Wheel bearing device

Abstract

To provide a wheel bearing device capable of suppressing deformation of the raceway surface of an inner ring and a tensile stress in the circumferential direction while preventing the creep of the inner ring, improving the ease of assembly, and maintaining a bearing preload.SOLUTION: A wheel bearing device includes: an outer member having an outer raceway surface; an inner member that comprises a hub wheel 3 having a small diameter stepped portion 3a and an inner ring 4 fixed to the small diameter stepped portion 3a, has an outer-side inner raceway surface 4a on the hub wheel 3 and an inner-side inner raceway surface on the inner ring 4; and double row rolling elements rollably received between both raceway surfaces of the outer member and the inner member. The inner ring 4 has a hardened portion 41 quenched along the inner-side inner raceway surface 4a. The inner ring 4 and hub ring 3 are fixed by press-cut joining and interference fit with an interference of 0.005 mm to 0.020 mm. The press-cut joining is joining of a hardened serration 32 formed on the outer peripheral surface of the small-diameter stepped portion 3a and an unhardened inner-side inner peripheral surface of the inner ring 4.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a wheel bearing device. [Background technology]

[0002] There is a so-called third-generation bearing device for a wheel that includes an outer ring, a hub ring having a small-diameter stepped portion on its outer periphery, an inner ring fixed to the small-diameter stepped portion, and rolling elements. In third-generation bearing devices for a wheel, the method of fixing the inner ring to the small-diameter stepped portion is generally a super tight fit (see Patent Document 1) or crimping of the hub ring end (see Patent Document 2) from the viewpoints of preventing creep of the inner ring, improving assembly ease, and maintaining bearing preload. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-57717 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-105343 Summary of the Invention [Problem to be solved by the invention]

[0004] However, fixing the inner ring by tight fitting or crimping can cause deformation of the raceway surface of the inner ring or excessive tensile stress in the circumferential direction, resulting in problems such as reduced durability of the wheel bearing device.

[0005] The present invention aims to provide a wheel bearing device that can prevent creep of the inner ring, improve assembly, maintain bearing preload, and suppress deformation of the inner ring raceway surface and circumferential tensile stress. [Means for solving the problem]

[0006] The wheel bearing device of the present invention comprises an outer member having a double-row outer raceway on its inner circumference, a hub ring having a small-diameter step extending axially on its outer circumference, and an inner ring fixed to the small-diameter step of the hub ring, wherein the hub ring has an outer-side inner raceway surface facing the outer-side outer raceway surface, and the inner ring has an inner-side inner raceway surface facing the inner-side outer raceway surface, and double-row rolling elements accommodated so as to roll freely between the raceway surfaces of the outer member and the inner member, wherein the inner ring has a hardened portion hardened along the inner-side inner raceway surface, and the inner ring and the hub ring are fixed together by press-cut joining and an interference fit with an interference of 0.005 mm or more and 0.020 mm or less. [Effects of the Invention]

[0007] According to the present invention, in a wheel bearing device, it is possible to prevent creep of the inner ring, improve assembly, and maintain bearing preload, while suppressing deformation of the inner ring raceway surface and circumferential tensile stress, thereby improving the durability of the wheel bearing device. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view of a wheel bearing device for a driving wheel according to an embodiment; [Figure 2] 1A and 1B are diagrams illustrating the joining form of the inner ring and the hub ring, in which FIG. 1A is a diagram showing the area around the small diameter step of the inner ring and the hub ring before joining, FIG. 1B is a diagram showing the area around the small diameter step of the inner ring and the hub ring during joining, and FIG. 1C is a diagram showing the area around the small diameter step of the inner ring and the hub ring after joining. [Figure 3] 10A and 10B are diagrams illustrating another joining form of the inner ring and the hub ring, in which FIG. 10A shows the area around the small diameter step of the inner ring and the hub ring before joining, FIG. 10B shows the area around the small diameter step of the inner ring and the hub ring during joining, and FIG. 10C shows the area around the small diameter step of the inner ring and the hub ring after joining. [Figure 4] 1 is a cross-sectional view of a wheel bearing device for a driven wheel according to an embodiment; DETAILED DESCRIPTION OF THE INVENTION

