JP4545819B2 - Grease - Google Patents

Description

  The present invention relates to a grease, and more particularly to a grease used for a wheel support rolling bearing unit for rotatably supporting a wheel with respect to an automobile suspension.

Regarding a rolling bearing unit for supporting a wheel of an automobile, a first example in which an inner ring is a stationary bearing ring and a hub is a rotating bearing ring, and an outer ring is a stationary bearing ring and a hub is a rotating bearing ring. The 2nd example of this is known (patent document 1).
First, a first example of a conventional structure of a wheel support rolling bearing unit will be described with reference to FIG. FIG. 5 is a cross-sectional view showing a first example of a conventional structure of a wheel bearing rolling bearing unit. A wheel 1 constituting a wheel is rotatably supported at an end portion of an axle 3 constituting a suspension device by a wheel bearing rolling bearing unit 2 as shown in FIG. That is, inner rings 5 and 5 that are stationary side bearing rings constituting the wheel support rolling bearing unit 2 are externally fitted to an axle 4 fixed to an end portion of the axle 3 and fixed by nuts 6. On the other hand, the wheel 1 is coupled and fixed to a hub 7, which is a rotating raceway wheel constituting the wheel support rolling bearing unit 2, by a plurality of studs 8, 8 and nuts 9, 9.

Double-row outer ring rolling surfaces 10a and 10b, each of which is a rotation-side rolling surface, are formed on the inner peripheral surface of the hub 7, and a mounting flange 11 is formed on the outer peripheral surface. The wheel 1 is coupled and fixed to one side surface (outer side surface in the illustrated example) of the mounting flange 11 by the studs 8 and 8 and nuts 9 and 9 together with a drum 12 for constituting a braking device. ing.
In the present specification, “outside” in the axial direction means the outside in the width direction when assembled to the vehicle, and “inside” means the center in the width direction.

Between the outer ring rolling surfaces 10a, 10b and the inner ring rolling surfaces 13, 13 formed on the outer peripheral surfaces of the inner rings 5, 5 are stationary rolling surfaces, respectively. A plurality of balls 14 and 14 are provided so as to be freely rollable in a state of being held by holders 15 and 15, respectively. By combining the constituent members in this way, a double-row angular contact type ball bearing which is a rear combination is formed, and the hub 7 is rotated around the inner rings 5 and 5 in a rotatable manner with radial load and thrust. The load is supported freely. In addition, seal rings 16a and 16b are provided between the inner peripheral surfaces of both ends of the hub 7 and the outer peripheral surfaces of the end portions of the inner rings 5 and 5, respectively, and a space in which the balls 14 and 14 are provided. The internal space 17 is shut off.
Further, the outer end opening of the hub 7 is closed by a cap 18.

  When using the wheel bearing rolling bearing unit 2 as described above, as shown in FIG. 5, the axle 4 with the inner rings 5, 5 fitted and fixed is fixed to the axle 3, and the mounting flange 11 of the hub 7 is illustrated. The wheel 1 and the drum 12 combined with tires that are not used are fixed. A drum brake for braking is configured by combining the drum 12 and a wheel cylinder and a shoe (not shown) supported by a backing plate 19 fixed to the end of the axle 3. During braking, a pair of shoes provided on the inner diameter side of the drum 12 is pressed against the inner peripheral surface of the drum 12. In addition, grease is enclosed in the internal space 17, and rolling contact between the outer ring rolling surfaces 10a and 10b, the inner ring rolling surfaces 13 and 13 and the rolling surfaces of the balls 14 and 14 is performed. The part is lubricated.

