JP5386212B2 - Cylinder - Google Patents

Description

  The present invention relates to a cylinder in which a piston slides on an inner wall surface thereof, and in particular, reciprocating friction with the piston can be reduced, and vertical scratches that may occur between the piston skirt portion of the piston and the cylinder The present invention relates to a cylinder capable of avoiding excessive wear.

Environmental issues such as global warming have been greatly highlighted on a global scale, and the development of fuel efficiency improvement technology for internal combustion engines to reduce CO _{2 in} the atmosphere has become a major issue. Reduction of the friction loss of the sliding member is required. In view of this, in recent years, the development of sliding member materials, surface treatment, and modification technologies that are excellent in wear resistance and seizure resistance and that can maximize the effect of reducing frictional force have been developed. It is being advanced.

  In order to improve the energy efficiency of a device using a cylinder, such as an improvement in fuel consumption of an internal combustion engine, reduction of friction loss is effective. In particular, friction reduction is effective between the piston (and piston ring) that reciprocates and the inner wall surface of the cylinder.

  In order to reduce the above-mentioned reciprocating friction, Patent Document 1 discloses a technique for reducing the reciprocating friction between the piston (and piston ring) and the cylinder liner by forming a recess (concave portion) on the inner wall surface of the cylinder liner. Yes. The document also discloses changing the size of the recessed portion and the opening area of the recessed portion in the portion of the inner wall surface of the cylinder liner that slides with the piston skirt of the piston and other portions.

JP 2007-46660 A

  However, in the invention of the above-mentioned Patent Document 1, it is considered as to how to form a recess in which part of the inner wall surface of the cylinder liner, and the portion of the recess that slides with the piston skirt and the recess Consideration of the relationship has not been done in detail and there is still room for improvement.

  The present invention has been made in such a current situation, and relates to a cylinder in which a piston slides on an inner wall surface thereof, and in particular, can reduce reciprocating friction with the piston, and a piston skirt portion of the piston. The main object is to provide a cylinder capable of avoiding vertical scratches and excessive wear that may occur between the cylinder and the cylinder.

  A first invention for solving the above-mentioned problem is a cylinder in which a piston slides on an inner wall surface, and of the inner wall surface of the cylinder, the ring groove of the lowest piston ring at the top dead center of the piston. At least one recess is present in all cross sections in the circumferential direction of the cylinder in the center area of the stroke, which is 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. As described above, a plurality of recesses are formed, and the recess is not formed in a region other than the stroke center region of the inner wall surface of the cylinder, and the area of the stroke center region is 100%. The total area of all the recesses is in the range of 1 to 80%, and the piston on the thrust side of the piston used in combination with the cylinder in the stroke center region is Of tons skirt and the sliding region, at least one-fourth or more, characterized in that it is a region in which the concave portion is not formed.

  Further, a second invention for solving the above-mentioned problem is a cylinder in which a piston slides on an inner wall surface, and the ring of the lowest piston ring at the top dead center of the piston among the inner wall surfaces of the cylinder There is at least one recess in all cross sections in the cylinder circumferential direction in the stroke center region, which is a region from the lower surface position of the groove to the upper surface position of the ring groove of the uppermost piston ring at the bottom dead center of the piston. A plurality of recesses are formed so that the recesses are not formed in the inner wall surface of the cylinder other than the stroke center region, and the area of the stroke center region is reduced. The thrust of the piston used in combination with the cylinder in the central region of the stroke when the total area of all the recesses is in the range of 1 to 80% when 100% Out of the piston skirt and the sliding region, at least one-fourth or more, and wherein the area ratio of the concave portion than in the region other than the region is lower region.

  Further, a third invention for solving the above-mentioned problem is a cylinder in which a piston slides on an inner wall surface, and of the inner wall surface of the cylinder, the ring of the lowest piston ring at the top dead center of the piston There is at least one recess in all cross sections in the cylinder circumferential direction in the stroke center region, which is a region from the lower surface position of the groove to the upper surface position of the ring groove of the uppermost piston ring at the bottom dead center of the piston. A plurality of recesses are formed so that the recesses are not formed in the inner wall surface of the cylinder other than the stroke center region, and the area of the stroke center region is reduced. The thrust of the piston used in combination with the cylinder in the central region of the stroke when the total area of all the recesses is in the range of 1 to 80% when 100% Out of the piston skirt and the sliding region, at least one-fourth or more, wherein the average length of the cylinder radial recess than in the region other than the region is a small area.

  The above cylinder may be composed of a cylinder body and a cylinder liner fixed to the inside of the cylinder body, and the plurality of recesses may be formed on the inner wall surface of the cylinder liner.

  In the above cylinder, the ten-point average roughness Rz of the portion where the concave portion is not formed in the central region of the stroke may be 4 μm or less.

  In the above cylinder, the average length of the concave portion in the cylinder axial direction may be equal to or less than the length of the uppermost piston ring in the cylinder axial direction among the piston rings used.

  Moreover, in said cylinder, the average length of the said recessed part in the cylinder radial direction may be in the range of 0.5-1000 micrometers.

  Further, the above cylinder may be used for an internal combustion engine.

  In the present invention, first, in which part the concave portion should be provided in the entire inner wall surface of the cylinder, the various requirements are limited. Specifically, since the concave portion is formed only in the stroke center region (the concave portion is not formed in a portion other than the stroke central region), the piston ring and the inner wall surface of the cylinder in the region where the piston ring slides. And reciprocating friction can be reduced. Further, by making the formation area ratio of the recesses in the center area of the stroke within a predetermined range, the contact area becomes small, and the frictional force due to the shear resistance of the lubricating oil can be kept small. Furthermore, in the present invention, the plurality of recesses formed in the center region of the stroke are formed so as to overlap in the cylinder axial direction (at least one recess is formed in all cross sections in the cylinder circumferential direction). Therefore, the contact area can be reduced efficiently and on average.

  In addition, the present invention secondly considers the positional relationship between the inner wall surface of the cylinder and the piston skirt of the piston that slides in the central region of the stroke of the inner wall surface of the cylinder. There are various limitations. Specifically, (1) Of the region that slides with the piston skirt portion on the thrust side of the piston used in combination with the cylinder in the stroke center region, at least 1/4 of the region is formed by the recess. The area is not. Or (2) In the region in the center of the stroke, in the region sliding with the piston skirt on the thrust side of the piston used in combination with the cylinder, at least 1/4 or more of the region is more than the region other than the region It can be said that the area ratio of the recesses is low. Or (3) Of the region that slides with the piston skirt on the thrust side of the piston used in combination with the cylinder in the central region of the stroke, at least ¼ or more of the region is more than the region other than the region The concave portion has a small average length in the cylinder radial direction.

