Internal combustion engines and vehicles

Abstract

To reduce friction between the piston and the inner wall surface over a wide range in the axial direction of the cylinder. [Solution] The internal combustion engine according to this embodiment comprises a cylinder and a piston. The cylinder has an inner wall surface in which a plurality of first recesses are formed. The piston is disposed in an internal space covered by the inner wall surface. The piston comprises a piston body, a piston ring disposed on the outer circumferential surface of the piston body, and a solid lubricating film. The solid lubricating film is applied to the outer circumferential surface of the piston ring. The solid lubricating film alters the relationship between the speed at which the piston moves and the friction between the region on the inner wall surface in which the plurality of first recesses are formed and the piston ring, compared to a configuration without the solid lubricating film.

Description

Technical Field

[0001] The present disclosure relates to an internal combustion engine and a vehicle.

Background Art

[0002] Conventionally, it is known that the friction between a piston that moves with respect to the inner wall surface of a cylinder provided in an internal combustion engine and the inner wall surface changes when a plurality of recesses are formed on the inner wall surface (see Patent Document 1). The piston moves at a low speed around the top dead center and bottom dead center, and moves at a high speed when facing the middle part of the inner wall surface. When a plurality of recesses are formed on the inner wall surface, the amount of friction reduction becomes large at the portion of the inner wall surface that faces the piston when moving at a high speed with respect to the inner wall surface. The amount of friction reduction varies depending on the type of recess, such as the depth and shape of the recess. When a specific type of recess is formed, the amount of friction reduction at the portion of the inner wall surface that faces the piston when moving at a high speed with respect to the inner wall surface is larger than when other types of recesses are formed on the inner wall surface.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] If the above-mentioned specific type of recess is formed in the portion of the inner wall surface that faces the piston when moving at a low speed with respect to the inner wall surface, there is a possibility that the friction is not reduced at that portion. For this reason, it is required to expand the range in which the above-mentioned specific type of recess is formed up to the portion of the inner wall surface that faces the piston when moving at a low speed with respect to the inner wall surface. And it is required to reduce the friction between the piston and the inner wall surface over a wide range in the axial direction of the cylinder.

[0005] This disclosure has been made in view of the above-mentioned problems and aims to reduce friction between the piston and the inner wall surface over a wide range in the axial direction of the cylinder. [Means for solving the problem]

[0006] An internal combustion engine according to this embodiment comprises a cylinder and a piston. The cylinder has an inner wall surface in which a plurality of first recesses are formed. The piston is disposed in an internal space covered by the inner wall surface. The piston comprises a piston body, a piston ring disposed on the outer circumferential surface of the piston body, and a solid lubricating film. The solid lubricating film is applied to the outer circumferential surface of the piston ring. The solid lubricating film alters the relationship between the friction between the region on the inner wall surface in which the plurality of first recesses are formed and the piston ring and the speed at which the piston moves, compared to a configuration without the solid lubricating film. [Effects of the Invention]

[0007] According to this disclosure, friction between the piston and the inner wall surface can be reduced over a wide range in the axial direction of the cylinder. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic diagram showing an example of the configuration of a vehicle according to the first embodiment. [Figure 2] Figure 2 is a schematic diagram showing an example of the configuration of an internal combustion engine according to the first embodiment. [Figure 3] Figure 3 is a schematic cross-sectional view showing an example of the configuration of the outer circumferential surface and its vicinity of the piston according to the first embodiment. [Figure 4] Figure 4 is a schematic diagram showing the configuration of the inner wall surface of the cylinder according to the first embodiment. [Figure 5] Figure 5 is a diagram illustrating a plurality of recesses according to the first embodiment. [Figure 6]Figure 6 is a diagram illustrating the relationship between the friction between the piston and the inner wall surface and the speed of the piston equipped with a piston ring, in two cases: when equipped with a piston ring according to the first embodiment, and when equipped with a piston ring according to a comparative example. [Figure 7] Figure 7 is a diagram illustrating the position of the inner wall surface 11 and other parameters determined based on the speed of a piston 3 equipped with a piston ring according to a comparative example. [Figure 8] Figure 8 is a diagram illustrating the relationship between the speed of the piston 3 and friction when each of the multiple piston rings contacts the inner wall surface 11, in a contact configuration different from the example shown in Figure 6. [Figure 9] Figure 9 is a schematic diagram showing the configuration of the inner wall surface of the cylinder according to the second embodiment. [Modes for carrying out the invention]

