JP4992602B2 - Double link type piston crank mechanism - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To optimize the rigidity of a lower link so that each bearing is symmetrically deformed against a load applied thereto. <P>SOLUTION: In this double-link piston crank mechanism, the lower link 5 comprises a crankpin bearing part 31 at the generally center part, a pin boss part 32 for an upper pin, and a pin boss part 33 for a control pin. A bush is stored in the pin boss part 32 for an upper pin. Where the wall thickness of the portion of the pin boss part 32 for an upper pin on the opposite side of the crankpin bearing part is L1, the wall thickness of the portion between the pin boss part 32 for an upper pin and the crankpin bearing part 31 is L2, the distance between the center of the pin boss part 32 for an upper pin and the center of the crankpin bearing part 31 is L3, and the distance between the center of the pin boss part 33 for a control pin and the center of the crankpin bearing part 31 is L4, L3+2L4:L4=L2:L1. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to an improvement of a multi-link type piston crank mechanism.

An upper link whose one end is 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 connected to the crank pin of the crankshaft, and one end on the engine body side And a control link having the other end connected to the lower link via a control pin. The lower link includes a crankpin bearing portion at a substantially center where the crankpin is fitted, and an upper link. A multi-link type piston crank having an upper pin pin boss portion for holding a pin and a control pin pin boss portion for the other end holding a control pin, and a bush accommodated in the upper pin pin boss portion There is a mechanism (see Patent Document 1).
JP 2005-180657 A

  By the way, since a lower link has a connection part with a crankpin, an upper pin, and a control pin, a high internal force is generated. In addition, the load is applied in the linear direction connecting the center of the connecting portion with the upper link and the center of the connecting portion of the crank pin, or in the linear direction connecting the center of the connecting portion with the control link and the center of the connecting portion of the crank pin. Since it is not input, asymmetric deformation occurs in the connecting portion with the upper link and the connecting portion with the control link. In a bearing in which such asymmetric deformation occurs, inward rotation occurs in the bush accommodated in the connecting portion with the upper link or the connecting portion with the control link. If the bush is inwardly rotated every time a load is input to the connecting portion with the upper link or the connecting portion with the control link, the durability of the bush is lowered.

  Accordingly, an object of the present invention is to provide a multi-link type piston crank mechanism capable of suppressing the inversion of the bush by optimizing the rigidity of the lower link so that each bearing is deformed symmetrically with respect to the received load. To do.

The present invention includes an upper link (6), a lower link (5), and a control link (11), and the lower link (5) is a substantially center crankpin bearing portion (31) to which a crankpin is fitted. And an upper pin pin boss portion (32) at one end for holding the upper pin and a control pin pin boss portion (33) at the other end for holding the control pin. In the multi-link type piston crank mechanism in which the bush is housed, the thickness of the portion of the upper pin pin boss portion (32) opposite to the side where the crank pin bearing portion (31) is located is L1, and the upper pin pin boss The thickness of the portion between the portion (32) and the crank pin bearing portion (31) is L2, the center of the pin boss portion (32) for the upper pin, and the crank pin bearing portion ( The distance between the center of 1) L3, the center of the control pin pin boss portion (33), when the distance between the center of the crankpin bearing portion (31) and L4,
L3 + 2L4: L4 = L2: L1 (a)
It becomes.

The present invention includes an upper link (6), a lower link (5), and a control link (11), and the lower link (5) is a substantially center crankpin bearing portion (31) to which a crankpin is fitted. And an upper pin pin boss portion (32) at one end holding the upper pin, and a control pin pin boss portion (33) at the other end holding the control pin, and the control pin pin boss portion (33) In the multi-link type piston crank mechanism in which the bush is housed, the thickness of the portion of the control pin pin boss portion (33) opposite to the side where the crank pin bearing portion (31) is located is L5, the control pin pin boss The thickness of the portion between the portion (33) and the crank pin bearing portion (31) is L6, the center of the pin boss portion (32) for the upper pin, and the crank When down bearing portion the distance between the center of the (31) L3, the center of the control pin pin boss portion (33), and the distance between the center of the crankpin bearing portion (31) and L4,
L4 + 2L3: L3 = L6: L5 (b)
It becomes.

The present invention includes an upper link (6), a lower link (5), and a control link (11), and the lower link (5) is a substantially center crankpin bearing portion (31) to which a crankpin is fitted. And an upper pin pin boss portion (32) at one end for holding the upper pin and a control pin pin boss portion (33) at the other end for holding the control pin. In the multi-link type piston crank mechanism in which the bush is housed, the load input to the upper pin pin boss part (32) is changed from the center of the upper pin pin boss part (32) to the crank pin bearing part (31). The angle of the straight line drawn to the center with respect to this load Fupper is θupper, the load input to the crankpin bearing (31) is Fcrank, and the crankpin bearing The angle of the straight line drawn from the center of (31) to the center of the upper pin pin boss part (32) with respect to this load Fcrank is θcrank, and the side of the upper pin pin boss part (32) where the crank pin bearing part (31) is located When the thickness of the portion on the opposite side is L1, and the thickness of the portion between the pin boss portion (32) for the upper pin and the crank pin bearing portion (31) is L2,
Fcrank · sinθcrank + Fupper · sinθupper: Fupper · sinθupper = L2: L1
... (c)
It becomes.

  According to the present invention, the lower link includes a crank pin bearing portion at the substantially center where the crank pin is fitted, a pin boss portion for the upper pin that holds the upper pin, and a control at the other end portion that holds the control pin. In a multi-link type piston crank mechanism having a pin boss portion for a pin and a bush accommodated in the pin boss portion for the upper pin, the portion of the upper pin pin boss portion opposite to the side where the crank pin bearing portion is located The thickness is L1, the thickness of the portion between the pin boss portion for the upper pin and the crank pin bearing portion is L2, the distance between the center of the pin boss portion for the upper pin and the center of the crank pin bearing portion is L3, the pin boss for the control pin When the distance between the center of the part and the center of the crankpin bearing part is L4, the above equation (a) is established. The load acting on the part between the pin boss part for the pin and the crank pin bearing part (B part in FIG. 5) and the part on the opposite side of the pin boss part for the upper pin to the side having the crank pin bearing part (in FIG. 5) The ratio (L3 + 2L4: L4) to the load acting on the A part) is equal to the ratio of the thickness of the B part to the thickness of the A part (L2: L1), and thus occurs in the A part and the B part. Asymmetric deformation can be suppressed, and the inversion of the bush accommodated in the pin boss portion for the upper pin can be prevented. In other words, among the upper pin pin bosses, the load on the side where the crank pin bearing part is located is different from that on the opposite side where there is no crank pin bearing part, and the load is input to the upper pin pin boss part. Even if the direction of the load input to the crank pin bearing part is not along the line connecting the center of the pin boss part for the upper pin and the center of the pin boss part for the control pin, it is stored in the pin boss part for the upper pin. The internal rotation of the bush can be prevented.

