JP7335195B2 - Internal combustion engine lower link - Google Patents

Description

The present invention relates to improvement of a lower link that constitutes a multi-link type piston crank mechanism of an internal combustion engine.

BACKGROUND ART Patent Document 1 and the like previously proposed by the applicant of the present invention are known as 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. This includes an upper link connected to the piston pin of the piston, a lower link connecting the upper link and the crankpin of the crankshaft, one end of which is swingably supported by the engine body, and the other end of which is 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 receives the combustion pressure received by the piston from the upper pin via the upper link, and moves the crank pin with a kind of "lever" action with the control pin as the fulcrum. transmit power.

Patent Document 1 discloses a configuration in which an oil hole for injecting lubricating oil to the outside when aligned with an oil hole on the crankpin side is formed through a crankpin bearing portion that is fitted to the crankpin substantially along the radial direction. is disclosed. Lubricating oil injected from this oil hole lubricates the bearing portion between the upper pin and the upper link.

JP 2016-196888 A

Assuming that the direction of motion of the piston is the vertical direction, the combustion load is applied downward to the upper pin at one end of the lower link, and the reaction force of the combustion load is applied downward to the control pin at the other end of the lower link. works. Then, the reaction force of the combustion load acts substantially upward on the crankpin bearing portion in which the crankpin positioned between the upper pin and the control pin is fitted. With such a load input, a large stress such as tensile stress and bending stress concentrates on the crankpin-side opening edge of the oil hole formed through the crankpin bearing portion. Therefore, the formation of the oil hole is a weak point in terms of the strength of the lower link, which limits the increase in output of an internal combustion engine having a multi-link type piston crank mechanism.

A lower link for an internal combustion engine according to the present invention has a circumferential position in which a maximum combustion load reaction force from the crankpin acts on an outer peripheral side surface of a crankpin bearing portion where the tip of the oil hole opens, and the oil hole. and is located within a circumferential angular range between and and is thinner than the thickness of the crankpin bearing portion at the position of the oil hole.

In the configuration in which the recessed portion that constitutes the thin wall portion is formed in this way, when the combustion load acts on the upper pin side of the lower link and the combustion load reaction force acting in the opposite direction acts on the crankpin bearing portion, the maximum combustion load reaction force is applied. The thin portion located between the position where the force acts and the oil hole is displaced relatively large, and the stress concentration at the opening edge of the oil hole on the crankpin side is reduced accordingly.

According to the present invention, the stress concentration at the inner peripheral side opening edge of the oil hole in the crankpin bearing portion, which is a weak point in the strength of the lower link, is alleviated, thereby ensuring the strength of the lower link and increasing the output of the internal combustion engine. be advantageous.

FIG. 2 is a configuration explanatory diagram of a multi-link type piston crank mechanism of one embodiment; 1 is a perspective view of a lower link of one embodiment; FIG. Sectional drawing of a lower link upper. FIG. 3 is a perspective view of a lower link upper in half section; The top view seen from the arrow A direction of FIG. FIG. 4 is a cross-sectional view taken along line BB of FIG. 3;

An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows constituent elements of a multi-link type piston crank mechanism to which the present invention is applied. This multi-link type piston crank mechanism itself is known from the above-mentioned Patent Document 1 and the like, and includes an upper link 3 having one end connected to a piston 1 via a piston pin 2, and an upper pin connected to the other end of the upper link 3. 4 and connected to a crankpin 5 of a crankshaft; and a control link 7 that regulates the degree of freedom of the lower link 6 . One end of the control link 7 is swingably supported by a support pin 8 on the engine body side, and the other end is connected to the lower link 6 via a control pin 9 . The multi-link type piston crank mechanism can be configured as a variable compression ratio mechanism by making the position of the support pin 8 variable.

As shown in FIG. 2, the lower link 6 has a cylindrical crankpin bearing portion 11 in the center to which the crankpin 5 is fitted. An upper pin pin boss portion 12 and a control pin pin boss portion 13 are provided at positions on the sides. The lower link 6 as a whole forms a parallelogram close to a rhombus. The lower link lower 6B including the portion 13 is divided into two parts. These lower link upper 6A and lower link lower 6B are fastened together by two bolts (not shown) after the crankpin bearing portion 11 is fitted into the crankpin 5 .