  Next, a second example of a conventional structure of a wheel support rolling bearing unit will be described with reference to FIG. FIG. 6 is a sectional view showing a second example of a conventional structure of a wheel bearing rolling bearing unit. In the case of the wheel support rolling bearing unit 2a shown in FIG. 6, a hub 7a that is a rotating raceway is provided on the inner diameter side of an outer ring 20 that is a stationary raceway, and a plurality of balls 14 each of which is a rolling element. 14 and 14 are supported rotatably. For this purpose, double row outer ring rolling surfaces 10a and 10b, each of which is a stationary rolling surface, are provided on the inner peripheral surface of the outer ring 20, and each of the outer peripheral surfaces of the hub 7a is a rotating side rolling surface. First and second inner ring rolling surfaces 21 and 22 are provided, respectively. The hub 7a is a combination of a hub body 23 and an inner ring 24. Of these, the mounting flange 11a for supporting the wheel on the outer end portion of the outer peripheral surface of the hub body 23, the first inner ring rolling surface 21 in the middle portion, and the first inner ring near the inner end portion of the hub. Small-diameter step portions 25 each having a smaller diameter than the portion where the inner ring rolling surface 21 is formed are provided. The inner ring 24 provided with the second inner ring rolling surface 22 having a circular arc cross section on the outer peripheral surface is externally fitted to the small diameter step portion 25. Further, the inner end surface of the inner ring 24 is held down by a caulking portion 26 formed by plastic deformation of the inner end portion of the hub main body 23 radially outward, and the inner ring 24 is fixed to the hub main body 23. .

Seal rings 16c and 16d are provided between the inner peripheral surface of both ends of the outer ring 20, the outer peripheral surface of the intermediate portion of the hub body 23, and the outer peripheral surface of the inner end of the inner ring 24, respectively. The inner space provided with the balls 14 and 14 and the outer space are shut off between the inner peripheral surface of the hub 7a and the outer peripheral surface of the hub 7a.
Grease is sealed in this internal space to lubricate rolling contact portions between the outer ring rolling surfaces 10a, 10b, the inner ring rolling surfaces 21, 22, and the rolling surfaces of the balls 14, 14. To do.
When the grease-filled rolling bearing is used as a wheel support bearing, the lubricating oil film of the lubricating grease is likely to break due to severe use conditions such as high speed and high load. When the lubricating oil film breaks, metal contact occurs, causing a problem that heat generation and frictional wear increase.
For this reason, it is necessary to improve lubricity and load resistance under high speed and high load, and to prevent metal contact due to breakage of the lubricating oil film. The extreme pressure agent-containing grease is used to reduce the problems.
In lubrication of the rolling bearing portion, in order to prevent the lubricating film of the lubricating grease from breaking, grease containing an extreme pressure agent (EP agent) is used to reduce the breaking of the lubricating oil film.
For example, an extreme pressure grease lubricant composition for a rolling bearing comprising an organic bismuth compound is known (Patent Document 2). Further, a grease composition containing molybdenum dithiocarbamate and polysulfide for the purpose of reducing wear is known (Patent Document 3).
However, as the usage conditions of rolling bearings become severe, such as lubrication under high speed conditions with a dN value of 100,000 or more, there is a problem that it becomes difficult to use rolling bearings with conventional greases.

JP 2001-221243 A JP-A-8-41478 Japanese Patent Laid-Open No. 10-324885

  An object of the present invention is to provide a grease capable of preventing frictional wear on the bearing lubrication surface under high speed and high load.

The grease of the present invention is a grease containing a base oil, a thickener, and inorganic bismuth, wherein the inorganic bismuth is bismuth powder, and the bismuth powder is blended in an amount of 0.01 to 15% by weight based on the whole grease. It is characterized by being.
The base oil is a mineral oil and has a kinematic viscosity of 30 to ²⁰⁰ mm ² / s at 40 ° C.
The thickener is a metal soap thickener.

  Since the grease of the present invention is formulated with a predetermined amount of bismuth powder as inorganic bismuth, it has excellent heat resistance and durability, and when sealed in a bearing unit, etc., inorganic bismuth rolls and is replenished to the contact portion, thereby providing extreme pressure properties. The effect can last for a long time. Therefore, it can be suitably used for a wheel bearing rolling bearing unit that is required to have long-term durability as well as wear resistance.

It is sectional drawing which shows the 1st example of the structure of the rolling bearing unit for wheel support which enclosed the grease of this invention. It is sectional drawing which shows the 2nd example of the structure of the rolling bearing unit for wheel support which enclosed the grease of this invention. It is sectional drawing which shows the 3rd example of the structure of the rolling bearing unit for wheel support which enclosed the grease of this invention. It is sectional drawing which shows the 4th example of the structure of the rolling bearing unit for wheel support which enclosed the grease of this invention. It is sectional drawing which shows the 1st example of the conventional structure of the rolling bearing unit for wheel support. It is sectional drawing which shows the 2nd example of the conventional structure of the rolling bearing unit for wheel support. It is a figure which shows an extreme pressure property evaluation test apparatus.

