JP2016142287A - Bearing and fuel injection pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress separation of an overlay layer in a bearing to be bent.SOLUTION: A bearing 1 has a back metal 11 bent in a first direction, and having surface roughness such that the surface roughness in a second direction vertical to the first direction is 10 μm or more, and the surface roughness in the first direction is smaller than the surface roughness in the second direction, and an overlay layer 12 formed on the back metal 11. Adhesion force between the overlay layer 12 and the back metal 11 is enhanced, and separation is suppressed though the bearing 1 does not have a copper sintered layer.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a bearing and a fuel injection pump.

  Bearings used under high pressure conditions, for example for fuel injection pumps, have been developed. Patent document 1 is disclosing the sliding member which formed the PTFE (fluorine-type resin) layer on the back metal. In general, since a fluorine-based resin has poor load resistance, in Patent Document 1, a porous metal layer (sintered layer) is formed on a back metal, and the porous metal layer is filled with a fluorine-based resin.

JP 2000-192961 A

  When used in a bearing, generally, an overlay layer (resin layer) is formed on the back metal, and then bent into the shape of the bearing. However, when bending is performed, stress concentration occurs in the overlay layer due to surface irregularities caused by the porous metal layer or the like, causing peeling of the overlay layer.

  In contrast, the present invention provides a technique for suppressing peeling of the overlay layer.

  In the present invention, the surface roughness in the second direction perpendicular to the first direction is greater than 10 μm, and the surface roughness in the first direction is smaller than the surface roughness in the second direction. A bearing having a backing metal and an overlay layer formed on the backing metal is provided.

  The surface roughness in the first direction may be less than 10 μm.

  The surface roughness in the second direction may be less than or equal to half the film thickness of the overlay layer.

  This bearing does not need to have a copper sintered layer between the back metal and the overlay layer.

  The glass transition point of the resin forming the overlay layer may be higher than 200 ° C.

  The present invention also provides a fuel injection pump using any one of the above bearings.

  According to the present invention, peeling of the overlay layer can be suppressed.

The figure which shows the external appearance of the bearing 1 which concerns on one Embodiment. 1 is a schematic diagram showing a cross-sectional structure of a bearing 1. FIG. The schematic diagram which shows the anisotropy of surface roughness. 3 is a flowchart illustrating a method for manufacturing the bearing 1. The figure which illustrates a roughening process. The figure which illustrates the stress at the time of shaping | molding of the bearing which concerns on a comparative example. The figure which illustrates the stress concentration location which concerns on fatigue failure. The figure which illustrates the fuel injection pump.

1. Structure FIG. 1 is a view showing an appearance of a bearing 1 according to an embodiment. In this example, the bearing 1 is a so-called bush having a cylindrical shape. The bearing 1 is used for a fuel injection pump, for example.

  FIG. 2 is a schematic diagram showing a cross-sectional structure of the bearing 1. FIG. 2 shows a cross section taken along line II-II in FIG. 1, that is, a cross section parallel to the axial direction. The bearing 1 has a back metal 11 and an overlay layer 12. The back metal 11 is a layer that provides mechanical strength as a bearing. The back metal 11 is made of, for example, steel.

  The overlay layer 12 is a layer for improving characteristics related to sliding with a counterpart material, such as friction coefficient, conformability, seizure resistance, corrosion resistance, and foreign material embedment property (foreign material robustness). is there. The overlay layer 12 has at least a binder resin. As the binder resin, for example, a thermosetting resin can be used. Specifically, the binder resin is at least one of a polyamideimide (PAI) resin, a polyimide (PI) resin, a polyamide resin, a phenol resin, a polyacetal resin, a polyether catheter ketone resin, a polyphenylene sulfide resin, and an epoxy resin. including.

  If used in a fuel injection pump, the glass transition point of the resin forming the overlay layer 12 is preferably 200 ° C. or higher, and more preferably 300 ° C. or higher. From this viewpoint, for example, a PI resin is used for the overlay layer 12.

  The overlay layer may contain an additive. As the additive, for example, at least one of a solid lubricant, a soft material, and a hard material is used. The content of the binder resin in the overlay layer 13 is determined according to the amount of other additives, but is preferably 30 to 70% by volume, and more preferably 40 to 65% by volume.

