JP6762657B2 - side rail - Google Patents

Description

The present invention relates to a side rail that is combined with an annular spacer expander to form a combined oil ring for an internal combustion engine together with the spacer expander.

In addition to the compression ring for sealing the combustion gas, the piston of the reciprocating engine (reciprocating internal combustion engine) is equipped with an oil ring for controlling the oil on the inner surface of the cylinder. As such an oil ring, a combination oil ring formed by combining an annular spacer expander with one or a pair of side rails is often used.

The side rail used for the combination oil ring is formed in the shape of a split ring with a joint, and is urged by a spacer expander to increase the diameter, and a predetermined contact pressure (surface pressure) is applied to the inner surface of the cylinder on the outer peripheral surface thereof. Contact with. Then, when the engine operates and the piston reciprocates, the side rail slides on the inner surface of the cylinder on the outer peripheral surface thereof to form an oil film of an appropriate thickness on the inner surface of the cylinder and remove excess oil adhering to the inner surface of the cylinder. Scratch it toward the crank chamber side to prevent oil from rising.

In recent years, as the performance of internal combustion engine engines has improved due to market demands such as low fuel consumption and low oil consumption, the combined oil ring also controls the oil scraping action during the piston ascending stroke (compression stroke and exhaust stroke) and piston lowering. By amplifying the oil scraping action during the stroke (suction stroke and combustion stroke), there is a demand for a product having the ability to reduce oil consumption while reducing friction with respect to the inner surface of the cylinder. Then, in order to meet such a demand, side rails having various shapes on the outer peripheral surface facing outward in the radial direction have been proposed.

For example, Patent Document 1 describes a side rail having an outer peripheral surface facing outward in the radial direction formed into a curved surface shape having an apex at the center position in the axial direction and protruding outward in the radial direction.

Further, it is generally known that the friction of the side rail with respect to the cylinder inner surface is reduced by reducing the contact width of the outer peripheral surface with the cylinder inner surface. In order to reduce the contact width, the outer peripheral surface of the side rail is generally known. Is formed into a vertically (front and back) asymmetrical shape having a slight shape change.

For example, in Patent Document 2, a pair of asymmetric regions including an outer peripheral apex portion and having an asymmetric shape in the axial direction are provided, and the outer peripheral surface is symmetrical with each other in the axial direction on both sides of the asymmetric region. A side rail having a symmetric region is described.

Japanese Unexamined Patent Publication No. 2003-194222 Japanese Patent No. 5833276

However, if the outer peripheral surface is formed in a vertically asymmetrical shape due to a slight change in shape as described above, it is difficult to determine the vertical direction (front and back) of the side rail, and it is difficult to determine the directionality of the side rail during manufacturing or the piston. There is a problem that the side rail may be assembled in an incorrect posture during the assembling work to the ring groove.

An object of the present invention is to solve such a point, and an object of the present invention is to provide a side rail which can easily determine the vertical direction.

The side rail of the present invention is a side rail formed in a split ring shape having a joint, combined with an annular spacer expander to form a combined oil ring for an internal combustion engine together with the spacer expander, and is a radial outer side. The outer peripheral surface facing inward, the inner peripheral surface facing inward in the radial direction, the first axial side surface facing one side in the axial direction, and the first axial side surface facing the other side in the axial direction and parallel to the first axial side surface. It has two axial side surfaces, has a chamfered portion between the outer peripheral surface and the second axial side surface , and has a diameter from the outer peripheral surface to the radial outer end of the second axial side surface. The directional distance is larger than the radial distance from the outer peripheral surface to the radial outer end of the first axial side surface, and the chamfered portion is formed from the first axial side surface to the second shaft. The tapered surface is formed by a tapered surface whose diameter is gradually reduced toward the side of the second axial side surface starting from a position on the outer peripheral surface which is 0.05 mm or more in the axial direction toward the directional side surface. It has a first tapered surface portion, and a second tapered surface portion provided between the first tapered surface portion and the outer peripheral surface and having a smaller inclination angle with respect to the axial direction than the first tapered surface portion. It is characterized by.

