JP6584243B2 - Piston ring and manufacturing method thereof - Google Patents

Description

  The present invention relates to a piston ring for an internal combustion engine, and more particularly, to a piston ring having improved friction characteristics and lubrication characteristics due to a surface fine structure of a sliding surface, and a method for manufacturing the same.

  A piston ring (hereinafter, also simply referred to as “ring”) used as a functional component of an internal combustion engine requires three functions: a gas seal function, a heat transfer function, and an oil control function. In order to secure the gas sealing function, that is, to seal the gap between the outer periphery of the piston and the inner wall of the cylinder so that the engine maintains a predetermined compression pressure, the ring has a self-tension for pushing the inner wall of the cylinder vertically. The shape is determined, and the ring circumferential length is determined so as to minimize the joint gap of the joint part required when the ring is set on the piston. Furthermore, the ring is made of a metal material to ensure the heat transfer function to transfer the heat of the piston top due to the high temperature and high pressure combustion gas to the cooled cylinder wall, and the outer peripheral shape of the ring to ensure the oil control function Is stipulated.

  Referring to the shape of the outer peripheral surface of the piston ring, the top ring (the ring attached to the most combustion chamber side of the piston, also referred to as the “first pressure ring”) is barrel-shaped in the cross section parallel to the ring axis on the outer peripheral surface. The barrel face shape with excellent oil film lubrication function is adopted, and the second ring (also called “second pressure ring”, which is a ring attached to the crank chamber side of the top ring) has an outer periphery in addition to the tapered face shape. A shape that improves the oil scraping performance by making the bottom edge as sharp as possible is adopted. Further, the oil ring is designed to increase the surface pressure per unit area and further improve the oil scraping performance by increasing the tension and decreasing the contact area with the inner wall of the cylinder.

In recent years, internal combustion engines are strongly required to reduce oil consumption and improve fuel efficiency in order to cope with environmental problems such as air pollution caused by oil combustion products and CO ₂ reduction. That is, the piston ring is required to further improve the oil consumption characteristics and the fuel consumption characteristics in addition to ensuring the above three functions.

  As a method of satisfying the oil consumption characteristics and the fuel consumption characteristics while ensuring the above three functions, first, the ring tension can be optimized. If the ring tension is too high, the gas seal characteristics and oil consumption are improved in the top ring and oil ring, but when the ring slides on the inner wall of the cylinder, the frictional force increases and the fuel consumption deteriorates. Further, the oil is excessively scraped and the lubricity is lowered. In the worst case, the ring and the cylinder are seized. On the other hand, if the ring tension is too low, the gas seal characteristics are lowered, the combustion gas is blown out, the output is lowered, the oil scraping performance is lowered, and the oil consumption is increased.

  For this reason, the ring tension needs to be optimized. However, since the combustion chamber itself changes from moment to moment, the optimum tension also changes accordingly. In order to ensure the most important characteristic of gas sealing, the ring tension tends to increase inevitably, which tends to cause a phenomenon of increased frictional force between the ring and the inner wall of the cylinder. This increase in frictional force tends to cause seizure due to a reduction in fuel consumption and insufficient lubrication.

  In this way, an increase in ring tension has a positive effect of improving gas seal characteristics and oil consumption characteristics, while it has a negative effect of worsening fuel efficiency characteristics due to increased frictional force and worsening lubrication characteristics due to improved oil scraping performance. Also brings the effect. Since these positive and negative effects are in a trade-off relationship, it seems difficult to find the optimum ring tension and bring all the characteristics in the preferred direction.

  The problem that can be seen in this situation is "How can we find a means to reduce the frictional force between the ring and the inner wall of the cylinder and ensure lubrication characteristics while ensuring sufficient gas seal characteristics and oil consumption characteristics?" In other words, "In order to ensure sufficient gas seal characteristics and oil consumption characteristics, even in a sliding environment where the ring tension is increased to some extent and the lubricating oil is insufficient, sliding frictional force reduction and Can you find a means to ensure lubrication properties that can prevent sticking? "

  For example, as a method to ensure the gas seal characteristics of the ring and to ensure lubrication so that seizure does not occur, and to reduce the frictional force between the ring and the cylinder wall, a dimple etc. A technique for imparting a fine structure is disclosed.

