JP2999544B2 - Needle roller bearings for starters - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a needle roller bearing for a starter for starting an automobile engine.

[Related Art] Electromagnetic push-types are mainly used as starters used for starting engines of automobiles, and among them, reduction types (with internal reduction gears) are often used.

As shown in FIG. 8, the reduction type starter is
A speed reducer 3 is provided between the drive shaft of the armature 1 and the pinion 2 of the output shaft, and the pinion 2 of the output shaft is configured to be disengaged from the ring gear 5 by a magnetic switch 4, so that the high speed rotation of the armature 1 is achieved. The speed is reduced by the speed reducer 3, and the output of the pinion 2 is set to another torque.

In the cranking for turning the output shaft to start the engine, the starter as described above has the armature 1 having the maximum torque when the rotation is 0 as shown in the relationship diagram between the cranking speed and the cranking torque in FIG. And the torque decreases as the rotation increases, so that the rotation of the armature 1 is higher in order to obtain a high output.

Since the characteristics of such a reduction type starter are high-speed rotation, bearings that are incorporated in the starter are required to have a function that is excellent in strength and grease life and has low torque.

10 and 11 show a conventional needle roller bearing used in a reduction type starter, and FIG. 10 shows a roller having a width in which the needle roller 7 fits on the inner peripheral surface of the outer ring 6. The driving groove 8 is cut, and a number of needle rollers 7 arranged in the rolling groove 8 are attached to the outer ring 6.
Is a solid needle roller bearing which is held at regular intervals by a cage 9 located inside.

FIG. 11 shows that an outer ring 10 is formed by bending a metal plate into a U-shaped cross section, a number of needle rollers 12 are arranged in an inner circumferential rolling groove 11 of the outer ring 10, and the needle rollers 12 are formed. This is a shell-shaped needle roller bearing which is held at regular intervals by a cylindrical cage 13 which is accommodated in the rolling groove 11.

It is well known that the life of the needle rollers 7, 12 and the outer rings 6, 10 in the needle roller bearing as described above is determined by the fact that the surface roughness of the rolling surface is an important factor. It was thought that it was better to make the running surface as smooth as possible.However, through repeated trial and error to improve the rolling contact fatigue life of the bearing, it was not necessary to improve the finish of the rolling surface. We found that it was effective for long life.

[Problems to be solved by the invention]

As described above, the needle roller bearing has the roller
ax 0.3-0.8μm is a structure formed on the rough surface of random scratches, can exert the effect of long life, but for a partner with a good finished surface, oil film formation becomes insufficient, Wear, peeling, peeling damage, and the like of the shaft, inner ring, and needle rollers may occur, and the need for improvement has been found in that the range of use for the finishing conditions of the mating shaft and the like is narrow.

In addition, since the cages 9 and 13 have a small cross-sectional area and a large amount of movement in the axial and radial directions, the cages are weak in strength and are difficult to cope with high-speed rotation. Since the vessel has a straight cross-sectional shape, the grease retention property is poor, and there is a problem that grease flows out due to centrifugal force during high-speed rotation, leading to a reduction in bearing life due to running out of grease.

Accordingly, the present invention focuses on the evaluation of the surface roughness of the surface of the needle roller not only in the axial direction but also in the rolling direction, and it is advantageous to form an oil film by suppressing the surface roughness in the axial direction and the circumferential direction to a certain range. It is an object of the present invention to provide a long-life needle roller bearing for a starter that can cope with any surface roughness of a mating surface.

Further, the present invention is for a starter which can increase the cross-sectional area of the cage and reduce the amount of movement in the axial and radial directions, improve the strength of the cage and the grease retention, and thereby also extend the life. It is an object to provide a needle roller bearing.

[Means for solving the problem]

In order to solve the above-described problems, the present invention provides an outer ring having a rolling groove on an inner peripheral surface, a large number of needle rollers arranged in the rolling groove, and a fixed interval between the needle rollers. The retainer is formed in a cross-sectional shape excellent in holding grease in the rolling groove, and minute independent depressions are randomly provided on the surface of the needle rollers, The surface roughness of the surface provided with the depressions is set such that the parameter SK value of the surface roughness is negative in both the axial direction and the circumferential direction, and the surface area ratio occupied by the minute depressions is 10 to
It adopts a 40% configuration.

