JP5062487B2 - Oil pump - Google Patents

Description

  The present invention relates to an oil pump for generating power for circulating oil in an engine, a hydraulic drive system or the like in, for example, an automobile.

  For example, in an automobile, an oil pump is used to generate power for circulating oil in an engine or a hydraulic drive system. The oil pump is disposed in a shape having a working chamber, a suction passage and a discharge passage communicating with the working chamber, and a plurality of divided bodies, and is rotatably disposed around the shaft in the working chamber. And a rotor that sucks oil through the suction passage as it rotates and discharges the oil through the discharge passage.

A rear housing that faces the working chamber among the plurality of divided bodies constituting the casing and faces the shaft end of the rotor is formed of an aluminum alloy for reducing the weight of the oil pump, and at least the rotor of the rear housing In order to improve the wear resistance of the surface facing the shaft end of the metal, it has been proposed to coat the surface with an anodized film (see Patent Document 1).
JP 2007-132237 A

  Recently, as an aluminum (Al) alloy forming the rear housing, for example, silicon (Si) is used to increase the strength of the rear housing in order to prevent the rear housing from being distorted in response to the high pressure of the oil pump (for example, 8 MPa → 15 MPa). ) Is being studied to use a high silicon-aluminum alloy containing 1 to 25% by mass. However, in that case, in the conventional anodizing treatment, the surface smoothness of the anodized film formed on the surface of the rear housing is lowered, and the anodized film wears the opposite end of the shaft of the rotor or the like. There is a problem that it is easy to express.

  An object of the present invention is that the rear housing is formed of an aluminum alloy such as a high silicon-aluminum alloy, and the surface of the rear housing that faces the rotor shaft end or the like faces the rotor shaft end or the like. An object of the present invention is to provide an oil pump that is coated with an anodized film that is not aggressive and has excellent wear resistance.

  The inventor examined the cause of the decrease in surface smoothness when an anodized film was formed on the surface of a rear housing made of a high silicon-aluminum alloy by a conventional anodizing process, and found the following facts. It was. That is, since the high silicon-aluminum alloy has a high silicon concentration, solid phase separation of silicon proceeds during cooling, and a crystalline structure in which a silicon phase is precipitated in an aluminum phase or a continuous phase composed of an eutectic phase of aluminum and silicon, The surface of the rear housing exhibits a state in which the silicon phase is exposed in an island shape in the continuous phase.

  However, the conductivity of the continuous phase containing aluminum is different from that of the silicon phase, and the silicon forming the silicon phase is hardly oxidized under conditions suitable for anodizing aluminum in the continuous phase, even if it is oxidized. Since the speed is remarkably small, the anodized film is selectively used in a region where the continuous phase on the surface of the rear housing is exposed, particularly in the initial stage of the formation (sometimes abbreviated as “continuous phase region”). grow up.

  When the growth proceeds to some extent, a slight amount of an anodized film is formed even in a region where the silicon phase is exposed (sometimes abbreviated as “silicon phase region”), and the anodized film grown in the continuous phase region is formed in the silicon phase. Grows around the area. Therefore, the anodized film is finally free from large defects corresponding to the silicon phase region (as is well known, the anodized film of aluminum is composed of an active layer in contact with the surface of the rear housing and a porous layer thereon. Thus, the porous layer is a continuous film (although it has a porous structure having very fine pores on the order of angstroms).

However, based on the difference in growth rate in the initial stage, the thickness of the anodic oxide film varies greatly between the two regions, resulting in a decrease in surface smoothness.
Therefore, the inventor uses the wrapping of the anodized film from the continuous phase region to the silicon phase region of the surface of the rear housing, particularly in the initial stage of the thickness of the anodized film formed between the two regions. We considered making the difference as small as possible. As a result, the current density of the current applied between the ^two electrodes in the initial stage within a few minutes after the start of the anodic oxidation process is 0.35 A / dm ² or less per minute until the predetermined current density is reached from 0 A / dm ^2. It was found that it should be gradually increased at a rate of.

  That is, when the current density is gradually increased at the above rate, in the initial stage, while suppressing the rapid growth of the anodic oxide film in the continuous phase region, the anodic oxide film is also circulated into the silicon phase region, thereby The difference in the thickness of the anodized film formed between the regions can be made smaller than before. Therefore, after the surface of the silicon phase is covered with an anodic oxide film, the entire surface of the rear housing is almost uniform in thickness and surface smoothness by continuing the anodic oxidation treatment at a constant current density by normal constant current control. It becomes possible to coat with an excellent anodic oxide film.