  In Patent Document 1, a concave portion that functions as an oil reservoir and improves lubricity is formed on a sliding surface with a pulse laser, and the concave portion has a diameter of 100 to 300 μm and a depth of 100 μm or more, and occupies the sliding surface. A piston ring having an area ratio of 5 to 50% is disclosed. Here, the depth is set to 100 μm or more so that the concave portion does not disappear even with the progress of wear.

  Patent Document 2 also discloses a piston ring that does not lower the gas seal and oil seal functions in addition to reducing friction. Patent Document 2 focuses on a non-recessed region where no recess is formed, and the area ratio of the non-recessed region to the barrel width region is 20 to 85%, and the non-recessed region is present in all axial cut surfaces. Teaches that it needs to exist. In addition, with regard to the dimensions of the recesses, an embodiment in which the opening width of the recesses is 0.19 mm × 0.16 mm and the depth is 10 μm is disclosed.

  In Patent Document 3, a large number of dimples formed on the outer peripheral sliding surface are formed to have a plurality of types of depth, and a plurality of types of dimples having different depths are alternately arranged in the circumferential direction of the piston ring. An installed piston ring is disclosed. Specifically, three types of dimples having a diameter of about 100 μm and a depth of 4 to 5 μm, 2 to 3 μm, and 1 to 1.5 μm are taught.

  Furthermore, Patent Document 4 discloses that as a method of forming a plurality of recesses even in a piston ring coated with a hard film, an oil pool is obtained by shot peening the piston ring base material before the hard film coating and then coating the hard film. It is disclosed that the fine dimples that act as an anti-wear can be formed on the outer peripheral sliding surface after the hard coating is coated. It is also disclosed that the micro dimple is a concave portion having a diameter of 0.1 to 5 μm with a substantially arc-shaped cross section.

  However, all of the above prior arts form a recess that acts as an oil reservoir on the sliding surface to hold a large amount of lubricating oil or how long the lubricating oil is held, The actual situation is that the frictional force is to be reduced and not to actively reduce the frictional force.

JP-A-5-340473 JP 2012-107710 A JP 2013-137080 JP JP 2004-60873 A

Shoichi Furahama, Tribology of automobile engines: Lubrication, airtightness, thermal load, Natsume, 5th edition (1984), page 83.

  It is an object of the present invention to provide a piston ring that exhibits excellent lubrication characteristics by reducing the frictional force between the ring and the cylinder inner wall while maintaining excellent gas seal characteristics and oil consumption characteristics, and a method for manufacturing the same. To do.

  Non-Patent Document 1 discloses that the pressure distribution generated in the lubricating oil between the cylinder inner wall and the barrel face surface when the barrel face-shaped piston ring slides is as shown in FIG. That is, the lubricating oil is compressed at the barrel face portion on the traveling direction side, and the generated compressive force cancels the ring tension, thereby reducing the frictional force. As a result of intensive research on whether or not the compressive force that cancels such ring tension can be introduced in relation to the microstructure formed on the sliding surface, the inventor squeezed the recess formed as the microstructure. It was conceived that the frictional force can be reduced at a micro level corresponding to the fine structure of the sliding surface by adopting a shape that makes it easy to exhibit.

  In addition to the concave portion having the effect of reducing the frictional force, it has also been conceived that it is effective to coexist with a concave portion having a shallow depth in order to exhibit excellent lubrication characteristics.

That is, the piston ring of the present invention is a barrel face shaped piston ring having a hard film coated on the outer peripheral sliding surface and having a number of recesses, and the recesses are of the first and second types having different depths. The first recesses are independent of each other, deeper than the second recesses, and the cross-sectional area substantially parallel to the outer peripheral sliding surface decreases in the depth direction, and the second recesses Is connected to a part of the other second recess . The opening diameter of the first recess is preferably an equivalent circle diameter of 100 μm or more and less than 300 μm and a depth of 100 μm or more and less than 300 μm. The first recess is preferably conical or pyramidal.

