JP2009036147A - Double-link piston-crank mechanism of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a corner-shaped lower edge part 26 of a cylinder 11 from being brought into contact with a piston 12 by so setting that a part of the piston 12 lowers more than the lower edge part 26 of the cylinder near the bottom dead center of the piston. <P>SOLUTION: The lower end of an upper link 14 connected to the piston 12 is connected to a lower link 17 attached to a crank pin 16 through an upper pin 15. The gravity center 12A of the piston is offset from the center 13A of the piston pin in the thrust-antithrust direction. At least near the bottom dead center of the piston, the upper pin 15 is offset from the center 13A of the piston pin to the anti-piston gravity center side R to bring the upper part of the piston on the piston gravity center side L into contact with the wall surface of the cylinder 11. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a multi-link piston-crank mechanism in which a piston of an internal combustion engine and a crank pin of a crankshaft are linked by a plurality of links.

As described in Patent Document 1, as a piston-crank mechanism for an internal combustion engine, the present applicant has disclosed a multi-link type piston-crank mechanism (hereinafter simply referred to as a piston-crank mechanism) in which a piston and a crank pin of a crankshaft are linked by a plurality of links. Previously proposed "multi-link mechanism". In this multi-link mechanism, a lower link rotatably attached to a crank pin and a piston are connected by an upper link, and a control link that restricts the movement is connected to the lower link. According to such a multi-link mechanism, the piston stroke is compared with a single-link piston-crank mechanism (hereinafter also simply referred to as “single link mechanism”) in which the piston and the crank pin are linked by a single connecting rod. The degree of freedom in setting the characteristics is high. For example, the piston stroke characteristics can be made close to simple vibrations to greatly reduce vibrations. Further, in such a multi-link mechanism, the position of the swing fulcrum on the engine body side of the control link is changed, so that the geometrical structure of the internal combustion engine that accompanies changes in the top dead center position and the bottom dead center position of the piston can be obtained. The compression ratio (hereinafter simply referred to as “engine compression ratio”) can be changed, and can easily function as a variable compression ratio mechanism.
JP 2004-162895 A

  In such a multi-link mechanism, if the piston stroke is increased in order to increase the compression ratio or increase the displacement, the increase in the size in the height direction of the cylinder in which the piston reciprocates, which in turn increases the size of the internal combustion engine. Tend to invite. In order to reduce or avoid such an increase in the height dimension of the cylinder as the piston stroke increases, the piston skirt is below the lower edge located at the lower end of the cylinder (bore) at the piston bottom dead center. The present applicant is considering setting to be exposed to a lower level.

  However, in the case where the skirt portion of the piston is exposed below the lower edge of the cylinder with the corner shape (edge shape) bent from the inner wall surface of the cylinder, the piston is placed on the lower edge of the cylinder with the corner shape. If the skirt portion contacts, the skirt portion may be damaged. In particular, when the engine compression ratio can be changed by the multi-link mechanism, the piston bottom dead center position tends to be lowered as the piston top dead center position is lowered on the low compression ratio side. In order to avoid knocking during rotation, the engine is often operated at a low compression ratio.Therefore, the inertia force near the bottom dead center and the thrust load acting on the piston from the cylinder to the piston are increased. There is a high risk of damage to the skirt when in contact with the edge.

  In the above multi-link mechanism, the movement of the upper link draws a unique trajectory different from that of the single-link mechanism, so that the piston outer periphery and the cylinder strongly come into contact with each other at an unexpected timing. There is a problem of generating. In order to reduce or avoid the occurrence of such a hitting sound, the present applicant has previously proposed a technique for offsetting the center of the piston pin and the center of gravity of the piston in the thrust-anti-thrust direction (Japanese Patent Laid-Open No. 2002-61501). These conventional ones do not consider the contact between the cylinder lower edge and the piston skirt as described above.