Accordingly, the present invention provides a housing (9) configured by a plurality of divided bodies in a shape having a working chamber (6), a suction passage (7) and a discharge passage (8) communicating with the working chamber, The housing of the oil pump (2) having a rotor (3) disposed in the working chamber so as to be rotatable about the shaft (4) and having the oil sucked in through the suction passage and discharged through the discharge passage with rotation. A rear housing (1) facing the working chamber of the divided body constituting the body and facing the shaft end of the rotor is formed of a high silicon-aluminum alloy, and at least facing the shaft end of the rotor of the rear housing In the state where the surface (25) to be immersed in the electrolyte together with the cathode with the rear housing as the anode,
(1) a first step of increasing the current density of the current applied between the ^two electrodes from 0 A / dm ^{2 at} a rate of 0.35 A / dm ² or less per minute;
(2) a second step of continuing the anodizing process while maintaining the predetermined current density after the current density reaches a predetermined value;
It is covered with the anodic oxide film formed through (Claim 1). The alphanumeric characters in parentheses represent corresponding components in the embodiments described later.

The rear housing is preferably formed of a high silicon-aluminum alloy containing silicon in a proportion of 1 to 25% by mass in consideration of increasing the strength of the rear housing in order to increase the pressure of the oil pump. Item 2).
The rotor is formed of an iron-nickel-molybdenum-carbon based high-density sintered body having a density of 7.25 g / cm ³ or more in consideration of improving wear resistance when combined with the rear housing. (Claim 3), and particularly preferably formed by a sintered body obtained by subjecting the high-density sintered body to vacuum carburizing and carburizing and quenching (Claim 4).

FIG. 1 is a cross-sectional view showing a cross section of the oil pump 2 of the present invention along the direction of the axis 5 of the shaft 4 of the rotor 3, and FIG. 2 is a side view showing a state where the rear housing 1 is removed from the oil pump 2. It is.
With reference to FIG. 1, an oil pump 2 of this example includes a housing 9 having a working chamber 6, an oil suction passage 7 and a discharge passage 8 communicating with the working chamber 6, and the working chamber 6. A rotor 3 is disposed so as to be rotatable about an axis 5 and sucks oil through the suction passage 7 and discharges it through the discharge passage 8 as the shaft 4 rotates.

  The housing 9 is constituted by a plurality of divided bodies in a shape having the above-described parts. That is, the housing 9 includes a front housing (divided body) 11 and a rear housing (divided body) 1 that can be divided by the dividing surface 10. The front housing 11 is made of, for example, an aluminum alloy, and includes a working chamber 6 that is recessed from the dividing surface 10. The front housing 11 and the rear housing 1 are sealed by a seal 12 provided on the dividing surface 10. The front housing 11 and the rear housing 1 are fixed to each other by screwing a bolt 15 into a screw hole 13 provided in the front housing 11 through a through hole 14 provided in the rear housing 1.

  A first side plate (divided body) 17 is fitted into the working chamber 6 via a seal 16. The rear housing 1 also functions as a member that sandwiches the rotor 3 from both sides together with the first side plate 17 and is also called a second side plate. A through-hole 18 through which the shaft 4 is inserted from the bottom in the direction of the axis 5 perpendicular to the dividing surface 10 is formed in the center of the front housing 11 in the surface direction of the bottom of the working chamber 6.

  The first side plate 17 includes a surface facing the rotor 3 accommodated in the working chamber 6 and a surface facing the bottom of the working chamber 6 in a state of being fitted in the working chamber 6. A through hole 19 is formed through which the shaft 4 is inserted in communication with the through hole 18. Discharge ports 20 penetrating between the both surfaces are formed in parallel with the through hole 19 at two positions around the through hole 19 and symmetrically across the axis 5.

  An annular discharge recess 21 connected to the discharge port 20 is provided around the through hole 18 at the bottom of the working chamber 6. The discharge port 20 and the discharge recess 21, and a passage 22 formed in the front housing 11 Are connected to form a discharge passage 8. A cylindrical metal bearing 23 that rotatably supports the shaft 4 is disposed in the through hole 18. A seal 24 that seals between the shaft 4 and the front housing 11 is disposed at the opening of the through hole 18 on the opposite side of the working chamber 6.