[0009] [Overall configuration of wheel bearing device] The overall configuration of the wheel support bearing device 1 will be described using Figure 1. In the following description, the inner side refers to the vehicle body side of the wheel support bearing device 1 when attached to the vehicle body, and the outer side refers to the wheel side of the wheel support bearing device 1 when attached to the vehicle body. The axial direction refers to the direction along the rotation axis A of the wheel support bearing device 1.

[0010] 1, the wheel bearing device 1 rotatably supports a wheel in a suspension system of a vehicle such as an automobile. The wheel bearing device 1 includes an outer ring 2, a hub ring 3, an inner ring 4, rolling elements 5, an inner seal member 6, and an outer seal member 7.

[0011] The outer ring 2, which is the outer member, supports the hub ring 3 and the inner ring 4. The inner peripheral surface of the inner end 2g of the outer ring 2 is provided with an inner fitting surface 2b into which an inner seal member 6 is fitted. The inner peripheral surface of the outer end 2f of the outer ring 2 is provided with an outer fitting surface 2c into which an outer seal member 7 is fitted. The outer peripheral surface 2e of the outer ring 2 is integrally formed with a vehicle body mounting flange 2d for mounting to a knuckle of a suspension system (not shown). The inner peripheral surface of the outer ring 2 is provided with double-row outer raceways 2a / 2a on both the inner and outer sides in the circumferential direction.

[0012] The inner member is composed of a hub ring 3 and an inner ring 4. The hub ring 3 rotatably supports a vehicle wheel (not shown). The inner end of the outer peripheral surface of the hub ring 3 is provided with a small-diameter step 3a that extends axially and is reduced in diameter. A wheel mounting flange 3b for mounting a wheel is integrally formed with the outer end of the hub ring 3. Hub bolts 3c are press-fitted into the wheel mounting flange 3b for fastening the hub ring 3 to the wheel or brake device. Note that the wheel mounting flange 3b may be provided with tapped holes for fastening the hub bolts. Furthermore, the outer peripheral surface of the hub ring 3 is provided with an inner raceway surface 3d that faces the outer outer raceway surface 2a. In other words, the hub ring 3 forms the inner raceway surface 3d on the outer side of the inner member. A sliding contact surface 3e with which the outer seal member 7 slides is provided on the base side of the wheel mounting flange 3b of the hub ring 3.

[0013] The inner ring 4 is fixed to the small diameter step portion 3a of the hub ring 3. The inner ring 4 applies preload to the rolling elements 5. The outer peripheral surface of the inner ring 4 is provided with an inner raceway surface 4a that faces the inner-side outer raceway surface 2a. In other words, the inner ring 4 forms the inner raceway surface 4a on the inner side of the inner member. In addition, the outer peripheral surface of the inner-side end portion 4c of the inner ring 4 is provided with a fitting surface 4b into which an inner-side seal member 6 is fitted.

[0014] The rolling elements 5 are composed of balls. The inner-side rolling elements 5 and the outer-side rolling elements 5 are each held in a cage 51. The inner-side rolling elements 5 are rollably sandwiched between the inner raceway surface 4a of the inner ring 4 and the inner-side outer raceway surface 2a of the outer ring 2. The outer-side rolling elements 5 are rollably sandwiched between the inner raceway surface 3d of the hub ring 3 and the outer-side outer raceway surface 2a of the outer ring 2. In other words, the inner-side rolling elements 5 and the outer-side rolling elements 5 are rollably housed between the raceway surfaces of the outer member and the inner member. In this way, in the wheel bearing device 1, the outer ring 2, the hub ring 3, the inner ring 4, and the double-row rolling elements 5 form a double-row angular contact ball bearing. Note that the wheel bearing device 1 may be configured as a double-row tapered roller bearing instead of a double-row angular contact ball bearing.

