing equipment and man-hours required, as well as the production of plastic deformation tools with protrusions.

[0009] Therefore, in view of the above problems, the present invention provides a sintered bearing and bearing device that have excellent lubrication performance (sliding characteristics) without requiring plastic deformation processes such as peening, rolling, or stamping.

[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 made by sintering raw material powder mainly composed of metal material, with one end in the axial direction being designated as a first bearing portion and the other end in the axial direction being designated as a second bearing portion, the sliding surface being formed by the inner diameter surface of the first bearing portion and the inner diameter surface of the second bearing portion, and an intermediate portion being formed in the center of the inner diameter of the bearing having a relief portion with a larger diameter than the inner diameter surface of the first bearing portion and the inner diameter surface of the second bearing portion, a density difference being provided between the first bearing portion, the second bearing portion and the intermediate portion, and the proportion of pores on the end face side of the first bearing portion being set to be greater than that on the second bearing side.

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

[0012] By setting the proportion of the number of pores occupied on the end face side of the first bearing portion to be greater than that on the second bearing side, more pores can be distributed on the bearing end face (the first bearing portion side) on the output side of the motor.

[0013] In this case, when the end face side of the first bearing portion is within the range of 10% of the total bearing length from the end face of the first bearing portion, the proportion of the number of pores may be 60% or more of the total number of pores in the entire bearing; or when the end face side of the first bearing portion is within the range of 1% of the total bearing length from the end face of the first bearing portion, the proportion of the number of pores may be 45% or more of the total number of pores in the entire bearing.

[0014] Preferably, the first bearing portion is a high-density region, the second bearing portion is a low-density region having a density lower than that of the high-density region, and between the high-density region and the low-density region, there are a minimum density portion having a density lower than that of the low-density region near the low-density region, and a density gradient portion in which the density increases from the minimum density portion to the high-density region.

[0015] By providing such a density difference, the circulation of lubricating oil from the escape portion side to the first bearing portion and the circulation of lubricating oil from the escape portion side to the second bearing portion can be stably performed.

[0016] The density of the first bearing portion is higher than that of the second bearing portion by 0.08 (g / cm 3 ) to 0.56 (g / cm 3 ), and the oil content of the first bearing portion is set to be 1% to 7% lower than that of the second bearing portion; or the density difference between the first bearing portion and the second bearing portion is 0.08 (g / cm 3 ) to 0.48 (g / cm 3 ), and the difference in oil content is set to be 1% to 6%; or 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 set to be 5% to 45%. By setting in this way, stable oil circulation can be obtained.

[0017] The bearing device according to the present invention is a bearing device using said sintered bearing, wherein the first bearing portion is arranged on the output side of the motor, and the second bearing portion is arranged on the non-output side of the motor.

[0018] By arranging the high-density region on the output side of the motor where sliding resistance increases, a large amount of lubricating oil is supplied to the output side, and the friction coefficient of the bearing surface can be reduced. Therefore, even when used in a wide temperature range, the circulation and supply of oil work smoothly, oil depletion is improved, and favorable sliding performance can be obtained. In particular, even at low temperatures where the viscosity of oil increases and makes it difficult for the circulation and supply of oil to work smoothly, the circulation and supply of oil work smoothly, oil depletion is improved, and favorable sliding performance can be obtained.

[0019] The density of the first bearing portion is 0.08 (g / cm 3 ) to 0.48 (g / cm 3 ) higher than that of the second bearing portion, the oil content of the first bearing portion is 1% to 6% lower than that of the second bearing portion, the density of the first bearing portion is 0.16 (g / cm 3 ) to 0.40 (g / cm 3 ) higher than that of the second bearing portion, the oil content of the first bearing portion is 2% to 5% lower than that 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 that of the inner diameter surface of the second bearing portion.

[0020] In the present invention, no special processing equipment, processing facilities or special plastic working tools are required, and by providing the sintered bearing with a density gradient function, a circulation path for lubricating oil is formed, and a sliding member having excellent lubricating performance / sliding characteristics can be provided.

[0021] In particular, when the sintered bearing according to the present invention is used in a bearing device in which the first bearing portion is arranged on the output side of the motor and the second bearing portion is arranged on the opposite output side of the motor, even when used in a wide temperature range, the circulation and supply of oil work smoothly, oil depletion is improved, and favorable sliding performance can be obtained. As a result, a decrease in the rotation speed of the motor and instability of the rotation speed can be improved, and reduction of power consumption can be achieved.