In the above configuration, the "split ring shape provided with the abutment portion" is formed in a C shape in which the oil ring main body is cut at a part in the circumferential direction and the cut portion is a abutment portion. Means that. Further, the "axial direction" means a direction along the axial center of the split ring-shaped side rail.

In the present invention, in the above configuration, it is preferable that the first tapered surface portion and the second tapered surface portion are smoothly connected by a curved tapered surface sub-section.

In the above configuration, the tapered surface is provided so as to sandwich the outer peripheral surface region in the axial direction when the region where the outer peripheral surface and the second tapered surface portion are combined is defined as the outer peripheral surface region. The region of the sub-part and the region of the outer peripheral lower end surface of the curved shape provided between the outer peripheral surface and the first axial side surface are the first axial side surface and the second axial side surface. It is preferable that the shapes are asymmetrical with respect to the virtual surface passing through the intermediate position in the axial direction.

In the present invention, in the above configuration, it is preferable that the first tapered surface portion is formed in a curved surface shape.

According to the present invention, since a chamfered portion having visibility is provided between the outer peripheral surface and the second axial side surface, even if the side rail has vertical (front and back) directions, it is manufactured at the time of manufacturing. The top and bottom of the side rail can be easily discriminated by visually observing the chamfered portion when assembling the piston to the ring groove.

As described above, according to the present invention, it is possible to provide a side rail that makes it easy to determine the vertical direction.

It is a top view of the combination oil ring provided with the side rail which is one Embodiment of this invention. It is a vertical cross-sectional view which shows the use state of the combination oil ring shown in FIG. It is a top view of the side rail shown in FIG. It is sectional drawing which follows the AA line in FIG. It is a modification of the side rail shown in FIG. 4, and is the cross-sectional view in the case where the tapered surface sub-section is provided between the first tapered surface portion and the second tapered surface portion. It is a modification of the side rail shown in FIG. 4, and is a cross-sectional view when the first tapered surface portion is formed in a curved surface shape.

Hereinafter, the present invention will be described in more detail with reference to the drawings.

As shown in FIG. 1, the side rail 1 according to the embodiment of the present invention constitutes a combination oil ring (oil control ring) 3 together with the spacer expander 2. In the case shown in the figure, the combination oil ring 3 is a three-piece type in which a pair of side rails 1 are combined on both sides in the axial direction of the spacer expander 2, and as shown in FIG. 2, a reciprocating internal combustion engine such as a gasoline engine is used. It is used by being mounted on a ring groove 4a formed on the outer peripheral surface of a piston 4 of an engine.

The combination oil ring 3 may be a two-piece type in which only one side rail 1 is combined with the spacer expander 2.

The spacer expander 2 is formed of a steel material in an annular shape that can be elastically deformed in the radial inward and outward directions, and is mounted in the ring groove 4a of the piston 4 in a state of being elastically deformed in the radial direction to attach the side rail 1 in the radial direction. It is urged to increase the diameter toward the outside and the outside in the axial direction.

The pair of side rails 1 according to the embodiment of the invention have the same configuration as each other, and as shown in FIG. 3, the abutment 10 is formed by bending a long flat steel material (steel material). It is formed in the shape of a split ring provided. That is, the side rail 1 is formed in a C shape in which a part of the side rail 1 is cut in the circumferential direction and the cut portion becomes a joint opening 10. The side rail 1 can be elastically deformed so as to increase the distance between the abutments 10 in the circumferential direction, and the diameter can be expanded toward the outside in the radial direction.