[0015] The inner seal member 6 and the outer seal member 7 are seal members that close the open ends of the annular space S formed by the outer member and the inner member. The inner seal member 6 is attached to the inner open end of the annular space S formed between the outer ring 2 and the inner ring 4. On the other hand, the outer seal member 7 is attached to the outer open end of the annular space S formed between the outer ring 2 and the hub wheel 3.

[0016] [Inner ring fixing structure] The inner ring 4 is fixed to the small diameter step 3a of the hub ring 3 by press-cut joining and an interference fit with an interference of 0.005 mm to 0.020 mm. The press-cut joining can be performed, for example, by joining hardened serrations formed on the outer peripheral surface of the small diameter step 3a to the unhardened inner peripheral surface of the inner ring 4.

[0017] Figure 2 is a diagram explaining the joining form between the inner ring 4 and the hub ring 3, where (a) is a diagram showing the area around the small diameter step 3a of the inner ring 4 and the hub ring 3 before joining, (b) is a diagram showing the area around the small diameter step 3a of the inner ring 4 and the hub ring 3 during joining, and (c) is a diagram showing the area around the small diameter step 3a of the inner ring 4 and the hub ring 3 after joining.

[0018] As shown in FIG. 2(a), the inner ring 4 has a hardened portion 41 that is hardened along the inner side inner raceway surface 4a, an inner side inner peripheral surface 42 located on the inner side of the inner peripheral surface, and an outer side inner peripheral surface 43 located on the outer side of the inner peripheral surface.

[0019] The hardened portion 41 is formed by partially hardening the inner raceway surface 4a in a heat treatment process. In the heat treatment process, hardening is performed using a method that allows the hardening depth to be set, such as induction hardening. The hardened portion 41 improves the surface hardness and strength of the inner raceway surface 4a, thereby improving the rolling fatigue life of the inner raceway surface 4a.

[0020] On the other hand, portions of the inner ring 4 other than the hardened portion 41, including the inner inner peripheral surface 42 and the outer inner peripheral surface 43, are unhardened. Therefore, the cold workability and mechanical strength, such as toughness, of the material can be maintained. The inner inner peripheral surface 42 has a smaller diameter than the outer inner peripheral surface 43. The axial length L1 of the outer inner peripheral surface 43 is longer than the axial length L2 of the portion of the inner inner peripheral surface 42 that faces the serrations 32 (described below).

[0021] The hub wheel 3 has a hardened portion 31 hardened along the small diameter step portion 3a, serrations 32 formed on the inner side of the outer peripheral surface of the small diameter step portion 3a, and an outer outer peripheral surface 33 located on the outer side of the outer peripheral surface of the small diameter step portion 3a.

[0022] The hardened portion 31 is formed by partial hardening along the small diameter step portion 3a in the heat treatment process. In the heat treatment process, hardening is performed using a method that allows for setting the hardening depth, such as induction hardening. The hardened portion 31 improves the surface hardness and strength of the small diameter step portion 3a.

[0023] The serrations 32 are formed before the heat treatment process and are hardened during the heat treatment process. The outer diameter of the serrations 32 is smaller than the outer peripheral surface 33. The outer diameter of the serrations 32 is slightly larger than the inner inner peripheral surface 42 of the inner ring 4. This allows the inner inner peripheral surface 42 of the inner ring 4 to be joined to the serrations 32. The axial length L2 of the serrations 32 may be any length that provides a strength that prevents the press-cut-joined inner ring 4 from falling out when a bearing preload is applied.