  According to the present invention, the lower link includes a crank pin bearing portion at the substantially center where the crank pin is fitted, a pin boss portion for the upper pin that holds the upper pin, and a control at the other end portion that holds the control pin. In a multi-link type piston crank mechanism having a pin boss portion for a pin and a bush accommodated in the pin boss portion for the control pin, the portion of the control pin pin boss portion opposite to the side where the crank pin bearing portion is located The thickness is L5, the thickness between the pin boss part for the control pin and the crank pin bearing part is L6, the distance between the center of the pin boss part for the upper pin and the center of the crank pin bearing part is L3, the pin boss for the control pin When the distance between the center of the portion and the center of the crankpin bearing portion is L4, the above equation (b) is satisfied. Therefore, the load acting on the portion (D portion in FIG. 5) between the pin boss portion for the control pin and the crank pin bearing portion and the portion on the opposite side of the control pin pin boss portion on the side where the crank pin bearing portion is located ( Since the ratio (L4 + 2L3: L3) to the load acting on the C portion in FIG. 5 is equal to the ratio of the thickness of the D portion to the thickness of the C portion (L6: L5), the C portion and the D portion As a result, asymmetric deformation occurring in the control pin can be suppressed, and the inward rotation of the bush accommodated in the pin boss portion for the control pin can be prevented. In other words, among the control pin pin bosses, the thickness is different between the part having the crank pin bearing part and the opposite part without the crank pin bearing part 31, and the load inputted to the control pin pin boss part. Even when each direction of the load input to the crank pin bearing portion is not along the line connecting the center of the pin boss portion for the control pin and the center of the pin boss portion for the upper pin, the control pin pin boss portion 33 The internal rotation of the stored bush can be prevented.

  According to the present invention, the lower link includes a crank pin bearing portion at the substantially center where the crank pin is fitted, a pin boss portion for the upper pin that holds the upper pin, and a control at the other end portion that holds the control pin. In a multi-link type piston crank mechanism having a pin boss part for pins and a bush accommodated in the pin boss part for upper pins, the load input to the pin boss part for upper pins is Fupper, from the center of the pin boss part for upper pins The angle of the straight line drawn to the center of the crankpin bearing part is θupper, the load input to the crankpin bearing part is Fcrank, and the straight line drawn from the center of the crankpin bearing part to the center of the pin boss part for the upper pin The angle with respect to the load Fcrank is θcrank, and the pin boss portion for the upper pin is on the side where the crank pin bearing portion is located. Since the thickness of the opposite portion is L1 and the thickness of the portion between the pin boss portion for the upper pin and the crank pin bearing portion is L2, the above formula (c) is established. The thickness of the pin boss part on the side where the crank pin bearing part is located is different from the part on the opposite side where the crank pin bearing part is not present, and the load input to the pin boss part for the upper pin and the crank pin bearing part Even if each direction of the input load is deviated from the piston movement direction, the inversion of the bush accommodated in the pin boss portion for the upper pin can be prevented.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of a reciprocating engine to which a multi-link type piston crank mechanism of the present invention is applied. Since the reciprocating engine itself provided with the multi-link type piston crank mechanism is known, for example, from Japanese Patent Application Laid-Open No. 2001-227367, etc., only its outline will be described.

  In FIG. 1, the crankshaft 2 is provided with a crank journal 3 that is rotatably supported by a main bearing (not shown) in a cylinder block 1 constituting a part of the engine body for each cylinder. Each crank journal 3 has an axis O that coincides with the axis (rotation center) of the crankshaft 2 and constitutes a rotating shaft portion of the crankshaft 2.

  The crankshaft 2 includes a crankpin 4 that is eccentric from the axis O and is provided for each cylinder, a crank arm 4a that connects the crankpin 4 to the crank journal 3, and a crankpin 4 that is connected to the axis O. The counterweight 4b is disposed on the opposite side and mainly reduces the rotational primary vibration component of the piston motion. The crank arm 4a and the counterweight 4b are integrally formed in this embodiment.

  In the present embodiment, the piston 9 slidably fitted to the cylinder 10 formed for each cylinder and the crank pin 4 are formed by a plurality of link members, that is, the upper link 6 and the lower link 5. It is mechanically linked. The upper end side of the upper link 6 is externally fitted to a piston pin 8 fixedly provided on the piston 9 so as to be relatively rotatable around the axis Oc. Also, the lower link side of the upper link 6 and the one main body 5a of the lower link 5 that is substantially divided into two halves are connected to each other around the axis Od by an upper pin 7 that passes through both of them.

  The lower link 5 is configured by attaching two main bodies 5a and 5b so as to sandwich the crank pin 4. The lower link 5 is mounted so as to be relatively rotatable around the crank pin 4 and the axis Oe. Yes. The other lower link main body 5b divided into approximately two parts and the upper end side of the control link (third link) 11 are connected to each other around the axis Of by a control pin 12 inserted therethrough.

  The lower end side of the control link 11 is externally fitted and supported on a control shaft 13 having an eccentric cam portion 14 that is rotatably supported by the cylinder block 1 so as to be swingable around its axis Ob. That is, an eccentric cam portion 14 is rotatably provided on the outer periphery of the control shaft 13, and the axis Oa of the eccentric cam portion 14 is eccentric by a predetermined amount with respect to the axis Ob of the control shaft 13. The eccentric cam portion 14 is controlled to rotate according to the operating state of the engine by a compression ratio control actuator 16 via a worm gear 15 and is held at an arbitrary rotation position.

  With such a configuration, as the crankshaft 2 rotates, the piston 9 moves up and down in the cylinder 10 via the crankpin 4, the lower link 5, the upper link 6 and the piston pin 8, and is connected to the lower link 5. The control link 11 swings with the swing axis Ob on the lower end side as a fulcrum.

  Further, the eccentric cam portion 14 is rotationally controlled by the compression ratio control actuator 16, so that the axis Ob of the control shaft 13 serving as the pivot axis of the control link 11 is moved around the axis Oa of the eccentric cam portion 14. Rotation, that is, the swing center position Ob of the control link 11 moves relative to the engine body (and crankshaft rotation center O). As a result, the stroke of the piston 9 changes, and the compression ratio of each cylinder of the engine is variably controlled. For reference, FIG. 2 schematically shows the posture of the three links 6, 5, 11 at the piston top dead center position. The left side of FIG. 2 is the high compression ratio position, and the right side of FIG. 2 is the low compression ratio position. Each link posture.

