Internal combustion engine and vehicle

Abstract

An internal combustion engine and a vehicle, the internal combustion engine according to the embodiment has a cylinder and a piston. The cylinder has an inner wall surface formed with a plurality of first recessed portions. The piston is disposed in an internal space covered by the inner wall surface. The piston has a piston main body, a piston ring disposed on an outer peripheral surface of the piston main body, and a solid lubricating film. The solid lubricating film is coated on the outer peripheral surface of the piston ring. The solid lubricating film changes a relationship of friction between a region of the inner wall surface formed with the plurality of first recessed portions and the piston ring with respect to a speed at which the piston moves, as compared with a structure in which the solid lubricating film is not coated.

Description

Technical Field

[0001] This invention relates to an internal combustion engine and a vehicle. Background Technology

[0002] Currently, it is known that, regarding the friction between a piston moving relative to the inner wall surface of an internal combustion engine cylinder, if multiple recesses are formed on the inner wall surface, the friction condition changes compared to when multiple recesses are not formed on the inner wall surface. The piston moves at low speed around its top and bottom dead centers and at high speed when facing the middle portion of the inner wall surface. If multiple recesses are formed on the inner wall surface, the reduction in friction is increased at the portion of the inner wall surface facing the piston when it moves at high speed relative to the inner wall surface. The reduction in friction varies depending on the type of recess, such as its depth and shape. If a specific type of recess is formed, the reduction in friction at the portion facing the piston when it moves at high speed relative to the inner wall surface is greater than when other types of recesses are formed on the inner wall surface (e.g., Japanese Patent Application Laid-Open No. 2017-26823).

[0003] If the aforementioned specific type of recess is also formed on the inner wall surface opposite the piston when it moves at low speed relative to the inner wall surface, friction may not be reduced at that location. Therefore, it is required that the range of recesses of the aforementioned specific type be extended to the portion of the inner wall surface opposite the piston when it moves at low speed relative to the inner wall surface. Furthermore, it is required that the friction between the piston and the inner wall surface be reduced over a larger area along the axial direction of the cylinder. Summary of the Invention

[0004] The present invention was proposed in view of the above-mentioned problems, and its object is to reduce the friction between the piston and the inner wall surface over a large area along the axial direction of the cylinder.

[0005] The internal combustion engine involved in the embodiment has a cylinder and a piston. The cylinder has an inner wall surface with a plurality of first recesses formed therein. The piston is disposed in an internal space covered by the inner wall surface. The piston has: a piston body; piston rings disposed on the outer peripheral surface of the piston body; and a solid lubricating film. The solid lubricating film covers the outer peripheral surface of the piston rings. The solid lubricating film causes the relationship between the speed of piston movement and the friction between the region in the inner wall surface with the plurality of first recesses and the piston rings to change relative to a structure without the solid lubricating film.

[0006] According to the present invention, friction between the piston and the inner wall surface can be reduced over a large area along the axial direction of the cylinder. Attached Figure Description

[0007] Figure 1 This is a schematic diagram illustrating an example of the structure of the vehicle according to the first embodiment.

[0008] Figure 2 This is a schematic diagram illustrating an example of the structure of the internal combustion engine according to the first embodiment.

[0009] Figure 3 This is a cross-sectional view schematically showing an example of the outer peripheral surface of the piston and the structure in the vicinity of the first embodiment.

[0010] Figure 4 This is a schematic diagram showing the structure of the inner wall surface of the cylinder according to the first embodiment.

[0011] Figure 5 This is a diagram used to illustrate the plurality of recesses involved in the first embodiment.

[0012] Figure 6 This diagram illustrates the relationship between the friction between the piston and the inner wall surface and the speed of the piston with piston rings in both cases: the case with piston rings according to the first embodiment and the case with piston rings according to the comparative example.

[0013] Figure 7 This is a diagram illustrating the position of the inner wall surface 11, etc., based on the speed of a piston with piston rings that are shown in the comparative proportion.

[0014] Figure 8 It is used for multiple piston rings to correspond to Figure 6 The figure illustrates the relationship between friction and piston velocity when in contact with the inner wall surface, for example with other contact methods that differ from the one shown in the figure.

