JP2019002570A - Vibration motor - Google Patents

Abstract

To provide a vibration motor capable of stably exhibiting high rotation performance over a long period.SOLUTION: A vibration motor 1 comprises: a shaft 3; a motor part M configured to rotationally drive the shaft 3; a sintered bearing 4 having a bearing surface 4a on an inner periphery, and rotatably supporting the shaft 3; a weight W provided in the shaft 3; and a cylinder housing 2 press-fitting and fixing the sintered bearing 4 to an inner periphery, wherein the shaft 3 is affected by the weight W to eccentrically rotate to a center of the bearing, thereby generating vibration. The sintered bearing 4 comprises a sintered body mainly composed of iron and containing copper of 10-30 mass%, and has radial crushing strength of 300 MPa or more.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a vibration motor.

  The vibration motor functions as a vibrator for notifying incoming calls or mails in a portable terminal such as a cellular phone. For example, the motor unit rotates a shaft to which a weight (eccentric weight) is attached. Thus, the entire mobile terminal can be vibrated. As a vibration motor adopting such a structure, there is one in which a shaft is supported by a sintered bearing (sintered oil-impregnated bearing) (for example, Patent Documents 1 and 2).

  FIG. 1 schematically shows a main part of a configuration example of a vibration motor using a sintered bearing. In the vibration motor 1 of the illustrated example, both sides of the shaft 3 protruding from both sides in the axial direction of the motor part M are rotatably supported by cylindrical sintered bearings 4 (41, 42) having bearing surfaces 4a on the inner periphery. doing. A weight W is provided at one end of the shaft 3. The sintered bearing 41 on the weight W side is disposed between the weight W and the motor unit M, and the sintered bearing 41 has an axial dimension (of the bearing surface 4a) than the sintered bearing 42 on the opposite side to the weight W. Area) is increasing. The two sintered bearings 4 (41, 42) are both fixed to the inner periphery of the housing 2. In the vibration motor 1, when the motor unit M is energized and the shaft 3 rotates, the shaft 3 rotates while swinging along the entire surface of the bearing surface 4 a under the influence of the weight W. That is, in this vibration motor 1, the shaft 3 rotates with its center Oa decentered in all directions with respect to the bearing center (center Ob of the sintered bearing 4) (see FIG. 2).

JP 2001-178100 A JP 2008-99355 A Japanese Patent No. 3613569

  In recent years, vibration motors are required to be further downsized in consideration of mounting on so-called smartphones. When the vibration motor is downsized, there is a limit to the increase in motor power. Even in such a situation, in order to ensure the predetermined vibration performance, we are trying to cope with it by rotating the motor at a high speed (10000 rpm or more) or increasing the unbalanced load. It tends to become. That is, in the vibration motor, as described above, the shaft swings along the entire bearing surface of the sintered bearing, and the bearing surface is frequently hit by the unbalanced load (the shaft frequently collides with the bearing surface). Therefore, the use conditions of the sintered bearing are even more severe than the sintered bearing for normal use (for example, a sintered bearing for a spindle motor), and the bearing surface is easily worn. Therefore, if the motor is rotated at a high speed in order to ensure the desired vibration performance, the wear of the bearing surface is further promoted, and the rotational fluctuation becomes large.

  In addition, not only the bearing surface accuracy of the sintered bearing alone but also the bearing surface accuracy in a state where the sintered bearing is fixed to the inner periphery of the housing are important in order to be able to exhibit the desired rotational performance. In other words, if the sintered bearing has insufficient mechanical strength (particularly the crushing strength), for example, when the sintered bearing is inserted into the inner periphery of the housing with press fitting, the bearing surface becomes the inner peripheral shape of the housing. It becomes easy to follow and deform. Even if the bearing surface of a sintered bearing is deformed, additional shape correction processing such as sizing can be used to finish the bearing surface to the specified shape and accuracy. To do.

  In particular, vibration motors used in mobile terminals such as mobile phones are required to have high impact resistance so that they cannot be easily rotated even when a large impact value is applied when the mobile terminal is dropped. .

  Accordingly, an object of the present invention is to provide a vibration motor that can stably exhibit high rotational performance over a long period of time at a low cost.

  Invented to achieve the above object, the present invention includes a shaft, a motor unit that rotationally drives the shaft, a sintered bearing that has a bearing surface on the inner periphery and rotatably supports the shaft, and a shaft. A vibration motor that includes a provided weight and a housing in which a sintered bearing is press-fitted and fixed to the inner periphery, and generates vibration by rotating the shaft eccentrically with respect to the center of the bearing with the weight. It is made of a sintered body containing iron as a main component and then containing a large amount of copper, and has a crushing strength of 300 MPa or more.

  As described above, in the vibration motor according to the present invention, the main component is iron, which is inexpensive but has excellent mechanical strength, and the next most is copper, which has excellent sliding characteristics such as initial conformability with the shaft. A sintered bearing made of a bonded body (iron-copper-based sintered body) is used. In this way, sintered bearings that are relatively inexpensive but have high strength and excellent wear resistance on the bearing surface are used. Therefore, when the motor is rotated at a high speed or the unbalance load is increased. Even so, high rotational performance can be ensured without incurring a particular increase in cost. In particular, since sintered bearings with a pressure ring strength of 300 MPa or more are used, even when the sintered bearing is press-fitted and fixed to the inner periphery of the housing, the bearing surface is deformed with the press-fitting, and the roundness and cylindricity of the bearing surface are reduced. Etc. can be prevented as much as possible. Therefore, it is not necessary to additionally perform processing for finishing the bearing surface with a predetermined shape and accuracy with respect to the sintered bearing fixed to the inner periphery of the housing. In other words, press fitting, which is a simple fixing means, can be adopted without any problem as a fixing means for the sintered bearing to the housing. In addition, if the sintered bearing has a crushing strength of 300 MPa or more, even if the mobile terminal incorporating the vibration motor falls, even if a large impact value is added to the vibration motor (sintered bearing), the bearing surface Can be prevented from being deformed as much as possible. As described above, according to the present invention, it is possible to provide a low-cost vibration motor that can stably exhibit high rotational performance over a long period of time.

