Piston ring for hydrogen fueled internal combustion engine and method for inhibiting corrosion of piston ring in hydrogen fueled internal combustion engine

Abstract

The present invention aims to suppress corrosion of the side surfaces of piston rings, including a compression ring, which is fitted in a ring groove of a piston in an internal combustion engine that uses hydrogen fuel. [Solution] A piston ring 1 for an internal combustion engine that uses hydrogen fuel is a piston ring including a top ring 10 that is fitted in a ring groove of a piston of an internal combustion engine that uses hydrogen fuel, and the top ring 10 has an annular main body portion 11 that includes an inner circumferential surface 11c, an outer circumferential surface 11d, side surfaces 11a and 11b that are substantially perpendicular to the inner circumferential surface 11c, and a pair of butt ends 13, 14 that face each other and form a butt 15. The main body portion 11 is configured so that a butt area ratio obtained by dividing the projected area of ​​a gap formed around the butt 15 in the main body portion 11 by the thickness of the main body portion 11 is equal to or less than a predetermined threshold value.

Description

[Technical field]

[0001] The present disclosure relates to a piston ring for an internal combustion engine that uses hydrogen fuel and a method for inhibiting corrosion of the piston ring in an internal combustion engine that uses hydrogen fuel. [Background technology]

[0002] Among the piston rings used in internal combustion engines, the compression ring maintains airtightness between the combustion chamber and the crank chamber when it is fitted into the ring groove of the piston and inserted into the cylinder bore, and functions to reduce oil consumption. As such a compression ring, a top ring with a gas leak type joint is known (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 10-331973 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, the suitability of piston rings, including pressure rings mounted in the ring grooves of pistons, for internal combustion engines using hydrogen fuel, including hydrogen gas, has been studied. The present inventors have discovered that a type of corrosion that did not occur in conventional internal combustion engines using diesel fuel and internal combustion engines using gasoline fuel can occur on the side of piston rings in internal combustion engines using hydrogen fuel. If such corrosion progresses, there is a risk that the piston rings will break, so there is room for improvement.

[0005] The present disclosure aims to suppress corrosion of the side surfaces of piston rings, including compression rings that are mounted in ring grooves of pistons, in internal combustion engines that use hydrogen fuel. [Means for solving the problem]

[0006] In order to solve the above problems, the present inventors have conducted extensive research. As a result, the present inventors have found that the corrosion of the side surface of the piston ring is caused by the mixture of the combustion gas of hydrogen fuel, unburned hydrogen gas, and lubricating oil. The present inventors have focused on reducing the amount of combustion gas of hydrogen fuel that flows into the opposite side of the compression ring from the combustion chamber. The present inventors have found that the corrosion of the side surface of the piston ring is suppressed by configuring the main body so that the gap area ratio, which is the projected area of ​​the gap formed around the gap in the main body divided by the thickness of the main body, is equal to or less than a predetermined threshold value.

[0007] A piston ring according to one embodiment of the present disclosure is a piston ring including a compression ring that is mounted in a ring groove of a piston of an internal combustion engine that uses hydrogen fuel, wherein the compression ring has an annular main body including an inner circumferential surface, an outer circumferential surface, one side and the other side that are approximately perpendicular to the inner circumferential surface, and a pair of joint ends that face each other to form a joint, and the main body is configured such that a joint area ratio obtained by dividing the projected area of ​​a gap formed around the joint in the main body by the thickness of the main body is equal to or less than a predetermined threshold value.

[0008] In a piston ring according to one aspect of the present disclosure, the main body is configured so that the gap area ratio is equal to or less than a predetermined threshold value. This makes it possible to suppress the combustion gas of hydrogen fuel burned in the combustion chamber from flowing through a gap formed around the gap in the main body of the compression ring to the side opposite the combustion chamber of the compression ring. As a result, the progression of corrosion of the side surface of the piston ring caused by the combustion gas of hydrogen fuel can be suppressed on the side opposite the combustion chamber of the compression ring. Therefore, in an internal combustion engine that uses hydrogen fuel, it is possible to suppress corrosion of the side surface of piston rings, including the compression ring that is fitted in the ring groove of the piston.

[0009] In one embodiment, the piston is provided with a groove under chamfered surface located between a lower side surface of the ring groove and an outer peripheral surface of the piston, and the main body is provided with a first butt chamfered surface located between a first butt end of one of the pair of butt ends and the outer peripheral surface, a second butt chamfered surface located between a second butt end of the other of the pair of butt ends and the outer peripheral surface, and an outer peripheral under chamfered surface located between one of the one side surface and the other side surface and the outer peripheral surface, and when the pressure ring is attached to the ring groove and inserted into a cylinder bore of the internal combustion engine, a first butt chamfered portion is formed between an inner peripheral surface of the cylinder bore and the first butt chamfered surface, a second butt chamfered portion is formed between the inner peripheral surface and the second butt chamfered surface, an outer peripheral under chamfered portion is formed between the inner peripheral surface and the outer peripheral under chamfered surface, and a groove under chamfered portion is formed between the inner peripheral surface of the cylinder bore and the groove under chamfered surface, and the joint area ratio R is expressed by the following formula, and the joint area ratio R may be 40% or less. Formula: R=(C1+C2+2×C3+C4) / a1×100 however, C1 is the projected area of ​​the first chamfered portion along the axial direction of the main body portion, C2 is the projected area of ​​the second chamfered portion along the axial direction of the main body portion, C3 is the projected area of ​​the outer peripheral underside chamfer along the circumferential direction of the main body, C4 is the area of ​​the gap of the joint along the axial direction of the main body, a1 is the thickness of the main body.

[0010] In one embodiment, the side roughness of the one side and the other side of the compression ring may be Ra 0.8 μm or less, or Rz 4 μm or less. In this case, deterioration of the side sealability of the one side and the other side of the compression ring is suppressed, and the combustion gas can be suppressed from flowing into the side opposite the combustion chamber of the compression ring through a gap between the one side and the other side and the ring groove.

