JP4581675B2 - Internal combustion engine - Google Patents

Description

  The present invention relates to an internal combustion engine in which a piston is connected to a crankshaft via a plurality of links.

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, and the other end of the upper link is connected to the piston via a first connection pin and is rotatably attached to the crank pin of the crankshaft. The piston and the crank pin are linked by the link, and one end of the control link is connected to the lower link via the second connecting pin so as to restrain the movement of the lower link. The other end of the control link is supported, for example, at the bottom 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 the way, in addition to loads such as gas pressure and inertial force, the sliding speed of the piston pin is extremely important for the lubrication of the piston pin. In general, in a part where a fluid oil film is difficult to be formed, such as a piston pin, the severity of the lubrication condition is estimated by the PV value that is the product of the load P and the sliding (swinging) speed V. That is, the higher the load applied to the piston pin and the higher the sliding speed of the piston pin under the load, the more severe the lubrication surface. In other words, the higher the load applied to the piston pin and the higher the rocking speed of the upper link connected to the piston pin under the load with respect to the piston reciprocating axis, the more severe the lubrication surface.

  The present invention provides an internal combustion engine in which sufficient lubrication performance of a piston pin is ensured by optimizing the link geometry so as to reduce the swing speed of the piston pin in the first half of the expansion stroke with a large load P. Is the main purpose.

The present invention relates to an internal combustion engine in which a piston reciprocating in a cylinder is connected to a crankshaft via a plurality of links, and the piston-crank mechanism constituted by the plurality of links has a sliding speed of a piston pin. The swing speed of the link connected to the equivalent piston pin with respect to the piston reciprocating axis is configured to have a maximum value in the compression stroke before the compression top dead center. As a result, the swing speed of the link connected to the piston pin monotonously decreases from the maximum value before the compression top dead center until the end of the compression stroke, and the swing speed of the link in the first half of the expansion stroke. Is reduced in size.

  According to the present invention, since the magnitude of the link swing speed in the first half of the expansion stroke can be reduced, sufficient lubrication performance of the piston pin can be ensured.

  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 using a multi-link type piston-crank mechanism used in an internal combustion engine according to the present invention, for example, a four-cycle 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 crankpin 3 is eccentric from the journal part 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 a first connecting pin 6, and an upper end side rotatably connected to a piston 8 by a piston pin 7. The piston 8 receives the combustion pressure and reciprocates in the cylinder 19 of the cylinder block 18.

  The control link 10 that restrains the movement of the lower link 4 is pivotally connected to the other end of the lower link 4 by a second connecting pin 11 at the upper end side, and the lower end side of the engine main body via a control shaft 12 as a control shaft. The lower part of the cylinder block 18 which is a part 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 can be rotated on the eccentric cam portion 12a. It is mated.

  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.

  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, compared to the piston stroke characteristics of a general single link type piston-crank mechanism, it is possible to achieve characteristics closer to simple vibration. 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 described above will be described in detail with reference to FIGS.

  The piston 8 is integrally cast using an aluminum alloy, and a plurality of, for example, three piston ring grooves 22 are formed on the outer peripheral surface of the piston head 21 having a relatively thick disk shape. In addition, 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 along the cylindrical surface of the cylinder 19 from the outer peripheral surface. As shown in FIG. 6, the skirt portion 23 has a substantially rectangular shape when viewed from a 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 at the center of the piston 8, that is, at the center of the back surface of the piston head 21 having a disk shape, and the end of the piston pin 7 is rotatably fitted to the pin boss 24. A matching pin hole 25 is formed through. A pair of oil grooves 26 are formed along the axial direction on the inner periphery of the pin hole 25.

  On the other hand, the upper link 5 is made of steel, and a piston pin 7 is press-fitted into one end on the piston 8 side as shown in FIG. The axial length of the upper piston pin 7 in the upper link 5 and the axial length of the lower first connecting pin 6 are equal to each other. Further, since the load received by the piston pin 7 and the load received by the first connecting pin 6 are basically equal, the piston pin 7 and the first connecting pin 6 can have the same diameter.

  Further, as shown in FIG. 7, the dimension in the piston pin axial direction of the piston coupling structure comprising 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. .

  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 in the vertical direction. The piston 8 can be made closer to the center of the crankshaft 1 than the configuration of FIG.