  The greatest feature of this compression ratio variable mechanism is that the top dead center position (combustion chamber volume) of the piston 9 can be changed by the angular position control of the control shaft 13, and the function as a so-called compression ratio variable mechanism is exhibited.

  The engine control unit 39 to which the engine load and rotation speed signals are input refers to the target compression ratio map based on the input engine load and rotation speed, and thereby the target compression according to the load and rotation speed at that time. The ratio is calculated, and the command value (drive amount to the compression ratio variable mechanism) given to the compression ratio control actuator 16 is controlled so that the calculated target compression ratio is obtained. According to the map of the target compression ratio, the lower the load, the larger the target compression ratio (the maximum value is, for example, 22) to improve the fuel consumption, and conversely, the target compression ratio is set in the full load region where knocking is likely to occur. It is small (the minimum value is 10 for example).

  Now, since the lower link 5 has a connecting portion with the crank pin 4, the upper pin 7 and the control pin 12, a high internal force is generated. Further, the direction along the straight line connecting the center of the connecting portion with the upper link 6 and the center of the connecting portion with the crank pin 4, the center of the connecting portion with the control link 11, and the center of the connecting portion with the crank pin 4. Since no load is input in the direction along the straight line connecting the two, asymmetrical deformation occurs in the connecting portion with the upper link 6 and the connecting portion with the control link 11. In the connecting portion (bearing) in which such asymmetric deformation occurs, inversion occurs in the bushes housed in the connecting portion with the upper link 6 or the connecting portion with the control link 11.

  Here, the principle that the inward rotation occurs in the bush accommodated in the connecting portion (bearing) will be described with reference to FIG. First, FIG. 3A shows a deformation of the connecting rod small end portion 21 in the conventional crank connecting rod mechanism. In this crank connecting rod mechanism, a load acts on a straight line (vertical direction in the figure) connecting the center of the connecting rod small end (center of the piston pin hole 22) and the center of the connecting rod large end (not shown), Since the thickness of the connecting rod small end portion 21 around the piston pin 8 in the load direction is the same in the left and right parts, the deformation amount is the same in the left part and the right part of the piston pin. Therefore, when a bush (not shown) is accommodated between the piston pin 8 and the piston pin hole 22, the contact portion between the bush and the piston pin 8 is symmetrical with respect to the piston pin 8, and the bush is dragged clockwise. No dragging in the counterclockwise direction occurs.

  On the other hand, FIG. 3B shows a deformation of the connecting portion of the conventional lower link 5 and the upper link 6. In the case of a connecting portion (bearing) such as the conventional lower link 5 shown in FIG. 1 in which the rigidity around the upper pin 7 is non-uniform, assuming that a load acts on the upper pin 7 downward, Since the thickness of the right portion of the upper pin 7 is different from the thickness of the left portion of the upper pin 7, and the thickness of the left portion is smaller than the thickness of the right portion as shown, the left portion is more The deformation in the load direction is larger than that on the right side. Therefore, when a bush (not shown) is accommodated between the upper pin 7 and the upper pin hole 25, asymmetrical contact between the upper pin 7 and the bush occurs at the left side portion and the right side portion of the upper pin 7. In FIG. 3B, the bush is dragged in the counterclockwise direction, and the bush is internally rotated. When the load is removed, the drag does not occur and the bush is prevented from being internally rotated. Thus, each time a load is applied to the connecting portion with the upper link 6, an internal rotation occurs in the bush due to the counterclockwise drag, and if the internal rotation of the bush is accumulated, the durability of the bush decreases. It ends up.

  Therefore, in the present invention, in order to avoid such internal rotation of the bush, the shape of the lower link is reviewed, and in each connection portion of the lower link, the upper pin and the control pin, The rigidity of the lower link 5 is optimized so that the left part and the right part are deformed symmetrically. This will be described in detail with reference to FIGS. 4 and 5. FIG. 4 is a simplified model diagram of the lower link 5 according to the first embodiment of the present invention, and FIG. 5 illustrates the deformation of each part of the lower link when a load is applied. Is.

  When simplified as shown in FIG. 4, the lower link 5 includes a substantially central cylindrical crankpin bearing portion 31 into which the crankpin 4 is fitted, a cylindrical upper pin pin boss portion 32, and a cylindrical control pin. The pin boss portion 33 for connecting, the rod portion 37 for connecting the crank pin bearing portion 31 and the upper pin pin boss portion 32, and the rod portion 38 for connecting the crank pin bearing portion 31 and the control pin pin boss portion 33 are basically constituted. Has been. However, the centers of the crank pin hole 34, the upper pin hole 35, and the control pin hole 36 are assumed to be on a horizontal straight line.

  The load input from the upper link 6 to the upper pin pin boss portion 32 is Fupper, the load input from the crankshaft 2 to the crankpin bearing portion 31 is input to Fcrank, and the control link 11 is input to the control pin pin boss portion 33. When the load to be controlled is Fcontrol, the load Fupper acts downward, the load Fcrank acts upward, and the load Fcontrol acts downward. Here, the maximum value of the combustion load (the value at the maximum combustion load) is considered as the load, and the direction of the load at the maximum combustion load is as shown in FIG. In addition, although the direction of each load is made to correspond with an up-down direction for simplification, it cannot be overemphasized even if it is a case where the direction of a load inclines in the predetermined range from an up-down direction. Further, the load is not limited to this case, and the load at the time of maximum inertial force may be considered.

  Since the deformation amount of the part located on the left and right of the upper pin 7 is related to the thickness of the part, as shown in FIG. 4, the upper pin pin boss part 32 is opposite to the side where the crank pin bearing part 31 is located. The thickness of the portion (A portion in FIG. 5) is L1, the thickness of the portion (B portion in FIG. 5) between the upper pin pin boss portion 32 and the crank pin bearing portion 31 is L2, and the upper pin pin boss portion. The distance between the center of the pin 32 and the center of the crank pin bearing 31 is L3, the distance between the center of the pin boss 33 for the control pin and the center of the crank pin bearing 31 is L4, and the crank of the pin boss 33 for the control pin The thickness of the portion opposite to the pin bearing portion 31 side (C portion in FIG. 5) is L5, and the portion between the control pin pin boss portion 33 and the crank pin bearing portion 31 (D portion in FIG. 5). Thickness is L6 That.

  Considering the deformation of the A part and the B part located on the left side of the crankpin hole 34 in FIG. 5 after preparing so far, first, the load of 1/2 of Fupper is the left side part of the upper pin 7. The other half of the load of Fupper acts downward on part B, which is the right part of upper pin 7. A load of 1/2 of Fcrank acts upward on the B part. According to Hook's law, strain (tensile strain) is known to be proportional to Young's modulus x stress, and the amount of deformation is a value obtained by multiplying the strain by the length. When acting downward and extending by a minute amount Δx1, the following equation is established.

