JP5136255B2 - Spark ignition direct injection engine - Google Patents

Description

  The present invention relates to a spark ignition direct injection engine, and more particularly to a spark ignition direct injection engine that promotes catalyst activation when the engine is cold.

  2. Description of the Related Art Conventionally, a direct injection engine that directly injects fuel into a cylinder has been adopted in order to improve fuel efficiency. According to such a direct injection engine, the compression ratio can be increased and the engine efficiency can be increased. Further, the fuel injection amount can be freely adjusted regardless of the intake air intake amount.

  On the other hand, in recent years, exhaust gas emission regulations have been strengthened, and it is required to activate the catalyst at an early stage. In order to activate such a catalyst early, it is necessary to raise the exhaust gas temperature as early as possible, and it is conceivable to raise the exhaust gas temperature by retarding the ignition timing as much as possible.

  However, if the ignition timing is significantly retarded, the combustion stability deteriorates. Therefore, a technique for retarding the ignition timing while ensuring this combustion stabilization has been demanded.

  Therefore, in the following Patent Document 1, fuel injection is performed in two parts, before and after the main injection that is performed at a timing that crosses the top dead center and the early injection that is performed at the timing such as the intake stroke, and the ignition timing is determined from the top dead center. However, an engine device that performs combustion at a greatly retarded angle has been proposed.

  In this way, by performing fuel injection in advance in the intake stroke or the like, the injected fuel can be diffused into the cylinder before the main injection, so the main injection spray is ignited and combustion starts. Sometimes, relatively slow combustion can be generated in the entire cylinder, and combustion can be stably generated.

  That is, the in-cylinder state is a so-called “weak stratification” in which a thick air-fuel mixture is placed around the spark plug and only air is present around the spark plug, so that a thin air-fuel mixture is located around the so-called “stratification state”. By setting the “state”, the combustion state of the engine is stabilized.

As described in Patent Document 1, it is conceivable that a multi-hole type injector is used as an injector for injecting fuel.
JP 2006-250050 A

  By the way, in the engine device of Patent Document 1, it is disclosed that the timing of the early injection is performed at an early timing of the intake stroke or the compression stroke, but it is not clear at what timing the injection is performed specifically.

  In view of setting the injection timing, it is conceivable to set the early injection timing at a time when the intake stroke is late or when the compression stroke is early. In this way, if the injection timing is set, the piston is positioned near the bottom dead center, so that it is possible to secure a wide space in the cylinder and promote the expansion of the spray in the cylinder. .

However, in the case of early activation of the catalyst, since the engine is also cold state, Cylinders side wall of the cylinder (liner) is also cold, the injected spray adheres to Cylinders side wall of the cylinder There is a possibility that it does not vaporize. In particular, since the combustion temperature in the combustion chamber is difficult to be transmitted in the lower part of the cylinder, there is a high possibility that the spray adheres to the lower part of the cylinder and liquefies when the engine is cold.

  As described above, when the spray is liquefied and adheres to the side wall in the cylinder, unburned gas is discharged as HC to the exhaust system, and the exhaust gas performance may be deteriorated. In addition, the fuel to be vaporized and atomized is reduced, the air-fuel mixture becomes thin, and the desired combustion state may not be obtained.

  In addition, in the engine device of Patent Document 1, it is described that the main spray is injected at a timing across the top dead center, but in order to position a rich air-fuel mixture around the spark plug, In order to inject fuel into a high-pressure cylinder, it is necessary to increase the injection pressure, and it is difficult to position an appropriately rich mixture around the spark plug. there were.

  Accordingly, the present invention provides a spark ignition type direct injection engine that promotes catalyst activation when the engine is cold, and is set so that spray by fuel injection does not adhere to the side wall in the cylinder as much as possible. Spark ignition direct injection that can achieve the desired combustion state by suppressing the discharge of gas, surely vaporizing and atomizing a lot of spray, and by reliably positioning a rich mixture around the spark plug The purpose is to provide an engine.

The spark ignition direct injection engine of the present invention includes an injector provided with a plurality of injection holes for injecting a plurality of sprays obliquely downward at the periphery of the combustion chamber ceiling wall, and an ignition plug at the center of the combustion chamber ceiling wall. A spark ignition direct injection engine provided with a concave cavity corresponding to the spark plug on a piston crown surface, and a lowest stage located at a lowermost position among a plurality of sprays injected from the injector The lowermost nozzle hole for injecting the spray and the uppermost nozzle hole for injecting the uppermost spray located at the uppermost position are set, and the injection directions of the uppermost nozzle hole and the lowermost nozzle hole are directed to the cavity in plan view. When the engine is cold, the fuel is injected in the intake stroke and the compression stroke twice, and the fuel injection in the intake stroke is performed before the lowermost spray drops. Set so as to impinge on the piston cavity, the fuel injection of the compression stroke, the top spray, configured to collide with the cavity of the piston rises, the the uppermost nozzle hole and the lowermost jetting nozzle A plurality of intermediate injection holes for injecting the intermediate spray located at the intermediate height are provided between the two, and the injection direction of the intermediate injection holes is set so as to be directed to the outside of the cavity in plan view .

