JP2006274946A - Spark ignition type direct injection engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the increase of HC and smoke due to the deterioration of combustion by sufficiently promoting the vaporization of atomized fuel when an engine is cool or rotating at a low speed in an intermediate or high load area and reducing the adherence of the fuel to the wall surface of a cylinder in the direct injection engine in which multi-nozzle hole type injectors are disposed on the peripheral edge part of a combustion chamber in the cylinder so that the fuel can be jetted toward near an ignition plug. <P>SOLUTION: The orientations of nozzle holes 18e are set so that the geometric jetting area of an atomized fuel S1 toward near the ignition plug 16 is positioned between the valve stems 11a of two intake valves 11 in a plan view as viewed along a cylinder centerline Z. An ECU 40 comprises a fuel injection control part 40a starting fuel injection at the former of the intake stroke of the cylinder 2 in a specific operating state such that the engine is cool or the engine is rotating at a low speed in an intermediate or high load area and a means 40d changing the distribution of the flow velocity of intake air by closing flow control valves 34 and 35. A high-speed intake air from the intake valve 11 is set to directly and effectively hit the atomized fuel S1 heading near the ignition plug 16. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a spark ignition direct injection engine in which fuel is directly injected into a cylinder and ignited by a spark plug, and more particularly to a technical field relating to the formation of a mixture of fuel injected into a cylinder. Belongs.

  Conventionally, in this type of direct injection engine, since fuel is directly injected into a combustion chamber in a cylinder at a high pressure, it is difficult to form a uniform air-fuel mixture in the combustion chamber. Therefore, in general, direct injection engines use the flow of air (swirl and tumble) sucked into a cylinder to promote mixing of the intake air and fuel spray and vaporization of fuel droplets. That alone is often insufficient.

  That is, for example, when fuel is injected by an injector disposed at the peripheral edge toward the combustion chamber, the distance between the injector nozzle and the opposing cylinder wall surface is relatively short. In many cases, some of the liquid droplets adhere to the cylinder wall surface, and the vaporization of the fuel adhering to the cylinder wall surface is delayed or insufficient, resulting in the formation of a locally rich mixture. This contributes to the non-uniformity of the air-fuel mixture.

  In particular, if the fuel injection amount is increased as the load increases in a low rotation range where the flow in the cylinder is weak, the amount of fuel attached to the cylinder wall surface tends to increase, and when the engine is cold, the temperature of the cylinder wall surface is low. Since the delay in vaporization of the adhering fuel droplets tends to increase, the degree of non-uniformity of the air-fuel mixture as described above increases. Furthermore, if a part of the fuel droplets adhering to the cylinder wall surface is mixed into the engine oil without being vaporized, it causes a problem such as so-called oil dilution.

  In this regard, for example, in the direct injection engine disclosed in Patent Document 1, the fuel injection direction from the injector is deflected downward toward the top surface of the piston so that the fuel spray does not directly reach the cylinder wall surface. In addition, when the engine is cold, the fuel injection pressure is reduced and the penetration force of the fuel spray is weakened to prevent the fuel bounced off the piston top surface from adhering to the cylinder wall surface.

  Incidentally, the injector used in the conventional direct injection engine as described above is generally a swirler type in which fuel is injected as a swirling flow from a single injection port to form a substantially conical fuel spray, Since the spread angle of the fuel spray changes according to the cylinder internal pressure, it is easy to stratify the air-fuel mixture when the fuel is injected in the compression stroke of the cylinder, and the fuel is injected when the fuel is injected in the intake stroke. It has the feature of being easily dispersed widely throughout the cylinder.

  On the other hand, with a swirler injector, the diameter of a single nozzle cannot be made too small, so the fuel droplets ejected from here cannot be made too small, and the injection pressure is increased to promote fuel splitting. Even so, there is a difficulty that the atomization cannot be sufficiently achieved. Therefore, in recent years, as disclosed in, for example, Patent Document 2, a multi-injector type injector has been developed in which a plurality of very small injection holes are provided at the tip of the injector so that fuel is ejected from the plurality of injection holes, respectively. Has been.

  The engine of Patent Document 2 takes advantage of the features of the multi-injector type in which the orientations of a plurality of injection holes can be set individually, and is directed from the most injection holes of the injector arranged at the peripheral edge of the combustion chamber to the lower piston top surface. The fuel is injected and dispersed widely in the cylinder, and for example, the fuel spray from the two injection holes is directed toward the spark plug so that a combustible air-fuel mixture is more reliably formed in the vicinity of the spark plug. .

Also, in the same document, it is better to increase the fuel injection pressure (fuel pressure) at the time of start-up, high-load high-rotation and cold-cooling, which require a large amount of fuel injection and atomization, as compared with other times. The knowledge that is disclosed.
JP-A-9-68072 JP 2003-161224 A

  However, when the multi-injector type injector as described above is employed, in order to inject fuel from the minute injection port as described above, it is usually necessary to increase the fuel injection pressure as compared with the swirler type. As a result, the penetration force of the fuel spray tends to be relatively strong. For this reason, when the fuel pressure is increased at the time of high load or cold as in the latter conventional example (Patent Document 2), the penetration force of the fuel spray from each nozzle becomes considerably strong, particularly toward the vicinity of the spark plug. In fuel spraying, the amount of fuel that reaches the cylinder wall surface as droplets increases.

  Even if it reaches the cylinder wall surface in the form of droplets, the fuel spray of the multi-injector type injector is sufficiently atomized, so even if it is cold or after warming up, a little fuel Even if the amount of deposit is large, most of the fuel will be vaporized before ignition, and it is unlikely to be mixed into the engine oil as it is, but the vaporization of the fuel adhering to the cylinder wall surface is relatively slow. It is inevitable.

  And when the fuel vaporization is delayed or insufficient, the concentration of the air-fuel mixture increases locally, soot is generated by the combustion of the excessively concentrated portion, so-called smoke is generated, There also arises a problem that the soot mixes with the engine oil to lower the viscosity (hereinafter referred to as oil dilution).

  Further, as described above, part of the fuel spray directed to the vicinity of the spark plug adheres from the ceiling portion of the combustion chamber to the vicinity of the boundary with the peripheral wall portion (cylinder wall surface). Since the area where the surface does not propagate is formed, if the fuel is insufficiently vaporized or an excessively rich air-fuel mixture is formed as described above, as a result, the HC concentration in the exhaust gas is considerably high. There is also the problem of becoming.

  On the other hand, in the former conventional example (Patent Document 1), as described above, a swirler type injector, which is difficult to atomize the fuel, is employed, and when the fuel pressure is reduced when the engine is cold, Even though the penetrating force of the fuel spray can be weakened by this and the fuel droplets can be prevented from adhering to the cylinder wall surface, the drop of the fuel pressure causes the droplet diameter to increase throughout the fuel spray, resulting in cold In combination with this, fuel vaporization is insufficient. This causes a problem of increase in HC and smoke due to deterioration of combustion.

  The present invention has been made in view of such various points, and the object of the present invention is to achieve excellent atomization of fuel when the injector is disposed at the peripheral portion of the combustion chamber of the cylinder, but the penetration force of the spray. Focusing on the features of the multi-hole type that is relatively strong, when the engine is in a predetermined operating state, it sufficiently promotes the vaporization of fuel spray, reduces fuel adhesion to the cylinder wall surface, and worsens combustion This is to suppress the increase of HC and smoke due to the above.

