Multilink-type internal combustion engine

A multilink-type internal combustion engine includes a power transmission structure capable of transmitting rotation of a crankshaft to a pivot shaft. The power transmission structure comprises: a planet gear mechanism having a sun gear mounted on the crankshaft; a drive gear provided on a ring gear section of the planet gear mechanism; a driven gear mounted on the pivot shaft and meshing with the drive gear; and an adjustment mechanism for switching a rotation direction of a carrier of the planet gear mechanism to thereby adjust a meshing phase of the driven gear relative to the drive gear.

FIELD OF THE INVENTION

The present invention relates to multilink-type internal combustion engines where a connection link is mounted on a crankshaft, connected to a piston via a con rod and connected to a pivot shaft via a swing rod.

BACKGROUND OF THE INVENTION

Among the conventionally-known internal combustion engines are a premixed compression auto-ignition or self-ignition type in which a compression ratio in a combustion chamber is increased so that an air-fuel mixture supplied to the combustion chamber is automatically or spontaneously ignited by being compressed by a piston.

An example of such premixed-compression-self-ignition-type internal combustion engines is disclosed in Japanese Patent Application Laid-Open Publication No. 2005-69097 (Patent Literature 1), in which the air-fuel mixture can be ignited at a plurality of positions in the internal combustion engine and burned or combusted uniformly by being highly compressed to be automatically or spontaneously ignited. With such an increased compression ratio in the combustion chamber, the air-fuel mixture can be highly compressed and spontaneously ignited without use of an ignition plug (i.e., spark plug). However, with the internal combustion engine disclosed in Patent Literature 1, where the air-fuel mixture is automatically ignited without use of an ignition plug, it is difficult to stabilize the ignition timing.

As a means for stabilizing the self-ignition timing of the air-fuel mixture, it has been known to secure a negative overlap state where both an exhaust and an (air) intake valve are closed in an exhaust stroke to cause a part of combustion gas to remain in the combustion chamber so that heat energy of the remaining or residual gas can be used for combustion of the air-fuel gas. Namely, an internal EGR (Exhaust-Gas-Recirculation) mechanism is employed for mixing the residual combustion gas into the air-fuel mixture, so that the self-ignition timing of the air-fuel gas can be stabilized using the heat energy of the residual combustion gas in a compression stroke (see, for example, Japanese Patent Application Laid-Open Publication No. 2005-201127 (Patent Literature 2)).

However, in the exhaust stroke of such an internal combustion engine, the piston ascends to its top dead center or point with a part of the combustion gas remaining in the combustion chamber. Thus, because the remaining combustion gas is compressed by the piston until the piston reaches to its top dead center, a temperature of the remaining combustion gas would increase to get higher than a temperature of a cylinder wall. Therefore, heat loss from the cylinder wall would increase so that the remaining combustion gas may undesirably lower in temperature.

Further, as the reaches the top dead center in the exhaust stroke, a stress (load) would be generated from the remaining combustion gas to act on the piston by the remaining combustion gas being compressed by the piston. Therefore, the thus-generated stress is transmitted via the piston to the interior (particularly, sliding portions) of the internal combustion engine, so that friction may be produced in the interior of the internal combustion engine.

Further, Japanese Patent Application Laid-Open Publication No. 2007-239555 (Patent Literature 3), for example discloses a multilink-type internal combustion engine where a top dead center of the piston at the time of switching from the exhaust stroke to the intake stroke (i.e., exhaust top dead center) is set different from a top dead center of the piston at the time of switching from the compression stroke to the expansion stroke. In the internal combustion stroke disclosed in Patent Literature 3, the exhaust top dead center of the piston is set higher than the expansion top dead center of the piston. Thus, in the internal combustion engine disclosed in Patent Literature 3, the remaining combustion gas in the combustion chamber would be compressed by the piston more strongly than in the internal combustion engine disclosed in Patent Literature 2, so that heat loss of the remaining combustion gas and friction produced in the interior of the internal combustion engine cannot be effectively suppressed.

SUMMARY OF THE INVENTION

In view of the foregoing prior art problems, it is an object of the present invention to provide an improved multilink-type internal combustion engine which can effectively suppress heat loss of the remaining combustion gas and suppress friction from being produced in the interior of the internal combustion engine due to the remaining combustion gas.

