JP2012241592A - Gasoline engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gasoline engine that achieves suitable compression self-ignition combustion by suitably raising the temperature of an air-fuel mixture by an ignition assist.SOLUTION: A control means 50 causes each of nozzles holes 21a of an injector 21 to inject fuel in a preset specific operation area A3 of the engine, causes an ignition plug 20 to supply ignition energy to the fuel injected from each of the nozzle holes 21a of the injector 21 before the fuel reach a wall surface of a combustion chamber 6 to raise the temperature of the air-fuel mixture with the ignition energy, and then the air-fuel mixture id combusted by self-ignition. The ignition plug 20 is arranged at a position where the separation distance L between ignition point S1 of the ignition plug 20 and a tip part I1 of the injector 21 is 20-25 mm.

Description

  The present invention relates to a gasoline engine in which a piston is reciprocated by burning an air-fuel mixture of at least a part of gasoline and air in a combustion chamber.

  Conventionally, in the gasoline engine field, a combustion mode in which an air-fuel mixture is forcibly ignited by spark discharge from an ignition plug has been common, but in recent years, instead of combustion by such spark ignition, so-called compression self-ignition Research is underway to apply combustion to gasoline engines. The compression self-ignition combustion is to compress the air-fuel mixture generated in the combustion chamber with a piston and to ignite the air-fuel mixture in a high temperature / high pressure environment regardless of spark ignition. Compressed self-ignition combustion is combustion in which self-ignition occurs at various locations in the combustion chamber at the same time, and is said to have a shorter combustion period and higher thermal efficiency than combustion by spark ignition.

  Here, in order to stably realize the compression self-ignition combustion, it is necessary to increase the temperature of the air-fuel mixture in the combustion chamber more reliably. On the other hand, for example, as disclosed in Patent Document 1, the internal EGR amount is increased to thereby increase the temperature of the air-fuel mixture, or the air-fuel mixture is ignited as disclosed in Patent Document 2. A method of performing so-called ignition assist that increases the temperature of an air-fuel mixture by supplying energy and burning a part of the air-fuel mixture has been studied.

JP 2007-85241 A JP 2011-021553 A

  When performing the ignition assist, depending on the state of the air-fuel mixture to which ignition energy is applied, SOOT and NOx may be generated and exhaust performance may deteriorate, or proper compression self-ignition combustion may not be realized after ignition.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a gasoline engine capable of appropriately increasing the temperature of the air-fuel mixture by ignition assist and realizing appropriate compression self-ignition combustion.

  The inventors of the present invention have found the following as a result of intensive studies to solve the above problems.

  That is, in order to suppress the generation of SOOT or the like, the equivalence ratio of the air-fuel mixture in the vicinity of the ignition point to which the ignition energy is applied needs to be sufficiently small, and most of the fuel in the vicinity of the ignition point needs to be steam. On the other hand, in a state where the fuel injected from the injector diffuses throughout the combustion chamber and the equivalence ratio of the air-fuel mixture in the combustion chamber is extremely small overall, the ignition energy required to burn the air-fuel mixture is increased. When the ignition energy is increased in this way, not only a part of the fuel is combusted, but the entire air-fuel mixture in the combustion chamber is combusted, and there is a possibility that the compression auto-ignition combustion may not be realized. Therefore, it is necessary to supply ignition energy to the fuel injected from the injector before it spreads over the entire combustion chamber, that is, before the fuel reaches the wall of the combustion chamber. And the position of the ignition point which satisfies such conditions is substantially common to a plurality of injection pressures, and is a position of 20 mm or more and 25 mm or less from the injection port.

  Therefore, based on this discovery, the present inventors have created a gasoline engine in which the ignition timing and ignition position satisfy the above conditions.

  That is, the present invention is a gasoline engine that reciprocates a piston by burning a mixture of fuel and air, at least part of which is made of gasoline, in a combustion chamber, and a plurality of nozzles that inject the fuel into the combustion chamber Is formed at the front end, and the front end portion faces the combustion chamber at the radial center of the combustion chamber ceiling, and the injector disposed on the combustion chamber ceiling and the combustion chamber ceiling An ignition plug that is disposed radially outside the injector and supplies ignition energy to the air-fuel mixture; and a control means for controlling the fuel injection operation by the injector and the ignition operation by the ignition plug; The injection holes of the injector expand radially outward as the fuel approaches the crown surface of the piston through the injection holes. So that each axis is inclined radially outward as the piston crown surface is approached, and the spark plug has a separation distance of 20 mm between its ignition point and the tip of the injector. It is disposed at a position that is 25 mm or less, and the control means injects fuel from each injection port of the injector and injects from each injection port of the injector in a predetermined specific operation region of the engine. Before the fuel reaches the wall of the combustion chamber, ignition energy is supplied from the spark plug, and after the temperature of the mixture is increased by the ignition energy, the mixture is burned by self-ignition. (Claim 1).

  According to the present invention, before the fuel injected from the injector reaches the wall surface of the combustion chamber, ignition energy is supplied to the air-fuel mixture containing the fuel, and the separation distance between the ignition point and the injection nozzle of the injector is 20 mm or more. It is set to 25 mm or less. Thereby, since the ignition energy is supplied in a state where the equivalence ratio is sufficiently small and the fuel is sufficiently vaporized, the generation of NOx and SOOT is suppressed, and only the air-fuel mixture near the ignition point is Combusting properly, the air-fuel mixture in the combustion chamber is heated appropriately, and proper compression self-ignition combustion is realized.

  In the present invention, it is preferable that the injector has eight or more nozzle holes at the tip thereof (claim 2).

  According to this configuration, fuel atomization, that is, fuel evaporation, is promoted, so that proper combustion in the vicinity of the ignition point is realized while the generation of NOx and SOOT is more reliably suppressed.

  In the present invention, it is preferable that the spark plug protrudes from the combustion chamber ceiling toward the combustion chamber so that the ignition point is located in the vicinity of an axis of a specific nozzle hole of the injector in a side view. (Claim 3).

  In this way, ignition energy is efficiently transmitted to the fuel injected from the specific nozzle, and proper combustion near the ignition point is realized.

  Further, in the above configuration, an injector storage portion that is recessed in a direction away from the piston crown surface is formed in a central portion in a radial direction of the combustion chamber ceiling, and a tip portion of the injector is a portion of the injector storage portion. It faces the inside of the injector housing in a state where it is located in the central portion in the radial direction, and the inner peripheral surface of the injector housing is radially outward from the fuel passage region from each nozzle hole of the injector toward the wall surface of the combustion chamber. It is preferable to have a shape surrounding the fuel passage region at a position spaced apart from each other.

  In this way, the amount of protrusion of the spark plug into the combustion chamber can be reduced while avoiding the deterioration of fuel atomization due to the collision and adhesion of the fuel injected from each nozzle to the inner peripheral surface of the injector housing. Can be small. That is, as the tip of the injector is disposed at a position further away from the piston crown surface, the ignition point can be separated from the piston crown surface. Therefore, the protruding amount of the spark plug can be reduced.

  Specifically, the inner peripheral surface of the injector storage portion has a substantially conical surface shape with the radial center portion of the combustion chamber ceiling as a top portion, and the tip portion of the injector is located at the top portion. (Claim 5).

  Further, in the present invention, the piston has a concave cavity that is provided in a central portion in the radial direction of the crown surface and is recessed in a direction away from the combustion chamber ceiling, and the ignition plug has an ignition point at the cavity. It is preferable that it is arrange | positioned in the position which becomes radial inner side rather than the radial direction outer edge of this (Claim 6).

  In this way, by retracting the tip of the spark plug into the cavity, the collision between the spark plug and the piston crown surface can be avoided more reliably.

  Here, the control means causes the fuel to be injected from the injector in at least two times of the front-stage injection and the rear-stage injection in the specific operation area, and the fuel injected at the time of the rear-stage injection is ignited by the ignition plug. In the first stage injection, fuel is injected during the compression stroke and before the second stage injection, and the outer peripheral part of the combustion chamber located radially outside the cavity of the piston by the injected fuel. In addition, the air-fuel mixture is richer than the inside of the cavity, and the post-injection is performed by injecting fuel at a predetermined time from the latter stage of the compression stroke to the early stage of the expansion stroke. It is preferable that a richer air-fuel mixture is formed inside the cavity than when the pre-injection is performed (Claim 7).

