JP2014084913A - Rolling bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve durability and reliability in a grease lubrication (grease encapsulation) rolling bearing supporting a rotation shaft of a motor of, in particular, an electric vehicle or a hybrid automobile.SOLUTION: In a grease lubrication rolling bearing made by encapsulating a grease composition, the grease composition comprises synthetic hydrocarbon oil as base oil and a urea compound as thickening agent, and apparent viscosity at -30°C is 30 Pa s or less and apparent at -40°C viscosity is 100 Pa s or less. Consequently, occurrence of abnormal sound at low temperature is suppressed.

Description

The present invention relates to a rolling bearing lubricated with a grease composition, and more particularly to a grease composition-enclosed rolling bearing for supporting a rotating shaft of a motor of an electric vehicle or a hybrid vehicle.

Sales of electric vehicles and hybrid vehicles are increasing year by year, and further increases are expected in the future. In other words, it has been mainly used in urban areas where the conditions of use are relatively mild, but in the future, it is expected that use in places with relatively severe conditions of use such as polar regions, mountainous areas, and deserts will be sufficient. It has become.

For this reason, the motors that are the driving source of these electric vehicles and hybrid vehicles are also required to have durability and reliability under severe use conditions.

In order to improve the durability and reliability of the motor, it is also necessary to improve the durability and reliability of the rolling bearing that supports the rotating shaft of the motor. To improve the durability and reliability of the rolling bearing, It is necessary to maintain good lubrication of the rolling bearing.

Therefore, for example, a rolling bearing in which a grease composition in which a diurea compound is used as a thickener, ester oil is used as a base oil, and a predetermined extreme pressure agent or the like is encapsulated has been suitably used.

Japanese Patent Laid-Open No. 9-208982

However, motors that are driving sources of electric vehicles and hybrid vehicles are required to have higher reliability and durability, and are also strongly required to reduce noise and torque. In particular, in an electric vehicle or a hybrid vehicle, there is a strong demand for low noise when only a motor is used as a drive source.

Further, in the rolling bearing, there exists a frequency that is easy to vibrate, which is unique to each of the bearing rings due to the undulation of the inner and outer ring raceway surfaces. On the other hand, the housings that accommodate the rolling bearings also have vibration frequencies that are inherent to the respective housings. If these frequencies match, there is a possibility that abnormal noise may occur due to resonance.

It is empirically known that such abnormal noise due to resonance is more likely to occur when used at low temperatures. That is, it is presumed that the use in a low temperature environment deteriorates the fluidity of the grease composition enclosed in the rolling bearing, and the lubrication state inside the rolling bearing deteriorates, so that the possibility of occurrence increases.

Here, as the condition of deterioration of the lubrication state, the grease composition whose fluidity has decreased due to low temperature adheres to the inner and outer ring raceway surfaces and rolling elements, the oil film thickness due to the grease composition becomes uneven, and apparently the raceway surface It will be in a state that will increase the swell. When used under such a condition, it is considered that vibration is further promoted and is likely to be detected as an abnormal sound. In addition, when the frequencies at which the inner and outer rings are likely to vibrate are close, grease having a reduced fluidity due to relative movement is formed in a bank shape, and vibration may be further promoted.

In view of the above problems, as a result of earnest study, the present inventor has come to provide means for solving with the following configurations.

That is, an outer ring, an inner ring, a plurality of rolling elements interposed between the outer ring and the inner ring and rotatably supporting them, a cage having a predetermined interval between the rolling elements, and between the outer ring and the inner ring In a rolling bearing having a seal that closes an opening and enclosing a grease composition for lubrication in an inner space defined by an outer ring, an inner ring, and a seal, the grease composition is based on a synthetic hydrocarbon oil. An oil is used, and a urea compound is used as a thickener. The apparent viscosity at −30 ° C. is 30 Pa · s or less, and the apparent viscosity at −40 ° C. is 100 Pa · s or less.

As the urea compound, a polyurea compound, a tetraurea compound, a triurea compound, a diurea compound, a urea-urethane compound, or a mixture thereof can be used. Preferably, a diurea compound represented by the following general formula is used.

