JP2992731B2 - Automotive alternator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alternator (alternating current generator) for a motor vehicle, and more particularly to an improved rolling bearing for supporting a rotating shaft which is easily affected by heat inside the alternator.

[0002]

2. Description of the Related Art Conventionally, rolling bearings for supporting a rotating shaft used in an alternator for an automobile have not adopted special ones, and each material of the bearing components is generally made of bearing steel or carburized steel. ing.

[0003]

By the way, in an alternator for a motor vehicle, particularly a stator coil of a motor composed of a rotor attached to a rotating shaft and a stator attached to a case in a normal operation is used. Since heat is generated, this heat is conducted from the case to the rolling bearing for supporting the rotating shaft and the rotating shaft.

[0004] These heats are appropriately radiated from the outer surface of the case and the rotating shaft protruding from the case to the outside, and are cooled by a cooling fan provided on the pulley.
The temperature of the entire rolling bearing for supporting the rotating shaft becomes higher than the tempering temperature (approximately 170 to 200 ° C.) of the general steel used for the inner and outer rings due to the heat generated by the rolling elements accompanying the high-speed and high-load rotation. It may be. In this case, the composition immediately below the raceway surfaces of the inner and outer races of the rolling bearing for supporting the rotating shaft changes and the hardness decreases significantly, and at the same time, the size increases due to martensite transformation in which the retained austenite of the steel turns into martensite. This results in an increase in bearing clearance. In particular, since the alternator is directly subjected to the vibration or impact of the engine to which the alternator is attached, the hardness of the inner and outer races of the rolling bearing is reduced as described above, so that indentations are easily generated on the rolling element raceway. In particular, since the load zone is constant on the outer ring on the fixed side, the influence of vibration and impact is large, and a large number of fine cracks and structural changes (generation of white layer) occur immediately below the raceway surface, and the raceway surface becomes rough. The rough track surface causes heat generation under high speed and high load, which further promotes the above phenomenon. As a result, the bearing may be depleted within a very short time, leading to an early end of the bearing life.

In such a case, it is considered that the deterioration of the function may be suppressed by forming the inner and outer rings with ceramics having heat resistance, but it can be said that there is much waste such as a significant increase in cost. In addition, in the case of ceramics, the difference in linear expansion coefficient with respect to the metal case becomes large, so that when the temperature rises, the fitting gap becomes considerably large, and there is a concern that the support state of the rotating shaft becomes unstable. .

On the other hand, as disclosed in Japanese Patent Application Laid-Open No. 4-244624, there is a type in which the rolling element is made of fine ceramics to prevent the occurrence of peeling due to hydrogen embrittlement of steel. Alone
In a small-diameter bearing used for an alternator or the like, the effect of suppressing the rise in the outer ring temperature is small, and the occurrence of peeling of the raceway surface cannot be sufficiently suppressed.

SUMMARY OF THE INVENTION In view of such circumstances, it is an object of the present invention to prevent a deterioration in function of a rolling bearing for supporting a rotating shaft due to a rise in temperature, and to minimize a cost increase associated with the deterioration.

[0008]

SUMMARY OF THE INVENTION The present invention is an alternator for an automobile having a rolling bearing for rotatably supporting a rotating shaft on a case, wherein the rolling element of the rolling bearing is made of ceramics mainly composed of silicon nitride. together are formed, the inner and outer rings are formed of steel, it is subjected a heat treatment of tempering temperature of which at least the outer ring is two hundred to three hundred eighty ° C.
HR at 9.8% or less of retained austenite
It is formed of a steel material with C56.0 to 60.5 .