  A concave surface 26 into which the tip of the shaft 4 is inserted is provided on the facing surface 25 of the rear housing 1 facing the rotor 3. A cylindrical metal bearing 27 that rotatably supports the shaft 4 is disposed in the recess 26. In the rear housing 1, a passage 28 (indicated by a broken line in the drawing) constituting the suction passage 7 is provided. Suction ports 29 (also indicated by broken lines in the figure) for connecting the passage 28 and the working chamber 6 are provided at two symmetrical positions on the opposite surface 25 around the recess 26 with respect to the axis 5. .

The front housing 11 forms the suction passage 7 together with the passage 28 and the suction port 29, and when the oil flowing through the discharge passage 8 is excessive, part of the oil is returned to the suction passage 7 through the bypass passage 30. Passage members 31 and 32 constituting a flow control valve are provided, and a suction cylinder 33 that is an oil inlet is connected to the passage member 32.
Referring to FIGS. 1 and 2, a cylindrical cam ring 34 surrounding the rotor 3 is fitted in the working chamber 6 so as to be sandwiched between the first side plate 17 and the rear housing 1. The inner peripheral surface of the cylinder of the cam ring 34 is a cam surface 35 whose shape in a direction orthogonal to the direction of the axis 5 is an ellipse.

  The rotor 3 is fitted into a rotor main body 36 integrally attached to the shaft 4 and a plurality of grooves 37 provided radially from the outer peripheral surface of the rotor main body 36 toward the axis 5 so as to be outside the outer peripheral surface. And a plurality of vanes 38 arranged radially. Each vane 38 is provided so as to be able to be inserted and removed from the groove 37 and is urged radially outward by the hydraulic pressure applied to the vane 38.

  When the shaft 4 is rotated, the vane 38 is urged radially outward by hydraulic pressure, and rotates together with the rotor body 36 while maintaining the state where the tip is in contact with the cam surface 35 of the cam ring 34. The suction ports 29 are provided at two locations corresponding to the chambers 39 and 40 partitioned by the adjacent vanes 38 in the state of FIG. 2 on the facing surface 25 of the rear housing 1. Further, the discharge port 20 is provided at two locations corresponding to the chambers 41 and 42 partitioned by the adjacent vanes 38 in the state of FIG. 2 in the first side plate 17.

  When the shaft 4 is rotated in the direction indicated by the solid arrow in FIG. 2, each chamber 39 partitioned by the vane 38 itself rotates from the suction port 29 toward the discharge port 20, thereby sucking in oil. It can be sucked through the passage 7 and discharged through the discharge passage 8. Further, at this time, the following suction force and discharge force are generated in the respective chambers 39 along with the rotation, thereby preventing the back flow of oil.

Suction force: the suction of sucking oil into the chambers 39, 40 through the suction passage 7 and the suction port 29 by increasing the volume of the chambers 39, 40 to be separated from the suction port 29 based on the shape of the cam surface 35. Force is generated.
Discharge force: Discharge that causes oil to be discharged from the chambers 41 and 42 through the discharge port 20 and the discharge passage 8 by reducing the volume of the chambers 41 and 42 that approach the discharge port 20 based on the shape of the cam surface 35. Force is generated.

  Of these parts, the rear housing 1 and the front housing 11 are both increased in strength to prevent distortion in response to the high pressure (for example, 8 MPa → 15 MPa) of the aluminum alloy, particularly the oil pump, in order to reduce the weight of the oil pump 2. Therefore, it is formed of, for example, a high silicon-aluminum alloy containing silicon at a ratio of about 1 to 25% by mass, particularly about 10 to 20% by mass. Further, the opposed surface 25 of the rear housing 1 facing the shaft end of the rotor 3, that is, the side surface of the rotor main body 36 and the side edge of the vane 38 and in which the both portions are slidably contacted is not shown in order to improve the wear resistance. It is covered with an anodized film.

However, when the rear housing 1 made of the high silicon-aluminum alloy is anodized under normal conditions, as described above, the surface smoothness of the anodized film decreases, and the rotor body 36 and vane 38 are reduced. This causes a problem of developing an aggressiveness against.
On the other hand, in the present invention, the rear housing 1 is used as an anode, and immersed in an electrolyte together with the cathode,
(1) a first step of increasing the current density of the current applied between the ^two electrodes from 0 A / dm ^{2 at} a rate of 0.35 A / dm ² or less per minute;
(2) a second step of continuing the anodizing process while maintaining the predetermined current density after the current density reaches a predetermined value;
Then, the surface smoothness of the anodized film can be improved by coating the facing surface 25 with the anodized film. Therefore, it is possible to impart good wear resistance to the facing surface 25 while suppressing the aggressiveness against the rotor body 36 and the vane 38.

