Piston ring

Abstract

The present invention relates to a piston ring. The piston ring includes a plurality of first ring segments, and the plurality of first ring segments are placed inside a ring groove in a stacked manner such that the first ring segments are attached to each other in the axial direction. Each of the first ring segments includes a corresponding piston ring gap portion, and each piston ring gap portion has an end surface that is separated from each other in the circumferential direction of the first ring segment such that the end surfaces face each other across a ring gap having a predetermined size. The corresponding piston ring gap portions of the first ring segments are displaced from each other in the circumferential direction. A closing member is provided to close the piston ring gap portions of the first ring segments in the radial direction of the first ring segments.

Description

Technical Field

[0001] The present invention relates to a piston ring attached to a piston of an internal combustion engine, and more particularly to a piston ring configured to mainly seal blow-by gas. Background Art

[0002] The piston ring is partially open and does not have a complete circular shape. The piston ring is configured such that its outer diameter elastically increases and decreases. Such an open portion is referred to as a piston ring gap (or piston ring gap portion). Since the piston ring gap portion is a portion that penetrates the piston ring in the width direction of the piston ring (the dimension measured in the axial direction of the piston ring is referred to as the width), the piston ring gap portion can be used as a passage for blow-by gas. In view of this, in the related art, as inventions, various techniques have been designed and proposed to prevent blow-by gas leakage or reduce the leakage to a feasible level.

[0003] For example, Japanese Unexamined Patent Application Publication No. 2010-31995 (JP 2010-31995 A) describes a piston ring composed of an upper ring and a lower ring stacked in the width direction of the piston ring such that the corresponding piston ring gap portions of the rings are displaced from each other in the circumferential direction of the piston ring. For example, the piston ring gap portion of the upper ring has a shape that is open only in the width direction or has a slit shape that is open at an angle of 45° from the width direction. On the other hand, the piston ring gap portion of the lower ring has a stepped shape in which the end portions facing each other in the piston ring gap portion overlap each other in the thickness direction of the lower ring, such that the inner peripheral portion of the first end portion is cut to half thickness (the thickness represents the dimension measured in the radial direction of the lower ring), and the outer peripheral portion of the second end portion is cut to half thickness. Alternatively, the piston ring gap portion of the lower ring is inclined in a direction opposite to the inclined piston ring gap portion in the upper ring.

[0004] In addition, Japanese Unexamined Patent Application Publication No. 2000-130257 (JP 2000-130257 A) describes a piston ring composed of an outer peripheral ring and an inner peripheral ring. The outer peripheral ring includes a piston ring gap portion having a stepped structure in the width direction. On the other hand, the inner peripheral ring may include any type of piston ring gap portion, such as a vertical piston ring gap, a diagonal piston ring gap, or a stepped piston ring gap. The piston ring gap portions of the outer peripheral ring and the inner peripheral ring are arranged to be displaced from each other in the circumferential direction.

[0005] In addition, Japanese Unexamined Patent Application Publication No. 2008-14424 (JP 2008-14424 A) describes a piston ring configured such that corresponding end surfaces that constitute a piston ring gap portion and face each other are provided as inclined surfaces, the inclined surfaces being formed such that an upper space between the end surfaces gradually increases in the width direction (vertical direction), and a triangular piston ring gap piece having an inclined surface that contacts the inclined surface is fitted into the piston ring gap portion from above. SUMMARY OF THE INVENTION

[0006] In the piston ring described in JP 2010-31995 A, the upper surface of the lower ring contacts the lower side of the piston ring gap portion of the upper ring, and similarly, the lower surface of the upper ring contacts the upper side of the piston ring gap portion of the lower ring. Accordingly, each of the piston ring gap portions is closed in the width direction (vertical direction) by its mating ring (lower ring or upper ring). That is, a gas passage that is connected in the width direction is not formed.

[0007] However, the ring groove in which the piston ring is placed is configured such that the piston ring expands and contracts radially. That is, the outer diameter of the bottom of the ring groove is smaller than the inner diameter of the piston ring, such that a gap is formed between the ring groove and the piston ring. In the configuration described in JP 2010-31995 A, the piston ring gap portion of the upper ring and the piston ring gap portion of the lower ring open to the gap on the bottom side of the ring groove and are connected to each other. Accordingly, the piston ring gap portion of the upper ring and the piston ring gap portion of the lower ring communicate with each other via the gap on the bottom side of the ring groove, such that a gas passage is formed. In this regard, the configuration described in JP 2010-31995 A may have poor airtightness.

[0008] Note that in the case where the piston ring gap portion of the lower ring has a stepped structure in the thickness direction, a thin plate portion extending from a first end portion and a thin plate portion extending from a second end portion overlap each other in the thickness direction, such that a straight passage is not formed in the thickness direction (radial direction). However, in order to avoid or suppress a bending load being applied to the respective base portions of the thin plate portions, the thin plate portions face each other with a minute gap therebetween such that they do not contact each other. Accordingly, the gap serves as a gas passage through which the inner peripheral side and the outer peripheral side communicate. Ultimately, the configuration described in JP 2010-31995 A does not solve the problem of the gas passage that may cause blow-by leakage, and there is room for improvement in this regard.

[0009] In addition, the piston ring described in JP 2000-130257 A is such a piston ring that it has a configuration which can be regarded as replacing the upper ring described in JP 2010-31995 A with an inner peripheral ring and replacing the lower ring described in JP 2010-31995 A with an outer peripheral ring. That is, the piston ring gap portion of the outer peripheral ring and the piston ring gap portion of the inner peripheral ring are displaced from each other in the circumferential direction. Accordingly, the inner peripheral side of the piston ring gap portion of the inner peripheral ring contacts the outer peripheral side of the piston ring gap portion of the outer peripheral ring to close the piston ring gap portion from the inner peripheral side, while the outer peripheral side of the piston ring gap portion of the outer peripheral ring contacts the inner peripheral side of the piston ring gap portion of the inner peripheral ring to close the piston ring gap portion from the outer peripheral side. As a result, no gas passage is formed through which the inner peripheral side and the outer peripheral side of the piston ring are linearly communicated with each other. However, the piston ring gap portion of the outer peripheral ring is a so-called stepped piston ring gap in which thin plate portions face each other in the thickness direction (radial direction). Therefore, a gap is formed between the thin plate portions, and this gap serves as a gas passage. This is similar to the configuration described in JP 2010-31995 A. Ultimately, the configuration described in JP 2000-130257 A does not solve the problem of the gas passage that may cause blow-by leakage, including the inconvenience caused by the stepped piston ring gap, and there is room for improvement in this regard.

[0010] In addition, the configuration described in JP 2008-14424 A is examined as follows. A piston ring needs to expand and contract according to temperature changes, and accordingly, the gap (space between end surfaces) in the piston ring gap portion changes according to temperature changes. In the configuration described in JP 2008-14424 A, a piston ring gap piece assembled in the piston ring gap portion contacts a facing surface that is open upward. Accordingly, the piston ring gap piece moves up and down in response to the change in the space between the facing surfaces. As a result, the piston ring gap piece is stuck in the piston ring gap portion, and the state in which the piston ring gap piece contacts the end surface is maintained. However, a gap needs to be provided on the upper side or the lower side of the piston ring gap piece so that the piston ring gap piece can move up and down, and this gap serves as a gas passage through which the outer peripheral side and the inner peripheral side of the piston ring are communicated with each other. JP 2008-14424 A describes a configuration in which a guide member is provided, and the guide member is configured to apply a load to the piston ring gap piece in the radial direction. However, the guide member is formed integrally with the piston ring gap piece, and as the piston ring gap piece moves up and down, the guide member also moves up and down. Ultimately, a gap is formed above or below the guide member, and this gap serves as a gas passage.

