JP6132057B2 - Lubrication structure of a multi-link piston-crank mechanism of an internal combustion engine - Google Patents

Description

  The present invention relates to a multi-link type piston-crank mechanism for an internal combustion engine, and more particularly to a lubricating structure for a pin bearing portion.

  As a prior art in which a piston pin and a crank pin of a reciprocating internal combustion engine are connected by a multi-link type piston-crank mechanism, Patent Document 1 previously proposed by the present applicant is known. This includes an upper link connected to the piston pin of the piston, a lower link connecting the upper link and the crank pin of the crankshaft, one end supported to be swingable to the engine body side, and the other end to the lower link. A control link coupled to the link. The upper link and the lower link are rotatably connected to each other via an upper pin, and the control link and the lower link are rotatably connected to each other via a control pin.

  The lower link in such a multi-link type piston-crank mechanism is a kind of “lever” that receives the combustion pressure (in-cylinder pressure) received by the piston from the upper pin via the upper link and uses the control pin as a fulcrum. The force is transmitted to the crank pin by movement. Accordingly, a large combustion pressure or inertial load received by the piston is input to the lower link from the upper pin bearing portion via the piston pin, the upper link, and the upper pin. At the same time, a load is also generated in the crank pin bearing portion and the control pin bearing portion so as to balance this load. Accordingly, the surface pressure of each bearing portion is stricter than that of a general single link type reciprocating engine, and it is required to maintain a sufficient lubrication state in order to prevent wear and seizure.

  In particular, for lubrication of the bearing portion of the upper pin that connects the lower link and the upper link, the lower link revolves around the crankshaft together with the crankpin in accordance with the rotation of the crankshaft during engine operation. However, it is structurally difficult to forcibly supply the lubricating oil using hydraulic pressure.

  Therefore, in Patent Document 1 described above, oil passages are respectively formed in the pin boss portions of the crank pin, the lower link, and the upper link, and the oil passage of the crank pin and the oil passage of the lower link communicate with each other at a predetermined crank angle. Then, by injecting the lubricating oil from the oil path of the lower link toward the oil path of the pin boss part, the lubricating oil is supplied to the bearing part of the pin boss part of the upper link through the oil path of the lower link. Yes.

JP 2010-185329 A

  However, in the thing of the said patent document 1, the influence of the inertia force by rotation of a crankshaft at the time of the injection of the lubricating oil from a lower link is not considered, and it injects from the oil path of a lower link at the time of high rotation. There is a risk that the lubricating oil will start to deviate from the position of the oil passage of the pin boss portion of the supply destination, and the amount of oil supplied will decrease.

  Further, when the oil passage is formed through the pin boss portion of the upper link as in Patent Document 1, stress concentration is likely to occur around the oil passage, and the strength is reduced, so that durability and reliability are ensured. It becomes difficult.

  The present invention has been made in view of such circumstances, and in the structure in which lubricating oil is supplied from the lower link oil passage to the upper link and the pin boss portion of the control link, much of the lubricating oil injected from the lower link is provided. A new multi-link type piston for an internal combustion engine that can improve the lubrication performance by securing the amount of lubricating oil by ensuring good guidance to the pin bearing part of the pin boss part and the strength of the pin boss part. An object of the present invention is to provide a lubrication structure for a crank mechanism.

  The present invention relates to a lubrication structure for a multi-link piston-crank mechanism of an internal combustion engine. The multi-link piston-crank mechanism includes an upper link having one end connected to a piston via a piston pin, and the upper link. The lower link is connected to the other end of the crankshaft via an upper pin, and is rotatably attached to the crankpin of the crankshaft. One end is swingably supported on the engine body side, and the other end is controlled by the lower link. And a control link connected through pins.

  The crank pin has a crank pin oil passage that extends in the radial direction and has one end opened on the outer peripheral surface of the crank pin, and is supplied with lubricating oil of a predetermined pressure. The lower link oil passage formed in the lower link has a pin boss facing surface facing a pin boss portion of the upper link in which the upper pin is rotatably fitted or a pin boss portion of the control link in which the control pin is rotatably fitted, and And the bearing surface of the crank pin.

