JP2022155552A - Slide structure for internal combustion engine - Google Patents

Abstract

To provide a cylinder which reduces friction resistance and improves fuel consumption efficiency or reduces oil consumption.SOLUTION: The present invention relates to a cylinder in which a piston including a piston ring slides on an inner wall surface. A plurality of recesses are formed in a process center region of the inner wall surface and on a side face of the recess, a sagging region which is defined as follows is formed. A lower reference height line is defined by offsetting to a recess bottom side by 0.50 μm from an upper reference height line offset to the recess bottom side by 0.15 μm from an inner wall surface reference height line transformed into a single straight line using the least square method regarding a plurality of inner wall surfaces. A line segment connecting an upper pint where a cross-sectional curve first crosses the upper reference height line in the vicinity of a boundary with the inner wall surface and a lower point where the cross-sectional curve first crosses the lower reference height line is defined as a virtual sagging cross section of the sagging region. An absolute value of a gradient with an inner wall surface of the virtual sagging cross section defined as a reference is set within a range from 0.00625 to 0.0167.SELECTED DRAWING: Figure 4

Description

The present invention relates to a sliding structure and the like for an internal combustion engine having a cylinder and a piston.

BACKGROUND ART Conventionally, in an internal combustion engine having a cylinder and a piston, efforts have been made to reduce the sliding resistance (frictional force) between the cylinder and the piston in order to improve fuel efficiency and reduce oil consumption. The applicant has developed a so-called dimple liner as a technique for reducing the frictional force between the piston ring and the cylinder (see, for example, Patent Document 1), in which a plurality of recesses are formed in the stroke central region of the inner wall surface of the cylinder. By doing so, the sliding resistance during operation is reduced.

Japanese Patent No. 5155924

Although it was unknown at the time of the filing of the present application, further research by the present inventors revealed that there is still room for improving fuel efficiency, etc., by further reducing frictional resistance with this dimple liner technology. became.

SUMMARY OF THE INVENTION In view of such circumstances, the present invention seeks to further improve fuel efficiency and reduce oil consumption with respect to dimpled liners.

The present invention for achieving the above object is a cylinder in which a piston having a piston ring slides on an inner wall surface, wherein the position of the lower surface of the ring groove of the lowest piston ring in the inner wall surface at the top dead center of the piston. to the upper surface position of the ring groove of the uppermost piston ring at the bottom dead center of the piston. , a sagging region defined by the following region conditions is formed, and (region condition) the shape of at least two of the recesses aligned in the cylinder axial direction is measured with a stylus surface roughness in a state including a plurality of adjacent inner wall surfaces. Using a measuring machine (JIS B 0651: 2001), the cross-sectional curve obtained by setting the measuring needle tip radius to 2 μm and the cutoff value (wavelength) λs for the cross-sectional curve to 2.5 μm is used as the reference: multiple The inner wall surface is extracted and converted to a single straight line using the least squares method. The line is defined as an upper reference height line that means the upper edge of the sagging region: a line offset by 0.50 μm from the upper reference height line to the bottom side of the recess is the lower edge of the sagging region defined as the lower reference height line: the upper point where the cross-sectional curve from the inner wall surface to the bottom surface of the recess first intersects the upper reference height line near the boundary with the inner wall surface , the line segment connecting the lower point that first intersects the lower reference height line is defined as the virtual sagging cross section of the sagging region: the absolute gradient of the virtual sagging cross section in the sagging region with respect to the inner wall surface A cylinder characterized by a value set within the range of 0.00625 to 0.0167.

In relation to the cylinder, at least a portion of the surface in contact with the piston ring in the stroke center region has an arithmetic average roughness Ra of the contour curve measured by a stylus type surface roughness measuring instrument of 0.5. A central low-roughness region of 140 μm or less is formed.

In relation to the cylinder, the concave portion having the sagging region is formed within the range of the central bottom roughness region.

In relation to the above cylinder, the arithmetic mean height Sa of the profile curved surface of the central low-roughness region measured by a non-contact surface roughness measuring machine is 0.20 μm or less.

In relation to the above cylinder, the protruding valley depth Svk of the central low-roughness region measured by a non-contact surface roughness measuring machine is 0.41 μm or less.

In relation to the cylinder, the height Spk of the central low-roughness region measured by a non-contact surface roughness measuring device is 0.16 μm or less.

In relation to the cylinder, the level difference Sk of the core portion of the central low-roughness region measured by a non-contact surface roughness measuring machine is 0.53 μm or less.

In relation to the cylinder, E (Spk) is the protruding peak height and I (Svk) is the protruding valley depth measured by the non-contact surface roughness measuring device in the central low-roughness region. In this case, I/E is 2.6 or less.

In relation to the above cylinder, the arithmetic mean roughness Ra of the contour curve of the central low roughness region measured by a stylus type surface roughness tester is 0.120 μm or less.

The present invention for achieving the above object is a sliding structure for an internal combustion engine having a cylinder and a piston, wherein the cylinder is located in the inner wall surface of the ring groove of the lowest piston ring at the top dead center of the piston. A plurality of recesses are formed in a stroke center region that is all or part of the area from the lower surface position to the upper surface position of the ring groove of the uppermost piston ring at the bottom dead center of the piston, and the side surfaces of the recess. , a sagging region defined by the following region conditions is formed, and (region conditions) the shape of at least two of the recesses lined up in the cylinder axial direction, including a plurality of adjacent inner wall surfaces, is a stylus type surface Based on the cross-sectional curve obtained by measuring with a roughness measuring machine (JIS B 0651: 2001) with a measuring needle tip radius of 2 μm and a cutoff value (wavelength) λs for the cross-sectional curve of 2.5 μm. : A line obtained by extracting a plurality of the inner wall surfaces and converting them into a single straight line using the method of least squares is defined as the inner wall surface reference height line: 0.15 μm from the inner wall surface reference height line to the bottom side of the recess. The offset line is defined as an upper reference height line that means the upper edge of the sagging region: a line offset by 0.50 μm from the upper reference height line to the bottom side of the recess is the sagging region Defined as a lower reference height line that means a lower edge: the cross-sectional curve from the inner wall surface to the bottom surface of the recess first intersects the upper reference height line near the boundary with the inner wall surface A line segment connecting a point and a lower point that first intersects the lower reference height line is defined as a virtual sagging cross section of the sagging region: a gradient of the virtual sagging cross section in the sagging region with respect to the inner wall surface is set within a range of 0.00625 to 0.0167.

In relation to the sliding structure of the internal combustion engine, at least part of the surface in contact with the piston ring in the stroke center region of the cylinder has a contour curve measured by a stylus surface roughness measuring machine. A central low-roughness region having an arithmetic mean roughness Ra of 0.140 μm or less is formed.

In relation to the sliding structure of the internal combustion engine, the concave portion having the sagging region is formed within the range of the central bottom roughness region.

In relation to the sliding structure of the internal combustion engine, the arithmetic mean height Sa of the contour curved surface of the central low-roughness region measured by a non-contact surface roughness measuring device is 0.20 μm or less. do.

In relation to the sliding structure of the internal combustion engine, the protruding trough depth Svk of the central low-roughness region measured by a non-contact surface roughness measuring device is 0.41 μm or less.

In relation to the sliding structure of the internal combustion engine, the protruding peak height Spk of the central low-roughness region measured by a non-contact surface roughness measuring device is 0.16 μm or less.

In relation to the sliding structure of the internal combustion engine, the level difference Sk of the core portion of the central low-roughness region measured by a non-contact surface roughness measuring device is 0.53 μm or less.

In relation to the sliding structure of the internal combustion engine, E (Spk) is the protruding peak height measured by the non-contact surface roughness measuring device in the central low roughness region, and I is the protruding valley depth. (Svk), the I/E is 2.6 or less.

In relation to the sliding structure of the internal combustion engine, the arithmetic mean roughness Ra of the profile curve of the central low roughness region measured by a stylus type surface roughness tester is 0.120 μm or less. do.

In relation to the sliding structure of the internal combustion engine, the central low-roughness region includes the vicinity of the upper edge and the vicinity of the lower edge in the stroke central region.

In relation to the sliding structure of the internal combustion engine, the entire stroke central region is the central low-roughness region.

The sliding structure for the internal combustion engine may employ the following configuration.

For example, μ is the kinematic viscosity (coefficient of kinematic viscosity) in the central low-roughness region, Q is the relative speed with the piston, W is the contact load on the piston, and f is the coefficient of friction with the piston, Stribeck When defining the evaluation parameter of the diagram as A = μ × Q / W, the minimum value fmin of the friction coefficient f in the central low roughness region is achieved when the evaluation parameter A is 0.0003 or less It can be characterized as being

For example, the minimum value fmin can be characterized by being achieved within a range of the evaluation parameter A of 0.0001 or more.

For example, μ is the kinematic viscosity (coefficient of kinematic viscosity) in the central low-roughness region, Q is the relative speed with the piston, W is the contact load on the piston, and f is the coefficient of friction with the piston, Stribeck When defining the evaluation parameter of the diagram as A = μ × Q / W, the friction coefficient f in the central low roughness region is 0 in any of the ranges where the evaluation parameter A is 0.0003 or less .07 or less.

For example, μ is the kinematic viscosity (coefficient of kinematic viscosity) in the central low-roughness region, Q is the relative speed with the piston, W is the contact load on the piston, and f is the coefficient of friction with the piston, Stribeck When defining the evaluation parameter of the diagram as A = μ × Q / W, the piston and the cylinder in the central low roughness region are in any range where the evaluation parameter A is 0.0003 or less It can be characterized by being in a fluid lubrication state.

For example, in a friction test in a non-combustion state using a top ring, a second ring and an oil ring corresponding to the piston ring, the rotation speed of the internal combustion engine is N (r / min), and the central low roughness region When the friction loss mean effective pressure (FMEP) between the piston rings is T (kPa), the minimum value Tmin of the friction loss mean effective pressure T in the central low roughness region is obtained when the rotational speed N is 700 It can be characterized as being achieved within the following range.

For example, in a friction test in a non-combustion state using a top ring, a second ring and an oil ring corresponding to the piston ring, the rotation speed of the internal combustion engine is N (r / min), and the central low roughness region When the friction loss average effective pressure (FMEP) between the piston ring and the piston ring is T (kPa), the friction loss in the central low roughness region in any range where the rotation speed N is 700 or less It can be characterized in that the average effective pressure T is 14 kPa or less.

