JP2006046353A - Wheel supporting hub bearing unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wheel supporting hub bearing unit having excellent productivity, light weight, and a long life span. <P>SOLUTION: A wheel supporting rolling bearing unit 1 is equipped with a hub 2 in whose an outer circumference surface a wheel mounting flange 6 and an inner-race raceway 20a are included, an inner race 3 which is fixed integrally to the hub 2 and includes an inner race raceway 20b in its outer circumference surface, an outer race 4 having a suspension device mounting flange 17 in its outer circumferential surface and besides outer-race raceways 21a, 21b facing the inner-race raceways 20a, 20b in its inner circumferential surface, and rolling elements 5 arranged in a double line in a freely rotatable manner. Further, a hardened layer processed by high-frequency hardening is formed in both the inner-race raceways 20a, 20b and the outer-race raceways 21a, 21b. Besides, the hub 2, the inner race 3 and the outer race 4 are made up from alloyed steel containing a given amount of carbon, silicon, manganese, chrome and vanadium. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a wheel support hub bearing unit that rotatably supports a wheel of an automobile or the like with respect to a suspension device.

  A wheel bearing hub bearing unit that rotatably supports a wheel of an automobile or the like with respect to a suspension device includes an inner member having a raceway surface on an outer peripheral surface, an outer member having a raceway surface on an inner peripheral surface, A plurality of rolling elements that are arranged to freely roll between the raceway surfaces. In addition, at least one of the outer peripheral surface of the inner member and the outer peripheral surface of the outer member is provided with a flange for attaching a wheel or a suspension device, and the inner member and the outer member have a complicated shape. Conventionally, many hub bearing units have been used.

FIG. 7 is a cross-sectional view showing the structure of a wheel support hub bearing unit that has been widely used conventionally. The wheel support hub bearing unit 101 includes a hub 102, an inner ring 103, an outer ring 104, and two rows of rolling elements 105, 105, and an outer end side portion of the outer peripheral surface of the hub 102 includes: A wheel mounting flange 106 for supporting a wheel (not shown) is provided.
In this specification, in a state where the wheel support hub bearing unit is attached to a vehicle such as an automobile, the portion facing the width direction outer side of the vehicle is referred to as an outer end side portion, and the portion facing the width direction center side Is referred to as an inner end portion. That is, in FIG. 7, the left side is the outer end side, and the right side is the inner end side.

  A step portion 108 having a small outer diameter is formed on the inner end side portion of the hub wheel 102, and the inner ring 103 is fitted into the step portion 108. A cylindrical portion 110 is formed on the inner end side portion of the hub 102 so as to protrude from the inner ring 103 toward the inner end side, and a male screw is formed on the outer peripheral surface of the cylindrical portion 110. The inner ring 103 is fixed integrally with the hub 102 by sandwiching the inner ring 103 between the nut 111 screwed into the male screw and the step surface 112 of the step portion 108. A locking recess 114 is provided at the tip of the cylindrical portion 110, and the nut 111 is prevented from loosening by caulking a portion of the nut 111 corresponding to the locking recess 114 radially inward. Yes.

  A raceway surface is formed on each of the intermediate portion in the axial direction of the outer peripheral surface of the hub 102 and the outer peripheral surface of the inner ring 103 to form inner raceway surfaces 120a and 120b. Further, outer ring raceway surfaces 121a and 121b corresponding to both inner ring raceway surfaces 120a and 120b are formed on the inner peripheral surface of the outer ring 104. Furthermore, between the inner ring raceway surfaces 120a and 120b and the outer ring raceway surfaces 121a and 121b, a plurality of rolling elements 105 are arranged so as to be freely rollable. A suspension device mounting flange 117 is provided on the outer peripheral surface of the outer ring 104 at an end portion on the side away from the wheel mounting flange 106.

In order to assemble such a wheel support hub bearing unit 101 to an automobile, the outer ring 104 is fixed to the suspension device by the suspension device mounting flange 117 formed on the outer peripheral surface of the outer ring 104, and the wheel is attached to the wheel mounting flange 106. Fix it. As a result, the wheel is supported rotatably by the wheel support hub bearing unit 101 with respect to the suspension device.
In the case of the wheel support hub bearing unit 101 having the above-described structure, an operation of forming the locking recess 114 at the tip of the cylindrical portion 110 and an operation of caulking a part of the nut 111 radially inward are necessary. become. Therefore, in recent years, the conventional nut system has been developed for the purpose of reducing the wheel support hub bearing unit by reducing the parts cost and assembly cost, and reducing the size and weight of the wheel support hub bearing unit by reducing the size of the parts. In addition, a caulking wheel support hub bearing unit as shown in FIG.

  In the wheel supporting hub bearing unit of FIG. 8, a caulking portion formed by caulking and expanding the cylindrical portion 110 projecting to the inner end side of the inner ring 103 at the inner end side portion of the hub 102 radially outward. The inner ring 103 is pressed against the step surface 112 of the step portion 108 by 118, and the inner ring 103 is integrally fixed to the hub 102. In this case, since the inner ring 103 is fixed to the hub 102 by caulking, there are advantages in that the cost can be reduced by reducing the component cost and the assembly cost, and the weight and space can be saved. In FIG. 8, the same reference numerals as in FIG. 7 are assigned to the same or corresponding parts as in FIG.