The opening diameter of the second recess is preferably an equivalent circle diameter of less than 100 μm, the depth is preferably 1 μm or more and less than 100 μm, and the area of the cross section substantially parallel to the outer peripheral sliding surface of the second recess is It is preferable to decrease in the depth direction .

  The total opening area ratio of the two types of recesses is preferably 20% or more and less than 80%.

  The hard film is preferably a hard film selected from a chromium plating film, an ion plating film and a nitride film.

The method for manufacturing a piston ring according to the present invention is characterized in that the first recess is formed by pressing a hard indenter or laser processing before coating the hard film. Further, it is preferable that the second recess is formed by a method selected from indentation of a hard indenter, laser processing, shot blasting, shot peening, or etching before or after the coating of the hard film.

  In the piston ring of the present invention, the first concave portion formed on the outer peripheral sliding surface has a shape in which the squeeze effect of the lubricating oil can be easily exerted, that is, independently, corresponding to or deeper than the ring / cylinder inner wall interval. Since the area of the cross section substantially parallel to the outer peripheral sliding surface is reduced in the depth direction, it is possible to cancel the ring tension at a micro level and to exert a friction reducing effect. In addition, since the second concave portion having a shallow depth exhibits excellent lubrication characteristics, the coexistence of the first concave portion and the second concave portion improves the fuel consumption performance by reducing the frictional force and the burning resistance by improving the lubricating properties. An improvement in adherence can be realized at the same time.

FIG. 3 is a diagram showing an example of a cross-sectional shape perpendicular to the outer peripheral sliding surface of the first recess according to the present invention. FIG. 6 is a view showing a micro-level pressure distribution of a compressive force generated in lubricating oil between a ring / cylinder inner wall in the vicinity of a first recess according to the present invention. It is a figure which shows the outline of a sliding test method. FIG. 3 is a view showing an example of a surface microstructure in which first and second types of concave portions of the present invention are arranged on an outer peripheral sliding surface. It is a figure which shows notionally the test conditions of a sliding test. FIG. 2 is a diagram showing a Stribeck diagram of the sliding test of Example 1. It is a figure which shows the pressure distribution of the compressive force which generate | occur | produces in the lubricating oil between a ring / cylinder inner wall at the time of barrel face shape piston ring sliding.

[1] Fine structure of outer peripheral sliding surface In the piston ring of the present invention, a large number of concave portions formed on the outer peripheral sliding surface are composed of first and second types of concave portions having different depths. The first recess is a deep recess for reducing the frictional force, and the second recess is a shallow recess for ensuring lubrication characteristics. The first concave portion is an independent concave portion, and the lubricating oil in the concave portion is squeezed in the depth direction at the time of sliding, so that a so-called squeeze effect is expressed and the compressive force generated in the lubricating oil is increased. The cross-sectional area substantially parallel to the moving surface is reduced in the depth direction. The compressive force generated in the lubricating oil acts in a direction that cancels the ring tension acting on the inner wall of the cylinder, and it is possible to reduce the frictional force during sliding. FIG. 1 is an example of a cross-sectional shape perpendicular to the outer peripheral sliding surface (2) of the first recess (1), and shows a (reverse) conical shape. In terms of the squeeze effect, the larger the area reduction rate of the cross-section, the greater the effect. Therefore, if it is within a predetermined opening size and depth range, a convex recess (for example, hemispherical) It can be said that the concave portion protruding outward is more effective than the concave portion). However, the concave portion protruding outward acts as a sharp crack at the tip and may cause chipping or peeling of the hard coating, which is not preferable. The shape of the first recess (1) is preferably (reverse) conical shape or (reverse) pyramid shape.