A rolling bearing unit for supporting a wheel enclosing grease of the present invention includes a stationary side race ring, a rotation side race ring, and a plurality of rolling elements. Of these, the stationary-side race is supported and fixed to the suspension device in use. The rotating raceway supports and fixes the wheel in a use state. Moreover, each said rolling element is provided between the stationary-side rolling surface and rotation-side rolling surface which exist in the mutually opposing peripheral surface of the said stationary-side track ring and the rotation-side track ring. And the rolling contact part of each of these rolling surfaces and the said rolling element is lubricated with grease.
As a result of examining the durability of such a conventional wheel support rolling bearing unit, the space where the rolling elements are installed is filled with grease containing 0.01 to 15% by weight of inorganic bismuth with respect to the entire grease. The rolling bearing unit has been found to improve the lubrication performance of the rolling contact portion between the rolling surfaces of the stationary side and the stationary side and the rolling surfaces of the rolling elements.
Further, it has been found that when the above-described conventional wheel support rolling bearing unit is improved in terms of structure and the above grease is applied, the rotational torque of the hub is reduced. The present invention is based on such knowledge.
Four examples of the structure of a rolling bearing unit for supporting a wheel that is more suitable when the present invention is implemented will be described below.

  FIG. 1 shows a first example of a structure suitable as a wheel bearing rolling bearing unit in which the grease of the present invention is enclosed. The first example is a structure for supporting driven wheels (front wheels of FR and RR vehicles, rear wheels of FF vehicles), and the rotational torque of the hub 7b is increased by improving the structure shown in FIG. The structure can be further reduced. For this purpose, in the case of the first example, the inner end opening of the outer ring 20 is closed with a cap 18a, and the outer end inner peripheral surface of the outer ring 20 and the intermediate outer peripheral surface of the hub body 23 are sealed. It is blocked by the ring 16c. Since the cap 18a is provided, the seal ring 16d between the inner peripheral surface of the inner end portion of the outer ring 20 and the outer peripheral surface of the inner ring 24 shown in FIG. 6 can be omitted. Prevention of entry of foreign matter such as muddy water into the internal space 17b in which the balls 14 and 14 are installed is prevented by the seal ring 16c and the cap 18a. The grease sealed in the internal space 17b contains 0.01 to 15% by weight of inorganic bismuth with respect to the whole grease. The structure of other parts is the same as the conventional structure shown in FIG. When the wheel bearing rolling bearing unit is applied to a driven wheel, the seal ring between the inner peripheral surface of the inner end of the outer ring and the outer peripheral surface of the inner ring is omitted, so the rotational torque of the hub is reduced compared to the conventional structure. can do.

Next, FIG. 2 shows a second example of a structure suitable as a wheel bearing rolling bearing unit filled with the grease of the present invention.
The second example is also a structure for supporting driven wheels (front wheels of FR and RR vehicles, rear wheels of FF vehicles). In the case of the second example, a male screw portion 27 is provided at the inner end of the hub main body 23a constituting the hub 7c, and a nut 28 screwed to the male screw portion 27 is externally fitted to the small diameter step portion 25 of the hub main body 23a. The inner end surface of the inner ring 24 is suppressed. In accordance with this, the shape of the cap 18b attached to the inner end opening of the outer ring 20 is expanded to prevent interference between the male screw portion 27 and the nut 28. Other configurations are the same as those of the first example described above.

Next, FIG. 3 shows a third example of a structure suitable as a wheel bearing rolling bearing unit filled with the grease of the present invention. The third example is a structure for supporting driving wheels (rear wheels of FR and RR vehicles, front wheels of FF vehicles, and all wheels of 4WD vehicles).
For this reason, in the case of the third example, a spline hole 29 is formed in the central portion of the hub main body 23b constituting the hub 7d that is the rotation side raceway ring that is rotatably supported on the inner diameter side of the outer ring 20 that is the stationary side raceway ring. Is forming. A spline shaft (not shown) attached to the constant velocity joint is inserted into the spline hole 29 in the assembled state to the vehicle.
In addition, when the wheel bearing rolling bearing unit is applied to a drive wheel, a spline hole is formed in the center of the hub body having a hub that is a rotating side race ring, and this spline hole is attached to a constant velocity joint. By connecting this spline shaft, the rotational torque of the constant velocity joint can be reliably transmitted to the hub.