The upper pin pin boss portion 12 and the control pin pin boss portion 13 are bifurcated so as to sandwich the upper link 3 and the control link 7 in their axial central portions. A pair of bearing flange portions 12a and 13a that respectively support the lower link 6 extends along the axial end surface of the lower link 6 (see FIG. 6). That is, the bearing flange portions 12a and 13a forming the pin boss portions 12 and 13 are connected to both axial end portions of the cylindrical crankpin bearing portion 11, respectively. The crankpin bearings 12a and 13a have circular through holes 12b and 13b, respectively, into which the ends of the upper pin 4 and the control pin 9 are press-fitted. The upper link 3 and the control link 7 are configured to swing in grooves 17 and 18 formed between the pair of bearing flanges 12a and 13a.

The crankpin bearing portion 11 is fitted to the crankpin 5 via a pair of semi-cylindrical bearing metals 16 . The crankpin 5 is internally provided with a lubricating oil passage (not shown) to which pressurized lubricating oil is supplied. ing. As will be described later, an oil hole 21 is formed through the crankpin bearing portion 11, and when the oil hole 21 coincides with the tip of the lubricating oil passage on the crankpin 5 side, the lubricating oil flows from the oil hole 21 into a so-called oil jet. It is configured to be jetted as

A combustion load acts on the upper pin pin boss portion 12 of the lower link 6 from the upper link 3 via the upper pin 4, and the lower link 6 swings about the control pin 9 as a fulcrum. 5 to transmit force. Therefore, while the combustion load acts downward in FIG. 1 on the pin boss portion 12 for the upper pin, the reaction force from the crankpin 5 acts upward in FIG. As a result, a large stress (bending stress or tensile stress) is generated in a region of the lower link upper 6A near the upper link 3 .

FIG. 3 shows a cross-sectional view of the lower link upper 6A having the oil hole 21 in the crankpin bearing portion 11 (a cross-sectional view along a plane perpendicular to the axial direction of the crankpin 5). In FIG. 3 , an arrow P1 indicates the combustion load acting on the pin boss portion 12 for the upper pin, and an arrow P2 indicates the reaction force of the combustion load acting on the crankpin bearing portion 11 . A combustion load P1 is input from the piston 1 to the upper pin pin boss portion 12 via the upper pin 4 in a direction along the longitudinal direction of the upper link 3 . The combustion load reaction force P2 acts in a direction determined by the attitude of the lower link 6 with the control pin 9 as a fulcrum. It acts toward a circumferential position closer to the control pin 9 than the other. Both P1 and P2 indicate the load acting direction at the crank angle when the combustion load is maximized.

The oil hole 21 is for lubricating the connecting portion of the upper link 3 connected to the lower link 6 at the upper pin pin boss portion 12, that is, the sliding surface between the upper pin 4 and the upper link 3. The crankpin bearing portion 11 is linearly penetrating along the radial line of the crankpin 5 in the direction of the connecting portion with the link 3 . Specifically, it is provided at a circumferential position closer to the upper pin 4 than the central position in the semicircular crankpin bearing portion 11 of the lower link upper 6A, for example, at a circumferential position near 45° from the dividing surface 14. there is

When the lower link 6 is formed by forging, the oil hole 21 is formed by secondary machining, that is, drilling. When the lower link 6 is precision-cast by the lost-wax method or the like, the oil hole 21 can be molded. The tip of the oil hole 21 toward the end of the upper link 3 opens to the outer peripheral surface of the crankpin bearing portion 11, in other words, the bottom surface of the groove portion 17 between the pair of bearing flange portions 12a. As for the axial direction of the crankpin 5 , the oil hole 21 is located in the center of the axial dimension of the crankpin bearing portion 11 in one embodiment.

