Cylinder, internal combustion engine, and vehicle

Abstract

A cylinder, an internal combustion engine, and a vehicle, the cylinder according to the embodiments has an inner wall surface formed with a plurality of kinds of recesses staggered according to each kind in a moving direction of a piston. Among the plurality of kinds of recesses, an influence on a relationship between the inner wall surface and friction between the inner wall surface and the piston with respect to a speed of the piston movement differs according to each kind. In the inner wall surface, according to the plurality of kinds of recesses, at least one of a plurality of recess rows is formed staggered with respect to other recess rows in the moving direction. Among the plurality of recess rows, two or more recesses of one kind are respectively arranged in a circumferential direction. In the recess rows adjacent in the moving direction, two or more recesses of the upper recess row and two or more recesses of the lower recess row are alternately arranged along the circumferential direction, and a lower end of the upper recess row is located at a position more on a lower side than an upper end of the lower recess row.

Description

Technical Field

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

[0002] Currently, 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. If multiple recesses are formed on the inner wall surface, the reduction in friction increases at the portion of the inner wall surface opposite the piston moving at high speed relative to the inner wall surface (hereinafter referred to as the high-speed region). 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 in the high-speed region is greater compared to forming other types of recesses on the inner wall surface. As mentioned above, there are types of recesses that are advantageous in the high-speed region (e.g., Japanese Patent Application Laid-Open No. 2007-46660).

[0003] When the range of recesses that are advantageous in the high-speed region is expanded to the portion of the inner wall surface opposite the piston when it moves at low speed relative to the inner wall surface (hereinafter referred to as the low-speed region), friction may not be reduced compared to the case where multiple recesses are not formed on the inner wall surface. Therefore, it is required to increase the amount of friction reduction in the high-speed region and also reduce friction in the low-speed region. Summary of the Invention

[0004] The present invention was proposed in view of the above-mentioned problems, and its purpose is to increase the reduction of friction in the high-speed region and also reduce friction in the low-speed region.

[0005] The cylinder according to the embodiment has an inner wall surface in which multiple types of recesses are formed staggered in the piston's direction of movement, according to each type. The influence of each type of recess on the relationship between friction between the inner wall surface and the piston and the piston's speed of movement varies depending on the type. In the inner wall surface, at least one of the multiple recess rows is staggered relative to other recess rows in the direction of movement, according to the multiple types of recesses. In each of the multiple recess rows, two or more recesses of one type are arranged circumferentially. In adjacent recess rows in the direction of movement, two or more recesses in the upper recess row and two or more recesses in the lower recess row are arranged alternately circumferentially, and the lower end of the upper recess row is located further down than the upper end of the lower recess row.

[0006] According to the present invention, the amount of friction reduction in the high-speed region can be increased, and friction can also be reduced in the low-speed region. Attached Figure Description

[0007] Figure 1This is a schematic diagram illustrating an example of the structure of a vehicle involved in the implementation method.

[0008] Figure 2 This is a schematic diagram illustrating an example of the structure of an internal combustion engine involved in the implementation.

[0009] Figure 3 This is a cross-sectional view schematically showing an example of the outer peripheral surface of the piston and the structure near it according to the embodiment.

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

[0011] Figure 5 This is a diagram used to illustrate the various recesses involved in the implementation method.

[0012] Figure 6 This is a diagram used to illustrate the area ratio of the multiple recesses involved in the implementation method.

[0013] Figure 7 This diagram illustrates the relationship between the friction between the piston and the inner wall surface and the piston speed in two comparative cases: one where a first recess is formed integrally in the shaped area of ​​the cylinder's inner wall, and the other where a second type of recess is formed integrally in the shaped area.

[0014] Figure 8 This diagram illustrates the relationship between piston speed and friction when a first recess is formed in the first region of the inner wall surface of the cylinder according to the embodiment, and a second recess of a certain type is formed in the second and third regions. Detailed Implementation

[0015] (Implementation Method)

[0016] Figure 1 This is a schematic diagram illustrating an example of the structure of the vehicle 100 according to the embodiment. (See diagram for example.) Figure 1 As shown, the vehicle 100 has an internal combustion engine 1, a transmission 30, and at least one wheel 40. If the vehicle 100 drives the internal combustion engine 1, driving force is transmitted to at least one wheel 40 via the transmission 30.