  When the crankpin oil passage and the lower link oil passage communicate with each other at a predetermined crank angle, the crankshaft rotation center is connected to the pin boss facing surface end of the lower link oil passage as viewed in the crankshaft direction. On the straight line, a pin boss portion that is a lubricant supply target is arranged. A concave portion recessed in the axial direction is provided on the axial side surface of the pin boss portion to be lubricated.

  As a result, when the crankpin oil passage and the lower link oil passage communicate with each other at a predetermined crank angle, the lubricating oil of a predetermined pressure supplied to the crankpin oil passage becomes the end portion on the pin boss facing surface side of the lower link oil passage. A portion of the jet boss is ejected and ejected, and a part thereof is supplied to the bearing portion of the upper pin and the control pin via a concave portion provided in the axial side surface of the pin boss portion. Here, the pin boss portion that is the lubricant supply target is arranged on a straight line connecting the rotation center of the crankshaft and the end portion on the pin boss facing surface side of the lower link oil passage through which the lubricant is injected. In addition, due to the inertial force due to the rotation of the crankshaft, most of the lubricant injected from the end of the lower link oil passage on the side facing the pin boss is directed to the pin boss that is the lubricant supply target and supplied to the pin boss. A sufficient amount of lubricating oil can be secured.

  In addition, as a structure that guides the lubricating oil injected and supplied to the pin boss part to the pin bearing part, a recess is formed on the side surface in the axial direction of the pin boss part. Concentration can be suppressed and a decrease in strength of the pin boss portion can be suppressed.

  According to the present invention, the lubricating oil is supplied to the pin bearing portions of the upper link and the control link through the recesses formed on the side surfaces in the axial direction of the crank pin oil passage, the lower link oil passage, and the pin boss portion. The amount of lubricating oil can be secured, and the lubricating performance can be improved. In addition, as a structure that guides the lubricating oil injected from the lower link to the pin bearing part of the pin boss part, since the concave part is formed on the side surface in the axial direction of the pin boss part, when the oil passage penetrates the pin boss part In comparison, the stress concentration can be suppressed, and the strength reduction of the pin boss portion can be suppressed.

1 is a cross-sectional view showing an example of a multi-link piston-crank mechanism of an internal combustion engine according to the present invention. Sectional drawing which shows the vicinity of a lower link. Explanatory drawing which compared the stress concentration coefficient (C) with the Example (A) which provided the recessed part in the pin boss | hub part, and the comparative example (B) which provided the through-hole. The load diagram (A) which shows the maximum torque and the maximum output which act on a lower link, and explanatory drawing (B) which shows the formation position of a lower link oil path. The load diagram (A) which shows the combustion load which acts on a crankpin, and explanatory drawing which shows the formation position of a crankpin oil path. Explanatory drawing which shows an example of the U injection period to an upper side pin boss | hub part, and the C injection period to a control side pin boss | hub part. The front view (A), side view (B), and perspective view (C) of the pin boss part vicinity which show an example of the said recessed part. The front view (A), side view (B), and perspective view (C) of the pin boss part vicinity which show the other example of the said recessed part. The front view (A), side view (B), and perspective view (C) of the pin boss part vicinity which show the further another example of the said recessed part.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory diagram showing a configuration example in which a multi-link piston-crank mechanism is configured as a variable compression ratio mechanism. This mechanism includes a multi-link type piston-crank mechanism mainly composed of a lower link 4, an upper link 5 and a control link 10. The crankshaft 1 includes a plurality of journal portions 2 and a crankpin 3, and the journal portion 2 is rotatably supported by a main bearing of the cylinder block 9. The crank pin 3 is eccentric from the journal portion 2 by a predetermined amount, and a lower link 4 is rotatably attached thereto.

