JP2021060048A - Internal combustion engine sliding structure and method for creating the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sliding structure of an internal combustion engine which realizes further improvement of fuel efficiency and reduction of oil consumption. SOLUTION: The sliding structure of an internal combustion engine having a cylinder bore 10, a piston 30 and a piston ring 40, the piston ring 40 has a top ring 50 and an oil ring 70, and is a top ring with respect to the cylinder bore 10. The actual contact width in the axial direction of the actual contact surface with which the 50 or the oil ring 70 can come into contact is 0.05 mm or more, and the surface pressure acting between the actual contact surface and the cylinder bore 10 is 2.0 MPa or less. [Selection diagram] Fig. 1

Description

The present invention relates to a sliding structure of an internal combustion engine having a cylinder and a piston.

It is effective to reduce the friction between the piston ring and the cylinder bore to reduce the fuel consumption of the engine. In recent years, the piston ring has been subjected to chrome nitride coating or DLC coating by PVD treatment, which is a low friction coefficient material, to reduce the friction, or the friction coefficient has been reduced by using an additive of lubricating oil. ing. This idea presupposes that most of the frictional force is generated in the boundary lubrication region or the solid contact region.

By the way, in recent piston rings, the sliding surface has a V-shaped cross section (strong barrel shape), so that the actual contact width with the cylinder bore on the outer peripheral surface of the piston ring is extremely reduced, and the surface is wear resistant. By coating with a material with a high hardness, the friction coefficient is reduced while increasing the hardness. Such recent piston rings are defined here as "V-shaped rings (Over strong covex shaped Piston Ring, or High Barrel shaped Piston Ring)". In the case of this V-shaped ring, the fluid lubrication function is not required for the lubricating oil, and the lower the viscosity, the better in terms of frictional force. Therefore, in recent years, in internal combustion engines such as gasoline engines, the viscosity of lubricating oil has been reduced. From the viewpoint of gas sealability and LOC, the V-shaped local actual contact surface is brought into an extremely high surface pressure state to improve it. In other words, by narrowing the actual contact width, both gas sealability and reduction of frictional force are achieved. On the other hand, it is necessary to withstand the wear caused by the high surface pressure of the actual contact surface, and the high hardness coating already described is required.

On the other hand, in the old piston rings before the adoption of the V-shaped ring in recent years, it was common to use cast iron as the material or to perform Cr plating on the sliding surface. Since these have low hardness, minute wear called "familiarity" occurs during the initial operation of the internal combustion engine. Due to this minute wear, the sliding surface of the piston ring becomes an extremely gentle convex shape (weak barrel shape), and by creating a fluid lubrication region between the piston ring and the cylinder bore, gas sealability, wear resistance, and the like are exhibited. This old-fashioned piston ring is defined as a "Running-in Piston Ring, or Proper Shaped Piston Ring by Running-in".

This "familiarity" will be described with reference to FIG. On the sliding surface of the piston ring R, a minute sagging shape having the dimension e is naturally formed inside the actual contact width f formed by the initial wear (familiarity) of the engine operation. It is said that this dimension e converges to about 1/1000 of the actual contact width f. As the sliding speed between the piston ring R and the cylinder bore B increases, the lubricating oil O is involved by the wedge effect of the sagging shape to generate the pressure P, so that the fluid lubrication region slides. Incidentally, with reference to the moving direction D of the piston ring R, the front side of the actual contact surface is the low pressure P2, and the front side of the actual contact surface is the high pressure P1.

In the familiar ring, at least the outer peripheral surface is made soft by Cr plating treatment, nitriding treatment, soft resin coating, or the like. In order to generate pressure in the oil film during lubrication, it is preferable that the barrel height (dimension e) in the convex shape in the actual contact width f is low. On the other hand, if the actual contact width f is secured too large, the surface pressure is lowered, so that familiarity due to the initial operation is less likely to occur (wear is less likely to occur).

Since the V-shaped ring is premised on sliding while making solid contact with the cylinder bore, it is necessary to reduce the tension and the surface pressure between the piston ring and the cylinder bore in order to reduce the friction coefficient. is there. However, it is difficult to increase the roundness of the outer circumference at the manufacturing stage of the piston ring. As a result, if the tension of the piston ring is reduced, there is a problem that a fine gap due to a manufacturing error is likely to be formed between the piston ring and the cylinder bore, and the gas sealability is deteriorated.

On the other hand, the familiar ring is premised on creating a fluid lubrication state between the cylinder bores by applying a high tension to the piston ring while using a high-viscosity lubricating oil. However, since the viscosity of lubricating oils has been reduced in recent years, it is difficult to use this familiar ring as it is.

In view of such circumstances, the present invention aims to further improve fuel efficiency and reduce oil consumption.

The present invention that achieves the above object is a sliding structure of an internal combustion engine having a cylinder, a piston and a piston ring, the piston ring having a top ring and an oil ring, and the top with respect to the cylinder. The actual contact width in the axial direction of the actual contact surface with which the ring or the oil ring can come into contact is 0.05 mm or more, and the surface pressure acting between the actual contact surface and the cylinder is 2.0 MPa or less. It is a sliding structure of an internal combustion engine.

The present invention that achieves the above object is a sliding structure of an internal combustion engine having a cylinder, a piston and a piston ring, wherein the piston ring has a top ring and an oil ring, and the top ring or the oil ring. When defining a partial outer peripheral surface located outside the reference cylinder radially inwardly offset by 0.5 μm from the outermost peripheral edge of the cylinder as a virtual actual contact surface of the top ring or the oil ring with respect to the cylinder, the virtual The internal combustion engine is characterized in that the virtual actual contact width in the axial direction on the actual contact surface is 0.05 mm or more, and the surface pressure acting between the virtual actual contact surface and the cylinder is 2.0 MPa or less. It is a sliding structure of an engine.

In relation to the sliding structure of the internal combustion engine, the lubricating oil used in the internal combustion engine has a kinematic viscosity at 100 ° C. of less than 16.3 [mm2 / s].

In relation to the sliding structure of the internal combustion engine, the oil film thickness measured by the capacitance method at the passing point through which the top ring or the oil ring passes at the maximum speed during the stroke is 0.5 μm to 4 It is characterized by being 0.0 μm.

When the surface roughness of the sliding surface of the cylinder is defined as Ra (μm) in relation to the sliding structure of the internal combustion engine, the top ring or the oil ring passes through at the maximum speed during the stroke. In terms of points, the oil film thickness calculated by the modified Reynolds equation is 3.0 × Ra (μm) or more.

In relation to the sliding structure of the internal combustion engine, the surface pressure of the top ring is 0.3 MPa or less.

In relation to the sliding structure of the internal combustion engine, the surface pressure of the oil ring is 1.4 MPa or less.

In relation to the sliding structure of the internal combustion engine, the surface pressure of the oil ring is 1.1 MPa or less.

In relation to the sliding structure of the internal combustion engine, the surface pressure of the oil ring is 0.8 MPa or less.

In relation to the sliding structure of the internal combustion engine, the surface pressure of the oil ring is 0.1 MPa or more.

The oil ring is a three-piece type in relation to the sliding structure of the internal combustion engine.

In relation to the sliding structure of the internal combustion engine, the surface pressure of the oil ring is three times or less the surface pressure of the top ring.

In relation to the sliding structure of the internal combustion engine, the amount of radial displacement of the top ring or the oil ring on the actual contact surface or the virtual actual contact surface when moving along the circumferential direction is 10 μm or less. It is characterized by being.

In relation to the sliding structure of the internal combustion engine, the internal combustion engine is characterized by being a gasoline engine.

The present invention that achieves the above object is a method for incorporating a sliding structure of an internal combustion engine having a cylinder, a piston and a piston ring, wherein the piston ring includes first and second side rails and the first and second side rails. It has a 3-piece type oil ring having a holding member for holding the side rail, and has a first outer peripheral surface of the first side rail and a second outer peripheral surface of the second side rail in a state independent of the holding member. Is polished with a polishing tool to form an initial barrel shape that is radially outwardly convex with respect to the first outer peripheral surface and the second outer peripheral surface, and the first polishing step that has undergone the initial polishing step. An assembling step in which the first and second side rails are incorporated into the piston together with the holding member so that the first and second side rails are tilted in the width direction to bring the first outer peripheral surface and the second outer peripheral surface closer to each other. By sliding the oil ring that has undergone the assembling step with the cylinder of the internal combustion engine, the axially outer region of the oil ring on the first outer peripheral surface and the second outer peripheral surface is formed on the first outer peripheral surface. And the second outer peripheral surface is worn more than the axially inner region of the oil ring to form a final barrel shape that is radially outwardly convex with respect to the first outer peripheral surface and the second outer peripheral surface. Through the operation process, the actual contact width in the axial direction of the actual contact surface where the oil ring can come into contact with the cylinder is set to 0.05 mm or more, and between the actual contact surface and the cylinder. This is a method for incorporating a sliding structure of an internal combustion engine, characterized in that the acting surface pressure is 2.0 MPa or less.

The present invention that achieves the above object is a method for incorporating a sliding structure of an internal combustion engine having a cylinder, a piston and a piston ring, wherein the piston ring includes first and second side rails and the first and second side rails. It has a three-piece type oil ring having a holding member for holding the side rail, and by incorporating the first and second side rails into the holding member or a jig similar to the holding member, the first A pre-assembly step of inclining the outer peripheral surface and the second outer peripheral surface in the width direction of the first and second side rails to bring the first outer peripheral surface and the second outer peripheral surface closer to each other, and using a polishing tool. Then, the axially outer region of the oil ring on the first outer peripheral surface and the second outer peripheral surface is polished more than the axial inner region of the oil ring on the first outer peripheral surface and the second outer peripheral surface. The initial polishing step of forming an initial barrel shape that is radially outwardly convex with respect to the first outer peripheral surface and the second outer peripheral surface, and the holding of the first and second side rails that have undergone the initial polishing step. The first outer peripheral surface and the second outer peripheral surface are abraded by sliding the oil ring that has undergone the final assembling step together with the member into the piston and the cylinder of the internal combustion engine to wear the first outer peripheral surface and the second outer peripheral surface. The actual contact surface where the oil ring can come into contact with the cylinder through a familiar operation step of forming a final barrel shape that is radially outwardly convex with respect to the outer peripheral surface and the second outer peripheral surface. The sliding structure of the internal combustion engine is characterized in that the actual contact width in the axial direction of the internal combustion engine is 0.05 mm or more, and the surface pressure acting between the actual contact surface and the cylinder is 2.0 MPa or less. It is a crowding method.

From the viewpoint of the method of forming the outer peripheral surface of the oil ring, the following method of forming the shape of the oil ring is also deeply related to the present invention, and is therefore described below.

A means deeply related to the present invention is a three-piece type oil ring that is installed in a piston of an internal combustion engine and has a holding member for holding the first and second side rails and the first and second side rails. By polishing the first outer peripheral surface of the first side rail and the second outer peripheral surface of the second side rail in a state independent of the holding member with a polishing tool, the first outer peripheral surface and the first outer peripheral surface and the second outer peripheral surface are polished. The initial polishing step of forming an initial barrel shape that is radially outwardly convex with respect to the second outer peripheral surface, and the first and second side rails that have undergone the initial polishing step are incorporated into the piston together with the holding member. The first outer peripheral surface and the second outer peripheral surface are tilted in the width direction of the first and second side rails to bring the first outer peripheral surface and the second outer peripheral surface closer to each other, and the assembling. By sliding the oil ring that has undergone the process with the cylinder of the internal combustion engine, the axially outer region of the oil ring on the first outer peripheral surface and the second outer peripheral surface is formed on the first outer peripheral surface and the second outer peripheral surface. A familiar operation step of forming a final barrel shape that is radially outwardly convex with respect to the first outer peripheral surface and the second outer peripheral surface by abrading more than the axially inner region of the oil ring on the outer peripheral surface. It is characterized by having.

In relation to the method of forming the shape of the oil ring, the familiarity with respect to the first outer peripheral surface of the first side rail and the second outer peripheral surface of the second side rail in a state independent of the holding member. It is characterized by including a soft layer forming step of forming a soft layer that can be worn in the operating step.

In relation to the method of forming the shape of the oil ring, the thickness of the soft layer is set to 3 μm or more in the soft layer forming step.

