JP2014101893A - Pressure ring attachment piston - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce oil consumption by easily separating a pressure ring from a ring groove surface in a pressure ring attachment piston.SOLUTION: A pressure ring attachment piston 18 comprises: a top ring 34 as a first pressure ring arranged to be movable in a piston movement direction in a first ring groove 40; and a second ring 36 as a second pressure ring arranged to be movable in the piston movement direction in a second ring groove 42. At least one of a first end surface in an axial direction of the top ring 34, a first ring groove surface of the first ring groove 40 opposed to the first end surface, a second end surface in the axial direction of the second ring 36, and a second ring groove surface of the second ring groove 42 opposed to the second end surface is an oppositely formed surface, and the oppositely formed surface has a recession or a protrusion in a dimension larger than the maximum depth of the surface roughness.

Description

  The present invention relates to a pressure ring mounting piston, and more particularly to a structure in which a pressure ring and an oil ring are sequentially arranged in a plurality of ring grooves of a piston from a combustion chamber side toward a crank chamber side.

  Conventionally, a plurality of ring grooves are provided on the outer peripheral surface of a piston for an internal combustion engine, and a pressure ring and an oil ring are disposed in the plurality of ring grooves.

  Patent Document 1 describes an oil ring having a two-piece structure. In order to suppress the oil ring from adhering to the lower surface of the ring groove by the oil film and to prevent the oil in the ring groove from being sucked up between the upper surface of the oil ring and the ring groove, the lower surface of the ring groove or the oil ring A recess is provided on the lower surface of the.

  In Patent Document 2, the top ring, which is the first pressure ring, has a disc spring-like cross section, and when the piston is fitted to the cylinder, the top ring faces the groove surface of the ring groove of the piston. It is described that a ring end surface at the direction end is provided, and a smooth portion parallel to or almost parallel to the groove surface is provided on the ring end surface.

  In Patent Document 3, the force that presses the lower surface of the second ring against the ring groove due to the pressure increase in the space facing the second land between the top ring and the second ring that is the second pressure ring on the outer peripheral surface of the piston. In order to reduce this, it is described that the lower surface of the second ring is tapered.

JP 2010-270868 A JP-A-61-11441 JP 2000-9225 A

  The first pressure ring and the second pressure ring move in the ring groove affected by the inertial force accompanying the reciprocating movement of the piston, the frictional force between the cylinder wall surface, the pressure difference between the two sides of the ring, and the like. In this case, in at least one of the first pressure ring and the second pressure ring, the oil is interposed between the pressure ring and the ring groove surface of the ring groove regardless of changes in the moving direction or moving speed of the piston. The pressure ring may remain adsorbed on the ring groove surface. In this case, there is a possibility that “oil rise” occurs in which the oil on the crank chamber side is carried to the combustion chamber side and consumed, and the oil consumption may increase.

  An object of the present invention is to reduce oil consumption by facilitating separation of a pressure ring from a ring groove surface in a pressure ring mounting piston.

  The pressure ring mounting piston according to the present invention includes a piston main body for an internal combustion engine in which a ring groove and an oil ring groove are formed in order from the combustion chamber side to the crank chamber side on the outer peripheral surface, and a piston moving direction in the ring groove. A pressure ring having an inner diameter larger than the groove bottom diameter of the ring groove, and an end face in the axial direction of the pressure ring, or a ring groove face facing the end face as an opposing formation surface, The opposing formation surface has a concave portion or a convex portion larger than the maximum depth of the surface roughness.

  In the pressure ring mounting piston according to the present invention, preferably, the piston main body has an outer diameter that increases toward the ring groove in a peripheral portion of the ring groove.

  In the pressure ring mounting piston according to the present invention, it is preferable that a wettability reducing process for reducing wettability with respect to oil is performed on the facing formation surface.

  In the pressure ring mounting piston according to the present invention, preferably, the concave portion is formed radially on the facing formation surface.

  According to the pressure ring mounting piston of the present invention, even when oil is present between the pressure ring and the ring groove surface, a gap is increased between the concave portion or the portion that is out of the convex portion and the portion facing the mating surface. Therefore, the degree of freedom of movement and deformation of the oil is increased, the adhesion force between the pressure ring and the ring groove surface is reduced as a whole, and the pressure ring is easily separated from the ring groove surface. For this reason, oil consumption can be suppressed and oil consumption can be reduced.