[0024] The outer-side outer peripheral surface 33 has a slightly larger diameter than the outer-side inner peripheral surface 43 of the inner ring 4. This allows the outer-side inner peripheral surface 43 of the inner ring 4 to be interference-fitted onto the outer-side outer peripheral surface 33. This interference fit need only be strong enough to provide a fitting force that prevents the inner ring 4 from slipping out when a bearing preload is applied. Specifically, the interference is preferably 0.005 mm or more and 0.020 mm or less. This prevents creep of the inner ring 4, improves assembly, and enables bearing preload to be maintained, while also suppressing deformation of the inner raceway surface 4a of the inner ring 4 and tensile stress in the circumferential direction. As a result, the durability of the wheel bearing device can be improved.

[0025] The axial length L1 of the outer peripheral surface 33 is the same as the axial length L1 of the outer inner peripheral surface 43 and is longer than the axial length L2 of the serrations 32.

[0026] As shown in Figures 2(a) to 2(c), the inner ring 4 is assembled to the hub ring 3 by moving the inner ring 4 from the inner side to the outer side relative to the hub ring 3. More specifically, when the inner ring 4 is inserted into the small diameter step 3a from the state shown in Figure 2(a), the outer end of the outer inner circumferential surface 43 of the inner ring 4 first contacts the inner end of the outer outer circumferential surface 33 of the small diameter step 3a, as shown in Figure 2(b). This is because L1 > L2, as mentioned above. As a result, the inner ring 4 is inserted while being guided by the outer outer circumferential surface 33 of the small diameter step 3a. This precisely aligns the rotational axis of the inner ring 4 and the rotational axis of the hub ring 3.

[0027] When the inner ring 4 is further inserted from the state shown in FIG. 2(b), the outer end of the inner inner peripheral surface 42 of the inner ring 4 comes into contact with the inner end of the serrations 32. The inner inner peripheral surface 42 of the inner ring 4 is then cut by the serrations 32 and fits into the serrations 32. Then, the inner ring 4 is joined to the hub ring 3, as shown in FIG. 2(c).

[0028] In addition to the above, press-cut joining and interference fit can also be achieved by the form shown in Fig. 3. Fig. 3 is a diagram illustrating another joining form between the inner ring 4 and the hub ring 3, with (a) showing the area around the small diameter step 3a of the inner ring 4 and the hub ring 3 before joining, (b) showing the area around the small diameter step 3a of the inner ring 4 and the hub ring 3 during joining, and (c) showing the area around the small diameter step 3a of the inner ring 4 and the hub ring 3 after joining.

[0029] As shown in FIG. 3(a), the inner ring 4 has a hardened portion 41 hardened along the inner side inner raceway surface 4a, a hardened portion 45 hardened along the inner side of the inner circumferential surface, serrations 46 formed on the inner side of the inner circumferential surface, and an outer side inner circumferential surface 47 located on the outer side of the inner circumferential surface.

[0030] The hardened portion 45 is formed by partial hardening along the inner side of the inner peripheral surface during a heat treatment process. The hardened portion 45 includes serrations 46. Meanwhile, the portions of the inner ring 4 other than the hardened portions 41, 45 are not hardened. This allows the material to maintain its cold workability, toughness, and other mechanical strengths.

[0031] The serrations 46 are formed before the heat treatment process and are hardened during the heat treatment process. The inner diameter of the serrations 46 is smaller than that of the outer inner peripheral surface 47. The inner diameter of the serrations 46 is slightly smaller than that of the inner outer peripheral surface 36 of the hub ring 3. This allows the serrations 46 of the inner ring 4 to be joined to the inner outer peripheral surface 36 of the hub ring 3. The axial length L4 of the portion of the serrations 46 facing the inner outer peripheral surface 36 of the hub ring 3 may be any length that has the strength to prevent the press-cut joined inner ring 4 from falling out when bearing preload is applied. The axial length L3 of the outer inner peripheral surface 47 is formed longer than the axial length L4 of the inner outer peripheral surface 36 of the hub ring 3.

[0032] The hub wheel 3 has a hardened portion 35 hardened along the outer portion of the small diameter step portion 3a, an inner outer peripheral surface 36 located on the inner side of the outer peripheral surface of the small diameter step portion 3a, and an outer outer peripheral surface 37 located on the outer side of the outer peripheral surface of the small diameter step portion 3a.