  The region that slides with the piston skirt portion on the thrust side of the piston used in combination with the cylinder in the center region of the stroke is the portion to which the pressure from the piston skirt portion is most applied, and is at least 1/4 or more of the portion. By limiting the above-mentioned area, it is possible to reduce the surface pressure of the part, thereby preventing vertical damage from occurring in the part and preventing excessive wear of the part. it can.

  In addition, the cylinder of the present invention can obtain the same effect regardless of whether it is a type in which the inner wall surface of the cylinder and the piston slide or a type in which the cylinder liner fixed to the inside of the cylinder and the piston slide. Can do.

  Further, in the cylinder of the present invention, the effect of reducing the reciprocating friction can be exhibited by setting the value of the ten-point average roughness Rz of the portion where the concave portion is not formed in the central region of the stroke to a predetermined value or less. it can. The ten-point average roughness Rz is defined in JIS B0601-1994.

  Further, in the cylinder of the present invention, by setting the average length of the recesses in the cylinder axial direction to be equal to or shorter than the length of the uppermost piston ring in the cylinder axial direction, the airtightness in the cylinder can be maintained high.

  In the cylinder of the present invention, the influence of the shearing resistance of the lubricating oil in the reciprocating friction can be efficiently reduced by setting the average length of the recesses in the cylinder radial direction within a predetermined range.

  Furthermore, a high effect can be obtained by using the cylinder liner of the present invention for an internal combustion engine which is a field in which improvement in energy efficiency is particularly required.

It is a partially notched front view which shows the state which combined the piston and cylinder of this invention. It is an expanded view of the axial direction of the inner wall surface of the cylinder of this invention. It is a schematic sectional drawing which shows an example of the range of the said process center part area | region in the cylinder liner fixed inside the cylinder main body of this aspect. It is a general | schematic expanded view which shows an example of the shape of the recessed part formed in the cylinder used in this invention. It is a general | schematic expanded view which shows an example of arrangement | positioning of a recessed part in the process center part area | region of FIG. 3 mentioned above. It is the general | schematic expanded view and schematic sectional drawing explaining the dimension position of the recessed part formed in the cylinder of this invention. It is a general | schematic expanded view which shows another example of arrangement | positioning of a recessed part in the cylinder used in this invention. It is the schematic sectional drawing explaining the area ratio in the cylinder used in this invention, and a schematic expanded view. It is an expanded view of the axial direction of the inner wall surface of the cylinder liner of this invention. It is a figure which compares the recessed part of the special process center part area | region, and the recessed part of area | regions other than the said area | region (general process center part area | region). It is the schematic which shows the dimension of the cylinder liner and piston used in this invention. It is explanatory drawing of the method of forming a recessed part in the cylinder liner of this invention. It is an expanded view of the cylinder liner of a reference experiment. It is explanatory drawing of the apparatus for measuring a reciprocating friction force. 5 is a graph showing measurement results of Reference Experiment 1. 6 is a graph showing measurement results of Reference Experiment 2. 10 is a graph showing measurement results of Reference Experiment 3.

  The present invention relates to a cylinder in which a recess is provided in a central region of a stroke of an inner wall surface. Specifically, a method of providing a recess for each region (existence of a recess) is not provided in the cylinder inner wall surface. This is characterized in that the presence / absence of the recess, the area ratio of the recess, and the average length (depth) of the recess in the cylinder radial direction are changed. That is, first, the inner wall surface of the cylinder is divided into a stroke center region and other regions, and second, the stroke center piston region is used in combination with the cylinder on the thrust side of the piston skirt. It is characterized in that it is divided into an area that slides with the part and other parts, and an optimum recess is provided in each area. According to such a cylinder of the present invention, reciprocating friction with the piston can be reduced, and occurrence of vertical scratches and excessive wear that can occur between the piston skirt portion of the piston and the cylinder can be avoided. .

  FIG. 1 is a partially cutaway front view showing a state in which a cylinder and a piston of the present invention are combined.

  As shown in FIG. 1, a piston 20 is inserted into a cylinder 10 having a cylindrical shape.

  Here, the piston 20 is connected to a connecting rod 22 that is rotatably provided via a piston pin 21, and is provided so as to be able to reciprocate in the vertical direction (see the arrow in the figure). Further, the piston 20 has a piston skirt portion 23 disposed in a direction perpendicular to the axis of the piston pin 21 with respect to the piston pin 21, and a piston ring groove 24.

  The piston 20 is known to slide so as to be pressed against a predetermined region (referred to as a thrust region and an anti-thrust region) of the inner wall surface 11 of the cylinder 10 by the rotation of the connecting rod 22. The skirts 23 are provided in portions corresponding to the thrust area and the anti-thrust area, respectively.

  On the other hand, the inner wall surface 11 of the cylinder 10 of the present invention is provided with a plurality of recesses 12 in a predetermined region. The cylinder 10 shown in FIG. 1 is a so-called “linerless type” cylinder in which the piston 20 slides directly on the inner wall surface of the cylinder. However, the present invention is not limited to this type. It may be a so-called “cylinder liner type” cylinder composed of a cylinder liner fixed to the inside thereof (described in detail below).

  FIG. 2 is an axial development of the inner wall surface of the cylinder of the present invention.

  The inner wall surface 11 of the cylinder 10 according to the present invention has a predetermined recess 12 formed only in the stroke center region 13, and no recess is formed in any region other than the stroke center region 13. It has the characteristics. Furthermore, in the stroke center region 13, at least a quarter of the region 14 that slides with the piston skirt 23 on the thrust side of the piston 20 used in combination with the cylinder 10 (FIG. 2). , The surface state (specifically, the concave portion 12 is different from the region 15 other than the region 14 in the stroke center region 13) having the same size as the region 14 and a portion indicated by reference numeral 14 in the drawing. It has the second feature in that it is not formed, or the area ratio of the recess 12 is reduced, or the average length of the recess 12 in the cylinder radial direction is reduced (the depth is reduced). . Thereby, it is possible to prevent vertical damage from occurring in the portion, and it is possible to prevent excessive wear of the portion.