  In order to achieve the above object, according to the present invention, when the engine is in a specific operating state such as when it is cold or during low rotation and high load, the intake valve and the intake port are at least against fuel spray directed toward the vicinity of the spark plug. Vaporization of the fuel droplets is promoted by directly and effectively blowing high-speed intake air flowing into the combustion chamber through an annular gap (curtain area) between the opening and the fuel. In addition to weakening the penetration force of the spray, the swirl flow in the cylinder was strengthened to reduce the adhesion of fuel spray to the cylinder wall.

  Specifically, in the invention of claim 1, a multi-injector type injector having a plurality of injection holes is disposed so as to inject fuel from a peripheral portion thereof into a combustion chamber in a cylinder, and from at least one injection hole. Is directed to a spark ignition direct injection engine in which the fuel spray is directed to the vicinity of the spark plug near the center of the combustion chamber and the fuel spray from another at least one nozzle is directed to the piston side. A fuel spray directed to the vicinity of the spark plug while the tip of the injector provided with the plurality of nozzle holes is located at the peripheral edge of the combustion chamber between two adjacent intake valves as viewed along the center line It is assumed that the direction of the nozzle hole from which the fuel spray is ejected is set so that the geometric spray area is located between the valve shafts of the two intake valves.

  Then, when the engine is in a specific operating state, it flows into the combustion chamber from an annular gap (hereinafter also referred to as a curtain area) between one of the two intake valves and the intake passage opening. An intake flow changing means for changing the flow of intake air so that the flow rate of intake air is greater than that of the other, and the flow velocity of the intake air toward at least the center of the cylinder is increased around the one intake valve; Fuel injection control means for controlling the injector so that fuel injection by the injector starts in the first half of the intake stroke of the cylinder.

  According to the above configuration, first, the fuel spray from at least one of the plurality of nozzle holes of the multi-hole injector is directed to the vicinity of the spark plug. The concentration can be adjusted to be appropriate. On the other hand, since the fuel spray from at least one other nozzle is directed to the piston side, it is advantageous to disperse the fuel widely in the cylinder to form a uniform air-fuel mixture.

  Further, the tip of the injector is located at the peripheral edge of the combustion chamber between the two intake valves, and the fuel spray toward the vicinity of the spark plug has a geometric spray area in plan view and the valve shafts of the two intake valves. Here, the geometric spray area is an area of fuel spray droplets when there is no flow of intake air or the like in the combustion chamber. The fuel spray positioned at the point passes through a position where high-speed intake air flowing into the combustion chamber directly from the curtain area of each of the two intake valves directly hits the fuel. can do.

  When the engine is in a specific operating state, the flow of intake air in the intake passage is changed by the intake flow changing means, and the flow rate of intake air flowing into the combustion chamber from one of the two intake valves is greater than the other. As a result, the swirl component of the intake air flow in the cylinder is strengthened. Further, the flow velocity of the intake air that radially flows out from the curtain area between the one intake valve and the intake passage opening is increased at least in the range toward the center of the cylinder.

  At the same time, the injection of fuel is started in the first half of the intake stroke of the cylinder by the control of the injector by the fuel injection control means, so that the fuel spray directed to the vicinity of the spark plug becomes the one intake air. When the intake flow velocity from the curtain area is highest during the lift of the valve, it passes through the vicinity of the high intake flow velocity range.

  In other words, when the engine is in a specific operating state, a range where the flow velocity is particularly increased among the high-speed intake air flow around the one intake valve, and near the spark plug when the intake air flow velocity is the highest. The fuel spray toward the vehicle passes, and a high-speed intake flow blows against the fuel spray. As a result, the vaporization of the fuel spray is promoted very effectively, and the fuel spray of the multi-injector type that is originally excellent in atomization is sufficiently vaporized to form a highly uniform mixture. It becomes like this.

  Since vaporization is promoted and the particle size of the droplet is further reduced, the momentum is reduced, so that the penetration force of the fuel spray toward the vicinity of the spark plug is weakened, and the droplet remains on the cylinder wall surface. The amount of fuel that reaches is reduced, and further, the fuel droplets that attempt to reach the cylinder wall surface are carried in the circumferential direction by the swirl flow in the cylinder that has been strengthened as described above. The amount of adhering to the cylinder wall surface decreases.

  Thus, the vaporization of the fuel spray is sufficiently promoted, the adhesion of fuel to the cylinder wall surface is reduced, and HC and smoke are increased and oil dilution is reduced even in specific operating conditions such as when the engine is cold or during low rotation and high load. Problems can be suppressed. As a result, it is possible to set the fuel injection timing in a wider range than before, so that an effect such as fuel consumption reduction can be obtained.

  In the spark ignition type engine having the above-described configuration, it is preferable that the fuel spray directed to the vicinity of the spark plug as described above has at least two geometrical spray areas of the fuel spray depending on the layout of the nozzle from which the fuel spray is ejected. The electrode is formed so as to be sandwiched from the side (invention of claim 2). In this way, the fuel droplets do not wet the electrode of the spark plug, and the gas mixture formed by the two fuel sprays on the side wraps around this electrode, so that the mixture formation suitable for stratified combustion is achieved. Yes.

  Preferably, as the intake flow changing means, the intake flow adjusting means for adjusting the flow of intake air so that the flow velocity distribution around one intake valve changes at least in the circumferential direction; Intake flow control means for controlling the intake flow adjustment means so that a relatively high flow velocity range around the intake valve moves toward the other intake valve side. Invention of 3).

  In this configuration, when the engine is in a specific operating state, the intake flow control means is controlled by the intake flow control means, and the flow velocity distribution of the intake air flow from the curtain area around one intake valve is circumferential. The range where the flow velocity is relatively high moves toward the other intake valve side. That is, among the high-speed intake air flowing from the curtain area into the combustion chamber, the flow velocity in the range where the fuel spray is directed toward the vicinity of the spark plug, in particular, is increased, thereby promoting fuel vaporization more effectively. be able to.

  More specifically, for example, when two intake passages communicating with the combustion chambers in the cylinders are provided so as to extend side by side, the intake flow adjusting means includes the two intake passages. Provided with a throttle valve that restricts the flow of intake air toward the other intake passage and an open / close valve that opens and closes the other intake passage. What is necessary is just to comprise so that the other intake passage may be closed by the said on-off valve when restrict | squeezing the flow of intake air (Invention of Claim 4).

  In this configuration, the other intake passage is closed by the open / close valve, whereby the amount of intake air flowing in one intake passage increases, and the flow rate of the intake air flowing from one intake passage through the curtain area into the combustion chamber is increased. The fuel vaporization becomes higher and fuel vaporization can be more effectively promoted, and the intake air flows into the combustion chamber from only one intake valve, thereby generating a strong swirl flow.

  In addition, the intake flow in the one intake passage is throttled by a throttle valve, and the intake flow is shifted toward the other intake passage so that the intake air flowing into the combustion chamber from the intake passage through the curtain area can be reduced. The flow velocity distribution can be changed so that a relatively high flow velocity range moves toward the other intake valve side.