[0022] By allowing a large number of pores to be distributed on the bearing end surface (the first bearing portion side) on the output side of the motor, lubricating oil that has oozed out from the bearing gap due to thermal expansion during operation or the like can be easily absorbed into the bearing, leakage to the outside is reduced, and a short service life caused by the reduction of lubricating oil can be prevented.

[0023] This is a cross-sectional view of the sintered bearing according to the present invention. This is an explanatory diagram showing the density distribution of the sintered bearing according to the present invention. This is an explanatory diagram of the oil circulation of the sintered bearing according to the present invention. This is a manufacturing process diagram of the sintered bearing according to the present invention. This is a simplified diagram of the core pin used in the compression molding process. This is a plan view of a motor using a bearing device having the sintered bearing according to the present invention. This is a graph showing the axial pore distribution of Example 5. This is a graph showing the axial pore distribution of Comparative Example 3.

[0024] Embodiments of the present invention will be described below with reference to Figures 1 to 6. Figure 6 shows a motor (fan motor) using the 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 circumference, and a shaft member 4 that is rotatably supported by the sintered bearing 2. The shaft member 4 is provided at the bottom of the housing 3 and supported by a thrust bearing 5.

[0025] The fan motor comprises a bearing device 1, a rotor 10 attached to one end (output side) of the shaft member 4 of the bearing device 1, and a stator 11 provided in the housing 3. The rotor 10 comprises a rotor yoke 12 fixed to the shaft member and a rotor magnet 13 fixed to the inner surface of the peripheral wall 12a of the rotor yoke 12. The stator 11 comprises a laminated core 15 fitted and fixed to the cylindrical portion 3a of the housing 3 and a coil 16 wound around the laminated core 15.

[0026] The sintered bearing 2 is constructed by sintering a cylindrical sintered body made of raw material powder mainly composed of metal material, and containing lubricating oil. As shown in Figures 1 and 3, one end in the axial direction is designated as the first bearing portion 21, and the other end in the axial direction is designated as the second bearing portion 22. The inner diameter surface 21a of the first bearing portion 21 and the inner diameter surface 22a of the second bearing portion 22 form a sliding surface 23 that slides against the mating shaft member 4. The sintered bearing 2 also has an intermediate portion 24 formed between the first bearing portion 21 and the second bearing portion 22, which has a relief portion 24a with a larger diameter than the inner diameter surface of the first bearing portion 21 and the inner diameter surface of the second bearing portion 22.

[0027] Further, a drawn portion 25 is formed on the outer diameter surface on the second bearing portion 22 side of the sintered bearing 2. The drawn portion 25 consists of a cylindrical surface portion 25a on the axially outer side of the second bearing portion 22, and a tapered surface portion 25b that increases in diameter toward the axially inner side from the cylindrical surface portion 25a. Therefore, the second bearing portion 22 includes a part of the tapered surface portion 25b extending from the cylindrical surface portion 25a. 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.

[0028] The inner diameter dimension of the first bearing portion 21 and the inner diameter dimension of the second bearing portion 22 are set to the same dimension, and both the inner diameter dimension of the first bearing portion 21 and the inner diameter dimension of the second bearing portion 22 are set to be slightly larger than the outer diameter dimension of the shaft member 4. That is, when the inner diameter dimension of the first bearing portion 21 is D1, the inner diameter dimension of the second bearing portion 22 is D2, and the outer diameter dimension of the shaft member 4 is D (see FIG. 6), the relationship D1=D2>D is satisfied. In this case, since the drawn portion 25 is formed on the outer diameter surface on the second bearing portion 22 side, the wall thickness of the second bearing portion 22 is smaller than the wall thickness of the first bearing portion 21. Further, the clearance C between the outer diameter surface of the shaft member 4 and the inner diameter surface of the first bearing portion 21 and the inner diameter surface of the second bearing portion 22 is, for example, approximately 2 μm to 8 μm. In addition, the term "same dimension" includes a range that falls within the dimensional tolerance.

