Piston ring for internal combustion engine using hydrogen fuel, and method for suppressing corrosion of piston ring in internal combustion engine using hydrogen fuel

Abstract

A piston ring 1 for an internal combustion engine using hydrogen fuel includes a top ring 10 mounted in a ring groove of a piston of the internal combustion engine using hydrogen fuel. The top ring 10 has an annular body portion 11 including an inner peripheral surface 11c, an outer peripheral surface 11d, side surfaces 11a and 11b substantially orthogonal to the inner peripheral surface 11c, and a pair of abutment end portions 13 and 14 facing each other to form an abutment portion 15. The body portion 11 is constructed such that an abutment area ratio obtained by dividing a projected area of a gap formed around the abutment portion 15 in the body portion 11 by a thickness of the body portion 11 is equal to or less than a predetermined threshold value.

Description

Piston Ring for Internal Combustion Engine Using Hydrogen Fuel and Method for Suppressing Corrosion of Piston Ring in Internal Combustion Engine Using Hydrogen Fuel

[0001] The present disclosure relates to a piston ring for an internal combustion engine using hydrogen fuel and a method for suppressing corrosion of the piston ring in an internal combustion engine using hydrogen fuel.

[0002] Among the piston rings used in internal combustion engines, the compression ring is mounted in the ring groove of the piston and inserted into the cylinder bore, and functions to maintain airtightness between the combustion chamber and the crank chamber and reduce oil consumption. As such a compression ring, a top ring having a gas leak type joint portion formed therein is known (for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 10-331973

[0004] In recent years, the compatibility of piston rings including compression rings mounted in the ring grooves of pistons with internal combustion engines using hydrogen fuel containing hydrogen gas has been studied. The present inventor has discovered that a type of corrosion that did not occur in conventional internal combustion engines using light oil fuel and gasoline fuel can occur on the side surfaces of piston rings in internal combustion engines using hydrogen fuel. If such corrosion progresses, the piston ring may break, so there is room for improvement.

[0005] An object of the present disclosure is to suppress corrosion on the side surfaces of piston rings including compression rings mounted in the ring grooves of pistons in internal combustion engines using hydrogen fuel.

[0006] To solve the above problems, the present inventor has conducted intensive studies. As a result, the present inventor has found that the corrosion on the side surfaces of the piston rings is caused by the mixing of combustion gas of hydrogen fuel, unburned hydrogen gas, and lubricating oil. The present inventor has focused on reducing the combustion gas of hydrogen fuel flowing into the side opposite to the combustion chamber of the compression ring. The present inventor has found that the corrosion on the side surfaces of the piston rings is suppressed by configuring the main body such that the joint area ratio obtained by dividing the projected area of the gap formed around the joint portion in the main body by the thickness of the main body is equal to or less than a predetermined threshold value.

[0007] A piston ring according to one aspect of the present disclosure is a piston ring including a pressure ring fitted into the ring groove of a piston of an internal combustion engine using hydrogen fuel, wherein the pressure ring has an annular 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 joint ends facing each other to form a joint portion, and the body portion is configured such that the joint area ratio obtained by dividing the projected area of ​​the gap formed around the joint portion in the body portion by the thickness of the body portion is less than or equal to a predetermined threshold.

[0008] In one aspect of the present disclosure, the piston ring is configured such that the joint area ratio is below a predetermined threshold. This prevents combustion gases from hydrogen fuel burned in the combustion chamber from flowing through the gap formed around the joint in the main body of the pressure ring to the side of the pressure ring away from the combustion chamber. As a result, the progression of corrosion on the side of the piston ring caused by the combustion gases of hydrogen fuel can be suppressed on the side of the pressure ring away from the combustion chamber. Therefore, in an internal combustion engine using hydrogen fuel, corrosion of the side of the piston ring, including the pressure ring fitted in the ring groove of the piston, can be suppressed.