[0011] Another aspect of the present disclosure is a method for inhibiting corrosion of a piston ring in an internal combustion engine that uses hydrogen fuel, comprising: a preparation step of preparing a piston ring including a pressure ring for an internal combustion engine that uses hydrogen fuel; and an installation step of installing the pressure ring in a ring groove of a piston of the internal combustion engine. In the preparation step, the pressure ring is configured to have an annular main body portion including an inner circumferential surface, an outer circumferential surface, one side and the other side substantially perpendicular to the inner circumferential surface, and a pair of abutment ends that face each other to form a butt portion, and the main body portion is configured such that a butt area ratio obtained by dividing a projected area of ​​a gap formed around the butt portion in the main body portion by a thickness of the main body portion is equal to or less than a predetermined threshold value.

[0012] In a method for suppressing corrosion of a piston ring in an internal combustion engine using hydrogen fuel according to another aspect of the present disclosure, the main body is configured so that the gap area ratio is equal to or less than a predetermined threshold value. This makes it possible to suppress the combustion gas of hydrogen fuel burned in the combustion chamber from flowing through a gap formed around the gap in the main body of the compression ring to the side opposite the combustion chamber of the compression ring. As a result, the progression of corrosion of the side surface of the piston ring caused by the combustion gas of hydrogen fuel can be suppressed on the side opposite the combustion chamber of the compression ring. Therefore, in an internal combustion engine using hydrogen fuel, it is possible to suppress corrosion of the side surface of piston rings, including the compression ring mounted in the ring groove of the piston. Effect of the Invention

[0013] According to some aspects of the present disclosure, in an internal combustion engine that uses hydrogen fuel, it is possible to suppress corrosion of the side surfaces of piston rings, including compression rings that are mounted in ring grooves of pistons. [Brief description of the drawings]

[0014] [Figure 1] FIG. 2 is a perspective view of a piston ring according to an embodiment. [Diagram 2] 13 is an enlarged view of a main portion for explaining a gap formed around the joint portion. FIG. [Diagram 3]1A is an enlarged view of a main portion of an example of an abutment portion of a top ring, and FIG. 1B is an enlarged view of a main portion of an example of a chamfered portion on an outer periphery of a bottom surface of the top ring. [Figure 4] FIG. 4 is an enlarged view of a main portion of an example of a ring groove. [Diagram 5] FIG. 13 is a diagram showing the relationship between a gap area ratio and a corrosion index. [Figure 6] FIG. 2 is a diagram showing the state of a side surface of the piston ring of the first embodiment. [Figure 7] FIG. 11 is a diagram showing the state of a side surface of a piston ring according to a second embodiment. [Figure 8] FIG. 2 is a diagram showing the state of a side surface of the piston ring of Comparative Example 1. [Figure 9] FIG. 11 is a diagram showing the state of a side surface of a piston ring of Comparative Example 2. [Figure 10] FIG. 11 is an enlarged perspective view showing an example of a joint portion having a double step shape. [Figure 11] FIG. 13 is an enlarged perspective view showing an example of a joint portion having a double angle shape. [Figure 12] FIG. 11 is an enlarged perspective view showing an example of a joint portion having a triple step shape. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. In the description of the drawings, the same or corresponding elements are given the same reference numerals, and duplicated descriptions are omitted as appropriate. In the following description, the "upper side" corresponds to the top side of the piston (top dead center side, combustion chamber side), and the "lower side" corresponds to the skirt side of the piston (bottom dead center side, crankcase side). In the following description, the cross-sectional shape refers to the cross-sectional shape along a cross section including the central axis of the piston ring. In the following description and drawings, each dimension and each projected area corresponds to a numerical value in a state in which the axis of the piston and the piston ring are not inclined (concentric) with respect to the axis of the cylinder bore.

[0016] Fig. 1 is a perspective view of a piston ring according to an embodiment. As shown in Fig. 1, the piston ring 1 includes a compression ring that is mounted in a ring groove of a piston of an internal combustion engine that uses hydrogen fuel. The piston ring 1 includes, for example, a top ring (compression ring) 10, a second ring 20, and an oil ring 30. The piston ring 1 is inserted into a cylinder bore of the internal combustion engine while being mounted in the ring groove of the piston. The piston ring 1 slides against the inner wall of the cylinder bore, thereby fulfilling a gas seal function between the combustion chamber side and the crank chamber side, and a function of reducing oil consumption.

[0017] The piston ring 1 is applied to an internal combustion engine that uses hydrogen fuel. The internal combustion engine here is, for example, a four-stroke reciprocating engine mounted on a vehicle or the like. The engine oil used in this internal combustion engine contains additives including metal elements. Examples of the metal elements contained in the engine oil include Ca, S, P, and Zn.

[0018] The top ring 10 has an annular main body 11. The main body 11 includes a side surface (one side surface) 11a, a side surface (the other side surface) 11b, an inner peripheral surface 11c, an outer peripheral surface 11d, a joint end (first joint end) 13, and a joint end (second joint end) 14. The side surfaces 11a and 11b are substantially perpendicular to the inner peripheral surface 11c. In the example of FIG. 1, the side surface 11a is the upper surface of the main body 11, and the side surface 11b is the lower surface of the main body 11. The joint ends 13 and 14 face each other to form a joint portion 15. In the following description, the direction connecting the side surfaces 11a and 11b is defined as the width direction of the top ring 10, and the direction connecting the inner peripheral surface 11c and the outer peripheral surface 11d is defined as the thickness direction of the top ring 10. The width direction of the top ring 10 corresponds to the axial direction D1 of the cylinder bore. The thickness direction of the top ring 10 corresponds to the radial direction D2 of the cylinder bore. The direction in which the main body portion 11 extends annularly corresponds to a circumferential direction D3 of the cylinder bore.

[0019] The main body 11 has a generally rectangular cross section with a long side in the thickness direction and a short side in the width direction. The main body 11 is made of, for example, cast iron or steel containing a plurality of metal elements, and is formed with sufficient strength, heat resistance, and elasticity.

