JP2007024208A - Bearing device for wheel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bearing device for a wheel suppressing the deformation of an inner ring caused by fastening work to improve durability of the inner ring. <P>SOLUTION: The bearing device for the wheel is of self-retained structure with the inner ring 3 pressed into a small diameter step part 2b of a hub wheel 2 and axially fixed to the hub wheel 2 by a fastening part 2c formed by plastically deforming the end of the small diameter step part 2b radially outward. The inner diameter 3c of the inner ring 3 is formed in tapered shape having a predetermined inclination angle &beta; gradually enlarging the diameter toward an end face from a position which corresponds to an inner end A of an inner rolling surface 3a, and a radial escape part 13 is provided at a fitting part to the small diameter step part 2b. The elastic deformation of an outer diameter 3b of the inner ring 3 caused by fastening load is thereby suppressed to reduce hoop stress generated to the outer diameter 3b, and the deformation quantity of the fastening part 2c is reduced to suppress the occurrence of damage such as a crack. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

  The present invention relates to a bearing device for a wheel that rotatably supports a wheel of an automobile or the like with respect to a suspension device, and more particularly to a self-retained structure in which an inner ring is fixed by swinging caulking of a hub ring. The present invention relates to a wheel bearing device that suppresses deformation of an inner ring and improves the durability of the inner ring.

  2. Description of the Related Art Wheel bearing devices for vehicles such as automobiles include those for driving wheels and those for driven wheels. In particular, a wheel bearing device that rotatably supports a wheel with respect to a suspension device of an automobile has been made lighter and more compact for improving fuel efficiency, not to mention cost reduction. As a typical example of the conventional structure, a wheel bearing device for a driven wheel as shown in FIG. 5 is known.

  This wheel bearing device is referred to as a third generation, and includes a hub wheel 51, an inner ring 52, an outer ring 53, and double row rolling elements 54, 54. The hub wheel 51 integrally has a wheel mounting flange 55 for mounting a wheel (not shown) at one end thereof, an inner rolling surface 51a on the outer periphery, and a small diameter extending in the axial direction from the inner rolling surface 51a. A step portion 51b is formed. Further, hub bolts 56 for fixing the wheels are planted at the circumferentially equidistant positions of the wheel mounting flanges 55.

  An inner ring 52 having an inner rolling surface 52a formed on the outer periphery is press-fitted into the small diameter step portion 51b of the hub wheel 51. The inner ring 52 is prevented from coming off from the hub wheel 51 in the axial direction by a caulking portion 51c formed by plastically deforming the end portion of the small diameter step portion 51b of the hub wheel 51 radially outward. .

  The outer ring 53 integrally has a vehicle body mounting flange 53b on the outer periphery, and double row outer rolling surfaces 53a and 53a are formed on the inner periphery. Between the double-row outer rolling surfaces 53a and 53a and the inner rolling surfaces 51a and 52a facing these, the double-row rolling elements 54 and 54 are accommodated so as to be freely rollable.

  The hub wheel 51 is integrally formed by forging a carbon steel material having a carbon content of 0.40 to 0.80% by weight, from the base of the wheel mounting flange 55 to the inner rolling surface 51a, And the surface is hardened by induction hardening etc. over the small diameter step 51b. In addition, the caulking part 51c is left with the raw material surface hardness after forging. On the other hand, the inner ring 52 is made of high carbon steel such as high carbon chromium bearing steel such as SUJ2, and is hardened and hardened to the core.

  Here, a conical concave inclined surface 57 whose inner diameter increases toward the inner end opening is formed on the inner peripheral surface of the inner end portion of the inner ring 52. The inclined surface 57 is inclined with respect to the central axis of the hub wheel 51, and the inclination angle θ is set to about 20 to 60 °. Further, a circular concave portion 58 is formed on the inner end surface of the small diameter step portion 51b, whereby a cylindrical portion 59 is formed on the inner end portion of the small diameter step portion 51b.