  The smaller the rate of increasing the current density in the first step, the more uniform the thickness of the anodized film formed through the first and second steps, and the smoother the surface. However, the smaller the rate of increasing the current density in the first step, the longer the treatment required to form the anodic oxide film having a predetermined thickness, and the lower the productivity of metal parts having the anodic oxide film. Tend to.

Therefore, considering that the rear housing 1 having an anodized film having excellent surface smoothness and the like is manufactured while maintaining good productivity, the ratio of increasing the current density in the first step is within the above range. It is preferably 0.15 A / dm ² or more per minute, particularly 0.16 to 0.34 A / dm ² per minute. The current density may be unilaterally increased from 0 A / dm ² to a predetermined value, or may be increased stepwise.

Maintaining the current density in the second step, the constant current control by 0.8 A / dm ² or more, 1.2A / dm ² or less, in particular 0.9 A / dm ² or more, the predetermined value of 1.1A / dm ² or less It is preferable to do this. If the current density is less than the above range, it takes a long time to form an anodic oxide film having a predetermined thickness, which may reduce the productivity of metal parts having the anodic oxide film. On the other hand, when the above range is exceeded, the surface roughness of the anodized film becomes large, which may reduce the wear resistance and the performance of the oil pump.

The anodizing treatment can be performed in the same manner as in the prior art except that the current density is controlled through the steps (1) and (2). For example, the rear housing 1 is preferably pretreated such as degreasing prior to being immersed in the electrolyte.
The anodic oxide coating only needs to cover at least the opposing surface 25 of the rear housing 1. To selectively cover only the opposing surface 25 with the anodic oxide coating, the other surface of the rear housing 1 must be masked. That's fine. However, in consideration of saving troubles such as masking and improving the wear resistance of the entire surface of the rear housing 1, it is preferable to cover the entire surface of the rear housing 1 including the facing surface 25 with an anodized film.

Lead (Pb), carbon (C) or the like is used as the cathode.
Examples of the electrolytic solution include a sulfuric acid bath, an oxalic acid bath, a chromic acid bath, a phosphoric acid bath, an alkaline bath, and the like, and a sulfuric acid bath is particularly preferable. The liquid temperature of the electrolyte solution is controlled to a certain extent while forming a dense anodic oxide film with as high a hardness as possible and suppressing the selective and rapid growth of the anodic oxide film in the continuous phase region, particularly in the initial stage of formation. In consideration of maintaining the growth rate of the rear housing 1 and maintaining the productivity of the rear housing 1, the temperature is preferably 10 to 40 ° C, particularly preferably 10 to 20 ° C.

The anodic oxide film formed by the anodic oxidation treatment is composed of an active layer in contact with the facing surface 25 of the rear housing 1 and a porous layer thereon as in the prior art, and the porous layer has a very small thickness of angstrom order. It has a porous structure with pores.
For this reason, it is expected that oil is held in the through holes of the porous layer to give good lubricity to the rotor body 36 and the vane 38. For example, when the oil pump 2 is used in a high temperature environment such as around the engine of an automobile, in order to prevent seizure between the rear housing 1 and the rotor main body 36 and the vane 38, the through hole is provided with, for example, disulfide. A solid lubricant such as molybdenum (MoS ₂ ) may be impregnated.

In order to improve the surface smoothness, corrosion resistance, etc., the formed anodic oxide film is preferably subjected to sealing treatment such as immersing in water and boiling.
As described above, the surface of the anodized film is required to be as smooth as possible in order to suppress the aggressiveness to the rotor body 36 and the vane 38. Specifically, the ten-point average roughness R defined in Appendix 1 of Japanese Industrial Standard JIS B0601: 2001 “Product Geometrical Specification (GPS) —Surface Properties: Contour Curve Method—Terms, Definitions, and Surface Property Parameters” _{It is preferable} that the ten-point average roughness R _{ZJIS94 of the} anodized film coated on the facing surface 25 finished with _ZJIS94 to 1 μm through the steps (1) and (2) is 3 μm or less. The lower limit value of the ten-point average roughness is 0 μm, that is, ideally the surface is completely smooth, but in reality, it is preferably about 2 μm.