For example, in a friction test in a non-combustion state using a top ring, a second ring and an oil ring corresponding to the piston ring, the rotation speed of the internal combustion engine is N (r / min), and the central low roughness region When the friction loss average effective pressure (FMEP) between the piston ring is T (kPa), the piston in the central low roughness region and the It can be characterized in that the cylinder is in a fluid lubrication state.

ADVANTAGE OF THE INVENTION According to this invention, it can show the outstanding effect of reducing frictional resistance, improving fuel consumption, or reducing oil consumption.

1 is an axial cross-sectional view of a cylinder liner applied to a sliding structure for an internal combustion engine according to a first embodiment of the present invention; FIG. (A) and (B) are developed views showing a state in which the inner peripheral wall of the cylinder liner is developed in the circumferential direction. Fig. 3 is a cross-sectional view of the inner peripheral wall of the cylinder liner in the direction perpendicular to the axis; (A) and (B) are cross-sectional views showing cross-sectional curves of an inner peripheral wall and a recess of the cylinder liner. (A) is a side view showing a piston and a piston ring applied to the sliding structure of the internal combustion engine, (B) is a partially enlarged sectional view showing the piston and the piston ring, and (C) is a top ring. , and (D) is a partially enlarged cross-sectional view of a second ring. (A) is a cross-sectional view of a two-piece oil ring, and (B) is a cross-sectional view of a three-piece oil ring. FIG. 2 is (A) a Stribeck diagram and (B) an FMEP diagram relating to sliding of a general internal combustion engine. (A) and (B) are graphs showing actual measurement results of the sagging region of the same cylinder liner. (A) and (B) are graphs showing actual measurement results of a sagging region of a cylinder liner according to a comparative example. 1 is a cross-sectional view showing a general friction unit measuring device for measuring the sliding state of an internal combustion engine; FIG. (A) is a graph showing the results of actual measurement of frictional forces of the first to third cylinder liners as an example, and (B) is a state in which the inner peripheral walls of the first to third cylinder liners are expanded in the circumferential direction. It is a developed view showing the. (A) is a Stribeck diagram using a verification cylinder liner for analyzing the sliding structure of the internal combustion engine of the first embodiment, and (B) is an FMEP diagram using the same verification cylinder liner. be. It is a side view showing a sliding stroke of a cylinder liner and a piston ring of the same internal combustion engine. (A) is a cross-sectional view along the axial direction of a cylinder liner applied to a sliding structure for an internal combustion engine according to a second embodiment of the present invention, and (B) is a sliding stroke of the cylinder liner and a piston ring; It is a side view showing FIG. 2 is a cross-sectional view along the axial direction of a cylinder liner showing an example of a cylinder liner to which the microtexture technology is applied;

Embodiments of the present invention will be described below with reference to the accompanying drawings. First, the sliding structure of the internal combustion engine according to the first embodiment of the invention will be described in detail. In the first embodiment, the internal combustion engine is a diesel engine, but the present invention is not limited to this, and can be applied to other types of internal combustion engines such as gasoline engines.

<Cylinder liner>

As shown in FIG. 1, a plurality of recesses 14 are formed in an inner wall surface 12 of a cylinder liner 10 according to the internal combustion engine of the first embodiment. The recess 14 is formed in a mid-stroke region 20 of the inner wall surface 12 . The stroke center region 20 extends from the lower surface position of the ring groove of the lowest piston ring at the top dead center T of the piston 30 to the upper surface position of the ring groove of the uppermost piston ring at the bottom dead center U of the piston 30. is the maximum, and it is all or part of the range (here, the entire range is the stroke center region 20, and the case where the recess 14 is formed in the whole is illustrated). If the area outside the stroke central area 20 is defined as an external area 25, this external area 25 consists of an upper external area 25A adjacent to the top dead center side of the stroke central area 20 and a bottom dead center area 25A of the stroke central area 20. It consists of a lower outer region 25B adjacent to the point side. When the piston 30 reciprocates in the cylinder liner 10, it repeatedly passes through the upper outer region 25A, the stroke central region 20, the lower outer region 25B, the stroke central region 20, and the upper outer region 25A in this order. The boundary between the upper outer region 25A and the stroke central region 20 is defined as an upper boundary 27A, and the boundary between the lower outer region 25B and the stroke central region 20 is defined as a lower boundary 27B.

Of course, it is possible to form a plurality of recesses 14 beyond the stroke center region 20, but from the viewpoint of oil consumption (LOC), the recesses 14 are formed only inside the stroke center region 20. preferably.

<Dimples Formed on Cylinder Liner>

The recesses 14 are arranged on the inner wall surface 12 of the stroke center region 20 such that at least one recess 14 exists in any cross-section perpendicular to the axis. That is, the recesses 14 are arranged so as to overlap each other in the axial direction. As a result, the outer peripheral surface of the piston ring passing through the mid-stroke region 20 always faces at least one recess 14 . On the other hand, the concave portion 14 is not formed in the upper outer region 25A and the lower outer region 25B.

The shape of the recesses 14 is a square (square or rectangle) arranged obliquely with respect to the axial direction, and as a result, the plurality of recesses 14 as a whole are arranged in an oblique lattice. In this way, as shown in the developed view of FIG. 2(A), when focusing on a certain recessed portion 14, the lowest point 14b in the axial direction of that recessed portion 14 is the highest point in the axial direction of the other recessed portion 14. It is located axially below the point 14a. In this way, since the plurality of recesses 14 overlap in the axial direction, the recesses 14 are always present in cross-sections perpendicular to the axis at all locations (for example, view A, view B, and view C) in the stroke center region 20. can. Here, in the stroke central region 20, a plurality of recesses 14 having the same area are uniformly arranged in the plane direction (axial direction and circumferential direction).

In addition, as shown in the developed view of FIG. 2B, a plurality of recesses 14 having the same area may be arranged non-uniformly in the planar direction. Here, the area occupied by the plurality of recesses 14 is small in the circumferential strip region 20P at the axial end of the stroke center region 20, and the circumferential strip region at the axial center of the stroke center region 20 is small. In 20Q, the area occupied by the plurality of recesses 14 is large.

The size and shape of the recess 14 are not particularly limited, but are appropriately selected according to the size and purpose of the cylinder and piston ring. For example, the recessed portion 14 can be formed in a slit shape or band shape so as to penetrate (or extend) through the stroke central region 20 in the axial direction of the cylinder. On the other hand, from the viewpoint of airtightness of the cylinder, the maximum average length J (see FIG. 2A) of the concave portion 14 in the cylinder axial direction is set to the cylinder axis of the piston ring (top ring) located at the highest position of the piston. The length (width) in the direction or less, specifically about 5 to 100% thereof, is preferable. The average length J of the recesses 14 means the average value of the maximum axial dimension of the plurality of recesses 14 when there is variation.

The maximum average length S of the recesses 14 in the cylinder circumferential direction is preferably in the range of 0.1 mm to 15 mm, more preferably in the range of 0.3 mm to 5 mm. If it is smaller than these ranges, the effect of reducing the sliding area by the concave portion 14 itself may not be sufficiently obtained. On the other hand, if it is larger than these ranges, a part of the piston ring tends to enter the recess, which may cause problems such as deformation of the piston ring.

As shown in FIG. 3A, the maximum average length R (maximum average depth R) of the concave portion 14 in the cylinder radial direction is preferably in the range of 0.1 μm to 1000 μm, more preferably in the range of 0.1 μm to 500 μm. is desirable. More desirably, it is set to 0.1 μm to 50 μm. If the maximum average length R of the recessed portion 14 in the cylinder radial direction is smaller than these ranges, the effect of reducing the sliding area of the recessed portion 14 itself may not be sufficiently obtained. On the other hand, if it is attempted to be larger than these ranges, processing becomes difficult, and problems such as the need to increase the wall thickness of the cylinder may occur. For convenience of explanation, the concave portion 14 in FIG. 3 is drawn with the maximum average length R direction greatly exaggerated with respect to the maximum average length J direction.

Returning to FIG. 2, the average value of the minimum distance Hc in the cylinder circumferential direction between the recesses 14 adjacent in the circumferential direction at the same position in the axial direction is preferably in the range of 0.05 mm to 15 mm, more preferably 0.1 mm to 5 mm. A range of 0.0 mm is particularly preferred. If it is smaller than these ranges, the contact area (sliding area) between the piston ring and the cylinder liner may be too small to stably slide. On the other hand, if it exceeds these ranges, the effect of reducing the sliding area of the concave portion 14 itself may not be sufficiently obtained.

The average value of the minimum distance Ha in the cylinder axial direction between the axially adjacent recesses 14 at the same position in the circumferential direction is preferably in the range of 0.05 mm to 15 mm, and more preferably in the range of 0.1 mm to 5.0 mm. Especially preferred. If it is smaller than these ranges, the contact area (sliding area) between the piston ring and the cylinder liner may be too small to stably slide. On the other hand, if it exceeds these ranges, the effect of reducing the sliding area of the concave portion 14 itself may not be sufficiently obtained.

Furthermore, regardless of the direction, the average minimum distance Hm between adjacent recesses 14 is preferably within the range of 0.001 mm to 15 mm, and particularly preferably within the range of 0.001 mm to 5.0 mm. If it exceeds these ranges, the effect of reducing the sliding area of the concave portion 14 itself may not be sufficiently obtained.

In other words, these intervals Hc, Ha, and Hm are synonymous with the minimum width in each direction of the inner wall surface 12 remaining between adjacent recesses 14 . Therefore, although the details will be described later with reference to FIG. 4B, these intervals Hc, Ha, and Hm are defined by the upper point GS that first intersects the upper reference height line G1 of one recess 14 and the other adjacent point GS. means the distance from the upper point GS that first intersects the upper reference height line G1 of the recess 14 .

In this embodiment, it is particularly preferable that the average value of the distance Ha in the axial direction of the cylinder is within the range of 0.05 mm to 15 mm, and more preferably within the range of 0.1 mm to 5.0 mm. . When expanding the range of the fluid lubrication region 114 of the piston ring 40 sliding in the cylinder axial direction shown in FIG. By ensuring the interval Ha between the inner wall surfaces 12 in the axial direction of the cylinder, it is possible to suppress local surface pressure fluctuations acting on the piston rings 40 .

