JP6986107B2 - Piston ring combination - Google Patents

Description

The present invention relates to a combination of piston rings.

The internal combustion engine installed in a general automobile is equipped with three piston rings, which are a combination of two compression rings (pressure rings) including a top ring and a second ring, and one oil ring. The configuration provided on the piston is adopted. In these three piston rings, the top ring, the second ring, and the oil ring are mounted in the ring groove formed on the outer peripheral surface of the piston in order from the upper side (combustion chamber side), and slide on the inner wall surface of the cylinder. The oil ring farthest from the combustion chamber has an oil seal function that suppresses the outflow of oil to the combustion chamber side (oil rise) by scraping off excess engine oil (lubricating oil) adhering to the inner wall surface of the cylinder to the crank side. By adjusting the amount of oil so that the lubricating oil film is appropriately held on the inner wall surface of the cylinder, it has a function of preventing seizure of the piston due to the operation of the internal combustion engine. The compression ring has a gas seal function that suppresses the outflow (blow-by) of combustion gas from the combustion chamber side to the crank chamber side by maintaining airtightness, and scrapes off excess oil that the oil ring could not scrape off. It has an oil seal function that suppresses oil rise. By such a combination of piston rings, blow-by gas is reduced and oil consumption is reduced in the internal combustion engine.

In this regard, Patent Document 1 and Patent Document 2 are provided with a top ring having a vertically symmetrical barrel shape, a second ring having a tapered shape, and a segment having a vertically symmetrical barrel shape or a straight shape. A combination of an oil ring and a piston ring including is disclosed. In the combination of the piston ring disclosed in Patent Document 1 and Patent Document 2, the oil consumption in the internal combustion engine is reduced by using the second ring having the outer peripheral surface having an excellent tapered shape for the oil seal in combination with the oil ring.

Japanese Unexamined Patent Publication No. 2001-241357 Japanese Unexamined Patent Publication No. 2012-215238

Here, in order to reduce fuel consumption of an internal combustion engine, it is important to reduce the friction generated between the outer peripheral surface (sliding surface) of each piston ring and the inner wall of the cylinder to reduce the friction loss of the internal combustion engine. Is. On the other hand, although the above-mentioned tapered shape exhibits excellent performance in an oil seal, it tends to be disadvantageous in reducing friction. Therefore, a combination of piston rings capable of further reducing the friction loss is desired, but it is difficult to achieve both the oil seal performance and the oil seal performance.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a technique capable of ensuring oil sealing performance while further reducing friction loss in a combination of piston rings. be.

In order to solve the above problems, the present invention has adopted the following means. That is, the present invention is a combination of a piston ring including a top ring, a second ring, and an oil ring provided in a ring groove formed on the outer peripheral surface of a piston mounted on a cylinder of an internal combustion engine. Is provided at the outer peripheral end portion of the top ring and is convex outward in the radial direction including the first top portion having the maximum diameter in the top ring in a cross section orthogonal to the peripheral length direction of the top ring. The second ring has a curved first outer peripheral end surface, and the second ring is arranged on the lower side of the ring groove, which is the crank chamber side in the axial direction of the piston, and a joint is formed in the main body ring and the ring groove. The main body ring includes a cover ring which is arranged on the upper side which is the combustion chamber side in the axial direction of the piston and slides on the inner wall of the cylinder together with the main body ring, and the main body ring has a cross section orthogonal to the peripheral direction of the main body ring. The cover ring is provided at the outer peripheral end portion of the main body ring and has a second outer peripheral end surface curved so as to be convex outward in the radial direction including the second top portion having the maximum diameter in the main body ring. Overlaps the main body ring so as to cover at least a part of the abutment of the main body ring from above in the ring groove, and the oil ring is formed in an annular shape around the axis of the oil ring, and the oil is formed. It has a pair of sliding portions provided side by side in the axial direction of the ring, and each of the pair of sliding portions has an outer peripheral end of the sliding portion in a cross section orthogonal to the peripheral length direction of the sliding portion. It is a combination of piston rings provided in the portion and having a third outer peripheral end surface curved so as to be convex outward in the radial direction including the third top portion having the maximum diameter in the sliding portion.

Here, in the present specification, for each piston ring of the top ring, the second ring, and the oil ring, the "peripheral length direction" refers to the peripheral length direction of the piston ring unless otherwise specified. The "radial direction" refers to the radial direction of the piston ring unless otherwise specified. "Diameter inside" refers to the inner peripheral surface side of the piston ring, and "diameter outside" refers to the opposite side (that is, the outer peripheral surface side of the piston ring). The "axial direction" refers to a direction along the central axis of the piston ring unless otherwise specified. Further, a surface shape curved so as to be convex outward in the radial direction including the top having the maximum diameter in the piston ring is referred to as a "barrel shape". Further, among the barrel shapes, the outer peripheral surface shape in which the lower edge is located radially outside the upper edge and the top portion is located below the axial center (center of the ring width) on the surface is referred to as "the shape of the outer peripheral surface". It is called "eccentric barrel shape". For each piston ring of the top ring, second ring, and oil ring, the "outer peripheral surface" refers to the surface connecting the outer peripheral edges of both end faces in the axial direction that define the width (axial dimension) of the ring. , "Inner peripheral surface" refers to a surface connecting the inner peripheral edges of both end faces in the axial direction.

The combination of the piston ring according to the present invention is a barrel in which the outer peripheral end faces of the top ring, the main body ring of the second ring, and the oil ring are curved so as to be convex outward in the radial direction including the top which is the maximum diameter of the ring. It has a shape. According to this, each piston ring slides on the inner wall of the cylinder on the curved surface. Therefore, according to the present invention, the friction generated between the cylinder inner wall and the cylinder inner wall can be reduced, and the friction loss in the internal combustion engine can be reduced. Further, when the outer peripheral surface of the piston ring has a barrel shape, the function of scraping off oil tends to deteriorate, but the second ring according to the present invention is configured so that the joint of the main body ring is covered with a covering. There is. As a result, it is possible to suppress the oil rising due to the oil existing in the gap between the cylinder and the piston passing through the joint of the main body ring from the lower side to the upper side. As a result, according to the present invention, the oil seal performance can be ensured while reducing the friction loss.

Further, in the present invention, the cover ring is formed with a joint, and the width of the cover ring in the axial direction may be smaller than the width of the main body ring in the axial direction. According to this, it becomes difficult for the oil existing in the ring groove to flow into the joint of the covering. As a result, it is possible to suppress the oil rising due to the oil existing in the ring groove passing through the joint of the covering, and the oil sealing performance can be further improved.

Further, in the present invention, the radial width of the covering is larger than the maximum separation distance secured between the inner wall of the cylinder and the outer peripheral surface of the piston when the piston is mounted on the cylinder. It may be large. According to this, even if the separation distance changes due to the swinging motion of the piston, the entire area of the joint of the main body ring located in the gap between the cylinder and the piston is covered from above by the covering. Can be maintained. As a result, stable sealing performance can be ensured.