In order to accomplish the above-mentioned object, the present invention provides an improved multilink-type internal combustion engine in which a connection link is pivotably mounted on a crankshaft and connected at one end portion thereof to a piston via a con rod and at another end portion thereof to a pivot shaft via a swing rod, and which includes a power transmission structure capable of transmitting rotation of the crankshaft to the pivot shaft. The power transmission structure comprises: a planet gear mechanism having a sun gear mounted on the crankshaft; a drive gear provided on a ring gear section of the planet gear mechanism; a driven gear mounted on the pivot shaft and meshing with the drive gear; and an adjustment mechanism for switching a rotation direction of a carrier of the planet gear mechanism to thereby adjust a meshing phase of the driven gear relative to the drive gear.

According to the present invention, the meshing phase of the driven gear relative to the drive gear can be adjusted by the adjustment mechanism switching the rotation direction of the planet gear mechanism (carrier). Thus, a top dead center in an exhaust stroke (i.e., exhaust top dead center) of the piston can be set at an opposite position, with respect to a combustion chamber, from a top dead center in a compression stroke (i.e., compression top dead center) of the piston; namely, the exhaust top dead center can be set at a lower position than the compression top dead center. By setting the exhaust top dead center of the piston at a lower position like this, the piston can be prevented from compressing residual combustion gas (combustion gas remaining in the combustion chamber) in the exhaust stroke. Thus, it is possible to suppress temperature increase of the residual combustion gas due to compression by the piston. As a consequence, it is possible to keep small a temperature difference between the residual combustion gas and a wall of a cylinder of a cylinder block and minimize heat loss from the cylinder (wall of the cylinder), so that an air-fuel mixture can be ignited spontaneously in a stabilized manner.

Further, because the piston can be prevented from compressing the residual combustion gas in the exhaust stroke, it is possible to prevent a load (stress) from being generated on the piston from the residual combustion gas. In this way, it is possible to suppress friction from being produced in the interior (particularly, sliding portions) of the combustion engine due to a load (stress) generated on the piston.

Because an air-fuel mixture can be ignited spontaneously (self-ignited) in a stabilized manner and friction can be suppressed from being produced in the interior of the internal combustion chamber, it is possible to enhance an operating efficiency of the internal combustion engine of the present invention.

Preferably, in the internal combustion engine of the present invention, the adjustment mechanism adjusts the meshing phase in such a manner that, during staring operation of the internal combustion chamber, the exhaust top dead center of the piston is set at the same position as the compression top dead center of the piston, and that, during steady operation of the internal combustion engine, a compression top dead center in the compression stroke of the piston is set at a position closer to the combustion chamber than the compression top dead center set during the starting operation, but also an exhaust top dead center in the exhaust stroke of the piston is set at an opposite position, with respect to the combustion chamber, from the compression top dead center set during the steady operation.

During the starting operation of the internal combustion engine, the exhaust top dead center of the piston is set at the same position as the compression top dead center of the piston, and thus, the air-fuel mixture can be ignited in a stabilized manner by means of an ignition plug (spark plug). As a result, it is possible to enhance the operating efficiency of the internal combustion engine of the present invention during the starting operation.

During the steady operation of the internal combustion engine, on the other hand, the exhaust top dead center of the piston is set at a lower position (at an opposite position, with respect to the combustion chamber, than (from) the compression top dead center set during the steady operation. Thus, the piston can be prevented from compressing the residual combustion gas in the exhaust stroke, so that it is possible to suppress temperature increase of the residual combustion gas. Therefore, it is possible to keep small the temperature difference between the residual combustion gas and the wall of the cylinder and minimize heat loss from the cylinder (wall of the cylinder). As a result, the air-fuel mixture can be ignited spontaneously in a stabilized manner. Further, because the piston can be prevented from compressing the residual combustion gas in the exhaust stroke, it is possible to prevent a load (stress) from being generated on the piston from the residual combustion gas. In this way, it is possible to suppress friction from being produced in the interior of the combustion engine due to a load (stress) generated on the piston.

Because the air-fuel mixture can be ignited spontaneously (self-ignited) in a stabilized manner and friction can be suppressed from being produced in the interior of the internal combustion chamber, it is possible to enhance the operating efficiency of the internal combustion engine of the present invention during the steady operation.

DETAILED DESCRIPTION OF THE INVENTION

Now, a description will be given about a multilink-type internal combustion engine10according to an embodiment of the present invention. The multilink-type internal combustion engine10is, for example, a 4-cycle, single-cylinder OHV engine which uses gas (urban gas, LP gas or the like) as fuel. Further, this internal combustion engine10is a utility engine for use as a drive source of power generators, agricultural machines, cogeneration apparatus, etc.

As shown inFIG. 1, the embodiment of the multilink-type internal combustion engine10includes: a crankshaft16provided in an engine case11; a link mechanism20interconnecting the crankshaft16and a piston18; and a power transmission structure30capable of changing the top dead center of the piston18by adjusting rotation of the link mechanism20.