As a material constituting the outer ring 104 and the hub 102, structural carbon steel such as Japanese Industrial Standards S53C and SAE1055 is often used. Since the outer ring raceway surfaces 121a and 121b and the inner ring raceway surfaces 120a and 120b are repeatedly subjected to a high surface pressure from the rolling element 105, a hardened layer by induction hardening is provided so as to have sufficient rolling fatigue life and wear resistance. Is formed. In addition, the portions other than the outer ring raceway surfaces 121a and 121b of the outer ring 104 and the portions other than the inner ring raceway surface 120a of the hub 102 are used in a hot forged state from the viewpoint of workability (hereinafter, The part in such a state is referred to as “non-tempered part”).
JP-A-10-324951 JP 2002-332535 A JP 2002-363700 A

  In recent years, in order to improve the fuel efficiency and driving performance of automobiles, there has been an increasing demand for weight reduction of hub bearing units for supporting wheels. For example, it is considered to further reduce the thickness of flanges for mounting wheels and suspension devices. Yes. However, when the flange is simply thinned, the stress applied to the flange increases, and there is a concern that the strength of the flange is insufficient and fatigue failure is likely to occur.

In particular, a bending stress is applied to the base portion of the flange provided on the member to which the wheel is attached while rotating. In addition, since a torsional stress is applied to the flange as the wheel rotates, fatigue failure occurs if sufficient strength cannot be ensured.
Also, the flange is formed with a through hole for inserting a stud or bolt for attaching the wheel and the disk rotor, but the strength of the flange is reduced when the thickness is reduced, so that the wheel is attached to the flange. When tightening the stud and nut, or tightening the bolt inserted through the through hole, there is a concern that the peripheral part of the through hole in which the base end portion of the stud of the flange is fitted is likely to be deformed. The

  When the peripheral portion of the through hole is deformed, the perpendicularity with respect to the rotation center of the hub of the disk rotor attached to the flange is deteriorated. That is, both side surfaces of the disk rotor, which is the surface to be braked, should be perpendicular to the center of rotation of the hub. As a result, both side surfaces of the disk rotor are displaced in the axial direction with rotation, and vibration occurs. Even if the amplitude of vibration caused by such a cause is about several tens of μm, vibration called judder may occur at the time of braking, and riding comfort and durability of the hub bearing unit are lowered. Therefore, when the flange is thinned to reduce the weight, sufficient fatigue strength, yield strength, etc. are indispensable in the non-heat treated portion.

However, in the case of a member having a flange as described above, it is necessary to accurately process a through hole for inserting a stud or bolt for attaching a wheel or a suspension device. When the hardness is increased, the workability is remarkably lowered and the productivity is greatly deteriorated.
In addition, in the caulking type wheel support hub bearing unit, in addition to applying an appropriate preload, it is necessary to form a caulking portion for preventing the inner ring fitted on the hub from coming out by plastic working. is there. If the hardness of the caulking part increases and the plastic workability decreases, it becomes difficult to apply an appropriate preload, or the cold workability deteriorates, and the soundness of the caulking part may be impaired. Concerned.

From the above viewpoint, in the wheel bearing hub bearing unit, not only the inner ring raceway surface and the outer ring raceway surface that are subject to rolling fatigue, but also other non-heat treated parts have sufficient strength and processing after hot forging. Sexuality is required.
In general, the strength of steel has a good correlation with the material hardness. For example, if the hardness after hot forging is improved using a high carbon steel containing 0.7% by mass or more of carbon, the strength is increased. It is possible to improve. However, on the other hand, the workability is remarkably lowered, and the cost is inevitably increased. In this case, in the caulking type hub bearing unit, the plastic workability of the caulking portion is lowered, and the caulking process itself becomes difficult.

  In Patent Document 1, as main alloy components, 0.5 to 0.7% by mass of carbon, 0 to 0.6% by mass of silicon, 0.4 to 1.2% by mass of manganese, and 0.8% of vanadium are disclosed. An alloy steel for rolling bearings containing 0.5 to 0.2% by mass and a hub bearing unit are disclosed. However, although the tensile strength and the yield strength of the alloy steel for rolling bearings are disclosed, the functions and quality required for the hub bearing unit such as workability and rolling fatigue life are not considered.

  In Patent Document 2, as main alloy components, carbon is 0.5 to 0.7 mass%, silicon is 0.5 to 0.9 mass%, manganese is 0.5 to 1.0 mass%, 0.4% by mass or less of chromium, 0.01 to 0.15% by mass of vanadium, and C% + 1 / 7Si% + 1 / 5Mn% + 1 / 9Cr% -5 / 7S% + V% A high-strength induction hardening steel with excellent machinability having a carbon equivalent Ceq of 0.75 to 0.9 is disclosed.

