JP2009036143A - Internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce or avoid the occurrence of piston slap by a double-link piston-crank mechanism, and to reduce the weight of an internal combustion engine by adopting a magnesium alloy piston 8. <P>SOLUTION: An upper link 5 having one end connected to the piston 8 through a piston pin 7 is connected to a lower link 4 rotatably attached to a crank pin 3 through an upper-lower link connection pin 6. The moving range 6A of the upper-lower link connection pin 6 by the reciprocating movement of the piston 8 is limited to one side of a reference axis 7A extending in the axial direction of a cylinder substantially through the center of the piston pin 7. The piston 8 is made of an alloy formed mainly of magnesium smaller in specific gravity than aluminum. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an internal combustion engine in which a piston reciprocates by a piston-crank mechanism, and more particularly to a technique for reducing the weight of the piston.

Patent Document 1 has been previously proposed by the present applicant, and discloses a variable compression ratio mechanism of an internal combustion engine using a multi-link type piston-crank mechanism. The upper link has one end connected to the piston via a piston pin, the other end of the upper link is connected via an upper-lower connection pin, and is rotatably attached to the crank pin of the crankshaft. With the lower link, the piston and the crank pin are linked, and one end of the control link is connected to the lower link via the lower-control connecting pin so as to restrain the movement of the lower link. The other end of the control link is supported by, for example, the lower part of the cylinder block. Then, by displacing the swing center of the other end of the control link by the cam mechanism, the piston top dead center position and thus the compression ratio of the engine can be changed.
JP 2001-227367 A

  By applying such a multi-link type piston-crank mechanism to an internal combustion engine, the piston stroke characteristics are set to desirable characteristics (for example, single vibration) as compared with the case of using a single-link type piston-crank mechanism. While the sound vibration performance and the like can be remarkably improved, and a great advantage that the function of changing the engine compression ratio can be easily realized as described above, an increase in weight accompanying an increase in the number of parts is a particularly big problem. Become.

  Therefore, in order to reduce the weight of the piston, the applicant of the present invention uses magnesium (hereinafter, “Mg”) made of an Al alloy mainly composed of aluminum (hereinafter also referred to as “Al”), which is often used as a material for the piston. However, in this case, there are the following problems.

  FIG. 13 shows the characteristics of aluminum (Al) and magnesium (Mg) materials. As shown in the figure, magnesium has a smaller specific gravity than aluminum and can reduce the piston weight by about 30%, but has a large coefficient of thermal expansion, ensuring a large gap between the piston skirt and cylinder. There is a need to. Here, in a general single link type piston-crank mechanism, the load acting on the piston from the connecting rod as the piston reciprocates is such that the connecting rod passes through the center of the piston pin and is parallel to the cylinder axis. Therefore, the load is an alternating load that changes its direction repeatedly in the thrust-anti-thrust direction. For this reason, when a large clearance between the piston and the cylinder is ensured as described above, the piston skirt is caused by the above alternating load in a state in which a large clearance is left between the piston and the cylinder as in the cold machine before thermal expansion. A so-called piston slap phenomenon that strongly collides with the wall surface of the cylinder repeatedly occurs frequently, causing undesirable vibrations and noises, and requiring high durability.

  Referring to FIG. 14, the piston is designed so as not to be in a lubrication NG region where lubrication performance cannot be ensured at high temperatures, and not in a slap sound NG region where piston slap phenomenon becomes a problem when cold. It should be noted that the condition that the above-mentioned gap becomes negative when the design dimension is used at a high temperature is allowed, but in reality, a gap corresponding to the oil film thickness of the sliding surface is secured by elastic deformation of the piston skirt portion. As shown in the figure, an Al alloy piston can be designed so as not to be in the NG region both in cold and high temperatures. However, with an Mg alloy piston mainly composed of Mg having a thermal expansion coefficient significantly higher than Al (about 15%), it has been difficult to avoid the NG region on both the lubrication side and the slap side. Further, since Mg has a low thermal conductivity, there is a problem that the heat in the piston is difficult to escape, and the piston temperature during operation becomes higher than that of Al, so that the above problem tends to be further deteriorated.