[0015] Figure 9 This is a schematic diagram showing the structure of the inner wall surface of the cylinder according to the second embodiment. Detailed Implementation

[0016] (First Embodiment)

[0017] Figure 1 This is a schematic diagram illustrating an example of the structure of the vehicle 100 according to the first embodiment. (See diagram for example.) Figure 1 As shown, vehicle 100 has an internal combustion engine 1, a transmission 30, and at least one wheel 40. For vehicle 100, if the internal combustion engine 1 is driven, driving force is transmitted to at least one wheel 40 via the transmission 30.

[0018] Figure 2 This is a schematic diagram illustrating an example of the structure of the internal combustion engine 1 according to the first embodiment. Figure 3 This is a cross-sectional view schematically showing an example of the outer peripheral surface of the piston 3 and its surrounding structure according to the first embodiment. For example... Figure 2 and Figure 3As shown, 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 internal combustion engine, and one working cycle consists of four processes: intake, compression, expansion, and exhaust. The internal combustion engine 1 according to the first embodiment is, for example, a diesel engine.

[0019] Cylinder 2 extends along central axis A1 and is formed into a cylindrical shape, such as a cylinder. Cylinder 2 has an inner wall surface 11. An internal space covered by the inner wall surface 11 is formed in cylinder 2. Thereafter, the direction around the central axis A1 of cylinder 2 is defined as circumferential. The inner wall surface 11 extends along both the axial and circumferential directions of cylinder 2.

[0020] The piston 3 is disposed in the aforementioned internal space and is connected to the crank arm via a piston pin 4 extending in a direction orthogonal or substantially orthogonal to the central axis A1 of the cylinder 2. The crank arm is rotatably mounted on the crankshaft. The piston 3 reciprocates within the internal space along the central axis A1 of the cylinder 2, parallel to the rotation of the crank arm, which serves as the axis of rotation of the crankshaft. The axial direction of the cylinder 2 is along the direction of movement of the piston 3.

[0021] During the intake process of the internal combustion engine 1, piston 3 descends relative to the intake valve towards the crankshaft, reaching bottom dead center (BDC). During compression, piston 3 rises from BDC towards the intake valve, reaching top dead center (TDC). During expansion, piston 3 descends again towards BDC. Then, during exhaust, it rises again from BDC towards the intake valve. As described above, piston 3 reciprocates between TDC and BDC.

[0022] Specifically, piston 3 is stationary relative to the inner wall surface 11 at top dead center, and moves towards bottom dead center while accelerating from top dead center. Between top dead center and bottom dead center, piston 3 transitions from acceleration to deceleration, and comes to rest relative to the inner wall surface 11 at bottom dead center. Then, piston 3 moves towards top dead center while accelerating from bottom dead center, transitions to deceleration between top dead center and bottom dead center, and comes to rest relative to the inner wall surface 11 at top dead center.

[0023] The piston 3 has a piston body 5 and multiple piston rings. In the piston body 5, for example from the intake valve side, a piston top surface 12, a top ring groove 14, a secondary ring groove 17, an oil ring groove 19, and a piston skirt 21 are formed sequentially. The piston top surface 12 in the piston body 5 is the intake valve side end face, facing the intake valve side. The piston skirt 21 in the piston body 5 forms a crankshaft side end face, with the crankshaft side end face of the piston skirt 21 facing the crankshaft side.

[0024] Multiple piston rings are disposed on the outer circumferential surface of the piston body 5. In one example, the multiple piston rings include, for example, a top ring 7, a secondary ring 8, and an oil ring 9. The top ring 7 is disposed in the top ring groove 14. The secondary ring 8 is disposed in the secondary ring groove 17. The oil ring 9 is disposed in the oil ring groove 19.

[0025] Each of the piston rings has a solid lubricating film coated on its outer circumferential surface. The solid lubricating film can be, for example, a diamond-like carbon (DLC) film, a resin-coated film, or a molybdenum disulfide film. A solid lubricating film 7a is coated on the outer circumference of the top ring 7, a solid lubricating film 8a is coated on the outer circumference of the secondary ring 8, and a solid lubricating film 9a is coated on the outer circumferential surface of the oil ring 9. The region of the piston 3 between the intake valve side edge of the top ring 7 and the crankshaft side edge of the oil ring 9 is referred to as region S.