<Sagging area in dimple>

As shown enlarged in FIG. 3B, a so-called sagging region 200 is formed in the vicinity of an edge (edge) approaching the inner wall surface 12 on the side surface 300 of the recess 14 . The sagging region 200 forms a small inclined surface that begins to fall into the recess 14 with the inner wall surface 12 as a reference surface. The sagging region 200 can be regarded as a partial region of the side surface 300 of the recess 14 , particularly a region near the inner wall surface 12 . Note that the sagging region 200 can also be regarded as a partial region formed at the end of the inner wall surface 12 . In any case, the sagging region 200 is locally formed near the boundary between the inner wall surface 12 and the recess 14 .

The sagging region 200 is formed on the inner wall surface 12 of the cylinder liner 10 in which the recessed portion 14 is formed by honing using a honing machine and polishing after the honing. In particular, it is preferable to form a smooth sagging region 200 by carefully performing polishing.

In this embodiment, in order to objectively evaluate the shape of the sagging region 200, the sagging region 200 is defined as follows.

As shown in FIG. 4A, the shape of at least two recesses 14 that exist at the same position in the cylinder circumferential direction and are aligned in the cylinder axial direction are arranged so that they pass through the minimum interval Ha and are adjacent to each other. The surface roughness including the wall surface 12 is measured with a stylus type surface roughness tester (JIS B 0651:2001). The tip radius of the measuring needle is a standard 2 μm, and the cutoff value (wavelength) λs for the cross-sectional curve is selected to be 2.5 μm. The cross-sectional curve DK to be measured includes two adjacent recesses 14, a pair of inner wall surfaces 12A and 12C extending on both outer sides of the two recesses 14 in the cylinder axial direction, and an inner wall surface existing between the two recesses 14. 12B is included at least.

In this cross-sectional curve DK, only the range of three inner wall surfaces 12A-12C is extracted, and these wall surface groups 12A-12C are converted into a single straight line 250 using the method of least squares. This straight line 250 corresponds to the smoothed position of the inner wall surface 12 and is defined as the inner wall surface reference height line GK.

Next, as shown in FIG. 4B, the sagging region 200 to be specified is enlarged and extracted from a total of four sagging regions 200 included in the two recesses 14 . The actual wall surfaces 12A to 12C include fine unevenness corresponding to surface roughness. Since the amplitude of this unevenness is approximately 0.3 μm, when defining the sagging region 200 , in order to exclude the influence of this surface roughness, the distance from the inner wall surface reference height line GK to the base side of the recessed portion 14 is 0.3 μm. A line offset by 15 μm is defined as an upper reference height line G1. This upper reference height line G1 means a virtual starting position (starting height) of the sagging region 200 in the depth direction. Further, a line offset by 0.50 μm from the upper reference height line G1 to the base side of the concave portion 14 is defined as a lower reference height line G2. This lower reference height line G2 means a virtual end position (end height) of the sagging region 200 . Accordingly, the length (sagging height) DH of the sagging region 200 in the cylinder radial direction is defined as 0.50 μm.

A cross-sectional curve DK extending from the inner wall surfaces 12A to 12C in the bottom direction (depth direction) of the recess 14 first intersects the upper reference height line G1 near the boundary of the inner wall surfaces 12A to 12C. Select the lower point GE that first intersects the reference height line G2. A line segment GG connecting the upper point GS and the lower point GE with a straight line is defined as an imaginary sagging section GG of the sagging region 200 . The length of the imaginary sag section GG in the direction parallel to the straight line 250 (here, the cylinder axial direction) is defined as the sag width DW of the sag region 200 . Using the straight line 250 as a reference, the absolute value of the gradient DH/DW of this virtual droop section GG (hereinafter defined as the droop gradient DA) is calculated. A small sag gradient DA means that the gentle sag region 200 is properly formed, and a large sag gradient DA means that the sag region 200 is incomplete.

Note that the cross-sectional curve DK includes minute irregularities and the like, and therefore varies from measurement to measurement. Therefore, with each sagging region 200 as a target, measurement is performed 60 times with a stylus type surface roughness measuring machine (JIS B 0651: 2001), and 15 from the maximum side of the 60 calculated sagging gradients DA, the minimum Cut 15 from the side and calculate the average value from 30 data in the middle. This average value is used as the evaluation sag gradient DA of the sag region 200 . Here, the case where the sag gradient DA is used when evaluating the formation state of the sag region 200 is exemplified.

In this embodiment, the evaluation sag gradient DA of the sag region 200 is set in the range of 0.00625 to 0.0167 (the evaluation sag width DW is 0.030 to 0.080).

By the way, although different from the dimpled liner in which a plurality of recesses are arranged so as to overlap in the axial direction, there is a micro-texture technology for forming the same kind of recesses, so this will be briefly described. As shown in FIG. 15, the microtexture is a state in which a region V in which recesses are formed and a region Z in which no recesses are present do not overlap in the axial direction along the cylinder axial direction of the inner wall surface of the cylinder liner. The theory is that each time the piston ring moves on this inner wall surface, the engine oil flows in and out of the recess, and the dynamic pressure thickens the oil film and reduces the frictional force. . The present invention is also applicable to such micro-texture technology. That is, the present invention can be effectively applied to any structure that reduces the contact area with the piston ring by forming a plurality of recesses in the stroke central region.

<Central low-roughness region formed in cylinder liner>

The inner wall surface 12 of the cylinder liner 10 has a surface roughness (arithmetic mean roughness of contour curve) measured by a stylus type surface roughness measuring instrument (JIS B 0651:2001) at least in part of the stroke central region 20. A central low-roughness region 22 having a surface roughness Ra (JIS B 0601:2013) of 0.140 (μm) or less and preferably a surface roughness Ra of 0.120 (μm) or less is formed. Specifically, the surface roughness Ra of at least a portion of the surface of the inner peripheral surface 12 that can come into contact with the piston ring 40, ie, the surface of the inner peripheral surface 12 excluding the recess 14, is set to 0.140 (μm). The central low-roughness region 22 is formed by processing below, more preferably processing to 0.120 (μm) or less. In the present embodiment, the surface roughness (arithmetic mean roughness of the contour curve) measured by the stylus surface roughness measuring instrument is represented by Ra, and is measured by the non-contact surface roughness measuring instrument to be described later. The three-dimensional surface roughness (arithmetic mean height of contour curved surface (JIS B 0681-2: 2018, ISO 25178-2: 2012)) is denoted as Sa.

The central low-roughness region 22 preferably has a surface roughness Ra of 0.090 (μm) or less, specifically 0.083 (μm).

For this central low-roughness region 22, a non-contact surface roughness measuring machine (measurement magnification: 1080 times, visual field size: 259.5 mm) using a laser microscope according to JIS B 0681-6: 2014 (ISO 25178-6: 2010) was used. 4 μm × 259.4 μm, no cutoff, height direction (Z direction) measurement pitch 0.06 μm) three-dimensional surface roughness value (JIS B 0681-2: 2018, ISO 25178-2: 2012) are shown below.
Arithmetic mean height Sa (μm): 0.192 or less, preferably 0.163 or less, more preferably 0.120 or less (specifically set to 0.110).
Projection peak height Spk (μm): 0.159 or less, preferably 0.144 or less, more preferably 0.121 or less (specifically set to 0.116).
Core portion level difference Sk (μm): 0.521 or less, preferably 0.449 or less, more preferably 0.340 or less (specifically set to 0.315).
Projection valley depth Svk (μm): 0.409 or less, preferably 0.342 or less, more preferably 0.241 or less (specifically set to 0.218).

Above all, in the present embodiment, not only the height of the protruded peak is reduced, but also the depth of the protruded valley is actively reduced, thereby reducing the frictional force during sliding. Incidentally, in the conventional cylinder liner, it is necessary to increase the depth of the protruding troughs to some extent in order to secure the lubricating oil retention force. There is a limit to the reduction of frictional force inside. On the other hand, in the present embodiment, since the lubricating oil is sufficiently retained in the adjacent concave portions 14, the contact surface itself with the piston ring 40 can form a sufficient oil film even if the lubricating oil retaining force is small. Under this gist, when the height of the protruding peak is E and the depth of the protruding valley is I, in the central low-roughness region 22 of the present embodiment, the value of I/E is set to 2.6 or less. It is preferably set to 2.4 or less, more preferably 2.0 or less.

In the present embodiment, the central low-roughness region 22 is the entire range of the surface of the stroke central region 20 that can come into contact with the piston ring 40 . As a result, the central low-roughness region 22 includes near the top edge and near the bottom edge of the mid-stroke region 20 in which the recess 14 is formed. Furthermore, an upper low-roughness region 23A having a surface roughness Ra of 0.120 (μm) or less is formed in the upper external region 25A adjacent to the stroke central region 20 on the top dead center side. For the lower outer region 25B adjacent to the bottom dead center side of 20, a lower low-roughness region 23B is formed. The upper low-roughness region 23A, the central low-roughness region 22, and the lower low-roughness region 23B are completely connected in a state of uniform surface roughness, forming an integral continuous surface as a whole.

Since the relative velocity Q between the cylinder liner 10 and the piston 30 decreases in the vicinity of the upper edge and the vicinity of the lower edge of the stroke central region 20, the fluid lubrication region is likely to transition to the boundary lubrication region. However, the presence of this central low-roughness region 22 allows the hydrodynamic lubrication region to be developed predominantly. Since the so-called dimple liner technology can exert its effect in the hydrodynamic lubrication region, the advantages of the dimple liner technology can be obtained also in the vicinity of the upper edge and the lower edge of the stroke center region 20 . Although it is possible to form the central low-roughness region 22 only in the vicinity of the upper edge and/or the vicinity of the lower edge of the stroke central region 20, as in the present embodiment, the stroke central region A central low-roughness region 22 is preferably formed throughout 20 . When the relative speed Q between the cylinder liner 10 and the piston 30 becomes lower, the boundary lubrication region approaches the center side of the stroke center region 20. It is possible to expand the range of the area.

The central low-roughness region 22 of the inner wall surface 12 of the cylinder liner 10 is formed by honing using a honing machine. As for the grain size of the honing grindstone at this time, it is preferable to use abrasive grains finer than F500 or #800 (JIS R 6001-2:2017, ISO8486-2:2007), for example.

Furthermore, after the central low-roughness region 22 is formed by this honing process, it is preferable not to perform a chemical conversion treatment on the surface. For example, if a phosphate coating or the like, which is commonly used in the manufacturing process of the cylinder liner 10, is applied, the surface properties of the central low-roughness region 22 will vary depending on the coating. On the other hand, it is also desirable to apply a chemical conversion treatment to the central low-roughness region 22 in the case of a film with small variations in surface properties.

