JP4063985B2 - Wheel bearing device - Google Patents

Description

【００２７】
試験結果を表１に示す。表中の耐久寿命は、Ｌ１０寿命（９０％の軸受が破損しないで使える時間）までの回転回数で評価した。また、寿命比は比較例４の耐久寿命を基準値とした。
【００２８】
実施例の複列円錐ころ軸受は、いずれも優れた耐久寿命を示し、比較例４に対する寿命比が３倍以上になっている。一方、浸炭窒化層は形成されているが、その残留オーステナイト量が本願の範囲を外れる比較例１〜２は、寿命比が３０〜４０％増に止まっている。残留オーステナイト量は本願の範囲に入るが、浸炭層のみの比較例３は、殆ど改善効果が認められない。
【００２９】
【発明の効果】
以上のように、この発明の車輪用軸受装置は、車輪を支持する円錐ころ軸受の内輪と円錐ころの表面に、炭素含有量０．８０重量％以上で、かつロックウェル硬さＨＲＣ５８以上の浸炭窒化層を形成し、この浸炭窒化層の残留オーステナイト量を２５〜３５体積％としたので、これらの部品の機械的性質と疲労特性を高めるとともに、部品表面層を適度な靱性を有する材質に安定して保ち、高荷重、高温下での耐久寿命を著しく改善することができる。
【図面の簡単な説明】
【図１】実施形態の車輪用軸受装置を示す一部省略縦断面図
【図２】ａは図１の円錐ころ軸受を示す縦断面図、ｂはａの要部拡大断面図
【図３】従来の車輪用軸受装置を示す一部省略縦断面図
【符号の説明】
１ 車軸
２ 円錐ころ軸受
３ 内輪
３ａ 浸炭窒化層
４ 外輪
５ フランジ
６ ハブ
７ ブレーキロータ
８ ボルト
９ ナット
１０ ボルト
１１、１２ 軌道面
１３ 円錐ころ
１３ａ 浸炭窒化層
１４ 大端面
１５ 大鍔
１６ ゴム製シール
１７ 鋼板製シールド
２１ 車軸
２２ 円錐ころ軸受
２３ 内輪
２４ 外輪
２５ フランジ
２６ ハブ
２７ ブレーキロータ
２８ ボルト
２９ ナット
３０ ボルト
３１、３２ 軌道面
３３ 円錐ころ
３４ 大端面
３５ 大鍔
３６ ゴム製シール
３７ キャップ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wheel bearing device in which a wheel is supported on an axle by a tapered roller bearing.
[0002]
[Prior art]
A tapered roller bearing is a bearing suitable for applying a radial load, an axial load, and a combined load thereof, and has a large load capacity, and is therefore widely used for supporting wheels of automobiles and the like.
[0003]
FIG. 3 shows an example of a bearing device for a driven wheel of a truck. In this wheel bearing device, an inner ring 23 of a double-row tapered roller bearing 22 is fitted to an axle 21, and a hub 26 and a brake rotor 27 are fixed by bolts 28 to an outward flange 25 provided at one end of an outer ring 24. Has been. The inner ring 23 is secured by a nut 29 and a wheel mounting bolt 30 is mounted on the hub 26.
[0004]
Two rows of raceway surfaces 31 are formed on the inner diameter side of the outer ring 24, and each row of raceway surfaces 32 is formed on a pair of symmetrically arranged inner rings 23 so as to face each of the raceway surfaces 31. ing. A plurality of tapered rollers 33 are arranged in two rows between the opposed raceway surfaces 31, 32, and the tapered rollers 33 have large end surfaces 34 provided at both ends of the pair of inner rings 23. Rolls in contact with. Therefore, the hub 26 and the brake rotor 27 fixed to the outer ring 24 are rotatably supported with respect to the axle 21.