  A sintered bearing made of a sintered body containing iron as a main component and then containing a large amount of copper, for example, as described in Patent Document 3 above, has a copper content of 10% by mass or more and less than 30% by mass with respect to iron powder. Can be obtained by compacting and sintering copper-coated iron powder having a particle size of 80 mesh or less. However, the present inventors have verified that when the sintered bearing described in Patent Document 3 is used for a vibration motor, the rotational fluctuation becomes large. This is because sintered bearings obtained by compacting and sintering copper-coated iron powder have low neck strength between the iron phase (iron structure) and the copper phase (copper structure), so the bearing surface wears out early. It is thought that there is one cause.

  Therefore, in the present invention, as a sintered bearing, a raw material powder containing a partial diffusion alloy powder obtained by partially diffusing copper powder into iron powder, a low melting point metal powder, and a solid lubricant powder is molded and sintered. A sintered body was used.

  In the partial diffusion alloy powder, since a part of the copper powder is diffused in the iron powder, a higher neck strength is obtained between the sintered iron structure and the copper structure than when the copper-coated iron powder is used. Moreover, according to said structure, the low melting metal powder contained in a green compact fuse | melts by sintering after shaping | molding. Since the low melting point metal has high wettability with respect to copper, the iron structure and the copper structure of adjacent partial diffusion alloy powders, or the copper structures can be firmly bonded by liquid phase sintering. In addition, among the individual partial diffusion alloy powders, the melted low melting point metal diffuses into the part where the Fe-Cu alloy is formed by diffusing a part of the copper powder on the surface of the iron powder, The neck strength between the iron and copper structures is further increased. From these facts, high strength has excellent crushing strength of 300 MPa or more with excellent wear resistance of the bearing surface even at low temperature sintering where the sintering temperature is set to a temperature at which the low melting point metal powder is melted (for example, 700 to 900 ° C.). It becomes possible to reliably obtain a sintered body (sintered bearing). And if the abrasion resistance of a bearing surface improves, rotation fluctuation of a vibration motor can be prevented. In this case, as the partial diffusion alloy powder to be included in the raw material powder, it is preferable to use a copper powder having an average particle size of 5 μm or more and less than 20 μm that partially diffuses in the iron powder and contains 10 to 30% by mass of copper. .

  As a result of repeated extensive studies by the present inventors, if the raw material powder contains a partially diffused alloy powder having a large particle size exceeding the average particle size of 106 μm, rough air holes are easily formed inside the sintered body, As a result, it has been found that there are cases in which the required wear resistance of the bearing surface, the crushing strength, and the like cannot be ensured. Accordingly, it is preferable to use a partially diffused alloy powder having an average particle size of 145 mesh or less (average particle size of 106 μm or less). By using such an alloy powder, it is possible to stably obtain a sintered body in which the sintered metal structure (porous structure) is homogenized and the generation of coarse air holes in the porous structure is suppressed. Can do. Thereby, it becomes possible to stably obtain a sintered bearing in which the wear resistance of the bearing surface and the crushing strength of the bearing are further improved.

  The sintered bearing can be obtained from a raw material powder using tin powder as the low melting point metal powder and graphite powder as the solid lubricant powder. In this case, the sintered bearing contains 10 to 30% by mass of Cu, 0.5 to 3.0% by mass of Sn and 0.3 to 1.5% by mass of C, with the balance being iron and inevitable impurities. It can comprise with the sintered compact. In this configuration, since an expensive material such as nickel (Ni) or molybdenum (Mo) is not used, a sintered bearing with improved mechanical strength and wear resistance of the bearing surface can be obtained at low cost. . Therefore, it is possible to provide a low-cost vibration motor with high rotational performance that hardly causes rotational fluctuation.

  If the iron structure of the sintered body is mainly composed of a soft ferrite phase, the aggressiveness of the bearing surface against the shaft can be weakened, so that shaft wear can be suppressed. An iron structure mainly composed of a ferrite phase can be obtained, for example, by sintering a green compact at a temperature of 900 ° C. or less at which iron and carbon (graphite) do not react.

  The iron structure mainly composed of the ferrite phase includes an iron structure in which a pearlite phase harder than the ferrite phase is present at the grain boundary of the ferrite phase in addition to a structure in which all of the ferrite phase is formed as a ferrite phase. Thus, by forming a pearlite phase at the grain boundary of the ferrite phase, it is possible to improve the wear resistance of the bearing surface as compared with the case where the iron structure is composed only of the ferrite phase. In order to achieve both suppression of shaft wear and improvement in wear resistance of the bearing surface, the proportions of the ferrite phase (αFe) and pearlite phase (γFe) in the iron structure are 80 to 95% and 5 to 20%, respectively. (ΑFe: γFe = 80 to 95%: 5 to 20%) is preferable. In addition, said ratio can be calculated | required by the area ratio of each of the ferrite phase and the pearlite phase in the arbitrary cross sections of a sintered compact, for example.