A solid lubricant is added to improve the friction characteristics. The solid lubricant is included in the overlay layer 13 by 30 to 70% by volume, for example. The solid lubricant includes, for example, at least one of graphite, MoS ₂ , WS ₂ , polytetrafluoroethylene (PTFE), h-BN, and SB ₂ O ₃ . For example, graphite has a high affinity with engine oil. MoS ₂ gives good lubricity. Further, PTFE has an effect of reducing the friction coefficient because of its low intermolecular cohesion.

The soft material is added in order to improve the foreign material burying property. The soft material includes, for example, at least one of Sn, Al, or Bi. The hard material is added to improve wear resistance. The hard material includes, for example, at least one of clay, mullite, and talc. The hard material may include at least one of SiC, Al ₂ O ₃ , TiN, AIN, CrO ₂ , Si ₃ N ₄ , ZrO ₂ , Fe ₃ P, Fe ₂ O ₃ , and FeO.

  In general, in order to improve the adhesion (adhesiveness) between the overlay layer and the back metal, a technique for forming a porous metal layer on the surface of the back metal and forming the overlay layer on the porous metal layer is widely known. The porous metal layer is formed by sintering powder metal.

  However, in the present embodiment, the bearing 1 does not have a porous metal layer, and the overlay layer 12 is formed directly on the back metal 11. In order to improve the adhesion of the overlay layer 12, irregularities are formed on the surface of the back metal 11. Here, the unevenness has anisotropy. Specifically, the surface roughness differs between the forming direction, that is, the bending direction (circumferential direction; hereinafter referred to as “first direction”) and the direction perpendicular thereto (axial direction; hereinafter referred to as “second direction”). ing.

  FIG. 3 is a schematic diagram showing the anisotropy of the surface roughness. 3A shows the surface roughness in the first direction, and FIG. 3B shows the surface roughness in the second direction. The surface roughness in the first direction is smaller than the surface roughness in the second direction.

  If the surface roughness in the second direction is too large, the surface roughness of the overlay layer 12 will increase and the seizure resistance will decrease. From this point of view, the surface roughness in the second direction is preferably less than or equal to half the film thickness of the overlay layer 12. Here, the film thickness of the overlay layer 12 refers to a film thickness based on a predetermined point (for example, a point of the maximum peak height) in the roughness curve of the back metal 11.

2. Manufacturing Method FIG. 4 is a flowchart illustrating a method for manufacturing the bearing 1.

  In step S1, a backing metal is prepared. At this time, the back metal is not formed into the shape of the bearing, and is, for example, a flat plate.

  In step S2, the surface of the back metal is roughened. The roughening treatment is a treatment for increasing the surface roughness of the back metal. For the roughening treatment, for example, a well-known technique such as laser irradiation or sanding is used. This roughening process is a process of roughening the surface so that anisotropy occurs rather than isotropically (randomly) roughening the surface.

  FIG. 5 is a diagram illustrating a roughening process. Here, laser irradiation is used. Laser light is irradiated in pulses (ie, intermittently). A spot-shaped or circular recess is formed by one irradiation. Laser light is irradiated while shifting the position little by little. The direction in which the irradiation position is shifted is the first direction (A direction in the figure). The irradiation position is shifted so that the spot formed after the position change overlaps a part of the spot formed by the immediately preceding irradiation. When laser light is irradiated from one end to the other end in the sliding direction, the laser light irradiation position is shifted in the second direction (B direction in the figure). Thereafter, the laser light is irradiated in order from one end to the other end in the sliding direction.

  Due to the roughening treatment, a portion that is not irradiated with a laser is mixed in the first direction, and the surface roughness in the first direction is increased due to the difference in height between the two. In the second direction, the laser-irradiated part and the non-irradiated part are not mixed, and the height difference is small compared to the first direction, that is, the surface roughness is small.

  Refer to FIG. 4 again. In step S3, the back metal is washed. The backing metal is cleaned by ultrasonic cleaning using an organic solvent such as alcohol.