  The present invention has been made in view of such a specific technical problem, and while reducing or avoiding an increase in the height dimension of the cylinder accompanying an increase in piston stroke, the piston skirt portion and the cylinder under the cylinder are provided. The main object is to provide a novel multi-link type piston-crank mechanism for an internal combustion engine that can prevent contact with the edge.

  The multi-link type piston-crank mechanism for an internal combustion engine according to the present invention includes an upper link having one end connected to a piston reciprocating in a cylinder of the internal combustion engine via a piston pin, and an upper pin at the other end of the upper link. A lower link that is connected to the crankpin of the crankshaft and is rotatably supported on the engine body side such as a cylinder block and the other end is provided with a control pin on the lower link. And a control link connected through a high degree of freedom of piston stroke characteristics as described above, which can greatly reduce vibration and reduce thrust load compared to a single link mechanism. It can be done. Further, by providing a variable compression ratio means that can change the engine compression ratio by changing the support position of the one end of the control link on the engine body side, this multi-link mechanism can easily function as a variable compression ratio mechanism. Can do.

  In the present invention, the link dimension and the piston stroke characteristic are set so that a part of the piston skirt portion is positioned below the lower edge portion of the cylinder at the piston bottom dead center. As a result, an increase in the dimension in the height direction of the cylinder accompanying the expansion of the piston stroke can be reduced, and consequently the increase in size of the internal combustion engine can be suppressed.

  Further, in the present invention, the center of gravity of the piston is offset in the thrust-anti-thrust direction with respect to the center of the piston pin, and at least at the bottom dead center of the piston, the upper pin is offset in the thrust-anti-thrust direction to the opposite side of the piston center of gravity. It is set to be. That is, in the vicinity of the bottom dead center of the piston, the upper link is inclined toward the piston center of gravity toward the piston pin connected to the piston, and the piston is pressed against the wall surface of the cylinder on the piston center of gravity side. Also, in the vicinity of the bottom dead center of the piston, a downward inertial force acts on the center of gravity of the piston, so a moment in the direction of rotation toward the piston center of gravity acts around the piston pin. Since the moment acts in the direction in which the cylinder approaches the cylinder, the upper part of the piston is maintained in strong contact with the cylinder, so that contact between the skirt at the lower part of the piston and the lower edge of the cylinder can be reliably prevented and avoided. it can.

  Further, in the vicinity of the top dead center including the piston top dead center, the upper pin is set to be offset to the opposite side of the piston center of gravity with respect to the piston pin center. In the vicinity of the top dead center of the piston, an upward inertial force acts on the piston center of gravity, and a large combustion pressure acts on the piston crown surface. At the center of gravity of the piston in contact with the cylinder at the moment, the lower part of the piston with the skirt part makes strong contact with the cylinder, which is relatively thin and soft compared to the upper part of the piston. The hitting sound caused by the collision with the cylinder is reduced / suppressed.

  ADVANTAGE OF THE INVENTION According to this invention, the contact with the skirt part of a piston and the lower edge part of a cylinder can be prevented effectively, reducing and avoiding the increase in the height direction dimension of a cylinder accompanying expansion of a piston stroke.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In this specification, the piston reciprocating direction is basically the “up and down” direction, the direction toward the piston top dead center is the “up” direction, and the direction toward the piston bottom dead center is the “down” direction.

  1 to 6 show a multi-link type piston-crank mechanism for an internal combustion engine according to an embodiment of the present invention. FIGS. 1 and 2 show the state when the piston is at bottom dead center, and FIGS. Indicates the state when the piston is at top dead center. 1 to 6 exaggerate the inclination of the piston, the clearance with the cylinder, and the like for easy understanding, and do not accurately depict the actual shape and dimensions.

