JP2006057659A - Needle roller bearing for hydraulic pump - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain long service life even under the condition that thickness of an oil film is extremely small in low viscosity and diluted lubrication. <P>SOLUTION: Numerous recessed parts having a minute recessed shape are provided on a surface of at least a rolling body 2 of the roller bearing 1 for the hydraulic pump in a random manner. Surface roughness parameter Ryni of the face provided with the recessed parts is in a scope of 0.4 to 1.0 μm, and an Sk value is -1.6 or less. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a roller bearing for shaft support used for a hydraulic pump or the like.

FIG. 10 shows a cross section of a general circumscribed gear pump as a representative example of the hydraulic pump. As is well known, the circumscribed gear pump is composed of a pair of circumscribed gears 34 and 38. That is, the pair of gears 34 and 38 are accommodated in the casing 42, and the shaft portions 36 and 40 of the gears 34 and 38 are rotatably supported via the needle roller bearings 48. The casing 42 has a suction port 44 and a discharge port 46. When the gears 34 and 38 are rotated, oil is sucked from the suction port 44, and pressurized oil is discharged from the discharge port 46.
JP-A-3-223548

  In recent years, hydraulic pumps tend to be used in high-load and high-temperature environments due to downsizing, higher output, lower viscosity of lubricating oil, etc., and wear and surface-induced peeling due to poor lubrication are likely to occur. It is coming.

  Patent Document 1 describes a roller bearing in which minute irregularities are formed on the surface of a rolling element to improve oil film forming ability. These conventional recesses having a small concave shape have a value Rqni (L) / value of the ratio of the axial surface roughness Rqni (L) and the circumferential surface roughness Rqni (C) when the surface roughness is expressed by the parameter Rqni. The value of Rqni (C) is 1.0 or less (Rqni ≧ 0.10), and the surface roughness parameter Sk is set to −1.6 or less, so that even if the mating surface is rough, Even a good surface finish has a long service life.

  However, when the oil film thickness is extremely thin under low viscosity and dilute lubrication, the effect may not be sufficiently exhibited.

  In the roller bearing for a hydraulic pump according to the present invention, an infinite number of minute concave recesses are provided at least on the surface of the rolling element, and the surface roughness parameter Ryni of the surface provided with the recesses is 0.4 μm ≦ Ryni ≦ 1. It is in the range of 0 μm, and the Sk value is −1.6 or less.

  Here, the parameter Ryni is the average value of the maximum height for each reference length, that is, the reference length is extracted in the direction of the average line from the roughness curve, and the interval between the peak line and the valley bottom line of this extracted portion is the roughness curve. It is a value measured in the direction of the vertical magnification (ISO 4287: 1997).

  The parameter Sk indicates the degree of skewness (skewness) of the roughness curve (ISO 4287: 1997), and is a statistic that is a measure of the asymmetry of the uneven distribution. The Sk value is close to 0 in a symmetric distribution such as a Gaussian distribution. That is, when the concave and convex portions are deleted, negative values are obtained, and in the opposite case, positive values are obtained. The Sk value can be controlled by selecting the rotational speed of the barrel sander, the processing time, the amount of workpiece input, the type and size of the chip, and the like. By setting the Sk value to -1.6 or less in both the width direction and the circumferential direction, the hollow with a minute concave shape becomes an oil reservoir, and even when compressed, there is little oil leakage in the sliding direction and the right-angle direction, so that an oil film is formed. Excellent, oil film formation is good, and has the effect of minimizing surface damage.

  As is well known, a roller bearing is a mechanical element that supports a shaft that rotates or swings by a rolling motion of a rolling element (roller). Usually, the rolling element is slidably interposed between the inner ring raceway and the outer ring raceway, but there are types that do not have an inner ring with the outer peripheral surface of the shaft as a direct raceway surface, and types that have neither an outer ring nor an inner ring. To do. The reason why at least the surface of the rolling element is used is that it does not exclude the formation of a concave indentation on the raceway surface, and the concave shape is not only on the rolling surface of the rolling element but also on the end face. The purpose is not to exclude the formation of the depression.

  According to a second aspect of the present invention, in the roller bearing for a hydraulic pump according to the first aspect, a surface roughness parameter Rymax of the surface provided with the recess is 0.4 to 1.0. The parameter Rymax is the maximum value of the maximum height for each reference length (ISO 4287: 1997).