  In step S4, an overlay layer is formed on the roughened surface of the back metal. For the formation of the overlay layer, an overlay precursor is first prepared. The overlay precursor is prepared by mixing the binder resin, additives, and solvent. The adjusted overlay precursor is applied to the back metal by pad printing, screen printing, air spray, airless spray, electrostatic coating, tumbling, squeeze method, and roll method. Upon application, the overlay precursor may be diluted with a diluent. After coating, the overlay precursor is dried and fired to become an overlay layer.

  In step S <b> 5, the back metal is bent into a shape as the bearing 1. Thus, the bearing 1 is manufactured.

3. Advantages The bearing 1 according to the present embodiment has the following advantages.

3-1. FIG. 6 is a diagram illustrating stress during molding of a bearing according to a comparative example. FIG. 6 is a schematic view of a cross section parallel to the first direction and perpendicular to the second direction. In this comparative example, a porous metal layer is formed on the surface of the back metal. That is, it can be said that random irregularities having no anisotropy are formed on the surface of the back metal. That is, the surface roughness in the first direction is large. Therefore, the unevenness is also formed along the first direction, and the unevenness is shown in this sectional view. When there is this unevenness, stress is concentrated on the uneven portion at the interface between the back metal and the overlay layer when the back metal is bent. Therefore, the overlay layer may be peeled off during bending or use.

  On the other hand, the bearing 1 according to this embodiment has a small surface roughness in the first direction, that is, the bending direction. Therefore, stress concentration at the interface is less likely to occur than in the comparative example, and the overlay layer is less likely to peel off.

  In addition, although FIG. 6 demonstrated the bearing which has a porous metal layer as a comparative example, even if it is a bearing which does not have a porous metal layer, with respect to the bearing in which the random unevenness | corrugation was formed in the surface of a back metal. The bearing according to this embodiment has the above advantages.

3-2. Suppression of Fatigue Failure FIG. 7 is a diagram illustrating stress concentration points related to fatigue failure. FIG. 7A shows a cross section of the bearing according to the comparative example, and FIG. 7B shows a cross section of the bearing according to the present embodiment. Although not shown, this comparative example has a porous metal layer on the surface of the back metal. Generally, when an overlay layer is formed via a porous metal layer, the thickness of the overlay layer (thickness from the back metal surface) becomes relatively thick. On the other hand, since the bearing 1 according to this embodiment does not have a porous metal layer on the surface of the back metal, the thickness of the overlay layer can be reduced.

  It is known that when the bearing slides with the mating member (shaft), stress concentrates at a predetermined depth (for example, 100 μm) from the sliding surface (surface layer). Therefore, if the overlay layer is thicker than 100 μm, stress concentration occurs inside the overlay layer, and the overlay layer is easily damaged by fatigue. On the other hand, if the overlay layer is thinner than 100 μm, the position where stress concentration occurs is inside the back metal, and fatigue failure is less likely to occur.

3-3. Suppression of fuel deterioration When a copper sintered layer is used for the porous metal layer and the bearing is used in an environment where biofuel is used, the copper in the sintered layer may deteriorate the biofuel. . Since the bearing 1 according to the present embodiment does not have a copper sintered layer, the biofuel is not deteriorated even when used in an environment where the biofuel is used.

3-4. Others Compared with PTFE resin, PI resin has higher strength. PTFE resin has a glass transition temperature of about 130 ° C., whereas PI resin has a glass transition temperature of 300 ° C. or higher, and is excellent in heat resistance. Therefore, when PI resin is used, fatigue resistance, adhesion, friction resistance, and seizure resistance can be improved as compared with PTFE resin. Further, when a solid lubricant such as graphite is used as an additive, the friction can be further reduced. Furthermore, since the damage to the resin is reduced when the friction is reduced, the fatigue resistance is further improved.

4). Example 4-1. Adhesion test 4-1-1. Test piece preparation A 1 mm thick steel plate (SPCC (JIS)) was used as the backing metal. The back metal surface was roughened along the first direction by laser irradiation. The overlay precursor coating was applied to the roughened back metal surface by a roll method. As the binder resin for the overlay layer, a PI resin having a glass transition temperature of about 330 ° C. was used. No additive was added. During the application, NMP was used as a diluent. The ratio of overlay precursor to diluent was 50:50 (weight ratio). After coating, it was dried at 100 ° C. for 15 minutes. Then, it heated up to 180 degreeC with the temperature increase rate of 10 degree-C / min, and baked in air | atmosphere for 1 hour. Note that the thickness of the overlay layer was 200 μm.

