JP2003230248A - AC generator for vehicles - Google Patents

Abstract

(57) [Problem] To prolong the life of a bearing on a drive pulley side with a large load among bearings supporting a rotating shaft of an automotive alternator. A grease composition is included in grease of a bearing (4) opposite to the drive pulley (5) among two bearings (3, 4) that cantileverly support a rotating shaft (2) having a drive pulley (5) attached to an end. 1.0 to 40% by volume of the total amount, preferably 2.0 to 3%
0% by volume, more preferably 6.0 to 20% by volume of an electrically conductive substance such as carbon black is mixed to eliminate static electricity generated between the driving pulley belt and avoid a discharge phenomenon between the inner and outer rings of the bearing. In addition, the generation of hydrogen due to the decomposition of water is avoided, thereby preventing the peeling accompanied by the structural change and extending the life.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle alternator that is driven by, for example, an engine and generates an alternating current. It is suitable for a vehicle AC generator to be supported.

[0002]

2. Description of the Related Art Recently, as automobiles have become smaller and lighter,
Engine accessories are also required to be smaller and lighter, have higher performance and higher output. Under such circumstances, for example, in an alternator which is an alternator for vehicles, high vibration and high load (about 4G to 20G in gravitational acceleration) act on the bearing of the rotating shaft that is rotated at high speed by the engine, and as a result, the drive pulley Premature separation occurred on the outer ring raceway that is the fixed ring of the bearing of
This is the cause of shortening the life of the bearing.

As a factor of this early separation, the stress due to high vibration increases, and it becomes difficult to form an oil film with it.
It is considered that this is because about% of the water is decomposed to easily cause surface contact (metal contact). Further, in a vehicle AC generator, static electricity is generally generated between the belt and the drive pulley due to the high-speed rotational movement transmitted from the crankshaft of the engine. Normally, while the bearing is rotating, the oil film of the lubricant causes the inner and outer rings to be in an insulated state, but the potential difference between the inner and outer rings becomes large (about 100 to 500 V).
Then, a discharge phenomenon occurs between the inner and outer rings, whereby the grease or water mixed in during lubrication is decomposed and hydrogen ions are generated. When hydrogen ions are generated, they are adsorbed on the orbital surface of the bearing ring and become hydrogen atoms that accumulate in the high strain field (near the maximum shear stress position), which is considered to be the cause of stress corrosion cracking-type delamination. To be In addition, as a cause of moisture generation in the bearing, the auxiliary machinery also becomes hot during engine operation,
Since the engine is cooled to the atmospheric temperature after the engine is stopped, it is conceivable that the air existing in a small space in the bearing may be condensed.

As a countermeasure against this, for example, Japanese Patent Laid-Open No. 11-11
It is conceivable to use the hybrid pulley described in Japanese Patent No. 7758. Since the inside of this hybrid pulley is made of an insulating material, the static electricity generated between the belt and the pulley does not flow to the rotating shaft, and as a result, the discharge phenomenon in the bearing can be suppressed.

[0005]

However, since the vehicular AC generator is expected to rotate at a higher speed, the flow of static electricity to the rotating shaft side, which increases with the increase, is suppressed by the hybrid pulley. There is also a limit. That is, it is necessary to positively avoid the discharge phenomenon itself between the inner and outer rings of the bearing that supports the rotating shaft.

The present invention was developed in order to solve the above problems, and an AC generator for a vehicle having an excellent bearing life is provided by avoiding a discharge phenomenon between the inner and outer rings of a bearing that supports a rotating shaft. It is intended to be provided.

[0007]

In order to solve the above problems, the present inventors have conducted a study on the phenomenon of electrostatic discharge between the belt and the pulley using the test apparatus shown in FIG. This test device is proposed in Japanese Patent Laid-Open No. 9-89724, and is a model of a vehicle AC generator, that is, a rotating shaft and a bearing of an alternator, a drive pulley and the like. In this test device, of the two bearings that support the rotating shaft, the bearing on the drive pulley side is used as the test bearing, and the aluminum housing that supports the test bearing is simply fastened to the housing body by fastening members such as bolts. There is.
On the other hand, since the rotating shaft itself is grounded via the slip ring, there is no potential difference between the bearing inner and outer rings. In this state, a load was applied to the drive pulley, and the life of the test bearing was tested while detecting the vibration state of the aluminum housing with a vibrometer. Then, for example 9000Min ^-1 rotational speed every predetermined time is set to about 9 seconds and 1800 min ^-1
The load condition was changed to P (load load) / C (dynamic load rating) = 0.10, the test temperature was kept constant at 80 ° C., and a life test was performed using E grease for bearing lubrication. The result of the life test was that the number of samplings was 10, no peeling occurred even when the test was continued for 2000 hours, and no change in the structure was observed inside the bearing. In other words, eliminating the potential difference between the inner and outer rings of the bearing is considered to be an effective means for improving the life of the test bearing, but it is impossible to ground the actual rotating shaft of the alternator using a slip ring. , Had to develop some other means.