[0009] In one embodiment, the piston is provided with a groove bottom chamfer surface located between the lower surface of the ring groove and the outer surface of the piston, the main body is provided with a first joint chamfer surface located between one of a pair of joint ends and the outer surface, a second joint chamfer surface located between the other of a pair of joint ends and the outer surface, and an outer surface bottom chamfer surface located between one side and one of the other sides and the outer surface, and when the pressure ring is fitted into the ring groove and inserted into the cylinder bore of the internal combustion engine, a first joint chamfer is formed between the inner surface of the cylinder bore and the first joint chamfer surface, a second joint chamfer is formed between the inner surface and the second joint chamfer surface, an outer surface bottom chamfer is formed between the inner surface and the outer surface bottom chamfer surface, and a groove bottom chamfer is formed between the inner surface of the cylinder bore and the groove bottom chamfer surface, 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 where C1 is the projected area of ​​the first chamfered joint portion along the axial direction of the main body, C2 is the projected area of ​​the second chamfered joint portion along the axial direction of the main body, C3 is the projected area of ​​the outer bottom chamfered portion along the circumferential direction of the main body, C4 is the area of ​​the gap in the joint portion along the axial direction of the main body, and a1 is the thickness of the main body.

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

[0011] Another aspect of the present disclosure is a method for suppressing corrosion of a piston ring in an internal combustion engine using hydrogen fuel, comprising: a preparation step of preparing a piston ring including a pressure ring for an internal combustion engine using hydrogen fuel; and a mounting step of mounting the pressure ring in the ring groove of a piston of the internal combustion engine. In the preparation step, the pressure ring is configured to have an annular 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 joint ends facing each other to form a joint portion, and the body portion is configured such that the joint area ratio obtained by dividing the projected area of ​​the gap formed around the joint portion in the body portion by the thickness of the body portion is less than or equal to a predetermined threshold.

[0012] In another aspect of the present disclosure, a method for suppressing corrosion of piston rings in an internal combustion engine using hydrogen fuel is configured such that the joint area ratio is below a predetermined threshold. This prevents combustion gases of hydrogen fuel burned in the combustion chamber from flowing through the gap formed around the joint in the main body of the pressure ring to the side of the pressure ring away from the combustion chamber. As a result, the progression of corrosion on the side of the piston ring caused by the combustion gases of hydrogen fuel can be suppressed on the side of the pressure ring away from the combustion chamber. Therefore, corrosion of the side of piston rings, including the pressure ring fitted in the ring groove of the piston, can be suppressed in an internal combustion engine using hydrogen fuel.

[0013] According to some aspects of this disclosure, corrosion of the sides of piston rings, including pressure rings fitted into the ring grooves of pistons, can be suppressed in an internal combustion engine using hydrogen fuel.

[0014] This is a perspective view of a piston ring according to an embodiment. This is an enlarged view of a key part to explain the gap formed around the joint. Figure 3(a) is an enlarged view of a key part of an example of the joint of a top ring. Figure 3(b) is an enlarged view of a key part of an example of the chamfered lower surface of the outer circumference of a top ring. This is an enlarged view of a key part of an example of a ring groove. This figure shows the relationship between the joint area ratio and the corrosion index. This figure shows the side view of the piston ring of Example 1. This figure shows the side view of the piston ring of Example 2. This figure shows the side view of the piston ring of Comparative Example 1. This figure shows the side view of the piston ring of Comparative Example 2. This is an enlarged perspective view showing an example of a double-step shaped joint. This is an enlarged perspective view showing an example of a double-angle shaped joint. This is an enlarged perspective view showing an example of a triple-step shaped joint.

[0015] Embodiments relating to this disclosure will be described below with reference to the drawings. In the description of the drawings, the same or equivalent elements will be denoted by the same reference numerals, and redundant explanations will be omitted as appropriate. In the following description, "upper side" corresponds to the top side of the piston (top dead center side, combustion chamber side), and "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 the cross-section including the central axis of the piston ring. In the following description and drawings, each dimension and each projected area will correspond to the values ​​when the axes of the piston and piston ring are not inclined with respect to the axis of the cylinder bore (concentric).