  In the following description, a region 15 (shaded region in FIG. 2) 13 in the stroke center region is referred to as a “general stroke center region”, and a region 14 (sliding with the piston skirt of the piston). The region at least 1/4 of the portion) may be referred to as a “special stroke center region”. The inner wall surface 11 of the cylinder 10 has a front area (reference F), a thrust area (reference T), a rear area (reference R), and an anti-thrust area (reference A) depending on the relationship with the piston 20 that slides there. ). In the cylinder 10 of the present invention, the “special stroke center region 14” exists in the thrust region (T). However, some pistons may have a piston skirt that exceeds the thrust region. In this case, the piston skirt portion is not limited to the thrust region.

  Hereinafter, the cylinder of the present invention will be described by taking a “cylinder liner type” as an example.

A. First aspect (cylinder liner type)
The cylinder according to the first aspect of the present invention includes a cylinder body and a cylinder liner fixed to the inside of the cylinder body, and the plurality of recesses are formed on the inner wall surface of the cylinder liner. In this aspect, the inner wall surface of the cylinder body and the outer wall surface of the cylinder liner are fixed, and the piston slides on the inner wall surface of the cylinder liner. Therefore, the cylinder to which the cylinder liner is fixed The inner wall surface of the main body need not be provided with a recess.

(1) Stroke Center Area First, the stroke center area will be described.

  FIG. 3 is a schematic cross-sectional view showing an example of a range of the stroke center region in the cylinder liner fixed to the inside of the cylinder main body according to this aspect.

  In the present embodiment, the “stroke center area” 30 refers to the upper surface of the ring groove of the uppermost piston ring at the bottom dead center of the piston from the position of the lower surface of the ring groove of the lowermost piston ring at the top dead center of the piston. It is the area between the positions.

  For example, as illustrated in FIG. 3, when three piston rings are arranged in the order of the first pressure ring, the second pressure ring, and the oil control ring from above the piston, the upper end of the stroke center region 30 is The position of the lower surface 34 of the ring groove 33 of the oil control ring 32 is the position of the upper surface 37 of the ring groove 35 of the first pressure ring 36 which is the uppermost piston ring. In this embodiment, the recess is formed only in the center area of the stroke, and no recess is formed in other areas. In addition, this aspect is not limited to the configuration in which three piston rings are used, but has two piston rings (one pressure ring and one oil control ring), or one piston ring. The same applies to the configuration (piston ring having both gas seal and oil control).

(2) 1st characteristic Here, the 1st characteristic of this aspect exists in the point which provided the predetermined recessed part only in the said process center part area | region 30. FIG. More specifically, a plurality of recesses are formed in the stroke center region 30 so that there is at least one recess in all cross sections in the cylinder circumferential direction, and in regions other than the stroke center region, The recess is not formed, and the total area of all the recesses is in the range of 1 to 80% when the area of the central region of the stroke is 100%.

  In order to improve the energy efficiency of the device in which the cylinder is used, for example, to improve the fuel efficiency of the engine, it is effective to reduce the friction loss between the piston ring and the inner wall surface of the cylinder (in this embodiment, the inner wall surface of the cylinder liner). It is. The method of reducing the friction loss differs depending on the sliding condition, but in particular, the piston has a feature such that the speed becomes 0 at the top dead center, and therefore, it varies depending on the sliding position. Therefore, in the cylinder liner constituting the cylinder of this aspect, a recess is formed only in the stroke center region 30 of the inner wall surface, and at least one of the plurality of recesses is formed in all cross sections in the cylinder circumferential direction. In other words, by forming the recesses so as to overlap in the cylinder axis direction, it is possible to reduce the frictional force in the entire region of the stroke center region 30.

  In other words, the reciprocating friction can be reduced by reducing the surface roughness of the inner wall surface of the cylinder liner near the top dead center and the bottom dead center where the moving speed of the piston is relatively low. However, in the stroke center region 30 where the sliding speed between the inner wall surface of the cylinder liner and the piston ring is high, the influence of the shear resistance of the lubricating oil becomes large. Therefore, in this aspect, by forming a recess only in the stroke center region 30 of the inner wall surface of the cylinder liner, the contact area between the piston ring and the inner wall surface of the cylinder liner is reduced, and the shear resistance of the lubricating oil is reduced. It was possible to reduce the influence of

  Here, when a plurality of recesses are formed randomly in the stroke center region 30, the contact area between the piston ring and the inner wall surface of the cylinder liner is small in the stroke center region 30 as a whole. The width of the sliding piston ring (the length in the axial direction of the cylinder) is very short compared to the stroke center region 30, so there may be a portion where no recess is formed depending on the location, In this portion, the piston ring sliding surface and the inner wall surface of the cylinder liner are in contact with each other 100%, and there is a possibility that the above effect cannot be sufficiently exhibited. As described above, all cross sections in the cylinder circumferential direction have at least one of the plurality of recesses, in other words, the recesses overlap in the cylinder axial direction. As a result, the sliding piston ring is always in contact with the recess. As a result, the contact area between the piston ring and the inner wall surface of the cylinder liner does not become 100%, and the above effect is always achieved. It can be demonstrated.

  In addition, when the concave portion is formed in the entire region where the piston ring slides, that is, when the concave portion is formed in the region other than the central region of the stroke, the contact surface pressure increases due to the decrease in the contact area, and top dead Since boundary lubrication occurs near the point and bottom dead center, the frictional force increases. In addition, if there is a recess in such a portion, it becomes an unnecessary oil pool, which may burn and increase the amount of oil consumed.

(3) Concave portion in the first feature (concave portion formed in the central region of the general stroke)
Next, the recessed part formed in the process center part area | region is demonstrated.

  In this aspect, the shape of the recess formed in the central region of the stroke is not particularly limited, and can be appropriately adjusted according to the arrangement of the recess. For example, as illustrated in FIGS. 4A to 4J, a concave portion having a shape constituted by a straight line and / or a curved line can be formed. The recesses may be horizontally long as shown in FIGS. 4A to 4C, vertically long as shown in FIGS. 4D to 4G, or vertically as shown in FIGS. 4H to 4J. A shape with a substantially equal ratio of width to width may be used.

  Here, in the cylinder of this aspect, at least one of the concave portions is formed in all cross sections in the cylinder circumferential direction in the stroke center region. Thereby, a contact area can be reduced efficiently and on average.