[0020] The surface of the main body 11 may be modified to form a hard film. The hard film is, for example, a physical vapor deposition film (PVD film) formed by using a physical vapor deposition method (PVD method). This allows the hard film to be formed with sufficient hardness. The hard film is an ion plating film containing at least one of titanium (Ti) and chromium (Cr) and at least one of carbon (C), nitrogen (N), and oxygen, or a diamond-like carbon film. Specific examples of the hard film include a titanium nitride film, a chromium nitride film, a titanium carbonitride film, a chromium carbonitride film, a chromium oxynitride film, a chromium film, or a titanium film. From the viewpoint of wear resistance and scuff resistance, the hard film may be a chromium nitride film. The hard film may be a laminate, and may include, for example, a chromium nitride film and a diamond-like carbon film.

[0021] The joint portion 15 is a gap formed by dividing a part of the main body portion 11. The joint ends 13 and 14 are free ends of the main body portion 11. The joint end 13 is one of the pair of joint ends 13 and 14. The joint end 14 is the other of the pair of joint ends 13 and 14. The joint ends 13 and 14 have end faces that are flat along the axial direction D1, and the joint portion 15 has a so-called straight joint. When the piston 2 with the top ring 10 attached to the ring groove is inserted into the cylinder bore 3, a gap (joint gap) having a dimension s1 in the circumferential direction D3 is formed between the joint ends 13 and 14 at room temperature (see FIG. 3(a)).

[0022] The second ring 20 has an annular main body 21. The main body 21 includes a side surface 21a, a side surface 21b, an inner circumferential surface 21c, an outer circumferential surface 21d, abutment ends 23, and abutment ends 24. The side surfaces 21a and 21b are substantially perpendicular to the inner circumferential surface 21c. In the example of FIG. 1, the side surface 21a is the upper surface of the main body 21, and the side surface 21b is the lower surface of the main body 21. The abutment ends 23 and 24 face each other to form a abutment 25.

[0023] The main body 21 has a generally rectangular cross section with the long side in the thickness direction and the short side in the width direction. The main body 21 is made of, for example, cast iron or steel containing a plurality of metal elements, and is formed with sufficient strength, heat resistance, and elasticity. The surface of the main body 21 may be modified to form a hard film, similar to the top ring 10.

[0024] The joint portion 25 is a gap formed by dividing a part of the main body portion 21. The joint ends 23 and 24 are free ends of the main body portion 21.

[0025] The oil ring 30 has a pair of rails 31 and a spacer expander 32 facing each other. Each of the pair of rails 31 is a side rail of the oil ring 30. The spacer expander 32 is disposed between the pair of rails 31. In this embodiment, the pair of rails 31 and the spacer expander 32 configure a three-piece oil ring 30. Each of the pair of rails 31 has a joint portion formed therein. Each rail 31 may be formed from the same material as the top ring 10. The oil ring 30 is a so-called three-piece oil ring, but is not limited to a three-piece oil ring. The oil ring may be a two-piece oil ring.

[0026] Fig. 2 is an enlarged view of a main part for explaining a gap formed around the joint. Fig. 3(a) is an enlarged view of a main part of an example of the joint of a top ring. Fig. 3(b) is an enlarged view of a main part of an example of a chamfered portion on the outer periphery of the top ring. As shown in Figs. 2, 3(a) and 3(b), the main body 11 includes chamfered surfaces 13a, 14a and chamfered surface 11e.

[0027] The chamfered surface 13a is a surface (first joint chamfered surface) located between the joint end 13 and the outer circumferential surface 11d and connecting the joint end 13 and the outer circumferential surface 11d. The chamfered surface 13a is a surface formed by chamfering the corner between the joint end 13 and the outer circumferential surface 11d. A joint chamfered portion (first joint chamfered portion) 16 is formed between the chamfered surface 13a and the inner circumferential surface 3a of the cylinder bore 3. The joint chamfered portion 16 is a gap corresponding to a portion removed from the main body portion 11 by chamfering the corner between the joint end 13 and the outer circumferential surface 11d.

[0028] The chamfered surface 14a is a surface (second joint chamfered surface) located between the joint end 14 and the outer peripheral surface 11d and connecting the joint end 14 and the outer peripheral surface 11d. The chamfered surface 14a is a surface formed by chamfering the corner between the joint end 14 and the outer peripheral surface 11d. A joint chamfered portion (second joint chamfered portion) 17 is formed between the chamfered surface 14a and the inner peripheral surface 3a of the cylinder bore 3. The joint chamfered portion 17 is a gap corresponding to a portion removed from the main body portion 11 by chamfering the corner between the joint end 14 and the outer peripheral surface 11d.

[0029] As shown in Fig. 2, in this embodiment, the chamfered surfaces 13a, 14a are surfaces obtained by chamfering the corners formed by the joint ends 13, 14 and the outer circumferential surface 11d at 45 degrees. In this case, as shown in Fig. 3(a), if the chamfering dimension of the chamfered surface 13a is x, the area (projected area) C1 of the joint chamfered portion 16 as viewed along the axial direction D1 can be expressed as the area of ​​an isosceles right triangle with the length of each side being x. Therefore, the area C1 is expressed as C1=x 2 Similarly, when the chamfer dimension of the chamfered surface 14a is y, the area (projected area) C2 of the joint chamfered portion 17 as viewed along the axial direction D1 is expressed as C2=y 2 / 2.

[0030] The chamfered surface 11e is located between the side surface 11b and the outer peripheral surface 11d and is a surface (outer peripheral lower surface chamfered surface) that connects the side surface 11b and the outer peripheral surface 11d. The chamfered surface 11e is a surface formed by chamfering the corner between the outer peripheral surface 11d and the side surface 11b. An outer peripheral lower surface chamfered portion 18 is formed between the chamfered surface 11e and the inner peripheral surface 3a of the cylinder bore 3. The outer peripheral lower surface chamfered portion 18 is a gap corresponding to a portion removed from the main body portion 11 by chamfering the corner between the side surface 11b and the outer peripheral surface 11d.