  As iron powder constituting the partial diffusion alloy powder (Fe—Cu partial diffusion alloy powder), reduced iron powder can be used. As the iron powder, for example, atomized iron powder can be used in addition to the reduced iron powder. However, since the reduced iron powder has a spongy shape (porous shape) having internal pores, it is compared with the atomized iron powder. The powder is soft and excellent in compression moldability. Therefore, the green compact strength can be increased even at low density, and chipping and cracking of the green compact can be prevented. Moreover, since reduced iron powder makes a spongy shape as described above, it also has an advantage of superior oil retention as compared with atomized iron powder.

  In the above configuration, the porosity of the surface layer portion of the sintered body, particularly the porosity of the surface layer portion including the bearing surface is preferably 5 to 20%. Here, the surface layer portion is a region from the surface to a depth of 100 μm.

The sintered bearing can be a so-called sintered oil-impregnated bearing in which the internal pores of the sintered body are impregnated with lubricating oil. In this case, the lubricating oil has a kinematic viscosity at 40 ° C. of 10 to 50 mm ² / s. Those within the range are preferably used. This is to suppress the increase in rotational torque while ensuring the rigidity of the oil film formed in the bearing gap. As the oil impregnated into the sintered body, liquid grease based on oil (lubricating oil) having a kinematic viscosity at 40 ° C. within the range of 10 to 50 mm ² / s may be employed.

  In the vibration motor configured as described above, the sintered bearings can be disposed on both sides of the motor portion in the axial direction. In this case, among the sintered bearings arranged on both sides in the axial direction of the motor part, the sintered bearing on one side is arranged between the weight and the motor part, and the axial dimension of the sintered bearing on one side is set to the other side. It can be larger than the axial dimension of the side sintered bearing. In this way, since the bearing surface area of the sintered bearing on the one side can be set large, the bearing capacity can be increased on the side close to the weight on which a relatively large unbalance load acts. . On the other hand, in the sintered bearing on the other side on which a relatively small unbalance load acts, the bearing surface area can be set small, so that an increase in rotational torque as the whole vibration motor can be suppressed. .

  As described above, according to the present invention, even when the motor is rotated at a high speed or the unbalance load is increased, the vibration capable of stably exhibiting high rotational performance over a long period of time. A motor can be provided at low cost.

It is sectional drawing which shows typically the principal part of the vibration motor which concerns on one Embodiment of this invention. It is an AA arrow expanded sectional view in FIG. 1, and is a figure which shows a mode that an axis | shaft rotates. It is a microscope picture of the X section in FIG. It is a figure which shows a partial diffusion alloy powder typically. It is a schematic sectional drawing which shows a formation process. It is a schematic sectional drawing which shows a formation process. It is a figure which shows a part of green compact conceptually. It is a figure which shows typically the metal structure of a sintered compact. It is a microscope picture of the bearing surface vicinity of the sintered bearing which concerns on a prior art.

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

A vibration motor according to an embodiment of the present invention will be described with reference to FIG. The vibration motor 1 in the illustrated example has a shaft 3, a rotor magnet and a stator coil (not shown), and the like. A motor unit M that can rotate the shaft 3 at a rotational speed of 10,000 rpm or more, and both sides of the motor unit M in the axial direction. The ring-shaped sintered bearing 4 (41, 42) which is disposed and has a bearing surface 4a on the inner periphery, is formed in a substantially cylindrical shape with a metal or resin material, and the motor part M and the sintered bearing 4 (41 on the inner periphery) , 42) and a cylindrical housing 2. The shaft 3 is formed of a metal material such as stainless steel, and a shaft having a diameter of 2 mm or less (preferably 1.0 mm or less) is used here. A weight W is integrally or separately provided at one end of the shaft 3, and the weight W according to the present embodiment is attached and fixed to one end of the shaft 3 so that its center is eccentric with respect to the center of the shaft 3. ing. The sintered bearing 4 (41, 42) is press-fitted and fixed to the inner periphery of the housing 2. The gap width of the gap (bearing gap) formed between the outer peripheral surface 3a of the shaft 3 and the bearing surface 4a of the sintered bearing 4 is set to about 4 μm on one side (radius value), for example. The internal pores of the sintered bearing 4 are impregnated with a lubricating oil having a kinematic viscosity at 40 ° C. in the range of 10 to 50 mm ² / s. The internal pores of the sintered bearing 4 are impregnated with grease based on oil (lubricating oil) having a kinematic viscosity at 40 ° C. in the range of 10 to 50 mm ² / s instead of the above lubricating oil. Also good.

  In the vibration motor 1 having the above configuration, when the motor unit M is energized and the shaft 3 is driven to rotate, the lubricating oil held in the internal pores of the sintered bearing 4 oozes into the bearing surface 4a as the temperature rises. put out. The oil that has oozed out forms an oil film in the bearing gap between the outer peripheral surface 3a of the opposed shaft 3 and the bearing surface 4a of the sintered bearing 4, and the shaft 3 is rotatably supported by the sintered bearing 4. The The shaft 3 rotates while swinging along the entire surface of the bearing surface 4a due to the influence of the weight W eccentrically fixed at one end thereof. That is, as shown in FIG. 2, the shaft 3 rotates with its center Oa decentered in all directions with respect to the center Ob of the sintered bearing 4 (41, 42). Along with this, vibration is generated in the motor unit M, and this vibration is transmitted to the housing 2 (motor housing) holding the motor unit M on the inner periphery, whereby the vibration motor 1 vibrates as a whole.

