Method for processing recessed portion of cylinder and inner wall surface of cylinder

Abstract

A cylinder in which a piston provided with a piston ring slides on an inner wall surface, a plurality of recesses (14) based on laser processing are formed in a stroke central portion region of the inner wall surface (12), a surface roughness of a bottom surface (14A) of the recesses (14) satisfies at least one of a first state in which a core portion height difference Rk after polishing processing of the bottom surface is less than 1.6 μm, a second state in which a protruding valley portion depth Rvk after polishing processing of the bottom surface is less than 1.3 μm, a third state in which a core portion height difference Rk after chemical conversion processing and polishing processing of the bottom surface is less than 1.1 μm, and a fourth state in which a protruding valley portion depth Rvk after chemical conversion processing and polishing processing of the bottom surface is less than 0.9 μm. Thereby, frictional resistance is reduced, fuel efficiency is improved, or oil consumption is reduced.

Description

Technical Field

[0001] This invention relates to a cylinder or the like with a recess formed on its inner wall surface. Background Technology

[0002] In the past, efforts have been made in internal combustion engines with cylinders and pistons to reduce the sliding resistance (friction) between the cylinder and piston in order to improve fuel efficiency and reduce fuel consumption. As a method to reduce the friction between the piston rings and the cylinder, the applicant has developed a so-called recessed gasket (for example, see Japanese Patent No. 5155924), which reduces sliding resistance during operation by forming multiple recesses in the central region of the cylinder's inner wall during the stroke. These recesses are typically formed by a process called sandblasting. Summary of the Invention

[0003] Technical issues When a recess is formed through sandblasting, it is difficult to maintain a stable recess shape and surface roughness due to various factors such as grid deviation and wear of the grid discharge nozzle. Specifically, because the recess contains grids of sizes other than the standard size, local unevenness can easily form on the sides and bottom of the recess. If a local convexity forms on the bottom, its protruding end may come into contact with the piston, causing piston damage. Furthermore, consider the possibility that such local unevenness might obstruct the flow of lubricating oil in and out of the recess.

[0004] In view of the above circumstances, the present invention provides a cylinder or the like with a high-precision recess.

[0005] Technical solution The present invention, which achieves the above-mentioned objective, is a cylinder characterized in that a piston having piston rings slides on an inner wall surface, and the cylinder has a plurality of laser-processed recesses formed in the central region of the stroke of the inner wall surface, from the lower surface of the annular groove of the lowermost piston ring at the top dead center of the piston to the upper surface of the annular groove of the uppermost piston ring at the bottom dead center of the piston. The surface roughness of the bottom surface of the recesses satisfies at least one of the following first to fourth states: The first state is that the core height difference Rk after the bottom surface is polished is less than 1.6μm. The second state is that the depth Rvk of the protruding valley after the bottom surface has been polished is less than 1.3μm. The third state is when the core height difference Rk is less than 1.1 μm after the bottom surface has undergone chemical conversion treatment and polishing. The fourth state is that the depth Rvk of the protruding valley is less than 0.9 μm after the bottom surface has undergone chemical conversion treatment and polishing.

[0006] The cylinder described above can be associated with the following feature: the surface roughness of the bottom surface of the recess satisfies either the fifth or sixth state below: The fifth state is that, after polishing the bottom surface, the combined value of the core height difference Rk and the protruding valley depth Rvk is less than 2.9 μm. The sixth state is that the combined value of the core height difference Rk and the protruding valley depth Rvk after the bottom surface has undergone chemical conversion treatment and polishing is less than 2.0 μm.

[0007] The cylinder described above may be associated with the following feature: the depth of the recess is 0.1 μm to 1000 μm.

[0008] The cylinder described above can be associated with the following feature: the recess is processed by a laser with a pulse width of less than 100 picoseconds.

[0009] Associated with the aforementioned cylinder is the feature that the periphery of the recess becomes a conical surface with an increasing number of overlapping irradiations based on the laser spot of the laser processing, extending from the outside of the recess toward the inside.

[0010] The cylinder described above can be associated with the following feature: when the maximum axial dimension of the cylinder of the recess is defined as WJ, the axial offset Z of the central position of the axial direction of a pair of recesses circumferentially adjacent to the inner wall surface is set to 0 < Z < WJ.

[0011] The present invention, which achieves the above-mentioned objective, is a method for machining a concave portion of the inner wall surface of a cylinder, characterized in that a laser spot is irradiated onto the inner wall surface of a cylindrical cylinder on which a piston with piston rings slides, thereby forming a concave portion larger than the diameter of the laser spot. The concave portion machining method includes: a first irradiation step, in which a laser spot with a pulse width of less than 100 picoseconds is irradiated onto a predetermined concave portion target area along a linear first moving path to machine a first strip-shaped region; and a second irradiation step, after the first irradiation step, in which the laser spot overlapping at least a portion of the first strip-shaped region is irradiated onto the concave portion target area along a linear second moving path parallel to the first moving path and having a centerline offset from the centerline of the first moving path, thereby machining a second strip-shaped region overlapping the first strip-shaped region.

[0012] Associated with the above-described recess processing method may be the following feature: a plurality of recessed object regions are spaced apart from each other along the circumferential direction of the inner wall surface; the recess processing method includes: a first irradiation group step, in which the laser spot is irradiated along a first circumferential moving path to perform the first irradiation group step on each of the plurality of recessed object regions; and a second irradiation group step, in which, after the first irradiation group step, the laser spot is irradiated along a second circumferential moving path to perform the second irradiation group step on each of the plurality of recessed object regions.

[0013] Associated with the above-described recess processing method is the following feature: the scanning path of the laser spot in the first irradiation group process is along a spiral path.

[0014] Associated with the above-described recess processing method is the configuration of the plurality of recesses formed on the inner wall surface along the spiral path.

[0015] Associated with the above-described method for processing recesses may be the following feature, wherein the surface roughness of the bottom surface of the recess satisfies at least one of the following first to fourth states: The first state is that the core height difference Rk after the bottom surface is polished is less than 1.6μm. The second state is that the depth Rvk of the protruding valley after the bottom surface has been polished is less than 1.3μm. The third state is when the core height difference Rk is less than 1.1 μm after the bottom surface has undergone chemical conversion treatment and polishing. The fourth state is that the depth Rvk of the protruding valley is less than 0.9 μm after the bottom surface has undergone chemical conversion treatment and polishing.

[0016] Associated with the above-mentioned concave processing method is the following feature: when the diameter of the laser spot is defined as C, and the offset between the center line of the first moving path and the center line of the second moving path is defined as OS, OS ≤ C / 2.

[0017] Associated with the above-described recess processing method is the feature that the axial dimension of the recess is larger than the contact width between the piston ring and the inner wall surface.

[0018] Technical effect According to the present invention, it is possible to achieve excellent effects such as reducing frictional resistance, improving fuel efficiency, or reducing fuel consumption. Attached Figure Description

[0019] Figure 1 This is an axial cross-sectional view of the cylinder liner of an internal combustion engine applicable to embodiments of the present invention.

[0020] Figure 2 (A) and Figure 2 (B) is a diagram showing the circumferentially unfolded state of the inner peripheral wall of the cylinder liner.

[0021] Figure 3 (A) and Figure 3 (B) is a cross-sectional view of the inner circumferential wall of the cylinder liner in a direction perpendicular to the axis.

[0022] Figure 4 (A) and Figure 4 (B) is a cross-sectional view showing the cross-sectional curves of the inner peripheral wall and the recess of the cylinder liner.

[0023] Figure 5 (A) is a side view showing the piston and piston rings suitable for this internal combustion engine. Figure 5 (B) is a partially enlarged cross-sectional view showing the piston and piston rings. Figure 5 (C) is a partially enlarged cross-sectional view of the top ring. Figure 5 (D) is a partially enlarged cross-sectional view of the second ring.

[0024] Figure 6 (A) is a cross-sectional view of the two-piece oil ring. Figure 6 (B) is a cross-sectional view of the three-piece oil ring.

[0025] Figure 7 (A) is a Stribeck line diagram of slip in a typical internal combustion engine. Figure 7 (B) is an FMEP line diagram of slip in a typical internal combustion engine.

[0026] Figure 8 This is a perspective view showing the device for machining the recess of the cylinder liner.

[0027] Figure 9 (A) ~ Figure 9 (D) is a diagram showing the machining sequence of the recess in the cylinder liner. Figure 9 (E) and Figure 9 Figure (F) is a diagram showing a variation of the laser scanning method.

[0028] Figure 10 (A) is a cross-sectional view along the scanning direction showing the machining sequence of the recess in the cylinder liner. Figure 10 (B) is a cross-sectional view in the orthogonal direction showing the machining sequence of the recess of the cylinder liner.

[0029] Figure 11 (A) ~ Figure 11 (D) is a diagram showing the sequence in which multiple recesses of the cylinder liner are machined together.

[0030] Figure 12(A) ~ Figure 12 (C) is a graph showing the surface roughness of the concave bottom surface of the cylinder liner.

[0031] Figure 13 (A) is a front view showing a modified example of the recess processing device.

[0032] Figure 14 (A) ~ Figure 14 (D) is a three-dimensional view conceptually illustrating the scanning path of the laser in the recess processing device.

[0033] Figure 15 This is a diagram showing the circumferentially unfolded inner wall of the cylinder liner.

