JP4411779B2 - Crank mechanism of reciprocating internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a crank mechanism of a reciprocating internal combustion engine in which a crankshaft rotates with the reciprocation of a piston, and more particularly to an improvement of a crank mechanism suitable for an internal combustion engine having a variable compression ratio mechanism.
[0002]
[Prior art]
As a variable compression ratio mechanism of a reciprocating internal combustion engine, a mechanism using a multi-link type crank mechanism as shown in FIG. 1 has recently been proposed (see Japanese Patent Application Laid-Open No. 2000-73804 for a similar structure). The upper link 21 is connected to the piston 3 that slides in the cylinder 2 of the cylinder block 1 via a piston pin 25 and is connected to the other end of the upper link 21 via a connecting pin 26. And a lower link 22 connected to the crankpin 11 of the crankshaft 10, and a control link 23 that connects the lower link 22 and the internal combustion engine body to limit the degree of freedom of the lower link 22. The swing support position of the control link 23 is controlled by the eccentric cam 24. In this case, the swing support position of the lower end of the control link 23 changes depending on the rotational position of the eccentric cam 24, and accordingly, the top dead center position of the piston 3 and thus the compression ratio change.
[0003]
Here, the crankshaft 10 includes a counterweight 12 extending to the opposite side to the crankpin 11 as in the case of a general single link crank mechanism. The counterweight 12 is formed integrally with a crank arm 15 that connects the crankpin 11 and the crank journal 14. The counterweight 12 has a substantially sector shape, and an outer edge 13 of the counterweight 12 is an arc centered on the rotation center of the crank journal 14. Has been processed.
[0004]
[Problems to be solved by the invention]
FIG. 2 shows a state when the piston 3 reaches the bottom dead center in the crank mechanism configured as described above. At this time, the crank pin 11 is near the lowest point, and conversely, The counterweight 12 is located above, that is, at a position facing the lower end of the cylinder 2. Therefore, at this position, the gap between the outer edge 13 of the counterweight 12 and the piston 3 is minimized (c2), and interference between the two becomes a problem. FIG. 3 shows the movements of the lower end point of the piston 3 (usually the lower end of the central pin boss part) and the outer edge 13 where the interference is a problem. , The position of the outer edge 13 is a fixed position determined by the radius r of the arc, and as the piston 3 descends, the gap between the two becomes narrower and the minimum (c2) at the bottom dead center position. It becomes.
[0005]
When the variable compression ratio mechanism is used to reduce the compression ratio, the bottom dead center position is lowered as the top dead center position is lowered, so that the minimum gap c2 in this cycle is further reduced. Therefore, if the total height of the internal combustion engine is defined to be a predetermined value due to various restrictions, the compression ratio range that can be variably controlled is limited by the gap between the outer edge 13 of the counterweight 12 at the bottom dead center position of the piston 3. Will be.
[0007]
[Means for Solving the Problems]
The invention according to claim 1 is a reciprocating type comprising: a piston that reciprocates in a cylinder; and a crankshaft connected to the piston, wherein the crankshaft includes a counterweight extending from a crank arm. In the crank mechanism of an internal combustion engine,
The outer edge of the counterweight has a basic shape of an arc centered on the rotation center of the crank journal, and a circumferential position where the distance between the piston and the arc becomes the smallest when the piston reaches bottom dead center. In the vicinity, it is characterized in that it has a shape retreated to the inner peripheral side from the arc.
In particular, the internal combustion engine includes a variable compression ratio mechanism in which the bottom dead center position of the piston changes in accordance with variable control of the compression ratio, and one end of the variable compression ratio mechanism is connected to the piston pin of the piston. An upper link, a lower link connecting the upper link and the crank pin of the crankshaft, a control link having one end connected to the lower link and the other end swingably supported by the main body of the internal combustion engine; And a control mechanism for changing the swing support position of the control link.
[0008]
That is, in the present invention, the outer edge of the counterweight is approximated to a virtual arc centered on the rotation center of the crank journal as in the prior art, but interference with the piston is a problem with this virtual arc. In the region, it is partially retracted toward the inner periphery. Therefore, a relatively large gap can be secured between the piston and the outer edge of the counterweight when it reaches bottom dead center. In other words, the bottom dead center position of the piston can be brought closer to the rotation center of the crank journal. In addition, the moment of inertia can be easily ensured as compared with the case where the entire counterweight is reduced in diameter.