In relation to the method of forming the shape of the oil ring, after the familiar operation step, the residual thickness of the soft layer on the axial outer edge of the oil ring on the first outer peripheral surface and the second outer peripheral surface is increased. It is characterized in that it is smaller than the residual thickness of the soft layer on the axial inner edge of the oil ring on the first outer peripheral surface and the second outer peripheral surface.

In relation to the method of forming the shape of the oil ring, in the familiar operation step, the amount of wear of the axially outer edge of the oil ring on the first outer peripheral surface and the second outer peripheral surface is the first outer peripheral surface and the first outer peripheral surface. It is characterized in that it is 1 μm or more larger than the amount of wear of the axial inner edge of the oil ring on the second outer peripheral surface.

In addition, in relation to the method of forming the shape of the oil ring, the maximum polishing allowance in the familiar operation step may be larger than the maximum polishing allowance in the initial polishing step.

In relation to the method of forming the shape of the oil ring, after the familiar operation step, the actual contact width in the axial direction at which the first outer peripheral surface and the second outer peripheral surface can come into contact with the cylinder is 0. It is characterized in that it is 15 mm or more.

A means deeply related to the present invention is a three-piece type oil ring which is installed in a piston of an internal combustion engine and has a holding member for holding the first and second side rails and the first and second side rails. By incorporating the first and second side rails into the holding member or a jig similar to the holding member, the first outer peripheral surface and the second outer peripheral surface are made into the first and second side surfaces. By tilting in the width direction of the rail to bring the first outer peripheral surface and the second outer peripheral surface closer to each other and by using a polishing tool, the oil on the first outer peripheral surface and the second outer peripheral surface. The axial outer region of the ring is polished more than the axial inner region of the oil ring on the first outer peripheral surface and the second outer peripheral surface to have a diameter with respect to the first outer peripheral surface and the second outer peripheral surface. An initial polishing step of forming an initial barrel shape that is convex outward in the direction, a final assembling step of assembling the first and second side rails that have undergone the initial polishing step into the piston together with the holding member, and the final assembling step. By sliding the passed oil ring with the cylinder of the internal combustion engine, the first outer peripheral surface and the second outer peripheral surface are abraded, and the first outer peripheral surface and the second outer peripheral surface are radially outward. It is characterized by having a familiar operation process for creating a convex final barrel shape.

In relation to the method of forming the shape of the oil ring, in the initial polishing step, the amount of polishing of the axial outer edge of the oil ring on the first outer peripheral surface and the second outer peripheral surface is the first outer peripheral surface and the polishing amount. It is characterized in that it is 1 μm or more larger than the amount of polishing of the axial inner edge of the oil ring on the second outer peripheral surface.

In relation to the method of forming the shape of the oil ring, the familiarity with respect to the first outer peripheral surface of the first side rail and the second outer peripheral surface of the second side rail in a state independent of the holding member. It is characterized by including a soft layer forming step of forming a soft layer that can be worn in the operating step.

In relation to the method of forming the shape of the oil ring, the soft layer forming step is executed before the initial polishing step, and after the initial polishing step and before the familiar operation, the first outer peripheral surface and the said The residual thickness of the soft layer on the axial outer edge of the oil ring on the second outer peripheral surface is the residual thickness of the soft layer on the axial inner edge of the oil ring on the first outer peripheral surface and the second outer peripheral surface. It is characterized by being smaller than the size.

In addition, in relation to the method of forming the shape of the oil ring, the maximum polishing allowance in the familiar operation step may be smaller than the maximum polishing allowance in the initial polishing step.

In relation to the method of forming the shape of the oil ring, after the familiar operation step, the actual contact width in the axial direction at which the first outer peripheral surface and the second outer peripheral surface can come into contact with the cylinder is 0. It is characterized in that it is 15 mm or more.

A means deeply related to the present invention is a three-piece type oil ring installed on a piston of an internal combustion engine and having a holding member for holding the first and second side rails and the first and second side rails. The position of the first apex that protrudes most radially outward on the first outer peripheral surface of the first side rail in a state independent of the holding member, and the contact surface of the piston ring formed on the first outer peripheral surface. The oil ring is characterized in that the radial difference between the positions of the outer edges in the axial direction of the oil ring is 1.5 μm to 5.0 μm.

According to the present invention, it is possible to achieve an excellent effect of improving fuel efficiency or reducing oil consumption.

(A) is a side view showing a piston and a piston ring applied to the sliding structure of the internal combustion engine according to the embodiment of the present invention, and (B) is a partially enlarged sectional view showing the piston and 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. It is a partially enlarged sectional view of the top ring of the piston ring. (A) is a cross-sectional view of a 3-piece type oil ring, and (B) is a cross-sectional view of a 2-piece type oil ring. It is a Strivec diagram about the sliding of a general internal combustion engine. It is sectional drawing which shows the friction unit measuring apparatus which measures the sliding state of the Example of this Embodiment. It is a partially enlarged sectional view of the outer peripheral surface of the piston ring which becomes a comparative example. (A) is a diagram showing the actual measurement result of the frictional force of the sliding structure of the internal combustion engine of Example 1, and (B) is a line showing the actual measurement result of the frictional force of the sliding structure of the internal combustion engine of Comparative Example 1. It is a figure. (A) is a diagram showing an axial profile of the outer peripheral surface of the piston ring of Example 1, and (B) is a diagram showing an axial profile of the outer peripheral surface of the piston ring of Comparative Example 1. (A) is a diagram showing a circumferential profile of the outer peripheral surface of the piston ring of Example 1, and (B) is a diagram showing a circumferential profile of the outer peripheral surface of the piston ring of Comparative Example 1. It is a diagram which shows the insulation test result of the sliding structure of the internal combustion engine of Example 1. FIG. (A) is a diagram showing the results of simulating the frictional force of the piston rings of Example 1 and Comparative Example 1, and (B) is the result of simulating the oil film thickness of the top rings of Example 1 and Comparative Example 1. (C) is a diagram showing the results of simulating the gas passage amount of the top ring of Example 1 and Comparative Example 1. It is a diagram which shows the actual measurement result of the friction force of the piston ring of Example 2 and Comparative Example 2. It is a diagram which shows the actual measurement result of the friction force of the oil ring alone of Example 2 and Comparative Example 2. (A) is a diagram showing actual measurement values and simulation results regarding the relationship between the actual contact width of the oil ring of Example 2 and Comparative Example 2 and FMEP, and (B) is the actual contact width in consideration of roughness. It is a diagram which shows the state which separated into fluid lubrication and solid contact about the simulation result of FMEP. It is a diagram which shows the result of having measured the time change of FMEP of the oil ring alone of Example 2 and Comparative Example 2. It is a figure explaining the fluid lubrication state of a piston ring and a cylinder bore. It is a flowchart explaining the 1st detailed procedure of making the shape of the outer peripheral surface of a 3-piece type piston ring. (A) to (D) are partially enlarged cross-sectional views showing the shape of the outer peripheral surface of the three-piece type piston ring. It is a flowchart explaining the 2nd detailed procedure of making the shape of the outer peripheral surface of a 3-piece type piston ring. (A) to (D) are partially enlarged cross-sectional views showing the shape of the outer peripheral surface of the three-piece type piston ring. It is a partially enlarged sectional view which shows the shape of the outer peripheral surface of the 3 piece type piston ring in the process of making a shape. (A) and (B) are partially enlarged cross-sectional views showing the shape of the outer peripheral surface when the three-piece type piston ring whose shape has been formed is disassembled.

Hereinafter, the sliding structure of the internal combustion engine according to the embodiment of the present invention will be described with reference to the accompanying drawings.

<Structure of piston and piston ring>

1 (A) and 1 (B) show a piston 30 and a piston ring 40 (top ring 50, second ring 60, oil ring 70) installed in the ring groove of the piston 30 as a part of a gasoline engine. Shown. The piston ring 40 reciprocates in the cylinder axial direction with the outer peripheral surface 42 facing the inner wall surface 12 of the cylinder bore 10. The top ring 50 eliminates the gap between the piston 30 and the cylinder bore 10 and prevents a gas leak phenomenon (Blowby) in which the compressed gas escapes from the combustion chamber to the crankcase side. Like the top ring 50, the second ring 60 also has a role of eliminating a gap between the piston 30 and the cylinder bore 10 and a role of scraping off excess engine oil adhering to the inner wall surface 12 of the cylinder bore 10. The top ring 50 and the second ring 60 may be referred to as a compression ring.

The oil ring 70 scrapes off excess engine oil attached to the inner wall surface 12 of the cylinder bore 10 to form an appropriate oil film, thereby preventing seizure of the piston 30.

<Top ring shape>

As shown enlarged in FIG. 1C, the top ring 50 is a single annular member, and when the outer peripheral surface 52 is viewed in cross section, it has a so-called weak barrel shape that is gently convex outward in the radial direction. ing. In FIG. 1C, for convenience of explanation, the convex shape of the outer peripheral surface is emphasized by greatly exaggerating the radial dimension with respect to the axial dimension.

The thickness of the top ring 50 (radial width) _{a 1,} for example 4.0mm is set below, preferably to 3.0mm or less. The width (axial width) h ₁ is set to, for example, 2.0 mm or less, preferably 1.5 mm or less.

An actual contact surface 53 is formed on a part of the outer peripheral surface 52 in the axial direction. The actual contact surface 53 has a central surface 55 that is substantially parallel to the inner wall surface 12 in the vicinity of the center in the axial direction, and a pair of inclined surfaces 54 and 54 located on both outer sides of the central surface 55 in the axial direction. The inclined surfaces 54, 54 are inclined in a direction away from the inner wall surface 12 toward the outside in the cylinder axial direction.

When the top ring 50 slides back and forth with respect to the inner wall surface 12, the outer peripheral surface 52 is slightly inclined or deformed. The actual contact surface 53 means a region that can substantially come into contact with the inner wall surface 12 while being inclined or deformed. The inclination of the inclined surfaces 54 and 54 is a so-called sagging shape, and the piston 30 and the piston ring 40 are operated in a familiar manner, and the shape is generated by the contact wear thereof.

The maximum separation distance (sag amount) e of the inclined surfaces 54 and 54 with respect to the tip of the outer peripheral surface 52 is 1/2000 to 1/500 of the actual contact width f in the axial direction of the actual contact surface 53. It is set, more preferably 1/1500 to 1/500. In this embodiment, it is set to about 1/1000.

The actual contact width f may be determined by removing the top ring 50 after the familiar operation and actually measuring the band-shaped range in which fine scratches (wear marks) are formed. The actual contact width f is preferably formed to be 0.15 mm or more. More preferably, it is formed to be 0.3 mm or more, more preferably it is set to be larger than 0.3 mm, and even more preferably it is 0.4 mm or more.

Incidentally, instead of the actual contact width f obtained from the actual measurement, as shown in FIG. 2, the virtual actual contact width g defined from the contour shape of the outer peripheral surface 52 of the top ring 50 may be used. In the top ring 50, a reference cylinder C offset radially inward by x = 0.5 μm from the outermost edge (outermost peripheral edge) Z in the radial direction is set, and the outer peripheral surface 52 is outside the reference cylinder C. The range located at is defined as the virtual actual contact surface 56 of the piston ring. The width of the virtual actual contact surface 56 in the axial direction is the virtual actual contact width g. In the present embodiment, the virtual actual contact width in the axial direction on the virtual actual contact surface is 0.15 mm or more. When calculating the virtual actual contact surface 56 and the virtual actual contact width g, it can be calculated from the shape of the outer peripheral surface 53 in the design, or the contour shape of the outer peripheral surface 52 of the top ring 50 can be measured and calculated from the values. .. In particular, when calculating the virtual actual contact width g of the piston ring after the familiar operation, it is necessary to actually measure the outer peripheral surface shape of the top ring 50 after the familiar operation. Although the top ring 50 is illustrated in FIG. 2, the same definition will be used for the second ring 60 and the oil ring 70 hereafter.

In the top ring 50, the virtual actual contact width g is formed to be 0.05 mm or more, preferably 0.10 mm or more, and more preferably 0.15 mm or more. More preferably, it is formed to be 0.3 mm or more, more preferably it is set to be larger than 0.3 mm, and even more preferably it is 0.4 mm or more.