However, although the hardness of the non-heat treated part is mentioned, the yield strength does not depend only on the hardness but also strongly depends on the microstructure or the like. There are cases in which it is not always possible to meet the weight reduction due to the increase in the weight. Further, no consideration is given to the hardness of the raceway surface, the depth of the hardened layer, and the like.
Furthermore, Patent Document 3 contains 0.5 to 0.7% by mass of carbon, 0.6 to 1.2% by mass of silicon, and 0.6 to 1.0% by mass of manganese as alloy elements. And L calculated by the formula 11271C% + 5796Si% + 2665Mn% -6955 is 5000 or more, and H calculated by the formula 48.0C% + 5.7Si% + 11.5Mn% -16.2 is 23-25. A certain rolling component having excellent workability, fatigue strength, and rolling fatigue life is disclosed. However, only the hardness of the non-tempered part and the surface hardness of the hardened layer are mentioned.

  Thus, the thing of patent documents 1-3 does not fully satisfy both the intensity | strength and workability of a non-tempered part. Further, since the hub bearing unit is subjected to rolling fatigue on the inner ring raceway surface and the outer ring raceway surface in the same manner as a general rolling bearing, a sufficient rolling fatigue life is required in the hardened layer of the raceway surface. No. 3 hardly considers the rolling fatigue life of the hardened layer on the raceway surface.

Furthermore, in the case of a hub bearing unit, the hardness, structure, and strength vary depending on the heating and cooling conditions during forging. Therefore, to improve product quality, the hub bearing unit is manufactured by forging. It is also necessary to consider the hardness and microstructure of the steel.
Accordingly, an object of the present invention is to solve the above-described problems of the prior art and to provide a wheel support hub bearing unit that is lightweight and has a long life in addition to excellent productivity.

  In order to solve the above problems, the present invention has the following configuration. That is, the hub support unit for wheel support according to claim 1 of the present invention includes an inner member having a raceway surface on an outer peripheral surface and a raceway surface facing the raceway surface of the inner member. An outer member disposed on the outer side, and a plurality of rolling elements arranged to be freely rollable between the raceway surface of the inner member and the raceway surface of the outer member, and the inner side In the wheel supporting hub bearing unit, a hardened layer formed by induction hardening is formed on at least one of a part including the raceway surface of the member and a part including the raceway surface of the outer member. And the member in which the said hardened layer was formed among the said outer members is comprised by the alloy steel which satisfies the following four conditions, It is characterized by the above-mentioned.

(Condition 1) Carbon content C% is 0.45 mass% or more and 0.65 mass% or less, silicon content Si% is 0.5 mass% or more and 1 mass% or less, and manganese content Mn% is 0. .2 mass% to 0.6 mass%, chromium content Cr% is 0.4 mass% to 1 mass%, vanadium content V% is 0 mass% or 0 mass% excess 0.2 mass% It is as follows.
(Condition 2) The ratio Cr% / Mn% of chromium content Cr% and manganese content Mn% is 0.8 or more and 3 or less.

(Condition 3) Carbon content C%, silicon content Si%, manganese content Mn%, chromium content Cr%, and vanadium content V% satisfy the following formula (I): .
0.75 ≦ C% + Si% / 10 + Mn% / 5 + 5 × Cr% / 22 + 1.65 × V% ≦ 0.95 (I)
(Condition 4) The carbon content C%, the silicon content Si%, the manganese content Mn%, and the chromium content Cr% satisfy the following formula (II).
(0.2 × C% + 0.14) × (0.64 × Si% + 1) × (4.1 × Mn% + 1) × (2.33 × Cr% + 1) ≧ 1.5 (II )

  Further, the wheel supporting hub bearing unit according to claim 2 of the present invention is the wheel supporting hub bearing unit according to claim 1, wherein the hardened layer has a surface hardness of 650 to 780 in terms of Vickers hardness Hv. Vickers hardness Hv is 500 or more, and the effective hardened layer depth is 1.5 mm or more and 4 mm or less, and the Vickers hardness Hv of the non-heat treated part which is a part where the hardened layer is not formed is 230. The above is 300 or less.

Further, the wheel supporting hub bearing unit according to claim 3 of the present invention is the wheel supporting hub bearing unit according to claim 2, wherein the non-heat treated portion has a ferrite content of 8% or more in area ratio. The prior austenite grain size measured by the method specified in Japanese Industrial Standard JIS G0551 is 20% or less, and the grain size number is 6 or more.
Furthermore, the hub support unit for wheel support of Claim 4 which concerns on this invention is a hub bearing unit for wheel support as described in any one of Claims 1-3, The said hardened layer is Japanese Industrial Standard JISG0551. The prior austenite grain size measured by a specified method is characterized by having a grain size number of 8 or more.

  Furthermore, the manufacturing method of the wheel support hub bearing unit of Claim 5 which concerns on this invention is a method of manufacturing the wheel support hub bearing unit as described in any one of Claims 1-4, Comprising: At least one of the side member and the outer member has a cooling rate of 0.5 ° C./s or more when cooled to 600 ° C. from the temperature at the end of forging when being processed into a predetermined shape by hot forging. 5 ° C./s or less.