[0005]
A contact-type rubber seal 36 is attached to the inner end of the annular space in which the tapered rollers 33 are arranged in two rows on the center side of the axle 21, and the nut 29 is attached to the outer side of the end of the axle 21. It is covered with a cap 37 together with the end of the axle 21 so that the grease for lubrication in the bearing is prevented from being scattered and dust and water from entering from the outside.
[0006]
[Problems to be solved by the invention]
The bearing portion of the wheel bearing device as described above is regularly greased and maintained. In recent years, the horsepower and loading capacity of vehicles such as automobiles have increased, and accordingly, wheel bearing devices are required to withstand high loads and temperature rises at high speeds. Furthermore, there is an increasing demand for long-term maintenance-free operation. Bearing parts of wheel bearing devices are subject to rapid deterioration of the encapsulated grease under high loads and high temperatures, so it is desirable to develop long-life greases with excellent heat resistance. On the other hand, bearing members have long life under high loads and high temperatures. Securement is required.
[0007]
As described above, in the tapered roller bearing, the large end surface of the tapered roller comes into contact with the large collar surface of the inner ring and rolls, so heat is generated at the sliding portion between the large end surface and the large collar surface, and the load load is high. As the contact pressure between the large end face and the large collar surface increases, the amount of heat generation increases.
[0008]
Therefore, an object of the present invention is to provide a wheel bearing device that can ensure a long life even under a high load and high temperature.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a wheel bearing device in which a wheel is rotatably supported on an axle by a tapered roller bearing, wherein the tapered roller bearing has a raceway surface on an inner diameter side. An outer ring, an inner ring having a raceway surface formed on the outer diameter side facing the raceway surface, and a plurality of tapered rollers arranged between the opposed raceway surfaces, at least the inner ring and A carbonitriding layer having a carbon content of 0.80% by weight or more and a Rockwell hardness of HRC58 or more is formed on the surface of the tapered roller, and the amount of retained austenite of the carbonitriding layer is 25 to 35% by volume. Adopted.
[0010]
The reason why the carbonitriding layer is formed on the surfaces of the inner ring and the tapered roller is as follows. Residual austenite in the carburized layer obtained by normal carburizing and quenching has high toughness and work-hardening properties. By appropriately including this, the hardness of the carburized layer is ensured and crack generation and progress are suppressed. Although it works, it has the disadvantage of being unstable to heat. On the other hand, when the nitriding treatment is performed under appropriate conditions, nitrogen atoms are dissolved in the retained austenite and serve to stabilize the retained austenite against heat. In the carbonitrided layer obtained by this nitriding treatment, a compressive residual stress larger than that of a normal carburized layer is formed, so that the fatigue strength can be further increased.
[0011]
The carbonitriding layer having a carbon content of 0.80% by weight or more and Rockwell hardness of HRC58 or more reduces wear at the sliding portion between the large end surface of the tapered roller and the large collar surface of the inner ring. This is because the amount of retained austenite is set to 25 to 35% by volume because it imparts appropriate toughness to the carbonitrided layer and is caused by excessive stress caused by the wear powder intervening in the grease generated from the sliding portion and the like. This is to mitigate the increase. That is, if the amount of retained austenite is less than 25% by volume, the toughness is insufficient, and if the amount of retained austenite exceeds 35% by volume, the hardness is excessively lowered and the surface roughness is deteriorated due to plastic deformation.
[0012]
The structure of the carbonitriding layer as described above can be formed by the following processing steps. That is, after maintaining the carbon potential in the carburizing atmosphere at 0.8% or more for a predetermined time, cooling in oil and performing carburizing and quenching, and then heating and holding in ammonia gas for a predetermined time to perform nitriding treatment Do. A method of performing nitriding treatment simultaneously during the carburizing process can also be adopted. In order to adjust the amount of retained austenite, sub-zero treatment or tempering treatment may be performed.
[0013]
As the tapered roller bearing, double row raceway surfaces are formed on the inner diameter side of the outer ring, and double row raceway surfaces are formed on the outer diameter side of the inner ring so as to face each of these raceway surfaces. It is possible to employ a double-row tapered roller bearing in which a plurality of tapered rollers are arranged in double rows between the raceway surfaces.