  The lower link 4 is divided into a pair of lower link dividing members 31 and 32 fastened by bolts (not shown) so that the lower link 4 can be assembled to the crankpin 3 later. In the upper link 5, the upper pin boss portion 5 </ b> A on the lower end side is connected to the first lower side pin boss portion 4 </ b> A of the lower link 4 by the upper pin 6 so as to be relatively rotatable, and the upper end side is connected to the piston 8 by the piston pin 7. Has been. The piston 8 receives the combustion pressure and reciprocates in the cylinder 9 </ b> A of the cylinder block 9.

  The control link 10 that restrains the movement of the lower link 4 is configured such that the control-side pin boss portion 10A on the upper end side is connected to the second lower-side pin boss portion 4B of the lower link 4 by the control pin 11 so as to be relatively rotatable, and the lower end side is connected to the control shaft 12. Is supported by a lower part of a cylinder block 9 which is a part of the engine body through a shaft so as to be relatively rotatable. Specifically, the control shaft 12 is rotatably supported by the engine body, and has an eccentric cam portion 12A that is eccentric from the center of rotation, and the lower end portion of the control link 10 is rotatable on the eccentric cam portion 12A. Is fitted. The rotation position of the control shaft 12 is controlled by a compression ratio control actuator (not shown) that operates based on a control signal from an engine control unit (not shown).

  In such a variable compression ratio mechanism using a multi-link type piston-crank mechanism, when the control shaft 12 is rotated by a compression ratio control actuator, the center position of the eccentric cam portion 12A, in particular, relative to the engine body. The position changes. Thereby, the rocking | fluctuation support position of the lower end of the control link 10 changes. When the swing support position of the control link 10 changes, the stroke of the piston 8 changes, and the position of the piston 8 at the piston top dead center (TDC) becomes higher or lower. This makes it possible to change the engine compression ratio. That is, the control shaft 12, the compression ratio control actuator, the engine control unit, and the like provided with the eccentric cam portion 12A constitute variable compression ratio means that makes the engine compression ratio variable.

  The first lower-side pin boss portion 4A of the lower link 4 is formed in a bifurcated shape so as to sandwich the upper-side pin boss portion 5A, and the hollow upper pin 6 is rotatably fitted and inserted into the upper-side pin boss portion 5A. At both ends, it is fixed by press-fitting to a bifurcated first lower pin boss portion 4A. Accordingly, the pin boss facing surface 4C provided between the bifurcated first lower pin boss portion 4A of the lower link 4 faces and faces the outer peripheral surface of the upper side pin boss portion 5A.

  Similarly, the second lower side pin boss part 4B of the lower link 4 is configured to be bifurcated so as to sandwich the control side pin boss part 10A, and the control pin 11 is fitted to the control side pin boss part 10A so as to be rotatable. It is inserted and fixed to the second lower pin boss 4B that is bifurcated at both ends by press-fitting. Accordingly, the pin boss facing surface 4D provided between the bifurcated second lower side pin boss portion 4B of the lower link 4 faces and faces the outer peripheral surface of the control side pin boss portion 10A.

  A crankpin oil passage 21 is formed in the crankpin 3. The crankpin oil passage 21 extends linearly in the radial direction, and one end of the crankpin oil passage 21 opens on the outer peripheral surface of the crankpin 3. The crankpin oil passage 21 is supplied with lubricating oil having a predetermined pressure pressurized by an oil pump (not shown) via an axial oil passage 20 extending in the axial direction of the crankshaft 1. A lower link oil passage 22 is formed in the lower link 4. The lower link oil passage 22 includes a bearing metal (not shown) fitted in the bearing portion of the crank pin 3 and the pin boss facing surface 4C and the crank pin bearing surface facing the outer peripheral surface of the upper side pin boss portion 5A. That is, it penetrates the inner peripheral surface of the bearing metal.

  Next, characteristic configurations and operational effects of the illustrated embodiment are listed below. In the following description, the lubrication structure of the upper side pin boss portion 5A of the upper link 5 is mainly described. However, the same lubrication structure can be applied to the control side pin boss portion 10A of the control link 10 as well. is there.

