# US 11,111,875 B2 · Sliding structure for internal combustion engine, method for controlling idling operation, and method for controlling operation of internal combustion engine

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- Number: US 11,111,875 B2
- Document ID: US11111875B2
- Status: Granted
- Kind: B2
- Application number: 16/305,657
- Filed: 2017-05-30
- Published: 2020-10-15
- Granted: 2021-09-07
- Earliest claimed: 2016-05-31
- Assignees: Nippon Piston Ring Co., Ltd.
- Applicants: Nippon Piston Ring Co., Ltd.
- Inventors: Mitsuru Urabe; Hirokazu Murata; Kazuhiko Kanno; Jyuta Tase; Kazumi Moroi
- Web page: https://patentgrep.com/patent/US11111875B2

## CPC

- F01M 1/06: Lubricating systems characterised by the provision therein of crankshafts or connecting rods with lubricant passageways, e.g. bores (crankshafts, connecting-rods, per se F16C)
- F02F 1/20: characterised by constructional features providing for lubrication
- F02F 1/00: Cylinders; Cylinder heads
- F02F 1/004: {Cylinder liners (F02F1/08, F02F1/16 take precedence)}
- F02F 3/00: Pistons
- F02F 5/00: Piston rings, e.g. associated with piston crown
- F16J 9/06: using separate springs {or elastic elements} expanding the rings; Springs therefor {; Expansion by wedging}
- F16J 9/12: Details
- F16J 9/20: Rings with special cross-section (L-section rings F16J9/02); Oil-scraping rings {(F16J9/06 takes precedence)}
- F16J 9/26: characterised by the use of particular materials
- F16J 10/04: Running faces; Liners
- F02D 2200/02: the parameters being related to the engine
- F01M: LUBRICATING OF MACHINES OR ENGINES IN GENERAL; LUBRICATING INTERNAL COMBUSTION ENGINES; CRANKCASE VENTILATING
- F02F: CYLINDERS, PISTONS OR CASINGS, FOR COMBUSTION ENGINES; ARRANGEMENTS OF SEALINGS IN COMBUSTION ENGINES
- F16J: PISTONS {(specially adapted for dampers F16F9/32)}; CYLINDERS; SEALINGS
- F02D: CONTROLLING COMBUSTION ENGINES (vehicle fittings, acting on a single sub-unit only, for automatically controlling vehicle speed B60K31/00; conjoint control of vehicle sub-units of different type or different function, road vehicle drive control systems for purposes other than the control of a single sub-unit B60W)

## Abstract

In a sliding structure for an internal combustion, a cylinder has recesses in a stroke center region. Piston rings have inclined surfaces on an outer circumferential surface, and a lubricating oil flows between the inner wall surface and the outer circumferential surface that relatively move via the inclined surfaces. At any RPM equal to or greater than at idle, a center friction coefficient at the stroke center region through which the piston rings pass at the highest speed is less than a center friction coefficient when no recesses are formed in the stroke center region. Contrarily, at the RPM, an outside friction coefficient when the piston rings pass through a region outside the stroke center region is less than an outside friction coefficient when the recesses are formed in the outside region. As a result, further improved low fuel efficiency is achieved for the dimple liner technique.

## Claims

### Claim 1

A sliding structure for an internal combustion engine having a cylinder and a piston, the sliding structure comprising:
the piston having:
an oil ring groove having a lower surface;
an oil ring being disposed in the oil ring groove;
a top ring groove having an upper surface, the top ring groove being located closer to a top of the piston than the oil ring groove along a piston stroke direction; and
a top ring being disposed in the top ring groove; and
the cylinder having:
an inner wall surface;
a reference stroke region of the inner wall surface, the reference stroke region being from a first position corresponding to the lower surface of the oil ring groove when the piston is at a top dead center to a second position corresponding to the upper surface of the top ring groove when the piston is at a bottom dead center;
a stroke center region of the inner wall surface within the reference stroke region, the stroke center region being located below the first position of the reference stroke region, the stroke center region having a plurality of recesses, the stroke center region having an upper edge and a lower edge opposite to each other, the upper edge being located closer to the first position than the lower edge; and
an upper smooth region of the inner wall surface within the reference stroke region, the upper smooth region being free from any of the plurality of recesses, an entirety of the upper smooth region being located from the first position of the reference stroke region to the upper edge of the stroke center region,
wherein an outer circumferential surface of each of the oil ring and the top ring is in contact with the inner wall surface of the cylinder and has inclined surfaces that are inclined with respect to a direction away from the inner wall surface of the cylinder, a gap between the inner wall surface of the cylinder and the outer circumferential surface is configured to flow a lubricating oil into the gap,
at any RPM equal to or greater than an RPM for an idling operation of the internal combustion engine, a center friction coefficient between the inner wall surface and the outer circumferential surface at a place of the stroke center region through which the oil ring and the top ring pass at a highest speed is set to be less than the center friction coefficient when it is assumed that the plurality of recesses are not formed in the stroke center region,
at any RPM equal to or greater than the RPM for the idling operation of the internal combustion engine, an outside friction coefficient between the inner wall surface and the outer circumferential surface when the oil ring and the top ring pass through any place in an outside region that is outside the stroke center region is set to be less than the outside friction coefficient when it is assumed that the plurality of recesses are formed in the outside region, and
a distance along the piston stroke direction of the upper smooth region is 30% or greater of a distance along the piston stroke direction of the reference stroke region.

