JP4380321B2 - Lower link in piston crank mechanism of internal combustion engine - Google Patents

Description

  The present invention relates to a piston crank mechanism of a reciprocating internal combustion engine, and more particularly to a lower link in a multi-link type piston crank mechanism.

  Patent Documents 1 and 2 are known as conventional techniques 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. Each of these 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 on the engine body side, and the other end Includes a control link coupled to the lower 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.

  A typical lower link shape is shown in FIG. 1 of Patent Document 1 or FIG. 4 of Patent Document 2, for example.

  In such a multi-link type piston crank mechanism, the lower link receives the combustion pressure received by the piston from the upper pin via the upper link, and moves to the crank pin by a kind of “lever” operation with the control pin as a fulcrum. Force is transmitted (however, the relationship between the fulcrum and the power point varies depending on the stroke of the intake, compression, combustion, and exhaust engines). Therefore, the lower link needs to have strength and rigidity sufficient to maintain the positional relationship when receiving the input from each pin while holding the upper pin, the control pin and the crank pin rotatably. Therefore, the lower link has a shape in which a bearing housing portion or a pin boss portion that rotatably holds the upper pin, the control pin, and the crank pin is integrated as a member. In addition, in order to ensure ease of assembly with respect to the crankshaft, the bearing housing portion of the crankpin is configured such that two parts having semicircular holes are fastened to each other with bolts.

The lower link is a moving part that oscillates around the center of the crankpin while translationally moving on the crankpin's locus circle. A large inertial force. Therefore, the lower link needs to be as light as possible in addition to strength requirements. Further, depending on the position of the center of gravity of the lower link, a large inertia force is generated by the above-described swing motion. In order to reduce the inertial force due to the swinging motion, it is generally desirable that the position of the center of gravity of the lower link is close to the center of the crankpin as described in Patent Document 3. However, when aiming at the effect of canceling out the inertial force due to the swinging motion of other moving parts, a position slightly shifted rather than a position that exactly coincides with the center of the crankpin may be desirable.
JP 2001-227367 A JP 2002-61501 A Japanese Patent Laid-Open No. 2002-129995

  By the way, as a specific structure of the lower link, as shown in FIGS. 4 and 5, the lower pin has an upper pin pin boss portion 5 and one of the half portions of the bearing housing 2 into which the crank pin is fitted. The link upper part 6 is divided into a lower link lower part 8 having a control pin pin boss part 7 and having the other half of the bearing housing 2, and the lower link upper part 6 and the lower link lower part 8 Are being fastened by bolts 9 and 10 at a portion 4A near the upper pin and a portion 4 near the control pin with the bearing housing 2 interposed therebetween.

  In the case of the lower link 1 shown in FIGS. 4 and 5, the bolts 9 and 10 arranged on both sides of the bearing housing 2 are tightened from the lower link lower part 8 side so that the head faces downward. The front end sides of 9 and 10 are screwed into the bag-like screw holes 11 and 124 of the lower link upper part 6.

  However, the lower link 1 having such a structure has the following problems.

  For example, considering the force input to the lower link 1 in the combustion stroke of the internal combustion engine, the combustion load 121 is input from the pin boss portion 5 for the upper pin, and the reaction 122 in which the lower link 1 transmits the combustion load to the crank pin is a bearing. A force 123 that is input from the housing 2 and controls the motion posture of the lower link 1 is input from the pin boss portion 7 for the control pin. At this time, when attention is paid to the input 122 from the crank pin and the input 123 from the control pin, they become forces in approximately opposite directions, which causes the bolt 10 to be pulled downward in the figure. In order to prevent the lower link upper part 6 and the lower link lower part 8 from separating when the bolt 10 is pulled in this manner, a sufficiently large axial force is applied to the bolts 9 and 10 in advance. When the above pulling force acts in addition to the axial force, a large force directed downward in the figure acts on the thread 125 of the screw hole 124 on the lower link upper part 6 side.

  If attention is paid only to the lower link upper part 6, the lower link upper part 6 tends to bend diagonally downward to the left with the bearing housing 2 as a fulcrum by the force 122 from the crank pin and the pulling force. Also, stress due to bending acts near the thread 125 of the screw hole 124.

  Therefore, in the structure of the lower link 1, a complex stress field is formed in the vicinity of the screw thread 125 by combining the pulling force and the bending force, and it is difficult to ensure sufficient strength. Is the actual situation.

  In the lower link 1, the angle formed by the respective loads 121 to 123 and the mating surface of the lower link upper part 6 and the lower link lower part 8 is not a right angle, and when these loads 121 to 123 are received, A component force that generates a shift acts. Such a misalignment of the mating surfaces causes troubles such as fine movement wear, and causes problems such as deterioration of the roundness of the bearing housing 2 and an increase in frictional resistance. Therefore, there is a demand to increase the axial force (tightening force) of the bolts 9 and 10, and securing the strength in the vicinity of the thread 125 is a bottleneck to satisfy such a demand.