[0029] Incidentally, as shown in FIG. 2, in the sintered bearing 2 of 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 portion adjacent portion 26 of the intermediate portion 24 form a high density region H1, and the second bearing portion 22 and the second bearing portion 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 set higher than the density of the density fluctuation region H3. The density fluctuation region H3 has a lowest density portion 28 (a portion set to a density lower than that of the low density region H2) in the vicinity of the low density region H2, and a density gradient portion 29 in which the density increases from the lowest density portion 28 toward the high density region H1.

[0030] The density of the first bearing portion 21 is higher than the density of the second bearing portion 22 by 0.08 (g / cm 3 ) to 0.56 (g / cm 3The oil content of the first bearing section 21 is set to be 1% to 7% lower than that of the second bearing section 22. The density difference between the first bearing section 21 and the second bearing section 22 is 0.08 (g / cm³). 3 ) ~ 0.48 (g / cm 3 The oil content difference is set to be between 1% and 6%. The difference in surface opening ratio between the inner diameter surface of the first bearing section and the inner diameter surface of the second bearing section is set to be between 5% and 45%. Surface opening ratio refers to the ratio of the sum of the areas of each opening (total area) to the area per unit area.

[0031] By adjusting the pressure balance during molding and the mold design, the density after sintering and sizing can be set to achieve the density distribution shown in Figure 2. Furthermore, for example, by creating a difference in the inner diameter dimensions of the output side and the non-output side after in-mold sizing, and by increasing the finishing allowance during rotary finishing on the output side, the surface opening ratio can be reduced. Therefore, by varying the finishing allowance during rotary finishing in each area, differences in the surface opening ratio can be achieved in each area.

[0032] Incidentally, as shown in Figure 4, the sintered bearing 2 is formed by performing a powder mixing step S1, a compression molding step S2, a sintering step S3, a sizing and rotational finishing step S4, and a cleaning and oiling step S5.

[0033] In the powder mixing step S1, the raw material powders include, for example, copper powder, tin powder, iron powder, etc., as shown in Figure 4, to form a mixed powder. In this case, various molding aids, such as lubricants to improve mold release properties (e.g., metal soap), are added to the mixed powder as needed. Note that the raw material powders used are not limited to these, and those commonly used for cylindrical sintered bearings can be used.

[0034] In the compression molding process S2, a compact is formed by press molding using a mold device. This mold device comprises cylindrical upper and lower punches, a core pin 30 (see Figure 5) for forming the inner shape of the compact, and a die for forming the outer shape of the compact. In this case, during the compression molding process, an inner diameter step (relief portion 24a) is formed between the core pin body 30c and only one side (the inner diameter surface 21a side of the first bearing portion 21), and in the sizing process described later, the other side (the inner diameter surface 22a side of the second bearing portion 22) is deformed by drawing from the outer diameter direction to reduce its diameter and form a relief portion 24b in the inner diameter. That is, the core pin 30 has a first molding portion 30a for forming one of the bearing surfaces (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 body 30c. Note that this is different from the undercut removal method that utilizes springback when the mold is released during the compression molding process.

[0035] In the sintering step S3, a sintered body is obtained by heating the compacted body obtained in the compaction step (compression molding step) to the sintering temperature of the metal powder used. That is, sintering is performed in a predetermined atmosphere and temperature conditions. The predetermined atmosphere can be a vacuum, a reducing gas, or an inert gas, and can be selected in various ways depending on the metal powder used.

[0036] In the sizing process S4, the sintered body, which has been dimensionally deformed by sintering, is compressed to reshape its dimensions. In this case, the dimensional changes (expansion and contraction) during sintering differ depending on the material composition, sintering temperature, and sintering atmosphere. Specifically, a core pin is inserted into the inner circumference of the sintered body, and with the axial width of the sintered body defined to a predetermined dimension by upper and lower punches, these are pressed together into the inner circumference of the die. As a result, the outer surface of the sintered body is compressed and shaped by the die, and the inner surface of the sintered body is pressed against the outer surface of the core rod (core rod) and shaped (in-mold sizing). That is, in this sizing process, a core pin (not shown) with a plastic deformation allowance on the other side (the inner diameter surface 22a side of the second bearing portion 22) is used, and the inner diameter is reduced by drawing deformation from the outer diameter direction, forming a relief portion 24b in the inner diameter. In other words, the core pin in the sizing process is an inverted version of the core pin 30 used in the compression molding process. The sizing process forms a relief portion 24b in the inner diameter and improves dimensional accuracy. Furthermore, after the sizing process, the voids opened on the inner surface of the sintered body may be further reduced by rotational sizing. The sizing process consists of a first sizing process (in-mold sizing process) and a second sizing process, and the second sizing process may be either a rotational sizing process or an in-mold sizing process.