<Piston and piston ring>

5A) and 5B show the piston 30 and the piston ring 40 (top ring 50, second ring 60, oil ring 70) installed in the ring groove of the piston 30. FIG. The piston ring 40 reciprocates in the cylinder axial direction with the outer peripheral surface 42 facing the inner wall surface 12 of the cylinder liner 10 . The top ring 50 eliminates a gap between the piston 30 and the cylinder liner 10 and prevents a phenomenon (blow-by) in which compressed gas escapes from the combustion chamber to the crankcase side. Like the top ring 50 , the second ring 60 serves both to eliminate the gap between the piston 30 and the cylinder liner 10 and to scrape off excess engine oil adhering to the inner wall surface 12 of the cylinder liner 10 . The oil ring 70 scrapes off excess engine oil on the inner wall surface 12 of the cylinder liner 10 to form an appropriate oil film, thereby preventing seizing of the piston 30. - 特許庁

As shown enlarged in FIG. 5(C), the top ring 50 is a single annular member, and when viewed in cross section from the outer peripheral surface 52, it has a so-called barrel shape that protrudes radially outward. Specifically, both outer edges in the cylinder axial direction of the outer peripheral surface 52 are inclined in a direction away from the inner wall surface 12 toward the outer side in the cylinder axial direction. The contact width f of the outer peripheral surface 52 of the cylinder liner 10 with respect to the inner wall surface 12 is preferably 0.3 mm or less, for example. In addition, the surface roughness (arithmetic mean roughness of contour curve Ra (JIS B 0601: 2013)) of the outer peripheral surface 52 measured by a stylus surface roughness measuring instrument (JIS B 0651: 2001) is 0.250. (μm) or less is preferable.

As shown enlarged in FIG. 5(D), the second ring 60 is a single annular member, and the vicinity of the outer circumference thereof has a tapered shape that increases in diameter from the upper end in the axial direction of the cylinder toward the lower side in the axial direction of the cylinder. It's becoming An outer peripheral surface 62 located at the outermost end of the tapered shape and in contact with the inner wall surface 12 of the cylinder liner 10 has a planar shape in a cross-sectional view. The contact width f of the outer peripheral surface 62 of the cylinder liner 10 with respect to the inner wall surface 12 is preferably set to 0.3 mm or less, for example. In addition, the surface roughness (arithmetic mean roughness of contour curve Ra (JIS B 0601: 2013)) of the outer peripheral surface 62 measured by a stylus type surface roughness measuring instrument (JIS B 0651: 2001) is 0.250. (μm) or less is preferable.

The tension of the top ring 50 and the second ring 60 is set to a relatively low value, and the surface pressure acting on the contact surfaces of the outer peripheral surfaces 52 and 62 is, for example, 0.5 MPa or less, preferably 0.3 MPa. It is as follows. As a result, the top ring 50 and the second ring 60 often slide in the fluid lubrication region except near the top dead center and bottom dead center.

An oil ring 70 enlarged in FIG. 6A is of a two-piece type and has a ring main body 72 and a coil expander 76 in the shape of a coil spring. The ring body 72 has a pair of annular rails 73, 73 arranged at both ends in the axial direction, and an annular column portion 75 arranged between the pair of rails 73, 73 and connecting them. The combined cross-sectional shape of the pair of rails 73, 73 and the column portion 75 is approximately I-shaped or H-shaped. An inner peripheral groove 79 having a semicircular cross section is formed. Also, the pair of rails 73, 73 are formed with annular projections 74, 74 projecting radially outward from the column portion 75, respectively. Outer peripheral surfaces 82 , 82 formed at the tips of the annular projections 74 , 74 abut the inner wall surface 12 of the cylinder liner 10 . The coil expander 76 is accommodated in the inner peripheral groove 79 to press and urge the ring body 72 radially outward. A plurality of oil return holes 77 are formed in the column portion 75 of the ring body 72 in the circumferential direction.

The contact width of each of the pair of outer peripheral surfaces 82, 82 in FIG. 6A is preferably formed to be 0.02 mm to 0.30 mm, and is set to 0.15 mm, for example. The surface pressure acting on the contact surface of the outer peripheral surface 82 of the oil ring 70 is, for example, 1.0 MPa to 2.0 MPa, for example, approximately 1.75 MPa. Therefore, when the engine speed is high, the oil ring 70 often slides in the fluid lubrication region, but when the engine speed decreases, it often slides in the boundary lubrication region. Although the shape of the radial cross section of the outer peripheral surfaces 82, 82 is a simple trapezoid in FIG. The outer peripheral surface 82 of the lower rail 73 may have a stepped shape (a so-called step land shape) in which the corners of the mutually facing sides (coil expander 76 side) are notched. In addition, the surface roughness (arithmetic mean roughness of contour curve Ra (JIS B 0601:2013)) of the outer peripheral surface 82 measured by a stylus surface roughness measuring instrument (JIS B 0651:2001) is 0.450. (μm) or less is preferable.

Note that the oil ring 70 is not limited to the two-piece type, and may be, for example, a three-piece type oil ring 70 shown in FIG. 6(B). The oil ring 70 has annular side rails 73a and 73b separated vertically and a spacer expander 76s arranged between the side rails 73a and 73b.

The spacer expander 76s is formed by plastically working a steel material into a wave shape that repeats unevenness in the cylinder axial direction. Using this corrugated shape, an upper side support surface 78a and a lower side support surface 78b are formed, and a pair of side rails 73a and 73b are supported in the axial direction. The inner peripheral end of the spacer expander 76s has ears 74m erected in an arch shape toward the outside in the axial direction. The ear portions 74m abut against the inner peripheral surfaces of the side rails 73a and 73b. The spacer expander 76s is assembled in the ring groove of the piston 30 in a contracted state in the circumferential direction, with the joints being joined. As a result, due to the restoring force of the spacer expander 76s, the ear portions 74m press and urge the side rails 73a and 73b radially outward.

The contact width f of each of the outer peripheral surfaces 82, 82 of the side rails 73a, 73b in FIG. 6(B) is preferably 0.02 mm to 0.40 mm.

<Friction mode between cylinder liner and piston ring>

Next, the manner of friction between the cylinder liner and the piston ring will be described. Changes in the coefficient of friction during general sliding are expressed as a Stribeck diagram shown in FIG. 7(A). In this Stribeck diagram, the friction mode of the solid contact region 110 that slides in direct contact, the friction mode of the boundary lubrication region 112 that slides through the oil film, and the fluid lubrication region 114 that slides through the viscous lubricating oil film. It is classified into the friction mode in Moreover, between the boundary lubrication region 112 and the hydrodynamic lubrication region 114, there exists a friction mode of a mixed lubrication region 113 in which both states are mixed. In this Stribeck diagram, the horizontal axis is a logarithmic representation of "kinematic viscosity (coefficient of kinematic viscosity) μ" × "speed Q" / "contact load W", and the vertical axis is a coefficient of friction (f ). Therefore, it is the hydrodynamic lubrication region 114 or the mixed lubrication region 113 where the frictional force can be minimized, and effective use of these regions 114 and 113 is effective in reducing friction, that is, in reducing fuel consumption. On the other hand, if the boundary lubrication region 112 cannot shift to the fluid lubrication region 114 from the middle of the boundary lubrication region 112 even if the speed Q increases, the boundary lubrication region 112 continues up to the high speed region as indicated by the dotted line.

Incidentally, most of the frictional force in the fluid lubrication region 114 is shear resistance of the oil, and this shear resistance is defined by (viscosity)×(velocity)×(area)/(oil film thickness). As a result, reducing the shear area directly leads to reducing the frictional force.

Therefore, in the present embodiment, by actively causing oil to flow into the contact surface of the outer peripheral surface 42 of the piston ring 40, the fluid lubrication region 114 can be quickly transitioned to achieve low friction. At the same time, by applying the so-called dimple liner technology to the cylinder liner 10, the recessed portion 14 is formed in the stroke central region 20 of the cylinder liner 10 to reduce the substantial area where the shear resistance of the oil is generated. To effectively reduce the frictional force.

The Stribeck diagram of FIG. 7(A) shows the dynamic change of the friction coefficient (f) during one stroke of the piston 40. As another index for evaluating the friction mode, the friction loss average There is an effective pressure (FMEP: Friction Mean Effective Pressure). This friction loss average effective pressure indicates the value obtained by dividing the friction work per cycle by the stroke volume. A diagram (FMEP diagram) of this friction loss average effective pressure is shown in FIG. 7(B). In the FMEP diagram, the horizontal axis represents the rotation speed (N), and the vertical axis represents the friction loss average effective pressure (kPa). The higher the number of revolutions (N), the greater the ratio of fluid lubrication region 114 in one stroke. On the other hand, when the number of rotations (N) decreases, the ratio of fluid lubrication region 114 in one stroke decreases, and the ratio of mixed lubrication region 113 (or boundary lubrication region 112) increases. Therefore, the shape of the FMEP diagram of FIG. 7(B) is relatively similar to the shape of the hydrodynamic lubrication region 114 and the mixed lubrication region 113 of the Stribeck diagram of FIG. 7(A).

<Actual measurement result of sagging area>

Next, actual measurement results of the sagging region 200 formed in the cylinder liner 10 of the first embodiment will be described with reference to FIG. 8A and 8B, the maximum average length R (maximum average depth R) of the recess 14 in the cylinder radial direction is set to 3.0 μm, and the sagging region 200 is actively formed at the edge of the recess 14 by polishing. It is formed.

FIG. 8A shows the frequency of the sag width DW when the cross-sectional curve of the sag region 200 is measured 60 times. Although the sagging width DW varies somewhat, the average value is 0.036 mm. When this average sag width DW is converted to a sag gradient DA, it is 0.0139. FIG. 8(B) shows the frequency of the droop width DW of the median excluding the top 15 points and the bottom 15 points from the 60 data in FIG. 8(A). The average value of the sagging width DW is 0.030 mm. When this average sag width DW is converted to a sag gradient DA, it is 0.0167.

FIG. 9 shows the result of actual measurement of the sagging region 200 formed in the cylinder liner 10 as a comparative example. 9A and 9B, the maximum average length R (maximum average depth R) of the recess 14 in the cylinder radial direction is set to 3.0 μm, and the droop region 200 is actively formed at the edge of the recess 14. It was not.

