JP7631508B2 - Spacer expander and oil ring - Google Patents

Description

The present invention relates to a spacer expander and an oil ring combining a segment and a spacer expander.

Internal combustion engines installed in general automobiles adopt a configuration in which piston rings including a compression ring (pressure ring) and an oil ring are attached to the ring groove of the piston. In the axial direction of the piston, the compression ring is provided on the combustion chamber side, and the oil ring is provided on the crank chamber side, and they perform their functions by sliding on the inner wall surface of the cylinder. The oil ring has an oil seal function that suppresses the outflow of oil to the combustion chamber side (oil rising) by scraping off excess engine oil (lubricating oil) attached to the inner wall surface of the cylinder to the crank chamber side, and a function to prevent piston seizure caused by the operation of the internal combustion engine by adjusting the amount of oil so that a lubricating oil film is appropriately maintained on the inner wall surface of the cylinder. The compression ring has a gas seal function that suppresses the outflow of combustion gas from the combustion chamber side to the crank chamber side (blow-by) by maintaining airtightness, and an oil seal function that suppresses oil rising by scraping off excess oil that the oil ring could not scrape off.

Here, a three-piece combined oil ring is widely used, which combines a pair of segments (also called side rails) that slide on the cylinder inner wall surface with a spacer expander that urges the pair of segments against the cylinder inner wall surface. In relation to such combined oil rings, a combined oil ring equipped with a spacer expander that is composed of multiple wavy periodic elements that are displaced in the axial direction and are connected in the circumferential direction has been disclosed (for example, Patent Document 1). When assembling a three-piece combined oil ring to a piston, the spacer expander is fitted into the ring groove, and then the segments are fitted into the ring groove. When fitting the spacer expander into the ring groove, the spacer expander is inserted into the ring groove while expanding the gap of the spacer expander, and the gap ends of the spacer expander are butted together in the ring groove to fit the ring groove.

International Publication No. 2013/069349 Japanese Utility Model Application Publication No. 56-85048 Japanese Utility Model Application Publication No. 1-25448 Japanese Utility Model Application Publication No. 3-38456 Japanese Utility Model Application Publication No. 60-18242

When a conventional axially wavy (a wavy shape that continues in the circumferential direction when viewed radially from the oil ring) spacer expander is fitted to the ring groove of a piston, there is a risk that the joint ends will overlap in the radial or axial direction of the oil ring. If this occurs, there is a concern that it will be difficult to assemble the segments. Furthermore, even if the segments can be assembled, there is a concern that they will not be able to properly apply a biasing force and will not be able to function as an oil ring. For example, the segments may hit the top and bottom surfaces of the ring groove hard, preventing them from protruding toward the cylinder inner wall.

The present invention has been made in consideration of the above-mentioned problems, and its purpose is to provide a technology that can prevent overlapping of the joint ends of a spacer expander in an oil ring having an axially wavy spacer expander.

In order to solve the above problems, the present invention employs the following configuration. That is, the present invention is a spacer expander provided between a pair of segments spaced apart in the axial direction of an oil ring assembled to a piston in an internal combustion engine, the spacer expander comprising an expander body formed in an annular shape along the circumferential direction of the oil ring and biasing the pair of segments outward in the radial direction of the oil ring, the expander body including a pair of abutment ends that face each other to form abutments and formed in a wavy shape that continues in the circumferential direction when viewed in the radial direction of the oil ring, an expander groove formed in the expander body so as to extend along the circumferential direction of the oil ring across the abutments, and a linear member including a fitting portion formed in an arc shape along the circumferential direction of the oil ring and fitted into the expander groove so as to straddle the abutments.

According to the present invention, the linear member maintains the expander body in a position where the pair of joint ends face each other, thereby preventing the pair of joint ends from overlapping in the radial or axial direction. This prevents the segments from becoming difficult to assemble when assembling the oil ring to the piston, and prevents the oil ring assembled to the piston from failing to function. Furthermore, since the axially wavy spacer expander has a narrow axial width and radial thickness, it is difficult to provide a hole for inserting the linear member. However, the present invention employs a structure in which a groove is provided in the expander body to fit the fitting portion. This makes it possible to prevent the pair of joint ends from overlapping even with an axially wavy spacer expander.

In addition, in the present invention, the expander body includes a plurality of upper pieces arranged at intervals along the circumferential direction of the oil ring, a plurality of lower pieces arranged so as to be located closer to the crank chamber side of the internal combustion engine than the plurality of upper pieces in the axial direction of the oil ring when the oil ring is assembled to the piston, and the lower pieces are arranged so that each of the lower pieces is alternately arranged with each of the upper pieces in the circumferential direction of the oil ring, and a plurality of connecting pieces connecting the upper pieces and the lower pieces adjacent to each other in the circumferential direction of the oil ring. The upper piece may include an upper base portion and an upper ear portion formed to rise from the inside of the upper base portion in the radial direction of the oil ring and pressing the upper segment of the pair of segments that is provided on the combustion chamber side of the internal combustion engine radially outwardly of the oil ring, and the lower piece may include a lower base portion and a lower ear portion formed to rise from the inside of the lower base portion in the radial direction of the oil ring and pressing the lower segment of the pair of segments that is provided on the crank chamber side of the internal combustion engine radially outwardly of the oil ring.

In the present invention, the expander groove is formed on the outer peripheral surface of the expander body by a plurality of notches provided at the outer ends of the plurality of connecting pieces, which are the radially outer ends of the oil ring, so as to be arranged along the circumferential direction of the oil ring, and the width of the fitting portion in the axial direction of the oil ring may be smaller than the width of the outer ends of the connecting pieces in the axial direction. This allows the fitting portion to be fitted onto the outer peripheral surface of the expander body.

In the present invention, the expander groove is formed on the inner peripheral surface of the expander body by a plurality of notches provided at the inner ends of the plurality of connecting pieces, which are the radially inner ends of the oil ring, so as to be arranged along the circumferential direction of the oil ring, and the width of the fitting portion in the axial direction of the oil ring may be smaller than the width of the inner ends of the connecting pieces in the axial direction. This allows the fitting portion to be fitted into the inner peripheral surface of the expander body.

In addition, in the present invention, the expander groove is formed on the outer peripheral surface of the expander body, and in a free state before the oil ring is assembled to the piston, the radius of curvature of the arc at the inner peripheral end of the fitting portion may be less than or equal to the radius of curvature of the outermost circumference of the expander body in a state in which the ends of the joints are butted against each other. According to this, when the radius of curvature of the arc at the inner peripheral end of the fitting portion is less than the radius of curvature of the outermost circumference of the expander body, the fitting portion is fitted into the expander groove, and the fitting portion is expanded in diameter, so that a self-tension that tries to reduce the diameter is generated in the linear member. As a result, in the spacer expander, the inner peripheral end of the fitting portion presses the expander body radially inward. As a result, the fitting portion can be maintained in a state of being fitted into the expander groove across the joint.

In the present invention, the expander groove is formed on the inner peripheral surface of the expander body, and in a free state before the oil ring is assembled to the piston, the radius of curvature of the arc at the outer peripheral end of the fitting portion may be equal to or greater than the radius of curvature of the innermost circumference of the expander body in a state in which the ends of the joints are butted against each other. According to this, when the radius of curvature at the outer peripheral end of the fitting portion exceeds the radius of curvature of the innermost circumference of the expander body, the fitting portion is fitted into the expander groove, thereby reducing the diameter of the fitting portion, and a self-tension that tries to expand the diameter is generated in the linear member. As a result, in the spacer expander, the outer peripheral end of the fitting portion presses the expander body radially outward. As a result, the fitting portion can be maintained in a state of being fitted into the expander groove across the joint.

In the present invention, the expander groove is formed by a plurality of notches provided in the upper base portion of the plurality of upper pieces so as to be arranged along the circumferential direction of the oil ring, and the thickness of the fitting portion in the radial direction of the oil ring may be smaller than the thickness of the upper base portion in the radial direction. This allows the fitting portion to be fitted into the combustion chamber side surface of the expander body.

In the present invention, the expander groove is formed by a plurality of notches provided in the lower base portion of the plurality of lower pieces so as to be arranged along the circumferential direction of the oil ring, and the thickness of the fitting portion in the radial direction of the oil ring may be smaller than the thickness of the lower base portion in the radial direction. This allows the fitting portion to be fitted into the crank chamber side surface of the expander body.