[0031] The chamfered surface 11e is a surface obtained by chamfering the corner formed by the outer peripheral surface 11d and the side surface 11b at an arbitrary angle (for example, 45 degrees), or by rounding the corner. As shown in FIG. 3(b), in this embodiment, the chamfered surface 11e is a surface obtained by chamfering the corner formed by the outer peripheral surface 11d and the side surface 11b at an arbitrary angle. In this case, as shown in FIG. 3(b), if the dimension of the chamfered surface 11e along the axial direction D1 is zh and the dimension of the chamfered surface 11e along the radial direction D2 is za, the area (projected area) C3 of the outer peripheral lower surface chamfered portion 18 as viewed along the circumferential direction D3 can be expressed as the area of ​​a right-angled triangle with the lengths of the sides that sandwich the right angle being dimensions zh and za. Therefore, the area C3 is expressed as C3=zh×za / 2.

[0032] 2, the combustion gas G flowing from the combustion chamber to the second ring 20 side through the top ring 10 passes through at least one of the joint portion 15, the joint chamfered portions 16 and 17, and the outer circumferential lower surface chamfered portion 18. It is considered that the combustion gas G passing through the outer circumferential lower surface chamfered portion 18 includes combustion gas G1 passing through the outer circumferential lower surface chamfered portion 18a adjacent to the joint end portion 13, and combustion gas G2 passing through the outer circumferential lower surface chamfered portion 18b adjacent to the joint end portion 14. Therefore, it is considered that the flow area of ​​the combustion gas G in the outer circumferential lower surface chamfered portion 18 corresponds to the sum of the area C31 of the outer circumferential lower surface chamfered portion 18a as viewed along the circumferential direction D3 and the area C32 of the outer circumferential lower surface chamfered portion 18b as viewed along the circumferential direction D3.

[0033] In this embodiment, the area C31 and the area C32 are equal to each other. Here, the area C31 and the area C32 may be representatively referred to as the area C3. The area C31 and the area C32 may be different from each other.

[0034] The flow rate of the combustion gas G flowing from the combustion chamber to the second ring 20 side through the top ring 10 increases or decreases according to the projected area of ​​the gap formed around the butt joint 15 in the main body 11. The projected area of ​​the gap formed around the butt joint 15 is the projected area in the flow direction of the combustion gas G of the gap corresponding to the portion removed from the main body 11 by each chamfered portion, and corresponds to the cross-sectional area of ​​the gap shape perpendicular to the flow direction of the combustion gas G. The projected area of ​​the gap here can be expressed as the sum of the area C1 of the butt joint chamfered portion 16 as viewed along the axial direction D1, the area C2 of the butt joint chamfered portion 17 as viewed along the axial direction D1, the area C3 of the outer circumferential lower surface chamfered portion 18 as viewed along the circumferential direction D3, and the area (projected area) C4 of the gap of the butt joint 15 as viewed along the axial direction D1, when the piston 2 with the top ring 10 attached to the ring groove is inserted into the cylinder bore 3.

[0035] 3(a), when the piston 2 with the top ring 10 attached to the ring groove is inserted into the cylinder bore 3, a gap of dimension g1 is formed in the radial direction D2 between the outer peripheral surface 2a of the piston 2 and the inner peripheral surface 3a of the cylinder bore 3. Specifically, the dimension g1 can be set to a value of (the inner diameter of the cylinder bore 3--the diameter of the upper end of the second land of the piston 2) / 2.

[0036] A plurality of ring grooves 2b are formed in the outer peripheral surface 2a of the piston 2. The plurality of ring grooves 2b includes, in order from the top surface side of the piston, a ring groove in which a top ring 10 is assembled, a ring groove in which a second ring 20 is assembled, and a ring groove in which an oil ring 30 is assembled. A plurality of piston rings 1 are assembled in the plurality of ring grooves 2b, respectively.

[0037] FIG. 4 is an enlarged view of a main part of an example of a ring groove. FIG. 4 shows a ring groove 2b to which a top ring 10 is assembled. The ring groove 2b is a recess recessed inward in the radial direction D2, and includes a pair of upper side surface 2c and lower side surface 2d that face each other in the axial direction D1. The piston 2 is provided with a groove bottom chamfered surface 2e located between the lower side surface 2d of the ring groove 2b and the outer circumferential surface 2a of the piston 2. A groove bottom chamfered portion 2f is formed between the inner circumferential surface 3a of the cylinder bore 3 and the groove bottom chamfered surface 2e. In FIG. 3(a), the dashed line of reference symbol 2a corresponds to a position along the radial direction D2 of the outer circumferential surface 2a of the piston 2, and corresponds to the position of reference symbol 2a (the lower end position of the groove bottom chamfered surface 2e) in FIG. 4.

[0038] The groove-bottom chamfered surface 2e is a surface formed by chamfering the corner between the outer peripheral surface 2a of the piston 2 and the lower side surface 2d of the ring groove 2b. A groove-bottom chamfered portion 2f is formed between the extension line of the outer peripheral surface 2a of the piston 2 and the groove-bottom chamfered surface 2e. The groove-bottom chamfered portion 2f is a gap corresponding to a portion removed from the outer end of the lower side surface 2d of the ring groove 2b of the piston 2 in the radial direction D2 by chamfering the corner between the outer peripheral surface 2a and the lower side surface 2d. The groove-bottom chamfered portion 2f defines a rectangular gap equivalent to the area C4 of the gap of the joint portion 15 together with the gap of dimension g1 between the outer peripheral surface 2a of the piston 2 and the inner peripheral surface 3a of the cylinder bore 3 by forming a gap of dimension pa in the radial direction D2. In other words, in this embodiment, the area C4 of the gap at the joint portion 15 when the top ring 10 attached to the piston 2 and inserted into the cylinder bore 3 is viewed along the axial direction D1 can be expressed as (g1 + pa) × s1.