As shown in FIG. 4, the side rail 1 has a first axial side surface 11 facing one side in the axial direction (lower side in the figure) and a second shaft facing the other side in the axial direction (upper side in the figure). It includes a directional side surface 12, an inner peripheral surface 13 facing inward in the radial direction, and an outer peripheral surface 14 facing outward in the radial direction, and the cross-sectional shape perpendicular to the circumferential direction is substantially uniform over the entire circumference. The "axial direction" is a direction along the axial center of the split ring-shaped side rail 1.

The first axial side surface 11 is formed on a flat surface perpendicular to the axial direction. As shown in FIG. 2, the first axial side surface 11 is directed toward the crank chamber side of the engine in a state where the combined oil ring 3 using the side rail 1 is mounted on the piston 4.

As shown in FIG. 4, the second axial side surface 12 is formed on a flat surface perpendicular to the axial direction, that is, parallel to the first axial side surface 11. As shown in FIG. 2, the second axial side surface 12 is directed toward the combustion chamber side of the engine in a state where the combination oil ring 3 using the side rail 1 is mounted on the piston 4.

In the case of illustration, the axial distance between the pair of axial side surfaces 11 and 12 of the side rail 1, that is, the axial thickness (rail width) W of the side rail 1 is 0.35 mm, and the inner peripheral surface 13 and the outer peripheral surface 14 The interval, that is, the radial length L is 1.52 mm.

As shown in FIG. 4, the inner peripheral surface 13 of the side rail 1 is formed in a curved surface shape (barrel face) having an apex at the center position in the axial direction. As shown in FIG. 2, the inner peripheral surface 13 of the side rail 1 comes into contact with the seat surface 2a of the spacer expander 2 in a state where the combined oil ring 3 using the side rail 1 is mounted on the piston 4.

The inner peripheral surface 13 is not limited to the above shape, and various shapes such as a cylindrical surface shape parallel to the axial direction can be adopted.

As shown in FIG. 4, the outer peripheral surface 14 of the side rail 1 is formed in a cylindrical surface shape parallel to the axial direction. As shown in FIG. 2, the side rail 1 is in contact with the cylinder inner surface 20 on the outer peripheral surface 14.

In the side rail 1, a chamfered portion 30 is provided at one end of both ends in the axial direction of the outer peripheral surface 14. That is, a chamfered portion 30 is provided between the outer peripheral surface 14 and the second axial side surface 12. The outer peripheral surface 14 and the first axial side surface 11 may be formed in a shape in which a chamfered portion is not provided, but may be formed in a rounded R shape. In this case, the R shape may be formed. Is formed to have a smaller radial width and axial width than the chamfered portion 30.

The chamfered portion 30 is located at a position on the outer peripheral surface 14 where the axial distance B from the first axial side surface 11 to the second axial side surface 12 is 0.05 mm or more, that is, from the first axial side surface 11. Starting from a position on the outer peripheral surface 14 that is 0.05 mm or more in the axial direction toward the second axial side surface 12, and gradually reducing the diameter from the starting point toward the second axial side surface 12. It is formed by a tapered surface 30a extending to the second axial side surface 12.

The axial distance B, which is the starting point of the chamfered portion 30, is more preferably set to 0.10 mm or more.

As shown in FIG. 4, the tapered surface 30a constituting the chamfered portion 30 is formed between the first tapered surface portion 30a1 inclined at an angle θ1 with respect to the axial direction, the first tapered surface portion 30a1, and the outer peripheral surface 14. It is configured to have a second tapered surface portion 30a2 that is provided and is inclined with respect to the axial direction at an angle θ2 smaller than that of the first tapered surface portion 30a1.

In the case shown in the drawing, both the first tapered surface portion 30a1 and the second tapered surface portion 30a2 are formed in a shape (conical surface shape) that linearly reduces the diameter, that is, a linear tapered surface. In this case, the angle θ1 formed by the first tapered surface portion 30a1 with respect to the axial direction is preferably set to be larger than 10 °, more preferably 30 ° or more.