  FIG. 2 shows the first recess (1) formed on the outer peripheral sliding surface (2) and the inner cylinder wall (3) in sliding between the outer peripheral sliding surface (2) of the piston ring and the cylinder inner wall (3). Fig. 4 schematically shows a micro level pressure distribution (5) of the compressive force generated in the lubricating oil (4) due to the squeeze effect of the lubricating oil in between. That is, in addition to the reduction of the frictional force corresponding to the barrel face shape, it is shown that the reduction of the frictional force at the micro level corresponding to the fine structure of the outer peripheral sliding surface (2) is added. Even in areas where the lubricating oil is insufficient, such as the boundary lubrication area, if the outer peripheral sliding surface (2) and the cylinder inner wall (3) are close to each other, the lubricating oil (4) and the first recess (1) existing between them Compressive force is generated in the retained lubricating oil. From the viewpoint that the pressure effect generated at the micro level is sufficiently exhibited by the squeeze effect, the first recess (1) has an opening diameter and depth between the outer peripheral sliding surface (2) and the cylinder inner wall (3). It is preferable that the dimension is equal to or larger than the gap and the lubricating oil is not easily discharged. Specifically, the opening diameter is preferably an equivalent circle diameter (diameter of a circle having an area equal to the opening area) of 100 μm or more and less than 300 μm and a depth of 100 μm or more and less than 300 μm. The opening diameter is preferably 120 μm or more and less than 280 μm, and the depth is preferably 120 μm or more and less than 280 μm, more preferably 140 μm or more and less than 260 μm, or 140 μm or more and less than 260 μm, respectively.

  The piston ring according to the present invention is characterized in that, in addition to the first recess, the second recess having a shallow depth for ensuring lubricity coexists. Since the second recess has a shallow depth, the oil pressure generation effect due to the squeeze effect as in the first recess is small, but the lubricating oil discharging effect is large. In terms of dimensions, it is preferable that the opening diameter is an equivalent circle diameter of less than 100 μm and the depth is 1 μm or more and less than 100 μm. The opening diameter is more preferably 5 μm or more and less than 100 μm, and the depth is more preferably 2 μm or more and less than 50 μm, and further preferably 10 μm or more and less than 100 μm and 3 μm or more and less than 30 μm, respectively. Moreover, although the compressive force generation effect by a squeeze effect is small, it is preferable that the area of the cross section substantially parallel to the outer peripheral sliding surface is reduced in the depth direction.

In the piston ring of the present invention, the first recess it was necessary a separate recess to exert a squeezing effect, the second recess is for lubrication properties securing, the second recess one It is assumed that the portion is connected to a part of the other second recess. Lubricating oil moves through the connecting portion to ensure good lubrication characteristics. Of course, in that case, the lubricating oil escapes and the compression force generation effect due to the squeeze effect cannot be expected.

  The first and second types of recesses preferably have a total opening area ratio of 20% or more and less than 80%. However, the recesses must not be connected to prevent gas sealing. The ratio of the area ratio of the first concave portion to the second concave portion depends on whether the frictional force is mainly reduced or the lubricity is mainly improved, and is determined according to the engine specifications.

[2] Hard coating The piston ring of the present invention is preferably used as a top ring (first pressure ring), and the outer peripheral sliding surface is coated with a hard coating. The hard film is preferably a hard film selected from a chromium plating film, an ion plating film and a nitride film. The thickness of the hard coating is related to the formation method of the first and second recesses described later, and if it is too thick, the first recess is filled and shallow, so it is necessary to pay attention to the coating thickness to cover. is there. In the ion plating film, it is preferably less than 60 μm, more preferably less than 45 μm, and even more preferably less than 30 μm. On the other hand, in the case of a nitride film, since nitrogen is formed by diffusing in the surface layer of the base material, the first and second recesses are not covered and the film thickness is not limited. Usually, the thickness of the diffusion layer having a Vickers hardness of 700 HV0.1 or more is preferably 30 μm or more, more preferably 50 μm or more, and further preferably 70 μm or more. In addition, regarding the chromium plating film, the thickness decreases in the depth direction due to the cancellation of the electric field in the first recess, and even if the opening diameter is slightly narrowed, the depth is almost the same, so it is classified according to the application. It is preferable. In a gasoline vehicle ring, it is preferably less than 80 μm, more preferably less than 60 μm, and even more preferably less than 40 μm. In the ring for diesel vehicles (particularly heavy duty), it is preferably less than 120 μm, more preferably less than 100 μm, and even more preferably less than 80 μm. In a marine ring, it is preferably less than 350 μm, more preferably less than 325 μm, and even more preferably less than 300 μm.