[0037] By the way, in the sintered bearing of this embodiment, a constricted portion 25 is formed on the outer diameter surface of the second bearing portion 22. For this reason, when sizing, a die is used which has an inner diameter bulge on the inner diameter surface for forming the constricted portion 25.

[0038] The second bearing section 22 side tends to have a higher density because it is deformed by pressure during in-mold sizing. Therefore, the final density after sintering and sizing is set to be lower than that of the output side by adjusting the pressure balance during molding and the mold design in advance.

[0039] After the sizing and rotary finishing process S4, the cleaning and oiling process S5 is performed. In other words, after cleaning, lubricating oil is applied.

[0040] In the impregnation process S5, the sintered bearing 2, which has been molded into a predetermined shape through the sizing process, is impregnated with lubricating oil, thereby completing the sintered bearing 2 in which the internal pores are 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. In this case, in order to ensure that the lubricating oil is impregnated reliably and in a short time, the impregnation work may be carried out with the lubricating oil heated.

[0041] By creating a density difference, oil is actively supplied to the direction of higher density and finer pores due to capillary action. Therefore, in the sintered bearing of the present invention, as shown by the arrows in Figure 3, a circulation path can be formed such that the lubricating oil circulates from the intermediate portion 24 to the first bearing portion 21, and also circulates from the intermediate portion 24 to the second bearing portion 22.

[0042] According to the sintered bearing of the present invention, by providing a relief portion 24a, the sliding surface area of ​​the shaft member relative to the sintered bearing can be reduced, thereby reducing sliding resistance. Furthermore, by forming an oil circulation path, the supply of lubricating oil to the sliding part is stabilized.

[0043] Therefore, the sintered bearing of the present invention does not require special processing equipment, processing tools, or special plastic deformation tools. By providing the sintered bearing with a density gradient function, it is possible to create a circulation path for lubricating oil and provide a sliding member with excellent lubrication performance and sliding characteristics.

[0044] Preferably, the first bearing portion 21 is a high-density region H1, and the second bearing portion 22 is a low-density region H2 with a density lower than that of the high-density region H1. Between the high-density region H1 and the low-density region H2, there is a minimum density portion 28 where the vicinity of the low-density region H2 has a density lower than that of the low-density region H2, and a density gradient portion 29 where the density increases from this minimum density portion 28 to the high-density region H1.

[0045] By creating this density difference, the lubricating oil can be stably circulated from the relief section to the first bearing section 21, and from the relief section to the second bearing section 22.

[0046] In particular, it is preferable to provide a density gradient section 29 where the density increases from the lowest density section 28 towards the high-density region H1. By providing a density gradient in this way, lubricating oil is supplied sequentially from the lowest density section 28 towards the high-density region H1, and oil circulation is stabilized.

[0047] The density of the first bearing section 21 and the second bearing section 22 is 0.08 g / cm³ lower than the density of the lowest density section. 3 ) ~ 0.56 (g / cm 3 ) is high, and the oil content of the first bearing section 21 and the second bearing section 22 is set to be 1% to 7% lower than the oil content of the lowest density section, or the density difference between the first bearing section and the second bearing section is 0.08 (g / cm³). 3 ) ~ 0.48 (g / cm 3 The difference in oil content can be set to 1% to 6%, and the difference in surface opening ratio of the inner diameter surface of the first bearing section 21 and the inner diameter surface of the second bearing section 22 can be set to 5% to 45%. By setting it in this way, stable oil circulation can be obtained.

[0048] Incidentally, as a sintered bearing, the proportion of pores on the end face 21 side of the first bearing portion 21 is set to be greater than that on the second bearing portion 22 side. In this case, the end face 21 side of the first bearing portion 21 is within 10% of the total bearing length from the end face 21A of the first bearing portion 21, and the proportion of pores on the end face 21 side of the first bearing portion 21 is set to 60% or more of the total number of pores of the bearing length. Alternatively, as a 22nd sintered bearing, the end face 21 side of the first bearing portion 21 is within 1% of the total bearing length from the end face 21A of the first bearing portion 21, and the proportion of pores on the end face 21 side of the first bearing portion 21 is set to 45% or more of the total number of pores of the bearing length.