[0039] The main body 11 has a gap area ratio obtained by dividing the above-mentioned projected area of ​​the gap formed around the gap 15 in the main body 11 by the thickness a1 of the main body 11. (ratio) is configured to be equal to or smaller than a predetermined threshold value. As an example, the gap area ratio R is expressed by the following formula (1). Formula 1: R=(C1+C2+2×C3+C4) / a1×100 ={(g1+pa)×s1+C1+C2+2×C3} / a1×100 however, C1: Area of ​​the chamfered portion 16 along the axial direction D1 of the main body portion 11 C2: Area of ​​the chamfered portion 17 along the axial direction D1 of the main body portion 11 C3: Area of ​​the outer peripheral underside chamfer 18 along the circumferential direction D3 of the main body 11 C4: Area of ​​the gap of the joint 15 along the axial direction D1 of the main body 11 a1: thickness of main body 11 g1: The dimension of the gap between the outer peripheral surface 2a of the piston 2 and the inner peripheral surface 3a of the cylinder bore 3 pa: Dimension of the groove lower chamfered portion 2f along the radial direction of the main body portion 11 s1: The dimension of the gap between the joint end 13 and the joint end 14

[0040] In addition, when the area C31 of the outer peripheral underside chamfered portion 18a viewed along the circumferential direction D3 and the area C32 of the outer peripheral underside chamfered portion 18b viewed along the circumferential direction D3 are different from each other, "2×C3" in the above formula (1) may be replaced with "C31+C32."

[0041] The predetermined threshold is a threshold of the joint area ratio R for setting the dimensions of each part of the top ring 10 so as to suppress the occurrence of corrosion on the side surface 21a of the second ring 20. The predetermined threshold may be a value of 40% or less. The predetermined threshold may be 40%, 35%, or 30%.

[0042] The side roughness of the side surface 11a and the side surface 11b of the main body 11 of the top ring 10 may be Ra 0.8 μm or less, or Rz 4 μm or less. When the side surface roughness of the side surface 11a and the side surface 11b is equal to or less than the above Ra or Rz roughness value, deep recesses are unlikely to be formed on the surfaces of the side surface 11a and the side surface 11b, and a state in which ions derived from components of hydrogen fuel or engine oil are unlikely to stagnate in the space of the recesses is unlikely to occur. It is expected that the promotion of corrosion by such ions and the physical retention of substances related to corrosion due to the surface irregularities according to the roughness, which induces corrosion, are unlikely to occur. The side surface roughness of the side surface 11a and the side surface 11b may be Ra 0.02 μm or more. The side surface roughness of the side surface 11a and the side surface 11b may be Rz 0.1 μm or more.

[0043] The method for suppressing corrosion of the piston ring 1 in an internal combustion engine that uses hydrogen fuel includes a preparation step and an installation step.

[0044] In the preparation step, piston rings 1 including a top ring 10 for an internal combustion engine that uses hydrogen fuel are prepared. In the preparation step, a second ring 20 located on the opposite side of the top ring 10 from the combustion chamber is prepared. In the preparation step, an oil ring 30 may also be prepared.

[0045] In the preparation step, the top ring 10 is constructed to have an annular main body portion 11 including an inner circumferential surface 11c, an outer circumferential surface 11d, side surfaces 11a and 11b that are approximately perpendicular to the inner circumferential surface 11c, and a pair of joint ends 13, 14 that face each other to form a joint portion 15.

[0046] In the preparation step, the main body 11 is configured so that a gap area ratio R, which is obtained by dividing the projected area of ​​the gap formed around the joint 15 in the main body 11 by the thickness a1 of the main body 11, is equal to or less than a predetermined threshold value. In the preparation step, the gap area ratio R may be calculated according to the above formula (1), and the main body 11 may be configured so that the gap area ratio R is 40% or less. Regarding the dimension pa of the piston 2, in the preparation step, the groove lower chamfered surface 2e of the piston 2 may be configured so that the gap area ratio R is 40% or less, or a piston 2 may be selected so that the gap area ratio R is 40% or less.

[0047] In the fitting step, the top ring 10 prepared in the preparation step is fitted into the ring groove 2b for the top ring 10 of the piston 2 of the internal combustion engine. In the fitting step, the second ring 20 prepared in the preparation step is fitted into the ring groove 2b for the second ring 20 of the piston 2 of the internal combustion engine.

[0048] The piston 2 with the top ring 10 and the second ring 20 attached in the ring groove 2b in this manner is inserted into the cylinder bore 3 of an internal combustion engine. In this state, the gap area ratio R is equal to or less than a predetermined threshold value at room temperature, so that corrosion of the side surface 21a of the main body 21 of the second ring 20 of the piston ring 1 can be suppressed in an internal combustion engine that uses hydrogen fuel.

[0049] In the piston ring 1 and the corrosion suppression method for the piston ring 1 described above, the main body portion 11 is configured so that the gap area ratio R is a predetermined threshold value (for example, 40%) or less. This makes it possible to suppress the combustion gas of the hydrogen fuel burned in the combustion chamber from passing through the gap formed around the gap 15 in the main body portion 11 of the top ring 10 and flowing into the second ring 20 located on the opposite side of the top ring 10 from the combustion chamber. As a result, the progress of corrosion of the side surface 21a of the second ring 20 caused by the combustion gas of the hydrogen fuel can be suppressed on the opposite side of the top ring 10 from the combustion chamber. Therefore, in an internal combustion engine using hydrogen fuel, it is possible to suppress corrosion of the side surface (side surface 21a of the second ring 20) of the piston ring 1 including the top ring 10 mounted in the ring groove 2b of the piston 2.

[0050] The side surface roughness of the side surface 11a and the side surface 11b of the main body 11 of the top ring 10 is Ra 0.8 μm or less, or Rz 4 μm or less, which suppresses deterioration of the side surface sealing performance of the side surface 11a and the side surface 11b of the top ring 10 and suppresses the combustion gas from flowing into the side opposite the combustion chamber of the top ring 10 through the gaps between the side surface 11a and the side surface 11b and the ring groove 2b.