[0014]
The outer ring may be integrally formed with a wheel mounting flange.
[0015]
By providing seal members for sealing the annular space at both ends of the annular space between the outer ring and the inner ring in which the tapered rollers are arranged in a double row, the inside of the bearing formed by the annular space can be compactly sealed. It is possible to prevent the outflow of the encapsulated grease and to stably ensure the encapsulated amount of grease. A contact rubber seal can be used as the inner seal member provided on the axle center side, and a non-contact steel plate shield can be used as the outer seal member provided on the axle end side.
[0016]
The wheel bearing device for supporting the above-described wheel with a tapered roller bearing is preferably applied to a driven wheel axle.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an embodiment of a wheel bearing device mounted on a driven wheel axle 1 of a truck. In this wheel bearing device, an inner ring 3 of a double-row tapered roller bearing 2 is fitted to an axle 1, and a hub 6 and a brake rotor 7 are fixed with bolts 8 to an outward flange 5 provided at one end of the outer ring 4. Has been. The inner ring 3 is secured by a nut 9 and a wheel mounting bolt 10 is attached to the hub 6.
[0018]
As shown in FIG. 2 (a), two rows of raceway surfaces 11 are formed on the inner diameter side of the outer ring 4, and a pair of symmetrically arranged inner races 3 are respectively opposed to these raceway surfaces 11. A track surface 12 is formed for each row. A plurality of tapered rollers 13 are arranged in two rows between the opposed raceway surfaces 11, 12, and each tapered roller 13 has a large flange 15 provided with a large end surface 14 at both ends of the pair of inner rings 3. Rolls in contact with.
[0019]
In the annular space in which the tapered rollers 13 are arranged in two rows, a contact type rubber seal 16 is provided at the inner side end portion on the center side of the axle 1 and a non-contact type end portion is provided on the outer side end portion on the axle 1 end side. A steel plate shield 17 is mounted, and the inside of the bearing formed in the annular space is compactly sealed, so that the sealed grease can be prevented from flowing out and the amount of grease charged can be secured stably. .
[0020]
Further, the inner ring 3 and the tapered roller 13 are manufactured using case-hardened steel SCr435, and as shown in an enlarged view in FIG. 2 (b), the carbon content is 0.80% by weight or more on these surfaces. Carbonitriding layers 3a and 13a having well hardness HRC58 or more and a residual austenite amount of 25 to 35% by volume are formed. The outer ring 4 was made of induction-hardened structural carbon steel S53C.
[0021]
In this embodiment, SCr435 is used as the material for the inner ring and the tapered roller, but other bearing steels such as SCM420, SCM430, SCM435, SCr420, SCr430, SAE5130, SAE8620 can also be used. The present invention can also be applied to a wheel bearing device using a single-row tapered roller bearing or a double-row tapered roller bearing having more than two rows.
[0022]
Examples and comparative examples are given below.
[0023]
【Example】
The inner ring and the tapered roller shown in FIG. 2 (a) are made of case-hardened steel SCr435, and the surface has a carbon content of 0.80% by weight or more, Rockwell hardness of HRC58 or more, and a retained austenite amount of 25 to 35 volumes. %, A double row tapered roller bearing (Examples 1 to 3 in Table 1) in which a carbonitriding layer in the range of% was formed was prepared. The bearings have an inner diameter of 65 mm and a width of 130 mm.
[0024]
[Comparative example]
Similar to the example, the inner ring and the tapered roller are made of case-hardened steel SCr435, and a carbonitriding layer having a carbon content of 0.80% by weight or more and a Rockwell hardness of HRC58 or more is formed on the surface, and only the retained austenite amount is formed. Double row tapered roller bearings outside of the scope of the present invention (Comparative Examples 1 and 2 in Table 1), the amount of retained austenite falls within the scope of the present application, but a double row in which only the carburized layer is formed on the surfaces of the inner ring and the tapered roller. A tapered roller bearing (Comparative Example 3 in Table 1) and a double-row tapered roller bearing (Comparative Example 4 in Table 1) having a retained austenite amount outside the scope of the present application with only a carburized layer were prepared. The dimensions of each bearing are the same as in the example.