[0009]
Further, even if the bottom dead center position approaches the crank journal due to the variable control of the compression ratio, it is possible to avoid the interference with the counterweight and to secure a larger variable range of the compression ratio.
[0011]
Further, in the invention 請 Motomeko 2, the rotation center of the crank journal is located on the center axis of the cylinder, the radial distance from the rotational center of the crank journal to the outer edge each part of the counterweight, the piston The radial distance (rc) in the direction corresponding to the center axis of the cylinder in the attitude of the crankshaft when the bottom dead center is reached is larger than the radial distance of the portion on the advance side and the portion on the delay side from the center axis. short.
[0012]
In general, interference between the piston and the outer edge of the counterweight may occur at the pin boss located at the center of the piston. Therefore, by retreating the corresponding part to the inner peripheral side, the interference can be avoided reliably. Is done. And since the part of the both sides has a relatively large radial distance centering on the rotation center of a crank journal, a large moment of inertia is ensured.
[0013]
The invention of claim 3 further reduced from the invention of claim 2 is configured such that when the piston reaches bottom dead center, the crank pin is positioned on the lag side from the lowest point, and the piston is When the crankshaft is at the bottom dead center, the radial distance of the portion on the leading side from the central axis of the cylinder is shorter than the radial distance of the portion on the delayed side from the central axis. .
[0014]
Depending on the structure of the linkage mechanism between the piston and crankshaft, when the piston reaches the bottom dead center, the crank pin is not at the lowest point and the position where the lowest point has not been reached yet, that is, the position behind the lowest point. May be located in The invention of claim 3 presupposes such a configuration, and when the crankpin reaches the lowest point, the piston starts to rise past the bottom dead center. Therefore, the counterweight outer edge portion corresponding to this can be positioned relatively on the outer peripheral side.
[0015]
According to a fourth aspect of the present invention, when the piston reaches the bottom dead center, the crank pin is configured to be positioned on the more advanced side than the lowest point, and when the piston reaches the bottom dead center. In the posture of the crankshaft, the radial distance of the portion that is delayed from the central axis of the cylinder is shorter than the radial distance of the portion that is advanced from the central axis.
[0016]
Contrary to the third aspect , when the piston reaches the bottom dead center, the crank pin may be located on the more advanced side than the lowest point, that is, the lowest point. The invention of claim 4 is based on such a configuration, and when the crank pin reaches the lowest point, the piston has not yet reached the bottom dead center. Therefore, the counterweight outer edge portion corresponding to this can be positioned relatively on the outer peripheral side.
[0017]
Next, the invention of claim 5 is a further reduction of the invention of claim 3 provided with a variable compression ratio mechanism, wherein the rotation center of the crank journal is offset to one side with respect to the center axis of the cylinder. , And the skirt portion bottom end position at the outer peripheral end of the piston in the offset direction is positioned relatively higher than the skirt portion bottom end position at the opposite outer peripheral end.
[0018]
When the rotation center of the crank journal is offset to one side, the lowermost end of the piston skirt on the offset side tends to interfere with the counterweight outer edge. Therefore, this interference can be avoided by making the bottom end position of the skirt part asymmetrical and disposing relatively upward on the offset side.
[0019]
Moreover, in the invention which concerns on Claim 6 , the said outer edge has comprised the circular arc shape centering on points other than the rotation center of the said crank journal. For example, it can be a circular arc with a constant radius centered on the crankpin. With such an arc shape, machining such as turning is easy.
[0020]
Furthermore, in the invention which concerns on Claim 7 , the said outer edge has comprised the polygon. In this case, the plane corresponding to the plurality of sides of the polygon may be linearly processed, and the processing is easy. In addition, the plane portion can be used as a positioning reference surface for other processing.
[0021]
In the invention according to claim 8 , the outer edge is formed of a linear portion that faces the piston when the piston reaches bottom dead center, and arc portions on both sides thereof. The arc portion can be, for example, an arc centered on the rotation center of the crank journal, similarly to the conventional crankshaft. Therefore, it is only necessary to linearly process one portion of the arc, and the processing is easy. In addition, the plane portion can be used as a positioning reference surface for other processing.