  As another configuration of the intake flow changing means, an intake flow adjusting means is provided with a curved passage portion formed by bending the vicinity of the opening portion of one intake passage toward the cylinder center toward the downstream side, and the other intake passage. And the intake flow control means can close at least a part of the other intake passage by the open / close valve when the engine is in a specific operating state ( Invention of Claim 5).

  In this way, by closing the other intake passage with the opening / closing valve, the flow rate of intake air in one intake passage is increased, and the flow velocity of intake air toward at least the cylinder center around one intake valve is increased. The flow of intake can be changed.

  In such a case, more preferably, when the specific operation state of the engine is at least in a specific operation region defined by a load, the intake flow control means is provided, and in the specific operation region, the other intake passage is provided by an on-off valve. On the other hand, in the operating region on the higher load side than that, it is opened (invention of claim 6). In this way, when the engine is on a higher load side than the specific operating range and it is necessary to increase the charging efficiency of the cylinder, the passage cross-sectional area is expanded by opening the on-off valve and the like, thereby reducing the intake flow resistance. Can do.

  More specifically, for example, when the engine is in an operation range set to a medium load or a high load range of a low rotation range, the specific operation state may be set (invention of claim 7). Since the piston speed is low in the low rotation range, the intake air flow becomes weak. Nevertheless, in the medium to high load range where the fuel injection amount is relatively large, it becomes difficult for the fuel to vaporize naturally and the fuel to the cylinder wall surface. This is because the amount of adhesion tends to increase.

  Further, for example, the specific operation state may be set when the engine is cold. This is because the temperature of the cylinder wall surface is low at this time, and the delay in vaporization of the adhering fuel droplets tends to increase. In that case, it is preferable to provide a fuel pressure changing means for changing the fuel injection pressure by the injector to be lower than that in the same operation state after warm-up (invention of claim 8).

  By reducing the fuel injection pressure in this way, the penetration force of the fuel spray is weakened, and it is also possible to reduce the adhesion of fuel to the cylinder wall surface. In addition, if the fuel pressure is reduced in this way, the atomization of the fuel is worsened. However, as described above, the fuel droplets are vaporized by directly and effectively blowing the high-speed intake air flow from the curtain area. Will not cause any problems.

  Furthermore, in the spark ignition engine having the above-described configuration, the fuel injection control means causes the injector to divide the fuel into a plurality of times and injects the fuel into the first half of the intake stroke of the cylinder. In addition, it is preferable to control the injector (the invention of claim 9). If it carries out like this, the penetration force of a fuel spray can be weakened as a whole by division | segmentation injection, and the adhesion of the fuel to a cylinder wall surface can also be reduced by this.

  As described above, according to the spark ignition direct injection engine according to the present invention, the multi-injector type injector is disposed in the peripheral portion of the combustion chamber of the cylinder, and at least one fuel spray is directed to the vicinity of the spark plug. When the fuel spray from at least one other nozzle is directed toward the piston, the fuel spray is directed toward the vicinity of the spark plug in a specific operating state such as when the engine is cold or when the engine speed is low and the engine speed is low. On the other hand, by directly and effectively blowing a high-speed intake flow from the annular gap (curtain area) between the intake valve and the intake port opening, the vaporization of the fuel droplets is sufficiently promoted. The fuel spray is weakened by reducing the penetration force of the fuel spray and increasing the intake flow rate from one of the two intake valves more than the other to generate a strong swirl flow in the cylinder. It is possible to reduce the adhesion to the cylinder wall. As a result, problems such as an increase in HC and smoke and oil dilution can be sufficiently suppressed, and effects such as a reduction in fuel consumption can be obtained.

  In particular, if the engine is in an operation range set to a medium load or a high load range of a low rotation range, the specific operation state, the fuel injection amount increases despite the weak intake flow as a whole. The following effects are obtained and are extremely effective (invention of claim 7).

  Further, if the engine is cold when the specific operating state is set, and further, the fuel pressure is lowered to weaken the fuel spray penetration force, the above-described effect can be obtained more reliably and is extremely effective. (Invention of Claim 8).

Furthermore, if the penetration force of the fuel spray is weakened by dividing and injecting the fuel, the above effect can be further enhanced (invention of claim 9).

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the following description of the preferred embodiment is merely illustrative in nature, and is not intended to limit the present invention, its application, or its use.

  FIG. 1 shows the overall configuration of a spark ignition direct injection engine 1 according to the present invention, which is a multi-cylinder gasoline engine mounted on a vehicle. The engine 1 has a cylinder block 3 provided with a plurality of cylinders 2, 2,... (Only one is shown), and a cylinder head 4 is disposed on the cylinder block 3. In each cylinder 2, a piston 5 is inserted so as to reciprocate along the center line Z (see FIG. 2), and combustion occurs between the top surface of the piston 5 and the bottom surface of the cylinder head 4. A chamber 6 is formed. The piston 5 is connected to the crankshaft 7 by a connecting rod, and a crank angle sensor 8 for detecting the rotation angle (crank angle) is disposed on one end side of the crankshaft 7.

  The combustion chamber 6 for each cylinder 2 is of a pent roof type in which the ceiling portion is composed of two inclined surfaces on the intake and exhaust sides as shown in detail in FIGS. On the top surface of the piston 5 opposite to the inclined surface, inclined surfaces are formed on the intake and exhaust sides so as to correspond to the two inclined surfaces, respectively, so as to avoid interference with a fuel spray S from an injector 18 which will be described later. Cavity 5a is formed in In this embodiment, for convenience in the description of the cylinder 2 and the like, the direction of the cylinder center line Z is referred to as the up-down direction, the ceiling portion is the upper side, and the piston 5 is the lower side.

  The intake ports 9 and 9 and the exhaust ports 10 and 10 are formed on the inclined surfaces on the intake and exhaust sides of the ceiling portion of the combustion chamber 6 so as to open two each, and the opening to the combustion chamber 6 is formed. Are provided with intake and exhaust valves 11 and 12, respectively. The two intake ports 9 and 9 respectively extend obliquely upward from the combustion chamber 6 and open independently on one side of the cylinder head 4, while the two exhaust ports 10 and 10 In the middle, they merge into one and extend substantially horizontally, and open on the other side of the cylinder head 4.

  The intake valve 11 and the exhaust valve 12 are respectively driven by the crankshaft 7 via the timing belt with the two camshafts 13 and 14 disposed in the cylinder head 4. An opening / closing operation is performed at a predetermined timing. Although only shown in FIG. 1, the camshaft 13 on the intake side is provided with a known variable valve mechanism 15 (hereinafter abbreviated as VVT) that continuously changes the rotational phase with respect to the crankshaft 7 within a predetermined angular range. The operation timing of the intake valve 11 can be changed by the operation of the VVT 15.

  In addition, a spark plug 16 is disposed substantially at the center of the ceiling portion of the combustion chamber 6 so as to be surrounded by the four intake and exhaust valves 11,. An ignition circuit 17 (shown only in FIG. 1) is connected to the unit, and the ignition plug 16 is energized at a predetermined ignition timing for each cylinder 2. On the other hand, an injector 18 is disposed on the intake side of the combustion chamber 6 so as to be sandwiched between the two intake ports 9 and 9 below them.