In order to positively form a sagging shape by familiar operation, the surface hardness of the outer peripheral surface 52 is preferably 1500 Hv or less, and here it is 1200 Hv. It is preferable to apply Cr plating treatment to the outer peripheral surface 52, and an appropriate sagging shape is formed.

<Shape of second ring>

As shown enlarged in FIG. 1D, the second ring 60 is a single annular member, and has a so-called tapered shape when the outer peripheral surface 62 is viewed in cross section. The flat surface on the tip side of this tapered shape has a so-called weak barrel shape that is gently convex outward in the radial direction. In FIG. 1D, for convenience of explanation, the convex shape of the outer peripheral surface is emphasized by greatly exaggerating the radial dimension with respect to the axial dimension.

The thickness of the second ring 60 (radial width) _{a 1,} for example 4.0mm is set below, preferably to 3.0mm or less. The width (axial width) h ₁ is set to, for example, 2.0 mm or less, preferably 1.5 mm or less. Similar to the top ring 50, an actual contact surface 63 is formed on a part of the outer peripheral surface 62 in the axial direction. The actual contact surface 63 has a central surface 65 that is substantially parallel to the inner wall surface 12 in the vicinity of the center in the axial direction, and a pair of inclined surfaces 64 and 64 located on both outer sides of the central surface 65 in the axial direction. The inclined surfaces 64, 64 are inclined in a direction away from the inner wall surface 12 toward the outside in the cylinder axial direction. The inclination of the inclined surfaces 64 and 64 is a so-called sagging shape, and the piston 30 and the piston ring 40 are operated in a familiar manner, and the shape is formed by contact wear thereof.

The maximum separation distance (sag amount) e of the inclined surfaces 64 and 64 with respect to the tip of the outer peripheral surface 62 is 1/2000 to 1/500 of the actual contact width f in the axial direction of the actual contact surface 63. It is set, more preferably 1/1500 to 1/500. In this embodiment, it is set to about 1/1000.

The actual contact width f may be determined by removing the second ring 60 after the familiar operation and actually measuring the wear state of the surface thereof. The actual contact width f is preferably formed to be 0.15 mm or more. More preferably, it is formed to be 0.3 mm or more, more preferably it is set to be larger than 0.3 mm, and even more preferably it is 0.4 mm or more.

Further, the virtual actual contact width g is preferably formed to be 0.15 mm or more. More preferably, it is formed to be 0.3 mm or more, more preferably it is set to be larger than 0.3 mm, and even more preferably it is 0.4 mm or more.

In order to positively form a sagging shape by familiar operation, the surface hardness of the outer peripheral surface 62 is preferably 1500 Hv or less, and here it is 1200 Hv. It is preferable to apply Cr plating treatment to the outer peripheral surface 62, and an appropriate sagging shape is formed.

It is not essential that both the top ring 50 and the second ring 60, which are compression rings, be set to the above conditions, and one of them may be set to the above conditions. At that time, preferably, by setting the top ring 50 side to the above conditions, a ring having a high hardness on the outer peripheral surface (a ring in which wear due to familiar operation hardly occurs) may be adopted as the second ring 60.

<Shape of oil ring>

The oil ring 70 enlarged and shown in FIG. 3 (A) is a three-piece type oil ring. The oil ring 70 has an annular side rail 73a, 73b separated vertically and a spacer expander 76s arranged between the side rails 73a, 73b.

The spacer expander 76s is formed by plastic working a steel material into a corrugated shape that repeats unevenness in the cylinder axial direction. Using this corrugated shape, an upper support surface 78a and a lower support surface 78b are formed, and a pair of side rails 73a and 73b are supported in the axial direction, respectively. The inner peripheral side end of the spacer expander 76s has an ear portion 74 m that is erected in an arch shape toward the outer side in the axial direction. The selvage portion 74m abuts on the inner peripheral surfaces of the side rails 73a and 73b. The spacer expander 76s is incorporated into the ring groove of the piston 30 in a state of contraction in the circumferential direction with the abutment attached. As a result, the restoring force of the spacer expander 76s causes the selvage portion 74m to press and urge the side rails 73a and 73b outward in the radial direction. Upon receiving this urging, the side rails 73a and 73b incline inward in the axial direction (combination nominal width direction) of the oil ring 70, as shown by the dotted line. That is, the pair of outer peripheral surfaces 82, 82 are brought closer to each other by that amount.

The combined radial thickness a _{11 of the} oil ring 70 (see FIG. 1 (B)) is set to, for example, 4.0 mm or less, preferably 3.0 mm or less. The combined axial width (nominal width) h ₁ (see FIG. 1 (B)) is set to, for example, 4.0 mm or less, preferably 2.0 mm or less. The thickness (radial width) a ₁ (see FIG. 1 (B)) of the side rails 73a and 73b alone is set to, for example, 4.0 mm or less, preferably 3.0 mm or less. The width (axial width) h _{12 of the} single unit (see FIG. 1 (B)) is set to, for example, 1.0 mm or less, preferably 0.5 mm or less, and more preferably 0.4 mm or less.

As shown in a further enlarged view in the region O of FIG. 3A, the outer peripheral surfaces 82 of the side rails 73a and 73b each have a so-called weak barrel shape that is gently convex outward in the radial direction. In the region O, for convenience of explanation, the convex shape of the outer peripheral surface is emphasized by greatly exaggerating the radial dimension with respect to the axial dimension. Similar to the top ring 50 and the second ring 60, the actual contact surface 83 is formed on a part of the outer peripheral surface 82 in the axial direction. The actual contact surface 83 has a central surface 85 that is substantially parallel to the inner wall surface 12 in the vicinity of the center in the axial direction, and a pair of inclined surfaces 84 and 84 located on both outer sides of the central surface 85 in the axial direction. The inclined surfaces 84, 84 are inclined in a direction away from the inner wall surface 12 toward the outside in the cylinder axial direction. The inclination of the inclined surfaces 84 and 84 is a so-called sagging shape, which is a shape formed by familiar operation of the piston 30 and the piston ring 40 and contact wear thereof.

The maximum separation distance (sag amount) e of the inclined surfaces 84 and 84 with respect to the tip of the outer peripheral surface 82 is 1/2000 to 1/500 of the actual contact width f in the axial direction of each actual contact surface 83. Is set to, and more preferably 1/1500 to 1/500. In this embodiment, it is set to about 1/1000.

The actual contact width f may be determined by removing the oil ring 70 after the familiar operation and actually measuring the wear state of the surfaces of the side rails 73a and 73b. The actual contact width f is preferably formed to be 0.10 mm or more. It is more preferably formed to be 0.15 mm or more, further preferably 0.2 mm or more, further preferably set to be larger than 0.2 mm, and even more preferably 0.3 mm or more. That is, the total actual contact width F, which is the sum of the actual contact widths f of the pair of outer peripheral surfaces 82, 82, is preferably formed to be 0.2 mm or more, more preferably 0.3 mm or more, and further preferably 0. It is set to 0.4 mm or more, more preferably set to be larger than 0.4 mm, and even more preferably set to 0.6 mm or more.

Further, it is preferable that the virtual actual contact width g of each of the side rails 73a and 73b is formed to be 0.10 mm or more. It is more preferably formed to be 0.15 mm or more, further preferably 0.2 mm or more, further preferably set to be larger than 0.2 mm, and even more preferably 0.3 mm or more. That is, the total virtual actual contact width G, which is the sum of the virtual actual contact widths g of the pair of outer peripheral surfaces 82, 82, is preferably formed to be 0.2 mm or more, more preferably 0.3 mm or more, and further. It is preferably set to 0.4 mm or more, more preferably set to be larger than 0.4 mm, and even more preferably set to 0.6 mm or more.

In order to positively form a sagging shape by familiar operation, the surface hardness of the outer peripheral surface 82 is preferably 1500 Hv or less, and here it is 1200 Hv. It is preferable to apply Cr plating treatment to the outer peripheral surface 82, and an appropriate sagging shape is formed.

The oil ring 70 is not limited to the three-piece type, and may be, for example, a two-piece type oil ring 70 enlarged in FIG. 3 (B). The oil ring 70 has a ring body 72 and a coil spring-shaped coil expander 76C. The ring body 72 is an annular pillar portion 75 arranged between the annular upper rail 73A and the lower rail 73B arranged at both ends in the axial direction and the upper rail 73A and the lower rail 73B and connecting them. Integrally. The cross-sectional shape of the pair of upper rails 73A, lower rails 73B, and pillars 75 is approximately I or H, and by utilizing this shape, the coil expander 76C is placed on the inner peripheral surface side. An inner peripheral groove 79 having a semi-arc-shaped cross section is formed to accommodate the above. Further, the upper rail 73A and the lower rail 73B are formed with an upper annular projection 74A and a lower annular projection 74B that project radially outward with respect to the pillar portion 75, respectively. A part of the upper outer peripheral surface 81A and the lower outer peripheral surface 81B formed at the tip of the upper annular protrusion 74A and the lower annular protrusion 74B comes into contact with the inner wall surface 12 of the cylinder bore 10. The coil expander 76C is housed in the inner peripheral groove 79 to press and urge the ring body 72 outward in the radial direction. A plurality of oil return holes 77 are formed in the pillar portion 75 of the ring main body 72 in the circumferential direction.

As shown in a further enlarged view in the region O of FIG. 3B, since the upper outer peripheral surface 81A and the lower outer peripheral surface 81B are integrally formed with the ring main body 72, both outer peripheral surfaces 81A and 81B Can be collectively defined as a single outer peripheral surface 81. A gap S is formed in the center of the single outer peripheral surface 81.

The single outer peripheral surface 81 has a so-called weak barrel shape that is gently convex outward in the radial direction. In the region O, for convenience of explanation, the convex shape of the outer peripheral surface is emphasized by greatly exaggerating the radial dimension with respect to the axial dimension. Similar to the top ring 50 and the second ring 60, the upper actual contact surface 83A and the lower actual contact surface 83B are formed on a part of the single outer peripheral surface 81 in the axial direction. The upper side actual contact surface 83A has an upper side central surface 85A that is substantially parallel to the inner wall surface 12 in the vicinity of the center in the axial direction of the single outer peripheral surface 81 and an upper side inclination that is located above the upper side central surface 85A in the axial direction. It has a surface 84A. The lower side actual contact surface 83B is a lower side central surface 85B that is substantially parallel to the inner wall surface 12 in the vicinity of the center in the axial direction of the single outer peripheral surface 81, and a lower side that is located on the lower side in the axial direction of the lower side central surface 85B. It has an inclined surface 84B. A gap is formed between the upper central surface 85A and the lower central surface 85B. The upper inclined surface 84A and the lower inclined surface 84B are inclined in a direction away from the inner wall surface 12 toward the outside in the cylinder axial direction. The inclination of the upper inclined surface 84A and the lower inclined surface 84B is a so-called sagging shape, and the piston 30 and the piston ring 40 are operated in a familiar manner, and the shape is formed by contact wear thereof.

The maximum distance e from the inner wall surface 12 on the upper inclined surface 84A and the lower inclined surface 84B is the upper actual contact width f1 of the upper actual contact surface 82A and the lower actual contact width f2 of the lower actual contact surface 82B. It is set to be 1/2000 to 1/500 of the total actual hit width F, which is the total value, and more preferably 1/1500 to 1/500. In this embodiment, it is set to about 1/1000.

The dimensions of the upper actual contact width f1 and the lower actual contact width f2 can be determined by removing the oil ring 70 after the familiar operation and actually measuring the wear state of the surfaces of the upper outer peripheral surface 82A and the lower outer peripheral surface 82B. good. It is preferable that each of the upper actual contact width f1 and the lower actual contact width f2 is formed to be 0.15 mm or more. It is more preferably formed to be 0.2 mm or more, more preferably set to be larger than 0.2 mm, and further preferably set to 0.3 mm or more. That is, the total actual contact width F, which is the sum of the upper actual contact width f1 and the lower actual contact width f2, is preferably formed to be 0.3 mm or more, more preferably 0.4 mm or more, and further preferably 0.4 mm or more. It is set to be larger than 0.4 mm, more preferably 0.6 mm or more.