Thereby, the deformation amount of the caulking portion 51c can be reduced as compared with the conventional structure. That is, in the case of the conventional structure, in order to form the crimped portion 51c, the cylindrical portion formed at the end of the small-diameter step portion 51b is bent radially outward by 90 °, whereas here, Since it is only necessary to deform the cylindrical portion 59 by the inclination angle θ (= 20 to 60 °), it is possible to suppress the occurrence of damage such as cracks in the crimping portion 51c and to the outside of the inner ring 52 in the radial direction. Therefore, the inner ring 52 can be prevented from being damaged.
JP-A-10-95203

  In such a conventional wheel bearing device, the cylindrical portion 59 only needs to be deformed by the inclination angle θ, so that the amount of deformation of the caulking portion 51c is less than that of the conventional structure, and the caulking portion 51c While it is possible to suppress the occurrence of damage such as cracks and to reduce the force applied to the outer side of the inner ring 52 in the radial direction, when a large moment load is applied to the wheel bearing device In this case, the caulking portion 51c is required to have a strength sufficient to firmly fix the inner ring 52. Generally, since the strength of the crimped portion 51c depends on the rigidity of the crimped portion 51c itself, it is difficult to ensure the strength of the crimped portion 51c simply by suppressing the amount of plastic deformation of the crimped portion 51c. .

  Here, if the rigidity of the caulking portion 51 c is increased, the molding load in the swing press processing is naturally increased, and accordingly, the inner diameter of the inner ring 52 is expanded, and a hoop stress is applied to the outer diameter 60 of the inner ring 52. It cannot be denied that it occurs. If a hoop stress is generated in the outer diameter 60 of the inner ring 52, the inner ring 52 may be damaged. Further, even when the inner ring is not damaged by the hoop stress, when corrosion occurs in this part, diffusible hydrogen existing in the environment enters the structure of the inner ring 52 and the metal grain boundary is destroyed, so-called “ “Delayed fracture” tends to occur, which is not preferable. Therefore, it can be said that the hoop stress generated at the outer diameter 60 of the inner ring 52 is reduced, and the deformation amount of the caulking portion 51c is reduced to prevent the caulking portion 51c from being damaged such as a crack. In other words, a countermeasure that can solve conflicting problems has been desired.

  Furthermore, in the conventional wheel bearing device, when the crimped portion 51c is formed by plastically deforming the end portion of the small diameter step portion 51b radially outward, as shown in FIG. Since the vicinity of the tightening portion 51c is also plastically deformed in the radial direction, the inner diameter of the inner ring 52 is expanded with the plastic deformation, and the outer diameter 60 of the inner ring 52 is elastically deformed into a tapered shape (oscillating tightening). The previous state is indicated by a two-dot chain line).

  Thus, when the outer diameter 60 of the inner ring 52 is elastically deformed into a tapered shape and the outer diameter 60 has an inclination angle α and the cylindricity is collapsed, when a seal or an encoder for detecting speed is pressed into this part, This is not preferable because not only the assemblability but also galling may occur.

  The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a wheel bearing device that suppresses deformation of the inner ring accompanying caulking and improves the durability of the inner ring. .

  In order to achieve such an object, the invention according to claim 1 of the present invention integrally has an outer member having a double row outer rolling surface formed on the inner periphery and a wheel mounting flange at one end. A hub wheel formed with a small-diameter step portion extending in the axial direction from the wheel mounting flange, and an inner ring press-fitted into the small-diameter step portion of the hub wheel, and a plurality of outer rings facing the double-row outer rolling surface on the outer periphery. An inner member in which an inner rolling surface of the row is formed, and a double row rolling element that is accommodated so as to roll freely between both rolling surfaces of the inner member and the outer member via a cage. A bearing unit for a wheel in which the inner ring is fixed in the axial direction by a caulking part formed by plastically deforming an end of the small diameter step part radially outward, and a fitting part between the inner ring and the small diameter step part Is provided with a radial relief portion, from which the relief portion corresponds to the inner end of the inner raceway surface of the inner ring. Adopting a structure which is formed to become gradually larger toward the surface.

  In this way, the inner ring is fixed to the hub ring in the axial direction by the caulking portion formed by press-fitting the inner ring into the small-diameter step portion of the hub wheel and plastically deforming the end of the small-diameter step portion radially outward. In the so-called self-retained wheel bearing device, a fitting portion between the inner ring and the small diameter step portion is provided with a radial relief portion, and the relief portion corresponds to the inner end portion of the inner raceway surface of the inner race. Since it is formed so as to gradually increase from the end to the end surface, the elastic deformation of the outer diameter of the inner ring caused by the caulking load is suppressed, and the hoop stress generated at the outer diameter is reduced, and the deformation amount of the caulking portion It is possible to reduce the occurrence of damage such as cracks in the caulking portion. Furthermore, the assemblability of an encoder or the like that is press-fitted into the outer diameter of the inner ring can be improved.