  According to this configuration, the fuel is injected in at least two injection timings (front-end injection and rear-stage injection) after the compression stroke, so that separate spaces in the combustion chamber (the outer periphery of the combustion chamber and the inside of the cavity) Therefore, these air-fuel mixtures can be self-ignited and burned independently near the compression top dead center. For this reason, the situation in which the separately injected fuel is mixed and combusted at the same time is avoided, and an increase in combustion noise due to a sudden rise in pressure in the combustion chamber and a large amount of SOOT due to local oxygen shortage are effectively prevented. The In addition, the spark plug is disposed radially inward from the radially outer end of the cavity and supplies ignition energy to the fuel injected at the time of subsequent injection, and this ignition energy is transmitted to the outer periphery of the combustion chamber. An adverse effect on the air-fuel mixture is suppressed. Specifically, this ignition energy is supplied to the mixture of fuel and air of the pre-injection existing in the outer peripheral portion of the combustion chamber, so that combustion starts at the outer peripheral portion before the compression top dead center. Thus, it is possible to more reliably suppress the situation where the work amount is reduced or the flame propagation starts and the compression self-ignition combustion is prevented.

  As described above, according to the present invention, it is possible to achieve proper compression self-ignition combustion while improving exhaust performance.

It is a figure showing the whole gasoline engine composition concerning one embodiment of the present invention. It is the schematic of the combustion chamber periphery of the gasoline engine shown in FIG. It is the schematic which expands and shows a part of FIG. It is the schematic for demonstrating the relationship between an ignition point, fuel spray, etc. FIG. (A)-(c) is a figure for demonstrating the relationship between the equivalence ratio at the time of ignition, and exhaust performance. (A)-(c) is a figure for demonstrating the relationship between the equivalence ratio at the time of ignition, and exhaust performance. It is the figure which showed the equivalence ratio and state of fuel spray. It is the figure which showed the relationship between the injection pressure and the elapsed time after injection, and the equivalent ratio and state of fuel spray. It is the figure which showed the relationship between the injection pressure and the elapsed time after injection, and the equivalent ratio and state of fuel spray. It is a block diagram which shows the control system of the said engine. It is a figure which shows an example of the control map for selecting the combustion form according to the driving | running state of an engine. It is a time chart for demonstrating the control content in the 1st driving | operation area | region (A1) of FIG. It is a time chart for demonstrating the control content in the 2nd driving | running area | region (A2) of FIG. It is a time chart for demonstrating the control content in the 3rd driving | running area | region (A3) of FIG. (A)-(f) is a figure for demonstrating typically the fuel injection performed in the said 2nd driving | operation area | region (A2), and combustion of the air-fuel mixture based on it. It is the figure which showed the combustion chamber periphery of the gasoline engine which concerns on other embodiment of this invention. It is the figure which showed the combustion chamber periphery of the gasoline engine which concerns on other embodiment of this invention. It is the figure which showed the combustion chamber periphery of the gasoline engine which concerns on other embodiment of this invention. It is the figure which showed the combustion chamber periphery of the gasoline engine which concerns on other embodiment of this invention shown in FIG.

(1) Overall Configuration of Engine FIG. 1 is a diagram showing an overall configuration of an engine according to an embodiment of the present invention. The engine shown in the figure is a reciprocating piston type multi-cylinder gasoline engine mounted on a vehicle as a power source for driving driving. An engine body 1 of this engine includes a cylinder block 3 having a plurality of cylinders 2 (only one of which is shown in the drawing) arranged in a direction orthogonal to the paper surface, and a cylinder head 4 provided on the upper surface of the cylinder block 3. And a piston 5 inserted in each cylinder 2 so as to be slidable back and forth. The fuel supplied to the engine body 1 is mainly composed of gasoline. The fuel only needs to have gasoline as a main component, and the contents thereof may be all gasoline, or may be gasoline containing ethanol (ethyl alcohol) or the like. The bore diameter of the cylinder block 3 is 60 mm to 100 mm. In this embodiment, the bore diameter is set to 86 mm.

  The piston 5 is connected to the crankshaft 7 via a connecting rod 8. In response to the reciprocating motion of the piston 5, the crankshaft 7 rotates about its central axis.

  A combustion chamber 6 is formed above the piston 5. An intake port 9 and an exhaust port 10 are opened in the combustion chamber 6. The cylinder head 4 is provided with an intake valve 11 and an exhaust valve 12 for opening and closing the ports 9 and 10, respectively. The illustrated engine is a so-called double overhead camshaft (DOHC) engine. Two intake ports 9 and two exhaust ports 10 are provided for each cylinder 2, and two intake valves 11 and two exhaust valves 12 are also provided.

  Here, the “combustion chamber”, in a narrow sense, refers to a space formed above the piston 5 when it is at top dead center, but the combustion chamber 6 here refers to the upper and lower sides of the piston 5. It refers to the space formed above it regardless of position (combustion chamber in a broad sense).

  The intake valve 11 and the exhaust valve 12 are driven to open and close in conjunction with the rotation of the crankshaft 7 by valve mechanisms 13 and 14 including a pair of camshafts (not shown) disposed in the cylinder head 4. The

  A CVVL 15 is incorporated in the valve operating mechanism 13 for the intake valve 11. The CVVL 15 is called a continuously variable valve lift mechanism and continuously (steplessly) changes the lift amount of the intake valve 11. The CVVL 15 is provided so that the lift amounts of all the intake valves 11 of the engine can be changed. When the CVVL 15 is driven, the lift amounts of the pair of intake valves 11 in each cylinder 2 are changed simultaneously. It has become.

  The CVVL 15 having such a configuration is already known, and as a specific example thereof, a link mechanism that reciprocally swings the cam for driving the intake valve 11 in conjunction with the rotation of the camshaft, and the arrangement of the link mechanism (lever ratio). And a stepping motor that changes the swing amount of the cam (the amount by which the intake valve 11 is pushed down) by electrically driving the control arm (for example, JP, 2007-85241, A).

  The valve mechanism 14 for the exhaust valve 12 incorporates a VVL 16 that is an ON / OFF type variable valve lift mechanism (variable valve lift mechanism) that enables or disables the function of depressing the exhaust valve 12 during the intake stroke. ing. That is, the VVL 16 has a function of enabling the exhaust valve 12 to be opened not only in the exhaust stroke but also in the intake stroke, and switching between performing or stopping the valve opening operation of the exhaust valve 12 during the intake stroke. Yes. The VVL 16 is provided corresponding to all the exhaust valves 12 of the engine, and can individually perform or stop the valve opening operation during the intake stroke with respect to the pair of exhaust valves 12 of each cylinder 2.

  The VVL 16 having such a configuration is already known, and as a specific example thereof, the exhaust valve 12 is pushed down during the intake stroke separately from a normal cam for driving the exhaust valve 12 (a cam for pushing the exhaust valve 12 during the exhaust stroke). Examples include a sub cam and a so-called lost motion mechanism that enables or disables transmission of the driving force of the sub cam to the exhaust valve 12 (see, for example, JP-A-2007-85241).

  When the exhaust valve 12 is opened during the intake stroke in addition to during the exhaust stroke due to the action of the VVL 16, the high-temperature exhaust flows back from the exhaust port 10 to the combustion chamber 6 during the exhaust stroke, and the combustion chamber 6 A large amount of exhaust remains. That is, a large amount of internal EGR gas is secured. On the other hand, when the exhaust valve 12 is opened only during the exhaust stroke, the internal EGR gas amount is suppressed to a small amount or not.

  An intake passage 28 and an exhaust passage 29 are connected to the intake port 9 and the exhaust port 10 of the engine body 1, respectively.

  The intake passage 28 is provided with a common passage portion 28c composed of a single passage, a surge tank 28b provided at an upstream end portion of the common passage portion 28c, and branched for each cylinder 2. The surge tank 28b And a branch passage portion 28 a that connects the intake port 9 of each cylinder 2.

  The exhaust passage 29 is provided for each cylinder 2 by branching to a common passage portion 29c composed of a single passage, and connects the upstream end of the common passage portion 29c and the exhaust port 10 of each cylinder 2. And a branch passage portion 29a.

  An external EGR device 30 is provided between the intake passage 28 and the exhaust passage 29 to recirculate a part of the exhaust gas passing through the exhaust passage 29 to the intake passage 28. The external EGR device 30 is provided with an EGR passage 31 communicating with the common passage portions 28c and 29c of the intake passage 28 and the exhaust passage 29 and a flow rate of exhaust gas that is provided in the middle of the EGR passage 31 and passes through the EGR passage 31. An EGR valve 32 to be controlled and a water-cooled EGR cooler 33 for cooling the exhaust gas passing through the EGR passage 31 are provided.

  A throttle valve 25 for adjusting the amount of intake air passing through the intake passage 28 is provided in the common passage portion 28 c of the intake passage 28. However, in this embodiment, the lift amount of the intake valve 11 is adjusted by the CVVL 15, the amount of internal EGR gas in the combustion chamber 6 is adjusted by the VVL 16, and further, the return to the intake passage 28 is returned by the external EGR device 30. The amount of exhaust gas is adjusted. Therefore, it is possible to adjust the amount of air (fresh air) introduced into the combustion chamber 6 without operating the throttle valve 25 based on these operations. For this reason, the throttle valve 25 is kept fully open or close to it except when the engine is stopped.

