JP2010024921A - Spark ignition type direct injection engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spark ignition type direct injection engine capable of stabilizing combustion state during a cold engine period by surely making a large quantity of spray stay in a cavity while keeping the compression ratio of the engine high, in the spark ignition type direct injection engine accelerating catalyst activation during the cold engine period. <P>SOLUTION: A receiving surface 37 receiving spray is formed on an inclined surface 31 at an intake side as indicated in (a). The receiving surface 37 forms a hollow part having a U-shape in a plane view which is one step hollowed. The U-shape is formed in such a manner that a cavity side (anti-injector side) is gradually widened. Injector side upper edge end 34a of the hollow cavity 34 is set to be positioned at a lower side of the anti-injector side upper edge end 34b as indicated in (b) by forming a part of an upper side of the receiving surface 37 to overlap the hollow cavity 34. <P>COPYRIGHT: (C)2010,JPO&INPIT

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, there has been proposed an engine device that performs combustion at a greatly retarded angle.

  In this way, by performing fuel injection in advance at the timing of the intake stroke or the like, the injected fuel can be diffused into the cylinder before the main injection, so that the main injection spray is ignited and combustion is performed. When started, 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.

Japanese Patent Application Laid-Open No. H10-228561 discloses a structure in which a concave portion of an engine crown surface is formed into a spherical curved surface centering on an ignition point of a spark plug. Thus, by making a recessed part into a spherical curved surface, a combustion chamber can be made into a substantially spherical shape, and a uniform and favorable combustion state can always be maintained.
JP 2006-250050 A JP 2007-154827 A

  By the way, in order to improve the fuel efficiency, the compression ratio is increased in order to increase the engine efficiency. As a method of increasing the compression ratio, it is conceivable to provide a raised portion having a pent roof-shaped slope along the pent roof shape of the combustion chamber on the piston crown surface.

  However, considering the early activation of the catalyst when the engine is cold as in the engine device of Patent Document 1, it is necessary to retain a rich air-fuel mixture around the spark plug at the timing of the ignition timing. As in Patent Document 2, it is conceivable that a concave cavity is formed at a position corresponding to the spark plug to make this cavity a combustion space.

  Here, in the engine device of Patent Document 1, the main fuel injection is configured to be injected toward the spark plug. However, if the time from the spray timing to the ignition timing is slightly shifted, the ignitability is increased. May deteriorate and a stable combustion state may not be obtained.

  Therefore, it is conceivable that the spray (dense mixture) is positioned around the spark plug for a long period of time by injecting fuel toward the concave cavity and retaining the spray in the cavity.

  However, when a multi-hole injector is used, there are multiple sprays that are sprayed and sprayed in various directions, so there is a problem of how to effectively put these sprays into the cavity. Become.

  Here, for example, the first spray injected from the first nozzle located above is directly injected into the cavity, and the second spray injected from the second nozzle positioned below is raised from the first cavity. It is conceivable that the second spray is drawn into the cavity by using the negative pressure generated by the passage of the first spray after the collision with the slope of the part. By doing so, not only the first spray but also the second spray can be put into the cavity.

  However, even if the second spray is drawn into the cavity by using the negative pressure generated by the passage of the first spray in this way, the state of the generated negative pressure is not constant, so the second spray is surely It may not be pulled into the cavity.

  In addition, even if the second spray is drawn into the cavity using negative pressure, if the first spray easily leaks out of the cavity, the effect of drawing the second spray will be halved. is there.

  Accordingly, the present invention provides a spark ignition type direct injection engine that promotes catalyst activation when the engine is cold, and reliably retains a large amount of spray in the cavity while maintaining a high compression ratio of the engine. By doing so, an object of the present invention is to provide a spark ignition direct injection engine that can stabilize the combustion state when the engine is cold.

  A spark ignition direct injection engine according to the present invention includes an injector provided with a plurality of nozzles for injecting a plurality of sprays obliquely downward on a peripheral edge of a combustion chamber ceiling wall, and a spark including an ignition plug at a center portion of the combustion chamber ceiling wall. In the ignition type direct injection engine, a concave cavity corresponding to the spark plug is formed on the piston crown surface, a pent roof-like slope is formed on the injector side of the cavity, and the injector has an upper side A first injection port that injects the first spray that is positioned so as to be directed toward the cavity in a plan view, and a second spray that is overlapped with the first spray in a plan view and is located below the first spray in a front view. At least two nozzle holes, and the pent roof-shaped slope is provided with a second lower slope on which the second spray collides, and the second slope is provided in the cavity. By forming them so as to be connected to each other, the injector side of the peripheral part of the cavity is set lower than the anti-injector side, and fuel is injected at a predetermined time in the second half of the compression stroke in the engine cold operating region. The second spray is set to collide with the second slope so that the spray enters the cavity.

