Cylinders, internal combustion engines, and vehicles

Abstract

The goal is to significantly reduce friction at high speeds while also reducing friction at low speeds. [Solution] The cylinder according to the embodiment has an inner wall surface in which multiple types of recesses are formed, offset by type in the direction of piston movement. Each type of recess has a different effect on the relationship between the friction between the inner wall surface and the piston with respect to the speed at which the piston moves. On the inner wall surface, at least one of the multiple recess rows is formed offset from other recess rows in the direction of movement by the multiple types of recesses. In each of the multiple recess rows, two or more of one type of recess are arranged in the circumferential direction. 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 along the circumferential direction, and the lower end of the upper recess row is located below the upper end of the lower recess row.

Description

Technical Field

[0004] , ,

[0005] ,

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

Background Art

[0002] Conventionally, it is known that the friction between a piston that moves relative 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). When a plurality of recesses are formed on the inner wall surface, the amount of friction reduction becomes large at a portion of the inner wall surface that faces the piston when moving at high speed relative to the inner wall surface (hereinafter referred to as the high-speed region). The amount of friction reduction varies depending on the type of recesses, such as the depth and shape of the recesses. When a specific type of recess is formed, the amount of friction reduction in the high-speed region is greater than when other types of recesses are formed on the inner wall surface. Thus, there are types of recesses that are advantageous in the high-speed region.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the range in which recesses having a specification advantageous in the high-speed region are formed is extended to a portion of the inner wall surface that faces the piston when moving at low speed relative to the inner wall surface (hereinafter referred to as the low-speed region), the friction may not be reduced as compared with the case where no plurality of recesses are formed on the inner wall surface. For this reason, while increasing the amount of friction reduction in the high-speed region, it is required to reduce the friction even in the low-speed region.

[0005] The present disclosure has been made in view of the above problems, and an object thereof is to increase the amount of friction reduction in the high-speed region and reduce the friction even in the low-speed region. <0000[Means for solving the problem]

[0006] The cylinder according to this embodiment has an inner wall surface in which multiple types of recesses are formed, offset by type in the direction of piston movement. Each type of recess has a different effect on the relationship between the friction between the inner wall surface and the piston with respect to the speed at which the piston moves. On the inner wall surface, at least one of the multiple recess rows is formed offset in the direction of movement relative to the other recess rows. In each of the multiple recess rows, two or more of one type of recess are arranged in the circumferential direction. 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 along the circumferential direction, and the lower end of the upper recess row is located below the upper end of the lower recess row. [Effects of the Invention]

[0007] According to this disclosure, it is possible to reduce friction at low speeds while significantly reducing friction at high speeds. [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 this embodiment. [Figure 2] Figure 2 is a schematic diagram showing an example of the configuration of an internal combustion engine according to this 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 embodiment. [Figure 4] Figure 4 is a schematic diagram showing the configuration of the inner wall surface of the cylinder according to the embodiment. [Figure 5] Figure 5 is a diagram illustrating a plurality of recesses according to the embodiment. [Figure 6] Figure 6 is a diagram illustrating the area ratio of the multiple recesses according to the embodiment. [Figure 7]Figure 7 illustrates the relationship between piston speed and friction between the piston and the inner wall surface in two comparative examples: one in which a first recess is formed over the entire application area on the inner wall surface of the cylinder, and another in which a second recess of one type is formed over the entire application area. [Figure 8] Figure 8 is a diagram illustrating the relationship between piston speed and friction when a first recess is formed in a first region on the inner wall surface of the cylinder according to the embodiment, and a second recess of one type is formed in the second and third regions. [Modes for carrying out the invention]

[0009] (Embodiment) Figure 1 is a schematic diagram showing an example of the configuration of a vehicle 100 according to an 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 embodiment. 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 3 according to the embodiment. As shown in Figures 2 and 3, the internal combustion engine 1 comprises 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 comprises a piston body 5 and a plurality of piston rings. The internal combustion engine 1 according to the 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 embodiment is, for example, a diesel engine. In this case, the plurality of piston rings according to the embodiment include, for example, a top ring 7, a second ring 8, and an oil ring 9. Hereafter, 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 will be referred to as region S.

[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 central axis A1 of cylinder 2 will be referred to as the circumferential direction.