[0011] The present invention has been made in view of the above technical problems, and an object of the present invention is to provide a piston ring capable of eliminating, to the extent possible, the gas passage that causes blow-by leakage.

[0012] To achieve the above object, the piston ring of the present invention is an annular piston ring that is open at the piston ring gap portion. The piston ring is placed inside a ring groove formed in the outer peripheral portion of the piston, and the piston is configured to reciprocate in the axial direction of the hole within the hole. The piston ring is configured to slide when the outer peripheral portion of the piston ring is pressed against the inner peripheral surface of the hole. The piston ring includes a plurality of first ring pieces that are stacked inside the ring groove in a stacked manner such that the first ring pieces are attached to each other in the axial direction. Each of the first ring pieces includes a corresponding piston ring gap portion, and each piston ring gap portion has end surfaces that are separated from each other in the circumferential direction of the first ring piece such that the end surfaces face each other across a ring gap having a predetermined size. The corresponding piston ring gap portions of the first ring pieces are displaced from each other in the circumferential direction. A closing member is also provided such that the piston ring gap portions of the first ring pieces are closed in the radial direction of the first ring pieces.

[0013] In the present invention, the closing member may be constituted by a second ring that is placed on the inner circumferential side of the first ring piece within the ring groove and is configured to close the open ends on the inner circumferential side of the corresponding piston ring gap portions of the first ring piece by contacting the inner circumferential surface of the first ring piece. The second ring may include a piston ring gap portion that is open in the circumferential direction. The piston ring gap portion of the second ring may be displaced in the circumferential direction at least with respect to the piston ring gap portion of the first ring piece that is placed on the uppermost side in the up-down direction of the piston among the first ring pieces.

[0014] In the present invention, the second ring may be constituted by a plurality of second ring pieces that are stacked in an attached manner in the same direction as the stacking direction of the first ring pieces.

[0015] In the present invention, each of the second ring pieces may include a corresponding piston ring gap portion that is open in the circumferential direction. The corresponding piston ring gap portions of the second ring pieces may be displaced from each other in the circumferential direction. The corresponding piston ring gap portions of the second ring pieces may be displaced in the circumferential direction with respect to the corresponding piston ring gap portions of the first ring pieces.

[0016] In the present invention, the piston ring gap portion of the first ring piece that is on the uppermost side in the axial direction may have a pair of first end surfaces that are arranged such that the first end surfaces are separated from each other in the circumferential direction across a predetermined ring gap. The ring gap that is the space between the first end surfaces may gradually decrease inward in the radial direction of the first ring piece on the uppermost side. The closing member may be constituted by a first plug piece that is placed between the first end surfaces from the outer circumferential side of the first ring piece on the uppermost side such that the first plug piece can move in the radial direction of the first ring piece on the uppermost side while maintaining the state where the first plug piece is attached to the first end surfaces.

[0017] In the present invention, the piston ring may further include a first pressing member configured to elastically press a first plug piece inward in a radial direction of a first ring piece on the uppermost side inside a piston ring gap portion of the first ring piece on the uppermost side.

[0018] In the present invention, a piston ring gap portion of a second first ring piece placed below the first ring piece on the uppermost side in an axial direction may have a pair of second end surfaces that are arranged such that the second end surfaces are separated from each other by a predetermined ring gap in a circumferential direction. The ring gap as a space between the second end surfaces may gradually decrease outward in a radial direction of the second first ring piece. The closing member may further include a second plug piece that is placed between the second end surfaces from an inner circumferential side of the second first ring piece such that the second plug piece can move in a radial direction of the second first ring piece while maintaining a state where the second plug piece is attached to the second end surfaces.

[0019] In the present invention, the piston ring may further include a second pressing member configured to elastically press the second plug piece outward in a radial direction of the second first ring piece inside the piston ring gap portion of the second first ring piece.

[0020] In the present invention, the closing member may be constituted by an inner circumferential side bending member that is disposed in an attached manner on an inner circumferential surface of each of the first ring pieces in the first ring pieces such that the inner circumferential side bending member closes the piston ring gap portion of each of the first ring pieces in the first ring pieces, and each piston ring gap portion is provided with an inner circumferential side bending member. Any one of opposite portions of the inner circumferential side bending member across the piston ring gap portion may be joined to each of the first ring pieces in the first ring pieces.

[0021] In the present invention, the piston ring includes first ring pieces stacked in an attached manner in an up-and-down direction. The piston ring gap portions of the first ring pieces are displaced from each other in a circumferential direction. Accordingly, the piston ring gap portion of each of the first ring pieces in the first ring pieces is closed by a second first ring piece placed above or below each of the first ring pieces in the first ring pieces. Therefore, a so-called gas passage as a gap portion allowing communication in the up-and-down direction is not formed. Further, each of the piston ring gap portions is closed in a radial direction by the closing member. Therefore, a so-called gas passage as a gap portion allowing communication in the radial direction due to the piston ring gap portion is not formed. Finally, with the present invention, a gas passage allowing communication between the upper side and the lower side of the piston ring is eliminated or restricted, so that blow-by leakage can be effectively prevented or reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, where like reference numerals represent like elements, and where:

[0023] Figure 1 is a partial cross-sectional front view showing an example of a piston to which a piston ring is attached;

[0024] Figure 2 is a perspective view showing an example of a piston ring according to the present invention in an exploded manner;

[0025] Figure 3 is a partial cross-sectional view of the piston ring in a state where the piston ring is received in the ring groove;

[0026] Figure 4A is similar to Figure 3 and is a partial cross-sectional view of the part indicated by the reference numeral "A" in Figure 2 ;

[0027] Figure 4B is similar to Figure 3 and is a partial cross-sectional view of the part indicated by the reference numeral "B" in Figure 2 ;

[0028] Figure 4C is similar to Figure 3 and is a partial cross-sectional view of the part indicated by the reference numeral "C" in Figure 2 ;

[0029] Figure 5A is a cross-sectional view showing a state where the piston ring is attached to the upper surface of the ring groove, and is a partial cross-sectional view of the part indicated by the reference numeral "A" in Figure 2 ;

[0030] Figure 5B is a cross-sectional view showing a state where the piston ring is attached to the upper surface of the ring groove, and is a partial cross-sectional view of the part indicated by the reference numeral "B" in Figure 2 ;

[0031] Figure 5C is a cross-sectional view showing a state where the piston ring is attached to the upper surface of the ring groove, and is a partial cross-sectional view of the part indicated by the reference numeral "C" in Figure 2 ;

[0032] Figure 6A is a partial cross-sectional view for describing an embodiment in which the inner peripheral ring is divided into two pieces in the vertical direction, and is a partial cross-sectional view showing a state where the piston ring is attached to the lower surface of the ring groove;

[0033] Figure 6BIt is a partial cross-sectional view for describing an embodiment in which the inner peripheral ring is divided into two pieces in the vertical direction, and is a partial cross-sectional view of a cross-section taken along a portion corresponding to the piston ring clearance portion of the upper-side ring piece of the inner peripheral ring when the piston ring is attached to the upper surface of the ring groove and the upper-side ring piece of the inner peripheral ring is deformed by air pressure; and

[0034] Figure 6C It is a partial cross-sectional view for describing an embodiment in which the inner peripheral ring is divided into two pieces in the vertical direction, and is a partial cross-sectional view of a cross-section taken along a portion corresponding to the piston ring clearance portion of the lower-side ring piece of the inner peripheral ring when the piston ring is attached to the upper surface of the ring groove and the upper-side ring piece of the inner peripheral ring is deformed by air pressure;