The surface hardness of the upper outer peripheral surface 82A and the lower outer peripheral surface 82B is preferably 1500 Hv or less, and is set to 1200 Hv here, in order to positively form a sagging shape by the familiar operation. When the Cr coating is formed on the upper outer peripheral surface 82A and the lower outer peripheral surface 82B, an appropriate sagging shape is formed.

<Friction mode between cylinder bore and piston ring>

Next, the friction mode between the cylinder bore and the piston ring will be described. For general friction during sliding, as represented by the Strivec diagram shown in FIG. 4, the friction mode of the solid contact region 110 that slides in direct contact and the boundary that slides through the oil-based coating film. It is classified into the friction mode of the contact region 112 and the friction mode of the fluid lubrication region 114 that slides through the viscous lubricating oil film. In this Strivec diagram, the horizontal axis is a logarithmic representation of "kinematic viscosity (kinematic viscosity) μ" x "velocity U" / "contact load W", and the vertical axis is the coefficient of friction (μ). ). Therefore, the frictional force can be minimized in the fluid lubrication region 114, and effective use of this region 114 is effective for reducing friction, that is, for fuel efficiency.

Incidentally, in recent V-shaped rings, since the actual contact width f is set to be extremely small, even if the speed U increases, it is not possible to shift from the middle of the boundary contact region 112 to the fluid lubrication region 114. As a result, as shown by the dotted line, it is presumed that the boundary contact region 112 is in a state of continuing to the high speed region as it is (or a mixed state with the fluid lubrication region 114).

Most of the frictional force of the fluid lubrication region 114 is the shear resistance of the oil, and this shear resistance is defined by (viscosity) × (velocity) × (area) / (oil film thickness). As a result, reducing the shear area is directly linked to the reduction of frictional force.

Therefore, in the present embodiment, the outer peripheral surface 42 of the piston ring 40 has a weak barrel shape, and the gently inclined surface thereof is used to actively flow oil into the actual contact surface to quickly reach the fluid lubrication region 114. Achieve low friction by shifting.

<Piston ring surface pressure setting>

Next, the surface pressure setting between the piston ring 40 and the cylinder bore 10 will be described. Here, the surface pressure of the piston ring 40 means the surface pressure acting on the contact surface forming the actual contact width f or the virtual actual contact surface g on the outer peripheral surface 42 of the piston ring 40. Specifically, the surface pressure is calculated by (2 × tension) / (cylinder bore diameter × (virtual) actual contact width).

In the present embodiment, the surface pressure of the piston ring 40 is set to be 2.0 MPa or less. Further, the surface pressure of the piston ring 40 is set to be 0.1 MPa or more.

More specifically, the surface pressure of the top ring 50 is preferably 1.0 MPa or less, preferably 0.5 MPa or less. The surface pressure of the top ring 50 is preferably 0.1 MPa or more. For example, it is set to 0.4 MPa. The surface pressure of the second ring 60 is preferably 1.0 MPa or less, preferably 0.5 MPa or less. The surface pressure of the second ring 60 is preferably 0.1 MPa or more. For example, it is set to 0.4 MPa.

The surface pressure of the oil ring 70 is preferably 2.0 MPa or less, preferably 1.4 MPa or less. More preferably, it is 1.1 MPa or less, and even more preferably 0.8 MPa or less. The surface pressure of the oil ring 70 is preferably 0.1 MPa or more, preferably 0.2 MPa or more, and more preferably 0.3 MPa or more.

Further, in the present embodiment, it is preferable that the surface pressure of the oil ring 70 is larger than the surface pressure of the top ring 50. Further, it is preferable that the surface pressure of the oil ring 70 is set to 3 times or less with respect to the surface pressure of the top ring 50.

<Notes on virtual surface pressure of V-shaped ring in recent years>

As a reference, the virtual surface pressure of the V-shaped ring in recent years will be described. The actual contact width of the V-shaped ring is less than 0.1 mm, and in reality, it is often 0.07 mm or less. Therefore, the actual surface pressure acting on the contact surface of the V-shaped ring is significantly larger than the surface pressure of the piston ring 40 of the present embodiment, but since the actual contact width is extremely narrow, the surface pressure measurement itself. Is becoming difficult. Therefore, in the definition of the surface pressure of the V-shaped ring in recent years, _{the virtual surface pressure calculated based on the width (axial width) h 1} of the piston ring, not the actual contact width, is often used as it is as the surface pressure. .. That is, the virtual surface pressure, since the total width (axial width) h ₁ is calculated on the assumption that in contact with the cylinder bore, are far from the actual surface pressure. That is, it should be noted that the definition of the surface pressure of the V-shaped ring itself is a virtual surface pressure, which is different from the actual surface pressure in the present embodiment.

<Selection of lubricating oil>

Next, the selection of the lubricating oil will be described. According to the viscosity classification by the Society of Automotive Engineers, Inc., the lubricating oil used in this embodiment preferably has a low temperature viscosity of 10 W or less and a high temperature viscosity of 40 or less. That is, the CCS viscosity [mPa · s] /-25 [° C.] is preferably 7,000 or less, the pumping viscosity [mPa · s] / -30 [° C.] is preferably 60,000 or less, and the minimum kinematic viscosity at 100 ° C. is 12 The maximum kinematic viscosity at 100 ° C is less than 16.3 [mm2 / s] at 1.5 [mm2 / s] or less, and the viscosity at high temperature and high shear at 150 ° C is 2.9 [mPa · s] or less. preferable.

More preferably, the low temperature viscosity is 5 W or less and the high temperature viscosity is 30 or less. That is, the CCS viscosity [mPa · s] / -30 [° C] is 6600 or less, the pumping viscosity [mPa · s] / −35 [° C] is 60,000 or less, and the minimum kinematic viscosity at 100 ° C is 9.3 [mm2 / It is desirable that the maximum kinematic viscosity at 100 ° C. is less than 12.5 [mm2 / s] and the viscosity at high temperature and high shear at 150 ° C. is 2.9 [mPa · s] or less.

Most preferably, the low temperature viscosity is 0 W or less and the high temperature viscosity is 20 or less. That is, the CCS viscosity [mPa · s] / −35 [° C.] is 6200 or less, the pumping viscosity [mPa · s] / −40 [° C.] is 60,000 or less, and the minimum kinematic viscosity at 100 ° C. is 5.6 [mm2 / It is desirable that the maximum kinematic viscosity at 100 ° C. is less than 9.3 [mm2 / s] and the viscosity at high temperature and high shear at 150 ° C. is 2.6 [mPa · s] or less.

In the present embodiment, at the same time as combining such a lubricating oil having a low viscosity tendency, the actual contact width f of the piston ring 40 is set large to reduce the surface pressure of the piston ring. As a result, the cylinder bore 10 and the piston ring 40 can be maintained in the friction mode of the fluid lubrication region 114 even though the lubricating oil tends to have a low viscosity. At the same time, since the oil film thickness is not made too large, the shear resistance of the lubricating oil can be reduced, and the friction state can be significantly reduced.

Regarding the oil film thickness, the oil film thickness measured by the distance sensor using the capacitance method at the passing point where the piston ring 40 passes through the cylinder bore 10 at the maximum speed during the stroke is 0.5 μm to 4. It is set to 0 μm. In the distance sensor using the capacitance method, the piston ring 40 measures the distance (gap) of the cylinder bore 10. This distance (gap) means the oil film thickness.

As the first embodiment of the internal combustion engine of the present embodiment, a piston ring 40 under the following conditions was prepared.

<Top ring>

As the top ring, the weak barrel-shaped top ring 50 of the present embodiment is adopted, and the thickness (diameter direction width) a ₁ is 2.5 mm and the width (axial width) h ₁ is 1.0 mm. The outer peripheral surface of the top ring 50 was plated with chrome to have a surface hardness of 1200 Hv. The actual contact width f of the actual contact surface 53 after the familiar operation was set to 0.3 mm. By setting the tension of the top ring 50 to 3.7 N, the surface pressure acting on the actual contact surface 53 was set to 0.3 MPa.

<Second ring>

The second ring adopts a tapered shape, and the thickness (diameter width) a ₁ is 2.3 mm and the width (axial width) h ₁ is 1.0 mm. The actual contact width f of the actual contact surface was set to about 0.23 mm. The tension of the second ring was set to 3.0 N. The outer peripheral surface of the second ring was plated with chrome to set the surface hardness to 1200 Hv.

<Oil ring>

As the oil ring, the weak barrel-shaped three-piece type oil ring 70 of the present embodiment is adopted. The combined radial thickness _{a 11} of the oil ring 70 2.50 mm, the combination axial width (nominal width) _{h 1} was set to 2.0 mm. Side rails 73a, the thickness of 73b (radial width) of _{a 1} 1.9 mm, the width (axial _{width) h 12} was 0.4 mm. In each of the side rails 73a and 73b, the actual contact width f of the actual contact surface 83 after the familiar operation was set to 0.15 mm (total actual contact width F0.3 mm). By setting the tension of the oil ring 70 to 19.0 N, the surface pressure acting on the actual contact surface was set to 1.6 MPa.

<Cylinder bore>

The cylinder bore 10 has an inner diameter of 80.5 mm, a material gray cast iron product FC250 (JIS standard), and an arithmetic average roughness Ra: 0.208 (μm) and a root mean square roughness Rq: 0.219 by honing the surface. It was set to (μm) (JIS B 0601: 2013).

<Lubricating oil>

As the lubricating oil for the friction test, a lubricant having a viscosity classification of 0W-20 by the American Automobile Association and an API grade of SN was adopted.

<Friction test>

FIG. 5 shows a friction unit measuring device 500 for measuring the friction mode between the cylinder bore (cylinder liner) 10 and the piston ring 40. The friction unit measuring device 500 measures the friction state between the two by fixing the piston ring 40 side and reciprocating the cylinder liner 10 side up and down. The friction unit measuring device 500 holds the virtual piston 510 in which the piston ring 40 is set by the fixed shaft 514 via the piezo type load cell 512. The load cell 512 measures the external force (friction force) in the vertical direction acting on the piston ring 40.

The cylinder liner 10 is held by a moving sleeve 530 on the outer wall side thereof. The lower end of the moving sleeve 530 is held by the driving piston 540, and the driving piston 540 is moved up and down by the connecting rod 550 to reciprocate the cylinder liner 10 in the vertical direction. A fixed sleeve 560 is arranged on the outer circumference of the moving sleeve 530. The fixing sleeve 560 is fixed to the base 570. The fixed shaft 514 is fixed to the lid member 562 at the upper end of the fixed sleeve 560. The outer peripheral surface of the moving sleeve 530 and the inner peripheral surface of the fixed sleeve 560 are slidable. A temperature control jacket 565 is provided inside the fixed sleeve 560, and the temperature of the fixed sleeve 560 can be controlled by circulating hot water or cold water in the temperature control jacket 565.

In the present embodiment, the oil temperature of the lubricating oil is set to 60 degrees as the measurement condition of the friction mode by the friction unit measuring device 500, and the lubricating oil is dropped and supplied from the upper part of the cylinder liner 10. During the break-in operation (familiar operation), a large amount of lubricating oil was supplied. If the lubricating oil is excessive, the frictional force becomes unstable. Therefore, when measuring each frictional force, the supply of the lubricating oil is stopped for about 5 minutes, and the place where the frictional force is stable is set as the measured value. For the measurement of each frictional force, the rotation speed and temperature were adjusted so that the Stribeck index (= viscosity x velocity / surface pressure) at the fastest point was the same.

In the first embodiment, the friction waveform (friction waveform before the familiar operation) is measured 5 minutes after the start of the friction unit measuring device 500, and 20 hours after the start (after the familiar operation of 15 hours has passed), the friction waveform is measured. After another 5 hours of operation), the friction waveform was measured. During the familiar operation for 15 hours, the piston ring 40 was manually rotated by 40 ° to 90 ° every 2 hours. This is to reproduce the piston ring 40 rotating in the circumferential direction during operation in a normal gasoline engine.

Since the actual fuel consumption evaluation point of the engine is set so that the FMEP (mean effective pressure) is 800 kPa at 1500 rpm, the friction test is also performed in the first embodiment on the condition that the engine temperature is 85 ° C. and the engine speed is 1500 rpm. went. If this condition is replaced with the friction unit measuring device 500, the temperature at the center of the stroke of the cylinder liner becomes 35 ° C. and the rotation speed becomes 400 rpm.