[0016] Figure 1 is a perspective view of a piston ring according to an embodiment. As shown in Figure 1, the piston ring 1 includes a pressure ring fitted into the ring groove of a piston in an internal combustion engine using hydrogen fuel. The piston ring 1 includes, for example, a top ring (pressure ring) 10, a second ring 20, and an oil ring 30. The piston ring 1 is inserted into the cylinder bore of the internal combustion engine while fitted into the ring groove of the piston. The piston ring 1 slides against the inner wall of the cylinder bore, thereby providing a gas seal function between the combustion chamber side and the crankcase side, and a function to reduce 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 installed in a vehicle. The engine oil used in this internal combustion engine contains additives including metallic elements. Examples of metallic elements contained in the engine oil include Ca, S, P, and Zn.

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

[0019] The main body 11 has a roughly rectangular cross-section, with the thickness direction being the longer side and the width direction being the shorter side. The main body 11 is made of, for example, cast iron or steel containing multiple metal elements, and is formed with sufficient strength, heat resistance, and elasticity.

[0020] The surface of the main body 11 may be subjected to surface modification to form a hard film. The hard film is, for example, a physically vapor-deposited film (PVD film) formed using the PVD method. This allows the hard film to be formed with sufficient hardness. The hard film is an ion-plated film or a diamond-like carbon film containing at least one of titanium (Ti) and chromium (Cr), and at least one of carbon (C), nitrogen (N), and oxygen. Specific examples of hard films include titanium nitride film, chromium nitride film, titanium carbonitride film, chromium carbonitride film, chromium oxynitride film, chromium film, or titanium film. From the viewpoint of wear resistance and scuff resistance, the hard film may also 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 when a part of the main body portion 11 is separated. The joint end portion 13 and the joint end portion 14 are the free ends of the main body portion 11, respectively. The joint end portion 13 is one of a pair of joint end portions 13 and 14. The joint end portion 14 is the other of the pair of joint end portions 13 and 14. The joint end portions 13 and 14 have end faces that are flat along the axial direction D1. The joint portion 15 is a so-called straight joint. With the piston 2, with the top ring 10 mounted in the ring groove, inserted into the cylinder bore 3, a gap (joint gap) of dimension s1 in the circumferential direction D3 at room temperature is formed between the joint end portion 13 and the joint end portion 14 (see Figure 3(a)).

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

[0023] The main body portion 21 has a substantially rectangular cross-section, with the thickness direction being the longer side and the width direction being the shorter side. The main body portion 21 is made of, for example, cast iron or steel containing multiple metallic elements, and is formed with sufficient strength, heat resistance, and elasticity. The surface of the main body portion 21 may be surface modified in the same way as the top ring 10 to form a hard film.

[0024] The joint portion 25 is a gap created when a part of the main body portion 21 is separated. The joint end portion 23 and the joint end portion 24 are the free ends of the main body portion 21, respectively.

[0025] The oil ring 30 has a pair of rails 31 and a spacer expander 32 that face each other. Each of the pair of rails 31 is a side rail of the oil ring 30. The spacer expander 32 is positioned between the pair of rails 31. In this embodiment, the pair of rails 31 and the spacer expander 32 constitute a three-piece oil ring 30. Each of the pair of rails 31 has a joint formed therein. Each rail 31 may be made of 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 also be a two-piece oil ring.

[0026] Figure 2 is a close-up view of a key part illustrating the gap formed around the joint. Figure 3(a) is a close-up view of a key part of an example of the joint of the top ring. Figure 3(b) is a close-up view of a key part of an example of the chamfered lower outer surface of the top ring. As shown in Figures 2, 3(a), and 3(b), the main body 11 includes chamfered surfaces 13a, 14a, and 11e.

[0027] The chamfered surface 13a is located between the joint end 13 and the outer circumferential surface 11d, and is the surface (first joint chamfered surface) that connects the joint end 13 and the outer circumferential surface 11d. The chamfered surface 13a is a surface formed by chamfering the corner formed by 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 the portion removed from the main body 11 by chamfering the corner formed by the joint end 13 and the outer circumferential surface 11d.