[0009]

[Function] Even if heat is conducted from the case to the outer ring of the rolling bearing for supporting the rotating shaft due to the heat generated by the alternator, the tempering temperature of the outer ring is set to 200 to 380 ° C., which is higher than usual, and the temperature remains.
HRC5 with surface hardness of less than 9.8% retained austenite
Since the steel is made 6.0 to 60.5, it is thermally stable, and the enlargement of the dimensions due to the martensitic transformation of the steel is suppressed, so that it is possible to maintain the initial appropriate bearing clearance. Therefore, even if the outer ring on the fixed side receives vibration or impact, the bearing clearance is appropriate, so the influence of vibration or impact on the raceway surface is negligible, and local structural changes due to microscopic plastic deformation and The occurrence of cracks can be suppressed.

[0010] By using ceramic rolling elements, the effect of centrifugal force on the outer ring can be reduced as compared with steel, and the contact ellipse of the outer ring can be reduced. Can be reduced. The microscopic slip region is reduced, the heat generation of the bearing due to the high-speed and high-load rotation is suppressed, the adhesion phenomenon does not occur, and the microscopic plastic change on the raceway surface can be suppressed. Also, since the thermal conductivity is small,
The temperature rise of the grease around the rolling elements can be suppressed, and the grease life can be optimized.

Since the outer race and the case are both made of steel and have almost the same linear expansion coefficient, no inconvenience occurs at the fitting portion.

[0012]

1 and 2 show an embodiment of the present invention. FIG. 1 shows a vertical sectional view of the alternator.
Is a case formed by bolting the front bracket 1a and the rear bracket 1b, and 2 is a rotating shaft rotatably supported on the case 1 via two rolling bearings 3, 3.
A stator 5 around which a coil 6 is wound is attached to the case 1, and a rotor 7 around which a coil 8 is wound, a pole 9, a pulley 10 integrated with a fan, and a slip ring 11 are attached to the rotating shaft 2. I have. A brush 12 is pressed against the slip ring 11 by a spring.

The two rolling bearings 3 for supporting the rotary shaft 2 are, for example, deep groove ball bearings, but are not particularly limited. By the way, in this rolling bearing 3, the rolling element 3c is a ceramic mainly composed of silicon nitride, and the outer ring 3a is obtained by subjecting the SAE5120 material to carburizing treatment to -7
Subzero treatment is performed at 5 ° C., and the tempering temperature is higher than the temperature (150 to 200 ° C.) of the stator coil (heat source) 6 during operation (for example, 270 ° C.).
b is a common bearing steel (such as SUJ-2, but with a tempering temperature of 185 ° C.), each of which is formed. 3d is a cage made of polyamide resin such as 66 nylon or 46 nylon or PES (polyether sulfone) resin. By being formed of such a synthetic resin, the transmission of heat is cut off in combination with the ceramic rolling elements 3c, the heat generation of the grease in the bearing is prevented, and the life of the bearing is extended. 3e is a seal.

The carburized depth of the surface of the outer ring 3a is 0.3
０．７0.7 mm and surface hardness of HRC 56.0-60.5
And the internal hardness is HRC 35.0 to 52.0
The amount of retained austenite is set to 3% or less. Since the inside is made of carburized steel that is softer than the surface, the inside serves as a buffer for vibration and shock, and alleviates the effects on the raceway surface. The surface hardness of the inner ring 3b is HRC5
8.0 to 62.0, and the amount of retained austenite is 11
１４14%. This embodiment is hereinafter referred to as a first embodiment.

Next, another embodiment will be described. Here, the outer ring 3a of the first embodiment is as follows.

In the outer ring 3a of the second embodiment, the SAE 5120
It is made of carburized steel that has been subjected to a carburizing treatment, then subjected to a sub-zero treatment at -196 ° C, and tempered at 210 ° C. At this time, the retained austenite amount was 5.7%.

In the outer ring 3a of the third embodiment, the SAE 5120
It is made of carburized steel that has been subjected to a carburizing treatment at -60 ° C after a carburizing treatment and then tempered at 200 ° C. At this time, the amount of retained austenite was 9.8%.

The outer ring 3a of the fourth embodiment is made of bearing steel which is quenched and heated at 845 ° C., oil-cooled, and then tempered at 350 ° C. for SUJ-2 material. At this time, the amount of retained austenite was 3% or less.