  A catalyst converter 35 for purifying exhaust gas is provided in the common passage portion 29 c of the exhaust passage 29. For example, a three-way catalyst is incorporated in the catalytic converter 35, and harmful components in the exhaust gas passing through the exhaust passage 29 are purified by the action of the three-way catalyst.

  Various sensors are attached to the engine body. For example, a water temperature sensor SW1 for detecting the temperature of the engine coolant, a rotation angle (crank angle) of the crankshaft 7, and a crank angle sensor SW2 for detecting the engine speed, and the camshaft angle are detected to detect the cylinder temperature. A cam angle sensor SW3 that outputs a signal for determination (determination of whether each cylinder is in an intake stroke, compression stroke, expansion stroke, or exhaust stroke) is attached to the engine body.

  FIG. 2 is a view showing the periphery of the combustion chamber 6. As shown in FIG. 2 and the like, a concave cavity 40 is provided in the radial center portion of the inner surface of the combustion chamber 6, that is, the crown surface of the piston 5 constituting a part of the wall surface. The cavity 40 has an upward opening 40a facing the injector 21 at the upper end, and the area (opening area) of the opening 40a is the maximum cross-sectional area inside the cavity 40 (each height of the cavity 40). The maximum horizontal cross-sectional area at the position) is set. That is, the cavity 40 is formed in a constricted shape so that the inner diameter becomes narrower toward the upper side in the range from the opening 40a to a predetermined depth.

  An annular concave portion 41 having an annular shape in plan view is provided on the crown surface of the piston 5 located radially outside the cavity 40 so as to surround the cavity 40. The annular recess 41 is formed so that the height decreases as it goes radially outward. The maximum depth of the annular recess 41 (the depth of the outermost peripheral portion) is set to be shallower than the depth of the cavity 40.

  Further, an annular standing wall portion 42 protruding upward from the annular recess 41 is provided on the outermost peripheral portion of the piston 5 positioned further radially outward than the annular recess 41. The protruding height of the standing wall portion 42 is set to be the same as the portion (lip portion) surrounding the opening 40 a at the upper end of the cavity 40.

  An injector storage portion 62 that is recessed in a direction away from the crown surface of the piston 5 is provided at a central portion in the radial direction of the ceiling surface 60 of the combustion chamber 6 constituted by the bottom surface of the cylinder head 4. Hereinafter, the crown surface side (lower side in FIG. 2) of the piston 5 will be referred to as the lower side, and the injector storage part 62 side (upper side in FIG. 2) will be referred to as the upper side. Of the ceiling surface 60 of the combustion chamber 6, a portion 63 radially outside the injector storage portion 62 is a plane orthogonal to the axis of the piston 5. That is, the ceiling surface 60 of the combustion chamber 6 has a shape in which the injector storage portion 62 that is recessed upward is formed in the central portion in the radial direction of a so-called flat head.

  The injector storage portion 62 has a substantially conical shape with the central portion in the radial direction of the ceiling surface 60 of the combustion chamber 6 as a top portion, and an inner peripheral surface 62a thereof has a substantially conical shape. More specifically, a mounting portion 66 that is formed inside the cylinder head 4 and to which the injector 21 is attached is opened at the central portion in the radial direction of the injector storage portion 62, and the inner peripheral surface of the injector storage portion 62 62a extends downward from the opening 66a of the mounting portion 66 in a truncated cone shape.

  The cylinder head 4 is provided with one set of spark plugs 20 and injectors 21 for each cylinder 2. FIG. 3 shows an enlarged view around the spark plug 20 and the injector 21.

  A fuel supply pipe 23 (see FIG. 1) is connected to the injector 21, and fuel (fuel mainly composed of gasoline) supplied through the fuel supply pipe 23 is injected from the tip end portion I 1 of the injector 21. The The injector 21 is a so-called multi-hole injector. In the present embodiment, as shown in FIG. 4, the injector 21 has twelve injection holes 21 a at its tip end portion I1.

  The tip end portion I1 of the injector 21 is located at the top portion of the injector storage portion 62, that is, the opening 66a of the attachment portion 66, and the axis line u1 thereof is the diameter of the top portion of the injector storage portion 62, that is, the ceiling surface 60 of the combustion chamber 6. It is attached to the attachment portion 66 so as to pass through the center in the direction and face the injector storage portion 62 from the top of the injector storage portion 62. The respective nozzle holes 21a are formed at equal intervals on a circumference centered on the axis u1 of the injector 21, and the axis line u2 of each nozzle hole 21a, that is, the opening direction of each nozzle hole 21a is inclined radially outward. It faces downward (the crown side of the piston 4). That is, the axis u2 of each nozzle hole 21a constitutes a generatrix of a conical surface having the tip end I1 of the injector 21 as a vertex and the axis u1 of the injector 21 as a central axis. When fuel is injected from each injection hole 21 a of the injector 21, the fuel is injected radially so as to expand radially outward as it approaches the crown surface of the piston 5. In the present embodiment, the axis u2 of each nozzle hole 21a is inclined 45 degrees with respect to the axis u1 of the injector 21. That is, the angle α1 in FIG. 3 is set to 45 degrees.

  The inner peripheral surface 62a of the injector housing portion 62 is located radially outside the fuel passage region F1 so that the fuel injected from the injector 21 does not collide with the inner peripheral surface 62a. In the present embodiment, the inner peripheral surface 62a of the injector storage portion 62 extends in parallel to the axis u2 of the injection hole 21a of the injector 21 at the radially outer side from the fuel passage region F1 in a side view. The fuel passage region F1 is a region through which the fuel injected from each nozzle 21a passes before reaching the wall surface of the combustion chamber 6, and the axis u2 of each nozzle 21a is the central axis with each nozzle 21a as a vertex. This is a conical region with the apex angle being the spray angle α2 (see FIG. 3) of each nozzle 21a. In the present embodiment, the spray angle α2 is set to 15 degrees.

  The spark plug 20 discharges sparks from its tip in response to power supply from an ignition circuit (not shown), supplies ignition energy to the air-fuel mixture in the combustion chamber 6, and ignites the air-fuel mixture. In the present embodiment, the spark plug 20 is connected to the inside of the combustion chamber 6 from a plane portion 63 (hereinafter, appropriately referred to as a flat head surface) 63 radially outside the injector storage portion 62 of the ceiling surface 60 of the combustion chamber 6. It is attached in a state of facing.

  In the present embodiment, in the mounted state, an intermediate portion between the outer electrode and the inner electrode provided at the tip of the spark plug 20, that is, the ignition point S 1, as shown in FIG. It is located in the middle of the axes u2_1 and u2_2 of the adjacent nozzle holes 21a.

  Further, in the attached state, as shown in FIG. 3, the ignition point S1 is located on the axis u2 of the injection hole 21a located closest to the ignition plug 20 in a side view. The separation distance L between the ignition point S1 and the tip end portion I1 of the injector 21 is more specifically, the separation distance between the ignition point S1 and the radial center portion of the tip end portion I1 of the injector 21 is 20 mm or more and 25 mm or less. Is set to The separation distance L is a line extending from the tip end portion I1 of the injector 21 toward the ignition point S1, and is a distance along a line passing through the middle of the axis lines u2_1 and u2_2 of the two injection holes 21a close to the ignition point S1. . In the present embodiment, the separation distance L is set to 20 mm. Setting criteria for the separation distance L will be described later.

  Further, in the attached state, the ignition point S <b> 1 is located radially inward from the outer peripheral edge of the cavity 40. In other words, the diameter of the cavity 40 is set such that the ignition point S <b> 1 is positioned radially inward from the outer peripheral edge of the cavity 40.

(2) Criteria for setting the position of the ignition point S1 FIGS. 5 (a) to 5 (c) and FIGS. It is the figure which showed how it receives supply of and changes with time. Time elapses in the order of (a), (b), and (c) in each figure. FIG. 5A and FIG. 6A show the state of the air-fuel mixture before ignition energy is supplied. (B) and (c) of FIG. 5 and FIG. 6 each show a change in the state of the air-fuel mixture accompanying a change in time after the ignition energy is supplied. As shown in each figure, when ignition energy is supplied, the air-fuel mixture starts to combust, and accordingly, the temperature of the air-fuel mixture (including burned gas) rises.

  Each of FIGS. 5 and 6 shows a region where SOOT and NOx are generated. Specifically, the region E1 where the equivalence ratio of the air-fuel mixture in the combustion chamber 6 is high (in a rich state) and is equal to or higher than a predetermined temperature is a region where SOOT is mainly generated. The region E2 where the temperature is high is a region where NOx is mainly generated.