In the formula 1, R1 is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, and R2 and R3 may be the same or different, and are each an alkyl group or alkenyl group having 8 to 20 carbon atoms, carbon A cyclohexyl group or a cyclohexyl group derivative having 6 to 12 carbon atoms or an aromatic group having 6 to 12 carbon atoms is shown. More preferably, in the formula 1, R1 is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, R2 and R3 may be the same or different, and each is an alkyl group having 8 to 20 carbon atoms, Alternatively, a diurea compound composed of a cyclohexyl group having 6 to 12 carbon atoms is used.

Most preferably, in Formula 1, R1 is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, R2 and R3 may be the same or different, and each is an alkyl group having 8 to 20 carbon atoms, Or it consists of a C6-C12 cyclohexyl group, The molar ratio of the said cyclohexyl group and the said alkyl group made into R2, R3 in the said diurea compound is 20-90 (cyclohexyl group): 80-10 (alkyl group) A diurea compound is used.

Preferably, the proportion of the thickener in the total amount of the grease composition is 7 to 14% by mass. In addition, when the usage condition of the rolling bearing is relatively low, such as when the usage frequency is -40 ° C. or less, the amount of the thickener is preferably 7 to 10% by mass. When the usage condition is relatively high, such as when the usage frequency is 140 ° C. or higher, the amount of thickener is 10 to 14% by mass.

Preferably, the grease composition has a penetration degree (JIS K 2220: 25 ° C.) of 300 to 330.

More preferably, the blending degree of the grease composition is 300 to 330, and the immiscibility degree at −20 ° C. is 200 to 250. Most preferably, the immiscibility penetration at 25 ° C. is also 250 to 300.

Preferably, the amount of the grease composition enclosed with respect to the volume of the internal space of the rolling bearing is 20 to 50% by volume. More preferably, it is 25-45 volume%, Most preferably, it is 30-40 volume%. The grease composition is preferably sealed so as not to be unevenly distributed in the bearing internal space.

Further, it is preferable that the radial bearing internal clearance at 20 ° C. of the rolling bearing is 0 or more.

Further, when the rolling bearing is a so-called deep groove ball bearing having a raceway groove for rolling the rolling element on the inner periphery of the outer ring and the outer periphery of the inner ring, the radius of curvature of the raceway groove of the outer ring is the rolling element diameter. 52.5% or more is preferable.

The seal is preferably a so-called non-contact rubber seal, and the rubber material is preferably NBR (acrylonitrile butadiene rubber).

With the above configuration, a rolling bearing having durability and high reliability can be obtained. Further, lubrication inside the rolling bearing becomes inadequate at low temperatures, and the phenomenon of generating abnormal noise can be suppressed.

It is a figure explaining the rolling bearing of this invention. It is a figure explaining the measuring method of apparent viscosity.

FIG. 1 shows an example of the rolling bearing of the present invention.
A rolling bearing 1 shown in FIG. 1 is a deep groove ball bearing, and an inner ring 10 having a raceway groove 10a on an outer peripheral surface, an outer ring 20 having a raceway groove 20a facing the raceway groove 10a of the inner ring 10 on an inner peripheral surface, and both raceways. A plurality of balls 30 rotatably arranged between the grooves 10a and 20a, a crown-shaped cage 40 that rotatably holds the balls 30 between the inner ring 10 and the outer ring 20, and a non-contact supported by the outer ring 20 Shaped seals 50, 50. In the seal 50 in the present embodiment, a rubber part 50a made of NBR is attached to a cored bar 50b made of SPCC steel plate by adhesion.

In the bearing inner space 60 surrounded by the inner ring 10, the outer ring 20, and the seals 50, 50, grease is used as a lubricant that lubricates between the raceway grooves 10 a, 20 a and the rolling surface 30 a of the ball 30. The composition is encapsulated. In the rolling bearing 1 of the present embodiment, the inner ring 10 and the outer ring 20 can be rotated relative to each other through rolling of balls 30 that are rolling elements.

The crown-shaped cage 40 is a substantially annular member, and a plurality of concave portions 41 for inserting the balls 30 are provided at one end in the axial direction at intervals along the circumferential direction, and are adjacent to each other. A convex portion 43 is formed between the concave portions 41. Further, the plurality of concave portions 41 have a shape that follows the contour shape of the ball 30, and specifically, a spherical shape.

