KR102558487B1 - Low torque seal assembly for bearing - Google Patents

Abstract

The present invention relates to a low-torque seal assembly for a bearing, which comprises an elastic body and a slinger, wherein the elastic part includes a protrusion and the slinger includes a slinger outer diameter part. The protrusion and the slinger outer diameter part are formed so that separation is prevented after assembly, a mud-collection radial rib and a mud-collection axial rib are formed in the elastic body so that the inflow of foreign substances into a seal is reduced, and a contact pressure of a contact part to the slinger, thereby enabling designing and manufacturing a bearing with reduced drag torque. A first mud collection groove and a second mud collection groove store a part of foreign substances and moisture introduced through an opening between the protrusion and the slinger outer diameter part. Since parts with the seal are not separated before assembly into the bearing, the inflow of foreign substances into an assembly part can be prevented and assembly is easy when the bearing is mounted. In addition, when the bearing is mounted on a car wheel and the wheel rotates, the protrusion formed on an end part of a reinforcing steel cylinder limits the flow of foreign substances including water into the bearing, thereby providing effects of extending the life of the bearing and improving performance due to minimizing sealing drag torque.

Description

Low torque seal assembly for bearing

The present invention relates to a low-torque seal assembly for a bearing for preventing separation of an assembly seal and preventing the inflow of foreign substances such as water into the seal and leakage of oil to the outside of the seal when the bearing rotates after mounting the bearing, thereby increasing the efficiency of the bearing to extend its life and minimizing the drag torque pressure attached to the lip of the seal and the slinger.

In general, a bearing is a device that is mounted between a rotating element and a non-rotating element to smoothly rotate the rotating element.

As one type of bearing, there is a wheel bearing used in a vehicle, and this wheel bearing performs a function of rotatably connecting a rotating wheel (wheel) to a non-rotating vehicle body or knuckle.

A wheel bearing for a vehicle includes an inner ring coupled to a wheel hub and an outer ring rotatably supporting the wheel hub and the inner ring via a rolling element. A bearing space is formed between the inner ring and the outer ring of the vehicle wheel bearing, and the vehicle wheel bearing may further include a seal mounted in a gap between the inner ring and the outer ring communicating with the bearing space. This seal has a sealing structure capable of blocking external foreign substances from entering the bearing space and preventing leakage of lubricating oil injected into the bearing space to the outside while the inner ring is relatively rotatable with respect to the outer ring.

In FIG. 2 , the seal of the wheel bearing for a vehicle includes a first support part 300 mounted on an inner circumferential surface of an outer ring 130 and a sealing part 500 coupled to the first support part 300 . The sealing portion 500 includes a plurality of lip members 600, 700, and 800 protruding toward the outer circumferential surface of the inner ring 120 opposite to the outer circumferential surface of the outer ring 130, and the sealing portion 500 is assembled with the first support portion 300 and the sealing portion 500 in a sense of unity. The lip members 600 , 700 , and 800 always come into contact with the part 400 to prevent leakage of oil, thereby preventing wear and tear of parts.

However, in the seal of this structure, although the first support part 300 supports the sealing part 500 to maintain its basic shape and maintains its shape, the lip members 600 and 700 having elasticity generate a large attachment pressure, that is, drag torque pressure, by the second support part 400, and deteriorate due to heat resistance generated by the rotational force that continues in this pressurized state, resulting in a decrease in elasticity and a gap through which oil leaks. There are problems that cannot be effectively blocked.

Korean Patent Application No. 10-2020-0127030 "Sealing device for wheel bearing" Korean Patent Registration No. 10-1532079 "Wheel bearing"

The problem to be solved by the present invention has been made to solve the problems of the conventional bearing assembly seal as described above, reducing the compression pressure attached to the slinger of the side lip to reduce the drag torque pressure, forming a curved shape on the slinger at the same time, and adding mud collecting lips to the elastic body to limit the inflow of foreign substances and solve the problem of separation between the slinger and the greased elastic body after mounting, thereby providing a low torque assembly seal for bearings that extends the life of the bearing and reduces the drag torque.