(1/2) Fupper≈Y × Δx1 × L1 (1)
Where Y: Young's modulus (constant value),
Similarly, in part B, when a tensile load of 1/2 of Fupper acts downward and extends by a minute amount Δx2, and a tensile load of 1/2 of Fcrank acts upward and extends by a minute amount Δx3, The following equation holds according to the law of

(1/2) Fupper + (1/2) Fcrank≈Y × (Δx2 + Δx3) × L2
... (2)
Where Y: Young's modulus (constant value),
Here, if the amount of deformation in the load direction of the portion A is equal to the amount of deformation in the load direction of the portion B, when a bush (not shown) is accommodated between the upper pin 7 and the upper pin hole 35, the left side of the upper pin 7 Contact between the asymmetric upper pin 7 and the bush does not occur between the portion (A portion) and the right portion (B portion), and neither counterclockwise dragging nor clockwise dragging occurs on the bush. From this request, it is assumed that the load direction deformation amount of the A part and the load direction deformation amount of the B part are equal, ie, Δx1 = Δx2 + Δx3. Since the ratio between the left sides of the above equations (1) and (2) is equal to the ratio between the right sides of the above equations (1) and (2), the following equation is obtained.

(1/2) Fupper + (1/2) Fcrank: (1/2) Fupper
= (Δx2 + Δx3) × Y × L2: Δx1 × Y × L1
= L2: L1
Multiplying the left side of this expression by 2 gives Fupper + Fcrank: Fupper, so the following expression is obtained.

Fupper + Fcrank: Fupper = L2: L1 (3)
On the other hand, the sum of moments inputted to the bearing portion 31 of the lower link 5 and the connecting portions 32 and 33 and the sum of loads (Fupper, Fcrank, Fcontrol) are approximately equal to each other by the lever principle.

Fupper = L4 / (L3 + L4) · Fcrank (4)
Fcontrol = L3 / (L3 + L4) · Fcrank (5)
When the equations (4) and (3) are solved simultaneously, the following equation is obtained.

L3 + 2L4: L4 = L2: L1 (6)
The expression (6) thus obtained is obtained by determining the dimensions of the lower link 5 so that the relationship of the expression (6) is established between L1, L2, L3, and L4. Even if the thicknesses of the parts (A part and B part) located at different positions are different and the load direction is not along the line connecting the center of the crank pin hole 34 and the center of the upper pin hole 35, The amount of deformation in the load direction of the parts (A part, B part) located on the left and right sides of the pin 7 is the same, which means that the inversion of the bush accommodated between the upper pin 7 and the upper pin hole 35 can be suppressed. To do.

  Next, the deformation of the C part and the D part located on the right side of the crankpin hole 34 is considered in the same manner as described above. First, a half load of Fcontrol acts downward on part C, which is the right part of the control pin 12, and the other half of the load of Fcontrol acts downward on part D, which is the left part of the control pin 12. To do. The remaining half load of Fcrank acts upward on the D portion. According to Hooke's law, strain (tensile strain) is known to be proportional to Young's modulus x stress, and the amount of deformation is the product of strain multiplied by length. Acts downward and extends by a minute amount Δx4, the following equation is established.

(1/2) Fcontrol≈Y × Δx4 × L5 (7)
Where Y: Young's modulus (constant value),
In D part, if a tensile load of 1/2 of Fcontrol acts downward and extends by a minute amount Δx5, and a tensile load of 1/2 of Fcrank acts upward and extends by a minute amount Δx6, then according to Hook's law The formula holds.

(1/2) Fcontrol + (1/2) Fcrank≈Y × (Δx5 + Δx6) × L6
(8)
Where Y: Young's modulus (constant value),
Here, if the amount of deformation in the load direction of the C portion is equal to the amount of deformation in the load direction of the D portion, when a bush (not shown) is accommodated between the control pin 12 and the control pin hole 36, the right side of the control pin 12 Contact between the asymmetrical control pin 12 and the bush does not occur between the part (C part) and the left part (D part), and neither the clockwise drag nor the counterclockwise drag occurs on the bush. From this request, it is assumed that the load direction deformation amount of the C part and the load direction deformation amount of the D part are equal, that is, Δx4 = Δx5 + Δx6. Since the ratio between the left sides of the above formulas (7) and (8) is equal to the ratio between the right sides of the above formulas (7) and (8), the following formula is obtained.

(1/2) Fcontrol + (1/2) Fcrank: (1/2) Fcontrol
= (Δx5 + Δx6) × Y × L6: Δx4 × Y × L5
= L6: L5
Multiplying the left side of this expression by 2 gives Fcontrol + Fcrank: Fcontrol, so the following expression is obtained.

Fcontrol + Fcrank: Fcontrol = L6: L5 (9)
When the above equation (5) and equation (9) are solved simultaneously, the following equation is obtained.

L4 + 2L3: L3 = L6: L5 (10)
When the dimensions of the lower link 5 are determined so that the relationship of the expression (10) is established between L3, L4, L5, and L6, the expression (10) obtained in this way is the left and right sides of the control pin 12. Even if the thicknesses of the parts (C part and D part) located at different positions are different and the load direction is not along the line connecting the center of the crank pin hole 34 and the center of the control pin hole 36, The amount of deformation in the load direction of the portions (C portion, D portion) located on both the left and right sides of the pin 12 becomes the same, thereby suppressing the inversion of the bush accommodated between the control pin 12 and the control pin hole 36. Means you can.

  The lower link 5 according to the second embodiment of the present invention, which is designed based on such a principle, that is, L1, L2, L3, L4, L5, and L6 are defined so as to satisfy the relationship of the above expressions (6) and (10). FIG. 6 is a schematic front view of the engine, and FIG. 8 is a schematic configuration diagram of a reciprocating engine including a multi-link type piston crank mechanism having a lower link 5 according to the second embodiment of the present invention. In FIG. 6, a pair of bolts 75 and 76 for fastening a lower link upper part 72 and a lower link lower part 73, which will be described later, are shown in an overlapping manner.

  In FIG. 6, the lower link 5 holds a crank pin bearing portion 41 at the substantially center where the crank pin 4 is fitted, an upper pin pin boss portion at one end (left end portion) for holding the upper pin 7, and a control pin. It has a control pin pin boss portion at the other end portion (left end portion), is formed in a parallelogram shape as a whole, and has a predetermined thickness in a direction perpendicular to the paper surface.