  In addition, 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. If the skirt portion 23 is reduced in size as described above, it is difficult to ensure a large rigidity. However, in the multi-link type piston-crank mechanism on which the present invention is based, a side thrust that acts to tilt the piston 8 is used. Since the load is smaller than that in the case of a general single link type piston-crank mechanism, the skirt portion 23 only needs to have a minimum size. 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. . Therefore, as described above, the pin boss portion 24 that holds the piston pin 7 can be downsized.

  In the four-cycle internal combustion engine having such a multi-link piston-crank mechanism, in the present invention, the link geometry of the multi-link piston-crank mechanism is optimized in order to ensure sufficient lubrication performance of the piston pin 7. .

  As shown in FIGS. 1 and 8, the specifications of the multi-link type piston-crank mechanism are those in which the cylinder is not offset with respect to the crankshaft 1 (hereinafter referred to as type A double link), As shown in FIG. 9, there is a specification in which the cylinder is offset with respect to the crankshaft 1 (hereinafter referred to as a type B double link). Here, the multi-link piston-crank mechanism schematically shown in FIG. 9 is the same as the multi-link piston-crank mechanism shown in FIGS. 1 and 8 except that the cylinder is offset with respect to the crankshaft. It is the composition. 8 and 9, the locus L1 represents the movement of the piston pin 7 coinciding with the piston reciprocating axis, the locus L2 represents the movement of the first connecting pin 6, and the locus L3 represents the crank pin 3. It shows the movement of.

  FIG. 10 shows the swing angle characteristic (characteristic line A1) of the above-mentioned type A double link upper link 5, the swing angle characteristic (characteristic line B1) of the above-mentioned type B double link upper link 5, and This is a comparison of the link swing angle characteristics (characteristic line C1) in a general single link type piston-crank mechanism. Here, the link in the single link type piston-crank mechanism is a connecting rod.

  As shown in FIG. 10, the double link type piston-crank mechanism, that is, the type A double link and the type B double link, unlike the single link type piston-crank mechanism, has a minimum upper link swing angle in the middle of the expansion stroke. It is set to be a value. As described above, this is effective in reducing the side pressure of the piston 8 as described above.

Then, in the present invention, multi-link piston - are I figure optimized for characteristics of the swing speed (rocking angular velocity) against the piston reciprocation axis of the upper link 5 in the crank mechanism. Here, the rocking speed of the upper link 5 with respect to the piston reciprocating axis is substantially equivalent to the sliding speed of the piston pin.

  FIG. 11 shows a swing speed characteristic (characteristic line A2) of the upper link 5 of type A double link, a swing speed characteristic (characteristic line B2) of the upper link 5 of type B double link, and a conventional general single unit. This is a comparison of the swing speed characteristics (characteristic line C2) of the link (connecting rod) in the link type piston-crank mechanism.

  In the case of the type A double link and the type B double link, the absolute value of the swing speed is generally smaller than that of the single link type piston crank mechanism. In the case of the type A double link and the type B double link, the swing speed (the absolute value thereof) is smaller in the first half of the expansion stroke than in the single link type piston crank mechanism. The reason why the swing speed of Type A double link and Type B double link is relatively small in the first half of the expansion stroke is that the maximum value (maximum value) of the swing speed is the same as in the single link type piston-crank mechanism. This is because the shift is not on the compression top dead center but on the compression stroke side, that is, on the front side of the compression top dead center. By doing in this way, the rocking speed of the upper link 5 of the type A double link and the type B double link monotonously decreases from the maximum value before the compression top dead center until the compression stroke is completed. .

  As a result, in the type A double link and the type B double link, the moment when the swing speed of the upper link 5 becomes zero is relatively shifted to the first half of the expansion stroke. If the swing speed is close to zero, the lubrication conditions can be greatly relaxed, for example, the temperature of the sliding surface of the piston pin 7 hardly rises even if the load applied to the piston pin 7 is large.

  The result of concrete calculation of the PV value of the piston pin 7 in the type B double link is shown in FIGS. Note that FIG. 12 corresponds to a middle load operation, and FIG. 13 corresponds to a high load operation. 12 and 13, the characteristic line M is the PV value of the piston pin 7 in the type B double link, and the characteristic line N is the PV value of the piston pin in the single link type piston-crank mechanism.