It is a schematic fragmentary sectional view which shows the engine incorporating the pressure ring mounting piston of embodiment of this invention. It is the A section enlarged view of FIG. It is the B section enlarged view of Drawing 2 showing a top ring. It is an end view of a top ring. It is CC sectional drawing of FIG. (A) is the D section enlarged view of FIG. 5, (b) is a figure which shows the adhesive force of the upper end surface of a top ring and the 1st ring groove surface according to the circumferential direction position of (a). In the embodiment of the present invention, the calculation result of the in-cylinder pressure Pa and the second land pressure P1 corresponding to the crank angle and the second land pressure P2 of the comparative example in the low load or no load operation state of the engine, and the piston It is a figure which shows a moving direction. It is a figure corresponding to FIG. 3 which shows the comparative example. FIG. 4 is an enlarged view corresponding to FIG. 3 for explaining the reason why the second land pressure increases in the embodiment of the present invention. It is a figure corresponding to Drawing 3 which shows the 1st example of another example of an embodiment of the present invention. It is a figure corresponding to Drawing 2 showing the 2nd example of another example of an embodiment of the present invention. It is the E section enlarged view of Drawing 11 showing movement of an oil film at the time of piston movement. It is a figure corresponding to FIG. 3 which shows the 3rd example of another example of embodiment of this invention. In FIG. 13, it is a figure which shows the oil behavior in a 1st ring groove when a top ring moves upwards with respect to a piston. FIG. 9 is an enlarged view corresponding to the F part in FIG. 2 showing a state in which the lower surface of the second ring is pressed against the second ring groove surface in a fourth example of another example of the embodiment of the present invention. It is GG sectional drawing of FIG. In the embodiment of FIG. 15, the calculation result of the in-cylinder pressure Pa and the second land pressure P1 according to the crank angle and the second land pressure P2 of the comparative example, and the moving direction of the piston in the high-load operation state of the engine. FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, although the following description demonstrates the case where a piston is used for a gasoline engine, it is applicable also to the other engine in which a piston reciprocates. In the following, the case of an in-line plural cylinder in which cylinders are formed in a substantially vertical direction will be described as an engine. However, the present invention is not limited to this, and other types such as a V-shaped plural cylinder, a horizontally opposed plural cylinder, etc. It may be applied to other engines. In the following description, the same symbols are used for the same elements in all drawings.

  FIG. 1 is a schematic partial cross-sectional view showing an engine incorporating a pressure ring mounting piston according to the present embodiment. A gasoline engine 10 that is an internal combustion engine includes a plurality of cylinders 16 formed in a substantially vertical direction on a cylinder block 14 that forms an engine body 12, and a pressure ring mounting piston 18 that reciprocates vertically inside each cylinder 16. The connecting rod 20 has an upper end coupled to the pressure ring mounting piston 18 and a crankshaft 22 to which the lower end of the coupling rod is coupled. Both ends of the crankshaft 22 are rotatably supported by the engine body 12. An intermediate portion in the axial direction of the crankshaft 22 is disposed in a crank chamber 24 inside the lower portion of the engine body 12. Lubricating oil, which is engine oil, is stored in the crank chamber 24. A cylinder head 26 is coupled to the upper side of the cylinder block 14, and a combustion chamber 28 is formed by the cylinder head 26, the cylinder block 14, and the upper surface of the pressure ring mounting piston 18.

  FIG. 2 shows an enlarged view of part A of FIG. The pressure ring mounting piston 18 includes a piston body 32, a top ring 34, a second ring 36, and an oil ring 38 that is an oil control ring. The piston main body 32 has a substantially cylindrical shape with the upper end closed, and the first ring groove 40, the second ring groove 42, and the oil ring groove on the upper side of the outer peripheral surface from the combustion chamber 28 side toward the crank chamber 24 side. 44 are formed in order. Each ring groove 40, 42, 44 has a rectangular cross section formed on the outer peripheral surface of the piston body 32 along the entire circumference.

  The piston body 32 includes a drain hole 48 that is an oil hole formed so as to pass through the oil ring groove 44 and the piston internal space 46. The piston internal space 46 communicates with the lower crank chamber 24. One end portion of the drain hole 48 is connected to the inner peripheral portion and the lower portion of the oil ring groove 44, and the other end portion of the drain hole 48 is open to the inner wall of the piston main body 32.