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

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

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

[0031] The chamfered surface 11e is a surface obtained by chamfering the corner between 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 Figure 3(b), in this embodiment, the chamfered surface 11e is a surface obtained by chamfering the corner between the outer peripheral surface 11d and the side surface 11b at an arbitrary angle. In this case, as shown in Figure 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, then the area (projected area) C3 of the outer peripheral lower surface chamfered portion 18 viewed along the circumferential direction D3 can be expressed as the area of ​​a right-angled triangle with sides of dimensions zh and za forming a right angle. Therefore, the area C3 is expressed as C3 = zh × za / 2.

[0032] As shown in Figure 2, the combustion gas G flowing from the combustion chamber through the top ring 10 to the second ring 20 passes through at least one of the joint portion 15, the joint chamfer portion 16, the joint chamfer portion 17, and the outer peripheral lower chamfer portion 18. The combustion gas G passing through the outer peripheral lower chamfer portion 18 is thought to include combustion gas G1 passing through the outer peripheral lower chamfer portion 18a adjacent to the joint end portion 13, and combustion gas G2 passing through the outer peripheral lower chamfer portion 18b adjacent to the joint end portion 14. Therefore, the flow area of ​​the combustion gas G in the outer peripheral lower chamfer portion 18 is thought to be the sum of the area C31 of the outer peripheral lower chamfer portion 18a viewed along the circumferential direction D3 and the area C32 of the outer peripheral lower chamfer portion 18b viewed along the circumferential direction D3.

[0033] In this embodiment, areas C31 and C32 are equal. Here, areas C31 and C32 may be represented as area C3. Note that areas C31 and C32 may be different from each other.

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

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

[0036] Multiple ring grooves 2b are formed on the outer circumferential surface 2a of the piston 2. The multiple ring grooves 2b include, in order from the top surface side of the piston, a ring groove into which the top ring 10 is assembled, a ring groove into which the second ring 20 is assembled, and a ring groove into which the oil ring 30 is assembled. Multiple piston rings 1 are assembled into each of the multiple ring grooves 2b.

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

[0038] The groove bottom chamfered surface 2e is a surface formed by chamfering the corner formed by the outer circumferential surface 2a of the piston 2 and the lower surface 2d of the ring groove 2b. A groove bottom chamfered portion 2f is formed between the extension of the outer circumferential surface 2a of the piston 2 and the groove bottom chamfered surface 2e. The groove bottom chamfered portion 2f is a gap corresponding to the portion removed from the radially outer end D2 of the lower surface 2d of the ring groove 2b in the piston 2 by chamfering the corner formed by the outer circumferential surface 2a and the lower surface 2d. The groove bottom chamfered portion 2f forms a gap of dimension pa in the radial direction D2, and together with the gap of dimension g1 between the outer circumferential surface 2a of the piston 2 and the inner circumferential surface 3a of the cylinder bore 3, defines a rectangular gap equivalent to the area C4 of the gap in the joint portion 15. In other words, in this embodiment, the area C4 of the gap at the joint 15 when the top ring 10, which is 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 part 11 is configured such that the joint area ratio obtained by dividing the above-described projected area of the gap formed around the joint part 15 in the main body part 11 by the thickness a1 of the main body part 11 is not more than a predetermined threshold value. As an example, the joint 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: the area of the joint chamfer part 16 along the axial direction D1 of the main body part 11 C2: the area of the joint chamfer part 17 along the axial direction D1 of the main body part 11 C3: the area of the outer peripheral lower surface chamfer part 18 along the circumferential direction D3 of the main body part 11 C4: the area of the gap of the joint part 15 along the axial direction D1 of the main body part 11 a1: the thickness of the main body part 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: the dimension along the radial direction of the main body part 11 of the groove chamfer part 2f s1: the dimension of the gap between the joint end part 13 and the joint end part 14

[0040] In addition, when the area C31 of the outer peripheral lower surface chamfer part 18a as viewed along the circumferential direction D3 is different from the area C32 of the outer peripheral lower surface chamfer part 18b as viewed along the circumferential direction D3, "2 × C3" in the above formula (1) may be replaced with "C31 + C32".