Further, in the present invention, the main body ring has an inner cut surface for connecting the inner peripheral end surface provided at the inner peripheral end portion of the main body ring and the upper surface or the lower surface of the main body ring, and the inner cut surface is , The intersection of the virtual inner peripheral end surface and the virtual end surface in the virtual corner portion formed by the intersection of the virtual inner peripheral end surface with the inner peripheral end surface extended and the virtual end surface with the upper surface or the lower surface of the main body ring extended. A predetermined portion including a portion may be formed so as not to be included in the main body ring. The inner cut surface may be formed so as to connect the inner peripheral end surface and the upper surface or the lower surface of the main body ring with one plane or a curved surface, or may be formed by a plurality of planes or curved surfaces as another method. According to this, the overall stress balance becomes asymmetric in the main body ring. When this main body ring is attached to the piston and attached to the cylinder, the main body ring is twisted. By twisting the main body ring, the cover ring is urged to the upper wall of the ring groove by the main body ring. As a result, the cover ring is strongly pressed against the upper wall of the ring groove, and the fluttering of the cover ring is suppressed. By suppressing the fluttering of the covering, the posture of the covering is stabilized. As a result, the state in which the joint of the main body ring is covered by the covering is maintained, and the oil sealing performance can be further improved.

Further, in the present invention, the third outer peripheral end surface of at least one of the pair of sliding portions has a lower edge located radially outside the upper edge, and the third peripheral end surface is located in the axial direction of the sliding portions. The top portion may be formed so as to be located on the lower edge side of the central position of the third outer peripheral end surface. According to this, by forming the third outer peripheral end surface of the sliding portion of the oil ring into an eccentric barrel shape, the oil can be suitably scraped off when the piston is lowered, and a wedge effect is obtained when the piston is raised. As a result, the third outer peripheral end surface rides on the oil, so that it is possible to prevent the oil from being scraped up. As a result, the oil seal performance can be further improved.

Further, in the present invention, the lower edge of the second outer peripheral end surface is located radially outside the upper edge, and the second top portion is located at the center position of the second outer peripheral end surface in the axial direction of the main body ring. May be formed so as to be located on the lower edge side. According to this, the oil sealing performance can be further improved by forming the second outer peripheral end surface of the main body ring of the second ring into an eccentric barrel shape.

According to the present invention, it is possible to secure the oil seal performance while further reducing the friction loss in the combination of the piston rings.

It is an overall view of the internal combustion engine provided with the combination of the piston ring which concerns on embodiment. It is an enlarged view near the ring groove of the internal combustion engine which concerns on embodiment. It is sectional drawing which is orthogonal to the circumferential length direction of the top ring which concerns on embodiment. It is sectional drawing which is orthogonal to the circumferential length direction of the main body ring which concerns on embodiment. It is sectional drawing which is orthogonal to the circumferential length direction of the side rail which concerns on embodiment. It is a perspective view of the second ring in the use state. It is sectional drawing which is orthogonal to the circumferential length direction of the oil ring when the oil ring which concerns on embodiment is in use. It is sectional drawing which is orthogonal to the circumference direction of the segment which concerns on embodiment. It is sectional drawing which is orthogonal to the peripheral direction of the second ring when the second ring which concerns on embodiment is in use (1). FIG. 2 is a cross-sectional view orthogonal to the circumferential length direction of the second ring when the second ring according to the embodiment is in use (2). It is a figure which shows the vicinity of the ring groove of the internal combustion engine provided with the combination of the piston ring which concerns on a comparative example. FIG. 3 is a cross-sectional view orthogonal to the circumferential length direction of the second ring when the second ring according to the embodiment is in use (3). It is sectional drawing which is orthogonal to the circumferential length direction of the second ring when the second ring which concerns on modification 1 is in use. It is a figure which shows the main body ring which concerns on the modification 1, FIG. 14A is a cross-sectional view orthogonal to the circumferential length direction of a main body ring, and FIG. It is an enlarged view which shows. It is sectional drawing which is orthogonal to the circumferential length direction of the oil ring when the oil ring which concerns on modification 2 is in use. It is sectional drawing which is orthogonal to the circumference direction of the segment which concerns on modification 2. FIG. It is sectional drawing which is orthogonal to the circumferential length direction of the second ring when the second ring which concerns on modification 3 is in use. It is sectional drawing which is orthogonal to the peripheral length direction of the main body ring which concerns on modification 3. FIG. It is sectional drawing which is orthogonal to the circumferential length direction of the oil ring which concerns on modification 4.

Hereinafter, preferred embodiments of the combination of piston rings according to the present invention will be described with reference to the drawings. The configurations described in the following embodiments are not intended to limit the technical scope of the invention to those alone unless otherwise specified.

FIG. 1 is an overall view of an internal combustion engine 100 provided with a combination of piston rings according to an embodiment. FIG. 2 is an enlarged view of the vicinity of the ring groove of the internal combustion engine 100. In FIGS. 1 and 2, for convenience, each configuration is shown in a simplified manner. As shown in FIG. 1, the internal combustion engine 100 according to the embodiment includes a cylinder 20 and a piston 10 mounted on the cylinder 20. In the axial direction of the piston 10, the combustion chamber side indicated by reference numeral 30 is the upper side, and the crank chamber side indicated by the reference numeral 40 is the lower side.

As shown in FIG. 2, in the internal combustion engine 100, a gap PC1 is formed by ensuring a predetermined separation distance between the piston outer peripheral surface 10a and the cylinder inner wall 20a. Further, on the outer peripheral surface 10a of the piston, a top ring groove 101, a second ring groove 102, and an oil ring groove 103 are formed in this order from the upper side (combustion chamber side) at predetermined intervals in the axial direction of the piston 10. The top ring groove 101, the second ring groove 102, and the oil ring groove 103 are each provided with a top ring 1, a second ring 2, and an oil ring 3. In the present specification, when the top ring groove 101, the second ring groove 102, and the oil ring groove 103 are described without distinction, they are simply referred to as "ring grooves". Further, when the top ring 1, the second ring 2, and the oil ring 3 are described without distinction, they are simply referred to as "piston ring". As shown in FIG. 2, the state in which each piston ring is mounted in the ring groove is referred to as a "use state".

Further, for each of the piston 10, the cylinder 20, the top ring 1, the second ring 2, and the oil ring 3, the axial direction of each is defined as the vertical direction, and the combustion chamber 30 side in these usage states is the "upper side" of each. It is defined as the "upward direction" in FIGS. 1 and 2, and the opposite side (that is, the side away from the combustion chamber and the crank chamber 40 side) is defined as the "lower side" of each.

Further, in the present specification, the "barrel shape" refers to a surface shape curved so as to be convex outward in the radial direction including the top having the maximum diameter in the piston ring, and is a symmetric barrel shape or an eccentric barrel. It shall include the shape. In the "symmetrical barrel shape", in the barrel shape, the upper edge (edge on the combustion chamber side) and the lower edge (edge on the crank chamber side) are aligned in the radial direction, and the top thereof is in the axial direction (ring width) on the surface. Refers to the surface shape located in the center of the direction). The "eccentric barrel shape" is an outer peripheral surface of the barrel shape in which the lower edge is located radially outside the upper edge and the top is located below the axial center (center of the ring width) on the surface. Refers to the shape.

As shown in FIG. 2, each ring groove is formed by a pair of inner walls facing vertically, and among these, the upper inner wall is referred to as an upper wall W1 and the lower inner wall is referred to as a lower wall W2. Each piston ring has a self-tension so that the outer peripheral surface of each piston ring presses the cylinder inner wall 20a in the used state.

Hereinafter, the shape of each piston ring in the combination of the piston rings according to the embodiment will be described.