  [1] As shown in FIG. 2, concave portions 23 that are recessed in the axial direction are provided on both side surfaces in the axial direction of the pin boss portion 5 </ b> A of the upper link 5. The recess 23 extends in the radial direction from the outer peripheral surface of the pin boss portion 5 </ b> A to the inner peripheral surface serving as the bearing surface of the upper pin 6. The crankpin oil passage 21 and the lower link oil passage 22 communicate with each other via a circumferential oil passage 24 to be described later at a predetermined crank angle, for example, a crank angle near the bottom dead center where the inertial load increases. The lubricating oil is injected and supplied from the end 22A of the lower link oil passage 22 on the side facing the pin boss toward the pin boss 5A. When the crank angle is such that the lubricant is injected and supplied, the rotation center 2A of the journal portion 2 of the crankshaft 1 and the end portion 22A of the lower link oil passage 22 on the pin boss facing surface side, The pin boss portion 5A is arranged on a straight line 25 that connects the two, more specifically, a concave portion 23 that is recessed on the axial side surface of the pin boss portion 5A is arranged.

  Therefore, in a link arrangement at a predetermined crank angle where the crankpin oil passage 21 and the lower link oil passage 22 communicate with each other, the lubricating oil having a predetermined pressure supplied to the crankpin oil passage 21 is pin boss of the lower link oil passage 22. It is sprayed from the end 22A on the opposite surface side and supplied to the bearing portion of the upper pin 6 via the recess 23 of the pin boss portion 5A.

  Here, on the straight line 25 connecting the rotation center 2A of the crankshaft 1 and the end portion 22A on the pin boss facing surface side of the lower link oil passage 22 through which the lubricating oil is injected, that is, the inertial force accompanying the rotation of the crankshaft 1 Since the concave portion 23 of the pin boss portion 5A to be supplied with the lubricating oil is arranged along the direction (25) in which the oil acts, the lower link oil is utilized by utilizing the inertial force accompanying the rotation of the crankshaft 1. Most of the lubricating oil injected from the end 22A on the side opposite to the pin boss of the path 22 is guided to the concave portion 23 of the pin boss portion 5A to be supplied with the lubricating oil, and is supplied from the concave portion 23 to the pin bearing portion. A sufficient amount of lubricating oil can be secured, and the lubrication performance of the pin bearing portion can be improved.

  Further, as a structure for guiding most of the lubricating oil injected from the lower link oil passage 22 to the recess 23, the end 22A on the pin boss facing surface side of the lower link oil passage 22 is arranged on a straight line 25 along the inertia direction. The shape and direction of the lower link oil passage 22 can be set appropriately in consideration of the strength of the lower link 4 and the like. It is possible to easily achieve both strength and security.

  Referring to FIG. 3, FIG. 3 (A) shows the structure of the above embodiment in which recesses 23 are formed on both side surfaces in the axial direction of the pin boss portion 5A as a structure for guiding the lubricating oil to the pin bearing portion of the pin boss portion 5A. FIG. 3B schematically shows the structure of a comparative example in which a through hole 26 is formed through the pin boss portion 5A as an oil passage that communicates the outer peripheral surface and the inner peripheral surface of the pin boss portion 5A. Is shown. In the example (A) and the comparative example (B), the link width 2b is the same, and the cross-sectional area of the recess 23 and the through hole 26, that is, the substantial flow rate is the same. In this case, the minimum link width L1 of the embodiment (A) is larger than the minimum link width L2 of the comparative example (B), and the curvature radius R1 of the recess 23 is larger than the curvature radius of the through hole 26. Therefore, as shown in FIG. 3C, in the structure of Example (A), compared to the structure of Comparative Example (B), the stress concentration coefficient with respect to the equivalent input load is reduced and the stress concentration is relaxed. Combined with the increase in link width (L1> L2), the strength of the pin boss portion 5A can be greatly improved.