FIG. 9A shows the frequency of the sag width DW when the cross-sectional curve of the sag region 200 is measured 60 times. Although the sagging width DW varies somewhat, the average value is 0.017 mm. When this average sag width DW is converted to a sag gradient DA, it is 0.0294. FIG. 9(B) shows the frequency of the droop width DW of the median excluding the top 15 points and the bottom 15 points from the 60 data in FIG. 9(A). The average value of the sagging width DW is 0.016 mm. When this average sag width DW is converted to a sag gradient DA, it is 0.0313.

<Action of sagging area>

According to the cylinder liner 10 of the present embodiment, the sagging region 200 is formed in the vicinity of the edge that serves as the boundary between the recess 14 and the inner wall surface 12, so interference between the piston ring 40 and the sagging region 200 is reduced. As a result, when the fluid lubrication region 114 or the mixed lubrication region 113 is formed between the piston ring 40 and the recess 14 and its surrounding inner wall surface 12, an oil film is stably formed to reduce the frictional force. In particular, in the cylinder liner 10 of this embodiment, the relative velocity Q between the cylinder liner 10 and the piston 30 becomes lower by forming the inner peripheral wall 12 around the recess 14 into the central low-roughness area 22. Even in such a case, the fluid lubrication region 114 is developed as dominantly as possible. In the present embodiment, by forming the sagging region 200 in the recessed portion 14 formed in the range overlapping with the central bottom roughness region 22, the range of the fluid lubrication region 114 can be further expanded.

Further, although actual measurement and analysis are difficult, it is presumed that by forming the sagging region 200 in the concave portion 14 , the lubricating oil flows smoothly in and out of the concave portion 14 . As a result, the lubricating oil in the concave portion 14 is smoothly guided to the surrounding inner wall surface 12, and it is assumed that the oil film formation on the inner wall surface 12 can be stabilized.

For example, if the recessed portion 14 is not sufficiently formed with the sagging region 200 , the edges of the piston ring 40 and the recessed portion 14 may interfere with each other. This interference directly leads to an increase in sliding resistance, and at the same time induces an unstable state in the formation of the oil film on the surrounding inner wall surface 12, and as a result, the range of the hydrodynamic lubrication region 114 is narrowed. Furthermore, if the piston ring 40 interferes with the edge of the recess 14 and the edge of the recess 14 or the piston ring is chipped, hairline-like scratches may be formed on the inner wall surface 12 by the chipped piece. This scratch also causes the formation of an oil film on the inner wall surface 12 to become unstable, making it difficult to maintain the fluid lubrication region 114 or the mixed lubrication region 113, leading to an increase in frictional force. In particular, when the inner peripheral wall 12 around the recess 14 is the central low-roughness region 22, the adverse effects of scratches are likely to become apparent.

Next, a method for measuring the friction state between the cylinder liner 10 and the piston ring 40 of the first embodiment, etc. will be described. Since the fixed positions of the top ring 50, the second ring 60, and the oil ring 70 installed on the piston 30 are relatively different in the axial direction of the cylinder, strictly speaking, the state of friction with the cylinder liner 10 is Although each piston ring has a slight difference, here the position of the second ring 60 is used as the reference position of the piston ring 40 for explanation. As for the fastest passing point C, the top ring 50 is used as a reference.

<Method for measuring friction mode (non-combustion friction test)>

FIG. 10 shows a friction unit measuring device 500 for measuring the friction state between the cylinder liner 10 and the piston ring 50 employed in the first embodiment. The friction unit measuring device 500 fixes the piston ring 40 side and vertically reciprocates the cylinder liner 10 side to measure the friction state between the two. That is, the measurement of this friction state is a friction test in a state in which no combustion occurs in the internal combustion engine (non-combustion friction test). A friction unit measuring device 500 holds a virtual piston 510 on which piston rings 40 (three rings of a top ring, a second ring, and an oil ring) are set by a fixed shaft 514 via a load cell 512 . The load cell 512 measures the vertical external force (frictional force) acting on the piston ring 40 .

The cylinder liner 10 is held by a moving sleeve 530 on its outer wall side. The lower end of the moving sleeve 530 is held by the driving piston 540 . This driving piston 540 is held by a connecting rod 550 that moves up and down by a crankshaft (not shown). As a result, the cylinder liner 10 reciprocates vertically. A stationary sleeve 560 is arranged around the moving sleeve 530 . Fixed sleeve 560 is fixed to base 570 . The fixed shaft 514 is fixed to a lid member 562 at the upper end of the fixed sleeve 560 . The outer peripheral surface of the moving sleeve 530 and the inner peripheral surface of the fixed sleeve 560 are slidable. A temperature control jacket 565 is provided inside the fixed sleeve 560 , and by circulating hot or cold water in the temperature control jacket 565 , the temperature of the fixed sleeve 560 can be controlled.

For example, as the conditions for measuring the friction mode by the friction unit measuring device 500, the lubricating oil standard is set to 10W-30, the oil temperature is set to 60 degrees, and the rotation speed of the crankshaft can be changed from 215 rpm to 2154 rpm.

Further, for example, the top ring 50 adopts a height (width) of 2.5 mm, the surface roughness Ra of the outer peripheral surface 52 is set to 0.180 (μm), and the tension is set to 16.7N. The second ring 60 has a height (width) of 2.0 mm, a surface roughness Ra of the outer peripheral surface 62 of 0.180 (μm), and a tension of 12.3N. The oil ring 70 adopts a height (width) of 3.0 mm, the surface roughness Ra of the outer peripheral surface 82 is set to 0.330 (μm), and the tension is set to 22.6N.

<Example: Friction force measurement result (non-combustion friction test)>

As an example, the first to third cylinder liners 10 ₀₁ , 10 ₀₂ , and 10 ₀₃ employed in the first embodiment were manufactured, and the frictional force of each was measured using the friction unit measuring device 500 shown in FIG. The results are shown in FIG. 11(A). The contour shape of the concave portion 14 of the first to third cylinder liners 10 ₀₁ , 10 ₀₂ , 10 ₀₃ is a perfect circle as shown in FIG. The maximum average length (maximum average depth) of the recess 14 in the radial direction of the cylinder was set to about 5 μm, and the sagging region 200 was positively formed at the edge of the recess 14 by polishing, and the subsequent chemical conversion treatment was not performed. The area occupation ratio of the recess 14 was set to 40% of the total area of the inner wall surface 12 and the recess 14 . The droop width DW in the axial direction of the cylinder is 0.030 mm for the first cylinder liner 1001 (the droop gradient DA is _0.0167 ), and 0.050 mm for the second cylinder liner 1002 (the droop gradient DA is _0.0100 mm). ), and the third cylinder liner 1003 was 0.080 mm (sag gradient DA was _0.0063 ).

Also, as a cylinder liner 1099 as a comparative example, the droop width DW is 0.019 mm (the _droop gradient DA is _0.0263 ), and the other specifications are the first to third cylinder liners ₁₀₀₁ , 1002, and ₁₀₀₃ . I made something similar.

In the graph of FIG. 11(A), when the frictional force of the cylinder liner ₁₀₉₉ serving as a comparative example is set to 100%, the ratio of the frictional forces of the first to third cylinder _{liners 1001} , ₁₀₀₂ , and 1003 is show. As can be seen from these results, the larger the sag width DW (the smaller the sag gradient DA), the more the frictional force decreases.

<Change in Friction Mode Due to Formation of Drooping Area>

In the cylinder liner 10 of the present embodiment, by measuring the friction state with the friction unit measuring device 500, it is possible to confirm the reduction of the frictional force due to the presence of the sagging region 200. FIG. In particular, in the cylinder liner 10 of the present embodiment, the relative velocity Q between the cylinder liner 10 and the piston 30 is increased due to the presence of the sagging region 200 in the recessed portion 14 formed in the range overlapping the central bottom roughness region 22. Even when the speed becomes low, it is possible to reduce the frictional force.

<Change in Friction Mode Depending on the Presence or Absence of Central Low-Roughness Region>

In the first embodiment, the cylinder liner 10 has both the sagging region 200 and the central low-roughness region 22 . It is important to clarify the effect of the chisel on the frictional force. Therefore, it is preferable to measure the friction mode by the friction unit measuring device 500 also for the verification cylinder liner that has the central low-roughness region 22 but does not form the sagging region 200 in the concave portion 14 . The actual measurement results are shown below.

<Friction mode between verification cylinder liner having only central low-roughness region and piston ring>

(About the Stribeck diagram)

In order to actualize the friction mode of the central low-roughness region in the first embodiment, the surface roughness Ra of the central low-roughness region 22 was set to 0.120 (μm) without forming the sagging region 200. A verification cylinder liner 10-A and a verification cylinder liner 10-B with a surface roughness Ra of 0.083 (μm) were prepared, and the friction mode was measured using the friction unit measuring device 500. For reference, a verification cylinder liner X having the same shape as the verification cylinder liner 10 (without the sagging region 200) and having a surface roughness Ra of 0.160 (μm), and a test cylinder liner X without forming the recess 14 itself, the surface A verification cylinder liner Y having a roughness Ra of 0.160 (μm) was prepared, and other conditions were set to the same conditions, and the friction mode was measured using the friction unit measuring device 500 . Note that chemical conversion treatment was not performed on any of the cylinder liners 10-A, 10-B, X, and Y for verification. The measurement result of the Stribeck diagram is shown in FIG. 12(A), and the measurement result of the FMEP diagram is shown in FIG. 12(B). 12(A) and 12(B) show a hypothetical cylinder liner K for verification in which the surface roughness Ra of the central low-roughness region 22 is Ra 0.140 (μm) without forming the sagging region 200. Estimated values for are also given.

First, Table 1 below shows a list of the surface roughnesses of the verification cylinder liners 10-A, 10-B, and K. Note that the arithmetic mean roughness Ra is a value measured by a stylus type surface roughness tester (JIS B 0651: 2001), arithmetic mean height Sa (μm), protrusion peak height Spk (μm) , protruded valley depth Svk (μm), and core portion level difference: Sk (μm) are values measured using a non-contact surface roughness measuring machine using a laser microscope as already described.

The verification cylinder liners 10-A and 10-B and the verification cylinder liner X are formed with recesses 14 over the entire stroke center region 20. As shown in FIG. As shown in FIG. 13, when the piston 30 slides from the top dead center T to the bottom dead center U of the verification cylinder liner, the variation in the coefficient of friction between the verification cylinder liner and the piston ring 40 is the relative Speed dependent. This relative speed is uniquely determined with respect to the number of revolutions (rpm) of the engine. The piston 30 descends from a state where the speed at the top dead center T of the verification cylinder liner is zero, goes through the stroke A, and reaches the maximum speed C on the way. After that, when reaching the bottom dead center U via the stroke B, the speed becomes zero. During this period, the coefficient of friction always changes along the Stribeck diagram of FIG. 12(A).

