Piston ring, sliding structure of cylinder and piston ring, sliding simulation device for internal combustion engine, and sliding simulation method

Abstract

Provided is a piston ring for use with hydrogen gas fuel. The piston ring is configured such that the rate of change of core roughness depth Rk on a sliding face of a cylinder calculated through a first sliding simulation is 35% or less, and the rate of change of reduced peak height Rpk on the sliding face is 20% or less. (First sliding simulation) · Calculate an initial core roughness depth Rk and an initial reduced peak height Rpk of the sliding face · Supply emulsified oil obtained by emulsifying lubricating oil having a moisture content of 8% to the sliding face · Set the actual contact pressure of the piston ring to 1.97 Mpa · Set the temperature of the sliding face to 20°C · Cause sliding between the cylinder and the piston at a rotational speed of 2000 r / min for 10 hours · Measure a post-sliding core roughness depth Rk (final core roughness depth Rk) of the sliding face, and calculate the rate of change of the post-sliding core roughness depth Rk relative to the initial core roughness depth Rk · Measure a post-sliding reduced peak height Rpk (final reduced peak height Rpk) of the sliding face, and calculate the rate of change of the post-sliding reduced peak height Rpk relative to the initial reduced peak height Rpk. The configuration described above provides a piston ring that makes it possible to achieve an optimal operating environment in, for example, an internal combustion engine in which hydrogen gas fuel or the like is used.

Description

Piston Ring, Sliding Structure of Cylinder and Piston Ring, Sliding Simulation Device for Internal Combustion Engine, Sliding Simulation Method

[0001] The present invention relates to a sliding structure of an internal combustion engine having a cylinder and a piston, etc.

[0002] In recent years, from the perspective of reducing environmental load, as a fuel for an internal combustion engine having a cylinder and a piston, hydrogen gas, or a fuel in which hydrogen gas is mixed with other fuels (hereinafter, these are collectively referred to as hydrogen gas fuel) is considered to be used. When hydrogen gas fuel is burned, water vapor is generated. For the purpose of suppressing the aggregation of this water vapor in the combustion chamber, a technique of not cooling the cylinder has also been studied (see Japanese Patent Application Laid-Open No. 2003-013765).

[0003] Further, when water vapor aggregates in the cylinder and becomes water, this water can affect the sliding state of the cylinder and the piston ring. A piston ring considering the influence of this water has also been studied (see International Publication WO2024 / 053065).

[0004] Regarding an internal combustion engine using hydrogen gas fuel, a sliding structure of a cylinder and a piston ring that can realize an optimal operating environment is required. Also, regarding an internal combustion engine using hydrogen gas fuel, it is required to evaluate how the water generated in the cylinder affects the sliding state of the cylinder and the piston ring.

[0005] In view of such circumstances, the present invention aims to provide a piston ring or the like that can realize an optimal operating environment in an internal combustion engine using hydrogen gas fuel.

[0006] The present invention, which achieves the above objective, is a piston ring used in an internal combustion engine using hydrogen gas fuel, characterized in that, as calculated by the following first sliding simulation, the rate of change of the core level difference Rk of the contour curve on the sliding surface of the cylinder that slides with the piston ring is 35% or less, and as calculated by the first sliding simulation, the rate of change of the protruding peak depth Rpk of the contour curve on the sliding surface is 20% or less. (First sliding simulation) - The sliding surface before the simulation is measured with a stylus-type surface roughness measuring instrument to calculate the core level difference Rk (initial core level difference Rk) and the protruding peak depth Rpk (initial protruding peak depth Rpk) of the contour curve. - Emulsified oil obtained by emulsifying lubricating oil with a water content of 8% is supplied to the sliding surface. - The actual surface pressure of the piston ring on the sliding surface is set to 1.97 MPa. - The temperature of the sliding surface is set to 20°C. - The cylinder and the piston are rotated at a speed of 2000 r / m - Slide the sliding surface at a speed of in for 10 hours. - Measure the core level difference Rk (final core level difference Rk) of the contour curve measured by a stylus-type surface roughness measuring instrument after 10 hours of sliding, and calculate the rate of change from the initial core level difference Rk. - Measure the protruding peak depth Rpk (final protruding peak depth Rpk) of the contour curve measured by a stylus-type surface roughness measuring instrument after 10 hours of sliding, and calculate the rate of change from the initial protruding peak depth Rpk.

[0007] In relation to the piston ring described above, the following second sliding simulation may be used to determine whether the rate of change of the core level difference Rk of the contour curve on the sliding surface of the cylinder that slides with the piston ring is 35% or less, and whether the rate of change of the protruding peak depth Rpk of the contour curve on the sliding surface is 20% or less. (Second sliding simulation) - Before the simulation, the sliding surface is measured using a stylus-type surface roughness measuring instrument to calculate the core level difference Rk (initial core level difference Rk) and the protruding peak depth Rpk (initial protruding peak depth Rpk) of the contour curve. - Emulsified oil, obtained by emulsifying lubricating oil with a water content of 10%, is supplied to the sliding surface. - The actual surface pressure of the piston ring on the sliding surface is set to 0.61 MPa. - The temperature of the sliding surface is set to 20°C. - The cylinder and the piston are rotated at a speed of 2000 r / - Slide the sliding surface at min speed for 10 hours. - Measure the core level difference Rk (final core level difference Rk) of the contour curve measured by a stylus-type surface roughness measuring instrument after 10 hours of sliding, and calculate the rate of change from the initial core level difference Rk. - Measure the protruding peak depth Rpk (final protruding peak depth Rpk) of the contour curve measured by a stylus-type surface roughness measuring instrument after 10 hours of sliding, and calculate the rate of change from the initial protruding peak depth Rpk.

[0008] In relation to the piston ring described above, the following third sliding simulation may be used to determine whether the rate of change of the core level difference Rk of the contour curve on the sliding surface of the cylinder that slides with the piston ring is 35% or less, and whether the rate of change of the protruding peak depth Rpk of the contour curve on the sliding surface is 20% or less. (Third sliding simulation) - Before the simulation, the sliding surface is measured using a stylus-type surface roughness measuring instrument to calculate the core level difference Rk (initial core level difference Rk) and the protruding peak depth Rpk (initial protruding peak depth Rpk) of the contour curve. - Emulsified oil, obtained by emulsifying lubricating oil with a water content of 4%, is supplied to the sliding surface. - The actual surface pressure of the piston ring on the sliding surface is set to 3.56 MPa. - The temperature of the sliding surface is set to 20°C. - The cylinder and the piston are rotated at a speed of 2000 r / m - Slide the sliding surface at a speed of in for 10 hours. - Measure the core level difference Rk (final core level difference Rk) of the contour curve measured by a stylus-type surface roughness measuring instrument after 10 hours of sliding, and calculate the rate of change from the initial core level difference Rk. - Measure the protruding peak depth Rpk (final protruding peak depth Rpk) of the contour curve measured by a stylus-type surface roughness measuring instrument after 10 hours of sliding, and calculate the rate of change from the initial protruding peak depth Rpk.

[0009] The present invention, which achieves the above objective, is a sliding structure for a cylinder and piston ring in an internal combustion engine using hydrogen gas fuel, characterized in that, as calculated by the following first sliding simulation, the rate of change of the core level difference Rk of the contour curve on the sliding surface between the cylinder and the piston ring is 35% or less, and as calculated by the first sliding simulation, the rate of change of the protruding peak depth Rpk of the contour curve on the sliding surface is 20% or less. (First sliding simulation) - Before the simulation, the sliding surface is measured with a stylus-type surface roughness measuring instrument to calculate the core level difference Rk (initial core level difference Rk) and the protruding peak depth Rpk (initial protruding peak depth Rpk) of the contour curve. - Emulsified oil obtained by emulsifying lubricating oil with a water content of 8% is supplied to the sliding surface. - The actual surface pressure of the piston ring on the sliding surface is set to 1.97 MPa. - The temperature of the sliding surface is set to 20°C. - The cylinder and piston ring are rotated at a speed of 2000 rpm. - Slide the sliding surface at a speed of / min for 10 hours. - Measure the core level difference Rk (final core level difference Rk) of the contour curve measured by a stylus-type surface roughness measuring instrument on the sliding surface after 10 hours of sliding, and calculate the rate of change from the initial core level difference Rk. - Measure the protruding peak depth Rpk (final protruding peak depth Rpk) of the contour curve measured by a stylus-type surface roughness measuring instrument on the sliding surface after 10 hours of sliding, and calculate the rate of change from the initial protruding peak depth Rpk.

[0010] In relation to the above sliding structure, the following second sliding simulation may be used to determine whether the rate of change of the core level difference Rk of the contour curve on the sliding surface between the cylinder and the piston ring is 35% or less, and whether the rate of change of the protruding peak depth Rpk of the contour curve on the sliding surface is 20% or less. (Second sliding simulation) - Before the simulation, the sliding surface is measured using a stylus-type surface roughness measuring instrument to calculate the core level difference Rk (initial core level difference Rk) and the protruding peak depth Rpk (initial protruding peak depth Rpk) of the contour curve. - Emulsified oil, obtained by emulsifying lubricating oil with a water content of 10%, is supplied to the sliding surface. - The actual surface pressure of the piston ring on the sliding surface is set to 0.61 MPa. - The temperature of the sliding surface is set to 20°C. - The cylinder and the piston ring are rotated at a speed of 2000 rpm. - Slide the sliding surface at a speed of / min for 10 hours. - Measure the core level difference Rk (final core level difference Rk) of the contour curve measured by a stylus-type surface roughness measuring instrument on the sliding surface after 10 hours of sliding, and calculate the rate of change from the initial core level difference Rk. - Measure the protruding peak depth Rpk (final protruding peak depth Rpk) of the contour curve measured by a stylus-type surface roughness measuring instrument on the sliding surface after 10 hours of sliding, and calculate the rate of change from the initial protruding peak depth Rpk.