[0034] Figure 16 This is an axial cross-sectional view of a cylinder liner that demonstrates an example of a cylinder liner to which microtexturing technology has been applied.

[0035] Symbol Explanation 10 Cylinder Liner 12 Inner wall surface 14 recess 14A Bottom 14a Highest Point 14b Lowest point 14e Terminal Area 14s starting region 20. Central Region 30 Piston 40 Piston Rings 70 oil ring 200 Collapsed Edge Area 500, 800 concave processing device 510 Laser Oscillator 570, 870 control devices 590, 890 lasers 590S laser spot 592 inter-pulse travel distance 594mm spot diameter 596 line spacing 611 First Movement Path 612 Second Movement Path 613 Third movement path 614 Recessed object area 620 strip area 621 First Strip Region 621e Terminal Area 622 Second Strip Region 623 Second Strip Region 623 Third Strip Region 624 Fourth Strip Region 625 Fifth Strip Region 626 Sixth Strip Region Detailed Implementation

[0036] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. First, the cylinder of the internal combustion engine according to the embodiments of the present invention will be described in detail. It should be noted that the cylinder of this embodiment exemplifies a cylinder liner embedded in the engine block when the internal combustion engine is a diesel engine, but the present invention is not limited to this and can also be applied to cylinders of other types of internal combustion engines such as gasoline engines.

[0037] <Cylinder Liner> like Figure 1 As shown, the inner wall surface 12 of the cylinder liner 10 of the internal combustion engine in this embodiment has a plurality of recesses 14. The recesses 14 are formed in the stroke center region 20 of the inner wall surface 12. For this stroke center region 20, the range from the lower surface of the ring groove of the lowermost piston ring at the top dead center T of the piston 30 to the upper surface of the ring groove of the uppermost piston ring at the bottom dead center U of the piston 30 is set to the largest, and it is either all or part of the region (here, the entire range is shown as the stroke center region 20, and the recesses 14 are formed therein). If the region outside the stroke center region 20 is defined as the outer region 25, then the outer region 25 is composed of an upper outer region 25A adjacent to the top dead center side of the stroke center region 20 and a lower outer region 25B adjacent to the bottom dead center side of the stroke center region 20. As the piston 30 reciprocates within the cylinder liner 10, it sequentially passes through the upper outer region 25A, the central region 20 of the stroke, the lower outer region 25B, the central region 20 of the stroke, and the upper outer region 25A again. It should be noted that the boundary between the upper outer region 25A and the central region 20 of the stroke is defined as the upper boundary 27A, and the boundary between the lower outer region 25B and the central region 20 of the stroke is defined as the lower boundary 27B.

[0038] Of course, it is possible to form multiple recesses 14 beyond the central region 20 of the stroke, but from the point of view of fuel consumption (LOC), it is preferable to form the recesses 14 specifically within the central region 20 of the stroke.

[0039] <Recesses (pits) formed in cylinder liners> The recess 14 is configured such that at least one recess 14 exists in any section perpendicular to the axis of the inner wall surface 12 of the stroke center region 20. That is, the recesses 14 are arranged to coincide axially in the cylinder. As a result, the outer circumferential surface of the piston ring passing through the stroke center region 20 is always opposite at least one recess 14. On the other hand, no recesses 14 are formed in the upper outer region 25A and the lower outer region 25B.

[0040] The recess 14 is shaped like a polygon (square, rectangle, hexagon) arranged at an angle relative to the cylinder axis; here, a hexagon is used. Thus, as... Figure 2 As shown in the unfolded diagram (A), when focusing on a particular recess 14, the lowest point 14b of this recess 14 in the axial direction is located lower than the highest point 14a in the cylinder axial direction of the other recesses 14. Thus, since the multiple recesses 14 overlap each other in the cylinder axial direction, a recess 14 can always be present in the cross-section perpendicular to the axis at all locations (e.g., arrows A, B, and C) in the stroke center region 20. Here, in the stroke center region 20, multiple recesses 14 of equal area are uniformly arranged in the planar direction (cylinder axial and cylinder circumferential directions).

[0041] Specifically, such as Figure 2 As shown in the unfolded diagram of (B), there are always multiple recesses 14 in the strip-shaped regions 20P, 20Q, and 20R where the piston ring contacts the central region 20 of the stroke.

[0042] The size and shape of the recess 14 are not particularly limited and are appropriately selected according to the size and purpose of the cylinder and piston rings. For example, the recess 14 can be formed in a slit-like or strip-like manner, extending (or passing through) the cylinder axial direction of the stroke center region 20. On the other hand, from the viewpoint of cylinder airtightness, it is preferable that the maximum average length J of the recess 14 in the cylinder axial direction (refer to...) Figure 2 The (A) value is set to be less than or equal to the cylinder axial length (width) of the piston ring (top ring) located at the top of the piston, specifically, preferably about 5% to 100% of it. The average length J of the recess 14 refers to the average length of the multiple recesses 14 when there is a deviation in the maximum cylinder axial dimension of the multiple recesses 14. In addition, when the lengths of the recesses 14 are mixed, the maximum dimension is set as the average length J, preferably not exceeding the cylinder axial length (width) of the piston ring (top ring) located at the top of the piston. The maximum average length J of the recess 14 in the cylinder axial direction is preferably in the range of 0.1 mm to 15 mm, and preferably in the range of 0.1 mm to 5 mm. It is further desirable to set it to 0.1 mm to 1.0 mm.

[0043] The maximum average length S of the cylinder circumference of the recess 14 is preferably in the range of 0.1 mm to 15 mm, and ideally in the range of 0.1 mm to 5 mm. It is further desirable to set it to 0.1 mm to 1.0 mm. If it is smaller than these ranges, the effect of reducing the sliding area brought by the recess 14 itself may not be fully obtained. On the other hand, if it is larger than these ranges, part of the piston ring may easily enter into the recess, which may sometimes cause piston ring deformation or, if the depth of the recess 14 is shallow, contact with the bottom surface of the recess, etc.

[0044] like Figure 3 As shown in (A), the maximum average length R (maximum average depth R) of the cylinder radial direction of the recess 14 is preferably in the range of 0.1 μm to 1000 μm, and preferably in the range of 0.1 μm to 500 μm. It is more desirable to set it to 0.1 μm to 50 μm, and even more desirable to set it to 0.1 μm to 10 μm. It should be noted that in this embodiment, the maximum average depth R is set to 2.5 μm. If the maximum average length R of the cylinder radial direction of the recess 14 is less than these ranges, the effect of reducing the sliding area of ​​the recess 14 itself may not be sufficiently obtained, or the bottom surface 14A of the recess 14 may come into contact with the piston ring. It should be noted that the definition of the maximum average depth R will be explained later.

[0045] On the other hand, if the maximum average depth R is greater than these ranges, it would require excessive machining time or an increase in cylinder wall thickness. It should be noted that for... Figure 3 For the concave portion 14, for ease of explanation, the direction of the maximum average length R is depicted in a significantly exaggerated manner relative to the direction of the maximum average length J.

[0046] Return to Figure 2 The average value of the minimum circumferential spacing Hc between adjacent recesses 14 at the same position along the cylinder axis is preferably in the range of 0.05 mm to 15 mm, and particularly preferably in the range of 0.1 mm to 5.0 mm. It is further desirable to set it to 0.1 mm to 1.0 mm. If it is smaller than these ranges, the contact area (sliding area) between the piston ring and the cylinder liner will be too small, and stable sliding may not be possible. On the other hand, if it is larger than these ranges, the effect of the recess 14 itself in reducing the sliding area may not be sufficiently obtained.

[0047] The average value of the minimum axial spacing Ha between adjacent recesses 14 at the same position in the cylinder circumferential direction is preferably in the range of 0.05 mm to 15 mm, and particularly preferably in the range of 0.1 mm to 5.0 mm. It is further desirable to set it to 0.1 mm to 1.0 mm. If it is less than these ranges, the contact area (sliding area) between the piston ring and the cylinder liner may be too small, and stable sliding may not be possible. On the other hand, if it is greater than these ranges, the effect of the recesses 14 themselves in reducing the sliding area may not be sufficiently obtained.

[0048] Furthermore, regardless of the orientation, the average value of the minimum spacing Hm between adjacent recesses 14 is preferably in the range of 0.001 mm to 15 mm, and particularly preferably in the range of 0.001 mm to 5.0 mm. If it is greater than these ranges, the effect of reducing the sliding area of ​​the recesses 14 themselves may not be sufficiently obtained.

[0049] In other words, these intervals Hc, Ha, and Hm are equivalent to the minimum widths in each direction of the inner wall surfaces 12 remaining between adjacent recesses 14. Therefore, details will be provided later. Figure 4 As described later in (B), these intervals Hc, Ha, and Hm refer to the distance between the evaluation starting point GS that first intersects the upper reference height line G1 of one recess 14 and the adjacent evaluation starting point GS that first intersects the upper reference height line G1 of another recess 14.