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

[0042] Further, the surface roughness of the side surfaces 11a and 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 surface roughness of the side surfaces 11a and 11b is below the above Ra or Rz roughness values, deep depressions are less likely to form on the surfaces of the side surfaces 11a and 11b, and a state in which ions derived from hydrogen fuel or engine oil components stagnate in the space of the depressions is less likely to occur. It is expected that the promotion of corrosion by such ions and the physical retention of corrosion-related substances due to the surface irregularities according to the roughness, which induce corrosion, are less likely to occur. The surface roughness of the side surfaces 11a and 11b may be Ra 0.02 µm or more. The surface roughness of the side surfaces 11a and 11b may be Rz 0.1 µm or more.

[0043] By the way, a method for suppressing corrosion of the piston ring 1 in an internal combustion engine using hydrogen fuel includes a preparation step and a mounting step.

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

[0045] In the preparation step, the top ring 10 is configured to have an annular main body 11 including an inner peripheral surface 11c, an outer peripheral surface 11d, side surfaces 11a and 11b substantially orthogonal to the inner peripheral surface 11c, and a pair of joint end portions 13 and 14 that face each other to form a joint portion 15.

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

[0047] In the mounting step, the top ring 10 prepared in the preparation step is mounted into the ring groove 2b for the top ring 10 of the piston 2 of the internal combustion engine. In the mounting step, the second ring 20 prepared in the preparation step is mounted 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 second ring 20 mounted in the ring groove 2b in this manner, is inserted into the cylinder bore 3 of the internal combustion engine. In this state, the gap area ratio R is below a predetermined threshold at room temperature, which can suppress corrosion of the side surface 21a of the main body portion 21 of the second ring 20 of the piston ring 1 in an internal combustion engine using hydrogen fuel.

[0049] In the piston ring 1 and the method for suppressing corrosion of the piston ring 1 described above, the main body 11 is configured such that the joint area ratio R is less than or equal to a predetermined threshold (for example, 40%). This prevents combustion gases of hydrogen fuel burned in the combustion chamber from flowing through the gap formed around the joint portion 15 in the main body 11 of the top ring 10 to the second ring 20 located on the opposite side of the top ring 10 from the combustion chamber. As a result, the progression of corrosion on the side surface 21a of the second ring 20 caused by the combustion gases of hydrogen fuel can be suppressed on the side of the top ring 10 opposite the combustion chamber. Therefore, in an internal combustion engine using hydrogen fuel, corrosion of the side surface (side surface 21a of the second ring 20) of the piston ring 1, including the top ring 10, which is mounted in the ring groove 2b of the piston 2 can be suppressed.

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

[0051] In addition, in the above embodiment, the side surface 11b of the main body portion 11 of the top ring 10, which is in the same environment as the side surface 21a of the second ring 20, can also suppress the flow of combustion gases, thereby suppressing the progression of corrosion caused by combustion gases of hydrogen fuel. Furthermore, even in cases where a piston ring including three or more pressure rings is used in an internal combustion engine using hydrogen fuel, if an environment similar to the "opposite side of the top ring 10 from the combustion chamber" in the above embodiment occurs, the side surfaces of the third and subsequent pressure rings from the combustion chamber side can be targeted for corrosion suppression.

[0052] The present disclosure will be further illustrated by the following examples, but the present disclosure is not limited to these examples.

[0053] Figure 5 shows the relationship between the joint area ratio and the corrosion index. The horizontal axis of the graph in Figure 5 represents the joint area ratio (%) of the top ring. The vertical axis of the graph in Figure 5 represents the corrosion index (%). The corrosion index is the percentage of the area on the side surface of the second ring where corrosion has occurred.