Among the embodiments, in the seal assembly for sealing the end of the bearing inner space formed between the inner ring and the outer ring of a bearing device formed between an inner ring coupled to a hub shaft to rotate together and an outer ring that does not rotate, a reinforcing iron cylindrical portion mounted on an inner circumferential surface of the outer ring that does not rotate toward the center with respect to the radial direction and arranged to be concentric with the bearing device; A slinger cylindrical portion mounted on the outer circumferential surface of the rotating inner ring toward the outer circumferential side with respect to the radial direction and arranged to be a concentric axis with the bearing device; Reinforcing iron that is bent and extended from the outer end of the reinforcing iron cylinder toward the center in the radial direction; a slinger bent and extending from the inner end of the cylindrical slinger toward the outer circumferential side in the radial direction; an elastic body fixed to the reinforcing iron so as not to fall from the reinforcing iron and formed of a material having elasticity; The elastic body is characterized in that it includes a protrusion formed at one end of the reinforcing iron cylindrical portion, a mud collecting lip that does not contact the slinger, a side lip that contacts the slinger, and a seal lip that contacts the slinger cylindrical portion.

The elastic body covers the entire radial central side surface of the reinforcing cylinder part, extends from the open end of the reinforcing cylinder part to the middle of the outer circumferential side, extends along the axial inner surface of the reinforcing iron and covers it, and covers the open end of the reinforcing iron. A protrusion that extends from the open end of the reinforcing cylinder to the middle of the outer surface and extends from the open end of the reinforcing cylinder toward the center in the radial direction; mud-collecting ribs that do not contact the slinger; a side lip that is in slanted contact with the slinger; It is characterized in that it includes; seal lips in contact with the slinger cylindrical portion.

The mud collecting lip extending from the inner surface of the reinforcing iron may include a mud collecting radial lip facing the radial outer circumferential side; It is characterized in that it includes; mud collecting axial lip facing inward in the axial direction.

a protrusion extending toward the center of the radial direction than the end of the outer diameter portion of the slinger and having a thickness of 0.15 to 0.25 mm; It is characterized in that the axial inner end surface of the slinger is located on a straight line with the axial inner end surface of the protrusion.

The slinger further includes an inclined portion, characterized in that the outer end surface in the axial direction of the protrusion and the inner end surface in the axial direction of the outer diameter portion of the slinger overlap each other.

The slinger further includes an inclination portion, and the outer diameter portion of the slinger is formed to be inclined by 10 to 20 ° from the slinger inclination portion toward the radial outer circumference, and the axial outer end surface of the protrusion and the inclination portion of the slinger overlap each other.

The material of the elastic body is characterized by any one of nitrile (NBR), hydrogenated nitrile (HNBR), polyacrylate (CM), and fluorocarbon (FKM) as an elastomer that is a rubber compound.

According to an embodiment of the present invention, it includes a configuration of an elastic body and a slinger, and the elastic part includes a protrusion, and the slinger includes a slinger outer diameter. In addition, the protrusion and the outer diameter of the slinger are formed to form a shape that is not separated after assembly, and the mud collecting radial lip and the mud collecting axial lip are formed on the elastic body to reduce the inflow of foreign substances into the seal and to minimize the contact pressure of the contact part to the slinger. As a result, it is possible to design and manufacture bearings for reducing drag torque. Since the parts with seals are not separated before being assembled to the bearing, it is possible to prevent the inflow of foreign substances into the assembly part, and it is easy to assemble when the bearing is mounted, and when the bearing is mounted on the wheel of a car and the wheel rotates, foreign substances including water are restricted from entering the bearing due to protrusions formed at the end of the reinforcing steel cylinder, thereby prolonging the life of the bearing and minimizing the sealing drag torque to improve performance.

1 is a view showing a partially cut away wheel bearing for a vehicle according to an embodiment of the present invention.
2 shows the configuration of a seal assembly for a bearing according to an embodiment of the prior art.
3 shows the configuration of a low-torque seal assembly for a bearing according to an embodiment of the present invention.
Figure 4 shows the configuration of a low-torque seal assembly for bearings according to an embodiment of the present invention.

EMBODIMENT OF THE INVENTION Hereinafter, each embodiment of this invention is described, referring drawings. However, this is not intended to limit the technology described in this document to specific embodiments, and should be understood to include various modifications, equivalents, and/or substitutes of the embodiments in this document. In connection with the description of the drawings, like reference numerals may be used for like elements.

Hereinafter, the first embodiment of the present invention will be described.