[0050] <Detailed shape definition within the recess> like Figure 3 As shown in enlarged view (B), the recess 14 has a bottom surface 14A and a side surface 300. Furthermore, a so-called collapsed edge region 200 is formed near the edge of the inner wall surface 12 on the side surface 300. This collapsed edge region 200 is a gently sloping surface that begins to slope inwards into the recess 14 with the inner wall surface 12 as a reference plane. The collapsed edge region 200 can be considered as a part of the side surface 300 of the recess 14, particularly as a region near the inner wall surface 12. It should be noted that the collapsed edge region 200 can also be considered as a part of the end of the inner wall surface 12. In any case, the collapsed edge region 200 is locally formed near the boundary between the inner wall surface 12 and the recess 14.

[0051] The bottom surface 14A and the collapsed edge region 200 are formed by further polishing the recess 14 formed by the laser processing described later. In particular, by carefully polishing, the bottom surface 14A of the recess 14 is further smoothed, while forming a smooth collapsed edge region 200.

[0052] In this embodiment, in order to objectively evaluate the shape of the bottom surface 14A (maximum average depth·bottom surface roughness) and the side surface 300 (including the collapsed edge region 200), the bottom surface 14A and the side surface 300 are defined as follows.

[0053] (Determination of cross-sectional curves) like Figure 4 As shown in (A), the shape of at least two recesses 14 is measured using a stylus-type surface roughness measuring machine (JIS B 0651:2001) at a point where the minimum interval Ha of at least two recesses 14 located at the same position in the circumferential direction of the cylinder and arranged along the cylinder axis is included, and the shape includes adjacent inner wall surfaces 12. It should be noted that the tip radius of the measuring stylus is a standard 2 μm, and the cutoff value (wavelength) λs for the cross-sectional profile is selected as 2.5 μm for measurement. The measured cross-sectional profile DK includes at least two adjacent recesses 14, a pair of inner wall surfaces 12A, 12C extending outwards from the two recesses 14 in the cylinder axis, and an inner wall surface 12B existing between the two recesses 14.

[0054] (Definition of the base) like Figure 4 As shown in (A), in the cross-sectional curve DK, the range of the three inner wall surfaces 12A to 12C (two recesses 14) is extracted, and these inner wall surfaces 12A to 12C are transformed into a single straight line 250 using the least squares method. This straight line 250 corresponds to the position after the inner wall surfaces 12 are smoothed, and is defined as the inner wall surface reference height line GK.

[0055] The actual wall surfaces 12A to 12C include minute irregularities corresponding to their surface roughness. These minute irregularities can be evaluated using Ra (arithmetic mean roughness). Therefore, when defining the starting point of the side surface 300, to eliminate the influence of these irregularities, a line offset by Ra from the inner wall reference height line GK towards the base side of the recess 14 is defined as the upper reference height line G1. However, even when Ra is small, the influence of irregularities in the boundary (edge) shape between the wall surfaces 12A to 12C and the side surface 300 is eliminated by offsetting by at least 0.2 μm. That is, the offset of the upper reference height line G1 is chosen to be either 0.2 μm or the larger of the Ra (arithmetic mean roughness) of the wall surfaces 12A to 12C.

[0056] The upper reference height line G1 refers to the virtual starting point position in the depth direction of the side surface 300. Therefore, the point where the cross-sectional curve DK, extending from the wall surface 12A to 12C towards the interior of the recess 14, finally intersects with the upper reference height line G1 is defined as the evaluation starting point GS of the side surface 300. The length GL obtained by connecting the two evaluations of the pair of side surfaces 300 that define the recess 14 using the starting points GS and GS is defined as the axial outer dimension of the recess 14. The midpoint of this axial outer dimension GL is defined as the center of the recess GM. Based on the center of the recess GM, the range of 1 / 4 GL (total range of 1 / 2 GL) on both outer sides is defined as the reference bottom surface range 14G at the bottom surface 14A.

[0057] (Definition of the maximum average depth of the concave portion) The least squares method is used to convert the cross-sectional curve DK of the reference bottom surface range 14G into a single straight line. This single straight line is defined as the bottom surface reference height line BK. Alternatively, as another calculation method, the cross-sectional curve DK can be expanded longitudinally by a factor of 5000 and laterally by a factor of 50 to extract the third highest peak and the third lowest valley of the cross-sectional curve DK. The height between the peak and valley is defined as the bottom surface reference height BK. The maximum average depth R of the recess 14 is set as the average of the distances between the inner wall reference height lines GK of the total 20 recesses 14 and the bottom surface reference height line BK.

[0058] (Parameters of surface roughness of the bottom surface) Furthermore, for the reference bottom surface range 14G of the total 20 recesses 14 defined above, the core height difference Rk and the protruding valley depth Rvk (JISB0671-2:2002) are calculated and averaged, and they are defined as the core height difference Rk and the protruding valley depth Rvk of the bottom surface 14 of the recesses 14.

[0059] The reasons for using the core height difference Rk and the protrusion valley depth Rvk when evaluating the surface roughness of the reference bottom surface area 14G are as follows: If the core height difference Rk is large, the risk of the piston ring contacting the reference bottom surface area 14G increases. If it is assumed that the piston ring is in contact with the reference bottom surface area 14G, the risk of damage during sliding increases. If the protrusion valley depth Rvk is large, the excess oil storage volume in the recess 14 increases, and oil consumption increases. In addition, the smaller these two values ​​are, the less likely it is to impede the flow of lubricating oil in and out of the recess 14.

[0060] It should be noted that when measuring the surface roughness of the reference bottom surface area 14G, two states may exist. One is the surface roughness after laser processing of the recess 14 followed by polishing (hereinafter referred to as "laser-polished surface roughness"). The other is the surface roughness after laser processing of the recess 14, followed by chemical conversion treatment (coating treatment), and then polishing (hereinafter referred to as "laser-coated-polished surface roughness"). Whether or not a coating treatment is performed depends on the required specifications of the cylinder liner 10. If a coating treatment is performed, the coating components penetrate the micro-undulations of the reference bottom surface area 14G, resulting in a corresponding reduction in surface roughness.

[0061] In this embodiment, the core height difference Rk is set to less than 1.6 μm as the surface roughness after laser polishing, and the protrusion valley depth Rvk is set to less than 1.3 μm. In another embodiment, the core height difference Rk is set to less than 1.1 μm as the surface roughness after laser coating and polishing, and the protrusion valley depth Rvk is set to less than 0.9 μm.

[0062] Furthermore, as the surface roughness after laser polishing, the value (Rk+Rvk) obtained by adding the core height difference Rk and the protrusion valley depth Rvk is set to be less than 2.9 μm. As the surface roughness after laser coating and polishing, the value (Rk+Rvk) obtained by adding the core height difference Rk and the protrusion valley depth Rvk is set to be less than 2.0 μm.

[0063] In this embodiment, as described above, by setting the core height difference Rk of the reference bottom surface range 14G to be small, the depth of the recess 14 is made shallower, making it difficult for contact scratches to form even when the piston ring contacts the bottom surface 14A. Furthermore, by actively reducing the depth Rvk of the protruding valley of the reference bottom surface range 14G, the fluidity of the lubricating oil in the recess 14 can be improved.

[0064] (Definition of lateral tilt angle) Next, the definition of the 300° tilt angle on the side will be explained. For example... Figure 4 As shown in (B), the cross-sectional curve DK of the side surface 300 of the recess 14 is enlarged and extracted. The line offset by R / 2 from the bottom reference height line BK towards the upper side of the recess 14 is defined as the lower side reference height line G3. The effect of the unevenness of the bottom surface 14A is reduced by offsetting this lower side reference height line G3. The radial length of the cylinder (height for side tilt evaluation) SH when evaluating the tilt angle of the side surface 300 is defined by the distance between the upper reference height line G1 and the lower side reference height line G3.

[0065] The point where the cross-sectional curve DK and the lower side reference height line G3 first intersect is defined as the endpoint SE for side slope evaluation. The line segment SS connecting the evaluation starting point GS of side 300 and the endpoint SE for side slope evaluation is defined as the virtual side section SS of side 300. The length of the virtual side section SS in the direction parallel to the straight line 250 (here, the cylinder axis) is defined as the side slope evaluation width SW of side 300. Using the straight line 250 as a reference, the absolute value of the slope SH / SW of this virtual side section SS is calculated (hereinafter, it is defined as the side slope SA).

[0066] It should be noted that due to the presence of minute irregularities in the cross-sectional curve DK, deviations will occur with each measurement. Therefore, using each side 300 as the target, 60 measurements were performed using a stylus-type surface roughness measuring machine (JIS B 0651:2001). Fifteen measurements were removed from the side with the largest calculated side slope SA, and 15 from the side with the smallest. The average value was calculated based on the remaining 30 data points. This average value was set as the side slope SA used to evaluate side 300.

[0067] (Definition of the collapsed area) like Figure 4 As shown in (B), the cross-sectional curve DK of the side surface 300 of the recess 14 is magnified and extracted. The line offset by 0.50 μm from the upper reference height line G1 to the base side of the recess 14 is defined as the lower reference height line G2 of the collapsed edge. This lower reference height line G2 of the collapsed edge refers to the virtual end position (end height) of the collapsed edge region 200 in the side surface 300. Therefore, the cylinder radial length (collapse height) DH of the collapsed edge region 200 is defined as 0.50 μm.