[0035] Figure 7 It is a partial cross-sectional view for describing an embodiment in which only the lower-side ring piece is provided with an inner peripheral ring;

[0036] Figure 8 It is a plan view showing an example of the relative positions between the respective piston ring clearance portions of the ring pieces of the outer peripheral ring and the inner peripheral ring and the joining position between the outer peripheral ring and the inner peripheral ring;

[0037] Figure 9A It is a schematic partial cross-sectional view for describing an example in which the outer peripheral ring presses against the lower side of the ring groove, and shows an example in which the outer peripheral surface of the inner peripheral ring is composed of a single inclined surface;

[0038] Figure 9B It is a schematic partial cross-sectional view for describing an example in which the outer peripheral ring presses against the lower side of the ring groove, and shows an example in which a spring is further provided on the inner peripheral side of the inner peripheral ring;

[0039] Figure 10A It is a schematic partial cross-sectional view showing an example in which the ring piece of the outer peripheral ring is restricted in the width direction by the inner peripheral ring, and shows an example in which the ring piece is restricted by a single recess;

[0040] Figure 10B It is a schematic partial cross-sectional view showing an example in which the ring piece of the outer peripheral ring is restricted in the width direction by the inner peripheral ring, and shows an example in which corresponding recesses are provided for the ring piece;

[0041] Figure 10C It is a schematic partial cross-sectional view showing an example in which the ring piece of the outer peripheral ring is restricted in the width direction by the inner peripheral ring, and shows an example in which the inner peripheral ring is divided into two pieces in the vertical direction;

[0042] Figure 10D It is a schematic partial cross-sectional view showing an example in which the ring piece of the outer peripheral ring is restricted in the width direction by the inner peripheral ring, and shows an example in which a spring is further provided on the inner peripheral side;

[0043] Figure 11 is a plan view showing an example in which an arcuate piece is set as a closing member;

[0044] Figure 12A is a partial plan view showing an example in which a plug piece is set as a closing member, and shows the plug piece and the piston ring clearance portion in the ring piece on the upper side;

[0045] Figure 12B is a partial plan view showing an example in which a plug piece is set as a closing member, and shows the plug piece and the piston ring clearance portion in the ring piece on the lower side; and

[0046] Figure 13 is a partial plan view showing a cylindrical plug piece. DETAILED DESCRIPTION

[0047] The present invention can be implemented for a piston ring attached to a piston in an internal combustion engine (such as a gasoline engine or a diesel engine). Embodiments of the present invention are described below. Note that the embodiments described below are merely examples of the present invention and do not limit the present invention.

[0048] Figure 1 The overall structure of the piston of the internal combustion engine is shown in a simplified manner. The piston 1 is accommodated inside the hole 2 of the cylinder so that the piston 1 reciprocates in the axial direction of the hole 2. Ring grooves 3 are formed in the outer peripheral portion on the upper end side of the piston 1, and corresponding piston rings 4 are assembled in the ring grooves 3. As an example, the piston ring 4 is composed of a total of three rings, namely, two compression rings and one oil ring. In Figure 1 the example shown, the two rings on the upper side are compression rings, and the one ring on the lower side is an oil ring.

[0049] The present invention is mainly applicable to compression rings, and Figure 2 an example of this case is shown in an exploded view in. The piston ring 4 shown herein is composed of an outer peripheral ring 7 and an inner peripheral ring 8. The outer peripheral ring includes two ring pieces 5 and 6 stacked in the direction (width direction) along the central axis of the piston ring 4. The inner peripheral ring is placed on the inner peripheral side of the ring pieces 5 and 6. The two ring pieces 5 and 6 in the outer peripheral ring 7 correspond to the first ring pieces in the present invention. The two ring pieces 5 and 6 are made of a metal similar to that used in conventional compression rings, and have a ring shape that is open at the piston ring clearance portions 9 and 10, and thus do not have a complete ring shape. The piston ring clearance portions 9 and 10 are portions where a ring gap with a predetermined size is provided so that the outer diameter of the ring pieces 5 and 6 increases or decreases. The space between the end surfaces 9a of the ring piece 5 facing each other in the circumferential direction and the space between the end surfaces 10a of the ring piece 6 facing each other in the circumferential direction correspond to the ring gap.

[0050] The outer diameters of the ring pieces 5 and 6 (the outer diameters in the free state without applied load) are larger than the inner diameter of the hole 2, and the inner diameters of the ring pieces 5 and 6 (the inner diameters in the use state where the piston 1 is assembled in the hole 2) are larger than the outer diameter of the bottom of the ring groove 3. In addition, the shape of the outer peripheral portion of the ring pieces 5 and 6 that slidably contacts the hole 2 can be any suitable known shape, such as barrel-shaped, tapered, bevel-shaped, or flat-shaped. In addition, the piston ring gap portions 9 and 10 can be any one of the so-called vertical piston ring gaps, diagonal piston ring gaps, stepped piston ring gaps, etc. that are well known.

[0051] The inner peripheral ring 8 corresponds to the closing member in the present invention and is an annular member assembled in an attached manner on the corresponding inner peripheral sides of the ring pieces 5 and 6 (i.e., the outer peripheral ring 7) stacked in the width direction. The inner peripheral ring 8 is configured to elastically deform such that the outer diameter of the inner peripheral ring 8 increases or decreases. To achieve such deformation, similar to the ring pieces 5 and 6, a piston ring gap portion 11 is provided in the inner peripheral ring 8. In the state where the outer peripheral ring 7 is assembled in the hole 2, the outer diameter of the inner peripheral ring 8 (the outer diameter in the so-called free state without applied load) is equal to or larger than the inner diameter of the outer peripheral ring 7, such that the inner peripheral ring 8 is configured to be attached to the inner peripheral surface of the outer peripheral ring 7 by elastic force. Note that since the inner peripheral ring 8 and the outer peripheral ring 7 are accommodated together inside the ring groove 3, the inner diameter of the inner peripheral ring 8 is larger than the outer diameter of the bottom of the ring groove 3. In addition, the inner peripheral ring 8 covers the entire inner peripheral sides of the piston ring gap portions 9 and 10 of the outer peripheral ring 7, thereby closing the corresponding open ends on the inner peripheral sides of the piston ring gap portions 9 and 10. Therefore, the width of the inner peripheral ring 8 (the dimension measured in the axial direction) is set to be equal to or larger than the width of the outer peripheral ring 7 (the total width of the ring pieces 5 and 6 stacked in an attached manner). Note that the shape of the piston ring gap portion 11 of the inner peripheral ring 8 can be any known shape, such as a vertical piston ring gap, a diagonal piston ring gap, or a stepped piston ring gap, which is similar to the shape of the piston ring gap portions 9 and 10 of the ring pieces 5 and 6.

[0052] In the state where the ring pieces 5 and 6 are stacked in an attached manner in the width direction and the inner peripheral ring 8 is assembled on the inner peripheral sides of the ring pieces 5 and 6, the ring pieces 5 and 6 are assembled inside the ring groove 3. Figure 3 This state is shown in a partial cross-sectional view in

[0053] The inner peripheral ring 8 assembled to the inner peripheral sides of the ring pieces 5 and 6 is elastically deformed due to the decrease in the diameters of the ring pieces 5 and 6, and is pressed against the inner peripheral surfaces of the ring pieces 5 and 6 in an attached manner by the tension caused by the elastic deformation. Accordingly, the ring pieces 5 and 6 are pressed against the inner peripheral surface of the hole 2 by their own tensions and the tension received from the inner peripheral ring 8. These tensions are designed such that the ring pieces 5 and 6 do not separate from the inner surface of the hole 2 due to air pressure and the frictional force between the piston 1 and the hole 2 does not become excessive when the piston 1 moves up and down. In addition, as Figure 3 shown, in a state where the piston ring 4 is in contact with the lower surface of the ring groove 3, no gap is formed between the piston ring 4 and the lower surface of the ring groove 3 except for the piston ring clearance portions 9, 10, and 11.