1 is a vertical sectional view showing a schematic configuration of a bearing device 1 for a vehicle. In Fig. 1, a bearing device 1 is provided with seals 2 and 3 according to the first embodiment.

As shown in FIG. 1, the bearing device 1 includes a hub 110, an inner ring 120, an outer ring 130, and a plurality of rolling elements 140. The hub 110 includes a substantially cylindrical hub shaft 111 and a substantially annular hub flange 112 . An axle A is inserted into the hub 110 . The hub shaft 111 and the axle shaft A are fixed to each other. As a result, the hub 110 rotates together with the axle A.

The hub flange 112 protrudes outward from the outer circumferential surface of the hub shaft 111 in the axial direction of the hub shaft 111 . A disk wheel (not shown) and a brake disk (not shown) are fixed to the hub flange 112 by a plurality of fastening members 150 .

The inner ring 120 is disposed at the end of the hub shaft 111 closer to the vehicle body in the axial direction of the bearing device 1. Hereinafter, in the axial direction of the bearing device 1, the side closer to the vehicle body is referred to as the inner side, the side farther from the vehicle body as the outer side, the radial center of the axle A as the center, and the outer side of the axle A as the outer circumferential side.

The inner ring 120 has a substantially cylindrical shape. The front end of the hub shaft 111 is inserted into the inner ring 120 . The inner ring 120 is fixed to the outer circumferential surface of the hub shaft 111. As a result, the inner ring 120 rotates together with the hub 110 and the axle A.

The outer ring 130 includes an outer ring body 131 and an outer ring flange 132. The outer ring body 131 has a substantially cylindrical shape. A hub shaft 111 and an inner ring 120 are inserted into the outer ring body 131 . The outer ring body 131 is arranged to be concentric with the hub shaft 111 and the inner ring 120.

The outer ring flange 132 protrudes from the outer circumferential surface of the outer ring body 131 toward the outer circumferential side in the radial direction of the outer ring body 131 . The outer ring flange 132 has a substantially annular shape. A knuckle (not shown) or the like is fixed to the outer ring flange 132, for example. That is, the bearing device 1 is supported on the vehicle body via a member such as a knuckle.

The outer wheel 130 may be fixed so as not to rotate by being coupled to a non-rotating body such as a car body or a knuckle disposed adjacent thereto.

A substantially cylindrical bearing inner space S is formed between the outer circumferential surfaces of the hub shaft 111 and the inner ring 120 and the inner circumferential surface of the outer ring body 131 . A plurality of rolling elements 140 are disposed in the bearing inner space (S). A plurality of rolling elements 140 are aligned along the circumferential direction of the bearing inner space (S). Lubricant is filled in the bearing inner space (S).

As shown in FIG. 1, seals 2 and 3 seal the bearing inner space S. Respectively, the seals 2 and 3 are approximately cylindrical in shape. The seals 2 and 3 block the ends of the bearing inner space S, respectively, to prevent foreign matter from penetrating into the bearing inner space S, and to prevent leakage of the lubricating oil filled in the bearing inner space S, and may be formed of an open type (3) (not shown) and a pack type (2). Here, the seal 2 is a pack type and seals the inner end of the bearing inner space S in the axial direction of the bearing device 1.

In the lip structure formed inside the seal 2, when the frictional area due to contact with the slinger 80 increases, the wheel hub 110 and the inner wheel 120 relative to the outer wheel 130 act as a large resistance during rotation, and in this case, the seal 2 reduces the driving force transmitted from the axle to the wheel. For this reason, the torque performance of the bearing device 1 can be improved by forming the lip structure formed inside the seal 2 into a structure in which friction due to contact is minimized. In the following embodiments, the structure of the seal 2 for improving the torque performance of the bearing device 1 will be described in detail.

Fig. 3 is a view showing a cut surface when the seal 2 is cut in a vertical plane through the central axis. As shown in FIG. 3 , the seal 2 includes reinforcing iron 10 and a slinger 80 .

As shown in FIG. 3, the reinforcing iron 10 includes a reinforcing iron cylindrical portion 10a. The material of the reinforcing iron 10 is not particularly limited, but metal can be used. For example, the reinforcing iron 10 may be formed of stainless steel.

The reinforcing iron cylindrical portion 10a has a substantially cylindrical shape. The reinforcing iron cylindrical portion 10a is arranged so as to be concentric with the bearing device 1. The reinforcing iron cylindrical portion 10a extends along the axial direction of the bearing device 1.