  Further, as in the invention described in claim 2, the inner ring may be formed so that the inner diameter of the inner ring gradually becomes larger toward the end face, and as in the invention described in claim 3, The outer peripheral surface of the end portion of the small diameter step portion may be formed so as to gradually decrease in diameter toward the end surface of the inner ring.

  Further, as in the invention according to claim 4, if the relief portion is formed in a tapered shape having a predetermined inclination angle, it is possible to suppress the outer diameter of the inner ring from being elastically deformed into a tapered shape. .

  In the invention according to claim 5, if the maximum amount of the relief portion is set in a range of 20 to 60 μm, the plastic deformation of the end portion of the small diameter step portion caused by the caulking process is suppressed, Elastic deformation of the outer diameter of the inner ring caused by the tightening load can be suppressed.

  The wheel bearing device according to the present invention integrally has an outer member having a double row outer raceway formed on the inner periphery and a wheel mounting flange at one end, and extends in an axial direction from the wheel mounting flange. A hub ring formed with a small-diameter step portion and an inner ring press-fitted into the small-diameter step portion of the hub ring, and a double-row inner rolling surface facing the double-row outer rolling surface is formed on the outer periphery. An inner member, and a double-row rolling element that is rotatably accommodated between both rolling surfaces of the inner member and the outer member via a cage, and an end portion of the small-diameter step portion is provided. In the wheel bearing device in which the inner ring is fixed in the axial direction by a caulking portion formed by plastic deformation radially outward, a radial relief portion is provided in a fitting portion between the inner ring and the small diameter step portion, The relief portion gradually increases from the position corresponding to the inner end portion of the inner raceway surface of the inner ring toward the end surface. Therefore, the elastic deformation of the outer diameter of the inner ring caused by the caulking load is suppressed to reduce the hoop stress generated in the outer diameter, and the deformation amount of the caulking portion is reduced to cause damage such as cracking. Occurrence can be suppressed. Furthermore, the assemblability of an encoder or the like that is press-fitted into the outer diameter of the inner ring can be improved.

  A vehicle body mounting flange is integrally formed on the outer periphery, an outer member having a double row outer rolling surface formed on the inner periphery, a wheel mounting flange is integrally formed on one end, and the double row outer rolling is formed on the outer periphery. One inner rolling surface facing the running surface, a hub wheel formed with a small-diameter step portion extending in the axial direction from the inner rolling surface, and press-fitted into the small-diameter step portion of the hub wheel, and the double row on the outer periphery An inner member made of an inner ring formed with the other inner rolling surface opposite to the outer rolling surface of the inner rolling surface, and can be rolled via a cage between both rolling surfaces of the inner member and the outer member. A double row rolling element housed in a bearing assembly for a wheel, wherein the inner ring is fixed in the axial direction by a caulking portion formed by plastically deforming an end portion of the small diameter step portion radially outward. The inner ring has a predetermined inner diameter that gradually increases from the position corresponding to the inner end of the inner rolling surface toward the end surface. It is tapered consisting oblique angle relief portion in the radial direction in the fitting portion between the cylindrical portion is provided.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a longitudinal sectional view showing a first embodiment of a wheel bearing device according to the present invention, and FIG. 2 is an enlarged view of a main part of FIG. In the following description, the side closer to the outer side of the vehicle when assembled to the vehicle is referred to as the outboard side (left side in the drawing), and the side closer to the center is referred to as the inboard side (right side in the drawing).

  This wheel bearing device is referred to as the third generation on the driven wheel side, and is a double row rolling element (ball) accommodated between the inner member 1 and the outer member 10 and between both members 1 and 10 so as to roll freely. 6 and 6. The inner member 1 includes a hub ring 2 and an inner ring 3 that is press-fitted into the hub ring 2 through a predetermined scissors.