  More specifically, a bifurcated portion is formed at the upper left corner of the lower link 5, and a pair of upper pin pin boss portions 45, 46 are provided at the bifurcated portion. This will be further described with reference to FIG. 7. FIG. 7 shows an assembled state in which the upper link 6 and the lower link 5 are connected. That is, the lower link 5 is formed with a bifurcated portion extending upward, and has a pair of upper pin pin boss portions 45 and 46 at the bifurcated portion. A space into which the lower end pin boss portion 51 of the upper link 6 is fitted is provided at the forked portion of the lower link 5. A pair of upper pin pin boss portions 45, 46 provided at the bifurcated portion of the lower link 5 supports both end portions of the upper pin 7. In this embodiment, the inner diameters of the upper pin holes 47, 48 formed in a cylindrical shape in the pair of upper pin pin boss portions 45, 46 are extremely slightly smaller than the outer diameter of the upper pin 7, and the upper pin 7 is press-fitted. It has become so. Further, a ring-shaped bush 53 is accommodated in the pin hole 52 of the lower end pin boss portion 51 of the upper link 6, and the inner diameter of the bush 53 is extremely slightly larger than the outer diameter of the upper pin 7. A predetermined clearance is generated. As a result, the lower end pin boss portion 51 of the upper link 6 is positioned so as to be sandwiched between the forked portions of the lower link 5 including the pair of upper pin pin boss portions 45 and 46, and both end portions of the upper pin 7 are connected to the lower link 5. The lower fork pin boss portion 51 of the upper link 6 is rotatably fitted to the center portion of the upper pin 7 supported by the forked portion side.

  Returning to FIG. 6, a bifurcated portion is also formed at the lower right corner of the lower link 5, and a pair of control pin pin boss portions 61 and 62 are provided at the bifurcated portion. Although not shown, the assembled state in which the control link 11 and the lower link 5 are connected has the same configuration as that in FIG.

  The center of the upper pin holes 47 and 48 formed in a cylindrical shape in the pair of pin boss portions 45 and 46 and the center of the control pin holes 63 and 64 formed in a cylindrical shape in the pair of pin boss portions 61 and 62 are connected. The position of the crank pin hole 42 is determined so that the center of the crank pin hole 42 of the crank pin bearing portion 41 is on the line m.

  On the other hand, the lower link 5 has a lower link upper part 72 having upper pin pin boss portions 45 and 46 and a control pin pin boss portions 61 and 62 in order to improve the assemblability to the crank pin 4. The lower part 73 is divided into two parts, and both are fastened by a pair of bolts 75 and 76. As shown in FIG. 8, the lower link upper part 72 is located on the upper side, and the lower link lower part 73 is located on the lower side.

  The lower link 5 is divided into a lower link upper part 72 and a lower link lower part 73 at a surface (joint surface) passing through the center of the crankpin bearing part 41 to which the crankpin 4 is fitted, and the crankpin bearing part 41 is As a half structure, one of the half parts is formed on the lower link upper part 72 and the other is formed on the lower link lower part 73.

  Bolts 75 and 76 for connecting both parts 72 and 73 are disposed in the upper pin portion and the control pin portion, with the crank pin bearing 41 interposed therebetween, of the joint surfaces of the two parts 72 and 73. The close bolt 75 is inserted from the lower surface side of the lower link lower part 73 and screwed into a bag-like screw hole 77 formed in the lower link upper part 72. On the other hand, the bolt 76 near the control pin is inserted from the upper surface side of the lower link upper part 72 and screwed into a screw hole 78 formed in the lower link lower part 73. In this way, the pair of bolts 75 and 76 are configured such that the front ends of the bolts are staggered.

  In addition, the bolt 75 near the upper pin has a bolt center axis n that coincides with a vertical line passing through the centers of the upper pin holes 47 and 48, whereas the bolt 76 near the control pin has a bolt center. The axis p is positioned so as to be slightly translated to the left side from the vertical line passing through the centers of the control pin holes 63 and 64.

  Furthermore, the bolt engagement tip of the bolt 75 near the upper pin is located away from the upper pin holes 47 and 48 and the crank pin hole 42, and the bolt engagement tip of the bolt 76 near the control pin is the control pin hole 63, 64. And a position away from the crankpin hole 42.

  In the first embodiment shown in FIG. 4, the simplified model in which the loads Fcrank, Fupper, and Fcontrol act in the vertical direction on the horizontal line connecting the centers of the three pin holes 34, 35, and 36 is considered. The lower link 5 swings within a predetermined angle range around the upper pin 7, and the direction in which each load Fcrank, Fupper, Fcontrol acts does not necessarily coincide with the piston movement direction. For example, assuming that the bolt center axes n and p are at positions parallel to the piston movement direction Q in FIG. 6, straight lines connecting the centers of the upper pin holes 47 and 48, the crank pin hole 42, and the control pin holes 63 and 64. m is inclined with respect to the piston movement direction Q, and the direction in which each load Fcrank, Fupper, Fcontol acts is not parallel to the piston movement direction Q. In such a case, an angle with respect to the load Fcrank of a straight line (m) drawn from the center of the crank pin hole 42 (crank pin bearing portion) to the center of the upper pin holes 47 and 48 (upper pin boss portions 45 and 46). Θcrank, the angle with respect to the load Fupper of the straight line (m) drawn from the center of the upper pin holes 47, 48 (upper pin pin boss portions 45, 46) to the center of the crank pin hole 42 (crank pin bearing portion 41), Then, only the component force (Fcrank · sinθcrank and Fupper · sinθupper) in the direction orthogonal to the straight line m of Fcrank and Fupper needs to be considered. That is, in the second embodiment, the following equation (11) is used instead of the above equation (3).

Fcrank · sinθcrank + Fupper · sinθupper: Fupper · sinθupper = L2: L1
... (11)
Similarly, the angle of the straight line (m) drawn from the center of the crank pin hole 42 (crank pin bearing portion 41) to the center of the control pin holes 63 and 64 (control pin pin boss portions 61 and 62) with respect to the load Fcrank is θcrank. When the angle with respect to the load Fcontrol of the straight line (m) drawn from the center of the control pin holes 63, 64 (control pin pin boss portions 61, 62) to the center of the crank pin hole 42 (crank pin bearing portion 41) is θcontrol, Since only the component forces (Fcrank · sinθcrank and Fcontrol · sinθcontrol) in the direction orthogonal to the straight line m of Fcrank and Fcontrol have to be considered, in the second embodiment, instead of the above equation (9), the following (12 ) Expression.

Fcrank ・ sinθcrank + Fcontrol ・ sinθcontrol ： Fcontrol ・ sinθcontrol
= L6: L5
(12)
As described above, in the second embodiment shown in FIG. 6, the lower link shape is designed by determining L1, L2, L5, and L6 so as to satisfy the expressions (11) and (12).