  In the present embodiment, the axial dimensions (the area of the bearing surface 4a) and the radial thickness of the two sintered bearings 41 and 42 are different from each other. Specifically, the area of the bearing surface 4a of the sintered bearing 41 on the side close to the weight W (sintered bearing 41 arranged between the weight W and the motor part M) is set to the sintered bearing on the side far from the weight W. 42 is set to be larger than the area of the bearing surface 4a. This is because, on the side closer to the weight W, a larger unbalance load acts on the shaft 3 than on the side farther from the weight W, so that the support capability of the shaft 3 is improved through the expansion of the area of the bearing surface 4a, while far from the weight W. This is because, on the side, the support capability closer to the weight W is not required, so the area of the bearing surface 4a is reduced to reduce the torque. The same sintered bearing 4 may be disposed on both sides in the axial direction of the motor part M, and the shaft 3 may be rotatably supported by these two sintered bearings 4.

  Although not shown, in order to prevent the lubricating oil impregnated in the internal pores of the sintered bearing 4 from leaking to the outside of the housing 2 or scattering, the vibration motor 1 has an opening in the housing 2. A sealing member for sealing may be provided.

  The sintered bearing 4 described above is composed of an iron-copper-based sintered body containing iron as a main component and then containing a large amount of copper (Cu: 10 to 30% by mass), and has a crushing strength of 300 MPa or more. . Such a sintered bearing 4 (sintered body) is mainly manufactured through (A) a raw material powder production step, (B) a forming step, and (C) a sintering step in this order. Hereinafter, each process of said (A)-(C) is demonstrated in detail. The two sintered bearings 4 (41, 42) are manufactured through the same manufacturing process except that the areas of the bearing surfaces 4a are different from each other and the other structures are substantially the same.

(A) Raw Material Powder Mixing Step In this step, the raw material powder that is a material for producing the sintered bearing 4 is made uniform by mixing a plurality of types of powders described later. The raw material powder used in the present embodiment is a mixed powder in which a partial diffusion alloy powder is used as a main raw material, and a low melting point metal powder and a solid lubricant powder are blended therein. Various molding lubricants (for example, a lubricant for improving releasability) may be added to the raw material powder as necessary. Hereinafter, each of the above powders will be described in detail.

[Partial diffusion alloy powder]
As shown in FIG. 4, as the partial diffusion alloy powder 11, Fe—Cu partial diffusion alloy powder in which copper powder 13 is partially diffused on the surface of iron powder 12 is used. In this embodiment, the surface of iron powder 12 is used. Moreover, Fe-Cu partial diffusion alloy powder obtained by partially diffusing a large number of copper powders 13 having an average particle size smaller than that of the iron powder 12 is used. The diffusion portion of the partial diffusion alloy powder 11 forms an Fe—Cu alloy, and as shown in the partial enlarged view in FIG. 4, the alloy portion has an arrangement in which iron atoms 12 a and copper atoms 13 a are bonded to each other. Having a crystal structure. As the partial diffusion alloy powder 11, only particles having an average particle size of 145 mesh or less (average particle size of 106 μm or less) that can pass through the mesh of a 145 mesh screen are used.

  In addition, an apparent density falls and the powder tends to float, so that the particle size becomes small. For this reason, if the raw material powder contains a large amount of the partially diffused alloy powder 11 having a small particle size, the filling ability of the raw material powder into the molding die (cavity) is lowered in the molding process described later, and the pressure of a predetermined shape and density It becomes difficult to obtain powder stably. Specifically, the present inventors have found that the above problem is likely to occur when the partial diffusion alloy powder 11 containing 25% by mass or more of particles having a particle size of 45 μm or less is used. Therefore, as the partial diffusion alloy powder 11, one having an average particle size of 145 mesh or less (average particle size of 106 μm or less) and not containing 25% by mass or more of particles having an average particle size of 350 mesh (average particle size of 45 μm) or less is selectively used. Is desirable. The average particle size is determined by irradiating a particle group with laser light, and calculating the particle size distribution from the intensity distribution pattern of diffraction / scattered light emitted from the particle group. (The average particle size of the powder described below can also be measured by the same method).

  As the iron powder 12 constituting the partial diffusion alloy powder 11, known iron powders such as reduced iron powder and atomized iron powder can be used, but reduced iron powder is used in the present embodiment. The reduced iron powder has an irregular shape that approximates a spherical shape and has a sponge shape (porous shape) having internal pores, and is also referred to as sponge iron powder. The iron powder 12 used preferably has an average particle size of 20 μm to 106 μm, and more preferably an average particle size of 38 μm to 75 μm.