### Claim 2 (depends on 1)

The sliding structure for the internal combustion engine according to claim 1, wherein
a center point of the stroke center region in the piston stroke direction is located closer to the second position of the bottom dead center of the piston than a center point of the reference stroke region in the piston stroke direction.

### Claim 3 (depends on 1)

The sliding structure for the internal combustion engine according to claim 1, wherein
when a position at which the top ring passes through the inner wall surface at the highest speed is defined as a fastest speed point, and
the upper edge of the stroke center region is located at or below the fastest speed point.

### Claim 4 (depends on 1)

The sliding structure for the internal combustion engine according to claim 1, wherein
a maximum distance of the inclined surfaces from the inner wall surface is set to 1/2000 or greater of a width of an actual contact area of the outer circumferential surface that is in contact with the inner wall surface.

### Claim 5 (depends on 1)

The sliding structure for the internal combustion engine according to claim 1, wherein
a sliding surface of each of the oil ring and the top ring with respect to the cylinder is configured with
a base member,
a first layer formed on the base member, and
a second layer which is deposited on the first layer and softer than the first layer.

### Claim 6 (depends on 5)

The sliding structure for the internal combustion engine according to claim 5, wherein
the first layer has a surface roughness (Ra) of 0.7 μm or less.

### Claim 7

A sliding structure for an internal combustion engine having a cylinder and a piston, the sliding structure comprising:
the piston having:
an oil ring groove having a lower surface;
an oil ring being disposed in the oil ring groove;
a top ring groove having an upper surface, the top ring groove being located closer to a top of the piston than the oil ring groove along a piston stroke direction; and
a top ring being disposed in the top ring groove; and
the cylinder having:
an inner wall surface;
a reference stroke region of the inner wall surface, the reference stroke region being from a first position corresponding to the lower surface of the oil ring groove when the piston is at a top dead center to a second position corresponding to the upper surface of the top ring groove when the piston is at a bottom dead center;
a stroke center region of the inner wall surface within the reference stroke region, the stroke center region being located below the first position of the reference stroke region, the stroke center region having a plurality of recesses, the stroke center region having an upper edge and a lower edge opposite to each other, the upper edge being located closer to the first position than the lower edge; and
an upper smooth region of the inner wall surface within the reference stroke region, the upper smooth region being free from any of the plurality of recesses, an entirety of the upper smooth region being located from the first position of the reference stroke region to the upper edge of the stroke center region,
wherein an outer circumferential surface of each of the oil ring and the top ring is in contact with the inner wall surface of the cylinder and has inclined surfaces that are inclined with respect to a direction away from the inner wall surface of the cylinder, a gap between the inner wall surface of the cylinder and the outer circumferential surface is configured to flow a lubricating oil into the gap,
at any RPM equal to or greater than an RPM for an idling operation of the internal combustion engine, a boundary center side friction coefficient when the oil ring and the top ring pass through a vicinity region in the stroke center region adjacent to a boundary between the stroke center region and an outside region outside the stroke center region is set to be less than a boundary outside friction coefficient when the oil ring and the top ring pass through a vicinity region in the outside region adjacent to the boundary, and
a distance along the piston stroke direction of the upper smooth region is 30% or greater of a distance along the piston stroke direction of the reference stroke region.

### Claim 8 (depends on 7)

The sliding structure for the internal combustion engine according to claim 7, wherein
a center point of the stroke center region in the piston stroke direction is located closer to the second position of the bottom dead center of the piston than a center point of the reference stroke region in the piston stroke direction.