[0068] The point where the cross-sectional curve DK first intersects the lower reference height line G2 is defined as the collapse edge endpoint GE. The line segment GG connecting the evaluation starting point GS of the side 300 and the collapse edge endpoint GE is defined as the virtual collapse edge section GG of the collapse edge region 200. The length of the virtual collapse edge section GG in the direction parallel to the straight line 250 (here, the cylinder axis) is defined as the collapse edge width DW of the collapse edge region 200. Using the straight line 250 as a reference, the absolute value of the slope DH / DW of this virtual collapse edge section GG is calculated (hereinafter, it is defined as the collapse edge slope DA).

[0069] It should be noted that since the cross-sectional curve DK contains minute irregularities, deviations will occur in each measurement. Therefore, each collapsed area 200 was used as a target, and 60 measurements were performed using a stylus-type surface roughness measuring machine (JIS B0651:2001). Fifteen measurements were removed from the side with the largest slope DA calculated from the largest side, and 15 from the side with the smallest slope DA. The average value was calculated based on the middle 30 data points. This average value was set as the collapsed slope DA for evaluating the collapsed area 200. It should be noted that while the case of using the collapsed slope DA is illustrated here when evaluating the formation of the collapsed area 200, the same meaning can be achieved by directly using the collapsed width DW for evaluation.

[0070] Incidentally, although different from the recessed gaskets configured as multiple overlapping recesses in the cylinder axis direction, microtexturing technology exists as a technique for forming the same type of recesses, and therefore will be briefly explained. Microtexturing refers to the following theory: Figure 16 As shown, regions V with recesses and ZX without recesses alternate along the inner wall of the cylinder liner in a non-overlapping manner along the cylinder axial direction. Whenever the piston ring moves along this inner wall, engine oil flows in and out relative to the recesses, thickening the oil film through dynamic pressure and reducing friction. This invention is also applicable to such microtexture techniques. That is, any structure that reduces the contact area with the piston ring by forming multiple recesses in the central region of the stroke can be effectively applied to this invention.

[0071] <Formed in the central low-roughness region of the cylinder liner> return Figure 1A central low-roughness region 22 is formed on at least a portion of the central region 20 of the stroke on the inner wall surface 12 of the cylinder liner 10. The surface roughness (arithmetic mean roughness Ra of the profile curve (JIS B 0601:2013)) of this central low-roughness region 22, as measured by a stylus-type surface roughness measuring machine (JIS B 0651:2001), is 0.140 (μm) or less, preferably 0.120 (μm) or less. Specifically, the central low-roughness region 22 is formed by machining the surface roughness Ra of at least a portion of the inner wall surface 12 that can contact the piston ring 40, i.e., the surface of the inner wall surface 12 excluding the recess 14, to 0.140 (μm) or less, more preferably 0.120 (μm) or less. It should be noted that in this embodiment, the surface roughness (arithmetic mean roughness of the profile curve) measured by the stylus-type surface roughness measuring machine is denoted as Ra, and the three-dimensional surface roughness (arithmetic mean height of the profile surface (JIS B 0681-2:2018, ISO 25178-2:2012)) measured by the non-contact surface roughness measuring machine described later is denoted as Sa.

[0072] The surface roughness Ra of the central low-roughness region 22 is preferably set to below 0.090 (μm), specifically to 0.083 (μm).

[0073] For the central low-roughness region 22, the following shows the three-dimensional surface roughness value (JIS B 0681-2:2018, ISO 25178-2:2012) measured using a non-contact surface roughness measuring machine (measuring magnification 1080x, field of view size 259.4μm×259.4μm, no cutoff, measuring line spacing in the height direction (Z direction) 0.06μm). This non-contact surface roughness measuring machine is a measuring machine using a laser microscope based on JIS B 0681-6:2014 (ISO 25178-6:2010).

[0074] Arithmetic mean height Sa (μm): 0.192 or less, preferably 0.163 or less, and further preferably 0.120 or less (specifically set to 0.110).

[0075] The height of the prominent peak Spk (μm) is 0.159 or less, preferably 0.144 or less, and further preferably 0.121 or less (specifically set to 0.116).

[0076] Core height difference Sk (μm): 0.521 or less, preferably 0.449 or less, and further preferably 0.340 or less (specifically set to 0.315).

[0077] The valley depth Svk (μm) is 0.409 or less, preferably 0.342 or less, and further preferably 0.241 or less (specifically set to 0.218).

[0078] Specifically, in this embodiment, by not only reducing the height of the protruding peaks of the inner wall surface 12, but also actively reducing the depth of the protruding valleys of the inner wall surface 12, the frictional force during sliding is reduced. Incidentally, in conventional cylinder liners, in order to ensure the retention force of the inner wall surface 12 on the lubricating oil, it is necessary to increase the depth of the protruding valleys to a certain extent. Consequently, it is difficult to reduce the height of the protruding peaks, and there are limitations to reducing the frictional force during sliding. On the other hand, in this embodiment, since the lubricating oil is adequately retained in the highly smooth recess 14 on the bottom surface 14A, the lubricating oil in the recess 14 can easily move along the surrounding inner wall surface 12. Therefore, even if the lubricating oil retention force is small, an oil film can be adequately formed on the contact surface (inner wall surface 12) with the piston ring 40.

[0079] Under this principle, when the height of the protruding peak of the inner wall surface 12 is set to Spk and the depth of the protruding valley of the inner wall surface 12 is set to Svk, in the central low roughness region 22 of this embodiment, it is preferable to set the value of Svk / Spk to 2.6 or less, more preferably to 2.4 or less, and even more desirable to set it to 2.0 or less.

[0080] In this embodiment, the entire area of ​​the surface in the central stroke region 20 that can contact the piston ring 40 is designated as the central low-roughness region 22. As a result, the central low-roughness region 22 includes the vicinity of the upper and lower edges of the central stroke region 20 where the recess 14 is formed. Furthermore, an upper low-roughness region 23A with a surface roughness Ra of 0.120 (μm) or less is formed in the upper outer region 25A adjacent to the top dead center side of the central stroke region 20, and a lower low-roughness region 23B is formed in the lower outer region 25B adjacent to the bottom dead center side of the central stroke region 20. The upper low-roughness region 23A, the central low-roughness region 22, and the lower low-roughness region 23B are completely connected with a uniform surface roughness, forming a continuous surface as a whole.

[0081] Near the upper and lower edges of the central stroke region 20, the relative speed Q between the cylinder liner 10 and the piston 30 decreases, making it easier to transition from the fluid lubrication region to the boundary lubrication region. However, the presence of the central low-roughness region 22 allows the fluid lubrication region to dominate. The so-called pit liner technology can be effective in the fluid lubrication region, thus the advantages of the pit liner technology can also be obtained near the upper and lower edges of the central stroke region 20. It should be noted that the central low-roughness region 22 can also be limited to the area near the upper and / or lower edges of the central stroke region 20, but it is preferable to form the central low-roughness region 22 throughout the entire central stroke region 20 as in this embodiment. Even when the relative speed Q between the cylinder liner 10 and the piston 30 is lower, the boundary lubrication region is closer to the central side of the central stroke region 20, but even in this case, the range of the fluid lubrication region can be expanded.

[0082] 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. The honing stone grit size is preferably finer than, for example, F500 or #800 (JIS R 6001-2:2017, ISO8486-2:2007).

[0083] <Regarding the chemical conversion treatment process> Furthermore, it is preferable not to perform chemical conversion treatment on the surface of the central low-roughness region 22 when it is formed by the honing process. This is because, for example, if a phosphate coating or similar process, which is commonly used in the manufacturing process of the cylinder liner 10, is performed, the surface properties of the central low-roughness region 22 will vary depending on the coating.

[0084] On the other hand, if the coating has minimal changes in surface properties, it is also desirable to apply a chemical conversion treatment to the central low-roughness region 22. In this embodiment, when the inner wall surface 12 is chemically converted, the following two steps can be performed. The first step is as follows: after forming the recess 14 on the inner wall surface 12 of the cylinder liner 10 using a laser, a chemical conversion treatment is performed, followed by polishing. In the case of the first step, since a coating is formed on the bottom surface 14A of the laser-processed recess 14, the coating is fused during the polishing process, thereby further reducing the fine unevenness of the bottom surface 14A of the recess 14. On the other hand, since the depth of the recess 14 reduces the thickness of the coating, it is necessary to pre-process the recess 14 with a depth equivalent to the coating thickness using a laser, which increases the processing time. For example, when a 0.5 μm film is formed by chemical conversion, a 0.5 μm deep recess 14 needs to be formed using a laser.

[0085] The second step is as follows: after chemically converting the inner wall surface 12 of the cylinder liner 10, a recess 14 is formed using a laser, followed by polishing. In this second step, although no coating is formed on the bottom surface 14A of the recess 14, the Rk and Rvk values ​​of the bottom surface 14A of the recess 14 formed by the laser are reduced, thus minimizing the need for coating. Furthermore, since the recess 14 can be processed using a laser without considering the thickness of the coating, it has the advantage of shortening the processing time.

[0086] Pistons and Piston Rings exist Figure 5 (A) and Figure 5 (B) shows a piston 30 and piston rings 40 (top ring 50, second ring 60, oil ring 70) disposed in the annular grooves of the piston 30. The piston rings 40 reciprocate along the cylinder axis with their outer peripheral surface 42 facing the inner wall surface 12 of the cylinder liner 10. The top ring 50 eliminates the gap between the piston 30 and the cylinder liner 10, preventing compressed gas from escaping from the combustion chamber to the crankcase side (blow-through). Similar to the top ring 50, the second ring 60 serves to eliminate the gap between the piston 30 and the cylinder liner 10, and also to scrape off excess engine oil adhering to the inner wall surface 12 of the cylinder liner 10. The oil ring 70 forms a suitable oil film by scraping off excess engine oil adhering to the inner wall surface 12 of the cylinder liner 10, thereby preventing the piston 30 from sticking.