According to the above configuration, the fuel injection when the engine is cold is divided into the intake stroke and the compression stroke, and the fuel injection in the intake stroke is set to collide with the piston cavity where the lowermost spray falls. In the fuel injection in the compression stroke, the uppermost spray is set to collide with the rising piston cavity.
That is, in the intake stroke, a spray space is secured above the piston, and injection is performed so that the lowermost spray is trapped (captured) in the piston cavity, and in the compression stroke, the space above the piston is reduced. The injection is carried out so that the uppermost spray is trapped in the cavity of the piston.
For this reason, in the fuel injection in the intake stroke, the spray is widely dispersed in the vertical direction in the cylinder, and the bottom spray is trapped by a piston having a high wall temperature, so that the spray is injected into the cylinder having a low wall temperature. Can be prevented from adhering to the lower wall surface. In addition, in fuel injection in the compression stroke, by receiving the uppermost spray in the cavity, a dense air-fuel mixture layer is reliably formed around the spark plug, and the ignition stability of the spark plug is improved, thereby improving combustion stability. Can be improved.

Further, a plurality of intermediate nozzles for injecting a middle spray located at an intermediate height are provided between the uppermost nozzle and the lowermost nozzle. From the intermediate nozzle, the uppermost spray and the lowermost spray are provided. By spraying a plurality of middle-stage sprays in between, a plurality of sprays can be dispersed and sprayed in the vertical direction in the cylinder. For this reason, the distribution of the air-fuel mixture in the cylinder that is long in the vertical direction can be substantially homogenized.
Therefore, even when the engine is cold, the vaporization and atomization of the fuel can be promoted, and the inside of the cylinder can be reliably stratified.

In addition, the injection direction of the intermediate nozzle is set to be directed to the outside of the cavity in plan view, and a plurality of sprays are generated by spraying the spray from the intermediate nozzle toward the outside of the cavity. It will be injected in the cylinder three-dimensionally. For this reason, the distribution of the air-fuel mixture in the cylinder of the three-dimensional space can be made substantially uniform.
Therefore, even when the engine is cold, vaporization and atomization can be further promoted, and the inside of the cylinder can be weakly stratified.

In one embodiment of the present invention, the fuel injection end timing of the intake stroke is set to the middle period when the intake stroke is divided into the first period, the middle period, and the latter period.
According to the above configuration, the fuel is injected in a state where the injection space is secured above the piston, and the fuel injection is completed in the middle of the intake stroke in which the intake flow is most generated in the intake stroke.
For this reason, fuel vaporization and atomization can be promoted by utilizing the intake air flow such as swirl, and the fuel can be vaporized and atomized effectively even when the engine is cold when the fuel is difficult to vaporize and atomize. .
Therefore, the vaporization atomization of the fuel injection in the intake stroke can be further promoted, and the exhaust gas performance and the combustion performance when the engine is cold can be improved.

In one embodiment of the present invention, the fuel injection end timing of the compression stroke is set to 3/4 or later of the compression stroke, and the ignition timing of the spark plug is set after top dead center.
According to the above configuration, by injecting fuel near the top dead center of the compression stroke, the distance from the piston is close, and the uppermost spray can be surely put into the cavity, and there is a strong concentration around the spark plug. A mixture layer can be formed. In addition, combustion stability can be improved by performing ignition after top dead center in the state where the inside of the cylinder is weakly stratified.
Therefore, combustion after top dead center, it is possible to stably performed, it is possible to increase the temperature of the exhaust gas, Ru can be reliably revitalize the catalyst.

In an embodiment of the present invention, the uppermost spray from the uppermost injection port is sprayed to a position below the spark plug so as to be detached from the spark plug.
According to the above configuration, since the uppermost spray is not applied to the spark plug during fuel injection, the spark plug does not get wet with the fuel, and deterioration of the ignition performance of the spark plug can be suppressed.
Therefore, even when the engine is cold, the spark plug can reliably ignite and the combustion stability can be improved.