### Claim 9 (depends on 7)

The sliding structure for the internal combustion engine according to claim 7, wherein
when a position at which the top ring passes through the inner wall surface at a highest speed is defined as a fastest speed point, and
the upper edge of the stroke center region is located at or below the fastest speed point.

### Claim 10 (depends on 7)

The sliding structure for the internal combustion engine according to claim 7, wherein
at any RPM equal to or greater than the RPM for the idling operation of the internal combustion engine, a center friction coefficient between the inner wall surface and the outer circumferential surface at a place of the stroke center region through which the oil ring and the top ring pass at a highest speed is set to be less than the center friction coefficient when it is assumed that the plurality of recesses are not formed in the stroke center region, and
at any RPM equal to or greater than the RPM for the idling operation of the internal combustion engine, an outside friction coefficient between the inner wall surface and the outer circumferential surface when the oil ring and the top ring pass through any place in an outside region that is outside the stroke center region is set to be less than the outside friction coefficient when it is assumed that the plurality of recesses are formed in the outside region.

### Claim 11 (depends on 7)

The sliding structure for the internal combustion engine according to claim 7, wherein
a ratio (μ1/μ2) of the boundary outside friction coefficient μ1 to the boundary center side friction coefficient μ2 is set to within a range of 2.5 or less.

### Claim 12 (depends on 11)

The sliding structure for the internal combustion engine according to claim 11, wherein
the ratio (μ1/μ2) of the boundary outside friction coefficient μ1 to the boundary center side friction coefficient μ2 is set to within a range of 1.5 or less.

### Claim 13 (depends on 7)

The sliding structure for the internal combustion engine according to claim 7, wherein
a maximum distance of the inclined surfaces from the inner wall surface is set to 1/2000 or greater of a width of an actual contact area of the outer circumferential surface that is in contact with the inner wall surface.

### Claim 14 (depends on 7)

The sliding structure for the internal combustion engine according to claim 7, wherein
a sliding surface of each of the oil ring and the top ring with respect to the cylinder is configured with
a base member,
a first layer formed on the base member, and
a second layer which is deposited on the first layer and softer than the first layer.

### Claim 15

A method for controlling an idling operation of an internal combustion engine having a cylinder and a piston, the method comprising the steps of:
providing the piston, the piston having:
an oil ring groove having a lower surface;
an oil ring being disposed in the oil ring groove;
a top ring groove having an upper surface, the top ring groove being located closer to a top of the piston than the oil ring groove along a piston stroke direction; and
a top ring being disposed in the top ring groove;
providing an inner wall surface of the cylinder;
providing a reference stroke region of the inner wall surface, the reference stroke region being from a first position corresponding to the lower surface of the oil ring groove when the piston is at a top dead center to a second position corresponding to the upper surface of the top ring groove when the piston is at a bottom dead center;
providing a stroke center region of the inner wall surface within the reference stroke region, the stroke center region being located below the first position of the reference stroke region, the stroke center region having a plurality of recesses, the stroke center region having an upper edge and a lower edge opposite to each other, the upper edge being located closer to the first position than the lower edge; and
providing an upper smooth region of the inner wall surface within the reference stroke region, the upper smooth region being free from any of the plurality of recesses, an entirety of the upper smooth region being located from the first position of the reference stroke region to the upper edge of the stroke center region,
wherein an outer circumferential surface of each of the oil ring and the top ring is in contact with the inner wall surface of the cylinder and has inclined surfaces that are inclined with respect to a direction away from the inner wall surface of the cylinder, a gap between the inner wall surface of the cylinder and the outer circumferential surface is configured to flow a lubricating oil into the gap,
a distance along the piston stroke direction of the upper smooth region is 30% or greater of a distance along the piston stroke direction of the reference stroke region, and
an RPM at an idling operation of the internal combustion engine is controlled so as to satisfy a condition A and a condition B below:
the condition A: a center friction coefficient between the inner wall surface and the outer circumferential surface at a place of the stroke center region through which the oil ring and the top ring pass at a highest speed is to be less than the center friction coefficient when it is assumed that the plurality of recesses are not formed in the stroke center region; and
the condition B: an outside friction coefficient between the inner wall surface and the outer circumferential surface at any place in an outside region that is outside the stroke center region is to be less than the outside friction coefficient when it is assumed that the plurality of recesses are formed in the outside region.

### Claim 16 (depends on 15)

The method according to claim 15, wherein
a center point of the stroke center region in the piston stroke direction is located closer to the second position of the bottom dead center of the piston than the center point of the reference stroke region in the piston stroke direction.