  Each of the injectors 18 is a multi-hole type having a plurality of minute nozzle holes for injecting fuel, and the tip portion provided with the plurality of nozzle holes is between the two intake valves 11, 11. Located at the peripheral edge of the combustion chamber 6, the fuel is directly injected into the combustion chamber 6. More specifically, as shown in an example in FIG. 4, six injection holes 18 a,..., 18 b,. Fuel is injected from the nozzle holes 18a,..., 18b,.

  4 is a diagram schematically showing the inclination angles of the nozzle holes 18a,..., 18b,... With respect to the axial center when the tip end portion is viewed along the axial center of the injector 18. The two nozzle holes 18a,... Are inclined upward from the axial center of the injector 18 in the direction in which the fuel flows, and the fuel sprays S1,. If there is no flow of intake air or the like in the combustion chamber 6, it proceeds linearly toward the vicinity of the ignition plug 16 near the center of the combustion chamber 6, and the ignition plug 16 is V-shaped when viewed in the traveling direction. The electrode (ignition position) is surrounded from below.

  More specifically, among the three V-shaped fuel sprays S1,..., One fuel spray S1 located in the lower part of the V shape has its geometric spray area passing directly below the spark plug 16 electrode. The two fuel sprays S1 and S1 located at the top of the V-shape are formed so that the geometric spray area sandwiches the electrode of the spark plug 16 from the side. As a result, the three fuel sprays S1,... Vaporize without the fuel droplets getting wet to the electrode of the spark plug 16, and the air-fuel mixture formed thereby encloses the electrode.

  Further, when it is assumed that the upper three fuel sprays S1,... Injected from the peripheral edge of the combustion chamber 6 to the vicinity of the spark plug 16 closer to the center have no intake flow as described above, As schematically shown in FIG. 5, the two intake valves 11 and 11 are positioned between the valve shafts 11 a and 11 a. Thus, the geometric spray areas of the upper three fuel sprays S1,... Are positioned between the valve shafts 11a, 11a of the two intake valves 11, 11 in plan view, so that, for example, the injector 18 is connected to the cylinder. Even when the intake valves 11 and 11 are lifted when operating in the intake stroke of 2, the interference between the intake valves 11 and 11 and the fuel sprays S1,.

  On the other hand, the direction of the lower three nozzle holes 18b,... Is set so that the fuel spray is separated from the upper three fuel sprays S1,. . That is, the upper one of the three is formed along the axis of the injector 18, and the remaining two nozzle holes 18 b and 18 b are inclined downward from the axis of the injector 18 in the direction of fuel flow. ing. Since the axis of the injector 18 itself is inclined downward with respect to the cross section of the cylinder 2, the fuel sprays S2,... Ejected from the three nozzle holes 18b,. It progresses downward (toward the piston 5).

  The layout of the nozzle holes 18a,..., 18b,... Can realize desirable air-fuel mixture formation in various combustion states such as stratified combustion, weakly stratified combustion, and uniform combustion. That is, even when the fuel injection amount is small as in the idling operation, if the injector 18 is operated at an appropriate time in the compression stroke of the cylinder 2, the fuel from the upper three injection holes 18a,. By the sprays S1,..., An air-fuel mixture having excellent ignitability can be formed in the vicinity of the electrode of the spark plug 16.

  On the other hand, during high load operation with a large amount of fuel injection, the injector 18 is operated in the intake stroke of the cylinder 2 so that the fuel sprays S1,..., S2,. It is possible to form a substantially uniform air-fuel mixture in the cylinder 2 by being dispersed. At this time, fuel sprays S1,... From the upper three nozzle holes 18a,... Flow into the combustion chamber 6 from an annular gap (curtain area) between the intake valve 11 being lifted and the intake port 9 opening. On the other hand, fuel sprays S2,... From the lower three injection holes 18b,... Are formed in the entire cylinder 2 while proceeding downward so as to follow the descending piston 5. Get involved in a big flow.

  Further, if fuel is injected by the injector 18 in both the intake stroke and the compression stroke of the cylinder 2, a substantially uniform mixture is formed in the entire cylinder 2, and the mixture concentration in the vicinity of the spark plug 16 is appropriately set. This can increase the ignition stability. This is particularly effective when, for example, the ignition timing is greatly retarded in order to quickly warm up the exhaust system catalyst 39 immediately after the engine 1 is started.

  A common fuel distribution pipe 19 is connected to all the cylinders 2, 2... To the injector 18 for each cylinder 2, and high-pressure fuel from the fuel supply system 20 is distributed and supplied. Yes. The fuel supply system 20 is configured, for example, schematically as shown in FIG. 6, and the main fuel passage 22 that connects the fuel distribution pipe 19 and the fuel tank 21 has a low pressure from the upstream side toward the downstream side. A fuel pump 23, a low pressure regulator 24, a fuel filter 25, a high pressure fuel pump 26, and a high pressure regulator 27 are arranged in this order.

  Then, the fuel sucked up from the fuel tank 21 by the low-pressure fuel pump 23 is regulated by the low-pressure regulator 24, filtered by the fuel filter 25, and pumped to the high-pressure fuel pump 26. A part of the fuel further boosted by the high-pressure fuel pump 26 is adjusted in flow rate by the high-pressure regulator 27 and supplied to the fuel distribution pipe 19, while the remaining fuel is pressure-adjusted by the low-pressure regulator 28 while being supplied to the fuel tank 21. Returned.

  In this manner, the pressure (fuel pressure) of the fuel supplied to the fuel distribution pipe 19 becomes approximately the fuel injection pressure by the injector 18. In this embodiment, a fuel pressure sensor 29 is disposed in the fuel distribution pipe 19 so as to detect the pressure state of the fuel therein, and based on a signal from the sensor 29, the ECU 40 performs the high pressure regulator as will be described later. By controlling 27 (fuel pressure changing means), the fuel pressure is adjusted within a preset range (for example, 12 to 20 MPa).

  In FIG. 1, an intake passage 30 is connected to one side surface of the cylinder head 4 located on the right side of the engine 1 so as to communicate with the intake ports 9 and 9 of each cylinder 2. The intake passage 30 is for supplying air filtered by an air cleaner (not shown) to the combustion chamber 6 of each cylinder 2 of the engine 1, and an electric motor (not shown) is connected to the common passage upstream of the surge tank 31. An electric throttle valve 32 driven by a motor and a throttle position sensor 33 for detecting the position of the valve body (throttle opening) are provided.

  On the other hand, the intake passage 30 is an independent passage for each cylinder 2 downstream of the surge tank 31, and the downstream end portion of each of the independent passages is further branched into two to communicate with the intake ports 9, 9 individually. is doing. The two branch passages 30a and 30b for each cylinder 2 extend side by side as indicated by phantom lines in FIG. 3, and flow control valves 34 and 35 as intake flow adjusting means are provided on both of them. Has been. Note that reference numerals 30a and 30b are attached to the branch passages only in FIG.

  As shown in FIG. 3, the flow control valves 34 and 35 are both made of butterfly valves, and are arranged in one of the two branch passages 30a and 30b (the one located on the left side of the figure). The provided flow control valve 34 has a substantially half of the valve body close to the other branch passage cut out, and in the closed state, the branch passage 30a is closed while leaving the substantially half passage cross section. It has become. When substantially half of one branch passage 30a is closed in this way, the flow of intake air is throttled and deviated closer to the other branch passage 30b. In this sense, the flow control valve 34 of the one branch passage 30a is Also referred to as a throttle valve.