[0049] By setting it in this way, a large number of pores can be distributed on the bearing end face on the output side of the motor (end face 21A side of the first bearing portion 21). This makes it easier for lubricating oil that seeps out from the bearing clearance due to thermal expansion during operation to be absorbed into the bearing, reducing leakage to the outside and preventing a shortened life due to a decrease in lubricating oil. Here, the bearing clearance is the difference between the outer diameter dimension of the shaft member 4 (see Figure 6) and the inner diameter dimension of the bearing (D1 or D2 in Figure 1). In particular, it is preferable that the ratio of the number of pores within 1% of the total bearing length from the end face 21A of the first bearing portion 21 is 45% or more of the total number of pores in the entire bearing length, as this allows for a larger distribution of pores on the bearing end face on the output side of the motor (end face 21A side of the first bearing portion 21).

[0050] The bearing device according to the present invention is a bearing device using a sintered bearing 2, wherein the first bearing portion 21 is on the output side of the motor and the second bearing portion 22 is on the non-output side of the motor. 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, thereby reducing the friction coefficient of the bearing surface. As a result, even when used in a wide temperature range, oil circulation and supply work smoothly, improving oil depletion and providing good sliding performance. In particular, even at low temperatures where the viscosity of the oil increases and oil circulation and supply become difficult, oil circulation and supply work smoothly, improving oil depletion and providing good sliding performance.

[0051] In such a bearing device, the density of the first bearing section 21 is set to be 0.08 (g / cm³) lower than the density of the second bearing section 22. 3 ) ~ 0.48 (g / cm 3 ) Higher, the oil content of the first bearing section 21 is 1% to 6% lower than that of the second bearing section 22, or the density of the first bearing section 21 is 0.16 (g / cm³) lower than that of the second bearing section 22. 3 ) ~ 0.40 (g / cm 3 ) is high, and the oil content of the first bearing portion can be made 2% to 5% lower than that of the second bearing portion, or the surface opening ratio of the inner diameter surface of the first bearing portion can be made 5 to 45% lower than that of the inner diameter surface of the second bearing portion.

[0052] 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, and may not have the constricted portion 25. Furthermore, in the embodiments, a gradient was 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.

[0053] Furthermore, the sintered bearing according to the present invention can be used not only in spindle motors for disk drive devices such as HDDs, but also in fan motors for cooling fans and polygon scanner motors for laser beam printers. In particular, it is suitable for bearings in automotive cooling fan motors and other applications that are used in a wide temperature range from low to high temperatures.

[0054] The motor characteristics when the sintered bearing according to the present invention is used in a fan motor were investigated. The results are shown in Table 1. In this case, sintered bearings for Examples 1 to 5 and Comparative Examples 1 to 3 were prepared. Each of the sintered bearings for Examples 1 to 5 and Comparative Examples 1 to 3 is a sintered bearing with the shape shown in Figure 1, where the first bearing portion 21 is on the output side and the second bearing portion 22 is on the non-output side, the inner diameter of the first bearing portion 21 and the second bearing portion 22 is φ3 mm, the outer diameter of the bearing is φ8 mm, the width (axial length) is 14 mm, the clearance between the bearing surface 23 (inner diameter surface of the first bearing portion 21 and inner diameter surface 22a of the second bearing portion 22) and the shaft member 4 is 4 μm, and the clearance between the relief portion 24a and the shaft member 4 is approximately 100 μm.

[0055] In Example 1, the density of the output side of A was set to 6.59 (g / cm³) for the bearing density. 3 ) and the density of the counter-output side of B is set to 6.11 (g / cm³). 3 ) and the density of the lowest density part of C is 6.03 (g / cm³). 3 In Example 2, the density on the output side of A was set to 6.51 (g / cm³). 3 ) and the density of the counter-output side of B is set to 6.11 (g / cm³). 3 ) and the density of the lowest density part of C is 6.03 (g / cm³). 3 In Example 3, the density on the output side of A was set to 6.43 (g / cm³). 3) and the density of the counter-output side of B is set to 6.19 (g / cm³). 3 ) and the density of the lowest density part of C is 6.11 (g / cm³). 3 In Example 4, the density on the output side of A was set to 6.35 (g / cm³). 3 ) and the density of the counter-output side of B is set to 6.19 (g / cm³). 3 ) and the density of the lowest density part of C is 6.11 (g / cm³). 3 In Example 5, the density on the output side of A was set to 6.35 (g / cm³). 3 ) and the density of the counter-output side of B is set to 6.27 (g / cm³). 3 ) and the density of the lowest density part of C is 6.19 (g / cm³). 3 )