[0054] The ring pieces 5 and 6 and the inner peripheral ring 8 are set inside the ring groove 3 such that the piston ring clearance portions 9, 10, and 11 are displaced from each other in the circumferential direction so that the piston ring clearance portions 9, 10, and 11 do not form a gas passage. In Figure 2 is shown a state where the piston ring clearance portions 9, 10, and 11 are displaced from each other in the circumferential direction. This is to prevent the piston ring clearance portions 9, 10, and 11 from forming a gas passage by closing the piston ring clearance portions 9, 10, and 11 with the ring pieces 5, 6 and the inner peripheral ring 8.

[0055] More specifically, Figure 4A is a cross-sectional view of the piston ring 4 cut at the position of "A" in Figure 2 in a state where the piston ring 4 is attached to the lower surface of the ring groove 3. The difference between the width of the piston ring 4 and the opening width of the ring groove 3 (the dimension measured in the up-and-down direction in Figure 4A ) is generally about 0.02 mm to 0.03 mm. Accordingly, a gap is formed on the upper side of the piston ring 4. In addition, the upper-side ring piece 5 is open at the piston ring clearance portion 9. As a result, the combustion chamber (not shown) communicates with the inside of the ring groove 3 through this gap and the piston ring clearance portion 9. At the same time, since the upper-side ring piece 5 is attached to the lower-side ring piece 6, the lower opening of the piston ring clearance portion 9 of the upper-side ring piece 5 is sealed by the lower-side ring piece 6. Accordingly, the piston ring clearance portion 9 does not penetrate in the up-and-down direction and does not serve as a gas passage from the combustion chamber to the crankshaft chamber (not shown). In addition, the lower-side ring piece 6 and the inner peripheral ring 8 attached to the inner peripheral surface of the lower-side ring piece 6 are attached to the lower surface of the ring groove 3, and an airtight state is formed between each of the lower-side ring piece 6 and the inner peripheral ring 8 and the lower surface of the ring groove 3. In addition, the outer peripheral end of the lower-side ring piece 6 is in airtight contact with the inner peripheral surface of the hole 2, and accordingly, the inside of the ring groove 3 is hermetically shielded from the crankshaft chamber. Thus, for example, even when blow-by flows in a curve as indicated by the arrow in Figure 4A and reaches the inside of the ring groove 3, the blow-by is in Figure 4AStop at the portion indicated by "X" in. That is, even when the piston ring clearance portion 9 is formed in the ring piece 5 on the upper side, the piston ring clearance portion 9 is not used as a gas passage through which the combustion chamber communicates with the crankshaft chamber.

[0056] Figure 4B is a cross-sectional view of the piston ring 4 cut at position "B" in Figure 2 with the piston ring 4 attached to the lower surface of the ring groove 3. The gap described above is formed between the piston ring 4 and the upper surface of the ring groove 3, and the inside of the ring groove 3 communicates with the combustion chamber through this gap. In addition, since the piston ring clearance portion 10 is provided in the ring piece 6 on the lower side, the inside of the ring groove 3 is partially communicated with the crankshaft chamber through the piston ring clearance portion 10. However, since the ring piece 5 on the upper side is attached to the upper side of the piston ring clearance portion 10, the upper side of the piston ring clearance portion 10 is closed by the ring piece 5 on the upper side. In addition, the inner peripheral ring 8 is attached to the inner peripheral surface of the ring piece 6 on the lower side, and the inner peripheral ring 8 is airtightly attached to the lower surface of the ring groove 3. Therefore, for example, even when blow-by flows in a curve as shown by the arrow in Figure 4B and reaches the inside of the ring groove 3, the blow-by stops at the portion indicated by "X" in Figure 4B . Therefore, the piston ring clearance portion 10 of the ring piece 6 on the lower side is sealed in the upward (axial direction) and radial directions by the ring piece 5 on the upper side and the inner peripheral ring 8, and thus, even when the piston ring clearance portion 10 is formed in the ring piece 6 on the lower side, the piston ring clearance portion 10 is not used as a gas passage through which the combustion chamber communicates with the crankshaft chamber.

[0057] Figure 4C is a cross-sectional view of the piston ring 4 cut at position "C" in Figure 2 with the piston ring 4 attached to the lower surface of the ring groove 3. Similar to the Figure 4A described above, Figure 4B a gap is formed between the piston ring 4 and the upper surface of the ring groove 3. Therefore, the inside of the ring groove 3 communicates with the combustion chamber. The inner peripheral surfaces of the ring pieces 5 and 6 are exposed to the inside of the ring groove 3 at the piston ring clearance portion 11 in the inner peripheral ring 8. The ring pieces 5 and 6 are attached to each other in a substantially airtight manner, and similarly, the ring piece 6 on the lower side is also airtightly attached to the lower surface of the ring groove 3. Therefore, blow-by does not pass through between the ring pieces 5 and 6 and between the lower surface of the ring piece 6 on the lower side and the lower surface of the ring groove 3. Therefore, for example, even when blow-by flows in a curve as shown by the arrow in Figure 4C and reaches the inside of the ring groove 3, the blow-by stops at the portion indicated by "X" in Figure 4C . Finally, even when the piston ring clearance portion 11 is formed in the inner peripheral ring 8, the piston ring clearance portion 11 is not used as a gas passage through which the combustion chamber communicates with the crankshaft chamber.

[0058] Note that in the embodiments described herein, the ring plates 5 and 6 are attached to each other, and this serves to eliminate the gas passage or prevent blow-by. The reasons are as follows. That is, the ring plates 5 and 6 are merely stacked on each other, and thus, the contact pressure between the ring plates 5 and 6 is not particularly limited, such that the ring plates 5 and 6 can firmly contact each other to the extent of applying a load to each other. On the other hand, for example, in the case of a structure such as a thin plate piece in a stepped piston ring gap, the thin plate piece may break due to the application of a bending load, or may break due to fatigue even with a very small bending load. In such a structure, it is necessary to set a minute gap such that the thin plate pieces do not contact each other. Due to this gap, the outer peripheral side of the piston ring gap portion or the upper opening of the piston ring gap portion communicates with the inner peripheral side of the piston ring gap portion or the lower opening of the piston ring gap portion, such that this gap serves as a gas passage. In the above-described embodiments, it is not necessary to provide such a gap between the ring plates 5 and 6. Therefore, the configuration in which the ring plates 5 and 6 are stacked in an attached manner in the width direction effectively serves to eliminate the gas passage, which is very different from the configuration in which thin plate pieces are stacked in a stepped piston ring gap.

[0059] Meanwhile, during high-speed operation, there is a case where the inertial force of the piston ring 4 becomes large and the piston ring 4 contacts the upper surface of the ring groove 3 during the expansion stroke or the intake stroke. Figure 5A This state is shown. Even in such a case, the embodiments of the present invention effectively serve to eliminate the gas passage. That is, in the state where the piston ring 4 is pressed against the upper surface of the ring groove 3 in an attached manner, no gap is formed between the piston ring 4 and the upper surface of the ring groove 3 except for the piston ring gap portions 9, 10, and 11. Further, in the piston ring gap portions 9, 10, and 11, the following sealing state is established such that no gas passage is formed.