  Moreover, as the copper powder 13 which comprises the partial diffusion alloy powder 11, the irregular-shaped and dendritic copper powder currently used widely can be used widely, for example, electrolytic copper powder, atomized copper powder, etc. are used. In the present embodiment, an atomized copper powder having a large number of irregularities on the surface, an irregular shape that approximates a spherical shape as a whole particle, and excellent in formability is used. As the copper powder 13, one having a smaller particle diameter than the iron powder 12 is used, and specifically, one having an average particle diameter of 5 μm or more and 20 μm or less (preferably less than 20 μm) is used. In addition, the ratio of Cu in each partial diffusion alloy powder 11 is 10 to 30% by mass (preferably 22 to 26% by mass), and the content of copper in the sintered body 4 ″ obtained in the sintering step described later ( Strictly speaking, this is the same as the copper content in the case where the sintered body 4 ″ does not contain Sn or C. That is, in this embodiment, no single copper powder or iron powder is blended in the raw material powder. The raw material powder may contain a single piece of copper powder or iron powder, but if a single piece of copper powder is added, the wear resistance of the bearing surface 4a can be improved (the strength of the bearing surface 4a is increased). It becomes difficult. Therefore, for example, when the shaft 3 collides with the bearing surface 4a as the shaft 3 rotates, an indentation (dent) is easily formed on the bearing surface 4a. Further, when a single iron powder is blended, it becomes difficult to obtain a sintered body 4 ″ (sintered bearing 4) having a desired crushing strength. Therefore, a single copper powder or iron powder is blended into the raw material powder. Preferably not.

[Low melting point metal powder]
As the low melting point metal powder, a metal powder having a melting point of 700 ° C. or less, for example, a powder of tin, zinc, phosphorus or the like is used. In this embodiment, among these, tin powder 14 (see FIG. 6), which is easily diffused into copper and iron (good compatibility) and can be used as a single powder, particularly atomized tin powder is used. As the tin powder (atomized tin powder) 14, one having an average particle diameter of 5 to 63 μm is preferably used, and one having an average particle diameter of 20 to 45 μm is more preferably used.

[Solid lubricant]
As the solid lubricant, one or more powders such as graphite and molybdenum disulfide can be used. In the present embodiment, graphite powder, particularly scaly graphite powder is used in consideration of cost.

(B) Molding Step In the molding step, the raw material powder 10 is compressed using a molding die 20 as shown in FIGS. 5A and 5B, so that the sintered bearing 4 shown in FIG. A green compact 4 ′ having an approximate shape (substantially finished product shape) is obtained. The molding die 20 has a core 21, upper and lower punches 22 and 23, and a die 24 that are coaxially arranged as main components. The molding die 20 is set in a die set of a cam type molding press, for example.

  In the molding die 20 having the above-described configuration, the raw powder 10 is filled in the cavity 25 defined by the core 21, the lower punch 23 and the die 24, and then the upper punch 22 is moved closer to the lower punch 23. When the raw material powder 10 is moved and compressed with an appropriate pressing force (set according to the shape and size of the green compact to be molded), the green compact 4 ′ is formed. Then, the upper punch 22 is moved up and the lower punch 23 is moved up, and the green compact 4 ′ is extracted out of the cavity 25. As schematically shown in FIG. 6, in the green compact 4 ′, the partial diffusion alloy powder 11, tin powder 14, and graphite powder (not shown) are uniformly dispersed. Since the partial diffusion alloy powder 11 used in the present embodiment uses reduced iron powder as the iron powder 12, the powder is softer than the partial diffusion alloy powder using atomized iron powder, and the compression moldability is improved. Excellent. Therefore, the strength of the green compact 4 ′ can be increased even at a low density, and chipping or cracking of the green compact 4 ′ can be prevented.

(C) Sintering step In the sintering step, the green compact 4 'is sintered to obtain a sintered body. The sintering conditions are such that carbon contained in graphite (graphite powder) does not react with iron (carbon does not diffuse). In the iron-carbon equilibrium state, there is a transformation point at 723 ° C., and when this is exceeded, the reaction between iron and carbon is initiated and a pearlite phase (γFe) is produced in the iron structure. After that, the reaction between carbon (graphite) and iron begins, and a pearlite phase (γFe) is generated. Since the pearlite phase (γFe) has high hardness (HV300 or more) and is highly aggressive against the mating material, if the pearlite phase (γFe) is excessively present in the iron structure of the sintered bearing 4, the wear of the shaft 3 may be advanced. There is. In a general sintered bearing manufacturing process, green compacts are heated in an atmosphere of endothermic gas (RX gas), which is a mixture of liquefied petroleum gas such as butane and propane and air, and pyrolyzed with Ni catalyst.・ It is often sintered. However, in the endothermic gas, carbon may diffuse and the surface of the green compact may be cured, and the same problem as described above is likely to occur.

  From the above viewpoint, the green compact 4 ′ is heated at 900 ° C. or lower, specifically 800 ° C. (preferably 820 ° C.) or higher and 880 ° C. or lower (low temperature sintering). The sintering atmosphere is a gas atmosphere containing no carbon (hydrogen gas, nitrogen gas, argon gas, etc.) or a vacuum. Under such sintering conditions, the reaction between carbon and iron does not occur in the raw material powder, and therefore the iron structure after sintering becomes a soft ferrite phase (HV200 or less). When various molding lubricants such as a fluid lubricant are included in the raw material powder, the molding lubricant volatilizes with sintering.