  The present invention includes an upper link having one end connected to a piston via a piston pin, a lower link connected to the other end of the upper link via an upper pin, and connected to a crank pin of a crankshaft. A piston crank mechanism of an internal combustion engine provided with a control link supported on the engine body side so as to be swingable and having the other end connected to the lower link via a control pin. The structure is improved.

  The lower link of the present invention is divided into a lower link upper part and a lower link lower part, and both of these parts are parts of the joint surfaces of the two parts closer to the upper pin with the bearing housing portion in between. The bolts are tightened from the lower link upper part side so that their heads are located on the lower link upper part side. did.

  According to the present invention, since the bolt disposed near the control pin is fastened from the lower link upper part side, the bolt insertion hole near the control pin of the lower link upper part is not threaded or meshed with the bolt. The hole shape can be reduced. Therefore, stress concentration is unlikely to occur in the periphery of the bolt insertion hole near the control pin of the lower link upper part where a large bending load is applied by the crank pin and the control pin, and the strength of this part can be easily and reliably ensured.

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

  1 to 3 show a lower link 101 according to the present invention. The lower link 101 is used in a multi-link type piston crank mechanism known from the above-mentioned Patent Documents 1 and 2, and includes an upper link, a control link, and a crank pin (crankshaft) (not shown). These are the parts that connect the three. The end of the control link opposite to the lower link 101 is rotatably supported by an eccentric cam on the control shaft, and the control shaft is controlled to rotate according to engine operating conditions. In this embodiment, variable compression ratio means for changing and controlling the engine compression ratio is constituted by an eccentric cam, a control shaft, an actuator for rotating the control shaft, and the like. The variable compression ratio means increases the engine compression ratio under light load conditions.

  FIG. 1 is a cross-sectional view of the lower link 101 cut along a central plane in the thickness direction (crankshaft axial direction) (a plane along the line AA in the top view of FIG. 3). FIG. FIG. 3 is a top view of the lower link 101 when the link 101 is viewed from the axial direction of the crankshaft.

  The lower link 101 is configured to be divided into a lower link upper part 6 having an upper pin pin boss part 5 and a lower link lower part 8 having a control pin pin boss part 7 for assembly to a crank pin. It is fastened by a pair of bolts 9 and 10. If cylinders (not shown) are arranged vertically, the lower link upper part 6 is located on the upper side and the lower link lower part 8 is located on the lower side in the crankcase.

  The lower link 101 is divided into a lower link upper part 6 and a lower link lower part 8 at a surface (joint surface) passing through the central axis 3 of the bearing housing 2 to which the crankpin is fitted, and the bearing housing 2 has a half structure. One of the halves is formed on the lower link upper part 6 and the other is formed on the lower link lower part 8. Bolts 9 and 10 for connecting the parts 6 and 8 are arranged at the upper pin side portion 4A and the control pin side portion 4 with the bearing housing 2 interposed therebetween, and the bolts near the upper pin. 9 is inserted from the lower surface side of the lower link lower part 8 and is screwed into a bag-like screw hole 111 formed in the lower link upper part 6. On the other hand, the bolt 10 near the control pin is inserted from the upper surface side of the lower link upper part 6 and screwed into a screw hole 12 formed in the lower link lower part 8.

  As can be seen from the top view of FIG. 3, the upper pin pin boss portion 5 is formed at one location so as to penetrate the center surface 16 in the thickness direction of the lower link 101, and the control pin pin boss portion 7 is the center. It is formed separately at two locations facing each other with the surface 16 in between. That is, the control pin pin boss portion 7 has a bifurcated structure, and one end portion of a control link (not shown) is arranged in a groove-like space 17 inside the bifurcated portion.

  When this lower link 101 receives the loads 121 to 123 during combustion as in the lower link 1 shown in FIGS. 4 and 5, the lower link upper 6 component and the lower link lower component 8 tend to be separated. 9, 10 prevents the separation. At this time, the bolt 10 on the control pin side receives a tensile load between the portion engaging with the thread of the screw hole 12 on the lower link lower part 8 side and the seating surface 13 on the lower link upper part 6 side. The peripheral part of the bolt insertion hole 14 of the link upper part 6 receives a compressive load between the joint surface of the parts 6 and 8 and the seat surface 13. In addition, the bolt insertion hole 14 has a hole shape with no screw thread or little screw engagement.