  5 and 6 are different from each other in the position (ignition point) of the combustion chamber 6 to which ignition energy is applied. FIG. 5 shows a result when the ignition point is set at a position where an air-fuel mixture with an equivalence ratio of 2 is present (point S1 in FIG. 5A). FIG. 6 shows a result when the ignition point is set at a position where an air-fuel mixture with an equivalence ratio of 1 is present (point S2 in FIG. 6A). Comparing FIG. 5 (b) and FIG. 6 (b) and FIG. 5 (c) and FIG. 6 (c), the amount of the air-fuel mixture contained in the NOx generation region E2 is almost the same, When the ignition point is set at a position where an air-fuel mixture with an equivalence ratio of 2 is present, the equivalence ratio is higher and the amount of the air-fuel mixture with a higher temperature is larger, that is, the mixture included in the SOOT generation region E1. The amount of energy is large and more SOOT is produced. Thus, when ignition energy is supplied to a high region where the equivalence ratio is close to 2, combustion starts in a region where air is insufficient and the temperature in this region increases, resulting in a large amount of SOOT being generated.

  For this reason, in order to suppress the amount of SOOT generated to a lower level and improve the exhaust performance, it is necessary to make the equivalent ratio of the air-fuel mixture in the region where the ignition energy is supplied sufficiently smaller than 1.

  Here, when the period from the time when the fuel is injected into the combustion chamber 6 to the time when the ignition energy is supplied to the air-fuel mixture in the combustion chamber 6 is long, the premixing of the air-fuel mixture proceeds to mix the fuel. The equivalent ratio of the whole gas becomes small. However, it is necessary to increase the ignition energy in order to burn the air-fuel mixture that is sufficiently mixed and has a very small equivalence ratio. If large ignition energy is supplied to the air-fuel mixture that has been sufficiently premixed in this way, there is a risk that flame propagation may start, not only the temperature rise of the air-fuel mixture, and a mixture with a moderately low equivalence ratio. I need to supply ignition energy.

  Further, it is known that when the ignition energy is supplied to the liquid fuel, SOOT is likely to occur, and it is necessary to supply the ignition energy to a region where most of the fuel is vapor.

  As described above, in order to appropriately increase the temperature of the air-fuel mixture to the ignition temperature during compression without increasing the flame performance while improving exhaust performance, the injected fuel diffuses throughout the combustion chamber 6 and is premixed. Before the injection, that is, before the injected fuel reaches the wall surface of the combustion chamber 6 and the equivalence ratio of the air-fuel mixture is sufficiently smaller than 1, and the region where most of the fuel is steam is ignited It can be said that it is necessary to supply energy.

  Accordingly, the present inventors set the equivalence ratio distribution of the air-fuel mixture in the combustion chamber 6 after fuel injection and the state of fuel spray (liquid) so as to set the region satisfying the above conditions as the ignition point. Or steam). Specifically, as shown in FIG. 7, the distribution of the equivalence ratio of the air-fuel mixture containing the fuel in the liquid state and the distribution of the equivalence ratio of the air-fuel mixture containing the fuel in the vapor state Each was examined. The graph on the left side of FIG. 7 shows the distribution of the equivalence ratio of the air-fuel mixture containing liquid fuel. In this graph, the horizontal axis r indicates the distance from the axis u1 of the injector 21 in the direction orthogonal to the axis u1, and the left side indicates that the distance from the axis u1 of the injector 21 is farther. On the other hand, the graph on the right side of FIG. 7 shows the distribution of the equivalence ratio of the air-fuel mixture containing fuel vapor. In this graph, the horizontal axis r indicates the distance from the axis u1 of the injector 21 in the direction orthogonal to the axis u1, and the right side indicates that the distance from the tip of the injector 21 is farther. In both the left and right graphs, the vertical axis Z is the distance from the tip end portion I1 of the injector 21 in the direction of the axis u2 of the injection hole 21a of the injector 21, and indicates that the distance from the tip end of the injector 21 is farther downward. Yes. Each numerical value in the left and right graphs indicates the range of the equivalence ratio of the indicated region. For example, the region indicated as 0.1 to 0.5 is a region having an equivalent ratio of 0.1 or more and less than 0.5, and the region indicated as 1.0 to is an equivalent ratio of 1.0 or more. It is an area.

  The time variation of the equivalence ratio distribution of the air-fuel mixture containing the liquid fuel and the distribution of the equivalence ratio of the air-fuel mixture containing the fuel as shown in FIG. 7 was examined for a plurality of injection pressures. The results are shown in FIGS. FIGS. 8 and 9 show the equivalence ratio distribution and fuel spray state when the injection pressure is 120, 80, 40, and 20 MPa, respectively. FIG. 8 shows the distribution of equivalence ratio and the state of fuel spray when the elapsed time after fuel injection is 0.2 ms, 0.5 ms, and 1.0 ms, respectively. FIG. 9 shows the equivalence ratio distribution and the fuel spray state when the elapsed time after fuel injection is 1.5 ms, 2.0 ms, and 2.5 ms, respectively.

  As shown in FIG. 8, the higher the injection pressure, the faster the fuel spray evaporates and the earlier this fuel vapor moves to a range far from the injector tip. However, as shown in FIGS. 8 and 9, at any injection pressure, the distance from the tip of the injector 21 along the value of Z, that is, the axis u2 of the nozzle 21a, at 1.0 ms and 1.5 ms after injection. In the region where the value is 20 mm or more and 25 mm or less, most of the fuel spray is steam, and the equivalent ratio of the air-fuel mixture containing the steam is about 0.2. Therefore, if the region where the ignition energy is supplied, that is, the ignition point S1 is set to a region where the distance from the tip end I1 of the injector 21 is 20 mm or more and 25 mm or less, the air-fuel mixture can be properly burned regardless of the injection pressure. Can do. Thus, in the present engine, the ignition point S1 is set to a position where the separation distance L between the ignition point S1 and the tip end portion I1 of the injector 21 is 20 mm or more and 25 mm or less.

(3) Control System FIG. 10 is a block diagram showing an engine control system. The ECU 50 shown in the figure is a device for comprehensively controlling each part of the engine, and includes a well-known CPU, ROM, RAM, and the like.

  Various information is input to the ECU 50 from various sensors such as the water temperature sensor SW1, the crank angle sensor SW2, and the cam angle sensor SW3 provided in the engine body. The ECU 50 also receives information from various sensors provided in the vehicle. For example, information on the accelerator opening is input to the ECU 50 from an accelerator opening sensor SW4 that detects the opening of an accelerator pedal (not shown) that is depressed by the driver.

  The ECU 50 includes a determination unit 51, an injector control unit 52, an intake control unit 53, an internal EGR control unit 54, an external EGR control unit 55, and an ignition control unit 56 as main functional elements.

  Based on the engine speed Ne and the load T (target torque) specified from the detected values of the crank angle sensor SW2 and the accelerator opening sensor SW4, the determination means 51 determines whether the current engine operating range is as shown in FIG. It is determined which operating region is in the control map.

  Specifically, in the control map of FIG. 11, the first operation region A1 is set in the region where the load T is relatively low over the entire rotational speed region. Further, in a region where the load T is higher than the first operation region A1 and the rotational speed Ne is lower than a predetermined value, the second operation region A2 is set and the load T is higher than that in the first operation region A1. The third operation region A3 is set in a region where the rotational speed Ne is higher and the rotational speed Ne is higher than the predetermined value. Further, a fourth operation region A4 and a fifth operation region A5 are respectively provided between the first operation region A1 and the second operation region A2 and between the first operation region A1 and the third operation region A3. Is set. In addition, the control map which consists of these 1st-5th operation area | regions A1-A5 is fundamentally in the time of the warm state where the cooling water temperature detected by engine water temperature sensor SW1 becomes more than predetermined value (for example, 80 degreeC). Is. The description of the control map when the engine is in a cold state is omitted here.

  The injector control means 52 controls the amount and timing of fuel injected from the injector 21 into the combustion chamber 6. Specifically, the injector control means 52 calculates a target fuel injection amount and injection timing based on the load T, the engine speed Ne, and the like, and drives the injector 21 based on the calculation result.

  The intake control means 53 drives the CVVL 15 to change the lift amount (valve opening amount) of the intake valve 11. For example, the intake control means 53 increases the lift amount of the intake valve 11 to introduce a large amount of air (fresh air) into the combustion chamber 6 when the engine load T is high. On the other hand, the intake control means 53 reduces the lift amount of the intake valve 11 when the engine load T is low.