In the present invention, the expander groove is formed on one of both end faces of the expander body in the axial direction of the oil ring, and in a free state before the oil ring is assembled to the piston, the radius of curvature of the arc at the outer peripheral end of the fitting portion may be within +10% of the radius of curvature of the outermost circumference of the expander body when the pair of joint ends are abutted against each other, and the radius of curvature of the arc at the inner peripheral end of the fitting portion may be -10% or more of the radius of curvature of the innermost circumference of the expander body when the pair of joint ends are abutted against each other. This makes it difficult for the fitting portion to come off the expander groove, and reduces resistance when the expander body is reduced or expanded in diameter. In addition, when the radius of curvature of the arc at the outer peripheral end of the fitting portion exceeds the radius of curvature of the outermost circumference of the expander body, the fitting portion is fitted into the expander groove to reduce the diameter of the fitting portion, so that self-tension is generated in the linear member, and the outer peripheral end of the fitting portion presses the expander body radially outward. As a result, the linear member is maintained in a state of being fitted into the expander groove across the joint. Similarly, when the radius of curvature of the arc at the inner peripheral end of the fitting portion is less than the radius of curvature of the innermost circumference of the expander body, the linear member is fitted into the expander groove to expand the diameter of the fitting portion, so that self-tension is generated in the linear member, and the inner peripheral end of the fitting portion presses the expander body radially inward. As a result, the fitting portion is maintained in a state of being fitted into the expander groove across the joint.

In the present invention, the expander groove is formed on the outer peripheral surface of the expander body, and the linear member further includes locking portions provided at both ends of the fitting portion, and the locking portions may include a first bent portion that bends from the end of the fitting portion and extends from the outer peripheral side to the inner peripheral side of the expander body through between the connecting pieces adjacent in the circumferential direction, and a second bent portion that bends from the tip of the first bent portion and engages with an inner end of the connecting piece that is the radially inner end of the oil ring. In this way, the locking portions provided at both ends of the fitting portion engage with the expander body, thereby maintaining the linear member fitted into the expander body.

The present invention can also be specified as an oil ring in which a pair of segments and the above-mentioned spacer expander are combined. That is, the present invention can be specified as an oil ring comprising a pair of segments spaced apart in the axial direction of the oil ring and a spacer expander provided between the pair of segments, the spacer expander being an expander body formed in an annular shape along the circumferential direction of the oil ring and biasing the pair of segments outward in the radial direction of the oil ring, the expander body including a pair of abutment ends that face each other to form abutments, and formed in a wavy shape that continues in the circumferential direction when viewed in the radial direction of the oil ring, an expander groove formed in the expander body so as to extend along the circumferential direction of the oil ring across the abutments, and a linear member including a fitting portion formed in an arc shape along the circumferential direction of the oil ring and fitted into the expander groove so as to straddle the abutments.

According to the present invention, in an oil ring having an axially wavy spacer expander, it is possible to prevent overlapping of the joint ends of the spacer expander.

1 is a partial cross-sectional view of an internal combustion engine equipped with an oil ring according to an embodiment. FIG. 2 is a perspective view of a portion of an expander body according to an embodiment. FIG. 2 is a cross-sectional view for explaining the outer circumferential diameter and the inner circumferential diameter of an expander body. FIG. 2 is a top view of a linear member according to the embodiment. FIG. 2 is a perspective view of a portion of a spacer expander according to an embodiment. FIG. 2 is a top view of a portion of a spacer expander according to an embodiment. This is a cross-sectional view taken along line AA in FIG. 6. 1 is a partial cross-sectional view of an internal combustion engine equipped with an oil ring according to a first modified example of an embodiment. FIG. 13 is a top view of a portion of a spacer expander according to a first modified example of an embodiment. This is a cross-sectional view taken along line BB of FIG. 9. 11 is a partial cross-sectional view of an internal combustion engine equipped with an oil ring according to a second modified example of the embodiment. FIG. 11 is a partial cross-sectional view of an internal combustion engine equipped with an oil ring according to a third modified example of the embodiment. FIG. 13 is a partial cross-sectional view of an internal combustion engine equipped with an oil ring according to a fourth modified example of the embodiment. FIG. 13 is a partial cross-sectional view of an internal combustion engine equipped with an oil ring according to a fifth modified example of the embodiment. FIG. 13 is a partial cross-sectional view of an internal combustion engine equipped with an oil ring according to a sixth modified example of the embodiment. FIG. 13 is a partial cross-sectional view of an internal combustion engine equipped with an oil ring according to a seventh modified example of the embodiment. FIG. FIG. 13 is a top view of a portion of a spacer expander according to an eighth modified example of the embodiment. FIG. 23 is a top view of a linear member according to an eighth modified example of the embodiment.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. Note that the configurations described in the following embodiments are not intended to limit the technical scope of the invention unless otherwise specified.

[Overall configuration]
FIG. 1 is a partial cross-sectional view of an internal combustion engine 100 including an oil ring 40 according to an embodiment. FIG. 1 illustrates a cross section perpendicular to the circumferential direction (circumferential length direction) of the oil ring 40. As shown in FIG. 1, in the internal combustion engine 100, a piston gap PC1 is formed by ensuring a predetermined separation distance between an inner wall surface 10a of a cylinder 10 and an outer peripheral surface 20a of a piston 20 mounted in the cylinder 10. In addition, a ring groove 30 having a substantially rectangular cross section is formed on the outer peripheral surface 20a of the piston 20. The ring groove 30 has an upper wall 301 formed on the combustion chamber side, a lower wall 302 formed on the crank chamber side and facing the upper wall 301, and a connecting wall 303 connecting the inner peripheral edges of the upper wall 301 and the lower wall 302. The oil ring 40 according to this embodiment is mounted in the ring groove 30.

The oil ring 40 is a sliding member that slides on the inner wall surface 10a of the cylinder 10 in association with the reciprocating motion of the piston 20. The oil ring 40 is a so-called three-piece type combination oil ring, and as shown in FIG. 1, comprises a pair of segments 1, 1 and a spacer expander 2. The spacer expander 2 further comprises an expander body 3, an expander groove 4, and a linear member 5. The oil ring 40 is assembled to the piston 20 by being fitted into the ring groove 30.

Hereinafter, as shown in FIG. 1, the direction along the central axis of the oil ring 40 (axial direction) is defined as the "up-down direction". In addition, in the axial direction of the oil ring 40, the combustion chamber side (upper side in FIG. 1) in the internal combustion engine 100 is defined as the "upper side", and the opposite side, i.e., the crank chamber side (lower side in FIG. 1) is defined as the "lower side". In the following description of the oil ring 40, unless otherwise specified, the "circumferential direction" refers to the circumferential direction of the oil ring 40, the "radial direction" refers to the radial direction of the oil ring 40, and the "axial direction" refers to the axial direction of the oil ring 40. In addition, in this specification, the state in which the oil ring is assembled to a piston attached to a cylinder of an internal combustion engine as shown in FIG. 1 is referred to as the "used state". In addition, the state before the oil ring is assembled to the piston is referred to as the "free state". More specifically, the free state refers to a state in which the oil ring 40 is disassembled into each of the components, i.e., the segments, the expander body, and the linear member, and each of these components is not constrained by other elements. Each component of the oil ring 40 will be described below.

[segment]
The pair of segments 1, 1 are formed in an annular shape along the circumferential direction of the oil ring 40, and are provided independently and spaced apart in the axial direction. In the oil ring 40 according to the embodiment, the pair of segments 1, 1 have the same shape. However, in the present invention, the shapes of the pair of segments may be different. Hereinafter, when the pair of segments 1, 1 are to be distinguished from one another, the segment 1 provided on the upper side (combustion chamber side) is referred to as the upper segment 1U, and the segment 1 provided on the lower side (crank chamber side) is referred to as the lower segment 1L. When there is no need to distinguish between these, they are simply referred to as the segment 1. The material of the segment 1 is not particularly limited. Examples of the material of the segment 1 include SUS and SWRH.

As shown in Figure 1, segment 1 has an outer peripheral surface 11, an inner peripheral surface 12, an upper surface 13, and a lower surface 14. The upper surface 13 and the lower surface 14 define the axial width of segment 1. Upper segment 1U is arranged so that upper surface 13 faces upper wall 301 of ring groove 30 in the used state. Lower segment 1L is arranged so that lower surface 14 faces lower wall 302 of ring groove 30 in the used state.