[0060] That is, Figure 5A is a cross-sectional view of the piston ring 4 cut at position "A" in Figure 2 in the state where the piston ring 4 is attached to the upper surface of the ring groove 3. Since the piston ring gap portion 9 of the ring plate 5 on the upper side opens upward, the piston ring gap portion 9 communicates with the combustion chamber. However, since the ring plate 6 on the lower side is attached to the ring plate 5 on the upper side, the lower opening of the piston ring gap portion 9 is sealed by the ring plate 6 on the lower side. Further, since the inner peripheral ring 8 is attached to the inner peripheral surface of the ring plate 5 on the upper side, the inner peripheral opening of the piston ring gap portion 9 is sealed by the inner peripheral ring 8. Since the upper surface of the inner peripheral ring 8 is attached to the upper surface of the ring groove 3, the piston ring gap portion 9 of the ring plate 5 on the upper side is finally closed with respect to the inside of the ring groove 3. Therefore, for example, even when blow-by flows along a curve as indicated by the arrow in Figure 5A and reaches the inside of the ring groove 3, the blow-by is in the state of being Figure 5AStop at the part indicated by "X" in. That is, even when the piston ring clearance portion 9 is formed in the ring piece 5 on the upper side, the piston ring clearance portion 9 is not used as a gas passage through which the combustion chamber communicates with the crankshaft chamber.

[0061] Figure 5B is a cross-sectional view of the piston ring 4 cut at the position "B" in Figure 2 in the state where the piston ring 4 is attached to the upper surface of the ring groove 3. As Figure 5B shown, in this part, the piston ring clearance portion 10 is formed in the ring piece 6 on the lower side. However, a part of the ring piece 5 on the upper side except for the piston ring clearance portion 9 is attached to the upper surface of the ring groove 3, and the outer peripheral end of the ring piece 5 is attached to the inner peripheral surface of the hole 2. Therefore, the gap between the piston 1 and the hole 2 is finally closed by the ring piece 5 on the upper side. Thus, for example, even when the blow-by gas flows like the curve indicated by the arrow in Figure 5B the blow-by gas stops at the part indicated by "X" in Figure 5B . That is, even in this part, no gas passage through which the combustion chamber communicates with the crankshaft chamber is formed.

[0062] Figure 5C is a cross-sectional view of the piston ring 4 cut at the position "C" in Figure 2 in the state where the piston ring 4 is attached to the upper surface of the ring groove 3. Even in this case, the ring piece 5 on the upper side closes the gap between the piston 1 and the hole 2 above the ring groove 3. Thus, for example, even when the blow-by gas flows like the curve indicated by the arrow in Figure 5C the blow-by gas stops at the part indicated by "X" in Figure 5C . That is, similar to the part shown in Figure 5B , no gas passage through which the combustion chamber communicates with the crankshaft chamber is formed.

[0063] As described above, the inner peripheral ring 8 functions to close the piston ring clearance portions 9 and 10 provided in the outer peripheral ring 7 from the inner peripheral side. In the above embodiment, the two piston ring clearance portions 9 and 10 on the upper and lower sides are closed by one inner peripheral ring 8. However, the present invention is not limited to this configuration. Similar to the outer peripheral ring 7, the inner peripheral ring 8 may be composed of two (or more) ring pieces stacked in the width direction (the stacking direction of the ring pieces 5 and 6). Figure 6A This example is shown. The inner peripheral ring pieces 12 and 13 corresponding to the ring pieces 5 and 6 are respectively provided on the inner peripheral sides of the ring pieces 5 and 6 constituting the outer peripheral ring 7. The inner peripheral ring pieces 12 and 13 correspond to the second ring pieces in the present invention. The inner peripheral ring pieces 12 and 13 are obtained by dividing the inner peripheral ring 8 into two pieces at the central portion of the inner peripheral ring 8 in the width direction. Therefore, the inner peripheral ring pieces 12 and 13 include corresponding piston ring clearance portions, although not specifically shown herein.

[0064] Figure 6A In the illustrated embodiments, the inner peripheral ring pieces 12 and 13 are attached to each other in the width direction in the normal state, and are also attached to the corresponding inner peripheral surfaces of their corresponding ring pieces 5 and 6 on the outer peripheral side. Therefore, in a state where the inner peripheral ring pieces 12 and 13 are attached to each other and operate integrally, the inner peripheral ring pieces 12 and 13 operate similarly to those in the embodiments described above Figure 2 such that no gas passage is formed, thereby avoiding or reducing the leakage of blow-by gas.

[0065] Note that in Figure 6A the illustrated configuration, when the piston ring 4 contacts the upper surface of the ring groove 3, the internal pressure (air pressure) in the cylinder causes the inner peripheral ring piece 12 on the upper side to bend in the piston ring clearance portion 9 of the ring piece 5 on the upper side. This state is shown in Figure 6B . When the air pressure is high, a part of the inner peripheral ring piece 12 may deform in the direction in which the inner diameter of the inner peripheral ring piece 12 decreases. Figure 6C shows a state in which a part of the inner peripheral ring piece 12 on the upper side is deformed as described above near the piston ring clearance portion 10 in the ring piece 6 on the lower side. In this state, the inner peripheral ring piece 12 on the upper side is separated from the inner peripheral surface of the ring piece 5 on the upper side, so that a gap is formed between the inner peripheral ring piece 12 on the upper side and the inner peripheral surface of the ring piece 5 on the upper side. However, since the inner peripheral ring 8 is composed of the inner peripheral ring pieces 12 and 13 separated in the vertical direction, the deformation of the inner peripheral ring piece 12 on the upper side does not affect the inner peripheral ring piece 13 on the lower side, and the inner peripheral ring piece 13 on the lower side is attached to the inner peripheral surface of the ring piece 6 on the lower side and closes the piston ring clearance portion 10. Thus, even when the inner peripheral ring piece 12 on the upper side is deformed due to the air pressure, a gas passage through which the combustion chamber communicates with the crankshaft chamber is not formed, thereby effectively preventing or suppressing the leakage of blow-by gas.

[0066] Note that when the piston ring 4 is attached to the upper surface of the ring groove 3, a specific effect obtained by separating the inner shaft ring 8 in the width direction (vertical direction) is exerted. Therefore, in an engine in which the piston ring 4 is not attached to the upper surface of the ring groove 3, or in an engine in which the piston ring 4 is hardly attached to the upper surface of the ring groove 3, the inner peripheral ring 8 may be provided only for the ring piece 6 on the lower side. An example of this case is shown in a partial cross-sectional view in Figure 7 . Note that the thickness (dimension measured in the radial direction) of the ring piece 5 on the upper side is equal to or greater than the thickness of the ring piece 6 on the lower side, preferably greater than the thickness of the ring piece 6 on the lower side. This is to reliably cover the piston ring clearance portion 10 of the ring piece 6 on the lower side with the ring piece 5 on the upper side.

[0067] In Figure 7In the configuration shown, a gap is formed between the piston ring 4 and the upper surface of the ring groove 3, and the ring piece 5 on the upper side is open at the piston ring gap portion 9. Further, an inner peripheral ring 8 for the ring piece 6 on the lower side is open at the piston ring gap portion 11 of the inner peripheral ring 8. Therefore, the gap between the piston 1 and the hole 2 or the inside of the combustion chamber communicates with the inside of the ring groove 3. However, since the inner peripheral ring 8 is attached to the inner peripheral surface of the ring piece 6 on the lower side, the piston ring gap portion 10 of the ring piece 6 on the lower side communicating with the crankcase is closed by the inner peripheral ring 8 relative to the inside of the ring groove 3. That is, similar to the example shown in Figure 3 and Figure 6A No gas passage through which the combustion chamber communicates with the crankcase is formed, so that leakage of blow-by gas can be prevented or suppressed.