[0009] (First embodiment) Figure 1 is a schematic diagram showing an example of the configuration of a vehicle 100 according to the first embodiment. As shown in Figure 1, the vehicle 100 comprises an internal combustion engine 1, a transmission 30, and at least one wheel 40. When the internal combustion engine 1 is driven, the driving force is transmitted to at least one wheel 40 via the transmission 30.

[0010] Figure 2 is a schematic diagram showing an example of the configuration of an internal combustion engine 1 according to the first embodiment. Figure 3 is a schematic cross-sectional view showing an example of the configuration of the outer circumferential surface of the piston 3 and its vicinity according to the first embodiment. As shown in Figures 2 and 3, the internal combustion engine 1 includes an intake valve (not shown), a cylinder 2, a piston 3, a piston pin 4, a crank arm (not shown), and a crankshaft (not shown). The internal combustion engine 1 according to the first embodiment is, for example, a four-stroke engine that constitutes one cycle consisting of four processes: intake, compression, expansion, and exhaust. The internal combustion engine 1 according to the first embodiment is, for example, a diesel engine.

[0011] Cylinder 2 extends along the central axis A1 and is formed in a cylindrical or other tubular shape. Cylinder 2 has an inner wall surface 11. Inside cylinder 2, an internal space is formed that is covered by the inner wall surface 11. Hereafter, the direction around the axis A1 of cylinder 2 will be referred to as the circumferential direction. The inner wall surface 11 is aligned with the axial and circumferential directions of cylinder 2.

[0012] The piston 3 is positioned in the internal space and connected to the crank arm via a piston pin 4 or the like, which extends in a direction perpendicular or nearly perpendicular to the central axis A1 of the cylinder 2. The crank arm is rotatably mounted on the crankshaft. The piston 3 reciprocates in the internal space along the central axis A1 of the cylinder 2, in parallel with the rotation of the crank arm with the crankshaft as the axis of rotation. The axial direction of the cylinder 2 is aligned with the direction of movement of the piston 3.

[0013] During the intake stroke of the internal combustion engine 1, piston 3 descends toward the crankshaft relative to the intake valve, reaching bottom dead center. During the compression stroke, piston 3 rises from bottom dead center toward the intake valve, reaching top dead center. During the expansion stroke, piston 3 descends again toward bottom dead center. Then, during the exhaust stroke, it rises again toward the intake valve from bottom dead center. In this way, piston 3 reciprocates between top dead center and bottom dead center.

[0014] Specifically, piston 3 is stationary relative to the inner wall surface 11 at top dead center, and moves toward the bottom dead center while accelerating from top dead center. Between top dead center and bottom dead center, piston 3 changes from acceleration to deceleration, and is stationary relative to the inner wall surface 11 at bottom dead center. Then, piston 3 moves toward the top dead center while accelerating from bottom dead center, changes from acceleration to deceleration between top dead center and bottom dead center, and is stationary relative to the inner wall surface 11 at top dead center.

[0015] The piston 3 includes a piston body 5 and a plurality of piston rings. In the piston body 5, for example, in order from the intake valve side, a piston top surface 12, a top ring groove 14, a second ring groove 17, an oil ring groove 19, and a piston skirt 21 are formed. The piston top surface 12 is an end surface on the intake valve side of the piston body 5 and faces the intake valve side. The piston skirt 21 forms an end surface on the crankshaft side of the piston body 5, and the end surface on the crankshaft side formed by the piston skirt 21 faces the crankshaft side.