  The present invention has been made in view of such problems. That is, in the internal combustion engine of the present invention, the piston-crank mechanism that connects the piston that reciprocates in the cylinder and the crankshaft includes an upper link that has one end connected to the piston via the piston pin, and other than this upper link. And a lower link having an end connected via an upper-lower connecting pin. For this reason, the piston stroke characteristics are more flexible than the single link type piston-crank mechanism. For example, by making the characteristics close to simple vibration, the piston acceleration is leveled and the vicinity of the top dead center. The maximum inertia force is reduced, which is advantageous in reducing the size of the piston pin and the pin boss. Moreover, it is advantageous in terms of noise vibration characteristics, and for example, it is possible to avoid the deterioration of the inertial secondary vibration of the piston accompanying the expansion of the piston stroke of the in-line four-cylinder engine.

  In the present invention, the piston is made of an alloy mainly composed of magnesium. This makes it possible to significantly reduce the weight of the piston (for example, 30% lighter) compared to an aluminum alloy piston. An effect is obtained.

  In order to enable such magnesiumation of the piston, in the present invention, the range of movement of the upper-lower connecting pin that accompanies the reciprocating movement of the piston is substantially the reference that extends in the cylinder axial direction through the center of the piston pin. Restricted to one side with respect to the axis.

  Thus, by setting the upper link so that it always swings to one side with respect to the reference axis, the piston behavior always slides to one side of the cylinder. This can significantly reduce or eliminate the swinging motion of the piston in the thrust-anti-thrust direction within a gap with the cylinder called piston slap. As a result, as described above, a piston made of Mg alloy mainly composed of Mg having a high coefficient of thermal expansion can be adopted, and the weight of the piston can be reduced.

  As described above, according to the invention, in the internal combustion engine employing the multi-link type piston-crank mechanism that can easily realize the optimization of the piston stroke characteristics and the variable control of the engine compression ratio, it is caused by the gap between the piston and the cylinder. It is possible to greatly reduce or eliminate the occurrence of the piston slap phenomenon, whereby the piston can be formed of an Mg alloy mainly composed of magnesium having a small specific gravity. For this reason, an increase in the weight of the internal combustion engine, which is a particularly important issue in adopting the multi-link type piston-crank mechanism, can be greatly reduced and suppressed.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is an explanatory diagram showing the configuration of a variable compression ratio mechanism used in an internal combustion engine according to the present invention, for example, a direct injection gasoline engine. This mechanism is composed of a multi-link type piston-crank mechanism mainly composed of a lower link 4, an upper link 5 and a control link 10.

  The crankshaft 1 includes a plurality of journal portions 2 and a crankpin 3, and the journal portion 2 is rotatably supported by a main bearing of the cylinder block 18. The crank pin 3 is eccentric from the journal portion 2 by a predetermined amount, and a lower link 4 is rotatably connected thereto. The counterweight 15 extends from the crank web 16 connecting the journal portion 2 and the crankpin 3 to the opposite side of the crankpin 3. The counter weight 15 is provided on both sides of the crank pin 3 so as to face each other, and an outer peripheral portion thereof is formed in an arc shape centering on the journal portion 2.

  The lower link 4 is configured to be split into two left and right members, and the crank pin 3 is fitted in a substantially central connecting hole. The upper link 5 has a lower end side rotatably connected to one end of the lower link 4 by an upper-lower connection pin 6, and an upper end side rotatably connected to a piston 8 by a piston pin 7. The piston 8 receives combustion pressure and reciprocates in the cylinder 19 of the cylinder block 18. The control link 10 that restricts the movement of the lower link 4 is pivotally connected to the other end of the lower link 4 at the upper end side by a lower-control connecting pin 11, and the lower end side is connected to a part of the engine body via the control shaft 12. The lower part of the cylinder block 18 is rotatably connected. Specifically, the control shaft 12 is rotatably supported by the engine body and has an eccentric cam portion 12a that is eccentric from the center of rotation, and the lower end portion of the control link 10 is rotatable on the eccentric cam portion 12a. Is fitted. The rotation position of the control shaft 12 is controlled by a compression ratio control actuator (not shown) that operates based on a control signal from an engine control unit (not shown).

  In the variable compression ratio mechanism using the multi-link type piston-crank mechanism as described above, when the control shaft 12 is rotated by the compression ratio control actuator, the center position of the eccentric cam portion 12a, particularly with respect to the engine main body. The relative position changes. Thereby, the rocking | fluctuation support position of the lower end of the control link 10 changes. When the swing support position of the control link 10 changes, the stroke of the piston 8 changes, and the position of the piston 8 at the piston top dead center (TDC) becomes higher or lower. This makes it possible to change the engine compression ratio.