  [2] As shown in FIG. 2, when the crankpin oil passage 21 and the lower link oil passage 22 communicate with each other at a predetermined crank angle, the rotation center 2A of the crankshaft 1 and the crankpin are viewed in the direction of the crankshaft. On the straight line 25 connecting the end portion 21A on the outer peripheral surface side of the oil passage 21 and the end portion 22A on the pin boss facing surface side of the lower link oil passage 22, a concave portion 23 of the pin boss portion 5A that is a lubricating oil supply target portion is formed. Has been placed. That is, the end portion 21A on the outer peripheral surface side of the crankpin oil passage 21 and the lower link oil passage along the inertia direction (straight line 25) of the crankshaft 1 toward the concave portion 23 of the pin boss portion 5A that is a lubricating oil supply target portion. 22, an end 22 </ b> A on the side facing the pin boss is disposed. Accordingly, the inertia force generated by the rotation of the crankshaft 1 is used to promote the flow of the lubricating oil that is injected from the crankpin oil passage 21 through the lower link oil passage 22 toward the recess 23 of the pin boss portion 5A. A sufficient amount of lubricating oil can be reliably supplied to the pin bearing portion of 5A.

  [3] As shown in FIG. 2, a circumferential oil passage 24 extending in the circumferential direction is formed in the bearing portion of the crank pin 3, and the circumferential oil passage 24 is formed within a predetermined crank angle range. The crankpin oil passage 21 and the lower link oil passage 22 are configured to communicate with each other. The circumferential oil passage 24 is recessed in the inner peripheral surface of the lower link 4 constituting the bearing surface of the crankpin 3 in the present embodiment, but may be recessed in the outer peripheral surface of the crankpin 3, or The circumferential oil passage 24 may be provided in a (semi) cylindrical bearing metal interposed between the three and the four. Thus, by providing the circumferential oil passage 24 in the bearing portion of the crankpin 3, the range of the crank angle where the crankpin oil passage 21 and the lower link oil passage 22 communicate with each other is expanded, and the lubricating oil injection period is increased. And the lubrication performance can be further improved by increasing the supply amount of the lubricating oil.

  [4] Referring to FIG. 4, the lower link oil passage 22 is disposed at a low load input position. That is, as shown in FIG. 4 (A), it is arranged in a range of a predetermined angle α with the crankpin bearing surface as the center so as to avoid the range in which the maximum torque Ta and the maximum output Tb act. More specifically, the lower link oil passage 22 is set within a range α of a predetermined angle (about 90 degrees) around a line connecting the center of the crank pin bearing surface to the center of the pin (6, 11), More specifically, it is set within a range α of a predetermined angle (about 90 degrees) from the mating surface 34 of the lower link dividing members 31 and 32 to the pin (6, 11) side. Thus, by arranging the lower link oil passage 22 at a position where the load input is low, it is easy to ensure the strength of the lower link 4 with respect to the load input, even though the lower link oil passage 22 is formed. The improvement of the lubrication performance and the securing of the strength of the lower link 4 can both be achieved.

  [5] Referring to FIG. 5, the crankpin oil passage 21 is arranged avoiding the input position of the combustion load. Specifically, in a coordinate system in which the counterclockwise direction is a positive rotation direction with the direction from the rotation center 2A of the crankshaft 1 toward the center of the crankpin as a reference (0 °), the combustion load input is about −25 °. Since the peak Tc is located, the crankpin oil passage is avoided so as to avoid a predetermined angle range β (about 90 degrees) around the peak Tc of the combustion load input, that is, a range β of about −70 degrees to about +20 degrees. The position of the end 21 </ b> A on the outer peripheral surface side of 21 is set. Thus, by arranging the crankpin oil passage 21 while avoiding the combustion load input position, it is easy to ensure the strength of the crankpin 3 against the combustion load input despite the formation of the crankpin oil passage 21. Therefore, it is possible to achieve both the improvement of the lubrication performance and the securing of the strength of the crankpin 3.