[0087] like Figure 5 As shown in magnification in (C), the top ring 50 is a single annular component, and when viewed in cross-section, the outer peripheral surface 52 becomes a so-called barrel shape that bulges radially outward. Specifically, the two outer edges of the outer peripheral surface 52 along the cylinder axis are inclined towards the outer side of the cylinder axis and away from the inner wall surface 12. It should be noted that the contact width f of the outer peripheral surface 52 relative to the inner wall surface 12 of the cylinder liner 10 is preferably formed to be, for example, 0.3 mm or less. In addition, the surface roughness (arithmetic mean roughness Ra of the profile curve (JIS B 0601:2013)) of the outer peripheral surface 52, as measured by a stylus-type surface roughness measuring machine (JIS B 0651:2001), is preferably 0.250 (μm) or less.

[0088] like Figure 5As shown in magnified view (D), the second ring 60 is a single annular component, with its outer periphery forming a tapered shape that expands in diameter from the upper end of the cylinder axial direction toward the lower side of the cylinder axial direction. The outer peripheral surface 62, located at the outermost end of this tapered shape and in contact with the inner wall surface 12 of the cylinder liner 10, is planar when viewed in cross-section. It should be noted that the contact width f of the outer peripheral surface 62 relative to the inner wall surface 12 of the cylinder liner 10 is preferably formed to be, for example, 0.3 mm or less. In addition, the surface roughness (arithmetic mean roughness Ra of the profile curve (JIS B 0601:2013)) of the outer peripheral surface 62, as measured by a stylus-type surface roughness measuring machine (JIS B 0651:2001), is preferably 0.250 (μm) or less.

[0089] It should be noted that 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 or less. As a result, the top ring 50 and the second ring 60 slide mostly in the fluid lubrication zone, except near the top dead center and the bottom dead center.

[0090] Figure 6 The oil ring 70 shown in enlarged view in (A) is a two-piece design, comprising a ring body 72 and a helical spring-shaped expander 76. The ring body 72 has a pair of annular tracks 73, 73 disposed at both axial ends, and an annular column 75 disposed between and connecting the tracks 73, 73. The cross-sectional shape of the combination of the tracks 73, 73 and the column 75 is approximately I-shaped or H-shaped, and using this shape, an inner circumferential groove 79 with a semi-circular cross-section for accommodating the expander 76 is formed on the inner circumferential surface. Furthermore, annular protrusions 74, 74 are formed on the tracks 73, 73, respectively, protruding radially outward from the column 75. The outer circumferential surfaces 82, 82 of the protruding ends of these annular protrusions 74, 74 abut against the inner wall surface 12 of the cylinder liner 10. The expander 76, by being accommodated in the inner circumferential groove 79, presses and applies force to the ring body 72 radially outward. It should be noted that multiple oil return holes 77 are formed circumferentially in the column portion 75 of the ring body 72.

[0091] Figure 6 The contact width of each of the outer peripheral surfaces 82, 82 in (A) is preferably formed to be 0.02 mm to 0.30 mm, for example, 0.15 mm. It should be noted that 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, about 1.75 MPa. Therefore, at high engine speeds, the oil ring 70 mostly slides in the fluid lubrication zone, but if the engine speed decreases, the oil ring 70 mostly slides in the boundary lubrication zone. It should be noted that the shape of the radial cross-section of the outer peripheral surfaces 82, 82 is... Figure 6Example (A) illustrates a simple trapezoidal shape, but the present invention is not limited to this. It can also be configured such that the corners of the opposite sides (the spiral expander 76 side) of the outer peripheral surfaces 82 of the upper track 73 and the lower track 73 are cut into a stepped shape (so-called step-land shape). In addition, the surface roughness (arithmetic mean roughness Ra of the profile curve (JIS B 0601:2013)) of the outer peripheral surface 82, as measured by a stylus-type surface roughness measuring machine (JIS B 0651:2001), is preferably 0.450 (μm) or less.

[0092] It should be noted that the oil ring 70 is not limited to a two-piece design; for example, it can also be... Figure 6 The three-piece oil ring 70 shown in (B) has upper and lower separated annular side rails 73a and 73b, and a spacer 76s disposed between the side rails 73a and 73b.

[0093] The spacer expander 76s is formed by plastically shaping steel into a repeating concave-convex wave shape along the cylinder axial direction. This wave shape forms an upper side support surface 78a and a lower side support surface 78b, with a pair of side rails 73a and 73b supported axially. At the inner circumferential end of the spacer expander 76s, there is an arched ear 74m extending axially outward. This ear 74m abuts against the inner circumferential surfaces of the side rails 73a and 73b. It should be noted that the spacer expander 76s, with its fitting opening, is inserted into the annular groove of the piston 30 in a contracted state in the circumferential direction. As a result, the ear 74m, through the restoring force of the spacer expander 76s, presses the side rails 73a and 73b radially outward.

[0094] It should be noted that the preferred option is... Figure 6 The contact width f of the outer peripheral surfaces 82 and 82 of the side rails 73a and 73b of (B) is formed to be 0.02mm to 0.40mm respectively.

[0095] <The friction mechanism between cylinder liner and piston ring> Next, the friction mechanism between the cylinder liner and piston rings will be explained. Typically, the change in the coefficient of friction during sliding is manifested as follows: Figure 7The Stribeck diagram shown in (A) illustrates the friction modes: a solid contact region 110 where friction occurs through direct contact and sliding; a boundary lubrication region 112 where friction occurs through an oil film; and a fluid lubrication region 114 where friction occurs through a viscous lubricating oil film. Furthermore, a mixed lubrication region 113 exists between the boundary lubrication region 112 and the fluid lubrication region 114, where both states coexist. It should be noted that the horizontal axis of this Stribeck diagram is a logarithmic representation of kinematic viscosity (kinematic viscosity ratio) μ × velocity Q / contact load W, and the vertical axis is the coefficient of friction (f). Therefore, the fluid lubrication region 114 or the mixed lubrication region 113 may have the lowest possible friction, and effectively utilizing these regions 114 and 113 is effective for low friction, i.e., low oil consumption. On the other hand, even if the speed Q increases, if it is impossible to transfer from the middle of the boundary lubrication region 112 to the fluid lubrication region 114, as shown by the dashed line, the boundary lubrication region 112 continues directly into the high-speed region.

[0096] Incidentally, most of the friction in the fluid lubrication zone 114 is the shear resistance of the oil, and this shear resistance is defined as (viscosity) × (velocity) × (area) / (oil film thickness). As a result, reducing the shear area directly leads to a reduction in friction.

[0097] Therefore, in this embodiment, low friction is achieved by actively allowing oil to flow into the contact surface of the outer peripheral surface 42 of the piston ring 40, thereby rapidly transferring it to the fluid lubrication region 114. Simultaneously, by applying a so-called recessed gasket technique to the cylinder liner 10, a recess 14 is formed in the central region 20 of the cylinder liner 10's stroke, reducing the actual area that generates oil shear resistance, thereby more effectively achieving a reduction in friction.

[0098] in addition, Figure 7 The Stribek graph (A) shows the dynamic change of the coefficient of friction (f) during one stroke of piston 30. As another indicator for evaluating friction, there is the friction mean effective pressure (FMEP). This friction mean effective pressure is the value obtained by dividing the frictional work of one cycle by the stroke volume. The FMEP graph is shown in... Figure 7 As shown in (B). In the FMEP graph, the horizontal axis represents the rotational speed (N), and the vertical axis represents the mean effective pressure of frictional losses (kPa). The higher the rotational speed (N), the greater the proportion of the fluid lubrication region 114 in a stroke. On the other hand, if the rotational speed (N) decreases, the proportion of the fluid lubrication region 114 in a stroke decreases, and the proportion of the mixed lubrication region 113 (or boundary lubrication region 112) increases. Therefore, Figure 7 The shape of the FMEP line graph of (B) and Figure 7 The shapes of fluid lubrication region 114 and mixed lubrication region 113 in the (A) Stribeck diagram are quite similar.

[0099] <Concave processing device> Next, the machining of the recess 14 in the cylinder liner 10 will be described. For example... Figure 8 As shown, the concave machining apparatus 500 employs a galvanometer-mirror method and includes a laser oscillator 510, an X-axis mirror 704 driven by an X-axis motor 702, a Y-axis mirror 714 driven by a Y-axis motor 712, a terminal mirror 718, and a control device 570. The laser 590 irradiated from the laser oscillator 510 is reflected by the X-axis mirror 704, the Y-axis mirror 714, and the terminal mirror 718 and reaches the cylinder liner 10. Therefore, the relative scanning directions can be freely controlled to the desired direction. This galvanometer-mirror method allows for easy and free change of the scanning direction while irradiating the laser 590. It should be noted that the present invention is not limited to this, and scanning methods such as polygonal mirror methods, in which the laser 590 is reflected and scanned by a polygonal rotating mirror, are also possible.