  The oil ring 38 is a three-piece type, and includes two upper and lower annular side rails 50 and 52 and an annular spacer 54 interposed between the annular side rails 50 and 52 and is mounted in the oil ring groove 44. . The annular spacer 54 is formed by connecting the outer peripheral portions of two upper and lower annular elements with a connecting portion, and the annular side rails 50 and 52 are pressed against the upper and lower ring groove surfaces of the oil ring groove 44 by each annular element. Yes. Further, the annular side rails 50 and 52 are pushed and spread on the outer peripheral side at the inner peripheral end portions of the respective annular elements, and a circumferential tension is applied, whereby the outer peripheral edges of the respective annular side rails 50 and 52 are used as the wall surface of the cylinder 16. In sliding contact. A hole penetrating in the thickness direction may be formed in the connecting portion of the annular spacer 54.

  The top ring 34 is a first pressure ring disposed in the first ring groove 40. The second ring 36 is a second pressure ring disposed in the second ring groove 42. As shown in FIG. 4 to be described later, the top ring 34 is formed in a substantially annular shape having a joint 56 in a part in the circumferential direction from a metal such as steel. The same applies to the second ring 36. The top ring 34 and the second ring 36 are respectively arranged inside the first ring groove 40 and the second ring groove 42 so as to be movable in the vertical direction that is the piston moving direction.

  The top ring 34 has an inner diameter da (FIG. 4) in a free state that is larger than the groove bottom diameter of the first ring groove 40. When the top ring 34 is mounted in the first ring groove 40 and the piston 18 is assembled in the cylinder 16, a radial gap is formed between the inner peripheral surface of the top ring 34 and the groove bottom of the first ring groove 40. Is done. Similarly, the second ring 36 has an inner diameter in a free state that is larger than the groove bottom diameter of the second ring groove 42. Further, when the second ring 36 is mounted in the second ring groove 42 and the piston 18 is assembled in the cylinder 16, a radial gap is formed between the inner peripheral surface of the second ring 36 and the second ring groove 42. The The outer peripheral edges of the top ring 34 and the second ring 36 are in sliding contact with the wall surface of the cylinder 16.

  A cylindrical top land 58 is formed on the outer peripheral surface of the piston body 32 on the combustion chamber 28 side of the first ring groove 40, and a cylindrical surface is formed between the first ring groove 40 and the second ring groove 42. A shaped second land 60 is formed. A cylindrical top land space 62 is formed between the top land 58 and the cylinder 16, and a cylindrical second land space 64 is formed between the second land 60 and the cylinder 16. A cylindrical third land 66 is formed between the second ring groove 42 and the oil ring groove 44 on the outer peripheral surface of the piston body 32. The pressure in the third land 66 portion is almost the same as the atmospheric pressure that is the pressure in the crank chamber 24.

  FIG. 3 is an enlarged view of a portion B in FIG. 2 showing the top ring 34, and FIG. 4 is an end view of the top ring 34. 5 is a cross-sectional view taken along the line CC of FIG. An upper end surface 70 that is a first end surface that is an end surface in the axial direction of the top ring 34 and that is an opposing formation surface has a plurality of recesses 68 that are formed in the radial direction of the upper end surface 70. The plurality of recesses 68 are formed at equal intervals in the circumferential direction of the upper end surface 70. Further, the depth and the width in the circumferential direction are the same between the plurality of recesses 68. In FIG. 4, the recessed part 68 is shown by the slanted lattice part.

  6A is an enlarged view of a portion C in FIG. 4, and FIG. 6B is an upper end surface 70 at one axial end of the top ring 34 corresponding to the circumferential position of FIG. 4A and the first ring groove 40. It is a figure which shows the adhesive force with the upper groove surface 72 which is the 1st ring groove surface. Each recess 68 formed in the upper end surface 70 of the top ring 34 is larger than the maximum depth of the surface roughness of the upper end surface 70. For example, the depth of the recess 68 is set to 10 times or more with respect to the maximum depth of the surface roughness. Further, when the maximum depth of the surface roughness is less than 50 μm, the depth of the recess 68 may be 50 μm or more. When the top ring 34 is pressed against the upper groove surface 72 of the first ring groove 40, the top ring 34 and the first ring groove 40 come into contact with each other within a range indicated by P in FIG. In the recessed portion 68 forming portion other than the range P, the top ring 34 and the upper groove surface 72 are sufficiently separated from each other.