[Top ring]
First, the top ring 1 according to the embodiment will be described. FIG. 3 is a cross-sectional view orthogonal to the peripheral length direction of the top ring 1 according to the embodiment. As shown in FIG. 3, the top ring 1 has a first upper surface 11 provided on the upper side, a first lower surface 12 provided on the lower side, and an outer peripheral edge E101 and a first lower surface 12 of the first upper surface 11. It has a first outer peripheral surface 13 connecting the peripheral edge E102, and a first inner peripheral surface 14 connecting the inner peripheral edge E103 of the first upper surface 11 and the inner peripheral edge E104 of the first lower surface 12. When the top ring 1 is mounted on the top ring groove 101, that is, in the used state, the first upper surface 11 is located on the upper side and faces the upper wall W1 of the top ring groove 101, and the first lower surface 12 is on the lower side. It is located on the side and faces the lower wall W2, and the first outer peripheral surface 13 slides on the cylinder inner wall 20a. The first upper surface 11 and the first lower surface 12 define the width of the top ring 1 in the axial direction.

As shown in FIG. 3, the first outer peripheral surface 13 connects the first outer peripheral end surface S11 provided at the outer peripheral end of the top ring 1, the first outer peripheral end surface S11, the first upper surface 11, and the first lower surface 12, respectively. Includes a pair of connecting surfaces S12, S12. One of the pair of connecting surfaces S12 and S12 connects the peripheral edge (hereinafter, upper edge) E11 on the upper side (combustion chamber 30 side) of the first outer peripheral end surface S11 and the outer peripheral edge E101 of the first upper surface 11. The other of the pair of connecting surfaces S12 and S12 connects the peripheral edge (hereinafter referred to as the lower edge) E12 on the lower side (crank chamber 40 side) of the first outer peripheral end surface S11 and the outer peripheral edge E102 of the first lower surface 12.

The first outer peripheral end surface S11 is formed in a barrel shape. That is, the first outer peripheral end surface S11 is curved so as to be convex outward in the radial direction including the first top portion P1 having the maximum diameter in the top ring 1 in a cross section orthogonal to the circumferential length direction of the top ring 1. There is. The first top portion P1 of the first outer peripheral end surface S11 is located on the first outer peripheral surface 13 at the outermost position in the radial direction of the top ring 1, and the first outer peripheral end surface S11 slides on the cylinder inner wall 20a in the used state. The first outer peripheral end surface S11 is further formed in a symmetrical barrel shape that is symmetrical in the axial direction with the first top portion P1 as a boundary. That is, the first outer peripheral end surface S11 is curved so as to be radially outward in a cross section orthogonal to the peripheral direction, and the upper edge E11 and the lower edge E12 of the first outer peripheral end surface S11 are aligned in the radial direction. The convex first top portion P1 is located at the center of the top ring 1 in the axial direction (vertical direction) on the first outer peripheral end surface S11.

The reference numeral CL1 in FIG. 3 is orthogonal to the central axis A1 of the top ring 1 and is the first outer peripheral end surface S1.
A straight line passing through the central position in the axial direction at 1 is shown. As shown in FIG. 3, the first top P1 is located on the center line CL1. Further, reference numerals a11 and a12 in FIG. 3 represent barrel heads. a11 indicates the barrel head on the combustion chamber 30 side of the top ring 1, that is, the radial distance between the first top portion P1 of the top ring 1 and the upper edge E11 of the first outer peripheral end surface S11. a11 is equal to the distance from the cylinder inner wall 20a in the used state to the upper edge E11 of the first outer peripheral end surface S11. Similarly, a12 indicates the barrel head on the crank chamber 40 side of the top ring 1, that is, the radial distance between the first top portion P1 of the top ring 1 and the lower edge E12 of the first outer peripheral end surface S11. a12 is equal to the distance from the cylinder inner wall 20a in the used state to the lower edge E12 of the first outer peripheral end surface S11. In this example, since the first outer peripheral end surface S11 is formed in a symmetrical barrel shape, the upper edge E11 and the lower edge E12 of the first outer peripheral end surface S11 are aligned in the radial direction. As a result, a11 and a12 are equal. Further, reference numeral b11 in FIG. 3 indicates a distance in the axial direction between the first top portion P1 of the first outer peripheral end surface S11 and the upper edge E11 of the first outer peripheral end surface S11. Further, b12 indicates the distance in the axial direction between the first top portion P1 of the first outer peripheral surface 13 and the lower edge E12 of the first outer peripheral end surface S11. In this example, since the first outer peripheral end surface S11 is formed in a symmetrical barrel shape, b11 and b12 are equal to each other.

In this example, the first outer peripheral end surface S11 is formed in a symmetrical barrel shape, but the shape of the first outer peripheral end surface S11 is not limited to this. The first outer peripheral end surface S11 may have a barrel shape and may not have a symmetrical barrel shape. That is, the first outer peripheral end surface S11 may have a shape curved so as to be convex outward in the radial direction including the first top portion P1 having the maximum diameter in the top ring 1. For example, the first outer peripheral end surface S11 may have an eccentric barrel shape. In that case, the lower edge E12 is located radially outside the upper edge E11, and the first top portion P1 is offset toward the crank chamber 40 side. Further, the top ring 1 may not have a pair of connecting surfaces S12 and S12, and the first outer peripheral end surface S11 may be connected to the first upper surface 11 and the first lower surface 12. That is, the entire area of the first outer peripheral surface 13 may be the first outer peripheral end surface S11.

[Second ring]
Next, the second ring 2 according to the embodiment will be described. As shown in FIG. 2, the second ring 2 according to the embodiment has a main body ring 4 arranged on the lower side in the second ring groove 102 and a main body ring 4 arranged on the upper side in the second ring groove 102, and the cylinder inner wall 20a is arranged together with the main body ring 4. Includes a sliding side rail 5.

FIG. 4 is a cross-sectional view orthogonal to the circumferential length direction of the main body ring 4 according to the embodiment. As shown in FIG. 4, the main body ring 4 has a second upper surface 41 provided on the upper side, a second lower surface 42 provided on the lower side, and an outer peripheral edge E401 and a second lower surface 42 of the second upper surface 41. It has a second outer peripheral surface 43 connecting the peripheral edge E402, and a second inner peripheral surface 44 connecting the inner peripheral edge E403 of the second upper surface 41 and the inner peripheral edge E404 of the second lower surface 42. When the main body ring 4 is mounted on the second ring groove 102 and is in use, the second upper surface 41 is located on the upper side and abuts on the side rail 5, and the second lower surface 42 is located on the lower side and is on the lower wall W2. The second outer peripheral surface 43 faces the cylinder inner wall 20a and slides on the cylinder inner wall 20a. The width of the main body ring 4 in the axial direction is defined by the second upper surface 41 and the second lower surface 42.

As shown in FIG. 4, the second outer peripheral surface 43 connects the second outer peripheral end surface S41 provided at the outer peripheral end of the main body ring 4, the second outer peripheral end surface S41, the second upper surface 41, and the second lower surface 42, respectively. Includes a pair of connecting surfaces S42 and S42. One of the pair of connecting surfaces S42 and S42 connects the upper edge E41 of the second outer peripheral end surface S41 and the outer peripheral edge E401 of the second upper surface 41. The other of the pair of connecting surfaces S42 and S42 connects the lower edge E42 of the second outer peripheral end surface S41 and the outer peripheral edge E402 of the second lower surface 42.