  According to the above configuration, the compression ratio of the engine can be increased by forming a pent roof-like slope on the piston crown surface. Further, when the engine is cold, the first spray is injected toward the cavity, and the second spray is injected so as to collide with the second slope, whereby the second spray is generated by the passage of the first spray. It is drawn into the cavity by negative pressure. Since the second slope is one step lower than the pent roof-like slope, the second spray is guided by the second slope and guided into the cavity. Furthermore, since the injector side of the peripheral part of the cavity is lower than the anti-injector side, the first spray and the second spray easily enter the cavity and are difficult to exit.

  For this reason, when the second spray is drawn into the cavity using the negative pressure while increasing the compression ratio of the engine, the second spray is surely put into the cavity without being greatly affected by the negative pressure state. be able to. In addition, even if the second spray is put into the cavity, the first spray or the like is not easily emitted from the cavity, so that a lot of spray can be retained in the cavity.

In one embodiment of the present invention, the second inclined surface has a substantially U shape formed so as to gradually spread toward the cavity in a plan view.
According to the said structure, after a 2nd spray collides with a 2nd slope, it is smoothly guided to the cavity side by forming the 2nd slope as a substantially U shape which spreads gradually to the cavity side. become.
Therefore, it becomes possible to put the second spray into the cavity more reliably, and it is possible to reliably position the rich air-fuel mixture around the spark plug.

In one embodiment of the present invention, there is provided a third injection hole for injecting a third spray that overlaps with the second spray in a plan view and is located below the second spray in a front view.
According to the above configuration, since the third spray is positioned below the second spray at the time of fuel injection, the third spray collides with the second inclined surface in addition to the second spray.
For this reason, the 2nd spray and the 3rd spray which are arranged up and down can be guided to the cavity side using the 2nd slope, etc., and more spray can be put in the cavity.
Therefore, a much richer air-fuel mixture (spray) can be retained around the spark plug.

In one embodiment of the present invention, the fuel injection end timing of the predetermined timing 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, when the piston is located in the vicinity of the top dead center, the fuel can be injected, so that the spray can be made to collide accurately with the piston crown surface. It can be accurately placed in the cavity. Even if the ignition timing of the ignition plug is set after top dead center and the ignition timing is delayed, the rich air-fuel mixture is retained around the ignition plug, so that the engine combustibility can be ensured.
Therefore, combustion can be performed with retarded ignition timing, and the exhaust gas temperature can be raised.

In one embodiment of the present invention, in addition to the fuel injection in the compression stroke, the fuel injection is also performed in the intake stroke.
According to the above configuration, the fuel can be injected even in the intake stroke, and the two-part injection can be performed, so that the inside of the cylinder can be weakly stratified.
Therefore, it is possible to improve the combustion stability when the ignition timing is retarded for combustion, and it is possible to raise the exhaust gas temperature more reliably.

According to the present invention, when the second spray is drawn into the cavity using the negative pressure while increasing the compression ratio of the engine, the second spray is surely inserted into the cavity without being greatly affected by the negative pressure state. Can be put inside. In addition, even if the second spray is put into the cavity, the first spray or the like is not easily emitted from the cavity, so that a lot of spray can be retained in the cavity.
Therefore, the present invention provides a spark ignition type direct injection engine that promotes catalyst activation when the engine is cold, and reliably retains a large amount of spray in the cavity while maintaining a high compression ratio of the engine. By doing so, the combustion state when the engine is cold can be stabilized.

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. The cylinder block 2 and the cylinder head 3 are 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 at the side edge of the combustion chamber 7 so as to face obliquely downward. The multi-hole injector 11 is configured such that fuel corresponding to the pulse width is injected into the combustion chamber 7 when the fuel supply system 12 receives a fuel injection pulse from the control unit 13.
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 spark plug 14 and is configured to be 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. 4 is connected to control the operating state of the engine.

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.