  As is clear from FIGS. 12 and 13, the PV value of the type B double link is reduced over the entire area with respect to the PV value of the single link type piston-crank mechanism, and particularly, the peak expansion. It is greatly reduced in the process.

  A method for greatly reducing the swing speed of the upper link 5 in the first half of the expansion stroke will be described in detail while comparing the above-described type A multiple link and type B multiple link.

  FIG. 14 is an explanatory view schematically showing the behavior of the type A double link in the expansion stroke, and FIG. 14A corresponds to the piston top dead center position (compression top dead center position). (C) of FIG. 14 corresponds to a position that is lowered by 90 ° in terms of crank angle from the piston top dead center position (compression top dead center), and FIG. 14 (b) is an intermediate position between (a) and (c) of FIG. Corresponds to position.

  FIG. 15 is an explanatory view schematically showing the behavior in the expansion stroke of the type B double link. FIG. 15A corresponds to the piston top dead center position (compression top dead center position). (C) of FIG. 15 corresponds to a position 90 degrees lower than the piston top dead center position (compression top dead center) in terms of crank angle, and FIG. 15 (b) is an intermediate position between (a) and (c) of FIG. Corresponds to position.

  ΔX in FIGS. 14 and 15 is a horizontal coordinate change of the first connecting pin 6 when the piston 8 is lowered by 90 ° in terms of crank angle from the top dead center. Roughly corresponds. In order to reduce this ΔX, it is effective to incline the ellipse (trajectory L2) that is the trajectory of the first connecting pin 6, and the type A multi-link type piston-crank mechanism is configured as such.

  Further, the upper link 5 is formed so that both ends thereof are bifurcated, and each of the bifurcated ends is configured to support both ends of the piston pin 7 and both ends of the first connecting pin 6. This is most reasonable, and the passage allowance of the counterweight 15 can be designed in the same manner. Since the piston pin 7 and the first connecting pin 6 have basically the same load level due to the combustion gas pressure, which is the maximum load, there is no problem with the same specifications. Regarding the inertial load, the first connecting pin 6 increases by the inertial force of the upper link 5, but this is more convenient when the lower link 4 is made of steel and the piston 8 is made of aluminum.

  The technical ideas of the present invention that can be grasped from the above embodiments will be listed.

  (1) In an internal combustion engine in which a piston that reciprocates in a cylinder is connected to a crankshaft via a plurality of links, the piston-crank mechanism including the plurality of links includes a link connected to a piston pin. The swing speed with respect to the piston reciprocating axis is configured to take a maximum value in the compression stroke before the compression top dead center. As a result, the swing speed of the link connected to the piston pin monotonously decreases from the maximum value before the compression top dead center until the end of the compression stroke, and the swing speed of the link in the first half of the expansion stroke. Is reduced in size. Therefore, since the magnitude of the link swing speed in the first half of the expansion stroke can be reduced, sufficient lubrication performance of the piston pin can be ensured.

  (2) In an internal combustion engine in which a piston reciprocating in a cylinder is connected to a crankshaft via a plurality of links, the piston-crank mechanism constituted by the plurality of links is connected to a piston pin in the first half of the expansion stroke. The average value of the rocking speed with respect to the piston reciprocating axis of the link is configured to be smaller than the average value of the rocking speed with respect to the piston reciprocating axis of the link connected to the piston pin in the latter half of the compression stroke.

  (3) In an internal combustion engine in which a piston that reciprocates in a cylinder is connected to a crankshaft via a plurality of links, the piston-crank mechanism constituted by the plurality of links has a piston pin in the first half of the expansion stroke. There is a moment when the rocking speed of the link coupled to the piston reciprocating axis is zero.

  (4) In the internal combustion engine according to any one of (1) to (3), each piston includes a skirt portion at a portion on the thrust-anti-thrust side in the circumferential direction. The width along the axial direction of the piston pin is substantially equal to the total length of the piston pin.

  (5) In the internal combustion engine according to any one of (1) to (3), each piston includes a skirt portion at a portion on the thrust-anti-thrust side in the circumferential direction. The width along the axial direction of the piston pin is shorter than the total length of the piston pin.

  (6) In the internal combustion engine according to any one of (1) to (5), the outermost diameter portion of the counterweight of the crankshaft intersects with an extension line in the axial direction of the piston pin in the vicinity of bottom dead center. To do.