The second outer peripheral end surface S41 is formed in a barrel shape like the first outer peripheral end surface S11 of the top ring 1. That is, the second outer peripheral end surface S41 is curved so as to be convex outward in the radial direction including the second top portion P4 having the maximum diameter in the main body ring 4 in a cross section orthogonal to the circumferential length direction of the main body ring 4. There is. The second top P4 of the second outer peripheral end surface S41 is located on the second outer peripheral surface 43 at the outermost position in the radial direction of the main body ring 4, and the second outer peripheral end surface S41 slides on the cylinder inner wall 20a in the used state. The second outer peripheral end surface S41 is further formed in a symmetrical barrel shape that is symmetrical in the axial direction with the second top P4 as a boundary. That is, the second outer peripheral end surface S41 is curved so as to be radially outward in a cross section orthogonal to the peripheral length direction, and the upper edge E41 and the lower edge E42 of the second outer peripheral end surface S41 are aligned in the radial direction. The convex second top P4 is located at the center of the main body ring 4 in the axial direction (vertical direction) on the second outer peripheral end surface S41.

Reference numeral CL4 in FIG. 4 indicates a straight line orthogonal to the central axis A4 of the main body ring 4 and passing through the central position in the axial direction on the second outer peripheral end surface S41. As shown in FIG. 4, the second top P4 is located on the center line CL4. Further, reference numerals a41 and a42 in FIG. 4 represent barrel heads. a41 indicates the barrel head on the combustion chamber 30 side of the main body ring 4, that is, the radial distance between the second top portion P4 of the main body ring 4 and the upper edge E41 of the second outer peripheral end surface S41. a41 is equal to the distance from the cylinder inner wall 20a in the used state to the upper edge E41 of the second outer peripheral end surface S41. Similarly, a42 indicates the barrel drop on the crank chamber 40 side of the main body ring 4, that is, the radial distance between the second top portion P4 of the main body ring 4 and the lower edge E42 of the second outer peripheral end surface S41. a42 is equal to the distance from the cylinder inner wall 20a in the used state to the lower edge E42 of the second outer peripheral end surface S41. In this example, since the second outer peripheral end surface S41 is formed in a symmetrical barrel shape, the upper edge E41 and the lower edge E42 of the second outer peripheral end surface S41 are aligned in the radial direction. As a result, a41 and a42 are equal. Further, reference numeral b41 in FIG. 4 indicates the distance in the axial direction between the second top portion P4 of the second outer peripheral end surface S41 and the upper edge E41 of the second outer peripheral end surface S41. Further, b42 indicates the distance in the axial direction between the second top portion P4 of the second outer peripheral surface 43 and the lower edge E42 of the second outer peripheral end surface S41. In this example, since the second outer peripheral end surface S41 is formed in a symmetrical barrel shape, b41 and b42 are equal to each other.

In this example, the second outer peripheral end surface S41 is formed in a symmetrical barrel shape, but the shape of the second outer peripheral end surface S41 is not limited to this. The second outer peripheral end surface S41 may have a barrel shape and may not have a symmetrical barrel shape. That is, the second outer peripheral end surface S41 may have a shape that includes the second top P4 having the maximum diameter in the main body ring 4 and is curved so as to be convex outward in the radial direction, and has an eccentric barrel shape as described later. May be. Further, the main body ring 4 may not have a pair of connecting surfaces S42 and S42, and the second outer peripheral end surface S41 may be connected to the second upper surface 41 and the second lower surface 42. That is, the entire area of the second outer peripheral surface 43 may be the second outer peripheral end surface S41.

FIG. 5 is a cross-sectional view orthogonal to the circumferential length direction of the side rail 5 according to the embodiment. Reference numeral A5 in FIG. 5 indicates the central axis of the side rail 5. As shown in FIG. 5, the side rail 5 includes a cover upper surface 51 provided on the upper side, a cover lower surface 52 provided on the lower side, an outer peripheral edge E501 of the cover upper surface 51, and an outer peripheral edge E502 of the cover lower surface 52. It has a cover outer peripheral surface 53 to be connected, and a cover inner peripheral surface 54 connecting the inner peripheral edge E503 of the cover upper surface 51 and the inner peripheral edge E504 of the cover lower surface 52. When the side rail 5 is mounted on the second ring groove 102 and is in use, the upper surface 51 of the cover is located on the upper side and faces the upper wall W1 of the second ring groove 102, and the lower surface 52 of the cover is located on the lower side of the main body. The cover outer peripheral surface 53 abuts on the ring 4 and slides on the cylinder inner wall 20a. The width of the side rail 5 in the axial direction is defined by the cover upper surface 51 and the cover lower surface 52. The side rail 5 is formed in a substantially rectangular shape in a cross section orthogonal to the circumferential length direction, and the outer peripheral surface 53 of the cover is formed in a flat straight shape extending along the axial direction. The outer peripheral surface 53 of the cover may be formed in a barrel shape or may have a tapered shape, but is not limited to this. The side rail 5 is an example of the "covering" according to the present invention.

FIG. 6 is a perspective view of the second ring 2 in a used state. In FIG. 6, the piston 10 and the cylinder 20 are not shown for convenience. Reference numeral G4 indicates a joint formed in the main body ring 4. Reference numeral B4 indicates a portion (main body portion) of the main body ring 4 excluding the abutment G4. Further, reference numeral G5 indicates a joint formed on the side rail 5. Reference numeral B5 indicates a portion (main body portion) of the side rail 5 excluding the abutment G5. As shown in FIG. 6, the second ring 2 is provided in the second ring groove 102 so that the abutment G4 of the main body ring 4 and the abutment G5 of the side rail 5 do not overlap in the axial direction of the main body ring 4. The main body portion B5 of the side rail 5 overlaps the abutment G4 of the main body ring 4 from above. That is, the side rail 5 overlaps the main body ring 4 in the second ring groove 102 so as to cover the abutment G4 of the main body ring 4 from above.

[Oil ring]
Next, the oil ring 3 according to the embodiment will be described. FIG. 7 is a cross-sectional view orthogonal to the circumferential length direction of the oil ring 3 when the oil ring 3 according to the embodiment is in use. Further, FIG. 8 is a cross-sectional view orthogonal to the peripheral length direction of the segment 7 according to the embodiment. FIG. 7 shows a usage state in which the oil ring 3 is mounted on the oil ring groove 103. As shown in FIG. 7, the oil ring 3 is a so-called three-piece oil ring. More specifically, the oil ring 3 is formed in an annular shape around the axis of the oil ring 3, and is provided with a pair of segments 7 and 7 independently of each other and arranged side by side in the axial direction of the oil ring 3, and a pair of segments. 7 and 7 are configured to include an expander spacer 6 for urging the outside in the radial direction (cylinder inner wall 20a). In the oil ring 3 according to the embodiment, the pair of segments 7 and 7 have the same shape. The pair of segments 7 and 7 is an example of the "pair of sliding portions" in the present invention. Hereinafter, of the pair of segments 7 and 7, the segment 7 arranged on the upper side (combustion chamber 30 side) is referred to as an upper segment 7U, and the segment 7 arranged on the lower side (crank chamber 40 side) is referred to as a lower segment 7L. When these are not distinguished, it is simply referred to as segment 7.