FIG. 4 is a perspective view of a half of the lower link upper 6A taken along a plane perpendicular to the axial direction of the crankpin 5 and viewed obliquely. As shown in FIGS. 3 and 4, a concave portion 23 for forming a partial thin portion 22 is formed by secondary machining on the outer peripheral surface of the crankpin bearing portion 11 of the lower link upper 6A. It is The concave portion 23 is positioned within a circumferential angular range between the oil hole 21 and the circumferential position in which the maximum combustion load reaction force P2 described above acts in the circumferential direction of the crankpin bearing portion 11 . In a specific example, one circumferential end 23a of the recessed portion 23 is adjacent to the tip opening of the oil hole 21 with a small distance left therebetween, and the other circumferential end 23b of the crankpin bearing portion 11 forms a semicircular shape. Located near the center. As shown in FIG. 3, the ends near the one end 23a and the other end 23b of the recess 23 (that is, both ends in the circumferential direction) form curved surfaces. In addition, in the intermediate portion of the recess 23 in the circumferential direction, the thin portion 22 is formed continuously over a certain angular range in the circumferential direction with a constant thickness. In other words, the thin portion 22 has an arcuate shape with a constant thickness.

FIG. 5 is a plan view of the concave portion 23 viewed from the direction of arrow A in FIG. As shown, the recessed portion 23 is formed between the pair of bearing flange portions 12a, and as can be easily understood from FIG. It has a shape. That is, the thin portion 22 having a constant thickness has a rectangular plate shape curved in an arc.

6 shows a cross-sectional view taken along line BB in FIG. As shown in FIG. 6, the concave portion 23 has both ends 23c and 23d in the axial direction that are curved in a substantially arc shape. It is connected to the opposing side surface 12c. As shown in FIG. 6, the thin portion 22 formed in the axial center portion of the concave portion 23 excluding both end portions 23c and 23d extends with a constant thickness in the axial direction. Moreover, as can be easily understood from FIG. 6 , the formation range of the concave portion 23 along the axial direction is larger than the diameter of the oil hole 21 . That is, when the oil hole 21 is projected onto the concave portion 23 in FIG.

After first machining the side surface 12c of the bearing flange portion 12a and the outer peripheral surface of the crankpin bearing portion 11, which serves as the bottom surface of the groove portion 17, the concave portion 23 is machined secondarily. The boundary between both end portions 23c, 23d of the recess 23 and the side surface 12c of the bearing flange portion 12a in FIG. That is, the concave portion 23 has a configuration in which the center portion in the axial direction is recessed toward the inner peripheral side of the crankpin 5 while leaving the reference contour 24 of the crankpin bearing portion 11 on the side surface 12c of the bearing flange portion 12a. As shown in FIG. 3, the reference contour 24 smoothly connects one end 23a and the other end 23b of the concave portion 23 in the circumferential direction along an arc substantially concentric with the crankpin 5 while maintaining a substantially constant wall thickness. shape.

Although the recess 23 in the embodiment is formed over the entire space between the pair of bearing flanges 12a, the dimension in the axial direction may be smaller. In this case, the reference contour 24 remains in a belt shape having a width.

t1, t2, and t3 in FIG. 3 indicate the thickness of each portion of the crankpin bearing portion 11. As shown in FIG. Both are thickness dimensions along the radial direction of the crankpin 5 . The thickness t1 is the thickness at the position where the oil hole 21 is formed. More specifically, the thickness t1 indicates the thickness of the cross section passing through the center of the opening of the oil hole 21 on the inner peripheral side of the crankpin bearing portion 11 . A thickness t2 is the thickness of the thin portion 22 formed by the recess 23 . The thickness t3 indicates the thickness dimension of the crankpin bearing portion 11 at the circumferential position in which the maximum combustion load reaction force P2 described above acts.

In the above embodiment, the thickness t2 of the thin portion 22 is smaller than the thickness t1 at the position where the oil hole 21 is formed. That is, the rigidity of the thin portion 22 is relatively low. Therefore, when the maximum combustion load P1 acts on the pin boss portion 12 for the upper pin and the maximum combustion load reaction force P2 acts on the crankpin bearing portion 11, the thin portion 22 is relatively less than the periphery of the oil hole 21. A large displacement occurs, and the stress concentration at the opening edge of the oil hole 21 on the crankpin 5 side is reduced accordingly. In other words, the load transmission from the position where the maximum combustion load reaction force P2 acts to the oil hole 21 is restricted by the thin portion 22 positioned in front of the oil hole 21, and stress concentration occurs at the opening edge of the oil hole 21. become difficult. In particular, in the illustrated example, the thin portion 22 is long and continuous in the circumferential direction with a constant thickness t2 and is formed to spread widely in the axial direction. It is possible to effectively suppress stress concentration at the oil hole 21 opening edge while avoiding local stress concentration at the oil hole 21 opening edge.