[Spacer expander]
As shown in FIG. 1, the spacer expander 2 is provided between a pair of segments 1, 1, and comprises an expander body 3 formed in a wavy shape in the axial direction, an expander groove 4 formed in the expander body 3, and a linear member 5 fitted into the expander groove 4.

The expander body 3 is formed in an annular shape along the circumferential direction of the oil ring 40. The expander body 3 includes an outer peripheral surface S1, an inner peripheral surface S2, an upper surface S3, and a lower surface S4. The upper surface S3 is the surface located on the upper side (combustion chamber side) of both axial end surfaces of the expander body 3. The lower surface S4 is the surface located on the lower side (crank chamber side) of both axial end surfaces of the expander body 3. In other words, the expander body 3 is arranged so that the upper surface S3 faces the upper segment 1U and the lower surface S4 faces the lower segment 1L in the usage state. The material of the expander body 3 is not particularly limited. Examples of the material of the expander body 3 include SUS and the like.

2 is a perspective view of a part of the expander body 3 according to the embodiment. As shown in FIG. 2, the expander body 3 is configured by a plurality of wavy periodic elements displaced in the axial direction, which are connected in the circumferential direction. In other words, the expander body 3 is formed in a wavy shape that continues in the circumferential direction when viewed in the radial direction of the oil ring 40 (when viewed from the outside or inside in the radial direction). Specifically, the expander body 3 includes a plurality of upper pieces 31 and lower pieces 32 that are spaced apart in the axial and circumferential directions and alternately arranged in the circumferential direction, and a connecting piece 33 that connects the upper pieces 31 and lower pieces 32 adjacent to each other in the circumferential direction. The plurality of upper pieces 31 are arranged at intervals along the circumferential direction. The plurality of lower pieces 32 are provided so as to be located below the plurality of upper pieces 31 when the oil ring 40 is assembled to the piston 20 (i.e., in the use state). The plurality of lower pieces 32 are also arranged so that each of the lower pieces 32 is alternately arranged with each of the upper pieces 31 in the circumferential direction. The upper piece 31 and the lower piece 32 are provided perpendicular to the axial direction and are spaced apart from each other in the axial direction. The connecting piece 33 connects the circumferential ends of the upper piece 31 and the lower piece 32 adjacent to each other in the axial direction. As shown in Fig. 2, the expander body 3 includes a pair of joint ends 3a, 3b that face each other to form a joint G1. Note that the structure of the expander body according to the present invention is not limited to this, and it is sufficient that it is formed in a wavy shape in the axial direction.

As shown in FIG. 1, the upper piece 31 includes an upper base portion 310, an upper ear portion 311, and an upper support portion 312. The upper base portion 310 extends in the radial direction perpendicular to the axial direction. The upper ear portion 311 is formed to stand on the inner side of the upper base portion 310 in the radial direction and protrudes upward from the upper base portion 310. In addition, the upper ear portion 311 presses the upper segment 1U radially outward by abutting against the inner peripheral surface 12 of the upper segment 1U in the use state. The upper support portion 312 is formed to stand on the outer side of the upper base portion 310 in the radial direction and protrudes upward from the upper base portion 310. In addition, the upper support portion 312 supports the upper segment 1U by abutting against the lower surface 14 of the upper segment 1U in the use state. In addition, a through hole 34 is formed at the base of the upper ear portion 311. It should be noted that the upper piece according to the present invention does not necessarily have to have the upper support portion 312 .

As shown in FIG. 1, the lower piece 32 includes a lower base portion 320, a lower ear portion 321, and a lower support portion 322. The lower base portion 320 extends in the radial direction perpendicular to the axial direction. The lower ear portion 321 is formed to stand on the inside of the lower base portion 320 in the radial direction and protrudes downward from the lower base portion 320. In addition, the lower ear portion 321 presses the lower segment 1L radially outward by abutting against the inner peripheral surface 12 of the lower segment 1L in the use state. The lower support portion 322 is formed to stand on the outside of the lower base portion 320 in the radial direction and protrudes downward from the lower base portion 320. In addition, the lower support portion 322 supports the lower segment 1L by abutting against the upper surface 13 of the lower segment 1L in the use state. In addition, a through hole 34 is formed at the base of the lower ear portion 321. It should be noted that the lower piece according to the present invention does not necessarily have to have the lower support portion 322 .

Here, the symbol E1 in FIG. 1 indicates the radially outer end (outer end) of the connecting piece 33, and the symbol E2 indicates the radially inner end (inner end) of the connecting piece 33. The axial width of the outer end E1 is b1, and the axial width of the inner end E2 is b2. At this time, as shown in FIG. 1, in this example, b1 is equal to the axial distance between the lower surface of the upper support part 312 and the upper surface of the lower support part 322, and b2 is equal to the axial distance between the lower surface of the upper ear part 311 and the upper surface of the lower ear part 321. The radial thickness of the upper base part 310 is a1, and the radial thickness of the lower base part 320 is a2. At this time, as shown in FIG. 1, in this example, a1 is equal to the radial distance between the upper ear part 311 and the upper support part 312, and a2 is equal to the radial distance between the lower ear part 321 and the lower support part 322.

As shown in Figs. 1 and 2, a notch 37 that opens radially outward (outer periphery) is formed in the outer end E1 of the connecting piece 33. The inner wall of the notch 37 is formed in an arc shape that is convex radially inward. However, the shape of the notch according to the present invention is not limited to an arc shape. The notches 37 are provided in a plurality of connecting pieces 33 so as to be arranged along the circumferential direction. As a result, an expander groove 4 that extends along the circumferential direction and opens to the outer periphery is formed in the outer periphery surface S1 of the expander body 3. The expander groove 4 is formed to include a plurality of notches 37, and extends across the joint G1 as shown in Fig. 2. The expander groove 4 according to the embodiment is formed around the entire circumference of the expander body 3. However, the expander groove according to the present invention is not limited to this. It is sufficient that the expander groove is formed in at least a part of the expander body so as to cross the joint. In this example, the expander groove 4 is formed in the center of the connecting piece 33 in the axial direction, but the position of the expander groove 4 in the axial direction may be closer to the upper piece 31 side or the lower piece 32 side.

Figure 3 is a cross-sectional view for explaining the outer diameter and inner diameter of the expander body 3. The symbol CA3 in Figure 3 indicates the central axis of the expander body 3. In this case, the outer diameter of the expander body 3, i.e., the radius of curvature of the outermost circumference of the expander body 3 (the distance from the central axis CA3 of the expander body 3 to the outer peripheral surface S1) is R1, and the inner diameter of the expander body 3, i.e., the radius of curvature of the innermost circumference of the expander body 3 (the distance from the central axis CA3 of the expander body 3 to the inner peripheral surface S2) is R2. In other words, R1 is the outer diameter of the expander body 3, and R2 is the inner diameter of the expander body 3.

4 is a top view (viewed from above in the axial direction) of the linear member 5 according to the embodiment. The linear member 5 is a linear member formed by bending a wire. The material of the linear member 5 is not particularly limited, but steel or resin can be used. Examples of the material of the linear member 5 include SUS, SWP, resin, etc. The linear member 5 includes a fitting portion 51 and a locking portion 52. The fitting portion 51 is formed in an arc shape along the circumferential direction of the oil ring 40 and extends along the circumferential direction of the oil ring 40. As shown in FIG. 1, the fitting portion 51 has a circular cross-sectional shape so as to correspond to the cross-sectional shape of the expander groove 4 formed in the expander body 3. However, the present invention is not limited to this. The cross-sectional shape of the notch 37 and the cross-sectional shape of the linear member 5 do not necessarily have to be the same. In addition, the cross-sectional shape of the linear member 5 does not have to be circular. In addition, the axial width w1 of the fitting portion 51 is smaller than the axial width b1 of the outer end portion E1 of the connecting piece 33, i.e., the axial distance between the lower surface of the upper support portion 312 and the upper surface of the lower support portion 322.

4, the locking portion 52 is connected to one end of the fitting portion 51 and is bent so as to protrude radially inward. The locking portion 52 includes a first bent portion 521 extending radially inward from one end of the fitting portion 51, and a second bent portion 522 bent from a tip of the first bent portion 521 and extending radially outward. The second bent portion 522 includes one end of the linear member 5.