  According to such a pressure ring mounting piston 18, the lubricating oil indicated by sand in FIG. 6 exists between the upper end surface 70 of the top ring 34 and the upper groove surface 72 of the first ring groove 40 facing the upper end surface. Even in this case, the contact area with the upper groove surface 72 is reduced as compared with the case where the entire upper end surface 70 is a flat surface having only surface roughness, so that the recess 68 and the opposing upper groove surface 72 are opposed to each other. Since the gap becomes large at the portion, the degree of freedom of movement and deformation of the oil increases. For this reason, the adhesive force between the top ring 34 and the upper groove surface 72 is reduced as a whole, and the top ring 34 is easily separated from the upper groove surface 72. That is, the adhesion force between the top ring 34 and the upper groove surface 72 due to the oil film acts greatly only in a portion that is out of the concave portion 68 that is a portion indicated by a range P in FIG. For this reason, the sum total of the adhesive force by an oil film can be reduced between the top ring 34 and the upper groove surface 72.

  Since the adhesion force due to the oil film can be reduced in this way, even when the top ring 34 moves in the axial direction in the first ring groove 40 and contacts the upper groove surface 72 of the first ring groove 40 during engine operation, the piston main body 32. The top ring 34 is easily separated from the first ring groove 40 in accordance with the inertial force due to the movement of the first ring groove, the pressure difference between the two sides of the top ring 34, and the like. For this reason, the design of the top ring 34 related to oil consumption can be facilitated, the oil on the crank chamber 24 side is conveyed to the combustion chamber 28, and the oil consumption consumed is suppressed. Oil consumption can be reduced.

  Next, the reason will be described in more detail. There are various forms of oil consumption in the engine. In the present embodiment, attention has been paid particularly to oil rising. There are the following (1) to (3) as factors of oil increase.

(1) The oil film formed on the sliding surface between the pressure ring and the piston ring, which is an oil ring, and the cylinder is evaporated and consumed.
(2) The piston ring scoops up the oil film formed on the sliding surface between the piston ring and the cylinder and is consumed.
(3) In a plurality of spaces (piston land portions) surrounded by the piston ring, the cylinder, and the piston, oil is transported and consumed above the piston due to a pressure difference between adjacent spaces (piston land portions). .

  (1) For (2), the shape including the surface pressure applied to the piston ring sliding surface related to the oil film forming ability on the sliding surface between the piston ring and the cylinder, the shape of the piston ring sliding surface and the surface shape of the cylinder In addition, an approximate design is possible by calculation based on the oil film temperature related to the amount of oil evaporation.

  On the other hand, for (3), the oil rises by calculating the vertical behavior in the ring groove of the piston ring based on the inertial force acting on the piston ring, the sliding surface frictional force, and the pressure difference on both sides of the ring. In order to avoid the undesirable piston ring behavior. However, in fact, when lubricating oil enters between the piston ring and the ring groove, it was found that the adhesion force due to the oil film acts on the piston ring in addition to the above three forces acting on the piston ring. . For this reason, the piston ring behavior may not always be achieved as designed, and an undesigned oil consumption phenomenon may occur. In particular, it has been found that the oil consumption increases rapidly because the movement of the lubricating oil due to the pressure difference becomes active in a portion where the pressure difference acting on the adjacent space across the piston ring is large. For example, a piston of an automobile engine often has a three-ring configuration of a top ring, a second ring, and an oil ring as in this embodiment. Among these, in the top ring and the second ring, the pressure difference between the upper and lower rings tends to be larger than that of the oil ring. For this reason, oil consumption related to (3) is likely to occur.

  The adhesion force of the oil film acting on the piston ring basically changes depending on the contact area between the piston ring and the ring groove surface and the amount of oil intervening there. The larger the contact area, the larger the oil amount. The smaller the number, the smaller. Roughness exists on the surface of the actual piston ring and ring groove surface. For this reason, until the thickness of the oil film interposed between the piston ring and the ring groove surface becomes equal to the surface roughness, the adhesion force increases due to the increase in the contact area between the piston ring and the ring groove surface, and the oil film If the thickness is more than that, the oil film tends to flow, and this tends to reduce the adhesion.

  According to this embodiment, the adhesive force with the upper groove surface 72 of the 1st ring groove 40 by an oil film can be reduced in the upper end surface 70 of the top ring 34 for such a reason. In FIG. 6, the adhesion force increases in accordance with the increase in the contact area in the range P, but the oil film tends to flow in a portion outside the range P indicated by R and the adhesion force decreases. For this reason, the behavior of the top ring 34 in the actual working state can be brought close to the state designed by the above three forces (inertial force, frictional force, and pressure). It is possible to reduce the occurrence of phenomena outside.