As shown in FIGS. 7 and 8, the segment 7 has a third upper surface 71 provided on the upper side, a third lower surface 72 provided on the lower side, and an outer peripheral edge E701 and a third lower surface 72 of the third upper surface 71. It has a third outer peripheral surface 73 connecting the outer peripheral edge E702 of the above, and a third inner peripheral surface 74 connecting the inner peripheral edge E703 of the third upper surface 71 and the inner peripheral edge E704 of the third lower surface 72. In the upper segment 7U, when the oil ring 3 is mounted on the oil ring groove 103, that is, in the used state, the third upper surface 71 faces the upper wall W1 of the oil ring groove 103, and the third lower surface 72 and the upper surface segment 7U The third inner peripheral surface 74 abuts on the expander spacer 6, and the third outer peripheral surface 73 is provided so as to slide on the cylinder inner wall 20a. In the lower segment 7L, when the oil ring 3 is in use, the third lower surface 72 faces the lower wall W2 of the oil ring groove 103, and the third upper surface 71 and the third inner peripheral surface 74 are the expander spacers 6. The third outer peripheral surface 73 is provided so as to slide on the inner wall 20a of the cylinder. The third upper surface 71 and the third lower surface 72 define the width of the segment 7 in the axial direction.

As shown in FIG. 8, the third outer peripheral surface 73 connects the third outer peripheral end surface S71 provided at the outer peripheral end portion of the segment 7, the third outer peripheral end surface S71, the third upper surface 71, and the third lower surface 72, respectively. Includes a pair of connecting surfaces S72, S72. One of the pair of connecting surfaces S72 and S72 connects the upper edge E71 of the third outer peripheral end surface S71 and the outer peripheral edge E701 of the third upper surface 71. The other of the pair of connecting surfaces S72 and S72 connects the lower edge E72 of the third outer peripheral end surface S71 and the outer peripheral edge E702 of the third lower surface 72.

The third outer peripheral end surface S71 is formed in a barrel shape like the first outer peripheral end surface S11 of the top ring 1 and the second outer peripheral end surface S41 of the main body ring 4 of the second ring 2. That is, the third outer peripheral end surface S71 is curved so as to be convex outward in the radial direction including the third top portion P7 having the maximum diameter in the segment 7 in the cross section orthogonal to the circumferential length direction of the segment 7. The third top portion P7 of the third outer peripheral end surface S71 is located on the third outer peripheral surface 73 at the outermost position in the radial direction of the segment 7, and the third outer peripheral end surface S71 slides on the cylinder inner wall 20a in the used state. The third outer peripheral end surface S71 is further formed in a symmetrical barrel shape that is symmetrical in the axial direction with the third top portion P7 as a boundary. That is, the third outer peripheral end surface S71 is curved so as to be radially outward in a cross section orthogonal to the peripheral length direction, and the upper edge E71 and the lower edge E72 of the third outer peripheral end surface S71 are aligned in the radial direction. The convex third top P7 is located at the center of the segment 7 in the axial direction (vertical direction) on the third outer peripheral end surface S71.

Reference numeral CL7 in FIG. 8 indicates a straight line orthogonal to the central axis A7 of the segment 7 and passing through the central position in the axial direction on the third outer peripheral end surface S71. As shown in FIG. 8, the third top P7 is located on the center line CL7. Further, reference numerals a71 and a72 in FIG. 8 represent barrel heads. a71 indicates the barrel head on the combustion chamber 30 side in the segment 7, that is, the radial distance between the third top portion P7 of the segment 7 and the upper edge E71 of the third outer peripheral end surface S71. a71 is equal to the distance from the cylinder inner wall 20a in the used state to the upper edge E71 of the third outer peripheral end surface S71. Similarly, a72 indicates the barrel head on the crank chamber 40 side in the segment 7, that is, the radial distance between the third top P7 of the segment 7 and the lower edge E72 of the third outer peripheral end surface S71. a72 is equal to the distance from the cylinder inner wall 20a in the used state to the lower edge E72 of the third outer peripheral end surface S71. In this example, since the third outer peripheral end surface S71 is formed in a symmetrical barrel shape, the upper edge E71 and the lower edge E72 of the third outer peripheral end surface S71 are aligned in the radial direction. As a result, a71 and a72 are equal. Further, reference numeral b71 in FIG. 8 indicates a distance in the axial direction between the third top portion P7 of the third outer peripheral end surface S71 and the upper edge E71 of the third outer peripheral end surface S71. Further, b72 indicates the distance in the axial direction between the third top portion P7 of the third outer peripheral surface 73 and the lower edge E72 of the third outer peripheral end surface S71. In this example, since the third outer peripheral end surface S71 is formed in a symmetrical barrel shape, b71 and b72 are equal to each other.

In this example, the third outer peripheral end surface S71 is formed in a symmetrical barrel shape, but the shape of the third outer peripheral end surface S71 is not limited to this. The third outer peripheral end surface S71 may have a barrel shape and may not have a symmetrical barrel shape. That is, the third outer peripheral end surface S71 may have a shape that includes the third top P7 having the maximum diameter in the segment 7 and is curved so as to be convex outward in the radial direction, and has an eccentric barrel shape as described later. There may be. Further, the segment 7 may not have a pair of connecting surfaces S72 and S72, and the third outer peripheral end surface S71 may be connected to the third upper surface 71 and the third lower surface 72. That is, the entire area of the third outer peripheral surface 73 may be the third outer peripheral end surface S71.

[About the oil seal function of the second ring]
9 and 10 are cross-sectional views orthogonal to the circumferential length direction of the second ring 2 when the second ring 2 according to the embodiment is in use. 9 and 10 show the state of the second ring 2 in the descending stroke of the piston 10. FIG. 9 corresponds to the AA cross section of FIG. That is, FIG. 9 shows a cross section of the second ring 2 in the portion where the main body portion B4 of the main body ring 4 and the main body portion B5 of the side rail 5 overlap. Further, FIG. 10 corresponds to the BB cross section of FIG. That is, in FIG. 10, a cross section of the second ring 2 at the abutment G4 portion of the main body ring 4 is shown. The white arrows in FIGS. 9 and 10 indicate the flow of oil.

As shown in FIGS. 9 and 10, in the descending stroke of the piston 10, the upper surface 51 of the cover of the side rail 5 is pressed against the upper wall W1 of the second ring groove 102 by the upward inertial force acting on the second ring 2, and the main body is formed. The second upper surface 41 of the ring 4 is pressed against the cover lower surface 52 of the side rail 5. When the cover upper surface 51 of the side rail 5 is pressed against the upper wall W1 of the second ring groove 102, the oil existing in the second ring groove 102 is between the cover upper surface 51 of the side rail 5 and the upper wall W1 of the second ring groove 102. It is suppressed that the oil flows out to the gap PC1 through the gap PC1. As described above, the outflow of oil from the second ring groove 102 to the gap PC1 (oil rise) to the combustion chamber 30 side is suppressed.