[3] Forming method of first recess The first recess is formed by pressing a hard indenter or laser processing. As a method of indentation, a method in which a diamond indenter or a super-hard indenter is pressed against the outer periphery of the ring base material before coating the hard film and plastically deformed to form a recess is excellent. The recess opening diameter is 100 μm or more and less than 300 μm, A recess having a length of 100 μm or more and 300 μm or less can be easily formed. The concave portion formed using a pyramid-shaped or conical-shaped hard indenter has a cross-sectional area substantially parallel to the outer peripheral sliding surface that is effectively reduced in the depth direction. Compressive force due to the effect is generated, and the effect of reducing the frictional force is exhibited. What is important is to provide a concave shape at the stage of the base material before coating the hard film. If the concave portion is formed after the hard coating is formed, the depth of the concave portion is 100 μm or more, which is not preferable because cracks or peeling occurs after the hard coating is coated, or a defect that becomes a destruction source is left inside.

  Also, in the laser processing method, it is possible to obtain a recess depth of 100 μm or more by increasing the laser output and concentrating the energy. Further, if the focal point is adjusted so as to decrease in accordance with the depth, it is possible to obtain a shape in which the cross-sectional area decreases in the depth direction of the recess.

[4] Method for forming second recess Compared to the first recess, the second recess has only the difference that the opening diameter and depth are less than 100 μm. Indentation and laser processing methods can be used. However, the indentation depth is reduced in the indentation of the hard indenter, and the output is reduced in the laser processing method. The second recess can also be formed by methods such as shot blasting, shot peening, and etching. Furthermore, the second recess can be formed either before or after the hard coating is applied, as long as the final recess dimensions are taken into consideration. Forming the recesses before coating the hard coating is superior in terms of not introducing defects into the hard coating, but if the coating of the hard coating greatly changes the shape of the recesses, It is preferable to form the second recess. In order to avoid the introduction of defects, for example, in a laser processing method, a pulse laser may be employed to reduce the thermal load as much as possible.

  Among the above-described recess forming methods, the indentation of the hard indenter and the laser processing method can form the first and second types of recesses in one step. In that case, the indentation load and the laser output are controlled corresponding to the first and second recesses arranged.

In the following examples and comparative examples, a sliding test capable of evaluating frictional force and seizure was performed instead of performing an engine test by forming a recess on the outer peripheral surface of the ring. The sliding test is a test piece (45 mm x 3.5 mm x 4 mm) with a barrel-shaped contact surface (5 mm x 3.5 mm) on both ends on a rotating disk (7) as shown in Fig. 3. This is a test in which the load P is gradually increased on the test piece (6) while placing (6) and dripping the lubricating oil (8). The base material of the test piece (6) is a steel material consisting of C: 0.85, Si: 0.38%, Mn: 0.34%, Cr: 17.56%, Mo: 1.0%, V: 0.11%, and the balance Fe. Used, on the disk (7), in mass%, C: 1.00%, Si: 2.10%, Mn: 0.32%, P: 0.16%, S: 0.002%, Cr: 1.36%, Ni: 0.08%, balance A steel material made of Fe was used. The barrel-like contact surface of the test piece (6) has a radius of curvature of 20 mm in consideration of the radius of curvature of the ring barrel face of 10 to 30 mm. The disk (7) was adjusted to a hardness of 54.5 to 56.0 HRC by quenching and tempering, and finished to a surface roughness of 0.8 to 1.2 μm by Rz _JIS by polishing.