  In particular, when the engine is under a low load or no load, for example, when an engine brake is applied, the combustion chamber has a negative pressure for many periods. FIG. 7 shows a calculation result of the in-cylinder pressure Pa and the second land pressure P1 according to the crank angle and the second land pressure P2 of the comparative example in the low load or no load operation state of the engine in the present embodiment, and It is a figure which shows the moving direction of a piston. In FIG. 7, the periods of suction, compression, expansion, and exhaust may be shifted depending on the valve timing.

  As shown in FIG. 7, there are many periods in which the in-cylinder pressure Pa is negative depending on the crank angle. The piston 18 reciprocates up and down according to the crank angle. In this case, the comparative example indicated by the broken line P2 is different from the present embodiment in that no recess is formed on the upper end surface 70 of the top ring 34 as shown in FIG. In an engine incorporating such a comparative pressure ring mounting piston, the second land pressure, which is the pressure in the second land space 64, changes as shown by the broken line P2 in FIG. That is, the in-cylinder pressure Pa increases rapidly from the second half of compression to the first half of expansion and then decreases rapidly. During this period (from the second half of compression to the first half of expansion), the top ring 34 adheres to the upper groove surface 72 of the first ring groove 40. If it remains, the second land pressure P2 remains negative regardless of the in-cylinder pressure Pa. For this reason, a large amount of lubricating oil is sucked into the second land space 64 from the crank chamber 24 through the third land 66 portion, resulting in an increase in oil consumption. In FIG. 7, the broken line P2 coincides with the one-dot chain line P1 at a crank angle equal to or less than the point U and a crank angle equal to or greater than the point V.

  On the other hand, in the case of the present embodiment indicated by the alternate long and short dash line P1 in FIG. 7, the top ring 34 has the first ring groove 40 due to the presence of the recess 68 as shown in FIG. It becomes easy to move away from the upper groove surface 72. Therefore, when the pressure in the top land space 62 increases in the latter half of the compression, the gas flows from the top land 58 side through the space between the top ring 34 and the first ring groove 40 as shown by the arrow in FIG. Flowing into. Therefore, as shown in FIG. 7, the second land pressure P1 increases rapidly with a slight delay from the increase in the in-cylinder pressure Pa. As a result, the period during which the second land space 64 is under negative pressure can be reduced, and oil consumption can be suppressed.

  On the other hand, in the configuration described in Patent Document 1, a recess is formed in the oil ring or the oil ring groove, but the oil can be passed from the oil ring joint in addition to the inside of the oil ring groove. is there. The oil that has passed through the oil ring may be carried to the combustion chamber due to the pressure relationship between the land spaces formed by the combination of the top ring and the second ring, and the oil may rise. Patent Document 1 does not disclose an effective means for such oil rising. In the present embodiment, the behavior of the top ring 34 can be appropriately designed, and the pressure acting on the upper side of the oil ring 38 can be optimized, thereby reducing the passage of oil through the joint of the oil ring 38. Can do. In addition, if the behavior of the second ring 36 can be optimized as shown in another example described later, the passage of oil passing through the oil ring 38 can be further reduced.

  In addition, in Patent Document 1, as a proposal to suppress adhesion to the ring groove due to high temperature and high pressure with respect to the pressure ring, a groove that holds lubricating oil that produces a cooling effect on the contact surface of the pressure ring with the ring groove is provided. It is described to form. However, this groove is considered for a purpose different from the recess 68 of the present embodiment, and is not a suggestion for conceiving the pressure ring mounting piston 18 of the present embodiment.

  Further, as shown in FIG. 3, when the recesses 68 are formed radially on the upper end surface 70 of the top ring 34 and both ends in the length direction of the recess 68 are opened to the outer peripheral surface and the inner peripheral surface of the top ring 34, the top ring Even when the upper end surface 70 of 34 is in contact with the first ring groove 40, the lubricating oil easily flows through the recess 68. In addition, the recessed part 68 is not limited to the case where it forms radially, The recessed part of various numbers and shapes can be employ | adopted. For example, the radial recess 68 may be formed only on the outer peripheral side of the upper end surface 70. Further, the recess may be formed in a substantially annular shape over the entire circumference on the outer peripheral side or the inner peripheral side of the upper end surface of the top ring 34. Also in this case, the contact area with the upper groove surface 72 can be reduced compared to the case where the entire upper end surface is a flat surface, and the top ring can be easily separated from the upper groove surface 72.