[0017] Figure 2 This is a schematic diagram illustrating an example of the structure of the internal combustion engine 1 according to the 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 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 piston 3 includes a piston body 5 and multiple piston rings. The internal combustion engine 1 according to the embodiment is, for example, a four-stroke internal combustion engine, whose one cycle consists of four processes: intake, compression, expansion, and exhaust. The internal combustion engine 1 according to the embodiment is, for example, a diesel engine. In this case, the multiple piston rings according to the embodiment include, for example, a top ring 7, a secondary ring 8, and an oil ring 9. Hereinafter, the portion between the intake valve side edge of the top ring 7 of the piston 3 and the crankshaft side edge of the oil ring 9 is referred to as region S.

[0018] Cylinder 2 extends along central axis A1 and is formed into a cylindrical shape or the like. 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.

[0019] 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, in parallel with the rotation of the crank arm, which rotates around the crankshaft. The axial direction of the cylinder 2 is along the direction of movement of the piston 3.

[0020] 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.

[0021] 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.

[0022] In piston 3, for example, starting 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 piston 3 is the end face on the intake valve side, facing the intake valve side. The piston skirt 21 in piston 3 forms the end face on the crankshaft side, and the crankshaft side end face of piston skirt 21 faces the crankshaft side.

[0023] A top ring 7 is configured in the top ring groove 14. A secondary ring 8 is configured in the secondary ring groove 17. An oil ring 9 is configured in the oil ring groove 19.

[0024] In this embodiment, the piston 3 used in a diesel engine within the internal combustion engine 1 is described as an example, but it is not limited to this. The piston 3 is not limited to use in a diesel engine, but can also be used in other internal combustion engines 1 such as a gasoline engine.

[0025] Figure 4 This is a schematic diagram showing the structure of the inner wall surface 11 of the cylinder 2 according to the embodiment. The inner wall surface 11 extends along the axial and circumferential directions of the cylinder 2. Figure 4 The diagram shows the state of a portion of the inner wall surface 11 of the cylinder 2 when the cylinder 2 is unfolded and viewed from the side of the internal space covered by the inner wall surface 11. The direction along the circumference of the cylinder 2 is defined as the X-axis direction, and the axial 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 and is referred to as the upper side. Conversely, the crankshaft side is defined as the negative direction and is referred to as the lower side. The portion o of the inner wall surface 11 opposite the oil ring 9 when the piston 3 is at top dead center is located on the upper side, relative to the portion t opposite the top ring 7 when the piston 3 is at bottom dead center.

[0026] In the inner wall surface 11 involved in the implementation method, in Figure 4 The defined shaped region R shown forms multiple recesses. Furthermore, the phrase "forming multiple recesses on the inner wall surface 11" can be replaced with the phrase "texturing the inner wall surface 11". In this embodiment, the upper end of the textured shaped region R is the same position as the portion o in the inner wall surface 11 that the oil ring 9 faces when the piston 3 is at top dead center. The lower end of the shaped region R is the same position as the portion t in the inner wall surface 11 that the top ring 7 faces when the piston 3 is at bottom dead center. However, it is not limited to this; the upper end of the shaped region R may, for example, be a position below and near portion o, and the lower end of the shaped region R may, for example, be a position above and near portion t. Alternatively, it may be a structure with a smaller area than the shaped region R in the inner wall surface 11 described in this embodiment. Furthermore, in this embodiment, the multiple recesses in the shaped region R are not limited to a structure formed throughout the entire circumference of the inner wall surface 11. In one example, multiple recesses in the shaped region R may also be formed without covering the entire circumference of the inner wall surface 11.