[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] In the piston 3, 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 in the piston 3 and faces the intake valve side. The piston skirt 21 forms an end surface on the crankshaft side in the piston 3, and the end surface on the crankshaft side formed by the piston skirt 21 faces the crankshaft side.

[0016] The top ring 7 is disposed in the top ring groove 14. The second ring 8 is disposed in the second ring groove 17. The oil ring 9 is disposed in the oil ring groove 19.

[0017] In the present 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 is not limited to being used in a diesel engine, and may be used in other internal combustion engines 1 such as a gasoline engine.

[0018] FIG. 4 is a schematic view showing the configuration of the inner wall surface 11 of the cylinder 2 according to the embodiment. The inner wall surface 11 extends along the axial direction and the circumferential direction of the cylinder 2. In FIG. 4, the cylinder 2 is developed, and a state in which 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 is shown. The direction along the circumferential direction 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 the positive direction of the Y-axis direction and is referred to as the upper side. Also, in the Y-axis direction, the crankshaft side is the negative direction of the Y-axis direction and is referred to as the lower side. Among the inner wall surface 11, a portion o that faces the oil ring 9 when the piston 3 is at the top dead center is located above a portion t that faces the top ring 7 when the piston 3 is at the bottom dead center.

[0019] In the inner wall surface 11 according to the embodiment, a plurality of recesses are formed in a predetermined application region R shown in FIG. 4. Note that the phrase "forming a plurality of recesses in the inner wall surface 11" may be rephrased as the phrase "applying texturing to the inner wall surface 11". In the embodiment, the upper end of the application region R to which texturing is applied is at the same position as the portion o facing the oil ring 9 when the piston 3 is at the top dead center in the inner wall surface 11. Also, the lower end of the application region R is at the same position as the portion t facing the top ring 7 when the piston 3 is at the bottom dead center in the inner wall surface 11. Note that it is not limited to this, and the upper end of the application region R may be, for example, a position below and near the portion o, and the lower end of the application region R may be, for example, a position above and near the portion t. Also, a configuration that is a range narrower than the application region R on the inner wall surface 11 according to the embodiment may be used. Also, in the embodiment, in the application region R, the plurality of recesses are not limited to being formed over the entire circumference of the inner wall surface 11. In one example, in the application region R, the plurality of recesses may not be formed over the entire circumference of the inner wall surface 11.

[0020] The designated region R according to the embodiment is divided into three regions, for example, a first region R1, a second region R2, and a third region R3, as shown in Figure 4. In Figure 4, a virtual boundary p is defined between part o and part t. A virtual boundary q is defined between boundary p and part t. The first region R1 corresponds to the region between boundary p and boundary q. The second region R2 corresponds to the region between part o and boundary p. The third region R3 corresponds to the region between boundary q and part t. 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. Note that the first region R1 and the second region R2 do not necessarily have to be continuous in the direction of movement of the piston 3. In this case, a recess does not need to be formed in the region between the upper end of the first region R1 and the lower end of the second region R2. Also, the first region R1 and the third region R3 do not necessarily have to be continuous in the direction of movement of the piston 3. In this case, a recess does not need to be formed in the region between the lower end of the first region R1 and the upper end of the second region R2.

[0021] When at least a portion of the region S of the piston 3 faces the first region R1, the piston 3 moves at a higher speed than when the entire region S faces the second region R2 or the third region R3. For this reason, the first region R1 is also called the high-speed region. The first region R1 is also called the bore middle. On the other hand, the second region R2 or the third region R3 is also called the low-speed region.

[0022] Figure 5 is a diagram illustrating a plurality of recesses according to the embodiment. Figure 5 shows a view from the internal space side where the inner wall surface 11 covers a part of the application area R. 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 embodiment, the shape of the opening is the same. Having the same shape includes, for example, that the shapes of the openings of the recesses are congruent, or that the difference in area between the recesses is small and the recesses are similar to each other. 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.

[0023] Here, the arrangement of each of the multiple recesses formed on the inner wall surface 11 according to the embodiment will be described. Multiple rows of recesses are formed in the application region R. Multiple rows of recesses are formed offset from each other in the direction of movement of the piston 3, from the upper end to the lower end of the application region R. In other words, at least one of the multiple rows of recesses is formed offset from the other rows of recesses in the direction of movement of the piston 3. As shown in Figure 5, in one example, the multiple rows of recesses are arranged at a constant pitch along the direction of movement of the piston 3.