Example 1
By pressing a cone-shaped carbide needle as a first recess on the barrel-shaped contact surface of the above test piece and plastically deforming it, as shown in FIG. 4, a cone-shaped with an opening diameter of 200 μm and a depth of 200 μm Recesses (9) were formed in a grid pattern with a center-to-center distance of 400 μm. Next, a chromium plating film is formed as a hard film, and chromic acid 250 g / L, sulfuric acid 1.1 g / L, fluoride 3.7 g / L is used as a raw material, liquid temperature 56 ° C., current density 50 A / dm ² For 3 hours, and the tip R was polished so that Rz _JIS was in the range of 1.0 to 1.5 μm. At this time, the first recess has an opening diameter of about 150 μm and a depth of about 200 μm, the chromium plating thickness is about 100 μm, and the hardness is 875 to 913 HV0.1 as a result of measuring Vickers hardness at five points. Was in the range. Furthermore, by using a masking plate having a circular opening with a diameter of 260 μm, blasting is performed at a position corresponding to the second recess (10) in FIG. A large number of second recesses (10) having an opening diameter of 10 to 96 μm and a depth of 1 to 5 μm were formed in a circle having a diameter of about 260 μm between (9). These second recesses (10) had few independent recesses and many connected recesses.

Comparative Example 1
The test piece of Comparative Example 1 was covered with the chromium plating film in the same manner as in Example 1 without forming the first recess, and the tip R was left as it was.

Example 2
A test piece having a first recess and a second recess was produced in the same manner as in Example 1 except that a nitride film was formed as the hard film. The nitride film is formed by treatment for 4.5 hours at 585 ° C in an NH ₃ gas atmosphere, polishing about 25μm by surface grinding machine R polishing to remove the surface white layer, and finally R finishing with a dedicated jig went. At this time, the first recess has an opening diameter of about 175 μm and a depth of about 175 μm, the surface hardness of the obtained nitride film is 1120 to 1175 HV0.1, the surface roughness is 0.3 to 0.4 μm in Rz _JIS The thickness of the diffusion layer having a hardness of 700 HV0.1 or more was about 75 μm. In addition, many second recesses formed by blasting were in the range of an opening diameter of 7 to 73 μm and a depth of 1 to 4 μm.

Comparative Example 2
The test piece of Comparative Example 2 was subjected to nitriding treatment in the same manner as in Example 2 without forming the first recess, and the tip R was left as it was.

Example 3
A test piece having a first recess and a second recess was formed in the same manner as in Example 1 except that the second recess was formed before the coating of the hard coating, and a CrN coating by ion plating was formed as the hard coating. Produced. The CrN film uses metallic Cr as the evaporation source, is evacuated, and is adjusted to 2.0 Pa while flowing N ₂ gas, with an ion current of 380 minutes at an arc current of 150 A, a bias voltage of 0 V, and a temperature of 500 ° C The film was formed by a finishing process, and further R-finished by R-polishing with a dedicated jig. At this time, the first recess had an opening diameter of about 180 μm and a depth of about 200 μm, and the second recess had an opening diameter of 1 to 50 μm and a depth of 1 to 2.5 μm. Further, the obtained CrN coating had a coating thickness of 20 μm, a surface hardness of 850 to 1150 HV0.1, and a surface roughness of 0.3 to 0.4 μm in Rz _JIS .

Comparative Example 3
The test piece of Comparative Example 3 was subjected to the ion plating process in the same manner as in Example 3 without forming the first concave portion and the second concave portion, and the tip R finish was left.

Sliding test As shown in Fig. 5, the sliding test consists of a break-in operation and the main test. This test increases the stepping pressure until seizure occurs with the pressing load P applied to the test piece at a constant sliding speed. Is what you do. The test conditions are as follows.
1. Break-in operation Sliding speed: 0.5 m / sec,
Pressing load: 500 N,
Lubricant: Nisseki Motor Oil (Motor P # 20),
Lubricating oil temperature: 100 ° C (oil bath),
Lubricating oil supply: 40 cc / min,
Driving time: 2 minutes.
2. Main test Sliding speed: 8 m / sec.
Pressing load: Increase pressure from initial 100 N by 20 N until scuffing.
Each load holding time is 30 seconds,
Lubricant: Nisseki Motor Oil (Motor P # 20),
Lubricating oil temperature: 100 ° C (oil bath),
Lubricating oil supply: 40 cc / min,
Seizure trigger: A seizure is determined when the friction coefficient is 0.1 or more.