[0056] In Comparative Example 1, the density of the output side of A was 6.27 (g / cm³). 3 ) and the density of the counter-output side of B is set to 6.35 (g / cm³). 3 ) and the density of the lowest density part of C is 6.19 (g / cm³). 3 In Comparative Example 2, the output density of A was set to 6.19 (g / cm³). 3 ) and the density of the counter-output side of B is set to 6.43 (g / cm³). 3 ) and the density of the lowest density part of C is 6.11 (g / cm³). 3 In Comparative Example 3, the density on the output side of A was set to 6.11 (g / cm³). 3 ) and the density of the counter-output side of B is set to 6.51 (g / cm³). 3 ) and the density of the lowest density part of C is 6.03 (g / cm³). 3 )

[0057] In sintered bearings with shapes like those shown in Figure 1, the non-output side is narrowed during in-mold sizing, so the density tends to be higher on that side. Therefore, in each example and Comparative Example 1, the density of the non-output side was lowered in advance by adjusting the pressure balance during molding and the mold design, so that the final density after sizing was lower than that of the output side. In Comparative Example 2, the density of the molded body was set so that the output side ≈ non-output side, and in Comparative Example 3, the density of the molded body was adjusted so that the output side < non-output side.

[0058] In Example 1, the oil content was 19% on the output side of A, 25% on the counter-output side of B, and 26% at the lowest density point of C. In Example 2, the oil content was 20% on the output side of A, 25% on the counter-output side of B, and 26% at the lowest density point of C. In Example 3, the oil content was 21% on the output side of A, 24% on the counter-output side of B, and 25% at the lowest density point of C. In Example 4, the oil content was 22% on the output side of A, 24% on the counter-output side of B, and 25% at the lowest density point of C. In Example 5, the oil content was 22% on the output side of A, 23% on the counter-output side of B, and 24% at the lowest density point of C.

[0059] In Comparative Example 1, the oil content was 23% on the output side of A, 22% on the non-output side of B, and 24% at the lowest density point of C. In Comparative Example 2, the oil content was 24% on the output side of A, 21% on the non-output side of B, and 25% at the lowest density point of C. In Comparative Example 3, the oil content was 25% on the output side of A, 20% on the non-output side of B, and 26% at the lowest density point of C.

[0060] The density difference between part A and part B (A-B) is 0.48 g / cm³ in Example 1. 3 ) and in Example 2 it was 0.40 (g / cm³). 3 ) and in Example 3 it was 0.24 (g / cm³). 3 ) and in Example 4 it was 0.16 (g / cm³). 3 ) and in Example 5 it was 0.08 (g / cm³). 3 ) The density difference between part A and part B (A-B) is -0.08 (g / cm³) in Comparative Example 1. 3 ) and in Comparative Example 2, it was -0.24 (g / cm³). 3 ) and in Comparative Example 3, it was -0.40 (g / cm³). 3 )

[0061] The difference in oil content between section A and section B (A-B) was -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 section A and section B (A-B) was +1 (%) in Comparative Example 1, +3 (%) in Comparative Example 2, and +5 (%) in Comparative Example 3.

[0062] As for the motor characteristics (in a -30°C environment), in Example 1 the rotational speed was 820 rpm, the current was 64 mA, and the starting voltage was 7.9 V; in Example 2 the rotational speed was 890 rpm, the current was 62 mA, and the starting voltage was 7.5 V; in Example 3 the rotational speed was 910 rpm, the current was 61 mA, and the starting voltage was 7.5 V; in Example 4 the rotational speed was 880 rpm, the current was 62 mA, and the starting voltage was 7.5 V; and in Example 5 the rotational speed was 830 rpm, the current was 65 mA, and the starting voltage was 7.8 V.

[0063] In the motor characteristics (at a -30°C environment), Comparative Example 1 had a rotational speed of 770 rpm, a current of 68 mA, and a starting voltage of 8.3 V. In Comparative Example 2, the rotational speed was 720 rpm, the current of 70 mA, and the starting voltage of 8.5 V. In Comparative Example 3, the rotational speed was 650 rpm, the current of 72 mA, and the starting voltage of 8.9 V.