[0100] The laser oscillator 510 is a short-pulse laser oscillator. The pulse width of the short pulse is preferably 100 picoseconds or less (100,000 femtoseconds or less), more preferably 20 picoseconds or less (20,000 femtoseconds or less), and even more desirablely less than 1 picosecond (less than 1,000 femtoseconds). It should be noted that a device whose pulse width can be set to less than 1 picosecond (less than 1,000 femtoseconds) is called a femtosecond laser oscillator, and a femtosecond laser oscillator is used in this embodiment. The laser oscillator includes a seed pulse section for oscillating a weak femtosecond laser (seed pulse), an amplification section for amplifying the seed pulse by exciting the laser, and a compensation section for dispersion compensation of the amplified laser. The pulse width of the laser 590 emitted from the laser oscillator 510 can be set to less than 1 picosecond (femtosecond unit). The pulse width of the laser oscillator 510 is, for example, set to 400 femtoseconds to 20,000 femtoseconds. Furthermore, the wavelength of the laser can be suitable for metal material processing, for example, a wavelength of 100 nm to 3000 nm can be used. The laser frequency can range from 20 kHz to 2000 kHz. The pulse energy can be, for example, up to 2000 μJ. It should be noted that although the laser wavelength is set to 1030 nm in this embodiment, there are no particular limitations as long as the wavelength is suitable for metal processing.

[0101] The control device 570 is a computer equipped with a central processing unit (CPU), memory, external storage devices, etc. In this control device 570, the recess machining process of the recess machining apparatus 500 is realized by executing a recess machining program.

[0102] <Processing method of concave unit> Next, the detailed control of the recess processing device 500 by the control device 570 will be explained. First, the processing method for each individual recess 14 will be explained. Figure 9 As shown in (A), a predetermined recessed object region 614 for forming a recess 14 is present on the inner wall surface 12. The recess processing apparatus 500 processes the first strip-shaped region 621 into a groove shape by irradiating each recessed object region 614 with a laser spot 590S of laser 590 along a linear first moving path 611. This process is defined as the first irradiation process. It should be noted that the two ends of the first moving path 611 intersect the contour of the recessed object region 614.

[0103] If the first irradiation process is completed, the heat accumulated at any point X in the first strip region 621 is diffused or released to the outside.

[0104] After the first irradiation process, such as Figure 9 As shown in (B), the recess processing apparatus 500 irradiates the recessed object region 614 with a laser spot 590S that overlaps with at least a portion of the first strip region 621 along a linear second moving path 612 that is parallel to the first moving path 611 and offset from the center line of the first moving path 611 by a line spacing 596. This process processes the second strip region 622 that overlaps with the first strip region 621 into a groove shape. This process is defined as the second irradiation process. It should be noted that the two ends of the second moving path 612 intersect the contour of the recessed object region 614. In addition, the scanning direction on the first moving path 611 (the moving direction of the laser spot 590S) and the scanning direction on the second moving path 612 are in the same direction (parallel).

[0105] When the offset of the line spacing 596 is defined as OS and the diameter of the laser spot is defined as C, it is preferable to set OS ≤ C / 2. This allows the strip-shaped regions to overlap on the bottom surface 14A of the recess 14.

[0106] If the second irradiation process is completed, the heat accumulated in the second strip region 622 is diffused or released to the outside.

[0107] like Figure 9 As shown in (C), the third irradiation process is performed using the same steps as the first and second irradiation processes described above, and the third strip region 623 is processed along the third movement path 613. Thereafter, the fourth irradiation process, the fifth irradiation process, and so on, are repeated. The result is as follows: Figure 9As shown in (D), by forming multiple strip-shaped regions 620 side by side in the width direction, the recessed object region 614 is expanded into a planar shape. The center lines of adjacent strip-shaped regions 620 are offset from each other by a predetermined line spacing 596 and become parallel to each other. Thus, the recess 14 is formed.

[0108] It should be noted that, in Figure 9 In steps (A) to (D), examples are shown where the scanning direction of all lasers is parallel (or approximately) to the circumferential direction of the cylinder liner 10. However, the present invention is not limited to this; scanning can also be performed in the axial direction of the cylinder liner 10 or in an inclined direction including both the axial and circumferential directions. Furthermore, as... Figure 9 As shown in (E), it is also possible to scan in a circular or spiral manner within a recess 14 along a circular line that approximates (or is similar to) its contour. Furthermore, as... Figure 9 As shown in (F), a scanning path can also be used in which the first moving path 611, the second moving path 612, and the third moving path 613, which are parallel to each other, meander continuously.

[0109] exist Figure 10Figure (A) schematically shows a cross-section of the cylinder liner 10 along the first moving path 611 during the processing using laser 590. For clarity, the upper part of the figure shows the first moving path 611 of the laser spot 590S, and the opening and closing times (pulse waveforms) of the laser spot 590S moving along the first moving path 611. The laser spot 590S moves along the first moving path 611 while repeatedly opening and closing. As a result, a groove-shaped first strip region 621 is formed in the cylinder liner 10. The moving distance between adjacent pulses of the laser spot 590S (inter-pulse moving distance) 592 is shorter than the spot diameter 594 of the laser spot 590S. The inter-pulse moving distance 592 is the value obtained by dividing the scanning speed A (mm / s) by the frequency B (kHz) of the laser 590 (A / B). Furthermore, the number of overlapping irradiations of the laser spot 590S at the deepest point X in the first strip region 621 formed in one scanning process along the first moving path 611 becomes the maximum. When the spot diameter 594 is defined as C (mm), this maximum number of overlapping irradiations is the value obtained by dividing the spot diameter C by the inter-pulse travel distance (A / B), i.e., C / (A / B). For example, with a scanning speed of 100mm / s, a frequency of 200kHz, and a spot diameter 594 of 0.04mm, the inter-pulse travel distance 592 becomes 0.0005mm, and the number of overlapping irradiations of the laser spot 590S at the deepest point X (reference bottom surface range 14G or recess center GM) of the first strip region 621 becomes 80. Thus, by repeatedly irradiating the deepest point X with the laser spot 590S, the desired groove is formed. It should be noted that in the terminal region 621e of the first strip region 621, the number of overlapping irradiations of the laser spot 590S decreases in stages towards the terminal, forming a conical surface (side surface 300). The same applies to the starting region of the first strip region 621.

[0110] (Number of overlapping light spots in the strip region) When forming each strip-shaped region, the number of times the laser spot 590S overlaps with the deepest point X (reference bottom surface range 14G or the center of the recess GM) (hereinafter referred to as the strip-shaped region spot overlap number) is preferably set to 2 or more, more preferably 3 or more, and ideally 5 or more. On the other hand, the strip-shaped region spot overlap number is preferably set to 50 or less, ideally 30 or less, further ideally 20 or less, and even more ideally 10 or less. Similarly, the number of virtual overlap irradiations (spot diameter / inter-pulse movement distance, hereinafter referred to as the virtual strip-shaped region spot overlap number) at the calculation level, which can be calculated based on the processing conditions, is preferably set to 2 or more, more preferably 3 or more, and ideally 5 or more. On the other hand, the virtual strip-shaped region spot overlap number is preferably set to 50 or less, ideally 30 or less, further ideally 20 or less, and even more ideally 10 or less.

[0111] (Number of overlapping light spots per unit depth in a strip-shaped region) To explain in more detail, the maximum amount of material removed (depth of material removed) in each strip area processed in a single scan can be adjusted appropriately according to the desired outcome. For example, to increase the maximum amount of material removed in a single scan, one can simply set a larger overlap number of the laser spot in the strip area, or increase the energy of the laser spot 590S to increase the amount of material removed during a single irradiation of the laser spot 590S. However, if the energy of the laser spot 590S is too high, the excess energy will be absorbed (accumulated) on the processing surface, resulting in energy loss, and the processing surface will melt, thus increasing the unevenness.

[0112] Conversely, to reduce the maximum amount of material removed in a single scan, one can simply reduce the overlap of the laser spot in the strip region, or reduce the energy of the laser spot 590S to decrease the amount of material removed per irradiation. However, if the energy of the laser spot 590S is too low, the processing efficiency deteriorates drastically, and as a result, processing itself becomes impossible.

[0113] To standardize the above concept, the inventors defined the unit excavation depth as 1 μm and the number of laser spot overlaps achieving this unit excavation depth as the number of laser spot overlaps per unit depth strip area (times / μm). Preferably, the laser irradiation and / or scanning conditions are adjusted to ensure that the number of laser spot overlaps per unit depth strip area (times / μm) is within the range of 5 to 500. Furthermore, it is desirable to adjust the laser irradiation and / or scanning conditions to ensure that the number of laser spot overlaps per unit depth strip area (times / μm) is within the range of 5 to 250, and even more desirable to adjust the laser irradiation and / or scanning conditions to ensure that the number of laser spot overlaps per unit depth strip area (times / μm) is within the range of 5 to 50.