[0033] The hardened portion 35 is formed by partial hardening in a heat treatment process. The hardened portion 35 improves the surface hardness and strength of the outer portion of the small diameter step portion 3a. Meanwhile, the inner side portions of the inner outer peripheral surface 36 and the outer outer peripheral surface 37 are not hardened. Therefore, the cold workability and mechanical strength, such as toughness, of the material can be maintained.

[0034] The inner-side outer peripheral surface 36 has a smaller diameter than the outer-side outer peripheral surface 37. The outer-side outer peripheral surface 37 has a slightly larger diameter than the outer-side inner peripheral surface 47 of the inner ring 4. This allows the outer-side inner peripheral surface 47 of the inner ring 4 to be interference-fitted onto the outer-side outer peripheral surface 37. As in the above embodiment, the interference is preferably 0.005 mm or more and 0.020 mm or less. The axial length L3 of the outer-side outer peripheral surface 37 is the same as the axial length L3 of the outer-side inner peripheral surface 47, and is longer than the axial length L4 of the inner-side outer peripheral surface 36.

[0035] As shown in Figures 3(a) to 3(c), the inner ring 4 is assembled to the hub wheel 3 by moving the inner ring 4 from the inner side to the outer side relative to the hub wheel 3. More specifically, when the inner ring 4 is inserted into the small diameter step 3a from the state shown in Figure 3(a), the outer end of the outer inner circumferential surface 47 of the inner ring 4 first contacts the inner end of the outer outer circumferential surface 37 of the small diameter step 3a, as shown in Figure 3(b). This is because L3 > L4, as mentioned above. As a result, the inner ring 4 is inserted while being guided by the outer outer circumferential surface 37 of the small diameter step 3a. This precisely aligns the rotational axis of the inner ring 4 and the rotational axis of the hub wheel 3.

[0036] When the inner ring 4 is further inserted from the state shown in Figure 3(b), the outer end portions of the serrations 46 of the inner ring 4 come into contact with the inner end portions of the inner outer peripheral surface 36 of the small diameter step portion 3a. The serrations 46 then cut the inner outer peripheral surface 36 of the small diameter step portion 3a and fit onto the inner outer peripheral surface 36. Then, as shown in Figure 3(c), the inner ring 4 is joined to the hub wheel 3.

[0037] As described above, the press-cut joining and interference fit between the hub ring 3 and the inner ring 4 are not used for torque transmission, but rather for the purposes of preventing creep of the inner ring 4 and maintaining bearing preload. Therefore, it is sufficient for the inner ring 4 to have sufficient strength to prevent slippage. This suppresses deformation of the inner raceway surface 4a of the inner ring 4 and circumferential tensile stress. As a result, the durability of the wheel bearing device can be improved. Furthermore, the use of press-cut joining and interference fit for fastening improves assembly ease compared to a tight fit or crimping of the hub ring end. Furthermore, the use of press-cut joining and interference fit for fastening can reduce weight compared to crimping of the hub ring end. Furthermore, the use of press-cut joining and interference fit for fastening eliminates the need for interference management, as is required with a tight fit.

[0038] [Inner ring material] The inner ring 4 is made of bearing steel that is cold-worked and has a carbon equivalent of 0.64 or more and 1.15 or less. The carbon equivalent (C-equivalent) is a value expressed as C + 1 / 7Si + 1 / 5Mn + 1 / 9Cr. Among bearing steels that are cold-worked, S53C is an example of a material with a carbon equivalent of 0.64 or more, and the materials exemplified in Patent No. 3374006 are examples of materials with a carbon equivalent of 1.15 or less. Using these materials makes it easier to partially harden the inner ring 4, reducing costs.