[0025]
The double row tapered roller bearings of the above examples and comparative examples were attached to the shaft of an endurance tester, and an endurance life test was performed.
The test conditions are as follows.
(Durability test)
Radial load: 63kN
Thrust load: 25kN
Rotation speed: 400rpm
[0026]
[Table 1]

[0027]
The test results are shown in Table 1. The endurance life in the table was evaluated by the number of rotations up to L10 life (time in which 90% of bearings can be used without being damaged). Further, the life ratio was determined based on the durable life of Comparative Example 4.
[0028]
The double row tapered roller bearings of the examples all have an excellent durability life, and the life ratio with respect to the comparative example 4 is three times or more. On the other hand, although the carbonitrided layer is formed, in Comparative Examples 1 and 2 in which the amount of retained austenite falls outside the scope of the present application, the life ratio is only increased by 30 to 40%. Although the amount of retained austenite falls within the scope of the present application, Comparative Example 3 with only the carburized layer shows almost no improvement effect.
[0029]
【The invention's effect】
As described above, the wheel bearing device of the present invention has a carbon content of 0.80% by weight or more and a Rockwell hardness of HRC58 or more on the inner ring and the surface of the tapered roller of the tapered roller bearing that supports the wheel. A nitrided layer is formed, and the amount of retained austenite of the carbonitrided layer is 25 to 35% by volume, so that the mechanical properties and fatigue characteristics of these parts are enhanced and the surface layer of the parts is stabilized to a material having appropriate toughness. The durability life under high load and high temperature can be remarkably improved.
[Brief description of the drawings]
1 is a partially omitted longitudinal sectional view showing a wheel bearing device of an embodiment. FIG. 2 is a longitudinal sectional view showing a tapered roller bearing of FIG. 1, and b is an enlarged sectional view of a main part of a. Partially omitted vertical sectional view showing a conventional wheel bearing device [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Axle 2 Tapered roller bearing 3 Inner ring 3a Carbonitriding layer 4 Outer ring 5 Flange 6 Hub 7 Brake rotor 8 Bolt 9 Nut 10 Bolts 11 and 12 Race surface 13 Tapered roller 13a Carbonitriding layer 14 Large end surface 15 Large flange 16 Rubber seal 17 Steel plate shield 21 Axle 22 Tapered roller bearing 23 Inner ring 24 Outer ring 25 Flange 26 Hub 27 Brake rotor 28 Bolt 29 Nut 30 Bolts 31, 32 Raceway surface 33 Tapered roller 34 Large end surface 35 Large flange 36 Rubber seal 37 Cap

Claims (1)

A wheel is rotatably supported on the axle by a tapered roller bearing, and the tapered roller bearing is formed with a double row raceway surface on the inner diameter side of the outer ring, and the outer diameter of the pair of inner rings is opposed to each raceway surface. A row of raceways is formed on each side, and a double row tapered roller bearing in which a plurality of tapered rollers are arranged in a double row between the opposed raceway surfaces, and grease is sealed inside the bearing, In the wheel bearing device in which a flange for mounting a wheel is integrally formed on the outer ring, the pair of inner rings are arranged symmetrically so that large flanges are provided at both ends with the end surfaces attached to each other, and the outer ring is structured. Carbon steel for induction use is induction hardened, and case hardening steel is used for the inner ring and the tapered roller, and the carbon content is 0.80% by weight or more on the surface of the inner ring and the tapered roller, and the Rockwell hardness is HRC58. More carburizing and nitriding To form a layer, the amount of retained austenite of the carbonitrided layer wheel bearing device is characterized in that a 25 to 35% by volume.

Images