  In the above description, the concave portion 68 is formed on the upper end surface 70 of the top ring 34. However, as shown in FIG. 10, the concave portion 74 is formed on the upper groove surface 72 of the first ring groove 40 facing the upper end surface 70. May be. For example, the concave portions 74 may be formed radially on the upper groove surface 72. In this case, the outer peripheral end of the recess 74 may be opened on the outer peripheral surface of the piston main body 32. Also in this case, the concave portions 74 are not limited to being formed in a radial shape, and various numbers and shapes of concave portions can be employed. For example, an annular concave portion is formed on the outer peripheral side of the upper groove surface 72, and the top ring and the upper groove surface 72 are arranged so that the upper end surface of the top ring can come into contact with the portion of the upper groove surface 72 that is off the inner peripheral side. It can also be made to face in an axial direction. Further, the recesses 68 and 74 may be formed on both the upper end surface 70 and the upper groove surface 72 of the top ring 34. Further, a recess may be formed in one or both of the lower end surface 76 that is the first end surface of the top ring 34 and the lower groove surface 78 that is the first groove surface of the first ring groove 40 that the lower end surface 76 faces. .

  FIG. 11 is a diagram corresponding to FIG. 2 showing a second example of another example of the embodiment of the present invention. In the case of this example, the second land 60 and the third land 66 on the outer peripheral surface of the piston body 32 are gently inclined in the direction in which the diameter increases toward the ring grooves 40, 42, 44 at both ends in the piston axial direction. Tapered surfaces S1, S2, S3, S4 are formed over the entire circumference. For this reason, the piston main body 32 is disposed outside the second land 60 and the third land 66 toward the ring grooves 40, 42, 44 around the first ring groove 40, the second ring groove 42, and the oil ring groove 44. The diameter is larger.

  According to such a configuration, when the lubricating oil adhering to the second land 60 and the third land 66 approaches the ring grooves 40, 42, 44 due to the acceleration accompanying the vertical movement of the piston main body 32, the lubricating oil flows into the ring grooves 40, 42, 44. Since it has a velocity component in the direction away from 42, 44, the intrusion of lubricating oil into each ring groove 40, 42, 44 can be suppressed. For example, as shown by the first ring groove 40 side portion of the second land 60 in FIG. 12, as the piston main body 32 is displaced in the direction of the arrow α, the oil film of the lubricating oil adhering to the second land 60 accompanies the gas flow. May tend to rise toward the first ring groove 40. In this case, it is possible to reduce the amount of lubricating oil that is guided to the cylinder 16 side along the tapered surface S <b> 1 and enters the first ring groove 40. For this reason, the oil film which exists between the end surface of the top ring 34 and the ring groove surface of the first ring groove 40 can be reduced, and the adhesion force of the end surface of the top ring 34 to the first ring groove 40 can be reduced. As a result, oil consumption can be reduced. The operation in the case of the other tapered surfaces S2, S3, S4 is the same. Other configurations and operations are the same as those in FIGS. 1 to 6 described above.

  In this example, instead of the tapered surfaces S1, S2, S3, S4, the ring grooves 40, 42, 44 are formed at both ends in the piston axial direction on the second land 60 and the third land 66 on the outer peripheral surface of the piston body 32. You may form the curved surface curved in the direction which a diameter becomes large toward the whole circumference. Further, a tapered surface or a curved surface whose diameter increases toward the first ring groove 40 may be formed around the first ring groove 40 of the top land 58. Further, in any one or two of the lands 58, 60, 66, a similar tapered surface or curved surface may be formed around the ring grooves 40, 42, 44.

  FIG. 13 is a diagram corresponding to FIG. 3 showing a third example of another example of the embodiment of the present invention. In the case of this example, wettability reduction processing for reducing wettability to oil is applied to the portions indicated by broken lines between the upper and lower end faces 70 and 76 of the top ring 34 and the upper and lower groove faces 72 and 78 of the first ring groove 40. ing. For example, as the wettability reduction treatment, an oil-repellent coating treatment such as forming a resin layer, or a surface treatment treatment for reducing wettability such as projection of polytetrafluoroethylene (PTFE) particles can be employed.

