Patent ID: 12196325

DESCRIPTION OF EMBODIMENTS

A preferred embodiment of a compression ring according to the present invention will be described below with reference to the drawings. While the embodiment described below is a compression ring according to the present invention applied to a top ring, this is merely an example, and application of the present invention is not limited to the top ring. The present invention is also applicable to a second ring. Note that a configuration described in the embodiment below is not intended to limit a technical scope of the invention unless otherwise specified.

FIG.1is an enlarged cross-section view of an internal combustion engine in which a top ring according to the embodiment is provided. As illustrated inFIG.1, an internal combustion engine1000according to the embodiment includes a cylinder200, and a piston100loaded to the cylinder200.

As illustrated inFIG.1, in the internal combustion engine1000, a piston clearance PC1is formed by a predetermined separation distance being secured between a piston outer peripheral surface110and a cylinder inner wall210. Further, on the piston outer peripheral surface110, a top ring groove101, a second ring groove102, and an oil ring groove103are formed in this order from a combustion chamber side at predetermined intervals in an axial direction of the piston100. The piston outer peripheral surface110is partitioned by the top ring groove101, the second ring groove102, and the oil ring groove103. As illustrated inFIG.1, a top ring10, a second ring20, and an oil ring30are respectively loaded in the top ring groove101, the second ring groove102, and the oil ring groove103. As illustrated inFIG.1, a state where each piston ring is loaded in the corresponding ring groove of the piston100loaded to the cylinder200will be referred to as a “use state”. Each piston ring has self tension so that each outer peripheral surface presses the cylinder inner wall210in the use state.

Further, in the following description, a “peripherally longitudinal direction” refers to a peripherally longitudinal direction of the piston ring unless otherwise specified. A “radial direction” refers to a radial direction of the piston ring unless otherwise specified. An “axial direction” refers to a direction along a central axis of the piston ring unless otherwise specified. Further, regarding the piston ring, an “outer peripheral surface” refers to a surface on which outer peripheral edges on both end surfaces in the axial direction, which specify a width (dimension in the axial direction) of a ring (or a segment) contact each other, and an “inner peripheral surface” refers to a surface on which inner peripheral edges on the both end surfaces in the axial direction contact each other.

Here, an arrow inFIG.1represents a vertical direction. In the present specification, a combustion chamber side is defined as an “upper side”, and a crankcase side is defined as a “lower side” regarding the internal combustion engine1000. Further, an axial direction of each of the piston100, the cylinder200, the top ring10, the second ring20, and the oil ring30is defined as a vertical direction, the combustion chamber side when they are in the use state is defined as an “upper side”, and an opposite side (that is, a side separate from the combustion chamber, which is the crankcase side) is defined as a “lower side”.

Further, in the present specification, a “barrel shape” refers to a surface shape that is curved so as to be convex outward in the radial direction while including a peak portion that has a maximum diameter in the piston ring, and a “symmetric barrel shape” refers to a barrel shape that is a surface shape symmetric in the axial direction (vertical direction) about the peak portion. As illustrated inFIG.1, the internal combustion engine1000according to the embodiment employs a combination of piston rings including the top ring10having an outer peripheral surface in a symmetric barrel shape, the second ring20having an undercut shape in which a lower portion of an outer peripheral portion is cut out, and the oil ring30including a pair of segments (side rails)30a,30a, and an expander spacer30bthat biases the pair of segments outward (to the cylinder inner wall210) in the radial direction. However, the present invention is not limited to this.

The top ring10according to the embodiment will be described in detail below.FIG.2is an enlarged cross-section view of a portion near the top ring groove101of the internal combustion engine1000in which the top ring10according to the embodiment is provided. As illustrated inFIG.2, the top ring groove101is formed by a pair of inner walls that vertically face each other, and between these, the inner wall on the upper side will be referred to as an upper wall W1, and the inner wall on the lower side will be referred to as a lower wall W2. As illustrated inFIG.2, the top ring10includes an upper surface1provided on the upper side, a lower surface2provided on the lower side, an outer peripheral surface3that connects an outer peripheral edge E1on the upper surface1and an outer peripheral edge E2on the lower surface2, and an inner peripheral surface4that connects an inner peripheral edge E3on the upper surface1and an inner peripheral edge E4on the lower surface2. When the top ring10is loaded in the top ring groove101, that is, the top ring10is in the use state, the upper surface1is located on the upper side and faces the upper wall W1of the top ring groove101, the lower surface2is located on the lower side and faces the lower wall W2, and the outer peripheral surface3is in sliding contact with the cylinder inner wall210.