  The hub wheel 2 integrally has a wheel mounting flange 4 for mounting a wheel (not shown) at an end portion on the outboard side, and is used for fixing the wheel at a circumferentially equidistant position of the wheel mounting flange 4. Hub bolts 5 are planted. Further, on the outer periphery of the hub wheel 2, an inner rolling surface 2a and an axial small-diameter step portion 2b extending in the axial direction from the inner rolling surface 2a are formed. The inner ring 3 having the inner raceway surface 3a formed on the outer periphery is press-fitted into the small-diameter step portion 2b, and the end portion of the small-diameter step portion 2b is plastically deformed outward in the radial direction. Thus, the inner ring 3 is prevented from coming off in the axial direction with respect to the hub ring 2.

  The outer member 10 integrally has a vehicle body mounting flange 10b for mounting to a vehicle body (not shown) on the outer periphery, and double row outer rolling surfaces 10a, 10a are formed on the inner periphery. And the double row rolling elements 6 and 6 are accommodated between each rolling surface 10a, 2a and 10a, 3a, and these double row rolling elements 6 and 6 are rollably hold | maintained by the holder | retainers 7 and 7. ing. In addition, a seal 8 and an end cap 9 are attached to the end portion of the outer member 10 to prevent leakage of lubricating grease sealed inside the bearing and intrusion of rainwater or dust from the outside into the bearing. Yes. A rotation speed sensor (not shown) is attached to the end cap 9 and detects the rotation speed of the wheel against the encoder 11 fitted to the outer diameter 3 b of the inner ring 3.

  Here, the wheel bearing device referred to as the third generation in which the inner raceway surface 2a is directly formed on the outer periphery of the hub wheel 2 is illustrated, but the wheel bearing device according to the present invention is not limited to such a structure. For example, it may be a first generation or second generation structure in which a pair of inner rings are press-fitted into a small diameter step portion of a hub ring. In addition, although the double row angular contact ball bearing which used the rolling elements 6 and 6 as the ball | bowl was illustrated, it is not restricted to this, The double row tapered roller bearing which uses a tapered roller for a rolling element may be sufficient.

  The hub wheel 2 is formed of medium carbon steel containing 0.40 to 0.80% by weight of carbon such as S53b, and includes an inner rolling surface 2a on the outboard side, a seal land portion with which the seal 8 is in sliding contact, and a small diameter. The surface hardness is set to a range of 58 to 64 HRC by induction hardening over the step 2b (indicated by cross-hatching in the figure). The caulking portion 2c is an unquenched portion having a material surface hardness of 25 HRC or less after forging. On the other hand, the inner ring 3 is made of high carbon chrome bearing steel such as SUJ2, and is hardened in the range of 58 to 64 HRC up to the core part by quenching.

  The outer member 10 is formed of medium carbon steel containing 0.40 to 0.80% by weight of carbon such as S53b, like the hub wheel 2, and the double row outer raceway surfaces 10a and 10a are formed by induction hardening. The surface hardness is set in the range of 58 to 64 HRC.

  The present applicant measured the amount of elastic displacement (the amount of radial expansion) of the outer diameter 3b of the inner ring 3 during swing caulking, and investigated the relationship between the amount of elastic displacement and the caulking load. It was found that the relationship between the two is a substantially linear proportional relationship. Accordingly, the hoop stress of the outer diameter 3b of the inner ring 3 generated by the caulking process sets the caulking load within a range in which the durability of the inner ring 3 is not affected, and the elasticity of the outer diameter 3b generated by the caulking load. In order to suppress the deformation, a means for previously providing an inclination angle β on the inner diameter 3c of the inner ring 3 corresponding to the amount of plastic deformation of the caulking portion 2c is employed.

  FIG. 2 is an enlarged view of the main part of FIG. 1 (the encoder 11 is omitted in this figure), but the inner ring 3 press-fitted into the small-diameter step portion 2b is rocked at the end of the small-diameter step portion 2b. By the dynamic caulking, the inner diameter 3c and the outer diameter 3b of the inner ring 3 are elastically deformed into a tapered shape (the state before the rocking caulking is indicated by a two-dot chain line). Here, in the present embodiment, in order to suppress this elastic deformation, an inclination angle β is formed in advance on the inner diameter 3c of the inner ring 3, and a relief portion 13 is provided with respect to the cylindrical portion 12 before caulking.