[0068] Similar to the piston rings known in the prior art, the piston ring 4 in the embodiment of the present invention is elastically deformed so that the inner diameter of the piston ring 4 increases, and in this state, the piston ring 4 is assembled on the outer peripheral side of the piston 1 and then assembled into the ring groove 3 so that the inner diameter decreases by its own elastic force. In the case of performing such an assembling operation, a plurality of ring pieces constituting the outer peripheral ring 7, the inner peripheral ring 8, etc. are integrally assembled to the piston 1 as the piston ring 4 in the embodiment of the present invention. In view of this, it is preferable to configure the piston ring 4 so that the ring pieces do not disassemble from each other. An example of such a configuration is shown in Figure 8 In the example shown herein, the ring pieces 5, 6 and the inner peripheral ring 8 assembled so that the piston ring gap portions 9, 10, 11 are displaced from each other in the circumferential direction are joined to each other at a portion P deviated from the piston ring gap portions 9, 10, 11. The joining can be performed by welding, joining with an adhesive, etc., or can be performed by binding with a cord, etc. that is removed after being assembled into the ring groove 3. Further, the adhesive can be an adhesive that melts or disappears over time. Furthermore, pits and protrusions configured to engage with each other can be used as a joining means.

[0069] At the same time, the inner peripheral ring 8 or the inner peripheral ring pieces 12, 13 expand by their own elastic force so that a radial force is generated between the inner peripheral ring 8 or the inner peripheral ring pieces 12, 13 and the outer peripheral ring 7. In the embodiment of the present invention, the radial force can be set to be used more effectively. Examples thereof will be described below. Figure 9A and Figure 9BThe example shown in [Fig. 0] is an example in which the outer peripheral ring 7 is pressed against the lower surface of the ring groove 3 by the radial force of the inner peripheral ring 8. The outer peripheral surface of the inner peripheral ring 8 shown herein is formed as an inclined surface 8a whose outer diameter increases toward the upper side. At the same time, the inner peripheral surface of the outer peripheral ring 7 in which the ring pieces 5 and 6 are stacked in the vertical direction is formed as an inclined surface 7a whose inner diameter increases toward the upper side to correspond to the outer peripheral surface of the inner peripheral ring 8. Therefore, a downward component force is generated between the outer peripheral surface of the inner peripheral ring 8 and the inner peripheral surface of the outer peripheral ring 7 based on the force that expands the inner peripheral ring 8 outward in the radial direction, so that the outer peripheral ring 7 can be pressed against the lower surface of the ring groove 3 by the component force, as shown in Figure 9A shown. Note that, as shown in Figure 9B , a spring SP configured to generate an elastic force in the expansion direction can be provided on the inner peripheral side of the inner peripheral ring 8.

[0070] Figures 10A to 10D An example is shown in which the ring pieces 5 and 6 constituting the outer peripheral ring 7 are configured to be restricted in the width direction. In the outer peripheral portion of the inner peripheral ring 8 shown in Figure 10A , a concave portion 8b having a V-shaped cross section is formed such that the central portion of the concave portion 8b is most recessed in the width direction (vertical direction). At the same time, a convex portion 5a having a right-angled triangular cross section is formed in the inner peripheral portion of the upper ring piece 5 constituting the outer peripheral ring 7 such that the upper surface side of the convex portion 5a gradually slopes downward toward the lower surface of the ring piece 5, and a convex portion 6a having a shape symmetric to the convex portion 5a is formed in the inner peripheral portion of the lower ring piece 6. That is, the convex portion 6a in the lower ring piece 6 has a right-angled triangular cross section in which the lower surface side of the convex portion 6a gradually slopes upward toward the upper surface of the ring piece 6. The convex portions 5a and 6a are combined to form a convex portion having a cross-sectional shape substantially the same as the cross-sectional shape of the concave portion 8b of the inner peripheral ring 8 and are inserted into the concave portion 8b.

[0071] An elastic force is applied to the inner peripheral ring 8 in the direction of expanding the outer diameter of the inner peripheral ring 8. Therefore, a force in the direction of firmly fitting each other is applied between the convex portions 5a and 6a formed in the ring pieces 5 and 6 of the outer peripheral ring 7 and the concave portion 8b of the inner peripheral ring 8. At the same time, the corresponding contact surfaces of the convex portions 5a and 6a and the concave portion 8b are inclined surfaces corresponding to their respective shapes. Finally, a force that tightens the convex portions 5a and 6a in the width direction (vertical direction) is applied between the convex portions 5a and 6a and the concave portion 8b, so that the ring pieces 5 and 6 are joined together in the width direction (vertical direction).

[0072] Figure 10BThe illustrated example is an example in which the annular plates 5 and 6 are respectively restricted by the inner peripheral ring 8 in the width direction. In the respective inner peripheral portions of the annular plates 5 and 6, convex portions 5b and 6b are formed, each having a triangular cross section that tapers toward the central portion in the width direction. In addition, in the outer peripheral portion of the inner peripheral ring 8, concave portions 8c and 8d are formed corresponding to the convex portions 5b and 6b and having the same cross-sectional shape as the cross-sectional shape of the convex portions 5b and 6b. Therefore, when the convex portions 5b and 6b of the annular plates 5 and 6 are assembled in the concave portions 8c and 8d, the annular plates 5 and 6 are restricted by the inner peripheral ring 8 in the width direction.

[0073] In addition, Figure 10C An example is shown in which the inner peripheral ring 8 having the Figure 10B illustrated configuration is divided into two pieces in the vertical direction. In addition, Figure 10D The illustrated example is an example in which, in addition to the Figure 10C illustrated configuration, a second inner peripheral ring 18 is provided on the inner peripheral side of the inner peripheral ring 8, and a spring 19 is provided on the inner side of the second inner peripheral ring 18, the spring being configured to generate an elastic force that radially outwardly presses the second inner peripheral ring 18. The second inner peripheral ring 18 contacts each of the two pieces obtained by separating the inner peripheral ring 8 in the vertical direction via a V-shaped concave portion and a convex portion assembled in the concave portion. Therefore, the second inner peripheral ring 18 and the inner peripheral ring 8 are configured to be restricted in the vertical direction.

[0074] Note that in any of the above embodiments, the annular plates 5 and 6 are attached to each other in the width direction, so that a gas passage can be avoided from being formed between the annular plates 5 and 6. Similarly, the annular plate 6 on the lower side or the inner peripheral ring 8 is attached to the lower surface of the annular groove 3, and the annular plate 5 or the inner peripheral ring 8 on the upper side is attached to the upper surface of the annular groove 3, so that a gas passage can be avoided from being formed. Therefore, in the embodiments of the present invention, it is preferably to apply a resin coating on the portions attached to their mating members (for example, the respective upper and lower surfaces of the annular plates 5 and 6 and the inner peripheral ring 8, the respective inner peripheral surfaces of the annular plates 5 and 6, and the outer peripheral surface of the inner peripheral ring 8, etc.).

[0075] The inner peripheral ring 8 in each of the above embodiments is a member configured to be attached to the inner peripheral surface of the outer peripheral ring 7 to function to close the piston ring gap portions 9 and 10 provided in the annular plates 5 and 6. Therefore, in each of the embodiments of the present invention, the member configured to be attached to the inner peripheral surface of the outer peripheral ring 7 can be arc-shaped pieces 8A and 8B provided respectively for the piston ring gap portions 9 and 10, instead of the annular member including the piston ring gap portion as described above. The arc-shaped pieces 8A and 8B correspond to the closing member or the inner peripheral side bending member in the present invention, and Figure 11An example of the arcuate pieces 8A and 8B is shown. The outer peripheral ring 7 is configured such that the ring piece 5 on the upper side and the ring piece 6 on the lower side are stacked in an attached manner in the width direction. The ring piece 5 on the upper side has a piston ring clearance portion 9, and the ring piece 6 on the lower side is configured similarly to the ring piece 5 and includes a piston ring clearance portion 10.