  According to a third aspect of the present invention, in the roller bearing for a hydraulic pump according to the first or second aspect, when the surface roughness of the surface provided with the recess is indicated by a parameter Rqni, the axial surface roughness Rqni (L) and the circumference A ratio value Rqni (L) / Rqni (C) to the directional surface roughness Rqni (C) is 1.0 or less. The parameter Rqni is the square root of the value obtained by integrating the square of the height deviation from the roughness center line to the roughness curve in the section of the measurement length and averaging it, and is also called the root mean square roughness. . Rqni is obtained by numerical calculation from the cross-sectional curve and roughness curve recorded in an enlarged manner, and measured by moving the stylus of the roughness meter in the width direction and the circumferential direction.

  According to the present invention, an oil film forming ability is improved by providing an innumerable number of minute concave concaves on the surface of the rolling element, and the oil film thickness is extremely thin under low viscosity and dilute lubrication. But it has a long life. In particular, the surface roughness parameter Ryni of the surface provided with the indentation is set within a range of 0.4 μm ≦ Ryni ≦ 1.0 μm, and is suppressed to be smaller than before, thereby preventing oil film breakage even under lean lubrication. It is possible, and a long life can be obtained even under conditions where the oil film thickness is extremely thin compared to conventional products. As for the Sk value, -1.6 or less is the range advantageous for oil film formation in terms of the shape and distribution of the surface recess depending on the processing conditions.

  The needle roller bearing for shaft support in the gear pump already described with reference to FIG. 10 has an inner ring, an outer ring, and a rolling element as main components. The needle roller bearing 10 shown in FIG. 10 is of a type that does not have an inner ring with the outer peripheral surfaces of the shafts 36 and 40 as direct raceways. And, at least one of the rolling surfaces and end surfaces of the rolling elements and the raceway surfaces of the inner and outer rings are randomly roughened by randomly forming innumerable minute concave recesses. This minute rough surface has a surface roughness parameter Rqni of a surface provided with a depression within a range of 0.4 μm ≦ Rqni ≦ 1.0 μm, and an Sk value of −1.6 or less, preferably −4.9. It is the range of -1.6. Further, the surface roughness parameter Rymax of the surface provided with the depression is 0.4 to 1.0. Further, when the surface roughness is obtained in the axial direction and the circumferential direction of each surface and displayed by the parameter Rqni, the ratio of the axial surface roughness Rqni (L) to the circumferential surface roughness Rqni (C) The value Rqni (L) / Rqni (C) is 1.0 or less. As the surface processing for obtaining such a fine rough surface, a desired finished surface can be obtained by special barrel polishing, but a shot or the like may be used.

The measurement method and conditions of the parameters Ryni, Rymax, Sk, Rqni are exemplified as follows. Note that when measuring the surface properties represented by these parameters for components such as rolling elements and races of roller bearings, a single measured value can be relied on as a representative value. Should be measured.
Parameter calculation standard: JIS B 0601: 1994 (Surfcom JIS 1994)
Cut-off type: Gaussian Measurement length: 5λ
Cut-off wavelength: 0.25mm
Measurement magnification: × 10000
Measurement speed: 0.30 mm / s
Measurement location: Roller center measurement number: 2
Measuring device: Surface roughness measuring device Surfcom 1400A (Tokyo Seimitsu Co., Ltd.)

  A needle roller bearing 1 for a gear pump shown in FIG. 1 is a needle roller bearing in which a needle roller 2 is incorporated in an outer ring 4 as a rolling element, and the other shaft (not shown) is supported by the needle roller 2. ing. The needle rollers 2 are held by a cage 6 so as to be able to roll evenly in the circumferential direction. A description will be given of the results of manufacturing a plurality of types of needle roller bearings on the surface of the needle roller 2 that have been subjected to surface treatments having different finishing surfaces and performing a life test. As shown in FIG. 2, the needle roller bearing used in the life test has 15 outer diameters Dr = 33 mm, an inner diameter dr = 25 mm, a diameter D = 4 mm of the needle roller 2, and a length L = 25.8 mm. 2 is a roller with a cage 6 (subunit consisting of a rolling element of a roller bearing and a cage). Three types of test roller bearings with different surface roughness finishes were produced. That is, there are a bearing A (comparative example) subjected to superfinish after grinding, and a bearing B (comparative example) and a bearing C (example) in which numerous indentations of minute concave shapes are randomly formed. FIGS. 3 to 5 show the finished surface condition of the needle roller of each test bearing. 3 shows the surface roughness of the bearing A, FIG. 4 shows the surface roughness of the bearing B, and FIG. 5 shows the surface roughness of the bearing C. Table 1 shows a list of characteristic value parameters of the surface finish of each test bearing. For Rqni (L / C), the bearings B and C are 1.0 or less, and the bearing A is a value around 1.0.