[0011] In relation to the above sliding structure, the following third sliding simulation may be used to determine whether the rate of change of the core level difference Rk of the contour curve on the sliding surface between the cylinder and the piston ring is 35% or less, and whether the rate of change of the protruding peak depth Rpk of the contour curve on the sliding surface is 20% or less. (Third sliding simulation) - Before the simulation, the sliding surface is measured using a stylus-type surface roughness measuring instrument to calculate the core level difference Rk (initial core level difference Rk) and the protruding peak depth Rpk (initial protruding peak depth Rpk) of the contour curve. - Emulsified oil, obtained by emulsifying lubricating oil with a water content of 4%, is supplied to the sliding surface. - The actual surface pressure of the piston ring on the sliding surface is set to 3.56 MPa. - The temperature of the sliding surface is set to 20°C. - The cylinder and the piston ring are rotated at a speed of 2000 rpm. - Slide the sliding surface at a speed of / min for 10 hours. - Measure the core level difference Rk (final core level difference Rk) of the contour curve measured by a stylus-type surface roughness measuring instrument on the sliding surface after 10 hours of sliding, and calculate the rate of change from the initial core level difference Rk. - Measure the protruding peak depth Rpk (final protruding peak depth Rpk) of the contour curve measured by a stylus-type surface roughness measuring instrument on the sliding surface after 10 hours of sliding, and calculate the rate of change from the initial protruding peak depth Rpk.

[0012] To achieve the above objective, the present invention is a sliding simulation device for simulating the sliding motion of a piston ring and a cylinder for an internal combustion engine, comprising: a ring holding mechanism for holding the piston ring to be simulated; a cylinder holding mechanism for holding the cylinder to be simulated; a relative movement device for sliding the piston ring and the cylinder by moving the ring holding mechanism and the cylinder holding mechanism relative to each other; and an emulsified oil supply device for supplying an emulsified oil, obtained by mixing at least lubricating oil and water, to the sliding parts of the piston ring and the cylinder.

[0013] In relation to the above-described sliding simulation apparatus, the piston ring held by the ring holding mechanism is ring-shaped with a joint, the cylinder held by the cylinder holding mechanism has a perfectly cylindrical inner wall surface, and the relative movement mechanism is characterized by causing the entire outer surface of the piston ring and the inner wall surface to slide against each other.

[0014] In relation to the above-mentioned sliding simulation apparatus, the ring holding mechanism may be characterized by having a tension application mechanism for applying tension to the piston ring.

[0015] In relation to the above-described sliding simulation apparatus, the emulsified oil supply device may be characterized by having a nozzle that sprays the emulsified liquid in a cone shape toward the inner wall surface of the cylinder.

[0016] In relation to the above-mentioned sliding simulation apparatus, the emulsified oil supply apparatus may be characterized by having a tank for storing the emulsified oil and a temperature control heater for adjusting the temperature of the emulsified oil.

[0017] The above-described sliding simulation device may be characterized by being equipped with a temperature control unit for adjusting the temperature of the cylinder.

[0018] To achieve the above objective, the present invention is a sliding simulation method for simulating the sliding motion of a piston ring and a cylinder for an internal combustion engine, characterized in that the piston ring and the cylinder to be simulated are moved relative to each other, and an emulsified oil, obtained by mixing at least lubricating oil and water, is supplied to the sliding parts of the piston ring and the cylinder.

[0019] In relation to the above-described sliding simulation method, the piston ring may be ring-shaped with a gap, the cylinder may have a completely cylindrical inner wall surface, and the entire outer surface of the piston ring may slide against the inner wall surface.

[0020] In relation to the above-described sliding simulation method, the method may be characterized by supplying multiple types of emulsified oils with different mixing ratios of lubricating oil and water to the sliding parts of the piston ring and the cylinder at different timings.

[0021] In relation to the above-described sliding simulation method, the emulsified oil may be characterized by being sprayed in a mist form onto the sliding parts of the piston ring and the cylinder.

[0022] In relation to the above-described sliding simulation method, it may be characterized by adjusting the temperature of the inner wall surface of the cylinder to be constant.

[0023] In relation to the above-described sliding simulation method, the method may be characterized by adjusting the temperature of the inner wall surface to 30 degrees Celsius or less.

[0024] According to the present invention, it is possible to provide piston rings and the like that can realize an optimal operating environment in an internal combustion engine using, for example, hydrogen gas fuel.

[0025] (A) is a cross-sectional view along the axial direction of the cylinder liner and piston ring of an internal combustion engine according to an embodiment of the present invention, (B) is a partially enlarged cross-sectional view showing the piston ring, (C) is a partially enlarged cross-sectional view of the top ring, and (D) is a partially enlarged cross-sectional view of the second ring. (A) is a cross-sectional view of a two-piece type oil ring, and (B) is a cross-sectional view of a three-piece type oil ring. This is a partially cross-sectional view along the axial direction of a sliding simulation device that simulates the sliding state of the cylinder liner and piston ring. (A) is a plan view of the sliding simulation device, and (B) is an end view taken along the line III-III in Figure 3. This is a Stribeck diagram relating to the sliding of an internal combustion engine. This is a chart showing the degree of influence of the piston ring on the inner wall surface of the cylinder liner simulated by the sliding simulation device. This is a diagram showing the sliding marks on the inner wall surface of the cylinder liner simulated for 10 hours using only lubricating oil with the sliding simulation device. This is a diagram showing the sliding marks on the inner wall surface of the cylinder liner simulated for 10 hours using 2% water-containing emulsified oil with the sliding simulation device. This figure shows the sliding marks on the inner wall surface of a cylinder liner simulated for 10 hours using an emulsified oil containing 4% water with the same sliding simulation device. This figure shows the sliding marks on the inner wall surface of a cylinder liner simulated for 10 hours using an emulsified oil containing 6% water with the same sliding simulation device. This figure shows the sliding marks on the inner wall surface of a cylinder liner simulated for 10 hours using an emulsified oil containing 8% water with the same sliding simulation device. This figure shows the sliding marks on the inner wall surface of a cylinder liner simulated for 10 hours using an emulsified oil containing 10% water with the same sliding simulation device. This figure shows the sliding marks on the inner wall surface of a cylinder liner simulated for 10 hours using an emulsified oil containing 8% water with the same sliding simulation device. This figure shows the sliding marks on the inner wall surface of a cylinder liner simulated for 20 hours using an emulsified oil containing 8% water with the same sliding simulation device. This figure shows the sliding marks on the inner wall surface of a cylinder liner simulated for 30 hours using an emulsified oil containing 8% water with the same sliding simulation device. This figure shows the sliding marks on the inner wall surface of a cylinder liner simulated for 40 hours using the same sliding simulation device with an emulsified oil containing 8% water.This figure shows the sliding marks on the inner wall surface of a cylinder liner simulated for 50 hours using the same sliding simulation device with an emulsified oil containing 8% water. This is a graph of the surface roughness of the inner wall surface of a cylinder liner simulated using the same sliding simulation device. This is a partial cross-sectional view showing a modified example of the same sliding simulation device.

[0026] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. First, the cylinder liner and piston ring of an internal combustion engine according to an embodiment of the present invention will be described.

[0027] <Cylinder Liner and Piston Ring>

[0028] As shown in Figure 1, the cylinder 10 of the internal combustion engine in the first embodiment is cylindrical in shape. The piston 30 reciprocates axially along the cylindrical inner wall surface (sliding surface) 12 of the cylinder 10. The piston 30 reciprocates within the range from top dead center to bottom dead center. Therefore, when multiple piston rings 40 are set on the piston 30, each piston ring 40 also reciprocates within the range from top dead center to bottom dead center. Note that this cylinder 10 is a concept that includes the cylinder liner as a component, the cylinder portion in the engine block, etc.

[0029] The inner wall surface 12 of the cylinder 10 is formed by honing using a honing machine. In this process, it is preferable to use a finer abrasive grain (JIS R 6001-2:2017, ISO8486-2:2007) than, for example, F500 or #800 for the honing wheel.

[0030] Furthermore, after this honing process, the surface can be treated with a chemical conversion coating. For example, a phosphate coating can be applied.

[0031] It is preferable to set the core level difference Rk (initial core level difference Rk) (JIS B0671-2:2002) of the inner wall surface 12 before the sliding simulation described later to within the range of 0.2 to 0.8 μm. It is also preferable to set the protruding peak depth Rpk (initial protruding peak depth Rpk) (JIS B0671-2:2002) of the inner wall surface 12 to within the range of 0.05 to 0.25 μm. These values ​​are measured along the circumferential direction of the inner wall surface 12 using a non-contact cylinder inner circumference measuring instrument (JIS B 0633:2001). Five arbitrary positions are randomly selected as measurement locations. The cutoff value (wavelength) λs for the cross-sectional curve is selected to 0.8 μm for measurement.

[0032] <Pistons and piston rings>

[0033] Figure 1(B) shows a magnified view of the piston 30 and the piston rings 40 (top ring 50, second ring 60, oil ring 70) installed in the ring groove of the piston 30. The piston rings 40 reciprocate in the cylinder axial direction with their outer circumferential surface 42 facing the inner wall surface 12 of the cylinder 10. The top ring 50 eliminates the gap between the piston 30 and the cylinder 10, preventing the phenomenon of compressed gas leaking from the combustion chamber to the crankcase (blow-by). The second ring 60, like the top ring 50, serves to eliminate the gap between the piston 30 and the cylinder 10 and also scrapes off excess engine oil adhering to the inner wall surface 12 of the cylinder 10. The oil ring 70 scrapes off excess engine oil adhering to the inner wall surface 12 of the cylinder 10, forming an appropriate oil film and preventing the piston 30 from seizing. Furthermore, in the piston ring 40, the top ring 50 and the second ring 60, excluding the oil ring 70, can be referred to as compression rings.

