A link component (150) with an oil hole (150E) is attached to a crankshaft (106) of an internal combustion engine (E), and the oil hole (150E) allows communication from an outside to the crankshaft (106) side. The oil hole (150E) has an inclined surface (150F) along an opening rim on the crankshaft (106) side. A surface other than the oil hole (150E) has a carbon concentration of 0.5 wt % or more. The inclined surface (150F) has a carbon concentration within a range of 0.7 wt % or more and 0.9 wt % or less. Production cost is suppressed, and at the same time, damage is prevented by increasing resistance of the oil-hole part on which stress is liable to concentrate.

An engine piston having a piston upper part, a piston lower part connected to the piston upper part, a piston pin mounted in the piston lower part connects the piston to a connecting rod, and a first cooling space between the piston upper and lower parts for cooling oil. The first cooling space is connected to a second cooling space formed between the piston upper part and a piston lower part via at least one transfer bore, a cooling oil conduction sleeve for conducting cooling oil through a bore in the connecting rod towards the first cooling space. A guiding surface of the cooling oil conduction sleeve adjoins a support face of the piston lower part. At least one groove circulating in the circumferential direction is introduced into the guiding surface of the cooling oil conduction sleeve and/or into the support face of the piston lower part.

Provided is a compression ratio varying mechanism, including a communication hole including: a first opening opened in an outer peripheral side surface of a piston rod; and a second opening, which is prevented from being opposed to the first opening in a radial direction of a piston rod, and is connected to an oil passage at a position apart from the first opening in a stroke direction.

An actuator of a variable compression ratio mechanism for an internal combustion engine includes an arm link 13 configured to change a posture of the variable compression ratio mechanism for the internal combustion engine by swinging, a second control shaft 11 fixed to the arm link 13, and a housing 20 including a first bearing hole 301a supporting the second control shaft 11. The housing 20 includes a lubricant oil supply oil passage 202 opened to a pressure-receiving range over which a contact pressure is received at the first bearing hole 301a from the second control shaft 11 during an expansion stroke of the internal combustion engine.

A lower link (6) is provided with an oil hole (30) in a crank pin bearing portion (11) in order to supply a jet of oil to a connecting portion between an upper pin (4) and an upper link (3). Oil hole (30) is composed of a first oil hole (31) linearly extending from the inner peripheral surface of crank pin bearing portion (11) outwardly in the radial direction, and a second oil hole (32) linearly extending from the outer surface of lower link (6) so as to intersect a distal end portion of first oil hole (31). An inclination angle () of first oil hole (31) with a divided surface (14) set as a reference becomes relatively small, and hence the position of an oil inlet (31b) involving a problem of stress concentration becomes closer to divided surface (14) exhibiting a relatively low stress. Consequently, the stress concentration at oil inlet (31b) is alleviated.

A variable-compression-ratio engine may include a piston pin configured to interconnect a piston and an end portion of a connecting rod; an eccentric cam rotatably provided around the end portion of the connecting rod so that the piston pin is provided eccentrically to the eccentric cam, the eccentric cam serving to eccentrically rotate the piston pin via rotation thereof to vary a height of a top dead point of the piston; a latching plate configured to eject an oil, supplied thereinto, outwards in a circumferential direction through an oil ejection hole formed in an external peripheral surface thereof, to be rotated by an ejection pressure of the oil, the latching plate being rotated with the eccentric cam; and an oil supply device configured to selectively supply the oil into the latching plate.

A variable-compression-ratio engine may include a piston pin configured to interconnect a piston and an end portion of a connecting rod; an eccentric cam rotatably provided around the end portion of the connecting rod so that the piston pin is provided eccentrically to the eccentric cam, the eccentric cam serving to eccentrically rotate the piston pin via rotation thereof to vary a height of a top dead point of the piston; a latching plate configured to eject an oil, supplied thereinto, outwards in a circumferential direction through an oil ejection hole formed in an external peripheral surface thereof, to be rotated by an ejection pressure of the oil, the latching plate being rotated with the eccentric cam; and an oil supply device configured to selectively supply the oil into the latching plate.

A pin including recesses extending longitudinally between opposite ends, and a piston assembly including the pin, for a two-stroke engine, is provided. The recesses preferably have a radius of curvature less than a radius of curvature of the remaining outer surface of the pin. The pin is rotationally fixed relative to the connecting rod. As the connecting rod swings back and forth during operation, some of the recesses rotate beyond the load bearing region of the pin joint where oil is located, allowing oil to fill the recesses. As the pin swings back, these recesses carrying the oil enter the load bearing region of the pin joint, transferring the oil with them. Preferably, at least one of the recesses aligns with an oil opening in the pin, which aligns with an oil hole in the connecting rod, to receive and distribute oil along the full length of the pin.

A lower link (6) is provided with an oil hole (30) in a crank pin bearing portion (11) in order to supply a jet of oil to a connecting portion between an upper pin (4) and an upper link (3). Oil hole (30) is composed of a first oil hole (31) linearly extending from the inner peripheral surface of crank pin bearing portion (11) outwardly in the radial direction, and a second oil hole (32) linearly extending from the outer surface of lower link (6) so as to intersect a distal end portion of first oil hole (31). An inclination angle (?) of first oil hole (31) with a divided surface (14) set as a reference becomes relatively small, and hence the position of an oil inlet (31b) involving a problem of stress concentration becomes closer to divided surface (14) exhibiting a relatively low stress. Consequently, the stress concentration at oil inlet (31b) is alleviated.

A small end of a connecting rod includes an oil supply hole extending from an outer surface to an inner surface of the small end. The oil supply hole includes an oil storage groove and a communication hole. The oil storage groove is recessed from the outer surface and extends along the circumference of the small end. The communication hole extends through a bottom surface of the oil storage groove and connects the outer and inner surfaces. Opposite edges of the oil storage groove contact the outer surface in a direction the oil storage groove extends. The bottom surface of the oil storage groove has an opening contacting a wall surface of the communication hole. When the small end includes a distal end of the connecting rod defining a top, the opposite edges are located between the top and the opening in the bottom surface of the oil storage groove.