[0026] In the first embodiment, the piston 3 used in a diesel engine in the internal combustion engine 1 will be described as an example, but it is not limited to this. The piston 3 is not limited to the case of being used in a diesel engine, but can also be used in other internal combustion engines 1 such as gasoline engines.

[0027] Figure 4 This is a schematic diagram showing the structure of the inner wall surface 11 of the cylinder 2 according to the first embodiment. Figure 4 The diagram shows the cylinder 2 with the cylinder 2 extended, and a portion of the inner wall 11 is viewed from the internal space side covered by the inner wall 11. The direction along the circumference of the cylinder 2 is defined as the X-axis, and the axial direction along the central axis A1 of the cylinder 2 is defined as the Y-axis. In the Y-axis direction, the intake valve side is defined as the positive direction and referred to as the upper side. Conversely, the crankshaft side is defined as the negative direction and referred to as the lower side. Here, the position in the inner wall 11 opposite to the oil ring 9 when the piston 3 is at top dead center is defined as the first defined position r1. Furthermore, the position opposite to the top ring 7 when the piston 3 is at bottom dead center is defined as the second defined position r2. Figure 4 As shown, the first specified position r1 is located on the upper side relative to the second specified position r2.

[0028] In the first embodiment, a plurality of recesses are formed on the inner wall surface 11. Hereinafter, in the first embodiment, the region where the plurality of recesses are formed is referred to as the first region R1. Furthermore, the expression "forming a plurality of recesses on the inner wall surface 11" can be replaced with the expression "giving texture 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 more than other recesses that can be used to replace the recess formed in the first region R1 when the piston 3 moves at a speed faster than a reference value. The reference value is defined based on the relationship between the piston 3's speed and the friction between the piston 3 and the inner wall surface 11 with the plurality of recesses, and the relationship between the piston 3's speed and the friction between the piston 3 and the inner wall surface 11 with other recesses. In the following description, during the reciprocating motion of the piston 3, the plurality of piston rings are respectively arranged to maintain solid contact with the recesses.

[0029] The upper end T of the first region R1, which is textured, is located below the first predetermined position r1. The lower end B of the first region R1 is located above the second predetermined position r2. Figure 4 In this context, the axial distance between the upper end T and the lower end B of the first region R1 is defined as d2, and the axial distance between the first specified position r1 and the second specified position r2 is defined as d1. In a certain example, the distance d2 is within the range of more than 55% and less than 85% of the distance d1.

[0030] exist Figure 4 In this example, the axial distance between the upper end T of the first region R1 and the first designated position r1 is defined as d3, and the axial distance between the second designated position r2 and the lower end B is defined as d4. In one example, distance d3 and distance d4 are the same or approximately the same.

[0031] Furthermore, in the first embodiment, the first region R1 is not limited to a structure in which multiple recesses are formed throughout the entire circumference of the inner wall surface 11. In one example, the multiple recesses may not be formed throughout the entire circumference of the inner wall surface 11 in the first region R1.

[0032] The region between the first predetermined position r1 and the second predetermined position r2 of the inner wall surface 11 involved in the embodiment is as follows: Figure 4As shown, the piston is divided into three regions: region 1 R1, region 2 R2, and region 3 R3. Region 2 R2 corresponds to the area between the first predetermined position r1 and the upper end T of region 1 R1. Region 3 R3 corresponds to the area between the lower end B of region 1 R1 and the second predetermined position r2. Region 1 R1 is located below region 2 R2 and above region 3 R3. Regions 1 R1 and 2 R2 are continuous in the direction of piston 3 movement. Similarly, regions 1 R1 and 3 R3 are continuous in the direction of piston 3 movement.