[0022]
【The invention's effect】
According to the present invention, the minimum gap between the piston and the counterweight outer edge can be secured relatively large without downsizing the counterweight, and the moment of inertia necessary for the counterweight can be secured sufficiently large. On the other hand, it is possible to realize an increase in margin or a reduction in the overall height of the internal combustion engine.
[0023]
In particular, Oite the internal combustion engine with a variable compression ratio mechanism, the bottom dead center position along with the variable control of the compression ratio is even closer to the crank journal, can avoid interfering with the counterweight, the variable range of the compression ratio Can be secured larger.
[0024]
According to the invention of claim 3 or claim 4 , when the timing when the piston reaches the bottom dead center and the timing when the crank pin becomes the lowest point are deviated, this timing deviation is taken into account. A large gap can be secured between the piston and the outer edge of the counterweight.
[0025]
Further, according to the invention of claim 5 , when the rotation center of the crank journal is offset to one side with respect to the center axis of the cylinder, it is possible to reliably avoid interference between the lowermost end of the piston skirt and the outer edge of the counterweight. A large variable range of the compression ratio can be secured.
[0026]
According to the invention of claim 6, the outer edge of the counterweight is formed into an arc shape having a constant radius, thereby facilitating machining such as turning.
[0027]
According to the invention of claim 7 , by making the outer edge of the counterweight polygonal, it becomes straight plane processing, and processing is easy, and the plane portion can be used as a positioning reference surface for other processing. It becomes possible.
[0028]
Similarly, according to the invention of claim 8 , it is only necessary to linearly planarize one place of the arc, the machining is easy, and the planar portion can be used as a positioning reference surface for other machining. Become.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
[0030]
FIG. 4 shows an embodiment in which the present invention is applied to a reciprocating internal combustion engine having a variable compression ratio mechanism. This crank mechanism has a piston 3 that slides in the cylinder 2 of the cylinder block 1, a crankshaft 10 that is rotatably supported by the cylinder block 1, and one end connected to the piston 3 via a piston pin 25. The upper link 21 is connected to the other end of the upper link 21 via a connecting pin 26, the lower link 22 connected to the crank pin 11 of the crankshaft 10, and the lower link 22 via a connecting pin 27. A control link 23 having one end connected to the internal combustion engine body and the other end swingably supported by the internal combustion engine body, and the swing support position of the control link 23 is controlled by an eccentric cam 24. It has become. The eccentric cam 24 is supported on the lower side of the bearing cap 20 that supports the crank journal 14 of the crankshaft 10. In this embodiment, the center of rotation of the crank journal 14 is located on the center axis L of the cylinder 2 and, as shown in the figure, when the piston 3 reaches bottom dead center, Is located at the lowest point.
[0031]
The crankshaft 10 includes a counterweight 12 that is integral with the crank arm 15 and extends to the opposite side of the crankpin 11. The outer edge 13 of the counterweight 12 is composed of a continuous curve and has a basic shape that approximates an arc centered on the rotation center of the crank journal 14, but from the rotation center of the crank journal 14 to each part of the outer edge 13. The radial distance is not completely constant, and the radial distance rc at the central portion is shorter than the radial distance rs at both side portions. More specifically, as shown in the drawing, in the posture of the crankshaft 10 when the piston 3 reaches the bottom dead center, the radial distance at the position corresponding to the cylinder center axis L is the shortest (rc), and the leading side is more than this. The radial distance rs in the part which becomes and the part which becomes the delay side are both relatively large. In the state shown in the figure, the counterweight 12 has a symmetrical shape with the cylinder center axis L in between.
[0032]
FIG. 5 is an explanatory view similar to FIG. 3 in the configuration of such an embodiment, and the position of the outer edge 13 is a radial distance at the bottom dead center of the piston 3 where the lower end of the pin boss portion of the piston 3 is at the lowest position. Since it is located below as indicated by rc, the gap c between the two at the bottom dead center position is enlarged. Therefore, the margin is increased and the variable range of the compression ratio is increased. Further, since the radial distance rs of the counterweight 12 can be secured large except for the portion closest to the piston 3 as described above, a sufficiently large moment of inertia can be obtained. In particular, the stroke change in the vicinity of the bottom dead center of the piston in a general single link type crank mechanism has a long stagnation time in the vicinity of the bottom dead center due to the influence of the rotational secondary component, whereas the double link type in this embodiment. In the crank mechanism, the movement of the piston 3 can be made close to a single vibration, so that the radial distance rs on both sides can be set larger than in the case of the single link type.