Further, the length T of the chamfered portion 30, that is, the tapered surface 30a in the radial direction is preferably 0.05 mm or more.

As described above, in the side rail 1 of the present invention, the chamfered portion 30 having visibility is provided at one end of both ends in the axial direction of the outer peripheral surface 14, and thus the chamfered portion 30 is provided. Even if the side rails have vertical (front and back) directions, the chamfered portion 30 can be visually observed during the manufacturing of the side rail 1 or the assembly work of the piston into the ring groove of the side rail 1. The top and bottom can be easily distinguished. Therefore, it is possible to prevent the side rail 1 from being erroneously assembled in the wrong posture during the work.

Further, the tapered surface 30a constituting the chamfered portion 30 has a first tapered surface portion 30a1 and a second tapered surface portion 30a2 inclined with respect to the axial direction at an angle θ2 smaller than that of the first tapered surface portion 30a1. Therefore, the radial length T of the chamfered portion 30 can be secured to improve the visibility thereof, and the incident angle with respect to the outer peripheral surface 14 can be reduced by the second tapered surface portion 30a2. As a result, the chamfered portion 30 can prevent the oil from being scraped up by the edge of the outer peripheral surface 14 with respect to the inner surface 20 of the cylinder, and the oil consumption can be reduced.

As shown in FIG. 5, the tapered surface 30a constituting the chamfered portion 30 is provided with a curved tapered surface sub portion 30a3 between the first tapered surface portion 30a1 and the second tapered surface portion 30a2, and the tapered surface sub portion 30a3 is provided. The first tapered surface portion 30a1 and the second tapered surface portion 30a2 may be smoothly connected by the portion 30a3. In this case, the tapered surface auxiliary portion 30a3 is preferably a curved surface having a constant radius of curvature, but may also be a curved surface in which the radius of curvature gradually changes.

In this way, the tapered surface 30a constituting the chamfered portion 30 is configured to have a curved tapered surface sub-section 30a3 provided between the first tapered surface portion 30a1 and the second tapered surface portion 30a2, thereby providing an outer circumference. Oil consumption can be further reduced by more effectively preventing oil scraping by the edges of the surface 14.

Further, as shown in FIG. 6, the first tapered surface portion 30a1 of the chamfered portion 30 can be formed in a curved surface shape. Also in this case, it is preferable that the first tapered surface portion 30a1 has a curved surface shape having a constant radius of curvature, but it can also be a curved surface shape in which the radius of curvature gradually changes.

In this way, by configuring the chamfered portion 30 to have the first tapered surface portion 30a1 having a curved surface shape, the chamfered portion 30 can be made more visible, and the vertical discrimination of the side rail 1 can be further facilitated. it can.

In the case shown in FIG. 6, the tapered surface sub-section 30a3 is not provided between the first tapered surface portion 30a1 and the second tapered surface portion 30a2, but the first tapered surface portion 30a1 and the second tapered surface portion 30a1 are provided. It is also possible to provide a tapered surface auxiliary portion 30a3 between the 30a2 and the 30a2.

As shown in FIG. 5, if the area of the chamfered portion 30 in which the second tapered surface portion 30a2 facing outward in the radial direction and the outer peripheral surface 14 are combined is defined as the outer peripheral surface region A1, it is easy to distinguish the top and bottom of the side rail 1. For this purpose, the outer circumference of the curved surface shape provided between the two regions sandwiching the outer peripheral surface region A1 in the axial direction, that is, the region A2 of the tapered surface auxiliary portion 30a3, and the outer peripheral surface 14 and the first axial side surface 11. It is preferable that the region A3 of the lower end surface 15 has an asymmetric shape with respect to the virtual surface S passing through the axial intermediate position between the first axial side surface 11 and the second axial side surface 12.