Furthermore, in the above embodiment, the thickness t2 of the thin portion 22 is smaller than the thickness t3 at the position where the maximum combustion load reaction force P2 acts. Therefore, the thin portion 22 exists between two circumferentially thick and rigid portions (the portion t1 and the portion t3). stress concentration is relaxed.

The thickness t3 at the position where the maximum combustion load reaction force P2 acts is smaller than the thickness t1 at the position where the oil hole 21 is formed. That is, the illustrated example has a relationship of "t2<t3<t1". Therefore, it is possible to obtain high rigidity and strength around the oil hole 21 while suppressing stress concentration at the opening edge of the oil hole 21 .

Also, the lower link 6 having the recess 23 as in the above embodiment has some additional advantages. First, since the wall thickness t3 is large at the position where the combustion load reaction force P2 acts, a large reaction force or pressure can be obtained against the outer peripheral surface of the bearing metal 16. Rotation is suppressed. Secondly, the reduced rigidity of the thin portion 22 adjacent to the oil hole 21 reduces the oil film pressure in the vicinity of the oil hole 21, thereby reducing the risk of the crankpin 5 seizing. Thirdly, lubricating oil can be collected in the concave portion 23 and sprayed toward the upper link 3 and the upper pin 4 as the lower link 6 moves. In addition, the formation of the recessed portion 23 contributes to weight reduction of the lower link 6 as well.

The lower link upper 6A (lower link 6) of the illustrated example has an oil hole 28 for supplying an oil jet toward the piston 1 (see FIG. 1) or the inner wall surface of the cylinder, in addition to the oil hole 21 described above. I have. The oil hole 28 is located closer to the control pin 9 than the position where the maximum combustion load reaction force P2 acts on the circumference of the crankpin bearing portion 11 . Therefore, the stress concentration at the opening edge due to the combustion load and combustion load reaction force described above is relatively small. Therefore, the oil hole 28 is not provided with a recessed portion or a thin portion.

6... Lower link 6A... Lower link upper 11... Crankpin bearing part 12... Upper pin pin boss part 12a... Bearing flange part 17... Groove part 21... Oil hole 22... Thin part 23... Recessed part 24... Reference contour t1, t2, t3... thickness

Claims (6)

An upper link having one end connected to a piston of an internal combustion engine via a piston pin, a lower link connected to the other end of the upper link via an upper pin and to a crankpin of a crankshaft, and an engine having one end a control link swingably supported on the body side, the other end of which is connected to the lower link via a control pin; Between the control pin and the control pin, there is a crankpin bearing portion rotatably fitted to the crankpin, and an oil hole directed to the connecting portion between the upper pin and the upper link is formed through the crankpin bearing portion. In the lower link of the internal combustion engine that has been
A circumferential angular range between the oil hole and a circumferential position where the maximum combustion load reaction force from the crankpin acts on the outer peripheral side surface of the crankpin bearing portion where the tip of the oil hole opens. a recess that is located inside the oil hole and that constitutes a thin-walled portion that is thinner than the thickness of the crankpin bearing portion at the position of the oil hole;
Lower link of internal combustion engine. 2. The lower link for an internal combustion engine according to claim 1, wherein said recess has a formation range in the axial direction of the crank pin that is larger than the diameter of said oil hole. 3. The lower link for an internal combustion engine according to claim 1, wherein the thickness of said thin portion is thinner than the thickness at a position in the circumferential direction in which said maximum combustion load reaction force acts. 4. The lower link for an internal combustion engine according to claim 3, wherein the wall thickness at the circumferential position in the direction in which the maximum combustion load reaction force acts is thinner than the wall thickness at the position of the oil hole. 4. The lower link for an internal combustion engine according to claim 1, wherein said recess is recessed so as to form a rectangular shape in plan view when expanded in the circumferential direction. A pin boss portion supporting the upper pin is bifurcated by a pair of bearing flange portions extending along the end surface of the lower link,
The oil hole and the recess are positioned at the bottom of the groove sandwiched between the pair of bearing flanges,
6. The lower part of the internal combustion engine according to claim 1, wherein the recess has a center portion in the axial direction recessed toward the inner peripheral side of the crankpin while leaving a reference contour of the surface on the side surface of the bearing flange portion. Link.

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