[0034] As shown in an enlarged view in Figure 1(C), the top ring 50 is a single annular member, and when viewed in cross-section, the outer circumferential surface 52 has a so-called barrel shape that is convex radially outward. Specifically, both outer edges of the outer circumferential surface 52 in the cylinder axial direction are inclined toward the outside in the cylinder axial direction, away from the inner wall surface 12. The contact width f of the outer circumferential surface 52 with respect to the inner wall surface 12 of the cylinder 10 is preferably formed to be, for example, 0.15 mm or less. Furthermore, it is preferable that the surface roughness of the outer circumferential surface 52, as measured by a stylus-type surface roughness measuring instrument (JIS B 0651:2001) (arithmetic mean roughness Ra of the contour curve (JIS B 0601:2013)), is 0.1 (μm) or less.

[0035] As shown in an enlarged view in Figure 1(D), the second ring 60 is a single annular member, and its outer circumference has a tapered shape that widens in diameter from, for example, the upper end in the cylinder axial direction towards the lower end in the cylinder axial direction. The outer peripheral surface 62, located at the outermost end of this tapered shape and in contact with the inner wall surface 12 of the cylinder 10, has a planar shape in cross-sectional view. The contact width f of the outer peripheral surface 62 with respect to the inner wall surface 12 of the cylinder 10 is preferably formed to be, for example, 0.3 mm or less. Furthermore, it is preferable that the surface roughness of the outer peripheral surface 62, as measured by a stylus-type surface roughness measuring instrument (JIS B 0651:2001), (arithmetic mean roughness Ra of the contour curve (JIS B 0601:2013)) is 0.1 (μm) or less.

[0036] Furthermore, when installed in an internal combustion engine (actual machine) using hydrogen gas fuel, the surface pressure acting on the contact surfaces of the outer circumferential surfaces 52 and 62 of the top ring 50 and second ring 60 will be, for example, 0.24 to 1.98 MPa. It is desirable that the top ring 50 and second ring 60 slide in the fluid lubrication region as much as possible, except near the top dead center and bottom dead center.

[0037] The oil ring 70, shown in an enlarged view in Figure 2(A), is a two-piece type and comprises a ring body 72 and a coil spring-shaped coil expander 76. The ring body 72 has a pair of annular rails 73, 73 positioned at both axial ends and an annular column 75 positioned between the pair of rails 73, 73 and connecting them. The combined cross-sectional shape of the pair of rails 73, 73 and the column 75 is approximately I-shaped or H-shaped, and this shape is used to form an inner circumferential groove 79 with a semicircular cross-section for housing the coil expander 76 on the inner circumferential surface. In addition, annular projections 74, 74 are formed on the pair of rails 73, 73, respectively, projecting radially outward with respect to the column 75. The outer circumferential surfaces 82, 82 formed at the ends of these annular projections 74, 74 abut against the inner wall surface 12 of the cylinder 10. The coil expander 76, when housed in the inner circumferential groove 79, biases the ring body 72 radially outward. Furthermore, multiple oil return holes 77 are formed in the circumferential direction in the column portion 75 of the ring body 72.

[0038] The contact width of each of the pair of outer peripheral surfaces 82, 82 in Figure 2(A) is preferably formed to be 0.08 to 0.2 mm, and is set to, for example, 0.15 mm. When installed in an internal combustion engine (actual machine) using hydrogen gas fuel, the surface pressure acting on the contact surface of the outer peripheral surface 82 of the oil ring 70 is, for example, 1.0 MPa to 2.0 MPa, and is approximately 1.75 MPa. Therefore, when the engine speed is high, the oil ring 70 often slides in the fluid lubrication region, but when the engine speed decreases, it often slides in the boundary lubrication region. In Figure 2(A), the radial cross-sectional shape of the outer peripheral surfaces 82, 82 is illustrated as a simple trapezoid, but the present invention is not limited to this, and the outer peripheral surfaces 82 of the upper rail 73 and the outer peripheral surfaces 82 of the lower rail 73 may have a stepped shape in which the corners on the sides facing each other (coil expander 76 side) are cut out (a so-called step land shape). Furthermore, it is preferable that the outer surface 82 has a surface roughness (arithmetic mean roughness Ra of the contour curve (JIS B 0601:2013)) of 0.3 (μm) or less, as measured by a stylus-type surface roughness measuring instrument (JIS B 0651:2001).

[0039] Note that the oil ring 70 is not limited to a two-piece type; for example, it may be a three-piece type oil ring 70 as shown in Figure 2(B). This oil ring 70 has annular side rails 73a and 73b that are separated vertically, and a spacer expander 76s positioned between these side rails 73a and 73b.

[0040] The spacer expander 76s is formed by plastically deforming a steel material into a corrugated shape with repeated ridges and depressions in the direction of the cylinder axis. This corrugated shape is used to form an upper support surface 78a and a lower support surface 78b, which support a pair of side rails 73a and 73b in the axial direction. The inner circumferential end of the spacer expander 76s has an arch-shaped lug 74m that extends outward in the axial direction. This lug 74m contacts the inner circumferential surfaces of the side rails 73a and 73b. The spacer expander 76s is then assembled into the ring groove of the piston 30 in a contracted state in the circumferential direction with its joints facing each other. As a result, the restoring force of the spacer expander 76s causes the lug 74m to press and bias the side rails 73a and 73b radially outward.

[0041] Furthermore, it is preferable that the contact width of each of the outer peripheral surfaces 82, 82 of the side rails 73a, 73b in Figure 2(B) be formed to be 0.02 mm to 0.40 mm.

[0042] <Surface characteristics of the actual contact surface of the piston ring> Next, the surface characteristics of the actual contact surface of the piston ring 40 will be described. In this embodiment, the "degree of frictional influence on the inner wall surface (sliding surface) 12 of the cylinder 10 (hereinafter referred to as the degree of frictional influence on the cylinder)" is used as an indicator of these surface characteristics. Specifically, the degree of frictional influence on the cylinder is calculated by a sliding simulation described later. Specifically, the rate of change of the core level difference Rk of the contour curve on the sliding surface of the cylinder 10 that slides with the piston ring 40 and the rate of change of the protruding peak depth Rpk are adopted. If the rate of change of the core level difference Rk is small even after the sliding simulation, it means that the basic shape of the unevenness of the inner wall surface 12 is small. Also, if the rate of change of the protruding peak depth Rpk is small even after the sliding simulation, it means that the shape of the protruding tips of the unevenness on the inner wall surface 12 is small.

[0043] As a result, in the combination of "the change rate (decrease rate) of the core part level difference Rk" and "the change rate (decrease rate) of the protruding peak depth Rp", when the change rates (decrease rates) of both are small, even if it is a lubricating oil (emulsified oil) containing moisture, the required lubricating function is appropriately exerted, and the wear amount of the unevenness on the inner wall surface 12 is small. On the other hand, when the change rates of both are large, the lubricating function by the lubricating oil (emulsified oil) containing moisture is insufficient, and the wear amount of the unevenness on the inner wall surface 12 is large. When the wear amount of the unevenness on the inner wall surface 12 of the cylinder 10 is large, some problems are likely to occur during the operation of an internal combustion engine using hydrogen gas fuel. Hereinafter, the sliding simulation will be described in detail.

[0044] (Sliding simulation device) First, a sliding simulation device 500 for simulating the friction mode of an internal combustion engine will be described in detail. In the present embodiment, an example of simulating the sliding situation of an internal combustion engine using hydrogen gas fuel is illustrated, but the present invention is not limited to this, and it is also applicable to the simulation of other types of internal combustion engines that can generate water vapor or water by combustion.

[0045] As shown in FIG. 3, the sliding simulation device 500 fixes the cylinder 10 side and moves the piston ring 40 side in the vertical direction to create a sliding state between the two. The simulation of this sliding state is a friction simulation (friction simulation during non-combustion) in a state where combustion as an internal combustion engine does not occur.

[0046] The sliding simulation device 500 includes a base 502, a cylinder holding mechanism 510, a ring holding mechanism 600, a relative movement device 700, an emulsified oil supply device 800, a temperature adjustment unit 900, and a control device 980 that serves as a computer.

[0047] (Ring Holding Mechanism) The ring holding mechanism 600 holds the piston ring 40 (at least one of the top ring, the second ring, and the oil ring) to be simulated. The ring holding mechanism 600 includes a virtual piston 610 that is a cylindrical member, a ring holding groove 614 provided on the circumferential surface of the virtual piston 610 and serving as a circumferential groove or slit into which the piston ring 40 is inserted, and a tension applying mechanism 650 disposed in the accommodation space 616 of the virtual piston 610.

[0048] The virtual piston 610 includes a disk-shaped first piston piece 610A disposed on the upper side and a disk-shaped second piston piece 610B disposed on the lower side, and they are fixed to each other by bolts 611. When the first piston piece 610A and the second piston piece 610B are fixed to each other, an annular gap is formed in the vicinity of the peripheral edges facing each other, and this becomes the ring holding groove 614. Further, an accommodation space 616 that is an annular or disk-shaped space is formed inside the virtual piston 610. This accommodation space 616 is continuous (communicates) with the radially inner side of the ring holding groove 614.