  Also, the flow control valve 35 disposed in the other branch passage 30b located on the right side in FIG. 3 is an on-off valve that opens and closes the entire passage section (hereinafter also simply referred to as an on-off valve 35). If the other branch passage 30b is closed, all of the intake air flows toward the one branch passage 30a, and flows into the cylinder 2 only from one intake port 9 (the left side in FIG. 3) connected to the branch passage 30a. It becomes like this. Here, the valve bodies of the throttle valve 34 and the on-off valve 35 are coupled to a common shaft, and when this shaft is rotated by an actuator (not shown) and the other branch passage 30b is closed by the on-off valve 35, Approximately half of the one branch passage 30 a is closed by the throttle valve 34.

  In this way, the intake air flows through only one of the two intake ports 9, 9, and the flow is throttled by the throttle valve 34, so that the flow of the intake air flowing into the cylinder 2 from the intake port 9 is considerably large. Get faster. In addition, since intake air does not flow to the other intake port 9, a strong intake swirl flow is generated in the cylinder 2. Further, in the branch passage 30 a communicating with the one intake port 9, the flow of intake air is shifted toward the other branch passage 30 b, so that the space between the opening portion (valve seat) of the intake port 9 and the umbrella portion of the intake valve 11. In the flow velocity distribution of the intake air flowing into the combustion chamber 6 from the curtain area, the flow from the intake valve 11 toward the center of the cylinder is the fastest as shown in FIG.

  That is, generally, the flow of the intake air flowing into the cylinder becomes faster in the direction in which the intake port extends, and in the four-valve type like this embodiment, the flow velocity is relatively high in the flow velocity distribution of the intake air around the intake valve. The high range (the angular range centered on the intake valve shaft) is not shown, but is generally toward the exhaust valve side (the same applies when the flow control valves 34 and 35 are opened in the engine 1 of this embodiment). Is).

  On the other hand, if the flow control valves 34 and 35 are closed as described above, as shown in FIG. 7, the overall flow of the intake air flowing radially toward the combustion chamber 6 in the curtain area of one intake port 9 is increased. At the same time, the flow of the intake air is shifted upstream of the intake port 9 so that the relatively high flow velocity range moves around the intake valve 11 toward the other intake valve 11 (counterclockwise in the figure). However, the flow in the direction indicated by the arrow in the figure is roughly the fastest.

  At this time, the flow velocity distribution of the intake air in the longitudinal section at the center of the cylinder shown as AA in FIG. 8 is as shown in FIG. 8 (a), and the flow of the intake air that is offset as described above blows radially from the curtain area. By taking out, it turns out that especially the flow velocity becomes high in the range (I) (range shown with a dotted line in a figure) near the ceiling part of the combustion chamber 6. FIG. Also, the flow velocity distribution in the cross section of the cylinder shown as B-B in the same figure is as shown in Fig. (B), and the flow velocity is particularly high in the same range (I) as described above and is generated in the cylinder 2. It can be seen that due to the strong swirl flow, a relatively fast circumferential flow is formed at the exhaust peripheral edge (range (II)).

  Here, the angle range C-C shown in FIGS. 8A and 8B is roughly the whole of the fuel sprays S1,..., S2, ... from the injection holes 18a, ..., 18b, ... of the injector 18. According to this figure, according to the figure, the area of fuel spray injected from the upper three injection holes 18a,... Toward the vicinity of the spark plug 16 has a particularly high flow rate as described above. It can be seen that it is included in the range (I). From this, if the fuel injection by the injector 18 is started at a predetermined timing in the intake stroke in synchronization with the opening operation of the intake valve 11, the upper three fuel sprays S1,. As described above, the intake air flow speeded up as described above is directly blown, thereby effectively promoting fuel vaporization.

  Exhaust gas for exhausting burned gas (exhaust gas) from the combustion chamber 6 of each cylinder 2 on the side of the cylinder head opposite to the side where the intake passage 30 is connected as shown in FIG. A passage 36 is connected. The upstream side of the exhaust passage 36 is composed of an exhaust manifold 37 that branches into each cylinder 2 and communicates with the exhaust port 10. A sensor for detecting the oxygen concentration in the exhaust is provided at a collection portion of the exhaust manifold 37. 38 is disposed. A catalyst 39 for purifying harmful components in the exhaust is disposed in the exhaust passage 36 downstream of the exhaust manifold 37.

  An engine control unit 40 (hereinafter referred to as ECU) is provided to perform operation control of the engine 1 configured as described above. As is well known, it includes a CPU, a memory, an I / O interface circuit, etc., and measures at least signals from the crank angle sensor 8, the fuel pressure sensor 29, the oxygen concentration sensor 38, and the air flow rate in the intake passage 30. A signal from the airflow sensor 41 that performs, a signal from the water temperature sensor 42 that detects a coolant temperature (engine water temperature) of a water jacket (not shown), and an accelerator opening that detects an operation amount (accelerator opening) of an accelerator pedal (not shown). The signal from the sensor 43 is input.

  Then, the ECU 40 determines the operating state (for example, load state and engine speed) of the engine 1 based on the signal from the sensor and the like, and according to this, the VVT 15, the ignition circuit 17, the injector 18, and the fuel supply system 20, the electric throttle valve 32, the flow control valves 34, 35 and the like are controlled. That is, for example, if the engine 1 is operated in a stratified combustion state, fuel is injected by the injector 18 in the compression stroke of the cylinder 2 as schematically shown in FIG. Is burned in a state of being distributed in layers.

  At this time, in order to reduce the pumping loss, the throttle valve 32 may be opened relatively large, and the average air-fuel ratio of the combustion chamber 6 at this time is the theoretical air-fuel ratio (A / F≈14.7). It becomes leaner than. If the flow control valves 34 and 35 are closed at that time, the swirl component of the flow generated in the combustion chamber 6 can be strengthened.

  On the other hand, if the engine 1 is operated in a uniform combustion state, fuel is injected by the injector 18 in the intake stroke of the cylinder 2 as shown in FIG. 9B, and a substantially uniform mixture is formed in the combustion chamber 6. Let it burn above. At this time, the fuel injection amount, throttle opening, etc. are controlled so that the air-fuel ratio of the air-fuel mixture becomes substantially the stoichiometric air-fuel ratio or richer than that. In order to reduce the intake resistance, it is preferable to open the flow control valves 34 and 35.

  At this time, the fuel is divided into a plurality of times and injected by the injector 18, and the plurality of fuel injections may all start in the first half of the intake stroke of the cylinder 2 as shown in FIG. 9 (c). it can. If split injection is performed in this way, the penetration force of the spray can be moderately reduced without significantly impairing the atomization of the fuel.

  Further, the control of the fuel pressure to the injector 18 is performed mainly on the basis of the engine rotation speed by switching the characteristics between when cold (cold) and after warm (warm) as shown in FIG. 10, for example. The high pressure regulator 27 of the fuel supply system 20 is controlled to change the fuel pressure in two stages so that it is relatively low on the low rotation side after warm-up and high on the high rotation side. In addition, the fuel pressure is lowered when the engine is cold compared to after the engine is warmed, and the degree of decrease is increased particularly on the low rotation side.