  FIG. 2 is a basic operation explanatory view of the above-described multi-link type piston-crank mechanism, and shows the operation of each part during one rotation (360 ° CA) of the crankshaft 1 every 90 ° CA. Yes. (B) in the figure corresponds to the piston top dead center position, and as is clear from this figure (b), if the position of the lower end of the control link 10 changes, the piston 8 is displaced vertically, and the compression ratio is increased. Will change.

  Here, in this embodiment, the piston 8 is made of a magnesium alloy mainly composed of magnesium. As described above, such a magnesium alloy piston enables a significant reduction in weight of the piston 8 as compared with an aluminum alloy piston. It is necessary to ensure a large gap with respect to 19, and how to suppress the occurrence of the piston slap phenomenon due to this gap becomes a problem.

  Embodiments 1 and 2 of a multi-link type piston-crank mechanism that can solve this problem are shown in FIGS. FIG. 4 also shows the piston stroke characteristics of the single link type piston-crank mechanism according to the comparative example. In both the first and second embodiments, the swing angle characteristic of the upper link 5 swings substantially only on one side (the right side in FIG. 3) with respect to the reference axis 7A extending in the cylinder axis direction through the center of the piston pin 7. Is set to That is, the movement range (movement locus) 6A of the upper-lower connecting pin 6 accompanying the reciprocating movement of the piston 8 is substantially limited to one side with respect to the reference axis 7A. In particular, in these embodiments, in the combustion stroke, the inclination of the upper link 5 with respect to the reference axis 7A is set to be small in the combustion stroke. Therefore, the piston 8 can always be slid to one side with respect to the cylinder 19 in the thrust-anti-thrust direction. Thus, unlike the single-link type piston-crank mechanism, the direction of the repeated load does not change in the thrust-anti-thrust direction with the reciprocating movement of the piston, and the cylinder 19 called piston slap caused by such an alternating load. Can be significantly reduced or eliminated. For this reason, even when the piston 8 is made of an alloy mainly composed of Mg having a large coefficient of thermal expansion, the occurrence of the slap phenomenon due to an increase in the gap during cooling can be greatly reduced or eliminated.

  In the first embodiment, the rotation center 2A of the crankshaft is disposed on the reference axis 7A. In the second embodiment, the reference axis 7A is disposed in the thrust-anti-thrust direction with respect to the rotation center 2A of the crankshaft. One side, more specifically, the side where the moving range 6A of the upper link 5 exists (the right side in FIG. 3) is offset by a predetermined amount Δα. As described above, in the second embodiment, the inclination direction of the upper link 5 can be completely restricted to one side by offsetting the reference axis 7A, and the piston 8 is reliably pressed against one cylinder wall. Reciprocates. On the other hand, in the case of the first embodiment, as compared with the second embodiment, the angle at which the piston 8 is pressed against the cylinder 19 is relaxed, so that it is slightly inclined in the opposite side in the middle of the expansion stroke. (See symbol 6B), the absolute value of the angle is slight and the period is extremely short, so the energy that can move the piston to the opposite side is negligibly small (the in-cylinder pressure is reduced in the intermediate stroke, and the inertial force is also low) The condition is almost zero). Therefore, in the first embodiment as well, since the state of pressing the piston to one side is overwhelmingly large, the occurrence of piston slap can be sufficiently reduced.

  Further, in the above-described multi-link variable compression ratio mechanism, a piston stroke characteristic close to simple vibration can be obtained by appropriately selecting a link dimension. In particular, as shown in FIG. 12, it is possible to obtain characteristics closer to simple vibrations than the piston stroke characteristics of a general single link type piston-crank mechanism. Then, the piston acceleration is leveled, and the maximum inertial force near the piston top dead center is greatly reduced. According to the piston stroke characteristics close to the simple vibration described above, the speed of the piston 8 near the top dead center is slowed by nearly 20% as compared with that of the single link type piston-crank mechanism.

  Next, the structure of the piston 8 and the upper link 5 will be described. 5 to 8 show the structure of the piston 8 used in the internal combustion engine of the present invention. As described above, the piston 8 is integrally cast with an Mg alloy mainly composed of magnesium, and a plurality of, for example, three piston ring grooves are formed on the outer peripheral surface of the piston head 21 having a relatively thick disk shape. 22 is formed, and a skirt portion 23 is formed in a part of the circumferential direction which is the thrust-anti-thrust direction of the piston 8 so as to extend from the outer peripheral surface along the cylindrical surface. As shown in FIG. 8, the skirt portion 23 has a substantially rectangular shape when viewed from the direction orthogonal to the piston pin 7, and the width along the piston pin axial direction is substantially equal to the total length of the piston pin 7. It is equal or shorter than the total length of the piston pin 7. That is, the skirt portion 23 is provided in a very small range in the circumferential direction.