Further, the embodiment of the multilink-type internal combustion engine10includes: an (air) intake valve37and an exhaust valve38accommodated in a cylinder head14; a valve (gear) mechanism40(FIG. 2) for actuating the intake valve37and the exhaust valve38; and an ignition plug (spark plug)46(FIG. 2) accommodated in the cylinder head14.

The crankshaft16has a cover47mounted on an end portion16athereof projecting beyond en engine case11. A cooling fan48is provided on an outer portion of the cover47, and a power generator49is accommodated in the cover47.

The multilink-type internal combustion engine10is switchable, in response to an operating state thereof, between spark ignition operation and premixed compression self-ignition operation. The “spark ignition operation” means operation where an air-fuel mixture in a combustion chamber15is combusted by the ignition plug (spark plug)46(FIG. 2), and the premixed compression self-ignition operation means operation where the air-fuel mixture is ignited spontaneously by being compressed by the piston18. For example, the spark ignition operation is selected during starting operation of the internal combustion engine10, and the premixed compression self-ignition operation is selected during steady operation of the internal combustion engine10.

The air-fuel mixture is generated by gas and air being mixed by a mixer52provided upstream of an intake path51. The air-fuel mixture thus generated by the mixer52is supplied via the intake path51to the combustion chamber15when the intake valve37is in an open position.

As shown inFIG. 2, the valve mechanism40includes: first and second intake cams (only one of which is shown in theFIG. 41mounted on a second shaft24; first and second exhaust cams (only one of which is shown in the figure)42; an intake lifter43that is selectively slidingly contacted by one of the first and second intake cams41; and an exhaust lifter42that is selectively slidingly contacted by one of the first and second exhaust cams42.

The valve mechanism40further includes an intake rocker arm45connected to the intake lifter43via an intake push rod44, and an exhaust rocker arm connected to the exhaust lifter via an exhaust push rod.

The intake valve37is switchable between an open position and a closed position by actuating movement of the intake rocker arm45, and the exhaust valve38is switchable between an open position and a closed position by actuating movement of the air exhaust rocker arm.

By the first and second intake cams41being moved in an axial direction of the pivot shaft24, any one of the first and second intake cams41is selected to slidingly contact the intake lifter43. Similarly, by the first and second exhaust cams42being moved in the axial direction of the pivot shaft24, any one of the first and second exhaust cams42is selected to slidingly contact the exhaust lifter.

By causing the first intake cam41to slidingly contact the intake lifter43and causing the first exhaust cam42to contact the exhaust lifter during the starting operation, the intake valve37and the exhaust valve38are switchable between the open position and the closed position for the spark ignition operation of the internal combustion engine10. On the other hand, by causing the second intake cam to contact the intake lifter and causing the second exhaust cam to contact the exhaust lifter during the steady operation, the intake valve37and the exhaust valve38are switchable between the open position and the closed position for the premixed compression self-ignition operation of the internal combustion engine10.

In the premixed compression self-ignition operation, settings are made such that valve closing timing of the exhaust valve38is advanced while valve opening timing of the intake valve37is retarded. Thus, a so-called “negative overlap” state where both of the intake valve37and the exhaust valve38are closed is maintained from a latter half of an exhaust stroke to a former half of an intake stroke.

By thus maintaining the negative overlap state, the instant embodiment allows a part of combustion gas to remain in the combustion chamber15, so that heat energy of the remaining gas (hereinafter referred to also as “residual combustion gas”) can be used for the next combustion. Namely, the instant embodiment employs an internal EGR (Exhaust Gas Recirculation) mechanism for mixing the residual combustion gas of the combustion chamber15with an air-fuel mixture supplied to the combustion chamber15, so that it can stabilize the self-ignition timing of the air-fuel mixture by use of the heat energy of the residual combustion gas.

In the spark ignition operation, on the other hand, the air-fuel mixture is combusted by the ignition plug46, and thus, there is no need to use the heat energy of the combustion gas at the time of combustion of the air-fuel mixture. Thus, during the spark ignition operation, the valve closing timing of the exhaust valve38is set to occur when the piston18is near the top dead center of the exhaust stroke while the valve opening timing of the intake valve37is set to occur when the piston18is near the top dead center of the intake stroke. In this way, the combustion gas can be discharged from the combustion chamber15without being caused to remain in the combustion chamber15.

Further, the first and second intake cams41and the first and second exhaust cams42of the valve mechanism40are mounted on the pivot shaft24. Thus, the pivot shaft24can function also as a cam shaft supporting the first and second intake cams41and the first and second exhaust cams42. Because there is no need to provide a separate cam shaft, it is possible to reduce the number of necessary components and thus reduce the size of the multilink-type internal combustion engine10.