  On the injection surface 11a of the multi-hole injector 11, five injection holes 40 are provided. Specifically, as shown in the detailed view of the injection surface, the first injection hole 40a is located at the center of the upper stage, the second injection hole 40b is located at the center of the second stage, and the third injection hole 40c and the fourth injection hole 40d are located on both sides of the third stage. The fifth nozzle holes 40e are provided in the center of the lower stage so as to be arranged in line.

  Thus, by providing each nozzle hole 40..., The spray G injected from each nozzle hole 40 can be evenly sprayed evenly into the cylinder in a diagonally downward direction. Therefore, at the time of homogeneous combustion during normal operation, the fuel is spread throughout the entire cylinder, and can be burned efficiently.

In addition, as will be described later, a weak stratification 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 ratio in the cylinder (4) is adjusted so that the concentration of the air-fuel mixture around the spark plug is increased and the air-fuel mixture around the spark plug is reduced.

  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 directing direction of each spray G ... is set corresponding to the position of each nozzle 40 ..., and the first spray Ga from the first nozzle 40a is directed most upward, and the second spray from the second nozzle 40b. The spray Gb is directed to the center below, the third spray Gc from the third nozzle 40c and the fourth spray Gd from the fourth nozzle 40d are further directed to the left and right outer sides below, The fifth spray Ge from the five nozzle holes 40e is set so as to be directed to the center at the lowest position. 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 the injector side and the non-injector side of the raised portion 31, horizontal plane portions 32 and 33 serving as reference surfaces for the piston crown surface 30 are provided, respectively. 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 shape. When the piston 6 is located at the top dead center, A substantially spherical combustion space centering on the electrode 14a of the spark 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 by a concave portion having a substantially U shape in plan view that is recessed by one step. This U-shape is formed so that the cavity side (anti-injector side) gradually becomes wider. As will be described later, when the spray G is received, the spray G is guided into the concave cavity 34. Yes.

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 becomes the anti-injector-side upper edge. It is set to be positioned below the end 34b.
For this reason, as will be described later, the spray (Ga, Gb...) Sprayed from the multi-hole injector 11 easily enters the concave cavity 34 and does not easily exit.

  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 set to two times, once in the intake stroke and once in the compression stroke, and the fuel injection per cycle is 2 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, the fuel can be vaporized and atomized in the cylinder at an early stage by the first fuel injection F1, and then around the spark plug 14 by the second fuel injection F2. In addition, a rich layer with a rich mixture can be formed. That is, the so-called weak stratification can be achieved in the cylinder 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.

  As described above, by retarding the ignition timing S, the combustion energy of the engine is largely used for heat energy, and the exhaust gas is discharged to the exhaust side while the exhaust temperature is high.

For this reason, exhaust gas having a high temperature is supplied to the catalyst capacitor 24, the temperature of the catalyst capacitor 24 can be raised at an early stage, and the catalyst can be activated.
Therefore, exhaust gas can be purified at an early stage when the engine is started.

  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 fifth spray Ge injected from the lowermost fifth injection port 40 e enters the concave cavity 34 of the piston crown surface 30. Is set to That is, the fifth spray Ge directed downward is injected so as to be directed to the piston crown surface 30 without reaching (attaching) the side wall surface 4 a (liner) of the cylinder 4.

  In this way, the fuel is injected so that the fifth spray Ge is directed to the piston crown surface 30, whereby the fuel adheres to the lower portion 4 a 1 of the side wall surface 4 a (liner) having the lowest temperature in the cylinder 4. In this way, the vaporization and atomization of the 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.

  Further, by injecting fuel in the vicinity of 90 ° CA, the fuel is injected at the time when the piston speed is the fastest and the in-cylinder flow is the largest, so vaporization atomization can be further promoted.

  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 is directed to the concave cavity 34 of the piston crown surface 30. Is set to That is, the first spray Ga directed upward is set to be directed to the inner peripheral surface 35 of the concave cavity 34.

  On the other hand, the second spray Gb is set so as to be directed to the receiving surface 37 in front of the concave cavity 34. However, even if the second spray Gb is directed to the receiving surface 37 as described above, the second spray Gb enters the concave cavity 34. That is, the second spray Gb that has collided with the receiving surface 37 and weakened momentum is drawn into the concave cavity 34 by the negative pressure generated after the first spray Ga passes.

  The fifth spray Ge located below the second spray Gb is also set so as to be directed to the receiving surface 37 and the horizontal surface portion 32 in front of it. However, like the second spray Gb, the fifth spray Ge is also drawn into the concave cavity 34 by the negative pressure generated by the first spray Ga.