  The multi-link piston-crank mechanism includes an upper link 14 having one end connected to a piston 12 reciprocating in a cylinder 11 provided in a cylinder block 10 via a piston pin 13, and the other end of the upper link 14. The lower link 17 is connected to the crankpin 16 of the crankshaft and is rotatably attached to the crankpin 16 of the crankshaft. One end of the lower link 17 is swingably supported on the side of the cylinder block 10 as the engine body, and the other end is supported. And a control link 19 connected to the lower link 17 via a control pin 18. The lower link 17 is divided into two members 17A and 17B so that the lower link 17 can be assembled to the crankpin 16.

  One end of the control link 19 is rotatably attached to an eccentric cam portion 20 of a control shaft that is rotatably supported on the cylinder block side. The shaft center of the outer peripheral cylindrical surface of the eccentric cam portion 20 is eccentric with respect to the rotation center of the control shaft, and the rotation position of the control shaft is changed by an appropriate actuator according to the engine operating state, thereby The position, that is, the position of the swing fulcrum of the control link 19 changes. Along with this, the movement restraint condition of the lower link 17 by the control link 19 changes, the piston top dead center position and the piston bottom dead center position change, and the geometric compression ratio (engine compression ratio) of the internal combustion engine. Changes. These control shafts and actuators constitute variable compression ratio means for allowing the above-mentioned multi-link mechanism to function as a variable compression ratio mechanism.

  In such a multi-link type piston-crank mechanism as a variable compression ratio mechanism, in addition to being able to change the engine compression ratio according to the engine operating state, the piston stroke characteristics can be freely set unlike the single link mechanism. By selecting the link dimension appropriately, it has characteristics close to simple vibration compared to the single link mechanism, and the inclination angle of the upper link 14 with respect to the reciprocating axis of the piston pin 13 is larger than the piston ascending stroke. It can be set to be smaller in the piston lowering stroke. As a result, the inertial force in the vicinity of the piston top dead center is greatly reduced, while the piston descending stroke in the vicinity of the piston top dead center where a large combustion load acts is applied in the thrust-anti-thrust direction acting on the piston from the cylinder. Thrust load can be reduced.

  The piston 12 is made of, for example, aluminum die casting, and a plurality of ring grooves 21 and land portions 22 into which piston rings (not shown) are fitted are alternately formed on the upper portion of the piston. Further, as shown in FIG. 5, two substantially cylindrical piston pin boss portions 23 formed with pin holes 23 </ b> A into which the piston pins 13 are fitted are arranged in parallel in the piston pin direction at the lower portion of the piston. An upper end portion of the upper link 14 is interposed between the pin boss portions 23. Further, at the lower part of the piston, two skirt portions 24 (24R, 24L) extending to the lowermost end of the piston on the outer peripheral portion in the thrust-anti-thrust direction (left-right direction in FIGS. 1 to 6) orthogonal to the center line 13A of the piston pin 13. ) Is formed.

  The center of gravity 12A of the piston 12 is offset in the thrust-anti-thrust direction with respect to the center (line) 13A of the piston pin 13 (that is, the center of the piston pin boss portion 23). The offset direction (left side of FIGS. 1 to 6) of the piston center of gravity 12A relative to the piston pin center 13A in the thrust-anti-thrust direction is referred to as “piston center of gravity L”, and the opposite direction (right side of FIGS. It is referred to as “anti-piston center of gravity R”. Further, if necessary, the configuration on the piston gravity center side L is denoted by “L” after the reference symbol, and the configuration on the anti-piston gravity center side R is denoted by “R” after the reference symbol to distinguish the two. To do.

  Of the two skirt portions 24R, 24L formed in the thrust-anti-thrust direction, the radial thickness 25L of the skirt portion 24L on the piston gravity center side L is the radial thickness of the skirt portion 24R on the anti-piston gravity center side R. It is set to be larger than 25R. That is, the skirt portion 24L on the piston gravity center side L is relatively thickened.