Further, as shown in FIG. 9, in the portion where the main body portion B4 of the main body ring 4 and the main body portion B5 of the side rail 5 overlap in the second ring 2, the main body portion B4 of the main body ring 4 slides on the cylinder inner wall 20a. By doing so, the oil existing in the gap PC1 is scraped down (cylinder chamber 40 side). On the other hand, as shown in FIG. 10, in the abutment G4 portion of the main body ring 4 in the second ring 2, the oil existing in the gap PC1 is on the lower side (crank chamber 40 side) of the abutment G4 which is a gap formed in the main body ring 4. May flow in from. On the other hand, in the second ring 2 according to the embodiment, as described above, the abutment G4 of the main body ring 4 is covered from the upper side (combustion chamber 30 side) by the main body portion B5 of the side rail 5. Therefore, the side rail 5 suppresses the oil flowing into the abutment G4 of the main body ring 4 from flowing out from the abutment G4 to the upper side. As described above, the oil rising due to the oil existing in the gap PC1 passing through the abutment G4 of the main body ring 4 from the lower side to the upper side is also suppressed.

[Comparison example]
Here, FIG. 11 is a diagram showing the vicinity of the ring groove of the internal combustion engine 200 provided with the combination of the piston rings according to the comparative example. The internal combustion engine 200 according to the comparative example is different from the internal combustion engine 100 in that the second ring 202 is used instead of the second ring 2. The second ring 202, unlike the second ring 2, does not have a side rail 5. Further, the ring outer peripheral surface 2023 that slides on the cylinder inner wall 20a in the second ring 202 is formed in a tapered shape that is gradually reduced in diameter toward the combustion chamber 30 side.

[Action / Effect]
Next, the action and effect of the combination of the piston rings according to the embodiment will be described in comparison with the comparative example. As described above, in the combination of the piston rings according to the embodiment, the top ring 1, the main body ring 4 of the second ring 2, and the outer peripheral end faces of the oil ring 3 have a barrel shape. That is, the outer peripheral end surface of each piston ring has a curved shape so as to be convex outward in the radial direction including the top portion which is the maximum diameter of the ring. As a result, each piston ring slides on the cylinder inner wall 20a on the curved surface. Therefore, according to the combination of the piston rings according to the embodiment, the friction generated between the cylinder inner wall 20a and the cylinder inner wall 20a is reduced as compared with the combination of the piston rings according to the comparative example in which the outer peripheral surface of the second ring is tapered. However, the friction loss in the internal combustion engine 100 can be reduced.

On the other hand, when the piston ring alone is evaluated, when the outer peripheral surface of the piston ring has a barrel shape, the function of scraping off oil tends to be lower than when the outer peripheral surface has a tapered shape. On the other hand, the second ring 2 according to the embodiment is configured so that the abutment G4 of the main body ring 4 is covered with the side rail 5 in the used state. As a result, it is possible to suppress the oil rising due to the oil existing in the gap PC1 passing through the abutment G4 of the main body ring 4 from the lower side to the upper side. As a result, the oil seal performance can be ensured.

That is, according to the combination of the piston rings according to the embodiment, the outer peripheral surface of each piston ring has a barrel shape, so that the friction loss is reduced as compared with the combination of the piston rings according to the comparative example, but the main body of the second ring 2 is used. The oil seal performance can be ensured by covering the abutment G4 of the ring 4 from above with the side rail 5.

As shown in FIGS. 9 and 10, in the second ring 2 according to the embodiment, the side rail 5 is configured to cover the entire joint G4 of the main body ring 4 from above. The second ring concerned is not limited to this. In the present invention, the covering may overlap the main body ring so as to cover at least a part of the joint of the main body ring from above. The cover ring according to the present invention is configured to slide on the inner wall of the cylinder together with the main body ring. Therefore, when the side rail 5 overlaps the main body ring 4, at least a part of the region (the region of the dot pattern represented by the reference numeral X1 in FIG. 10) located in the gap PC1 in the joint G4 in the used state is formed by the side rail 5. It will be covered from above. As a result, the side rail 5 can prevent the oil in the gap PC1 flowing into the abutment G4 of the main body ring 4 from passing through the abutment G4 from the lower side to the upper side, and the sealing performance can be ensured.

Here, reference numeral t1 in FIGS. 9 and 10 indicates the width of the side rail 5 in the radial direction. Further, reference numeral d1 indicates the maximum separation distance secured between the cylinder inner wall 20a and the piston outer peripheral surface 10a when the piston 10 is mounted on the cylinder 20. When the piston 10 reciprocates in the cylinder 20, the size of the gap PC1, that is, the separation distance between the cylinder inner wall 20a and the piston outer peripheral surface 10a may change due to the swinging motion of the piston 10 (also called a piston slap). .. The maximum separation distance d1 is assumed in consideration of the piston slap and the like. At this time, the second ring 2 according to the embodiment is configured so that t1 is larger than d1. As a result, even if the separation distance changes, the entire area of the above-mentioned region X1 can be covered from above by the side rail 5. As a result, stable sealing performance can be ensured.

Further, the second ring 2 has a detenting means for suppressing the side rail 5 from rotating relative to the main body ring 4 in the circumferential length direction due to vibration or the like accompanying the reciprocating motion of the piston 10. May be good. The detent means includes, for example, a protrusion formed on one of the second upper surface 41 of the main body ring 4 and the cover lower surface 52 of the side rail 5, and a groove (notch) formed on the other side and engaging with the protrusion. May be formed including. Since the rotation prevention means suppresses the relative rotation of the main body ring 4 and the side rail 5, it is possible to prevent the abutment G5 of the side rail 5 from overlapping the abutment G4 of the main body ring 4. As a result, the state in which the joint port G4 of the main body ring 4 is covered from above by the side rail 5 is maintained, and the oil sealing performance can be further improved.

Here, FIG. 12 is a cross-sectional view orthogonal to the circumferential length direction of the second ring 2 when the second ring 2 according to the embodiment is in use. FIG. 12 shows the state of the second ring 2 in the descending stroke of the piston 10. FIG. 12 corresponds to the CC cross section of FIG. That is, FIG. 12 shows a cross section of the second ring 2 at the abutment G5 portion of the side rail 5. The white arrows in FIG. 12 indicate the flow of oil.

At the abutment G5 portion of the side rail 5 in the second ring 2, oil existing in the second ring groove 102 may flow into the abutment G5 of the side rail 5 from the inside in the radial direction and flow out to the gap PC1. Here, reference numeral w4 in FIG. 12 indicates the width of the main body ring 4 in the axial direction, and reference numeral w5 indicates the width of the side rail 5 in the axial direction. At this time, the second ring 2 according to the embodiment is configured such that w5 is smaller than w4. That is, the side rail 5 is thinner in the axial direction than the main body ring 4. Since the side rail 5 has a thin width, it is difficult for the oil existing in the second ring groove 102 to flow into the abutment G5 of the side rail 5. As a result, it is possible to suppress the oil rising due to the oil existing in the second ring groove 102 passing through the abutment G5 of the side rail 5, and the oil sealing performance can be further improved.

<Modified example of the embodiment>
Hereinafter, the combination of the piston rings according to the modified example of the embodiment will be described. In the description of the modified example, the differences from the combination of the piston rings according to the embodiments described above will be mainly described, and the same points will be designated by the same reference numerals and detailed description thereof will be omitted.