The type of the cage is not limited to the crown-shaped cage shown in the figure, and various types such as a machined cage can be applied. The material of the cage is not particularly limited, but polyamide resin is preferable in consideration of high-speed rotation and adaptation to a wide temperature range from high temperature to low temperature. As the polyamide-based resin, 4,6 nylon and 6,6 nylon are preferable, and more preferably, fiber reinforced nylon in which glass fiber or carbon fiber is blended with the nylon can be used. Furthermore, since the nylon resin has good compatibility with the synthetic hydrocarbon oil, it is suitable as a material for the cage of the present invention.

H indicates the cross-sectional height of the rolling bearing 1, and B indicates the width of the rolling bearing 1.

In the rolling bearing of the present invention, in the rolling bearing formed by enclosing a grease composition for lubrication in an internal space defined by an outer ring, an inner ring, and a seal, the grease composition includes a synthetic hydrocarbon oil as a base oil. And a urea compound as a thickener, the apparent viscosity at −30 ° C. is 30 Pa · s or less, and the apparent viscosity at −40 ° C. is 100 Pa · s or less.

As a result, since the apparent viscosity is small even at low temperatures, the grease composition spreads inside the bearing, and good lubrication can be maintained, so that the occurrence of so-called low-temperature abnormal noise can be suppressed. Furthermore, the grease composition does not excessively soften at high temperatures, and leakage of the grease composition from the inside of the bearing can be suppressed. Further, since the base oil is a synthetic hydrocarbon oil excellent in heat resistance and water resistance, it is possible to prevent oxidative degradation at high temperatures and hydrolysis of the base oil due to the presence of moisture at high temperatures.

As the urea compound, a polyurea compound, a tetraurea compound, a triurea compound, a diurea compound, a urea-urethane compound, or a mixture thereof can be used. Preferably, a diurea compound represented by the following general formula is used.

In the formula 1, R1 is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, and R2 and R3 may be the same or different, and are each an alkyl group or alkenyl group having 8 to 20 carbon atoms, carbon A cyclohexyl group or a cyclohexyl group derivative having 6 to 12 carbon atoms or an aromatic group having 6 to 12 carbon atoms is shown.
By using the specific diurea compound, it becomes easy to realize the preferable range apparent viscosity of the grease composition. The diurea compound is also excellent in heat resistance, and can be suitably used from a high temperature to a low temperature.

More preferably, in the formula 1, R1 is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, R2 and R3 may be the same or different, and each is an alkyl group having 8 to 20 carbon atoms, Alternatively, a diurea compound composed of a cyclohexyl group having 6 to 12 carbon atoms is used.

Most preferably, in Formula 1, R1 is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, R2 and R3 may be the same or different, and each is an alkyl group having 8 to 20 carbon atoms, Or it consists of a C6-C12 cyclohexyl group, The molar ratio of the said cyclohexyl group and the said alkyl group made into R2, R3 in the said diurea compound is 20-90 (cyclohexyl group): 80-10 (alkyl group) A diurea compound is used.

Furthermore, by using the specific diurea compound as described above, it is possible to obtain a grease composition that is excellent in heat resistance and durability with less leakage at high temperatures while further suppressing the generation of abnormal noise at low temperatures. Thus, the reliability of the rolling bearing in which the grease composition is enclosed can be further improved.

A synthetic hydrocarbon oil is used as the base oil. As the synthetic hydrocarbon oil, poly α-olefin, alkylbenzene, polycyclic condensed naphthene, polybutene, a polymer of ethylene and polyα-olefin, or a mixture thereof can be used. As long as the effect of using the synthetic hydrocarbon oil is not impaired, it is also possible to use a mixture of mineral oil mainly composed of hydrocarbon. Among these, in consideration of heat resistance and low temperature fluidity, poly α-olefins can be preferably used.

Moreover, as a base oil viscosity, the thing of 10-300 mm2 / s can be used in 40 degreeC. In the case of relatively low temperature such as frequent use at −40 ° C. or lower, the base oil viscosity is preferably 10 to 250 mm 2 / s, and relatively frequently used at 140 ° C. or higher. When it is on the high temperature side, the base oil viscosity is preferably 40 to 300 mm2 / s.

In addition, synthetic hydrocarbon oils having different base oil viscosities can be mixed to obtain a base oil viscosity in the above range.

Additives such as a rust inhibitor and an antioxidant can be applied as long as the effects of the present invention are not impaired.