  As described above, when considering a cross section in the circumferential direction, if no recess is formed in a certain cross section, when the piston ring passes through the cross section, it passes through the cross section in which a plurality of recesses are formed. Compared to the case, the contact area between the piston ring and the inner wall surface of the cylinder liner is increased. Therefore, the influence of the shear resistance of the lubricating oil is increased, and as a result, the reciprocating friction is also increased.

  On the other hand, by forming at least one recess in all cross sections in the cylinder circumferential direction in the stroke center area, even if the piston ring passes through any circumferential section in the stroke center area, Since the contact area can be reliably and averagely reduced, the reciprocating friction can also be reliably reduced.

  As an example of the state of “a state where at least one of the plurality of recesses is formed in all cross sections in the circumferential direction of the cylinder” which is a feature of this aspect, the case of FIG. 5 can be given.

  FIG. 5 is a schematic development view showing an example of the arrangement of the recesses 50 in the stroke center region 30 in FIG. 3 described above. In FIG. 5, the vertical direction of the drawing is the axial direction of the cylinder, and the horizontal direction of the drawing is the circumferential direction of the cylinder. As illustrated in FIG. 5, in the line X drawn in the cylinder circumferential direction, the lowermost point 52 of the concave portion 51 is located below the uppermost point 54 of the concave portion 53 closest to the lower side thereof. In the line Y drawn in the cylinder circumferential direction, the lowest point 55 of the concave portion 53 is positioned below the uppermost point 57 of the concave portion 56 closest to the lower portion. In this way, by arranging the recesses close to each other in the vertical direction so as to overlap with each other in the cylinder axial direction, at least one of the plurality of recesses can be formed in all cross sections in the cylinder circumferential direction. From the above, when the piston reciprocates, the piston ring that slides in the central region of the stroke can reduce the contact area with the cylinder inner wall surface at any position in the cylinder axial direction, reducing reciprocating friction. There is an effect.

  In this embodiment, the size of the recess is not particularly limited, and can be appropriately adjusted according to the size of the cylinder and the piston ring used together. The concave portion may be formed so as to penetrate the center region of the stroke in the cylinder axial direction, but from the viewpoint of maintaining the airtightness of the cylinder, the average length of the concave portion in the cylinder axial direction is the piston ring used. The length of the uppermost piston ring is preferably equal to or less than the length in the cylinder axial direction. More specifically, it is preferable that the uppermost piston ring of the used piston rings is about 5 to 100% of the length in the cylinder axial direction.

  The average length of the recesses in the cylinder circumferential direction is preferably within a range of 0.1 mm to 15 mm, and particularly preferably within a range of 0.3 mm to 5 mm. When the cylinder circumferential direction average length is less than this range, the effect of forming the concave portion may not be sufficiently obtained. On the other hand, if the circumferential average length exceeds this range, a part of the piston ring may enter the recess and a problem such as deformation of the piston ring may occur.

  The average length of the recesses 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, and particularly preferably in the range of 0.1 μm to 50 μm. When the average length in the cylinder radial direction of the recess is less than this range, the effect of forming the recess may not be sufficiently obtained. On the other hand, when the radial average length exceeds this range, processing is difficult, and there is a problem such as the need to increase the radial length of the cylinder liner (thicken the wall thickness). There is.

  In this aspect, the cylinder circumferential direction average length (interval) between adjacent recesses is preferably in the range of 0.1 to 15 mm, and particularly preferably in the range of 0.3 mm to 5 mm. If the cylinder circumferential average length (interval) between adjacent recesses is less than this range, the inner wall surface of the cylinder liner on which the piston ring slides is too small, and the inner wall surface of the piston ring and the cylinder liner May not be able to slide stably. On the other hand, when it exceeds this range, the effect of forming the recess may not be sufficiently obtained.

  In addition, each average length of the recessed part mentioned in this aspect shall mean the average length of each location illustrated in FIG. FIG. 6A is a schematic development view showing the cylinder axial direction of the inner wall surface of the cylinder liner in the vertical direction of the drawing. FIG. 6B is a schematic cross-sectional view of the cylinder liner in the circumferential direction. The axial average length of the concave portion is an average length of the concave portion 50 in the cylinder axial direction as illustrated in FIG.

  Moreover, the circumferential direction average length of the said recessed part 50 is an average of the length of the recessed part 50 in a cylinder circumferential direction so that it may illustrate in Fig.6 (a). As illustrated in FIG. 6B, the average length in the circumferential direction of the recess 50 means the average length in the surface including the inner wall surface, and the same applies to the area of the recess.

  Moreover, the radial direction length of the said recessed part 50 is an average of the length from the bottom face of the recessed part 50 to the inner wall face of a cylinder liner so that it may illustrate in FIG.5 (b). Moreover, the cylinder circumferential direction average length (interval) between the said recessed parts is the average of the space | interval of the adjacent recessed part 50 so that it may illustrate in FIG. 6 (a) and (b). Note that the average length in the cylinder circumferential direction between the recesses when no recess is formed in the special stroke center region is considered excluding the special stroke center region.

  In this aspect, the arrangement of the recesses in the general stroke central region is particularly limited as described above, except that the recesses are arranged so that “at least one recess is formed in all cross sections in the cylinder circumferential direction”. It is not a thing. For example, FIG. 7 shows a partially developed view in which the inner periphery of the cylinder liner is opened in the circumferential direction. As illustrated in FIG. 7A, the recess is formed so as to penetrate the general stroke center region in the cylinder axial direction. Alternatively, as illustrated in FIG. 7B, it may be formed in a spiral shape on the inner wall surface of the cylinder liner. In addition, as illustrated in FIGS. 7C and 7D, concave portions having a specific length in the cylinder axis direction may be arranged at regular intervals. Furthermore, the recesses may be arranged irregularly (randomly). In addition, the shapes and dimensions of the plurality of recesses formed on the inner wall surface of one cylinder liner may be different or the same.

  In this aspect, a plurality of recesses are formed only in the stroke center region, and the total area of all recesses is within a range of 1 to 80% when the area of the stroke center region is 100%. The number of recesses formed per cross section in the cylinder circumferential direction may be at least one, and the others are not particularly limited. However, if the number of recesses formed in one cross section in the circumferential direction of the cylinder is too small, there is a possibility that the effect of reducing the reciprocating frictional force obtained by forming the recesses and reducing the contact area cannot be sufficiently obtained. is there. Therefore, it is preferable to form a recess that can sufficiently exhibit the effect for each cross section in the cylinder circumferential direction.