[0033] Figure 5 This is a diagram used to illustrate the plurality of recesses involved in the first embodiment. Figure 5 This indicates the state of a portion of the first region R1 as viewed from the interior space side covered by the inner wall surface 11. The multiple recesses are, for example, pit shapes. However, this is not a limitation; the multiple recesses can be other shapes. Additionally, as... Figure 5 As shown, in the plurality of recesses formed on the inner wall surface 11 according to the first embodiment, the shapes of their respective openings are the same. The so-called same shape includes, for example, the opening shapes of the plurality of recesses being identical; and the differences in the opening areas of the plurality of recesses being small and similar. In the plurality of recesses, the opening shape of each is, for example, circular, and the diameter of the opening... For example, it can be 0.25mm. In addition, its opening shape can also be rectangular, rhomboid, or other shapes.

[0034] Here, the arrangement of the plurality of recesses formed on the inner wall surface 11 according to the first embodiment will be described. A plurality of rows of recesses are formed in the first region R1. These rows of recesses are formed staggered from the upper end T to the lower end B of the first region R1 in the direction of movement of the piston 3. Figure 5 As shown, in one example, multiple rows of recesses are arranged at constant intervals along the direction of movement.

[0035] In multiple rows of recesses, two or more recesses are arranged circumferentially. Two or more recesses in adjacent rows of recesses are arranged alternately in the direction of piston 3's movement. In one example, two or more recesses constituting the upper side of an adjacent row of recesses in the direction of movement are respectively positioned circumferentially offset from two or more recesses constituting the lower row of recesses relative to each other in the inner wall surface 11. In the first region R1, a row of recesses and a row of recesses adjacent to that row on the lower side in the direction of piston 3's movement are arranged alternately.

[0036] Furthermore, in adjacent rows of recesses along the movement direction of piston 3, the lower end of the upper row of recesses is located further down than the upper end of the lower row of recesses. Specifically, in adjacent rows of recesses along the movement direction of piston 3, the lower ends of two or more recesses constituting the upper row of recesses are located lower than the upper ends of two or more recesses constituting the lower row of recesses. Furthermore, the statement "the lower end of the upper row of recesses is located further down than the upper end of the lower row of recesses" can be replaced with the statement "they overlap in the axial direction". Additionally, when the area ratio of the multiple recesses is defined as a value representing the proportion of the total opening area of ​​the multiple recesses to the entire first region R1, in one example, the area ratio is 20% or more and 50% or less.

[0037] Next, the effects achieved by the structure of the first embodiment will be explained. Figure 6 This diagram illustrates the relationship between the friction between the piston 3 and the inner wall surface 11 and the velocity of the piston 3 with piston rings in two cases: one with piston rings according to the first embodiment and the other with piston rings according to the comparative example. Figure 6 In the diagram, the horizontal axis represents the velocity of piston 3 relative to the inner wall surface 11, and the vertical axis represents the change in friction, D, from the friction when a recess is formed on the inner wall surface 11 to the friction when no recess is formed on the inner wall surface 11. That is, when the change in friction D is positive, the friction increases when a recess is formed on the inner wall surface 11 compared to the state where no recess is formed. Conversely, when the change in friction D is negative, the friction decreases when a recess is formed on the inner wall surface 11 compared to the state where no recess is formed. In the following explanation, in... Figure 6 In this example, V1 is used to represent the velocity of piston 3 when oil ring 9 passes through the upper end T of region 1 R1. At this time, the velocity of piston 3 when top ring 7 passes through the lower end B of region 1 R1 is the same as or approximately the same as V1. Furthermore, not limited to this, in another example, V1 can also represent the velocity of piston 3 when piston rings other than oil ring 9 pass through the upper end T of region 1 R1. Additionally, in... Figure 6 In this context, V2 represents the maximum speed of piston 3 when it transitions from acceleration to deceleration. When the speed of piston 3 is above V1 and below V2, at least a portion of region S of piston 3 is opposite to the first region R1.

[0038] Here, the portion of the inner wall surface 11 opposite to the secondary ring 8 when the piston 3's velocity is V2 is defined as the third specified position r3. For example... Figure 4As shown, the first region R1 is defined as the region including at least the third specified position r3. Furthermore, not limited to this, the third specified position r3 can also be defined as a position where the distance from the first specified position r1 along the direction of movement of the piston 3 is the same as or approximately the same as the distance from the second specified position r2 along the direction of movement of the piston 3.