According to the present invention, in the fuel injection in the intake stroke, the spray is dispersed in the vertical direction in the cylinder, and the bottom spray is trapped by the piston having the high wall surface temperature so that the spray has a low wall surface temperature. It can prevent adhering to the lower wall surface in a cylinder. In addition, in fuel injection in the compression stroke, the uppermost spray is received by the cavity, so that a rich air-fuel mixture layer is reliably formed around the spark plug, improving the ignition plug ignitability and improving combustion stability. can do.
Therefore, in a spark ignition direct injection engine that promotes catalyst activation when the engine is cold, unburned gas is discharged from the exhaust system by setting so that the spray from the fuel injection does not adhere to the side wall in the cylinder as much as possible. Therefore, a desired combustion state can be obtained by reliably vaporizing and atomizing a large amount of spray, and reliably positioning a rich air-fuel mixture around the spark plug.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a spark ignition direct injection engine according to an embodiment of the present invention.
As shown in FIG. 1, the engine E is a so-called four-cycle reciprocating engine, and includes a cylinder block 2 that rotatably supports the crankshaft 1 and a cylinder head 3 that is disposed above the cylinder block 2. It is composed integrally. Further, this cylinder block 2 and the cylinder head 3 is provided with a plurality of cylinders 4.

  Each cylinder 4 is provided with a piston 6 connected to the crankshaft 1 via a connecting rod 5 and a combustion chamber 7 formed above the piston.

  On the lower surface of the cylinder head 3, a ceiling wall portion 8 of the combustion chamber 7 is formed for each cylinder 4. The ceiling wall portion 8 is a so-called pent roof type having two opposing inclined surfaces 8a and 8b extending from the center portion to the lower end of the cylinder head 3.

  The ceiling wall 8 of the combustion chamber 7 is provided with two independent intake ports 9 and exhaust ports 10, and has a four-valve configuration of two intake valves 16 and two exhaust valves 17.

A multi-hole injector 11 connected to the fuel supply system is installed on the side edge of the combustion chamber 7 so as to face obliquely downward. The multi-hole injector 11 is configured such that when the fuel supply system 12 receives a fuel injection pulse from the control unit 13, fuel corresponding to the pulse width is injected into the combustion chamber 7.
The detailed structure of the multi-hole injector 11 will be described later.

  Further, each cylinder 4 is provided with a spark plug 14 that is fixed to the cylinder head 3 and is disposed with the electrode facing the combustion chamber 7. The spark plug 14 is disposed at a substantially central position of the combustion chamber 7. An ignition circuit 15 capable of controlling the ignition timing by electronic control is connected to the ignition plug 14 and is controlled by the ignition circuit 15.

  Tappet units 18 and 19 are provided on the intake valve 16 and the exhaust valve 17 of each cylinder 4, respectively. The tappet units 18 and 19 are configured to be periodically driven by cams 20 and 21 of a cam shaft of a valve mechanism provided in the cylinder head 3.

  A branch intake pipe 22 of an intake manifold is connected to the intake port 9 of the engine E. The branch intake pipe 22 is provided for each cylinder, and each of them is connected in a state in which an intake passage having an equal length is formed in the intake manifold.

  Next, the exhaust port 10 is connected to a bifurcated branch exhaust pipe 23 formed in pairs for each cylinder. A catalytic converter 24 for purifying exhaust gas is installed on the downstream side of each branch exhaust pipe 23. The catalytic converter 24 is provided with a catalyst temperature sensor 25 for detecting the catalyst temperature, and detects whether or not the temperature of the catalyst has risen to the activation temperature.

  The control unit 13 is composed of a CPU or the like, and includes input elements (not shown) such as an input sensor (crank angle sensor) and the catalyst temperature sensor 25 described above, and output elements such as the fuel supply system 12 and the ignition circuit 15 described above. By connecting to, the engine operating state is controlled.

2 is a perspective view showing a detailed structure of a multi-hole type injector, a piston, and a spark plug. FIG. 3 is (a) a plan view of a piston crown surface and (b) a cross section taken along line AA of the piston crown surface. FIG.
As shown in FIG. 2, the multi-hole injector 11 is installed such that the tip injection surface 11 a faces obliquely downward, and injects a plurality of sprays G toward the crown surface 30 side of the piston 6. It is composed.

  Six injection holes 40 are provided on the injection surface 11 a of the multi-hole injector 11. Specifically, as shown in the detailed view of the injection surface, the first injection port 40a is located at the upper center, the second injection port 40b and the third injection port 40c are provided on the left and right sides of the second stage, and the fourth injection port 40d is provided on the left and right ends of the third stage. And a fifth nozzle hole 40e, and a sixth nozzle hole 40f at the center of the lower stage, respectively.