[0064] In Table 1, ◎ (Excellent) indicates a rotational speed of 860 rpm or higher, a current of 62 mA or less, and a starting voltage of 7.6 V or less; ○ (Good) indicates a rotational speed of 800 rpm or higher, a current of 66 mA or less, and a starting voltage of 8.0 V or less; △ (Acceptable) indicates a rotational speed of 700 rpm or higher, a current of 70 mA or less, and a starting voltage of 8.6 V or less; and × (Unacceptable) indicates a rotational speed of less than 700 rpm, a current exceeding 70 mA, and a starting voltage exceeding 8.6 V. In other words, products marked with ◎, ○, and △ are acceptable, while × is unacceptable.

[0065] Thus, the density difference between the output side and the counter-output side is 0.08 to 0.48 (g / cm³). 3 It is preferable to set the oil content difference between the output side and the counter-output side to 1-6%, and furthermore, the density difference between the output side and the counter-output side should be 0.16-0.40 (g / cm³). 3 It is preferable to set the oil content difference between the output side and the non-output side to 2-5%, using a specific setting.

[0066] Next, the surface aperture ratio of the bearing surface and the motor characteristics (in a -30°C environment) were investigated. In this case, Examples 6 to 9 and Comparative Examples 4 and 5 were created by changing the surface aperture ratio of a sintered bearing with the same dimensions, shape, and density specifications as the sintered bearing of Example 3, and these were investigated. The surface aperture ratio of Example 6 was set to 10% on the output side of A and 55% on the non-output side of B; the surface aperture ratio of Example 7 was set to 25% on the output side of A and 55% on the non-output side of B; the surface aperture ratio of Example 8 was set to 35% on the output side of A and 55% on the non-output side of B; the surface aperture ratio of Example 9 was set to 50% on the output side of A and 55% on the non-output side of B; the surface aperture ratio of Comparative Example 4 was set to 5% on the output side of A and 55% on the non-output side of B; and the surface aperture ratio of Comparative Example 5 was set to 55% on the output side of A and 55% on the non-output side of B.

[0067] The difference in surface opening ratio between section A and section B (B-A) 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 ratio can be reduced by creating a difference in the inner diameter dimensions of the output side and the non-output side after in-mold sizing, and by increasing the finishing allowance during rotary finishing on the output side.

[0068] In Table 2, "Inner diameter NG" indicates a condition where the opening on the inner diameter surface of the output side is clogged or burnt, indicating that the condition of the inner diameter surface is not good. Furthermore, "Unable to manufacture" means that a sample with the target surface opening ratio could not be manufactured at the final rotational finishing stage. For a sintered bearing with the same dimensions, shape, and density specifications as the one in Example 3, the surface opening ratio was changed by rotational finishing, but even with the finishing allowance kept to a minimum, it was not possible to achieve a surface opening ratio of 55% on side A.

[0069] As for the motor characteristics (in a -30°C environment), in Example 6 the rotational speed was 870 rpm, the current was 63 mA, and the starting voltage was 7.6 V; in Example 7 the rotational speed was 920 rpm, the current was 61 mA, and the starting voltage was 7.5 V; in Example 8 the rotational speed was 910 rpm, the current was 61 mA, and the starting voltage was 7.5 V; in Example 9 the rotational speed was 840 rpm, the current was 64 mA, and the starting voltage was 7.7 V. In Comparative Example 4, the inner diameter surface on the output side was clogged and burnt, indicating a problem with the condition of the bearing's inner diameter surface; and in Comparative Example 5, a surface opening ratio of 55% on side A could not be produced. ◎ and ○ in Table 2 are the same as in Table 1.

[0070] The difference in surface aperture ratio between the output side and the non-output side is preferably set to 5 to 45%, and more preferably to 20 to 30%.