  In addition to forming the entire iron structure with a ferrite phase (αFe), as shown in FIG. 7, the iron structure can also be a two-phase structure of a ferrite phase αFe and a pearlite phase γFe. Thereby, the pearlite phase γFe harder than the ferrite phase αFe contributes to the improvement of the wear resistance of the bearing surface 4a, and the wear of the bearing surface 4a under high surface pressure can be suppressed to improve the bearing life. However, if the pearlite phase γFe is present in an excessive proportion and becomes equal to the ferrite phase αFe, the aggressiveness of the pearlite against the shaft 3 increases and the shaft 3 is likely to wear. In order to prevent this, as shown in FIG. 7, the pearlite phase γFe is suppressed to the extent that it exists (is scattered) at the grain boundary of the ferrite phase αFe. The term “grain boundary” as used herein means both a grain boundary formed between powder particles and a crystal grain boundary formed in the powder particle. When the iron structure is formed of a two-phase structure of a ferrite phase αFe and a pearlite phase γFe, the ratio of the ferrite phase αFe and the pearlite phase γFe in the iron structure is an area ratio in an arbitrary cross section of the sintered body. % And 5 to 20% (αFe: γFe = 80 to 95%: 5 to 20%) are desirable. Thereby, the wear suppression of the shaft 3 and the improvement of the wear resistance of the bearing surface can both be achieved.

  The precipitation amount of the pearlite phase γFe mainly depends on the sintering temperature and the atmospheric gas. Therefore, in order for the pearlite phase γFe to be present at the grain boundary of the ferrite phase αFe as described above, the sintering temperature is raised to about 820 ° C. to 900 ° C., and the gas containing carbon as the furnace atmosphere, such as natural gas, Sintering is performed using an endothermic gas (RX gas). As a result, carbon contained in the gas diffuses into iron during sintering, and pearlite phase γFe can be formed. As described above, when the green compact 4 ′ is sintered at a temperature exceeding 900 ° C., graphite (carbon) reacts with iron to form a pearlite phase γFe. Is preferably sintered.

After sintering, the sintered body 4 ″ is sized, and the sintered body 4 ″ is finished to a finished shape and size, and then the internal pores of the sintered body 4 ″ are impregnated with a lubricating oil by a method such as vacuum impregnation. 1 is completed. The lubricating oil impregnated in the internal pores of the sintered body 4 ″ has a low viscosity as described above, specifically, a kinematic viscosity at 40 ° C. is 10 to 50 mm. ^{A 2} / s lubricating oil (for example, a synthetic hydrocarbon-based lubricating oil) is used. This is to suppress the increase in rotational torque while ensuring the rigidity of the oil film formed in the bearing gap. The internal pores of the sintered body 4 ″ may be impregnated with grease based on a lubricating oil having a kinematic viscosity at 40 ° C. of 10 to 50 mm ² / s instead of the above lubricating oil. It is sufficient to apply sizing as necessary, and it is not always necessary.

  The sintered body 4 ″ (sintered bearing 4) obtained as described above has Cu of 10 to 30% by mass (preferably 22 to 26% by mass) and Sn of 0.5 to 3.0% by mass ( Preferably it is 1.0-3.0 mass%), C contains 0.3-1.5 mass% (preferably 0.5-1.0 mass%), and the balance consists of iron and inevitable impurities. And if it is said sintering conditions which made sintering temperature of green compact 4 '900 degrees C or less far lower than melting | fusing point (1083 degreeC) of copper, it is contained in green compact 4' (partial diffusion) The copper powder 13 (which constitutes the alloy powder 11) does not melt, and therefore, copper does not diffuse into the iron (iron structure) during sintering. Therefore, the surface of the sintered body 4 ″ (bearing surface 4a) An appropriate amount of copper structure containing a bronze phase is formed. Further, free graphite is also exposed on the bearing surface 4a. Therefore, the initial conformability with the shaft 3 is good, and the friction coefficient of the bearing surface 4a is small. Increasing the proportion of tin powder in the raw material powder increases the mechanical strength of the sintered body 4 ″. However, if the amount of Sn becomes excessive, the number of coarse air holes increases, so the above proportion (relative to the proportion of Cu) The blending ratio is about 10%).

  In the sintered body 4 ″, an iron structure mainly composed of iron and a copper structure composed of copper are formed. In the present embodiment, the iron powder alone or the copper powder alone is not added to the raw material powder. However, since the amount is very small, all the iron structure and copper structure of the sintered body 4 ″ are formed mainly of the partial diffusion alloy powder 11. In the partial diffusion alloy powder, since a part of the copper powder is diffused in the iron powder, a high neck strength can be obtained between the sintered iron structure and the copper structure. Further, at the time of sintering, the tin powder 14 in the green compact 4 ′ melts and wets the surface of the copper powder 13 included in the partial diffusion alloy powder 11. Along with this, liquid phase sintering proceeds, and as shown in FIG. 7, an iron structure and a copper structure of adjacent partial diffusion alloy powder 11, or a bronze phase (Cu—Sn) 16 that bonds the copper structures to each other is formed. Is done. In addition, among the individual partial diffusion alloy powders 11, molten Sn is diffused and Fe—Cu is diffused in a part where a part of the copper powder 13 is diffused on the surface of the iron powder 12 to form an Fe—Cu alloy. Since the -Sn alloy (alloy phase) 17 is formed, the neck strength between the iron structure and the copper structure constituting the sintered body 4 "is further increased. Therefore, it is high even in the sintering under the low temperature condition as described above. The crushing strength, specifically, the crushing strength of 300 MPa or more can be obtained, and the bearing surface 4a can be hardened to improve the wear resistance of the bearing surface 4a. αFe, pearlite phase γFe, etc. are represented by shades of color, specifically, the colors are darkened in the order of ferrite phase αFe → bronze phase 16 → Fe—Cu—Sn alloy 17 → pearlite phase γFe.