The following paragraphs describe in detail the link mechanism20and the power transmission structure30(FIG. 3) of the multilink-type internal combustion engine10. As shown inFIG. 1, the engine case11includes; a crankcase12having accommodated therein the crankshaft16, link mechanism20and power transmission structure30, and a cylinder block13having a cylinder13acommunicating with the interior of the crankcase12.

The cylinder13ais inclined at an inclination angle θ (seeFIG. 2), and the piston18is accommodated in the cylinder13afor sliding movement in an arrowed direction.

The crankshaft16includes a shaft body section55with opposite shaft portions rotatably supported by the crankcase12, and a crankpin56provided on a longitudinally-middle portion of the shaft body section55. More specifically, the crankpin56is disposed parallel to the shaft body section55at a position eccentric to the shaft body section55.

The piston18is accommodated coaxially in the cylinder13aof the cylinder block13for sliding movement in an arrowed direction along the axis of the cylinder13a.

As shown inFIGS. 2 and 3, the link mechanism20includes: a connection link (trigonal link)21pivotably provided on the crankpin56of the crankshaft16; a con rod (connecting rod)22connecting one end portion21bto the connection link21; a swing rod23connecting another end portion21cof the connection link21to the pivot shaft24; and a pivot shaft (eccentric shaft)24rotatably supported on the crankcase12.

The connection link21integrally has a central portion21arotatably mounted on the crankpin56, one end portion21bprovided on one side of the central portion21a, and another end portion21cprovided on the other side of the central portion21a.

The con rod22has its proximal end portion22arotatably connected to the one end portion21bof the connection link21via a connection pin61, and a distal end portion22brotatably connected to the piston18via a piston pin62.

Further, the swing rod23has its proximal end portion23arotatably connected to the other end portion21cof the connection link21via a connection pin63, and a distal end portion23brotatably connected to a pivot pin26of the pivot shaft24.

Further, as shown inFIG. 4, the pivot shaft24includes a shaft body section25rotatably supported by the crankcase12, and a pivot pin26provided on a longitudinally-middle portion of the shaft body section25. More specifically, the pivot pin26is disposed parallel to the shaft body section25at a position eccentric to the shaft body section25.

Further, as shown inFIGS. 3 and 4, the power transmission structure30includes: a planet gear mechanism31having a sun gear65mounted on the shaft body section55of the crankshaft16; a driven gear32provided on the shaft body section25of the pivot shaft24(FIG. 4) meshing with a ring gear72of the planet gear mechanism31; and an adjustment mechanism33capable of switching a carrier68of the planet gear mechanism31between a stationary state and a rotating state.

The planet gear mechanism31includes: the sun gear65mounted coaxially on the shaft body section55of the crankshaft16; a plurality of planetary gears66disposed on and at intervals around the outer periphery of the sun gear65and meshing with the sun gear65; the carrier68rotatably supporting the plurality of planetary gears66via planetary pins67; and a ring gear section71meshing with the plurality of planetary gears66.

Further, as shown inFIGS. 5 and 6, the carrier68, which is formed in a disk shape having a central opening, includes the plurality of planetary pins67rotatably supporting the respective planetary gears66, and an adjustment gear69formed on the outer periphery thereof. A drive pinion36of the adjustment mechanism33meshes with the adjustment gear69of the carrier68.

Thus, deactivation of an electric motor34of the adjustment mechanism33can keep the adjustment gear69(i.e., carrier68) in the stationary state. On the other hand, driving of the electric motor34of the adjustment mechanism33can keep the adjustment gear69(i.e., carrier68) in the rotating state.

The above-mentioned ring gear section71, which is formed in a generally cylindrical shape, includes the ring gear72formed on its inner peripheral wall, and a drive gear73formed on its outer peripheral wall. The ring gear72meshes with the plurality of planetary gears66, and the drive gear73meshes with the driven gear32.

The adjustment mechanism33includes the electric motor34mounted on the crankcase12, and a drive pinion36provided coaxially with a drive shaft35of the motor34and meshing with the adjustment gear69. The drive pinion36is kept in a stationary state by deactivation of the electric motor34and rotated by driving of the electric motor34.

With the drive pinion36kept in the stationary state, the carrier68is kept in the stationary state. On the other hand, with drive pinion36kept in the rotating state, the carrier68is kept rotating in a direction of arrow A1or A2.

The following describe, with reference toFIG. 6, behavior of the power transmission structure30. As shown inFIG. 6, the carrier68is kept in the stationary state by the electric motor34of the adjustment mechanism33being kept in the deactivated state. With the carrier68kept in the stationary state like this, the plurality of planetary pins67are kept in a stationary state.