FIG.3is an enlarged cross-section view of a portion near the outer peripheral surface3of the top ring10. A reference numeral CL1inFIG.3indicates a line (central line) that passes through a center of a width in the vertical direction (axial direction) of the top ring10. As illustrated inFIG.3, the outer peripheral surface3includes a barrel curved surface S1provided at an outer peripheral end portion of the top ring10, and a pair of connection surfaces S2, S2that respectively connect the barrel curved surface S1, and the upper surface1, and the lower surface2. One of the pair of connection surfaces S2, S2connects a peripheral edge (hereinafter, an upper edge) E11on the upper side (combustion chamber side) of the barrel curved surface S1and an outer peripheral edge E1of the upper surface1. The other of the pair of connection surfaces S2, S2connects a peripheral edge (hereinafter, a lower edge) E12on the lower side (the crankcase side40) of the barrel curved surface S1and the outer peripheral edge E2of the lower surface2. The pair of connection surfaces S2, S2are formed vertically symmetrically about the central line CL1.

As illustrated inFIG.3, the barrel curved surface S1is formed in a barrel shape. In other words, the barrel curved surface S1is curved with a predetermined curvature radius so as to be convex outward in the radial direction while including an outer peripheral peak P1that has a maximum diameter in the top ring10on a cross-section orthogonal to the peripherally longitudinal direction of the top ring10. The outer peripheral peak P1on the barrel curved surface S1is located outermost in the radial direction of the top ring10on the outer peripheral surface3, and the barrel curved surface S1is in sliding contact with the cylinder inner wall210in the use state. In the present embodiment, the outer peripheral peak P1is located on the central line CL1and coincides with a midpoint C1of the outer peripheral surface3in the vertical direction (axial direction). Further, the barrel curved surface S1is formed in a symmetric barrel shape. In other words, the barrel curved surface S1is formed vertically symmetrically about the outer peripheral peak P1on the cross-section orthogonal to the peripherally longitudinal direction. Here, a width of the outer peripheral surface3in the vertical direction is set as L1. In this event, the top ring10is configured so as to satisfy a condition of 0.2 mm<½×L.

As illustrated inFIG.3, on the cross-section orthogonal to the peripherally longitudinal direction of the top ring10, the barrel curved surface S1is divided into a large diameter region S11and a pair of small diameter regions S12, S12having different curvature radii. The large diameter region S11includes the outer peripheral peak P1and is curved with a first curvature radius R1. The pair of small diameter regions S12, S12are located on both sides of the large diameter region S11so that the large diameter region S11is put between the small diameter regions S12, S12in the vertical direction and are curved with a second curvature radius R2 smaller than R1. In other words, R2<R1. Here, a width of the large diameter region S11in the vertical direction is set as L2. In this event, the top ring10is configured to satisfy a condition of 0.2 mm≤L2≤½×L1.

Here, reference numerals P2and P3inFIG.3indicate two points on the barrel curved surface S1separate from the outer peripheral peak P1by 0.1 mm in the vertical direction. The point P2out of the two points is a point on the upper side (combustion chamber side), and the point P3out of the two points is a point on the lower side (crankcase side). The points P2and P3are located on the large diameter region S11. Further, reference numerals P4and P5inFIG.3indicate two points on the barrel curved surface S1separate from the outer peripheral peak P1by ¼×L1 in the vertical direction. The point P4out of the two points is a point on the upper side, and the point P5out of the two points is a point on the lower side. The point P4is located on the small diameter region S12on the upper side, and the point P5is located on the small diameter region S12on the lower side. Further, a distance in the radial direction between each of the points P2and P3and the outer peripheral peak P1is set as a drop d1, and a distance in the radial direction between each of the points P4and P5and the outer peripheral peak P1is set as a drop d2. In this event, the top ring10is configured to satisfy a condition of d1<d2.