### Claim 17 (depends on 15)

The method according to claim 15, wherein
when a position at which the top ring passes through the inner wall surface at the highest speed is defined as a fastest speed point, and
the upper edge of the stroke center region is located at or below the fastest speed point.

### Claim 18

A method for controlling an idling operation of an internal combustion engine having a cylinder and a piston, the method comprising the steps of:
providing the piston, the piston having:
an oil ring groove having a lower surface;
an oil ring being disposed in the oil ring groove;
a top ring groove having an upper surface, the top ring groove being located closer to a top of the piston than the oil ring groove along a piston stroke direction; and
a top ring being disposed in the top ring groove;
providing an inner wall surface of the cylinder;
providing a reference stroke region of the inner wall surface, the reference stroke region being from a first position corresponding to the lower surface of the oil ring groove when the piston is at a top dead center to a second position corresponding to the upper surface of the top ring groove when the piston is at a bottom dead center;
providing a stroke center region of the inner wall surface within the reference stroke region, the stroke center region being located below the first position of the reference stroke region, the stroke center region having a plurality of recesses, the stroke center region having an upper edge and a lower edge opposite to each other, the upper edge being located closer to the first position than the lower edge; and
providing an upper smooth region of the inner wall surface within the reference stroke region, the upper smooth region being free from any of the plurality of recesses, an entirety of the upper smooth region being located from the first position of the reference stroke region to the upper edge of the stroke center region,
wherein an outer circumferential surface of each of the oil ring and the top ring is in contact with the inner wall surface of the cylinder and has inclined surfaces that are inclined with respect to a direction away from the inner wall surface of the cylinder, a gap between the inner wall surface of the cylinder and the outer circumferential surface is configured to flow a lubricating oil into the gap,
a distance along the piston stroke direction of the upper smooth region is 30% or greater of a distance along the piston stroke direction of the reference stroke region, and
an RPM at an idling operation of the internal combustion engine is controlled so as to satisfy a condition C below:
the condition C: a boundary center side friction coefficient when the oil ring and the top ring pass through a vicinity region in the stroke center region adjacent to a boundary between the stroke center region and an outside region outside the stroke center region is set to be less than a boundary outside friction coefficient when the oil ring and the top ring pass through a vicinity region in the outside region adjacent to the boundary.

### Claim 19 (depends on 18)

The method according to claim 18, wherein
the RPM at the idling operation of the internal combustion engine is controlled so as to satisfy a condition A and a condition B below:
the condition A: a center friction coefficient between the inner wall surface and the outer circumferential surface at a place of the stroke center region through which the oil ring and the top ring pass at a highest speed is to be less than the center friction coefficient when it is assumed that the plurality of recesses are not formed in the stroke center region; and
the condition B: an outside friction coefficient between the inner wall surface and the outer circumferential surface at any place in an outside region that is outside the stroke center region is to be less than the outside friction coefficient when it is assumed that the plurality of recesses are formed in the outside region.

### Claim 20 (depends on 18)

The method according to claim 18, wherein
the RPM at the idling operation of the internal combustion engine is controlled so as to satisfy a condition D below:
the condition D: a ratio (μ1/μ2) of the boundary outside friction coefficient μ1 to the boundary center side friction coefficient μ2 is to be within the range of 2.5 or less.

### Claim 21 (depends on 18)

The method according to claim 18, wherein
a center point of the stroke center region in a stroke direction is located on a side of the bottom dead center of the piston with respect to the center point of the reference stroke region in the stroke direction.

### Claim 22 (depends on 18)

The method according to claim 18, wherein
when a position at which the top ring passes through the inner wall surface at a highest speed is defined as a fastest speed point,
the upper edge of the stroke center region is located at or below the fastest speed point.