As shown in Fig. 3, when the seal 2 is installed in the bearing device 1, the reinforcing iron 10 extends from the reinforcing iron cylindrical portion 10a toward the center with respect to the radial direction of the bearing device 1.

The seal 2 of one embodiment includes a reinforcing iron 10 mounted on the inner circumferential surface of the outer ring 130 facing the center with respect to the radial direction, an elastic body 20 fixedly attached to the reinforcing iron 10, and a slinger 80 mounted on the outer circumferential surface of the inner ring 120 facing the outer circumferential side with respect to the radial direction.

In the example of Fig. 3, one end of the reinforcing iron 10 in the axial direction of the bearing device 1 is connected to one end of the reinforcing iron cylindrical portion 10a.

The elastic body 20 is installed on the reinforcing iron 10. The elastic body 20 is fixed to the reinforcing iron 10 so as not to be separated from the reinforcing iron 10 .

The elastic body 20 may be formed of a material having elasticity. As the material of the elastic body 20, the elastomer, which is a rubber compound, is selected as a result of wear and torque tests for 20 hours at 2000 RPM in a grease-free state within 0.1 Nm, and includes nitrile (NBR), hydrogenated nitrile (HNBR), and fluorocarbon (FKM). When using an elastomer as the material of the elastic body 20, the elastic body 20 can be fixed to the reinforcing iron 10 by vulcanization bonding, for example.

The elastic body 20 covers the entire inner circumferential surface and the open end of the reinforcing iron cylindrical portion 10a. After the elastic body 20 extends along the inner surface of the reinforcing iron 10, it is folded back at the open end and extended to the middle of the outer circumferential surface.

The elastic body 20 includes a protrusion 30 at an axially inner end of the reinforcing iron cylindrical portion 10a. Due to the protrusion 30 formed at the inner end of the reinforcing cylindrical portion 10a, foreign substances are primarily prevented from permeating, and secondarily, the reinforcing cylindrical portion 10a and the slinger 80 are prevented from being separated after assembly.

The elastic body 20 further includes a mud collecting lip 50, a mud collecting radial lip 50a, a mud collecting axial lip 50b, a side lip 50b, and a seal lip 70. The side lip 50b and the seal lip 70 block the gap generated between the reinforcing iron 10 and the slinger 80.

Here, the protrusion 30 extends more toward the center of the radial direction than the inclined portion 40a of the slinger 80 to prevent the slinger 80 from being separated from the reinforcing iron 10, and at the same time, by the elasticity of the rubber, it acts on the external pressure of foreign substances and moisture introduced from the outside through the opening formed by the protrusion 30 and the inclined portion 40a of the slinger 80, and is bent toward the surface of the slinger to close the gap between the foreign substances and the moisture input path. Minimize. At this time, in order to support the slinger 80 and have appropriate flexibility by elasticity against external pressure, the thickness of the axial section of the projection 30 is 0.15 to 0.25 mm.

The slinger 80 includes an inclined portion 40a inclined outward in the axial direction.

The inner end surface in the axial direction of the slinger 80 is formed to be positioned on a straight line with the inner end surface in the axial direction of the protrusion 30.

The inner end surface in the axial direction of the slinger outer diameter portion 40 and the outer end surface in the axial direction of the protrusion 30 overlap each other.

The mud collecting radial lip 50a and the mud collecting axial lip 50b, which do not contact the slinger 80, suppress the penetration of some foreign substances and moisture that may come into the seal 2 from the outside. The mud collecting axial lip 50b collects some of the large particle foreign matter and moisture entering the axial direction through the opening between the protrusion 30 and the slinger outer diameter portion 40, thereby effectively preventing some foreign matter and mud from entering the bearing device 1.

Since there are first mud collecting troughs 101 and second mud collecting troughs 201, some of the foreign substances and moisture introduced through the opening between the protrusion 30 and the outer diameter of the slinger 40 are stored in the first mud collecting trough 101 and the second mud collecting trough 201 by the action of the mud collecting axial lip 50a and the mud collecting axial lip 50b.

Some foreign substances and water stored in the first mud collecting trough 101 and the second mud collecting trough 201, which are open to the outer circumferential side in the radial direction, are induced to be discharged through the opening between the protrusion 30 and the slinger outer diameter 40 by centrifugal force when the wheel hub 110 and the inner ring 120 rotate, and are easily discharged to the outside of the bearing device 1.