Here, typically, under conditions of a low oil temperature at which oil viscosity becomes high, friction increases in the fluid lubricating region where a relatively thick oil film between the cylinder inner wall and the ring outer peripheral surface becomes large. To reduce friction in the fluid lubricating region, it is effective to reduce a contact area between the cylinder inner wall and the ring outer peripheral surface and reduce shear resistance of the oil film. Meanwhile, if the contact area between the cylinder inner wall and the ring outer peripheral surface is reduced, a surface pressure of the ring outer peripheral surface becomes high with respect to the cylinder inner wall. If the surface pressure becomes too high, there is a possibility that oil is scraped off unnecessarily, which causes runout of the oil film in the boundary lubricating region where the oil film is thin and the cylinder inner wall is in solid contact with the outer peripheral surface, near top and bottom dead centers of the piston. Thus, in the top ring having the outer peripheral surface in the barrel shape, in a case where the contact area between the cylinder inner wall and the ring outer peripheral surface is reduced by uniformly reducing a curvature radius of the outer peripheral surface, to reduce friction in the fluid lubricating region, there is concern that friction rather increases due to runout of the oil film in the boundary lubricating region.

To address this, the present inventor has found that in the fluid lubricating region, an oil film forming range (range where a hydraulic pressure is high) is not located in an entire region of the outer peripheral surface but is narrowed around the outer peripheral peak, and further, the hydraulic pressure becomes maximum in the vicinity of the outer peripheral peak. On the basis of this, the present inventor has made a drop in a region adjacent to a region in the vicinity of the outer peripheral peak larger than a drop in the region in the vicinity of the outer peripheral peak. Specifically, in the present embodiment, the top ring10is configured so as to satisfy a condition of 0.2 mm<½×L1 and so that the distance d1 in the radial direction between the outer peripheral peak P1and each of the two points P2and P3on the barrel curved surface S1separate from the outer peripheral peak P1by 0.1 mm in the vertical direction (axial direction), and the distance d2 in the radial direction between the outer peripheral peak P1and each of the two points P4and P5on the barrel curved surface S1separate from the outer peripheral peak P1by ¼×L1 in the vertical direction satisfy a condition of d1<d2. According to this configuration, by securing a contact area between the cylinder inner wall210and the outer peripheral surface3by reducing the drop d1 at a position of 0.1 mm vertically from the outer peripheral peak P1in a region in the vicinity of the outer peripheral peak P1, it is possible to prevent increase in friction in the boundary lubricating region. On the other hand, by reducing shear resistance of the oil film by increasing the drop at the position of ¼×L1 vertically from the outer peripheral peak P1within the oil film forming range in the fluid lubricating region, it is possible to reduce friction in the fluid lubricating region. In other words, it is possible to reduce friction in the fluid lubricating region while preventing increase in friction in the boundary lubricating region.

Further, in the present embodiment, the top ring10is configured such that the barrel curved surface S1is divided into the large diameter region S11including the outer peripheral peak P1and curved with a first curvature radius R1, and small diameter regions S12located on both sides of the large diameter region S11in the vertical direction (axial direction) and curved with a second curvature radius R2 smaller than the first curvature radius R1, and a width L2 of the large diameter region S11in the vertical direction satisfies a condition of 0.2 mm≤L2≤½×L1. In other words, the top ring10is configured so that the two points P2and P3on the barrel curved surface S1, which are measurement positions of d1 and which are separate from the outer peripheral peak P1by 0.1 mm, are located on the large diameter region S11, and the two points P4and P5on the barrel curved surface S1, which are measurement positions of d2 and which are separate from the outer peripheral peak P1by ¼×L1, are located on the small diameter regions S12by setting a vertical width of the large diameter region S11with a large curvature radius at equal to or greater than 0.2 mm and equal to or less than ½×L1. This makes it possible to satisfy d1<d2 and can reduce friction. However, the present invention is not limited to this, and R1 may be equal to or substantially equal to R2.

Further, under conditions that d1<d2 is satisfied, d1 and d2 may be set such that 0.05 μm≤d1≤0.7 μm, and 4.0 μm≤d2≤15.0 μm, are preferably set such that 0.05 μm≤d1≤0.7 μm and 6.0 μm≤d2≤15.0 μm and are further preferably set such that 0.05 μm≤d1≤0.7 μm and 8.0 μm≤d2≤15.0 μm. By setting d1 and d2 as described above, friction can be further reduced. However, the present invention is not limited to this.