[0049] As shown enlarged in FIG. 4(B), the tension applying mechanism 650 disposed in the accommodation space 616 includes an inner support portion 652 and a pressing mechanism 656 that presses the inner support portion 652 radially outward. The inner support portion 652 is a ring-shaped or partial arc-shaped member and is movable radially while supporting the inner circumferential surface side of the piston ring 40. Here, four partial arc-shaped inner support portions 652 are disposed in the accommodation space 616. The pressing mechanism 656 is a compression spring and is disposed in the accommodation space 616 to bias the inner support portion 652 radially outward. As a result, indirectly, the piston ring 40 is biased radially outward to generate a desired surface pressure (tension). Note that the piston ring 40 is not a partial arc piece dedicated for testing but has a ring shape excluding the joint 40A.

[0050] The surface pressure that can be applied between the piston ring 40 and the cylinder 10 by the tension application mechanism 650 is preferably 0.2 MPa or more, more preferably 0.5 MPa or more, and even more preferably 0.8 MPa or more. In this way, by setting the surface pressure and tension of the piston ring 40 to a large level by the tension application mechanism 650, a more severe sliding environment can be simulated.

[0051] In this embodiment, the example of a pressing mechanism 656 is shown as one in which the inner support portion 652 is biased by a spring. However, any structure or mechanism other than a spring can be used as long as it can generate a force directed radially outward. Furthermore, in the case of a piston ring 40 that incorporates a tension biasing mechanism such as a coil expander 76, as shown in Figure 2, the coil expander 76 may be omitted and the desired tension may be applied by the tension application mechanism 650. Alternatively, the function of the tension application mechanism 650 may be omitted by fixing or omitting the inner support portion 652 while employing the coil expander 76.

[0052] In this embodiment, the case in which the ring holding groove 614 holds a single ring is illustrated, but the present invention is not limited thereto, and may simultaneously hold multiple rings arbitrarily selected from the top ring, second ring, and oil ring. In this case, multiple virtual pistons 610 may be stacked.

[0053] (Cylinder Holding Mechanism) Returning to Figure 3, the cylinder holding mechanism 510 holds the cylindrical cylinder 10 that is the subject of the simulation. Note that the cylinder 10 is not a partially arced cylinder for testing purposes, but one that has a complete cylindrical inner wall surface 12. The cylinder holding mechanism 510 has a holder 520, a ring-shaped first lid portion 530 positioned above the holder 520, and a ring-shaped second lid portion 540 positioned below the holder 520.

[0054] The holder 520 has a cylindrical structure, with a ring-shaped first diameter-reducing portion 524A formed on one axial side (upper side) of the cylindrical inner circumferential surface 522, and a ring-shaped second diameter-reducing portion 524B formed on the other axial side (lower side) of the inner circumferential surface 522. The first diameter-reducing portion 524A and the second diameter-reducing portion 524B are reduced in diameter radially inward relative to the inner circumferential surface 522. The annular inner end faces 526A and 526B of the first diameter-reducing portion 524A and the second diameter-reducing portion 524B support the outer wall surface 13 of the cylinder 10. As a result, a gap is formed between the inner circumferential surface 522 of the holder 520 and the outer wall surface 13 of the cylinder 10, and this gap becomes the temperature control space 910 of the temperature control unit 900, which will be described later, and functions as a temperature control jacket.

[0055] The holder 520 is fixed to the base 502 via a jig 570 and a load cell 575. The jig 570 is bolted to the holder 520. The load cell 575 measures the axial external force acting on the cylinder 10 (axial frictional force between the cylinder 10 and the piston ring 40).

[0056] The ring-shaped first cover portion 530 is fixed to the first axial end face 520A on one axial side (upper side) of the holder 520 by bolts 535. The first cover portion 530 has a first ring-shaped step 533 that extends axially toward the cylinder 10 near its inner periphery. The end of the cylinder 10 on one axial side (upper side) is sandwiched between this first ring-shaped step 533 and the first reduced diameter portion 524A of the holder 520. More specifically, the first cover portion 530 has an axial support surface 532 facing the first axial end face 520A of the holder 520, and a ring-shaped radial inner support surface 534 formed on the first ring-shaped step 533. The axial support surface 532 engages with the end face of the cylinder 10, thereby restricting the axial movement of the cylinder 10. The radially inner support surface 534 engages with the inner circumferential surface 12 of the cylinder 10, thereby restricting the radial movement of the cylinder 10. An annular housing groove for accommodating a rubber-like seal ring 537 is formed on the axial support surface 532. The liquid-tight performance of the temperature control space 910 is ensured when the seal ring 537 is sandwiched between the first lid portion 530 and the holder 520. An annular housing groove for accommodating a rubber-like seal ring 539 is formed on the radially inner support surface 534. The liquid-tight performance of the temperature control space 910 is ensured when the seal ring 539 is sandwiched between the first lid portion 530 and the cylinder 10.

[0057] The ring-shaped second cover portion 540 is fixed by bolts 545 to the second axial end face 520B on the other axial side (lower side) of the holder 520. The second cover portion 540 has a second ring-shaped step 543 that extends axially toward the cylinder 10 near its inner periphery. The other axial side (lower side) end of the cylinder 10 is sandwiched between this second ring-shaped step 543 and the second reduced diameter portion 524B of the holder 520. More specifically, the second cover portion 540 has an axial support surface 542 facing the second axial end face 520B of the holder 520, and a ring-shaped radially inner support surface 544 formed on the first ring-shaped step 543. The axial support surface 542 engages with the end face of the cylinder 10, thereby restricting the axial movement of the cylinder 10. The radially inner support surface 544 engages with the inner circumferential surface 12 of the cylinder 10, thereby restricting the radial movement of the cylinder 10. An annular housing groove for accommodating a rubber-like seal ring 547 is formed on the axial support surface 542. The liquid-tight performance of the temperature control space 910 is ensured when the seal ring 547 is sandwiched between the second lid portion 540 and the holder 520. An annular housing groove for accommodating a rubber-like seal ring 549 is formed on the radially inner support surface 544. The liquid-tight performance of the temperature control space 910 is ensured when the seal ring 549 is sandwiched between the second lid portion 540 and the cylinder 10.

[0058] (Relative Movement Device) The relative movement device 700 includes a linear slider 710 connected to the virtual piston 510 and performing linear reciprocating motion, a connecting rod 720 connected to the linear slider 710, a crankshaft 730 to which the connecting rod is connected, and a rotational drive source 740 such as a motor that rotates the crankshaft 730. When the crankshaft 730 is rotated by the rotational drive source 740, the connecting rod 720 oscillates due to the crank mechanism, and the linear slider 710 reciprocates in a linear direction. As a result, the virtual piston 510 reciprocates in the axial direction (up and down direction). Here, a crosshead method is adopted by interposing the linear slider 710 to prevent external force from being applied to the virtual piston 510 in the direction perpendicular to the rod axis of the connecting rod 720 (lateral direction). As a result, only the axial sliding component can be accurately simulated.

[0059] The crankshaft 730 is designed to allow adjustment of the eccentricity of the connecting rod 720, thereby enabling flexible changes to the stroke of the virtual piston 510.

[0060] In the relative movement device 700, it is preferable that the rotational speed of the rotational drive source 740 can be freely adjusted within a range including, for example, at least 500 rpm to 1500 rpm. Preferably, it can be freely adjusted within a range including at least 300 rpm to 2000 rpm. Similarly, in the relative movement device 700, it is preferable that the stroke of the relative movement between the cylinder 10 and the piston ring 40 can be freely adjusted within a range including, for example, at least 10 mm to 20 mm, and preferably within a range including 5 mm to 30 mm. In fact, in this embodiment, it is possible to set it within a range of 500 rpm, stroke 5 mm to 2000 rpm, stroke 30 mm. Furthermore, in the relative movement device 700, it is preferable that the maximum value of the relative movement speed between the cylinder 10 and the piston ring 40 (relative movement speed at the midpoint of the stroke) can be freely adjusted within a range including, for example, at least 0.08 to 2.0 m / sec. The control device 980 can adjust the maximum value of the relative moving speed, etc., by controlling the rotational speed of the rotational drive source 740. In doing so, the control device 980 also refers to the setting information of the eccentricity amount.

[0061] Here, we have illustrated a case where the cylinder holding mechanism 510 is fixed to the base 502 and the relative movement device 700 moves the virtual piston 510 up and down. However, the present invention is not limited to this, and the virtual piston 510 can also be fixed to the base 502 and the cylinder holding mechanism 510 can be moved up and down.

[0062] (Temperature Control Unit) The temperature control unit 900 includes a pair of pipes 920 connected to the temperature control space 910 and a temperature control device 940 connected to the pipes 920. A liquid medium such as water circulates in the temperature control space 910 and the pipes 920. The temperature control device 940 is a so-called chiller and can freely adjust the temperature of the circulating liquid medium. A temperature sensor (not shown) is installed on the inner wall surface 12 of the cylinder 10, and the temperature control unit 900 refers to the information from this temperature sensor and provides feedback adjustment to the temperature of the liquid medium so that the temperature of the inner wall surface 12 reaches a predetermined temperature. This adjustment control can also be performed by the control device 980. The temperature control range preferably includes at least a range of 0°C to 80°C, and more preferably at least a range of -10°C to 120°C. In particular, by controlling the temperature of the inner wall surface 12 within a range of 30°C or less, it is possible to simulate a harsh environment for the emulsified oil described later.

[0063] (Emulsified Oil Supply Device) The emulsified oil supply device 800 includes a plurality of (in this case, six) tanks 810A to 810F for storing a liquid (hereinafter referred to as emulsified oil) obtained by mixing lubricating oil and water in a desired ratio, a nozzle 820 from which the emulsified oil is discharged, branch pipes 830A to 830F each belonging to tanks 810A to 810F, an integrated pipe 832 connecting the confluence point of the branch pipes 830A to 830F to the nozzle 820, a liquid pump 840 installed in the middle of the integrated pipe 832 for supplying the emulsified oil, a flow control valve 842 and a flow meter 844 installed in the middle of the integrated pipe 830, six on-off valves 846A to 846F installed in each of the branch pipes, and temperature control heaters 850A to 850F installed in tanks 810A to 810F.