In the Stribeck diagram of FIG. 12(A), μ is the kinematic viscosity (kinematic viscosity) in the central low-roughness region 22, Q is the relative speed with the piston 30 (piston ring 40), and W is the contact load on the piston 30. , the coefficient of friction with the piston 30 is defined as f (vertical axis of the graph), and the evaluation parameter is defined as A=μ×Q/W (horizontal axis of the graph (logarithmic notation)).

In the verification cylinder liners 10-A and 10-B, the minimum value fmin of the friction coefficient f in the central low-roughness region 20 is located within the range where the evaluation parameter A is 0.0003 or less. More desirably, the minimum value fmin of the friction coefficient f is positioned within a range where the evaluation parameter A is 0.0002 or less. On the other hand, the minimum value fmin of the friction coefficient f in the central low-roughness region 20 is located within the range where the evaluation parameter A is 0.0001 or more.

Furthermore, in the verification cylinder liners 10-A and 10-B, the friction coefficient f in the central low-roughness region 20 is 0.07 or less in any of the ranges in which the evaluation parameter A is 0.0003 or less. Desirably, the coefficient of friction f is 0.06 or less.

As can be seen from the comparison with the test cylinder liner X (surface roughness Ra 0.160 (μm)/concave portion), the test cylinder liners 10-A and 10-B have a range in which the coefficient of friction is 0.07 or less. , spreads to the left of the graph when the evaluation parameter A is 0.0003 or less. This means that the range of the fluid lubrication region 114 and the mixed lubrication region 113 is widened even during low-speed sliding, resulting in a sliding mode with an extremely low coefficient of friction f.

As can be seen from the verification results of these verification cylinder liners, in addition to the above-described low friction coefficient state created by the central low roughness region 22, when the sagging region 200 is formed in the recess 14, this low friction coefficient However, it can be maintained for a long period of time.

As a reference, in the case of the verification cylinder liner X (surface roughness Ra 0.160 (μm)/with recesses), when the evaluation parameter A exceeds 0.0003, the effect of the recesses 14 appears and the friction coefficient f increases. The coefficient of friction f becomes smaller than that of the cylinder liner Y for verification (surface roughness Ra 0.160 (μm)/no concave portion). On the other hand, when the evaluation parameter A is within the range of 0.0003 to 0.0005, the graph of the verification cylinder liner X (surface roughness Ra 0.160 (μm) / with recessed portion) and the verification cylinder liner Y (surface roughness Ra 0 0.160 (μm)/no recesses) intersects, and when the evaluation parameter A becomes 0.0003 or less, the friction coefficient f of the verification cylinder liner X (surface roughness Ra 0.160 (μm)/with recesses) becomes It rises in a range exceeding 0.07 and exceeds the friction coefficient f of the cylinder liner Y for verification (surface roughness Ra 0.160 (μm)/no concave portion). That is, in the case of the verification cylinder liner X (surface roughness Ra 0.160 (μm)/with recesses), the recesses 14 act to reduce the friction coefficient f in the range where the evaluation parameter A exceeds 0.0003. , the evaluation parameter A is in the range of 0.0003 or less, the concave portion 14 increases the friction coefficient f. According to the inventors' unpublished consideration, in the case of the verification cylinder liner X (surface roughness Ra 0.160 (μm)/with recesses), the presence of the recesses 14 causes the actual contact area between the cylinder liner and the piston ring 40 to be Therefore, it is presumed that insufficient lubrication by lubricating oil tends to occur in the low-speed region, and that the lubrication tends to fall into the boundary lubrication region. The sagging region 200 of the cylinder liner 10 of the present embodiment can exhibit the effect of reducing insufficient lubrication (increased frictional force) due to the recess 14 .

In the verification cylinder liners 10-A and 10-B, the surface roughness Ra of the central low-roughness region 20 is set to 0.120 (μm) or less, so the evaluation parameter A is a low-speed region of 0.0003 or less. In addition, even if the actual contact area with the piston ring 40 is small due to the concave portion 14, the fluid lubrication region 114 or the mixed lubrication region 113 can be easily maintained. Further, even if boundary lubrication occurs, the coefficient of friction is kept small because the surface roughness is small. In general, when the surface roughness Ra of the inner peripheral surface of the cylinder liner is set to 0.120 (μm) or less, the lubricating oil retaining force of the contact surface is reduced and the lubricating oil tends to be insufficient. , The recessed portion 14 superimposed on the central low-roughness region 22 functions as a lubricating oil storage portion for the central low-roughness region 20, so there is also a synergistic effect that shortage of lubricating oil is less likely to occur in the central low-roughness region 20. can get.

At this time, it is presumed that if a sagging region 200 is further formed in the concave portion 14, the lubricating oil flows in and out of the concave portion 14 smoothly. As a result, the lubricating oil is smoothly guided to the central low-roughness region 22 from the concave portion 14, which serves as a reservoir for the lubricating oil. .

Furthermore, in the verification cylinder liners 10-A and 10-B, the friction coefficient f in the range (high-speed region) where the evaluation parameter A exceeds 0.0003 is / with concave portion), or smaller than it. That is, in the verification cylinder liners 10-A and 10-B, the central low-roughness region 20 contributes to the reduction of the friction coefficient f even in the high-speed region.

In the Stribeck diagram of FIG. 12(A), the surface roughness Ra of the central low-roughness region 20 of the central low-roughness region 20 is 0.140 (μm ), the friction coefficient of the verification cylinder liner K is estimated and displayed. The friction coefficient of the verification cylinder liner K is divided into the state of the verification cylinder liners X and Y with a surface roughness Ra of 0.160 (μm) and the state of the verification cylinder liner with a surface roughness Ra of 0.120 (μm). It can be assumed to approximate the median value of liner 10-A. Even with this verification cylinder liner K, the friction coefficient f in the central low-roughness region 20 is 0.07 or less within any range in which the evaluation parameter A is 0.0003 or less, and preferably the friction coefficient f is 0.06 or less. Furthermore, in the verification cylinder liner K, the friction coefficient f in the range where the evaluation parameter A exceeds 0.0003 (high-speed region) is the friction It approximates the factor f or is smaller than it.

(About FMEP diagram)

In the FMEP diagram of FIG. 12(B), the friction loss average effective pressure (FMEP) between the central low roughness region 22 and the piston ring 40 is defined as T (kPa) (vertical axis), and the rotation speed of the internal combustion engine is defined as N (r/min) (horizontal axis).

In the verification cylinder liners 10-A and 10-B, the minimum value Tmin of the friction loss mean effective pressure T in the central low-roughness region 20 is located within the range where the rotational speed N is 700 or less. More desirably, the minimum value Tmin of the friction loss mean effective pressure T is positioned within a range where the rotational speed N is 600 or less.

Further, in the verification cylinder liners 10-A and 10-B, the friction loss average effective pressure T in the central low-roughness region 20 is set to 14 kPa or less when the number of revolutions N is within the range of 700 or less. do.

As can be seen from a comparison with the verification cylinder liner X (surface roughness Ra 0.160 (μm)/concave portion), the verification cylinder liners 10-A and 10-B have a small friction loss average effective pressure T of 14 kPa or less. range extends to rotation speed N of 700 or less (left side of the graph). As a result, even at low rotation, a sliding mode with extremely low friction loss is obtained.

As a reference, in the case of the test cylinder liner X (surface roughness Ra 0.160 (μm)/with recesses), when the rotation speed N exceeds 700, the effect of the recesses 14 appears and the friction loss increase rate In particular, the friction loss becomes smaller than that of the test cylinder liner Y (surface roughness Ra 0.160 (μm)/no concave portion) when the number of revolutions N exceeds 1000. On the other hand, when the rotation speed N is within the range of 1000 to 1300, the graph of the verification cylinder liner X (surface roughness Ra 0.160 (μm) / with recessed portion) and the verification cylinder liner Y (surface roughness Ra 0.160 (μm) )/no recess) intersect. When the rotational speed N is 1000 or less, it exceeds the friction loss of the verification cylinder liner Y (surface roughness Ra: 0.160 (μm)/no recesses). That is, in the case of the verification cylinder liner X (surface roughness Ra 0.160 (μm)/with recesses), the recesses 14 act to reduce friction loss in a range where the rotation speed N exceeds 1000, but the rotation speed When N is in the range of 1000 or less, the concave portion 14 acts to increase friction loss. According to the inventors' unpublished consideration, in the case of the verification cylinder liner X (surface roughness Ra 0.160 (μm)/with recesses), the presence of the recesses 14 causes the actual contact area between the cylinder liner and the piston ring 40 to be becomes smaller, it is presumed that insufficient lubrication by lubricating oil tends to occur in the low speed region, and the ratio occupied by the boundary lubrication region tends to increase. The sagging region 200 of the cylinder liner 10 of the present embodiment can exhibit the effect of suppressing an increase in friction loss due to the recess 14 .

In the verification cylinder liners 10-A and 10-B, the surface roughness Ra of the central low-roughness region 20 is set to 0.120 (μm) or less. However, by maintaining the fluid lubrication region 114 or the mixed lubrication region 113, the friction loss is suppressed. Moreover, even if boundary lubrication occurs, friction loss is suppressed because the surface roughness is small. Specifically, when the rotational speed N is 700 or less, the test cylinder liner X (surface roughness Ra: 0.160 (μm)/with recesses) is used as a reference, and the test cylinder liner 10-A is about 2.0 kPa. In the case of the verification cylinder liner 10-B, a reduction effect of about 4.0 kPa can be obtained. In general, if the surface roughness Ra of the inner peripheral surface of the cylinder liner is set to 0.120 (μm) or less, the lubricating oil retaining force is reduced and the lubricating oil tends to be insufficient. Since the concave portion 14 superimposed on the roughness region 22 functions as a lubricating oil reservoir for the central low-roughness region 20, a synergistic effect is obtained in which insufficient lubricating oil is less likely to occur in the central low-roughness region 20.

In addition to the low friction loss state created by the central low-roughness region 22, further forming the sagging region 200 in the concave portion 14 leads to the ability to maintain this low friction loss state over a long period of time.