[0054] In the graph of Figure 5, the black square plots represent values ​​for internal combustion engines using hydrogen fuel. The white circular plots represent values ​​for diesel engines. The two black square plots on the left are hidden behind the white circular plots, but from left to right they correspond to Example 1 and Example 2. The two black square plots on the right correspond from left to right they correspond to Comparative Example 1 and Comparative Example 2. The three white circular plots correspond to the conventional example.

[0055] In Example 1, the dimensions of each part of the top ring were set so that the joint area ratio was 35%. As a specific example, the dimensions of each part of the top ring in Example 1 were as follows: the joint 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 gap dimension g1 along the radial direction D2 between the outer circumferential surface 2a of the piston 2 and the inner circumferential surface 3a of the cylinder bore 3 was 0.29 mm, and the dimension pa of the groove bottom chamfered part 2f along the radial direction of the main body 11 was 0.06 mm. The respective areas calculated from the dimensions of each part of the top ring in Example 1 were as follows: the area C1 of the joint chamfered part 16 was 0.35 mm ２ Therefore, the area C2 of the chamfered joint portion 17 is 0.35 mm ２ Therefore, the area C3 of the outer peripheral lower chamfer portion 18 is 0.35 mm ２ Therefore, the area C4 of the gap in the joint portion 15 is 0.0702 mm². ２ , and in this case the joint area ratio R was 35.0.

[0056] The dimension s1 of the joint gap can be measured by inserting a gap gauge between the pair of joint ends with the top ring inserted into the cylinder bore (or a cylindrical jig that mimics the cylinder bore). 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 with 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] To obtain the graph shown in Figure 5, the internal combustion engine was operated under evaluation conditions simulating actual vehicle driving of a vehicle equipped with an internal combustion engine using hydrogen fuel. The evaluation conditions involved repeatedly alternating between low and high oil and water temperatures. The evaluation conditions involved repeatedly alternating between low and high load states of the internal combustion engine. The evaluation conditions involved repeatedly alternating between low and high rotational speed states of the internal combustion engine. The evaluation conditions included periods of intermittent temporary shutdown of the internal combustion engine during the evaluation.

[0058] After operating the internal combustion engine under the evaluation conditions described above, the upper side surface of the second ring was photographed using a digital microscope. On the upper side surface of the second ring, the area of ​​most advanced corrosion was selected for photography. The entire side surface 21a of the second ring 20 was visually observed to identify the area (region) where corrosion was most advanced. Figures 6 to 9 show images taken at a magnification of 20x. In Figures 6 to 9, the areas where corrosion occurred appear darker. This is the color of compounds formed by chemical changes in the steel material of the second ring 20, and the color differs from the areas where corrosion did not occur.

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

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

[0061] Figure 8 is an image showing the condition of the upper side surface of the second ring in Comparative Example 1. In the image in Figure 8, the discoloration on the side surface of the second ring is unevenly visible, confirming that minor corrosion has occurred.

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

[0063] The areas shown in Figures 6 to 9 were captured using an electron microscope to obtain backscattered electron composition images (Compo images) (magnification 40x), and then analyzed by binarization using image analyzer software. The brightness threshold was set to 130. The area was divided into two phases: black where corrosion occurred and white where corrosion did not occur. The corrosion index was calculated by determining the percentage of the black area relative to the total area. The corrosion index represents the percentage of the area of ​​the upper side surface of the second ring that was corroded.

[0064] As shown in Figure 5, the corrosion index of Example 1, with a joint area ratio of 35%, was 0%. The corrosion index of Example 2, with a joint area ratio of 40%, was 0%. The corrosion index of Comparative Example 1, with a joint area ratio of 43%, was 18%. The corrosion index of Comparative Example 2, with a joint area ratio of 48%, was 57%.