[0064] Tanks 810A to 810F store, for example, different types of emulsified oil. These different types of emulsified oil include, for example, emulsified oil with different mixing ratios of lubricating oil and water, emulsified oil mixed with a third material (for example, foreign matter such as metal powder) in addition to lubricating oil and water, emulsified oil with different types of lubricating oil, and emulsified oil at different temperatures.

[0065] The nozzle 820 is fixedly positioned on one axial side (upper side) of the cylinder 10 or virtual piston 610. The nozzle 820 is, for example, a spray nozzle that discharges emulsified oil as a mist in a conical shape. By aligning the central axis of the nozzle 820 when spraying in a conical shape with the central axis of the cylinder 10, the emulsified oil is uniformly sprayed over the entire circumferential surface of the inner wall surface 12 of the cylinder 10.

[0066] The control device 980 controls the amount of emulsified oil supplied to the nozzle 820 by controlling the flow control valve 842 or the liquid supply pump 840 based on the measurement results of the flow meter 844. The control device 980 also selectively opens and closes the on / off valves 846A to 846F to supply the desired emulsified oil from one or more tanks 810A to 810F. The control device 890 can continuously supply different types of emulsified oil by sequentially switching between tanks 810A to 810F, for example, based on a timing chart.

[0067] Although this example illustrates a case where the type of emulsified oil is switched using multiple tanks 810A to 810F, the present invention is not limited to this, and simulations can also be performed by storing a specific emulsified oil in a single tank.

[0068] (Control device) The control device 980 is a computer equipped with a CPU, memory, etc., and controls the entire sliding simulation device 500 to perform sliding simulations by executing a sliding simulation program.

[0069] (Friction patterns between cylinder liner and piston ring) Next, the friction patterns between the cylinder liner and piston ring will be explained. The change in the coefficient of friction during general sliding is represented by the Stribeck diagram shown in Figure 5. In this Stribeck diagram, the friction patterns are divided into the solid contact region 110 where sliding occurs in direct contact, the boundary lubrication region 112 where sliding occurs via an oil film, and the fluid lubrication region 114 where sliding occurs via a viscous lubricating oil film. In addition, between the boundary lubrication region 112 and the fluid lubrication region 114, there is a mixed lubrication region 113 where both states coexist. In this Stribeck diagram, the horizontal axis is a logarithmic representation of "viscosity μ" × "velocity Q" / "contact load W", and the vertical axis is the coefficient of friction (f). Therefore, the area where frictional force can be minimized is the fluid lubrication region 114 or the mixed lubrication region 113. Effectively utilizing these regions 114 and 113 is effective in reducing friction, i.e., avoiding abnormal wear of the cylinder liner. On the other hand, if the transition from the boundary lubrication region 112 to the fluid lubrication region 114 is not possible even as the speed Q increases, the boundary lubrication region 112 will continue as is up to the high-speed region, as shown by the dotted line, resulting in a state where the cylinder liner is prone to wear.

[0070] In the reciprocating motion of the piston, near the top dead center and bottom dead center, the relative velocity Q between the cylinder 10 and the piston ring 40 decreases, making it easy to transition to the boundary lubrication region 112. If insufficient lubrication occurs in the boundary lubrication region 112, the cylinder 10 and the piston ring 40 come into contact, forming a solid contact region 110, causing wear on the cylinder 10 and the formation of wear marks.

[0071] Incidentally, the majority of the frictional force in the fluid lubrication region 114 is due to the shear resistance of the oil, which is defined as (viscosity) × (velocity) × (area) / (oil film thickness). As a result, reducing the shear area directly leads to a reduction in frictional force.

[0072] In the case of an internal combustion engine that burns hydrogen gas fuel, water vapor is generated during combustion, and this water vapor condenses on the inner wall surface of the cylinder liner to form water. This water mixes with the lubricating oil and is agitated and emulsified by the continuous sliding of the cylinder and piston rings, so the lubricating oil stored in the oil pan changes into emulsified oil over time. Furthermore, as the operating time of the internal combustion engine increases, the water content ratio in the emulsified oil stored in the oil pan also gradually increases. In other words, during the operation of an internal combustion engine using hydrogen gas fuel, emulsified oil, not lubricating oil, is supplied from the oil pan to the space between the cylinder and piston rings. Compared to the original lubricating oil, the lubricating function of emulsified oil is reduced, so it is presumed that the solid contact region 110 and boundary lubrication region 112 in Figure 5 expand to the right in the horizontal direction, and the mixed lubrication region 113 and fluid lubrication region 114 become relatively narrower.

[0073] In the sliding simulation device 500 of this embodiment, water and lubricating oil are mixed to pre-generate an emulsified oil, which is then supplied to the inner wall surface of the cylinder. Furthermore, the inner wall surface 12 of the cylinder 10 to be evaluated is made into a perfect cylindrical shape (i.e., not a partial arc), and the entire circumferential surface of the ring-shaped piston ring 40, excluding the joint 40A, is brought into contact with the inner wall surface 12 to approximate the actual operating environment of an internal combustion engine. In this way, by simulating using a perfectly cylindrical sliding area that becomes part of the inner wall surface 12, even a change of a few percent in the water content ratio of the emulsified oil can be reflected in the change in the surface properties of the sliding area. As a result, the sliding simulation device 500 of this embodiment can accurately simulate the wear condition of the cylinder 10 and piston ring 40 in an internal combustion engine burning hydrogen gas fuel, according to the purpose. By using the simulated cylinder and piston ring to evaluate minute changes in the surface roughness of the sliding surface and minute fluctuations in the frictional force during simulation, it becomes possible to objectively analyze the effect of the emulsified oil during combustion.

[0074] <First Sliding Simulation> The first sliding simulation using the sliding simulation device 500 will be explained, including the procedure.

[0075] (Initial Measurement) The inner wall surface 12 of the cylinder 10 to be evaluated is measured along the circumferential direction using a non-contact cylinder circumference measuring instrument (JIS B 0633:2001) within its sliding range. Five arbitrary positions are randomly selected as measurement locations. The cutoff value (wavelength) λs for the cross-sectional curve is set to 0.8 μm for measurement. From the measured cross-sectional curve, the core level difference Rk, the protruding peak depth Rpk, and the protruding valley depth Rvk (JIS B 0671-2:2002) are calculated. These values ​​are defined as "initial core level difference Rk," "initial protruding peak depth Rpk," and "initial protruding valley depth Rvk."

[0076] Furthermore, in order to improve the accuracy of the sliding simulation, the initial core level difference Rk is preferably set to 0.8 μm or less, and more preferably to 0.2 μm or more. Similarly, the initial protruding peak depth Rpk is preferably set to 0.25 μm or less, and more preferably to 0.05 μm or more.

[0077] (Preparation for simulation) Next, the cylinder 10 and piston ring 40 to be evaluated are placed in the sliding simulation device 500. At this time, the spring of the tension application mechanism 650 is adjusted so that the actual surface pressure on the actual contact surface of the piston ring 40 is 1.0 MPa or more. In the first sliding simulation, it is specifically set to 1.97 MPa.

[0078] The piston rings 40 are actual (or equivalent) parts used in an actual internal combustion engine employing hydrogen gas fuel. For accuracy, the cylinder 10 is a cylinder section cut from the engine block of an actual internal combustion engine employing hydrogen gas fuel. The stroke of the virtual piston 610 is set to, for example, a range of 5 mm to 30 mm, and is set to 15 mm.

[0079] For simulation purposes, an evaluation emulsion oil containing 8% water relative to the total amount of emulsion oil is prepared as a lubricating oil and emulsifying oil. The emulsion oil is produced by stirring lubricating oil (SAE standard 0W-20 viscosity) and pure water using a homogenizer. This evaluation emulsion oil is stored in six tanks 810A to 810F. The control device 980 controls the temperature control heaters 850A to 850F to control the evaluation emulsion oil in tanks 810A to 810F to a predetermined temperature (e.g., 20°C).

[0080] The control device 980 controls the temperature control unit 900 so that the inner wall surface 12 of the cylinder 10 is, for example, 20°C. By setting the temperature of the emulsified oil and / or the inner wall surface 12 to a low level in this way, the lubrication function of the emulsified oil is simulated under more stringent conditions.

[0081] (Simulation execution) The control device 980 controls the rotational drive source 740 of the relative movement device 700 to operate at a predetermined rotational speed (in this case, 2000 rpm), causing the virtual piston 610 to reciprocate. As a result, the maximum relative speed between the piston ring 40 and the cylinder 10 becomes 1.0 m / sec. Simultaneously with the operation of the relative movement device 700, the emulsified oil supply device 800 continuously supplies only the standard lubricating oil. This is operated continuously for 10 hours.

[0082] (Final measurement)

[0083] After the simulation is complete, the core level difference Rk, the protruding peak depth Rpk, and the protruding valley depth Rvk (JIS B 0671-2:2002) are measured within the sliding range of the inner wall surface 12 of the cylinder 10 under the same conditions as the initial measurement. These values ​​are defined as "final core level difference Rk," "final protruding peak depth Rpk," and "final protruding valley depth Rvk."

[0084] (Calculation of frictional impact on the cylinder) The difference value △Rk (absolute value) between the "initial core level difference Rk" and the "final core level difference Rk" is calculated, and the ratio (%) of the difference value △Rk to the initial core level difference Rk is defined as the "rate of change of core level difference Rk". In addition, the difference value △Rpk (absolute value) between the "initial protruding peak depth Rpk" and the "final protruding peak depth Rpk" is calculated, and the ratio (%) of the difference value △Rpk to the initial protruding peak depth Rpk is defined as the "rate of change of protruding peak depth Rpk". These represent the frictional impact on the cylinder.