  Thus, by providing each nozzle hole 40..., The spray G injected from each nozzle hole 40 can be sprayed evenly and evenly in the cylinder in an obliquely downward direction. For this reason, at the time of homogeneous combustion during normal operation, fuel spreads all over the cylinders and can be burned efficiently.

Further, as will be described later, a weakly stratified state can be generated in the cylinder (4) by appropriately controlling the injection timing when the engine is cold.
Here, the weakly stratified state refers to a state in which the mixture distribution in the cylinder (4) is adjusted so that the concentration of the mixture around the spark plug is increased and the mixture around the spark plug is thinned.

  Each of the nozzle holes 40 is formed with a very small diameter (for example, about 0.1 mm), and the injection amount and the directing direction from each of the nozzle holes 40 are determined by the diameter, the direction, and the like.

  The directivity direction of each of the nozzle holes 40 is set corresponding to the position of each of the nozzle holes 40, and the first spray Ga from the first nozzle hole 40a points most upward, and the first direction from the second nozzle hole 40b. The second spray Gb and the third spray Gc from the third nozzle 40c are directed in the left-right direction below, and the fourth spray Gd from the fourth nozzle 40d and the fifth spray Ge from the fifth nozzle 40e are further provided. It is set so that the sixth spray Gf from the sixth nozzle hole 40f is directed to the center at the bottom and directed to the left and right outer sides below. As shown in FIG. 2, the first spray Ga is set so as to be directed to a position below the electrode 14a so that fuel does not adhere to the electrode 14a of the spark plug 14.

  The piston 6 of this embodiment forms a raised portion 31 having a pair of inclined surfaces 31a and 31b facing the piston crown surface 30 along the crankshaft direction. The inclined surfaces 31a and 31b of the raised portion 31 are formed so as to be inclined in a pent roof shape along the pent roof type ceiling wall portion 8 of the combustion chamber 7 described above.

  Further, on both sides of the raised portion 31, horizontal plane portions 32 and 33 serving as reference surfaces for the piston crown surface 30 are provided. An intake valve recess 32a and an exhaust valve recess 33a are formed on the horizontal plane portions 32 and 33 so as to correspond to the intake valve 16 and the exhaust valve 17, respectively.

  A concave cavity 34 having a substantially circular shape in plan view is formed at the center of the raised portion 31. The concave cavity 34 includes an inner peripheral surface 35 formed in a substantially hemispherical shape and a flat bottom surface 36 formed in a substantially horizontal plane. When the piston 6 is located at the top dead center, ignition is performed. A substantially spherical combustion space centering on the electrode 14a of the plug 14 is formed.

  In this way, by forming the concave cavity 34 to form a substantially spherical combustion space, an engine with an extremely high compression ratio can be obtained, and the engine efficiency can be increased.

  As shown in FIG. 3A, a receiving surface 37 that receives the spray is formed on the inclined surface 31 on the intake side. The receiving surface 37 is formed of a concave portion having a substantially gourd shape in plan view that is recessed by one step.

By forming a part of the upper portion of the receiving surface 37 over the concave cavity 34, as shown in FIG. 3B, the injector-side upper edge 34a of the concave cavity 34 has an anti-injector-side upper edge. It is formed so as to be positioned below the end 34b.
Therefore, as described later, spray injected from the injector 11 (Ga) is in the cavity 34. enters easily, so do One out difficult.

  In addition, as shown to Fig.3 (a), the upper surface parts 38 and 38 are formed in the top part of the both sides of the concave cavity 34 of the protruding part 31. As shown in FIG. The upper surface portions 38 and 38 are formed by inclined surfaces with the outer ends slightly lowered. By doing so, even when the piston 6 is at the top dead center, a communication space that allows the intake side and the exhaust side to communicate with each other at the upper part of the cylinder (4) can be formed.

  Next, the engine operating state (fuel injection state) when the engine is cold will be described with reference to FIGS. 4 is a time chart of fuel injection timing and ignition timing when the engine is cold, FIG. 5 is a side view showing the fuel injection state in the intake stroke, and FIG. 6 is a side view showing the fuel injection state in the compression stroke. FIG.

  The multi-hole injector 11 and the spark plug 14 controlled by the control unit 13 are controlled as shown in the time chart of FIG. 4 when the engine is cold.

  That is, when the engine cold state is detected by the catalyst temperature sensor 25 or the like, the fuel injection timing is performed twice in total, one time in the intake stroke and one time in the compression stroke, and 2 fuel injections per cycle. It is done in divisions.

  Specifically, for example, the first fuel injection F1 is finished at a crank angle of 80 degrees (hereinafter referred to as “° CA”), and the second fuel injection F2 is finished at 325 ° CA. ing. The widths w1 and w2 of each injection pulse are set to be proportional to the fuel injection amount at each injection timing, and the fuel injection is such that the sum of the two fuel injection amounts is substantially the stoichiometric air-fuel ratio. The amount is set.