[0065] The inventors conducted an experiment in which they fitted a pressure ring with a joint area ratio of approximately 43-45 into the ring groove of a piston in an internal combustion engine using hydrogen fuel, and discovered corrosion on the side surface 21a of the second ring 20. In conventional diesel engines, corrosion did not occur even when the joint area ratio exceeded 40%. In contrast, in internal combustion engines using hydrogen fuel, corrosion was observed when the joint area ratio R exceeded 40%, and a rapid increase in corrosion was seen when the joint area ratio R was 47.8%. The inventors believe that this type of corrosion is a phenomenon unique to internal combustion engines using hydrogen fuel, caused by the mixing of combustion gases, unburned hydrogen gases, and lubricating oil.

[0066] In Examples 1 and 2, no corrosion occurred, while in Comparative Example 1, slight corrosion occurred. Figures 5 to 9 show that when the joint 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 significantly in Comparative Example 2 than in Comparative Example 1. It was found that when the joint area ratio exceeds 45%, corrosion on the upper side surface of the second ring is likely to progress. Therefore, in internal combustion engines using hydrogen fuel, it was confirmed that setting the top ring joint area ratio to 40% or less is important to suppress corrosion on the side surface of the second ring.

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

[0068] The shape of the outer circumferential surface 11d of the top ring 10 may be 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 a scraper, a balanced scraper, a napier, or a balanced napier. The shape of the outer circumferential surface 21d of the second ring 20 may be a tapered face shape, a barrel face shape, or an eccentric barrel face shape.

[0069] The joint of a pressure ring is not limited to a straight shape. For example, the joint of a pressure ring may be a special shape, such as a so-called double step. As shown in Figure 10, in the joint 45, the side surface 41a of the main body 41 may be provided with a first projection 46 projecting from one joint end 43 toward the other joint end 44, and a first receiving portion 47 at the other joint end 44 that receives the first projection 46. Furthermore, the side surface 41b of the main body 41 may be provided with a second projection 48 projecting from the other joint end 44 toward the one joint end 43, and a second receiving portion 49 at the one joint end 43 that receives the second projection 48.

[0070] The joint portion of the pressure ring may be a special joint portion with a so-called double angle shape. As shown in Figure 11, the joint portion 55 may be formed on a part of the annular main body portion 51. The main body portion 51 may have a substantially rectangular cross-section with the thickness direction being the longer side and the width direction being the shorter side, formed by one side surface 51a and the other side surface 51b which are the end faces in the width direction, and the inner circumferential surface 51c and outer circumferential surface 51d which are the end faces in the thickness direction. The joint portion 55 may be composed of one end surface 53 and the other end surface 54 of the main body portion 51, a projection 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 that extends from the middle of the side surface 51a to the outer circumferential surface 51d, and the projection 56 may have a shape corresponding to the receiving portion 57.

[0071] The joint portion of the pressure ring may be a special joint portion with a so-called triple step shape. As shown in Figure 12, the joint portion 65 may be formed on a part of the annular main body portion 61. The main body portion 61 may have a substantially rectangular cross-section with the thickness direction being the longer side and the width direction being the shorter side, formed by one side surface 61a and the other side surface 61b which are the end faces in the width direction, and the inner circumferential surface 61c and outer circumferential surface 61d which are the end faces in the thickness direction. If the outer circumferential surface 61d is inclined, the lengths of the side surfaces 61a and 61b may be different. The joint portion 65 may include joint ends 63 and joint ends 64 provided at both ends of the annular main body portion 61.

[0072] A triple-step shape refers to a joint portion 65 that exhibits a stepped shape when viewed from three directions. In the case of the top ring 60, the joint portion 65 may have a stepped shape when viewed from the upper side surface 61a, the lower side surface 61b, and the outer peripheral surface 61d. The opposing surfaces of the joint ends 63 and 64 may have irregularities formed on the outer peripheral surface 61d of the main body 61, such that the joint end 64 protrudes toward the joint end 63 on the side surface 61a, and the joint end 63 protrudes toward the joint end 64 on the side surface 61b, compared to the opposing surfaces 66 and 67 on approximately half of the inner peripheral surface 61c of the main body 61.