In this case, the outer peripheral surface region A1 of the side rail 1 is preferably formed in an asymmetrical shape in the axial direction. Although details are not shown, in this asymmetric shape, the line passing through the center in the axial direction is set as the first intermediate line, and the contour curve of the outer peripheral surface in the vertical cross section is traced in the outer peripheral tip portion in the radial direction from the outer peripheral apex. Of the two positions on the contour curve at a position with a distance of 3 μm toward the inner peripheral side, the position on the combustion chamber side of the engine is defined as position a1, the position on the side away from the combustion chamber of the engine is defined as position b1, and those positions a1 and b1 When the length of the line between and is L1 and the middle line of the line of the length L1 is the second middle line, the second middle line is farther from the combustion chamber of the engine than the first middle line. The outer peripheral apex of the side rail 1 located on the side is located on the second intermediate line or on the side away from the combustion chamber of the engine from the second intermediate line, and the contour curve of the outer peripheral surface in the vertical cross section is in the radial direction. The side rail 1 is traced from the outer peripheral apex to the inner peripheral side in the radial direction to at least 0.025 mm so that a symmetrical shape having a pair of both ends in the axial direction exists at the inner peripheral side position. The asymmetrical contour curve at the tip of the outer circumference is sandwiched between the outer peripheral apex and the outer peripheral apex at a distance of 1.5 μm toward the inner peripheral side in the radial direction. When it is divided into contour parts sandwiched by a distance of 3.0 μm, the first contour division, the second contour division, and the third contour division are set from the combustion chamber side of the engine of the cylinder, and the first contour division is the second contour division. The second contour division is provided in a part of a linear shape or a quadratic curve shape starting from the first end on the combustion chamber side of the engine, and the second contour division has an outer peripheral apex in the middle and is provided in an arc shape. Is provided so as to be a part of the quadratic curve shape starting from the second end portion on the side away from the combustion chamber of the engine of the second contour division, and the surface roughness of the asymmetric portion of the outer peripheral surface of the side rail 1. Is 0.6 μmRp or less, and among the outer peripheral tip portions in the contour curve, a line segment L1 which is a radial line orthogonal to the line segment between the position a1 and the position b1 and is divided by a line passing through the outer peripheral apex. The length on the position a1 side is L2, the length on the position b1 side is L3, and the positions on the combustion chamber side of the engine are set at two positions on the contour curve at a distance of 1.5 μm toward the inner peripheral side in the radial direction. When the position a2 and the position away from the combustion chamber of the engine are set to the position b2 and the length of the line between the position a2 and the position b2 is L4, 0.05 mm ≦ L1 ≦ 0.15 mm, L2 / L1 Satisfy the conditions of ≧ 0.5 and L3 / L1 ≦ 0.74, and pass through position a1 and position a2. When the angle formed by the first straight line and the axial direction of the cylinder is an angle θ3, the condition of 2 degrees ≤ θ3 ≤ 7 degrees is satisfied, and the position b1 and the second straight line passing through the position b2 and the axial direction of the cylinder are When the angle formed is the angle θ4, the shape can satisfy the condition of 9 degrees ≤ θ4.