  A caulking portion 26 is formed by plastically deforming the inner end portion of the inner ring 24 externally fitted to the small-diameter step portion 25 formed at the inner end portion of the hub main body 23b radially outward. Thus, the inner ring 24 is fixed to the hub body 23b to constitute the hub 7d. Seal rings 16c and 16d are provided between the inner peripheral surface of both ends of the outer ring 20, the outer peripheral surface of the intermediate part of the hub main body 23b, and the outer peripheral surface of the inner end part of the inner ring 24, respectively. Between the inner peripheral surface and the outer peripheral surface of the hub 7d, the internal space 17b provided with the balls 14 and 14 is blocked from the external space. Other configurations are the same as those in the first and second examples described above.

Next, FIG. 4 shows a fourth example of a structure suitable as a wheel bearing rolling bearing unit filled with the grease of the present invention. The fourth example is also a structure for supporting driving wheels (rear wheels of FR and RR vehicles, front wheels of FF vehicles, and all wheels of 4WD vehicles).
In the case of the fourth example, the inner end surface of the inner ring 24 that is externally fitted to the small diameter step portion 25 provided at the inner end portion of the hub main body 23c and forms the hub 7e together with the hub main body 23c is used as the inner end surface of the hub main body 23c. It protrudes inward rather than. The outer end surface of a constant velocity joint (not shown) hits the inner end surface of the inner ring 24 in the assembled state in the vehicle, and the inner ring 24 is prevented from falling off the small diameter step portion 25. Other configurations are the same as those of the third example described above.

The inorganic bismuth, the base oil, the thickener and the additive constituting the grease of the present invention that can be suitably applied to the four examples of the above structure that are wheel bearing rolling bearing units will be described below.
The wheel bearing rolling bearing unit capable of enclosing grease using inorganic bismuth is not limited to the four examples of the above structure, and the grease using inorganic bismuth is also applied to the two examples of the conventional structure described above. Can be applied.

  Examples of the inorganic bismuth that can be used in the grease of the present invention include bismuth powder, bismuth carbonate, bismuth chloride, bismuth nitrate and its hydrate, bismuth sulfate, bismuth fluoride, bismuth bromide, bismuth iodide, bismuth oxyfluoride. Bismuth oxychloride, bismuth oxybromide, bismuth oxyiodide, bismuth oxide and its hydrates, bismuth hydroxide, bismuth selenide, bismuth telluride, bismuth phosphate, bismuth oxyperchlorate, bismuth oxysulfate, bismuth acid Sodium, bismuth titanate, bismuth zirconate, bismuth molybdate, and the like are mentioned, but in the present invention, particularly preferable is bismuth sulfate and trioxide having a high extreme pressure effect because of excellent heat resistance and resistance to thermal decomposition. Bismuth and bismuth powder.

  Bismuth is a silver-white metal with the lowest thermal conductivity of all metals except mercury, a specific gravity of 9.8, and a melting point of 271.3 ° C. Bismuth powder is a relatively soft metal and tends to form a film when subjected to extreme pressure. Therefore, the particle size of the powder may be any particle size that can be dispersed in the grease. The bismuth powder used for the grease sealed in the wheel support device is preferably 5 to 500 μm.

It is essential to add inorganic bismuth as an extreme pressure agent to the grease of the present invention. One kind or two kinds of inorganic bismuth may be mixed and added to the grease.
The amount of inorganic bismuth added is 0.01 to 15% by weight based on the entire grease. Preferably, it is 1 to 10% by weight. If the amount added is less than 0.01% by weight, the effect of improving the wear resistance will not be exhibited. If the amount added exceeds 15% by weight, the torque during rotation increases, heat generation increases, and rotation trouble occurs. .