  In the example shown in the figure, the fuel pressure after warm-up is changed in two steps, high and low. However, the present invention is not limited to this, and the fuel pressure may be gradually increased as the engine speed increases. Alternatively, the fuel pressure may be maintained substantially constant regardless of the engine speed. In addition, the fuel pressure during cold operation is substantially constant on the low rotation side and gradually increased as the rotation increases on the high rotation side. However, the present invention is not limited to this, and the fuel pressure may be changed stepwise. Alternatively, it may be maintained substantially constant regardless of the engine speed.

  Control of the injector 18, the fuel supply system 20, the throttle valve 32, and the flow control valves 34 and 35 as described above is realized by executing a control program electronically stored in the memory of the ECU 40 by the CPU. . In that sense, the ECU 40, as described above, the fuel injection control unit 40a that controls the operation of the injector 18, the fuel pressure control unit 40b that controls the high pressure regulator 27 of the fuel supply system 20, the throttle control unit 40c that controls the throttle valve 32, An intake flow control unit 40d that controls the flow control valves 34 and 35 is provided in the form of software.

(Control in specific operating conditions)
By the way, when fuel is injected in the intake stroke of the cylinder 2 in order to make the engine 1 in a uniform combustion state as described above, the penetration force of the fuel spray becomes relatively strong because the inside of the cylinder 2 has a negative pressure. End up. In the fuel sprays S1,... Directed from the upper three injection holes 18a,... Of the multi-injector type injector 18 arranged at the peripheral edge of the combustion chamber 6 to the vicinity of the spark plug 16, as described above, from the injection holes 18a,. In combination with the relatively short distance to the cylinder wall surface, a part of the fuel does not vaporize but reaches the wall surface of the cylinder 2 as a droplet and adheres.

  Even when the liquid droplets reach the cylinder wall surface as they are, in the case of the multi-hole injector 18, the fuel liquid droplets are sufficiently atomized, so that most of them normally vaporize before ignition. Therefore, the possibility of being mixed into engine oil is low. However, the fuel droplets adhering to the cylinder wall surface are delayed in vaporization or insufficiently vaporized, so that an excessively rich portion of the air-fuel mixture is locally formed in the vicinity of the fuel droplets. Soot is generated and so-called smoke is generated, and the problem of oil dilution occurs that the soot mixes with engine oil and lowers its viscosity.

  Also, as described above, the upper three fuel sprays S1,... Directed toward the vicinity of the spark plug 16 are attached from the ceiling portion of the combustion chamber 6 to the vicinity of the boundary with the peripheral wall portion (cylinder wall surface). In the vicinity of the top dead center of the cylinder 2, the space between the ceiling portion of the combustion chamber 6 and the top surface of the piston 5 becomes very narrow, and a region where the flame surface does not propagate is formed. There is also a problem that a part of the rich portion of the air-fuel mixture is discharged from the cylinder 2 without burning, and the HC concentration in the exhaust gas becomes considerably high.

  Such a problem is caused by, for example, when the fuel injection amount is increased in response to an increase in engine load in a low rotation range where the piston speed is relatively low and the flow in the cylinder 2 is weak, thereby Since the amount of adhesion increases, it tends to be a big problem. Also, when the engine is cold, the temperature of the cylinder wall surface is low, and the delay in vaporization of the adhering fuel droplets becomes large.

  Therefore, in this embodiment, the engine 1 is operated at a low rotation speed and a medium and high load as shown by hatching in FIG. 11, for example. In a specific operating state such as when the engine is cold or when the engine is in a cold state, the fuel may adhere to the cylinder wall as described above. The high-speed intake air flow around the intake valve 11 is directly and effectively sprayed on the upper three fuel sprays S1,... To promote the vaporization of the fuel droplets, thereby penetrating the fuel spray. In addition to weakening the force, a strong swirl flow is generated in the cylinder 2 to reduce the adhesion of fuel spray to the cylinder wall surface.

  That is, when the engine 1 is cold or in the low-rotation medium-high load range after warm-up, the fuel injection control unit 40a of the ECU 40 first starts fuel injection in the first half of the intake stroke of the cylinder 2. The injector 18 is controlled. In this way, the fuel sprays S1,... Injected from the three injection holes 18a,... On the upper side of the injector 18 toward the vicinity of the spark plug 16 have the highest intake flow velocity from the curtain area during the lift of the intake valve 11. Furthermore, it passes through a high flow velocity range (range (I) shown in FIG. 8) near the curtain area.

  The fuel injection timing (start timing) may be, for example, between 1/5 of the intake stroke of the cylinder 2 and 1/2 of the intake stroke when the engine 1 is on the low speed side. More preferably, after intake top dead center (ATDC), 40 to 80 ° CA. By doing so, the high-speed intake flow blows directly on the fuel sprays S1,... In the high flow velocity range (I), and promotes the fuel vaporization.

  At this time, the flow control valves 34 and 35 are closed by the intake flow control unit 40d of the ECU 40, whereby the intake flow field in the cylinder 2 changes as described above with reference to FIGS. Vaporization is effectively promoted. That is, when intake air flows from only one of the two intake ports 9, 9, the intake flow velocity increases as a whole, and a strong intake swirl flow is generated in the cylinder 2.

  Further, the flow of intake air flowing into the combustion chamber 6 radially from the curtain area between the opening of the intake port 9 and the intake valve 11 is changed in the circumferential direction because the flow of intake air in the one intake port 9 is offset. The area of the upper three fuel sprays S1,... Toward the vicinity of the spark plug 16 is included in the particularly fast flow range (I), and the fuel spray S1,. The inspiratory flow comes to blow directly.

  That is, the fuel sprays S1,... Toward the vicinity of the spark plug 16 pass through the range (I) in which the flow velocity is particularly increased in the high-speed intake flow from the curtain area when the intake flow velocity is the highest. And vaporization is promoted very effectively. For this reason, in the fuel spray S1,... From the multi-injector type injector 18 which is originally excellent in atomization, the particle size of the droplet is further reduced and the momentum is reduced, so that the fuel spray S1,. The force is weakened, and the amount of fuel that reaches the cylinder wall surface as droplets decreases.

  Further, the fuel droplets that attempt to reach the cylinder wall surface are carried in the circumferential direction by the swirl flow in the cylinder 2 strengthened as described above (the range (II) in FIG. 8B). See), and the amount of fuel adhering to the cylinder wall surface is sufficiently reduced.

  In addition, when the engine is cold, the high pressure regulator 27 of the fuel supply system 20 is controlled by the fuel pressure control unit 40b of the ECU 40 so that the fuel pressure becomes lower than that in the same operating state after warming up (FIG. 10). (see (b)), the penetrating force of the fuel sprays S1,... is further weakened, and this can also reduce the adhesion of fuel to the cylinder wall surface.

  Reducing the fuel pressure in this manner is disadvantageous for the fuel splitting when ejected from the nozzle holes 18a,..., 18b,. As for the upper fuel sprays S1,..., There is no problem because the vaporization of the fuel droplets can be effectively promoted by the high-speed intake flow from the curtain area as described above. The advantage of having fewer drops is greater.

