Piston ring

Abstract

The invention relates to a piston ring for an internal combustion engine using hydrogen fuel. When the piston ring is subjected to a bending test under predetermined conditions, the bending index of the piston ring is defined as FP1, and when the piston ring is subjected to a bending test after a corrosion test in which the piston ring is immersed in a 1% aqueous nitric acid solution for 30 minutes, the post-corrosion bending index of the piston ring is defined as FP2. When the rupture strength retention rate (FPS) of the piston ring is set to be FPS = FP2 / FP1, the piston ring satisfies 0.75 < = FPS.

Description

Technical Field

[0001] The invention relates to a piston ring for an internal combustion engine using hydrogen fuel. Background Art

[0002] In recent years, there have been demands for reducing CO2 emissions and fossil fuel usage. From the perspective of environmental burden, research is underway on a technology involving an internal combustion engine that uses hydrogen or a fuel mixed with other fuels (hereinafter, both are collectively referred to as hydrogen fuel) as fuel.

[0003] In connection with this, for example, Patent Document 1 discloses a component used in a hydrogen engine and provided with a coating layer made of stainless steel in order to suppress hydrogen embrittlement fracture.

[0004] Patent Document 2 discloses a hydrogen engine component that has been subjected to physical and chemical treatments in order to prevent rusting of the component caused by water vapor generated by combustion of hydrogen.

[0005] Furthermore, Patent Document 3 shows that in a general hydrogen engine, cylinder cooling based on condensation of water vapor is not performed, and discloses a hydrogen engine for controlling condensation of water vapor in a cylinder forming a combustion chamber.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Utility Model Publication No. 51-137004

[0009] Patent Document 2: Japanese Patent Application Laid-Open No. 51-081203

[0010] Patent Document 3: Japanese Patent Application Publication No. 2003-013765 Summary of the invention

[0011] Problems to be solved by the invention

[0012] Unlike gasoline, hydrogen fuel produces a lot of H2O and NO during combustion. x , H2O backflow occurs in the cylinder, and corrosive wear caused by condensed water may occur on the upper and lower surfaces of the piston ring. In addition, if the corrosion resistance of the upper and lower surfaces of the piston ring is insufficient, the piston ring may be reduced in width, the upper and lower surfaces may become rough, and pitting may occur due to corrosion, and the piston ring may be damaged during operation. The problem of the present invention is to provide a piston ring with sufficient damage resistance in an internal combustion engine using hydrogen fuel.

[0013] Solutions for solving problems

[0014] The present inventors conducted research to solve the above-mentioned problems and found that the above-mentioned problems can be solved by the following piston ring, thereby completing the present invention: the piston ring is a piston ring for an internal combustion engine using hydrogen fuel, and the flexural strength maintenance rate of the piston ring when undergoing a specified flexural test meets the specified conditions.

[0015] The present invention is a piston ring for an internal combustion engine using hydrogen fuel, wherein:

[0016] The bending resistance index of the piston ring when the piston ring is subjected to a bending resistance test under prescribed conditions is denoted as FP1.

[0017] The post-corrosion flexural index of the piston ring when the flexural test is performed on the piston ring after the corrosion test of immersing the piston ring in a 1% nitric acid aqueous solution for 30 minutes is FP2,

[0018] When the flexural strength maintenance rate FPS of the piston ring is set to FPS=FP2 / FP1,

[0019] The piston ring satisfies 0.75≤FPS.

[0020] Furthermore, preferably, when the arithmetic mean roughness of the upper surface of the piston ring after the corrosion test is defined as Ra (μm) and the first strength maintenance coefficient KDA is defined as KDA=FPS / Ra,

[0021] The piston ring satisfies 0.2≤KDA.

[0022] Furthermore, when the maximum valley depth of the upper surface of the piston ring after the corrosion test is set to Rv (μm) and the second strength maintenance coefficient KDV is set to KDV=FPS / Rv,

[0023] The piston ring satisfies 0.06≤KDV.

[0024] Furthermore, it is preferred that the internal combustion engine is a spark ignition engine.

[0025] Effects of the Invention

[0026] According to the present invention, it is possible to provide a piston ring having sufficient breakage resistance in an internal combustion engine using hydrogen fuel. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic diagram of the fixing fixture used in the flexural test. Figure 1 (a) is a cross-sectional schematic diagram, Figure 1 (b) is a schematic top view.

[0028] Figure 2 It is a schematic diagram (top view) for explaining the force point length dg in the bending test.