The thickness of the anodized film is 6 to 15 μm, particularly 8 to 10 μm in consideration of imparting good wear resistance to the facing surface 25 of the rear housing 1 while maintaining the productivity of the rear housing 1. Is preferred.
The hardness of the anodic oxide film, considering that sufficient wear resistance is imparted to the facing surface 25 of the rear housing 1, has an internal hardness (hardness at a depth of 1 mm from the surface) of Japanese Industrial Standard JIS. Z2244: 2003 facing surface made of high silicon-aluminum, expressed as Vickers hardness HV0.01 at a test force of 0.09807N, 150, measured by the measurement method defined in “Vickers hardness test—test method” 25, it is preferable that the same Vickers hardness HV0.01 of the surface of the anodized film coated through the steps (1) and (2) is about 200 to 300.

In order to improve the wear resistance of the rotor body 36 constituting the rotor 3, an iron (Fe) -nickel (Ni) -molybdenum (Mo) -carbon (C) based sintered alloy, particularly iron (Fe)- Nickel (Ni) -copper (Cu) -molybdenum (Mo) -carbon (C) based sintered body, in particular, density ρ = 7.25 g / cm ³ or more, particularly 7.25 in order to increase its strength and wear resistance. -7.5 g / cm ³ high density sintered body, and further formed by carburizing and quenching the high density sintered body, ie, vacuum carburizing treatment and subsequent quenching treatment. The The first side plate 17 and the cam ring 34 are also preferably formed of the same sintered body.

The proportion of each component in the sintered body is such that when the sintered body is the rotor body 36, nickel is 0.5 to 5.5% by mass, particularly 3 to 4% by mass, molybdenum in order to ensure toughness by nickel. Is preferably 0.1 to 1.0% by mass, copper is 0.5 to 2.0% by mass, and carbon is 0.1 to 0.8% by mass, with the balance being iron and inevitable impurities. .
Further, when the sintered body is the first side plate 17 and the cam ring 34, nickel is 0.5 to 5.0% by mass, particularly 3 to 4% by mass, and molybdenum is 0.4% in order to ensure wear resistance by molybdenum. It is preferable that 5-1.5 mass%, copper is 0-2.0 mass%, carbon is 0.1-0.8 mass%, and the balance is iron and inevitable impurities.

In any case, the carbon content is the content after the treatment when carburizing and quenching described later.
The sintered body can be manufactured by high-density warm die lubrication using, for example, a raw material powder in which an iron-nickel-molybdenum-based or iron-nickel-copper-molybdenum-based metal powder and a carbon powder are blended. The reason why carbon powder is contained in advance is to compensate for the tendency of carburizing and quenching to be insufficient in a high-density sintered body. By including the carbon powder and adopting a vacuum carburizing process described later in the carburizing and quenching process, the high-density sintered body can be sufficiently carburized and quenched to improve its wear resistance. .

  In the high-density warm mold lubrication, first, a higher fatty acid-based lubricant such as lithium stearate is applied to the mold surface corresponding to the shape of the rotor body 36 and the like, and both the mold and the raw material powder are 150. The raw material powder is warm-filled in the mold while heating at a temperature not lower than ° C. and not higher than the melting point of the higher fatty acid-based lubricant (for example, up to about 200 ° C.). Under the present circumstances, you may mix | blend the powder of the same higher fatty acid-type lubricant with the raw material powder in the ratio of about 0.2 mass part per 100 mass parts.

Next, the raw material powder filled in the mold is pressed to about 600 to 700 MPa to form a compacted body, and then the compacted body taken out from the mold is sintered at about 1100 to 1400 ° C. for 40 to 80 minutes. A knot is obtained.
Higher fatty acid-based lubricants function as a lubricant during warm filling to increase the packing density of the raw material powder, and also have a mechanochemical reaction with iron under high pressure when forming a compacted body, for example, If lithium stearate is used, iron stearate is generated to improve lubricity and to improve the releasability of the compact from the mold. Therefore, the density of the compacted body can be increased, and a high-density sintered body satisfying the above-described density can be produced from the compacted body.