  In addition, since the powder having an average particle size of 145 mesh or less (average particle size of 106 μm or less) is used as the partial diffusion alloy powder 11, the structure of the sintered body 4 ″ can be made uniform to prevent the formation of rough atmospheric pores. Therefore, the sintered body 4 ″ can be densified to further enhance the crushing strength and the wear resistance of the bearing surface 4a.

As described above, the sintered body 4 ″ of this embodiment has a crushing strength of 300 MPa or more, and the value of this crushing strength is more than twice that of an existing copper-iron-based sintered body. the value. Further, from the density of the sintered body 4 "of the present embodiment is 6.8 ± 0.3g / cm ^3, and the density of the existing copper iron-based sintered body (about 6.6 g / cm ³⁾ Will also be dense. Even existing copper-iron-based sintered bodies can be densified by high compression in the green compact molding process, but this will prevent the internal fluid lubricant from burning during sintering. Because of gasification, the pores in the surface layer portion become coarse. In the present invention, it is not necessary to perform high compression at the time of forming the green compact, and such a problem can be prevented.

  Thus, while densifying the sintered body 4 ″, the oil content can be increased to 15 vol% or more, and an oil content comparable to that of an existing copper-iron sintered bearing can be secured. This is because the iron powder 12 constituting the partial diffusion alloy powder 11 is spongy and uses reduced iron powder excellent in oil retaining property. In this case, lubrication impregnated in the sintered body 4 ″ The oil is held not only in the pores formed between the particles of the sintered structure, but also in the pores of the reduced iron powder.

  The coarse air holes are particularly likely to occur in the surface layer portion (region from the sintered body surface to a depth of 100 μm) of the sintered body 4 ″, but if the sintered body 4 ″ obtained as described above is used, As described above, it is possible to prevent the formation of rough air holes in the surface layer portion and increase the density of the surface layer portion. Specifically, the porosity of the surface layer portion can be 5 to 20%. This porosity can be obtained, for example, by image analysis of the area ratio of the pores in an arbitrary cross section of the sintered body 4 ″.

  As the surface layer portion is densified in this way, the surface area ratio of the bearing surface 4a is also reduced. Specifically, the surface area ratio of the bearing surface 4a can be set within a range of 5% to 20%. When the surface open area ratio is less than 5%, it becomes difficult to exude a necessary and sufficient amount of lubricating oil into the bearing gap, and the merit as a sintered bearing cannot be obtained.

  In addition, as the raw material powder for obtaining this sintered body 4 ″, since the main raw material is the partial diffusion alloy powder 11 in which the copper powder 13 is partially diffused on the surface of the iron powder 12, the existing powder is used. It is possible to prevent segregation of copper, which is a problem with ferrous copper-based sintered bearings. In addition, with this sintered body 4 ″, mechanical strength can be increased without using expensive metal powders such as Ni and Mo. Since it can improve, the cost reduction of the sintered bearing 4 is also achieved.

  As described above, since the sintered bearing 4 used in the vibration motor 1 according to the present invention has high crushing strength (crushing strength of 300 MPa or more), it is press-fitted and fixed to the inner periphery of the housing 2 as shown in FIG. Even in this case, the bearing surface 4a does not deform following the shape of the inner peripheral surface of the housing 2, and the roundness, cylindricity, and the like of the bearing surface 4a can be stably maintained even after fixing. Therefore, after press-fitting and fixing the sintered bearing 4 to the inner periphery of the housing 2, a desired roundness can be obtained without additionally performing shape correction processing such as sizing in order to finish the bearing surface 4a with an appropriate shape and accuracy. (For example, roundness of 3 μm or less) can be obtained. Further, if the sintered bearing 4 has a crushing strength of 300 MPa or more, the vibration motor 1 incorporating the sintered bearing 4 (and thus a portable terminal equipped with the vibration motor 1) will drop, and the bearing surface 4a. Even when a large impact value is added to the bearing surface 4a, deformation of the bearing surface 4a can be prevented as much as possible.

  Further, as described above, (1) the sintered body 4 ″ constituting the sintered bearing 4 is mainly composed of iron, and the neck strength between the iron structure and the copper structure in the porous structure, and the copper structure. The bearing surface 4a has a high hardness due to the high neck strength between them, (2) the sintered bearing 4 has a uniform and dense porous structure with few rough air holes, and (3) the bearing surface 4a. Due to various factors such as the exposed copper structure (bronze phase) and free graphite, the bearing surface 4a has high wear resistance, so that the shaft 3 swings along the entire surface of the bearing surface 4a. Alternatively, even if the shaft 3 frequently collides with the bearing surface 4a, the wear and damage of the bearing surface 4a can be suppressed.According to the present invention, vibration capable of exhibiting high rotational performance over a long period of time is achieved. The motor 1 can be provided at low cost.

  Here, for reference, a micrograph of a surface layer portion of a sintered bearing (hereinafter referred to as “copper-coated iron powder bearing”) according to the technical means described in Patent Document 1 is shown in FIG. Comparing FIG. 8 with a micrograph (see FIG. 3) of the surface layer portion of the sintered bearing 4 used in the vibration motor 1 according to the present embodiment, the sintered bearing 4 according to the present embodiment is copper-coated. It is understood that the porous structure of the surface layer is denser than that of the iron powder bearing. Actually, the porosity of the surface layer portion of the sintered bearing 4 according to the present embodiment was 13.6%, whereas the porosity of the surface layer portion of the copper-coated iron powder bearing was about 25.5%. As a factor causing such a difference, copper-coated iron powder only has a copper film in close contact with the iron powder, and the neck strength between the iron structure and the copper structure is insufficient.