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

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

[0075] In the above embodiment, the main body 11 of the top ring 10 was configured such that the joint area ratio R is below a predetermined threshold. However, the embodiment is not limited to the example where the pressure ring is the top ring 10 and corrosion of the side surface 21a of the second ring 20 is suppressed. The pressure ring may be the second ring, and corrosion of the side surface of the piston ring located on the opposite side of the combustion chamber of the second ring may be suppressed.

[0076] 1...Piston ring, 2...Piston, 2a...Outer circumference, 2b...Ring groove, 2d...Lower side, 2e...Groove bottom chamfer, 2f...Groove bottom chamfer, 3...Cylinder bore, 3a...Inner circumference, 10...Top ring (pressure ring), 11...Main body, 11a...Side (one side), 11b...Side (other side), 11c...Inner circumference, 11d...Outer circumference, 13...Joint end (first joint end), 14...Joint end (second joint end), 15...Joint section, 16...Joint chamfer section (first joint chamfer section), 17...Joint chamfer section (second joint chamfer section), 18, 18a, 18b...Outer circumference lower chamfer section, 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 for an internal combustion engine using hydrogen fuel, comprising a pressure ring fitted into the ring groove of a piston, wherein the pressure ring has an annular 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 joint ends facing each other to form a joint portion, and the body portion is configured such that the joint area ratio obtained by dividing the projected area of ​​the gap formed around the joint portion in the body portion by the thickness of the body portion is less than or equal to a predetermined threshold.

2. The piston is provided with a groove bottom chamfer surface located between the lower surface of the ring groove and the outer circumferential surface of the piston, the main body is provided with a first joint chamfer surface located between one of the pair of joint ends and the outer circumferential surface, a second joint chamfer surface located between the other of the pair of joint ends and the outer circumferential surface, and an outer circumferential bottom chamfer surface located between one of the two sides and the outer circumferential surface, when the pressure ring is mounted in the ring groove and inserted into the cylinder bore of the internal combustion engine, a first joint chamfer is formed between the inner circumferential surface of the cylinder bore and the first joint chamfer surface, a second joint chamfer is formed between the inner circumferential surface and the second joint chamfer surface, an outer circumferential bottom chamfer is formed between the inner circumferential surface and the outer circumferential bottom chamfer surface, a groove bottom chamfer is formed between the inner circumferential surface of the cylinder bore and the groove bottom chamfer surface, the joint area ratio R is expressed by the following formula, The piston ring for an internal combustion engine using hydrogen fuel according to claim 1, wherein the joint area ratio R is 40% or less. Formula: R = (C1 + C2 + 2 × C3 + C4) / a1 × 100 where C1 is the projected area of ​​the first joint chamfer along the axial direction of the main body, C2 is the projected area of ​​the second joint chamfer along the axial direction of the main body, C3 is the projected area of ​​the outer peripheral lower chamfer along the circumferential direction of the main body, C4 is the area of ​​the gap in the joint along the axial direction of the main body, and a1 is the thickness of the main body.

3. The piston ring for an internal combustion engine using hydrogen fuel according to claim 1 or 2, wherein the surface roughness of one side and the other side of the pressure ring is Ra 0.8 μm or less, or Rz 4 μm or less.

4. A method for suppressing corrosion of a piston ring in an internal combustion engine using hydrogen fuel, comprising: a preparation step of preparing a piston ring including a pressure ring for an internal combustion engine using hydrogen fuel; and a mounting step of mounting the pressure ring in the ring groove of the piston of the internal combustion engine, wherein in the preparation step, the pressure ring is configured to have an annular body portion including an inner circumferential surface, an outer circumferential surface, one side and another side substantially perpendicular to the inner circumferential surface, and a pair of joint ends facing each other to form a joint portion, and the body portion is configured such that the joint area ratio obtained by dividing the projected area of ​​the gap formed around the joint portion in the body portion by the thickness of the body portion is less than or equal to a predetermined threshold.

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