Below, the hub bearing unit for wheel support of the present invention will be described in detail focusing on the critical significance of each of the aforementioned numerical values (content of alloying elements in alloy steel, etc.).
[Carbon content]
Carbon (C) is an element that is indispensable for ensuring the hardness of the non-heat treated portion after hot forging and the hardness of the hardened layer after quenching and tempering. 0.45% by mass or more is necessary from the viewpoint of rolling fatigue life, but if it is too much, the hardness after hot forging becomes too high, and the proeutectoid ferrite that becomes a chip breaker is reduced, so that the machinability and punchability are reduced. May decrease. Further, in the caulking type hub bearing unit, the plastic workability of the caulking portion may be deteriorated. Therefore, the C content in the alloy steel needs to be 0.45 mass% or more and 0.65 mass% or less.

[About silicon content]
Silicon (Si) acts as a deoxidizer during steelmaking and has the effect of improving the hardness and hardenability after hot forging. In particular, after quenching and tempering, not only strengthens the martensite structure and improves the rolling fatigue life, but in the non-tempered part, it dissolves in the ferrite and improves the strength of the ferrite structure, yield strength and Has the effect of increasing fatigue strength.
However, if there is too much Si, the hardness after hot forging becomes too high, and the machinability and drillability may be reduced. Further, in the caulking type hub bearing unit, the plastic workability of the caulking portion may be deteriorated. Therefore, Si content in alloy steel needs to be 0.5 mass% or more and 1 mass% or less.

[About manganese content]
Manganese (Mn) acts as a deoxidizer as well as Si, and has the effect of improving the hardness and hardenability after hot forging, so it is necessary to add 0.2% by mass or more. Yes, it is more preferable to add 0.3% by mass or more.
However, if there is too much Mn, the hardness after hot forging becomes too high, and the machinability and drillability may be reduced. Further, in the caulking type hub bearing unit, the plastic workability of the caulking portion may be deteriorated. Therefore, the Mn content in the alloy steel needs to be 0.6% by mass or less, and more preferably 0.55% by mass or less.

[Chromium content]
Chromium (Cr) has the effect of improving the hardness and hardenability after hot forging as well as Si and Mn, strengthening the martensite structure after quenching, and improving the rolling fatigue life. In addition, after hot forging, it has the effect of refining the structure and remarkably improving the balance between the strength and ductility of the non-heat treated part. It has the effect | action which improves the plastic workability of the caulking part accompanying a process. Further, by refining the prior austenite crystal grains, the ferrite is divided, and the balance between strength and workability is remarkably improved. Furthermore, even after induction hardening, it has the effect of suppressing the growth of crystal grains, and has the effect of improving both rolling fatigue life and fatigue strength, so it is necessary to add 0.4 mass% or more, It is more preferable to add 0.45% by mass or more.
However, if there is too much Cr, the hardness after hot forging becomes too high, and the machinability and drillability may be reduced. Further, in the caulking type hub bearing unit, the plastic workability of the caulking portion may be deteriorated. Therefore, the Cr content in the alloy steel needs to be 1% by mass or less.

[Vanadium content]
Vanadium (V) forms a stable carbide or carbonitride in the alloy steel and has an effect of effectively suppressing the growth of old austenite crystal grains during hot forging and induction hardening. ing. Further, by refining the prior austenite crystal grains, the ferrite is divided, and the balance between strength and workability is remarkably improved.
For this reason, V may be added as necessary, but in order to sufficiently obtain the effect, it is preferable to add 0.03% by mass or more. However, if there is too much V, the hardness after hot forging becomes too high, and the machinability and drillability may be reduced. Further, in the caulking type hub bearing unit, the plastic workability of the caulking portion may be deteriorated. Therefore, the V content in the alloy steel is preferably 0.2% by mass or less.

[About the balance of alloy steel]
The balance other than the alloy components described above is substantially iron (Fe), but may contain alloy components other than those described above. Inevitable impurities may include sulfur (S), phosphorus (P), aluminum (Al), titanium (Ti), oxygen (O) and the like.
Since the cleanliness of the alloy steel greatly affects the rolling fatigue life of the wheel bearing hub bearing unit particularly under clean lubrication conditions, the impurity content is preferably low. However, the extreme reduction of the amount of impurities may significantly increase the material cost. Therefore, the cleanliness of the grade that can be used as a bearing material (regulated by JIS G 4805) is not required, and the amount of impurities is not strictly regulated. If the quality (bearing quality) level that satisfies the requirements), there is no problem.

[Ratio Cr% / Mn% of Cr content Cr% and Manganese content Mn%]
If the ratio Cr% / Mn% is 0.8 or more, both the prior austenite crystal grains and proeutectoid ferrite are refined and the structure is densified. As a result, not only the yield strength and fatigue strength of the non-tempered portion, but also the workability such as impact strength, machinability, and plastic workability are greatly improved. However, if the ratio Cr% / Mn% is too large, the amount of pro-eutectoid ferrite may increase and the effect of improving the strength may not be obtained.