[0016] Each of the plurality of piston rings is arranged on the outer peripheral surface of the piston body 5. In one example, the plurality of piston rings includes, for example, a top ring 7, a second ring 8, and an oil ring 9. The top ring 7 is arranged in the top ring groove 14. The second ring 8 is arranged in the second ring groove 17. The oil ring 9 is arranged in the oil ring groove 19.

[0017] On each of the outer peripheral surfaces of the plurality of piston rings, a solid lubricating film is coated. The solid lubricating film is, for example, a diamond-like carbon film (DLC), a resin coating film, a molybdenum disulfide film, etc. On the outer peripheral surface of the top ring 7, a solid lubricating film 7a is coated, on the outer peripheral surface of the second ring 8, a solid lubricating film 8a is coated, and on the outer peripheral surface of the oil ring 9, a solid lubricating film 9a is coated. Hereinafter, the region of the piston 3 between the edge on the intake valve side of the top ring 7 and the edge on the crankshaft side of the oil ring 9 is referred to as region S.

[0018] In the first embodiment, the piston 3 used in the diesel engine of the internal combustion engine 1 is described as an example, but it is not limited thereto. The piston 3 may be used not only in a diesel engine but also in other internal combustion engines 1 such as a gasoline engine.

[0019] Figure 4 is a schematic diagram showing the configuration of the inner wall surface 11 of the cylinder 2 according to the first embodiment. In Figure 4, the cylinder 2 is unfolded, and a part of the inner wall surface 11 is viewed from the side of the internal space covered by the inner wall surface 11 of the cylinder 2. The direction along the circumferential direction of the cylinder 2 is defined as the X-axis direction, and the direction along the central axis A1 of the cylinder 2 is defined as the Y-axis direction. In the Y-axis direction, the intake valve side is defined as the positive direction in the Y-axis direction and is referred to as the upper side. Also, in the Y-axis direction, the crankshaft side is defined as the negative direction in the Y-axis direction and is referred to as the lower side. Here, the position of the inner wall surface 11 that faces the oil ring 9 when the piston 3 is at top dead center is defined as the first defined position r1. Also, the position that faces the top ring 7 when the piston 3 is at bottom dead center is defined as the second defined position r2. As shown in Figure 4, the first defined position r1 is located above the second defined position r2.

[0020] In the inner wall surface 11 according to the first embodiment, a plurality of recesses are formed. Hereafter, in the first embodiment, the region in which a plurality of recesses are formed will be referred to as the first region R1. Note that the phrase "a plurality of recesses are formed on the inner wall surface 11" may be rephrased as "texturing is applied to the inner wall surface 11". In the first embodiment, one type of recess is formed in the first region R1. The recess formed in the first region R1 is a type of recess that reduces friction between the piston 3 and the inner wall surface 11 compared to other recesses that may be applied in place of the recess formed in the first region R1 when the speed at which the piston 3 moves is faster than a reference value. The reference value is determined by the relationship between the speed of the piston 3 and the friction between the piston 3 and the inner wall surface 11 in which the plurality of recesses are formed, and the relationship between the speed of the piston 3 and the friction between the piston 3 and the inner wall surface 11 in which other recesses are formed. In the following description, it is assumed that each of the plurality of piston rings is always in solid contact with a recess during the reciprocating motion of the piston 3.

[0021] The upper end T in the axial direction of the first region R1 to which texturing is applied is located below the first specified position r1. The lower end B of the first region R1 is located above the second specified position r2. In Figure 4, let d1 be the axial distance between the upper end T and the lower end B of the first region R1, and let d2 be the axial distance between the first specified position r1 and the second specified position r2. In one example, the distance d1 is in the range of 55% or more and 85% or less of the distance d2.

[0022] In Figure 4, let d3 be the axial distance between the upper end T of the first region R1 and the first specified position r1, and let d4 be the axial distance between the second specified position r2 and the lower end B. In one example, distance d3 is the same as or approximately the same as distance d4.