[0027] like Figure 4 As shown, the shaping region R involved in the implementation is, for example, divided into three regions: a first region R1, a second region R2, and a third region R3. Figure 4In this diagram, a virtual boundary p is defined between part o and part t. Additionally, a virtual boundary q is defined between boundary p and part t. Region 1 R1 corresponds to the region between boundary p and boundary q. Region 2 R2 corresponds to the region between part o and boundary p. Region 3 R3 corresponds to the region between boundary q and part t. Region 1 R1 is the region located below Region 2 R2 and above Region 3 R3. Regions 1 R1 and 2 R2 are continuous in the direction of piston 3's movement. Furthermore, Regions 1 R1 and 3 R3 are continuous in the direction of piston 3's movement. However, Regions 1 R1 and 2 R2 are not necessarily continuous in the direction of piston 3's movement. In this case, a recess may not be formed in the region between the upper end of Region 1 R1 and the lower end of Region 2 R2. Similarly, Regions 1 R1 and 3 R3 are not necessarily continuous in the direction of piston 3's movement. In this case, a recess may not be formed in the region between the lower end of Region 1 R1 and the upper end of Region 2 R2.

[0028] When at least a portion of region S of piston 3 is opposite to region R1, piston 3 moves at a higher speed than when region S as a whole is opposite to region R2 and region R3. Therefore, region R1 is also referred to as the high-speed region. In addition, region R1 is also referred to as the cylinder bore center. On the other hand, region R2 or region R3 is also referred to as the low-speed region.

[0029] Figure 5 This is a diagram used to illustrate the various recesses involved in the implementation method. Figure 5 This shows a portion of the shaped region R 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 also be other shapes. Additionally, as... Figure 5 As shown, in the plurality of recesses formed on the inner wall surface 11 according to the embodiment, the shapes of their respective openings are identical. The identical shape includes, for example, the opening shapes of the recesses being the same; or the area difference between the recesses being small and the recesses being similar to each other. In the plurality of recesses, the shape of each opening 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.

[0030] Here, the arrangement of the plurality of recesses formed on the inner wall surface 11 according to the embodiment will be described. A plurality of recess rows are formed in the shaping region R. The plurality of recess rows are formed offset from each other in the moving direction of the piston 3, extending from the upper end to the lower end of the shaping region R. In other words, at least one of the plurality of recess rows is formed offset from the other recess rows in the moving direction of the piston 3. Figure 5As shown, in one example, multiple rows of recesses are arranged at a constant spacing along the direction of movement of piston 3.

[0031] In a plurality of recess rows, two or more recesses of one type are arranged circumferentially. Hereinafter, one of the recess rows is defined as recess row α. However, recess row α is defined as any recess row that is not the uppermost, lowermost, or the recess row adjacent above the lowermost recess row. Furthermore, the recess row adjacent above recess row α is defined as recess row β. Furthermore, the recess row adjacent below recess row α is defined as recess row γ. Furthermore, the recess row adjacent below recess row γ is defined as recess row δ.

[0032] In the direction of piston 3 movement, two or more recesses in adjacent rows of recesses are arranged alternately. Specifically, in adjacent rows of recesses in the direction of piston 3 movement, two or more recesses in the upper row and two or more recesses in the lower row are arranged alternately circumferentially. Figure 5 As shown, two or more recesses constituting recess row α are each located circumferentially offset from two or more recesses constituting recess row β adjacent to recess row α on the upper side. Furthermore, two or more recesses constituting recess row α are each located circumferentially offset from two or more recesses constituting recess row γ adjacent to recess row α on the lower side. The two or more recesses constituting recess row β adjacent to recess row α on the upper side are each located at the same or approximately the same position circumferentially as one of the corresponding recesses in the two or more recesses constituting recess row γ adjacent to recess row α on the lower side. That is, the two or more recesses constituting recess row β correspond one-to-one with the recesses in the two or more recesses constituting recess row γ that are located at the same or approximately the same position circumferentially on the inner wall surface 11. Here, in Figure 5 In this arrangement, when a straight line passing through the center of one of the two or more recesses constituting the recess row β, namely recess β1, and along the direction of movement of the piston 3 is defined as l1, the straight line l1 passes through the center of recess γ1 in the recess row γ. Furthermore, a recess adjacent to recess β1 and offset from recess β1 in the circumferential direction is called β2. A straight line passing through the center of recess β2 and along the direction of movement of the piston 3 is defined as l2. Thereafter, the side where recess β2 is located relative to recess β1 is called the first side D1. At this time, the straight line l2 passes through the center of recess γ2, which is adjacent to recess γ1 and offset from recess γ1 in the first side D1. In one example, the circumferential distance d1 between the straight lines l1 and l2 along the inner wall surface 11 is 0.744 mm. In one example, in the recess row, two or more recesses adjacent in the circumferential direction are arranged at a constant circumferential spacing.