  The concave portion to the extent that the effect of reducing the reciprocating friction force is different depending on the reciprocating speed of the piston used together, but in this aspect, when the area of the stroke center region is 100%, The total area of all the recesses is preferably 1 to 80%, more preferably 10 to 60%, and particularly preferably 20 to 50%. If the area ratio is less than this range, the effect of forming the recess may not be sufficiently obtained. On the other hand, if the area ratio exceeds this range, the contact area is too small, and the piston ring is in a cylinder liner. Inconveniences such as being unable to slide stably on the inner wall surface may occur. From the viewpoint of the effect of reducing the reciprocating frictional force, there is a preferable range of the size of the recess. Therefore, the number of recesses and the number of recesses are determined so that the area ratio is within the above range and at least one recess is formed in all cylinder circumferential cross-sections while taking into account the size of each recess. It is necessary to adjust the arrangement.

In this embodiment, “the total area of all the recesses when the area of the center area of the stroke is 100%” means that the area of the recess 50 is A as illustrated in FIGS. 8A and 8B. _{1, a 2,} a 3, when the _{··· a n, a 1, a} 2, a 3 to the area of the stroke center region is intended to mean the ratio of the sum of the · · · _{a n} . Area ratio, the area _A 1 of the recess 50 in the stroke center _region, A _2, A 3, and the total _{A total} of · · · _{A n,} the cylinder liner inner wall surface other than the recess 50 in the stroke center region area B Using the total B _total, it is expressed by the following formula. In addition, as illustrated in FIG. 8A, the area of the recess 50 means not the area of the bottom of the recess 50 but the area in the cross section including the inner wall surface.

（４）第２の特徴
次に、本態様の第２の特徴について説明する。

(4) Second Feature Next, the second feature of this aspect will be described.

  The second feature of this aspect is that in the stroke center region 30, there is a region that slides with the piston skirt portion on the thrust side of the piston used in combination with the cylinder (cylinder liner) (that is, the special stroke center region). Among them, at least a quarter or more of the region is in a surface state different from the region other than the region in the above-described stroke center region (that is, the general stroke center region). More specifically, in the central region of the special stroke, the concave portion 50 is not formed, the area ratio of the concave portion 50 is reduced, or the average length of the concave portion 50 in the cylinder radial direction is reduced (the depth is reduced). Shallow))).

  The so-called special stroke center region in the stroke center region is a portion to which the pressure from the skirt portion of the piston is most applied. By limiting the above for at least 1/4 of the region, the region It is possible to reduce the surface pressure, thereby preventing vertical damage from occurring in the area and preventing excessive wear in the area.

(5) Special process center area Next, the special process center area will be described.

  FIG. 9 is a development view in the axial direction of the inner wall surface of the cylinder liner according to this embodiment.

  As shown in FIG. 2, as shown in FIG. 9, the special stroke center region 90 exists in the thrust region (T) of the cylinder liner in the stroke center region 30, and the piston skirt portion of the piston. And at least 1/4 of the sliding part.

  FIG. 9A shows a case where the entire stroke portion of the piston and the piston skirt portion in the stroke center region 30 is a special stroke center region 90.

  FIG. 9B shows a case where in the stroke center region 30, 1/4 of the portion sliding with the piston skirt portion of the piston is the special stroke center region 90.

  As shown in FIG. 9 (b), in this embodiment, it is sufficient that a region of 1/4 or more of the portion sliding with the piston skirt portion is the special stroke center region 90, as shown in FIG. 9 (a). In addition, it is not always necessary to use the special stroke center region 90 as a whole for the portion sliding with the piston skirt portion.

  FIG. 9C shows a case where in the stroke center region 30, ½ of the portion sliding with the piston skirt portion of the piston is the special stroke center region 90.

  As shown in FIG. 9C, in this aspect, the special stroke center region 90 does not necessarily have to be integrated, and the total of two or more regions may be used as the special stroke center region 90.

(6) Concave portion in the second feature (concave portion formed in the central region of the special stroke)
Next, a description will be given of a recess (including a case where it is not formed) formed in the special stroke center region.

  In this aspect, the special stroke center region 90 has (1) a recess is not formed, (2) the area ratio of the recess is lower than a region other than the region, and (3) a region other than the region. The average length of the concave portion in the cylinder radial direction is small (the depth of the concave portion is shallow).

  Here, in the case where (1) the recess is not formed, the special stroke center region 90 has the same surface shape as that of the region other than the stroke center region (that is, the surface shape of a normal cylinder liner). It has become.

  The case (2) where the area ratio of the recesses is low means that the number of recesses in the special process center region 90 is small compared to the other regions, or the special area compared to the other regions. This means that the length in the cylinder circumferential direction of the recess in the stroke center region 90 is short.

  FIG. 10 is a diagram comparing the recesses in the special stroke center region with the recesses in regions other than the region (general stroke center region).

  FIG. 10A is a front view of the concave portion in the general stroke central region, and FIG. 10B is a schematic development view of the concave portion in the special stroke central region. As shown in the drawing, by increasing the interval between the recesses, the area ratio of the recesses in the special stroke center region 90 can be lowered.

  FIG. 10C is a cross-sectional view of the recess in the general stroke center region, and FIG. 10D is a cross-sectional view of the recess in the special stroke center region. As illustrated, the cylinder radial direction average length (depth) of the recess may be reduced.

  In this aspect, although the special stroke center region exists, the entire stroke center region satisfies all the various conditions described in the above-mentioned “(3) Recess in the first feature”. In other words, even if no recess is formed in the special stroke center region, the area ratio of the recess is within the above range in the entire stroke center region, and at least one recess is present in the cross section in the cylinder circumferential direction. It will be formed. Moreover, even when the concave portion is formed in the central region of the special stroke, the above conditions are satisfied, and the dimensions and the like of the concave portion are within the range described above.

(7) Cylinder liner The cylinder liner in this aspect is used by being fixed inside the cylinder body, and a piston ring mounted on the piston slides on its inner wall surface. The dimensions, materials, and the like of the cylinder liner of this aspect can be appropriately designed in consideration of the dimensions and materials of the cylinder body, compatibility with the piston rings used together, and the operating temperature.