  In this way, by injecting the fuel in two parts, first, the fuel is vaporized and atomized early in the cylinder by the first fuel injection F1, and then around the spark plug 14 by the second fuel injection F2. A rich layer with a rich mixture is formed. That is, the inside of the cylinder is so-called weakly stratified by such two-split injection timing.

  Then, after the top dead center (TDC) has elapsed, the spark plug 14 is ignited at 380 ° CA (= 20 ° CA of the exhaust stroke). That is, the ignition timing S is retarded until the timing for entering the exhaust stroke.

Thus, by retarding the ignition timing S, will be burning energy formic the engine is often used to heat energy formic, remains high exhaust gas temperature, so that the exhaust gas is discharged to the exhaust side .

Thus, the catalytic converter 24 is supplied a high exhaust gas temperature, early it is possible to raise the temperature of the catalytic converter 24, it is possible to activate the catalyst.
Therefore, exhaust gas can be purified at an early stage.

  Note that if the ignition timing S of the spark plug 14 is retarded, the combustion state becomes unstable, and combustion may not occur reliably. However, in the present embodiment, since the inside of the cylinder is reliably weakly stratified, a stable combustion state can be obtained even if the ignition timing S is significantly retarded.

As shown in FIG. 5, in the fuel injection in the intake stroke (first fuel injection F <b> 1), the sixth spray Gf injected from the lowest sixth injection port 40 f enters the concave cavity 34 of the piston crown surface 30. Is set to That is, the sixth spraying Gf directed most downwardly, reaches the side wall surface 4a of the cylinder 4 (liner) (adhesion) without, it being ejected to direct the piston crown surface 30.

Thus, as the sixth spraying Gf is directed to the piston crown surface 30, that the fuel is injected, the lower 4a1 most lower temperature side wall surface 4a in the cylinder 4 (liners), adhesion fuel Therefore, vaporization and atomization of fuel in the intake stroke can be promoted. For this reason, it can prevent that HC which is unburned gas is contained in exhaust gas.

  In addition, by injecting the fuel in the vicinity of 90 ° CA, the fuel is injected at a time when the piston speed is the fastest and the in-cylinder flow is the largest due to the flow of air such as a swirl. Can be promoted more.

  Further, the first spray Ga, the second spray Gb (third spray Gc), and the fourth spray Gd (fifth spray Ge) sprayed upward are also sprayed at this timing, so that a three-dimensional space can be obtained. In the cylinder (4) which comprises, it will inject uniformly and widely. Moreover, stirring of each spray in the cylinder (4) is promoted by the air flow of the swirl Q or the like, and it is possible to prevent droplets from adhering to the corners of the cylinder (4).

  For these reasons, the sprays Ga, Gb, Gc, Gd, and Ge other than the sixth spray Gf can also promote vaporization and atomization more uniformly in the cylinder (4), so that the fuel is burned efficiently. Can be made.

  As shown in FIG. 6, in the fuel injection in the compression stroke (second fuel injection F <b> 2), the first spray Ga injected from the uppermost first injection port 40 a enters the concave cavity 34 of the piston crown surface 30. Is set to That is, the first spray Ga that is directed upward is set so as to be directed to the inner peripheral surface 35 of the concave cavity 34.

  On the other hand, the second spray Gb (third spray Gc) is set to be directed to the inclined surface 31a (specifically, the receiving surface 37) in front of the concave cavity 34. However, even if the second spray Gb (third spray Gc) is directed to the receiving surface 37 as described above, the second spray Gb and the third spray Gc enter the concave cavity 34. That is, the second spray Gb and the third spray Gc, which have collided with the receiving surface 37 and weakened momentum, are drawn into the concave cavity 34 by the negative pressure generated after the first spray Ga passes.

  This pull-in behavior will be described using the schematic diagram of FIG. FIG. 7A is a schematic side view immediately after injection, and FIG. 7B is a schematic side view thereafter.

As shown in FIG. 7A, the first spray Ga is injected to the substantially hemispherical inner peripheral surface 35 of the concave cavity 34 so as to be directed.
For this reason, as shown in FIG. 7B , the first spray Ga is guided by the arc-shaped inclined surface 35a of the inner peripheral surface 35 and smoothly reverses upward, so that the spark plug 14 side (ceiling wall) Part 8 side).