  4B and 6, θx is the direction of splash injected from the crankpin oil passage 21, and the mating surface of the outer peripheral side end portion 21 </ b> A of the crankpin oil passage 21 with respect to the center of the crankpin 3. This corresponds to the angular position from 34. θU is an angular section in which the injection direction of the lubricating oil is directed to the upper side pin boss portion 5A. θC is an angle section in which the injection direction of the lubricating oil is directed to the control-side pin boss portion 5A. θUoil is an angular position from the mating surface 34 of the end 22A of the lower link oil passage 22 on the pin boss facing surface side. θpin is an angular position of the pin hole center with respect to the mating surface 34, and is a fixed value set in advance. 5 and 6, θCR1 is an angular position of the outer peripheral side end portion 21A of the crankpin oil passage 21 with respect to the center of the crankpin 3, and θCR2 is a crankpin oil passage with respect to the crank rotation center 2A. 21 is an angular position of the outer peripheral side end portion 21A, and θsp is an oil injection angle (θCR2 + 90 °). As shown in FIG. 6, the injection period (U injection period) to the upper pin boss portion 5A is set to a period in which the oil injection angle θsp is within the θU section. Similarly, the injection period (C injection period) to the control-side pin boss portion 10A is set to a period in which θsp is within the θC interval.

  [6] FIGS. 7 to 9 show examples of the recesses provided on both side surfaces in the axial direction of the upper link 5 (or the control link 10). The upper link 5 (or the control link 10) has a structure in which pin boss portions 5A at both ends are integrally connected by rod portions 5B. Therefore, if a line passing through the center of the pin boss portion 5A at both ends of the upper link 5 is a link center line 27A and a line passing through the center of the pin boss portion 5A and orthogonal to the link center line 27A is a pin boss orthogonal line 27B, this pin boss In the vicinity of the orthogonal line 27B, the tensile stress becomes maximum. Therefore, in the example shown in FIGS. 7 to 9, in order to ensure the strength of the pin boss portion 5A, the concave portion 23 is formed so as to avoid the pin boss orthogonal line 27B where the tensile stress is maximum.

  [7] The recess 23 is formed such that the outer peripheral surface side of the pin boss portion 5A is larger than the inner peripheral surface side. Specifically, the recess 23A shown in FIG. 7 is formed in a fan shape that gradually expands from the inner peripheral side toward the outer peripheral side. In the recesses 23B and 23C shown in FIGS. 8 and 9, an extension portion 28 extending in the circumferential direction is provided at the outer peripheral portion. Thus, by enlarging the outer peripheral side of the recess 23 into which the lubricating oil is injected and supplied, the inflow amount of the lubricating oil can be ensured and the lubricating performance can be improved. In addition, by reducing the inner peripheral side of the recess 23 relatively, it is possible to suppress a decrease in strength of the pin boss portion 5A due to the provision of the recess 23.

  [8] Of the pin boss portion 5A, the portion closer to the rod portion 5B has higher strength than the portion farther from the rod portion 5B. Therefore, the recessed part 23 is arrange | positioned in the position close | similar to the rod part 5B rather than the above-mentioned pin boss orthogonal line 27B among the pin boss parts 5A near the rod part with high intensity | strength. Specifically, the concave portion 23 is provided in the vicinity of the base portion where the rod portion 5B is connected to the pin boss portion 5A.

  [9] A curved portion 29 that bends with a predetermined curvature is provided at the corner portion on the outer peripheral side of the pin boss portion 5A. Thus, by providing the curved portion 29, a part of the lubricating oil flows into the concave portion 23 along the curved portion 29, thereby promoting the inflow of the lubricating oil into the concave portion 23 and improving the lubricating performance. it can.

  [10] In the example shown in FIG. 9, a plurality of recesses 23B and 23C are provided on each axial side surface of the pin boss portion 5A. In this example, two concave portions 23B and 23C are arranged symmetrically with respect to the link center line 27A. As described above, the one concave portion 23B is disposed at a position where the lubricating oil is injected and supplied from the lower link 4, and functions as a supply oil passage for supplying the lubricating oil to the pin bearing portion. The other recess 23C functions as a discharge oil passage for discharging the lubricant supplied to the pin bearing portion. Thus, by providing the oil discharge recess 23C separately from the oil supply recess 23B, the supply and discharge of the lubricant to the pin bearing portion is promoted, and the flow rate of the lubricant oil in the pin bearing portion is increased. The lubrication performance can be further improved.