<Insulation test>

An electrical insulation test was performed to confirm the fluid lubrication region of the cylinder bore 10 and the piston ring 40. This electrical insulation test utilizes the property that the fluid lubricating oil film formed between the cylinder bore 10 and the piston ring 40 enhances the electrical insulation of both. Specifically, in the friction unit measuring device 500 shown in FIG. 5, the piston ring 40 was electrically isolated from the surroundings by making the virtual piston 510 with a highly insulating resin. In this state, the piston ring 40 and the cylinder bore 10 were connected by conductive wiring, and a constant voltage generator 590 (3V) and a variable resistor 592 (2.4kΩ) were interposed in the middle of the wiring. Further, a voltage detector (oscilloscope) 594 for detecting the voltage (mV) was arranged in the middle of the wiring to detect the change in the resistance value of the fluid lubricating oil film. In this test, the absolute value of the oil film thickness cannot be clarified, but there is an advantage that the overall lubrication state of the oil film formed over the entire circumference can be estimated.

In Example 1, the oil film state of the oil ring 70 alone was measured by energizing only the oil ring 70. The reason for this is that the oil ring 70 has the highest surface pressure as compared with other rings and is a piston ring that does not easily move to the fluid lubrication region. In other words, if a sufficient oil film is formed on the oil ring 70, it can be inferred that the top ring 50 and the second ring 60 are always fluid lubrication regions. Further, since the outer peripheral surface 82 of the oil ring 70 is Cr-plated, it exhibits a stable resistance value, so that the measurement accuracy is high. In the case of a solid contact region or a boundary lubrication region where the piston ring and the cylinder bore are in direct contact with each other, an inconsistent noise waveform is likely to occur in this insulation test.

<Measurement of contour shape in the width direction of the piston ring after familiar operation>

The contour shape in the width direction of the actual contact surface of the piston ring 40 after the familiar operation was actually measured. The top ring 50 and the second ring 60 were removed from the virtual piston 510, and the profiles of the outer peripheral surfaces 52 and 62 were measured in the axial direction (actual contact width direction). The oil ring 70 was mounted on the virtual piston 510 and tension was applied by the spacer expander 76s, and the profiles of the outer peripheral surfaces 82 of the side rails 73a and 73b were measured in the axial direction (actual contact width direction).

<Measurement of the contour shape of the piston ring in the circumferential direction after familiar operation>

The contour shape of the actual contact surface of the piston ring 40 in the circumferential direction was actually measured. Here, the oil ring 70 was removed from the virtual piston 510, and the profile of the outer peripheral edge of the actual contact surface 83 was measured in the circumferential direction with respect to the single upper side rail 73a in the state where the spacer expander 76s was not attached. Before grasping the effect of familiar driving, both the profile before familiar driving and the profile after familiar driving were measured.

[Comparative Example 1]

As Comparative Example 1 for verifying the effect of Example 1, a piston ring 40 under the following conditions was prepared.

<Top ring>

A V-shaped ring (strong barrel-shaped top ring) is used for the top ring, the thickness (radial width) a ₁ is 2.5 mm, the width (axial width) h ₁ is 1.0 mm, and the outer peripheral surface is set. The surface hardness was set to 1800 Hv by PVD coating. The tension of the top ring was 3.7 N, which was the same as in Example 1.

FIG. 6 shows a concept for explaining the degree of protrusion of the V-shape on the outer peripheral surface of the piston ring as a comparative example. When selecting a reference surface Mk such that the width in the axial direction is Mf on the outer peripheral surface of the piston ring M, both edges Mka and Mkb in the width direction of the reference surface Mk have diameters from the outermost peripheral edge Z of the outer peripheral surface. The amount x that offsets inward in the direction was measured. The degree of curvature (V-shaped degree) of the outer peripheral surface was evaluated from the width Mf in the axial direction and the offset amount x.

The top ring of Comparative Example 1 had an offset amount x of 15 μm when the axial width Mf of the reference surface Mk was 0.3 mm. As can be seen from the fact that the general offset amount that can actually come into contact with the cylinder bore is 0.5 μm or less, it can be seen that the actual contact width of the actual contact surface of the top ring of the comparative example is extremely narrow.

<Second ring>

As the second ring, the one under exactly the same conditions as in Example 1 was adopted.

<Oil ring>

The oil ring is a V-shaped (strong barrel shape) 3-piece type oil ring. The combined radial thickness _{a 11} of the oil ring 2.55 mm, the combination axial width (nominal width) _{h 1} was set to 2.0 mm. The thickness of the pair of side rails (radial width) 2.0 mm the _{a 1,} a width (axial _{width) h 12} was 0.4 mm. The tension of the oil ring was 19.0 N, which was the same as in Example 1.

When the degree of protrusion of the V-shape of each side rail was measured, the offset amount x was 5 μm when the axial width Mf of the reference surface Mk was 0.15 mm. The outer peripheral surface was PVD coated to give a surface hardness of 1800 Hv.

All other conditions were the same as in Example 1, and a friction test, an insulation test, a contour shape measurement, and the like were performed.

(Friction test result)

FIG. 7 shows the results of the friction test. FIG. 7A shows the test results of Example 1, and the friction waveform (friction waveform before familiar operation) 5 minutes after the start of the friction unit measuring device 500 is shown by a dotted line, and the friction after 20 hours of familiar operation is shown. The waveform is shown by a solid line. Compared with before the familiar operation, the frictional force was greatly reduced after the familiar operation, and the FMEP (state in which the top ring, the second ring, and the oil ring were combined) was also reduced. The FMEP after the familiar operation was 10.07 kPa. From this, it can be seen that even if the piston ring of the first embodiment is applied to an actual internal combustion engine, a significant fuel consumption reduction effect can be obtained. The manifestation of the effect of the familiar operation varies depending on the initial shape of the piston ring, the material hardness, etc., but since the actual internal combustion engine has a higher rotation speed, it is estimated that the familiar operation is completed in less than 20 hours.

FIG. 7B shows the test results of Comparative Example 1, and the friction waveform (friction waveform before familiar operation) 5 minutes after the start of the friction unit measuring device 500 is shown by a dotted line, and the friction after 20 hours of familiar operation is shown. The waveform is shown by a solid line. However, since the frictional force hardly changes before and after the familiar operation, both graphs overlap. That is, the piston ring of Comparative Example 1 does not exhibit the effect of so-called familiar operation. It is presumed that this state is maintained even in an actual internal combustion engine. The FMEP after the familiar operation was 13.91 kPa.

Therefore, when comparing Example 1 and Comparative Example 1 after the familiar operation, it was clarified that Example 1 was about 28% lower in FMEP.

(Axial contour measurement result)

FIG. 8 shows the results of measuring the contour of the outer peripheral surface in the axial direction. As shown in FIG. 8A, in the top ring 50 of Example 1, the actual contact width f of the actual contact surface 53 was 300 μm, and the sagging amount e was 0.3 μm. In the second ring of Example 1, the actual contact width of the actual contact surface was 230 μm, and the sagging amount e was 0.3 μm.

In the oil ring 70 of Example 1, the actual contact width f of the actual contact surface 83 of one side rail 73a was 150 μm, and the sagging amount e was 0.2 μm. The actual contact width f of the actual contact surface 83 of the other side rail 73b was 130 μm, and the sagging amount e was 0.2 μm.

As shown in FIG. 8B, it is difficult to actually measure the width of the actual contact surface of the top ring of Comparative Example 1 because the outer peripheral surface is extremely curved, but it is estimated to be about 45 μm or less. Was done. Since the second ring of Comparative Example 1 was the same as that of Example 1, the actual contact width of the actual contact surface was 230 μm, and the sagging amount e was 0.3 μm. It is difficult to actually measure the width of the actual contact surface of each side rail of the oil ring of Comparative Example 1 because the outer peripheral surface is extremely curved, but it is estimated to be about 20 μm or less.

(Result of contour measurement in the circumferential direction)

FIG. 9 shows the results of contour measurement in the circumferential direction of the outer peripheral surface. As shown in FIG. 9A, it can be seen that in the side rail 73a of the oil ring 70 of the first embodiment, the outer peripheral edge of the actual contact surface 83 is displaced within a range of 10 μm in the radial direction before the familiar operation. .. Further, it can be seen that after the familiar operation, the outer peripheral edge of the actual contact surface 83 is displaced within a range of 3 μm in the radial direction. As a result, it can be seen that the amount of displacement in the circumferential direction of the outer peripheral edge of the actual contact surface 83 is significantly reduced by the effect of the familiar operation. It has been clarified that the reduction of the displacement amount in the circumferential direction, that is, the improvement of the roundness, plays an important role from the viewpoint of maintaining the fluid lubrication region during operation.

As shown in FIG. 9B, in the side rail 73a of the oil ring 70 of Comparative Example 1, the outer peripheral edge of the actual contact surface 83 is displaced to 30 μm or more in the radial direction even after 20 hours of familiar operation. You can see that it does. Of course, it is presumed that even the side rail 73a of Comparative Example 1 is deformed by being pressed against the cylinder bore by the expander, and the outer peripheral edge of the actual contact surface 83 approaches a perfect circle. However, in order to deform the actual contact surface 83 into a perfect circle, a corresponding tension is required, which causes a problem that the frictional force becomes high.

(Insulation test result)

FIG. 10 shows the insulation measurement result of the oil ring 70 of Example 1. The rotation speed at the time of measurement adopted the conditions corresponding to 1500 rpm, 1000 rpm, 600 rpm, 300 rpm, and 150 rpm in the internal combustion engine. As a reference, during the insulation test at each rotation speed, the fluctuation mode of the frictional force was also measured at the same time, so these are also shown together.

It can be seen that the resistance value increases as the rotation speed increases. This means that as the number of revolutions increases, the oil film thickness increases to form a fluid lubrication region. In particular, when the rotation speed is 600 rpm or more, the resistance value tends to increase significantly. When it reaches 1000 rpm or more, the resistance value hardly changes even if the rotation speed changes. This means that the oil film thickness has reached the upper limit. On the other hand, the resistance value becomes small at 150 rpm and 300 rpm where the frictional force is large. It can be inferred that the oil film is extremely thin, or that the oil ring 70 and the cylinder bore 10 are in contact with each other in part. However, in an internal combustion engine such as a gasoline engine, it is rare to operate at 150 rpm or 300 rpm. As a result, in the case of the piston ring of the first embodiment, it is presumed that the piston ring is always lubricated in the fluid lubrication region at a rotation speed higher than the idling operation.

By the way, in the case of Comparative Example 1, since the piston ring and the cylinder bore are in the solid contact region or the boundary lubrication region where they slide while being in direct contact with each other, an inconsistent noise waveform is generated even if the insulation test is performed. ..

(Verification of LOC)

Deterioration of gas seal performance and unscraped lubricating oil on the sliding surface have a large effect on the factors that determine LOC. As shown in Comparative Example 1 of FIG. 9B, deterioration of the roundness of the oil ring is directly linked to the unscraped residue of the lubricating oil. On the other hand, in the oil ring 70 of the first embodiment of FIG. 9A, since the roundness is significantly improved by the familiar operation, the residual lubricating oil on the sliding surface is reduced and the LOC (lubricating oil consumption) is consumed. Amount) is estimated to decrease.

(Additional verification of blow-by and wear by simulation test)

By simulating and calculating the frictional force, oil film thickness, and gas passage amount, gas sealability and wear in the fluid lubrication region where the oil film is formed will be verified.

Excite-PR manufactured by AVL was used as simulation software for calculating the oil film thickness, frictional force, amount of gas passing through the sliding surface, etc. of the sliding surface of the piston ring. For the oil film and friction calculation, the modified Reynolds equation (Patir and Cheng) and the Greenwood-Tripp model for calculating the solid contact pressure were used. The contraction coefficient was used to calculate the amount of leaked gas.