[0033]
Next, FIG. 6 shows a more specific shape of the outer edge 13 as described above. In the second embodiment, as shown in the drawing, a circle having a constant radius R from the center of the crankpin 11 is shown. An outer edge 13 is formed so as to form an arc shape, whereby the radial distance from the rotation center of the crank journal 14 is short (rc) at the center and long (rs) at both sides. According to such a configuration, turning processing around the crankpin 11 is possible, and the processing becomes easy.
[0034]
FIG. 7 shows different shapes of the outer edge 13. In this third embodiment, the outer edge 13 basically forms a shape along an arc of radius rs centered on the crank journal 14, and its central portion. Is cut off as a plane portion 13a parallel to the tangential direction. According to such a configuration, it is only necessary to delete a part of the arc having a constant radius in the plane, so that the processing is easy, and the plane portion 13a can be used as a positioning reference surface in other processing. it can.
[0035]
FIG. 8 shows a fourth embodiment in which the outer edge 13 is formed into a polygon by three plane portions 13a, 13b, and 13c. As shown in the figure, the central portion of the flat surface portion 13a has the shortest radial distance rc, and the four vertices have the longest radial distance rs. According to this configuration, the outer edge 13 can be formed only by plane machining, and the machining is easy, and each plane portion 13a, 13b, 13c can be used as a positioning reference plane in other machining.
[0036]
Next, FIGS. 9 and 10 show a fifth embodiment applied to a crank mechanism having a link structure in which the crank pin 11 does not yet reach the lowest point when the piston 3 reaches the bottom dead center. ing. The rotation direction of the crankshaft 10 is the clockwise direction in the figure as indicated by the arrow ω. That is, FIG. 9 shows a state when the piston 3 is at the bottom dead center position. At this time, the crank pin 11 is slightly behind the lowest point. Therefore, when the piston 3 reaches the bottom dead center, the position where the pin boss portion at the center of the piston 3 is closest is not the center of the outer edge 13 of the counterweight 12 but a position offset from the center of the counterweight 12 toward the advance side. Become. As shown also in FIG. 10, at this position, the radial distance of the outer edge 13 is the shortest (rc). That is, the radial distance rc at the position corresponding to the cylinder center axis L is the shortest in the posture of the crankshaft 10 when the piston 3 reaches bottom dead center. Further, the radial distance is longer than that at both side portions, and in particular, the radial distance rs1 of the portion on the advance side from the cylinder center axis L is shorter than the radial distance rs2 of the portion on the delay side. .
[0037]
Therefore, as apparent from FIG. 10, the height position of the outer edge 13 changes in a form corresponding to the movement locus of the lower end of the piston 3 during the cycle, and the gap is more appropriately near the bottom dead center of the piston 3. c can be secured.
[0038]
Although not shown, conversely, when applied to a crank mechanism having a link structure in which the crank pin 11 passes the lowest point when the piston 3 reaches bottom dead center, In addition, the radial distance rs1 of the portion on the advance side from the cylinder center axis L is set to be relatively longer than the radial distance rs2 of the portion on the delay side.
[0039]
Next, FIG. 11 shows a sixth embodiment in which the rotation center of the crank journal 14 is offset from the cylinder center axis L to the right side of the drawing. In the sixth embodiment, the shape of the outer edge 13 of the counterweight 12 is the same as that of the second embodiment described above, and has an arc shape with a radius R centered on the crankpin 11. In the configuration in which the crankshaft 10 is offset in this manner, the lowermost skirt portion 5 on the right side of the piston 3 easily interferes with the counterweight 12. FIG. 12 shows a comparative example. As shown in the figure, when the piston 3 reaches bottom dead center, the gap between the two becomes very small as indicated by c6. Therefore, in the sixth embodiment of FIG. 11, the position of the lowermost skirt part 5 on the right side of the piston 3 is positioned relatively higher than the position of the lowermost skirt part 4 on the left side of the figure. Yes. That is, the length of the skirt portion is relatively shorter in the right part of the figure than in the left part of the figure. According to such a configuration, a gap between the two is ensured to be large as shown by c7, and interference at this position can be avoided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an example of a conventional crank mechanism.