On the other hand, as shown in FIG. 7A, the second spray Gb (third spray Gc) is injected so as to be directed to the receiving surface 37.
For this reason, the second spray Gb (third spray Gc) collides with the receiving surface 37 to weaken the momentum, and drifts above the receiving surface 37. However, as shown in FIG. 7B , after the first spray Ga has passed, a negative pressure is drawn into the concave cavity 34, so the second spray Gb (third spray Gc) is This negative pressure draws it into the concave cavity 34.

  As described above, since the second spray Gb and the third spray Gc are drawn into the concave cavity 34, a rich mixture can be positioned around the spark plug 14.

  Further, not only the first spray Ga, but also the second spray Gb and the third spray Gc are drawn into the concave cavity 34, so that more air-fuel mixture can be positioned around the spark plug 14.

Further, as shown in the plan view showing the injection state in FIG. 8, the second spray Gb and the third spray Gc are injected from the inclined surface 31a onto the receiving surface 37 that is recessed by one step. Without being leaked to the inner side ) and reliably guided into the concave cavity 34.

Further, as shown in FIG. 8 , since the directing directions of the second spray Gb and the third spray Gc (the extension line is indicated by a one-dot chain line) are set so as to overlap the concave cavity 34 in plan view, The pull-in effect due to the negative pressure is more likely to occur.

9 to 11 are simulation diagrams of the injection state of this embodiment. 9 is a simulation diagram of 325 ° CA, FIG. 10 is a simulation diagram of 340 ° CA, FIG. 11 is a simulation diagram of 350 ° CA, and FIG. 12 is a simulation diagram of 360 ° CA. Moreover, in each figure, (a) is the injection state of the first spray, (b) is the injection state of the second spray and the third spray, (c) is the spray state of the first spray, the second spray and the third spray. The spray state is combined. And the upper stage is a plan view and the lower end is a side view. Each dot is a droplet of the spray.

  As shown in FIG. 9, at 325 ° CA immediately after the completion of injection, the first spray Ga is injected into the concave cavity 34 as shown in (a). The second spray Gb and the third spray Gc are reflected on the receiving surface 37 and drift upward as shown in FIG. For this reason, as shown in (c), many droplets are located on the injector side.

  As shown in FIG. 10, at the subsequent 340 ° CA, the first spray Ga is in contact with the inner peripheral surface 35 in the concave cavity 34 and guided upward as shown in FIG. The second spray Gb and the third spray Gc are drawn into the concave cavity 34 (upward in the drawing) by the negative pressure generated when the first spray Ga passes as shown in FIG. For this reason, as shown in (c), many droplets are located around the spark plug 14.

  As shown in FIG. 11, in the subsequent 350 ° CA, the first spray Ga is biased to one side of the concave cavity 34 as shown in (a). Moreover, the 2nd spray Gb and the 3rd spray Gc spread centering around the concave cavity 34 like (b). For this reason, as shown in (c), a droplet is positioned around the spark plug 14. It should be noted that the reason why the number of liquid droplets is decreasing as compared with FIG. 10 is that the liquid droplets are evaporated (vaporized) smoothly.

  As shown in FIG. 12, at 360 ° CA, which is the position of the top dead center, as shown in (a), the first spray Ga is vaporized in a state of being biased to one side of the concave cavity 34. Moreover, the 2nd spray Gb and the 3rd spray Gc spread and vaporize over the whole like (b). For this reason, as shown in (c), the liquid droplet is almost vaporized although it is located in a state of being partially biased to one side of the concave cavity 34.

FIG. 13 is a view showing the distribution of the air-fuel ratio (A / F) of the air-fuel mixture around the spark plug at 360 ° CA. In this figure, the R region indicates the richest region, and the L region indicates the leanest region.
As shown in FIG. 13, also in the 360 ° CA, the air-fuel ratio of the mixture is about relatively rose, towards the injector side of the spark plug 14, there will be rich mixture (R) . In addition, a rich air-fuel mixture (R) also exists on the side of the non-injector that is separated from the spark plug 14. And a thin air-fuel mixture (L) exists in a wide range.

On the other hand, FIG. 14 is a view showing the distribution of the air-fuel ratio (A / F) of the air-fuel mixture around the spark plug at 380 ° CA immediately before the ignition timing.
As shown in FIG. 14 , at 380 ° CA, the air-fuel ratio of the air-fuel mixture is such that there are many slightly rich air-fuel mixtures (R) around the spark plug 14 but overall the air-fuel ratio of the air-fuel mixture is Will be equalized. Thereby, the ignition performance by the spark plug 14 can be improved.

  As described above, since the fuel is vaporized and atomized to improve the ignition performance, even if the ignition timing S is delayed, the air-fuel mixture can be reliably burned and the temperature of the exhaust gas can be increased.