  Further, in most of the piston reciprocating stroke including the vicinity of the piston bottom dead center and the vicinity of the piston top dead center, the upper pin 15 provided at the lower end portion of the upper link 14 with respect to the piston pin center 13A is anti-pistoned in the thrust-anti-thrust direction. The piston stroke characteristic is set so as to be offset toward the center of gravity R. That is, the upper link 14 is set to incline upward toward the piston gravity center L. As a result, in most piston reciprocation strokes including the vicinity of the piston top dead center and the vicinity of the piston bottom dead center, the piston 12 is pressed against the wall surface of the cylinder 11 on the piston gravity center L, and the thrust-anti-thrust direction of the piston 12 It is possible to effectively reduce and avoid collision with the wall surface of the cylinder 11 due to movement of the cylinder 11.

  As shown in FIGS. 1 and 2, at least near the bottom dead center including the piston bottom dead center, a part of the piston skirt portion 24 is lower than the lower edge portion 26 having a corner shape located at the lower end of the cylinder 11. The piston stroke characteristics are set so as to be located at the position of the cylinder 11 and exposed below the cylinder 11. As a result, an increase in the dimension in the height direction of the cylinder accompanying the expansion of the piston stroke can be suppressed.

  Further, the height position of the lower edge portion 26 of the cylinder 11 is different in the thrust-anti-thrust direction. Specifically, the cylinder lower edge portion 26R on the anti-piston center-of-gravity side R is arranged above the cylinder lower edge portion 26L on the piston center-of-gravity side L that contacts the piston 12 at least near the piston bottom dead center. That is, on the anti-piston centroid side R, the cylinder 11R on the anti-piston centroid side is shortened as much as possible so that the lowermost link groove 21 descends to the vicinity of the cylinder lower edge portion 26R (see FIG. 1).・ We are trying to reduce weight.

  In the vicinity of the bottom dead center of the piston, an inertia force Fi downward to the piston acts on the piston center of gravity 12A. Therefore, the piston 12 rotates in the direction of rotation toward the anti-piston center of gravity L around the piston pin center 13A, that is, in the direction of FIG. A moment ML in the clockwise direction acts. As a result, as exaggeratedly depicted in FIG. 2, on the piston center of gravity L, the piston upper portion is inclined so as to approach the cylinder 11 </ b> L, and the piston upper portion is in strong contact with the cylinder 11 </ b> L, while the piston lower portion is It will leave | separate from the lower edge part 26L, and the contact with the cylinder lower edge part 26L and the piston 12 can be prevented and avoided reliably.

  In addition, since the skirt portion 24L on the piston gravity center side L in contact with the cylinder 11L is relatively thickened, the skirt portion 24R on the anti-piston gravity center side R is reduced in weight, and the piston gravity center L side It is possible to achieve both improvement in load resistance by increasing the thickness of the skirt portion 24L. Further, by making the thicknesses of the two skirt portions 24R, 24L in the thrust-anti-thrust direction different from each other in this manner, the piston pin center 13A is not offset in the thrust-anti-thrust direction with respect to the piston center. It is possible to easily offset the piston center of gravity 12A in the thrust-anti-thrust direction with respect to the center 13A.

  As shown in FIGS. 3 and 4, in the vicinity of the piston top dead center, an upward inertia force acts on the piston center of gravity 12A and a large combustion pressure Fc acts on the piston crown surface. In the rotational direction toward the anti-piston centroid side R, that is, the clockwise moment MR in FIGS. 3 and 4, the piston lower skirt portion 24L on the piston centroid side L comes into strong contact with the cylinder 11L. Here, since the lower part of the piston is thinner and softer than the upper part of the piston, it is possible to effectively reduce the hitting sound and vibration at the time of collision as compared with the case where the lower part of the piston makes contact.