  Specifically, as described above, the elastic displacement amount of the outer diameter 3b due to the caulking process is regulated to, for example, 75 μm or less from the range that does not affect the durability of the inner ring 3, that is, the allowable hoop stress. Yes. Here, although the allowable hoop stress is set to 300 MPa, when the inner ring 3 is used in an exposed state to the external environment, it is necessary to set it to 250 MPa or less.

  Here, the inner diameter 3c of the inner ring 3 is formed with an inclination angle β in a taper shape so as to increase in diameter from the position corresponding to the inner end A of the inner rolling surface 3a toward the end surface. A relief portion 13 is formed in the fitting portion by the cylindrical portion 12. The maximum amount of the escape portion 13 is set in a range of 20 to 60 μm. This corresponds to the amount of plastic deformation of the cylindrical portion 12 that occurs in the caulking process performed by the applicant. Thereby, elastic deformation of the outer diameter 3b of the inner ring 3 caused by the caulking load is suppressed to reduce hoop stress generated in the outer diameter 3b, and the deformation amount of the caulking portion 2c is reduced so that the caulking portion 2c is reduced. The occurrence of damage such as cracks can be suppressed. Furthermore, the assemblability of the encoder 11 (see FIG. 1) press-fitted into the outer diameter 3b of the inner ring 3 can be improved.

  Here, the relief angle 13 is formed by forming the tapered inclination angle β on the inner diameter 3 c of the inner ring 3. However, the present invention is not limited to this, and the position where the inner diameter 3 c of the inner ring 3 corresponds to the inner end A. It is sufficient that the diameter gradually increases from the end toward the end face. For example, although it is not illustrated, it may be formed in an arc shape.

  FIG. 3 is a modification of the embodiment shown in FIG. In this embodiment, only the configuration of the escape portion is different, and the same components and parts as those in the above-described embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the present embodiment, the inner diameter 3c 'of the inner ring 3' is formed on a cylindrical surface. On the other hand, the outer periphery of the cylindrical portion 14 before caulking at the end of the small-diameter step portion 2b is inclined so that the diameter decreases from the position corresponding to the inner end A of the inner raceway surface 3a of the inner ring 3 'toward the end surface. An angle β is formed, and an escape portion 15 is provided for the inner diameter 3c ′ of the inner ring 3 ′. Thus, as in the above-described embodiment, the elastic deformation of the outer diameter 3b of the inner ring 3 ′ caused by the caulking load is suppressed to reduce the hoop stress generated in the outer diameter 3b, and the deformation amount of the caulking portion 2c ′. It is possible to suppress the occurrence of damage such as cracks by reducing the amount of the damage.

  FIG. 4 is a longitudinal sectional view showing a second embodiment of the wheel bearing device according to the present invention. In addition, this embodiment is applied to the wheel bearing device on the drive wheel side, and the same components and parts having the same functions as those of the above-described embodiment are denoted by the same reference numerals to avoid redundant description. .

  This wheel bearing device is referred to as the third generation on the drive wheel side, and the inner member 16 and the outer member 10, and the double row rolling elements 6 and 6 accommodated between the members 16 and 10 so as to roll freely. And. The inner member 16 includes a hub ring 17 and an inner ring 3 press-fitted into the hub ring 17 through a predetermined shimiro.

  An inner rolling surface 2a and a cylindrical small-diameter step portion 2b extending in the axial direction from the inner rolling surface 2a are formed on the outer periphery of the hub wheel 17, and a serration (or spline) 17a for torque transmission is formed on the inner periphery. Is formed. The inner ring 3 is prevented from coming off in the axial direction with respect to the hub wheel 17 by a crimping part 2c formed by plastically deforming the end of the small diameter step part 2b radially outward.

  Seals 8 and 18 are attached to the end portions of the outer member 10 to prevent leakage of lubricating grease sealed inside the bearing and intrusion of rainwater, dust, and the like from the outside into the bearing. The inboard-side seal 18 is composed of annular first and second seal plates 19 and 20 having a substantially L-shaped cross section, and is disposed to face each other. The first seal plate 19 is fitted into the end portion of the outer member 10, and the second seal plate (slinger) 20 is press-fitted and fixed to the outer diameter 3 b of the inner ring 3.