Next, the effect of this embodiment comprised in this way is demonstrated.
In this embodiment, when the engine is cold, the fuel is injected in the intake stroke and the compression stroke twice, and the fuel injection in the intake stroke is performed in the concave cavity of the piston 6 where the sixth spray Gf descends. 34, the combustion injection in the compression stroke is set so as to collide with the concave cavity 34 of the piston 6 where the first spray Ga rises.

Thus, when the engine is cold, in the intake stroke, a fuel injection space is secured above the piston 6 and injection is performed so that the sixth spray Gf is trapped in the concave cavity 34 of the piston 6. The injection is performed so that the space above the piston 6 is reduced and the first spray Ga is trapped in the concave cavity 34 of the piston 6.
For this reason, in the fuel injection in the intake stroke, the spray is distributed on the wall surface by trapping the sixth spray Gf with the piston 6 having a high wall surface temperature while spraying the spray widely dispersed in the vertical direction in the cylinder (4). It can prevent adhering to lower part 4a1 (refer FIG. 5) of the side wall surface of a cylinder (4) with low temperature. In addition, in the fuel injection in the compression stroke, by receiving the first spray Ga in the concave cavity 34, a dense air-fuel mixture layer is reliably formed around the spark plug 14 and the ignitability of the spark plug 14 is improved. , Combustion stability can be improved.
Therefore, in a spark ignition direct injection engine that promotes catalyst activation when the engine is cold, it is set so that the spray by fuel injection does not adhere to the side wall surface (4a1) in the cylinder as much as possible, and unburned gas from the exhaust system. The engine combustion state in the cold state can be improved by suppressing the discharge of gas, surely vaporizing and atomizing a large amount of spray, and reliably positioning a rich air-fuel mixture around the spark plug 4 .

In this embodiment, the fuel injection end timing of the intake stroke is set to 80 ° CA, which is the middle period of the intake stroke.
As a result, fuel is injected in a state in which an injection space is secured above the piston 6, and fuel injection is completed in the middle of the intake stroke in which the intake flow is most generated in the intake stroke.
For this reason, fuel vaporization and atomization can be promoted by utilizing the intake air flow such as swirl, and the fuel can be vaporized and atomized effectively even when the engine is cold when the fuel is difficult to vaporize and atomize. .
Therefore, the vaporization atomization of the fuel injection in the intake stroke can be further promoted, and the exhaust gas performance and the combustion performance when the engine is cold can be improved.
The fuel injection end timing is not limited to 80 ° CA, and may be set in the range of 60 to 120 ° CA, which is the middle stage of the intake stroke.

Further, in this embodiment, the fuel injection end timing of the compression stroke is set to 325 ° CA that is 3/4 or later of the compression stroke, and the ignition timing of the spark plug 14 is set to 380 after top dead center (TDC). ° CA is set.
As a result, the fuel is injected at 325 ° CA in the vicinity of the top dead center (TDC) of the compression stroke, so that the distance from the piston 6 is close and the first spray Ga can be surely put into the concave cavity 34. And a dense air-fuel mixture layer can be formed around the spark plug 14. In addition, combustion stability can be improved by performing ignition after top dead center (TDC) in a state where the in-cylinder (4) is weakly stratified.
Therefore, since combustion after the top dead center can be stably performed, the temperature of the exhaust gas can be increased, and the catalyst can be reliably activated.

In this embodiment, the second spray Gb, the third spray Gc, the fourth spray Gd, and the fifth spray Ge, which are located at the intermediate height, are injected between the first nozzle hole 40a and the sixth nozzle hole 40f. A second nozzle 40b, a third nozzle 40c, a fourth nozzle 40d, and a fifth nozzle 40e are provided.
Thus, by spraying a plurality of sprays (Gb, Gc, Gd, Ge, Gf) between the first spray Ga and the sixth spray Gf, the plurality of sprays are dispersed vertically in the cylinder (4). Can be injected. For this reason, the distribution of the air-fuel mixture in the cylinder (4) that is long in the vertical direction can be made substantially uniform.
Therefore, even when the engine is cold, the vaporization of fuel can be promoted and the in-cylinder (4) can be reliably stratified.

In this embodiment, the injection directions of the second injection port 40b, the third injection port 40c, the fourth injection port 40d, and the fifth injection port 40e are set so as to be directed to the left and right outer sides of the concave cavity 34 in plan view. doing.
Thereby, a plurality of sprays Ga ... are jetted three-dimensionally in the cylinder (4). For this reason, the air-fuel mixture distribution in the cylinder (4) of the three-dimensional space can be substantially homogenized.
Therefore, even when the engine is cold, vaporization and atomization can be further promoted, and the in-cylinder (4) can be weakly stratified.