[0023] In the first embodiment, the plurality of recesses in the first region R1 are not limited to being formed around the entire circumference of the inner wall surface 11. In one example, the plurality of recesses in the first region R1 do not need to be formed around the entire circumference of the inner wall surface 11.

[0024] In the region between the first defined position r1 and the second defined position r2 of the inner wall surface 11 according to the embodiment, as shown in Figure 4, it is divided into three regions, for example, the first region R1, the second region R2, and the third region R3. The second region R2 corresponds to the region between the first defined position r1 and the upper end T of the first region R1. The third region R3 corresponds to the region between the lower end B of the first region R1 and the second defined position r2. The first region R1 is below the second region R2 and above the third region R3. The first region R1 and the second region R2 are continuous in the direction of movement of the piston 3. Also, the first region R1 and the third region R3 are continuous in the direction of movement of the piston 3.

[0025] Figure 5 is a diagram illustrating a plurality of recesses according to the first embodiment. Figure 5 shows a view from the internal space side where the inner wall surface 11 covers a part of the first region R1. Each of the plurality of recesses is, for example, dimple-shaped. However, it is not limited to this, and each of the plurality of recesses may have other shapes. Also, as shown in Figure 5, in each of the plurality of recesses formed in the inner wall surface 11 according to the first embodiment, the shape of the opening is the same. Having the same shape includes, for example, that the shapes of the openings of the plurality of recesses are congruent, and that the difference in the opening areas of the plurality of recesses is small and they are similar. In each of the plurality of recesses, the shape of the opening is, for example, circular, and the diameter of the opening φ is, for example, 0.25 mm. However, the shape of the opening may be other shapes such as rectangular or rhombus.

[0026] Here, the arrangement of each of the multiple recesses formed on the inner wall surface 11 according to the first embodiment will be described. In the first region R1, multiple rows of recesses are formed. The multiple rows of recesses are formed offset from each other in the direction of movement of the piston 3, from the upper end T to the lower end B of the first region R1. As shown in Figure 5, in one example, the multiple rows of recesses are arranged at a constant pitch along the direction of movement.

[0027] In each of the multiple rows of recesses, two or more recesses are arranged in the circumferential direction. Two or more recesses in adjacent rows of recesses in the direction of movement of the piston 3 are arranged in a staggered pattern. In one example, each of the two or more recesses constituting the upper row of recesses in adjacent rows of recesses in the direction of movement is offset in the circumferential direction of the inner wall surface 11 relative to each of the two or more recesses constituting the lower row of recesses. In the first region R1, a certain row of recesses and the rows of recesses adjacent to that row from below in the direction of movement of the piston 3 are arranged alternately.

[0028] Furthermore, in adjacent rows of recesses in the direction of movement of the piston 3, the lower end of the upper row of recesses is located below the upper end of the lower row of recesses. Specifically, in adjacent rows of recesses in the direction of movement of the piston 3, the lower end of each of the two or more recesses constituting the upper row of recesses is located below the upper end of each of the two or more recesses constituting the lower row of recesses. Note that the phrase "the lower end of the upper row of recesses is located below the upper end of the lower row of recesses" can be rephrased as "they overlap each other in the axial direction." Also, when the area ratio of multiple recesses is defined as a value indicating the ratio of the total opening area of ​​the multiple recesses to the entire first region R1, in one example, the area ratio is between 20% and 50%.