  In the lower link 101 of this embodiment, the bolt insertion hole 14 on the lower link upper part 6 side has a shape in which stress due to meshing is difficult to act, and the bolt 10 acting on the periphery of the bolt insertion hole 14. Therefore, the stress concentration around the bolt insertion hole 14 on the lower link upper part 6 side can be reliably prevented.

  The screw hole 12 on the lower link lower part 8 side may have problems such as stress concentration similar to the screw hole 124 on the lower link upper part 6 side in the lower link 1 shown in FIGS. The problem has been reduced for the following reasons.

  First, the direction of the input load during combustion is more advantageous on the lower link lower part 8 side than on the lower link upper part 6 side, and secondly, a bearing for supporting the pin boss portion 7 for the control pin. Since a large rib 15 is provided between the housing 2 and the pin boss portion 7 and the strength and rigidity of the peripheral portion thereof are sufficiently secured, stress concentration occurs in the peripheral portion of the screw hole 12 of the lower link lower part 8. Hateful.

  Third, the screw hole 12 of the lower link lower part 8 penetrates toward the space 17 between the bifurcated control pin pin bosses 5 and is not formed in a bag shape. Stress is less likely to concentrate in the vicinity of the site where the part is screwed.

  Further, in the lower link 101, the head of the bolt 9 near the upper pin is arranged on the lower surface side of the lower link lower part 8, while the head of the bolt 10 near the control pin is arranged on the upper surface side of the upper link part 6. Therefore, the heads of both bolts 9 and 10 are positioned approximately symmetrically across the bearing housing 2, and the center of gravity of the entire lower link 101 is brought closer to the crankpin center shaft 3 to suppress the inertial force. Is advantageous. In other words, the weight unbalance due to the bolt head is small even when the size of the bolt 10 is increased, and the bolt is used for fastening the lower link upper part 6 and the lower link lower part 8 more firmly. This is advantageous in increasing the size.

  Furthermore, the periphery of the seat surface 13 on the lower link upper part 6 side and the seat surface 18 on the lower link lower part 8 side where the heads of the bolts 10 and 9 come into contact are continuous from the standing block portion on the bearing housing 2 side. Reinforcing ribs 19 and 20 are provided respectively. Since the ribs 19 and 20 are provided, when the lower link 101 receives a combustion load from the piston or an inertial load of each moving part, the lower link 101 receives a load from the bearing housing 2 or the pin boss portions 5 and 7. It is possible to suppress the deformation of the link upper part 6 and the lower link lower part 8. In particular, it is possible to effectively prevent the members 21 from bending and deforming with the corners 21 and 22 from the bearing housing 2 of the bearing surfaces 13 and 18 as fulcrums and causing stress concentration in the corners 21 and 22.

  If it is assumed that the reinforcing ribs 19 and 20 are not provided, the thickness of the entire lower link is increased in order to avoid stress concentration at the corners 21 and 22, and both parts 6 are connected to the parts 6. , 8 must be increased in distance to the joint surface. In this case, the weight and moment of inertia of the entire lower link increase, which is disadvantageous in terms of restraining inertial force. However, by providing the reinforcing ribs 19 and 20 as in this embodiment, each seat is secured with sufficient strength and rigidity. The distance from the surfaces 13 and 18 to the joint surface can be reduced to reduce the size of the lower link 101. The reinforcing rib 19 extends from the bearing housing 2 side of the lower link upper part 6 to the outer side (right side in the figure) of the bolt 10 as shown in FIG. A sufficient reinforcing effect can be obtained.

  Further, as shown in FIG. 3, the heads of the bolts 9 and 10 are formed with an operation hole 30 having a hexagonal recess on the inner periphery, and a hexagonal tool is inserted into the operation hole 30 to 10 is rotated. It is conceivable that the bolt head has a hexagonal outer shape and the bolt head is rotated by a tool having a hexagonal recess, but in this case, it is sufficient to interpose the tool outside the bolt head. Since a large space must be secured, the clearance between the reinforcing rib and the bolt head must be increased. In this case, the thickness of the reinforcing rib may be limited, the size of the head of the bolt, and thus the thickness of the bolt screw portion may be limited. However, this embodiment is superior in space efficiency. The thick bolts 9 and 10 can be installed in a limited space. Therefore, it is advantageous for fastening the lower link upper part 6 and the lower link lower part 8 more firmly.

  In this embodiment, the operation hole 30 for rotating the bolts 9 and 10 has a hexagonal shape. However, these bolts 9 and 10 need to generate a large axial force and must be tightened with a large torque. Therefore, the operation hole 30 can be formed in a deformed polygonal shape other than a hexagonal shape that can be tightened with a large torque.

  Next, actions and effects unique to the invention of each claim will be listed.