In order to solve the above problems, the vehicle alternator according to claim 1 of the present invention is for a vehicle in which a rotating shaft having a drive pulley attached to an end thereof is supported in a cantilever manner by two bearings. In the AC generator, a conductive substance is mixed in the grease of the bearing on the side opposite to the drive pulley among the two bearings. The electrically conductive substance is preferably nanoscale powder such as carbon black. Further, the bearing in which the current-carrying substance is mixed in the grease needs to be on the side opposite to the drive pulley, not on the drive pulley side. This is because seizure resistance deteriorates when a current-carrying substance is mixed into the grease, and seizure may occur in the bearing on the drive pulley side having a large load.

According to a second aspect of the present invention, in the vehicle alternator of the first aspect, the electrically conductive substance is 1.0 to 40.0% by volume of the total amount of the grease composition.
It is characterized by that. Further, in order to ensure the electric conductivity of the inner and outer rings in the bearing, it is effective to use a conductive material for the seal member. Therefore, in the vehicle AC generator of the present invention, it is desirable to use a bearing provided with a conductive seal member.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. FIG. 1 is a cross-sectional view of the vehicle AC generator of this embodiment. The rotor of this vehicle alternator, the so-called rotor part, is housed inside the housing 1, and its rotating shaft 2
Is rotatably supported by two bearings 3 and 4. The left end portion of the rotary shaft 2 in the drawing protrudes from the housing 1 to the outside, and the drive pulley 5 is attached to the protruding portion. That is, the rotary shaft 2 having the drive pulley 5 attached to its end is supported in a cantilever manner by the two bearings 3 and 4. When the drive pulley 5 is rotated by the engine, the rotor rotates together with the rotary shaft 2 and an alternating current is generated in the coil.

Using this vehicle alternator, two bearings 3 and 4 for supporting the rotary shaft 2 were subjected to a life test. The bearing 3 on the side of the drive pulley 5 is JIS No. 6303.
And the test load is P (load load) / C (dynamic load rating)
= 0.1. The bearing 4 on the side opposite to the drive pulley 5 has a JIS nominal number 6202, and the test load is P.
(Load load) / C (dynamic load rating) = 0.05. The inner / outer rings and rolling elements of each bearing were all subjected to normal heat treatment (quenching heating at 830 to 850 ° C., oil cooling, and then tempering at 180 to 240 ° C.) using bearing steel type 2 (SUJ2). Surface hardness of inner / outer rings and rolling elements is HRC57 ~ 6
3, the amount of retained austenite is 0 to 20%, the surface roughness of the inner and outer rings is 0.015 μmRa, and the surface roughness of the rolling elements is 0.
003 to 0.010 μmRa.

[0012] Then, 9000min ^-1 and 1800 min ^-1 rotary speed every predetermined time set to, for example, about 9 seconds
Then, the bearings are filled with E grease having the composition shown in Table 1 below. A life test was carried out by changing variously the volume% of the electrically conductive substance added to the E grease.

[0013]

[Table 1]

The calculated service life of the bearing on the drive pulley side of the vehicle alternator is 1350 hours, and the calculated service life of the bearing on the side opposite to the drive pulley is 6430 hours. As described above, among the bearings that support the rotating shaft of this type of vehicle AC generator, it is the drive pulley side bearing that has the short life due to the occurrence of peeling accompanying structural changes. Was 1500 hours. In the test, when the vibration value increased 5 times with respect to the initial vibration, it was considered as the life, the test was interrupted, and the presence or absence of peeling and microstructure change was confirmed. The number of tests (the number of samplings) is 10, respectively. The results of the life test are shown in Table 2 and FIG.

[0015]

[Table 2]

As is clear from Table 2 and FIG. 2, in Examples 4 to 7, the bearings on the drive pulley side and the side opposite to the drive pulley were all 10 out of 10, and the life test termination time was 10 times. No peeling was observed even after 1500 hours. This is because the electrically conductive substance is mixed in the grease of the bearing on the side opposite to the drive pulley in an amount of 6.0 to 20.0% by volume, so that the inner and outer rings of the bearing on the side opposite to the drive pulley can be energized when the bearing rotates. By doing this, static electricity generated between the belt and pulley is discharged to the housing,
It is considered that this is because the discharge between the inner and outer rings of the bearing was avoided, and as a result, the generation of hydrogen due to the decomposition of water in the grease as described above could be suppressed and prevented.

In Examples 1 to 3, as compared with Examples 4 to 7, the conductive material in the grease of the bearing on the side opposite to the drive pulley was small, so that the conductivity during rotation of the bearing was high. It was not so good, and as a result, 1 to 2 peeled out of 10. In addition, in Examples 8 to 11, since a large amount of the electrically conductive substance was added, the electrical conductivity was good and peeling did not occur. The degree became low, and 1 to 2 out of 10 seizures occurred. However,
Compared with Comparative Examples 1 to 10 described later, the life is 3 to 6 times longer.