As detailed calculation conditions, the surface roughness of the cylinder bore: Rq = 0.219 (μm), the surface roughness of the piston ring: Rq = 0.000 (μm), the cylinder bore shape: cylindrical, the sliding surface temperature: TDC (top). Dead center) 150 ° C, MID (center point) 85 ° C, BDC (bottom dead center) 85 ° C, lubricating oil: 0W-20 (kinematic viscosity at 40 ° C 37 [mm2 / s], kinematic viscosity at 100 ° C 8 .7 [mm2 / s]). Further, the secondary vibration and friction of the piston were not considered, the friction coefficient of the boundary contact region was set to 0.072, and the maximum combustion pressure was set to 7.2 MPa. Further, it was assumed that an oil film having 3 × bore surface roughness Rq (= 0.657 μm) always remained in the cylinder bore.

For the shapes of the outer peripheral surfaces of the piston rings of Example 1 and Comparative Example 1, the contour measurement data in the axial direction of FIG. 8 was used. In this simulation, the contour shape data in the circumferential direction of FIG. 9 is not considered.

FIG. 11 shows the simulation results. FIG. 11A shows the total frictional force of the top ring, the second ring, and the oil ring of Example 1 (solid line) and Comparative Example 1 (dotted line). FIG. 11B shows the oil film thickness of the sliding surface of the top ring of Example 1 (solid line) and Comparative Example 1 (dotted line). FIG. 11C shows the amount of gas passing through the sliding surface of the top ring of Example 1 (solid line) and Comparative Example 1 (dotted line). Regarding the frictional force and the oil film, it can be seen that the simulation result of FIG. 10 and the result of the friction test and the insulation test of FIGS. 7 and 8 are similar except immediately after the top dead center (immediately after the crank angle 0 °). It is presumed that the difference immediately after top dead center is due to the fact that the combustion pressure is not taken into consideration in the friction test and the insulation test of FIGS. 7 and 8.

In order to analyze the gas sealability and wear, it is necessary to grasp the oil film thickness near the top dead center where the combustion pressure is high. As shown in FIG. 11B, in the top ring of Comparative Example 1, only the minimum oil film thickness on the cylinder bore side, which is a prerequisite, is obtained, and almost no oil film is formed on the top ring side over the entire stroke. That is, the result is contact sliding. Since the contact slides over the entire stroke, it can be inferred that wear occurs over the entire stroke and becomes particularly large near the top dead center where the combustion pressure is applied. As a result, in the top ring of Comparative Example 1, the amount of gas leakage increases as the combustion pressure increases.

On the other hand, as shown in FIG. 11B, the oil film thickness of the top ring of Example 1 depends on the sliding speed of the top ring, and the combustion pressure immediately after top dead center (immediately after the crank angle 0 °). It can be seen that an oil film is formed on the top ring side in the entire area except the moment when It can be seen that the oil film is maintained by the drawing film effect even at the bottom dead center (crank angle 180 °) where the sliding speed becomes zero. As a result, in the top ring of Example 1, the contact sliding range is extremely narrow, so that the amount of wear is reduced. Further, as described in the present embodiment, since the piston ring of the first embodiment has a low surface pressure setting, it acts more favorably against wear by synergistic action. Therefore, the need to coat the outer peripheral surface with a high-hardness material is reduced.

Further, as shown in FIG. 11C, the amount of gas passing through the top ring (gas leakage amount) is reduced by about 10% in Example 1 as compared with Comparative Example 1, but this also covers a wide range. This is due to the fact that the oil film is maintained. Maintaining the oil film is synonymous with the pressure generated in the oil film, and if the pressure in the oil film is equal to or higher than the combustion pressure, the gas can be sealed. In the top ring of Example 1, when stopped at the top dead center (crank angle 0 °), the oil film pressure depending on the sliding speed disappears, while a separate pressure is generated due to the throttle effect in the process of thinning the oil film, and the gas Maintains sealing properties. As a result, the top ring of Example 1 has a higher gas sealability than that of Comparative Example 1.

As the second embodiment of the internal combustion engine of the present embodiment, a piston ring 40 having the following conditions was prepared.

<Top ring> The same top ring as in Example 1 was used.

<Second ring> The same second ring as in Example 1 was used.

<Oil ring>

Three types of oil rings (A, B, C) with different actual contact widths were prepared. For all the oil rings, the weak barrel-shaped three-piece type oil ring 70 of the present embodiment was adopted. The combined radial thickness _{a 11} of the oil ring 70 2.50 mm, the combination axial width (nominal width) _{h 1} was set to 2.0 mm. The side rails 73a, the thickness of 73b (radial width) of _{a 1} 1.9 mm, the width (axial _{width) h 12} was 0.4 mm.

In the oil ring A, in each of the side rails 73a and 73b, the actual contact width f of the actual contact surface 83 after the familiar operation was set to 0.350 mm (total actual contact width F0.7 mm). By setting the tension of the oil ring A to 19.0 N, the surface pressure acting on the actual contact surface was set to 0.67 MPa. The method of forming the shape of the actual contact surface 83 of the oil ring A was performed by the "second forming method" described later.

In the oil ring B, in each of the side rails 73a and 73b, the actual contact width f of the actual contact surface 83 after the familiar operation was set to 0.250 mm (total actual contact width F0.50 mm). By setting the tension of the oil ring B to 19.0 N, the surface pressure acting on the actual contact surface was set to 0.94 MPa. The method of forming the shape of the actual contact surface 83 of the oil ring B was performed by the "first forming method" described later.

In the oil ring C, in each of the side rails 73a and 73b, the actual contact width f of the actual contact surface 83 after the familiar operation was set to 0.150 mm (total actual contact width F0.30 mm). By setting the tension of the oil ring C to 19.0 N, the surface pressure acting on the actual contact surface was set to 1.6 MPa. The method of forming the shape of the actual contact surface 83 of the oil ring C was performed by the "first forming method" described later.

All other conditions were the same as in Example 1.

[Comparative Example 2]

As Comparative Example 2 for verifying the effect of Example 2, a piston ring 40 under the following conditions was prepared. In Comparative Example 2, piston rings 40 of two groups (group X and group Y) were prepared.

<Group X top ring>

As the top ring, the V-shaped ring (strong barrel-shaped top ring) of the present embodiment is adopted, and the thickness (radial width) a ₁ is 2.5 mm and the width (axial width) h ₁ is 1.0 mm. The surface hardness was set to 1800 Hv by PVD coating the outer peripheral surface. The tension of the top ring was 3.7 N, which was the same as in Example 1.

As shown in FIG. 6, the outer peripheral surface of the top ring has an offset amount x of 6.5 μm when the axial width Mf of the reference surface Mk is 0.5 mm. Since the general offset amount that can actually come into contact with the cylinder bore is 0.5 μm or less, it can be seen that the actual contact width of the actual contact surface of the top ring of Comparative Example 2 is extremely narrow.

<Group X second ring>

As the second ring, the one under exactly the same conditions as in Comparative Example 1 was adopted.

<Group X oil ring>

The oil ring is a V-shaped (strong barrel shape) 3-piece type oil ring. The combined radial thickness _{a 11} of the oil ring was 2.5 mm, the width (axial width) _{h 1} and 2.0 mm. The thickness (radial width) a ₁ of the pair of side rails was 1.9 mm, and the width (axial width) h ₁₂ was 0.4 mm. The tension of the oil ring was 19.0 N, which was the same as in Example 2.

When the degree of protrusion of the V-shape of each side rail was measured, the offset amount x was 12 μm when the axial width Mf of the reference surface Mk was 0.15 mm. The outer peripheral surface was PVD coated to give a surface hardness of 1800 Hv.

<Group Y top ring>

The surface hardness was set to 1200 Hv by treating the outer peripheral surface with Cr plating while maintaining the same shape as the top ring of Group X.

<Group Y second ring>

As the second ring, the one under exactly the same conditions as in Comparative Example 1 was adopted.

<Group Y oil ring>

The surface hardness was set to 1200 Hv by treating the outer peripheral surface with Cr plating while maintaining the same shape as the oil ring of Group X.

The top ring and oil ring of this group Y are familiar because the outer peripheral surface of the base material itself is V-shaped and the actual contact width is extremely narrow (less than 0.15 mm), but the surface is Cr-plated. It can be worn finely by operation.

(Friction test result of piston ring set)

FIG. 12 shows the results of a friction test of a piston ring set composed of a top ring, a second ring, and an oil ring. Here, the friction waveform after the familiar operation for 20 hours is shown. The piston ring set of the top ring, the second ring, and the oil ring A (actual contact width of each side rail: 0.350 mm) of the second embodiment has significantly reduced frictional force. On the other hand, the piston ring set of the top ring, the second ring, and the oil ring (PVD coating on the outer peripheral surface) of the group X of Comparative Example 2 had a significantly large frictional force. It was revealed that the FMEP of the piston ring set of Example 2 was about 41% lower than that of the piston ring set of Comparative Example 2.

(Friction test result of oil ring only)

FIG. 13 shows the result of the friction test of the oil ring alone. Here, the friction waveform after the familiar operation for 20 hours is shown. The frictional force of the oil ring A of Example 2 (actual contact width of each side rail: 0.350 mm) was significantly reduced. The oil ring C of Example 2 (actual contact width of each side rail 0.150 mm) had a slightly larger frictional force than the oil ring A. On the other hand, the oil ring (PVD coating on the outer peripheral surface) of Group X of Comparative Example 2 had a significantly larger frictional force than the oil rings A and C. Comparing the oil ring A of Example 2 with the oil ring of Group X of Comparative Example 2, it was revealed that the oil ring A was about 46% lower in terms of FMEP.

(Verification of the relationship between the actual contact width of the oil ring and FMEP)

FIG. 14A shows the relationship between the actual contact width of the oil ring and FMEP. The graph (Experimental Result) shown by the solid line and the black circle is the measured value of the oil rings A, B, C of the second embodiment and the oil ring of the group Y of the comparative example 2. On the other hand, the graph shown by the solid line and the white circle (Simulation with Roughness) is the simulation result considering the flow of lubricating oil and the contact sliding by considering the roughness, and the graph shown by the dotted line and the "x" mark (Simulation without). Roughness) is a simulation result on the condition of complete fluid lubrication without considering the roughness. The simulation was calculated using Excite-PR manufactured by AVL. For the oil film and friction calculation, the modified Reynolds equation (Patir and Cheng's average flow model) and the Greenwood-Tripp model for calculating the solid contact pressure were used.

In FIG. 14 (B), the calculation result of the simulation result in which the flow of lubricating oil and the contact sliding are taken into consideration by considering the roughness in FIG. It is divided into white circles) and friction due to solid contact (solid line and "x" mark).

As can be seen from the actually measured values in FIG. 14 (A), the larger the actual contact width, the lower the friction, and when the actual contact width is less than 150 μm, the frictional force tends to increase sharply. This is because, as can be seen from the simulation result of FIG. 14 (B), when the actual contact width is less than 150 μm, the increase in the friction of the boundary lubrication reaches the limit, but the friction due to the solid contact increases sharply. It is presumed that it is.

By the way, in the measured values, the smallest FMEP was the actual contact width of 250 μm (oil ring B), but considering fluctuations in the operating conditions of the internal combustion engine, it is presumed that a slightly wider one is optimal. To. In general, an increase in the actual contact width leads to an increase in the frictional force, but according to measured values and simulations, a state in which the frictional force is small is sufficiently maintained until the actual contact width is about 400 μm. it is conceivable that. Therefore, when the lubricating oil is 0W-20, the actual contact width in the range of 250 μm to 400 μm (the surface pressure is in the range of 0.59 MPa to 0.94 MPa) is considered to be optimal. This optimum range varies slightly depending on the viscosity of the lubricating oil, but when a lubricating oil having a lower viscosity is used, it is considered preferable to increase the actual contact width or reduce the surface pressure.

(Actual measurement result of time change of FMEP of oil ring alone)

Next, in the friction test of the oil rings A, B, C of Example 2 and the oil rings of Group X and Group Y of Comparative Example 2, how the FMEP of each oil ring is timed during the familiar operation for 20 hours. The result of the change or the actual measurement is shown in FIG.

The group X oil ring (V-shaped, PVD coating) had a slight decrease in FMEP during 20 hours of familiar operation, but the amount of decrease was less than 10%. It is presumed that this is a state in which the so-called familiar effect is not exhibited without the outer peripheral surface being worn even by the familiar operation.