  According to such a structure, the wettability with respect to the oil of the surface which performed the wettability reduction process falls. Therefore, as shown in FIG. 14, the top ring 34 moves in the first ring groove 40 due to the pressure difference between the top ring 34 and the gas flow in the direction of the arrow between the top ring 34 and the first ring groove 40. When this occurs, the oil between the top ring 34 and the first ring groove 40 can be easily discharged. As a result, adhesion of the top ring 34 to the first ring groove 40 due to the oil film can be suppressed. Other configurations and operations are the same as those in FIGS. 1 to 6 described above. Note that wettability reduction processing may be performed only on a part of the upper and lower end faces 70 and 76 and the upper and lower groove surfaces 72 and 78 of the top ring 34.

  FIG. 15 is an enlarged view of part F in FIG. 2 showing a state in which the lower surface of the second ring 36 is pressed against the second ring groove surface of the second ring groove 42 in a fourth example of another example of the embodiment of the present invention. FIG. 16 is a cross-sectional view taken along the line GG in FIG. In the case of this example, the lower end surface 80 that is the second end surface of the second ring 36, is an opposing formation surface, and is an end surface in the axial direction has a recess 82 formed in the radial direction of the lower end surface 80. Each recess 82 is larger than the maximum depth of the surface roughness of the lower end surface 80. The basic shape of the second ring 36 is the same as that of the top ring 34 of FIG. 3, and the configuration of the recess 82 is the same as the recess 68 of the configuration of FIGS.

  According to such a configuration, when there is lubricating oil between the lower end surface 80 of the second ring 36 and the lower groove surface 84 that is the second ring groove surface of the second ring groove 42 facing the lower end surface 80. However, compared with the case where the entire lower end surface 80 is a flat surface with only surface roughness, the contact area with the lower groove surface 84 is reduced, and the facing portion between the concave portion 82 and the lower groove surface 84 which is the mating surface. Since the gap becomes large, the degree of freedom of movement and deformation of the oil increases. For this reason, the adhesive force to the lower groove surface 84 of the second ring 36 is reduced as a whole, and the second ring 36 is easily separated from the lower groove surface 84. As a result, the sum of the adhesion forces due to the oil film can be reduced between the second ring 36 and the lower groove surface 84, and the oil consumption on the crank chamber side can be suppressed and oil consumption can be reduced.

  In particular, in a load operation state involving combustion of the engine, the in-cylinder pressure of the combustion chamber 28 in FIG. 1 is positive or almost zero. FIG. 17 shows the calculation results of the in-cylinder pressure Pa and the second land pressure P1 corresponding to the crank angle and the second land pressure P2 of the comparative example, and the piston moving direction in the high-load operation state of the engine. FIG. Also in the case of FIG. 17, the periods of suction, compression, expansion, and exhaust may be shifted depending on the valve timing.

  As shown in FIG. 17, the in-cylinder pressure Pa increases rapidly from the second half of compression to the first half of expansion, and then rapidly decreases depending on the crank angle. On the other hand, unlike the present example, the comparative example indicated by the broken line P <b> 2 has no recess formed on the lower end surface of the second ring 36. In an engine incorporating such a comparative pressure ring mounting piston, the second land pressure changes as indicated by a broken line P2 in FIG. That is, the second ring 36 remains attached to the lower groove surface 84 of the second ring groove 42 regardless of the piston moving direction changing from the top to the bottom near the top dead center in the latter half of the compression. The second land pressure P2 becomes higher than the in-cylinder pressure Pa in the portion surrounded by the broken line β. In this case, the top ring 34 shown in FIG. 2 is pushed up by the pressure difference between the two sides, and the lubricating oil is sent from the second land space 64 to the combustion chamber, which causes an increase in oil consumption.

  On the other hand, in the case of the present example indicated by the one-dot chain line P1 in FIG. It becomes easy to separate. For this reason, the gas in the second land space 64 is reduced to the third land 66 side so that the second land pressure P1 becomes almost atmospheric pressure. As a result, the period during which the second land pressure P1 is higher than the in-cylinder pressure Pa can be eliminated or reduced, and oil consumption can be suppressed and oil consumption can be reduced. In addition, the recessed part formed in the 2nd ring 36 is not limited to the case where it forms radially, The recessed part of various numbers and shapes can be employ | adopted. For example, the concave portion may be formed in a substantially annular shape over the entire circumference on the outer peripheral side or inner peripheral side of the lower end surface of the second ring 36. Other configurations and operations are the same as those in FIGS. 1 to 6 described above. In the configuration of this example as well, the wettability reduction treatment is applied to part or all of the upper and lower end surfaces of the second ring 36 and the upper and lower groove surfaces of the second ring groove 42 as in the configurations of FIGS. May be.