[Formula (I)]
C, Si, Mn, Cr and V are all elements that increase the hardness of the alloy steel after hot forging, and have the effect of improving the strength and fatigue strength of the non-tempered part. However, if the non-tempered part is harder than necessary, there is a disadvantage in that the cutting property after hot forging, the drilling property, and the plastic workability are lowered, resulting in a significant cost increase. Strictly speaking, the hardness of the alloy steel after hot forging depends on the cooling rate after hot forging, but in order to make the hardness of the alloy steel suitable, the content of the alloy component is It is necessary to satisfy Formula (I).

[About Formula (II)]
In the hardened layer formed on the part including the raceway surface, sufficient surface hardness and hardened layer depth are required from the viewpoint of rolling fatigue life, but if the alloy steel does not have sufficient hardenability, An incompletely hardened structure may be generated and the rolling fatigue life may be reduced. If the content of the alloy component satisfies the formula (II), a hardened layer having sufficient surface hardness and effective hardened layer depth is obtained, and a sound hardened layer having no incompletely quenched structure is formed.

[Hardness of non-heat treated part]
As mentioned above in the section of “Formula (I)”, if the non-heat treated part is harder than necessary, the machinability, drilling ability and plastic workability after hot forging are lowered, resulting in a significant increase in cost. There is an inconvenience. Therefore, the Vickers hardness Hv of the non-heat treated part after forging is preferably 230 or more and 300 or less.

[Surface hardness of hardened layer and effective hardened layer depth]
The quality of the hardened layer varies depending on the conditions of induction hardening, as is the case with the quality of the non-tempered part, but in order to ensure a sufficient rolling fatigue life, the surface hardness of the hardened layer is Vickers hardness. It is preferable to set it as 650 or more and 780 or less in Hv, and it is preferable that the effective hardened layer depth (the range of the part where Vickers hardness Hv is 500 or more) of a hardened layer shall be 1.5 mm or more.
However, if an attempt is made to obtain an effective hardened layer depth that is greater than necessary, high hardenability is required for the alloy steel, and workability may be sacrificed, or depending on the heating conditions, etc., the grain size of the hardened layer may become coarse. Since the rolling fatigue life may be insufficient due to the invitation, the effective hardened layer depth is preferably 4 mm or less.

[The former austenite grain size of the hardened layer]
As described above in the section “Surface hardness and effective hardened layer depth of hardened layer”, rolling fatigue life may be insufficient if the old austenite crystal grains of hardened layer are coarse. It is preferable that the prior austenite grain size measured by the method prescribed in the industrial standard JIS G0551 is 8 or more in terms of grain size number.

[Regarding ferrite content and prior austenite grain size in non-tempered part]
As described above in the section “Ratio Cr% / Mn% of Cr content Cr% and manganese content Mn%”, there is a problem in strength when the ferrite content in the non-tempered part is large. Since there exists a possibility, it is preferable that it is 8% or more and 20% or less by area ratio. In addition, if the prior austenite crystal grains in the non-tempered part are fine, the structure is densified, and not only the yield strength and fatigue strength of the non-tempered part, but also the workability such as impact strength, machinability, plastic workability, etc. Greatly improved. Therefore, it is preferable that the prior austenite crystal grain size measured by the method prescribed in Japanese Industrial Standard JIS G0551 is 6 or more in terms of grain size number.

[Method of manufacturing wheel bearing hub bearing unit]
The optimum forging conditions for obtaining the above quality are preferably as follows from the viewpoint of workability. That is, a condition in which hot forging is performed at a temperature of 950 ° C. or more and 1200 ° C. or less, and a cooling rate from the temperature at the end of forging to cooling to 600 ° C. is 0.5 ° C./s or more and 5 ° C./s or less. It is. If the cooling rate is slower than 0.5 ° C / second, the hardness of the non-heat treated part described above is insufficient, and if it is faster than 5 ° C / second, the hardness increases more than necessary and the workability decreases. Or cracks.

  The wheel support hub bearing unit of the present invention is lightweight and has a long life in addition to excellent productivity.

An embodiment of a hub bearing unit for supporting a wheel according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a sectional view showing the structure of an embodiment of a wheel supporting hub bearing unit according to the present invention.
The wheel support hub bearing unit 1 shown in FIG. 1 includes a hub 2, an inner ring 3, an outer ring 4, and two rows of rolling elements 5, 5. Is provided with a wheel mounting flange 6 for supporting a wheel (not shown).

  A step portion 8 having a small outer diameter is formed on the inner end side portion of the hub wheel 2, and the inner ring 3 is fitted into the step portion 8. A cylindrical portion 10 is formed on the inner end side portion of the hub 2 so as to protrude from the inner ring 3 toward the inner end side, and a male screw is formed on the outer peripheral surface of the cylindrical portion 10. The inner ring 3 is fixed to the hub 2 integrally by sandwiching the inner ring 3 between the nut 11 screwed into the male screw and the step surface 12 of the step portion 8.

  A locking recess 14 is provided at the tip of the cylindrical portion 10, and the nut 11 is prevented from loosening by caulking a portion of the nut 11 corresponding to the locking recess 14 radially inward. Yes. Moreover, what fixed the inner ring | wheel 3 and the hub 2 integrally is corresponded to the inner member which is a structural requirement of this invention, and the outer ring | wheel 4 is equivalent to the outer member which is a structural requirement of this invention.