[0039] Although the above embodiment has been described with reference to a wheel bearing device 1 for a driving wheel, the present invention can also be applied to a wheel bearing device for a driven wheel. Fig. 4 is a cross-sectional view of a wheel bearing device 10 for a driven wheel according to one embodiment. In the wheel bearing device 10, the inner ring 4 is fixed to the hub wheel 3 by the press-cut joining method shown in Fig. 3, as an example. In the wheel bearing device 10, components having the same functions as those in the wheel bearing device 1 described above are designated by the same reference numerals, and detailed description thereof will be omitted.

[0040] The wheel bearing device 10 includes an outer ring 2, a hub ring 3, an inner ring 4, rolling elements 5, an outer seal member 7, an encoder ring 8, and a cap 9.

[0041] An inner fitting surface 2b for fitting a cap 9 is provided on the inner peripheral surface of the inner end portion 2g of the outer ring 2. A fitting surface 4b for fitting an encoder ring 8 is provided on the outer peripheral surface of the inner end portion 4c of the inner ring 4.

[0042] The encoder ring 8 includes a support member 81 and a magnetic encoder 82. The support member 81 is a ring-shaped body made of, for example, a steel plate, and is fitted onto the fitting surface 4b of the inner ring 4. The magnetic encoder 82 is made of synthetic rubber or the like, with magnetic poles (north and south poles) arranged alternately in the circumferential direction so that the magnetism alternates in the circumferential direction, and is bonded to the inner surface of the support member 81 by vulcanization bonding or the like. The magnetic encoder 82 is detected by a rotational speed sensor (not shown), which is a magnetic sensor.

[0043] The cap 9 is a member that closes the inner-side open end of the outer ring 2 and supports the rotational speed sensor. The cap 9 is fitted onto the inner-side fitting surface 2b of the outer ring 2. The cap 9 prevents foreign matter such as muddy water from entering from the outside and protects the encoder ring 8.

[0044] With this wheel bearing device 10, the inner ring 4 and hub ring 3 are fixed together by press-cut joining and interference fitting, eliminating the need to crimp the hub ring end as in the past. This improves assembly ease and reduces weight.

[0045] The above-described embodiment merely shows a typical form of the present invention, and various modifications can be made without departing from the gist of the present invention. [Explanation of symbols]

[0046] 1 Wheel bearing device 2 Outer ring (outer member) 2a Outer raceway surface 3 Hub ring (inner part) 3a Small diameter stepped section 3d inner raceway surface 4 Inner ring (inner part) 4a Inner raceway surface 5 rolling elements 32, 46 serrations 41 Hardened section

Claims

1. an outer member having a double-row outer raceway surface on its inner periphery; an inner member comprising a hub ring having a small diameter stepped portion extending axially on its outer periphery, and an inner ring fixed to the small diameter stepped portion of the hub ring, the hub ring having an outer side inner raceway surface facing the outer side outer raceway surface, and the inner ring having an inner side inner raceway surface facing the inner side outer raceway surface; a double row of rolling elements rollably accommodated between the raceway surfaces of the outer member and the inner member, the inner ring has a hardened portion that is hardened along the inner raceway surface on the inner side, The inner ring and the hub ring are fixed together by press-cut joining and interference fitting with an interference of 0.005 mm or more and 0.020 mm or less, A wheel bearing device according to claim 1, wherein the axial length of the portion fixed by the interference fit is longer than the axial length of the portion fixed by the press cut joint.

2. 2. The wheel bearing device according to claim 1, wherein the inner ring is made of bearing steel that is subjected to cold working and has a carbon equivalent of 0.64 to 1.

15.

3. 3. The wheel bearing device according to claim 1, wherein the press-cut joint is a joint between serrations formed on the outer peripheral surface of the small diameter step portion and hardened, and an unhardened inner peripheral surface of the inner ring.

4. 3. The wheel bearing device according to claim 1, wherein the press-cut joint is a joint between serrations formed on the inner peripheral surface of the inner ring and hardened, and an unhardened outer peripheral surface of the small diameter step portion.

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