Here, the reference numeral 511 in FIG. 4 indicates the outer peripheral end of the fitted portion 51 of the linear member 5. The outer peripheral end 511 is a part of the outer peripheral surface of the fitted portion 51 and is the part located at the radially outermost position in the fitted portion 51. The reference numeral 512 indicates the inner peripheral end of the fitted portion 51 of the linear member 5. The inner peripheral end 512 is a part of the inner peripheral surface of the fitted portion 51 and is the part located at the radially innermost position in the fitted portion 51. The reference numeral C5 indicates the center of the arc formed by the fitted portion 51. In this case, the radius of curvature of the linear member 5 at the outer peripheral end 511 of the fitted portion 51 (the distance from the center C5 of the arc of the fitted portion 51 to the outer peripheral end 511) is r1, and the radius of curvature of the linear member 5 at the inner peripheral end 512 of the fitted portion 51 (the distance from the center C5 of the arc of the fitted portion 51 to the inner peripheral end 512) is r2.

Figure 5 is a perspective view of a portion of the spacer expander 2 according to the embodiment. Figure 5 illustrates a state in which a pair of joint ends 3a, 3b are butted together (contacted). As shown in Figure 5, in the spacer expander 2, the fitting portion 51 of the linear member 5 is fitted into the expander groove 4 of the expander body 3 so as to straddle the joint G1. The fitting portion 51 and the expander groove 4 are fitted loosely together.

At this time, in the spacer expander 2 according to this example, the dimensions R1 and r2 are set so that in a free state, the radius of curvature r2 of the arc at the inner end 512 of the fitting portion 51 of the linear member 5 is equal to or smaller than the radius of curvature R1 of the outermost circumference of the expander body 3 in a state in which the pair of joint ends 3a, 3b are butted against each other. This allows the linear member 5 to be fitted into the expander groove 4. Here, if the dimension of r2 is less than the dimension of R1, the linear member 5 is fitted into the expander groove 4, and the linear member 5 is expanded in diameter, so that a self-tension that tries to reduce the diameter is generated in the linear member 5. As a result, in the spacer expander 2 in which the linear member 5 is fitted into the expander groove 4, the inner end 512 of the linear member 5 presses the expander body 3 radially inward. This maintains the state in which the linear member 5 is fitted into the expander groove 4 across the joint G1. At this time, the radius of curvature r2 of the linear member 5 in the free state is preferably within a range of 0 to -10% of the radius of curvature R1 of the expander body 3 in the state where the pair of joint ends 3a, 3b are abutted against each other in the free state, and more preferably within a range of 0 to -5%. This makes it possible to make the linear member 5 less likely to come off the expander groove 4.

Figure 6 is a top view of a portion of a spacer expander 2 according to an embodiment. As shown in Figure 6, in the spacer expander 2, the locking portion 52 of the linear member 5 engages with one of the multiple connecting pieces 33, thereby locking the linear member 5 to the expander body 3. In this example, the locking portion 52 engages with the connecting piece 33 on the side of the joint end 3a of the pair of joint ends 3a, 3b that sandwich the joint G1. The locking portion 52 may also engage with the connecting piece 33 on the side of the joint end 3b. Here, the symbol G2 in Figure 6 indicates the gap between adjacent connecting pieces 33 in the circumferential direction. As shown in FIG. 6, in the spacer expander 2, the first bent portion 521 connected to the end of the fitting portion 51 extends from the outer peripheral surface S1 side of the expander body 3 through the gap G2 to the opposite inner peripheral surface S2 side, and the second bent portion 522 connected to the first bent portion 521 is folded back and extends from the inner peripheral surface S2 side to the opposite outer peripheral surface S1 side through the adjacent gap G2. As a result, the connecting piece 33 is sandwiched from both sides in the circumferential direction by the first bent portion 521 and the second bent portion 522. In addition, the tip of the second bent portion 522 abuts against the connecting piece 33 and is not allowed to protrude to the outer peripheral side of the expander body 3. Here, FIG. 7 is a cross-sectional view showing the A-A cross section in FIG. 6. As shown in FIG. 7, the inner end E2 of the connecting piece 33 corresponding to the bent portion of the locking portion 52 has a notch 38 into which the locking portion 52 fits. As a result, the linear member 5 is not allowed to protrude to the inner peripheral side of the expander body 3. However, the linear member 5 may protrude to the inner peripheral side of the expander body 3 within a range where it does not interfere (contact) with the inner wall of the ring groove 30, and the notch 38 may not be formed in the expander body 3. In the spacer expander 2, the fitting portion 51 fits into the expander groove 4 formed on the outer peripheral surface S1 side of the expander body 3, and the locking portion 52 fits into the notch 38 formed on the inner peripheral surface S2 side of the expander body 3, thereby restricting the radial relative movement of the linear member 5 with respect to the expander body 3. In the spacer expander 2, the connecting piece 33 on the joint end 3a side is sandwiched from both sides in the circumferential direction by the first bent portion 521 and the second bent portion 522, and the tip of the second bent portion 522 abuts against the connecting piece 33 adjacent to the connecting piece 33, so that the circumferential relative movement of the linear member 5 with respect to the joint end 3a is restricted. As a result, one end (locking portion 52) of the linear member 5 is locked on the joint end 3a side of the expander body 3, preventing the linear member 5 from coming off from the expander body 3. On the other hand, the other end of the linear member 5 is not locked on the joint end 3b side of the expander body 3. Therefore, in the spacer expander 2, the joint end 3b is slidable in the circumferential direction along the fitting portion 51. Note that, in order to prevent the fitting portion 51 from coming off the expander groove 4 when the joint end 3b is slid in the circumferential direction along the fitting portion 51, the opening of at least a part of the notch 37 of the expander groove 4 may be closed with, for example, resin on the joint end 3b side.

At least one of the segments 1 and the expander body 3 may have a coating formed on its surface, the coating including at least one of a resin coating, a nitriding coating, a Ni-P plating coating, a chrome plating coating, a PVD coating, and a DLC coating. The term "resin coating" refers to a coating formed from a resin material. The term "nitriding coating" refers to a coating formed by infiltrating nitrogen into a metal surface by nitriding. The term "Ni-P plating coating" refers to a coating formed by electroless Ni-P plating. The term "chrome plating coating" refers to a coating formed by chrome plating. Chrome plating is also called industrial chrome plating. The term "PVD (physical vapor deposition) coating" refers to a coating formed by the PVD method. The term "DLC (Diamond Like Carbon) coating" refers to an amorphous hard carbon coating composed mainly of hydrocarbons and carbon allotropes. By forming such a coating, the wear resistance of the segment 1 or the expander body 3 can be increased.

[Installation of oil ring to piston]
Next, a method of assembling the oil ring 40 to the piston 20 according to the embodiment will be described. To assemble the oil ring 40 to the piston 20, first, the spacer expander 2 with the linear member 5 fitted in the expander groove 4 is fitted in the ring groove 30 of the piston 20, and then the pair of segments 1, 1 are fitted in the ring groove 30 so as to be separated via the spacer expander 2. When fitting the spacer expander 2 in the ring groove 30, the spacer expander 2 is inserted into the ring groove 30 while widening the joint G1 of the expander body 3, and the pair of joint ends 3a, 3b of the expander body 3 are butted against each other in the ring groove 30, thereby fitting the spacer expander 2 in the ring groove 30. As described above, in the spacer expander 2, the linear member 5 is maintained in a state of being fitted in the expander groove 4 across the joint G1, and the joint end 3b is slidable in the circumferential direction along the fitting portion 51 of the linear member 5. Therefore, when the joint G1 of the expander body 3 expands, the joint ends 3b move along the fitting portion 51 and expand while being guided by the fitting portion 51. Also, when the spacer expander 2 is attached to the ring groove 30 and the joint G1 is closed, the joint ends 3b move along the fitting portion 51 and close while being guided by the fitting portion 51. As a result, when the spacer expander 2 is assembled to the piston 20, the expander body 3 is maintained in a position in which the pair of joint ends 3a, 3b face each other, and the pair of joint ends 3a, 3b are prevented from overlapping each other.

[Action and Effects]
As described above, the spacer expander 2 according to the embodiment comprises the expander body 3 which is formed in an annular shape along the circumferential direction of the oil ring 40 and which is formed in a wavy shape that continues in the circumferential direction when viewed in the radial direction of the oil ring 40, the expander groove 4 which is formed in the expander body 3 so as to extend along the circumferential direction of the oil ring 40 across the joint G1, and the linear member 5 which includes the fitting portion 51 which is formed in an arc shape along the circumferential direction of the oil ring 40 and which is fitted into the expander groove 4 so as to straddle the joint G1, thereby maintaining the expander body 3 in a position in which the pair of joint end portions 3a, 3b face each other.