### Claim 23

A method for controlling an operation of an internal combustion engine having a cylinder and a piston, the method comprising the steps of:
providing the piston, the piston having:
an oil ring groove having a lower surface;
an oil ring being disposed in the oil ring groove;
a top ring groove having an upper surface, the top ring groove being located closer to a top of the piston than the oil ring groove along a piston stroke direction; and
a top ring being disposed in the top ring groove;
providing an inner wall surface of the cylinder;
providing a reference stroke region of the inner wall surface, the reference stroke region being from a first position corresponding to the lower surface of the oil ring groove when the piston is at a top dead center to a second position corresponding to the upper surface of the top ring groove when the piston is at a bottom dead center;
providing a stroke center region of the inner wall surface within the reference stroke region, the stroke center region being located below the first position of the reference stroke region, the stroke center region having a plurality of recesses, the stroke center region having an upper edge and a lower edge opposite to each other, the upper edge being located closer to the first position than the lower edge; and
providing an upper smooth region of the inner wall surface within the reference stroke region, the upper smooth region not having being free from any of the plurality of recesses, an entirety of the upper smooth region being located from the first position of the reference stroke region to the upper edge of the stroke center region,
wherein an outer circumferential surface of each of the oil ring and the top ring is in contact with the inner wall surface of the cylinder and has inclined surfaces that are inclined with respect to a direction away from the inner wall surface of the cylinder, a gap between the inner wall surface of the cylinder and the outer circumferential surface is configured to flow a lubricating oil into the gap,
a distance along the piston stroke direction of the upper smooth region is 30% or greater of a distance along the piston stroke direction of the reference stroke region,
an RPM of the internal combustion engine is controlled so as to satisfy a condition A and a condition B below:
the condition A: a center friction coefficient between the inner wall surface and the outer circumferential surface at a place of the stroke center region through which the oil ring and the top ring pass at a highest speed is to be less than the center friction coefficient when it is assumed that the plurality of recesses are not formed in the stroke center region; and
the condition B: an outside friction coefficient between the inner wall surface and the outer circumferential surface at any place in an outside region that is outside the stroke center region is to be less than the outside friction coefficient when it is assumed that the plurality of recesses are formed in the outside region.

### Claim 24 (depends on 23)

The method according to claim 23, wherein
a center point of the stroke center region in the piston stroke direction is located closer to the second position of the bottom dead center of the piston than a center point of the reference stroke region in the piston stroke direction.

### Claim 25 (depends on 23)

The method according to claim 23, wherein
when a position at which the top ring passes through the inner wall surface at the highest speed is defined as a fastest speed point, and
the upper edge of the stroke center region is located at or below the fastest speed point.

### Claim 26

A method for controlling an operation of an internal combustion engine having a cylinder and a piston, the method comprising the steps of:
providing the piston, the piston having:
an oil ring groove having a lower surface;
an oil ring being disposed in the oil ring groove;
a top ring groove having an upper surface, the top ring groove being located closer to a top of the piston than the oil ring groove along a piston stroke direction; and
a top ring being disposed in the top ring groove;
providing an inner wall surface of the cylinder;
providing a reference stroke region of the inner wall surface, the reference stroke region being from a first position corresponding to the lower surface of the oil ring groove when the piston is at a top dead center to a second position corresponding to the upper surface of the top ring groove when the piston is at a bottom dead center;
providing a stroke center region of the inner wall surface within the reference stroke region, the stroke center region being located below the first position of the reference stroke region, the stroke center region having a plurality of recesses, the stroke center region having an upper edge and a lower edge opposite to each other, the upper edge being located closer to the first position than the lower edge; and
providing an upper smooth region of the inner wall surface within the reference stroke region, the upper smooth region being free from any of the plurality of recesses, an entirety of the upper smooth region being located from the first position of the reference stroke region to the upper edge of the stroke center region,
wherein an outer circumferential surface of each of the oil ring and the top ring is in contact with the inner wall surface of the cylinder and has inclined surfaces that are inclined with respect to a direction away from the inner wall surface of the cylinder, a gap between the inner wall surface of the cylinder and the outer circumferential surface is configured to flow a lubricating oil into the gap,
a distance along the piston stroke direction of the upper smooth region is 30% or greater of a distance along the piston stroke direction of the reference stroke region, and
an RPM of the internal combustion engine is controlled so as to satisfy a condition C below:
the condition C: a boundary center side friction coefficient when the oil ring and the top ring pass through a vicinity region in the stroke center region adjacent to a boundary between the stroke center region and an outside region outside the stroke center region is set to be less than a boundary outside friction coefficient when the oil ring and the top ring pass through a vicinity region in the outside region adjacent to the boundary.

### Claim 27 (depends on 26)

The method according to claim 26, wherein
a ratio (μ1/μ2) of the boundary outside friction coefficient μ1 to the boundary center side friction coefficient μ2 is set to within a range of 2.5 or less.

### Claim 28 (depends on 26)

The method according to claim 26, wherein
a center point of the stroke center region in the piston stroke direction is located closer to the second position of the bottom dead center of the piston than a center point of the reference stroke region in the piston stroke direction.

### Claim 29 (depends on 26)

The method according to claim 26, wherein
when a position at which the top ring passes through the inner wall surface at a highest speed is defined as a fastest speed point, and
the upper edge of the stroke center region is located at or below the fastest speed point.