  A pair of pin bosses 24 are formed in the center of the piston 8, that is, in the center of the back surface of the piston head 21 having a disk shape, and the end of the piston pin 7 is rotatable on the pin boss 24. A pin hole 25 to be fitted is formed through. A pair of oil grooves 26 along the axial direction are formed on the inner periphery of the pin hole 25.

  On the other hand, the upper link 5 is made of steel, and as shown in FIG. 9, a piston pin 7 is press-fitted into one end on the piston 8 side. Further, as shown in FIG. 10, the other end of the upper link 5 connected to the lower link 4 branches into a bifurcated shape, and supports both ends of the upper-lower connecting pin 6.

  Here, the axial length of the upper piston pin 7 in the upper link 5 and the axial length of the lower upper-lower connecting pin 6 are equal to each other. Further, since the load received by the piston pin 7 and the load received by the upper-lower connecting pin 6 are basically equal, the piston pin 7 and the upper-lower connecting pin 6 can have the same diameter.

  Further, as shown in FIGS. 9 and 11, the dimension in the piston pin axial direction of the piston coupling structure including the pair of pin boss portions 24 and the piston pin 7 is considerably smaller than the diameter of the piston 8 or the cylinder 19. It has become.

  When the piston 8 is in the vicinity of bottom dead center, the outermost diameter portion of the counterweight 15 of the crankshaft 1 intersects with an extension line extending the piston pin 7 in the axial direction as shown in the figure. ing. In other words, when the piston 8 is in the vicinity of the bottom dead center, the outermost diameter portion of the counterweight 15 passes through the side of the pin boss portion 24 holding the piston pin 7. 2D is merely for explaining the operation, the piston pin 7 and the counterweight 15 are drawn apart from each other up and down, but by configuring as described above, The piston 8 can be made closer to the center of the crankshaft 1 than the configuration of FIG.

  FIG. 10 shows the piston stroke from the top dead center to the bottom dead center when the conventional general single link type piston-crank mechanism 101 and the piston 102 are combined for comparison. As is apparent from a comparison between FIG. 11 and FIG. 11, in the configuration of the present embodiment, the piston stroke from the top dead center to the bottom dead center is greatly increased, and the displacement can be increased. For example, the piston stroke can be expanded by about 20%.

  Further, as apparent from FIG. 11, since the skirt portion 23 is also downsized, the counterweight 15 does not interfere with the skirt portion 23 when passing the side of the pin boss portion 24 as described above. Absent. When the skirt portion 23 is downsized in this way, it is difficult to ensure a large rigidity, but as described above, in the present embodiment, the upper link 5 is substantially only on one side with respect to the reference axis 7A. Therefore, the side thrust load that acts to tilt the piston 8 is extremely smaller than that of a general single link type piston-crank mechanism, so the skirt portion 23 has the smallest size. That's all. Specifically, the maximum combustion pressure acts on the piston 8 in the first half of the expansion stroke, and the piston head 21 receives the maximum load in the vicinity of (c) in FIG. As shown in the drawing, the upper link 5 is in a substantially vertical posture, and the inclination of the cylinder 19 with respect to the axis is very small. In particular, the inclination of the cylinder 19 with respect to the axis 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, and the skirt portion 23 can be downsized.

  Furthermore, as an advantage of the above-mentioned double link type piston-crank mechanism, the piston acceleration is leveled by making the piston-stroke characteristic close to simple vibration, and the maximum inertial force near the top dead center of the piston is greatly reduced. . Accordingly, the pin boss portion 24 that holds the piston pin 7 can be downsized together with the effect of preventing the piston slap.

  In the configuration using the single link type piston-crank mechanism 101 shown in FIG. 10, if the crank radius of the crankpin is increased and the piston stroke is made longer, the side thrust load acting on the piston 102 is assumed. As the size of the skirt increases, it is difficult to reduce the size of the skirt, and it is difficult to establish a practical engine.