[Action]

The surface of the needle rollers is formed into a random micro-rough surface, and the parameter SK value of the finished surface roughness of the micro-rough surface is made negative in both the axial and circumferential directions, and the surface area ratio occupied by the micro-dents is reduced by 10%. Setting to ~ 40%, the oil film formation rate on the needle roller surface is improved, and there is no wear, peeling or peeling damage on the mating surface regardless of the surface roughness of the mating surface, and a long life can be obtained. it can.

Also, the cage has a large cross-sectional area when provided with radially outward bent portions on both sides thereof, and the amount of movement in the axial and radial directions by the outer ring rolling grooves is small, so that the strength of the cage is excellent, and the grease is retained. Can be performed reliably.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
Description will be made based on the drawings.

As shown in FIG. 1, a needle roller bearing 21 for a starter is used.
Are outer races 22 and rolling grooves 23 formed on the inner peripheral surface of the outer races 22.
A large number of needle rollers 24 housed therein comprise a retainer 25 for holding the needle rollers 24 at regular intervals in pockets, and the outer ring 22 is made of a metal plate and has side walls 27 on both sides of an annular wall 26. , 27
Is formed in a shell shape having a U-shaped cross section obtained by bending the above.

The retainer 25 is provided with bent portions 28, 28 that are bent outward in the radial direction on both sides of the annular portion provided with the pocket.
It is formed in a substantially U-shaped cross-sectional shape that fits in the rolling groove 23 of 22.

The retainer 25 that fits in the rolling groove 23 of the outer ring 22 is guided by the bent portions 28, 28 on both sides in the radial direction by the rolling surface of the rolling groove 23 and the axial direction by the side surface of the side wall 27, 27, respectively. The amount of movement in the axial and radial directions is small.

As described above, when the retainer 25 has a substantially U-shaped cross-sectional shape, the cross-sectional area becomes large and the amount of movement in the axial direction and the radial direction is small, so that the strength of the retainer 25 is improved.

Further, the retainer 25 is substantially U-shaped having the bent portions 28 on both sides.
By adopting the cross-sectional shape of a letter, the grease holding property in the rolling groove 23 is improved, which is advantageous in grease life.

The same effect can be obtained by forming the retainer 25 not only in the substantially U-shaped cross section shown in FIG. 1 but also in a U-shaped cross section in which bent portions are provided on both sides of a straight annular portion.

In order to reduce the contact friction between the retainer 25 and the needle rollers 24, the entire surface of the retainer 25 may be coated with ethylene tetrafluoride resin. For example, in the case of grease lubrication, the contact friction is reduced by 20%. It can be down and can meet the demand for low torque as a high-speed rotation starter bearing.

In the needle roller bearing 21, the surface of the needle roller 24 is formed as a micro-rough surface 24a in a random direction, and the micro-rough surface 24a has a surface roughness in the axial direction and the circumferential direction of the needle roller 24. Is obtained and expressed as a parameter RMS, the ratio RMS between the axial surface roughness RMS (L) and the circumferential surface roughness RMS (C)
(L) / RMS (C) is 1.0 or less, for example, 0.7 to 1.0, and the parameter SK value of the surface roughness is minus, preferably -1.6 or less in both the axial and circumferential directions.

In the surface processing for obtaining the rough surface condition as described above, a desired finished surface can be obtained by special barrel polishing.

The parameter SK value refers to the degree of distortion (SKEWNESS) of the distribution curve of the surface roughness, and a symmetric distribution such as a Gaussian distribution has an SK value of 0, but the parameter SK value is determined in both the circumferential direction and the axial direction. The set value of -1.6 or less is a range in which the shape and distribution of the surface concave portions are advantageous for forming an oil film.

The surface area ratio occupied by the fine dents provided on the surface of the needle rollers 24 is in the range of 10 to 40%, and the average area of the fine dents is 35 to 150 μm ² when arranged except for an equivalent circular diameter of 3 μmφ or less. It has become.

FIG. 2 shows the finished surface condition of the standard needle rollers, and FIG.
The figure shows a comparison of the finished surface condition of the micro-roughened surface of the present invention applied to the surface of the needle rollers.