The crankshaft16rotates in a direction of arrow C in response to the piston18sliding in a direction of arrow B (seeFIG. 3). In response to the crankshaft16rotating in the direction of arrow C, the sun gear65rotates in the direction of arrow C, so that the plurality of planetary gears66each rotate in a direction of arrow D by a predetermined number of rotations N1without revolving around the sun gear65.

In response to the plurality of planetary gears66rotating in the direction of arrow D as above, the ring gear72(i.e., ring gear section71) rotates in a direction of arrow E about the crankshaft16, so that the drive gear73of the ring gear section71rotates in the direction of arrow E about the crankshaft16. In response to the drive gear73rotating in the direction of arrow E, the driven gear32rotates in a direction of arrow F, so that the pivot shaft24rotates in the direction of arrow F by a predetermined number of rotations N2.

Namely, by causing the crankshaft16to rotate in the direction of arrow C with the carrier68kept in the stationary state, the power transmission structure30can cause the pivot shaft24to rotate in the direction of arrow F by the predetermined number of rotations N2.

Then, the electric motor34of the adjustment mechanism33is activated from the aforementioned state, so that the carrier68is rotated in the direction of arrow A1by means of the drive pinion36. In response to such rotation of the carrier68, the plurality of planetary gears66revolve in the direction of arrow A1; more specifically, the plurality of planetary gears66revolve in the direction of arrow A1but also rotate in the direction of arrow D by a predetermined number of rotations N3. Namely, by causing the plurality of planetary gears66to revolve in the direction of arrow A1, the planetary gears66can be adjusted into the number of rotations N3smaller than the number of rotations N1.

In response to the plurality of planetary gears66rotating in the direction of arrow D by the predetermined number of rotations N3as above, the pivot shaft24rotates in the direction of arrow F by a predetermined number of rotations N4, via the ring gear72, drive gear73and driven gear32, which is smaller than the number of rotations N2.

Namely, by causing the carrier68to rotate in the direction of arrow A1, the power transmission structure30can cause the pivot shaft24to rotate in the direction of arrow F by the number of rotations N4smaller than the number of rotations N2.

By driving of the electric motor34of the adjustment mechanism33, the carrier68is caused to rotate in the direction of arrow A2via the drive pinion36, so that the plurality of planetary gears66revolve in the direction of arrow A2. Namely, the plurality of planetary gears66revolve in the direction of arrow A2but also rotate in the direction of arrow D by the number of rotations N5greater than the number of rotations N1. Namely, by causing the plurality of planetary gears66to revolve in the direction of arrow A2, the power transmission structure30can be adjusted into the number of rotations N5greater than the number of rotations N1.

In response to the plurality of planetary gears66rotating in the direction of arrow D by the predetermined number of rotations N5as above, the pivot shaft24rotates in the direction of arrow F by a predetermined number of rotations N6, via the ring gear72, drive gear73and driven gear32, greater than the number of rotations N2.

Namely, by causing the carrier68to rotate in the direction of arrow A2, the power transmission structure30can cause the pivot shaft24to rotate in the direction of arrow F by the number of rotations N6greater than the number of rotations N2.

By the rotation direction of the planetary gear mechanism31(carrier68) being switched by the adjustment mechanism33between the direction of arrow A1and the direction of arrow A2as set forth above, the number of rotations of the driven gear32can be adjusted as desired.

In the aforementioned manner, it is possible to adjust the rotations of the first and second intake cams41and the first and second exhaust cams42mounted on the pivot shaft24. Further, by changing the number of rotations of the carrier68, it is possible to adjust as desired the meshing phase γ of the driven gear32relative to the drive gear73.

The following describe, with reference toFIG. 3, behavior of the link mechanism20in the instant embodiment. In response to the crankshaft16rotating in the direction of arrow C as shown inFIG. 3, the crankpin56rotates (revolves) in the direction of arrow C about the shaft body section55. In response to such rotation of the shaft body section55, the connection link21rotates (revolves) in the direction of arrow C together with the shaft body section55.

Further, the pivot shaft24is rotated by the power transmission mechanism30in the direction of arrow F, in response to which the pivot pin26rotates (revolves) in the direction of arrow F about the shaft body section25. In response to such rotation of the pivot pin26, the distal end portion23bof the swing rod23rotates (revolves) in the direction of arrow F together with the pivot pin26.

Further, in response to such revolution of the distal end portion23bof the swing rod23, the other end portion21cof the connection link21moves in a direction of arrow G together with the proximal end portion23aof the swing rod23, so that the connection link21pivots in a direction of arrow H about the crankpin56.