  Referring to FIG. 6A, the skirt portion 24 of the piston protrudes to the outer peripheral side in a barrel shape, and the height position 27 at which the outer diameter becomes maximum is set above the piston pin center 13A. ing. Therefore, as exaggeratedly depicted in FIG. 6B, in the vicinity of the bottom dead center of the piston, even if the skirt portion 24L on the piston center of gravity L comes into contact with the cylinder 11L, the contact position is the maximum outside. Since the skirt portion 24L is curved inward as it goes downward from the maximum outer diameter position 27 and the clearance from the cylinder 11L increases, the clearance from the cylinder 11L increases. Contact with the edge portion 26L can be avoided more reliably. Further, since the thickness of the skirt portion 24L decreases from the maximum outer diameter position 27 downward, it is possible to further reduce / avoid sound and vibration caused by a collision near the piston top dead center.

  As described above, the present invention has been described based on the specific embodiments. However, the present invention is not limited to the above-described embodiments, and includes various modifications and changes without departing from the spirit of the present invention. . For example, unlike the above embodiment, the piston centroid is offset with respect to the piston pin center by setting the two skirt portions of the piston to have the same thickness and offsetting the piston pin center with respect to the piston center. Also good.

The cross-sectional corresponding view in the piston bottom dead center which shows the double link type piston-crank mechanism of the internal combustion engine which concerns on one Example of this invention. The cross-section corresponding view which shows the attitude | position of the piston in a piston bottom dead center. The cross-sectional corresponding view in the piston top dead center which shows the multiple link type piston-crank mechanism of the said Example. The cross-section corresponding view which shows the attitude | position of the piston in a piston top dead center. The lower surface corresponding view which shows the piston of the said Example. (A) is explanatory drawing which shows the outer periphery shape of the skirt part of the said piston, (B) is a cross-sectional corresponding view which shows the attitude | position of the piston in the bottom dead center vicinity.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Cylinder 12 ... Piston 13 ... Piston pin 14 ... Upper link 15 ... Upper pin 16 ... Crank pin 17 ... Lower link 18 ... Control pin 19 ... Control link 24 ... Skirt part 26 ... Cylinder lower edge part

Claims (6)

An upper link whose one end is connected to a piston that reciprocates in a cylinder of an internal combustion engine via a piston pin, and is connected to the other end of the upper link via an upper pin and is rotatably attached to the crank pin of the crankshaft. A multi-link type piston for an internal combustion engine, comprising: a lower link, and 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. -In the crank mechanism,
The center of gravity of the piston is offset in the thrust-anti-thrust direction with respect to the center of the piston pin,
And at least at the bottom dead center of the piston, a part of the skirt provided at the lower part of the piston is positioned below the lower edge of the cylinder, and the upper pin is in a thrust-anti-thrust direction with respect to the piston pin center. A multi-link type piston-crank mechanism for an internal combustion engine, which is set so as to be offset to the side opposite to the piston center of gravity.   2. The multi-link type piston for an internal combustion engine according to claim 1, wherein at least at the top dead center of the piston, the upper pin is set to be offset to the opposite side of the piston center of gravity with respect to the center of the piston pin. Crank mechanism.   2. The skirt portion on the piston center of gravity side protrudes in a barrel shape toward the outer peripheral side, and a height position at which the maximum outer diameter is set is set above the piston pin center. Or a double-link type piston-crank mechanism for an internal combustion engine according to 2;   The multi-link type piston for an internal combustion engine according to any one of claims 1 to 3, wherein a thickness of the skirt portion on the piston gravity center side is larger than a thickness of the skirt portion on the opposite side to the piston gravity center side. Crank mechanism.   2. The lower edge of the cylinder on the opposite side to the piston center of gravity side is disposed above the lower edge of the cylinder on the piston center of gravity side in the thrust-anti-thrust direction. A multi-link type piston-crank mechanism for an internal combustion engine according to any one of -4.   6. A multi-link type piston for an internal combustion engine according to claim 1, further comprising variable compression ratio means capable of changing the engine compression ratio by changing a support position of one end of the control link. -Crank mechanism.

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