Furthermore, in the verification cylinder liners 10-A and 10-B, the friction loss in the high rotation range where the number of revolutions N exceeds 700 is Close to or less than friction loss. That is, in the verification cylinder liners 10-A and 10-B, the central low-roughness region 20 does not adversely affect the friction loss even in the high-speed region.

Incidentally, this FMEP diagram is based on a non-combustion friction test. Therefore, the FMEP value of an actual internal combustion engine in which actual combustion occurs is higher than this value due to the effect of the combustion pressure.

In the FMEP diagram of FIG. 12(B), the surface roughness Ra of the central low-roughness region 20 is 0.140 (μm) in the same configuration as the verification cylinder liner 10-A, although it is not an actual measurement value. FMEP of the verification cylinder liner K is estimated and displayed. The FMEP diagram of the verification cylinder liner K is the FMEP diagram of the verification cylinder liners X and Y with a surface roughness Ra of 0.160 (μm), and the FMEP diagram of the verification cylinder liner with a surface roughness Ra of 0.120 (μm). It can be assumed that it approximates the middle value of the 10-A FMEP diagram. In this verification cylinder liner K, the range in which the friction loss average effective pressure T is reduced to 14 kPa or less extends to rotation speed N of 700 or less (left side of the graph). As a result, even at low rotation, a sliding mode with extremely low friction loss is obtained.

That is, in the verification cylinder liner K, friction loss is suppressed by maintaining the fluid lubrication region 114 or the mixed lubrication region 113 even in the low rotational speed region where the rotational speed N is 700 or less. Moreover, even if boundary lubrication occurs, friction loss is suppressed because the surface roughness is small. In general, if the surface roughness Ra of the inner peripheral surface of the cylinder liner is set to 0.140 (μm) or less, the lubricating oil retaining force is reduced and the lubricating oil tends to be insufficient. Since the recessed portion 14 superimposed on the low-roughness region 22 functions as a lubricating oil reservoir for the central low-roughness region 20, a synergistic effect is obtained in which insufficient lubricating oil is unlikely to occur in the central low-roughness region 20. .

<Oil consumption>

In the case of the sliding structure of the cylinder liner 10 and the piston 30 of this embodiment, oil consumption is also suppressed. This is because the absolute amount of lubricating oil film formed in the central low-roughness region 22 is reduced. Even if the absolute amount of the oil film is reduced, since the concave portion 14 having the sagging region 200 is superimposed, the lubricating oil in the concave portion 14 is smoothly guided to the surrounding inner wall surface 12. , you will never run out of lubrication. That is, in this embodiment, it is possible to rationally solve both the reduction in oil consumption and the sufficient lubrication effect.

<Cylinder liner of the second embodiment>

Next, a sliding structure for an internal combustion engine according to a second embodiment of the invention will be described with reference to the accompanying drawings.

As shown in FIG. 14(A), a plurality of recesses 14 are formed in the inner wall surface 12 of the cylinder liner 10 according to the internal combustion engine of the second embodiment. A sagging region 200 similar to that of the first embodiment is formed in the plurality of concave portions 14 . The recess 14 is formed only in the stroke central region 20 of the inner wall surface 12 . The stroke center region 20 extends from the lower surface position 19A of the ring groove of the lowest piston ring at the top dead center T of the piston 30 (hereinafter also referred to as the top dead center side edge) to the bottom dead center U of the piston 30. It is part of the entire range (hereinafter referred to as the reference stroke area 19) up to the upper surface position 19B (hereinafter also referred to as the bottom dead center side edge) of the ring groove of the uppermost piston ring.

The stroke center region 20 of the present embodiment is positioned below the top dead center side edge 19A of the reference stroke region 19. As shown in FIG. As a result, a smooth upper smooth region 130A having no concave portion is formed entirely from the top dead center side edge 19A of the reference stroke region 19 to the top dead center side edge 27A of the stroke central region 20. It is formed. The upper smooth area 130A is an area through which the piston ring 40 passes.

Further, the stroke central region 20 of the present embodiment is shifted upward from the bottom dead center side edge 19B of the reference stroke region 19 . As a result, the entire area from the edge 19B on the bottom dead center side of the reference stroke area 19 to the edge 27B on the bottom dead center side of the central stroke area 20 is a smooth lower smooth area 130B that does not have recesses. is formed. The lower smooth area 130B is an area through which the piston ring 40 passes.

In the present embodiment, the edge 27A on the top dead center side of the stroke central region 20 may be referred to as an "upper boundary" which means a boundary line between a location where the recess 14 is formed and a location where the recess 14 is not formed. Also, the edge 27B of the stroke center region 20 on the bottom dead center side is sometimes called a "lower boundary" which means a boundary line between a place where the recess 14 is formed and a place where the recess 14 is not formed. The edge (lower boundary) 27B on the bottom dead center side of the stroke center region 20 may be aligned with the edge 19B on the bottom dead center side of the reference stroke region 19, or may be widened below it. Also good.

Further, if the area outside the stroke central area 20 is defined as an external area 25, this external area 25 includes an upper external area 25A adjacent to the top dead center side of the stroke central area 20, and an area between the stroke central area 20. It is composed of a lower outer region 25B adjacent to the bottom dead center side. The upper smooth region 130A is included in a portion of the upper external region 25A, and the lower smooth region 130B is included in a portion of the lower external region 23B.

In the present embodiment, in at least part of the stroke central region 20, the surface roughness (arithmetic mean roughness) Ra measured by a stylus surface roughness measuring instrument is 0.140 (μm) or less, which is preferable. A central low-roughness region 22 having a surface roughness Ra of 0.120 (μm) or less is formed. Here, the entire stroke central region 20 is the central low-roughness region 22 . As a result, the central low-roughness region 22 includes near the top edge and near the bottom edge of the mid-stroke region 20 in which the recess 14 is formed.

The surface roughness values of this central low-roughness region 22 measured by a non-contact surface roughness measuring machine using a laser microscope are shown below.
Arithmetic mean height Sa (μm): 0.192 or less, preferably 0.163 or less, more preferably 0.120 or less (specifically set to 0.110).
Projection peak height Spk (μm): 0.159 or less, preferably 0.144 or less, more preferably 0.121 or less (specifically set to 0.116).
Core portion level difference Sk (μm): 0.521 or less, preferably 0.449 or less, more preferably 0.340 or less (specifically set to 0.315).
Projection valley depth Svk (μm): 0.409 or less, preferably 0.342 or less, more preferably 0.241 or less (specifically set to 0.218).

Furthermore, the upper smooth region 130A adjacent to the upper side of the stroke central region 20 has a surface roughness (arithmetic mean roughness) Ra of 0.140 (μm) or less by a stylus type surface roughness measuring machine, preferably , an upper low-roughness region 23A having a surface roughness Ra of 0.120 (μm) or less is formed. The upper low-roughness region 23A of the present embodiment is formed to extend over the upper smooth region 130A while overlapping the upper smooth region 130A. In addition, the lower smooth region 130 adjacent to the lower side of the stroke central region 20 has a surface roughness (arithmetic mean roughness) Ra of 0.140 (μm) or less, preferably 0. A lower low-roughness region 23B of 0.120 (μm) or less is formed. The lower low-roughness region 23B of the present embodiment is formed to extend beyond the lower smooth region 130B while overlapping the lower smooth region 130B. The upper low-roughness region 23A, the central low-roughness region 22, and the lower low-roughness region 23B are completely connected with uniform surface roughness, and form an integral continuous plane as a whole.

The surface roughness values of the upper low-roughness region 23A and/or the lower low-roughness region 23B measured by a non-contact surface roughness measuring machine using a laser microscope are shown below.
Arithmetic mean height Sa (μm): 0.192 or less, preferably 0.163 or less, more preferably 0.120 or less (specifically set to 0.110).
Projection peak height Spk (μm): 0.159 or less, preferably 0.144 or less, more preferably 0.121 or less (specifically set to 0.116).
Core portion level difference Sk (μm): 0.521 or less, preferably 0.449 or less, more preferably 0.340 or less (specifically set to 0.315).
Projection valley depth Svk (μm): 0.409 or less, preferably 0.342 or less, more preferably 0.241 or less (specifically set to 0.218).

When the piston 30 reciprocates in the cylinder liner 10, the upper external region 25A (upper low roughness region 23A), the stroke central region 20 (central low roughness region 22), the lower external region 25B (lower low roughness 23B), the stroke central region 20 (central low-roughness region 22), and the upper outer region 25A (upper low-roughness region 23A) are repeatedly passed in this order.

The stroke-direction distance of the upper smooth region 130A is desirably set to 30% or more of the total stroke-direction distance of the reference stroke region 19 . In addition, the stroke direction center point 20M in the stroke center region 20 is positioned closer to the bottom dead center U side of the piston than the stroke direction center point 19M in the reference stroke region.

If the position where the uppermost piston ring (top ring 50 described later) passes through the inner wall surface 12 at the highest speed is defined as the fastest passing point C, the edge of the stroke center region 20 on the top dead center side (upper boundary) 27A is set below the fastest passing point C. In this embodiment, the edge 27A on the top dead center side and the fastest passing point C are set to coincide with each other.

The central low-roughness region 22, the upper low-roughness region 23A, and the lower low-roughness region 23B of the cylinder liner 10 are formed by honing using a honing machine. As for the grain size of the honing grindstone at this time, it is preferable to use abrasive grains finer than F500 or #800 (JIS R 6001-2:2017, ISO8486-2:2007), for example. After forming the central low-roughness region 22, the upper low-roughness region 23A, and the lower low-roughness region 23B by this honing process, it is preferable not to perform chemical conversion treatment on the surfaces thereof. For example, when a phosphate coating or the like is generally used in the manufacturing process of the cylinder liner 10, the surface properties of the central low-roughness region 22, the upper low-roughness region 23A, and the lower low-roughness region 23B are changed to that of the coating. This is because it fluctuates depending on On the other hand, if the film has a small variation in surface properties, it is desirable to apply chemical conversion treatment to the central low-roughness region 22, the upper low-roughness region 23A, and the lower low-roughness region 23B.

<Action of sagging area>

According to the cylinder liner 10 of the second embodiment, since the sagging region 200 is formed in the vicinity of the edge serving as the boundary between the recess 14 and the inner wall surface 12, interference between the piston ring 40 and the sagging region 200 is reduced. . As a result, when the fluid lubrication region 114 or the mixed lubrication region 113 is formed between the piston ring 40 and the recess 14 and its surrounding inner wall surface 12, an oil film is stably formed to reduce the frictional force.