[0033] Furthermore, two or more recesses forming the recess row α adjacent to the recess row γ on the upper side are each located at the same or approximately the same position in the circumferential direction as one corresponding recess in one or more recesses forming the recess row δ adjacent to the recess row γ on the lower side. That is, the two or more recesses forming the recess row α correspond one-to-one with the recesses in the two or more recesses forming the recess row δ that are located at the same or approximately the same position in the circumferential direction on the inner wall surface 11. Figure 5 In this model, the recess α1 is defined as the recess that is located on the first side D1 relative to recess β1 and on the second side D2 opposite to the first side D1 relative to recess β2 among two or more recesses constituting recess row α. Furthermore, when a straight line l3 is defined as the line passing through the center of recess α1 along the direction of movement of piston 3, the straight line l3 passes through the center of one of the two or more recesses constituting recess row δ, namely recess δ1. In one example, recess α1 is located at a position offset from recess β1 towards the first side D1 by half a distance, and also at a position offset from recess β2 towards the second side D2 by half a distance. Therefore, in one example, the circumferential distance d2 between straight lines l1 and l3 is half the length of distance d1, which is 0.372 mm. As described above, in the shaping region R, concave columns such as β or γ, which include the concave section through which the straight line l1 passes, and concave columns such as α or δ, which include the concave section through which the straight line l2 passes, are arranged alternately.

[0034] Furthermore, in adjacent rows of recesses along the moving 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. In other words, in adjacent rows of recesses along the moving direction of piston 3, the lower ends of two or more recesses constituting the upper row are located lower than the upper ends of two or more recesses constituting the lower row of recesses. Moreover, 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 each other axially." Specifically, as follows... Figure 5 As shown, in the adjacent rows of recesses in the moving direction of piston 3, the lower end βu of recess β1 constituting the upper row of recesses β is located on the lower side relative to the upper end αt of recess α1 constituting the lower row of recesses α.

[0035] exist Figure 5In this design, a straight line passing through the center of recess β1 and along the circumference of the inner wall surface 11 is defined as l4, and a straight line passing through the center of recess α1 and along the circumference of the inner wall surface 11 is defined as l5. Additionally, a straight line passing through the center of recess γ1 and along the circumference of the inner wall surface 11 is defined as l6. In this case, the distance d3 between straight lines l4 and l5 along the moving direction of the piston 3 is half the length of the distance d4 between straight lines l4 and l6 along the moving direction of the piston 3. For example, distance d3 is 0.215 mm, and distance d4 is 0.430 mm.

[0036] Furthermore, since the lower end of the upper recess column is located further down than the upper end of the lower recess column in the moving direction of piston 3, the boundaries p and q are not straight lines but curves.

[0037] Next, the area ratio of the multiple recesses will be explained. The area ratio is a value that represents the proportion of the total opening area of ​​the multiple recesses to the entire shaped region R. Figure 6 This is a diagram used to illustrate the area ratio of the multiple recesses involved in the embodiment. Specifically, in Figure 6 In the middle, as an example, a magnified view is shown. Figure 5 Part of the multiple recesses shown, namely recess β1, recess α1, and the vicinity of these recesses. Figure 6 The code defines a rectangular region R4. Region R4 is enclosed by four straight lines l1, l3, l4, and l5. The area ratio of the multiple recesses is defined as the ratio of the area occupied by the openings of the recesses within region R4 to the area of ​​region R4. In one example, the area ratio is greater than 20% and less than 50%.