[0051] In the above embodiment, the side surface 11b of the main body 11 of the top ring 10, which is in an environment similar to that of the side surface 21a of the second ring 20 as "the side opposite the combustion chamber of the top ring 10," is also prevented from flowing in, thereby suppressing the progression of corrosion caused by the combustion gas of hydrogen fuel. In addition to the above embodiment, even when a piston ring including three or more compression rings is used in an internal combustion engine that uses hydrogen fuel, the side surfaces of the third and subsequent compression rings from the combustion chamber side can be targeted for corrosion suppression as long as an environment similar to that of "the side opposite the combustion chamber of the top ring 10" in the above embodiment is created. EXAMPLES

[0052] The present disclosure will be described in more detail with reference to the following examples, but the present disclosure is not limited to these examples.

[0053] Fig. 5 is a diagram showing the relationship between the gap area ratio and the corrosion index. The horizontal axis of the graph in Fig. 5 is the gap area ratio (%) of the top ring. The vertical axis of the graph in Fig. 5 is the corrosion index (%). The corrosion index is the ratio of the area of ​​the part where corrosion has occurred on the side surface of the second ring.

[0054] In the graph of Fig. 5, the black square plots indicate values ​​for an internal combustion engine that uses hydrogen fuel, and the white circle plots indicate values ​​for a diesel engine. The two black square plots on the left are hidden behind the white circle plots, but correspond, from the left, to Example 1 and Example 2. The two black square plots on the right correspond, from the left, to Comparative Example 1 and Comparative Example 2. The three white circle plots correspond to the conventional example.

[0055] In Example 1, the dimensions of each part of the top ring were set so that the gap area ratio was 35%. As a specific example, the dimensions of each part of the top ring in Example 1 were as follows: the gap dimension s1 was 0.20 mm, the thickness a1 of the main body was 4.2 mm, the dimension za of the chamfered surface 11e along the radial direction D2 was 0.35 mm, the dimension zh of the chamfered surface 11e along the axial direction D1 was 0.35 mm, the dimension g1 of the gap along the radial direction D2 between the outer peripheral surface 2a of the piston 2 and the inner peripheral surface 3a of the cylinder bore 3 was 0.29 mm, and the dimension pa of the groove bottom chamfered portion 2f along the radial direction of the main body 11 was 0.06 mm. The areas calculated from the dimensions of each part of the top ring in Example 1 were: the area C1 of the gap chamfered portion 16 was 0.35 mm, 2 , the area C2 of the joint chamfer 17 is 0.35 mm 2 The area C3 of the outer peripheral lower chamfer 18 is 0.35 mm 2 , the area C4 of the gap at the joint 15 is 0.0702 mm 2 In this case, the joint area ratio R was 35.0.

[0056] The dimension s1 of the gap between the pair of ends of the joint can be measured by inserting a gap gauge between the pair of ends of the joint when the top ring is inserted into the cylinder bore (or a cylindrical jig simulating a cylinder bore). The dimensions x, y, zh, za, and pa can be measured from the contour shape of each chamfered portion. The contour shape may be measured manually or by image processing software. The thickness a1 of the main body of the top ring can be measured by a micrometer. In Example 2, the dimensions of each part of the top ring were set so that the joint area ratio was 40%. In Comparative Example 1, the dimensions of each part of the top ring were set so that the joint area ratio was 43%. In Comparative Example 2, the dimensions of each part of the top ring were set so that the joint area ratio was 47.8%.

[0057] In the experiment to obtain the graph of FIG. 5, the internal combustion engine was operated under evaluation conditions simulating actual driving of a vehicle equipped with an internal combustion engine that uses hydrogen fuel. The evaluation conditions were such that the oil temperature and water temperature alternated between low and high temperatures. The evaluation conditions were such that the internal combustion engine alternated between low and high load states. The evaluation conditions were such that the internal combustion engine alternated between low and high rotation states. The evaluation conditions included periods during which the internal combustion engine was intermittently paused during the evaluation.

[0058] After operating the internal combustion engine under the above-mentioned evaluation conditions, the upper side surface of the second ring was photographed with a digital microscope. The part of the upper side surface of the second ring where corrosion was most advanced was photographed. The entire side surface 21a of the second ring 20 was visually observed to identify the part (area) where corrosion was most advanced. Photographs taken at a magnification of 20 times are shown in Figs. 6 to 9. In Figs. 6 to 9, the color of the part where corrosion had occurred is dark. This is the color of a compound formed by a chemical change in the steel material of the second ring 20, and it appears different in color compared to the part where corrosion had not occurred.

[0059] Fig. 6 is an image showing the condition of the upper side surface of the second ring in Example 1. In the image in Fig. 6, no discoloration was observed on the side surface of the second ring, and no corrosion had occurred.

[0060] Fig. 7 is an image showing the condition of the upper side surface of the second ring of Example 2. In the image of Fig. 7, no discoloration was observed on the side surface of the second ring, and no corrosion had occurred.

[0061] Fig. 8 is an image showing the condition of the upper side surface of the second ring of Comparative Example 1. In the image of Fig. 8, it was confirmed that the discolored areas on the side surface of the second ring were uneven and that minor corrosion had occurred.

[0062] Fig. 9 is an image showing the condition of the upper side surface of the second ring in Comparative Example 2. In the image in Fig. 9, discoloration was observed over a wide area on the side surface of the second ring, and it was confirmed that corrosion was more advanced than in the example in Fig. 8.

[0063] The areas in Figures 6 to 9 were photographed with backscattered electron composition images (composite images) using an electron microscope (magnification 40x), and then analyzed by binarization using software called an image analyzer. The brightness threshold was set to 130. The areas were divided into two phases, black where corrosion had occurred and white where no corrosion had occurred, and the ratio of the area of ​​the black areas to the total area was calculated as a percentage to calculate the corrosion index. The corrosion index is the ratio of the area of ​​the corroded areas to the entire area of ​​the upper side of the second ring.