On the other hand, in Comparative Example 1, no electrically conductive substance was mixed in the grease on both the drive pulley side and the bearing on the side opposite to the drive pulley. The peeling occurred on the bearing on the drive pulley side in all 10 of them. In Comparative Example 2, an electrically conductive seal made of, for example, nitrile rubber containing graphite was used instead of mixing an electrically conductive substance in grease, and a long life tendency was recognized as compared with Comparative Example 1, but about 550. In about 10 hours, peeling occurred on the drive pulley side bearings in all 10 pieces. It is considered that this is because the seal was deformed as the life test was performed, and the inner and outer rings were in an insulating state, so that a potential difference was generated between the inner and outer rings and a discharge phenomenon occurred.

In Comparative Example 3, the grease of the bearing on the side opposite to the drive pulley is mixed with 0.5% by volume of an electrically conductive substance, but the electrical conductivity at the time of rotation of the bearing is not good,
In a relatively short time of about 410 hours, peeling occurred in 6 out of 10 bearings on the drive pulley side. In Comparative Example 4 and Comparative Example 5, the grease of the bearing on the side opposite to the drive pulley was mixed with 45% by volume and 55% by volume of the electrically conductive substance, respectively, and the electrical conductivity during rotation of the bearing was good. Therefore, peeling did not occur, but the consistency of the grease became low, and in each of the relatively short time of 590 hours and 390 hours, 5 out of 10, 7 out of 10 I got stuck.

In Comparative Example 6 and Comparative Example 7, the conductive material is mixed only in the grease of the bearing on the drive pulley side, but in each of the short time of 490 hours and 380 hours, respectively, 5 out of 10 pieces are used. Seizure occurred on the bearings on the drive pulley side, 7 out of 10 and 10. It is considered that this is because the bearing on the drive pulley side is seized because the load is twice as high as the bearing on the opposite side. Further, in Comparative Examples 8 to 10, the electrically conductive substance was mixed into the grease of the bearing on the drive pulley side and the grease of the bearing on the side opposite to the drive pulley, but 420 hours and 280 hours, respectively. 40
In a short time of 0 hour, seizure occurred in 8 of 10, 8 of 10, 7 of 10, and bearings on the drive pulley side, respectively. The reason for this is considered to be the same as in Comparative Examples 6 and 7.

As described above, in the vehicle alternator of the present invention, it is effective to mix the electrically conductive substance into the grease of the bearing on the side opposite to the drive pulley, and the addition amount is 1. It is 0 to 40.0 volume%. If the amount of conductive material mixed in the grease is less than this, sufficient conductivity cannot be obtained and peeling occurs due to hydrogen generation due to electrostatic discharge, and if it is more than this, the consistency of the grease decreases. Then the grease itself hardens and the seizure life is reduced. Ensure the conductivity of the inner and outer rings of the bearing,
Considering the reduction of the seizure life, the amount of the electrically conductive substance mixed is preferably 2.0 to 20.0% by volume, more preferably 6.0 to 20.0% by volume with respect to the total amount of grease. desirable. As a result, the grease consistency after the addition of the electrically conductive substance is NLGI No. 1-No. 3 is more desirable.

[0022]

As described above, according to the vehicle alternator of the present invention, of the two bearings that support the rotating shaft, the electrically conductive substance is mixed in the grease of the bearing on the side opposite to the drive pulley. By doing so, static electricity generated between the drive pulley and the belt is eliminated, and the discharge phenomenon itself between the inner and outer rings of the bearing that supports the rotating shaft is avoided, so that the life of the bearing can be extended.

The electrically conductive substance mixed in the grease is 1.0 to 40.0% by volume of the total amount of the grease composition, so that the electric discharge phenomenon between the inner and outer races of the rotating shaft can be surely avoided.
Therefore, the life of the bearing can be further extended.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of a vehicle AC generator of the present invention.

2 is an explanatory diagram of a result of a bearing life test in the vehicle AC generator of FIG.

FIG. 3 is an explanatory diagram of a bearing life test device simulating a vehicle alternator.

[Explanation of symbols]

1 is the housing 2 is the rotation axis Bearings 3 and 4 5 is a drive pulley

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 3J101 AA01 AA42 AA52 AA62 AA82                       CA12 EA64 EA72 FA11 FA32                       FA35 GA01 GA24                 5H605 AA12 BB01 CC04 EB10 FF13

Claims (2)

[Claims] 1. An alternator for a vehicle in which a rotary shaft having a drive pulley attached to an end thereof is supported by two bearings in a cantilever manner, wherein, of the two bearings, a bearing on the opposite side of the drive pulley is provided. An alternator for vehicles, characterized in that a conductive substance is mixed in the grease. 2. The vehicle alternator according to claim 1, wherein the electrically conductive substance is 1.0 to 40.0% by volume of the total amount of the grease composition.