  According to the invention of claim 2, the head of the bolt arranged near the control pin is located on the lower link upper part side, and the head of the bolt arranged near the upper pin is located on the lower link lower part side. Therefore, the heads of the bolts on both sides are substantially symmetrical across the bearing housing, and the position of the center of gravity of the lower link can be brought closer to the optimum position to minimize the transmission of inertial force to other parts. .

  According to the invention of claim 3, since the screw hole near the control pin of the lower link lower part to which the front end side of the bolt is screwed is not a bag shape, stress concentration at the screw front side screwing portion of the screw hole is effectively avoided. Can do.

  According to the fourth aspect of the present invention, even if a load that bends the lower link by a reverse load input from the bearing housing and each pin boss portion is applied, the lower link is formed from the corner portion of the seat surface of the bolt. The buckling deformation can be reliably restricted by the reinforcing rib.

  According to the invention of claim 5, since the reinforcing rib extends in a direction away from the center of the crank pin rather than the center axis of each bolt, buckling deformation due to load input from each pin boss portion is more effectively prevented. be able to. In other words, it is possible to bring the seating surface of the bolt head closer to the joint surface between the lower link upper part and the lower link lower part, under the constraint of ensuring sufficient strength and rigidity against bending deformation of the lower link. Become. Therefore, the lower link including the space for arranging the bolt head can be made smaller, and the weight and moment of inertia can be reduced, and the inertia force can be reduced.

  According to the invention of claim 6, the tool is less likely to interfere with the reinforcing rib as compared with the case where the tool is fitted to the outside of the bolt head and the bolt is screwed. Therefore, the bolt head can be enlarged and the bolt shaft can be thickened. Therefore, the lower link upper part and the lower link lower part can be tightened with a stronger axial force, and the joint surface of both parts can be opened or displaced. Such a problem can be avoided reliably.

Sectional drawing in alignment with the AA of FIG. 3 which shows one Embodiment of this invention. The front view which looked at the lower link of the embodiment from the crankshaft axial direction. The top view of the lower link of the embodiment. The front view which looked at the lower link conceived in the development stage of this invention from the crankshaft axial direction. The longitudinal cross-sectional view of the same lower link.

Explanation of symbols

DESCRIPTION OF SYMBOLS 2 ... Bearing housing 5 ... Upper pin pin boss part 6 ... Lower link upper part 7 ... Control pin pin boss part 8 ... Lower link lower part 9, 10 ... Bolt 12 ... Screw hole 19, 20 ... Reinforcement rib 30 ... Operation hole 101 ... Lower link

Claims (8)

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 crank pin of the crankshaft, and one end on the engine body side In a piston crank mechanism of an internal combustion engine comprising: a control link supported so as to be swingable and having the other end connected to the lower link via a control pin;
The lower link is
A lower link upper part having an upper pin pin boss part for holding the upper pin and having one of the half parts of the bearing housing part into which the crank pin is fitted;
A lower link lower part having a pin boss part for a control pin for holding the control pin and having the other half of the bearing housing part into which the crank pin is fitted,
The lower link upper part and the lower link lower part are fastened with bolts respectively at the upper pin side and the control pin side, with the bearing housing portion between the joint surfaces of the lower link upper part and the lower link lower part,
The lower link in the piston crank mechanism of the internal combustion engine, wherein the bolt arranged near the control pin is fastened from the lower link upper part side so that the head thereof is located on the lower link upper part side. . 2. The lower portion in the piston crank mechanism of the internal combustion engine according to claim 1, wherein the bolt arranged closer to the upper pin is fastened from the lower link lower part side so that a head thereof is positioned on the lower link lower part side. Link. The lower link in the piston crank mechanism of the internal combustion engine according to claim 1 or 2, wherein a screw hole of a lower link lower part into which a front end side of a bolt arranged near the control pin is screwed passes. 4. A reinforcing rib extending perpendicularly to each seating surface is formed in a peripheral region of the seating surface where the heads of the respective bolts of the lower link upper part and the lower link lower part abut. A lower link in the piston crank mechanism of the internal combustion engine according to any one of the above. 5. The lower link in a piston crank mechanism of an internal combustion engine according to claim 4, wherein the reinforcing rib is formed so as to extend in a direction away from the center of the crank pin rather than the center axis of the bolt. 6. A lower link in a piston crank mechanism of an internal combustion engine according to claim 4, wherein an operation hole into which a polygonal tool for screw operation is fitted is formed in a head portion of the bolt. The variable compression ratio means for changing / controlling the engine compression ratio by changing the swing fulcrum position of one end of the control link according to engine operating conditions. A lower link in the piston crank mechanism of the internal combustion engine described. 8. The lower link in a piston crank mechanism of an internal combustion engine according to claim 7, wherein the variable compression ratio means increases the engine compression ratio under light load conditions.

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