In addition, since the mud collecting radial lip 50a and the mud collecting axial lip 50b do not contact the slinger 80, the number of elastic bodies 20 that rotate in pressure contact with the non-rotating slinger 80 is reduced. Frictional force, that is, torque force generated by the elastic body 20 and the slinger 80 is reduced, and the performance of the bearing device 1 can be further improved.

The side lip 60 protrudes from the elastic body 20 toward the surface of the slinger 80 and is installed along the circumferential direction of the reinforcing iron 10 to form a substantially annular shape. The side lip 60 is in inclined pressure contact with the outer surface in the radial direction of the slinger 80, and the mud collecting radial lip 50a and the mud collecting axial lip 50b fail to partially block the sealing 2. By blocking foreign substances or moisture introduced into the bearing device 1, it is possible to more effectively block some foreign substances and moisture from entering the bearing device 1.

In addition, as the side lip 60 presses and contacts the surface of the slinger 80 at an angle toward the outer circumferential side in the radial direction through which foreign matter or moisture flows, it has a structure in which foreign matter or moisture is difficult to inflow while discharge is easy.

The seal lip 70 protrudes from the vicinity of the open end of the reinforcing iron 10 toward the slinger cylindrical portion 80a.

The seal lip 70 is installed along the circumferential direction of the end of the reinforcing iron 10, forming a substantially annular shape. The front end of the seal lip 70 is pressed against the slinger cylindrical portion 80a.

Therefore, the seal lip 70 prevents the oil inside the bearing device 1 from leaking out.

Grease is filled in the space formed by the combination of the slinger 80 and the reinforcing iron 10. This grease has excellent adhesiveness and water resistance, and excellent heat resistance, so it has excellent lubrication performance for lubricating parts at high temperatures. It is provided for smoother operation of automobile wheel bearings.

The grease filled in the wheel bearing is preferably lithium grease (HIREX OHD REASE).

The slinger 80 blocks the flow of foreign substances and moisture flowing into the opening.

The slinger cylindrical portion 80a has a substantially cylindrical shape. The slinger cylindrical portion 80a is arranged so as to be concentric with the bearing device 1. When the seal 2 is installed in the bearing device 1, the inner circumferential surface of the slinger cylindrical portion 80a is opposed to the outer circumferential surface of the inner ring 12. The slinger cylindrical portion 80a extends along the axial direction of the bearing device 1.

As shown in Fig. 3, the outer circumferential surface of the slinger cylindrical portion 80a is opposed to the open end of the reinforcing iron 10. The front end of the seal lip 70 presses into contact with the outer circumferential surface of the slinger cylindrical portion 80a.

The slinger 80 is approximately annular. When the seal 2 is installed in the bearing device 1, the slinger 80 is bent and extended from the slinger cylindrical portion 80a toward the outer circumferential side of the bearing device 1 in the radial direction. In the example of Fig. 3, one end of the slinger 80 in the axial direction of the bearing device 1 is connected to one end of the slinger cylindrical portion 80a.

When the seal 2 is installed in the bearing device 1, the axial directions of the reinforcing cylindrical portion 10a and the slinger cylindrical portion 80a coincide with the axial direction of the bearing device 1.

The surface of the slinger 80 is opposed to the surface of the reinforcing iron 10. The front end of the side lip 60 is in press contact with the surface of the slinger 80.

Although it does not specifically limit as a material of the slinger 80, For example, metal, such as stainless steel, can be used.

The sensor may include a wheel speed sensor capable of measuring wheel speed. In order to generate a magnetic signal, the protruding portion 30 may also include a material having the magnetic properties. As the protrusion 30 rotates around the rotational axis A, the magnetic field generated by the part containing the magnetic material of the protrusion 30 changes, and the sensor can detect this change in the magnetic field. In embodiments, the protrusion 30 may include a material having magnetism, such as ferrite and rare earth (rare earth elements) material, and specifically, neodymium (Nd), samarium (Sm), cobalt (Co), and the like.

Hereinafter, a second embodiment of the present invention will be described.

As shown in FIG. 4, the slinger 80 includes an inclined portion 40a inclined outward in the axial direction.