[0064] 5, the corrosion index of Example 1, in which the gap area ratio was 35%, was 0%. The corrosion index of Example 2, in which the gap area ratio was 40%, was 0%. The corrosion index of Comparative Example 1, in which the gap area ratio was 43%, was 18%. The corrosion index of Comparative Example 2, in which the gap area ratio was 48%, was 57%.

[0065] The inventors conducted an experiment by mounting a pressure ring with a gap area ratio of about 43 to 45 in the ring groove of a piston of an internal combustion engine using hydrogen fuel, and found that corrosion occurred on the side surface 21a of the second ring 20. In the conventional diesel engine, no corrosion occurred even when the gap area ratio exceeded 40%. In contrast, in the internal combustion engine using hydrogen fuel, corrosion was confirmed when the gap area ratio R was 40% or more, and a rapid increase in corrosion was observed at 47.8%. The inventors considered that such corrosion was a phenomenon specific to the internal combustion engine using hydrogen fuel, which is caused by the mixture of the combustion gas of hydrogen fuel, unburned hydrogen gas, and lubricating oil.

[0066] From the results of Figs. 5 to 9, it was found that, while no corrosion occurred in Examples 1 and 2, minor corrosion occurred in Comparative Example 1, and therefore, when the gap area ratio exceeds 40%, corrosion begins to occur on the upper side surface of the second ring. Furthermore, while no corrosion occurred in Examples 1 and 2, corrosion progressed more in Comparative Example 2 than in Comparative Example 1. It was found that, when the gap area ratio exceeds 45%, corrosion of the upper side surface of the second ring is likely to progress. Therefore, it was confirmed that, in an internal combustion engine using hydrogen fuel, it is important to set the top ring gap area ratio to 40% or less in order to suppress corrosion of the side surface of the second ring.

[0067] The present disclosure has been described in detail above based on the embodiments. However, the present disclosure is not limited to the above embodiments. The present disclosure can be modified in various ways without departing from the spirit and scope of the present disclosure.

[0068] The shape of the outer peripheral surface 11d of the top ring 10 may be any of a barrel face shape, an eccentric barrel face shape, or a tapered face shape. The cross-sectional shape of the second ring 20 may be any of a scraper, a balance scraper, a napier, or a balance napier. The shape of the outer peripheral surface 21d of the second ring 20 may be any of a tapered face shape, a barrel face shape, or an eccentric barrel face shape.

[0069] The joint of the pressure ring is not limited to a straight joint. For example, the joint of the pressure ring may be a joint having a special shape, so-called double step. As in the top ring 40 shown in FIG. 10, in the joint 45, a first protrusion 46 protruding from one joint end 43 toward the other joint end 44 and a first receiving portion 47 receiving the first protrusion 46 at the other joint end 44 may be provided on the side surface 41a of the main body 41. In addition, a second protrusion 48 protruding from the other joint end 44 toward one joint end 43 and a second receiving portion 49 receiving the second protrusion 48 at the one joint end 43 may be provided on the side surface 41b of the main body 41.

[0070] The joint of the pressure ring may be a joint having a special shape, so-called a double angle. As in the top ring 50 shown in FIG. 11, the joint 55 may be formed in a part of the annular main body 51. The main body 51 may have a substantially rectangular cross section with a long side in the thickness direction and a short side in the width direction, with one side surface 51a and the other side surface 51b as end faces in the width direction, and an inner peripheral surface 51c and an outer peripheral surface 51d as end faces in the thickness direction. The joint 55 may be composed of one end surface 53 and the other end surface 54 of the main body 51, a protruding portion 56 provided on the end surface 53, and a receiving portion 57 provided on the other end surface 54 side. The receiving portion 57 may have an inclined surface 58 extending from the middle of the side surface 51a to the middle of the outer peripheral surface 51d, and the protruding portion 56 may have a shape corresponding to the receiving portion 57.

[0071] The joint of the pressure ring may be a joint having a special shape, so-called triple step. As in the top ring 60 shown in FIG. 12, the joint 65 may be formed in a part of the annular main body 61. The main body 61 may have a substantially rectangular cross section with a long side in the thickness direction and a short side in the width direction, with one side 61a and the other side 61b as end faces in the width direction, and an inner peripheral surface 61c and an outer peripheral surface 61d as end faces in the thickness direction. When the outer peripheral surface 61d is inclined, the lengths of the side 61a and the side 61b may be different from each other. The joint 65 may include joint ends 63, 64 provided at both ends of the annular main body 61.

[0072] The triple step shape is a step shape when the joint portion 65 is viewed from three directions. In the case of the top ring 60, the joint portion 65 may have a step shape when viewed from the upper side surface 61a side, the lower side surface 61b side, and the outer circumferential surface 61d side. The opposing surfaces of the joint end portion 63 and the joint end portion 64 may be unevenly formed such that the joint end portion 64 protrudes toward the joint end portion 63 on the side surface 61a side and the joint end portion 63 protrudes toward the joint end portion 64 on the side surface 61b side in approximately half of the outer circumferential surface 61d side of the main body portion 61, compared with the opposing surfaces 66, 67 in approximately half of the inner circumferential surface 61c side of the main body portion 61.

[0073] In the above embodiment, the gap area ratio R is expressed by the above formula (1), but is not limited to this example. The gap area ratio may be any value obtained by dividing the projected area of ​​the gap formed around the gap in the main body of the compression ring by the thickness of the main body.

[0074] In the above embodiment, the side surface roughness of the side surface 11a and the side surface 11b of the main body 11 of the top ring 10 is Ra 0.8 μm or less, or Rz 4 μm or less, but is not limited to this example.