  These pull-in behaviors 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 to (a), the 1st spray Ga is injected so that it may direct to the substantially hemispherical inner peripheral surface 35 of the concave cavity 34.
For this reason, as shown in (b), 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 8 side) ).

On the other hand, as shown in (a), the second spray Gb is injected so as to be directed toward the receiving surface 37.
For this reason, the second spray Gb collides with the receiving surface 37 to weaken the momentum, and drifts above the receiving surface 37. However, as shown in (b), after the first spray Ga has passed, a negative pressure that is drawn into the concave cavity 34 is generated, so that the second spray Gb is generated in the concave cavity 34 by this negative pressure. Be drawn into.
As described above, since the second spray Gb is drawn into the concave cavity 34, a rich mixture can be positioned around the spark plug 14.

Then, not only the second spray Gb but also the fifth spray Ge behind the second spray Gb is drawn into the concave cavity 34 by the negative pressure in a state where the momentum is weakened by colliding with the receiving surface 37 and the horizontal surface portion 32.
For this reason, the fifth spray Ge is also drawn into the concave cavity 34, and a richer air-fuel mixture is located around the spark plug 14.
Further, as shown in the plan view showing the injection state in FIG. 8, the second spray Gb that is injected so as to overlap the first spray is injected from the inclined surface 31a to the receiving surface 37 that is recessed by one step. It does not leak to the side (liner side) and is surely guided into the concave cavity 34.

  In particular, the receiving surface 37 is formed in a substantially U shape that gradually widens toward the cavity side (anti-injector side), so that the flow of the second spray Gb is not hindered and the concave cavity is surely formed. 34 can be guided.

  Moreover, since the fifth spray Ge is also sprayed so as to be overlapped in a plan view like the first spray Ga and the second spray Gb, it can receive a guide function by the receiving surface 37, It is surely guided into the cavity.

  9 to 12 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, (c) is a combination of the spray state of the first spray and the spray state of the second spray. is there. And the upper stage is a plan view and the lower end is a side view. Each dod is a spray droplet.

  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 collides with the receiving surface 37 and drifts 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 is 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). Further, the second spray Gb spreads around the concave cavity 34 as shown in (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. Further, the second spray Gb spreads and vaporizes as a whole as shown in (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.

  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, a receiving surface 37 that is recessed in one step so as to be connected to the concave cavity 34 is formed on the inclined surface 31 a of the raised portion 31, and the injector-side upper edge 34 a of the concave cavity 34 is anti-injector-side upper edge 34 b. By setting it lower and injecting fuel in the second half of the compression stroke in the operating region when the engine is cold, the first spray Ga is injected so as to enter the concave cavity 34, and the second spray Gb is applied to the receiving surface 37. It is set to inject to collide.

  As a result, the pent roof-shaped raised portion 31 is formed on the piston crown surface 30 to increase the compression ratio of the engine, but the second spray Gb is concave due to the negative pressure generated by the passage of the first spray Ga. It is drawn into the cavity 34. Since the receiving surface 37 is one step lower than the inclined surface 31 a of the raised portion 31, the second spray Gb is guided by the receiving surface 37 and guided into the concave cavity 34. Furthermore, since the injector-side upper edge end 34a of the concave cavity 34 is lower than the anti-injector-side upper edge end 34b, the first spray Ga and the second spray Gb are likely to enter the concave cavity 34 and hardly come out.

  For this reason, when the second spray Gb is drawn into the concave cavity 34 using the negative pressure while increasing the compression ratio of the engine, the second spray Gb is surely not affected by the negative pressure state. It can be placed in the concave cavity 34. Further, even if the second spray Gb is placed in the concave cavity 34, the first spray Ga and the second spray Gb are not easily emitted from the concave cavity 34, so that a large amount of the spray G can be retained in the concave cavity 34.

  Therefore, in a spark ignition direct injection engine that promotes catalyst activation when the engine is cold, a large amount of spray G is reliably put and retained in the concave cavity 34 while maintaining a high compression ratio of the engine E. In this way, the combustion state when the engine is cold can be stabilized.

In this embodiment, the receiving surface 37 has a substantially U shape formed so as to gradually spread toward the concave cavity 34 in a plan view.
Thus, after the second spray Gb collides with the receiving surface 37, it is smoothly guided to the concave cavity 34 side.
Therefore, it becomes possible to put the second spray Gb into the concave cavity 34 more reliably, and a rich air-fuel mixture can be reliably positioned around the spark plug 14.