[0029] Next, the effects of the configuration of the first embodiment will be explained. Figure 6 is a diagram illustrating the relationship between the friction between the piston 3 and the inner wall surface 11 and the speed of the piston 3 equipped with the piston ring, in two cases: when equipped with the piston ring according to the first embodiment, and when equipped with the piston ring according to the comparative example. In Figure 6, the horizontal axis represents the speed of the piston 3 relative to the inner wall surface 11, and the vertical axis represents the change in friction D obtained by subtracting the friction when the inner wall surface 11 is not formed from the friction when a recess is formed in the inner wall surface 11. That is, when the change in D is positive, it means that the friction has increased as a result of forming a recess in the inner wall surface 11 compared to the state in which no recess is formed in the inner wall surface 11. On the other hand, when the change in D is negative, it means that the friction has decreased as a result of forming a recess in the inner wall surface 11 compared to the state in which no recess is formed in the inner wall surface 11. In the following explanation, V1 in Figure 6 will be described as representing the speed of the piston 3 when the oil ring 9 passes the upper end T of the first region R1. At this time, the speed of piston 3 when the top ring 7 passes the lower end B of the first region R1 is the same as or approximately the same as V1. However, this is not limited to this example; in another example, V1 may represent the speed of piston 3 when a piston ring other than the oil ring 9 passes the upper end T of the first region R1. Also, in Figure 6, V2 represents the maximum speed of piston 3 when piston 3 changes from acceleration to deceleration. When the speed of piston 3 is between V1 and V2, at least a portion of the region S of piston 3 faces the first region R1.

[0030] Here, the portion of the inner wall surface 11 that the second ring 8 faces when the piston 3 is moving at a speed of V2 is defined as the third specified position r3. As shown in Figure 4, the first region R1 is defined as a region that includes at least the third specified position r3. However, the third specified position r3 may also be defined as a position where the distance from the first specified position r1 along the direction of movement of the piston 3 coincides or approximately coincides with the distance from the second specified position r2 along the direction of movement of the piston 3.

[0031] In Figure 6, the solid line segment s1 represents the change D with respect to the speed of the piston 3, which is equipped with a piston ring coated with a solid lubricant film on its outer surface. As shown in Figure 6, when the speed of the piston 3 is between V1 and V2, the change D is negative. Therefore, when the piston 3 slides against the first region R1 in which multiple recesses are formed, the friction between the piston 3 and the inner wall surface 11 is reduced.

[0032] Here, an internal combustion engine 1 equipped with a piston ring without a solid lubricating film on its outer surface is given as a comparative example of the configuration according to the embodiment. Of the configuration of the internal combustion engine 1 according to the comparative example, all configurations other than the piston ring configuration are the same as those of the internal combustion engine 1 according to the embodiment. In Figure 6, the dashed line segment s2 represents the change in speed D of the piston 3 equipped with a piston ring according to the comparative example without a solid lubricating film on its outer surface. Both the solid line segment s1 and the dashed line segment s2 represent the change in speed D of the piston 3 when the speed of the piston 3 is V1 or greater and V2 or less.

[0033] As shown in Figure 6, line segment s2 intersects with line D=0. In Figure 7, let V3 be the speed of piston 3 when line segment s2 intersects with line D=0. Speed ​​V3 is less than V2 and greater than V1.

[0034] Figure 7 is a diagram illustrating the position of the inner wall surface 11, etc., as defined based on the speed of the piston 3 equipped with a piston ring according to a comparative example. As shown in Figure 7, the first region R1 is divided into the fourth region R4, the fifth region R5, and the sixth region R6. The boundary between the fourth region R4 and the fifth region R5 is denoted as boundary p. The boundary between the fourth region R4 and the sixth region R6 is denoted as boundary q. The fourth region R4 is the region between boundary p and boundary q. The fifth region R5 is the region between the upper end T of the first region R1 and boundary p. The sixth region R6 is the region between boundary q and the lower end B of the first region R1. The distance along the axial direction of the cylinder 2 between boundary p and boundary q is denoted as d5. The third defined position r3 is located between boundary p and boundary q.

[0035] In the following explanation, in Figure 7, of the two parts facing the oil ring 9 when the piston 3 speed is V3, the part above the third specified position r3 will be described as boundary p. Also, of the two parts facing the top ring 7 when the piston 3 speed is V3, the part below the third specified position r3 will be described as boundary q.