  In the above description, the concave portion 82 is formed on the lower end surface 80 of the second ring 36. However, the concave portion may be formed on the lower groove surface 84 of the second ring groove 42 facing the lower end surface 80. In this case, the recesses may be formed radially of the second ring groove 42. Further, the outer peripheral end of the recess may be opened on the outer peripheral surface of the piston main body 32. Also in this case, the recesses are not limited to the case where they are formed radially, and various numbers and shapes of recesses can be adopted. Further, a recess may be formed on both the lower end surface 80 and the lower groove surface 84 of the second ring 36. Further, a recess may be formed in one or both of the upper end surface 86 that is the second end surface of the second ring 36 and the upper groove surface 88 that is the second groove surface of the second ring groove 42 facing the upper end surface 86. .

  Further, in the above, the axial end surface of the top ring 34, the first groove surface of the first ring groove 40 facing the axial end surface, the axial end surface of the second ring 36, and the second ring groove facing the axial end surface. A case has been described in which at least one of the second groove surfaces of 42 is used as an opposing formation surface, and a recess is formed in the opposing surface. However, one or a plurality of convex portions larger than the maximum depth of the surface roughness of the opposing formation surface may be formed on at least one opposing formation surface. For example, on the upper end surface of the top ring 34 or the lower end surface of the second ring 36, a convex portion protruding in the axial direction in a straight line, a curved shape such as an arc or a circle, or a convex portion arranged in the form of dots is formed. May be. For example, a curved surface whose cross-sectional shape when cut along a plane perpendicular to the circumferential direction of the upper end surface of the top ring 34 or the lower end surface of the second ring 36 is an arc shape protruding in the axial direction is an upper end surface or a lower surface. You may form in an end surface. Also in this case, the contact area between the facing surface and the mating surface can be reduced, and the facing surface can be easily separated from the mating surface, so that oil consumption can be reduced.

  As mentioned above, although the form for implementing this invention was demonstrated, this invention is not limited to such embodiment at all, and it can implement with a various form in the range which does not deviate from the summary of this invention. Of course.

  10 Gasoline Engine, 12 Engine Body, 14 Cylinder Block, 16 Cylinder, 18 Pressure Ring Piston, 20 Connecting Rod, 22 Crankshaft, 24 Crank Chamber, 26 Cylinder Head, 28 Combustion Chamber, 32 Piston Body, 34 Top Ring, 36 Second ring, 38 Oil ring, 40 First ring groove, 42 Second ring groove, 44 Oil ring groove, 46 Piston inner space, 48 Drain hole, 50, 52 Ring side rail, 54 Ring spacer, 56 Joint, 58 Topland , 60 second land, 62 top land space, 64 second land space, 66 third land, 68 recess, 70 upper end surface, 72 upper groove surface, 74 recess, 76 lower end surface, 78 lower groove surface, 80 lower end surface, 82 recess, 84 lower groove Face, 86 Upper end surface, 88 upper groove surface.

Claims (4)

A piston body for an internal combustion engine in which a ring groove and an oil ring groove are sequentially formed on the outer peripheral surface from the combustion chamber side toward the crank chamber side;
A pressure ring disposed in the ring groove so as to be movable in the piston movement direction, and having an inner diameter larger than a groove bottom diameter of the ring groove;
An axial end face of the pressure ring, or a ring groove face facing the end face as an opposing formation face,
The pressure ring mounting piston, wherein the opposing formation surface has a concave portion or a convex portion larger than the maximum depth of surface roughness. The pressure ring mounting piston according to claim 1,
The pressure ring mounting piston, wherein the piston body has an outer diameter that increases toward the ring groove at a peripheral portion of the ring groove. The pressure ring mounting piston according to claim 1 or 2,
The pressure ring mounting piston, wherein the opposing formation surface is subjected to a wettability reduction process for reducing wettability to oil. The pressure ring mounting piston according to any one of claims 1 to 3,
The pressure ring mounting piston, wherein the recesses are radially formed on the facing forming surface.

Images