[0024] In each of the multiple rows of recesses, two or more recesses of one type are arranged in the circumferential direction. Hereinafter, one of the multiple rows of recesses will be defined as recess row α. However, recess row α is not the uppermost, lowermost, or the recess row adjacent to the lowermost recess row on the upper side. Furthermore, the recess row adjacent to recess row α on the upper side will be defined as recess row β. Furthermore, the recess row adjacent to recess row α on the lower side will be defined as recess row γ. Furthermore, the recess row adjacent to recess row γ on the lower side will be defined as recess row δ.

[0025] In the direction of movement of the piston 3, two or more recesses in adjacent rows of recesses are arranged in a staggered pattern. Specifically, in adjacent rows of recesses in the direction of movement of the piston 3, two or more recesses in the upper row of recesses and two or more recesses in the lower row of recesses are arranged alternately along the circumferential direction. As shown in Figure 5, each of the two or more recesses constituting recess row α is positioned offset in the circumferential direction of the inner wall surface 11 with respect to each of the two or more recesses constituting recess row β that is adjacent to recess row α on the upper side. Also, each of the two or more recesses constituting recess row α is positioned offset in the circumferential direction of the inner wall surface 11 with respect to each of the two or more recesses constituting recess row γ that is adjacent to recess row α on the lower side. Each of the two or more recesses constituting recess row β that is adjacent to recess row α on the upper side is in the same or approximately the same position in the circumferential direction as the corresponding one of the two or more recesses constituting recess row γ that is adjacent to recess row α on the lower side. In other words, for each of the two or more recesses constituting the recess row β, there is a one-to-one correspondence with the recess in the two or more recesses constituting the recess row γ that is located at the same or approximately the same position on the inner wall surface 11 in the circumferential direction. Here, in Figure 5, when we define l1 as the straight line passing through the center of recess β1, which is one of the two or more recesses constituting the recess row β, and along the direction of movement of the piston 3, the straight line l1 passes through the center of recess γ1 of recess row γ. Furthermore, the recess adjacent to recess β1 and positioned offset to one side in the circumferential direction relative to recess β1 is referred to as β2. We define l2 as the straight line passing through the center of recess β2 and along the direction of movement of the piston 3. Hereafter, the side on which recess β2 is located relative to recess β1 will be referred to as 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 positioned offset to the first side D1 relative to recess γ1. In one example, the distance d1 along the circumferential direction of the inner wall surface 11 between straight line l1 and straight line l2 is 0.744 mm. In another example, in a row of recesses, two or more recesses adjacent to each other in the circumferential direction are arranged at a constant pitch along the circumferential direction.

[0026] Furthermore, each of the two or more recesses constituting the recess row α adjacent to recess row γ on the upper side is located at the same or approximately the same circumferential position as the corresponding recess among the two or more recesses constituting recess row δ adjacent to recess row γ on the lower side. That is, for each of the two or more recesses constituting recess row α, there is a one-to-one correspondence with the recess in the two or more recesses constituting recess row δ that is located at the same or approximately the same circumferential position on the inner wall surface 11. In Figure 5, among the two or more recesses constituting recess row α, recess α1 is located on the first side D1 with respect to recess β1, and on the second side D2 opposite to the first side D1 with respect to recess β2. When a straight line passing through the center of recess α1 and along the direction of movement of the piston 3 is defined as l3, the straight line l3 passes through the center of recess δ1, which is one of the two or more recesses constituting recess row δ. In one example, recess α1 is located offset by half a pitch on the first side D1 with respect to recess β1, and also offset by half a pitch on the second side D2 with respect to recess β2. Therefore, in one example, the distance d2 along the circumferential direction between straight line l1 and straight line l3 is 0.372 mm, which is half the length of distance d1. In this way, in the assigned region R, rows of recesses such as recess row β and recess row γ, which include recesses passing through straight line l1, and rows of recesses such as recess row α and recess row δ, which include recesses passing through straight line l2, are arranged alternately.

[0027] 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. In other words, 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." Specifically, as shown in Figure 5, in adjacent rows of recesses in the direction of movement of the piston 3, the lower end βu of recess β1 constituting the upper row of recesses β is located below the upper end αt of recess α1 constituting the lower row of recesses α.

