JP2002031143A - Rolling bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prolong the life by inhibiting the occurrence of flaw and restraining a contact surface pressure by defining a groove shape against a rolling body (ball). SOLUTION: A contact surface pressure caused by a bearing load is restrained and a damage caused by a rolling fatigue is prevented by making a groove curvature Sr represented by a percent of a groove diameter to a ball diameter is from 52% to 55%. A generation of damage is prevented at the time of assembling of rolling body by making a groove depth ratio Sd represented by a percent of a groove depth to the ball diameter is from 18.5% to 25% or less. A riding-up phenomenon of the rolling body is relaxed and 'a riding-up flaw' is hardly caused on the rolling body to enhance a life by making a riding-up coefficient Kd to 20 or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a rolling bearing, and more particularly to an alternator, an electromagnetic clutch, an intermediate pulley,
It is suitable for rolling bearings used in engine accessories such as air compressors and water pumps.

[0002]

2. Description of the Related Art In recent years, as engines have become smaller and lighter,
Engine auxiliaries are also required to be smaller, lighter, and have higher performance and higher output. When the engine is running,
For example, high vibration and high load (approximately 4G to 30G by gravitational acceleration) due to high-speed rotation act simultaneously on the alternator bearing via the belt, and as a result, premature peeling occurs particularly on the outer ring raceway surface which is a fixed wheel. Cause short life.

As a conventional technique for improving the life of a bearing used under high vibration and high load, for example, Japanese Patent Application Laid-Open No. Hei 2-1906 is known.
No. 15 discloses a grease-filled bearing in which grease is sealed in a bearing.
One that forms an oxide film of 2.5 μm is disclosed. Japanese Unexamined Utility Model Publication No. 6-43349 discloses a roller bearing lubricated with a lubricant in which an oxide film having a thickness of 0.1 to 2.5 μm is formed on a rolling surface of a bearing race. I have. Also, Japanese Patent Application Laid-Open No. 5-26244 discloses that
A grease-filled bearing in which grease is sealed in a bearing is disclosed in which at least the fixed-side race is made of steel containing 1.5 to 6% Cr. This is intended to prevent brittle flaking by a passivation film of the material of the bearing ring itself.

[0004]

By the way, as a measure to prevent the early separation of the bearing race as described above, "SA
E Technical Paper: SAE950944 (Date 1)
(February 27-March 2, 995), the first to fourteenth items are to clarify the fatigue mechanism of alternator bearings, and to change the encapsulated grease from E grease to M grease with high damper effect. , High vibration with this M grease
It is disclosed that high loads are absorbed to prevent premature peeling.

[0005] This early raceway peeling phenomenon is caused by the fact that a slight amount of water contained in lubricating oil (for example, grease may contain about 0.1%) is decomposed due to high vibration and high load. The hydrogen ions are adsorbed on the orbital surface, become hydrogen atoms, and accumulate in the high strain field (near the maximum shear stress position).
It is thought to lead to stress corrosion cracking type delamination. Also, as a source of moisture in the bearing, one of the bearings for engine accessories is often used in a high temperature state.
It is conceivable that air existing in a small space in the bearing may condense when cooled to ambient temperature.

[0006] Further, as a series of these studies, as an example of the life reduction when water is mixed in a rolling bearing, JA
Cirura et al., `` Wear, 24 (1973) 107-118, The Effect of H
ydrogen on the Rolling Contact Fatigue Life of AIS
According to I 52100 and 440C Steel Balls, in a four-ball rolling test in which water was mixed with lubricating oil, the life was reduced to about 1/10 compared to before mixing with water, and a steel ball charged with hydrogen was used. In the rolling fatigue test, the results show that the stainless steel balls have a longer life than the bearing steel class 2 steel balls.

However, as shown in "Japan Tribology Conference Proceedings (Tokyo, 1995-5), pp. 551 to 554," the bearings for engine accessories used under high vibration and high load have a fixed wheel load. In order to cause rotation slip at the entrance of the sphere,
The results indicate that it is difficult to prevent early peeling of the fixed wheel because the oxide film that can serve as a damper effect is cut and directly receives a load on the outer ring where premature peeling frequently occurs.

That is, even if an oxide film is formed, if the film is broken, the long life effect is lost. The present invention has been developed in order to solve the above-mentioned problems, and provides a rolling bearing capable of favorably preventing early peeling due to high vibration and high load and greatly extending the life of the bearing. It is intended for.

[0009]

In order to solve the above-mentioned problems, a rolling bearing according to the present invention is a rolling bearing having a plurality of rolling elements disposed between an outer ring and an inner ring. The groove curvature Sr expressed as a percentage of the diameter is more than 52% and not more than 55%, and the groove depth ratio Sd expressed as a percentage of the groove depth with respect to the ball diameter is more than 18.5% and 25% The raising coefficient K which is the following and is represented by the following equation:
A rolling bearing, wherein the raceways of the outer ring and the inner ring are formed so as to satisfy d is 20 or more.