[0036] Since the speed V1 is smaller than V3, as shown in Figure 7, the upper end T of the first region R1 is located above the boundary p, and the lower end B of the first region R1 is located below the boundary q. For this reason, the distance d2 along the axial direction of the cylinder 2 between the upper end T and the lower end B of the first region R1, which is the recessed area on the inner wall surface 11 according to the embodiment, is greater than the distance d5 along the axial direction of the cylinder 2 between the boundary p and the boundary q. In other words, the fourth region R4 is narrower than the first region.

[0037] When the speed of piston 3 is greater than V3 and less than or equal to V2, at least a portion of the region S of piston 3 faces the fourth region R4. Also, when the speed of piston is greater than or equal to V1 and less than V3, the entire region S of piston 3 faces the fifth region or the sixth region R6.

[0038] In another example, boundary p may be the part above the third specified position r3 of the two parts facing the piston ring other than the oil ring 9 when the piston speed of 3 is V3. In yet another example, boundary q may be the part below the third specified position r3 of the two parts facing the piston ring other than the top ring 7 when the piston speed of 3 is V3.

[0039] As shown in Figure 6, when the speed of piston 3 is greater than V3 and less than or equal to V2, the change amount D is negative. Therefore, when at least a portion of the region S of piston 3 faces the fourth region R4, the friction between piston 3 and the inner wall surface 11 is reduced compared to the state in which no recess is formed on the inner wall surface 11.

[0040] On the other hand, when the speed of piston 3 is between V1 and V3, the change amount D is positive. Therefore, when the entire region S of piston 3 faces the fifth region R5 and the sixth region R6, friction increases compared to the state in which no recess is formed on the inner wall surface 11. In the comparative example, friction is reduced when at least a part of the region S of piston 3 slides against the fourth region R4, but when it slides against the fifth region R5 and the sixth region R6, friction increases, so friction is not reduced across the entire first region R1.

[0041] In contrast, the outer surface of the piston ring according to this embodiment is coated with a solid lubricant film. The presence of the solid lubricant film changes the relationship between the speed at which the piston 3 moves and the friction between the region where the multiple recesses are formed and the piston ring. Specifically, when the piston ring is coated with a solid lubricant film, the friction when the region where the multiple recesses are formed and the piston ring make solid contact is reduced. In the first embodiment, during the reciprocating motion of the piston 3, each of the multiple piston rings is always in solid contact with the multiple recesses. Therefore, by changing from a piston ring without a solid lubricant film to a piston ring with a solid lubricant film, in Figure 7, the relationship between the friction between the piston 3 and the inner wall surface 11 with respect to the speed of the piston 3 becomes a line segment s1, which is a parallel shift from line segment s2 to the negative side. That is, when the piston ring is coated with a solid lubricant film, the friction is reduced compared to when the piston ring is not coated with a solid lubricant film.

[0042] Furthermore, when the speed of the piston 3, which is equipped with a piston ring coated with a solid lubricating film, is between V1 and V2, the change amount D is negative, as shown in line segment s1. Therefore, in the inner wall surface 11 according to this embodiment, friction is reduced throughout the entire first region R1. Since the first region R1 is wider than the fourth region R4, the area in which a recess can be formed can be made wider compared to the inner wall surface 11 according to the comparative example, and friction can be reduced even in the part of the inner wall surface 11 that faces the piston 3 when it moves at a low speed relative to the inner wall surface 11. Specifically, the distance along the axial direction of the cylinder 2 between the upper end and lower end of the region in which the first recess is formed can be set to a range of 55% or more and 85% or less of the distance along the axial direction of the cylinder 2 between the first specified position and the second specified position.

