JP2005147067A - Cylinder direct injection internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make the compression ratio in a cylinder direct injection internal combustion engine such as a diesel engine changeable. <P>SOLUTION: In the cylinder direct injection diesel engine equipped with a fuel injection valve 29 at a central position of a cylinder 19, a variable compression ratio mechanism using a double link piston-crank mechanism to change a top dead center of a piston 8 is provided. A cavity 25 in a crown side of a piston 8 is formed to a shallow pan shape of the diameter which is near the outside diameter of the piston 8 so that a fundamental shape of a combustion chamber does not change even when the top dead center changes corresponding to the change in the compression ratio. In the diesel engine, at the top dead center in the condition in which the compression ratio is the lowest, the relationship of a cavity angle θp with a spray angle θi is set to be θi<θp. This makes piston-stroke characteristics be near a simple harmonic vibration with the double piston-crank mechanism without directly spraying on a cylinder 19 inner wall surface, and although a squish is not obtained, a combustion time can be fully obtained. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an in-cylinder direct injection internal combustion engine such as a diesel engine, and more particularly to an in-cylinder direct injection internal combustion engine combined with a variable compression ratio mechanism that variably controls the mechanical compression ratio of the engine by changing the piston top dead center position. Related to institutions.

  In the case of a diesel engine, the compression ratio is almost determined by the demand for startability, and the compression ratio during normal operation after warm-up can basically be significantly lower than at the start. However, until now, there has been no practical compression ratio variable means, and combustion control corresponding to changes in the piston top dead center position has been difficult, so variable compression ratio control of diesel engines has not been put into practical use.

  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.

On the other hand, unlike a gasoline engine, a diesel engine uses a rise in the intake air temperature due to compression without supplying a spark plug, and supplies high pressure fuel spray to it, so that light oil with a high cetane number is self-ignited. In this system, it reacts with the surrounding compressed air and burns. In this diesel engine, fuel supply with moderate penetration at high pressure is performed, and by utilizing the in-cylinder gas flow such as swirl and squish, the air utilization rate is increased, smoke at high loads, etc. Is avoided. Therefore, inhaling as much air as possible is important for increasing the output while avoiding the generation of smoke. Therefore, a diesel engine is often combined with a supercharger, but a variable compression ratio system that can reduce the maximum combustion pressure (Pmax) by reducing the compression ratio to an appropriate value during high supercharging is an important technology. It has the potential to improve output and exhaust performance while maintaining the durability and reliability of the engine.
JP 2001-227367 A

  However, when a variable compression ratio mechanism that changes the piston top dead center position is applied to a diesel engine, several major problems arise.

  1 and 2 show a configuration example when a compression ratio variable mechanism is combined with a conventional diesel engine, and depicts a state when the piston 101 is at the compression top dead center position. (A) of a figure shows a high compression ratio control state, (b) shows a low compression ratio control state. In conventional diesel engines, the piston 101 is provided with a relatively deep cavity 102, and the turbulence of intake air is effectively increased by the flow of compressed air entering from the surrounding squish area. Is injected and burned efficiently (FIGS. 1 (a) and 2 (a)).

  However, when the low compression ratio is controlled as shown in FIG. 1B by the variable compression ratio mechanism (generally, when it is necessary to inject a large amount of fuel at a high load, the low compression ratio state is set to increase the air amount. Since the clearance between the piston 101 and the cylinder head upper wall surface is enlarged even at the top dead center position, the effect of the squish is remarkably reduced. In addition, as for fuel spraying, as shown in FIG. 2B, the position of the cavity 102 is downward, so that in the cavity 102 having a relatively deep and small opening diameter as in the prior art, many fuel sprays are formed in the cavity 102. End up outside. Although this has a large impact on the combustion surface, the fuel that hits the cylinder wall at a relatively low temperature increases, so it is discharged as particulates without being burned, or the oil on the cylinder wall is diluted to improve lubrication. Problems also arise. Further, in such a situation where a large amount of fuel is directed to the outside of the cavity 102, it is impossible to efficiently meet a large amount of injected fuel at high load and maintain the air utilization rate at a high level.