In the group Y oil ring (V-shaped, Cr plating treatment), the FMEP decreased by about 15% to about 8.5 kPa after 20 hours of familiar operation as compared with immediately after the operation (about 10 kPa). Since the actual contact width is as small as less than 50 μm, it is considered that the sliding is due to solid contact or contact lubrication region, but it is presumed that the frictional force is slightly reduced with time due to surface wear.

In the oil ring C (actual contact width 0.150 mm, Cr plating treatment), the FMEP decreased by about 40% after 20 hours of familiar operation as compared with immediately after the operation (10 kPa), and became about 6.3 kPa.

In the oil ring B (actual contact width 0.250 mm, Cr plating treatment), the FMEP decreased by about 38% after 20 hours of familiar operation as compared with immediately after the operation (8 kPa), and became about 4.8 kPa.

The oil ring A (actual contact width 0.350 mm, Cr plating treatment) was about 4.0 kPa with almost no change in FMEP over the entire familiar operation. In addition, since this oil ring A incorporates the inclination of the side rail by the spacer expander at the time of manufacturing to form a barrel shape by the second fabrication method described later, FMEP is formed about 20 minutes after the start of familiar operation. It became the minimum value (about 4.0 kPa).

As a result of the above, it can be seen that the oil rings A, B, and C of Example 2 have a reduction in FMEP by 30% or more due to the effect of familiar operation in a single test. In particular, it was presumed that the oil ring A could slide in the optimum fluid lubrication region from the beginning because the contact width was set large even in the initial state due to the barrel shape created before the familiar operation. Further, in the oil ring A, it was estimated that the FMEP became smaller by further slightly modifying the barrel shape about 20 minutes after the start of the familiar operation.

As described above, according to the sliding structure of the internal combustion engine of the present embodiment, the actual contact width f at which the top ring or the oil ring can come into contact with the cylinder bore is 0.05 mm or more, and acts on the sliding surface. As a result of the surface pressure being reduced to 2.0 MPa or less, the fluid lubrication region allows sliding in a low friction state, so that the efficiency of the internal combustion engine can be significantly improved. This is the same even if it is defined by the virtual actual hit width g.

Further, in the sliding structure, when applied to a low-viscosity lubricating oil having a kinematic viscosity at 100 ° C. of less than 16.3 [mm2 / s], further reduction in friction of the sliding surface is achieved.

Further, in this sliding structure, the oil film thickness measured by the capacitance method is 0.5 μm to 4.0 μm at the passing point where the top ring or the oil ring passes at the maximum speed during the stroke. Set. By controlling the oil film thickness within an appropriate range, it is possible to keep the frictional force small.

Further, in this sliding structure, the surface pressure of the top ring is set to 0.3 MPa or less. As a result, the sliding resistance of the top ring is significantly reduced, and the efficiency of the internal combustion engine is improved.

Furthermore, in this sliding structure, the surface pressure of the oil ring is 1.4 MPa or less. As a result, the oil film thickness of the oil ring becomes large, the sliding resistance becomes small, and the efficiency of the internal combustion engine is improved. In particular, in order to exhibit the effect of familiar operation, it is preferable that the oil ring is a three-piece type.

Furthermore, in this sliding structure, the surface pressure of the oil ring is three times or less the surface pressure of the top ring for both the top ring and the oil ring. By bringing the surface pressures of both as close as possible, the overall sliding resistance is reduced and the efficiency of the internal combustion engine is improved.

Further, in this sliding structure, the displacement amount in the radial direction when moving along the circumferential direction on the actual contact surface or the virtual actual contact surface of the top ring and the oil ring when removed from the piston is 10 μm or less. Become. In this way, when reducing the surface pressure (lower tension) of the sliding surface, the gap between the cylinder bore, the top ring and the oil ring is made uniform, and the frictional force is reduced and gas leakage is reduced at the same time. Will be possible.

In particular, the present sliding structure is preferably applied to a gasoline engine, but the present invention is not limited to this, and can be applied to other internal combustion engines.

Next, two types of methods for forming the sliding structure of the internal combustion engine will be described. The method of creating the sliding structure of the internal combustion engine is synonymous with the method of creating the barrel shape of the outer peripheral surface of the oil ring.

<First method of making the shape of the outer peripheral surface of the oil ring>

Next, regarding the three-piece type oil ring 70 described with reference to FIG. 3 (A), a first detailed procedure for forming a weak barrel shape on the outer peripheral surface thereof will be described with reference to FIGS. 17 and 18. Although the radial cross-sectional shape of the outer peripheral surface is enlarged and shown in FIG. 18, the barrel shape is exaggeratedly displayed by significantly increasing the radial enlargement ratio with respect to the widthwise enlargement ratio. There is.

As shown in FIG. 18A, as the soft layer forming step S310, the first outer peripheral surface 82a and the second outer peripheral surface of the independent first side rail 73a and the second side rail 73b removed from the spacer expander 76s. With respect to 82b, soft layers 200a and 200b having low hardness that can be worn away in a familiar operation step described later are formed. The surface hardness of the soft layers 200a and 200b is formed to 1500 Hv or less by Cr plating treatment, nickel plating treatment (Ni-P plating treatment), galvanization treatment, gas nitriding treatment, low hardness DLC treatment, soft resin coating and the like. Just do it. The thickness of this soft layer is preferably 3 μm or more, more preferably 5 μm or more.

Next, as shown in FIG. 18B, as the initial polishing step S320, the first outer peripheral surface 82a and the second outer peripheral surface 82a of the independent first side rail 73a and the second side rail 73b removed from the spacer expander 76s. The outer peripheral surface 82b is polished with a polishing tool. As a result, an initial barrel shape that is convex outward in the radial direction is formed with respect to the first outer peripheral surface 82a and the second outer peripheral surface 82b. This polishing process is a so-called lapping process, in which abrasive grains are interposed in a tool having a cylindrical inner peripheral surface that is close to the outer diameter of the first side rail 73a and the second side rail 73b. The first outer peripheral surface 82a and the second outer peripheral surface 82b are relatively moved.

Next, as shown in FIG. 18C, as the assembling step S330, the first and second side rails 73a and 73b that have undergone the initial polishing step S320 are incorporated into the piston 30 together with the spacer expander 76s. At this time, the first outer peripheral surface 82a and the second outer peripheral surface 82b are inclined in the width directions 73a and 73b of the first and second side rails. It can be said that the diameter is reduced by inclining the first outer peripheral surface 82a and the second outer peripheral surface 82b. As a result, the first outer peripheral surface 82a and the second outer peripheral surface 82b are closer to each other than the inner peripheral surfaces of the first and second side rails 73a and 73b. The inclination angle of the first outer peripheral surface 82a and the second outer peripheral surface 82b is preferably 0.25 degrees or more.

Next, as shown in FIG. 18D, as the familiar operation step S340, the internal combustion engine is normally operated, so that the oil ring 70 that has undergone the incorporation step S330 is slid with the cylinder bore 10 of the internal combustion engine. By this sliding, the axial outer regions 82a-1 and 82b-1 of the oil ring of the actual contact surface formed on the first outer peripheral surface 82a and the second outer peripheral surface 82b are formed in the axial inner region 82a-2 of the oil ring. , 82b-2 wears more than. As a result, a final barrel shape that is radially outwardly convex with respect to the first outer peripheral surface 82a and the second outer peripheral surface 82b is formed. This final barrel shape is in a state in which the inclination angles generated on the first outer peripheral surface 82a and the second outer peripheral surface 82b in the assembling step S330 are reduced or almost eliminated.

After the familiar operation step S340, the residual thickness Oa of the soft layers 200a and 200b of the axial outer edges 88a and 88b of the oil ring of the actual contact surface formed on the first outer peripheral surface 82a and the second outer peripheral surface 82b. , Ob is smaller than the residual thicknesses Ia and Ib of the soft layers of the axial inner edges 89a and 89b of the oil ring on the first outer peripheral surface 82a and the second outer peripheral surface 82b. This difference in residual thickness (Ia-Oa, Ib-Ob) is preferably set to 1 μm or more. The maximum abrasion allowance Lm (see FIG. 18D) in the familiar operation step S340 may be larger than the maximum polishing allowance Sm in the initial polishing step S320 (see FIG. 18B). ..

As a result of the above, in the state after the familiar operation step, the actual contact width in the axial direction of the actual contact surface where the first outer peripheral surface 82a and the second outer peripheral surface 82b can come into contact with the cylinder bore 10 is 0.15 mm or more.

In the above-mentioned first preparation method, the initial polishing step S320 is performed after passing through the soft layer forming step S310, but the present invention is not limited to this. It is also possible to perform the soft layer forming step S310 after performing the initial polishing step S320.

The oil ring 70 completed according to FIG. 18D is removed from the piston 30, and further separated and separated from the spacer expander 76s, the first side rail 73a, the second side rail 73b, the first outer peripheral surface 82a, and the second outer circumference. The state of the surface 82b is shown in FIG. 22 (A). The first side rail 73a and the second side rail 73b released from the urging by the spacer expander 76s return from the inclined state.

When the first outer peripheral surface 82a and the second outer peripheral surface 82b are cross-sectionally viewed, the locations most protruding outward in the radial direction are defined as the first vertex Za and the second vertex Zb. The radial difference (outer edge side radial difference) Va-1 and Vb-1 between the positions of the first vertex Za and the second vertex Zb and the positions of the axial outer edges 88a and 88b of the oil ring on the actual contact surface is 1. It is set in the range of .5 μm to 5.0 μm. Va-1 and Vb-1 are preferably in the range of 2.0 μm to 4.0 μm. On the other hand, the radial difference (inner edge side radial difference) Va-2 and Vb-2 between the positions of the first vertex Za and the second vertex Zb and the positions of the axial inner edges 89a and 89b of the oil ring on the actual contact surface is , 0.0 μm to 1.5 μm. Va-2 and Vb-2 are preferably in the range of 0.1 μm to 1.0 μm. The case where Va-2 and Vb-2 are 0.0 μm means that the first apex Za and the second apex Zb coincide with the axial inner edges 89a and 89b of the oil ring on the actual contact surface. To do. Further, the outer edge side radial difference Va-1 and Vb-1 are set to be larger than the inner edge side radial difference Va-2 and Vb-2 (Va-1> Va-2, Vb-1> Vb-. 2) More specifically, the inner edge side radial difference is preferably 3 times or more, more preferably 4 times or more, as compared with the inner edge side radial difference.

Specifically, in the oil ring B (actual contact width 0.250 mm) of Example 2, the outer edge side radial difference is Va-1 = 2.4 μm and Vb-1 = 2.0 μm, and the inner edge side radial difference is. Va-2 = 0.5 μm and Vb-2 = 0.2 μm.

<Second method of making the shape of the outer peripheral surface of the oil ring>

Next, regarding the three-piece type oil ring 70 described with reference to FIG. 3 (A), a second detailed procedure for forming a weak barrel shape on the outer peripheral surface thereof will be described with reference to FIGS. 19 and 20. Although the radial cross-sectional shape of the outer peripheral surface is enlarged and shown in FIG. 20, the barrel shape is exaggeratedly displayed by significantly increasing the radial enlargement ratio with respect to the widthwise enlargement ratio. There is.

As shown in FIG. 20 (A), as the soft layer forming step S410, the first outer peripheral surface 82a and the second outer peripheral surface of the independent first side rail 73a and the second side rail 73b removed from the spacer expander 76s. With respect to 82b, soft layers 200a and 200b having low hardness that can be worn away in a familiar operation step described later are formed. The surface hardness of the soft layers 200a and 200b is formed to 1500 Hv or less by Cr plating treatment, nickel plating treatment (Ni-P plating treatment), galvanization treatment, gas nitriding treatment, low hardness DLC treatment, soft resin coating and the like. Just do it. The thickness of this soft layer is preferably 3 μm or more, more preferably 5 μm or more.

Next, as shown in FIG. 20B, as the pre-assembly step S420, the first and second side rails 73a and 73b are incorporated into the spacer expander 76s or a jig similar thereto. At this time, the first outer peripheral surface 82a and the second outer peripheral surface 82b are inclined in the width directions 73a and 73b of the first and second side rails. It can be said that the diameter is reduced by inclining the first outer peripheral surface 82a and the second outer peripheral surface 82b. As a result, the first outer peripheral surface 82a and the second outer peripheral surface 82b are closer to each other than the inner peripheral surfaces of the first and second side rails 73a and 73b. The inclination angle of the first outer peripheral surface 82a and the second outer peripheral surface 82b is preferably 0.25 degrees or more.