Further, in response to such pivoting movement of the connection link21, the one end portion21bof the connection link21moves in a direction of arrow I, so that the proximal end portion22aof the con rod22moves in the direction of arrow I. By such movement of the proximal end portion22aof the con rod22, it is possible to change (adjust) the top dead center of the piston18.

In such states, it is possible to adjust the meshing phase γ of the driven gear32relative to the drive gear73by switching the rotation direction of the planetary gear mechanism31(carrier68) between the direction of arrow A1and the direction of arrow A2.

The following paragraphs describe, with reference toFIGS. 3 and 7, a manner in which the meshing phase γ is adjusted to switch the internal combustion engine10to the starting operation (i.e., spark ignition operation) or to the steady operation (i.e., premixed compression self-ignition operation) and in which the top dead center of the piston18is changed in the steady operation.

FIG. 7Ais a view explanatory of the spark ignition operation and premixed compression self-ignition operation of the embodiment of the multilink-type internal combustion engine of the present invention.FIG. 7Bis a graph showing relationship among the meshing phase γ, height of the top dead center and height of the bottom dead center of the embodiment of the multilink-type internal combustion engine10, where G1represents the bottom dead center of the intake stroke, G2represents the top dead center of the compression stroke, G3represents the bottom dead center of the expansion stroke and G4represents the top dead center of the exhaust stroke. Further, inFIG. 7B, the vertical axis represents the heights of the bottom and top dead centers while the horizontal axis represents the meshing phase γ. Note that the meshing phase γ refers to a phase at which the driven gear32on the pivot shaft24meshes with the drive gear73on the shaft body section55of the crankshaft16.

As an example, in the embodiment of the multilink-type internal combustion engine10, link ratios of the link mechanism20and gear ratios of the power transmission structure30are set in such a manner that, when the carrier68of the power transmission structure30rotates in the direction of arrow A1, the meshing phase is set at γ1(seeFIG. 7B). With the meshing phase set at γ1like this, the starting operation (spark ignition operation) can be selected.

As shown inFIG. 7, the bottom dead center in the intake stroke (intake bottom dead center) is set at P1in response to the meshing phase being at γ1. Further, the top dead centers of the piston18in the compression stroke and exhaust stroke (i.e., compression top dead center and exhaust top dead center) of the piston18are set at the same position P2, and the bottom dead center in the expansion stroke (expansion bottom dead center) is set at P3.

In addition, the link ratios of the link mechanism20and the gear ratios of the power transmission structure30are set in such a manner that, when the carrier68rotates in the direction of arrow A2, the meshing phase γ is set at γ2as shown inFIG. 3. With the meshing phase set at γ2, the steady operation (premixed compression self-ignition operation) can be selected.

As shown inFIG. 7, the bottom dead centers in the intake stroke and expansion stroke (intake bottom dead center and expansion bottom dead center) are set at the same position P4in response to the meshing phase γ being at γ2as above. Further, the top dead center of the piston18in the compression stroke (compression top dead center) of the piston18is set at a position P5, and the top dead center of the piston18in the exhaust stroke (exhaust top dead center) of the piston18is set at a position P6.

During the steady operation (premixed compression self-ignition operation) of the multilink-type internal combustion engine10, as set forth above, the exhaust top dead center P6can be set at an opposite position, with respect to the combustion chamber15, from the compression top dead center P5(more specifically, at a position lower than the compression top dead center P5).

Namely, in the steady operation the multilink-type internal combustion engine10, the position of the top dead center of the piston18can be changed by the power transmission structure30adjusting the meshing phase γ.

Next, with reference toFIGS. 8 to 12, a description will be given about how the embodiment of the multilink-type internal combustion engine10is operated. To facilitate understanding of the top and bottom dead centers of the piston18, the following description will be given assuming that the cylinder13ais disposed in a vertical orientation.

First, the following describe, with reference toFIGS. 8 and 9, how the multilink-type internal combustion engine10behaves in the starting operation (i.e., spark ignition operation). The drive pinion36of the adjustment mechanism33is rotated during operation of the multilink-type internal combustion engine10, in response to which the carrier68of the internal combustion engine10rotates in the direction of arrow A1as shown inFIG. 8. Thus, the meshing phase γ of the driven gear32relative to the drive gear73changes to γ1(seeFIG. 7B), in response to which the multilink-type internal combustion engine10switches to the starting operation (i.e., spark ignition operation).