  A direct injection type internal combustion engine according to the present invention has a cavity in a crown surface of a piston that reciprocates in a cylinder, and includes a fuel injection valve so as to inject fuel directly into the combustion chamber. And a variable compression ratio mechanism that changes the position at the top dead center of the piston up and down. Therefore, the mechanical compression ratio is variably controlled according to the engine operating conditions.

  The relationship between the spray angle θi of the fuel injection valve and the angle θp with respect to the outermost diameter of the cavity around the injection hole position of the fuel injection valve at the piston top dead center position is the lowest in the compression ratio. In the condition, that is, when the piston top dead center position is the lowest, θi <θp. Therefore, no matter how the piston top dead center position is changed by the variable compression ratio mechanism, the spray collides into the cavity and the spray does not directly adhere to the cylinder wall.

  In the present invention, the cavity preferably has a shallow dish shape whose outermost diameter is close to the piston diameter. Further, the squish area on the outer periphery of the piston can be substantially absent. The squish area is rather harmful when the piston top dead center position is changed by the variable compression ratio mechanism, because the basic shape of the combustion chamber changes with the change of the compression ratio.

  A variable compression ratio mechanism suitable for the present invention includes an upper link having one end connected to the piston via a piston pin, the other end of the upper link being connected via a first connection pin, and a crankshaft. A lower link rotatably attached to the crank pin of the engine, and a control link having one end connected to the lower link via a second connecting pin and the other end supported to be swingable with respect to the internal combustion engine body. And a support position varying means for displacing the swing support position of the other end of the control link relative to the internal combustion engine body.

  In such a variable compression ratio mechanism, the link configuration is set so that the piston stroke characteristic of the piston with respect to the rotation of the crankshaft becomes a characteristic closer to the single vibration than the characteristic in the single link piston-crank mechanism. Is possible.

  By bringing the piston stroke characteristic close to simple vibration in this way, the piston speed near the top dead center becomes relatively slow. In other words, in a combustion chamber structure in which a squish effect cannot be obtained, such as a shallow dish-shaped cavity piston without a squish area, even if the combustion speed is slow, a larger time margin is given.

  Further, the link configuration of the variable compression ratio mechanism is set so that the inclination of the upper link with respect to the cylinder axis is smaller than that of a single-link piston-crank mechanism when the piston is at a position where the maximum combustion load is received. It is also easy to set. Thus, the side thrust load acting on the piston is relatively reduced by the posture of the upper link approaching the vertical. For example, if the cavity has a shallow dish shape, the frequency of the fuel spray reaching the cylinder wall is higher than that of the deep dish cavity, and the piston outer periphery is exposed to high-temperature combustion gas, so that the piston skirt is more difficult to lubricate. However, since the side thrust load is reduced as described above, the problem of lubrication of the skirt portion can be solved.

  According to this invention, even if the piston top dead center position is changed by the variable compression ratio mechanism, the fuel spray does not directly collide with the cylinder wall, thereby increasing the unburned components and diluting the oil on the cylinder wall. Etc. can be avoided.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 3 is an explanatory diagram showing the configuration of the variable compression ratio mechanism used in the direct injection type internal combustion engine according to the present invention. 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 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 combustion pressure and reciprocates in the cylinder 19 of the cylinder block 18.

  The control link 10 that constrains 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 the second connecting pin 11, and the lower end side becomes 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. 4 is a basic operation explanatory view of the above-mentioned multi-link type piston-crank mechanism, showing 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, as shown in FIG. 5, it is possible to make the characteristics closer to simple vibrations compared to the piston stroke characteristics of a general single link type piston-crank mechanism. Due to the piston stroke characteristic close to simple vibration, the speed of the piston 8 near the top dead center is reduced by nearly 20% compared to that of the single link type piston-crank mechanism. Further, as shown in FIG. 6 showing the characteristics of piston acceleration, the secondary inertia vibration can be reduced, which is advantageous in terms of vibration noise of the internal combustion engine.

  Next, the structure of the piston 8 and the combustion chamber, which are the main parts of the present invention, will be described. This example is an example of a turbocharged diesel engine.