[0075] In the above embodiment, the main body 11 of the top ring 10 is configured so that the gap area ratio R is equal to or less than a predetermined threshold value, but the present invention is not limited to an example in which the compression ring is the top ring 10 and corrosion of the side surface 21a of the second ring 20 is suppressed. The compression ring may be the second ring and corrosion of the side surface of the piston ring located on the opposite side of the second ring to the combustion chamber may be suppressed. [Explanation of symbols]

[0076] 1...piston ring, 2...piston, 2a...outer peripheral surface, 2b...ring groove, 2d...lower surface, 2e...groove lower chamfered surface, 2f...groove lower chamfered portion, 3...cylinder bore, 3a...inner peripheral surface, 10...top ring (pressure ring), 11...main body, 11a...side surface (one side surface), 11b...side surface (other side surface), 11c...inner peripheral surface, 11d...outer peripheral surface, 13...butt end (first butt end), 14...joint end (second joint end), 15...joint, 16...joint chamfered portion (first joint chamfered portion), 17...joint chamfered portion (second joint chamfered portion), 18, 18a, 18b...outer peripheral underside chamfered portion, C1, C2, C3, C4...area (projected area), D1...axial direction, D2...radial direction, D3...circumferential direction, g1, pa, s1, x, y, za, zh...dimensions, R...joint area ratio.

Claims

1. A piston ring including a compression ring mounted in a ring groove of a piston of an internal combustion engine that uses hydrogen fuel, The compression ring has an annular main body portion including an inner circumferential surface, an outer circumferential surface, one side surface and another side surface substantially perpendicular to the inner circumferential surface, and a pair of joint ends facing each other to form a joint, the main body portion is configured such that a ratio obtained by dividing a projected area of ​​a gap formed around the joint portion in the main body portion by a thickness of the main body portion is equal to or less than a predetermined threshold value, The piston is provided with a groove lower chamfered surface located between a lower side surface of the ring groove and an outer circumferential surface of the piston, The main body portion is provided with a first joint chamfered surface located between a first joint end portion of one of the pair of joint ends and the outer peripheral surface of the main body portion, a second joint chamfered surface located between a second joint end portion of the other of the pair of joint ends and the outer peripheral surface of the main body portion, and an outer peripheral lower surface chamfered surface located between one of the one side surface and the other side surface and the outer peripheral surface of the main body portion, In a state in which the compression ring is fitted into the ring groove and inserted into a cylinder bore of the internal combustion engine, a first butt chamfered portion is formed between the inner peripheral surface of the cylinder bore and the first butt chamfered surface, a second butt chamfered portion is formed between the inner peripheral surface of the cylinder bore and the second butt chamfered surface, and an outer peripheral lower surface chamfered portion is formed between the inner peripheral surface of the cylinder bore and the outer peripheral lower surface chamfered surface, a groove bottom chamfer portion is formed between the inner circumferential surface of the cylinder bore and the groove bottom chamfer surface, The ratio R is expressed by the following formula: A piston ring for an internal combustion engine that uses hydrogen fuel, wherein the ratio R is 40% or less. Formula: R=(C1+C2+2×C3+C4) / a1×100 however, C1 is the projected area of ​​the first abutment chamfered portion along the axial direction of the main body portion, C2 is the projected area of ​​the second chamfered portion along the axial direction of the main body portion, C3 is the projected area of ​​the outer peripheral lower surface chamfered portion along the circumferential direction of the main body portion, C4 is the area of ​​the gap of the joint along the axial direction of the main body, a1 is the thickness of the main body.

2. 2. The piston ring for an internal combustion engine that uses hydrogen fuel according to claim 1, wherein the one side surface and the other side surface of the compression ring have a side roughness of Ra 0.8 μm or less, or Rz 4 μm or less.

3. A method for inhibiting corrosion of a piston ring in an internal combustion engine that uses hydrogen fuel, comprising: a preparation step of preparing a piston ring including a compression ring for an internal combustion engine that uses hydrogen fuel; and a mounting step of mounting the compression ring in a ring groove of a piston of the internal combustion engine, In the preparation step, The pressure ring is configured to have an annular main body portion including an inner circumferential surface, an outer circumferential surface, one side surface and another side surface substantially perpendicular to the inner circumferential surface, and a pair of joint ends facing each other to form a joint portion, The main body is configured so that a ratio obtained by dividing a projected area of ​​a gap formed around the joint in the main body by a thickness of the main body is equal to or less than a predetermined threshold value; In the preparation step, a groove lower chamfered surface located between a lower side surface of the ring groove and an outer peripheral surface of the piston is provided on the piston; a first joint chamfered surface located between a first joint end of one of the pair of joint ends and the outer peripheral surface of the main body portion, a second joint chamfered surface located between a second joint end of the other of the pair of joint ends and the outer peripheral surface of the main body portion, and an outer peripheral lower surface chamfered surface located between one of the one side surface and the other side surface and the outer peripheral surface of the main body portion, In a state in which the compression ring is fitted into the ring groove and inserted into a cylinder bore of the internal combustion engine, a first butt chamfered portion is formed between an inner peripheral surface of the cylinder bore and the first butt chamfered surface, a second butt chamfered portion is formed between the inner peripheral surface of the cylinder bore and the second butt chamfered surface, and an outer peripheral lower surface chamfered portion is formed between the inner peripheral surface of the cylinder bore and the outer peripheral lower surface chamfered surface, a groove bottom chamfer portion is formed between the inner circumferential surface of the cylinder bore and the groove bottom chamfer surface; The ratio R is expressed by the following formula: The method for suppressing corrosion of a piston ring in an internal combustion engine that uses hydrogen fuel, wherein the ratio R is 40% or less. Formula: R=(C1+C2+2×C3+C4) / a1×100 however, C1 is the projected area of ​​the first abutment chamfered portion along the axial direction of the main body portion, C2 is the projected area of ​​the second chamfered portion along the axial direction of the main body portion, C3 is the projected area of ​​the outer peripheral lower surface chamfered portion along the circumferential direction of the main body portion, C4 is the area of ​​the gap of the joint along the axial direction of the main body, a1 is the thickness of the main body.

Images