[0038] In the inner wall surface 11, multiple types of recesses are formed staggered in the moving direction of the piston 3 according to each type. The influence of these recesses on the relationship between friction between the inner wall surface 11 and the piston 3 and the speed of piston 3 movement varies depending on the type. In the inner wall surface 11 according to the embodiment, for example, two types of recesses are formed. Hereinafter, the recess that minimizes friction to the greatest extent when the piston 3 moves at a first speed is referred to as the first recess. Furthermore, the recess that minimizes friction even more than the first recess when the piston 3 moves at a second speed slower than the first speed is referred to as the second recess. The second recess may have only one type or multiple types. The first speed is a speed faster than a reference value, and the second speed is a speed less than the reference value. That is, the first recess is the type that minimizes friction when the piston 3 moves at a speed faster than a reference value. The second recess is the type that minimizes friction even more than the first recess when the piston 3 moves at a speed slower than a reference value. The reference values ​​are specified based on the relationship between the speed of piston 3 and the friction between piston 3 and the inner wall surface 11 with the first recess, and the relationship between the speed of piston 3 and the friction between piston 3 and the inner wall surface 11 with the second recess.

[0039] Figure 7 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, in two comparative cases: one where a first recess is formed integrally in the shaping region R of the inner wall surface 11, and the other where a second type of recess is formed integrally in the shaping region R. Figure 7 In the diagram, the horizontal axis represents the velocity of the piston 3 relative to the inner wall surface 11, and the vertical axis represents the change in friction, D, between the friction when a recess is formed on the inner wall surface 11 and the friction when a recess is not 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 when a recess is not 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 when a recess is not formed. Figure 7 In this context, V1 represents the velocity of piston 3 when oil ring 9 passes through the upper end of shaping region R. Furthermore, the velocity of piston 3 when top ring 7 passes through the lower end of shaping region R is the same as or approximately the same as V1. Additionally, in... Figure 7 In this context, V2 represents the maximum speed of piston 3 when it transitions from acceleration to deceleration. Here, the portion of the inner wall surface 11 opposite to the secondary ring 8 when the piston 3's speed is V2 is defined as the specified position r. The first region R1 is defined as the region including at least the specified position r. In one example, the distance from part o to the specified position r along the direction of piston 3 movement is the same as or approximately the same as the distance from part t to the specified position r along the direction of piston 3 movement.

[0040] exist Figure 7 In the diagram, the solid line segment s1 represents the velocity change D relative to the piston 3 in the first comparative example where a first concave portion is formed throughout the shaped region R. Conversely, the dashed line segment s2 represents the velocity change D relative to the piston 3 in the second comparative example where a second type of concave portion is formed throughout the shaped region R. For example... Figure 7 As shown, line segment s1 intersects line segment s2. Figure 7 In this example, the velocity of piston 3 when line segment s1 intersects line segment s2 is set as V3. V3 is an example of a reference value.

[0041] In the following description of the embodiments, the portion of the two parts of the oil ring 9 that is above the predetermined position r when the piston 3 is at a speed of V3 will be described as the boundary p of the first region R1 and the second region R2. Similarly, the portion of the two parts of the top ring 7 that is below the predetermined position r when the piston 3 is at a speed of V3 will be described as the boundary q of the first region R1 and the third region R3. When the piston 3's speed is V1 or higher but less than V3, the entire region S of the piston 3 is opposite to either the second region R2 or the third region R3. Furthermore, when the piston 3's speed is V3 or higher but less than V2, at least a portion of the region S of the piston 3 is opposite to the first region R1.

[0042] In the inner wall surface 11 of the embodiment, a first recess is formed in a first region R1. Therefore, at least a portion of region S of the piston 3 slides facing the first region R1 where the first recess is formed when the speed of the piston 3 is greater than V3 and less than or equal to V2. The first speed is, for example, a speed greater than V3 and less than or equal to V2.