Alternatively, as the asymmetric shape of the outer peripheral surface region A1 of the side rail 1, the line passing through the center of the segment width is set as the first intermediate line, and the outer peripheral apex at the outer peripheral tip portion where the contour curve of the outer peripheral surface in the vertical cross section is traced. Of the two positions on the contour curve at a position with a distance of 3 μm toward the inner peripheral side in the radial direction, the position on the combustion chamber side of the engine is defined as position a1, and the position on the side away from the combustion chamber of the engine is defined as position b1. When the length of the line segment between a1 and the position b1 is L1 and the intermediate line of the line segment of the length L1 is the second intermediate line, the second intermediate line is more of the engine than the first intermediate line. The outer peripheral apex of the side rail 1 is located on the side away from the combustion chamber and is located on the second intermediate line or on the side away from the combustion chamber of the engine from the second intermediate line, and the contour curve of the outer peripheral surface in the vertical cross section is , At least 0.025 mm is traced from the outer peripheral apex of the side rail 1 toward the inner peripheral side in the radial direction so that there is a symmetrical shape with both ends in the axial direction at the inner peripheral side position in the radial direction. The asymmetrical contour curve at the outer peripheral tip of the third rail 1 is oriented toward the inner peripheral side in the radial direction and is sandwiched between the outer peripheral apex and the outer peripheral apex at a distance of 1.5 μm and the outer peripheral apex toward the inner peripheral side in the segment radial direction. When divided into contour parts sandwiched between a distance of 1.5 μm and a distance of 3.0 μm, the first contour division, the second contour division, and the third contour division are set from the combustion chamber side of the engine of the cylinder, and the first contour division is The second contour division is provided on a part of a linear shape or a quadratic curved shape starting from the first end portion on the combustion chamber side of the engine of the second contour division, and the second contour division has a flat portion in the middle thereof and the shaft of the flat portion. It consists of a part of a straight line shape or a quadratic curve shape from the end on the combustion chamber side of the engine in the direction, and has a shape continuous with the first contour division, and the end on the side away from the combustion chamber of the engine in the axial direction of the flat part. It is composed of a part of the quadratic curve shape and is provided in a shape continuous with the third contour division, and the third contour division is provided so as to be a part of the quadratic curve shape continuous with the second end portion. The surface roughness of the asymmetrical portion of the outer peripheral surface of the rail 1 is 0.6 μmRp or less, and is orthogonal to the line segment between the position a1 and the position b1 of the outer peripheral tip portion in the contour curve of the outer peripheral surface of the side rail 1. The length of the line segment L1 that is a radial line and is divided by the line passing through the outer peripheral apex is L2 on the position a1 side, L3 is the length on the position b1 side, and the distance is further toward the inner peripheral side in the radial direction. Positions on the combustion chamber side of the engine at two positions on the contour curve at 1.5 μm Is the position a2, the position away from the combustion chamber of the engine is the position b2, the length of the line segment between the position a2 and the position b2 is L4, and the axial length of the flat portion of the second contour division. Is L5, the conditions of 0.05 mm ≦ L1 ≦ 0.15 mm, L2 / L1 ≧ 0.5, L4 / L1 ≦ 0.76, and 0 <L5 ≦ 0.05 mm are satisfied, and the positions a1 and a2 are set. When the angle formed by the first straight line passing through and the axial direction of the cylinder is an angle θ3, the condition of 3 degrees ≤ θ3 ≤ 6 degrees is satisfied, and the second straight line passing through the position b1 and the position b2 and the axial direction of the cylinder form. When the angle is the angle θ4, the shape can satisfy the condition of 9 degrees ≤ θ4.

While the outer peripheral surface region A1 has such a shape, the region A2 of the tapered surface auxiliary portion 30a3 and the region A3 of the outer peripheral lower end surface 15 are axially intermediate positions between the first axial side surface 11 and the second axial side surface 12. By making the shapes asymmetrical with each other with respect to the virtual surface S passing through the above, it is possible to further facilitate the vertical discrimination of the side rail 1 while reducing the oil consumption.

Although details are not shown, a hard film (hard layer) may be provided on at least the outer peripheral surface 14 and the chamfered portion 30, that is, the tapered surface 30a. As the hard film, for example, a configuration including at least one of a nitriding treatment layer, a PVD treatment layer, a hard chrome plating treatment layer, and a DLC layer can be adopted.

The "PVD-treated layer" means a "layer formed by physical vapor deposition", and the "DLC (Diamond Like Carbon) layer" is a non-polycarbon or carbon homogeneous layer. It means a crystalline hard carbon film.