  The present invention is suitable for an in-line four-cylinder engine. In general, in the case of an in-line four-cylinder engine, the inertial secondary vibration of the piston 8 increases rapidly with the expansion of the piston stroke. Therefore, if the displacement is increased by increasing the stroke, the noise vibration characteristics deteriorate and the quality is significantly impaired. However, the multi-link type piston-crank mechanism used in the present invention has a piston stroke characteristic close to a single vibration, so that such a deterioration of the noise vibration characteristic can be avoided.

  Moreover, if the piston stroke characteristics are close to simple vibration, the speed of the piston 8 near the top dead center is slower than that of the single link type piston-crank mechanism. Thus, good combustion can be ensured even in a combustion chamber having a large displacement per cylinder.

  The piston 8 illustrated in FIGS. 5 to 8 has two compression rings as a piston ring, whereas the piston 8 illustrated in FIG. 9 has a single compression ring. . Since the weight of the lower half of the piston 8 in which the pin boss portion 24 and the piston pin 7 of the present invention are miniaturized becomes very light, the configuration with a single compression ring stabilizes the behavior of the piston 8 around the piston pin 7. Is advantageous. Further, it is advantageous in terms of expanding the piston stroke, which is the original object of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The structure explanatory drawing which shows the whole variable compression ratio mechanism of the internal combustion engine which concerns on this invention. Operation | movement explanatory drawing which shows the basic operation | movement. Explanatory drawing which shows the operation | movement characteristic of the multilink type piston-crank mechanism which concerns on Example 1 (A) and Example 2 (B) of this invention. The characteristic view which shows the piston stroke characteristic which concerns on the said Examples 1, 2 and a comparative example. Sectional drawing of the piston along the surface orthogonal to a crankshaft. Sectional drawing of the piston along a crankshaft axial direction. The perspective view which notches and shows a part of piston. The side view of a piston. Explanatory drawing which shows the positional relationship of the piston and counterweight in a bottom dead center. Explanatory drawing of the piston stroke in the conventional piston-crank mechanism. Explanatory drawing of the piston stroke in this embodiment. The characteristic view which shows the piston-stroke characteristic of this embodiment. Explanatory drawing which shows the comparison of the material characteristic of aluminum and magnesium. Explanatory drawing which shows the relationship between piston temperature-piston skirt part and the clearance gap between a cylinder.

Explanation of symbols

4 ... Lower link 5 ... Upper link 6 ... Upper-lower connecting pin 7 ... Piston pin 7A ... Reference axis 8 ... Piston 10 ... Control link 15 ... Counter weight 23 ... Skirt part 24 ... Pin boss part

Claims (7)

In an internal combustion engine having a piston-crank mechanism that connects a piston that reciprocates in a cylinder and a crankshaft,
The piston-crank mechanism has a multi-link type having an upper link whose one end is connected to the piston via a piston pin, and a lower link whose other end is connected via an upper-lower connecting pin. And
The piston is made of an alloy mainly composed of magnesium,
In addition, the moving range of the upper-lower connecting pin accompanying the reciprocating movement of the piston is limited to one side with respect to a reference axis extending substantially in the cylinder axial direction through the center of the piston pin. Internal combustion engine. The lower link is rotatably attached to the crankpin of the crankshaft,
The piston-crank mechanism includes a control link having one end connected to the lower link via a lower-control connecting pin and the other end supported to be swingable with respect to the internal combustion engine body. The internal combustion engine according to claim 1, wherein   3. A support position varying means for displacing a swing support position of the other end of the control link with respect to the internal combustion engine body, wherein the engine compression ratio is variably controlled by the displacement of the swing support position. The internal combustion engine described in 1.   The internal combustion engine according to any one of claims 1 to 3, wherein an inclination of the upper link with respect to a reference axis in the combustion stroke is set to be small in the combustion stroke.   The link configuration of the piston-crank mechanism is set so that the piston stroke characteristic of the piston with respect to the rotation of the crankshaft is closer to the single vibration than the characteristic of the single link piston-crank mechanism. An internal combustion engine according to any one of claims 1 to 4.   Each of the pistons includes a skirt portion at a portion on the thrust-anti-thrust side in the circumferential direction, and the width along the piston pin axial direction of the skirt portion is substantially equal to the total length of the piston pin, Or the internal combustion engine in any one of Claims 1-5 characterized by being shorter than the full length of a piston pin.   7. An outermost diameter portion of a counterweight of a crankshaft is configured to pass through a side of a pin boss portion of a piston that rotatably holds the piston pin in the vicinity of bottom dead center. An internal combustion engine according to any one of the above.

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