[0029] Figure 3 It is a schematic diagram for explaining the shape of the indenter 23 used in the bending test. DETAILED DESCRIPTION

[0030] One embodiment of the present invention is a piston ring for an internal combustion engine using hydrogen fuel. The specific embodiment thereof is described below. However, unless otherwise specified, the configuration described in the following embodiments is not intended to limit the technical scope of the invention to only this.

[0031] When in use, the piston ring of this embodiment is attached to a piston ring groove formed in a piston, and reciprocates while sliding on the inner peripheral surface of a cylinder bore by utilizing the reciprocating motion of the piston.

[0032] The piston ring of the present embodiment may be a so-called compression ring such as a top ring or a second ring, or may be an oil ring.

[0033] In this specification, the “upper surface” of the piston ring refers to the surface close to the combustion chamber when the piston ring is mounted on the piston, and the “lower surface” refers to the surface close to the crank chamber.

[0034] In this specification, hydrogen fuel refers to a fuel composed of only hydrogen (excluding impurities) or a fuel mixed with other fuels. The proportion of hydrogen in the entire fuel is 50% or more, and may be 60% or more, or 70% or more.

[0035] The piston ring of the present embodiment is a piston ring for an internal combustion engine using hydrogen fuel, wherein when the flexural index of the piston ring when the piston ring is subjected to a flexural test under prescribed conditions is set to FP1, when the piston ring is subjected to a corrosion test in which the piston ring is immersed in a 1% nitric acid aqueous solution for 30 minutes, the post-corrosion flexural index of the piston ring when the flexural test is conducted is set to FP2, and when the flexural strength maintenance rate FPS of the piston ring is set to FPS=FP2 / FP1, the piston ring satisfies 0.75≤FPS.

[0036] This means that the greater the flexural strength maintenance rate FPS, the smaller the reduction rate of the flexural index after corrosion.

[0037] If the FPS is less than 0.75, the flexural strength will be significantly reduced due to corrosion, and the piston ring may be damaged during operation when using hydrogen fuel.

[0038] Since the FPS is 0.75 or more, sufficient breakage resistance can be obtained even in an environment where corrosion caused by condensed water is likely to occur in an internal combustion engine using hydrogen fuel. If the FPS satisfies the above conditions, it can be achieved by appropriately selecting the material and surface treatment of the piston ring.

[0039] The flexural test is as follows.

[0040] Fix the piston ring on Figure 1 The fixing fixture shown is used to perform the flexural test using a flexural testing machine (universal testing machine). Figure 1 In the figure, (a) is a cross-sectional schematic diagram of the fixing fixture, and (b) is a top view schematic diagram of the fixing fixture. In the bending test, the piston ring 21 is fixed with the fastener 22 with the upper surface of the piston ring facing upward so that the distance L from the force point P to the fulcrum is 15 mm, and a load is applied to the piston ring 21 from the upper surface of the piston ring along the axial direction of the piston ring to perform the bending test. Figure 2 As shown, the force point length dg (mm) is obtained from the length of the chord of the piston ring 21 relative to the distance L from the force point P to the fulcrum. It should be noted that the length of the chord is obtained by the following formula based on the outer diameter d (nominal diameter) of the piston ring when it is attached to the cylinder bore.

[0041] θa=sin －1 (L / (d / 2))dg=d×sin(θa / 2)

[0042] The speed of the test load is set to 1 mm / min. Figure 3 As shown, the opening angle θ of the top of the pressure head 23 is set to 60 degrees, the pressure head width PW is set to 10 mm, the top shape is set to a rounded R shape, and the radius of the rounded corner R is 0.5 mm. The temperature during the test is set to room temperature, the environment is set to the atmosphere, and the load is detected by the attached load cell.

[0043] Here, the maximum axial width of the piston ring is set to h11 (mm), and the maximum radial thickness is set to a11 (mm). If the piston ring is damaged during the bending test, the test is terminated at that time, and the maximum load up to that time is set to the maximum load F1 (N). If the piston ring is not damaged at the time when the pressure head 23 drops to 10 mm, the maximum load up to that time is set to the maximum load F1 (N). The section modulus Z1 (mm 3 ) is set to Z1 = (a11 × h11 × h11) / 6, and the flexural index FP1 (N / mm 2 ) is set to FP1 = (F1×dg) / Z1.

[0044] When a test is performed using a piston ring after a corrosion test described later, the piston ring is fixed so that a portion corroded by the corrosion test serves as a fulcrum.