  In addition, in the example of FIG. 9, although two recessed parts are provided in each axial direction side surface of the pin boss | hub part 5A, you may comprise so that three or more recessed parts may be provided.

DESCRIPTION OF SYMBOLS 1 ... Crankshaft 3 ... Crankpin 4 ... Lower link 5 ... Upper link 6 ... Upper pin 7 ... Piston pin 8 ... Piston 10 ... Control link 11 ... Control pin 21 ... Crank pin oil passage 22 ... Lower link oil passage 23 ... Concave part

Claims (10)

An upper link having one end connected to the piston via a piston pin, a lower link connected to the other end of the upper link via an upper pin and rotatably attached to the crank pin of the crankshaft, and one end of the engine In a lubrication structure for a multi-link piston-crank mechanism of an internal combustion engine, comprising a control link supported on the main body side so as to be swingable and having the other end connected to the lower link via a control pin.
A crankpin oil passage extending radially inside the crankpin, having one end opened on an outer peripheral surface of the crankpin, and supplied with lubricating oil of a predetermined pressure;
A pin boss facing surface formed on the lower link and facing the pin boss portion of the upper link to which the upper pin is rotatably fitted, or a pin boss facing surface of the control link to which the control pin is rotatably fitted, and a bearing of the crank pin A lower link oil passage extending therethrough,
When the crank angle is near the bottom dead center where the crank pin oil passage communicates with the lower link oil passage, the rotation center of the crank shaft and the pin boss facing surface side of the lower link oil passage are viewed in the direction of the crankshaft. The pin boss part is arranged on a straight line connecting the end part,
A lubrication structure for a multi-link piston-crank mechanism for an internal combustion engine, wherein a concave portion that is recessed in the axial direction is provided on an axial end face of the pin boss portion.   When the crankpin oil passage and the lower link oil passage communicate with each other at a predetermined crank angle, as viewed in the crankshaft direction, the rotation center of the crankshaft and the outer peripheral surface end of the crankpin oil passage; 2. The multi-link type piston for an internal combustion engine according to claim 1, wherein the lubricating oil supply target portion is arranged on a straight line connecting the end portion on the pin boss facing surface side of the lower link oil passage. -Lubrication structure of the crank mechanism. A circumferential oil passage extending in the circumferential direction is formed in the bearing portion of the crank pin,
3. The multi-link type piston-crank for an internal combustion engine according to claim 1, wherein the crank pin oil passage and the lower link oil passage communicate with each other through the circumferential oil passage. Lubrication structure of the mechanism.   4. The lubrication structure for a multi-link piston-crank mechanism for an internal combustion engine according to claim 1, wherein the lower link oil passage is disposed at a position where load input is low.   The lubrication structure for a multi-link piston-crank mechanism for an internal combustion engine according to any one of claims 1 to 4, wherein the crank pin oil passage is disposed so as to avoid a combustion load input position.   The said recessed part is arrange | positioned so that it may avoid the pin boss orthogonal line which passes through the center of the said pin boss | hub part and is orthogonal to a link centerline by the axial direction view of the said pin boss | hub part. A lubrication structure for a multi-link piston-crank mechanism of an internal combustion engine according to claim 1.   The multi-link type piston for an internal combustion engine according to any one of claims 1 to 6, wherein the concave portion is formed so that an outer peripheral surface side of the pin boss portion is larger than an inner peripheral surface side. -Lubrication structure of the crank mechanism.   The said recessed part is arrange | positioned among the said pin boss | hub parts at the side close | similar to the rod part which connects the pin boss | hub part of the both ends of the said upper link or a control link, The Claim 1 characterized by the above-mentioned. A lubrication structure for a multi-link piston-crank mechanism of an internal combustion engine.   The lubrication structure for a multi-link piston-crank mechanism for an internal combustion engine according to any one of claims 1 to 8, wherein a curved portion is provided at a corner portion on the outer peripheral side of the pin boss portion. The lubrication structure for a multi-link piston-crank mechanism for an internal combustion engine according to any one of claims 1 to 9, wherein a plurality of recesses are provided on each axial end surface of the pin boss portion.

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