[0085] (Evaluation of frictional impact on the cylinder) In this embodiment, the surface properties of the actual contact surface of the piston ring 40 are set such that the "rate of change of core level difference Rk" is 35% or less, and the "rate of change of protruding peak depth Rpk" is 20% or less. More preferably, the "rate of change of core level difference Rk" is 25% or less, and the "rate of change of protruding peak depth Rpk" is 15% or less. Such a piston ring 40 has little adverse effect on the cylinder 10 in an internal combustion engine using hydrogen gas fuel, and can therefore be operated safely for a long period of time.

[0086] <Second Sliding Simulation> This section describes the second sliding simulation using the sliding simulation device 500. Note that this section will only describe two conditions that differ from those of the first sliding simulation.

[0087] In the second sliding simulation, an emulsified lubricating oil with a water content of 10% is used as the evaluation emulsified oil. Compared to the first sliding simulation, the water content of the lubricating oil has increased by 2%, so the lubricating function of the lubricating oil is more likely to deteriorate.

[0088] On the other hand, the actual surface pressure at the actual contact surface of the piston ring 40 is set to 0.61 MPa. Compared to the first sliding simulation, the actual surface pressure is smaller, so it is less likely to adversely affect the inner wall surface 12 of the cylinder 10.

[0089] Except for the two conditions mentioned above, the same procedure as the first sliding simulation procedure is adopted to calculate the "rate of change of core level difference Rk" and the "rate of change of protruding peak depth Rpk". Furthermore, the surface properties of the actual contact surface of the piston ring 40 are set such that the "rate of change of core level difference Rk" is 35% or less and the "rate of change of protruding peak depth Rpk" is 20% or less. More preferably, the "rate of change of core level difference Rk" is set to 25% or less and the "rate of change of protruding peak depth Rpk" is set to 15% or less. Such a piston ring 40 has little adverse effect on the cylinder 10 in an internal combustion engine using hydrogen gas fuel, and can therefore be operated safely for a long period of time.

[0090] <Third Sliding Simulation> This section describes the third sliding simulation using the sliding simulation device 500. Note that this section will only describe two conditions that differ from those of the first sliding simulation.

[0091] In the third sliding simulation, an emulsified lubricating oil with a water content of 4% is used as the evaluation emulsified oil. Compared to the first sliding simulation, the water content of the lubricating oil is reduced by 4%, thus maintaining a high level of lubrication function.

[0092] On the other hand, the actual surface pressure at the actual contact surface of the piston ring 40 is set to 3.56 MPa. Compared to the first sliding simulation, the higher actual surface pressure is likely to adversely affect the inner wall surface 12 of the cylinder 10.

[0093] Except for the two conditions mentioned above, the same procedure as the first sliding simulation procedure is adopted to calculate the "rate of change of core level difference Rk" and the "rate of change of protruding peak depth Rpk". Furthermore, the surface properties of the actual contact surface of the piston ring 40 are set such that the "rate of change of core level difference Rk" is 35% or less and the "rate of change of protruding peak depth Rpk" is 20% or less. More preferably, the "rate of change of core level difference Rk" is set to 25% or less and the "rate of change of protruding peak depth Rpk" is set to 15% or less. Such a piston ring 40 has little adverse effect on the cylinder 10 in an internal combustion engine using hydrogen gas fuel, and can therefore be operated safely for a long period of time.

[0094] In particular, if the piston ring 40 is such that the "rate of change of core level difference Rk" is 35% or less and the "rate of change of protruding peak depth Rpk" is 20% or less in all of the first to third sliding simulations, then in an internal combustion engine using hydrogen gas fuel, there will be less adverse effects on the cylinder 10, and it will be possible to operate it safely and continuously for a long period of time.

[0095] <Examples of Sliding Simulations> In the first to third sliding simulations, the water content of the emulsified oil was varied to 4%, 8%, and 10%, and the actual surface pressure on the actual contact surface of the piston ring 40 was varied to 0.61 MPa, 1.97 MPa, and 3.56 MPa. Therefore, there are nine possible combinations of water content and actual surface pressure. Simulations were performed for these nine combinations, and the results of calculating the "rate of change of core level difference Rk" and the "rate of change of protruding peak depth Rpk" are shown in Figure 6. As is clear from these results, the first to third sliding simulations described above represent boundary values.

[0096] In the above description, the surface properties of the actual contact surface of the piston ring 40 were exemplified as being defined by the rate of change of the core level difference Rk and the rate of change of the protruding peak depth Rpk from the viewpoint of the degree of frictional influence on the cylinder, but the present invention is not limited to this. For example, the sliding structure between the piston ring 40 and the inner wall surface 12 of the cylinder 10 may be defined by the rate of change of the core level difference Rk and the rate of change of the protruding peak depth Rpk from the viewpoint of the degree of frictional influence on the inner wall surface 12. In other words, the definition of the surface properties of the actual contact surface of the piston ring 40 can be directly applied to the definition of the sliding structure between the piston ring 40 and the inner wall surface 12 of the cylinder 10.

[0097] Next, we will describe another embodiment (modified embodiment) of sliding simulation using the sliding simulation device 500.

[0098] <First set of modified simulation examples> The first set of modified simulation examples using the sliding simulation device 500 will be explained, including the procedure.

[0099] (Preparation) The cylinder 10 and piston ring 40 to be evaluated were placed in the sliding simulation device 500. At this time, a tension (back pressure) of 1.0 MPa or more was applied to the piston ring 40 by adjusting the spring of the tension application mechanism 650. In this case, it was specifically set to 1.0 MPa. This resulted in a simulation under more stringent conditions regarding surface pressure.

[0100] The piston rings 40 were taken from actual internal combustion engines that use hydrogen gas fuel. For accuracy, the cylinder 10 was taken from the engine block of an actual internal combustion engine that uses hydrogen gas fuel, specifically the cylinder section. The stroke of the virtual piston 610 was set to a range of, for example, 5 mm to 30 mm, and was set to 15 mm.

[0101] For simulation purposes, lubricating oils and emulsified oils were prepared, for example, the lubricating oil itself (0% water content), a first emulsified oil containing 2% water relative to the total amount of emulsified oil, a second emulsified oil containing 4% water relative to the total amount of emulsified oil, a third emulsified oil containing 6% water relative to the total amount of emulsified oil, a fourth emulsified oil containing 8% water relative to the total amount of emulsified oil, and a fifth emulsified oil containing 10% water relative to the total amount of emulsified oil. Each emulsified oil was produced by stirring lubricating oil (SAE standard 0W-20 viscosity) and pure water using a homogenizer. These lubricating oils and first to fifth emulsified oils were stored in six tanks 810A to 810F. The control device 980 controlled the temperature control heaters 850A to 850F to control the lubricating oil or emulsified oil in tanks 810A to 810F to a predetermined temperature (e.g., 20°C).

[0102] The control device 980 controlled the temperature control unit 900 so that the inner wall surface 12 of the cylinder 10 was set to, for example, 20°C. By setting the temperature of the emulsified oil and / or the inner wall surface 12 to a lower level in this way, the lubrication function of the emulsified oil was simulated under more stringent conditions.

[0103] (Reference sliding simulation) The control device 980 controlled the rotational drive source 740 of the relative moving device 700 to operate at a predetermined rotational speed (for example, 2000 rpm), causing the virtual piston 610 to reciprocate. The maximum relative speed between the piston ring 40 and the cylinder 10 was 1.0 m / sec. Simultaneously with the operation of the relative moving device 700, the emulsified oil supply device 800 continuously supplied only the standard lubricating oil. This was operated continuously for 10 hours. After the reference simulation was completed, the sliding marks formed on the inner wall surface 12 of the cylinder 10 were observed and evaluated. A photograph taken during the observation is shown in Figure 7A.

[0104] (First Deformation Sliding Simulation) Next, the piston ring 40 and cylinder 10 were replaced with new ones, and after the above preparation steps, the first emulsified oil (emulsified oil containing 2% water) was supplied and the first deformation sliding simulation was performed. Except for the first emulsified oil, the conditions were the same as those for the reference sliding simulation. After the completion of the first deformation sliding simulation, the sliding marks formed on the inner wall surface 12 of the cylinder 10 were observed and evaluated. A photograph taken at the time of observation is shown in Figure 7B.

[0105] (Second Deformation Sliding Simulation) Next, the piston ring 40 and cylinder 10 were replaced with new ones, and after the above preparation steps, the second emulsified oil (emulsified oil containing 4% water) was supplied and the second deformation sliding simulation was performed. Except for the second emulsified oil, the conditions were the same as those for the reference sliding simulation. After the completion of the second deformation sliding simulation, the sliding marks formed on the inner wall surface 12 of the cylinder 10 were observed and evaluated. A photograph taken during the observation is shown in Figure 7C.

[0106] (Third Deformation Sliding Simulation) Next, the piston ring 40 and cylinder 10 were replaced with new ones, and after the above preparation steps, a third emulsified oil (emulsified oil containing 6% water) was supplied and a third deformation sliding simulation was performed. Except for the third emulsified oil, the conditions were the same as those for the standard sliding simulation. After the completion of the third deformation sliding simulation, the sliding marks formed on the inner wall surface 12 of the cylinder 10 were observed and evaluated. A photograph taken during the observation is shown in Figure 7D.

[0107] (Fourth Deformation Sliding Simulation) Next, the piston ring 40 and cylinder 10 were replaced with new ones, and after the above preparation steps, the fourth emulsified oil (emulsified oil containing 8% water) was supplied and the fourth deformation sliding simulation was performed. Except for the fourth emulsified oil, the conditions were the same as those for the standard sliding simulation. After the completion of the fourth deformation sliding simulation, the sliding marks formed on the inner wall surface 12 of the cylinder 10 were observed and evaluated. A photograph taken during the observation is shown in Figure 7E.