Moreover, in this embodiment, it sets so that the 1st spray Ga from the 1st nozzle hole 40a may be injected to the downward position of the spark plug 14, and it sets so that the 1st spray Ga may not be applied to the spark plug 14. .
Thereby, since the first spray Ga does not reach the spark plug 14, the spark plug 14 does not get wet with the fuel, and deterioration of the ignitability of the spark plug 14 can be suppressed.
Therefore, even when the engine is cold, the spark plug can reliably ignite and the combustion stability can be improved.

As described above, in the correspondence between the configuration of the present invention and the above-described embodiment,
The injector of the present invention corresponds to the multi-hole injector 11 of the embodiment,
Similarly,
The cavity corresponds to the concave cavity 34;
The uppermost spray corresponds to the first spray Ga,
The lowermost spray corresponds to the sixth spray Gf,
The top nozzle corresponds to the first nozzle 40a,
The lowermost nozzle hole corresponds to the sixth nozzle hole 40f,
Middle spray corresponds to the second spray Gb, the third spray Gc, the fourth spray Gd, the fifth spray Ge,
The intermediate nozzle holes correspond to the second nozzle hole 40b, the third nozzle hole 40c, the fourth nozzle hole 40d, and the fifth nozzle hole 40e,
The present invention is not limited to the above-described embodiment, but includes an embodiment applied to any spark ignition direct injection engine.

1 is a schematic configuration diagram of a spark ignition direct injection engine according to an embodiment of the present invention. The perspective view which showed the detailed structure of the multi-hole type injector, piston, and spark plug. (A) The top view of a piston crown surface, (b) AA sectional view taken on the line AA of a piston crown surface. A time chart of fuel injection timing and ignition timing when the engine is cold. The side view which shows the fuel-injection state in an intake stroke. The side view which shows the fuel-injection state in a compression stroke. (A) Side surface schematic diagram immediately after injection, (b) Lateral side schematic diagram. The top view which showed the injection state. The simulation figure of 325 degrees CA. The simulation figure of 340 degrees CA. Simulation diagram of 350 ° CA. The simulation figure of 360 degree CA. The figure which showed the distribution state of the air fuel ratio (A / F) of the air-fuel mixture around a spark plug in 360 degree CA. The figure which showed the distribution state of the air fuel ratio (A / F) of the air-fuel mixture around a spark plug in 380 degree CA.

6 ... Piston
8 ... Ceiling wall (combustion chamber ceiling wall)
11 ... Multi-hole type injector (injector)
14 ... Spark plug
30 ... Piston crown 34 ... Concave cavity (cavity)
40a ... First nozzle (top nozzle)
40f ... Sixth nozzle (lowermost nozzle)
40b, 40c, 40d, 40e ... Intermediate nozzle Ga ... First spray (top spray)
Gf ... 6th spray (top spray)
Gb, Gc, Gd, Ge ... middle spray

Claims (4)

The spark chamber direct injection engine is provided with an injector provided with a plurality of nozzles for injecting a plurality of sprays obliquely downward on the periphery of the combustion chamber ceiling wall, and an ignition plug at the center of the combustion chamber ceiling wall. And
The piston crown surface is provided with a concave cavity corresponding to the spark plug,
Among the plurality of sprays ejected from the injector, while setting the lowermost nozzle for injecting the lowest spray located in the lowermost and the uppermost nozzle for injecting the uppermost spray located in the uppermost,
The injection direction of the uppermost nozzle hole and the lowermost nozzle hole is set so as to face the cavity in plan view,
When the engine is cold, the fuel is set to be injected twice in the intake stroke and the compression stroke.
The fuel injection in the intake stroke is set so that the lowermost spray collides with the descending cavity of the piston;
The compression stroke combustion injection is set so that the uppermost spray hits the rising cavity of the piston ;
Between the uppermost nozzle hole and the lowermost nozzle hole, there are provided a plurality of intermediate nozzle holes for injecting a middle stage spray located at an intermediate height,
A spark ignition direct injection engine in which the injection direction of the intermediate nozzle is set to be directed to the outside of the cavity in plan view . The spark ignition type direct injection engine according to claim 1, wherein the fuel injection end timing of the intake stroke is set to the middle period when the intake stroke is divided into the first period, the middle period, and the latter period. The fuel injection end timing of the compression stroke is set to 3/4 or later of the compression stroke,
Wherein the ignition timing of the spark plug, according to claim 1 or 2 direct-injection spark-ignition engine according to set after top dead center. Direct-injection spark-ignition according to uppermost spray, what Re or one of the injected <br/> claims 1 to 3 as out of the ignition plug in the lower position of the spark plug from the top nozzle hole engine.

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