  Therefore, according to the spark ignition direct injection engine 1 according to this embodiment, the multi-injector type injector 18 is arranged at the peripheral edge of the combustion chamber 6 in the cylinder 2 and the ignition plug 16 is inserted from the upper three injection holes 18a,. The fuel is injected toward the vicinity of the fuel tank and the fuel is injected downward from the lower three nozzle holes 18b, which is desirable in any combustion state such as stratified combustion or uniform combustion. Mixture formation can be realized.

  Further, when the engine is in a specific operating state such as when it is cold or during a low rotation and high load, a high-speed intake flow from the curtain area with respect to the fuel sprays S1,. Is directly and effectively sprayed to sufficiently evaporate, thereby weakening the penetration force of the fuel sprays S1,... And generating a strong swirl flow in the cylinder 2, thereby Adhesion can be reduced.

  In this way, the vaporization of fuel spray can be sufficiently promoted and the adhesion of fuel to the cylinder wall surface can be reduced, so that the increase in HC and smoke and the problem of oil dilution can be sufficiently suppressed, resulting in a wider range than before. This makes it possible to set the fuel injection timing, so that the effect of reducing fuel consumption can be obtained.

  FIG. 12 shows how the smoke concentration changes in the direct injection engine having substantially the same configuration as that of this embodiment by changing the state of the intake air flow in the cylinder 2 and changing the fuel injection timing in the intake stroke. Show. In the figure, the solid line shows this embodiment, and the dotted line and broken line show a tumble flow and a swirl flow respectively generated in the cylinder. As shown in the figure, regardless of the state of intake air flow in the cylinder 2, if the fuel injection timing is advanced too much, the amount of fuel adhering to the top surface of the piston 5 increases, resulting in a high smoke concentration. Become.

  On the other hand, when the injection timing is retarded, the amount of fuel adhering to the cylinder wall surface increases due to the attenuation of the intake flow, the fuel vaporization worsens, and the time from injection to ignition is shortened. However, there is a tendency that the vaporization becomes insufficient, the combustion deteriorates, and the smoke concentration increases. However, if fuel vaporization is effectively promoted by a high-speed intake flow from the curtain area as in this embodiment, and a strong swirl flow is generated in the cylinder 2, a tumble flow or a swirl flow is used. It can be seen that the adhesion of the fuel to the cylinder wall surface can be greatly reduced as compared with the case where only the fuel injection is performed, the fuel vaporization is improved and the combustibility is improved, so that the injection timing can be greatly retarded as shown.

  In this way, it becomes possible to set the fuel injection timing in a wider range than before, which increases the degree of freedom in setting the ignition timing, which is advantageous for reducing fuel consumption and purifying exhaust gas, for example, cold start Immediately after that, the ignition timing can be significantly retarded for rapid warm-up of the catalyst 39.

  In addition, when the engine 1 is cold, by reducing the fuel pressure and weakening the penetration force of the fuel sprays S1,..., S2,. The increase in smoke can be suppressed more effectively.

  FIGS. 13 (a) and 13 (b) show the relationship between the fuel injection pressure (fuel pressure) and the HC and smoke concentrations in the exhaust in the direct injection engine 1 of this embodiment. As shown by the solid lines in FIG. It can be seen that the increase in HC and smoke can be suppressed by lowering the fuel pressure when cold. In particular, the effect of smoke is great, which indicates that the formation of a rich mixture is suppressed by reducing fuel adhesion to the cylinder wall surface.

  Note that after warming up (warm), HC does not change much regardless of the fuel pressure, but it can be seen that the smoke concentration can be reduced by increasing the fuel pressure as compared to cold as in this embodiment. This is considered to be due to further promotion of atomization of fuel spray.

(Other embodiments)
The configuration of the present invention is not limited to the above-described embodiment, but includes other various configurations. That is, in the embodiment, as shown in FIG. 4, six nozzle holes 18a,..., 18b,... Are laid out three at the top and bottom at the tip of the injector 18, but the number and layout of the nozzle holes are limited thereto. For example, as shown in FIGS. 14 (a) to (f), the number of nozzles may be 5 or less, and conversely, it may be 7 or more.

  The layout of the nozzle holes 18a,... Shown in FIGS. 11A and 11B is suitable for dispersing fuel in the cylinder 2 to achieve a uniform combustion state, and particularly in the case of FIG. A relatively large number of nozzles 18a,... Can be arranged so that the center of the fuel spray does not interfere with the lifted intake valve 11. Further, the layout of the nozzle holes 18a,..., 18b,... Shown in the same figure (c) to (f) are the nozzle holes 18a,. The nozzles 18b for injecting fuel so as to be dispersed in the other directions are provided so as to be adapted to both uniform combustion and stratified combustion.

  Further, in the above-described embodiment, as an intake flow adjusting means for adjusting the intake flow velocity distribution around the intake valve 11, as shown in FIG. 3, the two branch passages 30 a and 30 b are provided for each cylinder 2 of the intake passage 30. The flow control valves 34 (throttle valves) and 35 (open / close valves) disposed respectively are used, and the valve body of the throttle valve 34 is cut out from a substantially half near the other branch passage 30b. This is not a limitation.

  That is, as shown in FIG. 15, for example, only the upper half of the valve body of the throttle valve 34 that is close to the other branch passage 30b may be cut out, or conversely, only the lower side as shown in FIG. May be cut off. As shown in FIG. 15, if the upper quarter of the valve body close to the other branch passage 30b is cut away, the intake flow is shifted to the upper side of the intake port 9 when the valve body is closed. The flow in the extending direction becomes relatively strong, and the swirl component is further strengthened in the flow in the cylinder 2.

  On the other hand, as shown in FIG. 16, when the lower side of the valve body, which is close to the other branch passage 30b, is cut out by about 1/4, the intake flow is shifted to the lower side of the intake port 9 when the valve body is closed. Since the flow that radially expands between the opening to the combustion chamber 6 and the umbrella portion of the intake valve 11 is strengthened, the intake flow velocity directly hitting the fuel sprays S1,. Become.

  Further, for example, as schematically shown in FIG. 17, the intake flow changing means uses one intake port 9 (upper intake port in the same figure) as a so-called helical port, near the opening thereof, toward the center of the cylinder toward the downstream side. It is also possible to form a passage bending portion that curves toward the side and to arrange a flow control valve 35 that is an on-off valve in the other branch passage 30b as in the above embodiment.

  In this way, when the engine 1 is in a specific operation state, the flow of intake air from one branch passage 30a to the one intake port 9 is closed by closing the flow control valve 35 by the intake flow control unit 40d of the ECU 40. By increasing the amount, the flow velocity of the intake air flowing out from the curtain area between the one intake port opening and the intake valve 11 can be increased as a whole.

  Furthermore, in the above embodiment, the fuel pressure control characteristics are switched between when the engine 1 is cold and after it is warmed up so that the fuel pressure when it is cold is lower than that in the same operating state after warming up. However, the present invention is not limited to this, and the fuel pressure may be continuously changed according to the engine water temperature, for example, as shown in FIG. Further, the temperature state of the engine 1 can be detected based on the temperature of the engine oil, for example, regardless of the engine water temperature. In the figure, the broken line indicates the control characteristics when the fuel pressure is switched between when cold and after warming up as in the above embodiment.