[0114] (Number of overlapping bands) exist Figure 10 (B) shows a cross-section of the cylinder liner 10 along an orthogonal direction (cylinder axis) relative to the scanning direction of the laser 590. For example, multiple cross-sections are formed along the cylinder liner 10. Figure 10 (B) refers to a groove-shaped strip area extending in the depth direction of the paper surface. More specifically, it is formed sequentially in the width direction of the strip. Figure 10 The first strip region 621 to the sixth strip region 626 are arranged side by side on the left and right sides of the paper (B). After forming the first strip region 621, the laser spot 590S moves along the axial direction by a predetermined line spacing 596 to form the second strip region 622. Then, it moves along the axial direction by a predetermined line spacing 596 to form the third strip region 623. Then, it moves along the axial direction by a predetermined line spacing 596 to form the fourth strip region 624. Then, it moves along the axial direction by a predetermined line spacing 596 to form the fifth strip region 625. Then, it moves along the axial direction by a predetermined line spacing 596 to form the sixth strip region 626.

[0115] The line spacing 596 is shorter than the spot diameter 594 of the laser spot 590S. For example, when the line spacing 596 is 0.03 mm and the spot diameter 594 is 0.09 mm, three strip-shaped regions (third strip-shaped region 623 to fifth strip-shaped region 625) overlap at the deepest point X of the recess 14. It should be noted that in the axial terminal region 14e of the recess 14, the number of overlaps of the strip-shaped regions 620 decreases stepwise toward the terminal, thus forming a stepped conical surface (side surface 300). The same is true in the axial starting end region 14s.

[0116] It should be noted that the overlap number of the strip-shaped region opposite to the deepest point X of the recess 14 (hereinafter referred to as the strip-shaped region overlap number) is preferably set to 2 or more, and ideally to 3 or more. On the other hand, the strip-shaped region overlap number is preferably set to 10 or less, ideally to 8 or less, and further ideally to 5 or less. Similarly, the overlap number of the strip-shaped region (spot diameter / line spacing, hereinafter referred to as the virtual strip-shaped region overlap number) of the calculation layer that can be calculated according to the processing conditions is preferably set to 2 or more, and ideally to 3 or more. On the other hand, the virtual strip-shaped region overlap number is preferably set to 10 or less, ideally to 8 or less, and further ideally to 5 or less.

[0117] It should be noted that, in Figure 11 In order to facilitate explanation, the depth dimension of the recess 14 is exaggerated.

[0118] (Total number of overlapping light spots) The number of times the laser spot 590S overlaps with the reference bottom surface range 14G or the center GM of the recess 14 formed by laser processing (hereinafter referred to as the total number of spot overlaps) is the product of the number of spot overlaps in the strip region and the number of overlaps in the strip region. As a result, the total number of spot overlaps is preferably 4 times (the product of the number of spot overlaps in the strip region and the number of overlaps in the strip region) or more, preferably 6 times (the product of the number of spot overlaps in the strip region and the number of overlaps in the strip region) or more, preferably 9 times (the product of the number of spot overlaps in the strip region and the number of overlaps in the strip region) or more, preferably 10 times (the product of the number of spot overlaps in the strip region and the number of overlaps in the strip region) or more, and preferably 15 times (the product of the number of spot overlaps in the strip region and the number of overlaps in the strip region) or more. On the other hand, the total number of overlapping light spots is preferably 500 times or less (the product of the number of overlapping light spots in the strip region 50 and the number of overlapping light spots in the strip region 10), preferably 400 times or less (the product of the number of overlapping light spots in the strip region 50 and the number of overlapping light spots in the strip region 8), preferably 300 times or less (the product of the number of overlapping light spots in the strip region 30 and the number of overlapping light spots in the strip region 10), preferably 200 times or less (the product of the number of overlapping light spots in the strip region 20 and the number of overlapping light spots in the strip region 10), preferably 160 times or less (the product of the number of overlapping light spots in the strip region 20 and the number of overlapping light spots in the strip region 8), preferably 100 times or less (the product of the number of overlapping light spots in the strip region 10 and the number of overlapping light spots in the strip region 10), preferably 80 times or less (the product of the number of overlapping light spots in the strip region 10 and the number of overlapping light spots in the strip region 8), and preferably 50 times or less (the product of the number of overlapping light spots in the strip region 10 and the number of overlapping light spots in the strip region 5).

[0119] (Total number of overlapping light spots per unit depth) The total number of overlapping light spots can be adjusted by the maximum average depth R (in μm) of the recess 14. Therefore, 1 μm is defined as the unit recess depth, and the value obtained by dividing the total number of overlapping light spots by the maximum average depth R is defined as the total number of overlapping light spots per unit depth (times / μm). Preferably, the laser irradiation and / or scanning conditions are adjusted to have a total number of overlapping light spots per unit depth (times / μm) within the range of 5 to 500. Furthermore, it is desirable to adjust the laser irradiation and / or scanning conditions to have a total number of overlapping light spots per unit depth (times / μm) within the range of 5 to 250, and even more desirable to adjust the laser irradiation and / or scanning conditions to have a total number of overlapping light spots per unit depth (times / μm) within the range of 5 to 50.

[0120] <Machining methods for multiple recesses> Next, the machining method for cases where multiple recessed object regions 614 exist in the scanning direction (circumferential or axial) will be described. For example... Figure 11As shown in (A), a laser spot 590S is irradiated along a first linear moving path 611 in the circumferential or axial direction. This first moving path 611 is configured to span multiple recessed object regions 614. The aforementioned first irradiation process is performed sequentially on each of the multiple recessed object regions 614 from upstream to downstream along the first moving path 611. This process is defined as a first irradiation group process. As a result, groove-shaped first strip regions 621 are formed in each of the multiple recessed object regions 614. These are defined as a first strip region group.

[0121] After the first irradiation group process, such as Figure 11 As shown in (B), a laser spot 590S is irradiated along a second moving path 612, which is linear in shape and has a center line offset from the center line of the first moving path 611 by a predetermined line spacing 596. This second moving path 612 is configured to span multiple recessed object regions 614. The aforementioned second irradiation process is performed sequentially on each of the multiple recessed object regions 614 from upstream to downstream of the second moving path 612. This process is defined as a second irradiation group process. As a result, groove-shaped second strip regions 622 are formed in each of the multiple recessed object regions 614. These are defined as a second strip region group.

[0122] Focusing on each recessed object area 614, the recess processing apparatus 500 processes the other recessed object areas 614 during the period from after the first irradiation step to before the second irradiation step. As a result, each recessed object area 614 has the advantage of ensuring sufficient heat dissipation time immediately after processing in the first and second irradiation steps.

[0123] like Figure 11 As shown in (C), the third irradiation group process is performed in the same manner as the first and second irradiation group processes described above, forming multiple third strip-shaped regions 623 along the third movement path 613. The fourth, fifth, and subsequent irradiation group processes are repeated in the same way. The result is as follows: Figure 11 As shown in (D), multiple recesses 14 are formed.

[0124] <Example> Next, an embodiment of the cylinder liner 10 of this embodiment will be described. Using a recess machining apparatus 500, recesses 14 are machined into the four cylinder liners 10 that constitute the first to fourth embodiments. Alternatively, as a comparative example, the recesses 14 are machined into the cylinder liners 10 using a conventional sandblasting process.

[0125] like Figure 12As shown in (A) and (B), for the bottom surface 14A of the recess 14 in the first, second, third, and fourth embodiments, the core height difference Rk is less than 1.6 μm as the surface roughness after laser polishing, and the protrusion valley depth Rvk is less than 1.3 μm. In this embodiment, the core height difference Rk is less than 1.1 μm as the surface roughness after laser coating and polishing, and the protrusion valley depth Rvk is less than 0.9 μm.

[0126] On the other hand, in the comparative example where the recess was formed by sandblasting, the core height difference Rk was 1.6 μm or more, and the depth of the protruding valley Rvk was 1.3 μm or more, as the surface roughness after laser polishing. In the comparative example, the core height difference Rk was 1.1 μm or more, and the depth of the protruding valley Rvk was 0.9 μm or more, as the surface roughness after laser coating and polishing.

[0127] like Figure 12 As shown in (C), for the bottom surface 14A of the recess 14 in the first embodiment, second embodiment, third embodiment, and fourth embodiment, the value (Rk+Rvk) obtained by adding the core height difference Rk and the protruding valley depth Rvk as the surface roughness after laser polishing is less than 2.9 μm. The value (Rk+Rvk) obtained by adding the core height difference Rk and the protruding valley depth Rvk as the surface roughness after laser coating and polishing is less than 2.0 μm.

[0128] On the other hand, for the comparative example where the recess was formed by sandblasting, the value (Rk+Rvk) obtained by adding the core height difference Rk and the depth of the protruding valley Rvk as the surface roughness after laser polishing is 2.9 μm or more. Furthermore, in the comparative example, the value (Rk+Rvk) obtained by adding the core height difference Rk and the depth of the protruding valley Rvk as the surface roughness after laser coating and polishing is 2.0 μm or more.

[0129] <Fuel Consumption> In the case of the cylinder liner 10 in 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 though the absolute amount of oil film is reduced, since the recesses 14 with smooth bottom surfaces 14A are formed overlappingly, the lubricating oil in the recesses 14 is smoothly guided to the surrounding inner wall surfaces 12, preventing insufficient lubrication. That is, in this embodiment, both the reduction of oil consumption and sufficient lubrication effect can be reasonably solved.