Preferably, the proportion of the thickener in the total amount of the grease composition is 7 to 14% by mass. When the rolling bearing is used at a relatively low temperature, the amount of thickener is preferably 7 to 10% by mass, and the apparent viscosity at −40 ° C. is preferably 50 Pa · s or less. When the use conditions are on the relatively high temperature side, the thickener amount is preferably 10 to 14% by mass, and the apparent viscosity at −40 ° C. is preferably 50 to 100 Pa · s.

By setting the amount of the thickening agent within the above range, a suitable rolling bearing can be obtained in accordance with the use conditions.

Preferably, the grease composition has a penetration degree (JIS K 2220: 25 ° C.) of 300 to 330.

More preferably, the blending degree of the grease composition is 300 to 330, and the immiscibility degree at −20 ° C. is 200 to 250. Most preferably, the immiscibility penetration at 25 ° C. is also 250 to 300.

By setting the blending penetration and non-mixing penetration to the above ranges, it is possible to reduce the influence of the grease composition enclosed in the rolling bearing on the rotational torque of the rolling bearing.

Preferably, the amount of the grease composition enclosed with respect to the volume of the internal space of the rolling bearing is 20 to 50% by volume. More preferably, it is 25-45 volume%, Most preferably, it is 30-40 volume%. The grease composition is preferably sealed so as not to be unevenly distributed in the bearing internal space.

In order to make the durability of the rolling bearing in a favorable range, it is preferable to enclose the grease composition so that it becomes approximately 20% by volume or more. However, when the amount of the grease composition enclosed exceeds 50% by volume, the agitation resistance of the grease inside the bearing increases, and the possibility of inducing leakage of the grease composition and heat generation of the rolling bearing increases.

When the rolling bearing is a rolling bearing that can support a load in the radial direction, the radial internal bearing clearance at 20 ° C. is preferably 0 or more.

If the internal bearing clearance in the radial direction is 20 or more at 20 ° C, it is possible to avoid excessively negative clearance even when used at -30 ° C and -40 ° C. Further, since the gap becomes small at low temperatures, it is possible to prevent bearing vibration at low temperatures.

Further, when the rolling bearing is a so-called deep groove ball bearing having a raceway groove for rolling the rolling element on the inner periphery of the outer ring and the outer periphery of the inner ring, the radius of curvature of the raceway groove of the outer ring is the rolling element diameter. 52.5% or more is preferable.

By setting it as the said curvature radius, the heat_generation | fever from a rolling bearing in high speed rotation can be suppressed.

The seal is preferably a so-called non-contact rubber seal, and the rubber material is preferably NBR (acrylonitrile butadiene rubber).

NBR is relatively inexpensive and has excellent heat resistance and cold resistance.

In particular, since the rolling bearing of the present invention uses a synthetic hydrocarbon oil that is less aggressive to NBR even at high temperatures as a base oil, it is possible to suppress deterioration of the seal and maintain the sealing performance for a long period of time. Thus, a synergistic effect that grease leakage from the bearing can be suppressed over a long period of time can be obtained.

The apparent viscosity was measured with a rheometer while keeping the grease composition at a predetermined temperature. FIG. 2 is a cross-sectional view showing a configuration of a measurement unit provided in a rheometer for measuring the rheological characteristics of the grease composition. Flat stage 1 surrounded by heat insulation wall
2 above the gap G
A disk-shaped measurement plate 13 (parallel plate) is arranged through the flat plate, and the flat lower surface of the measurement plate 13 is parallel to the stage 12. The gap G formed between the measurement plate 13 and the stage 12 is filled with the grease composition.

Then, while controlling the temperature of the grease with a temperature control device built in the stage 12, the shear rate was applied to the grease by rotating the measuring plate 13 in one direction (arrow A direction), and the apparent viscosity was measured.

The rolling bearing of the present invention can be suitably used for supporting a motor rotation shaft of an electric vehicle or a hybrid vehicle.

1 Rolling bearing (deep groove ball bearing)

Claims (1)

In a grease-lubricated rolling bearing in which a grease composition is enclosed, the grease composition has a synthetic hydrocarbon oil as a base oil and a urea compound as a thickener, and an apparent viscosity at −30 ° C. of 30 Pa. A rolling bearing characterized by having an apparent viscosity at −40 ° C. of 100 Pa · s or less.

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