[0043] In the first embodiment, the case where each of the multiple piston rings is always in solid contact with the inner wall surface 11 during the reciprocating motion of the piston 3 was described as an example. However, it is also possible that each of the multiple piston rings is in contact with the inner wall surface 11 in a manner other than always being in solid contact. In this case, the relationship between the speed of the piston 3 and friction is different from the case shown in Figure 7. Figure 8 is a diagram to explain the relationship between the speed of the piston 3 and friction when each of the multiple piston rings is in contact with the inner wall surface 11 in a manner other than the contact manner corresponding to the example shown in Figure 6. In Figure 8, the speed of the piston 3 when the speed of the piston 3 is greater than V3 and less than V2 is defined as V4. The dashed line segment s3 is the same as the portion of the line segment s2 shown in Figure 6 in which the speed of the piston 3 is between V1 and V4. The solid line segment s4 is the same as the portion of the line segment s2 shown in Figure 6 in which the speed of the piston 3 is between V4 and V2. The solid line s5 represents the relationship between the speed of the piston 3 and friction when each of the multiple piston rings contacts the inner wall surface 11 in a different manner within the range of piston speed V1 to less than V4. As shown by line segment s3 and the broken line s5, even when each of the multiple piston rings contacts the inner wall surface 11 in a different manner, friction between the piston 3 and the inner wall surface 11 is reduced within the range of piston speed V1 to less than V4.

[0044] (Second embodiment) The internal combustion engine 1 according to the second embodiment has a configuration in which a recess of a different type from the recess formed in the first region R1 is formed in at least one of the second region R2 and the third region R3. Figure 9 is a schematic diagram showing the configuration of the inner wall surface 11 of the cylinder 2 according to the second embodiment.

[0045] On the inner wall surface 11, multiple types of recesses are formed, offset by type in the direction of movement of the piston 3. Each type of recess has a different effect on the relationship between the friction between the inner wall surface 11 and the piston 3 with respect to the speed at which the piston 3 moves. In Figure 9, in the first region R1, shown by a dashed line extending from the lower left to the upper right, similar to the first embodiment, a type of recess is formed that reduces the friction between the piston 3 and the inner wall surface 11 when the speed at which the piston 3 moves is above a reference value, compared to other recesses that can be applied in place of the recess formed in the first region R1. Hereafter, the recess formed in the first region R1 will be referred to as the first recess. Then, in at least one of the second region R2 and the third region R3, shown by a dashed line extending from the lower right to the upper left, one or more types of recesses are formed that have a different effect on the relationship between the friction with respect to the speed at which the piston 3 moves compared to the first recess. Hereafter, one or more types of recesses formed in at least one of the second region R2 and the third region R3 will be referred to as the second recess. The first recess is a type of recess that reduces friction when the piston 3 moves at a speed greater than or equal to a standard value, compared to one or more of the second recesses. On the other hand, one or more of the second recesses are a type of recess that reduces friction when the piston 3 moves at a speed slower than a standard value, compared to the first recess.

[0046] In one example, two types of recesses are formed on the inner wall surface 11. A first recess is formed in the first region R1, and a second recess of one type is formed in the second region R2 and the third region R3. As a result, two types of recesses are formed in the entire region between the first specified position r1 and the second specified position r2. The reference value is, for example, the speed at which the piston 3 passes over the upper end T of the first region R1 or the lower end B of the first region R1.

[0047] The depth of the first recess is formed to be greater than the depth of the second recess. For example, the depth of the first recess is 3.0 μm or more and 5.0 μm or less, and the depth of the second recess is 1.0 μm or more and 2.0 μm or less.

[0048] Furthermore, the above example is not limited to a configuration in which no recess is formed in the third region R3, and the second recess is formed only in the second region R2. Alternatively, no recess is formed in the second region R2, and the recess is formed only in the third region R3.

[0049] Furthermore, two or more types of second recesses may be formed in the second region. In this case, in the second region, the recesses formed at positions further away from the first region R1 are of a type that reduces friction when the piston 3 is moving at a slow speed. Similarly, in the third region, the recesses formed at positions further away from the first region R1 are of a type that reduces friction when the piston 3 is moving at a slow speed.