In the intake stroke, the crankshaft16continues to rotate as indicated by arrow J and the pivot shaft24continues to rotate as indicated by arrow K, as shown in (a) ofFIG. 9. Also, the intake valve37is switched to the open position, the exhaust valve38is switched to the closed position, and the piston18descends to the intake bottom dead center P1along the cylinder13aas indicated by arrow L. Then, with the intake valve37kept in the open position, an air-fuel mixture is supplied to the combustion chamber15as indicated by arrow M.

Then, by the crankshaft16continuing to rotate as indicated by arrow J and by the pivot shaft24continuing to rotate as indicated by arrow K as shown in (b) ofFIG. 9, the piston18of the internal combustion engine10switches from the intake stroke to the compression stroke.

In the compression stroke, the intake valve37and the exhaust valve38are switched to the closed position, and the piston18ascends from the intake bottom dead center P1to the compression top dead center P2along the cylinder13aas indicated by arrow N. Once the piston18ascends to the neighborhood of the compression top dead center P2, the air-fuel mixture in the combustion chamber15is ignited (combusted) by the ignition plug46.

Then, by the crankshaft16continuing to rotate as indicated by arrow J and by the pivot shaft24continuing to rotate as indicated by arrow K as shown in (c) ofFIG. 9, the internal combustion engine10switches from the compression stroke to the expansion stroke.

In the expansion stroke, the intake valve37and the exhaust valve38are kept in the closed position, and the piston18descends from the compression top dead center P2to the expansion bottom dead center P3along the cylinder13aas indicated by arrow O. The expansion bottom dead center P3is located lower than the intake dead center P1.

Then, by the crankshaft16continuing to rotate as indicated by arrow J and by the pivot shaft24continuing to rotate as indicated by arrow K as shown in (d) ofFIG. 9, the piston18of the internal combustion engine10switches from the expansion stroke to the exhaust stroke.

In the exhaust stroke, the intake valve37is kept in the closed position while the exhaust valve38is kept in the open position, and the piston18ascends from the expansion bottom dead center P1to the exhaust top dead center P2along the cylinder13aas indicated by arrow P. With the exhaust valve38kept in the open position as above, the combustion gas in the combustion chamber15is discharged as indicated by arrow Q. The exhaust top dead center P2is located at the same position as the compression top dead center P2.

In the starting operation (spark ignition operation), as set forth above, the air-fuel mixture is combusted by the ignition plug46, and thus, the air-fuel mixture can be ignited in a stabilized manner even without use of heat energy of combustion gas. Because the air-fuel mixture can be ignited in a stabilized manner, it is possible to enhance an operating efficiency during the starting operation of the internal combustion engine10.

During the spark ignition operation, the valve closing timing of the exhaust valve38in the exhaust stroke is set to occur when the piston18has reached the neighborhood of the exhaust top dead center P2. Further, the valve opening timing of the intake valve37in the intake stroke is set to occur immediately before the piston18reaches the exhaust top dead center P2. In addition, the exhaust top dead center P2is located at the same position as the compression top dead center P2. In this way, the combustion gas can be discharged from the combustion chamber15without being caused to remain in the combustion chamber15.

The following describe, with reference toFIGS. 10 and 12, how the multilink-type internal combustion engine10behaves in the steady operation (i.e., premixed compression self-ignition operation).FIG. 10is a graph explanatory of the premixed compression self-ignition operation, where the vertical axis represents positions of the piston18while the horizontal axis represents crank angles.

As shown inFIG. 10, in response to the drive pinion36being rotated in the reverse direction with the crankshaft16rotating as indicated by arrow J, the carrier68rotates as indicated by arrow A2. Thus, the meshing phase γ of the driven gear32relative to the drive gear73changes to γ2 (seeFIG. 7B), in response to which the multilink-type internal combustion engine10switches to the steady operation (i.e., premixed compression self-ignition operation).

Further, in the intake stroke, as shown inFIG. 11and (a) ofFIG. 12, the crankshaft16continue to rotate as indicated by arrow J, and the pivot shaft24continues to rotate as indicated by arrow K. The intake valve37is switched to the open position while the exhaust valve38is switched to the closed position, and the piston18descends to the intake bottom dead center P4along the cylinder13aas indicated by arrow R.

In the premixed compression self-ignition operation, the valve opening timing T1of the intake valve37is retarded, and an air-fuel mixture is supplied to the combustion chamber15as indicated by arrow S by the thus-retarded intake valve37being kept in the open position.