According to the spacer expander 2 of the embodiment, it is possible to prevent the pair of joint ends 3a, 3b from overlapping in the radial direction or the axial direction. This prevents the segment 1 from becoming difficult to assemble during the assembly work of the oil ring 40 to the piston 20, and prevents the oil ring 40 assembled to the piston 20 from failing to function. Furthermore, since the axially wavy spacer expander has a narrow width in the axial direction and a narrow thickness in the radial direction, it is difficult to provide a hole for inserting a linear member, but the spacer expander 2 of the embodiment adopts a structure in which the linear member 5 is fitted by providing a groove. This makes it possible to prevent the pair of joint ends from overlapping even though it is an axially wavy spacer expander. Furthermore, the spacer expander 2 of the embodiment adopts a structure in which the linear member 5 is fitted into the expander groove 4 formed in the expander body 3 and opened to the outside. This differs from a technique of fixing the joint ends together with a pin or the like, in that the expander body 3 can be guided by the linear member 5 to expand or contract the diameter, and therefore the spacer expander 2 can be easily attached and detached from the piston 20. This makes it easy to replace the oil ring 40 including the segment 1 and the spacer expander 2. This allows the oil ring 40 to be used as a spare part (repair part).

Furthermore, the expander groove 4 of the spacer expander 2 according to the embodiment is formed on the outer peripheral surface S1 of the expander body 3 by notches 37 provided on the outer ends E1 of the multiple connecting pieces 33 so as to be arranged along the circumferential direction of the oil ring 40. The width w1 of the fitting portion 51 of the linear member 5 in the axial direction is smaller than the width b1 of the outer ends E1 of the connecting pieces 33 in the axial direction (in this example, the distance between the lower surface of the upper support portion 312 and the upper surface of the lower support portion 322 in the axial direction). According to this, by making the width w1 of the fitting portion 51 in the axial direction smaller than the width b1 of the outer ends E1 of the connecting pieces 33 in the axial direction, the fitting portion 51 can be fitted between a pair of segments 1, 1.

Furthermore, in the spacer expander 2 according to the embodiment, the radius of curvature r2 of the arc at the inner peripheral end 512 of the fitting portion 51 of the linear member 5 in the free state is equal to or smaller than the radius of curvature R1 of the outermost circumference of the expander body 3 in the state where the pair of joint ends 3a, 3b are butted against each other in the free state. This allows the spacer expander 2 to maintain the state in which the linear member 5 is fitted into the expander groove 4 across the joint G1. Note that the radius of curvature r2 of the linear member 5 in the free state is preferably within the range of 0 to -10%, and more preferably within the range of 0 to -5%, of the radius of curvature R1 of the expander body 3 in the state where the pair of joint ends 3a, 3b are butted against each other in the free state. This makes it difficult for the linear member 5 to come off the expander groove 4. However, the present invention is not limited to this.

Here, the circumferential length of the fitting portion 51 of the linear member 5 is preferably 2 mm or more from one joint end (the joint end on the side where the locking portion 52 is fixed) to the other joint end. Also, the locking portion 52 is not an essential component of the present invention. In other words, the linear member according to the present invention may not have a locking portion, and the entire linear member may be the fitting portion. In that case, the circumferential length of the fitting portion is preferably 1/2 or more of the entire circumference of the expander body, and more preferably 2/3 or more. In this way, the inner peripheral surface of the linear member (more specifically, the inner peripheral end) and the outer peripheral surface of the expander body (more specifically, the bottom of the expander groove) are fitted together, making it difficult for the linear member to come off. Also, when the linear member does not have a locking portion, both of the pair of joint ends of the expander body can slide circumferentially along the linear member, and the joint ends are guided by the linear member, preventing the joint ends from overlapping with each other.

In addition, in the present invention, one end of the linear member may be fixed to the expander body by adhesive, welding, brazing, or other methods instead of the above-mentioned locking portion 52. Also, one end of the linear member may be locked to the expander body by using burrs formed on the linear member or the expander body so as to catch the burrs.

[Modification]
Modifications of the embodiment will be described below. In the following description, differences from the above-described oil ring 40 will be mainly described, and similar configurations will be denoted by the same reference numerals and detailed description will be omitted.

[Modification 1]
Fig. 8 is a partial cross-sectional view of an internal combustion engine 100A equipped with an oil ring 40A according to a first modified example of the embodiment. Fig. 8 illustrates a cross section perpendicular to the circumferential direction of the oil ring 40A. As shown in Fig. 8, the spacer expander 2A of the oil ring 40A according to the first modified example differs from the spacer expander 2 in that the expander groove 4A is formed on the inner circumferential surface S2 of the expander body 3A.

8, in the spacer expander 2A, a notch 37 that opens radially inward (inner circumferential side) is formed at the inner end E2, which is the radially inner end of the connecting piece 33 of the expander body 3A. The inner wall of the notch 37 is formed in an arc shape that is convex radially outward. The notches 37 are provided in a plurality of connecting pieces 33 so as to be arranged along the circumferential direction. As a result, an expander groove 4A that extends circumferentially across the joint G1 and opens to the inner circumferential side is formed on the inner circumferential surface S2 of the expander body 3A. In this example, the expander groove 4A is formed in the center of the connecting piece 33 in the axial direction, but the position of the expander groove 4A in the axial direction may be closer to the upper piece 31 side or the lower piece 32 side. The fitting portion 51 of the linear member 5A is fitted into the expander groove 4A so as to straddle the joint G1. The axial width w1 of the fitting portion 51 of the linear member 5A is smaller than the axial width b2 of the inner end portion E2 of the connecting piece 33, i.e., the distance between the lower surface of the upper ear portion 311 and the upper surface of the lower ear portion 321 in the axial direction.

Here, in the first modified example, the dimensions R2 and r1 are set so that in the free state, the radius of curvature r1 of the arc at the outer circumferential end 511 of the fitting portion 51 of the linear member 5A is equal to or greater than the radius of curvature R2 (the distance from the central axis to the inner circumferential surface S2) of the innermost circumference of the expander body 3A in the state where the pair of joint ends 3a, 3b are butted against each other. This allows the linear member 5A to be fitted into the expander groove 4A. Here, if the dimension of r1 exceeds the dimension of R2, the linear member 5A is fitted into the expander groove 4A, and the linear member 5A is reduced in diameter, so that a self-tension that tries to expand the diameter is generated in the linear member 5A. As a result, in the spacer expander 2A in which the linear member 5A is fitted into the expander groove 4A, the outer circumferential end 511 of the linear member 5A presses the expander body 3A radially outward. This maintains the state in which the linear member 5A is fitted into the expander groove 4A across the gap G1.

Figure 9 is a top view of a portion of a spacer expander 2A according to a first modified embodiment. The locking portion 52A of the linear member 5A according to the first modified embodiment is connected to one end of the fitting portion 51 and is bent so as to protrude radially outward. The locking portion 52A includes a first bent portion 521A extending radially outward from one end of the fitting portion 51, and a second bent portion 522A bent from the tip of the first bent portion 521A and extending radially inward. The second bent portion 522A includes one end of the linear member 5A. As shown in FIG. 9, in the spacer expander 2A, the first bent portion 521A connected to the end of the fitting portion 51 extends from the inner peripheral surface S2 side of the expander body 3A through the gap G2 to the opposite outer peripheral surface S1 side, and the second bent portion 522A connected to the first bent portion 521A is folded back and extends from the outer peripheral surface S1 side to the opposite inner peripheral surface S2 side through the adjacent gap G2. As a result, the connecting piece 33 is sandwiched from both sides in the circumferential direction by the first bent portion 521A and the second bent portion 522A. In addition, the tip of the second bent portion 522A abuts against the connecting piece 33 and does not protrude to the inner peripheral side of the expander body 3A. Here, FIG. 10 is a cross-sectional view showing the B-B cross section of FIG. 9. As shown in FIG. 10, a notch 38 into which the locking portion 52A fits is formed in the outer end E1 of the connecting piece 33 corresponding to the bent portion of the locking portion 52A. This prevents the linear member 5A from protruding outward from the outer periphery of the expander body 3A. In the spacer expander 2A, the fitting portion 51 fits into the expander groove 4A formed on the inner periphery S2 side of the expander body 3A, and the locking portion 52A fits into the notch 38 formed on the outer periphery S1 side of the expander body 3A, thereby restricting the radial movement of the linear member 5A relative to the expander body 3A. In addition, in the spacer expander 2A, the connecting piece 33 on the joint end 3a side is sandwiched from both sides in the circumferential direction by the first bent portion 521A and the second bent portion 522A, and the tip of the second bent portion 522A abuts against the connecting piece 33 adjacent to the connecting piece 33, so that the circumferential movement of the linear member 5A relative to the joint end 3a is restricted. As a result, one end (locking portion 52A) of the linear member 5A is locked on the joint end 3a side of the expander body 3A, preventing the linear member 5A from coming off the expander body 3A. On the other hand, the other end of the linear member 5A is not locked on the joint end 3b side of the expander body 3A, so that in the spacer expander 2A, the joint end 3b can slide in the circumferential direction along the fitting portion 51.