[0050] According to the second embodiment described above, a first recess is formed in the first region R1. In addition, one or more second recesses of a different type are formed in at least one of the second region R2 and the third region R3, which have a different effect on the relationship between the friction between the inner wall surface 11 and the piston ring with respect to the speed at which the piston 3 moves compared to the first recess. Specifically, in the first region R1, a first recess is formed that reduces friction when the piston 3 is moving at a high speed, compared to any of the one or more second recesses. Furthermore, in at least one of the second region R2 and the third region R3, a recess is formed that reduces friction when the piston 3 is moving at a slow speed compared to the first recess. As a result, friction can be further reduced in the portion of the inner wall surface facing the piston 3 when it is moving at a low speed relative to the inner wall surface 11.

[0051] It should be noted that the present invention is not limited to the embodiments described above, and can be modified in various ways during implementation without departing from its essence. Furthermore, each embodiment may be combined as appropriate, and in that case, the combined effects can be obtained. Moreover, the above embodiments include various inventions, and various inventions can be extracted by selecting combinations from the multiple constituent elements disclosed. For example, if the problem can be solved and effects obtained even if some constituent elements are deleted from all the constituent elements shown in the embodiment, then the configuration with these deleted constituent elements can be extracted as an invention. [Explanation of Symbols]

[0052] 1...Internal combustion engine, 2...Cylinder, 3...Piston, 4...Piston pin, 5...Piston body, 7...Top ring, 8...Second ring, 9...Oil ring, 7a, 8a, 9a...Solid lubricating film, 11...Inner wall surface, 12...Piston crown surface, 14...Top ring groove, 17...Second ring groove, 19...Oil ring groove, 21...Piston skirt, 100...Vehicle, A1...Central axis, B...Lower end of the first region, d1-d5...Distance, R1...First region, R2...Second region, R3...Third region, R4...Fourth region, R5...Fifth region, R6...Sixth region, r1...First specified position, r2...Second specified position, T...Upper end of the first region.

Claims

1. A cylinder having an inner wall surface in which a plurality of first recesses are formed, A piston is disposed in the internal space covered by the aforementioned inner wall surface, Equipped with, The aforementioned piston is The piston body and A piston ring is positioned on the outer circumferential surface of the piston body, A solid lubricating film is formed on the outer surface of the piston ring, Equipped with, The solid lubricating film alters the relationship between the friction between the region on the inner wall surface where the plurality of first recesses are formed and the piston ring, and the speed at which the piston moves, compared to a configuration without the solid lubricating film. An internal combustion engine equipped with [a specific feature].

2. The piston ring includes a top ring and an oil ring located below the top ring. On the inner wall surface, a first defined position is defined which is the position facing the oil ring when the piston is at top dead center, and a second defined position is defined which is the position facing the top ring when the piston is at bottom dead center. The upper end of the region where the plurality of first recesses are formed is located below the first specified position, The lower end of the region where the plurality of first recesses are formed is located above the second specified position. The internal combustion engine according to claim 1, wherein the distance along the axial direction of the cylinder between the upper end and the lower end is in the range of 55% or more and 85% or less of the distance along the axial direction between the first specified position and the second specified position.

3. The inner wall surface includes a first region in which the plurality of first recesses are formed, a second region above the upper end of the first region, and a third region below the lower end of the first region. In at least one of the second and third regions, one or more second recesses are formed that have an effect on the relationship between the friction between the inner wall surface and the piston ring with respect to the speed at which the piston moves, different from that of the first recess. The internal combustion engine according to claim 1.

4. The plurality of first recesses are of a type that reduces friction when the piston moves at a speed greater than or equal to a reference value, compared to any of the one or more second recesses. The internal combustion engine according to claim 3, wherein the one or more second recesses are of a type that reduces friction when the speed at which the piston moves is less than the reference value, compared to the first recess.

5. A vehicle equipped with an internal combustion engine according to any one of claims 1 to 4.

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