  The internal EGR control means 54 adjusts the amount of internal EGR gas remaining in the combustion chamber 6 by driving or stopping the VVL 16 to open or stop the exhaust valve 12 during the intake stroke. In this embodiment, since two exhaust valves 12 with VVL 16 are provided per cylinder, by switching the number of exhaust valves 12 opened during the intake stroke between 0, 1, and 2, It is possible to change the amount of internal EGR gas stepwise.

  The external EGR control means 55 adjusts the amount of exhaust gas recirculated from the exhaust passage 29 to the intake passage 28, that is, the amount of external EGR, by changing the opening degree of the EGR valve 32 provided in the EGR passage 31.

  The ignition control means 56 controls the timing (ignition timing) at which the spark plug 20 performs spark discharge.

(4) Specific Control Procedure for Each Operating Area Next, the control performed by the ECU 50 in the first operating area A1 and the second operating area A2 will be specifically described.

  First, when engine operation is started, the ECU 50 controls the engine operating point (load T and rotation speed Ne) based on the detected values of the crank angle sensor SW2 and the accelerator opening sensor SW4 as shown in FIG. It is sequentially determined which operation region in the map corresponds. And according to the determined driving | operation area | region, the following control is performed, respectively.

  As a premise of this explanation, it is assumed that the engine coolant temperature is sufficiently warm (that is, the engine is warm). In the present embodiment, the ECU 50 performs the control that realizes the compression self-ignition combustion even when the engine operating point is in any of the operation regions A1 to A5 during the warm period. However, in order to perform appropriate compression self-ignition combustion, the fuel injection timing from the injector 21, the presence / absence of internal EGR or external EGR, the presence / absence of ignition from the spark plug 20, and the like vary depending on the operation regions A1 and A2. It is necessary to let Therefore, the ECU 50 controls the injector 21, spark plug 20, CVVL15, VVL16, EGR valve 32, and the like while sequentially determining the operating point of the engine.

(I) 1st operation area A1
FIG. 12 is a diagram showing the fuel injection timing when the engine is operated in the first operating region A1, the lift characteristics of the intake and exhaust valves 11 and 12, and the heat generation rate (J / deg) generated by combustion based thereon. is there. As shown in the figure, in the first operation region A1, a general premixed compression self-ignition combustion is performed in which the air-fuel mixture injected before the compression stroke is self-ignited by the compression action of the piston 5. Executed. Specifically, in the first operation region A1, fuel is injected (P) from the injector 21 into the combustion chamber 6 at a predetermined time during the intake stroke, and the fuel injected by the fuel injection P is combusted from the intake passage 28. The mixture with the air (fresh air) introduced into the chamber 6 becomes high temperature and high pressure by the compression action of the piston 5, and self-ignites near the compression top dead center (TDC between the compression stroke and the expansion stroke). Then, based on such self-ignition, combustion accompanied by heat generation as shown by the waveform Qa occurs.

  However, since the load T is relatively low in the first operation region A1 and the amount of fuel injected from the injector 21 is small, misfire may occur unless the in-cylinder temperature is intentionally increased. Therefore, in the first operation region A1, the VVL 16 is driven to open the exhaust valve 12 during the intake stroke, whereby the exhaust gas generated in the combustion chamber 6 is caused to flow back to the combustion chamber 6 and the combustion chamber 6 A large amount of internal EGR is secured. In other words, the exhaust valve 12 opens in the intake stroke (lift curve EX ′) in addition to the exhaust stroke (lift curve EX in FIG. 12). Thus, when a large amount of high-temperature internal EGR gas is ensured, the temperature of the air-fuel mixture in the combustion chamber 6 becomes high, and self-ignition of the air-fuel mixture is promoted. The amount of internal EGR gas is set to be larger on the low load side and smaller on the high load side. As a control for that, for example, in the low load region (region close to no load) in the first operation region A1, the number of the exhaust valves 12 opened during the intake stroke is two, and the load becomes higher than that, The number of valve openings is reduced to one.

  As described above, in the first operation region A1, the introduction of the external EGR gas is stopped as the internal EGR gas amount based on the restart valve (opening during the intake stroke) of the exhaust valve 12 is increased. That is, when the opening degree of the EGR valve 32 provided in the EGR passage 31 is set to be fully closed, the recirculation of the exhaust gas from the exhaust passage 29 to the intake passage 28 is stopped. Further, the ignition of the air-fuel mixture by the spark plug 20 is stopped.

  In the first operation region A1, the excess air ratio λ, which is a value obtained by dividing the air-fuel ratio (actual air-fuel ratio) of the air-fuel mixture in the combustion chamber 6 by the theoretical air-fuel ratio (14.7), is about 2-2. It is set to a significantly lean value of about .4. Therefore, control for increasing or decreasing the lift amount of the intake valve 11 (lift curve IN) is executed by driving the CVVL 15, and the amount of fresh air introduced into the combustion chamber 6 is considerably excessive with respect to the fuel injection amount from the injector 21. It is controlled to become. In this way, when the air-fuel mixture set to be significantly lean is burned, the combustion temperature is greatly lowered, so that the cooling loss can be reduced and the thermal efficiency (fuel consumption) can be improved. Note that when λ = 2 to 2.4, the NOx purification action by the three-way catalyst can hardly be expected. However, if λ = 2 to 2.4, the amount of NOx produced by combustion (raw NOx amount) ) Is greatly reduced, the amount of NOx contained in the exhaust gas can be suppressed to a sufficiently small value without providing a special catalyst (for example, a NOx trap catalyst) in addition to the three-way catalyst.

(Ii) Second operation area A2
In the second operation region A2 in which the load T is higher than the first operation region A1 and the rotation speed Ne is relatively low, the control as shown in FIG. 13 is executed. That is, in the second operation region A2, split injection is performed in which fuel is injected from the injector 21 in two steps (P1, P2) across the compression top dead center. In the following description, the first fuel injection P1 executed during the compression stroke is performed as the pre-stage injection, and the second fuel injection P2 executed near the compression top dead center after that (in the illustrated example, very early in the expansion stroke). This is called post-injection.

  Specifically, in the second operation region A2, the timing of the front injection P1 is 50 to 60 ° CA before the top dead center (BTDC) with respect to the compression top dead center (TDC) (CA represents the crank angle). ) And the timing of the post-injection P2 is set within a period of about 0 to 10 ° CA after top dead center (ATDC). Further, regarding the ratio of each injection amount by the front stage injection P1 and the rear stage injection P2, the front stage injection P1 is about 60% and the rear stage injection from the pattern in which the front stage injection P1 is set to 10% or less and the rear stage injection P2 is set to 90% or more. Up to a pattern in which P2 is set to about 40%, it is set at an appropriate ratio depending on the operating conditions and the like.

  The total injection amount by the front injection P1 and the rear injection P2 is increased in comparison with the first operation region A1 (the injection amount by the fuel injection P) in accordance with the high load corresponding to the second operation region A2. Further, the CVVL 15 is driven to increase the lift amount of the intake valve 11 (lift curve IN) in order to introduce a large amount of fresh air corresponding to the fuel injection amount set to increase in this way into the combustion chamber 6. Then, as shown in the waveform Qb in the figure, two peaks having different timings are obtained by the self-ignition of the mixture of fuel and air (fresh air) separately injected as described above near the compression top dead center. Combustion accompanied by heat generation occurs. Note that such a shape of the waveform Qb is conceptual only, and there are naturally cases where two peaks do not appear clearly.

  The reason why the fuel is injected separately into the front injection P1 and the rear injection P2 as described above is in consideration of problems such as combustion noise. That is, in the second operation region A2 where the fuel injection amount is large, if the fuel is injected at one time, a sudden combustion occurs in which all of the injected large amount of fuel burns in a short period of time. May suddenly increase, resulting in a marked increase in combustion noise. Therefore, by dividing and injecting fuel as described above, relatively mild combustion is continuously caused to avoid the increase in combustion noise as described above.

  However, even if the fuel injection is divided into a plurality of times, depending on the arrangement of the injector 21 and the shape of the piston 5, the fuels injected at each time may be mixed and the mixed fuel may burn almost simultaneously. . In this way, if combustion occurs in a mixture of fuels with different injection timings, not only does combustion noise become excessive, but the oxygen required for combustion is significantly insufficient locally, resulting in a large amount of soot (carbonaceous matter). Particles) may occur.

  In order to deal with such a problem, in the present embodiment, the injector 21 is disposed at the center portion in the radial direction of the ceiling of the combustion chamber 6 and the crown surface of the piston 5 is formed in a special shape having the cavity 40 and the like. In addition, the separately injected fuel does not burn at the same time, and it is possible to avoid an increase in combustion noise and a large amount of soot as described above (detailed mechanism will be described later).