  Examples of the base oil that can be used in the grease of the present invention include mineral oil, poly-α-olefin (hereinafter abbreviated as PAO) oil, ester oil, phenyl ether oil, fluorine oil, and a Fischer-Tropsch reaction. And synthetic hydrocarbon oils (GTL base oil). Among these, it is preferable to use at least one selected from PAO oil, mineral oil, ester oil and ether oil. The PAO oil is usually an α-olefin or an isomerized α-olefin oligomer or polymer mixture. Specific examples of the α-olefin include 1-octene, 1-nonene, 1-decene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1 -Nonadecene, 1-eicosene, 1-docosene, 1-tetradocosene and the like can be mentioned, and usually a mixture thereof is used. Moreover, as mineral oil, what is normally used in the field | areas of normal lubricating oil and grease, such as a paraffinic mineral oil and a naphthenic mineral oil, can be used, for example.

The base oil that can be used in the grease of the present invention preferably has a kinematic viscosity at 40 ° C. of 30 to ²⁰⁰ mm ² / s. If it is less than 30 mm ² / s, the amount of evaporation increases and the heat resistance decreases, which is not preferable. On the other hand, if it exceeds 200 mm ² / s, the temperature rise of the bearing increases due to an increase in rotational torque, which is not preferable. .

（式（１）中のＲ₂ は、炭素数６〜１５の芳香族炭化水素基を、Ｒ₁およびＲ₃ は、炭素数６〜１２の芳香族炭化水素基または炭素数６〜２０の脂環族炭化水素基または炭素数６〜２０の脂肪族炭化水素基をそれぞれ示し、Ｒ₁ およびＲ₃ は、同一であっても異なっていてもよい。）
式（１）で表されるウレア系化合物は、例えば、ジイソシアネートとモノアミンの反応で得られる。ジイソシアネートとしては、フェニレンジイソシアネート、ジフェニルジイソシアネート、ジフェニルメタンジイソシアネート、１，５−ナフチレンジイソシアネート、２，４−トリレンジイソシアネート、３，３−ジメチル−４，４−ビフェニレンジイソシアネート、オクタデカンジイソシアネート、デカンジイソシアネート、ヘキサンジイソシアネー卜等が挙げられ、モノアミンとしては、オクチルアミン、ドデシルアミン、ヘキサデシルアミン、ステアリルアミン、オレイルアミン、アニリン、ｐ−トルイジン、シクロヘキシルアミン等が挙げられる。
ウレア化合物は、イソシアネート化合物とアミン化合物を反応させることにより得られる。反応性のある遊離基を残さないため、イソシアネート化合物のイソシアネート基とアミン化合物のアミノ基とは略当量となるように配合することが好ましい。
基油にウレア化合物を配合して各種配合剤を配合するためのベースグリースが得られる。ベースグリースは、基油中でイソシアネート化合物とアミン化合物とを反応させて作製する。 Thickeners that can be used in the grease of the present invention include metal soap thickeners such as aluminum, lithium, sodium, complex lithium, complex calcium, complex aluminum, and diurea compounds of the following formula (1). Preferably, it is a diurea compound or lithium soap. These thickeners may be used alone or in combination of two or more.

(R ₂ in the formula (1) is an aromatic hydrocarbon group having 6 to 15 carbon atoms, R ₁ and R ₃ are an aromatic hydrocarbon group having 6 to 12 carbon atoms or an oil having 6 to 20 carbon atoms. Each represents a cyclic hydrocarbon group or an aliphatic hydrocarbon group having 6 to 20 carbon atoms, and R ₁ and R ₃ may be the same or different.)
The urea compound represented by the formula (1) is obtained, for example, by reaction of diisocyanate and monoamine. Diisocyanates include phenylene diisocyanate, diphenyl diisocyanate, diphenylmethane diisocyanate, 1,5-naphthylene diisocyanate, 2,4-tolylene diisocyanate, 3,3-dimethyl-4,4-biphenylene diisocyanate, octadecane diisocyanate, decane diisocyanate, hexane diisocyanate. Examples of the monoamine include octylamine, dodecylamine, hexadecylamine, stearylamine, oleylamine, aniline, p-toluidine, and cyclohexylamine.
A urea compound is obtained by reacting an isocyanate compound and an amine compound. In order not to leave a reactive free radical, the isocyanate group of the isocyanate compound and the amino group of the amine compound are preferably blended so as to be approximately equivalent.
Base grease for blending various compounding agents by blending a urea compound with a base oil can be obtained. The base grease is produced by reacting an isocyanate compound and an amine compound in a base oil.