  In this aspect, from the viewpoint of reducing the reciprocating frictional force between the piston ring and the inner wall surface of the cylinder liner, the 10-point average roughness Rz of the portion where the concave portion is not formed in the central region of the stroke is 4 μm or less. Preferably, the thickness is 2 μm or less, more preferably 1 μm or less. Further, in this aspect, all the areas where the piston slides have the above-mentioned surface roughness, such as the area near the top dead center, the area near the bottom dead center, and the stroke center area on the inner wall surface of the cylinder liner. It is preferable. The ten-point average roughness Rz is defined in JIS B0601-1994.

(8) Cylinder main body The cylinder main body used in this aspect is only required to be able to fix the cylinder liner to the inside thereof, and its material, dimensions, etc. can be appropriately designed according to the application, operating temperature and the like.

(9) Method for forming recesses The method for forming a plurality of recesses in the stroke center region (general stroke center region and special stroke center region) of the cylinder of this aspect is not particularly limited, Any method can be adopted as long as the concave portion that satisfies the conditions can be formed.

  For example, in the blasting method (adopted in the examples described later) for forming recesses by spraying abrasive grains after masking, in the method for forming recesses by masking and then immersed in a corrosive solution, and in letterpress printing A corrosive processing method using a corrosive liquid instead of ink can be employed.

  Further, in the cylinder according to this aspect, it is only necessary that the concave portion is finally formed, and it is not always necessary to remove the cylinder surface in the manufacturing process to form the concave portion, and conversely, the convex portion is formed on the cylinder surface. As a result, a portion where the convex portion is not formed may be a concave portion.

  In this case, specifically, after predetermined masking, a method of forming a PVD film as a convex portion by various PVD methods, and plating of chromium, copper, tin, zinc, nickel, nickel-phosphorous, etc. in addition to the PVD film A film, other iron trioxide, manganese phosphate, molybdenum disulfide, a fluororesin, a graphite film, or the like can be used.

(10) Piston ring used in combination with cylinder The piston ring used in combination with the cylinder of this aspect is not particularly limited, and various piston rings that are currently known can be selected as appropriate.

  In particular, the outer peripheral sliding surface of the piston ring has various shapes depending on its purpose and application, but the cylinder of this aspect can be combined with all piston rings having different outer peripheral sliding surfaces. is there.

For example, in the case of a piston ring with a three-ring configuration (two pressure rings and one oil ring), the outer peripheral sliding surface of the first pressure ring has a barrel shape, an eccentric barrel shape, a tapered shape, etc. The outer peripheral sliding surface of the second pressure ring is preferably a taper shape, an undercut shape, an underhook shape, etc., and the abutment shape is preferably an interrupted undercut shape. For an oil ring, a coil expander and an oil A two-piece oil ring consisting of a ring body and a three-piece oil ring consisting of two side rails and a spacer expander can be used. Double bevel shape and barrel shape, upper surface side of upper rail of oil ring body and lower surface side of lower rail are barrel shape (11) Pistons used in combination with cylinders The pistons used in combination with the cylinders in this embodiment are also particularly limited. However, various pistons that are currently known can be appropriately selected.

  Since the cylinder of this aspect has a plurality of recesses in the stroke center region, the recesses function as an oil reservoir, and the amount of oil increases as compared with a conventional cylinder (no recesses). There is concern over deterioration of the LOC due to the oil left behind by the ring, the oil left in the recesses flowing out to the sliding surface, being lifted up by the rising piston ring, and remaining oil evaporating. The Therefore, in the piston used in combination with the cylinder of this aspect, in order to quickly drain the oil, 2 to 6 oil drain holes (holes for draining the oil to the crankcase) in the thrust direction and the anti-thrust direction, respectively. It may be devised such as forming or increasing the diameter of the oil drain hole. Furthermore, it is preferable that the number and size of the oil drain holes in the thrust direction be larger than the oil drain holes formed in the anti-thrust direction.

B. Second aspect (linerless type)
The cylinder according to the second aspect of the present embodiment does not use the cylinder liner as in the first aspect, and the recess is formed directly on the inner wall surface of the cylinder body, and the piston is on the inner wall surface of the cylinder. It slides directly.

  The cylinder body used in this aspect is not particularly limited as long as the concave portion is formed directly on the inner wall surface, and the dimensions and materials thereof are not particularly limited.

  The cylinder of this embodiment is the same as the cylinder liner type cylinder of the above “A. First embodiment” except that no cylinder liner is used and a recess is formed directly on the inner wall surface of the cylinder body. Therefore, the description here is omitted. That is, all items ((1) to (11)) of “A. First aspect” can be applied as they are to the linerless type of this aspect. By providing a predetermined recess in the predetermined area in the center area of the stroke, the same effect as the above “first aspect” is achieved.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention. For example, as the material for the cylinder inner wall surface of the present invention, various conventionally used materials such as aluminum, aluminum-based alloys, cast iron, cast steel, and steel can be used.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

<Preparation and processing of cylinder liner>
The cylinder liners of Conventional Example 1, Examples 1 to 5, and Comparative Examples 1 to 7 having recesses as shown in Table 1 below were prepared and processed. The dimensions of the cylinder liner are as shown in FIG.

  The cylinder liner machining method is as follows.

A conventionally known cylinder liner (material: FC250) (without recess) was prepared, and a masking plate (SUS420, thickness: 0.5 mm) was used in the center region of the stroke, and a recess was formed by the following procedure. In addition, the recessed part was made into the rhombus shape shown in FIG. 5, and arrangement | positioning was also the same as that of FIG.
(1) The masking plate was fixed to the inner wall surface of the cylinder liner.
(2) As shown in FIG. 12, the cylinder liner 100 was fixed to the turntable 101 of the blasting machine.
(3) As shown in FIG. 12, the abrasive grain outlet 102 of the blasting machine is inserted inside the cylinder liner 100, the turntable 101 is rotated, and the abrasive grain outlet 102 is moved up and down while moving the abrasive grain. The particles were discharged onto the inner wall surface of the cylinder liner 1000 (the abrasive particles were discharged only when the abrasive nozzle 102 was raised). As the abrasive material, alumina was used, and the abrasive particle size was 53 to 74 μm. The abrasive spray pressure was about 2 MPa, and the rotation speed of the turntable 101 was 4 rpm. The vertical movement time of the abrasive grain ejection port 102 was 5 min × 2 times.
(4) The cylinder liner 100 was removed from the turntable 101, and then the masking plate was removed from the cylinder liner.
(5) Honing was performed on the inner wall surface of the cylinder liner 100. The honing process is for removing wrinkles that may occur at the ends of the formed recesses.
(6) The shape of the formed recess was a rhombus as shown in FIG. 5, and both the axial length and the circumferential length were 1.4 mm. The length of the recess in the cylinder radial direction is as shown in Table 1.