Kd = (Sr−52) × 10 + (Sd−2) (1)

[0011]

Embodiments of the present invention will be described below. FIG. 1 is a cross-sectional view of the rolling bearing of the present embodiment. The rolling bearing 1 is a deep groove ball bearing of JIS call number 6303, in which the outer ring 2 is fixed to a housing 8,
The inner ring 3 through which the shaft 7 is inserted rotates. A number of rolling elements 4 held by a retainer 5 are arranged between the outer ring 2 and the inner ring 3, and a seal member 6 is mounted between the outer ring 2 and the inner ring 3 on both sides of the retainer 5. I have. The portion surrounded by the seal member 6 is filled with M grease having a high damper effect, and has a long life bearing specification in which high vibration and high load are absorbed to prevent early peeling. The wheel 3 that is not rotated with the rotation of the shaft 7 also rotates, and the vibration and load associated with the rotation act on the load zone of the outer ring 2 from the shaft 7 via the inner ring 3 and the rolling elements 4.

In the bearing life tests of Examples and Comparative Examples,
For the inner and outer rings of the bearing and the rolling elements, the bearing steel SUJ2 was used as the material for both the examples and comparative examples, and was subjected to normal heat treatment (quenching and heating at 840 ° C., oil cooling, and tempering at 180 ° C.) before testing. Provided. The surface hardness of the inner and outer rings is HRC57.
63, the amount of retained austenite is 7-20%, the surface roughness of the inner and outer rings is 0.01-0.03 μmRa, the surface roughness of the rolling elements is 0.003-0.010 μmRa, and the predetermined groove curvature (ball Grinding was performed so that the groove diameter ratio (percentage of the groove diameter with respect to the diameter) and the groove depth ratio (percentage of the groove depth with respect to the ball diameter) were obtained. A normal SUJ2 steel ball was used for the rolling element.
Then, after assembling, fill in M grease as described above,
Test bearings were made.

Here, the present inventors have conducted a detailed investigation on a large number of bearings in which a failure has occurred in a vehicle on the market, particularly for a bearing for an engine auxiliary device, and as a result, have found that a bearing with a defective product has a rolling element. Many were found to have scratches.
In particular, it should be noted that despite the fact that longevity measures such as a damper effect by the oxide film and the lubricant and prevention of hydrogen intrusion have been applied to the rolling bearings for the engine auxiliary devices, the rolling elements It was found that if a scratch occurred on the surface, a problem would occur.

Here, when the flaws generated in the rolling elements were further examined in detail, it was confirmed that the flaws were linear and, in some cases, boat-shaped flaws. In other words, as shown in FIG. 2, these flaws are “raising flaws” caused by the rolling elements climbing on the groove shoulders of the bearing, and are caused by handling of the bearing such as mounting the bearing to the housing or the shaft. It is determined that the wound has occurred. Incidentally, riding up means that when a thrust load is applied, the contact ellipse between the bearing ring and the rolling element goes out of the raceway surface at the portion indicated by ○ in FIG.

The present inventors have paid attention to "ride-in scratches" based on the results of this investigation, and have conducted various experiments on rolling bearings which are less likely to cause "ride-in scratches". Regarding the “raising scratch”, it is generally considered that the groove depth is increased to increase the groove depth ratio, the groove curvature is increased, or the bearing gap is reduced. For rolling bearings related to electrical accessories used at high speeds, seizure occurs if the bearing gap is made extremely small, so the gap should be the same as before, and the rise in groove depth ratio and groove curvature should be examined. Was done.

Generally, the riding load of a ball bearing can be calculated from the specifications of the bearing. An example is shown in the following two equations. Riding load _{= (2 × f m × (} cosα / cosα i over 1) / C) ^2/3 Number of balls × × ball diameter ² × ^sinα _i ......... ⁽²⁾ where, f _m: grooves of the inner ring and the outer ring Average value of curvature α: initial contact angle α _i : contact angle when riding up.

Next, a life test was performed on the rolling bearings of the above-described Examples and Comparative Examples using a test apparatus described in Japanese Patent Application Laid-Open No. 9-89724. In the test, the rotation speed was set to 5000 rpm and 1000 for every predetermined time (for example, 9 seconds).
In accordance with a rapid acceleration / deceleration test for switching to rpm. In each of the examples and the comparative examples, the JIS call number 6303 was used for the test bearing. The load condition of the test bearing is P
(Load) / C (dynamic load rating) = 0.10, and M grease was used as the sealed grease.

As shown in FIG. 2, a normal axial load is applied between the outer ring 2 and the inner ring 3 to the rolling bearing in which various groove shapes are formed on the rolling surface of the raceway, and the normal rolling is performed. In the case of bearings, a life test was performed after conditions were given under which "raising scratches" occurred. The axial load was 0.2 times the dynamic rated load, and the load time was 10 minutes. The test termination time was 1500 hours. The number of tests was n = 10, and the total rotation time required for the 10% of the ten rolling bearings to be separated from the short-lived side was determined by the Weibull distribution function. did. The test results are shown in Table 1 and FIG. The raising coefficient was determined according to the above equation (1).