  The friction coefficient μ (= F / P) can be obtained from the pressing load P and the shearing load F generated perpendicular to the pressing load measured by a load cell (not shown in FIG. 3), and the seizure stress σ (= Pmax / A) can be obtained from the seizure load Pmax and the contact area A of the sliding surface observed and measured after the end of the test.

  The results of Example 1 are shown in FIG. 6 as the relationship between the Stribeck parameter S (= ηV / P, where η is the viscosity of the lubricating oil, V is the sliding speed, P is the pressing load) and the friction coefficient μ. The frictional force was evaluated by the μ value at the left end where seizure occurred, and the lubricity was evaluated by seizure stress σ. In other examples and comparative examples, as shown in FIG. 6, three regions of fluid lubrication, mixed lubrication, and boundary lubrication clearly appeared from the right. The reason why the μ value decreases from the top to the left end of the boundary lubrication region in FIG. 6 is thought to be due to the “familiarity phenomenon (the true contact area increases and the friction coefficient decreases)”.

  The results of Examples 1 to 3 and Comparative Examples 1 to 3 are shown in Table 1. Compared with a combination of test pieces having the same hard coating, the first to third embodiments having the first concave portion and the second concave portion of the sliding surface are seized surfaces, compared to the comparative example having no concave portion on the sliding surface. The pressure increased by 4.2 to 9.5%, the friction coefficient decreased by about 0.001 to 0.002, and the shear load decreased. It is considered that the seizure surface pressure is improved by the presence of the first recess, and the reduction of the shear load is caused by the presence of the second recess.

1, 9… 1st recess
2… Peripheral sliding surface
3… Cylinder wall
4… Lubricating oil
5… Compressive force generated in lubricating oil
6… Test piece
7… disk
8… Lubricating oil
10… Region of presence of second recess

Claims (9)

A barrel face-shaped piston ring having a hard coating coated on the outer peripheral sliding surface and having a plurality of recesses, wherein the recess comprises first and second recesses having different depths, and the first recess Each independently, deeper than the second recess, the area of the cross section substantially parallel to the outer peripheral sliding surface decreases in the depth direction, a part of the second recess is the other second A piston ring connected to a part of the concave portion of the piston ring.   2. The piston ring according to claim 1, wherein an opening diameter of the first recess is an equivalent circle diameter of 100 μm or more and less than 300 μm, and a depth is 100 μm or more and less than 300 μm.   3. The piston ring according to claim 1, wherein the first concave portion has a conical shape or a pyramid shape.   4. The piston ring according to claim 1, wherein the opening diameter of the second recess is an equivalent circle diameter of less than 100 μm and the depth is 1 μm or more and less than 100 μm.   5. The piston ring according to claim 1, wherein an area of a cross section substantially parallel to the outer peripheral sliding surface of the second recess is reduced in a depth direction. In the piston ring according to any one of claims 1 to 5, piston ring, wherein the total open area ratio of the two types of recesses is less than 80% to 20%. The piston ring according to any one of claims 1 to 6 , wherein the hard film is a hard film selected from a chromium plating film, an ion plating film, and a nitride film. The method for manufacturing the piston ring according to any one of claims 1 to 7 , wherein the first concave portion is formed by pressing a hard indenter or laser processing before coating the hard coating. Manufacturing method of piston ring. 9. The method of manufacturing a piston ring according to claim 8 , wherein the second recess is selected from indentation of a hard indenter, laser processing, shot blasting, shot peening, or etching before or after coating of the hard coating. The manufacturing method of the piston ring characterized by the above-mentioned.

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