[0028] In Figure 5, the straight line passing through the center of recess β1 and along the circumferential direction of the inner wall surface 11 is defined as l4, and the straight line passing through the center of recess α1 and along the circumferential direction of the inner wall surface 11 is defined as l5. Also, the straight line passing through the center of recess γ1 and along the circumferential direction of the inner wall surface 11 is defined as l6. At this time, the distance d3 along the direction of movement of the piston 3 between the straight line l4 and the straight line l5 is half the length of the distance d4 along the direction of movement of the piston 3 between the straight line l4 and the straight line l6. For example, the distance d3 is 0.215 mm, and the distance d4 is 0.430 mm.

[0029] Furthermore, in adjacent rows of recesses in the direction of movement of piston 3, the lower end of the upper row of recesses is located below the upper end of the lower row of recesses, so the boundaries p and q are curves rather than straight lines.

[0030] Next, the area ratio of the multiple recesses will be explained. The area ratio is a value that indicates the ratio of the total opening area of ​​the multiple recesses to the entire given region R. Figure 6 is a diagram for explaining the area ratio of the multiple recesses according to the embodiment. Specifically, in Figure 6, as an example, recesses β1 and α1, which are part of the multiple recesses shown in Figure 5, and the vicinity of these recesses are shown in an enlarged view. In Figure 6, a rectangular region R4 is defined. Region R4 is the area enclosed by four straight lines l1, l3, l4, and l5. The area ratio of the multiple recesses is defined by the ratio of the area occupied by the openings of the recesses in region R4 to the area of ​​region R4. In one example, the area ratio is 20% or more and 50% or less.

[0031] 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 the inner wall surface 11 according to this embodiment, for example, two types of recesses are formed. Hereafter, the type of recess that reduces friction the most when the piston 3 moves at a first speed will be referred to as the first recess. The type of recess that reduces friction more than the first recess when the piston 3 moves at a second speed, which is slower than the first speed, will be referred to as the second recess. There may be only one type of second recess, or there may be multiple types. The first speed is a speed faster than a reference value, and the second speed is a speed less than or equal to the reference value. That is, the first recess is the type of recess that reduces friction the most when the piston 3 moves at a speed faster than a reference value. The second recess is the type of recess that reduces friction more than the first recess when the piston 3 moves at a speed slower than a reference value. The reference value is determined based on 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 first recess is 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 the second recess is formed.

[0032] Figure 7 illustrates the relationship between the speed of the piston 3 and the friction between the piston 3 and the inner wall surface 11 in two comparative cases: when a first recess is formed over the entire oil application region R on the inner wall surface 11, and when one type of second recess is formed over the entire oil application region R. In Figure 7, 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, which is obtained by subtracting the friction when no recess is formed on the inner wall surface 11 from the friction when a recess is formed on 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 on the inner wall surface 11 compared to the state when no recess is formed on 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 on the inner wall surface 11 compared to the state when no recess is formed on the inner wall surface 11. In Figure 7, V1 represents the speed of the piston 3 when the oil ring 9 passes over the upper end of the oil application region R. Furthermore, the speed of the piston 3 when the top ring 7 passes the lower end of the application region R is the same as or approximately the same as V1. Also, in Figure 7, V2 represents the maximum speed of the piston 3 when it changes from acceleration to deceleration. Here, the portion of the inner wall surface 11 that the second ring 8 faces when the speed of the piston 3 is V2 is defined as the specified position r. The first region R1 is defined as a region that includes at least the specified position r. In one example, the distance along the direction of movement of the piston 3 from portion o to the specified position r is the same as or approximately the same as the distance along the direction of movement of the piston 3 from portion t to the specified position r.

[0033] In Figure 7, the solid line segment s1 represents the change D in the speed of piston 3 in the first comparative example where a first recess is formed throughout the entire application region R. On the other hand, the dashed line segment s2 represents the change D in the speed of piston 3 in the second comparative example where one type of second recess is formed throughout the entire application region R. As shown in Figure 7, line segment s1 intersects with line segment s2. In Figure 7, let V3 be the speed of piston 3 when line segment s1 intersects with line segment s2. V3 is an example of a reference value.