[0076] The arcuate piece 8A is placed on the inner peripheral side of the piston ring clearance portion 9 of the ring piece 5 on the upper side such that the arcuate piece 8A extends to both sides in the circumferential direction across the piston ring clearance portion 9, and the arcuate piece 8A is attached to the inner peripheral surface of the ring piece 5 on the upper side and closes the piston ring clearance portion 9. In addition, a part of the arcuate piece 8A on either side of it in the circumferential direction across the piston ring clearance portion 9 is joined to the ring piece 5 on the upper side. The joined portion in the arcuate piece 8A is denoted by the reference numeral P1. This allows the ring piece 5 on the upper side to elastically deform such that its outer diameter increases or decreases, and also allows the unjoined end portion of the arcuate piece 8A to radially outwardly press the ring piece 5 from the inner peripheral side, such that the arcuate piece 8A and the ring piece 5 are attached to each other.

[0077] Similarly, the arcuate piece 8B is placed on the inner peripheral side of the piston ring clearance portion 10 of the ring piece 6 on the lower side such that the arcuate piece 8B extends to both sides in the circumferential direction across the piston ring clearance portion 10, and the arcuate piece 8B is attached to the inner peripheral surface of the ring piece 6 on the lower side and closes the piston ring clearance portion 10. In addition, a part of the arcuate piece 8B on either side of it in the circumferential direction across the piston ring clearance portion 10 is joined to the ring piece 6 on the lower side. The joined portion in the arcuate piece 8B is denoted by the reference numeral P2. This allows the ring piece 6 on the lower side to elastically deform such that its outer diameter increases or decreases, and also allows the unjoined end portion of the arcuate piece 8B to radially outwardly press the ring piece 6 from the inner peripheral side, such that the arcuate piece 8B and the ring piece 6 are attached to each other.

[0078] Another embodiment of the present invention is further described below. As described above, the closing member of the present invention is a member for closing the piston ring clearance portions 9 and 10 in the outer peripheral ring 7 in the radial direction, such as the inner peripheral ring 8 or the arcuate pieces 8A and 8B. In view of this, the closing member can be a member configured to close the piston ring clearance portions 9 and 10 by being assembled in the piston ring clearance portions 9 and 10, rather than closing the piston ring clearance portions 9 and 10 by being attached to the inner peripheral surface of the outer peripheral ring 7. An example of this is shown in Figure 12A 、 Figure 12B and is shown in the figure.

[0079] Figure 12ASchematically shown are the piston ring clearance portion 9 of the ring piece 5 on the upper side and the plug piece 14 assembled in the piston ring clearance portion 9. The end surfaces 9a that face each other in the circumferential direction and constitute the piston ring clearance portion 9 correspond to the first end surface of the present invention, and the end surfaces 9a form a shape in which the space (ring gap) between the end surfaces 9a gradually increases outward in the radial direction. That is, the end surfaces 9a are inclined in the radial direction or the circumferential direction such that the end surfaces 9a form a shape that opens outward in the radial direction.

[0080] The plug piece 14 assembled in the piston ring clearance portion 9 corresponds to the first plug piece of the present invention and is configured to fill the piston ring clearance portion 9 by making airtight contact with the end surfaces 9a. In Figure 12A the example shown, the plug piece 14 is substantially fan-shaped and is provided as a plate piece having the same width as the ring piece 5. Note that the surface of the plug piece 14 that contacts the end surfaces 9a may be a flat surface similar to the end surfaces 9a, or may be a convex curved surface that can make contact with the end surfaces 9a while maintaining an airtight state. The plug piece 14 is assembled in the piston ring clearance portion 9 from the outside toward the inside in the radial direction. Here, the end surfaces 9a are inclined surfaces as described above. Therefore, when the ring gap in the piston ring clearance portion 9 changes due to a change in the outer diameter of the ring piece 5, the plug piece 14 moves inward or outward in the radial direction to always airtightly fill the space between the end surfaces 9a. Further, the circumference (length in the circumferential direction) of the plug piece 14 is longer on the outer peripheral side and shorter on the inner peripheral side. In other words, in a state where the piston ring 4 is placed inside the ring groove 3 described above, the pressure-receiving area of the plug piece 14 on the outer peripheral side is wider than its pressure-receiving area on the inner peripheral side. Therefore, the plug piece 14 is pushed inward by the air pressure in the radial direction.

[0081] Figure 12B Schematically shown are the piston ring clearance portion 10 of the ring piece 6 on the lower side and the plug piece 15 assembled in the piston ring clearance portion 10. The piston ring clearance portion 10 and the plug piece 15 have a structure opposite to the Figure 12A structure shown, such that the plug piece 15 is extruded outward in the radial direction to airtightly close the piston ring clearance portion 10 in the radial direction. More specifically, the end surfaces 10a that face each other in the circumferential direction and constitute the piston ring clearance portion 10 correspond to the second end surface in the present invention, and the end surfaces 10a form a shape in which the space (ring gap) between the end surfaces 10a gradually decreases outward in the radial direction. That is, the end surfaces 10a are inclined in the radial direction or the circumferential direction such that the end surfaces 10a form a shape that opens inward in the radial direction.

[0082] The plug piece 15 assembled in the piston ring clearance portion 10 corresponds to the second plug piece of the present invention and is configured to fill the piston ring clearance portion 10 by making airtight contact with the end surfaces 10a. In Figure 12BIn the illustrated example, the plug piece 15 is substantially fan-shaped and is provided as a plate piece having the same width as the ring piece 6. Note that the surface of the plug piece 15 that contacts the end surface 10a may be a flat surface similar to the end surface 10a, or may be a convex curved surface that can contact the end surface 10a while maintaining an airtight state. The plug piece 15 is assembled into the piston ring gap portion 10 from the inner side toward the outer side in the radial direction. The end surface 10a is the inclined surface described above. Therefore, when the ring gap in the piston ring gap portion 10 changes due to a change in the outer diameter of the ring piece 6, the plug piece 15 moves inward or outward in the radial direction to always airtightly fill the space between the end surfaces 10a. In addition, the circumference (the length in the circumferential direction) of the plug piece 15 is longer on the inner peripheral side and shorter on the outer peripheral side. In other words, in a state where the piston ring 4 is placed inside the ring groove 3 described above, the pressure receiving area of the plug piece 15 on the inner peripheral side is wider than its pressure receiving area on the outer peripheral side, so that the plug piece 15 is pushed outward by air pressure in the radial direction.

[0083] The ring pieces 5 and 6 including the plug pieces 14 and 15 are respectively placed inside the ring groove 3 such that the ring pieces 5 and 6 are stacked in an attached state in a state where the piston ring gap portions 9 and 10 are displaced from each other in the circumferential direction. In a state where the piston ring 4 is attached to the lower surface of the ring groove 3, a gap is formed between the upper surface of the piston ring 4 and the upper surface of the ring groove 3, so that the combustion chamber communicates with the inside of the ring groove 3. In this case, since the plug piece 14 in the upper ring piece 5 is configured such that the pressure receiving area on the outer peripheral side is wider than the pressure receiving area on the inner peripheral side, the plug piece 14 presses inward against the piston ring gap portion 9 in the radial direction. Therefore, the plug piece 14 adheres to the end surface 9a of the piston ring gap portion 9, so that the piston ring gap portion 9 is hermetically sealed in the radial direction of the piston ring 4. In addition, when the plug piece 14 is deeply pushed into the piston ring gap portion 9 in the radial direction, a gap may be formed between the outer peripheral surface of the plug piece 14 and the inner peripheral surface of the hole 2. However, since the lower ring piece 6 is placed below the piston ring gap portion 9 in an attached state, this gap is sealed in the vertical direction (the width direction of the piston ring 4). That is, the piston ring gap portion 9 is not used as a gas passage through which the upper side and the lower side of the piston ring 4 communicate with each other (that is, the combustion chamber and the crankcase communicate with each other).