Further, although actual measurement and analysis are difficult, it is presumed that by forming the sagging region 200 in the concave portion 14 , the lubricating oil flows smoothly in and out of the concave portion 14 . As a result, the lubricating oil in the concave portion 14 is smoothly guided to the surrounding inner wall surface 12, and it is assumed that the oil film formation on the inner wall surface 12 can be stabilized.

Furthermore, the existence of the sagging region 200 makes it difficult for the piston ring 40 and the edge of the recess 14 to interfere with each other, thereby suppressing damage to the edge of the recess 14 and the piston ring. As a result, it is possible to reduce the occurrence of hairline-like flaws in the upper low-roughness region 23A due to the defective pieces.

<Significance of Existence of Upper Low Roughness Region 23A>

As already described, in the present embodiment, the upper low roughness region 23A in which no recesses are formed is provided on the top dead center side of the central low roughness region 22 in which the recesses are superimposed. The significance of the upper low-roughness region 23A is as follows. The top dead center side of the piston 30 is in a high temperature environment due to the existence of the combustion chamber. Therefore, if a recess is formed on the top dead center side of the cylinder liner 10 and the engine oil is retained in the recess, the engine oil becomes hot and evaporates, resulting in an increase in oil consumption. Therefore, by not forming a concave portion in the upper low-roughness region 23A, oil consumption is suppressed. On the other hand, if the upper low-roughness region 23A is reduced in roughness as in the present embodiment, insufficient lubrication may occur, or the recessed portion 14 formed overlapping the central low-roughness region 22 adjacent to the lower side may be It functions as a reservoir for lubricating oil, and the lubricating oil is positively supplied to the upper low-roughness region 23A via the recess 14, so that a synergistic effect is obtained in which insufficient lubrication is unlikely to occur.

In addition, since the viscosity of the engine oil decreases due to the high temperature environment on the side of the top dead center T of the piston 30, it is difficult to form an oil film. , preferably 0.100 (μm) or less, even if the oil film is small, the fluid lubrication region or the mixed lubrication region is positively established. Even if it is in the boundary lubrication region, the friction coefficient can be small because the roughness is low. Furthermore, since the lubricating oil accumulated in the concave portion 14 superimposed on the central low-roughness region 22 can supply lubricating oil to the upper low-roughness region 23A, shortage of lubricating oil in the upper low-roughness region 23A is unlikely to occur. There is an advantage.

<Sliding Structure Between Cylinder Liner and Piston Ring of Second Embodiment>

FIG. 14(B) shows a stroke in which the piston ring 40 moves relative to the cylinder liner 10 from the top dead center T toward the bottom dead center U. As shown in FIG. Stroke lines A and L are formed during the relative movement of the piston ring 40 in the upper low-roughness region 23A. A stroke line M is formed when the piston ring 40 passes through the central low-roughness region 22 . After that, the lower low-roughness region 23B of the cylinder liner 10 becomes stroke lines N and B while the piston ring 40 is relatively moving toward the bottom dead center side.

According to the sliding structure of the internal combustion engine of the second embodiment, as in the first embodiment, the central low-roughness region 22 can reduce the coefficient of friction during low-speed movement. In addition, it is possible to reduce friction loss during low rotation. Furthermore, the oil consumption can be suppressed by the upper low-roughness region 23A through which the piston ring 40 passes.

It should be noted that the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

10 cylinder liner 12 inner wall surface 14 concave portion 20 stroke central region 22 central low-roughness region 23A upper low-roughness region 23B lower low-roughness region 25 outer region 25A upper outer region 25B lower outer region 30 piston 40 piston ring 110 Solid contact area 112 Boundary lubrication area 113 Mixed lubrication area 114 Fluid lubrication area 200 Sagging area

Claims (20)

A cylinder in which a piston having a piston ring slides on an inner wall surface,
All of the inner wall surface between the lower surface position of the ring groove of the lowest piston ring at the top dead center of the piston and the upper surface position of the ring groove of the highest piston ring at the bottom dead center of the piston, or A plurality of recessed portions are formed in the stroke central region that becomes a part,
A sagging region defined by the following region conditions is formed on the side surface of the recess,
(area conditions)
The shape of the at least two recesses arranged in the cylinder axial direction is measured by a stylus surface roughness measuring machine (JIS B 0651: 2001) in a state including a plurality of adjacent inner wall surfaces, with a measuring needle tip radius of 2 μm and a cross-sectional curve. Based on the cross-sectional curve obtained by setting the cutoff value (wavelength) λs for 2.5 μm and measuring:
A line obtained by extracting a plurality of the inner wall surfaces and converting them into a single straight line using the method of least squares is defined as the reference height line of the inner wall surface:
A line offset from the inner wall surface reference height line to the bottom side of the recess by 0.15 μm is defined as an upper reference height line that means the upper edge of the sagging region:
A line offset by 0.50 μm from the upper reference height line to the bottom side of the recess is defined as a lower reference height line, which means the lower edge of the sagging region:
The cross-sectional curve extending from the inner wall surface to the bottom surface of the recess first intersects the lower reference height line and the upper point where the upper reference height line first intersects in the vicinity of the boundary with the inner wall surface. A line segment connecting the lower points is defined as a hypothetical sag section of the sag region:
A cylinder, wherein an absolute value of a gradient with respect to the inner wall surface of the imaginary sagging section in the sagging region is set within a range of 0.00625 to 0.0167. At least a part of the surface in contact with the piston ring in the stroke center region has a low central roughness such that the arithmetic mean roughness Ra of the profile curve measured by a stylus surface roughness measuring device is 0.140 μm or less. characterized in that a narrow region is formed,
A cylinder according to claim 1. characterized in that the recess having the sagging region is formed within the range of the central bottom roughness region,
3. A cylinder according to claim 2. The arithmetic mean height Sa of the contour curved surface of the central low-roughness region measured by a non-contact surface roughness measuring device is 0.20 μm or less,
A cylinder according to claim 2 or 3. The protruding valley depth Svk of the central low roughness region measured by a non-contact surface roughness measuring device is 0.41 μm or less,
A cylinder according to any one of claims 2-4. The height Spk of the central low-roughness region measured by a non-contact surface roughness measuring device is 0.16 μm or less,
A cylinder according to any one of claims 2-5. The level difference Sk of the core portion of the central low-roughness region measured by a non-contact surface roughness measuring device is 0.53 μm or less,
A cylinder according to any one of claims 2-6. When the protruding peak height measured by the non-contact surface roughness measuring device in the central low roughness region is E (Spk) and the protruding valley depth is I (Svk), I / E is 2.6 or less,
The cylinder according to any one of claims 2-7. The arithmetic mean roughness Ra of the contour curve of the central low roughness region measured by a stylus surface roughness measuring instrument is 0.120 μm or less,
The cylinder according to any one of claims 2-8. A sliding structure for an internal combustion engine having a cylinder and a piston,
The cylinder is
All of the inner wall surface between the lower surface position of the ring groove of the lowest piston ring at the top dead center of the piston and the upper surface position of the ring groove of the highest piston ring at the bottom dead center of the piston, or A plurality of recessed portions are formed in the stroke central region that becomes a part,
A sagging region defined by the following region conditions is formed on the side surface of the recess,
(area condition)
The shape of the at least two recesses arranged in the cylinder axial direction is measured by a stylus surface roughness measuring machine (JIS B 0651: 2001) in a state including a plurality of adjacent inner wall surfaces, with a measuring needle tip radius of 2 μm and a cross-sectional curve. Based on the cross-sectional curve obtained by setting the cutoff value (wavelength) λs for 2.5 μm and measuring:
A line obtained by extracting a plurality of the inner wall surfaces and converting them into a single straight line using the method of least squares is defined as the reference height line of the inner wall surface:
A line offset from the inner wall surface reference height line to the bottom side of the recess by 0.15 μm is defined as an upper reference height line that means the upper edge of the sagging region:
A line offset by 0.50 μm from the upper reference height line to the bottom side of the recess is defined as a lower reference height line, which means the lower edge of the sagging region:
The cross-sectional curve extending from the inner wall surface to the bottom surface of the recess first intersects the lower reference height line and the upper point where the upper reference height line first intersects in the vicinity of the boundary with the inner wall surface. A line segment connecting the lower points is defined as a hypothetical sag section of the sag region:
The absolute value of the gradient with reference to the inner wall surface of the virtual sag section in the sag region is set within the range of 0.00625 to 0.0167,
Sliding structure for internal combustion engines. At least part of the surface in contact with the piston ring in the stroke center region of the cylinder has an arithmetic mean roughness Ra of a profile curve measured by a stylus type surface roughness measuring instrument of 0.140 μm or less. characterized in that a central low-roughness region is formed,
The sliding structure for an internal combustion engine according to claim 10. characterized in that the recess having the sagging region is formed within the range of the central bottom roughness region,
The sliding structure for an internal combustion engine according to claim 11. The arithmetic mean height Sa of the contour curved surface of the central low-roughness region measured by a non-contact surface roughness measuring device is 0.20 μm or less,
The sliding structure for an internal combustion engine according to claim 11 or 12. The protruding valley depth Svk of the central low roughness region measured by a non-contact surface roughness measuring device is 0.41 μm or less,
A sliding structure for an internal combustion engine according to any one of claims 11 to 13. The height Spk of the central low-roughness region measured by a non-contact surface roughness measuring device is 0.16 μm or less,
A sliding structure for an internal combustion engine according to any one of claims 11 to 14. The level difference Sk of the core portion of the central low-roughness region measured by a non-contact surface roughness measuring device is 0.53 μm or less,
A sliding structure for an internal combustion engine according to any one of claims 11 to 15. When the protruding peak height measured by the non-contact surface roughness measuring device in the central low roughness region is E (Spk) and the protruding valley depth is I (Svk), I / E is 2.6 or less,
A sliding structure for an internal combustion engine according to any one of claims 11 to 16. The arithmetic mean roughness Ra of the contour curve of the central low roughness region measured by a stylus surface roughness measuring instrument is 0.120 μm or less,
A sliding structure for an internal combustion engine according to any one of claims 11 to 17. The central low-roughness region includes the vicinity of the upper edge and the vicinity of the lower edge in the stroke central region,
A sliding structure for an internal combustion engine according to any one of claims 11 to 18. The entire stroke central region is the central low-roughness region,
A sliding structure for an internal combustion engine according to any one of claims 11 to 19.

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