[0130] <Example of a modified recess machining device> exist Figure 8The recess processing apparatus 500 illustrates a galvanometer mirror method, but the present invention is not limited thereto. For example, Figure 13 The recess processing apparatus 800 shown includes: a laser oscillator 810 that emits a laser 890; a holding cylinder 81 disposed in the laser oscillator 810 and through which the laser 890 passes; a reflector 820 disposed inside the holding cylinder 815 and reflecting the laser 890 at an angle of 90 degrees; an axial moving device 830 that moves the laser oscillator 810 and the cylinder liner 10 relative to each other in the cylinder axial direction; a base 850 that holds the cylinder liner 10; a chuck 852 that fixes the cylinder liner 10 to the base 850; a rotation moving device 840 that rotates the cylinder liner 10 and the laser 890 relative to each other in the cylinder circumferential direction; and a control device 870 that controls the entire assembly.

[0131] The central axis of the retaining cylinder 815 extends parallel to the cylinder axis of the cylinder liner 10. The retaining cylinder 815 is inserted into the interior of the cylinder liner 10. The laser 890 passing through the interior of the retaining cylinder 815 is deflected (reflected) by the reflecting mirror 820 and travels radially along the cylinder of the cylinder liner 10, irradiating the inner wall surface 12 substantially perpendicularly. It should be noted that, although the case where the axial moving device 830 moves the laser oscillator 810 is illustrated here, the cylinder liner 10 can also be moved along the cylinder axis. In addition, although the case where the rotating moving device 840 rotates the cylinder liner 10 is illustrated here, the laser oscillator 810 as a whole or the reflecting mirror 820 (retaining cylinder liner 815) can also be rotated.

[0132] For example, Figure 14 As shown in the scanning path of (A), the recess processing apparatus 800 can repeat the following operation: after scanning 360 degrees along the first direction of the cylinder circumference with the laser 890, it moves a predetermined line spacing 596 along the cylinder axis, scans 360 degrees again along the first direction of the cylinder circumference with the laser 890, and then moves the predetermined line spacing 596 along the cylinder axis. Additionally, for example, as... Figure 14 As shown in the scanning path (B), the following actions can be repeated: after the laser 890 scans 360 degrees along the first direction of the cylinder circumference, a predetermined line spacing 596 is moved along the cylinder axis to scan 360 degrees along the second direction of the cylinder circumference (opposite to the first direction), and then the predetermined line spacing 596 is moved along the cylinder axis. Furthermore, for example, as... Figure 14 As shown in the scanning path (C), the laser 890 can scan in a spiral pattern along the cylinder circumference and cylinder axis while rotating 360 degrees and moving a predetermined line spacing of 596 along the cylinder axis. Furthermore, for example, as... Figure 14As shown in the scanning path of (D), the following actions can be repeated: after the laser 890 scans a predetermined distance along the first direction of the cylinder axis, the line spacing is moved by a predetermined line spacing 596 along the cylinder circumference, and then the predetermined distance is scanned along the second direction of the cylinder axis (the direction opposite to the first direction).

[0133] <Configuration of the recesses during spiral operation> exist Figure 15 The text shows how to achieve this. Figure 14 The scanning path of the spiral laser of (C) and Figure 11 The arrangement of multiple recesses 14 formed on the inner wall surface 12 of the cylinder liner 10 is achieved by combining machining methods for multiple recesses. It should be noted that... Figure 15 This diagram shows the state where the inner wall surface 12 is unfolded circumferentially. The center of the coaxial direction of the maximum average length J of the cylinder axial direction of the recess 14 is defined as the recess center GM. The scanning path (spiral path) of the laser 590 on the inner wall surface 12 is parallel to the line segment connecting the circumferentially arranged recess center GM. The angle at which the scanning path (spiral direction) intersects the circumferential direction of the cylinder liner is defined as the torsion angle β.

[0134] The torsion angle β is set to be greater than 0 degrees and less than 45 degrees. The torsion angle β is ideally set to less than 20 degrees, further ideally less than 10 degrees, even more ideally less than 5 degrees, and still even more ideally less than 1 degree. Specifically, the torsion angle β is preferably determined by the line spacing 596. If the circumference of the cylinder liner 10 is defined as KS, and the line spacing 596 is defined as LP, then the torsion angle β can be expressed as β = tan φ. -1 (LP / KS) is used for definition. For example, if the circumference of cylinder liner 10 is defined as 314mm and the line spacing 596 is defined as 0.010mm, then β becomes 1.825 × 10 -4 Spend.

[0135] The result is that the central GM of the plurality of recesses 14 arranged at intervals in the circumferential direction is configured to gradually shift along the cylinder axis along the torsion angle β. That is, the plurality of recesses 14 are arranged in a spiral scanning path. In addition, the distance difference KK between the central GM of the recesses of a pair of adjacent recesses 14 in the circumferential direction and in the cylinder axis is set to be smaller than the maximum average length J of the recesses 14, and is expected to be set to J / 2 or less.

[0136] It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

Claims

1. A cylinder, characterized in that, The piston, equipped with piston rings, slides on the inner wall surface. The cylinder has a plurality of laser-machined recesses formed in the central region of its stroke, which extends from the lower surface of the annular groove of the lowermost piston ring at the top dead center of the piston to the upper surface of the annular groove of the uppermost piston ring at the bottom dead center of the piston. The surface roughness of the bottom surface of the recess satisfies at least one of the following first to fourth states: The first state is that the core height difference Rk after the bottom surface is polished is less than 1.6μm. The second state is that the depth Rvk of the protruding valley after the bottom surface has been polished is less than 1.3μm. The third state is when the core height difference Rk is less than 1.1 μm after the bottom surface has undergone chemical conversion treatment and polishing. The fourth state is that the depth Rvk of the protruding valley is less than 0.9 μm after the bottom surface has undergone chemical conversion treatment and polishing.

2. The cylinder according to claim 1, characterized in that, The surface roughness of the bottom surface of the recess satisfies either the fifth or sixth state below: The fifth state is that, after polishing the bottom surface, the combined value of the core height difference Rk and the protruding valley depth Rvk is less than 2.9 μm. The sixth state is that the combined value of the core height difference Rk and the protruding valley depth Rvk after the bottom surface has undergone chemical conversion treatment and polishing is less than 2.0 μm.

3. The cylinder according to claim 1 or 2, characterized in that, The depth of the recess is 0.1 μm to 1000 μm.

4. The cylinder according to claim 1 or 2, characterized in that, The recess is processed using a laser with a pulse width of less than 100 picoseconds.

5. The cylinder according to claim 1 or 2, characterized in that, The area surrounding the recess forms a conical surface that increases in the number of overlapping irradiations of the laser spot based on the laser processing, moving from the outside of the recess toward the inside.

6. The cylinder according to claim 1 or 2, characterized in that, When the maximum axial dimension of the cylinder of the recess is defined as WJ, the axial offset Z of the central position of the axial direction of a pair of recesses circumferentially adjacent to the inner wall surface is set to 0 < Z < WJ.

7. A method for machining a recess on the inner wall of a cylinder, characterized in that, A laser spot is irradiated onto the inner wall surface of a cylindrical cylinder in which a piston equipped with piston rings slides, thereby forming a recess larger than the diameter of the laser spot. The method for processing the recess includes: In the first irradiation step, a laser spot with a pulse width of less than 100 picoseconds is irradiated along a linear first moving path onto a predetermined recessed object area to form the recess, thereby performing concave processing on the first strip-shaped area; and The second irradiation step, following the first irradiation step, involves irradiating the recessed object region with a laser spot that overlaps at least a portion of the first strip region along a second linear movement path that is parallel to the first movement path and has a center line offset from the center line of the first movement path, thereby performing concave processing on the second strip region that overlaps with the first strip region.

8. The method for machining the concave portion of the cylinder inner wall according to claim 7, characterized in that, Multiple recessed object regions exist, spaced apart from each other along the circumference of the inner wall surface. The method for processing the recess includes: The first irradiation process involves irradiating the laser spot along the first circumferential moving path, and performing the first irradiation process on each of the plurality of recessed object regions; and The second irradiation process, following the first irradiation process, involves irradiating the laser spot along the second circumferential moving path to perform the second irradiation process on each of the plurality of recessed object regions.

9. The method for machining the concave portion of the cylinder inner wall according to claim 8, characterized in that, The scanning path of the laser spot in the first irradiation group process is along a spiral path.

10. The method for machining the recessed portion of the cylinder inner wall according to claim 9, characterized in that, The arrangement of the plurality of recesses formed on the inner wall surface is along the spiral path.

11. The method for machining the recessed portion of the cylinder inner wall according to claim 7, characterized in that, The surface roughness of the bottom surface of the recess satisfies at least one of the following first to fourth states: The first state is that the core height difference Rk after the bottom surface is polished is less than 1.6μm. The second state is that the depth Rvk of the protruding valley after the bottom surface has been polished is less than 1.3μm. The third state is when the core height difference Rk is less than 1.1 μm after the bottom surface has undergone chemical conversion treatment and polishing. The fourth state is that the depth Rvk of the protruding valley is less than 0.9 μm after the bottom surface has undergone chemical conversion treatment and polishing.

12. The method for machining the recess on the inner wall surface of a cylinder according to any one of claims 7 to 11, characterized in that, When the diameter of the laser spot is defined as C, and the offset between the center line of the first moving path and the center line of the second moving path is defined as OS, then OS ≤ C / 2.

13. The method for machining the recessed portion of the cylinder inner wall surface according to any one of claims 7 to 11, characterized in that, The axial dimension of the recess is larger than the contact width between the piston ring and the inner wall surface.

Images