  The grease of the present invention can contain known additives in the grease as necessary. Examples of the additive include organic zinc compounds, amine-based, phenol-based and sulfur-based antioxidants, metal deactivators such as benzotriazole and sodium nitrite, viscosity index improvers such as polymethacrylate and polystyrene, Examples thereof include solid lubricants such as molybdenum sulfide and graphite. These can be added alone or in combination of two or more.

  The grease of the present invention can also be used for bearings that are subjected to high loads other than wheel-supporting rolling bearing units.

Example 1, Comparative Examples 1 to 10
In a reaction vessel, add a thickener to the base oil, homogenize it using a three-roll mill, and mix with Li soap / mineral oil grease (40 ° C base oil viscosity 100 mm ² / s, shown in Table 1). Concentration 220), urea / PAO oil grease (40 ° C base oil viscosity 46 mm ² / s, miscibility 280), Li soap / ester oil grease (40 ° C base oil viscosity 33 mm ² / s, miscibility) 250), urea / ether oil grease (40 ° C. base oil viscosity 100 mm ² / s, blending degree 300).
Further, inorganic bismuth as an extreme pressure agent was added to the grease in the ratio shown in Table 1 to prepare greases of Example 1 and Comparative Examples. The obtained grease was subjected to the following extreme pressure evaluation test and roller bearing test. The results are also shown in Table 1.

Comparative Example 11 to Comparative Example 18
In a reaction vessel, add a thickener to the base oil, homogenize using a three-roll mill, and mix with Li soap / mineral oil grease (40 ° C base oil viscosity 100 mm ² / s, mixed in Table 2). Concentration 220), urea / PAO oil grease (40 ° C base oil viscosity 46 mm ² / s, miscibility 280), Li soap / ester oil grease (40 ° C base oil viscosity 30 mm ² / s, miscibility) 250), urea / ether oil grease (40 ° C. base oil viscosity 100 mm ² / s, blending degree 300).
Further, as an extreme pressure agent, organic bismuth, MoDTC, or zinc powder was added to the grease in the ratio shown in Table 2 to prepare greases of respective comparative examples.

The obtained grease was subjected to an extreme pressure evaluation test and a roller bearing test in the same manner as in the example. The results are shown in Table 2.
Extreme pressure evaluation test:
An extreme pressure property evaluation test apparatus is shown in FIG. The evaluation test apparatus is composed of a φ40 × 10 ring-shaped test piece 2 fixed to the rotary shaft 30 and a ring-shaped test piece 31 in which the end faces are rubbed with each other at the end face 32. The roller bearing grease was applied to the end face 32 portion, and the extreme pressure property was evaluated by applying the axial load 490 N and the radial load 392 N in the right direction A in FIG. The extreme pressure property was measured by measuring the vibration of the rotating shaft 30 caused by an increase in frictional wear at the sliding portions of both test pieces with a vibration sensor, performing the test until the vibration value was twice the initial value, and measuring the time.
The longer the time it takes for the vibration value of the rotary shaft 30 to be twice the initial value, the greater the extreme pressure effect, and the better the heat resistance and durability. Therefore, the heat resistance durability of the grease was evaluated by comparing the examples with the comparative examples based on the measured length of time.
Roller bearing test:
3.620 g of grease was sealed in a 30206 tapered roller bearing and operated at an axial load of 980 N, a rotational speed of 2600 rpm at room temperature, and the surface temperature of the collar part during rotation was measured. After the start of operation, the average value of the collar surface temperature from 4 to 8 hours was calculated.
When the sliding friction generated between the collar portion and the “roller” increases, the surface temperature of the rotating collar portion increases. Therefore, the heat resistance durability of the grease was evaluated by comparing each example with each comparative example at the measured temperature. The standard for the heat resistance and durability of the grease was that the temperature was 70 ° C or less.