By the crankshaft16continuing to rotate as indicated by arrow J and by the pivot shaft24continuing to rotate as indicated by arrow K, the piston18of the internal combustion engine10switches from the intake stroke to the compression stroke, as shown inFIG. 11and (b) ofFIG. 12. In the compression stroke, the intake valve37and the exhaust valve38are switched to the closed position, and the piston18ascends from the intake bottom dead center P3to the compression top dead center P5along the cylinder13aas indicated by arrow T. During the premixed compression self-ignition operation, the compression top dead center P5is set higher (closer to the combustion chamber15) than the compression top dead center P2set during the spark ignition operation. The air-fuel mixture is ignited spontaneously by the piston18ascending to the compression top dead center P5to thereby compress the air-fuel mixture with a high compression ratio.

By the crankshaft16continuing to rotate as indicated by arrow J and by the pivot shaft24continuing to rotate as indicated by arrow K, the piston18of the internal combustion engine10switches from the compression stroke to the expansion stroke, as shown inFIG. 11and (c) ofFIG. 12. In the expansion stroke, the intake valve37and the exhaust valve38are switched to the closed position, and the piston18descends from the compression top dead center P5to the expansion bottom dead center P4along the cylinder13aas indicated by arrow U. The expansion bottom dead center P4is located at the same position as the intake bottom dead center P4.

By the crankshaft16continuing to rotate as indicated by arrow J and by the pivot shaft24continuing to rotate as indicated by arrow K, the piston18of the internal combustion engine10switches from the expansion stroke to the exhaust stroke, as shown inFIG. 11and (d) ofFIG. 12. In the exhaust stroke, the intake valve37is kept in the closed position while the exhaust valve38is kept in the opened position, and the piston18ascends from the expansion bottom dead center P3to the exhaust top dead center P6along the cylinder13aas indicated by arrow V. With the exhaust valve38kept in the open position as above, the combustion gas in the combustion chamber15is discharged as indicated by arrow W.

In the premixed compression self-ignition operation, the valve closing timing T2of the exhaust valve38is advanced. Further, the valve opening timing T1of the intake valve37is retarded in the intake stroke. Thus, the so-called “negative overlap” state where the both of the intake valve37and the exhaust valve38are closed can be secured in a time period Hov. Further, in the premixed compression self-ignition operation, the exhaust top dead center P6can be set lower than the compression top dead center P5(at an opposite position, with respect to the combustion chamber15, from the compression top dead center P5).

With the negative overlap state secured in the time period Hov and with the exhaust top dead center P6set at a lower position than the compression top dead center P5as noted above, a part of the combustion gas is caused to remain in a residual gas space V between the compression top dead center P5and the exhaust top dead center P6. Further, with the exhaust top dead center P6set at a lower position than the compression top dead center P5, it is possible to prevent the piston18from compressing the residual combustion gas in the exhaust stroke and thereby prevent a load (stress) from being generated on the piston18from the residual combustion gas. In this way, it is possible to suppress friction from being produced in the interior (particularly, sliding portions) of the multilink-type internal combustion engine10due to a load (stress) generated on the piston18.

In addition, because the piston18can be prevented from compressing the residual combustion gas in the exhaust stroke, it is possible to suppress temperature increase of the residual combustion gas. Thus, it is possible to keep small a temperature difference between the residual combustion gas and the wall of the cylinder13aand minimize heat loss from the cylinder13a(wall of the cylinder13a). In this way, heat energy of the residual combustion gas of the combustion chamber15can be used efficiently for spontaneous ignition (combustion)

In addition, the compression top dead center P5during the premixed compression self-ignition operation is set higher than (closer to the combustion chamber15) than the compression top dead center P2during the spark ignition operation (seeFIG. 9). By using the heat energy of the residual combustion gas and setting the compression top dead center P5during the premixed compression self-ignition operation at a higher position, it is possible to spontaneously ignite the air-fuel mixture in a stabilized manner. Namely, the spontaneous ignition (self-ignition) timing of the air-fuel mixture can be stabilized.

Because the spontaneous ignition timing of the air-fuel mixture can be stabilized and friction can be suppressed from being produced in the interior (particularly, sliding portions) of the multilink-type internal combustion engine10, it is possible to enhance the operating efficiency of the internal combustion engine10during the premixed compression self-ignition operation (i.e., steady operation).

The multilink-type internal combustion engine10of the present invention is not limited to the above-described embodiment and may be modified variously. For example, the shapes and constructions of the multilink-type internal combustion engine10, crankshaft16, piston18, connection link21, con rod22, swing rod23, pivot shaft24, power transmission structure30, planet gear mechanism31, driven gear32, adjustment mechanism33, sun gear65, carrier68, ring gear72, drive gear73, etc. are not limited to those shown and described above and may be modified variously.

The basic principles of the present invention are well suited for applications to multilink-type internal combustion engines where a connection link is mounted on a crankshaft and a piston and a pivot shaft are connected with the connection link.