A raceway surface is formed on each of the axially intermediate portion of the outer peripheral surface of the hub 2 and the outer peripheral surface of the inner ring 3 to form inner ring raceway surfaces 20a and 20b. Further, outer ring raceway surfaces 21 a and 21 b corresponding to both inner ring raceway surfaces 20 a and 20 b are formed on the inner peripheral surface of the outer ring 4. Furthermore, between the inner ring raceway surfaces 20a and 20b and the outer ring raceway surfaces 21a and 21b, a plurality of rolling elements 5 are arranged so as to be freely rollable. A suspension device mounting flange 17 is provided on an outer peripheral surface of the outer ring 4 at an end portion on the side away from the wheel mounting flange 6.
In order to assemble such a wheel support hub bearing unit 1 in an automobile, the outer ring 4 is fixed to the suspension device by the suspension device mounting flange 17 formed on the outer peripheral surface of the outer ring 4, and the wheel is attached to the wheel mounting flange 6. Fix it. As a result, the wheel is supported rotatably by the wheel support hub bearing unit 1 with respect to the suspension device.

In this wheel support rolling bearing unit 1, the hub 2, the inner ring 3, and the outer ring 4 are made of alloy steel that satisfies the following four conditions.
(Condition 1) Carbon content C% is 0.45 mass% or more and 0.65 mass% or less, silicon content Si% is 0.5 mass% or more and 1 mass% or less, and manganese content Mn% is 0. .2 mass% to 0.6 mass%, chromium content Cr% is 0.4 mass% to 1 mass%, vanadium content V% is 0 mass% or 0 mass% excess 0.2 mass% It is as follows.
(Condition 2) The ratio Cr% / Mn% of chromium content Cr% and manganese content Mn% is 0.8 or more and 3 or less.

(Condition 3) Carbon content C%, silicon content Si%, manganese content Mn%, chromium content Cr%, and vanadium content V% satisfy the following formula (I): .
0.75 ≦ C% + Si% / 10 + Mn% / 5 + 5 × Cr% / 22 + 1.65 × V% ≦ 0.95 (I)
(Condition 4) The carbon content C%, the silicon content Si%, the manganese content Mn%, and the chromium content Cr% satisfy the following formula (II).
(0.2 × C% + 0.14) × (0.64 × Si% + 1) × (4.1 × Mn% + 1) × (2.33 × Cr% + 1) ≧ 1.5 (II )

  Since a high surface pressure is repeatedly applied from the rolling elements 5 to the inner ring raceway surface 20a of the hub 2, the inner ring raceway surface 20b of the inner ring 3, and the outer ring raceway surfaces 21a and 21b of the outer ring 4, a sufficient rolling fatigue life is obtained. A hardened layer (not shown) is formed by induction hardening so as to have both wear resistance and wear resistance. Further, a hardened layer is not formed on the inner peripheral surface of the outer ring 4 other than the outer ring raceway surfaces 21a and 21b, and on the outer peripheral surface of the hub 2 other than the inner ring raceway surface 20a. From the point of view, it is considered as a non-tempered part that is still hot forged. However, the hardened layer may be formed up to the peripheral portions of the outer ring raceway surfaces 21a and 21b and the peripheral portion of the inner ring raceway surface 20a.

This hardened layer has a surface hardness of 650 to 780 in terms of Vickers hardness Hv, and an effective hardened layer depth of 1.5 to 4 mm in which the Vickers hardness Hv is 500 or more. The hardened layer has an old austenite grain size measured by the method defined in Japanese Industrial Standards JIS G0551 and a grain size number of 8 or more.
Moreover, the Vickers hardness Hv of the non-tempered part is 230 or more and 300 or less. The ferrite content is 8% or more and 20% or less in terms of area ratio, and the prior austenite grain size measured by the method defined in Japanese Industrial Standard JIS G0551 is 6 or more in grain size number.

Furthermore, the yield strength of the non-tempered part is 500 MPa or more, the 10 ⁷ cycle fatigue strength is 400 MPa or more, and it has better workability and higher durability than structural carbon steel such as S53C and SAE1055 of Japanese Industrial Standards. ing.
With such a configuration, the hub 2, the inner ring 3, and the outer ring 4 have excellent workability, strength, and rolling fatigue life. Since the strength is excellent, the flanges 6 and 17 can be thinned. Therefore, the wheel bearing hub bearing unit 1 is lightweight and has a long life in addition to being excellent in productivity.
In addition, this embodiment shows an example of this invention and this invention is not limited to this embodiment. For example, in the present embodiment, as an example of the wheel support hub bearing unit, the nut type as described above is illustrated, but a caulking type wheel support hub bearing unit as shown in FIG. 8 may be used.