In Tables 1 and 2, the data of Li soap / mineral oil-based grease is compared between the examples and the comparative examples. Excellent heat resistance and durability.
As shown in Example 1 and Comparative Example 15, it can be seen that bismuth powder, in particular, has a heat durability of about 6 times that of organic bismuth. Moreover, in Comparative Example 2 and Comparative Example 15, it can be seen that bismuth trioxide exhibits a heat durability of about 3 times that of organic bismuth. From these facts, inorganic bismuth is superior to organic bismuth in heat resistance and resistance to thermal decomposition, so it is considered that the extreme pressure effect can be maintained for a long time.
Among bismuth sulfate, bismuth trioxide and bismuth powder, bismuth powder showed the best heat resistance and durability.

  Although the extreme pressure effect tends to increase as the amount of bismuth trioxide added increases to 1% by weight of Comparative Example 5, 5% by weight of Comparative Example 2, and 15% by weight of Comparative Example 6, the addition of bismuth trioxide increases. Even if the amount is increased to 3 times the 15% by weight and 5% by weight added, the increase in extreme pressure effect is only about 1.4 times. This is probably because when the amount of bismuth trioxide added approaches 15% by weight, the torque during rotation increases, heat generation increases, and rotation failure tends to occur.

  Further, as shown in Comparative Example 18, when zinc powder was added, the heat resistance durability was remarkably deteriorated, and even if it was an inorganic compound, no extreme pressure effect was observed in the zinc powder. This is considered to be because the melting point of zinc was low and the heat resistance of the grease could not be improved.

  In Tables 1 and 2, the urea / PAO oil grease, Li soap / ester oil grease, and urea / ether oil grease data are compared with the comparative examples. As for the type of extreme pressure agent, inorganic bismuth such as bismuth sulfate and bismuth trioxide exhibits superior heat resistance and durability than organic bismuth. As shown in Comparative Example 3, Comparative Example 4 and Comparative Example 17, bismuth sulfate has a heat resistance of about 3 times that of organic bismuth, and bismuth trioxide has a heat resistance of about 4 times that of organic bismuth. It turns out that it shows durability. This is presumably because inorganic bismuth is superior to organic bismuth in heat resistance and resistance to thermal decomposition, so that the extreme pressure effect can be maintained for a long time.

Further, as shown in Comparative Example 7 and Comparative Example 13, in the case of Li soap / ester oil grease, heat resistance and durability is about 13 times higher when bismuth sulfate is used as an extreme pressure agent than when no extreme pressure agent is used. Showed sex.
Further, as shown in Comparative Example 8 and Comparative Example 14, in the case of urea / ether oil based grease, heat resistance and durability is about 6 times higher when bismuth trioxide is used as an extreme pressure agent than when no extreme pressure agent is used. Showed sex. From the above, it can be seen that inorganic bismuth such as bismuth sulfate and bismuth trioxide maintains the extreme pressure effect for a long time.

  Since the rolling bearing unit for supporting a wheel enclosing grease of the present invention uses a rolling bearing enclosing grease using inorganic bismuth excellent in heat resistance and durability, the extreme pressure effect can be maintained for a long period of time. Therefore, it can be suitably used for railway vehicles, construction machines, automobile electrical accessories and the like that are required to have long-term durability in addition to wear resistance.

DESCRIPTION OF SYMBOLS 1 Wheel 2 Rolling bearing unit 3 for wheel support 4 Axle 5 Axle 5 Inner ring 6 Nut 7 Hub 8 Stud 9 Nut 10 Outer ring rolling surface 11 Mounting flange 12 Drum 13 Inner ring rolling surface 14 Ball 15 Cage 16 Cage 16 Seal ring 17 Internal space 18 Cap 19 Backing plate 20 Outer ring 21, 22 Inner ring rolling surface 23 Hub 24 Inner ring 25 Small diameter step

Claims (3)

A grease containing a base oil, a thickener, and inorganic bismuth,
The thickener is at least one thickener selected from metal soap thickeners and urea compounds,
A grease characterized in that the inorganic bismuth is bismuth powder, and the bismuth powder is blended in an amount of 0.01 to 15% by weight based on the whole grease. The grease according to claim 1, wherein the base oil is a mineral oil, and the kinematic viscosity of the base oil at 40 ° C is 30 to ²⁰⁰ mm ² / s.   The grease according to claim 1 or 2, wherein the thickener is a metal soap thickener.

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