The outer ring 3a of the fifth embodiment is formed of bearing steel which is obtained by quenching and heating the SUJ-2 material at 845 ° C., oil-cooling, sub-zero treatment at −70 ° C., and then tempering at 200 ° C. At this time, the retained austenite amount was 7.9%.

As a comparative example, a general bearing (with inner and outer rings and balls made of SUJ-2, tempering temperature of 180 ° C.) was used.

A test machine incorporating the bearings of the above Examples and Comparative Examples was installed on a vibration table, and a load was applied.
A vibration test was performed by applying vibration while rotating the inner ring. The test conditions are as follows.

Bearing load (static load) / dynamic load rating ...
0.22 Inner ring rotation speed: 8000 rpm Calculated life (according to the above): 196 hours Vibration acceleration: 10 G (on a vibration table) Atmospheric temperature: 170 ° C. Test time: 500 hours And peeling The degree of fatigue was compared and evaluated from the time up to. Table 1 shows the test results. In addition, as a result of the test, no abnormality was recognized except for the outer ring, so the results are shown only for the outer ring.

Sample Rotation time until peeling Comparative Example 33 to 170 hours (n = 15) Example 1 No peeling until 500 hours (n = 6) Example 2 No peeling until 500 hours (n = 6) 3 No peeling up to 500 hours (n = 6) Example 4 No peeling up to 500 hours (n = 6) Example 5 No peeling up to 500 hours (n = 6) Degradation of the grease was observed along with a number of cracks and structural changes on the surface. However, in Examples 1, 2, and 4, neither cracks, structural changes nor deterioration of the grease were recognized. Only a change was noted. Thus, it can be seen that the life of the rolling bearings according to the present invention of Examples 1 to 5 is greatly improved as compared with the rolling bearing of the comparative example.

In the comparative example, when no vibration was applied in the above-mentioned test, no peeling occurred even after 1500 hours, and no crack or structural change was observed. It has been confirmed that there is no such thing.

Further, in the above-described embodiment, a special heat treatment is applied to the outer ring 3a. However, the present invention is not limited to the outer ring 3a but may be applied to the inner ring 3b.

[0026]

As described above, according to the present invention, the outer ring is made of a material that is thermally stable and the dimensional enlargement is suppressed, while the rolling elements are not thermally affected by the heat between the inner and outer rings. The material that blocks the conduction and reduces the effect of the rotational centrifugal force on the outer ring and does not cause the adhesion phenomenon. In addition, even if it receives vibration or shock, the influence on the raceway surface of the outer ring is negligible, so that it is possible to suppress local structural changes and cracks. Further, since the temperature rise of the grease around the rolling elements is suppressed, the grease life can be optimized. In addition, since the outer race and the case are both made of steel and have substantially the same linear expansion coefficient, no problem occurs at the fitting portion.

Therefore, according to the present invention, it is possible to prevent deterioration of the function of the rolling bearing for supporting the rotating shaft due to temperature rise,
The cost increase relating to this can be minimized.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of an embodiment of an automotive alternator according to the present invention.

FIG. 2 is a longitudinal sectional view of an upper half showing a rolling bearing according to the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Case 2 Rotating shaft 3 Rolling bearing 3a Outer ring 3b Inner ring 3c Rolling element

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F16C 33/62 F16C 33/32

Claims (1)

(57) [Claims] 1. An alternator for an automobile having a rolling bearing rotatably supporting a rotating shaft on a case, wherein a rolling element of the rolling bearing is formed of ceramics mainly composed of silicon nitride. Outer ring is made of steel
It is formed, of which at least the outer ring is 200 to 380 ° C.
Heat treatment at the tempering temperature of retained austenite
Is 9.8% or less and the surface hardness is HRC 56.0 to 60.5.
An alternator for an automobile, wherein the alternator is made of a steel material.