[0039] exist Figure 6 In the diagram, line segment s1, represented by a solid line, represents the change in velocity D relative to the piston 3, which has piston rings with a solid lubricating film covering its outer circumference. For example... Figure 6 As shown, when the speed of piston 3 is above V1 and below V2, the change in D is negative. Therefore, when piston 3 slides relative to the first region R1 with multiple recesses, the friction between piston 3 and inner wall surface 11 decreases.

[0040] Here, an internal combustion engine 1 having piston rings whose outer circumferential surface is not covered with a solid lubricating film is given as a comparative example of the structure according to the embodiment. The structure of the internal combustion engine 1 in the comparative example, except for the piston ring structure, is the same as that of the internal combustion engine 1 according to the embodiment. Figure 6 In the diagram, the dashed line segment s2 represents the change in velocity D of the piston 3 relative to the piston rings in the comparative example, which have no solid lubricating film covering their outer circumferential surface. Both the solid line segment s1 and the dashed line segment s2 represent the change in velocity D of the piston 3 relative to when the piston 3's velocity is above V1 and below V2.

[0041] like Figure 6 As shown, line segment s2 intersects the line D = 0. Figure 6 In the diagram, the velocity of piston 3 when line segment s2 intersects the line D = 0 is defined as V3. Velocity V3 is less than V2 and greater than V1.

[0042] Figure 7 This diagram illustrates the position of the inner wall surface 11, etc., based on the speed of the piston 3 with piston rings shown in the comparative example. Figure 7 As shown, region R1 is divided into region R4, region R5, and region R6. The boundaries of regions R4 and R5 are defined as boundary p. The boundaries of regions R4 and R6 are defined as boundary q. Region R4 is the area between boundary p and boundary q. Region R5 is the area between the upper end T of region R1 and boundary p. Region R6 is the area between boundary q and the lower end B of region R1. Furthermore, the distance between boundary p and boundary q along the axial direction of cylinder 2 is defined as d5. The third specified position r3 is located between boundary p and boundary q.

[0043] In the following explanation, Figure 7In this description, the portion of the oil ring 9 that is above the third predetermined position r3 among the two portions opposite to the piston 3 at a speed of V3 will be defined as boundary p. Similarly, the portion of the top ring 7 that is below the third predetermined position r3 among the two portions opposite to the piston 3 at a speed of V3 will be defined as boundary q.

[0044] Since the speed V1 is less than V3, therefore... Figure 7 As shown, the upper end T of the first region R1 is located on the upper side relative to the boundary p, and the lower end B of the first region R1 is located on the lower side relative to the boundary q. Therefore, the distance d2 along the axial direction of the cylinder 2 between the upper end T and the lower end B of the shaped recess of the inner wall surface 11 involved in the embodiment is greater than the distance d5 along the axial direction of the cylinder 2 between the boundary p and the boundary q. That is, the fourth region R4 is narrower than the first region.

[0045] When the speed of piston 3 is greater than V3 and less than or equal to V2, at least a portion of region S of piston 3 is opposite to region R4. Furthermore, when the speed of piston 3 is greater than V1 and less than V3, region S of piston 3 is entirely opposite to region R6 (either region R6 or region V1).

[0046] Furthermore, in another example, boundary p can also be the portion of one of the two portions of the piston rings (excluding the oil ring 9) opposite to the piston 3 at a speed of V3, located above the third predetermined position r3. Additionally, in another example, boundary q can also be the portion of one of the two portions of the piston rings (excluding the top ring 7) opposite to the piston 3 at a speed of V3, located below the third predetermined position r3.

[0047] like Figure 6 As shown, when the speed of piston 3 is greater than V3 and less than or equal to V2, the change D is negative. Therefore, when at least a portion of region S of piston 3 is opposite to region R4, the friction between piston 3 and inner wall surface 11 is reduced compared to the state where no recess is formed on inner wall surface 11.

[0048] On the other hand, when the speed of piston 3 is above V1 but less than V3, the change D is positive. Therefore, when region S of piston 3 is entirely opposite to region 5 R5 and region 6 R6, friction increases compared to the state where no recess is formed on the inner wall surface 11. In the comparative example, friction decreases when at least a portion of region S of piston 3 slides relative to region 4 R4, but increases when sliding relative to region 5 R5 and region 6 R6. Therefore, friction does not decrease in region 1 R1 as a whole.