Moreover, in this embodiment, the 5th nozzle 40e which injects the 5th spray Ge which overlaps with the 2nd spray Gb by planar view, and is located under the 2nd spray Gb by front view is provided.
Accordingly, since the fifth spray Ge is positioned below the second spray Gb during fuel injection, the fifth spray Ge collides with the receiving surface 37 and the like in addition to the second spray Gb.
Therefore, the second spray Gb and the fifth spray Ge arranged in the vertical direction can be guided to the concave cavity 34 side by using the receiving surface 37 and the horizontal surface portion 32, and more spray G can be contained in the concave cavity 34. Can be put in.
Therefore, a much richer air-fuel mixture (spray G) can be retained around the spark plug 14.

In this embodiment, the fuel injection end timing (F2) is set so that the injection end time is 345 ° CA, and the ignition timing (S) of the spark plug 14 is set after the top dead center. .
Thereby, when the piston 6 is positioned near the top dead center, it is possible to cause the spray to collide with the piston crown surface 30 accurately by injecting fuel, and the first spray Ga and the second spray Gb, etc. It is possible to enter the concave cavity 34 more precisely. Even if the ignition timing (S) of the spark plug 14 is set after the top dead center and the ignition timing is delayed, the rich air-fuel mixture is retained around the spark plug 14, so that the engine combustibility is ensured. can do.
Therefore, combustion can be performed with retarded ignition timing, and the exhaust gas temperature can be raised.

In this embodiment, in addition to the fuel injection (F2) in the compression stroke, the fuel injection (F1) is also performed in the intake stroke.
According to the above configuration, the cylinder interior can be so-called weakly stratified by performing the fuel injection in the two-split injection (F1, F2) performed in the intake stroke and the compression stroke.
Therefore, it is possible to improve the combustion stability when the ignition timing is retarded for combustion, and it is possible to raise the exhaust gas temperature more reliably.
Therefore, the temperature of the exhaust system can be raised while obtaining more stable combustion, and the catalyst can be activated.

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 pent roof-shaped slope corresponds to the slope 31a,
The second slope corresponds to the receiving surface 37,
The first nozzle hole corresponds to the first nozzle hole 40a,
The second nozzle hole corresponds to the second nozzle hole 40b,
The third nozzle hole corresponds to 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.

Explanation of symbols

6 ... Piston 11 ... Multi-hole injector 14 ... Spark plug 31 ... Raised portion 31a ... Inclined surface 34 ... Concave cavity 37 ... Receiving surface 40 ... Injection hole G ... Spray

Claims (5)

A spark ignition type direct injection engine comprising an injector provided with a plurality of injection holes for injecting a plurality of sprays obliquely downward on a peripheral edge of the combustion chamber ceiling wall, and having an ignition plug at the center of the combustion chamber ceiling wall,
A concave cavity corresponding to the spark plug is formed on the crown surface of the piston,
A pent roof-like slope is formed on the injector side of the cavity,
The injector has a first injection hole for injecting a first spray located on the upper side so as to be directed to the cavity in plan view;
Provided with at least two injection holes that overlap the first spray in a plan view and a second injection hole for injecting a second spray located below the first spray in a front view;
The pent roof-like slope is provided with a second slope that is one step lower where the second spray collides,
By forming the second inclined surface so as to be connected to the cavity, the injector side of the peripheral edge of the cavity is set lower than the anti-injector side,
A spark ignition type in which the second spray collides with the second slope so that the first spray enters the cavity by injecting fuel at a predetermined time in the second half of the compression stroke in the engine cold operating region. Direct injection engine. The spark-ignition direct injection engine according to claim 1, wherein the second inclined surface has a substantially U shape formed so as to gradually spread toward the cavity in a plan view. 3. The spark ignition direct injection engine according to claim 1, further comprising a third injection hole that injects a third spray that overlaps the second spray in a plan view and is located below the second spray in a front view. The fuel injection end timing of the predetermined timing is set to 3/4 or later of the compression stroke,
The spark ignition direct injection engine according to any one of claims 1 to 3, wherein an ignition timing of the spark plug is set after top dead center. The spark ignition type direct injection engine according to claim 4, wherein fuel injection is performed in an intake stroke in addition to fuel injection in the compression stroke.

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