The test apparatus used is a radial load tester 8 as schematically shown in FIG. 6, and the test bearings 1 are attached to both sides of the rotary shaft 9 and the test is performed by applying rotation and load. The finish of the inner race (mating shaft) used for the test is Ra 0.10 to 0.16 μm of the polished finish. The outer race (outer ring) is also common. The test conditions are as follows.
Bearing radial load: 2000kgf
Rotation speed: 4000rpm
Lubricant: Crisef Oil H8 (2 cst under test conditions)

  FIG. 7 shows the life test results under the oil film parameter Λ = 0.13. The vertical axis of the figure represents the L10 life (h). As is clear from the figure, bearing A was 78h and bearing B was 82h, while bearing C was 121h. As shown by this data, the bearing C as an example can obtain a long life effect even under extremely severe lubricating conditions with a low viscosity and a thin oil film parameter Λ = 0.13.

  The metal contact rate was evaluated using a two-cylinder tester shown in FIG. In FIG. 8, a driving side cylinder 22 (D cylinder: Driver) and a driven side cylinder 24 (F cylinder: Follower) are attached to one end of each rotating shaft, and two rotating shafts 26, 28 are pulleys 30, 32, respectively. Can be driven by a separate motor. The shaft 26 on the D cylinder 22 side was driven by a motor, and the F cylinder 24 was free-rolled to follow the D cylinder 22. For the F cylinder 24, two types of comparative examples and examples were prepared for the surface treatment. Details of the test conditions are shown in Table 2.

  The comparison data of metal contact ratio is shown in FIG. In this figure, the horizontal axis represents the elapsed time, the vertical axis represents the metal contact rate, FIG. 9A shows the metal contact rate of the rolling surface of the roller in the comparative example bearing, and FIG. 9B shows the example bearing. The metal contact ratios of the rolling surfaces of the rollers are shown respectively. Comparing these figures, it can be clearly confirmed that the metal contact ratio is improved in the embodiment as compared with the comparative example. In other words, the oil film formation rate (= 100% −metal contact rate) is about 10% at the start of operation and 2 at the end of the test (after 2 hours) in the bearing of the example compared to the bearing of the comparative example. % Improvement.

Cross section of needle roller bearing Cross section of needle roller bearing used for life test Roughness curve diagram showing the condition of the finished surface of the rolling element in the test bearing Roughness curve diagram showing the condition of the finished surface of the rolling element in the test bearing Roughness curve diagram showing the condition of the finished surface of the rolling element in the test bearing Schematic diagram of test equipment Graph showing life test results Overall schematic diagram of a 2-cylinder testing machine A is a graph showing the metal contact rate of the comparative example, and B is a graph showing the metal contact rate of the example. A is a transverse sectional view of the gear pump, B is a longitudinal sectional view

Explanation of symbols

1 Needle roller bearing 2 Rolling element 4 Outer ring 6 Cage

Claims (3)

  At least the surface of the rolling element is randomly provided with an infinite number of minute concave recesses, and the surface roughness parameter Ryni of the surface provided with the recesses is in the range of 0.4 μm ≦ Ryni ≦ 1.0 μm, and Sk A roller bearing for a hydraulic pump having a value of -1.6 or less.   2. The roller bearing for a hydraulic pump according to claim 1, wherein a surface roughness parameter Rymax of the surface provided with the recess is in a range of 0.4 to 1.0.   When the surface roughness of the surface provided with the depression is represented by the parameter Rqni, the value Rqni (L) / Rqni (R) of the ratio between the axial surface roughness Rqni (L) and the circumferential surface roughness Rqni (C) The roller bearing for a hydraulic pump according to claim 1 or 2, wherein C) is 1.0 or less.

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