  Here, also in the present embodiment, the inner ring 3 has an inner diameter 3c having a tapered inclination angle β such that the inner ring 3 has a larger diameter from the position corresponding to the inner end A of the inner rolling surface 3a toward the end face. The relief portion 13 is formed in the fitting portion by the inclination angle β and the cylindrical portion 12. Thereby, elastic deformation of the outer diameter 3b of the inner ring 3 caused by the caulking load is suppressed to reduce hoop stress generated in the outer diameter 3b, and the deformation amount of the caulking portion 2c is reduced so that the caulking portion 2c is reduced. The occurrence of damage such as cracks can be suppressed. Furthermore, the assemblability of the second seal plate 20 press-fitted into the outer diameter 3b of the inner ring 3 can be improved.

  The embodiment of the present invention has been described above, but the present invention is not limited to such an embodiment, and is merely an example, and various modifications can be made without departing from the scope of the present invention. Of course, the scope of the present invention is indicated by the description of the scope of claims, and further, the equivalent meanings described in the scope of claims and all modifications within the scope of the scope of the present invention are included. Including.

  In the wheel bearing device according to the present invention, the inner ring is fixed by a caulking portion formed by press-fitting an inner ring into a small-diameter step portion of a hub wheel and plastically deforming an end portion of the small-diameter step portion. It can be applied to a self-retained wheel bearing device.

It is a longitudinal section showing a 1st embodiment of a bearing device for wheels concerning the present invention. It is a principal part enlarged view of FIG. It is a principal part enlarged view which shows the modification of FIG. It is a longitudinal cross-sectional view which shows 2nd Embodiment of the wheel bearing apparatus which concerns on this invention. It is a longitudinal cross-sectional view which shows the conventional wheel bearing apparatus. It is a principal part enlarged view of FIG.

Explanation of symbols

1, 16... Inner member 2, 17... Hub wheel 2 a, 3 a... Inner rolling surface 2 b. '············································· 3 Mounting flange 5 ·········································································· End cap 10 Outer member 10a Outer rolling surface 10b Car body mounting flange 11 ... Encoders 12 and 14 ... Cylindrical parts 13 and 15 ... Relief part 17a ... Serration 19 ... First seal plate 20 ... .... Second seal plate 51 ·················· Hub wheels 51a, 52a ... Inner rolling surface 51b Inner ring 53 ... Outer ring 53a ... Outer rolling surface 53b ... Car body mounting flange 54 ... Rolling element 55 ... ··· Wheel mounting flange 56 ······································································・ ・ ・ ・ ・ ・ ・ ・ Outer diameter A ・ ・ ・ ・ ・ ・ ・ ・ ・ Inner ends α, β, θ of the inner raceway surface of the inner ring ・ ・ ・ ・ ・ Inclination angle

Claims (5)

An outer member having a double row outer raceway formed on the inner periphery;
It has a wheel mounting flange integrally at one end, a hub wheel formed with a small-diameter step portion extending in the axial direction from the wheel mounting flange, and an inner ring press-fitted into the small-diameter step portion of this hub wheel, An inner member formed with a double-row inner rolling surface facing the double-row outer rolling surface;
A double row rolling element that is accommodated so as to roll freely between the rolling surfaces of the inner member and the outer member via a cage,
In the wheel bearing device in which the inner ring is fixed in the axial direction by a caulking portion formed by plastically deforming an end portion of the small diameter step portion radially outwardly,
A fitting portion between the inner ring and the small-diameter step portion is provided with a radial relief portion, and the relief portion is formed so as to gradually increase from the position corresponding to the inner end portion of the inner raceway surface of the inner ring toward the end surface. A bearing device for a wheel, characterized in that   The wheel bearing device according to claim 1, wherein an inner diameter of the inner ring is gradually increased toward an end surface.   3. The wheel bearing device according to claim 1, wherein an outer peripheral surface of an end portion of the small diameter step portion is formed so as to gradually become a small diameter toward an end surface of the inner ring.   The wheel bearing device according to any one of claims 1 to 3, wherein the relief portion is formed in a tapered shape having a predetermined inclination angle.   The wheel bearing device according to any one of claims 1 to 4, wherein a maximum amount of the relief portion is set in a range of 20 to 60 µm.

Images