Sliding structure for internal combustion engine, method for controlling idling operation, and method for controlling operation of internal combustion engine

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.

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.

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.

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.

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.