  More specifically, FIG. 6 shows a case where θupper, θcrank, and θcontrol are not the same angle. However, if roughly handled, these angles may be the same, that is, θupper = θcrank = θcontrol. At this time, the above equations (11) and (12) are as follows.

Fcrank + Fupper: Fupper = L2: L1 (13)
Fcrank + Fcontrol: Fcontrol = L6: L5 (14)
These expressions (13) and (14) are the same as the above expressions (3) and (9). That is, the first embodiment corresponds to a case where the second embodiment is simplified.

  In the multi-link type piston crank mechanism, the side thrust load that acts to incline the piston 9 is smaller than that in a general single-link type piston crank mechanism. Specifically, the maximum combustion pressure acts on the piston 9 in the first half of the expansion stroke, and the piston head receives the maximum load. At this time, the upper link 6 is in a posture close to vertical. Yes, the inclination of the cylinder 10 with respect to the axis is very small. In particular, the inclination with respect to the axis of the cylinder 10 can be made smaller than the posture of the connecting rod in the case of a single link type piston crank mechanism. Accordingly, the side thrust load is reduced. More specifically, in the second embodiment, as shown in FIG. 9, the movement locus of the upper pin 7 is an ellipse having a long axis in the piston movement direction, so that the upper link 6 around the piston pin 8 is centered. The swing angle becomes smaller and the swing angular velocity of the upper link 6 becomes smaller. The combustion load acting on the upper link 6 is normally maximum at about 10 to 20 deg after the compression top dead center, and thereafter continues to receive the load until the cylinder internal pressure decreases. In the meantime, if the locus of the upper pin 7 is elliptical, the upper link 6 receives a load with almost no angle change, so the sliding speed with the piston pin 8 is reduced (almost zero), thereby side thrust load. Can be reduced. In other words, as shown in FIG. 6, in the second embodiment, the direction of the load Fupper at the maximum combustion load input to the pin boss portions 45 and 46 is quite close to the piston movement direction Q.

  In this way, the bolt central axis n of the bolt 75 near the upper pin is substantially parallel to the direction of the load Fupper when the combustion load is maximum, that is, the center axis of the upper link when the combustion load is maximum. The moment load on the bolt 75 near the pin can be reduced, and the durability of the bolt fastening portion can be improved. On the other hand, if the bolt center axis n of the bolt 75 near the upper pin is greatly deviated from the direction of the load Fupper at the maximum combustion load, a moment load acts on the bolt 75 near the upper pin, and the bolt fastening portion It is conceivable that the durability of the resin deteriorates.

  Further, at this time, as shown in FIG. 6, the direction of the load Fcontrol at the time of maximum combustion load inputted to the pin boss portions 61 and 62 is also very close to the piston movement direction Q. By making the bolt central axis p of the bolt 76 near the pin substantially parallel to the direction of the load Fcontrol at the maximum combustion load, that is, the central axis of the control link at the maximum combustion load, the bolt 76 near the control pin The moment load on the bolt can be reduced, and the durability of the bolt fastening portion can be improved. On the other hand, if the bolt center axis p of the bolt 76 near the control pin is greatly deviated from the direction of the load Fcontrol when the combustion load is maximum, a moment load acts on the bolt 76 near the control pin, and the bolt fastening portion It is conceivable that the durability of the resin deteriorates.

  Not only in the case of FIG. 6, the bolt central axis n of the bolt 75 near the upper pin is just parallel to the direction of the load Fupper at the maximum combustion load, that is, the central axis of the upper link at the maximum combustion load. It doesn't matter.

  Here, the effects of the two embodiments will be described together.

  According to the first embodiment (the invention described in claim 1), the upper link 6, the lower link 5, and the control link 11 are provided. The lower link 5 includes the crankpin bearing portion 31 at the substantially center and the upper link. It has an upper pin pin boss part 32 for holding the pin 7 and a control pin pin boss part 33 for the other end of the control pin 12, and a bush is accommodated in the upper pin pin boss part 32. In the multi-link type piston crank mechanism, the thickness of the portion of the upper pin pin boss portion 32 opposite to the side where the crank pin bearing portion 31 is located is L1, and between the upper pin pin boss portion 32 and the crank pin bearing portion 31. L2 is the thickness of the portion of L, and L3 is the distance between the center of the pin boss portion 32 for the upper pin and the center of the crank pin bearing portion 31. When the distance between the center of the pin boss portion 33 for the lupin and the center of the crank pin bearing portion 31 is L4, the above formula (6) is established, so the pin boss portion 32 for the upper pin and the crank pin bearing portion And the load acting on the portion between the upper pin pin boss portion 32 and the portion on the opposite side of the crank pin bearing portion 31 side (A portion in FIG. 5). Since the ratio (L3 + 2L4: L4) to the load is equal to the ratio (L2: L1) between the thickness of the B part and the thickness of the A part (L2: L1), asymmetric deformation occurring in the A part and the B part is suppressed. In addition, the inward rotation of the bush accommodated in the pin boss portion 32 for the upper pin can be prevented. In other words, the thickness of the upper pin pin boss portion 32 is different between the portion on the side where the crank pin bearing portion 31 is located and the portion on the opposite side where the crank pin bearing portion 31 is not present, and the input is input to the pin boss portion 32 for the upper pin. Even when the directions of the load Fupper and the load Fcrank input to the crank pin bearing portion 31 are not along the line connecting the center of the upper pin pin boss portion 32 and the center of the control pin pin boss portion 33. Further, the inward rotation of the bush accommodated in the pin boss portion 32 for the upper pin can be prevented.

  According to the first embodiment (the invention described in claim 2), the upper link 6, the lower link 5, and the control link 11 are provided. The lower link 5 includes the crankpin bearing portion 31 at the substantially center and the upper link. A multi-link type having an upper pin pin boss portion 32 for holding a pin and a control pin pin boss portion 33 for holding the control pin, and having a bush accommodated in the control pin pin boss portion In the piston crank mechanism, the thickness of the portion of the control pin pin boss portion 33 opposite to the side where the crank pin bearing portion is located is L5, and the thickness of the portion between the control pin pin boss portion 33 and the crank pin bearing portion 31 is. The thickness is L6, the distance between the center of the pin boss portion 32 for the upper pin and the center of the crank pin bearing portion 31 is L3, the controller When the distance between the center of the pin pin boss portion 33 and the center of the crank pin bearing portion 31 is L4, the above formula (10) is established, so the control pin pin boss portion 33 and the crank pin bearing portion And a load acting on a portion between the control pin pin boss portion 33 and a portion on the opposite side of the crank pin bearing portion 31 side (C portion in FIG. 5). The ratio (L4 + 2L3: L3) to the load is equal to the ratio (L6: L5) between the thickness of D part and the thickness of C part (L6: L5), so that asymmetric deformation occurring in C part and D part is suppressed. Thus, the internal rotation of the bush accommodated in the control pin pin boss portion 33 can be prevented. In other words, the wall thickness of the control pin pin boss part 33 is different between the part on the side where the crankpin bearing part 31 is located and the part on the opposite side where the crankpin bearing part 31 is not present, and is input to the pin boss part 33 for control pin. Even when the directions of the load Fcontrol and the load Fcrank input to the crank pin bearing portion 31 are not along the line connecting the center of the control pin pin boss portion 33 and the center of the upper pin pin boss portion 32 In addition, the inversion of the bush accommodated in the control pin pin boss portion 33 can be prevented.