By providing such a hard film, the shape of the outer peripheral surface 14 does not change due to wear, the shape of the outer peripheral surface is maintained, the surface pressure decrease is small, the oil control function is maintained, and the oil consumption is reduced over a long period of time. The effect of reducing the fuel consumption of the engine can be obtained while reducing the amount, and the hue of the chamfered portion 30 visually recognized can be changed more clearly with respect to the second axial side surface 12 and the outer peripheral surface 14. .. In particular, when the outer peripheral surface 14 is subjected to a wrapping process, the difference in hue becomes larger. Therefore, by providing the hard film, the chamfered portion 30 can be made more visible, and the vertical discrimination of the side rail 1 can be further facilitated.

In addition to having the shape shown in FIG. 4, the axial thickness (W) is 0.35 mm, the axial distance (B) indicating the chamfered position of the chamfered portion is 0.15 mm, and the chamfered portion has the shape with respect to the axial direction of the first tapered surface portion. We prepared 100 side rails with an angle (θ1) of 30 ° and an angle (θ2) of the second tapered surface with respect to the axial direction of 6 °, and 10 workers visually moved the side rails up and down. The direction of was determined. As a result, the operator was able to correctly determine the vertical direction of all the side rails.

It goes without saying that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the gist thereof.

For example, in the above-described embodiment, the outer peripheral surface 14 has a cylindrical surface shape parallel to the axial direction, but the outer peripheral surface 14 may be formed into another shape such as a vertically (front and back) asymmetric shape having a slight shape change. it can.

1 Side rail 2 Spacer expander 2a Seat surface 3 Combination oil ring 4 Piston 4a Ring groove 10 Abutment 11 First axial side surface 12 Second axial side surface 13 Inner peripheral surface 14 Outer outer surface 15 Outer outer lower end surface 20 Cylinder inner surface 30 chamfer Part 30a Tapered surface 30a1 First tapered surface part 30a2 Second tapered surface part 30a3 Tapered surface sub-part W Axial thickness L Radial length B Axial distance θ Angle T Radial length θ1 Angle θ2 Angle A1 Outer surface region A2 Area of the sub-tapered surface A3 Area of the lower end surface of the outer circumference S Virtual surface

Claims (4)

A side rail that is formed in the shape of a split ring with a joint and is combined with an annular spacer expander to form a combined oil ring for an internal combustion engine together with the spacer expander.
The outer peripheral surface facing outward in the radial direction and
The inner peripheral surface facing inward in the radial direction and
A first axial side surface facing one side in the axial direction,
It has a second axial side surface that faces the other side in the axial direction and is parallel to the first axial side surface.
A chamfered portion is provided between the outer peripheral surface and the second axial side surface.
The radial distance from the outer peripheral surface to the radial outer end of the second axial side surface is larger than the radial distance from the outer peripheral surface to the radial outer end of the first axial side surface. ,
The side of the second axial side surface with the chamfered portion starting from a position on the outer peripheral surface that is axially separated from the first axial side surface toward the second axial side surface by 0.05 mm or more in the axial direction. Formed by a tapered surface that gradually shrinks toward
The tapered surface is provided between the first tapered surface and the first tapered surface and the outer peripheral surface, and the second tapered surface has a smaller inclination angle with respect to the axial direction than the first tapered surface. A side rail characterized by having,. The side rail according to claim 1, wherein the first tapered surface portion and the second tapered surface portion are smoothly connected by a curved tapered surface auxiliary portion. When the region in which the outer peripheral surface and the second tapered surface portion are combined is defined as the outer peripheral surface region, the region of the tapered surface sub-part and the outer peripheral surface provided so as to sandwich the outer peripheral surface region in the axial direction. The region of the outer peripheral lower end surface of the curved surface shape provided between the first axial side surface and the first axial side surface is a virtual surface passing through an axial intermediate position between the first axial side surface and the second axial side surface. The side rail according to claim 2, wherein the side rails have an asymmetrical shape with respect to each other. The side rail according to any one of claims 1 to 3, wherein the first tapered surface portion is formed in a curved surface shape.

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