Further, when carburizing and quenching the sintered body, vacuum carburizing treatment is preferably employed. In the vacuum carburizing treatment, the carburized gas is introduced while heating the sintered body to approximately 800 to 1100 ° C. in vacuum, and further heated for about 200 to 300 minutes, so that the inside of the high-density sintered body can be sufficiently obtained. Can be carburized.
When the sintered body after carburizing is immersed in oil of 100 ° C. or less, particularly 50 to 70 ° C. and quenched, the carburizing and quenching process is completed. Then, you may perform the tempering process which heats a sintered compact at about 180-200 degreeC for 60 to 80 minutes as needed.

The density measured by the measuring method specified in the Japanese Industrial Standard JIS Z2505: 1989 “Sintering Density Test Method for Metal Sintered Materials” of the sintered body manufactured through the above-described steps is as described above. It is preferably 7.25 g / cm ³ or more and 7.5 g / cm ³ or less, particularly preferably 7.3 g / cm ³ or more and 7.45 g / cm ³ or less. When the density is less than the above range, the wear resistance of the sintered body, that is, the rotor main body 36, the vane 38, the first side plate 17, and the cam ring 34 may not be sufficiently improved. Moreover, when exceeding the said range, hardening may become inadequate and there exists a possibility that intensity | strength may fall.

  In particular, when the sintered body is the rotor main body 36, considering that it imparts good toughness while sufficiently maintaining the wear resistance of the surface, the internal hardness of the sintered body is JISZ2244: 2003 " The Vickers hardness HV at a test force of 0.2 N measured by the measurement method defined in “Vickers Hardness Test—Test Method” is 700 to 800 in a region having a depth of 0.1 to 0.2 mm from the surface. And it is preferable that it is 500-600 in the depth vicinity of 1 mm. A sintered body having such a hardness distribution can be manufactured by forming the above-described alloy having the composition for the rotor body 36 and subjecting it to carburizing and quenching.

The vane 38 can be formed of, for example, a steel material such as bearing steel SUJ2, or a material obtained by plating the surface of the steel material.
The configuration of the oil pump 2 of the present invention is not limited to the example shown in the drawings described above, and various modifications can be made without departing from the gist of the present invention.

Example 1
A high silicon-aluminum alloy plate having a silicon content of 14% by mass was prepared as a base material. The Vickers hardness HV0.01 at a depth of 1 mm from the surface of the high silicon-aluminum alloy forming the plate material was 150. The ten-point average roughness _RZJIS94 of the surface of the plate material was finished to 1 μm.

The plate material is degreased in advance and then connected to the anode of the power supply device and immersed in a sulfuric acid bath together with the lead cathode. First, the current density applied between the electrodes in the first step is changed from 0 A / dm ² to 0. Increased to 1 A / dm ² over 3 minutes at a rate of 333 A / dm ² .
Subsequently, after the current density reaches the predetermined value, the anodization treatment is further performed for a further 37 minutes while maintaining the current density by constant current control, and then the substrate is taken out from the sulfuric acid bath and washed with water. Further, the sample was sealed by boiling in water to produce a sample of a metal part having a surface coated with an anodized film.

(Comparative Example 1)
After increasing the current density of the current applied between the electrodes to 1A / dm ² over a period of 1 minute per minute 1A / dm ² from 0A / dm ² in a first step, maintaining the current density by the constant current control However, a sample of a metal part whose surface was coated with an anodized film was manufactured in the same manner as in Example 1 except that the anodizing treatment was further performed for 39 minutes for a total of 40 minutes.

(Surface roughness measurement)
The ten-point average roughness _RZJIS94 of the surface of the anodized film of the metal part samples produced in Example 1 and Comparative Example 1 was measured using a surface roughness meter. The measurement conditions were 6 sections, cut-off value λ _C = 0.8 mm, λ _S = 0.0025 mm, measurement speed: 0.5 mm / sec, and a 10-point average roughness R by applying a Gaussian filter to the measurement results. _ZJIS94 was determined.

(Thickness measurement)
Samples of metal parts manufactured in Example 1 and Comparative Example 1 were cut in the thickness direction of the anodized film, filled with resin, and the cut surface was polished. The average value of the measured thickness was determined and used as the thickness of the anodized film. Further, the difference between the maximum value and the minimum value of the ten measured values was determined to evaluate the thickness variation.

(Hardness measurement)
The sample of the metal part manufactured in Example 1 and Comparative Example 1 was lapped on the surface of the anodized film and then measured for Vickers hardness HV0.01.
The results are shown in Table 1.
(Real machine test)
A rear housing 1 having the shape shown in FIG. 1 is formed of a high silicon-aluminum alloy having a silicon content of 14% by mass, which is the same as that used in Example 1 and Comparative Example 1. At least the facing surface 25 facing the rotor 3 was anodized under the same conditions as in Example 1 and Comparative Example 1 to form an anodized film.