  FIG. 7 shows the structure of the piston 8 according to the present invention. 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 a piston head 21 having a relatively thick disk shape. A skirt portion 23 is formed on a part of the piston 8 in the circumferential direction that is the thrust-anti-thrust direction so as to extend from the outer circumferential surface along the cylindrical surface.

  A pair of pin bosses 24 are formed in the center of the piston 8, that is, on the back surface of the piston head 21 having a disc shape, and the piston boss 7 is rotatably supported by the pin boss 24. Link 5 is connected.

  A shallow dish-shaped cavity 25 is concentrically recessed on the crown surface of the piston 8 so that the outermost diameter is almost equal to the outer diameter of the piston 8. On the outer periphery of the cavity 25, the flat portion 26 for chamfering remains only in a very thin annular shape, and there is substantially no squish area for obtaining gas flow.

  FIG. 8 shows the structure of the combustion chamber using the piston 8 having the shallow dish-shaped cavity 25 as described above, and an intake valve and an exhaust valve (not shown) are provided on the cylinder head 28 side covering the upper end of the cylinder 19. And a fuel injection valve 29 at the center of the combustion chamber, that is, at the center of the cylinder 19. In the fuel injection valve 29, the central axis of the spray coincides with the cylinder center line, and the fuel is injected toward the cavity 25. The diesel engine of this embodiment includes a known common rail fuel injection device, and injects high-pressure fuel from the fuel injection valve 29 according to a control signal from the control unit. Here, as shown in the figure, the spray spread of the fuel injection valve 29 is defined as a spray angle θi, and the outermost diameter of the cavity 25 centered on the injection hole position of the fuel injection valve 29 at the top dead center position of the piston 8. When the angle with respect to (in the present embodiment, substantially equal to the outer diameter of the piston 8) is the cavity angle θp (which changes with variable control of the compression ratio), the condition with the lowest compression ratio (that is, the piston 8 Under the condition that the top dead center position is the lowest), various dimensional relationships and the like are set so that θi <θp.

  Therefore, in the above configuration, as shown in FIG. 9, even if the top dead center position of the piston 8 changes between the high compression ratio state (a) and the low compression ratio state (b), the basic shape of the combustion chamber. The fuel spray is injected into the cavity 25 and the spray does not directly adhere to the inner wall of the cylinder 19 having a low temperature.

  On the other hand, in the case of the shallow dish-shaped cavity 25 having no squish area as described above, if there is no combustion accelerating means instead of the squish, mixing with air and combustion cannot be performed well, and the effect of the variable compression ratio is very high. Cannot be demonstrated. However, as described above, in the multi-link type piston-crank mechanism constituting the variable compression ratio mechanism, a piston stroke characteristic close to simple vibration is obtained, and the speed of the piston 8 near the top dead center is Compared to that of a piston-crank mechanism, it is nearly 20% slower. Therefore, even if the combustion speed is slow, a sufficient time margin is provided, and good combustion can be ensured. In general, if the compression ratio is increased, the combustion speed is increased, so that there are fewer problems due to the absence of squish under the operating conditions of a high compression ratio such as partial load.

  Moreover, even if the fuel spray is injected into the cavity 25 by using the shallow dish-shaped cavity 25 as described above, the frequency at which the fuel spray bounced here reaches the inner wall surface of the cylinder 19 is a deep dish shape. It is larger than a cavity. Moreover, since the outer peripheral portion of the piston 8 is exposed to the high-temperature combustion gas, the piston skirt portion 23 is hard to be lubricated. When high supercharging is performed with a low compression ratio, the average piston load (due to the combustion pressure) during the expansion stroke becomes large, and the demand for lubrication further increases. However, in the above-described multi-link piston-crank mechanism, the side thrust load acting in the radial direction of the piston 8 is smaller than that in the case of a general single-link piston-crank mechanism. The problem of lubrication can be avoided. 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 demand for lubrication of the skirt portion 23 is reduced.