[0071] Next, the pore distribution of Example 5 and Comparative Example 3 was investigated. A JMC microfocus CT scanner (Phoenix V | tome | x m300) was used to measure the pores. The measurement conditions (maximum output) were set to 300 kV / 500 W. The measurement procedure involved taking an axial cross-sectional image of the object, constructing 3D data from the image data, and calculating the number of pores inside. These results are shown in Figure 7 (Example 5) and Figure 8 (Comparative Example 1). Generally, the detected pore volume was 0.000014 mm². 3 The above (equivalent circle diameter: 0.03 mm) is the pore volume present between average particle diameters (D50) of approximately 50 μm in the mixed powder used in this application, which is 0.000042 mm². 3 Pores larger than (equivalent circle diameter 0.02 mm) were defined as coarse pores. D50 is the median diameter, which is the diameter at which, when a powder is divided into two parts from a certain particle size, the larger and smaller parts are equal in volume. In other words, D50 is the particle size at which the cumulative particle size distribution of the powder reaches 50% from the small particle side.

[0072] As can be seen from Figure 7 of Example 5, a large number of pores can be distributed on the bearing end face side (first bearing section side) of the motor's output side. In contrast, as can be seen from Figure 8 of Comparative Example 3, pores are distributed throughout the entire structure, not just on the bearing end face side of the motor's output side.

[0073] This bearing can be applied to bearings in automotive cooling fan motors and other applications used in a wide temperature range from low to high temperatures. 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 and second bearing portions, thereby creating a density difference between the first, second, and intermediate bearing portions.

[0074] H1 High-density region H2 Low-density region H3 Density fluctuation region 1 Bearing device 2 Sintered bearing 21 First bearing section 21a Inner diameter surface 21A End surface 22 Second bearing section 22a Inner diameter surface 23 Sliding surface 24a Relief section 26 Adjacent section of bearing section 27 Adjacent section of bearing section 28 Lowest density section

Claims

1. A sintered bearing having a sliding surface that slides against a mating shaft member, comprising a cylindrical sintered body made by sintering raw material powder mainly composed of metal material and containing lubricating oil, wherein one end in the axial direction is designated as a first bearing portion and the other end in the axial direction is designated as a second bearing portion, the sliding surface is formed by the inner diameter surface of the first bearing portion and the inner diameter surface of 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 surface of the first bearing portion and the inner diameter surface of the second bearing portion, a density difference is provided between the first bearing portion, the second bearing portion and the intermediate portion, and the proportion of pores on the end face side of the first bearing portion is set to be greater than that on the second bearing side.

2. The sintered bearing according to claim 1, characterized in that the ratio of pores on the end face side of the first bearing portion is 60% or more of the total number of pores of the entire bearing portion, within a range of 10% of the total bearing length from the end face of the first bearing portion.

3. The sintered bearing according to claim 1, characterized in that the ratio of pores on the end face side of the first bearing portion is 45% or more of the total number of pores of the total bearing length, within a range of 1% of the total bearing length from the end face of the first bearing portion.

4. The sintered bearing according to claim 1, characterized in that the first bearing portion is a high-density region, the second bearing portion is a low-density region with a density lower than that of the high-density region, and between the high-density region and the low-density region, there is a minimum density portion where the vicinity of the low-density region has a density lower than that of the low-density region, and a density gradient portion where the density increases from this minimum density portion to the high-density region.

5. The density of the first bearing section is 0.08 (g / cm³) higher than the density of the second bearing section. 3 ) ~ 0.56 (g / cm 3 The sintered bearing according to claim 1, characterized in that the oil content of the first bearing portion is high and the oil content of the second bearing portion is 1% to 7% lower than that of the second bearing portion.

6. The density difference between the first bearing section and the second bearing section is 0.08 (g / cm³). 3 ) ~ 0.48 (g / cm 3 The sintered bearing according to claim 1 or 2, characterized in that the difference in oil content is 1% to 6%.

7. The sintered bearing according to claim 1, characterized in that 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%.

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

9. The density of the first bearing portion is 0.08 g / cm³ lower than the density of the second bearing portion. 3 ) ~ 0.48 (g / cm 3 The bearing device according to claim 8, characterized in that the oil content of the first bearing portion is high, and the oil content of the second bearing portion is 1% to 6% lower than that of the second bearing portion.

10. The density of the first bearing portion is 0.16 g / cm³ lower than the density of the second bearing portion. 3 ) ~ 0.40 (g / cm 3 The bearing device according to claim 8, characterized in that the oil content of the first bearing portion is high, and the oil content of the second bearing portion is 2% to 5% lower than that of the second bearing portion.

11. The bearing device according to claim 8, characterized in that 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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