  In the second operation region A2, in addition to the fuel split injection control as described above, the VVL 16 is driven so as to invalidate the function of depressing the exhaust valve 12 during the intake stroke, and the intake stroke of the exhaust valve 12 is determined. The valve opening inside is stopped. As a result, the exhaust gas hardly flows back into the combustion chamber 6 and internal EGR is prohibited.

  On the other hand, in the second operation region A2, external EGR is executed instead of the prohibited internal EGR as described above. That is, the operation of recirculating the exhaust gas from the exhaust passage 29 to the intake passage 28 is performed by opening the EGR valve 32 provided in the EGR passage 31 to a predetermined opening degree.

  The reason for switching from the internal EGR to the external EGR in this way is to ensure the amount of fresh air in the combustion chamber 6 and to avoid abnormal combustion. That is, in the second operation region A2, the engine load T is higher than that in the first operation region A1, a larger amount of fresh air is required, and pre-ignition and knocking are accompanied by a large amount of total fuel injected. Abnormal combustion may occur. Therefore, the volume of the EGR gas is reduced by switching from the internal EGR to the external EGR and returning the exhaust gas that has passed through the EGR passage 31 with the EGR cooler 33 (that is, cooled by the EGR cooler 33) to the intake passage 28. Thus, the amount of fresh air in the combustion chamber 6 is ensured, the temperature of the combustion chamber 6 is prevented from being increased, and abnormal combustion as described above is avoided. However, even in the second operation region A2, the external EGR is stopped in the vicinity of the full load of the engine in order to ensure a large amount of fresh air.

  Here, the combustion mode in the second operation region A2 realized based on the above control will be described more specifically with reference to FIGS. 15 (a) to 15 (f). FIG. 15A shows a state when the upstream injection P1 is performed from the injector 21. FIG. As described above, the piston 5 at this time is positioned at about 50 to 60 ° CA before compression top dead center (BTDC). When fuel is injected radially from the plural (12) nozzle holes provided at the tip end portion I1 of the injector 21 toward the crown surface of the piston 5 at such a position, the spray of the fuel is It goes to the annular recess 41 provided on the outer side in the radial direction of the crown surface.

  The fuel (spray) injected toward the annular recess 41 of the piston 5 is then dispersed while being guided upward by the standing wall portion 42 provided on the outermost peripheral portion of the piston 5, and based on the dispersed fuel, As shown in FIG. 15B, the air-fuel mixture X1 is formed in the outer peripheral portion of the combustion chamber 6 (mainly inside the annular recess 41 and the space above it). The air-fuel ratio of the air-fuel mixture X1 formed here is set to a theoretical air-fuel ratio (excess air ratio λ = 1) as a local air-fuel ratio only in the outer peripheral portion of the combustion chamber 6. That is, the injection timing and the injection amount of the pre-stage injection P1 are set so that the air-fuel mixture X1 having a concentration about the stoichiometric air-fuel ratio is locally formed on the outer periphery of the combustion chamber 6.

  Of course, a small amount of fuel may be present outside the outer peripheral portion of the combustion chamber 6 (for example, inside the cavity 40) by the front injection P1, but the concentration of the fuel is extremely higher than that of the outer peripheral portion of the combustion chamber 6. It is thin. In other words, the air-fuel mixture X1 that is extremely richer than the inside of the cavity 40 is formed in the outer peripheral portion of the combustion chamber 6 at the time when the front injection P1 is executed.

  The air-fuel mixture X1 formed on the outer peripheral portion of the combustion chamber 6 as described above is compressed by the rise of the piston 5 to become high temperature and pressure, and when the piston 5 reaches the vicinity of the compression top dead center, FIG. It burns by self-ignition as shown in (compression self-ignition). In the figure, the region where the air-fuel mixture X1 is burning is shown in black or gray. The region Y2 where the air-fuel mixture X1 burns is limited to the outer peripheral portion of the combustion chamber 6 corresponding to the region where the air-fuel mixture X1 is formed.

  When the combustion based on the front injection P1 as described above starts, the rear injection P2 as shown in FIG. 15 (d) is executed almost simultaneously or with a short period of time. As described above, the timing of the post-injection P2 is about 0 to 10 ° CA after top dead center (ATDC) shortly after the piston 5 starts to descend. Thus, when the fuel is injected from the injector 21 at the timing when the piston 5 is close to the top dead center, the spray of the fuel goes to the inside of the cavity 40 provided in the radial center portion of the crown surface of the piston 5. It will be. Then, the fuel (spray) injected toward the inside of the cavity 40 is dispersed while being guided upward along the peripheral wall of the cavity 40, and based on the dispersed fuel, as shown in FIG. The air-fuel mixture X2 is formed in the radially central portion of the combustion chamber 6 (mainly inside the cavity 40). The local air-fuel ratio of the air-fuel mixture X2 is also set to about the stoichiometric air-fuel ratio (excess air ratio λ = 1), similar to the air-fuel mixture X1 based on the pre-stage injection P1 described above. In other words, the rich air-fuel mixture X2 is formed inside the cavity 40 by the post-injection P2 than when the pre-injection P1 is executed.

  The mixture X2 based on the post-stage injection P2 as described above is formed in a state where the piston 5 is close to the compression top dead center and the combustion of the mixture X1 based on the pre-stage injection P1 has already occurred. For this reason, as shown in FIG. 15 (f), the air-fuel mixture X2 reaches self-ignition in a very short time after the post-injection P2, and burns. The region Y2 where the air-fuel mixture X2 burns is limited to the central portion in the radial direction of the combustion chamber 6 corresponding to the region where the air-fuel mixture X2 is formed. That is, the air-fuel mixture X1 based on the above-described front-stage injection P1 burns in the outer peripheral portion (fuel region Y1) of the combustion chamber 6 corresponding to the installation portion of the annular recess 41, whereas the air-fuel mixture X2 based on the rear-stage injection P2 Then, combustion occurs in the radial center portion (combustion region Y2) of the combustion chamber 6 corresponding to the installation portion of the cavity 40.

  As described above, in the second operation region A2, a relatively large amount of fuel corresponding to the load T is injected in a plurality of times (the front-stage injection P1 and the rear-stage injection P2), so that the air-fuel mixture (X1) , X2) and self-igniting and burning them independently. In the second operation region A2 in which such control is performed, the separately injected fuel is not mixed and combusted at the same time. Therefore, an increase in combustion noise due to a sudden rise in the in-cylinder pressure, and local oxygen There is no worry that a large amount of soot will occur due to shortage. Moreover, the air-fuel mixtures X1 and X2 based on the front-stage injection P1 and the rear-stage injection P2 are each locally set to an excess air ratio of about λ = 1, so that the exhaust gas generated by combustion in such an environment is used. If it exists, harmful components can be sufficiently purified only by the three-way catalyst.

  In particular, an annular recess 41 having a circular shape in plan view is formed on the crown surface of the piston 5 located radially outward from the cavity 40 and the height decreases toward the radially outer side. Therefore, when the fuel injected by the upstream injection P1 is received by the annular recess 41, the air-fuel mixture X1 based on the upstream injection P1 is introduced into the outer peripheral portion of the combustion chamber 6 corresponding to the installation portion of the annular recess 41. You can keep it securely. As a result, the air-fuel mixture X1 based on the preceding injection P1 can be clearly separated from the air-fuel mixture X2 formed in the cavity 40 based on the subsequent post-injection P2, and the combustion of the air-fuel mixtures X1 and X2 is independent of combustion. Sex can be secured more reliably.

  Further, an upright wall portion 42 that guides the fuel injected by the front injection P1 upward is provided further radially outward than the annular recess 41. Therefore, the fuel of the front injection P1 injected toward the annular recess 41 is wound up upward along the standing wall portion 42, so that the fuel is sufficiently dispersed, vaporized and atomized, and mixed in the outer peripheral portion of the combustion chamber 6. The formation of Qi X1 can be effectively promoted.

  Further, the cavity 40 is formed in a constricted shape, and the area of the opening 40 a at the upper end is set smaller than the maximum cross-sectional area inside the cavity 40. Therefore, the air-fuel mixture X2 based on the fuel injected by the post-injection P2 can be reliably kept inside the cavity 40, and the air-fuel mixture X2 based on the post-injection P2 is changed to the previous pre-injection P1. It can be formed clearly separated from the based air-fuel mixture X1.

(Iii) Third operation area A3
In the third operation region A3 where the load T is higher than that in the first operation region A1 and the rotational speed Ne is higher than that in the second operation region A2, the control as shown in FIG. 14 is executed. That is, in the third operation region A3, the fuel from the injector 21 is injected in three times from the intake stroke to the vicinity of the compression top dead center (P0, P1, P2). Of these, the second fuel injection P1 executed during the compression stroke and the third fuel injection P2 executed near the compression top dead center after that (in the illustrated example, very early in the expansion stroke) are: Each corresponds to the front-stage injection P1 and the rear-stage injection P2 (FIG. 13) in the second operation region A2 described above. On the other hand, the first fuel injection P0 executed during the intake stroke is an injection that is not performed in the second operation region A2, and is specific to the third operation region A3. Hereinafter, the first fuel injection P0 in the third operation region A3 is referred to as preliminary injection, the second fuel injection P1 is referred to as pre-injection, and the third fuel injection P2 is referred to as post-injection.