According to the spacer expander 2A of the first modification, as in the above-mentioned spacer expander 2, the pair of joint ends 3a, 3b are maintained in an opposing position in the expander body 3A, thereby preventing the pair of joint ends 3a, 3b from overlapping in the radial direction or axial direction. In addition, the expander groove 4A of the spacer expander 2A of the first modification is formed on the inner peripheral surface S2 of the expander body 3A by the notches 37 provided in the inner ends E2 of the multiple connecting pieces 33 so as to be arranged along the circumferential direction of the oil ring 40. The width w1 of the fitting portion 51 of the linear member 5A in the axial direction is smaller than the width b2 of the inner ends E2 of the connecting pieces 33 in the axial direction (in this example, the distance between the lower surface of the upper ear 311 and the upper surface of the lower ear 321 in the axial direction). According to this, by making the width w1 of the fitting portion 51 in the axial direction smaller than the width b2 of the inner end E2 of the connecting piece 33 in the axial direction, the fitting portion 51 can be fitted to the inner peripheral surface S2 of the expander body 3A. Furthermore, in the spacer expander 2A according to the first modification, the radius of curvature r1 of the arc at the outer peripheral end 511 of the fitting portion 51 of the linear member 5A in the free state is equal to or greater than the radius of curvature R2 of the innermost circumference of the expander body 3A in the state where the pair of joint ends 3a, 3b are butted against each other in the free state. This allows the linear member 5A to maintain a state in which it is fitted into the expander groove 4A across the joint G1. Note that the radius of curvature r1 of the linear member 5A in the free state is preferably within a range of 0 to +10% with respect to the radius of curvature R2 of the expander body 3 in the state where the pair of joint ends 3a, 3b are butted against each other in the free state, and more preferably within a range of 0 to +5%. This makes it possible to make it difficult for the linear member 5A to come off the expander groove 4A. However, the present invention is not limited to this.

[Modification 2]
Fig. 11 is a partial cross-sectional view of an internal combustion engine 100B equipped with an oil ring 40B according to the second modification of the embodiment. Fig. 11 shows a cross section perpendicular to the circumferential direction of the oil ring 40B. As shown in Fig. 11, the spacer expander 2B of the oil ring 40B according to the second modification differs from the spacer expander 2 in that the expander groove 4B is formed on the upper surface S3 of the expander body 3B.

11, in the spacer expander 2B, a notch 37 that opens upward (toward the combustion chamber) is formed in the upper piece 31 of the expander body 3B. More specifically, the notch 37 is formed between the upper ear 311 and the upper support 312 in the upper piece 31, that is, in the upper base portion 310. The inner wall of the notch 37 is formed in an arc shape that is convex toward the crank chamber side. The notches 37 are provided in a plurality of upper pieces 31 so as to be arranged along the circumferential direction. As a result, an expander groove 4B that extends along the circumferential direction across the joint G1 and opens upward is formed on the upper surface S3 of the expander body 3B. In this example, the expander groove 4B is formed in the center of the upper base portion 310 in the radial direction, but the position of the expander groove 4B in the radial direction may be closer to the outer circumferential side or the inner circumferential side. The fitting portion 51 of the linear member 5B is fitted into the expander groove 4B so as to straddle the gap G1. As shown in Fig. 11, the radial thickness t1 of the fitting portion 51 of the linear member 5B is smaller than the radial thickness of the expander body 3 (the radial distance between the outermost circumference and the innermost circumference). More specifically, the thickness t1 is smaller than the radial thickness a1 of the upper base portion 310 of the upper piece 31 (in this example, the radial distance between the upper ear portion 311 and the upper support portion 312). The linear member 5B according to the second modification is engaged with the expander body 3B by the engaging portion 52, similar to the linear member 5.

According to the spacer expander 2B of the modified example 2, as with the above-mentioned spacer expander 2, by maintaining the expander body 3B in a position in which the pair of joint ends 3a, 3b face each other, it is possible to prevent the pair of joint ends 3a, 3b from overlapping in the radial direction or axial direction. In addition, the spacer expander 2B of the modified example 2 can fit the fitting portion 51 to the upper base portion 310 by making the radial thickness t1 of the fitting portion 51 smaller than the radial thickness a1 of the upper base portion 310 (in this example, the radial distance between the upper ear portion 311 and the upper support portion 312).

Here, in the spacer expander 2B according to the second modification, it is preferable that the radius of curvature r1 of the arc at the outer peripheral end 511 of the fitted portion 51 of the linear member 5B in the free state is +10% or less of the radius of curvature R1 of the outermost circumference of the expander body 3B in the state where the pair of joint ends 3a, 3b are butted against each other in the free state, and that the radius of curvature r2 of the arc at the inner peripheral end 512 of the fitted portion 51 of the linear member 5B in the free state is -10% or more of the radius of curvature R2 of the innermost circumference of the expander body 3B in the state where the pair of joint ends 3a, 3b are butted against each other in the free state. This makes it difficult for the linear member 5B to come off the expander groove 4B, and reduces the resistance when the expander body 3B is contracted or expanded. Note that r1 may be equal to or less than R1, and r2 may be equal to or greater than R2. Here, when the radius of curvature r1 of the arc at the outer peripheral end 511 of the linear member 5B exceeds the radius of curvature R1 of the outermost circumference of the expander body 3B, that is, when r1 is greater than R1 and is not more than R1 +10%, the linear member 5B is fitted into the expander groove 4B, causing the linear member 5B to contract in diameter, generating self-tension in the linear member, and the outer peripheral end 511 of the linear member 5B presses the expander body 3B radially outward. Similarly, when the radius of curvature r2 of the arc at the inner peripheral end 512 of the linear member 5B is less than the radius of curvature R2 of the innermost circumference of the expander body 3B, that is, when r2 is -10% or more of R2 and less than R2, the linear member 5B is fitted into the expander groove 4B to expand the diameter of the linear member 5B, so that self-tension is generated in the linear member 5B, and the inner peripheral end 512 of the linear member 5B presses the expander body 3B radially inward. As a result, the linear member 5B is maintained in a state of being fitted into the expander groove 4B across the joint G1. However, the above-mentioned conditions of R1, R2, r1, and r2 do not limit the present invention.

[Modification 3]
Fig. 12 is a partial cross-sectional view of an internal combustion engine 100C equipped with an oil ring 40C according to Modification 2 of the embodiment. Fig. 12 illustrates a cross section perpendicular to the circumferential direction of the oil ring 40C. As shown in Fig. 12, a spacer expander 2C of the oil ring 40C according to Modification 3 differs from the spacer expander 2 in that an expander groove 4C is formed on the lower surface S4 of the expander body 3C.

12, in the spacer expander 2C, a notch 37 that opens downward (toward the crank chamber) is formed in the lower piece 32 of the expander body 3C. More specifically, the notch 37 is formed between the lower ear 321 and the lower support 322 in the lower piece 32, that is, in the lower base part 320. The inner wall of the notch 37 is formed in an arc shape that is convex toward the combustion chamber side. The notches 37 are provided in a plurality of lower pieces 32 so as to be arranged along the circumferential direction. As a result, an expander groove 4C that extends along the circumferential direction across the joint G1 and opens downward is formed on the lower surface S4 of the expander body 3C. In this example, the expander groove 4C is formed in the center of the lower base part 320 in the radial direction, but the position of the expander groove 4C in the radial direction may be closer to the outer circumferential side or the inner circumferential side. The fitting portion 51 of the linear member 5C is fitted into the expander groove 4C so as to straddle the gap G1. As shown in Fig. 12, the radial thickness t1 of the fitting portion 51 of the linear member 5C is smaller than the radial thickness of the expander body 3 (the radial distance between the outermost circumference and the innermost circumference). More specifically, the thickness t1 is smaller than the radial thickness a2 of the lower base portion 320 (in this example, the radial distance between the lower ear portion 321 and the lower support portion 322). The linear member 5C according to the third modification is engaged with the expander body 3C by the engaging portion 52, similar to the linear member 5.