[0034] In the following descriptions of embodiments, when the piston speed of 3 is V3, the portion of the two portions facing the oil ring 9 that is above the specified position r will be described as the boundary p between the first region R1 and the second region R2. Also, when the piston speed of 3 is V3, the portion of the two portions facing the top ring 7 that is below the specified position r will be described as the boundary q between the first region R1 and the third region R3. When the piston speed of 3 is V1 or greater and less than V3, the entire region S of the piston 3 faces either the second region R2 or the third region R3. Also, when the piston speed of 3 is V3 or greater and less than or equal to V2, at least a part of the region S of the piston 3 faces the first region R1.

[0035] In the inner wall surface 11 according to this embodiment, the first recess is formed in the first region R1. Therefore, at least a portion of the region S of the piston 3 slides against 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, greater than V3 and less than or equal to V2.

[0036] In this embodiment, a second recess of one type is formed in the second region R2 and the third region R3. Therefore, when the speed of the piston 3 is V1 or greater and V3 or less, 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. The second speed is, for example, a speed of V1 or greater and V3 or less. The second recess is formed in a region where the amount of deviation from the specified position r is greater than that of the region where the first recess is formed. In another example, boundary p may be the region above the specified position r of the two regions that face the piston ring other than the oil ring 9 when the speed of the piston 3 is V3. In yet another example, boundary q may be the region below the specified position r of the two regions that face the piston ring other than the top ring 7 when the speed of the piston 3 is V3.

[0037] As shown in Figure 7, when the piston speed of 3 is V1 or greater and less than V3, the change in D with the second recess formed is smaller than the change in D with the first recess formed on the inner wall surface 11. Therefore, the second recess has a greater friction reduction effect when the piston 3 moves at the second speed compared to the first recess, and is advantageous in the low-speed range. On the other hand, when the piston speed of 3 is V3 or greater and less than or equal to V2, the change in D with the first recess formed is smaller than the change in D when the second recess formed on the inner wall surface 11. Therefore, the first recess has a greater friction reduction effect when the piston 3 moves at the first speed compared to the second recess, and is advantageous in the high-speed range.

[0038] 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 between 3.0 μm and 5.0 μm. For example, the depth of the second recess is between 1.0 μm and 2.0 μm.

[0039] Figure 8 is a diagram illustrating the relationship between the speed of the piston 3 and friction 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. In Figure 8, the horizontal and vertical axes are the same as in Figure 7. In Figure 8, the solid line s3 represents the change in speed D of the piston 3 sliding on the inner wall surface 11 according to the embodiment. On the other hand, the dashed line segment s4 in Figure 8 represents the change in speed D of the piston 3 sliding on the inner wall surface 11 where the first recess is formed in the second region R2 and the third region R3. Also, the dashed line segment s5 represents the change in speed D of the piston 3 sliding on the inner wall surface 11 where the second recess is formed in the first region R1.

[0040] When the speed of piston 3 is between V1 and V3, piston 3 slides against the second region R2 or the third region R3, where a second recess is formed that has a greater friction reduction effect when the piston 3 is moving at a slow speed. Therefore, as shown by the broken line s3 and line segment s4 in Figure 8, friction can be reduced compared to the case where the first recess is formed in the second region R2 and the third region R3. On the other hand, when the speed of piston 3 is between V3 and V2, piston 3 slides against the first region R1, where a first recess is formed that has a greater friction reduction effect when the piston 3 is moving at a fast speed. Therefore, as shown by the broken line s3 and line segment s5, friction can be reduced compared to the case where the second recess is formed in the first region R1. Thus, according to the above embodiment, compared to the first and second comparative examples, the amount of friction reduction in the high-speed range is increased while also reducing friction in the low-speed range. Furthermore, since friction between the piston ring and the inner wall surface 11 is reduced, and friction between the piston body 5 and the inner wall surface 11 is also reduced, friction between the piston 3 and the inner wall surface 11 is also reduced.

[0041] In the embodiment, the inner wall surface 11 was described using as an example a configuration in which a first recess is formed in the first region R1 and a second recess is formed in the second region R2 and the third region R3, but the embodiment is not limited to this. For example, the second recess may not be formed in the third region R3, and may only be formed in the second region R2. Alternatively, the second recess may not be formed in the second region R2, and may only be formed in the third region R3.