The inner end surface of the slinger 80 in the axial direction is aligned with the inner end surface of the protrusion 30 in the axial direction.

The inclined portion 40a of the slinger 80 and the outer end surface in the axial direction of the protrusion 30 overlap each other.

The slinger 80 has a slinger outer diameter portion 40 extending to the inclined portion 40a curved outward in the axial direction.

The outer diameter portion 40 of the slinger is formed inclined at an angle of about 10 to 20 degrees from the inclined portion 40a toward the outer circumferential side in the radial direction.

The protrusion 30 extends toward the center in the radial direction rather than the curved portion 40a to prevent the slinger 80 from being separated from the reinforcing iron 10, and at the same time, the elasticity of the rubber minimizes the gap between the foreign matter and moisture input path by acting on the external pressure of foreign matter and moisture introduced through the opening formed by the protrusion 30 and the slinger 80. At this time, the thickness of the axial section of the protrusion 30 is 0.15 to 0.25 mm.

Therefore, some foreign substances and moisture stored in the first mud collection bone 101 and the second muff collection bone 201, which are opened in the outer circumferential side, are discharged by the centrifugal force when the wheel hub 110 and the inner wheel 120 are discharged by the centrifugal force, while the inflow of the foreign substance or moisture is difficult. The discharge is easy to discharge along the slope of the wealth 40.

In the description of the first and second preferred embodiments of the present invention, when the bearing device 1 is mounted and operating, the seal 160 formed between the rotating inner ring 120 and the stationary outer ring 110 has been described, but the rights of the present invention are not limited thereto.

10: reinforcement iron
10a; Reinforced iron cylinder
20: elastic body
20a: anti-stick
30: projection
40: slinger outer diameter
50a: Mud collecting radial lip
50b: mud collecting axial lip
60: side lip
70: seal lip
80: slinger
80a: slinger cylinder

Claims (2)

In the seal assembly for sealing the end of the bearing inner space formed between the inner ring and the outer ring of the bearing device formed between the inner ring coupled to the hub shaft and rotating together and the outer ring that does not rotate,
a reinforcing iron cylindrical portion mounted on an inner circumferential surface of the non-rotating outer ring toward the center with respect to the radial direction and arranged to be concentric with the bearing device;
a slinger cylindrical portion mounted on an outer circumferential surface of the rotating inner ring toward an outer circumferential side with respect to a radial direction and arranged to be a concentric axis with the bearing device;
Reinforcing iron bent and extending from the outer end of the reinforcing iron cylindrical portion toward the center in the radial direction;
a slinger bent and extending from an inner end of the cylindrical slinger toward an outer circumferential side in a radial direction;
an elastic body fixed to the reinforcing iron so as not to fall from the reinforcing iron and formed of a material having elasticity;
The elastic body covers the entire radial central side surface of the reinforcing iron cylinder part and extends from the open end of the reinforcing iron cylinder part to the middle of the outer circumferential side, and extends along the axial inner surface of the reinforcing iron to cover and cover the open end of the reinforcing iron.
A protrusion protruding from the open end of the reinforcing cylindrical portion toward the center in the radial direction beyond the end of the outer diameter portion of the slinger and having a thickness of 0.15 to 0.25 mm;
a mud collecting lip that does not contact the slinger;
a side lip that comes into contact with the slinger at an angle;
a seal lip contacting the slinger cylindrical portion;
The mud collecting ribs include a mud collecting radial lip facing radially outward; and a mud collecting axial lip facing axially inward;
an outer diameter portion of the slinger extending and protruding in a straight line from an end of the inclined portion of the slinger to a radial outer circumferential side and disposed in parallel with the mud collecting radial lip;
It includes a first mud collecting bone and a second mud collecting bone for storing some of the foreign substances and moisture introduced through the opening between the protrusion and the outer diameter of the slinger,
The material of the elastic body is an elastomer, which is a rubber compound, and is a low-torque seal assembly for bearings, characterized in that any one of nitrile (NBR), hydrogenated nitrile (HNBR), and fluorocarbon (FKM). According to claim 1, wherein the slinger is an outer diameter portion of the slinger extending outwardly in the axial direction to the curved inclined portion;
The low-torque seal assembly for bearings, characterized in that the slinger outer diameter portion is formed to be inclined by 10 to 20 ° from the inclined portion toward the outer circumferential side in the radial direction.