According to the spacer expander 2C of the modified example 3, as with the above-mentioned spacer expander 2, by maintaining the expander body 3C in a position in which the pair of joint ends 3a, 3b face each other, it is possible to prevent the pair of joint ends 3a, 3b from overlapping in the radial direction or axial direction. In addition, the spacer expander 2C of the modified example 3 can fit the fitting portion 51 into the lower base portion 320 by making the radial thickness t1 of the fitting portion 51 smaller than the radial thickness a2 of the lower base portion 320 (in this example, the radial distance between the lower ear portion 321 and the lower support portion 322).

Here, in the spacer expander 2C according to the third modification, as in the second modification, it is preferable that the radius of curvature r1 of the arc at the outer peripheral end 511 of the fitted portion 51 of the linear member 5C in the free state is +10% or less of the radius of curvature R1 of the outermost circumference of the expander body 3C in the state where the pair of joint ends 3a, 3b are butted against each other in the free state, and that the radius of curvature r2 of the arc at the inner peripheral end 512 of the fitted portion 51 of the linear member 5C in the free state is -10% or more of the radius of curvature R2 of the innermost circumference of the expander body 3C in the state where the pair of joint ends 3a, 3b are butted against each other in the free state. This makes it difficult for the linear member 5C to come off the expander groove 4C, and reduces the resistance when the expander body 3C is contracted or expanded. Note that r1 may be equal to or less than R1, and r2 may be equal to or greater than R2. Here, when r1 exceeds R1 (i.e., when r1 is greater than R1 and is equal to or less than +10% of R1) or when r2 is less than R2 (i.e., when r2 is equal to or greater than -10% of R2 and is less than R2), a self-tension is generated in the linear member 5C, so that the linear member 5C is maintained in a state of being fitted into the expander groove 4C across the gap G1. However, the above-mentioned conditions of R1, R2, r1, and r2 do not limit the present invention.

[Modification 4]
FIG. 13 is a partial cross-sectional view of an internal combustion engine 100D equipped with an oil ring 40D according to a fourth modified example of the embodiment. FIG. 13 illustrates a cross section perpendicular to the circumferential direction of the oil ring 40D. As shown in FIG. 13, the spacer expander 2D of the oil ring 40D according to the fourth modified example differs from the spacer expander 2 in that the expander body 3D does not have the upper support portion 312 and the lower support portion 322. As shown in FIG. 13, in the fourth modified example, the width b1 in the axial direction of the outer end E1 of the connecting piece 33 is equal to the distance in the axial direction between the lower surface of the upper base portion 310 and the upper surface of the lower base portion 320. In the spacer expander 4D according to the fourth modified example, the width w1 of the fitting portion 51 of the linear member 5D in the axial direction is made smaller than the width b1 of the outer end E1 of the connecting piece 33 in the axial direction, so that the fitting portion 51 can be fitted to the outer peripheral surface S1 of the expander body 3D.

[Modification 5]
Fig. 14 is a partial cross-sectional view of an internal combustion engine 100E including an oil ring 40E according to a fifth modified embodiment. Fig. 14 illustrates a cross section perpendicular to the circumferential direction of the oil ring 40E. As shown in Fig. 14, the spacer expander 2E of the oil ring 40E according to the fifth modified embodiment differs from the spacer expander 2A according to the first modified embodiment in that the expander body 3E does not have the upper support portion 312 and the lower support portion 322. The spacer expander 4E according to the fifth modified embodiment can fit the fitting portion 51 to the inner circumferential surface S2 of the expander body 3E by making the width w1 of the fitting portion 51 of the linear member 5E in the axial direction smaller than the width b2 of the inner end E2 of the connecting piece 33 in the axial direction.

[Modification 6]
FIG. 15 is a partial cross-sectional view of an internal combustion engine 100F including an oil ring 40F according to a sixth modified embodiment. FIG. 15 illustrates a cross section perpendicular to the circumferential direction of the oil ring 40F. As shown in FIG. 15, the spacer expander 2F of the oil ring 40F according to the sixth modified embodiment differs from the spacer expander 2B according to the second modified embodiment in that the expander body 3F does not have the upper support portion 312 and the lower support portion 322. In the sixth modified embodiment, the radial thickness a1 of the upper base portion 310 is equal to the radial distance between the upper ear portion 311 and the outer end E1 of the connecting piece 33. In the spacer expander 4F according to the sixth modified embodiment, the radial thickness t1 of the fitting portion 51 of the linear member 5F is made smaller than the radial thickness a1 of the upper base portion 310, so that the fitting portion 51 can be fitted into the upper base portion 310.

[Modification 7]
FIG. 16 is a partial cross-sectional view of an internal combustion engine 100G including an oil ring 40G according to a seventh modified embodiment. FIG. 16 illustrates a cross section perpendicular to the circumferential direction of the oil ring 40G. As shown in FIG. 16, the spacer expander 2G of the oil ring 40G according to the seventh modified embodiment differs from the spacer expander 2C according to the third modified embodiment in that the expander body 3G does not have the upper support portion 312 and the lower support portion 322. In the seventh modified embodiment, the radial thickness a2 of the lower base portion 320 is equal to the radial distance between the lower ear portion 321 and the outer end E1 of the connecting piece 33. In the spacer expander 4G according to the seventh modified embodiment, the radial thickness t1 of the fitting portion 51 of the linear member 5G is made smaller than the radial thickness a2 of the lower base portion 320, so that the fitting portion 51 can be fitted into the lower base portion 320.

[Modification 8]
Next, a spacer expander used in an oil ring according to Modification 8 of the embodiment will be described. Fig. 17 is a top view of a portion of a spacer expander 2H according to Modification 8 of the embodiment. Fig. 18 is a top view (viewed from above in the axial direction) of a linear member 5H according to Modification 8 of the embodiment.

As shown in Fig. 18, the linear member 5H used in the spacer expander 2H differs from the linear member 5 described in Fig. 4 etc. in that locking portions 53 are provided at both ends of the fitting portion 51. The locking portions 53 are formed by bending the ends of the linear member 5H. As shown in Fig. 18, the locking portions 53 include a first bent portion 531 extending radially inward from the end of the fitting portion 51, and a second bent portion 532 bent from the tip of the first bent portion 531 and extending circumferentially outward (in the opposite direction to the fitting portion 51). The linear member 5H is formed in a generally U-shape by the fitting portion 51 and the pair of locking portions 53, 53. In the following description, when the pair of locking portions 53, 53 of the linear member 5H are distinguished from one another, the locking portion 53 connected to one end of the fitting portion 51 is referred to as a first locking portion 53a, and the locking portion 53 connected to the other end of the fitting portion 51 is referred to as a second locking portion 53b. In this example, the first locking portion 53a engages with the connecting piece 33 on the joint end 3a side, and the first locking portion 53b engages with the connecting piece 33 on the joint end 3b side.

As shown in Fig. 17, the expander body 3H of the spacer expander 2H is the same as the expander body 3 described in Figs. 1 to 3, etc., except that the notches 38 are provided on the inner ends E2 of the two connecting pieces 38 located on opposite sides of the joint G1. In other words, the expander grooves 4 are formed on the outer peripheral surface S1 of the expander body 3 by the multiple notches 37 provided on the outer ends E1 of the multiple connecting pieces 33. As shown in Fig. 17, the expander body 3H is formed with a notch 38 for fitting the second bent portion 532 of the first locking portion 53a and a notch 38 for fitting the second bent portion 532 of the second locking portion 53b. The pair of notches 38, 38 are formed on the inner end E2 of the connecting piece 33 on the joint end 3a side and the inner end E2 of the connecting piece 33 on the joint end 3b side.

As shown in Figure 17, in the spacer expander 2H, the first bent portion 531 of a pair of engagement portions 53, 53 extends from the outer periphery to the inner periphery of the expander body 3H through the gap G2, and the second bent portion 532 engages with the inner end portion E2 of the connecting piece 33.

In the eighth modification, the expander body 3H is attached to the ring groove 30, and then the linear member 5 is fitted into the expander body 3H, so that the pair of joint ends 3a, 3b are prevented from overlapping with each other by the fitting portion 51. This allows the pair of segments 1, 1 to be assembled to the spacer expander 2H in a state in which the pair of joint ends 3a, 3b of the spacer expander 2H are prevented from overlapping with each other.