The rear housing 1 is formed into a predetermined shape by high-density warm die lubrication using a raw material powder in which iron-nickel-copper-molybdenum metal powder and carbon powder are mixed, and then vacuum carburized. The oil pump 2 shown in FIGS. 1 and 2 is configured in combination with the rotor body 36 formed in this way, the vane 38 made of bearing steel SUJ2, and the like.
The density of the rotor body 36 is 7.4 g / cm ³ , and the Vickers hardness HV at a test force of 0.2 N is 730 in a region 0.1 to 0.2 mm deep from the surface, and in the vicinity of 1 mm deep. 500.

The oil pump 2 was continuously operated for 110 hours under the following operating conditions.
(Operating conditions)
Lubricating oil: PS pump oil Oil temperature: 100 ° C. or higher Pump pressure: 15 MPa or higher Sliding speed at the tip of the vane 38: 3.9 m / s or higher Next, the rear housing 1 is removed, and the rotor body 36 and vane of the opposing surface 25 are removed. The wear depth (μm) of the region that was in contact with 38 was measured under the following measurement conditions using a contact-type roughness measuring machine, and the maximum value was determined. The measurement was performed in one direction from one point on the outer peripheral edge of the region through a central recess 26 to one point on the opposite side of the outer peripheral edge.

(Measurement condition)
Stylus tip R: 2 μm
Measurement speed: 0.5 mm / s
The results are shown in Table 1 and FIG. 3 together with the results in the case of using the rear housing 1 in which the opposed surface 25 and the like are not anodized for comparison (Comparative Example 2).

From Table 1, Example 1 in which the current density was increased at a rate of 0.35 A / dm ² or less per minute in the first step of the anodic oxidation treatment was Comparative Example 1 in which the current density was increased beyond the above range. It was confirmed that the variation in the thickness of the anodized film was smaller than that of No. 1, and the surface smoothness was excellent. Also, from Table 1 and FIG. 3, the rear housing configured as in Example 1 has its own wear resistance as compared with that of Comparative Example 1 and Comparative Example 2 in which no anodized film was formed. It was confirmed that the properties were excellent.

It is sectional drawing which shows the cross section along the direction of the axis of the axis | shaft of a rotor of the oil pump containing the rear housing as an example of the metal component manufactured by the manufacturing method of this invention. It is a side view which shows the state which removed the rear housing from the oil pump of FIG. It is a graph which shows the maximum value of the abrasion depth of an opposing surface measured after performing an actual machine test using the rear housing produced by the Example of this invention and the comparative example.

Explanation of symbols

  1: rear housing, 2: oil pump, 3: rotor, 4: shaft, 6: working chamber, 7: suction passage, 8: discharge passage, 9: housing, 25: surface (opposing surface).

Claims (4)

A casing formed of a plurality of divided bodies in a shape having a working chamber, and a suction passage and a discharge passage communicating with the working chamber, and is rotatably disposed around the shaft in the working chamber. The oil pump having a rotor that sucks oil through the suction passage and discharges it through the discharge passage faces the working chamber among the divided bodies constituting the housing, and the rear housing facing the rotor shaft end is made of high silicon The surface of the rear housing facing at least the shaft end of the rotor is formed of an aluminum alloy, and the surface of the rear housing is immersed in an electrolyte together with the cathode, using the rear housing as an anode.
(1) a first step of increasing the current density of the current applied between the ^two electrodes from 0 A / dm ^{2 at} a rate of 0.35 A / dm ² or less per minute;
(2) a second step of continuing the anodizing process while maintaining the predetermined current density after the current density reaches a predetermined value;
An oil pump, characterized in that it is covered with an anodized film formed through the process.   The oil pump according to claim 1, wherein the rear housing is formed of a high silicon-aluminum alloy containing silicon in a proportion of 1 to 25 mass%. The oil pump according to claim 1 or 2, wherein the rotor is formed of a high-density sintered body of iron-nickel-molybdenum-carbon system with a density of 7.25 g / cm ³ or more.   The oil pump according to claim 3, wherein the rotor is formed of a sintered body obtained by subjecting the high-density sintered body to carburizing and quenching by vacuum carburization.

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