Further, while in the present embodiment, the midpoint C1of the outer peripheral surface3coincides with the outer peripheral peak P1on the cross-section orthogonal to the peripherally longitudinal direction of the top ring10, the midpoint C1and the outer peripheral peak P1may be misaligned in the vertical direction. However, a distance in the vertical direction (axial direction) between the midpoint C1and the outer peripheral peak P1is preferably set at equal to or less than 0.05 mm and further preferably set at equal to or less than 0.02 mm.

Further, L1 is preferably set such that 0.8 mm≤L1≤2.5 mm, and is further preferably set such that 1.0 mm≤L1≤1.5 mm. However, the present invention is not limited to this.

Further, the outer peripheral surface of the compression ring according to the present invention may have a hard coating including at least one layer among a PVD processing film, a DLC film, and a chrome plating processing film. This can reduce friction force on the outer peripheral surface of the compression ring and improve abrasion resistance. Note that the “physical vapor deposition (PVD) processing film” refers to a coating formed using a PVD method. The PVD method is one type of a vapor-deposition method of forming a film on a surface of an opposite material by attaching particles emitted from a target and is also referred to as physical vapor deposition. Further, a “diamond like carbon (DLC) film” refers to an amorphous hard carbon film mainly constituted with allotropes of carbon hydride and carbon. Still further, the “chrome plating processing film” refers to a coating formed through chrome plating.

Further, the compression ring according to the present invention is preferably provided in a gasoline engine. However, an internal combustion engine to which the compression ring according to the present invention is to be applied is not limited to the gasoline engine. The internal combustion engine may be a diesel engine.

[Hydraulic Experiment]

An experiment of measuring a hydraulic pressure between the cylinder inner wall and the outer peripheral surface of the top ring in the fluid lubricating region was performed. Experiment machine used in the present experiment has an internal combustion engine structure with a bore diameter of 86 mm and a stroke of 60 mm. In the present experiment, the experiment machine was operated in each of experimental examples 1 to 3 described later, and distribution of hydraulic pressures between the cylinder inner wall and the outer peripheral surface of the top ring was measured. Experiment conditions were such that crank rotation speed was set at 1200 rpm, and an oil temperature was set at 80° C.

EXPERIMENTAL EXAMPLES

In the experimental examples 1 to 3, a top ring having an outer peripheral surface in a symmetric barrel shape was used. The outer peripheral peak P1in the experimental examples 1 to 3 is located at a vertical center of the outer peripheral surface3. In the experimental examples 1 to 3, L1 was set at 1.2 mm, and a magnitude of d2 was made different. d2 is a drop at a position of 0.3 mm (¼×L1) vertically from the outer peripheral peak P1located at the vertical center of the outer peripheral surface3. d2 was set at 15 m in the experimental example 1, d2 was set at 8 m in the experimental example 2, and d2 was set at 4 m in the experimental example 3. Note that the present invention is not limited by the experimental examples.

[Experimental Results]

FIG.4is a view illustrating distribution of hydraulic pressures in the experimental examples 1 to 3.FIG.4illustrates distribution of hydraulic pressures at a crank angle of 77° that is a midpoint of the piston stroke in which piston speed becomes maximum in a descending stroke. A graph inFIG.4indicates a height from the lower surface of the top ring on a vertical axis and indicates a hydraulic pressure on a horizontal axis. As can be seen from the experimental examples 1 to 3 inFIG.4, it can be confirmed that the oil film forming range with the hydraulic pressure in the fluid lubricating region of equal to or higher than 0.6 MPa is narrower than the vertical width of the ring. Further, by comparing the experimental examples 1 to 3, it can be confirmed that the oil film forming range is narrowed by increasing d2. By this means, it can be confirmed that in the fluid lubricating region, shear resistance of the oil film can be reduced when the drop at the position vertically separate from the outer peripheral peak P1by ¼×L1 is increased.

While the preferred embodiment of the present invention has been described above, the above-described various forms can be combined in every possible manner.

REFERENCE SIGNS LIST

1000: internal combustion engine100: piston200: cylinder10: top ring3: outer peripheral surfaceP1: outer peripheral peakS1: barrel curved surfaceS11: large diameter regionS12: small diameter region