  As shown in FIG. 1, in the case of a conventional apparatus in which the center of the crank pin bearing portion is below the line connecting the center of the upper pin boss portion and the center of the control pin boss portion, As a result of the rise, interference with the lower end of the cylinder bore increases, and it is necessary to reduce the thickness L1 on the side where the crank pin 4 is not provided, and L4 / L3 cannot be increased, so that the piston stroke cannot be increased. On the other hand, although not shown, if the center of the crank pin bearing is above the line connecting the center of the upper pin boss and the center of the control pin boss, the upper link 6 at the bottom dead center In order to prevent the interference of the lower link 5, the distance between the pin boss portion for the upper pin and the lower link 5 must be increased. Then, it is necessary to increase the thickness L1 of the portion where the crank pin 4 is not provided, and the interference with the lower end of the cylinder bore at the top dead center is increased. On the other hand, according to the second embodiment (the invention described in claim 3), the crank pin is on a line connecting the centers of the upper pin pin boss portions 45 and 46 and the control pin boss portions 61 and 62. Since there is the center of the hole 42 (crank pin bearing portion 41), such a problem does not occur.

  The lower link 5 includes a lower link upper part 72 having one half of the crankpin bearing 41 and upper pin pin bosses 45, 46, the other half of the crankpin bearing 41 and a control pin boss. The lower link upper part 72 and the lower link lower part 73 are divided into upper link pins with the crank pin bearing portion 41 between them. In the case where the bolts 75 and 76 are fastened at the shift part and the control pin, respectively, when the heads of the pair of bolts 75 and 76 are arranged on the same side in FIG. 6, for example, the bolt 75 near the upper pin. At the top of the pin bosses 45, 46, and at this time, the envelope of the lower link 5 (low -The outermost trajectory when the link 5 swings) not only prevents the cylinder block from being made compact, but also increases interference with the cylinder bore near the top dead center. 4), the bolt 75 arranged near the upper pin is fastened from the lower link lower part 73 side so that its head is located on the lower link lower part 73 side, and closer to the control pin. Since the bolt 76 arranged at the position is fastened from the lower link upper part 72 side so that the head is located at the lower link upper part 72 side, the heads of the pair of bolts 75 and 76 are arranged on the same side. The entire lower link 5 can be made more compact than the case.

  According to the second embodiment (invention described in claim 5), the bolt 75 arranged near the upper pin has an upper link central axis (direction of the load Fupper) when the bolt central axis n is at the maximum combustion load. The bolt 76 arranged in parallel or close to the control pin has its bolt center axis p parallel to the control link center axis (direction of the load Fcontrol) when the combustion load is maximum. The moment load to 75 and 76 can be reduced, the durability of the bolt fastening portion can be improved, and the configuration of the lower link 5 can be made compact.

  According to the second embodiment (the invention described in claim 6), the bolt 75 arranged near the upper pin has a bolt meshing tip separated from the upper pin pin boss portions 45 and 46 and the crank pin bearing portion 41. The bolt 76 located at the position and close to the control pin has a bolt engaging tip that is located away from the control pin pin boss portions 61 and 62 and the crank pin bearing portion 41. It is possible to separate the deformation of the tip of the portion from the pin boss portions 45, 46, 61, 62 and the crank pin bearing portion 41, and the deformation of the pin boss portions 45, 46, 61, 62 and the crank pin bearing portion 41 can be suppressed.

  According to the second embodiment (the invention described in claim 7), the upper link 6, the lower link 5, and the control link 11 are provided. The lower link 5 includes the crankpin bearing portion 31 at the substantially center and the upper link. A multi-link having an upper pin pin boss portion 32 for holding a pin and a control pin pin boss portion 33 for holding the control pin, and having a bush accommodated in the upper pin pin boss portion 32 In the type piston crank mechanism, a straight line (Fupper, a straight line obtained by pulling the load input to the upper pin pin boss portions 45, 46 from the center of the upper pin pin boss portions 45, 46 to the center of the crank pin hole 42 (crank pin bearing portion 41)) m) The angle of this load Fupper with θupper, the load input to the crankpin bearing 31 with Fcrank, and the crankpin hole The angle of the straight line (m) drawn from the center of the 42 (crank pin bearing portion 41) to the center of the upper pin pin boss portions 45, 46 with respect to this load Fcrank is θcrank, and of the upper pin pin boss portions 45, 46, the crank pin bearing When the thickness of the portion opposite to the side where the portion 41 is located is L1, and the thickness of the portion between the upper pin pin boss portions 45, 46 and the crank pin bearing portion 41 is L2, the above equation (11) is Since the upper pin pin boss part 32 is formed, the thickness of the part on the side where the crankpin bearing part 31 is present is different from the part on the opposite side where the crankpin bearing part 31 is not present, and for the upper pin. Even if the direction of the load input to the pin boss part 32 and the direction of the load input to the crank pin bearing part 31 are deviated from the piston movement direction Q, they are stored in the pin boss part 32 for the upper pin. It is possible to prevent the adduction of the stored bush.

  According to the second embodiment (the invention described in claim 9), the actuator (control shaft 13, eccentric cam portion 14, worm gear) that can change the compression ratio by changing the swing fulcrum position of one end of the control link 11. 15, compression ratio control actuator 16) and an engine control unit 39 (compression ratio variable control means for controlling the command value given to this actuator so that the compression ratio is low when the load is high so that the compression ratio is high when the load is low. ), The engine load increases, and the bush inversion suppressing effect is increased at low compression when the load Fupper input to the pin boss portions 45 and 46 of the lower link via the piston 9 and the upper link 6 is increased.

  In the embodiment, the case where the center of the crank pin bearing portion is on the line connecting the center of the pin boss portion for the upper pin and the center of the control pin boss portion has been described (see FIGS. 4 and 6). The present invention can also be applied to the case where the center of the crank pin bearing portion is not on the line connecting the center of the portion and the center of the control pin boss portion. That is, also in this case, the lower link 5 can be configured so that the above expressions (6), (10), (11), and (12) are established.