  In addition, when making the length in the cylinder radial direction (depth of the recess) of the recess on the thrust side shallower than other regions, a plurality of masking plates are prepared in the above processing method, and the cylinder radial direction of the recess While confirming the length, the plurality of masking plates were appropriately replaced.

<Measurement of friction force by actual machine test>
Each cylinder was mounted on an actual machine (engine) under the following conditions, and the frictional force was measured.

・ Actual machine type: diesel engine ・ Displacement: 9000cc
・ Number of cylinders: 6
・ Cylinder diameter: 112mm
・ Stroke: 150mm
・ Rotation speed: 2700 rpm
・ Load: Full load ・ Water temperature: 90 ℃
-Oil temperature: Result-Piston material: Spheroidal graphite cast iron-Circumferential length (width) of piston skirt of piston: 90 mm
<Evaluation>
Table 1 shows the results of the measurement of the frictional force and the observation of the surface properties on the thrust side of the cylinder liner in the conventional examples, examples and comparative examples.

  With respect to the frictional force, the frictional force of the conventional example (cylinder liner having no recesses) is used as a reference (100%), and the ratio of the frictional force of the example and the comparative example to this is shown.

  In addition, regarding the surface properties on the thrust side, “X” is indicated when a vertical flaw is confirmed visually, and “◯” is indicated when no vertical flaw is confirmed.

  For the overall evaluation, the frictional force ratio is less than 0.9 and the surface condition of the cylinder liner is not abnormal, “Good”, and the frictional force ratio is 0.9 or higher and the surface texture is not abnormal. “△” was given, and “X” was given to those having an abnormal surface texture regardless of the frictional force ratio.

  In Table 1, “recess area ratio” and “radial length” described in the column “T” are the area ratio and radial length of the recess in the central region of the special stroke, respectively. Even in the thrust region, the portions other than the region are the same as the “recess area ratio” and the “radial length” described in the columns “F” and “R”. .

  In Comparative Examples 2 and 4, a recess is formed on the anti-thrust side with the same width as the cylinder circumferential direction width of the special stroke center region, and can be compared with the “only thrust side” effect of the present invention. I did it.

  As shown in Table 1, it can be seen that the friction force can be reduced in both the example and the comparative example as compared with the conventional example having no recess in the central region of the stroke.

  However, as compared with the case where a recess is simply provided in the center area of the stroke, the recess in the so-called special process center area is eliminated or the area ratio is reduced as in the embodiment of the present invention. It can be seen that the vertical flaws generated on the thrust side of the cylinder liner can be eliminated by reducing the depth of the cylinder.

  On the other hand, when the special stroke center region was provided in the anti-thrust region instead of the thrust region, the effect of reducing the frictional force was inferior.

<Reference experiment 1: Measurement of reciprocating frictional force>
In the cylinder of the present invention, the reciprocating frictional force was measured in order to evaluate the relationship with the area ratio frictional force of the recess. Specifically, it is as follows.

  In the central region of the stroke that is hatched in FIG. 13, recesses are formed with various area ratios by the procedures (1) to (6) described above, and reciprocating friction is performed using the apparatus shown in FIG. 14. The force was measured. The axial length h1 of the test piece piston ring used at this time was 1.2 mm, the radial length a1 was 3.2 mm, and the tangential tension Ft of the piston ring was 9.8 N. Moreover, the rotation speed at the time of measurement of a reciprocating frictional force was 50-750 rpm, the piston ring ambient temperature was 80 degreeC, and the supply oil used SAE viscosity 10W-30.

<Evaluation of Reference Experiment 1>
The area ratio of the recesses is 0% when the 10-point average roughness Rz of the portion of the inner wall surface of the cylinder liner where the recesses are not formed is 2 μm, the average length of the recesses in the cylinder radial direction is 10 μm, and the rotational speed is 750 rpm. FIG. 15 shows the measurement results of the reciprocating friction force in the cases of 1%, 10%, 30%, 50%, 60%, 80%, and 90%. FIG. 15 shows the friction force ratio when the concave portion is not formed, that is, when the conventional cylinder liner friction force with the area ratio of 0% is set to 1.00.

  From FIG. 15, the frictional force is effectively reduced when the area ratio of the recesses is in the range of 1 to 80% over the entire region of the center of the stroke, and the frictional force is minimum when the area ratio of the recesses is 50%. I understand that This is because when the area ratio of the concave portion is increased, the frictional force is reduced by the effect of reducing the contact area up to 50%, and when the area ratio exceeds 50%, the contact area becomes smaller, thereby reducing the sliding portion. It is thought that this is because the surface pressure becomes excessively high and the frictional force increases.

<Reference Experiment 2: Measurement of mechanical loss due to frictional force>
Furthermore, in the cylinder of the present invention, mechanical loss (FMEP) due to frictional force was measured in order to evaluate the significance of forming a recess only in the central region of the stroke. Specifically, it is as follows.

  The mechanical loss (FMEP) due to the frictional force was determined using the apparatus shown in FIG. In this test method, a test piece piston ring was set on the piston, and after a familiar operation, the rotational speed corresponding to the engine speed was changed at an oil temperature of 80 ° C., and the frictional force was measured. In this reference experiment, a cylinder liner (reference example 1) in which a recess is formed only in the center region of the stroke, a cylinder liner (reference comparative example 1) in which no recess is formed, and a recess is formed only in the sliding end. Friction force was measured for the cylinder liner (Reference Comparative Example 2) and the cylinder liner (Reference Comparative Example 3) in which a concave portion was formed in the sliding end and stroke center region. In addition, when forming a recessed part in the said process center part area | region, when the area of the said process center part area | region was 100%, it formed so that the sum total of the area of all the recessed parts might be 50%. Further, the sliding end refers to a region (upper side sliding) of the cylinder liner of the apparatus illustrated in FIG. 14 from the upper end of the cylinder liner to the lower surface position of the ring groove of the piston ring of the test piece at the top dead center of the piston. End), and the region (lower sliding end) from the upper surface position of the ring groove of the test piece piston ring at the bottom dead center of the piston to the lower end of the cylinder liner.