[0043] In one embodiment, a second recess of one type is formed in the second region R2 and the third region R3. Therefore, the entire region S of the piston 3 slides against the second region R2 or the third region R3 where the second recess is formed when the piston 3's speed is above V1 and below V3. The second speed is, for example, a speed above V1 and below V3. The second recess is formed at a location with a greater offset relative to a predetermined position r compared to the location where the first recess is formed. Furthermore, in another example, the boundary p may be the upper part of one of the two parts opposite the piston rings other than the oil ring 9 when the piston 3's speed is V3, relative to the predetermined position r. Additionally, in another example, the boundary q may be the lower part of one of the two parts opposite the piston rings other than the top ring 7 when the piston 3's speed is V3, relative to the predetermined position r.

[0044] like Figure 7As shown, when the speed of piston 3 is above V1 and below V3, the change in friction D with the second recess formed is smaller than the change in friction D with the first recess formed on the inner wall surface 11. Therefore, compared to the first recess, the second recess has a greater friction reduction effect when piston 3 moves at a second speed, which is advantageous in the low-speed region. On the other hand, when the speed of piston 3 is above V3 and below V2, the change in friction D with the first recess formed is smaller than the change in friction D with the second recess formed on the inner wall surface 11. Therefore, compared to the second recess, the first recess has a greater friction reduction effect when piston 3 moves at a first speed, which is advantageous in the high-speed region.

[0045] 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. The depth of the second recess is, for example, 1.0 μm or more and 2.0 μm or less.

[0046] Figure 8 This diagram illustrates the relationship between the speed and friction of the piston 3 when a first recess is formed in the first region R1 of the inner wall surface 11 according to the embodiment, and a second recess of one type is formed in the second region R2 and the third region R3. Figure 8 In the middle, the horizontal and vertical axes are... Figure 7 Same. Figure 8 In the diagram, the broken line s3, represented by a solid line, represents the change in velocity D relative to the piston 3 sliding along the inner wall surface 11, according to the embodiment. On the other hand, in... Figure 8 In the diagram, the dashed line segment s4 represents the change in velocity D of the piston 3 relative to the inner wall surface 11 where the first recess is formed in the second region R2 and the third region R3. Similarly, the dashed line segment s5 represents the change in velocity D of the piston 3 relative to the inner wall surface 11 where the second recess is formed in the first region R1.

[0047] When the speed of piston 3 is greater than V1 but less than V3, piston 3 slides in the second region R2 or the third region R3 of the second recess, where the friction reduction effect is greater due to the slower movement speed of piston 3. Therefore, in Figure 8As shown by line s3 and line segment s4, compared to the case where the first recess is formed in the second region R2 and the third region R3, friction can be reduced. On the other hand, when the speed of piston 3 is above V3 and below V2, piston 3 slides in the first region R1 where the first recess, which has a greater friction-reducing effect when piston 3 moves at a faster speed, is formed. Therefore, as shown by line s3 and line segment s5, compared to the case where the second recess is formed in the first region R1, friction can be reduced. As described above, according to the above embodiment, compared to the first comparative example and the second comparative example, the amount of friction reduction in the high-speed region can be increased, and friction is also reduced in the low-speed region. Furthermore, since the friction between piston ring and inner wall surface 11 is reduced, and the friction between piston body 5 and inner wall surface 11 is also reduced, the friction between piston 3 and inner wall surface 11 is also reduced.

[0048] Furthermore, in the inner wall surface 11 described in the embodiment, an example is given of a structure in which a first recess is formed in a first region R1 and a second recess is formed in a second region R2 and a third region R3, but this is not a limitation. For example, it is also possible for a structure in which the second recess is not formed in the third region R3 but only in the second region R2. Alternatively, it is also possible for a structure in which the second recess is not formed in the second region R2 but only in the third region R3.

[0049] Furthermore, in the embodiment involving the inner wall surface 11, an example of a structure in which only one type of second recess is formed in the second region R2 and the third region R3 has been described, but it is not limited to this. Multiple types of second recesses may also be formed in at least one of the second region R2 and the third region R3. Specifically, when multiple types of second recesses are formed in the region between the upper end of the first region R1 and the part o, i.e., the second region R2, the recesses in the second region R2 that reduce friction the further away from the first region R1 are formed, the more friction is reduced when the piston 3 moves at the second speed. Similarly, when multiple types of second recesses are formed in the region between the part t and the lower end of the first region R1, i.e., the third region R3, the recesses in the third region R3 that reduce friction the further away from the first region R1 are formed, the more friction is reduced when the piston 3 moves at the second speed. The positions of the boundaries p and q vary depending on the combination of the types of recesses formed on the inner wall surface 11.