  The pre-stage injection P1 and the post-stage injection P2 executed in the third operation area A3 play the same role as that in the second operation area. That is, the pre-stage injection P1 executed during the compression stroke forms an air-fuel mixture X1 that is unevenly distributed in the outer peripheral portion of the combustion chamber 6 as shown in FIG. 15B, and is executed near the compression top dead center. By the post-injection P2, the air-fuel mixture X2 that is unevenly distributed in the radial center portion of the combustion chamber 6 as shown in FIG. 15 (e) is formed.

  However, in the third operation region A3, the engine rotation speed Ne is higher than that in the second operation region A2, and the piston speed is faster. Therefore, the injected fuel from the injector 21 is in the vicinity of the vicinity of the crown surface of the piston 5. The piston 5 moves relatively large. Considering this, the timings of the front injection P1 and the rear injection P2 are set slightly earlier than in the second operation region A2. Thereby, the air-fuel mixture X1, X2 based on the injections P1, P2 is separately formed at the same place as shown in FIGS. 15B and 15E regardless of the difference in the engine rotational speed Ne. (FIGS. 15C and 15F).

  On the other hand, in the third operation region A3, in addition to the front injection P1 and the rear injection P2, the preliminary injection P0 executed during the intake stroke is added because the third operation has a relatively high engine speed Ne. This is because in the region A3, it is difficult to inject a required amount of fuel within a short period of time. That is, in the third operating region A3 where the engine rotational speed Ne is high, unlike the second operating region A2 where the rotational speed Ne is relatively low, the piston speed is fast, so the required amount of fuel is injected over the same time. Even if it tries to do so, the position of the piston 5 may change significantly during that time, and the positional relationship between the piston 5 and the fuel spray may be destroyed.

  For example, in the third operation region A3, if the same amount of fuel as in the second operation region A2 is to be injected by the pre-injection P1, the fuel injection operation from the injector 21 (from the injection port of the injector 21 by opening the injection port) It is necessary to continue the fuel injection operation) for the same period as in the second operation region A2, but in the third operation region A3 where the piston speed is high, the piston 5 If the position of the valve is greatly raised, the proper positional relationship as shown in FIG. 15A may be lost, and the spray direction may deviate from the annular recess 41 of the piston 5. When such a situation occurs, the air-fuel mixture X1 cannot be unevenly distributed on the outer peripheral portion of the combustion chamber 6 corresponding to the installation portion of the annular recess 41, and the subsequent injection P1 after the compression top dead center. It is considered that the air-fuel mixture X1, X2 based on the post-injection P2 cannot be burned sufficiently independently.

  Therefore, in order to surely avoid the above situation, in the third operation region A3, first, the preliminary injection P0 is executed during the intake stroke to inject a small amount of fuel, and during the subsequent compression stroke and the compression top dead center. In the vicinity, the front injection P1 and the rear injection P2 are executed. As a result, the amount of fuel to be injected by the pre-stage injection P1 and the post-stage injection P2 is reduced, so the time required for the injection of the fuel is also reduced, and the above-described problems (the position of the piston 5 changes greatly during the fuel injection). ) Is avoided.

  As described above, when the fuel is injected in three times, that is, the preliminary injection P0, the pre-stage injection P1, and the post-stage injection P2, the pre-stage injection is performed in the extremely lean mixture previously formed in the combustion chamber 6 by the preliminary injection P0. Fuel from P1 and post-injection P2 is additionally injected. Then, in the combustion chamber 6, a rich air-fuel mixture of about λ = 1 based on the preliminary injection P0, the pre-stage injection P1, and the post-stage injection P2 is formed in the outer peripheral portion and the radial center portion (inside the cavity 40). On the other hand, in other regions, an extremely lean air-fuel mixture (for example, an air-fuel mixture that greatly exceeds λ = 2) based only on the preliminary injection P0 is formed.

  Here, the post-injection P2 is injected within a period of about 0 to 10 ° CA after top dead center (ATDC). For this reason, from the viewpoint of fuel efficiency, it is preferable that the fuel injected by the post-injection P2 starts and ends early after injection (early at the crank angle). On the other hand, in the third operation region A3, the engine speed is high. Therefore, when waiting for the fuel to sufficiently absorb heat until self-ignition is possible, there is a problem that the combustion start angle becomes very retarded from the top dead center, and the fuel consumption performance deteriorates. Further, in the third operation region A3, the load T is high and the amount of fresh air sucked into the combustion chamber 6 is large. Therefore, the temperature in the combustion chamber 6 becomes low, and compression self-ignition tends to be difficult. Therefore, in the third operation region A3, after the post-injection P2 is injected, the air-fuel mixture is sparked by the spark plug 20. As described above, in order to appropriately increase the temperature of the air-fuel mixture while improving the exhaust performance, it is necessary to supply ignition energy to the air-fuel mixture before the injected fuel reaches the wall surface of the combustion chamber. Therefore, in the third operation region A3, spark ignition is performed on the air-fuel mixture by the spark plug 20 immediately after the post-stage injection P2 is injected.

  As described above, the position of the ignition point S1 of the spark plug 20 is set to a position where the separation distance L from the tip end I1 of the injector 21 is 20 mm. Therefore, the ignition energy applied to the ignition point S1 is supplied to the fuel spray containing a sufficiently high equivalence ratio and containing a large amount of steam, and the mixture containing the fuel spray burns while the generation of SOOT and the like is suppressed. Thus, the air-fuel mixture is heated appropriately. Further, the ignition point S1 is located in the middle of the axial lines u2_1 and u2_2 of the nozzle holes 21a adjacent to each other in the injector 21 in plan view. Therefore, the ignition energy is efficiently supplied to the fuel spray injected from the two injection holes 21a that pass on both sides of the ignition point S1, and the air-fuel mixture burns more reliably.

  Further, as described above, the position of the ignition point S1 of the spark plug 20 is located on the radially inner side with respect to the outer peripheral edge of the cavity 40. Therefore, the ignition energy supplied into the combustion chamber by the spark plug 20 is not added to the air-fuel mixture formed by the front-stage injection P1 existing in the outer peripheral portion of the combustion chamber 6, but the air-fuel mixture formed by the rear-stage injection P2. Only added. Accordingly, also in the third operation region A3, as in the second operation region A2, the fuel injected by the front injection P1 and the fuel injected by the rear injection P2 are in different locations (in the combustion chamber 6). Burns independently (inside the perimeter and cavity 40). Specifically, the air-fuel mixture formed by the front-stage injection P1 starts self-ignition combustion near the compression top dead center, and the air-fuel mixture formed by the rear-stage injection P2 receives the ignition energy and then rises in temperature. Ignite and burn. As a result, the combustion chamber 6 as a whole, as shown conceptually in the waveform Qc of FIG. 8, undergoes combustion accompanied by heat generation having two peaks at different times. In addition, when the air-fuel ratio mixture as described above burns, the generated exhaust gas can be sufficiently purified by a three-way catalyst, or the amount of NOx generated is extremely small. Is cleared without problems.

  As shown in FIG. 14, in the third operation region A3, the same control as that in the second operation region A2 is executed except for the control related to the fuel split injection as described above. For example, in the third operation region A3, the internal EGR that opens the exhaust valve 12 during the intake stroke (returns the exhaust gas to the combustion chamber 6) is prohibited, and the exhaust gas is passed through the EGR passage 31 to the intake passage 28. External EGR to reflux is performed. However, external EGR is prohibited in the vicinity of the full load of the engine in order to ensure a large amount of fresh air.

(Iv) Fourth operation region A4 and fifth operation region A5
The fourth operation region A4 and the fifth operation region A5 are regions located between the first operation region A1 and the second operation region A2 or between the first operation region A1 and the third operation region A3. From the above, intermediate control of each control content described in the above (i) to (iii) is executed.

  Specifically, in the fourth operation region A4, the fuel injection timing from the injector 21 is retarded from the fuel injection timing in the first operation region A1, and is set to, for example, once during the compression stroke. The injection amount at that time is set so that the excess air ratio λ is about λ = 2 to 2.4, as in the first operation region A1. In addition, external EGR for returning the exhaust gas to the intake passage 28 through the EGR passage 31 is executed.