In order to perform the quantitative measurement of the minute depression, the surface of the rolling element or the rolling surface can be enlarged, and the image can be quantified by a commercially available image analysis system.

The white part of the image is analyzed as a flat surface part, and the minute dent is analyzed as a black part. For example, when an analysis is performed using an LA-525 image analysis system manufactured by Pierce Co., Ltd., the density of the original image is first clarified by an emphasis filter, and thereafter, an extremely fine black portion having an equivalent circular diameter of 3 μmφ or less is removed by a noise eraser.

Calculate the size, distribution, and surface area ratio of the minute dents left after removal with the noise eraser,
It evaluates the rolling element surface or the inner and outer ring rolling surfaces.

Next, the results of a durability test performed on a conventional needle roller bearing and the needle roller bearing of the present invention using a radial load tester under grease and oil lubrication conditions in an oil bath will be described.

As shown in the schematic diagram of FIG. 4, the radial load tester 31 used was a test in which test bearings A on both sides of a rotating shaft 32 were mounted, and a test was performed by applying rotation and load. Are shown together.

Table 2 shows the test results for grease lubrication and oil bath lubrication.
FIG. 5 further shows the cumulative damage establishment in FIG.

FIG. 6 shows the results of the area ratio of the minute depressions and the durability life, and FIG. 7 shows the results of the average area of the minute depressions and the durability life.

From the results of FIGS. 6 and 7, the durability life is 10% in area ratio.
% Or more and the average area is 35 μm ² or more, the ratio of the durable life (L ₁₀ ) to the calculated life is 4 or more, which is effective for the durable life.

In addition, the area ratio of the minute depression is 30% or more, and the average area
If it is 120 μm ² or more, the effective contact length tends to decrease, and the effect of long life tends to decrease.

〔effect〕

As described above, according to the present invention, the surface of the needle rollers is formed into a random micro-rough surface, and the surface area ratio occupied by the micro-dents is set to 10 to 40%. Advantageously, even when the mating surface is rough, a long life can be obtained even with a mating surface having a good finished surface, and there is an effect that there is no wear or peeling damage on the mating surface.

Further, since the bearing strength is high and the life of the grease is prolonged, it can be used as a starter bearing under conditions of high speed rotation and high load.

When the retainer is housed in the rolling groove of the outer race as shown in the illustrated embodiment, and radially outwardly bent portions are provided on both sides of the retainer, the amount of radial and axial movement of the retainer can be minimized. As well as maximize the cross-sectional area of the cage,
Accordingly, the strength of the cage is improved.

Further, when the cage is formed in a cross-sectional shape having bent portions on both sides thereof, the holding force of the grease is improved, and the movement amount of the cage is small, so that the grease life can be improved.

Further, since the bearing strength is high and the life of the grease is prolonged, it can be used as a starter bearing under conditions of high speed rotation and high load.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a needle roller bearing according to the present invention, FIGS. 2 and 3 are schematic views showing the finished surface condition of the needle roller surface, and FIG. 4 is a schematic view of a test device used for a life test. FIGS. 5 and 6 are graphs showing the establishment of cumulative damage, FIGS. 6 and 7 are graphs showing the results of a life test, FIG. 8 is a schematic explanatory diagram of a reduction type starter, and FIG. Diagram,
10 and 11 are sectional views showing a conventional needle roller bearing. 21: Needle roller bearing, 22: Outer ring, 23: Rolling groove, 24: Needle roller, 25: Cage, 27: Side wall, 28: Bend.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) F16C 19/46 F16C 33/34 F16C 33/46

Claims (1)

(57) [Claims] 1. An outer ring having a rolling groove provided on an inner peripheral surface thereof, a plurality of needle rollers arranged in the rolling groove, and a retainer for holding the needle rollers at a constant interval, This retainer is formed in a cross-sectional shape excellent in grease retention in the rolling grooves, and minutely independent indentations are randomly provided on the surface of the needle rollers, and the surface of the surface provided with the indentations is roughened. Say,
A needle roller bearing for a starter, wherein the surface roughness parameter SK value is negative in both the axial direction and the circumferential direction, and the surface area ratio occupied by the depression is 10 to 40%.