[0050] Furthermore, the depth of the recess that minimizes friction to the greatest extent when the piston moves at the first speed is greater than the depth of the recess that reduces friction when the piston moves at the first speed.

[0051] According to the above embodiment, the cylinder 2 has an inner wall surface 11 with multiple types of recesses formed staggered in the moving direction of the piston 3, depending on the type. Among the multiple types of recesses, the effect on the relationship between the friction between the inner wall surface 11 and the piston 3 and the speed of piston 3 movement varies depending on the type. That is, recesses with a greater friction reduction effect when the piston 3 moves at a faster speed are formed in the high-speed region of the inner wall surface 11, and recesses with a greater friction reduction effect when the piston 3 moves at a slower speed are formed in the low-speed region of the inner wall surface 11. Therefore, the amount of friction reduction in the high-speed region can be increased, and friction can also be reduced in the low-speed region.

[0052] Furthermore, according to the above embodiment, a first recess, which is one of multiple types of recesses, is formed in the first region R1 to minimize friction when the piston moves at a high speed. Compared to the first recess, one or more second recesses of a certain type formed in a region other than the first region on the inner wall surface 11 further reduce friction when the piston moves at a low speed. This further increases the amount of friction reduction in the high-speed region and also further reduces friction in the low-speed region. Moreover, when multiple types of second recesses are provided, the type of second recess formed further away from the first region R1 reduces friction more significantly when the piston moves at a low speed. This further increases the amount of friction reduction in the high-speed region and also further reduces friction in the low-speed region.

[0053] Furthermore, according to the embodiment, based on the aforementioned effects, it is also possible to provide an internal combustion engine 1 having a cylinder 2, which has an inner wall surface 11 that can increase the reduction of friction in the high-speed region and also reduce friction in the low-speed region. Moreover, it is possible to provide a vehicle 100 having the aforementioned internal combustion engine 1.

[0054] 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. A cylinder having an inner wall surface having a plurality of recesses formed in a staggered manner according to each type in the direction of piston movement. In each of the various types of recesses, the effect on the relationship between the friction between the inner wall surface and the piston and the speed of piston movement varies depending on the type. In the inner wall surface, according to the plurality of types of recesses, at least one of the plurality of recess rows is formed offset relative to the other recess rows in the direction of movement. In each of the plurality of recessed rows, there are two or more recesses of one type arranged circumferentially. In adjacent rows of recesses in the direction of movement, two or more recesses in the upper row and two or more recesses in the lower row are arranged alternately along the circumference, and the lower end of the upper row of recesses is located further down than the upper end of the lower row of recesses.

2. The cylinder according to claim 1, wherein, In the first region of the inner wall surface, a first recess of the type of the plurality of recesses is formed, which minimizes the friction between the inner wall surface and the piston to the greatest extent when the piston moves at a first speed. In the regions of the inner wall surface other than the first region, a second recess of one or more types is formed, which further reduces the friction compared to the first recess when the piston moves at a second speed slower than the first speed.

3. The cylinder according to claim 2, wherein, In the regions of the inner wall surface other than the first region, multiple types of second recesses are formed as one or more types of second recesses. Among the various types of second recesses, the type that is formed further away from the first region reduces friction as the piston moves at the second speed.

4. The cylinder according to claim 2, wherein, The depth of the first recess is greater than the depth of the second recess of one or more types.

5. The cylinder according to claim 1, wherein, The openings of the various types of recesses have the same shape.

6. The cylinder according to claim 5, wherein, The openings of the various types of recesses are circular in shape.

7. The cylinder according to claim 1, wherein, The area ratio of the various types of recesses is 20% or more and 50% or less.

8. An internal combustion engine, comprising: The cylinder according to any one of claims 1 to 7; and The piston is disposed in an internal space covered by the inner wall surface.

9. A vehicle having the internal combustion engine of claim 8.

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