[0108] (Fifth Deformation Sliding Simulation) Next, the piston ring 40 and cylinder 10 were replaced with new ones, and after the above preparation steps, the fifth emulsified oil (emulsified oil containing 10% water) was supplied and the fifth deformation sliding simulation was performed. Except for the fifth emulsified oil, the conditions were the same as those for the standard sliding simulation. After the completion of the fifth deformation sliding simulation, the sliding marks formed on the inner wall surface 12 of the cylinder 10 were observed and evaluated. A photograph taken during the observation is shown in Figure 7F.

[0109] In the baseline simulation shown in Figure 7A, the sliding marks were faint and no excessive wear was observed. In the first deformation sliding simulation shown in Figure 7B, the sliding marks were faint and no excessive wear was observed. In the second deformation sliding simulation shown in Figure 7C, the sliding marks were faint and no excessive wear was observed. In the third deformation sliding simulation shown in Figure 7D, white ring-shaped sliding marks were formed near the top and bottom dead centers of the piston ring 40. No excessive wear was observed. In the fourth deformation sliding simulation shown in Figure 7E, white ring-shaped sliding marks were formed near the top and bottom dead centers of the piston ring 40, with a wider band and a stronger white color. In addition, white linear sliding marks extending in the axial direction were formed near the joint 40A of the piston ring 40 (see Figure 4(B)). On the other hand, no excessive wear was observed on the surface. In the fifth deformation sliding simulation shown in Figure 7F, strong white band-shaped sliding marks were formed near the top and bottom dead centers of the piston ring 40, and sliding marks were formed throughout the entire stroke range (cylindrical sliding area). The entire sliding area became mirror-like due to wear, and steps (excessive wear) were formed at the upper and lower ends (dead centers) of the piston ring sliding range due to wear.

[0110] As described above, the first set of modified examples in the simulation revealed that when the water content in the emulsified oil is 8% or less, excessive wear does not occur in the cylinder 10, and when the water content is 10% or more, excessive wear (steps due to wear) occurs in the cylinder 10.

[0111] <Second set of simulation deformation examples>

[0112] In the first group of deformation examples, the fourth deformation sliding simulation using the fourth emulsion oil containing 8% water relative to the total emulsion oil had a simulation time of 10 hours. Therefore, in order to investigate the effects of long-term operation with this fourth emulsion oil, the following additional simulations were performed. Figure 8A shows photographs taken during the observation of the fourth deformation sliding simulation.

[0113] (Sixth Deformation Sliding Simulation) Based on the results of the fourth deformation sliding simulation described above, the fourth emulsifier was supplied and the system was operated continuously for an additional 10 hours, bringing the total operating time to 20 hours. Except for the fourth emulsifier, the conditions were the same as those for the reference sliding simulation. After the completion of the sixth deformation sliding simulation, the sliding marks formed on the inner wall surface 12 of the cylinder 10 were observed and evaluated. A photograph taken during the observation is shown in Figure 8B.

[0114] (Seventh Deformation Sliding Simulation) Based on the results of the sixth deformation sliding simulation described above, the fourth emulsifier was supplied and the system was operated continuously for an additional 10 hours, bringing the total operating time to 30 hours. Except for the fourth emulsifier, the conditions were the same as those for the standard sliding simulation. After the completion of the seventh deformation sliding simulation, the sliding marks formed on the inner wall surface 12 of the cylinder 10 were observed and evaluated. A photograph taken during the observation is shown in Figure 8C.

[0115] (Eighth Deformation Sliding Simulation) Based on the results of the seventh deformation sliding simulation described above, the fourth emulsifier was supplied and the system was operated continuously for an additional 10 hours, bringing the total operating time to 40 hours. Except for the fourth emulsifier, the conditions were the same as those for the standard sliding simulation. After the completion of the eighth deformation sliding simulation, the sliding marks formed on the inner wall surface 12 of the cylinder 10 were observed and evaluated. A photograph taken during the observation is shown in Figure 8D.

[0116] (Ninth Deformation Sliding Simulation) Based on the results of the eighth deformation sliding simulation described above, the fourth emulsifier was supplied and the system was operated continuously for an additional 10 hours, bringing the total operating time to 50 hours. Except for the fourth emulsifier, the conditions were the same as those for the standard sliding simulation. After the completion of the ninth deformation sliding simulation, the sliding marks formed on the inner wall surface 12 of the cylinder 10 were observed and evaluated. A photograph taken during the observation is shown in Figure 8E.

[0117] Comparing the fourth simulation in Figure 8A with the sixth simulation in Figure 8B, the sliding marks were more pronounced in the sixth simulation. On the other hand, in the range of the sixth to ninth simulations (Figures 8B to 8E), the rate of increase in sliding marks became extremely gradual. In other words, it became clear that sliding marks increase up to a maximum of 20 hours of total operation time, but do not increase much even with operation beyond that, and converge to a stable state.

[0118] Figure 9 shows the results of measuring the surface roughness of the sliding area of ​​the inner wall surface 12 of the cylinder 10 before simulation and after the fourth, sixth to ninth simulations.

[0119] The measurement method involved measuring the inner wall surface 12 along the circumferential direction using a non-contact cylinder inner circumference measuring instrument (JIS B 0633:2001) within its sliding range. Five arbitrary positions were randomly selected for measurement. The cutoff value (wavelength) λs for the cross-sectional curve was set to 0.8 μm for measurement. From the measured cross-sectional curve, the core level difference Rk, the protruding peak depth Rpk, and the protruding valley depth Rvk (JIS B 0671-2:2002) were calculated. The average value of the calculation results was used for evaluation.

[0120] As is clear from Figure 9, compared to the cylinder before simulation (0 Hr), the sliding area of ​​the cylinder after the fourth (10 Hr), sixth (20 Hr), seventh (30 Hr), eighth (40 Hr), and ninth (50 Hr) simulations is smoothed by initial wear. On the other hand, there is almost no variation in surface roughness between the fourth and sixth-to-ninth simulations. In other words, it is clear that the surface roughness stabilizes after the initial wear that occurs from before the simulation to the first 10 hours of operation.

[0121] Based on these results, in the case of the fourth emulsified oil, although the visual friction marks increased slightly after 10 to 50 hours of operation, the surface roughness hardly changed. Therefore, it could be estimated that even after more than 50 hours of operation, abnormal wear leading to scuffing would not progress. In other words, it became clear that as long as the water content relative to the total emulsified oil is maintained at 8% or less, abnormal wear will not form on the cylinder 10.

[0122] <Modified Sliding Simulation Device> Next, with reference to Figure 10, a modified sliding simulation device 1500 will be described. Note that, except for the emulsified oil supply device 800 and the control device 980, the sliding simulation device 500 in Figure 3 is the same, so the explanation will be omitted by using the same reference numerals in the figure.

[0123] The emulsified oil supply device 800 of the sliding simulation device 1500 includes a lubricating oil tank 870 for storing lubricating oil, a water tank 880 for storing water, a temperature control heater 870A provided in the lubricating oil tank 870, a temperature control heater 880A provided in the water tank 880, a lubricating oil pipe 872 connected to the lubricating oil tank 870, a water pipe 882 connected to the water tank 880, an integrated pipe 832 connecting the lubricating oil pipe 870 and the water pipe 882 from the confluence point to the nozzle 820, a lubricating oil pump 876 and a lubricating oil mass flow controller 874 provided in the lubricating oil pipe 872 for controlling the amount of lubricating oil supplied, a water pump 886 and a water mass flow controller 884 provided in the water pipe 882 for controlling the amount of water supplied, and a homogenizer 890 provided in the integrated pipe 832 for emulsifying the lubricating oil and water flowing through it.

[0124] In the sliding simulation device 1500, lubricating oil, whose temperature is controlled by a temperature-controlled heater 870A in the lubricating oil tank 870, can be supplied while adjusting the flow rate with a lubricating oil mass flow controller 874. Similarly, water, whose temperature is controlled by a temperature-controlled heater 880A in the water tank 880, can be supplied while adjusting the flow rate with a water mass flow controller 884. As a result, the mixing ratio of lubricating oil and water and the total flow rate can be controlled. Furthermore, the lubricating oil and water guided to the integrated piping 832 can be guided to the nozzle 820 in a pre-emulsified state by a homogenizer 890.

[0125] Therefore, the control device 980 can control the flow rate, temperature, and water mixing ratio of the emulsified oil in accordance with a timing chart of a sliding simulation set in advance by a program or the like.

[0126] It should be noted that the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the invention.

[0127] 10 Cylinder liner 12 Inner wall surface 13 Outer wall surface 30 Piston 40 Piston ring 110 Solid contact area 112 Boundary lubrication area 113 Mixed lubrication area 114 Fluid lubrication area 500 Sliding simulation device 502 Base 510 Cylinder holding mechanism 520 Holder 530 First cover 540 Second cover 600 Ring holding mechanism 610 Virtual piston 650 Tension application mechanism 700 Relative movement device 710 Linear slider 720 Connecting rod 730 Crankshaft 740 Rotational drive source 800 Emulsified oil supply device 820 Nozzle 900 Temperature control unit 910 Temperature control space 980 Control device

Claims

1. A piston ring used in an internal combustion engine using hydrogen gas fuel, characterized in that, as calculated by the following first sliding simulation, the rate of change of the core level difference Rk of the contour curve on the sliding surface of the cylinder that slides with the piston ring is 35% or less, and the rate of change of the protruding peak depth Rpk of the contour curve on the sliding surface is 20% or less, as calculated by the first sliding simulation. (First sliding simulation) - Before the simulation, the sliding surface is measured using a stylus-type surface roughness measuring instrument to calculate the core level difference Rk (initial core level difference Rk) and the protruding peak depth Rpk (initial protruding peak depth Rpk) of the contour curve. - Emulsified oil, obtained by emulsifying lubricating oil with a water content of 8%, is supplied to the sliding surface. - The actual surface pressure of the piston ring on the sliding surface is set to 1.97 MPa. - The temperature of the sliding surface is set to 20°C. - The cylinder and the piston are rotated at a speed of 2000 r / m - Slide the sliding surface at a speed of in for 10 hours. - Measure the core level difference Rk (final core level difference Rk) of the contour curve measured by a stylus-type surface roughness measuring instrument after 10 hours of sliding, and calculate the rate of change from the initial core level difference Rk. - Measure the protruding peak depth Rpk (final protruding peak depth Rpk) of the contour curve measured by a stylus-type surface roughness measuring instrument after 10 hours of sliding, and calculate the rate of change from the initial protruding peak depth Rpk.