  On the other hand, in the fifth operation region A5, the control for injecting the fuel is executed in two steps near the predetermined timing during the compression stroke and after the compression top dead center. The injection amount at that time is set so that the excess air ratio λ is locally about λ = 1. Further, the internal EGR for causing the exhaust gas to flow backward to the combustion chamber 6 is performed by opening the exhaust valve 12 during the intake stroke.

(5) Operational effects and the like As described above, in the gasoline engine of the present embodiment, the separation distance L between the ignition point S1 and the tip end portion I1 of the injector 21 is set at a position where the distance is 20 mm and the fuel is injected. Ignition energy is supplied to the fuel before it reaches the wall of the combustion chamber. Therefore, the air-fuel mixture is appropriately heated while suppressing the generation of SOOT and the like, and the subsequent compression self-ignition combustion can be properly realized.

  In particular, the ignition point S1 is located in the middle of the axial lines u2_1 and u2_2 of the nozzle holes 21a adjacent to each other of the injector 21 in plan view. Therefore, the ignition energy is efficiently supplied to the fuel spray injected from the two injection holes 21a passing on both sides of the ignition point S1, and the air-fuel mixture can be burned more reliably and appropriately.

  In the present embodiment, a concave cavity 40 is provided in the radial center portion of the crown surface of the piston 5, and fuel (gasoline is a main component) radially from the radial center portion of the combustion chamber 6 facing the cavity 40. The cylinder head 4 is provided with a multi-hole type injector 21 for injecting the fuel. In addition, the diameter of the cavity 40 is set such that the ignition point S <b> 1 is positioned radially inward from the outer peripheral edge of the cavity 40. And in 3rd operation area | region A3 (specific operation area | region) including a high load area, it isolate | separates into the separate space (the outer peripheral part of the combustion chamber 6, and the inside of the cavity 40) in the combustion chamber 6, and air-fuel | gaseous mixture X1, X2 Control is performed so that fuel is injected in at least two times, that is, the front injection P1 set during the compression stroke and the rear injection P2 set near the compression top dead center after that so as to be formed. At the same time, ignition energy is supplied only to the air-fuel mixture X2 formed inside the cavity 40. Therefore, these air-fuel mixtures X1, X2 can be self-ignited and burned independently in the vicinity of compression top dead center, and combustion noise increases due to a sudden rise in in-cylinder pressure due to the mixture of these fuels and simultaneous combustion In addition, a large amount of soot due to local oxygen shortage can be effectively prevented.

  Here, the operation region where the ignition assist is performed is not limited to the above. Further, the fuel injection control performed in the operation region where the ignition assist is performed is not limited to the above. For example, the ignition assist may be performed in a low load low speed region where the temperature in the combustion chamber is relatively low, the engine speed is low, and the engine load is small.

  Further, the injector storage 62 can be omitted. That is, as shown in FIG. 16, the entire ceiling surface of the combustion chamber 6 may be substantially flat. However, as in the above-described embodiment, if the injector storage portion 62 is provided on the ceiling surface of the combustion chamber 6 and the position of the tip end portion I1 of the injector 21 is arranged higher (in the direction away from the piston crown surface), the ignition point The amount of projection of the spark plug 20 into the combustion chamber 6 can be kept small while disposing S1 on the axis of each injection hole 21a of the injector 21 in a side view.

  Further, the ceiling surface 60 of the combustion chamber 6 is not limited to the one in which the surface radially outside of the injector storage portion 62 is a horizontal plane. For example, as shown in FIG. 17, the ceiling surface 60 of the combustion chamber 6 has a shape that inclines downward (in the direction approaching the piston crown surface) from the outer peripheral edge of the injector storage portion 62 toward the radially outer side. Also good.

  In the above embodiment, the case where the ignition point S1 is arranged in the middle of the axes u2_1 and u2_1 of the adjacent nozzle holes 21a in plan view has been described. However, as shown in FIG. The ignition point S1 may be arranged on the axis u2 of the predetermined injection hole 21a, that is, in the fuel passage region F1. However, it is known that the equivalence ratio is relatively large in the fuel passage region F1. Therefore, when the ignition point S1 is arranged in the fuel passage region F1 in this way, as shown in FIG. 19, the ignition point S1 is located above the axis u2 of the injection hole 21a (in the injector 21) in a side view. It is preferable to dispose at a position separated on the near side. For example, when the number of injection holes 21a of the injector 21 is larger than eight and the amount of fuel injected from one injection hole 21a is small, the ignition point S1 is adjacent so that ignition energy is supplied to more fuel. On the other hand, when the number of nozzle holes 21a of the injector 21 is less than 8, the ignition point S1 may be disposed in the spray region A1.

  Further, the number of nozzle holes of the injector 21 is not limited to 12, and may be more or less than 12. However, if the number of injection holes is too small, the concentration of the fuel injected from the injector 21 varies greatly in the circumferential direction. For this reason, it is desirable that the number of nozzle holes be eight or more. If the number of nozzle holes is eight or more, an air-fuel mixture having a substantially uniform air-fuel ratio in the circumferential direction can be formed in a very short time after the execution of the front injection P1 and the rear injection P2. It is possible to properly perform combustion by self-ignition (compression self-ignition combustion).

5 Piston 6 Combustion chamber 21 Injector 21a Injection hole 40 Cavity 50 ECU (control means)
60 ceiling surface 62 injector storage part A3 3rd operation area (specific operation area)
I1 Injector tip S1 Ignition point

Claims (7)

A gasoline engine that reciprocates a piston by burning a mixture of fuel and air, at least part of which is gasoline, in a combustion chamber,
A plurality of nozzle holes for injecting the fuel into the combustion chamber are formed at the tip, and the tip is disposed on the combustion chamber ceiling with the tip facing the combustion chamber at the radial center of the combustion chamber ceiling. Injectors,
An ignition plug that is disposed at a position radially outside the injector in the ceiling of the combustion chamber and supplies ignition energy to the air-fuel mixture;
Control means for controlling the fuel injection operation by the injector and the ignition operation by the spark plug;
Each nozzle hole of the injector expands radially outward as the fuel approaches the crown surface of the piston through each nozzle hole, and radially outwards as its axis line approaches the piston crown surface. Has an inclined shape,
The spark plug is disposed at a position where a separation distance between the ignition point and the tip of the injector is 20 mm or more and 25 mm or less,
The control means injects fuel from each injection port of the injector in a predetermined specific operation region of the engine, and before the fuel injected from each injection port of the injector reaches the wall surface of the combustion chamber, A gasoline engine characterized in that ignition energy is supplied from an ignition plug, the temperature of the mixture is increased by the ignition energy, and then the mixture is burned by self-ignition. The gasoline engine according to claim 1,
The gasoline engine has eight or more nozzle holes at its tip. The gasoline engine according to claim 1 or 2,
The gasoline engine, wherein the ignition plug protrudes from the ceiling of the combustion chamber toward the inside of the combustion chamber so that an ignition point thereof is located in the vicinity of an axis of a specific nozzle hole of the injector in a side view. The gasoline engine according to claim 3,
An injector housing portion that is recessed in a direction away from the piston crown surface is formed in a radially central portion of the combustion chamber ceiling,
The injector faces the injector storage portion in a state where a tip portion thereof is positioned at a radial central portion of the injector storage portion,
The inner peripheral surface of the injector storage portion has a shape surrounding the fuel passage region at a position spaced radially outward from the fuel passage region from each nozzle hole of the injector toward the wall surface of the combustion chamber. Gasoline engine. The gasoline engine according to claim 4, wherein
The inner peripheral surface of the injector storage portion has a substantially conical surface shape with the center portion in the radial direction of the combustion chamber ceiling as a top portion,
The gasoline engine according to claim 1, wherein a tip portion of the injector is located at the top. In the gasoline engine according to any one of claims 1 to 5,
The piston has a concave cavity that is provided in a central portion in the radial direction of the crown surface and is recessed in a direction away from the combustion chamber ceiling,
The gasoline engine according to claim 1, wherein the ignition plug is disposed at a position where an ignition point is radially inward of a radially outer edge of the cavity. The gasoline engine according to claim 6,
In the specific operation region, the control means injects fuel from the injector in at least two times of front-stage injection and rear-stage injection, and supplies ignition energy to the fuel injected during the rear-stage injection by the spark plug. ,
The pre-stage injection injects fuel during the compression stroke and before the post-stage injection, and the injected fuel causes the cavity to enter the outer peripheral portion of the combustion chamber located radially outside the cavity of the piston. Which forms a richer mixture than the interior of
In the latter-stage injection, fuel is injected at a predetermined time from the latter stage of the compression stroke to the early stage of the expansion stroke, and the injected fuel causes a richer air-fuel mixture to be formed in the cavity than when the preceding-stage injection is performed. A gasoline engine characterized by what is formed.