  As mentioned above, although the Example which applied this invention to the diesel engine was described, this invention is not limited to this, It applies similarly to the direct injection type gasoline engine which injects a fuel directly into a cylinder and performs stratified combustion. be able to. FIGS. 10A to 10F show various types of piston cavity structures used in a direct injection gasoline engine, and FIGS. 10A to 10C show stratification using swirl. , (D) to (f) are intended to be stratified using tumble, but the configurations of (a) to (c), (e) and (f) are not suitable for variable compression ratios. . Since (d) does not have a squish area, such a problem does not occur, but it is impossible to cause effective stratified combustion only by a tumble flow, and it is not so often employed in a conventional direct injection engine. However, as described above, if the piston stroke characteristic close to simple vibration is obtained by the multi-link piston-crank mechanism constituting the variable compression ratio mechanism, the speed of the piston 8 near the top dead center is -Since it is slower than that of the crank mechanism, a sufficient time margin is provided even when the combustion speed is slow, and good combustion can be ensured.

Explanatory drawing of the squish when the conventional direct injection type diesel engine is made into variable compression ratio. Explanatory drawing of the spray at the time of making variable compression ratio the conventional direct injection type diesel engine. BRIEF DESCRIPTION OF THE DRAWINGS Structure explanatory drawing which shows the variable compression ratio mechanism of the direct injection type internal combustion engine which concerns on this invention. Operation | movement explanatory drawing which shows the basic operation | movement. The characteristic view which shows the piston-stroke characteristic. The characteristic view which similarly shows the acceleration characteristic of a piston. The perspective view which cuts and shows a part of piston used for the internal combustion engine which concerns on this invention. Explanatory drawing which shows the relationship between spray angle (theta) i and cavity angle (theta) p. Explanatory drawing which compares and shows a high compression ratio state (a) and a low compression ratio state (b). Explanatory drawing which shows the various structural examples of the combustion chamber of a direct injection type gasoline engine.

Explanation of symbols

4 ... Lower link 5 ... Upper link 7 ... Piston pin 8 ... Piston 10 ... Control link 25 ... Cavity 29 ... Fuel injection valve

Claims (9)

In a cylinder direct injection internal combustion engine having a cavity on the crown surface of a piston that reciprocates in a cylinder, and having a fuel injection valve so as to inject fuel directly into the combustion chamber toward the cavity,
With a variable compression ratio mechanism that changes the position at the top dead center of the piston up and down,
The relationship between the spray angle θi of the fuel injection valve and the angle θp with respect to the outermost diameter of the cavity centering on the position of the injection hole of the fuel injection valve at the piston top dead center position is that the compression ratio is the lowest. In-cylinder direct injection internal combustion engine, wherein θi <θp.   The in-cylinder direct injection internal combustion engine according to claim 1, wherein the cavity has a shallow dish shape with an outermost diameter close to a piston diameter.   The in-cylinder direct injection internal combustion engine according to claim 2, wherein a squish area on the outer periphery of the piston does not substantially exist.   The variable compression ratio 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 lower link attached to the lower link, a control link whose one end is connected to the lower link via a second connecting pin and whose other end is swingably supported with respect to the internal combustion engine body, and the other end of the control link The cylinder direct injection internal combustion engine according to any one of claims 1 to 3, further comprising support position changing means for displacing a swing support position of the internal combustion engine with respect to the main body of the internal combustion engine.   The direct injection internal combustion engine according to any one of claims 1 to 4, wherein the direct injection internal combustion engine is a diesel engine.   6. The direct injection type internal combustion engine according to claim 1, wherein the fuel injection valve is positioned substantially at the center of the combustion chamber, and the center axis of the spray is parallel to the cylinder center line. .   The link configuration of the variable compression ratio mechanism is set so that the piston stroke characteristic of the piston with respect to the rotation of the crankshaft is a characteristic closer to a single vibration than the characteristic of a single link piston-crank mechanism. The in-cylinder direct injection internal combustion engine according to claim 4.   The link configuration of the variable compression ratio mechanism is set so that the inclination of the upper link with respect to the cylinder axis is smaller than that of a single link piston-crank mechanism when the piston is in a position to receive the maximum combustion load. 8. The direct injection type internal combustion engine according to claim 4, wherein the direct injection type internal combustion engine.   The direct injection type internal combustion engine according to any one of claims 1 to 8, further comprising a supercharger.