[0019]

[Table 1]

As can be seen from Table 1 and FIG. 3, in each of the embodiments, by setting the riding coefficient Kd to 20 or more, the occurrence of "riding scratches" can be minimized, and good life can be achieved. was gotten. However, in Example 1 in which the groove depth ratio Sd was less than 19%, although "small climbing" was confirmed although it was minute,
The groove depth ratio Sd is desirably 19% or more. Also, the groove curvature S
If the value of r is too large, the occurrence of "ride damage" can be prevented, but the contact surface pressure due to the test load is increased, so that the life is slightly reduced. Therefore, the groove curvature Sr is desirably 54% or less, and the rise coefficient Kd is desirably 22 or more and 30 or less.

On the other hand, in Comparative Examples 1 and 2, the groove curvature Sr is small, and in Comparative Example 3, the groove depth ratio Sd is small and the coefficient of rise Kd is all smaller than 20, so that the "loading" is increased by the axial load. It is considered that "scratch" occurs, and the above-described phenomenon of cutting the oxide film due to the sliding of the rolling element accelerates the short life phenomenon caused by the damage of the rolling element. In Comparative Example 4, the groove curvature Sr and the groove depth ratio Sd were within the recommended values of the present invention. However, since the rise coefficient Kd was smaller than 20, the interaction did not function, and “rare scratches” occurred. Occurrence and shortened service life. In Comparative Example 5, since the groove curvature Sr was too large, the contact surface pressure was too high, and a reduction in life due to rolling fatigue was confirmed.

As described above, when the riding-up coefficient Kd is 20 or more, the riding-up phenomenon is alleviated, and "rolling-up flaws" are less likely to occur on the rolling elements, so that the life is improved. By setting the raising coefficient Kd to 22 or more and 30 or less, a more stable life can be obtained. Further, if the groove curvature Sr is made unnecessarily large, the contact surface pressure due to the bearing load becomes too high and breakage due to general rolling fatigue occurs. Therefore, the upper limit of the groove curvature Sr is set to 55%. Also, if the groove depth ratio Sd is increased more than necessary, it becomes difficult to incorporate the rolling elements,
In some cases, the upper limit of the groove depth ratio Sd is set to 25% because the rolling elements may be damaged when assembled. In addition, when attention is paid only to the groove depth ratio Sd, the peeling is small at 19% or more and the life is long, which is more preferable.

On the other hand, "ride-up scratches", which are determined to be caused by handling of the rolling bearings, such as mounting the rolling bearings on a housing or a shaft, may be caused by handling when the outer ring is inserted into the housing. Also, there is a high possibility that some trouble occurs when the shaft is inserted into the inner ring. FIG. 4 shows an example. This is the housing 8
When the shaft 7 is inserted into the inner ring 3 of the rolling bearing 1 press-fitted into the shaft, an edge of the shaft 7 and an edge portion of the inner ring 3 (because it is actually chamfered, hereinafter referred to as a chamfer portion) are so-called. It is in a state of being seized and stuck, and the same axial load as in FIG.
There is a danger that the rolling elements will get "riding wounds". Normally, the chamfer portions of the bearing outer ring and the inner ring are not subjected to the grinding process and remain as a heat-treated skin. Therefore, the surface condition is poor and the surface roughness is not good, so that the galling is likely to occur. The surface roughness of the chamfer portion of the outer ring and inner ring of the bearing is set to 0.5 μmR in order to prevent the rolling element from “raising scratch” from the axial load due to the galling of the chamfer portion.
It is desirable to set it to a or less.

[0024]

As described above, according to the rolling bearing of the present invention, the riding coefficient Kd is set to 20 or more to prevent the rolling element from getting scratched, and the contact surface pressure is reduced by defining the groove curvature Sr. By preventing the height from becoming too high, or by defining the groove depth ratio Sd to prevent the occurrence of scratches when the rolling elements are incorporated, it is possible to significantly improve the overall life.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing one embodiment of a rolling bearing of the present invention.

FIG. 2 is an explanatory view of a riding wound of a rolling element.

FIG. 3 is an explanatory diagram showing a relationship between a riding coefficient and a rolling bearing life.

FIG. 4 is an explanatory diagram of a case where a rolling scratch occurs on a rolling element during assembly.

[Explanation of symbols]

 1 is a rolling bearing 2 is an outer ring 3 is an inner ring 4 is a rolling element 5 is a cage 6 is a seal 7 is a shaft 8 is a housing

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kazuo Matsushita 1-5-50 Kugenuma Shinmei, Fujisawa-shi, Kanagawa F-term in NSK Ltd. (reference) 3J101 AA02 AA32 AA42 AA52 AA62 BA53 BA54 EA03 EA63 FA31 GA24

Claims (1)

[Claims] 1. In a rolling bearing having a plurality of rolling elements disposed between an outer ring and an inner ring, a groove curvature Sr expressed as a percentage of a groove diameter with respect to a ball diameter is more than 52% and not more than 55%. And the groove depth ratio Sd expressed as a percentage of the groove depth with respect to the ball diameter exceeds 18.5% and not more than 25%, and the raising coefficient Kd expressed by the following formula is not less than 20. A rolling bearing, wherein the raceways of the outer ring and the inner ring are formed so as to satisfy the following. Kd = (Sr−52) × 10 + (Sd−2)