To fit the linear member 5H into the expander body 3H, the locking portion 53 is contracted circumferentially inward (toward the fitting portion 51) against the elastic force of the linear member 5H, the fitting portion 51 is fitted into the expander groove 4, the locking portion 53 is inserted between the connecting pieces 33, and the second bent portion 532 is fitted into the notch 38 to engage with the connecting piece 33. When the linear member 5H is fitted into the expander body 3H, a restoring force that tends to protrude circumferentially outward is generated in the locking portion 53 due to the elasticity of the linear member 5H, so that the first bent portion 531 is pressed against the connecting piece 33 (stretched state). Therefore, the second bent portion 532 is maintained in an engaged state with the connecting piece 33.

In the spacer expander 2H, the fitting portion 51 of the linear member 5H fits into the expander groove 4 formed on the outer circumferential surface S1 side of the expander body 3H, and a pair of locking portions 53, 53 provided at both ends of the fitting portion 51 engage with the inner end E2 of the connecting piece 33 of the expander body 3H, thereby restricting the radial and circumferential relative movement of the linear member 5H with respect to the expander body 3H. This locks the linear member 5H to the expander body 3H, preventing the linear member 5H from coming off the expander body 3H. In the modified example 8, by providing the locking portions 53 at both ends of the fitting portion 51, the linear member 5H can be more reliably maintained in the fitted state in the expander body 3H than when the locking portions 53 are provided only at one end. The shape of the locking portions 53 is not limited to the shape shown in FIG. 17. 4, the locking portion 53 may have a shape in which the second bent portion 532 is bent from the tip of the first bent portion 531 and extends radially outward. Also, the linear member 5H may protrude to the inner periphery side of the expander main body 3H within a range that does not interfere with (contact with) the inner wall of the ring groove 30, and the notch 38 may not be formed in the expander main body 3H.

＜Other＞
Although the preferred embodiments of the present invention have been described above, the above-mentioned various aspects can be combined to the extent possible.

100, 100A, 100B, 100C, 100D, 100E, 100F, 100G: Internal combustion engine 10: Cylinder 20: Piston 30: Ring groove 40, 40A, 40B, 40C, 40D, 40E, 40F, 40G: Oil ring 1: Segment 2, 2A, 2B, 2C, 2D, 2E, 2F, 2G, 2H: Spacer expander 3, 3A, 3B, 3C, 3D, 3E, 3F, 3G, 3H: Expander body 4, 4A, 4B, 4C, 4D, 4E, 4F, 4G: Expander groove 5, 5A, 5B, 5C, 5D, 5E, 5F, 5G, 5H: Linear member

Claims (10)

A spacer expander is provided between a pair of segments spaced apart in an axial direction of an oil ring that is assembled to a piston in an internal combustion engine, the spacer expander comprising:
an expander body that is formed in an annular shape along the circumferential direction of the oil ring and biases the pair of segments outward in the radial direction of the oil ring, the expander body including a pair of joint ends that face each other to form a joint, and that is formed in a wavy shape that is continuous in the circumferential direction when viewed in the radial direction of the oil ring;
an expander groove formed in the expander body so as to extend along a circumferential direction of the oil ring across the joint;
a linear member including a fitting portion formed in an arc shape along a circumferential direction of the oil ring, the fitting portion being fitted into the expander groove so as to span the gap ;
The linear member further includes a locking portion provided at one end of the fitting portion,
the locking portion includes a first bent portion extending from one end of the fitting portion toward the inside in the radial direction of the oil ring, and a second bent portion bent from a tip of the first bent portion and extending toward the outside in the radial direction of the oil ring,
Spacer expander. The expander body includes:
A plurality of upper pieces arranged at intervals along a circumferential direction of the oil ring;
a plurality of lower pieces provided so as to be located closer to a crank chamber in the internal combustion engine than the plurality of upper pieces in an axial direction of the oil ring when the oil ring is assembled to the piston, the lower pieces being arranged so as to be alternately disposed with the respective upper pieces in a circumferential direction of the oil ring;
a plurality of connecting pieces connecting the upper piece and the lower piece adjacent to each other in a circumferential direction of the oil ring,
the upper piece includes an upper base portion and an upper ear portion that is formed to rise from inside the upper base portion in a radial direction of the oil ring and presses an upper segment of the pair of segments that is provided on a combustion chamber side of the internal combustion engine outward in the radial direction of the oil ring,
the lower piece includes a lower base portion and a lower ear portion that is formed to stand on the inside of the lower base portion in the radial direction of the oil ring and presses the lower segment, of the pair of segments, that is provided on the crank chamber side of the internal combustion engine, outward in the radial direction of the oil ring.
2. The spacer expander of claim 1. The expander groove is formed in the outer peripheral surface of the expander body by a plurality of notches provided at outer ends, which are radially outer ends of the oil ring, of the plurality of connecting pieces so as to be arranged along the circumferential direction of the oil ring,
a width of the fitting portion in the axial direction of the oil ring is smaller than a width of the outer end portion of the connecting piece in the axial direction;
3. The spacer expander of claim 2. The expander groove is formed on the inner circumferential surface of the expander body by a plurality of notches provided at inner ends, which are radially inner ends of the oil ring, of the plurality of connecting pieces so as to be arranged along the circumferential direction of the oil ring,
a width of the fitting portion in the axial direction of the oil ring is smaller than a width of the inner end portion of the connecting piece in the axial direction;
3. The spacer expander of claim 2. The expander groove is formed on an outer circumferential surface of the expander body,
In a free state before the oil ring is assembled to the piston, a radius of curvature of the arc at the inner peripheral end of the fitting portion is equal to or smaller than a radius of curvature of the outermost circumference of the expander body in a state in which the pair of abutting ends are abutted against each other.
A spacer expander according to any one of claims 1 to 3. The expander groove is formed on an inner circumferential surface of the expander body,
In a free state before the oil ring is assembled to the piston, a radius of curvature of the arc at the outer circumferential end of the fitting portion is equal to or greater than a radius of curvature of the innermost periphery of the expander body in a state in which the pair of abutting ends are abutted against each other.
5. A spacer expander according to claim 1, 2 or 4. the expander groove is formed by a plurality of notches provided in the upper base portions of the plurality of upper pieces so as to be arranged along a circumferential direction of the oil ring,
a thickness of the fitting portion in a radial direction of the oil ring is smaller than a thickness of the upper base portion in the radial direction;
3. The spacer expander of claim 2. the expander groove is formed by a plurality of notches provided in the lower base portions of the plurality of lower pieces so as to be arranged along a circumferential direction of the oil ring,
a thickness of the fitting portion in a radial direction of the oil ring is smaller than a thickness of the lower base portion in the radial direction;
3. The spacer expander of claim 2. The expander groove is formed in one of both end faces of the expander body in the axial direction of the oil ring,
In a free state before the oil ring is assembled to the piston, the radius of curvature of the arc at the outer circumferential end of the fitting portion is within +10% of the radius of curvature of the outermost circumference of the expander body when the pair of joint ends are abutted against each other, and the radius of curvature of the arc at the inner circumferential end of the fitting portion is equal to or greater than -10% of the radius of curvature of the innermost circumference of the expander body when the pair of joint ends are abutted against each other.
3. A spacer expander according to claim 1 or 2. An oil ring to be assembled to a piston in an internal combustion engine,
a pair of segments spaced apart in an axial direction of the oil ring; and a spacer expander provided between the pair of segments,
The spacer expander includes:
an expander body that is formed in an annular shape along the circumferential direction of the oil ring and biases the pair of segments outward in the radial direction of the oil ring, the expander body including a pair of joint ends that face each other to form a joint, and that is formed in a wavy shape that is continuous in the circumferential direction when viewed in the radial direction of the oil ring;
an expander groove formed in the expander body so as to extend along a circumferential direction of the oil ring across the joint;
a linear member including a fitting portion formed in an arc shape along a circumferential direction of the oil ring, the fitting portion being fitted into the expander groove so as to span the gap ;
The linear member further includes a locking portion provided at one end of the fitting portion,
the locking portion includes a first bent portion extending from one end of the fitting portion toward the inside in the radial direction of the oil ring, and a second bent portion bent from a tip of the first bent portion and extending toward the outside in the radial direction of the oil ring,
Oil ring.

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