  The vibration motor 1 according to one embodiment of the present invention has been described above, but the embodiment of the present invention is not limited to the above-described one.

  For example, the case where all of the iron structure and the copper structure of the sintered bearing 4 are formed only by the partial diffusion alloy powder has been described, but one or both of the simple iron powder and the simple copper powder are added to the raw material powder, A part of the iron structure or copper structure can also be formed of simple iron powder or simple copper powder. In this case, in order to ensure the minimum wear resistance, strength, and sliding characteristics, the proportion of the partial diffusion alloy powder in the raw material powder is preferably 50% by mass or more. Further, in this case, the blending ratio of the solid lubricant powder in the raw material powder is 0.3 to 1.5% by mass. Furthermore, the blending ratio of the low melting point metal powder in the raw material powder is 0.5 to 5.0 mass%. This blending ratio is preferably set to about 10% by mass of the total amount of copper powder in the raw material powder (the sum of the copper powder in the partial diffusion alloy powder and the single copper powder added separately). The remainder of the raw material powder is formed of simple iron powder or simple copper powder (or simple powders of both) and inevitable impurities.

  In such a configuration, the bearing amount is maintained while maintaining the wear resistance, high strength, and good sliding characteristics obtained by using the partial diffusion alloy powder by changing the blending amount of the single iron powder and the single copper powder. The characteristics can be adjusted. For example, the addition of single iron powder can increase the wear resistance of the bearing while reducing the cost by reducing the amount of partially diffused alloy powder, and the addition of single copper powder can further improve the sliding characteristics. Can do. As a result, the development cost of sintered bearings suitable for various applications can be reduced, and it is possible to cope with the production of various types of sintered bearings in small quantities.

  Further, when the green compact 4 ′ is compression-molded, a so-called warm molding method in which at least one of the molding die 20 and the raw material powder 10 is heated and the green compact 4 ′ is compression-molded, A die lubrication molding method may be employed in which the green compact 4 ′ is compression molded in a state where a lubricant is applied to the molding surface of the mold 20 (the defined surface of the cavity 25). By adopting such a method, the green compact 4 ′ can be molded with higher accuracy.

  Furthermore, a dynamic pressure generating portion such as a dynamic pressure groove can be provided on the bearing surface 4a of the sintered bearing 4 or the outer peripheral surface 3a of the shaft 3 opposed via the bearing gap. In this way, since the rigidity of the oil film formed in the bearing gap can be increased, the rotational accuracy can be further increased.

DESCRIPTION OF SYMBOLS 1 Vibration motor 2 Housing 3 Shaft 4 Sintered bearing 4 'Compact 4 "Sintered body 4a Bearing surface 10 Raw material powder 11 Partially diffused alloy powder 12 Iron powder 13 Copper powder 14 Tin powder (low melting point metal powder)
16 Bronze phase 17 Fe-Cu-Sn alloy 20 Molding die αFe Ferrite phase γFe Pearlite phase M Motor part W Weight

Claims (11)

A shaft, a motor unit that rotationally drives the shaft, a sintered bearing that has a bearing surface on the inner periphery and rotatably supports the shaft, a weight provided on the shaft, and a sintered bearing that is press-fitted and fixed to the inner periphery A vibration motor that generates vibration by rotating the shaft eccentrically with respect to the bearing center with a weight,
A vibration motor, wherein the sintered bearing is made of a sintered body containing iron as a main component and then containing a large amount of copper, and has a crushing strength of 300 MPa or more.   The sintered bearing is formed of a sintered body obtained by forming and sintering a raw material powder including a partially diffused alloy powder obtained by partially diffusing copper powder in iron powder, a low melting point metal powder, and a solid lubricant powder. The vibration motor according to Item 1.   The vibration motor according to claim 2, wherein reduced iron powder is used as the iron powder of the partial diffusion alloy powder.   The vibration motor according to claim 2 or 3, wherein a partial diffusion alloy powder having an average particle size of 106 µm or less is used. Tin powder is used as the low melting point metal powder, and graphite powder is used as the solid lubricant powder.
Sintered bearing containing 10 to 30% by mass of Cu, 0.5 to 3.0% by mass of Sn, 0.3 to 1.5% by mass of C, the balance being iron and inevitable impurities The vibration motor according to any one of claims 2 to 4, comprising a body.   The vibration motor according to any one of claims 1 to 5, wherein the iron structure of the sintered body is mainly composed of a ferrite phase.   The vibration motor according to any one of claims 1 to 6, wherein the iron structure of the sintered body is composed of a ferrite phase and a pearlite phase existing at a grain boundary of the ferrite phase.   The vibration motor according to any one of claims 1 to 7, wherein the porosity of the surface layer portion of the sintered body is 5 to 20%. The vibration motor according to any one of claims 1 to 8, wherein the sintered bearing is obtained by impregnating a sintered body with a lubricating oil having a kinematic viscosity at 40 ° C of 10 to 50 mm ² / s.   The vibration motor according to any one of claims 1 to 9, wherein the sintered bearings are disposed on both axial sides of the motor unit.   Of the sintered bearings arranged on both sides in the axial direction of the motor part, the sintered bearing on one side is arranged between the weight and the motor part, and the axial dimension of the sintered bearing on one side is set to the sintering on the other side. The vibration motor according to claim 10, wherein the vibration motor is larger than an axial dimension of the bearing.