FIG. 2 is a sectional view showing a state when a piston reaches a bottom dead center.
FIG. 3 is an explanatory view showing a developed movement locus of a piston lower end and a counterweight outer edge.
FIG. 4 is a sectional view showing a first embodiment of the present invention.
FIG. 5 is an explanatory view similar to FIG. 3 showing the movement trajectory of the piston lower end and the counterweight outer edge in this embodiment.
FIG. 6 is a cross-sectional view showing a second embodiment of the present invention.
FIG. 7 is a sectional view showing a third embodiment.
FIG. 8 is a sectional view showing a fourth embodiment.
FIG. 9 is a cross-sectional view showing a fifth embodiment.
FIG. 10 is an explanatory view similar to FIG. 3 in the fifth embodiment.
FIG. 11 is a sectional view showing a sixth embodiment.
FIG. 12 is a sectional view showing a comparative example related to the sixth embodiment.
[Explanation of symbols]
3 ... Piston 10 ... Crank shaft 11 ... Crank pin 12 ... Counter weight 13 ... Outer edge 14 ... Crank journal 21 ... Upper link 22 ... Lower link 23 ... Control link

Claims (8)

In a crank mechanism of a reciprocating internal combustion engine comprising: a piston that reciprocates in a cylinder; and a crankshaft connected to the piston, wherein the crankshaft includes a counterweight extending from a crank arm.
The outer edge of the counterweight has a basic shape of an arc centered on the rotation center of the crank journal, and a circumferential position where the distance between the piston and the arc becomes the smallest when the piston reaches bottom dead center. In the vicinity, it is shaped to recede to the inner circumference side than the above arc ,
The internal combustion engine includes a variable compression ratio mechanism in which the bottom dead center position of the piston changes in accordance with variable control of the compression ratio, and the variable compression ratio mechanism is an upper link having one end connected to the piston pin of the piston. A lower link for connecting the upper link and the crank pin of the crankshaft, a control link having one end connected to the lower link and the other end swingably supported by the main body of the internal combustion engine, and the control A crank mechanism for a reciprocating internal combustion engine, comprising: a control mechanism that changes a swing support position of the link . The crankshaft when the rotation center of the crank journal is located on the central axis of the cylinder and the piston reaches the bottom dead center with respect to the radial distance from the rotation center of the crank journal to each outer edge portion of the counterweight. the radial distance direction corresponding to the central axis of the cylinder at position (rc) is, in claim 1, characterized in that less than radial distance portion to be a part and the delayed side to be also advanced side than the central axis The crank mechanism of the reciprocating internal combustion engine described. When the piston reaches the bottom dead center, the crank pin is positioned behind the lowest point, and the center axis of the cylinder in the attitude of the crankshaft when the piston reaches the bottom dead center 3. The crank mechanism of a reciprocating internal combustion engine according to claim 2, wherein a radial distance of a portion that is closer to the leading side is shorter than a radial distance of the portion that is behind the central axis. When the piston reaches the bottom dead center, the crank pin is positioned on the more advanced side than the lowest point, and the center axis of the cylinder in the attitude of the crankshaft when the piston reaches the bottom dead center 3. The crank mechanism of a reciprocating internal combustion engine according to claim 2 , wherein a radial distance of a portion that is further on the delay side is shorter than a radial distance of a portion that is on the more advanced side than the central axis. The rotation center of the crank journal is offset to one side with respect to the center axis of the cylinder, and the lowermost position of the skirt portion at the outer peripheral end in the offset direction of the piston is lower than the lowermost position of the skirt portion at the outer peripheral end on the opposite side. 2. The crank mechanism for a reciprocating internal combustion engine according to claim 1 , wherein the crank mechanism is positioned relatively upward. The outer edges, the crank mechanism of the reciprocating internal combustion engine according to any one of claims 1 to 5, characterized in that an arc shape around the point other than the center of rotation of the crank journal. The outer edges, the reciprocating internal combustion engine according to any one of claims 1 to 5, characterized in that forms a polygonal crank mechanism. The outer edges, and a straight portion opposed to the piston when the piston reaches the bottom dead center, according to any one of claims 1 to 5, characterized in that it is formed from an arcuate portion of the both sides, Crank mechanism for reciprocating internal combustion engine.

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