<Evaluation of Reference Experiment 2>
The measurement results are shown in FIG. FIG. 16 shows mechanical loss ratios of other cylinder liners when the mechanical loss of the cylinder liner of Reference Comparative Example 1 in which no recess is formed is 1.

  From FIG. 16, the cylinder liner of the reference example 1 in which the recess is formed only in the center region of the stroke has the cylinder liner of the reference comparative example 1 in which the recess is not formed, and the recess is formed in the sliding end. It can be seen that there is less mechanical loss than Reference Comparative Example 2 and Reference Comparative Example 3.

<Reference experiment 3: Measurement of reciprocating friction force>
In the cylinder of the present invention, the reciprocating frictional force was measured in order to evaluate the relationship between the average ten-point roughness Rz of the inner wall surface of the cylinder and the frictional force. Specifically, it is as follows.

  In the center area of the stroke that is hatched in FIG. 13, a recess is formed with an area ratio of 50% by the procedures (1) to (6) described above, and reciprocating friction is performed using the apparatus shown in FIG. The force was measured. The axial length h1 of the test piece piston ring used at this time was 1.2 mm, the radial length a1 was 3.2 mm, and the tangential tension Ft of the piston ring was 9.8 N. Further, the number of revolutions at the time of measuring the reciprocating frictional force was 750 rpm, the piston ring ambient temperature was 80 ° C., and the supply oil was SAE viscosity 10W-30.

<Evaluation of Reference Experiment 3>
When the average length in the cylinder radial direction of the recess is 10 μm and the rotational speed is 750 rpm, the ten-point average roughness Rz of the portion where the recess on the inner wall surface of the cylinder liner is not formed is 0.5 μm, 2 μm, 4 μm, 5 μm. The measurement result of the reciprocating friction force in this case is shown in FIG. In FIG. 17, the conventional cylinder liner frictional force in which no concave portion is formed, that is, the area ratio is 0% and the ten-point average roughness Rz of the inner wall surface is 2 μm is 1.00. The frictional force ratio is shown.

  From FIG. 17, it can be seen that even when the ten-point average roughness Rz is the same, the frictional force is significantly reduced in the case where the concave portion is formed compared to the case where the concave portion is not formed. Moreover, when the thing in which the recessed part is formed is compared, when the ten-point average roughness Rz exceeds 4 micrometers, it turns out that the frictional force becomes large rapidly. This is because the contact area is reduced by forming a recess, and the surface pressure of the sliding portion is higher than when no recess is formed, and therefore it is more susceptible to the surface roughness of the sliding surface. It is thought to be caused by

DESCRIPTION OF SYMBOLS 10 ... Cylinder 11 ... Cylinder inner wall surface, cylinder liner inner wall surface 12, 50 ... Recess 13, 30 ... Stroke center area 14, 90 ... Special stroke center area 15 ... General stroke center area 20 ... Piston 23 ... Piston skirt part

Claims (6)

A cylinder in which a piston slides on an inner wall surface,
Of the inner wall surface of the cylinder, 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 uppermost piston ring at the bottom dead center of the piston A plurality of recesses are formed in the center area of the stroke, which is an area, so that at least one recess exists in all cross sections in the cylinder circumferential direction.
Of the inner wall surface of the cylinder, the recess is not formed in a region other than the stroke center region,
When the area of the central region of the stroke is 100%, the total area of all the recesses is in the range of 30 to 50% ,
Of the region that slides with the piston skirt on the thrust side of the piston that is used in combination with the cylinder in the center region of the stroke, at least 1/4 of the region is the region where the recess is not formed ,
The average length in the cylinder axial direction of the recess is equal to or less than the length in the cylinder axial direction of the uppermost piston ring among the piston rings used ,
The average length of the concave portion in the cylinder radial direction is within a range of 0.1 to 10 μm,
The cylinder, wherein an average length of the concave portion in the cylinder circumferential direction is in a range of 0.1 to 15 mm . A cylinder in which a piston slides on an inner wall surface,
Of the inner wall surface of the cylinder, 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 uppermost piston ring at the bottom dead center of the piston A plurality of recesses are formed in the center area of the stroke, which is an area, so that at least one recess exists in all cross sections in the cylinder circumferential direction.
Of the inner wall surface of the cylinder, the recess is not formed in a region other than the stroke center region,
When the area of the central region of the stroke is 100%, the total area of all the recesses is in the range of 30 to 50% ,
Of the region that slides with the piston skirt on the thrust side of the piston that is used in combination with the cylinder in the central region of the stroke, at least 1/4 of the region has an area ratio of the recesses than the region other than the region. Low area ,
The average length in the cylinder axial direction of the recess is equal to or less than the length in the cylinder axial direction of the uppermost piston ring among the piston rings used ,
The average length of the concave portion in the cylinder radial direction is within a range of 0.1 to 10 μm,
The cylinder, wherein an average length of the concave portion in the cylinder circumferential direction is in a range of 0.1 to 15 mm . A cylinder in which a piston slides on an inner wall surface,
Of the inner wall surface of the cylinder, 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 uppermost piston ring at the bottom dead center of the piston A plurality of recesses are formed in the center area of the stroke, which is an area, so that at least one recess exists in all cross sections in the cylinder circumferential direction.
Of the inner wall surface of the cylinder, the recess is not formed in a region other than the stroke center region,
When the area of the central region of the stroke is 100%, the total area of all the recesses is in the range of 30 to 50% ,
Of the region that slides with the piston skirt on the thrust side of the piston that is used in combination with the cylinder in the central region of the stroke, at least 1/4 of the region is in the cylinder radial direction of the recess than the region other than the region an area average length of small,
The average length in the cylinder axial direction of the recess is equal to or less than the length in the cylinder axial direction of the uppermost piston ring among the piston rings used ,
The average length of the concave portion in the cylinder radial direction is within a range of 0.1 to 10 μm,
The average length of the concave portion in the cylinder circumferential direction is in the range of 0.1 to 15 mm.   The said cylinder is comprised from the cylinder main body and the cylinder liner fixed to the inner side, The said several recessed part is formed in the inner wall face of the said cylinder liner, The any one of Claims 1-3 characterized by the above-mentioned. A cylinder according to any one of the above.   5. The cylinder according to claim 1, wherein a ten-point average roughness Rz of a portion where the concave portion is not formed in the central region of the stroke is 4 μm or less. The cylinder according to any one of claims 1 to 5, wherein the cylinder is used in an internal combustion engine .

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