2. The piston ring according to claim 1, characterized in that, calculated by the second sliding simulation described below, the rate of change of the core level difference Rk of the contour curve on the sliding surface of the cylinder that slides with the piston ring is 35% or less, and the rate of change of the protruding peak depth Rpk of the contour curve on the sliding surface is 20% or less, calculated by the second sliding simulation described above. (Second sliding simulation) - The sliding surface before the simulation is measured using a stylus-type surface roughness measuring instrument to calculate the core level difference Rk (initial core level difference Rk) and the protruding peak depth Rpk (initial protruding peak depth Rpk) of the contour curve. - Emulsified oil obtained by emulsifying lubricating oil with a water content of 10% is supplied to the sliding surface. - The actual surface pressure of the piston ring on the sliding surface is set to 0.61 MPa. - The temperature of the sliding surface is set to 20°C. - The cylinder and the piston are rotated at a speed of 2000 r / - Slide the sliding surface at min speed for 10 hours. - Measure the core level difference Rk (final core level difference Rk) of the contour curve measured by a stylus-type surface roughness measuring instrument after 10 hours of sliding, and calculate the rate of change from the initial core level difference Rk. - Measure the protruding peak depth Rpk (final protruding peak depth Rpk) of the contour curve measured by a stylus-type surface roughness measuring instrument after 10 hours of sliding, and calculate the rate of change from the initial protruding peak depth Rpk.

3. The piston ring according to claim 1, characterized in that, calculated by the third sliding simulation described below, the rate of change of the core level difference Rk of the contour curve on the sliding surface of the cylinder that slides with the piston ring is 35% or less, and the rate of change of the protruding peak depth Rpk of the contour curve on the sliding surface is 20% or less, calculated by the third sliding simulation described above. (Third sliding simulation) - The sliding surface before the simulation is measured using a stylus-type surface roughness measuring instrument to calculate the core level difference Rk (initial core level difference Rk) and the protruding peak depth Rpk (initial protruding peak depth Rpk) of the contour curve. - Emulsified oil obtained by emulsifying lubricating oil with a water content of 4% is supplied to the sliding surface. - The actual surface pressure of the piston ring on the sliding surface is set to 3.56 MPa. - The temperature of the sliding surface is set to 20°C. - The cylinder and the piston are rotated at a speed of 2000 r / m - Slide the sliding surface at a speed of in for 10 hours. - Measure the core level difference Rk (final core level difference Rk) of the contour curve measured by a stylus-type surface roughness measuring instrument after 10 hours of sliding, and calculate the rate of change from the initial core level difference Rk. - Measure the protruding peak depth Rpk (final protruding peak depth Rpk) of the contour curve measured by a stylus-type surface roughness measuring instrument after 10 hours of sliding, and calculate the rate of change from the initial protruding peak depth Rpk.

4. A sliding structure for a cylinder and piston ring in an internal combustion engine using hydrogen gas fuel, characterized in that, as calculated by the following first sliding simulation, the rate of change of the core level difference Rk of the contour curve on the sliding surface between the cylinder and the piston ring is 35% or less, and as calculated by the first sliding simulation, the rate of change of the protruding peak depth Rpk of the contour curve on the sliding surface is 20% or less. (First sliding simulation) - Before the simulation, the sliding surface is measured using a stylus-type surface roughness measuring instrument to calculate the core level difference Rk (initial core level difference Rk) and the protruding peak depth Rpk (initial protruding peak depth Rpk) of the contour curve. - Emulsified oil obtained by emulsifying lubricating oil with a water content of 8% is supplied to the sliding surface. - The actual surface pressure of the piston ring on the sliding surface is set to 1.97 MPa. - The temperature of the sliding surface is set to 20°C. - The cylinder and piston ring are rotated at a speed of 2000 rpm. - Slide the sliding surface at a speed of / min for 10 hours. - Measure the core level difference Rk (final core level difference Rk) of the contour curve measured by a stylus-type surface roughness measuring instrument on the sliding surface after 10 hours of sliding, and calculate the rate of change from the initial core level difference Rk. - Measure the protruding peak depth Rpk (final protruding peak depth Rpk) of the contour curve measured by a stylus-type surface roughness measuring instrument on the sliding surface after 10 hours of sliding, and calculate the rate of change from the initial protruding peak depth Rpk.

5. A cylinder and piston ring sliding structure according to claim 4, characterized in that, calculated by the second sliding simulation described below, the rate of change of the core level difference Rk of the contour curve on the sliding surface between the cylinder and the piston ring is 35% or less, and the rate of change of the protruding peak depth Rpk of the contour curve on the sliding surface is 20% or less, calculated by the second sliding simulation described above. (Second sliding simulation) - Before the simulation, the sliding surface is measured using a stylus-type surface roughness measuring instrument to calculate the core level difference Rk (initial core level difference Rk) and the protruding peak depth Rpk (initial protruding peak depth Rpk) of the contour curve. - Emulsified oil obtained by emulsifying lubricating oil with a water content of 10% is supplied to the sliding surface. - The actual surface pressure of the piston ring on the sliding surface is set to 0.61 MPa. - The temperature of the sliding surface is set to 20°C. - The cylinder and the piston ring are rotated at a speed of 2000 rpm. - Slide the sliding surface at a speed of / min for 10 hours. - Measure the core level difference Rk (final core level difference Rk) of the contour curve measured by a stylus-type surface roughness measuring instrument on the sliding surface after 10 hours of sliding, and calculate the rate of change from the initial core level difference Rk. - Measure the protruding peak depth Rpk (final protruding peak depth Rpk) of the contour curve measured by a stylus-type surface roughness measuring instrument on the sliding surface after 10 hours of sliding, and calculate the rate of change from the initial protruding peak depth Rpk.

6. A cylinder and piston ring sliding structure according to claim 4, characterized in that, calculated by the third sliding simulation described below, the rate of change of the core level difference Rk of the contour curve on the sliding surface between the cylinder and the piston ring is 35% or less, and the rate of change of the protruding peak depth Rpk of the contour curve on the sliding surface is 20% or less, calculated by the third sliding simulation described above. (Third sliding simulation) - Before the simulation, the sliding surface is measured using a stylus-type surface roughness measuring instrument to calculate the core level difference Rk (initial core level difference Rk) and the protruding peak depth Rpk (initial protruding peak depth Rpk) of the contour curve. - Emulsified oil obtained by emulsifying lubricating oil with a water content of 4% is supplied to the sliding surface. - The actual surface pressure of the piston ring on the sliding surface is set to 3.56 MPa. - The temperature of the sliding surface is set to 20°C. - The cylinder and the piston ring are rotated at a speed of 2000 rpm. - Slide the sliding surface at a speed of / min for 10 hours. - Measure the core level difference Rk (final core level difference Rk) of the contour curve measured by a stylus-type surface roughness measuring instrument on the sliding surface after 10 hours of sliding, and calculate the rate of change from the initial core level difference Rk. - Measure the protruding peak depth Rpk (final protruding peak depth Rpk) of the contour curve measured by a stylus-type surface roughness measuring instrument on the sliding surface after 10 hours of sliding, and calculate the rate of change from the initial protruding peak depth Rpk.

7. A sliding simulation device for simulating the sliding motion of a piston ring and cylinder for an internal combustion engine, comprising: a ring holding mechanism for holding the piston ring to be simulated; a cylinder holding mechanism for holding the cylinder to be simulated; a relative movement device for sliding the piston ring and the cylinder by moving the ring holding mechanism and the cylinder holding mechanism relative to each other; and an emulsified oil supply device for supplying an emulsified oil, obtained by mixing at least lubricating oil and water, to the sliding parts of the piston ring and the cylinder.

8. The sliding simulation device according to claim 7, characterized in that the piston ring held by the ring holding mechanism is ring-shaped with a gap, the cylinder held by the cylinder holding mechanism has a perfectly cylindrical inner wall surface, and the entire outer surface of the piston ring and the inner wall surface are slid by the relative movement mechanism.

9. The sliding simulation apparatus according to claim 7, characterized in that the ring holding mechanism has a tension application mechanism for applying tension to the piston ring.

10. A sliding simulation method for simulating the sliding motion of a piston ring and a cylinder for an internal combustion engine, characterized in that the piston ring and the cylinder to be simulated are moved relative to each other, and an emulsified oil, obtained by mixing at least lubricating oil and water, is supplied to the sliding parts of the piston ring and the cylinder.

11. A sliding simulation method according to claim 10, characterized in that multiple types of emulsified oils with different mixing ratios of lubricating oil and water are supplied to the piston ring and the sliding portion of the cylinder at different timings.

12. The sliding simulation method according to claim 10, characterized in that the temperature of the inner wall surface is adjusted to 30 degrees or less.

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