[0084] In addition, at the same time, as Figure 12B shown, in the lower ring piece 6, the plug piece 15 is pushed from the inner peripheral side toward the outer peripheral side into the piston ring gap portion 10. The plug piece 15 is configured to close the piston ring gap portion 10 and is not configured to close the gap between the ring piece 6 and the inner peripheral surface of the hole 2. Therefore, as Figure 12BAs shown, minute gaps are formed on the outer peripheral side of the plug pieces 15, and the gaps communicate with the crankshaft chamber. Accordingly, the air pressure in the combustion chamber is applied to the inner peripheral surface of the plug pieces 15, such that the plug pieces 15 are pushed outward in the radial direction. Thus, the plug pieces 15 adhere to the end surface 10a of the piston ring clearance portion 10, such that the piston ring clearance portion 10 is hermetically sealed in the radial direction of the piston ring 4. Further, the ring piece 6 and the plug pieces 15 on the lower side adhere to the lower surface of the ring groove 3 and seal the inside of the ring groove 3 with respect to the crankshaft chamber. That is, the piston ring clearance portion 10 is not used as a gas passage through which the upper side and the lower side of the piston ring 4 communicate with each other (i.e., the combustion chamber and the crankshaft chamber communicate with each other).

[0085] Note that, in a state where the engine is operating, the air pressure in the combustion chamber increases such that the plug pieces 14, 15 can press against the end surfaces 9a, 10a of the piston ring clearance portions 9, 10. At the same time, in a state where the engine is not operating, the air pressure is not applied to the plug pieces 14, 15. Accordingly, the plug pieces 14, 15 can move inside the piston ring clearance portions 9, 10, such that collision noise or impact sound may be generated. To avoid such inconvenience, elastic members configured to apply a force in a corresponding direction to push the plug pieces 14, 15 into the piston ring clearance portions 9, 10 can be used. Examples of the elastic members are shown in Figure 12A and Figure 12B .

[0086] A leaf spring 16 is provided for the plug piece 14 in the upper-side ring piece 5 such that the leaf spring 16 is bent in a wave shape, where a central portion of the leaf spring 16 is coupled to the inner peripheral surface of the plug piece 14, and the left and right sides of the leaf spring 16 contact the inner peripheral surface of the ring piece 5. The leaf spring 16 corresponds to a first pressing member of the present invention. In a state where the left and right sides of the leaf spring 16 are elastically deformed toward the inside of the ring piece 5, the leaf spring 16 is assembled to the inside of the ring piece 5. Accordingly, an elastic force is generated in a direction in which the central portion of the leaf spring 16 to which the plug piece 14 is coupled is displaced inward in the radial direction. Due to this elastic force, the plug piece 14 is pulled inward in the radial direction inside the piston ring clearance portion 9 and adheres to the end surface 9a.

[0087] Similarly, a leaf spring 17 is provided for the plug piece 15 in the lower-side ring piece 6 such that the leaf spring 17 is bent in a wave shape, where a central portion of the leaf spring 17 is coupled to the inner peripheral surface of the plug piece 15, and the left and right sides of the leaf spring 17 are coupled to the inner peripheral surface of the ring piece 6. The leaf spring 17 corresponds to a second pressing member of the present invention. In a state where the central portion of the leaf spring 17 is elastically deformed toward the inside of the ring piece 6, the leaf spring 17 is assembled to the inside of the ring piece 6. Accordingly, an elastic force is generated in a direction in which the central portion of the leaf spring 17 contacting the plug piece 15 is displaced outward in the radial direction. Due to this elastic force, the plug piece 15 is pulled outward in the radial direction inside the piston ring clearance portion 10 and adheres to the end surface 10a.

[0088] Here, a plug piece corresponding to the closing member of the present invention is further described. The plug piece should be sandwiched between the end surfaces constituting the piston ring gap portion to fill the ring gap, so that the piston ring gap portion is closed in the radial direction. Therefore, the shape of the plug piece can be appropriately determined in design and can be, for example, cylindrical as shown in Figure 13 , rather than a shape similar to the shape of the opening of the piston ring gap portion. Note that in order to avoid forming a gap on either the upper side or the lower side of the plug piece, the plug piece is configured to have the same width as the width of the ring piece (the dimension in the vertical direction).

[0089] Embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments, and the outer peripheral ring is not limited to the configuration in which two ring pieces are stacked, and can be configured such that a plurality of ring pieces are stacked. In the case where three or more ring pieces are stacked, if the piston ring gap portion in the uppermost ring piece is displaced in the circumferential direction from the piston ring gap portion in the ring piece directly below the uppermost ring piece, all the piston ring gap portions are not necessarily displaced from each other in the circumferential direction. In addition, the present invention can be implemented by appropriately combining the configurations described in the embodiments. For example, a plug piece can be used for the ring piece on the upper side, and an inner peripheral ring can be provided for the ring piece on the lower side. Alternatively, an inner peripheral ring can also be provided for the ring piece on the upper ring, and a plug piece can be used for the ring piece on the lower side. In addition, the present invention is mainly applicable to compression rings, and the present invention is also applicable to other compression rings other than the top ring. Only the top ring among the plurality of piston rings can have the configuration of the present invention, and the other piston rings can be configured differently from the top ring.

Claims

1. A piston ring having an annular shape that is open at a piston ring gap portion, the piston ring being placed inside a ring groove formed in an outer peripheral portion of a piston, the piston being configured to reciprocate in an axial direction of a hole, the piston ring being configured to slide when an outer peripheral portion of the piston ring is pressed against an inner peripheral surface of the hole, the piston ring including a plurality of first ring pieces stacked inside the ring groove in a stacked manner such that the first ring pieces are attached to each other in the axial direction, wherein: the first ring pieces each include a corresponding piston ring gap portion, each of the piston ring gap portions having end surfaces that are separated from each other in a circumferential direction of the first ring piece such that the end surfaces face each other with a ring gap having a predetermined size therebetween; the corresponding piston ring gap portions of the first ring pieces are displaced from each other in the circumferential direction; and a closing member is further provided such that the piston ring gap portions of the first ring pieces are closed in a radial direction of the first ring piece, wherein: the closing member is constituted by a second ring placed inside the ring groove on an inner circumferential side of the first ring piece, and the second ring is configured to close an open end on an inner circumferential side of the corresponding piston ring gap portion of the first ring piece by contacting an inner circumferential surface of the first ring piece; and wherein the second ring is constituted by a plurality of second ring pieces stacked in an attached manner in a direction the same as a stacking direction of the first ring pieces.

2. The piston ring according to claim 1, wherein: the second ring includes a piston ring gap portion that is open in the circumferential direction; and the piston ring gap portion of the second ring is displaced in the circumferential direction at least relative to the piston ring gap portion of the first ring piece placed on an uppermost side in an up-and-down direction of the piston among the first ring pieces.

3. The piston ring according to claim 2, wherein: the second ring pieces each include a corresponding piston ring gap portion that is open in the circumferential direction; the corresponding piston ring gap portions of the second ring pieces are displaced from each other in the circumferential direction; and the corresponding piston ring gap portions of the second ring pieces are displaced in the circumferential direction relative to the corresponding piston ring gap portions of the first ring pieces.

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