[0049] In contrast, the outer circumferential surface of the piston ring in the embodiment is coated with a solid lubricating film. If a solid lubricating film is applied, the relationship between the speed of piston 3 movement and the friction between the region with the multiple recesses and the piston ring changes. Specifically, if a solid lubricating film is applied to the piston ring, the friction during solid contact between the region with the multiple recesses and the piston ring is reduced. In the first embodiment, during the reciprocating motion of piston 3, the multiple piston rings are respectively configured to maintain solid contact with the multiple recesses. Therefore, by changing the piston ring from one without a solid lubricating film to one with a solid lubricating film, the friction is reduced. Figure 6 In this context, the relationship between the friction between piston 3 and the inner wall surface 11 and the velocity of piston 3 becomes the line segment s1 after the line segment s2 has been moved parallel to the negative side. That is, when the piston rings are covered with a solid lubricating film, the friction is reduced compared to when the piston rings are not covered with a solid lubricating film.

[0050] Furthermore, when the speed of the piston 3, which has piston rings coated with a solid lubricating film, is V1 or higher and V2 or lower, the change D is negative, as shown by line segment s1. Therefore, in the inner wall surface 11 according to the embodiment, friction is reduced overall in the first region R1. Since the first region R1 is wider than the fourth region R4, the area where the recess can be formed can be expanded compared to the inner wall surface 11 according to the comparative example, and friction can also be reduced for the portion of the inner wall surface 11 opposite to the piston 3 when moving 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 and lower ends of the region where the first recess is formed can be set in the range of 55% or more and 85% or less of the distance along the axial direction of the cylinder 2 between the first predetermined position and the second predetermined position.

[0051] Furthermore, in the first embodiment, an example was given where multiple piston rings are always in solid contact with the inner wall surface 11 during the reciprocating motion of the piston 3. However, it is also conceivable that the multiple piston rings may contact the inner wall surface 11 in other ways that are not always in solid contact. In this case, the relationship between friction and the speed of the piston 3 is... Figure 6 The situation shown in the text is different. Figure 8 It is used to connect multiple piston rings to their corresponding... Figure 6 The figure illustrates the relationship between friction and the velocity of piston 3 when other contact methods, different from the example shown, contact the inner wall surface 11. Figure 8 In the diagram, the velocity of piston 3 when it is greater than V3 and less than V2 is defined as V4. The line segment s3, represented by the dashed line, and... Figure 6 The portion of line segment s2 shown in the diagram where the piston 3's velocity is above V1 and below V4 is the same. Line segment s4, represented by the solid line, is the same as... Figure 6The portion of line segment s2 shown in the figure where the piston 3's velocity is above V4 and below V2 is the same. The broken line s5, represented by the solid line, shows the relationship between the piston 3's velocity and friction when multiple piston rings are in contact with the inner wall surface 11 in other ways, within the range where the piston 3's velocity is above V1 and below V4. As shown by line segment s3 and broken line s5, when multiple piston rings are in contact with the inner wall surface 11 in other ways, the friction between the piston 3 and the inner wall surface 11 also decreases within the range where the piston 3's velocity is above V1 and below V4.

[0052] (Second Implementation)

[0053] The internal combustion engine 1 according to the second embodiment has a structure in which a type of recess is formed in at least one of the second region R2 and the third region R3, which is different from the recess formed in the first region R1. Figure 9 This is a schematic diagram showing the structure of the inner wall surface 11 of the cylinder 2 according to the second embodiment.

[0054] In the inner wall surface 11, various recesses are formed staggered in the direction of piston 3 movement, depending on the type. The effect of these various recesses on the relationship between friction between the inner wall surface 11 and piston 3 and the speed of piston 3 movement varies depending on the type. Figure 9 In the first region R1, represented by a dashed line extending obliquely from the lower left to the upper right, similar to the first embodiment, a recess is formed that reduces friction between the piston 3 and the inner wall surface 11 more than other recesses that can replace the recess formed in the first region R1 when the piston 3 moves at a speed of at least a reference value. Hereinafter, the recess formed in the first region R1 will be referred to as the first recess. Furthermore, in at least one of the second region R2 and the third region R3, represented by a dashed line extending obliquely from the lower right to the upper left, one or more recesses are formed that have a different effect on the relationship between friction and the piston 3's moving speed than the first recess. Hereinafter, one or more 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 recess that reduces friction more than any of the one or more second recesses when the piston 3 moves at a speed of at least a reference value. On the other hand, one or more second recesses are recesses that reduce friction when the piston 3 moves slower than the reference value compared to the first recess.