Next, as shown in FIG. 20C, as the initial polishing step S430, the first outer peripheral surfaces 82a of the first and second side rails 73a and 73b assembled to the spacer expander 76s or a jig similar thereto. , The second outer peripheral surface 82b is polished with a polishing tool. As a result, the axially outer regions 82a-1 and 82b-1 of the oil ring on the first outer peripheral surface 82a and the second outer peripheral surface 82b are polished more than the axial inner regions 82a-2 and 82b-2 of the oil ring. As a result, an initial barrel shape that is radially outwardly convex with respect to the first outer peripheral surface 82a and the second outer peripheral surface 82b is formed. This initial barrel shape is in a state in which the inclination angles generated on the first outer peripheral surface 82a and the second outer peripheral surface 82b in the assembling step S330 are reduced or almost eliminated. This polishing process is a so-called lapping process, and is a first process in which abrasive grains are interposed in a tool having a cylindrical inner peripheral surface that is close to the outer diameter of the first side rail 73a and the second side rail 73b. The outer peripheral surface 82a and the second outer peripheral surface 82b are relatively moved.

After the initial polishing step S430, the soft layers 200a and 200b of the axially outer edges 88a and 88b of the oil ring on the contact surfaces (surfaces to be polished) formed on the first outer peripheral surface 82a and the second outer peripheral surface 82b. The residual thicknesses Oa and Ob are smaller than the residual thicknesses Ia and Ib of the soft layers of the axial inner edges 89a and 89b of the oil ring on the first outer peripheral surface 82a and the second outer peripheral surface 82b. This difference in residual thickness (Ia-Oa, Ib-Ob) is preferably set to 1 μm or more.

Next, as shown in FIG. 20 (D), as the final assembling step S440, the first side rail 73a and the second side rail 73b that have undergone the initial polishing step S430 are incorporated into the piston together with the spacer expander 76s.

Further, as shown in FIG. 20 (D), as the familiar operation step S450, the internal combustion engine is normally operated, so that the oil ring 70 that has undergone the final assembly step S440 is slid with the cylinder bore 10 of the internal combustion engine. By this sliding, the first outer peripheral surface 82a and the second outer peripheral surface 82b are worn away, and a final barrel shape that is convex outward in the radial direction is created.

As a result of the above, in the state after the familiar operation step, the actual contact width in the axial direction of the actual contact surface where the first outer peripheral surface 82a and the second outer peripheral surface 82b can come into contact with the cylinder bore 10 is 0.15 mm or more.

Between the initial polishing step S430 and the final assembly step S440, it is necessary to temporarily disassemble the first side rail 73a and the second side rail 73b from the spacer expander 76s or the jig. As shown in FIG. 21, the first outer peripheral surface 82a and the second outer peripheral surface 82b of the first side rail 73a and the second side rail 73b whose tension is released after the initial polishing step S430 are paired with the first side rail 73a. , The second side rail 73b is inclined outward in the width direction. That is, the actual contact surfaces of the first outer peripheral surface 82a and the second outer peripheral surface 82b have an asymmetrical shape between the axial outer regions 82a-1 and 82b-1 and the axial inner regions 82a-2 and 82b-2. Therefore, in the subsequent final assembly step S440, the first side rail 73a and the second side rail 73b are opposed to the first side rail 73a and the second side rail 73b so as not to make a mistake in the direction in which the first side rail 73a and the second side rail 73b face each other. It is preferable to add a mark so that the side (inside in the axial direction) can be identified.

The maximum abrasion allowance Lm (see FIG. 20D) in the familiar operation step S450 may be smaller than the maximum polishing allowance Sm in the initial polishing step S320 (see FIG. 20C). ..

In the above-mentioned second making method, the initial polishing step S430 is performed after passing through the soft layer forming step S410, but the present invention is not limited to this. In the case of the lapping process in the initial polishing step S430, the surface of the base metal can be directly cut without forming a soft layer. On the other hand, in order to cause wear in the familiar operation step S450, it is necessary to form the soft layers 200a and 200b in advance. Therefore, it is also possible to perform the soft layer forming step after performing the initial polishing step S430 and before the familiar operation step S450. In this case, the thickness of the soft layers 200a and 200b can be small, for example, 3 μm or less.

The oil ring 70 completed according to FIG. 20 (D) is removed from the piston 30, and the first side rail 73a and the second side rail 73b are separated and separated from the spacer expander 76s. The state of the surface 82b is shown in FIG. 22 (B). The first side rail 73a and the second side rail 73b released from the urging by the spacer expander 76s return from the inclined state.

When the first outer peripheral surface 82a and the second outer peripheral surface 82b are cross-sectionally viewed, the locations most protruding outward in the radial direction are defined as the first vertex Za and the second vertex Zb. The radial difference (outer edge side radial difference) Va-1 and Vb-1 between the positions of the first vertex Za and the second vertex Zb and the positions of the axial outer edges 88a and 88b of the oil ring on the actual contact surface is 1. It is set in the range of .5 μm to 5.0 μm. Va-1 and Vb-1 are preferably in the range of 2.0 μm to 4.0 μm. On the other hand, the radial difference (inner edge side radial difference) Va-2 and Vb-2 between the positions of the first vertex Za and the second vertex Zb and the positions of the axial inner edges 89a and 89b of the oil ring on the actual contact surface is , 0.0 μm to 1.5 μm. Va-2 and Vb-2 are preferably in the range of 0.1 μm to 1.0 μm. The case where Va-2 and Vb-2 are 0.0 μm means that the first apex Za and the second apex Zb coincide with the axial inner edges 89a and 89b of the oil ring on the actual contact surface. To do. Further, the outer edge side radial difference Va-1 and Vb-1 are set to be larger than the inner edge side radial difference Va-2 and Vb-2 (Va-1> Va-2, Vb-1> Vb-. 2) More specifically, the inner edge side radial difference is preferably 3 times or more, more preferably 4 times or more, as compared with the inner edge side radial difference.

Specifically, in the oil ring A (actual contact width 0.350 mm) of Example 2, the outer edge side radial difference is Va-1 = 3.4 μm and Vb-1 = 3.6 μm, and the inner edge side radial difference is. Va-2 = 0.5 μm and Vb-2 = 0.2 μm.

It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

10 Cylinder bore 12 Inner wall surface 30 Piston 40 Piston ring 50 Top ring 60 Second ring 70 Oil ring 73a, 73b Side rail 76s Spacer expander 82 Outer peripheral surface 82A Upper outer peripheral surface 200a, 200b Soft layer 200a, 200b Soft layer

Claims (13)

A sliding structure of an internal combustion engine having a cylinder, a piston and a piston ring.
The piston ring has a top ring and an oil ring.
The actual contact width in the axial direction of the actual contact surface on which the top ring or the oil ring can come into contact with the cylinder is 0.05 mm or more.
A sliding structure of an internal combustion engine, characterized in that the surface pressure acting between the actual contact surface and the cylinder is 2.0 MPa or less. A sliding structure of an internal combustion engine having a cylinder, a piston and a piston ring.
The piston ring has a top ring and an oil ring.
A partial outer peripheral surface located outside the reference cylinder, which is offset inward by 0.5 μm in the radial direction from the outermost peripheral edge of the top ring or the oil ring, is used as a virtual actual contact surface of the top ring or the oil ring with respect to the cylinder. At the time of definition, the virtual actual contact width in the axial direction on the virtual actual contact surface is 0.05 mm or more.
A sliding structure of an internal combustion engine, characterized in that the surface pressure acting between the virtual actual contact surface and the cylinder is 2.0 MPa or less. The lubricating oil used in the internal combustion engine has a kinematic viscosity at 100 ° C. of less than 16.3 [mm2 / s].
The sliding structure of an internal combustion engine according to claim 1 or 2. The oil film thickness measured by the capacitance method is 0.5 μm to 4.0 μm at a passing point through which the top ring or the oil ring passes at the maximum speed during the stroke.
The sliding structure of an internal combustion engine according to any one of claims 1 to 3. When the surface roughness of the sliding surface of the cylinder is defined as Ra (μm), the oil film thickness calculated by the modified Reynolds equation at the passing point where the top ring or the oil ring passes at the maximum speed during the stroke. The feature is that the value is 3.0 × Ra (μm) or more.
The sliding structure of an internal combustion engine according to any one of claims 1 to 4. The surface pressure of the top ring is 0.3 MPa or less.
The sliding structure of an internal combustion engine according to any one of claims 1 to 5. The surface pressure of the oil ring is 1.4 MPa or less.
The sliding structure of an internal combustion engine according to any one of claims 1 to 6. The oil ring is a three-piece type.
The sliding structure of an internal combustion engine according to any one of claims 1 to 7. The surface pressure of the oil ring is 3 times or less the surface pressure of the top ring.
The sliding structure of an internal combustion engine according to any one of claims 1 to 8. The amount of displacement in the radial direction when moving along the circumferential direction on the actual contact surface or the virtual actual contact surface of the top ring or the oil ring is 10 μm or less.
The sliding structure of an internal combustion engine according to any one of claims 1 to 9. The internal combustion engine is a gasoline engine.
The sliding structure of an internal combustion engine according to any one of claims 1 to 10. It is a method of making a sliding structure of an internal combustion engine having a cylinder, a piston and a piston ring.
The piston ring has a three-piece type oil ring having a holding member for holding the first and second side rails and the first and second side rails.
By polishing the first outer peripheral surface of the first side rail and the second outer peripheral surface of the second side rail in a state independent of the holding member with a polishing tool, the first outer peripheral surface and the second outer peripheral surface are polished. The initial polishing process to create the initial barrel shape that is convex outward in the radial direction,
By incorporating the first and second side rails that have undergone the initial polishing step into the piston together with the holding member, the first outer peripheral surface and the second outer peripheral surface are aligned in the width direction of the first and second side rails. An assembling step in which the first outer peripheral surface and the second outer peripheral surface are brought close to each other by tilting.
By sliding the oil ring that has undergone the assembling step with the cylinder of the internal combustion engine, the axially outer region of the oil ring on the first outer peripheral surface and the second outer peripheral surface is formed on the first outer peripheral surface and the first outer peripheral surface. A familiar operation step in which the oil ring is worn more than the axially inner region of the oil ring on the second outer peripheral surface to form a final barrel shape that is radially outwardly convex with respect to the first outer peripheral surface and the second outer peripheral surface. By going through
The actual contact width in the axial direction of the actual contact surface that the oil ring can contact the cylinder is 0.05 mm or more, and the surface pressure acting between the actual contact surface and the cylinder is 2.0 MPa or less. A method of making a sliding structure of an internal combustion engine. It is a method of making a sliding structure of an internal combustion engine having a cylinder, a piston and a piston ring.
The piston ring has a three-piece type oil ring having a holding member for holding the first and second side rails and the first and second side rails.
By incorporating the first and second side rails into the holding member or a jig similar to the holding member, the first outer peripheral surface and the second outer peripheral surface are oriented in the width direction of the first and second side rails. A pre-assembly step of tilting the first outer peripheral surface and the second outer peripheral surface to bring them closer to each other.
By using a polishing tool, the axially outer region of the oil ring on the first outer peripheral surface and the second outer peripheral surface can be changed to the axial inner region of the oil ring on the first outer peripheral surface and the second outer peripheral surface. An initial polishing step of polishing more than the first to form an initial barrel shape that is radially outwardly convex with respect to the first outer peripheral surface and the second outer peripheral surface.
A final assembling step of incorporating the first and second side rails that have undergone the initial polishing step into the piston together with the holding member.
By sliding the oil ring that has undergone the final assembly step with the cylinder of the internal combustion engine, the first outer peripheral surface and the second outer peripheral surface are worn away, and the first outer peripheral surface and the second outer peripheral surface are subjected to. By going through the familiar operation process of creating the final barrel shape that is convex outward in the radial direction.
The actual contact width in the axial direction of the actual contact surface that the oil ring can contact the cylinder is 0.05 mm or more, and the surface pressure acting between the actual contact surface and the cylinder is 2.0 MPa or less. A method of making a sliding structure of an internal combustion engine.

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