[0045] The maximum axial width of the piston ring after the corrosion test is h12 (mm), the maximum radial thickness after corrosion is a12 (mm), the maximum load in the bending test after the corrosion test is F2 (N), and the section modulus after corrosion is Z2 (mm 3 ) is set to Z2 = (a12 × h12 × h12) / 6, and the flexural index after corrosion FP2 (N / mm 2 ) is set to FP2 = (F2×dg) / Z2.

[0046] The corrosion test was carried out as follows.

[0047] The nitric acid aqueous solution used in the corrosion test was prepared by mixing 8 g of nitric acid (1.38) (standard content 60% to 61%) manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. and 492 g of distilled water to give a nitric acid concentration of 1%.

[0048] A beaker filled with nitric acid aqueous solution was immersed in a water bath. After the temperature of the nitric acid aqueous solution in the beaker reached 80°C, the piston ring was immersed in the nitric acid aqueous solution. The nitric acid aqueous solution was stirred every 5 minutes while maintaining the liquid temperature at 80°C. The piston ring was immersed for 30 minutes. After 30 minutes, the piston ring was taken out and washed with distilled water.

[0049] In addition, in the piston ring of the present embodiment, it is preferable that the arithmetic mean roughness of the upper surface of the piston ring after the corrosion test is Ra (μm), the first strength maintenance coefficient KDA (μm) -1 ) is set to KDA=FPS / Ra, 0.2≤KDA is satisfied.

[0050] If KDA is less than 0.2, the bending strength will be reduced due to the roughness of the surface state such as pitting caused by corrosion, and the piston ring may be damaged during operation. On the other hand, by setting KDA to 0.2 or more, the bending strength maintenance rate after corrosion is large, or the surface roughness (damage starting point) is reduced, which can prevent the piston ring from being damaged.

[0051] If KDA is to meet the above conditions, it can be achieved by appropriately selecting the piston ring material, processing conditions such as heat treatment, and surface treatment to increase the FPS value or reduce Ra.

[0052] In addition, in the piston ring of the present embodiment, it is preferable that the maximum valley depth of the upper surface of the piston ring after the corrosion test is Rv (μm), the second strength maintenance coefficient KDV (μm) -1) is set to KDV=FPS / Rv, 0.06≤KDV is satisfied.

[0053] If KDV is less than 0.06, the reduction in flexural strength due to corrosion is significant, and the piston ring may be damaged during operation due to corrosion. On the other hand, by setting KDV to 0.06 or more, the flexural strength maintenance rate after corrosion is high, or the surface roughness (damage starting point) is reduced, which can prevent the piston ring from being damaged.

[0054] If KDV is to meet the above conditions, it can be achieved by appropriately selecting the material and surface treatment of the piston ring to increase the FPS value or reduce Rv.

[0055] It should be noted that for Ra and Rv, the roughness of the piston ring upper surface was measured at three locations with an evaluation length of 4 mm (sampling length of 0.8 mm) using a stylus surface roughness tester in accordance with ISO4287, and the average value of the three measured values ​​was used.

[0056] The arithmetic mean roughness Ra (μm) of the upper surface of the piston ring according to the present embodiment after the corrosion test may be 5 μm or less, or 4 μm or less.

[0057] The surface treatment method for the piston ring can be a known method that satisfies the above-mentioned preferred surface property parameters, for example, surface treatments such as PVD (Physical Vapor Deposition), DLC (Diamond Like Carbon), chemical conversion treatment, nitriding treatment, etc.

[0058] The maximum valley depth Rv (μm) of the upper surface of the piston ring of the present embodiment after the corrosion test may be 14 μm or less, or 12 μm or less.

[0059] The cross-sectional shape of the piston ring of the present embodiment relative to the circumferential direction is not particularly limited, and may be a rectangular shape, may include an undercut, or may include an inner cut. In addition, it may be a keystone shape.

[0060] The size of the opening gap of the piston ring of the present embodiment is not particularly limited, but is, as an example, within a range of 0.1 mm to 0.8 mm.

[0061] The axial width of the piston ring of the present embodiment is not particularly limited, but is usually 0.8 mm or more and usually 4.0 mm or less. In addition, the outer diameter d is usually 50 mm or more and 220 mm or less.