4-1-2. Test Method A dummy having a roughened surface with the same roughness as the test piece was prepared. The dummy and the test piece were bonded with an adhesive. Then, it pulled with the test machine (Shimadzu Corporation autograph AG-IS) at the pulling speed of 2 mm / min, and made the force required for both fracture | rupture into adhesive force.

4-1-3. Test results Table 1 shows the surface roughness of the back metal of each test piece and the adhesion of the overlay layer. In Experimental Example 1, the surface roughness Rz1 in the first direction is smaller than the surface roughness Rz2 in the second direction. In Experimental Examples 2 to 4, the surface roughnesses Rz1 and Rz2 are approximately the same. Considering experimental example 1 as an example and experimental examples 2 to 4 as comparative examples, those having the same surface roughness Rz1 and surface roughness Rz2 have poor adhesion, and the surface roughness Rz1 is the surface roughness Rz2. Smaller ones have better adhesion. Here, it was judged that the adhesiveness in the adhesiveness test was 30 MPa or more was good, and the adhesiveness less than 30 MPa was judged to be poor.

4-2. Peel test Test pieces having different surface roughness in the second direction were prepared, and the presence or absence of peeling of the overlay layer was evaluated for these test pieces. The method for preparing the test piece is as described in the adhesion test.

4-2-1. Test Method U-bending was performed with the back metal on which the overlay layer was formed facing inward and outward. After processing, the test piece was visually observed to confirm whether the overlay layer was peeled off or cracked.

4-2-2. Test results

  Table 2 shows the surface roughness of the back metal of each test piece and the presence or absence of peeling of the overlay layer. In Experimental Examples 5, 6, and 7, the surface roughness Rz1 in the first direction was 5 μm. The surface roughness Rz2 in the second direction was 30, 15 and 10 μm, respectively. The surface roughness referred to here is a ten-point average roughness according to JIS B0601-1994.

  In Experimental Example 7 in which the surface roughness Rz2 in the second direction was 10 μm, peeling of the overlay layer was observed, but in the test pieces having Rz2 exceeding 10 μm (Experimental Examples 5 and 6), no peeling of the overlay layer was observed. It was.

4-3. Conclusion In each of Experimental Examples 1, 5, and 6, the surface roughness Rz1 is smaller than the surface roughness Rz2, and the surface roughness Rz1 is less than 10 μm.

5. Application Example FIG. 8 is a diagram illustrating the structure of the fuel injection pump 100. The fuel injection pump 100 is an example of a device using the bearing 1. The fuel injection pump 100 includes a bearing 1, an eccentric cam 101, a ring cam housing 102, a housing 103, a high pressure valve 104, a plunger 105, a suction control valve 106, a supply pump 107, a cam shaft 108, a suction valve 109, and a connecting pipe 110. Have The bearing 1 supports the eccentric cam 101 on the inner surface of the cam housing 102. When used in a fuel injection pump, the repeated surface pressure applied to the bearing 1 becomes high, and the oil film thickness is very thin due to lubrication by fuel. This embodiment is also suitable for a fuel injection pump because peeling of the overlay layer 12 is suppressed.

DESCRIPTION OF SYMBOLS 1 ... Bearing 11 ... Back metal 12 ... Overlay layer

Claims (6)

A back metal that is bent in the first direction, the surface roughness in the second direction perpendicular to the first direction is more than 10 μm, and the surface roughness in the first direction is smaller than the surface roughness in the second direction;
A bearing having an overlay layer formed on the back metal and containing resin. The bearing according to claim 1, wherein the surface roughness in the first direction is less than 10 μm. The bearing according to claim 1 or 2, wherein the surface roughness in the second direction is not more than half of the thickness of the overlay layer. The bearing according to any one of claims 1 to 3, wherein a copper sintered layer is not provided between the back metal and the overlay layer. The bearing according to any one of claims 1 to 4, wherein a glass transition point of the resin forming the overlay layer is higher than 200 ° C.   A fuel injection pump using the bearing according to any one of claims 1 to 5.

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