〔Example〕
Hereinafter, the present invention will be described more specifically with reference to examples. Various wheel support hub bearing units (reference number: 49BWKH) having the same structure as the wheel support hub bearing unit 1 described above except that the hub, inner ring, and outer ring are made of the alloy steel shown in Table 1. ) Was prepared and various performances were evaluated. The formula value (I) shown in Table 1 means a value (C% + Si% / 10 + Mn% / 5 + 5 × Cr% / 22 + 1.65 × V%) calculated from the formula (I) described above. The formula value (II) is a value ((0.2 × C% + 0.14) × (0.64 × Si% + 1) × (4.1 × Mn%) calculated from the above formula (II). +1) × (2.33 × Cr% + 1)).

  First, a test piece was collected from the flange portion of the hub, and various physical properties and various performances related to the non-heat treated portion were evaluated. For the hub, inner ring, and outer ring, the material cut out from the steel bar is heated to 950 to 1200 ° C. by high frequency induction heating, hot forging mainly including upsetting is performed, and furnace cooling, air cooling, fan forced air cooling, etc. Manufactured by cooling. And the hardness of the non-tempered part was changed by changing various cooling rates. The temperature of the member was measured with an infrared radiation thermometer from the end of forging until it was cooled to 600 ° C., and the cooling rate was calculated from the measured value and the cooling time (see Tables 2 and 3).

[Measurement of hardness of non-tempered part, ferrite content, and prior austenite grain size]
The hardness of the non-heat treated part was measured using a Vickers hardness meter after cutting out the smooth part of the flange of the hub, embedding it in resin, and finishing and polishing the cut surface with emery paper. Further, after etching the same surface as the surface where the hardness was measured with a picral corrosion solution, the content (area ratio) of pro-eutectoid ferrite and the prior austenite grain size were measured by performing microstructure observation and image processing.

[Measurement method of yield strength, fatigue strength, and Charpy impact value of non-tempered part]
The yield strength of the non-heat treated part was measured using a JIS No. 14A test piece (diameter 8.5 mm) cut out from the flange of the hub. Further, the fatigue strength of the non-heat treated part was measured using an Ono type rotating bending fatigue tester. The test conditions are a rotation speed of 3700 min ⁻¹ and a rotation speed of 10 ⁷ cycles. The test piece used was a No. 1-8 test piece defined in JIS Z2271, which was cut out from the flange of the hub. Further, the Charpy impact value of the non-tempered portion was measured using a U-notched test piece cut out from the hub flange. The notch depth is 2 mm.

[Regarding the method for evaluating the turning performance of non-heat treated parts]
Grinding was performed under the following conditions in accordance with the bite test method defined in JIS B 4011. The time until the wear amount on the flank face of the cutting tool reached 0.2 mm was defined as the tool life, and the turning performance was evaluated by the length of the tool life.
Tool type: P10 defined in JIS B 4053
Cutting speed: 150 m / s
Feed amount: 0.2 mm / rev
Cutting depth: 0.5mm

[About the evaluation method of drilling property of non-heat treated parts]
Drilling was carried out under the following conditions, and the drillability was evaluated by the number of holes formed before the drilling became impossible.
Tool type: SKH51
Cutting speed: 30 m / min
Feed amount: 0.2 mm / rev
Drilling depth: 15mm

[Evaluation method for cold workability of non-heat treated parts]
A disk-shaped test piece (diameter: 10 mm) cut out from the flange of the hub is subjected to cold compression (forging) with an upsetting rate of 20 to 80%, and the limit upsetting rate at which cracks occur on the circumference Was used to evaluate the cold workability.
Tables 2 and 3 show the evaluation results of various physical properties and various performances related to the non-heat treated part. As can be seen from Tables 2 and 3, in each example, since the prior austenite grains and proeutectoid ferrite are refined by suitable alloy components, workability (turnability, drillability, cold workability) and The balance with strength (yield strength, fatigue strength, Charpy impact value) was excellent.

Next, a rotation test was performed on the wheel-supporting rolling bearing unit to evaluate its life. At that time, the suspension device mounting flange provided on the outer peripheral surface of the outer ring was fixed, a load was applied to the wheel mounting flange provided on the outer peripheral surface of the hub, and a rotation test was performed under the following conditions. . Then, the occurrence of flaking was detected by measuring the vibration of the hub and the outer ring, and the life was evaluated based on the total number of revolutions until flaking occurred on the inner ring raceway surface or the outer ring raceway surface. The results are shown in Tables 4 and 5. In addition, the numerical value of the lifetime shown to Table 4, 5 is shown by the relative value when the lifetime of the comparative example 3A is set to 1.
Radial load: 7000N
Axial load: 5000N
Rotational speed: 300 min ^-1
In addition, about Example 3, what has a hardened layer from which surface hardness etc. differed by changing the conditions of induction hardening (Example 3A, 3B, 3C) was prepared, and it used for the rotation test, respectively. The same applies to Comparative Examples 3 and 4.

As can be seen from Tables 4 and 5, the wheel-supporting rolling bearing unit of the example had a longer life than the wheel-supporting rolling bearing unit of the comparative example.
Next, the correlation between the Vickers hardness Hv and the yield strength of the non-tempered portion is shown in FIG. 2, the correlation between the Vickers hardness Hv of the non-tempered portion and the ferrite content is shown in FIG. Fig. 4 shows the correlation between Vickers hardness Hv and turning performance (tool life), and Fig. 5 shows the correlation between Vickers hardness Hv of non-heat-treated parts and drillability (number of holes formed before drilling becomes impossible). , Respectively.