[Modification 1]
FIG. 13 is a cross-sectional view orthogonal to the circumferential length direction of the second ring 2A when the second ring 2A according to the modified example 1 is in use. The combination of piston rings according to the first modification is different from the above-mentioned combination of piston rings in that the second ring 2A is used instead of the second ring 2 described above. 14A and 14B are views showing the main body ring 4A according to the first modification, FIG. 14A is a cross-sectional view orthogonal to the peripheral length direction of the main body ring 4A, and FIG. 14B is a main body ring. It is an enlarged view which shows the lower part on the inner peripheral side of 4A. As shown in FIG. 14A, the second inner peripheral surface 44 of the main body ring 4A has a second inner peripheral end surface 441 provided at the inner peripheral end portion of the main body ring 4A, a second inner peripheral end surface 441, and a second inner peripheral surface. 2 Includes an inner cut surface 442 that connects to the lower surface 42. The second inner peripheral end surface 441 is a surface constituting the innermost peripheral portion of the main body ring 4A, and is formed in a straight shape extending along the axial direction. Further, the second inner peripheral end surface 441 is formed on the upper side of the second lower surface 42 and on the inner side in the radial direction. Here, reference numeral VP4 in FIG. 14B indicates a virtual inner peripheral end surface obtained by extending the second inner peripheral end surface 441 downward. Further, the reference numeral VP2 indicates a virtual lower surface in which the second lower surface 42 is extended inward in the radial direction. The virtual lower surface corresponds to one form of the "virtual end face" referred to in the present application. The virtual corner portion formed by the intersection of the virtual inner peripheral end surface VP4 and the virtual lower surface VP2 is referred to as a virtual lower corner portion and is indicated by the reference numeral VC1. The virtual lower corner portion corresponds to one form of the "virtual corner portion" referred to in the present application.

As shown in FIG. 14B, the inner cut surface 442 does not include a predetermined portion of the virtual lower corner portion VC1 including the intersection portion VC11 between the virtual inner peripheral end surface VP4 and the virtual lower surface VP2 in the main body ring 4A. , The second inner peripheral end surface 441 and the second lower surface 42 are connected. As a result, an inner cut 45, which is a notch, is formed between the second inner peripheral end surface 441 and the second lower surface 42. As a result, the main body ring 4A has a shape (inner cut shape) in which the lower portion on the inner peripheral side is cut out.

In the main body ring 4A in which the inner cut surface 442 is formed in this way, the overall stress balance becomes asymmetric. When the main body ring 4A is attached to the piston 10 and attached to the cylinder 20, the main body ring 4A is twisted. By twisting the main body ring 4A, the side rail 5 is urged to the upper wall W1 of the second ring groove 102 by the main body ring 4. As a result, the side rail 5 is strongly pressed against the upper wall W1 of the second ring groove 102, and the fluttering of the side rail 5 is suppressed. By suppressing the fluttering of the side rail 5, the posture of the side rail 5 is stabilized. As a result, according to the combination of the piston rings according to the first modification, the state in which the joint port G4 of the main body ring 4A is covered by the side rail 5 is maintained, and the oil sealing performance can be further improved.

The inner cut surface 442 may be formed so as to connect the second inner peripheral end surface 441 and the second lower surface 42 with one flat surface or curved surface, and as another method, the second inner peripheral surface may be formed with a plurality of flat surfaces or curved surfaces. It may be formed so as to connect the end surface 441 and the second lower surface 42. For example, the inner cut surface is set so that the notched portion (the portion surrounded by the inner cut surface 442, the virtual inner peripheral end surface VP4, and the virtual lower surface VP2) in the cross-sectional view of FIG. 14B has a rectangular shape. You may. Alternatively, the inner cut surface 442 may be formed so as to connect the second inner peripheral end surface 441 and the second upper surface 41, that is, to cut out the upper portion on the inner peripheral side of the main body ring 4A. good. In this case, the virtual inner peripheral end surface having the second inner peripheral end surface 441 extended upward and the virtual upper surface having the second upper surface 41 extended radially inward (corresponding to one form of the "virtual end surface" in the present application) intersect. The main body ring 4A does not include a predetermined portion including the intersecting portion in the virtual upper corner portion (corresponding to one form of the “virtual corner portion” referred to in the present application) formed thereby. Even in this case, as described above, the main body ring 4A is twisted and the side rail 5 is suppressed from fluttering.

[Modification 2]
FIG. 15 is a cross-sectional view taken along the circumferential length direction of the oil ring 3B when the oil ring 3B according to the modified example 2 is in use. The combination of piston rings according to the second modification is different from the combination of piston rings described above in that the oil ring 3B is used instead of the oil ring 3 described above. FIG. 16 is a cross-sectional view orthogonal to the peripheral length direction of the segment 7B according to the modified example 2. As shown in FIG. 16, the third outer peripheral end surface S71 of the segment 7B according to the modified example 2 is formed in a barrel shape in the same manner as the above-mentioned segment 7. That is, the third outer peripheral end surface S71 of the segment 7B is provided at the outer peripheral end of the segment 7B in the cross section orthogonal to the circumferential length direction of the segment 7B, and includes the third top portion P7 having the maximum diameter in the segment 7B in the radial direction. It is curved so as to be convex outward. Further, the third outer peripheral end surface S71 of the segment 7B is formed in an eccentric barrel shape. Specifically, in the third outer peripheral end surface S71 of the segment 7B, the lower edge E72 is located radially outside the upper edge E71, and the third top portion P7 is the third outer peripheral end surface S71 in the axial direction of the segment 7B. It is formed so as to be located on the lower edge E72 side of the central position. As a result, the third outer peripheral end surface S71 is formed in an eccentric barrel shape that is asymmetric in the axial direction with the third top portion P7 as a boundary. In the second modification, since the third outer peripheral end surface S71 is formed in an eccentric barrel shape, a72 is smaller than a71 and b72 is smaller than b71.

According to the second modification, the third outer peripheral end surface S71 of the segment 7B of the oil ring 3B has an eccentric barrel shape, so that the cylinder inner wall 20a and the third cylinder inner wall 20a on the crank chamber 40 side are in use with the third top P7 as a boundary. The gap with the outer peripheral end surface S71 can be made smaller than the gap on the combustion chamber 30 side. As a result, the oil can be suitably scraped off when the piston 10 is lowered, and when the piston 10 is raised, the third outer peripheral end surface S71 rides on the oil due to the wedge effect, so that the oil is prevented from being scraped up. be able to. As a result, according to the combination of the piston rings according to the modified example 2, the oil sealing performance can be further improved.

As shown in FIG. 15, in the modified example 2, the third outer peripheral end faces S71 of both the pair of segments 7B and 7B have an eccentric barrel shape, but one of the pair of segments 7B and 7B has a third outer peripheral surface. Only the end face S71 may have an eccentric barrel shape. For example, the third outer peripheral end surface S71 of the upper segment 7U may have the above-mentioned eccentric barrel shape, and the third outer peripheral end surface S71 of the lower segment 7L may have a symmetric barrel shape, or vice versa. However, in the second modification, by forming the third outer peripheral end faces S71 of both of the pair of segments 7B and 7B into the above-mentioned eccentric barrel shape, the oil sealing performance is further enhanced as compared with the case where only one of the segments 7B and 7B has the eccentric barrel shape. Can be done.