  Moreover, in the said embodiment, although the specific operation area | region of the engine 1 is made into the low rotation middle high load area | region as shown, for example in FIG. 11, it is not restricted to this, The specific operation area | region is a medium load thru | or high load area | region of a low rotation area. May be set as appropriate, or may be defined only by the load state.

  Further, in the above embodiment, when the engine 1 is in a specific operating state, the fuel injection control unit 40a of the ECU 40 causes the injector 18 to supply the fuel a plurality of times (in the example shown in FIG. 9 twice). ), And the injector 18 may be controlled so that the plurality of fuel injections all start in the first half of the intake stroke of the cylinder 2. In this way, the penetration force of the fuel spray as a whole can be weakened by the divided injection, and this can further reduce the adhesion of fuel to the cylinder wall surface.

  As described above, the spark-ignition direct injection engine according to the present invention has a fuel injection even in a specific operation state such as cold, low rotation, medium / high load, etc., when a multi-injector type injector is arranged at the periphery of the combustion chamber. Vaporization of spray is sufficiently promoted, fuel adhesion to the cylinder wall surface is reduced, and problems such as increase in HC and smoke in exhaust and oil dilution can be suppressed, and effects such as fuel efficiency reduction can also be obtained. Therefore, it is suitable for an automobile engine, for example.

1 is a diagram illustrating an overall configuration of a spark ignition direct injection engine according to an embodiment of the present invention. It is a front view which expands and shows the structure of a cylinder. It is the same perspective view. It is a figure which shows typically the layout of each nozzle hole of an injector. It is explanatory drawing which shows the position of the geometric spray area of an upper fuel spray seeing along a cylinder centerline. It is explanatory drawing which shows the structure of a fuel supply system. It is the figure which calculated | required the flow velocity distribution around the intake valve when a flow control valve was closed by CFD. It is the figure which calculated | required the flow velocity distribution of the intake air of the range containing an upper fuel spray by CFD, (a) shows the longitudinal cross section near the center of a cylinder, (b) shows the cross section near a ceiling part. It is explanatory drawing which shows typically the injection timing of the fuel by an injector. It is explanatory drawing which shows the characteristic of the fuel pressure control based on an engine speed, (a) is after warm-up, (b) shows the time of cold. It is a map figure which shows an example of the specific driving | operation area | region of an engine. It is a graph which shows the change of the smoke density | concentration by the change of a fuel-injection timing compared with a prior art example. It is a graph which shows the change of HC and a smoke density | concentration by the change of a fuel pressure. FIG. 5 is a view corresponding to FIG. 4 showing another embodiment of the layout of the nozzle hole. FIG. 4 is a view corresponding to FIG. 3 showing another embodiment of the flow control valve. FIG. 4 is a view corresponding to FIG. 3 showing another embodiment of the flow control valve. FIG. 6 is a view corresponding to FIG. 5 showing another embodiment in which one intake port is a helical port. It is a characteristic view of other fuel pressure control based on engine water temperature.

Explanation of symbols

1 Engine 2 Cylinder 6 Combustion chamber 9 Intake port (intake passage)
DESCRIPTION OF SYMBOLS 11 Intake valve 16 Spark plug 18 Injector 18a At least 1 nozzle 18b Another at least 1 nozzle 27 High pressure regulator (fuel pressure change means)
30 Intake passage 30a, 30b Branch passage (intake passage)
34 Flow control valve (throttle valve)
35 Flow control valve (open / close valve)
40 ECU
40a Fuel injection control unit (fuel injection control means)
40b Fuel pressure control unit (fuel pressure changing means)
40d Intake flow control unit (intake flow control means)
Z cylinder center line

Claims (9)

A multi-hole type injector having a plurality of nozzle holes is disposed so as to inject fuel from a peripheral portion thereof into a combustion chamber in a cylinder, and the fuel spray from at least one nozzle hole is an ignition plug closer to the center of the combustion chamber In a spark ignition direct injection engine directed to the vicinity and fuel spray from another at least one nozzle to the piston side,
When viewed along the center line of the cylinder, the tip of the injector provided with the plurality of nozzle holes is located at the peripheral edge of the combustion chamber between two adjacent intake valves and directed toward the vicinity of the spark plug. The direction of the nozzle hole from which the fuel spray is ejected is set so that the geometric spray area of the fuel spray is located between the valve shafts of the two intake valves.
In a specific operation state, of the two intake valves, the flow rate of the intake air flowing into the combustion chamber from the annular clearance between one intake valve and the intake passage opening is larger than the other, and An intake flow changing means for changing the flow of the intake air so that the flow velocity of the intake air at least toward the cylinder center around the intake valve is increased;
And a fuel injection control means for controlling the injector so that fuel injection by the injector starts in the first half of the intake stroke of the cylinder in the specific operation state. The spark ignition direct injection engine of claim 1,
A spark ignition direct injection engine characterized in that the fuel spray toward the vicinity of the spark plug is formed so that at least two geometric spray areas of the fuel spray sandwich the electrode of the spark plug from the side. In the spark ignition direct injection engine according to claim 1 or 2,
The intake flow changing means is
Intake air flow adjusting means for adjusting the flow of intake air so that the flow velocity distribution around one intake valve changes at least in the circumferential direction;
An intake air flow control means for controlling the intake air flow adjusting means so that a relatively high flow velocity range around the one intake valve moves toward the other intake valve in the specific operation state. This is a spark ignition direct injection engine. The spark ignition direct injection engine according to claim 3,
Two intake passages communicating with the combustion chambers in the cylinders are provided to extend side by side,
The intake air flow adjusting means is disposed in one of the two intake air passages, and includes a throttle valve that restricts the flow of intake air so as to be biased toward the other air intake passage, and an open / close valve that opens and closes the other air intake passage. The spark ignition type direct injection engine is configured to close the other intake passage by the opening / closing valve when the throttle valve restricts the flow of intake air in the one intake passage. In the spark ignition direct injection engine according to claim 1 or 2,
The intake flow changing means is
An intake flow adjusting means having a passage bending portion formed by bending the vicinity of the opening portion of one intake passage toward the cylinder center toward the downstream side, and an on-off valve disposed in the other intake passage;
A spark ignition direct injection engine comprising: an intake flow control means for closing at least a part of the other intake passage by the on-off valve in a specific operation state. In the spark ignition direct injection engine according to claim 4 or 5,
The specific operation state is a specific operation region defined by at least the load,
The spark-ignition direct-injection engine is characterized in that the intake air flow control means closes the other intake passage by an on-off valve in the specific operation region, and opens it in an operation region on the higher load side. In the spark ignition direct injection engine according to any one of claims 1 to 6,
The spark-ignited direct injection engine characterized in that the specific operation state is an operation region set to a medium load to a high load region in a low rotation region. In the spark ignition direct injection engine according to any one of claims 1 to 6,
A spark ignition type direct current characterized by comprising a fuel pressure changing means for changing the fuel injection pressure by the injector at this time to be lower than that in the same operation state after warm-up when the specific operation state is cold. Jet engine. The spark ignition direct injection engine according to any one of claims 1 to 8,
The fuel injection control means divides and injects the fuel into a plurality of times by the injector, and controls the injector so that each of the plurality of fuel injections starts in the first half of the intake stroke of the cylinder. A spark ignition direct injection engine.

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