[0062] The piston ring of this embodiment may also have a coating on the upper and lower surfaces. When the piston ring has a coating on the upper and lower surfaces, for example, it may be any single coating selected from PVD treatment coating, DLC coating, hard chrome plating coating, nitriding treatment coating, ferroferric oxide coating, phosphate coating, manganese-based phosphate coating, resin coating, etc., or may be a laminated coating of any two or more thereof. In addition, the coating may be only on the upper surface or only on the lower surface, or on both the upper and lower surfaces, or on a part of the upper and lower surfaces instead of the entire surface.

[0063] In addition, when the upper surface has a soft film such as a resin film, the above-mentioned corrosion test is performed in a state where the lower soft film is peeled off.

[0064] When the piston ring of the present embodiment has a coating on the upper and lower surfaces, the thickness of the coating is not particularly limited, but is usually 0.001 mm or more, preferably 0.005 mm or more, and is usually 0.1 mm or less, preferably 0.05 mm or less.

[0065] It should be noted that, when the coating includes a DLC coating, the DLC coating may be a DLC coating containing hydrogen or a so-called hydrogen-free DLC coating.

[0066] The material of the piston ring base material needs to be appropriately selected to satisfy the above FPS. Examples of high alloy steel include martensitic stainless steel, low alloy steel include valve spring steel and spring steel, and examples of carbon steel include hard steel wire.

[0067] Example

[0068] Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples.

[0069] Examples 1 to 17, Comparative Examples 1 to 3

[0070] The axial length (width) of the piston ring was changed from 0.78 to 1.52, and the radial thickness was changed from 1.95 to 3.72, so that piston ring samples with different section moduli were produced as shown in Table 1. As shown in Table 1, the materials and upper surface surface treatments of the samples were different. It should be noted that even if the same type of surface treatment is used, changing the treatment conditions such as temperature and time will produce samples with different upper surface roughness.

[0071] These are referred to as Examples 1 to 17 and Comparative Examples 1 to 3.

[0072] In Table 1, the surface treatment of the piston ring upper surface is A: ferroferric oxide coating, B: manganese-based phosphate coating, C: nitriding coating, D: phosphate coating, and E: no treatment. In addition, the material is A for low alloy steel, B for high alloy steel, and C for cast iron.

[0073] Use in Figure 1 The piston rings produced in each example and comparative example were subjected to a bending test before and after the corrosion test using a bending test machine whose outline is shown in FIG. 1 , and FPS, KDA, and KDV were calculated. The results are shown in Table 1.

[0074] The piston rings used in the test all had an outer diameter d (nominal diameter) of 81 mm when attached to the cylinder bore, and a force point length dg obtained by calculation of the chord relative to L, dg = 15.3 mm.

[0075] [Table 1]

[0076] Table 1

[0077]

[0078] As described above, when the piston ring specified in the present invention is used in an internal combustion engine using hydrogen fuel, a piston ring having sufficient breakage resistance even in an environment where condensed water generated by combustion of hydrogen fuel exists can be provided.

[0079] Description of reference numerals:

[0080] 21: Piston ring;

[0081] 22: Fasteners;

[0082] 23: pressure head;

[0083] P: force point;

[0084] L: distance from the force point P to the fulcrum;

[0085] dg: force point length;

[0086] PW: head width;

[0087] θ: opening angle.

Claims

1. A piston ring for an internal combustion engine using hydrogen fuel, wherein: The bending resistance index of the piston ring when the piston ring is subjected to a bending resistance test under prescribed conditions is denoted as FP1. The post-corrosion flexural index of the piston ring when the flexural test is performed on the piston ring after the corrosion test of immersing the piston ring in a 1% nitric acid aqueous solution for 30 minutes is FP2, When the flexural strength maintenance rate FPS of the piston ring is set to FPS=FP2 / FP1, The piston ring satisfies 0.75≤FPS.

2. The piston ring according to claim 1, wherein: The arithmetic mean roughness of the upper surface of the piston ring after the corrosion test is defined as Ra, When the first strength maintenance coefficient KDA is set to KDA=FPS / Ra, The piston ring satisfies 0.2≤KDA, The unit of Ra is μm.

3. The piston ring according to claim 1, wherein: When the maximum valley depth of the upper surface of the piston ring after the corrosion test is set to Rv and the second strength maintenance coefficient KDV is set to KDV=FPS / Rv, The piston ring satisfies 0.06≤KDV, The unit of Rv is μm.

4. The piston ring according to any one of claims 1 to 3, wherein: The internal combustion engine is a spark ignition engine.

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