As can be seen from each graph, in the same hardness, both the yield strength and the ferrite content were superior to the comparative example. And since yield strength 500MPa and 10 ⁷ cycle fatigue strength 400MPa can be sufficiently achieved without significantly reducing workability (turnability, drillability), it is advantageous for weight reduction of the wheel bearing hub bearing unit. is there.
FIG. 6 shows the correlation between the prior austenite grain size and the lifetime of the hardened layer formed on the raceway surface. In addition to the alloy components, the surface hardness and hardened layer depth were optimized, and further, the coarsening of the prior austenite crystal grains was suppressed, so the wheel support rolling bearing unit of the example was more than the wheel support rolling bearing unit of the comparative example. The service life was significantly longer.

It is sectional drawing which shows the structure of one Embodiment of the wheel bearing hub bearing unit which concerns on this invention. It is a graph which shows the correlation with the Vickers hardness Hv and the yield strength of a non-tempered part. It is a graph which shows the correlation with Vickers hardness Hv of a non-tempered part, and content of a ferrite. It is a graph which shows the correlation with the Vickers hardness Hv of a non-tempered part, and turning property. It is a graph which shows the correlation with the Vickers hardness Hv of a non-tempered part, and drilling property. It is a graph which shows the correlation with the old austenite grain size of the hardened layer formed in the raceway surface, and the lifetime of the rolling bearing unit for wheel support. It is sectional drawing which shows the structure of the conventional wheel bearing hub bearing unit. It is sectional drawing which shows the structure of the conventional wheel bearing hub bearing unit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Wheel support hub bearing unit 2 Hub 3 Inner ring 4 Outer ring 5 Rolling element 6 Wheel attachment flange 17 Suspension attachment flange 20a Inner ring raceway surface 20b Inner ring raceway surface 21a Outer ring raceway surface 21b Outer ring raceway surface

Claims (5)

An inner member having a raceway surface on an outer peripheral surface, an outer member having a raceway surface facing the raceway surface of the inner member, and disposed on the outer side of the inner member; and a raceway surface of the inner member And a plurality of rolling elements arranged to be freely rollable between the raceway surface of the outer member, a flange provided on at least one of the inner member and the outer member, to which a wheel or a suspension device is attached, And a wheel bearing hub bearing in which a hardened layer formed by induction hardening is formed on at least one of the inner member including the raceway surface and the outer member including the raceway surface. In the unit
Of the inner member and the outer member, the member on which the hardened layer is formed is made of an alloy steel that satisfies the following four conditions.
(Condition 1) Carbon content C% is 0.45 mass% or more and 0.65 mass% or less, silicon content Si% is 0.5 mass% or more and 1 mass% or less, and manganese content Mn% is 0. .2 mass% to 0.6 mass%, chromium content Cr% is 0.4 mass% to 1 mass%, vanadium content V% is 0 mass% or 0 mass% excess 0.2 mass% It is as follows.
(Condition 2) The ratio Cr% / Mn% of chromium content Cr% and manganese content Mn% is 0.8 or more and 3 or less.
(Condition 3) Carbon content C%, silicon content Si%, manganese content Mn%, chromium content Cr%, and vanadium content V% satisfy the following formula (I): .
0.75 ≦ C% + Si% / 10 + Mn% / 5 + 5 × Cr% / 22 + 1.65 × V% ≦ 0.95 (I)
(Condition 4) The carbon content C%, the silicon content Si%, the manganese content Mn%, and the chromium content Cr% satisfy the following formula (II).
(0.2 × C% + 0.14) × (0.64 × Si% + 1) × (4.1 × Mn% + 1) × (2.33 × Cr% + 1) ≧ 1.5 (II )   The hardened layer has a surface hardness of 650 to 780 in terms of Vickers hardness Hv, an effective hardened layer depth of Vickers hardness Hv of 500 or more, and a thickness of 1.5 mm to 4 mm. 2. The wheel bearing hub bearing unit according to claim 1, wherein the Vickers hardness Hv of the non-heat treated portion which is a portion not formed is 230 or more and 300 or less.   The non-tempered part has a ferrite content of 8% or more and 20% or less in terms of area ratio, and the prior austenite grain size measured by the method defined in Japanese Industrial Standard JIS G0551 is 6 or more in grain size number. The wheel support hub bearing unit according to claim 2 characterized by things.   The wheel according to any one of claims 1 to 3, wherein the hardened layer has a grain size number of 8 or more as a prior austenite grain size measured by a method defined in Japanese Industrial Standard JIS G0551. Support hub bearing unit.   5. A method of manufacturing the wheel supporting hub bearing unit according to claim 1, wherein at least one of the inner member and the outer member is processed into a predetermined shape by hot forging. The method for producing a wheel bearing hub bearing unit, characterized in that a cooling rate from the temperature at the end of forging to cooling to 600 ° C. is 0.5 ° C./s or more and 5 ° C./s or less. .

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