[Modification 3]
FIG. 17 is a cross-sectional view orthogonal to the circumferential length direction of the second ring 2C when the second ring 2C according to the modified example 3 is in use. The combination of the piston rings according to the modified example 3 is different from the combination of the piston rings described above in that the second ring 2C is used instead of the second ring 2 described above. FIG. 18 is a cross-sectional view orthogonal to the circumferential length direction of the main body ring 4C according to the modified example 3. As shown in FIG. 18, the second outer peripheral end surface S41 of the main body ring 4C according to the modified example 3 is formed in a barrel shape like the main body ring 4 described above. That is, the second outer peripheral end surface S41 of the main body ring 4C is provided at the outer peripheral end portion of the main body ring 4C in a cross section orthogonal to the circumferential length direction of the main body ring 4C, and has a second top portion P4 having the maximum diameter in the main body ring 4C. It is curved so as to be convex outward in the radial direction including it. Further, the second outer peripheral end surface S41 of the main body ring 4C is formed in an eccentric barrel shape. Specifically, in the second outer peripheral end surface S41 of the main body ring 4C, the lower edge E42 is located radially outside the upper edge E41, and the second top P4 is the second outer peripheral end surface in the axial direction of the main body ring 4C. It is formed so as to be located on the lower edge E42 side of the central position of S41. As a result, the second outer peripheral end surface S41 is formed in an eccentric barrel shape that is asymmetric in the axial direction with the second top P4 as a boundary. In the third modification, since the second outer peripheral end surface S41 is formed in an eccentric barrel shape, a42 is smaller than a41 and b42 is smaller than b41.

According to the third modification, the second outer peripheral end surface S41 of the main body ring 4C of the second ring 2C has an eccentric barrel shape, so that the cylinder inner wall 20a and the second cylinder inner wall 20a on the crank chamber 40 side are bounded by the second top P4 in the used state. 2 The gap with the outer peripheral end surface S41 can be made smaller than the gap on the combustion chamber 30 side. As a result, the oil can be suitably scraped off when the piston 10 is lowered, and when the piston 10 is raised, the second outer peripheral end surface S41 rides on the oil due to the wedge effect, so that the oil is prevented from being scraped up. be able to. As a result, according to the combination of the piston rings according to the modified example 3, the oil sealing performance can be further improved.

[Modification 4]
FIG. 19 is a cross-sectional view orthogonal to the circumferential length direction of the oil ring 3D according to the modified example 4. The oil ring according to the present invention may be a so-called two-piece oil ring as in the oil ring 3D shown in FIG. The oil ring 3D includes an oil ring main body 8 formed in an annular shape around the axis of the oil ring 3D, and a coil expander EX1 that urges the oil ring main body 8 radially outward. Further, on the oil ring main body 8, a pair of rails 9 and 9 protruding outward in the radial direction are formed side by side in the axial direction of the oil ring 3D. Of the pair of rails 9 and 9, the upper rail 9 is referred to as a rail 9U, and the lower rail 9 is referred to as a rail 9L. The pair of rails 9U and 9L are portions corresponding to the pair of segments 7U and 7L in the oil ring 3, and are an example of the "pair of sliding portions" in the present invention.

As shown in FIG. 19, the third outer peripheral end surface S91 of the rail 9 is radially outwardly convex including the third top P9 having the maximum diameter in the rail 9 in a cross section orthogonal to the circumferential length direction of the rail 9. It is formed in a barrel shape that is curved so as to be. The third outer peripheral end surface S91 of the rail 9 may have a symmetrical barrel shape or an eccentric barrel shape. By forming the third outer peripheral end surface S91 in an eccentric barrel shape, the oil sealing performance can be further improved. Further, the third outer peripheral end surface S91 of the rail 9 is not limited to the barrel shape, but may be a straight shape or a tapered shape.

<Others>
Although the preferred embodiments of the present invention have been described above, the various embodiments described above can be combined as much as possible. For example, in the combination of piston rings, the outer peripheral surface of the top ring may have a barrel shape, the outer peripheral end surface of the main body ring of the second ring may have an eccentric barrel shape, and the outer peripheral end surface of the oil ring may have an eccentric barrel shape. Further, the outer peripheral end faces of the top ring, the main body ring of the second ring, and the oil ring may have an eccentric barrel shape.

100: Internal combustion engine 10: Piston 20: Cylinder 30: Combustion chamber 40: Crank chamber 1: Top ring 2: Second ring 3: Oil ring 4: Main body ring 5: Side rail (an example of covering)
6: Oil ring body 7: Segment (example of sliding part)

Claims (6)

A combination of a piston ring including a top ring, a second ring, and an oil ring provided in a ring groove formed on the outer peripheral surface of a piston mounted on a cylinder of an internal combustion engine.
The top ring is provided at the outer peripheral end portion of the top ring in a cross section orthogonal to the peripheral length direction of the top ring, and is convex outward in the radial direction including the first top portion having the maximum diameter in the top ring. It has a first outer peripheral end face that is curved so as to be
The second ring is arranged on the lower side of the ring groove, which is the crank chamber side in the axial direction of the piston, and has a main body ring having a joint, and the ring groove is on the combustion chamber side of the piston in the axial direction. Includes a covering that is located on the upper side and slides along with the body ring on the inner wall of the cylinder.
The main body ring is provided at the outer peripheral end portion of the main body ring in a cross section orthogonal to the peripheral length direction of the main body ring, and is convex outward in the radial direction including a second top portion having the maximum diameter in the main body ring. It has a second outer peripheral end face that is curved so as to be
The cover ring overlaps the main body ring so as to cover at least a part of the abutment of the main body ring from above in the ring groove.
The oil ring is formed in an annular shape around the axis of the oil ring, and has a pair of sliding portions provided side by side in the axial direction of the oil ring.
Each of the pair of sliding portions includes a third top portion provided at the outer peripheral end portion of the sliding portion and having the maximum diameter in the sliding portion in a cross section orthogonal to the circumferential length direction of the sliding portion. Has a third outer peripheral end face curved so as to be radially outwardly convex.
Piston ring combination. A joint is formed in the cover ring, and the cover ring has a joint.
The axial width of the covering is smaller than the axial width of the body ring.
The combination of piston rings according to claim 1. The radial width of the covering is greater than the maximum separation distance secured between the inner wall of the cylinder and the outer peripheral surface of the piston when the piston is mounted on the cylinder.
The combination of piston rings according to claim 1 or 2. The main body ring has an inner cut surface that connects the inner peripheral end surface provided at the inner peripheral end portion of the main body ring and the upper surface or the lower surface of the main body ring.
The inner cut surface is the virtual inner peripheral end surface and the virtual inner peripheral end surface in a virtual corner portion formed by the intersection of the virtual inner peripheral end surface on which the inner peripheral end surface is extended and the virtual end surface on which the upper surface or the lower surface of the main body ring is extended. A predetermined portion including an intersection with the virtual end face is formed so as not to be included in the main body ring.
The combination of piston rings according to any one of claims 1 to 3. The lower edge of the third outer peripheral end surface of at least one of the pair of sliding portions is located radially outside the upper edge, and the third top portion thereof is the third outer peripheral portion in the axial direction of the sliding portions. It is formed so as to be located on the lower edge side of the center position of the end face.
The combination of piston rings according to any one of claims 1 to 4. The lower edge of the second outer peripheral end surface is located radially outside the upper edge, and the second top portion is located on the lower edge side of the center position of the second outer peripheral end surface in the axial direction of the main body ring. Formed to do,
The combination of piston rings according to any one of claims 1 to 5.

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