[0055] In one example, two types of recesses are formed in the inner wall surface 11. A first recess is formed in the first region R1, and a second type of recess is formed in the second region R2 and the third region R3. Thus, two types of recesses are formed in the entire region between the first predetermined position r1 and the second predetermined position r2. The reference value is, for example, the velocity of the piston 3 when it passes the upper end T or the lower end B of the first region R1.

[0056] The depth of the first recess is greater than the depth of the second recess. The depth of the first recess is, for example, 3.0 μm or more and 5.0 μm or less, and the depth of the second recess is, for example, 1.0 μm or more and 2.0 μm or less.

[0057] Furthermore, not limited to the above examples, it is also possible to have a structure in which the second recess is formed only in the second region R2, and no recess is formed in the third region R3. Alternatively, it is also possible to have a structure in which the second region R2 is not formed, and the recess is formed only in the third region R3.

[0058] Alternatively, two or more types of second recesses can be formed in the second region. In this case, in the second region, the further away from the first region R1, the more the type of recess that reduces friction when the piston 3 moves at a slower speed is formed. Similarly, in the third region, the further away from the first region R1, the more the type of recess that reduces friction when the piston 3 moves at a slower speed is formed.

[0059] According to the second embodiment described above, a first recess is formed in the first region R1. Based on this, at least one second recess is formed in at least one of the second region R2 and the third region R3, and its effect on the relationship between friction between the inner wall surface 11 and the piston ring and the speed of piston 3 movement differs from that of the first recess. Specifically, in the first region R1, a first recess is formed that reduces friction more effectively than any of the first or second recesses when piston 3 moves at a faster speed. Furthermore, in at least one of the second region R2 and the third region R3, a recess is formed that reduces friction more effectively than the first recess when piston 3 moves at a slower speed. Therefore, friction can be further reduced at the portion of the inner wall surface opposite the piston 3 when it moves at a low speed relative to the inner wall surface 11.

[0060] Furthermore, the present invention is not limited to the above-described embodiments, and various modifications can be made during the implementation phase without departing from its spirit. Additionally, the embodiments can be appropriately combined, in which case combined effects can be obtained. Moreover, the above embodiments include various inventions, and various inventions can be derived by selecting combinations from multiple disclosed technical features. For example, if the problem can be solved and the effect obtained even if several technical features are deleted from all the technical features shown in the embodiments, the structure with those technical features deleted can be refined into an invention.

Claims

1. An internal combustion engine, comprising: A cylinder having an inner wall surface with a plurality of first recesses; and Piston, which is disposed in an internal space covered by the inner wall surface, The piston has: Piston body; Piston rings, disposed on the outer peripheral surface of the piston body; and A solid lubricating film covers the outer circumferential surface of the piston ring. The solid lubricating film causes the piston's movement speed to change relative to the friction between the region in the inner wall surface where the plurality of first recesses are formed and the piston rings, compared to a structure not covered by the solid lubricating film.

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

3. The internal combustion engine according to claim 1, wherein, The inner wall bread includes a first region having the plurality of first recesses, a second region located on the upper side relative to the upper end of the first region, and a third region located on the lower side relative to the lower end of the first region. One or more second recesses are formed in at least one of the second and third regions, and the effect of the second recess on the relationship between the friction between the inner wall surface and the piston ring and the speed of piston movement is different from that of the first recess.

4. The internal combustion engine according to claim 3, wherein, The plurality of first recesses are recesses that reduce the piston movement speed by a reference value or higher than any of the one or more second recesses, and the one or more second recesses are recesses that reduce the piston movement speed by a reference value or lower than the first recesses.

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

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