[0042] Furthermore, although the embodiment of the inner wall surface 11 has been described using as an example a configuration in which only one type of second recess is formed in the second region R2 and the third region R3, it is not limited to this. Multiple types of second recesses may 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 second region R2, which is the region between the upper end of the first region R1 and part o, in the second region R2, the recesses formed at positions further from the first region R1 are of a type that reduces friction when the piston 3 moves at the second speed. Also, when multiple types of second recesses are formed in the third region R3, which is the region between part t and the lower end of the first region R1, in the third region R3, the recesses formed at positions further from the first region R1 are of a type that reduces friction when the piston 3 moves at the second speed. The positions of boundary p and boundary q vary depending on the combination of types of recesses formed on the inner wall surface 11.

[0043] Furthermore, the depth of the recess that best reduces friction 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.

[0044] According to the embodiment described above, the cylinder 2 has an inner wall surface 11 on which multiple types of recesses are formed, each offset 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. Specifically, in the high-speed range of the inner wall surface 11, a type of recess is formed that has a large friction reduction effect when the piston 3 is moving at a high speed, while in the low-speed range of the inner wall surface 11, a type of recess is formed that has a large friction reduction effect when the piston 3 is moving at a slow speed. This makes it possible to reduce friction in the low-speed range while also reducing friction in the high-speed range.

[0045] Furthermore, according to the embodiment described above, in the first region R1, a first recess is formed that, among multiple types of recesses, most effectively reduces friction when the piston is moving at a high speed. One or more second recesses formed in regions of the inner wall surface 11 other than the first region reduce friction when the piston 3 is moving at a slower speed compared to the first recess. This further increases the reduction in friction at high speeds while also further reducing friction at low speeds. 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 effectively when the piston is moving at a slower speed. This further increases the reduction in friction at high speeds while also further reducing friction at low speeds.

[0046] Furthermore, according to the embodiment, in addition to the effects described above, it is possible to provide an internal combustion engine 1 equipped with a cylinder 2 having an inner wall surface 11 that reduces friction at low speeds while significantly reducing friction at high speeds. And it is possible to provide a vehicle 100 equipped with the above internal combustion engine 1.

[0047] 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]

[0048] 1...Internal combustion engine, 2...Cylinder, 3...Piston, 4...Piston pin, 5...Piston body, 7...Top ring, 8...Second ring, 9...Oil ring, 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, α, β, γ, δ...Row of recesses, α1, β1, β2, γ1, γ2, δ1...Recess, R...Applied area, R1~R4...Area.

Claims

1. The inner wall surface is equipped with multiple types of recesses that are offset by type in the direction of piston movement, In the aforementioned multiple types of recesses, the effect on the relationship between the friction between the inner wall surface and the piston with respect to the speed at which the piston moves differs for each type. On the inner wall surface, the plurality of types of recesses cause at least one of the plurality of recess rows to be formed to be offset in the direction of movement relative to the other recess rows. In each of the aforementioned rows of recesses, two or more recesses of one type are arranged in the circumferential direction. In adjacent rows of recesses in the direction of movement, two or more recesses in the upper row of recesses and two or more recesses in the lower row of recesses are arranged alternately along the circumferential direction, and the lower end of the upper row of recesses is located below the upper end of the lower row of recesses. Cylinder.

2. The cylinder according to claim 1, wherein in a first region of the inner wall surface, a first recess of the type that best reduces friction between the inner wall surface and the piston when the piston moves at a first speed is formed, and in regions of the inner wall surface other than the first region, one or more second recesses of the type that reduce friction more than the first recess when the piston moves at a second speed slower than the first speed are formed.

3. In the areas of the inner wall surface other than the first area, multiple types of second recesses are formed as one or more types of second recesses. Of the multiple types of second recesses, the type formed at a position further away from the first region reduces friction when the piston moves at the second speed. The cylinder according to claim 2.

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

5. The cylinder according to claim 1, wherein the shapes of the openings of the multiple types of recesses are the same.

6. The cylinder according to claim 5, wherein the shape of the openings of the multiple types of recesses is circular.

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

8. A cylinder according to any one of claims 1 to 7, The piston is disposed in the internal space covered by the inner wall surface, An internal combustion engine equipped with [a specific feature / technology].

9. A vehicle equipped with an internal combustion engine as described in claim 8.

Images