  (7) In the internal combustion engine according to any one of (1) to (6), the piston-crank mechanism includes an upper link whose one end is connected to the piston via a piston pin, and the other end of the upper link. The lower link is connected via the first connecting pin and is rotatably attached to the crankpin of the crankshaft. One end of the lower link is connected to the lower link via the second connecting pin, and the other end is connected to the internal combustion engine. A multi-link type piston-crank mechanism including a control link that is swingably supported with respect to a main body.

  (8) In the internal combustion engine described in (7) above, a multi-link type is used 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. The link configuration of the piston-crank mechanism is set.

  (9) In the internal combustion engine according to (7) or (8), the multi-link piston-crank mechanism further includes a support position changing unit that displaces a swing support position of the other end of the control link with respect to the internal combustion engine body. The engine compression ratio is variably controlled by displacement of the swing support position.

  (10) In the internal combustion engine according to any one of (7) to (9), the double link type piston-crank mechanism is configured such that an inclination of the upper link with respect to the cylinder reciprocating axis is small in an expansion stroke. Yes.

BRIEF DESCRIPTION OF THE DRAWINGS The structure explanatory drawing which shows the whole multilink type piston-crank mechanism of the internal combustion engine which concerns on this invention. Operation | movement explanatory drawing which shows the basic operation | movement of a multiple link type piston-crank mechanism. 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 which shows a type A double link typically. Explanatory drawing which shows a type B double link typically. Explanatory drawing which shows the rocking | fluctuation angle characteristic of the upper link of the multiple link type piston-crank mechanism of the internal combustion engine which concerns on this invention. Explanatory drawing which shows the rocking speed characteristic of the upper link of the multiple link type piston-crank mechanism of the internal combustion engine which concerns on this invention. Explanatory drawing which shows the PV value characteristic of the piston pin in a type B double link. Explanatory drawing which shows the PV value characteristic of the piston pin in a type B double link. Explanatory drawing which showed typically the behavior of the expansion stroke in a type A double link. Explanatory drawing which showed typically the behavior of the expansion stroke in a type B double link.

Explanation of symbols

4 ... Lower link 5 ... Upper link 7 ... Piston pin 8 ... Piston 10 ... Control link 15 ... Counterweight 23 ... Skirt part 24 ... Pin boss part

Claims (8)

In an internal combustion engine in which a piston that reciprocates in a cylinder is connected to a crankshaft via a plurality of links,
In the piston-crank mechanism constituted by the plurality of links, the swing speed of the link connected to the piston pin, which is equivalent to the sliding speed of the piston pin, with respect to the piston reciprocating axis is in the compression stroke before the compression top dead center. An internal combustion engine configured to take a maximum value. Each piston is provided with 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. The internal combustion engine according to claim 1 . Each piston is provided with a skirt portion at the thrust-anti-thrust side in the circumferential direction, and the width of the skirt portion along the piston pin axial direction is shorter than the total length of the piston pin. The internal combustion engine according to claim 1 . The internal combustion engine according to any one of claims 1 to 3 , wherein an outermost diameter portion of a counterweight of the crankshaft intersects an extension line in the axial direction of the piston pin in the vicinity of bottom dead center. The piston-crank mechanism has an upper link whose one end is connected to the piston via a piston pin, and the other end of the upper link is connected via a first connection pin, and is rotatable to the crank pin of the crankshaft. A multi-link type comprising: a lower link to be attached; and a control link having one end connected to the lower link via a second connecting pin and the other end swingably supported with respect to the internal combustion engine body The internal combustion engine according to any one of claims 1 to 4 , wherein the internal combustion engine is a piston-crank mechanism. Check that the link configuration of the multi-link piston-crank mechanism is set so that the piston stroke characteristics of the piston with respect to the rotation of the crankshaft are closer to simple vibrations than the characteristics of the single-link piston-crank mechanism. The internal combustion engine according to claim 5 , characterized in that: The multi-link type piston-crank mechanism further includes support position varying means for displacing the swing support position of the other end of the control link with respect to the internal combustion engine body, and the engine compression ratio is variable by the displacement of the swing support position. The internal combustion engine according to claim 5 or 6 , wherein the internal combustion engine is controlled. The internal combustion engine according to any one of claims 5 to 7 , wherein the multi-link type piston-crank mechanism is configured such that an inclination of the upper link with respect to a cylinder reciprocating axis is small in an expansion stroke.

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