  In the embodiment, the load (Fupper, Fcrank, Fcontrol) acting at the maximum combustion load is considered as the load input to the pin boss part for the upper pin, the crank pin bearing part, and the pin boss part for the control pin, but is not limited to this. The present invention can also be applied to a load that acts when the inertial force is maximum.

1 is a schematic configuration diagram of a reciprocating engine having a multi-link type piston crank mechanism. The posture figure of each link in a high compression ratio position and a low compression ratio position. Schematic for demonstrating the principle which bush inversion occurs. The simplified model figure of the lower link of 1st Embodiment. Schematic which illustrated the deformation | transformation of each part of the lower link at the time of the load effect | action of 1st Embodiment. The schematic front view of the lower link of 2nd Embodiment. Sectional drawing which shows the assembly | attachment state of the upper link and lower link of 2nd Embodiment. The schematic block diagram of a reciprocating engine provided with the multi-link type piston crank mechanism incorporating the lower link of 2nd Embodiment. Schematic for demonstrating the upper pin locus | trajectory of 2nd Embodiment.

Explanation of symbols

4 Crank pin 5 Lower link 6 Upper link 8 Piston pin 9 Piston 11 Control link 31 Crank pin bearing part 32 Pin boss part for upper pin 33 Pin boss part for control pin 39 Engine control unit (compression ratio variable control means)
41 Crank pin bearing part 42 Crank pin hole 45, 46 Pin boss part 47, 48 Upper pin hole 61, 62 Pin boss part 63, 64 Control pin hole 72 Lower link upper part 73 Lower link lower part 75 Bolt near upper pin 76 Control pin Bolt

Claims (9)

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 connected to the crankpin of the crankshaft;
A control link having one end swingably supported on the engine body side and the other end connected to the lower link via a control pin.
The lower link is for a crank pin bearing portion in the middle of which the crank pin is fitted, an upper pin pin boss portion for holding the upper pin, and a control pin for the other end portion of the control pin. Having a pin boss,
In the multi-link type piston crank mechanism in which the bush is stored in the pin boss part for the upper pin,
The thickness of the portion of the upper pin pin boss portion opposite to the side where the crank pin bearing portion is located is L1, and the thickness of the portion between the upper pin pin boss portion and the crank pin bearing portion is L2, When the distance between the center of the pin boss portion for the upper pin and the center of the crank pin bearing portion is L3, and the distance between the center of the pin boss portion for the control pin and the center of the crank pin bearing portion is L4,
L3 + 2L4: L4 = L2: L1 (a)
A multi-link type piston crank mechanism. 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 connected to the crankpin of the crankshaft;
A control link having one end swingably supported on the engine body side and the other end connected to the lower link via a control pin.
The lower link is for a crank pin bearing portion in the middle of which the crank pin is fitted, an upper pin pin boss portion for holding the upper pin, and a control pin for the other end portion of the control pin. Having a pin boss,
In the multi-link type piston crank mechanism in which the bush is housed in the pin boss part for the control pin,
The thickness of the portion of the control pin pin boss portion opposite to the side where the crank pin bearing portion is located is L5, and the thickness of the portion between the control pin pin boss portion and the crank pin bearing portion is L6, When the distance between the center of the pin boss portion for the upper pin and the center of the crank pin bearing portion is L3, and the distance between the center of the pin boss portion for the control pin and the center of the crank pin bearing portion is L4,
L4 + 2L3: L3 = L6: L5 (b)
A multi-link type piston crank mechanism.   3. The multi-link type piston crank mechanism according to claim 1, wherein the center of the crank pin bearing portion is on a line connecting the center of the pin boss portion for the upper pin and the center of the pin boss portion for control. . The lower link includes a lower link upper part having one of the half parts of the crank pin bearing part and the pin boss part for the upper pin, the other half part of the crank pin bearing part, and the control pin boss part. Divided into lower link lower parts,
The lower link upper part and the lower link lower part are fastened by bolts at the upper pin portion and the control pin portion, with the crank pin bearing portion in between, respectively,
The bolt arranged near the upper pin is fastened from the lower link lower part side so that its head is located on the lower link lower part side,
The bolt arranged near the control pin is fastened from the lower link upper part side so that its head is located on the lower link upper part side. The double link type piston crank mechanism as described.   The bolt arranged near the upper pin has a bolt central axis parallel to the upper link central axis when the combustion load is maximum or the inertial force is maximum, or the bolt arranged near the control pin is 5. The multi-link type piston crank mechanism according to claim 4, wherein the bolt center axis is parallel to the control link center axis when the combustion load is maximum or the inertia force is maximum.   The bolt arranged closer to the upper pin has a bolt engaging tip located at a position away from the pin boss portion for the upper pin and the crank pin bearing portion, or the bolt arranged closer to the control pin is engaged with the bolt. 6. The multi-link type piston crank mechanism according to claim 4, wherein a tip is located at a position away from the pin boss portion for the control pin and the crank pin bearing portion. 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 connected to the crankpin of the crankshaft;
A control link having one end swingably supported on the engine body side and the other end connected to the lower link via a control pin.
The lower link is for a crank pin bearing portion in the middle of which the crank pin is fitted, an upper pin pin boss portion for holding the upper pin, and a control pin for the other end portion of the control pin. Having a pin boss,
In the multi-link type piston crank mechanism in which the bush is stored in the pin boss part for the upper pin,
The load input to the pin boss for the upper pin is Fupper, and the angle of the straight line drawn from the center of the pin boss for the upper pin to the center of the crankpin bearing is θupper, and the angle is input to the crankpin bearing. Fcrank, the angle of the straight line drawn from the center of the crank pin bearing portion to the center of the upper pin pin boss portion with respect to the load Fcrank is θcrank, and the crank pin bearing portion of the upper pin pin boss portion is provided. When the thickness of the portion opposite to the side is L1, and the thickness of the portion between the pin boss portion for the upper pin and the crank pin bearing portion is L2,
Fcrank · sinθcrank + Fupper · sinθupper: Fupper · sinθupper = L2: L1
... (c)
A multi-link type piston crank mechanism.   The multi-link type piston crank mechanism according to claim 7, wherein the load is a load at the time of maximum combustion load or maximum inertia force. An actuator capable of changing the compression ratio by changing the swing fulcrum position of one end of the control link;
The compression ratio variable control means for controlling a command value given to the actuator so as to become a low compression ratio at a high load so as to become a high compression ratio at a low load. Double-link type piston crank mechanism.

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